Year-to-year variation in phthalate metabolites in the Midlife Women's Health Study

BACKGROUND

Humans are widely exposed to phthalates, which are metabolized in the body and excreted in urine. Phthalate metabolites are excreted within hours of exposure, making urinary phthalate biomarker concentrations highly variable.

OBJECTIVE

The goal of this study was to characterize the long-term variability in phthalate biomarker concentrations in women across the midlife transition and to identify factors that may be associated with increased variability in those phthalate biomarker concentrations by analyzing longitudinal urinary phthalate metabolite data from the Midlife Women's Health Study (2006-2015).

METHODS

A total of 741 women were enrolled in the study for a period of up to 4 years, during which they each provided 2-4 urine samples per year over 4 consecutive weeks that were pooled for analysis (1876 total pools). Nine phthalate metabolites were assessed individually and as molar sums representative of common compounds (all phthalates: ƩPhthalates; DEHP: ƩDEHP), exposure sources (plastics: ƩPlastic; personal care products: ƩPCP), and modes of action (anti-androgenic: ƩAA). Phthalate metabolites were analyzed by quartile using generalized linear models. In addition, the impact of explanatory variables (race, annual family income, and type of work) on phthalate quartile was examined using ordinal logistic regression models.

IMPACT STATEMENT

Phthalate biomarker concentrations are highly variable among midlife women over time, and annual sampling may not be sufficient to fully characterize long-term exposure.

Subacute and low dose of tributyltin exposure leads to brown adipose abnormalities in male rats

Tributyltin (TBT) is an obesogenic endocrine disrupting chemical (EDC) linked with several metabolic complications. Brown adipose tissue (BAT) is the principal site for thermogenesis, making it a potential target for obesity management and metabolic disease. However, few studies have evaluated TBT effect on BAT function. In this investigation, we assessed whether subacute (15 days) and low dose of TBT exposure (100 ng/kg/day) results in abnormal BAT morphophysiology in adult male rats. Body temperature, BAT morphology, inflammation, oxidative stress, collagen deposition and BAT metabolic gene expression markers were assessed in room temperature (Room, ∼24 ºC) and after cold tolerance test (Cold, ∼4 ºC) conditions. A reduction in body temperature was observed in both Room and Cold conditions in TBT rats, suggesting abnormal BAT thermogenic function. Changes in BAT morphology were observed in TBT rats, with an increase in BAT lipid accumulation, an increase in BAT unilocular adipocyte number and a decrease in BAT multilocular adipocyte number in Room condition. All these parameters were opposite in Cold condition TBT rats, leading to a borderline increase in BAT UCP1 protein expression. An increase in BAT mast cell number was observed in TBT rats in Room condition. An increase in ED1 protein expression (macrophage marker) was observed in TBT rats in Cold condition. Oxidative stress and collagen deposition increased in both Room and Cold conditions in TBT rats. TBT exposure caused a borderline increase in BAT COL1A1 protein expression in Cold condition. Further, strong negative correlations were observed between body temperature and BAT lipid accumulation, and BAT lipid accumulation and multilocular adipocyte number. Thus, these data suggest that TBT exposure impaired BAT morphophysiology through impacts on lipid accumulation, inflammation, fibrosis and oxidative stress in male rats.

Health impacts of artificial turf: Toxicity studies, challenges, and future directions

Many communities around the country are undergoing contentious battles over the installation of artificial turf. Opponents are concerned about exposure to hazardous chemicals leaching from the crumb rubber cushioning fill made of recycled tires, the plastic carpet, and other synthetic components. Numerous studies have shown that chemicals identified in artificial turf, including polycyclic aromatic hydrocarbons (PAHs), phthalates, and per- and polyfluoroalkyl substances (PFAS), are known carcinogens, neurotoxicants, mutagens, and endocrine disruptors. However, few studies have looked directly at health outcomes of exposure to these chemicals in the context of artificial turf. Ecotoxicology studies in invertebrates exposed to crumb rubber have identified risks to organisms whose habitats have been contaminated by artificial turf. Chicken eggs injected with crumb rubber leachate also showed impaired development and endocrine disruption. The only human epidemiology studies conducted related to artificial turf have been highly limited in design, focusing on cancer incidence. In addition, government agencies have begun their own risk assessment studies to aid community decisions. Additional studies in in vitro and in vivo translational models, ecotoxicological systems, and human epidemiology are strongly needed to consider exposure from both field use and runoff, components other than crumb rubber, sensitive windows of development, and additional physiological endpoints. Identification of potential health effects from exposures due to spending time at artificial turf fields and adjacent environments that may be contaminated by runoff will aid in risk assessment and community decision making on the use of artificial turf.

The Effects of Environmental Contaminant Exposure on Reproductive Aging and the Menopause Transition

PURPOSE OF REVIEW

Menopause marks the end of a woman's reproductive lifetime. On average, natural menopause occurs at 51 years of age. However, some women report an earlier age of menopause than the national average. This can be problematic for women who delay starting a family. Moreover, early onset of menopause is associated with increased risk of cardiovascular disease, depression, osteoporosis, and premature death. This review investigates associations between exposure to endocrine-disrupting chemicals (EDCs) and earlier onset of menopause.

RECENT FINDINGS

Recent data suggest exposure to certain EDCs may accelerate reproductive aging and contribute to earlier onset of menopause. Human and rodent-based studies identify positive associations between exposure to certain EDCs/environmental contaminants and reproductive aging, earlier onset of menopause, and occurrence of vasomotor symptoms. These findings increase our understanding of the detrimental effects of EDCs on female reproduction and will help lead to the development of strategies for the treatment/prevention of EDC-induced reproductive aging.

Perfluorooctanoic Acid Disrupts Ovarian Steroidogenesis and Folliculogenesis in Adult Mice

Perfluorooctanoic acid (PFOA) is a synthetic fluorosurfactant used in the manufacturing of fluorotelomers. Although PFOA is no longer produced in the United States, it is environmentally persistent and found in imported food packaging, cookware, and textiles. Previous studies have identified developmental toxicity of PFOA, but little is known about the effects of PFOA on the adult ovary. Thus, this study examined the effects of PFOA on hormone levels, ovarian steroidogenic gene expression, and folliculogenesis in mice in vitro and in vivo. For the in vitro studies, antral follicles from adult female mice were cultured with vehicle control or 1, 10, or 100 μg/ml PFOA for 96 h. For the in vivo studies, adult CD-1 female mice were orally dosed with vehicle control or 1, 5, 10, or 20 mg/kg/day PFOA for 10 days. Gene expression of steroidogenic enzymes, levels of sex steroid hormones, and follicle counts were analyzed. In vitro, PFOA (100 μg/ml) significantly decreased follicle growth, estradiol and estrone levels, and gene expression of StaR, Cyp11a1, and Hsd3b1 compared with controls. In vivo, exposure to PFOA significantly decreased progesterone and pregnenolone levels (5 mg/kg), increased testosterone levels (1 mg/kg), and increased gene expression of Cyp19a1 (1 mg/kg) compared with controls. Exposure to PFOA also significantly altered follicle counts by decreasing primordial follicles and increasing preantral and antral follicles (5 and 10 mg/kg) compared with controls. Collectively, these data show that PFOA disrupts adult ovarian function in a nonmonotonic matter and may pose a risk for premature ovarian failure.

Early postnatal exposure to di(2-ethylhexyl) phthalate causes sex-specific disruption of gonadal development in pigs

Di(2-ethylhexyl) phthalate (DEHP) is a chemical commonly used as a plasticizer to render polyvinyl chloride products more durable and flexible. Although exposure to DEHP has raised many health concerns due to the identification of DEHP as an endocrine disruptor, it is still used in consumer products, including polyvinyl chloride plastics, medical tubing, car interiors, and children's toys. To investigate the impact of early life exposure to DEHP on the ovary and testes, newborn piglets were orally dosed with DEHP (20 or 200 mg/kg/day) or vehicle control (tocopherol-stripped corn oil) for 21 days. Following treatment, ovaries, testes, and sera were harvested for histological assessment and measurement of steroid hormone levels. In male piglets, progesterone and pregnenolone levels were significantly lower in both treatment groups compared to control, whereas in female piglets, progesterone was significantly higher in the 20 mg group compared to control, indicating sex-specific effects in a non-monotonic manner. Follicle numbers and gene expression of steroidogenic enzymes and apoptotic factors were not altered in treated ovaries compared to controls. In DEHP-treated testes, germ cell migration was impaired and germ cell death was significantly increased compared to controls. Overall, the results of this study suggest that neonatal exposure to DEHP in pigs leads to sex-specific disruption of the reproductive system.

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.

Subchronic and Low Dose of Tributyltin Exposure Leads to Reduced Ovarian Reserve, Reduced Uterine Gland Number, and Other Reproductive Irregularities in Female Mice

Tributyltin (TBT) chloride is an endocrine disrupting chemical associated with reproductive complications. Studies have shown that TBT targets the reproductive tract, impairing ovarian folliculogenesis, and uterine morphophysiology. In this investigation, we assessed whether subchronic and low dose of TBT exposure results in abnormal ovarian follicular reserve and other irregularities in female mice. TBT was administered to female mice (500 ng/kg/day for 12 days via gavage), and reproductive tract morphophysiology was assessed. We further assessed reproductive tract inflammation and oxidative stress. Improper functioning of the reproductive tract in TBT mice was observed. Specifically, irregular estrous cyclicity and abnormal ovarian morphology coupled with reduction in primordial and primary follicle numbers was observed, suggesting ovarian reserve depletion. In addition, improper follicular development and a reduction in antral follicles, corpora lutea, and total healthy ovarian follicles together with an increase in cystic follicles were apparent. Evidence of uterine atrophy, reduction in endometrial gland number, and inflammation and oxidative stress were seen in TBT mice. Further, strong negative correlations were observed between testosterone levels and primordial, primary, and total healthy ovarian follicles. Thus, these data suggest that the subchronic and low dose of TBT exposure impaired ovarian follicular reserve, uterine gland number, and other reproductive features in female mice.

Urinary phthalate metabolite concentrations and hot flashes in women from an urban convenience sample of midlife women

CONTEXT

Phthalate exposure is associated with altered reproductive function, but little is known about associations of phthalate exposure with risk of hot flashes.

OBJECTIVE

To investigate associations of urinary phthalate metabolite levels with four hot flash outcomes in midlife women.

DESIGN

A cross-sectional study of the first year of a prospective cohort of midlife women, the Midlife Women's Health Study (2006-2015), a convenience sample from an urban setting.

PARTICIPANTS

728 multi-racial/ethnic pre- and perimenopausal women aged 45-54 years.

OUTCOME MEASURES

Women completed questionnaires about hot flash experience and provided 1-4 urine samples over four consecutive weeks that were pooled for analysis. Phthalate metabolites were assessed individually and as molar sums representative of common compounds (all phthalates: ƩPhthalates; DEHP: ƩDEHP), exposure sources (plastics: ƩPlastic; personal care products: ƩPCP), and modes of action (anti-androgenic: ƩAA). Covariate-adjusted logistic regression models were used to assess associations of continuous natural log-transformed phthalate metabolite concentrations with hot flash outcomes. Analyses were conducted to explore whether associations differed by menopause status, body mass index (BMI), race/ethnicity, and depressive symptoms.

RESULTS

Overall, 45% of women reported a history of hot flashes. Compared to women who never experienced hot flashes, every two-fold increase in ƩPlastic was associated with 18% (OR: 1.18; 95%CI: 0.98, 1.43) and 38% (OR: 1.38; 95%CI: 1.11, 1.70) higher odds of experiencing hot flashes in the past 30 days and experiencing daily/weekly hot flashes, respectively. Some associations of phthalates with certain hot flash outcomes differed by menopause status, BMI, race/ethnicity, and depressive symptoms.

CONCLUSIONS

This study suggests that phthalates are associated with hot flash experience and may impact hot flash risk in women who are susceptible to experiencing hot flashes.

Environmentally relevant mixtures of phthalates and phthalate metabolites differentially alter the cell cycle and apoptosis in mouse neonatal ovaries†

Phthalates are a group of chemicals used as additives in various consumer products, medical equipment, and personal care products. Phthalates and their metabolites are consistently detected in humans, indicating widespread and continuous exposure to multiple phthalates. Thus, environmentally relevant mixtures of phthalates and phthalate metabolites were investigated to determine the effects of phthalates on the function of the ovary during the neonatal period of development. Neonatal ovaries from CD-1 mice were cultured with dimethyl sulphoxide (DMSO; vehicle control), phthalate mixture (0.1-100 μg/mL), or phthalate metabolite mixture (0.1-100 μg/mL). The phthalate mixture was composed of 35% diethyl phthalate, 21% di(2-ethylhexyl) phthalate, 15% dibutyl phthalate, 15% diisononyl phthalate, 8% diisobutyl phthalate, and 5% benzylbutyl phthalate. The phthalate metabolite mixture was composed of 37% monoethyl phthalate, 19% mono(2-ethylhexyl) phthalate, 15% monobutyl phthalate, 10% monoisononyl phthalate, 10% monoisobutyl phthalate, and 8% monobenzyl phthalate. After 96 h of culture, ovaries were harvested for histological analysis of folliculogenesis, gene expression analysis of cell cycle and apoptosis regulators, and immune staining for cell proliferation and apoptosis. The metabolite mixture significantly decreased the number and percentage of abnormal follicles (100 μg/mL) compared to controls. The metabolite mixture also significantly increased the expression of cell cycle inhibitors (100 μg/mL) and the antiapoptotic factor Bcl2l10 (10 μg/mL) compared to controls. The phthalate mixture did not significantly alter gene expression or follicle counts, but ovaries exposed to the phthalate mixture (0.1 μg/mL) exhibited marginally significantly increased apoptosis as revealed by DNA fragmentation staining. Overall, these data show that parent phthalates and phthalate metabolites differentially impact ovarian function.

Endocrine disrupting chemicals and reproductive disorders in women, men, and animal models

This chapter covers the known effects of endocrine disrupting chemicals (EDCs) on reproductive disorders. The EDCs represented are highly studied, including plasticizers (bisphenols and phthalates), chemicals in personal care products (parabens), persistent environmental contaminants (polychlorinated biphenyls), and chemicals in pesticides or herbicides. Both female and male reproductive disorders are reviewed in the chapter. Female disorders include infertility/subfertility, irregular reproductive cycles, early menopause, premature ovarian insufficiency, polycystic ovarian syndrome, endometriosis, and uterine fibroids. Male disorders include infertility/subfertility, cryptorchidism, and hypospadias. Findings from both human and animal studies are represented.

Zero-Order Catalysis in TAML-Catalyzed Oxidation of Imidacloprid, a Neonicotinoid Pesticide

Bis-sulfonamide bis-amide TAML activator [Fe{4-NO₂ C₆ H₃ -1,2-(NCOCMe₂ NSO₂ )₂ CHMe}]^- (2) catalyzes oxidative degradation of the oxidation-resistant neonicotinoid insecticide, imidacloprid (IMI), by H₂ O₂ at pH 7 and 25 °C, whereas the tetrakis-amide TAML [Fe{4-NO₂ C₆ H₃ -1,2-(NCOCMe₂ NCO)₂ CF₂ }]^- (1), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra-low concentrations of both imidacloprid and 2, 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2. Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [2]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H₂ O₂ ]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [2]>[IMI]. A plausible mechanism of the TAML-catalyzed oxidations of imidacloprid is briefly discussed. Similar zero-order catalysis is presented for the oxidation of 3-methyl-4-nitrophenol by H₂ O₂ , catalyzed by the TAML analogue of 1 without a NO₂ -group in the aromatic ring.

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.

Mechanisms of action of agrochemicals acting as endocrine disrupting chemicals

Agrochemicals represent a significant class of endocrine disrupting chemicals that humans and animals around the world are exposed to constantly. Agrochemicals can act as endocrine disrupting chemicals through a variety of mechanisms. Recent studies have shown that several mechanisms of action involve the ability of agrochemicals to mimic the interaction of endogenous hormones with nuclear receptors such as estrogen receptors, androgen receptors, peroxisome proliferator activated receptors, the aryl hydrocarbon receptor, and thyroid hormone receptors. Further, studies indicate that agrochemicals can exert toxicity through non-nuclear receptor-mediated mechanisms of action. Such non-genomic mechanisms of action include interference with peptide, steroid, or amino acid hormone response, synthesis and degradation as well as epigenetic changes (DNA methylation and histone modifications). This review summarizes the major mechanisms of action by which agrochemicals target the endocrine system.

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.

Common bisphenol A replacements are reproductive toxicants

Replacements for the chemical bisphenol A (BPA) have become commonplace in plastics labelled BPA free. However, many of these chemicals have similar structures and properties to BPA. A new study reports that replacement bisphenols, which were discovered as laboratory contaminants, are reproductive toxicants and that their effects might persist for multiple generations.

Reactivity and operational stability of N-Tailed TAMLs through kinetic studies of the catalyzed oxidation of orange II by H2 O2 : synthesis and X-ray structure of an N-phenyl TAML

Invited for the cover of this issue are Terrence J. Collins and co-workers at Carnegie Mellon University (USA) and the National Chemical Laboratory (India). The image depicts five generations of tetraamido macrocyclic ligand (TAML) activators, which are small molecule, full-functional mimics of oxidizing enzymes that arguably outperform the peroxidase enzymes they mimic. Read the full text of the article at 10.1002/chem.201406061.