Factors affecting the yields of C1' and C5' oxidation products in radiation-damaged DNA: the indirect effect

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.

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.

Mitigation of gamma-radiation induced abasic sites in genomic DNA by dietary nicotinamide supplementation: metabolic up-regulation of NAD(+) biosynthesis

The search for non-toxic radio-protective drugs has yielded many potential agents but most of these compounds have certain amount of toxicity. The objective of the present study was to investigate dietary nicotinamide enrichment dependent adaptive response to potential cytotoxic effect of (60)Co γ-radiation. To elucidate the possible underlying mechanism(s), male Swiss mice were maintained on control diet (CD) and nicotinamide supplemented diet (NSD). After 6 weeks of CD and NSD dietary regimen, we exposed the animals to γ-radiation (2, 4 and 6Gy) and investigated the profile of downstream metabolites and activities of enzymes involved in NAD(+) biosynthesis. Increased activities of nicotinamide phosphoribosyltransferase (NAMPT) and nicotinamide mononucleotide adenylyltransferase (NMNAT) were observed up to 48h post-irradiation in NSD fed irradiated mice. Concomitant with increase in liver NAMPT and NMNAT activities, NAD(+) levels were replenished in NSD fed and irradiated animals. However, NAMPT and NMNAT-mediated NAD(+) biosynthesis and ATP levels were severely compromised in liver of CD fed irradiated mice. Another major finding of these studies revealed that under γ-radiation stress, dietary nicotinamide supplementation might induce higher and long-lasting poly(ADP)-ribose polymerase 1 (PARP1) and poly(ADP-ribose) glycohydrolase (PARG) activities in NSD fed animals compared to CD fed animals. To investigate liver DNA damage, number of apurinic/apyrimidinic sites (AP sites) and level of 8-hydroxy-2'-deoxyguanosine (8-oxo-dG) residues were quantified. A significant increase in liver DNA AP sites and 8-oxo-dG levels with concomitant increase in caspase-3 was observed in CD fed and irradiated animals compared to NSD fed and irradiated mice. In conclusion present studies show that under γ-radiation stress conditions, dietary nicotinamide supplementation restores DNA excision repair activity via prolonged activation of PARP1 and PARG activities. Present results clearly indicated that hepatic NAD(+) replenishment might be a novel and potent approach to reduce radiation injury.