Apoptosis of vascular smooth muscle cells induced by cholesterol and its oxides in vitro and in vivo

The ability of cholesterol and its oxides to induce apoptosis in vascular smooth muscle cells in tissue culture and in a rabbit model of atherosclerosis was evaluated. Apoptosis was detected using DNA laddering and in situ end-labelling of fragmented DNA. Cholesterol oxides, but not cholesterol, were found to inhibit proliferation and induce apoptosis of vascular smooth muscle cells in tissue culture. 7-ketocholesterol was found to be the most potent inhibitor of proliferation, while 25-hydroxycholesterol was found to be the most potent inducer of apoptosis. These data suggest that the inhibition of proliferation and the induction of apoptosis by cholesterol oxides within vascular smooth muscle cells use different pathways, suggesting a differential role for these cholesterol oxides within the arterial wall. Cholesterol feeding after balloon injury in a rabbit model of atherosclerosis is known to result in the accumulation of cholesterol oxides. However, we found that cholesterol feeding had no effect on the level of apoptosis in the rabbit aortic wall after balloon injury, suggesting that the major factor determining apoptosis in our model was the balloon injury.