ANTIOXIDANT REACTIONS OF VITAMIN-E IN THE PERFUSED-RAT-LIVER - PRODUCT DISTRIBUTION AND EFFECT OF DIETARY VITAMIN-E SUPPLEMENTATION

We have investigated the relationship between vitamin E (alpha-tocophe rol, TH) oxidation and antioxidant protection in a perfused rat liver model, Perfusion of a male Sprague-Dawley rat liver with 2 mM tert-but yl-hydroperoxide (t-BuOOH) for 10 min resulted in lipid peroxidation a nd metabolic changes reflecting oxidative stress, Mitochondria isolate d from the liver exhibited increases in state 3 and state 4 respiratio n and a decline in the respiratory control ratio, In livers from rats given supplementary vitamin E in the diet, TH content was 7- to 10-fol d higher than in controls and lipid peroxidation and metabolic changes induced by t-BuOOH were decreased, In mitochondria from these vitamin E-supplemented livers, the t-BuOOH-induced increase in state 4 respir ation was reduced and the respiratory control ratio was maintained, In livers from unsupplemented rats, t-BuOOH induced oxidation of TH to a lpha-tocopherolquinone, alpha-tocopherolhydroquinone, 2,3-epoxy-alpha- tocopherolquinone, and 5,6-epoxy-alpha-tocopherolquinone as determined by gas chromatography-mass spectrometry analysis, Yields of these pro ducts were approximately doubled by treatment of samples with dilute a cid, which indicated the presence of tocopherone and epoxytocopherone precursors, Oxidation of TH in vitamin E-supplemented livers yielded t he same products and the relative extent of TH oxidation appeared simi lar to that in unsupplemented livers, In livers from both unsupplement ed and vitamin E-supplemented animals, the distribution of oxidation p roducts was similar in whole liver and isolated mitochondria, These da ta provide the first simultaneous documentation of TH antioxidant reac tions and antioxidant effects in an intact organ system during oxidati ve stress. (C) 1997 Academic Press.