Antioxidant and prooxidant effects of polyphenol compounds on copper-mediated DNA damage Nathan R. Perron, Carla R. García, Julio R. Pinzón, Manuel N. Chaur, Julia L. Brumaghim ⁎ Department of Chemistry, Clemson University, Clemson, SC 29634-0973, United States abstract article info Article history: Received 25 August 2010 Received in revised form 16 February 2011 Accepted 17 February 2011 Available online 26 February 2011 Keywords: Polyphenol Antioxidants Copper DNA damage Redox cycling Radical scavenging Inhibition of copper-mediated DNA damage has been determined for several polyphenol compounds. The 50% inhibition concentration values (IC 50 ) for most of the tested polyphenols are between 8 and 480 μM 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 H 2 O 2 , it is likely that weak polyphenol-Cu I interactions permit a redox-cycling mechanism, whereby the necessary reactants to cause DNA damage (Cu I ,H 2 O 2 , 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. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Oxidative DNA damage has been implicated as a cause of cardiovascular disease [1,2,3–5] and cancer [6,7], as well as aging, Alzheimer's, and Parkinson's diseases [8–11]. Hydrogen peroxide oxidizes Cu I , resulting in the formation of hydroxyl radical (•OH) via a Fenton-type reaction [12,13] and causing DNA damage (Fig. 1). Cellular reductants such as ascorbate [14,15] then reduce Cu II to Cu I , the primary copper oxidation state in cells [16]. Evidence also suggests that Cu II causes oxidative DNA damage in the presence of H 2 O 2 via a copper-coordinated peroxy species or singlet oxygen ( 1 O 2 ) generation [17,18]. In addition, Cu II may react with O 2 •- to regenerate both H 2 O 2 and Cu I (Fig. 1) [19]. This redox cycling of copper makes formation of •OH catalytic in vivo [20]. Although iron-mediated oxidative DNA damage by •OH has been proposed as the primary cause of cell death under oxidative stress conditions in both prokaryotes and eukaryotes, including humans, Cu I can generate DNA damaging •OH 60 times faster than Fe II [21]. It has been calculated that the intracellular concentration of non- protein-bound copper is less than 10 -18 M in bacteria and yeast, corresponding to less than one non-protein-bound copper ion per cell [22]. However, free copper has recently been found in the mitochon- dria and neuronal cells of higher organisms [23,24], and localized on nucleic acids in vivo [25–27]. Using microprobe X-ray absorption measurements in mouse fibroblast cells, Yang, et al. observed a low- coordinate Cu I complex different from the Cu I bound to metallothio- nein or glutathione, suggesting a kinetically labile pool of copper in the mitochondria and Golgi apparatus [23]. Stöckel et al. reported normal concentrations of labile copper in human brain tissue to be 80 μM, with particular abundance in the locus ceruleus (1.3 mM) and the substantia nigra (0.4 mM) [28], the center for dopamine production [24]. Although copper is a required nutrient, due to its potential toxicity and ability to generate radical species, the intracellular transport of copper is tightly regulated by chaperone proteins that deliver copper ions to copper-requiring proteins, such as ATPases [29], CuZn superoxide dismutase [30], and cytochrome oxidase [31]. However, normal copper homeostasis in humans may be disrupted, as in Menkes and Wilson diseases [32]. Koizumi, et al. observed that Long Evans Cinnamon rats (an animal model for Wilson disease) showed a marked increase in plasma and liver concentrations of copper (0.26– 2.87 μM and 0.13–5.1 μmol per gram of protein, respectively). This increased copper pool resulted in liver dysfunction, hepatitis, and cancer [33]. Also, if dietary copper intake exceeds the recommended daily allowance for humans, hepatic accumulation of copper can occur, resulting in symptoms of oxidative stress [19,34,35]. While it is often believed that histone proteins offer some protection to DNA, oxidative damage to nuclear DNA has been observed in the presence of histones, and several studies have found that histones increase copper-mediated oxidative DNA damage [36–38]. Therefore, understanding and controlling copper-mediated DNA damage is a major motivation for the prevention and treatment of copper-related diseases. Journal of Inorganic Biochemistry 105 (2011) 745–753 ⁎ Corresponding author. Tel.: +1 864 656 0481; fax: +1 864 656 6613. E-mail address: brumagh@clemson.edu (J.L. Brumaghim). 0162-0134/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jinorgbio.2011.02.009 Contents lists available at ScienceDirect Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio