Study of DNA damage caused by dipyrone in presence of some transition metal ions.

The DNA damage in the presence of dipyrone (used as its sodium salt, NaDip) and some transition metal ions in an air saturated ([O2 ] ≈ 0.25 mM) non-buffered solution at T = (25.0 ± 0.5)°C was investigated by agarose gel electrophoresis. As metal ions Cu2+ , Fe3+ , Ni2+ and Mn3+ were selected and evaluated in the present study because of the important role they play in a biological system. pUC19 plasmid DNA damage-induced by NaDip (80-600 μM) was observed in the presence of 100 μM Cu2+ . The damage was proportional to the NaDip concentration provided that the order of addition of reagents (pUC19 plasmid DNA + Cu2+  + NaDip) is obeyed. Addition in the reaction medium of ligands for Cu2+ and Cu+ , respectively EDTA and neocuproine, promoted total inhibition or reduction of the pUC19 plasmid DNA damage suggesting the involvement of the Cu2+ /Cu+ cycle. Besides, the decrease in the pUC19 plasmid DNA damage after addition of catalase (1.0 × 10-4  mg μL-1 ) in the same reaction medium indicates that H2 O2 is also involved in the damage process. In NaDip concentration range (80-600 μM), and under same the experimental conditions, it was not possible to conclude whether there was pUC19 plasmid DNA damage caused by 10 μM Fe3+ . No damage was observed in the presence of Mn3+ or Ni2+ . Although the technique used in this study is sensitive to detect the pUC19 plasmid DNA damage it was not possible to identify in which DNA base this damage occurs. Further studies with other techniques should be made to unambiguously identify the oxidative intermediates that are responsible for the DNA damage. As far as we know, this is the first study dealing with the pUC19 plasmid DNA damage-induced by NaDip in presence of copper, iron, nickel and manganese ions.