The widely utilized brominated flame retardant tetrabromobisphenol A (TBBPA) is a potent inhibitor of the SERCA Ca2+ pump

Cytotoxicity by endocrine disruptors through effects on ER Ca2+ transporters, aberrations in Ca2+ signalling pathways and ER stress

Concerns regarding man-made organic chemicals pervading our ecosystem and having adverse and detrimental effects upon organisms, including man, have now been studied for several decades. Since the 1970s, some environmental pollutants were identified as having endocrine disrupting affects. These endocrine disrupting chemicals (EDC) were initially shown to have estrogenic or anti-estrogenic properties and some were also shown to bind to a variety of hormone receptors. However, since the 1990s it has also been identified that many of these EDC additionally, have the ability of causing abnormal alterations in Ca2+ signalling pathways (also commonly involved in hormone signalling), leading to exaggerated elevations in cytosolic [Ca2+] levels, that is known to cause activation of a number of cell death pathways. The major emphasis of this review is to present a personal perspective of the evidence for some types of EDC, specifically alkylphenols and brominated flame retardants (BFRs), causing direct effects on Ca2+ transporters (mainly the SERCA Ca2+ ATPases), culminating in acute cytotoxicity and cell death. Evidence is also presented to indicate that this Ca2+ATPase inhibition, which leads to abnormally elevated cytosolic [Ca2+], as well as a decreased luminal ER [Ca2+], which triggers the ER stress response, are both involved in acute cytotoxicity.

Cellular and physiological mechanisms of halogenated and organophosphorus flame retardant toxicity

Flame retardants (FRs) are chemical substances used to inhibit the spread of fire in numerous industrial applications, and their abundance in modern manufactured products in the indoor and outdoor environment leads to extensive direct and food chain exposure of humans. Although once considered relatively non-toxic, FRs are demonstrated by recent literature to have disruptive effects on many biological processes, including signaling pathways, genome stability, reproduction, and immune system function. This review provides a summary of research investigating the impact of major groups of FRs, including halogenated and organophosphorus FRs, on animals and humans in vitro and/or in vivo. We put in focus those studies that explained or referenced the modes of FR action at the level of cells, tissues and organs. Since FRs are highly hydrophobic chemicals, their biophysical and biochemical modes of action usually involve lipophilic interactions, e.g. with biological membranes or elements of signaling pathways. We present selected toxicological information about these molecular actions to show how they can lead to damaging membrane integrity, damaging DNA and compromising its repair, changing gene expression, and cell cycle as well as accelerating cell death. Moreover, we indicate how this translates to deleterious bioactivity of FRs at the physiological level, with disruption of hormonal action, dysregulation of metabolism, adverse effects on male and female reproduction as well as alteration of normal pattern of immunity. Concentrating on these subjects, we make clear both the advances in knowledge in recent years and the remaining gaps in our understanding, especially at the mechanistic level.

Tetrabromobisphenol A and hexabromocyclododecane, brominated flame retardants, trigger endoplasmic reticulum stress and activate necroptosis signaling in PC12 cells

Tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) are brominated flame retardants commonly used in a variety of industrial and consumer products. In this study, we performed RNA sequencing analysis of PC12 cells to clarify the mechanisms by which TBBPA and HBCD induce neurotoxicity. Differential expression analysis demonstrated that 636 and 271 genes were differentially expressed after TBBPA and HBCD treatment, respectively. Gene Ontology (GO) enrichment analysis revealed that genes annotated with the GO term "endoplasmic reticulum unfolded protein response" were upregulated in both TBBPA- and HBCD-treated groups. Furthermore, protein expression of endoplasmic reticulum stress markers, such as HSPA5 and DDIT3, as well as cleaved caspase-3, an apoptosis marker, were induced by TBBPA and HBCD. We also found that the cytotoxicity induced by TBBPA and HBCD was blocked by necrostatin-1, a necroptosis inhibitor, indicating the contribution of necroptosis. Our findings provide new insight into the mechanisms of toxicity induced by these chemicals.

The potential mechanisms of TBBPA bis(2-hydroxyethyl) ether induced developmental neurotoxicity in juvenile zebrafish (Danio rerio)

TBBPA bis(2-hydroxyethyl) ether (TBBPA-DHEE), one of the main derivatives of TBBPA, has been widely detected in environmental samples and been discovered to be potential neurotoxic. In this study, the juvenile zebrafish were selected as the research subject to explore the neurotoxicity and its mechanism of low-dose TBBPA-DHEE exposure, and to reveal the neurotoxicity susceptibility in different sexes. Behavioral studies revealed that TBBPA-DHEE could significantly reduce the swimming velocity, maximum acceleration and cumulative duration of high-speed mobility, significantly increasing the cumulative duration of low-speed mobility and average social distance. It significantly reduced the contents of ATP, glutamate and Ca²⁺ in the whole brain. The histopathological study demonstrated that TBBPA-DHEE could cause brain tissue damage in female and male juvenile zebrafish. The comprehensive data analysis indicated that female zebrafish were more susceptible to TBBPA-DHEE exposure than male zebrafish. Transcriptomic analysis showed that TBBPA-DHEE could significantly affect the expressions of behavioral and development-related genes. Furthermore, female and male juvenile zebrafish have different molecular mechanisms of neurotoxicity. For female juvenile zebrafish, the potential mechanism of neurotoxicity could be that it interfered with the feedback regulation of nerves by affecting the related genes expressions in the signaling pathways such as Ca²⁺ signaling, Wnt signaling and synapses. For male juvenile zebrafish, the potential mechanism of neurotoxicity may be through affecting the expression of related genes in hormones and neuro-related genes. This research could reveal the potential neurotoxicity of TBBPA-DHEE to aquatic organisms, which will be helpful to reveal the health effects of the emerging environmental pollutants.

Rapid debromination of tetrabromobisphenol A by Cu/Fe bimetallic nanoparticles in water, its mechanisms, and genotoxicity after treatments

Tetrabromobisphenol A (TBBPA), a widely used brominated flame retardants, has been detected in various environmental matrices and is known to cause various adverse effects on human bodies. This study examined the feasibility and effectiveness of remediating TBBPA using Cu/Fe bimetallic nanoparticles (Cu/Fe BNPs) at various environmental and operational conditions. In general, TBBPA removal rate and debromination efficiency increased with higher Cu doping, higher Cu/Fe BNPs loading, higher temperature, and lower pH. At optimal conditions, TBBPA was completed removed at a rate constant > 0.2 min^-1 where over 90% TBBPA was transformed to BPA within 30 min. The activation energy was found to be 35.6 kJ/mol, indicating that TBBPA was predominantly removed via surface-controlled reactions. Under pH 3-7 and ≥ 25 °C, debromination was the dominant removal mechanism compared to adsorption. The complete debromination pathway and the time-evolution of intermediates byproducts at different pHs were also presented. Cu/Fe BNPs can be reused for more than 6 times with performance constancy. Genotoxic tests showed that the treated solution did not find a significant hazardous potential. The byproducts can be further degraded by additional H₂O₂ through Fenton reaction. These results demonstrated the efficacy of Cu/Fe BNPs for treating TBBPA and its potential for degrading other halogenated organic compounds.

Occurrence of chemical pollutants in major e-waste sites in West Africa and usefulness of cytotoxicity and induction of ethoxyresorufin-O-deethylase (EROD) in determining the effects of some detected brominated flame retardants and e-waste soil-derived extracts

We investigated the occurrence of chemical pollutants in major e-waste sites in West Africa and usefulness of cytotoxicity and induction of ethoxyresorufin-O-deethylase (EROD) in determining the effects of some detected brominated flame retardants (BFRs) and e-waste soil-derived extracts. Analysis of the e-waste site samples using AAS and GC-MS techniques revealed the presence of a range of toxic metals as well as persistent and toxic organic pollutants, respectively, in the vicinity of the e-waste sites. As expected, the occurrence (%) of all the detected chemical pollutants in experimental soils significantly (P < 0.05) differs from occurrence (%) in control soil. The calculated LC₅₀ values on RBL-2H3 cells of the detected tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) were 3.75 μM and 4.2 μM, respectively. Tribromophenol (TBP), dibromobiphenyl (DBB), and decabromodiphenyl ether (DBDE) were remarkably less toxic on RBL-2H3 cells compared with TBBPA and HBCD as they did not reduce RBL-2H3 cell viability below 50% in the tested concentration range (0-20 μM). The study revealed that TBBPA and HBCD could induce significant RBL-2H3 cell death through caspase-dependent apoptosis. The study further shows that the cytotoxicity of some of these BFRs could increase synergistically when in mixtures and potentially activate inflammation through the stimulation of mast cell degranulation. The e-waste soil-derived extracts induced a concentration-dependent increase in EROD activity in the exposed RTG-W1 cells. Ultimately, nonpolar extracts had higher EROD-inducing potency compared with polar extracts and hence suggesting the presence in higher amounts of AhR agonists in nonpolar e-waste soil-derived extracts than polar extracts. Overall, there is urgent need for actions in order to improve the environmental quality of the e-waste sites.

Assessment of tetrabromobisphenol-A (TBBPA) content in plastic waste recovered from WEEE

Due to the variability of additives and polymer types used in electrical and electronic equipment (EEE), and in accordance with the European Directive 2012/19/EU, an implementation of sound management practices is necessary. This work focuses on assessing the content of tetrabromobisphenol-A (TBBPA) in acrylonitrile-butadiene-styrene (ABS), polypropylene (PP), polycarbonate (PC) and their polymer blends (i.e. PC/ABS). A total of 36 plastic housing samples originating from microwave ovens, electric irons, vacuum cleaners and DVD/CD players were subjected to microwave-assisted-extraction (MAE) and/or ultrasound-assisted-extraction (UAE). Maximum mean concentration values of TBBPA measured in DVD/CD players and vacuum cleaners ranged between 754-1146 μg/kg, and varied per polymer type, as follows: 510-2515 μg/kg in ABS and 55-3109 μg/kg in PP. The results indicated that MAE was more sufficient than UAE in the extraction of TBBPA from ABS. To optimize the UAE procedure, various solvents were tested. Higher amounts of TBBPA were obtained from ABS and PP using a binary mixture of a polar-non-polar solvent, isopropanol:n-hexane (1:1), whereas the sole use of isopropanol exhibited incomplete extraction.

Sarco/Endoplasmic Reticulum Calcium ATPase Inhibitors: Beyond Anticancer Perspective

The sarco/endoplasmic reticulum calcium ATPase (SERCA), which plays a key role in the maintenance of Ca²⁺ ion homeostasis, is an extensively studied enzyme, the inhibition of which has a considerable impact on cell life and death decision. To date, several SERCA inhibitors have been thoroughly studied and the most notable one, a derivative of the sesquiterpene lactone thapsigargin, is gradually approaching a clinical application. Meanwhile, new compounds with SERCA-inhibiting properties of natural, synthetic, or semisynthetic origin are being discovered and/or developed; some of these might also be suitable for the development of new drugs with improved performance. This review brings an up-to-date comprehensive overview of recently discovered compounds with the potential of SERCA inhibition, discusses their mechanism of action, and highlights their potential clinical applications, such as cancer treatment.

Structural Changes of Sarco/Endoplasmic Reticulum Ca2+-ATPase Induced by Rutin Arachidonate: A Molecular Dynamics Study

Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) maintains the level of calcium concentration in cells by pumping calcium ions from the cytoplasm to the lumen while undergoing substantial conformational changes, which can be stabilized or prevented by various compounds. Here we attempted to clarify the molecular mechanism of action of new inhibitor rutin arachidonate, one of the series of the acylated rutin derivatives. We performed molecular dynamics simulations of SERCA1a protein bound to rutin arachidonate positioned in a pure dipalmitoylphosphatidylcholine bilayer membrane. Our study predicted the molecular basis for the binding of rutin arachidonate towards SERCA1a in the vicinity of the binding site of calcium ions and near the location of the well-known inhibitor thapsigargin. The stable hydrogen bond between Glu771 and rutin arachidonate plays a key role in the binding. SERCA1a is kept in the E2 conformation preventing the formation of important salt bridges between the side chains of several residues, primarily Glu90 and Lys297. All in all, the structural changes induced by the binding of rutin arachidonate to SERCA1a may shift proton balance near the titrable residues Glu771 and Glu309 into neutral species, hence preventing the binding of calcium ions to the transmembrane binding sites and thus affecting calcium homeostasis. Our results could lead towards the design of new types of inhibitors, potential drug candidates for cancer treatment, which could be anchored to the transmembrane region of SERCA1a by a lipophilic fatty acid group.

Tetrabromobisphenol A-induced depolarization of rat cerebellar granule cells: ex vivo and in vitro studies

The brominated flame retardant tetrabromobisphenol A (TBBPA) is toxic to cultured brain neurons, and glutamate receptors partially mediate this effect; consequently, the depolarizing effect of TBBPA on neurons is to be expected, but it is yet to be actually demonstrated. The aim of this study was to detect TBBPA-evoked depolarization and identify the underlying mechanisms. The plasma membrane potential of rat cerebellar granule cells (CGC) in cerebellar slices or in primary cultures was measured using whole-cell current clamp recordings, or the fluorescent probe oxonol VI, respectively. The contribution of NMDA and AMPA receptors, voltage-gated sodium channels and intracellular calcium mobilization was tested using their selective antagonists or inhibitors. Direct interactions of TBBPA with NMDARs were tested by measuring the specific binding of radiolabeled NMDAR ligands to isolated rat cortical membrane fraction. TBBPA (25 μM) strongly depolarized CGC in cerebellar slices, and at ≥ 7.5 μM concentration-dependently depolarized primary CGC cultures. Depolarization of the primary CGC by 25 μM TBBPA was partly reduced when MK-801 was applied alone or in combination with either TTX or CNQX, or where bastadin 12 was applied in combination with ryanodine, whereas depolarization was completely prevented when MK-801, CNQX and TTX where combined. TBBPA had no effect on the specific binding of NMDAR radio-ligands to isolated cortical membranes. These results demonstrate the depolarizing effect of TBBPA on CGC, which is mainly mediated by ionotropic glutamate receptors, while voltage-gated sodium channels are also involved. We found no evidence for the direct activation of NMDARs by TBBPA.

Preparation of novel magnetic molecular imprinted polymers nanospheres via reversible addition - fragmentation chain transfer polymerization for selective and efficient determination of tetrabromobisphenol A

A well-defined molecularly imprinted polymer nanospheres with excellent specific recognition ability was prepared on Fe₃O₄ nanoparticles via the combination of click chemistry and surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization and using Tetrabromobisphenol A as template. Concretely, Fe₃O₄ nanoparticles were prepared by solvothermal method and then modified by 4-vinylbenylchloride through distillation-precipitation, which makes azide groups easily introduced on the surface of magnetic nanoparticles to form the relatively large amount of benzyl chloride groups. With high efficiency, alkyne terminated RAFT chain transfer agent were then immobilized onto the surface of Fe₃O₄ by means of click chemistry, which is Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The highly uniform imprinted thin film was finally fabricated on the surface of RAFT agent modified Fe₃O₄ nanoparticles. The binding results demonstrated that as-prepared imprinted beads exhibited remarkable molecular imprinting effects to the template molecule, fast rebinding kinetics and an excellent selectivity to compounds with similar configuration.

Altered expression of genes involved in programmed cell death in primary cultured rat cerebellar granule cells acutely challenged with tetrabromobisphenol A

In the present study, primary cultures of rat cerebellar granule cells (CGC) and the RT² Profiler PCR array were used to examine the effect of acutely applied brominated flame retardant tetrabromobisphenol A (TBBPA) on the expression of 84 genes related to the main modes of programmed cell death. CGC, at the 7th day of culture, were exposed to 10 or 25μM TBBPA for 30min. Then, 3, 6, and 24h later, the viability of the cells was examined by the staining with propidium iodide (PI) or using the calcein/ethidium homodimer (CA/ET) live/dead kit, and RNA was extracted for the evaluation of gene expression by RT-PCR. At 3, 6 and 24h after the treatment, the number of viable neurons decreased, according to the PI staining method, to 75%, 58% and 41%, respectively, and with the CA/ET method to 65%, 58% and 28%, respectively. In CGC analyzed 3h after the treatment with 25μM TBBPA or 6h after 10μM TBBPA, the only change in the gene expression was a reduction in the expression of Tnf, which is associated with autophagy and may activate some pro-apoptotic proteins. Six hours after 25μM TBBPA, only 2 genes were over-expressed, a pro-apoptotic Tnfrsf10b and Irgm, which is related to autophagy, and the genes that were suppressed included the anti-apoptotic gene Xiap, the necrosis-related Commd4, pro-apoptotic Abl1, 5 genes involved in autophagy (App, Atg3, Mapk8, Pten, and Snca) and 2 genes that participate in two metabolic pathways: Atp6v1g2 (pro-apoptotic and necrosis) and Tnf (pro-apoptotic, autophagy). Autophagy-related Snca and Tnf remained under-expressed 24h after treatment with 25μM TBBPA, which was accompanied by the over-expression of the pro-apoptotic Casp6, the anti-apoptotic Birc3, 2 genes related to autophagy (Htt and Irgm) and 2 genes (Fas and Tp53) that are involved in both apoptosis (pro-apoptotic) and autophagy. These results show a complex pattern of TBBPA-evoked changes in the expression of the genes involved in the programmed neuronal death, indicating no induction of programmed necrosis, an early suppression of the autophagy and anti-apoptotic genes, followed by a delayed activation of genes associated with apoptosis.

Tetrabromobisphenol A disturbs zinc homeostasis in cultured cerebellar granule cells: A dual role in neurotoxicity

The brominated flame retardant tetrabromobisphenol A (TBBPA) has recognized neurotoxic properties mediated by intracellular Ca²⁺ imbalance and oxidative stress. Although these factors are known to trigger the release of Zn²⁺ from intracellular stores, the effects of TBBPA on Zn²⁺ homeostasis in neurons and the role of Zn²⁺in TBBPA neurotoxicity have not yet been studied. Therefore, we investigated zinc transients in primary cultures of rat cerebellar granule cells and assessed their involvement in TBBPA neurotoxicity. The results demonstrate that TBBPA releases Zn²⁺ from the intracellular stores and increases its intracellular concentration, followed by Zn²⁺ displacement from the cells. TBBPA-evoked Zn²⁺ transients are partially mediated by Ca²⁺ and ROS. Application of TPEN, Zn²⁺ chelator, potentiates TBBPA- and glutamate-induced ⁴⁵Ca uptake, enhances TBBPA-induced ROS production and potentiates decreases in the ΔΨm in cells treated with 25 μM TBBPA, revealing the potential neuroprotective capacity of endogenous Zn²⁺. However, the administration of TPEN does not aggravate TBBPA neurotoxicity, and even slightly decreases neuronal death induced by 25 μM TBBPA. In summary, it was shown for the first time that TBBPA interferes with the cellular Zn²⁺ homeostasis in neuronal cultures, and we revealed complex roles for endogenous Zn²⁺ in cytoprotection and TBBPA toxicity in cultured neurons.

Divergent Mechanisms Leading to Signaling Dysfunction in Embryonic Muscle by Bisphenol A and Tetrabromobisphenol A

Bisphenol A (BPA) and its brominated derivative tetrabromobisphenol A (TBBPA) are high production volume chemicals used in the manufacture of various consumer products. Although regarded as endocrine disruptors, these chemicals are suspected to exert nongenomic actions on muscle function that are not well understood. Using skeletal muscle microsomes, we examined the effects of BPA and TBBPA on ryanodine receptor type 1 (RyR1), dihydropyridine receptor (DHPR), and sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA). We assessed the impact of these chemicals on Ca²⁺ dynamics and signaling in embryonic skeletal myotubes through fluorescent Ca²⁺ imaging and measurement of resting membrane potential (V_m). TBBPA activated RyR1 and inhibited DHPR and SERCA, inducing a net efflux of Ca²⁺ from loaded microsomes, whereas BPA exhibited little or no activity at these targets. Regardless, both compounds disrupted the function of intact myotubes. TBBPA diminished and eventually abrogated Ca²⁺ transients, altered intracellular Ca²⁺ equilibrium, and caused V_m depolarization. For some cells, BPA caused rapid Ca²⁺ transient loss without marked changes in cytosolic and sarcoplasmic reticulum Ca²⁺ levels, likely owing to altered cellular excitability as a result of BPA-induced V_m hyperpolarization. BPA and TBBPA both interfere with skeletal muscle function through divergent mechanisms that impair excitation-contraction coupling and may be exemplary of their adverse outcomes in other muscle types.

The Role of Ca2+ Imbalance in the Induction of Acute Oxidative Stress and Cytotoxicity in Cultured Rat Cerebellar Granule Cells Challenged with Tetrabromobisphenol A

Using primary cultures of rat cerebellar granule cells (CGC) we examined the role of calcium transients induced by tetrabromobisphenol A (TBBPA) in triggering oxidative stress and cytotoxicity. CGC were exposed for 30 min to 10 or 25 µM TBBPA. Changes in intracellular calcium concentration ([Ca²⁺]_i), in the production of reactive oxygen species (ROS), and in the potential of mitochondria (∆Ψm) were measured fluorometrically during the exposure. The intracellular glutathione (GSH) and catalase activity were determined after the incubation; cell viability was evaluated 24 h later. TBBPA concentration-dependently increased [Ca²⁺]_i and ROS production, and reduced GSH content, catalase activity, ∆Ψm and neuronal viability. The combination of NMDA and ryanodine receptor antagonists, MK-801 and bastadin 12 with ryanodine, respectively, prevented Ca²⁺ transients and partially reduced cytotoxicity induced by TBBPA at both concentrations. The antagonists also completely inhibited oxidative stress and depolarization of mitochondria evoked by 10 µM TBBPA, whereas these effects were only partially reduced in the 25 µM TBBPA treatment. Free radical scavengers prevented TBBPA-induced development of oxidative stress and improved CGC viability without having any effect on the rises in Ca²⁺ and drop in ∆Ψm. The co-administration of scavengers with NMDA and ryanodine receptor antagonists provided almost complete neuroprotection. These results indicate that Ca²⁺ imbalance and oxidative stress both mediate acute toxicity of TBBPA in CGC. At 10 µM TBBPA Ca²⁺ imbalance is a primary event, inducing oxidative stress, depolarization of mitochondria and cytotoxicity, whilst at a concentration of 25 µM TBBPA an additional Ca²⁺-independent portion of oxidative stress and cytotoxicity emerges.

Concentration of novel brominated flame retardants and HBCD in leachates and sediments from selected municipal solid waste landfill sites in Gauteng Province, South Africa

In this study leachate and sediment samples were collected from six municipal solid waste landfill sites across Gauteng Province in South Africa to determine the levels of 2-ethylhexyl 2,3,4,5 tetrabromobenzoate (EH-TBB), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), decabromodiphenyl ethane (DBDPE), bis(2-ethylhexyl)-3,4,5,6-tetrabromo-phthalate (BEH-TEBP) and hexabromocyclododecane (HBCD). Soxhlet as well as liquid-liquid extraction were employed for sediment and leachates respectively followed by GC-EIMS analysis. Concentrations of novel brominated flame retardants (NBFRs) ranged from below detection (<dl)-310ngg(-1) and <dl-142pgL(-1) for sediment and leachate samples while percentage proportions of detected NBFRs and HBCD analytes in leachate samples was observed to be approximately 64%, 22%, 9% and 5% for TBB, ∑HBCD, BTBPE and TBPH respectively. Frequency of detection was lower in sediment (<20-50%) compared to leachate (75-100%) samples. Decabromodiphenyl ethane levels in sediment and leachate samples were found below the limit of quantitation. A positive correlation with NBFRs was, however, observed with some water quality parameters except for sulphate.

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

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

Assessing developmental toxicity and estrogenic activity of halogenated bisphenol A on zebrafish (Danio rerio)

Halogenated bisphenol A (H-BPAs), widely used in industrial production, have been identified in various environmental matrices and detected in human serum and breast milk. The persistence and prevalence of H-BPAs in the environment underscore the need to in-depth understand their adverse effects to humans and other organisms. In the present study, zebrafish embryos/larvae were used as models to investigate the developmental toxicities of three H-BPAs, namely tetrabromobisphenol A (TBBPA), tetrachlorobisphenol A (TCBPA), and bisphenol AF (BPAF). The half lethal concentration (LC50) values indicated that the rank order of toxicities of the chemicals were TCBPA>TBBPA>BPAF. Three H-BPAs exposure resulted in a variety of developmental lesions in the embryos/larvae, such as a delay in time to hatch, edema, and hemorrhage. The estrogenic activities of H-BPAs were determined by means of in vivo vitellogenin (vtg) assay and in vitro MVLN assay. Here only BPAF specifically shows a stronger estrogenic activity than BPA both in in vivo and in vitro. These data suggest that TCBPA, TBBPA, and BPAF are more potent toxicants than BPA, and indicate that further research of the mechanisms on their toxicities is required.

Mammalian toxicology and human exposures to the flame retardant 2,2',6,6'-tetrabromo-4,4'-isopropylidenediphenol (TBBPA): implications for risk assessment

The compound 2,2',6,6'-Tetrabromo-4,4'-isopropylidenediphenol (tetrabromobisphenol A, TBBPA) is used as a reactive and additive flame retardant. This review evaluates the mammalian toxicology of TBBPA and summarizes recent human exposure and risk assessments. TBBPA has a low potential for systemic or reproductive toxicity, and no-observed-adverse-effect-levels were greater than 1,000 mg/kg body weight (bw)/day in a 90-day oral toxicity study, a developmental toxicity study and a two-generation reproductive and developmental toxicity study. Some interactions of TBBPA with hormone-mediated pathways were noted in vitro; however, when studied in vivo, TBBPA did not produce adverse effects that might be considered to be related to disturbances in the endocrine system. Therefore, in accordance with internationally accepted definitions, TBBPA should not be considered an "endocrine disruptor." Furthermore, TBBPA is rapidly excreted in mammals and therefore does not have a potential for bioaccumulation. Measured concentrations of TBBPA in house dust, human diet and human serum samples are very low. Daily intakes of TBBPA in humans were estimated to not exceed a few ng/kg bw/day. Due to the low exposures and the low potential for toxicity, margins of exposures for TBBPA in the human population were between 6 × 10(4) (infants) to 6 × 10(7) (adults). Exposures of the general population are also well below the derived-no-effect-levels derived for endpoints of potential concern in REACH.

Related flavonoids cause cooperative inhibition of the sarcoplasmic reticulum Ca²⁺ ATPase by multimode mechanisms

Flavonoids are group of plant-derived hydroxylated polycyclic molecules found in fruit and vegetables. They are known to bio-accumulate within humans and are considered to have beneficial health effects, including cancer chemoprotection. One mechanism proposed to explain this is that they are able to induce apoptosis in cancer cells by inhibiting a variety of kinases and also the Ca²⁺ ATPase. An investigation was undertaken with respect to the mechanism of inhibition for three flavonoids: quercetin, galangin and 3,6 dihydroxyflavone (3,6-DHF). Each inhibited the Ca²⁺ ATPase with K(i) values of 8.7, 10.3 and 5.4 μM, respectively, showing cooperative inhibition with n ~ 2. Given their similar structures, the flavonoids showed several differences in their mechanisms of inhibition. All three flavonoids stabilized the ATPase in the E₁ conformation and reduced [³²P]-ATP binding. However, both galangin and 3,6-DHF increased the affinity of Ca²⁺ for the ATPase by decreasing the Ca²⁺-dissociation rate constant, whereas quercetin had little effect. Ca²⁺-induced changes in tryptophan fluorescence levels were reduced in the presence of 3,6-DHF and galangin (but not with quercetin), indicating that Ca²⁺-associated changes within the transmembrane helices are altered. Both galangin and quercetin reduced the rates of ATP-dependent phosphorylation and dephosphorylation, whereas 3,6-DHF did not. Modelling studies suggest that flavonoids could potentially bind to two sites: one directly where nucleotides bind within ATP binding site and the other at a site close by. We hypothesize that interactions of these two neighbouring sites may account for both the cooperative inhibition and the multimode mechanisms of action seen with related flavonoids.

The sarcoplasmic-endoplasmic reticulum Ca(2+)-ATPase (SERCA) is the likely molecular target for the acute toxicity of the brominated flame retardant hexabromocyclododecane (HBCD)

Hexabromocyclododecane (HBCD) is a widely utilised brominated flame retardant (BFR). It has been shown to bio-accumulate within organisms, including man, and possibly cause neurological disorders. The acute neurotoxicity of HBCD, and six other unrelated BFRs, were assessed in SH-SY5Y human neuroblastoma cells by 24h viability assays and HBCD proved to be the most lethal (LC50, 3μM). In addition, the effects of these BFRs were also assessed for their potency at inhibiting the sarcoplasmic-endoplasmic reticulum Ca(2+) ATPase (SERCA) derived from the SH-SY5Y cells and again HBCD was the most potent (IC50, 2.7μM). The data for the other BFRs tested showed a direct correlation (coefficient 0.94) between the potencies of inducing cell death and inhibiting the Ca(2+) ATPase, indicating that SERCA is likely to be the molecular target for acute toxicity. Mechanistic studies of HBCD on the Ca(2+) ATPase suggest that it affects ATP binding, phosphorylation as well as the E2 to E1 transition step.

Structural requirements for inhibitory effects of bisphenols on the activity of the sarco/endoplasmic reticulum calcium ATPase

Bisphenols (BPs) are a class of small organic compounds with widespread industrial applications. Previous studies have identified several BPs that interfere with the activity of the ion-translocating enzyme sarco/endoplasmic reticulum calcium ATPase (SERCA). In order to define the molecular determinants of BP-mediated SERCA inhibition, we conducted enzyme activity assays with rabbit SERCA to determine the inhibitory potencies of 27 commercially available BPs, which were the basis for structure-activity relationships. The most potent BPs inhibited SERCA at low micromolar concentrations and carried at their two phenyl rings multiple non-polar substituents, such as small alkyl groups or halides. Furthermore, the presence of methyl groups or a cyclohexyl group at the central carbon atom connecting the two phenyl moieties correlated with good potencies. For a characterization and visualization of enzyme/inhibitor interactions, molecular docking was performed, which suggested that hydrogen bonding with Asp254 and hydrophobic interactions were the major driving forces for BP binding to SERCA. Calcium imaging studies with a selection of BPs showed that these inhibitors were able to increase intracellular calcium levels in living human cells, a behavior consistent with that of a SERCA inhibitor.

Multiple novel modes of action involved in the in vitro neurotoxic effects of tetrabromobisphenol-A

Neurotoxicological data on the widely used brominated flame retardant tetrabromobisphenol-A (TBBPA) is limited. Since recent studies indicated that inhibitory GABA(A) and excitatory α(4)β(2) nicotinic acetylcholine (nACh) receptors are sensitive targets for persistent organic pollutants, we investigated the effects of TBBPA on these receptors, expressed in Xenopus oocytes, using the two-electrode voltage-clamp technique. Our results demonstrate that TBBPA acts as full (≥ 10 μM) and partial (≥ 0.1 μM) agonist on human GABA(A) receptors, whereas it acts as antagonist (≥ 10 μM) on human α(4)β(2) nACh receptors. Next, neuronal B35 cells were used to further study the effects of TBBPA on calcium-permeable nACh receptors using single-cell fluorescent calcium imaging. These results demonstrate that TBBPA (≥ 1 μM) inhibits acetylcholine (ACh) receptors as evidenced by a reduction in the ACh-evoked increases in the intracellular calcium concentration ([Ca(2+)](i)). Additionally, TBBPA (> 1 μM) induced a strong and concentration-dependent increase in basal [Ca(2+)](i) in B35 cells. Similarly, TBBPA (> 1 μM) increases basal [Ca(2+)](i) in dopaminergic PC12 cells. This increase is also evident under calcium-free conditions, indicating it originates from intracellular calcium stores. Moreover, depolarization-evoked increases in [Ca(2+)](i) are strongly reduced by TBBPA (≥ 1 μM), indicating TBBPA-induced inhibition of voltage-gated calcium channels. Our in vitro studies thus demonstrate that TBBPA exerts several adverse effects on functional neurotransmission endpoints with effect concentrations that are only two orders of magnitude below the highest cord serum concentrations. Although epidemiological proof for adverse TBBPA effects is lacking, our data justify the quest for flame retardants with reduced neurotoxic potential.

Some commonly used brominated flame retardants cause Ca2+-ATPase inhibition, beta-amyloid peptide release and apoptosis in SH-SY5Y neuronal cells

Brominated flame retardants (BFRs) are chemicals commonly used to reduce the flammability of consumer products and are considered pollutants since they have become widely dispersed throughout the environment and have also been shown to bio-accumulate within animals and man. This study investigated the cytotoxicity of some of the most commonly used groups of BFRs on SH-SY5Y human neuroblastoma cells. The results showed that of the BFRs tested, hexabromocyclododecane (HBCD), tetrabromobisphenol-A (TBBPA) and decabromodiphenyl ether (DBPE), all are cytotoxic at low micromolar concentrations (LC₅₀ being 2.7±0.7µM, 15±4µM and 28±7µM, respectively). They induced cell death, at least in part, by apoptosis through activation of caspases. They also increased intracellular [Ca²⁺] levels and reactive-oxygen-species within these neuronal cells. Furthermore, these BFRs also caused rapid depolarization of the mitochondria and cytochrome c release in these neuronal cells. Elevated intracellular [Ca²⁺] levels appear to occur through a mechanism involving microsomal Ca²⁺-ATPase inhibition and this maybe responsible for Ca²⁺-induced mitochondrial dysfunction. In addition, µM levels of these BFRs caused β-amyloid peptide (Aβ-42) processing and release from these cells with a few hours of exposure. These results therefore shows that these pollutants are both neurotoxic and amyloidogenic in-vitro.

A diversity of SERCA Ca2+ pump inhibitors

The SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase) is probably the most extensively studied membrane protein transporter. There is a vast array of diverse inhibitors for the Ca2+ pump, and many have proved significant in helping to elucidate both the mechanism of transport and gaining conformational structures. Some SERCA inhibitors such as thapsigargin have been used extensively as pharmacological tools to probe the roles of Ca2+ stores in Ca2+ signalling processes. Furthermore, some inhibitors have been implicated in the cause of diseases associated with endocrine disruption by environmental pollutants, whereas others are being developed as potential anticancer agents. The present review therefore aims to highlight some of the wide range of chemically diverse inhibitors that are known, their mechanisms of action and their binding location on the Ca2+ ATPase. Additionally, some ideas for the future development of more useful isoform-specific inhibitors and anticancer drugs are presented.

Discovery of novel SERCA inhibitors by virtual screening of a large compound library

Two screening protocols based on recursive partitioning and computational ligand docking methodologies, respectively, were employed for virtual screens of a compound library with 345,000 entries for novel inhibitors of the enzyme sarco/endoplasmic reticulum calcium ATPase (SERCA), a potential target for cancer chemotherapy. A total of 72 compounds that were predicted to be potential inhibitors of SERCA were tested in bioassays and 17 displayed inhibitory potencies at concentrations below 100 μM. The majority of these inhibitors were composed of two phenyl rings tethered to each other by a short link of one to three atoms. Putative interactions between SERCA and the inhibitors were identified by inspection of docking-predicted poses and some of the structural features required for effective SERCA inhibition were determined by analysis of the classification pattern employed by the recursive partitioning models.

Design, synthesis, and biological evaluation of hydroquinone derivatives as novel inhibitors of the sarco/endoplasmic reticulum calcium ATPase

Analogues of the compound 2,5-di-tert-butylhydroquinone (BHQ) are capable of inhibiting the enzyme sarco/endoplasmic reticulum ATPase (SERCA) in the low micromolar and submicromolar concentration ranges. Not only are SERCA inhibitors valuable research tools, but they also have potential medicinal value as agents against prostate cancer. This study describes the synthesis of 13 compounds representing several classes of BHQ analogues, such as hydroquinones with a single aromatic substituent, symmetrically and unsymmetrically disubstituted hydroquinones, and hydroquinones with omega-amino acid tethers attached to their hydroxyl groups. Structure-activity relationships were established by measuring the inhibitory potencies of all synthesized compounds in bioassays. The assays were complemented by computational ligand docking for an analysis of the relevant ligand/receptor interactions.

P-type ATPases as drug targets: tools for medicine and science

P-type ATPases catalyze the selective active transport of ions like H+, Na+, K+, Ca2+, Zn2+, and Cu2+ across diverse biological membrane systems. Many members of the P-type ATPase protein family, such as the Na+,K+-, H+,K+-, Ca2+-, and H+-ATPases, are involved in the development of pathophysiological conditions or provide critical function to pathogens. Therefore, they seem to be promising targets for future drugs and novel antifungal agents and herbicides. Here, we review the current knowledge about P-type ATPase inhibitors and their present use as tools in science, medicine, and biotechnology. Recent structural information on a variety of P-type ATPase family members signifies that all P-type ATPases can be expected to share a similar basic structure and a similar basic machinery of ion transport. The ion transport pathway crossing the membrane lipid bilayer is constructed of two access channels leading from either side of the membrane to the ion binding sites at a central cavity. The selective opening and closure of the access channels allows vectorial access/release of ions from the binding sites. Recent structural information along with new homology modeling of diverse P-type ATPases in complex with known ligands demonstrate that the most proficient way for the development of efficient and selective drugs is to target their ion transport pathway.

Effects of bisphenol-A and other endocrine disruptors compared with abnormalities of schizophrenia: an endocrine-disruption theory of schizophrenia

In recent years, numerous substances have been identified as so-called "endocrine disruptors" because exposure to them results in disruption of normal endocrine function with possible adverse health outcomes. The pathologic and behavioral abnormalities attributed to exposure to endocrine disruptors like bisphenol-A (BPA) have been studied in animals. Mental conditions ranging from cognitive impairment to autism have been linked to BPA exposure by more than one investigation. Concurrent with these developments in BPA research, schizophrenia research has continued to find evidence of possible endocrine or neuroendocrine involvement in the disease. Sufficient information now exists for a comparison of the neurotoxicological and behavioral pathology associated with exposure to BPA and other endocrine disruptors to the abnormalities observed in schizophrenia. This review summarizes these findings and proposes a theory of endocrine disruption, like that observed from BPA exposure, as a pathway of schizophrenia pathogenesis. The review shows similarities exist between the effects of exposure to BPA and other related chemicals with schizophrenia. These similarities can be observed in 11 broad categories of abnormality: physical development, brain anatomy, cellular anatomy, hormone function, neurotransmitters and receptors, proteins and factors, processes and substances, immunology, sexual development, social behaviors or physiological responses, and other behaviors. Some of these similarities are sexually dimorphic and support theories that sexual dimorphisms may be important to schizophrenia pathogenesis. Research recommendations for further elaboration of the theory are proposed.

Hydroxylation increases the neurotoxic potential of BDE-47 to affect exocytosis and calcium homeostasis in PC12 cells

BACKGROUND

Oxidative metabolism, resulting in the formation of hydroxylated polybrominated diphenyl ether (PBDE) metabolites, may enhance the neurotoxic potential of brominated flame retardants.

OBJECTIVE

Our objective was to investigate the effects of a hydroxylated metabolite of 2,2',4,4'-tetra-bromodiphenyl ether (BDE-47; 6-OH-BDE-47) on changes in the intracellular Ca2+ concentration ([Ca2+]i) and vesicular catecholamine release in PC12 cells.

METHODS

We measured vesicular catecholamine release and [Ca2+]i using amperometry and imaging of the fluorescent Ca2+-sensitive dye Fura-2, respectively.

RESULTS

Acute exposure of PC12 cells to 6-OH-BDE-47 (5 microM) induced vesicular catecholamine release. Catecholamine release coincided with a transient increase in [Ca2+]i, which was observed shortly after the onset of exposure to 6-OH-BDE-47 (120 microM). An additional late increase in [Ca2+]i was often observed at > or =1 microM 6-OH-BDE-47. The initial transient increase was absent in cells exposed to the parent compound BDE-47, whereas the late increase was observed only at 20 microM. Using the mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) and thapsigargin to empty intracellular Ca2+ stores, we found that the initial increase originates from emptying of the endoplasmic reticulum and consequent influx of extracellular Ca2+, whereas the late increase originates primarily from mitochondria.

CONCLUSION

The hydroxylated metabolite 6-OH-BDE-47 is more potent in disturbing Ca2+ homeostasis and neurotransmitter release than the parent compound BDE-47. The present findings indicate that bioactivation by oxidative metabolism adds considerably to the neurotoxic potential of PBDEs. Additionally, based on the observed mechanism of action, a cumulative neurotoxic effect of PBDEs and ortho-substituted polychlorinated biphenyls on [Ca2+]i cannot be ruled out.