The flavonoid, eriodictyol, induces long-term protection in ARPE-19 cells through its effects on Nrf2 activation and phase 2 gene expression.

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. 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. 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 overexpress 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. 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.