Antitumor and antimetastatic activities of rhamnogalacturonan-II-type polysaccharide isolated from mature leaves of green tea via activation of macrophages and natural killer cells

To investigate the antitumor and antimetastatic polysaccharide from the mature leaves of green tea, GTE-II was purified using size exclusion chromatography. GTE-II consisted of 15 different sugars including rarely observed sugars such as 2-O-methyl-fucose, 2-O-methyl-xylose, apiose, aceric acid, 3-deoxy-d-manno-2-octulosonic acid, and 3-deoxy-d-lyxo-2-heptulosaric acid, which were characteristics of pectic polysaccharide rhamnogalacturonan-II. Treatment of peritoneal macrophages with GTE-II not only increased interleukin (IL)-6 and IL-12 production, but also had significantly increased tumoricidal activity against Yac-1 tumor cells than those obtained from untreated mice. In an assay of natural killer (NK) cell activity, intravenous administration of GTE-II significantly stimulated NK cytotoxicity against Yac-1 tumor cells. Furthermore, the depletion of NK cells by injection of rabbit anti-asialo GM1 serum eliminated the inhibitory effect of GTE-II on B16BL6 melanoma cells. These data suggest that GTE-II inhibits tumor metastasis, and its antitumor effect is associated with activation of macrophages and NK cells.