Structure and immunostimulatory activity studies on two novel Flammulina velutipes polysaccharides: revealing potential impacts of →6)-α-D-Glc p (1→ on the TLR-4/MyD88/NF-κB pathway.

Two novel Flammulina velutipes ( F. velutipes ) polysaccharides, FVPH1 and FVPH2, were isolated and purified after hot water extraction. The structural characterization revealed that the backbone of FVPH1 consisted mainly of →6)-α-D-Glc p (1→, →3,4)-α-D-Gal p (1→, →4)-α-L-Fuc p (1→, and →4)-β-D-Man p (1→, while the backbone of FVPH2 consisted of →3)-α-D-Gal p (1→, →3,4)-α-D-Man p (1→,→6)-α-D-Glc p (1→. The branches of FVPH1 contained →6)-α-D-Glc p (1→ and α-D-Glc p (1→ and the branches of FVPH2 consisted of →3)-α-D-Gal p (1→, →6)-α-D-Glc p (1→, and β-L-Fuc p (1→. FVPH2 exhibited significantly better immunostimulatory activity than FVPH1 ( P < 0.05), as evidenced by the increased expression of NO, IL-1β, IL-6, and TNF-α and pinocytic activity of RAW264.7 cells. As the most abundant structure in the polysaccharides of F. velutipes , the content of →6)-α-D-Glc p (1→ might play a crucial role in influencing the immunostimulatory activity of F. velutipes polysaccharides. The F. velutipes polysaccharide with a lower content of →6)-α-D-Glc p (1→ and a higher branching degree could significantly enhance the immunostimulatory activity of F. velutipes polysaccharides via activating the TLR-4/MyD88/NF-κB pathway more effectively.