Tocopherols antioxidant/vitamin properties

Any of the group of related substances (a-, P-, y, -d tocopherols) constitutes vitamin E which is a natural antioxidant. The a-form is the most potent having the following structural formula and properties [38] ... 

Vitamin Bg in its various forms has antioxidant properties that compare favorably with those of the well-established antioxidant vitamins such as vitamin C and the tocopherols. Pyridoxine and pyridoxamine inhibit superoxide radicals and prevent lipid peroxidation, protein glycosylation, and Na+,K+-ATPase activity in high glucose-treated erythrocytes and hydrogen peroxide-treated monocytes (2) and endothelial cells (3). In bovine endothelial cells, treatment with homocysteine and copper increased extracellular hydrogen peroxide levels. Treatment with pyridoxal or EDTA prevented such increases and enhanced the viability of the cells by supporting apoptosis. 

The structure of vitamin E in its most active form, o-tocopherol, is shown in Figure 18.38. a-Tocopherol is a potent antioxidant, and its function in animals and humans is often ascribed to this property. On the other hand, the molecular details of its function are almost entirely unknown. One possible role for... 

A large number of nonenzymatic compounds, including tocopherols, caroti-noids, vitamins C and D, steroids, ubiquinones, thiols, uric acid, bilirubin, ino-sine, taurine, pyruvate, CRP, and so on, demonstrate qualitative antioxidant properties under experimental conditions. However, the quantitative relevance of most findings remains unclear. 

Several different tocopherols are known to have vitamin E activity, but a-tocopherol, a trimethyltocol (Figure 12.9) is the most biologically active. Other less potent forms are the /3-, y- and S-tocopherols, which contain fewer methyl groups. They all have antioxidant properties and a deficiency results in a lack of protection of the unsaturated fatty acids in the membrane phospholipids against oxidation by molecular oxygen. 

Vitamin E may be indicated in some rare forms of anemia such as macrocytic, megaloblastic anemia observed in children with severe malnutrition and the hemolytic anemia seen in premature infants on a diet rich in polyunsaturated fatty acids. Also anemia s in malabsorption syndromes have shown to be responsive to vitamin E treatment. Finally, hemolysis in patients with the acanthocytosis syndrome, a rare genetic disorder where there is a lack of plasma jS-lipoprotein and consequently no circulating alpha tocopherol, responds to vitamin E treatment. In neonates requiring oxygen therapy vitamin E has been used for its antioxidant properties to prevent the development retrolental fibroplasia. It should be noted that high dose vitamin E supplements are associated with an increased risk in allcause mortality. 

In cow s milk, nearly all of the vitamin E is a-tocopherol and the level can vary with the cow s feed and the season of the year (Lampert 1975). For example, summer milk can contain five times more vitamin E (1.1 mg a-tocopherol per quart) than winter milk (0.2 mg/quart) (Hertig and Drury 1969 McLaughlin and Weihrauch 1979). It is suggested that vitamin E, due to its antioxidant properties, may have some effect in retarding the development of oxidized flavor in milk (Lampert 1975). 

To investigate the mode of action of vitamin E and related structures using the colon model, two hypotheses were tested (l)that their antioxidant properties contribute to the response and (2) that the vitamin was acting as an agonist on a receptor with structural requirements for producing activity in hypoxia. Testing the various available tocopherols on the colon model... 

Vitamin E (tocopherol) possesses antioxidative properties, which means it can protect polyunsaturated fatty acids from auto-oxidation. Deficiency of vitamin E causes increased peroxidation of lipids, which consequently leads to elevated production of prostaglandins. Increased concentration of prostaglandins, in turn, retards... 

More recent studies have shown that vitamin E also has roles in cell signaling, by inhibition or inactivation of protein kinase C, and in modulation of gene expression, inhibition of cell proliferation, and platelet aggregation. These effects are specific for a-tocopherol and are independent of the antioxidant properties of the vitamin. 

The antioxidant properties of vitamin E are well known and documented [5]. In particular, prevention by a-tocopherol of LDL oxidation has been studied [6]. Although the correlation between the level of LDL oxidation and atherosclerosis is not always evident [7], alternative studies have suggested that a-tocopherol protection against LDL oxidation may be secondary to the inhibition of protein kinase C (PKC). This enzyme seems to be responsible for the release of reactive oxygen species and lipid oxidation [8,9]. 

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