Structural elucidation and immunoregulatory activity of a new polysaccharide obtained from the edible part of Scapharca subcrenata

Scapharca subcrenata, a delicious and functional seafood, has been used as a tonic in traditional Chinese food and pharmacology for a long time. Polysaccharides have been considered as the key pharmacological ingredient in S. subcrenata. In this present study, a novel immunomodulatory polysaccharide SSPW50–1 (4.87 × 106 Da) was purified from S. subcrenata for the first time. NMR spectra and compositional analysis indicated that it was a glucan, with a backbone consisted of (1 → 4)-α-D-Glcp, and (1 → 4,6)-α-D-Glcp while the side chain was composed of (1→6)-α-D-Glcρ and (1→)-α-D-Glcp. SSPW50–1 increased RAW264.7 cell pinocytosis, endocytosis and secretion of inflammatory mediators. Results of flow cytometric analysis demonstrated that SSPW50–1 also caused the up-expression of the M1-type markers CD86 and MHC II in macrophages. The results suggested that SSPW50–1 activated macrophages via the TLR2 and MAPK/Akt/NF-κB signalling pathways. Furthermore, SSPW50–1 exerted an immunomodulatory effect in the 4T1 breast cancer mouse model by upregulating the proportion of M1-type tumour-associated macrophages (TAMs) to inhibit tumour growth. SSPW50–1 might serve as a good food supplement for enhancing immunity and preventing cancer.