Structure elucidation of arabinogalactan and arabinogalacturonan from the root of Scutellaria baicalensis Georgi and evaluation on their immunoregulating effects via TLR2 pathway

Polysaccharides were extracted from the roots of Scutellaria baicalensis Georgi using hot water and ethanol precipitation method. The SBP-1 and SBP-2, were obtained after eluting from DE-52 column. The molecular weight, monosaccharide composition and linkage types of SBP-1 and SBP-2 were determined by the high performance gel permeation chromatography, high-performance anion exchange chromatography, gas chromatography–mass spectroscopy and NMR spectra. SBP-1 and SBP-2 were characterized as a homogenous polysaccharide with Mw of 80.5 and 25.8 kDa, respectively. Moreover, there were seven linkage types in the SBP-1 and it was a type II arabinogalactan formed by a (1→6)-linked β-d-Galp main chain. Whereas, except for the linkage types of α-l-Araf-(1→, →5)-α-l-Araf-(1→ and →3,5)-α-l-Araf-(1→, the SBP-2 enriched with →3,4)-α-d-GalpA-(1→, →4)-α-d-GalpA-(1→ and →4)-α-d-GalpA(OMe)-(1→, indicating the pectic type arabinogalacturonan structure. Moreover, both SBP-1 and SBP-2 exhibited immunoregulatory effects on RAW 264.7 cells by modulating the toll-like receptor (TLR) signaling pathway, as demonstrated through RNA-seq analysis, western blotting, immunoprecipitation (IP) experiments, and surface plasmon resonance (SPR) analysis. These findings suggest an immunological basis for the therapeutic potential of S. baicalensis.