OBJECTIVETo investigate the effect of magnolol on proliferation and apoptosis of HL-60 cells and its mechanism.

METHODSMTT assay was used to measure the proliferation of HL-60 cells after treatment with different concentration of magnolol (5, 10, 20, 40, 80 and 160 µg/ml). The morphological changes of HL-60 cells were examined by light microscopy, and DAPI staining was performed to observe the nuclear morphology of HL-60 cells. The early cell apoptosis was detected by flow cytometry with Annexin V-FITC/PI double-staining. RT-PCR was carried out to examine the mRNA expression of BAX and BCL-2. Western blot was performed to detect the protein expression of caspase family.

RESULTSThe magnolol inhibited HL-60 cell proliferation, and the inhibitory rate of cell proliferation increased significantly in a dose- and time- dependent manner (P < 0.05). HL-60 cells became small, even apoptotic bodies appeared after treatment with magnolol. In addition, nuclear condensation or fragmentation could be observed, which is the typical morphological features of apoptosis. When HL-60 cells were treated with 40 µg/ml of magnolol for 24 h, the ratio of early apoptotic cells reached to (11.7 ± 2.4) %, which was significant different from control (1.4 ± 1.1) % (P < 0.05). RT-PCR results showed that treatment of HL-60 cells with magnolol up-regulated the expression of BAX, whereas down-regulated the expression of BCL-2. Western blot results showed that the cleavages of caspase-3, -8 and -9 were significantly enhanced by magnolol.

CONCLUSIONThe magnolol can significantly inhibit the proliferation of HL-60 cells and induce the apoptosis of HL-60 cells, which may occur through up-regulation of BAX, down-regulation of BCL-2 and the activation of caspases.