Tissue-specific metabolic responses of Cyprinus flammans to copper

Copper (Cu) contamination is serious in China, with ≤2.76 mg/L in some waters. Exposure to Cu causes a high toxicity to the aquatic organisms and subsequent ecological risk. To understand fish responses to Cu exposure, we analyzed the metabonomic changes in multiple tissues (gill, liver, and muscle) of Cyprinus flammans using an nuclear magnetic resonance-based metabonomic technique. Our results showed that metabolic alterations are dose-dependent. No significant metabolic alterations in three tissues of fish are caused by 0.25 mg/L Cu. However, 1.53 mg/L Cu caused changes of energy-related metabolites and amino acids, which we suggest are due to enhanced metabolic acidosis in gill and muscle, decreased tricarboxylic acid cycle activity in muscle, increased gluconeogenesis from amino acids in liver, and improved glycogenesis in liver and muscle. The Cori cycle between liver and muscle is concurrently triggered. Furthermore, high concentration of Cu resulted in the alteration of choline metabolism such that we hypothesize that Cu induces membrane damage and detoxification of CuSO4 in gill as well as altered osmoregulation in all three tissues. Choline-O-sulfate in gill may be used as a biomarker to provide an early warning of Cu exposure in C. flammans. Moreover, Cu exposure caused alterations of nucleoside and nucleotide metabolism in both gill and muscle. These findings provide a new insight into the metabolic effects of Cu exposure on C. flammans and highlight the value of metabonomics in the study of metabolic metal disturbance in fish.