Exploring the Comorbidity Mechanism among Functional Diarrhea, Irritable Bowel Syndrome with Predominant Diarrhea, and Functional Dyspepsia through the Gut-brain Axis and the Pharmacological Mechanisms of Shen-Ling-Bai-Zhu-San Therapy

Background: Functional Diarrhea (FDr), Irritable Bowel Syndrome with predominant diarrhea (IBS-D), and Functional Dyspepsia (FD) are common functional gastrointestinal disorders (FGIDs) with significant impacts on quality of life. While the gut-brain axis and key regulators like 5-hydroxytryptamine (5-HT), dopamine (DA), and butyrate are known to play crucial roles in these conditions, the mechanisms underlying their comorbidities remain unclear. Shen-Ling-Bai-Zhu-San (SLBZS), a traditional herbal formula, is effective in treating FGIDs. Still, the specific components and mechanisms mediating its therapeutic effects via the gut-brain axis are not well understood. Methods: This study identified molecular links among FDr, IBS-D, and FD from the gut-brain axis using integrated biological information. The pharmacological mechanisms of SLBZS were explored through network pharmacology, molecular docking, molecular dynamics simulations, and in vitro bio-layer interferometry (BLI) validation. Results: A total of 328 common targets were identified among FDr, IBS-D, and FD, with 22 hub genes in the protein-protein interaction (PPI) network associated with 5-HT/DA/butyrate pathways. Virtual screening revealed seven key targets (AKT1, CASP3, VEGFA, INS, CTNNB1, PTGS2, and IL1B) and 14 bioactive components (e.g., diosgenin and luteolin) from SLBZS. Molecular docking indicated strong binding affinities between key components and targets, while molecular dynamics simulations confirmed stable interactions, particularly between PTGS2 and diosgenin/luteolin. BLI experiments further validated the strong binding affinity of PTGS2 for diosgenin. Conclusion: This study elucidates potential targets shared by FDr, IBS-D, and FD through the gut-brain axis, highlighting diosgenin's interaction with PTGS2 as a potential mechanism of SLBZS's therapeutic effects. These findings provide valuable insights into the pharmacological mechanisms of SLBZS in treating FGIDs and suggest new avenues for targeted therapies.