Brass-Derived Copper and Zinc Induce Oxidative Stress and Autophagy-Mediated Nephrotoxicity in Channa punctatus

Brass toxicity has emerged as a pressing environmental concern, with its dual-metal burden of copper (Cu) and zinc (Zn) from industrial discharges continuing to jeopardize aquatic ecosystem health. This study investigates the effects of environmentally relevant concentrations (ERC) and 10% and 20% elevated levels of Cu (0.85, 0.935, and 1.02 mg/L) and Zn (1.2, 1.32, and 1.44 mg/L) on the kidney of Channa punctatus during a 60-day exposure, with sampling conducted at 15-day intervals under controlled laboratory conditions. Results revealed significant (p < 0.05), dose- and time-dependent accumulation of Cu and Zn in renal tissues, accompanied by elevated reactive oxygen species (ROS) and lipid peroxidation (LPO) levels, and increased superoxide dismutase (SOD) and catalase (CAT) activities, whereas reduced glutathione (GSH) content declined markedly. qRT-PCR analysis demonstrated pronounced upregulation of atg5, beclin1, lc3, and ulk1b with concomitant downregulation of mTOR, suggesting activation of the autophagic pathway in response to oxidative stress. Histopathological examination confirmed progressive renal degeneration, including glomerular degenerative cells, vacuolization, and epithelial disorganization, especially at higher concentrations. Principal component analysis (PCA) indicated a strong association among ROS, antioxidant enzymes, LPO, and autophagy genes, emphasizing redox-autophagy coupling in metal-induced stress responses. Collectively, these findings identify brass as a key driver of nephrotoxicity, where chronic Cu-Zn release disrupts redox balance and induces cytotoxic autophagy, with autophagy-related genes serving as sensitive biomarkers of brass toxicity in freshwater ecosystems.