Effects Of Adding Betaine Or/and TMAO In High-carbohydrate Diets On Hepatic Lipic Accumulation,Glycometabolism,and Amino Acid Metabolism In Megalobrama Amblycephala

Carbohydrates were widely used in commercial feeds based on the advantages such as low-cost,high-yield,and protein saving.However,compared to terrestrial animals,fishes were generally considered to have poor ability of utilizing carbohydrate and have low tolerance in glucose.Therefore,searching for new additives to improve the utilization ability of carbohydrates in fish has attracted increasing attention.Megalobrama amblycephala was a kind of herbivorous freshwater fish with fast growth rate and low farming cost,and was the seventh largest freshwater cultured fish in China.Thus,this study aimed to explore the effects of betaine or/and TMAO supplementations in high-carbohydrate diets on the growth performance,body composition,health of liver,gut microbe composition,and serum metabolite alteration in M.amblycephala.The research helped us to understand the underlying mechanism of glycolipid metabolism controlled by betaine and/or TMAO,which might provide a theoretical basis for the prevention and treatment of nutritional fatty liver disease and the search and application of feed additives with a high glucose tolerance.Simultaneously,this study helped us to find effective approaches to improve its carbohydrate utilization,and further promote the development of low-protein and high-energy feed for fish.And all of roles for the current study would contribute to the healthy and sustainable development of aquaculture industry.The main results were as follows:The healthy and uniformly sized juvenile M.amblycephala(450,average weight5.00±0.50 g)were selected and randomly divided into 5 groups,with 3 replicates per group.The fishes were randomly distributed in 15 plastic tanks with 300 L water capacity each tank(30 fishes per tank/replicate).After two weeks of domestication,a 90-day experiment was started.The diets were as follows: CD group(control diet,28.5%carbohydrate),HCD group(high-carbohydrate diet,38.2% carbohydrate),HBD group(betaine-added diet,38.3% carbohydrate + 1.2% betaine),HTD group(TMAO-added diet,38.2% carbohydrate + 0.2% TMAO),and HBT group(diet added with both betaine and TMAO,38.2% carbohydrate + 1.2% betaine + 0.2% TMAO).The results showed that compared to CD group,the hepatosomatic index(HSI),whole-body crude fat,hepatic lipid accumulation,m RNA expressions of glucokinase(gk),fructose-1,6-biphosphatase(fpbase),glucose-6-phosphatase(g6pase),acetohydroxy acid synthase(ahas),and branched-chain aminotransferase(bcat),serum branched-chain amino acids(BCAAs,including valine,isoleucine and leucine),ratio of Firmicutes-to-Bacteroidetes,and abundance of the genus Aeromonas were all significantly increased in HCD group,while the abundance levels of the genus Lactobacillus and phyla Tenericutes and Bacteroidetes were drastically decreased in the HCD group.Compared with the HCD group,the HSI,whole-body crude fat,hepatic lipid accumulation,relative expressions of fbpase,g6 pase,pepck,ahas,and bcat,circulating BCAA,ratio of Firmicutes-to-Bacteroidetes,and abundances of the genus Aeromonas were significantly downregulated in the HBD,HTD,and HBT groups.Meanwhile,the expressions of pk,the abundances of phyla Tenericutes and Bacteroidetes were drastically upregulated in the HBD,HTD,and HBT groups as well as the abundance of Lactobacillus in the HBT group.These results indicated that the supplementation of betaine and/or TMAO in high-carbohydrate diets could affect the hepatic lipid accumulation and glycometabolism of M.amblycephala by promoting glycolysis,inhibiting gluconeogenesis and biosynthesis of BCAA,and mitigating the negative alteration of gut microbiota.Among these groups,the combination of betaine and TMAO had the best effect.Compared with the CD group,the concentrations of Glutamate and Asparagine was increased significantly in the HCD group;and the m RNA expressions of glutamate dehydrogenase(gudb),asparagine synthetase(asna)and aspartate aminotransferase(got1)were also increased significantly.The concentrations of Glutamate and Asparagine in the HCD group were significantly lower than those of the HBD,HTD,and HBT groups,and the expressions of gudb,asna and got1 in the HCD group were significantly lower than those in the HBD,HTD,and HBT groups.The results of the current experiments demonstrated that the supplementation of betaine and/or TMAO in high-carbohydrate diets could significantly lower the gene expressions of Glutamate dehydrogenase,Asparagine synthetase and Aspartate aminotransferase in liver,simultaneously,could drastically reduce the serum contents of Glutamate and Asparagine to maintain the stability of amino acid metabolism and TCA cycle,which could promote a normal metabolism of the body.