Suppression of the formation of H
-induced ROS formation in PC12 cells by water extracts of the biennial flower. A: Cultured PC12 cells were pre-labeled DCFH-DA for one hour before the addition of various concentrations of H2O2 (0, 1.7, 3.4, 6.8 and 13.6 μg/ml) for another hour. The amount of ROS was fluorometrically measured with excitation at 485 nm and emission at 530 nm. B: Water and ethanol extracts of the biennial flower (1 mg/ml) were pre-treated with the PC12 cells for 24 hours. H2O2 (13.6 μg/ml) was used in the ROS formation assay as in A. Vitamin C (35.2 μg/ml) served as positive control. Data were expressed as% of inhibition where all the values were normalized by the control (no drug treatment), Mean ± SD, n = 4. Statistical significance is indicated as * P = 0.00419 for control (without extract) vs 30% EtOH and *** P = 0.000269 for control (without extract) vs water.