Structural characterization and immunomodulatory activity of an acidic polysaccharide from nine steaming and nine sun drying processed Polygonatum cyrtonema Hua.

A galactose-rich acidic polysaccharide, named NPCP-A1 (Mw = 55.138 kDa), was obtained from Polygonatum cyrtonema Hua processed by nine steaming and nine sun drying cycles. The structure of NPCP-A1 was elucidated by comprehensive analysis of results from high performance size exclusion chromatography-multi angle laser light scattering-refractive index detector (HPSEC-MALLS-RID), gas chromatography-mass spectrometry (GC-MS), and 1D/2D nuclear magnetic resonance (NMR) spectroscopy. NPCP-A1 was mainly comprised of Gal, along with a small amount of Ara, Rha, Man, GalA, Glc, Xyl, and GlcA, with a molar ratio of 79.48: 7.52: 5.18: 2.94: 2.47: 1.02: 0.71: 0.68. The glycosidic linkages were proposed as →4)-β-D-Galp-(1→, β-D-Galp-(1→, α-L-Araf-(1→, →3)-β-D-Galp-(1→, →4,6)-α-D-Glcp-(1→, →3,6)-β-D-Galp-(1→, →4)-α-D-GalpA-(1→, →2,4)-α-D-Rhap-(1→, and →4)-α-D-Manp-(1→. Congo red experiment indicated that NPCP-A1 does not form a triple helix structure and scanning electron microscope (SEM) revealed that the surface of NPCP-A1 is dense and flaky, with a rough and porous structure. Functionally, NPCP-A1 significantly promotes macrophage phagocytosis without cytotoxicity, and stimulates the release of nitric oxide (NO) and proinflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in RAW 264.7 cells.