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

Dimethylformamide (DMF) has been suspected to associate with cancers in exposed workers, whereas there has been inadequate evidence for carcinogenicity in experimental animals. We demonstrated that H2O2 was generated during the degradation of DMF under aerobic conditions, and that; the amount of H2O2 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 the degraded DMF induced DNA damage in the presence of Cu(II). However, purified 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(II). The degraded DMF caused Cu(II)-mediated DNA cleavage frequently at thymine and cytosine residues. The similar pattern of site-specific DNA damage was observed with purified DMF and H2O2 Bathocuproine and catalase inhibited the DNA damage, indicating the involvement of Cu(I) and H2O2. A typical free 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'-deoxyguanosine formation induced by H2O2 and Cu(II). ESR spectroscopic study demonstrated that carbon-centered radicals and nitrogen-centered radicals were generated in the reaction mixture of DMF, H2O2, and Cu(II). Inhibitory effects of scavengers on radical formation and DNA damage suggest that carbon-centered radicals and/or nitrogen-centered radicals may contribute to the DNA damage. These results suggest that H2O2 generation during DMF degradation is related to the possible carcinogenic activity of DMF.