Independent antioxidant action of vitamins E and C in cultured rat hepatocytes intoxicated with allyl alcohol

The relationship between the metabolism of alpha-tocopherol (vitamin E) and ascorbate (vitamin C) was examined in cultured hepatocytes intoxicated with allyl alcohol. Alcohol dehydrogenase rapidly metabolizes allyl alcohol to the potent electrophile acrolein. Acrolein depletes the glutathione (GSH) content of the hepatocytes, thereby sensitizing the cells to the constitutive flux of activated oxygen species. Supplementation of the medium with 1 mu M alpha-tocopherol phosphate (alpha-TP) prevents the 85% decline in cellular vitamin E seen after 16-18 hr in culture. In cells supplemented with alpha-TP, allyl alcohol produced a concentration-dependent decline in the cellular content of alpha-tocopherol, and these cells were more resistant to cell killing than hepatocytes not supplemented with alpha-TP. alpha-TP concentrations that raised the cellular alpha-tocopherol above the physiological level completely protected hepatocytes against the killing by allyl alcohol. In cells with physiological alpha-tocopherol, vitamin E declined within 30 min of exposure to allyl alcohol. This decrease paralleled the peroxidation of lipids, but preceded the decrease in cellular ascorbate. Under these conditions, a decline in ascorbate correlated with the loss of cell viability. Cells supplemented with at least 3 mM ascorbate prevented the decline in alpha-tocopherol. However, ascorbate acts as an independent antioxidant at these concentrations. In the absence of killing by allyl alcohol, the loss of cellular ascorbate did not depend on the presence or absence of cellular alpha-tocopherol. These data indicate that vitamins E and C act as separate antioxidants and that ascorbate does not regenerate the tocopheroxyl radical in cultured rat hepatocytes.