Vascular smooth muscle cell apoptosis induced by 7-ketocholesterol was mediated via Ca2+ and inhibited by the calcium channel blocker nifedipine

Previous reports indicate that 7-ketocholesterol (7KCHO) induces apoptosis of cultured human vascular smooth muscle cells (SMCs). We hypothesized that calcium channel blockers will inhibit SMC apoptosis induced by 7KCHO because caspase-3 activity is Ca2+ dependent and 7KCHO stimulates caspase-3 and SMC apoptosis. So, the protective effect of the calcium channel blocker nifedipine on SMC apoptosis induced by 7KCHO was investigated. When 7KCHO (50 μmol/L) was added to SMCs, terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate (dUTP)-biotin nick end-labeling was positive. DNA extracted from SMCs exposed to 7KCHO showed a ladder pattern on agarose electrophoresis. In the presence of extracellular Ca2+, the Ca2+ influx, caspase-3 activity, and fragmented DNA also increased in SMCs incubated with 7KCHO dose-dependently. However, in the absence of extracellular Ca2+, no effects of 7KCHO on caspase-3 activity and fragmented DNA were observed. In the presence of nifedipine, the 7KCHO-induced increases in Ca2+ influx, caspase-3 activity, and the amount of fragmented DNA decreased significantly. These results suggest that 7KCHO-induced apoptosis of SMCs is inhibited by calcium channel blockade, and that Ca2+ influx into cells mediated by 7KCHO plays an important role in 7KCHO-induced apoptosis.