Neurotoxicogenomic impact of 4-nonylphenol on Heteropneustes fossilis via molecular, histopathological and bioinformatic analysis.

Exposure to 4-Nonylphenol at concentrations of 64 µg/L (low) and 160 µg/L (high) for 30 to 60 days, spanning the pre-spawning to spawning phases in H. fossilis, induces significant adverse effects in the brain, particularly within the telencephalon and cerebellum regions. Additionally, protein content in brain decreases in treated group of 4-Nonylphenol (4-NP), brain acetylcholinesterase (AChE) activity decreases in a manner contingent upon the amount of dose and exposure period. In the brain tissue of H. fossilis, exposure to 4-Nonylphenol (4-NP) results in a dose-dependent decrement of antioxidant enzymes including Superoxide dismutase(SOD), Catalase, and Glutathione peroxidase(GPx), alongside a dose and duration-dependent increase in Lipid peroxidation (LPO) levels. Cortisol level in the brain increases with higher doses of 4-NP. The exposure to 4-NP induces a dose-dependent increase in cell death after both 30 and 60 days, with a marked increase in necrosis after 30 days. However, at 60 days, apoptosis becomes more prominent, suggesting a shift toward programmed cell death due to prolonged exposure. In the brain cells of H. fossilis, exposure to 4-Nonylphenol (4-NP) over 30 to 60 days caused an escalation in reactive oxygen species (ROS) and DNA fragmentation. Gene expression of brain aromatase (Cyp19a1b) and Gonadotropin-releasing hormone (GnRH) is downregulated in a dose-dependent manner. These findings indicate that both acute and chronic exposure to 4-NP induces neurotoxicity in male H. fossilis by crossing the blood-brain barrier. This was further validated through an in silico analysis using SwissADME, which predicted high intestinal absorption of 4-NP and its potential to cross the blood-brain barrier. Additionally, molecular docking and Molecular Dynamics (MD) simulations substantiated a strong binding affinity of 4-NP to acetylcholinesterase in the brain. Overall, this investigation demonstrates that 4-NP disrupts brain tissue, impairs antioxidant defenses, promotes ROS production, and impacts gene expression and brain enzyme activity.