Association of BER and NER pathway polymorphism haplotypes and micronucleus frequencies with global DNA methylation in benzene-exposed workers of China: Effects of DNA repair genes polymorphisms on genetic damage

The role of genetic polymorphisms for inducing genotoxicity in workers occupationally exposed to benzene: a systematic review

Benzene is used worldwide as a major raw material in a number of industrial processes and also a potent airborne pollutant emitted from traffic exhaust fume. The present systematic review aimed to identify potential associations between genetic polymorphisms and occupational benzene-induced genotoxicity. For this purpose, a total of 22 selected studies were carefully analysed. Our results revealed a positive relation between gene polymorphism and genotoxicity in individuals exposed to benzene, since 17 studies (out of 22) observed positive relations between genotoxicity and polymorphisms in xenobiotics metabolizing genes influencing, therefore, individuals' susceptibility to genomic damage induced by benzene. In other words, individuals with some genotypes may show increase or decrease DNA damage and/or higher or lower DNA-repair potential. As for the quality assessment, 17 studies (out of 22) were categorized as Strong or Moderate and, therefore, we consider our findings to be trustworthy. Taken together, such findings are consistent with the notion that benzene induces genotoxicity in mammalian cells being strongly dependent on the genetic polymorphism. Certainly, such findings are important for clarifying the role of biomarkers related to genotoxicity in human biomonitoring studies.

An exploration of biomarkers for noise exposure: mitochondrial DNA copy number and micronucleus frequencies in Chinese workers

Few studies have been conducted that use biomarkers as early warning signals for noise-associated health hazards. To explore potentially effective biomarkers for noise-exposed populations, we recruited 218 noise-exposed male workers in China. We calculated cumulative noise exposure (CNE) through noise intensity and noise-exposed duration. When the model was fully adjusted, ln-transformed relative mitochondrial DNA copy number (mtDNAcn) decreased by 0.014 (95% confidence interval (CI): -0.026, -0.003) units with each 1 dB(A)∙year increase in CNE levels. CNE was further included in the model as a grouping variable, and the results showed a negative dose-effect relationship between relative mtDNAcn and CNE (P-trend = 0.045). However, we did not find a correlation between CNE and micronucleus (MN) frequencies. Our findings suggest that CNE in workers was associated with a decrease in relative mtDNAcn which may provide a potential biomarker for noise and for certain health risk but not with MN frequencies.

Purebred dogs show higher levels of genomic damage compared to mixed breed dogs

Inbreeding is a common phenomenon in small, fragmented or isolated populations, typical conditions of many threatened species. In the present paper, we used a new non-invasive approach based on the buccal micronucleus assay to evaluate the possible relationships between inbreeding and genomic damage using the dog as model species. In particular, we assessed the frequencies of micronuclei and other nuclear aberrations in a group of purebred dogs (n = 77), comparing the obtained data with those from a control group represented by mixed breed dogs (n = 75). We found a significant increase of micronuclei, nuclear buds and total nuclear aberrations frequencies in purebred dogs compared to mixed-bred dogs. The absence of significant differences in the frequency of micronuclei and other nuclear aberrations amongst different breeds reinforces the hypothesis that the observed increased genomic damage amongst purebred dogs may not be due to a different genomic instability typical of a particular breed, but to inbreeding itself. This hypothesis is further confirmed by the fact that other endogen confounding factors, such as sex, age and weight, do not contribute significantly to the increase of genomic damage observed amongst purebred dogs. In conclusion, results presented in this study showed that, in purebred dogs, inbreeding may increase the levels of genomic damage. Considering that genomic damage is associated with increased physiological problems affecting animal health, the results we obtained may represent a stimulus to discourage the use of intensive inbreeding practices in captive populations and to reduce the fragmentation of wild populations.

Review on novel toxicological effects and personalized health hazard in workers exposed to low doses of benzene

Several recent reports indicate health hazards for workers with below occupational limit exposure to benzene (BZ). Our updated review indicates that such low exposures induced traditional as well as novel toxicity/genotoxicity, e.g., increased mitochondria copy numbers, prolongation of telomeres, impairment of DNA damage repair response (DDRR), perturbations of expression in non-coding RNAs, and epigenetic changes. These abnormalities were associated with alterations of gene expression and cellular signaling pathways which affected hematopoietic cell development, expression of apoptosis, autophagy, etc. The overarching mechanisms for induction of health risk are impaired DDRR, inhibition of tumor suppressor genes, and changes of MDM2-p53 axis activities that contribute to perturbed control for cancer pathways. Evaluation of the unusual dose-responses to BZ exposure indicates cellular over-compensation and reprogramming to overcome toxicity and to promote survival. However, these abnormal mechanisms also promote the induction of leukemia. Further investigations indicate that the current exposure limits for workers to BZ are unacceptable. Based on these studies, the new exposure limits should be less than 0.07 ppm rather than the current 1 ppm. This review also emphasizes the need to conduct appropriate bioassays, and to provide more reliable decisions on health hazards as well as on exposure limits for workers. In addition, it is important to use scientific data to provide significantly improved risk assessment, i.e., shifting from a population- to an individual-based risk assessment.

Polymorphisms in ERCC1, ERCC4 and ERCC5 genes as biomarkers of susceptibility for pesticide-induced DNA damage in North-West Indian agricultural workers

BACKGROUND

Occupational pesticides exposure has raised health concerns due to genotoxicity and accumulation of DNA damage. Polymorphisms in genes encoding enzymes involved in nucleotide excision repair (NER) may affect the individual's susceptibility to pesticide toxicity.

METHODS

This study evaluates the association of excision repair cross complementation group 1 (ERCC1) (8092 C > A, 3'UTR, rs3212986) and ERCC1 (19007 C > T, Asn118Asn, rs11615), ERCC4 (1244 G > A, Arg415Gln, rs1800067) and ERCC5 (3507 G > C, Asp1104His, rs17655) polymorphisms with pesticide-induced DNA damage in North-West Indian agricultural workers. The study population comprised 225 agricultural workers exposed to pesticides and 225 non-exposed controls.

RESULTS

Our study demonstrate that exposed workers carrying variant ERCC1 8092AA genotype showed higher total comet DNA migration (p = 0.015) as well as increased frequency of cells showing DNA migration (p = 0.027). Exposed agricultural workers with variant ERCC4 1244AA (415Gln/Gln) and ERCC5 3507CC (1104His/His) genotypes exhibited elevation in total comet DNA migration (p < 0.01). However, genotypes of ERCC1 19007 C > T (Asn118Asn) showed no association with total comet DNA migration (p = 0.963), frequency of cells showing DNA migration (p = 0.423) as well as mean tail length (p = 0.432).

CONCLUSION

ERCC1, ERCC4 and ERCC5 polymorphisms influence DNA damage and can be used as biomarkers of susceptibility for pesticide-induced DNA damage in North-West Indian agricultural workers.

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.

Gene-Environment Interactions Between Environmental Response Genes Polymorphisms and Mitochondrial DNA Copy Numbers Among Benzene Workers

OBJECTIVE

To determine the effect of mitochondrial DNA copy number (mtDNAcn) as a biomarker of benzene exposure.

METHODS

A total of 294 benzene-exposed workers and 102 controls were recruited. Biomarkers of mtDNAcn, cytokinesis-block micronucleus (MN) frequency, and peripheral blood white blood cells (WBC) were detected. Eighteen polymorphism sites in DNA damage repair and metabolic genes were analyzed.

RESULTS

Benzene exposure increased mtDNAcn and indicated a dose-response relationship (P < 0.001). mtDNAcn was negatively correlated with WBC count and DNA methylation and positively correlated with MN frequency. The AG type in rs1695 interacted with benzene exposure to aggravate mtDNAcn (β = 0.006, 95% CI: 0, 0.012, P = 0.050). rs13181, rs1695, rs1800975, and GSTM1 null were associated with benzene-induced mtDNAcn. Rs1695 interacted with benzene to increase mitochondrial damage.

CONCLUSIONS

Benzene exposure increases mtDNAcn levels in benzene-exposed workers.

Modulation of DNA damage by XPF, XPG and ERCC1 gene polymorphisms in pesticide-exposed agricultural workers of Punjab, North-West India

Inter-individual variations in DNA repair capacity (DRC) for repairing pesticide-induced DNA oxidation damage may influence adverse health outcomes. We aimed to evaluate whether polymorphisms in genes involved in nucleotide excision repair (NER) pathway could modulate DNA damage in pesticide-exposed agricultural workers. Xeroderma pigmentosum group F (XPF) (Arg415Gln, G1244A, rs1800067), xeroderma pigmentosum group G (XPG) (Asp1104His, G3507C, rs17655), excision repair cross complementation group 1 (ERCC1) (3'UTR, C8092A, rs3212986) and ERCC1 (Asn118Asn, C19007T, rs11615) polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique in 225 pesticide-exposed agricultural workers and 225 controls from Punjab, North-West India. The assessment of DNA damage was carried out by alkaline comet assay. Kruskal-Wallis test was used to evaluate the association of gene polymorphisms in NER pathway with DNA damage. Pesticide-exposed agricultural workers carrying variant XPF Gln/Gln (AA) genotype showed higher comet tail length (p < 0.01) than wild type Arg/Arg (GG) genotype. The comet tail length (p < 0.01) was found to be significantly increased in exposed agricultural workers carrying XPG His/His (CC) genotype than wild-type Asp/Asp (GG) genotype. In relation to the individuals carrying wild type ERCC1 3'UTR CC genotype, exposed individuals with variant ERCC1 3'UTR CA genotype showed elevation in the comet tail length (p = 0.029). However, we found no association of ERCC1 Asn118Asn (C19007T) genotype with DNA damage. These results indicate that XPF, XPG and ERCC1 genes of NER pathway may modulate the efficacy of the DNA repair system against pesticide exposure in our population.

Copper Ions Induce DNA Sequence Variation in Zygotic Embryo Culture-Derived Barley Regenerants

In vitro tissue culture could be exploited to study cellular mechanisms that induce sequence variation. Altering the metal ion composition of tissue culture medium affects biochemical pathways involved in tissue culture-induced variation. Copper ions are involved in the mitochondrial respiratory chain and Yang cycle. Copper ions may participate in oxidative mutations, which may contribute to DNA sequence variation. Silver ions compete with copper ions to bind to the complex IV subunit of the respiratory chain, thus affecting the Yang cycle and DNA methylation. The mechanisms underlying somaclonal variation are unknown. In this study, we evaluated embryo-derived barley regenerants obtained from a single double-haploid plant via embryo culture under varying copper and silver ion concentrations and different durations of in vitro culture. Morphological variation among regenerants and the donor plant was not evaluated. Methylation-sensitive Amplified Fragment Length Polymorphism analysis of DNA samples showed DNA methylation pattern variation in CG and CHG (H = A, C, or T) sequence contexts. Furthermore, modification of in vitro culture conditions explained DNA sequence variation, demethylation, and de novo methylation in the CHG context, as indicated by analysis of variance. Linear regression indicated that DNA sequence variation was related to de novo DNA methylation in the CHG context. Mediation analysis showed the role of copper ions as a mediator of sequence variation in the CHG context. No other contexts showed a significant sequence variation in mediation analysis. Silver ions did not act as a mediator between any methylation contexts and sequence variation. Thus, incorporating copper ions in the induction medium should be treated with caution.

Promoter hypermethylation in CSF3R induces peripheral neutrophil reduction in benzene-exposure poisoning

Benzene is a global pollutant and has been established to cause leukemia. To better understand the role of DNA methylation in benzene toxicity, peripheral blood mononuclear cells were collected from six benzene-poisoning patients and six matched controls for genome-wide DNA methylation screening by Illumina Infinium Methylation 450 BeadChip. The Gene Chip Human Gene 2.0 ST Array (Affymetrix) was used to analyze global mRNA expression. Compared with the corresponding sites of controls, 442 sites in patients were hypermethylated, corresponding to 253 genes, and 237 sites were hypomethylated, corresponding to 130 genes. The promoter methylation and mRNA expression of CSF3R, CREB5, and F2R were selected for verification by bisulfite sequencing and real-time PCR in a larger data set with 21 cases and 23 controls. The results indicated that promoter methylation of CSF3R (p = .005) and F2R (p = .015) was significantly higher in cases than in controls. Correlation analysis showed that the promoter methylation of CSF3R (p < .001) and F2R (p < .001) was highly correlated with its mRNA expression. In the poisoning cases, neutrophil percentage was significantly different among the high, middle, and low CSF3R-methylation groups (p = .002). In particular, the neutrophil percentage in the high CSF3R-methylation group (48.10 ± 9.63%) was significantly lower than that in the low CSF3R-methylation group (59.30 ± 6.26%) (p = .012). The correlation coefficient between promoter methylation in CSF3R and the neutrophil percentage was -0.445 (p = .020) in cases and - 0.398 (p = .060) in controls. These results imply that hypermethylation occurs in the CSF3R promoter due to benzene exposure and is significantly associated with a reduction in neutrophils.

Interaction effects of environmental response gene polymorphisms and benzene exposure on telomere length in shoe-making workers

Benzene is a globally occurring environmental and occupational pollutant that causes leukemia. To better understand telomere length (TL) as a function of benzene toxicity, we recruited 294 shoe-making workers and 102 controls from Wenzhou, China in 2011. Biomarkers of TL, cytokinesis-block micronucleus (MN) frequency, and white blood cells (WBC) were measured. In total, 18 polymorphic sites in environmental response genes, including metabolic and DNA repair genes, were analyzed. Results indicate that benzene exposure led to a longer TL at a threshold of 32 mg/m³-year of cumulative exposure dose (CED). Furthermore, the TL was longer in members of the damaged group, when evaluated for MN frequency (P < 0.001) and reduced WBC (P < 0.001), than in those of the normal group. Workers carrying genotype TT (β = 0.32, P = 0.042) in rs3212986 of ERCC1 and genotype TC (β = 0.24, P = 0.082) in rs1051740 of mEH exon3 were associated with a longer TL as compared to the wild-type group. TA (β = -0.53, P < 0.001) in rs6413432 of CYP2E1 was associated with a shorter TL. Benzene exposure interacted with the TA type in rs6413432 (β = 0.003, 95% CI: 0, 0.006, P = 0.042) and the CC type in rs1051740 (β = 0.007, 95% CI: 0.001, 0.013, P = 0.015) after adjusting for confounding factors. Our results indicate that benzene induces an increase in TL at a threshold of CED ≥32mg/m³-year. Rs1051740, rs3212986, and rs6413432 were found to be involved in benzene-induced telomere growth; in particular, rs1051740 and rs6413432 interacted with the benzene exposure, resulting in an extended TL.

CircRNAs in anticancer drug resistance: recent advances and future potential

CircRNAs are a novel class of RNA molecules with a unique closed continuous loop structure. CircRNAs are abundant in eukaryotic cells, have unique stability and tissue specificity, and can play a biological regulatory role at various levels, such as transcriptional and posttranscriptional levels. Numerous studies have indicated that circRNAs serve a crucial purpose in cancer biology. CircRNAs regulate tumor behavioral phenotypes such as proliferation and migration through various molecular mechanisms, such as miRNA sponging, transcriptional regulation, and protein interaction. Recently, several reports have demonstrated that they are also deeply involved in resistance to anticancer drugs, from traditional chemotherapeutic drugs to targeted and immunotherapeutic drugs. This review is the first to summarize the latest research on circRNAs in anticancer drug resistance based on drug classification and to discuss their potential clinical applications.

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.

Nickel Carcinogenesis Mechanism: DNA Damage

Nickel (Ni) is known to be a major carcinogenic heavy metal. Occupational and environmental exposure to Ni has been implicated in human lung and nasal cancers. Currently, the molecular mechanisms of Ni carcinogenicity remain unclear, but studies have shown that Ni-caused DNA damage is an important carcinogenic mechanism. Therefore, we conducted a literature search of DNA damage associated with Ni exposure and summarized known Ni-caused DNA damage effects. In vitro and vivo studies demonstrated that Ni can induce DNA damage through direct DNA binding and reactive oxygen species (ROS) stimulation. Ni can also repress the DNA damage repair systems, including direct reversal, nucleotide repair (NER), base excision repair (BER), mismatch repair (MMR), homologous-recombination repair (HR), and nonhomologous end-joining (NHEJ) repair pathways. The repression of DNA repair is through direct enzyme inhibition and the downregulation of DNA repair molecule expression. Up to now, the exact mechanisms of DNA damage caused by Ni and Ni compounds remain unclear. Revealing the mechanisms of DNA damage from Ni exposure may contribute to the development of preventive strategies in Ni carcinogenicity.