Abstract
Vitamin E, a generic term for tocopherol (T) and tocotrienol (T3), is one of the most potent lipid-soluble antioxidants present in the body. Vitamin E exists in eight isoforms such as α-, β-, γ-, and δ-T and α-, β-, γ-, and δ-T3 in which α-, β-, γ-, and δ-vitamin E isoforms have different chroman structures contributing to the function to scavenge free radicals. Vitamin E is classified into T and T3 based on the difference in the side chain structure. The reactivity of vitamin E against free radicals depends on the difference in the chroman structure, and T and T3 exhibit a similar capacity to scavenge free radicals. In contrast, they exert quite unique cytoprotective activities depending on the difference in the side chain structure in cultured cells. In this review, we summarize the chemical and antioxidative properties of vitamin E isoforms, particularly the difference in cytoprotective effect against oxidative stress between T and T3. In addition, we describe the relationship between vitamin E and the essential trace element “selenium”, which exhibits complementary antioxidant action on lipid peroxidation. Furthermore, we explain the difference in the molecular mechanism for the cytoprotective action of vitamin E oxidation products among vitamin E isoforms. Collectively, we discuss the various antioxidative actions of vitamin E, especially the different cytoprotective effects of vitamin E isoforms.
