Tumoricidal effects of a selenium (Se)-polysaccharide from Ziyang green tea on human osteosarcoma U-2 OS cells

Selenium(Se)-enriched green tea consumption in human diets is well-known to reduce the risk of a variety of diseases. Here, we isolated a Se-polysaccharide (Se-ZYTP) from Se-enriched Ziyang green tea and investigated its antitumor activity on human osteosarcoma U-2 OS cells in vitro and in vivo. Se-ZYTP contained 94.5% of carbohydrate and 2.1% of uronic acid, as well as 2.14 μg/g Se, revealing that Se-ZYTP was an acidic Se-conjugated polysaccharide. Monosaccharide composition analysis indicated that Se-ZYTP consisted of mannose, rhamnose and fucose in molar ratios of 2.4:1.5:1.2:0.2:0.1:0.3:0.3. In vitro, both MTT and LTH assays proved that Se-ZYTP (25, 50, 100 and 200 μg/ml) could significantly inhibit the proliferation of human osteosarcoma U-2 OS cells in a concentration-dependent fashion (P<0.05 or P<0.01). In U-2 OS cancer xenograft model in BALB/c athymic mice, Se-ZYTP oral administration at three doses of 100, 200 and 400mg/kg body weight (B.W.) daily for 28 days resulted in obvious tumor regression as compared to model control (P<0.05 or P<0.01). In addition, body weights of mice in control or Se-ZYTP treated groups did not differ significantly and no mice died during experiment, suggesting the safety of Se-ZYTP. Therefore, we postulate that Se-ZYTP might have cancer-preventive and cancer-therapeutic benefit for human osteosarcoma.