One widely accepted metabolic activation pathway of the prototypic carcinogenic
polycyclic aromatic hydrocarbon (PAH)
benzo[a]pyrene (BaP) proceeds through the "bay region diol
epoxide" BaP-(7R,8S)-diol-(9S,10R)-epoxide (2). However, few studies have addressed the analysis of human urinary metabolites of BaP, which result from this pathway.
Phenanthrene (Phe) is structurally related to BaP, but human exposure to Phe is far greater, and its metabolites can be readily detected in urine. Thus, Phe metabolites have been proposed as
biomarkers of PAH exposure and metabolic activation. Phe-tetraols in particular could be
biomarkers of the diol
epoxide pathway. While BaP-tetraols and Phe-tetraols have been previously quantified in human urine, no published studies have determined their enantiomeric composition. This is important because different enantiomers would result from the bay region diol
epoxide and "reverse" diol
epoxide pathways, the latter being associated with weak mutagenicity and carcinogenicity. We addressed this problem using chiral HPLC to separate the enantiomers of BaP-7,8,9,10-tetraol and Phe-1,2,3,4-tetraol. Urine samples from smokers were subjected to solid-phase extraction, chiral HPLC, and GC-NICI-MS/MS analysis for silylated Phe-1,2,3,4-tetraols. The results demonstrated that >96% of Phe-1,2,3,4-tetraol in smokers' urine was
Phe-(1S,2R,3S,4R)-tetraol (12), resulting from the "reverse" diol
epoxide pathway, whereas less than 4% resulted from the "bay region diol
epoxide" pathway of Phe metabolism. Urine from
creosote workers was similarly analyzed for BaP-7,8,9,10-tetraol enantiomers. In contrast to the results of the Phe-tetraol analyses, 78% of BaP-7,8,9,10-tetraol in these human urine samples was BaP-(7R,8S,9R,10S)-tetraol (3) resulting from the "bay region diol
epoxide" pathway of BaP metabolism. These results provide further support for the bay region diol
epoxide pathway of BaP metabolism in humans and demonstrate differences in BaP and Phe metabolism, which may be important when considering Phe-tetraols as
biomarkers of PAH metabolic activation.