DNA damage and 2′-deoxyguanosine oxidation induced by S(IV) autoxidation catalyzed by copper(II) tetraglycine complexes: Synergistic effect of a second metal ion

S(IV) (SO2,HSO3-andSO32-) autoxidation catalyzed by Cu(II)/tetraglycine complexes in the presence of DNA or 2′-deoxyguanosine (dGuo) resulted in DNA strand breaks and formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo), respectively. Ni(II), Co(II) or Mn(II) (1.0 × 10−4 M) complexes had much smaller effects. Cu(II)/tetraglycine (1.0 × 10−4 M) in the presence of Ni(II) or Mn(II) (10−7–10−6 M) and S(IV) showed remarkable synergistic effect with these metal ions producing a higher yield of 8-oxodGuo. Oxidation of dGuo and DNA damage were attributed to oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by transition metal ions. SO3- and HO radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline-N-oxide).