Urinary DNA Methylation and Hydroxymethylation Dynamics as Candidate Biomarkers of Occupational Chemical Exposure—An Exploratory Pilot Study

DNA methylation (5-mdC) and its oxidative derivatives reflect interactions between environmental exposures and genome regulation, yet their short-term responsiveness to occupational factors remains insufficiently characterized. This exploratory pilot study evaluated whether a standard workweek is associated with measurable changes in urinary epigenetic and oxidative DNA modification profiles across distinct occupational settings. A cohort representing three exposure scenarios—cyanoacrylate-based cosmetic services, toluene diisocyanate (TDI) exposure, and polyurethane (PUR) foam processing—was examined using a paired pre-/post-exposure design. Urinary levels of 5-methyl-2′-deoxycytidine (5-mdC), 5-hydroxymethylcytosine (5-hmCyt), 5-hydroxymethyl-2′-deoxycytidine (5-hmdC), 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), 5-hydroxymethyl-2′-deoxyuridine (5-hmdU), and 5-hydroxymethyluracil (5-hmUra) were quantified, and an epigenetic turnover ratio (5-hmdC/5-mdC) was derived. Although none of the observed shifts achieved formal statistical significance after False Discovery Rate (FDR) adjustment (p_FDR > 0.05), exposure-specific, directionally consistent non-significant trends were noted across cohorts. The isocyanate-exposed group demonstrated coordinated reductions in 5-mdC and 5-hmdC accompanied by an increase in 5-hmdU. The PUR-processing group exhibited the most pronounced response, including a marked elevation in 5-hmdU and an increased turnover ratio. In contrast, the beauty sector showed minimal median shifts but substantial inter-individual variability. These preliminary findings suggest that urinary epigenetic and oxidative DNA markers might reflect short-term, exposure-related biological trends, warranting further evaluation.