Abstract: Objective:To study the effects of Ginkgo Biloba extract(GBE) on the differentiation and bone resorptionof the osteoclasts, and to clarify their mechanisms. Methods:The RAW264.7 cells were cultured in vitro, then were treated with receptor activator for nuclear factor-κB ligand (RANKL) and different concentrations of GBE. The cells were divided into blank control group(0 μg·L^-1 RANKL), RANKL group(100 μg·L^-1 RANKL), RANKL+75 mg·L^-1 GBE group,and RANKL+150 mg·L^-1 GBE group.The morphology and number of osteoclasts were assessed with TRAP staining assay, and bone resorption of GBE was examined with bone resorption pits assay. Flow cytometry was applied to analyze the the apoptotic rate of RAW264.7 cells and the cell cycle;the expression levels of nuclear factor of activated T cells 1 (NFATc1), DC-STAMP, Casthepin K,matrix metalloprotein 9(MMP-9), Bcl-2, Bax,P27 and Cyclin-D1 in the RAW264.7 cells were analyzed by RT-PCR method. Results:Compared with blank control group, the number of osteoclasts in RANKL group were significantly increased(P<0.01); compared with RANKL group,the number of osteoclasts in RANKL+75 mg·L^-1 GBE and RANKL+150 mg·L^-1 GBE groups were significantly decreased (P<0.05). Compared with blank control group,the area of bone resorption pit of bone slice in RANKL group was significantly increased(P<0.05);compared with RANKL group, the areas of bone resorption pit of bone slice in RANKL+75 mg·L^-1 GBE and RANK+150 mg·L^-1 GBE groups were significantly decreased (P<0.05). Compared with blank control group, the apoptotic rates of the RAW264.7 cells in 75 and 150 mg·L^-1 GBE groups were increased, and the expression levels of Bcl-2 in the RAW264.7 cells were significantly decreased and the expression levels of Bax were significantly increased (P<0.05). Compared with RANKL group, the G₀-G₁ phase arrest of the RAW264.7 cells in RANKL+75 mg·L^-1 GBE and RANKL 150 mg·L^-1 GBE groups were shortened;the expression levels of P27 in the RAW264.7 cells were significantly decreased and the expression levels of Cyclin-D1 were significantly increased (P<0.05). Compared with blank control group, the expression levels of NFATc1, DC-STAMP, Casthepin K and MMP-9 in the RAW264.7 cells in RANKL group were significantly increased(P<0.05); compared with RANKL group, the expression levels of NFATc1, DC-STAMP, Casthepin K and MMP-9 in the RAW264.7 cells in RANKL+75 mg·L^-1 GBE and RANKL+150 mg·L^-1 GBE groups were significantly decreased (P<0.05). Conclusion:GBE could inhibit the differentiation and bone resorption of the osteoclasts, and their mechanisms may be related to promoting the apoptosis of RAW264.7 and shortening the G₀-G₁ phase of the RAW264.7 cells.

Key words: Ginkgo Biloba extract, osteoclast, cell cycle, apoptosis