The environmental pollutant BDE-209 regulates NO/cGMP signaling through activation of NMDA receptors in neurons

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

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

Toxic Effects and Mechanisms of Polybrominated Diphenyl Ethers

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

Evaluation of BDE-47-induced neurodevelopmental toxicity in zebrafish embryos

There are growing concerns about the neurodevelopmental toxicity of polybrominated diphenyl ethers (PBDEs), but the toxicological phenotypes and mechanisms are not well elucidated. Here, zebrafish (Danio rerio) were exposed to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from 4 to 72 h post-fertilization (hpf). The results showed that BDE-47 stimulated the production of dopamine and 5-hydroxytryptamine, but inhibited expression of Nestin, GFAP, Gap43, and PSD95 in 24 hpf embryos. Importantly, we unraveled the inhibitory effects of BDE-47 on neural crest-derived melanocyte differentiation and melanin syntheses process, evidenced by disrupted expression of wnt1, wnt3, sox10, mitfa, tyrp1a, tyrp1b, tryp2, and oca2 gene in 72 hpf embryos and decreased tyrosinase activities in embryos at 48 and 72 hpf. The transcriptional activities of myosin VAa, kif5ba, rab27a, mlpha, and cdc42 genes, which are associated with intracellular transport process, were also disturbed during zebrafish development. Ultimately, these alterations led to fast spontaneous movement and melanin accumulation deficit in zebrafish embryos upon BDE-47 exposure. Our results provide an important extension for understanding the neurodevelopmental effects of PBDEs and facilitate the comprehensive evaluation of neurotoxicity in embryos.

Differential binding of CREB and REST/NRSF to NMDAR1 promoter is associated with the sex-selective cognitive deficit following postnatal PBDE-209 exposure in mice

Neonatal exposure to decabromodiphenyl ether (PBDE-209), a widely used flame retardant, affects cognitive performances in the later stage of life in a sex-dependent manner. PBDE-209 interferes with glutamatergic signaling and N-methyl-D-aspartate receptor (NMDAR) subunits with unresolved regulatory mechanisms. This study exposed male and female mice pups through postnatal day (PND) 3-10 to PBDE-209 (oral dose: 0, 6, or 20 mg/kg body weight). The frontal cortex and hippocampus, collected from neonate (PND 11) and young (PND 60) mice, were analyzed for cAMP response element-binding protein (CREB) and RE1-silencing transcription factor/ Neuron-restrictive silencer factor (REST/NRSF) binding to NMDAR1 promoter and expression of NMDAR1 gene by electrophoretic mobility shift assay and semi-quantitative RT-PCR respectively. Behavioral changes were assessed using spontaneous alternation behavior and novel object recognition tests in young mice. In neonates, the binding of CREB was increased, while REST/NRSF was decreased significantly to their cognate NMDAR1 promoter sequences at the high dose of PBDE-209 in both the sexes. This reciprocal pattern of CREB and REST/NRSF interactions correlates with the up-regulation of NMDAR1 expression. Young males followed a similar pattern of CREB and REST/NRSF binding and NMDAR1 expression as in neonates. Surprisingly, young females did not show any alteration when compared to age-matched controls. Also, we found that only young males showed working and recognition memory deficits. These results indicate that early exposure to PBDE-209 interferes with CREB- and REST/NRSF-dependent regulation of the NMDAR1 gene in an acute setting. However, long-term effects persist only in young males that could be associated with cognitive impairment.

Melatonin alleviates BDE-209-induced cognitive impairment and hippocampal neuroinflammation by modulating microglia polarization via SIRT1-mediated HMGB1/TLR4/NF-κB pathway

Polybrominated diphenyl ethers (PBDEs) are persistent environmental contaminants with developmental neurotoxicity, the mechanism of which remains obscure. The present study aimed to evaluate cognitive deficits and microglia-originated neuroinflammation in the hippocampus of offspring rats exposed to BDE-209 (30 and 100 mg/kg) during perinatal period. Compared to the control, BDE-209-treated rats showed significant longer escape latency and less platform crossings in tests of Morris water maze. Besides obvious hippocampal neuron damage, increased microglial activation and pro-inflammatory markers (CD86, TNFα, and IL-1β), meanwhile, decreased anti-inflammatory molecules (CD206, IL-10, and Arg1) were induced by BDE-209. Furthermore, we investigated the neuroprotection of melatonin against BDE-209 and whether through sirtuin 1 (SIRT1). Consistent with restored SIRT1 activity, enhanced deacetylation of HMGB1 and inhibited cytoplasmic translocation of HMGB1, reduced expression of proteins involved in TLR4-NF-κB pathway and nuclear transfer of phosphorylated-NF-κB p65, and ultimately suppressed microglial activation and improved spatial memory were observed in 10 mg/kg melatonin-pretreated rats, compared with BDE-209-exposed alone. These results demonstrated that melatonin ameliorated BDE-209-caused cognitive impairment partially through shifting microglia polarization towards anti-inflammatory phenotype in a SIRT1-dependent manner, suggesting a potential mechanism for prevention.

A preliminary study on the mechanism of the neurosteroid-mediated ionotropic receptor dysfunction in neurodevelopmental toxicity induced by decabromodiphenyl ether

The mechanism of neurodevelopmental toxicity of decabromodiphenyl ether (BDE209) remains unclear. Recent evidence suggests that neurosteroids disorders play a vital role in BDE209 induced-neurodevelopmental toxicity. To explore the mechanism of it, pregnant ICR mice were orally gavaged with 0, 225, and 900 mg kg^-1 BDE209 for about 42 days. Spatial learning and memory abilities of offspring were tested on postnatal day (PND) 21. Offspring were euthanized at PND26, the neuronal structure, neurosteroids level, and related proteins including neurosteroids synthase, ionotropic receptors and cAMP-response element binding protein (CREB) pathway were evaluated, as well as Ca²⁺ concentration and the mitochondrial membrane potential (Mmp). Our results showed that BDE209 impaired learning and memory abilities and disrupted neuronal structure. Meanwhile, BDE209 decreased the pregnenolone (PREG), dehydroepiandrosterone (DHEA), progesterone (PROG) and allopregnanolone (ALLO) levels in the serum and brain, as well as the mRNA and protein levels of cholesterol-side-chain cleavage enzyme (P450scc), steroid 17α-hy-droxylase (P450C17), 3β-hydroxysteroid dehydrogenase (3β-HSD) and steroid 5α-reductase of type I (5α-R) in the hippocampi. Also, BDE209 suppressed mRNA and protein levels of NR1, NR2A and NR2B subunits of the N-methyl-D-aspartic acid receptor (NMDAR) and α1 subunit of the Gamma-amino butyric acid A receptor (GABAAR), but increased the levels of β2 and γ2 subunits of the GABAAR in the hippocampi. Moreover, BDE209 increased the Ca²⁺ concentration and phosphorylation extracellular regulated protein kinases (P-ERK) 1/2 level, but decreased the P-CREB and Mmp level in the hippocampi. These results indicate that BDE209 exposure during pregnancy and lactation is possible to affect learning and memory formation of offspring by the neurosteroid-mediated ionotropic receptors dysfunction.

Effects of Decabrominated Diphenyl Ether Exposure on Growth, Meat Characteristics and Blood Profiles in Broilers

Decabrominated diphenyl ether (BDE-209) is widely used as a flame retardant and is detected at high levels in the environment. Its toxicities have been reported and have attracted attention. In the present study, broilers were used to determine the response in growth performance, carcass traits, meat quality, blood profiles and antioxidant system to BDE-209 exposure at doses of 0, 0.02, 0.4 and 4 mg/kg. The results showed that BDE-209 exposure at levels of 0.02 or 0.4 mg/kg increased feed intake and decreased feed efficiency. BDE-209 altered the blood profiles, such as reducing the numbers of white blood cells, lymphocytes and neutrophilic granulocytes. As compared with the control, BDE-209 exposure significantly increased abdominal fat percentages of broilers at 64.9-159.5% and adversely affected the selected biochemical indicators, including alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine (CRE), which indicated its toxicity to liver and kidney functions. Moreover, BDE-209 exposure significantly increased plasma malondialdehyde (MDA) concentrations and decreased the activities of glutathione peroxidase (GSH-px) and superoxide dismutase (SOD), which implied aggravating oxidant stress and decline of antioxidant capacity in broilers. In conclusion, our data demonstrated that the environmental pollutant BDE-209 adversely influenced growth performance, increased the deposition of abdominal fat, impaired antioxidant capacity and the immune system and had potential toxicity to the liver and kidney of broilers.

Organophosphorus flame retardant (tricresyl phosphate) trigger apoptosis in HepG2 cells: Transcriptomic evidence on activation of human cancer pathways

Tricresyl phosphate (TCP) is one of the organophosphorus flame retardants (OPFRs) used as plasticizer in consumer products and mixed as a lubricant in commercial jet engine oil, reportedly induce neurotoxicity and aerodynamic syndrome. No studies have been attempted so far on TCP to induce hepatotoxicity in human cells. This study for the first time confirms the hepatotoxic potential and activation of cancer pathways in TCP treated human hepatocellular cells (HepG2). MTT and NRU data showed 39.3% and 49.85% decline in HepG2 survival when exposed to the highest concentration of TCP (400 μM) for 3 days. Comet assay showed 27.1-fold greater DNA damage in cells treated with TCP (400 μM). Flow cytometric analysis revealed an upsurge in the intracellular reactive oxygen species (ROS) and nitric oxide (NO) production in cells, affirming oxidative stress. TCP (400 μM) exposure resulted in 27% reduction in Rh123 fluorescence, indicating dysfunction of mitochondrial membrane potential (ΔΨm). Cell cycle analysis exhibited 62.53% cells in the subG1 apoptotic phase after TCP (400 μM) treatment, also a massive increase in Ca²⁺ influx validate the on-set of apoptosis in cells. Immunofluorescence of TCP exposed cells showed activation of p53, caspase3, caspase9 reaffirming the involvement of mitochondrial-dependent intrinsic apoptotic signaling. qPCR array of 84 genes unravel the transcriptomic alterations in HepG2 cells after TCP treatment. mRNA transcripts of ATP5A1, GADD45A, IGFBP5, SOD1, STMN1 genes were prominently upregulated providing candid evidence on TCP mediated activation of human cancer pathways to orchestrate the apoptotic death of HepG2 cells, specifying hepatotoxic potential of TCP.

An increase of estrogen receptor α protein level regulates BDE-209-mediated blood-testis barrier disruption during spermatogenesis in F1 mice

Deca-bromodiphenyl ether (BDE-209) regulates various aspects of spermatogenesis and male fertility through its effect on estrogen receptor α (ERα), but the underlying mechanism remains unclear. Because molecular mechanisms such as remodeling of the blood-testis barrier (BTB) play crucial roles in spermatogenesis, we investigated the disruptive effects of ERα agonists on the BTB in spermatogenesis. In this study, 0, 300, and 500 mg/kg/day of BDE-209 were administered to pregnant adult mice by oral gavage from gestation day 7 to postnatal day 21. SerW3 cells were treated with methylpiperidino pyrazole (MPP) for 30 min before being treated with 50 μg/mL of BDE-209. BDE-209 increases ERα in time- and dose-dependent manners and decreases formin 1 and BTB-associated protein in F1 male mice. Furthermore, BDE-209 impairs the structure and function of the BTB. Activation of ERα signaling could disrupt the BTB, leading to spermatogenesis dysfunction. The results identified the role of ERα in BTB disruption during spermatogenesis and suggested that BTB disruption occurs because of exposure to BDE-209, which could potentially affect spermatogenesis. In conclusion, Sertoli cells seem to be the primary target of BDE-209 in the perinatal period, and this period constitutes a critical window of susceptibility to BDE-209. Also, the SerW3 cell model may not be a particularly useful cell model for studying the function of the cytoskeleton.