Methylation of promoter regions of DNA repair and xenobiotic metabolism genes in coal-fired power plant workers

Introduction. Occupational exposure to a complex of genotoxic agents (coal dust, heavy metals, polycyclic aromatic hydrocarbons) at coal-fired thermal power plants (TPPs) can induce epigenetic changes, in particular, abnormal methylation of the promoters of key genome protection genes. However, the methylation status of DNA repair genes (XRCC1, XRCC2, XRCC3, ERCC2, ERCC5) and xenobiotic biotransformation genes (GSTP1, GSTT1, CYP1A1) in coal-fired TPP workers remains unstudied. Objective: To characterize the methylation profile of these promoters in coal-fired TPP workers compared with a control group and to evaluate the influence of occupational and individual factors.

Methods. A total of 936 individuals were examined: 445 workers at coal-fired power plants in Kemerovo and 491 residents not employed in industrial production. Promoter methylation status was determined using methylation-specific PCR after bisulfite conversion of DNA. Results were validated using whole-genome bisulfite sequencing (WGBS) on a subsample (n=5).

Results. A significant increase in the frequency of hypermethylated and partially methylated promoter status of all eight genes was revealed in thermal power plant workers compared to the controls (p <0.000001). The most pronounced differences were recorded for GSTP1, GSTT1 and ERCC5 (hypermethylation in workers was 4-5 times more frequent). Work experience of >20 years was associated with a higher frequency of hypermethylation of ERCC2, XRCC1, XRCC3 (p <0.02). Workers in the fuel and transport, repair, chemical shops and the thermal automation and measurements shop demonstrated the highest rates of hypermethylation of ERCC2, ERCC5 and GSTT1 (p < 0.02). No significant associations of methylation status with gender, age, smoking and the presence of chronic diseases were found (p > 0.05).

Conclusion. The obtained data demonstrate for the first time a significant shift in the epigenetic profile toward hypermethylation of repair and detoxification gene promoters during work at coal-fired power plants. Work experience and occupational location are key determinants of epigenetic changes. The obtained results substantiate the use of these markers for biomonitoring of occupational risks.

1. Jiménez-Garza O., Ghosh M., Barrow T.M., Godderis L. Toxicomethylomics revisited: A state-of-the-science review about DNA methylation modifications in blood cells from workers exposed to toxic agents. Front Public Health. 2023;11:1073658. doi: 10.3389/fpubh.2023.1073658

2. Wei Y., Zhou Y.F., Xiao L., et al. Associations of Heavy Metals with Cognitive Function: An Epigenome-Wide View of DNA Methylation and Mediation Analysis. Ann Neurol. 2024;96(1):87-98. doi: 10.1002/ana.26942

3. Graber J.M., Stayner L.T., Cohen R.A., et al. Respiratory disease mortality among US coal miners; results after 37 years of follow-up. Occup Environ Med. 2014;71(1):30-9. doi: 10.1136/oemed-2013-101597

4. Ku P., Tsui M.T., Liu S., et al. Examination of mercury contamination from a recent coal ash spill into the Dan River, North Carolina, United States. Ecotoxicol Environ Saf. 2021;208:111469. doi: 10.1016/j.ecoenv.2020.111469

5. Cerda S., Weitzman S.A. Influence of oxygen radical injury on DNA methylation. Mutat Res. 1997;386(2):141-52. doi: 10.1016/s1383-5742(96)00050-6. PMID: 9113115.

6. Zhang P., Wu Y., Piao C., et al. DNA methylome profiling in occupational radon exposure miners using an Illumina Infinium Methylation EPIC BeadChip. Toxicol Res (Camb). 2023;12(5):943-953. doi: 10.1093/toxres/tfad084

7. Duan H., He Z., Ma J., et al. Global and MGMT promoter hypomethylation independently associated with genomic instability of lymphocytes in subjects exposed to high-dose polycyclic aromatic hydrocarbon. Arch Toxicol. 2013;87(11):2013-2022. doi: 10.1007/s00204-013-1046-0

8. Yang J., Liu Y., Zhang H., et al. Urinary 1-hydroxypyrene and smoking are determinants of LINE-1 and AhRR promoter methylation in coke oven workers. Mutat Res Genet Toxicol Environ Mutagen. 2018;826:33-40. doi: 10.1016/j.mrgentox.2018.01.001

9. Xing C., Wang Q., Tian H., et al. [Hypermethylation and downregulation of tumor suppressor gene p16 in benzene poisoning]. Wei Sheng Yan Jiu. 2012;41(2):247-50.

10. Ren J., Cui J.P., Luo M., et al. The prevalence and persistence of aberrant promoter DNA methylation in benzene-exposed Chinese workers. PLoS One. 2019;14(8):e0220500. doi: 10.1371/journal.pone.0220500

11. Herceg Z., Ambatipudi S. Smoking-associated DNA methylation changes: no smoke without fire. Epigenomics. 2019;11(10):1117-1119. doi: 10.2217/epi-2019-0136

12. Unnikrishnan A., Freeman W.M., Jackson J., et al. The role of DNA methylation in epigenetics of aging. Pharmacol Ther. 2019;195:172-185. doi: 10.1016/j.pharmthera.2018.11.001

13. Seiler C.L., Fernandez J., Koerperich Z., et al. Maintenance DNA Methyltransferase Activity in the Presence of Oxidized Forms of 5-Methylcytosine: Structural Basis for Ten Eleven Translocation-Mediated DNA Demethylation. Biochemistry. 2018;57(42):6061-6069. doi: 10.1021/acs.biochem.8b00683

14. Kurita H., Ohuchi K., Inden M. Effects of Environmental Non-Essential Toxic Heavy Metals on Epigenetics During Development. Toxics. 2025;13(3):167. doi: 10.3390/toxics13030167

15. Rieke D.T., Ochsenreither S., Klinghammer K., et al. Methylation of RAD51B, XRCC3 and other homologous recombination genes is associated with expression of immune checkpoints and an inflammatory signature in squamous cell carcinoma of the head and neck, lung and cervix. Oncotarget. 2016;7(46):75379-75393. doi: 10.18632/oncotarget.12211

16. Strizhakov L.A., Babanov S.A., Vinnikov D.V., et al. «Effekt zdorovogo rabochego» i professional’nyy otbor v promyshlennoy meditsine [«The healthy worker effect» and occupational selection in industrial medicine]. Vrach [Doctor]. 2021;32(12):20-28. (In Russ.) doi: 10.29296/25877305-2021-12-03

17. Krylov D.A. Negativnoye vliyaniye elementov-primesey ot ugol’nykh TES na okruzhayushchuyu sredu i zdorov’ye lyudey [Negative effects of impurities from coal-fired thermal power stations on the environment and health]. Gornyy informatsionno-analiticheskiy byulleten’ [Mining Information and Analytical Bulletin]. 2017;12:77-87. (In Russ.) doi:10.25018/0236-1493-2017-12-0-77-87

18. Schärer O.D. Nucleotide excision repair in eukaryotes. Cold Spring Harb Perspect Biol. 2013;5(10):a012609. doi: 10.1101/cshperspect.a012609

19. Zhang X., Li J., He Z., et al. Associations between DNA methylation in DNA damage response-related genes and cytokinesis-block micronucleus cytome index in diesel engine exhaust-exposed workers. Arch Toxicol. 2016;90(8):1997-2008. doi: 10.1007/s00204-015-1598-2

20. Congues F., Wang P., Lee J., et al. Targeting aryl hydrocarbon receptor to prevent cancer in barrier organs. Biochem Pharmacol. 2024;223:116156. doi: 10.1016/j.bcp.2024.116156