Inflammation-mediated, neutrophil-derived
hypochlorous acid can damage
DNA and result in the chlorination damage products
5-chlorocytosine and
5-chlorouracil as well as the oxidation damage products
5-hydroxycytosine and
5-hydroxyuracil. While
5-chlorocytosine could potentially perturb epigenetic signals if formed at a CpG dinucleotide, the remaining products are miscoding and could result in transition mutations. In this article, we have investigated the reaction of
hypochlorous acid with an
oligonucleotide site-specifically enriched with 15N to probe the reactivity of
cytosine at CpG. These experiments demonstrate directly the formation of
5-chlorocytosine at a CpG dinucleotide in duplex
DNA. We observe that chlorination relative to oxidation damage is greater at CpG by
a factor of approximately two, whereas similar amounts of
5-chlorocytosine and
5-hydroxycytosine are formed at two non-CpG sites examined. The relative amounts of deamination of the
cytosine to
uracil derivatives are similar at CpG and non-CpG sites. Overall, we observe that the reactivity of
cytosine at CpG and non-CpG sites toward
hypochlorous acid induced damage is similar (5-
chlorocytosine > 5-hydroxycytosine > 5-hydroxyuracil > 5-chlorouracil), with a greater proportion of chlorination damage at CpG sites. These results are in accord with the potential of
inflammation-mediated DNA damage to both induce transition mutations and to perturb epigenetic signals.