Benzene In Mice Research Articles

Targeting IGF2BP1 alleviated benzene hematotoxicity by reprogramming BCAA metabolism and fatty acid oxidation

Benzene is the main environmental pollutant and risk factor of childhood leukemia and chronic benzene poisoning. Benzene exposure leads to hematopoietic stem and progenitor cell (HSPC) dysfunction and abnormal blood cell counts. However, the key regulatory targets and mechanisms of benzene hematotoxicity are unclear. In this study, we constructed a benzene-induced hematopoietic damage mouse model to explore the underlying mechanisms. We identified that Insulin like growth factor 2 mRNA binding protein 1 (IGF2BP1) was significantly reduced in benzene-exposed mice. Moreover, targeting IGF2BP1 effectively mitigated damages to hematopoietic function and hematopoietic molecule expression caused by benzene in mice. On the mechanics, by metabolomics and transcriptomics, we discovered that branched-chain amino acid (BCAA) metabolism and fatty acid oxidation were key metabolic pathways, and Branched-chain amino acid transaminase 1 (BCAT1) and Carnitine palmitoyltransferase 1a (CPT1A) were critical metabolic enzymes involved in IGF2BP1-mediated hematopoietic injury process. The expression of the above molecules in the benzene exposure population was also examined and consistent with animal experiments. In conclusion, targeting IGF2BP1 alleviated hematopoietic injury caused by benzene exposure, possibly due to the reprogramming of BCAA metabolism and fatty acid oxidation via BCAT1 and CPT1A metabolic enzymes. IGF2BP1 is a potential regulatory and therapeutic target for benzene hematotoxicity.

Chemopreventive Potential of Major Flavonoid Compound of Methanolic Bark Extract of Saraca asoca (Roxb.) in Benzene-induced Toxicity of Acute Myeloid Leukemia Mice.

Background:Saraca asoca (SA) (Roxb.) is one of the folk medicinal plants found in India, Bangladesh, and Sri Lanka. Its major biological activity appears due to the presence of flavonoid group of compounds in its bark extract.Objective:In this study, our research aims to analyze the chemopreventive effect of flavonoids, especially a natural phenol catechin present in the bark methanolic extract of SA on acute myeloid leukemia (AML) mice.Materials and Methods:The total bark extract was partitioned and analyzed on thin-layer chromatography (TLC) plate. The yellow-brown material of spot 4 was analyzed and identified as catechin. The yellowish brown material (YBM) was tested for their chemopreventive potential. An in vivo AML mice model was used to test the efficacy. Hematological parameters (Hb %, red blood cell, and white blood cell count), expression of cell cycle regulatory proteins, and DNA fragmentation analysis were performed.Results:After treatment of benzene-exposed mice with the major flavonoid compound, namely catechin, the above parameters increase significantly (P < 0.05). There was an upregulation of p53 and p21, caspase 11 myeloperoxidase, bcl2, and CYP2EI in catechin-treated group. DNA was less fragmented in flavonoid-treated group compared to that of control (P ≤ 0.05). The present study indicates that the secondary metabolites of SA methanolic bark extract, comprising flavonoid catechin as major constituents, have modulatory effect in cell cycle deregulation and hematological abnormalities induced by benzene in mice.Conclusions:Our data suggest that catechin from methanolic bark extract of SA effectively attenuates benzene-induced secondary AML in bone marrow, which is likely associated with the anticell cycle deregulation properties of this flavan-3-ol. This study was supported by the observation that catechin (YBM), like doxorubicin, can act as the neutralizer and protector of mortality in cancer cases.SUMMARY The catechin from methanolic bark extract of Saraca asoca has chemoprotective activity in benzene-induced secondary acute myeloid leukemia.(AML) in bone marrowHematological parameters, structural analysis of DNA showed that the purified catechin attenuates the conditions responsible for the development of AMLThe purified flavonol, catechin has a modulatory effect on different cell cycle deregulations induced by benzene in AML model.

New phenylpropanoid and other compounds from Illicium lanceolatum with inhibitory activities against LPS-induced NO production in RAW 264.7 macrophages

Illicium lanceolatum is a traditional Chinese medicine (TCM) for treating inflammatory diseases. Anti-inflammatory activities of I. lanceolatum stems and leaves were tested using ear edema models induced by dimethyl benzene in mice. Bioassay-guided fractionation of the ethanol extract of I. lanceolatum leaves and stems revealed that the ethyl acetate fraction exhibited inhibitory potency to dimethyl benzene-induced edema in the mouse ear. Phytochemical investigation on the active fraction led to the isolation of a new phenylpropanoid (1), together with fifteen known compounds. This is the first report of the isolation of 2–16 from I. lanceolatum. Of these compounds, compounds 1, 2 and 3 showed inhibitory activity on LPS-stimulated NO production in RAW 264.7 macrophages with IC50 values of 27.58, 26.59 and 34.35μg/mL, respectively. I. lanceolatum stems and leaves can be exploited to alleviate inflammatory diseases, which makes the rare medicinal plant resources sustainable.

Effect of Cassia nomame on Small Intestine Movement, Diuresis, and Anti-inflammation in Rats

ObjectiveTo investigate the preliminary pharmacological screening of Cassia nomame. MethodsThe effect of aqueous extract from C. nomame on gastrointestinal motor function was investigated by assessing the intestinal transit rate (ITR) of charcoal modeled into gastrointestinal motility dysfunction (GMD) by the administration of dopamine, atropine, or noradrenaline to the rats, respectively. Diuresis was studied in vivo by estimating the urine output. The anti-inflammatory activity was expressed as the percentage of swelling reduction by comparison on the mean thickness of ear swelling in mice. ResultsThe ITR in these GMD animals was significantly retarded compared to that in normal animals. The retardation, however, was significantly inhibited by the ig administration of C. nomame (2 g/kg) for all GMD animals. The results suggested that C. nomame had the potential for development into a prokinetic agent that could prevent or alleviate GMD in patients. C. nomame increased urine output and suppressed significantly ear swelling induced by dirnethyl benzene in mice. ConclusionC. nomame could increase the gastrointestinal contractile activity of rats and has the effects of diuresis and anti-inflammation.

Anti-Allergic Effect of Ulmus davidiana Cortex on Contact Dermatitis Induced by Dinitrofluoro- Benzene in Mice.

Objective:The root bark of Ulmus davidiana var. Japonica (Ulmi Radicis cortex, URC) is a medicinal herb used for promoting diuresis and treating dampness. In Korea, URC has long been used as an efficacious therapy for inflammation, burns, frostbite and skin diseases such as eczema and psoriasis.Methods:In the present study, we used 1-fluoro-2,4- dinitrofluorobenzene (DNFB)-induced contact dermatitis (CD) mouse model to investigate the antiallergic and the anti-inflammatory effects of URC on skin lesion, histopathological changes and specific antibody production.Results:URC treatment, 10 mg/mL, effectively inhibited skin lesions induced by repeated paintings with DNFB. In the histopathological observation, topical application of URC inhibited spongiosis. In addition, URC lowered the production levels of total immunoglobulin and IgG2a in serum.Conclusion:These data indicate that URC has an anti-inflammatory effect that produces an improvement of skin lesions in CD mice.

Effect of Methanolic Leaf Extract ofOcimum basilicumL. on Benzene-Induced Hematotoxicity in Mice

The aim of the present study was to investigate the protective role of methanolic leaf extract of Ocimum basilicum L. against benzene-induced hematotoxicity in Swiss albino mice. GC analysis and subacute toxicity level of the extract were tested. Mice were randomly divided into three groups among which II and III were exposed to benzene vapour at a dose 300 ppm × 6 hr/day × 5 days/week for 2 weeks and group I was control. Group III of this experiment was treated with the leaf methanolic extract at a dose of 100 mg/kg body weight, a dose in nontoxic range. Hematological parameters (Hb%, RBC and WBC counts), cell cycle regulatory proteins expression and DNA fragmentation analysis of bone marrow cells was performed. There was an upregulation of p53 and p21 and downregulation of levels of CDK2, CDK4, CDK6, and cyclins D1 and E in leaf extract-treated group. DNA was less fragmented in group III compared to group II (P < 0.05). The present study indicates that the secondary metabolites of O. basilicum L. methanolic leaf extract, comprising essential oil monoterpene geraniol and its oxidized form citral as major constituents, have modulatory effect in cell cycle deregulation and hematological abnormalities induced by benzene in mice.

Influence of toluene co-exposure on the metabolism and genotoxicity of benzene in mice using continuous and intermittent exposures

Benzene exposure in occupational settings often occurs with concurrent exposure to toluene, the methyl-substituted derivative of benzene. Toluene is also readily metabolized by CYP450 isozymes although oxidation primarily occurs in the methyl group. While earlier mouse studies addressing co-exposure to benzene and toluene at high concentrations demonstrated a reduction in benzene-induced genotoxicity, we have previously found, using an intermittent exposure regimen with lower concentrations of benzene (50 ppm) and toluene (100 ppm), that toluene enhances benzene-induced clastogenic or aneugenic bone marrow injury in male CD-1 mice with significantly increased CYP2E1, and depleted GSH and GSSG levels. The follow-up study reported here also used the same daily and total co-exposures but over consecutive days and compared the effects of co-exposure on genotoxicity and metabolism in CD-1 mice both with and without buthionine sulfoximine (BSO) treatment to deplete GSH. In this study the toluene co-exposure doubled the genotoxic response (as determined by the erythrocyte micronucleus test) to benzene alone. Further, GSH depletion caused a reduction in this genotoxicity in both benzene exposed and benzene/toluene co-exposed mice. The results are discussed in terms of the analyses of urinary metabolites from this consecutive day study and the intermittent exposure study as well as levels of CYP2E1, epoxide hydrolase, quinone reductase, alcohol dehydrogenase, and aldehyde dehydrogenase activities. The results suggest that the presence of glutathione is necessary for benzene genotoxicity either as a metabolite conjugate or through an indirect mechanism such as TNF-induced apoptosis.

A Multicompartment Liver-based Pharmacokinetic Model for Benzene and its Metabolites in Mice

Benzene is a highly flammable, colorless liquid. Ubiquitous exposures result from its presence in gasoline vapors, cigarette smoke, and industrial processes. After uptake into the body, benzene undergoes a series of metabolic transformations to multiple metabolites that exert toxic effects on the bone marrow. We developed a physiologically based pharmacokinetic model for the uptake and elimination of benzene in mice to relate the concentration of inhaled and orally administered benzene to the tissue doses of benzene and its key metabolites. This model takes into account the zonal distribution of enzymes and metabolism in the liver rather than treating the liver as one homogeneous compartment, and considers metabolism in tissues other than the liver. Analysis was done to examine the existence and uniqueness of solutions of the system. We then formulated an inverse problem to obtain estimates for the unknown parameters; data from multiple laboratories and experiments were used. Despite the sources of variability, the model simulations matched the data reasonably well in most cases. Our study shows that the multicompartment metabolism model does improve predictions over the previous model (Cole et al. in J. Toxicol. Environ. Health, 439-465, 2001) and that in vitro metabolic constants can be successfully extrapolated to predict in vivo data for benzene metabolism and dosimetry.

Transient disruption of liver gap junctional intercellular communication and induction of apoptosis after administration of 1,4-bis[2-(3,5 dichloropyridyloxy)]benzene in mice

Gap junctional intercellular communication (GJIC) and connexin expression (Cx26 and Cx32) in mouse liver were studied after administration of 4-bis[2-(3,5 dichloropyridyloxy)]benzene (TCPOBOP), a phenobarbital-like enzyme inducer. Female C57Bl/6 mice were administered TCPOBOP (5.8 mg/kg BW) and euthanized 0, 24, 48 and 72 hours later. Liver samples were snap frozen, or fixed in formalin, or submitted to GJIC analysis. The proliferating cell nuclear antigen (PCNA) immunohistochemistry and the Western blotting for Cx26 and Cx32 were performed. After 48 and 72 h of drug administration the liver-to-body weight ratio was increased 70% and 117% ( p<0.0001), respectively. There were temporal-dependent alterations in liver histopathology and a significant increase in cell proliferation was noted after 48 h and sustained after 72 h, though to a lesser extent ( p<0.0001). In addition, TCPOBOP administration induced apoptosis, which appeared to be time-dependent showing statistical significance only after 72 h ( p<0.0001). Interestingly, a transient disruption by nearly 50% of GJIC capacity was detected after 48 h of drug ingestion, which recovered after 72 h ( p=0.003). These GJIC changes were due to altered levels of Cx26 and Cx32 in the livers of TCPOBOP-treated mice. We concluded that a single administration of TCPOBOP transiently disrupted the levels of GJIC due to decreased expression of connexins and increased apoptotic cell death in mouse liver.

In Vivo and In Vitro Anti-inflammatory Activities of Neoandrographolide

Neoandrographolide, one of the principal diterpene lactones, isolated from a medicinal herb Andrographis paniculata Nees, was tested in vivo and in vitro for its anti-inflammatory activities and mechanism. Oral administration of neoandrographolide (150 mg/kg) significantly suppressed ear edema induced by dimethyl benzene in mice. Oral administration of neoandrographolide (100-150 mg/kg) also reduced the increase in vascular permeability induced by acetic acid in mice. In vitro studies were performed using the macrophage cell line RAW264.7 to study the effect of neoandrographolide on suppressing phorbol-12-myristate-13-acetate (PMA)-stimulated respiratory bursts and lipopolysaccharide (LPS)-induced production of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha). Respiratory bursts were quantified by chemiluminescence (CL) measurements. Results showed that neoandrographolide suppressed PMA-stimulated respiratory bursts dose-dependently from 30 muM to 150 muM. Neoandrographolide also inhibited NO and TNF-alpha production in LPS-induced macrophages, contributing to the anti-inflammatory activity of A. paniculata. These results indicate that neoandrographolide possesses significant anti-inflammatory effects, which implies that it would be one of the major contributing components to participate in the anti-inflammatory effect of A. paniculata. and a potential candidate for further clinical trial.

Attomole detection of in vivo protein targets of benzene in mice: evidence for a highly reactive metabolite.

Modified proteins were detected in liver and bone marrow of mice following treatment with [(14)C]benzene. Stained sections were excised from one-dimensional and two-dimensional gels and converted to graphite to enable (14)C/(13)C ratios to be measured by accelerator mass spectrometry. Protein adducts of benzene or its metabolites were indicated by elevated levels of (14)C. A number of proteins were identified by in-gel proteolysis and conventional mass spectrometric methods with the low molecular weight proteins identified including hemoglobin and several histones. The incorporation of (14)C was largely proportional to the density of gel staining, giving little evidence that these proteins were specific targets for selective labeling. This was also true for individual histones subfractionated with Triton-acid-urea gels. A representative histone, H4, was isolated and digested with endopeptidase Asp-N, and the resulting peptides were separated by high performance liquid chromatography. (14)C levels in collected fractions were determined, and the peptides were identified by conventional mass spectrometry. The modifications were distributed throughout the protein, and no particular amino acids or groups of amino acids were identified as selective targets. Thus chemical attack by one or more benzene metabolites upon histones was identified and confirmed, but the resulting modifications appeared to be largely nonspecific. This implies high reactivity toward proteins, enabling such attack to occur at multiple sites within multiple targets. It is not known to what extent, if any, the modification of the core histones may contribute to the carcinogenicity of benzene.

A model for the induction of aplastic anemia by subcutaneous administration of benzene in mice

Long-term exposure to benzene vapors is associated with hematological diseases such as leukemia, lymphoma and aplastic anemia. CD 1 male mice were randomly assigned to six groups: 1B 10, 1B 15, 1B 20, 2B 10, 2B 15, and 2B 20. 1B mice were administered 2 ml/kg (1940 mg/kg) subcutaneous injection (in the dorsal region) of benzene 5 days a week, and 2B mice were exposed 3 days a week (Monday, Wednesday and Friday) until a total of 10, 15 and 20 doses were completed. About 48 h after treatment completion, leukocyte, erythrocyte, and bone marrow cells were counted, and spleen histopathology was analyzed. 1B 15 and 1B 20 mice showed lethargy and irritability, 80% body and 42% spleen weight loss ( P<0.001), while body and spleen weight loss were less severe in 2B mice (12 and 48%, respectively). After exposure to 20 benzene doses, 1B 20 and 2B 20 mice showed decreased hemoglobin concentrations, and erythrocyte, leukocyte and bone marrow cell counts (37, 34, 80 and 50%, respectively in group 1B 20; P<0.001; and 12, 48, 62 and 62%, respectively in group 2B 20). Thrombocytopenia occurred only in group 2B. Both benzene-treatment schemes caused aplastic anemia, however, the disease was masked by spleen toxicity in group 1B. Scheme 2 allowed mice survival and caused less non-hematological effects. We establish here a reproducible and inexpensive experimental model to induce aplastic anemia in mice by subcutaneous injection of 2 ml/kg benzene, using two short-term treatment schemes.

Physiologically Based Pharmacokinetic Modeling of Benzene Metabolism in Mice Through Extrapolation from In Vitro to In Vivo

Benzene (C6H6) is a highly flammable, colorless liquid. Ubiquitous exposures result from its presence in gasoline vapors, cigarette smoke, and industrial processes. Benzene increases the incidence of leukemia in humans when they are exposed to high doses for extended periods; however, leukemia risks in humans at low exposures are uncertain. The exposure-dose-response relationship of benzene in humans is expected to be nonlinear because benzene undergoes a series of metabolic transformations, detoxifying and activating, in the liver, resulting in multiple metabolites that exert toxic effects on the bone marrow. We developed a physiologically based pharmacokinetic model for the uptake and elimination of benzene in mice to relate the concentration of inhaled and orally administered benzene to the tissue doses of benzene and its key metabolites, benzene oxide, phenol, and hydroquinone. As many parameter values as possible were taken from the literature; in particular, metabolic parameters obtained from in vitro studies with mouse liver were used since comparable parameters are also available for humans. Parameters estimated by fitting the model to published data were first-order rate constants for pathways lacking in vitro data and the concentrations of microsomal and cytosolic protein, which effectively alter overall enzyme activity. The model was constrained by using the in vitro metabolic parameters (maximum velocities, first-order rate constants, and saturation parameters), and data from multiple laboratories and experiments were used. Despite these constraints and sources of variability, the model simulations matched the data reasonably well in most cases, showing that in vitro metabolic constants can be successfully extrapolated to predict in vivo data for benzene metabolism and dosimetry. Therefore in vitro metabolic constants for humans can subsequently be extrapolated to predict the dosimetry of benzene and its metabolites in humans. This will allow us to better estimate the risks of adverse effects from low-level benzene exposures.

Reactive ring-opened aldehyde metabolites in benzene hematotoxicity.

The hematotoxicity of benzene is mediated by reactive benzene metabolites and possibly by other intermediates including reactive oxygen species. We previously hypothesized that ring-opened metabolites may significantly contribute to benzene hematotoxicity. Consistent with this hypothesis, our studies initially demonstrated that benzene is metabolized in vitro to trans-trans-muconaldehyde (MUC), a reactive six-carbon diene dialdehyde, and that MUC is toxic to the bone marrow in a manner similar to benzene. Benzene toxicity most likely involves interactions among several metabolites that operate by different mechanisms to produce more than one biological effect. Our studies indicate that MUC coadministered with hydroquinone is a particularly potent metabolite combination that causes bone marrow damage, suggesting that the involvement of ring-opened metabolites in benzene toxicity may be related to their biological effects in combination with other benzene metabolites. Studies in our laboratory and by others indicate that MUC is metabolized to a variety of compounds by oxidation or reduction of the aldehyde groups. The aldehydic MUC metabolite 6-hydroxy-trans-trans-2,4-hexadienal (CHO-M-OH), similar to MUC but to a lesser extent, is reactive toward glutathione, mutagenic in V79 cells, and hematotoxic in mice. It is formed by monoreduction of MUC, a process that is reversible and could be of biological significance in benzene bone marrow toxicity. The MUC metabolite 6-hydroxy-trans-trans-2,4-hexadienoic (COOH-M-OH) is an end product of MUC metabolism in vitro. Our studies indicate that COOH-M-OH is a urinary metabolite of benzene in mice, a finding that provides further indirect evidence for the in vivo formation of MUC from benzene. Mechanistic studies showed the formation of cis-trans-muconaldehyde in addition to MUC from benzene incubated in a hydroxyl radical-generating Fenton system. These results suggest that the benzene ring is initially opened to cis,cis-muconaldehyde, an unstable isomer that rearranges to cis-trans-muconaldehyde, which further rearranges to trans-trans-muconaldehyde. The latter is not formed from benzene dihydrodiol by reactive oxygen species in a Fenton system that contains reactive oxygen species.

Identification of 6-hydroxy-trans,trans-2,4-hexadienoic acid, a novel ring-opened urinary metabolite of benzene.

We studied the in vivo metabolism of benzene in mice to ring-opened compounds excreted in urine. Male CD-1 mice were treated intraperitoneally with benzene (110-440 mg/kg), [14C]benzene (220 mg/kg) or trans, trans-muconaldehyde (MUC; 4 mg/kg), a microsomal, hematotoxic metabolite of benzene. Urine, collected over 24 hr, was extracted and analyzed by HPLC with a diode-array detector and by scintillation counting. In addition to trans,trans-muconic acid, previously the only known ring-opened urinary benzene metabolite, a new metabolite, 6-hydroxy-trans,trans-2,4-hexadienoic acid, was detected in urine of mice treated with either benzene or MUC. We identified the new metabolite based on coelution of metabolites and UV spectral comparison with authentic standards in unmethylated and methylated urine extracts. Results presented here are consistent with the intermediacy of MUC in the in vivo metabolism of benzene to ring-opened metabolites.

Identification of 6-Hydroxy-trans,trans-2,4-Hexadienoic Acid, a Novel Ring-Opened Urinary Metabolite of Benzene

We studied the in vivo metabolism of benzene in mice to ring-opened compounds excreted in urine. Male CD-1 mice were treated intraperitoneally with benzene (110-440 mg/kg), [14C]benzene (220 mg/kg) or trans, trans-muconaldehyde (MUC; 4 mg/kg), a microsomal, hematotoxic metabolite of benzene. Urine, collected over 24 hr, was extracted and analyzed by HPLC with a diode-array detector and by scintillation counting. In addition to trans,trans-muconic acid, previously the only known ring-opened urinary benzene metabolite, a new metabolite, 6-hydroxy-trans,trans-2,4-hexadienoic acid, was detected in urine of mice treated with either benzene or MUC. We identified the new metabolite based on coelution of metabolites and UV spectral comparison with authentic standards in unmethylated and methylated urine extracts. Results presented here are consistent with the intermediacy of MUC in the in vivo metabolism of benzene to ring-opened metabolites.

Genotoxic effects of benzene in mice

Genotoxic effects of benzene in mice

Dose-related clastogenic effects induced by benzene in bone marrow cells and in differentiating sopermatogonia of Swiss CD1 mice

Cancer hazard is due to genotoxic events in somatic cells and genetic hazard in the strict sense is due to mutagenic events in germ cells. The investigation of sensitivity differences between somatic and germinal cells is pertinent to the question whether a genotoxic carcinogen is also a germ cell mutagen. Cytogenetic damage induced by benzene in mice was evaluated by determining the frequencies of chromosomal aberrations in bone marrow and spermatogonial cells of male Swiss CD1 mice. First, the analysis was performed by administering 1 ml/kg (880 mg/kg) of benzene as a single oral dose and sampling either cell type after a wide range of times (6, 12, 18, 24, 30, 36, 42 and 48 h) to determine the time of maximum response. At this dose benzene showed high clastogenic activity in bone marrow cells with a peak between 24 and 30 h. In differentiating spermatogonia the frequency of aberrant cells was highest 24 h after treatment. The overall effect in spermatogonia was lower than in bone marrow cells. Second, the dose response was determined 24 h after treatment with two additional doses of benzene: 0.1 ml/kg (88 mg/kg) and 0.5 ml/kg (440 mg/kg) for bone marrow cells; 0.25 ml/kg (220 mg/kg) and 0.5 ml/kg (440 mg/kg) for differentiating spermatogonia. The clastogenic effect was dose dependent in both cell types. The frequencies of aberrant cells increased in a linear-quadratic manner in bone marrow and linearly in differentiating spermatogonia. Furthermore, the per cell damage was higher in bone marrow than in spermatogonial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of ethanol on the stem cell toxicity of benzene in mice

BDF 1 mice were exposed to 100, 300, and 900 ppm benzene vapor, and the numbers of hematopoietic progenitor cells, early and late erythroid progenitors (BFU-E and CFU-E) and granuloid progenitors (CFU-C), were determined with and without additional exposure to ethanol (5, 10, 15 vol%) in the drinking water. The duration of benzene inhalation was up to 4 weeks, 6 hr per day, 5 days per week. It was shown that the number of CFU-E per femur was depressed in a dose-dependent manner by benzene alone and also by ethanol combined with a given benzene concentration. CFU-E showed rapid regeneration after the end of the exposure, but not BFU-E and CFU-C. Prolongation of the ethanol exposure after withdrawal of benzene had only a marginal effect on progenitor cell regeneration.

Cytogenetic assays in genotoxic studies: Somatic cell effects of benzene and germinal cell effects of dibromochloropropane

We have reviewed the results of our cytogenetic studies to evaluate the usefulness of these assays in genotoxic studies. In one study, we observed unusual dose-response in lymphocyte chromosome aberration frequencies after exposure of mice to low doses of a chemical mixture (benzene, chloroprene, epichlorohydrin, and xylene). The frequency in the high dose group is lower than those of the medium and low dose groups. This reduction of genotoxicity is correlated with a significant induction of a detoxifying enzyme, glutathione-S-transferase. The data also suggest that extrapolation of effects from high to low doses for risk assessment may be erroneous. Using benzene as a model clastogen, we found that the clastogenic effect persists for a long time after termination of exposure in mice. This phenomenon is probably due to a gradual release of benzene from absorption of the chemical in body fat. In an inhalation study, we observed that chromosome aberrations are induced in mice after exposure to benzene at below the occupational exposure limit of 1 ppm. Since benzene is a ubiquitous environmental contaminant, it may interact with other environmental agents to modify its genotoxic effects. We found that a nongenotoxic drug, praziquantel, and a free radical scavenger, DMSO, can enhance or reduce respectively the clastogenic activities of benzene in mice. Both modifying agents acted by altering the metabolic pathways of benzene. In a study with rats, we showed that carcinogenic doses of benzene can induce chromosome aberrations in lymphocytes of rats long before the expression of cancer. With dibromochloropropane, we observed that this chemical can induce dominant lethality in rats.(ABSTRACT TRUNCATED AT 250 WORDS)