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

The carbonate radical anion CO₃^?? is a potent reactive oxygen species (ROS) produced in vivo through enzymatic one-electron oxidation of bicarbonate or, mostly, via the reaction of CO₂ with peroxynitrite. Due to the vitally essential role of the carbon dioxide/bicarbonate buffer system in regulation of physiological pH, CO₃^?? is arguably one of the most important ROS in biological systems. So far, the studies of reactions of CO₃^?? with DNA have been focused on the pathways initiated by oxidation of guanines in DNA. In this study, low-molecular products of attack of CO₃^?? 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 CO₃^?? and the hydroxyl radical, though the relative contribution of the C1′ damage induced by CO₃^?? 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 CO₃^?? primarily as a one-electron oxidant with fairly low reactivity toward the sugar–phosphate backbone.