OBJECTIVETo explore the role of autophagy in quercetin (Que)-induced apoptosis in human bladder carcinoma BIU-87 cells in vitro.

METHODSTo determine the proliferative inhibition by MTT colorimetric assay after treating BIU-87 cells with quercetin at various concentrations. To identify autophagy and apoptosis in the BIU-87 cells after Que treatment by monodansylcadaverin (MDC) and Hoechst 33258 fluorescent staining, respectively. To examine the cytotoxic effect of Que and influence of autophagy on apoptosis by studying LDH leakage rate and flow cytometry, after blocking the autophagy with 3-methlyadenine (3-MA), a specific autophagy inhibitor.

RESULTSThere was an obvious inhibitory effect of Que on the proliferation of BIU-87 cells in a time- and dose-dependent manner. The inhibition rate of BIU-87 cells after 200 µmol/L Que treatment for 72 hours was 89.2%. Autophagy and apoptosis were induced and detected in Que-treated BIU-87 cells and autophagy occurred earlier than apoptosis. The apoptosis peak became much higher after the autophagy was blocked. Whenever the autophagy was blocked before or after Que treatment, the Que-induced cytotoxicity in BIU-87 cells was enhanced.

CONCLUSIONSQuercetin significantly inhibits the proliferation of BIU-87 cells, and the autophagy is induced earlier than apoptosis. In the process of Que-induced apoptosis of BIU-87 cells, autophagy may play a protective role at the initiation phase, delay apoptosis and reduce the Que-induced death of BIU-87 cells.