Structural Characterization and Screening for Anti‐inflammatory Activity of Polysaccharides with Different Molecular Weights from Astragali Radix

Astragali Radix polysaccharides (APSs) exhibit a broad spectrum of biological activity, which is mainly related to immune regulation. At present, most available studies focus on total APSs or a certain component of APSs. However, structural structure study and screening for the anti‐inflammatory activity of polysaccharides with different molecular weights (MW) have yet to be conducted. In this study, lipopolysaccharide (LPS)‐induced RAW264.7 macrophages were used as a model to investigate the anti‐inflammatory activity of APSs and its fractions. The results revealed that fraction APS‐I had better anti‐inflammatory effects than APS‐II. After APS‐Ⅰ was hydrolyzed by trifluoroacetic acid (TFA), the resulting degradation products oligosaccharides were fully methylated. These derivatized oligosaccharides were further analyzed by MALDI‐TOF‐MS and UPLC‐Q‐Exactive‐MS/MS. The results showed that APS‐Ⅰ was a hetero‐polysaccharide with a molecular weight of about 2.0 × 106 Da, mainly consisting of glucose (46.8%) and galactose (34.4%). The degree of polymerization of Astragali Radix oligosaccharides (APOS) was 2‐16. APOS were identified as 1,4‐glucooligosaccharides and 1,4‐galactooligosaccharides. The findings of this study lay the foundation for further elucidation of structure‐function relationships of APSs and provide guidance for the development of anti‐inflammatory drugs.