Numerous studies have demonstrated that biologically active, natural components of the diet may confer resistance to chemical carcinogens via induction and/or inhibition of biotransformation enzymes. In particular, specific chemical components of the diet, such as flavonoids, isocyanates, glucosinolates, indoles, dithiolthiones, and polyphenols have been identified as effective inducers and/or inhibitors of carcinogen activation/detoxification pathways in animal models. There is much supporting data from human epidemiological studies on the important relationship between diet and cancer in humans, although the diversity and complexity of the diet, and uncertainty of specific exposures, in such studies makes identification of specific active components nearly impossible. Although animal models are useful for """"""""hypothesis testing"""""""", species differences in carcinogen activation and detoxification pathways, as well as differences in gene regulation and expression in response to inducers, make extrapolation of animal data to the human situation tentative, at best. Thus, there is a need to develop model systems that utilize human cells/tissues to determine the efficacy of specific dietary components and/or putative chemoprotectant drugs to favorably modify the biotransformation of human carcinogens. One such model human carcinogen is aflatoxin B1. Aflatoxins are mycotoxins produced by the common fungal molds, Aspergillus flavus and Aspergillus parasiticus. Worldwide, aflatoxins are considered a major public health problem because of their potent carcinogenic effects. Human epidemiological data has documented that humans are susceptible to AFB-induced hepatocarcinogenesis, especially in combination with hepatitis B virus infection. However, there are large species differences in the susceptibility to aflatoxin carcinogenesis. Rats are highly sensitive, whereas mice are very resistant. The mechanism for this difference is associated with the expression of a specific enzyme, glutathione S-transferase A3-3 (mGSTA3-3), which is present in the livers of mice, but not rats. Treatment of rats with the drug, oltipraz, or the food additive, ethoxyquin, protects rats from aflatoxin-induced liver cancer. The mechanism for this protection is due to the ability of these chemicals to """"""""turn on"""""""" a gene for a glutathione S-transferase, rGSTA5-5, that is normally not expressed in rat liver, but which efficiently detoxifies aflatoxin. Human liver tissue has very low ability to detoxify aflatoxin -- in fact, worse than the poor ability of rats. There has been considerable interest in devising a dietary or chemointervention strategy for humans that increases resistance to AFB by induction of GSTs. The long range goals of this proposal are to: 1) establish in vitro models that utilize isolated human hepatocytes in culture and human cDNA expressing yeast, to assess the efficacy of specific dietary components as putative chemoprotectors against AFB and other chemical carcinogens, and 2) complete the characterization of species differences in glutathione S-transferases with activity toward AFB-epoxide.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Research Project (R01)
Project #
5R01ES005780-15
Application #
6524718
Study Section
Chemical Pathology Study Section (CPA)
Program Officer
Shreffler, Carol K
Project Start
1991-05-01
Project End
2004-07-31
Budget Start
2002-08-01
Budget End
2003-07-31
Support Year
15
Fiscal Year
2002
Total Cost
$318,555
Indirect Cost
Name
University of Washington
Department
Public Health & Prev Medicine
Type
Schools of Public Health
DUNS #
135646524
City
Seattle
State
WA
Country
United States
Zip Code
98195
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Gross-Steinmeyer, Kerstin; Stapleton, Patricia L; Tracy, Julia H et al. (2009) Modulation of aflatoxin B1-mediated genotoxicity in primary cultures of human hepatocytes by diindolylmethane, curcumin, and xanthohumols. Toxicol Sci 112:303-10
Zhou, Changcheng; Poulton, Emma-Jane; Grun, Felix et al. (2007) The dietary isothiocyanate sulforaphane is an antagonist of the human steroid and xenobiotic nuclear receptor. Mol Pharmacol 71:220-9
Peterson, Sabrina; Lampe, Johanna W; Bammler, Theo K et al. (2006) Apiaceous vegetable constituents inhibit human cytochrome P-450 1A2 (hCYP1A2) activity and hCYP1A2-mediated mutagenicity of aflatoxin B1. Food Chem Toxicol 44:1474-84
Guo, Yingying; Breeden, Linda L; Fan, Wenhong et al. (2006) Analysis of cellular responses to aflatoxin B(1) in yeast expressing human cytochrome P450 1A2 using cDNA microarrays. Mutat Res 593:121-42
Gross-Steinmeyer, K; Stapleton, P L; Tracy, J H et al. (2005) Influence of Matrigel-overlay on constitutive and inducible expression of nine genes encoding drug-metabolizing enzymes in primary human hepatocytes. Xenobiotica 35:419-38
Guo, Yingying; Breeden, Linda L; Zarbl, Helmut et al. (2005) Expression of a human cytochrome p450 in yeast permits analysis of pathways for response to and repair of aflatoxin-induced DNA damage. Mol Cell Biol 25:5823-33
Abel, Erika L; Bammler, Theo K; Eaton, David L (2004) Biotransformation of methyl parathion by glutathione S-transferases. Toxicol Sci 79:224-32
Abel, Erika L; Lyon, Robert P; Bammler, Theodore K et al. (2004) Estradiol metabolites as isoform-specific inhibitors of human glutathione S-transferases. Chem Biol Interact 151:21-32
Gross-Steinmeyer, K; Stapleton, P L; Liu, F et al. (2004) Phytochemical-induced changes in gene expression of carcinogen-metabolizing enzymes in cultured human primary hepatocytes. Xenobiotica 34:619-32

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