Oxidation Products of Vitamin E in the Peroxidation of Liposomal and Biological Systems

Abstract

The oXidation products of vitamin E, α-tocopherol, during the peroxidation of unsaturated lipids in the peroxidation of liposomal systems, human plasma, and some biological tissues have been reViewed. Free radical reactions of α-tocopherol take place via the α-tocopheroxyl radical as an intermediate. If suitable free radical is present, a non-radical product can be formed from the coupling of the free radical with the or-tocopheroxyl radical. The reaction products of α-tocopherol with lipid-peroxyl radicals, such as phosphatidylcholine-peroxyl radicals and cholesteryl ester-peroxyl radicals, are 8a-(lipid-dioxy)-α-tocopherones, which are hydrolyzed to or-tocopherylquinone. The other product-forming pathway yields 2, 3-and 5, 6-epoxy-α-tocopherylquinones and their precursors, epoxyhydroperoxy-α-tocopherylquinones. Other vitamin E compound, γ-tocopherol, is superior to α-tocopherol in the detoXification of reactive nitrogen oxide species and forms 5-nitro-γ-tocopherol as the reaction product. The oxidation products of vitamin E have been detectedin liposomal systems, plasma samples, a perfused rat liver model, and human atherosclerotic lesions. Thus, the formation of these products provides us with much information onthe antioxidant function of vitamin E in biological systems.