Tryptophan Metabolites Improve Intestinal Mucosal Barrier via the Aryl Hydrocarbon Receptor-Interleukin-22 Pathway in Murine Dextran Sulfate Sodium-Induced Pouchitis.

Background: Pouchitis is the commonest complication after ileal pouch-anal anastomosis for ulcerative colitis. The protective effect of tryptophan metabolites on the mucosal barrier may be an effective method for treating pouchitis. The role of tryptophan metabolites on pouchitis remained unclear.

Objective: We aimed to establish a murine model of dextran sulfate sodium-induced pouchitis to examine the roles of tryptophan metabolites in its pathogenesis.

Design: This is a study combined clinical patient data and animal research. A total of 22 patients were enrolled: 5 with familial adenomatous polyposis after ileal pouch-anal anastomosis, eight ulcerative colitis patients after ileal pouch-anal anastomosis patients with pouchitis, and 9 ulcerative colitis patients after ileal pouch-anal anastomosis with normal pouch. The demographic data and fecal samples of patients were collected. Male C57BL/6 mice were purchased from a licensed breeder and underwent ileal pouch-anal anastomosis to establish murine model of pouch. The bloods, feces, tissues of mice were collected.

Settings: This study was performed in an academic medical center in China.

Interventions: The demographic data of patients were observational collected. The mice underwent ileal pouch-anal anastomosis were divided into six groups: control group with chow diet, dextran sulfate sodium, 6-formylindolo[3,2-b] carbazole + dextran sulfate sodium, high tryptophan diet + dextran sulfate sodium, CH-223191 + dextran sulfate sodium, indole-3-carboxaldehyde + dextran sulfate sodium. Animals were sacrificed after dextran sulfate sodium for 7 days.

Main outcome measures: Fecal tryptophan metabolite level and microbiome composition, the severity of pouchitis, intestinal mucosal barrier function, and activation of the aryl hydrocarbon receptor-interleukin 22 pathway were assessed.

Results: Patients with pouchitis had lower fecal microbial diversity and indole-3-acetic acid levels. In murine pouchitis model, high-tryptophan diet increased fecal levels of 3-indoleglyoxylic acid, indole-3-aldehyde, and indole. A high-tryptophan diet and intraperitoneal aryl hydrocarbon receptor ligand 6-formylindolo[3,2-b] carbazole injection alleviated pouchitis. Tryptophan metabolites improved pouch mucosal barriers. aryl hydrocarbon receptor inhibitors exacerbated experimental pouchitis and disrupted the mucosal barrier; however, the aryl hydrocarbon receptor ligand indole-3-carboxaldehyde reversed this effect.

Limitations: This study was limited by small human sample size and lacking an Aryl hydrocarbon receptor knockout mouse model.

Conclusions: A high-tryptophan diet and aryl hydrocarbon receptor ligand alleviated dextran sulfate sodium-induced pouchitis in murine ileal pouch-anal anastomosis model, which might be through regulating epithelial tight junctions and promoting goblet-cell differentiation, as well as maintaining the integrity and function of the mucosal barrier. This study provides a rationale for the clinical application of Aryl hydrocarbon receptor ligands in the treatment of pouchitis. See Video Abstract.