Tryptophan metabolism, from nutrition to potential therapeutic applications

Abstract

Tryptophan is an indispensable amino acid that should to be supplied by dietary protein. Apart from its incorporation into body proteins, tryptophan is the precursor for serotonin, an important neuromediator, and for kynurenine, an intermediary metabolite of a complex metabolic pathway ending with niacin, CO(2), and kynurenic and xanthurenic acids. Tryptophan metabolism within different tissues is associated with numerous physiological functions. The liver regulates tryptophan homeostasis through degrading tryptophan in excess. Tryptophan degradation into kynurenine by immune cells plays a crucial role in the regulation of immune response during infections, inflammations and pregnancy. Serotonin is synthesized from tryptophan in the gut and also in the brain, where tryptophan availability is known to influence the sensitivity to mood disorders. In the present review, we discuss the major functions of tryptophan and its role in the regulation of growth, mood, behavior and immune responses with regard to the low availability of this amino acid and the competition between tissues and metabolic pathways for tryptophan utilization.

Effects of standardized ileal digestible tryptophan: lysine ratio on growth performance of nursery pigs12

“…The absorbed Trp is converted into 5-hydroxytryptophan, which is a metabolite that can cross the blood-brain barrier and work as a precursor for serotonin after being decarboxylated (Le Floc'h et al, 2011). As a result, the inclusion of different levels of Trp in pig diets has been shown to manipulate serotonin-mediated feed intake (Batterham et al, 1994;Simongiovanni et al, 2012).…”

Identification of novel biomarkers for Parkinson's disease by metabolomic technologies

“…However, it currently remains unclear whether low plasma serotonin levels are actually associated with psychotic symptoms in PD. In the body, serotonin plays a role in gastrointestinal regulation and is a modulator of blood vessel tone 20. Taken together, these findings suggest that there is some degree of autonomic dysfunction in advanced PD.…”

Role of Microbiota and Tryptophan Metabolites in the Remote Effect of Intestinal Inflammation on Brain and Depression

“…7 Intestinal inflammation and disrupted serotonin signaling system: from alterated gut functionality to development of depression Serotonin is a key signaling regulator that modulates a wide range of effects on host physiology, including the control of gut motility, secretory reflexes, platelet aggregation, regulation of immune responses, and regulation of mood and behavior [67]. Once tryptophan is absorbed in the gut, it crosses the blood-brain barrier to be partially metabolized into serotonin in the raphe nuclei within the brain stem [34]. However, the majority (~ 95%) of serotonin in the body is synthesized, stored, and released in the gut, mainly from a subset of enteroendocrine cells called enterochromaffin cells in the intestinal mucosa [19].…”