Early developmental lead exposure disrupts skeletal development in zebrafish

Lead (Pb) pollution is a critical environmental concern because of its high toxicity, persistence, and bioaccumulative nature. While the toxicological effects of Pb on the urinary, reproductive, and nervous systems have been extensively studied, its impact on skeletal development and the associated mechanisms remain insufficiently understood. In this study, zebrafish (Danio rerio) embryos were used as a model to investigate the developmental toxicity of Pb with a specific focus on bone development. Lead (II) acetate (PbAc) is used as a Pb donor. Embryos were exposed to Pb at 0, 10, 100, 1000, and 10,000 μg/L for 7 days, covering environmentally relevant levels and a higher worst-case concentration. Pb exposure induced dose-dependent morphological abnormalities in larvae, including spinal curvature and tail flexure, along with increased rates of deformity and mortality. In addition, hatching rate and survival rate were significantly reduced, while heart rate increased. Alcian blue, Alizarin red, and Calcein staining revealed that Pb significantly impaired craniofacial cartilage development and inhibited mineralization in the skull and vertebrae. Mechanistic analyses demonstrated that Pb exposure suppressed the activity of key bone-related enzymes, alkaline phosphatase (ALP) and acid phosphatase (ACP), and reduced total antioxidant capacity and superoxide dismutase (SOD) activity. qPCR analysis showed that high Pb concentrations significantly downregulated the expression of critical bone development-related genes, including Bmp2, Col2a1, Runx2, Wnt16, and Sparc. These findings suggest that Pb impairs zebrafish cartilage development and bone mineralization by disrupting phosphatase activity, antioxidant defense, and gene expression related to osteogenesis. This study provides novel insights into the mechanisms underlying Pb-induced skeletal toxicity and contributes to a better understanding of heavy metal toxicity in early vertebrate development, with implications for human health risk assessment.