Partial chemical structure and immunomodulating activities of RGAP (Red Ginseng acidic Polysaccharide) from Korean red ginseng (Panax ginseng C. A. Meyer)

A red ginseng acidic polysaccharide (RGAP) with immunomodulating antitumor activities was isolated from Korean red ginseng, steamed and dried ginseng (Panax ginseng C. A. Meyer). The molecular weight of RGAP was estimated to be 12–450 kDa by gel filtration chromatography. RGAP has been found to increase survival rate and to inhibit of tumor growth significantly in a dose dependent manner in mice transplanted with tumor cells. RGAP significantly promoted nitric oxide (NO) production from peritoneal macrophages both in vivo and in vitro. Western blot analysis exhibited a newly synthesized inducible nitric oxide synthase (iNOS) protein band in the RGAP treated group. It seems likely that immunomodulating antitumor activities of RGAP are mainly mediated by NO production of macrophage. RGAP was further purified by ultrafiltration and anion exchange chromatography on DEAE-sepharose, followed by gel filtration on Sephacryl S-300 to give an active fraction (GFP) with stronger NO production in murine macrophages. GFP increased survival rate ten times compared to RGAP in male ICR mice transplanted with sarcoma 180 and also showed more potent tumoricidal activities of natural killer cells than RGAP. Sugar composition(mol %) of GFP was found to be arabinose: rhamnose: xylose: galacturonic acid: mannose: galactose: glucose (10:9:1:25:8:20:27) by GC/MS. Partial acid hydrolysis of GFP resulted in acidic oligosaccharides, and a combination of enzymatic digestion(Endo-α-D-(1→4)-polygalacturonase) and methylation analysis, MALDI-TOF-MS, PSD analysis of the acidic oligosaccharides suggested that GFP comprised a galactogalacturonan core such as –α-D-GalA-(1→4)-α-D-GalA-(1→4)-α-D-GalA-(1→6)-α-D-Gal as the acidic moiety. The results suggest that certain galactogalacturonan core chains are responsible for immunomodulating antitumor activities as well as nitric oxide (NO) production.

Acknowledgement: This work was supported by a grant(GP-303) from Korea Ginseng Corporation.