Two polysaccharides from the roots of Uncaria rhynchophylla: Structural characteristics, immunopotentiation activity,...

Numerous studies have documented the abundant chemical constituents and broad pharmacological effects of Uncaria rhynchophylla, yet research on the structure and bioactivity of its polysaccharides remains unreported. This study aimed to explore the structural features and immunopotentiation activity of two polysaccharides (URP90-1 and URP90-3) from U. rhynchophylla roots. Structure analysis revealed that URP90-1 (3745 Da) mainly contained →1)-β-D-Manp-(4→, →1)-α-L-Araf-(3,5→, →1)-α-D-Glcp-(4→, and t-α-D-Glcp residues as backbone, with →1)-α-L-Araf-(5→, t-β-D-Manp, and t-α-D-Galp as side chains. Whereas, URP90-3 (3405 Da) exhibits a backbone of t-α-L-Araf, →1)-α-L-Araf-(3,5→, →1)-β-D-Galp-(4,6→, →1)-β-D-Galp-(6→, →1)-β-D-Manp-(3,6→, and t-β-D-Galp, bearing →1)-β-D-Galp-(4→, →1)-α-L-Araf-(5 →, and t-α-L-Araf side chains. A key structural distinction between them was the presence of glucose and a higher content of (1 → 4)-glycosidic linkages in URP90-1. Further pharmacological studies revealed that URP90-1 and URP90-3 exhibited immunopotentiation activity in vitro cell-based assays and in vivo zebrafish models by activating the TLR4/MyD88/NF-κB pathway. Biolayer Interferometry (BLI) assays confirmed the binding of both polysaccharides to the TLR4 receptor, with URP90-1 exhibiting better affinity. Furthermore, a structure-activity relationship analysis revealed that URP90-1 exhibits better immunopotentiating activity than URP90-3, likely due to a higher content of glucose and (1 → 4)-glycosidic linkages in URP90-1. Our results revealed that URP90-1 and URP90-3, particularly URP90-1, are promising candidates for development as immune enhancers.