The effect of fecal microbiota transplantation on levels of tryptophan metabolites in intestine and serum of gnotobiotic mice.

Gut microbiota is one of the key suppliers of tryptophan metabolites, which perform various functions in the host organism, including their role as signaling molecules. Fecal microbiota transplantation (FMT) is widely used as a method for determining the contribution of microorganisms to the content of various metabolites in the holoorganism. In this regard, the aim of our study was to investigate the effect of FMT on the level of tryptophan metabolites in feces and blood in gnotobiotic mice. It was found that both before and after FMT, indole-3-lactate, and quinolinic acid were the dominant tryptophan metabolites in the intestine. FMT increased the content of both indoles (indole-3-acetate, indole-3-acrylate, indole-3-butyrate, indole-3-lactate) and kynurenines (anthranilic and xanthurenic acids) in the intestine. In serum of mice after FMT, indole metabolites (indole-3-butyrate, indole-3-carboxaldehyde, indole-3-lactate, indole-3-propionate) predominantly increased; however, tryptamine and xanthurenic acid also demonstrated a clear increase. The use of FMT demonstrates that the intestinal microbiota is a source of not only indole derivatives of tryptophan, but also metabolites of the kynurenine pathway.