Cl-IB-MECA [2-Chloro-N6-(3-iodobenzyl)adenosine-5'-N-methylcarboxamide] Reduces Ischemia/Reperfusion Injury in Mice by Activating the A Adenosine Receptor

Abstract

We used pharmacological agents and genetic methods to determine whether the potent A3 adenosine receptor (AR) agonist 2-chloro-N6-(3-iodobenzyl)adenosine-5 -N-methylcarboxamide (Cl-IB-MECA) protects against myocardial ischemia/ reperfusion injury in mice via the A3AR or via interactions with other AR subtypes. Pretreating wild-type (WT) mice with Cl-IBMECA reduced myocardial infarct size induced by 30 min of coronary occlusion and 24 h of reperfusion at doses (30 and 100 姯kg) that concomitantly reduced blood pressure and stimulated systemic histamine release. The A3AR-selective antagonist MRS 1523 [3-propyl-6-ethyl-5[(ethylthio)carbonyl]-2-phenyl-4-propyl-3-pyridine-carboxylate], but not the A2AAR antagonist ZM 241385 [4-{2-7-amino-2-(2-furyl)[1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-ylamino]ethyl}phenol], blocked the reduction in infarct size provided by Cl-IB-MECA, suggesting a mechanism involving the A3AR. To further examine the selectivity of Cl-IB-MECA, we assessed its cardioprotective effectiveness in A3AR gene "knock-out" (A3KO) mice. Cl-IB-MECA did not reduce myocardial infarct size in A3KO mice in vivo and did not protect isolated perfused hearts obtained from A3KO mice from injury induced by global ischemia and reperfusion. Additional studies using WT mice treated with compound 48/80 [condensation product of ?-methoxyphenethyl methylamine with formaldehyde] to deplete mast cell contents excluded the possibility that Cl-IB-MECA was cardioprotective by releasing mediators from mast cells. These data demonstrate that Cl-IBMECA protects against myocardial ischemia/reperfusion injury in mice principally by activating the A3AR.