Effects of residual PAH exposure from firefighters' skin and turnout gear on biospecimen microRNA expression

Firefighters are routinely exposed to polycyclic aromatic hydrocarbons (PAHs) during fire suppression activities, molecular biomarkers reflecting such exposure remain underexplored. Thus, we explored an integrated exposure assessment framework linking PAH contamination on turnout gear and skin to changes in microRNA (miRNA) expression in skin and blood biospecimens. Our goals are to evaluate the relationship between fire-related PAH exposure and miRNA expression profiles in firefighters, and to identify candidate miRNA biomarkers of occupational exposure. This prospective study enrolled 25 firefighters. PAHs on turnout gear and skin were quantified post-fire using gas chromatography/mass spectrometry. Concurrently, skin tape strips and blood were collected and analyzed for miRNA expression using NanoString's nCounter platform. Bioinformatic analyses, including differential expression, pathway enrichment, and network modeling, were performed to evaluate PAH-associated miRNA dynamics. Five miRNAs showed significant differential expression following fire activity (q < 0.05), with miR-125a-3p showing a 60 % increase post-fire. Biospecimen comparisons showed six differentially expressed miRNAs, including a 91 % reduction in miR-451a expression in skin relative to blood. Network and pathway analyses identified PAH-specific interaction patterns, with Naphthalene emerging as a central node. Pathway enrichment highlighted necroptosis and Th17 cell differentiation as key biological processes affected by exposure. This study provides novel evidence that PAH exposure at fire scenes induces distinct miRNA expression profiles in firefighters. miR-125a-3p emerges as a potential biomarker responsive to fire-related exposures. These findings provide critical insights into PAH-associated transcriptional responses and suggest the potential of miRNA profiling in occupational exposure assessment and cancer risk stratification among firefighters.