Physicochemical properties and immune enhancement activity of oligosaccharide fraction purified from biomass of green macro-algal Ulva prolifera

Ulva prolifera (U. U. prolifera), ), as the dominant species of green macro-algal bloom, caused great damage to marine aquaculture and economy. This study was carried out to find its industrial utilization ways by determination the structure characteristics and the immune enhancement effect of oligosaccharide fractions produced from this alga. The result indicated that oligosaccharide fraction of F3 showed the best immune enhancement activity via RAW 264.7 macrophages and zebrafish assays. Chemical and structural analysis indicated that F3 with 11.14% sulfate content was composed of rhamnose, xylose, and glucose in ratio of 77.11:16.33:6.56. NMR spectroscopy showed that F3 contained (1-* 4)-alpha-L-rhamnopyranose-3-SO3 L-rhamnopyranose-3-SO 3 and alpha-L-rhamnopyranose-3-SO3-(1 L-rhamnopyranose-3-SO 3-(1-* 4)-(3-Dxylopyranose, with sulfate groups located at C-3 of rhamnopyranose. The results of immune effect in vitro demonstrated that F3 increased the production of nitric oxide (NO) and prostaglandin E2 (PGE2) 2 ) with up- regulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression. F3 also promoted the secretion of cytokines (TNF-alpha, IL-1(3 and IL-6) and activated the expression of mitogen-activated protein kinases (MAPK) and NF-kappa B signaling pathways. In vivo assay, F3 boosted the embryo survival rate and heart rate, as well as promoted the generation of NO and reactive oxygen species (ROS) in a dose-dependent manner. The novel structure and excellent activity in this study suggested that F3 could be the potential material for use as a natural immuno-enhancing agent in the biomedical and functional food industries.