Immunostimulating activities and anti-cancer efficacy of rhamnogalacturonan-I rich polysaccharide purified from Panax ginseng leaf

Abstract

This study aimed to evaluate the anti-cancer effects as well as stimulation of various immune related factors such as complementary system, macrophages, and NK cells of polysaccharides isolated from Panax ginseng (P. ginseng) leaf. The polysaccharide fractions (PGEP, PGEP-I, –II, and –III) isolated from P. ginseng were contained rhamnose (Rha), arabinose (Ara), galactose (Gal), galacturonic acid (GalA), and glucuronic acid (GlcA), all of which are typical sugar components of rhamnogalacturonan (RG)-I. Only PGEP-I reacted with the β-glucosyl Yariv reagent (37.29%), indicating the presence of type-II arabinogalactan. Additionally, methylation analysis indicated the PGEP-I mainly comprised 19 different sugar linkages including 4-linked GalpA, 2,4-linked Rhap, 3,6-linked Galp, 5-linked Araf, terminal GlcpA, and terminal Arap which are characteristics of RG-I. Meanwhile, PGEP-I enhanced the production of cytokines such as interleukin (IL)-6, IL-12, and tumor necrosis factor-α and augmented the complement system. The intravenous administration of PGEP-I activated the natural killer (NK) cells in a dose-dependent manner against YAC-1. Prophylactic intravenous administration of PGEP-I significantly suppressed Colon26-M3.1 carcinoma inoculation-induced lung cancer (48.7%). Moreover, the anti-cancer effects of PGEP-I were significant even though NK cell functions were blocked by anti-asialo GM1. The findings suggest that PGEP-I, an RG-I polysaccharide, not only activates the complement system, macrophages and NK cells, but also has strong anticancer effects that inhibit lung cancer.