Effects of vitamin E and selenium on antioxidant defense in rat heart

Heart mitochondria, isolated from rats fed diets deficient or supplemented with vitamin E (E) and/or selenium (Se), were subjected to time-course assays of lipid peroxidation stimulated by ascorbate/ADP/Fe3+. Mitochondria depleted of alpha-tocopherol (alpha-TH) peroxided rapidly as assessed by formation of thiobarbituric acid reactive substances (TBARS). Formation of TBARS was strongly inhibited in mitochondria from rats fed diets supplemented with E. Selenium deficiency, reduced glutathione (GSH), glutathione disulfide (GSSG) or GSH + GSSG did not affect the course of lipid peroxidation in mitochondria from rats supplemented or deficient in E. Combined E and Se deficiency resulted in significantly lower total (oxidized+reduced) mitochondrial coenzyme Q-9 (CoQ-9) concentration compared with control rats supplemented with dietary E and Se. Time-course changes in mitochondrial alpha-TH and total CoQ-9 during oxidizing conditions were minor in +E rats. Total CoQ-9 was reduced substantially, however, during the course of lipid peroxidation in mitochondria depleted of alpha-TH. Selenium-dependent glutathione peroxidase (Se-GSHPx) activity was reduced by approximately 96% in heart cytosol, and to a somewhat lesser extent in mitochondria, by dietary Se deficiency. Non-Se GSHPx activity was not detected in heart cytosol but was detected in very small amounts in heart mitochondria. Glutathione S-transferase activity of heart cytosol was decreased in E and/or Se deficiency. The results of these experiments indicate that membrane alpha-TH was most effective in inhibiting lipid peroxidation in heart mitochondria.