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Final Progress Reports: Oregon State University: Environmental PAH Mixtures as Skin and Transplacental Carcinogens

Superfund Research Program

Environmental PAH Mixtures as Skin and Transplacental Carcinogens

Project Leader: William M. Baird
Grant Number: P42ES016465
Funding Period: 2009-2013

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Final Progress Reports

Year:   2012 

 

Studies and Results

 

A 12-month transplacental cancer study investigated in utero exposure to a polycyclic aromatic hydrocarbon (PAH) mixture collected from the Willamette River Superfund site along with two concentrations of a mixture of air-borne PAHs, simulating filter samples collected in Beijing, China. These were compared the potent PAH, dibenzo[def,p]chrysene (DBC) which has been demonstrated in this model to produce an aggressive t-cell lymphoblastic leukemia and lung cancer. Pregnant mice were gavaged on GD 17, sub-samples of fetal tissue collected 24 hr later for gene expression profiles using arrays and DNA adducts using UPLC/MS/MS. The remaining progeny were weaned and monitored for 10 months. The DBC 15 mg/kg treatment group had 19.2% (n=47) survival due to lymphoma mortality at the end of 10 months while all other groups presented no lymphoma. The DBC group also had 100% lung tumors, characterized as either hyperplasia, adenoma, or carcinoma while the low air mixture of 53 mg/kg and the high air mixture of 95 mg/kg had an incidence of 13.3% (n=61) and 26.3% (n=57) respectively. The Portland Harbor mixture (0.39 mg/kg) did not result in any cancers or additional pathologies. Gene profile data and DNA adduct level analysis is in progress and will be correlated with the 10 month phenotypes.

This project is also investigating the effects of dietary intervention with the chemopreventative agent, chlorophyllin (CHL), during transplacental exposure to the model PAH, DBC. This is a follow-up of an earlier study which established distribution and excretion times of a single DBC dose on gestation day 17 for mother and fetus from 2-8 hours post gavage. In this study pregnant mice were treated with oral gavage of 14C-DBC, 15 mg/kg, 14C-DBC + CHL 1:1 molar ratio, 14C-DBC + CHL 1:10 molar ratio, or tricaprylin vehicle control. Four mothers and litters were euthanized at 4, 6, 8, 12, and 24 hours post gavage. Tissues were harvested for scintillation counting and HPLC analysis of DBC metabolites to determine if chlorophyllin changes the metabolic profile of DBC and/or binds DBC in the gut reducing the bioavailability.

A major collaboration between this project and Cross-Species Comparison of Transplacental Dosimetry PAHs has been completed using the relatively new technique of human microdosing and analyses with Accelerator Mass Spectrometry (AMS) to quantitate ultralow doses of 14C-DBC given to human subjects. 14C- DBC from NCI was purified and the radiochemical purity verified via HPLC fraction collection and scintillation counting. With full IRB and radiation safety approval, nine individuals were enrolled in the study. Utilizing the Integrative Health Sciences Facility Core, blood and urine were collected at time points over 72 hours. The volunteers enrolled in this study were males and females between 20 to 65 years old with BMIs of 23.5 - 34.8. Despite the variability expected in a human study, including any unidentified polymorphisms, a variety of ages, BMI, and sexes, the pharmacokinetic results were remarkably consistent.

The two projects continue to investigate important Phase I and Phase II enzyme expression levels and activity throughout mouse and human gestation to better understand the mode of action of PAH metabolism, recognize particularly susceptible times during pregnancy and develop pharmacokinetic models in pregnant rodents and humans. Fetal mouse were collected from the transplacental model described above and from the human tissue bank at the University of Washington Department of Pediatrics. Researchers are using an LC/MS proteomics approach to characterize activity in fetal thymus, lung, and liver.

A second skin tumor study is underway to follow up results from the study done in years 1-2 of this grant. C57B6 Cyp1b1 null mice were backcrossed to an FVB genetic background for 7 generations for this study. Female homozygous nulls and homozygous wild-type siblings were used to compare skin tumor response to initiation with benzo[a]pyrene (400 nmol), DBC (4 nmol), SRM 1597a coal tar extract (1 mg), and toluene vehicle control followed by a 25 week promotion with 12-O-tetradecanoylphorbol-13-acetate (6.5) nmol. Additional groups of animals were treated with the same initiation doses at early time points for investigating levels of DNA adduction and changes in gene or protein expression.

One of the missions of this Superfund Program is to develop new technologies for understanding, measuring, and predicting PAH exposures. A smart phone application has been developed which keeps track of and warns users about unwanted small particulate matter, coarse particulate matter, and ozone atmospheric exposures. The app was designed to be intuitive for the general population, presenting data as color-coded points on a Google map or graph and allowing users to set exposure warning levels via sliding color-coded bars. Warnings are sent to users whenever they are in or are approaching a location with predicted exposures above the set warning levels. With more than 1 billion active smartphone users in the world, the research team believes that the developed app has great potential to disseminate information to the general public, prevent unwanted foreseeable exposures, and facilitate interdisciplinary collaborations between research scientists and community outreach programs. The research team continues to seek new collaborations with other SRP cores. Recent consultations with the SRP Research Translation Core has identified several components of the application that can be modified to further enhance ease of use and interpretability in the general community, which researchers hope to implement before submitting the app for free public download on the iTunes and android stores later this year.

 

Significance

 

These studies will provide valuable and readily measurable biomarkers for predicting the potential risk environmental mixtures pose. Furthering the research team's knowledge of the underlying mechanisms involved in carcinogenesis, in particular specific pathways of bioactivation identified through early gene expression changes that correlate to later tumor formation, will help to translate who and why particular groups are at risk for developing cancer from PAH exposure. Comparisons of proteomics, metabolism, and PBPK models from rodents and humans enable scientists to understand and predict outcomes from human exposures to environmental PAHs which are an increasing risk on a global scale.

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