Cholesterol epoxide is a direct-acting mutagen.

A 24-hr treatment of V79 Chinese hamster lung fibroblasts with 12.4 microM cholesterol 5 alpha, 6 alpha-epoxide induced 8-azaguanine-resistant mutants at frequencies 4.6- to 11.8-fold higher than the spontaneous mutation rate. We show that cholesterol epoxide, which is produced by in vivo cholesterol oxidation, is a weak direct-acting mutagen. Cholesterol epoxide was found to be accumulated by cells and transformed to cholestane-3 beta, 5 alpha, 6 beta-triol, which was more toxic and a more potent inhibitor of DNA synthesis than the epoxide but, at concentrations less than 17.8 microM, was not significantly mutagenic. Consideration of the rates of cholesterol epoxide conversion to cholestane triol shows that this conversion can result in abolition of the mutagenicity of the epoxide. Conditions under which conversion of the epoxide to the triol is low, as in the case of low epoxide hydrolase activity, favor mutagenicity whereas rapid conversion to triol favors cytotoxicity.