Maternal-fetal transfer of endocrine disruptors in the induction of Calbindin-D9k mRNA and protein during pregnancy in rat model

Environmental health influences in pregnancy and risk of gestational diabetes mellitus: a systematic review

Background

Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications globally. Environmental risk factors may lead to increased glucose levels and GDM, which in turn may affect not only the health of the mother but assuming hypotheses of "fetal programming", also the health of the offspring. In addition to traditional GDM risk factors, the evidence is growing that environmental influences might affect the development of GDM. We conducted a systematic review analyzing the association between several environmental health risk factors in pregnancy, including climate factors, chemicals and metals, and GDM.

Methods

We performed a systematic literature search in Medline (PubMed), EMBASE, CINAHL, Cochrane Library and Web of Science Core Collection databases for research articles published until March 2021. Epidemiological human and animal model studies that examined GDM as an outcome and / or glycemic outcomes and at least one environmental risk factor for GDM were included.

Results

Of n = 91 studies, we classified n = 28 air pollution, n = 18 persistent organic pollutants (POP), n = 11 arsenic, n = 9 phthalate n = 8 bisphenol A (BPA), n = 8 seasonality, n = 6 cadmium and n = 5 ambient temperature studies. In total, we identified two animal model studies. Whilst we found clear evidence for an association between GDM and air pollution, ambient temperature, season, cadmium, arsenic, POPs and phthalates, the findings regarding phenols were rather inconsistent. There were clear associations between adverse glycemic outcomes and air pollution, ambient temperature, season, POPs, phenols, and phthalates. Findings regarding cadmium and arsenic were heterogeneous (n = 2 publications in each case).

Conclusions

Environmental risk factors are important to consider in the management and prevention of GDM. In view of mechanisms of fetal programming, the environmental risk factors investigated may impair the health of mother and offspring in the short and long term. Further research is needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-13965-5.

Birth outcome measures and prenatal exposure to 4-tert-octylphenol

Exposure to 4-tert-octylphenol (tOP) has been linked with adverse health outcomes in animals and humans, while epidemiological studies about associations between prenatal exposure to tOP and fetal growth are extremely limited. We measured urinary tOP concentrations in 1100 pregnant women before their delivery, and examined whether tOP levels were associated with birth outcomes, including weight, length, head circumference and ponderal index at birth. tOP could be detected in all samples, and the median uncorrected and creatinine-corrected tOP concentrations were 0.90 μg/L (range from 0.25 to 20.05 μg/L) and 1.33 μg/g creatinine (range from 0.15 to 42.49 μg/g creatinine), respectively. Maternal urinary log-transformed tOP concentrations were significantly negatively associated with adjusted birth weight [β (g) = -126; 95% confidence interval (CI): -197, -55], birth length [β (cm) = -0.53; 95% CI:-0.93, -0.14], and head circumference [β (cm) = -0.30; 95% CI: -0.54, -0.07], respectively. Additionally, considering sex difference, these significant negative associations were also found among male neonates, while only higher maternal tOP concentrations were associated with a significant decrease in birth weight among female neonates. This study suggested significant negative associations between maternal urinary tOP concentrations and neonatal sizes at birth, and they differed by neonatal sex. Further epidemiological studies are required to more fully elaborate the associations between prenatal tOP exposure and birth outcomes.

Low concentrations of Bisphenol A and para-Nonylphenol affect extravillous pathway of human trophoblast cells

Bisphenol A (BPA) and para-Nonylphenol (p-NP) are chemicals of industrial origin which may influence human reproductive health. The effects of these substances in the prenatal life is an important topic that is receiving greater attention in the developed countries. In this study, human trophoblast cells HTR-8/SVneo were exposed to BPA and p-NP (1 × 10(-15), 1 × 10(-13), 1 × 10(-11), 1 × 10(-9) and 1 × 10(-7) M) and incubated for 24, 48 and/or 72 h then, examined for the main physiological processes which characterize the extravillous trophoblast. Cell proliferation showed no changes while the processes of cell migration and invasion were both reduced by BPA and p-NP. For each chemical, the activity was higher at lower concentrations with a maximum activity between 1 × 10(-13) and 1 × 10(-11) M (p < 0.05 for 1 × 10(-9) and p < 0.001 for 1 × 10(-11) M). Co-culture studies with human umbilical cord endothelial cells (HUVEC) revealed that trophoblast/endothelial interaction was significantly reduced by p-NP at 1 × 10(-11) M. Moreover, both chemicals were inducing differentiation of HTR-8/SVneo toward polyploidy by the process of endoreduplication. The estrogen-receptor antagonist ICI significantly reduced p-NP action, while it had no effect on BPA treated cells. In conclusion, p-NP and BPA act on trophoblast cells altering key physiological processes in placenta development. The exact mechanism of action of the chemicals in human trophoblast still needs to be clarified.

Toxicological mechanism of endocrine disrupting chemicals:is estrogen receptor involved?

Endocrine disrupting chemicals (EDCs) have been shown to interfere with physiological systems, i.e., adversely affecting hormone balance (endocrine system) , or disrupting normal function, in the female and male reproductive organs. Although endocrine disruption is a global concern for human health, its impact and significance and the screening strategy for detecting these synthetic or man-made chemicals are not clearly understood in female and male reproductive functions. Thus, in this review, we summarize the interference of environmental EDCs on reproductive development and function, and toxicological mechanism (s) of EDCs in in vitro and in vivo models of male and female reproductive system. In addition, this review highlights the effect of exposure to multiple EDCs on reproductive functions, and brings attention to their toxicological mechanism (s) through estrogen receptors.

A systematic review of Bisphenol A "low dose" studies in the context of human exposure: a case for establishing standards for reporting "low-dose" effects of chemicals

Human exposure to the chemical Bisphenol A is almost ubiquitous in surveyed industrialized societies. Structural features similar to estrogen confer the ability of Bisphenol A (BPA) to bind estrogen receptors, giving BPA membership in the group of environmental pollutants called endocrine disruptors. References by scientists, the media, political entities, and non-governmental organizations to many toxicity studies as "low dose" has led to the belief that exposure levels in these studies are similar to humans, implying that BPA is toxic to humans at current exposures. Through systematic, objective comparison of our current, and a previous compilation of the "low-dose" literature to multiple estimates of human external and internal exposure levels, we found that the "low-dose" moniker describes exposures covering 8-12 orders of magnitude, the majority (91-99% of exposures) being greater than the upper bound of human exposure in the general infant, child and adult U.S. Population. "low dose" is therefore a descriptor without specific meaning regarding human exposure. Where human exposure data are available, for BPA and other environmental chemicals, reference to toxicity study exposures by direct comparison to human exposure would be more informative, more objective, and less susceptible to misunderstanding.

Molecular mechanism(s) of endocrine-disrupting chemicals and their potent oestrogenicity in diverse cells and tissues that express oestrogen receptors

Endocrine-disrupting chemicals (EDCs) are natural or synthetic compounds present in the environment which can interfere with hormone synthesis and normal physiological functions of male and female reproductive organs. Most EDCs tend to bind to steroid hormone receptors including the oestrogen receptor (ER), progesterone receptor (PR) and androgen receptor (AR). As EDCs disrupt the actions of endogenous hormones, they may induce abnormal reproduction, stimulation of cancer growth, dysfunction of neuronal and immune system. Although EDCs represent a significant public health concern, there are no standard methods to determine effect of EDCs on human beings. The mechanisms underlying adverse actions of EDC exposure are not clearly understood. In this review, we highlighted the toxicology of EDCs and its effect on human health, including reproductive development in males and females as shown in in vitro and in vivo models. In addition, this review brings attention to the toxicity of EDCs via interaction of genomic and non-genomic signalling pathways through hormone receptors.

Gene alterations of ovarian cancer cells expressing estrogen receptors by estrogen and bisphenol a using microarray analysis

Since endocrine disrupting chemicals (EDCs) may interfere with the endocrine system(s) of our body and have an estrogenicity, we evaluated the effect(s) of bisphenol A (BPA) on the transcriptional levels of altered genes in estrogen receptor (ER)-positive BG-1 ovarian cancer cells by microarray and real-time polymerase-chain reaction. In this study, treatment with 17β-estradiol (E₂) or BPA increased mRNA levels of E₂-responsive genes related to apoptosis, cancer and cell cycle, signal transduction and nucleic acid binding etc. In parallel with their microarray data, the mRNA levels of some altered genes including RAB31_MEMBER RAS ONCOGENE FAMILY (U59877), CYCLIN D1 (X59798), CYCLIN-DEPENDENT KINASE 4 (U37022), IGF-BINDING PROTEIN 4 (U20982), and ANTI-MULLERIAN HORMONE (NM_000479) were significantly induced by E₂ or BPA in this cell model. These results indicate that BPA in parallel with E₂ induced the transcriptional levels of E₂-responsive genes in an estrogen receptor (ER)-positive BG-1 cells. In conclusion, these microarray and real-time polymerase-chain reaction results indicate that BPA, a potential weak estrogen, may have estrogenic effect by regulating E₂-responsive genes in ER-positive BG-1 cells and BG-1 cells would be the best in vitro model to detect these estrogenic EDCs.

Estrogen receptor α is involved in the induction of Calbindin-D(9k) and progesterone receptor by parabens in GH3 cells: a biomarker gene for screening xenoestrogens

The effects of paraben, a xenoestrogen with known endocrine disrupting bioactivity were evaluated. We used the induction of an estrogenic biomarker gene - Calbindin-D(9k) (CaBP-9k) to investigate the xenoestrogenic activity of a panel of parabens (methyl-, ethyl-, propyl-, isopropyl-, butyl-, and isobutylparabens) in GH3 rat pituitary cancer cell line. Following 24-h treatment, a significant increase in CaBP-9k expression of transcript and protein was dependent on the concentration-treated as well as the linear length of the alkyl chain from methyl- to isobutylparabens. Interestingly, co-treatment with fulvestrant, a pure antiestrogen largely reversed the paraben-dependent induction of CaBP-9k mRNA and protein in GH3 cell line. To better understand the mechanism of CaBP-9k induction by these endocrine disrupting compounds, we measured the levels of estrogen receptor (ERα) and progesterone receptor (PR) expression following parabens exposure. Also, we monitored the transiently transfected with plasmids containing of estrogen response element (ERE) sequence into GH3. In the GH3 cells, a large increase in PR mRNA and protein was observed in a concentration-dependent manner after parabens treatment that was effectively blocked in the presence of antagonist of 17β-estradiol (fulvestrant). And, luciferase activity was expressed from the putative ERE and expression was stimulated by parabens. To confirm that ERα signaling is involved in parabens induction of CaBP-9k and PR mRNA and protein, we treated GH3 cells with an antiestrogen, fulvestrant, which blocked the paraben-induced upregulation of CaBP-9k and PR. Taken together, these results indicate that CaBP-9k and PR is induced by parabens via the ER pathway in GH3 cell line.

Embryonic exposure to octylphenol induces changes in testosterone levels and disrupts reproductive efficiency in rats at their adulthood

The purpose of the present study was to investigate the effects of prenatal exposure to octylphenol (OP) at the dose of 50mg/kg body weight on days 1, 7 and 14 of pregnancy on reproductive health of male rats at adulthood. F1 male rats from control and OP exposed animals were weaned and maintained up to postnatal day (PND) 100. The indices of testis, epididymis and seminal vesicles were significantly decreased in male rats exposed to OP during embryonic development when compared with controls. Significant reduction in the epididymal sperm count, viable sperms and motile sperms and number of tail coiled sperms (HOS-test) were observed in experimental rats when compared to control rats. The levels of serum testosterone and also activity levels of testicular hydroxysteroid dehydrogenases were significantly decreased with a significant increase in the serum follicle stimulating and leutinizing hormones in experimental rats. Furthermore, embryonic exposure to OP caused significant down regulation of StAR, 3ß hydroxysteroid dehydrogenase and 17ß hydroxysteroid dehydrogenase mRNAs in testis of adult rats as compared to control rats. The results of fertility studies revealed that there was an increase in the mating index in experimental rats with an increase in the pre- and post-implantation losses in rats cohabited with treated animals indicating poor male reproductive performance.

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.

In vitro exposure to xenoestrogens induces growth hormone transcription and release via estrogen receptor-dependent pathways in rat pituitary GH3 cells

In this study, we employed an in vitro model to examine the effects of endocrine disruptors (EDs) in the regulation of growth hormone (GH) gene, an important hormone in growth, development and body composition. The rat pituitary cells, GH3, were treated with alkyl-phenols (APs), i.e., 4-tert-octyl-phenol (OP), p-nonyl-phenol (NP) or bisphenol A (BPA) for 24h in a dose-dependent manner (10(-5), 10(-6) and 10(-7)M) and in a time-dependent fashion (1, 3, 6, 12 and 24h) at a high concentration (10(-5)M). An anti-estrogen, ICI 182,780, was used to examine the potential involvement of estrogen receptor (ER) in the induction of GH by EDs through an ER-mediated pathway. Treatment with OP, NP and BPA induced a significant increase in GH gene expression at high and medium doses at 24h. ED-exposure induced a marked increase in GH gene transcription as early as 6h and peaked at 12h. Co-treatment with ICI 182,780 significantly attenuated ED-induced GH expression in GH3 cells. Interestingly, the level of in vitro GH release was significantly increased at 24h in response to OP, NP or BPA, whereas co-treatment with ICI 182,780 significantly reversed ED-induced GH secretion, indicating that ER may take part in both GH gene transcription and its release in these cells. In addition, the activation of extracellular signal-regulated kinases (ERKs), protein kinases B (Akt) or G protein in response to OP, NP or BPA at 24h was observed in this study. Exposure to these APs resulted in a rapid and significant activation of ERK phosphorylation, reflecting that EDs-induced response may involve both genomic and non-genomic pathways in these cells. Taken together, these results may provide new insight into the mode of ED-induced action in GH gene regulation as well as the biological pathway underlying these molecular events.

Uterine and placental expression of TRPV6 gene is regulated via progesterone receptor- or estrogen receptor-mediated pathways during pregnancy in rodents

Transient receptor potential cation channel, subfamily V, member 6 (TRPV6) is an epithelial Ca2+ channel protein expressed in calcium absorbing organs. In the present study, we investigated the expression and regulation of uterine and placental TRPV6 during gestation in rodents. Uterine TRPV6 peaked at pregnancy day (P) 0.5, P5.5 and, P13.5 and was detected in uterine epithelium and glands of rats, while placental TRPV6 mRNA levels increased in mid-gestation. Uterine and placental TRPV6 mRNA levels in rats appear to cyclically change during pregnancy, suggesting that TRPV6 may participate in the implantation process. In addition, uterine TRPV6 mRNA is only expressed in placenta-unattached areas of the uterus, and uterine TRPV6 immunoreactivity was observed in luminal and glandular epithelial cells. In the placenta, TRPV6 was detected in the labyrinth and spongy zone. These results may indicate that TRPV6 has at least two functions: implantation of the embryo and maintenance of pregnancy. To investigate the pathway(s) mediating TRPV6 expression in rodents, anti-steroid hormone antagonists were injected prior to maximal TRPV6 expression. In rats, TRPV6 expression was reduced by RU486 (an anti-progesterone) through progesterone receptors, and ICI 182,780 (an anti-estrogen) blocked TRPV6 expression via estrogen receptors in mice. The juxtaposition of uterine and placental TRPV6 expressed in these tissues supports the notion that TRPV6 participates in transferring calcium ions between the maternal and fetal compartments. Taken together, TRPV6 gene may function as a key element in controlling calcium transport in the uterus between the embryo and the placenta during pregnancy.

Molecular mechanism of regulation of the calcium-binding protein calbindin-D9k, and its physiological role(s) in mammals: a review of current research

Calbindin-D_9k (CaBP-9k) is a cytosolic calcium-binding protein that is expressed in a variety of tissues, such as uterus, placenta, intestine, kidney, pituitary gland and bone. At present, the precise role(s) of CaBP-9k remains to be clarified. CaBP-9k-null mice are normal, which indicates that other calcium-transporter genes can compensate for the lack CaBP-9k. Uterine CaBP-9k has been shown to be involved in the regulation of myometrial activity by intracellular calcium. In the uterus and placenta, CaBP-9k expression is regulated by the sex steroid hormones oestrogen (E2) and progesterone (P4). Intestinal CaBP-9k is involved in intestinal calcium absorption, and is regulated at the transcriptional and post-transcriptional levels by 1,25-dihydroxyvitamin D3, the hormonal form of vitamin D. Thus, evidence to date suggests that CaBP-9k may be regulated in a tissue-specific manner. In this review, we will summarize current data on the molecular mechanism of regulation of CaBP-9k in mammals, including recent research data generated in our laboratories.

Phenotype of a calbindin-D9k gene knockout is compensated for by the induction of other calcium transporter genes in a mouse model

CaBP-9k may be involved in the active calcium absorption and embryo implantation. Although we generated CaBP-9k KO mice to explore its function, no distinct phenotypes were observed in these KO mice. It can be hypothesized that TRPV5 and 6 and plasma membrane calcium ATPase 1b may play a role in the regulation of calcium transport to compensate CaBP-9k deficiency in its KO model.

INTRODUCTION

Active calcium transport in the duodenum and kidney is carried in three steps: calcium entry through epithelial Ca2+ channels (TRPV5 and TRPV6), buffering and/or transport by calbindin-D9k (CaBP-9k) and -D28k (CaBP-28k), and extrusion through the plasma membrane calcium ATPase 1b (PMCA1b) and sodium/calcium exchanger 1. Although the molecular mechanism of calcium absorption has been studied using knockouts (KOs) of the vitamin D receptor and CaBP-28k in animals, the process is not fully understood.

MATERIALS AND METHODS

We generated CaBP-9k KO mice and assessed the phenotypic characterization and the molecular regulation of active calcium transporting genes when the mice were fed different calcium diets during growth.

RESULTS

General phenotypes showed no distinct abnormalities. Thus, the active calcium transport of CaBP-9k-null mice proceeded normally in this study. Therefore, the compensatory molecular regulation of this mechanism was elucidated. Duodenal TRPV6 and CaBP-9k mRNA of wildtype (WT) mice increased gradually during preweaning. CaBP-9k is supposed to be an important factor in active calcium transport, but its role is probably compensated for by other calcium transporter genes (i.e., intestinal TRPV6 and PMCA1b) during preweaning and renal calcium transporters in adult mice.

CONCLUSIONS

Depletion of the CaBP-9k gene in a KO mouse model had little phenotypic effect, suggesting that its depletion may be compensated for by calcium transporter genes in the intestine of young mice and in the kidney of adult mice.

The classical and a non-classical pathways associated with NF-kappaB are involved in estrogen-mediated regulation of calbindin-D9k gene in rat pituitary cells

Calbindin-D9k (CaBP-9k) is a high affinity calcium binding protein that is highly expressed in the duodenum, kidney, uterus, and pituitary glands. Previous studies have shown that CaBP-9k expression is regulated by several steroid hormones, such as 1,25-dihydroxyvitamin D3, glucocorticoids, 17beta-estradiol (E2), and progesterone (P4), in a tissue-specific manner. However, the promoter elements that mediate transcriptional regulation by these steroid hormones are not clearly understood, mainly due to the lack of an appropriate cell line expressing CaBP-9k. Recently it was shown that CaBP-9k was constitutively expressed in the rat pituitary gland, and is expressed in an E2-dependent manner in a pituitary gland tumor-derived cell line, GH3. In the current study, we examined the activity of the estrogen responsive element (ERE) in rat CaBP-9k gene in GH3 cells, using a luciferase gene reporter assay, electrophoretic mobility shift assay, and mutagenesis. A nuclear factor-kappaB (NF-kappaB) binding site in the CaBP-9k promoter region was identified (nucleotides -848 to -834 from the transcriptional start site), and we demonstrated that addition of an NF-kappaB blocker to GH3 cells reduced E2-induced CaBP-9k transcription. In the present study, we further showed a previously reported imperfect ERE (nucleotides +51 to +65) between exon I and intron A of CaBP-9k, indicating that the interaction of estrogen receptor (ER) alpha with this region is involved in the regulation of CaBP-9k promoter activity and its expression. Taken together, these results suggest that in GH3 cells, both the classical ERalpha-ERE pathway and a non-classical pathway involving NF-kappaB are involved in E2-mediatd regulation of CaBP-9k expression in the pituitary gland.

Induction of uterine calbindin-D9k through an estrogen receptor-dependent pathway following single injection with xenobiotic agents in immature rats

Various environmental chemicals, both natural and synthetic, are believed to act as endocrine disruptors (EDs) in mammals. In this study, a new in vivo model of immature rats was used to explore the induction of calbindin-D9k (CaBP-9k) following a single injection of EDs. In a time-dependent experiment, immature rats at postnatal day 16 were treated with high doses (600 mg/kg body weight [BW]) of 4-tert-octyphenol (OP), p-nonylphenol (NP), or bisphenol A (BPA), and euthanized at different time points (3, 6, 12, 24, or 48 h). For a dose-dependent study, immature rats were given different doses (200, 400, or 600 mg/kg BW) and euthanized at 24 h after injection. After treatment with these EDs, the effects on CaBP-9k mRNA and protein were examined by Northern and Western blot analyses, respectively. An anti-estrogen, ICI 182,780, was employed to examine the potential involvement of estrogen receptor (ER) in the induction of estrogen receptor-mediated physiologic responses in vivo. A single treatment with each of the chemicals, at 600 mg/kg BW, resulted in a significant increase in the expression of CaBP-9k mRNA and protein 24 h after injection. In addition, treatment with OP, NP, or BPA resulted in a positive uterotrophic response. Cotreatment with the ER antagonist ICI 182,780 completely prevented the ED-induced uterine weight gain. Taken together, these results demonstrate that a single injection of OP, NP, or BPA results in an increase of CaBP-9k mRNA and protein via an ER-dependent pathway in the uterus of immature rats. This new model may be important to elucidate the mechanism of action of xenoestrogens on estrogen-sensitive tissue.

Analysis of gene expression profiles in the offspring of rats following maternal exposure to xenoestrogens

Many environmental chemicals are known endocrine disruptors (EDs). These have the potential to alter endocrine systems via various mechanisms that include binding to hormone receptors, thereby either mimicking or blocking the hormone actions and causing abnormal gene expression. Here, to elucidate the molecular mechanism(s) underlying the detrimental effects associated with the estrogenicity of these chemicals, we determined whether gene profiles were altered in rats exposed to 4-tert-octyphenol (OP) and diethylstilbestrol (DES) in utero. Pregnant rats were treated with a high dose of OP (600 mg/kg BW per day) or DES (500 microg/kg BW per day) at gestational days (GD) 17, 18 and 19. Both dams and neonates were euthanized at lactation day (LD) 5. The transcript profiles of uterine tissue were compared in treated versus control in both maternal and neonatal sites using cDNA microarray to determine the expression levels of approximately 13,000 genes and expressed sequence tags (ESTs). The expression levels of some known estrogen-responsive genes, i.e., complement component 3, epidermal growth factor receptor or c-fos oncogene and calbindin 3, as well as some other randomly selected genes, including general transcription factor IIa, transcription factor 4 and lymphocyte specific 1, were increased by OP and/or DES treatment in the uteri of both maternal and neonate groups. However, the magnitude of these alterations in gene expression differed markedly between dams and neonates, most likely reflecting the temporal susceptibility of the reproductive tract to estrogenic chemicals. Importantly, the altered gene patterns identified by microarray analysis were confirmed by RT-PCR and real-time RT-PCR. Fifteen primers were designed to amplify specific altered genes. These genes were selected for validation because of their markedly increased expression levels and they were classified on the basis of gene ontology. Overall, a high correlation was observed between microarray and real-time PCR data. Taken together, these results indicate that placental exposure to OP or DES may cause temporal changes in gene expression in the uteri of dams and neonates. Moreover, these findings may provide useful indicators of the adverse effects of EDs and prove particularly important in elucidating the effects of xenoestrogens on estrogen-responsive tissues, such as the developing reproductive tract.

Anti-progestogenic effect of flutamide on uterine expression of calbindin-D9k mRNA and protein in immature mice

A calcium binding protein, calbindin-D9k (CaBP-9k), is a cytosolic protein and regulated by steroid hormones in the reproductive tissues. Mouse CaBP-9k gene was predominantly regulated by progesterone (P4), whereas rat CaBP-9k was mainly regulated by 17beta-estradiol (E2) in the uterus. The induction of CaBP-9k can be employed as a biomarker for steroidal substrates as endocrine disruptors (EDs). Flutamide (FLU) is a non-steroidal anti-androgen or pro-drug that is rapidly metabolized to hydroxyflutamide, which may have both an anti-androgenic and anti-progestogenic activities. Thus, in the present study, we employed immature mice (14-day-old) subcutaneously injected with P4 (20 mg/kg/day) and/or FLU (5 mg/kg/day) for 3 consecutive days in the presence or absence of RU486, a pure PR antagonist (30 mg/kg/day), to analyze uterine CaBP-9k expression in this model. When immature mice were treated with P4, the expression levels of CaBP-9k mRNA and protein were significantly increased by P4. P4-induced expression levels of CaBP-9k mRNA and protein were abolished by FLU, in part, suggesting that FLU is a partial antagonist of P4 in the regulation of uterine CaBP-9k in immature mice. In addition, P4-induced CaBP-9k expression was completely reversed by RU486. Increased expression levels of CaBP-9k mRNA and protein were maintained for 24h after final injection with P4 in a time-dependent manner. However, CaBP-9k mRNA rapidly disappeared after 48 h and its protein level is similar with its mRNA. Treatment with FLU suppressed partially P4-induced CaBP-9k mRNA and protein until 24 h. Taken together, these results indicate that FLU has an anti-progestogenic activity and plays a role as a partial antagonist of P4 in the regulation of uterine CaBP-9k in immature mouse model.

Effects of maternal 4-tert-octylphenol exposure on the reproductive tract of male rats at adulthood

Increases in human male reproductive disorders (testicular cancer, cryptorchidism, hypospadias, and low sperm counts) might stem from increased exposure of the developing male to environmental estrogens. In the present study, we investigated the effects of octylphenol (OP), an estrogenic compound, exposure on the male reproductive system during the fetal period in which the development of reproductive organs and sexual differentiation occurs. Male rats were treated with OP in utero at doses of control (vehicle), 100 or 250 mg/kg/day. After birth, male rats were allowed to grow until adulthood, and then testes, epididymides, and prostate glands were investigated histopathologically. Sperm counts and percentage of abnormal sperm were determined. Seminiferous and epididymal round tubules were evaluated for tubule diameter, lumen diameter, and height of tubule epithelium. Treatment with OP caused abnormalities in the histology of the testis and epididymis and induced atrophy of prostate glands tubules. Although there were no differences in sperm counts among treatment groups, abnormal sperm percentages in the high dose group increased significantly. The results of this study demonstrate that maternally injected OP causes adverse effects on male reproductive tract at adulthood, especially on sperm structure.

Identification of estrogen-regulated genes by microarray analysis of the uterus of immature rats exposed to endocrine disrupting chemicals

Environmental estrogenic compounds which bind to the estrogen receptor (ER) can block or alter endogenous functions of estrogen in reproductive and developmental stages. A microarray technology is a very valuable method for the prediction of hormone-responsive activities in various gene expressions. Thus, we investigated the altered gene expression by estrogen and endocrine disruptors (EDs) using microarray technology in the uterus of immature rats. In this study, the expression levels of only 555 genes (7.42%) among the 7636 genes spotted on microarray chips were enhanced by more than two-fold following treatment with estradiol (E2), suggesting that direct or rapid response to E2 is widespread at the mRNA levels in these genes. In addition, elevated expression levels of the genes (over 2-fold) were observed by diethylstilbestrol (DES; 9.01%), octyl-phenol (OP; 8.81%), nonyl-phenol (NP; 9.51%), bisphenol-A (BPA; 8.26%) or genistein (9.97%) in the uterus of immature rats. The expression levels of representative genes, i.e., calbindin-D9k (CaBP-9k; vitamin D-dependent calcium-binding protein), oxytocin, adipocyte complement related protein (MW 30 kDa), lactate dehydrogenase A and calcium binding protein A6 (S100a6; calcyclin), were confirmed in these tissues by real-time PCR. In addition, the mRNA levels of these genes by real-time PCR were increased at follicular phase when E2 level was elevated during estrous cycle of adult female rats. In conclusion, these results indicate distinct altered expression of responsive genes following exposure to E2 and estrogenic compounds, and implicate distinct effects of endogenous E2 and environmental endocrine disrupting chemicals in the uterus of immature rats.

Calcium Homeostasis in Human Placenta: Role of Calcium‐Handling Proteins

The human placenta is a transitory organ, representing during pregnancy the unique connection between the mother and her fetus. The syncytiotrophoblast represents the specialized unit in the placenta that is directly involved in fetal nutrition, mainly involving essential nutrients, such as lipids, amino acids, and calcium. This ion is of particular interest since it is actively transported by the placenta throughout pregnancy and is associated with many roles during intrauterine life. At term, the human fetus has accumulated about 25-30 g of calcium. This transfer allows adequate fetal growth and development, since calcium is vital for fetal skeleton mineralization and many cellular functions, such as signal transduction, neurotransmitter release, and cellular growth. Thus, there are many proteins involved in calcium homeostasis in the human placenta.

Biology and physiology of Calbindin-D9k in female reproductive tissues: involvement of steroids and endocrine disruptors

Although Calbindin-D9k (CaBP-9k), a cytosolic calcium binding protein which has calcium binding sites, is expressed in various tissues, i.e., intestine, uterus, and placenta, potential roles of this gene and its protein are not clearly understood. Uterine CaBP-9k may be involved in controlling myometrial activity related with intracellular calcium level and is not under the control of vitamin D despite the presence of vitamin D receptors. But, it is under the control of the sex steroid hormones, estrogen (E2) and progesterone (P4), in female reproductive systems including the uterus and placenta. Thus, in this review, we summarize recent research literature in regards to the expression and regulation of CaBP-9k in mammals and introduce the research data of recent studies by us and others.

Conflict of Estrogenic Activity by Various Phthalates between In Vitro and In Vivo Models Related to the Expression of Calbindin-D9k

Phthalates are suspected to disrupt the endocrine system, especially through estrogenic effects. In the present study, we investigated the effects of various phthalates and compared them with those of estrogenic compounds that disrupt the female reproductive system. To assess the effects of these phthalates, alteration of the Calbindin-D9k (CaBP-9k) gene was measured as a biomarker because rat CaBP-9k gene carries an estrogen response element (ERE) which is involved in estrogen responsiveness of the gene during the estrous cycle. In this study, phthalates were tested for estrogenic properties in in vitro and in vivo models. First, the E-Screen assay was used to measure the proliferation of MCF-7 cells, a human breast cancer cell line. Treatments with 17beta-estradiol (E2; 9-fold) and 17alpha-estradiol (EE; 9-fold) induced MCF-7 cell proliferation at concentrations of 10(-9) M. Phthalates induced an increase in MCF-7 proliferation at concentration of 10(-6) M up to 10(-4) M. Nbutyl benzyl phthalate (BBP; 6-fold vs. vehicle), dicyclohexyl phthalate (DCHP; 8-fold), 2-ethylhexyl phthalate (DEHP; 6-fold) and di-n-butyl phthalate (DBP; 7-fold) at the concentration of 10(-4) M induced in an increase in MCF-7 proliferation after 6 d of treatment compared to vehicle. However, significant increase in MCF-7 proliferation was induced by diethyl phthalate (DEP). Second, we investigated the expression of CaBP-9k in the uterus of immature rats after oral treatment with BBP, DCHP, DEHP, DBP or DBP (600 mg/kg per day) in this in vivo model, because the immature rat model is highly sensitive to exposure to estrogenic chemicals. None of the phthalates induced the expression of CaBP-9k mRNA and its protein in the neonatal uterus as analysed by Northern and Western blot analyses, respectively. Although phthalates induced an increase in MCF-7 cell proliferation by an estrogenic effect, they could not induce CaBP-9k expression in the in vivo system, suggesting that the assays of estrogenic effects of various phthalates conducted in vitro and in vivo expression of CaBP-9k may produce conflicting results.

Maternal Exposure to Bisphenol A during Late Pregnancy Resulted in an Increase of Calbindin-D9k mRNA and Protein in Maternal and Postnatal Rat Uteri

It has been reported that Calbindin-D9k (CaBP-9k) is rapidly and strongly induced by environmental estrogenic compounds, possibly through estrogen receptors (ERalpha) in the uterus of mammals. CaBP-9k can be evaluated as an early gene marker for assaying estrogenic effects of putative environmental chemicals in the rat uterus. This study was undertaken to investigate CaBP-9k mRNA and protein expression in the postnatal rat uterus following maternal exposure to 17beta-estradiol (E2) and bisphenol A (BPA) during the neonatal period. Treatment with a high dose of BPA (600 mg/kg body weight (BW) per day) resulted in a 3-fold increase in CaBP-9k mRNA expression for 3 days, while a single dose of E2 (40 microg/kg BW per day) induced 2-fold increase of this gene in the maternal uterus. In an agreement with maternal CaBP-9k mRNA, postnatal CaBP-9k mRNA in the uterus increased 4-fold when treated with BPA (600 mg/kg BW per day). In addition, treatment with increasing concentrations of BPA resulted in significant increases in CaBP-9k protein in the maternal rat uterus. It is of interest that increasing doses of BPA induced a significant ERalpha mRNA increase in the postnatal uterus. Furthermore, immunohistochemistry revealed that treatment with BPA induced CaBP-9k protein in the maternal uterus. We demonstrated that maternal exposure to BPA during late pregnancy induced CaBP-9k mRNA and protein in maternal and postnatal rat uteri. These results suggest that rapid absorption and distribution of environmental estrogenic compounds occurs in maternal and neonatal rat uteri and these chemicals can easily pass though the placenta during pregnancy to affect postnatal reproductive functions.

Induction of Calbindin-D9k Messenger RNA and Protein by Maternal Exposure to Alkylphenols During Late Pregnancy in Maternal and Neonatal Uteri of Rats1

Environmental chemicals are proposed to possess hormone-like properties, such as mimicking natural hormones, inhibiting the action of hormones, and inducing abnormal gene expression. Among environmental chemicals, the alkylphenol products (APs), octylphenol (OP) and nonylphenol (NP), are derived from alkylphenol ethoxylates and have been reported to be environmentally persistent. Thus, in the present study, we examined the effect of two APs, OP and NP, on the expression of Calbindin-D(9k) (CaBP-9k) following maternal exposure during late pregnancy in maternal and fetal uteri. Treatment with a high dose (600 mg/kg body weight [BW]) of OP and NP resulted in an induction of CaBP-9k mRNA at Day 5 of lactation, as did a single treatment with diethylstilbestrol (DES) and 17beta-estradiol (E2) in maternal uteri. The expression of CaBP-9k mRNA was also induced following treatment with a high dose (600 mg/kg BW) of OP, transferred from the mother, exposed to fetuses during late pregnancy, and persisted through Day 5 of lactation. It is of interest that treatments with high doses of OP (400 and 600 mg/kg BW) reduced the expression of maternal estrogen receptor alpha (ERalpha) mRNA, as E2 did. However, all doses of NP resulted in an inhibition of neonatal ERalpha, while only the high does of OP (600 mg/kg BW) induced the reduction of neonatal ERalpha mRNA expression, as E2 did. Parallel to mRNA, the expression of CaBP-9k protein was significantly induced by treatment with a high dose of OP and NP. In conclusion, maternal exposure to APs, OP and NP, during late pregnancy increased the expressions of CaBP-9k mRNA and protein in maternal and neonatal uteri. These results suggest that the absorption and distribution of environmental estrogenic compounds in maternal and neonatal uteri are extremely rapid, and these chemicals can easily pass though the placenta during pregnancy to affect functions of neonatal reproductive tissues.

Transfer of maternally injected endocrine disruptors through breast milk during lactation induces neonatal Calbindin-D9k in the rat model

The uterus is a highly estrogen-responsive tissue, which can be measured through changes in CaBP-9k expression. In this study, we investigated the potential for estrogenic compounds 4-tert-octylphenol (OP), nonylphenol (NP), bisphenol A (BPA), diethylstilbestrol (DES) and 17beta-estradiol (E2) to be transferred through breast milk from dam to neonate during lactation using the induction of CaBP-9k in uterine tissue as a biomarker. Dams were treated with OP, NP and BPA, dissolved in corn oil, at doses of 200, 400 and 600 mg/kg body weight per day l for 5 days after delivery. Dams and neonates were euthanized after 24h. Treatment with these estrogenic compounds increased the expression of CaBP-9k mRNA in the maternal uterus, in a dose-dependent manner. All doses of estrogenic compounds resulted in an increase in CaBP-9k protein levels. These compounds have an estrogenic effect on the maternal uterus during the lactation period as shown by the induction of both CaBP-9k mRNA and protein. In the neonatal uterus, the expression of CaBP-9k mRNA and protein significantly increased with DES exposure. There was a significant increase in CaBP-9k mRNA in neonatal uterus when the dams were treated with high doses of estrogenic compounds, but protein levels of CaBP-9k were undetectable. Taken together, these findings suggest that maternally injected estrogenic compounds may be transferred to neonates through breast milk and thus affecting uterine function, as shown by the induction of CaBP-9k gene expression in the neonatal uterus.