Anti-metastatic effect of polysaccharide isolated from Colocasia esculenta is exerted through immunostimulation.

In the present study, an edible corm of the plant Colocasia esculenta, commonly known as Taro was extracted with cold water (4˚C). Finally, 10.44 g (1.04%) of the crude polysaccharide (Taro-0) was obtained from Taro. The purified active compound (Taro-4-I) was isolated using DEAE-Sepharose FF and Sephadex G-100. The anti-complementary activity of Taro-4-I (57.3±4.5%) was similar to that of polysaccharide K (used as the positive control). The molecular weight of Taro-4-I was 200 kDa and it was a polysaccharide composed of 64.4% neutral sugars and 35.6% uronic acid. Taro-4-I activated the complement system through the classical and alternative pathways. The treatment of peritoneal macrophages with Taro-4-I significantly increased the production of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α) in a dose-dependent manner. However, IL-12 production showed maximal activity at 56 µg/ml and subsequently decreased. Splenocytes obtained from mice which were administered Taro-4-I intravenously showed a higher toxicity to Yac-1 cells compared to those obtained from untreated mice in a effector‑to‑target (E/T) ratio-dependent manner. The group treated with 50 µg/ml Taro-4-I showed a significantly increased toxicity to Yac-1 cells compared to the group treated with 500 µg/ml Taro-4-I. The administration of Taro-4-I significantly inhibited the lung metastasis of B16BL6 melanoma cells. However, the group treated with 50 µg/mouse Taro-4-I had a significantly lower number of tumors compared to the group injected with 500 µg/mouse Taro-4-I.