Prepubertal exposure to soy or its biologically active component genistein reduces later breast cancer risk in both animal models and human populations. We investigated whether that might be due to reported estrogenic properties of genistein. Our study indicated that daily prepubertal exposures between postnatal days 7 and 20 to 10 microg 17beta-estradiol (E2) reduced later risk of developing 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors. Assessment of mammary gland morphology revealed that both prepubertal E2 and genistein (50 microg daily) exposures reduced the size of mammary epithelial area and number of terminal end buds (TEBs) and increased the density of lobulo-alveolar structures, suggesting that these exposures induced elimination of targets for malignant transformation by differentiation. Next, the mechanisms mediating the protective effects of E2 and genistein were investigated. E2 is shown to up-regulate BRCA1, a tumor suppressor gene that participates in DNA damage repair processes and cell differentiation and that down-regulates the activity of estrogen receptor (ER)-alpha. The expression of BRCA1 mRNA was up-regulated in the mammary glands of rats exposed to E2 or genistein during prepuberty, when determined at the ages of 3, 8 and 16 weeks. Prepubertal E2 exposure reduced ER-alpha levels in the mammary gland, while prepubertal genistein exposure had an opposite effect. Our results suggest that prepubertal estrogenic exposures may reduce later breast cancer risk by inducing a persistent up-regulation of BRCA1 in the mammary gland.

At present, we do not know what causes sporadic breast cancer. Environmental factors,particularly diet, appear to explain at least 70% of newly diagnosed breast cancers, but it is not clear what these factors are. We propose that the lack of progress in this area is due to a lack of considering the effect of timing of environmental and dietary exposures on the breast. The evidence provided above suggests that an in utero exposure to an estrogenic environment-including that caused by diet [high (n-6) PUFA or genistein]-increases breast cancer risk. This increase may be mediated by an increased presence of TEB in the mammary epithelial tree and increased ER-alpha levels, reduced ER-beta levels or both. Prepubertal estrogenic exposure, in contrast, reduces later risk of developing breast cancer. The protective effect of estrogens may be mediated by early epithelial differentiation, reduced presence of ER-alpha and increased levels of ER-beta in the mammary gland. The challenge we are now facing is to determine whether the data obtained mainly through the use of animal models is relevant to women and if so, how we might be able to modulate pregnancy and childhood estrogenic exposure by appropriate dietary modifications to reduce breast cancer risk in women.

Maternal high fat diet has been shown to increase mammary cancer risk among female offspring. We investigated here if the increase is seen across multiple generations. For that purpose, pregnant C57BL/6NTac dams (F0) were fed either a control (CON, 6% corn oil) or an isocaloric high n-6 polyunsaturated fat (HF) diet (18% corn oil) between gestation days 8 and 21. Offspring in subsequent generations (F1-F3) were not exposed to any further dietary modifications, and kept on CON diet. Mammary tumors were initiated by priming the mammary glands with 15 mg medroxyprogesterone (MPA) at week 6, followed by a 1 mg dose of 7,12-dimethylbetz(a)anthracene (DMBA) given on weeks 7-9 for a total of 3 doses. Animals were monitored for 20 weeks after the final dose of DMBA for tumors. Both F1 and F3 generation female HF offspring exhibited a significantly higher mammary tumor incidence and tumor burden than the control offspring. In F3 generation, the increase was seen from week 12 of tumor monitoring until the end of the study. The increase in risk was preceded by a higher number of terminal end buds in the F1 and F3 generation mammary glands. Malondialdehyde (MDA) adduct levels were found to be significantly elevated in the HF group of F3 offspring, suggesting that the increased mammary cancer risk in this generation was attributed to oxidative stress. Western blot analysis of mammary glands identified significantly elevated Keap1 (a repressor of the antioxidant response) and PERK levels in HF F3 offspring; and elevated levels of Beclin-1 and p62 in both F1 and F3 generations compared with CON offspring, corroborating with the idea that oxidative stress was the culprit. miRNA analysis of F3 mammary glands showed decreased expression of mir-324-5p, mir-136 and mir-378 that target Keap1 and p62, potentially explaining the increase in Keap1 and p62 levels. Our results suggest that oxidative stress and antioxidant response plays a role in explaining transgenerational increase in mammary cancer risk among offspring exposed to high fat diet through F0 dams. Citation Format: Nguyen M. Nguyen, Fabia O. Andrade, Sonia DeAssis, Idalia Cruz, Carlos Benitez, Roger Godschalk, Leena Hilakivi-Clarke. Transgenerational inheritance of increased mammary cancer risk in the offspring of high fat diet fed dams: Changes in oxidative stress pathways. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 901.