Analysis of oxidative cytosine products in DNA exposed to ionizing radiation

From ionizing radiation studies, we have previously characterized a large number of modifications of cytosine and 2'-deoxycytidine which arise by way of hydroxyl radical or base radical cation reactions. However, it remains a great challenge today to detect and quantitate these lesions in DNA. In the present work, I have developed a method for the analysis of six oxidation products of cytosine in DNA using HF acid hydrolysis and gas chromatography/mass spectrometry with isotopic dilution. The analysis of gamma-irradiated DNA indicated that uracil 5,6-glycols 5-hydroxyuracil and 5-hydroxyhydantoin are the major stable decomposition products of cytosine residues, whereas alloxane and 1-carbamoyl-2-oxo-4,5-dihydroxy-imidazolidine are formed in comparatively lower yields. These results suggest that the major pathway of OH radical induced decomposition of cytosine in DNA involves initial deamination of intermediate 5-hydroxy-6-hydroperoxides