FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY FOR MAPPING OF ENDOGENOUS METHYLATED PURINE-BASES IN URINE EXTRACTS

Fast-atom bombardment (FAB) mass spectrometry, linked with tandem mass spectrometry (MS/MS), was employed for the identification of methylat ed purine bases in four urinary extracts of healthy subjects and fourt een urinary extracts of patients bearing colorectal tumors. In order t o obtain an easy structural identification of the species present in u rinary extracts, the MS/MS spectra of MH(+) species of twenty nine dia gnostically relevant purine bases were studied. Even if definitive qua ntitative data cannot be obtained by this approach, FAB mass spectra o f urine extracts lead to a readily reproducible mapping of endogenous purine bases, allowing a distinction between healthy and sick subjects . Bases such as 9-ethyladenine, N-6-2-isopentenyladenine and N-6-benzy ladenine were detected only in urine samples of colorectal tumor beari ng patients. The detection in urine of compounds such as 7-methylguani ne and 1-methylguanine, and their increase in the urine of colorectal tumor bearing patients, has been justified either by a more rapid turn over of nucleic acids in tumor tissue or by an increase in the extent of their methylation. The obtained results indicate that the method ca n be employed for diagnostic purposes. (C) 1997 by John Wiley & Sons, Ltd.