The structural discrepancy in the immunomodulatory potency of the polysaccharides RFHP-1 and RFHP-2 derived from Radix Fici Hirtae

Radix Fici Hirtae (RFH), a traditional Chinese medication, is said to be useful in controlling immunity. However, it remained unclear whether its polysaccharides components are associated with these immunomodulatory properties. Herein, two polysaccharides, designated RFHP-1 and RFHP-2, were isolated from RFH using water-soluble alcohol precipitation and column chromatography. Structural characterization by monosaccharide content analysis, methylation, and nuclear magnetic resonance spectroscopy (NMR) revealed that the main chain of RFHP-1 was formed by the interconnection of →4)-α-D-Glc p -(1→, →3,6)-β-D-Glc p -(1→, →3)-β-D-Glc p -(1→, and →4,6)-α-D-Glc p -(1→, and the main chain of RFHP-2 was formed by the interconnection of →4)-α-D-Glc p -(1→, →3,6)-β-D-Gal p -(1→, →3)-β-D-Gal p -(1→, →4,6)-α-D-Glc p -(1→ and →6)-β-D-Gal p -(1→. Both RFHP-1 and RFHP-2 raised the CD4/CD8 ratio and improved the expression of immune factors in immunocompromised mice. By activating the NF-κB pathway (promote phosphorylation of p65 and IκB), RFHP-1 and RFHP-2 both promoted release cytokines (NO, TNF-a, IL-6, and IFN-γ) at RAW 264.7 macrophages. The results of molecular docking (−8.4 kcal/mol vs. -6.0 kcal/mol) and isothermal titration calorimetry (ITC) (−7.75 kcal/mol vs. -7.46 kcal/mol) demonstrated that RFHP-1 exhibited stronger binding affinity with MD2, suggesting greater immunoactivating potential. These findings indicate that RFHP polysaccharides, particularly RFHP-1, may serve as promising candidates for development as dietary supplements for individuals with compromised immune systems.