Structure characterization and immunomodulating effects of polysaccharides isolated from Dendrobium officinale

A crude polysaccharide fraction (cDOP) has been determined to be the characteristic marker of Dendrobium officinale Kimura & Migo (Orchidaceae), an expensive tea material in Asia. cDOP was de-starched (DOP, 90% yield), and separated into two sub-fraction polysaccharides, DOPa and DOPb, using anion-exchange chromatography column. DOP, DOPa, and DOPb were characterized by monosaccharide composition and methylation analyses, and spectral analyses (FT-IR and 1 H and 13 C NMR). All of them are composed of mannose and glucose, at similar ratios; and have a similar structure with a backbone of 1, 4-linked β-D-mannopyranosyl and β-D-glucopyranosyl residues. Significant differences were observed only in their molecular weights. The molecular weights of DOP, DOPa, and DOPb are 7.3 × 10 5 , 8.1 × 10 5 , and 6.7 × 10 5 Da, respectively. DOP, DOPa, and DOPb enhanced cell proliferation, TNF-α secretion, and phagocytosis of RAW264.7 cells in a dose-dependent manner using MTT assays, ELISA, and flow cytometry, respectively. They also induced the proliferation of lymphocytes alone and with mitogens [1]. DOPa and DOPb are thus proven to be major, active polysaccharide markers of D. officinale. Rhodiola rosea extract has been proved to be a health product for fatigue resistance, so it was used as positive control for determining the anti-fatigue effect of DOP. Mice dosed with DOP and R. rosea extract showed significant increases weight-loaded swimming endurance duration time [2]. The swimming time of mice fed with DOP is much longer than that of mice fed with R. rosea extract. Thus, DOP, which exceeds 30% of the dry herb by weight, has stronger anti-fatigue activity than R. rosea extract. As such, DOP has significant potential for pharmaceutical development into health products to reduce fatigue. Acknowledgements: This study was supported by HKSAR Innovation and Technology 460 Fund (ITF), Tier 3, ITS/311/09, and Hong Kong Baptist University (RC-start up grant, MPCF-001 – 2014/2015, and FRG2/14 – 15/028).