The Flavonoid, Eriodictyol, Induces Long-term Protection in ARPE-19 Cells through Its Effects on Nrf2 Activation and Phase 2 Gene Expression

PURPOSE. Eriodictyol, a flavonoid found in citrus fruits, is among the most potent compounds reported to protect human RPE cells from oxidative stress-induced cell death. The present study sought to determine whether eriodictyol-induced phase 2 protein expression further enhances the resistance of human ARPE-19 cells to oxidative stress. METHODS. The ability of eriodictyol to activate Nrf2 and to induce the phase 2 proteins heme-oxygenase (HO)-1 and NAD-( P) H: quinone oxidoreductase (NQO)-1, and the cellular antioxidant glutathione (GSH) were analyzed. Cytoprotection assays in ARPE-19 cells that were overexpressing HO-1 or NQO-1 were performed, cell survival after short-term and long-term eriodictyol treatment was compared, and the mechanism of protection using a dominant negative Nrf2 and shRNA specific for HO-1 was tested. RESULTS. Eriodictyol induced the nuclear translocation of Nrf2, enhanced the expression of HO-1 and NQO-1, and increased the levels of intracellular glutathione. ARPE-19 cells that over-express HO-1 or NQO-1 were more resistant to oxidative stress-induced cell death than control cells. Eriodictyol induced long-term protection significantly greater than its short-term protection. This effect was correlated temporally with the activation of Nrf2 and the induction of phase 2 enzymes and could be blocked with the use of a dominant negative Nrf2 and shRNA specific to HO-1. CONCLUSIONS. These findings indicate that the greatest benefit from eriodictyol may be its ability to regulate gene expression and enhance multiple cellular defenses to oxidative injury. (Invest Ophthalmol Vis Sci. 2009;50:2398-2406) DOI:10.1167/iovs.08-2088