Cell Signaling by Tryptophan Catabolism

Tryptophan (Trp) metabolism follows three main branches: the kynurenine (KP), serotonin, and indole (IP) pathways. These pathways generate bioactive metabolites that regulate immune responses, redox balance, neurotransmission, metabolic homeostasis, inflammation, and circadian rhythms. A common theme across these pathways is the activation of the aryl hydrocarbon receptor (AhR). Several metabolites from KP, IP, and serotonin act as endogenous AhR ligands or interact indirectly with AhR, but the