Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a seleno-organic compound with glutathione peroxidase-like activity, has been shown to be protective against brain ischemic injury and Parkinson's disease. This study was undertaken to investigate the protective effects of ebselen on oxidative DNA damage induced by dopamine in the presence of copper ions. Incubation of phiX-174 plasmid DNA with micromolar dopamine in the presence of Cu(II) resulted in a concentration-dependent induction of DNA strand breaks. Both a Cu(II)/Cu(I) redox cycle and H(2)O(2) formation were critically involved in the induction of DNA strand breaks by the dopamine/Cu(II) system. The presence of ebselen at micromolar concentrations led to a marked concentration-dependent inhibition of DNA strand breaks induced by the dopamine/Cu(II) system. Further studies showed that ebselen did not affect either the Cu(II)-mediated oxidation of dopamine to dopamine quinone or the reduction of Cu(II) to Cu(I) by dopamine. Instead, the presence of ebselen resulted in a marked decrease in the levels of H(2)O(2) derived from the Cu(II)-mediated oxidation of dopamine. Taken together, our results demonstrate for the first time that ebselen is able to inhibit the dopamine/Cu(II)-induced oxidative DNA damage, which appears to be attributable to the ability of ebselen to decrease the levels of H(2)O(2) derived from the dopamine/Cu(II) system. Since oxidative DNA damage has been implicated in the pathogenesis of various neurodegenerative diseases, the inhibition of oxidative DNA damage by ebselen may be responsible, at least partially, for its neuroprotective activities observed in both humans and experimental animals.