Structural characterization and oxidative stress modulation activity of an acidic Heteropolysaccharide from Microctis...

Microctis folium has served as a traditional edible and medicinal herb for centuries. While extensive studies have focused on its secondary metabolites, the structural and functional roles of its polysaccharides remain underexplored. Here, we isolated and characterized of MFP-I, an acidic heteropolysaccharide (8.38 kDa) from M. folium aqueous extract. MFP-I primarily comprises glucuronic acid (33.6 %), D-galactose (25.9 %), L-rhamnose (18.2 %), and galacturonic acid (11.3 %). Structural analysis (methylation, 1D/2D-NMR) revealed a backbone of →3,6)-β-D-Galp-(1 → 2,4)-α-L-Rhap-(1 → 4)-α-D-GalAp-(1 → 3)-α-L-Rhap-(1 → 3)-β-D-GlcAp-(1→, with a β-D-Galp-(1 → 6)-β-D-Galp-(1 side chain attached to the O-3 position of the →3,6)-β-D-Galp-(1 → residue, and another α-D-Glcp-(1 → 6)-α-D-Glcp-(1 → 4,6)-α-D-Glcp-(1 → linked to the O-2 position of the →2,4)-α-L-Rhap-(1 → residue. Additionally, an α-L-Araf-(1 → 5)-α-L-Araf-(1 → motif is linked to the O-4 position of →4,6)-α-D-Glcp-(1 → in the latter branched chain. MFP-I exhibited potent antioxidative activity via DPPH· and ·OH radical scavenging, and conferred neuroprotection in H₂O₂-stressed HT-22 cells and LPS-stimulated BV2 microglia. Mechanistically, its efficacy was linked to Keap1-Nrf2 pathway modulation and neuroinflammation attenuation. Furthermore, MFP-I significantly reduced tBHP-induced ROS levels (p < 0.01), and extended the mean lifespan of tBHP-challenged Caenorhabditis elegans by 11.12 % (200 μg/mL) and 19.15 % (400 μg/mL), as well as the whole lifespan curves (p < 0.05). This work bridges a critical knowledge gap in M. folium polysaccharides and highlights their therapeutic potential.