Structural characterization of a low-methylated RG-I pectin from Sonchus oleraceus Linn. And its protective effects against DSS-induced colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease with limited effective therapeutic options. Plant-derived polysaccharides have emerged as promising candidates for UC treatment. In this study, a novel pectic polysaccharide, designated SOP, was isolated from the traditional medicinal plant Sonchus oleraceus L. SOP is homogeneous polysaccharide (≈169 kDa), mainly composed of galacturonic acid (72.13%), accompanied by galactose (10.57%), arabinose (9.51%), and rhamnose (4.23%). Comprehensive NMR spectroscopic analysis (1H, 13C, HSQC, HMBC, COSY) elucidated its backbone structure, characteristic of rhamnogalacturonan-I (RG-I) type pectin. It is classfied as a low-methylated pectin with coexistence pyranose and furanose ring configurations, along with moderate esterification (≈23.8%), methylation(22.45%) and minor acetylation (1.36%). Functionally, SOP exhibited superior emulsifying activity (56.05%) and dose-dependent DPPH radical scavenging activity. In a DSS-induced colitis mouse model, oral administration of SOP significantly alleviated disease symptoms, reduced disease activity index scores, restored colon length, and ameliorated colonic histopathological damage in a dose-dependent manner. Mechanistic studies revealed that SOP treatment significantly downregulated the expression of M1 macrophage markers (iNOS, CD86) and pro-inflammatory cytokine IL-6 in colonic tissues. Furthermore, SOP suppressed the phosphorylation of NF-κB p65, JNK, and ERK1/2, indicating its anti-inflammatory effects are mediated via inhibition NF-κB and MAPK signaling pathways. These findings demonstrate that SOP, a structurally unique low-methylated RG-I pectin from Sonchus oleraceus L, has promising antioxidant and anti-inflammatory properties, exerts therapeutic effects against experimental colitis by modulating key inflammatory pathways, and provides a scientific basis for its traditional use and clinical UC prevention and management.