This project continues to focus on the use of immunologic techniques to monitor human exposure to aflatoxin B1 (AFB1) which, in conjunction with hepatitis B virus (HBV) infection, is believed to be a causative factor in elevated levels of hepatocellular carcinoma (HCC) in Taiwan. Monoclonal antibodies developed against the DNA and protein adducts of AFB1 will be used to monitor AFB1 exposure. Genetic differences in metabolic capacity, which may be responsible for the interindividual differences observed in adduct levels, will be investigated. Cytochrome P450 1A1, 1A2 and 3A4 and glutathione S transferase mu (GSTM1) levels will be determined in tumor and nontumor tissue of HCC patients and controls by Western blot analysis. GSTM1 will also be genotyped by PCR. This data will be correlated with AFB1-DNA adduct levels determined by competitive ELISA of isolated DNA and quantitative immunohistochemical analysis of tissue sections. Specific p53 mutations will be analyzed in the liver tumors by both immunohistochemical methods and single strand conformation polymorphism followed by sequencing. Two case-control studies will determine the potential role of AFB1- albumin adducts as predictors of risk for HCC induction. The first will use banked serum samples from a community based nested case-control study in 6 townships in Taiwan. AFB1-albumin adducts will be determined by competitive ELISA and the inter-relationship between AFB1 exposure, family history, HBV carrier status and risk for developing HCC will be investigated. The second will use samples being collected in an ongoing cancer screening program throughout Taiwan which has to date, banked samples from 20,000 individuals. Since white blood cells as well as serum are being stored, GSTM1 genotype will also be determined. The relationship between AFB1-albumin adducts and GSTM1 genotype will be investigated as well as their relationship to HCC induction. This proposal will provide important information on the role of AFB1 in HCC induction in Taiwan and an understanding of some genetic factors influencing individual cancer risk.
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