Dose-dependent effects of the water extract of the biennial flower against H
-induced cytotoxicity in PC12 cells. A: Extracts (1 mg/ml) of biennial flower by water and ethanol extractions were pre-treated with PC12 cells for 24 hours before the addition of H2O2 (13.6 μg/ml) for cytotoxicity test as in Figure 2. Vitamin C (35.2 μg/ml) served as positive control. B: Dose-dependent response was performed by pre-treating the culture with various concentrations of the water extract of the biennial flower (0.01-10 mg/ml). Data were expressed as% of control where the value of untreated culture was set as 100%, Mean ± SD, n = 4. Statistical significance is indicated as * P = 0.00471 for control (without extract) vs 30% EtOH and *** P = 0.000693 for control (without extract) vs water.