A DNA methylation pattern represents an original plan of the function settings of individual cells and tissues. The basic strategies of its development and changes during the human lifetime are known, but the details related to its modification over the years on an individual basis have not yet been studied. Moreover, current evidence shows that environmental exposure could generate changes in DNA methylation settings and, subsequently, the function of genes. In this study, we analyzed the effect of chronic exposure to nanoparticles (NP) in occupationally exposed workers repeatedly sampled in four consecutive years (2016-2019). A detailed methylation pattern analysis of 14 persons (10 exposed and 4 controls) was performed on an individual basis. A microarray-based approach using chips, allowing the assessment of more than 850 K CpG loci, was used. Individual DNA methylation patterns were compared by principal component analysis (PCA). The results show the shift in DNA methylation patterns in individual years in all the exposed and control subjects. The overall range of differences varied between the years in individual persons. The differences between the first and last year of examination (a three-year time period) seem to be consistently greater in the NP-exposed subjects in comparison with the controls. The selected 14 most differently methylated cg loci were relatively stable in the chronically exposed subjects. In summary, the specific type of long-term exposure can contribute to the fixing of relevant epigenetic changes related to a specific environment as, e.g., NP inhalation.

Department of Aerosol Chemistry and Physics Institute of Chemical Process Fundamentals CAS Rozvojova 1 165 02 Prague 6 Czech Republic

Department of Genetic Toxicology and Epigenetics Institute of Experimental Medicine CAS Videnska 1083 142 20 Prague 4 Czech Republic

Department of Machining and Assembly Department of Engineering Technology Department of Material Science Faculty of Mechanical Engineering Technical University in Liberec Studentska 1402 2 461 17 Liberec Czech Republic

Department of Nanotoxicology and Molecular Epidemiology Institute of Experimental Medicine CAS Videnska 1083 142 20 Prague 4 Czech Republic

Department of Occupational Medicine 1st Faculty of Medicine Charles University Prague and General University Hospital Prague Na Bojisti 1 120 00 Prague 2 Czech Republic

Experimental Medicine Centre Institute for Clinical and Experimental Medicine Videnska 1958 9 140 21 Prague 4 Czech Republic

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