adenosine-5--(n-ethylcarboxamide) and Myocardial-Infarction

While it is well known that adenosine receptor activation protects the heart from ischemia/reperfusion injury, the precise mitochondrial mechanism responsible for the action remains unknown. This study probed the mitochondrial events associated with the cardioprotective effect of 5'-(N-ethylcarboxamido) adenosine (NECA), an adenosine A

Topics: Adenosine-5'-(N-ethylcarboxamide); Animals; Electron Transport Complex I; Humans; Membrane Potential, Mitochondrial; Mitochondria; Mutation; Myocardial Infarction; Myocardial Reperfusion Injury; Myocytes, Cardiac; NADH Dehydrogenase; Oxidative Stress; Purines; Pyrimidines; Rats; Receptors, Adenosine A2; Triazoles

Pre- and postconditioning depend on the activation of adenosine receptors (ARs) at the end of the index ischemia. The aim of this study was to determine which receptor subtypes must be activated. In situ mouse hearts underwent 30 min of regional ischemia, followed by 2 h of reperfusion. As expected, either ischemic postconditioning (6 cycles of 10 s of reperfusion and 10 s of coronary occlusion) or infusion of the selective A(2b) adenosine receptor (A(2b)AR) agonist BAY60-6583 (BAY60) for 60 min, starting 5 min before reperfusion reduced infarct size in wild-type C57Bl/6N mice. Protection from either was abolished by the selective A(2b)AR antagonist MRS-1754, confirming a role for A(2b)AR. Additionally, the coadministration of ischemic postconditioning and a selective A(2a)AR antagonist led to the loss of protection as well. 5'-Ectonucleotidase (CD73) is thought to be necessary for the production of adenosine during ischemia. As predicted, ischemic postconditioning did not protect CD73 knockout mice. Selective agonists of either A(2b)AR (BAY60) or A(2a)AR (CGS-21680), as well as the coadministration of ischemic postconditioning and BAY60, also failed to protect hearts of the CD73 knockout mice. But the nonselective A(1)/A(2)AR agonist 5'-(N-ethylcarboxamido)adenosine (NECA) was protective, suggesting that the activation of multiple AR subtypes might be required. The coadministration of CGS-21680 and BAY60 also elicited profound protection, indicating that two AR subtypes, A(2a) and A(2b), must be simultaneously activated for protection to occur.

Topics: 5'-Nucleotidase; Acetamides; Adenosine; Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Adenosine-5'-(N-ethylcarboxamide); Aminopyridines; Animals; Mice; Mice, Inbred C57BL; Mice, Knockout; Models, Animal; Myocardial Infarction; Myocardial Reperfusion Injury; Phenethylamines; Purines; Receptor, Adenosine A2A; Receptor, Adenosine A2B

Although protein kinase C (PKC) plays a key role in ischemic preconditioning (IPC), the actual mechanism of that protection is unknown. We recently found that protection from IPC requires activation of adenosine receptors during early reperfusion. We, therefore, hypothesized that PKC might act to increase the heart's sensitivity to adenosine. IPC limited infarct size in isolated rabbit hearts subjected to 30-min regional ischemia/2-h reperfusion and IPC's protection was blocked by the PKC inhibitor chelerythrine given during early reperfusion revealing involvement of PKC at reperfusion. Similarly chelerythrine infused in the early reperfusion period blocked the increased phosphorylation of the protective kinases Akt and ERK1/2 observed after IPC. Infusing phorbol 12-myristate 13-acetate (PMA), a PKC activator, during early reperfusion mimicked IPC's protection. As expected, the protection triggered by PMA at reperfusion was blocked by chelerythrine, but surprisingly it was also blocked by MRS1754, an adenosine A(2b) receptor-selective antagonist, suggesting that PKC was somehow facilitating signaling from the A(2b) receptors. NECA [5'-(N-ethylcarboxamido) adenosine], a potent but not selective A(2b) receptor agonist, increased phosphorylation of Akt and ERK1/2 in a dose-dependent manner. Pretreating hearts with PMA or brief preconditioning ischemia had no effect on phosphorylation of Akt or ERK1/2 per se but markedly lowered the threshold for NECA to induce their phosphorylation. BAY 60-6583, a highly selective A(2b) agonist, also caused phosphorylation of ERK1/2 and Akt. MRS1754 prevented phosphorylation induced by BAY 60-6583. BAY 60-6583 limited infarct size when given to ischemic hearts at reperfusion. These results suggest that activation of cardiac A(2b) receptors at reperfusion is protective, but because of the very low affinity of the receptors endogenous cardiac adenosine is unable to trigger their signaling. We propose that the key protective event in IPC occurs when PKC increases the heart's sensitivity to adenosine so that endogenous adenosine can activate A(2b)-dependent signaling.

Topics: Acetamides; Adenosine A2 Receptor Agonists; Adenosine-5'-(N-ethylcarboxamide); Alkaloids; Aminopyridines; Animals; Benzophenanthridines; Ischemic Preconditioning, Myocardial; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Myocardial Infarction; Myocardial Reperfusion Injury; Perfusion; Phosphorylation; Protein Kinase C; Purines; Rabbits; Receptor, Adenosine A2B; Signal Transduction; Tetradecanoylphorbol Acetate

Ischemic postconditioning protects the reperfused heart from infarction, and this protection is dependent on the occupancy of adenosine receptors. We further explored the role of adenosine receptors in this salvage.. In situ rabbit hearts underwent 30 min of regional ischemia and 3 h of reperfusion, and postconditioning was effected with four cycles of 30-s reperfusion/30-s coronary artery occlusion at the end of ischemia.. Postconditioning reduced infarct size from 40.2+/-3.4% of the risk zone in untreated hearts to 15.5+/-2.5%. Protection by postconditioning was blocked by either the non-selective adenosine receptor blocker 8-p-(sulfophenyl)theophylline or the A2b-selective antagonist MRS 1754, injected intravenously 5 min before reperfusion. The protein kinase C (PKC) antagonist chelerythrine also aborted postconditioning's salvage, indicating a PKC-dependent mechanism. Neither the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine nor the A2a-selective antagonist 8-(13-chlorostyryl)caffeine had an effect on protection. The non-selective but A2b-potent adenosine agonist 5'-(N-ethylcarboxamido)adenosine (NECA) infused from 5 min before to 1h after reperfusion mimicked postconditioning's effect on infarct size (17.2+/-2.7% infarction) and MRS 1754 blocked the NECA-induced cardioprotection, confirming that A2b activation was protective. The PKC activator phorbol 12-myristate 13-acetate delivered just before reperfusion also duplicated the protective effect of postconditioning (16.3+/-4.1% infarction), and co-administration of the PKC antagonist chelerythrine aborted PMA's protection, confirming that the protection was the result of PKC activation. NECA's protective effect was not affected by chelerythrine, but rather MRS 1754 blocked PMA's salutary effect (42.8+/-1.0% infarction), suggesting that the A2b receptor's effect is under control of PKC. Finally, wortmannin, a blocker of phosphatidylinositol 3-kinase, also abrogated protection by PMA.. Salvage of ischemic myocardium by postconditioning is dependent on activation of A2b receptors, which in turn depends on activation of PKC. It is still unclear why PKC activation is required to make the heart's adenosine become protective.

Topics: Acetamides; Adenosine; Adenosine A2 Receptor Antagonists; Adenosine-5'-(N-ethylcarboxamide); Alkaloids; Androstadienes; Animals; Aorta; Benzophenanthridines; Constriction; Enzyme Activators; Female; Male; Myocardial Infarction; Myocardial Reperfusion Injury; Myocardium; Perfusion; Phenanthridines; Phosphoinositide-3 Kinase Inhibitors; Protein Kinase C; Purines; Rabbits; Receptor, Adenosine A2B; Signal Transduction; Tetradecanoylphorbol Acetate; Wortmannin; Xanthines

The A1/A2 adenosine agonist 5'-(N-ethylcarboxamido) adenosine (NECA) limits infarction when administered at reperfusion. The present study investigated whether p70S6 kinase is involved in this anti-infarct effect. Adult rat ventricular myocytes were isolated and incubated in tetramethylrhodamine ethyl ester (TMRE, 100 nM), which causes cells to fluoresce in proportion to their mitochondrial membrane potential. A reduction in TMRE fluorescence serves as an indicator of collapse of the mitochondrial transmembrane potential. Cells were subjected to H2O2 (200 microM), which like ischemia induces loss of mitochondrial membrane potential. Fluorescence was measured every 3 min and to facilitate quantification membrane potential was arbitrarily considered as collapsed when fluorescence reached less than 60% of the starting value. Adding NECA (1 mM) to the cells prolonged the time to fluorescence loss (48.0+/-3.2 min in the NECA group versus 29.5+/-2.2 min in untreated cells, P<0.001) and the mTOR/p70S6 kinase inhibitor rapamycin (5 nM) abolished this protection (31.3+/-3.4 min). Since cyclosporine A offered similar protection, mitochondrial permeability transition pore formation is a likely cause of the H2O2-induced loss of potential. The direct GSK-3beta inhibitor SB216763 (3 microM) also prolonged the time to fluorescence loss (49.2+/-2.1 min, P<0.001 versus control), and its protection could not be blocked by rapamycin (42.2+/-2.3 min, P<0.001 versus control). NECA treatment (100 nM) of intact isolated rabbit hearts at reperfusion after 30 min of regional ischemia decreased infarct size from 33.0+/-3.8% of the risk zone in control hearts to 11.8+/-2.0% (P<0.001), and rapamycin blocked this NECA-induced protection (38.3+/-3.7%). A comparable protective effect was seen for SB216763 (1 microM) with infarct size reduction to 13.5+/-2.3% (P<0.001). NECA treatment (200 nM) of intact rabbit hearts at reperfusion also resulted in phosphorylation of p70S6 kinase more than that seen in untreated hearts. This NECA-induced phosphorylation was blocked by rapamycin. These experiments reveal a critical role for p70S6 kinase in the signaling pathway of NECA's cardioprotection at reperfusion.

Topics: Adenosine-5'-(N-ethylcarboxamide); Animals; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Hydrogen Peroxide; In Vitro Techniques; Membrane Potentials; Mitochondrial Membrane Transport Proteins; Mitochondrial Membranes; Mitochondrial Permeability Transition Pore; Myocardial Infarction; Myocytes, Cardiac; Phosphorylation; Rabbits; Rats; Rats, Wistar; Reperfusion Injury; Ribosomal Protein S6 Kinases, 70-kDa; Vasodilator Agents

Stimulation of adenosine A1 receptors is known to reduce infarct size in the rabbit heart. The aim of the present study was to verify whether a protective activity similar to that of the selective A1 receptor agonist, 2-chloro-N6-cyclopentyladenosine (CCPA), could also be obtained by inducing comparable hemodynamic effects with drugs having different mechanisms of action. The effects of the beta-adrenoceptor blocker atenolol, the calcium channel blocker felodipine, the A2A-selective adenosine receptor agonist 2-hexynyl-5'-N-ethyl-carboxamidoadenosine (2HE-NECA), and the non-selective adenosine receptor agonist 5'-N-ethyl-carboxamidoadenosine (NECA) were tested. Groups of 12-15 anesthetized open-chest rabbits received a 5-min infusion of CCPA (50 micrograms kg-1 min-1), atenolol (1 mg kg-1 min-1), felodipine (50 micrograms kg-1 min-1), 2HE-NECA (1 microgram kg-1 min-1), and NECA ( 1 microgram kg-1 min-1). Myocardial infarction was induced by a 30-min occlusion of a branch of the left coronary artery, followed by 3-h reperfusion. Infarct size was measured by tetrazolium staining. In controls, infarct size was about 40% of the zone at risk. Pretreatment with CCPA induced a marked decrease in heart rate (-40%) and blood pressure (-48%), and showed antiischemic activity (28% of the zone at risk). The other drugs tested produced similar effects on either heart rate (atenolol, -25%), or blood pressure (felodipine, 2HE-NECA and NECA, about -45%), but did not affect infarct size. IN this model, the reduction in infarct size by CCPA is most likely mediated by A1 receptors, since comparable hemodynamic effects, induced by other means, are not effective. A2A receptor stimulation does not appear to exert a protective effect.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Analysis of Variance; Animals; Antihypertensive Agents; Atenolol; Calcium Channel Blockers; Felodipine; Hemodynamics; Male; Myocardial Infarction; Purinergic P1 Receptor Agonists; Rabbits; Vasodilator Agents