Benzene Exposure Assessed by Metabolite Excretion in Estonian Oil Shale Mineworkers: Influence of Glutathione S-Transferase Polymorphisms

Exogenous 24-epibrassinolide enhanced benzene detoxification in Chlorophytum comosum via overexpression and conjugation by glutathione

Benzene, a hydrophobic xenobiotic, induces cell damage in both humans and plants. Due to its volatilization, benzene is an airborne environmental problem. The potential of an exogenous bioactive brassinosteroid phytohormone to enhance benzene removal for phytoremediation was investigated. Chlorophytum comosum had higher brassinosteroids content under benzene stress. Plant treated with 24-epibrassinolide (EBR) removed significantly more gaseous benzene than untreated plants under both light and dark conditions at an initial benzene of 12.75 μmol in the systematic chambers (P < 0.05). Although benzene increased malondialdehyde in plant tissue, EBR-treated plants lowered this lipid peroxidation by enhancing their antioxidant content and increasing benzene detoxification-related genes expression, including ascorbic acid (AsA), homogentisate phytyltransferase (HPT), and glutathione synthethase (GS). This contributed to maintaining higher photosynthetic performances. Moreover, EBR-treated plants had higher gene expression of ferredoxin-NADP reductase (FNR) and glucose-6-phosphate 1-dehydrogenase (G6PDH), thus promoting NADPH biosynthesis to cope with benzene under light and dark conditions, respectively. Further, higher glutathione biosynthesis promoted more glutathione conjugate of benzene products including S-phenylcysteine (SPC) in EBR-treated plants. Hence, application of exogenous EBR as foliar spray provided for enhanced benzene detoxification via antioxidant content, benzene detoxification-related genes and benzene conjugation products with glutathione (GSH) and consequently greater gaseous benzene removal.

Residents' Self-Reported Health Effects and Annoyance in Relation to Air Pollution Exposure in an Industrial Area in Eastern-Estonia

Eastern Estonia has large oil shale mines and industrial facilities mainly focused on electricity generation from oil shale and shale oil extraction, which produce high air pollution emissions. The "Study of the health impact of the oil shale sector-SOHOS" was aimed at identifying the impacts on residents' health and annoyance due to the industrial processing. First, a population-wide survey about health effects and annoyance was carried out. Second, the total and oil shale sectors' emitted concentrations of benzene, phenol, and PM2.5 were modelled. Third, the differences between groups were tested and relationships between health effects and environmental pollution studied using multiple regression analysis. Compared to the control groups from non-industrial areas in Tartu or Lääne-Viru, residents of Ida-Viru more frequently (p < 0.05) reported wheezing, chest tightness, shortness of breath, asthma attacks, a long-term cough, hypertension, heart diseases, myocardial infarction, stroke, and diabetes. All health effects except asthma were reported more frequently among non-Estonians. People living in regions with higher levels of PM2.5, had significantly higher odds (p < 0.05) of experiencing chest tightness (OR = 1.13, 95% CI 1.02-1.26), shortness of breath (1.16, 1.03-1.31) or an asthma attack (1.22, 1.04-1.42) during the previous year. People living in regions with higher levels of benzene had higher odds of experiencing myocardial infarction (1.98, 1.11-3.53) and with higher levels of phenol chest tightness (1.44, 1.03-2.00), long-term cough (1.48, 1.06-2.07) and myocardial infarction (2.17, 1.23-3.83). The prevalence of adverse health effects was also higher among those who had been working in the oil shale sector. Next to direct health effects, up to a quarter of the residents of Ida-Viru County were highly annoyed about air pollution. Perceived health risk from air pollution increased the odds of being annoyed. Annoyed people in Ida-Viru had significantly higher odds of experiencing respiratory symptoms during the last 12 months, e.g., wheezing (2.30, 1.31-4.04), chest tightness (2.88, 1.91-4.33 or attack of coughing (1.99, 1.34-2.95).

Utilização de biomarcadores de genotoxicidade e expressão gênica na avaliação de trabalhadores de postos de combustíveis expostos a vapores de gasolina

Resumo Introdução: a avaliação de uma exposição mensura sua intensidade, frequência e duração, podendo detectar danos precoces que, se ignorados, podem evoluir para um quadro nocivo. Nos campos da saúde ambiental e ocupacional, os biomarcadores de genotoxicidade tem sido largamente utilizados para essa avaliação. Objetivo: identificar, descrever e discutir os principais bioindicadores de genotoxicidade e seu uso conjunto com técnicas de avaliação de expressão gênica em estudos de exposição ocupacional ao benzeno em postos de revenda de combustíveis (PRC). Métodos: revisão bibliográfica de trabalhos publicados entre 1995 e 2015. Resultados: as técnicas identificadas foram: ensaio cometa, estresse oxidativo, micronúcleos, aberrações cromossômicas, polimorfismos, adutos de DNA e proteínas, fatores epigenéticos e expressão gênica. Foi observado que testes de danos genéticos e epigenéticos são utilizados em frentistas de PRC que participam de programas de saúde do trabalhador ou de pesquisas, embora um baixo número de publicações sobre o tema tenha sido identificado. Esse fato talvez possa ser explicado pelos poucos países onde a profissão persiste e pelas limitações para o desenvolvimento de pesquisas nesses países. Conclusão: os bioindicadores de genotoxicidade e as técnicas de expressão gênica são úteis na detecção de dano precoce desta exposição ocupacional e devem ser avaliados em conjunto.

Benzene Uptake and Glutathione S-transferase T1 Status as Determinants of S-Phenylmercapturic Acid in Cigarette Smokers in the Multiethnic Cohort

Research from the Multiethnic Cohort (MEC) demonstrated that, for the same quantity of cigarette smoking, African Americans and Native Hawaiians have a higher lung cancer risk than Whites, while Latinos and Japanese Americans are less susceptible. We collected urine samples from 2,239 cigarette smokers from five different ethnic groups in the MEC and analyzed each sample for S-phenylmercapturic acid (SPMA), a specific biomarker of benzene uptake. African Americans had significantly higher (geometric mean [SE] 3.69 [0.2], p<0.005) SPMA/ml urine than Whites (2.67 [0.13]) while Japanese Americans had significantly lower levels than Whites (1.65 [0.07], p<0.005). SPMA levels in Native Hawaiians and Latinos were not significantly different from those of Whites. We also conducted a genome-wide association study in search of genetic risk factors related to benzene exposure. The glutathione S-transferase T1 (GSTT1) deletion explained between 14.2-31.6% (p = 5.4x10-157) and the GSTM1 deletion explained between 0.2%-2.4% of the variance (p = 1.1x10-9) of SPMA levels in these populations. Ethnic differences in levels of SPMA remained strong even after controlling for the effects of these two deletions. These results demonstrate the powerful effect of GSTT1 status on SPMA levels in urine and show that uptake of benzene in African American, White, and Japanese American cigarette smokers is consistent with their lung cancer risk in the MEC. While benzene is not generally considered a cause of lung cancer, its metabolite SPMA could be a biomarker for other volatile lung carcinogens in cigarette smoke.

Biomonitoring of benzene and 1,3-butadiene exposure and early biological effects in traffic policemen

The objective of this study was to determine benzene and 1,3-butadiene exposure through ambient air and personal air monitoring, as well as through biomarkers of exposure, and to evaluate the potential health risk of exposure through the use of biomarkers of early biological effects in central Bangkok traffic policemen. Ambient air concentrations of benzene and 1,3-butadiene at the roadsides were significantly higher than in police offices used as control sites (p<0.001). Traffic policemen had a significantly higher exposure to benzene (median 38.62 microg/m(3)) and 1,3-butadiene (median 3.08 microg/m(3)) than office policemen (median 6.17 microg/m(3) for benzene and 0.37 microg/m(3) for 1,3-butadiene) (p<0.001). Biomarkers of benzene exposure, blood benzene, and urinary metabolite, trans, trans-muconic acid were significantly higher in traffic policemen than office policemen (p<0.001). No significant difference between traffic and office policemen was found in urinary benzene metabolite, S-phenyl mercapturic acid, or in urinary 1,3-butadiene metabolite, monohydroxy-butenyl mercapturic acid. Biomarkers of early biological effects, 8-hydroxy-2'-deoxyguanosine in leukocytes (8-OHdG), DNA-strand breaks, and DNA-repair capacity, measured as an increase in gamma ray-induced chromosome aberrations were significantly higher in traffic policemen than controls (p<0.001 for 8-OHdG, p<0.01 for tail length, p<0.001 for olive tail moment, p<0.05 for dicentrics and p<0.01 for deletions). Multiple regression model including individual exposure, biomarkers of exposure, ages and years of work as independent variables showed that only the levels of individual 1,3-butadiene exposure were significantly associated with 8-OHdG and olive tail moment at p<0.0001 indicating more influence of 1,3-butadiene on DNA damage. These results indicated that traffic policemen, who are exposed to benzene and 1,3-butadiene at the roadside in central Bangkok, are potentially at a higher risk for development of diseases such as cancer than office policemen.

Genetic Polymorphism in Glutathione Transferases (GST): Population distribution of GSTM1, T1, and P1 conjugating activity

Glutathione transferases (GST) catalyze the conjugation of glutathione (GSH) with electrophiles, many of which may otherwise interact with protein or DNA. In select cases such as halogenated solvents, GST-mediated conjugation may lead to a more toxic or mutagenic metabolite. Polymorphisms that exert substantial effects on GST function were noted in human populations for several isozymes. This analysis focuses on three well-characterized isozymes, GSTM1, T1, and P1, in which polymorphisms were extensively studied with respect to DNA adducts and cancer in molecular epidemiologic studies. The current review and analysis focused upon how polymorphisms in these GST contributed to population variability in GST function. The first step in developing this review was to characterize the influence of genotype on phenotype (enzyme function) and the frequency of the polymorphisms across major population groups for all three GST. This information was then incorporated into Monte Carlo simulations to develop population distributions of enzyme function. These simulations were run separately for GSTM1, T1, and P1, and also for the combination of these isozymes, to assess the possibility of overlapping substrate specificity. Monte Carlo simulations indicated large interindividual variability for GSTM1 and T1 due to the presence of the null (zero activity) genotype, which is common in all populations studied. Even for GSTM1 or T1 non-null individuals, there was considerable interindividual variability with a bimodal distribution of enzyme activity evident. GSTP1 polymorphisms are associated with somewhat less variability due to the absence of null genotypes. However, in all cases simulated, the estimated variability is sufficiently large to warrant consideration of GST function distributions in assessments involving GST-mediated activation or detoxification of xenobiotics. Ideally, such assessments would involve physiologically based toxicokinetic (PBTK) modeling to assess population variability in internal dose.

Association between GST genetic polymorphism and dose-related production of urinary benzene metabolite markers, trans, trans-muconic acid and S-phenylmercapturic acid

The urinary benzene metabolites, trans, trans-muconic acid (ttMA) and S-phenylmercapturic acid (SPMA), are widely used as benzene exposure biomarkers. The influence of the glutathione S-transferase (GST) genetic polymorphism on the excretion levels of urinary ttMA and/or SPMA has been investigated. The association between dose-related production of urinary benzene metabolites and benzene exposure level was also reported. However, the association between the dose-related productions of urinary benzene metabolites and GST genetic polymorphism was not described in the literature. The purpose of this study was to investigate the association between the GST genetic polymorphism and dose-related production of the two widely used biomarkers, urinary ttMA and SPMA. Seventy male workers in a chemical factory were measured for their benzene exposure levels and provided blood and urine specimens at the end of work-shift. The atmospheric benzene exposure levels of these workers were determined by passive samplers with gas chromatograph mass spectrometer. The urinary ttMA and SPMA levels were quantitated by an online dual-loop cleanup device with an electrospray ionization tandem mass spectrometer. The analyses of GST genotypes, including M(1), T(1), and P(1), were done using PCR. Mean (+/- SD) of benzene exposure levels in participants was 7.2 +/- 15 ppm. The ttMA and SPMA levels in the high benzene exposure group (> or =1 ppm) were higher than those in the low benzene exposure group (<1 ppm; P < 0.001). Among the GST genotypes investigated in this study, the results showed that only the GSTT1 genotype was related to the level and dose-related production of SPMA. Using SPMA for evaluating benzene exposure, the results suggest that the GSTT1 genetic polymorphism, especially in a comparison study between two populations with different GSTT1 genotype frequencies, should be considered. Additionally, the biological exposure index value of SPMA should be set based on the levels of subjects with GSTT1-deficient genotypes for protection of all subjects.

Oxidative DNA damage and influence of genetic polymorphisms among urban and rural schoolchildren exposed to benzene

Traffic related urban air pollution is a major environmental health problem in many large cities. Children living in urban areas are exposed to benzene and other toxic pollutants simultaneously on a regular basis. Assessment of benzene exposure and oxidative DNA damage in schoolchildren in Bangkok compared with the rural schoolchildren was studied through the use of biomarkers. Benzene levels in ambient air at the roadside adjacent to Bangkok schools was 3.95-fold greater than that of rural school areas. Personal exposure to benzene in Bangkok schoolchildren was 3.04-fold higher than that in the rural schoolchildren. Blood benzene, urinary benzene and urinary muconic acid (MA) levels were significantly higher in the Bangkok schoolchildren. A significantly higher level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in leukocytes and in urine was found in Bangkok children than in the rural children. There was a significant correlation between individual benzene exposure level and blood benzene (rs=0.193, P<0.05), urinary benzene (rs=0.298, P<0.05), urinary MA (rs=0.348, P<0.01), and 8-OHdG in leukocyte (rs=0.130, P<0.05). In addition, a significant correlation between urinary MA and 8-OHdG in leukocytes (rs=0.241, P<0.05) was also found. Polymorphisms of various xenobiotic metabolizing genes responsible for susceptibility to benzene toxicity have been studied; however only the GSTM1 genotypes had a significant effect on urinary MA excretion. Our data indicates that children living in the areas of high traffic density are exposed to a higher level of benzene than those living in rural areas. Exposure to higher level of benzene in urban children may contribute to oxidative DNA damage, suggesting an increased health risk from traffic benzene emission.

Genetic susceptibility to benzene toxicity in humans

Human metabolism of benzene involves pathways coded for by polymorphic genes. To determine whether the genotype at these loci might influence susceptibility to the adverse effects of benzene exposure, 208 Bulgarian petrochemical workers and controls, whose exposure to benzene was determined by active personal sampling, were studied. The frequency of DNA single-strand breaks (DNA-SSB) was determined by alkaline elution, and genotype analysis was performed for five metabolic loci. Individuals carrying the NAD(P)H:quinone oxidoreductase 1 (NQO1) variant had significantly twofold increased DNA-SSB levels compared to wild-type individuals. The same result was observed for subjects with microsomal epoxide hydrolase (EPHX) genotypes that predict the fast catalytic phenotype. Deletion of the glutathione S-transferase T1 (GSTT1) gene also showed a consistent quantitative 35-40% rise in DNA-SSB levels. Neither glutathione S-transferase M1 (GSTM1) nor myeloperoxidase (MPO) genetic variants exerted any effect on DNA-SSB levels. Combinations of two genetic polymorphisms showed the same effects on DNA-SSB as expected from the data on single genotypes. The three locus genotype predicted to produce the highest level of toxicity, based on metabolic pathways, produced a significant 5.5-fold higher level of DNA-SSB than did the genotype predicted to yield the least genotoxicity.

A critique of benzene exposure in the general population

Benzene risk assessment indicates that exposure to a time-weighted average (TWA) of 1-5 parts per million (ppm) benzene in ambient air for 40 years is associated with an increased risk of acute myeloid leukemia. Decreased white blood cell count, platelet count and other hematological indices have also been observed in persons exposed to as low as 1 ppm airborne benzene. Evidence from studies worldwide consistently shows elevated levels of benzene biomarkers that are equivalent to 0.1-2 ppm benzene in ambient air, or even higher in the general population without occupational exposure to benzene (including children). The public health significance of these observations depends on to what extent these levels reflect actual benzene exposure, and whether such exposures are life-long or at least occur frequently enough to pose a possible health threat. We reviewed the evidence and discussed possible explanations for these observations. It was concluded that while there is reason to suspect that benzene contributes significantly to elevated levels of biomarkers in the general population, there is growing concern that this cannot be definitively ascertained without concomitant consideration of the role of other factors such as metabolic polymorphisms and sources of biomarkers other than benzene, which have been insufficiently studied to date. Such studies are urgently needed for valid assessment of this potential public health problem.