Anti-inflammatory activity of alkali-soluble polysaccharides from Arctium lappa L. and its effect on gut microbiota of mice with inflammation

In this study, an alkali-soluble polysaccharide (ASALP) from Arctium lappa L. were extracted and purified. Our results indicated that ASALP was a homogeneous polysaccharide with a molecular weight of 1.2 × 105 Da composed of rhamnose, arabinose, xylose, glucose and galactose in a molar ratio of 1.2: 4.4: 0.9: 0.9: 2.6. The structure characterization indicated that ASALP was mainly consisted of →5-α-L-Araf-(1 → backbone and α-Araf-(1→,→2)-α-Rhap-(1 → T-Glcp-(1→, →3)-β-D-Xylp-(1 → 4)-α-GalpA-(1 → branches. In vitro and in vivo assay showed that ASALP could effectively alleviate inflammation by improving the dysregulation of pro-inflammatory and anti-inflammatory cytokines. Specifically, ASALP significantly inhibited the production of nitric oxide (NO) and pro-inflammatory cytokines (IL-6, IL-1β and TNF-α) in lipopolysaccharide (LPS)-treated macrophages and in the serum of inflammatory mice, but increased the production of the anti-inflammatory cytokines IL-10. The results from 16S rRNA (V3-V4) amplicon sequencing showed that the relative abundance of Firmicutes, Alistipes, Odoribacter and Lactobacillus in mice was significantly increased after ASALP treatment. Lower levels of Proteobacteria, Staphylococcus and Bacteroidetes were detected in LPS + ASALP treatment group. ASALP alleviated inflammation by improving the reduction of microbial diversity and affecting the composition of the gut microbiota. Our study could provide the basis for the subsequent research and application of ASALP.