HO ^• radicals induce an unexpected high proportion of tandem base lesions refractory to repair by DNA glycosylases

Abstract

Reaction of HO• radicals with double-stranded calf thymus DNA produces high levels of and, to a minor extent, . Formation of the hydroxylated purine lesions is explained by addition of HO • to the C8 position of the purine moiety. It has been reported that tandem lesions containing a formylamine residue neighboring 8-oxodGuo could be produced through addition of a transiently generated pyrimidine peroxyl radical onto the C8 of an adjacent purine base. Formation of such tandem lesions accounted for ≈10% of the total 8-oxodGuo. In the present work we show that addition of HO • onto the C8 of purine accounts for only ∼5% of the generated 8-oxodGuo. About 50% of the 8-hydroxylated purine lesions, including 8-oxodGuo and 8-oxodAdo, are involved in tandem damage and are produced by peroxyl addition onto the C8 of a vicinal purine base. In addition, the remaining 45% of the 8-oxodGuo are produced by an electron transfer reaction, providing an explanation for the higher yield of formation of 8-oxodGuo compared to 8-oxodAdo. Interestingly, we show that >40% of the 8-oxodGuo involved in tandem lesions is refractory to excision by DNA glycosylases. Altogether our results demonstrate that, subsequently to a single oxidation event, peroxidation reactions significantly increase the yield of formation of hydroxylated purine modifications, generating a high proportion of tandem lesions partly refractory to base excision repair.DNA damage | DNA repair | peroxidation reaction | tandem lesions F ormation of oxidatively generated DNA lesions is associated with the occurrence of degenerative diseases, cancer, and aging (1). Therefore, reactions of reactive oxygen species, and among them the highly genotoxic hydroxyl radical (HO • ), with DNA constituents have been extensively studied during the last three decades (2). 8-Oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) and, to a minor extent the corresponding adenine derivative 8-oxo-7,8-dihydro-2′-deoxyadenosine (8-oxodAdo), have been shown to be significantly generated in cellular DNA under various conditions of oxidative stress. More than 20 years ago (3) it was established that in the presence of HO• (produced either by the indirect effect of ionizing radiation or by Fenton-type reactions) the mechanism of formation of 8-hydroxylated purine lesions (8-oxoPur), including both 8-oxodGuo and 8-oxodAdo, involves addition of HO• to the C8 position of the purine bases, followed by an oxidation reaction (for a review see refs. 2 and 4). In addition, 8-oxoPur could be also produced by a one-electron oxidation process followed by hydration of the purine radical cation thus generated, producing following oxidation mainly 8-oxodGuo due to efficient charge transfer processes (5, 6) combined with the relatively low ionization potential of guanine compared to other DNA constituents.In addition, the pioneering work of Box and coworkers (7-10) suggested the possible formation of tandem lesions, constituted of two adjacent modifications. Recent works have demonstrated that in dinucleoside monophosp...

Meiosis and the Paradox of Sex in Nature

“…This is just one of the many reactions and products of free radicals with DNA, which have been reviewed comprehensively elsewhere [22,33,34]. Hydroxyl radicals can cause not only single, but tandem lesions of purine bases [35]. An important feature of free radicals is that single initiation events have the potential to generate multiple reactions and multiple peroxide molecules by complex chain reactions [22].…”

Non-B DNA-forming Sequences and WRN Deficiency Independently Increase the Frequency of Base Substitution in Human Cells

“…In addition, the migration of a charge from a distal base toward G (X ⅐ ϩ ϩ G 3 X ϩ G ⅐ ϩ ) (hole migration) through -stacking (55-59) has been proposed to contribute to mutagenesis (60). Hole migration behavior (55)(56)(57)(58)(59) would predict that the number of mutations at any given G in the context of NGNN should increase with increasing local base stacking and with a decrease in ionization potentials afforded by 3Ј base stacking (54) (Fig.…”

Sequestration and Scavenging of Iron in Infection

“…Ferrous iron is potentially toxic through its ability to catalyze the production of reactive oxygen and nitrogen species, including the highly reactive hydroxyl radical (1). These reactive species can damage biological molecules, including DNA (2). Iron within heme is in the ferrous (Fe 2ϩ ) state and readily participates in redox reactions.…”