POSSIBLE INVOLVEMENT OF STRESS-ACTIVATED PROTEIN-KINASE SIGNALING PATHWAY AND FAS RECEPTOR EXPRESSION IN PREVENTION OF ISCHEMIA REPERFUSION-INDUCED CARDIOMYOCYTE APOPTOSIS BY CARVEDILOL/

Carvedilol, a new vasodilating beta-adrenoceptor antagonist and a pote nt antioxidant, produces a high degree of cardioprotection in a variet y of experimental models of ischemic cardiac injury. Recent clinical s tudies in patients with heart failure have demonstrated that carvedilo l reduces morbidity and mortality and inhibits cardiac remodeling. The present study was designed to explore whether the protective effects of carvedilol on the ischemic myocardium include inhibition of apoptos is of cardiomyocytes and, if so, to determine its mechanism of action. Anesthetized rabbits were subjected to 30 minutes of coronary artery occlusion followed by 4 hours of reperfusion. Detection of apoptosis o f cardiomyocytes was based on the presence of nucleosomal DNA fragment s on agarose gels (DNA ladder) and in situ nick end labeling. Carvedil ol (1 mg/kg IV), administered 5 minutes before reperfusion, reduced th e number of apoptotic myocytes in the ischemic area from 14.7+/-0.4% t o 3.4+/-1.8% (77% reduction, P<.001). Propranolol, administered at equ ipotent beta-blocking dosage, reduced the number of apoptotic myocytes to 8.9+/-2.1% (39% reduction, P<.05). DNA ladders were observed in th e hearts of all six vehicle-treated rabbits but only one of six carved ilol-treated rabbits (P<.01). Immunocytochemical analysis of rabbit he arts demonstrated an upregulation of Fas protein in ischemic cardiomyo cytes, and treatment with carvedilol reduced both the intensity of sta ining as well as the area stained. Myocardial ischemia/reperfusion led to a rapid activation of stress-activated protein kinase (SAPK) in th e ischemic area but not in nonischemic regions. SAPK activity was incr eased from 2.1+/-0.3 mU/mg (basal) to 8.9+/-0.8 mU/mg after 30 minutes of ischemia followed by 20 minutes of reperfusion. Carvedilol inhibit ed the activation of SAPK by 53.4+/-6.5% (P<.05). Under the same condi tions, propranolol (1 mg/kg) had no effect on SAPK activation. Taken t ogether, these results suggest that carvedilol prevents myocardial isc hemia/reperfusion-induced apoptosis in cardiomyocytes possibly by down regulation of the SAPK signaling pathway, by inhibition of Fas recepto r expression, and by beta-adrenergic blockade. The former two actions represent novel and important mechanisms that may contribute to the ca rdioprotective effects of carvedilol.