RESUMO
The aim of this study was to investigate the effect of betulinic acid on inducing apoptosis of human multiple myeloma RPMI-8226 cell line. The inhibitory effect of betulinic acid on proliferation and its inducing apoptosis effect, influence on cell cycle and induced morphological changes of RPMI-8226 were evaluated by MTT, flow cytometry Annexin-V/PI double staining, flow cytometry with PI staining and fluorescence microscopy with Hoechst33258 staining, respectively. The transcription level changes of bcl-xl gene and caspase 3 which are two kinds of apoptosis related protein gene were determined by RT-PCR. The results showed that within a certain range of concentration (0, 5, 10, 15, 20 microg/ml), IC50 of betulinic acid to RPMI-8226 at 24 hours was 10.156+/-0.659 microg/ml, while the IC50 at 48 hours was 5.434+/-0.212 microg/ml, and its inhibiting effect on proliferation of RPMI-8226 showed both time-and dose-dependent manners. Flow cytometry with Annexin-V/PI double staining revealed that apoptotic rate of RPMI-8226 cells increased as betulinic acid concentration increased. Flow cytometry with PI staining showed that the ratio of cells in G0/G1 phase increased, while it in S phase decreased, and ratio of cells at G2/M phase did not present a significant change. Morphological differences were typical and obvious between cells in treated and control groups under fluorescence microscope using Hoechst33258 staining. RT-PCR detection of caspase 3 gene indicated that its transcription level showed an increasing trend as the concentration of betulinic acid increased, while the bcl-xl showed the opposite trend. It is concluded that the betulinic acid can induce apoptosis of RPMI-8226 within a certain range of concentration in a time- and dose-dependent manners. This phenomenon may be related to the transcriptional level increase of caspase 3 gene and decrease of bcl-xl. Betulinic acid also affects G1/S in cell cycle which arrests cells at phase G0/G1.