Estrogenic activity of phthalate esters by in vitro VTG assay using primary-cultured Xenopus hepatocytes

Phthalates and uterine disorders

Humans are ubiquitously exposed to environmental endocrine disrupting chemicals such as phthalates. Phthalates can migrate out of products and enter the human body through ingestion, inhalation, or dermal application, can have potential estrogenic/antiestrogenic and/or androgenic/antiandrogenic activity, and are involved in many diseases. As a female reproductive organ that is regulated by hormones such as estrogen, progesterone and androgen, the uterus can develop several disorders such as leiomyoma, endometriosis and abnormal bleeding. In this review, we summarize the hormone-like activities of phthalates, in vitro studies of endometrial cells exposed to phthalates, epigenetic modifications in the uterus induced by phthalate exposure, and associations between phthalate exposure and uterine disorders such as leiomyoma and endometriosis. Moreover, we also discuss the current research gaps in understanding the relationship between phthalate exposure and uterine disorders.

Mono-(2-ethyl-5-hydroxyhexyl) phthalate promotes uterine leiomyoma cell survival through tryptophan-kynurenine-AHR pathway activation

Uterine leiomyoma is the most common tumor in women and causes severe morbidity in 15 to 30% of reproductive-age women. Epidemiological studies consistently indicate a correlation between leiomyoma development and exposure to endocrine-disrupting chemical phthalates, especially di-(2-ethylhexyl) phthalate (DEHP); however, the underlying mechanisms are unknown. Here, among the most commonly encountered phthalate metabolites, we found the strongest association between the urine levels of mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), the principal DEHP metabolite, and the risk of uterine leiomyoma diagnosis (n = 712 patients). The treatment of primary leiomyoma and smooth muscle cells (n = 29) with various mixtures of phthalate metabolites, at concentrations equivalent to those detected in urine samples, significantly increased cell viability and decreased apoptosis. MEHHP had the strongest effects on both cell viability and apoptosis. MEHHP increased cellular tryptophan and kynurenine levels strikingly and induced the expression of the tryptophan transporters SLC7A5 and SLC7A8, as well as, tryptophan 2,3-dioxygenase (TDO2), the key enzyme catalyzing the conversion of tryptophan to kynurenine that is the endogenous ligand of aryl hydrocarbon receptor (AHR). MEHHP stimulated nuclear localization of AHR and up-regulated the expression of CYP1A1 and CYP1B1, two prototype targets of AHR. siRNA knockdown or pharmacological inhibition of SLC7A5/SLC7A8, TDO2, or AHR abolished MEHHP-mediated effects on leiomyoma cell survival. These findings indicate that MEHHP promotes leiomyoma cell survival by activating the tryptophan-kynurenine-AHR pathway. This study pinpoints MEHHP exposure as a high-risk factor for leiomyoma growth, uncovers a mechanism by which exposure to environmental phthalate impacts leiomyoma pathogenesis, and may lead to the development of novel druggable targets.

Prioritizing phthalate esters (PAEs) using experimental in vitro/vivo toxicity assays and computational in silico approaches

Phthalate esters (PAEs) pose prominent ecological risks owing to their multiplex toxicity potentials and ubiquitous detection in the environment. Therefore, this study aims to prioritize the individual and mixtures of six PAEs based on their toxicological implications using in vitro and vivo models exposed at environmentally relevant concentrations. Results were further confirmed using in silico Combination index (CI) and Independent action (IA), and molecular docking models. Among PAEs, DEHP revealed prominent in vitro/vivo toxicity followed by DEP, DBP, and DMP. Importantly, binary mixtures particularly C2-C6 and C11-C15 exhibited greater developmental toxicity, apoptosis, and perturbed the HPG pathway. The CI and IA models forecasted antagonistic and additive effects at Fa = 0.5 and Fa = 0.9 using in vitro Acinetobacter sp. Tox2. Conversely, in zebrafish, the IA model predicted mixture effects in the following order: additive > synergistic > antagonistic on the regulation of the HPG pathway, which was consistent with experimental results from Acridine Orange (AO) staining and apoptosis gene expression. Molecular docking for estrogen receptors (ERα, ERβ) revealed the highest binding energy scores for DEHP, compared to other PAEs. In short, our findings confirm that individual and mixtures of PAEs behave as xenoestrogens in the freshwater ecosystem with DEHP as a priority compound.

Chronic exposure to mono-(2-ethylhexyl)-phthalate causes endocrine disruption and reproductive dysfunction in zebrafish

Phthalic acid esters are frequently detected in aquatic environments. In the present study, zebrafish were exposed to low concentrations (0 µg/L, 0.46 µg/L, 4.0 µg/L, and 37.5 µg/L) of mono-(2-ethylhexyl) phthalate (MEHP) for 81 d, and the effects on reproduction, gamete quality, plasma vitellogenin (VTG), sex steroids, and transcriptional profiles of key genes involved in steroidogenesis were investigated. The results demonstrated that egg production and sperm quality were decreased after exposure to MEHP, which also resulted in reduced egg diameter and eggshell as well as decreased egg protein content. Significant inductions in plasma testosterone and 17β-estradiol (E2) were observed in females, which might have resulted from up-regulation of CYP19a and 17β-HSD gene transcription in the ovary. A significant increase in plasma E2 along with a decrease in plasma 11-keto testosterone was also observed in males, which was accompanied by up-regulation of CYP19a and inhibition of CYP11b transcription in the testis. In addition, plasma vitellogenin levels were significantly increased after MEHP exposure in both sexes. Moreover, continuous MEHP exposure in the F1 embryos resulted in worse hatching rates and increased malformation rates compared with embryos without MEHP exposure. Taken together, these results demonstrate that MEHP has the potential to cause reproductive dysfunction and impair the development of offspring. However, it should be noted that most of the significant effects were observed at higher concentrations, and MEHP at typically measured concentrations may not have major effects on fish reproduction and development. Environ Toxicol Chem 2016;35:2117-2124. © 2016 SETAC.

Plasticizer endocrine disruption: Highlighting developmental and reproductive effects in mammals and non-mammalian aquatic species

Due to their versatility, robustness, and low production costs, plastics are used in a wide variety of applications. Plasticizers are mixed with polymers to increase flexibility of plastics. However, plasticizers are not covalently bound to plastics, and thus leach from products into the environment. Several studies have reported that two common plasticizers, bisphenol A (BPA) and phthalates, induce adverse health effects in vertebrates; however few studies have addressed their toxicity to non-mammalian species. The aim of this review is to compare the effects of plasticizers in animals, with a focus on aquatic species. In summary, we identified three main chains of events that occur in animals exposed to BPA and phthalates. Firstly, plasticizers affect development by altering both the thyroid hormone and growth hormone axes. Secondly, these chemicals interfere with reproduction by decreasing cholesterol transport through the mitochondrial membrane, leading to reduced steroidogenesis. Lastly, exposure to plasticizers leads to the activation of peroxisome proliferator-activated receptors, the increase of fatty acid oxidation, and the reduction in the ability to cope with the augmented oxidative stress leading to reproductive organ malformations, reproductive defects, and decreased fertility.

Toxicity and estrogenic endocrine disrupting activity of phthalates and their mixtures

Phthalates, widely used in flexible plastics and consumer products, have become ubiquitous contaminants worldwide. This study evaluated the acute toxicity and estrogenic endocrine disrupting activity of butyl benzyl phthalate (BBP), di(n-butyl) phthalate (DBP), bis(2-ethylhexyl) phthalate (DEHP), diisodecyl phthalate (DIDP), diisononyl phthalate (DINP), di-n-octyl phthalate (DNOP) and their mixtures. Using a 72 h zebrafish embryo toxicity test, the LC₅₀ values of BBP, DBP and a mixture of the six phthalates were found to be 0.72, 0.63 and 0.50 ppm, respectively. The other four phthalates did not cause more than 50% exposed embryo mortality even at their highest soluble concentrations. The typical toxicity symptoms caused by phthalates were death, tail curvature, necrosis, cardio edema and no touch response. Using an estrogen-responsive ChgH-EGFP transgenic medaka (Oryzias melastigma) eleutheroembryos based 24 h test, BBP demonstrated estrogenic activity, DBP, DEHP, DINP and the mixture of the six phthalates exhibited enhanced-estrogenic activity and DIDP and DNOP showed no enhanced- or anti-estrogenic activity. These findings highlighted the developmental toxicity of BBP and DBP, and the estrogenic endocrine disrupting activity of BBP, DBP, DEHP and DINP on intact organisms, indicating that the widespread use of these phthalates may cause potential health risks to human beings.

Presence of phthalates in gastrointestinal medications: Is there a hidden danger?

Pharmaceutical companies that produce gastrointestinal (GI) medications often utilize phthalates for their ability to localize medication release. Commonly prescribed GI medications that may utilize phthalates are 5-Aminosalicylates, proton pump inhibitors, and pancreatic enzymes. Our understanding of the cumulative health effects of phthalates from medications remains unclear, and there is increasing evidence that phthalates are not harmless. Experimental studies in animals have shown that phthalates, specifically dibutyl phthalate and Di-(2-ethyl-hexyl) phthalate, have the potential to alter and/or inhibit reproductive biology and in utero development. Despite the lack of definitive human data, many cohort and cross-sectional studies demonstrate concerning associations between phthalates and poor health status, specifically developmental problems. Longitudinal studies and studies with larger sample sizes are required to determine whether phthalates actually cause negative health consequences. It is also important that physicians regularly review and discuss with patients the medicinal ingredients in their medications and supplements, specifically in pregnant woman with inflammatory bowel disease.

Alternatives to in vivo tests to detect endocrine disrupting chemicals (EDCs) in fish and amphibians--screening for estrogen, androgen and thyroid hormone disruption

Endocrine disruption is considered a highly relevant hazard for environmental risk assessment of chemicals, plant protection products, biocides and pharmaceuticals. Therefore, screening tests with a focus on interference with estrogen, androgen, and thyroid hormone pathways in fish and amphibians have been developed. However, they use a large number of animals and short-term alternatives to animal tests would be advantageous. Therefore, the status of alternative assays for endocrine disruption in fish and frogs was assessed by a detailed literature analysis. The aim was to (i) determine the strengths and limitations of alternative assays and (ii) present conclusions regarding chemical specificity, sensitivity, and correlation with in vivo data. Data from 1995 to present were collected related to the detection/testing of estrogen-, androgen-, and thyroid-active chemicals in the following test systems: cell lines, primary cells, fish/frog embryos, yeast and cell-free systems. The review shows that the majority of alternative assays measure effects directly mediated by receptor binding or resulting from interference with hormone synthesis. Other mechanisms were rarely analysed. A database was established and used for a quantitative and comparative analysis. For example, a high correlation was observed between cell-free ligand binding and cell-based reporter cell assays, between fish and frog estrogenic data and between fish embryo tests and in vivo reproductive effects. It was concluded that there is a need for a more systematic study of the predictive capacity of alternative tests and ways to reduce inter- and intra-assay variability.

Di (n-butyl) Phthalate Inhibits Testosterone Synthesis Through a Glucocorticoid-Mediated Pathway in Rats

The present study focused on investigating whether the inhibitory effect of di (n-butyl) phthalate (DBP) on testosterone (T) biosynthesis was mediated by the glucocorticoid (GC) pathway in prepubertal male rats and T production after the exposure to DBP ceased. Prepubertal male rats were administered DBP in corn oil orally at 0, 250, 500, 1000, and 2000 mg/kg daily for 30 days. Serum T and GC were measured by radioimmunoassay and enzyme-linked immunosorbent assay, respectively. The responses, including glucocorticoid receptor (GR), type I 11β-hydroxysteroid dehydrogenase (11β-HSD1), and steroidogenesis acute regulatory protein (StAR) in the testes tissues, were determined by Western blotting and reverse transcriptase PCR. DBP exposure resulted in testicular toxicity, such as seminiferous tubule degeneration and a decrease in the number of spermatogenic cells. T was decreased and GC was increased in a DBP concentration-dependent manner in the exposure group. The expression of GR and 11β-HSD1 was significantly increased, with an associated decrease in expression of StAR. Neither the expression of the GR nor 11β-HSD1 and StAR were statistically significantly different in the postexposure group compared with the control. However, the weight and morphology of the testes did not recover in the postexposure group. These data suggest that DBP inhibits testosterone production through a GC-mediated pathway in prepubertal male rats, and after exposure to DBP ceases, testosterone biosynthesis returns.

A critical analysis of the biological impacts of plasticizers on wildlife

This review provides a critical analysis of the biological effects of the most widely used plasticizers, including dibutyl phthalate, diethylhexyl phthalate, dimethyl phthalate, butyl benzyl phthalate and bisphenol A (BPA), on wildlife, with a focus on annelids (both aquatic and terrestrial), molluscs, crustaceans, insects, fish and amphibians. Moreover, the paper provides novel data on the biological effects of some of these plasticizers in invertebrates, fish and amphibians. Phthalates and BPA have been shown to affect reproduction in all studied animal groups, to impair development in crustaceans and amphibians and to induce genetic aberrations. Molluscs, crustaceans and amphibians appear to be especially sensitive to these compounds, and biological effects are observed at environmentally relevant exposures in the low ng l(-1) to microg l(-1) range. In contrast, most effects in fish (except for disturbance in spermatogenesis) occur at higher concentrations. Most plasticizers appear to act by interfering with the functioning of various hormone systems, but some phthalates have wider pathways of disruption. Effect concentrations of plasticizers in laboratory experiments coincide with measured environmental concentrations, and thus there is a very real potential for effects of these chemicals on some wildlife populations. The most striking gaps in our current knowledge on the impacts of plasticizers on wildlife are the lack of data for long-term exposures to environmentally relevant concentrations and their ecotoxicity when part of complex mixtures. Furthermore, the hazard of plasticizers has been investigated in annelids, molluscs and arthropods only, and given the sensitivity of some invertebrates, effects assessments are warranted in other invertebrate phyla.

Cytocompatibility of a tissue conditioner containing vinyl ester as a plasticizer

In the current study, we examined the cytocompatibility of eight vinyl esters as candidate plasticizers for producing phthalate- and ethanol-free tissue conditioners. We measured the estrogenic activity and cytotoxicity of vinyl esters in human fibroblasts and keratinocytes using an E-screen assay and a mitochondrial dye conversion assay, respectively. We also assessed the cytotoxicity of three prototype materials and commercially available tissue conditioners on human fibroblasts grown in collagen gels. Finally, we measured the effects of these materials on the expression of cytokines in three-dimensional cultures by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assays. None of the tested vinyl esters had estrogenic activity. Vinyl octanoate and vinyl pivalate were the least cytotoxic of the eight tested vinyl esters. In the same vein, a prototype tissue conditioner containing vinyl octanoate had equivalent or weaker cytotoxicity and induction of cytokine expression than conventional materials.

Immobilization of simulated reducing agent at the surface of SiO2 fillers in dental composite resins

To reduce the leachability of reducing agents from composite resins, immobilization of a simulated reducing agent at the surface of SiO2 fillers was examined. SiO2 plates were immersed in 2% 3-aminopropyltriethoxy silane/ethanol solution, and then immersed in dimethyl sulfoxide with 0.25 wt% 4-dimethyl amino benzoic acid (DMABA), 2.0 wt% 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride, and 0.5 wt% N-hydroxysuccinimide. Wide-scan spectrum of X-ray photoelectron spectroscopy did not detect carbon contamination. However, narrow scan detected an O=C-N peak at 399.8 eV, suggesting that DMABA could be immobilized on silane-coupled SiO2 plates. Further, surface plasmon resonance analysis indicated the adsorption of MMA at the surface of reducing agent-immobilized plate.