Phenanthrene Metabolism in Smokers: Use of a Two-Step Diagnostic Plot Approach to Identify Subjects with Extensive Metabolic Activation

Abstract

Polycyclic aromatic hydrocarbons (PAHs) in cigarette smoke are among the most likely causes of lung cancer. PAHs require metabolic activation to initiate the carcinogenic process. Phenanthrene (Phe), a noncarcinogenic PAH, was used as a surrogate of benzo [␣]pyrene and related PAHs to study the metabolic activation of PAHs in smokers. A dose of 10 g of deuterated Phe ([D 10 ]Phe) was administered to 25 healthy smokers in a crossover design, either as an oral solution or by smoking cigarettes containing [D 10 ]Phe. Phe was deuterated to avoid interference from environmental Phe. Intensive blood and urine sampling was performed to quantitate the formation of deuterated r- 1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D 10 ]PheT), a biomarker of the diol epoxide metabolic activation pathway. In both the oral and smoking arms approximately 6% of the dose was metabolically converted to diol epoxides, with a large intersubject variability in the formation of [D 10 ]PheT observed. Two diagnostic plots were developed to identify subjects with large systemic exposure and significant lung contribution to metabolic activation. The combination of the two plots led to the identification of subjects with substantial local exposure. These subjects produced, in one single pass of [D 10 ]Phe through the lung, a [D 10 ]PheT exposure equivalent to the systemic exposure of a typical subject and may be an indicator of lung cancer susceptibility. Polymorphisms in PAH-metabolizing genes of the 25 subjects were also investigated. The integration of phenotyping and genotyping results indicated that GSTM1-null subjects produced approximately 2-fold more [D 10 ]PheT than did GSTM1-positive subjects.

Structure–Function Studies of Naphthalene, Phenanthrene, Biphenyl, and Their Derivatives in Interaction with and Oxidation by Cytochromes P450 2A13 and 2A6

“…53–55 Several metabolites—including 1-, 4-, and 9-hydroxyphenanthrene—have been identified in human urine, 53–55 and in vitro studies have suggested that a number of P450 enzymes are involved in the formation of several hydroxylated and dihydrodiol metabolites of phenanthrene in humans. 18,56 Our present results support the conclusion that 9-hydroxyphenanthrene is a major metabolite during incubation of phenanthrene with P450s 2A13 and 2A6.…”

Longitudinal study of [D10]phenanthrene metabolism by the diol epoxide pathway in smokers

“…In our previous study of [D 10 ]phenanthrene, the mean percentage of dose excreted in the 6 h urine was 3.3% (Wang et al 2012). Other urinary metabolites of phenanthrene in humans have been identified as phenols and mercapturic acids.…”

Investigation of the presence in human urine of mercapturic acids derived from phenanthrene, a representative polycyclic aromatic hydrocarbon

“…It is possible of course that our previous observations regarding the effects of GSTM1 null status on levels of [D 10 ]Phe-tetraols 5 and 21 after administration of [D 10 ]Phe were due to chance [18]. The study involved only 25 subjects who received 10 μg [D 10 ]Phe either orally or by smoking cigarettes to which [D 10 ]Phe had been added so that the cigarettes delivered approximately the same dose of [D 10 ]Phe as in the oral administration arm [19].…”

“…We hypothesize that smokers who extensively metabolically activate PAH by the diol epoxide pathway will be at higher risk for lung cancer, all other factors considered equal. As a test of this hypothesis, we are administering [D 10 ]phenanthrene ([D 10 ]Phe, a single dose of 1 – 10 μg) to smokers and analyzing the amounts of [D 10 ]Phe-tetraols 5 and 21 excreted in 6h urine, a protocol which has been previously validated [18–20]. The use of [D 10 ]Phe allows us to focus only on the metabolic activation process, setting aside exposure variables such as diet and polluted air which contain Phe and would complicate the interpretation of levels of unlabeled Phe-tetraols 5 and 21 excreted by smokers.…”

“…In one study of subjects to whom [D 10 ]Phe was administered, we found that individuals who were null for the GSTM1 gene, among 12 genetic polymorphisms tested, had a significantly higher approximately doubled level of [D 10 ]Phe-tetraols 5 and 21 than did those who were GSTM1 competent [18]. The simplest explanation for this phenomenon would be that GSTM1 catalyzes the detoxification of Phe-diol epoxides 4 and 20 , competing with tetraol formation; therefore the null individuals would have higher levels of [D 10 ]Phe-tetraols 5 and 21 .…”