Mechanistic study on curcumin alleviating hepatic cell injury in common carp ( <i>Cyprinus carpio</i> ) via regulation of mitochondrial function

Intensive aquaculture practices often expose fish to hepatic injuries induced by dietary and environmental stressors, with mitochondrial dysfunction playing a pivotal role. Curcumin, a natural polyphenol, has demonstrated hepatoprotective activity in mammals; however, its mitochondria-targeted mechanism of action in the hepatocytes of aquatic animals remains unclear. This study aimed to investigate whether curcumin alleviates carbon tetrachloride (CCl₄)-induced injury in common carp hepatocytes by regulating mitochondrial function, and to elucidate its dose-dependent effects. Primary hepatocytes isolated from common carp were used as an in vitro model. A hepatic injury system was established using CCl₄, with interventions of curcumin at low (2.5 μM) and high (10 μM) concentrations. The regulatory effects of curcumin on mitochondrial function and hepatocyte homeostasis were systematically assessed by measuring the activities of mitochondrial respiratory chain complexes, adenosine triphosphate (ATP) and reactive oxygen species (ROS) levels, mitochondrial membrane potential, and the expression of genes related to mitophagy and apoptosis. Results revealed a significant dose-dependent hormetic effect of curcumin intervention: a low dose (2.5 μM) comprehensively improved mitochondrial respiratory function, enhanced ATP synthesis, reduced ROS accumulation, and activated the PINK1/Parkin-mediated mitophagy pathway, thereby markedly inhibiting the caspase-3-dependent apoptosis pathway. In contrast, a high dose (10 μM), despite exhibiting stronger direct antioxidant capacity, showed weaker restorative effects on overall mitochondrial metabolic function，which including impaired restoration of CS and SDH activities and ATP synthesis, and impaired maintenance of mitophagy. Collectively, 2.5 μM curcumin confers a core hepatoprotective effect by coordinately regulating mitochondrial bioenergetics, mitophagy, and apoptosis signaling pathways. This study elucidates the dose-dependent, mitochondria-targeted protective mechanism of curcumin in an aquatic animal model, providing important theoretical and experimental evidence for its application as a precision nutritional strategy in aquafeed formulations.