Objective: To observe the effect of different concentrations of Celastrus orbiculatus extract (COE) on proliferation and apoptosis of U251 cells (a glioblastoma cancer cell line)

and its possible molecular mechanism. Method: U251 cells at the logarithmic growth phase were divided into control group and COE-treated group. 3-(4

5-dimethyl-2-thiazolyl)-2

5-diphenyl-2-H-tetrazolium bromide(MTT) assay and 5-bromo-2-deoxy uridine(BrdU) incorporation experiment were performed to observe the inhibitory effect on cell viability and proliferation

respectively. Annexin V/PI double staining was used to detect the effect of COE on U251 cell apoptosis. Ultrastructural changes of U251 cells after COE treatment were observed under transmission electron microscope; the protein expressions of apoptosis marker B-cell lymphoma-2/Bcl-2-associated X (Bcl-2/Bax) and Caspase-3 were detected by Western blot. Result: Compared to control group

the proliferation of U251 cells in COE-treated group were significant inhibited by COE (P<0.05). COE could induce the early apoptosis and ultrastructure changes of U251 cells

and apoptotic bodies were observed under transmission electron microscope. The protein expressions of Bcl-2/Bax and Caspase-3 were changed in a concentration dependent manner. Conclusion: COE can effectively inhibit the proliferation of U251 cells by down-regulating the expression of Bcl-2/Bax and increasing the protein expression of Caspase-3

and promoting the apoptosis of cell

suggesting that COE can be used as a drug candidate for treating glioblastoma.