Tryptophan Metabolism: A New Look at the Role of Tryptophan Derivatives in the Human Body

In modern scientific literature, close attention is paid to the biological role of tryptophan catabolites both in normal conditions and in various pathologies. There are more and more reports that tryptophan metabolism catabolites play a signaling role in the human body and in the intestinal microbial community. Receptors and signaling pathways in the human body, the so-called tryptophan signaling molecules (TrpSM), their cellular targets, and their physiological and metabolic effects are being actively studied. It has now been established that almost all catabolites of tryptophan metabolism are signaling molecules. Many of them realize their signaling role through arylhydrocarbon receptors (АhR). The dominant pathway of tryptophan metabolism for the human body is the kynurenine pathway, which is the source of universal the signaling molecules—kynurenine, quinolinic and kynurenic acids. The indole pathway of tryptophan catabolism, the main pathway for the microbiota, with the exception of indole formation reactions in immunocompetent cells, is a source of interregional and interspecies signaling molecules—indole and its derivatives: indole-3-pyruvate, indole-3-lactate, indole-3-acetate, indole-3-propionate, indole-3-acrylate, indole-3-butyrate and indole-3-acetaldehyde. Serotonin and melatonin are also universal signaling molecules and have been widely studied in various diseases of the nervous system.