Role of mitochondrial cytochrome c in cocaine-induced apoptosis in coronary artery endothelial cells

Cocaine induces apoptosis in coronary artery endothelial cells. Yet the cel lular and molecular mechanisms are not clear. Given that cocaine has profou nd toxic effects on the mitochondria, the present study examined the role o f mitochondrial cytochrome c in cocaine-mediated apoptosis. Using cultured bovine coronary artery endothelial cells, we found that cocaine-induced apo ptosis was dose dependently inhibited by cyclosporin A with IC50 of 0.2 muM . The maximum of 65% inhibition was obtained with 3 muM cyclosporin A. Coca ine induced a translocation of cytochrome c from the mitochondria to the cy tosol with a 1.8-fold increase in cytosolic cytochrome c levels, and a corr esponding decrease in mitochondrial cytochrome c. In accordance with its in hibition of cocaine-induced apoptosis, cyclosporin A blocked cocaine-induce d cytochrome c translocation. Correspondingly, cocaine-induced activation o f caspase-9 preceded that of caspase-3. Caspase-8 was not activated. Cocain e 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 casp ase-3 inhibitor Ac-DEVD-CHO. Collectively, these data indicate that the rel ease 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 th ese cells. Furthermore, the down-regulation of the Bcl-2 protein may play a n important role in cocaine-induced release of cytochrome c.