Determination of styrene oxide adducts in DNA and DNA components

The reaction of styrene oxide with DNA components was studied using separation by capillary zone electrophoresis (CZE) and detection by negative-ion electrospray mass spectrometry (MS). The CZE-MS interface was built for a sector field mass spectrometer. The reaction of styrene oxide with mononucleotides (dGMP, dAMP) was used to optimize the relevant separation parameters and to gather the first information about the behaviour of the possible products. With these mixtures, sample stacking procedures were developed and the scope of collision-induced dissociations were studied. From the fragments recorded, information about the reaction sites in the nucleotides was obtained. Further, the reaction with intact calf thymus DNA was investigated. The DNA was digested into oligonucleotides using the previously described approach with Benzonase, an unspecific nuclease, and alkaline phosphatase. Styrene oxide mono-adducts in dinucleotides, trinucleotides and tetranucleotides were detected, whereas pentanucleotides exhibit mono- and discernible amounts of di-adducts. The hexanucleotides were generally modified twice. The alkylated species moved faster than the unmodified oligomers.

A new mass spectrometric approach to detect modifications in DNA

A new approach is described for the enzymatic digestion of DNA yielding oligonucleotides ranging from dinucleoside monophosphates to octanucleoside heptaphosphates. DNA was digested by means of the benzon nuclease, an unspecific nuclease, and alkaline phosphatase to remove the terminal phosphate. The mixture of oligonucleotides was separated using capillary-zone electrophoresis with a buffer system, yielding a rather strong electro-osmotic flow. The oligomers are separated into groups with nucleotides of the same chain length. The separation capillary was used as the innermost capillary of an electrospray spraying system. Negative molecular ions of the nucleotides were recorded using a home-built interface and ion source for a sector-field mass spectrometer. This approach allows the facile detection of DNA modifications since they lead not only to differences in mass, but also can possess altered electrophoretic mobility. For modifying reactions which exhibit sequence specificity, the information is retained in the oligomers. Thus, reactions of DNA with electrophiles can be evaluated at different levels, since in longer chains, even complex sequence specificity may be apparent. Results from calf thymus DNA digests and preliminary experiments with DNA adducts with styrene oxide are discussed.