A2 Adenosine Receptor-mediated Cardioprotection Against Reperfusion Injury in Rat Hearts Is Associated With Autophagy Downregulation

This study was undertaken to determine and confer the cardioprotective effects of the adenosine A2 receptor (A2AR) and its impact on myocardial autophagy in the setting of reperfusion. We established a rat ischemia model by subjecting rats to 30 minutes of ischemia (I) and 120 minutes of reperfusion (R). The A2AR agonists CGS21680 (A2aAR specific) and BAY60-6583 (A2bAR specific) were administered separately and in combination 5 minutes before reperfusion (postconditioning). No visible improvements in the rats' hemodynamic changes in response to either CGS or BAY were observed compared with untreated control groups (I/R). BAY significantly reduced infarct sizes, whereas CGS did not. Electron microscopy, enzyme-linked immunosorbent assay and TUNEL apoptosis staining results demonstrated that CGS and BAY play cardioprotective roles by maintaining mitochondria structural stability, decreasing serum cardiac troponin I (cTnI) concentrations and decreasing the number of apoptotic cells. CGS21680 and BAY60-6583 slightly increased the expression (vs. I/R group) of Bcl-2 and significantly attenuated the expression of Beclin-1, LC3B, and LAMP-2, as analyzed by Western blot, compared with the I/R alone group. Notably, BAY60-6583 exerts a predominant effect on mitochondria structural stabilization, apoptotic inhibition, and attenuation of LC3B/LAMP-2 expression. No synergistic effects were observed for the 2 agonists. Our data suggest that A2AR-mediated cardioprotection is associated with Beclin-1-induced autophagy downregulation in the setting of reperfusion. A2bAR activation exerts stronger cardioprotective effects against I/R injury compared with A2aAR.