Shouhui Tongbian Capsules alleviate constipation by modulating the gut microbiota–tryptophan metabolism–AhR signaling axis: a mechanistic study

Objective Constipation is a prevalent functional gastrointestinal disorder characterized by impaired intestinal barrier function, often driven by gut microbiota dysbiosis and metabolic disturbances. Shouhui Tongbian Capsules (SHTB), a traditional Chinese medicine formulation, has demonstrated clinical efficacy in constipation management. This study aimed to elucidate the molecular mechanisms underlying SHTB's anti-constipation effects through modulation of the gut microbiota–tryptophan metabolism–aryl hydrocarbon receptor (AhR) signaling axis. Methods A loperamide-induced murine constipation model was established to evaluate the therapeutic efficacy of SHTB, as assessed by time to first black stool defecation, fecal pellet count, fecal water content, and small intestinal propulsion rate. Colonic histopathology was examined by hematoxylin and eosin (H&E) and Alcian blue–periodic acid–Schiff (AB-PAS) staining. 16S rRNA gene sequencing and metabolomic profiling were used to characterize gut microbiota composition and metabolite alterations in SHTB-treated constipated mice. Key findings were subsequently validated through fecal microbiota transplantation (FMT) and pharmacological AhR inhibition. Results SHTB significantly improved defecation parameters in constipated mice ( P < 0.001). Mechanistically, SHTB may promote tryptophan metabolic flux through gut microbiota remodeling, particularly through enrichment of Bifidobacterium ( P < 0.05) and Alistipes ( P < 0.01), leading to activation of colonic AhR signaling ( P < 0.05) and reinforced intestinal barrier integrity. FMT with SHTB-conditioned microbiota restored key bacterial populations and reactivated AhR expression ( P < 0.05) in recipient mice. Critically, pharmacological blockade of AhR with CH223191 abolished all SHTB-mediated therapeutic benefits, with no significant differences observed between the CH223191 + Lop and CH223191 + Lop + SHTB groups ( P > 0.05), thereby identifying AhR as an indispensable mediator of SHTB's anti-constipation mechanism. Conclusion SHTB alleviates constipation in a murine model by enhancing intestinal barrier integrity through modulation of the gut microbiota–tryptophan metabolism–AhR signaling axis, thereby providing mechanistic support for its clinical application in managing constipation.