THE ANTIOXIDANT FUNCTION OF THE PHYSIOLOGICAL CONTENT OF VITAMIN-C

The synthesis of vitamin C is substantially reduced in Osteogenic Diso rder Shionogi (ODS) rats, Hepatocytes prepared from these rats contain ed similar to 12% of the wild-type content of this vitamin. In culture , the ascorbate content remained low in the absence of supplementation of the medium. Independent of their vitamin C status, cultured hepato cytes became depleted of vitamin E. Supplementation of the culture med ium with 100 mu M ascorbate and 1.2 mu M alpha-tocopherol phosphate ma intained the physiological content of both vitamins C and E in ODS hep atocytes. Thus, the antioxidant function of vitamins C and E could be evaluated in the presence of both or either vitamin or in the absence of both vitamins, Hepatocytes deficient in both vitamins were the most susceptible to lipid peroxidation (as measured by thiobarbituric acid ) and to cell kilting within a 90-min exposure to 125-500 mu M tert-bu tyl hydroperoxide (TBHP). Supplementation to achieve a physiological c ontent of both vitamins C and E reduced the evidence of lipid peroxida tion and abolished the cell killing. Supplementation with either vitam in alone resulted in an intermediate degree of both lipid peroxidation and cell killing. In ODS hepatocytes treated with TBHP, the decline i n vitamin E preceded the decline in vitamin C. In ODS hepatocytes depl eted of vitamin C, the loss of vitamin E after exposure to TBHP was gr eater than that in the presence of physiological levels of ascorbate, This greater loss of vitamin E in the face of a depletion of vitamin C was readily attributable to the increased peroxidation of lipids. Thu s, the physiological level of vitamin C in cells does not seem to rege nerate vitamin E. In contrast, the rate and extent of the depletion of vitamin C correlate with the degree of cell killing. These data docum ent the antioxidant function of the physiological level of cellular vi tamin C and relate this function to protection against peroxidative ce ll injury.