Brominated Flame Retardants alter Cytokine Production in Mast Cells

Abstract

Polybrominated diphenyl ethers (PBDEs), extensively used as flame‐retardants have been classified as persistent environmental pollutants. PBDEs have also been shown to cause neurotoxicity, immunotoxicity and endocrine disruption; however, the exact mechanisms are largely unknown. In this study, we propose to investigate PBDE‐induced immunotoxicity in mast cells. We examined the effects of two of the most commonly occurring brominated diphenyl ether (BDE) congeners, BDE‐47 and −99, and a metabolite of BDE‐47, 6‐OH‐BDE‐47 on MC/9 mast cells. MC/9 cells treated with BDE‐47, −99 and 6‐OH‐BDE‐47 (0.25, 0.5, 5, 20 and 40μM, 24h) were stimulated with IgE/antigen (1μg/ml), and levels of IL‐6 and TNF‐α were measured by ELISA. Our results indicate that PBDEs inhibit the IgE‐mediated cytokine release in MC/9 cells in a concentration‐dependent manner. Interestingly, exposure to BDE‐47 and 6‐OH‐BDE47 decreased IL‐6 release in a concentration‐dependent manner; however, BDE‐99 decreased IL‐6 release only at concentrations above 20 μM. These results demonstrate that tetra‐brominated BDE‐47 and its 6‐OH metabolite can suppress cytokine release with increasing concentrations, while penta‐brominated BDE‐99 congener inhibits IL‐6 release only at higher concentrations. Mast cell degranulation measured by β‐hexoaminidase also showed that BDE congeners decreased degranulation in a concentration‐dependent manner in IgE stimulated mast cells. In order to test effects on cell viability, we exposed the MC/9 cells to increasing concentrations of the BDE congeners and measured cytotoxicity at 24 and 48h by MTS assay. We found that tetra‐brominated BDE‐47 exhibited more potent cytotoxicity (EC50 μM =42.38 at 24h and 32.33 at 48h) in comparison to the penta‐brominated BDE‐99 (EC50 μM =48.41 and 35.04 at 48h) in the MC/9 cells. However, the 6‐OH metabolite of BDE‐47 was more cytotoxic in comparison to its parent compound BDE‐47 as well as penta‐brominated BDE‐99 (EC50 μM =25.82 at 24h and 20.16 at 48h). We are further characterizing development of apoptosis in the MC9 cells in the presence of BDE congeners. Our results suggest that PBDE congeners can modulate cytokine release in mast cells and the extent of inhibition is dependent on the bromination of PBDEs. These results address the need to better understand the molecular and cellular mechanisms by which PBDE exposure can mediate immunotoxicity.