An Investigation of the Single and Combined Phthalate Metabolite Effects on Human Chorionic Gonadotropin Expression in Placental Cells

Molecular pathways in placental-fetal development and disruption

The first trimester of pregnancy ranks high in priority when minimizing harmful exposures, given the wide-ranging types of organogenesis occurring between 4- and 12-weeks' gestation. One way to quantify potential harm to the fetus in the first trimester is to measure a corollary effect on the placenta. Placental biomarkers are widely present in maternal circulation, cord blood, and placental tissue biopsied at birth or at the time of pregnancy termination. Here we evaluate ten diverse pathways involving molecules expressed in the first trimester human placenta based on their relevance to normal fetal development and to the hypothesis of placental-fetal endocrine disruption (perturbation in development that results in abnormal endocrine function in the offspring), namely: human chorionic gonadotropin (hCG), thyroid hormone regulation, peroxisome proliferator activated receptor protein gamma (PPARγ), leptin, transforming growth factor beta, epiregulin, growth differentiation factor 15, small nucleolar RNAs, serotonin, and vitamin D. Some of these are well-established as biomarkers of placental-fetal endocrine disruption, while others are not well studied and were selected based on discovery analyses of the placental transcriptome. A literature search on these biomarkers summarizes evidence of placenta-specific production and regulation of each biomarker, and their role in fetal reproductive tract, brain, and other specific domains of fetal development. In this review, we extend the theory of fetal programming to placental-fetal programming.

Longitudinal Associations between Prenatal Exposure to Phthalates and Steroid Hormones in Maternal Hair Samples from the SEPAGES Cohort

We assessed phthalate-hormone associations in 382 pregnant women of the new-generation SEPAGES cohort (2014-2017, France) using improved exposure and outcome assessments. Metabolites from seven phthalate compounds and the replacement di(isononyl)cyclohexane-1,2-dicarboxylate (DINCH) were measured in within-subject pools of repeated urine samples collected at the second and third pregnancy trimesters (≈21 samples/trimester). Metabolites from five steroid hormones were measured in maternal hair samples collected at delivery, reflecting cumulative levels over the previous weeks to months. Adjusted linear regression and Bayesian weighted quantile sum (BWQS) mixture models were performed. Each doubling in third-trimester urinary mono-benzyl phthalate (MBzP) concentrations was associated with an average increase of 13.3% (95% CI: 2.65, 24.9) for ∑cortisol, 10.0% (95% CI: 0.26, 20.7) for ∑cortisone, 17.3% (95% CI: 1.67, 35.4) for 11-dehydrocorticosterone, and 16.2% (95% CI: 2.20, 32.1) for testosterone, together with a suggestive 10.5% (95% CI: -1.57, 24.1) increase in progesterone levels. Each doubling in second-trimester urinary di-isononyl phthalate (DiNP) concentrations was inversely associated with testosterone levels (-11.6%; 95% CI: -21.6, -0.31). For most hormones, a nonsignificant trend toward a positive phthalate mixture effect was observed in the third but not in the second trimester. Our study showed that exposure to some phthalate metabolites, especially MBzP, may affect adrenal and reproductive hormone levels during pregnancy.

Association of endocrine disrupting chemicals exposure with human chorionic gonadotropin concentrations in pregnancy

BACKGROUND

Human chorionic gonadotropin (hCG) is produced by the placenta and plays an essential role in the maintenance of pregnancy. Endocrine disrupting chemicals (EDCs) have the potential to interfere with functions related to the production and secretion of hCG; however associations between exposure to EDCs and hCG concentrations in humans remain to be elucidated.

OBJECTIVES

To investigate the association of urinary, serum and plasma concentrations of EDCs during pregnancy with serum hCG concentrations.

METHODS

We utilized data form the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study. We investigated the association of 26 EDCs measured in early pregnancy urine or blood with serum hCG concentrations using multi-variable adjusted linear regression models per EDC and Weighted Quantile Sum (WQS) regression with repeated holdout validation for the EDCs mixture.

RESULTS

In 2,039 included women, higher exposure to bisphenol A was associated with lower hCG (beta [95% CI]: -0.06 [-0.11 to -0.002]) while higher triclosan exposure was associated with a higher hCG (0.02 [0.003 to 0.04]). Higher exposure to several phthalates, including mono-ethyl and mono-butyl phthalates (MEP and MBP) as well as metabolites of di-2-ethylhexyl phthalate (DEHP) was associated with a lower hCG (beta [95% CI] for sum of DEHP metabolites: -0.13 [-0.19 to -0.07]). Likewise, higher exposure to several polychlorinated biphenyls (PCBs) was associated with a lower hCG. In the WQS regression, each quartile increase in the EDCs mixture was associated with -0.27 lower hCG (95% CI: -0.34 to -0.19).

DISCUSSION

Higher exposure to several EDCs during pregnancy was associated with a lower hCG; and despite the small effect sizes, still indicating that the exposure may negatively affect production or secretion of hCG by the placenta. Our results provide the impetus for future experimental studies to investigate the placenta as a target organ for adverse effects of EDCs.

Associations between prenatal exposure to phthalates and birth weight: A meta-analysis study

Previous studies have suggested that phthalates are associated with birth weight. However, most phthalate metabolites have not been fully explored. Therefore, we conducted this meta-analysis to assess the relationship between phthalate exposure and birth weight. We identified original studies that measured phthalate exposure and reported its association with infant birth weight in relevant databases. Regression coefficients (β) with 95% confidence intervals (CIs) were extracted and analyzed for risk estimation. Fixed-effects (I² ≤ 50%) or random-effects (I² > 50%) models were adopted according to their heterogeneity. Overall summary estimates indicated negative associations of prenatal exposure to mono-n-butyl phthalate (pooled β = -11.34 g; 95% CI: -20.98 to -1.70 g) and mono-methyl phthalate (pooled β = -8.78 g; 95% CI: -16.30 to -1.27 g). No statistical association was found between the other less commonly used phthalate metabolites and birth weight. Subgroup analyses indicated that exposure to mono-n-butyl phthalate was associated with birth weight in females (β = -10.74 g; 95% CI: -18.70 to -2.79 g). Our findings indicate that phthalate exposure might be a risk factor for low birth weight and that this relationship may be sex specific. More research is needed to promote preventive policies regarding the potential health hazards of phthalates.

Cumulative Exposure to Phthalates and Their Alternatives and Associated Female Reproductive Health: Body Burdens, Adverse Outcomes, and Underlying Mechanisms

The global birth rate has recently shown a decreasing trend, and exposure to environmental pollutants has been identified as a potential factor affecting female reproductive health. Phthalates have been widely used as plasticizers in plastic containers, children's toys, and medical devices, and their ubiquitous presence and endocrine-disrupting potential have already raised particular concerns. Phthalate exposure has been linked to various adverse health outcomes, including reproductive diseases. Given that many phthalates are gradually being banned, a growing number of phthalate alternatives are becoming popular, such as di(isononyl) cyclohexane-1,2-dicarboxylate (DINCH), di(2-ethylhexyl) adipate (DEHA), and di(2-ethylhexyl) terephthalate (DEHTP), and they are beginning to have a wide range of environmental effects. Studies have shown that many phthalate alternatives may disrupt female reproductive function by altering the estrous cycle, causing ovarian follicular atresia, and prolonging the gestational cycle, which raises growing concerns about their potential health risks. Herein, we summarize the effects of phthalates and their common alternatives in different female models, the exposure levels that influence the reproductive system, and the effects on female reproductive impairment, adverse pregnancy outcomes, and offspring development. Additionally, we scrutinize the effects of phthalates and their alternatives on hormone signaling, oxidative stress, and intracellular signaling to explore the underlying mechanisms of action on female reproductive health, because these chemicals may affect reproductive tissues directly or indirectly through endocrine disruption. Given the declining global trends of female reproductive capacity and the potential ability of phthalates and their alternatives to negatively impact female reproductive health, a more comprehensive study is needed to understand their effects on the human body and their underlying mechanisms. These findings may have an important role in improving female reproductive health and in turn decreasing the number of complications during pregnancy.

Mono(2-ethylhexyl) phthalate induces transcriptomic changes in placental cells based on concentration, fetal sex, and trophoblast cell type

Phthalates are ubiquitous plasticizer chemicals found in consumer products. Exposure to phthalates during pregnancy has been associated with adverse pregnancy and birth outcomes and differences in placental gene expression in human studies. The objective of this research was to evaluate global changes in placental gene expression via RNA sequencing in two placental cell models following exposure to the phthalate metabolite mono(2-ethylhexyl) phthalate (MEHP). HTR-8/SVneo and primary syncytiotrophoblast cells were exposed to three concentrations (1, 90, 180 µM) of MEHP for 24 h with DMSO (0.1%) as a vehicle control. mRNA and lncRNAs were quantified using paired-end RNA sequencing, followed by identification of differentially expressed genes (DEGs), significant KEGG pathways, and enriched transcription factors (TFs). MEHP caused gene expression changes across all concentrations for HTR-8/SVneo and primary syncytiotrophoblast cells. Sex-stratified analysis of primary cells identified different patterns of sensitivity in response to MEHP dose by sex, with male placentas being more responsive to MEHP exposure. Pathway analysis identified 11 KEGG pathways significantly associated with at least one concentration in both cell types. Four ligand-inducible nuclear hormone TFs (PPARG, PPARD, ESR1, AR) were enriched in at least three treatment groups. Overall, we demonstrated that MEHP differentially affects placental gene expression based on concentration, fetal sex, and trophoblast cell type. This study confirms prior studies, as enrichment of nuclear hormone receptor TFs were concordant with previously published mechanisms of phthalate disruption, and generates new hypotheses, as we identified many pathways and genes not previously linked to phthalate exposure.

Associations of urinary phthalate metabolites and inflammatory biomarkers among pregnant women in Puerto Rico

Phthalates are ubiquitous environmental exposures that may be implicated in inflammatory processes, as demonstrated by previous in vivo and in vitro studies. Few human studies have substantiated these observations. This study sought to examine whether maternal phthalate exposures impact inflammatory processes, as measured by circulating inflammatory biomarkers, in the PROTECT cohort in northern Puerto Rico. Inflammatory biomarkers included matrix metalloproteinases 1, 2, and 9 (MMPs), C-reactive protein (CRP), vascular cell adhesion molecule-1 (VCAM), and intercellular cell adhesion molecule-1 (ICAM). Biomarkers were measured in maternal serum samples collected during pregnancy. 19 phthalate metabolites were assessed in urinary samples collected at three study visits across pregnancy. Phthalates with <50 % of measurements above the limit of detection were excluded from analysis. We utilized linear mixed effect models to estimate associations between interquartile range increases in phthalate metabolite concentrations and percent changes in inflammatory biomarkers. Our results revealed significant associations between mono-n-butyl phthalate (MBP) and higher MMP1 by 7.86 % (95 % CI: 0.49, 15.76) and between mono oxononyl phthalate (MONP) and higher MMP2 by 8.30 % (95 % CI: 2.22, 14.75). We observed negative or null associations between phthalate metabolites and MMP2, MMP9, ICAM, VCAM, and CRP. Many results were significantly modified by fetal sex, particularly those between di-2-ethylhexyl phthalate (DEHP) metabolites and MMP1 (p-interaction: MEHHP = 0.01, MEOHP = 0.04, MECPP = 0.01) and MMP2 (p-interaction: MEHHP = 0.03, MEOHP = 0.01, MECPP = 0.01), for which associations were positive among only women carrying female fetuses. MMPs have been previously associated with preeclampsia and hypertensive pregnancy disorders as mediators of artery remodeling. Hence, our findings suggest a potential role for phthalates in mediating the maternal inflammatory response, as well as significant sexual dimorphism in these relationships, which has implications for several adverse pregnancy outcomes.

Killing two birds with one stone: Pregnancy is a sensitive window for endocrine effects on both the mother and the fetus

Pregnancy is a complex process requiring tremendous physiological changes in the mother in order to fulfill the needs of the growing fetus, and to give birth, expel the placenta and nurse the newborn. These physiological modifications are accompanied with psychological changes, as well as with variations in habits and behaviors. As a result, this period of life is considered as a sensitive window as impaired functional and physiological changes in the mother can have short- and long-term impacts on her health. In addition, dysregulation of the placenta and of mechanisms governing placentation have been linked to chronic diseases later-on in life for the fetus, in a concept known as the Developmental Origin of Health and Diseases (DOHaD). This concept stipulates that any change in the environment during the pre-conception and perinatal (in utero life and neonatal) period to puberty, can be "imprinted" in the organism, thereby impacting the health and risk of chronic diseases later in life. Pregnancy is a succession of events that is regulated, in large part, by hormones and growth factors. Therefore, small changes in hormonal balance can have important effects on both the mother and the developing fetus. An increasing number of studies demonstrate that exposure to endocrine disrupting compounds (EDCs) affect both the mother and the fetus giving rise to growing concerns surrounding these exposures. This review will give an overview of changes that happen during pregnancy with respect to the mother, the placenta, and the fetus, and of the current literature regarding the effects of EDCs during this specific sensitive window of exposure.

The sex-specific association of prenatal phthalate exposure with low birth weight and small for gestational age: A nationwide survey by the Taiwan Maternal and Infant Cohort Study (TMICS)

The Taiwan Maternal and Infant Cohort Study (TMICS) was launched with the aim to assess the effects of prenatal exposure to phthalic acid esters (PAEs) on infant health. A total of 1102 pregnant women were enrolled in this study from 2012 to 2015. All participants completed a structured questionnaire, and provided urine specimens. The urinary concentrations of PAE metabolites in the third trimester were measured using liquid chromatography-electrospray ionization tandem mass spectrometry. Generalized additive model-penalized regression splines and logistic regression models were employed to determine the risk for low birth weight (LBW) or small for gestational age (SGA) among pregnant women exposed to PAEs. After adjustments for other covariates, each incremental unit of ln-transformed mono-n-butyl phthalate (MnBP) for pregnant women increased the odds of SGA in male neonates by 1.44 (95% CI: 0.92-2.23). An inverse association between SGA and maternal MnBP exposure level was observed in female neonates. An increase in one ln-transformed MnBP concentration unit decreased the risk of female SGA to 0.50 (95% CI: 0.24-0.97). In the penalized regression splines, increased risks of LBW/SGA in male neonates were presented while pregnant women exposed to increased MnBP levels. However, an association in the opposite direction was observed between maternal MnBP and LBW or SGA for male and female neonates. This study indicated that high maternal MnBP exposure in the third trimester was associated with LBW or SGA for male infants. Adverse effects on susceptible populations exposed to high levels of PAEs should be of concern.

Association of phthalate exposure with thyroid function during pregnancy

BACKGROUND

The extent of thyroid disruptive effects of phthalates during pregnancy remains unclear.

AIM

To investigate the association of maternal urinary phthalates with markers of the thyroid system during early pregnancy.

METHODS

Urinary concentrations of phthalate metabolites and serum concentrations of thyroid stimulating hormone (TSH), free and total thyroxine (FT4 and TT4) and free and total triiodothyronine (FT3 and TT3) were measured in pregnant women in early pregnancy in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy study (2007-ongoing), a population-based prospective cohort.

RESULTS

In the 1,996 included women, higher di-ethyl-hexyl phthalate (DEHP) metabolites were associated with a lower FT4 (β [SE] for the molar sum: -0.13 [0.06], P = 0.03) and a higher TSH/FT4 ratio (0.003 [0.001], P = 0.03). Higher concentrations of di-iso-nonyl phthalate (DINP) metabolites were associated with a lower TT4 (β [SE] for the molar sum: 0.93 [0.44], P = 0.03) as well as with lower TT4/FT4 and TT4/TT3 ratios. Higher metabolites of both dibutyl and butyl-benzyl phthalate (DBP and BBzP) were associated with lower T4/T3 ratio (free and total) and higher FT4/TT4 and FT3/TT3 ratios. A higher diisononyl cyclohexane dicarboxylate (DINCH) metabolite concentration was associated with a higher TT3.

CONCLUSIONS

These results translate results from experimental studies suggesting that exposure to phthalates may interfere with the thyroid system during pregnancy. This is also true for compounds that have been introduced to replace known disruptive phthalates. Further experimental studies should take into account the human evidence to better investigate the potential underlying mechanisms of thyroid disruption by phthalates.

The exposure levels of phthalates in pregnant women and impact factors of fetal malformation

METHODS

Urine samples were collected from 157 women with fetal malformations (case group) and 147 women with normal fetuses (control group). High-performance liquid chromatography-mass spectrometry (HPLC-MS) was used to detect the content of eight metabolites of phthalate compounds in urine, including monoethyl phthalate (MEP), mononbutyl phthalate (MBP), monoisobutyl phthalate (MiBP), mono-(2-ethylhexyl) phthalate (MEHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-benzyl phthalate (MBzP). Demographic data were collected from questionnaires administered in specimen collection.

RESULTS

The exposure level of MEOHP and MEHP in the case group was higher than the others. And there were significant differences between structural malformations and chromosomal malformations in the levels of MEHHP and MEOHP. Pregnant women with low income, high body mass index (BMI), frequent plastic contact, and low nutrients intake were at risk of suffering from fetal malformation.

CONCLUSION

This study provides evidence for the correlation between the concentration of phthalates and fetal malformation. In addition, decreasing plastic exposure and supplementing nutrients may reduce the incidence of fetal malformations.

Sexual dimorphism in placental development and its contribution to health and diseases

According to the Developmental Origin of Health and Disease (DOHaD), intrauterine exposure to adverse environments can affect fetus and birth outcomes and lead to long-term disease susceptibility. Evidence has shown that neonatal outcomes and the timing and severity of adult diseases are sexually dimorphic. As the link between mother and fetus, the placenta is an essential regulator of fetal development programming. It is found that the physiological development trajectory of the placenta has sexual dimorphism. Furthermore, under pathological conditions, the placental function undergoes sex-specific adaptation to ensure fetal survival. Therefore, the placenta may be an important mediator of sexual dimorphism in neonatal outcomes and adult disease susceptibility. Few systematic reviews have been conducted on sexual dimorphism in placental development and its underlying mechanisms. In this review, sex chromosomes and sex hormones, as the main reasons for sexual differentiation of the placenta, will be discussed. Besides, in the etiology of fetal-originated adult diseases, overexposure to glucocorticoids is closely related to adverse neonatal outcomes and long-term disease susceptibility. Studies have found that prenatal glucocorticoid overexposure leads to sexually dimorphic expression of placental glucocorticoid receptor isoforms, resulting in different sensitivity of the placenta to glucocorticoids, and may further affect fetal development. The present review examines what is currently known about sex differences in placental development and the underlying regulatory mechanisms of this sex bias. This review highlights the importance of placental contributions to the origins of sexual dimorphism in health and diseases. It may help develop personalized diagnosis and treatment strategies for fetal development in pathological pregnancies.

Transcriptomics and Other Omics Approaches to Investigate Effects of Xenobiotics on the Placenta

The conceptus is most vulnerable to developmental perturbation during its early stages when the events that create functional organ systems are being launched. As the placenta is in direct contact with maternal tissues, it readily encounters any xenobiotics in her bloodstream. Besides serving as a conduit for solutes and waste, the placenta possesses a tightly regulated endocrine system that is, of itself, vulnerable to pharmaceutical agents, endocrine disrupting chemicals (EDCs), and other environmental toxicants. To determine whether extrinsic factors affect placental function, transcriptomics and other omics approaches have become more widely used. In casting a wide net with such approaches, they have provided mechanistic insights into placental physiological and pathological responses and how placental responses may impact the fetus, especially the developing brain through the placenta-brain axis. This review will discuss how such omics technologies have been utilized to understand effects of EDCs, including the widely prevalent plasticizers bisphenol A (BPA), bisphenol S (BPS), and phthalates, other environmental toxicants, pharmaceutical agents, maternal smoking, and air pollution on placental gene expression, DNA methylation, and metabolomic profiles. It is also increasingly becoming clear that miRNA (miR) are important epigenetic regulators of placental function. Thus, the evidence to date that xenobiotics affect placental miR expression patterns will also be explored. Such omics approaches with mouse and human placenta will assuredly provide key biomarkers that may be used as barometers of exposure and can be targeted by early mitigation approaches to prevent later diseases, in particular neurobehavioral disorders, originating due to placental dysfunction.

A Comprehensive Assessment of Associations between Prenatal Phthalate Exposure and the Placental Transcriptomic Landscape

BACKGROUND

Phthalates are commonly used endocrine-disrupting chemicals that are ubiquitous in the general population. Prenatal phthalate exposure may alter placental physiology and fetal development, leading to adverse perinatal and childhood health outcomes.

OBJECTIVE

We examined associations between prenatal phthalate exposure in the second and third trimesters and the placental transcriptome at birth, including genes and long noncoding RNAs (lncRNAs), to gain insight into potential mechanisms of action during fetal development.

METHODS

The ECHO PATHWAYs consortium quantified 21 urinary phthalate metabolites from 760 women enrolled in the CANDLE study (Shelby County, TN) using high-performance liquid chromatography-tandem mass spectrometry. Placental transcriptomic data were obtained using paired-end RNA sequencing. Linear models were fitted to estimate separate associations between maternal urinary phthalate metabolite concentration during the second and third trimester and placental gene expression at birth, adjusted for confounding variables. Genes were considered differentially expressed at a Benjamini-Hochberg false discovery rate (FDR) p<0.05. Associations between phthalate metabolites and biological pathways were identified using self-contained gene set testing and considered significantly altered with an FDR-adjusted p<0.2.

RESULTS

We observed significant associations between second-trimester phthalate metabolites mono (carboxyisooctyl) phthalate (MCIOP), mono-2-ethyl-5-carboxypentyl phthalate, and mono-2-ethyl-5-oxohexyl phthalate and 18 genes in total, including four lncRNAs. Specifically, placental expression of NEAT1 was associated with multiple phthalate metabolites. Third-trimester MCIOP and mono-isobutyl phthalate concentrations were significantly associated with placental expression of 18 genes and two genes, respectively. Expression of genes within 27 biological pathways was associated with mono-methyl phthalate, MCIOP, and monoethyl phthalate concentrations.

DISCUSSION

To our knowledge, this is the first genome-wide assessment of the relationship between the placental transcriptome at birth and prenatal phthalate exposure in a large and diverse birth cohort. We identified numerous genes and lncRNAs associated with prenatal phthalate exposure. These associations mirror findings from other epidemiological and in vitro analyses and may provide insight into biological pathways affected in utero by phthalate exposure. https://doi.org/10.1289/EHP8973.

Placental outcomes of phthalate exposure

Proper placental development and function relies on hormone receptors and signaling pathways that make the placenta susceptible to disruption by endocrine disrupting chemicals, such as phthalates. Here, we review relevant research on the associations between phthalate exposures and dysfunctions of the development and function of the placenta, including morphology, physiology, and genetic and epigenetic effects. This review covers in vitro studies, in vivo studies in mammals, and studies in humans. We also discuss important gaps in the literature. Overall, the evidence indicates that toxicity to the placental and maternal-fetal interface is associated with exposure to phthalates. Further studies are needed to better elucidate the mechanisms through which phthalates act in the placenta as well as additional human studies that assess placental disruption through pregnancy with larger sample sizes.

Endocrine disrupting chemicals (EDCs) and placental function: Impact on fetal brain development

Pregnancy is a critical time of vulnerability for the development of the fetal brain. Exposure to environmental pollutants at any point in pregnancy can negatively impact many aspects of fetal development, especially the organization and differentiation of the brain. The placenta performs a variety of functions that can help protect the fetus and sustain brain development. However, disruption of any of these functions can have negative impacts on both the pregnancy outcome and fetal neurodevelopment. This review presents current understanding of how environmental exposures, specifically to endocrine disrupting chemicals (EDCs), interfere with placental function and, in turn, neurodevelopment. Some of the key differences in placental development between animal models are presented, as well as how placental functions such as serving as a xenobiotic barrier and exchange organ, immune interface, regulator of growth and fetal oxygenation, and a neuroendocrine organ, could be vulnerable to environmental exposure. This review illustrates the importance of the placenta as a modulator of fetal brain development and suggests critical unexplored areas and possible vulnerabilities to environmental exposure.

First trimester mechanisms of gestational sac placental and foetal teratogenicity: a framework for birth cohort studies

BACKGROUND

The function of the gestational sac (GS) and the placenta in the closely related processes of embryogenesis and teratogenicity in the first trimester has been minimally described. The prevailing assumption is that direct teratogenic effects are mediated by the critical extraembryonic organ, the placenta, which either blocks or transfers exposures to the foetus. Placental transfer is a dominant mechanism, but there are other paradigms by which the placenta can mediate teratogenic effects. Knowledge of these paradigms and first trimester human developmental biology can be useful to the epidemiologist in the conduct of biomarker-based studies of both maternal and child health.

OBJECTIVE AND RATIONALE

Our aim is to provide a causal framework for modelling the teratogenic effects of first trimester exposures on child health outcomes mediated by the GS and placenta using biomarker data collected in the first trimester. We initially present first trimester human developmental biology for the sake of informing and strengthening epidemiologic approaches. We then propose analytic approaches of modelling placental mechanisms by way of causal diagrams using classical non-embryolethal teratogens (diethylstilboestrol [DES], folic acid deficiency and cytomegalovirus [CMV]) as illustrative examples. We extend this framework to two chronic exposures of particular current interest, phthalates and maternal adiposity.

SEARCH METHODS

Information on teratogens was identified by a non-systematic, narrative review. For each teratogen, we included papers that answered the five following questions: (i) why were these exposures declared teratogens? (ii) is there a consensus on biologic mechanism? (iii) is there reported evidence of a placental mechanism? (iv) can we construct a theoretical model of a placental mechanism? and (v) can this knowledge inform future work on measurement and modelling of placental-foetal teratogenesis? We prioritized literature specific to human development, the organogenesis window in the first trimester and non-embryolethal mechanisms.

OUTCOMES

As a result of our review of the literature on five exposures considered harmful in the first trimester, we developed four analytic strategies to address first trimester placental mechanisms in birth cohort studies: placental transfer and direct effects on the foetus (DES and maternal adiposity), indirect effects through targeted placental molecular pathways (DES and phthalates), pre-placental effects through disruptions in embryonic and extraembryonic tissue layer differentiation (folic acid deficiency), and multi-step mechanisms that involve maternal, placental and foetal immune function and inflammation (DES and CMV).

WIDER IMPLICATIONS

The significance of this review is to offer a causal approach to classify the large number of potentially harmful exposures in pregnancy when the exposure occurs in the first trimester. Our review will facilitate future research by advancing knowledge of the first trimester mechanisms necessary for researchers to effectively associate environmental exposures with child health outcomes.

A pathway level analysis of PFAS exposure and risk of gestational diabetes mellitus

Per- and polyfluoroalkyl substances (PFAS) have been found to be associated with gestational diabetes mellitus (GDM) development, a maternal health disorder in pregnancy with negative effects that can extend beyond pregnancy. Studies that report on this association are difficult to summarize due to weak associations and wide confidence intervals. One way to advance this field is to sharpen the biologic theory on a causal pathway behind this association, and to measure it directly by way of molecular biomarkers. The aim of this review is to summarize the literature that supports a novel pathway between PFAS exposure and GDM development. Epidemiological studies demonstrate a clear association of biomarkers of thyroid hormones and glucose metabolism with GDM development. We report biologic plausibility and epidemiologic evidence that PFAS dysregulation of maternal thyroid hormones and thyrotropin (TSH) may disrupt glucose homeostasis, increasing the risk of GDM. Overall, epidemiological studies demonstrate that PFAS were positively associated with TSH and negatively with triiodothyronine (T3) and thyroxine (T4). PFAS were generally positively associated with glucose and insulin levels in pregnancy. We propose dysregulation of thyroid function and glucose metabolism may be a critical and missing component in the accurate estimation of PFAS on the risk of GDM.

The impact of Di-(2-ethylhexyl) Phthalate and Mono(2-ethylhexyl) Phthalate in placental development, function, and pathophysiology

Di(2-ethylhexyl) phthalate (DEHP) is a chemical widely distributed in the environment as is extensively used in the plastic industry. DEHP is considered an endocrine disruptor chemical (EDC) and humans are inevitably and unintentionally exposed to this EDC through several sources including food, beverages, cosmetics, medical devices, among others. DEHP exposure has been associated and may be involved in the development of various pathologies; importantly, pregnant women are a particular risk group considering that endocrine alterations during gestation may impact fetal programming leading to the development of several chronic diseases in adulthood. Recent studies have indicated that exposure to DEHP and its metabolite Mono(2-ethylhexyl) phthalate (MEHP) may impair placental development and function, which in turn would have a negative impact on fetal growth. Studies performed in several trophoblastic and placental models have shown the negative impact of DEHP and MEHP in key processes related to placental development such as implantation, differentiation, invasion and angiogenesis. In addition, many alterations in placental functions like hormone signaling, metabolism, transfer of nutrients, immunomodulation and oxidative stress response have been reported. Moreover, clinical-epidemiological evidence supports the association between DEHP exposure and adverse pregnancy outcomes and pathologies. In this review, we aim to summarize for the first time current knowledge about the impact of DEHP and MEHP exposure on placental development and pathophysiology, as well as the mechanisms involved. We also remark the importance of exploring DEHP and MEHP effects in different trophoblast cell populations and discuss new perspectives regarding this topic.

A toolkit for the application of placental-fetal molecular biomarkers in epidemiologic studies of the fetal origins of chronic disease

Purpose of review

In this review, we provide essential background knowledge and an analytical framework for the application of placental-fetal molecular biomarkers in fetal origins chronic disease epidemiology. The widely available and highly quantitative placental hormone human chorionic gonadotropin (hCG) is used as an example. hCG is currently used for diagnosing fetal genetic disorders; yet it can and should be expanded to understanding the fetal origins of chronic diseases. We provide justification and methods to do this.

Recent findings

Ten papers published in the last 5 years were identified with supportive findings relevant to the application of biomarkers of hCG in epidemiologic studies on the developmental origins of health and disease (DOHaD).

Summary

There is increasing and consistent evidence that placental-fetal biomarkers may be highly informative in observational studies, as exemplified by hCG, with the correct approaches for measurement and data analysis.

Testing the low dose mixtures hypothesis from the Halifax project

In 2013, 60 scientists, representing a larger group of 174 scientists from 26 nations, met in Halifax, Nova Scotia to consider whether - using published research - it was logical to anticipate that a mixture of chemicals, each thought to be non-carcinogenic, might act together in that mixture as a virtual carcinogen. The group identified 89 such chemicals, each one affecting one or more Hallmark(s) - collectively covering all Hallmarks of Cancer - confirming the possibility that a chemical mixture could induce all the Hallmarks and function as a virtual carcinogen, thereby supporting the concern that chemical safety research that does not evaluate mixtures, is incomplete. Based on these observations, the Halifax Project developed the Low-Dose Carcinogenesis Hypothesis which posits "…that low-dose exposures to [mixtures of] disruptive chemicals that are not individually carcinogenic may be capable of instigating and/or enabling carcinogenesis." Although testing all possible combinations of over 80,000 chemicals of commerce would be impractical, prudence requires designing a methodology to test whether low-dose chemical mixtures might be carcinogenic. As an initial step toward testing this hypothesis, we conducted a mini review of published empirical observations of biological exposures to chemical mixtures to assess what empirical data exists on which to base future research. We reviewed studies on chemical mixtures with the criteria that the studies reported both different concentrations of chemicals and mixtures composed of different chemicals. We found a paucity of research on this important question. The majority of studies reported hormone related processes and used chemical concentrations selected to facilitate studying how mixtures behave in experiments that were often removed from clinical relevance, i.e., chemicals were not studied at human-relevant concentrations. New research programs must be envisioned to enable study of how mixtures of small doses of chemicals affect human health, starting, when at all possible, from non-malignant specimens when studies are done in vitro. This research should use human relevant concentrations of chemicals, expand research beyond the historic focus on endocrine endpoints and endocrine related cancers, and specifically seek effects that arise uniquely from exposure to chemical mixtures at human-relevant concentrations.

The sex-specific association of phthalate exposure with DNA methylation and characteristics of body fat in children

The present study assessed the association between phthalate exposure and mitochondrial DNA (mtDNA) polymerase γ (POLG) methylation along with the potential effect on the characteristics of body fat in children. A total of 152 children were enrolled. The urinary concentrations of phthalate metabolites were measured using ultraperformance liquid chromatography-tandem mass spectrometry. Genomic DNA was extracted from the buffy coat, and bisulfite-treated DNA was subjected to a pyrosequencing assay. In total, 17 CpG sites in the exon 2 region of POLG were included in the analysis. A multivariable regression model was applied to determine whether characteristics of body fat were associated with phthalate exposure and methylation of POLG. After adjustment for covariates, male children with a ten-fold increase in mono-methyl phthalate (MMP) or mono-benzyl phthalate (MBzP) concentrations had significantly higher measurements for total body fat (MMP: β = 6.47%; MBzP: β = 3.54%), and trunk fat (MMP: β = 6.67%; MBzP: β = 3.90%). Male children who had hypermethylation at the 2nd CpG site in exon 2 of POLG also had high measurements for BMI (β = 1.66 kg/m2), waist (β = 4.49 cm) and hip (β = 4.81 cm) circumference, total body fat (β = 5.48%), and trunk fat (β = 6.21%). A dose-response relationship existed between methylation at the 2nd CpG site in exon 2 of POLG and characteristics of body fat (p for trend<0.01). This study suggested that male children who are exposed to phthalic acid esters have high body weight, BMI, and body and trunk fat percentages. Methylation of the exon 2 region of POLG is a possible mechanism behind the causal effect of endocrine-disrupting substances.

Sex-specific difference in placental inflammatory transcriptional biomarkers of maternal phthalate exposure: a prospective cohort study

Previous epidemiologic research has shown that phthalate exposure in pregnant women is related to birth outcomes in a sex-specific manner. These outcomes may be mediated by placental inflammation, which is the proposed biological mechanism. This is the first study to address the relationship between phthalate exposure and gene expression in placental inflammation in a sex-specific manner. We performed quantitative PCR to measure placental inflammatory mRNAs (CRP, TNF-α, IL-1β, IL-6, IL-10, MCP-1, IL-8, CD68, and CD206) in 2469 placentae that were sampled at birth. We estimated the associations between mRNA and urinary phthalate monoesters using multiple linear regression models. Mono-n-butyl phthalate (MBP) was correlated with higher IL-1β, IL-6, and CRP expression in placentae of male fetuses and with higher IL-6, CRP, MCP-1, IL-8, IL-10, and CD68 expression in placentae of female fetuses. Mono benzyl phthalate (MBzP) increased the expression of TNF-α, MCP-1, and CD68 only in placentae of male fetuses. Mono (2-ethyl-5-oxohexyl) phthalate (MEOHP) was negatively correlated with CRP, MCP-1, and CD68 in placentae of female fetuses. Maternal phthalate exposure was associated with inflammatory variations in placental tissues. The associations were stronger in placentae of male than of female fetuses. Compared with the other metabolites, MBP plays a strong role in these associations. The placenta is worth being further investigated as a potential mediator of maternal exposure-induced disease risk in children.

Placenta Disrupted: Endocrine Disrupting Chemicals and Pregnancy

Endocrine disrupting chemicals (EDCs) are chemicals that can interfere with normal endocrine signals. Human exposure to EDCs is particularly concerning during vulnerable periods of life, such as pregnancy. However, often overlooked is the effect that EDCs may pose to the placenta. The abundance of hormone receptors makes the placenta highly sensitive to EDCs. We have reviewed the most recent advances in our understanding of EDC exposures on the development and function of the placenta such as steroidogenesis, spiral artery remodeling, drug-transporter expression, implantation and cellular invasion, fusion, and proliferation. EDCs reviewed include those ubiquitous in the environment with available human biomonitoring data. This review also identifies critical gaps in knowledge to drive future research in the field.

Associations of a mixture of urinary phthalate metabolites with blood lipid traits: A repeated-measures pilot study

Evidence is available about the associations of phthalates or their metabolites with blood lipids, however, the mixture effects of multiple phthalate metabolites on blood lipid traits remain largely unknown. In this pilot study, 106 individuals at three age groups of <18, 18- and ≥60 years were recruited from the residents (n = 1240) who were randomly selected from two communities in Wuhan city, China. The participants completed the questionnaire survey and physical examination as well as provided urine samples in the winter of 2014 and the summer of 2015. We measured urinary levels of nine phthalate metabolites using a high-performance liquid chromatography-tandem mass spectrometry. We estimated the associations of individual phthalate metabolite with blood lipid traits by linear mixed effect (LME) models, and assessed the overall association of the mixture of nine phthalate metabolites with blood lipid traits using Bayesian kernel machine regression (BKMR) models. LME models revealed the negative association of urinary mono-2-ethylhexyl phthalate (MEHP) with total cholesterol (TC) as well as of urinary mono-benzyl phthalate or urinary MEHP with low density lipoprotein cholesterol (LDL-C). BKMR models revealed the negative overall association of the mixture of nine phthalate metabolites with TC or LDL-C, and DEHP metabolites (especially MEHP) had a greater contribution to TC or LDL-C levels than non-DEHP metabolites. The findings indicated the negative overall association of the mixture of nine phthalate metabolites with TC or LDL-C. Among nine phthalate metabolites, MEHP was the most important component for the changes of TC or LDL-C levels, implying that phthalates exposure may disrupt lipid metabolism in the body.

Occurrence and Distribution of Phthalates in Sanitary Napkins from Six Countries: Implications for Women's Health

Chemicals in feminine hygiene products can exert adverse health effects as a result of strong absorptive capacity of the vagina and vulva. However, little information is available on phthalates in sanitary napkins. We measured the concentrations of 15 phthalates in sanitary napkins collected from six countries and found total concentrations in the range of 1733-11942 ng/g. Di(isobutyl)phthalate (DiBP), bis(2-ethylhexyl)phthalate (DEHP), and di-n-butyl phthalate (DnBP) were the dominant congeners, representing a median of 27.3, 26.7, and 20.4% of the total median phthalate concentrations across all countries, respectively. The phthalates likely originated mainly from the introduction in the manufacturing process, and some may have been from the use of plastic or paper materials. The estimated intake (at the 90th percentile) of DiBP, DnBP, and DEHP from sanitary napkins approximately represented 6.35-23.6, 3.35-9.90, and 1.06-9.57%, respectively, of the total exposure, indicating that sanitary napkins are a relevant source of exposure to these chemicals. The calculated health risks of phthalates in sanitary napkins were generally low, but the carcinogenic risks in some samples exceeded acceptable levels. More research is required to investigate the contaminations in sanitary napkins and those associated with risks to women.

Prenatal phthalate exposure in relation to gestational age and preterm birth in a prospective cohort study

This study enrolled 3266 pregnant women, to explore the relationship of prenatal phthalate exposure with the risk of preterm birth and gestational age. All participants filled questionnaires and provided with up to three urine samples during three trimesters. Seven phthalate metabolites in urines were measured. The incidences of very preterm, late preterm, early-term, late-term and postterm births were 0.58%, 3.52%, 24.22%, 10.53%, and 0.34%, respectively. Non-linear relationships were shown between phthalate metabolites and gestational age. Except for monomethyl phthalate (OR = 1.65, 95%CI = 1.17-2.34), the average concentrations of phthalate metabolites were associated with a slightly and insignificantly increased risk of overall preterm birth (<37⁺⁰ gestational weeks). Through a restricted cubic spline regression, phthalate metabolites were found to be related to the risk of overall preterm birth in a linear manner (p-value >0.05) or a non-linear manner (p-value <0.05). All curves indicated the overall preterm birth risk rose with the increase of phthalate metabolite concentrations. Finally, compared with full-term birth (39⁺⁰ to 40⁺⁶ gestational weeks), phthalate metabolites were associated with the elevated risks of very preterm, late preterm and postterm births, although some relationships were not statistically significant. In conclusion, these findings suggested non-linear associations between phthalate metabolites and gestational age. Exposure to some phthalate metabolites was associated with increased risks of overall preterm birth and postterm birth.

Ovarian Metabolism of an Environmentally Relevant Phthalate Mixture

Phthalates are synthetic chemicals with widespread human exposure due to their use as additives in consumer products. Phthalate diesters are hydrolyzed in the environment and in the body to monoesters that may be more toxic than the parent compounds. This study tested the hypothesis that adult mouse antral follicles, but not neonatal ovaries, are able to metabolize an environmentally relevant mixture of phthalates. Whole neonatal ovaries and isolated adult antral follicles from CD-1 mice were cultured in media treated with vehicle control or 0.1-10 µg/ml of a mixture composed of 35% diethyl phthalate (DEP), 21% di(2-ethylhexyl) phthalate (DEHP), 15% dibutyl phthalate (DBP), 15% diisononyl phthalate (DiNP), 8% diisobutyl phthalate (DiBP), and 5% benzylbutyl phthalate (BzBP). After 4 days of culture, media were subjected to high-performance liquid chromatography tandem mass spectrometry to measure the amounts of diester phthalates and monoester metabolites. Ovaries and follicles were collected to measure the gene and protein expression of the enzymes required for phthalate metabolism. Monoester metabolites for all phthalates except DiNP were detected in the media for both culture types at most doses. The long-chain phthalates (BzBP, DEHP, and DiNP) were metabolized less than the short-chain phthalates (DEP, DBP, and DiBP) compared with respective controls. Expression of metabolizing enzymes was observed for all treatment groups in both culture types. These data indicate that mouse ovaries are capable of metabolizing low doses of phthalates and suggest that metabolic capacity differs for follicles at different stages of development.

The Role of Peroxisome Proliferator–Activated Receptor Gamma (PPARγ) in Mono(2-ethylhexyl) Phthalate (MEHP)-Mediated Cytotrophoblast Differentiation

BACKGROUND

Phthalates are environmental contaminants commonly used as plasticizers in polyvinyl chloride (PVC) products. Recently, exposure to phthalates has been associated with preterm birth, low birth weight, and pregnancy loss. There is limited information about the possible mechanisms linking maternal phthalate exposure and placental development, but one such mechanism may be mediated by peroxisome proliferator–activated receptor γ (PPARγ). PPARγ belongs to the nuclear receptor superfamily that regulates, in a ligand-dependent manner, the transcription of target genes. Studies of PPARγ-deficient mice have demonstrated its essential role in lipid metabolism and placental development. In the human placenta, PPARγ is expressed in the villous cytotrophoblast (VCT) and is activated during its differentiation into syncytiotrophoblast.

OBJECTIVES

The goal of this study was to investigate the action of mono(2-ethylhexyl) phthalate (MEHP) on PPARγ activity during in vitro differentiation of VCTs.

METHODS

We combined immunofluorescence, PPARγ activity/hCG assays, western blotting, and lipidomics analyses to characterize the impacts of physiologically relevant concentrations of MEHP (0.1, 1, and 10 μM) on cultured VCTs isolated from human term placentas.

RESULTS

Doses of 0.1 and 1 μM MEHP showed significantly lower PPARγ activity and less VCT differentiation in comparison with controls, whereas, surprisingly, a 10 μM dose had the opposite effect. MEHP exposure inhibited hCG production and significantly altered lipid composition. In addition, MEHP had significant effects on the mitogen-activated protein kinase (MAPK) pathway.

CONCLUSIONS

This study suggests that MEHP has a U-shaped dose–response effect on trophoblast differentiation that is mediated by the PPARγ pathway and acts as an endocrine disruptor in the human placenta. https://doi.org/10.1289/EHP3730.

Associations between repeated measures of maternal urinary phthalate metabolites during pregnancy and cord blood glucocorticoids

BACKGROUND

Previous studies have suggested that phthalates might disrupt fetal steroidogenesis. However, the evidence of the effects of prenatal phthalate exposure across pregnancy on fetal glucocorticoids was insufficient.

OBJECTIVE

We investigated the associations between urinary phthalate metabolites across pregnancy and cord blood glucocorticoids in a prospective birth cohort.

METHODS

Our study included 553 mother-infant pairs from a prospective birth cohort conducted in Wuhan, China. Maternal urine samples were collected at 14, 24 and 36 weeks of gestation (mean). Urinary phthalate metabolites and cord blood glucocorticoids (cortisol and cortisone) were measured. Generalized estimating equation models were conducted to explore the relationships of phthalate metabolite concentrations at each trimester and glucocorticoid levels.

RESULTS

Among the participants, mono‑benzyl phthalate (MBzP) in the first trimester was associated with higher cortisol/cortisone ratio concentrations, and mono‑(2‑ethyl‑5‑carboxypentyl) phthalate (MECPP) and mono‑(2‑ethyl‑5‑oxohexyl) phthalate (MEOHP) measured in the third trimester were associated with decreased cortisone. Moreover, the associations between phthalates and glucocorticoids varied by sex. Among the female infants, each 10-fold increase in several maternal urinary phthalate metabolite concentrations in 1st and 3rd trimester was associated with the increased glucocorticoid levels with percent changes ranged from 16.2%-55.9%. However, among male infants, each 10-fold increase in maternal urinary MECPP, mono‑(2‑ethyl‑5‑hydroxyhexyl) phthalate (MEHHP) and MEOHP in 3rd trimester was associated with 20.8%-36.3% decreased cortisol and cortisone levels, respectively.

CONCLUSION

We have shown that prenatal phthalate exposure during early and late trimester disrupted the infant steroidogenesis and these associations might be modified by infant sex. To the best of our knowledge, this is the first study to evaluate phthalate exposure at three trimesters during pregnancy in relation to infant glucocorticoids.