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.


CONCLUSIONS
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.
Dingemans
Milou M L
MM
Toxicology Division, Institute for Risk Assessment Sciences, Utrecht University, Utrecht, the Netherlands. m.dingemans@uu.nl
de Groot
Aart
A
van Kleef
Regina G D M
RG
Bergman
Ake
A
van den Berg
Martin
M
Vijverberg
Henk P M
HP
Westerink
Remco H S
RH
D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D004781:Environmental Exposure; D005089:Exocytosis / Q000187:drug effects*; D005411:Flame Retardants / Q000633:toxicity*; D055768:Halogenated Diphenyl Ethers; D006706:Homeostasis / Q000187:drug effects*; D006900:Hydroxylation; D016716:PC12 Cells / Q000187:drug effects* / Q000378:metabolism; D011075:Polybrominated Biphenyls / Q000378:metabolism / Q000633:toxicity*; D051381:Rats
D002395:Catecholamines; D005411:Flame Retardants; D055768:Halogenated Diphenyl Ethers; D011075:Polybrominated Biphenyls; C511295:2,2',4,4'-tetrabromodiphenyl ether; D002118:Calcium