Polychlorinated biphenyls PCB 52, PCB 180, and PCB 138 impair the glutamate-nitric oxide-cGMP pathway in cerebellar neurons in culture by different mechanisms

Association between mixed exposure to endocrine-disrupting chemicals and cognitive function in elderly Americans

OBJECTIVES

Studies exploring the relationship between mixed exposure to endocrine-disrupting chemicals (EDCs) and cognition are limited, with even more scarce studies conducted in the elderly. The aim of this study was to investigate the association between mixed exposure to five categories of EDCs and cognition in elderly Americans.

STUDY DESIGN

Cross-sectional study.

METHODS

727 participants from the 2011-2014 National Health and Nutrition Examination Survey were incorporated into this study, and the levels of 47 EDC metabolites were measured. Cognitive function was assessed using immediate recall test (IRT), delayed recall test (DRT), animal fluency test (AFT), and digit symbol substitution test (DSST), and all the cognitive test scores were standardized. The individual and combined effects of EDC metabolites on the cognitive function in older adults were assessed using three analytical methods.

RESULTS

The results showed that exposure to perfluorononanoic acid, polychlorinated biphenyl (PCB) 199, and PCB 206 was associated with the z-scores on the cognitive tests. Negative associations between mixed exposure to EDCs and the AFT and Global z-scores and a positive relationship with the DRT z-score were found in the WQS regression. The BKMR results revealed a positive trend between the mixture of EDCs and the DRT z-score. However, compared to the median, exposure to mixtures in the 45th percentile and below was associated with a decreased DRT z-score.

CONCLUSIONS

Mixed exposure to EDCs may adversely affect the global cognitive function in elderly individuals. Necessary measures are needed to restrict EDCs use to protect the cognitive health of older adults.

Assessment of neurotransmitter release in human iPSC-derived neuronal/glial cells: a missing in vitro assay for regulatory developmental neurotoxicity testing

Human induced pluripotent stem cell (hiPSC)-derived neural stem cells (NSCs) and their differentiated neuronal/glial derivatives have been recently considered suitable to assess in vitro developmental neurotoxicity (DNT) triggered by exposure to environmental chemicals. The use of human-relevant test systems combined with in vitro assays specific for different neurodevelopmental events, enables a mechanistic understanding of the possible impact of environmental chemicals on the developing brain, avoiding extrapolation uncertainties associated with in vivo studies. Currently proposed in vitro battery for regulatory DNT testing accounts for several assays suitable to study key neurodevelopmental processes, including NSC proliferation and apoptosis, differentiation into neurons and glia, neuronal migration, synaptogenesis, and neuronal network formation. However, assays suitable to measure interference of compounds with neurotransmitter release or clearance are at present not included, which represents a clear gap of the biological applicability domain of such a testing battery. Here we applied a HPLC-based methodology to measure the release of neurotransmitters in a previously characterized hiPSC-derived NSC model undergoing differentiation towards neurons and glia. Glutamate release was assessed in control cultures and upon depolarization, as well as in cultures repeatedly exposed to some known neurotoxicants (BDE47 and lead) and chemical mixtures. Obtained data indicate that these cells have the ability to release glutamate in a vesicular manner, and that both glutamate clearance and vesicular release concur in the maintenance of extracellular glutamate levels. In conclusion, analysis of neurotransmitter release is a sensitive readout that should be included in the envisioned battery of in vitro assays for DNT testing.

Placenta and fetal brain share a neurodevelopmental disorder DNA methylation profile in a mouse model of prenatal PCB exposure

Polychlorinated biphenyls (PCBs) are developmental neurotoxicants implicated as environmental risk factors for neurodevelopmental disorders (NDDs). Here, we report the effects of prenatal exposure to a human-relevant mixture of PCBs on the DNA methylation profiles of mouse placenta and fetal brain. Thousands of differentially methylated regions (DMRs) distinguish placenta and fetal brain from PCB-exposed mice from sex-matched vehicle controls. In both placenta and fetal brain, PCB-associated DMRs are enriched for functions related to neurodevelopment and cellular signaling and enriched within regions of bivalent chromatin. The placenta and brain PCB DMRs overlap significantly and map to a shared subset of genes enriched for Wnt signaling, Slit/Robo signaling, and genes differentially expressed in NDD models. The consensus PCB DMRs also significantly overlap with DMRs from human NDD brain and placenta. These results demonstrate that PCB-exposed placenta contains a subset of DMRs that overlap fetal brain DMRs relevant to an NDD.

Combining in vitro assays and mathematical modelling to study developmental neurotoxicity induced by chemical mixtures

Prenatal and postnatal co-exposure to multiple chemicals at the same time may have deleterious effects on the developing nervous system. We previously showed that chemicals acting through similar mode of action (MoA) and grouped based on perturbation of brain derived neurotrophic factor (BDNF), induced greater neurotoxic effects on human induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared to chemicals with dissimilar MoA. Here we assessed the effects of repeated dose (14 days) treatments with mixtures containing the six chemicals tested in our previous study (Bisphenol A, Chlorpyrifos, Lead(II) chloride, Methylmercury chloride, PCB138 and Valproic acid) along with 2,2'4,4'-tetrabromodiphenyl ether (BDE47), Ethanol, Vinclozolin and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)), on hiPSC-derived neural stem cells undergoing differentiation toward mixed neurons/astrocytes up to 21 days. Similar MoA chemicals in mixtures caused an increase of BDNF levels and neurite outgrowth, and a decrease of synapse formation, which led to inhibition of electrical activity. Perturbations of these endpoints are described as common key events in adverse outcome pathways (AOPs) specific for DNT. When compared with mixtures tested in our previous study, adding similarly acting chemicals (BDE47 and EtOH) to the mixture resulted in a stronger downregulation of synapses. A synergistic effect on some synaptogenesis-related features (PSD95 in particular) was hypothesized upon treatment with tested mixtures, as indicated by mathematical modelling. Our findings confirm that the use of human iPSC-derived mixed neuronal/glial models applied to a battery of in vitro assays anchored to key events in DNT AOP networks, combined with mathematical modelling, is a suitable testing strategy to assess in vitro DNT induced by chemical mixtures.

Exposure to human relevant mixtures of halogenated persistent organic pollutants (POPs) alters neurodevelopmental processes in human neural stem cells undergoing differentiation

Halogenated persistent organic pollutants (POPs) like perfluorinated alkylated substances (PFASs), brominated flame retardants (BFRs), organochlorine pesticides and polychlorinated biphenyls (PCBs) are known to cause cancer, immunotoxicity, neurotoxicity and interfere with reproduction and development. Concerns have been raised about the impact of POPs upon brain development and possibly neurodevelopmental disorders. The developing brain is a particularly vulnerable organ due to dynamic and complex neurodevelopmental processes occurring early in life. However, very few studies have reported on the effects of POP mixtures at human relevant exposures, and their impact on key neurodevelopmental processes using human in vitro test systems. Aiming to reduce this knowledge gap, we exposed mixed neuronal/glial cultures differentiated from neural stem cells (NSCs) derived from human induced pluripotent stem cells (hiPSCs) to reconstructed mixtures of 29 different POPs using concentrations comparable to Scandinavian human blood levels. Effects of the POP mixtures on neuronal proliferation, differentiation and synaptogenesis were evaluated using in vitro assays anchored to common key events identified in the existing developmental neurotoxicity (DNT) adverse outcome pathways (AOPs). The present study showed that mixtures of POPs (in particular brominated and chlorinated compounds) at human relevant concentrations increased proliferation of NSCs and decreased synapse number. Based on a mathematical modelling, synaptogenesis and neurite outgrowth seem to be the most sensitive DNT in vitro endpoints. Our results indicate that prenatal exposure to POPs may affect human brain development, potentially contributing to recently observed learning and memory deficits in children.

PCB52 exposure alters the neurotransmission ligand-receptors in male offspring and contributes to sex-specific neurodevelopmental toxicity

Polychlorinated biphenyls (PCBs) in the air are predominantly the less chlorinated congeners. Non-dioxin-like (NDL) low-chlorinated PCBs are more neurotoxic, and cause neurodevelopmental and neurobehavioral alterations in humans. However, the underlying mechanisms for this neurodevelopmental toxicity remain unknown. In the present study, Wistar rats were treated by gavage with PCB52 (1 mg/kg body weight) or corn oil from gestational day 7 to postnatal day 21. Both the body lengths and weights of the suckling rats at birth were significantly decreased by PCB52 treatment, suggesting developmental toxicity. Although no obvious histopathological changes were observed in the brain, using RNA-sequencing, 208 differentially expressed genes (DEGs) were identified in the striatum of PCB52-treated male offspring, while just 13 DEGs were identified in female offspring, suggesting sex-specific effects. Furthermore, using Gene Ontology enrichment analysis, neurodevelopmental processes, neurobehavioral alterations, and neurotransmission changes were enriched from the 208 DEGs in male offspring. Similarly, using Kyoto Encyclopedia of Genes and Genomes enrichment analysis, neuroactive ligand receptor interactions and multiple synapse pathways were enriched in male offspring, implying dysfunction of the neurotransmission system. Reductions in the protein expressions of these ligand receptors were also identified in the striatum, cerebral cortex, and hippocampus using western blotting methods. Taken together, our findings indicate that PCB52 exposure during gestation and lactation results in the abnormal expression of neurotransmission ligand-receptors in male offspring with a sex bias, and that this may contribute to neurodevelopmental toxicity.

Hexachloronaphthalene Induces Mitochondrial-Dependent Neurotoxicity via a Mechanism of Enhanced Production of Reactive Oxygen Species

Hexachloronaphthalene (PCN67) is one of the most toxic among polychlorinated naphthalenes. Despite the known high bioaccumulation and persistence of PCN67 in the environment, it is still unclear to what extent exposure to these substances may interfere with normal neuronal physiology and lead to neurotoxicity. Therefore, the primary goal of this study was to assess the effect of PCN67 in neuronal in vitro models. Neuronal death was assessed upon PCN67 treatment using differentiated PC12 cells and primary hippocampal neurons. At 72 h postexposure, cell viability assays showed an IC₅₀ value of 0.35 μg/ml and dose-dependent damage of neurites and concomitant downregulation of neurofilaments L and M. Moreover, we found that younger primary neurons (DIV4) were much more sensitive to PCN67 toxicity than mature cultures (DIV14). Our comprehensive analysis indicated that the application of PCN67 at the IC₅₀ concentration caused necrosis, which was reflected by an increase in LDH release, HMGB1 protein export to the cytosol, nuclear swelling, and loss of homeostatic control of energy balance. The blockage of mitochondrial calcium uniporter partially rescued the cell viability, loss of mitochondrial membrane potential (ΔΨ_m), and the overproduction of reactive oxygen species, suggesting that the underlying mechanism of neurotoxicity involved mitochondrial calcium accumulation. Increased lipid peroxidation as a consequence of oxidative stress was additionally seen for 0.1 μg/ml of PCN67, while this concentration did not affect ΔΨ_m and plasma membrane permeability. Our results show for the first time that neuronal mitochondria act as a target for PCN67 and indicate that exposure to this drug may result in neuron loss via mitochondrial-dependent mechanisms.

The developmental neurotoxicity of legacy vs. contemporary polychlorinated biphenyls (PCBs): similarities and differences

Although banned from production for decades, PCBs remain a significant risk to human health. A primary target of concern is the developing brain. Epidemiological studies link PCB exposures in utero or during infancy to increased risk of neuropsychiatric deficits in children. Nonclinical studies of legacy congeners found in PCB mixtures synthesized prior to the ban on PCB production suggest that non-dioxin-like (NDL) congeners are predominantly responsible for the developmental neurotoxicity associated with PCB exposures. Mechanistic studies suggest that NDL PCBs alter neurodevelopment via ryanodine receptor-dependent effects on dendritic arborization. Lightly chlorinated congeners, which were not present in the industrial mixtures synthesized prior to the ban on PCB production, have emerged as contemporary environmental contaminants, but there is a paucity of data regarding their potential developmental neurotoxicity. PCB 11, a prevalent contemporary congener, is found in the serum of children and their mothers, as well as in the serum of pregnant women at increased risk for having a child diagnosed with a neurodevelopmental disorder (NDD). Recent data demonstrates that PCB 11 modulates neuronal morphogenesis via mechanisms that are convergent with and divergent from those implicated in the developmental neurotoxicity of legacy NDL PCBs. This review summarizes these data and discusses their relevance to adverse neurodevelopmental outcomes in humans.

Assessment of developmental neurotoxicity induced by chemical mixtures using an adverse outcome pathway concept

BACKGROUND

In light of the vulnerability of the developing brain, mixture risk assessment (MRA) for the evaluation of developmental neurotoxicity (DNT) should be implemented, since infants and children are co-exposed to more than one chemical at a time. One possible approach to tackle MRA could be to cluster DNT chemicals in a mixture on the basis of their mode of action (MoA) into 'similar' and 'dissimilar', but still contributing to the same adverse outcome, and anchor DNT assays to common key events (CKEs) identified in DNT-specific adverse outcome pathways (AOPs). Moreover, the use of human in vitro models, such as induced pluripotent stem cell (hiPSC)-derived neuronal and glial cultures would enable mechanistic understanding of chemically-induced adverse effects, avoiding species extrapolation.

METHODS

HiPSC-derived neural progenitors differentiated into mixed cultures of neurons and astrocytes were used to assess the effects of acute (3 days) and repeated dose (14 days) treatments with single chemicals and in mixtures belonging to different classes (i.e., lead(II) chloride and methylmercury chloride (heavy metals), chlorpyrifos (pesticide), bisphenol A (organic compound and endocrine disrupter), valproic acid (drug), and PCB138 (persistent organic pollutant and endocrine disrupter), which are associated with cognitive deficits, including learning and memory impairment in children. Selected chemicals were grouped based on their mode of action (MoA) into 'similar' and 'dissimilar' MoA compounds and their effects on synaptogenesis, neurite outgrowth, and brain derived neurotrophic factor (BDNF) protein levels, identified as CKEs in currently available AOPs relevant to DNT, were evaluated by immunocytochemistry and high content imaging analysis.

RESULTS

Chemicals working through similar MoA (i.e., alterations of BDNF levels), at non-cytotoxic (IC20/100), very low toxic (IC5), or moderately toxic (IC20) concentrations, induce DNT effects in mixtures, as shown by increased number of neurons, impairment of neurite outgrowth and synaptogenesis (the most sensitive endpoint as confirmed by mathematical modelling) and increase of BDNF levels, to a certain extent reproducing autism-like cellular changes observed in the brain of autistic children.

CONCLUSIONS

Our findings suggest that the use of human iPSC-derived mixed neuronal/glial cultures applied to a battery of assays anchored to key events of an AOP network represents a valuable approach to identify mixtures of chemicals with potential to cause learning and memory impairment in children.

Mechanisms of Action Point Towards Combined PBDE/NDL-PCB Risk Assessment

At present, human risk assessment of the structurally similar non-dioxin-like (NDL) PCBs and polybrominated diphenylethers (PBDEs) is done independently for both groups of compounds. There are however obvious similarities between NDL-PCBs and PBDEs with regard to modulation of the intracellular calcium homeostasis (basal calcium levels, voltage-gated calcium channels, calcium uptake, ryanodine receptor) and thyroid hormone (TH) homeostasis (TH levels and transport). which are mechanisms of action related to neurobehavioral effects (spontaneous activity, habituation and learning ability). There also similarities in agonistic interactions with the hepatic nuclear receptors PXR and CAR. Several effects on developmental (reproductive) processes have also been observed, but results were more dispersed and insufficient to compare both groups of compounds. The available mechanistic information is sufficient to warrant a dose addition model for NDL-PCBs and PBDEs, including their hydroxylated metabolites.Although many of the observed effects are similar from a qualitative point of view for both groups, congener or tissue specific differences have also been found. As this is a source of uncertainty in the combined hazard and risk assessment of these compounds, molecular entities involved in the observed mechanisms and adverse outcomes associated with these compounds need to be identified. The systematical generation of (quantitative) structure-activity information for NDL-PCBs and PBDEs on these targets (including potential non-additive effects) will allow a more realistic risk estimation associated with combined exposure to both groups of compounds during early life. Additional validation studies are needed to quantify these uncertainties for risk assessment of NDL-PCBs and PBDEs.

Amperometric Microsensors Monitoring Glutamate-Evoked In Situ Responses of Nitric Oxide and Carbon Monoxide from Live Human Neuroblastoma Cells

In the brain, nitric oxide (NO) and carbon monoxide (CO) are important signaling gases which have multifaceted roles, such as neurotransmitters, neuromodulators, and vasodilators. Even though it is difficult to measure NO and CO in a living system due to their high diffusibility and extremely low release levels, electrochemical sensors are promising tools to measure in vivo and in vitro NO and CO gases. In this paper, using amperometric dual and septuple NO/CO microsensors, real-time NO and CO changes evoked by glutamate were monitored simultaneously for human neuroblastoma (SH-SY5Y) cells. In cultures, the cells were differentiated and matured into functional neurons by retinoic acid and brain-derived neurotrophic factor. When glutamate was administrated to the cells, both NO and CO increases and subsequent decreases returning to the basal levels were observed with a dual NO/CO microsensor. In order to facilitate sensor’s measurement, a flower-type septuple NO/CO microsensor was newly developed and confirmed in terms of the sensitivity and selectivity. The septuple microsensor was employed for the measurements of NO and CO changes as a function of distances from the position of glutamate injection. Our sensor measurements revealed that only functionally differentiated cells responded to glutamate and released NO and CO.

Potential role of organochlorine pesticides in the pathogenesis of neurodevelopmental, neurodegenerative, and neurobehavioral disorders: A review

Organochlorine pesticides (OCPs) are persistent and bioaccumulative environmental contaminants with potential neurotoxic effects. The growing body of evidence has demonstrated that prenatal exposure to organochlorines (OCs) is associated with impairment of neuropsychological development. The hypothesis is consistent with recent studies emphasizing the correlation of environmental as well as genetic factors to the pathophysiology of neurodevelopmental and neurobehavioral defects. It has been suggested that maternal exposure to OCPs results in impaired motor and cognitive development in newborns and infants. Moreover, in utero exposure to these compounds contributes to the etiology of autism. Although impaired neurodevelopment occurs through prenatal exposure to OCs, breastfeeding causes postnatal toxicity in the infants. Parkinson's disease (PD) is another neurological disorder, which has been associated with exposure to OCs, leading to α-synuclein accumulation and depletion of dopaminergic neurons. The study aimed to review the potential association between pre- and post-natal exposure to OCs and impaired neurodevelopmental processes during pregnancy and neuropsychological diseases such as PD, behavioral alterations, seizures and autism.

Lactational exposure to low levels of the six indicator non-dioxin-like polychlorinated biphenyls induces DNA damage and repression of neuronal activity, in juvenile male mice

Previously, we evaluated the effects of lactational exposure to a representative mixture of the six indicator non-dioxin-like polychlorinated biphenyls (∑6 NDL-PCBs) at low levels on the neurobiological changes and developmental/behavioral performances in mice. In this study, we analyzed the global gene expression profile in cerebellar neurons isolated from male mice presenting the most significant induction of anxiety-like behavior in our previous study (10 ng/kg ∑6 NDL-PCBs). Our results revealed changes in the expression of 16658 genes in the neurons of the exposed mice. Among these, 693 upregulated [fold change (FC)>2; p<0.05] and 665 downregulated (FC<2; p<0.05) genes were statistically linked to gene ontology terms (GO). Overexpressed genes belonged to GO terms involved with the cell cycle, DNA replication, cell cycle checkpoint, response to DNA damage stimulus, regulation of RNA biosynthetic processes, and microtubule cytoskeleton organization. Downregulated genes belonged to terms involved with the transmission of nerve impulses, projection neurons, synapse hands, cell junctions, and regulation of RNA biosynthetic processes. Using qPCR, we quantified gene expression related to DNA damage and validated the transcriptomic study, as a significant overexpression of Atm-Atr Bard1, Brca2, Fancd2, Figf, Mycn, p53 and Rad51 was observed between groups (p<0.001). Finally, using immunoblots we determined the expression level of six selected proteins. We found that changes in the protein expression of Atm Brca1, p53, Kcnma1, Npy4r and Scn1a was significant between exposed and control groups (p<0.05), indicating that the expression pattern of these proteins agreed with the expression pattern of their genes by qPCR, further validating our transcriptomic findings. In conclusion, our study showed that early life exposure of male mice to a low level of ∑6 NDL-PCBs induced p53-dependent responses to cellular stress and a decrease in the expression of proteins involved in the generation, conduction, and transmission of electrical signals in neurons.

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.

Applicability of the TCDD-TEQ approach to predict sublethal embryotoxicity in Fundulus heteroclitus

The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalent quantity (TCDD-TEQ) approach was used successfully to predict lethal embryotoxicity in salmonids, but its applicability to sublethal effects of mixtures of organohalogenated compounds in other fish species is poorly known. The sublethal toxicity of two dioxin-like compounds (DLCs), 3,3',4,4'-tetrachlorobiphenyl (PCB77) and 2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-PnCDF), two non-dioxin-like (NDL) polychlorinated biphenyls (PCBs), 2,2',5,5'-tetrachlorobiphenyl (PCB52) and 2,3,3',4',6-pentachlorobiphenyl (PCB110), and of Aroclor 1254, a complex commercial mixture of PCBs, was assessed in Fundulus heteroclitus embryos exposed by intravitelline injection. At 16 days post-fertilization, the two DLCs and Aroclor 1254 altered prey capture ability in addition to inducing classical aryl hydrocarbon receptor-mediated responses: ethoxyresorufin-O-deethylase (EROD) induction, craniofacial deformities and reduction in body length. None of these responses was induced by the two NDL PCBs, at doses up to 5400 ng g(-1)wet weight. Dose-response curves for prey capture ability for the 2 DLCs tested were not parallel to that of TCDD, violating a fundamental assumption for relative potency (ReP) estimation. Dose-response curves for EROD induction were parallel for 2,3,4,7,8-PnCDF and TCDD, but the ReP of 2,3,4,7,8-PnCDF for F. heteroclitus was 5-fold higher than the World Health Organization (WHO) fish toxic equivalent factor (TEF) based on embryolethality in salmonids. The chemically derived TCDD-TEQs of Aroclor 1254, calculated using 3,3',4,4',5-pentachlorobiphenyl (PCB126) concentrations and it ReP for F. heteroclitus, overestimated its potency to induce EROD activity possibly due to antagonistic interactions among PCBs. This study highlights the limitations of using TEFs based on salmonid toxicity data alone for risk assessment to other fish species. There is a need to assess the variability of RePs of DLCs in different species for a variety of endpoints and to better understand interactions between DLCs and other toxic chemicals.

The presence of polychlorinated biphenyls in yellow pigment products in China with emphasis on 3,3'-dichlorobiphenyl (PCB 11)

A non-Aroclor PCB congener, 3,3'-dichlorobiphenyl (PCB 11) has recently attracted wide concerns because of its environmental ubiquity and specific sources potentially associated with yellow pigment production. In order to investigate PCB 11 and other PCBs in the yellow pigment products, 24 yellow pigment samples were collected from three different manufacturing plants in China. ∑20PCBs and PCB 11 were in the range of 50.7-9.19×10(5) ng g(-1) and 41.7-9.18×10(5) ng g(-1), respectively, which was much higher than those reported in previous study. The corresponding TEQ values ranged between 0.16 and 4.21×10(3) ng WHO2005-TEQ kg(-1). The contribution of PCB 11 to ∑20PCBs reached up to 85.5% (median value) followed by PCB 28, PCB 77, and PCB 52 with contributions of 10.5%, 6.70%, and 5.40%, respectively. Significant differences were observed for PCB 11 concentrations among the different types of yellow pigment from the same plant and among the same sample types from different plants. The PCB 11 concentrations in diarylide yellow pigments produced from 3,3'-dichlorbenzidine were the highest in all the samples. It demonstrates that yellow pigment is a significant source not only for the widespread pollution of PCB 11 but also for other PCBs, especially for the lower chlorinated congeners.

Influence of prenatal exposure to environmental pollutants on human cord blood levels of glutamate

Some chemicals released into the environment, including mercury and some organochlorine compounds (OCs), are suspected to have a key role on subclinical brain dysfunction in childhood. Alteration of the glutamatergic system may be one mechanistic pathway. We aimed to determine whether mercury and seven OCs, including PCBs 138, 153, and 180, DDT and DDE, hexachlorobenzene (HCB), and beta-hexachlorocyclohexane (β-HCH) influence the cord levels of two excitatory amino acids, glutamate and aspartate. Second, we evaluated if this association was mediated by glutamate uptake measured in human placental membranes. The study sample included 40 newborns from a Spanish cohort selected according to cord mercury levels. We determined the content of both amino acids in cord blood samples by means of HPLC and assessed their associations with the contaminants using linear regression analyses, and the effect of the contaminants on glutamate uptake by means of [(3)H]-aspartate binding in human placenta samples. PCB138, β-HCH, and the sum of the three PCBs and seven OCs showed a significant negative association with glutamate levels (decrease of 51, 24, 56 and 54%, respectively, in glutamate levels for each 10-fold increase in the contaminant concentration). Mercury did not show a significant correlation neither with glutamate nor aspartate levels in cord blood, however a compensatory effect between T-Hg and both PCB138, and 4,4'-DDE was observed. The organo-metallic derivative methylmercury completely inhibited glutamate uptake in placenta while PCB138 and β-HCH partially inhibited it (IC50 values: 4.9±0.8 μM, 14.2±1.2 nM and 6.9±2.9 nM, respectively). We conclude that some environmental toxicants may alter the glutamate content in the umbilical cord blood, which might underlie alterations in human development.

Prenatal exposure to organochlorine compounds and neuropsychological development up to two years of life

Polychlorinated biphenyls (PCB), hexachlorobenzene (HCB), and dichlorodiphenyl dichloroethylene (pp'DDE) are persistent, bioaccumulative, and toxic environmental pollutants with potential neurotoxic effects. Despite a growing body of studies investigating the health effects associated with these compounds, their specific effects on early neuropsychological development remain unclear. We investigated such neuropsychological effects in a population-based birth cohort based in three regions in Spain (Sabadell, Gipuzkoa, and Valencia) derived from the INMA [Environment and Childhood] Project. The main analyses in this report were based on 1391 mother-child pairs with complete information on maternal levels of organochlorine compounds and child neuropsychological assessment (Bayley Scales of Infant Development) at age 14 months. We found that prenatal PCB exposure, particularly to congeners 138 and 153, resulted in impairment of psychomotor development (coefficient=-1.24, 95% confidence interval=-2.41, -0.07), but found no evidence for effects on cognitive development. Prenatal exposure to pp'DDE or HCB was not associated with early neuropsychological development. The negative effects of exposure to PCBs on early psychomotor development suggest that the potential neurotoxic effects of these compounds may be evident even at low doses.

Insight into the neuroproteomics effects of the food-contaminant non-dioxin like polychlorinated biphenyls

Recent studies showed that food-contaminant non-dioxin-like polychlorinated biphenyls (NDL-PCBs) congeners (PCB52, PCB138, PCB180) have neurotoxic potential, but the cellular and molecular mechanisms underlying neuronal damage are not entirely known. The aim of this study was to assess whether in-vitro exposure to NDL-PCBs may alter the proteome profile of primary cerebellar neurons in order to expand our knowledge on NDL-PCBs neurotoxicity. Comparison of proteome from unexposed and exposed rat cerebellar neurons was performed using state-of-the-art label-free semi-quantitative mass-spectrometry method. We observed significant changes in the abundance of several proteins, that fall into two main classes: (i) novel targets for both PCB138 and 180, mediating the dysregulation of CREB pathways and ubiquitin-proteasome system; (ii) different congeners-specific targets (alpha-actinin-1 for PCB138; microtubule-associated-protein-2 for PCB180) that might lead to similar deleterious consequences on neurons cytoskeleton organization. Interference of the PCB congeners with synaptic formation was supported by the increased expression of pre- and post-synaptic proteins quantified by western blot and immunocytochemistry. Expression alteration of synaptic markers was confirmed in the cerebellum of rats developmentally exposed to these congeners, suggesting an adaptive response to neurodevelopmental toxicity on brain structures. As such, our work is expected to lead to new insights into the mechanisms of NDL-PCBs neurotoxicity.

Postnatal exposure to PCB 153 and PCB 180, but not to PCB 52, produces changes in activity level and stimulus control in outbred male Wistar Kyoto rats

Background

Polychlorinated biphenyls (PCBs) are a class of organic compounds that bioaccumulate due to their chemical stability and lipophilic properties. Humans are prenatally exposed via trans-placental transfer, through breast milk as infants, and through fish, seafood and fatty foods as adolescents and adults. Exposure has several reported effects ranging from developmental abnormalities to cognitive and motor deficiencies. In the present study, three experimental groups of rats were orally exposed to PCBs typically found in human breast milk and then behaviorally tested for changes in measures of stimulus control (percentage lever-presses on the reinforcer-producing lever), activity level (responses with IRTs > 0.67 s), and responses with short IRTs (< 0.67 s).

Methods

Male offspring from Wistar Kyoto (WKY/NTac) dams purchased pregnant from Taconic Farms (Germantown, NY) were orally given PCB at around postnatal day 8, 14, and 20 at a dose of 10 mg/kg body weight at each exposure. Three experimental groups were exposed either to PCB 52, PCB 153, or PCB 180. A fourth group fed corn oil only served as controls. From postnatal day 25, for 33 days, the animals were tested for behavioral changes using an operant procedure.

Results

PCB exposure did not produce behavioral changes during training when responding was frequently reinforced using a variable interval 3 s schedule. When correct responses were reinforced on a variable interval 180 s schedule, animals exposed to PCB 153 or PCB 180 were less active than controls and animals exposed to PCB 52. Stimulus control was better in animals exposed to PCB 180 than in controls and in the PCB 52 group. Also, the PCB 153 and PCB 180 groups had fewer responses with short IRTs than the PCB 52 group. No effects of exposure to PCB 52 were found when compared to controls.

Conclusions

Exposure to PCBs 153 and 180 produced hypoactivity that continued at least five weeks after the last exposure. No effects of exposure to PCB 52 were observed.

Nitric oxide signaling as a common target of organohalogens and other neuroendocrine disruptors

Organohalogen compounds such as polychlorinated biphenyls (PCB) and polybrominated diphenyl ethers (PBDE) are global environmental pollutants and highly persistent, bioaccumulative chemicals that produce adverse effects in humans and wildlife. Because of the widespread use of these organohalogens in household items and consumer products, indoor contamination is 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. Toxicological studies on organohalogen pollutants primarily focused on sex steroid and thyroid hormone actions, and findings have largely shaped the way one envisions their disruptive effects occurring. Organohalogens exert additional effects on other systems including other complex endocrine systems that may be disregulated at various levels of organization. Over the last 20 years evidence has mounted in favor of a critical role of nitric oxide (NO) in numerous functions ranging from neuroendocrine functions to learning and memory. With its participation in multiple systems and action at several levels of integration, NO signaling has a pervasive influence on nervous and endocrine functions. Like blockers of NO synthesis, PCBs and PBDEs produce multifaceted effects on physiological systems. Based on this unique set of converging information it is proposed that organohalogen actions occur, in part, by hijacking processes associated with this ubiquitous bioactive molecule. The current review examines the emerging evidence for NO involvement in selected organohalogen actions and includes recent progress from our laboratory that adds to our current understanding of the actions of organohalogens within hypothalamic neuroendocrine circuits. The thyroid, vasopressin, and reproductive systems as well as processes associated with long-term potentiation were selected as sample targets of organohalogens that rely on regulation by NO. Information is provided about other toxicants with demonstrated interference of NO signaling. Our focus on the convergence between NO system and organohalogen toxicity offers a novel approach to understanding endocrine and neuroendocrine disruption that is particularly problematic for developing organisms. This new working model is proposed as a way to encourage future study in elucidating common mechanisms of action that are selected with a better operational understanding of the systems affected.