Metabolites, gene expression, and gut microbiota profiles suggest the putative mechanisms via which dietary creatine increases the serum taurine and g-ABA contents in Megalobrama amblycephala.

A 90-day experiment was conducted to explore the effects of creatine on growth performance, liver health status, metabolites, and gut microbiota in Megalobrama amblycephala. There were 6 treatments as follows: control (CD, 29.41% carbohydrates), high carbohydrate (HCD, 38.14% carbohydrates), betaine (BET, 1.2% betaine + 39.76% carbohydrates), creatine 1 (CRE1, 0.5% creatine + 1.2% betaine + 39.29% carbohydrates), creatine 2 (CRE2, 1% creatine + 1.2% betaine + 39.50% carbohydrates), and creatine 3 (CRE3, 2% creatine + 1.2% betaine + 39.44% carbohydrates). The results showed that supplementing creatine and betaine together reduced the feed conversion ratio significantly (P < 0.05, compared to CD and HCD) and improved liver health (compared to HCD). Compared with the BET group, dietary creatine significantly increased the abundances of Firmicutes, Bacteroidota, ZOR0006, and Bacteroides and decreased the abundances of Proteobacteria, Fusobacteriota, Vibrio, Crenobacter, and Shewanella in the CRE1 group. Dietary creatine increased the content of taurine, arginine, ornithine, γ-aminobutyric acid (g-ABA), and creatine (CRE1 vs. BET group) and the expression of creatine kinase (ck), sulfinoalanine decarboxylase (csad), guanidinoacetate N-methyltransferase (gamt), glycine amidinotransferase (gatm), agmatinase (agmat), diamine oxidase1 (aoc1), and glutamate decarboxylase (gad) in the CRE1 group. Overall, these results suggested that dietary supplementation of creatine (0.5-2%) did not affect the growth performance, but it altered the gut microbial composition at the phylum and genus levels, which might be beneficial to the gut health of M. amblycephala; dietary creatine also increased the serum content of taurine by enhancing the expressions of ck and csad and increased the serum content of g-ABA by enhancing the arginine content and the expressions of gatm, agmat, gad, and aoc1.

Dietary betaine and/or TMAO affect hepatic lipid accumulation and glycometabolism of Megalobrama amblycephala exposed to a high-carbohydrate diet.

A 12-week experiment was conducted to explore the effects of betaine and/or TMAO on growth, hepatic health, gut microbiota, and serum metabolites in Megalobrama amblycephala fed with high-carbohydrate diets. 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 the hepatosomatic index (HSI); whole-body crude fat; hepatic lipid accumulation; messenger RNA expression levels of gk, fpbase, g6pase, ahas, and bcat; serum branched-chain amino acids (BCAAs); ratio of Firmicutes-to-Bacteroidetes; and abundance of the genus Aeromonas were all significantly increased, 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; expression levels of fbpase, g6pase, pepck, ahas, and bcat; circulating BCAA; ratio of Firmicutes-to-Bacteroidetes; and abundance levels of the genus Aeromonas and phyla Tenericutes and Bacteroidetes were significantly downregulated in the HBD, HTD, and HBT groups. Meanwhile, the expression levels of pk 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 them, the combination of betaine and TMAO had the best effect.