Grantee Research Project Results
2001 Progress Report: Fetal Metabolism of Aflatoxin B1 and Susceptibility to Childhood Cancer
EPA Grant Number: R827441Title: Fetal Metabolism of Aflatoxin B1 and Susceptibility to Childhood Cancer
Investigators: Gallagher, Evan
Institution: University of Florida
EPA Project Officer: Aja, Hayley
Project Period: July 1, 1999 through June 30, 2002 (Extended to March 30, 2004)
Project Period Covered by this Report: July 1, 2000 through June 30, 2001
Project Amount: $523,123
RFA: Children's Vulnerability to Toxic Substances in the Environment (1999) RFA Text | Recipients Lists
Research Category: Children's Health , Human Health
Objective:
The specific objectives of this project are to: (1) fully characterize and compare the expression of enzymes that catalyze aflatoxin (AFB1) oxidation and AFB1-8,9-epoxide (AFBO) detoxification in human prenatal liver and maternal placenta; (2) compare the rates of AFBO-DNA binding and DNA repair, and the frequency of AFB1-induced p53 mutations among adult and prenatal liver tissues; and (3) evaluate the effects of chemoprotective agents on ameliorating AFB1-induced precancerous lesions in human prenatal liver slices.Progress Summary:
In the second year of the project, we finished the quantitative analysis of the expression levels of AFB1 metabolizing enzymes in a panel of prenatal and adult liver tissues (experiments under specific aim #1) as well as the in vitro DNA and protein binding studies (specific aim #2). Substantial individual and ontogenic variation in the hepatic expression of certain AFB1 metabolizing enzymes were noted. We originally had hypothesized that such differences, if present, would lead to a marked difference in susceptibility among adult liver and prenatal liver tissues with regards to in vitro AFB1-macromolecular binding. However, the prenatal liver tissues did not exhibit a marked susceptibility to the formation of AFBO-macromolecular adducts in vitro. In addition, high interindividual variability was observed with respect to rates of in vitro formation of AFBO-DNA and AFBO-protein adducts among a panel of 10 adult donors, but little variation was observed among the 10 prenatal liver tissue donors. We also observed that the expression of some AFB1 oxidative enzymes (e.g., prenatal liver CYP3A7 and adult liver CYP1A2 and CYP3A4/5) were correlated with AFBO-macromolecular adduct formation; however, the levels of putative AFBO detoxification enzymes glutathione S-transferase M1-1 (hGSTM1-1), microsomal epoxide hydrolase, and aldehyde keto-reductase 7A were not. Collectively, these results indicate that despite ontogenic differences in the expression of AFB1 metabolizing enzymes, prenatal liver tissues do not exhibit a marked susceptibility to the in vitro formation of AFBO-DNA or AFBO-protein adducts relative to adults.A detailed comparative study of the expression of individual alpha class GST isoenzymes in prenatal and adult liver GST isoenzymes (experiments relative to specific aim #1) also was completed during this reporting period. These studies revealed the presence of alpha class GST isozyme hGSTA4-4 and hGSTA1/2 mRNAs in prenatal liver cytosol and mitochondria, and multiple tissue array analysis demonstrated considerable tissue-specific and developmental variation in hGSTA4 and hGSTA1/2 mRNA expression. Although prenatal liver cytosolic GSTs were active toward a variety of GST substrates, glutathione-dependent peroxidase and GST-dependent peroxidase activities were 9- and 18-fold lower in prenatal liver relative to adult liver. Thus, while prenatal liver tissues were generally not highly susceptible to the procarcinogen AFB1, it is possible that the relatively inefficient prenatal reduction of hydroperoxides may underlie an increased susceptibility to maternally transferred pro-oxidants. Accordingly, pro-oxidant transplacental carcinogens may be investigated in future spinoff studies.
Progress on studies using cultured prenatal liver slices and placental AFB1-metabolizing enzyme expression was hampered by technical issues related to the availablity of high-quality human liver tissue for culture. Experiments using relevant cell line models such as placental trophoblast cell lines and CD34+ cell lines are being investigated to conduct these studies.
Future Activities:
Our major focus for the next reporting period will be to use a cultured hematopoietic precursor (CD34+) cell line as a model to assess the effects of low, dietary relevant levels of AFB1 exposure on DNA injury and gene expression.Journal Articles on this Report : 1 Displayed | Download in RIS Format
| Other project views: | All 18 publications | 5 publications in selected types | All 5 journal articles |
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Gallagher EP, Gardner JL. Comparative expression of two alpha class glutathione S-transferases in human adult and prenatal liver tissues. Biochemical Pharmacology 2002;63(11):2025-2036. |
R827441 (2001) R827441 (Final) |
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Supplemental Keywords:
risk, risk assessment, effects, health effects, human health, metabolism, vulnerability, sensitive populations, carcinogen, teratogen, mutagen, cellular, population, enzymes, infants, children, age, diet, genetic predisposition, susceptibility, chemicals, toxics, decision making, southeast, EPA Regions., RFA, Health, Scientific Discipline, Susceptibility/Sensitive Population/Genetic Susceptibility, Health Risk Assessment, Risk Assessments, genetic susceptability, Epidemiology, Molecular Biology/Genetics, Children's Health, Biochemistry, Genetics, epidemeology, environmental hazard exposures, sensitive populations, bioactivated environmental toxicants, biotransformation, heterocyclic amines, cytochrome P450, DNA reactive metabolites, transplacental exposure to mutagenic agents, aflotoxin, human exposure, genetic risk factors, childhood cancer, genetic susceptibility, susceptibility, cancer risks, carcinogenesis, adolescents, children, exposure, biomedical research, children's vulnerablity, fetal metabolism, dietary procarcinogens, detoxification enzymes, environmentally caused disease, toxics, aflatoxin B1Relevant Websites:
http://www.ufbi.ufl.edu/physdept/gallagher.htm
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.