OBJECTIVE

2

To investigate the mechanism of Huangqin decoction in improving ulcerative colitis （UC） through the gut microbiota-tryptophan metabolism-aryl hydrocarbon receptor （AhR） axis.

METHODS

2

Mice were randomly divided into normal group （normal saline）， model group （normal saline）， microbiota depletion-model group （normal saline）， microbiota depletion-Huangqin decoction group （9.1 g/kg， by crude drug， similarly hereinafter）， Huangqin decoction group and mesalazine group （positive control group， 0.4 g/kg）， with 6 mice in each group. Microbiota depletion was achieved by providing free access to a mixed antibiotics for 10 days. The UC model was induced by administering 2.5% dextran sulfate sodium solution for 7 days. After successful modeling， each treatment group received corresponding drugs or normal saline intragastrically once daily for 10 days. After the final administration， body weight change ratio， disease activity index （DAI） score， and colon length were evaluated； colon pathological changes were observed； serum levels of interleukin-6 （IL-6）， IL-10， IL-22， and tumor necrosis factor-α （TNF-α） were measured； the expressions of Occludin， zonula occluden-1 （ZO-1）， and AhR in colon tissue were detected； fecal samples were subjected to high-throughput sequencing to analyze targeted tryptophan metabolomics.

RESULTS

2

Compared with the model group， Huangqin decoction group showed reduced infiltration of inflammatory cells in the colon tissue and restoration of the intestinal mucosal structure. Body weight change ratio， colon length， serum content of IL-10， the expressions of Occludin， ZO-1 and AhR in colon

tissue and the contents of tryptophan metabolites indole-3-propionic acid （IPA），

N

-acetylserotonin （NAS） and indole-3-acetic acid （IAA） were all significantly increased （

P

＜0.05）； DAI score， serum levels of IL-6， TNF-α， and IL-22 and the content of tryptophan metabolite indole-3-ethanol were significantly decreased （

P

＜0.05）； gut microbiota structure was improved， with increased relative abundances of beneficial bacteria such as

Lactobacillus

， and decreased relative abundances of pathogenic bacteria such as

Escherichia-Shigella

. However， after antibiotic-induced microbiota depletion， although Huangqin decoction significantly increased the content of NAS in the feces of mice， the expression of AhR protein in colon tissue did not increase concurrently.

CONCLUSIONS

2

Huangqin decoction can repair the intestinal mucosal barrier in UC mice by regulating the gut microbiota and promoting the production of IPA and IAA， thereby activating AhR. This suggests that an intact gut microbiota is an important prerequisite for Huangqin decoction to exert its AhR-regulating effects.