Abstract
Purpose: :
To determine whether exposure to flavonoids will provide long–term protection from oxidative stress–induced death in human RPE cells and to investigate the mechanisms of action of this protection.
Methods: :
ARPE19 cells were exposed to various dietary flavonoids in RPMI media for 24–48 hours prior to exposure to cytotoxic concentrations of either t–BOOH or H2O2. ARPE19 cell survival was determined 24 hours later using the MTT assay. We compared the intracellular levels of reactive oxygen species (ROS) and the intracellular levels of glutathione between RPE cells that had been treated with flavonoids and RPE cells that were exposed to oxidants alone. Additionally, we examined the expression of the transcription factor, Nrf2, and various downstream phase 2 detoxification enzymes, including heme–oxygenase 1, to determine whether there was an association between the flavonoids which provided long–term protection and those which induced phase 2 detoxification enzymes.
Results: :
Specific dietary flavonoids provide long–term protection of ARPE19 cells from oxidative stress–induced cell death. Exposure to specific flavonoids is associated with an increase in intracellular levels of glutathione, a decrease in reactive oxygen species (ROS) and an induction of phase 2 detoxification enzymes. Interestingly, some compounds that showed minimal protection with short–term (1 hr.) exposure to flavonoids showed excellent protection with long–term exposure (24–48 hrs).
Conclusions: :
The induction of phase 2 detoxification enzymes in human RPE cells may play an important role in the long–term protection seen with flavonoid treatment in the setting of oxidative stress. These results suggest that specific dietary flavonoids may be beneficial for the treatment of patients with macular diseases associated with oxidative stress in vivo.
Keywords: oxidation/oxidative or free radical damage • protective mechanisms • age-related macular degeneration