Unraveling the Mechanisms of Osteoporosis Triggered by Methylparaben and Monomethyl Phthalate through Integrated Mendelian Randomization, In Silico Simulations, and Experimental Validation

Endocrine-disrupting chemicals (EDCs) are pervasive environmental hazards that have been linked to osteoporosis (OP), though causal mechanisms remain elusive. Employing an integrated multiomics framework, this study combined bidirectional Mendelian randomization (MR), network toxicology, machine learning, molecular simulations, and ovariectomized rat models to elucidate causal relationships between EDCs and osteoporosis, and to identify the molecular underpinnings of these relationships. MR analyses leveraging European GWAS data identified methylparaben (MP; OR = 0.973, p < 0.001) and monomethyl phthalate (MMP; OR = 0.984, p = 0.006) as causal agents reducing bone mineral density (BMD), validated across two independent cohorts. Network toxicology revealed CYP3A4 as a shared target for both EDCs, with HSPA5-driven endoplasmic reticulum (ER) stress implicated in MP-induced bone loss and CRP-mediated inflammation central to MMP pathology. Molecular dynamics simulations confirmed stable binding of MP/MMP with hub targets. Crucially, ribosomal genes (RPL9/RPL37A/RPS19) altered by MP were mechanistically linked to ER stress-induced osteotoxicity rather than direct EDC binding. In vivo validation demonstrated that MP and MMP exposure in OVX rats significantly exacerbated trabecular degradation, suppressed osteogenic markers, and elevated osteoclastic activity. This work establishes CYP3A4 as a high-value therapeutic target for countering EDC-induced osteoporosis and resolves longstanding controversies regarding the osteotoxic mechanisms of parabens and phthalates.