Teratogenic phthalate esters and metabolites activate the nuclear receptors PPARs and induce differentiation of F9 cells

Combination of computational new approach methodologies for enhancing evidence of biological pathway conservation across species

The ability to predict which chemicals are of concern for environmental safety is dependent, in part, on the ability to extrapolate chemical effects across many species. This work investigated the complementary use of two computational new approach methodologies to support cross-species predictions of chemical susceptibility: the US Environmental Protection Agency Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) tool and Unilever's recently developed Genes to Pathways - Species Conservation Analysis (G2P-SCAN) tool. These stand-alone tools rely on existing biological knowledge to help understand chemical susceptibility and biological pathway conservation across species. The utility and challenges of these combined computational approaches were demonstrated using case examples focused on chemical interactions with peroxisome proliferator activated receptor alpha (PPARα), estrogen receptor 1 (ESR1), and gamma-aminobutyric acid type A receptor subunit alpha (GABRA1). Overall, the biological pathway information enhanced the weight of evidence to support cross-species susceptibility predictions. Through comparisons of relevant molecular and functional data gleaned from adverse outcome pathways (AOPs) to mapped biological pathways, it was possible to gain a toxicological context for various chemical-protein interactions. The information gained through this computational approach could ultimately inform chemical safety assessments by enhancing cross-species predictions of chemical susceptibility. It could also help fulfill a core objective of the AOP framework by potentially expanding the biologically plausible taxonomic domain of applicability of relevant AOPs.

Phthalate monoesters act through peroxisome proliferator-activated receptors in the mouse ovary

Widespread use of phthalates as solvents and plasticizers leads to everyday human exposure. The mechanisms by which phthalate metabolites act as ovarian toxicants are not fully understood. Thus, this study tested the hypothesis that the phthalate metabolites monononyl phthalate (MNP), monoisononyl phthalate (MiNP), mono(2-ethylhexyl) phthalate (MEHP), monobenzyl phthalate (MBzP), monobutyl phthalate (MBP), monoisobutyl phthalate (MiBP), and monoethyl phthalate (MEP) act through peroxisome proliferator-activated receptors (PPARs) in mouse granulosa cells. Primary granulosa cells were isolated from CD-1 mice and cultured with vehicle control (dimethyl sulfoxide) or MNP, MiNP, MEHP, MBzP, MBP, MiBP, or MEP (0.4-400 μM) for 24 h. Following culture, qPCR was performed for known PPAR targets, Fabp4 and Cd36. Treatment with the phthalate metabolites led to significant changes in Fabp4 and Cd36 expression relative to control in dose-dependent or nonmonotonic fashion. Primary granulosa cell cultures were also transfected with a DNA plasmid containing luciferase expressed under the control of a consensus PPAR response element. MNP, MiNP, MEHP, and MBzP caused dose-dependent changes in expression of luciferase, indicating the presence of functional endogenous PPAR receptors in the granulosa cells that respond to phthalate metabolites. The effects of phthalate metabolites on PPAR target genes were inhibited in most of the cultures by co-treatment with the PPAR-γ inhibitor, T0070907, or with the PPAR-α inhibitor, GW6471. Collectively, these data suggest that some phthalate metabolites may act through endogenous PPAR nuclear receptors in the ovary and that the differing structures of the phthalates result in different levels of activity.

Phthalate Exposure, PPARα Variants, and Neurocognitive Development of Children at Two Years

Background: The PPARα gene may be crucial to the neurotoxic effect of phthalates. However, epidemiological studies considering the neurodevelopmental influence of phthalates interacting with genetic susceptibility are limited. We hypothesized phthalates could interact with the PPARα gene, synergistically affecting neurocognitive development.

Methods: A total of 961 mother-infant pairs were involved in this study. The concentrations of phthalate metabolites in maternal urine during pregnancy were detected. Children’s neurocognitive development was estimated with the Bailey Infant Development Inventory (BSID). Genetic variations in PPARα were genotyped with the Illumina Asian Screening Array. We applied generalized linear regression models to estimate genotypes and phthalate metabolites’ association with children’s neurocognitive development.

Results: After adjusting for potential confounders, the mono-n-butyl phthalate (MnBP) concentration was negatively associated with Psychomotor Development Index (PDI) (β = −0.86, 95% CI: −1.67, −0.04). The associations between MnBP and neurocognitive development might be modified by PPARα rs1800246. Compared with low-MnBP individuals carrying rs1800246 GG genotypes, high-MnBP individuals with the AG + AA genotype had a higher risk of neurocognitive developmental delay, with the odds ratio of 2.76 (95% CI:1.14, 6.24).

Conclusions: Our current study revealed that prenatal exposure to MnBP was negatively correlated with children’s neurocognitive development, and PPARα rs1800246 might modify the association.

Reproductive toxic potential of phthalate compounds - State of art review

Phthalates are pervasive compounds, and due to the ubiquitous usage of phthalates, humans or even children are widely exposed to them. Since phthalates are not chemically bound to the plastic matrix, they can easily leach out to contaminate the peripheral environment. Various animal and human studies have raised vital health concern including developmental and reproductive toxicity of phthalate exposure. The present review is based upon the available literature on phthalates with respect to their reproductive toxic potential. Common reproductive effects such as declined fertility, reduced testis weight, variations in accessory sex organs and several female reproductive disorders appeared to be largely associated with the transitional phthalates. Among the higher molecular weight phthalates (≥ C7), di-isononyl phthalate (DINP) produces some minor effects on development of male reproductive tract and among low molecular weight phthalates (≤C3), di-methyl (DMP) and di-isobutyl (DIBP) phthalate produce some adverse effects on male reproductive system. Whereas transitional phthalates such as di-butyl phthalate, benzyl butyl phthalate, and di-(2-ethylhexyl) phthalate have shown adverse effects on female reproductive system. Owing to these, non-toxic alternatives to phthalates may be developed and use of phthalates could be rationalized as an important issue where human reproduction system is involved. Though, more epidemiological studies are needed to substantiate the reported findings on phthalates.

The effects of a phthalate metabolite mixture on antral follicle growth and sex steroid synthesis in mice

Phthalates are used as solvents and plasticizers in a wide variety of consumer products. Most people are exposed to phthalates as parent compounds through ingestion, inhalation, and dermal contact. However, these parent compounds are quickly metabolized to more active compounds in several tissues. Although studies indicate that phthalate metabolites reach the ovary, little is known about whether they are ovarian toxicants. Thus, this study tested the hypothesis that phthalate metabolites influence the expression of genes involved in sex steroid synthesis, cell cycle regulation, cell death, oxidative stress, and key receptors, as well as production of sex steroid hormones by mouse antral follicles. The selected metabolite mixture consisted of 36.7% monoethyl phthalate (MEP), 19.4% mono(2-ethylhexyl) phthalate (MEHP), 15.3% monobutyl phthalate (MBP), 10.2% monoisobutyl phthalate (MiBP), 10.2% monoisononyl phthalate (MiNP), and 8.2% monobenzyl phthalate (MBzP). Antral follicles from adult CD-1 mice were cultured for 96 h with vehicle control (DMSO) or metabolite mixture (0.065-325 μg/mL). Growth of follicles in culture was monitored every 24 h. Total RNA was isolated after 24 and 96 h and used for gene expression analysis. Media were collected and subjected to hormone analysis. Exposure to the phthalate mixture inhibited follicle growth, decreased expression of steroidogenic enzymes, and altered the levels of sex steroids relative to control. The mixture, primarily at the two highest doses, also altered expression of cell cycle regulators, apoptotic factors, oxidative stress genes, and some receptors. Collectively, these data suggest that mixtures of phthalate metabolites can directly impact follicle health.

The association between prenatal exposure to phthalates and cognition and neurobehavior of children-evidence from birth cohorts

BACKGROUND

Phthalate have been detected widely in the environment; while several studies have indicated that prenatal phthalate exposure has adverse effects on neurodevelopment, the results were inconsistent.

OBJECTIVE

We aimed to determine the current research status of the relationship between prenatal exposure to different types of phthalate and cognition and behavioral development in children. We conducted a systematic review to evaluate the current state of knowledge.

METHODS

We systematically searched PubMed, Web of Science, and EMBASE electronic databases up to May 2018 with manual searches of the references of retrieved publications and relevant reviews. Only birth cohort studies that reported on the association between phthalate exposure and cognitive or behavioral development were included in this review. We evaluated the risk of bias for each of the included studies using a modified instrument based on the Cochrane Collaboration's "Risk of Bias" tool.

RESULT

Twenty-six birth cohort studies met our inclusion criteria, nine of which investigated the impact of phthalate exposure during pregnancy on cognition, 13 on neurobehavior, and 4 on both cognition and neurobehavior. However, ten articles reported that the effect of prenatal exposure to phthalates on cognitive development was statistically significant, 15 articles reported that the effect of prenatal exposure to phthalates on neurobehavior was statistically significant. The effect of prenatal phthalate exposure on neurodevelopment differed according to sex, but the results are inconsistent, for instance, among the five studies investigating the association between mental development index (MDI) and Mono-n-butyl phthalate (MnBP), two of them showed a significantly decreasing MDI scores with increasing concentrations of MnBP among girls, but among boys one study showed the inverse association, another showed the positive association.

CONCLUSION

Di(2-ethylhexyl) phthalate, dibutyl phthalate, butyl-benzyl phthalate and di-ethyl phthalate exposure during pregnancy was associated with lower cognitive scores and worse behavior in offspring, and sex-specific effects on cognitive, psychomotor, and behavioral development were identified, especially the impact of phthalate exposure on neurobehavior in boys.

The Role of Dietary Phytoestrogens and the Nuclear Receptor PPARγ in Adipogenesis: An in Vitro Study

BACKGROUND

Phytoestrogens, naturally occurring plant chemicals, have long been thought to confer beneficial effects on human cardiovascular and metabolic health. However, recent epidemiological studies, have yielded conflicting outcomes, in which phytoestrogen consumption was both positively and negatively correlated with adiposity. Interestingly, several dietary phytoestrogens are known to stimulate or inhibit the activity of the peroxisome proliferator-activated receptor gamma (PPARγ), a key physiological regulator of adipogenesis.

OBJECTIVE

The objective of this study was to test the hypothesis that the pro- or anti-adipogenic activity of phytoestrogen chemicals is related to the ability to activate PPARγ in adipocytes.

METHODS

The effects of resveratrol and the soy isoflavones genistein and daidzein on adipogenesis were examined in cell-based assays using the 3T3-L1 cell model. In parallel, ligand-mediated alterations in PPARγ target gene expression were measured by quantitative polymerase chain reaction. The agonist/antagonist activities of phytoestrogens on PPARγ were further assessed by quantifying their ability to affect recruitment of transcriptional cofactors to the receptor.

RESULTS

Resveratrol displayed significant anti-adipogenic activities as exhibited by the ability to antagonize PPARγ-dependent adipocyte differentiation, down-regulate genes involved in lipid metabolism, block cofactor recruitment to PPARγ, and antagonize the effects of the PPARγ agonist rosiglitazone. In contrast, genistein and daidzein functioned as PPARγ agonists while also displaying pro-adipogenic activities.

CONCLUSIONS

These data provide biological evidence that the pro- or anti-obesity effects of phytoestrogens are related to their relative agonist/antagonist activity on PPARγ. Thus, PPARγ-activation assays may enable the screening of dietary components and identification of agents with adipogenic activities. https://doi.org/10.1289/EHP3444.

Prenatal and postnatal exposure to di-(2-ethylhexyl) phthalate and neurodevelopmental outcomes: A systematic review and meta-analysis

BACKGROUND

Di-(2-ethylhexyl) phthalate (DEHP), the most widely used phthalate, has recently been associated with neurodevelopmental disturbances in children. However, the risk is yet to be quantified. Therefore, a systematic review and meta-analysis focusing on the association between exposure to DEHP and neurodevelopmental outcomes is necessary, with particular attention to study design (longitudinal vs. cross-sectional).

METHODS

We performed a comprehensive literature search for associations between exposure to DEHP and neurodevelopmental outcomes. Among 106 published studies found in public databases, eight longitudinal studies and two cross-sectional studies were included in the meta-analysis.

RESULTS

We observed a statistically significant association between the concentrations of DEHP metabolites and the neurodevelopment outcomes of children among cross-sectional results, and found significant association between DEHP exposure measured in prenatal period and the psychomotor development outcomes measured later in childhood.

CONCLUSIONS

To our knowledge, this is the first meta-analysis of studies investigating the association between DEHP exposure and neurodevelopment in children. A need exists for more researches and a precautionary policy for potential health hazard of DEHP, the most commonly used phthalate, to promote healthier neurodevelopment in children.

Dietary sources of cumulative phthalates exposure among the U.S. general population in NHANES 2005-2014

BACKGROUND

Anti-androgenic phthalates are reproductive toxicants that may have additive effects on male development. Diet is the primary exposure source for most phthalates, which contaminate the food supply through food contact materials and industrialized production.

OBJECTIVE

To compare dietary sources of cumulative phthalates exposure between "food at home" (e.g. food consumed from a grocery store) and "food away from home" (e.g. food consumed from fast food/restaurants and cafeterias) in the U.S. general population.

METHODS

We estimated cumulative phthalates exposure by calculating daily intake from metabolite concentrations in urinary spot samples for 10,253 participants (≥6 years old) using National Health and Nutrition Examination Survey (NHANES, 2005-2014) data. We constructed a biologically relevant metric of phthalates daily intake (∑androgen-disruptor, μg/kg/day) by converting phthalates into anti-androgen equivalent terms prior to their summation. Particular foods and the percent of total energy intake (TEI) consumed from multiple dining out sources were ascertained from 24-h recall surveys. Associations with ∑androgen-disruptor levels were estimated for children, adolescents, and adults using multivariable linear regression.

RESULTS

We observed a consistent positive association between dining out and Σandrogen-disruptor levels across the study population (p-trend <0.0001). Among adolescents, high consumers of foods outside the home had 55% (95% CI: 35%, 78%) higher Σandrogen-disruptor levels compared to those who only consumed food at home. The contribution of specific dining out sources to Σandrogen-disruptor levels varied by age group. For example, cafeteria food was associated with 15% (95% CI: 4.0%, 28%) and 64% (95% CI: 40%, 92%) higher Σandrogen-disruptor levels in children and adults, respectively. Particular foods, especially sandwiches (i.e. cheeseburgers), were associated with increased Σandrogen-disruptor levels only if they were purchased away from home (p < 0.01).

CONCLUSION

Dining out may be an important source of biologically relevant cumulative phthalates exposure among the U.S.

POPULATION

Future studies should evaluate modifiable production practices that remove phthalates from the food supply in addition to the efficacy of interventions that promote eating fresh foods prepared at home.

Proposed Mode of Action for In Utero Effects of Some Phthalate Esters on the Developing Male Reproductive Tract

Phthalate esters containing a straight-chain backbone of 4–6 carbons have demonstrated testicular toxicity and infertility in adult and pre-adolescent rats, mice, hamsters, and ferrets. In recent years, these same phthalates have been shown to interfere with the normal development of the male reproductive tract in rodents and rabbits. The review presented here summarizes studies that provide evidence of a mode of action for these effects. The data indicate that C4–C6 phthalate esters inhibit processes in the Leydig cell, such as the synthesis of testosterone (T) and production of insulin-like factor 3 (insl3), both of which are required for normal development of male genitalia. A proposed secondary effect of reduced androgen production is on Sertoli cells, resulting in failure to proliferate and interference with cell-cell communication (gap-junction intracellular communication) leading to the development of large multinucleate gonocytes. The possibility that phthalates act directly on the Sertoli cells to interfere with intracellular communication is not excluded. The strength, consistency, and plausibility of the proposed mode of action and alternate modes of action are discussed.

In vivo chronic and in vitro acute effects of di(2-ethylhexyl) phthalate on pseudopregnant rabbit corpora lutea: possible involvement of peroxisome proliferator-activated receptor gamma

The in vivo chronic and in vitro acute effects of di(2-ethylhexyl) phthalate (DEHP) on the reproductive function of peroxisome proliferator-activated receptor gamma (PPARG) were studied in rabbit corpora lutea (CL) at early stage (Day 4), midstage (Day 9), and late stage (Day 13) of pseudopregnancy. The rabbits were in vivo treated with DEHP for 15 days before induction of pseudopregnancy. Immunohistochemistry provided evidence for the presence of PPARG, prostaglandin endoperoxide synthase 1 (PTGS1), PTGS2, prostaglandin E2-9-ketoreductase (PGE2-9-K), and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in all the luteal cells during pseudopregnancy. DEHP decreased progesterone plasma levels and CL production in all the luteal stages and PPARG protein and gene expressions in early and mid-CL. DEHP in vivo treatment reduced PTGS2 protein expression at the late stage and that of PGE2-9-K at all the stages, whereas PTGS1 and 3beta-HSD were not affected. In in vitro cultured CL, DEHP alone, the PPARG antagonist T0070907 alone, or DEHP plus T0070907 diminished progesterone production and 3beta-HSD activity and increased PGF2alpha and PTGS2 in early and mid-CL, whereas DEHP plus the PPARG agonist 15d-PGJ2 did not affect these hormones and enzymes. All the in vitro treatments did not affect PGE2 secretion as well as PTGS1 and PGE2-9-K enzymatic activities in all the luteal stages. These results provided evidence that DEHP favors functional luteolysis of pseudopregnant rabbit CL, with a mechanism that seems to involve PPARG expression down-regulation, an increase of PTGS2 activity and prostaglandin F2alpha secretion, 3beta-HSD down-regulation, and decrease in progesterone.

Phthalate levels in cord blood are associated with preterm delivery and fetal growth parameters in Chinese women

Data concerning the effects of phthalate exposure on preterm delivery and fetal growth are limited in humans. In this paper, we assessed the relationship between 15 phthalate levels in cord blood and preterm delivery and fetal growth parameters in 207 Chinese women going into labor. Exposure to phthalates except DCHP was associated with gestational age reduction and preterm delivery (p<0.05). There were associations between phthalates and fetal growth parameters, many of which disappeared when analyses were adjusted for gestational age, especially in male infants (Only DEEP was associated with birth weight; DEP, DNHP, BBP, DNP with abdominal circumference; DEP, DBP, DCHP, DEHP with femur length in female infants. And DPP, DBEP was associated with birth length in male infants. p<0.05). This study indicates that prenatal exposure to phthalates is associated with younger gestational age and preterm delivery. Also, phthalate exposure may adversely affect fetal growth parameters via gestational age reduction and preterm delivery with a significant gender effect.

Differential effects of environmental chemicals and food contaminants on adipogenesis, biomarker release and PPARγ activation

Eleven environmental relevant chemicals were investigated for their ability to affect adipogenesis in vitro, biomarker release from adipocytes and PPARα and γ activation. We found that butylparaben stimulated adipogenesis in 3T3-L1 adipocytes and increased release of leptin, adiponectin and resistin from the cells. Butylparaben activated PPARγ as well, which may be a mediator of the adipogenic effect. Polychlorinated biphenyl (PCB)153 also stimulate adipogenesis and biomarker release, but did not affect PPARs. The data indicates that PPARγ activating chemicals often stimulate adipocyte differentiation although PPARγ activation is neither a requirement nor a guarantee for stimulation. Four out of the eleven chemicals (bisphenol A, mono-ethylhexyl phthalate, butylparaben, PCB 153) caused increased adipogenesis. The release of adipocyte-secreted hormones was sometimes but not always correlated with the effect on adipocyte differentiation. Eight chemicals were able to cause increased leptin release. These findings strengthen the hypothesis that chemicals can interfere with pathways related to obesity development.

Chronic exposure to contaminated drinking water stimulates PPAR expression in mice livers

Mice were fed with source water (SW) and tap water (TW) for 90 d to evaluate hepatotoxicity induced by the drinking water. Histopathologic observation showed no obvious damage to hepatic tissue in the SW and TW groups. However, microarray analysis indicated that the SW and TW exposures affected many metabolic pathways, among which PPAR (peroxisome proliferator-activated receptors) signaling was most susceptible. Immunohistochemical staining demonstrated that both PPAR-α and PPAR-γ were significantly increased in the exposure groups compared to control. Enzyme-linked immunosorbent assay revealed that PPAR-α expression level was increased from 23.37±0.53 ng g(-1) liver weight in control group to 26.60±1.43 ng g(-1) liver weight in SW group and 27.68±1.10 ng g(-1) liver weight in TW group (p<0.05). For PPAR-γ, the expression level was also significantly enhanced from 0.83±0.07 ng g(-1) liver weight in control group to 1.11±0.20 ng g(-1) liver weight in SW group and 1.16±0.07 ng g(-1) liver weight in TW group (p<0.05). The SW and DW posed no obvious hepatotoxicity on mice and PPAR-α/-γ could be used as a novel biomarker to assess public health risk induced by slightly contaminated drinking water.

Associations between circulating levels of bisphenol A and phthalate metabolites and coronary risk in the elderly

Studies have pointed out associations between various chemicals with estrogenic activity and cardiovascular disease. Being ubiquitous, the plastic additive substances bisphenol A (BPA), and phthalates have been detected in almost all types of analyzed human samples. The aim of this study was to investigate whether circulating levels of BPA and/or four selected phthalate metabolites are associated to coronary risk in an elderly population. In the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study, coronary risk was assessed by the Framingham Risk Score (FRS) together with circulating serum levels of BPA and the four phthalate metabolites monoisobutyl phthalate (MiBP), monomethyl phthalate (MMP), monoethyl phthalate (MEP), mono-(2-ethylhexyl) phthalate (MEHP) in 1016 subjects aged 70 years. BPA, MEHP, and MMP were associated to LDL-cholesterol and MEHP to HDL-cholesterol, MEP to diastolic blood pressure and MiBP to fasting glucose when the compounds were investigated one by one. After Bonferronni correction, only the relations for MMP to LDL-cholesterol (p<0.0001), MEP to diastolic blood pressure (p<0.0002), and MiBP to fasting glucose (p<0.0001) remained significant. MMP was associated to the FRS (p=0.02), but after Bonferronni correction, this association was not significant. In conclusion, associations were found between MMP and LDL-cholesterol, MEP and diastolic blood pressure, and MiBP and fasting glucose. We did not observe any strong associations between BPA nor any of the four phthalate metabolites and Framingham Risk Score in this elderly population.

Mechanistic considerations for human relevance of cancer hazard of di(2-ethylhexyl) phthalate

Di(2-ethylhexyl) phthalate (DEHP) is a peroxisome proliferator agent that is widely used as a plasticizer to soften polyvinylchloride plastics and non-polymers. Both occupational (e.g., by inhalation during its manufacture and use as a plasticizer of polyvinylchloride) and environmental (medical devices, contamination of food, or intake from air, water and soil) routes of exposure to DEHP are of concern for human health. There is sufficient evidence for carcinogenicity of DEHP in the liver in both rats and mice; however, there is little epidemiological evidence on possible associations between exposure to DEHP and liver cancer in humans. Data are available to suggest that liver is not the only target tissue for DEHP-associated toxicity and carcinogenicity in both humans and rodents. The debate regarding human relevance of the findings in rats or mice has been informed by studies on the mechanisms of carcinogenesis of the peroxisome proliferator class of chemicals, including DEHP. Important additional mechanistic information became available in the past decade, including, but not limited to, sub-acute, sub-chronic and chronic studies with DEHP in peroxisome proliferator-activated receptor (PPAR) α-null mice, as well as experiments utilizing several transgenic mouse lines. Activation of PPARα and the subsequent downstream events mediated by this transcription factor represent an important mechanism of action for DEHP in rats and mice. However, additional data from animal models and studies in humans exposed to DEHP from the environment suggest that multiple molecular signals and pathways in several cell types in the liver, rather than a single molecular event, contribute to the cancer in rats and mice. In addition, the toxic and carcinogenic effects of DEHP are not limited to liver. The International Agency for Research on Cancer working group concluded that the human relevance of the molecular events leading to cancer elicited by DEHP in several target tissues (e.g., liver and testis) in rats and mice can not be ruled out and DEHP was classified as possibly carcinogenic to humans (Group 2B).

Genomic biomarkers of phthalate-induced male reproductive developmental toxicity: a targeted RT-PCR array approach for defining relative potency

Male rat fetuses exposed to certain phthalate esters (PEs) during sexual differentiation display reproductive tract malformations due to reductions in testosterone (T) production and the expression of steroidogenesis- and INSL3-related genes. In the current study, we used a 96-well real-time PCR array containing key target genes representing sexual determination and differentiation, steroidogenesis, gubernaculum development, and androgen signaling pathways to rank the relative potency of several PEs. We executed dose-response studies with diisobutyl (DIBP), dipentyl (DPeP), dihexyl (DHP), diheptyl (DHeP), diisononyl (DINP), or diisodecyl phthalate (DIDP) and serial dilutions of a mixture of nine phthalates. All phthalates, with the exception of DIDP, reduced fetal testicular T production. Several genes involved in cholesterol transport, androgen synthesis, and Insl3 also were downregulated in a dose-responsive manner by DIBP, DPeP, DHP, DHeP, DINP, and the 9-PE mixture. Despite speculation of peroxisome proliferator activated receptor (PPAR) involvement in the effects of PEs on the fetal testis, no PPAR-related genes were affected in the fetal testes by exposure to any of the tested PEs. Furthermore, the potent PPARα agonist, Wy-14,643, did not reduce fetal testicular T production following gestational day 14-18 exposure, suggesting that the antiandrogenic activity of PEs is not PPARα mediated. The overall sensitivity of the fetal endpoints (gene expression or T production) for the six phthalates from most to least was Cyp11b1 > Star = Scarb1 > Cyp17a1 = T production > Cyp11a1 = Hsd3b = Insl3 > Cyp11b2. The overall potency of the individual phthalates was DPeP > DHP > DIBP ≥ DHeP > DINP. Finally, the observed mixture interaction was adequately modeled by the dose-addition model for most of the affected genes. Together, these data advance our understanding of the collective reproductive toxicity of the PE compounds.

Tributyltin is a potent inhibitor of piscine peroxisome proliferator-activated receptor α and β

Increasing evidence suggests that common environmental contaminants can act as endocrine disrupters in fish. However, current data are biased towards environmental estrogens, highlighting the need to elucidate potential pollutant impact on other endocrine axes. Here, we report a high-throughput assay to identify chemicals interacting with piscine peroxisome proliferator-activated receptors (PPARs). Our transactivation assay employs a fish cell line and uses recombinant proteins combining the yeast Gal4 DNA-binding domain with the ligand-binding domain of PPARs from plaice (Pleuronectes platessa). Compared to assays with full-length PPARs, this approach circumvents interaction of chemicals binding to retinoid X receptors, which form heterodimers with PPAR and many other nuclear receptors. Plaice PPARα and PPARβ are activated by fibrate drugs and by phthalate mono-esters at concentrations similar to those activating the homologous mammalian receptors. In line with their assumed role as central transcriptional regulators of energy homeostasis, a number of fatty acids activate plaice PPARα and PPARβ. In contrast, tributyl tin oxide (TBTO) is a potent antagonist of PPARα and PPARβ, showing activity at environmentally relevant concentrations of TBTO (1-50 nM). Given the ubiquitous and persistent nature of TBTO, the possibility that chronic environmental effects are occurring via disruption of PPAR signalling in fish should be further investigated.

Endocrine disruptors, environmental oxygen, epigenetics and pregnancy

The placenta and its myriad functions are central to successful reproductive outcomes. These functions can be influenced by the environment encountered throughout pregnancy, thereby altering the appropriate genetic programming needed to allow for sustained pregnancy and appropriate fetal development. This altered programming may result from epigenetic alterations related to environmental exposures. Epigenetic alterations are now being linked to several important reproductive outcomes, including early pregnancy loss, intrauterine growth restriction, congenital syndromes, preterm birth, and preeclampsia. The diversity of environmental exposures linked to adverse reproductive effects continues to grow. Much attention has focused on the role of endocrine disruptors in infertility, but recent work suggests that these chemicals may also have adverse effects in pregnancy and development. Environmental oxygen is also critical in pregnancy success. There are clear links between altered oxygen levels and placentation amongst other effects. As research continues to enhance our understanding of the molecular processes including epigenetic regulation that influence pregnancy, it will be critical to specifically examine how the environment, broadly defined, may play a role in altering these critical functions.

A recombinant peroxisome proliferator response element-driven luciferase assay for evaluation of potential environmental obesogens

A recombinant Huh7-PPRE-Luc cell line for analyzing the peroxisome proliferator response element (PPRE)-driven luciferase activity was established. The cells exhibited a good dose-response induction in PPRE-driven luciferase activity by three subtypes of peroxisome proliferator-activated receptor (PPAR) agonists as well as by a retinoid X receptor agonist, 9-cis-retinoic acid. Among five environmental chemicals tested, benzyl butyl phthalate and bisphenol induced PPRE-driven luciferase activation in Huh7-PPRE-Luc cells and caused adipogenic differentiation of 3T3-L1 cells. This recombinant Huh7-PPRE-Luc cell line would be useful for screening potential environmental obesogens with PPAR activity.

Improving in vitro Sertoli cell/gonocyte co-culture model for assessing male reproductive toxicity: Lessons learned from comparisons of cytotoxicity versus genomic responses to phthalates

Gonocytes exist in the neonatal testis and represent a transient population of male germ-line stem cells. It has been shown that stem cell self-renewal and progeny production is probably controlled by the neighboring differentiated cells and extracellular matrix (ECM) in vivo known as niches. Recently, we developed an in vitro three-dimensional (3D) Sertoli cell/gonocyte co-culture (SGC) model with ECM overlay, which creates an in vivo-like niche and supports germ-line stem cell functioning within a 3D environment. In this study, we applied morphological and cytotoxicity evaluations, as well as microarray-based gene expression to examine the effects of different phthalate esters (PE) on this model. Known in vivo male developmentally toxic PEs (DTPE) and developmentally non-toxic PEs (DNTPE) were evaluated. We observed that DTPE induced significantly greater dose-dependent morphological changes, a decrease in cell viability and an increase in cytotoxicity compared to those treated with DNTPE. Moreover, the gene expression was more greatly altered by DTPE than by DNTPE and non-supervised cluster analysis allowed the discrimination of DTPE from the DNTPE. Our systems-based GO-Quant analysis showed significant alterations in the gene pathways involved in cell cycle, phosphate transport and apoptosis regulation with DTPE but not with DNTPE treatment. Disruptions of steroidogenesis related-gene expression such as Star, Cyp19a1, Hsd17b8, and Nr4a3 were observed in the DTPE group, but not in the DNTPE group. In summary, our observation on cell viability, cytotoxicity, and microarray-based gene expression analysis induced by PEs demonstrate that our in vitro 3D-SGC system mimicked in vivo responses for PEs and suggests that the 3D-SGC system might be useful in identifying developmental reproductive toxicants.

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.

Association of urinary phthalate metabolite concentrations with body mass index and waist circumference: a cross-sectional study of NHANES data, 1999-2002

BACKGROUND

Although diet and activity are key factors in the obesity epidemic, laboratory studies suggest that endocrine disrupting chemicals may also affect obesity.

METHODS

We analyzed associations between six phthalate metabolites measured in urine and body mass index (BMI) and waist circumference (WC) in National Health and Nutrition Examination Survey (NHANES) participants aged 6-80. We included 4369 participants from NHANES 1999-2002, with data on mono-ethyl (MEP), mono-2-ethylhexyl (MEHP), mono-n-butyl (MBP), and mono-benzyl (MBzP) phthalate; 2286 also had data on mono-2-ethyl-5-hydroxyhexyl (MEHHP) and mono-2-ethyl-5-oxohexyl (MEOHP) phthalate (2001-2002). Using multiple regression, we computed mean BMI and WC within phthalate quartiles in eight age/gender specific models.

RESULTS

The most consistent associations were in males aged 20-59; BMI and WC increased across quartiles of MBzP (adjusted mean BMI = 26.7, 27.2, 28.4, 29.0, p-trend = 0.0002), and positive associations were also found for MEOHP, MEHHP, MEP, and MBP. In females, BMI and WC increased with MEP quartile in adolescent girls (adjusted mean BMI = 22.9, 23.8, 24.1, 24.7, p-trend = 0.03), and a similar but less strong pattern was seen in 20-59 year olds. In contrast, MEHP was inversely related to BMI in adolescent girls (adjusted mean BMI = 25.4, 23.8, 23.4, 22.9, p-trend = 0.02) and females aged 20-59 (adjusted mean BMI = 29.9, 29.9, 27.9, 27.6, p-trend = 0.02). There were no important associations among children, but several inverse associations among 60-80 year olds.

CONCLUSION

This exploratory, cross-sectional analysis revealed a number of interesting associations with different phthalate metabolites and obesity outcomes, including notable differences by gender and age subgroups. Effects of endocrine disruptors, such as phthalates, may depend upon endogenous hormone levels, which vary dramatically by age and gender. Individual phthalates also have different biologic and hormonal effects. Although our study has limitations, both of these factors could explain some of the variation in the observed associations. These preliminary data support the need for prospective studies in populations at risk for obesity.

Survey of 2-ethylhexanoic acid in baby food

A solid-phase microextraction method was developed and used to perform a survey of 2-ethylhexanoic acid (2-EHA) in 63 samples of baby food from 13 European Union countries, as well as from Norway and Switzerland. The levels of 2-EHA did not exceed 3.4 mg kg(-1). The concentrations of 2-EHA in 53 samples (84%) were in the range between <0.1 and 0.5 mg kg(-1). Ten samples showed the presence of the compound in the range between 0.5 and 3.4 mg kg(-1). An exposure assessment showed that the intake of 2-EHA does not exceed the tolerable daily intake (TDI) for infants of 6-12 months of age except one occurrence when taking the worst-case food consumption data available and the highest level of contamination of the survey. In the other cases, the levels of 2-EHA are at 13-fold below the TDI.

Computational screening of phthalate monoesters for binding to PPARgamma

Phthalate esters are ubiquitous environmental contaminants that interact with peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptors. Molecular docking and free energy calculations were performed in an effort to identify novel phthalate ligands of PPARgamma, a subtype expressed in a wide range of human tissues. The method was validated using several agonists and partial agonists of PPARgamma, whose binding orientations were correctly reproduced; however, reduced accuracy in docking was observed with ligands of increasing size and flexibility. Improved results were obtained by introduction of a more accurate scoring function based on the all-atom molecular mechanics potential CHARMM and a generalized Born/surface area solvation term ACE (analytical continuum electrostatics). Comparison of the lowest CHARMM/ACE energy of each phthalate vs the logarithm of the experimentally determined EC(50) value for PPARgamma trans-activation yielded a good correlation (R(2) = 0.82). Thus, we can reliably distinguish phthalates that bind and activate PPARgamma from those that do not, with the computational method predicting relative PPARgamma binding activities with some degree of accuracy. We have applied this method to screen a series of 73 mono-ortho-phthalate esters listed in the Available Chemicals Directory. Several putative PPARgamma binding phthalates were identified, including compounds that are known PPARgamma agonists. These findings support the use of computational methods to identify environmental chemicals that warrant further experimental evaluation for PPAR binding and trans-activation potential in cell-based models.

The Toxicology of Ligands for Peroxisome Proliferator-Activated Receptors (PPAR)

Peroxisome proliferator-activated receptors (PPARs) are ligand activated transcription factors that modulate target gene expression in response to endogenous and exogenous ligands. Ligands for the PPARs have been widely developed for the treatment of various diseases including dyslipidemias and diabetes. While targeting selective receptor activation is an established therapeutic approach for the treatment of various diseases, a variety of toxicities are known to occur in response to ligand administration. Whether PPAR ligands produce toxicity via a receptor-dependent and/or off-target-mediated mechanism(s) is not always known. Extrapolation of data derived from animal models and/or in vitro models, to humans, is also questionable. The different toxicities and mechanisms associated with administration of ligands for the three PPARs will be discussed, and important data gaps that could increase our current understanding of how PPAR ligands lead to toxicity will be highlighted.

Mono(2-ethylhexyl)phthalate and mono-n-butyl phthalate activation of peroxisome proliferator activated-receptors alpha and gamma in breast

The phthalates di(2-ethylhexyl)phthalate (DEHP) and di-n-butyl phthalate (DBP) are environmental contaminants with significant human exposures. Both compounds are known reproductive toxins in rodents and DEHP also induces rodent hepatocarcinogenesis in a process believed to be mediated via the peroxisome proliferator-activated receptor alpha (PPARalpha). DEHP and DBP are metabolised to their respective monoesters, mono-(2-ethylhexyl)phthalate (MEHP) and mono-n-butyl phthalate (MBP), which are the active metabolites. MEHP also activates another member of the PPAR subfamily, PPARgamma. The effects of PPARalpha and PPARgamma activation in human breast cells appears to be opposing; PPARalpha activators in breast cells cause an increase in proliferation, while PPARgamma activation in breast cells is associated with differentiation and an inhibition of cell proliferation. Further to this the activation of the PPARs is cell and ligand specific, suggesting the importance of examining the effect of MEHP and MBP on the activation of PPARalpha, PPARbeta and PPARgamma in human breast. We used the common model of human breast cancer MCF-7 and examined the ability of MEHP and MBP to activate human PPARs in this system. The ability of MBP and MEHP to block PPAR responses was also assessed. We found that both human PPARalpha and PPARgamma were activated by MEHP whereas MEHP could not activate PPARbeta. MBP was unable to activate any PPAR isoforms in this breast model, despite being a weak peroxisome proliferator in liver, although MBP was an antagonist for both PPARgamma and PPARbeta. Our results suggest that the toxicological consequences of MEHP in the breast could be complex given the opposing effects of PPARalpha and PPARgamma in human breast cells.

All-trans retinoic acid enhances differentiation and influences permeability of intestinal Caco-2 cells under serum-free conditions

Vitamin A and retinoids are essential nutrients for the differentiation of epithelia. Vitamin A deficiency is accompanied by an impairment in intestinal integrity. We investigated whether retinoids influence the differentiation and permeability of Caco-2 cells under serum-free culture conditions as a model for the intestinal epithelium. Treatment of the Caco-2 cells with retinoic acids (RA) resulted in an increased specific activity, enhanced mRNA expression, and induction of the 5'-flanking promoter activity of the marker enzyme for the differentiation intestinal alkaline phosphatase. Surprisingly, permeability of the Caco-2 monolayer, as measured by transepithelial electric resistance and [3H]-mannitol flux, was found to be enhanced by RA. Treatment with RA had only a slight effect on the mRNA expression of the tight junction-associated proteins occludin, ZO-1, claudin-1, -3, and -4, but enhanced the expression of claudin-2, which was recently suggested to form a paracellular ion channel. The role of retinoids as potent inducers of epithelial differentiation was confirmed for the Caco-2 cells under serum-free culture conditions and it was concluded that IAP is a target gene of RA. The inverse regulation of the permeability by RA under these serum-free conditions showed that other mechanisms, which are essential to regulate intestinal epithelial integrity with respect to decreased permeability, have to be identified.

Molecular and cellular effects of cis-9, trans-11-conjugated linoleic acid in enterocytes: Effects on proliferation, differentiation, and gene expression

It has been hypothesized that dietary conjugated linoleic acids (CLA) may inhibit colon tumorigenesis. The aim of our study was to investigate the cellular and molecular effects of cis-9 (9Z), trans-11 (11E)-CLA on the proliferation, differentiation, interaction with peroxisome proliferator-activated receptors (PPARs), and expression of genes relevant in the APC-beta-catenin-TCF4 signalling pathway in human HT-29 and Caco-2 colon cells. We found that 9Z,11E-CLA inhibited the proliferation of HT-29 and Caco-2 cells. Trans-vaccenic acid (VA) showed no antiproliferative effects at all. We determined that 9Z,11E-CLA induced cell differentiation as measured by intestinal alkaline phosphatase (IAP) enzyme activity in Caco-2 cells, mRNA expression of IAP, and activation of a 5' flanking region of IAP. The 9Z,11E-CLA activated human PPARdelta as measured in a reporter gene assay. Treatment of HT29 cells in the poliferation phase with 9Z,11E-CLA repressed mRNA-expression of proliferation genes such as c-myc, cyclin D1 and c-jun in a concentration dependent manner. The promoter activities of c-myc and AP1 were also inhibited after incubation with 9Z,11E-CLA. beta-Catenin mRNA and protein expression was also repressed by the treatment with 9Z,11E-CLA. In addition, the mRNA expression of PPARdelta was repressed by treatment of the HT-29 cells with 9Z,11E-CLA. We conclude that 9Z,11E-CLA has an antiproliferative effect at the cellular and molecular levels in human colon cells. The results indicate that the preventive effects of CLA in the development of colon cancer may be due to their downregulation of some target genes of the APC-beta-catenin-TCF-4- and PPARdelta signalling pathway.

Role of PPARα in mediating the effects of phthalates and metabolites in the liver

Phthalate esters belong to a large class of compounds known as peroxisome proliferators (PP). PP include chemicals that activate different subtypes of the peroxisome proliferator-activated receptor (PPAR) family. The ability of phthalate esters and their metabolites to activate responses through different PPAR subtypes is not fully characterized. We investigated the ability of two phthalate esters di-(2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP) and selected metabolites to activate PPAR (alpha, beta/delta, gamma) using a transient transfection assay. The monoester of DEHP, mono-(2-ethylhexyl) phthalate (MEHP) activated all three subtypes of PPAR, but preferentially activated PPARalpha. A second metabolite of DEHP, 2-ethylhexanoic acid (2-EHXA) was a weaker activator of all three subtypes. DBP, but not the primary metabolite mono-n-butyl phthalate weakly activated all three PPAR subtypes. MEHP and DBP but not DEHP and MBP interacted directly with human PPARalpha and PPARgamma as determined by scintillation proximity assays. Both DEHP and DBP activated expression of PP-inducible gene products in wild-type but not PPARalpha-null mice suggesting that both of these phthalates exert their effects by activation of PPARalpha in vivo. The preferential activation of PPARalpha by phthalate ester metabolites suggests that these phthalates mediate their toxic effects in rodent liver in a manner indistinguishable from other PP.

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.

Altered expression of genes related to zinc homeostasis in early mouse embryos exposed to di-2-ethylhexyl phthalate

Numerous studies have shown that di-2-ethylhexyl phthalate (DEHP) is teratogenic in animals but the mechanism of developmental toxicity is not well understood. One hypothesis is altered zinc homeostasis. The present study has investigated the effect of DEHP exposure on several key genes in zinc metabolism (MT-I, MT-II, ZnT-1) for early mouse embryos exposed in utero. Time- and dose-dependent effects were examined using expression polymerase chain reaction (PCR) (relative to ACTB) and Western blot analysis of the maternal liver, embryonic brain, and visceral yolk sac at 9 days post-coitus (d.p.c.). Maternal exposure to 800 mg/kg DEHP increased the abundance of MT-I and MT-II transcripts in maternal liver at 3.0, 4.5 and 6.0 h after administration. MT-I and MT-II protein induction was confirmed by Western blot analysis. On the other hand, this exposure down-regulated both transcripts (MT-I, MT-II), as well as transcripts for a zinc transporter (ZnT-1), in the embryonic brain, but not the visceral yolk sac. To examine dose-response relationships, the experiment was repeated for DEHP exposures of 50, 200 and 800 mg/kg. The effect to MT-I and MT-II expression in the maternal liver became significant at the 200 mg/kg dose level. The contrasting effect to MT-I, MT-II and ZnT-1 expression in the embryo was also dose-dependent, and a benchmark computation for the dose resulting in a 5% change in the mean (BMD5) was estimated as 11.6 mg/kg for MT-I, 8.9 mg/kg for MT-II, and 6.6 mg/kg for ZnT-1. We conclude that DEHP exposure to pregnant dams at reasonably low levels during organogenesis stages can alter the expression of several key genes in embryonic zinc homeostasis.

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.

Occurrence of 2-ethylhexanoic acid in foods packed in glass jars

After simultaneous distillation-extraction (SDE) of commercial baby foods (n = 20) and fruit juices (n = 15) (among them 15 and eight products labelled 'organic', respectively) from 11 different suppliers, analyses performed by coupled capillary gas chromatography-mass spectrometry (GC-MS) revealed the presence of 2-ethylhexanoic acid (2-EHA), a known teratogenic compound. 2-EHA was found in 80 and 73% of the baby foods and fruit juices, respectively. Amounts ranged from 0.25 to 3.2 mg kg(-1)(average, 0.55 mg kg(-1)) and from 0.01 to 0.59 mg l(-1) (average, 0.18 mg l(-1)) in baby foods and fruit juices, respectively. GC-MS analysis of the SDE extracts obtained from the plastic gaskets inside the metal lids of the samples under study revealed the gaskets to be the origin of 2-EHA. As shown from the non-contaminated samples under study, obviously technology is available to avoid 2-EHA contamination of glass jar-packed food.