University of North Carolina Chapel Hill

Center for Environmental Health and Susceptibility

James A Swenberg, Ph.D.
james_swenberg@unc.edu
http://cehs.sph.unc.edu/

Project Description

The UNC-Chapel Hill Center for Environmental Health and Susceptibility brings population science, medical and biomedical researchers together to examine major issues in environmental health resulting from gene environment interactions that affect an individual's susceptibility to disease. The highly complex nature of such interactions demands in-depth expertise in many different disciplines to understand the influence of genetic, metabolic, endocrine, developmental and toxicological issues on disease outcomes. The Center achieves this goal by fostering enhanced interaction and collaboration among researchers, so that the expertise of experts in diverse fields of environmental health can expand the vision and capabilities of a preeminent cadre of researchers to excel far beyond the norm. Such interaction and collaboration is demonstrated among the five research cores: Genetic Susceptibility, Developmental Susceptibility, Toxicokinetic Susceptibility, Transomics, and Obesity Research. The core support also makes state-of-the-art resources and expertise available to our scientists through the support of four facility cores. Molecular Epidemiology provides centralized resources for biospecimen collection, preparation, storage and tracking, and high throughput genetic analysis. Biostatistical and Epidemiologic Methods provides consultation on statistical and study design and analysis to help ensure that valid scientific conclusions emerge from our environmental health research. The Biomarkers core makes available training, expertise and sample analysis using expensive and sophisticated instrumentation for mass spectrometry, molecular biology, genomics, proteomics and metabolomics. Finally, the Nutrient Assessment core supplies analysis and dietary assessment of nutrients and biomarkers of nutritional status that may modulate environmental health and disease.

The core support also provides funds for a multifaceted Pilot Project Program that promotes interdisciplinary collaboration, encourages young investigators to enter environmental health research, and enhances use of the facility cores. In addition, the requested support provides a diverse enrichment program that will increase interactions with visiting investigators and broaden the scope of environmental health research. Support for a Community Outreach and Education Program facilitates translational activities that communicate the scientific advances of the Center to the lay community, concerned citizens groups, and government. This NIEHS Center of Excellence is coordinated by an Administrative core that reports through the School of Public Health at the University of North Carolina.

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Program Highlights

Long Island Breast Cancer Study Project (LIBCSP)

The LIBCSP is a population-based study undertaken to identify environmental factors associated with breast cancer risk and survival. LIBCSP began as a case-control study in response to federal legislation, and was jointly funded by NIEHS and NCI. Primary aims focused on breast cancer risk associated with: (1) polycyclic aromatic hydrocarbon (PAH)-DNA adducts (with Dr. Regina Santella, Director of the NIEHS Center for Environmental Health in Northern Manhattan at Columbia University); (2) blood levels of organochlorines including DDT, DDE, PCBs, and chlordane (with Dr. Mary Wolff, Director of the NIEHS-funded Mount Sinai Center for Children’s Environmental Health and Disease Prevention Research); and (3) electromagnetic fields (in a companion study with Dr. Christina Leske, Department of Preventive Medicine at Stony Brook Medical Center). Despite community concern and biologic plausibility of such associations, little or no effects were found for organochlorine levels or electromagnetic fields.

A postnatal paraquat and maneb model was the first report of a developmental model that could reproduce the phenotype. It has since been shown to exhibit progressive cell loss indicative of both silent and cumulative toxicity across life. This model is critical in that it documents the 1) a potential role for pesticides that impact dopamine systems as contributory risk factors for the human disease, 2) a separation of risk factor exposures from disease onset, demonstrating the importance of silent and cumulative toxicity over the lifespan; and 3) a role for oxidative stress as a component of the associated pathophysiology. A prenatal maneb exposure model also resulted in expression of this phenotype. Both models are consistent with a fetal basis for the adult disease. [1-3].

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Inhibitory Effects of Caffeine on the Development of Skin Cancer

Center investigators have found that oral administration of caffeine to SKH-1 mice twice a week for several months inhibited UVB-induced skin cancer; oral or topical administration of caffeine to UVB pretreated mice in the absence of further UVB irradiation (high risk mice) inhibited the development of skin tumors. Mechanistic studies indicated that caffeine enhanced apoptosis in epidermal cells and in tumors in mice. The proapoptotic effect of caffeine was selective for DNA-damaged epidermis, since caffeine administration to normal non UVB-treated epidermis, or to areas of the epidermis distant from tumors in mice did not stimulate apoptosis.

In 2002 and 2004 we reported a 29-35% increase associated with breast cancer risk in relation to PAH-DNA adducts measured in lymphocytes. Our findings, based on the largest epidemiologic study conducted to date on this issue (with a population-based sample of over 1800 women), are consistent with much smaller reports. PAH are ubiquitous combustion products from diesel fuel, cigarette smoke, and grilled and smoked foods, and are known carcinogens in the lung, and have been found to increase mammary tumors in laboratory animals, although effects on the breast in humans are unclear. Our data suggest that increasing levels of exposure to PAH sources are not associated with stronger effect estimates for the association between adducts and breast cancer. Therefore, the biomarker appears to better reflect how the body responds to the PAH exposure, rather than the exposure amount. To test this hypothesis, we have turned to examining effects associated with: (1) other PAH sources and (2) variations in genetic susceptibility, particularly in genes involved in DNA repair, oxidative stress, and carcinogen metabolism/detoxification pathways. In 2004, we reported a doubling of risk associated with long-term exposure to residential environmental tobacco smoke, and in 2007 we found a 50% increase in risk associated with the average lifetime intake of grilled and smoked foods. In 2004 we also reported a modest 21% increase in the association between those subjects with at least one variant Gln allele at exon 23 of the XPD gene (also called ERCC2) and breast cancer risk; the increase in risk for homozygosity of the variant allele was more pronounced among those with PAH-DNA adduct levels above the median (OR, 1.61; 95% CI, 0.99-2.63), and among current smokers (OR, 1.97; 95% CI, 1.02-3.81). Recently we considered multiple genes in the NER pathway, and our findings suggest that the risk of breast cancer was positively associated with carrying multiple variant alleles in a dose-response manner, with a 50% increase associated with carrying more than 6 variants. In 2005, we reported a 90% elevation in risk for the interaction between the 399Gln allele of XRCC1 and detectable PAH-DNA adducts. In 2006, findings from LIBCSP indicate that smokers with the GSTA1 (AG/GG) genotypes had an 89% increased breast cancer risk compared to wildtype nonsmokers. Further, our data indicate that carrying multiple variants in several GST markers is associated with more than a 3-fold increase in breast cancer risk. These data support the hypothesis that PAH-DNA adducts, and PAH sources, are associated with breast cancer risk, and that the associations are modified by variations in genetic polymorphisms in biologically plausible pathways.

Gammon MD, Sagiv SK, Eng SM, Shantakumar S, Gaudet MM, Teitelbaum SL, Britton JA, Terry MB, Wang LW, Wang Q, Stellman SD, Beyea J, Hatch M, Kabat GC, Wolff MS, Levin B, Neugut AI, Santella RM.Polycyclic aromatic hydrocarbon-DNA adducts and breast cancer: a pooled analysis. Arch Environ Health. 2004 Dec;59(12):640-9.

Beyea J, Hatch M, Stellman SD, Santella RM, Teitelbaum SL, Prokopczyk B, Camann D, Gammon MD. Validation and calibration of a model used to reconstruct historical exposure to polycyclic aromatic hydrocarbons for use in epidemiologic studies. Environ Health Perspect. 2006 Jul;114(7):1053-8.

Ahn J, Gammon MD, Santella RM, Gaudet MM, Britton JA, Teitelbaum SL, Terry MB, Neugut AI, Eng SM, Zhang Y, Garza C, Ambrosone CB. Effects of glutathione S-transferase A1 (GSTA1) genotype and potential modifiers on breast cancer risk. Carcinogenesis. 2006 Sep;27(9):1876-82.

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Development and Application of Biomarkers of Exposure

Benzene is a common contaminant in hazardous waste sites, also emitted from gasoline and organic combustion products. Although benzene toxicity has been linked to its metabolism, the dose-related production of metabolites is not well understood in humans, particularly at low exposure levels. We used natural spline (NS) models to investigate nonlinear relationships between levels of benzene urinary metabolites [E,E-muconic acid (MA), S-phenylmercapturic acid (SPMA), phenol (PH), hydroquinone (HQ), and catechol (CA)] and benzene exposure among 386 exposed and control workers in Tianjin, China. After adjusting for background levels (estimated from the 60 control subjects with lowest benzene exposures), expected mean trends of all metabolite levels increased with benzene air concentrations over the range from 0.03 to 88.9 ppm. Molar fractions for PH, HQ and MA changed continuously with increasing air concentrations, suggesting that competing CYP-mediated metabolic pathways favored MA and HQ below 20 ppm and favored PH above 20 ppm. Mean trends of dose-specific levels (μM/ppm benzene) of MA, PH, HQ, and CA all decreased with increasing benzene exposure, with an overall 9-fold reduction of total metabolites. Surprisingly, 90% of the reductions in dose-specific levels occurred below about 3 ppm for each major metabolite. Using general linear models (GLM) with NS-smoothing functions we detected significant effects upon metabolite levels of gender, age and smoking status. Metabolite levels were about 20% higher in females and decreased between one and two percent per year of life. Also, levels of HQ and CA were greater in smoking subjects. We then extended the GLM+NS models to investigate 9 single nucleotide polymorphisms (SNPs) of metabolizing genes, thought to be responsible for production of benzene metabolites [cytochrome P450 2E1 (CYP2E1), NAD(P)H: quinone oxidoreductase (NQO1), microsomal epoxide hydrolase (EPHX1), glutathione-S-transferases (GSTT1, GSTM1 and GSTP1) and myeloperoxidase (MPO)]. After adjusting for benzene exposure, gender, age and smoking status, NQO1*2 affected all five metabolites, CYP2E1 affected all metabolites except CA, EPHX1 affected CA and SPMA, and GSTT1 and GSTM1 affected SPMA. Significant interactions were also detected between benzene exposure and all four genes and between smoking status and NQO1*2 and EPHX. No significant effects were detected for GSTP1 or MPO. Results generally support prior associations between benzene hematotoxicity and specific gene mutations, confirm earlier evidence that GSTT1 affects production of SPMA, and provide additional evidence that SNPs in NQO1*2, CYP2E1, and EPHX1 affect metabolism of benzene in the human liver. Although all of these effects of metabolism genes and gene-environment interactions were significant, the magnitudes of the effects were small, generally less than two-fold. This study represents the most comprehensive analysis ever reported of the effects of benzene exposure, metabolism genes, and gene-environment interactions on the levels of benzene metabolites. Overall, our results indicate that benzene metabolism is highly nonlinear with increasing benzene exposure above 0.03 ppm and that current human toxicokinetic models do not accurately predict benzene metabolism below 3 ppm. Since the dose-specific levels of benzene metabolites are much higher at low levels of exposure, current estimates of human risks of leukemia, which were derived from studies of humans and animals exposed to high levels of benzene, may be substantially underestimated at low levels of exposure. Our results also indicate that the effects of genes and gene-environment interactions upon benzene metabolite levels are rather small and are dwarfed by the large effects of benzene exposure per se. Finally, our results suggest that GLM+NS models are ideal for evaluating nonlinear relationships between environmental exposures and levels of human biomarkers that have plagued prior studies.

Kim S, Vermeulen R, Waidyanatha S, Johnson BA, Lan Q, Smith MT, Zhang L, Li G, Shen M, Yin S, Rothman N, Rappaport SM. Modeling human metabolism of benzene following occupational and environmental exposures. Cancer Epidemiol Biomarkers Prev. 2006 Nov;15(11):2246-52.

Kim S, Lan Q, Waidyanatha S, Chanock S, Johnson BA, Vermeulen R, Smith MT, Zhang L, Li G, Shen M, Yin S, Rothman N, Rappaort S. Genetic polymorphisms and benzene metabolism in humans exposed to a wide range of air concentrations. Pharmacogenetics and Genomics 2006 (in press).

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