Structural characterization and anti-neuroinflammatory activity of a heteropolysaccharide isolated from the rhizomes of Polygala tenuifolia

Polygala tenuifolia Willd. is a vital industrial-export plant in Southeast Asia, particularly China. The rhizomes of P. tenuifolia are known for their nootropic and cognition-improving effects. As such, they have been widely used in traditional Chinese medicine (TCM) for centuries. However, the active constituents responsible for the biological benefits of P. tenuifolia remain unclear. In this study, P. tenuifolia rhizomes were extracted with hot water and then isolated and purified using diethylaminoethyl cellulose (DEAE-C) 52 and Sephacryl S-100 chromatographic columns. A homogeneous heteropolysaccharide (PTP70-2) with a relative molecular weight (MW) of 65.2 kDa was obtained. Based on monosaccharide composition, Fourier-transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC/MS), and nuclear magnetic resonance (NMR) analyses, PTP70-2 was composed of 11 residues: →5)-α-L-Araf-(1→, →2,5)-α-L-Araf-(1→, →3,5)-α-L-Araf-(1→, →6)-β-D-Galp-(1→, →6)-α-L-Manp-(1→, →4)-β-D-Galp-(1→, →4,6)-β-D-Galp-(1→, α-L-Araf, α-L-Rhap, α-D-GlcAp, and α-L-Manp, at a molar ratio of 7.3:1.4:5.2:15.0:2.1:2.4:5.6:8.2:1.3:1.5:1.3. Scanning electron microscopy (SEM) results showed that PTP70-2 had an irregular surface with scattered strips. Pharmacological assessments showed that PTP70-2 inhibited the production of nitric oxide (NO) in lipopolysaccharide (LPS)–induced pro-inflammatory BV2 microglial cells, and the inhibitory effect of 3.08 μM PTP70-2 was even greater than that of the positive control, 12.5 μM minocycline. In addition to NO, PTP70-2 significantly suppressed the expression of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Based on these results, the authors believe PTP70-2 is a new anti-neuroinflammatory agent that has great potential for the treatment and prevention of Alzheimer disease.