Bromination pattern of hydroxylated metabolites of BDE-47 affects their potency to release calcium from intracellular stores in PC12 cells.
BACKGROUND
Brominated flame retardants, including the widely used polybrominated diphenyl ethers (PBDEs), have been detected in humans, raising concern about possible neurotoxicity. Recent research demonstrated that the hydroxylated metabolite 6-OH-BDE-47 increases neurotransmitter release by releasing calcium ions (Ca2+) from intracellular stores at much lower concentrations than its environmentally relevant parent congener BDE-47. Recently, several other hydroxylated BDE-47 metabolites, besides 6-OH-BDE-47, have been detected in human serum and cord blood.


OBJECTIVE
To investigate the neurotoxic potential of other environmentally relevant PBDEs and their metabolites, we examined and compared the acute effects of BDE-47, BDE-49, BDE-99, BDE-100, BDE-153, and several metabolites of BDE-47-6-OH-BDE-47 (and its methoxylated analog 6-MeO-BDE-47), 6 -OH-BDE-49, 5-OH-BDE-47, 3-OH-BDE-47, and 4 -OH-BDE-49--on intracellular Ca2+ concentration ([Ca2+]i), measured using the Ca2+-responsive dye Fura-2 in neuroendocrine pheochromocytoma (PC12) cells.


RESULTS
In contrast to the parent PBDEs and 6-MeO-BDE-47, all hydroxylated metabolites induced Ca2+ release from intracellular stores, although with different lowest observed effect concentrations (LOECs). The major intracellular Ca2+ sources were either endoplasmic reticulum (ER; 5-OH-BDE-47 and 6 -OH-BDE-49) or both ER and mitochondria (6-OH-BDE-47, 3-OH-BDE-47, and 4 -OH-BDE-49). When investigating fluctuations in [Ca2+]i, which is a more subtle end point, we observed lower LOECs for 6-OH-BDE-47 and 4 -OH-BDE-49, as well as for BDE-47.


CONCLUSIONS
The present findings demonstrate that hydroxylated metabolites of BDE-47 cause disturbance of the [Ca2+]i. Importantly, shielding of the OH group on both sides with bromine atoms and/or the ether bond to the other phenyl ring lowers the potency of hydroxylated PBDE metabolites.
Dingemans
Milou M L
MM
Neurotoxicology Research Group, Toxicology Division, Institute for Risk Assessment Sciences, Utrecht University, Utrecht, the Netherlands. m.dingemans@uu.nl
Heusinkveld
Harm J
HJ
Bergman
Ake
A
van den Berg
Martin
M
Westerink
Remco H S
RH
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D055768:Halogenated Diphenyl Ethers; D054879:Halogenation; D016716:PC12 Cells / Q000187:drug effects* / Q000378:metabolism*; D011075:Polybrominated Biphenyls / Q000737:chemistry* / Q000494:pharmacology*; D051381:Rats; D013329:Structure-Activity Relationship
D055768:Halogenated Diphenyl Ethers; D011075:Polybrominated Biphenyls; C511295:2,2',4,4'-tetrabromodiphenyl ether; D002118:Calcium