| Background and objectUrsolic acid (UA) is a kind of triterpenoid compound which exists widely in natural plants and has a variety of activities such as hepatoprotection, anti-inflammation, anti-atherosis, anti-tumor and immunomodulation. Recently, considerable attention has been devoted to its anti-tumor effect. It was found that UA had growth inhibiting, apoptosis inducing and cytotoxic effects on many cancer cell lines. But the exact mechanism of UA such effects is poorly understood. The present study was designed to investigate the anti-tumor effect of UA on human gastric carcinoma BGC-823 cells. MethodsHuman gastric carcinoma BGC-823 cells were cultured in RPMI-1640. Cell proliferation inhibition was detected by MTT assay. DNA fragmentation was determined by DNA electrophoresis. Cell cycle and apoptosis rate was analyzed by flow cytometry. Fas antigen expression on BGC-823 cells surface was detected with Fas monoclonal antibody and then analyzed by FCM. The expression of Bcl-2 and activity of caspase-8, -3 were detected by western blot. Results1. MTT assay showed that UA can inhibit proliferation of BGC-823 cells effectively in a dose- and time-dependent manner. After BGC-823 cells were treated by UA for 24h, the IC50 value was 43.10μmol/L.2. After treatment with 50, 60μmol/L UA for 24h, DNA ladder of apoptosis was observed by gel electrophoresis, The cells treated with 0, 20, 30,40μmol/L of UA for 24h could not observe the DNA ladder.3. Cell cycle and apoptosis rate analysis found that treatment with UA for 24 hours resulted in a S-phase arrest and G1-phase decline, while no significant change was observed in G2/M-phase. The Apo-peak was observed in DNA content frequency histograms. After treated with 0, 20, 30, 40, 50 and 60μmol/L UA for 24h, the cellsapoptosis rate was increased, respectively.4. The Fas expression on BGC-823 cell was very low (0.92%), after the treatment with U A for 24h, the expression of Fas was not changed.5. Western blot analysis indicated that UA decreased Bcl-2 protein levels in a dose manner. After cells were treated with UA, the procaspase-8 cleavaged to the intermediate cleavage products of 43kD and 41kD, and the active subunit of 18kD. Procaspase-3, which is a 32 kD protein, diminished in treated groups in a dose-dependent manner, meanwhile, cleavaged active fraction, which is 17 kD and 19 kD, increased.ConclusionUA has inhibitory and apoptosis-inducing effects on BGC-823 cells in a time-and dose-dependent manner. UA may function towards BGC-823 cells in S-phase and inhibit its into G2/M phase, which may result in DNA injury and induce cell apoptosis. UA can down-regulate the expression of Bcl-2, release cytochrome c and induce the activation of caspase-3, these suggest that UA may induce the apoptosis by mitochondria pathway. In addition, UA lead to activation of caspase-8, which also can activate caspase-3 and induce the apoptosis of BGC-823 cells.
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