Transient estrogen exposure of female mice during early development permanently affects osteoclastogenesis in adulthood

Exposure to BPA and BPS during pregnancy disrupts the bone mineralization in the offspring

Exposure to plastic-derived estrogen-mimicking endocrine-disrupting bisphenols can have a long-lasting effect on bone health. However, gestational exposure to bisphenol A (BPA) and its analogue, bisphenol S (BPS), on offspring's bone mineralization is unclear. The effects of in-utero bisphenol exposure were examined on the offspring's bone parameters. BPA and BPS (0.0, 0.4 μg/kg bw) were administered to pregnant Wistar rats via oral gavage from gestational day 4-21. Maternal exposure to BPA and BPS increased bone mineral content and density in the offspring aged 30 and 90 days (P < 0.05). Plasma analysis revealed that alkaline phosphatase, and Gla-type osteocalcin were significantly elevated in the BPS-exposed offspring (P < 0.05). The expression of BMP1, BMP4, and their signaling mediators SMAD1 mRNAs were decreased in BPS-exposed osteoblast SaOS-2 cells (P < 0.05). The expression of extracellular matrix proteins such as ALPL, COL1A1, DMP1, and FN1 were downregulated (P < 0.05). Bisphenol co-incubation with noggin decreased TGF-β1 expression, indicating its involvement in bone mineralization. Altered mineralization could be due to dysregulated expression of bone morphogenetic proteins and signalling mediators in the osteoblast cells. Thus, bisphenol exposure during gestation altered growth and bone mineralization in the offspring, possibly by modulating the expression of Smad-dependent BMP/TGF-β1 signalling mediators.

Associations of urinary metabolite concentrations of phthalates and phthalate replacements with body composition from mid-childhood to early adolescence

BACKGROUND

Phthalates may adversely influence body composition by lowering anabolic hormones and activating peroxisome-proliferator activated receptor gamma. However, data are limited in adolescence when body mass distributions rapidly change and bone accrual peaks. Also, potential health effects of certain phthalate/replacements [e.g., di-2-ethylhexyl terephthalate (DEHTP)] have not been well studied.

METHODS

Among 579 children in the Project Viva cohort, we used linear regression to evaluate associations of urinary concentrations of 19 phthalate/replacement metabolites from mid-childhood (median: 7.6 years; 2007-2010) with annualized change in areal bone mineral density (aBMD) and lean, total fat, and truncal fat mass as measured by dual-energy X-ray absorptiometry between mid-childhood and early adolescence (median: 12.8 years). We used quantile g-computation to assess associations of the overall chemical mixture with body composition. We adjusted for sociodemographics and tested for sex-specific associations.

RESULTS

Urinary concentrations were highest for mono-2-ethyl-5-carboxypentyl phthalate [median (IQR): 46.7 (69.1) ng/mL]. We detected metabolites of most replacement phthalates in a relatively small number of participants [e.g., 28% for mono-2-ethyl-5-hydrohexyl terephthalate (MEHHTP; metabolite of DEHTP)]. Detectable (vs. non-detectable) MEHHTP was associated with less bone and greater fat accrual in males and greater bone and lean mass accrual in females [e.g., change in aBMD Z-score/year (95% CI): -0.049 (-0.085, -0.013) in males versus 0.042 (0.007, 0.076) in females; pinteraction<0.01]. Children with higher concentrations of mono-oxo-isononyl phthalate and mono-3-carboxypropyl phthalate (MCPP) had greater bone accrual. Males with higher concentrations of MCPP and mono-carboxynonyl phthalate had greater accrual of lean mass. Other phthalate/replacement biomarkers, and their mixtures, were not associated with longitudinal changes in body composition.

CONCLUSIONS

Concentrations of select phthalate/replacement metabolites in mid-childhood were associated with changes in body composition through early adolescence. As use of phthalate replacements such as DEHTP may be increasing, further investigation can help better understand the potential effects of early-life exposures.

Associations of maternal gestational urinary environmental phenols concentrations with bone mineral density among 12-year-old children in the HOME Study

BACKGROUND

Early life environmental exposures may affect bone mass accrual in childhood, but only one study has assessed the role of environmental phenols on child bone health.

METHODS

We used data from 223 mother-child dyads enrolled in the Health Outcomes and Measures of the Environment (HOME) Study (Cincinnati, OH; 2003-2006). We quantified benzophenone-3, bisphenol A (BPA), 2,5-dichlorophenol, and triclosan in maternal urine collected at 16- and 26-weeks gestation and calculated the average of creatinine-adjusted concentrations. We performed dual x-ray absorptiometry at age 12 years and calculated Z-scores for whole body (less head), total hip, femoral neck, and 1/3rd distal radius bone mineral content (BMC) and areal bone mineral density (aBMD) as well as ultra-distal radius aBMD and spine BMC and bone mineral apparent density (BMAD). We estimated covariate-adjusted associations per doubling of maternal urinary environmental phenol concentrations in linear regression models. We also examined effect measure modification by child's sex and estimated associations of the environmental phenol mixture with BMC and aBMD using quantile g-computation.

RESULTS

We observed generally null associations for all analytes and bone measures. Yet, in adjusted models, higher urinary 2,5-dichlorophenol concentrations were associated with higher 1/3rd distal radius BMC (β: 0.09; 95% CI: 0.02, 0.17) and aBMD (β: 0.09; 95% CI: 0.02, 0.17) Z-scores in the overall sample. In sex-stratified analyses, the magnitude of the BMC association was positive for females (β: 0.16; 95% CI: 0.06, 0.26) and null for males (β: 0.02; 95% CI: 0.08, 0.13). The environmental phenol mixture was associated with greater 1/3rd distal radius BMC and aBMD Z-scores in both sexes, which was mostly driven by benzophenone-3 in males and 2,5-dichlorophenol in females.

CONCLUSION

In this prospective cohort study, we observed generally null associations for environmental phenols with BMC and aBMD at age 12 years. While there was a positive association of 2,5-dichlorophenol concentrations during fetal development with distal radius BMC and aBMD at age 12 years, future studies utilizing methods capable of differentiating cortical and trabecular bone are needed to elucidate potential mechanisms and implications for bone strength and microarchitecture.

Estrogen Signaling Influences Nephron Segmentation of the Zebrafish Embryonic Kidney

Despite significant advances in understanding nephron segment patterning, many questions remain about the underlying genes and signaling pathways that orchestrate renal progenitor cell fate choices and regulate differentiation. In an effort to identify elusive regulators of nephron segmentation, our lab conducted a high-throughput drug screen using a bioactive chemical library and developing zebrafish, which are a conserved vertebrate model and particularly conducive to large-scale screening approaches. 17β-estradiol (E2), which is the dominant form of estrogen in vertebrates, was a particularly interesting hit from this screen. E2 has been extensively studied in the context of gonad development, but roles for E2 in nephron development were unknown. Here, we report that exogenous estrogen treatments affect distal tubule composition, namely, causing an increase in the distal early segment and a decrease in the neighboring distal late. These changes were noted early in development but were not due to changes in cell dynamics. Interestingly, exposure to the xenoestrogens ethinylestradiol and genistein yielded the same changes in distal segments. Further, upon treatment with an estrogen receptor 2 (Esr2) antagonist, PHTPP, we observed the opposite phenotypes. Similarly, genetic deficiency of the Esr2 analog, esr2b, revealed phenotypes consistent with that of PHTPP treatment. Inhibition of E2 signaling also resulted in decreased expression of essential distal transcription factors, irx3b and its target irx1a. These data suggest that estrogenic compounds are essential for distal segment fate during nephrogenesis in the zebrafish pronephros and expand our fundamental understanding of hormone function during kidney organogenesis.

Early life organophosphate ester exposures and bone health at age 12 years: The Health Outcomes and Measures of the Environment (HOME) Study

BACKGROUND

No human studies have evaluated early life organophosphate ester (OPE) exposures with bone health outcomes, despite evidence of osteotoxicity.

OBJECTIVES

We assessed associations of urinary OPE metabolites measured across early life with areal bone mineral density (aBMD) and bone mineral content (BMC) at age 12 years.

METHODS

Among 223 mother-child dyads enrolled in the Health Outcomes and Measures of the Environment (HOME) Study, we quantified concentrations of bis-2-chloroethyl phosphate (BCEP), bis-(1,3-dichloro-2-propyl) (BDCIPP), di-n-butyl phosphate (DnBP), and diphenyl phosphate (DPHP) in urine collected from mothers during pregnancy and children at ages 1, 2, 3, 5, and 8 years. At age 12 years, we performed dual energy x-ray absorptiometry and calculated aBMD and BMC z-scores at six skeletal sites. We estimated overall and sex-stratified BMD/BMC z-score differences per interquartile range (IQR) increase in OPE concentrations at multiple exposure timepoints: gestation (average) and 1-3 (average), 5, and 8 years.

RESULTS

In adjusted models, overall associations of BCEP and BDCIPP with total hip and 1/3rd distal radius aBMD and BMC varied significantly by exposure timepoint, as did BDCIPP with whole body aBMD. For example, differences (95 % CI) in total hip aBMD z-score per IQR increase in BDCIPP were 0.33 (0.01, 0.64), -0.10 (-0.34, 0.14), -0.18 (-0.40, 0.05), and 0.14 (-0.09, 0.38) for concentrations during gestation and at 1-3, 5, and 8 years, respectively. Overall DnBP and DPHP associations were generally null at all timepoints. We observed sex-specific associations for some timepoints and skeletal sites. For example, an IQR increase in 8-year DPHP was associated with a 0.21 (0.05, 0.38) greater total hip aBMD z-score among females but -0.19 (-0.43, 0.05) lower z-score among males.

DISCUSSION

Early life OPE exposures may be associated with sex- and exposure period-dependent alterations in early adolescent bone mineral accrual and strength.

Developmental programming of macrophages by early life adversity

Macrophages are central elements of all organs, where they have a multitude of physiological and pathological functions. The first macrophages are produced during fetal development, and most adult organs retain populations of fetal-derived macrophages that self-maintain without major input of hematopoietic stem cell-derived monocytes. Their developmental origins make macrophages highly susceptible to environmental perturbations experienced in early life, in particular the fetal period. It is now well recognized that such adverse developmental conditions contribute to a wide range of diseases later in life. This chapter explores the notion that macrophages are key targets of environmental adversities during development, and mediators of their long-term impact on health and disease. We first briefly summarize our current understanding of macrophage ontogeny and their biology in tissues and consider potential mechanisms by which environmental stressors may mediate fetal programming. We then review evidence for programming of macrophages by adversities ranging from maternal immune activation and diet to environmental pollutants and toxins, which have disease relevance for different organ systems. Throughout this chapter, we contemplate appropriate experimental strategies to study macrophage programming. We conclude by discussing how our current knowledge of macrophage programming could be conceptualized, and finally highlight open questions in the field and approaches to address them.

Associations of pregnancy phthalate concentrations and their mixture with early adolescent bone mineral content and density: The Health Outcomes and Measures of the Environment (HOME) study

BACKGROUND

The developing fetus may be particularly susceptibility to environmental osteotoxicants, but studies of pregnancy phthalate exposures and childhood bone health are scarce.

OBJECTIVES

To examine relations of pregnancy phthalate exposure biomarkers with early adolescent bone mineral density (BMD) and bone mineral content (BMC) in a prospective birth cohort.

METHODS

We used data from 223 pregnant mothers and their children enrolled in a Cincinnati, OH area cohort from 2003 to 2006. We quantified monoethyl phthalate (MEP), monoisobutyl phthalate, monobutyl phthalate, monobenzyl phthalate, mono-(3-carboxypropyl) phthalate (MCPP), and four metabolites of di-2-ethylhexyl phthalate in maternal urine collected at 16 and 26 weeks gestation, and calculated the average of creatinine-standardized concentrations. Using dual x-ray absorptiometry measures at age 12 years, we calculated BMD and BMC Z-scores for six skeletal sites. In overall and sex-stratified models, we estimated covariate-adjusted associations per 2-fold increase in phthalate biomarker concentrations using linear regression, and estimated joint effects of the phthalate biomarkers mixture using Bayesian kernel machine regression (BKMR) and quantile g-computation.

RESULTS

In single phthalate models, several biomarkers were positively associated with BMC and BMD. For example, each doubling of MEP and MCPP, 1/3rd distal radius BMD Z-score increased by 0.09 (95% CI: 0.01, 0.17) and 0.16 (95% CI: 0.01, 0.31), respectively. For phthalate mixtures, associations were generally U-shaped among males and positive-linear among females, using both statistical methods. Mixture associations were strongest with forearm sites: in BKMR models, increasing all biomarkers from the 50th to 90th percentile was associated with a 0.64 (95% CI: 0.01, 1.28) greater 1/3rd distal radius BMD Z-score in males, and a 0.49 (95% CI: -0.13, 1.10) greater ultradistal radius BMD Z-score in females.

DISCUSSION

In this study, phthalate exposures during gestation were associated with increased BMD Z-scores in early adolescence, though further research is needed to determine implications for long-term skeletal health.

Phosphodiesterase Type-5 Inhibitor Tadalafil Modulates Steroid Hormones Signaling in a Prostate Cancer Cell Line

Background: The androgen receptor (AR) plays a key role in normal prostate homeostasis and in prostate cancer (PCa) development, while the role of aromatase (Cyp19a1) is still unclear. We evaluated the effects of a treatment with Tadalafil (TAD) on both these proteins. Methods: Androgen-sensitive human PCa cell line (LnCAP) was incubated with/without TAD (10⁻⁶ M) and bicalutamide (BCT) (10⁻⁴ M) to evaluate a potential modulation on cell proliferation, protein and mRNA expression of Cyp19a, AR and estrogen receptor-β (ERβ), respectively. Results: TAD increased early AR nuclear translocation (p < 0.05, after 15 min of exposure), and increased AR transcriptional activity (p < 0.05) and protein expression (p < 0.05) after 24 h. Moreover, after 24 h this treatment upregulated Cyp19a1 and ERβ mRNA (p < 0.05 and p < 0.005 respectively) and led to an increase in protein expression of both after 48 h (p < 0.05). Interestingly, TAD counteracted Cyp19a1 stimulation induced by BCT (p < 0.05) but did not alter the effect induced by BCT on the AR protein expression. Conclusion: We demonstrate for the first time that TAD can significantly modulate AR expression and activity, Cyp19a1 and ERβ expression in PCa cells, suggesting a specific effect of these proteins. In addition, TAD potentiates the antiproliferative activity of BCT, opening a new clinical scenario in the treatment of PCa.

Loss of Lgals3 Protects Against Gonadectomy-Induced Cortical Bone Loss in Mice

Sex hormone deprivation commonly occurs following menopause in women or after androgen-depletion during prostate cancer therapy in men, resulting in rapid bone turnover and loss of bone mass. There is a need to identify novel therapies to improve bone mass in these conditions. Previously, we identified age- and sex-dependent effects on bone mass in mice with deletion of the gene encoding the β-galactoside binding lectin, galectin-3 (Lgals3-KO). Due to the influence of sex on the phenotype, we tested the role of sex hormones, estrogen (β-estradiol; E₂), and androgen (5α-dihydroxytestosterone; DHT) in Lgals3-KO mice. To address this, we subjected male and female wild-type and Lgals3-KO mice to gonadectomy ± E₂ or DHT rescue and compared differential responses in bone mass and bone formation. Following gonadectomy, male and female Lgals3-KO mice had greater cortical bone expansion (increased total area; T.Ar) and reduced loss of bone area (B.Ar). While T.Ar and B.Ar were increased in response to DHT in wild-type mice, DHT did not alter these parameters in Lgals3-KO mice. E₂ rescue more strongly increased B.Ar in Lgals3-KO compared to wild-type female mice due to a failure of E₂ to repress the increase in T.Ar following gonadectomy. Lgals3-KO mice had more osteoblasts relative to bone surface when compared to wild-type animals in sham, gonadectomy, and E₂ rescue groups. DHT suppressed this increase. This study revealed a mechanism for the sex-dependency of the Lgals3-KO aging bone phenotype and supports targeting galectin-3 to protect against bone loss associated with decreased sex hormone production.

Effects of Di(2-ethylhexyl)phthalate on Bone Metabolism in Ovariectomized Mice

Background

The molecular pathways of how endocrine disruptors affect bone mineral density (BMD) and bone remodeling are still unclear. The purpose of this experimental study is to determine the effects of di(2-ethylhexyl)phthalate (DEHP) on bone metabolism in ovariectomized mice.

Methods

Twenty-six-month-old female CD-1 mice were divided into 4 groups: control, low-dose DEHP, high-dose DEHP, and estrogen groups (n=5, each group). All mice were subjected to ovariectomy for the induction of artificial menopause and then exposed to corn oil, DEHP, and estrogen for 2 months. Micro-computed tomography (Micro-CT) of the bone and analysis of blood samples for bone markers were performed to observe the changes in bone metabolism.

Results

Osteocalcin level was decreased in the control, low-dose and high-dose DEHP group, the reduction width was greater in the high-dose DEHP group (-0.219 ng/mL) than control group (-0.077 ng/mL, P<0.05). C-terminal telopeptide of type I collagen level was increased in the control, low-dose and high-dose DEHP group, the increase range of low-dose DEHP group (0.329 ng/mL) showed greater than control group (0.093 ng/mL, P<0.05). Micro-CT analysis revealed that the BMD was significantly lower in the high-dose DEHP group (19.8×10^-2 g/cm³) than control group (27.2×10^-2 g/cm³, P<0.05). The structure model index was significantly higher in the high-dose DEHP group (2.737) than low-dose DEHP group (2.648) and estrogen group (2.63, P<0.05). It means the progression of osteoporosis in the high-dose DEHP group.

Conclusions

These results confirm the negative effects of DEHP on bone health in ovariectomized mice. Further continuous studies on genetic pathways and other endocrine disruptors will be necessary to validate these findings.

Bone Manifestation of Faulty Perinatal Hormonal Imprinting: A Review

Hormonal imprinting takes place at the first encounter between the developing receptor and its target hormone and the encounter determines the receptor's binding capacity for life. In the critical period of development, when the window for imprinting is open, the receptor can be misdirected by related hormones, synthetic hormones, and industrial or communal endocrine disruptors which cause faulty hormonal imprinting with life-long consequences. Considering these facts, the hormonal imprinting is a functional teratogen provoking alterations in the perinatal (early postnatal) period. One single encounter with a low dose of the imprinter in the critical developmental period is enough for the formation of faulty imprinting, which is manifested later, in adult age. This has been justified in the immune system, in sexuality, in animal behavior and brain neurotransmitters etc. by animal experiments and human observations. This review points to the faulty hormonal imprinting in the case of bones (skeleton), by single or repeated treatments. The imprinting is an epigenetic alteration which is inherited to the progeny generations. From clinical aspect, the faulty imprinting can have a role in the pathological development of the bones as well, as in the risk of osteoporotic fractures, etc.

Role of TGFβ Signaling in Maternal Ethanol-Induced Fetal Articular Cartilage Dysplasia and Adult Onset of Osteoarthritis in Male Rats

Based on our previous findings that prenatal ethanol exposure in offspring increased susceptibility to adult osteoarthritis, this study aimed to further investigate the direct toxicity of ethanol on fetal articular cartilage development. Rat bone marrow-derived stroma cells were capsulated in alginate beads, incubated in a chondrogenic differentiation medium, and cultured for 4 weeks with ethanol treatment at concentrations of 0, 4, 20, and 100 mM. Pregnant rats were treated with ethanol (4 g/kg/day) from gestational days (GDs) 9 to 20. At GD20 and postnatal weeks 2, 6, and 12, 8 male offspring were sacrificed, and 8 male offspring rats of 8-weeks old in each group were treated with or without intraarticular injection of papain for 4 weeks to verify the susceptibility of adult osteoarthritis. Ethanol treatment resulted in poor differentiation of bone marrow-derived stroma cells to chondrocytes and suppressed the expression of the transforming growth factor-β (TGFβ)-smad2/3-Sox9 signaling pathway. In animal experiments, the shape of articular cartilage in the ethanol treatment group was more disordered than that of the control group, the matrix was not deep, and the cartilage was thin, which showed poor cartilage development. The TGFβ signaling pathway in the ethanol treatment group was persistently low at all time points. After intraarticular injection of papain, histological analyses, and the Mankin score revealed increased cartilage destruction in the ethanol treatment group. Ethanol caused articular cartilage dysplasia that was programmed in adulthood via a low-functional TGFβ signaling pathway, and the tolerance of this articular cartilage to external stimuli was significantly decreased.

Low-dose developmental exposure to bisphenol A alters the femoral bone geometry in wistar rats

BACKGROUND

Bisphenol A (BPA) is a chemical produced in large volumes for use in manufacturing of consumer products and industrial applications, and an endocrine disruptor known to affect several hormonal systems. Bone produces hormones and is additionally a sensitive hormone target tissue, and is thus potentially sensitive to low doses of endocrine disruptors such as BPA, especially during development.

METHODS

110 pregnant Wistar rats were gavaged with 0; 25 μg; 250 μg; 5000 μg or 50,000 μg BPA/kg bodyweight (bw)/day from gestational day 7 until weaning at postnatal day 22. The three-month-old offspring were sacrificed and right femurs collected for length measurements, geometrical measurements by peripheral quantitative computed tomography (pQCT), as well as for analyses of biomechanical properties using the three-point-bending method.

RESULTS

The femur was elongated in female offspring of dams exposed to 25 or 5000 μg BPA/kg bw/day (1.8% and 2.1%, respectively), and increased cortical thickness (4.7%) was observed in male offspring of dams exposed to 25 μg BPA/kg bw/day, compared to controls (p < 0.005). The biomechanical properties of the bone were not significantly altered.

CONCLUSIONS

In utero and lactational exposure to the lowest BPA dose used in this study altered femoral geometry in both male and female offspring. This was observed at 25 μg BPA/kg bw/day, a dose lower than the Human Equivalent Dose (HED) applied by EFSA to set a temporary TDI (609 μg BPA/kg bw/day), and far lower than the No-Observed-Adverse-Effect-Level (NOAEL) (5000 μg BPA/kg bw/day) on which the US FDA TDI is based.

A Mouse Model for Studying Nutritional Programming: Effects of Early Life Exposure to Soy Isoflavones on Bone and Reproductive Health

Over the past decade, our research group has characterized and used a mouse model to demonstrate that "nutritional programming" of bone development occurs when mice receive soy isoflavones (ISO) during the first days of life. Nutritional programming of bone development can be defined as the ability for diet during early life to set a trajectory for better or compromised bone health at adulthood. We have shown that CD-1 mice exposed to soy ISO during early neonatal life have higher bone mineral density (BMD) and greater trabecular inter-connectivity in long bones and lumbar spine at young adulthood. These skeletal sites also withstand greater forces before fracture. Because the chemical structure of ISO resembles that of 17-β-estradiol and can bind to estrogen receptors in reproductive tissues, it was prudent to expand analyses to include measures of reproductive health. This review highlights aspects of our studies in CD-1 mice to understand the early life programming effects of soy ISO on bone and reproductive health. Preclinical mouse models can provide useful data to help develop and guide the design of studies in human cohorts, which may, depending on findings and considerations of safety, lead to dietary interventions that optimize bone health.

Assessment of safety and efficacy of perinatal or peripubertal exposure to daidzein on bone development in rats

Neonatal exposure to isoflavones improved bone health in thereafter in previous animal studies. However, since isoflavones possess hormonal activity, it may interfere with reproductive development. In the present study, we assessed the safety and efficiency of perinatal or peripubertal exposure to daidzein on bone and reproductive organ development at early adulthood in rats. Sprague-Dawley pregnant rats (n = 18) were divided into 3 groups: (1) dams and their offspring were fed the control diet. (2) Dams were fed the daidzein diet (0.5 g daidzein/kg diet) during pregnancy and then the control diet at postnatal day 13 and their offspring were fed the control diet. (3) Dams and their offspring were fed the daidzein diet through the experiment. While perinatal exposure to daidzein did not confer a positive effect on bone mineral density on postnatal day 35, peripubertal exposure to daidzein protected against a decline in bone mineral density. Meanwhile, exposure to daidzein during the perinatal or peripubertal period did not affect reproductive organ weights at early adulthood in rats. Further investigations should assess the mechanisms underlying these responses of bone metabolism to daidzein, as well as the safety of daidzein exposure during the perinatal period and throughout life.

In vivo dynamics of estrogen receptor activity: the ERE-Luc model

In recent years several studies demonstrated the presence of estrogen receptors in mammalian tissues and significantly improved our understanding of their ability to control biological processes in reproductive as well as non-reproductive organs. Considering the manifold mechanisms and organs that are involved in estrogen action and the implication of estrogens in human female physiology, innovative approaches are required to shed light on the widespread activities of estrogen receptors in woman physiology. This is particularly relevant for the definition of novel, more efficacious hormonal replacement therapies or for the evaluation of the risk associated with the exposure to endocrine disruptors. The introduction of genetic engineering and the development and application of in vivo imaging techniques offer new tools for pre-clinical studies. The generation of the ERE-Luc mouse, a reporter animal developed for in vivo studies of the estrogen receptor activity, allows assessing the activity state of the ER signaling pathway in all target tissues and organs at once, under physiological stimuli or as a result of a pharmacological treatment. This review summarizes the main steps in the generation and appraisal of the estrogen receptor reporter mouse ERE-Luc, designed for in vivo molecular imaging studies, and describes examples demonstrating the suitability of the ERE-Luc model for drug development and for the investigation of the effects of endogenous, environmental, and dietary estrogens in vivo. This article is part of a Special Issue entitled 'Phytoestrogens'.

Endocrine disruptors and bone metabolism

Bone microenvironment is a complex dynamic equilibrium between osteoclasts and osteoblasts and is modulated by a wide variety of hormones and osteocyte mediators secreted in response to physiological and pathological conditions. The rate of remodeling involves tight coupling and regulation of both cells population and is regulated by a wide variety of hormones and mediators such as parathyroid hormone, prostaglandins, thyroid hormone, sex steroids, etc. It is also well documented that bone formation is easily influenced by the exposure of osteoblasts and osteoclasts to chemical compounds. Currently, humans and wildlife animals are exposed to various environmental xenoestrogens typically at low doses. These compounds, known as endocrine disruptor chemicals (EDCs), can alter the systemic hormonal regulation of the bone remodeling process and the skeletal formation. This review highlights the effects of the EDCs on mammalian bone turnover and development providing a macro and molecular view of their action.

The estrogenic endocrine disrupting chemical bisphenol A (BPA) and obesity

There is increasing experimental and epidemiological evidence that fetal programming of genetic systems is a contributing factor in the recent increase in adult obesity and other components of metabolic syndrome. In particular, there is evidence that epigenetic changes associated with the use of manmade chemicals may interact with other factors that influence fetal and postnatal growth in contributing to the current obesity epidemic. The focus of this review is on the developmental effects of estrogenic endocrine disrupting chemicals (EDCs), and more specifically on effects of exposure to the estrogenic EDC bisphenol A (BPA), on adipocytes and their function, and the ultimate impact on adult obesity; BPA exposure also results in impaired reproductive capacity. We discuss the interaction of EDCs with other factors that impact growth during fetal and neonatal life, such as placental blood flow and nutrient transport to fetuses, and how these influence fetal growth and abnormalities in homeostatic control systems required to maintain normal body weight throughout life.

Developmental exposure to xenoestrogens at low doses alters femur length and tensile strength in adult mice

Developmental exposure to high doses of the synthetic xenoestrogen diethylstilbestrol (DES) has been reported to alter femur length and strength in adult mice. However, it is not known if developmental exposure to low, environmentally relevant doses of xenoestrogens alters adult bone geometry and strength. In this study we investigated the effects of developmental exposure to low doses of DES, bisphenol A (BPA), or ethinyl estradiol (EE(2)) on bone geometry and torsional strength. C57BL/6 mice were exposed to DES, 0.1 μg/kg/day, BPA, 10 μg/kg/day, EE(2), 0.01, 0.1, or 1.0 μg/kg/day, or vehicle from Gestation Day 11 to Postnatal Day 12 via a mini-osmotic pump in the dam. Developmental Xenoestrogen exposure altered femoral geometry and strength, assessed in adulthood by micro-computed tomography and torsional strength analysis, respectively. Low-dose EE(2), DES, or BPA increased adult femur length. Exposure to the highest dose of EE(2) did not alter femur length, resulting in a nonmonotonic dose response. Exposure to EE(2) and DES but not BPA decreased tensile strength. The combined effect of increased femur length and decreased tensile strength resulted in a trend toward decreased torsional ultimate strength and energy to failure. Taken together, these results suggest that exposure to developmental exposure to environmentally relevant levels of xenoestrogens may negatively impact bone length and strength in adulthood.

Neonatal administration of isoflavones attenuates deterioration of bone tissue in female but not male mice

Neonatal exposure to soy isoflavones at levels similar to that of infants fed soy protein formula resulted in higher bone mineral density (BMD), improved bone structure, and greater bone strength at young adulthood in female CD-1 mice (1,2). Our objective in this study was to determine whether these improvements in bone quantity and quality at 4 mo of age provide protection against the deterioration of bone tissue that occurs after a decline in endogenous sex steroid production. Male and female CD-1 mice (n = 8-18 pups per group per gender) were randomized to subcutaneous injections of corn oil [negative control (CON)], daidzein + genistein (DG; 7 mg x kg body weight(-1) x d(-1)), or diethylstilbestrol [(DES); positive control, 2 mg x kg body weight(-1) x d(-1)) from postnatal d 1 to 5. At 4 mo of age, mice were ovariectomized (females) or orchidectomized (males) and studied to 8 mo of age. Females treated with DG had higher (P < 0.05) femur and vertebral bone mineral content (BMC) and BMD compared with the CON group. Microstructural analysis revealed that improvements in BMD induced by DG and DES were coupled with greater trabecular thickness at the lumbar spine. Importantly, structural improvements resulted in bones that were more resistant to fracture, as the peak load of the femoral midpoint and lumbar vertebra 2 were higher (P < 0.05) with DG compared with CON. Effects in males were not significant. In conclusion, short-term neonatal exposure to isoflavones provides protection against the deterioration of bone tissue in females but not males after a decline of endogenous sex steroid production.

Neonatal exposure to daidzein, genistein, or the combination modulates bone development in female CD-1 mice

Neonatal exposure to genistein (GEN), an isoflavone abundant in soy, favorably modulates bone mineral density (BMD) and bone strength in mice at adulthood. The study objective was to determine whether early exposure to a combination of the soy isoflavones daidzein (DAI) and GEN that naturally exists in soy protein-based infant formula results in greater benefits to bone at adulthood than either treatment alone. Male and female CD-1 mice (n = 8-16 pups per group per gender) were randomized to subcutaneous injections of DAI (2 mg x kg body weight(-1) x d(-1)), GEN (5 mg x kg body weight(-1) x d(-1)), DAI+GEN (7 mg x kg body weight(-1) x d(-1)), diethylstilbesterol (DES; positive control) (2 mg x kg body weight(-1) x d(-1)), or control (CON) from postnatal d 1-5 and were studied to 4 mo of age. BMD, biomechanical bone strength, and bone microarchitecture were assessed at the femur and lumbar vertebrae (LV). Females treated with DAI, GEN, DAI+GEN, or DES had greater (P < 0.05) BMD at the LV compared with CON and vertebra in the DAI and DES group were more resistant to compression fractures. Microstructural analyses demonstrated that treatment with DAI and GEN resulted in greater (P < 0.05) trabecular connectivity and trabecular thickness, respectively, than the CON. In conclusion, neonatal exposure to DAI and/or GEN had a positive effect on the skeleton of female mice at adulthood, but, compared with individual treatments, DAI+GEN did not have a greater benefit to bone in females or males.

Diethylstilbesterol has gender-specific effects on weight gain and bone development in mice

Neonatal exposure to diethylstilbesterol (DES) in female mice programs estrogen-sensitive tissues, resulting in greater body weight gain and positive effects on bone architecture at adulthood. Using the CD-1 mouse model, the objective of the present study was to examine how short-term neonatal exposure to DES modulates weight gain as well as bone mineral density (BMD), bone strength, and bone microarchitecture in both males and females at adulthood. Male and female offspring (n = 8-12 pups/treatment/gender) were randomized to DES (2 mg/kg bw/d) or control (corn oil) from postnatal day 1 to 5 (subcutaneous injection, once daily) and sacrificed at 4 mo of age. Body weight was measured weekly, while bone mineral, strength, and microarchitecture were measured at 4 mo of age. DES treatment resulted in significantly higher body weight in females but lower weight in males at 4 mo of age. In DES-treated females, markedly higher BMD of lumbar vertebrae (LV1-LV3) was translated into significantly stronger LV2 that was more resistant to fracture; similar effects were observed at the femur midpoint. At the spine, males had a markedly lower BMD and peak load, suggesting an adverse effect. Microstructural analyses demonstrated that functional changes in femurs, i.e., peak load, were primarily due to modulation of cortical bone. In conclusion, neonatal exposure to DES exerted gender-specific effects on body weight gain and bone health.

Prenatal ethanol exposure disrupts the histological stages of fetal bone development

Maternal ethanol intake during pregnancy results in impairments in general growth and skeletal development in the offspring. We have previously shown that ethanol retards skeletal ossification at doses lower than those that affect growth. Moreover, skeletal sites vary in their sensitivity to ethanol effects, with more severe effects occurring in bones that undergo a greater proportion of their development in utero. Taken together, these data suggest that ethanol has specific effects on bone development, and that later stages in the ossification process may be particularly affected. Such effects could have important implications for the offspring's long-term bone health, as studies suggest that the intrauterine environment can program the skeleton. The present study examined the histological stages of bone development to determine if prenatal ethanol exposure alters the morphological development of the growth plate in the fetal rat. Rats were fed a liquid diet containing ethanol (Ethanol, E group), or without ethanol (Pair-Fed, PF, or Control, C groups) for 6 weeks: 3 weeks prior to breeding and during 3 weeks of pregnancy. Fetal tibiae were fixed, decalcified and stained for histological analysis on day 21 of gestation. Maternal ethanol intake resulted in a significant decrease in fetal total bone and diaphysis lengths, compared with tibiae from PF and C fetuses. Although the lengths of the epiphyses were not affected, ethanol disrupted the organization of the histological zones within the epiphyses. Prenatal ethanol exposure decreased the length of the resting zone, but increased the length of the hypertrophic zone. Enlargement of the hypertrophic zone is consistent with an effect of ethanol on the later stages of bone development; however, ethanol's effect on the resting zone indicates that earlier stages of bone development may also be disrupted. The functional significance of these morphological changes to long-term bone health remains to be determined.

Bone mass, bone strength, and their relationship in developing CD-1 mice

Optimizing nutrition during development may provide effective prevention strategies to protect against osteoporosis during later life. Because the mouse model is commonly used to test nutritional interventions on bone health, the overall objective of this study was to determine how bone develops during the first 4 months of life by assessing bone mass (bone mineral content (BMC) and bone mineral density (BMD)) and biomechanical strength properties such as peak load in male and female CD-1 mice. Bone outcomes were assessed at 1 month intervals from 1 to 4 months of age. Femur and spine BMC and BMD at 3 months were similar to 4 months, indicating that the accumulation of bone mass occurs primarily during the first 3 months of life. In contrast, the timing of changes in peak load, a measure of bone strength, varied by skeletal site. Regression analyses demonstrated that femur BMC is a significant predictor of femur peak load at the femur midpoint and neck. The study findings suggest that nutritional interventions aimed at optimizing peak bone mass to prevent osteoporosis may be most effective during pubertal growth.

Effect of neonatal exposure to genistein on bone metabolism in mice at adulthood

Infants fed soy-based infant formulas are exposed to high levels of genistein, an isoflavone, with potential estrogen-like activity. This study determined whether neonatal exposure of mice to genistein resulted in higher bone mineral density (BMD) and greater resistance to fracture at adulthood. Male and female CD-1 mice (n = 4-14/group) were randomized to control (CON) (corn oil, s.c.), diethylstilbestrol (DES) (2 microg/pup/d, s.c.), or genistein (GEN) (4 microg/pup/d, s.c.) from d 1 through 5 of life. At 21 d of age, pups were weaned and studied until 4 mo of age when tissues were collected. Among females, femur (p = 0.016) and lumbar vertebrae (LV1-LV4) (p < 0.001) BMD were higher among DES and GEN groups compared with CON group. Importantly, the higher LV1-LV4 BMD was associated with stronger vertebrae that were more resistant to fracture as the peak load of LV3 (p = 0.012) was higher in the GEN and DES groups compared with CON group. In males, DES and GEN had divergent effects on femur and lumbar vertebrae BMD and peak load. In conclusion, early exposure to GEN has positive effects on femur and lumbar spine of females, likely due to estrogenic effects, while only the lumbar spine of males benefits from early exposure to GEN.

Hormonal imprinting: phylogeny, ontogeny, diseases and possible role in present-day human evolution

Hormonal (chemical) imprinting which was first observed (and named) by us in the seventies of the last century, is a general biological phenomenon which takes place when the developing receptor meets its target hormone for the first time. Under the effect of imprinting, receptors mature and reach their maximal binding capacity. It also influences the cells' hormone production and different functions depending on receptors and hormones. Hormonal imprinting is present already at the unicellular level causing the development of specific receptors and helping the easier recognition of useful or harmful surrounding molecules. The phenomenon is an important factor in the survival of the species, as the effect of imprinting is transmitted to the progeny cell generations. At the same time it possibly helps the selection of molecules which are suitable for acting as hormones in higher ranked animals. In mammals, hormonal imprinting takes place perinatally and determines the function of receptor-signal-transduction systems as well as hormone production for life. However, there are other critical imprinting periods for continuously developing cells. Excess of the target hormones or presence of foreign molecules which are able to bind to the receptors, provoke faulty imprinting in the critical periods with life-long morphological, biochemical, functional or behavioural consequences. As many receptor-bound foreign molecules are used as medical treatments and many such molecules are present around us and inside us as environmental pollutants, they--causing faulty imprinting--are able to predispose the (human) organism to cardiovascular, endocrine, metabolic and cancerous diseases. It seems likely that this effect is connected with disturbance of DNA methylation process in the critical periods of life. There are some signs of the transgenerational effect of faulty imprinting and this could be manifested in the evolution of humans by an epigenetic route.

Impact of oral contraceptives on sex hormone-binding globulin and androgen levels: a retrospective study in women with sexual dysfunction

INTRODUCTION

Oral contraceptives (OCs) have been the preferred method of birth control because of their high rate of effectiveness. OC use, however, has been associated with women's sexual health complaints and androgen insufficiency. OC use is associated with a decrease of androgen ovarian synthesis and an increase in the production of sex hormone-binding globulin (SHBG). There have been limited studies assessing SHBG values after discontinuation of OC use.

AIM

To retrospectively investigate SHBG levels before and after discontinuation of OC use.

MAIN OUTCOME MEASURE

Sex hormone-binding globulin values were compared at baseline, while on the OC, and well beyond the 7-day half-life of SHBG at 49-120 (mean 80) days and >120 (mean 196) days after discontinuation of OCs.

METHODS

A total of 124 premenopausal women with sexual health complaints for >6 months met inclusion/exclusion criteria. Three groups of women were defined: (i) "Continued-Users" (N = 62; mean age 32 years) had been on OCs for >6 months and continued taking them; (ii) "Discontinued-Users" (N = 39; mean age 33 years) had been on OCs for >6 months and discontinued them; and (iii) "Never-Users" (N = 23; mean age 36 years) had never taken OCs.

RESULTS

Sex hormone-binding globulin values in the "Continued-Users" were four times higher than those in the "Never-User" group (mean 157 +/- 13 nmol/L vs. 41 +/- 4 nmol/L; P < 0.0001). Despite a decrease in SHBG values after discontinuation of OC use, SHBG levels in "Discontinued-Users" remained elevated in comparison with "Never-Users" (N = 26; P < 0.0001 for >120 days).

CONCLUSION

In women with sexual dysfunction, SHBG changes in "Discontinued-Users" did not decrease to values consistent with "Never-Users." Long-term sexual, metabolic, and mental health consequences might result as a consequence of chronic SHBG elevation. Does prolonged exposure to the synthetic estrogens of OCs induce gene imprinting and increased gene expression of SHBG in the liver in some women? Prospective research is needed.

Multigenerational exposure to genistein does not increase bone mineral density in rats

Genistein has been shown to prevent bone loss in ovariectomized adult rats. However, the effects of genistein on bone in developing and reproductively-intact rats have not been examined. A large multigenerational experiment involved feeding 0, 5, 100, or 500 ppm genistein in the diet to intact male and female rats from conception until either weaning, postnatal day 140, or continuously for 2 years. Vertebrae (lumbar and caudal) were collected from these animals at necropsy at 2 years of age and subjected to dual-energy x-ray absorptiometry (DXA) scanning to measure bone mineral density (BMD), bone mineral content (BMC), and bone area. Femurs were collected, and length, cross-sectional area, and cortical bone area were measured directly. Serum was collected for measurement of pyridinoline (PYD) and alkaline phosphatase (ALP). BMD was not affected by genistein in any phase of the experiment. In female rats treated continuously with genistein, BMC and bone area were reduced in the 500 ppm group compared to the 5 ppm group in the lumbar vertebrae, and in all treatment groups compared to control in the caudal vertebrae. In both males and females treated continuously, the cross-sectional area of the femur was reduced in rats treated with 500 ppm compared to those treated with 5 ppm. In female rats treated continuously, PYD was higher in the 100 and 500 ppm groups than in the 0 and 5 ppm groups. In conclusion, the effects of genistein on reproductively-intact rats were not dramatic. High dose of genistein throughout the lifespan resulted in decreased bone size, which may reduce the force required to break the bone.

Prenatal ethanol exposure has differential effects on fetal growth and skeletal ossification

There is increasing evidence suggesting that the intrauterine environment may influence long-term bone health and the risk of developing osteoporosis in later life. Alcohol (ethanol) is one factor whose presence in the prenatal environment has long-term consequences for the offspring, including permanent growth retardation. Moreover, prenatal ethanol exposure retards both fetal and postnatal bone development. It is unknown if ethanol's effects on skeletal development result from generalized growth retardation or effects specific to skeletal development. Furthermore, the level of ethanol exposure required to produce skeletal effects is unknown. The objectives of this study were to determine (1) if ethanol exerts specific effects on fetal skeletal development that are independent from its effects on general growth, and (2) the level of prenatal ethanol exposure required to affect fetal growth and skeletal ossification. Rats were fed isocaloric diets with ethanol (15%, 25%, or 36% ethanol-derived calories (EDC), approximating low, moderate, and high exposure levels), or without ethanol (pair-fed, PF, or control, C groups), prior to and throughout 21 days of gestation. The degree of E-induced delay in development was determined by comparison of E fetuses on d21 gestation to C fetuses on d17-d21 gestation. Prenatal ethanol exposure at 36% EDC decreased fetal body weight, length, and skeletal ossification compared with PF and C fetuses on d21 gestation. Importantly, effects on ossification, but not body weight or length, were also seen at the more moderate dose of 25% EDC, and the number of bones affected and the severity of effects on ossification tended to increase with dose of ethanol. Comparison of E fetuses on d21 gestation with C fetuses from d17 to 21 gestation indicated that the ethanol-induced delay in development differed for weight and skeletal ossification, and was not uniform among skeletal sites. Taken together, these data suggest that prenatal ethanol exposure has effects on fetal skeletal development that are independent of those on overall fetal growth, and that these effects occur even at moderate levels of maternal drinking. Effects of prenatal ethanol exposure on fetal skeletal development could potentially increase the offspring's risk of osteoporosis later in life.

Estrogenic endocrine disruptive components interfere with calcium handling and differentiation of human trophoblast cells

During development, calcium (Ca) is actively transported by placental trophoblasts to meet fetal nutritional and the skeletal mineralization needs. Maternal exposure to estrogenic pesticides, such as 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT) and methoxychlor (MTC), has been shown to result in reproductive disorders and/or abnormal fetal development. In this study, we have examined the effects of exposure of trophoblastic cells to MTC and DTT, in comparison to 17beta-estradiol (E2) and diethylstilbestrol (DES), to test the hypothesis that cellular Ca handling is a target for these endocrine disruptive components. Treatment with DDT, MTC, DES, or E2 increased cellular Ca uptake, and the expression of trophoblast-specific human Ca binding protein (HCaBP) was down-regulated by both MTC and DDT. Treatment with MTC, DDT, and DES inhibited cell proliferation, induced apoptosis, and suppressed expression of several trophoblast differentiation marker genes. These effects were reversed by overexpression of metallothionein IIa, a gene highly responsive to cadmium and other metals. These results strongly suggest that trophoblast Ca handling functions are endocrinally modulated, and that their alteration by candidate endocrine disruptors, such as MTC and DDT, constitutes a possible pathway of the harmful effects of these components on fetal development.

Estrogen activates cyclin-dependent kinases 4 and 6 through induction of cyclin D in rat primary osteoblasts

Estrogen plays important roles in maintaining bone density and protecting against osteoporosis, but the underlying mechanisms of estrogen action via estrogen receptors (ERs) in bone remain to be clarified. In the present study, we isolated primary osteoblasts derived from transgenic rats harboring a dominant negative ER mutant, rat ERalpha (1-535) cDNA, and from their wild-type littermates. We observed that the rate of cell growth of osteoblasts from the transgenic rats was reduced compared to that of wild-type osteoblasts. Utilizing cDNA microarray analysis, we found that mRNA level of cyclin D2 was lower in the osteoblasts from the transgenic rats. D-type cyclins including cyclin D1, cyclin D2, and cyclin D3 are cell cycle regulators that promote progression through the early-to-mid G1 phase of the cell cycle. The protein levels of D-type cyclins including cyclin D2 and cyclin D3 but not cyclin D1 were elevated in wild-type osteoblasts with 17beta-estradiol treatment, resulting in the activation of cyclin-dependent kinases 4 and 6 (Cdk4/6) activities and the promotion of cell growth. Moreover, an anti-estrogen ICI 182,780 abolished the induction of the expression of D-type cyclins by 17beta-estradiol. Our findings indicate that estrogen and its receptors enhance Cdk4/6 activities through the induction of D-type cyclins, leading to the growth promotion of osteoblasts.

The selective estrogen receptor modulator raloxifene regulates osteoclast and osteoblast activity in vitro

Raloxifene is a selective estrogen receptor modulator (SERM) that prevents bone loss. Although it is largely used for the treatment of osteoporosis, the mechanisms by which this compound modulates the activity of bone cells are still poorly understood. In this study we investigate whether raloxifene affects osteoclast and osteoblast activity in vitro. Bone marrow cultures were established from neonatal mice and treated with 1,25(OH)(2) vitamin D(3) (VitD(3), 10(-8) mol/L) to induce osteoclast generation. Similar to 17beta-estradiol, raloxifene significantly reduced the number of osteoclasts in a concentration-dependent manner, with maximal inhibition at 10(-11) mol/L (-48%). However, as for 17beta-estradiol, at a high concentration (10(-7) mol/L), the inhibitory effect of raloxifene was abolished. In a pit assay, raloxifene inhibited bone resorption. A maximal effect was observed at 10(-9) mol/L, and maintained at a high concentration, indicating that inhibition of osteoclast formation and inhibition of bone resorption may be due to activation of, at least in part, different pathways. Osteoblasts from neonatal mice calvariae were also exposed to raloxifene. In these cells, this compound induced a concentration-dependent increase of proliferation, which was blocked by the estrogen-receptor antagonist ICI 164,384. Raloxifene also increased the osteoblast-specific transcription factor Cbfa1/Runx2 and alpha2 procollagen type I chain mRNAs, with a pattern that only partially coincided with that of 17beta-estradiol. Consistent with decreased osteoclastogenesis, raloxifene inhibited the mRNA expression of interleukin (IL)-1beta and IL-6 at a low concentration, but not at a high concentration, whereas 17beta-estradiol had similar effects on IL-6 and inhibited IL-1beta at both concentrations. Furthermore, both compounds were able to inhibit tumor necrosis factor (TNF)-alpha-induced IL-1beta, but not IL-6, increase. In conclusion, these data show that raloxifene negatively modulates osteoclasts, and positively affects osteoblasts, suggesting not only an antiresorptive role, but also an osteoblast stimulatory role.