Chapter 12: Role of kynurenine pathway in gastrointestinal diseases

In the course of obtaining nutrients from the environment to sustain life, the gastrointestinal (GI) tract encounters a myriad diversity of foreign antigens, microbiota, and environmental toxins. To maintain homeostasis in this setting, the GI mucosal immune system employs a multitude of techniques to distinguish the helpful from harmful. Recent studies reveal amino acid metabolism pathways as an integral mechanism to maintaining homeostasis at the mucosal interface. Tryptophan metabolism along the kynurenine pathway in particular is now recognized as an important feature of both GI infl ammation and malignancy. Indoleamine 2,3 dioxygenase (IDO1), the most prevalent of the tryptophan catabolizing enzymes, is expressed widely across tissues and cell types within the GI tract. This chapter will address the current knowledge of kynurenine pathway functions in the diseased GI tract and highlight the potential benefi ts of exploiting this pathway for therapeutic purposes.