Damaging Capacity of Five Metal Cations on Escherichia coli Plasmid DNA
The toxic effects of five metal cations, frequently in contact with humans, have been analyzed in this study. Anthropogenic activities, such as mining, cause elevated levels of cobalt in soil and water. Other common environmental pollutants found in mining effluent include the heavy metals: copper, iron, and manganese. Stannous chloride (SnCl2) is widely used in nuclear medicine as a reducing agent for products radiolabeled with technetium-99m. The ability of these five heavy metals to mediate a Fenton-like reaction was observed through the alteration of plasmid topology. Treatment of Escherichia coli plasmid DNA with CuCl, SnCl2, and FeCl2 resulted in DNA singlestrand breaks in a dose-dependent manner. Sodium benzoate, a free radical scavenger, and EDTA, a metal ion chelator, both inhibit the DNA damage. The data indicate a correlation between the formation of reactive oxygen species and DNA damage. Also, the presence of a slow-migrating band after treatment with copper, tin, and iron suggests these metal cations produce an additional plasmid topology.