Molecular Mechanisms of Hippocampal Neurotoxicity Across Three Generations of Brominated Flame Retardants

Abstract

<b>Abstract ID 28060</b> <b>Poster Board 459</b> Brominated Flame Retardants (BFRs) are ubiquitously utilized to reduce flammability in a wide range of household products including carpets, upholstery, and paints. While useful chemicals, BFRs also migrate from their products into the environment. This has resulted in continuous, population-level exposure that has been correlated to impaired learning and memory. To determine the effects of different BFR generations on hippocampal cells, HT-22 cells were exposed to tetrabromobisphenol-A (TBBPA), hexabromocyclododecane (HBCD), or 2,29,4,49-tetrabromodiphenyl ether (BDE-47) (current, phasing out, and phased out BFRs, respectively). Cell viability analysis was assessed by MTT staining, as well as nuclear morphology after 48 hr of exposure. HBCD exposure resulted in lower IC₅₀ values in HT-22 cells (15 mM IC₅₀), as compared to TBBPA (70 mM) and BDE-47 (60 mM). HT-22 cellular and nuclear morphology suggested the presence of apoptosis after exposure to the IC₅₀for each BFR after both 24 and 48 hr exposure. To understand the mechanisms of toxicity, cell cycle and cell death were evaluated. Each BFR induced cell cycle alterations with increasing exposure time. Upon 24 hr exposure, HBCD (50 or 100 mM) induced significant S-phase arrest which was maintained upon 48 hr exposure. However, only upon 48 hr exposure did BDE-47 (50 and 100 mM) and TBBPA (100 mM) induce significant S-phase arrest. Annexin-PI staining verified a time and concentration-dependent neurotoxic effect, as evidenced by an increase in annexin V staining in cells, indicating the presence of apoptotic cell death. Both 24 and 48 hr exposure to HBCD (50 or 100 mM) or BDE-47 (100 mM) induced significant increases in apoptosis, although 100 mM TBBPA only induced apoptosis and necrosis after 48 hr. Further evaluation of the mechanisms of toxicity indicates that p53 and p21 may play a central role in the onset of cell cycle arrest and apoptosis. RNA-Sequencing was performed to understand the molecular mechanisms underlying flame retardant neurotoxicity. These data demonstrate that BFRs can induce chemical-dependent toxicity in neural cells <i>in&nbsp;vitro</i>; however, additional study will be necessary to determine if BFR-induced neural cytotoxicity would adversely affect learning and memory <i>in&nbsp;vivo</i>.