Unraveling the active ingredients and molecular mechanisms of Qinghua Changyan granule against irritable bowel syndrome with diarrhea: Effects on gut microbiota and glutamine transport via an integrative approach combining UHPLC-MS/MS and experimental verification.

Irritable bowel syndrome with diarrhea (IBS-D) is a prevalent functional gut disorder, with conventional treatments limited by incomplete symptom relief and side effects. Qinghua Changyan Granules (QHCYG), a traditional Chinese medicine, has clinical efficacy in treating IBS-D, though its molecular mechanisms are unclear. This study aimed to elucidate these mechanisms. Key components of QHCYG were identified via UHPLC-MS/MS and network pharmacology, with quercetin, kaempferol, luteolin, naringenin, and nobiletin confirmed as major active components. Pharmacodynamic results showed QHCYG significantly ameliorated IBS-D-related symptoms, including reduced fecal water content, diarrhea frequency, Bristol stool scale scores, and visceral hypersensitivity. Furthermore, QHCYG restored gut microbial diversity, increased the abundance of beneficial taxa (Akkermansia, Bifidobacterium) and decreased Allobaculum proportion; it also upregulated the expression of key intestinal barrier proteins, including zonula occludens-1 (ZO-1), epithelial cadherin (E-cadherin), catenin beta-1 (β-catenin), Claudin-1. Molecular docking indicated QHCYG's active components could bind to alanine-serine-cysteine-preferring transporter 2 (ASCT2), and QHCYG further elevated intestinal glutamine concentrations and ASCT2 expression. Notably, depletion of gut microbiota by antibiotics abolished all these therapeutic effects, confirming a microbiota-dependent mechanism. In conclusion, QHCYG alleviates IBS-D through restoring gut microbiota, enhancing intestinal barrier function, and promoting ASCT2-mediated glutamine transport, revealing a "Microbiota-Glutamine axis-Intestinal barrier" multi-target regulatory mechanism.