Extraction, Structure and Immunoregulatory Activity of Low Molecular Weight Polysaccharide from Dendrobium officinale

Abstract

The ethanol precipitation method has been widely-used for Dendrobium officinale polysaccharides preparation. However, the alcohol-soluble fractions have always been ignored, which causes significant wastes of resources and energies. In this study, the extraction, physicochemical properties, and immune regulation activity of an edible D. officinale polysaccharide (DOPs) isolated from the supernatant after 75% ethanol precipitation were systematically investigated. The structural characteristics determination results showed that DOPs was mainly composed of glucose and mannose at a molar ratio of 1.00:5.78 with an average molecular weight of 4.56 × 10³ Da, which was made up of α-(1,3)-Glcp as the main skeleton, and the α-(1,4)-Glcp and β-(1,4)-Manp as the branches. Subsequently, the cyclophosphamide (CTX)-induced immunosuppressive mice model was established, and the results demonstrated that DOPs could dose-dependently protect the immune organs against CTX damage, improve the immune cells activities, and promote the immune-related cytokines (IL-2, IFN-γ and TNF-α) secretions. Furthermore, DOPs treatment also effectively enhanced the antioxidant enzymes levels (SOD, GSH-Px) in sera and livers, therefore weakening the oxidative damage of CTX-treated mice. Considering these above data, DOPs presented great potential to be explored as a natural antioxidant and supplement for functional foods.

Keywords: D. officinale; immunoregulatory activity; low-molecular weight polysaccharide; structural characteristics.

Figure 1

The flow diagram of extraction and purification process for DOPs (a); UV-vis spectrum (b) and HPGPC profile (c) in DOPs.

Figure 2

GC spectra of six monosaccharide standards (a) and DOPs (b) (Peaks identity: 1- L-rhamnose; 2- D-arabinose; 3- D-xylose; 4- D-mannose; 5- D-glucose; 6- D-galactose; 7- myo-inositol hexaacetate); FT-IR spectrum (c) of DOPs.

Figure 3

The 1D ¹H (a) and 2D COSY (b) spectra of DOPs (solvent: D₂O).

Figure 4

The 2D HSQC (a)/HMBC (b) spectra and possible chemical structure (c) of DOPs.

Figure 5

Flow chart of animal experiment (a) and effects of DOPs on the organ indices (b). Note: ^α p < 0.05 vs. the blank group; ^β p < 0.05 vs. the model group.

Figure 6

Effects of DOPs on the splenic T lymphocytes proliferations induced by Con A (a), the splenic B lymphocytes proliferations induced by LPS (b), phagocytic activity of peritoneal macrophages (c), and splenic NK cytotoxic activity (d) in immunosuppressed mice. Note: ^α p < 0.05 vs. the blank group; ^β p < 0.05 vs. the model group.