149 THYROID HORMONE MARKER DEIODINASE 1 INDUCED BY 2,4,6-TRIBROMOPHENOL IN GH3 PITUITARY CELLS

Abstract

Numerous medical materials and products in daily use are made of chemicals that are rarely found in the environment. Some of these chemicals may alter reproductive and thyroid function by interfering with endogenous estrogens, progesterone, and thyroid hormones. They are called endocrine-disrupting chemicals (EDC). To inhibit ignition and to reduce flammability of products, brominated flame retardants (BFR) are added to some products. 2,4,6-Tribromophenol (TBP) is an emerging EDC that is produced in some countries. To compare this emerging chemical to traditional EDC, we investigated this chemical in a rat pituitary cell line, GH3 cells. The GH3 cells were starved without phenol red for 7 days to eliminate any steroidogenic effect. Then, GH3 cells were incubated with 1–850 (thyroid receptor antagonist; 5.0 × 10^–6 M) for 1 day before treatment with vehicle, triiodothyronine (T3; 1.0 × 10^–9 M) and TBP (1.0 × 10^–6 M) for 24 h, respectively. The TBP dose was determined from a previous pilot experiment using high, middle, and low doses. Each group of cells was prepared in triplicate and experiments were performed twice. Type I iodothyronine deiodinase (Dio1; thyromimetic marker), thyroid hormone receptor β, isoform 2 (Thrβ2), and growth hormone (Gh) were quantified by RT-qPCR. All data were analysed with a one-way ANOVA and Tukey’s studentized range test. Statistical analyses were performed with SAS software (SAS Institute Inc., Cary, NC, USA); P-values <0.05 were considered significant. RT-qPCR analysis was performed using the 2^–ΔΔCT method employing 18S RNA (18S) as endogenous reference gene. Each gene of interest was normalized to vehicle. The mRNA expression of Dio1 and Gh were up-regulated via TBP treatment, but was lower than that of the T3-treated positive control. In pretreatments of 1–850 with T3 or TBP, mRNA levels of Dio1 were diminished through inhibition of thyroid receptor, but Gh mRNA level was not diminished. The mRNA expression of Thrβ2 was decreased in independent treatment of T3 or TBP, and no change in pretreatments of 1–850 with T3 or TBP. Although interfering effects of TBP on thyroid function have been partly studied, the dangers of TBP have been not yet obviously verified. In this study, we confirmed a thyromimetic effect of TBP mediated by thyroid receptor on GH3 cells.