Bromobenzene-glutathione excretion into bile reflects toxic activation of bromobenzene in rats

Pre-treatment with Beta Carotene Gives Protection Against Nephrotoxicity Induced by Bromobenzene via Modulation of Antioxidant System, Pro-inflammatory Cytokines and Pro-apoptotic Factors

Bromobenzene is an environmental toxin which causes hepatotoxicity, and the secondary metabolites on biotransformation cause nephrotoxicity. The objective of this study was to assess the alleviation of the nephrotoxic effect of bromobenzene by beta carotene in female Wistar albino rats. Beta carotene (10 mg/kg b.w.p.o.) was delivered orally to the rats for 9 days before bromobenzene (10 mM/kg b.w.p.o.) was intragastrically intubated. Kidney markers, antioxidant status and lipid peroxidation were evaluated. In addition, the levels of TNF-α, IL-6 and IL-1β were measured in serum and in kidney tissue homogenate using ELISA. Caspase, COX-2 and NF-κB were measured with the help of Western blotting. Histopathological analysis of the kidney was done for the control and experimental rats. Bromobenzene induction caused elevation in levels of creatinine, urea, uric acid, cytokines and lipid per oxidation along with deterioration in histological observations and antioxidant status. Pre-treatment with beta carotene significantly (*p < 0.05) normalised the levels of kidney markers and pro-inflammatory cytokines. It also reduced oxidative stress and lipid peroxidation, as shown by improved antioxidant status. The anti-apoptotic activity was evidenced by inhibition of protein expression of caspase, COX-2 and NF-κB. This significant reversal (*p < 0.05) of the above variations in comparison with the control group as noticed in the bromobenzene-administered rats demonstrates that beta carotene possesses promising nephroprotective effect through its antioxidant, anti-inflammatory and anti-apoptotic activity and therefore suggests its use as a potential therapeutic agent for protection from bromobenzene and hence environmental pollutant toxicity.

Bromobenzene-induced lethal toxicity in mouse is prevented by pretreatment with zinc sulfate

In the current study, we evaluated the protective effect of zinc (Zn) against bromobenzene (BB) -induced lethal toxicity. We used Zn because this element is known to be an inducer of metallothionein (MT), which is in turn known to serve as an endogenous scavenger of free radicals. We administered Zn (as ZnSO4) at 50 mg/kg subcutaneously once-daily for 3 successive days prior to a single intraperitoneal administration of 1.2 g/kg BB in male ddY mice. Our results showed that pretreatment with Zn completely abolished the BB-induced mortality of mice until 48 h. We also found that pretreatment of mice with Zn significantly decreased the functional marker levels and reduced the histological damage both in liver and kidney as assessed at 18 h post-BB. We also showed that pretreatment with Zn enhanced antioxidative activity, resulting in decreased lipid peroxidation in both liver and kidney. Moreover, BB-induced calcium levels were downregulated by pretreatment with Zn. In addition, Zn-induced MT was decreased in Zn + BB-treated animals, implying that MT was consumed by BB-induced radicals. These findings suggest that prophylaxis with Zn protects mice from BB-induced lethal toxicity by decreasing oxidative stress in liver and kidney, presumably by induction of MT, which scavenges radicals induced by BB exposure.

In vitro and in vivo antioxidant and antimutagenic activities of polyphenols extracted from hops (Humulus lupulus L.)

BACKGROUND

Hops (Humulus lupulus L.) contain 40-140 mg g(-1) polyphenols. The objective of this study was to determine the phenolic composition of a high-purity (total phenolic content = 887 mg g(-1) ) hop polyphenol extract (HPE) and evaluate its antioxidant activities in vivo and in vitro and its antimutagenic activity. The antioxidant activity of HPE was compared with the activity of green tea polyphenols.

RESULTS

The phenolic compositions of HPE were more than 55% proanthocyanidins and more than 28% flavonoid glycosides. In vitro, HPE effectively scavenged α,α-diphenyl-β-picrylhydrazyl, hydroxyl and superoxide anion radicals, and inhibited DNA oxidative damage. In vivo, oral HPE at a polyphenol dose of 200-800 mg kg(-1) body weight significantly prevented a bromobenzene-induced decrease in liver superoxide dismutase and glutathione peroxidase activity, and decreased levels of liver thiobarbituric acid reactive substances in bromobenzene-treated mice. An oral dose of 20-80 mg kg(-1) body weight HPE significantly reduced the frequency of bone marrow micronuclei induced by cyclophosphamide. The antioxidant activities of hop polyphenols in vitro and in vivo were higher than green tea polyphenols at the same concentration.

CONCLUSION

Hop polyphenols had the same or higher antioxidant activity than tea polyphenols. Hop polyphenols might be useful as natural antioxidants and antimutagens.

Hazard Evaluation Support System (HESS) for predicting repeated dose toxicity using toxicological categories

Repeated dose toxicity (RDT) is one of the most important hazard endpoints in the risk assessment of chemicals. However, due to the complexity of the endpoints associated with whole body assessment, it is difficult to build up a mechanistically transparent structure-activity model. The category approach, based on mechanism information, is considered to be an effective approach for data gap filling for RDT by read-across. Therefore, a library of toxicological categories was developed using experimental RDT data for 500 chemicals and mechanistic knowledge of the effects of these chemicals on different organs. As a result, 33 categories were defined for 14 types of toxicity, such as hepatotoxicity, hemolytic anemia, etc. This category library was then incorporated in the Hazard Evaluation Support System (HESS) integrated computational platform to provide mechanistically reasonable predictions of RDT values for untested chemicals. This article describes the establishment of a category library and the associated HESS functions used to facilitate the mechanistically reasonable grouping of chemicals and their subsequent read-across.

Protective effect of Cassia fistula fruit extract on bromobenzene-induced nephrotoxicity in mice

The efficacy of a crude hydro-alcoholic extract of Cassia fistula (golden shower tree) fruit to protect the kidney against bromobenzene-induced toxicity was studied. Negative control mice received normal saline; positive control mice were given 460 mg/kg of bromobenzene; Cassia fistula treated mice received 200, 400, 600 and 800 mg/kg of Cassia fistula fruit extract followed by 460 mg/kg bromobenzene (daily by oral gavage for 10 days). On the 11th day, the mice were sacrificed, blood samples were obtained to assess blood urea nitrogen (BUN) and creatinine levels, and kidneys were removed for histological examination. We found that bromobenzene induced significant nephrotoxicity reflected by an increase in levels of BUN and creatinine that was dose dependently prevented by the Cassia fistula fruit extract. The nephroprotective effect of the Cassia fistula fruit extract was confirmed by the histological examination of the kidneys. To the best of our knowledge, this is the first study to demonstrate the protective effect of Cassia fistula in nephrotoxicity.

Protective effect of ginger extract against bromobenzene-induced hepatotoxicity in male rats

The bromobenzene (BB)-induced hepatotoxicity comes from its reactive metabolites. The efficacy of different doses of ginger (Zingiber officinalesRose) extract in alleviating hepatotoxicity was investigated in male albino rats. Oxidative stress parameters were monitored. The drugs metabolizing enzymes; cytochrome P450 and GST, pro-inflammatory marker; COX-2 and the apoptotic marker; caspase-3 were assessed. Animals were assigned to 1 of 5 groups: control group; bromobenzene (460 mg/kg BW) alone, three animal groups 3-5 treated with different doses of ethanolic ginger extract (100, 200, 300 mg/kg BW, respectively) 2 weeks prior bromobenzene (460 mg/kg BW) treatment. Rats received orally ginger extract daily for 21 days whereas bromobenzene treatment for 7 days starting from 15th day of treatment. Oral treatment of BB was found to elicit a significant decrease in the activities of the antioxidant enzymes; SOD, GPx and the GSH level, while the activities of GR and drug metabolizing enzymes; GSTs and Cyt P450 were enhanced. Also, BB-treatment resulted in a great enhanced production of nitric oxide products and activation of COX-2 and caspase-3. Pre-treatment with different doses of ginger extract prior to BB-treatment alleviated its toxic effects on the tested parameters in the three animal groups.

Alterations in xenobiotic metabolism in the long-lived Little mice

Our previous microarray expression analysis of the long-lived Little mice (Ghrhr(lit/lit)) showed a concerted up-regulation of xenobiotic detoxification genes. Here, we show that this up-regulation is associated with a potent increase in resistance against the adverse effects of a variety of xenobiotics, including the hepatotoxins acetaminophen and bromobenzene and the paralyzing agent zoxazolamine. The classic xenobiotic receptors Car (Constitutive Androstane Receptor) and Pxr (Pregnane X Receptor) are considered key regulators of xenobiotic metabolism. Using double and triple knockout/mutant mouse models we found, however, that Car and Pxr are not required for the up-regulation of xenobiotic genes in Little mice. Our results suggest instead that bile acids and the primary bile acid receptor Fxr (farnesoid X receptor) are likely mediators of the up-regulation of xenobiotic detoxification genes in Little mice. Bile acid levels are considerably elevated in the bile, serum, and liver of Little mice. We found that treatment of wild-type animals with cholic acid, one of the major bile acids elevated in Little mice, mimics in large part the up-regulation of xenobiotic detoxification genes observed in Little mice. Additionally, the loss of Fxr had a major effect on the expression of the xenobiotic detoxification genes up-regulated in Little mice. A large fraction of these genes lost or decreased their high expression levels in double mutant mice for Fxr and Ghrhr. The alterations in xenobiotic metabolism in Little mice constitute a form of increased stress resistance and may contribute to the extended longevity of these mice.

Dansyl Glutathione as a Trapping Agent for the Quantitative Estimation and Identification of Reactive Metabolites

A sensitive and quantitative method was developed for the estimation of reactive metabolite formation in vitro. The method utilizes reduced glutathione (GSH) labeled with a fluorescence tag as a trapping agent and fluorescent detection for quantitation. The derivatization of GSH was accomplished by reaction of oxidized glutathione (GSSG) with dansyl chloride to form dansylated GSSG. Subsequent reduction of the disulfide bond yielded dansylated GSH (dGSH). Test compounds were incubated with human liver microsomes in the presence of dGSH and NADPH, and the resulting mixtures were analyzed by HPLC coupled with a fluorescence detector and a mass spectrometer for the quantitation and mass determination of the resulting dGSH adducts. The comparative chemical reactivity of dGSH vs GSH was investigated by monitoring the reaction of each with 1-chloro-2,4-dinitrobenzene or R-(+)-pulegone after bioactivation. dGSH was found to be equivalent to GSH in chemical reactivity toward both thiol reactive molecules. dGSH did not serve as a cofactor for glutathione S-transferase (GST)-mediated conjugation of 3,4-dichloronitrobenzene in incubations with either human liver S9 fractions or a recombinant GST, GSTM1-1. Reference compounds were tested in this assay, including seven compounds that have been reported to form GSH adducts along with seven drugs that are among the most prescribed in the current U.S. market and have not been reported to form GSH adducts. dGSH adducts were detected and quantitated in incubations with all seven positive reference compounds; however, there were no dGSH adducts observed with any of the widely prescribed drugs. In comparison with existing methods, this method is sensitive, quantitative, cost effective, and easy to implement.

Bromobenzene-induced hepatotoxicity at the transcriptome level

Rats were exposed to three levels of bromobenzene, sampled at 6, 24, and 48 h, and liver gene expression profiles were determined to identify dose and time-related changes. Expression of many genes changed transiently, and dependent on the dose. Few changes were identified after 6 h, but many genes were differentially expressed after 24 h, while after 48 h, only the high dose elicited large effects. Differentially expressed genes were involved in drug metabolism (upregulated GSTs, mEH, NQO1, Mrps, downregulated CYPs, sulfotransferases), oxidative stress (induced HO-1, peroxiredoxin, ferritin), GSH depletion (induced GCS-l, GSTA, GSTM) the acute phase response, and in processes like cholesterol, fatty acid and protein metabolism, and intracellular signaling. Trancriptional regulation via the electrophile and sterol response elements seemed to mediate part of the response to bromobenzene. Recovery of the liver was suggested in response to BB by the altered expression of genes involved in protein synthesis and cytoskeleton rearrangement. Furthermore, after 48 h, rats in the mid dose group showed no toxicity, and gene expression patterns resembled the normal situation. For certain genes (e.g., CYP4A, metallothioneins), intraday variation in expression levels was found, regardless of the treatment. Selected cDNA microarray measurements were confirmed using the specific and sensitive branched DNA signal amplification assay.