High-carbohydrate diet altered conversion of metabolites, and deteriorated health in juvenile largemouth bass

Abstract

To explore the effects of dietary carbohydrate level on nutrients metabolism, largemouth bass juveniles (initial weight, 4.0 ± 0.2 g) were fed three isonitrogenous and isoenergetic diets containing 9.66% (L), 14.32% (M) or 19.11% (H) carbohydrate for 8 weeks. The lowest weight gain (15.75 ± 0.76 g) was observed in group H. Feeding high carbohydrate diet (HCD) led to increased pyruvate (PA), lactic acid (LD), triglyceride (TG) and free fatty acids (NEFA) levels in plasma. Also, HCD enhanced vacuolation, glycogen granule and lipid accumulation in fish liver. Activities of hepatic glycolysis enzymes such as hexokinase, pyruvate kinase and lactate dehydrogenase did not significantly differ among treatments ( P > 0.05). HCD resulted in enhancement of hepatic phosphoenolpyruvate carboxykinase (PEPCK) and lipase (LPS) activities, and increased glycogen and triglyceride (TG) concentrations. Similarly, expression of glucose and lipid metabolism related genes such as glycogen phosphorylase (PYG) and carnitine palmitoyl transferases (CPT1, CPT2) were up-regulated with increasing carbohydrate level. Hepatic catalase (CAT) and glutathione peroxidase (GSH-PX) activities, and total antioxidant capacity (T-AOC) were decreased in HCD group. UPLC-MS metabolomics revealed that glucose metabolism, lipid metabolism, and antioxidant defense system were influenced by dietary carbohydrate level. HCD raised the accumulation of carbohydrate metabolites (phosphohydroxypyruvic acid), unsaturated fatty acids (19( R )-HETE, 9( S )-HPOT, alpha-Linolenic acid and oleic acid), cholesterol, and antioxidant functional substance (oxidized glutathione). Additionally, these differential metabolites were enriched in the metabolic pathways such as galactose metabolism, fructose and mannose metabolism, unsaturated fatty acid biosynthesis, primary bile acid biosynthesis, cholesterol-butyrate metabolism, glutathione metabolism, serine and threonine metabolism. Overall, our results revealed the details of metabolites conversion in juvenile largemouth bass fed HCD. • High-carbohydrate diet (HCD) led to the accumulation of glycogen, lipid droplets and occurrence of vacuolation in liver. • HCD induced antioxidant response through the glutathione antioxidant system. • HCD promoted the conversion of glucose to other carbohydrates, lipids and protein components.