Comparison of the apoptotic processes induced by the oxysterols 7β-hydroxycholesterol and cholesterol-5β,6β-epoxide

Oxysterols have been shown to induce apoptosis in a variety of cell lines. The mechanism of oxysterol-induced apoptosis is mainly known at the post-mitochondrial level. The aim of the present study was to compare the pathway of apoptosis induced by the oxysterols 7β-hydroxycholesterol (7β-OH) and cholesterol-5β,6β-epoxide (β-epoxide) in U937 cells. To this end, we employed a range of inhibitors of apoptosis; a broad-spectrum caspase inhibitor, a specific caspase-3 inhibitor and an inhibitor of cytochromec release and the antioxidants; trolox, ebselen and resveratrol. The three inhibitors of apoptosis prevented cell death induced by 7β-OH; however, in β-epoxide-treated cells, the inhibitor of cytochromec release did not protect against apoptosis. The cellular antioxidant glutathione was depleted in 7β-OH-treated cells but not in cells incubated with β-epoxide. Trolox, a water-soluble synthetic analogue of α-tocopherol, prevented 7β-OH-induced apoptosis but did not protect against cell death induced by β-epoxide. Ebselen and resveratrol did not protect U937 cells against apoptosis induced by either 7β-OH or β-epoxide. Our results suggest that differences occur in the pathways of apoptosis induced by 7β-OH and β-epoxide in U937 cells.