α-Tocopherol[edit]
Sample of α-tocopherol, one of the various forms of vitamin E
alpha-Tocopherol is an important lipid-soluble antioxidant. It performs its functions as antioxidant in the glutathione peroxidase pathway,[12] and it protects cell membranes from oxidation by reacting with lipid radicals produced in the lipid peroxidation chain reaction.[7][13] This would remove the free radical intermediates and prevent the oxidation reaction from continuing. The oxidized α-tocopheroxyl radicals produced in this process may be recycled back to the active reduced form through reduction by other antioxidants, such as ascorbate, retinol or ubiquinol.[14] Other forms of vitamin E have their own unique properties; for example, γ-tocopherol is a nucleophile that can react with electrophilic mutagens.[15]
Tocotrienols[edit]
Compared with tocopherols, tocotrienols are sparsely studied.[16][17][18] In 2006, less than 1% of PubMed papers on vitamin E relate to tocotrienols.[19] Continuing investigations into the potential pharmacological potential of tocotrienols continues. Tocotrienols may have specialized roles in protecting neurons from damage[19] and cholesterol reduction[20] by inhibiting the activity of HMG-CoA reductase; δ-tocotrienol blocks processing of sterol regulatory element‐binding proteins (SREBPs).
Oral consumption of tocotrienols is also thought to protect against stroke-associated brain damage in vivo.[21]