Synergistic Effects of Maternal PM _2.5 and Ozone Co-exposure on Gestational Diabetes Mellitus: A Metabolomic Mechanistic Insight

Environmental pollutants represent critical controllable risk factors for gestational diabetes mellitus (GDM) requiring urgent investigation in maternal-fetal medicine. Emerging evidence has associated individual exposure to particulate matter with aerodynamic diameter ≤ 2.5 μm (PM_2.5) or ozone (O₃) with GDM risk, but their synergistic effects and underlying metabolic mechanisms remain unclear. In this nested case-control study involving 90 matched GDM-control pairs, we employed high-resolution metabolomics to identify co-exposure- and GDM-related metabolic signatures across four exposure scenarios: low-PM_2.5/low-O₃, high-PM_2.5/low-O₃, low-PM_2.5/high-O₃, and high-PM_2.5/high-O₃. We found that PM_2.5 and O₃ co-exposure exerted synergistic effects on maternal metabolism. Dysregulated aspartate/asparagine and amino-sugar metabolism potentially bridge PM_2.5-O₃ co-exposure to GDM pathogenesis. High-dimensional mediation analysis revealed a meet-in-the-middle-derived factor that significantly mediated the co-exposure-GDM association (mediation proportion, 13.7%). Among 1945 metabolic features linked to PM_2.5/O₃ exposure and 271 correlated with GDM, 12 were confirmedly annotated. Incorporating these 12 metabolites into a classical risk factor-based receiver operating characteristic model increased area under the curve from 0.64 to 0.77 (<i>p</i> = 0.003). This study identifies PM_2.5-O₃ co-exposure as a controllable GDM risk factor, mechanistically linked to aspartate/asparagine and amino-sugar metabolic disruption. The identified exposure-responsive metabolites not only provide biological insights but also demonstrate translational potential for improving GDM risk prediction models.