| 1. |
- Dingemans, Milou M. L., et al.
(författare)
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Hexabromocyclododecane Inhibits Depolarization-Induced Increase in Intracellular Calcium Levels and Neurotransmitter Release in PC12 Cells
- 2009
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Ingår i: Toxicological Sciences. - : Oxford University Press (OUP). - 1096-6080 .- 1096-0929. ; 107:2, s. 490-497
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Tidskriftsartikel (refereegranskat)abstract
- Environmental levels of the brominated flame retardant (BFR) hexabromocyclododecane (HBCD) have been increasing. HBCD has been shown to cause adverse effects on learning and behavior in mice, as well as on dopamine uptake in rat synaptosomes and synaptic vesicles. For other BFRs, alterations in the intracellular Ca2+ homeostasis have been observed. Therefore, the aim of this study was to investigate whether the technical HBCD mixture and individual stereoisomers affect the intracellular Ca2+ concentration ([Ca2+](i)) in a neuroendocrine in vitro model (PC12 cells). [Ca2+](i) and vesicular catecholamine release were measured using respectively single-cell Fura-2 imaging and amperometry. Exposure of PC12 cells to the technical HBCD mixture or individual stereoisomers did neither affect basal [Ca2+](i), nor the frequency of basal neurotransmitter release. However, exposure to HBCD (0-20 mu M) did cause a dose-dependent reduction of a subsequent depolarization-evoked increase in [Ca2+](i). This effect was apparent only when HBCD was applied at least 5 min before depolarization (maximum effect after 20 min exposure). The effects of alpha- and beta-HBCD were comparable to that of the technical mixture, whereas the inhibitory effect of gamma-HBCD was larger. Using specific blockers of L-, N- or P/Q-type voltage-gated Ca2+ channels (VGCCs) it was shown that the inhibitory effect of HBCD is not VGCC-specific. Additionally, the number of cells showing depolarization-evoked neurotransmitter release was markedly reduced following HBCD exposure. Summarizing, HBCD inhibits depolarization-evoked [Ca2+](i) and neurotransmitter release. As increasing HBCD levels should be anticipated, these findings justify additional efforts to establish an adequate exposure, hazard and risk assessment.
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| 2. |
- Dingemans, Milou M L, et al.
(författare)
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Hydroxylation increases the neurotoxic potential of BDE-47 to affect exocytosis and calcium homeostasis in PC12 cells.
- 2008
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Ingår i: Journal of Environmental Health Perspectives. - : Environmental Health Perspectives. - 0091-6765 .- 1552-9924. ; 116:5, s. 637-43
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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