Genetic Variability in Iron-Related Oxidative Stress Pathways (Nrf2, NQ01, NOS3 , and HO-1 ), Iron Intake, and Risk of Postmenopausal Breast Cancer Chi-Chen Hong, 1 Christine B. Ambrosone, 1 Jiyoung Ahn, 2 Ji-Yeob Choi, 1 Marjorie L. McCullough, 3 Victoria L. Stevens, 3 Carmen Rodriguez, 3 Michael J. Thun, 3 and Eugenia E. Calle 3 1 Department of Cancer Prevention and Control, Roswell Park Cancer Institute, Buffalo, New York; 2 Nutritional Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland; and 3 Department of Epidemiology and Surveillance Research, American Cancer Society, Atlanta, Georgia Abstract Oxidative stress resulting from excess reactive oxygen species and/or deficiencies in antioxidant capabilities may play a role in breast cancer etiology. In a nested case-controlstudyofpostmenopausalwomen(505cases and 502 controls) from the American Cancer Society Prevention II Nutrition Cohort, we examined relation- ships between breast cancer risk and genetic poly- morphisms of enzymes involved in the generation and removalofiron-mediatedreactiveoxygenspecies.Using unconditional logistic regression, genetic variations in Nrf2 (11108C>T ), NQO1 (609C>T ), NOS3 (894G>T ),and HO-1 [(GT ) n dinucleotide length polymorphism] were not associated with breast cancer risk in a multivariate model. A significant dose trend (P trend = 0.04), however, was observed for total number of putative ‘‘at-risk’’ alleles (Nrf T, NQO1 T, NOS T ,and HO-1 LL and LM genotypes), with those carrying three or more at-risk alleles having an odds ratio (OR) of 1.56 [95% confidence interval (95% CI), 0.97-2.51] compared with those having none. When examined in relation to iron, carriage of three or more high-risk alleles in the highesttertileofironintake(OR,2.27;95%CI,0.97-5.29; P trend = 0.02; P interaction = 0.30) or among users of supplementaliron(OR,2.39;95%CI,1.09-5.26; P trend= 0.02; P interaction=0.11)resultedinagreaterthan2-fold increasedriskcomparedwithwomenwithnohigh-risk alleles.Increasedriskwasalsoobservedamongsupple- mentuserswiththe HO-1 LL or LM genotypes(OR,1.56; 95% CI, 1.01-2.41; P interaction = 0.32) compared with S allele carriers and MM genotypes combined. These results indicate that women with genotypes resulting in potentially higher levels of iron-generated oxidative stressmaybeatincreasedriskofbreastcancerandthat this association may be most relevant among women with high iron intake. (Cancer Epidemiol Biomarkers Prev 2007;16(9):1784–94) Background There is evidence that oxidative stress, resulting from either an excess of reactive oxygen species (ROS) or a deficiency in antioxidant capabilities, may play a role in the etiology of breast cancer (1, 2). The balance of endogenous oxidants and antioxidants is likely affected by variation in genes involved in the generation and removal of oxidative species, with ultimate effects dependent in part on the presence of relevant exogenous exposures (3-5). Indeed, we have noted such interactions in studying associations between breast cancer risk and dietary antioxidants in concert with polymorphisms in myeloperoxidase (6) and catalase (7). One source of ROS generation among postmenopausal women is high dietary iron and high iron stores (8). Iron can cause oxidative tissue damage by catalyzing Haber- Weiss and Fenton reactions that convert hydrogen peroxide (H 2 O 2 ) to free radicals (9-12). In women, neoplastic breast tissue contains higher levels of iron and ferritin compared with normal tissue (13, 14), and rats fed excess iron develop earlier and more numerous mammary tumors (15), whereas those fed iron-deficient diets are protected (16). Currently, some epidemiologic studies support a role for excessive dietary iron intake and risk of total cancers (17-19) as well as risk of lung and colon cancers (17, 20-23), but there are few data on relationships with breast cancer (24-26). Several enzymes are important in the formation and reduction of iron-generated ROS (Fig. 1). NAD(P)H:qui- none oxidoreductase 1 (NQO1) may be particularly relevant for breast carcinogenesis because of its role in reduction of endogenous catechol estrogens generated in the metabolism of estrogen. By catalyzing the obligatory two-electron reduction of catechol estrogens and other quinones, the reactive semiquinone intermediate that drives the Fenton reaction is bypassed, and superoxide- mediated release of iron from ferritin stores is prevented (27). In animals, NQO1 suppression increases estradiol- dependent tumor formation (28, 29). A C609T polymor- phism (rs1800566) in NQO1 (30) leads to a proline to serine substitution in the NQO1 protein that results in Cancer Epidemiol Biomarkers Prev 2007;16(9). September 2007 Received 3/22/07; revised 6/1/07; accepted 6/19/07. 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. Requests for reprints: Chi-Chen Hong, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263. Phone: 716-845-7785; Fax: 716-845-5125. E-mail: Chi-Chen.Hong@roswellpark.org Copyright D 2007 American Association for Cancer Research. doi:10.1158/1055-9965.EPI-07-0247 1784 Downloaded from http://aacrjournals.org/cebp/article-pdf/16/9/1784/2266104/1784.pdf by guest on 15 February 2023