Proteomic evaluation of neonatal exposure to 2,2 ,4,4 ,5-pentabromodiphenyl ether

Serum proteome profiles in cats with chronic enteropathies

BACKGROUND

Serum protein biomarkers are used to diagnose, monitor treatment response, and to differentiate various forms of chronic enteropathies (CE) in humans. The utility of liquid biopsy proteomic approaches has not been examined in cats.

HYPOTHESIS/OBJECTIVES

To explore the serum proteome in cats to identify markers differentiating healthy cats from cats with CE.

ANIMALS

Ten cats with CE with signs of gastrointestinal disease of at least 3 weeks duration, and biopsy-confirmed diagnoses, with or without treatment and 19 healthy cats were included.

METHODS

Cross-sectional, multicenter, exploratory study with cases recruited from 3 veterinary hospitals between May 2019 and November 2020. Serum samples were analyzed and evaluated using mass spectrometry-based proteomic techniques.

RESULTS

Twenty-six proteins were significantly (P < .02, ≥5-fold change in abundance) differentially expressed between cats with CE and controls. Thrombospondin-1 (THBS1) was identified with >50-fold increase in abundance in cats with CE (P < 0.001) compared to healthy cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

Damage to the gut lining released marker proteins of chronic inflammation that were detectable in serum samples of cats. This early-stage exploratory study strongly supports THBS1 as a candidate biomarker for chronic inflammatory enteropathy in cats.

Studying the Impact of Persistent Organic Pollutants Exposure on Human Health by Proteomic Analysis: A Systematic Review

Persistent organic pollutants (POPs) are organic chemical substances that are widely distributed in environments around the globe. POPs accumulate in living organisms and are found at high concentrations in the food chain. Humans are thus continuously exposed to these chemical substances, in which they exert hepatic, reproductive, developmental, behavioral, neurologic, endocrine, cardiovascular, and immunologic adverse health effects. However, considerable information is unknown regarding the mechanism by which POPs exert their adverse effects in humans, as well as the molecular and cellular responses involved. Data are notably lacking concerning the consequences of acute and chronic POP exposure on changes in gene expression, protein profile, and metabolic pathways. We conducted a systematic review to provide a synthesis of knowledge of POPs arising from proteomics-based research. The data source used for this review was PubMed. This study was carried out following the PRISMA guidelines. Of the 742 items originally identified, 89 were considered in the review. This review presents a comprehensive overview of the most recent research and available solutions to explore proteomics datasets to identify new features relevant to human health. Future perspectives in proteomics studies are discussed.

Polybrominated diphenyl ether (PBDE) and poly- and perfluoroalkyl substance (PFAS) exposures during pregnancy and maternal depression

BACKGROUND

Experimental studies in rodents suggest that polybrominated diphenyl ethers (PBDEs) and poly- and perfluoroalkyl substances (PFAS) may contribute to depressive symptoms. Few studies have examined the impact of these chemicals on depression in adults.

OBJECTIVE

To examine the associations between serum PBDE and PFAS concentrations during pregnancy and repeated measures of depressive symptoms in women assessed from pregnancy to 8 years postpartum.

METHODS

This study was based on 377 women from the Health Outcomes and Measures of the Environment Study, a birth cohort in Cincinnati, OH (USA). PBDEs (BDE-28, -47, -99, -100, -153, and ∑PBDEs) and PFAS (perfluorooctanoate [PFOA], perfluorooctane sulfonate [PFOS], perfluorohexane sulfonate [PFHxS], perfluorononanoate [PFNA]) were quantified in maternal serum at 16 ± 3 weeks gestation. Depressive symptoms were measured using the Beck Depression Inventory-II (BDI-II) at ~20 weeks gestation and up to seven times during postpartum visits (4 weeks, 1, 2, 3, 4, 5, and 8 years). We used linear mixed models to estimate covariate-adjusted associations between chemical concentrations and repeated measures of BDI-II. Multinomial logistic regression models were used to estimate the relative risk ratios of having a medium or high depression trajectory.

RESULTS

We found that a 10-fold increase in BDE-28 at 16 ± 3 weeks gestation was associated with significantly increased BDI-II scores (β = 2.5 points, 95% confidence interval [CI] 0.8, 4.2) from pregnancy to 8 years postpartum. Significant positive associations were also observed with BDE-47, -100, -153, and ∑PBDEs. A 10-fold increase in ∑PBDEs was associated with a 4.6-fold increased risk (95% CI 1.8, 11.8) of a high trajectory for BDI-II compared to a low trajectory. We observed no significant associations between PFAS and BDI-II scores.

CONCLUSION

PBDEs during pregnancy were associated with more depressive symptoms among women in this cohort.

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

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

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.

2,2',4,4'-Tetrabromodiphenyl ether injures cell viability and mitochondrial function of mouse spermatocytes by decreasing mitochondrial proteins Atp5b and Uqcrc1

Our object was to explore direct effects and mechanism of BDE47 on GC2 (immortalized mouse spermatocyte). GC2 were exposed to DMSO, 0.1, 1, 10, 100μM BDE47 for 48h. Cell viability was detected by trypan-blue exclusion; ultrastructure by electron-microscopy; cell cycle, mitochondrial membrane motential (MMP), reactive oxygen species (ROS) by flow-cytometry; ATP production by luminometer; Atp5b, Uqcrc1, Bcl-2 level by WB. To explore whether the decreased mitochondrial proteins play an important role in apoptosis, MMP and apoptosis were detected after Atp5b or Uqcrc1 knockdown in GC2. Results showed BDE47 reduced cell viability, caused condensation of nuclear and vacuolated mitochondria, decreased MMP and ATP, induced ROS, cell cycle arrest at S and G2/M phase, reduced Atp5b, Uqcrc1, Bcl-2 in GC2. Knockdown of Atp5b or Uqcrc1 decreased MMP, induced apoptosis in GC2. Results suggested that BDE47 reduced cell viability, injured mitochondria in spermatocytes probably by decreasing mitochondrial protein Atp5b and Uqcrc1.

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.

The developmental neurotoxicity of polybrominated diphenyl ethers: Effect of DE-71 on dopamine in zebrafish larvae

The potential neurotoxicity of polybrominated diphenyl ethers (PBDEs) is still a great concern. In the present study, the authors investigated whether exposure to PBDEs could affect the neurotransmitter system and cause developmental neurotoxicity in zebrafish. Zebrafish embryos (2 h postfertilization) were exposed to different concentrations of the PBDE mixture DE-71 (0-100 μg/L). The larvae were harvested at 120 h postfertilization, and the impact on dopaminergic signaling was investigated. The results revealed significant reductions in content of whole-body dopamine and its metabolite, dihydroxyphenylacetic acid, in DE-71-exposed larvae. The transcription of genes involved in the development of dopaminergic neurons (e.g., manf, bdnf, and nr4a2b) was significantly downregulated upon exposure to DE-71. Also, DE-71 resulted in a significant decrease of tyrosine hydroxylase and dopamine transporter protein levels in dopaminergic neurons. The expression level of tyrosine hydroxylase in forebrain neurons was assessed by whole-mount immunofluorescence, and the results further demonstrated that the tyrosine hydroxylase protein expression level was reduced in dopaminergic neurons. In addition to these molecular changes, the authors observed reduced locomotor activity in DE-71-exposed larvae. Taken together, the results of the present study demonstrate that acute exposure to PBDEs can affect dopaminergic signaling by disrupting the synthesis and transportation of dopamine in zebrafish, thereby disrupting normal neurodevelopment. In accord with its experimental findings, the present study extends knowledge of the mechanisms governing PBDE-induced developmental neurotoxicity.

Bioconcentration, metabolism and neurotoxicity of the organophorous flame retardant 1,3-dichloro 2-propyl phosphate (TDCPP) to zebrafish

Organophosphate flame retardants are ubiquitous environmental contaminants; however, knowledge is limited regarding their environmental health risks and toxicity. Here, we investigated the effects of acute and long-term exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCPP) to the nervous system of zebrafish. Zebrafish embryos (2 h post-fertilization) were exposed to TDCPP (0-100 μg/L) for 6 months up until sexual maturation. Concentrations of TDCPP and its metabolic product (bis(1,3-dichloro-2-propyl) phosphate, BDCPP) were measured in the tissues of 5 day post-fertilization (dpf) larvae. There was no effect on locomotion, acetylcholinesterase activity, levels of the neurotransmitters dopamine and serotonin, and expression of mRNAs and proteins related to central nervous system development (e.g., myelin basic protein, α1-tubulin) in any exposure group. However, in adult fish, reductions of dopamine and serotonin levels were detected in the brains of females but not males. Downregulation of nervous system development genes was observed in both the male and female brain tissues. TDCPP concentrations were measured in adult fish tissues including the brain, and greater levels were detected in females. Our results showed that females are more sensitive to TDCPP stress than males in terms of TDCPP-induced neurotoxicity. We demonstrate that long-term exposure to lower concentrations of TDCPP in fish can lead to neurotoxicity.

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.

Identification of differentially expressed genes in the digestive gland of manila clam Ruditapes philippinarum exposed to BDE-47

Suppression subtractive hybridization (SSH) was used to identify alterations in gene transcription of the manila clam Ruditapes philippinarum after exposure to 5μg/L 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) for 15days. The ability to accumulate BDE-47 in digestive gland and gill was also evaluated in order to provide information for food safety. Analysis of tissue extracts indicated that digestive gland had the higher BDE-47 levels (12,463.1±1334.8 ng/g d.w.) compared to gill (6368.6±738.7ng/g d.w.) after a 15-day exposure period. Forward and reverse SSH libraries were made from pooled digestive glands of R. philippinarum, from which 75 high quality sequences were obtained by BLAST analysis. The expression of 39 genes with significant homology (E-value<10(-5)) out of the 75 sequences was investigated by quantitative RT-PCR. Among the 39 genes, 27 genes were found up-regulated while 12 genes were found down-regulated after the BDE-47 exposure. The 39 genes were involved in cellular cycle, cytoskeleton, substance and energy metabolism, stress response, innate immunity and cell signaling and transport which were extensively discussed. This study provides a preliminary basis for studying the response of marine bivalves upon exposure to PBDEs in terms of regulated gene expression.

Effects of dechlorane plus on the hepatic proteome of juvenile Chinese sturgeon (Acipenser sinensis)

Dechlorane Plus (DP), an alternative to decabromodiphenyl ether (BDE-209), is a widely used polychlorinated flame retardant that is frequently detected in aquatic ecosystems. While the mechanisms of toxicity of BDE-209 have been well documented, less is known about the toxicity of DP. In this study, juvenile Chinese sturgeon (Acipenser sinensis) were treated with DP at doses of 1, 10, and 100mg/kg wet weight for 14 days via a single intraperitoneal injection (i.p.). After 14 days, liver proteomes of juvenile Chinese sturgeon were analyzed using two-dimensional electrophoresis (2-DE) coupled matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF/TOF-MS). A total of 39 protein spots were significantly altered in abundance (>2-fold) and of these proteins, 27 were successfully identified. Proteins related to the stress response that included heat shock cognate protein 70 and T-complex protein 1 were significantly increased and decreased in abundance, respectively. Moreover, Ras-related protein Rab-6B and GDP dissociation inhibitor 2, proteins that are involved in small G-protein signal cascades, were decreased in abundance 2- to 5-fold. Annexin A4, which is associated with Ca(2+) signaling pathways, was also markedly decreased by 2-fold in the liver. Pathway analysis of differentially regulated proteins revealed that DP interfered with metabolism and was associated with proteins related to apoptosis and cell differentiation. Based upon protein responses, we suggest that DP has effects on the generalized stress response, small G-protein signal cascades, Ca(2+) signaling pathway, and metabolic process, and may induce apoptosis in the liver. This study offers novel mechanistic insight into the protein responses induced in the liver with DP, an increasingly used and understudied flame retardant.

The added value of proteomics for toxicological studies

Proteomics has the potential to elucidate complex patterns of toxic action attributed to its unique holistic a posteriori approach. In the case of toxic compounds for which the mechanism of action is not completely understood, a proteomic approach may provide valuable mechanistic insight. This review provides an overview of currently available proteomic techniques, including examples of their application in toxicological in vivo and in vitro studies. Future perspectives for a wider application of state-of-the-art proteomic techniques in the field of toxicology are discussed. The examples concern experiments with dioxins, polychlorinated biphenyls, and polybrominated diphenyl ethers as model compounds, as they exhibit a plethora of sublethal effects, of which some mechanisms were revealed via successful proteomic studies. Generally, this review shows the added value of including proteomics in a modern tool box for toxicological studies.

Nonparametric Bayesian evaluation of differential protein quantification

Arbitrary cutoffs are ubiquitous in quantitative computational proteomics: maximum acceptable MS/MS PSM or peptide q value, minimum ion intensity to calculate a fold change, the minimum number of peptides that must be available to trust the estimated protein fold change (or the minimum number of PSMs that must be available to trust the estimated peptide fold change), and the "significant" fold change cutoff. Here we introduce a novel experimental setup and nonparametric Bayesian algorithm for determining the statistical quality of a proposed differential set of proteins or peptides. By comparing putatively nonchanging case-control evidence to an empirical null distribution derived from a control-control experiment, we successfully avoid some of these common parameters. We then apply our method to evaluating different fold-change rules and find that for our data a 1.2-fold change is the most permissive of the plausible fold-change rules.

Alterations to the circuitry of the frontal cortex following exposure to the polybrominated diphenyl ether mixture, DE-71

Recent studies have identified exposure to polybrominated diphenyl ethers (PBDEs) as a risk factor for deficits in cognitive functioning seen in children as well as adults. Additionally, similar alterations in learning and memory have also been observed in animal models of PBDE exposure. However, given these findings, the molecular alterations that may underlie these neurobehavioral endpoints have not been identified. As the frontal cortex is involved in modulating several cognitive functions, the purpose of our study was to investigate the possible changes to the GABAergic and glutamatergic neurotransmitter systems located in the frontal cortex following exposure to the PBDE mixture, DE-71. Primary cultured neurons isolated from the frontal cortex showed a dose-dependent reduction in neurons as well as neurite outgrowth. Furthermore, evaluation of DE-71 neurotoxicity in the frontal cortex using an in vivo model showed alterations to specific proteins involved in mediating GABA and glutamate neurotransmission, including GAD67, vGAT, vGlut, and GABA(A) 2α receptor subunit. Interestingly, these alterations appeared to be preferential for the GABA and glutamate systems located in the frontal cortex. These findings identify specific targets of PBDE neurotoxicity and provide a possible molecular mechanism for PBDE-mediated neurobehavioral deficits that arise from the frontal cortex.

Lactation exposure to BDE-153 damages learning and memory, disrupts spontaneous behavior and induces hippocampus neuron death in adult rats

OBJECTIVE

To study the effects of 2,2',4,4',5,5'-hexa-brominated diphenyl ether (BDE-153) exposure during lactation on the learning and memory abilities, spontaneous behavior and brain cells of adult rats and to elicit basic information on PBDE's developmental neurotoxicity.

METHODS

Newborn male rat pups were randomly categorized into the following groups (15 pups per group), according to their weights and litters: a control group, and 1mg/kg, 5mg/kg and 10mg/kg BDE-153 groups. At postnatal day 10 (PND10), the pups in the BDE-153 groups were intraperitoneally injected once with BDE-153 plant oil solutions at 0.1ml/10g body weight, and the controls were injected with plant oil. Throughout the entire experiment, physiological measures were recorded, such as food and water consumption, body weight and clinical symptoms. At 1 month and 2 months after treatment, the learning and memory abilities of the rats were tested by the Morris water maze test, the step-down test, and the step-through test; spontaneous behavior was tested by the open-field test. After all tests were accomplished, rats were weighed and sacrificed, and the brain tissue was immediately isolated and divided into two parts. Sections were fabricated from one part, and changes in the morphology and ultrastructure in CA3 region of hippocampus were observed under an optical microscope and transmission electron microscope, along with the detection of apoptotic cells with the terminal-deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) method. The tissue of the second part was digested into single-cell suspension liquid, and the cell apoptosis was assayed with flow cytometry and the lactate dehydrogenase (LDH) leakage was detected with spectrophotometry.

RESULTS

There was no obvious change in food and water consumption, body weight and the ratio of brain to body weight, or any overt clinical symptoms in the BDE-153-treated rats. Compared to the control group, rats' latency time in the test session (LT2) in the step-down test was significantly increased in the 10mg/kg BDE-153 group at 2 months after treatment (P<0.05), and the BDE-153-treated rats' swimming times and distances in the target quadrant were significantly decreased at 1 month and 2 months after treatment (P<0.05 or P<0.01). These parameters were also significantly increased in the opposite quadrant at 1 month after treatment (P<0.05 or P<0.01). The spontaneous behavior was significantly reduced in the treated groups compared to the controls (P<0.05 or P<0.01). The severity of neurobehavioral dysfunction was dependent on the exposure dose of BDE-153, and worsened with age. Under an optical microscope, the treated rats' neurons in the CA3 region of the hippocampus were observed to be reduced and disarranged, and the cell junctions were loosened and the intercellular spaces were enlarged. Under a transmission electron microscope, the cell nucleus was observed to shrink; the chromatin was condensed and gathered near the nuclear membrane, the Nissl bodies and other organelles in the perikaryon were reduced, and the vacuole was observed to degenerate and even disappear. Moreover, compared to the controls, the cell apoptosis rates were significantly increased in the 5 and 10mg/kg BDE-153 groups (P<0.05), and the LDH activity was significantly increased in the 10mg/kg BDE-153 groups (P<0.01).

CONCLUSION

Lactation exposure to BDE-153 damaged adult rats' learning and memory abilities, disrupted their spontaneous behavior (hypoactivity) and induced hippocampus neuron apoptosis.

A three-generational study of In ovo exposure to PBDE-99 in the zebra finch

Based on a literature review of avian data for polybrominated diphenyl ethers (PBDEs), ecologically relevant doses, low (10 ng/egg), medium (100 ng/egg), and high (1,000 ng/egg) of the 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) congener along with dimethylsulfoxide (DMSO) control were injected into the yolk sac of un-incubated eggs of zebra finch, Taeniopygia guttata. Offspring development and adult phenotype were followed over three generations. No effects of in ovo PBDE exposure on hatching success, chick growth, thyroid hormone levels, or hematological traits were measured at sexual maturity (90 d posthatching). However, the authors did detect significant effects of BDE-99 treatment on adult phenotype of in ovo-exposed birds by breeding observations, in which clutch size was significantly smaller in all PBDE-dosed birds (low, medium, and high) compared with controls. A trend was also seen for longer laying intervals in PBDE-dosed birds (13-14 d) compared with control birds (8 d). In addition, a significant effect of PBDE was found on growth of the second-generation offspring of in ovo-treated females; body mass was significantly lower in the high-PBDE dosed birds compared with controls from hatch through to fledging (day 30). The authors found no evidence of effects over the longer term and in successive generations, whether in adult, reproductive phenotype of the second-generation offspring of in ovo-treated birds, or in the growth of their (third-generation) offspring. Their results suggest that egg levels as low as 10 ng/g BDE-99 may affect reproduction in small passerines by reducing clutch size.

Maternal transfer of BDE-47 to offspring and neurobehavioral development in C57BL/6J mice

Polybrominated diphenyl ethers (PBDEs) are flame retardants used worldwide in a variety of commercial goods, and are now widely found in both environmental and biological samples. BDE-47 is one of the most pervasive of these PBDE congeners and therefore is of particular concern. In this study C57BL/6J mice were exposed perinatally to 0.03, 0.1 or 1mg/kg/day of BDE-47, a dose range chosen to encompass human exposure levels. Tissue levels of BDE-47 were measured in the blood, brain, fat and milk of dams and in whole fetal homogenate and blood and brain of pups on gestational day (GD) 15, and postnatal days (PNDs) 1, 10 and 21. From GD 15 to PND 1 levels of BDE-47 increased within dam tissues and then decreased from PNDs 1 to 21. Over the period of lactation levels in dam milk were comparatively high when compared to both brain and blood for all dose groups. Measurable levels of BDE-47 were found in the fetus on GD 15 confirming gestational exposure. From PNDs 1 to 21, levels of BDE-47 in pup tissue increased over the period of lactation due to the transfer of BDE-47 through milk. Behavioral tests of fine motor function and learning and memory were carried out between postnatal weeks 5-17 in order to evaluate the neurobehavioral toxicity of BDE-47. Behavioral deficits were only seen in the Barnes spatial maze where mice in the three exposure groups had longer latencies and traveled longer distances to find the escape hole when compared to vehicle control mice. These results support the conclusions that perinatal exposure to BDE-47 can have neurodevelopmental consequences, and that lactational exposure represents a significant exposure risk during development.

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.

Prenatal transfer of polybrominated diphenyl ethers (PBDEs) results in developmental neurotoxicity in zebrafish larvae

Parental exposure to polybrominated diphenyl ethers (PBDEs) in animals has been found to be transferred to the offspring. The environmental health risk and toxicity to the offspring are still unclear. The objective of the present study was to identify environmentally relevant concentrations of PBDEs for parental exposure that would cause developmental neurotoxicity in the offspring. Adult zebrafish were exposed to environmentally relevant concentrations of DE-71 (0.16, 0.8, 4.0 μg/L) via water. The results showed that PBDE exposure did not affect larvae hatching, malformation, or survival. The residue of PBDEs was detected in F1 eggs upon parental exposure. Acetylcholinesterase (AChE) activity was significantly inhibited in F1 larvae. Genes of central nervous system development (e.g., myelin basic protein, synapsin IIa, α1-tubulin) were significantly downregulated in larvae. Protein levels of α1-tubulin and synapsin IIa were also reduced. Decreased locomotion activity was observed in the larvae. This study provides the first evidence that parental exposure to environmentally relevant concentrations of PBDEs could cause adverse effects on neurodevelopment in zebrafish offspring.

Organic anion transporting polypeptides in the hepatic uptake of PBDE congeners in mice

BDE47, BDE99 and BDE153 are the predominant polybrominated diphenyl ether (PBDE) congeners detected in humans and can induce drug metabolizing enzymes in the liver. We have previously demonstrated that several human liver organic anion transporting polypeptides (humans: OATPs; rodents: Oatps) can transport PBDE congeners. Mice are commonly used to study the toxicity of chemicals like the PBDE congeners. However, the mechanism of the hepatic PBDE uptake in mice is not known. Therefore, the purpose of the current study was to test the hypothesis that BDE47, BDE99, and BDE153 are substrates of mouse hepatic Oatps (Oatp1a1, Oatp1a4, Oatp1b2, and Oatp2b1). We used Human Embryonic Kidney 293 (HEK293) cells transiently expressing individual Oatps and quantified the uptake of BDE47, BDE99, and BDE153. Oatp1a4, Oatp1b2, and Oatp2b1 transported all three PBDE congeners, whereas Oatp1a1 did transport none. Kinetic studies demonstrated that Oatp1a4 and Oatp1b2 transported BDE47 with the greatest affinity, followed by BDE99 and BDE153. In contrast, Oatp2b1 transported all three PBDE congeners with similar affinities. The importance of hepatic Oatps for the liver accumulation of BDE47 was confirmed using Oatp1a4-, and Oatp1b2-null mice.

Aroclor 1254, a developmental neurotoxicant, alters energy metabolism- and intracellular signaling-associated protein networks in rat cerebellum and hippocampus

The vast literature on the mode of action of polychlorinated biphenyls (PCBs) indicates that PCBs are a unique model for understanding the mechanisms of toxicity of environmental mixtures of persistent chemicals. PCBs have been shown to adversely affect psychomotor function and learning and memory in humans. Although the molecular mechanisms for PCB effects are unclear, several studies indicate that the disruption of Ca(2+)-mediated signal transduction plays significant roles in PCB-induced developmental neurotoxicity. Culminating events in signal transduction pathways include the regulation of gene and protein expression, which affects the growth and function of the nervous system. Our previous studies showed changes in gene expression related to signal transduction and neuronal growth. In this study, protein expression following developmental exposure to PCB is examined. Pregnant rats (Long Evans) were dosed with 0.0 or 6.0mg/kg/day of Aroclor-1254 from gestation day 6 through postnatal day (PND) 21, and the cerebellum and hippocampus from PND14 animals were analyzed to determine Aroclor 1254-induced differential protein expression. Two proteins were found to be differentially expressed in the cerebellum following PCB exposure while 18 proteins were differentially expressed in the hippocampus. These proteins are related to energy metabolism in mitochondria (ATP synthase, sub unit β (ATP5B), creatine kinase, and malate dehydrogenase), calcium signaling (voltage-dependent anion-selective channel protein 1 (VDAC1) and ryanodine receptor type II (RyR2)), and growth of the nervous system (dihydropyrimidinase-related protein 4 (DPYSL4), valosin-containing protein (VCP)). Results suggest that Aroclor 1254-like persistent chemicals may alter energy metabolism and intracellular signaling, which might result in developmental neurotoxicity.

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.

Neurotoxicity of brominated flame retardants: (in)direct effects of parent and hydroxylated polybrominated diphenyl ethers on the (developing) nervous system

BACKGROUND/OBJECTIVE

Polybrominated diphenyl ethers (PBDEs) and their hydroxylated (OH-) or methoxylated forms have been detected in humans. Because this raises concern about adverse effects on the developing brain, we reviewed the scientific literature on these mechanisms.

DATA SYNTHESIS

Many rodent studies reported behavioral changes after developmental, neonatal, or adult exposure to PBDEs, and other studies documented subtle structural and functional alterations in brains of PBDE-exposed animals. Functional effects have been observed on synaptic plasticity and the glutamate-nitric oxide-cyclic guanosine monophosphate pathway. In the brain, changes have been observed in the expression of genes and proteins involved in synapse and axon formation, neuronal morphology, cell migration, synaptic plasticity, ion channels, and vesicular neurotransmitter release. Cellular and molecular mechanisms include effects on neuronal viability 
(via apoptosis and oxidative stress), neuronal differentiation and migration, neurotransmitter release/uptake, neurotransmitter receptors and ion channels, calcium (Ca²⁺) homeostasis, and intracellular signaling pathways.

DISCUSSION

Bioactivation of PBDEs by hydroxylation has been observed for several endocrine end points. This has also been observed for mechanisms related to neurodevelopment, including binding to thyroid hormone receptors and transport proteins, disruption of Ca²⁺ homeostasis, and modulation of GABA and nicotinic acetylcholine receptor function.

CONCLUSIONS

The increased hazard for developmental neurotoxicity by hydroxylated (OH-)PBDEs compared with their parent congeners via direct neurotoxicity and thyroid disruption clearly warrants further investigation into a) the role of oxidative metabolism in producing active metabolites of PBDEs and their impact on brain development; b) concentrations of parent and OH-PBDEs in the brain; and c) interactions between different environmental contaminants during exposure to mixtures, which may increase neurotoxicity.

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.

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.

Modified expression of several sperm proteins after chronic exposure to the antiandrogenic compound vinclozolin

Little is known about the molecular impact of in vivo exposure to endocrine disruptors (EDs) on sperm structures and functions. We recently reported that the lifelong exposure of rats to the antiandrogenic compound vinclozolin results in low epididymal weight, changes in sperm kinematic parameters, and immature sperm chromatin condensation, together with the impairment of several fertility end points. These results led us to focus specifically on possible molecular abnormalities in sperm. Sperm samples were recovered from the frozen epididymides of rats exposed during the previous study. The proteins present in the samples from six exposed and six control rats were analyzed in pairs, by two-dimensional fluorescence difference gel electrophoresis, to investigate possible exposure-induced changes to sperm protein profiles. Twelve proteins, from the 380 matched spots observed in at least five gels, were present in larger or smaller amounts after vinclozolin exposure. These proteins were identified by mass spectrometry, and several are known to play a crucial role in the sperm fertilizing ability, among which, two mitochondrial enzymes, malate dehydrogenase 2 and aldehyde dehydrogenase (both of which were present in smaller amounts after treatment) and A-kinase anchor protein 4 (larger amounts of precursor after treatment). Finally, Ingenuity Pathway Analysis revealed highly significant interactions between proteins over- and underexpressed after treatment. This is the first study to show an association between in vivo exposure to an ED and changes to the sperm protein profile. These modifications may be at least partly responsible for the reproductive abnormalities and impaired fertility recently reported in this rat model of vinclozolin exposure.

The potential of selected brominated flame retardants to affect neurological development

Various brominated flame retardants (BFR), including polybrominated diphenyl ether (PBDE) congeners, hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), are commonly used in household items and electronics and have been detected in the environment and/or the bodily fluids of people, including children. Some studies in animals suggest that exposure to PBDE congeners, HBCD, or TBBPA during the perinatal period may affect locomotor activity and/or memory and learning. Epidemiological studies showing similar effects in humans, however, are lacking. To assess whether an association exists between perinatal exposure and development of consistent neurobehavioral alterations, published animal studies investigating perinatal exposure to PBDE congeners, HBCD, or TBBPA with specific neurobehavioral evaluations-particularly, assessments of motor activity-were reviewed for consistency of results. Our analysis shows that although the majority of studies suggest that perinatal exposure affects motor activity, the effects observed were not consistent. This lack of consistency includes the type of motor activity (locomotion, rearing, or total activity) affected, the direction (increase or decrease) and pattern of change associated with exposure, the existence of a dose response, the permanency of findings, and the possibility of gender differences in response. Interestingly, Good Laboratory Practices (GLP)-compliant studies that followed U.S. Environmental Protection Agency (EPA)/Organization for Economic Cooperation and Development (OECD) guidelines for developmental neurotoxicity testing found no adverse effects associated with exposure to PBDE209, HBCD, or TBBPA at doses that were orders of magnitude higher and administered over longer durations than those used in the other studies examined herein. The lack of consistency across studies precludes establishment of a causal relationship between perinatal exposure to these substances and alterations in motor activity.

Proteomic studies in zebrafish liver cells exposed to the brominated flame retardants HBCD and TBBPA

Proteomic effect screening in zebrafish liver cells was performed to generate hypotheses regarding single and mixed exposure to the BFRs HBCD and TBBPA. Responses at sublethal exposure were analysed by two-dimensional gel electrophoresis followed by MALDI-TOF and FT-ICR protein identification. Mixing of HBCD and TBBPA at sublethal doses of individual substances seemed to increase toxicity. Proteomic analyses revealed distinct exposure-specific and overlapping responses suggesting novel mechanisms with regard to HBCD and TBBPA exposure. While distinct HBCD responses were related to decreased protein metabolism, TBBPA revealed effects related to protein folding and NADPH production. Overlapping responses suggest increased gluconeogenesis (GAPDH and aldolase) while distinct mixture effects suggest a pronounced NADPH production and changes in proteins related to cell cycle control (prohibitin and crk-like oncogene). We conclude that mixtures containing HBCD and TBBPA may result in unexpected effects highlighting proteomics as a sensitive tool for detecting and hypothesis generation of mixture effects.

Facing the challenge of data transfer from animal models to humans: the case of persistent organohalogens

A well-documented fact for a group of persistent, bioaccumulating organohalogens contaminants, namely polychlorinated biphenyls (PCBs), is that appropriate regulation was delayed, on average, up to 50 years. Some of the delay may be attributed to the fact that the science of toxicology was in its infancy when PCBs were introduced in 1920's. Nevertheless, even following the development of modern toxicology this story repeats itself 45 years later with polybrominated diphenyl ethers (PBDEs) another compound of concern for public health. The question is why? One possible explanation may be the low coherence between experimental studies of toxic effects in animal models and human studies. To explore this further, we reviewed a total of 807 PubMed abstracts and full texts reporting studies of toxic effects of PCB and PBDE in animal models. Our analysis documents that human epidemiological studies of PBDE stand to gain little from animal studies due to the following: 1) the significant delay between the commercialisation of a substance and studies with animal models; 2) experimental exposure levels in animals are several orders of magnitude higher than exposures in the general human population; 3) the limited set of evidence-based endocrine endpoints; 4) the traditional testing sequence (adult animals--neonates--foetuses) postpones investigation of the critical developmental stages; 5) limited number of animal species with human-like toxicokinetics, physiology of development and pregnancy; 6) lack of suitable experimental outcomes for the purpose of epidemiological studies. Our comparison of published PCB and PBDE studies underscore an important shortcoming: history has, unfortunately, repeated itself. Broadening the crosstalk between the various branches of toxicology should therefore accelerate accumulation of data to enable timely and appropriate regulatory action.

Gender-specific proteomic responses in zebrafish liver following exposure to a selected mixture of brominated flame retardants

Proteomic effect screening in zebrafish liver was performed to generate hypotheses following exposure (21 days) to a structurally diverse mixture of brominated flame retardants (BFRs). Fish were exposed to two doses (10 and 100 nmol/g feed). Two-dimensional gel-electrophoresis, image analysis and MALDI-TOF mass-spectrometry revealed 13 and 19 significant responses in males and females, respectively. Effects on proteins related to cellular maintenance and stress were observed in both genders. Regulated proteins were gender-specific, but functionally indicated common protective responses (peroxiredoxin 6 and Zgc:92891 in males and transketolase in females) suggesting oxidative stress. Betaine homocysteine methyltransferase (BHMT) was induced in both genders. In addition a female-specific downregulation of ironhomeostatic proteins (iron-regulatory protein 1 and transferrin) were observed. Our proteomic approach revealed novel responses that suggest important gender-specific sensitivity to BFRs that should be considered when interpreting adverse effects of BFRs.

Overview of toxicological aspects of polybrominated diphenyl ethers: a flame-retardant additive in several consumer products

Polybrominated diphenyl ethers (PBDEs) are ubiquitous environmental contaminants due to their long half-life and widespread use as flame retardants in several consumer products, including plastics. In addition to other actions, these compounds are characterized as thyroid hormone disruptors. Thyroid hormones affect the function of nearly all tissues via their effects on cellular metabolism and the essential roles they play in differentiation and growth. Interference with thyroid hormone homeostasis by these environmental compounds, therefore, has the potential to impact development and every system in the body. Their presence in human breast milk is particularly troubling due to exposure of nursing children. The last trimester of pregnancy up to 2 years of age corresponds to a time of rapid neurodevelopment and represents a period of vulnerability to environmental insults. Rodent studies indicate that PBDEs may act as developmental neurotoxicants and effects on the reproductive system have been reported as well. Concerns exist regarding possible impacts of exposure, in particular ones which occur during development, on human health. This paper is part of a series of articles regarding contaminants in plastic and provides an overview regarding PBDEs, a class of flame-retardant additives to plastic. PBDEs possess a similar structure to the polychlorinated biphenyls (PCBs) previously used as lubricants in electrical generators and transformers until production was prohibited approximately 25 years ago. Parallels between the two compounds will be briefly made and in particular, as more epidemiological studies on PCBs are available than on PBDEs, a few examples concerning thyroid homeostasis, cognitive function and sexually dimorphic behavior in humans will be mentioned.

New insights into the endocrine disrupting effects of brominated flame retardants

The objective of this review is to provide an overview of recent studies demonstrating the endocrine disrupting (ED) effects of brominated flame retardants (BFRs), while highlighting interesting data presented at the recent international BFR workshop in Amsterdam in April, 2007. A review written in 2002 was used as a starting point and about 60 publications published since 2003 were reviewed. New insights into the in vivo effects of BFRs on thyroid hormone, estrogen and androgen pathways in both mammalian and non-mammalian models are provided, and novel (in vitro) findings on the mechanisms underlying ED effects are highlighted. Special attention is also given to reports on neurotoxicological effects at relatively low doses of BFRs, although an endocrine-related mechanism is disputable. Convincing evidence has been published showing that BFRs and importantly, BFR metabolites, have the potential to disrupt endocrine systems at multiple target sites. While some studies suggest a wide margin of safety between effect concentrations in rodent models and levels encountered in humans and the environment, other studies demonstrate that exposure to low doses relevant for humans and wildlife at critical time points in development can result in profound effects on both endocrine pathways and (neuro)development.

Neurotoxicity of a polybrominated diphenyl ether mixture (DE-71) in mouse neurons and astrocytes is modulated by intracellular glutathione levels

Polybrominated diphenyl ether (PBDE) flame retardants have become widespread environmental contaminants. Body burden in the U.S. population has been shown to be higher than in other countries, and infants and toddlers have highest exposure through maternal breast milk and household dust. The primary concern for adverse health effects of PBDEs relates to their potential developmental neurotoxicity, which has been found in a number of animal studies. Information on the possible mechanisms of PBDE neurotoxicity is limited, though some studies have suggested that PBDEs may elicit oxidative stress. The present study examined the in vitro neurotoxicity of DE-71, a penta-BDE mixture, in primary neurons and astrocytes obtained from wild-type and Gclm knockout mice, which lack the modifier subunit of glutamate-cysteine ligase and, as a consequence, have very low levels of glutathione (GSH). These experiments show that neurotoxicity of DE-71 in these cells is modulated by cellular GSH levels. Cerebellar granule neurons (CGNs) from Gclm (-/-) mice displayed a higher sensitivity to DE-71 toxicity compared to CGNs from wild-type animals. DE-71 neurotoxicity in CGNs from Gclm (+/+) mice was exacerbated by GSH depletion, and in CGNs from both genotypes it was antagonized by increasing GSH levels and by antioxidants. DE-71 caused an increase in reactive oxygen species and in lipid peroxidation in CGNs, that was more pronounced in Gclm (-/-) mice. Toxicity of DE-71 was mostly due to the induction of apoptotic cell death. An analysis of DE-71-induced cytotoxicity and apoptosis in neurons and astrocytes from different brain areas (cerebellum, hippocampus, cerebral cortex) in both mouse genotypes showed a significant correlation with intracellular GSH levels. As an example, DE-71 caused cytotoxicity in hippocampal neurons with IC50s of 2.2 and 0.3 microM, depending on genotype, and apoptosis with IC50s of 2.3 and 0.4 microM, respectively. These findings suggest that the developmental neurotoxicity of PBDE may involve oxidative stress, and that individual with genetic polymorphisms leading to lower GSH levels may be more susceptible to their adverse effects.

Exposure to brominated flame retardant PBDE-99 affects cytoskeletal protein expression in the neonatal mouse cerebral cortex

Polybrominated diphenyl ethers (PBDEs) are environmental contaminants found in human and animal tissues worldwide. Neonatal exposure to the flame retardant 2,2', 4,4',5-pentabromodiphenyl ether (PBDE-99) disrupts normal brain development in mice, and results in disturbed spontaneous behavior in the adult. The mechanisms underlying the late effects of early exposure are not clear. To gain insight into the initial neurodevelopmental damage inflicted by PBDE-99, we investigated the short-term effects of PBDE-99 on protein expression in the developing cerebral cortex of neonatal mice, and the cytotoxic and apoptotic effects of PBDE-99 in primary cultures of fetal rat cortical cells. We used two-dimensional difference gel electrophoresis (2D-DIGE) to analyze protein samples isolated from the cortex of NMRI mice 24h after exposure to a single oral dose of 12 mg/kg PBDE-99 on post-natal day 10. Protein resolution was enhanced by sample pre-fractionation. In the cell model, we determined cell viability using the trypan blue exclusion assay, and apoptosis using immunocytochemical detection of cleaved caspase-3. We determined the identity of 111 differentially expressed proteins, 32 (29%) of which are known to be cytoskeleton-related. Similar to previous findings in the striatum, we found elevated levels of the neuron growth-associated protein Gap43 in the cortex. In cultured cortical cells, a high concentration of PBDE-99 (30 microM) induced cell death without any apparent increase in caspase-3 activity. These results indicate that the permanent neurological damage induced by PBDE-99 during the brain growth spurt involve detrimental effects on cytoskeletal regulation and neuronal maturation in the developing cerebral cortex.

In utero exposure to low doses of environmental pollutants disrupts fetal ovarian development in sheep

Epidemiological studies of the impact of environmental chemicals on reproductive health demonstrate consequences of exposure but establishing causative links requires animal models using ‘real life’ in utero exposures. We aimed to determine whether prolonged, low-dose, exposure of pregnant sheep to a mixture of environmental chemicals affects fetal ovarian development. Exposure of treated ewes (n = 7) to pollutants was maximized by surface application of processed sewage sludge to pasture. Control ewes (n = 10) were reared on pasture treated with inorganic fertilizer. Ovaries and blood were collected from fetuses (n = 15 control and n = 8 treated) on Day 110 of gestation for investigation of fetal endocrinology, ovarian follicle/oocyte numbers and ovarian proteome. Treated fetuses were 14% lighter than controls but fetal ovary weights were unchanged. Prolactin (48% lower) was the only measured hormone significantly affected by treatment. Treatment reduced numbers of growth differentiation factor (GDF9) and induced myeloid leukaemia cell differentiation protein (MCL1) positive oocytes by 25–26% and increased pro-apoptotic BAX by 65% and 42% of protein spots in the treated ovarian proteome were differently expressed compared with controls. Nineteen spots were identified and included proteins involved in gene expression/transcription, protein synthesis, phosphorylation and receptor activity. Fetal exposure to environmental chemicals, via the mother, significantly perturbs fetal ovarian development. If such effects are replicated in humans, premature menopause could be an outcome.

Striatal proteomic analysis suggests that first L-dopa dose equates to chronic exposure

L-3,4-dihydroxypheylalanine (L-dopa)-induced dyskinesia represent a debilitating complication of therapy for Parkinson's disease (PD) that result from a progressive sensitization through repeated L-dopa exposures. The MPTP macaque model was used to study the proteome in dopamine-depleted striatum with and without subsequent acute and chronic L-dopa treatment using two-dimensional difference in-gel electrophoresis (2D-DIGE) and mass spectrometry. The present data suggest that the dopamine-depleted striatum is so sensitive to de novo L-dopa treatment that the first ever administration alone would be able (i) to induce rapid post-translational modification-based proteomic changes that are specific to this first exposure and (ii), possibly, lead to irreversible protein level changes that would be not further modified by chronic L-dopa treatment. The apparent equivalence between first and chronic L-dopa administration suggests that priming would be the direct consequence of dopamine loss, the first L-dopa administrations only exacerbating the sensitization process but not inducing it.

Developmental neurotoxicity of polybrominated diphenyl ether (PBDE) flame retardants

Polybrominated diphenyl ethers (PBDEs) are a class of flame retardants used in a variety of consumer products. In the past 25 years, PBDEs have become ubiquitous environmental contaminants. They have been detected in soil, air, sediments, birds, marine species, fish, house dust, and human tissues, blood and breast milk. Diet and house dust appear to be the major sources of PBDE exposure in the general population, though occupational exposure can also occur. Levels of PBDEs in human tissues are particularly high in North America, compared to Asian and European countries, and have been increasing in the past 30 years. Concentrations of PBDEs are particularly high in breast milk, resulting in high exposure of infants. In addition, for toddlers, dust has been estimated to account for a large percentage of exposure. PBDEs can also cross the placenta, as they have been detected in fetal blood and liver. Tetra-, penta- and hexaBDEs are most commonly present in human tissues. The current greatest concern for potential adverse effects of PBDEs relates to their developmental neurotoxicity. Pre- or postnatal exposure of mice or rats to various PBDEs has been shown to cause long-lasting changes in spontaneous motor activity, mostly characterized as hyperactivity or decreased habituation, and to disrupt performance in learning and memory tests. While a reduction in circulating thyroid hormone (T(4)) may contribute to the developmental neurotoxicity of PBDEs, direct effects on the developing brain have also been reported. Among these, PBDEs have been shown to affect signal transduction pathways and to cause oxidative stress. Levels of PBDEs causing developmental neurotoxicity in animals are not much dissimilar from levels found in highly exposed infants and toddlers.

Two-dimensional fluorescence difference gel electrophoresis for comparative proteomics profiling

Quantitative proteomics is the workhorse of the modern proteomics initiative. The gel-based and MuDPIT approaches have facilitated vital advances in the measurement of protein expression alterations in normal and disease phenotypic states. The methodological advance in two-dimensional gel electrophoresis (2DGE) has been the multiplexing fluorescent two-dimensional fluorescence difference gel electrophoresis (2D-DIGE). 2D-DIGE is based on direct labeling of lysine groups on proteins with cyanine CyDye DIGE Fluor minimal dyes before isoelectric focusing, enabling the labeling of 2-3 samples with different dyes and electrophoresis of all the samples on the same 2D gel. This capability minimizes spot pattern variability and the number of gels in an experiment while providing simple, accurate and reproducible spot matching. This protocol can be completed in 3-5 weeks depending on the sample size of the experiment and the level of expertise of the investigator.

Neonatal exposure to brominated flame retardant BDE-47 reduces long-term potentiation and postsynaptic protein levels in mouse hippocampus

BACKGROUND

Increasing environmental levels of brominated flame retardants raise concern about possible adverse effects, particularly through early developmental exposure.

OBJECTIVE

The objective of this research was to investigate neurodevelopmental mechanisms underlying previously observed behavioral impairments observed after neonatal exposure to polybrominated diphenyl ethers (PBDEs).

METHODS

C57Bl/6 mice received a single oral dose of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on postnatal day (PND) 10 (i.e., during the brain growth spurt). On PND17-19, effects on synaptic plasticity, levels of postsynaptic proteins involved in long-term potentiation (LTP), and vesicular release mechanisms were studied ex vivo. We investigated possible acute in vitro effects of BDE-47 on vesicular catecholamine release and intracellular Ca(2+) in rat pheochromocytoma (PC12) cells.

RESULTS

Field-excitatory postsynaptic potential (f-EPSP) recordings in the hippocampal CA1 area demonstrated reduced LTP after exposure to 6.8 mg (14 micromol)/kg body weight (bw) BDE-47, whereas paired-pulse facilitation was not affected. Western blotting of proteins in the postsynaptic, triton-insoluble fraction of hippocampal tissue revealed a reduction of glutamate receptor subunits NR2B and GluR1 and autophosphorylated-active Ca(2+)/calmodulin-dependent protein kinase II (alphaCaMKII), whereas other proteins tested appeared unaffected. Amperometric recordings in chromaffin cells from mice exposed to 68 mg (140 micromol)/kg bw BDE-47 did not reveal changes in catecholamine release parameters. Modest effects on vesicular release and intracellular Ca(2+) in PC12 cells were seen following acute exposure to 20 microM BDE-47. The combined results suggest a post-synaptic mechanism in vivo.

CONCLUSION

Early neonatal exposure to a single high dose of BDE-47 causes a reduction of LTP together with changes in postsynaptic proteins involved in synaptic plasticity in the mouse hippocampus.