Dietary supplementation with succinic acid improves growth performance and flesh quality of adult Nile tilapia (Oreochromis niloticus) fed a high-carbohydrate diet.

To evaluate the effects of dietary supplementation with succinic acid on growth performance, flesh quality, glucose, and lipid metabolism of Nile tilapia (Oreochromis niloticus) fed a high-carbohydrate diet (HCD), five iso-nitrogenous and iso-lipidic diets were prepared as follows: HCD (control group) consisting of 55% corn starch and HCD supplemented with 0.5%, 1.0%, 2.0%, and 4.0% succinic acid, respectively. Tilapia with an initial body weight of 204.90 ± 1.23 g randomly assigned to 15 tanks with 3 replicates per group and 10 fish per tank fed for 8 weeks. Increasing dietary succinic acid supplementation resulted in significant second-order polynomial relationship in the weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency rate (PER), viscerosomatic index, condition factor, and contents of muscular crude lipid and glycogen (P < 0.05). The hepatosomatic index, mesenteric fat index, liver glycogen content and crude lipid contents of the whole-body and liver demonstrated significantly linear and second-order polynomial relationship (P < 0.05). Quadratic curve model analysis based on WGR, SGR, PER, and FCR demonstrated that optimal supplementation with succinic acid in the HCD of Nile tilapia ranged from 1.83% to 2.43%. Fish fed with 1.0% succinic acid had higher muscular hardness, increased the contents of alkali-soluble hydroxyproline in collagen, docosahexaenoic acid (DHA) and n-3 polyunsaturated fatty acid (n-3PUFA) in muscle, and lower total fatty acid content in muscle (P < 0.05) compared with the control group. Compared to the control group, dietary supplementation with 1.0% succinic acid significantly increased the contents of total bounding amino acid (arginine, histidine, isoleucine, lysine, methionine, alanine, proline), total flavor amino acid (free aspartic acid), the catalase (CAT) activity and total antioxidant capacity, and the mRNA relative expression levels of CAT, superoxide dismutase (SOD), and nuclearfactor erythroidderived 2-like 2 (Nrf2) in muscle (P < 0.05). Furthermore, succinic acid supplementation significantly up-regulated mRNA relative expression levels of glycolysis genes (hexokinase 2 [HK2], phosphofructokinase, muscle-A [PFKMA], and phosphofructokinase, muscle-B [PFKMB]), a key glycogen synthesis gene (glycogen synthase [GYS]), and lipid catabolism genes (carnitine palmitoyltransferase-1B [CPT1B], hormone sensitive lipase [HSL], and lipoprotein lipase [LPL]), while down-regulating the mRNA relative expression level of fatty acid synthase (FASN) in muscle (P < 0.05). In conclusion, dietary supplementation with 1.83% to 2.43% succinic acid improved muscle quality by increasing muscle antioxidant capacity and hardness, changing muscle amino acid and fatty acid composition, and regulating muscle glucose and lipid metabolism.

Molecular cloning and gene expression of acc2 from grass carp (Ctenopharyngodon idella) and the regulation of glucose metabolism by ACCs inhibitor.

BACKGROUND: Acetyl-CoA carboxylase (ACC) catalyzes the carboxylation of acetyl-CoA to malonyl-CoA. Malonyl-CoA, which plays a key role in regulating glucose and lipid metabolism, is not only a substrate for fatty acid synthesis but also an inhibitor of the oxidation pathway. ACC exists as two isoenzymes that are encoded by two different genes. ACC1 in grass carp (Ctenopharyngodon idellus) has been cloned and sequenced. However, studies on the cloning, tissue distribution, and function of ACC2 in grass carp were still rare. METHODS AND RESULTS: The full-length cDNA of acc2 was 8537 bp with a 7146 bp open reading frame encoding 2381 amino acids. ACC2 had a calculated molecular weight of 268.209 kDa and an isoelectric point of 5.85. ACC2 of the grass carp shared the closest relationship with that of the common carp (Sinocyclocheilus grahami). The expressions of acc1 and acc2 mRNA were detected in all examined tissues.  The expression level of acc1 was high in the brain and fat but absent in the midgut and hindgut. The expression level of acc2 in the kidney was significantly higher than in other tissues, followed by the heart, brain, muscle, and spleen. ACCs inhibitor significantly reduced the levels of glucose, malonyl-CoA, and triglyceride in hepatocytes. CONCLUSIONS: This study showed that the function of ACC2 was evolutionarily conserved from fish to mammals. ACCs inhibitor inhibited the biological activity of ACCs, and reduced fat accumulation in grass carp.