Polybrominated diphenyl ethers in human gestational membranes from women in southeast Michigan

The regulation of endocrine-disrupting chemicals to minimize their impact on health

Endocrine-disrupting chemicals (EDCs) are substances generated by human industrial activities that are detrimental to human health through their effects on the endocrine system. The global societal and economic burden posed by EDCs is substantial. Poorly defined or unenforced policies can increase human exposure to EDCs, thereby contributing to human disease, disability and economic damage. Researchers have shown that policies and interventions implemented at both individual and government levels have the potential to reduce exposure to EDCs. This Review describes a set of evidence-based policy actions to manage, minimize or even eliminate the widespread use of these chemicals and better protect human health and society. A number of specific challenges exist: defining, identifying and prioritizing EDCs; considering the non-linear or non-monotonic properties of EDCs; accounting for EDC exposure effects that are latent and do not appear until later in life; and updating testing paradigms to reflect 'real-world' mixtures of chemicals and cumulative exposure. A sound strategy also requires partnering with health-care providers to integrate strategies to prevent EDC exposure in clinical care. Critical next steps include addressing EDCs within global policy frameworks by integrating EDC exposure prevention into emerging climate policy.

Triiodothyronine or Antioxidants Block the Inhibitory Effects of BDE-47 and BDE-49 on Axonal Growth in Rat Hippocampal Neuron-Glia Co-Cultures

We previously demonstrated that polybrominated diphenyl ethers (PBDEs) inhibit the growth of axons in primary rat hippocampal neurons. Here, we test the hypothesis that PBDE effects on axonal morphogenesis are mediated by thyroid hormone and/or reactive oxygen species (ROS)-dependent mechanisms. Axonal growth and ROS were quantified in primary neuronal-glial co-cultures dissociated from neonatal rat hippocampi exposed to nM concentrations of BDE-47 or BDE-49 in the absence or presence of triiodothyronine (T3; 3-30 nM), N-acetyl-cysteine (NAC; 100 µM), or α-tocopherol (100 µM). Co-exposure to T3 or either antioxidant prevented inhibition of axonal growth in hippocampal cultures exposed to BDE-47 or BDE-49. T3 supplementation in cultures not exposed to PBDEs did not alter axonal growth. T3 did, however, prevent PBDE-induced ROS generation and alterations in mitochondrial metabolism. Collectively, our data indicate that PBDEs inhibit axonal growth via ROS-dependent mechanisms, and that T3 protects axonal growth by inhibiting PBDE-induced ROS. These observations suggest that co-exposure to endocrine disruptors that decrease TH signaling in the brain may increase vulnerability to the adverse effects of developmental PBDE exposure on axonal morphogenesis.

Critical review of analytical methods for the determination of flame retardants in human matrices

Human biomonitoring is a powerful approach in assessing exposure to environmental pollutants. Flame retardants (FRs) are of particular concern due to their wide distribution in the environment and adverse health effects. This article reviews studies published in 2009-2020 on the chemical analysis of FRs in a variety of human samples and discusses the characteristics of the analytical methods applied to different FR biomarkers of exposure, including polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), novel halogenated flame retardants (NHFRs), bromophenols, incl. tetrabromobisphenol A (TBBPA), and organophosphorous flame retardants (PFRs). Among the extraction techniques, liquid-liquid extraction (LLE) and solid phase extraction (SPE) were used most frequently due to the good efficiencies in the isolation of the majority of the FR biomarkers, but with challenges for highly lipophilic FRs. Gas chromatography-mass spectrometry (GC-MS) is mainly applied in the instrumental analysis of PBDEs and most NHFRs, with recent inclusions of GC-MS/MS and high resolution MS techniques. Liquid chromatography-MS/MS is mainly applied to HBCD, bromophenols, incl. TBBPA, and PFRs (including metabolites), however, GC-based analysis following derivatization has also been used for phenolic compounds and PFR metabolites. Developments are noticed towards more universal analytical methods, which enable widening method scopes in the human biomonitoring of FRs. Challenges exist with regard to sensitivity required for the low concentrations of FRs in the general population and limited sample material for some human matrices. A strong focus on quality assurance/quality control (QA/QC) measures is required in the analysis of FR biomarkers in human samples, related to their variety of physical-chemical properties, low levels in most human samples and the risk of contamination.

Women with high plasma levels of PBDE-47 are at increased risk of preterm birth

OBJECTIVES

Nearly 100% of North American women have detectable levels of flame retardants such as polybrominated diphenyl ethers (PBDEs) in their plasma. These molecules have structural homology to thyroid hormones and may function as endocrine disruptors. Thyroid dysfunction has previously been associated with increased risk for preterm birth. Therefore, we conducted a multi-center, case-cohort study to evaluate if high plasma concentrations of a common PBDE congener in the first trimester increases the risk of preterm birth and its subtypes.

METHODS

Pregnant women were recruited at the onset of initiation of prenatal care at Kaiser-Permanente Southern California (KPSC)-West Los Angeles and KPSC-San Diego medical centers. Plasma samples from women whose pregnancies ended preterm and random subset of those delivering at term were assayed for PBDE-47 and thyroid-stimulating hormone (TSH) by immunoassay. Quartile cutoffs were calculated for the patients at term and used to determine if women with exposures in the 4th quartile are at increased risk for preterm birth using logistic regression.

RESULTS

We found that high concentrations of PBDE-47 in the first trimester significantly increased the odds of both indicated (adjusted odds ratio, adjOR=2.35, 95% confidence interval [CI]: 1.31, 4.21) and spontaneous (adjOR=1.76, 95% CI: 1.02, 3.03) preterm birth. Regardless of pregnancy outcome, TSH concentrations did not differ between women with high and low concentrations of PBDE-47.

CONCLUSIONS

These results suggest that high plasma concentrations of PBDE-47 in the first trimester, increases the risk of indicated and spontaneous preterm birth.

Toxicant Disruption of Immune Defenses: Potential Implications for Fetal Membranes and Pregnancy

In addition to providing a physical compartment for gestation, the fetal membranes (FM) are an active immunological barrier that provides defense against pathogenic microorganisms that ascend the gravid reproductive tract. Pathogenic infection of the gestational tissues (FM and placenta) is a leading known cause of preterm birth (PTB). Some environmental toxicants decrease the capacity for organisms to mount an immune defense against pathogens. For example, the immunosuppressive effects of the widespread environmental contaminant trichloroethylene (TCE) are documented for lung infection with Streptococcus zooepidemicus. Group B Streptococcus (GBS; Streptococcus agalactiae) is a bacterial pathogen that is frequently found in the female reproductive tract and can colonize the FM in pregnant women. Work in our laboratory has demonstrated that a bioactive TCE metabolite, S-(1, 2-dichlorovinyl)-L-cysteine (DCVC), potently inhibits innate immune responses to GBS in human FM in culture. Despite these provocative findings, little is known about how DCVC and other toxicants modify the risk for pathogenic infection of FM. Infection of the gestational tissues (FM and placenta) is a leading known cause of PTB, therefore toxicant compromise of FM ability to fight off infectious microorganisms could significantly contribute to PTB risk. This Perspective provides the current status of understanding of toxicant-pathogen interactions in FM, highlighting knowledge gaps, challenges, and opportunities for research that can advance protections for maternal and fetal health.

Brominated diphenyl ether-47 differentially regulates cellular migration and invasion in a human first trimester trophoblast cell line

Polybrominated diphenyl ethers (PBDEs) are flame retardant compounds detected in human placenta and linked to adverse pregnancy outcomes. Impaired trophoblast migration and invasion during early pregnancy have been implicated as potential mechanisms of pregnancy disorders. The present study investigated the effect of BDE-47, a prevalent PBDE congener, on cell migration, invasion, and matrix metalloproteinase (MMP) expression in a human first trimester extravillous trophoblast cell line, HTR-8/SVneo. BDE-47 stimulated cell migration in HTR-SV/neo cells while decreasing invasion of cells into Matrigel. In addition, BDE-47 led to differential expression of MMP-1, -2, -3, and -9 at protein and mRNA levels. In summary, BDE-47 differentially regulated cellular migration and invasion with divergent changes in MMP expression in trophoblasts. Because proper regulation of trophoblast migration and invasion is critical for placental development and function, further research is warranted to determine if exposure to PBDEs disrupts trophoblast functions with increased risk for adverse pregnancy outcomes.

Endocrine disrupting chemicals: Impact on human health, wildlife and the environment

Endocrine disrupting chemicals are a group of pollutants that can affect the endocrine system and lead to diseases and dysfunctions across the lifespan of organisms. They are omnipresent. They are in the air we breathe, in the food we eat and in the water we drink. They can be found in our everyday lives through personal care products, household cleaning products, furniture and in children's toys. Every year, hundreds of new chemicals are produced and released onto the market without being tested, and they reach our bodies through everyday products. Permanent exposure to those chemicals may intensify or even become the main cause for the development of diseases such as type 2 diabetes, obesity, cardiovascular diseases and certain types of cancer. In recent years, legislation and regulations have been implemented, which aim to control the release of potentially adverse endocrine disrupting chemicals, often invoking the precautionary principle. The objective of this review is to provide an overview of research on environmental aspects of endocrine disrupting chemicals and their effects on human health, based on evidence from animal and human studies. Emphasis is given to three ubiquitous and persistent groups of chemicals, polychlorinated biphenyls, polybrominated diphenyl ethers and organochlorine pesticides, and on two non-persistent, but ubiquitous, bisphenol A and phthalates. Some selected historical cases are also presented and successful cases of regulation and legislation described. These led to a decrease in exposure and consequent minimization of the effects of these compounds. Recommendations from experts on this field, World Health Organization, scientific reports and from the Endocrine Society are included.

Effects of biochar on 2, 2', 4, 4', 5, 5'-hexabrominated diphenyl ether (BDE-153) fate in Amaranthus mangostanus L.: Accumulation, metabolite formation, and physiological response

The accumulation and metabolism of 2, 2', 4, 4', 5, 5'-hexabrominated diphenyl ether (BDE-153) in Amaranthus mangostanus L. (amaranth) as affected by different concentrations of biochar (1.3 to 26.6 g/L) under hydroponic conditions exposed to 10 μg/L BDE-153 after 10 days were investigated. Biochar significantly reduced BDE-153 shoot and root content by 27.5-61.6% and 73-95.3%, respectively. In general, BDE-153 migration from solution to amaranth decreased with increasing the doses of biochar. BDE-153 metabolites altered with doses of biochar. The ratio of de-BDEs to BDE-153 in root was polynomial correlated to biochar dose (R² = 0.9356**). Root and shoot Fe content was positively correlated with the BDE-153 amounts (R² = 0.948** and 0.822*, respectively). Though the higher biochar dose could obviously control BDE-153 uptake by the vegetable, the toxicity was caused more significantly. For instances, the high concentration of biochar at 26.6 g/L reduced pigment content, increased total ROS, and elevated antioxidant enzyme activity. At the same time, the O₂^- intensity was linearly positively correlated with de-BDEs in root (R² = 0.7324*) while photosynthetic parameter F_v/fm intensity was polynomial correlated to BDEs in shoot (R² = 0.9366*). Transmission electron microscopy (TEM) confirmed that exposure to BDE-153 and high concentration biochar at 26.6 g/L severely altered the chloroplasts in terms of the organelle shape and the presence of starch granules in the chloroplast. Taken together, biochar as a soil amendment could significantly control BDE-153 uptake and enhance BDE-153 metabolism in vegetables, but considering the dose of biochar to avoid its toxicity with higher dose.

Proteomic evaluation of human umbilical cord tissue exposed to polybrominated diphenyl ethers in an e-waste recycling area

Parental exposure to polybrominated diphenyl ethers (PBDEs) is associated with adverse birth outcomes. This study aims to examine differentially-expressed protein profiles in umbilical cord tissue, derived from mothers exposed to PBDEs, and investigate candidate biomarkers to reveal the underlying molecular mechanisms. Umbilical cord samples were obtained from women residing in an electronic waste (e-waste) recycling area (Guiyu) and reference area (Haojiang) in China. The concentration of PBDEs in umbilical cord tissue was determined by gas chromatography and mass spectrometry (GC/MS). Isobaric tagging for relative and absolute quantification (iTRAQ)-based proteomic technology was conducted to analyze differentially-expressed protein profiles. The total PBDE concentration was approximately five-fold higher in umbilical cords from Guiyu than from Haojiang (median 71.92ng/g vs. 15.52ng/g lipid, P<0.01). Neonatal head circumference, body-mass index (BMI) and Apgar1 score were lower in Guiyu and negatively correlated with PBDE concentration (P<0.01). Proteomic analysis showed 697 proteins were differentially expressed in the e-waste-exposed group compared with the reference group. The differentially-expressed proteins were principally involved in antioxidant defense, apoptosis, cell structure and metabolism. Among them, catalase and glutathione S-transferase omega-1, were down-regulated, and cytochrome c was found to be up-regulated, changes which were further verified by enzyme-linked immunosorbent assays. These results suggest that an antioxidant imbalance and cell apoptosis in the umbilical cord following PBDE exposure is associated with neonatal birth outcomes.

From the Cover: BDE-47 and BDE-49 Inhibit Axonal Growth in Primary Rat Hippocampal Neuron-Glia Co-Cultures via Ryanodine Receptor-Dependent Mechanisms

Polybrominated diphenyl ethers (PBDEs) are widespread environmental contaminants associated with adverse neurodevelopmental outcomes in children and preclinical models; however, the mechanisms by which PBDEs cause developmental neurotoxicity remain speculative. The structural similarity between PBDEs and nondioxin-like (NDL) polychlorinated biphenyls (PCBs) suggests shared toxicological properties. Consistent with this, both NDL PCBs and PBDEs have been shown to stabilize ryanodine receptors (RyRs) in the open configuration. NDL PCB effects on RyR activity are causally linked to increased dendritic arborization, but whether PBDEs similarly enhance dendritic growth is not known. In this study, we quantified the effects of individual PBDE congeners on not only dendritic but also axonal growth since both are regulated by RyR-dependent mechanisms, and both are critical determinants of neuronal connectivity. Neuronal-glial co-cultures dissociated from the neonatal rat hippocampus were exposed to BDE-47 or BDE-49 in the culture medium. At concentrations ranging from 20 pM to 2 µM, neither PBDE congener altered dendritic arborization. In contrast, at concentrations ≥ 200 pM, both congeners delayed neuronal polarization resulting in significant inhibition of axonal outgrowth during the first few days in vitro. The axon inhibitory effects of these PBDE congeners occurred independent of cytotoxicity, and were blocked by pharmacological antagonism of RyR or siRNA knockdown of RyR2. These results demonstrate that the molecular and cellular mechanisms by which PBDEs interfere with neurodevelopment overlap with but are distinct from those of NDL PCBs, and suggest that altered patterns of neuronal connectivity may contribute to the developmental neurotoxicity of PBDEs.

Autism, Mitochondria and Polybrominated Diphenyl Ether Exposure

BACKGROUND

Autism spectrum disorders (ASD) are a growing concern with more than 1 in every 68 children affected in the United States by age 8. Limited scientific advances have been made regarding the etiology of autism, with general agreement that both genetic and environmental factors contribute to this disorder.

OBJECTIVE

To explore the link between exposure to PBDE, mitochondrial dysfunction and autism risk.

RESULTS

Perinatal exposures to PBDEs may contribute to the etiology or morbidity of ASD including mitochondrial dysfunction based on (i) their increased environmental abundance and human exposures, (ii) their activity towards implicated in neuronal development and synaptic plasticity including mitochondria, and (iii) their bioaccumulation in mitochondria.

CONCLUSION

In this review, we propose that PBDE, and possibly other environmental exposures, during child development can induce or compound mitochondrial dysfunction, which in conjunction with a dysregulated antioxidant response, increase a child's susceptibility of autism.

Protective effect of (±)α-tocopherol on brominated diphenyl ether-47-stimulated prostaglandin pathways in human extravillous trophoblasts in vitro

Brominated diphenyl ether (BDE)-47 is a prevalent flame retardant chemical found in human tissues and is linked to adverse pregnancy outcomes in humans. Because dysregulation of the prostaglandin pathway is implicated in adverse pregnancy outcomes, the present study investigates BDE-47 induction of prostaglandin synthesis in a human extravillous trophoblast cell line, HTR-8/SVneo, examining the hypothesis that BDE-47 increases generation of reactive oxygen species (ROS) to stimulate the prostaglandin response. Treatment with 20 μM BDE-47 significantly increased mRNA expression of prostaglandin-endoperoxide synthase 2 (PTGS2) at 4, 12 and 24 h, and 24-h treatment significantly increased cyclooxygenase (COX)-2 cellular protein expression and prostaglandin E2 (PGE2) concentration in culture medium. The BDE-47-stimulated PGE2 release was inhibited by the COX inhibitors indomethacin and NS398, implicating COX activity. Exposure to 20 μM BDE-47 significantly increased ROS generation as measured by carboxydichlorofluorescein fluorescence, and this response was blocked by cotreatment with the peroxyl radical scavenger (±)-α-tocopherol. (±)-α-Tocopherol cotreatment suppressed BDE-47-stimulated increases of PGE2 release without significant effects on COX-2 mRNA and protein expression, implicating a role for ROS in post-translational regulation of COX activity. Because prostaglandins regulate trophoblast functions necessary for placentation and pregnancy, further investigation is warranted of BDE-47 impacts on trophoblast responses.

Human exposure to PBDE and critical evaluation of health hazards

Polybrominated diphenyl ethers (PBDEs) are used in large quantities as flame-retardant additives in a number of commercial products. Biomonitoring data show that, in recent years, PBDE concentrations have increased rapidly in the bodies of wildlife and humans. Usually, PBDE levels in North America have been reported to be higher than those in Europe and Asia. Moreover, body burden of PBDEs is three- to ninefold higher in infants and toddlers than in adults, showing these last two age groups the highest levels of these compounds, due to exposure via maternal milk and through dust. Tetra-, Penta-, and Hexa-BDEs are the isomers most commonly found in humans. Based on studies on experimental animals, the toxicological endpoints of exposure to PBDEs are likely to be thyroid homeostasis disruption, neurodevelopmental deficits, reproductive changes, and even cancer. Experimental studies in animals and epidemiological observations in humans suggest that PBDEs may be developmental neurotoxicants. Pre- and/or postnatal exposure to PBDEs may cause long-lasting behavioral abnormalities, particularly on motor activity and cognition. This paper is focused on reviewing the current status of PBDEs in the environment, as well as the critical adverse health effects based on the recent studies on the toxic effects of PBDEs.

Does exposure to flame retardants increase the risk for preterm birth?

During the past 40 years, polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants and nearly all women have some level of exposure. PBDEs have been isolated from amniotic fluid and cord plasma indicating vertical transmission; however, their effects on pregnancy outcome are largely unknown. Therefore, we quantified PBDE-47, the most common congener in maternal plasma samples collected at the time of labor from women who subsequently had term or preterm birth (PTB). Women were then scored based on whether or not they had very low, low, medium, high or very high peripheral plasma concentrations of PBDE-47. Probit regression analysis suggested that women in the PTB group had a greater chance of scoring higher on this scale (P<0.001). Women with high (OR=3.8, CI: 1.6, 9.7; P=0.003) or very high PBDE-47 concentrations were at greater odds (OR=5.6, CI: 2.2, 15.2; P<0.001) for PTB than women with very low levels of PBDE-47. Results became even more significant after adjustment for maternal race, age, and marital status. These findings suggest that high levels of maternal exposure to PBDEs might increase the risk for PTB.

A mechanistic view of polybrominated diphenyl ether (PBDE) developmental neurotoxicity

Polybrominated diphenyl ethers (PBDEs), extensively used in the past few decades as flame retardants in a variety of consumer products, have become world-wide persistent environmental pollutants. Levels in North America are usually higher than those in Europe and Asia, and body burden is 3-to-9-fold higher in infants and toddlers than in adults. The latter has raised concern for potential developmental toxicity and neurotoxicity of PBDEs. Experimental studies in animals and epidemiological observations in humans suggest that PBDEs may be developmental neurotoxicants. Pre- and/or post-natal exposure to PBDEs may cause long-lasting behavioral abnormalities, particularly in the domains of motor activity and cognition. The mechanisms underlying the developmental neurotoxic effects of PBDEs are not known, though several hypotheses have been put forward. One general mode of action relates to the ability of PBDEs to impair thyroid hormone homeostasis, thus indirectly affecting the developing brain. An alternative or additional mode of action involves a direct effect of PBDEs on nervous system cells; PBDEs can cause oxidative stress-related damage (DNA damage, mitochondrial dysfunction, apoptosis), and interfere with signal transduction (particularly calcium signaling), and with neurotransmitter systems. Important issues such as bioavailability and metabolism of PBDEs, extrapolation of results to low level of exposures, and the potential effects of interactions among PBDE congeners and between PBDEs and other contaminants also need to be taken into account.

Protective effect of nuclear factor E2-related factor 2 on inflammatory cytokine response to brominated diphenyl ether-47 in the HTR-8/SVneo human first trimester extravillous trophoblast cell line

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardants, and BDE-47 is a prevalent PBDE congener detected in human tissues. Exposure to PBDEs has been linked to adverse pregnancy outcomes in humans. Although the underlying mechanisms of adverse birth outcomes are poorly understood, critical roles for oxidative stress and inflammation are implicated. The present study investigated antioxidant responses in a human extravillous trophoblast cell line, HTR-8/SVneo, and examined the role of nuclear factor E2-related factor 2 (Nrf2), an antioxidative transcription factor, in BDE-47-induced inflammatory responses in the cells. Treatment of HTR-8/SVneo cells with 5, 10, 15, and 20μM BDE-47 for 24h increased intracellular glutathione (GSH) levels compared to solvent control. Treatment of HTR-8/SVneo cells with 20μM BDE-47 for 24h induced the antioxidant response element (ARE) activity, indicating Nrf2 transactivation by BDE-47 treatment, and resulted in differential expression of redox-sensitive genes compared to solvent control. Pretreatment with tert-butyl hydroquinone (tBHQ) or sulforaphane, known Nrf2 inducers, reduced BDE-47-stimulated IL-6 release with increased ARE reporter activity, reduced nuclear factor kappa B (NF-κB) reporter activity, increased GSH production, and stimulated expression of antioxidant genes compared to non-Nrf2 inducer pretreated groups, suggesting that Nrf2 may play a protective role against BDE-47-mediated inflammatory responses in HTR-8/SVneo cells. These results suggest that Nrf2 activation significantly attenuated BDE-47-induced IL-6 release by augmentation of cellular antioxidative system via upregulation of Nrf2 signaling pathways, and that Nrf2 induction may be a potential therapeutic target to reduce adverse pregnancy outcomes associated with toxicant-induced oxidative stress and inflammation.

Performance and storage integrity of dried blood spots for PCB, BFR and pesticide measurements

Dried blood spots (DBSs) can provide accurate and valuable estimates of exposure to environmental toxicants, and the use of information derived from archived newborn DBSs has enormous potential to open up new research on the impacts of early chemical exposure on disease. Broad application of DBS for the purpose of quantitative exposure estimation requires robust and validated methods. This study investigates the suitability of DBS analyses for population studies of exposure to three chemical groups: polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs), and chlorinated pesticides. It examines background (matrix) contamination, recovery and extraction variability, sensitivity, and storage stability. DBS samples prepared using 50 μL of adult blood were analyzed by GC/MS, and method performance was confirmed by using certified materials and paired DBS-blood samples from six volunteers. Several of the target compounds and their degradation products have not been previously measured in DBSs. All target compounds were detected in DBS samples collected from the volunteers. Sample DBS cards showed background contamination of several compounds. When stored at room temperature, target compounds, excluding PBDEs, were stable for up to one month. When refrigerated or frozen, stability was acceptable for all compounds up to one year, and multiyear storage appears acceptable at colder (e.g., -80°C) temperatures. Multicompartment models may be used to estimate or correct for storage losses. Considering concentrations of contaminants for adults and children reported in the literature, and experimental values of detection limits and background contamination, DBS samples are suitable for quantifying exposures to many PCBs, BFRs and persistent pesticides.

Involvement of reactive oxygen species in brominated diphenyl ether-47-induced inflammatory cytokine release from human extravillous trophoblasts in vitro

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardant compounds. Brominated diphenyl ether (BDE)-47 is one of the most prevalent PBDE congeners found in human breast milk, serum and placenta. Despite the presence of PBDEs in human placenta, effects of PBDEs on placental cell function are poorly understood. The present study investigated BDE-47-induced reactive oxygen species (ROS) formation and its role in BDE-47-stimulated proinflammatory cytokine release in a first trimester human extravillous trophoblast cell line, HTR-8/SVneo. Exposure of HTR-8/SVneo cells for 4h to 20μM BDE-47 increased ROS generation 1.7 fold as measured by the dichlorofluorescein (DCF) assay. Likewise, superoxide anion production increased approximately 5 fold at 10 and 15μM and 9 fold at 20μM BDE-47 with a 1-h exposure, as measured by cytochrome c reduction. BDE-47 (10, 15 and 20μM) decreased the mitochondrial membrane potential by 47-64.5% at 4, 8 and 24h as assessed with the fluorescent probe Rh123. Treatment with 15 and 20μM BDE-47 stimulated cellular release and mRNA expression of IL-6 and IL-8 after 12 and 24-h exposures: the greatest increases were a 35-fold increased mRNA expression at 12h and a 12-fold increased protein concentration at 24h for IL-6. Antioxidant treatments (deferoxamine mesylate, (±)α-tocopherol, or tempol) suppressed BDE-47-stimulated IL-6 release by 54.1%, 56.3% and 37.7%, respectively, implicating a role for ROS in the regulation of inflammatory pathways in HTR-8/SVneo cells. Solvent (DMSO) controls exhibited statistically significantly decreased responses compared with non-treated controls for IL-6 release and IL-8 mRNA expression, but these responses were not consistent across experiments and times. Nonetheless, it is possible that DMSO (used to dissolve BDE-47) may have attenuated the stimulatory actions of BDE-47 on cytokine responses. Because abnormal activation of proinflammatory responses can disrupt trophoblast functions necessary for placental development and successful pregnancy, further investigation is warranted of the impact of ROS and BDE-47 on trophoblast cytokine responses.

Aerobic biotransformation of decabromodiphenyl ether (PBDE-209) by Pseudomonas aeruginosa

Aerobic biodegradation of decabromodiphenyl ether (PBDE-209) by Pseudomonas aeruginosa under the influence of co-metabolic substrates and heavy metal cadmium ion was studied, The results showed that certain amount of co-metabolic substrates, such as glucose, sucrose, lactose, starch, and beef extract, would promote the biodegradation of PBDE-209, among which glucose most favorably accelerated PBDE-209 degradation by about 36% within 5d. The highest degradation efficiency was reached at the ratio of PBDE-209 and glucose 1:5 while excessive carbon source would actually hamper the degradation efficiency. Exploration of influences of cadmium ion on PBDE-209 biodegradation indicated that degradation efficiency was stimulated at low concentrations of Cd(2+) (0.5-2 mg L(-1)) while inhibited at higher levels (5-10 mg L(-1)), inferring that the heavy metals of different concentrations possessed mixed reactions on PBDE-209 bioremoval. Bromine ion was produced during the biotransformation process and its concentration had a good negative correlation with the residues of PBDE-209. Two nonabromodiphenyl ethers (PBDE-208, PBDE-207), four octabromodiphenyl ethers (PBDE-203, PBDE-202, PBDE-197, PBDE-196) and one heptabromodiphenyl ethers (PBDE-183) were formed with the decomposition of PBDE-209, demonstrating that the main aerobic transformation mechanism of PBDE-209 was debromination.

Simultaneous determination of polybrominated diphenyl ethers and polychlorinated biphenyls by gas chromatography-tandem mass spectrometry in human serum and plasma

Sensitive and reliable methods for simultaneous determination of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in limited volumes of human serum or plasma need to be further documented especially when they accumulate at low levels that are still capable of disrupting endocrine and immune functions, and affecting neurodevelopment and reproduction. The objective of this study was to develop and validate a sensitive and quantitative method that simultaneously quantifies PBDEs and PCBs in 0.5 ml of human serum or plasma. We optimized a solid-phase extraction (SPE) method and used silica particle purification for the extraction of PBDEs and PCBs. Two multiple reactions monitoring (MRM) transitions were optimized for each congener. The sum of the transitions was used for quantification, and their abundance ratios were used for identification. The combined method optimization techniques resulted in limits of detection from 3 to 145 pg/ml for 10 PBDEs and 1-12 pg/ml for 15 PCBs. Method was solidly validated by analyzing serum fortified with a certified PBDE and PCB standard mixture from the National Institute of Standards and Technology (NIST). The accuracy was 88-118% and day-to-day precision was within 19%. The method was successfully applied to quantify native concentrations of PBDE and PCB in commercially available human serum. The sensitivity and selectivity of the GC/EI-MS/MS analysis enables it to be the method of choice for investigations of exposures to PBDE and PCB congeners, especially when sample volume is limited.

Toxicity of the flame-retardant BDE-49 on brain mitochondria and neuronal progenitor striatal cells enhanced by a PTEN-deficient background

Polybrominated diphenyl ethers (PBDEs) represent an important group of flame retardants extensively used, tonnage of which in the environment has been steadily increasing over the past 25 years. PBDEs or metabolites can induce neurotoxicity and mitochondrial dysfunction (MD) through a variety of mechanisms. Recently, PBDEs with < 5 Br substitutions (i.e., 2,2',4,4'-tetrabromodiphenyl ether [BDE-47] and 2,2',4,5'-tetrabromodiphenyl ether [BDE-49]) have gained interest because of their high bioaccumulation. In particular, congeners such as BDE-49 arise as one of the most biologically active, with concentrations typically lower than those observed for BDE-47 in biological tissues; however, its potential to cause MD at biologically relevant concentrations is unknown. To this end, the effect of BDE-49 was studied in brain mitochondria and neuronal progenitor striatal cells (NPC). BDE-49 uncoupled mitochondria at concentrations < 0.1 nM, whereas at > 1 nM, it inhibited the electron transport at Complex V (mixed type inhibition; IC(50) = 6 nM) and Complex IV (noncompetitive inhibition; IC(50) = 40 nM). These concentrations are easily achieved in plasma concentrations considering that BDE-49 (this study, 400-fold) and other PBDEs accumulate 1-3 orders of magnitude in the cells, particularly in mitochondria and microsomes. Similar effects were observed in NPC and exacerbated with PTEN (negative modulator of the PI3K/Akt pathway) deficiency, background associated with autism-like behavior, schizophrenia, and epilepsy. PBDE-mediated MD per se or enhanced by a background that confers susceptibility to this exposure may have profound implications in the energy balance of brain.

Serum and follicular fluid concentrations of polybrominated diphenyl ethers and in-vitro fertilization outcome

There is evidence of endocrine disruption and reproductive effects in animals following exposure to certain PBDEs, but human studies are limited. The goal of this study was to investigate the use of serum and follicular fluid as biomarkers of exposure to PBDEs and to explore whether a relationship between PBDE exposure and early pregnancy loss exists. We measured 8 PBDE congeners in archived serum and ovarian follicular fluid samples from 65 women undergoing in-vitro fertilization (IVF). Logistic regression models were used to predict the odds of failed embryo implantation associated with higher levels of PBDEs among the women in the study. There were moderate Kendall's Tau-beta correlations between serum and follicular fluid concentrations of BDE 28, 47, 100 and 154 (T(β)=0.29-0.38, all p-values<0.005), but BDE 99 and 153 were not correlated between the two matrices (T(β)<0.2, p-values>0.05). Women with detectable concentrations of BDE 153 (39% had detectable levels) in follicular fluid had elevated odds of failed implantation compared with women who had non-detectable concentrations (adjusted OR=10.0; 95%CI: 1.9 to 52; p=0.006; adjusted by age and body mass index). These findings suggest that exposure to BDE 153 may be associated with failed embryo implantation. Due to our observation of only moderate correlations between matrices, serum PBDE concentrations may not be a good indicator of follicular fluid concentrations when studying early pregnancy endpoints in women undergoing IVF.

Polybrominated diphenyl ethers enhance the production of proinflammatory cytokines by the placenta

Polybrominated diphenyl ether(s) (PBDE) are ubiquitous environmental contaminants that bind and cross the placenta but their effects on pregnancy outcome are unclear. It is possible that environmental contaminants increase the risk of inflammation-mediated pregnancy complications such as preterm birth by promoting a proinflammatory environment at the maternal-fetal interface. We hypothesized that PBDE would reduce IL-10 production and enhance the production of proinflammatory cytokines associated with preterm labor/birth by placental explants. Second-trimester placental explants were cultured in either vehicle (control) or 2 μM PBDE mixture of congers 47, 99 and 100 for 72 h. Cultures were then stimulated with 10(6) CFU/ml heat-killed Escherichia coli for a final 24 h incubation and conditioned medium was harvested for quantification of cytokines and PGE(2). COX-2 content and viability of the treated tissues were then quantified by tissue ELISA and MTT reduction activity, respectively. PBDE pre-treatment reduced E. coli-stimulated IL-10 production and significantly increased E. coli-stimulated IL-1β secretion. PBDE exposure also increased basal and bacteria-stimulated COX-2 expression. Basal, but not bacteria-stimulated PGE(2), was also enhanced by PBDE exposure. No effect of PBDE on viability of the explants cultures was detected. In summary, pre-exposure of placental explants to congers 47, 99, and 100 enhanced the placental proinflammatory response to infection. This may increase the risk of infection-mediated preterm birth by lowering the threshold for bacteria to stimulate a proinflammatory response(s).

BDE 49 and developmental toxicity in zebrafish

The polybrominated diphenyl ethers (PBDEs) are a group of brominated flame retardants. Human health concerns of these agents have largely centered upon their potential to elicit reproductive and developmental effects. Of the various congeners, BDE 49 (2,2',4,5'-tetrabromodiphenyl ether) has been poorly studied, despite the fact that it is often detected in the tissues of fish and wildlife species. Furthermore, we have previously shown that BDE 49 is a metabolic debromination product of BDE 99 hepatic metabolism in salmon, carp and trout, underscoring the need for a better understanding of biological effects. In the current study, we investigated the developmental toxicity of BDE 49 using the zebrafish (Danio rerio) embryo larval model. Embryo and larval zebrafish were exposed to BDE 49 at either 5 hours post fertilization (hpf) or 24 hpf and monitored for developmental and neurotoxicity. Exposure to BDE 49 at concentrations of 4iμ-32 μM caused a dose-dependent loss in survivorship at 6 days post fertilization (dpf). Morphological impairments were observed prior to the onset of mortality, the most striking of which included severe dorsal curvatures of the tail. The incidence of dorsal tail curvatures was dose and time dependent. Exposure to BDE 49 caused cardiac toxicity as evidenced by a significant reduction in zebrafish heart rates at 6 dpf but not earlier, suggesting that cardiac toxicity was non-specific and associated with physiological stress. Neurobehavioral injury from BDE 49 was evidenced by an impairment of touch-escape responses observed at 5 dpf. Our results indicate that BDE 49 is a developmental toxicant in larval zebrafish that can cause morphological abnormalities and adversely affect neurobehavior. The observed toxicities from BDE 49 were similar in scope to those previously reported for the more common tetrabrominated congener, BDE 47, and also for other lower brominated PBDEs, suggest that these compounds may share similarities in risk to aquatic species.

Concentrations and speciation of polybrominated diphenyl ethers in human amniotic fluid

Polybrominated diphenyl ethers (PBDEs) are persistent organic chemicals used as flame retardants in textiles, plastics, and consumer products. Although PBDE accumulation in humans has been noted since the 1970s, few studies have investigated PBDEs within the gestational compartment, and none to date has identified levels in amniotic fluid. The present study reports congener-specific brominated diphenyl ether (BDE) concentrations in second-trimester clinical amniotic fluid samples collected in 2009 from fifteen women in southeast Michigan, USA. Twenty-one BDE congeners were measured by GC/MS/NCI. The average total PBDE concentration was 3795 pg/ml amniotic fluid (range: 337-21,842 pg/ml). BDE-47 and BDE-99 were identified in all samples. Based on median concentrations, the dominant congeners were BDE-208, 209, 203, 206, 207, and 47 representing 23, 16, 12, 10, 9 and 6%, respectively, of the total detected PBDEs. PBDE concentrations were identified in all amniotic fluid samples from southeast Michigan, supporting a need for further investigations of fetal exposure pathways and potential impacts on perinatal health.

Para- and ortho-substitutions are key determinants of polybrominated diphenyl ether activity toward ryanodine receptors and neurotoxicity

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardants that bioaccumulate in human tissues. Their neurotoxicity involves dysregulation of calcium ion (Ca(2+))signaling; however, specific mechanisms have yet to be defined.

OBJECTIVE

We aimed to define the structure-activity relationship (SAR) for PBDEs and their metabolites toward ryanodine receptors type 1 (RyR1) and type 2 (RyR2) and to determine whether it predicts neurotoxicity.

METHODS

We analyzed [3H]ryanodine binding, microsomal Ca(2+) fluxes, cellular measurements of Ca(2+) homeostasis, and neurotoxicity to define mechanisms and specificity of PBDE-mediated Ca(2+) dysregulation.

RESULTS

PBDEs possessing two ortho-bromine substituents and lacking at least one para-bromine substituent (e.g., BDE-49) activate RyR1 and RyR2 with greater efficacy than corresponding congeners with two para-bromine substitutions (e.g., BDE-47). Addition of a methoxy group in the free para position reduces the activity of parent PBDEs. The hydroxylated BDEs 6-OH-BDE-47 and 4´-OH-BDE-49 are biphasic RyR modulators. Pretreatment of HEK293 cells (derived from human embryonic kidney cells) expressing either RyR1 or RyR2 with BDE-49 (250 nM) sensitized Ca2+ flux triggered by RyR agonists, whereas BDE-47 (250 nM) had negligible activity. The divergent activity of BDE-49, BDE-47, and 6-OH-BDE-47 toward RyRs predicted neurotoxicity in cultures of cortical neurons.

CONCLUSIONS

We found that PBDEs are potent modulators of RyR1 and RyR2. A stringent SAR at the ortho and para position determined whether a congener enhanced, inhibited, or exerted nonmonotonic actions toward RyRs. These results identify a convergent molecular target of PBDEs previously identified for noncoplanar polychlorinated biphenyls (PCBs) that predicts their cellular neurotoxicity and therefore could be a useful tool in risk assessment of PBDEs and related compounds.

Exposure of the Flemish population to brominated flame retardants: model and risk assessment

Human exposure to brominated flame retardants (BFRs) varies widely throughout the world as it depends on country-related usage, production and legislation of these chemicals. US and UK exposure assessments show very diverse levels and patterns which in turn, are likely to differ from those in background exposed countries such as Belgium, where levels tend to be about an order of magnitude lower. The current study assessed human exposure to BFRs through the indoor and outdoor environment (e.g. dust, soil, and air) and food for all age groups in Flanders, Belgium. Most relevant food groups were identified based on a national food consumption survey and food items with Flemish origin were collected. Dust samples were collected using a standardized protocol in 43 homes and 10 offices throughout Flanders. Food, human milk and dust samples were analysed for their polybrominated diphenylethers (PBDE) and hexabromocyclodecane (HBCD) content using GC/MS and LC/MS-MS. An exposure model was developed including all analysed data, complemented with literature data. The model covered human exposure of infants, children and adults through human milk, food, dust/soil ingestion and air inhalation. Total human exposure was compared to the existing toxicological criteria and previous exposure estimates. In general, the exposure levels through human milk are consistent with those of a background exposed European population, whereas dust and food intake are at the low end of what has been reported in previous European intake assessments. Total average intake of SigmaHBCD and SigmaBDE(5) at 50th percentile (P50) levels by newborns equals 3.1 and 12.0ng/kg body weight (bw) day, respectively. This intake increases to 15.2 and 20.9ng/kgbwday for SigmaHBCD and SigmaBDE(5), for higher exposed newborns (95th percentile=P95 levels). Due to the limited database on health-based limit values for PBDEs and HBCD, it is difficult to assess the immediate health concern for any of the age groups, although the higher intake of newborns indicates the need for ongoing monitoring. For median exposed individuals, the average SigmaHBCD intake peaked at the age 3 to 6years with an intake of 6.59ng/kgbwday and declines to approximately 1ng/kgbwday at later age. SigmaBDE(5) intake exhibited a different profile compared to SigmaHBCD with maximal levels for newborns and a decline to approximately 0.7ng/kgbwday at adulthood.

Polybrominated diphenyl ethers in marine ecosystems of the American continents: foresight from current knowledge

Polybrominated diphenyl ethers (PBDEs) are a class of synthetic halogenated organic compounds used in commercial and household products, such as textiles, furniture, and electronics, to increase their flame ignition resistance and to meet fire safety standards. The demonstrated persistence, bioaccumulation, and toxic potential of these compounds in animals and in humans are of increasing concern. The oceans are considered global sinks for PBDEs, as higher levels are found in marine organisms than in terrestrial biota. For the past three decades, North America has dominated the world market demand for PBDEs, consuming 95% of the penta-BDE formulation. Accordingly, the PBDE concentrations in marine biota and people from North America are the highest in the world and are increasing. Despite recent restrictions on penta- and octa-BDE commercial formulations, penta-BDE containing products will remain a reservoir for PBDE release for years to come, and the deca-BDE formulation is still in high-volume use. In this paper, we review all available data on the occurrence and trends of PBDEs in the marine ecosystems (air, water, sediments, invertebrates, fish, seabirds, and marine mammals) of North and South America. We outline here our concerns about the potential future impacts of large existing stores of banned PBDEs in consumer products, and the vast and growing reservoirs of deca-BDE as well as new and naturally occurring brominated compounds on marine ecosystems.