The Effects Resveratrol And Nicotinamide On Growth And Glycolipid Metabolism Of Blunt Snout Bream Megalobrama Amblycephala Fed High-carbohydrate Diets

Carbohydrates are generally deemed as the most economical energy source in feed,because of their relatively low cost and protein-sparing and lipid effect.The inclusion of high levels of carbohydrates is favored by the aquaculture industry,as could usually result in a decrease in feed cost.However,unlike the case of most mammals,fish generally have a limited ability to use glucose for energy purposes.High-carbohydrate diets usually result in metabolic disorders of fish,as inevitably leads to nutritional and metabolic diseases.In view of this,finding an effective approach to improve the carbohydrate utilization by fish is of great significance.Both resveratrol(RSV/R)and nicotinamide(N)have been proven to play an important role in regulating the I and II diabetes mellitus of mammals.However,relevant information in fish has been quite limited until now.Bearing this in mind,using Megalobrama amblycephala as the target animal,this study evaluated the effects of resveratrol and nicotinamide on the growth and glycolipid metabolism of blunt snout bream fed high-carbohydrate diets in order to improve the carbohydrate utilization by fish.It will facilitate our understanding of the carbohydrate metabolism of fish,as would also benefit the development and application of high-carbohydrate feeds in the aquaculture industry.This study mainly includes two parts presented as follows:Experiment 1 Effects of resveratrol on the growth,energy sensing and glycolipid metabolism of blunt snout bream Megalobrama amblycephala fed high-carbohydrate diets.This study investigated the effects of resveratrol on the growth,energy sensing,glycolipid metabolism and glucose and insulin load of blunt snout bream Megalobrama amblycephala fed high-carbohydrate diets.Fish(39.44±0.06 g)were randomly fed three diets:a control diet(30%carbohydrate),a high-carbohydrate diet(HC,41%carbohydrate),and the HC diet supplemented with 0.04%resveratrol(HCR)for 12 weeks.Fish fed the HC diet had significantly high values of nitrogen and energy retention efficiency,hepatosomatic index,intraperitoneal fat ratio,whole-body lipid content and intraperitoneal fat glycogen and lipid contents compared to the control group,but showed little difference with the HCR treatment.Liver and muscle lipid contents and plasma levels of glucose,glycated serum protein,advanced glycation end products and total cholesterol of fish fed the HC diet were significantly higher than those of the control group,whereas the opposite was found with resveratrol supplementation.Fish fed the HC diet obtained significantly low values of plasma insulin levels and hepatic adenosine monophosphate(AMP)contents and NAD+/NADH ratio compared to HCR treatment,but showed little difference with the control group.The opposite was found for hepatic adenosine triphosphate(ATP)contents and the ATP/AMP ratio.In addition,fish fed the HC diet showed significantly high transcriptions of glucose transporter 2(GLUT2),glucose-6-phosphate dehydrogenase,glycogen synthase,fatty acid synthetase(FAS),acetyl-CoA carboxylase a(ACCα),peroxisome proliferator-activated receptor y(PPARy)and PPARa compared to the control group,whereas the opposite was found for protein levels of AMP-activated protein kinase a(t-AMPK2),phosphorylated AMP-activated protein kinase a(p-AMPKα),sirtuin-1(SIRT1),and p-AMPKα/t-AMPKα ratio as well as the transcriptions of AMPKal,AMPKα2,SIRT1,PPARγ coactivator-1a(PGC-1α),phosphoenolpyruvate carboxykinase,fructose-1,6-bisphosphatase(FBPase),glucose-6-phosphatase,carnitine palmitoyl transferase I(CPTI)and acyl-CoA oxidase.Resveratrol supplementation significantly up-regulated the protein levels of t-AMPK,p-AMPK,and SIRT1,p-AMPK/t-AMPK ratio as well as the transcriptions of AMPKal,AMPKa2,SIRT1,PGC-1α,GLUT2,FBPase,and CPTI compared to HC group,while the opposite was found for sterol regulatory element-binding protein-1,FAS and ACCα.Furthermore,resveratrol improved glucose and insulin tolerance of fish fed the HC diet after glucose and insulin load.Overall,these findings indicated that resveratrol benefited the glycolipid metabolism of Megalobrama amblycephala by activating the AMPKα/SIRT1/PGC1α network,the up-regulation of the genes related to glucose transportation,glycogenesis and fatty acid β-oxidation coupled with the depression of lipogenesis.Experiment 2 Effects of nicotinamide on the growth and glycolipid metabolism of blunt snout bream Megalobrama amblycephala fed different carbohydrate levels.A 12-week feeding trial was conducted to evaluate the effects of nicotinamide on growth,glycolipid metabolism and glucose tolerance and insulin levels of blunt snout bream fed different carbohydrate levels.Four isonitrogenous and isolipidic diets were formulated,including two dietary carbohydrate levels(30 and 43%)and two nicotinamide levels(0 and 31.0 mg/kg).High carbohydrate levels significantly(P<0.05)increased HSI,IPF,whole-body lipid content,tissue glycogen and lipid contents,plasma levels of glucose,GSP,AGES,insulin,triglyceride,pyruvate and lactic acid,hepatic the transcriptions of uncoupling protein 2(UCP2),PPARy,PPARα,GLUT2,glucokinase(GK),pyruvate kinase(PK),GS,glucose-6-phosphate dehydrogenase(G6PDH),SREBP1,FAS,ACCα,whereas the opposite was true for NAD+,NADH,SIRT1,PGC1-α,forkhead transcription factor 1(FOXO1),PEPCK,FBPase,CPTI and ACO.In addition,nicotinamide supplementation remarkably(P<0.05)increased whole-body lipid and tissue glycogen contents,plasma insulin level,hepatic NAD+content and NAD+/NADH ratio,SIRT1 protein level and the transcriptions of PGC1-α,FOXO1,PPARα,GLUT2,GK,PK,GS and CPTI,while the opposite was true for the remaining indicators.Furthermore,an significant(P<0.001)interaction between dietary carbohydrate levels and nicotinamide were also observed in IPF,liver glycogen and muscle and intraperitoneal fat lipid contents,hepatic NAD+/NADH ratio,plasma metabolites,the protein level of SIRT1 and the transcriptions of SIRT1,PGC1-α,UCP2,PPARγ,PPARα,GLUT2,GK,PEPCK,G6PDH,FAS,ACCα,CPT I and ACO.Furthermore,nicotinamide improved the glucose tolerance and increased insulin secretion of fish fed high-carbohydrate diets after glucose loading.Overall,present findings showed that nicotinamide should be benefits the intermediary metabolism of Megalobrama amblycephala fed high-carbohydrate diets via the mediation of sirtuinl and the enhancement of glycolysis,glycogenesis and fatty acid oxidation coupled with the suppression of gluconeogenesis and lipogenesis.