Cardiac injury and purine metabolic remodeling in Carassius auratus under environmentally relevant carbonate alkalinity exposure.

With the intensification of global warming and human activities, inland freshwaters are increasingly salinized and alkalized, often with carbonate alkalinity predominating. Such conditions disrupt acid-base and ion homeostasis in freshwater fish and may induce systemic energy metabolic reprogramming. However, the effects of carbonate alkalinity stress on the heart, an organ with high energy demands, remain poorly understood. Therefore, Carassius auratus (C. auratus), which exhibits relatively high tolerance to carbonate alkalinity, was selected as the experimental species in the present study. The fish were exposed to 0, 20, or 40 mM NaHCO3, representing carbonate alkalinity levels reported in saline-alkaline lakes of the Songnen Plain. Carbonate alkalinity exposure caused cardiac injury, evidenced by increased TUNEL-positive signals and mitochondrial swelling, cristae disruption, and vacuolization. These changes were accompanied by reduced mitochondrial membrane potential (P < 0.0001) and ATP content, increased cardiac ammonia, and disrupted redox homeostasis. Reactive oxygen species increased by 1.08- and 1.65-fold in the 20 and 40 mM groups, respectively, whereas glutathione content and glutathione peroxidase and superoxide dismutase activities decreased. Untargeted metabolomics revealed marked remodeling of purine metabolism, glycolysis, oxidative phosphorylation, starch and sucrose metabolism, glycerophospholipid metabolism, and unsaturated fatty acid biosynthesis. Targeted assays further showed increased cardiac ADP, AMP, IMP, hypoxanthine, xanthine, and uric acid, together with decreased xanthine dehydrogenase activity and increased xanthine oxidase activity, indicating that altered terminal purine oxidation may contribute to cardiac oxidative stress. Collectively, carbonate alkalinity stress was associated with cardiac injury in C. auratus, potentially via increased cardiac ammonia burden, mitochondrial energy dysfunction, perturbed purine metabolism, and xanthine oxidase-related oxidative stress.