Neural Cellular Response Upon Exposure to Brominated Flame Retardants

Abstract

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 which has been correlated to impaired learning and memory. To determine the effects of multiple BFRs on different stages of neuronal development, human Neural Stem Cells (NSCs) and mouse hippocampal HT-22 cells were exposed to Tetrabromobisphenol-A (TBBPA), Hexabromocyclododecane (HBCD), or 2,2',4,4'-Tetrabromodiphenyl ether (BDE-47) (current, phasing out, and phased out BFRs, respectively). Cell viability analysis was assessed by MTT staining after 48 hr of exposure, and demonstrated that HBCD was more toxic to both NSCs (3 μM IC50) and HT-22 cells (15 μM IC50) than TBBPA (NSC 20 μM, HT-22 50 μM) and BDE-47 (NSC 9 μM, HT-22 60 μM). HT-22 cellular and nuclear morphology demonstrated evidence of apoptosis and altered morphology at the IC50 for each BFR after both 24 and 48 hr exposure. Flow cytometry analysis provided further support for a time and concentration-dependent increase in apoptosis as indicated by an increase in annexin V staining in cells. Both 24 and 48 hr HBCD (50 or 100 μM) or BDE-47 (100 μM) exposure induced significant increases in apoptosis, although 100 μM TBBPA only induced apoptosis and necrosis after 48 hr. Interestingly, these chemicals also induced cell cycle alterations with increasing exposure time. Upon 24 hr exposure, HBCD (50 or 100 μM) induced significant S-phase arrest which was maintained upon 48 hr exposure. However, only upon 48 hr exposure did BDE-47 (50 and 100 μM) and TBBPA (100 μM) induce significant S-phase arrest. These data demonstrate that BFRs can induce chemical-dependent toxicity in neural cells, possibly by multiple mechanisms. Further study is needed to determine if BFR-induced neural cell death would adversely affect learning and memory in vivo.