Isolation, structure identification and anti-inflammatory activity of a polysaccharide from Phragmites rhizoma

Phragmites rhizoma (PR) is comprised of polysaccharides as its main active component. Currently, there are few studies on polysaccharides from PR, especially in purification and structure. In this study, an acidic polysaccharide (PRP-2) was obtained from PR by ultrasonic assisted extraction and secondary column chromatography purification (Diethylaminoethyl cellulose-52 (DEAE-52) and Sephadex G-100). Its structural characteristics were investigated by the gel permeation chromatography (GPC), gas chromatography and mass spectrometry (GC-MS), infrared spectroscopy (IR) and nuclear magnetic resonance (NMR) spectroscopy. The results showed that PRP-2 possessed the molecular weight of 20,332 Da and contained total sugars (71.73%), uronic acids (7.51%), proteins (0.57%) and sulfate radical (9.38%). The polysaccharide was composed of Galactose (34.70%), Fucose (36.15%) and a small amount of Rhamnose (0.88%) with a molar ratio of 39.50: 41.15: 1.00. It consisted of three sugar residues, →3)-β-D-GalpA-(1→, →2, 3)-α-L-Fucp-(1→ and α-L-Fucp (4SO₃^-) -(1→. PRP-2 could protect RAW246.7 macrophages from the cytotoxic effect induced by lipopolysaccharide (LPS), inhibit the LPS-induced NO production in RAW246.7 macrophages, which displayed its anti-inflammatory activity. Therefore, PRP-2 has the potential to be used as a functional component.