Background. Human genetic polymorphisms in metabolic activation and detoxification pathways are a major source of inter-individual variation in susceptibility to environmentally induced disease. The group has developed genotyping assays for the """"""""at-risk"""""""" variants of enzymes that protect against carcinogens in cigarette smoke, diet, industrial processes and environmental pollution. Following genotyping of over 15,000 individuals for these candidate susceptibility genes, it has been found that the frequency of the at-risk genotypes for glutathione transferase M1 (GSTM1), theta 1 (GSTT1), Pi (GSTP1) and N-acetyltransferase (NAT1 and NAT2), XRCC1, XPD, vary significantly between Asians, European- and African-Americans. This suggests that some of the ethnic differences in cancer incidence may be due to genetic metabolic differences as well as exposure differences. Mission: Our long-term goal is to understanding how genes and environment interact to influence risk of environmentally induced disease. To this end we are engaged in """"""""Environmental Genomics."""""""" This encompasses: 1) identification of candidate environmental response genes, 2) discovery and functional characterization of genetic and phenotypic variation in these genes, and; 3) the analysis in population studies of environmental disease susceptibility associated with functional polymorphisms, acquired susceptibility factors and exposures; and the interactions between these factors. Eventually we hope these genomic approaches will help us to develop assays using genotype, gene expression, and other biomarkers of exposure and effect, that will be predictive of future risk. This information will allow us to more carefully determine the bounds of human variability in risk assessment and will be useful in developing prevention strategies to reduce disease incidence. The Genetic Susceptibility Project takes the candidate susceptibility factors from the laboratory genotype/phenotype studies and tests them in population studies. We are collaborating with numerous NIH, and university-based epidemiology groups to design and carryout appropriate tests of these factors in population-based epidemiology studies. Progress/accomplishments: 1) Breast cancer. N-acetyltransferases (NATs) are important catalytic enzymes that metabolize carcinogenic arylamines. NAT2 genotype might modify the role of cigarette smoking, a source of arylamine exposure, in breast cancer. We conducted a nested case-control study to investigate the association between NAT2 genotype, smoking and breast cancer risk among women (110 cases, 113 matched controls) from the CLUE II cohort in Washington County, MD. Compared to women with the slow acetylator genotype, the main effects odds ratios (OR) for NAT2 were 1.4 for the intermediate acetylator genotype (95% confidence limits (CL) 0.7, 2.7) and 3.6 for the homozygous rapid acetylator genotype (95% CL 1.1, 11.4) (P for trend = 0.05). Smoking was associated in the direction of increased breast cancer risk in slow acetylators (e.g., >15 pack-years versus never smokers OR 2.0; 95% CL 0.7, 5.8) but not in rapid acetylators. These associations were not statistically significant in the total study population, but a statistically significant interaction between smoking and NAT2 acetylator status was present in postmenopausal women. The main effect of NAT2 in the direction of increased risk suggests that exposures to NAT2-activated carcinogens other than cigarette smoke may be important in this study population. The results for smoking were consistent with an inactivation role for NAT2 in breast cancer. 2) Bladder cancer. Previous epidemiological studies of fruit and vegetable intake and bladder cancer risk have yielded inconsistent results, especially with respect to the role of cigarette smoking as a possible modifier of the diet-bladder cancer association. Methods: A population-based case-control study was conducted in non-Asiaaaans of Los Angeles, California. 3- and 4-aminobiphenyl (ABP) hemoglobin adducts, and glutathione S-transferases M1/T1/P1 (GSTM1/T1/P1) and N-acetyltransferase-1 (NAT1) genotypes, cytochrome P4501A2 (CYP1A2) and N-acetyltransferase-2 (NAT2) phenotypes were measured in 724 (69%) case patients and 689 (70%) control subjects. Results: After adjustment for non-dietary risk factors including cigarette smoking, there were strong inverse associations between bladder cancer risk and intake of dark-green vegetables (p value for linear trend (p) = 0.01), yellow-orange vegetables (p = 0.01), citrus fruits/juices (p = 0.002), and tomato products (p = 0.03). In terms of nutrients, bladder cancer risk was inversely associated with intake of both total carotenoids (p = 0.001) and vitamin C (p = 0.02). There was a close correlation (r = 0.58, p = 0.0001) between intakes of total carotenoids and vitamin C in study subjects. When both nutrients were included in a multivariate logistic regression model, only total carotenoids exhibited a residual effect that was of borderline statistical significance (p = 0.06 and p = 0.27 for total carotenoids and vitamin C, respectively). Cigarette smoking was a strong modifier of the observed dietary effects; these protective effects were confined largely to ever smokers, and were stronger in current than ex-smokers. Smokers showed a statistically significant or boorderline statistically significant decrease in 3- and 4-aminobiphenyl (ABP)- hemoglobin adduct level with increasing intake of carotenoids (p = 0.04 and 0.05, respectively). The protective effect of carotenoids on bladder cancer seemed to be influenced by NAT1 genotype, NAT2 phenotype and CYP1A2 phenotype; the association was mainly confined to subjects possessing the putative NAT1*10, NAT2-rapid and CYP1A2-rapid genotype/phenotype. The carotenoid-bladder cancer association was not affected by the GSTM1, GSTT1 and GSTP1 genotypes. 3) Breast Cancer. Previous epidemiologic studies suggest that women with variant cytochrome P4501A1 (CYP1A1) genotypes who smoke cigarettes are at increased risk for breast cancer. Methods We evaluated the association of breast cancer with CYP1A1 polymorphisms and cigarette smoking in a population-based, case-control study of invasive breast cancer in North Carolina. The study population consisted of 688 cases ( 271 African Americans and 417 whites) and 702 controls ( 285 African Americans and 417 whites). Four polymorphisms in CYP1A1 were genotyped using PCR/restriction fragment length polymorphism analysis: M1 ( also known as CYP1A1*2A), M2 (CYP1A1*2C), M3 (CYP1A1*3), and M4 (CYP1A1*4). Results No associations were observed for CYP1A1 variant alleles and breast cancer, ignoring smoking. Among women who smoked for longer than 20 years, a modest positive association was found among women with one or more M1 alleles (odds ratio [OR] = 2.1, 95% confidence interval [CI] = 1.2-3.5) but not among women with non-M1 alleles (OR = 1.2, 95% Cl = 0.9-1.6). Odds ratios for smoking longer than 20 years were higher among African-American women with one or more M3 alleles (OR = 2.5, 95% CI = 0.9-7.1) compared with women with non-M3 alleles (OR = 1.3, 95% Cl = 0.8-2.2). ORs for smoking in white women did not differ appreciably based upon M2 or M4 genotypes. Conclusions Cigarette smoking increases breast cancer risk in women with CYP1A1 M1 variant genotypes and in African-American women with CYP1A1 M3 variant genotypes, but the modifying effects of the CYP1A1 genotype are quite weak. Continued in accomplishments section
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