Metal Ions Modify in Vitro DNA Damage Yields With High-LET Radiation

Cu 2+ and Co 2+ are metals known to increase DNA damage in the presence of hydrogen peroxide through a Fenton type reaction. We hypothesized that these metals could increase DNA damage following irradiations of increasing LET values as hydrogen peroxide is a product of the radiolysis of water. The reaction mixtures contain either double- or single-stranded DNA in solution with Cu 2+ or Co 2+ and was irradiated either with X-ray, carbon-ion or iron-ion beams or was treated with hydrogen peroxide or bleomycin at increasing radiation dosages or chemical concentrations. DNA damage was then assessed by gel electrophoresis followed by band intensity analysis. DNA in solution with metals demonstrated the most DNA damage when treated with hydrogen peroxide followed by irradiation with low-LET (X-Ray), high-LET (carbon-ion and iron-ion), respectively, and demonstrated the least damage with treatment of bleomycin. Cu 2+ portrayed greater DNA damage than Co 2+ following all experimental conditions. The metals effect caused more DNA damage and was observed to be LET dependent for single-strand break formation but inversely dependent for double-strand break formation. These results suggest that Cu 2+ is more efficient than Co 2+ at inducing both DNA single-strand and double-strand breaks following all irradiations and chemical treatments.