Chemoprevention of Tumor Metastasis by Liposomal β-Sitosterol Intake

To investigate chemopreventive effect of liposomal β-sitosterol on tumor metastasis, we prepared liposomal β-sitosterol composed of egg yolk phosphatidylcholine for oral delivery. Although orally administered β-sitosterol (4μmol as β-sitosterol/mouse) was not absorbed into plasma, the amount of immune response cytokines such as IL-12 and IL-18 was increased in the small intestine after the liposome intake. Moreover, after daily oral administration of the liposome for 7 d, natural killer (NK) cell activity in the mice was increased, suggesting that the immune surveillance activity of mice was enhanced by the liposomal β-sitosterol intake. Thus, we examined metastatic potential of B16BL6 melanoma cells, which were intravenously injected into mice after sequential administration of liposomal β-sitosterol for 7 d. The number of metastatic colonies in the lungs was significantly less than that of control group two weeks after the injections of the cells. These results suggest that daily liposomal β-sitosterol intake prevents tumor metastasis may be due to enhancement of gut immune surveillance systems.