Identification and quantification of mutagenic halogenated cytosines by gas chromatography, fast atom bombardment, and electrospray ionization tandem mass spectrometry
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Abstract
Oxidative modification of nucleic acids has been implicated in carcinogenesis. One
potential mechanism involves halogenation by the myeloperoxidase and eosinophil peroxidase
systems of phagocytes. In the current studies, three mass spectrometric methods for
the in vitro and in vivo analysis of halogenated cytosines and deoxycytidines were
compared: gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) with
a quadrupole instrument, fast atom bombardment or electrospray ionization (ESI) tandem
MS with a four-sector magnetic instrument, and liquid chromatography ESI tandem MS
(HPLC-ESI-MS/MS) with an ion-trap instrument. GC-EI-MS with selected ion monitoring
of dimethyl-tert-butylsilyl derivatives of nucleobases was the most sensitive method.
High-energy collisionally induced dissociation MS/MS analysis with a four-sector magnetic
instrument yielded detailed structural information about halogenated nucleoside adducts
but required relatively large amounts of material. The most sensitive analysis of
intact halogenated deoxycytidine was achieved with extracted ion chromatograms using
HPLC-ESI-MS/MS with an ion-trap instrument. Our results indicate that GC-EI-MS is
the methodology of choice for ultrasensitive analysis of halogenated cytosines. HPLC-ESI-MS/MS
provides greater structural detail for these compounds and may rival GC-EI-MS in sensitivity
with more advanced liquid chromatography applications. The mass spectrometric methods
we have developed should be useful for evaluating the role of phagocyte-derived oxidants
in halogenating nucleobases, nucleosides, and DNA at sites of inflammation.