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

Abstract

2'-Deoxycytidine glycols (5,6-dihydroxy-5, 6-dihydro-2'-deoxycytidine) are major 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 been characterized. Instead, the impetus has been placed on the primary decomposition products of 2'-deoxycytidine glycols, which includes 5-hydroxy-2'-deoxycytidine, 5-hydroxy-2'-deoxyuridine, and 2'-deoxyuridine glycols. Here, we have identified one of the four possible diastereomers of 2'-deoxycytidine glycols by product analyses of decomposition products, (1)H NMR, and mass spectrometry. This glycol was observed to decompose with a half-life of 50 min at 37 degrees C in buffered neutral solutions and preferentially undergo dehydration to 5-hydroxy-2'-deoxycytidine. The rate of decomposition was strongly dependent on pH (2-10) and the concentration of phosphate ion (10-300 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-hydroxycytosine and 5-hydroxyuracil. The results showed that the lifetime of cytosine 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. The relatively long lifetime of cytosine glycols in DNA suggests that this important class of DNA oxidation products will be significantly involved in repair and mutagenesis processes.