Characterization of Macrophage-Activating Polysaccharide Isolated from Fermented Brown Rice

Brown rice has nutritional benefits due to its abundant nutrients and high dietary fiber content. However, it is often consumed in a fermented form for improved chewy texture and digestibility. In this study, a polysaccharide, FBR-4a, was isolated from fermented brown rice and its chemical composition was analyzed. In addition, its immune-stimulating activity was determined using RAW264.7 cells. FBR-4a is a carbohydrate and consists of nine types of monosaccharides, including galactose, arabinose, rhamnose, mannose, fucose, xylose, glucose, galacturonic acid, and glucuronic acid. FBR-4a increased the gene expression of iNOS and IL-6 and enhanced the production of immune-stimulatory molecules (nitric oxide [NO], IL-6, and TNF-α) in RAW264.7 cells. Western blot analysis showed that FBR-4a phosphorylated the mitogen-activated protein kinases, NF-κB and c-Jun (major component of AP-1 transcription factor) in RAW264.7 cells, in a concentration-dependent manner. FBR-4a-induced IL-6 and NO production was completely suppressed by IκBα and JNK inhibition, but not by ERK and p38 inhibition. Furthermore, the phosphorylation of c-Jun was also suppressed by IκBα and JNK inhibition. These findings suggest that FBR-4a isolated from fermented brown rice has immune potentiation activity on macrophages through IκBα and JNK signaling pathways, which play a central role in IL-6 and NO production.