Short communication No reduction of a-tocopherol quinone by glutathione in rat liver microsomes

The cell membrane is protected against lipid peroxidation by endogenous antioxidants such as vitamin E (a-tocopherol). The oxidised form of a-tocopherol (a-tocopherol quinone) does not have this antioxidant function. However, the literature indicates that a-tocopherol quinone can be reduced to a-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 a-tocopherol quinone, either directly in solution or in rat liver microsomes fortified witha-tocopherol quinone. This renders GSH a less likely candidate for a-tocopherol quinone reduction in vivo. In addition, a-tocopherol quinone did not enhance GSH-dependent protection against lipid peroxidation, either in control microsomes, or in vitamin E-extracted microsomes. Indeed, a-tocopherol quinone blocked GSH-dependent protection against lipid peroxidation in vitamin E-extracted microsomes. This indicates that a-tocopherol quinone can act as a pro-oxidant. © 2001 Elsevier Science Inc. All rights reserved.