Metabolism of cholesteryl palmitate by rat brain in vitro; formation of cholesterol epoxides and cholestane-3β,5α,6β-triol

Abstract

Incubation of [4-14C] cholesteryl palmitate with the 12,000 g supernatant fraction of adult rat brain fortified with an NADPH-generating system and β-mercaptoethylamine resulted in formation (2–5%) of more polar metabolites characterized as a mixture of cholesterol-5,6-epoxides. Under extended incubation conditions, cholestane-3β,5α,6β-triol was isolated as the major end product of the incubations. Free [4-14C]cholesterol incubated under similar conditions was not oxidized, whereas oxidation of [4-14C]cholesteryl palmitate appeared to be dependent upon hydrolysis of the ester by the rat brain microsomal subcellular fraction. Elimination of the NADPH-generating system or the addition of EDTA to the incubation mixture inhibited epoxide formation, suggesting that the products are derived from an NADPH-dependent enzymatic lipoperoxidation mechanism. The in vitro conversion of [4-14C] cholesterol-5α,6α-epoxide to cholestane-3β,5α,6β-triol was also demonstrated in rat brain subcellular fractions in the absence of added cofactors.

Keywords

• brain cholesterol
• cholesterol oxidation