Oxidatively Generated Nucleobase Modifications in Isolated and CellularDNA

Abstract

The main oxidation reactions of the main pyrimidine bases (thymine and cytosine) and purine bases (adenine and guanine), and 5‐methylcytosine mediated by hydroxyl radical ( · OH) as well as one‐electron oxidants and singlet oxygen ( 1 O 2 ) leading to about 80 single‐oxidized‐type lesions are reported and the mechanism of their formation critically discussed. In addition, a few complex modifications including tandem base modifications involving either carbon‐centered radical or peroxyl radicals derived from radical oxidation of pyrimidine bases are also described. One may add modifications that arise from initial OH‐mediated hydrogen atom abstraction at C5 and C4 of the 2‐deoxyribose moiety of DNA giving rise to purine 5 ′ ,8‐cyclonucleosides and four diastereomeric aldehyde adducts to opposite cytosine bases in double‐stranded DNA, respectively. With the high level of product identification and thanks to the high sensitivity of high performance liquid chromatography (HPLC)‐electrospray ionization‐tandem mass spectrometry analysis, relevant information is gained on the formation of oxidation products in cells. Thus, 12 single and 5 complexes oxidatively generated base lesions have been detected in cellular DNA on exposure to 1 O 2 , γ rays and high‐intensity ultraviolet C (UVC) laser pulses. The information thus gained is strongly supportive of the oxidation mechanisms that were inferred from mechanistic studies on model systems in aerated aqueous solutions.

Photoinduced Damage to Cellular DNA: Direct and Photosensitized Reactions†

“…This clearly shows that biphotonic ionization takes place and that, like for other reactions leading to the formation of radical cations in DNA, guanine is the main direct or indirect target of one-electron oxidation. The formation of 8-oxoGua, 8-oxoAde and ThyGl is rationalized in terms of initial hydration reaction of the guanine, adenine and thymine radical cations, respectively, whereas the generation of HmUra and FoUra involves initial deprotonation of thymine radical cation (129,130). This does not only apply to isolated DNA as similar results were obtained in human cells exposed to highintensity nanosecond UVC pulses (128).…”

DNA Base Damage by Reactive Oxygen Species, Oxidizing Agents, and UV Radiation

“…These advances have been possible because of the development of sensitive and powerful high-performance liquid chromatography-mass spectrometry (HPLC-MS)/ mass spectrometry (MS) methods allowing one to revise previously reported data obtained using methods such as gas chromatographymass spectrometry (GC-MS), immunoassays, and HPLC with single MS detection (Cadet et al , 2012a. Considerable progress has also been made in the elucidation of oxidative degradation pathways of isolated DNA and related model compounds (for recent comprehensive reviews, see Gimisis and Cismaş 2006;Neeley and Essigmann 2006;Pratviel and Meunier 2006;von Sonntag 2006;Cadet et al 2008Cadet et al , 2010Cadet et al , 2012bDedon 2008;Burrows 2009;Wagner and Cadet 2010). In addition, there is much complementary information on solar-radiation-induced formation of bipyrimidine photoproducts in the DNA of fibroblasts, keratinocytes, and human skin.…”

Radical-induced purine lesion formation is dependent on DNA helical topology

“…a rise from 0.2 for SC to $8.0 for OC and L was observed. We suggest that the 8-oxo lesions are generated by the addition of HO onto C8 position and the higher yield of 8-oxo-dG formation compared with 8-oxo-dA reflects additional mechanisms such as one-electron oxidation in dsDNA that occurs via hole transfer and water assistance and/ or the formation of 8-oxo-dG through the intramolecular tandem damage involving base-derived peroxyl radicals [2,10]. Overall, it is noteworthy how supercoiled DNA structure attenuates solution-borne HO -free radical damage, with 8-oxo-dG and 8-oxo-dA levels increasing !10-fold within both circular and linear conformers.…”

“…exposure to ionizing radiation or redox metal ion overload, are known to produce HO and related reactive oxygen species (ROS) [1]. With regard to DNA chemical reactivity, diffusible HO are known to either add to base moieties [2], with the majority of HO attacks occurring at this location, or abstract a Hatom from 2-deoxyribose units [3]. Indeed, given the proximity of deoxyribose C5 pathway [5] with recent work demonstrating ca.…”

“…4) that impact on genome structural integrity, mutagenicity, excision repair, and polymerase fidelity [2,7]. DNA lesion quantification methods, developed and extensively used within the last decade, are mainly based on liquid chromatography coupled with highly sensitive mass detectors.…”