Antioxidant and prooxidant effects of polyphenol compounds on copper-mediated DNA damage

Inhibition of copper-mediated DNA damage has been determined for several polyphenol compounds. The 50% inhibition concentration values (IC50) for most of the tested polyphenols are between 8 and 480 mu M for copper-mediated DNA damage prevention. Although most tested polyphenols were antioxidants under these conditions, they generally inhibited Cu-I-mediated DNA damage less effectively than Fe-II-mediated damage, and some polyphenols also displayed prooxidant activity. Because semiquinone radicals and hydroxyl radical adducts were detected by EPR spectroscopy in solutions of polyphenols, Cu-I, and H2O2, it is likely that weak polyphenol-Cu-I interactions permit a redox-cycling mechanism, whereby the necessary reactants to cause DNA damage (Cu-I, H2O2, and reducing agents) are regenerated. The polyphenol compounds that prevent copper-mediated DNA damage likely follow a radical scavenging pathway as determined by EPR spectroscopy. (C) 2011 Elsevier Inc. All rights reserved.