OBJECTIVEThe aim of this study was to explore the molecular mechanism of apoptosis in esophageal cancer cells induced by Isodon rubescens.

METHODSThe DNA-damage effect of Jaridonin was detected by single cell gel electrophoresis (SCGE). The p53 protein was determined by Western blot. GSH assay kit was employed to determine the GSH content in human esophageal cancer EC-1 cells. Intracellular levels of hydrogen peroxide (H2O2) or superoxide (O(2).-) were determined using the redox-sensitive probes 2', 7'-dichlorodihydrofluorescein diacetate (DCF) or dihydroethidium (DHE), and the fluorescence signal was assayed by fluorescence microscopy and by flow cytometry.

RESULTSJaridonin induced DNA damage in EC-1 cells remarkably. The olive tail moments (OTM) of control and 20, 40 µmol/L Jaridonin were 3.2, 45.2 and 89.0, respectively. Compared with the control, the differences were significant (P < 0.01 for both). Jaridonin resulted in extensive p53 up-regulation in the EC-1 cells. More importantly, the p53 up-regulation occurred as early as 2 h after Jaridonin incubation, and in a time-dependent manner (P < 0.05). p53 siRNA transfection inhibited apoptosis in the EC-1 cells, and the Jaridonin-induced apoptosis rate was reduced from 38.5% to 8.8%. Intracellular level of H2O2 was increased by Jaridonin, whereas the level of O(2).- was barely changed. The GSH content in EC-1 cells was reduced from (10.3 ± 1.6) nmol/mg protein to (4.6 ± 2.1) nmol/mg protein after 20 µmol/L Jaridonin incubation for 8 h, and it was further reduced with the increase of Jaridonin concentration. Jaridonin induced DNA damage, H2O2 accumulation and apoptosis were significantly attenuated in the presence of GSH, but Jaridonin showed little effect on normal human liver L-02 cells.

CONCLUSIONSJaridonin selectively induces apoptosis in esophageal cancer EC-1 cells through H2O2-mediated DNA damage by depleting GSH.