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

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 × 104, 5.09 × 104, and 2.58 × 105, 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 Araf residues, and the side chains branched at the O-3 position by the single Araf residues. The arabinogalactan region comprised alternating (1 → 4)-, (1 → 6)- or (1 → 3)-linked Galp along with small amounts of branches mainly at the O-3 position of the (1 → 6)-linked Galp or O-6 position of the (1 → 3)-linked Galp residues by terminally linked Araf 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.