Mechanisms of action of selenium and vitamin E in protection of biological membranes.

Opinions vary as to the mode of action of vitamin E and selenium. Some argue that they act as nonspecific biological antioxidants. Others propose that the functions of the two substances are distinct and that vitamin E acts as a true vitamin in addition to functioning as a lipid-soluble antioxidant. Support for the "Biological Antioxidant Theory" is largely circumstantial. However, lipoperoxides have been detected in adipose tissues of vitamin E-deficient animals, and increased rates of in vitro peroxidation have been demonstrated in homogenates of several tissues of selenium and vitamin E-deficient animals. The basis of the antioxygenic role of selenium in these systems was elucidated by the discovery of Rotruck et al. (1973) that selenium is a component of rat erythrocyte glutathione peroxidase. Further studies in this laboratory have demonstrated the important role of glutathione peroxidase in protection against the vitamin E- and selenium-deficiency disease of chicks, exudative diathesis, which results from increased capillary permeability. Also shown were the activities of both dietary selenium and vitamin E in prevention of ascorbate-induced peroxidation in mitochondrial and microsomal preparations from chick liver. Recent results demonstrate that both selenium and vitamin E are required to protect hepatic mitochondria and microsomes from peroxidative degradation. Dietary requirements of the chick for both nutrients for this function have been determined: approximately 0.06 ppm selenium in the presence of adequate vitamin E; 30-50 IU vitamin E per kg in the presence of adequate selenium.