Effects of transplacental 17-α-ethynyl estradiol or bisphenol A on the developmental profile of steroidogenic acute regulatory protein in the rat testis

Previous research from our laboratory has determined the transcript profiles for developing fetal rat female and male reproductive tracts following transplacental exposure to estrogens. Prenatal exposure to bisphenol A (BPA) or 17-α-ethynyl estradiol (EE) significantly affects steroidogenic acute regulatory (StAR) protein transcript levels in the developing male rat reproductive tract. The purpose of this study was to establish the intratesticular distribution and temporal expression pattern of StAR, a key gene involved in steroidogenesis. Beginning on gestation day (GD) 11, pregnant Sprague-Dawley rats were exposed daily to 10μg/kg/day EE and fetal testes were harvested at GD16, 18, or 20. Quantitative reverse transcriptase PCR (QRT-PCR) demonstrated no significant difference in StAR transcript levels present at GD16. However, at GD18, StAR transcripts were significantly decreased following exposure. Immunohistochemistry demonstrated similar StAR protein levels in interstitial region of GD16 testes and an obvious decrease in StAR protein levels in the interstitial region of GD18 testes. Moreover, starting at GD11 additional dams were dosed with 0.001 or 0.1 μg/kg/day EE or 0.02, 0.5, 400 mg/kg/day BPA via subcutaneous injections. QRT-PCR validated previous microarray dose-related decreases in StAR transcripts at GD20, whereas immunohistochemistry results demonstrated decreases in StAR protein levels in the interstitial region at the highest EE and BPA doses only. Neither EE nor BPA exposure caused morphological changes in the developing seminiferous cords, Sertoli cells, gonocytes, or the interstitial region or Leydig cells at GD16-20. High levels of estrogens decrease StAR expression in the fetal rat testis during late gestation.

Uterine Temporal Response to Acute Exposure to 17α-Ethinyl Estradiol in the Immature Rat

The rat uterus responds to acute estrogen treatment with a series of well-characterized physiological responses; however, the gene expression changes required to elicit these responses have not been fully characterized. In order to understand early events induced by estrogen exposure in vivo, we evaluated the temporal gene expression in the uterus of the immature rat after a single dose of 17 alpha-ethinyl estradiol (EE) by microarray analysis, evaluating the expression of 15,923 genes. Immature 20-day-old rats were exposed to a single dose of EE (10 microg/kg), and the effects on uterine histology, weight, and gene expression were determined after 1, 2, 8, 24, 48, 72, and 96 h. EE induced changes in the expression of 3867 genes, at least at one time point (p < or = 0.0001), and at least 1.5-fold (up- or downregulated). Specifically, the expression of 8, 116, 3030, 2076, 381, 445, and 125 genes was modified at 1, 2, 8, 24, 48, 72, or 96 h after exposure to EE, respectively (p < or = 0.0001, t-test). At the tissue and organ level, a clear uterotrophic response was elicited by EE after only 8 h, reaching a maximum after 24 h and remaining detectable even after 96 h of exposure. The uterine phenotypic changes were induced by sequential changes in the transcriptional status of a large number of genes, in a program that involves multiple molecular pathways. Using the Gene Ontology to better understand the temporal response to estrogen exposure, we determined that the earliest changes were in the expression of genes whose products are involved in transcriptional regulation and signal transduction, followed by genes implicated in protein synthesis, energy utilization, solute transport, cell proliferation and differentiation, tissue remodeling, and immunological responses among other pathways. The compendium of genes here presented represents a comprehensive compilation of estrogen-responsive genes involved in the uterotrophic response.

Gene expression changes induced in the testis by transplacental exposure to high and low doses of 17{alpha}-ethynyl estradiol, genistein, or bisphenol A

The purpose of this study was to determine (1) the transcriptional program elicited by exposure to three estrogen receptor (ER) agonists: 17 alpha-ethynyl estradiol (EE), genistein (Ges), and bisphenol A (BPA) during fetal development of the rat testis and epididymis; and (2) whether very low dosages of estrogens (evaluated over five orders of magnitude of dosage) produce unexpected changes in gene expression (i.e., a non-monotonic dose-response curve). In three independently conducted experiments, Sprague-Dawley rats were dosed (sc) with 0.001-10 microg EE/kg/day, 0.001-100 mg Ges/kg/day, or 0.002-400 mg BPA/kg/day. While morphological changes in the developing reproductive system were not observed, the gene expression profile of target tissues were modified in a dose-responsive manner. Independent dose-response analyses of the three studies identified 59 genes that are significantly modified by EE, 23 genes by Ges, and 15 genes by BPA (out of 8740), by at least 1.5 fold (up- or down-regulated). Even more genes were observed to be significantly changed when only the high dose is compared with all lower doses: 141, 46, and 67 genes, respectively. Global analyses aimed at detecting genes consistently modified by all of the chemicals identified 50 genes whose expression changed in the same direction across the three chemicals. The dose-response curve for gene expression changes was monotonic for each chemical, with both the number of genes significantly changed and the magnitude of change, for each gene, decreasing with decreasing dose. Using the available annotation of the gene expression changes induced by ER-agonist, our data suggest that a variety of cellular pathways are affected by estrogen exposure. These results indicate that gene expression data are diagnostic of mode of action and, if they are evaluated in the context of traditional toxicological end-points, can be used to elucidate dose-response characteristics.

Cardiac abnormalities induced by zinc deficiency are associated with alterations in the expression of genes regulated by the zinc-finger transcription factor GATA-4

Zinc (Zn) deficiency during pregnancy results in a wide variety of developmental abnormalities. The objective of this study was to determine if expression of cardiac developmental genes regulated by Zn-finger transcription factors could be modulated during dietary Zn deficiency. Rats were fed 0.5 (low Zn) or 90 (controls) microg Zn/g diet throughout pregnancy. Fetal development was examined and RNA isolated at gestation day (GD) 13 and 20. Cardiac abnormalities were detected at GD 20 in 82% of fetuses from dams fed low Zn diets compared with only 2% in controls. Cardiac developmental gene expression regulated by the Zn-finger transcription factor, GATA-4, was measured by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In GD 13 and 20 hearts, two genes critical for heart development, alpha-myosin heavy chain (alpha-MHC) and cardiac troponin I (cTnI), were down-regulated in Zn-deficient fetuses. Expression of alpha-MHC was 66 and 40% lower at GD 13 and 20, respectively, in fetuses from dams fed low Zn diets compared with fetuses from control dams (p<0.05). Fetal cardiac TnI RNA levels were reduced 40 and 45% at GD 13 and 20 in the Zn-deficient group compared with controls (p<0.05). Fetal cardiac transcript levels of GATA-4 and MHox, a gene regulated by a helix-loop-helix transcription factor, whose expressions are not Zn-dependent, were unaffected by diet. These data indicated that alterations in gene regulation might be an underlying mechanism of cardiac abnormalities. Dysfunction of other Zn-dependent transcription factors may be an integral part of the extensive teratogenesis associated with Zn deficiency.

Impact of the phytoestrogen content of laboratory animal feed on the gene expression profile of the reproductive system in the immature female rat

The effect of the dietary background of phytoestrogens on the outcome of rodent bioassays used to identify and assess the reproductive hazard of endocrine-disrupting chemicals is controversial. Phytoestrogens, including genistein, daidzein, and coumestrol, are fairly abundant in soybeans and alfalfa, common ingredients of laboratory animal diets. These compounds are weak agonists for the estrogen receptor (ER) and, when administered at sufficient doses, elicit an estrogenic response in vivo. In this study, we assessed the potential estrogenic effects of dietary phytoestrogens at the gene expression level, together with traditional biologic end points, using estrogen-responsive tissues of the immature female rat. We compared the gene expression profile of the uterus and ovaries, as a pool, obtained using a uterotrophic assay protocol, from intact prepubertal rats fed a casein-based diet (free from soy and alfalfa) or a regular rodent diet (Purina 5001) containing soy and alfalfa. Estrogenic potency of the phytoestrogen-containing diet was determined by analyzing uterine wet weight gain, luminal epithelial cell height, and gene expression profile in the uterus and ovaries. These were compared with the same parameters evaluated in animals exposed to a low dose of a potent ER agonist [0.1 microg/kg/day 17alpha-ethynyl estradiol (EE) for 4 days]. Exposure to dietary phytoestrogens or to a low dose of EE did not advance vaginal opening, increase uterine wet weight, or increase luminal epithelial cell height in animals fed either diet. Although there are genes whose expression differs in animals fed the soy/alfalfa-based diet versus the casein diet, those genes are not associated with estrogenic stimulation. The expression of genes well known to be estrogen regulated, such as progesterone receptor, intestinal calcium-binding protein, and complement component 3, is not affected by consumption of the soy/alfalfa-based diet when assessed by microarray or quantitative reverse transcriptase-polymerase chain reaction analysis. Our results indicate that although diet composition has an impact on gene expression in uterus and ovaries, it does not contribute to the effects of an ER agonist.

Gene expression profile induced by 17 alpha-ethynyl estradiol in the prepubertal female reproductive system of the rat

The profound effects of 17beta-estradiol on cell growth, differentiation, and general homeostasis of the reproductive and other systems, are mediated mostly by regulation of temporal and cell type-specific expression of different genes. In order to understand better the molecular events associated with the activation of the estrogen receptor (ER), we have used microarray technology to determine the transcriptional program and dose-response characteristics of exposure to a potent synthetic estrogen, 17 alpha-ethynyl estradiol (EE), during prepubertal development. Changes in patterns of gene expression were determined in the immature uterus and ovaries of Sprague-Dawley rats on postnatal day (PND) 24, 24 h after exposure to EE, at 0.001, 0.01, 0.1, 1 and 10 micro g EE/kg/day (sc), for four days (dosing from PND 20 to 23). The transcript profiles were compared between treatment groups and controls using oligonucleotide arrays to determine the expression level of approximately 7000 annotated rat genes and over 1740 expressed sequence tags (ESTs). Quantification of the number of genes whose expression was modified by the treatment, for each of the various doses of EE tested, showed clear evidence of a dose-dependent treatment effect that follows a monotonic response, concordant with the dose-response pattern of uterine wet-weight gain and luminal epithelial cell height. The number of genes whose expression is affected by EE exposure increases according to dose. At the highest dose tested of EE, we determined that the expression level of over 300 genes was modified significantly (p < or = 0.0001). A dose-dependent analysis of the transcript profile revealed a set of 88 genes whose expression is significantly and reproducibly modified (increased or decreased) by EE exposure (p < or = 0.0001). The results of this study demonstrate that, exposure to a potent estrogenic chemical during prepubertal maturation changes the gene expression profile of estrogen-sensitive tissues. Furthermore, the products of the EE-regulated genes identified in these tissues have a physiological role in different intracellular pathways, information that will be valuable to determine the mechanism of action of estrogens. Moreover, those genes could be used as biomarkers to identify chemicals with estrogenic activity.

Gene expression profile induced by 17alpha-ethynyl estradiol, bisphenol A, and genistein in the developing female reproductive system of the rat

Exposure to some compounds with estrogenic activity, during fetal development, has been shown to alter development of reproductive organs, leading to abnormal function and disease either after birth or during adulthood. In order to understand the molecular events associated with the estrogenicity of different chemicals and to determine whether common sets of gene expression changes can be predictive of estrogenic activity, we have used microarray technology to determine the transcriptional program influenced by exposure to this class of compounds during organogenesis and development. Changes in patterns of gene expression were determined in the developing uterus and ovaries of Sprague-Dawley rats on GD 20, exposed to graded dosages (sc) of 17alpha-ethynyl estradiol (EE), genistein, or bisphenol A (BPA) from GD 11 to GD 20. Dose levels were roughly equipotent in estrogenic activity. We compared the transcript profiles between treatment groups and controls, using oligonucleotide arrays to determine the expression level of approximately 7000 rat genes and over 1000 expressed squence tags (ESTs). At the highest tested doses of EE, BPA, or genistein, we determined that less than 2% of the mRNA detected by the array showed a 2-fold or greater change in their expression level (increase or decrease). A dose-dependent analysis of the transcript profile revealed a common set of genes whose expression is significantly and reproducibly modified in the same way by each of the 3 chemicals tested. Additionally, each compound induces changes in the expression of other transcripts that are not in common with the others, which indicated not all compounds with estrogenic activity act alike. The results of this study demonstrate that transplacental exposure to chemicals with estrogenic activity changes the gene expression profile of estrogen-sensitive tissues, and that the analysis of the transcript profile of these tissues could be a valuable approach to determining the estrogenicity of different compounds.

Repeated administration of alpha-hederin results in alterations in maternal zinc status and adverse developmental outcome in the rat

The administration of alpha-hederin, an inducer of metallothionein, results in a secondary zinc deficiency that may be an important maternally mediated mechanism of developmental toxicity. Previous studies have shown adverse developmental outcome with a single administration of alpha-hederin to rats on gestation day (GD) 8 or 11. The objective of this study was to determine whether dosing of alpha-hederin throughout organogenesis would result in a sustained elevation of maternal hepatic metallothionein and subsequent developmental abnormalities. Rats were administered dosage levels of 0 (vehicle only), 20, or 30 mumol/kg from GD 6-15. Maternal hepatic metallothionein levels were 10-fold higher on GD 16 in the treatment groups than the controls. Consequently, liver zinc concentrations increased 60% and 54%, whereas plasma levels decreased 23% and 33% in the 20 and 30 mumol/kg treatment groups, respectively. At GD 20, mean fetal weights of the treatment litters were 11% less than control litters. The administration of alpha-hederin resulted in a threefold increase in the number of offspring that exhibited developmental abnormalities, including visceral and skeletal malformations. Following an oral pulse of 65Zn subsequent to treatment with 0 or 20 mumol/kg of alpha-hederin, the distribution of 65Zn to the liver of treated dams was twice that of controls, whereas the radiolabeled zinc apportioned to the decidua and uterus decreased by 44%. Furthermore, the 65Zn detected in the embryos from treated dams was 70% lower than in embryos from control dams. In conclusion, low doses of a metallothionein inducer administered to the dam from GD 6-15 resulted in a sustained elevation of hepatic metallothionein and a subsequent redistribution of zinc leading to a decrease in the zinc available to the embryo and ultimately to adverse development of the offspring. Repeated dosing throughout organogenesis, as required in regulated safety assessment testing, increased the severity of the effects previously observed with single large dosages of the toxicant administered during midgestation.

Altered Zn status by alpha-hederin in the pregnant rat and its relationship to adverse developmental outcome

The hypothesis that an acute-phase reaction in the pregnant animal causes a systemic redistribution of Zn, resulting in a transient but developmentally adverse Zn deficiency in the embryo, was tested by treating pregnant rats during organogenesis with alpha-hederin, an agent reported to induce substantial metallothionein (MT) synthesis in rat liver, and determining hepatic MT concentration, hepatic and plasma Zn concentration, and systemic distribution of a pulse of 65Zn after treatment. Developmental toxicity was assessed by evaluating morphologic development in term fetuses. A single dose of alpha-hederin, injected sc at dosages of 3 to 300 mumol/kg, caused an acute phase response, indicated by decreased Fe and Zn, and increased Cu, alpha 1-acid glycoprotein, and ceruloplasmin concentration in plasma, along with a dosage-related increase in maternal hepatic MT concentration. The maximum induction of MT was 11 to 15-fold greater than control and occurred at dosages of 30 mumol/kg and higher, and MT concentration reached its peak 12 to 24 h after treatment. Zn concentration in liver and liver cytosol increased along with MT, reaching a maximum level at dosages of 30 mumol/kg and higher. Plasma Zn concentration decreased after alpha-hederin treatment to a level approximately 75% of control at a dosage of 30 mumol/kg and 50% of control at 300 mumol/kg. Therefore, hepatic MT induction was associated with most, but not all, of the decrease in plasma Zn concentration. Zn distribution was evaluated by giving an oral pulse of 65Zn 8 h after treatment with 0, 30, or 300 mumol/kg alpha-hederin on gestation day 11, and measuring 65Zn levels 18 h after treatment. The fraction of 65Zn distributed to the liver of treated rats (either dosage) was twice that of control, but distribution of 65Zn to other maternal tissues was decreased. 65Zn accumulation by conceptuses was significantly decreased, attributable to decreased accumulation in decidua, but not in visceral yolk sacs or embryos; however, at this stage of development the decidua accounts for a greater quantity of Zn than either of the other products of conception and may serve as the Zn-storing tissue for the conceptus. Both 30 and 300 mumol/kg increased resorption incidence, and 300 mumol/kg also decreased fetal weight and increased the incidence of abnormal fetuses. Serum collected from rats two hours after alpha-hederin treatment (i.e., before the onset of MT synthesis) supported rat embryo development in vitro, whereas serum collected 18 h after treatment did not. Adding Zn to this serum restored normal embryonic development.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of metallothionein induction and altered zinc status in maternally mediated developmental toxicity: comparison of the effects of urethane and styrene in rats

We hypothesize that maternal metallothionein (MT) induction by toxic dosages of chemicals may contribute to or cause developmental toxicity by a chain of events leading to a transient but developmentally adverse decrease in Zn availability to the embryo. This hypothesis was tested by evaluating hepatic MT induction, maternal and embryonic Zn status, and developmental toxicity after exposure to urethane, a developmental toxicant, or styrene, which is not a developmental toxicant. Pregnant Sprague-Dawley rats were given 0 or 1 g/kg urethane ip, or 0 or 300 mg/kg styrene in corn oil po, on Gestation Day 11 (sperm positive = Gestation Day 0). These were maternally toxic dosages. As both treatments decreased food consumption, separate pair-fed control groups were also evaluated for effects on MT and Zn status and development. In addition, Gestation Day 11 rat embryos were exposed to urethane in vitro in order to determine whether urethane has the potential to be directly embryotoxic. Urethane treatment induced hepatic MT 14-fold over control; styrene treatment induced MT 2.5-fold. The MT induction by styrene could be attributed to decreased food intake, as a similar level of induction was observed in a pair-fed untreated control group. However, the level of MT induction by urethane was much greater than that produced by decreased food intake alone. Hepatic Zn concentration, particularly in the cytosol, was increased in the presence of increased hepatic MT concentration. Plasma Zn concentration was significantly decreased (approximately 30%) by urethane treatment, but not by styrene or food restriction (pair-feeding). Distribution of 65Zn to the liver of urethane-treated dams was significantly greater (by 30%), while distribution to embryonic tissues was significantly lower (by at least 50%) than in pair-fed or ad lib.-fed controls. Styrene treatment had no effect on 65Zn distribution. Urethane was developmentally toxic, causing an 18% decrease in fetal weight and a significant delay in skeletal ossification, but was not toxic to rat embryos in vitro. Styrene was not developmentally toxic. The changes observed after urethane treatment, namely substantial hepatic MT induction and altered maternal and embryonic Zn status, along with the lack of direct embryotoxicity of urethane in vitro, support the hypothesis that these maternal effects contribute to developmental toxicity. The lack of similar changes in styrene-intoxicated dams provides one explanation for its low developmental toxicity at maternally toxic dosages.

Association and dissociation of Escherichia coli heat-stable enterotoxin from rat brush border membrane receptors

Escherichia coli heat-stable enterotoxin (ST) binds to receptors on rat intestinal cells and brush border membranes (BBM). We devised experiments to examine the reversibility of ST binding. We found that both 125I-labeled ST and native ST were spontaneously dissociable from the BBM receptor. Radiolabeled ST bound to BBM was also dissociated by the addition of avid goat anti-ST antiserum. Furthermore, using a computer program for analysis of ligand binding, we calculated an apparent Ka of 10(8) liters/mol from competitive inhibition and saturation-binding data. This is significantly lower than the value previously reported by others. Our findings, of a lower Ka and a reversible ST-binding process, suggest that a therapeutic strategy of removing bound ST from its receptor or competing with the enterocyte receptor for unbound ST might be successful in terminating ST-induced secretion.