Prenatal Exposure of Pesticide Mixtures and the Placental Transcriptome: Insights from Trimester-specific, Sex-Specific and Metabolite-Scaled Analyses in the SAWASDEE Cohort

We investigated the effect of exposure to pesticide mixtures during pregnancy on the placental transcriptome, to link these exposures and placental functions. The Study of Asian Women and their Offspring's Development and Environmental Exposures (SAWASDEE) enrolled pregnant farmworkers from Thailand (n=248), who were primarily exposed to organophosphate (OP) and pyrethroid pesticides. We measured maternal urinary levels of six non-specific OP metabolites expressed as three summary measures (dimethylalkylphosphates (DMAP), diethylalkylphosphates (DEAP), and dialkylphosphates (DAP) and three pyrethroid metabolites (3-phenoxybenzoic acid (3-PBA), cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (Cis-DCCA, Trans-DCCA) during early, middle, and late pregnancy, and adjusted for urine dilution using creatinine. RNA-sequencing was used to profile the placental transcriptome from which 21 co-expression network modules were identified by Weighted Gene Co-expression Network Analysis. Quantile g-computation analysis identified an average pregnancy positive mixture exposure effect on the E2f Target Module (β=0.013, p=0.012) and a negative mixture exposure effect (β=-0.016, p=0.008) on the Myogenesis Module. The pesticide metabolites driving the associations differed for each module, highlighting differential susceptibilities within the placental transcriptome to various pesticides. When stratifying by infant sex, the average pregnancy mixture exhibited a significant negative effect (β=-0.018, P=0.016) on the Myogenesis Module only in females; other modules, such as epithelial-mesenchymal transition, though not demonstrating an overall mixture effect, did demonstrate differential impacts of the mixture by sex. Pesticide mixtures in both the second trimester (β=-0.013, p=0.015) and the third trimester (β =-0.012, p=0.028) exhibited consistently significant negative associations with the Myogenesis module. These findings underscore the importance of considering the prenatal environment more holistically, understanding the placenta's susceptibility to contaminants, and incorporating sex-specific analyses to understand differential impacts.