Rauvolfia verticillata-derived pectic polysaccharides alleviate ulcerative colitis via regulating macrophage polarization and inhibiting the JAK2/STAT3-NOS2 pathway

Objective: To investigate the effect of pectic polysaccharides isolated from Rauvolfia verticillata on ulcerative colitis and its underlying mechanisms. Methods: Pectic polysaccharides were characterized using high-performance liquid chromatography with 1-phenyl-3-methyl-5-pyrazolone pre-column derivatization, phenol-sulfuric acid assay, and gel permeation chromatography. HT-29 cells were stimulated with lipopolysaccharide and then treated with pectic polysaccharides; conditioned medium was applied to THP-1-derived macrophages to assess cell viability and polarization, while tight junction protein expression was analyzed in HT-29 cells. Furthermore, a mouse model of dextran sulfate sodium-induced colitis was treated with oral pectic polysaccharides or NOS2 overexpression. Body weight, disease activity index, colon length, histopathology, and the protein expression related to the JAK2/STAT3-NOS2 signaling were evaluated. Results: The pectic polysaccharide was characterized as an acidic pectic polysaccharide, primarily composed of galacturonic acid and various neutral sugars, with a narrow molecular weight distribution and high purity. Pectic polysaccharides significantly enhanced THP-1 macrophage viability, promoted M1 to M2 polarization, and upregulated the expression of epithelial tight junction proteins. In addition, pectic polysaccharide treatment attenuated body weight loss, lowered disease activity index scores and improved colon histology in mice with dextran sulfate sodium-induced colitis. It also reduced JAK2/STAT3 phosphorylation and NOS2 expression, and increased the expression of tight junction proteins (ZO-1, occludin, and claudin-1). Conclusions: Pectic polysaccharides attenuate ulcerative colitis by increasing M2-related macrophage markers, inhibiting the JAK2/ STAT3-NOS2 signaling, and enhancing epithelial barrier-related protein expression. These findings support pectic polysaccharides as a natural candidate for the treatment of ulcerative colitis.