The Thyroid Disruptor 1,1,1-Trichloro-2,2-Bis(p-Chlorophenyl)-Ethane Appears to Be an Uncompetitive Inverse Agonist for the Thyrotropin Receptor

Abstract

In this study, we aimed at establishing whether two previously identified thyroid disruptors, the insecticide 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and Aroclor 1254 (a complex mixture of polychlorinated water), may inhibit thyrotropin (TSH) receptor (TSHr) activity. DDT and Aroclor 1254 were shown to inhibit both the basal and bovine TSH (bTSH)-stimulated accumulation of cAMP in Chinese hamster ovary (CHO)-K1 cells stably transfected with the TSHr. Furthermore, both DDT and Aroclor 1254 did indeed prevent cAMP accumulation, as induced by the constitutive activity of a point mutant TSHr(I486M) transiently transfected in African green monkey kidney fibroblast (COS)-7 cells. Neither trypsin digestion of the extracellular domain (ECD) nor deletion of the ECD in a mutant TSHr trunk transiently transfected in COS-7 cells counteracted the inhibitory activity of DDT and Aroclor 1254. DDT exerted a weak inhibitory activity against forskolin in both CHO-K1 and COS-7 cells, whereas it was nil against the agonists dopamine and 5Ј-(N-ethyl-carboxamido)-adenosine (NECA) in CHO cells stably transfected with the dopamine D 1 receptor and in COS-7 cells transiently transfected with the adenosine type 2a receptor (A 2 a) receptor. Furthermore, DDT was inactive against the stimulation by isoproterenol of the endogenously expressed ␤ 2 adrenergic receptor in COS-7 cells. Conversely, Aroclor 1254 inhibited completely forskolin activity in CHO-K1 cells but not in COS-7 cells. Furthermore, it did not prevent accumulation of cAMP as induced by NECA in A 2 a transfected cells. The analog of DDT, diphenylethylene, was inactive against bTSH-induced increase in cAMP in CHO-K1 cells stably transfected with the TSHr. We interpreted these results as indicating that DDT and possibly Aroclor 1254 may have an uncompetitive inverse agonist activity for the TSHr.

Thyroid disruptor 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) prevents internalization of TSH receptor

“…More recently, we have analysed in detail whether this effect on thyroid homeostasis occurs via interaction with the TSHr. We have thus established that DDT inhibits both the basal and the TSH-stimulated accumulation of cAMP in Chinese hamster ovary CHO-K1 cells stably transfected with TSHr (Rossi et al 2007). Furthermore, DDT can still inhibit the basal TSHr activity, even when deprived of the extracellular domain, suggesting that DDT interacts directly with the transmembrane domain of the TSHr.…”

“…As controls, cells transfected with dopamine D1 and adenosine type A2a receptors have been shown to respond specifically to their respective agonists, even when stimulated in the presence of DDT. These observations have been interpreted as indicating that DDT acts specifically as an inverse agonist of the TSHr itself (Rossi et al 2007).…”

Dichlorodiphenyltrichloroethane (DDT) induced extracellular vesicle formation: a potential role in organochlorine increased risk of Parkinson's disease

“…We studied in detail the mechanism by which DDT causes this effect and we demonstrated that DDT inhibits TSH receptor function by modifying the lipid organization of the cell membrane (De Gregorio et al 2011, Picchietti et al 2009, Rossi et al 2007). The fact that DDT is highly lipophilic might count for these inhibitory effects on the TSH receptor activity, inasmuch highly lipophilic molecules are known to deplete the cholesterol content in the cell membrane, which results in a defective organization of the raft microdomains that contain the TSH receptors (De Gregorio et al 2011).…”

“…The literature available for DDT, due to its use as an insecticide worldwide, indicates around 10 μM the serum concentration of this compound in chronically exposed subjects (Chen et al 2005, De Jager et al 2006, and this is the concentration at which DDT begins to have an effect in our experimental setting (Rossi et al 2007). …”

“…The results observed with DDT then, suggested that the diffuse chlorination of DDT, together with its high lipophilicity, were responsible for the effects on the vesicle formation and on TSH receptor activity, and more importantly that, other organochlorine pesticides might show similar properties. For instance, Aroclor 1254, an organochlorine derivative structurally related to DDT, clearly alter the function of TSH receptors (Rossi et al 2007). Furthermore, Choi and others (2012) have shown that several polychlorinated biphenyl modify the blood brain barrier permeability in mice by altering lipid rafts organization, and this is consistent with the data of Eum and colleagues (2015) who demonstrated that the polychlorinated biphenyls PCB153 disrupts the brain endothelial barrier by altering the function of lipid raft-associated proteins such as phosphatase 2A and matrix metalloproteinase-2.…”