ToxSci Advance Access originally published online on September 22, 2005
Toxicological Sciences 2005 88(2):367-374; doi:10.1093/toxsci/kfi330
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Detection of Thyroid System–Disrupting Chemicals Using in Vitro and in Vivo Screening Assays in Xenopus laevis
* Department of Biology, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan; and BioResource Center, RIKEN Tsukuba Institute, Tsukuba 305-0074, Japan
Received July 29, 2005; accepted September 14, 2005
We developed a thyroid hormone (TH) inducible primary screening assay for the identification and assessment of man-made chemicals that interfere with the TH-signalling pathway within target cells. The assay was developed in a Xenopus laevis cell line that was transduced with a self-inactivating (SIN) lentivirus vector (LV) containing a luciferase gene. The luciferase activation in this cell line was TH-specific: 3,3',5-L-triiodothyronine (T3) > 3,3'5-L-triiodothyroacetic acid (Triac) > 3,3',5-D-triiodothyronine (D-T3), > L-thyroxine (T4) > 3,3',5'-L-triiodothyronine (rT3). The application of the ligand-dependent luciferase assay for screening for thyroid system-disrupting chemicals revealed that three phthalates (dicyclohexyl phthalate, n-butylbenzyl phthalate, and di-n-butyl phthalate), two herbicides (ioxynil and pentachlorophenol) and a miticide (dicofol) had 3,3',5-L-triiodothyronine- T3- antagonist activity at concentrations ranging from 10–6 to 10–5 M. These chemicals also inhibited the expression of the endogenous primary T3-response TH nuclear receptor ß (TRß) gene. The inhibitory characteristics of these chemicals were similar for both assays performed, although the assay for T3-dependent activation of TRß gene was more sensitive than the luciferase assay. These results indicate that the luciferase assay was a rapid method with a small intra-assay variation for the primary screening of thyroid system-disrupting chemicals. Of the six chemicals, only n-butylbenzyl phthalate and pentachlorophenol exhibited T3-antagonist activity in an in vivo metamorphosis-based assay. It should be noted that chemicals elicited thyroid system-disrupting activity in the luciferase assay did not always interfere with the thyroid system in vivo.
Key Words: endocrine toxicology – endocrine; thyroid, gene expression/regulation – receptor; nuclear hormone, endocrine toxicology – endocrine disruptors.
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