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

## TL;DR

Adding TMAO to a high-carb diet in largemouth bass improves liver health, metabolism, and disease resistance through changes in gut bacteria and liver function.

## Contribution

TMAO supplementation is shown to reprogram hepatic metabolism and enhance intestinal microbiota for improved fish health.

## Key findings

- TMAO reduced glycogen accumulation in the liver by altering gene expression related to glycogen metabolism.
- TMAO increased synthesis of long-chain fatty acids and amino acids while decreasing stress-related cortisol levels.
- TMAO enhanced disease resistance against Nocardia seriolae by boosting immune gene expression and reducing liver damage.

## Abstract

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 (Micropterus salmoides). 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 gys2 and ugp2b but up-regulated pygl 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 Romboutsia, 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 Nocardia seriolae. TMAO supplementation significantly enhanced the immune clearance function of largemouth bass against invading N. seriolae, with alleviated granulomatous nodules within liver but enhanced hepatic expression levels of nlrp3, caspase1, il-1β and il-18. These results collectively underscore the finding that TMAO may promote intestinal Romboutsia growth and reprogram hepatic metabolism to improve liver health, giving TMAO potential as a feed additive for growth and health promotion in largemouth bass.