Role of Genetic Polymorphism of Glutathione-S-Transferase T1 and Microsomal Epoxide Hydrolase in Aflatoxin-associated Hepatocellular Carcinoma 1 Edine W. Tiemersma, Ragaa E. Omer, Annelies Bunschoten, Pieter van’t Veer, Frans J. Kok, Mohamed O. Idris, Abdelgadir M. Y. Kadaru, Suliman S. Fedail, and Ellen Kampman 2 Division of Human Nutrition and Epidemiology, Wageningen University, 6700 EV Wageningen, the Netherlands [E. W. T., R. E. O., J. E. B., P. v. V., F. J. K., E. K.]; Department of Crop Protection, Faculty of Agriculture [R. E. O., M. O. I.] and Department of Medicine, Faculty of Medicine [A. M. Y. K.], University of Khartoum, Khartoum, 11123 Sudan; and National Center for Gastrointestinal and Liver Diseases, Khartoum, Sudan [S. S. F.] Abstract Exposure to aflatoxins is a risk factor for hepatocellular carcinoma (HCC). Aflatoxins occur in peanut butter and are metabolized by genetically polymorphic enzymes such as glutathione-S-transferases encoded by glutathione-S- transferase  1 gene (GSTM1) and glutathione-S- transferase  1 gene (GSTT1) and microsomal epoxide hydrolase encoded by epoxide hydrolase gene (EPHX). The rate at which aflatoxins become activated or detoxified may depend on polymorphisms in the encoding genes. GSTM1 homozygous deletion was indeed found to modify the association between peanut butter consumption and HCC. In this study, we investigate possible roles of GSTT1 and EPHX polymorphisms in this relationship. From a Sudanese case-control study on HCC, we analyzed data of 112 incident cases and 194 controls. All participants were interviewed using a standardized questionnaire inquiring about social and demographic factors, peanut butter consumption, and other known HCC risk factors. Univariate analysis showed that GSTT1 polymorphism was not associated with HCC, whereas EPHX 113HH and 139HH genotypes increased the risk of HCC (Odds ratio, 3.10; 95% Confidence interval, 1.18 – 8.12). Adjustment for age and region of origin slightly attenuated this association (Odds ratio, 2.56; 95% Confidence interval, 0.83–7.95). Interestingly, unlike GSTM1, both GSTT1 and EPHX polymorphism did not modify the association between peanut butter consumption and HCC. In conclusion, these epidemiological findings do not suggest significant roles of GSTT1 and EPHX in aflatoxin metabolism, although EPHX polymorphism is possibly related to the increased risk of HCC. Further studies are needed to investigate mechanisms by which the EPHX polymorphism potentially modifies cancer risk. Introduction HCC 3 is one of the major cancer types in developing countries, where most significant risk factors are chronic hepatitis virus infection and exposure to aflatoxins (1). Aflatoxins are pro- duced by Aspergillus fungi, which mainly occur in poorly stored maize and peanuts. In Sudan, aflatoxin exposure most likely occurs via consumption of peanut butter (2), which is a popular food. As we reported previously (3), peanut butter consumption is indeed related to the increased risk of HCC in Sudan. Genetic differences in aflatoxin metabolism may ex- plain the observed differences between prevalence rates of HCC in populations with similar aflatoxin exposures and hep- atitis infection rates (4). The most potent mutagenic and carcinogenic of the afla- toxins is AFB1. Fig. 1 depicts the metabolism of AFB1, which is mainly metabolized by cytochrome P450 3A4 into the geno- toxic metabolite AFB1– 8,9-exo-epoxide. This metabolite can bind to DNA, causing G-to-T transversions (5) that may ulti- mately lead to cancer. Detoxification prevents formation of DNA adducts; the metabolite may be conjugated to glutathione by GSTs or may be hydrolyzed. Hydrolysis occurs spontane- ously or is catalyzed by mEH (6, 7). Two genetically polymorphic GSTs play a role in AFB1 detoxification: GST- encoded by the GSTM1 gene and GST- encoded by GSTT1. Homozygous deletion of part of these genes (null genotype) results in enzyme deficiency and might therefore lead to hampered detoxification (8). Several studies (9, 10), among which our own Sudanese case-control study (3), showed that of populations exposed to aflatoxins, only subjects carrying the GSTM1-null genotype are at increased risk of HCC. After GST-, GST- showed highest efficiency for con- jugation of glutathione to AFB1– 8,9-exo-epoxide (Refs. 11 and 12; Fig. 1). Homozygous deletion of the GSTT1 gene was recorded in 24 to 38% of people from African origin (13). One study showed a positive association between GSTT1-null gen- otype and aflatoxin-albumin adduct levels among chronic HBV antigen carriers (10), but this was not confirmed by another study (14). Received 9/8/00; revised 5/11/01; accepted 5/11/01. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported partially by the Sudanese Standard and Meteorology Organization, SSMO. Wageningen University provided scientific support and facilitated per- sonnel exchange. 2 To whom requests for reprints should be addressed, at Division of Human Nutrition and Epidemiology, Wageningen University, John Snow Building (bode 154), Dreijenlaan 1, 6703 HA Wageningen, the Netherlands. 3 The abbreviations used are: HCC, hepatocellular carcinoma; AFB1, aflatoxin B1; mEH, microsomal epoxide hydrolase enzyme; GST, glutathione-S-transfer- ase; GST-, glutathione-S-transferase  enzyme; GSTM1, glutathione-S-trans- ferase  1 gene; GST-, glutathione-S-transferase  enzyme; GSTT1, glutathione- S-transferase  1 gene; EPHX, epoxide hydrolase gene; HBV, hepatitis B virus; OR, odds ratio; CI, confidence interval; SE, standard error. 785 Vol. 10, 785–791, July 2001 Cancer Epidemiology, Biomarkers & Prevention Research. on December 15, 2021. © 2001 American Association for Cancer cebp.aacrjournals.org Downloaded from