Dihydrothymine lesion in X-irradiated DNA: characterization at the molecular level and detection in cells

Purpose: To study the formation of the dihydrothymine lesion produced in DNA by ionizing radiation in an anaerobic environment. Materials and methods: The dihydrothymine lesion, along with other lesions, was isolated from an X-irradiated aqueous solution of the dinucleoside monophosphate d(TpA) and analysed by correlated two-dimensional nuclear magnetic resonance spectroscopy. The dihydrothymine lesion was obtained by enzymatic digestion of irradiated DNA in the form of modified dinucleoside monophosphates, d(TdA), where Td stands for dihydrothymidine. Liquid chromatography-tandem mass spectrometry was used to detect the lesion in the DNA of X-irradiated mouse fibroblast cells. Results: The modified dinucleoside monophosphate, d(TdpA), fragments by two pathways so that altogether the lesion could be detected using two different sets of tandem mass spectrometry (precursor ion mass/daughter ion mass) values. Conclusion: The dihydrothymine lesion is a significant lesion in cells exposed to ionizing radiation in an anaerobic environment.