Metabolism of cholesteryl palmitate by rat brain in vitro; formation of cholesterol epoxides and cholestane-3beta,5alpha,6beta-triol.
Incubation of [4-(14)C]cholesteryl palmitate with the 12,000 g supernatant fraction of adult rat brain fortified with an NADPH-generating system and beta-mercaptoethylamine resulted in formation (2-5%) of more polar metabolites characterized as a mixture of cholesterol-5,6-epoxides. Under extended incubation conditions, cholestane-3beta-5alpha-6beta-triol was isolated as the major end product of the incubations. Free [4-(14)C]cholesterol incubated under similar conditions was not oxidized, whereas oxidation of [4-(14)C]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-(14)C]cholesterol-5alpha,6alpha-epoxide to cholestane-3beta,5alpha,6beta-triol was also demonstrated in rat brain subcellular fractions in the absence of added cofactors.
D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002474:Cell-Free System; D002784:Cholesterol / Q000032:analysis / Q000378:metabolism*; D002849:Chromatography, Gas; D002855:Chromatography, Thin Layer; D004988:Ethers, Cyclic / Q000378:metabolism*; D005958:Glucosephosphates; D066298:In Vitro Techniques; D008624:Mercaptoethylamines; D000432:Methanol; D008861:Microsomes / Q000032:analysis; D008928:Mitochondria / Q000032:analysis; D009249:NADP; D010169:Palmitic Acids / Q000378:metabolism*; D051381:Rats; D013261:Sterols / Q000378:metabolism*
D002250:Carbon Radioisotopes; D004988:Ethers, Cyclic; D005958:Glucosephosphates; D008624:Mercaptoethylamines; D010169:Palmitic Acids; D013261:Sterols; D009249:NADP; D002784:Cholesterol; D000432:Methanol