Tryptophan metabolism in inter-organ communication and its potential applications for disease prevention and control

<p>Tryptophan (Trp) is an indispensable amino acid which, in addition to being incorporated into proteins, is involved in energy metabolism and gives rise to metabolites with pivotal functions in modulating a variety of physiological processes in mammals. These metabolites are generated in the body through two major metabolic pathways, namely the kynurenine and the 5-hydroxytryptamine pathways. Within the intestinal microbiota, Trp is a precursor for the synthesis of indole and indole-related compounds that have been shown to be active on several host’s tissues and organs. Increasing experimental and clinical studies demonstrated the versatile functions of Trp metabolites in various aspects of physiological and pathophysiological processes involved in energy and nutrient metabolism, as well as organ development and inter-organ communication through both peripheral and local regulatory networks. Recent research highlights the importance of such inter-organ communication in the maintenance of the host health. In this context, this review comprehensively summarizes the function of Trp metabolites and their physiological implications in communication between different organs and tissues, and between the intestinal microbiota and the lodging host’s cells. The metabolic connection between the intestine and other organs such as brain, liver, lung, kidney, and muscle are presented. The potential therapeutic applications of the regulation of Trp metabolism in different pathophysiological situations are discussed.</p>