Role of Mitochondrial Cytochrome c in Cocaine-Induced Apoptosis in Coronary Artery Endothelial Cells

Cocaine induces apoptosis in coronary artery endothelial cells. Yet the cellular and molecular mechanisms are not clear. Given that cocaine has profound toxic effects on the mitochondria, the present study examined the role of mitochondrial cytochrome c in cocaine-mediated apoptosis. Using cultured bovine coronary artery endothelial cells, we found that cocaine-induced apoptosis was dose dependently inhibited by cyclosporin A with IC50 of 0.2 μM. The maximum of 65% inhibition was obtained with 3 μM cyclosporin A. Cocaine induced a translocation of cytochrome c from the mitochondria to the cytosol with a 1.8-fold increase in cytosolic cytochrome c levels, and a corresponding decrease in mitochondrial cytochrome c . In accordance with its inhibition of cocaine-induced apoptosis, cyclosporin A blocked cocaine-induced cytochrome c translocation. Correspondingly, cocaine-induced activation of caspase-9 preceded that of caspase-3. Caspase-8 was not activated. Cocaine also produced a dose-dependent decrease in Bcl-2 protein levels, but had no effect on Bax protein levels. The cocaine-induced decrease in the Bcl-2 protein was not affected by cyclosporin A but was partially blocked by caspase-3 inhibitor Ac-DEVD-CHO. Collectively, these data indicate that the release of cytochrome c from the mitochondria and the subsequent activation of caspase-9 and caspase-3 play a key role in cocaine-induced apoptosis in these cells. Furthermore, the down-regulation of the Bcl-2 protein may play an important role in cocaine-induced release of cytochrome c .