Structural characterization and anti-rheumatoid arthritis effects of polysaccharides from Anoectochilus xingrenensis

The first chemical and biological investigation on Anoectochilus xingrenensis, a closely related species of A. roxburghii, revealed that the crude polysaccharide of A. xingrenensis (AXP) displayed significant anti-rheumatoid arthritis (RA) effects against collagen-induced arthritis (CIA) in rats. X21, a new polysaccharide with a molecular weight of 2.71 × 10⁴ Da, was purified as a major fraction from AXP and characterized as a heteroglycan backbone consisting of →4)-β-D-Galp-(1→, →4)-α-D-Glcp-(1→, and →4,6)-α-D-Glcp-(1→, and with a terminal residue of α-D-Manp-(1→. Pharmacological study demonstrated that X21 significantly reduced the arthritis score, increased the body weight, alleviated articular bone destruction, and decreased the levels of pro-inflammatory factors in the serum of CIA rats. Moreover, 16S rRNA sequencing indicated that X21 could restore the gut microbiota of RA rats by decreasing the relative abundance of Lactobacillus and increasing that of Roseburia, leading to increased levels of short chain fatty acids. In addition, X21 significantly suppressed macrophage M1 polarization and promoted M2 polarization both in vitro and in vivo, potentially by down-regulating the expressions of p-p65, p-IκB, p-JNK and p-p38 in NF-κB and MAPK pathways and up-regulating that of p-STAT6 in JAK/STAT pathway, respectively. Our study suggests that X21 from A. xingrenensis could be regarded as a promising drug candidate and prebiotic for RA treatment.