Inhibition and Induction of Aromatase (CYP19) Activity by Brominated Flame Retardants in H295R Human Adrenocortical Carcinoma Cells

Abstract

Brominated flame retardants (BFRs) are persistent and ubiquitous chemicals in the environment, and they are found at increasing levels in tissues of wildlife and humans. Previous in vitro studies with the BFR class of polybrominated diphenyl ethers (BDEs) have shown endocrine-disrupting properties. Our study assessed the potential effects of nineteen BDEs, five hydroxylated BDEs (OH-BDEs), one methoxylated BDE (CH(3)O-BDE), tetrabromobisphenol-A (TBBPA), its dibromopropane ether derivative (TBBPA-DBPE), and the brominated phenols/anisols 2,4,6-tribromophenol (TBP), 4-bromophenol (4BP) and 2,4,6-tribromoanisole (TBA) on the catalytic activity of the steroidogenic enzyme aromatase (CYP19) in H295R human adrenocortical carcinoma cells. Effects were studied in the concentration range from 0.5 to 7.5 microM; exposures were for 24 h. Both 6-OH-BDE47 and 6-OH-BDE99 showed an inhibitory effect on aromatase activity at concentrations >2.5 microM and >5 microM, respectively. However, 6-OH-BDE47 also caused a statistically significant increase in cytotoxicity (based on mitochondrial MTT reduction and lactate dehydrogenase-leakage [LDH]) at concentrations >2.5 microM that could explain in part the apparent inhibitory effect on aromatase activity. Compared to 6-OH-BDE47, the methoxy analog (6-CH(3)O-BDE47) did not elicit a cytotoxic effect, whereas significant inhibition of aromatase remained. TBP caused a concentration-dependent induction of aromatase activity between 0.5 and 7.5 microM (with a maximum of 3.8-fold induction at 7.5 microM). This induction was not observed when a OH- group replaced the CH(3)O- group or when bromine atoms adjacent to this OH- group were absent. These in vitro results provide a basis for studies of more detailed structure-activity relationships between these brominated compounds and the modulation of aromatase activity.

Chronic exposure to environmental levels of tribromophenol impairs zebrafish reproduction

“…Previous studies on the effects of this chemical revealed that TBP causes developmental neurotoxicity, embryotoxicity, and fetotoxicity in rats (Lyubimov et al, 1998). In addition, it is a potent competitor of the thyroid hormone (thyroxine, T4), which was indicated by the results of the in vitro TTR-binding assay (Legler and Brouwer, 2003;Hamers et al 2006;Suzuki et al, 2008); it showed weak estrogen-like activity in the human breast cancer cellline MCF-7 (Olsen et al, 2002); TBP caused an induction of aromatase activity in human adrenocortical (H295R) cell line (Cantón et al, 2005), and it induces neuroblastoma cell differentiation (Ríos et al, 2003) and disturbs cellular Ca 2+ signaling in neuroendocrine cells (PC12) (Hassenklöver et al, 2006). Exposure to TBP has also been shown to affect the development of zebrafish embryos .…”

The marine secondary metabolites 2,4-dibromophenol and 2,4,6-tribromophenol differentially modulate voltage dependent ion currents in neuroendocrine (PC12) cells

“…The selectivity of 2,4,6-TBP for calcium signals (reduction of calcium entry and release from intracellular stores) indicates the toxicity of this substance and therefore its impact on developmental processes, since calcium signals are crucial for hormonal and therefore developmental regulation. In addition, 2,4,6-TBP induces aromatase activity, which balances estrogen levels (Cantón et al, 2005). 2,4-DBP comparably reduces in-and outward currents; this interesting finding suggests more general target structures and target molecules for this compound and in support of this, 2,4-DBP binds to estrogen receptors as possible endocrine disruptors (Olsen et al, 2002).…”

Effects of tris(2,3-dibromopropyl) isocyanurate on steroidogenesis in H295R cells

“…Reduction of CYP19 gene expression might result in a loss of aromatase enzyme concentrations and activities. It has been hypothesized that the alteration of aromatase activity by various chemicals represents a potential mechanism of endocrine disruption (Cantón et al 2005;Sanderson et al 2000Sanderson et al , 2004. It is possible that TBC might exert anti-estrogenic effects via aromatase inhibition if this mechanism could occur in vitro and in vivo models.…”