Fig. 2From: Tryptophan-kynurenine metabolism: a link between the gut and brain for depression in inflammatory bowel diseaseThe link between intestinal inflammation, KP, and depression in IBD. In the process of IBD, inflammatory activity stimulates intestinal cells to produce a series of inflammatory cytokines such as IFN-γ, IL-6, and IL-1. Activation of IDO by inflammatory cytokines results in increased degradation of TRP to KYN, which crosses the blood-brain barrier and is metabolized by different branches to QUIN and KYNA. In an inflammatory environment, a higher rate of production of neurotoxic molecules such as QUIN, 3-HK, and 3-HAA may cause depression by damaging hippocampal neurons. In contrast, KYNA is a neuroprotective factor. These KP metabolites affect the mood of IBD patients through a complex series of neurobiological responses. IFN, interferon; IL, interleukin; α7nAChRs, α7 nicotinic acetylcholine receptors; Glu, glutamate; NMDA, N-methyl-D-aspartateBack to article page