Application of the lymphocyte Cytokinesis-Block Micronucleus Assay to populations exposed to petroleum and its derivatives: Results from a systematic review and meta-analysis

Biomarkers of occupational benzene exposure: A Systematic Review to estimate the exposure levels and individual susceptibility at low doses

Benzene is associated with diverse occupational and public health hazards. It exhibits an ability to rapidly permeate the skin and contaminate water and food sources, leading to dermal and ingestion exposures. Despite numerous studies examining the associations between benzene and various indicators of harm, the findings have yielded inconsistent results. Furthermore, relying solely on air concentration as a measure of benzene exposure is limited, as it fails to account for internal exposure dose and individual susceptibility. This study aimed to conduct a comprehensive review in order to present current knowledge on benzene biomarkers and their significance in evaluating exposure levels and associated health hazards. The search methodology adhered to the PRISMA guidelines and involved the application of specific inclusion and exclusion criteria across multiple databases including PubMed, Embase, and Web of Science. Two researchers independently extracted and evaluated the relevant data based on predetermined criteria. Following the screening process, a total of 80 articles were considered eligible out of the initially retrieved 1053 articles after undergoing screening and assessment for inclusion. As the level of exposure decreased, specific biomarkers demonstrated a gradual increase in limitations, including heightened background concentrations and vulnerability to confounding factors. The advancement of sampling and analysis techniques will yield new biomarkers. Additionally, when conducting practical work, it is crucial to employ a comprehensive utilization of diverse biomarkers while excluding individual metabolic variations and combined exposure factors.

Association of glutathione-S-transferase polymorphism with genetic damage in paint workers

BACKGROUND

Occupational exposure to toluene causes serious health problems ranging from drowsiness to lethal diseases such as cancer. Paint workers are exposed to toluene through inhalation or the dermal route, which can induce genetcic damage. The increased DNA damage could be linked to genetic polymorphism. Therefore, we evaluated the association of glutathione-S-transferase polymorphism with DNA damage in paint workers.

METHODS

First, we included skilled paint workers (n = 30) as exposed and healthy individuals (n = 30) as control belonging to the same socio-economic strata. The genotoxicity biomarkers, Cytokinesis-block micronucleus (CBMN), and single-cell gel electrophoresis (SCGE)/Comet assay were used to assess genotoxicity while Multiplex-PCR and PCR-RFLP were used to assess polymorphism in glutathione-s-transferase (GST) genes. Using linear curve regression analysis, we assessed the association between genetic damage and polymorphism in the glutathione-s-transferase (GST) gene in the exposed and control subjects.

RESULTS

A significantly higher frequency of CBMN (4.43 ± 1.50) and tail moment (TM) (11.23 ± 1.0) respectively in paint workers as compared to the control(1.50 ± 0.86 and (0.54 ± 0.37) underlined significantly high genetic damage in paint workers.Regression curve analysis reveals that polymorphism in the GST gene is significantly associated with higher MN and TM in paint workers.

CONCLUSION

Overall, our study provides a strong rationale for identifying a clear association between glutathione-S-transferase polymorphism and genetic damage in paint workers.

A Quantitative Meta-Analysis of the Relation between Occupational Benzene Exposure and Biomarkers of Cytogenetic Damage

BACKGROUND

The genotoxicity of benzene has been investigated in dozens of biomonitoring studies, mainly by studying (classical) chromosomal aberrations (CAs) or micronuclei (MN) as markers of DNA damage. Both have been shown to be predictive of future cancer risk in cohort studies and could, therefore, potentially be used for risk assessment of genotoxicity-mediated cancers.

OBJECTIVES

We sought to estimate an exposure-response curve (ERC) and quantify between-study heterogeneity using all available quantitative evidence on the cytogenetic effects of benzene exposure on CAs and MN respectively.

METHODS

We carried out a systematic literature review and summarized all available data of sufficient quality using meta-analyses. We assessed the heterogeneity in slope estimates between studies and conducted additional sensitivity analyses to assess how various study characteristics impacted the estimated ERC.

RESULTS

Sixteen CA (1,356 individuals) and 13 MN studies (2,097 individuals) were found to be eligible for inclusion in a meta-analysis. Studies where benzene was the primary genotoxic exposure and that had adequate assessment of both exposure and outcomes were used for the primary analysis. Estimated slope estimates were an increase of 0.27% CA [(95% CI: 0.08%, 0.47%); based on the results from 4 studies] and 0.27% MN [(95% CI: -0.23%, 0.76%); based on the results from 7 studies] per parts-per-million benzene exposure. We observed considerable between-study heterogeneity for both end points (I2>90%).

DISCUSSION

Our study provides a systematic, transparent, and quantitative summary of the literature describing the strong association between benzene exposure and accepted markers of genotoxicity in humans. The derived consensus slope can be used as a best estimate of the quantitative relationship between real-life benzene exposure and genetic damage in future risk assessment. We also quantitate the large between-study heterogeneity that exists in this literature, a factor which is crucial for the interpretation of single-study or consensus slopes. https://doi.org/10.1289/EHP6404.

Occupational benzene exposure and the risk of genetic damage: a systematic review and meta-analysis

Background

Benzene, an important component of organic solvents, is commonly used in industry. Meanwhile, benzene is a human carcinogen leading to leukemia. Although the links between benzene and various types of genetic damage indicators have been evaluated in several studies, but their results remain inconsistent. So we conducted a meta-analysis, and to explore the influence of low concentration benzene exposure on workers’ genetic damage indicators using 3.25 mg/m³ as the boundary value, in order to provide a basis for improved prevention and control of the harm from benzene exposure to the occupational population.

Methods

We conducted a search of five databases, including Pub Med, Web of Science, China National Knowledge Infrastructure (CNKI), Wan Fang Data and Chongqing VIP, to identify relevant articles up to December 25, 2018. Two researchers independently extracted and evaluated the data according to the inclusion and exclusion criteria of the literature. The imported articles were managed by Endnote X7, and the data were extracted and sorted by Excel 2013. We utilized Stata 12.0 software to perform the meta-analysis in the present study.

Results

A total of 68 eligible articles were finally included for the synthetic analyses. The meta-analysis results showed that occupational benzene exposure led to significantly increased Micronucleus (MN) frequency, Sister chromatid exchange (SCE) frequency, Chromosome aberration (CA) frequency, Olive Tail moment (OTM), Tail moment (TM), Tail length (TL), and Tail DNA% (T DNA%) compared to the control group (P < 0.05), and the pooled effect value estimates were 1.36, 0.98, 0.76, 1.06, 0.96, 1.78, and 1.42, respectively. Subsequent analysis of the effect of low concentration benzene exposure on genetic damage found significantly increased MN frequency increased compared with the control group (P < 0.05).

Conclusions

Occupational benzene exposure can affect multiple genetic damage indicators. Even at an exposure concentration lower than 3.25 mg/m³, benzene exposure has genotoxicity. These data provide an important scientific basis for the further revision of occupational disease prevention strategies. At the same time, increased attention should be focused on the health monitoring of the occupational population exposed to benzene, and health management should be strengthened to improve the health of the occupational population.

Effects of Micronucleus Frequencies and Mitochondrial DNA Copy Numbers among Benzene-Exposed Workers in China

To provide a more comprehensive understanding of genotoxic effects from benzene exposure, its effects on induction of mitochondrial DNA copy number (MtDNAcn) and of micronucleus (MN) were investigated using peripheral blood from workers in China. Changes in mtDNAcn and MN were determined using quantitative real-time polymerase chain reaction (PCR) and cytokinesis-block micronucleus assays (CBMN), respectively, in 58 control and 174 benzene-exposed workers in Shanghai, China. Among the exposed workers, relative mtDNAcn increased and then decreased with increasing doses of benzene exposure. Significant and dose-dependent increase in MN frequencies were observed among the different exposure groups. In addition, the relative mtDNAcn were significantly associated with the MN frequencies in the low-level exposure group (P = 0.046), but not in the high dose groups. Therefore, the mechanisms for induction of MtDNAcn and MN by benzene may be similar from exposure to low doses but different from high doses. Similar increase of MN frequencies and MtDNAcn may be due to oxidative stress induced by benzene at low concentrations, while higher concentrations may start to initiate the cell death pathway. The pathway may be associated with excessive MtDNAcn which can initiate apoptosis while MN can continue to be induced. However, the differential mechanisms need to be investigated because they may represent different levels of risk for different health consequences. On the other hand, our data indicate that induction of MtDNAcn may be a sensitive genotoxic biomarker for workers with exposure to low dose of benzene. Environ. Mol. Mutagen. 61:355-360, 2020. © 2020 Wiley Periodicals, Inc.

Absence of mutations in the human interferon alpha-2b gene in workers chronically exposed to ionising radiation

Individuals chronically exposed to low-level ionising radiation (IR) run the risk of harmful and long-term adverse health effects, including gene mutations and cancer development. The search for reliable biomarkers of IR exposure in human population is still of great interest, as they may have a great implementation potential for the surveillance of occupationally exposed individuals. In this context, and considering previous literature, this study aimed to identify mutations in the human interferon alpha-2b (hIFNα-2b) as a potential biomarker of occupational chronic low-dose IR exposure linking low-IR exposure to the effects on haematopoiesis and reduced immunity. The analysis was performed in the genomic DNA of 51 uranium miners and 38 controls from Kazakhstan, and in 21 medical radiology workers and 21 controls from Italy. hIFNα-2b gene mutations were analysed with the real-time polymerase chain reaction (PCR) or Sanger sequencing. However, none of the investigated workers had the hIFNα-2b mutation. This finding highlights the need for further research to identify biomarkers for early detection of health effects associated with chronic low-dose IR exposure.

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.