Polysaccharide from alfalfa activates RAW 264.7 macrophages through MAPK and NF-κB signaling pathways

Alfalfa polysaccharide (APS), a bioactive compound extracted from alfalfa, has been proposed to exhibit potential growth-promoting and immune-enhancing functions. But, little is known about the cellular immunomodulatory and intrinsic molecular mechanisms. Here we extracted the APS, and performed in vitro experiments to characterize the immunomodulatory functions as well as the molecular mechanisms of APS on RAW 264.7 macrophages cells. Chemical analyses showed that APS was mainly composed of fucose, arabinose, galactose, glucose, xylose, mannose, galacturonic acid and glucuronic acid. The results of in vitro assays demonstrated that 50 and 100 μg/mL APS increased the cell viability of RAW 264.7 cells. The secretion and gene expression of NO/iNOS, IL-6 and TNF-α in APS-induced macrophage cell were significantly enhanced. However, APS-induced TNF-α production was decreased by blocking the MAPK or NF-κB signaling pathways, especially for the blockade of p38. Moreover, APS enhanced the phosphorylation of p38, ERK, and JNK, promoted the degradation of IκBα, and increased the nuclear translocation of NF-κB p65 subunit. Therefore, we demonstrated that APS could improve the immune functions of RAW 264.7 macrophages cells by promoting the cell viability and increasing secretion and gene expressions of NO/iNOS, IL-6 and TNF-α through the MAPK and NF-κB signaling pathways.