Effects of perinatal exposure to a polybrominated diphenyl ether (PBDE 99) on mouse neurobehavioural development

Toxicity of persistent organic pollutants: a theoretical study

CONTEXT

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are two families of persistent organic pollutants that are dangerous as they remain in the atmosphere for long periods and are toxic for humans and animals. They are found all over the world, including the penguins of Antarctica. One of the mechanisms that explains the toxicity of these compounds is related to oxidative stress. The main idea of this theoretical research is to use conceptual density functional theory as a theory of chemical reactivity to analyze the oxidative stress that PCBs and PBDEs can produce. The electron transfer properties as well as the interaction with DNA nitrogenous bases of nine PCBs and ten PBDEs found in Antarctic penguins are investigated. From this study, it can be concluded that compounds with more chlorine or bromine atoms are more oxidizing and produce more oxidative stress. These molecules also interact directly with the nitrogenous bases of DNA, forming hydrogen bonds, and this may be an explanation for the toxicity. Since quinone-type metabolites of PCBs and PBDEs can cause neurotoxicity, examples of quinones are also investigated. Condensed Fukui functions are included to analyze local reactivity. These results are important as the reactivity of these compounds helps to explain the toxicity of PCBs and PBDEs.

METHODS

All DFT computations were performed using Gaussian16 at M06-2x/6-311 + g(2d,p) level of theory without symmetry constraints. Electro-donating (ω-) and electro-accepting (ω +) powers were used as global response functions and condensed Fukui functions as local parameters of reactivity.

Polybrominated diphenyl ether (PBDE) exposure and adverse maternal and infant health outcomes: Systematic review

Polybrominated diphenyl ethers (PBDEs) are flame retardants found in ambient environment and are measured in humans. There are reports on general PBDE toxicity, including endocrine disrupting properties. Studies on adverse maternal and infant outcomes and underlying toxicity mechanisms needs to be understood. The objective of this study was to conduct a systematic review to examine the state of science on the relationship between PBDE and adverse maternal/infant health outcomes and related maternal biomarker changes. This literature review was conducted using PubMed, Scopus, Embase and Web of Science for published articles from January 2005-February 2022. Article quality was assessed using Newcastle-Ottawa Scale. Of the 1518 articles, only 54 human observational studies were screened in for this review. A second reviewer examined the validity of these articles. Reports on associations between PBDE and maternal health outcomes included gestational hypertension/preeclampsia (N = 2) and gestational diabetes mellitus/glycemic index (N = 6). Meanwhile, reports on PBDE and infant outcomes (N=32) included effects on infant birth weight, birth length and cephalic perimeter, preterm birth, fetal growth restriction and APGAR scores. Although findings on PBDE exposure and adverse infant outcomes showed inconsistencies across studies, in general, negative correlations between maternal PBDEs and infant birth weight, birth length and cephalic perimeter were seen, in few cases, after stratification by sex. Association between maternal PBDE and maternal biomarkers (N=18) suggested negative impact of PBDE exposure on markers relevant to neuro-endocrine system and inflammatory processes. The review findings identified potential associations between maternal PBDE and adverse maternal/infant health outcomes. Furthermore, PBDE-related biomarker changes suggest disturbances in maternal mechanisms relevant to endocrine disrupting properties of PBDEs. The observed study heterogeneity can be attributed to factors namely, sample size, study design and statistical analysis. Overall review findings imply the necessity for further research to validate PBDE exposure-related adverse maternal/infant health effects and to validate underlying toxicity mechanisms.

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Ex vivo exposure to polybrominated diphenyl ether (PBDE) selectively affects the immune response in autistic children

Children on the autism spectrum have been shown to have immune dysregulation that often correlates with behavioral deficits. The role of the post-natal environment in this dysregulation is an area of active investigation. We examined the association between plasma levels of polybrominated diphenyl ether (PBDE) and immune cell function in age-matched autistic children and non-autistic controls. Plasma from children on the autism spectrum (n = 38) and typically developing controls (TD; n = 60) were analyzed for 14 major PBDE congeners. Cytokine/chemokine production was measured in peripheral blood mononuclear cell (PBMC) supernatants with and without ex vivo BDE-49 exposure. Total plasma concentration (∑PBDE14) and individual congener levels were also correlated with T cell function. ∑PBDE14 did not differ between diagnostic groups but correlated with reduced immune function in children on the autism spectrum. In autistic children, IL-2 and IFN-γ production was reduced in association with several individual BDE congeners, especially BDE-49 (p = 0.001). Furthermore, when PBMCs were exposed ex vivo to BDE-49, cells from autistic children produced elevated levels of IL-6, TNF-α, IL-1β, MIP-1α and MCP-1 (p < 0.05). Therefore, despite similar plasma levels of PBDE, these data suggest that PBMC function was differentially impacted in the context of several PBDE congeners in autistic children relative to TD children where increased body burden of PBDE significantly correlated with a suppressed immune response in autistic children but not TD controls. Further, acute ex vivo exposure of PBMCs to BDE-49 stimulates an elevated cytokine response in AU cases versus a depressed response in TD controls. These data suggest that exposure to the toxicant BDE-49 differentially impacts immune cell function in autistic children relative to TD children providing evidence for an underlying association between susceptibility to PBDE exposure and immune anomalies in children on the autism spectrum.

Toxic Effects and Mechanisms of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants used in plastics, textiles, polyurethane foam, and other materials. They contain two halogenated aromatic rings bonded by an ester bond and are classified according to the number and position of bromine atoms. Due to their widespread use, PBDEs have been detected in soil, air, water, dust, and animal tissues. Besides, PBDEs have been found in various tissues, including liver, kidney, adipose, brain, breast milk and plasma. The continued accumulation of PBDEs has raised concerns about their potential toxicity, including hepatotoxicity, kidney toxicity, gut toxicity, thyroid toxicity, embryotoxicity, reproductive toxicity, neurotoxicity, and immunotoxicity. Previous studies have suggested that there may be various mechanisms contributing to PBDEs toxicity. The present study aimed to outline PBDEs' toxic effects and mechanisms on different organ systems. Given PBDEs' bioaccumulation and adverse impacts on human health and other living organisms, we summarize PBDEs' effects and potential toxicity mechanisms and tend to broaden the horizons to facilitate the design of new prevention strategies for PBDEs-induced toxicity.

Adipose tissue levels of polybrominated diphenyl ethers in relation to prognostic biomarkers and progression-free survival time of breast cancer patients in eastern area of southern China: A hospital-based study

Evidence indicates that individual or groups of polybrominated diphenyl ethers (PBDEs) are associated with risk of breast cancer (BC). Epidemiological studies of PBDEs and BC progression are scarce. This study aimed to investigate the relationships between PBDE burdens in adipose tissues and prognostic biomarkers of BC as well as progression-free survival (PFS) of patients for the first time. The concentrations of 14 PBDE congeners in breast adipose tissues of 183 cases from the eastern area of southern China were analyzed by gas chromatography-mass spectrometry (GC-MS). Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression models for the associations between PBDE levels and prognostic biomarkers. Kaplan-Meier and Cox regression analyses were conducted to identify the correlations between PBDEs and PFS. The results showed that BDE-99 and 190 levels were positively associated with clinical stage and N stage respectively (OR = 2.61 [1.26-5.40], OR = 2.78 [1.04-7.46]). Concentrations of BDE-28 and BDE-183 were negatively associated with the expression of estrogen receptor (ER) (OR = 0.30 [0.11-0.81]; 0.39 [0.15-0.99]) and progesterone receptor (PR) (OR = 0.36 [0.14-0.92]; 0.37 [0.15-0.91]), and increased BDE-47 was associated with lower human epidermal growth factor receptor 2 (HER2) expression (OR = 0.44 [0.23-0.86]). Adipose levels of BDE-71, 99, 138, 153, 154 and total PBDEs were positively associated with p53 expression (all P < 0.05). Finally, BDE-47, 99 and 183 were considered as independent prognostic factors for shorter PFS in the Cox models (adjusted hazard ratios = 3.14 [1.26-7.82]; 2.25 [1.03-4.94]; 2.60 [1.08-6.25], respectively). The recurrence risk and prognosis of BC may be closely bound to the body burdens of certain PBDE congeners. Further epidemiological and experimental studies are needed for confirmation.

Persistent autism-relevant behavioral phenotype and social neuropeptide alterations in female mice offspring induced by maternal transfer of PBDE congeners in the commercial mixture DE-71

Polybrominated diphenyl ethers (PBDEs) are ubiquitous persistent organic pollutants (POPs) that are known neuroendocrine disrupting chemicals with adverse neurodevelopmental effects. PBDEs may act as risk factors for autism spectrum disorders (ASD), characterized by abnormal psychosocial functioning, although direct evidence is currently lacking. Using a translational exposure model, we tested the hypothesis that maternal transfer of a commercial mixture of PBDEs, DE-71, produces ASD-relevant behavioral and neurochemical deficits in female offspring. C57Bl6/N mouse dams (F0) were exposed to DE-71 via oral administration of 0 (VEH/CON), 0.1 (L-DE-71) or 0.4 (H-DE-71) mg/kg bw/d from 3 wk prior to gestation through end of lactation. Mass spectrometry analysis indicated in utero and lactational transfer of PBDEs (in ppb) to F1 female offspring brain tissue at postnatal day (PND) 15 which was reduced by PND 110. Neurobehavioral testing of social novelty preference (SNP) and social recognition memory (SRM) revealed that adult L-DE-71 F1 offspring display deficient short- and long-term SRM, in the absence of reduced sociability, and increased repetitive behavior. These effects were concomitant with reduced olfactory discrimination of social odors. Additionally, L-DE-71 exposure also altered short-term novel object recognition memory but not anxiety or depressive-like behavior. Moreover, F1 L-DE-71 displayed downregulated mRNA transcripts for oxytocin (Oxt) in the bed nucleus of the stria terminalis (BNST) and supraoptic nucleus, and vasopressin (Avp) in the BNST and upregulated Avp1ar in BNST, and Oxtr in the paraventricular nucleus. Our work demonstrates that developmental PBDE exposure produces ASD-relevant neurochemical, olfactory processing and behavioral phenotypes that may result from early neurodevelopmental reprogramming within central social and memory networks.

Endocrine disrupting chemicals and breast cancer: a systematic review of epidemiological studies

BACKGROUND

Endocrine-disrupting compounds (EDCs) are ubiquitous substances that are found in our everyday lives, including pesticides, plasticizers, pharmaceutical agents, personal care products, and also in food products and food packaging. Increasing epidemiological evidence suggest that EDCs may affect the development or progression of breast cancer and consequently lead to lifelong harmful health consequences, especially when exposure occurs during early life in humans. Yet so far no appraisal of the available evidence has been conducted on this topic.

OBJECTIVE

To systematically review all the available epidemiological studies about the association of the levels of environmental exposures of EDCs with breast cancer risk.

METHODS

The search was performed in accordance with the PRISMA guidelines. We retrieved articles from PubMed (MEDLINE) until 10 March 2021. The key words used in this research were: "Endocrine disruptor(s)" OR "Endocrine disrupting chemical(s)" OR any of the EDCs mentioned below AND "Breast cancer" to locate all relevant articles published. We included only cohort studies and case-control studies. All relevant articles were accessed in full text and were evaluated and summarized in tables.

RESULTS

We identified 131 studies that met the search criteria and were included in this systematic review. EDCs reviewed herein included pesticides (e.g. p,p'-dichlorodiphenyltrichloroethane (DDT), p,p'-dichlorodiphenyldichloroethylene (DDE), atrazine, 2,3,7,8-tetrachloridibenzo-p-dioxin (TCDD or dioxin)), synthetic chemicals (e.g. bisphenol A (BPA), phthalates, per- and polyfluoroalkyl substances (PFAS), parabens, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), contraceptive pills), phytoestrogens (e.g. genistein, resveratrol), and certain mycotoxins (e.g. zearalenone). Most studies assessed environmental EDCs exposure via biomarker measurements.

CONCLUSION

We identified certain EDC exposures could potentially elevate the risk of breast cancer. As majority of EDCs are highly persistent in the environment and bio-accumulative, it is essential to assess the long-term impacts of EDC exposures, especially multi-generational and transgenerational. Also, since food is often a major route of exposure to EDCs, well-designed exposure assessments of potential EDCs in food and food packing are necessary and their potential link to breast cancer development need to be carefully evaluated for subsequent EDC policy making and regulations.

Clarifying the in-situ cytotoxic potential of electronic waste plastics

Plastics in waste electronics (E-plastics) account for approximately 20% of the entire global electronic waste (E-waste) stream. Most of the E-plastics are not recycled as the presence of toxic additives (e.g. heavy metals, brominated flame retardants (BFRs), antimony, etc.) have associated environmental and health concerns. However, the majority of the studies are focused on quantitative assessment of the toxic constituents in E-plastics, while empirical information regarding the potential toxic effects in humans is largely lacking. To gain a deeper appreciation into the toxicological profile of E-plastics, in situ time-dependent exposures of 6 different human cell lines to a panel of 8 representative E-plastics recovered from liquid crystal displays (LCD), keyboards, screen frames, and wire insulators were conducted. Although several hazardous elements (e.g. Pb, As, Sb, Zn, Cu, etc) were detected at concentrations that far exceed the limit values permitted by the Restriction of Hazardous Substances Directive and EU Directives in the panel E-plastics, in-depth analysis of the 144 unique cell viability data points and live-dead staining experiments suggest that the acute and sub-chronic toxic effects of E-plastics in direct contact with human cells are negligible. These observations agreed with the inductively coupled plasma-optical emission spectrometry data, which revealed that leaching of these toxic additives into the biological milieu is not sufficiently high to trigger a cytotoxic response up to a continuous culture period of 2 weeks. The novel insights gained from this study are posited to further clarify the uncertainty associated with the safety and circular economy implementation of E-plastics.

Prenatal exposure to polybrominated diphenyl ethers (PBDEs) and cognitive ability in early childhood

BACKGROUND

Prenatal exposure to polybrominated diphenyl ethers (PBDEs) has been associated with adverse neurodevelopmental outcomes in children, but evidence remains mixed regarding sex differences in this association.

OBJECTIVE

To examine the prospective association between prenatal PBDE exposure and cognitive ability in young children, as well as potential sex differences.

METHODS

The study was conducted in a multi-site Canadian pregnancy cohort recruited in 2008-11. PBDEs were measured in maternal plasma samples collected early in pregnancy. Cognitive ability was assessed using the Wechsler Preschool and Primary Scale of Intelligence (WPPSI-III) in children at age 3 years (mean = 3.4). Multiple linear regression was used to analyze the association between maternal PBDE plasma concentrations (lipid-standardized and log10-transformed) and Verbal, Performance, and Full Scale IQ scores on the whole sample and stratified by sex, adjusting for confounders.

RESULTS

The sample was composed of 592 children (291 boys and 301 girls). A tenfold increase in maternal blood PBDE concentration (sum of BDE-47, -99, -100, and -153) was associated with lower Full Scale scores in boys (-3.4 points; 95% CI: -7.0, 0.1), after adjusting for confounders. BDE-47 was the congener with the highest concentrations in maternal blood and a tenfold increase in exposure was associated with significantly lower Full Scale IQ scores in boys (-4.4 points; 95% CI: -7.9, -0.9), after adjusting for confounders. Verbal and Performance IQ scores were similarly associated with PBDE exposure. Maternal blood PBDE concentrations were not associated with IQ scores in girls.

CONCLUSIONS

Prenatal exposure to background levels of PBDEs, especially BDE-47, was associated with lower IQ scores in boys, but not in girls. Our results support that exposure to PBDEs during early development may be sex-dependent and detrimental to a child's neurodevelopmental trajectory.

Long-Term Fipronil Treatment Induces Hyperactivity in Female Mice

Fipronil is an insecticide widely used for veterinary and agricultural purposes. While its insecticidal properties mostly rely on its high affinity antagonistic activity on insect γ aminobutyric acid (GABA) receptors, fipronil and its main metabolite fipronil sulfone nevertheless display non-negligible affinity for mammalian GABAA receptor. As several environmental toxicants have been shown to raise the risk of developing various neurodegenerative disorders, the aim of this study was to evaluate whether long-term low dose administration of fipronil could lead to cognitive deficiencies. Our results indicate that long-term fipronil treatment leads to behavioral perturbations in mice, indicating an accumulative effect of sustained exposure to low dose of fipronil. Although no memory impairment was observed during the course of our study, we noticed a significant hyperlocomotion behavior after 43 weeks of weekly fipronil administration, which is consistent with its direct effect on the GABAergic system.

Pro-neurogenic effect of fluoxetine in the olfactory bulb is concomitant to improvements in social memory and depressive-like behavior of socially isolated mice

Although loneliness is a human experience, it can be estimated in laboratory animals deprived from physical contact with conspecifics. Rodents under social isolation (SI) tend to develop emotional distress and cognitive impairment. However, it is still to be determined whether those conditions present a common neural mechanism. Here, we conducted a series of behavioral, morphological, and neurochemical analyses in adult mice that underwent to 1 week of SI. We observed that SI mice display a depressive-like state that can be prevented by enriched environment, and the antidepressants fluoxetine (FLX) and desipramine (DES). Interestingly, chronic administration of FLX, but not DES, was able to counteract the deleterious effect of SI on social memory. We also analyzed cell proliferation, neurogenesis, and astrogenesis after the treatment with antidepressants. Our results showed that the olfactory bulb (OB) was the neurogenic niche with the highest increase in neurogenesis after the treatment with FLX. Considering that after FLX treatment social memory was rescued and depressive-like behavior decreased, we propose neurogenesis in the OB as a possible mechanism to unify the FLX ability to counteract the deleterious effect of SI.

Functional connectivity of the reading network is associated with prenatal polybrominated diphenyl ether concentrations in a community sample of 5 year-old children: A preliminary study

Genetic factors explain 60 percent of variance in reading disorder. Exposure to neurotoxicants, including polybrominated diphenyl ethers (PBDEs), may be overlooked risk factors for reading problems. We used resting-state functional magnetic resonance imaging (rs-fMRI) to examine associations between prenatal PBDE concentrations and functional connectivity of a reading-related network (RN) in a community sample of 5-year-old children (N = 33). Maternal serum PBDE concentrations (∑PBDE) were measured at 12.2 ± 2.8 weeks gestation (mean ± SD). The RN was defined by 12 regions identified in prior task-based fMRI meta-analyses; global efficiency (GE) was used to measure network integration. Linear regression evaluated associations between ∑PBDE, word reading, and GE of the RN and the default mode network (DMN); the latter to establish specificity of findings. Weighted quantile sum regression analyses evaluated the contributions of specific PBDE congeners to observed associations. Greater RN efficiency was associated with better word reading in these novice readers. Children with higher ∑PBDE showed reduced GE of the RN; ∑PBDE was not associated with DMN efficiency, demonstrating specificity of our results. Consistent with prior findings, ∑PBDE was not associated word reading at 5-years-old. Altered efficiency and integration of the RN may underlie associations between ∑PBDE concentrations and reading problems observed previously in older children.

Gestational Exposure to Common Endocrine Disrupting Chemicals and Their Impact on Neurodevelopment and Behavior

Endocrine disrupting chemicals are common in our environment and act on hormone systems and signaling pathways to alter physiological homeostasis. Gestational exposure can disrupt developmental programs, permanently altering tissues with impacts lasting into adulthood. The brain is a critical target for developmental endocrine disruption, resulting in altered neuroendocrine control of hormonal signaling, altered neurotransmitter control of nervous system function, and fundamental changes in behaviors such as learning, memory, and social interactions. Human cohort studies reveal correlations between maternal/fetal exposure to endocrine disruptors and incidence of neurodevelopmental disorders. Here, we summarize the major literature findings of endocrine disruption of neurodevelopment and concomitant changes in behavior by four major endocrine disruptor classes:bisphenol A, polychlorinated biphenyls, organophosphates, and polybrominated diphenyl ethers. We specifically review studies of gestational and/or lactational exposure to understand the effects of early life exposure to these compounds and summarize animal studies that help explain human correlative data.

Polybrominated diphenyl ethers (PBDEs) and hydroxylated PBDEs in human serum from Shanghai, China: a study on their presence and correlations

Polybrominated diphenyl ethers (PBDEs) are becoming a public health concern because of their potential toxicity, from endocrine disruption system to neurodevelopmental impairments. Nonetheless, information on their levels in human blood is scarce. In this study, human serum samples collected in Shanghai, China, were analyzed for the concentrations of PBDEs and their hydroxylated metabolites (OH-PBDEs). Eight PBDE congeners and six OH-PBDE congeners were quantified in serum samples by gas chromatography with mass spectrometry (GC-MS) and high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). As a result, total PBDE concentration ranged from 0.280 to 12.330 ng g^-1 on a lipid weight basis lw (median: 1.100 ng g^-1 lw) and the total OH-PBDE level ranged from 0.045 to 0.363 ng g^-1 (lw) (median: 0.187 ng g^-1 lw). Among them, BDE-47 and 6-OH-BDE-47 were the predominant PBDEs and OH-PBDEs, respectively. In addition, based on the results of the Bartelett X ² test, BDE-47 significantly (p < 0.05) correlated with BDE-28, BDE-100, BDE-85, and BDE-154, whereas 3'-OH-BDE-7 significantly (p < 0.01) correlated with 3-OH-BDE-47, 2-OH-BDE-68, and 6'-OH-BDE-99. Among all donors, no significant association between age and PBDEs (or OH-PBDEs) was found. Further research on the exposure routes in the environment and metabolic processing of PBDEs in human blood is necessary.

Persistent 6-OH-BDE-47 exposure impairs functional neuronal maturation and alters expression of neurodevelopmentally-relevant chromatin remodelers

Polybrominated diphenyl ethers (PBDEs) are a pervasive class of brominated flame retardants that are present in the environment at particularly high levels, especially in the United States. Their environmental stability, propensity for bioaccumulation, and known potential for neurotoxicity has evoked interest regarding their effects on the developing nervous system. Exposure to PBDEs has been strongly associated with neurodevelopmental disorders. However, the details of their mechanistic roles in such disorders are incompletely understood. Here, we report the effects of one of the most prevalent congeners, BDE-47, and its hydroxylated metabolites on the maturation and function of embryonic rat cortical neurons. Prolonged exposure to 6OH-BDE-47 produces the strongest effects amongst the parent BDE-47 congener and its tested hydroxylated metabolites. These effects include: i) disruption of transcriptional responses to neuronal activity, ii) dysregulation of multiple genes associated with neurodevelopmental disorders, and intriguingly, iii) altered expression of several subunits of the developmentally-relevant BAF (Brg1-associated factors) chromatin remodeling complex, including the key subunit BAF170. Taken together, our data indicate that persistent exposure to 6OH-BDE-47 may interfere with neurodevelopmental chromatin remodeling mechanisms and gene transcription programs, which in turn are likely to interfere with downstream processes such as synapse development and overall functional maturity of neurons. Results from this study have identified a novel aspect of 6OH-BDE-47 toxicity and open new avenues to explore the effects of a ubiquitous environmental toxin on epigenetic regulation of neuronal maturation and function.

Differential neurotoxic effects of in utero and lactational exposure to hydroxylated polychlorinated biphenyl (OH-PCB 106) on spontaneous locomotor activity and motor coordination in young adult male mice

We investigated whether in utero or lactational exposure to 4-hydroxy-2',3,3',4',5'-pentachlorobiphenyl (OH-PCB 106) affects spontaneous locomotor activity and motor coordination in young adult male mice. For in utero exposure, pregnant C57BL/6J mice received 0.05 or 0.5 mg/kg body weight of OH-PCB 106 or corn oil vehicle via gavage every second day from gestational day 10 to 18. For lactational exposure, the different groups of dams received 0.05 or 0.5 mg/kg body weight of OH-PCB 106 or corn oil vehicle via gavage every second day from postpartum day 3 to 13. At 6-7 weeks of age, the spontaneous locomotor activities of male offspring were evaluated for a 24-hr continuous session in a home cage and in an open field for 30-min. Motor coordination function on an accelerating rotarod was also measured. Mice exposed prenatally to OH-PCB 106 showed increased spontaneous locomotor activities during the dark phase in the home cage and during the first 10-min in the open field compared with control mice. Mice exposed lactationally to OH-PCB 106, however, did not show a time-dependent decrease in locomotor activity in the open field. Instead, their locomotor activity increased significantly during the second 10-min block. In addition, mice exposed lactationally to OH-PCB 106 displayed impairments in motor coordination in the rotarod test. These results suggest that perinatal exposure to OH-PCB 106 affects motor behaviors in young adult male mice. Depending on the period of exposure, OH-PCB 106 may have different effects on neurobehavioral development.

Developmental exposure to low concentrations of two brominated flame retardants, BDE-47 and BDE-99, causes life-long behavioral alterations in zebrafish

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) were widely used as flame retardants until the early 2000s, mainly in home furnishings and electronics. The persistence of PBDEs in the environment leads to continued ubiquitous exposure to low levels, with infants and children experiencing higher exposures than adults. Accumulating evidence suggest that low-level exposures during early life stages can affect brain development and lead to long-term behavioral impairments. We investigated the effects of zebrafish exposure to low doses of the two prominent PBDEs; 2,2',4,4',5,-Pentabromodiphenyl ether (BDE-99) and 2,2',4,4',-Tetrabromodiphenyl ether (BDE-47), during embryo-development on short- and long-term behavioral endpoints. We included the organophosphate pesticide chlorpyrifos (CPF) due to its well documented neurotoxicity across species from zebrafish to humans.

METHODS

Zebrafish embryos were exposed to the following individual treatments; 0.1% DMSO (vehicle control); 0.3μM CPF; 0.01, 0.03, 0.1, 0.3μM BDE-47; 0.003, 0.03, 0.3, 1, 3, 10, 20μM BDE-99 from 5 until 120h post fertilization (hpf). Low exposure levels were determined as those not causing immediate overt toxicity, and behavior assays were conducted in the low-level range. At 144 hpf the larvae were tested for locomotor activity. At approximately 6 months of age adult zebrafish were tested in a behavioral battery including assays for anxiety-related behavior, sensorimotor response and habituation, social interaction, and predator avoidance.

RESULTS

In the short-term, larval locomotor activity was reduced in larvae treated with 0.3μM CPF and 0.1μM BDE-47. BDE-99 treatment caused non-monotonic dose effects, with 0.3μM causing hyperactivity and 1μM or higher causing hypoactivity. In the long-term, adult anxiety-related behavior was reduced in all treatments as measured in both the novel tank dive test and tap test.

DISCUSSION

We show that exposure of zebrafish embryos to low concentrations of the brominated flame retardants BDE-47 and BDE-99, and the organophosphate pesticide CPF, caused both short- and long-term behavioral impairments. Interestingly, we also found that at very low exposure concentrations, where there were no visible effects on larval activity, adult behavior was still strongly affected.

A Review on Polychlorinated Biphenyls (PCBs) and Polybrominated Diphenyl Ethers (PBDEs) in South Asia with a Focus on Malaysia

Malaysia is a developing country in Southeast Asia, with rapid industrial and economic growth. Speedy population growth and aggressive consumerism in the past five decades have resulted in environmental pollution issues, including products containing polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). PCBs and PBDEs are classified as persistent organic pollutants (POPs) by the Stockholm Convention due to their persistence, bioaccumulation in the environment and toxicity to humans and wildlife. These compounds are known to cause liver dysfunction, thyroid toxicity, developmental neuro-toxicity and possibly cancer. PCBs in air, mussels, pellets, seawater, fresh water, and human breast milk samples were analyzed in Malaysia, while studies on the pollution level of PBDEs in Malaysia were conducted on mussels, soils, leachate and sediment samples. PCBs in breast milk collected from Malaysia was the highest among Asian developing countries, with mean concentration of 80 ng/g lipid weight. On the other hand, the mean concentration of PCBs in mussels collected from Malaysia recorded the second lowest, with 56 ng/g and 89 ng/g lipid weight in two studies respectively. The concentrations of PBDEs in mussels taken from Malaysia fall in the range of 0.84-16 ng/g lipid weight, which is considerably low compared to 104.5 ng/g lipid weight in Philippines and 90.59 ng/g in Korea. Nevertheless, there are limited studies on these compounds in Malaysia, particularly there is no research on PBDEs in breast milk and sediment samples. This review will summarize the contamination levels of PCBs and PBDEs in different samples collected from Asian countries since 1988 until 2010 with a focus on Malaysia and will provide needed information for further research in this field.

Metabolite profiling study on the toxicological effects of polybrominated diphenyl ether in a rat model

Polybrominated diphenyl ethers (PBDEs) are commonly used to retard the combustion of materials such as foam padding, textiles, or plastics, and numerous studies have confirmed the accumulation thereof in the environment and in fish, mammals, and humans. In this study, we used metabolomics to conduct an environmental risk assessment of the PBDE-209. We profiled the urinary metabolites of control and PBDE-treated rats (exposed to PBDE-209) using nuclear magnetic resonance (NMR) and mass spectrometry (MS). Global metabolic profiling indicated that the effects of PBDE-209 on the urinary metabolic profile were not significant. However, targeted metabolic profiling revealed progressive effects of PBDE-209 over a 7-day PBDE-209 treatment. Moreover, despite the weak PBDE-209 effects, we observed that choline, acetylcholine, 3-indoxylsulfate, creatinine, urea, and dimethyl sulfone levels were decreased, whereas that of pyruvate was significantly increased. Furthermore, we suggest that the increased pyruvate level and decreased levels of choline, acetylcholine, and uremic toxins were suggestive of endocrine disruption and neurodevelopmental toxicity caused by PBDEs. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1262-1272, 2017.

Gestational and Lactational Exposure to an Environmentally-Relevant Mixture of Brominated Flame Retardants: Effects on Neurodevelopment and Metabolism

BACKGROUND

Developmental exposure to brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD), has been associated with impaired neurodevelopment and some symptoms of metabolic syndrome. However, there are inconsistencies in studies reporting neurodevelopmental effects with studies of pure substances more likely to report effects than studies of technical products. In addition, the influence of early BFR exposures on later development of metabolic disease-like symptoms has not been investigated. This study examined the effects of perinatal exposure to an environmentally relevant mixture of BFRs based on relative levels observed in house dust, on several markers of neurodevelopment and metabolism in offspring.

METHODS

Sprague-Dawley female rats were fed a diet estimated to deliver daily doses of 0, 0.06, 20, or 60 mg/kg of a mixture of PBDEs and HBCDD from before mating to weaning. Offspring were weaned to control diet and subjected to neurobehavioral and metabolic assessments.

RESULTS

Exposure to BFRs decreased vertical movement in at postnatal day (PND) 32 and increased time to emerge to a lighted area on PND 105 in offspring of both sexes. Although early life exposure to the BFR mixture did not impact measures of glucose or insulin action, male offspring had significantly decreased fat pad weights at PND 46. Total cholesterol was increased in male and female offspring exposed to the highest dose at PND 21.

CONCLUSIONS

These results suggest that gestational and lactational exposure to an environmentally relevant BFR mixture may induce changes in neurodevelopment and lipid metabolism in offspring. Birth Defects Research 109:497-512, 2017.© 2017 The Authors Birth Defects Research Published by Wiley Periodicals, Inc.

BDE-99 impairs differentiation of human and mouse NPCs into the oligodendroglial lineage by species-specific modes of action

Polybrominated diphenyl ethers (PBDEs) are bioaccumulating flame retardants causing developmental neurotoxicity (DNT) in humans and rodents. Their DNT effects are suspected to involve thyroid hormone (TH) signaling disruption. Here, we tested the hypothesis whether disturbance of neural progenitor cell (NPC) differentiation into the oligodendrocyte lineage (O4⁺ cells) by BDE-99 involves disruption of TH action in human and mouse (h,m)NPCs. Therefore, we quantified differentiation of NPCs into O4⁺ cells and measured their maturation via expression of myelin-associated genes (hMBP, mMog) in presence and absence of TH and/or BDE-99. T3 promoted O4⁺ cell differentiation in mouse, but not hNPCs, and induced hMBP/mMog gene expression in both species. BDE-99 reduced generation of human and mouse O4⁺ cells, but there is no indication for BDE-99 interfering with cellular TH signaling during O4⁺ cell formation. BDE-99 reduced hMBP expression due to oligodendrocyte reduction, but concentrations that did not affect the number of mouse O4⁺ cells inhibited TH-induced mMog transcription by a yet unknown mechanism. In addition, ascorbic acid antagonized only the BDE-99-dependent loss of human, not mouse, O4⁺ cells by a mechanism probably independent of reactive oxygen species. These data point to species-specific modes of action of BDE-99 on h/mNPC development into the oligodendrocyte lineage.

Pregnant Women's perceptions of exposure to brominated flame retardants

BACKGROUND

Recent media reports on human studies associating brominated flame retardants (BFRs) in household products in pregnancy with urogenital anomalies in boys and endocrine disruption in both sexes. We sought to explore the perceptions of pregnant women of brominated flame retardant (BFR) exposure, in light of recent media reports on the adverse health effects of BFR exposure prenatally.

METHODS

Pregnant women were recruited for interviews through posters and pamphlets in prenatal clinics, prenatal fairs and community centres. Interviews were audiotaped and transcribed verbatim for Charmaz-based qualitative analysis supported by NVIVO 10™.

RESULTS

Theoretical sufficiency was reached after analyzing the interviews of 23 pregnant women. Themes co-constructed were: I-Lack of Awareness of BFRs; II-Factors Influencing BFR Exposure; III-Responsibility; IV-Informed Choice. Almost all participants felt it was difficult to make informed choices to avoid BFRs, and wanted communication from clinicians and regulation from governments regarding decreasing BFR exposure.

CONCLUSION

Pregnant women in Canada may be unaware of the potential risks of exposure to BFRs. Professional organizations and governments should further study risk associated with BFR exposure in pregnancy and provide educational materials for pregnant women and clinicians regarding BFR exposure.

Implications of Applying Minimal Risk Standards in Clinical Research to Information Provision in Prenatal and Pre-conception Care

BACKGROUND

There have long been minimal risk thresholds beneath which risks may not need to be discussed in clinical research. This threshold concept may be applied to clinical practice. Our research explored application of minimal risk standards in research regulations to providing information in prenatal and pre-conception care.

METHODS

A case study approach applied minimal risk standards in research regulations to prenatal and pre-conception care with respect to the risks of excess alcohol consumption, folic acid insufficiency, exposure to phthalate plasticizers, and exposure to brominated flame retardants (BFRs).

RESULTS

Excess alcohol consumption and folic acid insufficiency were found to be above the minimal risk standards as outlined in research regulations, while exposure to phthalates and BFRs requires more evidence to determine whether they are above minimal risk. However, applying the minimal risk standard based on the daily life of a healthy adult or a fetus in a healthy pregnant woman, phthalates and BFRs are at the minimal risk threshold regardless of their potential harm since all pregnant women may be exposed to these chemicals in their daily life. Nevertheless, if there is demonstration of sufficient evidence of harm, they may be above minimal risk if such harm can be reduced by individual choice to avoid exposure.

CONCLUSION

The minimal risk concept in research regulations as applied to clinical practice may be useful to help clinicians and professional organizations determine what risks need be discussed in prenatal and pre-conception care.

Cross-Sectional Study of Polybrominated Flame Retardants and Self-Reported Attention Deficit Hyperactivity Disorder in US Youth Aged 12-15 (NHANES 2003-2004)

Background. Animal toxicity tests and epidemiological studies suggest that exposure to PBDEs can alter attention behavior, yet few studies have examined their association with diagnosis of attention deficit hyperactivity disorder (ADHD) in adolescents. Methods. Logistic regression was used to examine the cross-sectional association between ADHD and lipid and non-lipid adjusted blood serum concentrations of 2′,4-tribromodiphenyl ether (BDE-28), 2,2′,4,4′-tetrabromodiphenylether (BDE-47), 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99), 2,2′,4,4′,5,5′-pentabromodiphenyl ether (BDE-100), 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE-153), serum PBDEs, above/below the 75th percentile of serum PBDEs, and tertiles of serum PBDE in 12–15-year-olds (N = 292) using the National Health and Nutrition Examination Survey (NHANES) 2003-2004. Results. The ADHD weighted prevalence was 13.57%. The weighted adjusted odds ratios (AOR) and 95% confidence interval (CI) between ADHD diagnosis and lipid adjusted BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, serum total PBDE, serum PBDE concentrations above the 75th percentile, and serum PBDE concentrations in the second or third tertile were 1.16 (95% CI: 0.51, 2.67), 1.36 (95% CI: 0.72, 2.56), 1.51 (95% CI: 0.70, 3.25), 1.53 (95% CI: 0.73, 3.23), 1.43 (95% CI: 0.57, 3.56), 1.41 (0.71, 2.83), 0.59 (0.10, 3.56), 6.16 (1.19, 31.90), and 0.99 (0.23, 4.29). Conclusions. We observed no association between serum PBDE concentrations and ADHD in US youths.

Thyroid hormone disruption and cognitive impairment in rats exposed to PBDE during postnatal development

Polybrominated diphenyl ether flame-retardants (PBDEs) are thyroid-disrupting environmental chemicals. We investigated the effects of postnatal exposure to DE-71 (a mixture of tetra- and penta-brominated congeners), n-propylthiouracil (PTU) and thyroxine (T4) replacement on open-field (OF) and radial maze (RAM) tests. Wistar rats (5 males/5 females per litter, 32 litters) were treated orally (PND 5-22) with PTU (4mg/kg bw/d), DE-71 (30mg/kg bw/d), with and without co-administration of T4 (15μg/kg bw/d, sc). PTU depressed T4 serum levels and body weight gain and enlarged thyroid gland. Although decreasing T4 levels, DE-71 did not change thyroid and body weights. PTU-treated rats showed hyperactivity (PND 42 and 70), and working and reference memory learning deficits (RAM, PND 100). Although not altering motor activity and working memory, DE-71 caused a reference memory deficit (females only). T4 co-administration averted hypothyroxinemia and long-term cognitive deficits caused by PTU and DE-71.

Prenatal polybrominated diphenyl ether and perfluoroalkyl substance exposures and executive function in school-age children

Executive function is a critical behavioral trait rarely studied in relation to potential neurotoxicants. Prenatal exposure to polybrominated diphenyl ethers (PBDEs) and perfluoroalkyl substances (PFASs) has been associated with adverse neurodevelopment, but there is limited research on executive function. Data from 256 mother-child pairs in the Health Outcomes and Measures of the Environment Study, a prospective birth cohort (2003-2006, Cincinnati, OH), was used to examine maternal serum PBDEs and PFASs and executive function in children ages 5 and 8 years. Maternal serum PBDEs and PFASs were measured at 16±3 weeks gestation. Executive function was assessed with the parent-rated Behavior Rating Inventory of Executive Function (BRIEF), which yields composite measures: behavioral regulation index, metacognition index, and global executive composite. Higher BRIEF scores indicate executive function impairments. Linear mixed models and generalized estimating equations were used to estimate covariate-adjusted associations between PBDEs and PFASs and executive function. A 10-fold increase in BDE-153 was associated with poorer behavior regulation (β=3.23, 95% CI 0.60, 5.86). Higher odds of having a score ≥60 in behavior regulation (OR=3.92, 95% CI 1.76, 8.73) or global executive functioning (OR=2.34, 95% CI 1.05, 5.23) was observed with increased BDE-153. Each ln-unit increase in perfluorooctane sulfonate (PFOS) was associated with poorer behavior regulation (β=3.14, 95% CI 0.68, 5.61), metacognition (β=3.10, 95% CI 0.62, 5.58), and global executive functioning (β=3.38, 95% CI 0.86, 5.90). However, no association was observed between perfluorooctanoate (PFOA) and executive function. Prenatal exposures to BDE-153 and PFOS may be associated with executive function deficits in school-age children.

Abdominal Obesity and Insulin Resistance in People Exposed to Moderate-to-High Levels of Dioxin

Obesity, a risk factor for developing metabolic complications, is a major public health problem. Abdominal obesity is strongly accompanied by a cluster of metabolic abnormalities characterized by insulin resistance. The link between persistent organic pollutants (POPs) and insulin resistance has been investigated in animal and epidemiological studies. We aimed to examine whether insulin resistance is greater in people with abdominal obesity (AO) and concomitant exposure to serum dioxins (PCDD/Fs). We conducted a cross-sectional descriptive study of 2876 participants living near a PCDD/Fs contaminated area. Seventeen 2,3,7,8-substituted PCDD/Fs congeners were measured, and then the associations between the main predictor variable, serum TEQ_DF-1998, abdominal obesity (AO), dependent variables, and insulin resistance were examined. Twelve of the 17 congeners, widely distributed among PCDDs, and PCDFs, had trends for associations with abdominal adiposity. In men, the highest quintiles of 1,2,3,7,8-PeCDF; 1,2,3,7,8-PeCDD; 2,3,7,8-TCDD; 2,3,7,8-TCDF; and 2,3,4,7,8-PeCDF had the top five adjusted odds ratios (AORs) + 95% confidence intervals (CIs):[4.2; 2.7–6.4], [3.6; 2.3–5.7], [3.2; 2.1–5.0], [3.0; 2.0–4.5], and [2.9; 1.9–4.7], respectively. In women, the highest quintiles of 1,2,3,4,7,8,9-HpCDF; 1,2,3,6,7,8-HxCDF; and 1,2,3,4,6,7,8-HpCDF had the top three AORs + 95% CIs:[3.0; 1.9–4.7], [2.0; 1.3–3.1], and [1.9; 1.3–2.9], respectively. After confounding factors had been adjusted for, men, but not women, with higher serum TEQ_DF-1998 levels or abdominal obesity had a significantly (P_trend < 0.001) greater risk for abnormal insulin resistance. The groups with the highest joint serum TEQ_DF-1998 and abdominal obesity levels were associated with elevated insulin resistance at 5.0 times the odds of the groups with the lowest joint levels (AOR 5.23; 95% CI: 3.53–7.77). We hypothesize that serum TEQ_DF-1998 and abdominal obesity affect the association with insulin resistance in general populations.

Role of glutamate receptors in tetrabrominated diphenyl ether (BDE-47) neurotoxicity in mouse cerebellar granule neurons

The polybrominated diphenyl ether (PBDE) flame retardants are developmental neurotoxicants, as evidenced by numerous in vitro, animal and human studies. PBDEs can alter the homeostasis of thyroid hormone and directly interact with brain cells. Induction of oxidative stress, leading to DNA damage and apoptotic cell death is a prominent mechanism of PBDE neurotoxicity, though other mechanisms have also been suggested. In the present study we investigated the potential role played by glutamate receptors in the in vitro neurotoxicity of the tetrabromodiphenyl ether BDE-47, one of the most abundant PBDE congeners. Toxicity of BDE-47 in mouse cerebellar neurons was diminished by antagonists of glutamate ionotropic receptors, but not by antagonists of glutamate metabotropic receptors. Antagonists of NMDA and AMPA/Kainate receptors also inhibited BDE-47-induced oxidative stress and increases in intracellular calcium. The calcium chelator BAPTA-AM also inhibited BDE-47 cytotoxicity and oxidative stress. BDE-47 caused a rapid increase of extracellular glutamate levels, which was not antagonized by any of the compounds tested. The results suggest that BDE-47, by still unknown mechanisms, increases extracellular glutamate which in turn activates ionotropic glutamate receptors leading to increased calcium levels, oxidative stress, and ultimately cell death.

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.

Human health risk associated with brominated flame-retardants (BFRs)

The purposes of this review are to assess the human exposure and human and experimental evidence for adverse effects of brominated flame-retardants (BFRs) with specific focus on intake from seafood. The leakage of BFRs from consumer products leads to exposure of humans from fetal life to adulthood. Fish and fish products contain the highest levels of BFRs and dominate the dietary intake of frequent fish eaters in Europe, while meat, followed by seafood and dairy products accounted for the highest US dietary intake. House dust is also reported as an important source of exposure for children as well as adults. The levels of BFRs in the general North American populations are higher than those in Europe and Japan and the highest levels are detected in infants and toddlers. The daily intake via breast milk exceeds the RfD in 10% of US infants. BFRs including PBDEs, HBCDs and TBBP-A have induced endocrine-, reproductive- and behavior effects in laboratory animals. Furthermore, recent human epidemiological data demonstrated association between exposure to BFRs and similar adverse effects as observed in animal studies. Fish including farmed fish and crude fish oil for human consumption may contain substantial levels of BFRs and infants and toddlers consuming these products on a daily basis may exceed the tolerable daily intake suggesting that fish and fish oil alone represent a risk to human health. This intake comes in addition to exposure from other sources (breast milk, other food, house dust). Because potential harmful concentrations of BFRs and other toxicants occur in fish and fish products, research on a wider range of products is warranted, to assess health hazard related to the contamination of fish and fish products for human consumption.

Epigenetic effects of low perinatal doses of flame retardant BDE-47 on mitochondrial and nuclear genes in rat offspring

Polybrominated diphenyl ethers (PBDEs) are known endocrine disrupting chemicals used commonly as flame retardants in everything from electronics to furniture. Exposure to PBDEs during early development has been linked to neurodevelopmental delays. Despite mounting evidence of neurological harm from PBDE exposure, the molecular mechanisms underlying these effects on brain function remain unknown. We examined the effects of perinatal exposure to BDE-47, the most biologically active and prevalent BDE congener in North America, on epigenetic patterns in the frontal lobe of Wistar rats. Dams were gavaged with BDE-47 (0.002 and 0.2mg/kg body weight) at gestation days 9 and 16, and postnatal days 1, 8, and 15. Frontal lobes from offspring at postnatal day 41 were collected to measure 5-methylcytosine (5mC) in mitochondrial cytochrome c oxidase genes (Mt-co1, Mt-co2, and Mt-co3), global nuclear 5-hydroxymethylcytosine (5hmC) content, 5mC in repetitive elements L1Rn, and 5mC in nuclear genes (Bdnf, Crhr1, Mc2r, Nr3c1, and Snca) related to behavioral and brain functions in the nuclear genome. We observed a significant decrease in %5mC in Mt-co2 (difference from control=-0.68%, p=0.01 at the 0.2mg/kg BDE-47). 5mC in repetitive elements L1Rn decreased at 0.002 mg/kg BDE-47 (difference=-1.23%, p=0.02). Decreased nuclear 5mC was observed in Bdnf and Nr3c1 in BDE-47 exposed rats. However, we did not observe significant effects of PBDE toxicity on DNA methylation patterns for the majority of genes in the brain.

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.

Assessment of neurotoxic effects and brain region distribution in rat offspring prenatally co-exposed to low doses of BDE-99 and methylmercury

Exposure to polybrominated diphenyl ether (PDBE) and methylmercury (MeHg) can occur simultaneously as both contaminants are found in the same food sources, especially fish, seafood, marine mammals and milk. The aim of this study was to assess the effects of exposure to low levels of MeHg (2.0 μg mL(-1) in drinking water) and BDE-99 (0.2 mg kg(-1) d(-1)) from gestational day 6 to postnatal day (PND) 21, alone and in combination, on neurobehavioral development and redox responses in offspring. The present study demonstrated an interaction due to co-exposure with low doses of MeHg and BDE-99 enhanced developmental neurotoxic effects. These effects were manifested as the delayed appearance of negative geotaxis reflexes, impaired motor coordination, and induction of oxidative stress in the cerebellum. In particular, the cerebellum may be a sensitive target for combined MeHg and BDE-99 toxicity. The neurotoxicity of low dose MeHg was exacerbated by the presence of low dose of BDE-99. It is concluded that prenatal co-exposure to MeHg and BDE-99 causes oxidative stress in the cerebellum of offspring by altering the activity of different antioxidant enzymes and producing free radicals. Hg retention was not affected by co-exposure to BDE-99. However, MeHg co-exposure seemed to increase BDE-99 concentrations in selected brain regions in pups compared to pups exposed to BDE-99 only. These results showed that the adverse effects following prenatal co-exposure to MeHg and BDE-99 were associated with tissue concentrations very close to the current human body burden of this persistent bioaccumulative compound.

Developmental Exposure to Polybrominated Diphenyl Ethers and Neurodevelopment

Exposure to polybrominated diphenyl ethers (PBDE) during sensitive developmental windows can interfere with cognitive function and behavior, which are critical components of neurodevelopment. The association between developmental exposure to PBDEs and neurodevelopment has been extensively studied using animal models. In this review, we focus on the accumulating evidence in humans. Despite methodological, geographical, and temporal differences between studies, the majority of the epidemiologic evidence supports that early life exposure to PBDEs measured during pregnancy and/or during childhood is detrimental to child neurodevelopment in domains related to child behavior, cognition, and motor skills. While the precise mechanism of action of PBDEs on neurodevelopment is unknown, PBDE-induced neurotoxicity via thyroid hormone disruption and direct action of PBDEs on the developing brain have been proposed and tested. Additional studies are suggested to better understand how early life and/or childhood PBDE exposures, including exposure to specific PBDE congeners, impact neurodevelopmental indices.

Expression of obesity markers and Persistent Organic Pollutants levels in adipose tissue of obese patients: reinforcing the obesogen hypothesis?

Introduction

Persistent Organic Pollutants (POPs) accumulate in adipose tissue and some are described to possess endocrine disrupting capacities. Therefore, it is important to evaluate their effects on key endocrine pathways in adipose tissue (AT), to further evaluate their potential role in metabolic pathologies such as obesity.

Objectives

The aim is twofold: (i) evaluate gene expression levels of obesity marker genes, i.e. the adipokines leptin (LEP), adiponectin (ADIPOQ) and Tumor Necrosis Factor α (TNFα) and the nuclear receptor, Peroxisome Proliferator Activated Receptor γ (PPARγ) in paired subcutaneous (SAT) and visceral (VAT) AT of obese subjects (n = 50) and to relate these values to serum concentrations of LEP and ADIPOQ (ii) evaluate the association of expression levels of marker genes in AT and serum with POP concentrations in AT.

Results and Conclusions

Leptin and adiponectin levels in serum were positively correlated to respectively expression levels of leptin in SAT and adiponectin in VAT. Our study shows more significant correlations between gene expression of obesity marker genes and POP concentrations in VAT compared to SAT. Since VAT is more important than SAT in pathologies associated with obesity, this suggests that POPs are able to influence the association between obesity and the development of associated pathologies. Moreover, this finding reveals the importance of VAT when investigating the obesogen hypothesis. Concerning PPARγ expression in VAT, negative correlations with polychlorinated biphenyls (PCBs) concentrations were found in non T2D patients. LEP serum concentrations correlated with several PCBs in women whereas in men no correlations were found. This strengthens the potential importance of gender differences in obesity and within the obesogen hypothesis.

Effects of decabromodiphenyl ether (BDE-209) on mRNA transcription of thyroid hormone pathway and spermatogenesis associated genes in Chinese rare minnow (Gobiocypris rarus)

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants, which are ubiquitous environmental contaminant found in both abiotic and biotic environmental samples. Deca-BDE (BDE-209) is the principal component, which is currently used worldwide. In this study, the effect of BDE-209 on the mRNA levels of thyroid hormone (TH) related genes and spermatogenesis associated genes were determined from larvae and adult rare minnow (Gobiocypris rarus) exposed to concentrations 0.01, 0.1, 1, and 10 μg/L for 21 days. The results showed that the type II deiodinase (dio2) and sodium iodide symporter (nis) mRNA levels were significantly up-regulated in the larvae at 10 μg/L treatment. In adult, histopathological observations showed that liver of female fish were degenerated at 10 μg/L treatment, and inhibition of spermatogenesis were observed in testis of male fish. In addition, the thyroid hormone receptor α (trα), dio2, and nis mRNA levels in the liver of male and female fish were significantly up-regulated, whereas dio2 and nis mRNA levels were significantly down-regulated in the brain. These results indicate that exposure to BDE-209 could result in tissue-specific alternations of TH-related genes expression in adults. Moreover, the mRNA levels of the testis-specific apoptosis genes, the spermatogenesis-associated 4 (spata4) and spermatogenesis-associated 17 (spata17), were down-regulated at 10 μg/L treatment in testis of male fish. Our results suggest that BDE-209 may pose threat to normal thyroid and reproductive function in fish.

Mass spectrometric characterization of halogenated flame retardants

RATIONALE

Concerns about the adverse health effects of ubiquitous flame retardants spurred our interest in the development of a sensitive and reliable analytical method for these toxic compounds in various sample matrices. This study focuses on the investigation of fragmentation pathways and the structures of target ions of thirteen new halogenated flame retardants.

METHODS

In this study, we use gas chromatography (GC)/high-resolution double-focusing sector mass spectrometry to characterize the fragmentation pathways of these new flame retardants. Along with the isotope patterns, accurate mass data were acquired to verify the molecular formula.

RESULTS

The fragmentation pathways are classified based on the types of bond dissociations, e.g. σ-bond cleavage, α-bond cleavage and multiple-bond dissociations with a hydrogen shift. The α-bond dissociation occurs among 1,2-bis-(2,4,6-tribromophenoxy)ethane, allyl 2,4,6-tribromophenyl ether (ATE), 2,3-dibromopropyl 2,4,6-tribromophenyl ether (DPTE) and 2-bromoallyl 2,4,6-tribromophenyl ether (BATE). The peak clusters that dominated ATE, BATE and hexachlorocyclopentenyl-dibromocyclooctane (HCDBCO) spectra correspond to two fragments as proved by accurate mass data and isotope patterns. These two fragments are formed as the result of two competing fragmentation pathways of radical loss and hydrogen shift. Fragmentation pathways of the other compounds are complex, involving cleavage of multiple bonds and hydrogen shifts.

CONCLUSIONS

The accurate-mass-based GC/MS method offers great selectivity and sensitivity for quantitative analysis of the persistent organic pollutants. Thus, elucidation of the structures of the fragments is of prime importance for building an accurate-mass-based isotopic method. In addition, this study is useful for GC/MS/MS method development because multiple reaction monitoring (MRM) transitions of precursor ions and product ions may be easily elucidated based on these fragmentation patterns.

Environmental enrichment effects on the neurobehavioral profile of selective outbred trait anxiety rats

Environmental enrichment attenuates the response to psychostimulants and has been shown to reduce both anxiety and stress-related behaviors. Since stress is a major vulnerability factor for addiction, we investigated whether enrichment could reverse stress profiles in high anxious rats as well as reduce their amphetamine sensitivity. Using selectively-bred high and low anxiety males (filial 3) from enriched, social or isolated environments, we tested elevated plus maze exploration, novelty place preference and amphetamine (AMPH; 0.5mg/kg, IP)-induced hyperactivity. We measured plasma corticosterone (CORT) response after forced novel object exposure, phosphorylation of the tropomyosin-related kinase B receptor (pTrkB) in the hippocampus and striatum, and dopamine (D2) receptor mRNA levels in the striatum and nucleus accumbens. Results indicate that high anxiety animals reared in social or enriched environments spent more time on open arms of the EPM while low anxiety animals raised in enriched environments spent more time on open arms when compared to either isolated or social groups. There were no group differences or interactions found for novelty place preference. Enriched environments decreased the response to AMPH and stress-induced CORT regardless of trait but selectively decreased pTrkB and increased D2 mRNA levels in high anxiety animals. The results suggest that selectively-bred trait anxiety rats show state anxiety that is influenced by rearing environments, and D2 protein levels and BDNF/TrkB signaling may differentially contribute to integrating these effects.

Neurobehavioral effects, c-Fos/Jun expression and tissue distribution in rat offspring prenatally co-exposed to MeHg and PFOA: PFOA impairs Hg retention

Exposure to methylmercury (MeHg) and perfluorooctanoic acid (PFOA) can occur simultaneously as both contaminants are found in the same food sources, especially fish, seafood, marine mammals and milk. The aim of this study was to assess the effects of exposure to MeHg (10 μg mL(-1) in drinking water) and PFOA (10 μg mL(-1) in drinking water) from gestational day 1 to postnatal day (PND) 21, alone and in combination, on neurobehavioral development and the expression of c-Fos/Jun in different brain regions in the offspring. Our findings showed that exposure to MeHg alone, and exposure to MeHg combined with PFOA significantly induced cliff avoidance reflexes and negative geotaxis reflexes. And these effects appeared to be greater following exposure to MeHg alone. MeHg and/or PFOA exposure did not significantly impair motor coordination functions, or cause significant changes in c-Fos expression in the hippocampus and cerebellum, and spatial learning tests were similar to those in the controls, thus it was impossible to determine whether combined exposure to MeHg and PFOA had any additional effects on both hippocampus and cerebellum regions. However, a significant increase in the frequency of line crossing was observed in rats treated with MeHg or PFOA alone, and there were no significant differences between the MeHg+PFOA-treated group and the controls, suggesting that PFOA was antagonistic to MeHg toxicity in the locomotor activity test. Co-exposure to MeHg and PFOA decreased all tissue Hg concentrations in pups compared to the group exposed to MeHg only, suggesting that PFOA impaired Hg retention in different tissues.