alpha-Tocopherol acetate supplementation enhances rat hepatic cytochrome PROD activity in the presence of phenobarbital induction

Protective role of Vitamin E pre-treatment on N-nitrosodiethylamine induced oxidative stress in rat liver

Nitrosamine compounds are known hepatic carcinogens. In the metabolism of nitrosamines, such as N-nitrosodiethylamine (NDEA), there is evidence of the formation of reactive oxygen species (ROS) resulting in oxidative stress, which may be one of the factors in the etiology of cancer. The formation of ROS may alter the antioxidant system, while the presence of Vitamin E may counteract NDEA induced oxidative stress. This study was planned to determine whether pre-treatment with Vitamin E (40 mg/kg body weight, i.p., twice a week for 4 weeks) to NDEA induced rats provides protection against oxidative stress in liver caused by the carcinogen. A single necrogenic dose of NDEA (200mg/kg body weight) was administered i.p. to the male albino rats with or without Vitamin E pre-treatment and the animals were sacrificed on Days 7, 14 or 21 after the administration of NDEA. The result showed enhanced levels of hepatic lipid peroxidation (LPO) and conjugated dienes of NDEA treated rats as the indices of oxidative stress, however, Vitamin E pre-treated rats administered NDEA showed decreased LPO and conjugated dienes (Day 21). Superoxide dismutase (SOD) activity in liver was not altered significantly in NDEA treated rats with or without Vitamin E pre-treatment. Catalase (CAT) activity was inhibited with NDEA treatment, however, Vitamin E pre-treatment showed recovery in hepatic CAT activity (Days 14 and 21). Total and Se-glutathione peroxidase (GSH-Px) activities and glutathione-S-transferase (GST) activity in liver increased in NDEA treated rats irrespective of Vitamin E pre-treatment. Glutathione reductase (GSH-R) activity as well as total glutathione (GSH) content in liver decreased in NDEA treated animals, both of which were recovered in Vitamin E pre-treated rats administered NDEA. Activities of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) were increased significantly following NDEA treatment to rats with or without Vitamin E pre-treatment. The activities of AST and ALT enzymes were significantly reduced on Days 14 and 21 and ALP activity was reduced on Day 21 in NDEA+Vitamin E treated animals when compared to NDEA treated alone. LDH enzyme activity was normalized on Day 14 in Vitamin E pre-treated animals administered NDEA. However, the AST, ALT and ALP enzyme activities remained high in all treatment groups as compared to control group. Normal control and Vitamin E treated alone rats revealed normal histology of liver. On the other hand, NDEA treated animals showed alterations in normal hepatic histoarchitecture, which comprised of necrosis and vacuolization of the cells. However, the rats treated with Vitamin E+NDEA showed that the liver cells were normal, with very little necrosis (Day 21). This study concludes that the pre-treatment with Vitamin E prior to the administration of NDEA, reduced the degree of oxidative stress, although this vitamin produced only slight changes in the hepatic injury, in a time-dependent manner.

Dietary selenium supplementation prolongs pentobarbital induced hypnosis

The present studies characterized the influence of dietary selenium (Na2SeO3) on the duration of pentobarbital (PB) induced hypnosis (sleep) in the rat. Rats were fed semipurified diets varying from 0.01 to 2.0 mg Se/kg for up to 4 weeks. Consumption of diets containing 1.0 and 2.0 mg Se/kg significantly prolonged PB induced hypnosis. Hepatic selenium, but not hepatic glutathione peroxidase activity, correlated with the length of PB induced hypnosis. The prolongation of hypnosis caused by diets containing 1.0 mg Se/kg was substantially reduced or eliminated by repeated exposure to PB. Although single exposure to increasing quantities of PB (60-100 mg/kg body weight) led to a progressive increase in sleep duration, the proportional increase caused by supplemental selenium (2.0 vs 0.1 microg Se/g) remained relatively constant (approximately 25%). Increasing maturity was inversely related to the duration of PB induced hypnosis, regardless of dietary selenium provided. Consumption of the 2.0 mg Se/kg diet prolonged PB induced hypnosis to a greater degree in immature than in mature rats (P < 0.05). Consumption of the selenium enriched diet (2 microg Se/g) resulted in an increase in cytochrome 2B, but had no effect on cytochrome 1A compared to controls (0.1 microg Se/g). Pretreatment of rats with P450 enzymes activators (i.e., PB, Aroclor 1254, or 3-methylcholanthrene) shortened the duration of PB induced sleep and masked the effects of dietary selenium. The current studies document that dietary selenium can influence the response to pentobarbital induced hypnosis and likely relates to changes in drug detoxification enzymes.

Effect of 4-coumaric and 3,4-dihydroxybenzoic acid on oxidative DNA damage in rat colonic mucosa

The effect of 4-coumaric and 3,4-dihydroxybenzoic (protocatechuic) acid on the basal oxidative DNA damage of rat colonic mucosa in vivo was studied, relative to vitamin E. F344 rats were treated with 4-coumaric or protocatechuic acid mixed in the diet (25 or 50 mg/kg for 2 weeks). It was observed that 4-coumaric acid (50 mg/kg) significantly decreased the basal level of the oxidative damage assessed as 8-OH-2'-deoxyguanosine levels in DNA and by the comet assay. Moreover, it was found that vitamin E (10 mg/kg) had no effect on colonic mucosa oxidation damage, whereas at a higher dose (55 mg/kg) it actually enhanced oxidative stress. The effect of 4-coumaric acid (50 mg/kg) on the expression of some glutathione-related enzymes (glutathione-S-transferase (GST)-P, GST-M2, GST-M1, gamma-glutamylcysteine synthetase, glutathione peroxidase (GSPX)1 and GSPX4) was also investigated at the level of the colonic mucosa. Only the expression of GST-M2 was significantly induced by 4-coumaric acid, while protocatechuic acid was inactive. The data suggest that 4-coumaric acid acts as an antioxidant in the colonic mucosa in vivo.

Vitamin E inhibits hepatic NF-kappaB activation in rats administered the hepatic tumor promoter, phenobarbital

Phenobarbital (PB) is an efficacious hepatic tumor promoter. Although the promoting activity of PB is likely related to altered cell proliferation or apoptosis, the induction of an oxidative stress environment may also be important. PB has been shown to activate the transcription factor nuclear factor-kappaB (NF-kappaB). In this study, we hypothesized that PB-induced NF-kappaB activation can be decreased by dietary vitamin E in rats. Male Sprague-Dawley rats (n = 39) were fed a purified diet with varying levels of dietary vitamin E (10, 50 or 250 mg/kg of dl-alpha-tocopherol acetate) for 28 d, at which time 8 rats per level of dietary vitamin E were fed the same diet with 500 mg/kg PB for 10 d. In the rats fed the low vitamin E diet, PB increased NF-kappaB DNA binding, but it did not affect NF-kappaB activation in rats fed higher levels of vitamin E (50 and 250 mg/kg). Vitamin E may decrease the oxidative stress created by PB by also enhancing other antioxidants; therefore, we also measured hepatic glutathione S-transferase, glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase and NAD(P)H:quinone reductase (DT-diaphorase) activities and glutathione and ascorbic acid concentrations. Increased dietary alpha-tocopherol did not affect the antioxidants and antioxidant enzymes altered by PB treatment. Thus, the effect of alpha-tocopherol acetate on NF-kappaB activation does not appear to be mediated by alterations in the antioxidant system. These results demonstrate that the activation of NF-kappaB, a transcription factor that affects cell proliferation- and apoptosis-related gene expression, can be inhibited by dietary vitamin E.

Dietary fat and garlic oil independently regulate hepatic cytochrome p(450) 2B1 and the placental form of glutathione S-transferase expression in rats

The individual and combined effects of dietary fat and garlic oil on two drug-metabolizing enzymes, cytochrome P(450) 2B1 and the placental form of glutathione (GSH) S-transferase (PGST), in rat liver were examined in this study. Rats were fed a low corn oil, high corn oil or high fish oil diet and received various amount of garlic oil (0, 30, 80, 200 mg/kg body) orally three times per week for 6 wk. The fat energy in the low and high fat diets accounted for 11.6 and 45.7% of total energy, respectively. Final body weights did not differ among the three dietary fat groups and were not affected by garlic oil treatment. The fatty acid profile in hepatic phospholipids revealed higher eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic acid [22:6(n-3)] levels in the fish oil-fed group than in the low and high corn oil-fed groups (P < 0.05). In contrast, the corn oil-fed groups had greater hepatic phospholipid arachidonic acid [20:4(n-6)] levels (P < 0.05). Both dietary fat and garlic oil significantly affected hepatic cytochrome 7-pentoxyresorufin O-dealkylase (PROD) activity and GST activity toward ethacrynic acid. Rats fed the high fish oil diet had 85 and 51% higher PROD activity compared with those fed the low or the high corn oil diet, respectively (P < 0.05). The GST activity in the high fish oil and the high corn oil groups was 33 and 18% higher than that in the low corn oil group (P < 0.05), respectively, and the GST activity in rats fed the high fish oil diet was higher than in those fed the high corn oil diet (P < 0.05). Garlic oil dose-dependently increased GST activity. No interaction between dietary fat and garlic oil on PROD or GST activity was noted. Northern and Western blot analysis revealed that dietary fish oil increased both cytochrome P(450) 2B1 and PGST mRNA and protein levels. Cytochrome P(450) 2B1 and PGST mRNA and protein levels were also dose-dependently increased by garlic oil treatment. The effects of garlic oil and dietary fat on P(450) 2B1 and PGST mRNA and protein expression were independent. These results indicate that dietary fat and garlic oil independently modulate P(450) 2B1 and PGST expression at transcriptional and/or post-transcriptional stages.