Gestational Exposure to Tri- <i>n</i> -butyl Phosphate Induces Maternal Insulin Resistance and Glucose Intolerance by Antagonizing Estrogen Receptor Alpha

Epidemiological evidence links tri-<i>n</i>-butyl phosphate (TNBP) exposure to gestational diabetes mellitus (GDM), but mechanistic insights remain unclear. This study demonstrated that gestational TNBP exposure induced a GDM-like phenotype in pregnant mice, characterized by glucose intolerance, but not in nonpregnant female mice. This pregnancy-specific susceptibility might be attributed to significantly higher internal levels of TNBP and its metabolites dibutyl phosphate (DNBP) and dibutyl-3-hydroxybutyl phosphate (3-OH-TNBP) than the nonpregnant mice, subsequently exacerbating insulin resistance in the pregnant mice. The hyperglycemia in pregnant mice was closely associated with the reduced expression of estrogen receptors (<i>p</i> < 0.01). Through integrated biomolecular approaches (e.g., Western blotting and surface plasmon resonance), estrogen receptor alpha (ERα) was identified as the primary binding target, resulting in decreased ERα protein expression and transcriptional activity. Transcriptomics further revealed that exposure to TNBP disrupted ERα-regulated gene networks and the ERα/PI3K/Akt pathway in the pregnant mice, consequently downregulating glucose transporter 2 and impairing glucose metabolism. <i>In vitro</i> validation using pregnancy hormone-primed HepG2 cells confirmed that TNBP and its metabolites induced ERα-mediated glucose dysregulation, with a potency order of 3-OH-TNBP > DNBP > TNBP. These findings establish a novel mechanism by which gestational TNBP exposure disrupts maternal glucose homeostasis via ERα signaling suppression.