title: Multiple novel modes of action involved in the in vitro neurotoxic effects of tetrabromobisphenol-A.
abstract: Neurotoxicological data on the widely used brominated flame retardant tetrabromobisphenol-A (TBBPA) is limited. Since recent studies indicated that inhibitory GABA(A) and excitatory α(4)β(2) nicotinic acetylcholine (nACh) receptors are sensitive targets for persistent organic pollutants, we investigated the effects of TBBPA on these receptors, expressed in Xenopus oocytes, using the two-electrode voltage-clamp technique. Our results demonstrate that TBBPA acts as full (≥ 10 μM) and partial (≥ 0.1 μM) agonist on human GABA(A) receptors, whereas it acts as antagonist (≥ 10 μM) on human α(4)β(2) nACh receptors. Next, neuronal B35 cells were used to further study the effects of TBBPA on calcium-permeable nACh receptors using single-cell fluorescent calcium imaging. These results demonstrate that TBBPA (≥ 1 μM) inhibits acetylcholine (ACh) receptors as evidenced by a reduction in the ACh-evoked increases in the intracellular calcium concentration ([Ca(2+)](i)). Additionally, TBBPA (> 1 μM) induced a strong and concentration-dependent increase in basal [Ca(2+)](i) in B35 cells. Similarly, TBBPA (> 1 μM) increases basal [Ca(2+)](i) in dopaminergic PC12 cells. This increase is also evident under calcium-free conditions, indicating it originates from intracellular calcium stores. Moreover, depolarization-evoked increases in [Ca(2+)](i) are strongly reduced by TBBPA (≥ 1 μM), indicating TBBPA-induced inhibition of voltage-gated calcium channels. Our in vitro studies thus demonstrate that TBBPA exerts several adverse effects on functional neurotransmission endpoints with effect concentrations that are only two orders of magnitude below the highest cord serum concentrations. Although epidemiological proof for adverse TBBPA effects is lacking, our data justify the quest for flame retardants with reduced neurotoxic potential.
authors.affiliation: Neurotoxicology Research Group, Toxicology Division, Institute for Risk Assessment Sciences (IRAS), Utrecht University, NL-3508 TD Utrecht, The Netherlands.
authors.forename: Hester S
authors.initials: HS
authors.lastname: Hendriks
authors.forename: Regina G D M
authors.initials: RG
authors.lastname: van Kleef
authors.forename: Martin
authors.initials: M
authors.lastname: van den Berg
authors.forename: Remco H S
authors.initials: RH
authors.lastname: Westerink
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D018384:Oxidative Stress; D016716:PC12 Cells; D018408:Patch-Clamp Techniques; D011075:Polybrominated Biphenyls / Q000633:toxicity*; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects; D014981:Xenopus
chemical_list: D011075:Polybrominated Biphenyls; D011963:Receptors, GABA-A; D053148:Caspase 3; C020806:tetrabromobisphenol A; D000109:Acetylcholine; D002118:Calcium