Synergistic Effects of Maternal PM2.5 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 (PM2.5) 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-PM2.5/low-O3, high-PM2.5/low-O3, low-PM2.5/high-O3, and high-PM2.5/high-O3. We found that PM2.5 and O3 co-exposure exerted synergistic effects on maternal metabolism. Dysregulated aspartate/asparagine and amino-sugar metabolism potentially bridge PM2.5–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 PM2.5/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 (p = 0.003). This study identifies PM2.5–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.