ASSOCIATION BETWEEN 8-HYDROXY-2'-DEOXYGUANOSINE FORMATION AND DNA STRAND BREAKS MEDIATED BY COPPER AND IRON

Oxidative DNA damage is involved in diverse biological phenomena and c onsists of several kinds of lesions, mainly, strand breaks, base modif ications, and DNA-protein crosslinking, However, little is known about the existence of a chemical relationship among them or the ratio by w hich these different types of lesions are produced. In the present stu dy we investigated whether a relationship exists between DNA strand br eakage and base modification. We selected cupric [Cu(ll)] and ferric [ Fe(III)I ions for this study because these transition metals are activ e catalysts of DNA damage in vivo. Supercoiled plasmid DNA pZ189 was t reated with Cu(II) or Fe(III) in the presence of different reducing ag ents. We measured in each sample both the number of DNA single-strand breaks (SSB) by quantitative electrophoresis and the amount of a modif ied DNA base, 8-hydroxy- 2'-deoxyguanosine (8-OHdG) by HPLC with simul taneous electrochemical (EC) and spectrophotometric detection. The num ber of DNA SSBs produced was linearly related to the number of 8-OHdG present. The regression of the number of SSBs as a function of the num ber of 8-OHdG is expressed by the equation [SSBs] = b x [8-OHdG], wher e b = 1.7, 2.0, 2,7, 1.7, and 9.4, for Cu(II) in the presence of H2O2, L-cysteine and L-ascorbate, and for Fe(III) in the presence of H2O2 a nd L-ascorbate, respectively. The linear correlation we observed betwe en the production of SSB and 8-OHdG mediated by Fe(III) and by Cu(II) suggests that these products may arise via a common chemical mechanism and could allow an easier and more precise estimation of DNA breakage .