Integrated transcriptomic and metabolomic analysis of copper sulfate-induced hepatotoxicity in Oreochromis niloticus via glutathione depletion and energy metabolic reprogramming.

Copper is a widespread heavy metal pollutant in aquatic ecosystems, but the systemic molecular mechanisms of copper-induced hepatotoxicity in fish remain incompletely understood. Here, we integrated histopathological examination, biochemical assays, transcriptomics, and metabolomics to investigate the hepatotoxic effects of copper sulfate (CuSO₄) exposure in Oreochromis niloticus. CuSO₄ exposure caused typical pathological damage, including hepatocyte swelling, vacuolar degeneration, and pyknosis. Biochemical assays revealed significantly reduced activities of superoxide dismutase (SOD) and catalase (CAT), decreased glutathione (GSH) content, and elevated malondialdehyde (MDA) levels, indicating severe oxidative stress. Transcriptomic analysis identified 896 differentially expressed genes (DEGs) enriched in pathways related to lipid and fatty acid metabolism, cytochrome P450, and PPAR signaling. Metabolomic analysis detected 738 differentially expressed metabolites (DEMs), primarily involved in glutathione metabolism, oxidative phosphorylation, and amino acid metabolism. Integrated multi-omics analysis uncovered two core mechanisms: depletion of the glutathione system (significantly reduced GSH and GSSG) and energy metabolic reprogramming (marked decreases in NADH, citrate, and acylcarnitines). Concurrently, immune- and inflammation-related genes (IL1B, IL8, C3, C7) were strongly upregulated. Notably, copper homeostasis genes (ATP7B, CP) were downregulated, suggesting that copper accumulation may drive mitochondrial dysfunction and metabolic collapse. In conclusion, CuSO₄ induces hepatotoxicity in tilapia primarily by triggering oxidative stress, which is characterized by glutathione depletion and disruption of energy and lipid metabolic homeostasis. These findings provide multi-omics evidence for understanding copper toxicity and offer potential biomarkers for environmental risk assessment of copper pollution in aquatic ecosystems.