Effect of juglone in Qinglongyi on cell cycle status and apoptosis in A-549 cells

To explore the inhibition of juglone in Qinglongyi on A-549 cells in vitro, MTT assay was used. Laser confocal scanning microscope with AV-PI staining was used to observe apoptotic morphology. Changes of cell cycle are studied by flow cytometry analysis. The result of MTT assay showed that juglone had a marked growth inhibition in A-549 cells and the IC50 is respectively 3.4 times 10^-5mol/L, 1.8 times 10^-5mol/L and 2.6 times 10^-6 mol/L after treatment for 24, 48 and 72 h by juglone. Through Laser confocal scanning microscope, we can see that juglone can induce the apoptosis, cells in the early stage of apoptosis were only stained by Annexin V-FITC, while necrotic cells and cells in the late stage of apoptosis were stained by both Annexin V-FITC and PI and appeared to be red inside and green outside. Cell cycle changes are analyzed by flow cytometry with cells at G₁ phase significantly less than those of control and cells at G₂ phase significantly more than those of control. This study has demonstrated for the first time that juglone from Qinglongyi can inhibit the proliferation of A-549 cells and block their cell cycle at the G₂ phase, thus inducing apoptosis in these cells in distinct dose-dependent manner. But the specific mechanism responsible for the blocking of cell cycle and the induction of apoptosis has to await further research.