Bromobenzene Administration Research Articles

Different Hepatic Concentrations of Bromobenzene, 1,2-Dibromobenzene, and 1,4-Dibromobenzene in Humanized-Liver Mice Predicted Using Simplified Physiologically Based Pharmacokinetic Models as Putative Markers of Toxicological Potential.

Bromobenzene is an industrial solvent that elicits toxicity predominantly in the liver. In this study, the hepatic concentrations of bromobenzene and its related compounds 1,2-dibromobenzene and 1,4-dibromobenzene in humanized-liver mice were predicted after single oral administrations by simplified physiologically based pharmacokinetic (PBPK) models that had been set up on experimental plasma concentrations after single oral doses of 100 mg/kg to rats and 100-250 mg/kg to control mice and humanized-liver mice. The output values by simplified PBPK models were consistent with measured blood substrate concentrations in rats, control mice, and humanized-liver mice with suitable input parameter values derived from in silico prediction and the literature or estimated by fitting the measured plasma substrate concentrations. The predicted time-dependent hepatic concentrations after virtual administrations in humanized-liver mice were partly confirmed with single measured hepatic concentrations of bromobenzene and 1,4-dibromobenzene 2 h after oral doses of 150-250 mg/kg to humanized-liver mice. Moreover, leaked human albumin mRNA, a marker of the extent of human hepatic injuries, in humanized-liver mouse plasma was detected after oral administration of bromobenzene, 1,2-dibromobenzene, and 1,4-dibromobenzene. These results suggest that dosimetry approaches for determining tissue and/or blood exposures of hepatic toxicants bromobenzene, 1,2-dibromobenzene, and 1,4-dibromobenzene in humanized-liver mice were useful after virtual oral doses using simplified PBPK models. Using simplified PBPK models and plasma data from humanized-liver mice has potential to predict and evaluate the hepatic toxicity of bromobenzenes and related compounds in humanized-liver mice and in humans.

A biochemical approach to the anti-inflammatory, antioxidant and antiapoptotic potential of beta-carotene as a protective agent against bromobenzene-induced hepatotoxicity in female Wistar albino rats.

Bromobenzene is a compound which has contributed much in understanding the mechanisms involved in xenobiotic hepatotoxicity induced by drugs and environment pollutants. In the present study, the protective and ameliorative effect of beta-carotene was investigated against bromobenzene-induced hepatotoxicity and compared with silymarin, a standard hepatoprotective reference drug. Beta-carotene (10 mg/kg b.w. p.o.) was administered to the rats for 9 days before intragastric intubation of bromobenzene (10 mmol/kg b.w.). Liver marker enzymes (aspartate transaminase, alanine transaminase and alkaline phosphatase), total protein content, bilirubin, total cholesterol, high-density lipoproteins, triglycerides, antioxidant status (reduced glutathione, superoxide dismutase, catalase, glutathione-S-transferase and glutathione peroxidase) were assessed along with histopathological analysis. ELISA was performed for analysing the levels of cytokines such as TNF-α, IL-1β and IL-6 in serum and in the liver. Caspase-3, COX-2 and NF-κB were evaluated by Western blotting. Administration of bromobenzene resulted in elevated levels of liver marker enzymes, bilirubin, lipid peroxidation and cytokines but deterioration in total protein content, antioxidant levels and histopathological conditions. Pre-treatment with beta-carotene not only significantly decreased the levels of liver markers, lipid peroxidation and cytokines but also improved histo-architecture and increased antioxidant levels minimising oxidative stress, and reduced factors contributing to apoptosis. This significant reversal of the biochemical changes on pre-treatment with beta-carotene in comparison with rats administered with bromobenzene clearly demonstrates that beta-carotene possesses promising hepatoprotective effect through its antioxidant, anti-inflammatory and antiapoptotic activity and hence is suggested as a potential therapeutic agent for protection from bromobenzene.

Protective effect of aqueous extract of Phyllanthus fraternus against bromobenzene induced changes on cytosolic glutathione S-transferase isozymes in rat liver

The aim of this study was to investigate beneficial effect of aqueous extract of Phyllanthus fraternus (AEPF) on bromobenzene (BB) induced changes on cytosolic glutathione S-transferase (GST) isozymes in rat liver. Administration of BB significantly decreased the activity of GST, however, prior administration of AEPF prevented the BB induced decrease in GST activity. Further the cytosolic GSTs were purified from 3 groups of animals (control, BB and AEPF+BB administered) and resolved into three protein bands on SDS-PAGE. Densitometric analysis showed a significant decrease in BB group compared to control. Further, 2D PAGE analysis resolved these proteins into 8 bands which were identified as five isozymes of alpha, two of Mu and one of theta by MALDI-TOF MS and also observed decreased levels of isozymes in BB group. However, on prior administration of AEPF significantly prevented the BB induced decrease in GSTs and restored to normal levels.

Alleviation of the hepatotoxic effect of bromobenzene by the Indian traditional herbal formulation Triphala in experimental rats

The present study is an attempt to investigate the efficacy of Triphala in ameliorating the hepatotoxic effects of bromobenzene (BB) in experimental rats. Hepatotoxicity was induced in rats by oral administration of BB (1.57 mg/kg b.w.) and Triphala was given orally at two doses of 250 and 500 mg/kg b.w. for a period of 8 days. The antioxidant status was studied by measuring lipid peroxidation, total reduced glutathione levels and enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S-transferase (GST) in liver tissue homogenates. In addition, the levels of cytokines such as tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were measured in serum. The hepatoprotective role of Triphala was compared with that of the standard hepatoprotective agent silymarin. The treatment of BB-intoxicated rats with Triphala showed significant (p < 0.05) increase in the antioxidant status and significant (p < 0.05) reduction in the levels of Tumour Necrosis Factor-α (TNF-α), Interleukin-1β (IL-1β). The histopathological findings further confirmed the protective role of Triphala against BB-induced hepatotoxicity in rats. From the results obtained in this study, it can be concluded that treatment with Triphala alleviated the hepatotoxic effect of BB in experimental rats.

Amelioration of bromobenzene hepatotoxicity by Withania somnifera pretreatment: Role of mitochondrial oxidative stress

The present study investigated the possible protective role of Withania somnifera (Linn.) Dunal (Solanaceae) root powder against bromobenzene-induced oxidative damage in rat liver mitochondria. Administration of bromobenzene (10 mmol/kg body weight) to rats resulted in increased levels of liver marker enzymes, lipid peroxidation, TNF-α, IL-1β and VEGF. There was also marked depletion in the levels of mitochondrial enzymes and antioxidant activity. Pre-treatment with W. somnifera significantly decreased the levels of liver marker enzymes, TNF-α, IL-1β, VEGF and ameliorated histopathological manifestations in bromobenzene-treated rats. The molecular docking analysis predicted that the pro-inflammatory mediator NF-κB showed significant interaction with selected various active components of W. somnifera (withaferin A, withanolide D and withanolide E). This study demonstrates a good protective effect of W. somnifera against bromobenzene-induced oxidative stress.

Protective effect of Phyllanthus fraternus against bromobenzene-induced mitochondrial dysfunction in rat kidney

Phyllanthus fraternus(PF) (Euphorbiaceae) is used in ancient Indian traditional phytomedicine to treat various human diseases including hepatic and renal disorders. The present study was designed to investigate the protective effect of PF aqueous extract against bromobenzene-induced mitochondrial dysfunction in rat kidney, compared with vitamin E used as positive control. Male Wistar rats divided into six (A-F) groups and the experimental animals were administered bromobenzene with or without prior administration of PF extract or vitamin E. Animals were sacrificed and the kidneys obtained for studying mitochondrial function and histopathology. Administration of bromobenzene caused significant changes, including decrease in the mitochondrial respiration and P/O ratios, an increase in lipid peroxidation and protein oxidation, and a decrease in the activities of antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase, and glutathione peroxidase) in mitochondria with significant histopathological changes in the kidney. However, prior administration of the PF extract showed significant protection against bromobenzene induced renal damage by reversing all above parameters. Mitochondrial dysfunction induced by bromobenzene was protected much better with the PF extract than with vitamin E. These results suggested that the Phyllanthus fraternus extract is an efficient armament against nephrotoxicity induced by bromobenzene.

Protective Effect of Hemidesmus indicus L. R. Br. Against Bromobenzene-Induced Mitochondrial Dysfunction in Rat Kidney

Hemidesmus indicus (HI) is used in ancient Indian traditional herbal medicine to treat hepatic and renal disorders. The present study was designed to investigate the protective effect of HI aqueous extract against bromobenzene induced mitochondrial dysfunction in rat kidneys. Rats were administered bromobenzene with or without prior administration of HI or vitamin E. At the end of the experiment animals were sacrificed and kidneys were obtained to study mitochondrial function, oxidative stress parameters and histopathology. Administration of bromobenzene caused significant changes like: decrease in the mitochondrial respiration and P/O ratios, increase in lipid peroxidation and protein oxidation, and decrease in the activities of antioxidant enzymes (catalase, glutathione reductase, glutathione peroxidase and superoxide dismutase) in mitochondria with significant histopathological changes in the kidney. Prior administration of HI extract showed a significant protection against bromobenzene induced changes in the kidney and this effect is attributed to the antioxidant and free radical scavenging potential of the HI. The protection was much better with HI compared to vitamin E.

Protective effect of Phyllanthus fraternus against bromobenzene induced mitochondrial dysfunction in rat liver mitochondria

The objective of the current study was to investigate the protective effect of an aqueous extract of Phyllanthus fraternus (AEPF) against bromobenzene induced mitochondrial dysfunction in rat liver mitochondria. Administration of bromobenzene (10 mmol/kg body wt.) significantly decreased the rate of respiration (with glutamate + malate or succinate as substrates), abolished respiratory control ratio (RCR) and P/O ratios completely. There was a significant increase in the levels of lipid peroxides and protein carbonyls and a significant decrease in the total sulphydryl groups. The activities of antioxidant enzymes like catalase, glutathione peroxidase (GPx), glutathione reductase (GR) and superoxide dismutase (SOD) were decreased. The levels of antioxidants like reduced and oxidized glutathione were significantly decreased compared to control. Administration of rats with an AEPF (100 mg/kg body wt.) prior to bromobenzene administration showed several beneficial effects like: (i) complete protection on mitochondrial respiration, RCR and P/O ratios (ii) lipid peroxides and protein carbonyl levels were significantly lowered (iii) increased the levels of sulphydryl groups and the activity of antioxidant enzymes and (iv) significant increase in the levels of reduced and oxidized glutathione. Vitamin E was used as positive control and bromobenzene induced mitochondrial dysfunction was protected better with AEPF compared to vitamin E.

Beneficial effect of the administration of Hemidesmus indicus against bromobenzene induced oxidative stress in rat liver mitochondria

Aim of the study To study the beneficial effect of the prior administration of an aqueous extract of Hemidesmus indicus against bromobenzene induced oxidative damage in rat liver mitochondria. Materials and methods Oxidative stress was induced in rats with bromobenzene (10 mmol/kg body wt.). The rate of respiration, P/O ratios, lipid peroxides, protein carbonyls and sulphydryls were studied. Results When the rats were administered with bromobenzene, the rate of respiration was decreased significantly and the P/O ratio was completely abolished. There was a significant increase on the levels of lipid peroxide and protein carbonyl and a significant decrease on total sulphydryl groups when compared with control. Administration of rats with an aqueous extract (100 mg/kg) prior to bromobenzene administration showed significant beneficial effects like, stimulation in respiration, prevented the rise in lipid peroxides and protein carbonyls, increased the level of sulphydryl groups back to control level. Administration of vitamin E could not reverse as effectively as Hemidesmus indicus. Conclusions This study demonstrates a good protective effect of Hemidesmus indicus against the bromobenzene induced oxidative stress.

Investigation of the effect of a panel of model hepatotoxins on the Nrf2-Keap1 defence response pathway in CD-1 mice

The Keap1-Nrf2-ARE signalling pathway has emerged as an important regulator of the mammalian defence system to enable detoxification and clearance of foreign chemicals. Recent studies by our group using paracetamol (APAP), diethylmaleate and buthionine sulphoximine have shown that for a given xenobiotic molecule, Nrf2 induction in the murine liver is associated with protein reactivity and glutathione depletion. Here, we have investigated, in vivo, whether the ability of four murine hepatotoxins, paracetamol, bromobenzene (BB), carbon tetrachloride (CCl 4) and furosemide (FS) to deplete hepatic glutathione (GSH) is related to induction of hepatic Nrf2 nuclear translocation and Nrf2-dependent gene expression. Additionally, we studied whether hepatic Nrf2 nuclear translocation is a general response during the early stages of acute hepatic chemical stress in vivo. Male CD-1 mice were administered APAP (3.5 mmol/kg), FS (1.21 mmol/kg), BB (4.8 mmol/kg) and CCl 4 (1 mmol/kg) for 1, 5 and 24 h. Each compound elicited significant serum ALT increases after 24 h (ALT U/L: APAP, 3036 ± 1462; BB, 5308 ± 2210; CCl 4, 5089 ± 1665; FS, 2301 ± 1053), accompanied by centrilobular damage as assessed by histopathology. Treatment with APAP also elicited toxicity at a much earlier time point (5 h) than the other hepatotoxins (ALT U/L: APAP, 1780 ± 661; BB, 161 ± 15; CCl 4, 90 ± 23; FS, 136 ± 27). Significant GSH depletion was seen with APAP (9.6 ± 1.7% of control levels) and BB (52.8 ± 6.2% of control levels) 1 h after administration, but not with FS and CCl 4. Western Blot analysis revealed an increase in nuclear Nrf2, 1 h after administration of BB (209 ± 10% control), CCl 4 (146 ± 3% control) and FS (254 ± 41% control), however this was significantly lower than the levels observed in the APAP-treated mice (462 ± 36% control). The levels of Nrf2-dependent gene induction were also analysed by quantitative real-time PCR and Western blotting. Treatment with APAP for 1 h caused a significant increase in the levels of haem oxygenase-1 (HO-1; 2.85-fold) and glutamate cysteine ligase (GCLC; 1.62-fold) mRNA. BB and FS did not affect the mRNA levels of either gene after 1 h of treatment; however CCl 4 significantly increased HO-1 mRNA at this time point. After 24 h treatment with the hepatotoxins, there was evidence for the initiation of a late defence response. BB significantly increased both HO-1 and GCLC protein at this time point, CCl 4 increased GCLC protein alone, although FS did not alter either of these proteins. In summary, we have demonstrated that the hepatotoxins BB, CCl 4 and FS can induce a small but significant increase in Nrf2 accumulation in hepatic nuclei. However, this was associated with modest changes in hepatic GSH, a delayed development of toxicity and was insufficient to activate an early functional adaptive response to these hepatotoxins.

Changes in hepatic drug metabolizing enzymes and lipid peroxidation by methanol extract and major compound of Orostachys japonicus

The effects of methanol extract and gallic acid (3,4,5-trihydroxybenzoic acid) of Orostachys japonicus A. Berger on hepatic drug metabolizing enzymes and lipid peroxidation were investigated in rats treated with bromobenzene. The methanol extract of Orostachys japonicus reduced the activities of phase I enzymes, aminopyrine N-demethylase and aniline hydroxylase, that had been increased by i.p. injection of bromobenzene. Gallic acid isolated from Orostachys japonicus also reduced the aniline hydroxylase activity, while it did not affect the aminopyrine N-demethylase activity. The methanol extract and gallic acid restored the activity of epoxide hydrolase which had been decreased by bromobenzene. Hepatic glutathione content was lowered, along with increase in hepatic lipid peroxide, by bromobenzene administration. The hepatic lipid peroxidation induced by bromobenzene was prevented with the methanol extract and gallic acid of Orostachys japonicus. However, the decrease in glutathione was not altered by gallic acid. The present results suggest that the methanol extract and gallic acid of Orostachys japonicus may protect liver from bromobenzene toxicity through, at least in part, inhibiting the cytochrome P450-dependent monooxygenase activities and enhancing the activity of epoxide hydrolase. Antioxidant effect also may contribute to the protection of Orostachys japonicus against the bromobenzene-induced hepatotoxicity.

Subliminal Fas stimulation increases the hepatotoxicity of acetaminophen and bromobenzene in mice.

The hepatotoxicity of several drugs is increased by mild viral infections. During such infections, death receptor ligands are expressed at low levels, and most parenchymal cells survive. We tested the hypothesis that subliminal death receptor stimulation may aggravate the hepatotoxicity of drugs, which are transformed by cytochrome P-450 cytochrome P-450 into glutathione-depleting reactive metabolites. Twenty-four-hour-fasted mice were pretreated with a subtoxic dose of the agonistic Jo2 anti-Fas antibody (1 microg per mouse) 3 hours before acetaminophen (500 mg/kg) or 1 hour before bromobenzene (400 mg/kg) administration. Administration of Jo2 alone increased hepatic inducible nitric oxide synthase nitric oxide synthase but did not modify serum alanine aminotransferase (ALT), hepatic adenosine triphosphate (ATP), glutathione (GSH), cytochrome P-450, cytosolic cytochrome c, caspase-3 activity or hepatic morphology. However, pretreating mice with Jo2 further decreased both hepatic GSH and ATP by 40% 4 hours after acetaminophen administration, and further increased serum ALT and the area of centrilobular necrosis at 24 hours. In mice pretreated with the Jo2 antibody before bromobenzene administration, hepatic GSH 4 hours after bromobenzene administration was 51% lower than in mice treated with bromobenzene alone, and serum ALT activity at 24 hours was 47-fold higher. In conclusion, administration of a subtoxic dose of an agonistic anti-Fas antibody before acetaminophen or bromobenzene increases metabolite-mediated GSH depletion and hepatotoxicity. Subliminal death receptor stimulation may be one mechanism whereby mild viral infections can increase drug-induced toxicity.

Toxicogenomics of bromobenzene hepatotoxicity: a combined transcriptomics and proteomics approach

Toxicogenomics is a novel approach integrating the expression analysis of thousands of genes (transcriptomics) or proteins (proteomics) with classical methods in toxicology. Effects at the molecular level are related to pathophysiological changes of the organisms, enabling detailed comparison of mechanisms and early detection and prediction of toxicity. This report addresses the value of the combined use of transcriptomics and proteomics technologies in toxicology. Acute hepatotoxicity was induced in rats by bromobenzene administration resulting in depleted glutathione levels and reduced average body weights, 24 hr after dosage. These physiological symptoms coincided with many changes of hepatic mRNA and protein content. Gene induction confirmed involvement of glutathione- S-transferase isozymes and epoxide hydrolase in bromobenzene metabolism and identified many genes possibly relevant in bromobenzene toxicity. Observed glutathione depletion coincided with induction of the key enzyme in glutathione biosynthesis, γ-glutamylcysteine synthetase. Oxidative stress was apparent from strong upregulation of heme oxygenase, peroxiredoxin 1 and other genes. Bromobenzene-induced protein degradation was suggested from two-dimensional gel electrophoresis, upregulated mRNA levels for proteasome subunits and lysosomal cathepsin L, whereas also genes were upregulated with a role in protein synthesis. Both protein and gene expression profiles from treated rats were clearly distinct from controls as shown by principal component analysis, and several proteins found to significantly change upon bromobenzene treatment were identified by mass spectrometry. A modest overlap in results from proteomics and transcriptomics was found. This work indicates that transcriptomics and proteomics technologies are complementary to each other and provide new possibilities in molecular toxicology.

Role of perivenous hepatocytes in taurolithocholate-induced cholestasis in vivo

The magnitude of cholestasis induced by taurolithocholic acid (TLCA) and its relationship with phase I metabolism were analyzed in rats treated with bromobenzene (BZ), a chemical that causes selective necrosis of perivenous (zone 3) hepatocytes. Forty-eight hours after BZ administration (600 mg/Kg bw), a single dose of 20 μmol/Kg bw of TLCA was injected. Bile was collected during 180 min and bile flow and total bile acid excretion rate were determined. Biliary bile acid composition was analyzed by gas–liquid chromatography-mass spectrometry. BZ administration did not affect the development of TLCA-induced cholestasis, but exacerbated the bile acid-induced decrease in bile flow during the period of recovery from cholestasis. Biliary excretion of total bile acids after TLCA injection relative to basal value was not effected by BZ. The analysis of bile acid composition in bile revealed that TLCA was partially converted to hyodeoxycholic and muricholic acids. The cumulative excretion of all exogenous bile acids and their contribution to the composition of the biliary bile acid pool were not substantially affected by zone 3 necrosis, suggesting that synthesis and secretion of hydroxylated derivatives of TLCA were maintained by zone 1 and 2 hepatocytes. The relative content of endogenous bile acids was not affected by BZ during TLCA-induced cholestasis. Thus, it seems unlikely that the exacerbation of the cholestasis in BZ-treated rats is due to different choleretic properties and/or toxicity of the bile acid pool.

Inhibition of Glutathione Synthesis with Propargylglycine Enhances N-Acetylmethionine Protection and Methylation in Bromobenzene-Treated Syrian Hamsters

The finding that liver necrosis caused by the environmental glutathione (GSH)-depleting chemical, bromobenzene (BB) is associated with marked impairment in O- and S-methylation of BB metabolites in Syrian hamsters raises questions concerning the role of methyl deficiency in BB toxicity. N-Acetylmethionine (NAM) has proven to be an effective antidote against BB toxicity when given after liver GSH has been depleted extensively. The mechanism of protection by NAM may occur via a replacement of methyl donor and/or via an increase of GSH synthesis. If replacement of the methyl donor is an important process, then blocking the resynthesis of GSH in the methyl-repleted hamsters should not decrease NAM protection. This hypothesis was examined in this study. Propargylglycine (PPG), an irreversible inhibitor of cystathionase, was used to inhibit the utilization of NAM for GSH resynthesis. Two groups of hamsters were pretreated with an intraperitoneal (ip) dose of PPG (30 mg/kg) or saline 24 h before BB administration (800 mg/kg, ip). At 5 h after BB treatment, an ip dose of NAM (1200 mg/kg) was given. Light microscopic examinations of liver sections obtained 24 h after BB treatment indicated that NAM provided better protection (P < 0.05) in the PPG + BB + NAM group than in the BB + NAM group. Liver GSH content, however, was lower in the PPG + BB + NAM group than in the BB + NAM group. The Syrian hamster has a limited capability to N-deacetylated NAM. The substitution of NAM with methionine (Met; 450 mg/kg) resulted in a higher level of GSH in the BB + Met group than in the BB + NAM group (P < 0.05). The enhanced protection by PPG in the PPG + BB + NAM group was accompanied by higher (P < 0.05) urinary excretions of specificO- and S-methylated bromothiocatechols than in the BB + NAM group. The results suggest that NAM protection occurs primarily via a replacement of the methyl donor and that methyl deficiency occurring in response to GSH repletion plays a potential role in BB toxicity.

Role of SAM-dependent thiol methylation in the renal toxicity of several solvents in mice.

The role of S-adenosylmethionine (SAM)-dependent thiol methylation in the nephrotoxicity of seven industrial solvents was studied in mice. The seven following solvents were utilized: bromobenzene (BB), styrene (STY), tetrachloroethylene (TTCE), trichloroethylene (TCE), 1,1-dichloroethylene (DCE), 1,2-dichloroethane (DCA) and hexachlorobutadiene (HCB). The experimental model comprised mice pretreated with periodate oxidized adenosine (ADOX) (100 micromol kg(-1) i.p.) 30 min before injection of solvents. In the first 4 h after ADOX treatment, the SAM levels were about fourfold higher than controls for the liver and kidney. The S-adenosylhomocysteine (SAH) levels were increased by factors of 11 and 14 and the SAM/SAH ratios were decreased by factors of 3 and 10 for the liver and kidney, respectively. These results show that ADOX treatment probably induces an inhibition of methyltransferase SAM-dependent in the liver and kidney and thus decreases the methylation capabilities. A single oral administration of BB (500 or 800 mg kg(-1)), TTCE (3500 or 4000 mg kg(-1)), TCE (3000 or 3500 mg kg(-1)) or STY (400 or 600 mg kg(-1)) did not induce renal toxicity, evaluated by the percentage of damaged tubules compared to controls. On the other hand, the three solvents DCE, HCB and DCA were nephrotoxic and the percentage of damaged tubules observed for each solvent was significantly different from the value of <1.8% for controls: 19% and 40% for DCE (130 and 200 mg kg(-1)), 50% and 46% for HCB (80 and 100 mg kg(-1)) and 5.1% and 7.6% for DCA (1000 and 1500 mg kg(-1)). The ADOX treatment in the mice did not modify the renal toxicity of the seven solvents. Thus, their renal toxicity, when it existed, was probably independent of the SAM-dependent thiolmethyltransferase activity in the mice. The results of this study are discussed from two viewpoints. The first concerns the general considerations on inhibition of thiol methyltransferase activities in mice and the second is related to the different solvents that are evoked individually.

Lowering of lipid peroxidation and acute toxicity of bromobenzene by a polymeric form of zinc-metallothionein

Plasma and liver contents of malonic aldehyde are studied one day after administration of bromobenzene to mice pretreated with a polymeric form of zinc-metallothionein from rat liver. It is found that zinc-metallothionein injected in a dose of 1–4 mg/kg 5–10 min prior to injection of bromobenzene (2 g/kg, about 56% of LD50) markedly lowers the malonic dialdehyde level and active toxicity of this xenobiotic. Administration of a mixture modeling Zn-metallothionein (albumin, cysteine, and zinc) in a dose of 4 mg/kg has no appreciable effect on the malonic dialdehyde level raised after bromobenzene injection, and does not change its LD50. It is concluded that the protective effect of exogenous zinc-metallothionein is due to its antioxidant activity, which allows for normalization of lipid peroxidation.

Prevention of Bromobenzene Toxicity by N-Acetylmethionine: Correlation between Toxicity and the Impairment in O-Methylation and S-Methylation of Bromothiocatechols

Bromobenzene (800 mg/kg, ip) caused severe liver necrosis with massive hemorrhage in the golden Syrian hamster within the first 24 hr. Kidney injury was also observed. Treatment with N-acetylmethionine (NAM) at an ip dose of 1200 mg/kg at 5 hr after bromobenzene administration significantly protected the liver and kidney against injuries. Plasma glutamate pyruvate transaminase and blood urea nitrogen levels were substantially decreased in the NAM-treated animals. Histological evaluations confirmed these results. When the urinary neutral and phenolic metabolites of bromobenzene from NAM-treated and untreated hamsters were isolated and compared by GC and GC/ MS, a striking result was observed in terms of 0- and S-methylated thiol-containing metabolite formation. The NAM-treated animals showed approximately a 8- to 14-fold increase in the excretion of the four isomeric O and S-methylated bromothiocatechols. These thiocatechols, which are now known to be the 3,4- series metabolites of bromobenzene, can undergo methylation at either the thiol or the hydroxyl functional group. The excretion of 3-S- and 4-S-methylated bromodihydrobenzene thiolols was also increased significantly in the NAM-treated hamster, but other neutral and phenolic metabolites were relatively unchanged. These results suggest that bromobenzene toxicity in the Syrian hamster may be associated with impaired methylation capabilities, an impairment that could be due to methionine and glutathione depletion.

Severe monochlorobenzene-induced liver cell necrosis

Benzene derivatives can induce severe liver cell necrosis in animals. A case of a 40-year-old man whose daily consumption of alcohol was 200 g and who had a severe monochlorobenzene-induced liver necrosis is described. Liver biopsy specimen showed centrilobular and mediolobular necrosis, similar to that in mice after experimental bromobenzene administration. Monochlorobenzene serum concentration, assayed from day 3 to day 15 after poisoning, decreased monoexponentially with a half-life of 40.3 hours. Prostaglandin E1 was administered from day 3 to day 8. The patient ultimately recovered. The mechanism of monochlorobenzene-induced liver injury and the possible aggravating role of chronic alcohol consumption are discussed.

Short Term Inhalation of Bromobenzene: Methodology and Absorption Characteristics in Mouse, Rat and Rabbit

In a dynamic inhalation system, mice, rats and rabbits were exposed to bromobenzene vapour (250-3400 p.p.m.) for 4 hr. Blood concentrations of bromobenzene were determined by head-space gas chromatography. After inhalation of 1000 p.p.m. for 4 hr, concentrations of 153, 102 and 47 micrograms bromobenzene/ml blood were found in mice, rats and rabbits, respectively. In vitro experiments showed a blood/air partition coefficient at 37 degrees of approximately 200, which was reflected by a linear uptake of bromobenzene up to an air concentration of 2500 p.p.m. Compared with results obtained previously by intraperitoneal bromobenzene administration inhalation resulted in higher blood concentrations.