Effects of rhamnogalacturonan-I type polysaccharide purified from Curcuma longa on immunostimulatory and intracellular signaling pathway mechanisms of macrophages

Abstract

In previous study, potent anti-metastatic activities of turmeric-derived pectic polysaccharide (TP) via immune enhancing effects of intravenous and oral administration were evaluated. The present study was designed to elucidate intracellular signaling pathway for macrophage activation by the rhamnogalacturonan-I type polysaccharide (TPE-I) purified from TP. TPE-I increased the production of interleukin (IL)-6, tumor necrosis factor (TNF)-α, and nitric oxide (NO) by RAW264.7 cells. In addition, immunoblotting analysis indicated that TPE-I dose-dependently phosphorylated the mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) pathways. Subsequently, TPE-I induced the translocation of activated NF-κB into the nuclei, which was observed by confocal laser scanning microscopy. In the specific inhibitor experiments, cytokines and chemokine secretions were found to be suppressed by BAY11-7082, JNK inhibitor II, and SB20358. Furthermore, the experiments with neutralizing antibodies showed that pattern recognition receptors, such as dectin-1, toll-like receptor (TLR)2, TLR4, cluster of differentiation (CD)14, complement receptors (CR)3, mannose receptor (MR), and scavenger receptor (SR) were involved in cytokine and chemokine secretions by TPE-I in RAW264.7 cells. Consequently, these results suggest that TPE-I phosphorylated the MAPK and NF-κB signaling pathways via mainly the dectin-1, TLR2, TLR4, CD14, CR3, MR, and SR receptors to macrophage, and subsequently induced the secretion of IL-6, TNF-α and NO.