Chemical characterization of aconite polysaccharide and its ameliorative effect on ulcerative colitis by regulating gut microbiota and THDCA-driven TGR5/cAMP/PKA/NLRP3 pathway

Aconite shows potential to improve ulcerative colitis (UC). However, the specific impact and mechanisms of aconite polysaccharides (APs) on UC remain poorly understood. This study aims to elucidate the chemical structures of APs, among which one was further evaluated for its effects on dextran sulfate sodium (DSS)-induced UC, and the underlying mechanism was explored with a focus on gut microbiota (GM). Four distinct APs were isolated, among which aconite polysaccharide A-1 (APA-1) was the predominant one. APA-1 is characterized as a glucan composed of →4)-α-glucose (Glc)-(1→, with residues such as →3, 4)-α-Glc-(1→, →2, 4)-α-Glc-(1→ and →4, 6)-α-Glc-(1→ functioning as branching points. APA-1 significantly ameliorated disease symptoms and colonic pathological alterations in UC mice. Furthermore, APA-1 restored GM diversity and richness, counteracting dysbiosis marked by a decrease in beneficial microorganisms such as Dubosiella and Lactobacillus, and an increase in potentially pathogenic ones including Proteobacteria and Escherichia-Shigella. Fecal microbiota transplantation (FMT) recapitulated the effects of APA-1 on UC mice, thereby confirming the role of APA-1-regulated GM in UC. Metabolomic analysis revealed that APA-1 may exert its effects by enhancing microbial metabolite taurohyodeoxycholic acid (THDCA). Oral administration of THDCA, in conjunction with transcriptomic and Western blotting (WB) analyses, demonstrated that both APA-1 and THDCA ameliorate UC by inhibiting the nucleotide-binding domain, leucine-rich-repeat-containing family, pyrin domain-containing 3 (NLRP3) inflammasome through the Takeda G protein-coupled receptor 5/cyclic adenosine monophosphate/protein kinase A (TGR5/cAMP/PKA) signaling pathway. In summary, APA-1 effectively mitigates UC by modulating GM and microbial metabolite THDCA, which subsequently targets the NLRP3 inflammasome via the TGR5/cAMP/PKA pathway.