Molecular markers of contaminant/carcinogen exposure are an increasingly important tool for toxicologists and epidemiologists in assessing human health risk. The most direct evidence of recent exposure and genetic damage is through the measurement of DNA carcinogen adducts in cells. The long-term objective of this program is to improve our understanding of the relationship between certain diet-generated DNA adducts and tumorigenesis. Heterocyclic aromatic amines (HAA's), a class of potent carcinogens formed during the cooking of meat and fish, are the focus of this study. Epidemiological studies suggest that the consumption of foods that contain HAA's increases the risk to colorectal and pancreatic cancer. The DNA adducts of three specific heterocyclic aromatic amines, 2-amino-1-methyl- 6-phenylimidazo[4,5b]pyridine (PhIP), 2-amino-3-methylimidazo[4,5-f] quinoline (IQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), which are associated with a variety of carcinogenic functions including lymphomas in mice, colon cancer in rats and liver cancer in non-human primates, are targeted for examination. Improved methods for detection and characterization of their DNA adducts is an important first step toward accomplishing this goal and is emphasized in the program. Animal models, which have interspecies similarities to humans, will be used as surrogates in order to develop biomarkers to assess human health risk due to HAA's. In vitro reactions will also be examined to provide larger quantities of reference adducts. Capillary separation methods (liquid chromatography or capillary zone electrophoresis) coupled to electrospray ionization (ESI)/tandem mass spectrometry, which permits the analysis of intact DNA adducts, and 32/P post-labelling will be used and compared in parallel to characterize the HAA-DNA adduct content of liver tissues. The high information content of the capillary LC-(or CZE)-MS/MS method of analysis will complement that of the high sensitivity/low structural information content method of 32/P post-labelling. The MS data will thus serve as evaluation and validation of the 32/P method for its subsequent application to the examination of human specimens where the exposure levels are significantly lower. It is expected that the information generated from the proposed study will provide new insights on the use of biomarkers for risk assessment and diet modifications in order to minimize risk to dietary cancer.
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