In vitro and in vivo immune-enhancing effects of polysaccharides with different molecular weights and structural characteristics from Gastrodia elata Blume

Research on high-molecular-weight polysaccharides tends to be more difficult and lag in terms of their fine structures and bioavailability. We focused on Gastrodia elata Blume polysaccharides (GEPs) with different molecular weights and structural characteristics to reveal their bioactivities, especially those abundant high-molecular-weight GEPs. A novel high-yield polysaccharide (GEP1-2) with the high molecular weight of 3.21 × 10⁶ Da was first purified. Through conventional and enzymolysis-assisted analyses, GEP1-2 was an α-D-(1,4)(1,6)-glucan with unique linkages of →2)-β-D-Frucf-(1→, →4)-β-D-Glcp-(1→ and p-hydroxybenzyl alcohol citrate (HAC), and its main local fine structure had α-1-Glcp, α-1,4-Glcp, α-1,6-Glcp, β-1,6-Galp, and α-1,4,6-Glcp at the molar ratio of 1.20∶17.74∶2.71∶0.98∶0.76. Another refined GEP3-3 with 1.91 × 10⁴ Da was identified as an α-1,4- and α-1,4,6-glucan (molar ratio of 4.91∶1.02). It was noteworthy that all GEPs could induce the release and mRNA expressions of NO and cytokines in RAW264.7 macrophages. Specially, the high-molecular-weight polysaccharides showed comparable in vitro immune-enhancing effects to the low-molecular-weight polysaccharide. Furthermore, the macromolecular GEP1-2 could dose-dependently increase the organ coefficient of thymus and cytokine levels of TNF-α and IL-6 in mouse serum as well as in splenic lymphocytes. These efforts will be of great significance when proceeding to the safe relief or therapy of macromolecular GEPs for immunologic diseases.