Antioxidant effect of flavonoids after ascorbate/Fe2+-induced oxidative stress in cultured retinal cells

In this study, we investigated the structure-activity relationship of four flavonoids, i.e. eriodictyol, luteolin, quercetin, and taxifolin, in cultur ed retinal cells after ascorbate/Fe2+-induced oxidative stress. The relativ e order of antioxidant efficacy, determined by the thiobarbituric acid meth od, was the following: eriodictyol > quercetin > luteolin > taxifolin. Upon preincubation, the flavonoids were also effective in reducing the extent o f lipid peroxidation. Oxidative stress, determined by the changes in fluore scence of 2',7'-dichlorodihydrofluorescein, was also decreased in the prese nce of the flavonoids, showing the following order of antioxidant efficacy: eriodictyol > taxifolin approximate to quercetin > luteolin. Ascorbate/Fe2 +-induced oxidative stress or incubation in the presence of the flavonoids did not significantly affect the viability of retinal cells. We also evalua ted the degree of membrane partition of the flavonoids. In this system, the results strongly suggest that the higher antioxidant activity of the flavo noids is not correlated with the presence of a double bond at C-2-C-3 and/o r a hydroxyl group at C-3 on the C ring, but rather may depend on the capac ity to inhibit the production of reactive oxygen species to interact hydrop hobically with membranes. Eriodictyol was shown to be the most efficient an tioxidant in protecting against oxidative stress induced by ascorbate/Fe2in the retinal cells. (C) 2001 Elsevier Science Inc. All rights reserved.