Changes in miR-222 expression, DNA repair capacity, and MDM2-p53 axis in association with low-dose benzene genotoxicity and hematotoxicity.

Mechanisms for hematotoxicity and health effects from exposure to low doses of benzene (BZ) remain to be identified. To address the information gap, our investigation was focused onto using appropriate populations and cell cultures to investigate novel BZ-induced effects such as disruption of DNA repair capacity (DRC). From our study, abnormal miRNAs were identified and validated using lymphocytes from 56 BZ-poisoned workers and 53 controls. In addition, 173 current BZ-exposed workers and 58 controls were investigated for key miRNA expression using RT-PCR and for cellular DRC using a challenge assay. Subsequently, the observed activities in lymphocytes were verified using human HL-60 (p53 null) and TK6 (p53 wild-type) cells via 1,4-benzoquinone (1,4-BQ) treatment and miR-222 interferences. The targeting of MDM2 by miR-222 was validated using a luciferase reporter. Our results indicate induction of genotoxicity in lymphocytes from workers with low exposure doses to BZ. In addition, miR-222 expression was up-regulated among both BZ-poisoned and BZ-exposed workers together with inverse association with DRC. Our in vitro validation studies using both cell lines indicate that 1,4-BQ exposure increased expression of miR-222 and Comet tail length but decreased DRC. Loss of miR-222 reduced DNA damage, but induced S-phase arrest and apoptosis. However, silencing of MDM2 failed to activate p53 in TK6 cells. In conclusion, our in vivo observations were confirmed by in vitro studies showing that BZ/1,4-BQ exposures caused genotoxicity and high expression of miR-222 which obstructed expression of the MDM2-p53 axis that led to failed activation of p53, abnormal DRC and serious biological consequences.

Aberrant lncRNA Profiles Are Associated With Chronic Benzene Poisoning and Acute Myelocytic Leukemia.

OBJECTIVE: This study investigates the mechanisms of benzene hematotoxicity. METHODS: We used microarray to detect expression profiles of long non-coding RNAs (lncRNAs) and mRNAs in peripheral lymphocytes from chronic benzene poisoning, acute myelocytic leukemia, and healthy controls. The lncRNAs and mRNAs were validated using real-time quantitative PCR (RT-qPCR). Cytokinesis-block micronucleus assay was used to analyze chromosomal aberration. RESULTS: We found 173 upregulated and 258 downregulated lncRNAs, and 695 upregulated and 804 downregulated mRNAs. The lncRNA CUST_40243 and mRNA PDGFC and CDKN1A associated with chronic benzene poisoning. Relevant inflammatory response, hematopoietic cell lineage, and cell cycle may be important pathways for the sifted lncRNAs and mRNAs. Furthermore, micronuclei frequency was significantly higher in off-post chronic benzene poisoning patients. CONCLUSIONS: Chromosomal aberration induced by benzene exposure is irreversible. The lncRNA CUST_40243 and mRNA PDGFC and CDKN1A are related to chronic benzene poisoning.

Relative telomere length and gene expression of shelterin complex proteins among vinyl chloride monomer-exposed workers in China.

Vinyl chloride monomer (VCM) is a confirmed carcinogen. The effects of VCM on telomeres and the gene expression of telomere complex proteins, shelterin, have not been well studied but could be of potential relevance to the carcinogenic mechanism of VCM and the health surveillance of VCM-exposed workers. A group of 241 VCM-exposed workers and 101 internal controls from the same plant in Shandong, China were recruited and quantitative polymerase chain reaction was preformed to measure relative telomere length (RTL) and gene expression of shelterin proteins. VCM cumulative exposure dose (CED) was estimated for the exposed workers. The differences in RTL and gene expression between groups were compared by Wald test fitted with robust regression. Shorter RTL was observed in VCM-exposed workers than in the controls (P < 0.001) and was related to CED of VCM. Shortened RTL was also significantly related to increasing age (P = 0.012) and high blood pressure (P = 0.056). Levels of gene expression of shelterin components in exposed workers were all lower than in controls except increased TIN2 expression, and the gene expression differences in TIN2 and POT1 among exposed and control groups were significant (P = 0.014 for TIN2 and P < 0.001 for POT1, respectively). VCM exposure is found associated with altered telomere length and gene expression of shelterin components. This provides new insights into the potential carcinogenic mechanisms of VCM and could be helpful for the health surveillance for VCM-exposed workers. Environ. Mol. Mutagen. 60:361-367, 2019. © 2018 Wiley Periodicals, Inc.

Hypermethylation of CpG islands is associated with increasing chromosomal damage in chinese lead-exposed workers.

Lead is a widely existing environmental pollutant with potential carcinogenicity. To investigate the association of blood lead level (B-Pb) with potential chromosomal damage and cancer, we analyzed micronucleus (MN) frequency of peripheral blood lymphocytes (PBLs) and the methylation status of six human tumor suppressor genes (TSGs) post lead exposure. In the study, 147 lead-exposed workers were divided into two groups according to their B-Pb P50 value, with other 50 lead-unexposed workers as a control group. The cytokinesis-blocked micronucleus (CBMN) assay was performed to detect chromosomal damage of PBLs of both lead-exposed and -unexposed workers. The methylation-specific polymerase chain reaction (MSP-PCR) was further used to examine the methylation status of six TSGs (GSTP1, hMLH1, MGMT, p14, p15, and p16). Results showed that MN frequencies of high B-Pb workers 8.1 ± 3.1‰ and low B-Pb workers 5.7 ± 2.3‰ were significantly higher than that of control group 2.8 ± 1.9‰ (P < 0.01), while the MN frequency of high B-Pb workers was also higher than that of the low B-Pb workers (P < 0.01). The MN frequency in PBLs of lead-exposed group with the methylated TSGs was significantly higher than that in PBLs with the unmethylated TSGs (P < 0.05). Notably, the CpG island methylator phenotype (CIMP) correlated with chromosome damage (P < 0.05). Additionally, workers with high B-Pb had higher chromosome damage than those with low B-Pb (P < 0.05). Taken altogether, the results suggest that lead-exposed workers with CIMP positive and high B-Pb have a higher risk of being vulnerable to tumorigenesis. Environ. Mol. Mutagen. 59:549-556, 2018. © 2018 Wiley Periodicals, Inc.

Association of Telomere Length With Chromosomal Damage Among Chinese Workers Exposed to Vinyl Chloride Monomer.

OBJECTIVE: To explore the relationship between relative telomere length (RTL) and chromosomal damage represented by micronucleus (MN) frequencies among vinyl chloride monomer (VCM) -exposed workers. METHODS: A group of 126 VCM-exposed workers, 60 internal controls, and 25 external controls were examined for RTL by Quantitative polymerase chain reaction and MN frequencies by cytokinesis-block micronucleus test. Cumulative exposure dose was used to estimate the exposure of VCM-exposed workers. RESULTS: The RTL were significantly shorter in exposed workers and internal controls than in external controls. The exposed workers had significantly increased MN frequencies than both control groups. Additionally, MN frequencies were negatively associated with RTL in VCM-exposed group. CONCLUSIONS: VCM exposure may alter telomere length, which could be a potential biomarker of susceptibility to chromosomal damage.

Benchmark Doses Based on Abnormality of WBC or Micronucleus Frequency in Benzene-Exposed Chinese Workers.

OBJECTIVES: The aim of the study was to calculate benchmark dose for chromosomal damage and reduced white blood cell (WBC) associated with exposure to benzene (BZ). METHODS: A group of 317 exposed workers and 102 controls were examined for WBC count and genotoxicity by micronucleus (MN) frequency. The cumulative exposure concentration of BZ was calculated by ambient air BZ concentration at worksites in conjunction with job type and associated service duration. RESULTS: MN frequency (P < 0.01) was higher and WBC count was lower (P < 0.01) in exposed workers on average than in the controls. MN frequency was a more sensitive than WBC; workers older than 30 were more susceptible to abnormal MN frequency and WBC count reduction than those younger than 30. CONCLUSIONS: Benchmark dose estimates indicated that BZ exposure at levels below the current occupational exposure standard can induce genotoxicity and hematotoxicity.

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

BACKGROUND: Genetic variations in metabolic enzyme genes may enhance hematotoxicity in benzene-exposed populations. OBJECTIVE: To investigate the association between polymorphisms of metabolism genes and white blood cells (WBCs). METHODS: Three hundred and eighty-five benzene-exposed workers and 220 unexposed indoor workers were recruited in China. We explored the relationship between metabolic enzymes polymorphisms [glutathione S-transferase T1/M1 (GSTT1/M1) null, glutathione S-transferase P1 (GSTP1)rs1695, Cytochrome P450 2E1 (CYP2E1) rs3813867, rs2031920, rs6413432, microsomal epoxide hydrolase (mEH) rs1051740, rs2234922] by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) analysis and WBC. RESULTS: The exposed group had lower WBC counts (P<0·001) than the unexposed group. Increased susceptibility to hematotoxicity, as evidenced by lower WBC counts, was found in workers with null-GSTT1 (P = 0·045), null-GSTM1 (P = 0·030), rs2031920 (P = 0·020), and rs3813867 (P = 0·014) genotypes. White blood cell counts were also lower in workers with null-GSTT1 and null-GSTM after adjusting for age, gender, smoking, and alcohol consumption. CONCLUSION: Null-GSTT1 and null-GSTM1 genotypes and Cytochrome P4502E1 (CYP2E1: rs2031920, rs3813867) may support the hematotoxicity of benzene-exposed workers in China, and we can make use of it to select susceptible population.