Fetal Metabolism of Aflatoxin B1 and Susceptibility to Childhood Cancer

EPA Grant Number: R827441
Title: Fetal Metabolism of Aflatoxin B1 and Susceptibility to Childhood Cancer
Investigators: Gallagher, Evan
Institution: University of Florida
EPA Project Officer: Deener, Kacee
Project Period: July 1, 1999 through June 30, 2002 (Extended to March 30, 2004)
Project Amount: $523,123
RFA: Children's Vulnerability to Toxic Substances in the Environment (1999) RFA Text |  Recipients Lists
Research Category: Children's Health , Health Effects , Human Health , Health

Description:

Cancer is the second leading cause of death for children under fourteen years of age in the United States. The initial peak of cancer incidence occurs during the first five years of life, and available evidence indicates that a primary risk factor for childhood cancer involves transplacental exposure to either mutagenic or pro-mutagenic agents. The rapid changes that occur during fetal development may result in critical windows of susceptibility to toxic injury. A primary determinant of this susceptibility is the balance among in utero conversion of procarcinogens to DNA-reactive metabolites (e.g. by cytochrome P450s, lipoxygenases) and the detoxification of reactive intermediates (e.g. by glutathione S-transferases and other phase II enzymes). The long term objective of this proposal is to characterize the metabolism of the transplacental dietary carcinogen aflatoxin B1 (AFB1) in fetal liver and maternal placenta in order to understand the genetic and developmental risk factors for AFB1 and other dietary procarcinogens. Our hypothesis is that a primary risk factor the childhood cancer human fetus is at increased risk to transplacental AFB1-induced DNA injury due to efficient fetal activation of AFB1 to the mutagenic metabolite AFB1-8,9-exo-epoxide (AFBO), and due to inefficient AFBO detoxification. We further hypothesize that there are important interindividual and developmental differences in the biotransformation of dietary carcinogens that result in critical windows and differing susceptibility to childhood cancer.

Approach:

The specific aims of this grant will be addressed by using biochemical, immunohistochemical, and molecular techniques in isolated human fetal liver tissues and culture of adult and fetal precision liver slices. We will conduct detailed in vitro biochemical studies to establish the kinetics of AFB1 activation and to identify the high affinity AFB1 bioactivation enzyme and AFBO detoxification enzymes in maternal placenta and fetal liver. Cellular targets of AFBO will be analyzed in fetal liver hepatocytes and hematopoietic precursor cells. Quantitative Western blotting will be used to determine ontogenic expression of the key AFB1 bioactivation and AFBO detoxification enzymes among fetal donors. Studies using cultured precision fetal liver slices will determine the sensitivity of fetal tissues to AFBO-DNA binding in situ, and the functional relationships among fetal AFB1 biotransformation, AFBO-DNA binding, AFBO-DNA adduct repair (by unscheduled DNA synthesis), and p53 tumor suppressor gene mutation frequency (by restriction fragment length polymorphism polymerase chain reaction (RFLP/PCR) analysis). The metabolism of other pertinent dietary procarcinogens may also be investigated in our model system.

Expected Results:

At the completion of this project, we will understand the mechanisms and risk factors associated with a potent rodent transplacental carcinogen and probable human transplacental carcinogen positively associated with high rates of certain childhood cancers. In addition, we will have identified particularly sensitive age groups and windows of developmental susceptibility to transplacental carcinogen exposure. Once risk factors and critical susceptibility windows are identified, then appropriate risk avoidance or minimization strategies can be employed. Finally, this project generates and integrates mechanistic data based upon human tissues and cultured precision human liver slices, and thus minimizes uncertainty associated with animal data in the human risk assessment of transplacental carcinogen exposure and childhood disease.

Publications and Presentations:

Publications have been submitted on this project: View all 18 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 5 journal articles for this project

Supplemental Keywords:

aflatoxin, heterocyclic amines, transplacental carcinogenesis, sensitive populations, p53, human liver slices., RFA, Health, Scientific Discipline, Genetics, Health Risk Assessment, Epidemiology, Risk Assessments, Susceptibility/Sensitive Population/Genetic Susceptibility, Biochemistry, Children's Health, genetic susceptability, Molecular Biology/Genetics, aflatoxin B1, sensitive populations, heterocyclic amines, childhood cancer, cytochrome P450, fetal metabolism, detoxification enzymes, adolescents, carcinogenesis, DNA reactive metabolites, dietary procarcinogens, exposure, children, genetic risk factors, assessment of exposure, children's vulnerablity, susceptibility, human exposure, cancer risks, biotransformation, epidemeology, environmentally caused disease, bioactivated environmental toxicants, transplacental exposure to mutagenic agents, biomedical research, genetic susceptibility, aflotoxin, environmental hazard exposures

Relevant Websites:

http://www.ufbi.ufl.edu/physdept/gallagher.htm

Progress and Final Reports:

2000 Progress Report
2001 Progress Report
2002 Progress Report
Final Report