Can nucleotides prevent Cu-induced oxidative damage?

Cu-induced oxidative damage is associated with cancer, diabetes, neurodegenerative and age related diseases. The quest for Cu-chelators as potential antioxidants spans the past decades. Yet, biocompatible Cu-chelators that do not alter the normal metal-ion homeostasis are still lacking. Here, we explored the potential of natural and synthetic nucleotides and inorganic phosphates as inhibitors of the Cu(I)/(II)-induced ^{{radical dot}}OH formation via either the Fenton or Haber-Weiss mechanisms. For this purpose, we studied by ESR the modulation of Cu-induced ^{{radical dot}}OH production, from the decomposition of H₂O₂, by nucleotides and phosphates. ATP inhibited both Cu(I) and Cu(II) catalyzed reactions (IC₅₀ 0.11 and 0.04 mM, respectively). Likewise, adenosine 5′-β,γ-methylene triphosphate (AMP-PCP), adenosine 5′-O-(3-thiotriphosphate) (ATP-γ-S), ADP and tripolyphosphate were identified as good inhibitors. However, AMP and adenosine were poor inhibitors in the Cu(I)-H₂O₂ system, IC₅₀ ca. 1.2 mM, and radical enhancers in the Cu(II)-H₂O₂ system. The best antioxidant was adenosine 5′-[β,γ-imino] triphosphate (AMP-PNP) (IC₅₀ 0.05 mM at Cu(I)-H₂O₂ system) which was 15 times more active than the known antioxidant Trolox. ATP and analogues inhibit Cu-induced ^{{radical dot}}OH formation through an ion chelation rather than a scavenging mechanism. Two phosphate groups are required for making active Fenton-reaction inhibitors. Nucleotides and phosphates triggered a biphasic modulation of the Haber-Weiss reaction, but a monophasic inhibition of the Fenton reaction. We conclude that nucleotides at sub mM concentrations can prevent Cu-induced OH radical formation from H₂O₂, and hence may possibly prevent oxidative damage.