DNA damage by dimethylformamide: Role of hydrogen peroxide generated during degradation

Dimethylformamide (DMF) has been suspected to associate with cancers in exp osed workers, whereas there has been inadequate evidence for carcinogenicit y in experimental animals. We demonstrated that H2O2 was generated during t he degradation of DMF under aerobic conditions, and that; the amount of H2O 2 was enhanced by exposure to solar light or by the contamination of trace metal. Experiments using P-32-5'-end-labeled DNA fragments revealed that th e degraded DMF induced DNA damage in the presence of Cu(II). However, purif ied DMF did not induce DNA damage even in the presence of Cu(II). Addition of purified DMF enhanced DNA damage induced by H2O2 in the presence of Cu(I I). The degraded DMF caused Cu(II)-mediated DNA cleavage frequently at thym ine and cytosine residues. The similar pattern of site-specific DNA damage was observed with purified DMF and H2O2 Bathocuproine and catalase inhibite d the DNA damage, indicating the involvement of Cu(I) and H2O2. A typical f ree hydroxy radical scavenger showed no inhibitory effect on the DNA damage . Addition of purified DMF enhanced about 3-4-fold 8-oxo-7,8-dihydro-2'-deo xyguanosine formation induced by H2O2 and Cu(II). ESR spectroscopic study d emonstrated that carbon-centered radicals and nitrogen-centered radicals we re generated in the reaction mixture of DMF, H2O2, and Cu(II). Inhibitory e ffects of scavengers on radical formation and DNA damage suggest that carbo n-centered radicals and/or nitrogen-centered radicals may contribute to the DNA damage. These results suggest that H2O2 generation during DMF degradat ion is related to the possible carcinogenic activity of DMF.