Formation and repair of oxidatively generated damage in cellular DNA

In this review article, emphasis is placed on the critical survey of available data concerning modified nucleobase and 2-deoxyribose products that have been identified in cellular DNA following exposure to a wide variety of oxidizing species and agents including, hydroxyl radical, one-electron oxidants, singlet oxygen, hypochlorous acid and ten-eleven translocation enzymes. In addition, information is provided about the generation of secondary oxidation products of 8-oxo-7,8-dihydroguanine and nucleobase addition products with reactive aldehydes arising from the decomposition of lipid peroxides. It is worth noting that the different classes of oxidatively generated DNA damage that consist of single lesions, intra- and interstrand cross-links were unambiguously assigned and quantitatively detected on the basis of accurate measurements involving in most cases high performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The reported data clearly show that the frequency of DNA lesions generated upon severe oxidizing conditions, including exposure to ionizing radiation is low, at best a few modifications per 106 normal bases. Application of accurate analytical measurement methods has also allowed the determination of repair kinetics of several well-defined lesions in cellular DNA that however concerns so far only a restricted number of cases.

Efficacy and site specificity of hydrogen abstraction from DNA 2-deoxyribose by carbonate radicals

The carbonate radical anion CO(3)(•-) is a potent reactive oxygen species (ROS) produced in vivo through enzymatic one-electron oxidation of bicarbonate or, mostly, via the reaction of CO(2) with peroxynitrite. Due to the vitally essential role of the carbon dioxide/bicarbonate buffer system in regulation of physiological pH, CO(3)(•-) is arguably one of the most important ROS in biological systems. So far, the studies of reactions of CO(3)(•-) with DNA have been focused on the pathways initiated by oxidation of guanines in DNA. In this study, low-molecular products of attack of CO(3)(•-) on the sugar-phosphate backbone in vitro were analyzed by reversed phase HPLC. The selectivity of damage in double-stranded DNA (dsDNA) was found to follow the same pattern C4' > C1' > C5' for both CO(3)(•-) and the hydroxyl radical, though the relative contribution of the C1' damage induced by CO(3)(•-) is substantially higher. In single-stranded DNA (ssDNA) oxidation at C1' by CO3(•-) prevails over all other sugar damages. An approximately 2000-fold preference for 8-oxoguanine (8oxoG) formation over sugar damage found in our study identifies CO(3)(•-) primarily as a one-electron oxidant with fairly low reactivity toward the sugar-phosphate backbone.

Mitochondrial DNA: Radically free of free-radical driven mutations

Mitochondrial DNA has long been posited as a likely target of oxidative damage induced mutation during the ageing process. Research over the past decades has uncovered the accumulation of mitochondrial DNA mutations in association with a mosaic pattern of cells displaying mitochondrial dysfunction in ageing individuals. Unfortunately, the underlying mechanisms are far less straightforward than originally anticipated. Recent research on mitochondria reveals that these genomes are far less helpless than originally envisioned. Additionally, new technologies have allowed us to analyze the mutational signatures of many more somatic mitochondrial DNA mutations, revealing surprising patterns that are inconsistent with a DNA-oxidative damage based hypothesis. In this review, we will discuss these recent observations and new insights into the eccentricities of mitochondrial genetics, and their impact on our understanding of mitochondrial mutations and their role in the ageing process. This article is part of a Special Issue entitled: Mitochondrial Dysfunction in Aging.

Oxidatively generated base damage to cellular DNA by hydroxyl radical and one-electron oxidants: similarities and differences

Hydroxyl radical (OH) and one-electron oxidants that may be endogenously formed through oxidative metabolism, phagocytosis, inflammation and pathological conditions constitute the main sources of oxidatively generated damage to cellular DNA. It is worth mentioning that exposure of cells to exogenous physical agents (UV light, high intensity UV laser, ionizing radiation) and chemicals may also induce oxidatively generated damage to DNA. Emphasis is placed in this short review article on the mechanistic aspects of OH and one-electron oxidant-mediated formation of single and more complex damage (tandem lesions, intra- and interstrand cross-links, DNA-protein cross-links) in cellular DNA arising from one radical hit. This concerns DNA modifications that have been accurately measured using suitable analytical methods such as high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Evidence is provided that OH and one-electron oxidants after generating neutral radicals and base radical cations respectively may partly induce common degradation pathways. In addition, selective oxidative reactions giving rise to specific degradation products of OH and one-electron oxidation reactions that can be used as representative biomarkers of these oxidants have been identified.