2-(4-(2-carboxyethyl)phenethylamino)-5--n-ethylcarboxamidoadenosine and Ischemia

The aim of the present study was to explore whether endogenous activation of different purine receptors by ATP and adenosine contributes to or inhibits excess glutamate release evoked by ischemic-like conditions in rat hippocampal slices. Combined oxygen-glucose deprivation (OGD) elicited a substantial, [Ca(2+)](o)-independent release of [(3)H]glutamate, which was tetrodotoxin (1 microM)-sensitive and temperature-dependent. The P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, 0.1-10 microM), and the selective P2X(7) receptor antagonist Brilliant Blue G (1-100 nM), decreased OGD-evoked [(3)H]glutamate efflux indicating that endogenous ATP facilitates ischemia-evoked glutamate release. The selective A(1)-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 0.1-250 nM) and the selective A(2A) receptor antagonists 4-(2-[7-amino-2-)2-furyl(triazolo-[1,3,5]triazin-5-ylamino]ethyl)phenol (ZM241385, 0.1-20 nM) and 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH58261, 2-100 nM) decreased OGD-evoked [(3)H]glutamate efflux, indicating that endogenous adenosine also facilitates glutamate release under these conditions. The effect of DPCPX and ZM241385 was reversed, whereas the action of P2 receptor antagonists was potentiated by the selective ecto-ATPase inhibitor 6-N,N-diethyl-D-beta,gamma-dibromomethyleneATP (ARL67156, 50 microM). The binding characteristic of the A(2A) ligand [(3)H]CGS21680 to hippocampal membranes did not change significantly in response to OGD. Taken together these data suggest that while A(1) receptors might became desensitized, A(2A) and P2X receptor-mediated facilitation of glutamate release by endogenous ATP and its breakdown product adenosine remains operational under long-term OGD. Therefore the inhibition of P2X/A(2A) receptors rather than the stimulation of A(1) adenosine receptors could be an effective approach to attenuate glutamatergic excitotoxicity and thereby counteract ischemia-induced neurodegeneration.

Topics: Adenosine; Adenosine Triphosphate; Analgesics; Animals; Dose-Response Relationship, Drug; Glucose; Glutamic Acid; Hippocampus; Hypoxia; In Vitro Techniques; Ischemia; Male; Phenethylamines; Purinergic Agonists; Purinergic Antagonists; Pyrimidines; Rats; Rats, Wistar; Receptors, Purinergic; Sodium Channel Blockers; Tetrodotoxin; Triazines; Triazoles; Xanthines

Selective A(1)adenosine receptor agonists produced a considerable neuroprotective effect during global cerebral ischemia. The neuroprotective effect decreased in the order: A(1)agonists-NECA-adenosine-A(2A)agonist CGS 21680, while selective A(3)adenosine receptor agonist was ineffective. Inhibitory analysis showed that A(1)adenosine receptors mediate the neuroprotective effect of CPA, are involved in the effects of NECA and adenosine (but not CGS 21680), and participate in natural resistance to cerebral ischemia. The role of A(2B)adenosine receptors in the realization of neuroprotective effects was also demonstrated.

Topics: Adenosine; Animals; Antihypertensive Agents; Brain Ischemia; Dose-Response Relationship, Drug; Female; Ischemia; Male; Mice; Neurons; Phenethylamines; Receptors, Purinergic P1

To examine whether adenosine reduces ischemia/reperfusion (I/R)-induced liver injury by inhibiting leukocyte activation via A(2) receptor (A(2)R) stimulation, we investigated the effects of adenosine and selective A(2A) receptor (A(2A)R) agonists (YT-146 and CGS21680C) on I/R-induced liver injury in rats. Adenosine, YT-146, and CGS21680C, in the concentration of 10(-7) to 10(-5) M, significantly inhibited neutrophil elastase release by about 30 to 40% and increased intracellular Ca(2+) concentrations in isolated neutrophils stimulated with formyl-methionyl-leucyl-phenylalanine (fMLP) in vitro. Adenosine, YT-146, and CGS21680C, in the concentration of 10(-7) to 10(-5) M, significantly inhibited tumor necrosis factor (TNF)-alpha production by monocytes stimulated with endotoxin by about 50%. Although ZM241385, a selective A(2A)R antagonist, significantly enhanced the increase in neutrophil elastase release and intracellular Ca(2+) concentrations in neutrophils stimulated with fMLP, this agent did not affect the endotoxin-induced TNF-alpha production by monocytes. Rats were subjected to liver ischemia for 60 min. Serum levels of transaminases increased after hepatic I/R, peaking at 12 h after reperfusion. The i.v. infusion of adenosine (1 and 10 mg/kg/h), YT-146 (0.1 and 1 mg/kg/h), and CGS21680C (0.1 and 1 mg/kg/h) significantly inhibited the I/R-induced increase in serum transaminase levels 12 h after reperfusion. The I/R-induced decrease in hepatic tissue blood flow was significantly prevented by adenosine and YT-146. Hepatic levels of TNF-alpha, cytokine-induced neutrophil chemoattractant (equivalent to human interleukin-8), and myeloperoxidase were significantly increased after I/R. These increases were significantly inhibited by the administration of adenosine, YT-146, and CGS21680C. Although the histological neutrophil accumulation in the liver was significantly increased after I/R as evaluated by the naphthol AS-D chloroacetate technique, the administration of adenosine, YT-146, and CGS21680C significantly inhibited this increase. These findings suggest that adenosine reduces I/R-induced liver injury both by inhibiting the synthesis of inflammatory mediators and by inhibiting neutrophil degranulation directly, probably through A(2A)R stimulation.

Topics: Adenosine; Alkynes; Animals; Calcium; Cells, Cultured; Chemokine CXCL1; Chemokines, CXC; Chemotactic Factors; Growth Substances; Humans; Intercellular Signaling Peptides and Proteins; Ischemia; Leukocyte Elastase; Lipopolysaccharides; Liver; Male; Monocytes; Neutrophil Activation; Peroxidase; Phenethylamines; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Rats; Rats, Wistar; Receptor, Adenosine A2A; Reperfusion Injury; Triazines; Triazoles; Tumor Necrosis Factor-alpha

The adhesion of leukocytes to the endothelium of postcapillary venules hallmarks a key event in ischemia-reperfusion injury. Adenosine has been shown to protect from postischemic reperfusion injury, presumably through inhibition of postischemic leukocyte-endothelial interaction. This study was performed to investigate in vivo by which receptors the effect of adenosine on postischemic leukocyte-endothelium interaction is mediated. The hamster dorsal skinfold model and fluorescence microscopy were used for intravital investigation of red cell velocity, vessel diameter, and leukocyte-endothelium interaction in postcapillary venules of a thin striated skin muscle. Leukocytes were stained in vivo with acridine orange (0.5 mg kg-1 min-1 i.v.). Parameters were assessed prior to induction of 4 h ischemia to the muscle tissue and 0.5 h, 2 h, and 24 h after reperfusion. Adenosine, the adenosine A1-selective agonist 2-chloro-N6-cyclopentyladenosine (CCPA), the A2-selective agonist CGS 21,680, the non-selective adenosine receptor antagonist xanthine amine congener (XAC), and the adenosine uptake blocker S-(p-nitrobenzyl)-6-thioinosine (NBTI) were infused via jugular vein starting 15 min prior to release of ischemia until 0.5 h after reperfusion. Adenosine and CGS 21,680 significantly reduced postischemic leukocyte-endothelium interaction 0.5 h after reperfusion (p less than 0.01), while no inhibitory effect was observed with CCPA. Coadministration of XAC blocked the inhibitory effects of adenosine. Infusion of NBTI alone effectively decreased postischemic leukocyte-endothelium interaction. These findings indicate that adenosine reduces post-ischemic leukocyte-endothelium interaction via A2 receptor and suggest a protective role of endogenous adenosine during ischemia-reperfusion.

Topics: Adenosine; Animals; Cell Adhesion; Cricetinae; Endothelium, Vascular; Ischemia; Leukocytes; Mesocricetus; Muscles; Phenethylamines; Receptors, Purinergic; Reperfusion Injury; Thioinosine; Xanthines