Influence Of Dietary α-lipoic Acid(LA) On The Lipid Metabolism,Protein Metabolism And Antioxidant Ability In Grass Carp,Ctenopharyngodon Idellus

In present study,we use grass carp to evalue the application effect of lipoic acid in aquatic diet.The experiments in vivo and in vitro were carried out to evaluate the effects of lipoic acid on the grass carp in present study.The results will further indicate the role of lipoic acid in freshwater fish and provide theoretical basis for the regulation of antioxidant stress and lipid accumulation in cultured fish,which has great theoretical and practical significance.Trial 1 Effects of lipoic acid on the lipolysis and protein synthesis of juvenile grass carp(Ctenopharyngodon idellus).It has been reported that α-lipoic acid could promote antioxidant defenses,but the underlying mechanism of lipid metabolic regulation of α-lipoic acid is unknown in fish.Grass carp(initial body weight: 18.99 ± 1.82 g)were fed 0,600 or 1200 mg α-lipoic acid /kg diet for 56 d.The hepatocytes were exposed with 250 μM palmitic acid(PA)for 24 h,and then were treated with α-lipoic acid for 24 h at the presence or absence of 20 μM Compound C,the inhibitor of phosphorylation of AMPK.Triglyceride(TG)concentrations,mRNA and protein expression of genes involved in lipolysis and protein synthesis were measured.The crude lipid content of whole body,liver and muscle showed a significant decrease in fish fed the diet with α-lipoic acid in vivo(P<0.05).Further,α-lipoic acid activated phosphorylation of AMPK and notably increase protein content of adipose triglyceride lipase(ATGL)in intraperitoneal fat,liver and muscle in vivo.Meanwhile,α-lipoic acid significantly up-regulated mRNA expression of genes involved in lipolysis and fatty acid β-oxidation in intraperitoneal fat,liver and muscle in vivo(P<0.05),including adipose triglyceride lipase(ATGL),hormone-sensitive lipase(HSL),forkhead box o1(Foxo1),peroxisome proliferator activated receptor α(PPARα)and carnitine palmitoyltransferase-1(CPT-1α).The compound C markedly prevented the ability of α-lipoic acid to promote lipolysis in hepatocyte in vitro.Interestingly,the crude protein content of whole body and muscle,protein efficiency ratio and protein productive value had a significant increase in fish fed the diet with α-lipoic acid compared to control group in vivo(P<0.05).Furthermore,α-lipoic acid significantly elevated the phosphorylation level of mTOR,AKT,S6 K and 4EBP in muscle of experimental fish,and α-lipoic acid significantly up-regulated gene expression of mTOR and decreased GLDH mRNA level(P<0.05).Taken together,α-lipoic acid promoted lipolysis via activating phosphorylation of AMPK to increase the expression of ATGL,and promoted fatty acid β-oxidation by regulating PPARα and CPT-1α to increase energy supply from lipid catabolism and economize on the protein from energy production to increase protein deposition.Besides,α-lipoic acid might promote protein synthesis via regulating mTOR pathway directly.Trial 2 a-lipoic acid ameliorates n-3 long chain poly-unsaturated fatty acids induced lipid peroxidation via regulating antioxidant defenses in grass carp(Ctenopharyngodon idellus).This study evaluated the protective effect of α-lipoic acid(LA)on n-3 long chain poly unsaturated fatty acids(LC-PUFAs)-induced lipid peroxidation in grass carp.The result indicated that diets with n-3 LC-PUFAs increased the production of malondialdehyde(MDA)(P<0.05),thereby inducing lipid peroxidation in liver and muscle of grass carp.Meanwhile,compared with control group,the hepatosomatic index(HSI)and kidney index(KI)of grass carp were markedly increased in n-3 LC-PUFAs-only group.However,diets with LA remarkably inhibited the n-3 HUFAs-induced increase of HSI,KI,and MDA level in serum,liver and muscle(P<0.05).Interestingly,LA also significantly elevated the ratio of total n-3 LC-PUFAs in fatty acid composition of muscle and liver(P<0.05).Furthermore,LA significantly promoted the activity of antioxidant enzymes in serum,muscle and liver of grass carp(P<0.05),including superoxide dismutase(SOD),catalase(CAT),and glutathione s-transferase(GST).The further results showed that LA significantly elevated mRNA expression of antioxidant enzymes with promoting the mRNA expression of NF-E2-related nuclear factor 2(Nrf2)and decreasing Kelch-like-ECH-associated protein 1(Keap1)mRNA level.From the above,these results suggested that LA could attenuate n-3 LC-PUFAs-induced lipid peroxidation,remit the toxicity of the lipid peroxidant,and protect n-3 LC-PUFAs against lipid peroxidation to promote its deposition in fish,likely strengthening the activity of antioxidant enzymes through regulating mRNA expressions of antioxidant enzyme genes via mediating Nrf2-Keap1 signaling pathways.Overall,dα-lipoic acid promoted lipolysis via activating phosphorylation of AMPKATGL pathway,and promoted fatty acid β-oxidation by regulating PPARα-CPT1α pathway to increase energy supply from lipid catabolism and economize on the protein from energy production to increase protein deposition.Besides,α-lipoic acid might promote protein synthesis via regulating mTOR pathway directly.On the other hand,LA could attenuate n-3 LC-PUFAs-induced lipid peroxidation,remit the toxicity of the lipid peroxidant,and protect n-3 LC-PUFAs against lipid peroxidation to promote its deposition in fish,likely strengthening the activity of antioxidant enzymes through regulating mRNA expressions of antioxidant enzyme genes via mediating Nrf2-Keap1 signaling pathways.