Structural characterization and immunoregulatory activity of polysaccharides from Dendrobium officinale leaves

In this study, two kinds of polysaccharides from leaves of Dendrobium officinale, namely DLP‐1 and DLP‐2, were obtained by hot water extraction, ethanol sedimentation, and chromatographic separation using DEAE‐52 cellulose and Sephadex G‐100 columns. They were composed of different monosaccharides and the content of monosaccharides varied significantly while DLP‐1 (Mw 1.38 × 106 Da) was mainly composed of mannose (71.69%) and glucose (22.89%), and DLP‐2 (Mw 1.93 × 106 Da) was constituted by rhamnose (35.05%), arabinose (24.12%), and galactose (25.65%). A triple‐helical conformation was exhibited by both of them. The scanning electron microscope image of DLP‐1 showed an irregular and large lamellar shape, as well as a smooth surface and a porous interior, illustrating they had an amorphous structure. In contrast, DLP‐2 revealed a rough, loose, and uneven surface consisting of large sponge‐like particles. Nuclear magnetic resonance analysis showed that (1→4)‐β‐D‐Manp, (1→4)‐β‐D‐Glcp, and (1→4)‐2‐O‐acetyl‐β‐D‐Manp were the main linkage types of DLP‐1, whereas DLP‐2 was constituted by a large amount of (1→4)‐β‐D‐Manp, (1→4)‐β‐D‐Glcp, and other residues. Besides, DLP‐1 and DLP‐2 stimulated the proliferation and phagocytic capacities of RAW 264.7 cells and improved the production of nitric oxide, interleukin‐6, TNF‐α, and IL‐1β. These results proved that both DLP‐1 and DLP‐2 possessed excellent immunoregulatory bioactivities and could be functional food or adjuvant drug. Practical applications The leaf of Dendrobium officinale is a by‐product with huge biomass. The lack of systematic research on its chemical composition and pharmacologic effect, leading to a great waste of resources. In order to maximize the value of D. officinale, this study aimed to investigate the structural characteristics and immunologic effects of two polysaccharide fractions (DLP‐1 and DLP‐2) from D. officinale leaves, showing that DLP‐1 and DLP‐2 in D. officinale leaves could be used as anti‐inflammatory agents to avoid wasting. Two novel polysaccharides were extracted from the leaves of Dendrobium officinale. The structural features of the two polysaccharides were investigated. Both polysaccharides showed potential immunoregulatory activities.