Developmental exposure to benzalkonium chloride induces defects in mechanosensory hair cells and nociceptive responses in zebrafish

Sensory neurotoxicity involves damage to the sensory nerves, often resulting from exposure to chemicals, medications, toxins, infections, or neurological disorders. Benzalkonium chloride (BKC) is a widely used quaternary ammonium compound with antiseptic properties, commonly present in pharmaceuticals, household products, and cosmetics. While the potential neurotoxicity of BKC has been previously explored in ocular and nasal epithelia, its impact on other sensory systems and the underlying mechanisms remain largely unclear. In this study, we used zebrafish (Danio rerio) embryos to assess the developmental neurotoxicity of BKC. Embryonic exposure to 0.72, 1.28, and 2.24 mg/L BKC led to dose-dependent impairments in mechanosensory hair cells, reduced startle responses, and heightened nociceptive sensitivity upon noxious stimulation. BKC exposure induced pronounced oxidative stress, evidenced by increased reactive oxygen species levels, reduced antioxidant enzyme activity, and altered expression of redox-regulating genes. Moreover, BKC significantly upregulated inflammatory and pain-associated genes, including tnfa, il1b, cox2, bdnf, and trpa1b. Expression profiling of hair cell differentiation markers revealed increased pou4f3 and decreased tmc2a/tmc2b, suggesting that BKC disrupts both terminal differentiation and mechanotransduction processes in sensory hair cells. Collectively, these findings uncover a novel mechanistic link between oxidative stress, impaired hair-cell maturation, and sensory dysfunction, offering new insights into the mechanisms underlying BKC-induced sensory neurotoxicity. This study emphasizes the ecological and toxicological relevance of quaternary ammonium compounds in aquatic environments.