Recent Aspects of Oxidative DNA Damage: Guanine Lesions, Measurement and Substrate Specificity of DNA Repair Glycosylases

Abstract

This review discusses recent aspects of oxidation reactions of DNA and model compounds involving mostly OH radicals, one-electron transfer process and singlet oxygen (1O2). Emphasis is placed on the formation of double DNA lesions involving a purine base on one hand and either a pyrimidine base or a 2-deoxyribose moiety on the other hand. Structural and mechanistic information is also provided on secondary oxidation reactions of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), a major DNA marker of oxidative stress. Another major topic which is addressed here deals with recent developments in the measurement of oxidative base damage to cellular DNA. This has been mostly achieved using the accurate and highly specific HPLC method coupled with the tandem mass spectrometry detection technique. Interestingly, optimized conditions of DNA extraction and subsequent work-up allow the accurate measurement of 11 modified nucleosides and bases within cellular DNA upon exposure to oxidizing agents, including UVA and ionizing radiations. In addition, the modified comet assay, which involves the use of bacterial DNA N-glycosylases to reveal two main classes of oxidative base damage, is applicable to isolated cells and is particularly suitable when only small amounts of biological material are available. Finally, recently available data on the substrate specificity of DNA repair enzymes belonging to the base excision pathways are briefly reviewed.

DNA repair glycosylases with a [4Fe–4S] cluster: A redox cofactor for DNA-mediated charge transport?

“…These results indicate that guanine radical formation, one of the first DNA damage products generated under oxidizing conditions [64], facilitates the oxidation of DNA-bound MutY. By oxidizing the [4Fe-4S] cluster in MutY, guanine radical may initiate the searching process for BER enzymes in accordance with our proposed model ( Figure 5).…”

“…Guanine radicals, with an oxidation potential of 1 V versus NHE [63], have sufficient driving force to oxidize both Endo III and MutY. Moreover, these radicals are being generated under conditions of oxidative stress in the cell [64], when the DNA is in need of repair. Experimentally, we can generate guanine radicals via flash-quench of a Ru(II)dipyridophenazine (dppz) complex intercalated into the DNA helix (Figure 4) [65].…”

Oxidative DNA Damage Associated with Combination of Guanine and Superoxide Radicals and Repair Mechanisms via Radical Trapping

“…Guanine is the most easily oxidizable nucleic acid base in DNA (1) and is therefore a primary target of oxidative modification (2). In neutral aqueous solutions, the one-electron oxidation of guanine residues first produces the guanine radical cation (G .…”

“…10). In living systems, superoxide radicals, the products of normal metabolic activity, are rapidly deactivated by superoxide dismutases (SOD) that catalyze the conversion of O 2 . to the less reactive H 2 O 2 and O 2 (7)(8)(9).…”

“…A laser flash photolysis method developed by our group (15)(16)(17) was employed to generate O 2 . and G(ϪH) ⅐ radicals in DNA.…”