Abstract: Objective: To explore the selective effects of cyclamin on the proliferation and apoptosis of the liver cancer cells in vitro, and to clarify the molecular target and the underlying mechanisms.Methods: The human liver cancer HepG2 cells or normal human HL-7702 liver cells were divided into cyclamin groups (added with 0, 2.5, 5.0 and 10.0 μmol·L^-1 cyclamin), cholesterol intervention group (cyclamin + 20.0 mg·L^-1 cholesterol) and control group (0.5% DMSO only). MTT assay was performed to determine the survival rates of cells in various groups. The cellular cholesterol level was measured by Filipin staining. Lactate dehydrogenase (LDH) release assay was used to determine the LDH realease levels in cells. Flow cytometry was used to detect the apoptotic rates of cells. The expressions of Fas, FADD and caspase-8 proteins were measured by Western blotting method.Results: The survival rates of HepG2 cells in 5.0 and 10.0 μmol·L^-1 cyclamin groups were significantly lower than those of HL-7702 cells (P<0.05).The Filipin staining results showed that the cholesterol level in HepG2 cells was higher than that in HL-7702 cells (P<0.05).The LDH release levels in HepG2 cells in cyclamin groups were higher than those in than HL-7702 cells(P<0.05). Compared with 5.0 μmol·L^-1 cyclamin group, the LDH release level and the apoptotic rate in cholesterol intervention group were decreased(P<0.05).The Western blotting results showed that the expression levels of Fas,FADD and caspase-8 proteins in HepG2 cells in cyclamin groups were increased compared with control group(P<0.05);compared with cyclamin group, the expression levels of Fas, FADD and caspase-8 proteins in cholesterol intervention group were decreased(P<0.05).Conclusion: Cyclamin can selectively inhibit the proliferation of liver cancer cells, and its molecular mechanisms may be related to the increased cell membrane permeabilization via targeting membrane cholesterol component and the consequent ligand-independent activation of Fas signaling pathway.

Key words: cyclamin, liver neoplasms, cholesterol, Fas signaling pathway, apoptosis