Adenosine attenuates reperfusion-induced apoptotic cell death by modulating expression of Bcl-2 and Bax proteins

This study tests the hypothesis that infarct reduction with adenosine (Ado) is associated with inhibition of apoptotic cell death by modulating expression of anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins and reducing neutrophil accumulation. In three groups of dogs, the left anterior descending coronary artery was occluded for 60 min and reperfused for 6 h. Either saline (Control, n = 8), Ado (140 mug/kg/min, n = 8) or CGS21680, an adenosine A(2A) receptor analogue, (0.2 mug/kg/min, n = 7) were infused during the first 2 h of reperfusion. Myocardial apoptosis was detected by histological TUNEL staining and DNA laddering. Expression of Bcl-2 and Bax proteins was analyzed using Western blot assay, Neutrophil localization was detected by immunohistochemistry with monoclonal anti-neutrophil CD18 antibody. There was no group difference in collateral blood now (colored microspheres) during ischemia. Intra-left atrial administration of Ado and CGS21680 significantly decreased infarct size from 26 +/- 2% in Control to 13 +/- 1%* and 16 +/- 3%*, respectively. TUNEL positive cells in the peri-necrotic zone of the ischemic myocardium were also significantly reduced from 16 +/- 2% in Control group to 9 +/- 1%* and 10 +/- 2%*, respectively, consistent with the absence of DNA laddering in these two groups. Densitometrically, Ado and CGS21680 at reperfusion significantly increased the expression (% of normal myocardium) of downregulated Bcl-2 from 45 +/- 6% in Control group to 78 +/- 12%* and 69 +/- 10%*, respectively, and attenuated expression of upregulated Bax from 198 +/- 16% in Control group to 148 +/- 10%* and 158 +/- 12%*, respectively. Furthermore, the number of positive CD18 cells (mm(2) myocardium), which was significantly correlated with TUNEL positive cells in peri-necrotic zone, was significantly reduced from 403 +/- 42 in Control group to 142 +/- 18* in Ado group and 153 +/- 20%* in CGS21680 group, respectively. In conclusion, the present study suggests that inhibition of apoptosis by Ado at reperfusion involves alterations in anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins and neutrophil accumulation, primarily mediated by an adenosine A(2A) receptor. *P<0.05 v Control group. (C) 2000 Academic Press.