Generation of Strand Breaks and Formation of 8-Hydroxy-2′-deoxyguanosine in DNA by a Thiol/Fe3+/O2-Catalyzed Oxidation System

Strand breaks are produced in pBluescript plasmid DNA by a metal-catalyzed oxidation system composed of Fe3+, O2, and a thiol as an electron donor. Formation of 8-hydroxy-2′-deoxyguanosine (8-OH-dG) in calf thymus DNA was also observed utilizing the same system. DNA damage was observed with the physiological thiols dihydrolipoic acid, glutathione, and cysteine as well as with the synthetic thiols dithiothreitol and 2-mercaptoethanol under a wide range of conditions. Both strand breaks and formation of 8-OH-dG in DNA were temperature dependent, occurring more rapidly at higher temperatures. Sodium azide and mannitol as well as a metal chelator, diethylenetriaminepentaactic acid, decreased strand breaks and 8-OH-dG formation in DNA. Superoxide dismutase did not block damage to DNA, whereas a thiol-dependent protector protein from Saccharomyces cerevisiae and catalase inhibited DNA damage in a concentration-dependent manner. The results of the present study indicate that H2O2 may be generated from a thiol/Fe3+/O2 system and that hydroxyl free radicals may be produced by metal-catalyzed Fenton reactions and may be the ultimate species mediating the DNA damage.