Hydroxylation Increases the Neurotoxic Potential of BDE-47 to Affect Exocytosis and Calcium Homeostasis in PC12 Cells

• Published in: Environmental health perspectives Vol. 116; no. 5; pp. 637 - 643
• Main Authors: Dingemans, Milou M. L., de Groot, Aart, van Kleef, Regina G. D. M., Bergman, Åke, van den Berg, Martin, Vijverberg, Henk P. M., Westerink, Remco H. S.
• Format: Journal Article
• Language: English
• Published: United States National Institute of Environmental Health Sciences. National Institutes of Health. Department of Health, Education and Welfare 01.05.2008; National Institute of Environmental Health Sciences
• Subjects: Animals; Calcium - analysis; Calcium - metabolism; Catecholamines; Catecholamines - secretion; Chemical hazards; Environmental Exposure; Exocytosis; Exocytosis - drug effects; Flame retardants; Flame Retardants - toxicity; Halogenated Diphenyl Ethers; Health aspects; Homeostasis; Homeostasis - drug effects; Hydroxylation; Metabolites; Neurons; PC12 cells; PC12 Cells - drug effects; PC12 Cells - metabolism; Polybrominated Biphenyls - metabolism; Polybrominated Biphenyls - toxicity; Polychlorinated biphenyls; Rats; United States; calcium; catecholamine; neurotoxicity; brominated flame retardants; bioactivation; persistent organic pollutants; exocytosis; poly-brominated diphenyl ether; neurotransmitter release; intra-cellular calcium stores
• ISSN: 0091-6765; 1552-9924; 1552-9924
• DOI: 10.1289/ehp.11059

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 2,2',4,4'-tetrabromodiphenyl ether (BDE-47; 6-OH-BDE-47) on changes in the intracellular ${\rm Ca}^{2+}$ concentration $([{\rm Ca}^{2+}]_{i})$ and vesicular catecholamine release in PC12 cells. Methods: We measured vesicular catecholamine release and $[{\rm Ca}^{2+}]_{i}$ using amperometry and imaging of the fluorescent ${\rm Ca}^{2+}\text{-sensitive}$ dye Fura-2, respectively. Results: Acute exposure of PC12 cells to 6-OH-BDE-47 (5 μM) induced vesicular catecholamine release. Catecholamine release coincided with a transient increase in $[{\rm Ca}^{2+}]_{i}$, which was observed shortly after the onset of exposure to 6-OH-BDE-47 (120 μM). An additional late increase in $[{\rm Ca}^{2+}]_{i}$ was often observed at ≥ 1 μM 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 μM. Using the mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) and thapsigargin to empty intracellular ${\rm Ca}^{2+}$ stores, we found that the initial increase originates from emptying of the endoplasmic reticulum and consequent influx of extracellular ${\rm Ca}^{2+}$, whereas the late increase originates primarily from mitochondria. Conclusion: The hydroxylated metabolite 6-OH-BDE-47 is more potent in disturbing ${\rm Ca}^{2+}$ 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 $[{\rm Ca}^{2+}]_{i}$ cannot be ruled out.