2’, 7’-dichlorodihydrofluorescein diacetate H2DCFDA (Molecular Probes, Invitrogen) was used for the detection of reactive oxygen species (ROS). HFL-1 cells treated with 2 μg/ml QUER, 0.5, 2 and 5 μg/ml QU-CAP or the diluents (0.1% DMSO or 0.1% CAP) for 24 h, were resuspended in PBS ± the dye at a final concentration of 10 μM (loading buffer) and incubated at 37°C for 30 min. The loading buffer was then removed; cells were resuspended in prewarmed complete medium and incubated at 37°C for 5 min. The absorption and the emission of the oxidation product were measured at 493 and 520 nm respectively. Each sample was measured in triplicates. In replica cultures, cells were additionally incubated with 300 μM H2O2 in the presence or absence of the substances for 2.5 h and cells were then collected for detection of ROS.