Bisphenol S as an emerging osteotoxicant: Mechanistic insights from osteoblasts and zebrafish models.

Bisphenol S (BPS) exposure has been shown to induce osteopathies such as osteoporosis, yet the underlying mechanisms remain poorly understood. To comprehensively evaluate the toxic effects and mechanisms of BPS on osteoblast differentiation and bone development, an integrated approach combining the hFOB1.19 human osteoblast cell line (in vitro) and zebrafish larvae (in vivo) were utilized. In hFOB1.19 cells, exposure to BPS (0, 1, 5, 10 and 50 µM) for 96 h (n = 3-4 replicates) disrupted osteogenic differentiation by downregulating key markers (RUNX2 and OPG) and induced mitochondrial dysfunction through reduced membrane potential and metabolic alterations. BPS triggered excessive ROS production with compensatory antioxidant upregulation (SOD, CAT), while activating mitochondrial apoptosis pathways via Bax/Cytochrome c/Caspase-3 signaling. Notably, BPS promoted NLRP3 inflammasome activation (ASC, CAS1) and GSDMD cleavage, driving pyroptosis through inflammatory cytokine release. These dual cell death pathways collectively impaired osteoblast formation. In zebrafish larvae, exposure to BPS (0, 0.5, 1, 10 and 50 µM) for 5- and 7-dpf (n = 3-4 replicates) caused pharyngeal cartilage shortening, and delayed bone mineralization, accompanied by altered bone metabolism markers (ALP, osteocalcin, Ca, and P) and disrupted differentiation genes (col2a1 and bmp15). Parallel upregulation of apoptosis (p53 and cas9) and pyroptosis genes (nlrp3) mirrored cellular findings, suggesting conserved mechanisms across species. Collectively, these findings highlight BPS as a significant environmental risk factor for bone health, emphasizing the need for further toxicological and regulatory evaluation.