Oxidative catabolism of alpha-tocopherol in rat liver microsomes

The goal of this study was to clarify the mechanism responsible for the cat abolism of a-tocopherol. The vitamin, bound to albumin, was incubated with rat liver microsomes and appeared to be broken down. Optimal production of the metabolite was obtained when 1 mg of microsomal protein was incubated w ith 36 muM of alpha -tocopherol in the presence of 1.5 mM of NADPH. Chromat ographic and mass spectrometric analyses of the metabolite led to the concl usion that it consists of an omega -acid with an opened chroman ring, altho ugh we could not perform nuclear magnetic resonance analysis to confirm thi s. Our data show that ol-tocopherol is omega -oxidized to a carboxylic acid and that this process can occur in rat liver microsomes in the presence of NADPH and O-2. The oxidation to the quinone structure appears to be a subs equent event that may be artifactual and/or catalyzed by a microsomal enzym e(s).