Da-Jian-Zhong decoction restores the gut-brain balance in diarrhea-predominant irritable bowel syndrome rats via gut microbiota-bile acid axis

Ethnopharmacological relevance Da- Jian-Zhong decoction (DJZD), a Chinese medicinal formula, exhibits therapeutic effects in the clinical management of diarrhea-predominant irritable bowel syndrome (IBS-D). Accumulating studies have demonstrated that DJZD can regulate the gut-brain balance in IBS-D model rats; however, its underlying molecular mechanism remains unclear. Aim of the study To explore the potential mechanism by which DJZD restores the gut-brain axis in IBS-D model rats. Materials and methods Firstly, the therapeutic effects of DJZD in IBS-D model rats were evaluated based on the Bristol stool scale, abdominal withdrawal reflex (AWR) score, open field test (OFT) behavior, intestinal barrier integrity, and brain-gut peptide levels. Moreover, alterations in gut microbiota was detected using sequencing of the whole microbial genome. Subsequently, fecal microbiota transplantation (FMT) was performed to explore whether the regulatory effect of DJZD on the gut-brain axis against IBS-D was dependent on gut microbiota. The UHPLC-QTRAP-MS/MS was utilized to analyze bile acids (BAs) profiles and identify gut microbiota-derived BAs metabolites responsible for the beneficial effects of DJZD. Finally, the role of BAs metabolites in restoring the gut-brain axis was further verified using the IBS-D model rats. Results Treatment with DJZD not only decreased AWR score, improved stool score and intestinal barrier integrity, but also enhanced sucrose preference and changed OFT performance of IBS-D rats. Meanwhile, DJZD normalized the levels of 5-hydroxytryptamine (5-HT) and substance P (SP) in both the colon and hippocampus. Fecal microbiota harvested from DJZD-treated rats also reversed these IBS-D-associated pathological manifestations. Moreover, DJZD notably elevated the levels of secondary BAs (SBAs) in colonic contents of IBS-D rats, particularly norchenodeoxycholic acid (NorDCA), lithocholic acid (LCA), deoxycholic acid (DCA), and 3β-ursodeoxycholic acid (3β-UDCA). The elevated SBAs were positively correlated with the relative abundances of Akkermansia sp., Ruminococcus sp., and Clostridium sp. This could be attributed to the ability of these bacteria to produce bile salt hydrolases (BSH) and 7α-hydroxysteroid dehydrogenases (7α-HSDH). Additionally, administration of an LCA and DCA mixture was found to improve intestinal and brain dysfunction and restored abnormal 5-HT and SP levels in IBS-D rats. Conclusion DJZD restores gut-brain balance in IBS-D rats by regulating gut microbiota-bile acid axis, which provides a promising therapeutic strategy for IBS-D via targeting bile acid metabolites and intestinal bacteria.