探討霍山石斛多醣體的結構與活性

Abstract

霍山石斛是一種珍稀且具有多功能的中草藥，《本草綱目拾遺》曾經記載霍山石斛具有抗發炎，防癌，明目以及調節免疫的功能。然而，霍山石斛的多醣體結構與活性關係尚未建立。在本篇研究中，第一，探討具有免疫活性的霍山石斛多醣體結構。結果指出具有免疫活性的霍山石斛多醣體萃取物之單醣組成為甘露醣(79%) 和葡萄醣(21%)，且是一種包含部分乙醯基的葡萄甘露聚醣，而經鹼液處理去除乙醯基之霍山石斛多醣體則失去刺激細胞激素產生的能力。第二，探討霍山石斛多醣體對老鼠以及人類的細胞實驗中，誘導細胞激素和趨化素表現的能力。結果發現霍山石斛多醣體可以表現數種細胞激素如干擾素-伽瑪 (IFN-γ), 介白素-6 (IL-6), 介白素-10 (IL-10), 顆粒球巨噬細胞聚落刺激因子 (GM-CSF)和白血球生長激素 (G-CSF)。特別的是，霍山石斛多醣體比靈芝多醣體能誘導更多的G-CSF，它是一種能夠刺激骨髓性細胞生長的重要細胞激素。第三，探討具免疫活性的最小寡醣片段。初步結果指出，5-10顆甘露醣所組成的β-1,4-甘露寡醣片段，可經由結合接受器DC-SIGN, 活化MEK1和轉錄因子NF-κB，進而引發訊息傳導來刺激G-CSF的表現，因此是擁有免疫活性的最小寡醣片段。本篇提供一個清楚的證據在研究霍山石斛之多醣體結構和免疫活性之間的關係，因此霍山石斛多醣體萃取物可作為刺激G-CSF分泌或是保健食品開發之藥用植物。

Dendrobium huoshanense (DH) is a valuable and versatile Chinese herbal medicine with the anecdotal claims of anti-inflammatory, cancer prevention, eye-benefiting and immune-modulatory effects. However, structure and bioactivity of the polysaccharide in medicinal plant DH are limited. In this report, first, characteristics of polysaccharide extracted from DH (DHPS) were determined. DHPS was demonstrated a partial acetylated gluco-mannan with monosaccharide composition of Man (79%) and Glc (21%). Moreover, deacetyl-DHPS failed to induce cytokine production. Second, we investigated the effects of DHPS on inducing cytokines and chemokines in mice and human models in vitro. We found that DHPS induced IFN-γ, IL-6, IL-10, GM-CSF and G-CSF. Notably, DHPS induced larger amounts of G-CSF than Reishi F3. Third, we identified the minimal active oligosaccharide for further intracellular signaling of G-CSF elucidation. We demonstrated that M13, a putative minimal active structure from DH, involves G-CSF production through DC-SIGN-mediated activation of MEK1 and NF-κB. Here we provided clear evidence for the structure and activity relationship of the DHPS. Therefore, polysaccharide extracted from medicinal plants Dendrobium huoshanense can be used as immune-modulatory agent for G-CSF production and/or potential applications for health food development.