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 (Ca(2+)) 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 AND METHODS: 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 Ca(2+) concentration ([Ca(2+)](i)), measured using the Ca(2+)-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 Ca(2+) release from intracellular stores, although with different lowest observed effect concentrations (LOECs). The major intracellular Ca(2+) 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 [Ca(2+)](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 [Ca(2+)](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.