Effect Of ?-lipoic Acid Supplementation In High Lipid Level Diets On Nutritional Metabolism,Growth And Food Intake In Two Species Of Cyprinidae Fish

Lipid is one of the most important energy sources in diet and body components for fish.Higher lipid level diets can cause excessive lipid accumulation while promoting the growth of farmed fish.?-lipoic acid is a carboxylic acid which contains eight carbon,and has many functions such as enhancing animal immunity,antioxidant properties and reducing lipid accumulation.The research of?-lipoic acid in fish was mainly concerned with its antioxidant function.Only a few studies have indicated that?-lipoic acid can reduce lipid accumulation and increase protein deposition in grass carp,but the effect of?-lipoic acid on nutrient metabolism in fish was still unknown.In this study,the zebrafish was used to explore the systemic effect of?-lipoic acid supplementation in high lipid level diets on nutrition metabolism in fish,and designed vitro experiments to further explore the effect of?-lipoic acid on lipid metabolism of grass carp adipocyte.Finally,?-lipoic acid was applied to the grass carp diet and evaluated the effect of?-lipoic acid on growth,food intake and proximate composition in grass carp.The results of these trials expect to provide some reference for health aquaculture and new functional feed development.Major results and conclusions were presented as follows:1.Dietary?-lipoic acid supplementation can promote zebrafish nutrient metabolism in normal lipid level.High lipid diets supplementation?-lipoic acid decreased lipid content which caused by high lipid level diets,and inhibited protein catabolism to increase protein content.This trial included two states,540 male zebrafish?0.17 g?were randomly divided into two groups,6 tanks per group,fed with normal?CT,lipid level 5%?and high lipid?HL,lipid level 10%?diets for 6 weeks as the first stage,then9 fish per tank were sampled.Then each group were randomly chosen 3 tanks trail fish to fed with 1000 mg kg^-1?-lipoic acid supplementation diets for another 6 weeks as the second stage.The Results demonstrated that?-lipoic acid increased whole fish protein content,and decreased the expression of protein catabolism-related genes in muscle of high lipid level groups?P<0.05?.Furthermore,high lipid level diets increased the whole fish lipid content and the expression of gluconeogenesis and lipogenesis-related genes?P<0.05?,and?-lipoic acid counteracted these effects,decreased the whole fish triglycerides and cholesterol contents and expression of lipogenesis-related genes,with the enhanced expression of lipolytic genes,especially in high lipid groups?P<0.05?.High lipid level diets supplementation?-lipoic acid increased hepatocyte mitochondrial quantity and the mRNA expression of mitochondrial biogenesis and electron transport chain-related genes?P<0.05?.2.?-lipoic acid can promote lipid catabolism and decrease triglyceride content in grass carp adipocyte.In the experiment,the mature adipocyte in grass carp were cultured in0,50 and 200?M?-lipoic acid supplementation medium for 6h,and the lipid metabolism related indicators were detected.The results showed that 200?M?-lipoic acid treatment significantly decreased TG content in adipocyte of grass carp and increased the release of glycerol and NEFA content?P<0.05?.The mRNA expression of lipid catabolism related genes?HSL,PPAR?,CPT1 and CD36?in 200?M?-lipoic acid adipocyte group were significantly higher than that in control group.3.?-lipoic acid supplementation indifferent lipid level diets can reduce lipid accumulation in grass carp,while reducing food intake by regulating peripheral appetite factors,thereby reduced growth performance.In the experiment,1200 mg kg^-1?-lipoic acid was supplemented in 4%and 8%lipid level diets and fed juvenile grass carp?16.28±0.85 g?for 8 weeks,then detected growth performance,food intake,proximate composition and peripheral appetite factors gene expression.The final body weight,weight gain rate,and food intake were significantly decreased by dietary?-lipoic acid supplementation,and the food intake was reduced by high lipid level?P<0.05?.Dietary high lipid level resulted in a increase of intraperitoneal fat index and whole body lipid content.The hepatopancreas lipid content in HL+LA group was significantly lower than that in HL group?P<0.05?.The further study indicated that 1200 mg kg^-1?-lipoic acid significantly increased mRNA expression of CCK and PYY of intestine,also decreased ghrelin gene expression in CT+LA group?P<0.05?.The leptin and LEPR gene expression of intraperitoneal fat and liver showed a tendency of increase in CT+LA group,while they were significantly decreased in the liver of HL+LA group?P<0.05?.The leptin and LEPR gene expression of intraperitoneal fat and liver were significantly increased by dietary high lipid level?P<0.05?.Overall,high lipid diet?-lipoic acid supplementation can reduce body lipid content in fish by promoting lipid catabolism and enhancing mitochondrial oxidation function,and promote protein deposition.Furthermore,a certain level?-lipoic acid supplementaton in diets inhibited food intake and growth performance by regulating peripheral appetite factors.The present study considered that high lipid level diets supplementation?-lipoic acid can reduce lipid accumulation in fish,and suggested that?-lipoic acid may reduce food intake by regulating appetite factors.