Huanglian-Wendan Decoction alleviates DSS-induced colitis by modulating the gut microbiota and protecting against intestinal injury via suppression of colonic apoptosis and endoplasmic reticulum stress.

Inflammatory bowel disease (IBD) is a chronic disorder characterized by recurrent intestinal inflammation and gut microbiota dysbiosis. Huanglian-Wendan Decoction (HLWDD) has been clinically used for IBD treatment; however, its underlying mechanisms remain unclear. In this study, a dextran sulfate sodium (DSS, 2.25%)-induced IBD mouse model was established to evaluate the therapeutic effects of HLWDD. The protective mechanisms were investigated in colon tissues of DSS-induced mice using ELISA, immunoblotting, histological, and immunohistochemical analyses. In addition, the impact of HLWDD on gut microbiota dysbiosis was analyzed using 16S rRNA sequencing. Antibiotic treatment was applied before DSS administration to deplete gut microbiota and verify the role of microbial modulation. Furthermore, the phytochemical constituents of HLWDD were characterized using liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (LC-QTOF-MS/MS). The results demonstrated that HLWDD markedly alleviated DSS-induced colitis, as evidenced by reduced body weight loss, rectal bleeding, colon shortening, and disease activity index (DAI) scores. Mechanistically, HLWDD suppressed inflammatory responses in colon tissues by inhibiting the TLR4/MyD88/NF-κB and IL-6/JAK2/STAT3 signaling pathways, while enhancing epithelial barrier integrity through upregulation of ZO-1, Occludin, Claudin-1, and Mucin-2. In addition, HLWDD attenuated endoplasmic reticulum stress (ERS) and apoptosis by downregulating CHOP, phospho-eIF2α, cleaved caspase-3, and Bax, while increasing Bcl-2 expression in colonic tissues. Microbiota analysis revealed an increased abundance of beneficial bacterial genera such as Akkermansia and Escherichia-Shigella-related commensals, along with enrichment of beneficial bacterial families including Ruminococcaceae, Lachnospiraceae, and Verrucomicrobiaceae, whereas potentially harmful taxa such as Escherichia and Paraprevotella were reduced. HLWDD also increased the production of short-chain fatty acids (SCFAs), including acetate, butyrate, and isobutyrate, thereby promoting intestinal homeostasis. Importantly, the protective effects of HLWDD were largely abolished following antibiotic-mediated gut microbiota depletion, confirming the essential role of microbial modulation in its therapeutic action. Collectively, these findings suggest that HLWDD ameliorates IBD by regulating gut microbiota composition and function, thereby inhibiting colonic ER stress and apoptosis and restoring intestinal barrier integrity. This study provides mechanistic evidence supporting the potential clinical application of HLWDD as a novel therapeutic strategy for IBD.