Site-specific DNA damage induced by hydrazine in the presence of manganese and copper ions. The role of hydroxyl radical and hydrogen atom.

The mechanism of DNA damage by hydrazine in the presence of metal ions was investigated by DNA sequencing technique and ESR-spin trapping method. Hydrazine caused DNA damage in the presence of Mn(III), Mn(II), Cu(II), Co(II), and Fe(III). The order of inducing effect on hydrazine-dependent DNA damage (Mn(III) greater than Mn(II) approximately Cu(II) much greater than Co(II) approximately Fe(III)) was related to that of the accelerating effect on the O2 consumption rate of hydrazine autoxidation. DNA damage by hydrazine plus Mn(II) or Mn(III) was inhibited by hydroxyl radical scavengers and superoxide dismutase, but not by catalase. On the other hand, bathocuproine and catalase completely inhibited DNA damage by hydrazine plus Cu(II), whereas hydroxyl radical scavengers and superoxide dismutase did not. Hydrazine plus Mn(II) or Mn(III) caused cleavage at every nucleotide with a little weaker cleavage at adenine residues, whereas hydrazine plus Cu(II) induced piperidine-labile sites frequently at thymine residues, especially of the GTC sequence. ESR-spin trapping experiments showed that hydroxyl radical is generated during the Mn(III)-catalyzed autoxidation of hydrazine, whereas hydrogen atom adducts of spin trapping reagents are generated during Cu(II)-catalyzed autoxidation. The results suggest that hydrazine plus Mn(II) or Mn(III) generate hydroxyl free radical not via H2O2 and that this hydroxyl free radical causes DNA damage. A possibility that the hydrogen atom releasing compound participates in hydrazine plus Cu(II)-induced DNA damage is discussed.