Metformin improves insulin resistance, liver healthy and abnormal hepatic glucolipid metabolism via IR/PI3K/AKT pathway in Ctenopharyngodon idella fed a high-carbohydrate diet

The effects and underlying mechanisms of metformin which can improve glucose homeostasis of fish have rarely been explored. This experiment aimed to explore the influence of metformin on growth performance, body composition, liver health, hepatic glucolipid metabolic capacity and IR/PI₃K/AKT pathway in grass carp (Ctenopharyngodon idella) fed high-carbohydrate diets. A normal diet (Control) and high carbohydrate diets with metformin supplementation (0.00 %, 0.20 %, 0.40 %, 0.60 % and 0.80 %) were configured. Six groups of healthy fish were fed with the experimental diet for eight weeks. The results showed that the growth performance of grass carp was impaired in high carbohydrate diet. Impairment of IR/PI₃K/AKT signalling pathway reduced insulin sensitivity, while hepatic oxidative stress damage and decreased immunity affected liver metabolic function. The glycolysis and lipolysis decrease while the gluconeogenesis and fat synthesis increase, which triggers hyperglycaemia and lipid deposition in the body. Metformin supplementation restored the growth performance of grass carp. Metformin improved IR/PI₃K/AKT pathway signalling and alleviated insulin resistance, while liver antioxidant capacity and immunity were enhanced resulting in the restoration of liver health. The elevation of glycolysis and lipolysis maintains glycaemic homeostasis and reduces lipid deposition, respectively. These results suggest that metformin supplementation restores liver health and activates the IR/PI₃K/AKT signalling pathway, ameliorating insulin resistance and glucose-lipid metabolism disorders caused by a high-carbohydrate diet. As judged by HOMA-IR, the optimum supplementation level of metformin in grass carp (C. idella) fed a high-carbohydrate diet is 0.67 %.