An anti-colitis polysaccharide isolated from Bletilla striata: structural characterization and bioactivity evaluation

A novel high-molecular-weight neutral polysaccharide, BSPN, was extracted and purified from Bletilla striata. The structural characteristics of BSPN were comprehensively analyzed using conventional structural analysis techniques, including infrared spectroscopy, monosaccharide composition analysis, methylation analysis, and nuclear magnetic resonance spectroscopy. To further resolve the fine structure of BSPN, particularly the presence and distribution of acetyl substitutions, we employed enzyme-assisted hydrolysis combined with UPLC-QTOF-MS/MS to analyze the resulting oligosaccharide fragments. Structural analysis revealed that BSPN primarily consists of mannose and glucose at a molar ratio of 83.6:16.4, with a molecular weight of 1.78×10⁵ g/mol. The main chain of BSPN is composed of→4)-β-D-Manp-(1→, →4)-β-DGlcp-(1→, →3)-β-D-Manp-(1→ and →3)-β-D-Glcp-(1→ linkages, with branched chains connected via→4, 6)-β-D-Manp-(1→. Additionally, acetyl substitutions were identified at the C-2 and C-3 positions of →4)-β-D-Manp-(1→. The successful identification of these acetyl substitutions at the C-2 and C-3 positions was achieved by analyzing specific ion fragments in mass spectrometry. The therapeutic potential of BSPN was evaluated in a dextran sodium sulfate (DSS)-induced UC mouse model, which demonstrated that BSPN effectively alleviates UC symptoms in a dose-dependent manner. By correlating the biological activity of BSPN with its well-defined structure, we provide new insights into its mechanism of action in UC treatment. This study establishes a theoretical foundation for developing BSPN as a functional agent to treat UC.