Superfund Research Program
Comparative Toxicogenomics and Individual Differences in the Human Response to Dermal Exposure to Polycyclic Aromatic Hydrocarbons
Project Leader: Leena A. Nylander-French
Grant Number: P42ES005948
Funding Period: 2000 - 2011
The researchers are investigating the capacity of the human skin to metabolize polycyclic aromatic hydrocarbons (PAHs) and contribute to systemic internal exposure, the individual differences in quantitative exposure analysis, and the use of biomarkers as quantitative measures for exposure assessment. They have shown that skin, along with lungs, is an important route for PAH exposure and that dermal exposure can contribute to the total body burden in a PAH-exposed population. They have established that naphthalene (a model PAH) and its metabolites 1- and 2-naphthol can be used as quantitative biomarkers of exposure for a complex fuel mixture to the skin. They have shown that highly specific polyclonal antibodies developed to synthetic epitopes of naphthalene metabolites can be used for an inexpensive and sensitive ELISA for quantification of keratin adducts as biomarkers of dermal exposure. During this past year, they performed a candidate gene single nucleotide polymorphism (SNP) and a genome-wide association study using 250K SNP markers in relation to a range of biomarkers of exposure to identify highly significant quantitative trait nucleotides in 121 U.S. Air Force personnel exposed to jet fuel. They are investigating the association between biomarkers of naphthalene exposure (i.e., naphthalene-keratin adducts in the epidermis, urine metabolites, breath naphthalene levels), dermal and inhalation exposure levels, workplace variables (e.g., exposure time, personal protection equipment use) to the genotypes of individuals in the exposed population. The data indicate that quantitative individual differences in naphthalene exposure predictors exist in relation to highly associated SNP genotypes and JP-8 exposure biomarker levels in occupationally exposed workers. Highly significant SNP associations (-log10P≥ 5) were observed for total adducted epidermal keratin and total urine naphthol levels. Thus far, they have identified fucosyltransferase 9 (FUT9; 6q16), a critical enzyme in keratan sulfate biosynthesis and glycosylation of keratin in the epidermis that is in linkage disequilibrium with a nicotinic acetylcholine receptor component (CHRNA10, 11p15.5), which plays a critical role in coordinating adhesion and motility of keratinocytes. Bioinformatics analysis of these and other SNPs is in progress and candidates selected for further investigation and functional validation using reverse genetics strategy with RNAi specific knockdown experiments using transduced context-specific reconstructed human epidermis. The data show the power of genotype-phenotype association studies in limited populations to identify highly significant associated SNPs in intermediate phenotypes. By using quantitative measures of biomarkers and individuals stratified by documented real-time measures of epicutaneous and inhalation exposure, the gene-by-environment interactions (GEI) can be identified with sufficient statistical power to select candidate genes for bioinformatic analysis and functional validation. Ultimately, the final proof will be in functional validation of the role of the genic sequences (cis regulatory functions) in the GEI and the exposure-induced phenotype. Determination of the significance of individual differences in detoxification as a variable in exposure and risk assessment using mathematical, statistical, and toxicokinetic modeling is critical to developing our knowledge base and refining exposure-assessment methodology.