Metabolism Of Bromobenzene Research Articles

Protective effect of 16,16-dimethyl prostaglandin E 2 on the hepatotoxicity of bromobenzene in mice

It has been suggested that 16,16-dimethyl prostaglandin E 2 may have a cytoprotective effect in the liver. To assess this hypothesis, we determined the effects of this prostaglandin on the metabolism and toxicity of bromobenzene in mice. Administration of 16,16-dimethyl prostaglandin E 2 (50 μg/kg s.c., 30 min before, and every 6 hr after, the administration of bromobenzene) did not modify the disappearance curves of unchanged bromobenzene from plasma and liver, and did not modify the amount of bromobenzene metabolites covalently bound to hepatic proteins 1–24 hr after the administration of a toxic dose of bromobenzene (0.36 ml/kg i.p.). The prostaglandin, however, markedly reduced serum alanine aminotransferase activity, the extent of liver cell necrosis, the depletion of glutathione, and the disappearance of cytochrome P-450 after administration of this toxic dose of bromobenzene (0.36 ml/kg i.p.). It also markedly reduced mortality after administration of a lethal dose of bromobenzene (0.43 ml/kg i.p.). We conclude that 16,16-dimethyl prostaglandin E 2 can prevent hepatic necrosis without decreasing the covalent binding of bromobenzene metabolites to hepatic proteins. The mechanism for this dissociation between covalent binding and toxicity remains unknown.

Mechanisms for modification of bromobenzene hepatotoxicity by coadministered toluene and chlorobenzene

Hepatotoxicity of bromobenzene (2 mmole/kg) in combination with toluene or chlorobenzene (4 mmole/kg each) were studied in vivo on the basis of GPT elevation and histological examinations. Both toluene and chlorobenzene suppressed bromobenzene hepatotoxicity 24 hr after the treatment, and chlorobenzene dramatically potentiated the toxicity at 48 hr. The glutathione level became lower at 12 hr and recovered at 24 hr when bromobenzene was given alone. The recovery delayed until 48 hr when chlorobenzene was coadministered. In experiments in vitro with microsomes from phenobarbital-pretreated rats, both toluene and chlorobenzene at 0.6 mM inhibited p-bromophenol formation noncompetitively but had no effect on o-isomer formation. Multiple factors may determine overall hepatotoxicity in combined exposure; bromobenzene hepatotoxicity will be suppressed in the early phase owing to metabolic inhibition of 3,4-epoxidation, but potentiated later because of delayed recovery in the glutathione level. A time-saving yet reliable assay system with an ECD-gas chromatograph was developed for bromobenzene metabolism study.

Time and dose dependency of bromobenzene metabolism and toxicity using isolated rat hepatocytes

Time and dose dependency of bromobenzene metabolism and toxicity using isolated rat hepatocytes

Metabolic activation and hepatotoxicity: Toxicity of bromobenzene in hepatocytes isolated from phenobarbital- and diethylmaleate-treated rats

Hepatocytes freshly isolated from diethylmaleate-treated rats exhibited a markedly decreased concentration of reduced glutathione (GSH) which increased to the level present in hepatocytes from nontreated rats upon incubation in a complete medium. When bromobenzene was present in the medium, however, this increase in GSH concentration upon incubation was reversed and a further decrease occurred that resulted in GSH depletion and cell death. This was prevented by metyrapone, an inhibitor of the cytochrome P-450-linked metabolism of bromobenzene. Bromobenzene metabolism in hepatocytes was accompanied by a fraction of metabolites covalently binding to cellular proteins. The size of this fraction, relative to the amount of total metabolites, was increased in hepatocytes isolated from diethylmaleate-treated rats and in hepatocytes from phenobarbital-treated rats incubated with bromobenzene in the presence of 1,2-epoxy-3,3,3-trichloropropane, an inhibitor of microsomal epoxide hydrase which, however, also acted as a GSH-depleting agent. In addition, the metabolism of bromobenzene by hepatocytes was associated with a marked decrease in various coenzyme levels, including coenzyme A, NAD(H), and NADP(H). Cysteine and cysteamine inhibited the formation of protein-bound metabolites of bromobenzene in microsomes, but did not prevent bromobenzene toxicity in hepatocytes when added at higher concentrations to the incubation medium (containing 0.4 m m cysteine). Methionine, on the other hand, did not cause a significant effect on bromobenzene metabolism in microsomes and prevented toxicity in hepatocytes, presumably by stimulating GSH synthesis and thereby decreasing the amount of reactive metabolites available for interaction with other cellular nucleophiles. It is concluded that, in contrast to hepatocytes with normal levels of GSH, hepatocytes from diethylmaleate-treated rats were sensitive to bromobenzene toxicity under our incubation conditions. In this system, bromobenzene metabolism led to GSH depletion and was associated with a progressive decrease in coenzyme A and nicotinamide nucleotide levels and a moderate increase in the formation of metabolites covalently bound to protein. Methionine was a potent protective agent which probably acted by enhanced GSH synthesis via the formation of cystathionine.

Metabolic activation and hepatotoxicity: Metabolism of bromobenzene in isolated hepatocytes

Rat liver microsomes and isolated rat hepatocytes metabolized bromobenzene to watersoluble and protein-bound metabolites. The latter fraction—which normally accounted for 2–5% of the total products—was slightly increased when 1,2-epoxy-3,3,3-trichloropropane, an inhibitor of microsomal epoxide hydrase, was added to the microsomal incubate. The presence of reduced glutathione (GSH), on the other hand, caused an almost complete inhibition of the formation of protein-bound metabolites from bromobenzene in microsomes. The rates of bromobenzene metabolism were similar in liver microsomes and hepatocytes, and increased severalfold after phenobarbital pretreatment of the rats. Metyrapone and SKF 525-A were inhibitory in both systems. Bromobenzene metabolism in hepatocytes isolated from phenobarbital-treated rats was associated with a rapid and marked decrease in the level of intracellular GSH. When the cells were incubated in a complete medium, however, the decrease in GSH leveled off at about 40% of the original concentration and there was no evidence of any accelerated rate of cell death even when the incubation with bromobenzene was prolonged to 10 h. This was most probably due to resynthesis of GSH by the hepatocytes, which partly compensated for the loss of this thiol associated with bromobenzene metabolism. Accordingly, in a deficient medium (lacking amino acids), the cytotoxic effect of bromobenzene metabolism was pronounced—less than 5% of the zerotime level of GSH and only 25% cell viability remaining after 5 h of incubation. It is concluded that the intracellular level of GSH is of major importance in regard to the cytotoxic effect of bromobenzene metabolism and that hepatocytes incubated in a complete medium are protected against toxicity by their ability to resynthesize this thiol.

3148. Epoxidation likely in bromobenzene metabolism: Ruzo, L. O., Safe S. & Hutzinger, O. (1976). Metabolism of bromobenzenes in the rabbit. J. agric. Fd Chem. 24, 291.

3148. Epoxidation likely in bromobenzene metabolism: Ruzo, L. O., Safe S. & Hutzinger, O. (1976). Metabolism of bromobenzenes in the rabbit. J. agric. Fd Chem. 24, 291.

Mechanism of renal necrosis induced by bromobenzene

Treatment of mice or rats with a single intraperitoneal dose of [ 14C]-bromobenzene or [ 14C]-chlorobenzene produced necrosis of the proximal convoluted renal tubules within 24–48 hr. The development of renal necrosis was associated with the covalent binding of substantial amounts of radiolabeled material to kidney proteins, and autoradiograms revealed that most of the covalently bound material was localized within the necrotic tubular cells. Prior inhibition of [ 14C]-bromobenzene metabolism in vivo with piperonyl butoxide blocked both the necrosis and the binding, suggesting that the necrosis and binding are caused by a toxic metabolite. Studies on the metabolism and covalent binding of [ 14C]-bromobenzene in hepatic and renal microsomes in vitro were compatible with the interpretation that the renal necrosis was caused by a metabolite formed in the liver and transported by the circulation to binding sites in the renal tubules.

Active products of fetal drug metabolism.

Theoretical relationships between the activities of placental and fetal enzymes and their ability to perturb the steady‐state tissue levels of drugs have been calculated. Although the calculations suggest that the activities of the enzymes that metabolize desipramine and 3,4‐benzpyrene in human placentas and fetuses may be high enough to decrease the steady‐state concentrations of these substances, the rates of metabolism of most drugs are probably too slow to affect the fetal levels of most lipid‐soluble compounds. It is also probable that the rate of bromobenzene metabolism by cytochrome P‐450 enzymes in fetal liver is too slow to cause liver necrosis caused by this toxicant. Nevertheless, it is possible that enzymes that catalyze the reduction of nitro compounds, such as nitrofurazone, to hydroxylamino derivatives may mediate various drug toxicities in fetuses.

Bromobenzene metabolism and hepatic necrosis.

Treatment of rats with Phenobarbital stimulates the metabolism of bromobenzene and potentiates the hepatic necrosis elicited by the hydrocarbon. In contrast, administration of SKF 525-A or of piperonyl butoxide blocks bromobenzene metabolism and prevents the damage to the liver. These results indicate that the hepatotoxic effect of bromobenzene is mediated by a metabolite.

Biochemical studies of toxic agents. The isolation of premercapturic acids from the urine of animals dosed with chlorobenzene and bromobenzene

1. A premercapturic acid, i.e. a compound that yields a mercapturic acid when decomposed by acid, was isolated as a dicyclohexylammonium salt from the urine of rats and rabbits that had been dosed with bromobenzene. 2. Another premercapturic acid was isolated as its dicyclohexylammonium salt from the urine of rats that had been dosed with chlorobenzene. 3. When decomposed by acid, the premercapturic acid from the urine of animals dosed with bromobenzene gave p-bromophenylmercapturic acid, m-and p-bromophenol and NN'-diacetylcystine. 4. The premercapturic acid derived from chlorobenzene gave the corresponding chloro compounds together with NN'-diacetylcystine when decomposed by acid. 5. On the basis of these and other observations it is suggested that the premercapturic acid formed in the metabolism of bromobenzene is N-acetyl-S-(4-bromo-1,2-dihydro-2-hydroxyphenyl)-l-cysteine. 6. It is also suggested that the premercapturic acid derived from chlorobenzene has an analogous structure.

Metabolism of Bromobenzene in Growing Dogs and Mice Maintained on Adequate Diets.

Monohalogen benzenes, when fed, are excreted in the urine of adult dogs,1 cats,2 rats,3 and rabbits,4 partly as ethereal sulfates, partly as mercapturic acids. Hele,5 in an attempt to compare the synthesis of mercapturic acid in dogs and pigs, has come to the conclusion that the pig does not synthesize mercapturic acid readily. Hele5 used young growing pigs as experimental animals in comparing the metabolism of bromobenzene in pigs to that in the adult dog. Inasmuch as Abderhalden6 believes that the synthesis of mercapturic acid is limited in the animal body by the need of that animal for sulfur for reactions more essential than the detoxication of bromobenzene, it seemed probable that the limitation of synthesis of mercapturic acid in the pig as found by Hele5 was due to the fact that he employed young growing pigs instead of the adult animal. White and Jackson7 have adduced evidence which seems to indicate that bromobenzene, when fed to growing rats, affects the utilization by the animals of cystine nec...