Structural differences of polysaccharides from Astragalus before and after honey processing and their effects on colitis mice

Honey-processed Astragalus is a dosage form of Radix Astragali processed with honey, which exhibits better efficacy of tonifying Qi than the raw product. Polysaccharides are its main water-soluble active components. This work was designed to study the structural differences of homogeneous honey-processed Astragalus polysaccharides (HAPS3a) and Astragalus polysaccharides (APS3a) and their effects on colitis mice. The results showed that HAPS3a (Mw = 2463.5 kDa) and APS3a (Mw = 3373.2 kDa) differed in molecular weight, monosaccharide compositions, glycosidic bonds and degree of branching (DB). Notably, the molar ratios of galactose and galacturonic acid in HAPS3a were 22.66% and 33.24%, while those in APS3a were 11.87% and 49.55%, respectively. The uronic acid residues 1,4-β-GalpA and 1,6-α-GlcpA of the backbone in APS3a were converted into the corresponding neutral residues in HAPS3a after honey processing. The different DB of HAPS3a (15.35%) and APS3a (25.13%) suggested that the chain conformation became smoother. The anti-inflammatory effects on colitis mice revealed that HAPS3a exhibited better effects than APS3a by protecting intestinal mucosa, regulating the expression of cytokines and influencing microbiota diversity. Taken together, the differences in anti-inflammatory activity might be related to structural differences caused by honey processing. Our findings have laid a foundation for the processing mechanism of Astragalus.