Prepubertal genistein treatment modulates TGF-alpha, EGF and EGF-receptor mRNAs and proteins in the rat mammary gland

Molecular Pathways of Genistein Activity in Breast Cancer Cells

The most common malignancy in women is breast cancer. During the development of cancer, oncogenic transcription factors facilitate the overproduction of inflammatory cytokines and cell adhesion molecules. Antiapoptotic proteins are markedly upregulated in cancer cells, which promotes tumor development, metastasis, and cell survival. Promising findings have been found in studies on the cell cycle-mediated apoptosis pathway for medication development and treatment. Dietary phytoconstituents have been studied in great detail for their potential to prevent cancer by triggering the body's defense mechanisms. The underlying mechanisms of action may be clarified by considering the role of polyphenols in important cancer signaling pathways. Phenolic acids, flavonoids, tannins, coumarins, lignans, lignins, naphthoquinones, anthraquinones, xanthones, and stilbenes are examples of natural chemicals that are being studied for potential anticancer drugs. These substances are also vital for signaling pathways. This review focuses on innovations in the study of polyphenol genistein's effects on breast cancer cells and presents integrated chemical biology methods to harness mechanisms of action for important therapeutic advances.

ERBB Receptors and Their Ligands in the Developing Mammary Glands of Different Species: Fifteen Characters in Search of an Author

The ERBB tyrosine kinase receptors and their ligands belong to a complex family that has diverse biological effects and expression profiles in the developing mammary glands, where its members play an essential role in translating hormone signals into local effects. While our understanding of these processes stems mostly from mouse models, there is the potential for differences in how this family functions in the mammary glands of other species, particularly in light of their unique histomorphological features. Herein we review the postnatal distribution and function of ERBB receptors and their ligands in the mammary glands of rodents and humans, as well as for livestock and companion animals. Our analysis highlights the diverse biology for this family and its members across species, the regulation of their expression, and how their roles and functions might be modulated by varying stromal composition and hormone interactions. Given that ERBB receptors and their ligands have the potential to influence processes ranging from normal mammary development to diseased states such as cancer and/or mastitis, both in human and veterinary medicine, a more complete understanding of their biological functions should help to direct future research and the identification of new therapeutic targets.

Genistein: A Potent Anti-Breast Cancer Agent

Genistein is an isoflavonoid present in high quantities in soybeans. Possessing a wide range of bioactives, it is being studied extensively for its tumoricidal effects. Investigations into mechanisms of the anti-cancer activity have revealed many pathways including induction of cell proliferation, suppression of tyrosine kinases, regulation of Hedgehog-Gli1 signaling, modulation of epigenetic activities, seizing of cell cycle and Akt and MEK signaling pathways, among others via which the cancer cell proliferation can be controlled. Notwithstanding, the observed activities have been time- and dose-dependent. In addition, genistein has also shown varying results in women depending on the physiological parameters, such as the early or post-menopausal states.

Effects of Pubertal Exposure to Dietary Soy on Estrogen Receptor Activity in the Breast of Cynomolgus Macaques

Endogenous estrogens influence mammary gland development during puberty and breast cancer risk during adulthood. Early-life exposure to dietary or environmental estrogens may alter estrogen-mediated processes. Soy foods contain phytoestrogenic isoflavones (IF), which have mixed estrogen agonist/antagonist properties. Here, we evaluated mammary gland responses over time in pubertal female cynomolgus macaques fed diets containing either casein/lactalbumin (n = 12) or soy protein containing a human-equivalent dose of 120 mg IF/day (n = 17) for approximately 4.5 years spanning menarche. We assessed estrogen receptor (ER) expression and activity, promoter methylation of ERs and their downstream targets, and markers of estrogen metabolism. Expression of ERα and classical ERα response genes (TFF1, PGR, and GREB1) decreased with maturity, independent of diet. A significant inverse correlation was observed between TFF1 mRNA and methylation of CpG sites within the TFF1 promoter. Soy effects included lower ERβ expression before menarche and lower mRNA for ERα and GREB1 after menarche. Expression of GATA-3, an epithelial differentiation marker that regulates ERα-mediated transcription, was elevated before menarche and decreased after menarche in soy-fed animals. Soy did not significantly alter expression of other ER activity markers, estrogen-metabolizing enzymes, or promoter methylation for ERs or ER-regulated genes. Our results demonstrate greater ER expression and activity during the pubertal transition, supporting the idea that this life stage is a critical window for phenotypic modulation by estrogenic compounds. Pubertal soy exposure decreases mammary ERα expression after menarche and exerts subtle effects on receptor activity and mammary gland differentiation. Cancer Prev Res; 9(5); 385-95. ©2016 AACR.

Transcriptome alterations in zebrafish embryos after exposure to environmental estrogens and anti-androgens can reveal endocrine disruption

Exposure to environmental chemicals known as endocrine disruptors (EDs) is in many cases associated with an unpredictable hazard for wildlife and human health. The identification of endocrine disruptive properties of chemicals certain to enter the aquatic environment relies on toxicity tests with fish, assessing adverse effects on reproduction and sexual development. The demand for quick, reliable ED assays favored the use of fish embryos as alternative test organisms. We investigated the application of a transcriptomics-based assay for estrogenic and anti-androgenic chemicals with zebrafish embryos. Two reference compounds, 17α-ethinylestradiol and flutamide, were tested to evaluate the effects on development and the transcriptome after 48h-exposures. Comparison of the transcriptome response with other estrogenic and anti-androgenic compounds (genistein, bisphenol A, methylparaben, linuron, prochloraz, propanil) showed commonalities and differences in regulated pathways, enabling us to classify the estrogenic and anti-androgenic potencies. This demonstrates that different mechanism of ED can be assessed already in fish embryos.

Microsatellite polymorphisms in the EGFR, NOTCH4 and E2F4 genes and their association with breast cancer risk

BACKGROUND

The sequences of many human genes that encode proteins involved in cancer contain polymorphic microsatellites. Variations in microsatellite length may constitute risk factors in several human diseases, a possibility that has been little explored in breast cancer. Among the genes that contain polymorphic microsatellites are EGFR, NOTCH4 and E2F4. The length of some of these microsatellites has been associated with breast cancer risk.

PURPOSE AND METHODS

To determine whether the length of the microsatellites (CA)n in EGFR, (CTG)n in NOTCH4 and (AGC)n in E2F4 was associated with breast cancer risk, we genotyped these 3 microsatellites in 212 women with breast cancer and a control group of 308 women from the general population who did not have this disease.

RESULTS AND CONCLUSIONS

The allelic distribution observed for the 3 microsatellites matched that found in other white populations, with the exception of some (AGC)n alleles in E2F4, which have not been described previously. The length of (CA)n in EGFR and (CTG)n in NOTCH4 was not associated with breast cancer (OR=0.99; 95% CI 0.59-1.37; p=0.619 and OR=1.08; 95% CI 0.71-1.65; p=0.725, respectively). Short alleles (<13 repeats) of (AGC)n in E2F4 were less frequent in women with cancer than in the control sample.

Endocrine-active chemicals in mammary cancer causation and prevention

Endocrine-active chemicals alter or mimic physiological hormones. These compounds are reported to originate from a wide variety of sources, and recent studies have shown widespread human exposure to several of these compounds. Given the role of the sex steroid hormone, estradiol, in human breast cancer causation, endocrine-active chemicals which interfere with estrogen signaling constitute one potential factor contributing to the high incidence of breast cancer. Thus, the aim of this review is to examine several common endocrine-active chemicals and their respective roles in breast cancer causation or prevention. The plastic component, bisphenol A (BPA), the synthetic estrogen, diethylstilbestrol (DES), the by-product of organic combustion, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the soy component, genistein, and the red grape phytoalexin, resveratrol, have some degree of structural similarities to each other and estradiol. However, despite these structural similarities, the in vitro and in vivo properties of each of these chemicals vary greatly in terms of breast cancer causation and prevention. Early life exposure to BPA and DES increases rodent susceptibility to chemically induced mammary carcinogenesis, presumably through retardation of normal mammary gland maturation and/or disrupting the ratio of cell proliferation and apoptosis in the mammary gland. On the other hand, early exposures to genistein and resveratrol protect rodents against chemically induced and spontaneous mammary cancers. This is reported to occur through the ability of genistein and resveratrol to accelerate mammary gland maturation. Interestingly, TCDD, which is the most structurally dissimilar to the above chemicals and functions as an anti-estrogen, also increases chemically induced mammary carcinogenesis through retardation of mammary gland maturation. This article is part of a Special Issue entitled 'Endocrine disruptors'.

In Utero and Lactational Exposure to Low-Dose Genistein-Vinclozolin Mixture Affects the Development and Growth Factor mRNA Expression of the Submandibular Salivary Gland in Immature Female Rats

It has been suggested that hormonally controlled submandibular salivary gland (SSG) development and secretions may be affected by endocrine disruptor compounds. We investigated the effects of oral gestation-lactation exposure to 1 mg/kg body weight daily dose of the estrogenic soy-isoflavone genistein and/or the anti-androgenic food contaminant vinclozolin in female rats. The SSGs of female offspring were collected at postnatal day 35 to study gland morphogenesis and mRNA expression of sex-hormone receptors and endocrine growth factors as sex-dependent biomarkers. Because of high expression in neonatal SSG, mRNA expression of transforming growth factor α was also studied. Exposure to genistein, vinclozolin, or a genistein+vinclozolin mixture resulted in significantly lower numbers of striated ducts linked to an increase in their area and lower acinar proliferation (Ki-67–positive nuclei). Exposure to the mixture had the highest significant effects, which were particularly associated with repression of epidermal growth factor, nerve growth factor, and transforming growth factor α expression. In conclusion, early exposure to low doses of genistein and vinclozolin can affect glandular structure and endocrine gene mRNA expression in prepubertal SSG in female rats, and the effects are potentialized by the genistein+vinclozolin mixture. Our study provides the first evidence that SSG are targeted by both estrogenic and anti-androgenic disrupting compounds and are more sensitive to mixtures.

Factors to consider in the association between soy isoflavone intake and breast cancer risk

It has been suggested that soy isoflavones have protective effects against breast cancer. However, data from epidemiological studies are not conclusive. A recent meta-analysis showed that soy intake was inversely associated with breast cancer risk in Asian but not Western populations, which indicates that protection against breast cancer may require that women consume levels of soy typical in Asian diets. In addition to the amount of soy isoflavones consumed, the form and food source of isoflavones, timing of isoflavone exposure, estrogen receptor status of tumors, and equol-producer status and hormonal profile of individuals may modify the association between soy isoflavone intake and the risk of breast cancer. These factors might explain the heterogeneity of results from studies. This present report contrasts background data from Japanese and Western women to identify the potential modifying of these factors.

Effects of selenite and genistein on G2/M cell cycle arrest and apoptosis in human prostate cancer cells

Combination of chemopreventive agents with distinct molecular mechanisms is considered to offer a potential for enhancing cancer prevention efficacy while minimizing toxicity. Here we report two chemopreventive agents, selenite and genistein, that have synergistic effects on apoptosis, cell cycle arrest, and associated signaling pathways in p53-expressing LNCaP and p53-null PC3 prostate cancer cells. We show that selenite induced apoptosis only, whereas genistein induced both apoptosis and G2/M cell cycle arrest. Combination of these two agents exhibited enhanced effects, which were slightly greater in LNCaP than PC3 cells. Selenite or genistein alone upregulated protein levels of p53 in LNCaP cells only and p21(waf1) and Bax in both cell lines. Additionally, genistein inhibited AKT phosphorylation. Downregulation of AKT by siRNA caused apoptosis and G2/M cell cycle arrest and masked the effects of genistein. Treatment with insulin-like growth factor I (IGF-I) elevated levels of total and phosphorylated AKT and suppressed the effects of genistein. Neither downregulation of AKT nor IGF-I treatment altered the cellular effects of selenite. Our study demonstrates that selenium and genistein act via different molecular mechanisms and exhibit enhanced anticancer effects, suggesting that a combination of selenium and genistein may offer better efficacy and reduction of toxicity in prostate cancer prevention.

Adolescent and adult soy food intake and breast cancer risk: results from the Shanghai Women's Health Study

BACKGROUND

Soy food is a rich source of isoflavones--a class of phytoestrogens that has both antiestrogenic and anticarcinogenic properties.

OBJECTIVE

The objective was to evaluate the association of adolescent and adult soy food intake with breast cancer risk in a cohort of 73,223 Chinese women who participated in the Shanghai Women's Health Study.

DESIGN

A validated food-frequency questionnaire was used to assess usual dietary intake during adulthood and adolescence. After a mean follow-up of 7.4 y, 592 incident cases of breast cancer were identified for longitudinal analyses by using Cox regressions.

RESULTS

Adult soy food consumption, measured either by soy protein or isoflavone intake, was inversely associated with the risk of premenopausal breast cancer, and the association was highly statistically significant (P for trend < 0.001). The multivariate-adjusted relative risks (RRs) for the upper intake quintile compared with the lowest quintile were 0.41 (95% CI: 0.25, 0.70) for soy protein intake and 0.44 (95% CI: 0.26, 0.73) for isoflavone intake. High intake of soy foods during adolescence was also associated with a reduced risk of premenopausal breast cancer (RR: 0.57; 95% CI: 0.34, 0.97). Women who consumed a high amount of soy foods consistently during adolescence and adulthood had a substantially reduced risk of breast cancer. No significant association with soy food consumption was found for postmenopausal breast cancer.

CONCLUSION

This large, population-based, prospective cohort study provides strong evidence of a protective effect of soy food intake against premenopausal breast cancer.

Isoflavones and the prevention of breast and prostate cancer: new perspectives opened by nutrigenomics

Epidemiological evidence together with preclinical data from animal and in vitro studies strongly support a correlation between soy isoflavone consumption and protection towards breast and prostate cancers. The biological processes modulated by isoflavones, and especially by genistein, have been extensively studied, yet without leading to a clear understanding of the cellular and molecular mechanisms of action involved. This review discusses the existing gaps in our knowledge and evaluates the potential of the new nutrigenomic approaches to improve the study of the molecular effects of isoflavones. Several issues need to be taken into account for the proper interpretation of the results already published for isoflavones. Too often knowledge on isoflavone bioavailability is not taken into account; supra-physiological doses are frequently used. Characterization of the individual variability as defined by the gut microflora composition and gene polymorphisms may also help to explain the discrepancies observed so far in the clinical studies. Finally, the complex inter-relations existing between tissues and cell types as well as cross-talks between metabolic and signalling pathways have been insufficiently considered. By appraising critically the abundant literature with these considerations in mind, the mechanisms of action that are the more likely to play a role in the preventive effects of isoflavones towards breast and prostate cancers are reviewed. Furthermore, the new perspectives opened by the use of genetic, transcriptomic, proteomic and metabolomic approaches are highlighted.

Rats fed soy protein isolate (SPI) have impaired hepatic CYP1A1 induction by polycyclic aromatic hydrocarbons as a result of interference with aryl hydrocarbon receptor signaling

Consumption of soy diets has been found to reduce cancer incidence in animals and is associated with reduced cancer risk in humans. Previously, we have demonstrated that female Sprague-Dawley rats fed purified AIN-93G diets with soy protein isolate (SPI) as the sole protein source had reduced CYP1A1 induction and basal aryl hydrocarbon receptor (AhR) levels relative to those fed the same diet containing casein (CAS). In the present study, the molecular mechanisms underlying reduced AhR expression have been studied. The SPI-effect on AhR was not observed after feeding diets containing the purified soy isoflavones genistein or daidzein. Rat hepatoma FGC-4 cells were treated with the serum obtained from rats fed CAS- or SPI-containing diets. Reduced AhR levels (P<0.05) were observed after 24 h exposure to SPI-serum without any changes in the overall expression of chaperone proteins--HSP90 and XAP2. SPI-serum-stimulated AhR degradation was inhibited by treating the cells with the proteasome inhibitor, MG132, and was observed to be preceded by ubiquitination of the receptor. A reduced association of XAP2 with the immunoprecipitated AhR complex was observed. SPI-serum-mediated AhR degradation was preceded by nuclear translocation of the receptor. However, the translocated receptor was found to be unable to heterodimerize with ARNT or to bind to XRE elements on the CYP1A1 enhancer. These data suggest that feeding SPI-containing diets antagonizes AhR signaling by a novel mechanism which differs from those established for known AhR antagonists.

Genistein and resveratrol: mammary cancer chemoprevention and mechanisms of action in the rat

The environment, including diet, plays a critical role in a woman's subsequent risk of breast cancer. Two dietary polyphenols that have received attention from the health and research communities for their ability to protect against breast cancer are: genistein, a component of soy; and resveratrol, a phytoalexin found in red grapes and red wine. We and others have shown that both genistein and resveratrol can protect against mammary cancer in rodents. The timing of exposure to genistein appears critical for its mammary protective effects. It has been reported that genistein early in life causes enhanced mammary gland differentiation, alterations in cell proliferation and apoptosis, and upregulation of tumor-suppressor genes. With resveratrol in the diet, changes in cell proliferation and apoptosis in terminal ductal structures of the mammary gland might help to explain its protective effects. We conclude that genistein and resveratrol can protect against breast cancer by regulating important mammary growth and differentiation pathways.

Adolescent dietary phytoestrogen intake and breast cancer risk (Canada)

OBJECTIVE

It has been suggested that dietary phytoestrogen intake during adolescence may reduce the risk of developing breast cancer. This population-based case-control study evaluated the association between adolescent dietary phytoestrogen intake and adult breast cancer risk among women in Ontario, Canada.

METHODS

Pathology-confirmed, population-based breast cancer cases, aged 25-74 years, diagnosed between June 2002 and April 2003, were identified using the Ontario Cancer Registry. Population-based controls were recruited, and matched to cases within 5-year age groups. Adolescent phytoestrogen intake was obtained using a brief food frequency questionnaire (n = 3,024 cases, n = 3,420 controls). Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Higher phytoestrogen intake (both isoflavones and lignans) during adolescence was associated with a reduced breast cancer risk, and a monotonic trend was observed from the lowest to the highest quartile (OR [Q2] = 0.91, 95% CI 0.79-1.04, OR[Q3] = 0.86, 95% CI 0.75-0.98, and OR[Q4] = 0.71, 95% CI 0.62-0.82, p-trend < 0.001).

CONCLUSION

Adolescent dietary phytoestrogen intake may be associated with a decreased risk of adult breast cancer. If verified, this finding has important implications with regard to breast cancer prevention since diet is a potentially modifiable factor.

Heavy water labeling method for measuring the effect of genistein on mammary gland carcinogenesis

Heavy water labeling method was applied to measure the effect of genistein on mammary gland carcinogenesis by incoporating (2)H from (2)H(2)O into the deoxyribose (dR) moiety of purine deoxyribonucleotides in dividing cells. In the present study, we followed the study design of Lamartiniere group to evaluate the efficacy of (2)H(2)O labeling on the measurement of mammary gland carconogenesis. Female Sprague-Dawley rats were fed estrogen-free AIN-93G diet starting 1 week before breeding and continuing through pregnancy and lactation. Female pups were assigned to the following groups on postnatal day 16 and fed AIN-93G diet: vehicle (dimethylsulfoxide) (DMSO), genistein, and estradiol benzoate (EB). On postnatal days 16, 18, and 20, female pups were injected subcutaneously with 500 mug genistein/g body wt, 500 ng EB/g body wt, or an equivalent volume of the vehicle. At day 50 postpartum, half of each group were gavaged with 60 mg dimethylbenz[a]anthracene (DMBA) in perila oil. After 1 week of DMBA treatment, all animals were labeled with (2)H(2)O by administration of 4% (2)H(2)O in drinking water after single intraperitonial bolus injection with 99.9% (2)H(2)O until sacrifice on postnatal day 81. The time-dependent weight gains were observed in all groups throughout the experimental period. The enrichment of body (2)H(2)O was attained at 1.84-2.47% through oral administration of (2)H(2)O. Mammary epithelial cell proliferation was measured by enrichment (EM1) of dA from rats. DMBA-treated groups showed higher fractional synthesis than DMBA non-treated groups. The group exposed only to genistein showed significantly lower EM1 (1.46 +/- 0.87%) than those of control groups, i.e., the DMBA non-treated group (2.28 +/- 0.29%) and the DMBA-treated group (2.32 +/- 0.28%). Bromodeoxyuridine (BrdU) immunostaining of mammary tissue revealed that genistein reduced proliferation of the mammary epithelial, and the number of cells stained positive for BrdU both in DMBA-treated groups and DMBA non-treated groups. H&E staining of mammary epithelium also showed that the exposure to genistein decreased proliferation of the mammary epithelium. The epithelium in the rats treated with DMBA showed mostly multiple cell layers, in contrast to the mostly double layer shown in the DMBA non-treated rats. The exposure to genistein in the prepubertal period inhibited mammary epithelial cell proliferation. In conclusion, the (2)H(2)O labeling results were in good agreement with the results of BrdU incorporation and histomorphometry, which demonstrates that (2)H(2)O labeling can be used as a tool to measure carcinogenesis.

Reduction in 7,12-dimethylbenz[a]anthracene-induced hepatic cytochrome-P450 1A1 expression following soy consumption in female rats is mediated by degradation of the aryl hydrocarbon receptor

Consumption of a soy diet has been found to reduce cancer incidence in animals and is associated with reduced cancer risk in humans. In this study, the effect of consuming soy protein isolate (SPI) on the aryl hydrocarbon receptor (AhR)-mediated signaling pathway was investigated. Female Sprague-Dawley rats were fed AIN-93G diets with (+) or without (-) SPI-bound phytochemicals or casein (CAS) protein and gavaged orally with 7,12-dimethylbenz[a]anthracene (DMBA) or sesame oil. We found reduced (P < 0.05) DMBA-induced hepatic cytochrome-P450 1A1 (CYP1A1) activity, apoprotein, and mRNA expression along with the reduced binding of AhR-AhR nuclear translocator complex to CYP1A1 gene promoter in SPI(+)-fed rats compared with CAS- or SPI(-)-fed rats. Basal AhR protein expression was lower (P < 0.05) in SPI(+)-fed rats compared with CAS- or SPI(-)-fed groups. AhR levels were reduced (P < 0.05) after rats were fed SPI(+) for >20 d. Experiments in which SPI(+)-fed rats were weaned to CAS diets demonstrated that AhR reduction by SPI(+) is not imprinted metabolically. To determine the molecular mechanisms of SPI(+)-mediated AhR reduction, an ex vivo model was developed using FGC-4 cells treated with serum from CAS- or SPI(+)-fed rats. SPI(+) serum treatment of FGC-4 cells reduced AhR expression and DMBA-induced CYP1A1 expression (P < 0.05). The reduction in AhR expression was in part due to the shorter half-life of AhR protein. Our findings suggest that the cancer preventive effect of soy-based diets is mediated in part by reduction in AhR protein level posttranslationally, which reduces procarcinogen-induced CYP1A1 induction and metabolic activation.

(CA)n Microsatellite polymorphism of ERBB-1 in breast cancer

The aim of this study was to determine polymorphism of repeated sequences (CA)(n) in the ERBB-1 gene. The study group included 197 breast cancer patients and 180 healthy women. DNA was isolated from fresh-frozen tumour tissue and from peripheral blood. ERBB-1 (CA)(n) microsatellite polymorphism was examined by polymerase chain reaction (PCR). A polymorphic simple sequence repeat region of 9-23 CA repeats was detected in both groups. Homozygotes comprised 22% and 34% of breast cancer patients and controls, respectively (P=0.009). An allelic imbalance (AI), mostly in the shorter allele, was found in 27% of breast cancer patients. AI occurrence was associated with the lack of oestrogen receptors in tumour cells (P=0.05); otherwise, there were no correlations between histoclinical features and (CA)(n) microsatellite polymorphism of ERBB-1. It was concluded that an allelic imbalance is a common feature in breast cancer patients and may coincide with the lack of oestrogen receptors in tumour cells. The clinical relevance of ERBB-1 microsatellite polymorphism in breast cancer remains to be established.

Meta-Analysis of Soy Intake and Breast Cancer Risk

BACKGROUND

High intake of soy foods has been proposed to contribute to the low breast cancer risk in Asian countries. However, results of epidemiologic studies of this association are highly variable, and experimental data suggest that soy constituents can be estrogenic and potentially risk enhancing. Thus, rigorous evaluation of available epidemiologic data is necessary before appropriate recommendations can be made, especially for women at high risk of breast cancer or those who have survived the disease.

METHODS

We performed a meta-analysis of 18 epidemiologic studies (12 case-control and six cohort or nested case-control) published from 1978 through 2004 that examined soy exposure and breast cancer risk. Pooled relative risk estimates were based on either the original soy exposure measure defined in each study or on an estimate of daily soy protein intake.

RESULTS

Risk estimates, levels and measures of soy exposure, and control for confounding factors varied considerably across studies. In a pooled analysis, among all women, high soy intake was modestly associated with reduced breast cancer risk (odds ratio [OR] = 0.86, 95% confidence interval [CI] = 0.75 to 0.99); the association was not statistically significant among women in Asian countries (OR = 0.89, 95% CI = 0.71 to 1.12). Among the 10 studies that stratified by menopausal status the inverse association between soy exposure and breast cancer risk was somewhat stronger in premenopausal women (OR = 0.70, 95% CI = 0.58 to 0.85) than in postmenopausal women (OR = 0.77, 95% CI = 0.60 to 0.98); however, eight studies did not provide menopause-specific results, six of which did not support an association. When exposure was analyzed by soy protein intake in grams per day, a statistically significant association with breast cancer risk was seen only among premenopausal women (OR = 0.94, 95% CI = 0.92 to 0.97).

CONCLUSIONS

Soy intake may be associated with a small reduction in breast cancer risk. However, this result should be interpreted with caution due to potential exposure misclassification, confounding, and lack of a dose response. Given these caveats and results of some experimental studies that suggest adverse effects from soy constituents, recommendations for high-dose isoflavone supplementation to prevent breast cancer or prevent its recurrence are premature.

Chemoprevention of breast cancer, proteomic discovery of genistein action in the rat mammary gland

Genistein, the primary isoflavone component of soy, consumed in the diet during the prepubertal period only, and the combined prepubertal and adult periods, suppresses chemically induced mammary cancer in rats. Gestational or adult-only exposures do not provide protection. An inverse relation exists between cancer susceptibility and mammary gland differentiation. The current study used proteomic technology to investigate genistein mechanisms of action as related to programming against chemically induced mammary cancer. Rats were injected subcutaneously with 500 microg genistein/g body weight on d 16, 18, and 20 postpartum. At d 21, mammary glands were subjected to 2-dimensional polyacrylamide gel electrophoresis. After gel scanning, image analysis, and MS, 6 proteins were determined to be differentially regulated and identified. One protein, GTP-cyclohydrolase 1 (GTP-CH1), was confirmed as being significantly upregulated at d 21 by immunoblot analysis. Investigation of downstream signaling from GTP-CH1 showed that tyrosine hydroxylase was upregulated and vascular endothelial growth factor receptor 2 (VEGFR2) was downregulated in the mammary glands of 50-d-old rats treated with genistein in the prepubertal period. This and previous work suggest that early prepubertal exposure to genistein enhances cell proliferation by upregulating GTP-CH1 and the epidermal growth factor (EGF)-signaling pathway, and hence cell differentiation and gland maturation. This unique developmental maturation leads to a new biochemical blueprint, whereby the cells have reduced EGF signaling and VEGFR2, which renders the mature mammary gland less proliferative and less susceptible to cancer. This study demonstrated the usefulness of proteomics for the discovery of novel pathways that may be involved in cancer prevention.

The soy isoflavone genistein promotes apoptosis in mammary epithelial cells by inducing the tumor suppressor PTEN

The isoflavone genistein (GEN), a biologically active component of soy foods, is associated with reduced breast cancer risk in women who consume soy-rich diets. GEN has been reported to influence many biological processes, of which suppression of cell proliferation and stimulation of apoptosis are considered to be the major pathways underlying its inhibition of tumorigenesis. This study evaluated the mechanism by which diets containing GEN promote mammary epithelial cell death. We report that mammary glands of young adult female rats exposed from gestation day 4 to postnatal day 50, to AIN-93G diets containing as sole protein source, casein (CAS) supplemented with GEN, or soy protein isolate (SPI+) had increased apoptosis, relative to rats fed CAS diet devoid of GEN. Mammary gland proliferation was unaffected by diet. The increased apoptotic index in mammary glands of GEN and SPI+ rats was accompanied by increased levels of the tumor suppressor protein PTEN (phosphatase and tensin homolog deleted in chromosome ten), albeit enhanced mammary expression of the pro-apoptotic p21, Bax and Bok genes was observed only in GEN-fed rats. GEN-induced apoptosis in MCF-7 cells was concomitant with increased PTEN expression, and this was abrogated by PTEN siRNA. MCF-7 cells treated with serum from GEN- or SPI(+)-fed rats had increased apoptosis as well as increased levels of the PTEN transcript. PTEN siRNA attenuated the increased apoptotic response of MCF-7 cells to serum from rats fed SPI+ or GEN, although the inhibition to basal (CAS serum) apoptotic levels was achieved only for cells treated with GEN serum. Decreased p21 and Bok gene expression accompanied the inhibition of apoptosis by PTEN siRNA. Data implicate PTEN in the induction of apoptosis by GEN and suggest that the promotion of apoptosis leading to inhibition of tumorigenesis in vivo by diets containing GEN may also involve the distinct activities of yet unknown GEN metabolite(s) and/or other systemic factors induced by GEN.

Dynamic profiling of estrogen receptor and epidermal growth factor signaling in the uteri of genistein- and estrogen-treated rats

The pharmacokinetics and time course actions of the soy isoflavone, genistein, and estradiol benzoate (EB) on sex steroid and growth factor signaling were compared in the rat uterus. Following one s.c. injection of 500 mg genistein/kg BW or 500 microg EB/kg BW, AUC for genistein was 20171.8 ng h/ml and was 15.7 ng h/ml for estradiol-17-beta. Estrogen receptor-alpha (ER-alpha) decreased within 2 h of genistein or EB treatment, returning to basal levels within 24 and 48 h, respectively. In response to genistein and EB, progesterone receptors (PRs) A and B increased between 16 and 24 h, with a significant increase at 24 and 48 h. Epidermal growth factor receptor (EGFR) expression peaked 16 h after genistein or EB treatment, inversely correlating with extracellular regulating kinase (ERK) phosphorylation. These effects were inhibited by antiestrogen pretreatment, demonstrating a requirement for ER. At 16 h, uterine weight, epithelial cell height, and cell proliferation increased. While EGFR levels increased, phosphorylated EGFR was not altered. Reduced phosphorylation of downstream kinases corresponded with decreased stromal phosphorylated-ERK (P-ERK) immunolabeling, suggesting signal attenuation. Dynamic profiling of sex steroid receptors and EGF signaling molecules suggest a similar mechanism of action for genistein and EB in the uterus, albeit at approximately 1000-fold concentration.

Analysis of the dinucleotide repeat polymorphism in the epidermal growth factor receptor (EGFR) gene in head and neck cancer patients

BACKGROUND

Epidermal growth factor receptor (EGFR) overexpression is associated with poor prognosis in head and neck cancer. The first intron of EGFR gene is polymorphic (9-23 CA repeats) and transcription declines when the number of repeats increases.

PATIENTS AND METHODS

EGFR polymorphism (fluorescent genotyping) and expression (ligand-binding assay) were analyzed in tumors and normal tissues from 112 patients (100 men, 12 women; mean age 60 years).

RESULTS

The number of CA repeats varied from 15 to 22. Allelic distribution was trimodal (predominance of 16, 20 and 18 CA repeats). EGFR concentrations were significantly higher (P=0.02) in homozygous tumors as compared with heterozygous. Considering homozygous tumors, or classifying genotypes as short/long/intermediary (two alleles <17 versus two alleles > or =17 versus others), no relationship was observed between tumoral EGFR genotype and expression. In the 76 tumors exhibiting at least one 16-CA allele, the length of the remaining allele was inversely correlated to EGFR expression (P=0.047). Tumoral EGFR expression, performance status (WHO criteria) and node involvement were independent predictors of specific survival (P <0.01). Tumoral or normal tissue EGFR genotype did not influence survival.

CONCLUSIONS

Intron 1 EGFR polymorphism may be implicated in the regulation of EGFR expression in head and neck tumors.

Genistein alters growth factor signaling in transgenic prostate model (TRAMP)

Genistein, a component of soy, has been reported to protect against spontaneously developing prostate tumors in the transgenic adenocarcinoma of mouse prostate (TRAMP) model. This is consistent with reports showing that Asians eating a diet high in soy have reduced incidence of clinically manifested prostate cancer. In order to understand the mechanism of action of genistein, we have investigated the expression of androgen and estrogen receptors, four growth factor receptors that signal via tyrosine protein kinases, and specific growth factor proteins in the dorsolateral prostates of TRAMP mice fed 250 mg genistein/kg diet, starting at 5 weeks of age. These analyses were carried out at 12 weeks, prior to the development of solid tumors, allowing us to readily investigate cell proliferation and biomarkers in premalignant tissue. Cell proliferation, AR, ER-alpha, EGFR, ErbB2, EGF, IGF-1R, IGF-1, VEGFR2, ERKs-1 and 2 proteins and TGF-alpha mRNA, but not ER-beta and VEGF, were significantly increased in prostates of TRAMP compared to C57BL/6 mice. Genistein in the diet significantly down-regulated cell proliferation, EGFR, IGF-1R, ERK-1 and ERK-2, but not AR, ER-alpha, ER-beta, ErbB2, EGF, TGF-alpha, IGF-1, VEGF and VEGFR in prostates of TRAMP mice. Serum testosterone and dihydrotestosterone concentrations were not significantly different in C57BL/6 or TRAMP male mice fed control or genistein-containing diets. The up-regulation of sex steroid receptors and multiple growth signaling pathways in TRAMP mice supports the concept of multiple dysregulation contributing to carcinogenesis. Down-regulation of the tyrosine kinase regulated proteins, EGFR and IGF-1R, and of the downstream mitogen-activated protein kinases, ERK-1 and 2, with genistein in the diet provides a possible mechanism for prostate cancer chemoprevention.

Modification of breast cancer risk in young women by a polymorphic sequence in the egfr gene

The regulation of the epidermal growth factor receptor (egfr) gene in human cancer is not yet fully understood. Recent data on a polymorphic CA repeat located at the 5'-regulatory sequence in intron 1 of the egfr gene [egfr CA simple sequence repeat (SSR) I] point to a possible inheritance of cancer risk associated with the egfr gene. Furthermore, we have detected frequent allelic imbalances restricted to the egfr CA SSR I in breast cancer tissue and nontumorous breast tissue adjacent to invasive and in situ breast cancer representing amplifications. Therefore, we conducted a population-based case-control study to assess the relationship between the egfr polymorphism and breast cancer risk. Cases with a first primary breast cancer by age 50 years and age-matched population controls provided information on known and suspected risk factors. The allelic length of the egfr CA SSR was determined in 616 cases and 1072 population-sampled controls. Genotypes were categorized for analysis by allele length. Multivariate logistic regression was used to compare genotype distributions, accounting for other risk factors, and to investigate gene-environment interactions. We found a modifying effect, albeit no main effect, of the allelic length of the egfr polymorphism on breast cancer risk. The presence of two long alleles (>/==" BORDER="0">19 CA) was associated with a significantly elevated odds ratio (OR) of 10.4 [95% confidence interval (CI), 1.85-58.70] among women with a first-degree family history of breast cancer (P = 0.015 for interaction). The risk increase associated with high red meat consumption (OR, 10.68; 95% CI, 1.57-72.58) and the protective effect of high vegetable intake (OR, 0.07; 95% CI, 0.004-1.07) was also most pronounced among carriers of two long alleles (>/==" BORDER="0">19 CA). The length of the egfr CA SSR may increase the risk for familial breast cancers, and its effect could be modulated by dietary factors.

Mammary gland morphogenesis is enhanced by exposure to flaxseed or its major lignan during suckling in rats

The exposure of rats to 10% flaxseed (FS) or an equivalent level of its major lignan, secoisolariciresinol diglucoside (SDG), during suckling enhances mammary gland differentiation, which protects against mammary carcinogenesis at adulthood. We determined whether this diet-induced mammary gland differentiation is mediated through the estrogenic pathway via epidermal growth factor receptor (EGFR) and estrogen receptor (ER) signaling. Rats were fed the AIN-93G basal diet (BD) from day 7 of pregnancy until delivery and then randomized to consume BD, FS, or SDG during lactation. After weaning, female offspring were fed BD throughout the experiment. At postnatal day (PND) 21 and the proestrus phase on PND 49-51, mammary glands of offspring were analyzed for morphology, cell proliferation, and expression of EGFR, epidermal growth factor (EGF), transforming growth factor-alpha, ER-alpha, and ER-beta. At PND 21, compared with the BD control, the number of terminal end buds (TEBs) and terminal ducts were increased by FS, whereas mammary epithelial cell proliferation was increased by both FS and SDG, suggesting that mammary morphogenesis was enhanced. Epithelial EGFR and stromal fibroblast EGF were increased by SDG, whereas epithelial ER-beta was decreased by FS. Conversely, at PND 49-51, a lower number of TEBs but a higher ratio of lobules to TEBs with decreased expression of EGFR or EGF was observed in both treatment groups. EGFR expression was positively associated with EGF expression and cell proliferation in TEB epithelium at PND 21. Urinary lignans of lactating dams were related to their offspring's indices of mammary gland development. In conclusion, exposure to FS or SDG during suckling enhanced mammary gland morphogenesis by modulation of EGFR and ER signaling, which led to more differentiated mammary glands at PND 49-51. The physiological outcomes of FS and SDG were similar, which suggests that SDG is partly responsible for the mammary gland differentiation effect.

Exposure to flaxseed or its purified lignan during suckling inhibits chemically induced rat mammary tumorigenesis

Previous studies have shown that feeding flaxseed (FS) or its lignan secoisolariciresinol diglucoside (SDG) to rat dams during lactation enhances the differentiation of rat mammary gland in the female offspring. This study determined whether exposure to a diet with 10% FS or SDG (equivalent to the amount in 10% FS) during suckling could protect against 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced rat mammary tumorigenesis later in life. Dams were fed the AIN-93G basal diet (BD) throughout pregnancy. After delivery, dams were randomized to continue on BD or were fed BD supplemented with 10% FS or SDG during lactation. Three-day urine of dams was analyzed for mammalian lignans. After weaning, all offspring were fed BD. At postnatal Days 49 to 51, during proestrus phase, offspring were gavaged with 5 mg of DMBA. At Week 21 post-DMBA administration, compared with the BD group, the FS and SDG groups had significantly lower (P < 0.05) tumor incidence (31.3% and 42.0% lower, respectively), total tumor load (50.8% and 62.5% lower, respectively), mean tumor size (43.9% and 67.7% lower, respectively), and tumor number (46.9% and 44.8% lower, respectively) per rat. There was a significant decreasing trend (P < 0.05) in final tumor weights in rats fed FS or SDG. The high urinary lignan excretion in dams fed with FS or SDG corresponded with the reduced tumor development. The FS and SDG groups did not differ significantly in tumor indices, indicating that the effect of FS is primarily due to its SDG. There were no significant changes in selective reproductive indices measured among dams and offspring. In conclusion, exposure to FS or SDG during suckling suppressed DMBA-induced rat mammary tumorigenesis, suggesting that exposure to lignans at this early stage of mammary gland development reduces susceptibility to mammary carcinogenesis later in life without adverse effects on selective reproductive indices in dams or offspring.

Dietary diethylstilbestrol but not genistein adversely affects rat testicular development

Isoflavones, including genistein, contribute to the health benefits of a soy diet. However, the estrogenic activity of genistein suggests that there may be adverse effects on reproductive tract development. We investigated the potential of exposure to genistein (250 and 1000 mg/kg diet) and the synthetic estrogen and known male reproductive toxicant, diethylstilbestrol (DES, 75 micro g/kg diet) from d 21 to d 35 to alter rat testicular development. These dietary genistein concentrations resulted in serum concentrations that approximate or exceed concentrations in Asian men on a soy-containing diet. DES exposure reduced testicular weights, altered morphology and increased apoptosis in the seminiferous tubules. The effects of DES were accompanied by a reduction in androgen receptor (AR) protein concentrations, predominantly localized to Sertoli cells. Increased expression and immunostaining for the epidermal growth factor receptor (EGFR) and its downstream extracellular signal-regulated kinases (ERK) 1 and 2 in spermatagonia and spermatocytes were also observed. Immunohistochemical analysis of serial sections demonstrated that greater EGFR expression correlated with increased cellular proliferation, rather than apoptosis, and reflected impaired testicular development in DES-treated rats. Genistein in the diet did not significantly alter testicular weights, morphology, AR, EGFR and ERK expression or apoptosis. However, the higher concentration significantly reduced testicular aromatase activity, an effect that may contribute to reduced estrogen concentrations and suppression of prostate cancer development. These data suggest that exposure to genistein in the diet at concentrations that result in serum concentrations at the upper limit of humans consuming soy products does not adversely affect testicular development, but may provide health benefits.

Flavonoids and gene expression in mammalian cells

Flavonoids appear to regulate the expression of many genes. As expected, when multiple flavonoids were compared in one study, structure-specificity was always observed. Unfortunately, little information is available regarding the proportion of contribution of various structural elements. Also, we have very limited information on their molecular mechanisms of action. The affinity of flavonoids for ER could explain the stimulatory effect on genes with ERE but other modes of action apparently also exist and need to be further explored. Physiological relevance is always a concern when investigating the regulation of gene expression by environmental chemicals such as flavonoids. One factor of concern is the in vivo concentration of flavonoids. Besides intestinal cells, liver cells and skin cells, other tissues obtain flavonoids through blood circulation. Thus, plasma concentrations of flavonoids are normally discussed. Steady state plasma concentrations of flavonoids are usually not much higher than 1 microM even in populations that consume large amounts of plant material. This concentration is relatively low compared to the concentrations of flavonoids that were commonly used in cell culture systems to demonstrate their effectiveness. Nevertheless, we have evidence that some flavonoids may accumulate in the cell. The effect of quercetin on metallothionein expression in Caco-2 cells persisted for at least 24 hours after its removal from the culture medium (Kuo et al., 1998). Also, long-term treatment of cultured cells with quercetin at low concentrations led to a similar effect on metallothionein expression as one high concentration treatment (Kuo et al., 2001). If intracellular accumulation of certain flavonoids is a shared characteristic for various cell types, it implies that routine ingestion of flavonoids could lead to biological effects at the concentration lower than predicted from a single treatment. Experiments to address possible cell/tissue accumulation of flavonoids are greatly needed.

Phytoestrogens and breast cancer

The role of phytoestrogens and consumption of phytoestrogen-rich foods such as soy containing isoflavones and whole grain products with lignans for the prevention of breast cancer is reviewed. It is concluded that soy-containing diet in adult women is not or only slightly protective with regard to breast cancer, but that it may be beneficial if consumed in early life before puberty or during adolescence supporting results of immigrant and epidemiological studies. No negative effects of soy on breast cancer have been observed. On the other hand, a diet low in lignans, resulting in a low plasma enterolactone concentration, increases risk both in a case-control and a prospective study, but some controversial results have also been obtained. Some of these results may be explained by the fact that the determinants of plasma or urinary enterolactone concentration are very different in different countries. In Scandinavia, the main determinants are whole grain cereal food, vegetables and berries. Whether the protective effect is caused by the phytoestrogens in the diet or whether they are only biomarkers of a healthy diet has not been established.

Estrogen receptor expression in the prostate of rats treated with dietary genistein

Steroid hormones and their receptors play critical roles in the growth, development, and maintenance of the male reproductive tract. Genistein, a naturally occurring isoflavonoid primarily found in soybeans, interacts with estrogen receptors alpha and beta (ER alpha and beta), with preferential affinity for ER beta. This is one mechanism whereby genistein may affect growth and development and potentially alter susceptibility to carcinogenesis. Previous studies have indicated effects of soy and/or genistein in the male rodent reproductive tract under certain exposure conditions. The current study was undertaken to determine if modulation of the expression of ER alpha and ER beta by dietary genistein may contribute to those effects. Rats in a two-generation study were fed 0, 5, 100, or 500 ppm genistein prior to mating and through pregnancy and lactation. At weaning, male pups were selected in each of the F(1) and F(2) generations and half of the pups continued on the same diet as their dams (G/G, continuous exposure) while their litter mates were placed on control chow (G/C, gestational and lactational exposure) until sacrifice on PND 140. Male reproductive organ weights, serum levels of testosterone and dihydrotestosterone (DHT), and ER alpha and ER beta protein levels in the ventral and dorsolateral prostate were the endpoints measured. Prostate sections were also evaluated microscopically. Statistically significant elevations in testosterone and DHT were observed in PND 140 animals from the F(1) generation, but they were not accompanied by organ weight changes. Body weight in the continuously dosed 500 ppm F(1) PND 140 animals was depressed relative to control, but organ weights in animals of either generation showed few treatment-related effects. While estrogen receptor levels were quite variable, levels of ER beta in the dorsolateral prostate were significantly depressed in all dose groups in the G/C exposure and the high dose group of the G/G exposure in F(1) rats, but not in F(2) rats. Given the growing body of knowledge on the significance of ER beta in the prostate, the evidence for apparent down regulation of this receptor by genistein may have implications for reproductive toxicity and carcinogenesis that warrant further investigation.

Genistein chemoprevention: timing and mechanisms of action in murine mammary and prostate

We investigated the potential of genistein, the primary isoflavone of soy, to protect against breast and prostate cancers in animal models. For mammary cancer studies, Sprague-Dawley rats were fed AIN-76A diet plus minus 250 mg genistein/kg diet. Dimethylbenz[a]anthracene was administered by gavage at d 50 postpartum to induce mammary tumors. Mammary cancer chemoprevention was demonstrated after prepubertal and combined prepubertal and adult genistein treatments but not after prenatal- or adult-only treatments, demonstrating that the timing of exposure to genistein is important for mammary cancer chemoprevention. The cellular mechanism of action was found to be mammary gland and cell differentiation, as shown by whole-mount analysis and beta-casein expression. An imprinting effect was shown for epidermal growth factor receptor expression in mammary terminal end buds. For prostate cancer studies, we used two models. The first was a chemically (N-methylnitrosourea) induced prostate cancer rat model. Genistein in the diet inhibited the development of invasive adenocarcinomas in a dose-dependent manner. The second model was a transgenic mouse model that resulted in spontaneously developing adenocarcinoma tumor of the prostate. Genistein in the diet reduced the incidence of poorly differentiated prostatic adenocarcinomas in a dose-dependent manner and down-regulated androgen receptor, estrogen receptor-alpha, progesterone receptor, epidermal growth factor receptor, insulin-like growth factor-I, and extracellular signal-regulated kinase-1 but not estrogen receptor-beta and transforming growth factor-alpha mRNA expressions. We conclude that dietary genistein protects against mammary and prostate cancers by regulating specific sex steroid receptors and growth factor signaling pathways.

Effects of dietary genistein exposure during development on male and female CD (Sprague-Dawley) rats

Genistein is a naturally occurring isoflavone that interacts with estrogen receptors and multiple other molecular targets. Human exposure to genistein is predominantly through consumption of soy products, including soy-based infant formula and dietary supplements. A dose range-finding study was conducted as a prelude to a multigeneration bioassay to assess potential toxicities associated with genistein consumption. Genistein was administered in a soy- and alfalfa-free diet at 0, 5, 25, 100, 250, 625, or 1250 ppm to pregnant dams starting on Gestation day 7 and continuing throughout pregnancy. Dietary exposure of the dams continued through lactation, and pups were maintained on the same dosed feed as their mother after weaning until sacrifice at Postnatal day 50. Body weight and feed consumption of the treated dams prior to parturition showed a decreasing trend with a significant reduction at the highest dose. Litter birth weight was depressed in the 1250 ppm dose group, and pups of both sexes in that dose group had significantly decreased body weights relative to controls at the time of sacrifice. The most pronounced organ weight effects in the pups were decreased ventral prostate weight in males at the 1250 ppm dose and a trend toward higher pituitary gland to body weight ratios in both sexes. Histopathologic examination of female pups revealed ductal/alveolar hyperplasia of the mammary glands at 250 to 1250 ppm. Ductal/alveolar hyperplasia and hypertrophy also occurred in males, with significant effects seen at 25 ppm and above. Abnormal cellular maturation in the vagina was observed at 625 and 1250 ppm, and abnormal ovarian antral follicles were observed at 1250 ppm. In males, aberrant or delayed spermatogenesis in the seminiferous tubules relative to controls was observed at 1250 ppm. There was a deficit of sperm in the epididymis at 625 and 1250 ppm relative to controls, although testicular spermatid head counts and epididymal spermatozoa counts did not show significant differences from controls at these doses. Both sexes showed an increase in the incidence and/or severity of renal tubal mineralization at doses of 250 ppm and above. Dietary genistein thus produced effects in multiple estrogen-sensitive tissues in males and females that are generally consistent with its estrogenic activity. These effects occurred within exposure ranges achievable in humans.

Exposure to flaxseed or purified lignan during lactation influences rat mammary gland structures

Previous investigation demonstrated that feeding a 10% flaxseed (10F) diet during pregnancy and lactation enhanced the differentiation of highly proliferative terminal end bud (TEB) structures of rat mammary gland into less proliferative alveolar buds and lobules. From this study, it was hypothesized that the lignan component in flaxseed mediated the observed effects. Because mammary glands with more TEBs are more susceptible to carcinogens, exposure to flaxseed during early postnatal life may reduce the risk of developing mammary cancer. Our objectives were to elucidate whether exposure to flaxseed during lactation only and during pregnancy and lactation can similarly influence the differentiation of mammary gland structures and also to identify whether the lignan component of flaxseed is the biologically active agent. Offspring were exposed to a 10F diet or a dose of purified lignan equivalent to that in a 10F diet (10S) during lactation only or from lactation to postnatal Day 50. Compared with controls, exposure to 10F or 10S during lactation only or from lactation to postnatal Day 50 reduced the number of TEBs and resulted in a rise in the number of alveolar buds. In conclusion, exposure to flaxseed or its purified lignan during lactation is a critical period in which mammary gland development may be promoted by enhancing the differentiation of the mammary gland structures. However, continuous exposure, particularly to purified lignans, resulted in the most differentiation of the mammary gland. The next step is to determine whether the changes in mammary gland structures are chemopreventive in rats challenged with a carcinogen.

Animal models impacted by phytoestrogens in commercial chow: implications for pathways influenced by hormones

It is generally not known that most commercial rodent diets are formulated with soy protein and deliver large daily doses of isoflavones to animals throughout their lifespan, including the in utero period. Here, we demonstrate that isoflavones are bioavailable and show that commercial rodent diets universally used by animal facilities lead to very high steady-state serum isoflavone concentrations in adult rats (2613 +/- 873 ng/mL) and mice (2338 +/- 531 ng/mL), exceeding the animal's endogenous estrogen level by 30,000- to 60,000-fold. We demonstrate the maternal-fetal intrauterine transfer of isoflavones in animals fed a standard Purina 5001 soy-containing diet and show that newborn rat pups have high serum isoflavones levels (540 +/- 174 ng/mL) that are maintained throughout the suckling period by passage of isoflavones into maternal milk. These findings have profound implications for all animal experiments, including multigenerational studies and studies of transgenic animals, especially if biochemical or morphological end-points are influenced by the hormonal or nonhormonal properties of phytoestrogens. These compounds have the potential to modulate genotypic and phenotypic expression in general, and therefore, all investigators should be vigilant to the phytoestrogen composition of commercial rodent diets because there is a history of potent biological effects in larger animals and in humans from high circulating isoflavone concentrations.

Sex steroid receptor regulation by genistein in the prepubertal rat uterus

We evaluated the mechanism of action by the phytoestrogen genistein in the prepubertal rat uterus, when administered pharmacologically or physiologically. Female rats were injected with genistein (500 microg/g body weight), estradiol benzoate (EB) (500 ng/g body weight) or vehicle, dimethylsulfoxide (DMSO), on days 16, 18, and 20 postnatal. In 21-day-old rats, both compounds increased circulating estradiol and decreased progesterone concentrations. Uterine estrogen receptor alpha (ER-alpha) and androgen receptor (AR) proteins were reduced, and progesterone receptors (PR) were increased, as measured by western blot analyses. Immunohistochemistry for ER-alpha was confirmatory. Reverse transcription-polymerase chain reaction (RT-PCR) analyses indicated a decrease in ER-alpha, but not in ER-beta, PR and AR mRNA levels following genistein treatment. In prepubertal rats exposed perinatally to 250 mg genistein per kg AIN-76A diet or 250 microg estradiol per kg diet, uterine ER-alpha, AR, and PR proteins were not altered significantly. We conclude that pharmacologic, but not physiologic concentrations of genistein can modulate sex steroid receptor expression in the rat uterus.

Maternal and prepubertal diet, mammary development and breast cancer risk

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.

Protection against breast cancer with genistein: a component of soy

Breast cancer is the most common cancer in women. Because genetics is believed to account for only 10-15% of breast cancer cases, the environment, including nutrition, is thought to play a significant role in predisposing women to this cancer. Studies of Asian women suggest that those who consume a traditional diet high in soy products have a low incidence of breast cancer, but that among emigrants to the United States, the second generation, but not the first, loses this protection. These findings suggest a possible common mechanism of action for breast cancer protection from early, specific nutritional exposure. Genistein, an isoflavone found in soy, has been reported to have weak estrogenic and antiestrogenic properties, to be an antioxidant, to inhibit topoisomerase II and angiogenesis, and to induce cell differentiation. In studies of the mammary glands of immature rats, we showed that genistein up-regulates the expression of the epidermal growth factor receptor shortly after treatment, which may be responsible for the increased cell proliferation seen at that age. We hypothesize that the early genistein action promotes cell differentiation that results in a less active epidermal growth factor signaling pathway in adulthood that, in turn, suppresses the development of mammary cancer. We speculate that breast cancer protection in Asian women consuming a traditional soy-containing diet is derived from early exposure to soybean products containing genistein. We believe that early events are essential for the benefits of cancer protection.

Influence of perinatal genistein exposure on the development of MNU-induced mammary carcinoma in female Sprague-Dawley rats

Genistein, a phytoestrogen, was subcutaneously (s.c.) injected to pregnant Sprague-Dawley CD rats on gestational days 16-20 at either 25 mg (Group 1) or 5 mg/day (Group 2). Female offspring of mothers not exposed to genistein during pregnancy received 12.5 mg genistein s.c. at neonatal days 15 and 18 (Group 3), or received vehicle only (Group 4). At 35 days of age, 4-9 female offspring from each group were autopsied to observe the influence of genistein, and remainder of female offspring received 50 mg/kg N-methyl-N-nitrosourea (MNU) intraperitoneally and were sacrificed when mammary tumors were larger than 1 cm in size or when they reached 35 weeks of age. Genistein treatment during the perinatal period resulted in lower body weight and lower relative uterine-ovarian weight at 35 days, and a prolonged estrus cycle with a long estrus phase at 12-16 weeks. However, at 35 days (time at MNU administration), mammary gland development, cell proliferation rate (PCNA labeling index), and the number of estrogen receptor (ER)- and progesterone receptor (PgR)-positive cells were similar between genistein-treated and untreated rats. Twenty-five or 5 mg genistein/day in utero (between days 16 and 20 of gestation) or 12.5 mg genistein/day on neonatal days 15 and 18 did not affect the incidence of mammary tumors > 1 cm or the latency but did increase the number of mammary cancer lesions when MNU was administered at the time when the mammary gland growth in genistein-treated and untreated rats was similar. Thus, perinatal genistein is an endocrine disrupter and increases the multiplicity of MNU-induced mammary carcinoma in rats.