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1

Plasma Calcium and Magnesium in Newborn Babies  

PubMed Central

Normal values for plasma calcium and magnesium levels during the first week of life, in breast- and bottle-fed babies, have been determined. It has been shown on the sixth day that plasma levels of calcium, magnesium, and protein are all significantly lower in bottle-fed babies than in breast-fed babies, while the reverse is true of the plasma inorganic phosphorus. The normal babies have been compared with 30 babies who had convulsions, beginning towards the end of the first week of life. In only six of the babies was the plasma calcium outside our normal range and only four had abnormally low magnesium levels. As so many of these babies had calcium and magnesium levels within the normal range it must seriously be questioned whether hypocalcaemia or hypomagnesaemia could have been the sole cause of the convulsions.

Harvey, D. R.; Cooper, Lesley V.; Stevens, J. F.

1970-01-01

2

Effects of calcium and magnesium on strontium distribution coefficients  

USGS Publications Warehouse

The effects of calcium and magnesium on the distribution of strontium between a surficial sediment and simulated wastewater solutions were measured as part of an investigation to determine strontium transport properties of surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. The investigation was conducted by the U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy. Batch experimental techniques were used to determine strontium linear sorption isotherms and distribution coefficients (K(d)'s) using simulated wastewater solutions prepared at pH 8.0??0.1 with variable concentrations of calcium and magnesium. Strontium linear sorption isotherm K(d)'s ranged from 12??1 to 85??3 ml/g, increasing as the concentration of calcium and magnesium decreased. The concentration of sorbed strontium and the percentage of strontium retained by the sediment were correlated to aqueous concentrations of strontium, calcium, and magnesium. The effect of these cation concentrations on strontium sorption was quantified using multivariate least-squares regression techniques. Analysis of data from these experiments indicates that increased concentrations of calcium and magnesium in wastewater discharged to waste disposal ponds at the INEL increases the availability of strontium for transport beneath the ponds by decreasing strontium sorption to the surficial sediment.

Bunde, R. L.; Rosentreter, J. J.; Liszewski, M. J.; Hemming, C. H.; Welhan, J.

1997-01-01

3

DETERMINATION OF CALCIUM AND MAGNESIUM CARBONATES IN SOIL  

Microsoft Academic Search

For determining the alkaline earth carbonate conteni of calcareous soils ; by the present methods, calcium and magnesium carbonates are measured together ; and results are expressed as calcium carbonate equivalent. A new method has been ; devised for the determination of each compound separately. It involves the use ; of Ca⁴⁵ and a cation exchange resin. The method is

Amer

1959-01-01

4

STUDIES ON CALCIUM AND MAGNESIUM METABOLISM IN DISEASE  

PubMed Central

In leprosy there is a definite retention of calcium. The more advanced the stage of the disease the greater is the degree of retention. This behavior on the part of leprous individuals may be taken as an indication that the organism is in need of calcium. Magnesium may also be retained in leprosy, but .the degree of retention is much less marked than in the case of calcium. With the exception of the retention of calcium and magnesium the leprous organism responds to changes in the intake of calcium and magnesium in the same manner as normal individuals. The results of this investigation suggest that in leprosy administration of calcium may be of benefit as an additional therapeutic measure in an endeavor to retard or arrest the progress of the bone changes characteristic of the disease.

Underhill, Frank P.; Honeij, James A.; Bogert, L. Jean

1920-01-01

5

Precipitation of calcium and magnesium carbonates from homogeneous supersaturated solutions  

Microsoft Academic Search

Homogeneous (unseeded) precipitation of calcium and magnesium carbonates in the CaOMgOCO2H2O system in supersaturated solutions was investigated. The induction period (?) of spontaneous nucleation and the composition of precipitated solid phases were determined. The influence of saturation degree (chemical affinity) and Mg2+\\/Ca2+ activity ratio in solution on the kinetics of CaCO3 nucleation was studied. The order of CaCO3 homogeneous nucleation

O. S. Pokrovsky

1998-01-01

6

Automatic photometric titrations of calcium and magnesium in carbonate rocks  

USGS Publications Warehouse

Rapid nonsubjective methods have been developed for the determination of calcium and magnesium in carbonate rocks. From a single solution of the sample, calcium is titrated directly, and magnesium is titrated after a rapid removal of R2O3 and precipitation of calcium as the tungstate. A concentrated and a dilute solution of disodium ethylenediamine tetraacetate are used as titrants. The concentrated solution is added almost to the end point, then the weak solution is added in an automatic titrator to determine the end point precisely.

Shapiro, L.; Brannock, W. W.

1955-01-01

7

Determination of Nitrogen, Sulphur, Phosphorus, Potassium, Sodium, Calcium, and Magnesium in Plant Material by Automatic Analysis.  

National Technical Information Service (NTIS)

Methods are proposed for the rapid determination of nitrogen, sulphur, phosphorus, potassium, sodium, calcium, and magnesium in plant material by automated chemical analysis. Phosphorus, potassium, calcium, magnesium, and sodium are determined in nitric-p...

C. H. Williams J. R. Twine

1967-01-01

8

Myocardial Calcium and Magnesium in Acute Ischemic Injury  

PubMed Central

The effect of ischemic injury on calcium and magnesium distribution in dog myocardial cells was investigated in tissue damaged by occlusion of the circumflex branch of the left coronary artery for 60 minutes or for 40 minutes followed by 20 minutes of reperfusion of the damaged tissue by arterial blood. No significant change in the concentration of these cations was noted in permanently ischemic, irreversibly injured myocardial cells, but tissue calcium was markedly increased in cells killed by an episode of transient ischemia. Tissue water and sodium also were increased and magnesium was decreased significantly in the transient ischemia model. Investigation of the localization of the increased Ca-- by cellular fractionation and chemical analysis as well as by electron miscroscopy and microincineration showed that much of it was localized in dense bodies within the mitochondria. Within the intramitochondrial dense bodies, the calcium appeared to be a precipitate of an as yet undefined form of calcium phosphate. ImagesFig 5Fig 1Fig 2Fig 6AFig 6BFig 3AFig 3BFig 4

Shen, Anthony C.; Jennings, Robert B.

1972-01-01

9

Regulation of Intracellular Calcium Concentrations by Calcium and Magnesium in Cardioplegic Solutions Protects Rat Neonatal Myocytes from Simulated Ischemia  

Microsoft Academic Search

The effects of calcium and magnesium ions in cardioplegic solutions on cardioprotection and intracellular calcium ion handling during ischemia and reoxygenation were investigated in cultured neonatal rat myocardial cells. Myocytes were subjected to simulated ischemia for 60 min at 37C in hyperkalemic cardioplegic solutions containing various concentrations of calcium and magnesium ions, followed by 30 min of reoxygenation. For each

Takashi Ichiba; Naruto Matsuda; Naoaki Takemoto; Shingo Ishiguro; Hiroaki Kuroda; Tohru Mori

1998-01-01

10

A SIMPLE AND RAPID METHOD FOR THE SIMULTANEOUS DETERMINATION OF CALCIUM AND MAGNESIUM FROM THE SAME SAMPLE OF BLOOD SERUM  

PubMed Central

A simple and rapid procedure has been developed for the complexometric titration of serum calcium and magnesium using plasmocorinth B as indicator. Both determinations can be carried out from the same 0.5 ml. sample. The method is in good agreement with the established calcium and magnesium methods.

Kovacs, G. S.; Tarnoky, K. E.

1960-01-01

11

A simple and rapid method for the simulataneous determination of calcium and magnesium from the same sample of blood serum.  

PubMed

A simple and rapid procedure has been developed for the complexometric titration of serum calcium and magnesium using "plasmocorinth B" as indicator. Both determinations can be carried out from the same 0.5 ml. sample. The method is in good agreement with the established calcium and magnesium methods. PMID:14411396

KOVACS, G S; TARNOKY, K E

1960-03-01

12

Disorders of calcium and magnesium balance: a physiology-based approach.  

PubMed

Disorders of calcium and magnesium balance are physiologically interesting and clinically challenging. In this review, we attempt to bridge the gap between physiology and practice by providing a physiology-based approach to understanding hypocalcemia, hypercalcemia and hypomagnesemia. Calcium and, to a lesser extent, magnesium balance is achieved through a complex interplay between the parathyroid gland, bone, the intestine and the kidney. Our understanding of the molecular physiology of calcium and magnesium balance has grown considerably following the discovery of the calcium-sensing receptor (CaSR) and the main intestinal and renal transporters for calcium and magnesium, namely, the transient receptor potential channels TRPV5, TRPV6 and TRPM6. The regulation of parathyroid hormone (PTH) secretion by CaSR and the subsequent effects of PTH and vitamin D on TRPV5 constitute an increasingly characterized regulatory loop. In contrast, no truly magnesiotropic hormones have been identified, although the recently established interactions between the epidermal growth factor and TRPM6 suggest a possible candidate. Overall, the aim of this review is to illustrate the clinical disorders of calcium and magnesium balance from the perspective of their integrated physiology. PMID:23142866

Hoorn, Ewout J; Zietse, Robert

2013-08-01

13

A field method for the determination of calcium and magnesium in limestone and dolomite  

USGS Publications Warehouse

The method is an adaptation of a procedure described by Betz and Noll1 in 1950. Calcium and magnesium are determined by visual titration using Versene (disodium ethylenediamine tetraacetate) with Murexide (ammonium purpurate) as the indicator for calcium and Eriochrome Black T as the indicator for magnesium.

Shapiro, Leonard; Brannock, Walter Wallace

1957-01-01

14

Determination of Calcium and Magnesium in Serum, Urine, Diet, and Stool by Atomic Absorption Spectrophotometry  

Microsoft Academic Search

ATOMIC ABSORPTION was developed by Walsh and his associates (1) as an analytical technic applicable to the determination of many metals. Willis (2-4) found that this technic was applicable in particular to tile determination of calcium and magnesium in Serum and urine. These published results indicated that atomic absorption spectrophotometry would be a simple, rapid, and practical method for tile

Elizabeth G. Gimblet; Amy F. Marney; Roy W. Bonsnes

15

Extraction of phosphorus, potassium, calcium, and magnesium from soils by an ion?exchange resin procedure  

Microsoft Academic Search

A procedure for the simultaneous extraction of phosphorus, potassium, calcium and magnesium from soils, by an ion?exchange resin procedure applicable to large?scale advisory soil testing, is described. The important steps are the disaggregation of soil by shaking in water during 15 minutes with a glass marble, the transference of the elements from the soil to a sodium bicarbonate treated mixture

B. van Raij; J. A. Quaggio; N. M. da Silva

1986-01-01

16

Leaching of nitrate, calcium and magnesium under maize cultivation on an oxisol in Togo  

Microsoft Academic Search

In tropical regions, crop yields generally decrease with time, partly due to a decline in the levels of exchangeable bases linked to acidification of the upper layers of the soil. Nitrogen, calcium and magnesium balances were studied on an oxisol in southern Togo under continuous maize cropping with mineral fertilization and crop residue return, by measuring inputs and outputs.

R. Poss; H. Saragoni

1992-01-01

17

Calcium and magnesium dietary intakes and plasma and milk concentrations of Nepalese lactating women13  

Microsoft Academic Search

ABSTRACF Dietary calcium and magnesium intakes of 26 Nepalese lactating women were determined from analysis of 24-h duplicate food and beverage composites. In addition, blood, urine, and milk samples were collected. The mean Ca intake ofthese Nepalese mothers, 482 249 mg\\/d, was less than halfthat ofAmerican lactating women yet the Ca concentration ofthe milk was similar for the two

Phylis B Moser; Robert D Reynolds; Suniti Acharya; M Pat Howard; Mark B Andon

18

Simultaneous determination of calcium and magnesium in water using artificial neural network spectro-photometric method  

NASA Astrophysics Data System (ADS)

A new analytical method using Back-Propagation (BP) artificial neural networks and spectrophotometry for simultaneous determination of calcium and magnesium in tap water, the Yellow River water and seawater is established. By condition experiment, the optimum analytical conditions for calcium, magnesium and Arsenazo (III) color reactions are obtained. Levenberg-Marquart (L-M) algorithm is used for calculation in BP neural network. The topological structure of three-layer BP ANN network architecture is chosen as 11-10-2 (nodes). The initial value of gradient coefficient ? is fixed at 0.001 and the increase factor and reduction factor of ? take the default values of the system. The data are processed by computers with our own programs written in MATLAB 7.0. The relative standard deviations of the calculated results for calcium and magnesium are 2.31% and 2.14%, respectively. The results of standard addition method show that the recoveries of calcium and magnesium are 103.6% and 100.8% in the tap water, 103.2% and 96.6% in the Yellow River water (Lijin district of Shandong Province), and 98.8%-103.3% and 98.43%-103.4% in seawater from Jiaozhou Bay of Qingdao. It is found that 14 common cations and anions do not interfere with the determination of calcium and magnesium under the optimum experimental conditions. The comparative experiments do not show any obvious difference between the results obtained by this new method and those obtained by the classical complexometric titration method in seawater medium. This method exhibits good reproducibility and high accuracy in the determination of calcium and magnesium and can be used for the simultaneous determination of Ca2+ and Mg2+ in tap water and natural water.

Ji, Hongwei; Li, Shuang; Xin, Huizhen; Cao, Hengxia

2010-09-01

19

The initial phases of calcium and magnesium phosphates precipitated from solutions of high to medium concentrations  

NASA Astrophysics Data System (ADS)

The precipitation of calcium and magnesium phosphates is performed at 25C by mixing solutions of ammonium phosphate and solutions of calcium and magnesium chlorides under the condition [ P] = [ Ca] + [ Mg] in large pH intervals. Before any nucleation the phosphate concentration ranges from 0.50M to 0.01M. The phases first precipitated are CaHPO 42H 2O (brushite), CaHPO 4 (monetite), Ca 3(PO 4) 2 xH 2O (amorphous calcium phosphate), MgNH 4PO 46H 2O (struvite), and MgHPO 43H 2O (newberyite). The precipitation fields of each phase are determined and discussed as a function of pH, composition and supersaturation. The solutions are even supersaturated with respect to several other calcium phosphates but they never occur first even if their supersaturation is the highest.

Abbona, F.; Madsen, H. E. Lundager; Boistelle, R.

1986-04-01

20

A rapid method for the estimation of calcium and magnesium carbonates in limestones, dolomite and other calcareous materials  

Microsoft Academic Search

Summary Calcium and magnesium carbonates are determined in minerals by dissolving the sample in ammonium chloride solution and subsequent chelatometric titration. Iron and aluminium are dissolved, it any, in traces only.

Suresh Singh; Kali Prasad Gupta

1964-01-01

21

Rate of sulfur dioxide oxidation in aqueous suspensions of calcium and magnesium carbonates  

Microsoft Academic Search

Determinations of the quantitative dependence of the rate of sulfur dioxide oxidation in aqueous suspensions of calcium and magnesium carbontes on the temperature, oxygen concentration in the gas, rate of mass transfer in the liquid and gaseous phases, and the presence of catalytic additives showed that increase of the temperature from 40 to 80°C in the bubbling regime (w\\/sub g\\/

E. A. Orlov; B. A. Kopylev; N. N. Treushchenko; G. V. Belchenko

1980-01-01

22

Dissolved Calcium and Magnesium Carbonates Promote Arsenate Release From Ferrihydrite in Flow Systems  

Microsoft Academic Search

Field data from water systems around the world have shown that arsenic can reach toxic concentrations in dynamic groundwater systems. This is generally in contrast to analogous static systems at circumneutral pH, where arsenic is strongly retained by sorption to iron (hydr)oxides. Our research examines the effect of calcium and magnesium carbonates on As(V) mobility. In both dynamic flow and

S. L. Saalfield; B. C. Bostick

2007-01-01

23

Complexometric titration of the sum of calcium and magnesium using aluminon as metal indicator  

Microsoft Academic Search

Calcium and magnesium were estimated separately and in a mixture with EDTA (Titriplex III) using aluminon as metal indicator. Methylene blue is used for screening the yellow colour at the end point. The estimation should be carried out in theph range 8.59.9. Ammonia-ammonium chloride buffer was required for the estimation. Total hardness for a number of water samples was also

Phatik Kundu

1963-01-01

24

Simultaneous determination of calcium and magnesium by derivative spectrophotometry in pharmaceutical products  

NASA Astrophysics Data System (ADS)

First- and second-derivative spectrophotometric methods for the simultaneous determination of calcium and magnesium in their mixtures are described. The methods are based on the colored complexes formed by calcium and magnesium with bromopyrogallol red in presence of Tween 80 as a surfactant. The zero-crossing method has been utilized to measure the first- and second-derivative value of the derivative spectrum. Calcium (0.8-4.8 ?g ml -1) is determined in the presence of magnesium (0.5-3.5 ?g ml -1) at the pH 10 and vice versa at zero-crossing wavelengths of 544.5 and 570 nm in the first-derivative procedure and 574 and 531 nm in the second-derivative procedure, respectively. The detection limits achieved were 0.0575 ?g ml -1 of calcium and 0.03 ?g ml -1 of magnesium. The relative standard deviations were in all instances less than 2%. The proposed method has been applied to the simultaneous determination of calcium and magnesium in different samples: commercial multivitamin, human serum and drinking water where excellent agreement between reported and obtained results was achieved.

Benamor, M.; Aguerssif, N.

2008-02-01

25

Improved methods for reducing calcium and magnesium concentrations in tissue culture medium: Application to studies of lymphoblast proliferation in vitro  

Microsoft Academic Search

SummaryWe have compared several methods for reducing calcium and magnesium concentrations in tissue culture medium, with the objective\\u000a of producing selective deficiency effects on the growth of mouse (L5178Y) and human (P1R) lymphoblasts. In experiments in\\u000a which calcium- and magnesium-free McCoys medium was supplemented with 15% horse or fetal calf serum, enough calcium and\\u000a magnesium was provided by serum to

James K. Brennan; James Mansky; Geraldine Roberts; Marshall A. Lichtman

1975-01-01

26

Nephrolithiasis in a neonate with transient renal wasting of calcium and magnesium.  

PubMed

Following an uneventful full-term pregnancy, a 3-day-old girl presented with a focal seizure. Serological evaluation revealed hypomagnesemia and hypocalcemia. Renal ultrasonography performed because of hematuria showed bilateral nephrolithiasis. Renal wasting of calcium and magnesium was detected and urine citrate excretion was low. The hypocalcemia was refractory to calcium therapy, but responded briskly to magnesium supplementation. After 8 weeks of treatment with magnesium and calcium supplementation plus potassium citrate, the hypomagnesemia and hypocalcemia normalized spontaneously, as did the urinary calcium, magnesium, and citrate excretion. We speculate that our patient had a transient tubular defect in the thick ascending loop of Henle. PMID:12042901

Stoll, Matthew L; Listman, James A

2002-05-01

27

Calcium and Magnesium Absorption from the Colon and Rectum Are Increased in Rats Fed Fructooligosaccharides1  

Microsoft Academic Search

ABSTRACT We,investigated,the,effects,of,fruc- tooligosaccharides on the absorption of calcium, mag nesium,and water from,the colon and rectum,of rats fed a control diet or the control diet containing,50 g fruc- tooligosaccharides\\/kg.,Chromium-mordanted,cellulose was,used,as an unabsorbable,marker,to calculate,ap parent absorption,of calcium,and magnesium.,There was a positive correlation (r = 0.982, P < 0.001 in rats fed the control diet and r = 0.975, P < 0.001 in

ATSUTANE OHTA; MASAKO OHTSUKI; SEGO BABA; TAKASHI ADACHI

28

Effects of dietary vitamin D on calcium and magnesium levels in mice with abnormal calcium metabolism  

SciTech Connect

In previous studies vitamin D has been used to induce cardiac calcium overload in laboratory animals. Interrelationships between calcium and magnesium metabolism are also documented. The authors have investigated the effect of varying vitamin D in the diet on calcium and magnesium levels in plasma, kidney and heart of DBA mice which exhibit genetic abnormalities in cardiac calcium metabolism. Weanling DBA mice were maintained for 28 days on an AIN-76 diet containing either 1,000 I.U. of vitamin D{sub 3} per kg of diet (control); 4,000 I.U. of vitamin D{sub 3} per kg of diet; or no vitamin D. When compared to controls, supplemented animals showed significantly higher plasma magnesium, kidney calcium and kidney magnesium levels; animals receiving the vitamin D-deficient diet exhibited increases in cardiac calcium levels. The authors results support previous findings that vitamin D deficiency increases cardiac calcium uptake and suggest a possible role of vitamin D in magnesium metabolism.

Spurlock, B.G.; West, W.L.; Knight, E.M. (Howard Univ., Washington, DC (United States))

1991-03-11

29

Thyroxine-induced stimulation of hepatic cell transport of calcium and magnesium  

PubMed Central

The effect of L-thyroxine on the bidirectional transport of calcium and magnesium in rat liver was assessed in vitro. An increase of 34% in the fractional coefficient for calcium influx was observed 24 hr after the administration of 500 ?g of thyroxine. Chronic treatment with thyroxine for 1 and 3 wk at a dose of 750 ?g/wk resulted in increases in calcium influx of 57 and 51%, respectively. Calcium efflux was increased irregularly, by 14-26%. Magnesium transport measured in a similar system was not altered by 24 or 48 hr of treatment with thyroxine, but continuation of treatment for 1-3 wk resulted in increases in magnesium influx of 47-49%. Magnesium efflux was not significantly affected. Neither increased cellular binding of divalent cations nor enhanced protein synthesis could be incriminated in the stimulatory effect of thyroxine on divalent cation transport. Actinomycin-D and D,L-ethionine, inhibitors of protein synthesis, stimulated calcium and magnesium transport in liver independently of the effects of thyroxine. These data present the possibility that certain actions of thyroid hormone may be mediated or modulated by associated, direct changes in the cellular transport and intracellular concentrations of divalent cations.

Wallach, Stanley; Bellavia, J. V.; Gamponia, P. J.; Bristrim, P.

1972-01-01

30

Calcium and Magnesium Prophylaxis for Oxaliplatin-Related Neurotoxicity: Is It a Trade-off Between Drug Efficacy and Toxicity?  

PubMed Central

Oxaliplatin-based chemotherapy regimens are the current standard treatment in the management of colorectal cancer. Neurotoxicity is the major cause of treatment delay, dose reduction, and cessation of oxaliplatin. Evidence regarding the role of calcium and magnesium prophylaxis to prevent oxaliplatin-related neurotoxicity is conflicting and further randomized data are needed to answer this question accurately. The purpose of this paper is to provide a critical overview of various studies that have been conducted so far to evaluate the preventative role of calcium and magnesium prophylaxis against oxaliplatin-related neurotoxicity.

2011-01-01

31

STUDYING THE EFFECTS OF CALCIUM AND MAGNESIUM ON SIZE-DISTRIBUTED NITRATE AND AMMONIUM WITH EQUISOLV II. (R823186)  

EPA Science Inventory

Abstract A chemical equilibrium code was improved and used to show that calcium and magnesium have a large yet different effect on the aerosol size distribution in different regions of Los Angeles. In the code, a new technique of solving individual equilibrium equation...

32

Calcium and magnesium cations enhance the adhesion of motile and nonmotile pseudomonas aeruginosa on alginate films.  

PubMed

We investigated the impact of calcium and magnesium ions on the deposition kinetics of flagellated and nonflagellated Pseudomonas aeruginosa onto an alginate conditioning film in a radial stagnation point flow system. The bacterial deposition/adhesion behavior was related to structural changes of the alginate film in the presence of the divalent cations. Our results showed that adhesion of nonmotile bacteria was governed by cation bridging interactions between high-affinity sites at the bacterial surface and either clean or alginate-conditioned substrate surfaces. For motile bacteria, the adhesion onto clean quartz was governed by electrostatic interactions while adhesion onto alginate-conditioned quartz was dependent on the structure and viscoelastic properties of the alginate film in the presence of calcium or magnesium. We demonstrate that bacterial adhesion behavior is governed both by the effects of divalent cations on the surface properties of the bacteria and the substrate and by the type of specific interactions occurring between these two surfaces. PMID:18302437

Kerchove, Alexis J de; Elimelech, Menachem

2008-04-01

33

Sensitive methods for the titrimetric micro-determination of biological calcium and magnesium  

PubMed Central

New reagents containing high concentrations of urea are developed for micro-titration of calcium and magnesium, with ethylenediamine tetra-acetic acid (E.D.T.A.) as titrant and Corinth Ca (Plasmocorinth B) as indicator. Magnesium is determined as the difference between calcium plus magnesium and calcium. Quantitative aspects are studied, and accurate titration of untreated serum or urine is believed to be possible; precision is satisfactory. The methods are simple, robust, and suitable for routine use. Normal ranges are established for serum from blood donors of each sex. The mean serum calcium level for women is found to be lower than for men, while the mean magnesium contents are approximately the same. The latter appear to be somewhat lower than values found by flame emission spectrophotometry; in very good agreement with a mean value for plasma obtained by flame absorption spectrophotometry; and intermediate when compared with the values obtained by two other titrimetric procedures.

Beale, R. N.; Bostrom, J. O.

1963-01-01

34

[Forensic value of phenobarbital, calcium and magnesium determination in vitreous humor].  

PubMed

The concentrations of phenobarbital, magnesium and total calcium vitreous humor obtained postmortem from sheep receiving phenobarbital, were investigated. Phenobarbital, 20 mg/kg bw was administered i.v. Two hours later the animals were killed. The vitreous humor from one eye was obtained immediately. The vitreous human from the second eye was obtained after 3 days storage of the head at 22 degrees C. The levels of phenobarbital were determined ba EMIT, calcium and magnesium levels by complexometric titration. The results showed a significant increase of the phenobarbital and magnesium concentrations after the postmortem interval. It appears from these data that the phenobarbital and also magnesium concentrations in vitreous humor can be useful in the evaluation of the time of death approximately in phenobarbital intoxications. PMID:1580732

Balabanova, S; Gras, V

1992-01-01

35

[Simultaneous determination of calcium and magnesium by calculative spectrophotometric complexometric titration].  

PubMed

A new spectrophotometric complexometric titration method coupled with chemometrics for the determination of mixtures of metal ions has been developed. In the method described here, the titrant is a mixture of EDTA and two indicators. In the process of titration, both the volumetric addition of titrant and the progress of titration reaction can be characterized simultaneously by chemometric calculation with the absorption spectra, and then the titration curves can be obtained. With the titration curves, a matrix equation can be established, and thus the concentration of each component in the mixture of metal ions can be calculated with principal component regression. The method only needs the information of absorption spectra to obtain the analytical results, and is free of volumetric measurements. So the method is simple, convenient and precise, and has been applied to the simultaneous determination of mixtures of calcium and magnesium using malachite green and Cu-PAN as indicators with satisfactory results. PMID:18330321

Liao, Li-fu; Xiao, Xi-lin; Yang, Ming-hui; Yang, Jing

2007-12-01

36

The final phases of calcium and magnesium phosphates precipitated from solutions of high to medium concentration  

NASA Astrophysics Data System (ADS)

The phases of calcium and magnesium phosphates, which are obtained by evolution at 25C of the first precipitates in their mother solutions, are described in terms of pH and composition of solutions. The initial conditions were: 0.050M ? [P] ? 0.500M; [P] = [Ca] + [Mg]; 0 ? [Mg]/[Ca] ? 1. The most abundant final phases are brushite, CaHPO 42H 2O; monetite, CaHPO 4; newberyite, MgHPO 43H 2O and struvite, MgNH 4PO 46H 2O. At low concentration whitlockite, Ca 9MgH(PO 4) 7, occurs with the amorphous phase previously precipitated, Ca 3(PO 4) 2nH 2O. The conditions for stability are discussed and the changes observed are interpreted.

Abbona, Francesco; Lundager Madsen, Hans Erik; Boistelle, Roland

1988-07-01

37

Continental weathering following a Cryogenian glaciation: Evidence from calcium and magnesium isotopes  

NASA Astrophysics Data System (ADS)

A marked ocean acidification event and elevated atmospheric carbon dioxide concentrations following the extreme environmental conditions of the younger Cryogenian glaciation have been inferred from boron isotope measurements. Calcium and magnesium isotope analyses offer additional insights into the processes occurring during this time. Data from Neoproterozoic sections in Namibia indicate that following the end of glaciation the continental weathering flux transitioned from being of mixed carbonate and silicate character to a silicate-dominated one. Combined with the effects of primary dolomite formation in the cap dolostones, this caused the ocean to depart from a state of acidification and return to higher pH after climatic amelioration. Differences in the magnitude of stratigraphic isotopic changes across the continental margin of the southern Congo craton shelf point to local influences modifying and amplifying the global signal, which need to be considered in order to avoid overestimation of the worldwide chemical weathering flux.

Kasemann, Simone A.; Pogge von Strandmann, Philip A. E.; Prave, Anthony R.; Fallick, Anthony E.; Elliott, Tim; Hoffmann, Karl-Heinz

2014-06-01

38

Factors modulating the pH at which calcium and magnesium phosphates precipitate from human urine.  

PubMed

The factors controlling the rate at which crystalline bacterial biofilms develop on indwelling bladder catheters are poorly understood. It is known that normally the pH of voided urine (pHv) is lower than the pH at which calcium and magnesium phosphates come out of urine solution (pHn). In patients who develop infections with urease producing bacteria, however, the pHv rises above the pHn and precipitation of the phosphates occurs in the urine and the biofilm. The aim of this study was to examine ways of manipulating the pHn of urine so that more of its calcium and magnesium remain in solution under alkaline conditions. The experimental data show that pHn can be elevated by decreasing the calcium, magnesium and phosphate concentrations. Increasing the fluid intake of a human subject so that the urinary calcium fell from 120 mg/l to 25 mg/l, for example, resulted in the pHn increasing from 6.48 to 8.22. The addition of citrate to urine also produced a rise in the pHn. The daily consumption of 500 ml of fresh orange juice increased urinary citrate concentrations from 0.35 to around 1.21 mg/ml and the pHn rose from 7.24 to 8.2. The pHn of urine is thus a highly variable parameter. It can be manipulated by controlling the urinary concentrations of magnesium, calcium, phosphate and citrate ions. We suggest that increasing fluid intake with citrate containing drinks would reduce the extent of encrustation on catheters in patients infected with urease producing bacteria. PMID:15981006

Suller, M T E; Anthony, V J; Mathur, S; Feneley, R C L; Greenman, J; Stickler, D J

2005-08-01

39

Lack of blood pressure effect with calcium and magnesium supplementation in adults with high-normal blood pressure  

Microsoft Academic Search

Phase I of the Trials of Hypertension Prevention (TOHP) was a randomized, multicenter investigation that included double-blind, placebo-controlled testing of calcium and magnesium supplementation among 698 healthy adults (10.5% blacks and 31% women) aged 30 to 54 years with high-normal diastolic blood pressure (DBP) (80 to 89 mm Hg). Very high compliance (94 to 96% by pill counts) with daily

Monica E. Yamamoto; William B. Applegate; Michael J. Klag; Nemat O. Borhani; Jerome D. Cohen; Kent A. Kirchner; Edward Lakatos; Frank M. Sacks; James O. Taylor; Charles H. Hennekens

1995-01-01

40

Calcium and magnesium levels in isolated mitochondria from human cardiac biopsies.  

PubMed

A non-enzymatic method is presented for isolating mitochondria from small-sized human cardiac samples, including ventricular needle biopsies of 15-25 mg of wet weight. Electron microscopy demonstrates that these fractions are rich in structurally well preserved mitochondria. Calcium and magnesium levels of fractions are determined by atomic absorption flame spectroscopy. Comparative analyses are made in similar fractions of the mouse ventricle. Calcium concentrations of mitocondria isolated in the presence of ruthenium red do not differ significantly between the human auricle and ventricle, averaging 61 nmol Ca/mg protein and 68 nmol Ca/mg protein, respectively. Mitochondrial calcium level is lower in the mouse ventricular fractions, averaging 7 nmol Ca/mg protein. Mitochondrial magnesium amounts to slightly less than 60% of the calcium levels in the human heart, while it exceeds the calcium level by more than 100 per cent in the mouse heart. There is no significant difference of mitochondrial calcium between normal auricles, and, auricles of patients with increased right atrial mean pressure and/or volume overload. PMID:7410123

Saetersdal, T; Engedal, H; Rli, J; Myklebust, R

1980-01-01

41

Effect of cold-setting calcium- and magnesium phosphate matrices on protein expression in osteoblastic cells.  

PubMed

Bone loss due to accidents or tissue diseases requires replacement of the structure by either autografts, allografts, or artificial materials. Reactive cements, which are based on calcium phosphate chemistry, are commonly used in nonload bearing areas such as the craniofacial region. Some of these materials are resorbed by the host under physiological conditions and replaced by bone. The aim of this study was to test different calcium and magnesium cement composites in vitro for their use as bone substitution material. Phase composition of calcium deficient hydroxyapatite (Ca(9) (PO(4) )(5) HPO(4) OH), brushite (CaHPO(4) 2H(2) O), and struvite (MgNH(4) PO(4) 6H(2) O) specimens has been determined by means of X-ray diffraction, and compressive strength was measured. Cell growth and activity of osteoblastic cells (MG 63) on the different surfaces was determined, and the expression of bone marker proteins was analyzed by western blotting. Cell activity normalized to cell number revealed higher activity of the osteoblasts on brushite and struvite when compared to hydroxyapatite and also the expression of osteoblastic marker proteins was highest on brushite scaffolds. While brushite sets under acidic conditions, formation of struvite occurs under physiological pH, similar to hydroxyapatite cements, providing the possibility of additional modifications with proteins or other active components. PMID:21210513

Ewald, Andrea; Helmschrott, Kerstin; Knebl, Georg; Mehrban, Nazia; Grover, Liam M; Gbureck, Uwe

2011-02-01

42

In vivo degradation of low temperature calcium and magnesium phosphate ceramics in a heterotopic model.  

PubMed

Bone replacement using synthetic and degradable materials is desirable in various clinical conditions. Most applied commercial materials are based on hydroxyapatite, which is not chemically degradable under physiological conditions. Here we report the effect of a long-term intramuscular implantation regime on the dissolution of various low temperature calcium and magnesium phosphate ceramics in vivo. The specimens were analysed by consecutive radiographs, micro-computed tomography scans, compressive strength testing, scanning electron microscopy and X-ray diffractometry. After 15months in vivo, the investigated materials brushite (CaHPO(4)2H(2)O), newberyite (MgHPO(4)3H(2)O), struvite (MgNH(4)PO(4)6H(2)O) and hydroxyapatite (Ca(9)(PO(4))(5)HPO(4)OH) showed significant differences regarding changes of their characteristics. Struvite presented the highest loss of mechanical performance (95%), followed by newberyite (67%) and brushite (41%). This was accompanied by both a distinct extent of cement dissolution as well as changes of the phase composition of the retrieved cement implants. While the secondary phosphate phases (brushite, newberyite, struvite) completely dissolved, re-precipitates of whitlockite and octacalcium phosphate were formed in either particulate or whisker-like morphology. Furthermore, for the first time the possibility of a macropore-free volume degradation mechanism of bioceramics was demonstrated. PMID:21658480

Klammert, Uwe; Ignatius, Anita; Wolfram, Uwe; Reuther, Tobias; Gbureck, Uwe

2011-09-01

43

Dietary calcium and magnesium intakes and the risk of type 2 diabetes: the Shanghai Women's Health Study123  

PubMed Central

Background: Diet plays a key role in the development of type 2 diabetes (T2D), but little is known about the contributions of specific nutrients in populations in which dietary patterns differ from Western populations. Objective: We examined associations between calcium and magnesium intakes and the risk of T2D in a Chinese population. Design: We used data from a population-based, prospective study of 64,191 women who were free of T2D or other chronic diseases at study recruitment and were living in urban Shanghai, China. Dietary intake, physical activity, and anthropometric measurements were assessed through in-person interviews. A Cox regression model was used to evaluate the association of the exposures under study with the risk of T2D. Results: An inverse association between calcium and magnesium intakes and T2D risk was observed. The relative risks for the lowest to the highest quintiles of calcium intake were 1.00, 0.82, 0.73, 0.67, and 0.74 (P for trend < 0.001), and for magnesium they were 1.00, 0.84, 0.84, 0.79, and 0.86 (P for trend < 0.001). Milk intake was also inversely associated with the risk of T2D. Conclusion: Our data suggest that calcium and magnesium intakes may protect against the development of T2D in this population.

Villegas, Raquel; Gao, Yu-Tang; Dai, Qi; Yang, Gong; Cai, Hui; Li, Honglan; Zheng, Wei; Shu, Xiao Ou

2009-01-01

44

Calcium and magnesium in exocrine secretion--an X-ray microanalytical study  

SciTech Connect

Calcium and magnesium distribution in mammalian exocrine glands under resting, stimulated and pathological conditions was investigated by X-ray microanalysis of thick and ultrathin cryosections. Ultrathin sections were cut from tissue frozen in the presence of a polymer cryoprotectant, dextran. The effect of this treatment on isolated rabbit pancreas. Dextran caused a disturbance in water and ion transport, partly due to an osmotic effect and the impermeability of the pancreatic epithelium to dextran; this does, however, not necessarily invalidate intracellular measurements on frozen-dried sections. Cholinergic stimulation of the rat pancreas caused a change of Ca distribution from the basal to the apical part of the cell; this may be a component of the secretory Ca flux. Kinetic considerations make a significant Ca movement via the ER-Golgi endomembrane space less likely. The mitochondrial Ca concentration is low, and not significantly changed by cholinergic stimulation. X-ray microanalysis was carried out on submandibular glands of rats after chronic treatment with reserpin and/or isoproterenol (an animal model for cystic fibrosis, CF). The acinar cells had elevated Mg and Ca and lowered K concentrations. Analysis of ultrathin cryosections showed high levels of Ca and Mg in secretory granules, mucus globules and the ER. Ca and Mg in the ER may be transported intracellularly with secretory proteins to secretion granules or mucus globules. The decrease in cell K may be due to efflux of K caused by elevated cytoplasmic Ca levels. A similar decrease in cell K was caused by incubation of rat salivary glands with diluted serum from CF patients, a treatment which has been reported to mimic the effect of a rise in cytoplasmic Ca.

Roomans, G.M.; Barnard, T.

1982-01-01

45

Fast Pressure Jumps Can Perturb Calcium and Magnesium Binding to Troponin C F29W  

PubMed Central

We have used rapid pressure jump and stopped-flow fluorimetry to investigate calcium and magnesium binding to F29W chicken skeletal troponin C. Increased pressure perturbed calcium binding to the N-terminal sites in the presence and absence of magnesium and provided an estimate for the volume change upon calcium binding (-12 mL.mol-1). We observed a biphasic response to a pressure change which was characterized by fast and slow reciprocal relaxation times of the order 1000 s-1 and 100 s-1. Between pCa 8-5.4 and at troponin C concentrations of 8-28 ?M, the slow relaxation times were invariant indicating that a protein isomerization was rate-limiting. The fast event was only detected over a very narrow pCa range (5.6-5.4). We have devised a model based on a Monod-Wyman-Changeux cooperative mechanism with volume changes of -9 and +6 mL/mol for the calcium binding to the regulatory sites and closed to open protein isomerization steps respectively. In the absence of magnesium, we discovered that calcium binding to the C-terminal sites could be detected, despite their position distal to the calcium sensitive tryptophan, with a volume change of +25 mL/mol. We used this novel observation to measure competitive magnesium binding to the C-terminal sites and deduced an affinity in the range 200 - 300 ?M (and a volume change of +35 mL/mol). This affinity is an order of magnitude tighter than equilibrium fluorescence data suggest based on a model of direct competitive binding. Magnesium thus indirectly modulates binding to the N-terminal sites, which may act as a fine-tuning mechanism in vivo.

Pearson, David S.; Swartz, Darl R.; Geeves, Michael A.

2009-01-01

46

Continuous on-line feedback based flow titrations. Complexometric titrations of calcium and magnesium.  

PubMed

The methodology of continuous feedback-based flow titrations and the principle of compensating errors [Anal. Chem. 72 (2000) 4713; Anal. Chim. Acta 435 (2001) 289] were applied to the determination of calcium and magnesium ions with EDTA. The flow of the titrant, EDTA, varied linearly in response to a controller output voltage while the total flow (F(T), the sum of the metal ion sample flow and the titrant flow) was held constant. The sample was pre-doped with a metal ion indicator; the status of the indicator color in the mixed stream was monitored by an optical detector and was used for governing the controller output as well as for interpreting the results of the titrations. The titrant flow initially ramped upward linearly. As a change in the color corresponding to the equivalence point was sensed by the detector, the controller output (instantaneous value V(H)) reversed its ramp direction, thus decreasing the titrant flow linearly at the same ramp rate. When the predefined absorbance corresponding to the equivalence point was sensed again, the controller voltage (instantaneous value V(L)) was ramped in reverse once more, going upward. Because of the lag time between a change in the controller output and its effect being sensed by the detector, the controller voltage corresponding to the actual equivalence point was the average of V(H) and V(L). Continuous sensor-governed operation of the controller resulted in a triangular waveform. The mean of this waveform during any cycle gives the equivalence point controller voltage V(E). This principle allowed true titrations with good reproducibility (0.2-0.7% R.S.D.) and throughput (33-42 s per titration). PMID:18969033

Jo, Kyoo Dong; Dasgupta, Purnendu K

2003-05-28

47

Determination of sodium, potassium, calcium and magnesium content in milk products by flame atomic absorption spectrometry (FAAS): A joint ISO\\/IDF collaborative study  

Microsoft Academic Search

A flame atomic absorption spectrometry method to determine sodium, potassium, calcium and magnesium content in milk products using dry ashing or wet digestion was evaluated in an international collaborative trial. The study involved 18 participants from six countries. The method was tested on a total of eight milk products: whey protein concentrate, whole milk powder, two processed cheeses, whey powder,

Laurent Nol; Michael Carl; Christelle Vastel; Thierry Gurin

2008-01-01

48

Measurement and calculation of the Stark-broadening parameters for the resonance lines of singly ionized calcium and magnesium.  

NASA Technical Reports Server (NTRS)

The electron-impact-broadened profiles of the resonance lines of singly ionized calcium and magnesium have been measured using an electromagnetically driven shock tube and a rapid-scanning Fabry-Perot spectrometer. For an electron density of 10 to the 17th power per cu cm and a temperature of 19,000 K, we found the Lorentzian half-width of the Ca+ line to be 0.086 A plus or minus 10% and of the Mg+ line to be 0.044 A plus or minus 10%. Using the quantum-mechanical theory of Barnes and Peach and our semiclassical calculation for the calcium lines, we found that the temperature dependence of the theoretical curves is close to that measured, although both theories predict actual values which are somewhat large.

Jones, W. W.; Sanchez, A.; Greig, J. R.; Griem, H. R.

1972-01-01

49

TRPM7 is involved in angiotensin II induced cardiac fibrosis development by mediating calcium and magnesium influx.  

PubMed

Cardiac fibrosis is involved in a lot of cardiovascular pathological processes. Cardiac fibrosis can block conduction, cause hypoxia, strengthen myocardial stiffness, create electrical heterogeneity, and hamper systolic ejection, which is associated with the development of arrhythmia, heart failure and sudden cardiac death. Besides the initial stimulating factors, the cardiac fibroblasts (CFs) are the principal responsible cells in the fibrogenesis cascade of events. TRPM7, a member of the TRPM (Melastatin) subfamily, is a non-selective cation channel, which permeates both Ca(2+) and Mg(2+). Here we demonstrated TRPM7 expression in CFs, and 2-APB (TRPM7 inhibitor), inhibited Ang II-induced CTGF, ?-SMA expression and CFs proliferation. Besides, knocking down TRPM7 by shRNA, we proved that TRPM7 mediated both calcium and magnesium changes in cardiac fibroblasts which contribute to fibrosis progress. This study suggested that TRPM7 should play a pivotal role in cardiac fibroblast functions associated to cardiac fibrosis development. PMID:24680379

Yu, Yang; Chen, Shaorui; Xiao, Chuyao; Jia, Yanyan; Guo, Jinlei; Jiang, Jianmin; Liu, Peiqing

2014-05-01

50

Vitamin B6 depletion followed by repletion with animal- or plant-source diets and calcium and magnesium metabolism in young women1'2  

Microsoft Academic Search

An 84-98.4 study was conducted in young women to determine the effect ofvitamin B-6-defieient diets on calcium and magnesium metabolism. A vitamin B-6-defieient formula diet fed initially was followed by either animal- or plant- source protein food diets containing four increasing amounts of vitamin B-6. Calcium balance was negative during vitamin B-6 depletion. Serum calcium was higher and calcium balance

Judith R Turniund; Antoinette A Betschart; Michael Liebman; Mary J Kretsch; Howerde E Sauberlich

51

Effect of calcium and magnesium on the antimicrobial action of enterocin LR/6 produced by Enterococcus faecium LR/6.  

PubMed

Enterococci are well-known producers of antimicrobial peptides (enterocins) that possess potential as biopreservatives in food. In this study, divalent cations and release of intracellular potassium were used to assess the mechanism of interaction and killing of enterocin LR/6 produced by Enterococcus faecium LR/6 on three target Gram-positive and Gram-negative bacteria, namely Micrococcus luteus, Enterococcus sp. strain LR/3 and Escherichia coli K-12. Whilst treatment with enterocin LR/6 in all cases led to a significant loss of viability, suggesting a bactericidal mode of action, E. coli K-12 showed better tolerance than the other two strains. Bacteriocins have generally been reported to create pores in the membrane of sensitive cells and this function is diminished by divalent cations. In this study it was shown that Ca(2+) and Mg(2+) markedly improved the viability of enterocin LR/6-treated cells in a concentration-dependent manner. K(+) release as a sign of membrane leakiness was higher in M. luteus compared with the other two test strains. In agreement with the viability response, pre-exposure to Ca(2+) and Mg(2+) substantially reduced the amount of K(+) leakage by M. luteus and Enterococcus sp.; in the case of E. coli K-12, no leakage of K(+) was recorded. These results suggest that enterocin LR/6, which possesses good antibacterial potential, may not be very effective as a preservative in foods containing high concentrations of calcium and magnesium. PMID:21411293

Kumar, Manoj; Srivastava, Sheela

2011-06-01

52

Effect of Metal Chelators on ?-Secretase Indicates That Calcium and Magnesium Ions Facilitate Cleavage of Alzheimer Amyloid Precursor Substrate.  

PubMed

Gamma-secretase is involved in the production of A? amyloid peptides. It cleaves the transmembrane domain of the amyloid precursor protein (APP) at alternative sites to produce A? and the APP intracellular domain (AICD). Metal ions play an important role in A? aggregation and metabolism, thus metal chelators and ligands represent potential therapeutic agents for AD treatment. A direct effect of metal chelators on ?-secretase has not yet been investigated. The authors used an in vitro? ?-secretase assay consisting of cleavage of APP C100-3XFLAG by endogenous ?-secretase from rodent brains and human neuroblastoma SH-SY5Y, and detected AICD production by western blotting. Adding metalloprotease inhibitors to the reaction showed that clioquinol, phosphoramidon, and zinc metalloprotease inhibitors had no significant effect on ?-secretase activity. In contrast, phenanthroline, EDTA, and EGTA markedly decreased ?-secretase activity that could be restored by adding back calcium and magnesium ions. Mg(2+) stabilized a 1,000?kDa presenilin 1 complex through blue native gel electrophoresis and size-exclusion chromatography. Data suggest that Ca(2+) and Mg(2+) stabilize ?-secretase and enhance its activity. PMID:21253550

Ho, Michael; Hoke, David E; Chua, Yee Jia; Li, Qiao-Xin; Culvenor, Janetta G; Masters, Colin; White, Anthony R; Evin, Genevive

2010-01-01

53

Flow injection flame atomic absorption spectrometry for slurry atomization. Determination of iron, calcium and magnesium in samples with high silica content.  

PubMed

A study on the use of slurries in flame atomic absorption spectrometry is reported. Samples with a very high silica content are ground and then slurried in a solution containing 2% hydrochloric and 3% v/v hydrofluoric acids. The suspensions are prepared in the 0.01-1% m/v range and introduced into the flame by means of a simple flow injection manifold. Relative standard deviations for the measurements of iron, calcium and magnesium in diatomaceous earth samples are in the 1.5-2.8, 2.2-5.3 and 2.8-5.0% ranges, respectively. To avoid the use of suspensions prepared with a very low percentage of solid sample and to improve the reproducibility, an on-line dilution manifold is tried. The use of an easy-to-construct variable volume dilution chamber allows the on-line dilution of the slurries, thus permitting the determination of calcium and magnesium over a wide range of concentrations. Calibration is performed using aqueous standards. The experimental conditions, optimized for the determination of iron, calcium and magnesium in diatomaceous earth samples, can also be applied to other silica-based materials, as is shown by the analysis of several standard reference materials. PMID:18965839

Garca, I L; Cortz, J A; Crdoba, M H

1993-11-01

54

Alterations of serum zinc, copper, manganese, iron, calcium, and magnesium concentrations and the complexity of interelement relations in patients with obsessive-compulsive disorder.  

PubMed

The purpose of the present study was to evaluate the status of serum trace elements: zinc, copper, manganese, iron, calcium, and magnesium concentrations in obsessive-compulsive disorder patients. Forty-eight obsessive-compulsive disorder patients and 48 healthy volunteers were included in this study. Patients were recruited from Bangabandhu Sheikh Mujib Medical University by random sampling. Serum trace element concentrations were determined using flame atomic absorption spectroscopy (for zinc, copper, iron, calcium, and magnesium) as well as graphite furnace atomic absorption spectroscopy (for manganese). Data were analyzed using independent t test, Pearson's correlation analysis, regression analysis, and ANOVA. Statistical analysis of these data showed a definite pattern of variation among certain elements in patients with obsessive-compulsive disorder compared to controls. In patients' serum, zinc, iron, and magnesium concentrations decreased significantly (p<0.05) compared to the controls. Serum manganese and calcium concentrations were significantly higher (p<0.05) in patients compared to the controls. These data showed a definite imbalance in the interelement relations in obsessive-compulsive disorder patients compared to controls and therefore suggest a disturbance in the element homeostasis. PMID:22383079

Shohag, Hasanuzzaman; Ullah, Ashik; Qusar, Shalahuddin; Rahman, Mustafizur; Hasnat, Abul

2012-09-01

55

Short term spatio-temporal variability of soil water-extractable calcium and magnesium after a low severity grassland fire in Lithuania.  

NASA Astrophysics Data System (ADS)

Fire has important impacts on soil nutrient spatio-temporal distribution (Outeiro et al., 2008). This impact depends on fire severity, topography of the burned area, type of soil and vegetation affected, and the meteorological conditions post-fire. Fire produces a complex mosaic of impacts in soil that can be extremely variable at small plot scale in the space and time. In order to assess and map such a heterogeneous distribution, the test of interpolation methods is fundamental to identify the best estimator and to have a better understanding of soil nutrients spatial distribution. The objective of this work is to identify the short-term spatial variability of water-extractable calcium and magnesium after a low severity grassland fire. The studied area is located near Vilnius (Lithuania) at 54 42' N, 25 08 E, 158 masl. Four days after the fire, it was designed in a burned area a plot with 400 m2 (20 x 20 m with 5 m space between sampling points). Twenty five samples from top soil (0-5 cm) were collected immediately after the fire (IAF), 2, 5, 7 and 9 months after the fire (a total of 125 in all sampling dates). The original data of water-extractable calcium and magnesium did not respected the Gaussian distribution, thus a neperian logarithm (ln) was applied in order to normalize data. Significant differences of water-extractable calcium and magnesium among sampling dates were carried out with the Anova One-way test using the ln data. In order to assess the spatial variability of water-extractable calcium and magnesium, we tested several interpolation methods as Ordinary Kriging (OK), Inverse Distance to a Weight (IDW) with the power of 1, 2, 3 and 4, Radial Basis Functions (RBF) - Inverse Multiquadratic (IMT), Multilog (MTG), Multiquadratic (MTQ) Natural Cubic Spline (NCS) and Thin Plate Spline (TPS) - and Local Polynomial (LP) with the power of 1 and 2. Interpolation tests were carried out with Ln data. The best interpolation method was assessed using the cross validation method. Cross-validation was obtained by taking each observation in turn out of the sample pool and estimating from the remaining ones. The errors produced (observed-predicted) are used to evaluate the performance of each method. With these data, the mean error (ME) and root mean square error (RMSE) were calculated. The best method was the one which had the lower RMSE (Pereira et al. in press). The results shown significant differences among sampling dates in the water-extractable calcium (F= 138.78, p< 0.001) and extractable magnesium (F= 160.66; p< 0.001). Water-extractable calcium and magnesium was high IAF decreasing until 7 months after the fire, rising in the last sampling date. Among the tested methods, the most accurate to interpolate the water-extractable calcium were: IAF-IDW1; 2 Months-IDW1; 5 months-OK; 7 Months-IDW4 and 9 Months-IDW3. In relation to water-extractable magnesium the best interpolation techniques were: IAF-IDW2; 2 Months-IDW1; 5 months- IDW3; 7 Months-TPS and 9 Months-IDW1. These results suggested that the spatial variability of these water-extractable is variable with the time. The causes of this variability will be discussed during the presentation. References Outeiro, L., Aspero, F., Ubeda, X. (2008) Geostatistical methods to study spatial variability of soil cation after a prescribed fire and rainfall. Catena, 74: 310-320. Pereira, P., Cerd, A., beda, X., Mataix-Solera, J. Arcenegui, V., Zavala, L. Modelling the impacts of wildfire on ash thickness in a short-term period, Land Degradation and Development, (In Press), DOI: 10.1002/ldr.2195

Pereira, Paulo; Martin, David

2014-05-01

56

The influence of calcium and magnesium in drinking water and diet on cardiovascular risk factors in individuals living in hard and soft water areas with differences in cardiovascular mortality  

Microsoft Academic Search

BACKGROUND: The role of water hardness as a risk factor for cardiovascular disease has been widely investigated and evaluated as regards regional differences in cardiovascular disease. This study was performed to evaluate the relation between calcium and magnesium in drinking water and diet and risk factors for cardiovascular disease in individuals living in hard and soft water areas with considerable

Christina Nerbrand; Lars Agrus; Ragnhild Arvidsson Lenner; Per Nyberg; Kurt Svrdsudd

2003-01-01

57

Stimulation of ovine placental transport of calcium and magnesium by mid-molecule fragments of human parathyroid hormone-related protein.  

PubMed

Perfusion in situ of the placenta of intact or previously parathyroidectomized fetal lambs has been used to assess the ability of three mid-molecule fragments of the human parathyroid hormone-related protein (PTHrP) molecule to stimulate the placental transport of calcium and magnesium. PTHrP(67-86 amide) was most effective but some activity was also shown by PTHrP(75-86 amide) and by PTHrP (75-84) in decreasing order. This placental action of PTHrP(67-86 amide) was rapid and could be observed using the placenta from an intact fetus, whereas it was necessary to use the placenta from a previously parathyroidectomized fetus to demonstrate stimulation of placental calcium transport by PTHrP(1-84). PTHrP(67-86 amide) may resemble the molecule that activates the placental calcium pump. PMID:2223059

Care, A D; Abbas, S K; Pickard, D W; Barri, M; Drinkhill, M; Findlay, J B; White, I R; Caple, I W

1990-07-01

58

THE BEHAVIOR OF ISOLATED HEARTS OF THE GRASSHOPPER, CHORTOPHAGA VIRIDIFASCIATA, AND THE MOTH, SAMIA WALKERI, IN SOLUTIONS WITH DIFFERENT CONCENTRATIONS OF SODIUM, POTASSIUM, CALCIUM, AND MAGNESIUM  

PubMed Central

1. The blood of Chortophaga viridifasciata was analyzed. The average concentrations of inorganic cations expressed as milligrams per cent are: sodium, 250.66; potassium, 13.52; calcium, 11.40; and magnesium, 51.15. The osmotic pressure of the blood at 0C. is 10.7 atmospheres. Protein and non-protein nitrogen, expressed as milligrams per cent, are 253.4 and 140.0, respectively. 2. The blood of Samia walkeri has an osmotic pressure of 13.36 atmospheres at 0C. Its protein nitrogen is 628.58, and its non-protein nitrogen, 441.20 milligrams per cent. 3. The effects of isotonic chloride solutions of sodium, potassium, calcium, and magnesium and of distilled water on the heart beat of these two species were determined. The heart of the grasshopper failed to beat in isotonic solutions of KCl, MgCl2, or in distilled water. For both insects, sodium was found to be the least toxic ion. In the case of the grasshopper, calcium ranks next in order. In the case of the moth, potassium ranks next after sodium and is followed by calcium and magnesium. 4. The ratio of sodium to potassium in milligrams per cent, necessary for maintaining the normal heart beat of Chortophaga viridifasciata is 3 to 1, but it may be increased to at least 34 to 1 without any appreciable effects. The ratio of potassium to calcium necessary for maintaining the normal heart beat of this insect is 1 to 1, and may be increased to as much as 3 to 1. 5. The ratio of sodium to potassium, in milligrams per cent, necessary for maintaining the normal heart beat of Samia walkeri was found to be equal to or to exceed 1 to 13.8. The sodium content may be increased so that the ratio of sodium to potassium is 34 to 1 without any toxic effects. The ratios of potassium to calcium required for normal heart beat in this insect may be 1 to 1, 2 to 1, or 3 to 1. 6. The hearts of the grasshoppers beat normally in isotonic solutions having an osmotic pressure of 10.7 atmospheres. They beat equally well in solutions having an osmotic pressure of 13.4 atmospheres. The hearts of the cynthia pupae beat normally in isotonic solutions having an osmotic pressure of 13.36 atmospheres. However, they also beat normally in solutions having an osmotic pressure of 10.02 atmospheres. Therefore, although the blood of the cynthia moth and of the grasshopper have different osmotic pressures, their hearts are tolerant to solutions having the same tonicity. Because of this, and since the ratios of potassium to calcium necessary for maintaining normal heart beats of both insects are the same, solutions favorable to the grasshopper may also be favorable to the cynthia moth.

Barsa, Mary C.

1954-01-01

59

The Levels of Calcium and Magnesium, and of Selected Trace Elements, in Whole Blood and Scalp Hair of Children with Growth Retardation  

PubMed Central

Objective Metals such as copper (Cu), zinc (Zn), iron (Fe) are essential for human beings. Chronic metabolic disturbances may result from an excess or deficiency of these metals. Ca and Mg are also nutrient elements and play an important role in biological systems. Thus, it is very important to check regularly trace elements concentration in the body. The purpose of this study was to measure the content of Fe, Cu, Zn, Ca and Mg in whole blood and hair of children with growth retardation compared to that of controls. Methods A quantitative elemental analysis of whole blood and scalp hair of children with constitutional growth retardation (n = 27) and matched controls (n = 21) was used to find out correlation and possible changes, between growth retardation and healthy controls. Atomic absorption spectrophotometric (AAS) analysis of quantitative method was used to determine iron, zinc, copper, calcium and magnesium levels of whole blood and scalp hair. Findings The whole blood levels of Fe and Zn were significantly lower in children with growth retardation (P<0.05), but there were no differences in Cu, Ca and Mg concentrations in whole blood between children with growth retardation and healthy controls. The hair levels of Fe, Zn, Ca and Mg were significantly lower in children with growth retardation when compared to that of controls (P<0.05). The Cu concentrations in the hair of children with growth retardation and healthy controls showed no significant differences (P>0.05). Conclusion The usefulness and significance of these elements in growth retardation should be discussed more detailed in the light of the most recent data.

Ozmen, Habibe; Akarsu, Saadet; Polat, Fatih; Cukurovali, Alaaddin

2013-01-01

60

Phase I drug-interaction study of effects of calcium and magnesium infusions on oxaliplatin pharmacokinetics and acute neurotoxicity in colorectal cancer patients  

PubMed Central

Background Calcium and magnesium (Ca/Mg) infusions have been suggested as an effective intervention for preventing oxaliplatin-induced neurotoxicity, but the effects of Ca/Mg infusions on oxaliplatin pharmacokinetics, motor nerve hyperexcitability and acute neurotoxicity symptoms are unclear. Methods In this double blind crossover study, colorectal cancer patients undergoing oxaliplatin-based chemotherapy were randomised to receive Ca/Mg (1g Ca Gluconate plus 1g MgSO4) on cycle 1 and placebo (vehicle alone) on cycle 2, or to receive the same treatments in the opposite sequence. Study endpoints included plasma pharmacokinetics of intact oxaliplatin and free platinum; electromyography (EMG) detection of abnormal spontaneous high-frequency motor unit action potential discharges; and patient-reported acute neurotoxicity symptoms and their preferred study treatment for reducing these symptoms. Results Nineteen of 20 enrolled patients completed the study. Plasma pharmacokinetics of intact oxaliplatin and free platinum were similar when oxaliplatin was given with Ca/Mg or placebo (ratio of geometric means of AUC0-t with Ca/Mg or placebo: intact oxaliplatin, 0.95 (90% CI, 0.90 1.01); free platinum, 0.99 (90% CI, 0.94 1.05)). EMG motor nerve hyperexcitability scores were similar with Ca/Mg and placebo (mean difference in EMG score between Ca/Mg and placebo: -0.3 (95% CI, -2.2 1.6)). Patient-reported acute neurotoxicity symptoms were similar in frequency with Ca/Mg and placebo. For reducing neurotoxic symptoms, fewer patients preferred Ca/Mg than placebo or neither treatment (26% versus 74%; P<0.01). Conclusions Ca/Mg infusions do not alter the clinical pharmacokinetics of oxaliplatin and do not seem to reduce its acute neurotoxicity. Trial registration Trial registration identifier ACTRN12611000738921

2013-01-01

61

Kinetic characterization and gene expression of adenosine deaminase in intact trophozoites of Trichomonas vaginalis.  

PubMed

Trichomonas vaginalis is a parasite that resides in the human urogenital tract and causes trichomonosis, the most prevalent nonviral sexually transmitted disease. Nucleoside triphosphate diphosphohydrolase (NTPDase), which hydrolyzes extracellular di- and triphosphate nucleotides, and ecto-5'-nucleotidase, which hydrolyzes AMP, have been characterized in T. vaginalis. The aim of this study was to characterize the adenosine deaminase (ADA) activity in intact trophozoites of T. vaginalis. A strong inhibition in adenosine deamination was observed in the presence of calcium and magnesium, which was prevented by EDTA. The apparent K(M) value for adenosine was 1.13 0.07mM. The calculated V(max) was 2.61 0.054 nmol NH(3) min(-1) mg(-1) protein. Adenosine deamination was inhibited in the presence of erythro-9-(2-hydroxy-3-nonyl)adenine. Semi-quantitative reverse transcriptase-PCR experiments were performed and both ADA-related genes ada(125) and ada(231) mRNA were expressed, although ada(231) in higher quantity when compared with the ada(125) : ?-tubulin ratio. Furthermore, a phylogenetic analysis showed that the T. vaginalis sequences formed a clade with Entamoeba histolytica and Dictyostelium discoideum sequences, and it strongly suggests homologous functions in the T. vaginalis genome. The presence of ADA activity in T. vaginalis may be important to modulate the adenosine/inosine levels during infection and, consequently, to maintain the anti-inflammatory properties through different nucleoside-signalling mechanisms. PMID:21477257

Weizenmann, Marina; Frasson, Amanda Piccoli; de Barros, Muriel Primon; Vieira, Patrcia de Brum; Rosemberg, Denis Broock; De Carli, Geraldo Attilio; Bogo, Maurcio Reis; Bonan, Carla Denise; Tasca, Tiana

2011-06-01

62

Preventive effects of (-) epicatechin on altered adenosine triphosphatases and minerals in isoproterenol-induced myocardial infarcted rats.  

PubMed

The present study was aimed to evaluate the preventive effects of (-) epicatechin on alterations in the activities/levels of adenosine triphosphatases and minerals in isoproterenol-induced myocardial infarcted rats. Male albino Wistar rats were pretreated with (-) epicatechin (20 mg/kg body weight) daily for a period of 21 days. After the pretreatment period, rats were induced myocardial infarction by isoproterenol (100 mg/kg body weight) on 22nd and 23rd day. The activity of sodium/potassium-dependent adenosine triphosphatase was decreased, and the activities of calcium- and magnesium-dependent adenosine triphosphatases were increased in the heart of isoproterenol-induced myocardial infarcted rats. In addition, the concentrations of potassium were decreased and the concentrations of sodium and calcium were increased in the heart of isoproterenol-induced rats. Elevated plasma lipid peroxidation was noted in isoproterenol-induced rats. Prior treatment with (-) epicatechin significantly prevented the alterations in the activities and concentrations of adenosine triphosphatases, minerals, and plasma lipid peroxidation. The in vitro study confirmed the reducing property of (-) epicatechin. The observed effects in this study are attributed to the membrane-stabilizing and antioxidant properties of (-) epicatechin. The findings of this study will be beneficial to prevent the occurrence of myocardial infarction. PMID:23225614

Stanely Mainzen Prince, P

2012-12-01

63

Calcium and magnesium distribution in potato tubers  

Microsoft Academic Search

The calcium present in the potato tuber is partially extractable by water and by dilute HCl. Either of these procedures may\\u000a show higher calcium content than dry-ashing. A degree of fractionation of calcium can be obtained by extraction by 1N HCl,\\u000a first at room temperature and then at 70 C. Wet-ashing yielded consistently higher results for calcium than dry ashing.

Carl W. Bretzloff

1971-01-01

64

Adenosine dysfunction in epilepsy  

PubMed Central

Extracellular levels of the brains endogenous anticonvulsant and neuroprotectant adenosine largely depend on an astrocyte-based adenosine cycle, comprised of ATP release, rapid degradation of ATP into adenosine, and metabolic reuptake of adenosine through equilibrative nucleoside transporters and phosphorylation by adenosine kinase (ADK). Changes in ADK expression and activity therefore rapidly translate into changes of extracellular adenosine, which exerts its potent anticonvulsive and neuroprotective effects by activation of pre- and postsynaptic adenosine A1 receptors. Increases in ADK increase neuronal excitability, whereas decreases in ADK render the brain resistant to seizures and injury. Importantly, ADK was found to be overexpressed and associated with astrogliosis and spontaneous seizures in rodent models of epilepsy, as well as in human specimen resected from patients with hippocampal sclerosis and temporal lobe epilepsy. Several lines of evidence indicate that overexpression of astroglial ADK and adenosine deficiency are pathological hallmarks of the epileptic brain. Consequently, adenosine augmentation therapies constitute a powerful approach for seizure prevention, which is effective in models of epilepsy that are resistant to conventional antiepileptic drugs. The adenosine kinase hypothesis of epileptogenesis suggests that adenosine dysfunction in epilepsy undergoes a biphasic response: An acute surge of adenosine that can be triggered by any type of injury might contribute to the development of astrogliosis via adenosine receptor dependent and independent mechanisms. Astrogliosis in turn is associated with overexpression of ADK, which was shown to be sufficient to trigger spontaneous recurrent electrographic seizures. Thus, ADK emerges as a promising target for the prediction and prevention of epilepsy.

Boison, Detlev

2011-01-01

65

Adenosine and memory storage  

Microsoft Academic Search

Rationale: Caffeine is a non-selective A1\\/A2 adenosine receptor antagonist which is known to improve cognitive performance in humans. This effect of caffeine has been\\u000a attributed to its antagonism of adenosine receptors. Objective: The present study was devised to identify the role of A1 and A2A adenosine receptors in the facilitation of memory consolidation in mice performing a passive avoidance task.

Silvia R. Kopf; Alessia Melani; Felicita Pedata; Giancarlo Pepeu

1999-01-01

66

Molecular Structure of Adenosine  

NSDL National Science Digital Library

Adenosine is an endogenous nucleoside occurring in all of the cells of the body. It is chemically 6-amino-9-B-D-ribofuanosyl-9-H-purine and has the chemical formula of C10H13N5O4. Adenosine naturally hydrogen bonds to thymidine by two hydrogen bonds to construct a stable structure. Adenosine is a purine, meaning that it is a single ring structure. A carbon sugar ring attaches to nitrogen in the base to form an N-glycosylic bond. The nitrogenous bases, which are primarily nonpolar, pack tightly enough to exclude water and form a stable, primarily nonpolar environment in the helix interior.

2002-08-19

67

Adenosine and ATP Receptors  

Microsoft Academic Search

Adenosine and ATP, via P1 and P2 receptors respectively, can modulate pain transmission under physiological, inflammatory,\\u000a and neuropathic pain conditions. Such influences reflect peripheral and central actions and effects on neurons as well as\\u000a other cell types. In general, adenosine A1 receptors produce inhibitory effects on pain in a number of preclinical models\\u000a and are a focus of attention. In

J. Sawynok

68

Adenosine bronchoconstriction in asthma  

PubMed Central

1 Inhaled adenosine and its parent nucleotide, adenosine 5?-monophosphate (AMP) provoke bronchoconstriction in atopic and asthmatic individuals but not in normal subjects. 2 In clinical studies, histamine H1-receptor antagonists, cyclo-oxygenase inhibitors and the mast cell `stabilising' drugs, sodium cromoglycate and nedocromil, protect against the effects of adenosine bronchoprovocation suggesting the involvement of secondary mast cell mediator release. 3 Adenosine and its analogues potentiate histamine and leukotriene release from mast cells activated by other stimuli in vitro, and may also increase net mediator release from mast cells by counteracting the inhibitory effect of circulating adrenaline. 4 Although adenosine fulfils many of the criteria required for a mediator in asthma, its importance is not fully understood, and the mechanisms by which it provokes bronchoconstriction in asthmatic subjects is far from concluded. 5 Two possibilities are that either adenosine acts directly on luminal mast cells to upregulate histamine secretion, or it acts to initiate neuronal reflexes which stimulate histamine release indirectly and possibly activate peptidergic and/or cholinergic pathways.

Ng, W. H.; Polosa, R.; Church, M. K.

1990-01-01

69

Adenosine Receptors and Asthma  

PubMed Central

The pathophysiological processes underlying respiratory diseases like asthma are complex, resulting in an overwhelming choice of potential targets for the novel treatment of this disease. Despite this complexity, asthmatic subjects are uniquely sensitive to a range of substances like adenosine, thought to act indirectly to evoke changes in respiratory mechanics and in the underlying pathology, and thereby to offer novel insights into the pathophysiology of this disease. Adenosine is of particular interest because this substance is produced endogenously by many cells during hypoxia, stress, allergic stimulation, and exercise. Extracellular adenosine can be measured in significant concentrations within the airways; can be shown to activate adenosine receptor (AR) subtypes on lung resident cells and migrating inflammatory cells, thereby altering their function, and could therefore play a significant role in this disease. Many preclinical in vitro and in vivo studies have documented the roles of the various AR subtypes in regulating cell function and how they might have a beneficial impact in disease models. Agonists and antagonists of some of these receptor subtypes have been developed and have progressed to clinical studies in order to evaluate their potential as novel antiasthma drugs. In this chapter, we will highlight the roles of adenosine and AR subtypes in many of the characteristic features of asthma: airway obstruction, inflammation, bronchial hyperresponsiveness and remodeling. We will also discuss the merit of targeting each receptor subtype in the development of novel antiasthma drugs.

Wilson, Constance N.; Nadeem, Ahmed; Spina, Domenico; Brown, Rachel; Page, Clive P.; Jamal Mustafa, S.

2013-01-01

70

Adenosine and Bone Metabolism  

PubMed Central

Bone is a dynamic organ that undergoes continuous remodeling whilst maintaining a balance between bone formation and resorption. Osteoblasts, which synthesize and mineralize new bone, and osteoclasts, the cells that resorb bone, act in concert to maintain bone homeostasis. In recent years, there has been increasing appreciation of purinergic regulation of bone metabolism. Adenosine, released locally, mediates its physiologic and pharmacologic actions via interactions with G-protein coupled receptors and recent work has indicated that these receptors are involved in the regulation of osteoclast differentiation and function, as well as osteoblast differentiation and bone formation. Moreover, adenosine receptors also regulate chondrocyte and cartilage homeostasis. These recent findings underscore the potential therapeutic importance of adenosine receptors in regulating bone physiology and pathology.

Mediero, Aranzazu; Cronstein, Bruce N.

2013-01-01

71

Water soluble adenosine kinase inhibitors  

US Patent & Trademark Office Database

This invention relates to adenosine kinase inhibitors and to nucleoside analogs, specifically to water soluble, aryl substituted 4-amino pyrrolo[2,3-d] pyrimidine and pyrazolo[3,4-d] pyrimidine nucleoside analogs having activity as adenosine kinase inhibitors The invention also relates to the preparation and use of these adenosine kinase inhibitors in the treatment of cardiovascular, and cerebrovascular diseases, inflammation and other diseases which can be regulated by increasing the local concentration of adenosine.

1998-08-18

72

Regulation of Inflammation by Adenosine  

PubMed Central

Adenosine, a purine nucleoside generated by the dephosphorylation of adenine nucleotides, is a potent endogenous physiologic and pharmacologic regulator of many functions. Adenosine was first reported to inhibit the inflammatory actions of neutrophils nearly 30?years ago and since then the role of adenosine and its receptors as feedback regulators of inflammation has been well established. Here we review the effects of adenosine, acting at its receptors, on neutrophil and monocyte/macrophage function in inflammation. Moreover, we review the role of adenosine in mediating the anti-inflammatory effects of methotrexate, the anchor drug in the treatment of Rheumatoid Arthritis and other inflammatory disorders.

Hasko, Gyorgy; Cronstein, Bruce

2013-01-01

73

Adenosine and sleep  

SciTech Connect

Behavioral and biochemical approaches have been used to determine the relative contribution of endogenous adenosine and adenosine receptors to the sleep-wake cycle in the rat. Adenosine concentrations in specific areas of the rat brain were not affected by 24 hours of total sleep deprivation, or by 24 or 48 hours of REM sleep deprivation. In order to assess the effect of REM sleep deprivation on adenosine A/sub 1/ receptors, /sup 3/H-L-PIA binding was measured. The Bmax values for /sup 3/H-L-PIA binding to membrane preparations of the cortices and corpus striata from 48 hour REM sleep-deprived animals were increased 14.8% and 23%, respectively. These increases were not maintained following the cessation of sleep deprivation and recovered within 2 hours. The results of a 96 hour REM deprivation experiment were similar to those of the 48 hour REM sleep deprivation experiment. However, these increases were not evident in similar structures taken from stress control animals, and conclusively demonstrated that the changes in /sup 3/H-L-PIA binding resulted from REM sleep deprivation and not from stress.

Yanik, G.M. Jr.

1987-01-01

74

Adenosine and the Auditory System  

PubMed Central

Adenosine is a signalling molecule that modulates cellular activity in the central nervous system and peripheral organs via four G protein-coupled receptors designated A1, A2A, A2B, and A3. This review surveys the literature on the role of adenosine in auditory function, particularly cochlear function and its protection from oxidative stress. The specific tissue distribution of adenosine receptors in the mammalian cochlea implicates adenosine signalling in sensory transduction and auditory neurotransmission although functional studies have demonstrated that adenosine stimulates cochlear blood flow, but does not alter the resting and sound-evoked auditory potentials. An interest in a potential otoprotective role for adenosine has recently evolved, fuelled by the capacity of A1 adenosine receptors to prevent cochlear injury caused by acoustic trauma and ototoxic drugs. The balance between A1 and A2A receptors is conceived as critical for cochlear response to oxidative stress, which is an underlying mechanism of the most common inner ear pathologies (e.g. noise-induced and age-related hearing loss, drug ototoxicity). Enzymes involved in adenosine metabolism, adenosine kinase and adenosine deaminase, are also emerging as attractive targets for controlling oxidative stress in the cochlea. Other possible targets include ectonucleotidases that generate adenosine from extracellular ATP, and nucleoside transporters, which regulate adenosine concentrations on both sides of the plasma membrane. Developments of selective adenosine receptor agonists and antagonists that can cross the blood-cochlea barrier are bolstering efforts to develop therapeutic interventions aimed at ameliorating cochlear injury. Manipulations of the adenosine signalling system thus hold significant promise in the therapeutic management of oxidative stress in the cochlea.

Vlajkovic, Srdjan M; Housley, Gary D; Thorne, Peter R

2009-01-01

75

Calcium and magnesium status is not impaired in pregnant women.  

PubMed

Deficiencies in calcium (Ca) and magnesium (Mg) are associated with various complications during pregnancy. To test the hypothesis that the status of these minerals is inadequate in pregnancy, a cross-sectional study was conducted of the dietary intake and status of Ca and Mg in pregnant women (n = 50) attending a general public university hospital in Brazil. Dietary intake was assessed from 4-day food records; levels of plasma Mg, erythrocyte Mg, and urinary Ca and Mg excretion were determined by flame atomic absorption spectroscopy; and type I collagen C-telopeptides were evaluated by enzyme-linked immunosorbent assay. Probabilities of inadequate Ca and Mg intake were exhibited by 58 and 98% of the study population, respectively. The mean levels of urinary Ca and Mg excretion were 8.55 and 3.77 mmol/L, respectively. Plasma C-telopeptides, plasma Mg, and erythrocyte Mg were within normal levels. Multiple linear regression analysis revealed positive relationships among urinary Ca excretion, Ca intake (P = .002) and urinary Mg excretion (P < .001) and between erythrocyte Mg and Mg intake (P = .023). It is concluded that the Ca and Mg status of participants was adequate even though the intake of Ca and Mg was lower than the recommended level. PMID:22901563

Rocha, Vivianne S; Lavanda, Ivana; Nakano, Eduardo Y; Ruano, Rodrigo; Zugaib, Marcelo; Colli, Clia

2012-07-01

76

Spectrophotometric Titration of a Mixture of Calcium and Magnesium.  

ERIC Educational Resources Information Center

Describes a spectrophotometric titration experiment which uses a manual titration spectrophotometer and manually operated buret, rather than special instrumentation. Identifies the equipment, materials, and procedures needed for the completion of the experiment. Recommends the use of this experiment in introductory quantitative analysis

Fulton, Robert; And Others

1986-01-01

77

Responses in extracellular and intracellular calcium and magnesium in aldosteronism.  

PubMed

We hypothesized the hypercalciuria and hypermagnesuria that accompany aldosteronism could be pharmacologically attenuated to prevent shifts in extracellular and intracellular levels of these divalent cations and the adverse outcomes associated with them. Accordingly, rats administered aldosterone/salt treatment (ALDOST) were cotreated with either hydrochlorothiazide (Hctz), to selectively reabsorb urinary Ca2+, or with Hctz plus spironolactone (Hctz+Spi), where Spi retards the excretion of these cations in both urine and feces. We monitored urinary excretion and responses in extracellular and intracellular Ca2+ and Mg2+, together with indices of oxi/nitrosative stress in plasma and ventricular tissue. At 4 weeks ALDOST we found the following: (1) hypercalciuria was reduced by Hctz and normalized by Hctz+Spi, and this combination, unlike Hctz alone, also rescued hypermagnesuria; (2) the decrease in plasma-ionized [Ca2+]o was not seen with Hctz or Hctz+Spi, whereas Spi cotreatment protected against a decline in [Mg2+]o; (3) the Ca2+ loading of peripheral blood mononuclear cells and cardiac tissue was not seen with Hctz+Spi; and (4) the induction of oxi/nitrosative stress, expressed as reduced plasma alpha1-antiproteinase activity and activation of gp91(phox) subunit of NADPH oxidase in inflammatory cells invading intramural coronary arteries of the right and left ventricles, together with vascular fibrosis, was completely prevented by Spi cotreatment. In rats with aldosteronism, cotreatment with Hctz+Spi more effectively (vis--vis Hctz alone) protects against adverse iterations in extracellular and intracellular concentrations of Ca2+ and Mg2+, as well as the appearance of oxi/nitrosative stress to prevent the proinflammatory vascular phenotype. PMID:16099237

Runyan, Aliye L; Sun, Yao; Bhattacharya, Syamal K; Ahokas, Robert A; Chhokar, Vikram S; Gerling, Ivan C; Weber, Karl T

2005-08-01

78

Complexometric Titration of Calcium and Magnesium by a Semiautomated Procedure  

Microsoft Academic Search

A semiautomatic procedure for the direct estimation of both serum calcium and magnesiumis described. The indicator used, Eriochromeblue SE (EBSE), has the advantageof stability and freedom from interference by naturally occurring sub- stances. The procedurerequires3-5 mm. per sampleand is very reproducible. The valuesobtainedagreewith thoseobtainedbyback-titration of excesschelator andare consistently0.3 mg.\\/100 ml. lessthan thoseobtainedbyastandardoxalateprecipita- tion method. C OMPLEXOMETRIC TITRATION s of calcium

James D. Jonesand; Warren F. McGuckin

79

Metal Ion Dependence of Cooperative Collapse Transitions in RNA  

SciTech Connect

Positively charged counterions drive RNA molecules into compact configurations that lead to their biologically active structures. To understand how the valence and size of the cations influences the collapse transition in RNA, small-angle X-ray scattering was used to follow the decrease in the radius of gyration (R{sub g}) of the Azoarcus and Tetrahymena ribozymes in different cations. Small, multivalent cations induced the collapse of both ribozymes more efficiently than did monovalent ions. Thus, the cooperativity of the collapse transition depends on the counterion charge density. Singular value decomposition of the scattering curves showed that folding of the smaller and more thermostable Azoarcus ribozyme is well described by two components, whereas collapse of the larger Tetrahymena ribozyme involves at least one intermediate. The ion-dependent persistence length, extracted from the distance distribution of the scattering vectors, shows that the Azoarcus ribozyme is less flexible at the midpoint of transition in low-charge-density ions than in high-charge-density ions. We conclude that the formation of sequence-specific tertiary interactions in the Azoarcus ribozyme overlaps with neutralization of the phosphate charge, while tertiary folding of the Tetrahymena ribozyme requires additional counterions. Thus, the stability of the RNA structure determines its sensitivity to the valence and size of the counterions.

Moghaddam, Sarvin; Caliskan, Gokhan; Chauhan, Seema; Hyeon, Changbong; Briber, R.M.; Thirumalai, D.; Woodson, Sarah A.; (Chung-Ang); (JHU); (Maryland)

2010-10-12

80

N?-(?ISOPENTENYL)ADENOSINE  

Microsoft Academic Search

N?-(?-Isopentenyl)adenosine is a cytokinin, that is, it promotes cell division, growth and differentiation in certain plant tissues. Some aspects of the metabolism and biological effects of i?Ado were studied. These studies have contributed to scientific knowledge in several areas: the biological effects of i?Ado on animal and plant cells; the metabolism of i?Ado by animal cells; and the origin of

Michel Piers Rathbone

1972-01-01

81

Adenosine and Gastrointestinal Inflammation  

PubMed Central

Nucelosides such as adenosine (Ado) influence nearly every aspect of physiology and pathophysiology. Extracellular nucleotides liberated at local sites of inflammation are metabolized through regulated phosphohydrolysis by a series of ecto-nucleotidases including ectonucleoside triphosphate diphosphohydrolase-1 (CD39) and ecto-5?-nucleotidase (CD73), found on the surface of a variety of cell types. Once generated, Ado is made available to bind and activate one of four G-protein-coupled Ado receptors. Recent in vitro and in vivo studies implicate Ado in a broad array of tissue protective mechanisms that provide new insight into adenosine actions. Studies in cultured cells and murine tissues have indicated that Ado receptors couple to novel post-translational protein modifications, including Cullin deneddylation, as a new anti-inflammatory mechanism. Studies in Ado receptor-null mice have been revealing and indicate a particularly important role for the Ado A2B receptor in animal models of intestinal inflammation. Here, we review contributions of Ado to cell and tissue stress responses, with a particular emphasis on the gastrointestinal mucosa.

Colgan, Sean P.; Fennimore, Blair; Ehrentraut, Stefan F.

2013-01-01

82

Adenosine and Adenosine Receptors in the Cardiovascular System: Biochemistry, Physiology, and Pharmacology  

Microsoft Academic Search

Cardiomyocytes and vascular cells readily form, transport, and metabolize the endogenous adenine nucleoside adenosine and act to regulate both interstitial and plasma adenosine concentrations. Cardiovascular cells also have membrane adenosine receptors. Cell and tissue distributions, signal transduction pathways, and pharmacology of each of the four subtypes of adenosine receptors are subjects of intense investigation. The A1-adenosine receptors mediate the negative

1997-01-01

83

Adenosine receptors as therapeutic targets  

PubMed Central

Adenosine receptors are major targets of caffeine, the most commonly consumed drug in the world. There is growing evidence that they could also be promising therapeutic targets in a wide range of conditions, including cerebral and cardiac ischaemic diseases, sleep disorders, immune and inflammatory disorders and cancer. After more than three decades of medicinal chemistry research, a considerable number of selective agonists and antagonists of adenosine receptors have been discovered, and some have been clinically evaluated, although none has yet received regulatory approval. However, recent advances in the understanding of the roles of the various adenosine receptor subtypes, and in the development of selective and potent ligands, as discussed in this review, have brought the goal of therapeutic application of adenosine receptor modulators considerably closer.

Jacobson, Kenneth A.; Gao, Zhan-Guo

2012-01-01

84

Extracellular guanosine regulates extracellular adenosine levels  

PubMed Central

The aim of this investigation was to test the hypothesis that extracellular guanosine regulates extracellular adenosine levels. Rat preglomerular vascular smooth muscle cells were incubated with adenosine, guanosine, or both. Guanosine (30 ?mol/l) per se had little effect on extracellular adenosine levels. Extracellular adenosine levels 1 h after addition of adenosine (3 ?mol/l) were 0.125 0.020 ?mol/l, indicating rapid disposition of extracellular adenosine. Extracellular adenosine levels 1 h after addition of adenosine (3 ?mol/l) plus guanosine (30 ?mol/l) were 1.173 0.061 ?mol/l, indicating slow disposition of extracellular adenosine. Cell injury increased extracellular levels of endogenous adenosine and guanosine, and the effects of cell injury on endogenous extracellular adenosine were modulated by altering the levels of endogenous extracellular guanosine with exogenous purine nucleoside phosphorylase (converts guanosine to guanine) or 8-aminoguanosine (inhibits purine nucleoside phosphorylase). Extracellular guanosine also slowed the disposition of extracellular adenosine in rat preglomerular vascular endothelial cells, mesangial cells, cardiac fibroblasts, and kidney epithelial cells and in human aortic and coronary artery vascular smooth muscle cells and coronary artery endothelial cells. The effects of guanosine on adenosine levels were not mimicked or attenuated by 5-iodotubericidin (adenosine kinase inhibitor), erythro-9-(2-hydroxy-3-nonyl)-adenine (adenosine deaminase inhibitor), 5-aminoimidazole-4-carboxamide (guanine deaminase inhibitor), aristeromycin (S-adenosylhomocysteine hydrolase inhibitor), low sodium (inhibits concentrative nucleoside transporters), S-(4-nitrobenzyl)?6-thioinosine [inhibits equilibrative nucleoside transporter (ENT) type 1], zidovudine (inhibits ENT type 2), or acadesine (known modulator of adenosine levels). Guanosine also increases extracellular inosine, uridine, thymidine, and cytidine, yet decreases extracellular uric acid. In conclusion, extracellular guanosine regulates extracellular adenosine levels.

Cheng, Dongmei; Jackson, Travis C.; Verrier, Jonathan D.; Gillespie, Delbert G.

2013-01-01

85

Adenosine: An Old Drug Newly Discovered  

PubMed Central

Over decades, anesthesiologists have used intravenous adenosine as mainstay therapy for diagnosing or treating supraventricular tachycardia in the perioperative setting. More recently, specific adenosine receptor therapeutics or gene-targeted mice deficient in extracellular adenosine production or individual adenosine receptors became available. These models enabled physicians and scientists to learn more about the biological functions of extracellular nucleotide metabolism and adenosine signaling. Such functions include specific signaling effects through adenosine receptors expressed by many mammalian tissues, for example vascular endothelia, myocytes, heptocytes, intestinal epithelia or immune cells. At present, pharmacological approaches to modulate extracellular adenosine signaling are evaluated for their potential use in perioperative medicine, including attenuation of acute lung injury, renal, intestinal, hepatic and myocardial ischemia, or vascular leakage. If these laboratory studies can be translated into clinical practice, adenosine receptor based therapeutics may become an integral pharmacological component of daily anesthesiology practice.

Eltzschig, Holger K.

2009-01-01

86

Adenosine induced coronary spasm - A rare presentation  

PubMed Central

Adenosine is commonly used as a pharmacological agent in myocardial perfusion imaging, as an antiarrhythmic agent, and in Cath Lab. during PCI for treating no reflow phenomenon. Coronary spasm has been reported following adenosine injection during stress imaging. We report a rare complication with ST segment elevation, following adenosine injection, given for treatment of supraventricular tachycardia.

Arora, P.; Bhatia, V.; Arora, M.; Kaul, U.

2014-01-01

87

Adenosine induced coronary spasm - a rare presentation.  

PubMed

Adenosine is commonly used as a pharmacological agent in myocardial perfusion imaging, as an antiarrhythmic agent, and in Cath Lab. during PCI for treating no reflow phenomenon. Coronary spasm has been reported following adenosine injection during stress imaging. We report a rare complication with ST segment elevation, following adenosine injection, given for treatment of supraventricular tachycardia. PMID:24581102

Arora, P; Bhatia, V; Arora, M; Kaul, U

2014-01-01

88

Adenosine Receptors and Cancer  

PubMed Central

The A1, A2A, A2B and A3 G-protein-coupled cell surface adenosine receptors (ARs) are found to be upregulated in various tumor cells. Activation of the receptors by specific ligands, agonists or antagonists, modulates tumor growth via a range of signaling pathways. The A1AR was found to play a role in preventing the development of glioblastomas. This antitumor effect of the A1AR is mediated via tumor-associated microglial cells. Activation of the A2AAR results in inhibition of the immune response to tumors via suppression of T regulatory cell function and inhibition of natural killer cell cytotoxicity and tumor-specific CD4+/CD8+ activity. Therefore, it is suggested that pharmacological inhibition by specific antagonists may enhance immunotherapeutics in cancer therapy. Activation of the A2BAR plays a role in the development of tumors via upregulation of the expression levels of angiogenic factors in microvascular endothelial cells. In contrast, it was evident that activation of A2BAR results in inhibition of ERK1/2 phosphorylation and MAP kinase activity, which are involved in tumor cell growth signals. Finally, A3AR was found to be highly expressed in tumor cells and tissues while low expression levels were noted in normal cells or adjacent tissue. Receptor expression in the tumor tissues was directly correlated to disease severity. The high receptor expression in the tumors was attributed to overexpression of NF-?B, known to act as an A3AR transcription factor. Interestingly, high A3AR expression levels were found in peripheral blood mononuclear cells (PBMCs) derived from tumor-bearing animals and cancer patients, reflecting receptor status in the tumors. A3AR agonists were found to induce tumor growth inhibition, both in vitro and in vivo, via modulation of the Wnt and the NF-?B signaling pathways. Taken together, A3ARs that are abundantly expressed in tumor cells may be targeted by specific A3AR agonists, leading to tumor growth inhibition. The unique characteristics of these A3AR agonists make them attractive as drug candidates.

Fishman, P.; Bar-Yehuda, S.; Synowitz, M.; Powell, J.D.; Klotz, K.N.; Gessi, S.; Borea, P.A.

2013-01-01

89

Xanthines as Adenosine Receptor Antagonists  

PubMed Central

The natural plant alkaloids caffeine and theophylline were the first adenosine receptor (AR) antagonists described in the literature. They exhibit micromolar affinities and are non-selective. A large number of derivatives and analogs have subsequently been synthesized and evaluated as AR antagonists. Very potent antagonists have thus been developed with selectivity for each of the four AR subtypes.

Jacobson, Kenneth A.

2013-01-01

90

Adenosine receptors as therapeutic targets  

Microsoft Academic Search

Adenosine receptors are major targets of caffeine, the most commonly consumed drug in the world. There is growing evidence that they could also be promising therapeutic targets in a wide range of conditions, including cerebral and cardiac ischaemic diseases, sleep disorders, immune and inflammatory disorders and cancer. After more than three decades of medicinal chemistry research, a considerable number of

Zhan-Guo Gao; Kenneth A. Jacobson

2006-01-01

91

Adenosine-induced activation of esophageal nociceptors  

PubMed Central

Clinical studies implicate adenosine acting on esophageal nociceptive pathways in the pathogenesis of noncardiac chest pain originating from the esophagus. However, the effect of adenosine on esophageal afferent nerve subtypes is incompletely understood. We addressed the hypothesis that adenosine selectively activates esophageal nociceptors. Whole cell perforated patch-clamp recordings and single-cell RT-PCR analysis were performed on the primary afferent neurons retrogradely labeled from the esophagus in the guinea pig. Extracellular recordings were made from the isolated innervated esophagus. In patch-clamp studies, adenosine evoked activation (inward current) in a majority of putative nociceptive (capsaicin-sensitive) vagal nodose, vagal jugular, and spinal dorsal root ganglia (DRG) neurons innervating the esophagus. Single-cell RT-PCR analysis indicated that the majority of the putative nociceptive (transient receptor potential V1-positive) neurons innervating the esophagus express the adenosine receptors. The neural crest-derived (spinal DRG and vagal jugular) esophageal nociceptors expressed predominantly the adenosine A1 receptor while the placodes-derived vagal nodose nociceptors expressed the adenosine A1 and/or A2A receptors. Consistent with the studies in the cell bodies, adenosine evoked activation (overt action potential discharge) in esophageal nociceptive nerve terminals. Furthermore, the neural crest-derived jugular nociceptors were activated by the selective A1 receptor agonist CCPA, and the placodes-derived nodose nociceptors were activated by CCPA and/or the selective adenosine A2A receptor CGS-21680. In contrast to esophageal nociceptors, adenosine failed to stimulate the vagal esophageal low-threshold (tension) mechanosensors. We conclude that adenosine selectively activates esophageal nociceptors. Our data indicate that the esophageal neural crest-derived nociceptors can be activated via the adenosine A1 receptor while the placodes-derived esophageal nociceptors can be activated via A1 and/or A2A receptors. Direct activation of esophageal nociceptors via adenosine receptors may contribute to the symptoms in esophageal diseases.

Ru, F.; Surdenikova, L.; Brozmanova, M.

2011-01-01

92

Fluorescent Ligands for Adenosine Receptors  

PubMed Central

Interest is increasing in developing fluorescent ligands for characterization of adenosine receptors (ARs), which hold a promise of usefulness in the drug discovery process. The size of a strategically labeled AR ligand can be greatly increased after the attachment of a fluorophore. The choice of dye moiety (e.g. Alexa Fluor 488), attachment point and linker length can alter the selectivity and potency of the parent molecule. Fluorescent derivatives of adenosine agonists and antagonists (e.g. XAC and other heterocyclic antagonist scaffolds) have been synthesized and characterized pharmacologically. Some are useful AR probes for flow cytometry, fluorescence correlation spectroscopy, fluorescence microscopy, fluorescence polarization, fluorescence resonance energy transfer, and scanning confocal microscopy. Thus, the approach of fluorescent labeled GPCR ligands, including those for ARs, is a growing dynamic research field.

Kozma, Eszter; Jayasekara, P Suresh; Squarcialupi, Lucia; Paoletta, Silvia; Moro, Stefano; Federico, Stephanie; Spalluto, Giampiero; Jacobson, Kenneth A.

2012-01-01

93

Adenosine: trigger and mediator of cardioprotection  

Microsoft Academic Search

Adenosine, a purine nucleoside, is ubiquitous in the body, and is a critical component of ATP. Its concentration jumps 100-fold\\u000a during periods of oxygen depletion and ischemia. There are four adenosine receptors: A1 and A3 coupled to Gi\\/o and the high-affinity A2A and low-affinity A2B coupled to Gs. Adenosine is one of three autacoids released by ischemic tissue which are

Michael V. Cohen; James M. Downey

2008-01-01

94

Adenosine A 3 Receptors in Muscle Protection  

Microsoft Academic Search

\\u000a A growing body of evidence has accumulated to indicate an important cyto-protective role of the adenosine A3 receptor. This protective function, originally discovered in ameliorating ischemiareperfusion injury in the heart, is now\\u000a also extended to the skeletal muscle. Understanding the pharmacology of various adenosine receptor subtypes allowed their\\u000a selective activation and delineated the protective role of adenosine A3 receptors as

Bruce T. Liang; Maria Urso; Edward Zambraski; Kenneth A. Jacobson

95

Role of endogenous adenosine in vasovagal syncope  

Microsoft Academic Search

Adenosine may be a potential mediator in the pathogenesis of vasovagal syncope. Intravenous adenosine increases sympathetic\\u000a discharge and provokes vasovagal syncope in sensitive subjects. No data are available for endogenous adenosine. The authors\\u000a compared the results of head-up tilt-table testing (HUT) (45 minutes at 60) of three arbitrary groups of subjects: sensitive\\u000a (n=25, age 34 y, vasovagal syncope, positive HUT),

Matja inkovec; Anton Grad; Peter Rakovec

2001-01-01

96

Partial separation of platelet and placental adenosine receptors from adenosine A2-like binding protein  

SciTech Connect

The ubiquitous adenosine A2-like binding protein obscures the binding properties of adenosine receptors assayed with 5'-N-({sup 3}H)ethylcarboxamidoadenosine (({sup 3}H)NECA). To solve this problem, we developed a rapid and simple method to separate adenosine receptors from the adenosine A2-like binding protein. Human platelet and placental membranes were solubilized with 1% 3-((3-cholamidopropyl)dimethylammonio)-1-propanesulfonate. The soluble platelet extract was precipitated with polyethylene glycol and the fraction enriched in adenosine receptors was isolated from the precipitate by differential centrifugation. The adenosine A2-like binding protein was removed from the soluble placental extract with hydroxylapatite and adenosine receptors were precipitated with polyethylene glycol. The specificity of the ({sup 3}H)NECA binding is typical of an adenosine A2 receptor for platelets and an adenosine A1 receptor for placenta. This method leads to enrichment of adenosine A2 receptors for platelets and adenosine A1 receptors for placenta. This provides a useful preparation technique for pharmacologic studies of adenosine receptors.

Zolnierowicz, S.; Work, C.; Hutchison, K.; Fox, I.H. (University Hospital, Ann Arbor, MI (USA))

1990-04-01

97

Regulation of neutrophil function by adenosine  

PubMed Central

Adenosine is an endogenously released purine nucleoside that signals via four widely expressed G-protein coupled receptors: A1, A2A, A2B, and A3. In the setting of inflammation, the generation and release of adenosine is greatly enhanced. Neutrophils play an important role in host defense against invading pathogens and are the cellular hallmark of acute inflammation. Neutrophils both release adenosine and can respond to it via expression of all four adenosine receptor subtypes. At low concentrations, adenosine can act via the A1 and A3 adenosine receptor subtypes to promote neutrophil chemotaxis and phagocytosis. At higher concentrations, adenosine acts at the lower-affinity A2A and A2B receptors to inhibit neutrophil trafficking and effector functions such as oxidative burst, inflammatory mediator production, and granule release. Modulation of neutrophil function by adenosine is relevant in a broad array of disease models, including ischemia reperfusion injury, sepsis, and non-infectious acute lung injury. This review will summarize relevant research in order to provide a framework for understanding how adenosine directly regulates various elements of neutrophil function.

Barletta, Kathryn E.; Ley, Klaus; Mehrad, Borna

2012-01-01

98

Resveratrol inhibits metal ion-dependent and independent peroxidation of porcine low-density lipoproteins  

Microsoft Academic Search

Resveratrol, a phytoalexin (3, 4?, 5, trihydroxystilbene) present in some red wines, has been reported to inhibit copper-mediated low-density lipoprotein (LDL) oxidation. In this study, we examined the efficiency of this compound in inhibiting metal ion-dependent and independent peroxidation of porcine LDL. At 0.5, 1, or 1.5 ?M, transresveratrol prolonged the lag time preceding the onset of conjugated diene formation

Leila Belguendouz; Lucie Fremont; Alain Linard

1997-01-01

99

Characterization of adenosine transport in H9c2 cardiomyoblasts  

Microsoft Academic Search

Adenosine plays a significant role in various physiological processes including cardioprotection. Nucleoside transporters modulate adenosine levels in the vicinity of adenosine receptors, which in turn modulate adenosine functional efficacy. In the current study, adenosine transport in the rat heart myoblast cell line H9c2 was characterized. Kinetic analysis of adenosine transport in H9c2 cells revealed a Km of 8.90.001?M and a

George P. H. Leung; Chung-Ming Tse; Ricky Y. K. Man

2007-01-01

100

Regulation of atherosclerosis and associated risk factors by adenosine and adenosine receptors.  

PubMed

Adenosine is an endogenous metabolite that has an anti-inflammatory effect across the vasculature. Extracellular adenosine activates 4G-protein coupled receptors (A1, A3, A2A, and A2B) whose expression varies in different cells and tissues, including the vasculature and blood cells. Higher levels of adenosine are generated during stress, inflammation, and upon tissue damage. Some of the adenosine receptors (AR), such as the A2BAR, are further up-regulated following such stresses. This review discusses the role of adenosine and adenosine receptors in the development of atherosclerosis and some of the risk factors associated with this pathology. These include adenosine receptor-regulated changes in atherosclerosis, blood pressure, thrombosis, and myocardial infarction. Potential therapeutic applications are reviewed, as well as reasons for phenotypic differences occasionally observed between receptor knockout and pharmacological inhibition via drug administration. PMID:22850979

Koupenova, Milka; Johnston-Cox, Hillary; Ravid, Katya

2012-10-01

101

Endogenous adenosine and adenosine receptors localized to ganglion cells of the retina  

SciTech Connect

Using specific sensitive antisera against adenosine, we have immunocytochemically localized endogenous adenosine to specific layers of rat, guinea pig, monkey, and human retina. Highest adenosine immunoreactivity was observed in ganglion cells and their processes in the optic nerve fiber layer. Substantial staining was also found throughout the inner plexiform layer and in select cells in the inner nuclear layer. Adenosine A1 receptors, labeled with the agonists L-(/sup 3/H)phenylisopropyladenosine and /sup 125/I-labeled hydroxy-phenylisopropyladenosine, were autoradiographically localized. The highest levels of binding sites occurred in the nerve fiber, ganglion cell, and inner plexiform layers of the retina in all the species examined. The distribution of adenosine A1 receptor sites closely parallels that of retinal neurons and fibers containing immunoreactive adenosine. These results suggest a role for endogenous adenosine as a coneurotransmitter in ganglion cells and their fibers in the optic nerve.

Braas, K.M.; Zarbin, M.A.; Snyder, S.H.

1987-06-01

102

Regulation of Atherosclerosis and Associated Risk Factors by Adenosine and Adenosine Receptors  

PubMed Central

Adenosine is an endogenous metabolite that has an anti-inflammatory effect across the vasculature. Extracellular adenosine activates four G-protein coupled receptors (A1, A3, A2A, and A2B) whose expression varies in different cells and tissues, including the vasculature and blood cells. Higher levels of adenosine are generated during stress, inflammation, and upon tissue damage. Some of the adenosine receptors (AR), such as the A2BAR, are further upregulated following such stresses. This review will discuss the role of adenosine and adenosine receptors in the development of atherosclerosis and some of the risk factors associated with this pathology. These include adenosine receptor-regulated changes in atherosclerosis, blood pressure, thrombosis, and myocardial infarction.

Koupenova, Milka; Johnston-Cox, Hillary; Ravid, Katya

2013-01-01

103

The role of adenosine in pulmonary angiogenesis  

Microsoft Academic Search

Angiogenesis is a feature of chronic lung diseases such as asthma and pulmonary fibrosis; however, the pathways controlling pathological angiogenesis during lung disease are not completely understood. Adenosine is a signaling nucleoside that accumulates as a result of tissue hypoxia and damage. Adenosine has been implicated in the exacerbation of chronic lung disease and in the regulation of angiogenesis; however,

Amir Mohsenin

2006-01-01

104

Enzymatic regeneration of adenosine triphosphate cofactor  

NASA Technical Reports Server (NTRS)

Regenerating adenosine triphosphate (ATP) from adenosine diphosphate (ADP) by enzymatic process which utilizes carbamyl phosphate as phosphoryl donor is technique used to regenerate expensive cofactors. Process allows complex enzymatic reactions to be considered as candidates for large-scale continuous processes.

Marshall, D. L.

1974-01-01

105

Capillary transport of adenosine1,2  

PubMed Central

We tested the hypothesis that capillary exchange of adenosine is influenced by the ability of endothelial cells (ECs) to take up adenosine. Triple-indicator diffusion experiments were performed by injecting [14C]adenosine, [3H]9-?-d-arabinofuranosylhypoxanthine ([3H]araH), and radioiodinated serum albumin (RISA) into the arterial perfusate of isolated nonworking guinea pig hearts. Tracer appearance in venous effluent was observed over time. The early extraction of [14C]adenosine was much higher than that of [3H]araH. Extracted [3H]araH returned to the vascular space, but [14C]adenosine did not. Quantitative analysis of the curves by using a mathematical model indicates that approximately half of the extracted adenosine enters ECs and is metabolized. The remainder enters the interstitium and is taken up by myocytes, ECs, or other cells and is metabolized. We conclude that uptake of adenosine by ECs represents a significant influence on the capillary exchange of adenosine.

SPARKS, HARVEY V.; DEWITT, DONALD F.; WANGLER, ROGER D.; GORMAN, MARK W.; BASSINGTHWAIGHTE, JAMES B.

2010-01-01

106

Blocking of sodium and potassium ion-dependent adenosine triphosphatase-?1 with ouabain and vanadate suppresses cell-cell fusion during RANKL-mediated osteoclastogenesis.  

PubMed

To examine the possible enrolment of Na(+)/K(+)-ATPase during osteoclast differentiation, Na(+)/K(+)-ATPase inhibitors, including ouabain and vanadate, were used in this study. These inhibitors significantly inhibited cell-cell fusion of RAW264.7 cells and bone marrow cells induced by RANKL. Interestingly, in response to RANKL-stimulation, ouabain and vanadate decreased the number of large TRAP+ osteoclasts in the culture of RAW264.7 cells, as well as bone marrow cells. In contrast, the number of small TRAP+ osteoclasts either increased in RAW264.7 cells or were otherwise less affected in bone marrow cells than large TRAP+ osteoclasts. Large TRAP+ osteoclasts are defined as having ? 10 nuclei/cell and having more potency in bone resorption than small multinuclear osteoclasts with <9 nuclei/cell. Na(+)/K(+)-ATPase ?1 and ?2 mRNAs were detected in sRANKL-stimulated RAW264.7 cells. Moreover, real-time quantitative PCR showed that ouabain and vanadate suppressed the RANKL-dependent induction of the osteoclast fusion-promotion molecule DC-STAMP at the mRNA level. Finally, and importantly, RNAi-mediated suppression of Na(+)/K(+)-ATPase ?1 resulted in a diminished number of large TRAP+ osteoclasts in the sRANKL-stimulated RAW264.7 cells, along with the decreased level of DC-STAMP mRNA expression. These findings strongly suggest that blockage of the Na(+)/K(+)-ATPase ?1 subunit by ouabain or vanadate caused the inhibition of RANKL-induced cell-cell fusion, resulting in the generation of large osteoclasts through suppression of DC-STAMP expression. Thus, in addition to its known function of sodium and potassium ion exchange during bone resorption by mature osteoclasts, this study has revealed a novel molecular role of the Na(+)/K(+)-ATPase ?1 subunit in osteoclastogenesis. PMID:21945676

Makihira, Seicho; Nikawa, Hiroki; Kajiya, Mikihito; Kawai, Toshihisa; Mine, Yuichi; Kosaka, Eduardo; Silva, Marcelo J B; Tobiume, Kei; Terada, Yoshihiro

2011-11-30

107

Potassium ion-dependent trehalose phosphorylase from halophilic Bacillus selenitireducens MLS10.  

PubMed

We discovered a potassium ion-dependent trehalose phosphorylase (Bsel_1207) belonging to glycoside hydrolase family 65 from halophilic Bacillus selenitireducens MLS10. Under high potassium ion concentrations, the recombinant Bsel_1207 produced in Escherichia coli existed as an active dimeric form that catalyzed the reversible phosphorolysis of trehalose in a typical sequential bi bi mechanism releasing ?-D-glucose 1-phosphate and D-glucose. Decreasing potassium ion concentrations significantly reduced thermal and pH stabilities, leading to formation of inactive monomeric Bsel_1207. PMID:24021648

Nihira, Takanori; Saito, Yuka; Chiku, Kazuhiro; Kitaoka, Motomitsu; Ohtsubo, Ken'ichi; Nakai, Hiroyuki

2013-11-01

108

Homeostatic control of synaptic activity by endogenous adenosine is mediated by adenosine kinase.  

PubMed

Extracellular adenosine, a key regulator of neuronal excitability, is metabolized by astrocyte-based enzyme adenosine kinase (ADK). We hypothesized that ADK might be an upstream regulator of adenosine-based homeostatic brain functions by simultaneously affecting several downstream pathways. We therefore studied the relationship between ADK expression, levels of extracellular adenosine, synaptic transmission, intrinsic excitability, and brain-derived neurotrophic factor (BDNF)-dependent synaptic actions in transgenic mice underexpressing or overexpressing ADK. We demonstrate that ADK: 1) Critically influences the basal tone of adenosine, evaluated by microelectrode adenosine biosensors, and its release following stimulation; 2) determines the degree of tonic adenosine-dependent synaptic inhibition, which correlates with differential plasticity at hippocampal synapses with low release probability; 3) modulates the age-dependent effects of BDNF on hippocampal synaptic transmission, an action dependent upon co-activation of adenosine A2A receptors; and 4) influences GABAA receptor-mediated currents in CA3 pyramidal neurons. We conclude that ADK provides important upstream regulation of adenosine-based homeostatic function of the brain and that this mechanism is necessary and permissive to synaptic actions of adenosine acting on multiple pathways. These mechanistic studies support previous therapeutic studies and implicate ADK as a promising therapeutic target for upstream control of multiple neuronal signaling pathways crucial for a variety of neurological disorders. PMID:22997174

Digenes, Maria Jos; Neves-Tom, Raquel; Fucile, Sergio; Martinello, Katiuscia; Scianni, Maria; Theofilas, Panos; Lopatr, Jan; Ribeiro, Joaquim A; Maggi, Laura; Frenguelli, Bruno G; Limatola, Cristina; Boison, Detlev; Sebastio, Ana M

2014-01-01

109

Halobacterial adenosine triphosphatases and the adenosine triphosphatase from Halobacterium saccharovorum  

NASA Technical Reports Server (NTRS)

Membranes prepared from various members of the genus Halobacterium contained a Triton X-l00 activated adenosine triphosphatase. The enzyme from Halobacterium saccharovorum was unstable in solutions of low ionic strength and maximally active in the presence of 3.5 M NaCl. A variety of nucleotide triphosphates was hydrolyzed. MgADP, the product of ATP hydrolysis, was not hydrolyzed and was a competitive inhibitor with respect to MgATP. The enzyme from H. saccharovorum was composed of at least 2 and possibly 4 subunits. The 83-kDa and 60-kDa subunits represented about 90 percent of total protein. The 60-kDa subunit reacted with dicyclohexyl-carbodiimide when inhibition was carried out in an acidic medium. The enzyme from H. saccharovorum, possesses properties of an F(1)F(0) as well as an E(1)E(2) ATPase.

Kristjansson, Hordur; Sadler, Martha H.; Hochstein, Lawrence I.

1986-01-01

110

Regulation of cell proliferation by the guanosine-adenosine mechanism: role of adenosine receptors  

PubMed Central

A recent study (American Journal of Physiology Cell Physiology 304:C406C421, 2013) suggests that extracellular guanosine increases extracellular adenosine by modifying the disposition of extracellular adenosine (guanosineadenosine mechanism) and that the guanosineadenosine mechanism is not mediated by classical adenosine transport systems (SLC28 and SLC29 families) nor by classical adenosine-metabolizing enzymes. The present investigation had two aims (1) to test the hypothesis that the guanosineadenosine mechanism affects cell proliferation; and (2) to determine whether the transporters SLC19A1, SLC19A2, SLC19A3, or SLC22A2 (known to carrier guanosine analogs) might be responsible for the guanosineadenosine mechanism. In the absence of added adenosine, guanosine had little effect on the proliferation of coronary artery vascular smooth muscle cells (vascular conduit cells) or preglomerular vascular smooth muscle cells (vascular resistance cells). However, in the presence of added adenosine (3 or 10 ?mol/L), guanosine (10100 ?mol/L) decreased proliferation of both cell types, thus resulting in a highly significant (P < 0.000001) interaction between guanosine and adenosine on cell proliferation. The guanosineadenosine interaction on cell proliferation was abolished by 1,3-dipropyl-8-(p-sulfophenyl)xanthine (adenosine receptor antagonist). Guanosine (30 ?mol/L) increased extracellular levels of adenosine when adenosine (3 ?mol/L) was added to the medium. This effect was not reproduced by high concentrations of methotrexate (100 ?mol/L), thiamine (1000 ?mol/L), chloroquine (1000 ?mol/L), or acyclovir (10,000 ?mol/L), archetypal substrates for SLC19A1, SLC19A2, SLC19A3, and SLC22A2, respectively; and guanosine still increased adenosine levels in the presence of these compounds. In conclusion, the guanosineadenosine mechanism affects cell proliferation and is not mediated by SLC19A1, SLC19A2, SLC19A3, or SLC22A2.

Jackson, Edwin K; Gillespie, Delbert G

2013-01-01

111

Adenosine Kinase: Exploitation for Therapeutic Gain  

PubMed Central

Adenosine kinase (ADK; EC 2.7.1.20) is an evolutionarily conserved phosphotransferase that converts the purine ribonucleoside adenosine into 5?-adenosine-monophosphate. This enzymatic reaction plays a fundamental role in determining the tone of adenosine, which fulfills essential functions as a homeostatic and metabolic regulator in all living systems. Adenosine not only activates specific signaling pathways by activation of four types of adenosine receptors but it is also a primordial metabolite and regulator of biochemical enzyme reactions that couple to bioenergetic and epigenetic functions. By regulating adenosine, ADK can thus be identified as an upstream regulator of complex homeostatic and metabolic networks. Not surprisingly, ADK dysfunction is involved in several pathologies, including diabetes, epilepsy, and cancer. Consequently, ADK emerges as a rational therapeutic target, and adenosine-regulating drugs have been tested extensively. In recent attempts to improve specificity of treatment, localized therapies have been developed to augment adenosine signaling at sites of injury or pathology; those approaches include transplantation of stem cells with deletions of ADK or the use of gene therapy vectors to downregulate ADK expression. More recently, the first human mutations in ADK have been described, and novel findings suggest an unexpected role of ADK in a wider range of pathologies. ADK-regulating strategies thus represent innovative therapeutic opportunities to reconstruct network homeostasis in a multitude of conditions. This review will provide a comprehensive overview of the genetics, biochemistry, and pharmacology of ADK and will then focus on pathologies and therapeutic interventions. Challenges to translate ADK-based therapies into clinical use will be discussed critically.

2013-01-01

112

Adenosine receptors as drug targets -- what are the challenges?  

PubMed Central

Adenosine signalling has long been a target for drug development, with adenosine itself or its derivatives being used clinically since the 1940s. In addition, methylxanthines such as caffeine have profound biological effects as antagonists at adenosine receptors. Moreover, drugs such as dipyridamole and methotrexate act by enhancing the activation of adenosine receptors. There is strong evidence that adenosine has a functional role in many diseases, and several pharmacological compounds specifically targeting individual adenosine receptors either directly or indirectly have now entered the clinic. However, only one adenosine receptor-specific agent the adenosine A2A receptor agonist regadenoson (Lexiscan; Astellas Pharma) has so far gained approval from the US Food and Drug Administration (FDA). Here, we focus on the biology of adenosine signalling to identify hurdles in the development of additional pharmacological compounds targeting adenosine receptors and discuss strategies to overcome these challenges.

Chen, Jiang-Fan; Eltzschig, Holger K.; Fredholm, Bertil B.

2014-01-01

113

Mast Cell Adenosine Receptors Function: A Focus on the A3 Adenosine Receptor and Inflammation  

PubMed Central

Adenosine is a metabolite, which has long been implicated in a variety of inflammatory processes. Inhaled adenosine provokes bronchoconstriction in asthmatics or chronic obstructive pulmonary disease patients, but not in non-asthmatics. This hyper responsiveness to adenosine appears to be mediated by mast cell activation. These observations have marked the receptor that mediates the bronchoconstrictor effect of adenosine on mast cells (MCs), as an attractive drug candidate. Four subtypes (A1, A2a, A2b, and A3) of adenosine receptors have been cloned and shown to display distinct tissue distributions and functions. Animal models have firmly established the ultimate role of the A3 adenosine receptor (A3R) in mediating hyper responsiveness to adenosine in MCs, although the influence of the A2b adenosine receptor was confirmed as well. In contrast, studies of the A3R in humans have been controversial. In this review, we summarize data on the role of different adenosine receptors in mast cell regulation of inflammation and pathology, with a focus on the common and distinct functions of the A3R in rodent and human MCs. The relevance of mouse studies to the human is discussed.

Rudich, Noam; Ravid, Katya; Sagi-Eisenberg, Ronit

2012-01-01

114

Adenosine inhibits glutamatergic input to basal forebrain cholinergic neurons  

PubMed Central

Adenosine has been proposed as an endogenous homeostatic sleep factor that accumulates during waking and inhibits wake-active neurons to promote sleep. It has been specifically hypothesized that adenosine decreases wakefulness and promotes sleep recovery by directly inhibiting wake-active neurons of the basal forebrain (BF), particularly BF cholinergic neurons. We previously showed that adenosine directly inhibits BF cholinergic neurons. Here, we investigated 1) how adenosine modulates glutamatergic input to BF cholinergic neurons and 2) how adenosine uptake and adenosine metabolism are involved in regulating extracellular levels of adenosine. Our experiments were conducted using whole cell patch-clamp recordings in mouse brain slices. We found that in BF cholinergic neurons, adenosine reduced the amplitude of AMPA-mediated evoked glutamatergic excitatory postsynaptic currents (EPSCs) and decreased the frequency of spontaneous and miniature EPSCs through presynaptic A1 receptors. Thus we have demonstrated that in addition to directly inhibiting BF cholinergic neurons, adenosine depresses excitatory inputs to these neurons. It is therefore possible that both direct and indirect inhibition may synergistically contribute to the sleep-promoting effects of adenosine in the BF. We also found that blocking the influx of adenosine through the equilibrative nucleoside transporters or inhibiting adenosine kinase and adenosine deaminase increased endogenous adenosine inhibitory tone, suggesting a possible mechanism through which adenosine extracellular levels in the basal forebrain are regulated.

Hawryluk, J. M.; Ferrari, L. L.; Keating, S. A.

2012-01-01

115

Brain Adenosine Triphosphate: Decreased Concentration Precedes Convulsions.  

National Technical Information Service (NTIS)

The concentration of adenosine triphosphate in the brain decreased before the onset of generalized convulsions in unanesthetized rats subjected to acute hypoxia or treated with hydroxylamine or pentylenetetrazole (Metrazol). As the convulsive episode cont...

A. P. Sanders R. S. Kramer B. Woodhall W. D. Currie

1970-01-01

116

Internalization and desensitization of adenosine receptors  

Microsoft Academic Search

Until now, more than 800 distinct G protein-coupled receptors (GPCRs) have been identified in the human genome. The four subtypes\\u000a of the adenosine receptor (A1, A2A, A2B and A3 receptor) belong to this large family of GPCRs that represent the most widely targeted pharmacological protein class. Since\\u000a adenosine receptors are widespread throughout the body and involved in a variety of

Elisabeth C. Klaasse; Adriaan P. IJzerman; Willem J. de Grip; Margot W. Beukers

2008-01-01

117

Adenosine Receptors, Cystic Fibrosis, and Airway Hydration  

Microsoft Academic Search

\\u000a Adenosine (Ado) regulates diverse cellular functions in the lung through its local production, release, metabolism, and subsequent\\u000a stimulation of G-protein-coupled P1 purinergic receptors. The A2B adenosine receptor (A2BAR) is the predominant P1 purinergic receptor isoform expressed in surface airway epithelia, and Ado is an important regulator\\u000a of airway surface liquid (ASL) volume through its activation of the cystic fibrosis transmembrane

J. P. Clancy

118

Adenosine receptor activation ameliorates type 1 diabetes  

Microsoft Academic Search

Growing evidence indicates that adeno- sine receptors could be promising therapeutic targets in autoimmune diseases. Here we studied the role of adenosine receptors in controlling the course of type 1 diabetes. Diabetes in CD-1 mice was induced by multi- ple-low-dose-streptozotocin (MLDS) treatment and in nonobese diabetic (NOD) mice by cyclophosphamide injection. The nonselective adenosine receptor agonist 5-N-ethylcarboxamidoadenosine (NECA) prevented diabetes

Zoltan H. Nemeth; David Bleich; Balazs Csoka; Pal Pacher; Jon G. Mabley; Leonora Himer; E. Sylvester Vizi; Edwin A. Deitch; Csaba Szabo; Bruce N. Cronstein; Gyorgy Hasko

2007-01-01

119

RNA Tertiary Structure Mediation by Adenosine Platforms  

Microsoft Academic Search

The crystal structure of a group I intron domain reveals an unexpected motif that mediates both intra- and intermolecular interactions. At three separate locations in the 160-nucleotide domain, adjacent adenosines in the sequence lie side-by-side and form a pseudo-base pair within a helix. This adenosine platform opens the minor groove for base stacking or base pairing with nucleotides from a

Jamie H. Cate; Anne R. Gooding; Elaine Podell; Kaihong Zhou; Barbara L. Golden; Alexander A. Szewczak; Craig E. Kundrot; Thomas R. Cech; Jennifer A. Doudna

1996-01-01

120

Characterization of the adenosine receptor in porcine coronary arteries.  

PubMed Central

1. Relaxant responses of ring preparations from porcine ventricular coronary arteries to adenosine and various stable adenosine analogues were investigated in vitro. 2. The adenosine analogues did not produce contraction but elicited almost complete relaxation of coronary arteries preconstricted with 3 microM prostaglandin F2 alpha (PGF2 alpha), even after removal of the endothelium. 3. The order of potency, was 5'-N-ethylcarboxamide-adenosine (NECA) greater than 2-(2-phenylethylamino)5'-N-ethylcarboxamide-adenosine (2-PEA-NECA) greater than 2-phenylamino-adenosine (CV-1808) greater than N6-[R(-)-1-phenyl-2-propyl]adenosine (R-PIA) greater than N6-[S(+)-1-phenyl-2-propyl]adenosine (S-PIA) greater than N6-cyclopentyl-adenosine (CPA) greater than adenosine greater than ATP offDP which suggested the presence of adenosine A2-receptor subtypes. 4. There was an excellent correlation between the calculated pD2 values on coronary arteries and the pKD values at adenosine A2 binding sites, whereas no correlation was obtained when the pD2 values were compared to the pKD values at adenosine A1-binding sites on membranes from porcine striata. 5. The relaxant effects of adenosine and its analogues were competitively antagonized by 8-(p-sulphophenyl)-theophylline (8-SPT), producing pA2 values similar to the respective pKD value of the antagonist at adenosine A2 binding sites. 6. It is suggested that the porcine coronary artery possesses adenosine A2 receptors which seem to be similar to the adenosine A2 binding site in pig striatum, whereas no evidence was obtained for the presence of adenosine A1 receptors.

King, A. D.; Milavec-Krizman, M.; Muller-Schweinitzer, E.

1990-01-01

121

Adenosine mediates IL-13-induced inflammation and remodeling in the lung and interacts in an IL-13-adenosine amplification pathway.  

PubMed

IL-13 is an important mediator of inflammation and remodeling. We hypothesized that adenosine accumulation, alterations in adenosine receptors, and adenosine-IL-13 autoinduction are critical events in IL-13-induced pathologies. To test this, we characterized the effects of IL-13 overexpression on the levels of adenosine, adenosine deaminase (ADA) activity, and adenosine receptors in the murine lung. We also determined whether adenosine induced IL-13 in lungs from ADA-null mice. IL-13 induced an inflammatory and remodeling response that caused respiratory failure and death. During this response, IL-13 caused a progressive increase in adenosine accumulation, inhibited ADA activity and mRNA accumulation, and augmented the expression of the A1, A2B, and A3 but not the A2A adenosine receptors. ADA enzyme therapy diminished the IL-13-induced increase in adenosine, inhibited IL-13-induced inflammation, chemokine elaboration, fibrosis, and alveolar destruction, and prolonged the survival of IL-13-transgenic animals. In addition, IL-13 was strongly induced by adenosine in ADA-null mice. These findings demonstrate that adenosine and adenosine signaling contribute to and influence the severity of IL-13-induced tissue responses. They also demonstrate that IL-13 and adenosine stimulate one another in an amplification pathway that may contribute to the nature, severity, progression, and/or chronicity of IL-13 and/or Th2-mediated disorders. PMID:12897202

Blackburn, Michael R; Lee, Chun G; Young, Hays W J; Zhu, Zhou; Chunn, Janci L; Kang, Min Jong; Banerjee, Suman K; Elias, Jack A

2003-08-01

122

Photoaffinity labeling of A1-adenosine receptors  

SciTech Connect

The ligand-binding subunit of the A1-adenosine receptor has been identified by photoaffinity labeling. A photolabile derivative of R-N6-phenylisopropyladenosine, R-2-azido-N6-p-hydroxyphenylisopropyladenosine (R-AHPIA), has been synthesized as a covalent specific ligand for A1-adenosine receptors. In adenylate cyclase studies with membranes of rat fat cells and human platelets, R-AHPIA has adenosine receptor agonist activity with a more than 60-fold selectivity for the A1-subtype. It competes for (TH)N6-phenylisopropyladenosine binding to A1-receptors of rat brain membranes with a Ki value of 1.6 nM. After UV irradiation, R-AHPIA binds irreversibly to the receptor, as indicated by a loss of (TH)N6-phenylisopropyladenosine binding after extensive washing; the Ki value for this photoinactivation is 1.3 nM. The p-hydroxyphenyl substituent of R-AHPIA can be directly radioiodinated to give a photoaffinity label of high specific radioactivity ( SVI-AHPIA). This compound has a KD value of about 1.5 nM as assessed from saturation and kinetic experiments. Adenosine analogues compete for SVI-AHPIA binding to rat brain membranes with an order of potency characteristic for A1-adenosine receptors. Dissociation curves following UV irradiation at equilibrium demonstrate 30-40% irreversible specific binding. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that the probe is photoincorporated into a single peptide of Mr = 35,000. Labeling of this peptide can be blocked specifically and stereoselectively by adenosine receptor agonists and antagonists in a manner which is typical for the A1-subtype. The results indicate that SVI-AHPIA identifies the ligand-binding subunit of the A1-adenosine receptor, which is a peptide with Mr = 35,000.

Klotz, K.N.; Cristalli, G.; Grifantini, M.; Vittori, S.; Lohse, M.J.

1985-11-25

123

A model for adenosine transport and metabolism.  

PubMed Central

1. A model is presented for adenosine transport and metabolism in different steady states. The model considers steady-state equations for metabolic enzymes based on information from the literature on their kinetic behaviour. 2. Assuming that extracellular adenosine and inosine are translocated by three transporters, we have devised rate equations for these nucleoside transporters which are valid when both nucleosides are present. Since the Na(+)-independent transporter can either incorporate nucleosides into the cell or release them, various conditions have been simulated in which inosine was either incorporated or released. 3. Control analyses are reported which show that the fluxes towards intracellular adenine nucleosides are controlled by ecto-5'-nucleotidase in some circumstances and by the nucleoside transporters in others. The nucleoside transporter is responsible for five fluxes (two Na+ dependent adenosine transport mechanisms, a Na(+)-dependent inosine transport, a Na(+)-independent adenosine transport and a Na(+)-independent inosine influx or efflux) but the control is not always positive for all these fluxes. The control patterns of these five fluxes indicate that, in the presence of extracellular adenosine and inosine, the intracellular metabolism of adenine derivatives would be highly dependent on the extracellular and intracellular concentrations of both nucleosides, on the ectoenzymes (5'-nucleotidase and adenosine deaminase) and on the transporter. 4. Predictions of the model were examined. The results indicate that a change in one independent variable (extracellular AMP concentration) makes the system evolve towards a new steady state which is far from the initial one and has a different control pattern. In contrast, simulation of inhibition of the carriers produces only slight modification of the fluxes since the concentrations of the metabolites change to counteract the effect. Thus, for instance, a 50% inhibition of the three carriers does not affect the flux towards intracellular adenine nucleotides. Finally, our model has confirmed that the evolution of the concentration of extracellular adenosine, when an increase in extracellular AMP is produced, agrees with the behaviour expected for a neurohormone.

Centelles, J J; Cascante, M; Canela, E I; Franco, R

1992-01-01

124

Determination of adenosine effects and adenosine receptors in murine corpus cavernosum.  

PubMed

This study tested the hypothesis that adenosine, in murine corpora cavernosa, produces direct relaxation of smooth muscle cells and inhibition of contractile responses mediated by sympathetic nerve stimulation. Penes were excised from anesthetized male C57BL/6 mice, dissected, and cavernosal strips were mounted to record isometric force. Adenosine, 2-chloroadenosine (stable analog of adenosine), and 2-phenylaminoadenosine (CV1808) (A2(A)/A2(B) agonist) produced concentration-dependent relaxations of phenylephrine-contracted tissues. Relaxation to 2-chloroadenosine was inhibited, in a concentration-dependent manner, by 2-(2-furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine (SCH58261; A2(A) antagonist; 10(-9)-10(-6) M) and N-(4-acetylphenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)phenoxy]acetamida (MRS1706; A2(B) antagonist; 10(-8)-10(-6) M). The combination of both antagonists abrogated 2-chloroadenosine-induced relaxation. Electrical field stimulation (EFS; 1-32 Hz) of adrenergic nerves produced frequency-dependent contractions that were inhibited by compounds that increase adenosine levels, such as 5'-iodotubercidin (adenosine kinase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine (adenosine deaminase inhibitor), and dipyridamole (inhibitor of adenosine transport). The adenosine A1 receptor agonist N(6)-cyclopentyladenosine (C8031) right-shifted contractile responses to EFS, with a significant inhibitory effect at 10(-6) M. Blockade of adenosine A1 receptors with 8-cyclopentyl-1,3-dipropylxanthine (C101) (10(-7) M) enhanced contractile responses to EFS and eliminated the inhibitory effects of 5'-iodotubercidin. Dipyridamole and 5'-iodotubercidin had no effect on adenosine-mediated relaxation. In summary, adenosine directly relaxes cavernosal smooth muscle cells, by the activation of A2(A)/A2(B) receptor subtypes. In addition, adenosine negatively modulates sympathetic neurotransmission, by A1 receptor subtype activation, in murine corpora cavernosa. Adenosine may subserve dual roles in modulating the physiological mechanisms of erection in mice. PMID:17494861

Tostes, Rita C; Giachini, Fernanda R C; Carneiro, Fernando S; Leite, Romulo; Inscho, Edward W; Webb, R Clinton

2007-08-01

125

Adenosiland: walking through adenosine receptors landscape.  

PubMed

Adenosine receptors (ARs) belong to the family of G protein-coupled receptors. Four distinct subtypes are known, termed adenosine A(1), A(2A), A(2B) and A(3). receptors and they are regulated by adenosine which is one of the most ancient and widespread chemical messengers in the animal and plant kingdoms. Moreover, ARs are widely distributed in human body and they are expressed with different density in diverse tissues. It is not surprising that they are involved in the regulation of several physiopathological processes. Adenosiland represents the first tentative of an integrated bioinformatics and chemoinformatics web-resource dedicated to adenosine receptors. This informatics platform provides a wide-ranging of structure based and ligand based query functions to facilitate the exploration of adenosine receptor structures from primary sequences to three-dimensional architectures. Here, we present an overview of Adenosiland platform describing the most valuable searching tools and their functionalities. Adenosiland can be freely accessed at http://mms.dsfarm.unipd.it/Adenosiland/. PMID:23127988

Floris, Matteo; Sabbadin, Davide; Medda, Ricardo; Bulfone, Alessandro; Moro, Stefano

2012-12-01

126

The adenosine kinase hypothesis of epileptogenesis  

PubMed Central

Current therapies for epilepsy are largely symptomatic and do not affect the underlying mechanisms of disease progression, i.e. epileptogenesis. Given the large percentage of pharmacoresistant chronic epilepsies, novel approaches are needed to understand and modify the underlying pathogenetic mechanisms. Although different types of brain injury (e.g. status epilepticus, traumatic brain injury, stroke) can trigger epileptogenesis, astrogliosis appears to be a homotypic response and hallmark of epilepsy. Indeed, recent findings indicate that epilepsy might be a disease of astrocyte dysfunction. This review focuses on the inhibitory neuromodulator and endogenous anticonvulsant adenosine, which is largely regulated by astrocytes and its key metabolic enzyme adenosine kinase (ADK). Recent findings support the ADK hypothesis of epileptogenesis: (i) Mouse models of epileptogenesis suggest a sequence of events leading from initial downregulation of ADK and elevation of ambient adenosine as an acute protective response, to changes in astrocytic adenosine receptor expression, to astrocyte proliferation and hypertrophy (i.e. astrogliosis), to consequential overexpression of ADK, reduced adenosine and finally to spontaneous focal seizure activity restricted to regions of astrogliotic overexpression of ADK. (ii) Transgenic mice overexpressing ADK display increased sensitivity to brain injury and seizures. (iii) Inhibition of ADK prevents seizures in a mouse model of pharmacoresistant epilepsy. (iv) Intrahippocampal implants of stem cells engineered to lack ADK prevent epileptogenesis. Thus, ADK emerges both as a diagnostic marker to predict, as well as a prime therapeutic target to prevent, epileptogenesis.

Boison, Detlev

2008-01-01

127

Pain-relieving prospects for adenosine receptors and ectonucleotidases  

PubMed Central

Adenosine receptor agonists have potent antinociceptive effects in diverse preclinical models of chronic pain. In contrast, the efficacy of adenosine or adenosine receptor agonists at treating pain in humans is unclear. Two ectonucleotidases that generate adenosine in nociceptive neurons were recently identified. When injected spinally, these enzymes have long-lasting adenosine A1 receptor (A1R)-dependent antinociceptive effects in inflammatory and neuropathic pain models. Furthermore, recent findings indicate that spinal adenosine A2A receptor activation can enduringly inhibit neuropathic pain symptoms. Collectively, these studies suggest the possibility of treating chronic pain in humans by targeting specific adenosine receptor subtypes in anatomically defined regions with agonists or with ectonucleotidases that generate adenosine.

Zylka, Mark J.

2010-01-01

128

Adenine and adenosine salvage in Leishmania donovani.  

PubMed

6-aminopurine metabolism in Leishmania is unique among trypanosomatid pathogens since this genus expresses two distinct routes for adenine salvage: adenine phosphoribosyltransferase (APRT) and adenine deaminase (AAH). To evaluate the relative contributions of APRT and AAH, adenine salvage was evaluated in ?aprt, ?aah, and ?aprt/?aah null mutants of L. donovani. The data confirm that AAH plays the dominant role in adenine metabolism in L. donovani, although either enzyme alone is sufficient for salvage. Adenosine salvage was also evaluated in a cohort of null mutants. Adenosine is also primarily converted to hypoxanthine, either intracellularly or extracellularly, but can also be phosphorylated to the nucleotide level by adenosine kinase when the predominant pathways are genetically or pharmacologically blocked. These data provide genetic verification for the relative contributions of 6-aminopurine metabolizing pathways in L. donovani and demonstrate that all of the pathways can function under appropriate conditions of genetic or pharmacologic perturbation. PMID:23845934

Boitz, Jan M; Ullman, Buddy

2013-08-01

129

Effect of A2B adenosine receptor gene ablation on proinflammatory adenosine signaling in mast cells.  

PubMed

Pharmacological studies suggest that A(2B) adenosine receptors mediate proinflammatory effects of adenosine in human mast cells in part by up-regulating production of Th2 cytokines and angiogenic factors. This concept has been recently challenged by the finding that mast cells cultured from bone marrow-derived mast cells (BMMCs) of A(2B) knockout mice display an enhanced degranulation in response to FcepsilonRI stimulation. This finding was interpreted as evidence of anti-inflammatory functions of A(2B) receptors and it was suggested that antagonists with inverse agonist activity could promote activation of mast cells. In this report, we demonstrate that genetic ablation of the A(2B) receptor protein has two distinct effects on BMMCs, one is the previously reported enhancement of Ag-induced degranulation, which is unrelated to adenosine signaling; the other is the loss of adenosine signaling via this receptor subtype that up-regulates IL-13 and vascular endothelial growth factor secretion. Genetic ablation of A(2B) receptors had no effect on A(3) adenosine receptor-dependent potentiation of Ag-induced degranulation in mouse BMMCs, but abrogated A(2B) adenosine receptor-dependent stimulation of IL-13 and vascular endothelial growth factor secretion. Adenosine receptor antagonists MRS1706 and DPCPX with known inverse agonist activity at the A(2B) subtype inhibited IL-13 secretion induced by the adenosine analog NECA, but did not mimic the enhanced Ag-induced degranulation observed in A(2B) knockout BMMCs. Thus, our study confirmed the proinflammatory role of adenosine signaling via A(2B) receptors and the anti-inflammatory actions of A(2B) antagonists in mouse BMMCs. PMID:18490720

Ryzhov, Sergey; Zaynagetdinov, Rinat; Goldstein, Anna E; Novitskiy, Sergey V; Dikov, Mikhail M; Blackburn, Michael R; Biaggioni, Italo; Feoktistov, Igor

2008-06-01

130

Quantitative analysis of the ion-dependent folding stability of DNA triplexes  

NASA Astrophysics Data System (ADS)

A DNA triplex is formed through binding of a third strand to the major groove of a duplex. Due to the high charge density of a DNA triplex, metal ions are critical for its stability. We recently developed the tightly bound ion (TBI) model for ion-nucleic acids interactions. The model accounts for the potential correlation and fluctuations of the ion distribution. We now apply the TBI model to analyze the ion dependence of the thermodynamic stability for DNA triplexes. We focus on two experimentally studied systems: a 24-base DNA triplex and a pair of interacting 14-base triplexes. Our theoretical calculations for the number of bound ions indicate that the TBI model provides improved predictions for the number of bound ions than the classical Poisson-Boltzmann (PB) equation. The improvement is more significant for a triplex, which has a higher charge density than a duplex. This is possibly due to the higher ion concentration around the triplex and hence a stronger ion correlation effect for a triplex. In addition, our analysis for the free energy landscape for a pair of 14-mer triplexes immersed in an ionic solution shows that divalent ions could induce an attractive force between the triplexes. Furthermore, we investigate how the protonated cytosines in the triplexes affect the stability of the triplex helices.

Chen, Gengsheng; Chen, Shi-Jie

2011-12-01

131

Adenosine A peripheral neuronal modulator of pain and inflammation  

Microsoft Academic Search

\\u000a In the central nervous system, adenosine plays an important physiological role in the regulation of neuronal activity and\\u000a in neuroprotection. Adenosine actions are mediated by cell surface adenosine receptors (A1, A2A, A2B, A3) which are all linked to G-proteins, and activation of these receptors can recruit a number of second messenger systems [1,2] (Tab. 1). Adenosine has a high affinity

Jana Sawynok

132

Differential distribution of adenosine receptors in rat cochlea  

Microsoft Academic Search

Adenosine is a constitutive cell metabolite that can be released from cells via specific bi-directional transporters and is\\u000a an end-point for nucleotide hydrolysis. In the extracellular space, adenosine becomes a signalling molecule for P1 (adenosine)\\u000a receptors that modulate physiological responses in a wide range of mammalian tissues. Whereas adenosine signalling has been\\u000a implicated in the regulation of cochlear blood flow

Srdjan M. Vlajkovic; Shukri Abi; Carol J. H. Wang; Gary D. Housley; Peter R. Thorne

2007-01-01

133

Emerging adenosine receptor agonists--an update  

PubMed Central

Adenosine receptors (ARs), the major targets of caffeine and theophylline, comprise four receptor subtypes designated as A1, A2A, A2B and A3. Over a dozen AR agonists are currently in clinical trials for various conditions, including cardiac arrhythmias, neuropathic pain, myocardial perfusion imaging, cardiac ischemia, inflammatory diseases and cancer. Adenosine (non-selective), regadenoson (A2A) and dipyridamole (act indirectly via ARs) have received regulatory approval for clinical use. The present editorial will give a brief update on the current status of AR agonists in clinical trials.

Gao, Zhan-Guo; Jacobson, Kenneth A

2012-01-01

134

Ticagrelor Inhibits Adenosine Uptake In Vitro and Enhances Adenosine-Mediated Hyperemia Responses in a Canine Model  

Microsoft Academic Search

Aims: A routine secondary pharmacology screen indicated that reversibly binding oral P2Y12 receptor antagonist ticagrelor could inhibit adenosine uptake in human erythrocytes, suggesting that ticagrelor may potentiate adenosine-mediated responses in vivo. The aim of this study was to further characterize the adenosine uptake inhibition in vitro and study possible physiological consequences of adenosine uptake inhibition by ticagrelor in an anesthetized

J. J. J. van Giezen; James Sidaway; Philip Glaves; Ian Kirk; Jan-Arne Bjrkman

2012-01-01

135

Shaping of monocyte and macrophage function by adenosine receptors  

PubMed Central

Adenosine is an endogenous purine nucleoside that, following its release into the extracellular space, binds to specific adenosine receptors expressed on the cell surface. Adenosine appears in the extracellular space under metabolically stressful conditions, which are associated with ischemia, inflammation, and cell damage. There are 4 types of adenosine receptors (A1, A2A, A2B and A3) and all adenosine receptors are members of the G protein-coupled family of receptors. Adenosine receptors are expressed on monocytes and macrophages and through these receptors adenosine modulates monocyte and macrophage function. Since monocytes and macrophages are activated by the same danger signals that cause accumulation of extracellular adenosine, adenosine receptors expressed on macrophages represent a sensor system that provide monocytes and macrophages with information about the stressful environment. Adenosine receptors, thus, allow monocytes and macrophages to fine-tune their responses to stressful stimuli. Here, we review the consequences of adenosine receptor activation on monocyte/macrophage function. We will detail the effect of stimulating the various adenosine receptor subtypes on macrophage differentiation/proliferation, phagocytosis, and tissue factor (TF) expression. We will also summarize our knowledge of how adenosine impacts the production of extracellular mediators secreted by monocytes and macrophages in response to toll-like receptor (TLR) ligands and other inflammatory stimuli. Specifically, we will delineate how adenosine affects the production of superoxide, nitric oxide (NO), tumor necrosis factor-?, interleukin (IL)-12, IL-10, and vascular endothelial growth factor (VEGF). A deeper insight into the regulation of monocyte and macrophage function by adenosine receptors should assist in developing new therapies for inflammatory diseases.

Hasko, Gyorgy; Pacher, Pal; Deitch, Edwin A.; Vizi, E. Sylvester

2008-01-01

136

Neuromuscular transmission modulation by adenosine upon aging.  

PubMed

In infant rats adenosine A(2A) receptor-mediated modulation of neuromuscular transmission predominates over A1 receptor-mediated neuromodulation. We investigated whether aging affects this A(2A)/A(1) receptor balance. Evoked (EPPs) and miniature end plate potentials (MEPPs) were recorded from single fibers of (weeks-old) infant (3-4), young adult (12-16), older (36-38), and aged (80-90) male rat-diaphragm. The non A1/A(2A) selective agonist, 2-chloroadenosine (CADO; 30 nM) and the adenosine kinase inhibitor, iodotubericidin (ITU; 10 ?M) increased mean amplitude and quantal content of EPPs in infant, young adult, and older adult rats, but not in aged rats. The facilitatory effects were prevented by the A(2A) receptor antagonist, ZM241385 (50 nM) and mimicked by the A(2A) receptor agonist, CGS21680 (10 nM). The A1 receptor agonist, 6-cyclopentyladenosine (CPA; 100 nM), decreased EPPs amplitude in all age groups. It is concluded that aging differently influences adenosine A1 receptor and A(2A) receptor-mediated presynaptic modulation of neuromuscular transmission, so that the facilitatory influence decreases upon aging, whereas the inhibitory influence remains unchanged in aged animals. The reduction of adenosine A(2A) receptors upon aging may contribute to the age-related changes in neuromuscular function. PMID:22365485

Pousinha, Paula A; Correia, Alexandra M; Sebastio, Ana M; Ribeiro, Joaquim A

2012-12-01

137

Adenosine: an endogenous regulator of innate immunity  

Microsoft Academic Search

Although inflammatory and immunological reactions protect the host from invasion by microorganisms and eliminate debris at sites of tissue injury, they can also be responsible for significant tissue damage. Thus, regulatory mechanisms that limit damage from an overly exuberant immune response have evolved. It is increasingly apparent that adenosine, a purine nucleoside that is elaborated at injured and inflamed sites,

Gyrgy Hask; Bruce N. Cronstein

2004-01-01

138

Photoconduction of Adenosine in Various Morphological Forms  

Microsoft Academic Search

OPTICALLY clear films can be cast on a substrate when a neutral adenosine aqueous solution is slowly evaporated at about 60 C. Along the perimeter of the film, white needle-shaped crystallites are observed. If the film is exposed afterwards to high humidity, its clear portion will become cloudy. When viewed under the microscope between crossed nicols, this cloudy portion is

C. Y. Liang; E. G. Scalco

1963-01-01

139

Fluorescence sensing of adenosine deaminase based on adenosine induced self-assembly of aptamer structures.  

PubMed

A new approach is proposed for simple detection of adenosine deaminase (ADA) based on adenosine induced self-assembly of two pieces of single-stranded DNA (ssDNA). These ssDNA are two fragments of the aptamer that has a strong affinity for adenosine and are labeled with carboxyfluorescein and black hole quencher-1, respectively. The complementarities of the bases in the two pieces of ssDNA are insufficient to form a stable structure. In the presence of adenosine, however, the ssDNA can be assembled into the intact aptamer tertiary structure, which results in fluorescence quenching of the carboxyfluorescein-labeled aptamer fragment. As a result, the adenosine-ssDNA complex shows a low background signal, which is rather desired for achieving sensitive detection. Reaction of the complex with ADA causes a great fluorescence enhancement by converting adenosine into inosine that has no affinity for the aptamer. This behaviour leads to the development of a simple and sensitive fluorescent method for assaying ADA activity, with a detection limit of 0.05 U mL(-1), which is more sensitive than most of the existing approaches. Furthermore, the applicability of the method has been demonstrated by detecting ADA in mouse serum samples. PMID:23462984

Feng, Tingting; Ma, Huimin

2013-04-21

140

Adenosine augmentation ameliorates psychotic and cognitive endophenotypes of schizophrenia  

PubMed Central

An emerging theory of schizophrenia postulates that hypofunction of adenosine signaling may contribute to its pathophysiology. This study was designed to test the adenosine hypothesis of schizophrenia and to evaluate focal adenosine-based strategies for therapy. We found that augmentation of adenosine by pharmacologic inhibition of adenosine kinase (ADK), the key enzyme of adenosine clearance, exerted antipsychotic-like activity in mice. Further, overexpression of ADK in transgenic mice was associated with attentional impairments linked to schizophrenia. We observed that the striatal adenosine A2A receptor links adenosine tone and psychomotor response to amphetamine, an indicator of dopaminergic signaling. Finally, intrastriatal implants of engineered adenosine-releasing cells restored the locomotor response to amphetamine in mice overexpressing ADK, whereas the same grafts placed proximal to the hippocampus of transgenic mice reversed their working memory deficit. This functional double dissociation between striatal and hippocampal adenosine demonstrated in Adk transgenic mice highlights the independent contributions of these two interconnected brain regions in the pathophysiology of schizophrenia and thus provides the rationale for developing local adenosine augmentation therapies for the treatment of schizophrenia.

Shen, Hai-Ying; Singer, Philipp; Lytle, Nikki; Wei, Catherine J.; Lan, Jing-Quan; Williams-Karnesky, Rebecca L.; Chen, Jiang-Fan; Yee, Benjamin K.; Boison, Detlev

2012-01-01

141

Adenosine: An immune modulator of inflammatory bowel diseases  

PubMed Central

Inflammatory bowel disease (IBD) is a common and lifelong disabling gastrointestinal disease. Emerging treatments are being developed to target inflammatory cytokines which initiate and perpetuate the immune response. Adenosine is an important modulator of inflammation and its anti-inflammatory effects have been well established in humans as well as in animal models. High extracellular adenosine suppresses and resolves chronic inflammation in IBD models. High extracellular adenosine levels could be achieved by enhanced adenosine absorption and increased de novo synthesis. Increased adenosine concentration leads to activation of the A2a receptor on the cell surface of immune and epithelial cells that would be a potential therapeutic target for chronic intestinal inflammation. Adenosine is transported via concentrative nucleoside transporter and equilibrative nucleoside transporter transporters that are localized in apical and basolateral membranes of intestinal epithelial cells, respectively. Increased extracellular adenosine levels activate the A2a receptor, which would reduce cytokines responsible for chronic inflammation.

Ye, Jeff Huaqing; Rajendran, Vazhaikkurichi M

2009-01-01

142

Internalization and desensitization of adenosine receptors  

PubMed Central

Until now, more than 800 distinct G protein-coupled receptors (GPCRs) have been identified in the human genome. The four subtypes of the adenosine receptor (A1, A2A, A2B and A3 receptor) belong to this large family of GPCRs that represent the most widely targeted pharmacological protein class. Since adenosine receptors are widespread throughout the body and involved in a variety of physiological processes and diseases, there is great interest in understanding how the different subtypes are regulated, as a basis for designing therapeutic drugs that either avoid or make use of this regulation. The major GPCR regulatory pathway involves phosphorylation of activated receptors by G protein-coupled receptor kinases (GRKs), a process that is followed by binding of arrestin proteins. This prevents receptors from activating downstream heterotrimeric G protein pathways, but at the same time allows activation of arrestin-dependent signalling pathways. Upon agonist treatment, adenosine receptor subtypes are differently regulated. For instance, the A1Rs are not (readily) phosphorylated and internalize slowly, showing a typical half-life of several hours, whereas the A2AR and A2BR undergo much faster downregulation, usually shorter than 1h. The A3R is subject to even faster downregulation, often a matter of minutes. The fast desensitization of the A3R after agonist exposure may be therapeutically equivalent to antagonist occupancy of the receptor. This review describes the process of desensitization and internalization of the different adenosine subtypes in cell systems, tissues and in vivo studies. In addition, molecular mechanisms involved in adenosine receptor desensitization are discussed.

Klaasse, Elisabeth C.; de Grip, Willem J.; Beukers, Margot W.

2007-01-01

143

[3H]Adenosine Triphosphate: Release during Stimulation of Enteric Nerves  

Microsoft Academic Search

The isolated taenia coli of the guinea pig takes up tritiated adenosine, adenosine monophosphate, adenosine diphosphate, and adenosine triphosphate, in preference to tritiated inosine and adenine. After uptake, [3H]adenosine is converted and retained primarily as [3H]adenosine triphosphate. Tritium is released from taenia coli treated with [3H]adenosine upon activation of the nonadrenergic inhibitory nerves. These results are consistent with the previous

Che Su; John A. Bevan; Geoffrey Burnstock

1971-01-01

144

Experimental study of aluminum-, calcium-, and magnesium-acetate complexing at 80 degree C  

Microsoft Academic Search

The stabilities of Al-, Ca-, and Mg-acetate complexes were determined separately at 80°C by measuring the solubilities of gibbsite, portlandite, and brucite as functions of acetate concentrations. The experiments were conducted using geologically realistic acetate concentrations in order to observe the acetate complexes that are important in sedimentary basin fluids. The experimental measurements are used to calculate the stoichiometries and

J FEIN

1991-01-01

145

Experimental study of aluminum-, calcium-, and magnesium-acetate complexing at 80C  

NASA Astrophysics Data System (ADS)

The stabilities of Al-, Ca-, and Mg-acetate complexes were determined separately at 80C by measuring the solubilities of gibbsite, portlandite, and brucite as functions of acetate concentrations. The experiments were conducted using geologically realistic acetate concentrations in order to observe the acetate complexes that are important in sedimentary basin fluids. The experimental measurements are used to calculate the stoichiometries and thermodynamic properties of the important Al-, Ca-, and Mg-acetate complexes. The data indicate that Al(OAc) 2+ and Al(OAc) 2+ are the important Al-acetate complexes in the gibbsite system. Ca(OAc) + and Mg(OAc) + are the dominant acetate complexes in the portlandite and the brucite systems, respectively. The calculated values of the log of the dissociation constants for Al(OAc) 2+, Al(OAc) 2+, Ca(OAc) +, and Mg(OAc) + are -4.8 0.2, -2.9 0.1, -1.2 0.2, and -1.3 0.3, respectively. Thermodynamic models that incorporate these results indicate that the presence of acetate in sedimentary basin fluids can not markedly enhance rock porosity through mineral dissolution.

Fein, Jeremy B.

1991-04-01

146

Experimental study of aluminum-, calcium-, and magnesium-acetate complexing at 80 degree C  

SciTech Connect

The stabilities of Al-, Ca-, and Mg-acetate complexes were determined separately at 80{degree}C by measuring the solubilities of gibbsite, portlandite, and brucite as functions of acetate concentrations. The experiments were conducted using geologically realistic acetate concentrations in order to observe the acetate complexes that are important in sedimentary basin fluids. The experimental measurements are used to calculate the stoichiometries and thermodynamic properties of the important Al-, Ca-, and Mg-acetate complexes. The data indicate that Al(OAc){sup 2+} and Al(OAc){sup +}{sub 2} are the important Al-acetate complexes in the gibbsite system. Ca(OAc){sup +} and Mg(OAc){sup +} are the dominant acetate complexes in the portlandite and the brucite systems, respectively. The calculated values of the log of the dissociation constants for Al(OAc){sup +}{sub 2}, Al (OAc){sup 2+}, Ca(OAc){sup +}, and Mg(OAc){sup +} are -4.8 {plus minus} 0.2, -2.9 {plus minus} 0.1, -1.2 {plus minus} 0.2, and -1.3 {plus minus} 0.3, respectively. Thermodynamic models that incorporate these results indicate that the presence of acetate in sedimentary basin fluids can not markedly enhance rock porosity through mineral dissolution.

Fein, J.B. (Illinois State Water Survey, Champaign, IL (USA))

1991-04-01

147

Effect of Calcium and Magnesium on Phosphatidylserine Membranes: Experiments and All-Atomic Simulations  

PubMed Central

It is known that phosphatidylserine (PS?) lipids have a very similar affinity for Ca2+ and Mg2+ cations, as revealed by electrokinetic and stability experiments. However, despite this similar affinity, experimental evidence shows that the presence of Ca2+ or Mg2+ induces very different aggregation behavior for PS? liposomes as characterized by their fractal dimensions. Also, turbidity measurements confirm substantial differences in aggregation behavior depending on the presence of Ca2+ or Mg2+ cations. These puzzling results suggest that although these two cations have a similar affinity for PS? lipids, they induce substantial structural differences in lipid bilayers containing each of these cations. In other words, these cations have strong ion-specific effects on the structure of PS? membranes. This interpretation is supported by all-atomic molecular-dynamics simulations showing that Ca2+ and Mg2+ cations have different binding sites and induce different membrane hydration. We show that although both ions are incorporated deep into the hydrophilic region of the membrane, they have different positions and configurations at the membrane. Absorbed Ca2+ cations present a peak at a distance ?2nm from the center of the lipid bilayer, and their most probable binding configuration involves two oxygen atoms from each of the charged moieties of the PS molecule (phosphate and carboxyl groups). In contrast, the distribution of absorbed Mg2+ cations has two different peaks, located a few angstroms before and after the Ca2+ peak. The most probable configurations (corresponding to these two peaks) involve binding to two oxygen atoms from carboxyl groups (the most superficial binding peak) or two oxygen atoms from phosphate groups (the most internal peak). Moreover, simulations also show differences in the hydration structure of the membrane: we obtained a hydration of 7.5 and 9 water molecules per lipid in simulations with Ca2+ and Mg2+, respectively.

Martin-Molina, Alberto; Rodriguez-Beas, Cesar; Faraudo, Jordi

2012-01-01

148

Determination of sodium, potassium, calcium and magnesium cations in biodiesel by ion chromatography.  

PubMed

This work reports an ion chromatographic (IC) method for the quantitative determination of inorganic cations (Na(+), K(+), Mg(2+) and Ca(2+)) in biodiesel samples that were synthesized from different vegetable oils and fat. The proposed method uses water extraction, heating and ultrasound. The limits of detection (LOD) for each ion, in milligrams of the analyte per kilogram of biodiesel (mgkg(-1)), were respectively: 0.11 (Na(+)); 0.42 (K(+)); 0.23 (Ca(2+)); and 0.36 (Mg(2+)). The accuracy of the method was studied through recovery tests. For comparison, two samples were also analyzed using an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) procedure. The paired Student t test and the Snedecor F test showed that both methods offer equivalent results in terms of accuracy and precision. The operational simplicity, accuracy and precision of the proposed method suggest that it can be a good alternative for the determination of inorganic cations in biodiesel samples. PMID:22305906

de Caland, Lilia Basilio; Silveira, Eva Lcia Cardoso; Tubino, Matthieu

2012-03-01

149

Calcium and magnesium transport by in situ mitochondria: electron probe analysis of vascular smooth muscle  

SciTech Connect

The extent, time course, and reversibility of mitochondrial Ca/sup 2 +/ uptake secondary to cellular Ca/sup 2 +/ influx stimulated by massive Na+ efflux were evaluated by electron probe microanalysis of rabbit portal vein smooth muscle. Strips of portal vein were Na+ loaded for 3 hours at 37/sup 0/C in a K+-free 1 mM ouabain solution, after which rapid Na+ efflux was induced by washing with a Na+-free K+-Li+ solution (1 mM ouabain). Li+ washing Na+-loaded portal vein produced a large transient contraction accompanied by an increase (over 100-fold) in mitochondrial Ca/sup 2 +/ and also significant (p less than 0.05) increases in phosphorus and Mg/sup 2 +/. The Ca/sup 2 +/ loading of the mitochondria was reversed during prolonged Li+ wash, and by 2 hours, mitochondrial Ca/sup 2 +/, Mg/sup 2 +/, and phosphorus had returned to control levels. The maximal contractile response to stimulation remained normal, demonstrating that pathologic Ca/sup 2 +/ loading of mitochondria is reversible in situ and compatible with normal maximal force developed by the smooth muscle. Mitochondrial Ca/sup 2 +/ and phosphorus uptake were reduced but still significant when the Li+ wash contained 0.2 mM Ca/sup 2 +/ or when ouabain was omitted. The fact that mitochondrial Ca/sup 2 +/ loading accompanied submaximal contractions during 0.2 mM Ca/sup 2 +/-Li wash suggests supranormal affinity of mitochondria for Ca/sup 2 +/ and may be due, in part, to reverse operation of the mitochondrial Na+-Ca/sup 2 +/ exchanger. Mitochondrial Ca/sup 2 +/, Mg/sup 2 +/, and phosphorus uptake were eliminated when the Li+ wash was performed at 2/sup 0/C or when the wash contained no Ca/sup 2 +/.

Broderick, R.; Somlyo, A.P.

1987-10-01

150

Factors affecting ex-situ aqueous mineral carbonation using calcium and magnesium silicate minerals  

SciTech Connect

Carbonation of magnesium- and calcium-silicate minerals to form their respective carbonates is one method to sequester carbon dioxide. Process development studies have identified reactor design as a key component affecting both the capital and operating costs of ex-situ mineral sequestration. Results from mineral carbonation studies conducted in a batch autoclave were utilized to design and construct a unique continuous pipe reactor with 100% recycle (flow-loop reactor). Results from the flow-loop reactor are consistent with batch autoclave tests, and are being used to derive engineering data necessary to design a bench-scale continuous pipeline reactor.

Gerdemann, Stephen J.; Dahlin, David C.; O'Connor, William K.; Penner, Larry R.; Rush, G.E.

2004-01-01

151

Effects of calcium and magnesium ions and host viability on growth of bdellovibrios  

Microsoft Academic Search

Bdellovibrio spp. strains 6-5-S, 100, 109 (Davis), and A3.12 multiply in the presence of viable but non-proliferating or heat-killed (70\\u000a or 100 C, 10 min; 121 C, 5 min) cells ofSpirillum serpens strain VHL suspended in buffers supplemented with Ca++ and\\/or Mg++. Ca++ (optimal, 2 10?3\\u000a m) and Mg++ (optimal, 2 10?5\\u000a m) independently stimulate the groth of

J. C.-C. Huang; M. P. Starr

1973-01-01

152

Chemical, microstructural and strength development of calcium and magnesium carbonate binders  

Microsoft Academic Search

The influence of magnesium on the chemistry of calcium carbonate formation has been studied. It was found that the type of carbonate formed by subjecting compacts of Ca(OH)2 and Mg(OH)2 to carbon dioxide (up to 20atm CO2 pressure) for variable periods of time is largely controlled by the molar proportion of calcium to magnesium in the initial mixture. Increasing magnesium

P. De Silva; L. Bucea; V. Sirivivatnanon

2009-01-01

153

Synthesis and Properties of Modified Fillers Based on Calcium and Magnesium Carbonates  

Microsoft Academic Search

A possibility of modifying natural carbonate fillers for paint and varnish industry by solutions of salts of some nonferrous metals was studied. Reactions of carbonates with metal ions and physicotechnical properties of the resulting materials were considered.

I. L. Shashkova; A. I. Rat'ko; V. D. Koshevar; N. V. Kitikova; A. G. D'yachenko

2002-01-01

154

Calcium and magnesium carbonate concentrations in different growth regions of gorgonians  

Microsoft Academic Search

Four of the most abundant gorgonian species from the southwestern Cape waters, Eunicella papillosa (Esper, 1797), E. alba (Esper, 1797), E. tricoronata Velimirov, 1971 and Lophogorgia flamea (Ellis and Solander, 1786) were analysed for Ca and Mg by atomic absorption spectroscopy (AAS) and ethylenediaminetetraacetate (EDTA) titration. The total mineral content in the peripheral tissues, excluding the axial skeleton, expressed as

B. Velimirov; E. L. Bhm

1976-01-01

155

Effects of improved glycaemic control on calcium and magnesium homeostasis in type II diabetes.  

PubMed

Poorly controlled type II diabetic patients with hypomagnesaemia, hypermagnesuria, and hypercalciuria were allocated to treatment with either metformin or glipizide, to determine the effects on some indices of mineral metabolism. Despite comparable improvement in glycaemic control, assessed by glucose and haemoglobin A1, there were significant differences between the two groups in the handling of magnesium. Patients receiving metformin showed a reduction in magnesium excretion but remained hypomagnesaemic and hypercalciuric. In contrast, patients receiving glipizide exhibited little change in either magnesium or calcium excretion but showed a significant rise in serum magnesium. PMID:3192752

McBain, A M; Brown, I R; Menzies, D G; Campbell, I W

1988-09-01

156

Effects of improved glycaemic control on calcium and magnesium homeostasis in type II diabetes  

Microsoft Academic Search

Poorly controlled type II diabetic patients with hypomagnesaemia, hypermagnesuria, and hypercalciuria were allocated to treatment with either metformin or glipizide, to determine the effects on some indices of mineral metabolism. Despite comparable improvement in glycaemic control, assessed by glucose and haemoglobin A1, there were significant differences between the two groups in the handling of magnesium. Patients receiving metformin showed a

A M McBain; I R Brown; D G Menzies; I W Campbell

1988-01-01

157

Effect of Mineral Water Containing Calcium and Magnesium on Calcium Oxalate Urolithiasis Risk Factors  

Microsoft Academic Search

Calcium oxalate kidney stone formers are invariably advised to increase their fluid intake. In addition, magnesium therapy is often administered. Recently, a prospective study showed that a high dietary intake of calcium reduces the risk of symptomatic kidney stones. The present study was performed to test whether simultaneous delivery of these factors high fluid intake, magnesium ingestion and increased

Allen L. Rodgers

1997-01-01

158

Calcium and magnesium levels in isolated cardiac mitochondria from mice injected with isoproterenol  

Microsoft Academic Search

Calcium (Ca) and Magnesium (Mg) are determined by atomic absorption flame spectrometry in isolated cardiac mitochondria from mice receiving subcutaneous injections of DL-isoproterenol HC1 (ISO), and in mitochondria of untreated controls. In the controls, mitochondria were isolated in the presence or absence of ruthenium red. On the absence of ruthenium red in the isolation medium, mitochondrial Ca levels increase by

Thorvald Stersdal; Hogne Engedal; Jakob Rli; Harald Jodalen; Svein Rotevatn

1981-01-01

159

Ca2+-activated K+ Channels in Murine Endothelial Cells: Block by Intracellular Calcium and Magnesium  

PubMed Central

The intermediate (IKCa) and small (SKCa) conductance Ca2+-sensitive K+ channels in endothelial cells (ECs) modulate vascular diameter through regulation of EC membrane potential. However, contribution of IKCa and SKCa channels to membrane current and potential in native endothelial cells remains unclear. In freshly isolated endothelial cells from mouse aorta dialyzed with 3 ?M free [Ca2+]i and 1 mM free [Mg2+]i, membrane currents reversed at the potassium equilibrium potential and exhibited an inward rectification at positive membrane potentials. Blockers of large-conductance, Ca2+-sensitive potassium (BKCa) and strong inward rectifier potassium (Kir) channels did not affect the membrane current. However, blockers of IKCa channels, charybdotoxin (ChTX), and of SKCa channels, apamin (Ap), significantly reduced the whole-cell current. Although IKCa and SKCa channels are intrinsically voltage independent, ChTX- and Ap-sensitive currents decreased steeply with membrane potential depolarization. Removal of intracellular Mg2+ significantly increased these currents. Moreover, concomitant reduction of the [Ca2+]i to 1 ?M caused an additional increase in ChTX- and Ap-sensitive currents so that the currents exhibited theoretical outward rectification. Block of IKCa and SKCa channels caused a significant endothelial membrane potential depolarization (?11 mV) and decrease in [Ca2+]i in mesenteric arteries in the absence of an agonist. These results indicate that [Ca2+]i can both activate and block IKCa and SKCa channels in endothelial cells, and that these channels regulate the resting membrane potential and intracellular calcium in native endothelium.

Ledoux, Jonathan; Bonev, Adrian D.; Nelson, Mark T.

2008-01-01

160

Effects of ion pairing with calcium and magnesium on selenate availability to higher plants  

SciTech Connect

The effects of solution speciation on the bioavailability of trace metals are well documented, but the role of speciation in the bioavailability of oxyanionic trace elements that may form significant ion pairs with Ca and Mg in saline media has not been investigated. The authors assessed the effects of such ion pairing on the availability of selenate to representative monocotyledonous and dicotyledonous higher plants. Formation constants for the CaSO{sub 4}{sup 0} formation was confirmed, but the value of 10{sup 2.7} for CaSeO{sub 4}{sup 0} was found to be in error; a value of 10{sup 2.0} is proposed here as the correct formation constant. Five solution culture experiments were conducted using alfalfa (Medicago sativa L.) or tall wheatgrass (Elytrigia pontica [Podp.] Holub) with treatments consisting of NaSeO{sub 4} levels in combination with various levels of MgCl{sub 2} or CaCl{sub 2}. Both shoot Se concentrations and whole-plant Se contents were highly correlated with the free SeO{sub 4}{sup 2{minus}} activity but were poorly correlated with the sum of the free ion plus Ca and Mg ion pair species. Thus, the authors have shown, for the first time, that the free ion model of trace metal bioavailability is also valid for oxyanions that form complexes with Ca and Mg in saline media but that this conclusion hinges critically on the accuracy of the pertinent formation constants.

Parker, D.R.; Tice, K.R.; Thomason, D.N. [Univ. of California, Riverside, CA (United States). Dept. of Soil and Environmental Sciences

1997-03-01

161

Effects of improved glycaemic control on calcium and magnesium homeostasis in type II diabetes.  

PubMed Central

Poorly controlled type II diabetic patients with hypomagnesaemia, hypermagnesuria, and hypercalciuria were allocated to treatment with either metformin or glipizide, to determine the effects on some indices of mineral metabolism. Despite comparable improvement in glycaemic control, assessed by glucose and haemoglobin A1, there were significant differences between the two groups in the handling of magnesium. Patients receiving metformin showed a reduction in magnesium excretion but remained hypomagnesaemic and hypercalciuric. In contrast, patients receiving glipizide exhibited little change in either magnesium or calcium excretion but showed a significant rise in serum magnesium.

McBain, A M; Brown, I R; Menzies, D G; Campbell, I W

1988-01-01

162

The effects of aluminum loading on selected tissue calcium and magnesium concentrations in rats  

Microsoft Academic Search

Considerable evidence implicates elevated brain aluminum (Al) concentration in the pathogenesis of several forms of central\\u000a nervous system dysfunction seen particularly among dialysis patients. In animals Al intoxication also leads to cerebral dysfunction.\\u000a Since increased brain calcium (Ca) concentration has been associated with similar disturbances of cerebral function, this\\u000a study was initiated to examine the effects of increased Al concentration

Maria A. Burnatowska-Hledin; Gilbert H. Mayor

1984-01-01

163

Crystallization of calcium and magnesium phosphates from solutions of low concentration  

NASA Astrophysics Data System (ADS)

The precipitation and evolution of calcium phosphates in solutions of low concentration ([Ca] = [P] = 0.005M) were studied at 25 C in the presence of magnesium the concentration of which ranged from 0.5mM to 50mM. The initial and final phases are described in terms of initial composition and pH of solutions. The first precipitating phase is an amorphous calcium phosphate, Ca 3(PO 4) 2 nH 2O, which transforms into apatite-like phosphate, Ca 5(PO 4) 3OH, or whitlockite, Ca 9MgH(PO 4) 7, or remains unaltered, according to the magnesium concentration. Brushite, CaHPO 42H 2O, dominates in the poorly supersaturated solutions. Octacalcium phosphate, Ca 4H(PO 4) 32.5H 2O, rarely occurs. The conditions for phase stability, and the role of magnesium and supersaturation are discussed.

Abbona, F.; Franchini-Angela, M.

1990-08-01

164

Passive and active in vitro resorption of calcium and magnesium phosphate cements by osteoclastic cells.  

PubMed

Biocements are clinically applied materials for bone replacement in non-load-bearing defects. Depending on their final composition, cements can be either resorbed or remain stable at the implantation site. Degradation can occur by two different mechanisms, by simple dissolution (passive) or after osteoclastic bone remodeling (active). This study investigated both the passive and active in vitro resorption behavior of brushite (CaHPO?? 2H?O), monetite (CaHPO?), calcium-deficient hydroxyapatite (CDHA; Ca?(PO?)?HPO?OH), and struvite (MgNH?PO???6H?O) cements. Passive resorption was measured by incubating the cement samples in a cell culture medium, whereas active resorption was determined during the surface culture of multinuclear osteoclastic cells derived from RAW 264.7 macrophages. Osteoclast formation was confirmed by showing tartrate resistant acid phosphatase (TRAP) activity on CDHA, brushite, and monetite surfaces, as well as by measuring calcitonin receptor (CT-R) expression as an osteoclast-specific protein by Western blot analysis for struvite ceramics. An absence of passive degradation and only marginally active degradation of <0.01% were found for CDHA matrices. For the secondary calcium phosphates brushite and monetite, active degradation was predominant with a cumulative Ca+ release of 2.02 (1.20) ?mol during 13 days, whereas passive degradation released only 0.788 (0.04) ?mol calcium ions into the medium. The struvite cement was the most degradable with a passive (active) release of 9.26 (2.92) Mg+ ions and a total weight loss of 4.7% over 13 days of the study. PMID:20673025

Grossardt, Christian; Ewald, Andrea; Grover, Liam M; Barralet, Jake E; Gbureck, Uwe

2010-12-01

165

Solid state metathesis synthesis of metal silicides; reactions of calcium and magnesium silicide with metal oxides  

Microsoft Academic Search

Reactions of transition metal oxides (V2O3, V2O5, Nb2O5, LiNbO3, Ta2O5, LiTaO3, MoO3 and Li2MoO4) with lithium silicide (Li2Si) and calcium silicidemagnesium silicide mix (CaSi2, Mg2Si) could be initiated by grinding, flame, filament or bulk thermal methods to produce a range of single phase transition metal silicides (VSi2, NbSi2 and TaSi2) in good yields (approximately 90%). The silicides were characterised by

Artur M. Nartowski; Ivan P. Parkin

2002-01-01

166

Extracellular cAMP-adenosine pathways in the mouse kidney  

PubMed Central

The renal extracellular 2?,3?-cAMP-adenosine and 3?,5?-cAMP-adenosine pathways (extracellular cAMPs?AMPs?adenosine) may contribute to renal adenosine production. Because mouse kidneys provide opportunities to investigate renal adenosine production in genetically modified kidneys, it is important to determine whether mouse kidneys express these cAMP-adenosine pathways. We administered (renal artery) 2?,3?-cAMP and 3?,5?-cAMP to isolated, perfused mouse kidneys and measured renal venous secretion rates of 2?,3?-cAMP, 3?,5?-cAMP, 2?-AMP, 3?-AMP, 5?-AMP, adenosine, and inosine. Arterial infusions of 2?,3?-cAMP increased (P < 0.0001) the mean venous secretion of 2?-AMP (390-fold), 3?-AMP (497-fold), adenosine (18-fold), and inosine (adenosine metabolite; 7-fold), but they did not alter 5?-AMP secretion. Infusions of 3?,5?-cAMP did not affect venous secretion of 2?-AMP or 3?-AMP, but they increased (P < 0.0001) secretion of 5?-AMP (5-fold), adenosine (17-fold), and inosine (6-fold). Energy depletion (metabolic inhibitors) increased the secretion of 2?,3?-cAMP (8-fold, P = 0.0081), 2?-AMP (4-fold, P = 0.0028), 3?-AMP (4-fold, P = 0.0270), 5?-AMP (3-fold, P = 0.0662), adenosine (2-fold, P = 0.0317), and inosine (7-fold, P = 0.0071), but it did not increase 3?,5?-cAMP secretion. The 2?,3?-cAMP-adenosine pathway was quantitatively similar in CD73 ?/? vs. +/+ kidneys. However, 3?,5?-cAMP induced a 6.7-fold greater increase in 5?-AMP, an attenuated increase (61% reduction) in inosine and a similar increase in adenosine in CD73 ?/? vs. CD73 +/+ kidneys. In mouse kidneys, 1) 2?,3?-cAMP and 3?,5?-cAMP are metabolized to their corresponding AMPs, which are subsequently metabolized to adenosine; 2) energy depletion activates the 2?,3?-cAMP-adenosine, but not the 3?,5?-cAMP-adenosine, pathway; and 3) although CD73 is involved in the 3?,5?-AMP-adenosine pathway, alternative pathways of 5?-AMP metabolism and reduced metabolism of adenosine to inosine compensate for life-long deficiency of CD73.

Ren, Jin; Cheng, Dongmei; Mi, Zaichuan

2011-01-01

167

Extracellular Adenosine-Mediated Modulation of Regulatory T Cells  

PubMed Central

Extracellular adenosine-dependent suppression and redirection of pro-inflammatory activities are mediated by the signaling through adenosine receptors on the surface of most immune cells. The immunosuppression by endogenously-produced adenosine is pathophysiologically significant since inactivation of A2A/A2B adenosine receptor (A2AR/A2BR) and adenosine-producing ecto-enzymes CD39/CD73 results in the higher intensity of immune response and exaggeration of inflammatory damage. Regulatory T cells (Treg) can generate extracellular adenosine, which is implicated in the immunoregulatory activity of Tregs. Interestingly, adenosine has been shown to increase the numbers of Tregs and further promotes their immunoregulatory activity. A2AR-deficiency in Tregs reduces their immunosuppressive efficacy in vivo. Thus, adenosine is not only directly and instantly inhibiting to the immune response through interaction with A2AR/A2BR on the effector cells, but also adenosine signaling can recruit other immunoregulatory mechanisms, including Tregs. Such interaction between adenosine and Tregs suggests the presence of a positive feedback mechanism, which further promotes negative regulation of immune system through the establishment of immunosuppressive microenvironment.

Ohta, Akio; Sitkovsky, Michail

2014-01-01

168

Characterization of adenosine receptors in bovine corneal endothelium  

PubMed Central

Previous studies indicated that adenosine can increase [cAMP]i and stimulate fluid transport by corneal endothelium. The purpose of this study was to determine which adenosine receptor subtype(s) are expressed and to examine their functional roles in modulating [cAMP]i, [Ca2+]i and effects on Cl? permeability in corneal endothelium. We screened bovine corneal endothelium (BCE) for adenosine receptor subtypes by RT-PCR and immunoblotting, and examined the effects of pharmacological agents on adenosine stimulated Cl? transport, [cAMP]i and [Ca2+]i. RT-PCR indicated the presence of A1 and A2b adenosine receptors, while A2a and A3 were negative. Western blot (WB) confirmed the presence of A2b (?50 kDa) and A1 (?40 kDa) in fresh and cultured BCE. Ten micromolar adenosine increased [cAMP]i by 27-fold over control and this was inhibited 66% by 10 ?m alloxazine, a specific A2b blocker. A1 activation with 1 ?m N6-CPA (a specific A1 agonist) or 100 nm adenosine decreased [cAMP]i by 23 and 6%, respectively. Adenosine had no effect on [Ca2+]i mobilization. Indirect immunofluorescence localized A2b receptors to the lateral membrane and A1 to the apical surface in cultured BCE. Adenosine significantly increased apical Cl? permeability by 22 times and this effect was nearly abolished by DMPX (10 ?m), a general A2 blocker. Adenosine-induced membrane depolarization was also inhibited by 33% (n=6) in the presence of alloxazine. Bovine corneal endothelium expresses functional A1 and A2b adenosine receptors. A1, preferentially activated at <1 ?m adenosine, acts to decrease [cAMP]i and A2b, activated at >1 ?m adenosine, increase [cAMP]i.

Tan-Allen, Kah Y.; Sun, Xing Cai; Bonanno, Joseph A.

2014-01-01

169

Involvement of adenosine in the neurobiology of schizophrenia and its therapeutic implications  

Microsoft Academic Search

Based on the neuromodulatory and homeostatic actions of adenosine, adenosine dysfunction may contribute to the neurobiological and clinical features of schizophrenia. The present model of adenosine dysfunction in schizophrenia takes into consideration the dopamine and glutamate hypotheses, since adenosine exerts neuromodulatory roles on these systems, and proposes that adenosine plays a role in the inhibitory deficit found in schizophrenia. Given

Diogo R. Lara; Oscar P. Dall'Igna; Eduardo S. Ghisolfi; Miriam G. Brunstein

2006-01-01

170

Adenosine thallium 201 myocardial perfusion scintigraphy  

SciTech Connect

Pharmacologic coronary vasodilation as an adjunct to myocardial perfusion imaging has become increasingly important in the evaluation of patients with coronary artery disease, in view of the large number of patients who cannot perform an adequate exercise test or in whom contraindications render exercise inappropriate. Adenosine is a very potent coronary vasodilator and when combined with thallium 201 scintigraphy produces images of high quality, with the added advantages of a very short half-life (less than 10 seconds) and the ability to adjust the dose during the infusion, which may enhance safety and curtail the duration of side effects. The reported sensitivity and specificity of adenosine thallium 201 scintigraphy for the detection of coronary artery disease are high and at least comparable with imaging after exercise or dipyridamole administration. 23 refs.

Verani, M.S. (Baylor College of Medicine and Nuclear Cardiology, The Methodist Hospital, Houston, TX (USA))

1991-07-01

171

Adenosine-to-inosine RNA editing.  

PubMed

Ribonucleic acid (RNA) editing is a mechanism that generates RNA and protein diversity, which is not directly encoded in the genome. The most common type of RNA editing in vertebrates is the conversion of adenosine to inosine in double-stranded RNA which occurs in the higher eukaryotes. This editing is carried out by the family of adenosine deaminase acting on RNA (ADAR) proteins. The most-studied substrates of ADAR proteins undergo editing which is very consistent, highly conserved, and functionally important. However, editing causes changes in protein-coding regions only at a small proportion of all editing sites. The vast majority of editing sites are in noncoding sequences. This includes microRNAs, as well as the introns and 3' untranslated regions of messenger RNAs, which play important roles in the RNA-mediated regulation of gene expression. PMID:20835992

Zinshteyn, Boris; Nishikura, Kazuko

2009-01-01

172

Adenosine receptors: expression, function and regulation.  

PubMed

Adenosine receptors (ARs) comprise a group of G protein-coupled receptors (GPCR) which mediate the physiological actions of adenosine. To date, four AR subtypes have been cloned and identified in different tissues. These receptors have distinct localization, signal transduction pathways and different means of regulation upon exposure to agonists. This review will describe the biochemical characteristics and signaling cascade associated with each receptor and provide insight into how these receptors are regulated in response to agonists. A key property of some of these receptors is their ability to serve as sensors of cellular oxidative stress, which is transmitted by transcription factors, such as nuclear factor (NF)-?B, to regulate the expression of ARs. Recent observations of oligomerization of these receptors into homo- and heterodimers will be discussed. In addition, the importance of these receptors in the regulation of normal and pathological processes such as sleep, the development of cancers and in protection against hearing loss will be examined. PMID:24477263

Sheth, Sandeep; Brito, Rafael; Mukherjea, Debashree; Rybak, Leonard P; Ramkumar, Vickram

2014-01-01

173

Chemoelectrical energy conversion of adenosine triphosphate  

NASA Astrophysics Data System (ADS)

Plant and animal cell membranes transport charged species, neutral molecules and water through ion pumps and channels. The energy required for moving species against established concentration and charge gradients is provided by the biological fuel - adenosine triphosphate (ATP) -synthesized within the cell. The adenosine triphosphatase (ATPases) in a plant cell membrane hydrolyze ATP in the cell cytoplasm to pump protons across the cell membrane. This establishes a proton gradient across the membrane from the cell exterior into the cell cytoplasm. This proton motive force stimulates ion channels that transport nutrients and other species into the cell. This article discusses a device that converts the chemical energy stored in adenosine triphosphate into electrical power using a transporter protein, ATPase. The V-type ATPase proteins used in our prototype are extracted from red beet(Beta vulgaris) tonoplast membranes and reconstituted in a bilayer lipid membrane or BLM formed from POPC and POPS lipids. A pH7 medium that can support ATP hydrolysis is provided on both sides of the membrane and ATP is dissolved in the pH7 buffer on one side of the membrane. Hydrolysis of ATP results in the formation of a phosphate ion and adenosine diphosphate. The energy from the reaction activates ATPase in the BLM and moves a proton across the membrane. The charge gradient established across the BLM due to the reaction and ion transport is converted into electrical current by half-cell reference electrodes. The prototype ATPase cell with an effective BLM area of 4.15 mm2 carrying 15 ?l of ATPase proteins was observed to develop a steady state peak power output of 70 nW, which corresponds to a specific power of 1.69 ?W/cm2 and a current density of 43.4 ?A/cm2 of membrane area.

Sundaresan, Vishnu Baba; Sarles, Stephen Andrew; Leo, Donald J.

2007-03-01

174

Adenosine receptors as potential targets in melanoma.  

PubMed

Melanoma is one of the most aggressive types of cancer, that is difficult to manage clinically. A major feature of melanoma cells is their ability to escape immune surveillance. Adenosine receptors play a pivotal role in host immune-surveillance. A2a (A2aR) and, partially, A2bR receptors mediate the adenosine-induced immune-suppression, which markedly facilitates tumor development/progression. On the contrary, A3R stimulation enhances the anti-tumor immune response and thus limits tumor growth. A3R also inhibits the proliferation of many cancer cells. Given that A2aR and A3R have profound effects on tumor growth and metastasis, they are attractive targets for novel therapeutic anti-cancer agents. Here, we review the role played by A2aR and A3R in regulating cancer pathogenesis, with a focus on melanoma, and the therapeutic potential of adenosine receptors pharmacological modulation. PMID:23856527

Montinaro, Antonella; Iannone, Raffaella; Pinto, Aldo; Morello, Silvana

2013-10-01

175

The role of adenosine signaling in sickle cell therapeutics.  

PubMed

Data suggest a role for adenosine signaling in the pathogenesis of sickle cell disease (SCD). Signaling through the adenosine A2A receptor (A2AR) has demonstrated beneficial effects. Activation of A2ARs decreases inflammation with SCD by blocking activation of invariant natural killer T cells. Decreased inflammation may reduce the severity of vasoocclusive crises. Adenosine signaling through the adenosine A2B receptor (A2BR) may be detrimental in SCD. Whether adenosine signaling predominantly occurs through A2ARs or A2BRs may depend on differing levels of adenosine and disease state (steady state versus crisis). There may be opportunities to develop novel therapeutic approaches targeting A2ARs and/or A2BRs for patients with SCD. PMID:24589267

Field, Joshua J; Nathan, David G; Linden, Joel

2014-04-01

176

Use of adenosine echocardiography for diagnosis of coronary artery disease  

SciTech Connect

Two-dimensional echocardiography combined with exercise is sensitive and specific in the detection of coronary artery disease (CAD) by demonstrating transient abnormalities in wall motion. Frequently, however, patients cannot achieve maximal exercise because of various factors. Pharmacologic stress testing with intravenous adenosine was evaluated as a means of detecting CAD in a noninvasive manner. Patients with suspected CAD underwent echocardiographic imaging and simultaneous thallium 201 single-photon emission computed tomography during the intravenous administration of 140 micrograms/kg/min of adenosine. An increase in heart rate, decrease in blood pressure, and increase in double product were observed during adenosine administration. Initial observations revealed that wall motion abnormalities were induced by adenosine in areas of perfusion defects. The adenosine infusion was well tolerated, and symptoms disappeared within 1 to 2 minutes after termination of the infusion. Therefore preliminary observations suggest that adenosine echocardiography appears to be useful in the assessment of CAD.

Zoghbi, W.A. (Section of Cardiology Baylor College of Medicine, Methodist Hospital, Houston, TX (USA))

1991-07-01

177

Adenosine receptors: therapeutic aspects for inflammatory and immune diseases  

PubMed Central

Adenosine is a key endogenous molecule that regulates tissue function by activating four G-protein-coupled adenosine receptors: A1, A2A, A2B and A3. Cells of the immune system express these receptors and are responsive to the modulatory effects of adenosine in an inflammatory environment. Animal models of asthma, ischaemia, arthritis, sepsis, inflammatory bowel disease and wound healing have helped to elucidate the regulatory roles of the various adenosine receptors in dictating the development and progression of disease. This recent heightened awareness of the role of adenosine in the control of immune and inflammatory systems has generated excitement regarding the potential use of adenosine-receptor-based therapies in the treatment of infection, autoimmunity, ischaemia and degenerative diseases.

Hasko, Gyorgy; Linden, Joel; Cronstein, Bruce; Pacher, Pal

2008-01-01

178

Adenosine receptors: therapeutic aspects for inflammatory and immune diseases  

Microsoft Academic Search

Adenosine is a key endogenous molecule that regulates tissue function by activating four G-protein-coupled adenosine receptors: A1, A2A, A2B and A3. Cells of the immune system express these receptors and are responsive to the modulatory effects of adenosine in an inflammatory environment. Animal models of asthma, ischaemia, arthritis, sepsis, inflammatory bowel disease and wound healing have helped to elucidate the

Joel Linden; Bruce Cronstein; Pl Pacher; Gyrgy Hask

2008-01-01

179

Low-dose adenosine stress echocardiography: Detection of myocardial viability  

Microsoft Academic Search

OBJECTIVE: The aim of this study was to evaluate the diagnostic potential of low-dose adenosine stress echocardiography in detection of myocardial viability. BACKGROUND: Vasodilation through low dose dipyridamole infusion may recruit contractile reserve by increasing coronary flow or by increasing levels of endogenous adenosine. METHODS: Forty-three patients with resting dyssynergy, due to previous myocardial infarction, underwent low-dose adenosine (80, 100,

Ana Djordjevic-Dikic; Miodrag Ostojic; Branko Beleslin; Ivana Nedeljkovic; Jelena Stepanovic; Sinisa Stojkovic; Zorica Petrasinovic; Milan Nedeljkovic; Jovica Saponjski; Vojislav Giga

2003-01-01

180

Stimulation of Wound Revascularization by Adenosine Receptor Activation  

Microsoft Academic Search

\\u000a Adenosine is an endogenous mediator implicated in wound healing. The exact mechanisms and receptors involved are still under\\u000a evaluation. We have observed that topical application of a selective adenosine A2A receptor agonist promotes wound healing in experimental animals, both healthy and with impaired healing. Histological analysis\\u000a revealed that adenosine promoted granulation tissue formation, with increased cellularity, matrix deposition, and vessel

M. Carmen Montesinos; Mara D. Valls

181

A 1 Adenosine Receptor: Role in Diabetes and Obesity  

Microsoft Academic Search

\\u000a Adenosine mediates its diverse effects via four subtypes (A1, A2A, A2B and A3) of G-protein-coupled receptors. The A1 adenosine receptor (A1AR) subtype is the most extensively studied and is well characterized in various organ systems. The A1ARs are highly expressed in adipose tissue, and endogenous adenosine has been shown to tonically activate adipose tissue A1ARs. Activation of the A1ARs in

Arvinder K. Dhalla; Jeffrey W. Chisholm; Gerald M. Reaven; Luiz Belardinelli

182

A 1-adenosine receptor gene expression in fetal rat brain  

Microsoft Academic Search

Adenosine influences neurotransmitter release, neuronal excitability, and firing rate, through A1-adenosine receptors (A1-R). Caffeine and related methylxanthines are adenosine receptor antagonists. Exposure of developing rodents to caffeine is associated with subtle, long-term changes in neurochemistry and behavior. The developmental appearance of A1-R gene expression was examined in rats by in situ hybridization. On gestational day (GD) 10, A1-R mRNA was

1996-01-01

183

Ionic basis of the electrophysiological actions of adenosine on cardiomyocytes.  

PubMed

The purpose of this review is to examine the role of the extracellular A1-adenosine (Ado) receptor in modulating membrane potential and currents in cardiac cells. The cellular electrophysiological effects of adenosine are both cell type- and species-dependent. In supraventricular tissues (SA, AV node, and atrium) of all species studied, the "direct" cAMP-independent activation of the inwardly rectifying K+ current IKAdo seems to be the most important action of adenosine. This current is activated by both adenosine and acetylcholine and flows through K+ channels with unitary slope conductance of about 45 pS and an open time constant of 1.4 ms. The density of K(+)-ACh,Ado channels is much less in ventricular than in atrial myocytes, and thus adenosine has little or no effect on the ventricular action potential. In atrial myocytes adenosine has a small inhibitory effect on basal L-type calcium current (ICa,L), but no effect on T-type calcium current (ICa,T). In ventricular myocytes, adenosine does not inhibit ICa,L (except ferret), ICa,T, or the sodium inward current INa. Adenosine has recently been shown to activate IKATP in ventricular membrane patches, but the relevance of this finding remains to be defined. Irrespective of cell type and species, adenosine inhibits membrane currents that are stimulated by beta-adrenergic agonists and other agents known to stimulate the activity of the enzyme adenylyl cyclase. This indirect cAMP-dependent mechanism of action has been shown to be responsible for the inhibition by adenosine of isoproterenol-stimulated ICa,L, delayed rectifier K+ current (IK), chloride current (ICl), the transient inward current ITi, and the pacemaker current IF. The importance of the actions of adenosine on membrane currents in modulation of atrial, ventricular, sinoatrial, and atrioventricular nodal function are discussed. Likewise, the antiarrhythmic and proarrhythmic actions of adenosine are discussed and the clinical implications of these actions are noted. PMID:7896004

Belardinelli, L; Shryock, J C; Song, Y; Wang, D; Srinivas, M

1995-03-01

184

Adenosine Receptors in Wound Healing, Fibrosis and Angiogenesis  

Microsoft Academic Search

\\u000a Wound healing and tissue repair are critical processes, and adenosine, released from injured or ischemic tissues, plays an\\u000a important role in promoting wound healing and tissue repair. Recent studies in genetically manipulated mice demonstrate that\\u000a adenosine receptors are required for appropriate granulation tissue formation and in adequate wound healing. A2A and A2B adenosine receptors stimulate both of the critical functions

Igor Feoktistov; Italo Biaggioni; Bruce N. Cronstein

185

Adenosine receptors in regulation of dendritic cell differentiation and function  

PubMed Central

Differentiation of functional dendritic cells (DCs) critically depends on the microenvironment. DCs differentiate in hypoxic tumor sites and inflamed or damaged tissue. Because local concentrations of adenosine reach high physiologically relevant levels in these conditions, we assessed the expression of adenosine receptors and the effect of their activation on differentiation of human monocytes and mouse peritoneal macrophages and hematopoietic progenitor cells (HPCs) into myeloid DCs. Stimulation of adenosine receptors skews DC differentiation toward a distinct cell population characterized by expression of both DC and monocyte/macrophage cell surface markers. Pharmacologic analysis and experiments with cells from A2B adenosine receptor knockout mice identified A2B receptor as the mediator of adenosine effects on DCs. Unlike normal myeloid DCs, adenosine-differentiated DCs have impaired allostimulatory activity and express high levels of angiogenic, pro-inflammatory, immune suppressor, and tolerogenic factors, including VEGF, IL-8, IL-6, IL-10, COX-2, TGF-?, and IDO. They promoted tumor growth if injected into tumors implanted in mice. Using adenosine desaminase knockout animals, we showed that DCs with proangiogenic phenotype are highly abundant under conditions associated with elevated levels of extracellular adenosine in vivo. Adenosine signaling through A2B receptor is an important factor of aberrant DC differentiation and generation of tolerogenic, angiogenic, and proinflammatory cells.

Novitskiy, Sergey V.; Ryzhov, Sergey; Zaynagetdinov, Rinat; Goldstein, Anna E.; Huang, Yuhui; Tikhomirov, Oleg Y.; Blackburn, Michael R.; Biaggioni, Italo; Carbone, David P.; Feoktistov, Igor

2008-01-01

186

Adenosine receptors in regulation of dendritic cell differentiation and function.  

PubMed

Differentiation of functional dendritic cells (DCs) critically depends on the microenvironment. DCs differentiate in hypoxic tumor sites and inflamed or damaged tissue. Because local concentrations of adenosine reach high physiologically relevant levels in these conditions, we assessed the expression of adenosine receptors and the effect of their activation on differentiation of human monocytes and mouse peritoneal macrophages and hematopoietic progenitor cells (HPCs) into myeloid DCs. Stimulation of adenosine receptors skews DC differentiation toward a distinct cell population characterized by expression of both DC and monocyte/macrophage cell surface markers. Pharmacologic analysis and experiments with cells from A(2B) adenosine receptor knockout mice identified A(2B) receptor as the mediator of adenosine effects on DCs. Unlike normal myeloid DCs, adenosine-differentiated DCs have impaired allostimulatory activity and express high levels of angiogenic, pro-inflammatory, immune suppressor, and tolerogenic factors, including VEGF, IL-8, IL-6, IL-10, COX-2, TGF-beta, and IDO. They promoted tumor growth if injected into tumors implanted in mice. Using adenosine desaminase knockout animals, we showed that DCs with proangiogenic phenotype are highly abundant under conditions associated with elevated levels of extracellular adenosine in vivo. Adenosine signaling through A(2B) receptor is an important factor of aberrant DC differentiation and generation of tolerogenic, angiogenic, and proinflammatory cells. PMID:18559975

Novitskiy, Sergey V; Ryzhov, Sergey; Zaynagetdinov, Rinat; Goldstein, Anna E; Huang, Yuhui; Tikhomirov, Oleg Y; Blackburn, Michael R; Biaggioni, Italo; Carbone, David P; Feoktistov, Igor; Dikov, Mikhail M

2008-09-01

187

Adenosine potentiates human lung mast cell tissue plasminogen activator activity.  

PubMed

We investigated whether adenosine, a potent contributor to the regulation of pulmonary function, can modulate human lung mast cell (HLMC) fibrinolytic activity. Tissue plasminogen activator (tPA) activity and tPA transcript expression levels from a human mast cell line (HMC-1) and HLMC were monitored following adenosine application. Adenosine potentiated mast cell tPA activity and tPA gene expression in a dose-dependent manner. Adenosine effects were abolished in the presence of adenosine deaminase. HMC-1 cells and HLMC predominantly expressed adenosine A(2A) and A(2B) receptor transcripts (A(2B) ? A(2A) > A(3) > A(1)). Pharmacological and signaling studies suggest that the A(2A) receptor is the major subtype accounting for adenosine-induced mast cell tPA activity. Finally, the supernatant from HMC-1 cells and HLMC treated with adenosine (for 24 h) significantly increased fibrin clot lysis, whereas ZM241385, an A(2A) receptor antagonist, abolished this effect. To our knowledge, this study provides the first data to demonstrate the potentiating effect of adenosine on mast cell tPA activity and fibrin clot lysis. PMID:21149610

Sereda, Michal J; Bradding, Peter; Vial, Catherine

2011-01-15

188

Solubilization of stable adenosine A1 receptors from rat brain.  

PubMed Central

Despite numerous reports of solubilization of adenosine A1 receptors, little progress has been made in isolating or purifying the receptor, owing to the extreme lability of the preparations. The present solubilization strategies recognized the possible role of endogenous adenosine to produce adenosine-receptor-N-protein complexes, which are intrinsically unstable, and instead attempted to use caffeine to solubilize free adenosine receptors, which might be more stable. Endogenous adenosine was removed from membranes by using adenosine deaminase along with GTP to accelerate the release of receptor-bound adenosine. The receptors were then occupied with caffeine and solubilized with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulphonate (CHAPS) in the presence of glycerol. These soluble preparations exhibited the characteristics of free adenosine receptors. They bound the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPDPX) with high affinity to a single class of binding sites, which were insensitive to GTP. The binding activity was extremely stable, with a half-life of about 5 days at 4 degrees C; there was little change in either receptor number or affinity during 3 days at 4 degrees C. This methodology should greatly facilitate the characterization, isolation and purification of the adenosine A1 receptor.

Helmke, S M; Cooper, D M

1989-01-01

189

Adenosine A2A Receptor as a Drug Discovery Target.  

PubMed

The adenosine A2A receptor is a G-protein-coupled receptor (GPCR) that has been extensively studied during the past few decades because it offers numerous possibilities for therapeutic applications. Herein we describe adenosine A2A receptor distribution, signaling pathways, pharmacology, and molecular structure, followed by a summary and SAR discussion of the most relevant series of adenosine A2A agonists and antagonists. This review also provides an update of the A2A ligands that are undergoing or have undergone clinical studies, including the two currently marketed agonists adenosine and regadenoson. PMID:24164628

de Lera Ruiz, Manuel; Lim, Yeon-Hee; Zheng, Junying

2014-05-01

190

An Essential Role for Adenosine Signaling in Alcohol Abuse  

PubMed Central

In the central nervous system (CNS), adenosine plays an important role in regulating neuronal activity and modulates signaling by other neurotransmitters, including GABA, glutamate, and dopamine. Adenosine suppresses neurotransmitter release, reduces neuronal excitability, and regulates ion channel function through activation of four classes of G protein-coupled receptors, A1, A2A, A2B, and A3. Central adenosine levels are largely controlled by nucleoside transporters, which regulate adenosine levels across the plasma membrane. Adenosine has been shown to modulate cortical glutamate signaling and ventral-tegmental dopaminergic signaling, which are involved in several aspects of alcohol use disorders. Acute ethanol elevates extracellular adenosine levels by selectively inhibiting the type 1 equilibrative nucleoside transporter, ENT1. Raised adenosine levels mediate the ataxic and sedative/hypnotic effects of ethanol through activation of A1 receptors in the cerebellum, striatum, and cerebral cortex. Recently, we have shown that pharmacological inhibition or genetic deletion of ENT1 reduces the expression of excitatory amino acid transporter 2 (EAAT2), the primary regulator of extracellular glutamate, in astrocytes. These lines of evidence support a central role for adenosine-mediated glutamate signaling and the involvement of astrocytes in regulating ethanol intoxication and preference. In this paper, we discuss recent findings on the implication of adenosine signaling in alcohol use disorders.

Ruby, Christina L.; Adams, Chelsea; Knight, Emily J.; Nam, Hyung Wook; Choi, Doo-Sup

2014-01-01

191

Pretreatment with adenosine and adenosine A1 receptor agonist protects against intestinal ischemia-reperfusion injury in rat  

PubMed Central

AIM: To examine the effects of adenosine and A1 receptor activation on reperfusion-induced small intestinal injury. METHODS: Rats were randomized into groups with sham operation, ischemia and reperfusion, and systemic treatments with either adenosine or 2-chloro-N6-cyclopentyladenosine, A1 receptor agonist or 8-cyclopentyl-1,3-dipropylxanthine, A1 receptor antagonist, plus adenosine before ischemia. Following reperfusion, contractions of ileum segments in response to KCl, carbachol and substance P were recorded. Tissue myeloperoxidase, malondialdehyde, and reduced glutathione levels were measured. RESULTS: Ischemia significantly decreased both contraction and reduced glutathione level which were ameliorated by adenosine and agonist administration. Treatment also decreased neutrophil infiltration and membrane lipid peroxidation. Beneficial effects of adenosine were abolished by pretreatment with A1 receptor antagonist. CONCLUSION: The data suggest that adenosine and A1 receptor stimulation attenuate ischemic intestinal injury via decreasing oxidative stress, lowering neutrophil infiltration, and increasing reduced glutathione content.

Ozacmak, V Haktan; Sayan, Hale

2007-01-01

192

Putative role of the adenosine A 3 receptor in the antiproliferative action of N 6 -(2-isopentenyl)adenosine  

Microsoft Academic Search

We tested a panel of naturally occurring nucleosides for their affinity towards adenosine receptors. Both N\\u000a 6-(2-isopentenyl)adenosine (IPA) and racemic zeatin riboside were shown to be selective human adenosine A3 receptor (hA3R) ligands with affinities in the high nanomolar range (K\\u000a i values of 159 and 649nM, respectively). These values were comparable to the observed K\\u000a i value of adenosine

Clara C. Blad; Jacobien K. von Frijtag Drabbe Knzel; Henk de Vries; Thea Mulder-Krieger; Sara Bar-Yehuda; Pnina Fishman; Adriaan P. IJzerman

193

Separation of adenosine diphosphate-adenosine triphosphate-exchange activity from the cerebral microsomal sodium-plus-potassium ion-stimulated adenosine triphosphatase  

PubMed Central

1. A microsomal fraction from ox cerebral cortex catalysed [14C]ADPATP exchange at a speed similar to that at which it liberated Pi from ATP in the presence of Na+, K+ and Mg2+. 2. Repeated washing the fraction with MgATP solutions solubilized most of the exchange activity and left the adenosine triphosphatase insoluble and little changed in activity. The exchange activity was accompanied by negligible adenosine-triphosphatase activity and was enriched by precipitation at chosen pH and by DEAE-Sephadex. At no stage was its activity affected by Na+, K+ or ouabain. 3. The washed microsomal fraction was exposed to a variety of reagents; a sodium iodidecysteine treatment increased both adenosine-triphosphatase and exchange activities, as also did a synthetic zeolite. Preparations were obtained with exchange activities less than 3% of their Na+-plus-K+-stimulated adenosine-triphosphatase activity. Some contribution to the residual exchange activity was made by an adenylate kinase. 4. Thus over 95% of the microsomal ADPATP-exchange activity does not take part in the Na+-plus-K+-stimulated adenosine-triphosphatase reaction. Participation of some of the residual 3% of the ADPATP-exchange activity has not been excluded, but there appears no firm evidence for its participation in the adenosine triphosphatase; the bearing of this conclusion on mechanisms proposed for the Na+-plus-K+-stimulated adenosine triphosphatase is indicated.

Stahl, W. L.; Sattin, A.; McIlwain, H.

1966-01-01

194

Characterization of adenosine binding proteins in human placental membranes  

SciTech Connect

We have characterized two adenosine binding proteins in human placenta. In membranes, one site is detected with ({sup 3}H) -N-ethylcarboxamidoadenosine (({sup 3}H)NECA). This site is similar to the adenosine A{sub 2} receptor. We call this site the adenosine A{sub 2}-like binding site. In detergent extracts, the second site is detected and has the characteristics of an adenosine A{sub 1} receptor. The soluble adenosine A{sub 2}-like binding site cannot be detected without a rapid assay. Binding to the adenosine A{sub 1} receptor with ({sup 3}H)-2-chloroadenosine and ({sup 3}H)NECA is time dependent, saturable, and reversible. Equilibrium displacement analysis with adenosine agonists reveals an A{sub 1} specificity: 2-chloroadenosine > R-phenylisopropyladenosine > 5{prime}-N-ethylcarboxamidoadenosine. The antagonist potency order is 1,3-diethyl-8-phenylxanthine > isobutylmethylxanthine > theophylline. Competition analysis of membranes with the A,-selective ligands ({sup 3}H)-cyclohexyladenosine ({sup 3}H) cylopentylxanthine revealed adenosine A{sub 1} agonist and antagonist potency orders. We have purified the adenosine A{sub 2}-like binding site. The adenosine A{sub 2}-like binding site is an ubiquitous major cellular protein. It is glycosylated, highly asymmetric, and acidic. The native protein is an homodimer with a subunit molecular mass of 98 kDa. The sedimentation coefficient and partial specific volume of the binding complex are 6.9 s and 0.698 ml/g, respectively. The Stokes' radius is 70 {Angstrom}. The native molecular mass of the detergent-protein complex is 230 kDa. The adenosine A{sub 2}-like binding site has an agonist potency order of 5'-N-ethylcarboxamidoadenosine > 2-chloroadenosine >> R-phenylisopropyladenosine and an antagonist potency order of isobutylmethylxanthine > theophylline >> 1,3-diethyl-8-phenylxanthine.

Hutchison, K.A.

1989-01-01

195

Adenosine augments interleukin-10 production by microglial cells through an A2B adenosine receptor-mediated process  

PubMed Central

Microglia are activated by pathogen-associated molecular patterns and produce pro-inflammatory cytokines, such as TNF-?, IL-6, and IL-12, and the anti-inflammatory cytokine IL-10. Adenosine is an endogenous purine nucleoside and is a ligand of four G protein-coupled adenosine receptors (ARs), which are the A1AR, A2AAR, A2BAR and A3AR. ARs have been shown to suppress TNF-? production by microglia, but their role in regulating IL-10 production has not been studied. Here, we demonstrate that adenosine augments IL-10 production by activated murine microglia while suppressing the production of pro-inflammatory cytokines. Since the order of potency of selective AR agonists in inducing IL-10 production was 5?-N-ethylcarboxamidoadenosine (NECA) > N6-(3-iodobenzyl)-adenosine-5?-N-methyluronamide (IB-MECA) > 2-chloro-N6-cyclopentyladenosine (CCPA) ? 2-p-(2-carboxyethyl)phenethylamino-5?-N-ethyl-carboxamidoadenosine (CGS21680), and the A2BAR antagonist MRS-1754 prevented the effect of NECA, we conclude that the stimulatory effect of adenosine on IL-10 production is mediated by the A2BAR. Mechanistically, adenosine augmented IL-10 mRNA accumulation by a transcriptional process. Using mutant IL-10 promoter constructs we showed that a CREB-binding region in the promoter mediated the augmenting effect of adenosine on IL-10 transcription. Chromatin immunoprecipitation analysis demonstrated that adenosine induced CREB phosphorylation at the IL-10 promoter. Silencing CREB using lentivirally delivered shRNA blocked the enhancing effect of adenosine on IL-10 production confirming a role for CREB in mediating the stimulatory effect of adenosine on IL-10 production. In addition, adenosine augmented IL-10 production by stimulating p38 MAPK. Collectively, our results establish that A2BARs augment IL-10 production by activated murine microglia.

Koscso, Balazs; Csoka, Balazs; Selmeczy, Zsolt; Himer, Leonora; Pacher, Pal; Virag, Laszlo; Hasko, Gyorgy

2011-01-01

196

Adenosine receptors in wound healing, fibrosis and angiogenesis.  

PubMed

Wound healing and tissue repair are critical processes, and adenosine, released from injured or ischemic tissues, plays an important role in promoting wound healing and tissue repair. Recent studies in genetically manipulated mice demonstrate that adenosine receptors are required for appropriate granulation tissue formation and in adequate wound healing. A(2A) and A(2B) adenosine receptors stimulate both of the critical functions in granulation tissue formation (i.e., new matrix production and angiogenesis), and the A(1) adenosine receptor (AR) may also contribute to new vessel formation. The effects of adenosine acting on these receptors is both direct and indirect, as AR activation suppresses antiangiogenic factor production by endothelial cells, promotes endothelial cell proliferation, and stimulates angiogenic factor production by endothelial cells and other cells present in the wound. Similarly, adenosine, acting at its receptors, stimulates collagen matrix formation directly. Like many other biological processes, AR-mediated promotion of tissue repair is critical for appropriate wound healing but may also contribute to pathogenic processes. Excessive tissue repair can lead to problems such as scarring and organ fibrosis and adenosine, and its receptors play a role in pathologic fibrosis as well. Here we review the evidence for the involvement of adenosine and its receptors in wound healing, tissue repair and fibrosis. PMID:19639289

Feoktistov, Igor; Biaggioni, Italo; Cronstein, Bruce N

2009-01-01

197

Adenosine receptors in regulation of dendritic cell differentiation and function  

Microsoft Academic Search

Differentiation of functional dendritic cells (DCs) critically depends on the microenvi- ronment. DCs differentiate in hypoxic tu- mor sites and inflamed or damaged tis- sue. Because local concentrations of adenosine reach high physiologically rel- evant levels in these conditions, we as- sessed the expression of adenosine re- ceptors and the effect of their activation on differentiation of human monocytes and

Sergey V. Novitskiy; Sergey Ryzhov; Rinat Zaynagetdinov; Anna E. Goldstein; Yuhui Huang; Oleg Y. Tikhomirov; Michael R. Blackburn; Italo Biaggioni; David P. Carbone; Igor Feoktistov; Mikhail M. Dikov

2008-01-01

198

Adenosine Receptors in Wound Healing, Fibrosis and Angiogenesis  

PubMed Central

Wound healing and tissue repair are critical processes, and adenosine, released from injured or ischemic tissues, plays an important role in promoting wound healing and tissue repair. Recent studies in genetically manipulated mice demonstrate that adenosine receptors are required for appropriate granulation tissue formation and in adequate wound healing. A2A and A2B adenosine receptors stimulate both of the critical functions in granulation tissue formation (i.e., new matrix production and angiogenesis), and the A1 adenosine receptor (AR) may also contribute to new vessel formation. The effects of adenosine acting on these receptors is both direct and indirect, as AR activation suppresses antiangiogenic factor production by endothelial cells, promotes endothelial cell proliferation, and stimulates angiogenic factor production by endothelial cells and other cells present in the wound. Similarly, adenosine, acting at its receptors, stimulates collagen matrix formation directly. Like many other biological processes, AR-mediated promotion of tissue repair is critical for appropriate wound healing but may also contribute to pathogenic processes. Excessive tissue repair can lead to problems such as scarring and organ fibrosis and adenosine, and its receptors play a role in pathologic fibrosis as well. Here we review the evidence for the involvement of adenosine and its receptors in wound healing, tissue repair and fibrosis.

Feoktistov, Igor; Biaggioni, Italo; Cronstein, Bruce N.

2013-01-01

199

Adenosine A1 receptor antagonists in clinical research and development  

Microsoft Academic Search

Selective adenosine A1 receptor antagonists targeting renal microcirculation are novel pharmacologic agents that are currently under development for the treatment of acute heart failure as well as for chronic heart failure. Despite several studies showing improvement of renal function and\\/or increased diuresis with adenosine A1 antagonists, particularly in chronic heart failure, these findings were not confirmed in a large phase

Berthold Hocher

2010-01-01

200

Adenosine metabolism in cultured chick-embryo heart cells.  

PubMed

Adenosine, a coronary vasodilator, in involved in the regulation of coronary blood flow, but the mechanism (s) of vasodilation especially with respect to the influence of dipyridamole and aminophylline are not clearly understood. Cultured cardiac cells of 16-day-old chick embryos were used as a model for the mammalian heart. Hypoxia produced a twofold increase in the production of adenosine and its metabolic products in this preparation, indicating that the source of adenosine in the hypoxic heart is the myocardial cell. Neither dipyridamole (1 times 10-minus 6M) nor aminophylline (1 times 10-minus 5M) blocked the release of adenosine from the myocardial cells, but dipyridamole aminophylline was without effect. These data suggest that dipyridamole exerts its vasodilator effect by blocking the uptake of adenosine into the cells, thereby increasing its extracellular levels and the concentration of adenosine in the vicinity of coronary resistance vessels. The mechanism whereby aminophylline attenuates the vasodilation produced by adenosine is not known. However, aminophylline does not interfere with the release or uptake of adenosine. PMID:1130550

Mustafa, S J; Berne, R M; Rubio, R

1975-05-01

201

Characterization of cuckoo-pint (Arum maculatum) mitochondrial adenosine triphosphatases.  

PubMed

The catalytic properties of cuckoo-pint (Arum maculatum) mitochondrial adenosine triphosphatase have been analysed. The pH profile, effect of inhibitors, cold-stability and substrate specificity are characteristic of mitochondrial adenosine triphosphatases, although a high guanosine triphosphatase activity does appear to be restricted to plant mitochondrial adenosine triphosphatases. The kinetic properties of nucleoside 5'-triphosphate hydrolysis by membrane-bound and soluble enzymes have been studied by means of double-reciprocal plots. These plots were linear in the absence of an activating anion, which may indicate that the catalytic and/or regulatory mechanism of Arum maculatum adenosine triphosphatase is different from that of other enzyme preparations. It is suggested that the differences in subunit composition of plant and mammalian adenosine triphosphatases reported previously [Dunn, Slabas & Moore (1985) Biochem. J. 225, 821-824] are structurally, rather than functionally, significant. PMID:2939828

Dunn, P P; Slabas, A R; Moore, A L

1986-02-01

202

Characterization of cuckoo-pint (Arum maculatum) mitochondrial adenosine triphosphatases.  

PubMed Central

The catalytic properties of cuckoo-pint (Arum maculatum) mitochondrial adenosine triphosphatase have been analysed. The pH profile, effect of inhibitors, cold-stability and substrate specificity are characteristic of mitochondrial adenosine triphosphatases, although a high guanosine triphosphatase activity does appear to be restricted to plant mitochondrial adenosine triphosphatases. The kinetic properties of nucleoside 5'-triphosphate hydrolysis by membrane-bound and soluble enzymes have been studied by means of double-reciprocal plots. These plots were linear in the absence of an activating anion, which may indicate that the catalytic and/or regulatory mechanism of Arum maculatum adenosine triphosphatase is different from that of other enzyme preparations. It is suggested that the differences in subunit composition of plant and mammalian adenosine triphosphatases reported previously [Dunn, Slabas & Moore (1985) Biochem. J. 225, 821-824] are structurally, rather than functionally, significant.

Dunn, P P; Slabas, A R; Moore, A L

1986-01-01

203

Adenosine reduces postbypass transfusion requirements in humans after heart surgery.  

PubMed Central

OBJECTIVE: The objective of this study was to determine the effect, if any, of adenosine blood cardioplegia on blood component usage after heart surgery. SUMMARY BACKGROUND DATA: The most common cause of nonsurgical postcardiopulmonary bypass bleeding is platelet dysfunction. For this reason, pharmacologic agents are under investigation in an effort to reduce the need for transfusion in this setting. METHODS: A posthoc analysis of blood product usage was performed in data obtained from a Phase I, single center, open label, randomized study performed in 63 patients. The trial was designed to test the safety and tolerance of adenosine when added to blood cardioplegia in increasing doses to enhance myocardial protection. The database provided information regarding the effect of adenosine cardioplegia on venous plasma adenosine concentrations, the amount of platelets, fresh frozen plasma and packed erythrocytes used, and the association between the adenosine dose and postoperative thoracic drainage. RESULTS: The postoperative thoracic drainage at 6 hours, 24 hours, and at the time of chest tube removal in the high-dose adenosine cardioplegia group was 68%, 76%, and 75% of the placebo and low-dose adenosine cardioplegia group (p < 0.05). The highest dose of adenosine studied increased baseline adenosine venous plasma levels 360-fold, from 0.17 +/- 0.09 mumol/L to 42.30 +/- 11.20 mumol/L (p < 0.05). This marked increase was associated with a 68%, 56%, and 58% reduction in platelet, fresh frozen plasma, and packed erythrocyte usage, respectively (p < 0.05). CONCLUSIONS: In addition to enhancing the heart's tolerance to ischemia, adenosine-supplemented cardioplegic solution also may reduce bleeding after cardiopulmonary bypass.

Mentzer, R M; Rahko, P S; Canver, C C; Chopra, P S; Love, R B; Cook, T D; Hegge, M O; Lasley, R D

1996-01-01

204

Adenosine potentiates mediator release from human lung mast cells.  

PubMed

Micromolar concentrations of adenosine were found to potentiate the release of histamine and leukotriene C4 (LTC4) from immunologically activated human lung mast cells (HLMC). Structurally modified congeners of adenosine including 5'-N-ethylcarboxamideadenosine (NECA) and R-phenylisopropyladenosine (R-PIA) also potentiated mediator release. A rank order of potency was established where NECA greater than R-PIA for the potentiation of both LTC4 production and histamine secretion. Mast cells isolated by either enzymatic or mechanical means from human lung parenchyma were both similarly responsive to the modulatory effects of adenosine and analogues, and the potency series of NECA greater than R-PIA also applied. Moreover, histamine release induced by the calcium ionophore A23187 was augmented by NECA, R-PIA, and adenosine and in that potency order. Dipyridamole, an agent thought to impede the intracellular uptake of adenosine, failed to reverse the nucleoside's enhancement of IgE-mediated secretion. The irreversible inhibitor of adenosine deaminase, deoxycoformycin, did not modify the adenosine enhancement of stimulated secretion. Low concentrations of methylxanthines, which antagonize responses mediated at cell surface adenosine receptors, were inconsistent in their effects. Theophylline modestly reversed the adenosine-induced potentiation of IgE-mediated LTC4 generation but not histamine release. Studies employing 8-phenyltheophylline were complicated by the methylxanthine possessing inhibitory properties of its own at concentrations expected to antagonize a nucleoside-mediated effect. In total, these results suggest that the response of HLMC to adenosine describes properties most consistent with an A2/Ra-like process, although an interaction via an, as yet, uncharacterized cell surface receptor cannot be excluded. PMID:2462385

Peachell, P T; Columbo, M; Kagey-Sobotka, A; Lichtenstein, L M; Marone, G

1988-11-01

205

A High-Affinity Adenosine Kinase from Anopheles Gambiae  

SciTech Connect

Genome analysis revealed a mosquito orthologue of adenosine kinase in Anopheles gambiae (AgAK; the most important vector for the transmission of Plasmodium falciparum in Africa). P. falciparum are purine auxotrophs and do not express an adenosine kinase but rely on their hosts for purines. AgAK was kinetically characterized and found to have the highest affinity for adenosine (K{sub m} = 8.1 nM) of any known adenosine kinase. AgAK is specific for adenosine at the nucleoside site, but several nucleotide triphosphate phosphoryl donors are tolerated. The AgAK crystal structure with a bound bisubstrate analogue Ap{sub 4}A (2.0 {angstrom} resolution) reveals interactions for adenosine and ATP and the geometry for phosphoryl transfer. The polyphosphate charge is partly neutralized by a bound Mg{sup 2+} ion and an ion pair to a catalytic site Arg. The AgAK structure consists of a large catalytic core in a three-layer {alpha}/{beta}/{alpha} sandwich, and a small cap domain in contact with adenosine. The specificity and tight binding for adenosine arise from hydrogen bond interactions of Asn14, Leu16, Leu40, Leu133, Leu168, Phe168, and Thr171 and the backbone of Ile39 and Phe168 with the adenine ring as well as through hydrogen bond interactions between Asp18, Gly64, and Asn68 and the ribosyl 2'- and 3'-hydroxyl groups. The structure is more similar to that of human adenosine kinase (48% identical) than to that of AK from Toxoplasma gondii (31% identical). With this extraordinary affinity for AgAK, adenosine is efficiently captured and converted to AMP at near the diffusion limit, suggesting an important role for this enzyme in the maintenance of the adenine nucleotide pool. mRNA analysis verifies that AgAK transcripts are produced in the adult insects.

M Cassera; M Ho; E Merino; E Burgos; A Rinaldo-Matthis; S Almo; V Schramm

2011-12-31

206

A High Affinity Adenosine Kinase from Anopheles gambiae  

PubMed Central

Genome analysis revealed a mosquito orthologue of adenosine kinase in Anopheles gambiae (AgAK; the most important vector for the transmission of Plasmodium falciparum in Africa). P. falciparum are purine auxotrophs and do not express an adenosine kinase but rely on their hosts for purines. AgAK was kinetically characterized and found to have the highest affinity for adenosine (Km 8.1 nM) of any known adenosine kinase. AgAK is specific for adenosine at the nucleoside site but several nucleotide triphosphate phosphoryl donors are tolerated. The AgAK crystal structure with a bound bisubstrate analogue Ap4A (2.0 resolution) reveals interactions for adenosine, ATP and the geometry for phosphoryl transfer. The polyphosphate charge is partly neutralized by a bound Mg2+ ion and an ion pair to a catalytic site Arg. The AgAK structure consists of a large catalytic core in a three-layered ?/?/? sandwich, and a small cap domain in contact with adenosine. The specificity and tight-binding for adenosine arises from hydrogen bond interactions of Asn14, Leu16, Leu40, Leu133, Leu168, Phe168 and Thr171 and the backbone of Ile39 and Phe168 with the adenine ring as well as through hydrogen bond interactions between Asp18, Gly64 and Asn68 and the ribosyl 2?- and 3?-hydroxyl groups. The structure is more similar to human adenosine kinase (48% identity) than to AK from Toxoplasma gondii (31% identity). With this extraordinary affinity for AgAK, adenosine is efficiently captured and converted to AMP at near the diffusion limit, suggesting an important role of this enzyme to maintain the adenine nucleotide pool. mRNA analysis verifies that AgAK transcripts are produced in the adult insects.

Cassera, Maria B.; Ho, Meng-Chiao; Merino, Emilio F.; Burgos, Emmanuel S.; Rinaldo-Matthis, Agnes; Almo, Steven C.; Schramm, Vern L.

2011-01-01

207

Constitutively released adenosine diphosphate regulates proplatelet formation by human megakaryocytes  

PubMed Central

Background The interaction of adenosine diphosphate with its P2Y1 and P2Y12 receptors on platelets is important for platelet function. However, nothing is known about adenosine diphosphate and its function in human megakaryocytes. Design and Methods We studied the role of adenosine diphosphate and P2Y receptors on proplatelet formation by human megakaryocytes in culture. Results Megakaryocytes expressed all the known eight subtypes of P2Y receptors, and constitutively released adenosine diphosphate. Proplatelet formation was inhibited by the adenosine diphosphate scavengers apyrase and CP/CPK by 60-70% and by the P2Y12 inhibitors cangrelor and 2-MeSAMP by 50-60%, but was not inhibited by the P2Y1 inhibitor MRS 2179. However, the active metabolites of the anti-P2Y12 drugs, clopidogrel and prasugrel, did not inhibit proplatelet formation. Since cangrelor and 2-MeSAMP also interact with P2Y13, we hypothesized that P2Y13, rather than P2Y12 is involved in adenosine diphosphate-regulated proplatelet formation. The specific P2Y13 inhibitor MRS 2211 inhibited proplatelet formation in a concentration-dependent manner. Megakaryocytes from a patient with severe congenital P2Y12 deficiency showed normal proplatelet formation, which was inhibited by apyrase, cangrelor or MRS 2211 by 50-60%. The platelet count of patients with congenital delta-storage pool deficiency, who lack secretable adenosine diphosphate, was significantly lower than that of patients with other platelet function disorders, confirming the important role of secretable adenosine diphosphate in platelet formation. Conclusions This is the first demonstration that adenosine diphosphate released by megakaryocytes regulates their function by interacting with P2Y13. The clinical relevance of this not previously described physiological role of adenosine diphosphate and P2Y13 requires further exploration.

Balduini, Alessandra; Di Buduo, Christian Andrea; Malara, Alessandro; Lecchi, Anna; Rebuzzini, Paola; Currao, Manuela; Pallotta, Isabella; Jakubowski, Joseph A.; Cattaneo, Marco

2012-01-01

208

Targeted deletion of adenosine A(3) receptors augments adenosine-induced coronary flow in isolated mouse heart.  

PubMed

To determine whether adenosine A(3) receptors participate in adenosine-induced changes in coronary flow, isolated hearts from wild-type (WT) and A(3) receptor knockout (A(3)KO) mice were perfused under constant pressure and effects of nonselective and selective agonists were examined. Adenosine and the selective A(2A) agonist 2-[p-(2-carboxyethyl)]phenylethylamino-5'-N-ethylcarboxamidoadenosine (CGS-21680) produced augmented maximal coronary vasodilation in A(3)KO hearts compared with WT hearts. Selective activation of A(3) receptors with 2-chloro-N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA) at nanomolar concentrations did not effect coronary flow, but at higher concentrations it produced coronary vasodilation both in WT and A(3)KO hearts. Cl-IB-MECA-induced increases in coronary flow were susceptible to both pharmacological blockade and genetic deletion of A(2A) receptors. Because deletion or blockade of adenosine A(3) receptors augmented coronary flow induced by nonselective adenosine and the selective A(2A) receptor agonist CGS-21680, we speculate that this is due to removal of an inhibitory influence associated with the A(3) receptor subtype. These data indicate that the presence of adenosine A(3) receptors may either inhibit or negatively modulate coronary flow mediated by other adenosine receptor subtypes. PMID:12003827

Talukder, M A Hassan; Morrison, R Ray; Jacobson, Marlene A; Jacobson, Kenneth A; Ledent, Catherine; Mustafa, S Jamal

2002-06-01

209

Synthesis and biological evaluation of adenosines with heterobicyclic and polycyclic N(6)-substituents as adenosine A(1) receptor agonists.  

PubMed

A concise synthesis of a series of N(6)-substituted adenosines with bicyclo[3.2.1]octan-6-yl and polycyclic N(6)-substituents has been developed. The adenosine A(1) receptor (A(1)R) affinity and potency of these compounds was initially assessed using competitive binding assays and cyclic adenosine monophosphate (cAMP) accumulation assays in DDT(1) MF-2 cells. The potency and receptor subtype selectivity of selected examples was further evaluated by measuring their effects on cAMP accumulation at all human adenosine receptor subtypes expressed in CHO cells. The results of these assays indicated that all of the synthesised N(6)-substituted adenosines are full agonists at A(1) R and activate this receptor selectively over the other adenosine receptor subtypes. The two standout compounds in terms of potency were N(6)-(3-thiabicyclo[3.2.1]octan-6-yl)adenosine and N(6)-(cubanylmethyl)adenosine with EC(50) values at human A(1)R of 2.3 nM and 1.1 nM, respectively. The cubanylmethyl derivative in particular proved to be highly receptor subtype selective. These two compounds were further evaluated in a simulated ischaemia model in cultured cardiomyoblasts, where they were found to impart protective effects under hypoxic conditions that resulted in a significant reduction in cell death. PMID:22684887

Gosling, Joshua I; Baker, Stephen P; Haynes, John M; Kassiou, Michael; Pouton, Colin W; Warfe, Lyndon; White, Paul J; Scammells, Peter J

2012-07-01

210

Excess adenosine in murine penile erectile tissues contributes to priapism via A2B adenosine receptor signaling.  

PubMed

Priapism, abnormally prolonged penile erection in the absence of sexual excitation, is associated with ischemia-mediated erectile tissue damage and subsequent erectile dysfunction. It is common among males with sickle cell disease (SCD), and SCD transgenic mice are an accepted model of the disorder. Current strategies to manage priapism suffer from a poor fundamental understanding of the molecular mechanisms underlying the disorder. Here we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected priapic activity. ADA enzyme therapy successfully corrected the priapic activity both in vivo and in vitro, suggesting that it was dependent on elevated adenosine levels. Further genetic and pharmacologic evidence demonstrated that A2B adenosine receptor-mediated (A2BR-mediated) cAMP and cGMP induction was required for elevated adenosine-induced prolonged penile erection. Finally, priapic activity in SCD transgenic mice was also caused by elevated adenosine levels and A2BR activation. Thus, we have shown that excessive adenosine accumulation in the penis contributes to priapism through increased A2BR signaling in both Ada -/- and SCD transgenic mice. These findings provide insight regarding the molecular basis of priapism and suggest that strategies to either reduce adenosine or block A2BR activation may prove beneficial in the treatment of this disorder. PMID:18340377

Mi, Tiejuan; Abbasi, Shahrzad; Zhang, Hong; Uray, Karen; Chunn, Janci L; Xia, Ling Wei; Molina, Jose G; Weisbrodt, Norman W; Kellems, Rodney E; Blackburn, Michael R; Xia, Yang

2008-04-01

211

Adenosine 5?-monophosphate ameliorates D-galactosamine/lipopolysaccharide-induced liver injury through an adenosine receptor-independent mechanism in mice  

PubMed Central

D-galactosamine (GalN)/lipopolysaccharide (LPS)-induced lethality and acute liver failure is dependent on endogenously produced inflammatory cytokines. Adenosine has been proven to be a central role in the regulation of inflammatory response. It is not entirely clear that which adenosine action is actually crucial to limiting inflammatory tissue destruction. Here we showed that GalN/LPS challenge elevated hepatic adenosine and induced lethality in adenosine receptor-deficient mice with equal efficiency as wild-type mice. In GalN/LPS-treated mice, pretreatment with adenosine 5?-monophosphate (5?-AMP) significantly elevated hepatic adenosine level and reduced mortality through decreasing cytokine and chemokine production. In RAW264.7 cells, 5?-AMP treatment inhibited the production of inflammatory cytokines, which is not mediated through adenosine receptors. 5?-AMP failed to attenuate LPS-induced nuclear factor-?B (NF-?B) p65 nuclear translocation, but reduced LPS-induced recruitment of NF-?B p65 to inflammatory gene promoters and decreased LPS-induced enrichment of H3K4 dimethylation at the tumor necrosis factor-? (TNF-?) promoter, which was involved in 5?-AMP-induced elevation of cellular adenosine and a decline of methylation potential. In vitro biochemical analysis revealed that adenosine directly attenuated recruitment of NF-?B to the TNF-? and interleukin-6 promoters. Our findings demonstrate that 5?-AMP-inhibiting inflammatory response is not mediated by adenosine receptors and it may represent a potential protective agent for amelioration of LPS-induced liver injury.

Zhan, Y; Wang, Z; Yang, P; Wang, T; Xia, L; Zhou, M; Wang, Y; Wang, S; Hua, Z; Zhang, J

2014-01-01

212

Estimation of Skeletal Muscle Interstitial Adenosine During Forearm Dynamic Exercise in Humans  

Microsoft Academic Search

It has been proposed that adenosine is a metabolic signal that triggers activation of muscle afferents involved in the exercise pressor reflex. Furthermore, exogenous adenosine induces sympathetic activation that mimics the exercise pressor reflex, and blockade of adenosine receptors inhibits sympathetic activation induced by exercise. Thus, we hypothesize that adenosine is released locally by the muscle during exercise. We used

Fernando Costa; John Heusinkveld; Robert Ballog; Stephen Davis; Italo Biaggioni

2010-01-01

213

Elevated expression of adenosine A1 receptor in bronchial biopsy specimens from asthmatic subjects  

Microsoft Academic Search

Asthmatics, unlike healthy subjects, experience bronchoconstriction in response to inhaled adenosine, and extracellular adenosine concentrations are elevated in the bronchoalveolar lavage fluid and exhaled breath condensate of asthmatic subjects. However, little is known about the location and expression of adenosine receptors in asthmatic airways. The aim of the present study was to investigate the distribution of adenosine A1 receptors in

R. A. Brown; G. W. Clarke; C. L. Ledbetter; M. J. Hurle; J. C. Denyer; D. E. Simcock; J. E. Coote; T. J. Savage; R. D. Murdoch; C. P. Page; D. Spina; B. J. O'Connor

2008-01-01

214

Coronary microembolization does not induce acute preconditioning against infarction in pigsthe role of adenosine  

Microsoft Academic Search

Objective: After coronary microembolization (ME) adenosine is released from ischemic areas of the microembolized myocardium. This adenosine dilates vessels in adjacent nonembolized myocardium and increases coronary blood flow. For ischemic preconditioning (IP) to protect the myocardium against infarction, an increase in the interstitial adenosine concentration (iADO) prior to the subsequent ischemia\\/reperfusion is necessary. We hypothesized that the adenosine release after

Andreas Skyschally; Rainer Schulz; Petra Gres; Ina Konietzka; Claus Martin; Michael Haude; Raimund Erbel; Gerd Heusch

215

HIF-dependent induction of adenosine A2B receptor in hypoxia  

Microsoft Academic Search

Adenosine has been widely associated with hypoxia of many origins, including those associ- ated with inflammation and tumorogenesis. A number of recent studies have implicated metabolic control of adenosine generation at sites of tissue hypoxia. Here, we examine adenosine receptor control and amplifica- tion of signaling through transcriptional regulation of endothelial and epithelial adenosine receptors. Initial studies confirmed previous findings

Tianqing Kong; Karen A. Westerman; Marion Faigle; Holger K. Eltzschig; Sean P. Colgan

2006-01-01

216

THE ROLE AND REGULATION OF ADENOSINE IN THE CENTRAL NERVOUS SYSTEM  

Microsoft Academic Search

? Abstract Adenosine is a modulator that has a pervasive and generally inhibitory effect on neuronal activity. Tonic activation of adenosine receptors by adenosine that is normally present in the extracellular space in brain tissue leads to inhibitory effects that appear to be mediated by both adenosine A1 and A2A receptors. Relief from this tonic inhibition by receptor antagonists such

Thomas V. Dunwiddie; Susan A. Masino

2001-01-01

217

Effect of adenosine on carotid chemoreceptor activity in the cat.  

PubMed Central

1 The effects of intracarotid (i.c.) injections or infusions of adenosine on chemoreceptor activity recorded from the peripheral end of a sectioned carotid sinus nerve have been studied in cats anaesthetized with pentobarbitone. 2 Adenosine injections (0.1-100 micrograms) caused a rapid and marked increase of spontaneous chemoreceptor discharge, the intensity, duration and onset of which was dose-dependent. Infusion of adenosine, 50 microgram/min, also evoked an increase in discharge which persisted for the duration of the infusion. 3 Both theophylline (1 mg i.c.) and aminophylline (1 mg i.c.) caused short-lasting decreases in spontaneous discharge but did not prevent the excitatory effect of adenosine. Theophylline increased the excitatory action of adenosine. 4 Naloxone (400 micrograms i.c.) antagonized the depressant effect of morphine on chemoreceptor discharge but not the excitatory action of adenosine. 5 It is concluded that exogenous adenosine can excite the cat carotid chemoreceptors, an effect which is not prevented by theophylline in the doses studied. The physiological significance of the findings is discussed.

McQueen, D. S.; Ribeiro, J. A.

1981-01-01

218

The pulmonary effects of intravenous adenosine in asthmatic subjects  

PubMed Central

Background We have shown that intravenous adenosine in normal subjects does not cause bronchospasm, but causes dyspnea, most likely by an effect on vagal C fibers in the lungs [Burki et al. J Appl Physiol 2005; 98:180-5]. Since airways inflammation and bronchial hyperreactivity are features of asthma, it is possible that intravenous adenosine may be associated with an increased intensity of dyspnea, and may cause bronchospasm, as noted anecdotally in previous reports. Methods We compared the effects of placebo and 10 mg intravenous adenosine, in 6 normal and 6 asthmatic subjects. Results Placebo injection had no significant (p > 0.05) effect on the forced expiratory spirogram, heart rate, minute ventilation (Ve), or respiratory sensation. Similarly, adenosine injection caused no significant changes (p > 0.05) in the forced expiratory spirogram; however, there was a rapid development of dyspnea as signified visually on a modified Borg scale, and a significant (p < 0.05) tachycardia in each subject (Asthmatics +18%, Normals + 34%), and a significant (p < 0.05) increase in Ve (Asthmatics +93%, Normals +130%). The intensity of dyspnea was significantly greater (p < 0.05) in the asthmatic subjects. Conclusion These data indicate that intravenous adenosine does not cause bronchospasm in asthmatic subjects, and supports the concept that adenosine-induced dyspnea is most likely secondary to stimulation of vagal C fibers in the lungs. The increased intensity of adenosine-induced dyspnea in the asthmatic subjects suggests that airways inflammation may have sensitized the vagal C fibers.

Burki, Nausherwan K; Alam, Mahmud; Lee, Lu-Yuan

2006-01-01

219

Animal models for the study of adenosine receptor function.  

PubMed

Adenosine receptors represent a family of G-protein coupled receptors that are ubiquitously expressed in a wide variety of tissues. This family contains four receptor subtypes: A1 and A3, which mediate inhibition of adenylyl cyclase; and A2a and A2b, which mediate stimulation of this enzyme. Currently, all receptor subtypes have been genetically deleted in mouse models except for the A2b adenosine receptor, and some have been overexpressed in selective tissues of transgenic mice. Studies involving these transgenic mice indicated that receptor levels are rate limiting, as effects were amplified upon increases in receptor level. The knockout models pointed to clusters of activities related to the physiologies of the cardiovascular and the nervous systems, which are either reduced or enhanced upon specific receptor deletion. Interestingly, the trend of effects on these systems is similar in the A1 and A3 adenosine receptor knockout mice and opposite to the effects observed in the A2a adenosine receptor knockout model. This review summarizes in vitro studies on pathways affected by each adenosine receptor, and primarily focuses on the above in vivo models generated to investigate the physiologic role of adenosine receptors. Furthermore, it illustrates the need for multiple adenosine receptor subtype deficiency studies in mice and the deletion of the A2b subtype. PMID:15389588

Yaar, R; Jones, M R; Chen, J-F; Ravid, Katya

2005-01-01

220

Adenosine A3 receptor activation modulates the capillary endothelial glycocalyx.  

PubMed

The endothelial glycocalyx is a dynamic extracellular matrix composed of cell surface proteoglycans, glycoproteins, and adsorbed serum proteins that has been implicated in the regulation and modulation of capillary tube hematocrit, permeability, and hemostasis. High tissue adenosine levels have been shown to adversely affect microvascular function and tissue survival after an ischemic episode, and previous work in this laboratory has shown that adenosine causes arteriolar constriction and degranulation of mast cells via the A3 receptor (A3AR). We hypothesized that adenosine exerts at least part of its effect through modification of the glycocalyx via the A3AR. We used an in vivo cremaster model (hamster and mouse) in which circulating plasma was labeled with a 70-kDa FITC-dextran, and the capillaries were examined before and after superfusion with varying concentrations of adenosine (or other vasoactive molecules). Measurements of the dextran exclusion from an endothelial cell surface layer and red cell separation from the endothelial cell surface were made for up to 30 minutes. Our data indicate that adenosine causes a rapid and profound decrease in the ability of the glycocalyx to exclude dextran but only affects red blood cell exclusion at pharmacological levels. Knockout mice deficient in the A3AR were completely protected from glycocalyx changes attributable to adenosine. These data show a potential link between a known vasoactive tissue metabolite, adenosine, and regulation of the glycocalyx, which may be important during (patho)physiological changes in microvascular function during inflammatory insults. PMID:14630725

Platts, Steven H; Duling, Brian R

2004-01-01

221

Extracellular adenosine controls NKT-cell-dependent hepatitis induction.  

PubMed

Extracellular adenosine regulates inflammatory responses via the A2A adenosine receptor (A2AR). A2AR deficiency results in much exaggerated acute hepatitis, indicating nonredundancy of adenosine-A2AR pathway in inhibiting immune activation. To identify a critical target of immunoregulatory effect of extracellular adenosine, we focused on NKT cells, which play an indispensable role in hepatitis. An A2AR agonist abolished NKT-cell-dependent induction of acute hepatitis by concanavalin A (Con A) or ?-galactosylceramide in mice, corresponding to downregulation of activation markers and cytokines in NKT cells and of NK-cell co-activation. These results show that A2AR signaling can downregulate NKT-cell activation and suppress NKT-cell-triggered inflammatory responses. Next, we hypothesized that NKT cells might be under physiological control of the adenosine-A2AR pathway. Indeed, both Con A and ?-galactosylceramide induced more severe hepatitis in A2AR-deficient mice than in WT controls. Transfer of A2AR-deficient NKT cells into A2AR-expressing recipients resulted in exaggeration of Con A-induced liver damage, suggesting that NKT-cell activation is controlled by endogenous adenosine via A2AR, and this physiological regulatory mechanism of NKT cells is critical in the control of tissue-damaging inflammation. The current study suggests the possibility to manipulate NKT-cell activity in inflammatory disorders through intervention to the adenosine-A2AR pathway. PMID:24448964

Subramanian, Meenakshi; Kini, Radhika; Madasu, Manasa; Ohta, Akiko; Nowak, Michael; Exley, Mark; Sitkovsky, Michail; Ohta, Akio

2014-04-01

222

Adenosine release into venous plasma during free flow exercise.  

PubMed

We measured adenosine release into venous plasma as an index of interstitial adenosine concentration during free flow exercise hyperemia. Isolated, blood-perfused dog calf muscles were stimulated at 6 Hz for 10 min at free flow. Plasma samples were collected before, during, and after the exercise period for analysis of plasma adenosine concentration [( ADO]) by HPLC. Adenosine release (Rado) was calculated as plasma flow times venous-arterial [ADO] difference. Rado (nmole/min/100 g) went from -0.1 +/- 0.1 at rest to 6.6 +/- 4.6 during 6-Hz exercise. Isoproterenol infusion, which caused an increase in blood flow equivalent to 6-Hz exercise, did not result in increased Rado. Infusion of the 5'-nucleotidase inhibitor, alpha, beta, methylene adenosine 5'-diphosphate (AOPCP) did not prevent the increase in Rado during exercise. These results support the hypothesis that interstitial adenosine concentration increases during sustained free flow twitch exercise and that this results in increased release of adenosine into venous plasma. PMID:3814246

Fuchs, B D; Gorman, M W; Sparks, H V

1986-03-01

223

Plasma adenosine during investigation of hypoxic ventilatory response.  

PubMed

Adenosine, an endogenous nucleoside, is released by hypoxic tissue, causes vasodilation, and influences ventilation. Its effects are mediated by P1-purinoceptors. We examined to what extent the plasma adenosine concentration in the peripheral venous blood correlates with hypoxic ventilatory response (HVR) and ventilatory drive P0.1 to find out whether endogenously formed adenosine has an influence on the individual ventilatory drive under hypoxic conditions. While investigating the HVR of 14 healthy subjects, the ventilatory drive P0.1 was measured with the shutter of a spirometer. Determination of the ventilatory drive P0.1(RA) started under room air conditions (21% O (2)) and then inspiratory gas was changed to a hypoxic mixture of 10% O (2) in N (2) to determine P0.1(Hyp). At the time of the P0.1 measurements, two blood samples were taken to determine the adenosine concentrations. After removal of cellular components and proteins, samples were analyzed by high-pressure liquid chromatography (HPLC). Both adenosine concentrations in plasma under room air (r = 0.59, p < 0.05) and adenosine concentrations under hypoxia (r = 0.75, p < 0.01) correlated significantly with the ventilatory drive P0.1. In addition, plasma adenosine concentrations during hypoxic conditions showed a significant correlation with HVR on the 0.01 level (r = 0.71, p < 0.01). The results indicate a possible role of endogenous adenosine in the regulation of breathing in humans. We assume that endogenous adenosine influences the HVR and the ventilatory drive, probably by modulating the carotid body chemoreceptor response to hypoxia. PMID:15026936

Drumm, Dirk; Hoefer, Markus; Juhsz, Janos; Huszr, Eva; Sybrecht, Gerhard W

2004-03-01

224

Immunosuppression via adenosine receptor activation by adenosine monophosphate released from apoptotic cells  

PubMed Central

Apoptosis is coupled with recruitment of macrophages for engulfment of dead cells, and with compensatory proliferation of neighboring cells. Yet, this death process is silent, and it does not cause inflammation. The molecular mechanisms underlying anti-inflammatory nature of the apoptotic process remains poorly understood. In this study, we found that the culture supernatant of apoptotic cells activated the macrophages to express anti-inflammatory genes such as Nr4a and Thbs1. A high level of AMP accumulated in the apoptotic cell supernatant in a Pannexin1-dependent manner. A nucleotidase inhibitor and A2a adenosine receptor antagonist inhibited the apoptotic supernatant-induced gene expression, suggesting AMP was metabolized to adenosine by an ecto-5-nucleotidase expressed on macrophages, to activate the macrophage A2a adenosine receptor. Intraperitoneal injection of zymosan into Adora2a- or Panx1-deficient mice produced high, sustained levels of inflammatory mediators in the peritoneal lavage. These results indicated that AMP from apoptotic cells suppresses inflammation as a calm down signal. DOI: http://dx.doi.org/10.7554/eLife.02172.001

Yamaguchi, Hiroshi; Maruyama, Toshihiko; Urade, Yoshihiro; Nagata, Shigekazu

2014-01-01

225

Relationship between adenosine concentration and oxygen supply in rat brain.  

PubMed

Since adenosine is present in normal brain tissue and cerebrosipinal fluid and since it dilates the pial vessels, it is possible that adenosine, in addition to H-+, is also a mediator of the metabolic regulation of cerebral blood flow. Evidence supporting this hypothesis was obtained under various experimental conditions characterized by achange in brain oxygen supply. The brain was frozen in situ by means of a small bonerongeur precooled in liquid N2 and the tissue was processed for adenosine determination (nmol/g of tissue). Electrical stimulation of the cortex at 0, 15, 30, and 45 Hz yielded adenosine levels of 5.4 plus or minus 0.7, 10.5 plus or minus 1.7, 13.0 plusor minus 1.2, and 9.0 plus or minus 2.1 nmol/g. Arterial pressures of 87, 60, and 40mmHg gave adenosine levels of 7.5 plus or minus 0.76, 13 plus or minus 2.6, and 26.6plus or minus 3.3, respectively. Ventilation with 29.7, 20, 10.7, and5.5% O2 significantly increased the adenosine levels to 9.4 plus or minus 3.0, 6.4 plus or minus 1.2, 30.0 plus or minus 9.3, and 63.3 plus or minus 18.2 nmol/g, respectively. Hyperventilation significantly increased adenosine form 6.7 plus or minus 1.0 to 11.8 plus or minus 1.4 nmol/g. This increased adenosine level was reduced by additionof CO2 to the ventilating gas mixture. Lactate, the main H-+ donor, pyruvate, and cAMP changed in a fashion parallel to adenosine. However, cAMP showedonly a small increase in adenosine. These findings are in accordance with the concept that adenosine and H-+ may act synergistally to regulate cerebral blood flow and that endogenous adenosine may exert a small effect on cAMP formation. PMID:168787

Rubio, R; Berne, R M; Bockman, E L; CURNISH, R R

1975-06-01

226

Serum adenosine deaminase activity in cutaneous anthrax  

PubMed Central

Background Adenosine deaminase (ADA) activity has been discovered in several inflammatory conditions; however, there are no data associated with cutaneous anthrax. The aim of this study was to investigate serum ADA activity in patients with cutaneous anthrax. Material/Methods Sixteen patients with cutaneous anthrax and 17 healthy controls were enrolled. We measured ADA activity; peripheral blood leukocyte, lymphocyte, neutrophil, and monocyte counts; erythrocyte sedimentation rate; and C reactive protein levels. Results Serum ADA activity was significantly higher in patients with cutaneous anthrax than in the controls (p<0.001). A positive correlation was observed between ADA activity and lymphocyte counts (r=0.589, p=0.021) in the patient group. Conclusions This study suggests that serum ADA could be used as a biochemical marker in cutaneous anthrax.

Sunnetcioglu, Mahmut; Karadas, Sevdegul; Aslan, Mehmet; Ceylan, Mehmet Resat; Demir, Halit; Oncu, Mehmet Resit; Karahocagil, Mustafa Kas?m; Sunnetcioglu, Aysel; Aypak, Cenk

2014-01-01

227

Serum adenosine deaminase activity in cutaneous anthrax.  

PubMed

Background Adenosine deaminase (ADA) activity has been discovered in several inflammatory conditions; however, there are no data associated with cutaneous anthrax. The aim of this study was to investigate serum ADA activity in patients with cutaneous anthrax. Material and Methods Sixteen patients with cutaneous anthrax and 17 healthy controls were enrolled. We measured ADA activity; peripheral blood leukocyte, lymphocyte, neutrophil, and monocyte counts; erythrocyte sedimentation rate; and C reactive protein levels. Results Serum ADA activity was signi?cantly higher in patients with cutaneous anthrax than in the controls (p<0.001). A positive correlation was observed between ADA activity and lymphocyte counts (r=0.589, p=0.021) in the patient group. Conclusions This study suggests that serum ADA could be used as a biochemical marker in cutaneous anthrax. PMID:24997584

Sunnetcioglu, Mahmut; Karadas, Sevdegul; Aslan, Mehmet; Ceylan, Mehmet Resat; Demir, Halit; Oncu, Mehmet Resit; Karahocagil, Mustafa Kas?m; Sunnetcioglu, Aysel; Aypak, Cenk

2014-01-01

228

The adenosine system modulates Toll-like receptor function: basic mechanisms, clinical correlates and translational opportunities  

PubMed Central

Adenosine is an endogenous purine metabolite whose concentration in human blood plasma rises from nanomolar to micromolar during stress or hypoxia. Leukocytes express seven-transmembrane adenosine receptors whose engagement modulates Toll-like receptor-mediated cytokine responses, in part via modulation of intracellular cyclic adenosine monophosphate (cAMP). Adenosine congeners are used clinically to treat arrhythmias and apnea of prematurity. Herein we consider the potential of adenosine congeners as innate immune response modifiers to prevent and/or treat infection.

Coombs, Melanie R. Power; Belderbos, Mirjam E.; Gallington, Leighanne C.; Bont, Louis; Levy, Ofer

2014-01-01

229

Effect of A2B Adenosine Receptor Gene Ablation on Proinflammatory Adenosine Signaling in Mast Cells1  

PubMed Central

Pharmacological studies suggest that A2B adenosine receptors mediate proinflammatory effects of adenosine in human mast cells in part by up-regulating production of Th2 cytokines and angiogenic factors. This concept has been recently challenged by the finding that mast cells cultured from bone marrow-derived mast cells (BMMCs) of A2B knockout mice display an enhanced degranulation in response to Fc?RI stimulation. This finding was interpreted as evidence of anti-inflammatory functions of A2B receptors and it was suggested that antagonists with inverse agonist activity could promote activation of mast cells. In this report, we demonstrate that genetic ablation of the A2B receptor protein has two distinct effects on BMMCs, one is the previously reported enhancement of Ag-induced degranulation, which is unrelated to adenosine signaling; the other is the loss of adenosine signaling via this receptor subtype that up-regulates IL-13 and vascular endothelial growth factor secretion. Genetic ablation of A2B receptors had no effect on A3 adenosine receptor-dependent potentiation of Ag-induced degranulation in mouse BMMCs, but abrogated A2B adenosine receptor-dependent stimulation of IL-13 and vascular endothelial growth factor secretion. Adenosine receptor antagonists MRS1706 and DPCPX with known inverse agonist activity at the A2B subtype inhibited IL-13 secretion induced by the adenosine analog NECA, but did not mimic the enhanced Ag-induced degranulation observed in A2B knockout BMMCs. Thus, our study confirmed the proinflammatory role of adenosine signaling via A2B receptors and the anti-inflammatory actions of A2B antagonists in mouse BMMCs.

Ryzhov, Sergey; Zaynagetdinov, Rinat; Goldstein, Anna E.; Novitskiy, Sergey V.; Dikov, Mikhail M.; Blackburn, Michael R.; Biaggioni, Italo; Feoktistov, Igor

2013-01-01

230

Fine-tuning modulation of myenteric motoneurons by endogenous adenosine: on the role of secreted adenosine deaminase.  

PubMed

Besides the well-characterized inhibitory effect of adenosine in the gastrointestinal tract mediated by A1 receptors, we recently demonstrated that endogenously generated adenosine facilitates [3H]acetylcholine release from myenteric neurons through preferential activation of prejunctional A2A receptors. The co-existence of both receptor subtypes on cholinergic neurons prompted the question of how does adenosine discriminate between these receptors to regulate synaptic transmission in the longitudinal muscle-myenteric plexus (LM-MP) of the rat ileum. Electrical stimulation of the LM-MP increased the outflow of adenosine, inosine and hypoxanthine. Myenteric neurons seem to be the main source of endogenous adenosine, since blockade of action potentials with tetrodotoxin (1 microM) or omission of Ca2+ (plus EGTA, 1 mM) in the buffer essentially abolished nucleosides release, while adenosine outflow remained unchanged when smooth muscle contractions were prevented by nifedipine (1 microM). Inhibition of ecto-5'-nucleotidase by concanavalin A (0.1 mg ml-1) produced only a moderate decrease (approximately 25%) on adenosine accumulation in the LM-MP, indicating that the extracellular catabolism of released ATP might not be a major source of the nucleoside. Data using the acetylcholinesterase inhibitor, physiostigmine (10 microM), and several subtype-specific muscarinic receptor antagonists, 4-DAMP (100 nM), AF-DX 116 (10 microM) and muscarinic toxin-7 (1 nM), suggest that cholinergic motoneurons are endowed with muscarinic M3 autoreceptors facilitating the outflow of adenosine. Surprisingly, bath samples collected after stimulating the LM-MP exhibited a relatively high adenosine deaminase (ADA) activity (0.60+/-0.07 U ml-1), which increased in parallel with the accumulation of adenosine and its deamination products. Our findings are in keeping with the hypothesis that ADA secretion, along with a less-efficient dipyridamole-sensitive nucleoside transport system, may restrict endogenous adenosine actions to the synaptic region channelling to facilitatory A2A receptors activation. Such a local environment may also limit diffusion of exogenously added adenosine towards the active zones, as we showed that this constrain may be overcome by inhibiting ADA activity with erythro-9(2-hydroxy-3-nonyl) adenine (50 microM). PMID:16563876

Correia-de-S, Paulo; Ades, Sara; Timteo, M Alexandrina; Vieira, Ctia; Magalhes-Cardoso, Teresa; Nascimento, Carlos; Duarte-Arajo, Margarida

2006-06-30

231

Adenosine triphosphate (ATP) in the marine environment: a bibliography  

SciTech Connect

This bibliography lists published works on adenosine triphosphate (ATP) detected in the marine environment. Over 100 citations are listed in four categories: field measurements; macroscopic organisms; benthic populations; and papers on analytical methods.

Jones, A.T.; Hartwig, E.O.; Quinby-Hunt, M.S.

1981-03-01

232

Methylxanthine Discrimination in the Rat: Possible Benzodiazepine and Adenosine Mechanisms.  

National Technical Information Service (NTIS)

Rats were trained to discriminate either caffeine or theophylline form saline using a two-lever discrimination paradigm. Since methylxanthines have been found to interfere with agonist binding at both adenosine and benzodiazepine (BDZ) receptors, chlordia...

F. A. Holloway H. E. Modron R. C. Michaelis

1985-01-01

233

Sulfur-Containing Xanthine Derivatives as Adenosin Antagonists.  

National Technical Information Service (NTIS)

The invention provides for means of synthesis compounds with increasingly selective activity as adenosine receptor antagonists in xanthine drugs. Xanthines and thioxanthines were synthesized and further derivatized by forming an imidazole ring in the comp...

K. A. Jacobson W. Pfleiderer J. W. Daly J. L. Neumeyer

1989-01-01

234

Relaxation of the mouse isolated aorta and carotid artery in response to adenosine analogues in genetically-modified mice lacking the adenosine A 2A receptor  

Microsoft Academic Search

The aim of this study was to characterise the receptor(s) mediating responses to adenosine and\\/or adenosine analogues in mouse isolated aorta and carotid artery. In addition, since mice lacking the A2A adenosine receptor are reported to be hypertensive, the possibility that this gene deletion or the altered phenotype results in alteration of responses mediated via adenosine analogues was investigated. This

D. J. Prentice; M. D. W. Kelly; C. Ledent; S. M. O. Hourani

2002-01-01

235

Direct Interaction of Adenosine with the TRPV1 Channel Protein  

Microsoft Academic Search

Vanilloid receptor 1 (TRPV1), a nonspecific cation channel expressed primarily in small sensory neurons, mediates inflammatory thermal pain sensation. The function and expression of TRPV1 are enhanced during inflammation and certain neuropathies, leading to sustained hyperalgesia. Activation of TRPV1 in the spinal cord and periphery promotes release of adenosine, which produces analgesia by activating A1 and A2A adenosine receptor (AR)

Preeti Puntambekar; Jeremy Van Buren; Manish Raisinghani; Louis S. Premkumar; Vickram Ramkumar

2004-01-01

236

Hemodynamic Effects of Adenosine in Conscious Hypertensive and Normotensive Rats  

Microsoft Academic Search

SUMMARY Mean arterial pressure and heart rate were measured during intra-aortic arch (i.a.a.), intravenous, and suprarenal artery (s.r.a.) infusions of adenosine in conscious, unrestrained normo- tensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) in the absence and presence of ganglionic blockade. In both groups, i.a.a. and i.v. infusions of adenosine induced comparatively larger dose-dependent reductions in mean arterial pressure

AKIHIRO OHNISHI; ITALO BIAGGIONI; GILBERT DERAY; ROBERT A. BRANCH; EDWIN K. JACKSON

2009-01-01

237

Adenosine receptor subtype-selective antagonists in inflammation and hyperalgesia  

Microsoft Academic Search

In this study, we examined the effects of systemic and local administration of the subtype-selective adenosine receptor antagonists\\u000a PSB-36, PSB-1115, MSX-3, and PSB-10 on inflammation and inflammatory hyperalgesia. Pharmacological blockade of adenosine receptor\\u000a subtypes after systemic application of antagonists generally led to a decreased edema formation after formalin injection and,\\u000a with the exception of A3 receptor antagonism, also after the

Andras Bilkei-Gorzo; Osama M. Abo-Salem; Alaa M. Hayallah; Kerstin Michel; Christa E. Mller; Andreas Zimmer

2008-01-01

238

A 3 Adenosine Receptor: Pharmacology and Role in Disease  

Microsoft Academic Search

\\u000a The study of the A3 adenosine receptor (A3AR) represents a rapidly growing and intense area of research in the adenosine field. The present chapter will provide an\\u000a overview of the expression patterns, molecular pharmacology and functional role of this A3AR subtype under pathophysiological conditions. Through studies utilizing selective A3AR agonists and antagonists, or A3AR knockout mice, it is now clear

P. A. Borea; S. Gessi; S. Bar-Yehuda; P. Fishman

239

Emerging role of extracellular nucleotides and adenosine in multiple sclerosis  

Microsoft Academic Search

Extracellular nucleotides and adenosine play important roles in inflammation. These signaling molecules interact with the\\u000a cell-surface-located P2 and P1 receptors, respectively, that are widely distributed in the central nervous system and generally\\u000a exert opposite effects on immune responses. Indeed, extracellular ATP, ADP, UTP, and UDP serve as alarmins or damage-associated\\u000a molecular patterns that activate mainly proinflammatory mechanisms, whereas adenosine has

Marek Cie?lak; Filip Kukulski; Micha? Komoszy?ski

240

Hypoxia-Inducible Factors and Adenosine Signaling in Vascular Growth  

Microsoft Academic Search

\\u000a Low oxygen environment or hypoxia is conducive towards vascular growth and endothelial proliferation. Therefore it is an essential\\u000a element in both disease and development. Hypoxia stabilizes the hypoxia-inducible transcription factors -1? and -2? and also\\u000a increases adenosine levels thereby activating the adenosine receptor signaling pathways. While these pathways have been described\\u000a independently to a greater extent, increasing evidence suggests that

Aftab Ahmad; Carl W. White; Shama Ahmad

241

Expression and function of adenosine receptors in human dendritic cells  

Microsoft Academic Search

Dendritic cells (DCs) are specialized an- tigen-presenting cells characterized by their ability to migrate into target sites, process antigens, and activate naive T cells. In this study, we analyzed the biological activity and intracellular signaling of adenosine by using reverse transcriptase-polymerase chain reaction assays to investigate mRNA expression of A1 ,A 2a and A3 adenosine receptors in immature and mature

ELISABETH PANTHER; MARCO IDZKO; YARED HEROUY; HENRIETTE RHEINEN; PETER J. GEBICKE-HAERTER; ULRICH MROWIETZ; STEFAN DICHMANN; JOHANNES NORGAUER

2001-01-01

242

Diagnosis of Sick Sinus Syndrome with Intravenous Adenosine Injection  

Microsoft Academic Search

Background:The most widely utilized indexes of sinus node dysfunction are the sinus node recovery time (SNRT and the corrected sinus node recovery time (CSNRT, both of which generally require catheterization. Adenosine exhibits negative chronotropic effects on the sinoatrial node. The use\\/accuracy of the Nnon-invasive and reliable sinus node function test with intravenous adenosine was investigated. Methods and Results: The clinical

Jae-Sup Eum; Tae-Joon Cha; Ki-Bum Kwon; Chan-Ock Kim; Seong-Hoon Shin; Seong-Man Kim; Su-Seung Kang; Ik-Soo Jeon; Min-Dae Kim; Seong-Jae Joo; Jae-Woo Lee

2001-01-01

243

Adenosine release during seizures attenuates GABAA receptor-mediated depolarization.  

PubMed

Seizure-induced release of the neuromodulator adenosine is a potent endogenous anticonvulsant mechanism, which limits the extension of seizures and mediates seizure arrest. For this reason several adenosine-based therapies for epilepsy are currently under development. However, it is not known how adenosine modulates GABAergic transmission in the context of seizure activity. This may be particularly relevant as strong activation of GABAergic inputs during epileptiform activity can switch GABA(A) receptor (GABA(A)R) signaling from inhibitory to excitatory, which is a process that plays a significant role in intractable epilepsies. We used gramicidin-perforated patch-clamp recordings to investigate the role of seizure-induced adenosine release in the modulation of postsynaptic GABA(A)R signaling in pyramidal neurons of rat hippocampus. Consistent with previous reports, GABA(A)R responses during seizure activity transiently switched from hyperpolarizing to depolarizing and excitatory. We found that adenosine released during the seizure significantly attenuated the depolarizing GABA(A)R responses and also reduced the extent of the after-discharge phase of the seizure. These effects were mimicked by exogenous adenosine administration and could not be explained by a change in chloride homeostasis mechanisms that set the reversal potential for GABA(A)Rs, or by a change in the conductance of GABA(A)Rs. Rather, A(1)R-dependent activation of potassium channels increased the cell's membrane conductance and thus had a shunting effect on GABA(A)R currents. As depolarizing GABA(A)R signaling has been implicated in seizure initiation and progression, the adenosine-induced attenuation of depolarizing GABA(A)R signaling may represent an important mechanism by which adenosine can limit seizure activity. PMID:22496577

Ilie, Andrei; Raimondo, Joseph V; Akerman, Colin J

2012-04-11

244

Genetic and biochemical consequences of adenosine deaminase deficiency in humans.  

PubMed

Adenosine deaminase deficiency accounts for approximately 15-20% of severe combined immunodeficiency in humans. The gene for adenosine deaminase is located on chromosome 20q12-q13.11 and codes for an aminohydrolase that catalyzes the deamination of adenosine and deoxyadenosine to inosine and deoxyinosine, respectively. Absence of the enzyme causes a build-up of the substrates in addition to excess deoxyadenosine triphosphate, thereby compromising the regenerative capacity of the immune system. Due to underlying allelic heterogeneity, the disorder manifests as a spectrum, ranging from neonatal onset severe combined immunodeficiency to apparently normal partial adenosine deaminase deficiency. Tandem mass spectrometry coupled with high efficiency separation systems enables postnatal diagnosis of the disorder, while prenatal diagnosis relies on assaying enzyme activity in cultured amniotic fibroblasts or chorionic villi sampling. Screening of adenosine deaminase deficiency for relatives-at-risk may reduce costs of treatment and ensure timely medical intervention as applicable. This article reviews the genetic, biochemical and clinical aspects of adenosine deaminase deficiency. PMID:24772956

Bose, Rahul; Nandagopal, Krishnadas

2013-10-01

245

Modulation of sensory irritation responsiveness by adenosine and malodorants.  

PubMed

Respiratory tract reflex responses are an important defense mechanism against noxious airborne materials. This study was aimed at defining the effects of adenosine on sensory irritation responsiveness and its role in odorant-irritant interactions. These experiments were aimed at testing the hypothesis that adenosine, through the A2 receptor, enhances trigeminal nerve responses to multiple irritants and that odorants enhance responsiveness to irritants through A2 pathways in the female C57Bl/6 mouse. The adenosine precursor, AMP, immediately and markedly increased the sensory irritation response to capsaicin, cyclohexanone, and styrene, irritants that activate chemosensory nerves through differing receptor pathways. The neuromodulatory effect was blocked by the general adenosine receptor antagonist theophylline and by the A2 receptor-specific antagonist DMPX. Multiple odorants were examined, including R-carvone (spearmint), linalool (lavender), trimethylamine (rotting fish), mercaptoethanol, and ethyl sulfide (stench and rotten eggs). Of these, only mercaptoethanol and ethyl sulfide exhibited neuromodulatory effects, enhancing the sensory irritation response to styrene or cyclohexanone. This effect was blocked by theophylline and DMPX indicating the importance of adenosine A2 receptor pathways in this effect. These results highlight that trigeminal chemosensory responsiveness is not static, but can be quickly modulated by adenosine and select odors resulting in hyperresponsive states. PMID:23162088

Willis, Daniel N; Morris, John B

2013-01-01

246

Adaptations in adenosine signaling in drug dependence: therapeutic implications.  

PubMed

Adenosine is an important endogenous purine neuromodulator in the central nervous system that modulates many important cellular processes in neurons. The physiological effects of adenosine are transduced through four pharmacologically classified receptor types i.e., A1, A2A, A2B and A3. All adenosine receptors are G-protein coupled receptors (GPCR) of the type 1 variety. Adaptations in adenosine signaling have been implicated in a wide range of pathophysiological processes, such as epilepsies, sleep disorders, pain, and drug addictions. Knowledge relating to the etiology of addictive processes is far from complete, and as a result the therapeutic options to deal with drug dependence issues are limited. Drugs of abuse mediate their effects through many distinct cellular effectors, such as neurotransmitter transporters, ion channels, and receptor proteins. However, a unifying feature of the major drugs of abuse-i.e., opiates, cocaine, and alcohol-is that they all directly or indirectly modulate adenosine signaling in neurons. Agents targeting adenosine receptors may therefore offer novel avenues for the development of therapies to manage or treat addictions. A consistent cellular adaptation to long-term drug use is the up- or down-regulation of signaling pathways driven by adenylyl cyclase/cyclic AMP (cAMP) in several brain regions linked to addiction. Withdrawal from mu-opioids or cocaine following their chronic administration leads to an upregulation of adenylyl cyclase-mediated signaling, resulting in high levels of cAMP. Cyclic AMP produced in this way acts as a substrate for the endogenous production of adenosine. Increased levels of endogenous adenosine interact with presynaptic A1 receptors to inhibit the excessive neuronal excitation often seen during morphine/cocaine withdrawal. These pre-clinical findings fit well with other data indicating that drugs which boost endogenous adenosine levels or directly interact with inhibitory A1 receptors can alleviate many of the negative consequences of opioid/cocaine withdrawal. Ethanol interacts directly with the adenosine system by blocking nucleoside transporters in the cell membrane. The effect of this inhibition is an increase in extracellular adenosine levels and adenosine receptor activation. Depending on the time course of ethanol exposure and the receptor population present, cAMP levels are either reduced or increased. Chronic ethanol treatment tends to reduce cAMP levels as a consequence of the desensitization of stimulatory GPCRs (such as A2-type receptors) seen following prolonged receptor activation. Unlike opiates and cocaine, adenosine receptor activation worsens the behavioral effects of drug ingestion, and evidence indicates that agents that negatively modulate adenosine receptor function have some utility in attenuating the effects of ethanol use. Taken together, these data suggest that pharmacological manipulation of adenosine signaling represents a potentially useful means of managing drug dependence. PMID:15248812

Hack, Stephen P; Christie, Macdonald J

2003-01-01

247

Intracellular ATP Concentration Contributes to the Cytotoxic and Cytoprotective Effects of Adenosine  

PubMed Central

Extracellular adenosine (Ade) interacts with cells by two pathways: by activating cell surface receptors at nanomolar/micromolar concentrations; and by interfering with the homeostasis of the intracellular nucleotide pool at millimolar concentrations. Ade shows both cytotoxic and cytoprotective effects; however, the underlying mechanisms remain unclear. In the present study, the effects of adenosine-mediated ATP on cell viability were investigated. Adenosine treatment was found to be cytoprotective in the low intracellular ATP state, but cytotoxic under the normal ATP state. Adenosine-mediated cytotoxicity and cytoprotection rely on adenosine-derived ATP formation, but not via the adenosine receptor pathway. Ade enhanced proteasome inhibition-induced cell death mediated by ATP generation. These data provide a new pathway by which adenosine exerts dual biological effects on cell viability, suggesting an important role for adenosine as an ATP precursor besides the adenosine receptor pathway.

Guo, Haiping; Liu, Shouting; Huang, Hongbiao; Liu, Ningning; Yang, Changshan; Tang, Ping; Liu, Jinbao

2013-01-01

248

Adenosine A2A and A2B receptors are both required for adenosine A1 receptor-mediated cardioprotection  

PubMed Central

All four adenosine receptor subtypes have been shown to play a role in cardioprotection, and there is evidence that all four subtypes may be expressed in cardiomyocytes. There is also increasing evidence that optimal adenosine cardioprotection requires the activation of more than one receptor subtype. The purpose of this study was to determine whether adenosine A2A and/or A2B receptors modulate adenosine A1 receptor-mediated cardioprotection. Isolated perfused hearts of wild-type (WT), A2A knockout (KO), and A2BKO mice, perfused at constant pressure and constant heart rate, underwent 30 min of global ischemia and 60 min of reperfusion. The adenosine A1 receptor agonist N6-cyclohexyladenosine (CHA; 200 nM) was administrated 10 min before ischemia and for the first 10 min of reperfusion. Treatment with CHA significantly improved postischemic left ventricular developed pressure (74 4% vs. 44 4% of preischemic left ventricular developed pressure at 60 min of reperfusion) and reduced infarct size (30 2% with CHA vs. 52 5% in control) in WT hearts, effects that were blocked by the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (100 nM). Treatments with the A2A receptor agonist CGS-21680 (200 nM) and the A2B agonist BAY 60-6583 (200 nM) did not exert any beneficial effects. Deletion of adenosine A2A or A2B receptor subtypes did not alter ischemia-reperfusion injury, but CHA failed to exert a cardioprotective effect in hearts of mice from either KO group. These findings indicate that both adenosine A2A and A2B receptors are required for adenosine A1 receptor-mediated cardioprotection, implicating a role for interactions among receptor subtypes.

Zhan, Enbo; McIntosh, Victoria J.

2011-01-01

249

Functional characterization of adenosine A 2 receptors in Jurkat cells and PC12 cells using adenosine receptor agonists  

Microsoft Academic Search

The effect of several adenosine analogues on cyclic AMP accumulation was examined in the rat phaeochromocytoma cell PC12 and in the human T-cell leukaemia cell Jurkat, selected as prototypes of cells predominantly expressing adenosine A2A or A2B receptors. Using the reverse transcription-polymerase chain reaction it was, however, demonstrated that the Jurkat cell and the PC12 cell express both A2A and

Ingeborg Ploeg; Susanne Ahlberg; Fiona E. Parkinson; Bertil B. Fredholm; Ray A. Olsson

1996-01-01

250

8-substituted adenosine and theophylline-7-riboside analogues as potential partial agonists for the adenosine A1 receptor.  

PubMed

A series of 8-substituted adenosine and theophylline-7-riboside analogues (28 and 9 compounds, respectively) was tested on adenosine A1 and A2A receptors as an extensive exploration of the adenosine C8-region. Alkylamino substituents at the 8-position cause an affinity decrease for adenosine analogues, but an affinity increase for theophylline-7-riboside derivatives. The affinity decrease is probably due to a direct steric hindrance between the C8-substituent and the binding site as well as to electronic effects, not to a steric influence on the ribose moiety to adopt the anti conformation. The 8-substituents increase the affinity of theophylline-7-riboside analogues probably by binding to a lipophilic binding site. The intrinsic activity was tested in vitro for some 8-substituted adenosine analogues, by determining the GTP shift in receptor binding studies and the inhibition of adenylate cyclase in a culture of rat thyroid FRTL-5 cells, and in vivo in the rat cardiovascular system for 8-butylaminoadenosine. Thus, it was shown that 8-ethyl-, 8-butyl-, and 8-pentylamino substituted analogues of adenosine may be partial agonists in vitro, and that 8-butylaminoadenosine is a partial agonist for the rat cardiovascular A1 receptor in vivo. PMID:7589213

Van der Wenden, E M; Hartog-Witte, H R; Roelen, H C; von Frijtag Drabbe Knzel, J K; Pirovano, I M; Matht, R A; Danhof, M; Van Aerschot, A; Lidaks, M J; IJzerman, A P

1995-08-15

251

A3 adenosine receptor signaling contributes to airway inflammation and mucus production in adenosine deaminase-deficient mice.  

PubMed

Adenosine signaling has been implicated in chronic lung diseases such as asthma and chronic obstructive pulmonary disease; however, the specific roles of the various adenosine receptors in processes central to these disorders are not well understood. In this study, we have investigated the role(s) of the A(3) adenosine receptor in adenosine-dependent pulmonary inflammation observed in adenosine deaminase (ADA)-deficient mice. The A(3) receptor (A(3)R) was found to be expressed in eosinophils and mucus-producing cells in the airways of ADA-deficient mice. Treatment of ADA-deficient mice with MRS 1523, a selective A(3)R antagonist, prevented airway eosinophilia and mucus production. Similar findings were seen in the lungs of ADA/A(3) double knockout mice. Although eosinophils were decreased in the airways of ADA-deficient mice following antagonism or removal of the A(3)R, elevations in circulating and lung interstitial eosinophils persisted, suggesting signaling through the A(3)R is needed for the migration of eosinophils into the airways. These findings identify an important role for the A(3)R in regulating lung eosinophilia and mucus production in an environment of elevated adenosine. PMID:15240734

Young, Hays W J; Molina, Jose G; Dimina, Dawn; Zhong, Hongyan; Jacobson, Marlene; Chan, Lee-Nien L; Chan, Teh-Sheng; Lee, James J; Blackburn, Michael R

2004-07-15

252

Evidence that adenosine diphosphate can activate adenylate cyclase via conversion to adenosine in platelet-rich plasma containing magnesium.  

PubMed

When adenosine diphosphate (ADP) is added to hirudinized platelet-rich plasma (PRP) in which the level of platelet cAMP has been pharmacologically elevated, there is an initial rapid fall in the level of cAMP brought about by inhibition of adenylate cyclase. This may be followed by a subsequent activation of adenylate cyclase that does not occur when citrated PRP is used in place of hirudinized PRP, and is more pronounced in the presence of added Mg2+. Here we provide evidence that a) the Mg2+-dependent activation of adenylate cyclase seen in hirudinized PRP is mediated by adenosine, b) the adenosine produced synergizes with forskolin and with DN9693 to raise the level of cAMP in platelets. but not with iloprost, c) Mg2+ does not influence directly the rate or extent of cAMP production and so is more likely to influence the rate of adenosine production, and d) activation of adenylate cyclase by adenosine can lead to inhibition of platelet aggregation. ARL 66096, a P2T purinoceptor antagonist which inhibits ADP-induced platelet aggregation, prevented inhibition of adenylate cyclase by ADP. Conversely, ARL 66096 did not appear to inhibit conversion of ADP to adenosine and subsequent activation of adenylate cyclase. PMID:9716160

Glenn, J R; Heptinstall, S

1998-08-01

253

Adenosine-mediated cyclic AMP-dependent inhibition of ciliary activity in rabbit tracheal epithelium.  

PubMed

We wished to determine whether adenosine, a purine nucleotide, modulates activity of respiratory cilia and, to this end, we studied cultured rabbit tracheal epithelium in response to adenosine and related substances in vitro. Ciliary beat frequency (CBF) as determined by a photoelectric method was depressed by adenosine (10(-3) M), the maximal decrease from the baseline value (965 +/- 29 beats/min, mean +/- SE) being 31.6 +/- 5.0% (p less than 0.001). The adenosine A2-receptor agonist N-ethylcarboxamide adenosine had only a small effect on ciliary activity, whereas other adenosine analogs elicited decreases in CBF in a dose-dependent fashion. The order of potency of cilia-inhibitory action was N-cyclohexyladenosine (an agonist for adenosine A1-receptor) greater than phenylisopropyladenosine greater than adenosine greater than N-ethylcarboxamide adenosine. Intracellular cyclic AMP (cAMP) levels were decreased by 10(-3) M adenosine from 39.2 +/- 6.5 to 25.3 +/- 4.8 pM/mg protein (p less than 0.05). The effect of adenosine on CBF was enhanced by dipyridamole, an adenosine uptake inhibitor, and by deoxycoformycin, an adenosine deaminase inhibitor. The adenosine-induced decreases in CBF and cAMP content were reversed by 8-phenyltheophylline, an adenosine receptor antagonist. These results suggest that there is an adenosine A1-receptor on rabbit tracheal epithelium that inhibits adenylate cyclase, which may result in the impairment of respiratory ciliary activity, and that adenosine-induced ciliary inhibition may be modulated by adenosine uptake and its catabolism by airway epithelial cells. PMID:2536529

Tamaoki, J; Kondo, M; Takizawa, T

1989-02-01

254

Ion-dependent conformational switching by a DNA aptamer that induces remyelination in a mouse model of multiple sclerosis  

PubMed Central

We recently reported that a guanosine-rich 40-mer DNA aptamer (LJM-3064) mediates remyelination in the Theilers murine encephalomyelitis virus mouse model of multiple sclerosis. Here, we characterize the G-quadruplex forms of this aptamer in vitro, and demonstrate using circular dichroism spectroscopy that LJM-3064 undergoes a monovalent ion-dependent conformational switch. In the presence of sodium ions and no potassium ions, LJM-3064 adopts an antiparallel-stranded G-quadruplex structure. When presented with low concentrations of potassium ions in a buffer that mimics the composition of interstitial fluid and blood plasma, LJM-3064 rapidly switches to a parallel-stranded G-quadruplex conformation, which is presumably the physiologically active folded form. We characterize these conformational states using dimethyl sulfate reactivity studies and Bal 31 nuclease probing. Our analysis indicates that only the 5?-terminal 26 nucleotides are involved in G-quadruplex formation. Thermodynamic characterization of LJM-3064 at physiologically relevant ion concentrations reveals the G-quadruplex to be metastable at human body temperature. These data provide important structural and thermodynamic insights that may be valuable in optimizing LJM-3064 as a therapeutic remyelinating agent.

Smestad, John; Maher, L. James

2013-01-01

255

[Serum adenosine deaminase activity in pulmonary tuberculosis].  

PubMed

Adenosine deaminase (ADA) activity has been helpful for the diagnosis of tuberculous pleurisy. However, there are few studies about the role of ADA in the diagnosis and follow-up of pulmonary tuberculosis. In our study, serum ADA activity was determined in order to investigate the role of the enzyme in the diagnosis of pulmonary tuberculosis and monitoring the efficiency of therapy. The ADA activity was (mean +/- SD) 21.77 +/- 8.51 U/L in pulmonary tuberculosis patients (n= 44), 6.24 +/- 3.25 U/L in old tuberculosis patients (n= 24), 8.58 +/- 4.38 U/L in healthy control subjects (n= 20), whereas the mean for the patients with bronchial cancer (n= 20) was 18.51 +/- 7.85 U/L. There was no statistical difference between the results of pulmonary tuberculosis patients and the patients with bronchial cancer. On the contrary, the result of these two group were significantly different from both old tuberculosis patients and healthy control subjects (p< 0.001 for both). In 10 pulmonary tuberculosis patients, ADA activities were determined both before and after treatment and a significant decrease was observed in ADA activities after treatment (p< 0.001). In conclusion, serum ADA activity is increased in pulmonary tuberculosis patients, therefore it may be a helpful parameter for monitoring therapy. PMID:15143406

Alata?, Fsun; Uslu, Sema; Moral, Hale; Alata?, Ozkan; Metinta?, Muzaffer; Erginel, Sinan; Ugun, Irfan

2003-01-01

256

Effect of adenosine on the growth of human T-lymphocyte leukemia cell line MOLT-4.  

PubMed

Adenosine has been observed to suppress the growth of MOLT-4 human leukemia cells in vitro. Changes in the cell cycle, especially increased percentage of cells in S phase, prolonged generation time, and induction of apoptosis at higher adenosine concentrations have been found to be responsible for the growth suppression. Dipyridamole, a drug inhibiting the cellular uptake of adenosine, reversed partially but significantly the adenosine-induced growth suppression. It follows from these results that the action of adenosine on the MOLT-4 cells comprises its cellular uptake and intracellular operation. These findings present new data on anticancer efficacy of adenosine. PMID:17882653

Streitov, Denisa; Weiterov, Lenka; Hofer, Michal; Hol, Jirina; Horvth, Viktor; Kozubk, Alois; Znojil, Vladimr

2007-09-01

257

Adenosine deaminase from Streptomyces coelicolor: recombinant expression, purification and characterization.  

PubMed

The sequencing of the genome of Streptomyces coelicolor A3(2) identified seven putative adenine/adenosine deaminases and adenosine deaminase-like proteins, none of which have been biochemically characterized. This report describes recombinant expression, purification and characterization of SCO4901 which had been annotated in data bases as a putative adenosine deaminase. The purified putative adenosine deaminase gives a subunit Mr=48,400 on denaturing gel electrophoresis and an oligomer molecular weight of approximately 182,000 by comparative gel filtration. These values are consistent with the active enzyme being composed of four subunits with identical molecular weights. The turnover rate of adenosine is 11.5 s? at 30 C. Since adenine is deaminated ?10 slower by the enzyme when compared to that of adenosine, these data strongly show that the purified enzyme is an adenosine deaminase (ADA) and not an adenine deaminase (ADE). Other adenine nucleosides/nucleotides, including 9-?-D-arabinofuranosyl-adenine (ara-A), 5'-AMP, 5'-ADP and 5'-ATP, are not substrates for the enzyme. Coformycin and 2'-deoxycoformycin are potent competitive inhibitors of the enzyme with inhibition constants of 0.25 and 3.4 nM, respectively. Amino acid sequence alignment of ScADA with ADAs from other organisms reveals that eight of the nine highly conserved catalytic site residues in other ADAs are also conserved in ScADA. The only non-conserved residue is Asn317, which replaces Asp296 in the murine enzyme. Based on these data, it is suggested here that ADA and ADE proteins are divergently related enzymes that have evolved from a common ?/? barrel scaffold to catalyze the deamination of different substrates, using a similar catalytic mechanism. PMID:21511036

Pornbanlualap, Somchai; Chalopagorn, Pornchanok

2011-08-01

258

Enhancement of tetrodotoxin-induced axonal blockade by adenosine, adenosine analogues, dibutyryl cyclic AMP and methylxanthines in the frog sciatic nerve.  

PubMed Central

The effects of adenosine, adenosine analogues (N6-cyclohexyladenosine (CHA), L-N6-phenylisopropyladenosine (L-PIA), D-N6-phenylisopropyladenosine (D-PIA), N6-methyladenosine and 2-chloroadenosine), adenine, inosine, hypoxanthine, cyclic AMP and its analogue the dibutyryl cyclic AMP (db cyclic AMP), and methylxanthines (theophylline, caffeine and isobutylmethylxanthine (Ibmx) on compound action potentials were investigated in de-sheathed sciatic nerve preparations of the frog. Adenosine and its analogues enhanced, in a concentration-dependent manner, the inhibitory action of tetrodotoxin (TTX) on nerve conduction. The order of potencies was: CHA greater than D-PIA greater than L-PIA greater than N6-methyladenosine greater than 2-chloroadenosine greater than adenosine. The adenosine metabolites, inosine and hypoxanthine, were inactive on TTX-induced axonal blockade. Adenine enhanced the inhibitory action of TTX on nerve conduction, but was less effective than adenosine. db Cyclic AMP, but not cyclic AMP, mimicked the inhibitory effect of adenosine on nerve conduction. Methylxanthines did not antagonize the effect of adenosine on TTX-induced axonal block and in high concentrations also mimicked the effect of adenosine on nerve conduction. The possibility of adenosine acting on TTX-induced axonal block through an adenosine receptor positively coupled to adenylate cyclase is discussed.

Ribeiro, J. A.; Sebastiao, A. M.

1984-01-01

259

Enhancement of tetrodotoxin-induced axonal blockade by adenosine, adenosine analogues, dibutyryl cyclic AMP and methylxanthines in the frog sciatic nerve.  

PubMed

The effects of adenosine, adenosine analogues (N6-cyclohexyladenosine (CHA), L-N6-phenylisopropyladenosine (L-PIA), D-N6-phenylisopropyladenosine (D-PIA), N6-methyladenosine and 2-chloroadenosine), adenine, inosine, hypoxanthine, cyclic AMP and its analogue the dibutyryl cyclic AMP (db cyclic AMP), and methylxanthines (theophylline, caffeine and isobutylmethylxanthine (Ibmx) on compound action potentials were investigated in de-sheathed sciatic nerve preparations of the frog. Adenosine and its analogues enhanced, in a concentration-dependent manner, the inhibitory action of tetrodotoxin (TTX) on nerve conduction. The order of potencies was: CHA greater than D-PIA greater than L-PIA greater than N6-methyladenosine greater than 2-chloroadenosine greater than adenosine. The adenosine metabolites, inosine and hypoxanthine, were inactive on TTX-induced axonal blockade. Adenine enhanced the inhibitory action of TTX on nerve conduction, but was less effective than adenosine. db Cyclic AMP, but not cyclic AMP, mimicked the inhibitory effect of adenosine on nerve conduction. Methylxanthines did not antagonize the effect of adenosine on TTX-induced axonal block and in high concentrations also mimicked the effect of adenosine on nerve conduction. The possibility of adenosine acting on TTX-induced axonal block through an adenosine receptor positively coupled to adenylate cyclase is discussed. PMID:6091833

Ribeiro, J A; Sebastio, A M

1984-10-01

260

Ribose-modified adenosine analogues as potential partial agonists for the adenosine receptor.  

PubMed

We have adopted a practical three-step route for the synthesis of 2'- and 3'-deoxy analogues of N6-substituted adenosines: protection of the hydroxyl groups, replacement of the N6-amino by a better leaving group, and combined deprotection and N6-amination in the last step. This route was used to synthesize deoxy analogues of CPA, CHA, and R- and S-PIA. The compounds were tested on the adenosine A1 and A2a receptors in our search for partial agonists for these receptors. The GTP shift was used as an in vitro measure for the intrinsic activity of these compounds; the in vivo intrinsic activities of the deoxy analogues of CPA and R-PIA were determined in the rat cardiovascular system. Thus, it was shown that the hydroxyl groups are determinants for the affinity and intrinsic activity of these analogues. Removal of the 2'- and 3'-hydroxyl groups affects affinity and intrinsic activity, whereas removal of the 5'-hydroxyl group decreases only affinity. PMID:7562934

van der Wenden, E M; von Frijtag Drabbe Knzel, J K; Matht, R A; Danhof, M; IJzerman, A P; Soudijn, W

1995-09-29

261

Mechanism of adenylate kinase. Dose adenosine 5'-triphosphate bind to the adenosine 5'-monophosphate site  

SciTech Connect

Although the subtrate binding properties of adenylate kinase (AK) have been studied extensively by various biochemical and biophysical techniques, it remains controversial whether uncomplexed adenosine 5'-triphosphate (ATP) binds to the adenosine 5'-monophosphate (AMP) site of AK. The authors present two sets of experiments which argue against binding of ATP to the AMP site. (a) /sup 31/P nuclear magnetic resonance titration of ATP with AK indicated a 1:1 stoichiometry on the basis of changes in coupling constants and line widths. This ruled out binding of ATP to both sites. (b) ATP and MgATP were found to behave similarly by protecting AK from spontaneous inactivation while AMP showed only a small degree of protection. Such inactivation could also be protected or reversed by dithioerythritol and is most likely due to oxidation of sulfhydryl groups, one of which (cysteine-25) is located near the MgATP site. The results support binding of ATP to the MgATP site predominantly, instead of the AMP site, in the absence of Mg/sup 2 +/.

Shyy, Y.J.; Tian, G.; Tsai, M.D.

1987-10-06

262

Intracellularly transported adenosine induces apoptosis in HuH7 human hepatoma cells by downregulating c-FLIP expression causing caspase-3\\/-8 activation  

Microsoft Academic Search

Extracellular adenosine induced apoptosis of HuH-7 cells, a Fas-deficient human hepatoma cell line. The adenosine action was inhibited by dipyridamole, an adenosine transporter inhibitor, or 5?-amino-5?-deoxyadenosine, an inhibitor of adenosine kinase to convert from adenosine to AMP, but it was not affected by inhibitors for adenosine A1, A2a, A2b, and A3 adenosine receptors. Adenosine activated caspase-3 and -8, but not

Dongqin Yang; Takahiro Yaguchi; Hideyuki Yamamoto; Tomoyuki Nishizaki

2007-01-01

263

Effect of Adenosine on Melanogenesis in B16 Cells and Zebrafish  

PubMed Central

Background Adenosine is a nucleoside, in which an adenine molecule is attached to a ribofuranose sugar moiety. It can be released into the microenvironment by metabolically active cells, and then fulfills a multitude of functions in regulation of cell proliferation, by activating four subtypes of G protein-coupled adenosine receptors. Objective In this study, we investigated the effect of adenosine on melanogenesis, using B16 melanoma cells. Methods The toxic effects of adenosine on B16 melanoma cells were assessed. To understand the mechanism of the effect of adenosine on melanogenesis in B16 cells, melanin content and tyrosinase activity were measured. Tyrosinase, tyrosinase-related protein-1, and dopachrome tautomerase were monitored by Western blotting. Finally, adenosine was applied to zebrafish embryos, and its in vivo effect on pigmentation investigated. Results At a low concentration, adenosine increased melanin content and tyrosinase activity, while a high dose of adenosine resulted in inhibition of tyrosinase activity. Western blotting showed that adenosine increased tyrosinase protein levels slightly, while high-dose adenosine decreased the expression of tyrosinase. In zebrafish tests, adenosine slightly inhibited body pigmentation. Conclusion In this study, we investigated the effect of adenosine on melanogenesis, using the well-established B16 melanoma cell and zebrafish models. The results suggest that adenosine may inhibit pigmentation, through negative regulation of tyrosinase.

Kim, Mi Yoon; Lee, Hae-Eul; Im, Myung; Lee, Young; Kim, Chang-Deok; Lee, Jeung-Hoon

2014-01-01

264

Adenosine agonists reduce voltage-dependent calcium conductance of mouse sensory neurones in cell culture.  

PubMed Central

Adenosine and several of its analogues produced a concentration-dependent shortening of calcium-dependent action potential (c.a.p.) duration of mouse dorsal root ganglion (d.r.g.) neurones in dissociated cell culture. The following rank order of potency was obtained: N6-(L-phenylisopropyl)adenosine greater than N6-(D-phenylisopropyl)adenosine greater than N6-cyclohexyladenosine greater than 2-chloroadenosine much greater than 1-methylisoguanosine greater than adenosine. Effects of adenosine agonists on c.a.p. duration were blocked by methylxanthine adenosine antagonists. Adenosine monophosphate (AMP) and cyclic AMP shortened c.a.p.s in d.r.g. neurones, while ATP also depolarized cells. Voltage-clamp analysis revealed that the effect arose from reduction of a voltage-dependent calcium conductance. Adenosine agonists reduced depolarization-evoked inward currents but did not alter membrane conductance following blockade of calcium channels by cadmium. Additionally, adenosine reduced the instantaneous current-voltage slope (chord conductance) during step commands that produced maximal activation of voltage-dependent calcium conductance. If effects of adenosine on neuronal somata and synaptic terminals are similar, adenosine agonists may inhibit neurotransmitter release in the central nervous system by inhibiting a voltage-dependent calcium conductance. Since effects of adenosine agonists did not correspond with their relative potencies as modulators of adenylate cyclase activity or inhibitors of neurotransmitter release in peripheral tissues, a novel adenosine receptor may be involved in regulation of this conductance.

MacDonald, R L; Skerritt, J H; Werz, M A

1986-01-01

265

Anti-inflammatory activity of non-nucleoside adenosine deaminase inhibitor FR234938.  

PubMed

Adenosine has anti-inflammatory activity. Adenosine deaminase (EC 3.5.4.4) metabolizes extracellular adenosine, resulting in an exacerbation of inflammation. Consequently, it was hypothesized that adenosine deaminase inhibitors produce anti-inflammatory activity by increasing extracellular adenosine concentration. This group recently developed a non-nucleoside adenosine deaminase inhibitor, FR234938, by using rational structure-based drug design. FR234938 inhibits recombinant human adenosine deaminase enzyme competitively. FR234938 inhibits interleukin (IL)-6-dependent immunoglobulin (Ig) M production by SKW6.4 cells, in the presence of adenosine. Inhibitory effect of FR234938/adenosine combination is blocked by an A2a adenosine receptor antagonist. FR234938 also inhibits anti-type II collagen delayed type hypersensitivity (DTH) in a dose-dependent manner, both in the presence and absence of recombinant human adenosine deaminase. Moreover, FR234938 inhibits tumor necrosis factor (TNF)-alpha and IL-10 production in a lipopolysaccharide (LPS)-induced cytokine production model in mice. These results indicate that FR234938 has potential anti-inflammatory activity. Non-nucleoside adenosine deaminase inhibitor FR234938 has good potential as a new type of anti-rheumatic and anti-inflammatory drug, by modulating host-defense concentrations of adenosine. PMID:16515782

Kuno, Masako; Seki, Nobuo; Tsujimoto, Susumu; Nakanishi, Isao; Kinoshita, Takayoshi; Nakamura, Katsuya; Terasaka, Tadashi; Nishio, Nobuya; Sato, Akihiro; Fujii, Takashi

2006-03-18

266

2-Chloroadenosine but not adenosine induces apoptosis in rheumatoid fibroblasts independently of cell surface adenosine receptor signalling  

PubMed Central

The apoptotic effect of adenosine and its analogues was studied in fibroblast-like synoviocytes derived from rheumatoid arthritis patients (RA-FLSs). Evoked cell death was quantitatively examined by assessing DNA fragmentation using an enzyme-liked immunosorbent assay and by measuring phosphatidylserine exposure through flow cytometric analysis of annexin V binding.Exposing cells for 24?h to 2-chloroadenosine (2-CADO), a nonspecific, adenosine deaminase (ADA)-resistant, adenosine receptor (AdoR) agonist, induced DNA fragmentation, and thus apoptosis, in RA-FLSs at concentrations ?50??M. By contrast, incubation with adenosine for up to 72?h did not evoke DNA fragmentation, even in the presence of ADA inhibitor coformycin and nucleoside transporter inhibitor nitrobenzylmercaptopurin (NBMPR). Transcription of all four AdoR isoforms was detected in RA-FLSs; nevertheless selective AdoR agonists similarly failed to induce DNA fragmentation.DNA fragmentation evoked by 2-CADO was inhibited by NBMPR and by 5?-iodotubercidin, an adenosine kinase inhibitor, but not by xanthine amine congener, an A1 and A2 receptor antagonist, or by selective AdoR antagonists.The nonspecific caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone abolished the apoptotic effect of 2-CADO.These results suggest that 2-CADO induces apoptosis in RA-FLSs independently of AdoR-mediated signalling. Instead, 2-CADO, but not adenosine, is taken up into RA-FLSs via human equilibrative nucleoside transporter-1, where it is phosphorylated by adenosine kinase. The resultant phospho-2-CADO induces DNA fragmentation by activating a caspase pathway.

Koshiba, Masahiro; Kosaka, Hidekazu; Nakazawa, Takashi; Hayashi, Nobuhide; Saura, Ryuichi; Kitamura, Noriko; Kumagai, Shunichi

2002-01-01

267

Manipulation of adenosine kinase affects sleep regulation in mice  

PubMed Central

Sleep and sleep intensity are enhanced by adenosine and its receptor agonists, while adenosine receptor antagonists induce wakefulness. Adenosine kinase (ADK) is the primary enzyme metabolizing adenosine in adult brain. To investigate whether adenosine metabolism or clearance affects sleep we recorded sleep in mice with engineered mutations in Adk. Adk-tg mice over-express a transgene encoding the cytoplasmic isoform of ADK in the brain, but lack the nuclear isoform of the enzyme. Wild-type mice and Adk+/? mice that have a 50% reduction of the cytoplasmic and the nuclear isoforms of ADK served as controls. Adk-tg mice showed a remarkable reduction of EEG power in low frequencies in all vigilance states and in theta activity (6.2511 Hz) in REM sleep and waking. Adk-tg mice were awake 58 min more per day than wild-type mice and spent significantly less time in REM sleep (1023 vs 1283 min in wild-type). After sleep deprivation slow-wave activity (0.754 Hz), the intensity component of NREM sleep, increased significantly less in Adk-tg mice and their slow-wave energy was reduced. In contrast, the vigilance states and EEG spectra of Adk+/? and wild-type mice did not differ. Our data suggest that over-expression of the cytoplasmic isoform of ADK is sufficient to alter sleep physiology. ADK might orchestrate neurotransmitter pathways involved in the generation of EEG oscillations and regulation of sleep.

Palchykova, Svitlana; Winsky-Sommerer, Raphaelle; Shen, Hai-Ying; Boison, Detlev; Gerling, Andrea; Tobler, Irene

2010-01-01

268

Medicinal chemistry of A2A adenosine receptor antagonists.  

PubMed

Due to the clearly demonstrated receptor-receptor interaction between adenosine A(2A) and dopamine D(2) receptors in the basal ganglia, the discovery and development of potent and selective A(2A)adenosine receptor antagonists became, in the last ten years, an attractive field of research to discovery new drugs for the treatment of neurodegenerative disorders, such as Parkinsons disease. Different compounds have been deeply investigated as A(2A) adenosine receptor antagonists, which could be classified in two great families: xanthine derivatives and nitrogen poliheterocyclic systems. These studies led to the discovery of some highly potent and selective A(2A) adenosine receptor antagonists such as ZM241385, SCH58261 and some xanthine derivatives (KW6002), which have been used as pharmacological tools for studying this receptor subtype. However, those compounds showed some problems that do not permit their use in clinical studies, such as poor water solubility (SCH58261, and xanthine derivatives) or good affinity for A(2B) adenosine receptor subtype (ZM241385). In the last few years great efforts have been made to overcome these problems, trying to optimize not only the pharmacological profile but also the pharmacokinetic character of this class of compounds. The aim of this report is to briefly summarize the recent progress made in this attractive field of research. PMID:12570758

Cacciari, Barbara; Pastorin, Giorgia; Spalluto, Giampiero

2003-01-01

269

Characterization of Two Adenosine Analogs as Fluorescence Probes in RNA  

PubMed Central

The fluorescence properties of two adenosine analogs, 2-(3-phenylpropyl)adenosine [A-3CPh] and 2-(4-phenylbutyl)adenosine [A-4CPh], are reported. As monomers, the quantum yields and the mean lifetimes are 0.011 and 6.22 ns for A-3CPh and 0.007 and 7.13 ns for A-4CPh, respectively. Surprisingly, the quantum yields of the two probes are enhanced 1182 fold upon incorporation into RNA, while the mean lifetimes decrease 2340%. The data suggest that a subpopulation of molecules is responsible for the fluorescence characteristics and that the distribution of emitting and non-emitting structures is altered upon incorporation of the probes into RNA. Thus, although both adenosine analogs have low quantum yields as monomers, their fluorescence signals are significantly enhanced in RNA. Thermodenaturation experiments and CD spectroscopy indicate that incorporation of the adenosine analogs into three different RNAs does not alter their global structure or stability. Therefore, these probes should be useful for probing events occurring close to the site of modification.

Zhao, Ying; Knee, Joseph L.; Baranger, Anne M.

2008-01-01

270

Vitamin C prevents metal ion-dependent initiation and propagation of lipid peroxidation in human low-density lipoprotein.  

PubMed

Lipid peroxidation and oxidative modification of low-density lipoprotein (LDL) have been implicated as causal factors in the pathogenesis of atherosclerosis, and prevention of LDL oxidation by antioxidants may be an effective strategy to inhibit the progression of the disease. We investigated the effects of the reduced form of vitamin C (L-ascorbic acid, AA) and its two-electron oxidation product (dehydro-L-ascorbic acid, DHA) upon metal ion-dependent oxidative modification of human LDL. We found that low micromolar concentrations of both AA and DHA protect LDL against oxidation induced by Cu2+ or by hemin and hydrogen peroxide. In a dose-dependent manner, AA and DHA prevented the initiation of lipid peroxidation in LDL, as determined by a sensitive and selective assay for lipid hydroperoxides utilizing HPLC with chemiluminescence detection. AA and DHA also preserved the LDL-associated antioxidants alpha-tocopherol, beta-carotene, and lycopene, but not ubiquinol-10. Furthermore, AA was able to stop propagation of lipid peroxidation in LDL, whereas DHA lacked this ability. The addition of 60 microM AA to LDL containing up to 38 nmol/mg protein of pre-formed lipid hydroperoxides led to their rapid disappearance; this activity of AA was dependent on the presence of redox-active copper, but did not lead to the formation of lipid hydroxides, the reduced form of lipid hydroperoxides. Our data show that in Cu(2+)-exposed LDL (i) vitamin C primarily spares, rather than regenerates, alpha-tocopherol and other endogenous antioxidants, except for AA and DHA prevent initiation of lipid peroxidation in LDL; and (iii) AA can terminate lipid peroxidation, thereby protecting partially oxidized LDL against further oxidative modification. PMID:7647104

Retsky, K L; Frei, B

1995-08-01

271

Variation in One Residue Associated with the Metal Ion-Dependent Adhesion Site Regulates ?IIb?3 Integrin Ligand Binding Affinity  

PubMed Central

The Asp of the RGD motif of the ligand coordinates with the ? I domain metal ion dependent adhesion site (MIDAS) divalent cation, emphasizing the importance of the MIDAS in ligand binding. There appears to be two distinct groups of integrins that differ in their ligand binding affinity and adhesion ability. These differences may be due to a specific residue associated with the MIDAS, particularly the ?3 residue Ala252 and corresponding Ala in the ?1 integrin compared to the analogous Asp residue in the ?2 and ?7 integrins. Interestingly, mutations in the adjacent to MIDAS (ADMIDAS) of integrins ?4?7 and ?L?2 increased the binding and adhesion abilities compared to the wild-type, while the same mutations in the ?2?1, ?5?1, ?V?3, and ?IIb?3 integrins demonstrated decreased ligand binding and adhesion. We introduced a mutation in the ?IIb?3 to convert this MIDAS associated Ala252 to Asp. By combination of this mutant with mutations of one or two ADMIDAS residues, we studied the effects of this residue on ligand binding and adhesion. Then, we performed molecular dynamics simulations on the wild-type and mutant ?IIb?3 integrin ? I domains, and investigated the dynamics of metal ion binding sites in different integrin-RGD complexes. We found that the tendency of calculated binding free energies was in excellent agreement with the experimental results, suggesting that the variation in this MIDAS associated residue accounts for the differences in ligand binding and adhesion among different integrins, and it accounts for the conflicting results of ADMIDAS mutations within different integrins. This study sheds more light on the role of the MIDAS associated residue pertaining to ligand binding and adhesion and suggests that this residue may play a pivotal role in integrin-mediated cell rolling and firm adhesion.

Wu, Xue; Xiu, Zhilong; Li, Guohui; Luo, Bing-Hao

2013-01-01

272

Investigating real-time activation of adenosine receptors by bioluminescence resonance energy transfer technique  

NASA Astrophysics Data System (ADS)

Adenosine receptors play important roles in many physiological and pathological processes, for example regulating myocardial oxygen consumption and the release of neurotransmitters. The activations of adenosine receptors have been studied by some kinds of techniques, such as western blot, immunohistochemistry, etc. However, these techniques cannot reveal the dynamical response of adenosine receptors under stimulation. In this paper, bioluminescence resonance energy transfer technique was introduced to study the real-time activation of adenosine receptors by monitoring the dynamics of cyclic adenosine monophosphate (cAMP) level. The results showed that there were significant differences between adenosine receptors on real-time responses under stimulation. Moreover, the dynamics of cAMP level demonstrated that competition between adenosine receptors existed. Taken together, our study indicates that monitoring the dynamics of cAMP level using bioluminescence resonance energy transfer technique could be one potential approach to investigate the mechanism of competitions between adenosine receptors.

Huang, Yimei; Yang, Hongqin; Zheng, Liqin; Chen, Jiangxu; Wang, Yuhua; Li, Hui; Xie, Shusen

2013-02-01

273

Role of Adenosine Analogs and Growth Hormone in Waking and Sleep.  

National Technical Information Service (NTIS)

The role of adenosine in sleep has been further investigated using electroencephalography to document the dose response effects of newly developed specific adenosine A1 and A2 receptor stimulants and 8-cyclopropyltheophylline (CPRT), a substituted xanthin...

M. Radulovacki

1987-01-01

274

Mechanisms of induction of adenosine receptor genes and its functional significance  

PubMed Central

Adenosine is a metabolite generated and released from cells, particularly under injury or stress. It elicits protective or damaging responses via signaling through the adenosine receptors, including the adenylyl cyclase inhibitory A1, and A3, and the adenylyl cyclase stimulatory A2A and A2B. Multiple adenosine receptor types, including stimulatory and inhibitory, can be found in the same cell, suggesting that a careful balance of adenosine receptor expression in a particular cell is necessary for a specific adenosine-induced response. This balance could be controlled by differential expression of the adenosine receptor genes under different stimuli. Here, we have reviewed an array of studies that have characterized basal or induced expression of the adenosine receptors and common as well as distinct mechanisms of effect, in hopes that ongoing studies on this topic will further elucidate detailed mechanisms of adenosine receptor regulation, leading to potential therapeutic applications.

St. Hilaire, Cynthia; Carroll, Shannon H.; Chen, Hongjie; Ravid, Katya

2012-01-01

275

Adenosine induces growth-cone turning of sensory neurons  

PubMed Central

The formation of appropriate connections between neurons and their specific targets is an essential step during development and repair of the nervous system. Growth cones are located at the leading edges of the growing neurites and respond to environmental cues in order to be guided to their final targets. Directional information can be coded by concentration gradients of substrate-bound or diffusible-guidance molecules. Here we show that concentration gradients of adenosine stimulate growth cones of sensory neurons (dorsal root ganglia) from chicken embryos to turn towards the adenosine source. This response is mediated by adenosine receptors. The subsequent signal transduction process involves cAMP. It may be speculated that the in vivo function of this response is concerned with the formation or the repair and regeneration of the peripheral nervous system. Electronic supplementary material The online version of this article (doi:10.1007/s11302-008-9121-3) contains supplementary material, which is available to authorised users.

Grau, Benjamin; Eilert, John-Christian; Munck, Sebastian

2008-01-01

276

Characterization of adenosine receptors in the human bladder carcinoma T24 cell line  

Microsoft Academic Search

The molecular and pharmacological properties of adenosine receptors in the T24 human bladder epithelial carcinoma cell line were assessed by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), Ca2+ Flux, cAMP production and interleukin-8 measurements. RT-PCR experiments detected the presence of transcripts for the adenosine A1, A2A and A2B receptors but not for the adenosine A3 subtype. Application of specific adenosine receptor ligands

P. Tara Phelps; John C. Anthes; Craig C. Correll

2006-01-01

277

A2B Receptors Mediate the Antimitogenic Effects of Adenosine in Cardiac Fibroblasts  

Microsoft Academic Search

Adenosine inhibits growth of cardiac fibroblasts; however, the adenosine receptor subtype that mediates this antimitogenic effect remains undefined. Therefore, the goals of this study were to determine which adenosine receptor subtype mediates the antimitogenic effects of adenosine and to investigate the signal transduction mechanisms involved. In rat left ventricular cardiac fibroblasts, PDGF-BB (25 ng\\/mL) stimulated DNA synthesis (3H-thymidine incorpora- tion),

Raghvendra K. Dubey; Delbert G. Gillespie; Lefteris C. Zacharia; Zaichuan Mi; Edwin K. Jackson

278

Vesnarinone Inhibits Adenosine Uptake in Endothelial Cells, Smooth Muscle Cells and Myocytes, and Mediates Cytoprotection  

Microsoft Academic Search

Vesnarinone is a novel synthetic inotropic agent. Recently, it has been reported that vesnarinone inhibits adenosine uptake in the B-lymphocytoid cell line. Since extracellular adenosine is cardioprotective, we examined whether vesnarinone inhibits adenosine uptake in cells constituting the cardiovascular system. 1?Ci of [3H]adenosine was added to cells of the myocyte cell line (C2C12), human coronary smooth muscle cell line (HCASMC),

Masafumi Kitakaze; Miranda Fong; Masuhiro Yoshitake; Tetsuo Minamino; Koichi Node; Yuji Okuyama; Naohiro Terada; Taku Kambayashi; Masatsugu Hori

1997-01-01

279

Adenosine and cardioprotection: what can we learn from nature's genetic polymorphism?  

PubMed

Adenosine is an endogenous nucleoside that has been shown to be beneficial for the myocardium in different settings by a large number of experimental studies. In this article, we 1) outline adenosine's metabolic pathways, 2) address cardioprotective properties of adenosine, and 3) discuss possible implications of the two recently published clinical studies disclosing a positive effect of adenosine monophosphate deaminase 1 (AMPD1) gene mutation on cardiovascular survival in heart failure and ischemic heart disease. (Fig. 2, Ref. 84.) PMID:12448564

Skalova, K; Luptak, I; Turcani, M; Hulin, I

2002-01-01

280

Stability of Diluted Adenosine Solutions in Polyolefin Infusion Bags  

PubMed Central

Background: Intravenous or intracoronary adenosine is used in the cardiac catherization lab to achieve maximal coronary blood flow and determine fractional flow reserve. Objective: To determine the stability of adenosine 10 and 50 g/mL in either 0.9% sodium chloride injection or 5% dextrose injection in polyolefin infusion bags stored at 2 temperatures, refrigeration (2C-8C) or controlled room temperature (20C-25C). Methods: Adenosine 10 g/mL and 50 g/mL solutions were prepared in 50 mL polyolefin infusion bags containing 0.9% sodium chloride injection or 5% dextrose injection and stored at controlled room temperature or under refrigeration. Each combination of concentration, diluent, and storage was prepared in triplicate. Samples were assayed using stability-indicating, reversed-phase high-performance liquid chromatography immediately at time 0 and at 24 hours, 48 hours, 7 days, and 14 days. Stability was defined as retaining 90% to 110% of the initial adenosine concentration. The samples were also visually inspected against a light background for clarity, color, and the presence of particulate matter. Results: After 14 days, all samples retained 99% to 101% of the initial adenosine concentration. No considerable change in pH or visual appearance was noted. The stability data indicated no significant loss of drug due to chemical degradation or physical interactions during storage. Conclusion: Adenosine solutions of 10 and 50 g/mL were stable for at least 14 days in 50 mL polyolefin infusion bags of 0.9% sodium chloride injection or 5% dextrose injection stored at controlled room temperature and refrigerated conditions.

Almagambetova, Elise; Hutchinson, David; Blais, Danielle M.; Zhao, Fang

2013-01-01

281

Potential roles of adenosine deaminase-2 in diabetic retinopathy.  

PubMed

The early activation of microglia that induces retinal inflammation in DR may serve as a target for therapeutic intervention of DR. Our demonstration that retinal inflammation is attenuated via adenosine receptor A(2A)AR supports the hypothesis that a mechanism to maintain extracellular concentrations of adenosine important in normal physiology is impaired in DR. Extracellular concentrations of adenosine are regulated by the interplay of equiliberative nucleoside transporter (ENT)s with enzymes of adenosine metabolism including adenosine deaminase-1 (ADA1), adenosine kinase (AK) and CD73. In the vertebrates but not rodents, a macrophage-associated ADA2 is identified. The role of ADA2 is, therefore, understudied as the sequencing probes or antibodies to mouse ADA2 are not available. We identified increased ADA2 expression and activity in human and porcine retinas with diabetes, and in Amadori glycated albumin (AGA)- or hyperglycemia-treated porcine and human microglia. In rodent as well as porcine cells, modulation of TNF-? release is mediated by A(2A)AR. Quantitative analysis of normal and diabetic porcine retinas reveals that while the expression levels of ADA2, A2AAR, ENT1, TNF-? and MMP9 are increased, the levels of AK are reduced during inflammation as an endogenous protective mechanism. To determine the role of ADA2, we found that AGA induces ADA2 expression, ADA2 activity and TNF-? release, and that TNF-? release is blocked by ADA2-neutralizing antibody or ADA2 siRNA, but not by scrambled siRNA. These results suggest that retinal inflammation in DR is mediated by ADA2, and that the anti-inflammatory activity of A(2A)AR signaling is impaired in diabetes due to increased ADA2 activity. PMID:23685153

Elsherbiny, Nehal M; Naime, Mohammad; Ahmad, Saif; Elsherbini, Ahmed M; Mohammad, Shuaib; Fulzele, Sadanand; El-Remessy, Azza B; Al-Gayyar, Mohammed M; Eissa, Laila A; El-Shishtawy, Mamdouh M; Han, Guichun; White, Richard; Haroldo, Toque Flores; Liou, Gregory I

2013-07-01

282

Adenosine Produces Pulmonary Vasoconstriction in Sheep Evidence for Thromboxane A2\\/Prostaglandin Endoperoxide- Receptor Activation  

Microsoft Academic Search

Adenosine, an intermediate product in the metabolism of ATP, is thought to produce vasodilatation in all vascular beds with the exception of the kidney. Due to its theoretical potential as a pulmonary vasodilator, we studied the hemodynamic effects of adenosine in the pulmonary vasculature of chronically instrumented awake sheep. Adenosine produced signifi- cant pulmonary vasoconstriction instead of the expected vasodilatation.

Italo Biaggioni; Landon S. King; Nigar Enayat; David Robertson; John H. Newman

2010-01-01

283

Adenosine Receptor Activation Induces Vascular Endothelial Growth Factor in Human Retinal Endothelial Cells  

Microsoft Academic Search

Adenosine, released in increased amounts by hypoxic tissues, is thought to be an angiogenic factor that links altered cellular metabolism caused by oxygen deprivation to compensatory angiogenesis. Adenosine interacts with 4 subtypes of G protein- coupled receptors, termed A1 ,A 2A ,A 2B, and A3. We investigated whether adenosine causes proliferation of human retinal endothelial cells (HRECs) and synthesis of

Maria B. Grant; Roy W. Tarnuzzer; Sergio Caballero; Mark J. Ozeck; Margaret I. Davis; Polyxenie E. Spoerri; Igor Feoktistov; Italo Biaggioni; John C. Shryock; Luiz Belardinelli

284

Adenosine, a Metabolic Trigger of the Exercise Pressor Reflex in Humans  

Microsoft Academic Search

There is substantial evidence that adenosine activates muscle afferent nerve fibers leading to sympathetic stimulation, but the issue remains controversial. To further test this hypothesis, we used local injections of adenosine into the brachial artery while monitoring systemic muscle sympathetic nerve activity (MSNA) with peroneal microneurography. The increase in MSNA induced by 3 mg intrabrachial adenosine (106632%) was abolished if

Fernando Costa; Andre Diedrich; Benjamin Johnson; Paulgun Sulur; Ginnie Farley; Italo Biaggioni

285

Intravascular Source of Adenosine During Forearm Ischemia in Humans Implications for Reactive Hyperemia  

Microsoft Academic Search

It is believed that adenosine is released in ischemic tissues and contributes to reactive hyperemia. We tested this hypothesis in the human forearm using microdialysis to estimate interstitial and intravascular levels of adenosine and caffeine withdrawal to potentiate endogenous adenosine and determine its effect on reactive hyperemia. Forearm blood flow response to ischemia was measured by air plethysmography before and

Fernando Costa; Mark Angel; Virginia Haile; Brian Christman; Italo Biaggioni

286

Adenosine and IFN synergistically increase IFN production of human NK cells  

Microsoft Academic Search

Prevention of overwhelming immune reactions is essential for an organism to survive. Adenosine, a ribonucleoside produced by various cell types during inflammatory processes, has been shown to inhibit effector functions of different im- mune cells. Here, we show that the adenosine A3 receptor agonist iodobenzyl methylcarboxamido- adenosine potently inhibited proliferation, IFN- production, and cytotoxicity of activated human lymphoid cells. Stimulation

Florian Jeffe; Kerstin A. Stegmann; Felix Broelsch; Michael P. Manns; Markus Cornberg; Heiner Wedemeyer

2008-01-01

287

Temporal and mechanistic dissociation of ATP and adenosine release during ischaemia in the mammalian hippocampus1  

PubMed Central

Abstract Adenosine is well known to be released during cerebral metabolic stress and is believed to be neuroprotective. ATP release under similar circumstances has been much less studied. We have now used biosensors to measure and compare in real time the release of ATP and adenosine during in vitro ischaemia in hippocampal slices. ATP release only occurred following the anoxic depolarisation, whereas adenosine release was apparent almost immediately after the onset of ischaemia. ATP release required extracellular Ca2+. By contrast adenosine release was enhanced by removal of extracellular Ca2+, whilst TTX had no effect on either ATP release or adenosine release. Blockade of ionotropic glutamate receptors substantially enhanced ATP release, but had only a modest effect on adenosine release. Carbenoxolone, an inhibitor of gap junction hemichannels, also greatly enhanced ischaemic ATP release, but had little effect on adenosine release. The ecto-ATPase inhibitor ARL 67156, whilst modestly enhancing the ATP signal detected during ischaemia, had no effect on adenosine release. Adenosine release during ischaemia was reduced by pre-treament with homosysteine thiolactone suggesting an intracellular origin. Adenosine transport inhibitors did not inhibit adenosine release, but instead they caused a twofold increase of release. Our data suggest that ATP and adenosine release during ischaemia are for the most part independent processes with distinct underlying mechanisms. These two purines will consequently confer temporally distinct influences on neuronal and glial function in the ischaemic brain.

Frenguelli, Bruno G; Wigmore, Geoffrey; Llaudet, Enrique; Dale, Nicholas

2007-01-01

288

Rational design and performance testing of aptamer-based electrochemical biosensors for adenosine  

Microsoft Academic Search

This work emphasizes on the design criteria of aptamer-based biosensors for adenosine and the comparison of their performances by using both electrochemical and biochemical methods. The adenosine biosensors have been typically prepared by hybridizing a short bridging DNA (modified with a thiol for the attachment to gold electrode) to the aptamer strand that releases upon adenosine binding. We have carefully

Banani Chakraborty; Zhifeng Jiang; Yunchao Li; Hua-Zhong Yu

2009-01-01

289

Modulation of cardiac A 1 -adenosine receptors in rats following treatment with agents affecting heart rate  

Microsoft Academic Search

Effects of chronic treatment affecting heart rate on A1 adenosine receptor levels and their functions were studied. Treatment of rats with isoproterenol for 10 days accelerated heart rate and increased the level of adenosine receptors, in both the atria and ventricles. Negative dromotropic response of isolated heart to adenosine was enhanced in isoproterenol-treated rats. Similar results were obtained following treatment

Nissim Balas; Michael Arad; Babeth Rabinowitz; Asher Shainberg

2002-01-01

290

Adenosine A 3 Receptor Signaling in the Central Nervous System  

Microsoft Academic Search

\\u000a Adenosine A3 receptors are widely distributed in the central nervous system but are expressed at a low level and have lower affinity for\\u000a adenosine in comparison to the A1 and A2A receptors. Nevertheless, they appear to tonically modulate motor activity as pointed out in A3 receptor-deleted mice.\\u000a \\u000a \\u000a The role of A3 receptor in several pathophysiological conditions is often controversial. In

Felicita Pedata; Anna Maria Pugliese; Ana M. Sebastio; Joaquim A. Ribeiro

291

A 3 Adenosine Receptor Agonists: History and Future Perspectives  

Microsoft Academic Search

\\u000a IB-MECA, the first selective A3 adenosine receptor (A3AR) agonist, was reported in 1993, and since then numerous adenosine derivatives have been modified to optimize their interaction\\u000a with the A3AR. IB-MECA (CF101) and its 2-chloro analogue, Cl-IB-MECA (CF102) are in Phase II clinical trials for treatment of autoimmune\\u000a inflammatory diseases and cancer, respectively. Additional structural modifications made at the N\\u000a 6

Kenneth A. Jacobson; Zhan-Guo Gao; Dilip K. Tosh; Gangadhar J. Sanjayan; Sonia de Castro

292

The 2?,3?-cAMP-adenosine pathway  

PubMed Central

Our recent studies employing HPLC-tandem mass spectrometry to analyze venous perfusate from isolated, perfused kidneys demonstrate that intact kidneys produce and release into the extracellular compartment 2?,3?-cAMP, a positional isomer of the second messenger 3?,5?-cAMP. To our knowledge, this represents the first detection of 2?,3?-cAMP in any cell/tissue/organ/organism. Nuclear magnetic resonance experiments with isolated RNases and experiments in isolated, perfused kidneys suggest that 2?,3?-cAMP likely arises from RNase-mediated transphosphorylation of mRNA. Both in vitro and in vivo kidney experiments demonstrate that extracellular 2?,3?-cAMP is efficiently metabolized to 2?-AMP and 3?-AMP, both of which can be further metabolized to adenosine. This sequence of reactions is called the 2?,3?-cAMP-adenosine pathway (2?,3?-cAMP ? 2?-AMP/3?-AMP ? adenosine). Experiments in rat and mouse kidneys show that metabolic poisons increase extracellular levels of 2?,3?-cAMP, 2?-AMP, 3?-AMP, and adenosine; however, little is known regarding the pharmacology of 2?,3?-cAMP, 2?-AMP, and 3?-AMP. What is known is that 2?,3?-cAMP facilitates activation of mitochondrial permeability transition pores, a process that can lead to apoptosis and necrosis, and inhibits proliferation of vascular smooth muscle cells and glomerular mesangial cells. In summary, there is mounting evidence that at least some types of cellular injury, by triggering mRNA degradation, engage the 2?,3?-cAMP-adenosine pathway, and therefore this pathway should be added to the list of biochemical pathways that produce adenosine. Although speculative, it is possible that the 2?,3?-cAMP-adenosine pathway may protect against some forms of acute organ injury, for example acute kidney injury, by both removing an intracellular toxin (2?,3?-cAMP) and increasing an extracellular renoprotectant (adenosine).

2011-01-01

293

Phosphorylation of adenosine in renal brush-border membrane vesicles by an exchange reaction catalysed by adenosine kinase.  

PubMed Central

Uptake of [3H]adenosine in brush-border membrane (BBM) vesicles from either rat or pig kidney leads to an accumulation of intravesicular [3H]AMP. The lack of significant levels of ATP and the presence of AMP in BBM indicated that a phosphotransfer between [3H]adenosine and AMP occurs. The phosphotransfer activity is inhibited by iodotubercidin, which suggests that it is performed by adenosine kinase acting in an ATP-independent manner. The existence of a similar phosphotransferase activity was demonstrated in membrane-free extracts from pig kidney. From the compounds tested it was shown that a variety of mononucleotides could act as phosphate donors. The results suggest that phosphotransfer reactions may be physiologically relevant in kidney.

Sayos, J; Solsona, C; Mallol, J; Lluis, C; Franco, R

1994-01-01

294

Elevated Ecto-5'-nucleotidase-Mediated Increased Renal Adenosine Signaling Via A2B Adenosine Receptor Contributes to Chronic Hypertension  

PubMed Central

Rationale Hypertension is the most prevalent life-threatening disease worldwide and is frequently associated with chronic kidney disease (CKD). However, the molecular basis underlying hypertensive CKD is not fully understood. Objective We sought to identify specific factors and signaling pathways that contribute to hypertensive CKD and thereby exacerbate disease progression. Methods and Results Using high-throughput quantitative reverse-transcription polymerase chain reaction profiling, we discovered that the expression level of 5?-ectonucleotidase (CD73), a key enzyme that produces extracellular adenosine, was significantly increased in the kidneys of angiotensin IIinfused mice, an animal model of hypertensive nephropathy. Genetic and pharmacological studies in mice revealed that elevated CD73-mediated excess renal adenosine preferentially induced A2B adenosine receptor (ADORA2B) production and that enhanced kidney ADORA2B signaling contributes to angiotensin IIinduced hypertension. Similarly, in humans, we found that CD73 and ADORA2B levels were significantly elevated in the kidneys of CKD patients compared with normal individuals and were further elevated in hypertensive CKD patients. These findings led us to further discover that elevated renal CD73 contributes to excess adenosine signaling via ADORA2B activation that directly stimulates endothelin-1 production in a hypoxia-inducible factor-?dependent manner and underlies the pathogenesis of the disease. Finally, we revealed that hypoxia-inducible factor-? is an important factor responsible for angiotensin IIinduced CD73 and ADORA2B expression at the transcriptional level. Conclusions Overall, our studies reveal that angiotensin IIinduced renal CD73 promotes the production of renal adenosine that is a prominent driver of hypertensive CKD by enhanced ADORA2B signalingmediated endothelin-1 induction in a hypoxia-inducible factor-?dependent manner. The inhibition of excess adenosine-mediated ADORA2B signaling represents a novel therapeutic target for the disease.

Zhang, Weiru; Zhang, Yujin; Wang, Wei; Dai, Yingbo; Ning, Chen; Luo, Renna; Sun, Kaiqi; Glover, Louise; Grenz, Almut; Sun, Hong; Tao, Lijian; Zhang, Wenzheng; Colgan, Sean P.; Blackburn, Michael R.; Eltzschig, Holger K.; Kellems, Rodney E.; Xia, Yang

2013-01-01

295

Ecto-5?-Nucleotidase (CD73)-Mediated Formation of Adenosine Is Critical for the Striatal Adenosine A2A Receptor Functions  

PubMed Central

Adenosine is a neuromodulator acting through inhibitory A1 receptors (A1Rs) and facilitatory A2ARs, which have similar affinities for adenosine. It has been shown that the activity of intracellular adenosine kinase preferentially controls the activation of A1Rs, but the source of the adenosine activating A2ARs is unknown. We now show that ecto-5?-nucleotidase (CD73), the major enzyme able to convert extracellular AMP into adenosine, colocalizes with A2ARs in the basal ganglia. In addition to astrocytes, striatal CD73 is prominently localized to postsynaptic sites. Notably, CD73 coimmunoprecipitated with A2ARs and proximity ligation assays confirmed the close proximity of CD73 and A2ARs in the striatum. Accordingly, the cAMP formation in synaptosomes as well as the hypolocomotion induced by a novel A2AR prodrug that requires CD73 metabolization to activate A2ARs were observed in wild-type mice, but not in CD73 knock-out (KO) mice or A2AR KO mice. Moreover, CD73 KO mice displayed increased working memory performance and a blunted amphetamine-induced sensitization, mimicking the phenotype of global or forebrain-A2AR KO mice, as well as upon pharmacological A2AR blockade. These results show that CD73-mediated formation of extracellular adenosine is responsible for the activation of striatal A2AR function. This study points to CD73 as a new target that can fine-tune A2AR activity, and a novel therapeutic target to manipulate A2AR-mediated control of striatal function and neurodegeneration.

Augusto, Elisabete; Matos, Marco; Sevigny, Jean; El-Tayeb, Ali; Bynoe, Margaret S.; Muller, Christa E.

2013-01-01

296

Acetate supplementation modulates brain adenosine metabolizing enzymes and adenosine A2A receptor levels in rats subjected to neuroinflammation  

PubMed Central

Background Acetate supplementation reduces neuroglia activation and pro-inflammatory cytokine expression in rat models of neuroinflammation and Lyme neuroborreliosis. Because single-dose glyceryl triacetate (GTA) treatment increases brain phosphocreatine and reduces brain AMP levels, we postulate that GTA modulates adenosine metabolizing enzymes and receptors, which may be a possible mechanism to reduce neuroinflammation. Methods To test this hypothesis, we quantified the ability of GTA to alter brain levels of ecto-5-nucleotidase (CD73), adenosine kinase (AK), and adenosine A2A receptor using western blot analysis and CD73 activity by measuring the rate of AMP hydrolysis. Neuroinflammation was induced by continuous bacterial lipopolysaccharide (LPS) infusion in the fourth ventricle of the brain for 14 and 28days. Three treatment strategies were employed, one and two where rats received prophylactic GTA through oral gavage with LPS infusion for 14 or 28days. In the third treatment regimen, an interventional strategy was used where rats were subjected to 28days of neuroinflammation, and GTA treatment was started on day 14 following the start of the LPS infusion. Results We found that rats subjected to neuroinflammation for 28days had a 28% reduction in CD73 levels and a 43% increase in AK levels that was reversed with prophylactic acetate supplementation. CD73 activity in these rats was increased by 46% with the 28-day GTA treatment compared to the water-treated rats. Rats subjected to neuroinflammation for 14days showed a 50% increase in levels of the adenosine A2A receptor, which was prevented with prophylactic acetate supplementation. Interventional GTA therapy, beginning on day 14 following the induction of neuroinflammation, resulted in a 67% increase in CD73 levels and a 155% increase in adenosine A2A receptor levels. Conclusion These results support the hypothesis that acetate supplementation can modulate brain CD73, AK and adenosine A2A receptor levels, and possibly influence purinergic signaling.

2014-01-01

297

Effect of A2B adenosine receptor gene ablation on adenosine-dependent regulation of proinflammatory cytokines.  

PubMed

Pharmacological studies suggest that A(2B) adenosine receptors mediate proinflammatory effects of adenosine. This concept was recently challenged by the finding that A(2B) adenosine receptor knockout (A(2B)KO) mice had moderate inflammation due to elevated basal plasma tumor necrosis factor (TNF)-alpha and an exaggerated response to lipopolysaccharide (LPS) challenge. However, it is unclear whether this phenomenon actually reflects the loss of putative taming of proinflammatory cytokine production via activation of A(2B) receptors by endogenous adenosine. In this report, we examined adenosine receptor-dependent regulation of interleukin (IL)-6 and TNF-alpha blood plasma levels in A(2B)KO and wild-type mice in vivo and their release from peritoneal macrophages ex vivo. Stimulation of adenosine receptors with 5'-N-ethylcarboxamidoadenosine (NECA) up-regulated IL-6 and suppressed LPS-induced TNF-alpha in wild-type mice. The selective A(2B) antagonists 3-isobutyl-8-pyrrolidinoxanthine and 8-[4-[((4-cyanophenyl)carbamoylmethyl)oxy]phenyl]-1,3-di(n-propyl)xanthine (MRS 1754) inhibited NECA-induced IL-6 release but not the suppression of LPS-induced TNF-alpha secretion from macrophages. Genetic ablation of A(2B) receptors abrogated NECA-induced increases in IL-6 release from mouse peritoneal macrophages and dramatically reduced the ability of NECA to raise IL-6 plasma levels in vivo. In contrast, the absence of A(2B) adenosine receptors did not affect NECA-induced suppression of LPS-activated TNF-alpha release in macrophages, nor did it reduce the ability of NECA to suppress LPS-induced increase in TNF-alpha plasma levels in vivo. Thus, our results indicate that stimulation of A(2B) receptors up-regulates the proinflammatory cytokine IL-6 and argue against the recently suggested anti-inflammatory role of A(2B) receptors in suppression of LPS-stimulated TNF-alpha production by adenosine. PMID:17965229

Ryzhov, Sergey; Zaynagetdinov, Rinat; Goldstein, Anna E; Novitskiy, Sergey V; Blackburn, Michael R; Biaggioni, Italo; Feoktistov, Igor

2008-02-01

298

Evaluation of calcium and magnesium in scalp hair samples of population consuming different drinking water: risk of kidney stone.  

PubMed

The objective of this study was to examine the relationship between calcium (Ca) and magnesium (Mg) in underground water (UGW), bottled mineral water (BMW), and domestic treated water (DTW) with related to risk of kidney stones. The water samples were collected from different areas of Sindh, Pakistan. The scalp hair samples of both genders, age ranged 30-60 years, consuming different types of water, have or have not kidney disorders, were selected. The Ca and Mg concentrations were determined in scalp hair of study subjects and water by flame atomic absorption spectroscopy. The Ca and Mg contents in different types of drinking water, UGW, DTW, and BMW, were found in the range of 79.1-466, 23.7-140, and 45-270 mg/L and 4.43-125, 5.23-39.6, and 7.16-51.3 mg/L, respectively. It was observed that Ca concentration in the scalp hair samples of kidney stone patients consuming different types of drinking water was found to be higher (2,895-4721 ?g/g) while Mg level (84.3-101 ?g/g) was lower as compare to referents subjects (2,490-2,730 ?g/g for Ca, 107-128 ?g/g for Mg) in both genders. The positive correlation was found between Ca and Mg levels in water with related to kidney stone formations in population, especially who consumed underground water. A relative risk and odd ratio were calculated; the relative risk had a strong positive association with incidence of kidney stone which depends on types of drinking water. PMID:24218227

Panhwar, Abdul Haleem; Kazi, Tasneem Gul; Afridi, Hassan Imran; Shaikh, Haffeezur Rehman; Arain, Salma Aslam; Arain, Sadaf Sadia; Brahman, Kapil Dev

2013-12-01

299

Intravenous Calcium and Magnesium for Oxaliplatin-Induced Sensory Neurotoxicity in Adjuvant Colon Cancer: NCCTG N04C7  

PubMed Central

Purpose Cumulative sensory neurotoxicity (sNT) is the dose-limiting toxicity of oxaliplatin, which commonly leads to early discontinuation of oxaliplatin-based therapy in the palliative and adjuvant settings. In a nonrandomized, retrospective study, intravenous (IV) calcium/magnesium (Ca/Mg) was associated with reduced oxaliplatin-induced sNT. Methods Patients with colon cancer undergoing adjuvant therapy with infusional fluorouracil, leucovorin, and oxaliplatin (FOLFOX) were randomly assigned to Ca/Mg (1g calcium gluconate plus 1g magnesium sulfate pre- and post-oxaliplatin) or placebo, in a double-blinded manner. The primary end point was the percentage of patients with grade 2 or greater sNT at any time during or after oxaliplatin-based therapy by National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE; version 3) criteria. An oxaliplatin-specific sNT scale and patient questionnaires were also used to assess sNT. After 104 of 300 planned patients were enrolled, the study was closed. This was due to preliminary reports from another trial that suggested that Ca/Mg decreased treatment efficacy; these data were subsequently found to be incorrect. Results Overall, 102 patients were available for analysis. Ca/Mg decreased the incidence of chronic, cumulative, grade 2 or greater sNT, as measured by NCI CTCAE (P = .038) and also by the oxaliplatin-specific sNT scale (P = .018). In addition, acute muscle spasms associated with oxaliplatin were significantly reduced (P = .01) No effect on acute, cold-induced sNT was found. No substantial differences in adverse effects were noted between Ca/Mg and placebo. Conclusion Despite early termination and decreased statistical power, this study supports IV Ca/Mg as an effective neuroprotectant against oxaliplatin-induced cumulative sNT in adjuvant colon cancer.

Grothey, Axel; Nikcevich, Daniel A.; Sloan, Jeff A.; Kugler, John W.; Silberstein, Peter T.; Dentchev, Todor; Wender, Donald B.; Novotny, Paul J.; Chitaley, Umesh; Alberts, Steven R.; Loprinzi, Charles L.

2011-01-01

300

Thermodynamics of the conversion of calcium and magnesium fluorides to the parent metal oxides and hydrogen fluoride  

SciTech Connect

The authors have used thermodynamic modeling to examine the reaction of calcium fluoride (CaF{sub 2}) and magnesium fluoride (MgF{sub 2}) with water (H{sub 2}O) at elevated temperatures. The calculated, equilibrium composition corresponds to the global free-energy minimum for the system. Optimum, predicted reaction temperatures and reactant mole ratios are reported for the recovery of hydrogen fluoride (HF), a valuable industrial feedstock. Complete conversion of MgF{sub 2} is found at 1,000 C and a ratio of 40 moles of H{sub 2}O per 1 mole of MgF{sub 2}. For CaF{sub 2}, temperatures as high as 1,400 C are required for complete conversion at a corresponding mole ratio of 40 moles of H{sub 2}O per 1 mole of CaF{sub 2}. The authors discuss the presence of minor chemical constituents as well as the stability of various potential container materials for the pyrohydrolysis reactions at elevated temperatures. CaF{sub 2} and MgF{sub 2} slags are available as wastes at former uranium production facilities within the Department of Energy Complex and other facilities regulated by the Nuclear Regulatory Commission. Recovery of HF from these wastes is an example of environmental remediation at such facilities.

West, M.H.; Axler, K.M.

1997-02-01

301

Effects of Calcium, Fluoride and Magnesium Supplementations on Tissue Mineralization in Calcium and Magnesium-Deficient Rats1  

Microsoft Academic Search

There is considerable uncertainty about the interrelated effects of calcium (Ca), magnesium (Mg) and fluoride (F) on hypocalcification of the skeleton and Ca accumulation in vital soft tissues. This paper describes experiments with rats fed a diet deficient in Ca and Mg, the latter deficiency being accentuated by a low potassium content. For different groups the drinking water was supplemented

YNGVE ERICSSON; HEIKKI LUOMA; OLLE EKBERG

302

Comparing the Effects of Sodium and Potassium Diet with Calcium and Magnesium Diet on Sex Ratio of Rats` Offspring  

Microsoft Academic Search

Sex determination has scientific basis for prevention of genetic sex linked diseases in addition to social backgrounds. There are many methods for sex determination. This study was designed to investigate the effects of adding different ions to the drinking water of rats on determination of rats' offspring sexes. In total, 72 female Vistar rats were chosen and randomly divided into

2007-01-01

303

Effect of calcium and magnesium on the antimicrobial action of enterocin LR\\/6 produced by Enterococcus faecium LR\\/6  

Microsoft Academic Search

Enterococci are well-known producers of antimicrobial peptides (enterocins) that possess potential as biopreservatives in food. In this study, divalent cations and release of intracellular potassium were used to assess the mechanism of interaction and killing of enterocin LR\\/6 produced by Enterococcus faecium LR\\/6 on three target Gram-positive and Gram-negative bacteria, namely Micrococcus luteus, Enterococcus sp. strain LR\\/3 and Escherichia coli

Manoj Kumar; Sheela Srivastava

2011-01-01

304

The Effect of Calcium and Magnesium on Carbonate Mineral Precipitation during Reactive Transport in a Model Subsurface Pore Structure  

NASA Astrophysics Data System (ADS)

Carbonate mineral precipitation in the subsurface at the interface of two advecting fluids can result in physical and chemical changes in the pore network. This can affect various applications including carbon sequestration. In this work, we evaluate the precipitation kinetics of carbonates in a microfluidic pore network when carbonate in water is mixed transverse to flow with a synthetic brine containing an equimolar concentration of calcium (Ca, 10 mM) and concentrations of magnesium (Mg) ranging from 2 to 40 mM. Mineral precipitation was monitored using reflected brightfield microscopy and mineral polymorphs were determined using Raman spectroscopy. Although Mg was present, only calcium carbonate (CaCO3) polymorphs were observed. The presence of Mg affected both the rate of precipitation and the prevalence of different CaCO3 morphologies. The rate of precipitation with 40mM Mg was about half of the rate as when no Mg was present. The calcium carbonate polymorph aragonite increased from <5% of the precipitated crystal area to >20% as the Mg concentration increased from 0 mM to 40 mM. Energy dispersive spectroscopy (EDS) results showed Mg2+ incorporated into the crystal lattice of the CaCO3 polymorph calcite at 8 to 14 mole% when Mg concentration in solution was highest. The incorporation of Mg2+ into the crystals was likely responsible for the reduction in precipitation rate at high solution concentrations of Mg. Significant pore blockage occurred along the mixing zone, indicating that carbonate precipitation may be of concern along the CO2 plume margins and affect the efficiency of CO2 injection.

Boyd, V.; Werth, C. J.; Valocchi, A. J.; Fouke, B. W.

2012-12-01

305

Determination of calcium and magnesium in magnesite by a complexometric method employing co-precipitation of calcium with strontium sulphate  

Microsoft Academic Search

In the classical gravimetric method calcium is precipitated as phosphate along with the magnesium and recovered by adding sulphuric acid and alcohol, then Ca2+ and Mg2+ are determined separately by the usual method [1]. In the proposed method calcium is co-precipitated with strontium sulphate and in the filtrate magnesium ions are determined by EDTA. Then calcium is calculated by difference

Ramesh Chandra Nigam

1968-01-01

306

Foliar application of calcium and magnesium improves growth, yield, and essential oil yield of oregano ( Origanum vulgare ssp. hirtum)  

Microsoft Academic Search

Oregano is one of the most important spices, is used all over the world, and includes many species. One of the most important commercially grown species is Origanum vulgare ssp. hirtum (Link) Ietsw (syn.: O. heracleoticum.), which is endemic to the Mediterranean area. O. vulgare ssp. hirtum is a crop species which is well adapted to both dry land conditions

Christos Dordas

2009-01-01

307

Evaluation of the content and bioaccessibility of iron, zinc, calcium and magnesium from groats, rice, leguminous grains and nuts.  

PubMed

The objective of this study was to determine the content and the bioaccessibility of minerals (Fe, Zn, Ca and Mg) in commonly consumed food products, such as cereal groats, rice, leguminous grains and nuts purchased from the local market. The contents of Fe, Zn, Ca and Mg in foods were assayed after dry ashing of samples, while the bioaccessibility of these minerals after enzymatic in vitro digestion, was determined by flame atomic absorption spectrometry. A relatively high content of Fe was found in cashew nuts and green lentils, while cashew nuts and buckwheat groats had the highest concentration of Zn. It was found that the highest amount of macro-elements was generally in nuts, in particular: brazil nuts (Ca and Mg), cashews (Mg) and hazelnuts (Ca and Mg). Concerning the mineral bioaccessibility, the highest values for Fe were obtained in cashew nuts and green lentils (2.8 and 1.7mg/100g), for Zn in green lentils (2.1mg/100g), for Ca in brazil nuts and shelled pea (32.6 and 29.1mg/100g), while for Mg in shelled peas and green lentils (43.4 and 33.9mg/100g). Generally, the best sources of bioaccessible minerals seem to be leguminous grains and nuts. PMID:24587537

Suliburska, Joanna; Krejpcio, Zbigniew

2014-03-01

308

Aluminium, calcium and magnesium content of Hungarian foods and dietary intakes by children aged 3.9 and 14 years.  

PubMed

The Al, Ca and Mg content of 147 kinds of foods and beverages, representing a large proportion of the Hungarian diet, has been determined using replicate samples. Dietary intakes of these minerals by 67 kindergarten children and 139 schoolchildren have been assessed. The richest sources of Al were: parsley, celery, gherkins, barley-malt; of Ca: dairy products, celery, parsley, savoy; of Mg: dried beans and peas, parsley, dill, maize-flour, rice, gherkins, chocolate. Flavouring agents (e.g. salt, pepper, paprika, caraway-seed) had very high concentrations of all three minerals and poppy-seeds that of Ca and Mg. The presence of bone-dust or fragments elevated the Ca content of some meats and cooked dishes. The main source of dietary intake of all three minerals was food; as opposed to F, the contribution of water-borne Al, Ca and Mg was negligible. Based on average values, the daily intake of all three minerals was satisfactory in both age groups. Mg intake was marginally below the recommended limit for a few children, but no signs of Mg deficiency were seen. PMID:3227864

Schamschula, R G; Sugr, E; Un, P S; Duppenthaler, J L; Tth, K; Barmes, D E

1988-01-01

309

Strontium/Calcium and Magnesium/Calcium Ratios: Geochemical Constraints on Biomineralization in a Deep-Sea Coral  

NASA Astrophysics Data System (ADS)

Mg/Ca and Sr/Ca are both used as proxies for temperature in scleractinian coral skeletons. These tracers can also be influenced by biomineralization (vital effects) complicating proxy interpretation. We measure Sr/Ca and Mg/Ca across skeletal features in Desmophyllum dianthus, a deep-sea scleractinian coral. Since the growth environment of the deep-sea is typically invariant during the ~100 year lifetime of an individual coral, trace metal variability is attributed to biomineralization rather than environmental influences. By combining micromilling and isotope dilution- ICP-MS we determine detailed co-located Sr/Ca and Mg/Ca ratios in two individuals from the same oceanographic setting. Sr/Ca ratios vary by a relatively small amount across skeletal features, <5%. Sr/Ca within the optically dense central band, composed of centers of calcification, varies significantly less than the surrounding skeleton (F-Test, >98% loc) and has a mean value of 10.6+/-0.2. This value agrees with the inorganic aragonite temperature relationship at the temperature of coral growth for precipitation from seawater. Since Sr/Ca in the central band exhibits little variance, sampling localized to this region should yield the most precise test of a Sr/Ca paleothermometer. Unlike Sr/Ca, Mg/Ca varies dramatically across the coral skeleton. Coincident with the optically dense central band, Mg/Ca was greater than 3 mmol/mol, nearly twice that of the surrounding skeleton. The relative Mg/Ca ratios of three other D. dianthus individuals collected from separate oceanographic locations also nearly double within the central band. Outside the central band, Mg/Ca increases with decreasing Sr/Ca. Rayleigh fractionation from a closed pool may explain this behavior. Within the central band, however, Mg/Ca increases nearly twofold while Sr/Ca varies little from the surrounding skeleton. This observation suggests that a process of greater magnitude than Rayleigh fractionation influences Mg in this region. In order to take into account both metal/Ca ratios, any model explaining high Mg in the center of calcification must decouple Mg and Sr. Sr/Ca and Mg/Ca combined with other, previously measured, tracers in D. dianthus are powerful tools towards the goal of a comprehensive model governing geochemical tracers in biomineralization. Understanding these processes can help us better interpret paleothermometers in biogenic carbonates.

Gagnon, A. C.; Adkins, J. F.; Fernandez, D. P.; Robinson, L. F.

2006-12-01

310

A putative osmoreceptor system that controls neutrophil function through the release of ATP, its conversion to adenosine, and activation of A2 adenosine and P2 receptors  

Microsoft Academic Search

We have previously shown that hyper- tonic stress (HS) can suppress chemoattractant- induced neutrophil responses via cyclic adenosine monophosphate and enhance these responses through p38 mitogen-activated protein kinase (MAPK) activation. The underlying mechanisms are unknown. Here, we report that HS dose-depen- dently releases adenosine 5-triphosphate (ATP) from neutrophils and that extracellular ATP is rap- idly converted to adenosine or activates

Yu Chen; Alok Shukla; Sachiko Namiki; Paul A. Insel; Wolfgang G. Junger

2004-01-01

311

Ethanol Blocks Adenosine Uptake via Inhibiting the Nucleoside Transport System in Bronchial Epithelial Cells  

PubMed Central

Adenosine uptake into cells by nucleoside transporters plays a significant role in governing extracellular adenosine concentration. Extracellular adenosine is an important signaling molecule that modulates many cellular functions via four G-protein-coupled receptor subtypes (A1, A2A, A2B, and A3). Previously, we demonstrated that adenosine is critical in maintaining airway homeostasis and airway repair and that airway host defenses are impaired by alcohol. Taken together, we hypothesized that ethanol impairs adenosine uptake via the nucleoside transport system. To examine ethanol-induced alteration on adenosine transport, we used a human bronchial epithelial cell line (BEAS-2B). Cells were preincubated for 10 min in the presence and absence of varying concentrations of ethanol (EtOH). In addition, some cells were pretreated with S - (4-Nitrobenzyl)-6-thioinosine (100 ?M: NBT), a potent adenosine uptake inhibitor. Uptake was then determined by addition of [3H]-adenosine at various time intervals. Increasing EtOH concentrations resulted in increasing inhibition of adenosine uptake when measured at 1 min. Cells pretreated with NBT effectively blocked adenosine uptake. In addition, short-term EtOH revealed increased extracellular adenosine concentration. Conversely, adenosine transport became desensitized in cells exposed to EtOH (100 mM) for 24 hr. To determine the mechanism of EtOH-induced desensitization of adenosine transport, cAMP activity was assessed in response to EtOH. Short-term EtOH exposure (10 min) had little or no effect on adenosine-mediated cAMP activation, whereas long-term EtOH exposure (24 hr) blocked adenosine-mediated cAMP activation. Western blot analysis of lysates from unstimulated BEAS-2B cells detected a single 55 kDa band indicating the presence of hENT1 and hENT2, respectively. Real-time RT-PCR of RNA from BEAS-2B revealed transcriptional expression of ENT1 and ENT2. Collectively, these data reveal that acute exposure of cells to EtOH inhibits adenosine uptake via a nucleoside transporter, and chronic exposure of cells to EtOH desensitizes the adenosine transporter to these inhibitory effects of ethanol. Furthermore, our data suggest that inhibition of adenosine uptake by EtOH leads to an increased extracellular adenosine accumulation, influencing the effect of adenosine at the epithelial cell surface, which may alter airway homeostasis.

Allen-Gipson, D.S.; Jarrell, J. C.; Bailey, K. L.; Robinson, J. E.; Kharbanda, K.K.; Sisson, J.H.; Wyatt, T.A.

2009-01-01

312

Host A(2B) adenosine receptors promote carcinoma growth.  

PubMed

Recent studies suggest that tumor-infiltrating immune cells can benefit the tumor by producing factors that promote angiogenesis and suppress immunity. Because the tumor microenvironment is characterized by high adenosine levels, we hypothesized that the low-affinity A(2B) adenosine receptor located on host immune cells may participate in these effects. In the current study, we tested this hypothesis in a Lewis lung carcinoma isograft model using A(2B) receptor knockout (A(2B)KO) mice. These mice exhibited significantly attenuated tumor growth and longer survival times after inoculation with Lewis lung carcinoma compared to wild type (WT) controls. Lewis lung carcinoma tumors in A(2B)KO mice contained significantly lower levels of vascular endothelial growth factor (VEGF) compared to tumors growing in WT animals. This difference was due to VEGF production by host cells, which comprised 30 +/- 2% of total tumor cell population. Stimulation of adenosine receptors on WT tumor-infiltrating CD45+ immune cells increased VEGF production fivefold, an effect not seen in tumor-associated CD45+ immune cells lacking A(2B) receptors. In contrast, we found no significant difference in VEGF production between CD45- tumor cells isolated from WT and A(2B)KO mice. Thus, our data suggest that tumor cells promote their growth by exploiting A(2B) adenosine receptor-dependent regulation of VEGF in host immune cells. PMID:18714400

Ryzhov, Sergey; Novitskiy, Sergey V; Zaynagetdinov, Rinat; Goldstein, Anna E; Carbone, David P; Biaggioni, Italo; Dikov, Mikhail M; Feoktistov, Igor

2008-09-01

313

Host A2B Adenosine Receptors Promote Carcinoma Growth1  

PubMed Central

Recent studies suggest that tumor-infiltrating immune cells can benefit the tumor by producing factors that promote angiogenesis and suppress immunity. Because the tumor microenvironment is characterized by high adenosine levels, we hypothesized that the low-affinity A2B adenosine receptor located on host immune cells may participate in these effects. In the current study, we tested this hypothesis in a Lewis lung carcinoma isograft model using A2B receptor knockout (A2BKO) mice. These mice exhibited significantly attenuated tumor growth and longer survival times after inoculation with Lewis lung carcinoma compared to wild type (WT) controls. Lewis lung carcinoma tumors in A2BKO mice contained significantly lower levels of vascular endothelial growth factor (VEGF) compared to tumors growing in WT animals. This difference was due to VEGF production by host cells, which comprised 30 2% of total tumor cell population. Stimulation of adenosine receptors on WT tumor-infiltrating CD45+ immune cells increased VEGF production fivefold, an effect not seen in tumor-associated CD45+ immune cells lacking A2B receptors. In contrast, we found no significant difference in VEGF production between CD45- tumor cells isolated from WT and A2BKO mice. Thus, our data suggest that tumor cells promote their growth by exploiting A2B adenosine receptor-dependent regulation of VEGF in host immune cells.

Ryzhov, Sergey; Novitskiy, Sergey V; Zaynagetdinov, Rinat; Goldstein, Anna E; Carbone, David P; Biaggioni, Italo; Dikov, Mikhail M; Feoktistov, Igor

2008-01-01

314

Adenosine A3 Receptor Activation Modulates the Capillary Endothelial Glycocalyx  

Microsoft Academic Search

The endothelial glycocalyx is a dynamic extracellular matrix composed of cell surface proteoglycans, glycoproteins, and adsorbed serum proteins that has been implicated in the regulation and modulation of capillary tube hematocrit, permeability, and hemostasis. High tissue adenosine levels have been shown to adversely affect microvascular function and tissue survival after an ischemic episode, and previous work in this laboratory has

Steven H. Platts; Brian R. Duling

2010-01-01

315

Adenosine: a potential mediator of immunosuppression in multiple organ failure  

Microsoft Academic Search

Multiple organ failure following a variety of insults, including, trauma, shock and pancreatitis, is the cause of 5080% of all deaths in surgical intensive care units. In most patients, infections secondary to a general immunosuppressive state serve to trigger the development of multiple organ failure. This immunosuppressive state may be a consequence of excessive release of adenosine into the extracellular

Gyrgy Hask; Edwin A Deitch; Csaba Szab; Zoltn H Nmeth; E. Sylvester Vizi

2002-01-01

316

Adenosine-Sensitive Ventricular Tachycardia From the Anterobasal Left Ventricle  

Microsoft Academic Search

Objectives. This study demonstrates that exercise-provocable tachycardia resembling right ventricular outflow tract tachycardia may originate from the anterobasal left ventricle.Background. Reentry is the operative mechanism of idiopathic left ventricular tachycardia, with a QRS complex of right bundle branch block and superior axis that is responsive to verapamil but not adenosine. Whether some mechanism other than reentry is operative in some

San-Jou Yeh; Ming-Shien Wen; Chun-Chieh Wang; Fun-Chung Lin; Delon Wu

1997-01-01

317

Epigenetic changes induced by adenosine augmentation therapy prevent epileptogenesis.  

PubMed

Epigenetic modifications, including changes in DNA methylation, lead to altered gene expression and thus may underlie epileptogenesis via induction of permanent changes in neuronal excitability. Therapies that could inhibit or reverse these changes may be highly effective in halting disease progression. Here we identify an epigenetic function of the brain's endogenous anticonvulsant adenosine, showing that this compound induces hypomethylation of DNA via biochemical interference with the transmethylation pathway. We show that inhibition of DNA methylation inhibited epileptogenesis in multiple seizure models. Using a rat model of temporal lobe epilepsy, we identified an increase in hippocampal DNA methylation, which correlates with increased DNA methyltransferase activity, disruption of adenosine homeostasis, and spontaneous recurrent seizures. Finally, we used bioengineered silk implants to deliver a defined dose of adenosine over 10 days to the brains of epileptic rats. This transient therapeutic intervention reversed the DNA hypermethylation seen in the epileptic brain, inhibited sprouting of mossy fibers in the hippocampus, and prevented the progression of epilepsy for at least 3 months. These data demonstrate that pathological changes in DNA methylation homeostasis may underlie epileptogenesis and reversal of these epigenetic changes with adenosine augmentation therapy may halt disease progression. PMID:23863710

Williams-Karnesky, Rebecca L; Sandau, Ursula S; Lusardi, Theresa A; Lytle, Nikki K; Farrell, Joseph M; Pritchard, Eleanor M; Kaplan, David L; Boison, Detlev

2013-08-01

318

CD39/Adenosine Pathway Is Involved in AIDS Progression  

PubMed Central

HIV-1 infection is characterized by a chronic activation of the immune system and suppressed function of T lymphocytes. Regulatory CD4+ CD25high FoxP3+CD127low T cells (Treg) play a key role in both conditions. Here, we show that HIV-1 positive patients have a significant increase of Treg-associated expression of CD39/ENTPD1, an ectoenzyme which in concert with CD73 generates adenosine. We show in vitro that the CD39/adenosine axis is involved in Treg suppression in HIV infection. Treg inhibitory effects are relieved by CD39 down modulation and are reproduced by an adenosine-agonist in accordance with a higher expression of the adenosine A2A receptor on patients' T cells. Notably, the expansion of the Treg CD39+ correlates with the level of immune activation and lower CD4+ counts in HIV-1 infected patients. Finally, in a genetic association study performed in three different cohorts, we identified a CD39 gene polymorphism that was associated with down-modulated CD39 expression and a slower progression to AIDS.

Limou, Sophie; Younas, Mehwish; Kok, Ayrin; Hue, Sophie; Seddiki, Nabila; Hulin, Anne; Delaneau, Olivier; Schuitemaker, Hanneke; Herbeck, Joshua T.; Mullins, James I.; Muhtarova, Maria; Bensussan, Armand; Zagury, Jean-Francois; Lelievre, Jean-Daniel; Levy, Yves

2011-01-01

319

Role of Extracellular Adenosine in Acute Lung Injury  

NSDL National Science Digital Library

Acute lung injury (ALI) is a lung disease characterized by pulmonary edema and severe hypoxia. The past decade hosted a search for endogenous mechanisms controlling lung inflammation and pulmonary edema during ALI. As such, recent evidence indicates extracellular adenosine in orchestrating the resolution of pulmonary edema and inflammation during ALI.

Tobias Eckle (University of Colorado Denver Anesthesiology, Mucosal Inflammation Program); Michael Koeppen (University of Colorado Denver Anesthesiology); Holger K. Eltzschig (University of Colorado Denver Anesthesiology)

2009-10-01

320

Synthesis of oligo-RNAs with photocaged adenosine 2?-hydroxyls  

Microsoft Academic Search

This protocol describes a general method for the preparation of RNAs in which the reactivity or hydrogen-bonding properties of the molecule are modified in a photoreversible fashion by use of a caging strategy. A single caged adenosine, modified at the 2? position as a nitro-benzyl ether, can be incorporated into short RNAs by chemical synthesis or into long RNAs by

Steven G Chaulk; Andrew M MacMillan

2007-01-01

321

Pharmacological blockade of adenosine A2A receptors diminishes scarring  

PubMed Central

Adenosine A2A receptor (A2AR) stimulation promotes wound healing and is required for the development of fibrosis in murine models of scleroderma and cirrhosis. Nonetheless, the role of A2AR in the formation of scars following skin trauma has not been explored. Here, we examined the effect of pharmacological blockade of A2AR, with the selective adenosine A2AR-antagonist ZM241385 (2.5 mg/ml), in a murine model of scarring that mimics human scarring. We found that application of the selective adenosine A2AR antagonist ZM241385 decreased scar size and enhanced the tensile strength of the scar. Within the scar itself, collagen alignment and composition (marked reduction in collagen 3), but not periostin, biglycan, or fibronectin accumulation, was improved by application of ZM241385. Moreover, A2AR blockade reduced the number of myofibroblasts and angiogenesis but not macrophage infiltration in the scar. Taken together, our work strongly suggests that pharmacological A2AR blockade can be used to diminish scarring while improving the collagen composition and tensile strength of the healed wound.Perez-Aso, M., Chiriboga, L., Cronstein, B. N. Pharmacological blockade of adenosine A2A receptors diminishes scarring.

Perez-Aso, Miguel; Chiriboga, Luis; Cronstein, Bruce N.

2012-01-01

322

Adenosine in cold blood cardioplegia - a placebo-controlled study  

PubMed Central

OBJECTIVE Adenosine as an additive in blood cardioplegia is cardioprotective in animal studies, but its clinical role in myocardial protection remains controversial. The aim of this study was to investigate whether the addition of adenosine in continuous cold blood cardioplegia would enhance myocardial protection. METHODS In a prospective double-blind study comparing adenosine 400?moll?1 to placebo in continuous cold blood cardioplegia, 80 patients undergoing isolated aortic valve replacement were randomized into four groups: antegrade cardioplegia with adenosine (n=19), antegrade cardioplegia with placebo (n=21), retrograde cardioplegia with adenosine (n=21) and retrograde cardioplegia with placebo (n=19). Myocardial arteriovenous differences in oxygen and lactate were measured before, during and after aortic occlusion. Myocardial concentrations of adenine nucleotides and lactate were determined from left ventricular biopsies obtained before aortic occlusion, after bolus cardioplegia, at 60min of aortic occlusion and at 20min after aortic occlusion. Plasma creatine kinase (CK-MB) and troponin T were measured at 1, 3, 6, 9, 12 and 24h after aortic occlusion. Haemodynamic profiles were obtained before surgery and 1, 8 and 24h after cardiopulmonary bypass. Repeated-measures analysis of variance was used for significance testing. RESULTS Adenosine had no effects on myocardial metabolism of oxygen, lactate and adenine nucleotides, postoperative enzyme release or haemodynamic performance. When compared with the antegrade groups, the retrograde groups showed higher myocardial oxygen uptake (17.311.4 versus 2.53.6mll?1 at 60min of aortic occlusion, P<0.001) and lactate accumulation (43.120.7 versus 36.323.0molg?1 at 60min of aortic occlusion, P=0.052) in the myocardium during aortic occlusion, and lower postoperative left ventricular stroke work index (27.28.4 versus 30.17.9gנmנm?2, P=0.034). CONCLUSIONS Adenosine 400?moll?1 in cold blood cardioplegia showed no cardioprotective effects on the parameters studied. Myocardial ischaemia was more pronounced in patients receiving retrograde cardioplegia.

Ahlsson, Anders; Sobrosa, Claudio; Kaijser, Lennart; Jansson, Eva; Bomfim, Vollmer

2012-01-01

323

Pharmacokinetics of adenosine and cordycepin, a bioactive constituent of Cordyceps sinensis in rat.  

PubMed

Cordycepin is a bioactive constituent of Cordyceps sinensis that has been shown to regulate homeostatic function. As an adenosine analogue, it is possible cordycepin goes through a similar metabolic pathway to that of adenosine. To investigate this hypothesis, a sensitive liquid chromatography with photodiode-array detector (HPLC-PDA) coupled to a microdialysis sampling system was developed to monitor cordycepin and adenosine in rat blood and liver. Other endogenous nucleosides were simultaneously measured to further understand the downstream metabolic pathway. The experiments were divided into six parallel groups for drug administration: (1) normal saline vehicle, (2) adenosine, (3) cordycepin, (4) normal saline + erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA; a potent adenosine deaminase inhibitor), (5) adenosine + EHNA, and (6) cordycepin + EHNA. The pharmacokinetic results suggest that the levels of both adenosine and cordycepin decreased rapidly in blood around 30 min after drug administration. When adenosine was given, the concentrations of adenosine metabolites, hypoxanthinosine and hypoxanthine, increased in rat blood. This phenomenon was inhibited by EHNA pretreatment. An unidentified peak was observed in the blood and liver samples after cordycepin administration. The decline of this unidentified peak paralleled the decreased of the concentration of cordycepin, and it was not observed in the presence of the adenosine deaminase inhibitor. It is concluded that adenosine and cordycepin had short elimination half-lives and high rates of clearance and their biotransformation was suppressed by EHNA. PMID:20302371

Tsai, Yung-Jen; Lin, Lie-Chwen; Tsai, Tung-Hu

2010-04-28

324

Adenosine augmentation therapies (AATs) for epilepsy: prospect of cell and gene therapies  

PubMed Central

Deficiencies in the brains own adenosine-based seizure control system contribute to seizure generation. Consequently, reconstitution of adenosinergic neuromodulation constitutes a rational approach for seizure control. This review will critically discuss focal adenosine augmentation strategies and their potential for antiepileptic and disease modifying therapy. Due to systemic side effects of adenosine focal adenosine augmentation ideally targeted to an epileptic focus becomes a therapeutic necessity. This has experimentally been achieved in kindled seizure models as well as in post status epilepticus models of spontaneous recurrent seizures using three different therapeutic strategies that will be discussed here: (i) Polymer-based brain implants that were loaded with adenosine; (ii) Brain implants comprised of cells engineered to release adenosine and embedded in a cell-encapsulation device; (iii) Direct transplantation of stem cells engineered to release adenosine. To meet the therapeutic goal of focal adenosine augmentation, genetic disruption of the adenosine metabolizing enzyme adenosine kinase (ADK) in rodent and human cells was used as a molecular strategy to induce adenosine release from cellular brain implants, which demonstrated antiepileptic and neuroprotective properties. New developments and therapeutic challenges in using AATs for epilepsy therapy will critically be evaluated.

Boison, Detlev

2009-01-01

325

Adenosine signalling at immature parallel fibre-Purkinje cell synapses in rat cerebellum  

PubMed Central

The purine adenosine is an extracellular signalling molecule involved in a large number of physiological and pathological conditions throughout the mammalian brain. However little is known about how adenosine release and its subsequent clearance change during brain development. We have combined electrophysiology and microelectrode biosensor measurements to investigate the properties of adenosine signalling at early stages of cerebellar development, when parallel fibrePurkinje cell synapses have recently been formed (postnatal days 912). At this stage of development, we could detect little or no inhibitory A1 receptor tone in basal conditions and during trains of stimuli. Addition of pharmacological agents, to inhibit adenosine clearance, had only minor effects on synaptic transmission suggesting that under basal conditions, the concentration of adenosine moving in and out of the extracellular space is small. Active adenosine release was stimulated with hypoxia and trains of electrical stimuli. Although hypoxia released significant concentrations of adenosine, the release was delayed and slow. No adenosine release could be detected following electrical stimulation in the molecular layer. In conclusion, at this stage of development, although adenosine receptors and the mechanisms of adenosine clearance are present there is very little adenosine release.

Atterbury, Alison; Wall, Mark J

2009-01-01

326

Modulation of bladder function by luminal adenosine turnover and A1 receptor activation  

PubMed Central

The bladder uroepithelium transmits information to the underlying nervous and musculature systems, is under constant cyclical strain, expresses all four adenosine receptors (A1, A2A, A2B, and A3), and is a site of adenosine production. Although adenosine has a well-described protective effect in several organs, there is a lack of information about adenosine turnover in the uroepithelium or whether altering luminal adenosine concentrations impacts bladder function or overactivity. We observed that the concentration of extracellular adenosine at the mucosal surface of the uroepithelium was regulated by ecto-adenosine deaminase and by equilibrative nucleoside transporters, whereas adenosine kinase and equilibrative nucleoside transporters modulated serosal levels. We further observed that enriching endogenous adenosine by blocking its routes of metabolism or direct activation of mucosal A1 receptors with 2-chloro-N6-cyclopentyladenosine (CCPA), a selective agonist, stimulated bladder activity by lowering the threshold pressure for voiding. Finally, CCPA did not quell bladder hyperactivity in animals with acute cyclophosphamide-induced cystitis but instead exacerbated their irritated bladder phenotype. In conclusion, we find that adenosine levels at both surfaces of the uroepithelium are modulated by turnover, that blocking these pathways or stimulating A1 receptors directly at the luminal surface promotes bladder contractions, and that adenosine further stimulates voiding in animals with cyclophosphamide-induced cystitis.

Prakasam, H. Sandeep; Herrington, Heather; Roppolo, James R.; Jackson, Edwin K.

2012-01-01

327

The relationship between the neuromodulator adenosine and behavioral symptoms of autism  

PubMed Central

The neuromodulator adenosine is an endogenous sleep promoter, neuroprotector and anticonvulsant, and people with autism often suffer from sleep disruption and/or seizures. We hypothesized that increasing adenosine can decrease behavioral symptoms of autism, and, based on published research, specific physiological stimuli are expected to increase brain adenosine. To test the relationship between adenosine and autism, we developed a customized parent-based questionnaire to assess child participation in activities expected to influence adenosine and quantify behavioral changes following these experiences. Parents were naive to study hypotheses and all conditions were pre-assigned. Results demonstrate significantly better behavior associated with events pre-established as predicted to increase rather than decrease or have no influence on adenosine. Understanding the physiological relationship between adenosine and autism could open new therapeutic strategies - potentially preventing seizures, improving sleep, and reducing social and behavioral dysfunction.

Masino, Susan A.; Kawamura, Masahito; Plotkin, Louisa M.; Svedova, Julia; DiMario, Francis J.; Eigsti, Inge-Marie

2013-01-01

328

Neuronal adenosine release, and not astrocytic ATP release, mediates feedback inhibition of excitatory activity  

PubMed Central

Adenosine is a potent anticonvulsant acting on excitatory synapses through A1 receptors. Cellular release of ATP, and its subsequent extracellular enzymatic degradation to adenosine, could provide a powerful mechanism for astrocytes to control the activity of neural networks during high-intensity activity. Despite adenosine's importance, the cellular source of adenosine remains unclear. We report here that multiple enzymes degrade extracellular ATP in brain tissue, whereas only Nt5e degrades AMP to adenosine. However, endogenous A1 receptor activation during cortical seizures in vivo or heterosynaptic depression in situ is independent of Nt5e activity, and activation of astrocytic ATP release via Ca2+ photolysis does not trigger synaptic depression. In contrast, selective activation of postsynaptic CA1 neurons leads to release of adenosine and synaptic depression. This study shows that adenosine-mediated synaptic depression is not a consequence of astrocytic ATP release, but is instead an autonomic feedback mechanism that suppresses excitatory transmission during prolonged activity.

Lovatt, Ditte; Xu, Qiwu; Liu, Wei; Takano, Takahiro; Smith, Nathan A.; Schnermann, Jurgen; Tieu, Kim; Nedergaard, Maiken

2012-01-01

329

Special sensitization pattern in adenosine-induced myocardial responses after thyroxine-treatment.  

PubMed

Chronic thyroxine treatment reduces the susceptibility of atrial myocardium to adenosine. While the possible role of membrane adenosine receptors in this action is supported by several studies, the involvement of intracellular adenosine mechanisms has not been defined. The present experiments were carried out in electrically driven euthyroid and hyperthyroid guinea pig atrial myocardium. The extracellular and intracellular actions of adenosine were analyzed pharmacologically by the use of specific blockers of membrane adenosine transport and intracellular adenosine deaminase (ADA). The involvement of phosphoprotein phosphatase, phospholamban, and sarcoplasmic reticulum Ca2+ ATPase (SERCA) in the adenosine-induced responses was also studied. The major findings were as follows: i) pD(2)- and E(max)-values for adenosine-induced decrease of mechanical activity were significantly reduced after an 8-day thyroxine treatment in atrial tissues; ii) in atria of thyroxine-treated animals, membrane purine transport inhibitors (dipyridamole, NBTI) induced similar leftward shifts in concentration-response curves for adenosine in both euthyroid and hyperthyroid atrial myocardium without altering the depressed E(max) values; iii) the leftward displacement evoked by inhibitors of intracellularly located ADA (coformycin, EHNA) was more striking in hyperthyroid than euthyroid myocardia. ADA inhibitors induced a complete reversal of the maximum adenosine actions; iv) inhibition by cantharidin of phosphoprotein phosphatases (after inhibition of ADA) reduced the adenosine-induced responses. This inhibition was stronger in hyperthyroid atria; v) pharmacological elimination of sarcoplasmic reticulum Ca2+ ATPase by cyclopiazonic acid did not alter the cardiac responses to adenosine and this was independent of thyroid status. It is suggested that distinct modulation of the extra- and intracellular adenosine actions is present in eu- and hyperthyroid hearts. In the latter, a predominance of intracellular adenosine mechanisms can be proposed. PMID:12719658

Gesztelyi, Rudolf; Zsuga, Judit; Cseppent, Agnes; Bajza, Agnes; Varga, Angelika; Szab, Judit Zs; Szentmiklsi, A Jzsef

2003-04-01

330

Molecular modeling of adenosine receptors. The ligand binding site on the rat adenosine A2A receptor.  

PubMed

The amino acid sequence of the rat adenosine A2A receptor and the atomic coordinates of bacteriorhodopsin were combined to generate a three-dimensional model for the adenosine A2A receptor. This model consists of seven amphipathic alpha-helices, forming a pore that is rather hydrophilic compared to the hydrophobic outside of the protein. Subsequently, a highly potent and selective ligand for this receptor, 2-(cyclohexylmethylidinehydrazino)adenosine (SHA 174), was docked into this cavity. A binding site is proposed that takes into account the conformational characteristics of the ligand. Moreover, it involves two histidine residues that were shown to be important for ligand coordination from chemical modification studies. Subsequently, the deduced binding site was used to model other potent ligands, including 8-(3-chlorostyryl)caffeine, a new A2-selective antagonist, that could all be accommodated consistent with earlier biochemical and pharmacological findings. Finally, some thoughts on how adenosine receptor activation might proceed are put forward, based on structural analogies with the enzyme family of serine proteases. PMID:7925617

IJzerman, A P; van der Wenden, E M; van Galen, P J; Jacobson, K A

1994-06-15

331

Sustained adenosine exposure causes lung endothelial apoptosis: a possible contributor to cigarette smoke-induced endothelial apoptosis and lung injury  

PubMed Central

Pulmonary endothelial cell (EC) apoptosis has been implicated in the pathogenesis of emphysema. Cigarette smoke (CS) causes lung EC apoptosis and emphysema. In this study, we show that CS exposure increased lung tissue adenosine levels in mice, an effect associated with increased lung EC apoptosis and the development of emphysema. Adenosine has a protective effect against apoptosis via adenosine receptor-mediated signaling. However, sustained elevated adenosine increases alveolar cell apoptosis in adenosine deaminase-deficient mice. We established an in vitro model of sustained adenosine exposure by incubating lung EC with adenosine in the presence of an adenosine deaminase inhibitor, deoxycoformicin. We demonstrated that sustained adenosine exposure caused lung EC apoptosis via nucleoside transporter-facilitated intracellular adenosine uptake, subsequent activation of p38 and JNK in mitochondria, and ultimately mitochondrial defects and activation of the mitochondria-mediated intrinsic pathway of apoptosis. Our results suggest that sustained elevated adenosine may contribute to CS-induced lung EC apoptosis and emphysema. Our data also reconcile the paradoxical effects of adenosine on apoptosis, demonstrating that prolonged exposure causes apoptosis via nucleoside transporter-mediated intracellular adenosine signaling, whereas acute exposure protects against apoptosis via activation of adenosine receptors. Inhibition of adenosine uptake may become a new therapeutic target in treatment of CS-induced lung diseases.

Sakhatskyy, Pavlo; Newton, Julie; Shamirian, Paul; Hsiao, Vivian; Curren, Sean; Gabino Miranda, Gustavo Andres; Pedroza, Mesias; Blackburn, Michael R.; Rounds, Sharon

2013-01-01

332

Adenosine protected against pulmonary edema through transporter- and receptor A2-mediated endothelial barrier enhancement  

PubMed Central

We have previously demonstrated that adenosine plus homocysteine enhanced endothelial basal barrier function and protected against agonist-induced barrier dysfunction in vitro through attenuation of RhoA activation by inhibition of isoprenylcysteine-O-carboxyl methyltransferase. In the current study, we tested the effect of elevated adenosine on pulmonary endothelial barrier function in vitro and in vivo. We noted that adenosine alone dose dependently enhanced endothelial barrier function. While adenosine receptor A1 or A3 antagonists were ineffective, an adenosine transporter inhibitor, NBTI, or a combination of DPMX and MRS1754, antagonists for adenosine receptors A2A and A2B, respectively, partially attenuated the barrier-enhancing effect of adenosine. Similarly, inhibition of both A2A and A2B receptors with siRNA also blunted the effect of adenosine on barrier function. Interestingly, inhibition of both transporters and A2A/A2B receptors completely abolished adenosine-induced endothelial barrier enhancement. The adenosine receptor A2A and A2B agonist, NECA, also significantly enhanced endothelial barrier function. These data suggest that both adenosine transporters and A2A and A2B receptors are necessary for exerting maximal effect of adenosine on barrier enhancement. We also found that adenosine enhanced Rac1 GTPase activity and overexpression of dominant negative Rac1 attenuated adenosine-induced increases in focal adhesion complexes. We further demonstrated that elevation of cellular adenosine by inhibition of adenosine deaminase with Pentostatin significantly enhanced endothelial basal barrier function, an effect that was also associated with enhanced Rac1 GTPase activity and with increased focal adhesion complexes and adherens junctions. Finally, using a non-inflammatory acute lung injury (ALI) model induced by ?-naphthylthiourea, we found that administration of Pentostatin, which elevated lung adenosine level by 10-fold, not only attenuated the development of edema before ALI but also partially reversed edema after ALI. The data suggest that adenosine deaminase inhibition may be useful in treatment of pulmonary edema in settings of ALI.

Lu, Qing; Harrington, Elizabeth O.; Newton, Julie; Casserly, Brian; Radin, Gregory; Warburton, Rod; Zhou, Yang; Blackburn, Michael R.

2010-01-01

333

Adenosine and inosine increase cutaneous vasopermeability by activating A(3) receptors on mast cells.  

PubMed

Adenosine has potent effects on both the cardiovascular and immune systems. Exposure of tissues to adenosine results in increased vascular permeability and extravasation of serum proteins. The mechanism by which adenosine brings about these physiological changes is poorly defined. Using mice deficient in the A(3) adenosine receptor (A(3)AR), we show that increases in cutaneous vascular permeability observed after treatment with adenosine or its principal metabolite inosine are mediated through the A(3)AR. Adenosine fails to increase vascular permeability in mast cell-deficient mice, suggesting that this tissue response to adenosine is mast cell-dependent. Furthermore, this response is independent of activation of the high-affinity IgE receptor (FcepsilonR1) by antigen, as adenosine is equally effective in mediating these changes in FcepsilonR1 beta-chain-deficient mice. Together these results support a model in which adenosine and inosine induce changes in vascular permeability indirectly by activating mast cells, which in turn release vasoactive substances. The demonstration in vivo that adenosine, acting through a specific receptor, can provoke degranulation of this important tissue-based effector cell, independent of antigen activation of the high-affinity IgE receptor, supports an important role for this nucleoside in modifying the inflammatory response. PMID:10675362

Tilley, S L; Wagoner, V A; Salvatore, C A; Jacobson, M A; Koller, B H

2000-02-01

334

Activation of murine lung mast cells by the adenosine A3 receptor.  

PubMed

Adenosine has been implicated to play a role in asthma in part through its ability to influence mediator release from mast cells. Most physiological roles of adenosine are mediated through adenosine receptors; however, the mechanisms by which adenosine influences mediator release from lung mast cells are not understood. We established primary murine lung mast cell cultures and used real-time RT-PCR and immunofluorescence to demonstrate that the A(2A), A(2B), and A(3) adenosine receptors are expressed on murine lung mast cells. Studies using selective adenosine receptor agonists and antagonists suggested that activation of A(3) receptors could induce mast cell histamine release in association with increases in intracellular Ca(2+) that were mediated through G(i) and phosphoinositide 3-kinase signaling pathways. The function of A(3) receptors in vivo was tested by exposing mice to the A(3) receptor agonist, IB-MECA. Nebulized IB-MECA directly induced lung mast cell degranulation in wild-type mice while having no effect in A(3) receptor knockout mice. Furthermore, studies using adenosine deaminase knockout mice suggested that elevated endogenous adenosine induced lung mast cell degranulation by engaging A(3) receptors. These results demonstrate that the A(3) adenosine receptor plays an important role in adenosine-mediated murine lung mast cell degranulation. PMID:12817016

Zhong, Hongyan; Shlykov, Sergiy G; Molina, Jose G; Sanborn, Barbara M; Jacobson, Marlene A; Tilley, Stephen L; Blackburn, Michael R

2003-07-01

335

Targeting the A2B adenosine receptor during gastrointestinal ischemia and inflammation  

PubMed Central

Extracellular adenosine functions as an endogenous distress signal via activation of four distinct adenosine receptors (A1, A2A, A2B and A3). Conditions of limited oxygen availability or acute inflammation lead to elevated levels of extracellular adenosine and enhanced signaling events. This relates to a combination of four mechanisms: i) increased production of adenosine via extracellular phosphohydrolysis of precursor molecules (particularly ATP and ADP); ii) increased expression and signaling via hypoxia-induced adenosine receptors, particularly the A2B adenosine receptor; iii) attenuated uptake from the extracellular towards the intracellular compartment; and iv) attenuated intracellular metabolism. Due to their large surface area, mucosal organs are particularly prone to hypoxia and ischemia associated inflammation. Therefore, it is not surprising that adenosine production and signaling plays a central role in attenuating tissue inflammation and injury during intestinal ischemia or inflammation. In fact, recent studies combining pharmacological and genetic approaches demonstrated that adenosine signaling via the A2B adenosine receptor dampens mucosal inflammation and tissue injury during intestinal ischemia or experimental colitis. This review outlines basic principles of extracellular adenosine production, signaling, uptake and metabolism. In addition, we discuss the role of this pathway in dampening hypoxia-elicited inflammation, specifically in the setting of intestinal ischemia and inflammation.

Eltzschig, Holger K; Rivera-Nieves, Jesus; Colgan, Sean P

2014-01-01

336

Transcriptional control of adenosine signaling by hypoxia-inducible transcription factors during ischemic or inflammatory disease  

PubMed Central

Inflammatory lesions, ischemic tissues or solid tumors are characterized by the occurrence of severe tissue hypoxia within the diseased tissue. Subsequent stabilization of hypoxia-inducible transcription factors particularly of hypoxia-inducible factor 1? (HIF1A) - results in significant alterations of gene expression of resident cells or inflammatory cells that have been recruited into such lesions. Interestingly, studies of hypoxia-induced changes of gene expression identified a transcriptional program that promotes extracellular adenosine signaling. Adenosine is a signaling molecule that functions through the activation of four distinct adenosine receptors - the ADORA1, ADORA2A, ADORA2B and ADORA3 receptor. Extracellular adenosine is predominantly derived from the phosphohydrolysis of precursor nucleotides such as ATP or AMP. HIF1A-elicited alterations in gene expression enhance the enzymatic capacity within inflamed tissues to produce extracellular adenosine. Moreover, hypoxia-elicited induction of adenosine receptors particularly of the ADORA2B results in increased signal transduction. Functional studies in genetic models for HIF1A or adenosine receptors implicate this pathway in an endogenous feedback loop that dampens excessive inflammation and promotes injury resolution, while at the same time enhancing ischemia-tolerance. Therefore, pharmacological strategies to enhance HIF-elicited adenosine production or to promote adenosine signaling through adenosine receptors are being investigated for the treatment of acute inflammatory or ischemic diseases characterized by tissue hypoxia.

Poth, Jens M.; Brodsky, Kelley; Ehrentraut, Heidi; Grenz, Almut; Eltzschig, Holger K.

2012-01-01

337

Mechanical stimulation evokes rapid increases in extracellular adenosine concentration in the prefrontal cortex.  

PubMed

Mechanical perturbations can release ATP, which is broken down to adenosine. In this work, we used carbon-fiber microelectrodes and fast-scan cyclic voltammetry to measure mechanically stimulated adenosine in the brain by lowering the electrode 50?m. Mechanical stimulation evoked adenosine in vivo (average: 3.30.6?M) and in brain slices (average: 0.80.1?M) in the prefrontal cortex. The release was transient, lasting 182s. Lowering a 15-?m-diameter glass pipette near the carbon-fiber microelectrode produced similar results as lowering the actual microelectrode. However, applying a small puff of artificial cerebral spinal fluid was not sufficient to evoke adenosine. Multiple stimulations within a 50-?m region of a slice did not significantly change over time or damage cells. Chelating calcium with EDTA or blocking sodium channels with tetrodotoxin significantly decreased mechanically evoked adenosine, signifying that the release is activity dependent. An alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, did not affect mechanically stimulated adenosine; however, the nucleoside triphosphate diphosphohydrolase 1,2 and 3 (NTDPase) inhibitor POM-1 significantly reduced adenosine so a portion of adenosine is dependent on extracellular ATP metabolism. Thus, mechanical perturbations from inserting a probe in the brain cause rapid, transient adenosine signaling which might be neuroprotective. We have discovered immediate changes in adenosine concentration in the prefrontal cortex following mechanical stimulation. The adenosine increase lasts only about 20s. Mechanically stimulated adenosine was activity dependent and mostly because of extracellular ATP metabolism. This rapid, transient increase in adenosine may help protect tissue and would occur during implantation of any electrode, such as during deep brain stimulation. PMID:24606335

Ross, Ashley E; Nguyen, Michael D; Privman, Eve; Venton, B Jill

2014-07-01

338

Role of adenosine receptors in the regulation of angiogenic factors and neovascularization in hypoxia.  

PubMed

Because hypoxia increases extracellular adenosine levels and stimulates angiogenesis, we evaluated the relative roles of reduced oxygen concentrations and adenosine receptor activation in the production of angiogenic factors. In vitro, we analyzed the effects of hypoxia and adenosine on the secretion of angiogenic factors from human microvascular endothelial cells (HMEC-1). To study the effects of hypoxia alone, we scavenged adenosine from the hypoxic medium with adenosine deaminase, and we used the stable adenosine analog 5'-N-ethylcarboxamidoadenosine (NECA) to study the effects of stimulation of adenosine receptors. In the absence of adenosine, hypoxia stimulated vascular endothelial growth factor (VEGF) but not interleukin-8 (IL-8) secretion from HMEC-1. In contrast, NECA stimulated both VEGF and IL-8 secretion. VEGF secretion was increased 1.9 +/- 0.04-fold with NECA (10 microM) and 1.7 +/- 0.1-fold with hypoxia (5% O(2)) but 3.8 +/- 0.1-fold when these two stimuli were combined. Thus, adenosine receptors act in a cooperative fashion with hypoxia to stimulate VEGF and induce IL-8 secretion not stimulated by hypoxia alone. In vivo, antagonism of adenosine receptors with caffeine abrogated VEGF up-regulation induced by local injection of NECA into the mouse hind limb and produced a 46% reduction of neovascularization in a mouse ischemic hind limb model. Our study suggests that adenosine actions are not redundant but rather are complementary to the direct effects of hypoxia. Stimulation of adenosine receptors not only contributes to the overall effect of hypoxia but also has additional actions in the regulation of angiogenic factors. Thus, adenosine receptors represent a potential therapeutic target for regulation of neovascularization. PMID:17132813

Ryzhov, Sergey; McCaleb, Jennifer L; Goldstein, Anna E; Biaggioni, Italo; Feoktistov, Igor

2007-02-01

339

Extracellular 2?,3?-cAMP Is a Source of Adenosine*  

PubMed Central

We discovered that renal injury releases 2?,3?-cAMP (positional isomer of 3?,5?-cAMP) into the interstitium. This finding motivated a novel hypothesis: renal injury leads to activation of an extracellular 2?,3?-cAMP-adenosine pathway (i.e. metabolism of extracellular 2?,3?-cAMP to 3?-AMP and 2?-AMP, which are metabolized to adenosine, a retaliatory metabolite). In isolated rat kidneys, arterial infusions of 2?,3?-cAMP (30 ?mol/liter) increased the mean venous secretion of 3?-AMP (3,400-fold), 2?-AMP (26,000-fold), adenosine (53-fold), and inosine (adenosine metabolite, 30-fold). Renal injury with metabolic inhibitors increased the mean secretion of 2?,3?-cAMP (29-fold), 3?-AMP (16-fold), 2?-AMP (10-fold), adenosine (4.2-fold), and inosine (6.1-fold) while slightly increasing 5?-AMP (2.4-fold). Arterial infusions of 2?-AMP and 3?-AMP increased secretion of adenosine and inosine similar to that achieved by 5?-AMP. Renal artery infusions of 2?,3?-cAMP in vivo increased urinary excretion of 2?-AMP, 3?-AMP and adenosine, and infusions of 2?-AMP and 3?-AMP increased urinary excretion of adenosine as efficiently as 5?-AMP. The implications are that 1) in intact organs, 2?-AMP and 3?-AMP are converted to adenosine as efficiently as 5?-AMP (previously considered the most important adenosine precursor) and 2) because 2?,3?-cAMP opens mitochondrial permeability transition pores, a pro-apoptotic/pro-necrotic process, conversion of 2?,3?-cAMP to adenosine by the extracellular 2?,3?-cAMP-adenosine pathway would protect tissues by reducing a pro-death factor (2?,3?-cAMP) while increasing a retaliatory metabolite (adenosine).

Jackson, Edwin K.; Ren, Jin; Mi, Zaichuan

2009-01-01

340

Adenosine receptors mediate cellular adaptation to ethanol in NG108-15 cells.  

PubMed

Acute ethanol treatment of NG108-15 neuroblastoma x glioma hybrid cells results in inhibition of adenosine uptake with consequent increases in extracellular adenosine and intracellular cAMP concentrations. Chronic exposure to ethanol, however, causes heterologous desensitization of receptors coupled to adenylyl cyclase via stimulatory guanine nucleotide regulatory protein. This heterologous desensitization is correlated with a decrease in the amount of protein and mRNA for the GTP-binding subunit of stimulatory guanine nucleotide regulatory protein. In addition, after chronic exposure to ethanol, the adenosine transporter becomes tolerant to acute ethanol inhibition of adenosine uptake, and there is no longer an increase in extracellular adenosine. We have previously shown that extracellular adenosine is required for the development of ethanol-induced heterologous desensitization. To examine the role of adenosine receptors in mediating these responses to ethanol, we used BW A1434U, an adenosine receptor antagonist that does not inhibit nucleoside transport. BW A1434U caused a concentration-dependent inhibition of (-)-N6-(R-phenyl-isopropyl)-adenosine-stimulated cAMP production in NG108-15 cells. BW A1434U also completely blocked acute ethanol-induced increases in intracellular cAMP levels and prevented the development of ethanol-induced heterologous desensitization and the reduction in the GTP-binding subunit of stimulatory guanine nucleotide regulatory protein. In addition, BW A1434U prevented the development of tolerance to ethanol-induced inhibition of adenosine transport. Our results indicate that in NG108-15 cells, adenosine receptors mediate ethanol-induced changed in cAMP signal transduction and adenosine transport and that an adenosine receptor antagonist can block both these acute and chronic affects of ethanol. PMID:7965754

Sapru, M K; Diamond, I; Gordon, A S

1994-10-01

341

Content of antioxidants, preformed lipid hydroperoxides, and cholesterol as predictors of the susceptibility of human LDL to metal ion-dependent and -independent oxidation.  

PubMed

Oxidative modification of low density lipoprotein (LDL) has been suggested to play a casual role in human atherosclerosis, and prevention of LDL oxidation may be an effective strategy to prevent or slow the progression of this disease. It is important, therefore, to identify the factors that determine LDL's susceptibility to oxidation. We have analyzed 62 human LDL samples for content of antioxidants, preformed lipid hydroperoxides, and cholesterol. To investigate their oxidative susceptibility, the LDL samples were exposed to either a metal ion-dependent (Cu2+) or -independent (aqueous peroxyl radicals) oxidizing system; the length of the lag phase of inhibited lipid peroxidation was measured, as well as the rate of lipid peroxidation during the lag and ensuing propagation phases. The susceptibility of LDL to metal ion-dependent oxidation was not related to its susceptibility to metal ion-independent oxidation. A strong predictor of an increased susceptibility of LDL to metal ion-dependent oxidation was a decreased vitamin E-to-cholesterol ratio, in contrast to the vitamin E-to-protein ratio. Elevated levels of performed lipid hydroperoxides in LDL and an increased cholesterol content were also associated with an increased susceptibility of the lipoprotein to Cu(2+)-induced oxidation. Remarkably, a strong predictor of an increased susceptibility of LDL to metal ion-independent oxidation was an increased, rather than decreased, vitamin E content relative to protein. An increased cholesterol content also was associated with an increased oxidative susceptibility of LDL to aqueous peroxyl radicals, while preformed lipid hydroperoxides showed no significant correlation. Ubiquinol-10, beta-carotene, and lycopene, whether quantitated relative to cholesterol or protein, did not show significant protective effects against both metal ion-dependent and -independent oxidation of LDL. Our data suggest that a high lipid content of LDL, relative to its protein content, renders the lipoprotein more susceptible to oxidative modification, while vitamin E may have either a protective or promoting effect on LDL oxidation, depending on the oxidative stress conditions. Other known antioxidants in LDL do not appear to play a significant role in protecting LDL against oxidative modification. PMID:8301232

Frei, B; Gaziano, J M

1993-12-01

342

Structure-Activity Relationships of 9-Alkyladenine and Ribose-Modified Adenosine Derivatives at Rat A3 Adenosine Receptors  

PubMed Central

9-Alkyladenine derivatives and ribose-modified N6-benzyladenosine derivatives were synthesized in an effort to identify selective ligands for the rat A3 adenosine receptor and leads for the development of antagonists. The derivatives contained structural features previously determined to be important for A3 selectivity in adenosine derivatives, such as an N6-(3-iodobenzyl) moiety, and were further substituted at the 2-position with halo, amino, or thio groups. Affinity was determined in radioligand binding assays at rat brain A3 receptors stably expressed in Chinese hamster ovary (CHO) cells, using [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)adenosine-5?-(N-methyluronamide)), and at rat brain A1 and A2a receptors using [3H]-N6-PIA ((R)-N6-phenylisopropyladenosine) and [3H]CGS 21680 (2-[[[4-(2-carboxyethyl)-phenyl]ethyl]amino]-5?-(N-ethylcarbamoyl)adenosine), respectively. A series of N6-(3-iodobenzyl) 2-amino derivatives indicated that a small 2-alkylamino group, e.g., methylamino, was favored at A3 receptors. N6-(3-Iodobenzyl)-9-methyl-2-(methylthio)adenine was 61-fold more potent than the corresponding 2-methoxy ether at A3 receptors and of comparable affinity at A1 and A2a receptors, resulting in a 36-fold selectivity for A3 receptors. A pair of chiral N6-(3-iodobenzyl) 9-(2,3-dihydroxypropyl) derivatives showed stereoselectivity, with the R-enantiomer favored at A3 receptors by 5.7-fold. 2-Chloro-9-(?-d-erythrofuranosyl)-N6-(3-iodobenzyl)adenine had a Ki value at A3 receptors of 0.28 M. 2-Chloro-9-[2-amino-2,3-dideoxy-?-d-5-(methylcarbamoyl)-arabinofuranosyl]-N6-(3-iodobenzyl)adenine was moderately selective for A1 and A3 vs A2a receptors. A 3?-deoxy analogue of a highly A3-selective adenosine derivative retained selectivity in binding and was a full agonist in the inhibition of adenylyl cyclase mediated via cloned rat A3 receptors expressed in CHO cells. The 3?-OH and 4?-CH2OH groups of adenosine are not required for activation at A3 receptors. A number of 2?,3?-dideoxyadenosines and 9-acyclic-substituted adenines appear to inhibit adenylyl cyclase at the allosteric P site.

Jacobson, Kenneth A.; Siddiqi, Suhaib M.; Olah, Mark E.; Ji, Xiao-duo; Melman, Neli; Bellamkonda, Kamala; Meshulam, Yakov; Stiles, Gary L.; Kim, Hea O.

2012-01-01

343

Effect of adenosine kinase, adenosine deaminase and transport inhibitors on striatal dopamine and stereotypy after methamphetamine administration.  

PubMed

The effect of adenosine kinase (AKA), adenosine deaminase (ADA) and transport inhibitors on the release of dopamine (DA) induced by methamphetamine (MTH) in rat striatum was assessed using in vivo microdialysis in freely moving rats. MTH injected in a dose of 3 x 5 mg/kg i.p. at 2-hour intervals produced a massive release of DA. This excessive release of DA was inhibited by the ADA inhibitor 2'-deoxycoformycin (DCF), the AKA inhibitor 5'-iodotubercidin (IOT) and the adenosine uptake inhibitor dilazep (DIL), each of them given locally to the striatum via a microdialysis probe at a concentration of 100 microM. Perfusion with the same concentrations of erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and 5'-amino-5'-deoxyadenosine (NH(2)dAD), ADA and AKA inhibitors, respectively, induced a considerably weaker effect on DA release. The non-selective antagonist of adenosine A(1)/A(2A) receptor caffeine (75 microM) significantly prevented the inhibitory effect of DCF, IOT and DIL on the MTH-induced DA release. Intrastriatal administration of DCF, IOT and DIL (5 nmol/microl before each injection of MTH) inhibited the stereotypy induced by MTH. The striatal content of DA and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), decreased by MTH administration and measured 5 days after treatment with the toxin, was reversed by all the inhibitors at the order of potency as follows: IOT>DCF>DIL. Direct agonists of adenosine A(1) and A(1)/A(2A) receptors, N(6)-cyclopentyladenosine (CPA) and 5'-N-ethylcarboxamidoadenosine (NECA), respectively, given intrastriatally (5 nmol/microl) completely abolished the MTH-induced stereotypy and the fall in the striatal content of DA, DOPAC and HVA. The above results show that augmentation of endogenous adenosine in rat striatum by inhibition of its metabolism or uptake-despite the differences in the efficacy of various inhibitors-may provide neuroprotection against a toxic action of MTH. PMID:10963755

Go?embiowska, K; Zylewska, A

2000-08-23

344

Soluble Ecto-5?-nucleotidase (5?-NT), Alkaline Phosphatase, and Adenosine Deaminase (ADA1) Activities in Neonatal Blood Favor Elevated Extracellular Adenosine*  

PubMed Central

Extracellular adenosine, a key regulator of physiology and immune cell function that is found at elevated levels in neonatal blood, is generated by phosphohydrolysis of adenine nucleotides released from cells and catabolized by deamination to inosine. Generation of adenosine monophosphate (AMP) in blood is driven by cell-associated enzymes, whereas conversion of AMP to adenosine is largely mediated by soluble enzymes. The identities of the enzymes responsible for these activities in whole blood of neonates have been defined in this study and contrasted to adult blood. We demonstrate that soluble 5?-nucleotidase (5?-NT) and alkaline phosphatase (AP) mediate conversion of AMP to adenosine, whereas soluble adenosine deaminase (ADA) catabolizes adenosine to inosine. Newborn blood plasma demonstrates substantially higher adenosine-generating 5?-NT and AP activity and lower adenosine-metabolizing ADA activity than adult plasma. In addition to a role in soluble purine metabolism, abundant AP expressed on the surface of circulating neonatal neutrophils is the dominant AMPase on these cells. Plasma samples from infant observational cohorts reveal a relative plasma ADA deficiency at birth, followed by a gradual maturation of plasma ADA through infancy. The robust adenosine-generating capacity of neonates appears functionally relevant because supplementation with AMP inhibited whereas selective pharmacologic inhibition of 5?-NT enhanced Toll-like receptor-mediated TNF-? production in neonatal whole blood. Overall, we have characterized previously unrecognized age-dependent expression patterns of plasma purine-metabolizing enzymes that result in elevated plasma concentrations of anti-inflammatory adenosine in newborns. Targeted manipulation of purine-metabolizing enzymes may benefit this vulnerable population.

Pettengill, Matthew; Robson, Simon; Tresenriter, Megan; Millan, Jose Luis; Usheva, Anny; Bingham, Taiese; Belderbos, Mirjam; Bergelson, Ilana; Burl, Sarah; Kampmann, Beate; Gelinas, Laura; Kollmann, Tobias; Bont, Louis; Levy, Ofer

2013-01-01

345

Adenosine closes the K+ channel KCa3.1 in human lung mast cells and inhibits their migration via the adenosine A2A receptor  

PubMed Central

Human lung mast cells (HLMC) express the Ca2+-activated K+ channel KCa3.1, which opens following IgE-dependent activation. This hyperpolarises the cell membrane and potentiates both Ca2+ influx and degranulation. In addition, blockade of KCa3.1 profoundly inhibits HLMC migration to a variety of diverse chemotactic stimuli. KCa3.1 activation is attenuated by the ?2adrenoceptor through a G?s-coupled mechanism independent of cyclic AMP. Adenosine is an important mediator that both attenuates and enhances HLMC mediator release through the G?s-coupled A2A and A2B adenosine receptors, respectively. We show that at concentrations that inhibit HLMC degranulation (105103 M), adenosine closes KCa3.1 both dose-dependently and reversibly. KCa3.1 suppression by adenosine was reversed partially by the selective adenosine A2A receptor antagonist ZM241385 but not by the A2B receptor antagonist MRS1754, and the effects of adenosine were mimicked by the selective A2A receptor agonist CGS21680. Adenosine also opened a depolarising current carried by non-selective cations. As predicted from the role of KCa3.1 in HLMC migration, adenosine abolished HLMC chemotaxis to asthmatic airway smooth muscle-conditioned medium. In summary, the G?s-coupled adenosine A2A receptor closes KCa3.1, providing a clearly defined mechanism by which adenosine inhibits HLMC migration and degranulation. A2A receptor agonists with channel-modulating function may be useful for the treatment of mast cell-mediated disease.

Duffy, S Mark; Cruse, Glenn; Brightling, Christopher E; Bradding, Peter

2007-01-01

346

Adenosine closes the K+ channel KCa3.1 in human lung mast cells and inhibits their migration via the adenosine A2A receptor.  

PubMed

Human lung mast cells (HLMC) express the Ca2+-activated K+ channel KCa3.1, which opens following IgE-dependent activation. This hyperpolarises the cell membrane and potentiates both Ca2+ influx and degranulation. In addition, blockade of KCa3.1 profoundly inhibits HLMC migration to a variety of diverse chemotactic stimuli. KCa3.1 activation is attenuated by the beta2adrenoceptor through a Galphas-coupled mechanism independent of cyclic AMP. Adenosine is an important mediator that both attenuates and enhances HLMC mediator release through the Galphas-coupled A2A and A2B adenosine receptors, respectively. We show that at concentrations that inhibit HLMC degranulation (10(-5)-10(-3) M), adenosine closes KCa3.1 both dose-dependently and reversibly. KCa3.1 suppression by adenosine was reversed partially by the selective adenosine A2A receptor antagonist ZM241385 but not by the A2B receptor antagonist MRS1754, and the effects of adenosine were mimicked by the selective A2A receptor agonist CGS21680. Adenosine also opened a depolarising current carried by non-selective cations. As predicted from the role of KCa3.1 in HLMC migration, adenosine abolished HLMC chemotaxis to asthmatic airway smooth muscle-conditioned medium. In summary, the Galphas-coupled adenosine A2A receptor closes KCa3.1, providing a clearly defined mechanism by which adenosine inhibits HLMC migration and degranulation. A2A receptor agonists with channel-modulating function may be useful for the treatment of mast cell-mediated disease. PMID:17474152

Duffy, S Mark; Cruse, Glenn; Brightling, Christopher E; Bradding, Peter

2007-06-01

347

Partial agonism of theophylline-7-riboside on adenosine receptors.  

PubMed

Theophylline-7-riboside was evaluated as a partial agonist for rat adenosine receptors. Radioligand binding experiments were performed on both A1 and A2a adenosine receptors, using several methodologies to discriminate between agonists and antagonists. Mainly from thermodynamic data it was concluded that on A1 receptors theophylline-7-riboside had characteristics intermediate between full agonists, such as N6-cyclopentyladenosine, and full antagonists, such as the xanthines. The partial agonistic behaviour of theophylline-7-riboside was further explored in second messenger studies in intact cells. In FRTL-5 rat thyroid cells theophylline-7-riboside behaved as a partial agonist for A1 receptors, slightly inhibiting forskolin-stimulated cyclic AMP levels. The implications of these biochemical findings were further analysed in in vivo pharmacology. The infusion of theophylline-7-riboside in conscious, normotensive rats led to marked changes in cardiovascular parameters, although less outspoken than observed with full agonists for either A1 or A2a receptors. The concomitant determination of the blood concentrations of theophylline-7-riboside and its metabolite theophylline allowed the estimation of in vivo pharmacokinetic and pharmacodynamic parameters. Thus, the EC50 value of theophylline-7-riboside for lowering the mean arterial pressure was 47 +/- 12 micrograms/ml blood. The short duration of action of theophylline-7-riboside makes it improbable that its metabolite theophylline interferes with its effects. In conclusion, theophylline-7-riboside is one of the first partial agonists for adenosine receptors. It may serve as a tool in further investigations of adenosine receptor partial agonism. PMID:7708121

IJzerman, A P; van der Wenden, E M; von Frijtag Drabbe Knzel, J K; Matht, R A; Danhof, M; Borea, P A; Varani, K

1994-12-01

348

Adenosine Receptor Antagonists and Retinal Neovascularization in Vivo  

Microsoft Academic Search

PURPOSE. The role of adenosine receptor (AdoR) antagonists in human retinal endothelial cell function in vitro has previously been determined. In this study, efficacy of AdoR antagonist administration in reducing retinal neovascularization was ex- amined in a mouse pup model of oxygen-induced retinopathy. METHODS. A previously described model of oxygen-induced retinal neovascularization in newborn mouse pups was used to examine

Robert P. Mino; Polyxenie E. Spoerri; Sergio Caballero; Luiz Belardinelli; Italo Biaggioni; Maria B. Grant

2001-01-01

349

Adenosine: An Effective and Safe Antiarrhythmic Drug in Pediatrics  

Microsoft Academic Search

. Adenosine is an effective, safe drug for the diagnosis and treatment of paroxysmal tachycardias in adult and pediatric patients.\\u000a A starting dose of 0.050.10 mg\\/kg as a rapid bolus injection is recommended for infants and children. An electrophysiologic\\u000a effect can be expected within 20 seconds after injection. Dosage may be increased up to 0.3 mg\\/kg in steps of 0.050.10

T. Paul; J. P. Pfammatter

1997-01-01

350

The chemical basis of adenosine conservation throughout the Tetrahymena ribozyme.  

PubMed Central

Adenosines are present at a disproportionately high frequency within several RNA structural motifs. To explore the importance of individual adenosine functional groups for group I intron activity, we performed Nucleotide Analog Interference Mapping (NAIM) with a collection of adenosine analogues. This paper reports the synthesis, transcriptional incorporation, and the observed interference pattern throughout the Tetrahymena group I intron for eight adenosine derivatives tagged with an alpha-phosphorothioate linkage for use in NAIM. All of the analogues were accurately incorporated into the transcript as an A. The sites that interfere with the 3'-exon ligation reaction of the Tetrahymena intron are coincident with the sites of phylogenetic conservation, yet the interference patterns for each analogue are different. These interference data provide several biochemical constraints that improve our understanding of the Tetrahymena ribozyme structure. For example, the data support an essential A-platform within the J6/6a region, major groove packing of the P3 and P7 helices, minor groove packing of the P3 and J4/5 helices, and an axial model for binding of the guanosine cofactor. The data also identify several essential functional groups within a highly conserved single-stranded region in the core of the intron (J8/7). At four sites in the intron, interference was observed with 2'-fluoro A, but not with 2'-deoxy A. Based upon comparison with the P4-P6 crystal structure, this may provide a biochemical signature for nucleotide positions where the ribose sugar adopts an essential C2'-endo conformation. In other cases where there is interference with 2'-deoxy A, the presence or absence of 2'-fluoro A interference helps to establish whether the 2'-OH acts as a hydrogen bond donor or acceptor. Mapping of the Tetrahymena intron establishes a basis set of information that will allow these reagents to be used with confidence in systems that are less well understood.

Ortoleva-Donnelly, L; Szewczak, A A; Gutell, R R; Strobel, S A

1998-01-01

351

Adenosine receptor antagonist and augmented vasodilation during hypoxic exercise  

PubMed Central

We tested the hypothesis that adenosine contributes to augmented skeletal muscle vasodilation during hypoxic exercise. In separate protocols, subjects performed incremental rhythmic forearm exercise (10% and 20% of maximum) during normoxia and normocapnic hypoxia (80% arterial O2 saturation). In protocol 1 (n = 8), subjects received an intra-arterial administration of saline (control) and aminophylline (adenosine receptor antagonist). In protocol 2 (n = 10), subjects received intra-arterial phentolamine (?-adrenoceptor antagonist) and combined phentolamine and aminophylline administration. Forearm vascular conductance (FVC; in mlmin?1100 mmHg?1) was calculated from forearm blood flow (in ml/min) and blood pressure (in mmHg). In protocol 1, the change in FVC (?FVC; change from normoxic baseline) during hypoxic exercise with saline was 172 29 and 314 34 mlmin?1100 mmHg?1 (10% and 20%, respectively). Aminophylline administration did not affect ?FVC during hypoxic exercise at 10% (190 29 mlmin?1100 mmHg?1, P = 0.4) or 20% (287 48 mlmin?1100 mmHg?1, P = 0.3). In protocol 2, ?FVC due to hypoxic exercise with phentolamine infusion was 313 30 and 453 41 mlmin?1100 mmHg?1 (10% and 20% respectively). ?FVC was similar at 10% (352 39 mlmin?1100 mmHg?1, P = 0.8) and 20% (528 45 mlmin?1100 mmHg?1, P = 0.2) hypoxic exercise with combined phentolamine and aminophylline. In contrast, ?FVC to exogenous adenosine was reduced by aminophylline administration in both protocols (P < 0.05 for both). These observations suggest that adenosine receptor activation is not obligatory for the augmented hyperemia during hypoxic exercise in humans.

Madery, Brandon D.; Pike, Tasha L.; Eisenach, John H.; Dietz, Niki M.; Joyner, Michael J.; Wilkins, Brad W.

2009-01-01

352

Evidence for functional adenosine A3 receptors in microglia cells.  

PubMed

Adenosine exerts its effects through four subtypes of G-protein-coupled receptors (GPCRs): adenosine A1 and A3 receptors (A3R), which generally couple to Gi proteins and adenosine A2A and A2B receptors that activate Gs proteins. Though there is evidence for the expression of mRNA for the A3R in the central nervous system, evidence for functional receptors has depended on drugs with uncertain specificity. Here, we show that A3Rs mediating functional responses are present in microglia cells. By selectively stimulating the A3R in both primary mouse microglia cells and the N13 microglia cell line with the agonist Cl-IB-MECA, we have found a biphasic, partly Gi protein-dependent influence on the phosphorylation of the extracellular signal-regulated protein kinase 1/2 (ERK1/2). ERK1/2 activation was assessed by immunoblotting with phospho-specific antibodies. The involvement of the A3R in Cl-IB-MECA-induced ERK1/2 phosphorylation was confirmed by demonstrating that those effects are absent in primary mouse microglia cells isolated from mice lacking the gene for the A3R. PMID:12887702

Hammarberg, Christian; Schulte, Gunnar; Fredholm, Bertil B

2003-08-01

353

Identification of widespread adenosine nucleotide binding in Mycobacterium tuberculosis  

SciTech Connect

The annotation of protein function is almost completely performed by in silico approaches. However, computational prediction of protein function is frequently incomplete and error prone. In Mycobacterium tuberculosis (Mtb), ~25% of all genes have no predicted function and are annotated as hypothetical proteins. This lack of functional information severely limits our understanding of Mtb pathogenicity. Current tools for experimental functional annotation are limited and often do not scale to entire protein families. Here, we report a generally applicable chemical biology platform to functionally annotate bacterial proteins by combining activity-based protein profiling (ABPP) and quantitative LC-MS-based proteomics. As an example of this approach for high-throughput protein functional validation and discovery, we experimentally annotate the families of ATP-binding proteins in Mtb. Our data experimentally validate prior in silico predictions of >250 ATPases and adenosine nucleotide-binding proteins, and reveal 73 hypothetical proteins as novel ATP-binding proteins. We identify adenosine cofactor interactions with many hypothetical proteins containing a diversity of unrelated sequences, providing a new and expanded view of adenosine nucleotide binding in Mtb. Furthermore, many of these hypothetical proteins are both unique to Mycobacteria and essential for infection, suggesting specialized functions in mycobacterial physiology and pathogenicity. Thus, we provide a generally applicable approach for high throughput protein function discovery and validation, and highlight several ways in which application of activity-based proteomics data can improve the quality of functional annotations to facilitate novel biological insights.

Ansong, Charles; Ortega, Corrie; Payne, Samuel H.; Haft, Daniel H.; Chauvigne-Hines, Lacie M.; Lewis, Michael P.; Ollodart, Anja R.; Purvine, Samuel O.; Shukla, Anil K.; Fortuin, Suereta; Smith, Richard D.; Adkins, Joshua N.; Grundner, Christoph; Wright, Aaron T.

2013-01-24

354

Inhibition of Dengue Virus RNA Synthesis by an Adenosine Nucleoside ?  

PubMed Central

We recently reported that (2R,3R,4R,5R)-2-(4-amino-pyrrolo[2,3-d]pyrimidin-7-yl)-3-ethynyl-5-hydroxy-methyl-tetrahydro-furan-3,4-diol is a potent inhibitor of dengue virus (DENV), with 50% effective concentration (EC50) and cytotoxic concentration (CC50) values of 0.7 ?M and >100 ?M, respectively. Here we describe the synthesis, structure-activity relationship, and antiviral characterization of the inhibitor. In an AG129 mouse model, a single-dose treatment of DENV-infected mice with the compound suppressed peak viremia and completely prevented death. Mode-of-action analysis using a DENV replicon indicated that the compound blocks viral RNA synthesis. Recombinant adenosine kinase could convert the compound to a monophosphate form. Suppression of host adenosine kinase, using a specific inhibitor (iodotubercidin) or small interfering RNA (siRNA), abolished or reduced the compound's antiviral activity in cell culture. Studies of rats showed that 14C-labeled compound was converted to mono-, di-, and triphosphate metabolites in vivo. Collectively, the results suggest that this adenosine inhibitor is phosphorylated to an active (triphosphate) form which functions as a chain terminator for viral RNA synthesis.

Chen, Yen-Liang; Yin, Zheng; Duraiswamy, Jeyaraj; Schul, Wouter; Lim, Chin Chin; Liu, Boping; Xu, Hao Ying; Qing, Min; Yip, Andy; Wang, Gang; Chan, Wai Ling; Tan, Hui Pen; Lo, Melissa; Liung, Sarah; Kondreddi, Ravinder Reddy; Rao, Ranga; Gu, Helen; He, Handan; Keller, Thomas H.; Shi, Pei-Yong

2010-01-01

355

The role of adenosine receptors in rheumatoid arthritis.  

PubMed

Rheumatoid arthritis (RA), is the most common inflammatory musculoskeletal disease inducing diminished quality-of-life in the affected individuals and having major impact on society due to decrease work ability. Early diagnosis and immediate, effective therapy are crucial in order to prevent unfavorable outcome. Treatment of RA has progressed during the past two decades thanks to the advent of a large number of new agents targeting different specific molecules and pathways involved in the modulation of the inflammation. In this scenario an important role is covered by adenosine, a purine nucleoside released from a variety of cells in response to metabolic and inflammatory stress, which is considered to be a potent endogenous regulator acting through its interaction with 4 cell surface receptors named as A(1), A(2A), A(2B) and A(3). Adenosine receptor stimulation has complex effects on the release of pro-inflammatory cytokines depending on selective receptor engagement. Recent data show the involvement of adenosine pathways in RA and its potential therapeutic implications. PMID:20691813

Varani, Katia; Padovan, Melissa; Govoni, Marcello; Vincenzi, Fabrizio; Trotta, Francesco; Borea, Pier Andrea

2010-12-01

356

Pathophysiological roles for purines: adenosine, caffeine and urate  

PubMed Central

The motor symptoms of Parkinson's disease (PD) are due primarily to the degeneration of the dopaminergic neurons in the nigrostriatal pathway. However, several other brain areas and neurotransmitters other than dopamine such as noradrenaline, 5-hydroxytryptamine and acetylcholine are affected in the disease. Moreover, adenosine because of the extensive interaction of its receptors with the dopaminergic system has been implicated in the in the pathophysiology of the disease. Based on the involvement of these nondopaminergic neurotransmitters in PD and the sometimes severe adverse effects that limit the mainstay use of dopamine-based antiparkinsonian treatments, recent assessments have called for a broadening of therapeutic options beyond the traditional dopaminergic drug arsenal. In this review we describe the interactions between dopamine and adenosine receptors that underpin the preclinical and clinical rationale for pursuing adenosine A2A receptor antagonists as symptomatic and potentially neuroprotective treatment of PD. The review will pay particular attention to recent results regarding specific A2A receptor-receptor interactions and recent findings identifying urate, the end product of purine metabolism, as a novel prognostic biomarker and candidate neuroprotectant in PD.

Morelli, Micaela; Carta, Anna R; Kachroo, Anil; Schwarzschild, Michael A.

2011-01-01

357

Adenosine receptor localization in rat testes: biochemical and autoradiographic evidence for association with spermatocytes.  

PubMed

[3H]Cyclohexyladenosine ( [3H]CHA) labels adenosine receptors in rat testes. Testicular adenosine receptors are regulated by guanine nucleotides and divalent cations in a similar fashion to brain adenosine receptors. Endocrine manipulations which selectively decrease sperm cells reduce biochemically determined numbers of [3H]CHA labeled adenosine receptors, whereas adenosine receptor number is not affected by manipulations that primarily influence Leydig cells. Autoradiographic analysis of [3H]CHA binding in the rat testes reveals a localization within seminiferous tubules. Receptor related silver grains occur within tubular epithelium as well as in the lumen of tubules but are absent in interstitial tissue and blood vessels. These data suggest an association of adenosine receptors with spermatocytes within the seminiferous tubule epithelium. PMID:6311515

Murphy, K M; Goodman, R R; Snyder, S H

1983-10-01

358

Optimization of Adenosine 5?-Carboxamide Derivatives as Adenosine Receptor Agonists Using Structure-Based Ligand Design and Fragment Screening  

PubMed Central

Structures of G protein-coupled receptors (GPCRs) have a proven utility in the discovery of new antagonists and inverse agonists modulating signaling of this important family of clinical targets. Applicability of active-state GPCR structures to virtual screening and rational optimization of agonists, however, remains to be assessed. In this study of adenosine 5? derivatives, we evaluated the performance of an agonist-bound A2A adenosine receptor (AR) structure in retrieval of known agonists and then employed the structure to screen for new fragments optimally fitting the corresponding subpocket. Biochemical and functional assays demonstrate high affinity of new derivatives that include polar heterocycles. The binding models also explain modest selectivity gain for some substituents toward the closely related A1AR subtype and the modified agonist efficacy of some of these ligands. The study suggests further applicability of in silico fragment screening to rational lead optimization in GPCRs.

Tosh, Dilip K.; Phan, Khai; Gao, Zhan-Guo; Gakh, Andrei A.; Xu, Fei; Deflorian, Francesca; Abagyan, Ruben; Stevens, Raymond C.; Jacobson, Kenneth A.; Katritch, Vsevolod

2012-01-01

359

5'-substituted adenosine analogs as new high-affinity partial agonists for the adenosine A1 receptor.  

PubMed

5'-(Alkylthio)-, 5'-(methylseleno)-, and 5'-(alkylamino)-substituted analogues of N6-cyclopen-tyladenosine (CPA) were synthesized in 30-50% overall yields. The affinities of these compounds for the adenosine A1 and A2A receptors were determined in rat brain membranes. The 5'-substituted CPA analogues proved selective for the adenosine A1 receptors, displaying affinities in the nanomolar range. The compounds were also evaluated for their ability to stimulate [35S]GTP gamma S binding, also in rat brain membranes. The Ki values in receptor binding studies corresponded well to the EC50 values thus obtained. Intrinsic activities of the compounds were tested in vitro by determining the GTP shift in receptor binding studies as well as the maximal binding of [35S]GTP gamma S. It appeared that the 5'-thio and 5'-seleno derivatives in particular behaved as partial agonists. PMID:9438026

van der Wenden, E M; Carnielli, M; Roelen, H C; Lorenzen, A; von Frijtag Drabbe Knzel, J K; IJzerman, A P

1998-01-01

360

The Brain In Vivo Expresses the 2?,3?-cAMP-Adenosine Pathway  

PubMed Central

Although multiple biochemical pathways produce adenosine, studies suggest that the 2?,3?-cAMP-adenosine pathway (2?,3?-cAMP ? 2?-AMP/3?-AMP ? adenosine) contributes to adenosine production in some cells/tissues/organs. To determine whether the 2?,3?-cAMP-adenosine pathway exists in vivo in the brain, we delivered to the brain (gray matter and white matter separately) via the inflow perfusate of a microdialysis probe either 2?,3?-cAMP, 3?,5?-cAMP, 2?-AMP, 3?-AMP, or 5?-AMP and measured the recovered metabolites in the microdialysis outflow perfusate with mass spectrometry. In both gray and white matter, 2?,3?-cAMP increased 2?-AMP, 3?-AMP and adenosine, and 3?,5?-cAMP increased 5?-AMP and adenosine. In both brain regions, 2?-AMP, 3-AMP and 5?-AMP were converted to adenosine. Microdialysis experiments in 2?,3?-cyclic nucleotide-3?-phosphodiesterase (CNPase) wild-type mice demonstrated that traumatic brain injury (TBI; controlled cortical impact model) activated the brain 2,3?-cAMP-adenosine pathway; similar experiments in CNPase knockout mice indicated that CNPase was involved in the metabolism of endogenous 2?,3?-cAMP to 2?-AMP and to adenosine. In CSF from TBI patients, 2?,3?-cAMP was significantly increased in the initial 12 hours after injury and strongly correlated with CSF levels of 2?-AMP, 3?-AMP, adenosine and inosine. We conclude that in vivo, 2?,3?-cAMP is converted to 2?-AMP/3?-AMP, and these AMPs are metabolized to adenosine. This pathway exists endogenously in both mice and humans.

Verrier, Jonathan D.; Jackson, Travis C.; Bansal, Rashmi; Kochanek, Patrick M.; Puccio, Ava M.; Okonkwo, David O.; Jackson, Edwin K.

2012-01-01

361

Redox-sensitive synchronizing action of adenosine on transmitter release at the neuromuscular junction.  

PubMed

The kinetics of neurotransmitter release was recognized recently as an important contributor to synaptic efficiency. Since adenosine is the ubiquitous modulator of presynaptic release in peripheral and central synapses, in the current project we studied the action of this purine on the timing of acetylcholine quantal release from motor nerve terminals in the skeletal muscle. Using extracellular recording from frog neuromuscular junction we tested the action of adenosine on the latencies of single quantal events in the pro-oxidant and antioxidant conditions. We found that adenosine, in addition to previously known inhibitory action on release probability, also synchronized release by removing quantal events with long latencies. This action of adenosine on release timing was abolished by oxidants whereas in the presence of the antioxidant the synchronizing action of adenosine was further enhanced. Interestingly, unlike the timing of release, the inhibitory action of adenosine on release probability was redox-independent. Modulation of release timing by adenosine was mediated by purinergic A1 receptors as it was eliminated by the specific A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and mimicked by the specific A1 agonist N(6)-cyclopentyl-adenosine. Consistent with data obtained from dispersion of single quantal events, adenosine also reduced the rise-time of multiquantal synaptic currents. The latter effect was reproduced in the model based on synchronizing effect of adenosine on release timing. Thus, adenosine which is generated at the neuromuscular junction from the breakdown of the co-transmitter ATP induces the synchronization of quantal events. The effect of adenosine on release timing should preserve the fidelity of synaptic transmission via "cost-effective" use of less transmitter quanta. Our findings also revealed important crosstalk between purinergic and redox modulation of synaptic processes which could take place in the elderly or in neuromuscular diseases associated with oxidative stress like lateral amyotrophic sclerosis. PMID:23806718

Tsentsevitsky, A; Kovyazina, I; Nikolsky, E; Bukharaeva, E; Giniatullin, R

2013-09-17

362

Estimation of skeletal muscle interstitial adenosine during forearm dynamic exercise in humans  

NASA Technical Reports Server (NTRS)

It has been proposed that adenosine is a metabolic signal that triggers activation of muscle afferents involved in the exercise pressor reflex. Furthermore, exogenous adenosine induces sympathetic activation that mimics the exercise pressor reflex, and blockade of adenosine receptors inhibits sympathetic activation induced by exercise. Thus, we hypothesize that adenosine is released locally by the muscle during exercise. We used microdialysis probes, placed in the flexor digitorium superficialis muscle, to estimate muscle interstitial adenosine levels in humans. We estimated resting in vivo muscle interstitial adenosine concentrations (0.292+/-0.058 micromol/L, n=4) by perfusing increasing concentrations of adenosine to determine the gradient produced in the dialysate. Muscle interstitial adenosine concentrations increased from 0.23+/-0.04 to 0.82+/-0.14 micromol/L (n=14, P<0.001) during intermittent dynamic exercise at 50% of maximal voluntary contraction. Lactate increased from 0.8+/-0.1 to 2.3+/-0.3 mmol/L (P<0.001). Lower intensity (15% maximal voluntary contraction) intermittent dynamic exercise increased adenosine concentrations from 0.104+/-0.02 to 0.42+/-0.16 micromol/L (n=7). The addition of ischemia to this low level of exercise produced a greater increase in adenosine (from 0.095+/-0.02 to 0.48+/-0.2 micromol/L) compared with nonischemic exercise (0. 095+/-0.02 to 0.25+/-0.12 micromol/L). These results indicate that microdialysis is useful in estimating adenosine concentrations and in reflecting changes in muscle interstitial adenosine during dynamic exercise in humans.

Costa, F.; Heusinkveld, J.; Ballog, R.; Davis, S.; Biaggioni, I.

2000-01-01

363

Adenosine A2B receptors: a novel therapeutic target in asthma?  

Microsoft Academic Search

Adenosine is an endogenous nucleoside that modulates many physiological processes. Its actions are mediated by interaction with specific cell membrane receptors. Four subtypes of adenosine receptor have been cloned: A1, A2A, A2B and A3. Significant advancement has been made in our understanding of the molecular pharmacology and physiological relevance of adenosine receptors but our knowledge of A2B receptors lags behind

I. Feoktistov; I. Biaggioni; R. Polosa; S. T. Holgate

1998-01-01

364

Adenosine Inhibition of Lipopolysaccharide-Induced Interleukin6 Secretion by the Osteoblastic Cell Line MG63  

Microsoft Academic Search

Adenosine is known to inhibit inflammatory responses in many cell systems via a family of purine receptors termed P1. The\\u000a P1 family consists of the adenosine receptors (ADORA) of subtypes A1, A2a, A2b, and A3. In order to assess whether adenosine has anti-inflammatory actions in osteoblastic cells, we investigated its effects on\\u000a lipopolysaccharide (LPS)-induced interleukin 6 (IL-6) release in an

Joseph M. Russell; Graham S. Stephenson; Clare E. Yellowley; Hilary P. Benton

2007-01-01

365

Adenosine A 1 receptors are crucial in keeping an epileptic focus localized  

Microsoft Academic Search

Adenosine is an endogenous neuromodulator with anticonvulsant and neuroprotective properties presumably mediated by activation of adenosine A1 receptors (A1Rs). To study the involvement of A1Rs in neuroprotection during epileptogenesis, we induced status epilepticus by a unilateral intrahippocampal kainic acid (KA) injection (1 nmol) in wild-type C57BL\\/6 and homozygous adenosine A1R knock out (A1R-KO) mice of the same genetic background. Whereas

Denise E. Fedele; Tianfu Li; Jing Q. Lan; Bertil B. Fredholm; Detlev Boison

2006-01-01

366

The dynamics of single spike-evoked adenosine release in the cerebellum  

PubMed Central

The purine adenosine is a potent neuromodulator in the brain, with roles in a number of diverse physiological and pathological processes. Modulators such as adenosine are difficult to study as once released they have a diffuse action (which can affect many neurones) and, unlike classical neurotransmitters, have no inotropic receptors. Thus rapid postsynaptic currents (PSCs) mediated by adenosine (equivalent to mPSCs) are not available for study. As a result the mechanisms and properties of adenosine release still remain relatively unclear. We have studied adenosine release evoked by stimulating the parallel fibres in the cerebellum. Using adenosine biosensors combined with deconvolution analysis and mathematical modelling, we have characterised the release dynamics and diffusion of adenosine in unprecedented detail. By partially blocking K+ channels, we were able to release adenosine in response to a single stimulus rather than a train of stimuli. This allowed reliable sub-second release of reproducible quantities of adenosine with stereotypic concentration waveforms that agreed well with predictions of a mathematical model of purine diffusion. We found no evidence for ATP release and thus suggest that adenosine is directly released in response to parallel fibre firing and does not arise from extracellular ATP metabolism. Adenosine release events showed novel short-term dynamics, including facilitated release with paired stimuli at millisecond stimulation intervals but depletion-recovery dynamics with paired stimuli delivered over minute time scales. These results demonstrate rich dynamics for adenosine release that are placed, for the first time, on a quantitative footing and show strong similarity with vesicular exocytosis.

Klyuch, Boris P; Richardson, Magnus J E; Dale, Nicholas; Wall, Mark J

2011-01-01

367

Caffeine Acts via A1 Adenosine Receptors to Disrupt Embryonic Cardiac Function  

Microsoft Academic Search

BackgroundEvidence suggests that adenosine acts via cardiac A1 adenosine receptors (A1ARs) to protect embryos against hypoxia. During embryogenesis, A1ARs are the dominant regulator of heart rate, and A1AR activation reduces heart rate. Adenosine action is inhibited by caffeine, which is widely consumed during pregnancy. In this study, we tested the hypothesis that caffeine influences developing embryos by altering cardiac function.Methodology\\/Principal

Daniela L. Buscariollo; Gregory A. Breuer; Christopher C. Wendler; Scott A. Rivkees

2011-01-01

368

Synthesis of eudistomin D analogues and its effects on adenosine receptors  

Microsoft Academic Search

Six analogues (16) of eudistomin D, a ?-carboline alkaloid from a marine tunicate Eudistoma olivaceum, were synthesized, and their affinity and selectivity for adenosine receptors A1, A2A, and A3 were examined. All the synthetic compounds 16 did not show affinity to the adenosine A1 receptor. ?-Carboline 3 exhibited the most potent affinity to the adenosine receptor A3 among compounds 16.

Haruaki Ishiyama; Kengo Ohshita; Tetsuro Abe; Hiroyasu Nakata; Junichi Kobayashi

2008-01-01

369

Relationship between adenosine deaminase activity and cytokine-secreting T cells in normal pregnancy  

Microsoft Academic Search

OBJECTIVE:To evaluate the relationship between plasma adenosine deaminase activity and the proportion of cytokine-secreting T cells as causes of changes in adenosine deaminase activity in normal pregnancy.METHODS:Plasma adenosine deaminase activity and the proportions of cytokine-secreting T cells were measured in the peripheral blood of 26 nonpregnant and normal pregnant women in the third trimester. The proportion of CD4-positive T cells

Yoshio Yoneyama; Rintaro Sawa; Shunji Suzuki; Koichi Yoneyama; Daisuke Doi; Tsutomu Araki

2002-01-01

370

Immunoprecipitation of At Adenosine Receptor-GTP- Binding Protein Complexes In Ciliary Epithelial Cells  

Microsoft Academic Search

approach and (3H)DPCPX, a selective radioligand to adenosine receptor. Methods. Solubilized preparations of adenosine receptors from PE and NPE cell lines were immunoprecipitated with G protein specific antisera 8730 (anti-Gia), 3646 (anti-Gial), 1521 (anti-Gia2) an d 1518 (anti-Gia3), and of adenosine receptor-G protein complexes were de- tected by the binding of radioactive (3H)DPCPX. Results. Data indicate that (3H)DPCPX forms high-affinity

Martin B. Wax; Rajkumar V. Patil

371

Adenosine A2A receptors play a role in the pathogenesis of hepatic cirrhosis  

PubMed Central

Adenosine is a potent endogenous regulator of inflammation and tissue repair. Adenosine, which is released from injured and hypoxic tissue or in response to toxins and medications, may induce pulmonary fibrosis in mice, presumably via interaction with a specific adenosine receptor. We therefore determined whether adenosine and its receptors contribute to the pathogenesis of hepatic fibrosis. As in other tissues and cell types, adenosine is released in vitro in response to the fibrogenic stimuli ethanol (40?mg?dl?1) and methotrexate (100?nM). Adenosine A2A receptors are expressed on rat and human hepatic stellate cell lines and adenosine A2A receptor occupancy promotes collagen production by these cells. Liver sections from mice treated with the hepatotoxins carbon tetrachloride (CCl4) (0.05?ml in oil, 50?:?50 v?:?v, subcutaneously) and thioacetamide (100?mg?kg?1 in PBS, intraperitoneally) released more adenosine than those from untreated mice when cultured ex vivo. Adenosine A2A receptor-deficient, but not wild-type or A3 receptor-deficient, mice are protected from development of hepatic fibrosis following CCl4 or thioacetamide exposure. Similarly, caffeine (50?mg?kg?1?day?1, po), a nonselective adenosine receptor antagonist, and ZM241385 (25?mg?kg?1 bid), a more selective antagonist of the adenosine A2A receptor, diminished hepatic fibrosis in wild-type mice exposed to either CCl4 or thioacetamide. These results demonstrate that hepatic adenosine A2A receptors play an active role in the pathogenesis of hepatic fibrosis, and suggest a novel therapeutic target in the treatment and prevention of hepatic cirrhosis.

Chan, Edwin S L; Montesinos, Maria Carmen; Fernandez, Patricia; Desai, Avani; Delano, David L; Yee, Herman; Reiss, Allison B; Pillinger, Michael H; Chen, Jiang-Fan; Schwarzschild, Michael A; Friedman, Scott L; Cronstein, Bruce N

2006-01-01

372

Effects of targeted deletion of A1 adenosine receptors on postischemic cardiac function and expression of adenosine receptor subtypes.  

PubMed

To examine ischemic tolerance in the absence of A(1) adenosine receptors (A(1)ARs), isolated wild-type (WT) and A(1)AR knockout (A(1)KO) murine hearts underwent global ischemia-reperfusion, and injury was measured in terms of functional recovery and efflux of lactate dehydrogenase (LDH). Hearts were analyzed by real-time RT-PCR both at baseline and at intervals during ischemia-reperfusion to determine whether compensatory expression of other adenosine receptor subtypes occurs with either A(1)AR deletion and/or ischemia-reperfusion. A(1)KO hearts had higher baseline coronary flow (CF) and left ventricular developed pressure (LVDP) than WT hearts, whereas heart rate was unchanged by A(1)AR deletion. After 20 min of ischemia, CF was attenuated in A(1)KO compared with WT hearts, and this reduction persisted throughout reperfusion. Final recovery of LVDP was decreased in A(1)KO hearts (54.4 +/- 5.1 vs. WT 81.1 +/- 3.4% preischemic baseline) and correlated with higher diastolic pressure during reperfusion. Postischemic efflux of LDH was greater in A(1)KO compared with WT hearts. Real-time RT-PCR demonstrated the absence of A(1)AR transcript in A(1)KO hearts, and the message for A(2A), A(2B), and A(3) adenosine receptors was similar in uninstrumented A(1)KO and WT hearts. Ischemia-reperfusion increased A(2B) mRNA expression 2.5-fold in both WT and A(1)KO hearts without changing A(1) or A(3) expression. In WT hearts, ischemia transiently doubled A(2A) mRNA, which returned to preischemic level upon reperfusion, a pattern not observed in A(1)KO hearts. Together, these data affirm the cardioprotective role of A(1)ARs and suggest that induced expression of other adenosine receptor subtypes may participate in the response to ischemia-reperfusion in isolated murine hearts. PMID:16679400

Morrison, R Ray; Teng, Bunyen; Oldenburg, Peter J; Katwa, Laxmansa C; Schnermann, Jurgen B; Mustafa, S Jamal

2006-10-01

373

Up-regulation of A 2B adenosine receptor in A 2A adenosine receptor knockout mouse coronary artery  

Microsoft Academic Search

In this study, we looked into possible compensatory changes of other adenosine receptors (ARs) in A2A genetic knockout mice (A2AKO) as well as the functional role of nitric oxide (NO) in A2A AR-mediated vasodilation. Gene expression of ARs from coronary arteries of A2A AR wild type mice (A2AWT) and A2AKO was studied using real-time PCR. Functional studies were carried out

Bunyen Teng; Catherine Ledent; S. Jamal Mustafa

2008-01-01

374

Adenosine kinase inhibition promotes survival of fetal adenosine deaminase-deficient thymocytes by blocking dATP accumulation.  

PubMed

Thymocyte development past the CD4(-)CD8(-) stage is markedly inhibited in adenosine deaminase-deficient (ADA-deficient) murine fetal thymic organ cultures (FTOCs) due to the accumulation of ADA substrates derived from thymocytes failing developmental checkpoints. Such cultures can be rescued by overexpression of Bcl-2, suggesting that apoptosis is an important component of the mechanism by which ADA deficiency impairs thymocyte development. Consistent with this conclusion, ADA-deficient FTOCs were partially rescued by a rearranged T cell receptor beta transgene that permits virtually all thymocytes to pass the beta-selection checkpoint. ADA-deficient cultures were also rescued by the adenosine kinase inhibitor 5'-amino-5'-deoxyadenosine (5'A5'dAdo), indicating that the metabolite responsible for the inhibition of thymocyte development is not adenosine or deoxyadenosine, but a phosphorylated derivative of an ADA substrate. Correction of ADA-deficient FTOCs by 5'A5'dAdo correlated with reduced accumulation of dATP, implicating this compound as the toxic metabolite. In ADA-inhibited FTOCs rescued with a Bcl-2 transgene, however, dATP levels were superelevated, suggesting that cells failing positive and negative selection continued to contribute to the accumulation of ADA substrates. Our data are consistent with dATP-induced mitochondrial cytochrome c release followed by apoptosis as the mechanism by which ADA deficiency leads to reduced thymic T cell production. PMID:12163459

Van De Wiele, C Justin; Vaughn, James G; Blackburn, Michael R; Ledent, Catherine A; Jacobson, Marlene; Jiang, Hong; Thompson, Linda F

2002-08-01

375

Molecular Vibration-Activity Relationship in the Agonism of Adenosine Receptors  

PubMed Central

The molecular vibration-activity relationship in the receptor-ligand interaction of adenosine receptors was investigated by structure similarity, molecular vibration, and hierarchical clustering in a dataset of 46 ligands of adenosine receptors. The resulting dendrogram was compared with those of another kind of fingerprint or descriptor. The dendrogram result produced by corralled intensity of molecular vibrational frequency outperformed four other analyses in the current study of adenosine receptor agonism and antagonism. The tree that was produced by clustering analysis of molecular vibration patterns showed its potential for the functional classification of adenosine receptor ligands.

Chee, Hyun Keun

2013-01-01

376

Adenosine-induced coronary vasospasm following drug-eluting stent implantation.  

PubMed

We present the case of coronary vasospasm during adenosine stress in a patient with a prior drug-eluting stent implantation. The patient had a stent implantation in the left anterior descending coronary artery 3 years ago. Recently, he developed a chest pain and underwent adenosine stress myocardial perfusion single photon emission CT (SPECT). During the adenosine stress, he felt severe chest pain and ST elevation on electrocardiogram. An invasive coronary angiography showed no in-stent restenosis. This phenomenon deemed to be adenosine-induced coronary vasospasm after stent implantation. PMID:24518394

Matsumoto, Naoya; Nagao, Ken; Hirayama, Atsushi; Kasama, Shu

2014-01-01

377

Adenosine receptor-mediated adhesion of endothelial progenitors to cardiac microvascular endothelial cells.  

PubMed

Intracoronary delivery of endothelial progenitor cells (EPCs) is an emerging concept for the treatment of cardiovascular disease. Enhancement of EPC adhesion to vascular endothelium could improve cell retention within targeted organs. Because extracellular adenosine is elevated at sites of ischemia and stimulates neovascularization, we examined the potential role of adenosine in augmenting EPC retention to cardiac microvascular endothelium. Stimulation of adenosine receptors in murine embryonic EPCs (eEPCs) and cardiac endothelial cells (cECs) rapidly, within minutes, increased eEPC adhesion to cECs under static and flow conditions. Similarly, adhesion of human adult culture-expanded EPCs to human cECs was increased by stimulation of adenosine receptors. Furthermore, adenosine increased eEPC retention in isolated mouse hearts perfused with eEPCs. We determined that eEPCs and cECs preferentially express functional A1 and A2B adenosine receptor subtypes, respectively, and that both subtypes are involved in the regulation of eEPC adhesion to cECs. We documented that the interaction between P-selectin and its ligand (P-selectin glycoprotein ligand-1) plays a role in adenosine-dependent eEPC adhesion to cECs and that stimulation of adenosine receptors in cECs induces rapid cell surface expression of P-selectin. Our results suggest a role for adenosine in vasculogenesis and its potential use to stimulate engraftment in cell-based therapies. PMID:18032734

Ryzhov, Sergey; Solenkova, Nataliya V; Goldstein, Anna E; Lamparter, Mathias; Fleenor, Todd; Young, Pampee P; Greelish, James P; Byrne, John G; Vaughan, Douglas E; Biaggioni, Italo; Hatzopoulos, Antonis K; Feoktistov, Igor

2008-02-15

378

Adenosine Receptor-Mediated Adhesion of Endothelial Progenitors to Cardiac Microvascular Endothelial Cells  

PubMed Central

Intracoronary delivery of endothelial progenitor cells (EPCs) is an emerging concept for the treatment of cardiovascular disease. Enhancement of EPC adhesion to vascular endothelium could improve cell retention within targeted organs. Because extracellular adenosine is elevated at sites of ischemia and stimulates neovascularization, we examined the potential role of adenosine in augmenting EPC retention to cardiac microvascular endothelium. Stimulation of adenosine receptors in murine embryonic EPCs (eEPCs) and cardiac endothelial cells (cECs) rapidly, within minutes, increased eEPC adhesion to cECs under static and flow conditions. Similarly, adhesion of human adult culture-expanded EPCs to human cECs was increased by stimulation of adenosine receptors. Furthermore, adenosine increased eEPC retention in isolated mouse hearts perfused with eEPCs. We determined that eEPCs and cECs preferentially express functional A1 and A2B adenosine receptor subtypes, respectively, and that both subtypes are involved in the regulation of eEPC adhesion to cECs. We documented that the interaction between P-selectin and its ligand (P-selectin glycoprotein ligand-1) plays a role in adenosine-dependent eEPC adhesion to cECs and that stimulation of adenosine receptors in cECs induces rapid cell surface expression of P-selectin. Our results suggest a role for adenosine in vasculogenesis and its potential use to stimulate engraftment in cell-based therapies.

Ryzhov, Sergey; Solenkova, Nataliya V.; Goldstein, Anna E.; Lamparter, Mathias; Fleenor, Todd; Young, Pampee P.; Greelish, James P.; Byrne, John G.; Vaughan, Douglas E.; Biaggioni, Italo; Hatzopoulos, Antonis K.; Feoktistov, Igor

2009-01-01

379

Adenosine and inosine release during hypoxia in the isolated spinal cord of neonatal rats  

PubMed Central

BACKGROUND AND PURPOSE Adenosine and inosine accumulate extracellularly during hypoxia/ischaemia in the brain and may act as neuroprotectants. In spinal cord, there is pharmacological evidence for increases in extracellular adenosine during hypoxia, but no direct measurements of purine release. Furthermore, the efflux pathways and origin of extracellular purines are not defined. To characterize hypoxia-evoked purine accumulation, we examined the effect of acute hypoxia on the extracellular levels of adenosine and inosine in isolated spinal cords from rats. EXPERIMENTAL APPROACH Extracellular adenosine and inosine concentrations were assayed in an in vitro preparation of the isolated spinal cord of the neonatal rat by HPLC. KEY RESULTS The extracellular level of inosine was about 10-fold higher than that of adenosine. Acute hypoxia (10 min) caused a temperature-dependent increase in these two purines, which were inhibited by an increase in external Ca2+, but not by several inhibitors of efflux pathways or metabolic enzymes of adenine nucleotides. Inhibitors of adenosine deaminase or the equilibrative nucleoside transporter (ENT) abolished the hypoxia-evoked increase in inosine but not adenosine. The inhibition of glial metabolism abolished the increase of both purines evoked by hypoxia but not by oxygen-glucose deprivation, hypercapnia or an adenosine kinase inhibitor. CONCLUSIONS AND IMPLICATIONS Our data suggest that hypoxia releases adenosine itself from intracellular sources. Inosine formed intracellularly may be released through ENTs. During hypoxia, astrocytes appear to play a key role in purine release from neonatal rat spinal cord.

Takahashi, T; Otsuguro, K; Ohta, T; Ito, S

2010-01-01

380

Interactions between the effects of adenosine and calcium on synaptic responses in rat hippocampus in vitro.  

PubMed Central

The effect of adenosine on synaptic responses in the in vitro rat hippocampus was examined. As has been previously described, adenosine had a profound depressant effect on synaptic transmission at excitatory synapses on the CA1 pyramidal cells. Although adenosine also produced small decreases in the amplitude of the presynaptic fibre spike, this was unable to account for the relatively much greater decrease in the amplitude of the extracellularly recorded field excitatory post-synaptic potential (e.p.s.p.). The effect of the calcium concentration of the bathing medium on responses to adenosine was also examined. Adenosine generally had a greater depressant effect on field e.p.s.p.s from slices maintained in low concentrations of calcium (1 mM) than in high (10 mM-calcium). However, at low response amplitudes, the effect of adenosine in the two kinds of medium was quite similar. When corrections were made for non-linear summation of e.p.s.p.s, it was found that the effects of adenosine appeared to be independent of the calcium concentration of the medium. These data suggest that adenosine inhibits synaptic transmission by a calcium-independent regulatory mechanism, and that adenosine does not interfere with calcium influx or calcium levels in the presynaptic terminal. Comparisons of dose-response relationships in media containing different concentrations of calcium suggest that a maximal drug response can occur with less than maximal receptor occupancy at physiological calcium concentrations (less than 2.5 mM).

Dunwiddie, T V

1984-01-01

381

Intracoronary Adenosine versus Intravenous Adenosine during Primary PCI for ST-Elevation Myocardial Infarction: Which One Offers Better Outcomes in terms of Microvascular Obstruction?  

PubMed Central

Aims. Previous studies have suggested that intravenous administration of adenosine improves myocardial reperfusion and reduces infarct size in ST-elevation myocardial infarction (STEMI) patients. Intracoronary administration of adenosine has shown conflicting results. Methods. In this retrospective, single-centre, blinded clinical study, we assessed whether selective intracoronary administration of adenosine distal to the occlusion site immediately before initial balloon inflation reduces microvascular obstruction (MVO) as assessed with cardiac magnetic resonance imaging (MRI). Using contrast-enhanced sequences, microvascular obstruction (MVO) was calculated. We found 81 patients presenting with STEMI within 12?h from symptom onset who were eligible for the study. In 80/81 (100%) patients receiving the study drug, MRI was performed on Day 1 after primary angioplasty. Results. The prevalence of MVO was reduced in the patients treated with intracoronary adenosine, (45%) compared to 85% of patients who were administered intravenous adenosine (P = 0.0043). We found that the size of MVO in patients receiving intracoronary adenosine was significantly reduced compared to 0.91?g in the intravenous-treated group (P = 0.027). There was no statistically significant difference in TIMI flow and clinical outcomes after primary PCI. Conclusion. We found significant evidence that selective high-dose intracoronary administration of adenosine distal to the occlusion site of the culprit lesion in STEMI patients results in a decrease in microvascular obstruction.

Doolub, Gemina; Dall'Armellina, Erica

2013-01-01

382

The 1976C>T polymorphism in the adenosine A2A receptor gene does not affect the vasodilator response to adenosine in humans in vivo.  

PubMed

The 1976C>T polymorphism in the adenosine A2A receptor gene (ADORA2A) modulates the psychological response to administration of the adenosine receptor antagonist caffeine. We quantified the vascular response to adenosine and caffeine to determine the relevance of this variant allele in the physiological response to these agents. We selected 10 study participants with the TT genotype and 10 CC controls, matched for activities of other proteins involved in the metabolism of adenosine. The vasodilator response to the intrabrachial administration of adenosine (0.5, 1.5, 5.0, 15.0, and 50.0 microg/min/dl; venous occlusion plethysmography) was not different between the groups (P=0.4). In addition, the effect of subsequent administration of caffeine (90 microg/min/dl) was not different (P=0.7). We conclude that the 1976C>T polymorphism does not affect the vascular response to adenosine and caffeine in humans in vivo. Therefore, this polymorphism does not contribute to the variation in the effects of adenosine receptor stimulation. PMID:17558310

Riksen, Niels P; Franke, Barbara; van den Broek, Petra; Smits, Paul; Rongen, Gerard A

2007-07-01

383

Search for new purine- and ribose-modified adenosine analogues as selective agonists and antagonists at adenosine receptors.  

PubMed

The binding affinities at rat A1, A2a, and A3 adenosine receptors of a wide range of derivatives of adenosine have been determined. Sites of modification include the purine moiety (1-, 3-, and 7-deaza; halo, alkyne, and amino substitutions at the 2- and 8-positions; and N6-CH2-ring, -hydrazino, and -hydroxylamino) and the ribose moiety (2'-, 3'-, and 5'-deoxy; 2'- and 3'- O-methyl; 2'-deoxy 2'-fluoro; 6'-thio; 5'-uronamide; carbocyclic; 4'- or 3'-methyl; and inversion of configuration). (-)- and (+)-5'-Noraristeromycin were 48- and 21-fold selective, respectively, for A2a vs A1 receptors. 2-Chloro-6'-thioadenosine displayed a Ki value of 20 nM at A2a receptors (15-fold selective vs A1). 2-Chloroadenin-9-yl(beta-L-2'-deoxy-6'- thiolyxofuranoside) displayed a Ki value of 8 microM at A1 receptors and appeared to be an antagonist, on the basis of the absence of a GTP-induced shift in binding vs a radiolabeled antagonist (8-cyclopentyl-1,3-dipropyl-xanthine). 2-Chloro-2'-deoxyadenosine and 2-chloroadenin-9-yl(beta-D-6'-thioarabinoside) were putative partial agonists at A1 receptors, with Ki values of 7.4 and 5.4 microM, respectively. The A2a selective agonist 2-(1-hexynyl)-5'-(N-ethylcarbamoyl)adenosine displayed a Ki value of 26 nM at A3 receptors. The 4'-methyl substitution of adenosine was poorly tolerated, yet when combined with other favorable modifications, potency was restored. Thus, N6-benzyl-4'-methyladenosine-5'-(N-methyluronamide) displayed a Ki value of 604 nM at A3 receptors and was 103- and 88-fold selective vs A1 and A2a receptors, respectively. This compound was a full agonist in the A3-mediated inhibition of adenylate cyclase in transfected CHO cells. The carbocyclic analogue of N6-(3-iodobenzyl)adenosine-5'-(N-methyluronamide) was 2-fold selective for A3 vs A1 receptors and was nearly inactive at A2a receptors. PMID:7707320

Siddiqi, S M; Jacobson, K A; Esker, J L; Olah, M E; Ji, X D; Melman, N; Tiwari, K N; Secrist, J A; Schneller, S W; Cristalli, G

1995-03-31

384

Activity-dependent adenosine release may be linked to activation of Na(+)-K(+) ATPase: an in vitro rat study.  

PubMed

In the brain, extracellular adenosine increases as a result of neuronal activity. The mechanisms by which this occurs are only incompletely understood. Here we investigate the hypothesis that the Na(+) influxes associated with neuronal signalling activate the Na(+)-K(+) ATPase which, by consuming ATP, generates intracellular adenosine that is then released via transporters. By measuring adenosine release directly with microelectrode biosensors, we have demonstrated that AMPA-receptor evoked adenosine release in basal forebrain and cortex depends on extracellular Na(+). We have simultaneously imaged intracellular Na(+) and measured adenosine release. The accumulation of intracellular Na(+) during AMPA receptor activation preceded adenosine release by some 90 s. By removing extracellular Ca(2+), and thus preventing indiscriminate neuronal activation, we used ouabain to test the role of the Na(+)-K(+) ATPase in the release of adenosine. Under conditions which caused a Na(+) influx, brief applications of ouabain increased the accumulation of intracellular Na(+) but conversely rapidly reduced extracellular adenosine levels. In addition, ouabain greatly reduced the amount of adenosine released during application of AMPA. Our data therefore suggest that activity of the Na(+)-K(+) ATPase is directly linked to the efflux of adenosine and could provide a universal mechanism that couples adenosine release to neuronal activity. The Na(+)-K(+) ATPase-dependent adenosine efflux is likely to provide adenosine-mediated activity-dependent negative feedback that will be important in many diverse functional contexts including the regulation of sleep. PMID:24489921

Sims, Robert Edward; Dale, Nicholas

2014-01-01

385

The ionic basis of adenosine receptor actions on post-ganglionic neurones in the rat.  

PubMed Central

Adenosine inhibited three Ca2+-dependent potentials recorded intracellularly from post-ganglionic neurones of the rat superior cervical ganglion. A shoulder on the falling phase of the action potential elicited in normal Locke solution, a hyperpolarizing after-potential (h.a.p.) that follows the spike, and a regenerative Ca2+ spike elicited in Locke solution containing TTX and TEA were all reversibly inhibited by adenosine analogues in a dose-dependent fashion. The maximum rate of rise of the Ca2+ spike (dV/dt) was markedly reduced suggesting that the underlying mechanism of adenosine action is inhibition of the Ca2+ conductance mechanism and thus, the voltage-sensitive Ca2+ current. I/V curves in low Ca2+, high Mg2+, TTX, TEA, and Co2+ to block the Ca2+ current show no change in resistance in the presence of 2-chloroadenosine. The actions of adenosine were nearly eliminated in the presence of 1 mM-theophylline, an adenosine receptor antagonist. The order of agonist potency on the inhibition of the h.a.p. was: N-6-[L-phenylisopropyl] adenosine (L-PIA) greater than 2-chloroadenosine greater than adenosine greater than cyclic AMP = 5' AMP. The concentration of L-PIA which produced a half-maximal effect (EC50) was 0.5 microM and that for cyclic AMP was 100 microM. Dipyridamole, an adenosine uptake blocker, potentiated the effects of low concentrations of adenosine and shifted the dose-response curve for adenosine towards that of 2-chloroadenosine (EC50 = 1 microM). These results are consistent with the concept of an external adenosine receptor, but we are unable to assign a receptor subtype. Cyclic AMP mimicked the effects of adenosine, but these effects were eliminated by adenosine deaminase. Our results suggest that the electrogenic effects of bath-applied cyclic AMP may result from the metabolism of cyclic AMP to adenosine by ganglionic tissue. We conclude that adenosine activates a receptor on the neuronal cell surface to inhibit the voltage-dependent Ca2+ current.

Henon, B K; McAfee, D A

1983-01-01

386

Characterization of spontaneous, transient adenosine release in the caudate-putamen and prefrontal cortex.  

PubMed

Adenosine is a neuroprotective agent that inhibits neuronal activity and modulates neurotransmission. Previous research has shown adenosine gradually accumulates during pathologies such as stroke and regulates neurotransmission on the minute-to-hour time scale. Our lab developed a method using carbon-fiber microelectrodes to directly measure adenosine changes on a sub-second time scale with fast-scan cyclic voltammetry (FSCV). Recently, adenosine release lasting a couple of seconds has been found in murine spinal cord slices. In this study, we characterized spontaneous, transient adenosine release in vivo, in the caudate-putamen and prefrontal cortex of anesthetized rats. The average concentration of adenosine release was 0.170.01 M in the caudate and 0.190.01 M in the prefrontal cortex, although the range was large, from 0.04 to 3.2 M. The average duration of spontaneous adenosine release was 2.90.1 seconds and 2.80.1 seconds in the caudate and prefrontal cortex, respectively. The concentration and number of transients detected do not change over a four hour period, suggesting spontaneous events are not caused by electrode implantation. The frequency of adenosine transients was higher in the prefrontal cortex than the caudate-putamen and was modulated by A1 receptors. The A1 antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine, 6 mg/kg i.p.) increased the frequency of spontaneous adenosine release, while the A1 agonist CPA (N(6)-cyclopentyladenosine, 1 mg/kg i.p.) decreased the frequency. These findings are a paradigm shift for understanding the time course of adenosine signaling, demonstrating that there is a rapid mode of adenosine signaling that could cause transient, local neuromodulation. PMID:24494035

Nguyen, Michael D; Lee, Scott T; Ross, Ashley E; Ryals, Matthew; Choudhry, Vishesh I; Venton, B Jill

2014-01-01

387

Adenosine Inhibits the Excitatory Synaptic Inputs to Basal Forebrain Cholinergic, GABAergic, and Parvalbumin Neurons in Mice  

PubMed Central

Coffee and tea contain the stimulants caffeine and theophylline. These compounds act as antagonists of adenosine receptors. Adenosine promotes sleep and its extracellular concentration rises in association with prolonged wakefulness, particularly in the basal forebrain (BF) region involved in activating the cerebral cortex. However, the effect of adenosine on identified BF neurons, especially non-cholinergic neurons, is incompletely understood. Here we used whole-cell patch-clamp recordings in mouse brain slices prepared from two validated transgenic mouse lines with fluorescent proteins expressed in GABAergic or parvalbumin (PV) neurons to determine the effect of adenosine. Whole-cell recordings were made from BF cholinergic neurons and from BF GABAergic and PV neurons with the size (>20??m) and intrinsic membrane properties (prominent H-currents) corresponding to cortically projecting neurons. A brief (2?min) bath application of adenosine (100??M) decreased the frequency but not the amplitude of spontaneous excitatory postsynaptic currents (EPSCs) in all groups of BF cholinergic, GABAergic, and PV neurons we recorded. In addition, adenosine decreased the frequency of miniature EPSCs in BF cholinergic neurons. Adenosine had no effect on the frequency of spontaneous inhibitory postsynaptic currents in cholinergic neurons or GABAergic neurons with large H-currents but reduced them in a group of GABAergic neurons with smaller H-currents. All effects of adenosine were blocked by a selective, adenosine A1 receptor antagonist, cyclopentyltheophylline (CPT, 1??M). Adenosine had no postsynaptic effects. Taken together, our work suggests that adenosine promotes sleep by an A1 receptor-mediated inhibition of glutamatergic inputs to cortically projecting cholinergic and GABA/PV neurons. Conversely, caffeine and theophylline promote attentive wakefulness by inhibiting these A1 receptors in BF thereby promoting the high-frequency oscillations in the cortex required for attention and cognition.

Yang, Chun; Franciosi, Serena; Brown, Ritchie E.

2013-01-01

388

Adenosine signaling contributes to ethanol-induced fatty liver in mice  

PubMed Central

Fatty liver is commonly associated with alcohol ingestion and abuse. While the molecular pathogenesis of these fatty changes is well understood, the biochemical and pharmacological mechanisms by which ethanol stimulates these molecular changes remain unknown. During ethanol metabolism, adenosine is generated by the enzyme ecto-5?-nucleotidase, and adenosine production and adenosine receptor activation are known to play critical roles in the development of hepatic fibrosis. We therefore investigated whether adenosine and its receptors play a role in the development of alcohol-induced fatty liver. WT mice fed ethanol on the Lieber-DeCarli diet developed hepatic steatosis, including increased hepatic triglyceride content, while mice lacking ecto-5?-nucleotidase or adenosine A1 or A2B receptors were protected from developing fatty liver. Similar protection was also seen in WT mice treated with either an adenosine A1 or A2B receptor antagonist. Steatotic livers demonstrated increased expression of genes involved in fatty acid synthesis, which was prevented by blockade of adenosine A1 receptors, and decreased expression of genes involved in fatty acid metabolism, which was prevented by blockade of adenosine A2B receptors. In vitro studies supported roles for adenosine A1 receptors in promoting fatty acid synthesis and for A2B receptors in decreasing fatty acid metabolism. These results indicate that adenosine generated by ethanol metabolism plays an important role in ethanol-induced hepatic steatosis via both A1 and A2B receptors and suggest that targeting adenosine receptors may be effective in the prevention of alcohol-induced fatty liver.

Peng, Zhongsheng; Borea, Pier Andrea; Wilder, Tuere; Yee, Herman; Chiriboga, Luis; Blackburn, Michael R.; Azzena, Gianfranco; Resta, Giuseppe; Cronstein, Bruce N.

2009-01-01

389

Suppression of kindling epileptogenesis by adenosine releasing stem cell-derived brain implants.  

PubMed

Epilepsy therapy is largely symptomatic and no effective therapy is available to prevent epileptogenesis. We therefore analysed the potential of stem cell-derived brain implants and of paracrine adenosine release to suppress the progressive development of seizures in the rat kindling-model. Embryonic stem (ES) cells, engineered to release the inhibitory neuromodulator adenosine by biallelic genetic disruption of the adenosine kinase gene (Adk-/-), and respective wild-type (wt) cells, were differentiated into neural precursor cells (NPs) and injected into the hippocampus of rats prior to kindling. Therapeutic effects of NP-derived brain implants were compared with those of wt baby hamster kidney cells (BHK) and adenosine releasing BHK cell implants (BHK-AK2), which were previously shown to suppress seizures by paracrine adenosine release. Wild-type NP-graft recipients were characterized by an initial delay of seizure development, while recipients of adenosine releasing NPs displayed sustained protection from developing generalized seizures. In contrast, recipients of wt BHK cells failed to display any effects on kindling development, while recipients of BHK-AK2 cells were only moderately protected from seizure development. The therapeutic effect of Adk(-/-)-NPs was due to graft-mediated adenosine release, since seizures could transiently be provoked after blocking adenosine A1 receptors. Histological analysis of NP-implants at day 26 revealed cell clusters within the infrahippocampal cleft as well as intrahippocampal location of graft-derived cells expressing mature neuronal markers. In contrast, BHK and BHK-AK2 cell implants only formed cell clusters within the infrahippocampal cleft. We conclude that ES cell-derived adenosine releasing brain implants are superior to paracrine adenosine release from BHK-AK2 cell implants in suppressing seizure progression in the rat kindling-model. These findings may indicate a potential antiepileptogenic function of stem cell-mediated adenosine delivery. PMID:17472985

Li, Tianfu; Steinbeck, Julius A; Lusardi, Theresa; Koch, Philipp; Lan, Jing Q; Wilz, Andrew; Segschneider, Michaela; Simon, Roger P; Brstle, Oliver; Boison, Detlev

2007-05-01

390

Adenosine A1 receptors mediate mobilization of calcium in human bronchial smooth muscle cells.  

PubMed

Adenosine stimulates contraction of airway smooth muscle, but the mechanism is widely considered indirect, depending on release of contractile agonists from mast cells and nerves. The goal was to determine whether adenosine, by itself, directly regulates calcium signaling in human bronchial smooth muscle cells (HBSMC). Primary cultures of HBSMC from normal subjects were loaded with fura 2-AM, and cytosolic calcium concentrations ([Ca(2+)](i)) were determined ratiometrically by imaging single cells. The nonselective adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA), and the adenosine A(1) receptor agonist, N(6)-cyclopentyladenosine (CPA), both stimulated rapid, transient increases in [Ca(2+)](i). In contrast, there were no calcium responses to 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamido-adenosine (100 nM) or N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (100 nM), selective agonists at adenosine A(2A) receptors and adenosine A(3) receptors, respectively. Calcium responses to NECA and CPA were inhibited by 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A(1) receptor antagonist, and by pertussis toxin (PTX). In other experiments, NECA stimulated calcium transients in the absence of extracellular calcium, but not when cells were preincubated in cyclopiazonic acid or thapsigargin to empty intracellular calcium stores. Calcium responses were attenuated by xestospongin C and 2-aminoethoxydiphenylborane, inhibitors of inositol trisphosphate (IP(3)) receptors, and by U73122, an inhibitor of phospholipase C. It was concluded that stimulation of adenosine A(1) receptors on HBSMC rapidly mobilizes intracellular calcium stores by a mechanism dependent on PTX-sensitive G proteins, and IP(3) signaling. These findings suggest that, in addition to its well-established indirect effects on HBSMC, adenosine also has direct effects on contractile signaling pathways. PMID:16709961

Ethier, Michael F; Madison, J Mark

2006-10-01

391

Plasma concentration of adenosine during normoxia and moderate hypoxia in humans.  

PubMed

Adenosine, a purine nucleoside, plays a variety of roles in cardiovascular and ventilatory control, and may be a marker of tissue hypoxia. There is, however, no direct evidence of an increase in plasma or in tissue levels of adenosine during moderate hypoxia in humans. We measured the plasma concentrations of adenosine in an artery and the median cubital vein simultaneously in 12 normal volunteers, and also in the internal jugular vein in seven of them during normoxia and moderate hypoxia (SaO2 = 80%, 20 min) with or without dipyridamole (0.6 mg/kg) pretreatment. Dipyridamole was expected to block reuptake of adenosine by red blood cells and vascular endothelial cells so that the plasma level of adenosine would more likely reflect the tissue level. Blood was sampled with an appropriate stopping solution, and adenosine was measured with a high-pressure liquid chromatographic (HPLC)-fluorometric technique. The plasma concentration of adenosine did not rise either in the artery or in the vein at any phase of hypoxia without the dipyridamole pretreatment. However, when subjects were pretreated with dipyridamole, the plasma concentration of adenosine increased significantly and markedly in a time-dependent manner during hypoxia in the vein, but not in the artery. The adenosine level rose from 20. 7 +/- 2.5 nM (mean +/- SE) during normoxia to 50.7 +/- 10.7 nM at 20 min of hypoxia, and returned to the baseline level in the recovery phase. The plasma concentration of adenosine in the jugular vein did not change during hypoxia either with or without dipyridamole pretreatment. These data provide evidence that in humans, the local production of adenosine increases during moderate hypoxia in forearm tissue, although this is not reflected in plasma unless the subject is pretreated with dipyridamole. PMID:10051286

Saito, H; Nishimura, M; Shinano, H; Makita, H; Tsujino, I; Shibuya, E; Sato, F; Miyamoto, K; Kawakami, Y

1999-03-01

392

Adenosine Release Evoked by Short Electrical Stimulations in Striatal Brain Slices Is Primarily Activity Dependent  

PubMed Central

Adenosine is an important neuromodulator in the brain. Traditionally, adenosine is thought to arise in the extracellular space by either an extracellular mechanism, where it is formed outside the cell by the breakdown of released ATP, or an intracellular mechanism, where adenosine made inside the cell is transported out. Recently, a third mechanism of activity dependent adenosine release has also been proposed. Here, we used fast-scan cyclic voltammetry to compare the time course and mechanism of adenosine formation evoked by either low- or high-frequency stimulations in striatal rat brain slices. Low-frequency stimulations (5 pulses at 10 Hz) resulted in an average adenosine efflux of 0.22 0.02 ?M, while high-frequency stimulations (5 pulses, 60 Hz) evoked 0.36 0.04 ?M. Blocking intracellular formation by inhibiting adenosine transporters with S-(4-nitrobenzyl)-6-thioinosine (NBTI) or propentofylline did not decrease release for either frequency, indicating that the release was not due to the intracellular mechanism. Blocking extracellular formation with ARL-67156 reduced low-frequency release about 60%, but did not affect high-frequency release. Both low- and high-frequency stimulated release were almost completely blocked by the removal of calcium, indicating activity dependence. Reducing dopamine efflux did not affect adenosine release but inhibiting ionotropic glutamate receptors did, indicating that adenosine release is dependent on downstream effects of glutamate. Therefore, adenosine release after short, high-frequency physiological stimulations is independent of transporter activity or ATP metabolism and may be due to the direct release of adenosine after glutamate receptor activation.

2010-01-01

393

Early adenosine receptor activation ameliorates spinal cord reperfusion injury  

PubMed Central

Objectives Adenosine receptor activation at reperfusion has been shown to ameliorate ischemiareperfusion injury of the spinal cord, but the effects of therapy given in response to ischemic injury are unknown. We hypothesized that adenosine receptor activation with ATL-146e would produce similar protection from ischemic spinal cord injury, whether given at reperfusion or in a delayed fashion. Methods Twenty-two New Zealand white rabbits were divided into three groups. All three groups, including the ischemiareperfusion group (IR, n = 8), underwent 45 min of infrarenal aortic occlusion. The early treatment group (early, n = 8) received 0.06 ?g/kg/min of ATL-146e for 3 h beginning 10 min prior to reperfusion. The delayed treatment group (delayed, n = 6) received ATL-146e starting 1 h after reperfusion. After 48 h, hind limb function was graded using the Tarlov score. Finally, lumbar spinal cord neuronal cytoarchitecture was evaluated. Results Hemodynamic parameters were similar among the groups. Hind limb function at 48 h was significantly better in the early group (3.5 1.0) compared to the IR group (0.625 0.5, P? 0.01). There was a trend towards better hind limb function in the early group compared to the delayed group (2.4 1.1, P=0.08). Hind limb function was similar between delayed and IR groups. Hematoxylineosin spinal cord sections demonstrated preservation of viable motor neurons in the early group compared to the delayed and IR groups. Conclusions Early therapy with ATL-146e provided better protection in this study; therefore, therapy should not be delayed until there is evidence of ischemic neurological deficit. This study suggests that adenosine receptor activation is most effective as a preventive strategy at reperfusion for optimal protection in spinal cord ischemiareperfusion injury. J Cardiovasc Med 9:363?367 2008 Italian Federation of Cardiology.

Reece, T. Brett; Tribble, Curtis G.; Okonkwo, David O.; Davis, Jonathon D.; Maxey, Thomas S.; Gazoni, Leo M.; Linden, Joel; Kron, Irving L.; Kern, John A.

2008-01-01

394

Inhibition of adenosine kinase by phosphonate and bisphosphonate derivatives.  

PubMed

The enzyme adenosine kinase (AK) plays a central role in regulating the intracellular and interstitial concentration of the purine nucleoside adenosine (Ado). In view of the beneficial effects of Ado in protecting tissues from ischemia and other stresses, there is much interest in developing AK inhibitors, which can regulate Ado concentration in a site- and event-specific manner. The catalytic activity of AK from different sources is dependent upon the presence of activators such as phosphate (Pi). In this work we describe several new phosphorylated compounds which either activate or inhibit AK. The compounds acetyl phosphate, carbamoyl phosphate, dihydroxyacetone phosphate and imidodiphosphate were found to stimulate AK activity in a dose-dependent manner comparable to that seen with Pi. In contrast, a number of phosphonate and bisphosphonate derivatives, which included clodronate and etidronate, were found to inhibit the activity of purified AK in the presence of Pi. These AK inhibitors (viz. clodronate, etidronate, phosphonoacetic acid, 2-carboxyethylphosphonic acid, N-(phosphonomethyl)-glycine and N-(phosphonomethyl)iminodiacetic acid), at concentrations at which they inhibited AK, were also shown to inhibit the uptake of (3)H-adenosine and its incorporation into macromolecules in cultured mammalian cells, indicating that they were also inhibiting AK in intact cells. The drug concentrations at which these effects were observed showed limited toxicity to the cultured cells, indicating that these effects are not caused by cellular toxicity. These results indicate that the enzyme AK provides an additional cellular target for the clinically widely used bisphosphonates and related compounds, which could possibly be exploited for a new therapeutic application. Our structure-activity studies on different AK activators and inhibitors also indicate that all of the AK activating compounds have a higher partial positive charge (delta(+)) on the central phosphorous atom in comparison to the inhibitors. This information should prove helpful in the design and synthesis of more potent inhibitors of AK. PMID:16444581

Park, Jae; Singh, Bhag; Gupta, Radhey S

2006-02-01

395

Structure and mechanism of HpcH: a metal ion dependent class II aldolase from the homoprotocatechuate degradation pathway of Escherichia coli.  

PubMed

Microorganisms are adept at degrading chemically resistant aromatic compounds. One of the longest and most well characterized aromatic catabolic pathways is the 4-hydroxyphenylacetic acid degradation pathway of Escherichia coli. The final step involves the conversion of 4-hydroxy-2-oxo-heptane-1,7-dioate into pyruvate and succinic semialdehyde. This reaction is catalyzed by 4-hydroxy-2-oxo-heptane-1,7-dioate aldolase (HpcH), a member of the divalent metal ion dependent class II aldolase enzymes that have great biosynthetic potential. We have solved the crystal structure of HpcH in the apo form, and with magnesium and the substrate analogue oxamate bound, to 1.6 A and 2.0 A, respectively. Comparison with similar structures of the homologous 2-dehydro-3-deoxygalactarate aldolase, coupled with site-directed mutagenesis data, implicate histidine 45 and arginine 70 as key catalytic residues. PMID:17881002

Rea, Dean; Flp, Vilmos; Bugg, Timothy D H; Roper, David I

2007-11-01

396

The value of adenosine test in the diagnosis of sick sinus syndrome: susceptibility of sinus and atrioventricular node to adenosine in patients with sick sinus syndrome and unexplained syncope  

Microsoft Academic Search

Aims Patients (pts) with sick sinus syndrome (SSS) and unexplained syncope show increased suscepti- bility of sinus and atrioventricular node (AVN) to intravenous adenosine, respectively. Our aim is to assess the diagnostic value of adenosine test in pts with SSS, as well as to evaluate the response of AVN to adenosine either in pts with unexplained syncope or in pts

Nikolaos Fragakis; Ilias Iliadis; Emmanouil Sidopoulos; Alexandra Lambrou; Evangelos Tsaritsaniotis; George Katsaris

397
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