Comparison of (32)P-postlabeling and high-resolution GC/MS in quantifying N7-(2-Hydroxyethyl)guanine adducts

This study compares (32)P-postlabeling and high-resolution gas chromatography/mass spectrometry (GC/MS) in the quantification of N7-(2-hydroxyethyl)guanine adducts (7-HEG) in DNA obtained from the same tissue samples of control rats and rats exposed to ethene. The samples were obtained from two independent studies. In one study, male Sprague-Dawley rats were exposed to 300 ppm ethene for 12 h/day for 3 days ("Euro samples"). In the other study, male F-344 rats were exposed to 3000 ppm ethene for 6 h/day for 5 days ("U.S. samples"). DNA from liver and kidney from the European study was isolated in the European laboratory, and DNA from liver and spleen from the U.S. study was isolated in the U.S. laboratory. The DNA samples were coded, divided into two portions, and exchanged between the two laboratories. All DNA samples from both laboratories were analyzed with respect to 7-HEG adducts by (32)P-postlabeling and high-resolution GC/MS in the European and U.S. laboratories, respectively. However, the U.S. samples were repurified in the European laboratory before the postlabeling analysis. The data from the Euro and the U.S. samples were therefore treated separately in the regression analysis of the (32)P-postlabeling versus GC/MS data. The slope of the regression line for the Euro samples was 1.19 (r = 0.97), implying that the GC/MS data were slightly lower than the postlabeling data (one possible outlier was excluded). The slope of the regression line for the U.S. samples was 0.61 (r = 0.94), implying that the GC/MS data were somewhat higher than the postlabeling data. The main conclusion from this study is that there is very good agreement between the (32)P-postlabeling and high-resolution GC/MS methods in quantifying 7-HEG adducts to DNA, particularly when identical DNA samples are analyzed and the RNA content is <2%. The paper also discusses the background levels of adducts, the interorgan distribution, comparison between different strains, and exposure conditions.