Jaceosidin, a Natural Flavonoid From Artemisia argyi , Alleviates Colitis by Remodeling Gut Microbiota to Promote Treg Differentiation via the 5‐HIAA‐AhR Axis

Dysregulated gut microbiota-immune interactions are increasingly recognized as key contributors to inflammatory bowel disease (IBD), highlighting strategies that restore this crosstalk. Among these, jaceosidin (JAC), a natural flavonoid from Artemisia argyi, represents a potential candidate, and this study investigated its anti-colitis effect and underlying mechanism. TNBS-induced colitis was established in mice, and JAC (10, 20, 40 mg/kg) was administered orally, with 5-ASA as a positive control. Immune cell composition was assessed by flow cytometry. The contribution of the gut microbiota was tested via antibiotic depletion (ABX) and fecal microbiota transplantation (FMT). 16S rDNA sequencing and untargeted metabolomics identified microbial and metabolic changes. The involvement of the aryl hydrocarbon receptor (AhR) pathway was assessed using the AhR antagonist StemRegenin 1 (SR1). JAC dose-dependently alleviated TNBS-induced colitis, with greater improvement at medium and high doses than with 5-ASA under the present experimental conditions; no overt short-term toxicity was observed at the tested doses. Interestingly, JAC increased regulatory T (Treg) cell frequencies in vivo but did not further enhance Treg differentiation in vitro under the tested conditions. ABX attenuated the anti-colitis and Treg-promoting effects of JAC, whereas FMT from JAC-treated donors reproduced these effects, supporting a contribution of the gut microbiota. Fecal supernatants from JAC-treated mice enhanced Treg differentiation under Treg-polarizing conditions, suggesting that soluble fecal factors may contribute to Treg induction. Untargeted metabolomics revealed that JAC markedly altered the fecal tryptophan metabolite profile, with the greatest elevation observed for 5-hydroxyindole-3-acetic acid (5-HIAA) among indole derivatives. Exogenous 5-HIAA alleviated colitis and increased Treg frequencies in vivo, and enhanced Treg differentiation in vitro. Furthermore, both JAC and 5-HIAA increased colonic Cyp1a1 expression, supporting AhR pathway involvement in vivo; pharmacological blockade of AhR attenuated their anti-colitis effects and reduced 5-HIAA-induced Treg differentiation in vitro. JAC alleviates experimental colitis in association with microbiota remodeling and increased fecal 5-HIAA. Exogenous 5-HIAA shows anti-colitis and Treg-promoting activity, supporting further investigation of its contribution to JAC efficacy.