VANADIUM(IV)-MEDIATED FREE-RADICAL GENERATION AND RELATED 2'-DEOXYGUANOSINE HYDROXYLATION AND DNA-DAMAGE

Free radical generation, 2'-deoxyguanosine (dG) hydroxylation and DNA damage by vanadium(IV) reactions were investigated. Vanadium(IV) cause d molecular oxygen dependent dG hydroxylation to form 8-hydroxyl-2'deo xyguanosine (8-OHdG). During a 15 min incubation of 1.0 mM dG and 1.0 mM VOSO4 in phosphate buffer solution (pH 7.4) at room temperature und er ambient air, dG was converted to 8-OHdG with a yield of about 0.31% . Catalase and formate inhibited the 8-OHdG formation while superoxide dismutase enhanced it. Metal ion chelators, DTPA and deferoxamine, bl ocked the 8-OHdG formation. Incubation of vanadium(IV) with dG in argo n did not generate any significant amount of 8-OHdG, indicating the ro le of molecular oxygen in the mechanism of vanadium(IV)induced dG hydr oxylation. Vanadium(IV) also caused molecular oxygen-dependent DNA str and breaks in a pattern similar to that observed for dG hydroxylation. ESR spin trapping measurements demonstrated that the reaction of vana dium(IV) with H2O2 generated (OH)-O-. radicals, which were inhibited b y DTPA and deferoxamine. Incubation of vanadium(IV) with dG or with DN A in the presence of H2O2 resulted in an enhanced 8-OHdG formation and substantial DNA double strand breaks. Sodium formate inhibited 8-OHdG formation while DTPA had no significant effect. Deferoxamine enhanced the 8-OHdG generation by 2.5-fold. ESR and UV measurements provided e vidence for the complex formation between vanadium(IV) and deferoxamin e. UV-visible measurements indicate that dG, vanadium(IV) and deferoxa mine are able to form a complex, thereby, facilitating site-specific 8 -OHdG formation. Reaction of vanadium(IV) with t-butyl hydroperoxide g enerated hydroperoxide-derived free radicals, which caused 8-OHdG form ation from dG and DNA strand breaks. DTPA and deferoxamine attenuated vanadium(IV)/t-butyl-OOH-induced DNA strand breaks.