Diallyl sulfide pretreatment protects against DSS-induced colitis by reshaping the gut microbiota and enhancing microbiota-associated tryptophan metabolism.

ETHNOPHARMACOLOGICAL RELEVANCE: Allium sativum L. has a long-standing use in traditional medicine for gastrointestinal disorders. Diallyl sulfide (DAS), a key organosulfur compound derived from garlic, exhibits anti-inflammatory activity; however, its specific role in colitis and the underlying microbiota-metabolite mechanisms remain unresolved.

MATERIALS AND METHODS: Colitis was induced in mice using DSS following DAS pretreatment. Disease severity, intestinal barrier integrity, inflammation, gut microbiota composition, tryptophan metabolites, AhR signaling, colonic IL-22 levels, and STAT3 phosphorylation were evaluated. Fecal microbiota transplantation (FMT), IPA/IAld supplementation, parallel pharmacodynamic comparisons, and AhR blockade with CH223191 were executed to explore the microbiota-metabolite-host signaling axis.

RESULTS: DAS pretreatment conferred protection against DSS-induced colitis, evidenced by reduced disease activity, preserved colon length, improved histological injury, suppressed inflammatory responses, and restored tight-junction proteins. DAS modified the gut microbiota and elevated local intestinal levels of IPA and IAld. FMT and IPA/IAld supplementation partially recapitulated the protective phenotype associated with DAS, while combined supplementation of IPA + IAld yielded broader protective effects, nearing the protective outcomes provided by DAS. AhR blockade via CH223191 diminished DAS-mediated protection, characterized by decreases in AhR and Cyp1a1 expression, colonic IL-22 levels, and the p-STAT3/STAT3 ratio.

CONCLUSION: DAS pretreatment offers prophylactic protection against DSS-induced colitis by altering the gut microbiota and enhancing local indole-producing tryptophan metabolism, effects mediated at least in part by the AhR/IL-22/STAT3 pathway.