Study on Differences in Structure and Anti-Inflammatory Activity of Polysaccharides in Five Species of Dendrobium

Dendrobium is a famous edible and medicinal plants, and polysaccharides are their main bioactive components. Polysaccharides from five species, namely, DO (<i>Dendrobium officinale</i> Kimura et Migo), DH (<i>Dendrobium huoshanense</i> C. Z. Tang et S. J. Cheng), DNL (<i>Dendrobium nobile</i> Lindl.), DFH (<i>Dendrobium fimbriatum</i> Hook.), and DCL (<i>Dendrobium chrysanthum</i> Lindl.), were compared based on molecular weight (Mw), monosaccharide composition, and glycosidic bond types. The results showed that <i>Dendrobium</i> polysaccharides (DPs) contain relatively simple compositional monosaccharides and mainly consist of mannose (Man) and glucose (Glc), along with small amounts of arabinose (Ara), xylose (Xyl), and galactose (Gal). The Am/Ag (the ratio of Man to Glc) values in DO, DH, and DNL polysaccharides were 3.23, 3.81, and 3.88, while those in DFH and DCL were 0.45 and 0.81. DPs are mainly composed of →4)Man<i>p</i>(1→ and →4)Glc<i>p</i>(1→, but their molar ratios were different. →4)Man<i>p</i>(1→ and →4)Glc<i>p</i>(1→ ratios were 2.85, 2.92, 1.50, 1.45, and 1.05 in DO, DH, DNL, DFH, and DCL, respectively. Hierarchical cluster analysis (HCA) showed that there were significant differences in structural information, especially in glycosidic bond types and proportions. DH, DO, and DCL were clustered into different groups based on glycosidic bond types and proportions, respectively. Moreover, the five species of Dendrobium could significantly inhibit NO production and apoptosis induced by LPS in RAW 264.7, especially DH. The results of a correlation analysis of structure and anti-inflammatory activity showed that polysaccharides with a high →4)Man<i>p</i>(1→/→4)Glc<i>p</i>(1→ ratio and a molecular weight distribution between 3.343 × 10⁵ Da and 13.540 × 10⁵ Da had better anti-inflammatory activity. The results indicated that the quality evaluation of Dendrobium in clinical applications should investigate molecular weight and the composition of the glycoside bond types and proportions to ensure the consistency of curative effects.