Tocopherylquinone and tocopherylhydroquinone

Abstract

Tocopherylquinone (TQ) is formed in the antioxidant action of tocopherol (T). TQ was found in human subjects and it was observed that the ratio αTQ/αT increased in general with increasing oxidative stress. TQ is reduced to tocopheryl hydroquinone (TQH2) but the ratio TQH2/TQ in vivo has not been reported. TQH2 acts as a potent radical-scavenging antioxidant. αTQH2 is more reactive toward radicals than ubiquinol, a reduced form of coenzyme Q, and αT. The overall efficacy of TQH2 as an antioxidant is determined by the fate of semiquinone radical formed from TQH2 as well as the reactivity toward oxygen radicals. Partly substituted TQ, but not αTQ, exerts cytotoxicity by both redox cycling and reaction with protein thiols and glutathione. © W. S. Maney & Son Ltd.