Evaluation of the toxicity of the brominated flame retardants, PBDE-47 and HBCD, in neuronal cell lines

摘要

Polybrominated diphenyl ether (PBDE-47) and hexabromocyclododecane (HBCD) are brominated flame retardants (BFRs) commonly used in a wide range of consumer products. They bioaccumulate and persist in the environment, and have been detected in humans and wildlife. Their ability to pass the blood-brain barrier (BBB) and to accumulate in the brain has raised concern about the potential of BFRs to cause neurotoxicity. Functional genomics was used to investigate the modes of action of PBDE-47 and HBCD in two neuronal cell models namely mouse neuroblastoma (N2A) and neuroblastoma x spinal cord (NSC-19). It was established that PBDE-47 and HBCD reduce cell viability, increase lactate dehydrogenase (LDH) leakage and cause apoptosis as indicated by increased caspase-3 activity at low micromolar concentrations (1 - 4μM). A pre-incubation with the omega-3 fatty acid, docosahexaenoic acid (DHA), mitigated the toxic effect of HBCD in the N2A cell line, with a significant decrease in the LDH leakage. Transcriptome profiling revealed that exposure to PBDE-47 and HBCD affects expression of genes with overlapping functionalities. Both toxicants regulated genes related to calcium homeostasis, endoplasmic reticulum stress and lipid metabolism. Genes involved in thyroid hormone signalling, neurodegenerative diseases and nervous system development were also preferentially regulated. The fatty acid DHA altered the expression of genes that were also regulated by PBDE-47 or HBCD, and HBCD modulated DHA-induced gene expression. It was also established that HBCD exposure affect cellular zinc homeostasis, increasing the level of intracellular weakly bound Zn2+. This effect was ameliorated by the antioxidant NAC, suggesting that the [Zn2+] increase could have been caused by oxidative stress with release of Zn2+ from zinc-binding proteins. This result indicates for the first time that zinc signalling is a potential target of POP toxicity. In conclusion, we established that PBDE-47 and HBCD have toxicity effects on cells of neuronal origin starting at a concentration of 1μM and that exposure to either of these BFRs causes regulation of genes related to many cellular functions, several of which have been observed as BFR phenotypes in animal studies. It was also shown that zinc is a POP toxicity target and that cellular effects of BFRs are modulated by DHA.