Drug metabolism and hepatic heme proteins in the vitamin E-deficient rat

Effect of vitamin E on rat hepatic cytochrome P-450 activity

Hepatic cytochrome P-450 activity has been shown to be affected by various dietary factors including vitamin E. However, reports of the effect of dietary vitamin E on cytochrome P-450 activity have been inconsistent. The aim of the present study was to investigate the influence of dietary vitamin E on rat hepatic cytochrome P-450 activity. Three groups of six male weanling Sprague-Dawley rats were fed semipurified diets containing 0, 100, or 1,500 ppm vitamin E for eight weeks. Vitamin E was given in the form of alpha-tocopheryl acetate. Dietary vitamin E significantly affected liver vitamin E content (p < 0.05) but had no effect on rat hepatic total P-450 content, N-nitrosodimethylamine demethylase, and NADPH-cytochrome-P-450 reductase activities. Hepatic pentoxyresorufin O-dealkylase and glutathione S-transferase activities were significantly greater in rats fed 100 and 1,500 ppm vitamin E than in rats fed no vitamin E (p < 0.05). Dietary vitamin E induced changes in hepatic phospholipid fatty acid composition. Hepatic phospholipid linoleate was significantly greater in rats fed 0 and 1,500 ppm vitamin E than in rats fed 100 ppm vitamin E (p < 0.05). Hepatic phospholipid eicosapentaenoate was increased significantly by dietary vitamin E (p < 0.05). Hepatic thiobarbituric acid-reactive substance was significantly greater in rats fed no vitamin E than in rats fed 100 and 1,500 ppm vitamin E (p < 0.05). The results suggest that vitamin E may influence cytochrome P-450 IIB1 enzyme activity and may affect hepatic phospholipid fatty acid composition.

[Hematological parameters, selenium concentration and glutathione peroxidase activities in serum and the liver of rats at different selenium and vitamin E levels]

The aim of the both experiments was to determine whether selenium or selenium/vitamin E supply of rats significantly influences the most important hematological criteria. With experiment 1 the influence of Se deficiency should be determined at two different times of growing. So 36 weaned rats were divided into 2 groups of 18 animals each, the half of them being decapitated at day 22, the rest on day 45. In experiment 2 with the aim to investigate a combination of deficient, adequate and excessive Se and vitamin E supply 90 weaned rats in 9 groups were decapitated at day 44. The basic diet contained 0.04 mg Se and 8 mg vitamin E per kg dry matter and was supplemented in exp. 1 with 0 mg or 0.2 mg Se and 30 mg vitamin E and in exp. 2 with 0 mg, 0.2 mg or 1.0 mg Se and 0 mg, 30 mg or 200 mg vitamin E. With Se deficiency Se concentration and GSH-Px activity in serum and liver were significantly reduced. With excessive Se supply Se concentration in serum was higher; there was no effect on GSH-Px activity. Vitamin E supply had no influence neither on Se content nor on GSH-Px activity in serum or in liver. In exp. 1 Se deficiency caused no clear changes of the analysed hematological criteria although the increase of MCV (+3%) and hematocrit (+7%) on day 22 and the increase of leucocytes (+43%) and the decrease of MCH (-3%) and MCHC (-6%) on day 45 were statistically significant. In exp. 2 these results could not be repeated. The vitamin E supply was without significant effects on the examined hematological parameters.

Vitamins E and K induce aryl hydrocarbon hydroxylase activity in human cell cultures

Two fat soluble vitamins, Vitamins E and K, when added into culture medium, were found to increase aryl hydrocarbon hydroxylase activity in human cultured cells. The extent of induction in a hepatoma-derived cell line (Hep G2) by these vitamins is of similar magnitude to those cells receiving benz[a]anthracene; whereas in a mammary tumor-derived cell line (MCF-7), benz[a]anthracene is the best inducer for the hydroxylase activity. The increase of the hydroxylase activity is associated with increased levels of a specific mRNA coding for polynuclear aromatic hydrocarbons-induced form of cytochrome P-450 with Vitamins E and K treatment. The size of the induced mRNA is 3.3 kilobase which is the same as that of benz[a]anthracene treatment.

Interaction of vitamin E and selenium with the hepatotoxic agent dimethylnitrosamine

Pretreatment of rats with vitamin E, 0.02% w/w of the diet and a sc dose, 200 mg/kg, given 48 hrs. before dimethylnitrosamine, DMNA, was found to ameliorate the acute hepatotoxicity of DMNA (30 mg/kg) as reflected in reduced plasma asparagine-amino-transferase (AspAT) activity. This effect was confirmed by histological evaluation. No significant effect of DMNA on plasma levels of vitamin E was observed, however, DMNA significantly increased the hepatic level of vitamin E supplemented rats. Pretreatment with selenium, 0.5 mg/kg given intraperitoneally 48 hrs. before DMNA, was found to enhance the acute hepatotoxicity of DMNA as reflected in increased elevation of plasma AspAT activity. This effect was not confirmed morphologically. DMNA did not have any effect on the hepatic selenium state in selenium pretreated rats; however, selenium pretreatment tended to decrease hepatic and plasma tocopherol levels. To explain the effects observed in the present investigation, various mechanisms were discussed. If the compounds were acting as antioxidants, then the difference in intracellular localization had to be important. More likely a specific biochemical function involving drug metabolizing enzymes could be involved. Finally vitamin E could protect membranes from damage during the necrotizing action of DMNA.