Lycopene alleviates splenic injury in grass carp (Ctenopharyngodon idella) caused by endoplasmic reticulum stress-autophagy axis induced by sulfamethoxazole through regulating AKT/AMPK pathway

Sulfamethozole (SMZ), an antibiotic widely used in aquaculture, is bioaccumulating and resistant to degradation, posing ecological risks. Although environmentally relevant SMZ concentrations (0.3 μg/L) are known to impair piscine immune function, the molecular mechanisms driving its toxicity remain elusive. Lycopene (LYC) is a potent bioactive compound that alleviates SMZ-induced toxicity by regulating the endoplasmic reticulum (ER) stress autophagy axis. This experiment chooses 120 grass carps, divided into 4 groups: control group (CON), SMZ exposure group (0.3 μg/L), the LYC supplement group (10 mg/kg) and SMZ + LYC combined treatment group. The toxicity of SMZ (0.3 μg/L) to grass carp and the mitigation effect of LYC (10 mg/kg) to SMZ were studied through a 30-day experiment. Histopathological alterations were evaluated via hematoxylin-eosin (H&E) staining, ultrastructural changes were visualized by transmission electron microscopy (TEM), and key biomarkers of ER stress, autophagy, and AKT/AMPK signaling were quantified through qRT-PCR and Western blotting. Results demonstrated that SMZ exposure induced disorganization of white pulp, cellular vacuolation, and activation of melanomacrophage centers (MMCs), accompanied by significant upregulation of ER stress markers (IRE1, PERK, ATF6, GRP78, eif2α) and autophagy-related genes (LC3, P62, Beclin1, ATG5). TEM revealed nuclear pyknosis, mitochondrial swelling, and increased autophagosomes in SMZ-treated splenocytes. LYC intervention markedly attenuated these pathological injuries and suppressed ER stress and excessive autophagy by modulating the AKT/AMPK pathway. Molecular docking analysis confirmed binding affinity between LYC and AKT/AMPK proteins, with a binding energy of −8.8 kcal/mol. Our findings establish a mechanistic foundation for developing LYC-enriched functional feeds to counteract antibiotic-associated ecological risks in sustainable aquaculture.