Structure and bioactivity of a polysaccharide extracted from protocorm-like bodies of Dendrobium huoshanense

The crude polysaccharides of Dendrobium huoshanense were fractionated by anion-exchange chromatography and gel permeation chromatography, giving one homogeneous fraction DHP-4A with molecular weight of 2.32 × 105 Da. UV spectrum indicated that there was no existence of proteins and nucleic acids in DHP-4A. Monosaccharide analysis revealed that DHP-4A was made up of glucose, arabinose, mannose and rhamnose with a molar ratio of 13.8:3.0:6.1:2.1. The backbone of DHP-4A consisted of (1→6)-linked glucose, (1→6)-linked mannose and (1→3,6)-linked mannose. The β-l-Rhap-(1→2)-β -l-Rhap-(1→4)-β-d-Manp-(1→ and α-l-Araf-(1→3)- α-l-Araf -(1→3)- α-l-Araf-(1→ were regarded as the branches attached to the C-3 position of (1→6)-linked mannose in the backbone. The sugar residue sequence was further determined by NMR spectra including 1H NMR, 13C NMR, HSQC and HMBC. Pharmacological tests showed that DHP-4A can significantly stimulate RAW 264.7 macrophage cells to secrete NO, TNF-α, IL-6 and IL-10 via activation of p38, ERK, JNK and translocation of nuclear NF-κB, indicating this polysaccharide possesses good immunoregulatory activity.