Vitamin E: action, metabolism and perspectives

Abstract

Natural vitamin E includes four tocopherols and four tocotrienols. RRR-alpha-tocopherol is the most abundant form in nature and has the highest biological activity. Although vitamin E is the main lipid-soluble antioxidant in the body, not all its properties can be assigned to this action. As antioxidant, vitamin E acts in cell membranes where prevents the propagation of free radical reactions, although it has been also shown to have pro-oxidant activity. Non-radical oxidation products are formed by the reaction between alpha-tocopheryl radical and other free radicals, which are conjugated to glucuronic acid and excreted through the bile or urine. Vitamin E is transported in plasma lipoproteins. After its intestinal absorption vitamin E is packaged into chylomicrons, which along the lymphatic pathway are secreted into the systemic circulation. By the action of lipoprotein lipase (LPL), part of the tocopherols transported in chylomicrons are taken up by extrahepatic tissues, and the remnant chylomicrons transport the remaining tocopherols to the liver. Here, by the action of the "alpha-tocopherol transfer protein", a major proportion of alpha-tocopherol is incorporated into nascent very low density lipoproteins (VLDL), whereas the excess of alpha-tocopherol plus the other forms of vitamin E are excreted in bile. Once secreted into the circulation, VLDL are converted into IDL and LDL by the action of LPL, and the excess of surface components, including alpha-tocopherol, are transferred to HDL. Besides the LPL action, the delivery of alpha-tocopherol to tissues takes place by the uptake of lipoproteins by different tissues throughout their corresponding receptors. Although we have already a substantial information on the action, effects and metabolism of vitamin E, there are still several questions open. The most intriguing is its interaction with other antioxidants that may explain how foods containing small amounts of vitamin E provide greater benefits than larger doses of vitamin E alone.

FREE RADICALS AND ANTIOXIDANTS: ANTIOXIDATIVE AND OTHER PROPERTIES OF SWISS CHARD (Beta vulgaris L. subsp. cicla)

“…Unlike water-soluble antioxidants, α-tocopherol efficiently protects glutathione peroxidase deficient cells from cell death. GP is the only enzyme that efficiently reduces lipidperoxides within biological membranes (Herrera and Barbas, 2001).…”

Augmentation of antioxidant system: Contribution to antimalarial activity of Clerodendrum violaceum leaf extract

“…Vitamin C is the major circulating water soluble antioxidant and acts as a free radical scavenger; it has been shown to take part in the metabolism of folic acid, red blood cell formation and maturation, bone formation and immune response mechanisms (De Tullio, 2010;Rao, 2006). Vitamin E is a lipid soluble vitamin and its main function is to prevent the peroxidation of membrane phospholipids and avoid cell damage through its antioxidant action (Herrera and Barbas, 2001;Padayatty et al, 2003). Selenium protects the cells by inhibiting free oxygen radical production but is best known for its role in glutathione enzyme system (Balakrishnan and Anuradha, 1998;Yalçin et al, 2003).…”

Proximate Composition, Phytochemical Analysis and in vivo Antioxidant Activity of Pomegranate Seeds (Punica granatum) in Female Albino Mice

“…There is the existence of a synergistic network of antioxidant enzymes such as catalase, superoxide dismutase (SOD) in vivo which acts as a defence mechanism against oxidative stress to cells. However, there are also dietary sources of antioxidants such as vitamin C [3]; vitamin A and E [4] and other endogenous molecules such as glutathione [5].…”