Anemoside B4 alleviates ulcerative colitis by attenuating intestinal oxidative stress and NLRP3 inflammasome via activating aryl hydrocarbon receptor through remodeling the gut microbiome and metabolites

Ulcerative colitis (UC) is a chronic, non-specific inflammatory disease of the intestines with a significant increase in global incidence in recent years. Oxidative stress and inflammation are two hallmarks of UC pathogenesis. Anemoside B4 (AB4), a pentacyclic triterpenoid saponin, exhibits significant antioxidant and anti-inflammatory properties and shows potential for preventing UC. Here, an animal model induced by dextran sodium sulfate (DSS) was used to investigate the effect of AB4 on UC. The results demonstrated that AB4 significantly reduces intestinal oxidative stress and inflammation in UC mice, while also protecting intestinal barrier function. Furthermore, AB4 helps restore intestinal microbial balance primarily by modulating the abundance of Lactobacillus, which enhances the metabolism of short-chain fatty acids and upregulates the production of butyric acid (BA). Pseudogerm-free mice and fecal microbiota transplantation (FMT) demonstrated that AB4 significantly mitigated UC in a gut microbe-dependent manner. Both AB4 and BA markedly activate the aromatic hydrocarbon receptor (AhR). The intestinal organoid results suggest BA may activate the AhR to inhibit ROS production and activation of NLRP3 inflammasome, thereby protecting intestinal integrity. Administration of AhR antagonists abolished the protective effects, thus confirming the involvement of AhR in the underlying mechanism. Overall, these results indicate that AB4 is an effective agent against UC mainly by activating the AhR through gut microbial short-chain fatty acid metabolites to inhibit intestinal oxidative stress and inflammation.