Analysis of the benzene oxide-DNA adduct 7-phenylguanine by liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry-parallel reaction monitoring: application to DNA from exposed mice and humans.

Benzene oxide, the initial metabolite of the human carcinogen benzene, reacts with DNA producing 7-phenylguanine (7-PhG) and other products. We developed a highly sensitive liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry-parallel reaction monitoring method for the analysis of 7-PhG in DNA. Accuracy and precision of the method were established and the detection limit was about 8amol of 7-PhG injected on the column and less than 1 adduct per 10(9) nucleotides in DNA. 7-PhG was detected in calf thymus DNA reacted with 1μM to 10mM benzene oxide. The method was applied for the analysis of DNA isolated from bone marrow, lung, and liver of B6C3F1 mice treated by gavage with 50mg/kg benzene in corn oil 5 times weekly for 4weeks. 7-PhG was not detected in any of these DNA samples. The method was applied to DNA from mouse hepatocytes exposed to 100μM benzene oxide and human TK-6 lymphoblasts exposed to 100μM, 1, and 10mM benzene oxide. 7-PhG was only detected in TK-6 cell DNA from the 10mM exposure. The method was also applied to leukocyte DNA from 10 smokers and 10 nonsmokers. 7-PhG was detected in only one DNA sample, from a nonsmoker. The results of this study do not support the hypothesis that the benzene oxide-DNA adduct 7-PhG is involved in carcinogenesis by benzene.