Structural characterization of three polysaccharides from the roots of Codonopsis pilosula and their immunomodulatory effects on RAW264.7 macrophages

Abstract Three polysaccharides were isolated from the roots of Codonopsis pilosula by ion-exchange and gel-filtration chromatography. They were named RCNP, RCAP-1, and RCAP-2, and had apparent molecular weights of 1.14 × 10 4 , 5.09 × 10 4 , and 2.58 × 10 5 , respectively. Their structures were characterized by HPGPC, chemical derivative analysis, GC–MS and NMR analyses. Results showed that RCNP contained arabinan and arabinogalactan regions. The arabinan region had a main chain comprising (1 → 5)-linked Ara f residues, and the side chains branched at the O-3 position by the single Ara f residues. The arabinogalactan region comprised alternating (1 → 4)-, (1 → 6)- or (1 → 3)-linked Gal p along with small amounts of branches mainly at the O-3 position of the (1 → 6)-linked Gal p or O-6 position of the (1 → 3)-linked Gal p residues by terminally linked Ara f residues. RCAP-1 and RCAP-2 were highly methyl-esterified pectin-type polysaccharides with long homogalacturonan regions interrupted by a short rhamnogalacturonan I (RG-I) region. The side chains of the RG-I region consisted of (1 → 2)-linked Rha residues attached to the position O-4 of rhamnose. Their degrees of methyl-esterification were approximately 60.6% and 68.1%, respectively. Bioactivity tests showed that RCAP-1 and RCAP-2 exerted a significant immunostimulatory effect based on NO production from RAW264.7 macrophages. These results suggested that these two pectin-type polysaccharides were potential immunostimulation agents.