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K.–. Ha, Y. Chen, J. Cai, P. Sternberg, Jr.; Zinc Activates the ARE–Dependent Antioxidant Response in the RPE . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1376.
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The Age–Related Eye Disease Study (AREDS) demonstrated that zinc, alone or with antioxidants, significantly reduced the risk of progression from moderate to advanced age–related macular degeneration (AMD) and the risk of moderate vision loss. The aim of this study is to determine the molecular mechanisms underlying the protective effects of zinc against oxidative stress induced retinal pigment epithelial (RPE) cell damage, which has been implicated in AMD pathogenesis.
Cultured ARPE–19 cells were treated with zinc at different concentrations and for varying time periods. Cellular glutathione (GSH) and glutathione disulfide (GSSG) levels were measured by high performance liquid chromatography (HPLC). Glutamate–cysteine ligase (GCL) expression was measured by quantitative reverse transcriptase polymerase chain reaction (RT–PCR). Nrf2 (nuclear factor erythroid2–related factor) activity was measured using a dual luciferase assay after transfection of ARPE–19 cells with reporter plasmids containing the antioxidant response element (ARE). Small interference RNA (siRNA) approach was used to knock down the expression of Nrf2, which was confirmed by Western blot analysis.
Zinc significantly increased the intracellular GSH level in ARPE–19 cells through induction of the de novo synthesis pathway. At 150 µM, zinc increased the GSH level by 70%. At similar concentrations, zinc upregulated the GCL mRNA level and activated the ARE–Nrf2 pathway. The effects of zinc on ARE–Nrf2 activation and GSH synthesis were abolished by knock down of Nrf2 expression using the siRNA approach.
Induction of the ARE–Nrf2 pathway in cultured RPE cells by zinc provides powerful and prolonged antioxidation and detoxification that may explain the beneficial effects of zinc observed in the treatment of AMD.
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