Immunostimulatory effects of rhamnogalacturonan-I fraction purified from Glycyrrhiza glabra roots on cyclophosphamide-induced immunosuppressed mice

The present study aimed to investigate the immunostimulatory activities of polysaccharides purified from Glycyrrhiza glabra root. First, five polysaccharide fractions were separated from G. glabra through hot water extraction, ethanol precipitation, enzymatic hydrolysis, and size exclusion chromatography. Among them, G. glabra polysaccharide-enzyme (GRPE)-I showed the potent stimulation effect on cytokine secretion from peritoneal macrophage. Moreover, glycosidic linkage analysis indicated the GRPE-I mainly comprised 4-linked galacturonic acid, 2,4-linked rhamnose, 3,6-linked galactose, 4,6-linked galactose, and 5-linked arabinosef, which are characteristics of rhamnogalacturonan (RG)-I type polysaccharide. Immunostimulatory effect of GRPE-I in vivo was investigated in cyclophosphamide (CTX)-induced immunosuppressed mice model. As a results, the pre-administration of GRPE-I demonstrated significant benefits against reducing body weight and damaging lymphoid tissue. Additionally, GRPE-I affected regulation of various immunocytes population such as macrophage, natural killer cell, CD4+ T cell, CD8+ T cell. Serum and spleen tissue analysis results indicate improvement about immunoglobulin and cytokine levels by GRPE-I. These results are strongly correlated with the activation of the mitogen-activated protein kinase and nuclear factor-kappa B pathways. Furthermore, CTX-induced short chain fatty acid impairment was reversed by GRPE-I. In conclusion, GRPE-I, which is a RG-I type polysaccharide isolated from G. glabra, exhibits significant potential as a novel immunomodulator.