mrs-1191 and Myocardial-Ischemia

Extracellular adenosine concentrations increase within the heart during ischemia, and any exogenous adenosine receptor agonists therefore work in the context of significant local agonist concentrations. We evaluated the interactions between A1, A2A, A2B, and A3 receptors in the presence and absence of adenosine deaminase (ADA, which is used to remove endogenous adenosine) in a cardiac cell ischemia model. Simulated ischemia (SI) was induced by incubating H9c2(2-1) cells in SI medium for 12 hours in 100% N2 gas before assessment of necrosis using propidium iodide (5 microM) or apoptosis using AnnexinV-PE flow cytometry. N6-Cyclopentyladenosine (CPA; 10(-7)M) and N6-(3-iodobenzyl) adenosine-5'-N-methyluronamide (IB-MECA; 10(-7)M) reduced the proportion of nonviable cells to 30.87 +/- 2.49% and 35.18 +/- 10.30%, respectively (% of SI group). In the presence of ADA, the protective effect of CPA was reduced (62.82 +/- 3.52% nonviable), whereas the efficacy of IB-MECA was unchanged (35.81 +/- 3.84% nonviable; P < 0.05, n = 3-5, SI vs. SI + ADA). The protective effects of CPA and IB-MECA were abrogated in the presence of their respective antagonists DPCPX (8-cyclopentyl-1,3-dipropylxanthine) and MRS1191 [3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate], whereas A2A and A2B agonists had no significant effect. CPA-mediated protection was abrogated in the presence of both A2A (ZM241385, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-lamino]ethyl)phenol; 50 nM) and A2B (MRS1754, 8-[4-[((4-cyanophenyl)carbamoylmethyl)oxy]phenyl]-1,3-di(n-propyl)xanthine; 200 nM) antagonists (n = 3-5, P < 0.05). In the absence of endogenous adenosine, significant protection was observed with CPA in presence of CGS21680 (4-[2-[[6-amino-9-(N-ethyl-b-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid) or LUF5834 [2-amino-4-(4-hydroxyphenyl)-6-(1H-imidazol-2-ylmethylsulfanyl)pyridine-3,5-dicarbonitrile] (P < 0.05 vs. SI + ADA + CPA). Apoptosis (14.35 +/- 0.15% of cells in SI + ADA group; P < 0.05 vs. control) was not significantly reduced by CPA or IB-MECA. In conclusion, endogenous adenosine makes a significant contribution to A1 agonist-mediated prevention of necrosis in this SI model by cooperative interactions with both A2A and A2B receptors but does not play a role in A3 agonist-mediated protection.

Topics: Acetamides; Adenosine; Adenosine A1 Receptor Agonists; Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Adenosine A3 Receptor Agonists; Adenosine A3 Receptor Antagonists; Aminopyridines; Animals; Apoptosis; Cardiotonic Agents; Cell Line; Cell Survival; Dihydropyridines; Imidazoles; Myocardial Ischemia; Phenethylamines; Purines; Rats; Triazines; Triazoles; Xanthines

Adenosine released during cardiac ischemia exerts a potent, protective effect in the heart. A newly recognized adenosine receptor, the A3 subtype, is expressed on the cardiac ventricular cell, and its activation protects the ventricular heart cell against injury during a subsequent exposure to ischemia. A cultured chicken ventricular myocyte model was used to investigate the cardioprotective role of a novel adenosine A3 receptor. The protection mediated by prior activation of A3 receptors exhibits a significantly longer duration than that produced by activation of the adenosine A1 receptor. Prior exposure of the myocytes to brief ischemia also protected them against injury sustained during a subsequent exposure to prolonged ischemia. The adenosine A3 receptor-selective antagonist 3-ethyl 5-benzyl-2-methyl-6-phenyl-4-phenylethynyl-1, 4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS1191) caused a biphasic inhibition of the protective effect of the brief ischemia. The concomitant presence of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) converted the MRS1191-induced dose inhibition curve to a monophasic one. The combined presence of both antagonists abolished the protective effect induced by the brief ischemia. Thus, activation of both A1 and A3 receptors is required to mediate the cardioprotective effect of the brief ischemia. Cardiac atrial cells lack native A3 receptors and exhibit a shorter duration of cardioprotection than do ventricular cells. Transfection of atrial cells with cDNA encoding the human adenosine A3 receptor causes a sustained A3 agonist-mediated cardioprotection. The study indicates that cardiac adenosine A3 receptor mediates a sustained cardioprotective function and represents a new cardiac therapeutic target.

Topics: Adenosine; Animals; Chick Embryo; Dihydropyridines; Gene Transfer Techniques; Humans; Myocardial Ischemia; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Receptor, Adenosine A3; Receptors, Purinergic P1; Ventricular Function; Xanthines