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BACKGROUND Momordica charantia exerts anti-inflammatory effect against ulcerative colitis. Momordica charantia polysaccharides (MCPs) attenuate gastritis through inhibition of ethanol-induced inflammatory response. OBJECTIVE The role of MCPs in diarrhea-predominant irritable bowel syndrome (IBS-D) is investigated. MATERIALS AND METHODS Chemical stimulation followed by acute and chronic pressure stimulation was used to establish rats model with IBS-D. The model rats were then administrated with MCPs. Defecation frequency, fecal water content and abdominal withdrawal reflex (AWR) score were then recorded. Pathologic changes in the colonic tissues were evaluated by hematoxylin and eosin staining. Inflammation was detected by ELISA and qRT-PCR, and immunohistochemistry was used to assess intestinal mucosal permeability. RESULTS First, IBS-D of mice wasIBS-D ratsmice exhibited many abnormal clinical manifestations, including increased frequency of defecation, fecal water content, and abdominal withdrawal reflex (AWR) score. Second, the mice were administrated with MCPs, which reduced frequency of defecation, fecal water content, and AWR score, and 100-mg/kg MCPs indicated therapeutic effect on IBS-D mice equivalent to rifaximin. Moreover, MCPs also ameliorated pathologic changes in the colonic tissues of IBS-D mice. Third, inflammatory response in IBS-D mice was also suppressed by MCPs through up-regulation of Interleukin (IL)-10, and down-regulation of tumor necrosis factor-α (TNF-α), Interleukin(IL)-1β, and IL-6. MCPs enhanced levels of occludin (OCLN) and zona occludens protein-1 (ZO-1) in IBS-D mice to improve intestinal mucosal permeability. Finally, phosphorylation of p65 in IBS-D mice was reduced by MCP treatment. CONCLUSION MCPs ameliorated intestinal permeability and repressed intestinal inflammation to attenuate IBS-D by inactivating nuclear factor kappa B (NF-κB) signaling.