Oral tryptophan activates duodenal aryl hydrocarbon receptor in healthy subjects: a crossover randomized controlled trial.

Tryptophan is an essential amino acid transformed by host and gut microbial enzymes into metabolites that regulate mucosal homeostasis through aryl hydrocarbon receptor (AhR) activation. Alteration of tryptophan metabolism has been associated with chronic inflammation; however, whether tryptophan supplementation affects the metabolite repertoire and AhR activation under physiological conditions in humans is unknown. We performed a randomized, double blind, placebo-controlled, crossover study in 20 healthy volunteers.