Electrochemical simulation of oxidation processes involving nucleic acids monitored with electrospray ionization–mass spectrometry

Oxidation is commonly involved in the alteration of nucleic acids giving rise to diverse effects including mutation, cell death, malignancy, and aging. We demonstrate that electrochemistry represents an efficient and fast method to mimic oxidative modification of nucleic acids occurring in biological systems. Oxidation reactions were performed in a thin-layer cell employing a conductive diamond electrode as the working electrode and were monitored with electrospray ionization–mass spectrometry. Mass voltammograms were acquired for guanosine, adenosine, cytidine, and uridine. The observed oxidation potentials increased in the order guanosine<<adenosine<cytidine<uridine. Oxidation products of guanosine were characterized using high-resolution (tandem) mass spectrometry performed with a quadrupole–quadrupole time-of-flight instrument. On the basis of these experiments, it was concluded that the initial electrode reaction involves a one-electron, one-proton step to give a free radical. The primary oxidation product represents the starting point for a number of follow-up reactions, including guanosine dimerization as well as further oxidation to 8-hydroxyguanosine. Similar results were obtained for guanosine monophosphate and the corresponding dinucleotide. Furthermore, the guanosine radical was identified as an important intermediate for the formation of a covalent adduct with acetaminophen. This observation sheds new light on the mechanism of adduct formation as it demonstrates that oxidative activation of both the nucleobase and the adduct-forming agent is necessary to observe a detectable amount of adduct species. Figure On-line electrochemistry/mass spectrometry is fast, simple, and convenient method to study the impact of oxidation reactions on different kinds of nucleic acid species, including nucleosides, nucleotides and small oligomers. The initial electrode reaction involves a 1e⁻, 1H⁺ step to give a free radical. The primary oxidation product represents the starting point for a number of follow-up reactions.