A₃ adenosine receptor activation during reperfusion reduces infarct size through actions on bone marrow-derived cells

The goal of this study was to examine whether the A₃ adenosine receptor (A₃AR) agonist Cl-IB-MECA protects against myocardial ischemia/reperfusion injury when administered at the time of reperfusion in an in vivo mouse model of infarction induced by 30min of coronary occlusion and 24h of reperfusion. Treating B6 wild-type with Cl-IB-MECA during the reperfusion phase (100μg/kg i.v. bolus+0.3μg/kg/min subcutaneously via implantation of Alzet mini-osmotic pumps) reduced myocardial infarct size ~37% from 50.1±2.5% in vehicle-treated mice to 31.6±2.8% in Cl-IB-MECA-treated mice, and significantly reduced the number of leukocytes that infiltrated into the ischemic-reperfused myocardium. Cl-IB-MECA did not reduce infarct size or limit leukocyte accumulation in studies using B6 congenic A₃AR gene "knock-out" mice or in chimeric mice lacking the expression of A₃ARs in bone marrow (BM)-derived cells. Subsequent mechanistic studies demonstrated that Cl-IB-MECA inhibited migration of mouse neutrophils isolated from BM towards the chemotactic substance c5a in trans-well migration assays, and inhibited leukocyte migration into the peritoneal cavity in a mouse model of thioglycollate-induced peritonitis. We conclude that treating with the A₃AR agonist Cl-IB-MECA at the time of reperfusion provides effective protection from ischemia/reperfusion injury in the heart through activation of the A₃AR expressed in BM-derived cells, potentially by suppressing the robust inflammatory reaction that occurs during reperfusion and neutrophil-mediated tissue injury.