[Mechanism of Huangqin Decoction in repairing intestinal barrier of ulcerative colitis by regulating tryptophan metabolism and activating AhR].

This study aims to elucidate the mechanism of Huangqin Decoction(HQD) in treating ulcerative colitis(UC) by investigating the relationship between tryptophan metabolism and intestinal barriers. In the in vivo experiments, 3% dextran sulfate sodium(DSS) was used to induce a mouse model of acute colitis, with mesalazine as a positive control. The therapeutic effect of HQD on mice with UC was evaluated according to body weight, disease activity index(DAI), colon length, and pathological changes. Targeted metabolomics was used to detect the concentration of tryptophan and its metabolites in mouse feces. Western blot and RT-qPCR techniques were used to assess the expression levels of colonic aryl hydrocarbon receptor(AhR), myosin light chain kinase(MLCK), myo-sin light chain(MLC), and p-MLC. Serum FITC-dextran concentration, bacterial culture of mesenteric lymph nodes and spleen, as well as fluorescence probe in situ hybridization technique were used to evaluate intestinal epithelial permeability. Alcian blue and nuclear fast red staining, Western blot, and RT-qPCR techniques were used to detect the expression of mucin secreted by the mouse's intestinal epithelial goblet cells. Transmission electron microscopy was utilized to observe the connections of the mouse's intestinal epithelial cells. Immunofluorescence, Western blot, and RT-qPCR techniques were used to assess the expression of tight junction proteins in the mouse's intestinal epithelium. In the in vitro experiments, lipopolysaccharide(LPS) was used to induce intestinal epithelial barrier injury model in Caco2 cells, and AhR siRNA was used to further clarify the mechanism of HQD in activating AhR to improve intestinal barrier function. The results demonstrated that HQD effectively alleviated symptoms and pathological changes in the colon of DSS-induced mice with colitis. Treatment with HQD could regulate tryptophan metabolism in the feces of mice with colitis, activate AhR, and improve the intestinal epithelial barrier. Additionally, the results of the in vitro experiments confirmed that HQD could restore the expression of tight junction proteins in the intestinal epithelium of colitis cells by activating AhR to regulate the MLCK/p-MLC signaling pathway.