ascorbic-acid and 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 microM 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.

Topics: 1-Propanol; Animals; Antioxidants; Ascorbic Acid; Cell Death; Cells, Cultured; Drug Interactions; Liver; Malondialdehyde; Propanols; Rats; Vitamin E

1. The ability of ascorbic acid to protect from prooxidant-induced toxic injury was investigated in isolated, intact rat hepatocytes, whose ascorbic acid content had been restored by means of exogenous supplementation. 2. Ascorbate-supplemented and ascorbate-non-supplemented cells in suspension were treated with a series of different prooxidants (allyl alcohol, diethyl maleate, carbon tetrachloride, menadione), and the development of lipid peroxidation and cell injury was evaluated. 3. With allyl alcohol and diethyl maleate, ascorbic acid was able to protect cells from both lipid peroxidation and cell injury. The same protection was offered by ascorbate also in hepatocytes obtained from vitamin E-deficient animals. 4. With carbon tetrachloride, ascorbate supplementation did not affect the initial steps of lipid peroxidation, but nevertheless provided a marked protection against lipid peroxidation and cell injury at later times of incubation. The protection was unaffected by the vitamin E content of cells. 5. With menadione, a toxin which does not induce lipid peroxidation, ascorbic acid did not protect cells against injury. 6. It is concluded that ascorbic acid can act as an efficient antioxidant in isolated rat liver cells, with protection against cell injury. The antioxidant effect appears primarily to involve membrane lipids, and can be independent from the cellular content of vitamin E, thus suggesting that ascorbic acid can play a direct and independent role in the intact cell, in addition to its synergistic interaction with vitamin E described in other models.

Topics: 1-Propanol; Animals; Antioxidants; Ascorbic Acid; Carbon Tetrachloride; Cell Survival; Glutathione; Lipid Peroxidation; Liver; Male; Maleates; Malondialdehyde; Propanols; Rats; Rats, Sprague-Dawley; Vitamin E; Vitamin K

Topics: 1-Propanol; Animals; Ascorbic Acid; Bromobenzenes; Chemical and Drug Induced Liver Injury; Dehydroascorbic Acid; Diet; Glutathione; Lipid Peroxidation; Liver; Male; Maleates; Mice; Propanols; Vitamin E

The mechanisms of the liver damage produced by three glutathione (GSH) depleting agents, bromobenzene, allyl alcohol and diethylmaleate, was investigated. The change in the antioxidant systems represented by alpha-tocopherol (vitamin E) and ascorbic acid were studied under conditions of severe GSH depletion. With each toxin liver necrosis was accompanied by lipid peroxidation that developed only after severe depletion of GSH. The hepatic level of vitamin E was decreased whenever extensive lipid peroxidation developed. In the case of bromobenzene intoxication, vitamin E decreased before the onset of lipid peroxidation. Changes in levels of the ascorbic and dehydroascorbic acid indicated a redox cycling of vitamin C with the oxidative stress induced by all the three agents. Such a change of the redox state of vitamin C (increase of the oxidized over the reduced form) may be an index of oxidative stress preceding lipid peroxidation in the case of bromobenzene. In the other cases, such a change is likely to be a consequence of lipid peroxidation. Experiments carried out with vitamin E deficient or supplemented diets indicated that the pathological phenomena occurring as a consequence of GSH depletion depend on hepatic levels of vitamin E. In vitamin E deficient animals, lipid peroxidation and liver necrosis appeared earlier than in animals fed the control diet. Animals fed a vitamin E supplemented diet had an hepatic vitamin E level double that obtained with a commercial pellet diet. In such animals, bromobenzene and allyl alcohol had only limited toxicity and diethylmaleate none in spite of comparable hepatic GSH depletion. Thus, vitamin E may largely modulate the expression of the toxicity by GSH depleting agents.

Topics: 1-Propanol; Animals; Antioxidants; Ascorbic Acid; Bromobenzenes; Chromatography, High Pressure Liquid; Glutathione; Lipid Peroxidation; Liver; Male; Maleates; Malondialdehyde; Mice; Necrosis; Propanols; Time Factors; Vitamin E