IDO1 and type 2 diabetes mellitus: The shift of Trp toward the kynurenine pathway has also been linked to the pathophysiology of T2D; that is, the overexpression of TDO/IDO induced by low-grade inflammation and intestinal dysbiosis reduces the availability of this amino acid for other, more beneficial catabolic pathways such as the production of indoles and serotonin [27].