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

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.

Stability of microsomal mono-oxygenase during incubations for the liver microsomal assay with S9 fractions of mouse liver under various inductions

Aminopyrine-N-demethylase and p-nitroanisole-O-demethylase activities were determined in incubation mixtures for the liver microsomal assay at time zero and after 1 h of incubation in the conditions for the mutagenic assay. The experiments were performed with the S9 liver fraction of mice in the basal state and induced with sodium phenobarbital, beta-naphthoflavone or both. Lipid peroxidation was also determined. The experiments were repeated with female mice and also in the presence of styrene, as an example of a xenobiotic substance. The activity of pNAD was much more stable than that of APD in all the conditions tested. The pattern of stability, however, was similar for the two activities: more stable than controls with S9 fractions from beta-NF-induced mice, less stable than controls in PB-induced mice, intermediate between controls and PB-induced mice in those with combined induction by PB + beta NF. Styrene 50 mM in the incubation mixtures led to a marked inactivation of enzymic activity, similar in all cases and reaching about 90% in 1 h. S9 fractions from female mice gave enzymes slightly more stable in almost all cases. Lipid peroxidation was appreciably more elevated in basal than in induced animals. It was concluded that, for a mutagenesis test on an unknown xenobiotic, S9 fractions from mice following PB and beta-NF induction are to be preferred from the point of view of activation.

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.