Structure and immunostimulatory activity studies on two novel Flammulina velutipes polysaccharides: revealing potential impacts of →6)-α-d-Glcp(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)-alpha-D-Glcp(1 ->, -> 3,4)-alpha-D-Galp(1 ->, -> 4)-alpha-L-Fucp(1 ->, and -> 4)-beta-D-Manp(1 ->, while the backbone of FVPH2 consisted of -> 3)-alpha-D-Galp(1 ->, -> 3,4)-alpha-D-Manp(1 ->,-> 6)-alpha-D-Glcp(1 ->. The branches of FVPH1 contained -> 6)-alpha-D-Glcp(1 -> and alpha-D-Glcp(1 -> and the branches of FVPH2 consisted of -> 3)-alpha-D-Galp(1 ->, -> 6)-alpha-D-Glcp(1 ->, and beta-L-Fucp(1 ->. FVPH2 exhibited significantly better immunostimulatory activity than FVPH1 (P < 0.05), as evidenced by the increased expression of NO, IL-1 beta, IL-6, and TNF-alpha and pinocytic activity of RAW264.7 cells. As the most abundant structure in the polysaccharides of F. velutipes, the content of -> 6)-alpha-D-Glcp(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)-alpha-D-Glcp(1 -> and a higher branching degree could significantly enhance the immunostimulatory activity of F. velutipes polysaccharides via activating the TLR-4/MyD88/NF-kappa B pathway more effectively.