Formation of 2′-deoxyuridine hydrates upon exposure of nucleosides to gamma radiation and UVC-irradiation of isolated and cellular DNA

The two diastereoisomers of 6-hydroxy-5,6-dihydro-2'-deoxyuridine (dUrd hydrates) are produced upon deamination of the related 2'-deoxycytidine derivatives. Liquid chromatography coupled to tandem mass spectrometry was used to quantify dUrd hydrates. Their rate constant of formation within UVC-irradiated solutions of dCyd was first determined. Their formation was also shown to occur within solutions of either dUrd or dCyd exposed to gamma-rays in the absence of oxygen. dUrd hydrates were then quantified within isolated and cellular DNA exposed to UVC light. In both cases, their yield of formation was found to be, at least, 2 orders of magnitude lower than the overall yield of bipyrimidine photoproducts such as cyclobutane dimers and (6-4) photoproducts.