Effect of CYP2E1 induction by ethanol on the immunotoxicity and genotoxicity of extended low-level benzene exposure

Human CYP2E1-dependent mutagenicity of benzene and its hydroxylated metabolites in V79-derived cells: Suppression and enhancement by ethanol pretreatment

Benzene is a human carcinogen that requires metabolic activation. We previously observed that benzene and its hydroxylated metabolites induce micronuclei in mammalian cells expressing human CYP2E1. This study was initially aimed to study another endpoint, the induction of gene mutations by those compounds in the same cell models. A V79-derived cell line expressing human CYP2E1 and sulfotransferase (SULT) 1A1 (V79-hCYP2E1-hSULT1A1) pretreated with ethanol (a CYP2E1 stabilizer) was used in the hprt gene mutagenicity assay. Phenol, hydroquinone, catechol, and 1,2,4-trihydroxybenzene all induced gene mutations, while they were inactive, or only weakly positive (hydroquinone), in parental V79-Mz cells. Unexpectedly, benzene was non-mutagenic in both cell lines, but it became positive in V79-hCYP2E1-hSULT1A1 cells using regimes of short exposure/long recovery without ethanol pretreatment, for both gene mutations and micronuclei formation. In silico molecular simulation showed binding energies and positions favorable for each compound to be oxidized by human CYP2E1, benzene demonstrating the highest affinity. By tunnel analysis, ethanol binding did not limit benzene to pass tunnel S, which was specifically active for benzene. However, its end product, acetic acid, decreased the occurrence of tunnel S from 5.4 to 2.2% and extended the length of its bottleneck from 5.5 to 9.0 Å. With residual ethanol molecules still being present in CYP2E1 for a period of time after benzene exposure, the acetic acid formed could limit the entrance of benzene, thus inhibit its metabolic activation. In summary, ethanol may interfere with the activation of benzene to mutagenic metabolites, at least in cultured cells.

Effects of low concentrations of benzene exposure on levels of platelet-associated antibodies and platelet parameters

OBJECTIVE

To evaluate the impact of exposure to low concentrations of benzene on the platelet-associated antibodies and platelet parameters.

METHODS

We carried out an analysis on 121 benzene-exposed workers and 110 healthy workers whose blood samples were collected and the levels of platelet-associated antibodies and platelet parameters were assessed. Benzene emissions were monitored over 5 years.

RESULTS

Large-platelet cell ratios (P-LCR), platelet distribution width (PDW), and mean platelet volume (MPV) were significantly higher in benzene-exposed participants than in control participants. In participants who smoke cigarettes or drank alcohol, P-LCR, PDW, and MPV were more significantly elevated in the benzene-exposed group than in nonsmokers and nondrinkers. Platelet-associated immunoglobulin (PAIg) levels in benzene-exposed participants were higher than those in the control group, and PAIgA and PAIgM levels correlated with cumulative benzene exposure.

CONCLUSIONS

Exposure to low concentrations of benzene can induce changes in PAIg levels and platelet parameters.

Acrylonitrile has Distinct Hormetic Effects on Acetyl-Cholinesterase Activity in Mouse Brain and Blood that are Modulated by Ethanol

Acrylonitrile(AN) is a neurotoxin both in animals and humans, but its effects on acetylcholinesterase (AChE) activity remain controversial. This study aimed to determine the dose-response effects of AN on AChE activity and the modulatory role of ethanol pre-treatment. A total of 144 Kunming mice were randomly divided into 18 groups: nine groups received 5% ethanol in their drinking water, and the remaining nine groups received regular tap water. One week later, both the ethanol and tap water only groups were given an intraperitoneal injection of AN at the following doses: 0 (control), 0.156, 0.3125, 0.625, 1.25, 2.5, 5, 10 or 20 mg AN/kg body weight. AChE activity was determined on whole blood and brain 24 h later. Blood AChE activity was higher in AN-injected mice than in controls at all doses. AChE activity in blood increased in a dose-dependent manner, peaking at 0.156 mg/kg, after which a gradual decrease ensued, displaying a β-typed dose-response relationship. In contrast, brain AChE activity, following a single AN injection, was consistently lower than in control mice, and continued to fall up to a dose of 0.313 mg/kg, and thereafter increased gradually with higher doses. Mice receiving a 20 mg/kg dose of AN exhibited AChE brain activity indistinguishable from that of control mice, demonstrating a typical U-typed dose-response relationship. The activity of AChE in the blood and brain of the AN + ethanol-treated groups displayed a shift to the right, and the magnitude of the decrease in AChE activity induced by AN was attenuated relative to the AN-only group. These results suggest that AN affects AChE activity in both mouse blood and brain in a hormetic manner. Pretreatment with ethanol modifies the effect of AN on AChE, indicating that parent AN has a more prominent role than its metabolites in modulating enzyme activity.

Association between metabolic gene polymorphisms and susceptibility to peripheral nerve damage in workers exposed ton-hexane: A preliminary study

Chronic exposure to n-hexane may result in peripheral neuropathy. 2,5-Hexanedione (2,5-HD) has been identified as a toxic metabolite of n-hexane. The CYP2E1, CYP1A1 and GST genes are involved in the formation of 2,5-hexanedione from n-hexane as well as the elimination of 2,5-HD-formed electrophile, and these genes are highly polymorphic in the general population. A nested case-control study in an industrial cohort was conducted to evaluate the associations between polymorphisms in these metabolic genes and n-hexane-induced peripheral nerve damage. The study subjects included 22 cases, who worked in a printing factory with symptoms of peripheral nerve damage, and 163 controls, who came from the same factory of cases. DNA was extracted from blood samples and genotyping was conducted for CYP2E1 Pst, CYP2E1 Dra, CYP2E1 Ins96, CYP1A1 Msp, GSTT1 null, GSTM1 null and GSTP1 105V. Unconditional logistic regression was applied to estimate the odds ratio and 95% confidence intervals. There were no significant differences between the two groups regarding age, sex, smoking and alcohol status. A significant association between Dra polymorphism and peripheral nerve damage was found. The frequency of CYP2E1 Dra homozygous mutation in the case group (18.2%) was higher than that in the control group (3.7%, p=0.015). Individuals with homozygote genotype (CC) of CYP2E1 Dra had a significantly higher risk of peripheral nerve damage compared with those with DD genotype (adjusted OR=?.58, 95% CI=1.32-23.65) after n-hexane exposure duration, sex, age, smoking and alcohol status were adjusted. No significant association was found that CYP2E1 Pst, CYP2E1 Ins96, CYP1A1 Msp, GSTT1, GSTM1, GSTP gene polymorphisms associated with the susceptibility of peripheral nerve damage. These findings suggested that CYP2E1 gene might increase the susceptibility to n-hexane-induced peripheral damage.

Polymorphisms of DNA repair genes XRCC1 and XRCC3, interaction with environmental exposure and risk of chronic gastritis and gastric cancer

AIM

To evaluate the association between polymorphisms XRCC1 Arg194Trp and Arg399Gln and XRCC3 Thr241Met and the risk for chronic gastritis and gastric cancer, in a Southeastern Brazilian population.

METHODS

Genotyping by PCR-RFLP was carried out on 202 patients with chronic gastritis (CG) and 160 patients with gastric cancer (GC), matched to 202 (C1) and 150 (C2) controls, respectively.

RESULTS

No differences were observed among the studied groups with regard to the genotype distribution of XRCC1 codons 194 and 399 and of XRCC3 codon 241. However, the combined analyses of the three variant alleles (194Trp, 399Gln and 241Met) showed an increased risk for chronic gastritis when compared to the GC group. Moreover, an interaction between the polymorphic alleles and demographic and environmental factors was observed in the CG and GC groups. XRCC1 194Trp was associated with smoking in the CG group, while the variant alleles XRCC1 399Gln and XRCC3 241Met were related with gender, smoking, drinking and H pylori infection in the CG and GC groups.

CONCLUSION

Our results showed no evidence of a relationship between the polymorphisms XRCC1 Arg194Trp and Arg399Gln and XRCC3 Thr241Met and the risk of chronic gastritis and gastric cancer in the Brazilian population, but the combined effect of these variants may interact to increase the risk for chronic gastritis, considered a premalignant lesion. Our data also indicate a gene-environment interaction in the susceptibility to chronic gastritis and gastric cancer.

Phenotype analysis of lymphocytes of workers with chronic benzene poisoning

Lifetime exposure to benzene is associated to a variety of blood disorders, and except for the risk of cancer, almost nothing is known concerning health impairment in individuals who are no longer exposed. In Brazil, this exposure is one of the serious problems in workplaces, and many workers have been laid off their jobs due to this intoxication, particularly in the State of Bahia, the largest producer of benzene in Latin America, which is the area of this study. From a larger study to describe health effects and genetic polymorphisms among workers with chronic benzene poisoning (CBP), this previous specific investigation analyzes the association between CBP and the pattern of sub-populations of lymphocytes. The study was performed with a CBP group (n=24) and a control group with other occupational diseases (n=24); both were selected at the Workers Health Study Center in the State of Bahia, Brazil. Clinical and epidemiologic variables were collected from medical records and from a detailed questionnaire. The average age was similar in the two groups (51.1 and 50.7, respectively). Analyzing the mean proportions of the sub-populations of lymphocytes, statistically significant differences were found for T cytotoxic cells (TCD8) (27.9; 19.4; p=0.002) and T helper memory cell (CD4CD45RO) (31.2; 37.0; p=0.015), respectively, for the CBP group and control group. These results should be viewed with caution because of the small sample size, but they strengthen a previous impression that workers exposed to benzene have their immune system impaired, even in the long term, which may contribute to some disorders and carcinogenesis process. These workers must be strictly followed up in a medical surveillance program. Although this problem has been known for a long time, this is the first attempt to study these specific effects in Brazil.

DNA damage in lymphocytes of benzene exposed workers correlates with trans,trans-muconic acids and breath benzene levels

Benzene causes many kinds of blood disorders in workers employed in many different environments. These diseases include myelodisplastic syndrome and acute and chronic myelocytic leukemia. In the present study, five occupational work places, including six industrial process types, namely, printing, shoe-making, methylene di-aniline (MDA), nitrobenzene, carbomer, and benzene production were selected, and the levels of breath benzene, and trans,trans-muconic acids (t,t-MA) and phenol in urine were evaluated, as well as hematological changes and lymphocyte DNA damage. The concentration of benzene in breath was less than 3 ppm in the workplaces, and benzene exposure was found to be higher in work places where benzene is used, than in those where benzene is produced. At low levels of benzene exposure, urinary t,t-MA correlated strongly with benzene in air. Highest Olive tail moments were found in workers producing carbomer. Levels of breathzone benzene were found to be strongly correlated with Olive tail moment values in the lymphocytes of workers, but not with hematological data in the six workplaces types. In conclusion, the highest benzene exposures found occurred in workers at a company, which utilized benzene in the production of carbomer. In terms of low levels of exposure to benzene, urinary t,t-MA and DNA damage exhibited a strong correlation with breath benzene, but not with hematological data. We conclude that breath benzene, t,t-MA and lymphocytic DNA damage are satisfactory biomonitoring markers with respect to benzene exposure in the workplace.

Single strand DNA breaks in T- and B-lymphocytes and granulocytes in workers exposed to benzene

Comet assays were carried out to evaluate DNA damage in T- and B-lymphocytes and granulocytes from 41 workers exposed to benzene in a printing company and 41 unexposed donors. In T-lymphocytes, DNA damage was slightly higher in exposed workers than in controls. The tail moments in the two groups were 1.75+/-0.29 and 1.47+/-0.41, respectively (P<0.0006). DNA damage of B-lymphocytes in the two groups showed the most significant difference among the three cell types. The tail moments were 3.86+/-0.71 and 1.51+/-0.39, respectively (P<0.0001). In granulocytes, DNA damage was also different, the tail moments being 3.61+/-0.75 and 2.60+/-0.59, respectively (P<0.0001). The comparison of DNA damage in both groups shows that B-lymphocytes could be a useful target in biomonitoring of human exposure to low levels of benzene.

Differential STAT5 activation and phenotypic marker expression by immune cells following low levels of ethanol consumption in mice

Ethanol has been recognized as an immunosuppressive agent for many years. Effects of high levels of ethanol consumption on immune functions have been extensively studied, but little is known about the effects of low levels (scuh as 5% ethanol) of ethanol consumption. Herein we report that exposure of mice to 5% ethanol for 4-8 weeks decreases IL-2-augmented splenic NK cell activity, decreases the numbers of NK cells in spleen and liver, decreases the number of granulocytes (Gr-l+) in bone marrow and spleen, and decreases the percentages of B cells in liver. In contrast, the percentages of CD4+CD8+ thymocytes, CD4+CD8- splenocytes, CD4+CD8- liver nonparenchymal cells, CD3+ splenocytes, and CD3+ bone marrow cells were increased. Furthermore, exposure to 5% ethanol increases STAT5 activation in T cells and liver cells while decreases STAT5 activation in NK cells. Taken together, these findings suggest that low levels of ethanol consumption can differentially modulate immune cells in thymus, spleen, bone marrow and liver, which may be due to differential regulation of STAT5 activation by ethanol.

Genetic polymorphisms of XRCC1 and risk of the esophageal cancer

A variety of environmental factors were identified to be associated with the risk of esophageal cancer. The variation in capacity of DNA repair might influence environmental chemical-associated carcinogenesis. We hypothesized that the polymorphic XRCC1 genes might modify cancer susceptibility of the esophagus. To investigate the effect of XRCC1 genetic polymorphisms on codons 194, 280 and 399, we evaluated data from 105 patients of esophageal squamous cell carcinoma and 264 healthy controls, matching with age (+/-3 years), gender and ethnicity. The distribution of the 3 genotypes were not significantly different among patients and controls. However, among alcohol drinkers, the XRCC1399 Arg/Arg genotype was more frequently found in patients with esophageal cancer. After adjustment with other environmental confounders, the OR for the genotype of XRCC1399 Arg/Arg was 2.78 (95% CI =1.15-6.67) as compared with the XRCC1(399) Arg/Gln and XRCC1(399) Gln/Gln genotypes in the alcohol drinkers. Similar trends were observed among cigarette smokers and areca chewers. However, they did not reach a statistical significance. Our findings suggest that the polymorphic XRCC1 genes might modify the risk of alcohol-associated esophageal cancers.