TMAO Supplementation to High-Carbohydrate Diet Reprogrammed Hepatic Metabolism and Intestinal Microbiota to Improve Liver Health and Disease Resistance of Micropterus salmoides

This study aimed to evaluate the effects of trimethylamine oxide (TMAO) supplementation (0.5% and 1%) to a high-carbohydrate diet on the growth performance, liver health, hepatic metabolome, intestinal microbiota and disease resistance of largemouth bass (<i>Micropterus salmoides</i>). After an eight-week feeding trial with three replicates, fish fed with TMAO-supplemented diets showed growth-promoting potential with increased difference with a prolonged rearing period. Importantly, TMAO supplementation significantly improved liver structure and function, with reduced intrahepatic glycogen accumulation due to reprogrammed glycogen metabolism, including down-regulated <i>gys2</i> and <i>ugp2b</i> but up-regulated <i>pygl</i> expression levels. Targeted liver metabolomics analysis indicated the enhanced synthesis of long-chain fatty acid and amino acid in the 1% TMAO group, accompanied by decreased cortisol, indicating the attenuation of the stress response. Furthermore, TMAO supplementation changed the structure of the intestinal microbiota and particularly the intestinal content of <i>Romboutsia</i>, an important probiotic that can effectively utilize different kinds of dietary carbohydrate, showed an increasing trend with the increased TMAO supplementation levels. Finally, after sampling, all remaining fish were challenged with <i>Nocardia seriolae</i>. TMAO supplementation significantly enhanced the immune clearance function of largemouth bass against invading <i>N. seriolae</i>, with alleviated granulomatous nodules within liver but enhanced hepatic expression levels of <i>nlrp3</i>, <i>caspase1</i>, <i>il-1β</i> and <i>il-18</i>. These results collectively underscore the finding that TMAO may promote intestinal <i>Romboutsia</i> growth and reprogram hepatic metabolism to improve liver health, giving TMAO potential as a feed additive for growth and health promotion in largemouth bass.