The immature mouse is a suitable model for detection of estrogenicity in the uterotropic bioassay

Female Mice Exposed to Pyriproxyfen Since Prepuberty Showed Reproductive Impairment During Sexual Maturity and Increased Fetal Death in Their Offspring

Pyriproxyfen (PPF) is an insecticide used in agriculture, which is approved for use in drinking water tanks for human consumption. However, some studies indicate that it may act as an endocrine disruptor and affect nontarget organisms. This study aimed to evaluate the effects of PPF on reproduction and general health status in female mice exposed from pre-puberty to adulthood. In the first experiment, females were treated by gavage from postnatal day (PND) 23 to (PND) 75 and were distributed into three experimental groups: control (vehicle), PPF 0.1 mg/kg, and PPF 1 mg/kg. Female mice were assessed for the age of puberty onset, body mass, water and food consumption, and the estrous cycle. On PDN 75, a subgroup was euthanized, when vital and reproductive organs were collected and weighed. The thyroid, ovary, and uterus were evaluated for histomorphometry. The other subgroup was assessed in relation to reproductive performance and fetal parameters. In a second experiment, the uterotrophic assay was performed with juvenile females (PND 18) using doses of 0.01, 0.1, or 1 mg/kg of PPF. PPF treatment reduced thyroid mass and increased liver mass. Furthermore, there was an increase in ovarian interstitial tissue and, in the uterus, a decrease in the thickness of the endometrial stroma with reduced content of collagen fibers. There was also a reduction of 30% in pregnancy rate in the treated groups and an increase in the frequency of fetal death. This study suggests that, based on this experimental model, the insecticide may pose a reproductive risk for females chronically exposed to the substance from the pre-pubertal period until adulthood. These results raise concerns about prolonged exposure of women to the same compound.

4,4'-(9-Fluorenylidene)dianiline (BAFL) is antiestrogenic and has adverse effects on female development in CD-1 mice

Many phenolic compounds have been found to have endocrine disrupting activities, but their arylamine analogs, the phenolic hydroxyl groups substituted by aniline amino groups, have rarely been reported. 4,4'-(9-Fluorenylidene)dianiline (BAFL) is an arylamine analog of fluorene-9-bisphenol (BHPF) and BHPF has been reported to be a strong antiestrogen which could cause endometrial atrophy, ovarian damage and adverse pregnancy outcomes in animals. BAFL has been widely used as material to synthetize polymers, such as polyimides, polyamide, and polyamine, for various uses since the 1970s. Here, we assessed the antiestrogenicity of BAFL using a variety of methods and looked into its impacts on the development of females in CD-1 mice. With the aid of a yeast estrogen screen assay, we found BAFL possessed obviously antiestrogenic activity (IC₅₀ = 8.15 × 10^-6 M), which close to that of tamoxifen and BHPF. Using a 10-d mouse uterotrophic assay, we found that BAFL obviously decreased uterine weight in a dose-dependent way. Histological analyses of mouse uteri revealed that BAFL induced marked endometrial atrophy and inhibited the uterine development. Immunohistochemical analyses showed that Sprr2d, an estrogen-responsive gene encoding protein, was mainly expressed in endometrial epithelial cells and BAFL decreased the areas and levels of Sprr2d staining in mouse uteri. It was clear from uterine transcriptome investigations that BAFL significantly downregulated the expressions of multiple genes responding to estrogen. Molecular docking showed that BAFL could effectively occupy the antagonist-binding pocket of hERα, and one of the amino groups of BAFL formed hydrogen bonds with the side chains of Arg394 and Glu353 in the receptor. These results indicated that BAFL exhibited clearly antiestrogenic characteristics and could interfere with normal female development in mice, which should be avoided using in commodities that come into direct contact with humans. Moreover, this study indicated that the arylamine analogs of phenolic endocrine disrupting chemicals might also have endocrine disrupting activities.

Antiestrogenic property of 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (BPEF) and its effects on female development in CD-1 mice

Identifying chemicals with endocrine disrupting properties linked to disease outcomes is a key concern, as stated in the WHO-UNEP 2012 report on endocrine-disrupting chemicals. The chemical 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (BPEF) is widely and increasingly applied in synthesizing fluorene-based cardo polymers with superior optical, thermal and mechanical properties for various uses. However, little toxicological information is available regarding its safety. Here, we studied the endocrine disrupting property of BPEF by multiple toxicological tools and investigated its effects on female development in adolescent mice. Using the yeast two-hybrid bioassay, BPEF showed strong antiestrogenicity which was similar to that of tamoxifen, an effective antiestrogenic drug. In adolescent CD-1 mice, BPEF significantly decreased the uterine weight at relatively low doses and induced marked endometrial atrophy. Immunohistochemical staining and transcriptome analyses of the mice uteri revealed that BPEF could repressed the expressions of estrogen-responsive genes. Molecular simulation indicated that BPEF could be docked into the antagonist pocket of human estrogen receptor α, and the formation of hydrogen bonds and hydrophobic interactions between BPEF and the active site of receptor maintained their strong binding. All of the data demonstrated that BPEF possessed strong antiestrogenic property and might disrupt female development, suggesting it should be avoided in making products that might directly expose to people, particularly immature women.

In Vivo Study of The Oestrogenic Activity of Milk

Introduction

Milk has been suggested to be a possible source of oestrogenically active compounds. In order to assess the health risk for milk consumers and ensure the safety of this staple part of the human diet, it is important to study the effect of xenooestrogen mixtures present in milk. This investigation used the available in vivo model to learn to what extent such compounds may be endocrine disruptors.

Material and Methods

The recommended immature golden hamster uterotrophic bioassay was chosen. A total of 132 animals were divided into nine groups of experimental animals and positive and negative control groups, each of 12 animals. The experimental females received ad libitum either one of five samples of raw cow’s milk from individual animals or one of four samples of pasteurised or ultra-high temperature treated cow’s milk as retail products. After 7 days, the animals were sacrificed and necropsied. Uterine weight increases were measured as the endpoint of oestrogenic activity in milk.

Results

The milk samples from individual cows and the retail milk samples did not show oestrogenic activity. However, in three groups, decreased uterine weights were observed.

Conclusion

Considering that milk supplies are beneficial to health, contamination in this food should be avoided. There is a need for further animal experiments and epidemiological studies are warranted to evaluate any causative role of milk in human endocrinological disorders.

Tris(4-hydroxyphenyl)ethane (THPE), a trisphenol compound, is antiestrogenic and can retard uterine development in CD-1 mice

Tris (4-hydroxyphenyl)ethane (THPE), a trisphenol compound widely used as a branching agent and raw material in plastics, adhesives, and coatings is rarely regarded with concern. However, inspection of in vitro data suggests that THPE is an antagonist of estrogen receptors (ERs). Accordingly, we aimed to evaluate the antiestrogenicity of THPE in vivo and tested its effect via oral gavage on pubertal development in female CD-1 mice. Using uterotrophic assays, we found that THPE either singly, or combined with 17β-estradiol (E₂) (400 μg/kg bw/day) suppressed the uterine weights at low doses (0.1, 0.3, and 1 mg/kg bw/day) in 3-day treatment of weaning mice. When mice were treated with THPE during adolescence (for 10 days beginning on postnatal day 24), their uterine development was significantly retarded at doses of at least 0.1 mg/kg bw/day, manifest as decreased uterine weight, atrophic endometrial stromal cells and thinner columnar epithelial cells. Transcriptome analyses of uteri demonstrated that estrogen-responsive genes were significantly downregulated by THPE. Molecular docking shows that THPE fits well into the antagonist pocket of human ERα. These results indicate that THPE possesses strong antiestrogenicity in vivo and can disrupt normal female development in mice at very low dosages.

Fenugreek seeds estrogenic activity in ovariectomized female rats

The estrogenic activities of fenugreek seeds (Trigonella foenum-graecum L.), widely used in traditional pharmacopoeia, are reflected in the uterus of ovariectomized female rats, with a slight increase in dry and wet weight, a thickening of the stroma and the uterine epithelium and the development of the endometrial glands. In the vagina, the estrogenic action is shown through an increase in the epidermal cell number and a tendency to keratinization, leading to vaginal opening.

Furthermore, this estrogenic potential of fenugreek seeds is confirmed by the over-expression of progesterone receptors in the uterine tissues supporting possible interactions between phytoestrogens and estrogen receptors.

Therefore, Fenugreek seeds may be capable of promoting the development of reproductive tissues of immature ovariectomized rats, and its estrogenic activity may take its action by holding phystoestrogens that interact with estrogen binding sites and activate the same estradiol-mediated cell signaling pathways.

Thus, our results give added scientific support to the popular use of Fenugreek seeds as an alternative for several health problems such as fertility and menopause related disorders.

Analysis of individual and combined estrogenic effects of bisphenol, nonylphenol and diethylstilbestrol in immature rats with mathematical models

BACKGROUND

Traditional toxicological studies focus on individual compounds. However, this single-compound approach neglects the fact that the mixture exposed to human may act additively or synergistically to induce greater toxicity than the single compounds exposure due to their similarities in the mode of action and targets. Mixture effects can occur even when all mixture components are present at levels that individually do not produce observable effects. So the individual chemical effect thresholds do not necessarily protect against combination effects, an understanding of the rules governing the interactive effects in mixtures is needed. The aim of the study was to test and analyze the individual and combined estrogenic effects of a mixture of three endocrine disrupting chemicals (EDCs), bisphenol A (BPA), nonylphenol (NP) and diethylstilbestrol (DES) in immature rats with mathematical models.

METHOD

In the present study, the data of individual estrogenic effects of BPA, NP and DES were obtained in uterotrophic bioassay respectively, the reference points for BPA, NP and DES were derived from the dose-response ralationship by using the traditional no observed adverse effect (NOAEL) or lowest observed adverse effect level (LOAEL) methods, and the benchmark dose (BMD) method. Then LOAEL values and the benchmark dose lower confidence limit (BMDL10) of single EDCs as the dose design basis for the study of the combined action pattern. Mixed prediction models, the 3 × 2 factorial design model and the concentration addition (CA) model, were employed to analyze the combined estrogenic effect of the three EDCs.

RESULTS

From the dose-response relationship of estrogenic effects of BPA, NP and DES in the model of the prepuberty rats, the BMDL10(NOAEL) of the estrogenic effects of BPA, NP and DES were 90(120) mg/kg body weight, 6 mg/kg body weight and 0.10(0.25) μg/kg body weight, and the LOAEL of the the estrogenic effects of three EDCs were 240 mg/kg body weight, 15 mg/kg body weight and 0.50 μg/kg body weight, respectively. At BMDL10 doses based on the CA concept and the factorial analysis, the mode of combined effects of the three EDCs were dose addition. Mixtures in LOAEL doses, NP and DES combined effects on rat uterine/body weight ratio indicates antagonistic based on the CA concept but additive based on the factorial analysis. Combined effects of other mixtures are all additive by using the two models.

CONCLUSION

Our results showed that CA model provide more accurate results than the factorial analysis, the mode of combined effects of the three EDCs were dose addition, except mixtures in LOAEL doses, NP and DES combined effects indicates antagonistic effects based on the CA model but additive based on the factorial analysis. In particular, BPA and NP produced combination effects that are larger than the effect of each mixture component applied separately at BMDL doses, which show that additivity is important in the assessment of chemicals with estrogenic effects. The use of BMDL as point of departure in risk assessment may lead to underestimation of risk, and a more balanced approach should be considered in risk assessment.

Effects of Huang Bai (Phellodendri Cortex) on bone growth and pubertal development in adolescent female rats

Background

To evaluate the effects of Huang Bai (Phellodendron amurense) on growth and maturation in adolescent female rats.

Methods

Female Sprague-Dawley rats (28 days old; n = 72) were divided into six daily treatment groups: control (distilled water), Huang Bai (100 and 300 mg/kg), recombinant human GH (rhGH; 20 μg/kg), estradiol (1 μg/kg), and triptorelin (100 μg). Body weight, food intake, and vaginal opening were measured daily from postnatal day (PND) 28 to PND 43. Tetracycline (20 mg/kg) was injected on PND 41. After sacrifice on PND 43, the ovaries and uterus were weighed, and the tibias were fixed in 4% paraformaldehyde. Decalcified and dehydrated tibias were sectioned at a thickness of 40 μm, and sectioned tissues were examined with a fluorescence microscope. Insulin-like growth factor (IGF)-1 and bone morphogenetic protein (BMP)-2 were detected using immunohistochemistry.

Results

Relative to controls, body weight was higher in the triptorelin group. Bone growth rate increased in the Huang Bai 100 mg/kg (354.00 ± 31.1 μm/day), rhGH (367.10 ± 27.11 μm/day), and triptorelin (374.50 ± 25.37 μm/day) groups. Expression of IGF-1 and BMP-2 in the hypertrophic zone was higher in all experimental groups. Vaginal opening occurred earlier in the estradiol group (PND 33.58 ± 1.62) than in controls and later in the triptorelin group (PND > 43). Ovarian and uterine weights were lower in the oestradiol and triptorelin groups. However, Huang Bai had nonsignificant effects on vaginal opening and the weights of ovaries and the uterus.

Conclusions

Huang Bai stimulated bone growth by upregulating IGF-1 and BMP-2 in the growth plate. However, it had no effect on pubertal development.

Maternal exposure to an environmentally relevant dose of triclocarban results in perinatal exposure and potential alterations in offspring development in the mouse model

Triclocarban (TCC) is among the top 10 most commonly detected wastewater contaminants in both concentration and frequency. Its presence in water, as well as its propensity to bioaccumulate, has raised numerous questions about potential endocrine and developmental effects. Here, we investigated whether exposure to an environmentally relevant concentration of TCC could result in transfer from mother to offspring in CD-1 mice during gestation and lactation using accelerator mass spectrometry (AMS). ¹⁴C-TCC (100 nM) was administered to dams through drinking water up to gestation day 18, or from birth to post-natal day 10. AMS was used to quantify ¹⁴C-concentrations in offspring and dams after exposure. We demonstrated that TCC does effectively transfer from mother to offspring, both trans-placentally and via lactation. TCC-related compounds were detected in the tissues of offspring with significantly higher concentrations in the brain, heart and fat. In addition to transfer from mother to offspring, exposed offspring were heavier in weight than unexposed controls demonstrating an 11% and 8.5% increase in body weight for females and males, respectively. Quantitative real-time polymerase chain reaction (qPCR) was used to examine changes in gene expression in liver and adipose tissue in exposed offspring. qPCR suggested alterations in genes involved in lipid metabolism in exposed female offspring, which was consistent with the observed increased fat pad weights and hepatic triglycerides. This study represents the first report to quantify the transfer of an environmentally relevant concentration of TCC from mother to offspring in the mouse model and evaluate bio-distribution after exposure using AMS. Our findings suggest that early-life exposure to TCC may interfere with lipid metabolism and could have implications for human health.

Effects of a glyphosate-based herbicide on the uterus of adult ovariectomized rats

Glyphosate is the active ingredient of several herbicide formulations. Different reports suggest that glyphosate-based herbicides (GBHs) may act as endocrine disruptors. We evaluated the potential estrogenic effects of a GBH formulation using the uterotrophic assay. Adult ovariectomized rats were sc injected for 3 consecutive days with: saline solution (vehicle control), 2.10-5  g E2 /kg/day (uterotrophic dose; UE2 ), 2.10-7  g E2 /kg/day (nonuterotrophic dose; NUE2 ), or 0.5, 5, or 50 mg GBH/kg/day of the. Twenty-four hours after the last injection, the uterus was removed and weighed and processed for histopathology and mRNA extraction. Epithelial cell proliferation and height and expression of estrogen-responsive genes were evaluated (estrogen receptors, ERα and ERβ; progesterone receptor, PR; complement 3, C3). Uterine weight and epithelial proliferation were not affected by GBH. However, the luminal epithelial cell height increased at GBH0.5. ERα mRNA was downregulated by all GBH doses and E2 groups, whereas PR and C3 mRNA were diminished by GBH0.5. GBH5-, GBH50-, and UE2 -treated rats showed downregulated ERα protein expression in luminal epithelial cells, while the receptor was upregulated in the stroma. GBH upregulated ERβ (GBH0.5-50) and PR (GBH5) expressions in glandular epithelial cells, similar effect to that of NUE2 group. These results indicate that, although the uterine weight was not affected, GBH modulates the expression of estrogen-sensitive genes. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1191-1201, 2017.

Long-term effects of in utero and lactational exposure to butyl paraben in female rats

Parabens are used as preservatives in cosmetic, pharmaceutical, and food industries, and are frequently detected as contaminants in human fluids and tissues. The endocrine disrupting effects of parabens in female rodents include uterotrophic response, steroidogenesis impairment, and ovarian disturbances. The objective of this study was to determine the effects of maternal butyl paraben (BP) exposure on female sexual development. Pregnant Wistar rats were treated subcutaneously with either corn oil or BP at doses of 10, 100, or 200 mg/kg, from gestational day (GD) 12 until GD 20 for female foetal gonad evaluation, and from GD 12 until the end of lactation to evaluate sexual parameters on the female offspring. Immature female rats were also used in the uterotrophic assay to evaluate the possible estrogenic action of parabens. Our results revealed that, in this experimental protocol, BP did not show estrogenic activity at the doses used and did not impair sexual development and fertility capacity in the female rats, but impaired sexual behavior. We conclude that brain sexual development may be more sensitive to BP effects and we speculate that doses higher than 100 mg/kg (the male lowest observed adverse effect level (LOAEL) for rodent reproductive parameters) would be necessary to promote damages in the female reproduction, regarding the same protocol of exposure. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 776-788, 2017.

Effects of chronic exposure to triclosan on reproductive and thyroid endpoints in the adult Wistar female rat

Triclosan (TCS), an antibacterial, has been shown to be an endocrine disruptor in the rat. Previously, subchronic TCS treatment to female rats was found to advance puberty and potentiate the effect of ethinyl estradiol (EE) on uterine growth when EE and TCS were co-administered prior to weaning. In the pubertal study, a decrease in serum thyroxine (T₄) concentrations with no significant change in serum thyroid-stimulating hormone (TSH) was also observed. The purpose of the present study was to further characterize the influence of TCS on the reproductive and thyroid axes of the female rat using a chronic exposure regimen. Female Wistar rats were exposed by oral gavage to vehicle control, EE (1 μg/kg), or TCS (2.35, 4.69, 9.375 or 37.5 mg/kg) for 8 months and estrous cyclicity monitored. Although a divergent pattern of reproductive senescence appeared to emerge from 5 to 11 months of age between controls and EE-treated females, no significant difference in cyclicity was noted between TCS-treated and control females. A higher % control females displayed persistent diestrus (PD) by the end of the study, whereas animals administered with positive control (EE) were predominately persistent estrus (PE). Thyroxine concentration was significantly decreased in TCS-administered 9.375 and 37.5 mg/kg groups, with no marked effects on TSH levels, thyroid tissue weight, or histology. Results demonstrate that a long-term exposure to TCS did not significantly alter estrous cyclicity or timing of reproductive senescence in females but suppressed T₄ levels at a lower dose than previously observed.

Estrogenic effect of the extract of Renshen (Radix Ginseng) on reproductive tissues in immature mice

OBJECTIVE

To evaluate the estrogenic efficacy of Renshen (Radix Ginseng) (GS) on reproductive target tissues in immature mice.

METHODS

One hundred and ten female immature Kunming (KM) mice, 21-day-old, were randomly assigned to eleven groups, 10 for each; one served as control group treated with 0.154 mg/kg estradiol valerate (EV, n = 10), the rest were treated respectively with GS intragastrically at a daily dose of 0.5, 1.0, 1.5, 3.0, 6.0, 12.0, 18.0, 24.0 and 30.0 g/kg (n = 10 in per group) for 7 days. The estrous cycle, uterine weight, hormone levels in circulation and histomorphology changes of uterus and vagina were scrupulously examined. The estrogen receptor (ER) α and ERβ expressions in the uterus and vagina were detected by immunohistochemistry and western blotting.

RESULTS

Treatment with GS at the dose of 12.0, 18.0 and 24.0 g/kg resulted significant estrogenic activity in the mice, as indicated by advanced and prolonged estrous stage and increased uterine weight (all P < 0.05). GS treatment substantially promoted development of reproductive tisue by thickening the uterine endometrium and increasing vaginal epithelial layers. In addition, treatment with GS induced significant up-regulation of ERα and ERβ expressions in reproductive tissues, and ERα up-regulation was stronger than that of ERβ. GS could raise levels of circulating estrogen, simultaneously decrease levels of luteinizing hormone and follicle-stimulating hormone (all P < 0.001) compared with the control group.

CONCLUSION

Our findings suggest that GS had estrogenic effect on reproductive tissues in immature mice by stimulating biosynthesis of estrogen in circulation and up-regulating ERs.

Diosgenin does not express estrogenic activity: a uterotrophic assay

This study assessed the effects of diosgenin on estrogenic activity using a uterotrophic assay. Immature female rats received diosgenin orally at doses of 200, 100, or 20 mg/kg body mass; and 17α ethynylestradiol at doses of 1 or 0.3 μg/kg, daily, for 3 consecutive days from day 19 to day 21. Controls were distributed among 2 groups: an intact control group and a vehicle control group. Animals were sacrificed 24 h after the last application of diosgenin, estradiol, or vehicle (22nd day of life). Uterine wet weight, stereological and histomorphometrical changes, immunohistochemical expression of estrogen receptor alpha (ERα), progesterone receptor (PR), and the expression of lactoferrin (LF) were examined. Diosgenin did not affect the uterine wet weight, epithelium height, volume densities of endometrium, endometrial epithelia, number of endometrial glands, or histological appearance of vaginal epithelia. ERα, PR, and LF immunostaining intensity were not altered in the animals that received diosgenin. High-potency reference ER agonist 17α-ethynylestradiol induced a significant increase in all of the measured parameters, and as expected, decreased ERα immunostaining intensity. Based on these data, it can be concluded that diosgenin, at doses of 20–200 mg/kg, did not act as an estrogen agonist in the immature rat uterotrophic assay.

The estrogenic effects of apigenin, phloretin and myricetin based on uterotrophic assay in immature Wistar albino rats

Chemicals that occur in vegetal food and known as phytoestrogens, because of their structures similarity to estrogen, have benefits on chronic diseases. Despite this, when they are taken at high amounts, they can cause harmful effects on endocrine system of human and animals. In this study, it has been intended to determine the estrogenic potencies of phytoestrogens apigenin, phloretin and myricetin whose affinities for estrogen receptors in vitro. The female rats divided into 17 groups, each containing six rats. There was a negative control group and there were positive control dose groups which contains ethinyl estradiol, ethinyl estradiol+tamoxifen and genistein. The other dose groups which were tested for estrogenic activity contains apigenin, myricetin and phloretin All chemicals have been given to Wistar immature female rats with oral gavage for 3 consecutive days. By using uterotrophic analysis, uterus wet and blotted weights, vaginal opening, uterus length of female rats has been recorded at the end of the experiment. For detect of cell response, luminal epithelium height, gland number and lactoferrin intensity in luminal epithelium of uterus were evaluated. Biochemical analysises in blood were performed. Relative uterus weights of rats in 100 mg/kg/day dose group of myricetin were statistically increased according to vehicle control and positive control groups. In dose groups of apigenin and phloretin it was found that there were cell responses in uterus. All treatment groups had a significant difference in the high intensity of lactoferrin and uterine gland count compared to oil control group. There was no difference between phloretin and apigenin treatment groups in uterine weight statictically. Uterine heights were increased in positive control groups and 100 mg/kg/day dose group of myricetin. Epithelial cell heights were increased in treatment groups except apigenin and phloretin dose groups. There was no difference between all treatment groups in vaginal opening values according to positive control.

Rapid oestrogenic regulation of social and nonsocial learning

Much research on oestrogens has focused on their long-term action, exerting behavioural effects within hours to days through gene transcription. Oestrogens also affect behaviour on a much shorter time scale. These rapid effects are assumed to occur through cell signalling and can elicit a behavioural effect as early as 15 min after treatment. These effects on behaviour have primarily been explored through the action of oestradiol at three well-known oestrogen receptors (ERs): ERα, ERβ and the more recently described G protein-coupled ER1 (GPER1). The rapid effects of oestradiol and ER agonists have been tested on both social and nonsocial learning paradigms. Social learning refers to a paradigm in which an animal acquires information and modifies its behaviour based on observation of another animal, commonly studied using the social transmission of food preferences paradigm. When administered shortly before testing, oestradiol rapidly improves social learning on this task, although no ER agonist has definitive, comparable improving effects. Some evidence points to GPER1, whereas ERα impairs, and ERβ activation has no effect on social learning. Conversely, ERα and GPER1 play a larger role than ERβ in the rapid improving effect of oestrogens on nonsocial learning, including social and object recognition. In addition, when administered immediately post-acquisition, oestrogens also rapidly improve memory consolidation in a variety of learning paradigms: object recognition, object placement, inhibitory avoidance and the Morris water maze, indicating that oestradiol affects the consolidation of multiple types of memory. Evidence suggests that these improvements are the result of oestrogens acting in the dorsal hippocampus where selective activation of all three ERs shows rapid improving effects on spatial learning comparable to oestradiol. However, the hippocampus is not necessary for rapid oestradiol improvements on social recognition. Although acute treatment with oestradiol enhances learning and memory on various social and nonsocial learning paradigms, the specific ERs play different roles in each type of learning. Future research should aim to further determine the roles of ERs with respect to the enhancing effects of oestradiol on learning and memory, and also determine where in the brain oestradiol acts to affect social and nonsocial learning.

Assessment and molecular actions of endocrine-disrupting chemicals that interfere with estrogen receptor pathways

In all vertebrate species, estrogens play a crucial role in the development, growth, and function of reproductive and nonreproductive tissues. A large number of natural or synthetic chemicals present in the environment and diet can interfere with estrogen signaling; these chemicals are called endocrine disrupting chemicals (EDCs) or xenoestrogens. Some of these compounds have been shown to induce adverse effects on human and animal health, and some compounds are suspected to contribute to diverse disease development. Because xenoestrogens have varying sources and structures and could act in additive or synergistic effects when combined, they have multiple mechanisms of action. Consequently, an important panel of in vivo and in vitro bioassays and chemical analytical tools was used to screen, evaluate, and characterize the potential impacts of these compounds on humans and animals. In this paper, we discuss different molecular actions of some of the major xenoestrogens found in food or the environment, and we summarize the current models used to evaluate environmental estrogens.

Metals and breast cancer

Metalloestrogens are metals that activate the estrogen receptor in the absence of estradiol. The metalloestrogens fall into two subclasses: metal/metalloid anions and bivalent cationic metals. The metal/metalloid anions include compounds such as arsenite, nitrite, selenite, and vanadate while the bivalent cations include metals such as cadmium, calcium, cobalt, copper, nickel, chromium, lead, mercury, and tin. The best studied metalloestrogen is cadmium. It is a heavy metal and a prevalent environmental contaminant with no known physiological function. This review addresses our current understanding of the mechanism by which cadmium and the bivalent cationic metals activate estrogen receptor-α. The review also summarizes the in vitro and in vivo evidence that cadmium functions as an estrogen and the potential role of cadmium in breast cancer.

Genetic control of estrogen-regulated transcriptional and cellular responses in mouse uterus

The uterotropic response of the uterus to 17β-estradiol (E2) is genetically controlled, with marked variation observed depending on the mouse strain studied. Previous genetic studies from our laboratory using inbred mice that are high [C57BL/6J (B6)] or low [C3H/HeJ (C3H)] responders to E2 led to the identification of quantitative trait (QT) loci associated with phenotypic variation in uterine growth and leukocyte infiltration. The mechanisms underlying differential responsiveness to E2, and the genes involved, are unknown. Therefore, we used a microarray approach to show association of distinct E2-regulated transcriptional signatures with genetically controlled high and low responses to E2 and their segregation in (C57BL/6J×C3H/HeJ) F1 hybrids. Among the 6664 E2-regulated transcripts, analysis of cellular functions of those that were strain specific indicated C3H-selective enrichment of apoptosis, consistent with a 7-fold increase in the apoptosis indicator CASP3, and a 2.4-fold decrease in the apoptosis inhibitor Naip1 (Birc1a) in C3H vs. B6 following treatment with E2. In addition, several differentially expressed transcripts reside within our previously identified QT loci, including the ERα-tethering factor Runx1, demonstrated to enhance E2-mediated transcript regulation. The level of RUNX1 in uterine epithelial cells was shown to be 3.5-fold greater in B6 compared to C3H. Our novel insights into the mechanisms underlying the genetic control of tissue sensitivity to estrogen have great potential to advance understanding of individualized effects in physiological and disease states.

Low doses of 17β-estradiol rapidly improve learning and increase hippocampal dendritic spines

While a great deal of research has been performed on the long-term genomic actions of estrogens, their rapid effects and implications for learning and memory are less well characterized. The often conflicting results of estrogenic effects on learning and memory may be due to complex and little understood interactions between genomic and rapid effects. Here, we investigated the effects of low, physiologically relevant, doses of 17β-estradiol on three different learning paradigms that assess social and non-social aspects of recognition memory and spatial memory, during a transcription independent period of memory maintenance. Ovariectomized female CD1 mice were subcutaneously administered vehicle, 1.5 μg/kg, 2 μg/kg, or 3 μg/kg of 17β-estradiol 15 minutes before social recognition, object recognition, or object placement learning. These paradigms were designed to allow the testing of learning effects within 40 min of hormone administration. In addition, using a different set of ovariectomized mice, we examined the rapid effects of 1.5 μg/kg, 2 μg/kg, or 3 μg/kg of 17β-estradiol on CA1 hippocampal dendritic spines. All 17β-estradiol doses tested impacted learning, memory, and CA1 hippocampal spines. 17β-Estradiol improved both social and object recognition, and may facilitate object placement learning and memory. In addition, 17β-estradiol increased dendritic spine density in the stratum radiatum subregion of the CA1 hippocampus, but did not affect dendritic spines in the lacunosum-moleculare, within 40 min of administration. These results demonstrate that the rapid actions of 17β-estradiol have important implications for general learning and memory processes that are not specific for a particular type of learning paradigm. These effects may be mediated by the rapid formation of new dendritic spines in the hippocampus.

Histopathologic changes in the uterus, cervix and vagina of immature CD-1 mice exposed to low doses of perfluorooctanoic acid (PFOA) in a uterotrophic assay

The estrogenic and antiestrogenic potential of perfluorooctanoic acid (PFOA) was assessed using an immature mouse uterotrophic assay and by histologic evaluation of the uterus, cervix and vagina following treatment. Female offspring of CD-1 dams were weaned at 18days old and assigned to groups of equal weight, and received 0, 0.01, 0.1, or 1mg PFOA/kg BW/d by gavage with or without 17-β estradiol (E(2), 500μg/kg/d) from PND 18-20 (n=8/treatment/block). At 24h after the third dose (PND 21), uteri were removed and weighed. Absolute and relative uterine weights were significantly increased in the 0.01mg/kg PFOA only group. Characteristic estrogenic changes were present in all E(2)-treated mice; however, they were minimally visible in the 0.01 PFOA only mice. These data suggest that at a low dose PFOA produces minimal histopathologic changes in the reproductive tract of immature female mice, and does not antagonize the histopathologic effects of E(2).

Effects of environmentally-relevant levels of perfluorooctane sulfonate on clinical parameters and immunological functions in B6C3F1 mice

In the first part of a series of studies to account for perfluorooctane sulfonate (PFOS)-induced sheep red blood cell (SRBC)-specific immunoglobulin M (IgM) antibody suppression in mice, a survey of clinical and immunotoxicological endpoints was examined. Adult female B₆C₃F₁ mice were exposed orally for 28 days to a total administered dose (TAD) of 0, 0.1, 0.5, 1, or 5 mg PFOS/kg. Uterus wet weight was significantly decreased compared with control at the 5 mg/kg dose. No indications of wasting syndrome, malnutrition, alteration of thyroid homeostasis, or signs of overt toxicity were observed. Numbers of splenic CD19+/CD21⁻, CD19+/CD21+, B220+/CD40+, CD4+/CD154⁻, CD4+/CD154+, and MHC-II+ cells were not altered. Additionally, ex vivo interleukin-4 (IL-4), IL-5, and IL-6 production by in vitro anti-CD3- or phorbol myristate acetate-stimulated CD4+ T-cells was not affected. Ex vivo IL-6 production by B-cells was significantly increased by in vitro stimulation with either anti-CD40 or lipopolysaccharide. Increased IL-6 production by B-cells was the most sensitive endpoint assessed resulting in alterations at the lowest dose tested (0.1 mg/kg TAD) following anti-CD40 stimulation. Further studies are required to characterize effects on inflammatory markers such as IL-6 at environmentally relevant concentrations of PFOS and to determine the key events associated with PFOS-induced IgM suppression to address potential human health risks.

Maternal exposure to triclosan impairs thyroid homeostasis and female pubertal development in Wistar rat offspring

Although the effects of triclosan have been examined in male reproductive functions, it is unknown whether this potent antibacterial agent affects pregnancy and female pubertal development. Effects of maternal exposure to triclosan on thyroid homeostasis (TH) and reproductive-tract development in female Wistar rats were thus studied. Dams were exposed daily to triclosan (0, 1, 10, or 50 mg/kg/d) from 8 d before mating to lactation day 21. Offspring were also exposed after weaning. In vivo triclosan estrogenic activity was screened by uterotrophic assay and vaginal opening (VO), with first estrus and uterus and ovarian weight determined in offspring. Dam blood samples were taken during pregnancy and lactation to examine the effect of triclosan on TH. No apparent external signs of toxicity or differences in mean numbers of implantation sites were observed in treated rats. Triclosan treatment decreased total serum T(4) and T(3) in pregnant rats and also lowered sex ratio, lowered pup body weights on postnatal day (PND) 20, and delayed VO in offspring. In addition, the highest dose of triclosan significantly reduced the live birth index (percentage) and 6-d survival index. Data indicate that triclosan impairs thyroid homeostasis and reproductive toxicity in adult rats and produces fetal toxicity in offspring exposed in utero, during lactation, and after weaning.

Uterotrophic effects of cow milk in immature ovariectomized Sprague-Dawley rats

OBJECTIVES

Milk contains considerable quantities of estrogens and progesterone and as such may be one of the risk factors for hormone-related cancers. To determine the hormonal effects of commercial and traditional types of milk, we performed uterotrophic tests.

METHODS

Forty-five rats were ovariectomized and divided into three groups of 15 animals each. The animals were kept for 7 days on powdered chow and one of three different liquids: commercial milk (C), traditional milk (T), or water. At autopsy, wet and dry uterine weights were determined. The cell heights of the uterine epithelium and endometrium were determined. The uterine 5-bromo-2-deoxyuridine (BrdU) labeling index of the epithelium and endometrium gland epithelium was also assessed.

RESULTS

The weights of wet and dry uterus were 142 ± 13 and 112 ± 10 mg in the C group, 114 ± 30 and 91 ± 24 mg in the T group, and 87 ± 6 and 69 ± 5 mg in the W group. Significant differences in wet and dry uterus weights were found between all pairs of groups. The ratio of the wet uterine weight to body weight was significantly higher in the C and T groups than in the W group. The heights of the uterine epithelium and endometrium were higher and BrdU labeling index was greater in the C group than in the T and W groups.

CONCLUSIONS

Commercially available milk and traditional milk have uterotrophic effects on young ovariectomized rats. Our findings indicate that these uterotrophic effects in the milk groups were partly due to the estrogen and progesterone in the milk.

Supplemental dietary racemic equol has modest benefits to bone but has mild uterotropic activity in ovariectomized rats

Soy isoflavones and their metabolites, with estrogenic activity, have been considered candidates for reducing postmenopausal bone loss. In this study, we examined the effect of dietary equol, a bioactive metabolite of the soy isoflavone daidzein, on equol tissue distribution, bone parameters, and reproductive tissue activity using an adult ovariectomized (OVX) rat model. An 8-wk feeding study was conducted to compare 4 dietary treatments of equol (0, 50, 100, 200 mg/kg diet) in 6-mo-old OVX female Sprague-Dawley rats. A dose response increase in tissue equol concentrations was observed for serum, liver, kidney, and heart, and a plateau occurred at 100 mg equol/kg diet for intestine. In OVX rats receiving 200 mg equol/kg diet, femoral calcium concentration was greater than those receiving lower doses but was still less than SHAM (P < 0.05), and other bone measures were not improved. Tibia calcium concentrations were lower in OVX rats receiving 100 and 200 mg equol/kg diet compared with the OVX control rats. Trabecular bone mineral density of tibia was also lower in equol-fed OVX rats. At this dietary equol intake, uterine weight was higher (P < 0.05) than in other OVX groups but lower than the SHAM-operated intact rats. The 200 mg/kg diet dose of dietary equol significantly increased proliferative index in the uterine epithelium. Dietary equol had no stimulatory effect on mammary gland epithelium. We conclude that in OVX rats, a dietary equol dose that had modest effect on bone also exerts mild uterotropic effects.

An evaluation of estrogenic activity of parabens using uterine calbindin-d9k gene in an immature rat model

In the present study, calbindin-D9k (CaBP-9k), a potent biomarker for screening estrogen-like environmental chemicals in vivo and in vitro, was adopted to examine the potential estrogen-like property of the following parabens: propyl-, isopropyl-, butyl-, and isobutylparaben. Immature female rats were administered for 3 days from postnatal day 14 to 16 with 17alpha-ethinylestradiol (EE, 1 mg/kg body weight [BW]/day) or parabens (62.5, 250, and 1000 mg/kg BW/day). In uterotrophic assays, significantly increased uterus weights were detected in the EE-treated group and in the groups treated with the highest dose of isopropyl-, butyl-, and isobutylparaben. In addition, these parabens induced uterine CaBP-9k messenger RNA (mRNA) and protein levels, whereas cotreatment of parabens and fulvestrant, a pure estrogen receptor (ER) antagonist, completely reversed the paraben-induced gene expression and increased uterine weights. To investigate the ER-mediated mechanism(s) by which parabens exert their effects, the expression level of ER-alpha and progesterone receptor (PR) was analyzed. Exposure to EE or parabens caused a dramatic decrease in expression of both ER-alpha mRNA and protein levels, whereas cotreatment with fulvestrant reversed these effects. These data showed the difference of CaBP-9k and ER-alpha expression, suggesting that CaBP-9k may not express via ER-alpha pathway. In the effect of parabens on CaBP-9k expression through PR mediation, a significantly increased expression of uterine PR gene, a well-known ER-regulating gene, at both transcriptional and translational levels was indicated in the highest dose of isopropyl- and butylparaben. These parabens-induced PR gene expression was completely blocked by fulvestrant. This result indicates that CaBP-9k expression may involve with PR mediates in the estrogenic effect of paraben in immature rat uteri. Taken together, parabens exhibited an estrogen-like property in vivo, which may be mediated by a PR and/or ER-alpha signaling pathway. In addition, our results expanded the current understanding of the potential adverse effects of parabens associated with their estrogen-like activities. Further investigation is needed to elucidate in greater detail the adverse effects of parabens in humans and wildlife.

Estrogenic activity of bovine milk high or low in equol using immature mouse uterotrophic responses and an estrogen receptor transactivation assay

BACKGROUND

Cow's milk contain phytoestrogens especially equol depending on the composition of the feed ration. However, it is unknown whether milk differing in equol exhibits different estrogenicity in model systems and thereby potentially in humans as milk consumers.

METHODS

The estrogenicity of high and low equol milk (HEM and LEM, respectively) and purified equol was investigated in immature female mice including mRNA expression of six estrogen-sensitive genes in uterine tissue. Extracts of HEM and LEM were also tested for estrogenicity in vitro in an estrogen receptor (ER) reporter gene assay with MVLN cells.

RESULTS

The total content of phytoestrogens was approximately 10 times higher in HEM compared with LEM, but levels of endogenous milk estrone and 17beta-estradiol were similar in the two milk types (503-566 and 60-64.6pg/ml, respectively). There was no difference in uterine weight between mice receiving LEM and HEM, and no difference from controls. Equol (50 times the concentration in HEM) was not uterotrophic. The ERbeta mRNA expression was down-regulated in the uteri of HEM mice compared with LEM and controls, but there was no difference between milk types for any of the other genes. Extracts of HEM showed a higher estrogenicity than extracts of LEM in MVLN cells, and there was a dose-dependent increase in estrogenicity by equol.

CONCLUSION

The higher in vitro estrogenicity of HEM was not reflected as a higher uterine weight in vivo although the down-regulation of ERbeta in uterine tissue of HEM mice could suggest some estrogenic activity of HEM at the gene expression level.

Tamoxifen-elicited uterotrophy: cross-species and cross-ligand analysis of the gene expression program

BACKGROUND

Tamoxifen (TAM) is a well characterized breast cancer drug and selective estrogen receptor modulator (SERM) which also has been associated with a small increase in risk for uterine cancers. TAM's partial agonist activation of estrogen receptor has been characterized for specific gene promoters but not at the genomic level in vivo.Furthermore, reducing uncertainties associated with cross-species extrapolations of pharmaco- and toxicogenomic data remains a formidable challenge.

RESULTS

A comparative ligand and species analysis approach was conducted to systematically assess the physiological, morphological and uterine gene expression alterations elicited across time by TAM and ethynylestradiol (EE) in immature ovariectomized Sprague-Dawley rats and C57BL/6 mice. Differential gene expression was evaluated using custom cDNA microarrays, and the data was compared to identify conserved and divergent responses. 902 genes were differentially regulated in all four studies, 398 of which exhibit identical temporal expression patterns.

CONCLUSION

Comparative analysis of EE and TAM differentially expressed gene lists suggest TAM regulates no unique uterine genes that are conserved in the rat and mouse. This demonstrates that the partial agonist activities of TAM extend to molecular targets in regulating only a subset of EE-responsive genes. Ligand-conserved, species-divergent expression of carbonic anhydrase 2 was observed in the microarray data and confirmed by real time PCR. The identification of comparable temporal phenotypic responses linked to related gene expression profiles demonstrates that systematic comparative genomic assessments can elucidate important conserved and divergent mechanisms in rodent estrogen signalling during uterine proliferation.

Estrogenic activity of environmental polycyclic aromatic hydrocarbons in uterus of immature Wistar rats

Polycyclic aromatic hydrocarbons (PAHs) are an important group of environmental pollutants, known for their mutagenic and carcinogenic activities. Many PAHs are aryl hydrocarbon receptor (AhR) ligands and several recent studies have suggested that PAHs or their metabolites may activate estrogen receptors (ER). The present study investigated possible estrogenic/antiestrogenic effects of abundant environmental contaminants benzo[a]pyrene (BaP), benz[a]anthracene (BaA), fluoranthene (Fla) and benzo[k]fluoranthene (BkF) in vivo, using the immature rat uterotrophic assay. The present results suggest that BaA, BaP and Fla behaved as estrogen-like compounds in immature Wistar rats, when applied for 3 consecutive days at 10mg/kg/day, as documented by a significant increase of uterine weight and hypertrophy of luminal epithelium. These effects were likely to be mediated by ERalpha, a major subtype of ER present in uterus, as they were inhibited by treatment with ER antagonist ICI 182,780. BaA, the most potent of studied PAHs, induced a significant estrogenic effect within a concentration range 0.1-50mg/kg/day; however, it did not reach the maximum level induced by reference estrogens. The proposed antiestrogenicity of the potent AhR agonist BkF was not confirmed in the present in vivo study; the exposure to BkF did not significantly affect the uterine weight, although a weak suppression of ERalpha immunostaining was observed in luminal and glandular epithelium, possibly related to its AhR-mediated activity. The PAHs under study did not induce marked genotoxic damage in uterine tissues, as documented by the lack of Ser-15-phoshorylated p53 protein staining. With the exception of Fla, all three remaining compounds increased CYP1-dependent monooxygenation activities in liver at the doses used, suggesting that the potential tissue-specific antiestrogenic effects of PAHs mediated by metabolization of 17beta-estradiol also cannot be excluded. Taken together, these environmentally relevant PAHs induced estrogenic effects in vivo, which might affect their toxic impact and carcinogenicity.

Relationship between the results of in vitro receptor binding assay to human estrogen receptor α and in vivo uterotrophic assay: Comparative study with 65 selected chemicals

For screening chemicals possessing endocrine disrupting potencies, the uterotrophic assay has been placed in a higher level in the OECD testing framework than the ER binding assay to detect ER-mediated activities. However, there are no studies that can demonstrate a clear relationship between these assays. In order to clarify the relationship between the in vitro ER binding and in vivo uterotrophic assays and to determine meaningful binding potency from the ER binding assay, we compared the results from these assays for 65 chemicals spanning a variety of chemicals classes. Under the quantitative comparison between logRBAs (relative binding affinities) and logLEDs (lowest effective doses), the log RBA was well correlated with both logLEDs of estrogenic and anti-estrogenic compounds at r(2)=0.67 (n=28) and 0.79 (n=23), respectively. The RBA of 0.00233% was found to be the lowest ER binding potency to elicit estrogenic or anti-estrogenic activities in the uterotrophic assay, accordingly this value is considered as the detection limit of estrogenic or anti-estrogenic activities in the uterotrophic assay. The usage of this value as cutoff provided the best concordance rate (82%). These findings are useful in a tiered approach for identifying chemicals that have potential to induce ER-mediated effects in vivo.

Variations in phytoestrogen content between different mill dates of the same diet produces significant differences in the time of vaginal opening in CD-1 mice and F344 rats but not in CD Sprague-Dawley rats

BACKGROUND

The optimum test diet and rodent species/strain for evaluating endocrine-disrupting compounds (EDCs) are critical.

OBJECTIVES

We conducted studies to evaluate rodent species sensitivity and the effects of diets varying in phytoestrogen content on the time of vaginal opening (VO) in CD-1 mice, Fischer 344 (F344) rats, and CD Sprague-Dawley (S-D) rats.

METHODS

Mice were weaned on postnatal day (PND) 15 and rats on PND19 and randomly assigned to control or test diets. Body weights, food consumption, and time of VO were recorded.

RESULTS

The time of VO was significantly advanced in F344 rats fed diets containing daidzein and genistein, whereas these same diets did not advance VO in S-D rats. When animals were fed the AIN-76A diet spiked with genistein, time of VO was significantly advanced at all doses in CD-1 mice, at the two highest doses in F344 rats, and at the highest dose in S-D rats. The time of VO in F344 rats was more highly correlated with the phytoestrogen content than with the total metabolizable energy (ME) of 12 diets.

CONCLUSIONS

The S-D rat is less sensitive to dietary phytoestrogens compared with the F344 rat or the CD-1 mouse, suggesting that the S-D rat is not the ideal model for evaluating estrogenic activity of EDCs. The profound effects of dietary phytoestrogens on the time of VO, an estrogen-sensitive marker, indicate that a standardized open-formula phytoestrogen-free diet containing a low ME level should be used to optimize the sensitivity of estrogenic bioassays.

Drinking water with uranium below the U.S. EPA water standard causes estrogen receptor-dependent responses in female mice

BACKGROUND

The deleterious impact of uranium on human health has been linked to its radioactive and heavy metal-chemical properties. Decades of research has defined the causal relationship between uranium mining/milling and onset of kidney and respiratory diseases 25 years later.

OBJECTIVE

We investigated the hypothesis that uranium, similar to other heavy metals such as cadmium, acts like estrogen.

METHODS

In several experiments, we exposed intact, ovariectomized, or pregnant mice to depleted uranium in drinking water [ranging from 0.5 microg/L (0.001 microM) to 28 mg/L (120 microM).

RESULTS

Mice that drank uranium-containing water exhibited estrogenic responses including selective reduction of primary follicles, increased uterine weight, greater uterine luminal epithelial cell height, accelerated vaginal opening, and persistent presence of cornified vaginal cells. Coincident treatment with the antiestrogen ICI 182,780 blocked these responses to uranium or the synthetic estrogen diethylstilbestrol. In addition, mouse dams that drank uranium-containing water delivered grossly normal pups, but they had significantly fewer primordial follicles than pups whose dams drank control tap water.

CONCLUSIONS

Because of the decades of uranium mining/milling in the Colorado plateau in the Four Corners region of the American Southwest, the uranium concentration and the route of exposure used in these studies are environmentally relevant. Our data support the conclusion that uranium is an endocrine-disrupting chemical and populations exposed to environmental uranium should be followed for increased risk of fertility problems and reproductive cancers.

Effect of postnatal exposure to benzo[a]pyrene on the uterus of immature rats

The objective of this study was to investigate the morphological effects of postnatal exposure to benzo[a]pyrene (B[a]P) on the development of the uterus, uterine estrogen receptor (ERalpha) expression, and the uterine response to estrogen stimulation using the uterotrophic bioassay in rats. Neonates were injected on each postnatal day (PND) 1-14 with B[a]P (0.1, 1.0 and 10.0mg/kg), ethynylestradiol (EE; 1.0 microg/kg) or vehicle (control group). All animals were killed on PND 23. Postnatal administration of B[a]P with doses of 1.0 and 10.0 mg/kg induced significant (P<0.01) reduction of uterine weight and significantly lowered (P<0.05) ERalpha expression in the luminal epithelium. The increase in uterine weight and luminal epithelium heights after EE stimulation (1.0 microg/kg) on PND 20-22 was significantly higher (P<0.01) in all groups in comparison with corresponding non-stimulated groups. However, the uterotrophic response in rats postnatally exposed to EE and B[a]P was significantly lower (P<0.01) than in controls. In the control and EE groups, EE stimulation on PND 20-22 induced a significant (P<0.01) decrease in ERalpha immunoreactivity of the luminal epithelium. In contrast, rats postnatally treated with B[a]P showed no change in the density of ERalpha immunostaining when detected after estrogenic stimulation. The present study showed that postnatal exposure to B[a]P caused pathological changes in constitution and maturation of uterine ERalpha resulting in disturbed morphological development and uterine dysfunction in immature rats.

Estrogen Deprivation and Inhibition of Breast Cancer Growth in Vivo through Activation of the Orphan Nuclear Receptor Liver X Receptor

Estrogen plays an important role in normal physiology. It is also a risk factor for breast cancer, and antiestrogen therapies have been shown to be effective in the treatment and prevention of breast cancers. The liver is important for estrogen metabolism, and a compromised liver function has been linked to hyperestrogenism in patients. In this report, we showed that the liver X receptor (LXR) controls estrogen homeostasis by regulating the basal and inducible hepatic expression of estrogen sulfotransferase (Est, or Sult1e1), an enzyme critical for metabolic estrogen deactivation. Genetic or pharmacological activation of LXR resulted in Est induction, which in turn inhibited estrogen-dependent uterine epithelial cell proliferation and gene expression, as well as breast cancer growth in a nude mouse model of tumorigenicity. We further established that Est is a transcriptional target of LXR, and deletion of the Est gene in mice abolished the LXR effect on estrogen deprivation. Interestingly, Est regulation by LXR appeared to be liver specific, further underscoring the role of liver in estrogen metabolism. Activation of LXR failed to induce other major estrogen-metabolizing enzymes, suggesting that the LXR effect on estrogen metabolism is Est specific. In summary, our results have revealed a novel mechanism controlling estrogen homeostasis in vivo and may have implications for drug development in the treatment of breast cancer and other estrogen-related cancerous endocrine disorders.

Suppression of humoral immunity following exposure to the perfluorinated insecticide sulfluramid

Perfluorinated hydrocarbons have been manufactured for over 40 yr and have numerous applications in industry. This group of compounds has recently generated much interest, as some of these compounds such as perfluorooctane sulfonate (PFOS) and perfluoroctanic acid (PFOA) are persistent in the environment and detectable in blood samples of both wildlife and humans. Studies show that these perfluorinated compounds induce peroxisomal proliferation, induce hepatomegaly, alter steroidogenesis, and decrease body weight, accompanied by a wasting syndrome; however, effects on immune function have not been addressed at length. This study examined sulfluramid, a perfluorinated pesticide that is currently available in the marketplace and is a representative member of this class of chemicals. Adult female B6C3F1 mice were exposed via gavage to either an oil carrier control or sulfluramid for 14 d (1, 3, 10, or 30 mg/kg/d) or 28 d (0.3, 1, 3, or 10 mg/kg/d). Although responses were normal in natural killer cell activity and lymphocyte proliferation, dose-responsive suppression was noted in the plaque forming cell (PFC) response at exposure levels as low as 3 mg/kg/d in the 14-d exposure and 0.3 mg/kg/d for 28 d. Dose-responsive increases in liver mass were observed following treatment with 1, 3, 10, or 30 mg/kg/d for 14 d and 0.3, 1, 3, or 10 mg/kg/d for 28 d. A significant reduction in body weight was observed at the highest dose level in each study. Novel findings in this study indicate that sulfluramid suppresses immunoglobulin (Ig) M production. Additional immunotoxicity studies are required to understand potential mechanisms of suppression and determine potential health risks associated with exposure to perfluorinated hydrocarbons.

Disruption of the developing female reproductive system by phytoestrogens: Genistein as an example

Studies in our laboratory have shown that exposure to genistein causes deleterious effects on the developing female reproductive system. Mice treated neonatally on days 1-5 by subcutaneous injection of genistein (0.5-50 mg/kg) exhibited altered ovarian differentiation leading to multioocyte follicles (MOFs) at 2 months of age. Ovarian function and estrous cyclicity were also disrupted by neonatal exposure to genistein with increasing severity observed over time. Reduced fertility was observed in mice treated with genistein (0.5, 5, or 25 mg/kg) and infertility was observed at 50 mg/kg. Mammary gland and behavioral endpoints were also affected by neonatal genistein treatment. Further, transgenerational effects were observed; female offspring obtained from breeding genistein treated females (25 mg/kg) to control males had increased MOFs. Thus, neonatal treatment with genistein at environmentally relevant doses caused adverse consequences on female development which is manifested in adulthood. Whether adverse effects occur in human infants exposed to soy-based products such as soy infant formulas is unknown but the neonatal murine model may help address some of the current uncertainties since we have shown that many effects obtained from feeding genistin, the glycosolated form of genistein found in soy formula, are similar to those obtained from injecting genistein.

Perinatal bisphenol A exposure increases estrogen sensitivity of the mammary gland in diverse mouse strains

BACKGROUND

Studies of low-dose effects of xenoestrogens have yielded conflicting results that may be attributed to differences in estrogen sensitivity between the rodent strains examined. Perinatal exposure of CD-1 mice to low doses of the xenoestrogen bisphenol A (BPA) alters peripubertal mammary gland development. Future studies to assess the role of estrogen receptors as mediators of BPA action require estrogen receptor knock-out mice that were generated on a C57Bl6 background. The sensitivity of the C57Bl6 strain to estradiol and BPA is unknown.

OBJECTIVES

In the present study we examined whether the mammary glands of CD-1 and C57Bl6 mice exhibited similar responses to 17beta-estradiol (E(2)) and whether perinatal exposure to BPA equally enhanced sensitivity of the mammary glands to E(2) at puberty.

METHODS

Immature mice were ovariectomized and treated for 10 days with one of eight doses of E(2). Morphological mammary gland parameters were examined to identify doses producing half-maximal effects. Mice were exposed perinatally to 0 or 250 ng BPA/kg body weight (bw)/day from gestational day 8 until postnatal day (PND) 2. On PND25, female offspring were ovariectomized and given an estrogen challenge of 0, 0.5, or 1 microg E(2)/kg bw/day for 10 days. Morphometric parameters of the mammary gland were compared between strains.

RESULTS

Both strains exhibited similar responses to E(2). Perinatal BPA exposure altered responses to E(2) at puberty for several parameters in both strains, although the effect in CD-1 was slightly more pronounced.

CONCLUSION

Both mouse strains provide adequate models for the study of perinatal exposure to xenoestrogens.

Developmental exposure to diethylstilbestrol (DES) alters uterine response to estrogens in prepubescent mice: low versus high dose effects

Outbred CD-1 mice received subcutaneous injections on neonatal days 1-5 with DES (0.0001-1000 microg/kg per day), a model xenoestrogen. At 17 days of age, uterine wet weight increase in response to estrogen was altered in neonatally DES-treated mice compared to controls. The response varied depending on the neonatal DES dose; a low dose (0.01 microg/kg) caused an enhanced uterine response but higher neonatal doses dampened the response. Western blots and immunolocalization of estrogen receptor alpha (ERalpha) showed high ER levels at DES 0.01 microg/kg, but decreased levels at higher doses compared to controls. Genes responding through ER-mediated pathways (c-fos, proliferating cell nuclear antigen (PCNA), and lactoferrin (LF)) mirrored altered wet weight responses, i.e., enhancement at low doses and dampening at higher doses. A similar dose-response curve was seen in 4 months old ovariectomized DES-treated mice suggesting the altered response was long-term. These data suggest xenoestrogen exposure during critical developmental windows alters hormone programming so that the uterus responds abnormally to estrogen later in life, and that the response differs following high versus low doses of neonatal exposure.

Estrogenicity of the Isoflavone Metabolite Equol on Reproductive and Non-Reproductive Organs in Mice1

Equol, a metabolite of the phytoestrogen daidzein, is present at significant levels in some humans who consume soy and in rodents fed soy-based diets. Equol is estrogenic in vitro, but there have been limited studies of its activity in vivo. We evaluated equol effects on reproductive and non-reproductive endpoints in mice. Ovariectomized age-matched (30-day-old) female C57BL/6 mice were fed phytoestrogen-free diets and given a racemic mixture of equol by daily injections (0, 4, 8, 12, or 20 mg [kg body weight](-1) day(-1)) or in the diet (0, 500, or 1,000 ppm) for 12 days. Mice were killed, and serum concentrations of total and aglycone equol were measured. Total serum equol concentrations ranged from 1.4 to 7.5 microM with increasing doses of injected equol, but uterine weight increased significantly only at 12 and 20 mg (kg body weight)(-1) day(-1). Dietary equol at 500 or 1,000 ppm produced total serum equol concentrations of 5.9 and 8.1 microM, respectively, comparable with those in rodents consuming certain high-soy chows; the proportion of equol present as the free aglycone was much lower with dietary administration than injections, which may be a factor in the greater biological effects induced by injections. Dietary equol did not significantly increase uterine weight. Increasing dietary and injected equol doses caused a dose-dependent increase in vaginal epithelial thickness. Uterine epithelial proliferation was increased by equol injections at 8-20 mg (kg body weight)(-1) day(-1) and 1,000 ppm dietary equol. Neither dietary nor injected equol decreased thymic or adipose weights. In conclusion, equol is a weak estrogen with modest effects on endpoints regulated by estrogen receptor alpha when present at serum levels seen in rodents fed soy-based diets, but quantities present in humans may not be sufficient to induce estrogenic effects, although additive effects of equol with other phytoestrogens may occur.

17-β Estradiol Independently Regulates Erythropoietin Synthesis and NOS Activity during Hypoxia

We reported previously that 17-beta estradiol (E2-beta) attenuates hypoxic induction of erythropoietin (EPO) synthesis in rats. We hypothesized this attenuation is mediated by increased nitric oxide (NO) bio-availability. To investigate this hypothesis, ovariectomized estrogen-depleted rats were instrumented with arterial and venous catheters and treated with either E2-beta (20 microg/24 hrs) or vehicle (polypropylene glycol) for 7 days. Rats were placed in Plexiglas boxes and administered a bolus of either the NO synthase inhibitor, Nomega-nitro-L-arginine (l-NNA, 15 mg/kg) or saline. Following this bolus, saline or l-NNA was continuously infused (15 mg/kg/h) throughout the 8 hours of hypoxic exposure (12% O2). Hypoxia increased plasma NO metabolites (NOx) in both saline groups but more in E2-beta-treated rats. l-NNA prevented this increase in both groups. Renal endothelial NO synthase (NOS) expression was unaltered by hypoxia, l-NNA, or E2-beta. Despite preventing increases in plasma NOx during hypoxia, l-NNA did not affect E2-beta attenuation of EPO synthesis. We conclude that E2-beta independently attenuates hypoxic induction of EPO and augments hypoxic increases in NO synthesis.

Biotransformations of bisphenol A in a mammalian model: answers and new questions raised by low-dose metabolic fate studies in pregnant CD1 mice

We investigated the metabolic fate of a low dose (25 micro g/kg) of bisphenol A [2,2-bis(4-hydroxy-phenyl)propane] (BPA) injected subcutaneously in CD1 pregnant mice using a tritium-labeled molecule. Analytic methods were developed to allow a radio-chromatographic profiling of BPA residues in excreta and tissues, as well as in mothers' reproductive tracts and fetuses, that contained more than 4% of the administered radioactivity. BPA was extensively metabolized by CD1 mice. Identified metabolite structures included the glucuronic acid conjugate of BPA, several double conjugates, and conjugated methoxylated compounds, demonstrating the formation of potentially reactive intermediates. Fetal radioactivity was associated with unchanged BPA, BPA glucuronide, and a disaccharide conjugate. The latter structure, as well as that of a dehydrated glucuronide conjugate of BPA (a major metabolite isolated from the digestive tract), showed that BPA metabolic routes were far more complex than previously thought. The estrogenicity of the metabolites that were identified but not tested for hormonal activity cannot be ruled out; however, in general, conjugated BPA metabolites have significantly lower potency than that of the parent compound. Thus, these data suggest the parental compound is responsible for the estrogenic effects observed in fetuses exposed to BPA during gestation in this mammalian model.

Immunomodulation by diethylstilbestrol is dose and gender related: effects on thymocyte apoptosis and mitogen-induced proliferation

It is believed, but not proven, that the immunomodulatory effects of DES may vary with the dose and/or gender. To address these critical gaps in the literature, diethylstilbestrol (DES) was administered to female and male CD-1 mice as four subcutaneous injections for 1 week at 0, 5, 15, and 30 microg/kg bw doses, and immunological and reproductive effects examined a day after the last injection. Female thymuses were significantly larger than their male counterparts. Short-term administration of DES to female or male mice neither induced thymic atrophy nor altered the relative percentages of thymic subsets. Nevertheless, DES treatment of female or male mice induced a dose-related apoptosis of CD4(+)8(+), CD4(+)8(-) and CD4(-)8(+) subsets as analyzed by 7-amino-actinomycin D (7-AAD). Immature CD4(-)8(-) subset of thymocytes from females was also affected by high dose DES. The pattern of mitogen-induced proliferation of splenic lymphocytes varied with the dose of hormone and the gender. In females, splenic lymphocytes from low dose DES (5 microg/kg bw)-treated mice exhibited an increased proliferative response to Con-A, LPS or PMA/ionomycin compared with controls. Similar cultures from mice treated with higher doses of DES (15 or 30 microg/kg bw) did not manifest an increased proliferative response, but rather showed a trend for suppressed proliferation, especially in response to Con-A. In males, DES had minimal effects with the exception of increased proliferative response to Con-A in splenocytes from medium-dose-DES-treated mice. The changes in mitogen-induced proliferation in DES-treated female mice were not mirrored by similar changes in the relative numbers of CD90(+) or CD45R(+) cells, or in ratios of anti-apoptotic Bcl-2 to apoptotic Bax proteins. Con-A-activated splenocytes from DES-treated mice, particularly from females, had a decreased ability to secrete interferon-gamma compared with controls. Taken together, these findings suggest that short-term exposure to DES has differential immunological effects depending upon the dose of hormone and sex.

Assessing estrogenic activity of phytochemicals using transcriptional activation and immature mouse uterotrophic responses

The estrogenic responses of several phytoestrogens including genistein, daidzein, coumestrol, alpha-zearalanol, zearalenone, naringenin, taxifolin and biochanin A were compared over a wide dose range using an in vitro assay that measures transcriptional activation of the estrogen receptor (ER) and an in vivo immature mouse uterotrophic assay consisting of measuring uterine wet weight increase plus sensitive morphological and biochemical endpoints in the uterus. The transcriptional activation assay showed activation of the ER by all compounds tested except taxifolin with varying magnitudes of response as compared to estradiol or diethylstilbestrol. Results from the uterotropic bioassay showed that genistein, coumestrol, zearalanol, and zearalenone caused an increase in uterine wet weight, while naringenin, taxifolin, daidzein and biochanin A failed to do so over the dose range tested. However, sensitive morphological and biochemical parameters such as uterine epithelial cell height increase, uterine gland number increase, and induction of the estrogen-responsive protein lactoferrin demonstrated that all compounds tested in this study gave some measure of estrogenicity although a wide range of estrogenic responses across compounds was shown. Use of multiple in vitro and in vivo estrogenic endpoints as described in this paper will be useful in developing estrogenic profiles for individual compounds and ultimately mixtures of compounds. Furthermore, having an estrogenic "fingerprint" for each phytochemical is an essential first step in determining potential adverse effects of exposure to phytoestrogens.