Are polymorphisms in metabolism protective or a risk for reduced white blood cell counts in a Chinese population with low occupational benzene exposures?

Occupational health hazards and wide spectrum of genetic damage by the organic solvent fumes at the workplace: A critical appraisal

Long-term exposure to organic solvents is known to affect human health posing serious occupational hazards. Organic solvents are genotoxic, and they can cause genetic changes in the exposed employees' somatic or germ cells. Chemicals such as benzene, toluene, and gasoline induce an excessive amount of genotoxicity results either in genetic polymorphism or culminates in deleterious mutations when concentration crosses the threshold limits. The impact of genotoxicity is directly related to the time of exposure, types, and quantum of solvent. Genotoxicity affects almost all the physiological systems, but the most vulnerable ones are the nervous system, reproductive system, and blood circulatory system. Based on the available literature report, we propose to evaluate the outcomes of such chemicals on the exposed humans at the workplace. Attempts would be made to ascertain if the long-term exposure makes a person resistant to such chemicals. This may seem to be a far-fetched idea but has not been studied. The health prospect of this study is envisaged to complement the already existing data facilitating a deeper understanding of the genotoxicity across the population. This would also demonstrate if it correlates with the demographic profile of the population and contributes to comorbidity and epidemiology.

Genetic variations in ATM and H2AX loci contribute to risk of hematological abnormalities in individuals exposed to BTEX chemicals

Background

Loci controlling DNA double‐strand breaks (DSBs) repair play an important role in defending against the harmful health effects of benzene, toluene, ethylbenzene, and xylene (BTEX), but their gene variants may alter their repair capacity. The aim of the current study was to determine the relationship of functional polymorphisms ATM‐rs228589 A>T, WRN‐rs1800392 G>T and H2AX‐rs7759 A>G in DBS repair loci with the abnormal hematological indices in workers who exposed to BTEXs.

Methods

We included 141 cases with one or more abnormal hematological parameters, who had been occupationally exposed to BTEX chemicals and 152 controls with a similar exposure condition but without any abnormal hematological parameters. Atmospheric concentrations of BTEXs were measured and whole blood samples were taken from the participants to determine hematologic parameters and SNP genotyping.

Results

Results showed that T allele of ATM‐rs228589 and G allele of H2AX‐rs7759 had a higher frequency in cases than controls (p = 0.012 and p = 0.001, respectively). Also, AT and TT genotypes of ATM‐rs228589 and AG and GG genotypes of H2AX‐rs7759 were higher in cases compared to controls. The AT and TT genotypes of ATM‐rs228589 have significant associations with a risk of hematological abnormalities in the codominant (AT vs. AA, p = 0.018), dominant (AT + TT vs. AA, p = 0.010) and overdominant (AT vs. AA + TT, p = 0.037) models. The GG and AG genotypes of H2AX‐rs7759 were in relation with increased risk of abnormal hematological indices under codominant (GA vs. AA, p = 0.009 & GG vs. AA, p = 0.005), dominant (AG + GG vs. AA, p = 0.001), and recessive (GG vs. AA + AG, p = 0.025) models.

Conclusions

These observations may help to understand the mechanisms of BTEX hematotoxicity and identify useful biomarkers of risk assessment for workers exposed to BTEX.

LincRNA-p21 promotes p21-mediated cell cycle arrest in benzene-induced hematotoxicity by sponging miRNA-17-5p

Benzene is widely employed in manufacturing and causes hematotoxic effects and leukemia in humans. A long intergenic noncoding RNA (lincRNA)-microRNA (miRNA)-mRNA coexpression and competing endogenous RNA (ceRNA) regulatory network was constructed by bioinformatics analysis based on a benzene-induced aplastic anemia (BIAA) mouse model. In this population-based study, we observed a trend consistent with that in the BIAA mice: lincRNA-p21 and p21 were upregulated, while miRNA-17-5p expression was downregulated in benzene-exposed workers. Moreover, multiple linear regressions indicated that lincRNA-p21 was negatively associated with white blood cell (WBC) counts. Predictive thresholds of hematotoxicity were identified by ROC curve analysis with S-phenylmercapturic acid (SPMA) and lincRNA-p21 showing a better predictive ability than the other parameters and the combination of SPMA and lincRNA-p21 exhibiting the highest predictive value for hematotoxicity. LincRNA-p21 was predominantly present in the cytoplasm of bone marrow cells (BMCs) and K562 cells as assessed by fluorescence in situ hybridization (FISH). Upon exploring the underlying mechanism by which lincRNA-p21 mediates benzene-induced hematotoxicity, we observed that the negative regulation of 1,4-benzoquinone (1,4-BQ) on cell cycle arrest and inhibition of K562 cell proliferation was partially relieved by lincRNA-p21 knockdown, which can inhibit the expression of P21 and thereby suppress the toxic effects of 1,4-BQ. Finally, dual-luciferase reporter gene and RIP assay showed that, by acting as a sponge, lincRNA-p21 reduced the activity of miRNA-17-5p and consequently increased the expression of p21. In conclusion, our research suggested that benzene induces hematotoxicity via the lincRNA-p21/miRNA-17-5p/p21 signaling which might contribute to the underlying mechanism of lincRNA-p21 in benzene-induced hematotoxicity. Therefore, lincRNA-p21 can serve as a potential biomarker for the early detection of hematopoiesis inhibition in individuals with long-term exposure to low-dose benzene.

The effects of genetic polymorphisms on benzene-exposed workers: A systematic review

BACKGROUND AND AIMS

Benzene is a group I carcinogen, which has been associated with leukemia and myelodysplastic syndrome. Moreover, it has been proposed that polymorphisms in benzene metabolizing genes influence the outcomes of benzene exposure in the human body. This systematic review aims to elucidate the existent relationship between genetic polymorphisms and the risk of developing adverse health effects in benzene-exposed workers.

METHODS

Three databases were systematically searched until April 2020. The preferred reporting items for systematic reviews and meta-analyses method was used to select articles published between 2005 and 2020. Quality assessment and risk of bias were evaluated by the Newcastle-Ottawa scale.

RESULTS

After full-text evaluation, 36 articles remained out of 645 initially screened. The most studied health effects within the reviewed papers were chronic benzene poisoning, hematotoxicity, altered urinary biomarkers of exposure, micronucleus/chromosomal aberrations, and gene methylation. Furthermore, some polymorphisms on NQO1, GSTT1, GSTM1, MPO, and CYP2E1, among other genes, showed a statistically significant relationship with an increased risk of developing at least one of these effects on benzene-exposed workers. However, there was no consensus among the reviewed papers on which specific polymorphisms were the ones associated with the adverse health-related outcomes, except for the NQO1 rs1800566 and the GSTT1 null genotypes. Additionally, the smoking habit was identified as a confounder, demonstrating worse health outcomes in exposed workers that smoked.

CONCLUSION

Though there is a positive relationship between genetic polymorphisms and detrimental health outcomes for benzene-exposed workers, broader benzene-exposed cohorts that take into account the genetic diversity of the population are needed in order to determine which specific polymorphisms incur in health risks.

Association between air particulate matter pollution and blood cell counts of women preparing for pregnancy: Baseline analysis of a national birth cohort in China

BACKGROUND

Limited evidence is known about whether long-term exposures to air borne particulate matters of 2.5 μm or less (PM_2.5) impact human hematologic index for women preparing for pregnancy. No study assessed the effect of PM₁, which is small enough to reach the blood circulation.

OBJECTIVE

To evaluate whether exposure to PM₁ and PM_2.5 is associated with blood cell count of woman preparing for pregnancy.

METHOD

Based on the baseline data of a national birth cohort in China, we analysed the white blood cell (WBC), red blood cells (RBC) and thrombocyte counts of 1,203,565 women who are aged 18-45 years, being Han ethnicity, had no chronic disease and preparing for pregnancy. We matched their home addresses and examination date with daily concentrations of PM₁ and PM_2.5 which were estimated by a machine learning method with remote sensing, meteorological and land use information. Generalized additive mixed model to examine the associations between exposure to one-year average exposure to PMs prior to the health examination and the blood cells counts, after adjustment for potential individual variables.

RESULTS

A 10 μg/m³ PM₁ increment was associated with -1.49% (95%CI: 1.56%, -1.42%) difference in WBC count; with 0.33% (95%CI: 0.30%, 0.36%) difference of RBC count; and with 1.08% (95%CI: 1.01%, 1.15%) difference of thrombocyte count. For PM_2.5, the corresponding difference was -0.47% (95%CI: 0.54%, -0.39%) for WBC; was 0.06% (95%CI: 0.03%, 0.09%) for RBC; and was 1.10% (95%CI: 1.02%, 1.18%) for thrombocyte. Women working as workers, being overweight and with tobacco smoking exposure had higher associations between PMs and hematologic index than their counterparts (p < 0.05 for interaction test).

CONCLUSION

Long-term exposure to PMs were associated with decrement in WBC, as well as increment in RBC and thrombocytes among Han Chinese women preparing for pregnancy. Measures such as using air purifiers and wearing a mask in polluted areas should be improved to prevent women from the impact of PMs.

Derivation of an occupational exposure limit for benzene using epidemiological study quality assessment tools

This paper derives an occupational exposure limit for benzene using quality assessed data. Seventy-seven genotoxicity and 36 haematotoxicity studies in workers were scored for study quality with an adapted tool based on that of Vlaanderen et al., 2008 (Environ Health. Perspect. 116 1700-5). These endpoints were selected as they are the most sensitive and relevant to the proposed mode of action (MOA) and protecting against these will protect against benzene carcinogenicity. Lowest and No- Adverse Effect Concentrations (LOAECs and NOAECs) were derived from the highest quality studies (i.e. those ranked in the top tertile or top half) and further assessed as being "more certain" or "less certain". Several sensitivity analyses were conducted to assess whether alternative "high quality" constructs affected conclusions. The lowest haematotoxicity LOAECs showed effects near 2 ppm (8 h TWA), and no effects at 0.59 ppm. For genotoxicity, studies also showed effects near 2 ppm and showed no effects at about 0.69 ppm. Several sensitivity analyses supported these observations. These data define a benzene LOAEC of 2 ppm (8 h TWA) and a NOAEC of 0.5 ppm (8 h TWA). Allowing for possible subclinical effects in bone marrow not apparent in studies of peripheral blood endpoints, an OEL of 0.25 ppm (8 h TWA) is proposed.

Regulatory loop between lncRNA FAS-AS1 and DNMT3b controls FAS expression in hydroquinone-treated TK6 cells and benzene-exposed workers

Hydroquinone (HQ), one of the main metabolites of benzene, is a well-known human leukemogen. However, the specific mechanism of how benzene or HQ contributes to the development of leukemia is unknown. In a previous study, we demonstrated the upregulation of DNA methyltransferase (DNMT) expression in HQ-induced malignant transformed TK6 (HQ-TK6) cells. Here, we investigated whether a regulatory loop between the long noncoding RNA FAS-AS1 and DNMT3b exists in HQ-TK6 cells and benzene-exposed workers. We found that the expression of FAS-AS1 was downregulated in HQ-TK6 cells and workers exposed to benzene longer than 1.5 years via histone acetylation, and FAS-AS1 expression was negatively correlated with the time of benzene exposure. Restoration of FAS-AS1 in HQ-TK6 cells promoted apoptosis and inhibited tumorigenicity in female nude mice. Interestingly, treatment with a DNMT inhibitor (5-aza-2-deoxycytidine), histone deacetylase inhibitor (trichostatin A), or DNMT3b knockout led to increased FAS-AS1 through increased H3K27ac protein expression in HQ-TK6 cells, and DNMT3b knockout decreased H3K27ac and DNMT3b enrichment to the FAS-AS1 promoter region, which suggested that DNMT3b and/or histone acetylation involve FAS-AS1 expression. Importantly, restoration of FAS-AS1 resulted in reduced expression of DNMT3b and SIRT1 and increased expression of FAS in both HQ-TK6 cells and xenograft tissues. Moreover, the average DNMT3b expression in 17 paired workers exposed to benzene within 1.5 years was decreased, but that of the remaining 103 paired workers with longer exposure times was increased. Conversely, DNMT3b was negatively correlated with FAS-AS1 expression. Both FAS-AS1 and DNMT3b influenced the enrichment of H3K27ac in the FAS promoter region by regulating the expression of SIRT1, consequently upregulating FAS expression. Taken together, these observations demonstrate crosstalk between FAS-AS1 and DNMT3b via a mutual inhibition loop and indicate a new mechanism by which FAS-AS1 regulates the expression of FAS in benzene-related carcinogenesis.

Hypermethylation in Gene Promoters Are Induced by Chronic Exposure to Benzene, Toluene, Ethylbenzene and Xylenes

BACKGROUND AND OBJECTIVE

Gas station attendants are occupationally exposed to benzene, toluene, ethylbenzene and xylene (BTEX) compounds and thus more susceptible to the biological effects of this mixture present in gasoline, especially due to the carcinogenicity of benzene. Furthermore, the harmful effects of BTEX exposure may be potentiated by genetic and epigenetic inactivation of critical genes. The objective was to evaluate such gene-BTEX interactions accessing the promoter methylation status of p14ARF, p16INK4A and GSTP1 in peripheral blood leukocyte samples.

MATERIALS AND METHODS

The 59 exposed and 68 unexposed participants from Rio de Janeiro, Brazil, were included. The promoter methylation status was accessed by methylation-specific PCR (MSP) and GSTP1 Ile105Val polymorphism was investigated by PCR-restriction fragment length polymorphism (PCR-RFLP) technique.

RESULTS

Both p14ARF and p16INK4A were significantly hypermethylated in exposed subjects compared to unexposed (p = 0.004 and p<0.001, respectively). Additionally, p16INK4A hypermethylation in the exposed group was correlated with chromosomal abnormalities (CAs) (p = 0.018), thus highlighting the influence of the gene-environment interactions on genome instability. Noteworthy, p16INK4A methylation was significantly associated with miscarriage among female attendants (p = 0.047), in which those who reported miscarriage exhibited hypermethylation in at least 2 of the 3 genes analyzed. The GSTP1 heterozygote genotype, which could affect the metabolism of benzene detoxification, was found in both groups but was more frequent in those occupationally exposed. No significant association was observed between GSTP1 genotypes and methylation status.

CONCLUSION

Together, these findings indicate that gas station attendants with the aforementioned epigenetic and genetic profiles may be at greater risk of occupational BTEX exposure-induced genome instability, which could require concerted efforts to establish more preventive actions and constant biomonitoring in gas station attendants.

Benzene Exposure Induces Insulin Resistance in Mice

Benzene is a ubiquitous pollutant associated with hematotoxicity but its metabolic effects are unknown. We sought to determine if and how exposure to volatile benzene impacted glucose handling. We exposed wild type C57BL/6 mice to volatile benzene (50 ppm × 6 h/day) or HEPA-filtered air for 2 or 6 weeks and measured indices of oxidative stress, inflammation, and insulin signaling. Compared with air controls, we found that mice inhaling benzene demonstrated increased plasma glucose (p = .05), insulin (p = .03), and HOMA-IR (p = .05), establishing a state of insulin and glucose intolerance. Moreover, insulin-stimulated Akt phosphorylation was diminished in the liver (p = .001) and skeletal muscle (p = .001) of benzene-exposed mice, accompanied by increases in oxidative stress and Nf-κb phosphorylation (p = .025). Benzene-exposed mice also demonstrated elevated levels of Mip1-α transcripts and Socs1 (p = .001), but lower levels of Irs-2 tyrosine phosphorylation (p = .0001). Treatment with the superoxide dismutase mimetic, TEMPOL, reversed benzene-induced effects on oxidative stress, Nf-κb phosphorylation, Socs1 expression, Irs-2 tyrosine phosphorylation, and systemic glucose intolerance. These findings suggest that exposure to benzene induces insulin resistance and that this may be a sensitive indicator of inhaled benzene toxicity. Persistent ambient benzene exposure may be a heretofore unrecognized contributor to the global human epidemics of diabetes and cardiovascular disease.

Environmental exposure to benzene: evaluation of urinary S-PMA and polymorphism (CYP2E1-1293G>C and NQO1 609C>T) in Campos Elíseos residents, Duque de Caxias, Rio de Janeiro State, Brazil

Benzene is one of the most important substances for assessment, due to its significant use, the environmental contamination resulting from its emission and the effects on human health. It is classified by the International Agency for Research on Cancer (IARC) as a known carcinogen to humans (group 1) and associated with the development of leukemia. In general, the population is exposed to this substance by inhaling contaminated air, which varies according to the location and intensity of its potential sources. The petrochemical industry is one of the most important sources of this compound. The municipality of Duque de Caxias, specifically the Campos Elíseos district, in Rio de Janeiro State, Brazil, houses the Industrial Complex of Campos Elíseos (PICE), a grouping of over 25 industries, which includes the second largest oil refinery in Brazil. Environmental contamination from the PICE has been recognized, but there is a lack of studies concerning its impact on the health of the surrounding population. S-phenylmercapturic acid (S-PMA) concentrations ranging from 0.80 to 8.01μg.g-1 creatinine were observed in the local population, apparently related to hematological changes also observed in exposed population. The quantifiable presence of urinary S-PMA from the benzene metabolism is associated with the fact that 60% of the participants present specific hematological changes, which may be due to the environmental benzene exposure. The allele and genotype frequencies of the CYP2E1 and NQO1 enzymes observed in the study population were similar to those reported in other studies. The presence of the variant allele in the NQO1 genotype may be a risk factor for the observed hematological changes.

Assessment of interaction between maternal polycyclic aromatic hydrocarbons exposure and genetic polymorphisms on the risk of congenital heart diseases

The major causes of congenital heart diseases (CHDs) are the interactions of genetic and environmental factors. We conducted a case–control study in 357 mothers of CHDs fetuses and 270 control mothers to investigate the association of maternal PAHs exposure, AHR, CYP1A1, CYP1A2, CYP1B1 and CYP2E polymorphisms, the interaction between PAHs exposure and genetic variants with the risk of CHDs. The higher level PAHs exposure was associated with the risk of CHDs (aOR = 2.029, 95% CI: 1.266, 3.251) or subtypes. The haplotypes of AHR or CYP1A2 were associated with the risk of CHDs: AHR: C-G-A-C: aOR = 0.765; T-A-G-A: aOR = 1.33; CYP1A2: A-T:aOR = 1.75; C-C: aOR = 0.706. When exposed to higher level PAHs, the risk of CHDs among the mothers carrying rs2158041 “C/T or T/T” genotype or rs7811989 “G/A or A/A” genotype in AHR was 1.724 (χ² = 7.209, P = 0.007) or 1.735 (χ² = 7.364, P = 0.007) times greater than the aOR in the mothers carrying wild genotype. The multiplicative-scale interactions between PAHs exposure and polymorphisms of CYP1A2 rs4646425 (P = 0.03) or CYP2E1 rs915908 (P = 0.0238) on the risk of CHDs were observed. Our study suggests that maternal AHR polymorphisms may modify the association of PAHs exposure with CHDs, CYP1A2 or CYP2E1 polymorphisms significantly interact with PAHs exposure on CHDs.

Association between polymorphism of GSTP1, GSTT1, GSTM1 and CYP2E1 genes and susceptibility to benzene-induced hematotoxicity

Occupational exposure to benzene has been associated with leukemia, anemia, leukopenia, and thrombocytopenia. Genetic susceptibility to benzene toxicity in humans may be related to variations in benzene metabolizing genes. The main objective of this study was to ascertain whether polymorphism of GSTP1, GSTM1, GSTT1 and CYP2E1 genes might influence susceptibility to the adverse effects of benzene among employees of a petrochemical plant. In this cross-sectional study, 124 employees of a petrochemical plant who had been occupationally exposed to benzene and had one or more abnormal hematological parameter (cases) and 184 subjects with a similar exposure scenario, free from any abnormal hematological parameters (referent) were studied. Atmospheric concentrations of benzene were measured and GSTM1 and GSTT1 genotypes were evaluated using the multiplex polymerase chain reaction (PCR) technique. Additionally, GSTP1 and CYP2E1 genotypes were determined by PCR- restriction fragment length polymorphism (PCR–RFLP). The frequency of null GSTT1 genotype in cases was significantly higher than that of referent group (32.3 vs. 18.5%, OR 2.1, 95% CI 1.23–3.56, p = 0.004). The mean value of platelets in subjects with null GSTT1 genotype was significantly lower than that of individuals with positive GSTT1 genotype (p = 0.015). Conversely, the mean value of leukocytes was significantly higher in subjects with null GSTM1 genotype as compared to those with positive GSTM1 genotype (p = 0.026). Logistic regression analysis showed that, subjects with null GSTT1 genotype had a significantly higher risk for hematological disorders, as compared to those with positive GSTT1 genotype (OR 2.1, 95% CI 1.23–3.56). Moreover, subjects with both null GSTT1 and GSTM1 genotypes had a significantly higher risk for hematological disorders as compared to subjects with positive GSTT1 and GSTM1 genotypes (OR 2.35, 95% CI 1.14–4.8). The results of this study showed that, individuals carrying null GSTT1 or both null STT1 and GSTM1 genotypes had a higher risk and were more susceptible to benzene-induced hematological disorders.

Do mutations in DNMT3A/3B affect global DNA hypomethylation among benzene-exposed workers in Southeast China?: Effects of mutations in DNMT3A/3B on global DNA hypomethylation

Global DNA hypomethylation is commonly observed in benzene-exposed workers, but the underlying mechanisms remain unclear. We sought to discover the relationships among reduced white blood cell (WBC) counts, micronuclear (MN) frequency, and global DNA methylation to determine whether there were associations with mutations in DNMT3A/3B. Therefore, we recruited 410 shoe factory workers and 102 controls from Wenzhou in Zhenjiang Province. A Methylated DNA Quantification Kit was used to quantify global DNA methylation, and single nucleotide polymorphisms (SNPs) in DNMT3A (rs36012910, rs1550117, and R882) and DNMT3B (rs1569686, rs2424909, and rs2424913) were identified using the restriction fragment length polymorphism method. A multilinear regression analysis demonstrated that the benzene-exposed workers experienced significant global DNA hypomethylation compared with the controls (β = -0.51, 95% CI: -0.69 to -0.32, P < 0.001). The DNMT3A R882 mutant allele (R882H and R882C) (β = -0.25, 95% CI: -0.54 to 0.04, P = 0.094) and the DNMT3B rs2424909 GG allele (β = -0.37, 95% CI: -0.70 to -0.03, P = 0.031) were significantly associated with global DNA hypomethylation compared with the wild-type genotype after adjusting for confounding factors. Furthermore, the MN frequency in the R882 mutant allele (R882H and R882C) (FR = 1.18, 95% CI: 0.99 to 1.40, P = 0.054) was higher than that of the wild-type. The results imply that hypomethylation occurs due to benzene exposure and that mutations in DNMTs are significantly associated with global DNA methylation, which might have influenced the induction of MN following exposure to benzene. Environ. Mol. Mutagen. 58:678-687, 2017. © 2017 Wiley Periodicals, Inc.

Comparison of hematological alterations and markers of B-cell activation in workers exposed to benzene, formaldehyde and trichloroethylene

Benzene, formaldehyde (FA) and trichloroethylene (TCE) are ubiquitous chemicals in workplaces and the general environment. Benzene is an established myeloid leukemogen and probable lymphomagen. FA is classified as a myeloid leukemogen but has not been associated with non-Hodgkin lymphoma (NHL), whereas TCE has been associated with NHL but not myeloid leukemia. Epidemiologic associations between FA and myeloid leukemia, and between benzene, TCE and NHL are, however, still debated. Previously, we showed that these chemicals are associated with hematotoxicity in cross-sectional studies of factory workers in China, which included extensive personal monitoring and biological sample collection. Here, we compare and contrast patterns of hematotoxicity, monosomy 7 in myeloid progenitor cells (MPCs), and B-cell activation biomarkers across these studies to further evaluate possible mechanisms of action and consistency of effects with observed hematologic cancer risks. Workers exposed to benzene or FA, but not TCE, showed declines in cell types derived from MPCs, including granulocytes and platelets. Alterations in lymphoid cell types, including B cells and CD4+ T cells, and B-cell activation markers were apparent in workers exposed to benzene or TCE. Given that alterations in myeloid and lymphoid cell types are associated with hematological malignancies, our data provide biologic insight into the epidemiological evidence linking benzene and FA exposure with myeloid leukemia risk, and TCE and benzene exposure with NHL risk.