Many studies have investigated the effects of
glutathione S-transferase (GST) polymorphisms on
cancer incidence in people exposed to carcinogenic
polycyclic aromatic hydrocarbons (PAHs). The basis for this is that the carcinogenic bay region diol
epoxide metabolites of several PAH are detoxified by
GSTs in in vitro studies. However, there are no reports in the literature on the identification in urine of the
mercapturic acid metabolites that would result from this process in humans. We addressed this by developing a method for quantitation in human urine of mercapturic
acids which would be formed from angular ring diol
epoxides of
phenanthrene (Phe), the simplest PAH with a bay region, and a common
environmental pollutant. We prepared standard mercapturic
acids by reactions of syn- or anti-Phe-1,2-diol-3,4-epoxide and syn- or anti-Phe-3,4-diol-1,2-epoxide with
N-acetylcysteine. Analysis of human urine conclusively demonstrated that the only detectable
mercapturic acid of this type--N-acetyl-S-(r-4,t-2,3-trihydroxy-1,2,3,4-tetrahydro-c/t-1-phenanthryl)-
L-cysteine (anti-PheDE-1-NAC)--was derived from the 'reverse diol
epoxide', anti-Phe-3,4-diol-1,2-epoxide, and not from the bay region diol
epoxides, syn- or anti-Phe-1,2-diol-3,4-epoxide. Levels of anti-PheDE-1-NAC in the urine of 36 smokers were (mean +/- SD) 728 +/- 859 fmol/ml urine. The results of this study provide the first evidence for a
mercapturic acid of a PAH diol
epoxide in human urine, but it was not derived from a bay region diol
epoxide as molecular epidemiologic studies have presumed, but rather from a reverse diol
epoxide, representative of metabolites with little if any carcinogenic activity. These results demonstrate the need for integration of genotyping and phenotyping information in molecular epidemiology studies.