Polybrominated diphenyl ether (PBDE) effects in rat neuronal cultures: 14C-PBDE accumulation, biological effects, and structure-activity relationships

Perspective on halogenated organic compounds

During the past century, a vast number of organic chemicals have been manufactured and used in industrial, agricultural, public health, consumer products, and other applications. The widespread use in bulk quantities of halogenated organic chemicals (HOCs; also called Organohalogens), including chlorinated, brominated, and fluorinated compounds, and their persistent nature have resulted in global environmental contamination. Increasing levels of HOCs in environmental media (i.e., air, water, soil, sediment) and in human tissues including adipose tissue, breast milk, and placenta continue to be a cause of ecological and human health concern. Human exposure can occur through multiple pathways including direct skin contact, inhalation, drinking water, and mainly through food consumption. HOCs exposure has been implicated in a myriad of health effects including reproductive, neurological, immunological, endocrine, behavioral, and carcinogenic effects in both wildlife and humans. In addition, recent studies indicate that exposure to HOCs contributes to obesity and type 2 diabetes. Because of these adverse health effects, several regulatory agencies either banned or placed severe restrictions on their production and usage. In turn, many industries withdrew from production and usage of HOCs. This action resulted in decline of older HOCs such as polychlorinated biphenyls (PCBs), but more recent HOCs such as polybrominated diphenyl ethers (PBDEs) and perfluoroalkyl substances (PFAS) show a steady increase/stable with time in the global environment. Based on their use pattern and their persistent chemical properties, human exposure to HOCs will likely continue. Hence, understanding human health effects and taking preventive measures for such exposures are necessary.

Use of enzymatic biomarkers of Labeo rohita to study the effect of polybrominated diphenyl ether (BDE- 209) via dietary exposure in laboratory conditions

Fishes have been widely used as a representative to estimate the health of an aquatic ecosystem. In the present study, Labeo rohita was selected for biomarker study against decabromodiphenyl ether (BDE-209), a persistent organic pollutant (POP), as it is a widely used Indian carp. The results suggested significant effects on the optimum metabolism of Labeo rohita. After 48 to 72 h of exposure, most of the biomarkers such as lactate dehydrogenase (LDH), creatine kinase (CK), serum glutamic pyruvic transaminase (SGPT), serum glutamic oxaloacetic transaminase (SGOT), and hepatosomatic index (HSI) increased drastically indicating the higher index of tissue and liver damage. On the contrary, succinic dehydrogenase (SDH), acetylcholinesterase (AChE), and alkaline phosphatase (ALP) showed a reverse trend suggesting the shifting of fish metabolism towards anaerobic respiration mode because of induced stress. Increased catalase (CAT) activity was also observed, which indicated increased abundance of reactive hydroxyl species and therefore a possible oxidative stress in fishes. It is further suggested to understand and examine the biotransformation characteristics and degradation pathways of polybrominated diphenyl ether (PBDE)s, which would be useful to comprehend their environmental fate.

Perfluorohexane sulfonate induces memory impairment and downregulation of neuroproteins via NMDA receptor-mediated PKC-ERK/AMPK signaling pathway

Perfluorohexane sulfonate (PFHxS) is a widely used industrial chemical detected in human umbilical cord blood and breast milk, and has been suggested to exhibit developmental neurotoxicity. Previous studies on mice reported that neonatal exposure to PFHxS altered neuroprotein levels in the developing brain, and caused behavioral toxicity and cognitive dysfunction in the mature brain. However, the underlying mechanisms responsible for PFHxS-induced neuroprotein dysregulation are poorly understood. In this study, we examined the effect of neonatal exposure to PFHxS on memory function using an in vivo mice model. Furthermore, we examined the levels of growth associated protein-43 (GAP-43) and calcium/calmodulin dependent protein kinase II (CaMKII) (biomarkers of neuronal development) and the involved signaling pathways using differentiated neuronal PC12 cells. PFHxS decreased cell viability, GAP-43 and CaMKII levels, and neurite formation. These effects were mediated by the NMDA receptor, PKC-α, PKC-δ, AMPK and ERK pathways. MK801, an NMDA receptor antagonist, reduced the activation of PKC-α, PKC-δ, ERK and AMPK. The activation of ERK was suppressed by pharmacological and knockdown inhibition of PKC-α and -δ. Interestingly, the AMPK pathway was selectively inhibited by inhibiting PKC-δ but not PKC-ɑ. Consistent with PFHxS-induced neuronal death, and GAP-43 and CaMKII downregulation, neonatal exposure to PFHxS caused significant memory impairment in adult mice. Collectively, these results demonstrate that PFHxS induces persistent developmental neurotoxicity, as well as GAP-43 and CaMKII downregulation via the NMDA receptor-mediated PKCs (α and δ)-ERK/AMPK pathways.

Brominated and chlorinated contaminants in food (PCDD/Fs, PCBs, PBDD/Fs PBDEs): Simultaneous determination and occurrence in Italian produce

Validated methodology for the simultaneous determination of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) and polybrominated diphenyl ethers (PBDEs) in foods of animal origin is presented. Method performance indicators were equivalent or better than those required for the control of EU regulated (EU, 2017/644) PCDD/F and PCB congeners in these foods, and for risk assessment through dietary intake. The method uses a high (>90%) proportion of ¹³Carbon-labelled surrogates for internal standardisation combined with high resolution mass spectrometry that allow accurate quantitation, and this was confirmed by multiple successful participations in proficiency testing for PCDD/Fs, PCBs and PBDEs in food. The same validation and method performance requirements as used for PCDD/Fs were followed for PBDD/Fs. The analysis of a range of food samples (eggs, milk, fish, shellfish, pork, beef and poultry), showed the occurrence of all four classes of contaminants at varying concentration ranges. In general, PCBs were the most prominent contaminant, both, in terms of dioxin-like toxicity, as well as in the occurrence of non-dioxin-like congeners, an observation that concurs with those made in other studies on Italian foods. The levels of PCDD/F and PCB occurrence are consistent with a gradual decline in contamination as reported by some other similar studies. Although all the determined contaminants were detected in the sampled foods, there was poor correlation between the occurrences of the brominated and chlorinated contaminants, and between PBDEs and PBDD/Fs, but better associations were observed between the occurrences of the chlorinated contaminants.

Hexachloronaphthalene (HxCN) impairs the dopamine pathway in an in vitro model of PC12 cells

Among polychlorinated naphthalenes (PCNs), listed by the Stockholm convention as Persistent Organic Pollutants (POPs), hexachloronaphthalenes are considered the most toxic and raise the highest concern. Of these, 1,2,3,5,6,7-hexachloronaphthalanene (PCN67) is considered the main congener affecting human health due to its hepatotoxicity and its ability to disturb the reproductive, endocrine, and hematological systems. It is also prevalent in human serum/plasma, milk, and adipose tissue. However, little is known about its neurotoxicity, despite the fact that anorectic effects have been observed in workers occupationally exposed to PCNs and in animal research on PCN67. Since dopamine is involved in many aspects of food intake, the aim of this study was to confirm whether PCN67 affects dopamine synthesis in differentiated PC12 cells, a widely used model of neurosecretion. Our results show that exposure to PCN67 resulted in diminished dopamine content and release. Moreover, PCN67 also affected the expression of tyrosine hydroxylase and lowered the expression of vesicular monoamine transporter 1 (VMAT1). In addition, significantly lower expression of antioxidant enzymes, including catalase, glutathione peroxidase and copper/zinc superoxide dismutase, was observed in comparison to the vehicle. In conclusion, PCN67 appears to disturb dopaminergic transmission by altering tyrosine hydroxylation, reducing VMAT1 expression and impairing antioxidant protection. Our study provides a potential mechanism for how PCN67 may cause dopamine deficiency and contribute to neuronal death by affecting cellular antioxidant potency; however, this conclusion requires further research.

Effects of a human-based mixture of persistent organic pollutants on the in vivo exposed cerebellum and cerebellar neuronal cultures exposed in vitro

Exposure to persistent organic pollutants (POPs), encompassing chlorinated (Cl), brominated (Br) and perfluoroalkyl acid (PFAA) compounds is associated with adverse neurobehaviour in humans and animals, and is observed to cause adverse effects in nerve cell cultures. Most studies focus on single POPs, whereas studies on effects of complex mixtures are limited. We examined the effects of a mixture of 29 persistent compounds (Cl + Br + PFAA, named Total mixture), as well as 6 sub-mixtures on in vitro exposed rat cerebellar granule neurons (CGNs). Protein expression studies of cerebella from in vivo exposed mice offspring were also conducted. The selection of chemicals for the POP mixture was based on compounds being prominent in food, breast milk or blood from the Scandinavian human population. The Total mixture and sub-mixtures containing PFAAs caused greater toxicity in rat CGNs than the single or combined Cl/Br sub-mixtures, with significant impact on viability from 500x human blood levels. The potencies for these mixtures based on LC₅₀ values were Br + PFAA mixture > Total mixture > Cl + PFAA mixture > PFAA mixture. These mixtures also accelerated induced lipid peroxidation. Protection by the competitive N-methyl-D-aspartate (NMDA) receptor antagonist 3-((R)-2-Carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) indicated involvement of the NMDA receptor in PFAA and Total mixture-, but not Cl mixture-induced toxicity. Gene-expression studies in rat CGNs using a sub-toxic and marginally toxic concentration ((0.4 nM-5.5 µM) 333x and (1 nM-8.2 µM) 500x human blood levels) of the mixtures, revealed differential expression of genes involved in apoptosis, oxidative stress, neurotransmission and cerebellar development, with more genes affected at the marginally toxic concentration. The two important neurodevelopmental markers Pax6 and Grin2b were downregulated at 500x human blood levels, accompanied by decreases in PAX6 and GluN2B protein levels, in cerebellum of offspring mice from mothers exposed to the Total mixture throughout pregnancy and lactation. In rat CGNs, the glutathione peroxidase gene Prdx6 and the regulatory transmembrane glycoprotein gene Sirpa were highly upregulated at both concentrations. In conclusion, our results support that early-life exposure to mixtures of POPs can cause adverse neurodevelopmental effects.

Acute in vitro effects on embryonic rat dorsal root ganglion (DRG) cultures by in silico predicted neurotoxic chemicals: Evaluations on cytotoxicity, neurite length, and neurophysiology

The Hard-Soft Acid and Base hypothesis can be used to predict the potential bio-reactivity (electrophilicity) of a chemical with intracellular proteins, resulting in neurotoxicity. Twelve chemicals predicted to be neurotoxic were evaluated in vitro in rat dorsal root ganglia (DRG) for effects on cytotoxicity (%LDH), neuronal structure (total neurite length/neuron, NLPN), and neurophysiology (mean firing rate, MFR). DRGs were treated acutely on days in vitro (DIV) 7 (1-100 μM) with test chemical; %LDH and NLPN were measured after 48 h. 4-cyclohexylhexanone (4-C) increased %LDH release at 50 (29%) and 100 μM (56%), citronellal (Cit) and 1-bromopropane increased %LDH at 100 μM (22% and 26%). 4-C, Cit, 2,5 Hexanedione (2,5Hex), phenylacetylaldehyde (PAA) and 2-ethylhexanal decreased mean NLPN at 48 h; 50 and 100 μM for 4-C (28% and 60%), 100 μM Cit (52%), 100 μM 2,5- Hex (37%) 100 μM PAA (41%) and 100 μM for 2-ethylhexanal (23%). Separate DRG cultures were treated on DIV 14 and changes in MFR measured. Four compounds decreased MFR at 50 or 100 μM: Acrylamide (-83%), 3,4-dichloro-1-butene (-93%), 4-C (-89%) and hexane (-79%, 50 μM). Changes in MFR and NLPN occurred in absence of cytotoxicity. While the current study showed little cytotoxicity, it gave insight to initial changes in MFR. Results provide insight for future chronic exposure experiments to evaluate neurotoxicity.

Childhood polybrominated diphenyl ether (PBDE) serum concentration and reading ability at ages 5 and 8 years: The HOME Study

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) exist extensively in the environment and human beings. PBDE concentrations are higher in children than adults. A previous study found that prenatal PBDE exposure was associated with decreased reading skills in children; however, evidence is limited on the potential impact of childhood exposure to PBDEs. The study examined the association between childhood PBDE exposures and reading ability in children at ages 5 and 8 years.

METHODS

The study included 230 children from an ongoing prospective pregnancy and birth cohort study, the Health Outcomes and Measures of Environment (HOME) Study, conducted in Cincinnati, Ohio. Children's serum concentrations of eleven PBDE congeners were measured at 1, 2, 3, 5, and 8 years. The Woodcock-Johnson Tests of Achievement - III and the Wide Range Achievement Test - 4 were administered to assess children's reading skills at ages 5 and 8 years, respectively. We used multiple informant models to examine the associations between repeated measures of PBDEs and reading scores at ages 5 and 8 years. We also estimated the βs and 95% CIs of the association of PBDE measure at each age by including interaction terms between PBDE concentrations and child age in the models.

RESULTS

All childhood BDE-153 concentrations were inversely associated with reading scores at 5 and 8 years, but associations were not statistically significant after covariate adjustment. For example, a 10-fold increase in BDE-153 concentrations at ages 3 and 5 years was associated with a -5.0 (95% confidence interval (CI): -11.0, 1.0) and -5.5 (95% CI: -12.5, 1.4) point change in Basic Reading score at age 5 years, respectively. Similarly, the estimates for Brief Reading score at age 5 years were -4.5 (95% CI: -10.5, 1.5) and -5.2 (95% CI: -12.2, 1.7) point changes, respectively. Serum concentration of BDE-47, -99, -100, and Sum₄PBDEs (sum of BDE-47, 99, 100, and 153) at every age were inversely associated with reading scores at ages 5 and 8 years in unadjusted analyses. While the adjusted estimates were much attenuated and became non-significant, the direction of most of the associations was not altered.

CONCLUSION

Our study has shown a suggestive but non-significant trend of inverse associations between childhood PBDE serum concentrations, particularly BDE-153, and children's reading skills. Future studies with a larger sample size are needed to examine these associations.

Magnetic effervescent tablet-assisted ionic liquid-based dispersive liquid-liquid microextraction of polybrominated diphenyl ethers in liquid matrix samples

Herein, a novel method, magnetic effervescent tablet-assisted ionic liquid-based dispersive liquid-liquid microextraction (META-IL-DLLME), was pioneered for extraction and preconcentration of polybrominated diphenyl ethers (PBDEs) in liquid matrix samples. In this proposed method, a magnetic effervescent tablet, containing CO₂ sources, ionic liquids and Fe₃S₄ magnetic nanoparticles (MNPs), combines extractant dispersion and magnetic recovery into one-step. Fe₃S₄ was synthesized, characterized and applied it for the first time to the newly developed method, and its extraction recoveries (ERs) for PBDEs were 20.8-32.0% higher than those of conventional Fe₃O₄ MNPs. The increased ERs of Fe₃S₄ resulted from its larger specific surface area and pore size. Some important parameters were rigorously optimized, such as kinds of magnetic nanoparticles, effervescent agents, extraction solvents and their volumes, elution solvents, extraction temperature and salt addition. Under the optimized conditions, the META-IL-DLLME method combined with HPLC-DAD analysis gave the linear ranges of 0.1-0.5-100 µg L^-1 with correlation coefficients of > 0.9990. The ERs ranged from 80.7% to 99.3%, and the limits of detection and quantitation were 0.012-0.078 µg L^-1 and 0.04-0.26 µg L^-1, respectively. The intra- and inter-day precisions, expressed as relative standard deviations (RSD, n = 6), were 1.32-4.83% and 1.99-4.25%, respectively. To evaluate its matrix effect, the relative recoveries of PBDEs from tap and river water, skim and whole milk, pregnant women and women serum samples at three fortification levels (2.0, 5.0 and 20.0 µg L^-1) were in the range of 77.3-106.7%. Overall, the commercial Fe₃O₄ MNPs can only be used for magnetic separation in microextraction procedures, while Fe₃S₄ MNPs gave the higher adsorption and extraction efficiency for organic analytes besides the convenient magnetic separation. Therefore, the results obtained in this study provide a superior alternative for the conventional magnetic separation and adsorbent material. Also, this newly developed method has a great potential in routine monitoring of liquid matrix samples.

The Role of MicroRNAs in Environmental Risk Factors, Noise-Induced Hearing Loss, and Mental Stress

SIGNIFICANCE

MicroRNAs (miRNAs) are important regulators of gene expression and define part of the epigenetic signature. Their influence on every realm of biomedicine is established and progressively increasing. The impact of environment on human health is enormous. Among environmental risk factors impinging on quality of life are those of chemical nature (toxic chemicals, heavy metals, pollutants, and pesticides) as well as those related to everyday life such as exposure to noise or mental and psychosocial stress. Recent Advances: This review elaborates on the relationship between miRNAs and these environmental risk factors.

CRITICAL ISSUES

The most relevant facts underlying the role of miRNAs in the response to these environmental stressors, including redox regulatory changes and oxidative stress, are highlighted and discussed. In the cases wherein miRNA mutations are relevant for this response, the pertinent literature is also reviewed.

FUTURE DIRECTIONS

We conclude that, even though in some cases important advances have been made regarding close correlations between specific miRNAs and biological responses to environmental risk factors, a need for prospective large-cohort studies is likely necessary to establish causative roles. Antioxid. Redox Signal. 28, 773-796.

Enantioseparation and identification for the rationalization of the environmental impact of 4 polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are harmful and persistent organic pollutants that have long been used in industrial manufacturing. Their persistence leads to accumulation in the food chain causing potential toxic effects. As 19 out of 78 of the chiral congeners have stable atropisomers at ambient temperature, we studied some typical enantiomers: PCB45, PCB95, PCB136, and PCB149. The chiral stationary phases OD-H and OJ-H were used for separation in analytic high-performance liquid chromatography (HPLC), as well as for collection in semi-preparative HPLC. The resolution was optimized with respect to n-hexane-based mobile phases, temperature, and flow rate. All pure enantiomers were recovered from semi-preparative HPLC within 15 minutes for practical purpose. Characterization of the absolute configurations were conducted with a combination of theoretical and experimental electronic circular dichroism measurements. The enantiomers of PCB45, PCB95, PCB136, and PCB149 proved to be eluted as R > S, S > R, R > S, and S > R, respectively. Molecular structures (eg, substituent groups) and properties (eg, bond lengths, bond angles, and dipole moments) were quantitatively analyzed to understand the toxicity effect of PCBs. In summary, we have developed a well-established methodology of collection and configuration identification for analogous PCB derivatives.

The flame retardant 2,2',4,4'-Tetrabromodiphenyl ether enhances the expression of corticotropin-releasing hormone in the placental cell model JEG-3

Polybrominated diphenyl ethers (PBDEs) are chemicals used as flame retardants in household products. After disposing of these items, PBDEs leach from the products by surface water. BDE-47 is a PBDE congener commonly isolated from contaminated food and is the most studied isomer. The placenta is the major source of hormones during pregnancy, and an elevated level of corticotrophin-releasing hormone (CRH) is associated with premature delivery. In the present study, we examined changes in the placental CRH expression under BDE-47 exposure in the JEG-3 cell model system. These placental cells are derived from human choriocarcinoma. Our result showed that this pollutant induced the CRH mRNA expression at 0.5 nM or above in the cells. A similar trend was observed when CRH peptide was determined by Western analysis in the cell lysates. As previous studies have shown the importance of signal transduction pathways in the gene regulation, the status of some protein kinases in the present study was investigated. The phosphorylated PKCα, JNK, and P38 were increased by the toxicant treatment, and administering the specific inhibitors could counteract the induced CRH expression. It appeared that the signaling transduction pathway of PKC was a significant contributor in the transcriptional regulation. Further study by using Electrophoretic Mobility Shift Assay suggested that AP-2 was the ultimate DNA-binding element for the initiation of gene transcription. Because an untimely increased CRH may compromise fetal development and induce preterm birth, the present study suggested that endocrine changes in pregnancy should be taken into consideration in the next assessment.

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.

Role of Ryanodine and NMDA Receptors in Tetrabromobisphenol A-Induced Calcium Imbalance and Cytotoxicity in Primary Cultures of Rat Cerebellar Granule Cells

The study assessed the role of ryanodine receptors (RyRs) and NMDA receptors (NMDARs) in the Ca²⁺ transients and cytotoxicity induced in neurons by the brominated flame retardant tetrabromobisphenol A (TBBPA). Primary cultures of rat cerebellar granule cells (CGC) were exposed to 7.5, 10, or 25 µM TBBPA for 30 min, and cell viability was assessed after 24 h. Moreover, ⁴⁵Ca uptake was measured, and changes in the intracellular Ca²⁺ concentration ([Ca²⁺]_i) were studied using the fluo-3 probe. The involvement of NMDARs and RyRs was verified using the pertinent receptor antagonists, 0.5 µM MK-801 and 2.5 µM bastadin 12, which was co-applied with 200 µM ryanodine, respectively. The results show that TBBPA concentration-dependently induces an increase in [Ca²⁺]_i. This effect was partly suppressed by the inhibitors of RyRs and NMDARs when administered separately, and completely abrogated by their combined application. A concentration-dependent activation of ⁴⁵Ca uptake by TBBPA was prevented by MK-801 but not by RyR inhibitors. Application of ≥10 µM TBBPA concentration-dependently reduced neuronal viability, and this effect was only partially and to an equal degree reduced by NMDAR and RyR antagonists given either separately or in combination. Our results directly demonstrate that both the RyR-mediated release of intracellular Ca²⁺ and the NMDAR-mediated influx of Ca²⁺ into neurons participate in the mechanism of TBBPA-induced Ca²⁺ imbalance in CGC and play a significant, albeit not exclusive, role in the mechanisms of TBBPA cytotoxicity.

Developmental exposure to a commercial PBDE mixture: effects on protein networks in the cerebellum and hippocampus of rats

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are structurally similar to polychlorinated biphenyls (PCBs) and have both central (learning and memory deficits) and peripheral (motor dysfunction) neurotoxic effects at concentrations/doses similar to those of PCBs. The cellular and molecular mechanisms for these neurotoxic effects are not fully understood; however, several studies have shown that PBDEs affect thyroid hormones, cause oxidative stress, and disrupt Ca2+-mediated signal transduction. Changes in these signal transduction pathways can lead to differential gene regulation with subsequent changes in protein expression, which can affect the development and function of the nervous system.

OBJECTIVE

In this study, we examined the protein expression profiles in the rat cerebellum and hippocampus following developmental exposure to a commercial PBDE mixture, DE-71.

METHODS

Pregnant Long-Evans rats were dosed perinatally with 0 or 30.6 mg/kg/day of DE-71 from gestation day 6 through sampling on postnatal day 14. Proteins from the cerebellum and hippocampus were extracted, expression differences were detected by two-dimensional difference gel electrophoresis, and proteins were identified by tandem mass spectrometry. Protein network interaction analysis was performed using Ingenuity® Pathway Analysis, and the proteins of interest were validated by Western blotting.

RESULTS

Four proteins were significantly differentially expressed in the cerebellum following DE-71 exposure, whereas 70 proteins were significantly differentially expressed in the hippocampus. Of these proteins, 4 from the cerebellum and 47 from the hippocampus, identifiable by mass spectrometry, were found to have roles in mitochondrial energy metabolism, oxidative stress, apoptosis, calcium signaling, and growth of the nervous system.

CONCLUSIONS

Results suggest that changes in energy metabolism and processes related to neuroplasticity and growth may be involved in the developmental neurotoxicity of PBDEs.

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.

Food risk assessment for perfluoroalkyl acids and brominated flame retardants in the French population: results from the second French total diet study

To determine the exposure of the French population to toxic compounds contaminating the food chain, a total diet study was performed in France between 2007 and 2009. This study was designed to reflect the consumption habits of the French population and covered the most important foods in terms of consumption, selected nutrients and contribution to contamination. Based on French consumption data, the present study reports the dietary exposure to perfluoroalkyl acids (16 congeners) and brominated flame retardants (polybrominated diphenyl ethers, hexabromocyclododecane and polybrominated biphenyls). Comparison of the calculated dietary exposures with the generally accepted health-based guidance values revealed that most compounds do not pose any risk. There are however knowledge gaps for some congeners in these large chemical classes.

Modulation of cell viability, oxidative stress, calcium homeostasis, and voltage- and ligand-gated ion channels as common mechanisms of action of (mixtures of) non-dioxin-like polychlorinated biphenyls and polybrominated diphenyl ethers

Non-dioxin-like polychlorinated biphenyls (NDL-PCBs) and polybrominated diphenyl ethers (PBDEs) are environmental pollutants that exert neurodevelopmental and neurobehavioral effects in vivo in humans and animals. Acute in vitro neurotoxic effects include changes in cell viability, oxidative stress, and basal intracellular calcium levels. Though these acute cellular effects could partly explain the observed in vivo effects, other mechanisms, such as effects on calcium influx and neurotransmitter receptor function, likely contribute to the disturbance in neurotransmission. This concise review combines in vitro data on cell viability, oxidative stress and basal calcium levels with recent data that clearly demonstrate that (hydroxylated) PCBs and (hydroxylated) PBDEs can exert acute effects on voltage-gated Ca(2+) channels as well as on excitatory and inhibitory neurotransmitter receptors in vitro. These novel mechanisms of action are shared by NDL-PCBs, OH-PBDEs, and some other persistent organic pollutants, such as tetrabromobisphenol-A, and could have profound effects on neurodevelopment, neurotransmission, and neurobehavior in vivo.

Potential effects of environmental chemical contamination in congenital heart disease

There is compelling evidence that prenatal exposures to environmental xenobiotics adversely affect human development and childhood. Among all birth defects, congenital heart disease (CHD) is the most prevalent of all congenital malformations and remains the leading cause of death. It has been estimated that in most cases the causes of heart defects remain unknown, while a growing number of studies have indicated the potential role of environmental agents as risk factors in CHD occurrence. In particular, maternal exposure to chemicals during the first trimester of pregnancy represents the most critical window of exposure for CHD. Specific classes of xenobiotics (e.g. organochlorine pesticides, organic solvents, air pollutants) have been identified as potential risk factors for CHD. Nonetheless, the knowledge gained is currently still incomplete as a consequence of the frequent heterogeneity of the methods applied and the difficulty in estimating the net effect of environmental pollution on the pregnant mother. The presence of multiple sources of pollution, both indoor and outdoor, together with individual lifestyle factors, may represent a further confounding element for association with the disease. A future new approach for research should probably focus on individual measurements of professional, domestic, and urban exposure to physical and chemical pollutants in order to accurately retrace the environmental exposure of parents of affected offspring during the pre-conceptional and pregnancy periods.

Polybrominated diphenyl ether congener (BDE-100) induces mitochondrial impairment

Brominated flame retardants are used in various consumer products to increase their resistance to fire and/or high temperatures. Polybrominated diphenyl ethers (PBDEs) are representatives of this class and among the most widely used congeners, and BDE-100 is produced on a large scale. There is a lack of toxicological data about these compounds, which has recently become a matter of concern to the scientific community. The mitochondria are recognized as the main energy-producing organelles, as well as playing a vital role in the maintenance of many cell functions. Therefore, mitochondria were used in the present work as an experimental model to evaluate the effects of the BDE-100 congeners at concentrations ranging from 0.1 μM to 50 μM. The results showed that high concentrations of BDE-100 were able to induce mitochondrial alterations. It was observed that the substance had an affinity for the hydrophilic portion of the mitochondrial membrane, as monitored by ANS, inhibiting the glutamate + malate-stimulated mitochondrial respiration and also inducing dissipation of the mitochondrial membrane potential, deregulation of calcium homoeostasis and mitochondrial swelling, the latter being insensitive to cyclosporin A (CsA) but partially inhibited by Ruthenium Red and N-ethyl maleimide. In addition, a significant reduction in mitochondrial ATP content was found, but on the other hand, no oxidative stress was observed after exposure of the mitochondria to BDE-100. These results show the key role of mitochondria in the cytotoxicity induced by BDE-100.

Exposure to the polybrominated diphenyl ether mixture DE-71 damages the nigrostriatal dopamine system: role of dopamine handling in neurotoxicity

In the last several decades polybrominated diphenyl ethers (PBDEs) have replaced the previously banned polychlorinated biphenyls (PCBs) in multiple flame retardant utilities. As epidemiological and laboratory studies have suggested PCBs as a risk factor for Parkinson's disease (PD), the similarities between PBDEs and PCBs suggest that PBDEs have the potential to be neurotoxic to the dopamine system. The purpose of this study was to evaluate the neurotoxic effects of the PBDE mixture, DE-71, on the nigrostriatal dopamine system and address the role of altered dopamine handling in mediating this neurotoxicity. Using an in vitro model system we found DE-71 effectively caused cell death in a dopaminergic cell line as well as reducing the number of TH+ neurons isolated from VMAT2 WT and LO animals. Assessment of DE-71 neurotoxicity in vivo demonstrated significant deposition of PBDE congeners in the brains of mice, leading to reductions in striatal dopamine and dopamine handling, as well as reductions in the striatal dopamine transporter (DAT) and VMAT2. Additionally, DE-71 elicited a significant locomotor deficit in the VMAT2 WT and LO mice. However, no change was seen in TH expression in dopamine terminal or in the number of dopamine neurons in the substantia nigra pars compacta (SNpc). To date, these are the first data to demonstrate that exposure to PBDEs disrupts the nigrostriatal dopamine system. Given their similarities to PCBs, additional laboratory and epidemiological research should be considered to assess PBDEs as a potential risk factor for PD and other neurological disorders.

Polybrominated diphenyl ethers fate in China: a review with an emphasis on environmental contamination levels, human exposure and regulation

Because of their highly effective flame-retardant capability, polybrominated diphenyl ethers (PBDEs) have been extensively used as flame retardants in consumer goods. However, compelling evidence shows that many congeners of PBDEs have been accumulating in the environment, in biota and in human populations worldwide. In China, although octabrominated diphenyl ether (octaBDE) has never been produced or used, pentabrominated diphenyl ether (pentaBDE) and decabrominated diphenyl ether (decaBDE) have been produced and used in large quantities. In the face of increasing evidence about PBDE pollution and the adoption of international conventions, there is a growing push for China to develop more stringent methods of managing PBDE waste. This paper summarizes the information about PBDE production and application, describes the flame-retarding mechanism, and then reviews the toxicity and levels of PBDEs in China's environmental media and human tissues. Based on international regulations on PBDEs, the paper finally puts forward some suggestions for Chinese policy making and for self-regulation within the flame retardant industry.

The contribution of waste water treatment plants to PBDEs in ambient air

Air samples were collected at different sites in and around two wastewater treatment plants (WWTPs) located in central Italy to determine the concentrations, compositional profiles and contribution to ambient levels of eight polybrominated diphenyl ethers (PBDEs). The investigated WWTPs were selected as they treat industrial wastewater produced by local textile industries along with municipal wastewater. PBDE concentrations within the WWTPs were higher than those measured at reference sites located 4 and 5 km away with BDE-209 dominating the BDE congener composition in all air samples in 2008. Ambient PBDE concentrations measured in and around the WWTPs and estimates of emissions from aeration tanks suggest that WWTPs are sources of PBDEs to ambient air. Principal component analysis and Pearson correlations confirmed this result. The effect of distance from the plant and wind direction on atmospheric concentrations was also investigated. Although the primary fate of PBDEs in WWTPs will be partitioning to sewage sludge, this study suggests that plants can provide a measurable source of these compounds to local ambient air.

Using mouse models of autism spectrum disorders to study the neurotoxicology of gene-environment interactions

To better study the role of genetics in autism, mouse models have been developed which mimic the genetics of specific autism spectrum and related disorders. These models have facilitated research on the role genetic susceptibility factors in the pathogenesis of autism in the absence of environmental factors. Inbred mouse strains have been similarly studied to assess the role of environmental agents on neurodevelopment, typically without the complications of genetic heterogeneity of the human population. What has not been as actively pursued, however, is the methodical study of the interaction between these factors (e.g., gene and environmental interactions in neurodevelopment). This review suggests that a genetic predisposition paired with exposure to environmental toxicants plays an important role in the etiology of neurodevelopmental disorders including autism, and may contribute to the largely unexplained rise in the number of children diagnosed with autism worldwide. Specifically, descriptions of the major mouse models of autism and toxic mechanisms of prevalent environmental chemicals are provided followed by a discussion of current and future research strategies to evaluate the role of gene and environment interactions in neurodevelopmental disorders.

Developmental coexposure to polychlorinated biphenyls and polybrominated diphenyl ethers has additive effects on circulating thyroxine levels in rats

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are widespread environmental contaminants found in seafood and dairy products. PCBs and PBDEs are structurally similar chemicals and affect thyroid hormone function and behavior in children and laboratory rodents. Although coexposure frequently exists, the in vivo developmental effects of combined exposure to PCBs and PBDEs on thyroxine (T4) levels are unknown. We examined the effects of PCB and PBDE coexposure from gestational day 6 through postnatal day (p) 21, alone and in combination, on T4 levels in rat offspring. In males, exposure to PCBs and PBDEs at 1.7, 5, 10, 20, 40, and 60 μmol/kg/day induced equivalent and dose-dependent reductions in T4 from p 7 to p 21. Exposure to equimolar mixtures of PCBs and PBDEs at 3.4, 10, 20, 40, and 80 μmol/kg/day additively reduced T4 from p 7 to p 21 in males. In a second series of experiments, we determined sex effects on the mixture exposures and found that coexposure to PCBs and PBDEs had similar additive effects on T4 levels in male and female offspring. This study demonstrates that equimolar exposure to PCBs and PBDEs induces similar reductions in T4 levels and that coexposure to a mixture of PCBs and PBDEs has additive effects on T4 levels. These thyroid hormone effects of coexposure to PCBs and PBDEs are important when considering the cumulative effects of coexposure to multiple environmental thyroid hormone-disrupting agents in risk assessment for developmental disorders.

Effects of BDE-85 on the Oxidative Status and Nerve Conduction in Rodents

BDE-85 is a congener of a class of flame-retardant compounds called polybrominated diphenyl ethers (PBDEs). Although there are some studies on other congeners of PBDEs, there are none on the toxicity potential of this penta-BDE member. This study, therefore, reports the oxidative status and sciatic nerve conduction properties following BDE-85 treatment in rodents. The oxidative stress markers, lipid hydroperoxides, and the activities of antioxidant enzymes, namely superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione-S-transferase (GST), and catalase, in the exposed mice liver and brain tissues showed tissue-specific alterations following intraperitoneal injection of 0.25 mg/kg body weight of BDE-85 for 4 days. The results indicate a significant disruption in the oxidant/antioxidant equilibrium and setting in of oxidative stress. Isolated sciatic nerves of rats exposed to 5 µg/mL or 20 µg/mL of BDE-85 showed a significant reduction in nerve conduction velocity and compound action potential amplitudes, indicating physiological damage to the sciatic nerves.

In vitro neurotoxicity data in human risk assessment of polybrominated diphenyl ethers (PBDEs): overview and perspectives

Polybrominated diphenyl ethers (PBDEs) are flame retardants routinely detected in samples of cord blood and breast milk. Concerns have been raised with regard to the toxicity of both pre- and postnatal exposures towards the developing nervous system. Although there is an increasing body of literature on the disruption of brain cell functions by certain PBDE congeners in vitro, some challenges have yet to be tackled to enable the translation of in vitro findings into their in vivo counterparts. In this paper, we review findings on the PBDE neurotoxicity in human cells and discuss the research gaps to be addressed. Moreover, we propose a scheme for the incorporation of in vitro data in human risk assessment, namely through (i) the determination of in vitro cell benchmark levels; (ii) the consideration of uncertainties in establishing equivalency between the in vitro and the in vivo tissue benchmark levels (e.g., chronic vs. acute exposure, interactions with other chemicals); and (iii) relating tissue benchmark levels to surrogate levels of internal exposure. Alongside the assessment of brain dosimetry following exposure to PBDEs, in vitro neurotoxicity data provide a unique opportunity to evaluate the risks of prenatal and early life exposures on children neurodevelopment.

Plunger-in-needle solid-phase microextraction with graphene-based sol-gel coating as sorbent for determination of polybrominated diphenyl ethers

A solid-phase microextraction (SPME) device, assembled with a commercially available plunger-in-needle microsyringe, with the plunger coated with graphene via a sol-gel approach, was developed for the gas chromatographic-mass spectrometric determination of polybrominated diphenyl ethers (PBDEs) in environmental samples. This is the first application of graphene-based sol-gel coating as SPME sorbent. Parameters affecting the extraction efficiency were investigated in detail. The new coating exhibited enrichment factors for PBDEs between 1378 and 2859. The unique planar structure of graphene enhanced the π-π interaction with the aromatic PBDEs; additionally, the sol-gel coating technique created a porous three-dimensional network structure which offered larger surface area for extraction. The stainless steel plunger provided firm support for the coating and enhanced the durability of the assembly. The plunger-in-needle microsyringe represents a ready-made tool for SPME implementation. Under the optimized conditions, the method detection limits for five PBDEs were in the range of 0.2 and 5.3 ng/L (at a signal/noise ratio of 3) and the precision (% relative standard deviation, n=5) was 3.2-5.0% at a concentration level of 100 ng/L. The linearities were 5-1000 or 10-1000 ng/L for different PBDEs. Finally, the proposed method was successfully applied to the extraction and determination by gas chromatography-mass spectrometry of PBDEs in canal water samples.

Bioaccumulation and behavioral effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in perinatally exposed mice

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardants that have become pervasive environmental contaminants and may contribute to adverse health outcomes. We evaluated in mice the developmental neurotoxicity of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), one of the most abundant PBDE congeners detected in animal and human tissues. Female C57BL/6J mice were exposed to daily doses of 0, 0.03, 0.1 or 1mg/kg beginning 4 weeks prior to conception, continuing through gestation and lactation, and ending at weaning on postnatal day (PND) 21. Levels of BDE-47 in blood, brain, liver and adipose tissues of dams were markedly increased after 4 weeks of exposure, around the time of mating, and continued to increase through the time of parturition. Blood levels of BDE-47 in the dosed dams were within the range reported in humans. BDE-47 tissue levels in the dams decreased between parturition and weaning, possibly reflecting mobilization during lactation. Brain BDE-47 levels in the offspring at PND 1 approached those of the dams at parturition. Perinatal exposure to BDE-47 resulted in significant dose dependent growth retardation, slower motor performance in several behavioral tests, and mice exposed to 1mg/kg/day BDE-47 showed altered performance in the Morris water maze. There were no differences between groups in the numbers of pyramidal neurons in hippocampus CA1. These results document accumulation of BDE-47 in several organ systems following exposure to low-levels of BDE-47, and provide evidence that such exposure is associated with early behavioral deficits in exposed neonates.

Cell signaling and neurotoxicity: protein kinase C in vitro and in vivo

There is a growing concern about the effects of chemicals on the developing nervous system. Chemical exposure at critical periods of development can be associated with effects ranging from subtle to profound on the structure and/or function of the nervous system. Understanding critical biological molecular targets, which underlie chemical-induced neurotoxicity, will provide a scientific basis for risk assessment. Cell signaling molecules such as protein kinase C (PKC) have been shown to play critical roles in motor activity, development of the nervous system, and in learning and memory. PKC also has been shown to be associated with several neurological disorders including Alzheimer's disease, status epilepticus, and cerebellar ataxia. In the literature, there is abundant information linking PKC to cognitive function, long-term potentiation, or brain structural changes. Here, we show the relationship between changes in PKC (as assayed using radioactive material or by western blots) and the neurotoxic effects caused by environmental chemicals in vitro and in vivo.

Neuroendocrine actions of organohalogens: thyroid hormones, arginine vasopressin, and neuroplasticity

Organohalogen compounds are global environmental pollutants. They are highly persistent, bioaccumulative, and cause adverse effects in humans and wildlife. Because of the widespread use of these organohalogens in household items and consumer products, indoor contamination may be a significant source of human exposure, especially for children. One significant concern with regard to health effects associated with exposure to organohalogens is endocrine disruption. This review focuses on PCBs and PBDEs as old and new organohalogens, respectively, and their effects on two neuroendocrine systems; thyroid hormones and the arginine vasopressin system (AVP). Regarding neuroendocrine effects of organohalogens, there is considerable information on the thyroid system as a target and evidence is now accumulating that the AVP system and associated functions are also susceptible to disruption. AVP-mediated functions such as osmoregulation, cardiovascular function as well as social behavior, sexual function and learning/memory are discussed. For both thyroid and AVP systems, the timing of exposure seems to play a major role in the outcome of adverse effects. The mechanism of organohalogen action is well understood for the thyroid system. In comparison, this aspect is understudied in the AVP system but some similarities in neural processes, shown to be targeted by these pollutants, serve as promising possibilities for study. One challenge in understanding modes of action within neuroendocrine systems is their complexity stemming, in part, from interdependent levels of organization. Further, because of the interplay between neuroendocrine and neural functions and behavior, further investigation into organohalogen-mediated effects is warranted and may yield insights with wider scope. Indeed, the current literature provides scattered evidence regarding the role of organohalogen-induced neuroendocrine disruption in the neuroplasticity related to both learning functions and brain structure but future studies are needed to establish the role of endocrine disruption in nervous system function and development.

Application of mass spectrometry in the analysis of polybrominated diphenyl ethers

This review summarized the applications of mass spectrometric techniques for the analysis of the important flame retardants polybrominated diphenyl ethers (PBDEs) to understand the environmental sources, fate and toxicity of PBDEs that were briefly discussed to give a general idea for the need of analytical methodologies. Specific performance of various mass spectrometers hyphenated with, for example, gas chromatograph, liquid chromatograph, and inductively coupled plasma (GC/MS, LC/MS, and ICP/MS, respectively) for the analysis of PBDEs was compared with an objective to present the information on the evolution of MS techniques for determining PBDEs in environmental and human samples. GC/electron capture negative ionization quadrupole MS (GC/NCI qMS), GC/high resolution MS (GC/HRMS) and GC ion trap MS (GC/ITMS) are most commonly used MS techniques for the determination of PBDEs. New analytical technologies such as fast tandem GC/MS and LC/MS become available to improve analyses of higher PBDEs. The development and application of the tandem MS techniques have helped to understand environmental fate and transformations of PBDEs of which abiotic and biotic degradation of decaBDE is thought to be one major source of Br(1-9)BDEs present in the environment in addition to direct loading from commercial mixtures. MS-based proteomics will offer an insight into the molecular mechanisms of toxicity and potential developmental and neurotoxicity of PBDEs.

Polychlorinated biphenyls and polybrominated diphenyl ethers alter striatal dopamine neurochemistry in synaptosomes from developing rats in an additive manner

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are widespread environmental contaminants associated with changes in behavior and neurochemical function in laboratory animals and behavioral deficits in children. PCBs and PBDEs are found in food, especially in seafood and dairy products, and coexposure to these contaminants is likely. We examined the effects of an environmentally relevant mixture of PCBs (Fox River Mix [FRM]) and a PBDE mixture (DE-71) alone and in combination on synaptosomal and medium dopamine (DA) levels and the levels of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in striatal synaptosomes derived from postnatal days (PND) 7, PND14, or PND21 rats. FRM elevated medium DA and reduced synaptosomal DA concentrations with greater potency than equimolar concentrations of DE-71. The effects of FRM, but not DE-71, were dependent on the age of the animals from which the synaptosomes were derived, with greater effects observed in synaptosomes from the youngest animals. We used Bliss' model of independence to assess the possible interaction(s) of a 1:1 mixture of FRM and DE-71 on synaptosomal DA function and found that the effects of the FRM/DE-71 mixture were additive. Furthermore, as for FRM alone, the effects of the FRM/DE71 mixture were greater in synaptosomes prepared from PND7 rats than in synaptosomes from PND14 and PND21 rats. Because the effects of these contaminants are additive, it is necessary to take into account the cumulative exposure to organohalogen contaminants such as PCBs and PBDEs during risk assessment.

Developmental exposure to a commercial PBDE mixture, DE-71: neurobehavioral, hormonal, and reproductive effects

Developmental effects of polybrominated diphenyl ethers (PBDEs) have been suspected due to their structural similarities to polychlorinated biphenyls (PCBs). This study evaluated neurobehavioral, hormonal, and reproductive effects in rat offspring perinatally exposed to a widely used pentabrominated commercial mixture, DE-71. Pregnant Long-Evans rats were exposed to 0, 1.7, 10.2, or 30.6 mg/kg/day DE-71 in corn oil by oral gavage from gestational day 6 to weaning. DE-71 did not alter maternal or male offspring body weights. However, female offspring were smaller compared with controls from postnatal days (PNDs) 35-60. Although several neurobehavioral endpoints were assessed, the only statistically significant behavioral finding was a dose-by-age interaction in the number of rears in an open-field test. Developmental exposure to DE-71 caused severe hypothyroxinemia in the dams and early postnatal offspring. DE-71 also affected anogenital distance and preputial separation in male pups. Body weight gain over time, reproductive tissue weights, and serum testosterone concentrations at PND 60 were not altered. Mammary gland development of female offspring was significantly affected at PND 21. Congener-specific analysis of PBDEs indicated accumulation in all tissues examined. Highest PBDE concentrations were found in fat including milk, whereas blood had the lowest concentrations on a wet weight basis. PBDE concentrations were comparable among various brain regions. Thus, perinatal exposure to DE-71 leads to accumulation of PBDE congeners in various tissues crossing blood-placenta and blood-brain barriers, causing subtle changes in some parameters of neurobehavior and dramatic changes in circulating thyroid hormone levels, as well as changes in both male and female reproductive endpoints. Some of these effects are similar to those seen with PCBs, and the persistence of these changes requires further investigation.

Cytotoxicity and apoptosis induction on RTG-2 cells of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209)

Recently, the environmental residues of polybrominated diphenyl ethers (PBDEs) have markedly increased. In particular, the levels of certain PBDE congeners in fish have raised concern regarding potential risks associated with dietary PBDEs exposures. However, little is known regarding PBDE-mediated cell injury in relevant in vitro fish cell models. In this study, the cytotoxic effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209) on RTG-2 cells were investigated. RTG-2 cells were incubated with different concentrations of BDE-47 and BDE-209 (1-100 microM) for 72 h, and a set of bioassays were conducted to measure: cell viability (evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and neutral red (NR) uptake), lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation and cell apoptosis. The results showed that BDE-47 and BDE-209 inhibited the cells viability, increased LDH leakage, and induced cell apoptosis in time and concentration-dependent manner. All significant effects were observed at concentrations of 12.5 microM and above for BDE-47 and 25 microM and above for BDE-209 (P<0.05). At the concentration of 100 microM BDE-47 and BDE-209, the cell viability of the exposed cells dropped to about 40% and 50% of the control, and the apoptotic rates were 52.6% and 34.6%, respectively. After 12h exposure, a concentration-dependent increases of BDE-47 and BDE-209 (12.5-100 microM) in ROS formation were observed. Collectively, the results of cell viability, LDH leakage, cell apoptosis and ROS formation demonstrated that the toxic mechanism of PBDEs on RTG-2 might be mediated by oxidative stress.

Effects of individual polybrominated diphenyl ether (PBDE) congeners on harbour seal immune cells in vitro

Effects of polybrominated diphenyl ethers (PBDEs) on the immune system of marine mammals are poorly understood. One important innate immune function of granulocytes is the respiratory burst which generates reactive oxygen species (ROS) used to kill engulfed microorganisms. The present study investigates in vitro the effects of BDE-47, -99 and -153, on the formation of ROS, on intracellular level of thiols, on activity and efficiency of phagocytosis and on apoptosis in granulocytes of harbour seals. Compounds were tested at four different concentrations ranging from 1.5 to 12 microM. Results showed that ROS levels, thiol levels and phagocytosis were all affected when harbour seal cells were exposed to the highest concentration (12 microM) of PBDE congeners. Apoptosis was not affected by PBDEs. The observed effects were similar in adults, pups and in the 11B7501 cell line of harbour seals.

Quantitative structure-activity relationship (QSAR) studies for predicting activation of the ryanodine receptor type 1 channel complex (RyR1) by polychlorinated biphenyl (PCB) congeners

A quantitative structure-activity relationship (QSAR) was developed to predict the congener specific ryanodine receptor type RyR1 activity of all 209 polychlorinated biphenyl (PCB) congeners. A three-variable QSAR equation was obtained via stepwise forward linear regression on an unsupervised forward selection reduced data set from an initial database. Application of the QSAR towards predicting EC(2x) values for all 209 PCB congeners indicated good agreement in substitution pattern trends between the experimental and estimated data sets. The QSAR model predicts a less than two-fold increase in maximal potency among all congeners outside the experimental database, and it appears that no high-potency PCB congeners with EC(2x) values much less than 0.2 microM exist. Increasing RyR1-neuro toxicity equivalents with increasing homologue number and Aroclor chlorination likely reflect indirect molecular controls on toxicity, since congeners with multiple ortho substituents-the primary structural feature controlling a lack of coplanarity and resulting neurotoxicity-are more likely to be found in higher homologues.

Comparative cytotoxicity and intracellular accumulation of five polybrominated diphenyl ether congeners in mouse cerebellar granule neurons

Polybrominated diphenyl ethers (PBDEs), a group of flame retardants comprising 209 congeners, have become widespread environmental pollutants. High levels of PBDEs have been detected in human tissues, particularly in North America, and body burden is especially high in infants and toddlers because of exposure through breast milk and house dust. Increasing evidence, provided by animal studies, suggests that PBDEs are developmental neurotoxicants, although the underlying mechanisms are still unknown. Various PBDEs have been reported to cause oxidative stress and to induce apoptotic cell death in several cell types. In the present study, we investigated the comparative neurotoxicity in mouse cerebellar granule neurons of five brominated diphenyl ether (BDE) congeners, chosen among the most commonly found at the highest levels in human tissues. All BDE congener tested (BDE-47, BDE-99, BDE-100, BDE-153, and BDE-209) decreased cell viability and induced apoptotic cell death, which was prevented by antioxidants. They also caused oxidative stress, as indicated by an increase in reactive oxygen species and in lipid peroxidation. For all end points measured, the potency ranking of the congeners was BDE-100 > BDE-47 > BDE-99 > BDE-153 >> BDE-209. Measurement of BDE congener levels in neurons after exposure to different concentrations showed a significant accumulation in cells, which followed the same relative ranking. The findings suggest that all BDE congeners tested exhibit the same general mode of action (induction of oxidative stress-mediated apoptosis) and that the ability of each isomer to elicit such effects is dependent upon their accumulation in neurons, particularly in the microsomal fraction and the mitochondria.

Behavioral changes in aging but not young mice after neonatal exposure to the polybrominated flame retardant decaBDE

BACKGROUND

After several decades of commercial use, the flame-retardant chemicals polybrominated diphenyl ethers (PBDEs) and their metabolites are pervasive environmental contaminants and are detected in the human body. Decabrominated diphenyl ether (decaBDE) is currently the only PBDE in production in the United States.

OBJECTIVES

Little is known about the health effects of decaBDE. In the present study we examined the effects of neonatal decaBDE exposure on behavior in mice at two ages.

METHODS

Neonatal male and female C57BL6/J mice were exposed to a daily oral dose of 0, 6, or 20 mg/kg decaBDE from postnatal days 2 through 15. Two age groups were examined: a cohort that began training during young adulthood and an aging cohort of littermates that began training at 16 months of age. Both cohorts were tested on a series of operant procedures that included a fixed-ratio 1 schedule of reinforcement, a fixed-interval (FI) 2-min schedule, and a light-dark visual discrimination.

RESULTS

We observed minimal effects on the light-dark discrimination in the young cohort, with no effects on the other tasks. The performance of the aging cohort was significantly affected by decaBDE. On the FI schedule, decaBDE exposure increased the overall response rate. On the light-dark discrimination, older treated mice learned the task more slowly, made fewer errors on the first-response choice of a trial but more perseverative errors after an initial error, and had lower latencies to respond compared with controls. Effects were observed in both dose groups and sexes on various measures.

CONCLUSIONS

These findings suggest that neonatal decaBDE exposure produces effects on behavioral tasks in older but not younger animals. The behavioral mechanisms responsible for the pattern of observed effects may include increased impulsivity, although further research is required.

Low concentrations of the brominated flame retardants BDE-47 and BDE-99 induce synergistic oxidative stress-mediated neurotoxicity in human neuroblastoma cells

Polybrominated diphenyl ether (PBDE) flame retardants have become widespread environmental contaminants. The highest body burden has been found in toddlers and infants, due to their exposure through breast milk and house dust, and the current concern for potential adverse health effects of PBDEs relates to their developmental neurotoxicity. The mechanisms underlying the neurotoxicity of PBDEs are largely not understood, though there is evidence that PBDEs may elicit oxidative stress. In this study, two different mathematical models were used to evaluate the interaction between BDE-47 and BDE-99 on viability of neuronal cells. The combined exposure to these compounds induced synergistic effects at concentrations of BDE-47 below its threshold doses, and in a wide range of BDE-99 concentrations below its IC(50). In contrast, at concentrations of BDE-47 near its IC(50) value, and in a wide range of BDE-99 concentrations, antagonistic effects were observed. The interactions observed on cell viability were confirmed by an assessment of induction of oxidative stress. The finding that co-exposure to BDE-47 and BDE-99 could induce synergistic neurotoxic effects, in particular at low doses of BDE-47, is of much toxicological interest, as humans are exposed to mixtures of PBDEs, most notably tetra- and penta-BDE congeners.

An assessment of sources and pathways of human exposure to polybrominated diphenyl ethers in the United States

Polybrominated diphenyl ethers (PBDEs) are ubiquitous in the indoor environment, owing to their use in consumer products ranging from electronics to mattresses, furniture, and carpets. People are exposed to PBDEs through inhalation of indoor air and ingestion, and dermal absorption of dust particles present in the air. In this study, concentrations of PBDEs were determined in indoor air and house dust collected from homes in Albany, New York, USA. Based on the measured concentrations of PBDEs in indoor air and dust, we estimated daily exposure dose (DED) of PBDEs. In addition, we used previously published PBDE concentrations reported for breast milk from Massachusetts, USA [Johnson-Restrepo, B., Addink, R., Wong, C., Arcaro, K., Kannan, K., 2007. Polybrominated diphenyl ethers and organochlorine pesticides in human breast milk from Massachusetts. USA. J. Environ. Monitor. 9, 1205-1212] and foodstuffs collected from Texas and Florida, USA [Schecter, A., Päpke, O., Harris, T.R., Tung, K.C., Musumba, A., Olson, J., Birnbaum, L., 2006. Polybrominated diphenyl ether (PBDE) levels in an expanded market basket survey of U.S. food and estimated PBDE dietary intake by age and sex. Environ. Health Perspect. 114, 1515-1520, Johnson-Restrepo, B., Kannan, K., Addink, R., Adams, D.H., 2005b. Polybrominated diphenyl ethers and polychlorinated biphenyls in a marine foodweb of coastal Florida. Environ. Sci. Technol. 39, 8243-8250], in an estimation of dietary exposure to PBDEs. The exposure assessment was performed for five age groups: infants (<1yr), toddlers (1-5yr), children (6-11yr), teenagers (12-19yr), and adults (20yr). The dust ingestion and air inhalation factors that we used were the US Environmental Protection Agency's (EPA) exposure factors, while the daily food intake rates (g/day) were derived from the US Department of Agriculture's (USDA) food intake surveys. The total DED of PBDEs was calculated by summation of the exposures from diet, indoor air, and house dust. The average estimated DED of PBDEs was the highest for breastfed infants (86.4ng/kg-bw/day), contributed primarily (91%) from the consumption of breast milk. The average DED of PBDEs for toddlers, children, teenagers, and adults was respectively, 13.3, 5.3, 3.5, and 2.9ng/kg-bw/day. Ingestion and dermal absorption of house dust are the major pathways of PBDE exposure in toddlers, children, teenagers, and adults accounting for, on average, 56-77% of the total PBDE intake.