Studies on liver toxicants. Influence of bromobenzene on hepatic microsomal enzymes in rats

Comparison of in vivo and in vitro methods for assessing the effects of repeated dosing with carbon tetrachloride on the hepatic drug-metabolizing enzyme system

The effect of 7 daily i.p. injections of 0, 2, 20, or 200 microliters/kg carbon tetrachloride on the activity of the hepatic drug-metabolizing enzyme system was measured in the rat by a model substrate assay, employing lindane (gamma-hexachlorocyclohexane), and by a battery of in vitro enzyme assays. The data in this study indicated that repeated administration of CCl4 for 7 days significantly increased phase I and phase II reactions in vivo and in vitro. Though there were differences between the responses of the in vivo and in vitro assays, this is the first report of increased hepatic drug-metabolizing enzyme activity from repeated treatment with CCl4.

Comparison of in vivo and in vitro methods for assessing the effects of bromobenzene on the hepatic-metabolizing enzyme system

The effect of daily i.p. injections of 0, 0.05, 0.5 and 5.0 mmol/kg bromobenzene for 1 week on the activity of the hepatic drug-metabolizing enzyme system was measured in the rat by a model substrate assay employing lindane (gamma-hexachlorocyclohexane) and by a battery of in vitro enzyme assays. The data in this study indicated that repeated pretreatment with bromobenzene for 1 week stimulated a dose-related increase in phase I reactions while inducing phase II reactions at the high dose (5 mmol/kg bromobenzene). The in vivo and in vitro assays showed good agreement.

Studies on liver toxicants. Mixed-function oxidase activities and hemoprotein contents in livers of rats poisoned with bromobenzene

In liver microsomes of rats 5 h after intraperitoneal administration of bromobenzene, the activities of a series of drug-metabolizing mixed-function oxidases, i.e., ketamine and aminopyrine N-demethylases, methylayapanine and methoxybiphenyl O-demethylases, and ethoxycoumarin O-deethylase, as well as glutathione and cytochrome b5 contents were found to be decreased, whereas the activities of microsomal, NADPH-dependent cytochrome c and neotetrazolium reductases as well as cytochrome P-450 were unchanged.

Increased activity of certain hepatic drug-metabolizing enzymes due to subchronic exposure to bromobenzene

Male Sprague-Dawley rats were treated i.p. with different doses of bromobenzene (0, 0.1, 0.2, 0.3 and 0.5 mmol/kg) in corn oil for 4 weeks. The animals were killed 24 h after the end of the treatment for hepatic drug metabolism studies. A significant induction of the activities of microsomal aniline hydroxylase (51%) and aminopyrine N-demethylase (58%) was observed at 0.5 mmol/kg dose level. Liver microsomal cytochrome P-450 content was significantly increased (approx. 38%) at subchronic doses of 0.3 and 0.5 mmol/kg. Hepatic glutathione (GSH) concentrations were increased (approx. 30%) in comparison to control values at subchronic doses of 0.3 and 0.5 mmol/kg, whereas a significant induction (46-72%) of the activities of conjugating enzymes, cytosolic glutathione S-transferases was noticed at any subchronic dose level of bromobenzene studied. These results suggest that, under certain conditions, subchronic pretreatment with bromobenzene may have the potential to modify the acute toxicity of its own as well as those of other environmental pollutants which require metabolic activation.

Dose-dependent metabolic excretion of bromobenzene and its possible relationship to hepatotoxicity in rats

Male Sprague-Dawley rats received an intraperitoneal injection of 0.25-, 0.5-, 1.0-, 2.5-, and 5.0-mmol/kg dose of bromobenzene in corn oil. The metabolic fate of bromobenzene was studied by measuring its various urinary metabolites 24 h following bromobenzene administration. The hepatotoxicity of bromobenzene was estimated by determination of the serum glutamic-oxaloacetic and glutamic-pyruvic transaminase activities (SGOT and SGPT) 24 h after dosing. Treatment of rats with bromobenzene at up to 0.5 mmol/kg did not influence the transaminase activities, but significant increases in such activities began to manifest at a dose of 1 mmol/kg. However, no further increase in hepatotoxic response was induced on exposure to higher doses (2.5 and 5.0 mmol/kg) of bromobenzene. The urinary excretion of toxic doses of bromobenzene was nonlinear, based on the quantitative composition of various urinary metabolites. Furthermore, the fraction of the dose converted to thioethers, p-bromophenol, m-bromophenol, and total phenolic metabolites decreased with increasing toxic dose, suggesting their formation to be capacity-limited. The ratios of thioethers to total phenolic metabolites, of thioethers to p-bromophenol, and of thioethers to o-bromophenol decreased with increasing dose of bromobenzene. The correlation of the dose-dependent fate of metabolic excretion of bromobenzene with the results of the dose-hepatotoxic response curves supports the conclusion that there exists an apparent threshold dose (approximately 1-2.5 mmol/kg) for the toxic effects of bromobenzene that coincides with saturation of the metabolic pathways involving both glutathione/glutathione S-transferase(s) and formation of certain phenolic derivatives for its detoxification. All these results further suggest a role of a saturable, metabolic activation process involving 3,4-epoxide rather than 2,3-epoxide of bromobenzene in the development of its hepatotoxicity.

Short-term inhalation test for evaluating industrial hepatotoxicants in rats

Liver damage was investigated in rat using serum enzyme activities measurements. Responses were recorded 24 h after whole body inhalation exposure to vapors of bromobenzene, carbon tetrachloride, chloroform, o-dichlorobenzene, 1,2-dichloroethane and dimethylformamide as model toxicants. First, rats were exposed during a single 4 h period to different concentrations of each solvent and the minimally active concentration was determined. Second, repeated exposures to chemicals at this concentration level (6 h daily, 2 or 4 days) were used in order to examine whether hepatotoxicity was enhanced. GLDH and SDH are more sensitive and more constant indices than GOT and GPT. It appears that a single exposure period induced more marked serum activities enhancement than repeated exposures.

Studies on liver toxicants: influence of bromobenzene on hepatic microsomal drug-metabolizing enzymes in the hamster

The effect of bromobenzene on hepatic microsomal drug-metabolizing enzymes was investigated in hamsters after oral applications of 1.5 and 3.0 g/kg body weight. After 1.5 g/kg a decrease of aminopyrine N-demethylase as well as an increase of hepatic hydroperoxide formation occurred. At 3.0 g/kg, most mixed-function oxidases were inhibited with the exception of ketamine N-demethylase, methylayapanine O-demethylase, and coumarin 7-hydroxylase. Hydroperoxide formation was increased but lipoperoxidation was reduced. Neither glucuronyltransferase I nor glucuronyltransferase II were affected by bromobenzene treatment.

Action of ammonium meta vanadate on hepatic enzymes in vitro

In an in vitro study with rat liver, ammonium meta vanadate (NH4VO3) was found to inhibit microsomal ketamine N-demethylation, lipid peroxidation, and hydrogen peroxide formation; to have no effects on 4-methylaminoantipyrine N-demethylation and on glucuronyltransferase I activity, and to enhance glucuronyltransferase II. Mitochondrial succinate dehydrogenase and cytochrome c reductase were inhibited but cytochrome oxidase activity was enhanced by ammonium vanadate. Ammonium meta vanadate increased malate dehydrogenase activity but had no effect on glutamate, lactate, glycerophosphate, isocitrate, glucose-6-phosphate, and 6-phosphogluconate dehydrogenases.

Interaction of organic dyes with hepatic microsomal drug-metabolizing monoöxygenases in vitro

Organic dyes such as malachite green, methylene blue, fuchsin, safranine T, neutral red, phenazine methosulphate, riboflavin, dichlorophenolindophenol, phenolphthalein, and fluorescein, inhibit hepatic microsomal mixed-function oxidases and, partly, enhance, partly, inhibit hepatic microsomal NADPH-dependent cytochrome c and neotetrazolium reductases, in contrast to other inhibitors of drug metabolism which do not affect cytochrome c reductase but only interact with cytochrome P-450.

Studies on liver toxicants: influence of bromobenzene on hepatic microsomal enzymes in mice

The effect of acute bromobenzene intoxication on drug-metabolizing liver enzymes was studied. After an oral dose of 3000 mg/kg body weight of bromobenzene, the glucuronyltransferases I and II were increased, indicating an enzyme activation by this organic solvent via membrane irritation. The mixed-function oxidases were inhibited with the exception of the ketamine N-demethylase. Microsomal lipoperoxidation was reduced whilst H2O2 formation was unchanged.