This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Over the last 15 years we have been studying the role of diet on cancer. The cooking, heat processing, and pyrolysis of protein-rich foods result in the formation of a group of structurally related heterocyclic aromatic amines that have been found to be potent mutagens in a number of assay systems. These same compounds produce tumors at multiple organ sites in both male and female mice and rats and 100 percent of non-human primates given one of these heterocyclic amines developed hepatocarcinomas after a very short latency. Given these very compelling data, it is important to determine the extent to which these dietary mutagens/carcinogens contribute to the human cancer incidence and to devise strategies to limit their impact. This NIH program project attempts to achieve these goals by: - Identifying and quantifying the human intake of these heterocyclic amines in the diet; - Understanding the chronic toxicology of these compounds by analysis of DNA binding, cytogenetic damage and mutational effects following chronic long-term feeding exposure of rodents; - Understanding the mechanistic relevance of animal studies for humans by characterizing important metabolic pathways (rodents, non-human primates, humans) with the additional goal of understanding the nature of the tissue specificity in tumor formation induced by these heterocyclic amines; - Understanding the dose-relevance of high dose animals studies for human risk assessment by assessing the dosimetry from ingestion of these potent mutagens at low doses; - Characterizing the structural features of carcinogens and DNA adducts that are correlated with mutation; - Predicting the importance of individual differences in repair and metabolism using CHO cells and rodent strains having genetic differences in DNA repair and metabolic activation; - Identifying and validating biomarkers that may be useful for human risk or susceptibility determinations and; - Evaluating data generated from this project and data from the literature to produce quantitative cancer-risk assessment. It is clear that the AMS resource is having a major impact on this NIH funded Program Project, as aspects of this work can only be accomplished utilizing accelerator mass spectrometry. In particular, AMS allows us to conduct studies of metabolism and DNA damage at low dose that impacts every sub-project of our program project grant. Current study abstract: Cytochrome P450-mediated hydroxylation and UDP-glucuronosyltransferase (UGT)-catalyzed glucuronidation are major metabolic pathways in the biotransformation of many xenobiotics including heterocyclic amines (HAs). Studies have shown that, in humans, the bioactivation of the HA PhIP is highly dependent upon cytochrome P4501A2-mediated N-hydroxylation to the corresponding N-hydroxy-PhIP. Subsequent N-glucuronidation results in the formation of the less reactive N-hydroxy-PhIP-N2-glucuronide and N-hydroxy-PhIP-N3-glucuronide, which can be excreted through urine or bile, or can be transported to extrahepatic tissue where further metabolism can occur. Recent studies have shown that, in humans, glucuronidation of N-hydroxy-PhIP is a major pathway in the biotransformation of PhIP and that the UGT1A1 isozyme is a major contributor to N-hydroxy-PhIP glucuronidation. In addition, polymorphic expression of several UGTs has led to differential metabolism of many substrates. This inter-individual variation in UGT expression could potentially alter the bioactivation of pro-carcinogens such as PhIP in certain individuals. Therefore, understanding the N-glucuronidation of PhIP and N-hydroxy-PhIP in humans is especially important because the failure to conjugate N-hydroxy-PhIP by glucuronidation could result in further activation by esterifying reactions. These reactions would result in highly reactive compounds that can bind DNA, potentially causing mutations. Since PhIP bioactivation has been shown to be responsible for the formation of DNA adducts in multiple tissues in animal models, by determining the role glucuronidation has on tissue-specific bioactivation/detoxification of PhIP in rodent models, a better understanding of how PhIP metabolism contributes to DNA adduct formation in whole animals can be established. By using accelerator mass spectrometry we can analyze DNA adduct formation in tumor target tissues and dietary relevant doses of PhIP. We hypothesize that animals and/or tissues with diminished glucuronidation capacity will be more susceptible to PhIP induced DNA adducts in tumor target tissues than animals with increased UGT activity. This work resulted in the following InPress publication: Malfatti, M.A., Ubick E.A. and Felton, J.S. (2005) The impact of glucuronidation on the bioactivation and DNA adduction of the cooked-food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in vivo. Carcinogenesis, in press.
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