The effects of perchlorate on thyroidal gene expression are different from the effects of iodide deficiency.

Perchlorate (ClO4⁻), which is a ubiquitous and persistent ion, competitively interferes with iodide (I) accumulation in the thyroid, producing I deficiency (ID), which may result in reduced thyroid hormone synthesis and secretion. Human studies suggest that ClO4⁻ presents little risk in healthy individuals; however, the precautionary principle demands that the sensitive populations of ID adults and mothers require extra consideration. In an attempt to determine whether the effects on gene expression were similar, the thyroidal effects of ClO4⁻ (10 mg/kg) treatment for 14 d in drinking water were compared with those produced by 8 wk of ID in rats. The thyroids were collected (n = 3 each group) and total mRNA was analyzed using the Affymetrix Rat Genome 230 2.0 GeneChip. Changes in gene expression were compared with appropriate control groups. The twofold gene changes due to ID were compared with alterations due to ClO4⁻ treatment. One hundred and eighty-nine transcripts were changed by the ID diet and 722 transcripts were altered by the ClO4⁻ treatment. Thirty-four percent of the transcripts changed by the I-deficient diet were also altered by ClO4⁻ and generally in the same direction. Three specific transporter genes, AQP1, NIS, and SLC22A3, were changed by both treatments, indicating that the membrane-specific changes were similar. Iodide deficiency primarily produced alterations in retinol and calcium signaling pathways and ClO4⁻ primarily produced changes related to the accumulation of extracellular matrix proteins. This study provides evidence that ClO4⁻, at least at this dose level, changes more genes and alters different genes compared to ID.

A method for the analysis of six thyroid hormones in thyroid gland by liquid chromatography-tandem mass spectrometry.

Perchlorate can competitively inhibit iodide uptake by the thyroid gland (TG) via the sodium/iodide symporter, consequently reducing the production of thyroid hormones (THs). Until recently, the effects of perchlorate on TH homeostasis are being examined through measurement of serum levels of TH, by immunoassay (IA)-based methods. IA methods are fast, but for TH analysis, they are compromised by the lack of adequate specificity. Therefore, selective and sensitive methods for the analysis of THs in TG are needed, for assessment of the effects of perchlorate on TH homeostasis. In this study, we developed a method for the analysis of six THs: L-thyroxine (T(4)), 3,3',5-triiodo-L-thyronine (T(3)), 3,3',5'-triiodo-L-thyronine (rT(3)), 3,5-diiodo-L-thyronine (3,5-T(2)), 3,3'-diiodo-L-thyronine (3,3'-T(2)), and 3-iodo-L-thyronine (3-T(1)) in TG, using liquid chromatography (LC)-tandem mass spectrometry (MS/MS). TGs used in this study were from rats that had been placed on either iodide-deficient diet or iodide-sufficient diet, and that had either been provided with perchlorate in drinking water (10 mg/kg/day) or control water. TGs were extracted by pronase digestion and then analyzed by LC-MS/MS. The instrumental calibration range for each TH ranged from 1 to 200 ng/ml and showed a high linearity (r>0.99). The method quantification limits (LOQs) were determined to be 0.25 ng/mg TG for 3-T(1); 0.33 ng/mg TG for 3,3'- and 3,5-T(2); and 0.52 ng/mg TG for rT(3), T(3), and T(4). Rats were placed on an iodide-deficient or -sufficient diet for 2.5 months, and for the last 2 weeks of that period were provided either perchlorate (10 mg/kg/day) in drinking water or control water. Iodide deficiency and perchlorate administration both reduced TG stores of rT(3), T(3), and T(4). In iodide-deficient rats, perchlorate exacerbated the reduction in levels of THs in TG. With the advances in analytical methodology, the use of LC-MS/MS for measurement of hormone levels in TG will allow more comprehensive evaluations of the hypothalamic-pituitary-thyroid axis.