The EtOAc fraction from Taraxacum coreanum showed the strongest radical scavenging activity. The protective activity of active EtOAc fraction against the oxidative stress was investigated under cellular system using LLC-PK₁ renal epithelial cell. The LLC-PK₁ cells showed loss of the cell viability and elevation for lipid peroxidation by the treatment with generator of peroxynitrite (ONOO^－), 3-morpholinosydnonimine, and its precursors, nitric oxide (NO) and superoxide anion (O₂^－), produced by sodium nitroprusside and pyrogallol, respectively. However, the treatment of the EtOAc fraction significantly, dose-dependently, recovered cell viability and inhibited lipid peroxidation against both ONOO^－ itself, and its precursors of NO and O₂^－. At 100Ռg/ml of the EtOAC fraction, the cell viability was significantly increased to 93.4% from 61.0%, and lipid peroxidation was inhibited to 0.104 nmol/mg protein from 0.494 nmol/mg protein. The present study suggests that T. coreanum would have the protective potential from ONOO^－-induced oxidative stress. (Cancer Prev Res 17, 0-256, 2012)

Keywords: Taraxacum coreanum, LLC-PK₁, Peroxynitrite, Superoxide anion, Nitric oxide