α-Ketoglutarate modulates the mechanisms of toxicity in crucian carp kidneys chronically exposed to NaHCO3: Metabolomics insights

Due to the unique physicochemical properties of saline-alkaline water, aquatic organisms find it challenging to survive under such conditions. This study established a freshwater control group (C), a 20 mmol/L NaHCO₃ exposure group (T), a 40 mmol/L NaHCO₃ exposure group (F), a 20 mmol/L NaHCO₃ exposure with α-ketoglutarate (AKG)-supplemented feed group (TA), and a 40 mmol/L NaHCO₃ exposure with AKG-supplemented feed group (FA). Histopathological analysis, biochemical assays, and UPLC-QTOF/MS metabolomics were employed to explore the potential mechanisms by which AKG alleviates oxidative damage in freshwater teleosts induced by saline-alkaline stress. Histopathological results showed that as the concentration of carbonate alkali exposure increased, the severity of kidney lesions in crucian carp (Carassius auratus) worsened. However, in the TA and FA groups, the damage showed varying degrees of repair, with the kidney tissue morphology in the TA group almost restored to the state of the C group. Under carbonate alkali exposure, compared to the C group, the activity of antioxidant enzymes Catalase and Superoxide dismutase in crucian carp kidneys decreased in a dose-dependent manner, but increased upon AKG supplementation. Conversely, the levels of Malondialdehyde, blood ammonia, Urea nitrogen, and Uric acid showed the opposite trend. Metabolomics analysis revealed that carbonate-alkali stress caused a series of metabolic disruptions in fish, including amino acid metabolism, lipid metabolism, and energy metabolism. AKG positively regulated metabolic pathways such as the pentose phosphate pathway, arachidonic acid metabolism, and amino acid metabolism, thereby enhancing the antioxidant, anti-inflammatory, and immune capabilities of fish under saline-alkaline stress, alleviating oxidative damage induced by the stress. Overall, our research indicates that saline-alkaline stress significantly alters kidney function and metabolic characteristics, disrupts the antioxidant system and energy homeostasis, inhibits protein catabolism, and induces kidney damage in crucian carp. Exogenous AKG supplementation effectively mitigates oxidative damage and metabolic disorders in crucian carp kidneys under carbonate-alkaline stress. This study elucidates the physiological mechanisms by which AKG alleviates kidney tissue damage under saline-alkaline stress at the metabolic level, providing scientific evidence for the development of aquaculture in saline-alkaline water.