Dual activation of PPARalpha and PPARgamma by mono-(2-ethylhexyl) phthalate in rat ovarian granulosa cells

Di-(2-ethylhexyl) phthalate and mono-(2-ethylhexyl) phthalate inhibit growth and reduce estradiol levels of antral follicles in vitro

Any insult that affects survival of ovarian antral follicles can cause abnormal estradiol production and fertility problems. Phthalate esters (PEs) are plasticizers used in a wide range of consumer and industrial products. Exposure to these chemicals has been linked to reduced fertility in humans and animal models. Di-(2-ethylhexyl) phthalate (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) decrease serum estradiol levels and aromatase (Arom) expression, prolong estrous cycles, and cause anovulation in animal and culture models. These observations suggest PEs directly target antral follicles. We therefore tested the hypothesis that DEHP (1-100 microg/ml) and MEHP (0.1-10 microg/ml) directly inhibit antral follicular growth and estradiol production. Antral follicles from adult mice were cultured with DEHP or MEHP, and/or estradiol for 96 h. During culture, follicle size was measured every 24 h as a measurement of follicle growth. After culture, media were collected for measurement of estradiol levels and follicles were subjected to measurement of cylin-D-2 (Ccnd2), cyclin-dependent-kinase-4 (Cdk4), and Arom. We found that DEHP and MEHP inhibited growth of follicles and decreased estradiol production compared to controls at the highest doses. DEHP and MEHP also decreased mRNA expression of Ccnd2, Cdk4, and Arom at the highest dose. Addition of estradiol to the culture medium prevented the follicles from DEHP- and MEHP-induced inhibition of growth, reduction in estradiol levels, and decreased Ccnd2 and Cdk4 expression. Collectively, our results indicate that DEHP and MEHP may directly inhibit antral follicle growth via a mechanism that partially includes reduction in levels of estradiol production and decreased expression of cell cycle regulators.

Minireview: Nuclear receptor-controlled steroid hormone synthesis and metabolism

Steroid hormones are essential in normal physiology whereas disruptions in hormonal homeostasis represent an important etiological factor for many human diseases. Steroid hormones exert most of their functions through the binding and activation of nuclear hormone receptors (NRs or NHRs), a superfamily of DNA-binding and often ligand-dependent transcription factors. In recent years, accumulating evidence has suggested that NRs can also regulate the biosynthesis and metabolism of steroid hormones. This review will focus on the recent progress in our understanding of the regulatory role of NRs in hormonal homeostasis and the implications of this regulation in physiology and diseases.

Placental biomarkers of phthalate effects on mRNA transcription: application in epidemiologic research

BACKGROUND

CYP19 and PPARgamma are two genes expressed in the placental trophoblast that are important to placental function and are disrupted by phthalate exposure in other cell types. Measurement of the mRNA of these two genes in human placental tissue by quantitative real-time polymerase chain reaction (qPCR) offers a source of potential biomarkers for use in epidemiologic research. We report on methodologic challenges to be considered in study design.

METHODS

We anonymously collected 10 full-term placentas and, for each, sampled placental villi at 12 sites in the chorionic plate representing the inner (closer to the cord insertion site) and outer regions. Each sample was analyzed for the expression of two candidate genes, aromatase (CYP19) and peroxisome proliferator activated receptor protein gamma (PPARgamma) and three potential internal controls: cyclophilin (CYC), 18S rRNA (18S), and total RNA. Between and within placenta variability was estimated using variance component analysis. Associations of expression levels with sampling characteristics were estimated using mixed effects models.

RESULTS

We identified large within-placenta variability in both transcripts (>90% of total variance) that was minimized to <20% of total variance by using 18S as an internal control and by modelling the means by inner and outer regions. 18S rRNA was the most appropriate internal control based on within and between placenta variability estimates and low correlations of 18S mRNA with target gene mRNA. Gene expression did not differ significantly by delivery method. We observed decreases in the expression of both transcripts over the 25 minute period after delivery (CYP19 p-value for trend = 0.009 and PPARgamma (p-value for trend = 0.002). Using histologic methods, we confirmed that our samples were comprised predominantly of villous tissue of the fetal placenta with minimal contamination of maternally derived cell types.

CONCLUSION

qPCR-derived biomarkers of placental CYP19 and PPARgamma gene expression show high within-placental variability. Sampling scheme, selection of an appropriate internal control and the timing of sample collection relative to delivery can be optimized to minimize within-placenta and other sources of underlying, non-etiologic variability.

Maternal urinary metabolites of Di-(2-Ethylhexyl) phthalate in relation to the timing of labor in a US multicenter pregnancy cohort study

Di-(2-ethylhexyl) phthalate (DEHP) is a plasticizer used in consumer and medical products that can cross the placenta, disrupt steroid hormone synthesis, and activate peroxisome proliferator-activated receptor gamma. The authors examined DEHP exposure in relation to the timing of labor in a pregnancy cohort study of 283 women recruited in 4 US states (California, Iowa, Minnesota, and Missouri) between 2000 and 2004. The authors estimated associations between concentrations of DEHP metabolites and gestational age at delivery using linear regression models and associations between DEHP metabolites and clinical outcomes using logistic regression models. After covariate adjustment, women at the 75th percentile of DEHP metabolite concentrations had a 2-day-longer mean length of gestation than women at the 25th percentile (95% confidence interval: 1.4, 3.3). Log-unit increases in mono-2-ethylhexyl phthalate and mono-2-ethyl-5-oxohexyl phthalate concentrations were associated with increased odds of cesarean section delivery (30% and 50% increased odds, respectively), increased odds of delivering at 41 weeks or later (100% and 120% increased odds), and reduced odds of preterm delivery (50% and 60% decreased odds). These data suggest that DEHP may interfere with signaling related to the timing of parturition.

Phthalate-induced testicular dysgenesis syndrome: Leydig cell influence

Phthalates, the most abundantly produced plasticizers, leach out from polyvinyl chloride plastics and disrupt androgen action. Male rats that are exposed to phthalates in utero develop symptoms characteristic of the human condition referred to as testicular dysgenesis syndrome (TDS). Environmental influences have been suspected to contribute to the increasing incidence of TDS in humans (i.e. cryptorchidism and hypospadias in newborn boys and testicular cancer and reduced sperm quality in adult males). In this review, we discuss the recent findings that prenatal exposure to phthalates affects Leydig cell function in the postnatal testis. This review also focuses on the recent progress in our understanding of how Leydig cell factors contribute to phthalate-mediated TDS.

Reproductive and developmental toxicity of phthalates

The purposes of this review are to (1) evaluate human and experimental evidence for adverse effects on reproduction and development in humans, produced by exposure to phthalates, and (2) identify knowledge gaps as for future studies. The widespread use of phthalates in consumer products leads to ubiquitous and constant exposure of humans to these chemicals. Phthalates were postulated to produce endocrine-disrupting effects in rodents, where fetal exposure to these compounds was found to induce developmental and reproductive toxicity. The adverse effects observed in rodent models raised concerns as to whether exposure to phthalates represents a potential health risk to humans. At present, di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DBP), and butyl benzyl phthalate (BBP) have been demonstrated to produce reproductive and developmental toxicity; thus, this review focuses on these chemicals. For the general population, DEHP exposure is predominantly via food. The average concentrations of phthalates are highest in children and decrease with age. At present, DEHP exposures in the general population appear to be close to the tolerable daily intake (TDI), suggesting that at least some individuals exceed the TDI. In addition, specific high-risk groups exist with internal levels that are several orders of magnitude above average. Urinary metabolites used as biomarkers for the internal levels provide additional means to determine more specifically phthalate exposure levels in both general and high-risk populations. However, exposure data are not consistent and there are indications that secondary metabolites may be more accurate indicators of the internal exposure compared to primary metabolites. The present human toxicity data are not sufficient for evaluating the occurrence of reproductive effects following phthalate exposure in humans, based on existing relevant animal data. This is especially the case for data on female reproductive toxicity, which are scarce. Therefore, future research needs to focus on developmental and reproductive endpoints in humans. It should be noted that phthalates occur in mixtures but most toxicological information is based on single compounds. Thus, it is concluded that it is important to improve the knowledge of toxic interactions among the different chemicals and to develop measures for combined exposure to various groups of phthalates.

Phthalate exposure in girls during early puberty

The aim of this study was to determine the levels of phthalate ester metabolites in girls in early puberty, and the associated environmental factors for phthalate exposure. A case-control study was conducted in which we recruited girls in early puberty, including 30 girls with premature thelarche (PT) and 26 with central precocious puberty (CPP), and 33 normal controls. The mean urine levels of monomethyl phthalate (MMP) were significantly higher in the PT group (96.5 +/- 134.0 ng/ml) than in the control group (26.4 +/- 30.0 ng/ml; p = 0.005). The levels of monobutyl phthalate (MBuP) correlated with the intake of seafood, drink and the use of plastic cups. The levels of mono-(2-ethylhexyl) phthalate (MEHP) correlated with the intake of seafood and meat and exposure plastic handi-wrap. Significantly higher MMP in the PT girls revealed that phthalate may be one of the environmental causes of early puberty in Taiwanese girls.

An endogenous prostaglandin enhances environmental phthalate-induced apoptosis in bone marrow B cells: activation of distinct but overlapping pathways

Phthalate esters are ubiquitous environmental contaminants that are produced for a variety of common industrial and commercial purposes. We have shown that mono-(2-ethylhexyl) phthalate (MEHP), the toxic metabolite of di-(2-ethylhexyl) phthalate, induces bone marrow B cell apoptosis that is enhanced in the presence of the endogenous prostaglandin 15-deoxy-Delta((12, 14))-PGJ(2) (15d-PGJ(2)). Here, studies were performed to determine whether 15d-PGJ(2)-mediated enhancement of MEHP-induced apoptosis represents activation of an overlapping or complementary apoptosis pathway. MEHP and 15d-PGJ(2) induced significant apoptosis within 8 and 5 h, respectively, in a pro/pre-B cell line and acted cooperatively to induce apoptosis in primary pro-B cells. Apoptosis induced with each chemical was accompanied by activation of a combination of initiator caspases (caspases-2, -8, and -9) and executed by caspase-3. Apoptosis induced with MEHP and 15d-PGJ(2) was reduced in APAF1 null primary pro-B cells and accompanied by alteration of mitochondrial membranes, albeit with different kinetics, indicating an intrinsically activated apoptosis pathway. Significant Bax translocation to the mitochondria supports its role in initiating release of cytochrome c. Both chemicals induced Bid cleavage, a result consistent with a truncated Bid-mediated release of cytochrome c in an apoptosis amplification feedback loop; however, significantly more Bid was cleaved following 15d-PGJ(2) treatment, potentially differentiating the two pathways. Indeed, Bid cleavage and cytochrome c release following 15d-PGJ(2) but not MEHP treatment was profoundly inhibited by Z-VAD-FMK, suggesting that 15d-PGJ(2) activates apoptosis via two pathways, Bax mobilization and protease-dependent Bid cleavage. Thus, endogenous 15d-PGJ(2)-mediated enhancement of environmental chemical-induced apoptosis represents activation of an overlapping but distinct signaling pathway.

Impact of diisobutyl phthalate and other PPAR agonists on steroidogenesis and plasma insulin and leptin levels in fetal rats

Endocrine disrupting chemicals can induce malformations and impairment of reproductive function in experimental animals and may have similar effects in humans. Recently, the environmental obesogen hypothesis was proposed, suggesting that environmental chemicals contribute to the development of obesity and insulin resistance. These effects could be related to chemical interaction with nuclear receptors such as the peroxisome proliferator activated receptors (PPARs). As several testosterone-reducing drugs are PPAR activators, we aimed to examine whether four PPAR agonists were able to affect fetal testosterone production and masculinization of rats. Additionally, we wished to examine whether these chemicals affected fetal plasma levels of insulin and leptin, which play important roles in the developmental programming of the metabolic system. Pregnant Wistar rats were exposed from gestation day (GD) 7-21 to diisobutyl phthalate (DiBP), butylparaben, perfluorooctanoate, or rosiglitazone (600, 100, 20, or 1 mg/kg bw/day, respectively). Endocrine endpoints were studied in offspring at GD 19 or 21. DiBP, butylparaben and rosiglitazone reduced plasma leptin levels in male and female offspring. DiBP and rosiglitazone additionally reduced fetal plasma insulin levels. In males, DiBP reduced anogenital distance, testosterone production and testicular expression of Insl-3 and genes related to steroidogenesis. PPARalpha mRNA levels were reduced by DiBP at GD 19 in testis and liver. In females, DiBP increased anogenital distance and increased ovarian aromatase mRNA levels. This study reveals new targets for phthalates and parabens in fetal male and female rats and contributes to the increasing concern about adverse effects of human exposure to these compounds.

Mono-(2-ethylhexyl) phthalate stimulates basal steroidogenesis by a cAMP-independent mechanism in mouse gonadal cells of both sexes

Phthalates are widely used as plasticizers in a number of daily-life products. In this study, we investigated the influence of mono-(2-ethylhexyl) phthalate (MEHP), the active metabolite of the frequently used plasticizer di-(2-ethylhexyl) phthalate (DEHP), on gonadal steroidogenesisin vitro. MEHP (25–100 μM) stimulated basal steroid synthesis in a concentration-dependent manner in immortalized mouse Leydig tumor cells (MLTC-1). The stimulatory effect was also detected in KK-1 granulosa tumor cells. MEHP exposure did not influence cAMP or StAR protein levels and induced a gene expression profile of key steroidogenic proteins different from the one induced by human chorionic gonadotropin (hCG). Simultaneous treatment with MEHP and a p450scc inhibitor (aminoglutethimide) indicated that MEHP exerts its main stimulatory effect prior to pregnenolone formation. MEHP (10–100 μM) up-regulated hormone-sensitive lipase and 3-hydroxy-3-methylglutaryl coenzyme A reductase, suggesting that MEHP increases the amount of cholesterol available for steroidogenesis. Our data suggest that MEHP, besides its known inhibitory effect on hCG action, can directly stimulate gonadal steroidogenesis in both sexes through a cAMP- and StAR-independent mechanism. The anti-steroidogenic effect of DEHP has been proposed to cause developmental disorders such as hypospadias and cryptorchidism, whereas a stimulation of steroid synthesis may prematurely initiate the onset of puberty and theoretically affect the hypothalamic–pituitary–gonadal axis.

Effect of mono-(2-ethylhexyl) phthalate (MEHP) on resumption of meiosis, in vitro maturation and embryo development of immature mouse oocytes

The purpose of this study was to evaluate the effect of MEHP on in vitro maturation of mouse oocytes and resulting embryo development. Denuded oocytes (DO) were cultured in maturation medium supplemented with 0, 50, 100, 200 and 400 microM levels of MEHP for 24 h. The matured oocytes then were fertilized and cultured for 4 days. The percentage of Germinal Vesicle (GV) stage oocytes were significantly higher in 200 and 400 microM MEHP treatment comparing to the control (P < 0.05). The proportion of oocytes that progressed to the metaphase II (MII) stage was significantly decreased by adding of MEHP in a dose related pattern. The 2-cell embryo formation was significantly decreased with 400 microM treatments than the control. Moreover with further culture in experimental groups none of the embryos comparing to that of the control group were developed to morulla stage (P < 0.05). These results indicate that MEHP could negatively modulate mouse oocyte meiotic maturation in vitro and embryo development, suggesting possible risks for human and other mammalians reproductive health.

Time-response effects of testicular gene expression profiles in Sprague-Dawley male rats treated with di(n-butyl) phthalate

Phthalate esters were reported to damage fetal and postnatal testes of experimental animals, but the molecular mechanisms underlying these effects remain unknown. The time-response effects of di(n-butyl) phthalate (DBP) on the expression patterns of the testicular genes in male Sprague-Dawley rats were examined for different periods of exposure (1, 7, 14, or 28 d). The steroidogenic- or spermatogenic-related gene expression patterns were measured using reverse-transcription polymerase chain reaction (RT-PCR). After 28 d of exposure, the serum concentrations of DBP and monobutyl phthalate (MBP) increased in a dose-dependent manner, and were significantly higher in the DBP-treated rats than in the control rats. Liver weight was increased markedly at 28 d after DBP exposure at 750 mg/kg/d. Testicular weight was reduced significantly after 14 and 28 d of exposure. DBP (750 mg/kg/d) produced a significant increase in scavenger receptor class B1 (SR-B1) and steroidogenic acute regulatory (StAR) mRNA after 14 and 28 d of exposure. The level of cytochrome P-450 (P450) side-chain cleavage (P450scc) mRNA decreased in the group treated with DBP at 750 mg/kg/d at 7 d. After 14 and 28 d of exposure, there was an apparent increase in P450scc mRNA. High doses of DBP significantly increased the Cyp17 mRNA level after 28 d of exposure. At 7 d, a significant decrease in Cyp19 mRNA was observed only in the group exposed to 750 mg/kg/d DBP. In addition, DBP significantly decreased the levels of a spermatid-specific gene (Spag4) and lactate dehydrogenase A (LDHA) mRNA after 7 d of exposure. The levels of androgen receptor (AR), estrogen receptor-alpha (ER-alpha), and retinoid X receptor-gamma (RXR-r) expression decreased significantly in a time- or dose-dependent manner. DBP significantly increased the peroxisome proliferator-activated receptor-gamma (PPAR-r) and phosphorylated extracellular-signal-regulated kinase (p-ERK1/2) levels in the testis. These results suggest that the acute and chronic effects of DBP on the steroidogenic pathways in the testes show mechanistically distinct patterns. Data thus provide some insights into the molecular mechanisms underlying DBP-induced testicular dysgenesis.

Mono-(2-ethylhexyl) phthalate (MEHP) induces nuclear receptor 4A subfamily in NCI-H295R cells: a possible mechanism of aromatase suppression by MEHP

Phthalate esters are widely used as plasticizers for polyvinylchloride and are suspected of functioning as endocrine disrupters. Di-(2-ethylhexyl) phthalate (DEHP), the most important phthalate ester in commercial use, has been reported to act as a rodent reproductive toxicant. In the present study, we investigated the effects of phthalate esters on aromatase (CYP19) activity and on its gene expression in a human adrenocortical carcinoma cell line, NCI-H295R. Mono-(2-ethylhexyl) phthalate (MEHP), a principle metabolite of DEHP, dose-dependently suppressed aromatase activity and its transcription level. Furthermore, MEHP rapidly and transiently induced transcription of the genes which encode nuclear receptor 4A subfamily members (Nur77, Nurr1 and NOR-1), and up-regulated Nur77 promoter activation and Nur77 protein expression in the cells. MEHP-induced Nur77 transcription was inhibited by bisindolylmaleimide I (protein kinase C inhibitor) and wortmannin (phosphoinositide 3-kinase inhibitor). Finally, ectopic expression of Nur77 markedly suppressed forskolin-induced transcriptional activation of promoters I.3 and II of the CYP19 gene. These results suggest that the suppression of aromatase activity and its transcription level by MEHP exposure to NCI-H295R cells was regulated through the rapid and transient expression of Nur77 gene.

A dose–response study following in utero and lactational exposure to di-(2-ethylhexyl) phthalate (DEHP): Reproductive effects on adult female offspring rats

Di(2-ethylhexyl) phthalate (DEHP) is used in numerous consumer products, mainly imparting flexibility and durability to polyvinyl chloride (PVC) based plastics. It is a known reproductive and developmental toxicant in male rodents. However, data regarding effects of DEHP on female reproductive health are particularly sparse. We performed an extensive dose-response study following developmental exposure to DEHP and evaluated the effects on adult female reproductive function. Two wide ranges of doses, low and high, were tested. Female Wistar rats were treated daily with DEHP and peanut oil (vehicle control) by gavage from gestation day 6 to lactation day 21. The low doses were: 0.015, 0.045, 0.135, 0.405 and 1.215mgDEHP/kg/bw/day and the high doses were: 5, 15, 45, 135 and 405mg DEHP/kg/bw/day. At the doses tested, no effects on organ (liver, kidney, spleen, thymus, thyroid, ovary and uterus) or body weights were detected. Female offspring presented a normal pattern of estrous cyclicity with no hormonal alterations (serum estradiol and progesterone). A statistically significant increase in tertiary atretic follicles was observed at the highest dose (405mgDEHP/kg/day). Morphometric analysis indicated that uterus and vagina luminal epithelial cell height were unaffected by treatment. An increase in the number of ovarian atretic tertiary follicles was the only effect observed in adult female offspring exposed in utero and during lactation to DEHP.

In vitro screening of 200 pesticides for agonistic activity via mouse peroxisome proliferator-activated receptor (PPAR)alpha and PPARgamma and quantitative analysis of in vivo induction pathway

Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors and key regulators of lipid metabolism and cell differentiation. However, there have been few studies reporting on a variety of environmental chemicals, which may interact with these receptors. In the present study, we characterized mouse PPARalpha and PPARgamma agonistic activities of 200 pesticides (29 organochlorines, 11 diphenyl ethers, 56 organophosphorus pesticides, 12 pyrethroids, 22 carbamates, 11 acid amides, 7 triazines, 8 ureas and 44 others) by in vitro reporter gene assays using CV-1 monkey kidney cells. Three of the 200 pesticides, diclofop-methyl, pyrethrins and imazalil, which have different chemical structures, showed PPARalpha-mediated transcriptional activities in a dose-dependent manner. On the other hand, none of the 200 pesticides showed PPARgamma agonistic activity at concentrations <or =10(-5) M. To investigate the in vivo effects of diclofop-methyl, pyrethrins and imazalil, we examined the gene expression of PPARalpha-inducible cytochrome P450 4As (CYP4As) in the liver of female mice intraperitoneally injected with these compounds (< or =300 mg/kg). RT-PCR revealed significantly high induction levels of CYP4A10 and CYP4A14 mRNAs in diclofop-methyl- and pyrethrins-treated mice, whereas imazalil induced almost no gene expressions of CYP4As. In particular, diclofop-methyl induced as high levels of CYP4A mRNAs as WY-14643, a potent PPARalpha agonist. Thus, most of the 200 pesticides tested do not activate PPARalpha or PPARgamma in in vitro assays, but only diclofop-methyl and pyrethrins induce PPARalpha agonistic activity in vivo as well as in vitro.

Effects of luteinizing hormone on peroxisome proliferator-activated receptor gamma in the rat ovary before and after the gonadotropin surge

We have shown previously that mRNA for peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed in granulosa cells and downregulated by the luteinizing hormone (LH) surge. The current studies were undertaken to test the hypothesis that LH stimulates a decrease in the expression of PPARgamma, as well as its activity, in granulosa cells. Ovaries were collected from immature rats 0 and 48 h after they received pregnant mares' serum gonadotropin (PMSG), and 4 and 24 h after administration of human chorionic gonadotropin (hCG), and used for protein isolation or processed for immunolocalization of PPARgamma. The amount of phosphorylated PPARgamma was measured by immunoblot analysis to determine how LH affects the phosphorylation status, and therefore the activity, of PPARgamma. Granulosa cells were also collected from immature rats 48 h after PMSG. Cells were cultured with LH in the absence and presence of H89 and cycloheximide to investigate the role of PKA and protein synthesis in the LH-mediated decline in mRNA for PPARgamma respectively. Protein corresponding to PPARgamma was localized to nuclei of granulosa cells 0 and 48 h after PMSG. Expression was greatly reduced by 4 h after hCG, with expression in mural granulosa cells lost before that in cumulus cells. The amount of phosphorylated PPARgamma did not change during the periovulatory period. Blocking PKA activity had no effect on levels of mRNA for PPARgamma. However, levels of mRNA for PPARgamma were significantly increased in cells treated with cycloheximide (P < 0.05, ANOVA followed by Tukey's HSD). These data suggest that PPARgamma is tightly regulated in the ovary and that its expression is the primary mechanism by which LH influences the activity of PPARgamma. In addition, protein synthesis may be involved in modulating levels of PPARgamma in granulosa cells.

The methoxychlor metabolite, 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane, inhibits steroidogenesis in rat ovarian granulosa cells in vitro

The exquisitely balanced hormonal mechanisms that control female fertility can be affected by several internal and external factors including pathogens, genetic maladies, and environmental agents. In the latter group are natural and synthetic agents known as endocrine disruptors. One such compound, 2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), is the predominant metabolite of the pesticide methoxychlor. The effects of HPTE on ovarian steroidogenesis have not been previously reported and were investigated in the present study. Granulosa cells harvested from immature rats were treated with follicle-stimulating hormone (FSH) or N(6),2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (db-cAMP) in the presence or absence of HPTE. After 48h, progesterone (P4) and estradiol-17beta (E2) concentrations were measured in the culture media. Steady-state levels of the mRNAs encoding steroidogenic acute regulatory protein (StAR), P450 side-chain cleavage (P450scc), 3beta-hydroxysteroid dehydrogenase type 1 (3beta-HSD), and P450 aromatase (P450arom) were examined using real-time PCR. Both FSH- and db-cAMP-stimulated P(4) accumulation were impaired by HPTE. In contrast, FSH-, but not db-cAMP-stimulated, E2 content was suppressed by HPTE. The FSH-dependent increase in the abundance of P450scc, 3beta-HSD, and P450arom mRNAs was blocked by HPTE; however, StAR expression was not altered. Although db-cAMP-dependent P450arom was moderately reduced by HPTE, the levels of db-cAMP-dependent StAR, P450scc, and 3beta-HSD mRNAs were increased in the presence of HPTE. These data collectively show that HPTE can disrupt P4 and E2 production in granulosa cells, with implications for sites of action both preceding and following the generation of cAMP. The steroid-modulatory effects of HPTE in granulosa cells appear to involve the general suppression of the FSH-dependent expression of mRNAs encoding steroid pathway proteins, whereas the disparate effects of HPTE on cAMP-dependent mRNA content in this regard suggest a broader and more complex mechanism of action.

An assessment of the potential developmental and reproductive toxicity of di-isoheptyl phthalate in rodents

Di-isoheptyl phthalate (DIHP) is a branched, phthalate ester with seven carbon alkyl side chains. Since structurally similar phthalates have been shown to produce developmental and/or reproductive effects in rodents, the potential for DIHP to produce developmental and reproductive toxicity was assessed. In a developmental toxicity study, female rats were given DIHP by oral gavage on gestational days 6-20. There were significant reductions in uterine weight, increased resorptions and reduced fetal weight in the high dose (750 mg/kg) group. Fetal examination revealed malformations and variations of both the skeletal system and the viscera including ectopic testes. The intermediate dose, 300 mg/(kg/day), was a no effect level in this study. In a two-generation reproductive toxicity study, DIHP was given in the diet at 1000, 4500 and 8000 ppm. In the 8000 ppm group of the first (F1) generation, anogenital distance was reduced, time to balanopreputial separation was increased, there was a significant increase in thoracic nipples and testicular abnormalities, and weights of testes and accessory reproductive organs were significantly reduced. Testicular sperm counts and daily sperm production were significantly reduced. Fertility was also significantly reduced in the 8000 ppm group. In the second (F2) generation offspring, anogenital distance was significantly reduced and there was evidence of reduced weight gain during lactation in both the 4500 and 8000 ppm groups. The overall no effect level (NOEL) in the reproductive toxicity study was in the range of 64-168 mg/(kg/day) (gestation-lactation periods). By comparison, estimated average human exposures in the general population are <1 microg/(kg/day).

Estrogen in men: effects on bone accrual, maintenance and prevention of bone loss

Sex steroid hormones play an important role in the maintenance of bone mass in males as well as in females. Even though androgens represent the major sex steroid class in men, their primacy in regulating male skeletal remodeling has been questioned increasingly as direct and indirect evidence has emerged suggesting that estrogens also play a major role in male skeletal health. This review summarizes clinical and experimental evidence that estrogens are essential for bone accrual in the growing skeleton, maintenance of bone mass and prevention of bone loss in men.

Endocrine-disrupting chemicals as modulators of sex steroid synthesis

Endocrine-disrupting chemicals (EDCs) are typically identified as compounds that can interact with oestrogen or androgen receptors and thus act as agonists or antagonists of endogenous hormones. Growing evidence shows that they may also modulate the activity/expression of steroidogenic enzymes. These are expressed not only in the adrenal glands and gonads but also in many tissues that have the ability to convert circulating precursors into active hormones. In this way, EDCs may impact both on sexual differentiation and development and on hormone-dependent cancers. This review summarizes the evidence for EDCs as modulators of steroidogenic enzymes, identifies the structure/activity relationship in terms of inhibiting specific enzyme activity, questions whether experimental observations can equate with natural in vivo exposure or dietary intake of EDCs, and finally looks at the mechanisms through which these chemicals may disrupt normal steroidogenesis. In summarizing the evidence, the question of whether or not the dietary intake of these endocrine disrupters could pose a threat to human sexual development and health will be addressed.

Peroxisome proliferator-activated receptors (PPARs) and ovarian function--implications for regulating steroidogenesis, differentiation, and tissue remodeling

The peroxisome proliferator-activated receptors (PPARs) are a family of transcription factors involved in varied and diverse processes such as steroidogenesis, angiogenesis, tissue remodeling, cell cycle, apoptosis, and lipid metabolism. These processes are critical for normal ovarian function, and all three PPAR family members--alpha, delta, and gamma, are expressed in the ovary. Most notably, the expression of PPARgamma is limited primarily to granulosa cells in developing follicles, and is regulated by luteinizing hormone (LH). Although much has been learned about the PPARs since their initial discovery, very little is known regarding their function in ovarian tissue. This review highlights what is known about the roles of PPARs in ovarian cells, and discusses potential mechanisms by which PPARs could influence ovarian function. Because PPARs are activated by drugs currently in clinical use (fibrates and thiazolidinediones), it is important to understand their role in the ovary, and how manipulation of their activity may impact ovarian physiology as well as ovarian pathology.

Differential Effects of Phthalates on the Testis and the Liver1

Phthalates have been shown to elicit contrasting effects on the testis and the liver, causing testicular degeneration and promoting abnormal hepatocyte proliferation and carcinogenesis. In the present study, we compared the effects of phthalates on testicular and liver cells to better understand the mechanisms by which phthalates cause testicular degeneration. In vivo treatment of rats with di-(2-ethylhexyl) phthalate (DEHP) caused a threefold increase of germ cell apoptosis in the testis, whereas apoptosis was not changed significantly in livers from the same animals. Western blot analyses revealed that peroxisome proliferator-activated receptor (PPAR) alpha is equally abundant in the liver and the testis, whereas PPAR gamma and retinoic acid receptor (RAR) alpha are expressed more in the testis. To determine whether the principal metabolite of DEHP, mono-(2-ethylhexyl) phthalate (MEHP), or a strong peroxisome proliferator, 4-chloro-6(2,3-xylindino)-2-pyrimidinylthioacetic acid (Wy-14,643), have a differential effect in Sertoli and liver cells by altering the function of RAR alpha and PPARs, their nuclear trafficking patterns were compared in Sertoli and liver cells after treatment. Both MEHP and Wy-14,643 increased the nuclear localization of PPAR alpha and PPAR gamma in Sertoli cells, but they decreased the nuclear localization of RAR alpha, as previously shown. Both PPAR alpha and PPAR gamma were in the nucleus and cytoplasm of liver cells, but RAR alpha was predominant in the cytoplasm, regardless of the treatment. At the molecular level, MEHP and Wy-14,643 reduced the amount of phosphorylated mitogen-activated protein kinase (activated MAPK) in Sertoli cells. In comparison, both MEHP and Wy-14,643 increased phosphorylated MAPK in liver cells. These results suggest that phthalates may cause contrasting effects on the testis and the liver by differential activation of the MAPK pathway, RAR alpha, PPAR alpha, and PPAR gamma in these organs.

Activation of peroxisome proliferator-activated receptor-gamma and retinoid X receptor inhibits aromatase transcription via nuclear factor-kappaB

Our previous studies demonstrated that a peroxisome proliferator-activated receptor (PPAR)-gamma ligand, troglitazone (TGZ),and/or a retinoid X receptor (RXR) ligand, LG100268 (LG), decreased the aromatase activity in both cultured human ovarian granulosa cells and human granulosa-like tumor KGN cells. In the present study, we further found that a combined treatment of TGZ+LG decreased aromatase promoter II (ArPII) activity in both ovarian KGN cells and fibroblast NIH-3T3 cells in a PPARgamma-dependent manner. Furthermore, the inhibition of both aromatase activity and the transcription of ArPII by TGZ+LG was completely eliminated when nuclear factor-kappaB (NF-kappaB) signaling was blocked by specific inhibitors, suggesting NF-kappaB, which is endogenously expressed in both fibroblast and granulosa cells, might be a mediator of this inhibition. Interestingly, activation of NF-kappaB by either forced expression of the p65 subunit or NF-kappaB-inducing kinase up-regulated ArPII activity. Positive regulation of aromatase by endogenous NF-kappaB was also suggested by the fact that NF-kappaB-specific inhibitors suppress basal activity of the aromatase gene. A concomitant formation of high-order complex between NF-kappaB p65 and ArPII was also observed by chromatin immunoprecipitation assay. Although activation of PPARgamma and RXR affected endogenous expression levels of neither inhibitory kappaBalpha nor p65, it impaired the interaction between NF-kappaB and ArPII and the p65 based transcription as well. Altogether, these results indicate that activation of a nuclear receptor system, constituted by PPARgamma and RXR, down-regulates aromatase expression through the suppression of NF-kappaB-dependent aromatase activation and thus provide a new insight in the mechanism of regulation of the aromatase gene.

Effects of estradiol, benzophenone-2 and benzophenone-3 on the expression pattern of the estrogen receptors (ER) alpha and beta, the estrogen receptor-related receptor 1 (ERR1) and the aryl hydrocarbon receptor (AhR) in adult ovariectomized rats

The estrogen receptors (ERs) are members of a super family of ligand-activated transcription factors mediating estrogenic responses. A close functional kinship was found for the structurally related estrogen receptor-related receptor1 (ERR1), a constitutively active transcription factor. The aryl hydrocarbon receptor (AhR) mediates the toxic and estrogenic effects of a wide variety of environmental contaminants and industrial pollutants. Both the ERR1 and the AhR are known to modulate the ER's signalling pathways in multiple ways. Organic chemicals with a certain structural relationship to steroid hormones often induce a tissue- or cell-specific variety of responses distinct from estrogenic responses and this may involve ERR1 and AhR. The UV-screens benzophenone-2 and benzophenone-3 (BP2, BP3), structurally related to known steroid receptor ligands, are used in cosmetics and plastics to improve product stability and durability. Both BP2 and BP3 were shown to exert uterotrophic effects and BP2 was shown to bind to the estrogen receptors. Whether such effects are also exerted in other organs is unknown. Therefore, an approach to a multi-organic risk assessment for these substances was made by measuring the gene-expression of the four mentioned receptors in the pituitary, the uterus and the thyroid after a five-day treatment in comparison to estradiol. Though BP2 seems to exert an estrogen-like effect while BP3 does not, there are regulatory effects on receptor expression for both substances that indicate a kind of endocrine disruption that is not assessed by "classical" estrogenic markers.

Unequivocal estrogen receptor-binding affinity of phthalate esters featured with ring hydroxylation and proper alkyl chain size

The effect of plasticizers phthalate esters (PEs) on health is a controversial subject. PEs are likely to be estrogenic, but the results on the potency obtained by many investigators are still inconsistent and the endocrine disrupting mechanism remains to be clarified. Here, we show that PEs acquire unequivocal binding affinities for human estrogen receptors (ERs) through ring hydroxylation that is possible in the environment and through metabolism. Unexpectedly, the acquired affinities of hydroxylated PEs (PEs-OH) were enhanced by elongation and branching of the ester alkyl chains. PEs-OH with alkyl chains more than six carbons may grope for a new binding site, which is inaccessible to PEs-OH with short chains. The strongest ER-binding affinity among the tested PEs-OH was close to that of diethylstilbestrol, the most potent synthetic ER-binder. Ring hydroxylation would be a new clue to the clarification of the endocrine disruption mechanism of PEs.

Evidence for a new human CYP1A1 regulation pathway involving PPAR-alpha and 2 PPRE sites

BACKGROUND AND AIMS

Cytochrome P450 1A1 catalyzes the degradation of endobiotics (estradiol, fatty acids, and so on) and the bioactivation of numerous environmental procarcinogens, such as arylamines and polycyclic aromatic hydrocarbons, that are found in food. Several peroxisome proliferators and arachidonic acid derivatives enhance cytochrome P450 1A1 activity, but the mechanisms involved remain unknown. The aim of this work was to study the role of peroxisome proliferator-activated receptors in cytochrome P450 1A1 gene induction.

METHODS

The role of peroxisome proliferator-activated receptor transcription factors in cytochrome P450 1A1 induction was assessed by means of enzymatic activities, quantitative real-time polymerase chain reaction, gene reporter assays, mutagenesis, and electrophoretic mobility shift assay.

RESULTS

We show that peroxisome proliferator-activated receptor-alpha agonists (WY-14643, bezafibrate, clofibrate, and phthalate) induce human cytochrome P450 1A1 gene expression, whereas 2,4-thiazolidinedione, a specific peroxisome proliferator-activated receptor-gamma agonist, represses it. The induction of cytochrome P450 1A1 transcripts by WY-14643 was associated with a marked increase of ethoxyresorufin O -deethylase activity (10-fold at 200 mumol/L). Transfection of peroxisome proliferator-activated receptor-alpha complementary DNA enhanced cytochrome P450 1A1 messenger RNA induction by WY-14643, although WY-14643 failed to activate xenobiotic responsive element sequences. Two peroxisome proliferator response element sites were located at positions -931/-919 and -531/-519 of the cytochrome P450 1A1 promoter. Their inactivation by directed mutagenesis suppressed the inductive effect of WY-14643 on cytochrome P450 1A1 promoter activation. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay experiments showed that the 2 cytochrome P450 1A1 peroxisome proliferator response element sites bind the peroxisome proliferator-activated receptor-alpha/retinoid X receptor-alpha heterodimer.

CONCLUSIONS

We describe here a new cytochrome P450 1A1 induction pathway involving peroxisome proliferator-activated receptor-alpha and 2 peroxisome proliferator response element sites, indicating that peroxisome proliferator-activated receptor-alpha ligands, which are common environmental compounds, may be involved in carcinogenesis.

Peroxisome Proliferator-Activated Receptors: Mediators of Phthalate Ester-Induced Effects in the Male Reproductive Tract?

Many phthalate ester plasticizers are classified as peroxisome proliferators (PP), a large group of industrial and pharmaceutical chemicals. Like PP, exposure to some phthalates increases hepatocyte peroxisome and cellular proliferation, as well as the incidence of hepatocellular adenomas in mice and rats. Most effects of PP are mediated by three nuclear receptors called peroxisome proliferator-activated receptors (PPARalpha,beta,gamma). An obligate role for PPARalpha in PP-induced events leading to liver cancer is well-established. Exposure of rats in utero or in the neonate to a subset of phthalate esters causes profound, sometimes irreversible malformations in the male reproductive tract. We review here the data that supports or discounts roles for PPARs in phthalate-induced testis toxicity including (1) toxic effects of phthalates on the male reproductive tract, (2) expression of PPARs in the testis, (3) activation of PPARs by phthalates, (4) role of PPARalpha in testis toxicity, (5) gene targets of phthalates involved in steroid biosynthesis and catabolism, and (6) interactions between PPARs and other nuclear receptors that play roles in testis development and homeostasis. Critical research needs are identified that will help determine the significance of PPARs in phthalate-induced effects in the rat male reproductive tract and the relevance of toxicity to humans.

Diverse developmental toxicity of di-n-butyl phthalate in both sexes of rat offspring after maternal exposure during the period from late gestation through lactation

To evaluate developmental toxicity of di-n-butyl phthalate (DBP) with exposure during the period from late gestation to following lactation, maternal rats were given DBP at dietary concentrations of 0, 20, 200, 2000 and 10,000 ppm from gestational day 15 to postnatal day (PND) 21. At 10,000 ppm, male offspring showed a decreased neonatal anogenital distance and retention of nipples (PND 14), while females showed a slight non-significant delay in the onset of puberty. At PND 21, reduction of testicular spermatocyte development was evident from 20 ppm, as well as mammary gland changes at low incidence in both sexes. At this time point, population changes of pituitary hormone-immunoreactive cells were observed at 10,000 ppm with a similar pattern of increase in the percentages of luteinizing hormone (LH)-positive and decrease in follicle-stimulating hormone (FSH) and prolactin producing cells in both sexes, effects also being evident on FSH from 200 ppm and LH from 2000 ppm in females. During postnatal week (PNW) 8-11, marginal increase of the number of cases with extended diestrus was found at 10,000 ppm. At adult stage necropsy, testicular lesions appeared to be very faint in most cases, but degeneration and atrophy of mammary gland alveoli were observed in males from 20 ppm. Although without clear monotonic dose-dependence, relative pituitary weights were increased with the intermediate doses in males at PNW 11. In females, relative pituitary weights were decreased after 10,000 ppm at PNW 11, and from 200 ppm at PNW 20. The proportion of FSH-positive cells in the pituitaries at PNW 11 was increased in both sexes at 10,000 ppm. Thus, developmental exposure to DBP affected female sexual development involving pituitary function, while in males testicular toxicity was mostly reversible but mammary gland toxicity was persistent at a dose level as low as 20 ppm.

Environmental and Endogenous Peroxisome Proliferator-Activated Receptor γ Agonists Induce Bone Marrow B Cell Growth Arrest and Apoptosis: Interactions between Mono(2-ethylhexyl)phthalate, 9-cis-Retinoic Acid, and 15-Deoxy-Δ12,14-prostaglandin J2

The common commercial use of phthalate esters has resulted in significant human exposure to these bioactive compounds. The facts that phthalate ester metabolites, like endogenous PGs, are peroxisome proliferator-activated receptor (PPAR) agonists, and that PPARgamma agonists induce lymphocyte apoptosis suggest that phthalate esters are immunosuppressants that could act together with PGs to modulate early B cell development. In this study we examined the effects of a metabolite of one environmental phthalate, mono(2-ethylhexyl)phthalate (MEHP), and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), on developing B cells. MEHP inhibited [(3)H]thymidine incorporation by primary murine bone marrow B cells and a nontransformed murine pro/pre-B cell line (BU-11). Cotreatment with a retinoid X receptor alpha ligand, 9-cis-retinoic acid, decreased [(3)H]thymidine incorporation synergistically, thereby implicating activation of a PPARgamma-retinoid X receptor alpha complex. These results were similar to those obtained with the natural PPARgamma ligand 15d-PGJ(2). At moderate MEHP concentrations (25 or 100 microM for primary pro-B cells and a pro/pre-B cell line, respectively), inhibition of [(3)H]thymidine incorporation resulted primarily from apoptosis induction, whereas at lower concentrations, the inhibition probably reflected growth arrest without apoptosis. Cotreatment of bone marrow B cells with 15d-PGJ(2) and MEHP significantly enhanced the inhibition of [(3)H]thymidine incorporation seen with MEHP alone, potentially mimicking exposure in the bone marrow microenvironment where PG concentrations are high. Finally, MEHP- and 15d-PGJ(2)-induced death does not result from a decrease in NF-kappaB activation. These data demonstrate that environmental phthalates can cooperate with an endogenous ligand, 15d-PGJ(2), to inhibit proliferation of and induce apoptosis in developing bone marrow B cells, potentially via PPARgamma activation.

Human chorionic gonadotropin-dependent regulation of 17beta-hydroxysteroid dehydrogenase type 4 in preovulatory follicles and its potential role in follicular luteinization

17Beta-hydroxysteroid dehydrogenase type 4 (17betaHSD4) has a unique multidomain structure, with one domain involved in 17beta-estradiol inactivation. The objective of the study was to investigate the regulation of 17betaHSD4 during human chorionic gonadotropin (hCG)-induced ovulation/luteinization. The equine 17betaHSD4 cDNA was cloned and was shown to encode a 735-amino acid protein that is highly conserved (81-87% identity) compared with other mammalian orthologs. RT-PCR/Southern blot analyses were performed to study the regulation of 17betaHSD4 transcripts in equine preovulatory follicles isolated between 0-39 h after hCG treatment. Results showed the presence of basal 17betaHSD4 mRNA expression before hCG treatment, but an increase was observed in follicles obtained 24 h after hCG (P < 0.05). Analyses of isolated preparations of granulosa and theca interna cells identified basal mRNA expression in both layers, but granulosa cells appeared as the predominant site of follicular 17betaHSD4 mRNA induction. A specific polyclonal antibody was raised against a fragment of the equine protein and used to study regulation of the 17betaHSD4 protein. Immunoblots showed an increase in full-length 17betaHSD4 protein in follicles 24 h after hCG (P < 0.05), in keeping with mRNA results. Immunohistochemical data confirmed the induction of the enzyme in follicular cells after hCG treatment. Collectively, these results demonstrate that the gonadotropin-dependent induction of follicular luteinization is accompanied by an increase in 17betaHSD4 expression. Considering the estrogen-inactivating function of 17betaHSD4, its regulated expression in luteinizing preovulatory follicles appears as a potential complementary mechanism to reduce circulating levels of 17beta-estradiol after the LH surge.

Activation of PPARalpha and PPARgamma by environmental phthalate monoesters

Phthalate esters are widely used as plasticizers in the manufacture of products made of polyvinyl chloride. Mono-(2-ethylhexyl)-phthalate (MEHP) induces rodent hepatocarcinogenesis by a mechanism that involves activation of the nuclear transcription factor peroxisome proliferator-activated receptor-alpha (PPARalpha). MEHP also activates PPAR-gamma (PPARgamma), which contributes to adipocyte differentiation and insulin sensitization. Human exposure to other phthalate monoesters, including metabolites of di-n-butyl phthalate and butyl benzyl phthalate, is substantially higher than that of MEHP, prompting this investigation of their potential for PPAR activation, assayed in COS cells and in PPAR-responsive liver (PPARalpha) and adipocyte (PPARgamma) cell lines. Monobenzyl phthalate (MBzP) and mono-sec-butyl phthalate (MBuP) both increased the COS cell transcriptional activity of mouse PPARalpha, with effective concentration for half-maximal response (EC50) values of 21 and 63 microM, respectively. MBzP also activated human PPARalpha (EC50=30 microM) and mouse and human PPARgamma (EC50=75-100 microM). MEHP was a more potent PPAR activator than MBzP or MBuP, with mouse PPARalpha more sensitive to MEHP (EC50=0.6 microM) than human PPARalpha (EC50=3.2 microM). MEHP activation of PPARgamma required somewhat higher concentrations, EC50=10.1 microM (mouse PPARgamma) and 6.2 microM (human PPARgamma). No significant PPAR activation was observed with the monomethyl, mono-n-butyl, dimethyl, or diethyl esters of phthalic acid. PPARalpha activation was verified in FAO rat liver cells stably transfected with PPARalpha, where expression of several endogenous PPARalpha target genes was induced by MBzP, MBuP, and MEHP. Similarly, activation of endogenous PPARgamma target genes was evidenced for all three phthalates by the stimulation of PPARgamma-dependent adipogenesis in the 3T3-L1 cell differentiation model. These findings demonstrate the potential of environmental phthalate monoesters for activation of rodent and human PPARs and may help to elucidate the molecular basis for the adverse health effects proposed to be associated with human phthalate exposure.