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

Abstract

BackgroundOxidative metabolism, resulting in the formation of hydroxylated polybrominated diphenyl ether (PBDE) metabolites, may enhance the neurotoxic potential of brominated flame retardants.ObjectiveOur 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.MethodsWe measured vesicular catecholamine release and [Ca2+]i using amperometry and imaging of the fluorescent Ca2+-sensitive dye Fura-2, respectively.ResultsAcute exposure of PC12 cells to 6-OH-BDE-47 (5 μM) 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 μM). An additional late increase in [Ca2+]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 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.ConclusionThe 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.

Metabolic pathways of decabromodiphenyl ether (BDE209) in rainbow trout (Oncorhynchus mykiss) via intraperitoneal injection

“…Such differences might be due to different exposure routes and tested species (Montory and Barra, 2006). OH-BDEs metabolites were of particular interest because they might elicit a variety of effects on organisms, such as disruption of thyroid hormone homeostasis and neurotoxic effects (Meerts et al, 2001;Harju et al, 2007;Dingemans et al, 2008;). OH-BDEs have been detected in different organisms.…”

Molecular toxicology of polybrominated diphenyl ethers: nuclear hormone receptor mediated pathways

“…7 Furthermore, metabolism of PBDEs was reported to enhance the toxicity of PBDEs. 11 The mechanisms of PBDE toxicity are complex and have not been fully resolved. Since the chemical structures of PBDEs and their metabolites are similar to thyroid hormones, polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Fig.…”

Determination of environmentally relevant exposure concentrations of polybrominated diphenyl ethers for in vitro toxicological studies

“…In general, previous studies of PBDEs in vitro have incorporated micromolar (lM) levels in the culture media, although several reports have used nanomolar (nM) levels (Barber et al, 2006;Cantón et al, 2006;Dingemans et al, 2007Dingemans et al, , 2008Fery et al, 2009;Giordano et al, 2008Giordano et al, , 2009He et al, 2008aHe et al, ,b, 2009Hu et al, 2007;Madia et al, 2004;Mercado-Feliciano and Bigsby, 2008;Peters et al, 2004Peters et al, , 2006Stavenes Andersen et al, 2009;Song et al, 2009;Stapleton et al, 2009;Tagliaferri et al, 2010;Zhang et al, 2007). None of these studies measured the cellular PBDE concentrations but it is assumed that the concentrations used may not be environmentally relevant because they are much higher than the picomolar (pM) or lower levels typically found in environmental water or body fluids (Frederiksen et al, 2009;Gill et al, 2004;Streets et al, 2006;Wu et al, 2008).…”