Receptor

Organic chemistry

Stereochemistry

Pollutant

Biology

Binding site

Transthyretin

Endocrinology

Nursing

Chemistry

Fire retardant

Thyroxine-binding globulin

Tetrabromobisphenol A

Diphenyl ether

Polybrominated diphenyl ethers

Thyroid hormones

Ether

Docking (animal)

Biochemistry

Hormone

Medicine

Environmental Health Perspectives

Background: Tetrabromobisphenol A (TBBPA) mono-ether structural analogs, identified as the by-products or transformation products of commercial TBBPA bis-ether derivatives, have been identified as emerging widespread pollutants. However, there is very little information regarding their toxicological effects. Objective: We aimed to explore the potential thyroid hormone (TH) system–disrupting effect of TBBPA mono-ether structural analogs. Methods: The binding potencies of chemicals toward human TH transport proteins [transthyretin (TTR) and thyroxine-binding globulin (TBG)] and receptors [TRα ligand-binding domain (LBD) and TRβ-LBD] were determined by fluorescence competitive binding assays. Molecular docking was used to simulate the binding modes of the chemicals with the proteins. The cellular TR-disrupting potencies of chemicals were assessed by a GH3 cell proliferation assay. The intracellular concentrations of the chemicals were measured by high-performance liquid chromatography and mass spectrometry. Results: TBBPA mono-ether structural analogs bound to TTR with half maximal inhibitory concentrations ranging from 0.1μM to 1.0μM but did not bind to TBG. They also bound to both subtypes of TR-LBDs with 20% maximal inhibitory concentrations ranging from 4.0μM to 50.0μM. The docking results showed that the analogs fit into the ligand-binding pockets of TTR and TR-LBDs with binding modes similar to that of TBBPA. These compounds likely induced GH3 cell proliferation via TR [with the lowest effective concentrations (LOECs) ranging from 0.3μM to 2.5μM] and further enhanced TH-induced GH3 cell proliferation (with LOECs ranging from 0.3μM to 1.2μM). Compared with TBBPA, TBBPA-mono(2,3-dibromopropyl ether) showed a 4.18-fold higher GH3 cell proliferation effect and 105-fold higher cell membrane transportation ability. Conclusion: This study provided a possible mechanism underlying the difference in TTR or TR binding by novel TBBPA structural analogs. These compounds might exert TH system–disrupting effects by disrupting TH transport in circulation and TR activity in TH-responsive cells. https://doi.org/10.1289/EHP6498

Binding and Activity of Tetrabromobisphenol A Mono-Ether Structural Analogs to Thyroid Hormone Transport Proteins and Receptors