No reduction of α-tocopherol quinone by glutathione in rat liver microsomes

Abstract The cell membrane is protected against lipid peroxidation by endogenous antioxidants such as vitamin E (α-tocopherol). The oxidised form of α-tocopherol (α-tocopherol quinone) does not have this antioxidant function. However, the literature indicates that α-tocopherol quinone can be reduced to α-tocopherol in vivo and thereby will add to the total antioxidant potential (Moore AN, Ingold KU. Free Radic Biol Med 1997;22:931–4). We found that GSH (reduced glutathione) did not mediate the reduction of α-tocopherol quinone, either directly in solution or in rat liver microsomes fortified with α-tocopherol quinone. This renders GSH a less likely candidate for α-tocopherol quinone reduction in vivo . In addition, α-tocopherol quinone did not enhance GSH-dependent protection against lipid peroxidation, either in control microsomes, or in vitamin E-extracted microsomes. Indeed, α-tocopherol quinone blocked GSH-dependent protection against lipid peroxidation in vitamin E-extracted microsomes. This indicates that α-tocopherol quinone can act as a pro-oxidant.