RECYCLING AND ANTIOXIDANT ACTIVITY OF TOCOPHEROL HOMOLOGS OF DIFFERING HYDROCARBON CHAIN LENGTHS IN LIVER-MICROSOMES

Tocopherols (vitamin E) function as inhibitors of lipid peroxidation in biomembranes by donating a hydrogen atom to the chain propagating lipid radicals, thus giving rise to chromanoxyl radicals of the antioxidant. We have shown that α-tocopherol homologs differing in the lengths of their hydrocarbon side chains (α-Cn) manifest strikingly different antioxidant potencies in membranes. The antioxidant activity of tocopherol homologs during (Fe2+ + ascorbate)- or (Fe2+ + NADPH)-induced lipid peroxidation in rat liver microsomes increased in the order α-tocopherol (α-C16) < α-C11 < α-C6 < α-C1. Chromanoxyl radicals generated from α-tocopherol and its more polar homologs by an enzymatic oxidation system (lipoxygenase + linolenic acid) can be recycled in rat liver microsomes by NADPH-dependent electron transport or by ascorbate. The efficiency of recycling increased in the same order: α-tocopherol (α-C16) < α-C11 < α-C6 < α-C1. Thus the high efficiency of regeneration of short-chain homologs of vitamin E may account for their high antioxidant potency. © 1990.