CHAPTER 13. Oxidation Products of Vitamin E with Lipid-derived Free Radicals

Vitamin E is the most important lipophilic antioxidant in vivo and in vitro, which scavenges lipid-derived free radicals. This chapter has reviewed the oxidation products of two vitamin E compounds, α- and γ-tocopherols (αTH and γTH), during the degradation process of lipid hydroperoxides. Lipid hydroperoxides, the primary products of lipid peroxidation, are decomposed by transition metal ions or heme compounds to produce a wide range of secondary products, such as some toxic aldehydes. Since this process takes place via free radical reactions in lipophilic circumstances, THs can suppress the formation of such secondary products by trapping free-radical intermediates in micellar and liposomal systems. The oxidation products of αTH during the degradation process of lipid hydroperoxides are α-tocopherylquinone, 8a-(epoxylipid-dioxy)-α-tocopherones, 6-O-epoxylipid-αTHs, and αTH dimer. The products of γTH with lipid hydroperoxide-derived free radicals are tocored, γ-tocopherylquinone, 8a-(epoxylipid-dioxy)-γ-tocopherones, 6-O-epoxylipid-γTHs, and two γTH dimers. The produced γTH dimers are still effective in trapping lipid hydroperoxide-derived free radicals and form some addition products.