Physicochemical properties and immunomodulatory effects of polysaccharides isolated from Styela plicata

The physicochemical properties and immunomodulatory effects of polysaccharides isolated from the sea squirt Styela plicata were investigated. The crude polysaccharide (SP) was further fractionated into an unabsorbed fraction (SF-1) and absorbed fractions (SF-2 and SF3) to isolate polysaccharides with different molecular weights. The major constituents in the crude and fractionated polysaccharides were total carbohydrate (28.03-42.65%), uronic acid (9.88-23.76%), sulfate (18.03-29.25%), and protein (1.48-26.47%). The average molecular weights of the fractionated polysaccharides ranged from 28 to 1,187 kDa. The significant monosaccharide components of the polysaccharides were galactose (27.91-62.21%), glucose (14.79-37.63%), and glucosamine (10.74-28.31%). FT-IR analysis indicates that SP, SF-1, SF-2, and SF-3 were sulfated polysaccharides. SF-1 increased the production of nitric oxide and cytokines, such as tumor necrosis factor alpha and interleukin 6, in a dose-dependent manner in RAW 264.7 cells. Further, polymerase chain reaction analysis revealed that the mRNA expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) was markedly increased. These results indicate that SF-1 can enhance the activation of macrophages and that increasing the molecular weight and the uronic acid and sulfate content of fractionated polysaccharides can enhance their immunomodulatory function.