DNA-BASE MODIFICATIONS AND MEMBRANE DAMAGE IN CULTURED-MAMMALIAN-CELLS TREATED WITH IRON IONS

We investigated DNA base damage in mammalian cells exposed to exogenou s iron ions in culture. Murine hybridoma cells were treated with Fe(II ) ions at concentrations of 10 mu M, 100 mu M, and 1 mM. Chromatin was isolated from treated and control cells and analyzed by gas chromatog raphy/mass spectrometry for DNA base damage. Ten modified DNA bases we re identified in both Fe(II)-treated and control cells. The quantifica tion of modified bases was achieved by isotope-dilution mass spectrome try. In Fe(II)-treated cells, the amounts of modified bases were incre ased significantly above the background levels found in control cells. Dimethyl sulfoxide at concentrations up to 1 M in the culture medium did not significantly inhibit the formation of modified DNA bases. A m athematical simulation used to evaluate the plausibility of DNA damage upon Fe(II) treatment predicted a dose-dependent response, which agre ed with the experimental results. In addition, Fe(II) treatment of cel ls increased the cell membrane permeability and caused production of l ipid peroxides. The nature of DNA base lesions suggests the involvemen t of the hydroxyl radical in their formation. The failure of dimethyl sulfoxide to inhibit their formation indicates a site-specific mechani sm for DNA damage with involvement of DNA-bound metal ions. Fe(II) tre atment of cells may increase the intracellular iron ion concentration and/or cause oxidative stress releasing metal ions from their storage sites with subsequent binding to DNA. Identified DNA base lesions may be promutagenic and play a role in pathologic processes associated wit h iron ions.