Utilization of raw and gelatinized starch by blunt snout bream Megalobrama amblycephala as evidenced by the glycolipid metabolism, glucose tolerance and mitochondrial function

Abstract

This study aimed to evaluate the influences of dietary raw and gelatinized wheat starch and their ratios on the glycolipid metabolism, glucose tolerance and mitochondrial function of blunt snout bream Megalobrama amblycephala. Three diets incorporating 100% raw starch (R100), 100% gelatinized starch (G100) and 75% raw starch +25% gelatinized starch (R75/G25) were randomly assigned to 15 cages of fish for 10 weeks, after which fish were sampled. Then the remaining fish within each treatment were combined and later split into 6 tanks for a time series sampling in a glucose tolerance test. Daily gain index, relative feed intake and plasma levels of glucose, triglyceride, pyruvate and lactate all showed little difference among all the treatments. The R75/G25 group obtained the highest feed efficiency and tissue (namely liver and the abdominal fat tissue) glycogen contents. However, the highest tissue (namely muscle, liver and the abdominal fat tissue) lipid contents and plasma total cholesterol levels were both observed in the G100 group. In addition, the G100 group obtained significantly higher transcriptions of glucose transporter 2, glucokinase, peroxisome proliferator activated receptor γ and acetyl-CoA carboxylase α, but relatively low transcripts of the genes involved in gluconeogenesis and fatty acid β-oxidation, compared with the R100 group. The R100 group showed the highest glucose clearance rate, while the area under the glucose curve showed no statistical difference. Furthermore, the R100 group had relatively low activities of mitochondrial complex I, II, III and V as well as the transcriptions of cytochrome c oxidase 2, cytochrome b and NADH dehydrogenase 1 and ATP synthase 6 compared with other groups. Overall, our results suggested that high dietary inclusions of gelatinized starch could enhance the glucose transportation, glycolysis, lipogenesis, lipid deposition, glucose tolerance and mitochondrial function of blunt snout bream, while depress the gluconeogenesis and fatty acid oxidation.