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| 2. |
- Hamers, Timo, et al.
(författare)
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Biotransformation of brominated flame retardants into potentially endocrine-disrupting metabolites, with special attention to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47).
- 2008
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Ingår i: Mol Nutr Food Res. - 1613-4125. ; 52:2, s. 284-298
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the endocrine-disrupting (ED) potency of metabolites from brominated flame retardants (BFRs) was determined. Metabolites were obtained by incubating single-parent compound BFRs with phenobarbital-induced rat liver microsomes. Incubation extracts were tested in seven in vitro bioassays for their potency to compete with thyroxine for binding to transthyretin (TTR), to inhibit estradiol-sulfotransferase (E2SULT), to interact with thyroid hormone-mediated cell proliferation, and to (in-)activate the androgen, progesterone, estrogen, or aryl hydrocarbon receptor. For most BFRs, TTR-binding potencies, and to a lesser extent E2SULT-inhibiting potencies, significantly increased after biotransformation. Microsomal incubation had less pronounced effects on other ED modes of action, due to low biotransformation efficiency and background activities determined in control incubations without BFRs. Moreover, cell-based bioassays suffered from cytotoxicity from metabolites of lower-brominated polybrominated diphenyl ethers. For the environmentally relevant 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), six hydroxylated metabolites were identified. Individual metabolites had TTR-binding and E2SULT-inhibiting potencies 160-1600 and 2.2-220 times higher than BDE-47 itself, whereas their combined potencies in a realistic mixture were well predicted via concentration addition. In combination with other environmentally relevant hydroxylated organohalogens acting on TTR-binding and E2SULT inhibition, internal exposure to BFR metabolites may significantly contribute to the overall risk of endocrine disruption.
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| 3. |
- Hamers, Timo, et al.
(författare)
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In vitro profiling of the endocrine-disrupting potency of brominated flame retardants
- 2006
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Ingår i: Toxicological Sciences. - : Oxford University Press (OUP). - 1096-6080 .- 1096-0929. ; 92:1, s. 157-73
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Over the last few years, increasing evidence has become available that some brominated flame retardants (BFRs) may have endocrine-disrupting (ED) potencies. The goal of the current study was to perform a systematic in vitro screening of the ED potencies of BFRs (1) to elucidate possible modes of action of BFRs in man and wildlife and (2) to classify BFRs with similar profiles of ED potencies. A test set of 27 individual BFRs were selected, consisting of 19 polybrominated diphenyl ether congeners, tetrabromobisphenol-A, hexabromocyclododecane, 2,4,6-tribromophenol, ortho-hydroxylated brominated diphenyl ether 47, and tetrabromobisphenol-A–bis(2,3)dibromopropyl ether. All BFRs were tested for their potency to interact with the arylhydrocarbon receptor, androgen receptor (AR), progesterone receptor (PR), and estrogen receptor. In addition, all BFRs were tested for their potency to inhibit estradiol (sulfation by estradiol sulfotransferase (E2SULT), to interfere with thyroid hormone 3,3',5-triiodothyronine (T3)–mediated cell proliferation, and to compete with T3-precursor thyroxine for binding to the plasma transport protein transthyretin (TTR). The results of the in vitro screening indicated that BFRs have ED potencies, some of which had not or only marginally been described before (AR antagonism, PR antagonism, E2SULT inhibition, and potentiation of T3-mediated effects). For some BFRs, the potency to induce AR antagonism, E2SULT inhibition, and TTR competition was higher than for natural ligands or clinical drugs used as positive controls. Based on their similarity in ED profiles, BFRs were classified into five different clusters. These findings support further investigation of the potential ED effects of these environmentally relevant BFRs in man and wildlife.
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| 4. |
- Harju, Mikael, et al.
(författare)
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Quantitative Structure–Activity Relationship Modeling on in Vitro Endocrine Effects and Metabolic Stability Involving 26 Selected Brominated Flame Retardants
- 2007
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Ingår i: Environmental Toxicology and Chemistry. - 1552-8618. ; 26:4, s. 816-26
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Tidskriftsartikel (refereegranskat)abstract
- In this work, quantitative structure–activity relationships (QSARs) were developed to aid human and environmental risk assessment processes for brominated flame retardants (BFRs). Brominated flame retardants, such as the high-production-volume chemicals polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A, and hexabromocyclododecane, have been identified as potential endocrine disruptors. Quantitative structure–activity relationship models were built based on the in vitro potencies of 26 selected BFRs. The in vitro assays included interactions with, for example, androgen, progesterone, estrogen, and dioxin (aryl hydrocarbon) receptor, plus competition with thyroxine for its plasma carrier protein (transthyretin), inhibition of estradiol sulfation via sulfotransferase, and finally, rate of metabolization. The QSAR modeling, a number of physicochemical parameters were calculated describing the electronic, lipophilic, and structural characteristics of the molecules. These include frontier molecular orbitals, molecular charges, polarities, log octanol/water partitioning coefficient, and two- and three-dimensional molecular properties. Experimental properties were included and measured for PBDEs, such as their individual ultraviolet spectra (200–320 nm) and retention times on three different high-performance liquid chromatography columns and one nonpolar gas chromatography column. Quantitative structure–activity relationship models based on androgen antagonism and metabolic degradation rates generally gave similar results, suggesting that lower-brominated PBDEs with bromine substitutions in ortho positions and bromine-free meta- and para positions had the highest potencies and metabolic degradation rates. Predictions made for the constituents of the technical flame retardant Bromkal 70-5DE found BDE 17 to be a potent androgen antagonist and BDE 66, which is a relevant PBDE in environmental samples, to be only a weak antagonist.
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| 5. |
- Weiss, Jana M, et al.
(författare)
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Competitive Binding of Poly- and Perfluorinated Compounds to the Thyroid Hormone Transport Protein Transthyretin
- 2009
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Ingår i: Toxicological sciences : an official journal of the Society of Toxicology. - : Oxford University Press of the Society of Toxicology. - 1096-0929. ; 109:2, s. 206-16
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Tidskriftsartikel (refereegranskat)abstract
- Due to their unique surfactant properties, poly- and perfluorinated compounds (PFCs) have been extensively used, and can be found all over the environment.. Concern about their environmental fate and toxicological properties have initiated several research projects. In the present study, we investigated if PFCs can compete with thyroxin (T4, i.e. the transport form of thyroid hormone) for binding to the human thyroid hormone transport protein transthyretin (TTR). Such competitive capacity may lead to decreased thyroid hormone levels as previously reported for animals exposed to PFCs. Twenty four PFCs, together with six structurally similar natural fatty acids, were tested for binding capacity in a radioligand binding assay. The binding potency decreased in the order: PFHxS>PFOS/PFOA>PFHpA>L-PFOSi>PFNA, with TTR binding potencies 12.5-50 times lower than the natural ligand thyroxine (T4). Some lower molecular weight compounds with structural similarity to these PFCs were >100 times less potent than T4. Simple descriptors based on the two dimensional molecular structures of the compounds were used to visualize the chemical variation and to model the structure-activity relationship for the competitive potencies of the TTR-binding compounds. The models indicated the dependence on molecular size and functional group(s), but demanded a more detailed description of the chemical properties and data for validation and further QSAR development. Competitive binding of PFCs to TTR as observed for human TTR in the present study, may explain altered thyroid hormone levels described for PFC-exposed rats and monkeys. Median human blood levels of the most potent TTR-binding PFCs are 1-2 orders of magnitude lower than IC50-values determined in the present study. In addition, this study contributes to the understanding of the bioaccumulation of PFCs in man and possibly in other wildlife species.
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