2 '-deoxycytidine glycols, a missing link in the free radical-mediated oxidation of DNA

2'-Deoxycytidine glycols (5,6-dihydroxy-5,6-dihydro-2'-deoxycytidine) are m ajor products of the hydroxyl radical-induced oxidation of 2'-deoxycytidine resulting from either a Fenton reaction or exposure to ionizing radiation. Because of their instability, however, the glycols have not previously bee n characterized. Instead, the impetus has been placed on the primary decomp osition products of 2'-deoxycytidine glycols, which includes 5-hydroxy-2'-d eoxycytidine, 5-hydroxy-2'-deoxyuridine, and 2'-deoxyuridine glycols. Here, we have identified one of the four possible diastereomers of 2'-deoxycytid ine glycols by product analyses of decomposition products, H-1 NMR, and mas s spectrometry. This glycol was observed to decompose with a half-life of 5 0 min at 37 degrees C in buffered neutral solutions and preferentially unde rgo dehydration to 5-hydroxy-2'-deoxycytidine. The rate of decomposition wa s strongly dependent on pH (2-10) and the concentration of phosphate ion (1 0-300 mM), Next, we report on the deamination of cytosine glycols to uracil glycols in oxidized DNA using acid hydrolysis and high performance liquid chromatography analysis with electrochemical detection to monitor 5-hydroxy cytosine and 5-hydroxyuracil, The results showed that the lifetime of cytos ine glycols is greatly enhanced in DNA (34-fold; half-life, 28 h), and that deamination accounts for at least one-third of the total decomposition. Th e relatively long lifetime of cytosine glycols in DNA suggests that this im portant class of DNA oxidation products will be significantly involved in r epair and mutagenesis processes.