Kynurenine Attenuates Ulcerative Colitis Mediated by the Aryl Hydrocarbon Receptor

The higher prevalence of ulcerative colitis (UC) and the side effects of its therapeutic agents contribute to finding novel treatments. This study aimed to investigate whether kynurenine (KYN), a tryptophan metabolite, has the possibility of alleviating UC and further clarifying the underlying mechanism. The effect of KYN on treating UC was evaluated by intestinal pathology, inflammatory cytokines, and tight-junction proteins in colitis mice and LPS-stimulated Caco-2 cells. Our results revealed that KYN relieved pathological symptoms of UC, improved intestinal barrier function, enhanced AhR expression, and inhibited NF-κB signaling pathway activation in the colon of colitis mice. Moreover, the improved intestinal barrier function, the decreased inflammasome production, and the inhibited activation of the NF-κB signaling pathway by KYN were dependent on AhR in Caco-2 cells. KYN could trigger AhR activation, inactivate the NF-κB signaling pathway, and inhibit NLRP3 inflammasome production, thus alleviating intestinal epithelial barrier dysfunction and reducing intestinal inflammation. In conclusion, the present study reveals that KYN ameliorates UC by improving the intestinal epithelial barrier and activating the AhR-NF-κB-NLRP3 signaling pathway, and it can be a promising therapeutic agent and dietary supplement for alleviating UC.