Many naturally occurring phenolic compounds, such as bioactive substances in plants, grape seed proanthocyanidins, tea polyphenol, curcumin, and ginger oleoresin, have been reported to possess antioxidant properties [15-20].
Ginger oleoresin, which is extracted from ginger by a supercritical C[O.sub.2] fluid-extracted method, is a nonvolatile pungent mixture .
Treatment with Ginger Oleoresin and Irradiation Schedule.
The absorbance of formazan solution can be quantified by a spectrophotometer, and hence, this method can be applied to assess the cytoprotective ability and the toxicity of ginger oleoresin based on the viability of cells.
The treated cell samples (hMSCs, hMSCs + ginger oleoresin, hMSCs + [gamma]-ray irradiation, and hMSCs + ginger oleoresin + [gamma]-ray irradiation) were incubated in the presence of 10 [micro]M DCF[H.sub.2]-DA in DMEM-F12 medium at 37[degrees]C for 20 min and then washed three times with DMEM-F12 medium to remove the extracellular DCF[H.sub.2]-DA.
For comet assay, hMSCs were pretreated with [10.sup.-4] g/mL ginger oleoresin and cultured for 2 h followed by exposure to [gamma]-rays at the Irradiation Center.
After treatment with or without ginger oleoresin and [gamma]-ray irradiation, cells were cultured for 24 h.
Nrf2 siRNA was used for knocking down Nrf2 in hMSCs to explore whether the antioxidant effect of ginger oleoresin was through the Nrf2 pathways.