Polybrominated diphenylethers (PBDEs) are used as additive flame-retardants in consumer products to reduce the chances of ignition and burning. Levels of certain PBDE congeners have been increasing in fish, wildlife, and human tissues during the last decades. Some PBDEs are lipophilic and persistent, resulting in bioaccumulation in the environment. The structural similarity of PBDEs to other polyhalogenated aromatic hydrocarbons such as PCBs, has raised concerns that PBDEs might act as agonists for the aryl hydrocarbon receptor (AhR). To study the possible AhR-mediated effects of the environmentally relevant PBDEs (BDE47, 77, 99, 100, 153, 154, 183, 209), the induction of cytochrome P450-1A1 (CYP1A1) was studied in human breast carcinoma (MCF-7), human hepatocellular carcinoma (HepG2), and rat hepatoma (H4IIE) cells. 7-Ethoxyresorufin-O-deethylase (EROD) was used as a marker for CYP1A1 activity. Cells were exposed for 72 h to various PBDE concentrations (0.01-10 microM). Positive controls were 2,3,7,8-TCDD (0.001-2.5 nM) and PCB126 (0.01-10 nM). None of these PBDEs was capable of inducing EROD activity; this was confirmed by real time RT-PCR for CYP1A1 mRNA. However, in cells exposed to PBDEs in combination with TCDD, a concentration-dependent decrease in TCDD-induced EROD activity occurred. Co-exposure of BDE153 (10 muM) and a maximally inducing concentration of TCDD (1 nM) reduced EROD activity to 49% of the maximum induction by TCDD alone. All tested PBDEs showed similar effects in each cell line, though quantitative differences were observed. The observed decrease in CYP1A1 activity was not due to PBDE-dependent catalytic inhibition of EROD activity or cytotoxicity, nor were decreased CYP1A1 mRNA levels observed. However, inhibition of luciferase induction in mouse (Hepa) and rat (H4IIE) hepatoma cells containing a stably transfected AhR-responsive luciferase reporter gene, suggests that BDE77 is a weak AhR antagonist or partial agonist.
Polybrominated diphenyl ethers (PBDEs) are brominated flame retardants that have been in use as additives in various consumer products. Structural similarities of PBDEs with other polyhalogenated aromatic hydrocarbons that show affinity for the aryl hydrocarbon receptor (AhR), such as some polychlorinated biphenyls, raised concerns about their possible dioxin-like properties. We studied the ability of environmentally relevant PBDEs (BDE-47, -99, -100, -153, -154, and -183) and the "planar" congener BDE-77 to bind and/or activate the AhR in stably transfected rodent hepatoma cell lines with an AhR-responsive enhanced green fluorescent protein (AhR-EGFP) reporter gene (H1G1.1c3 mouse and H4G1.1c2 rat hepatoma). 7-Ethoxyresorufin-O-deethylation (EROD) was used as a marker for CYP1A1 activity. Dose- and bromination-specific inhibition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced responses was measured by their ability to inhibit the induction of AhR-EGFP expression and EROD activity. Individual exposure to these PBDEs did not result in any increase in induction of AhR-EGFP or CYP1A1 activity. The lower brominated PBDEs showed the strongest inhibitory effect on TCDD-induced activities in both cell lines. While the highest brominated PBDE tested, BDE-183, inhibited EROD activity, it did not affect the induction of AhR-EGFP expression. Similar findings were observed after exposing stably transfected human hepatoma (xenobiotic response element [XRE]-HepG2) cells to these PBDEs, resulting in a small but statically significant agonistic effect on XRE-driven luciferase activity. Co-exposure with TCDD resulted again in antagonistic effects, confirming that the inhibitory effect of these PBDEs on TCDD-induced responses was not only due to direct interaction at receptor level but also at DNA-binding level. This antagonism was confirmed for BDE-99 in HepG2 cells transiently transfected with a Gal4-AhR construct and the corresponding Gal4-Luc reporter gene. In addition, a chromatin immunoprecipitation assay further confirmed that BDE-99 could bind to the AhR and activate the AhR nuclear translocation and dioxin responsive element (DRE) binding in the context of the CYP1A1 promoter. However, the transactivation function of the BDE-99-activated AhR seems to be very weak. These combined results suggest that PBDEs do bind but not activate the AhR-AhR nuclear translocator protein-XRE complex.
The ability of murine-derived embryonic stem cells (D3) to differentiate into cardiomyocytes is the basis of the embryonic stem cell test (EST). With the EST, chemicals and pharmaceuticals can be assessed for their embryotoxic potency early on in the development process. In order to come to a higher throughput EST, a 96-well based method was developed based on low attachment well plates that allow for the formation of embryonic bodies from which the stem cells can differentiate. Twelve test compounds were selected based on their reported in vitro and in vivo embryotoxic potency. In the 96-well based EST, reportedly strong embryotoxic compounds 5-fluorouracil, 6-aminonicotinamide (6AN), methylmercury chloride, and hydroxyurea were correctly ranked with corresponding Relative Embryotoxic Potency values (REP, based on the EC(50) (microM) value of 6AN) of 2.6 +/- 2.9, 1, 2.0 +/- 3.1, and 0.07 +/- 0.05, respectively. Moderately embryotoxic compounds valproic acid, boric acid, methoxyacetic acid, and lithium chloride resulted in a correct ranking with REP values of 0.01 +/- 0.003, 0.001 +/- 0.001, 0.0007 +/- 0.001, and 0.0006 +/- 0.0004, respectively. The included nonembryotoxic compounds Penicillin G, acrylamide, and saccharin did not result in an inhibition of D3 cells to differentiate into cardiomyocytes, other than related to cytotoxicity (REP value of 0.00001). However, diphenhydramine resulted in an inhibitory effect similarly to the strong embryotoxic compound hydroxyurea, with a REP value of 0.40 +/- 0.36. However, further evaluation suggested this was due to direct inhibition of the contractile capacity of the D3 cardiomyocytes, rather than an embryotoxic mechanism. The 96-well based EST is a promising addition to the screening process of newly developed chemicals and pharmaceuticals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.