Intracellular iron, but not copper, plays a critical role in hydrogen peroxide-induced DNA damage

The role of intracellular iron, copper, and calcium in hydrogen peroxide-in duced DNA damage was investigated using cultured Jurkat cells. The cells we re exposed to low rates of continuously generated hydrogen peroxide by the glucose/glucose oxidase system, and the formation of single strand breaks i n cellular DNA was evaluated by the sensitive method, single cell gel elect rophoresis or "comet" assay. Pre-incubation with the specific ferric ion ch elator desferrioxamine (0.1-5.0 mM) inhibited DNA damage in a time- and dos e-dependent manner. On the other hand, diethylenetriaminepentaacetic acid ( DTPA), a membrane impermeable iron chelator, was ineffective. The lipophili c ferrous ion chelator 1,10-phenanthroline also protected against DNA damag e, while its nonchelating isomer 1,7-phenanthroline provided no protection. None of the above iron chelators produced DNA damage by themselves. In con trast, the specific cuprous ion chelator neocuproine (2,9-dimethyl-1,10-phe nanthroline), as well as other copper-chelating agents, did not protect aga inst H2O2-induced cellular DNA damage. In fact, membrane permeable copper-c helating agents induced DNA damage in the absence of H2O2. These results in dicate that, under normal conditions, intracellular redox-active iron, but not copper, participates in H2O2-induced single strand break formation in c ellular DNA. Since BAPTA/AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraa cetic acid acetoxymethyl ester), an intracellular Ca2+-chelator, also prote cted against H2O2-induced DNA damage, it is likely that intracellular Ca2changes are involved in this process as well. The exact role of Ca2+ and it s relation to intracellular transition metal ions, in particular iron, need s to be further investigated. (C) 2001 Elsevier Science Inc.