Comparison of effects of Iodine-deficiency and perchlorate on thyroid

Perchlorate, which is a ubiquitous and persistent ion, competitively interferes with iodide accumulation in the thyroid, causing iodine deficiency, which may result in reduced thyroid hormone synthesis and secretion. Human studies suggest that perchlorate presents very little risk in healthy individuals; however, the precautionary principle demands that the sensitive populations of iodine deficient adults and mothers require extra consideration. In an attempt to determine if the effects on gene expression were similar, we compared the thyroidal effects of perchlorate (10 mg/kg) treatment for 14 days in drinking water with those caused by 8 weeks of Iodine-deficiency 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. We compared the 2-fold gene changes due to I-deficiency with changes due to perchlorate treatment. 189 transcripts were changed by the Iodine-deficient diet and 722 transcripts were changed by the perchlorate treatment. 34% of the transcripts changed by the I-deficient diet were also changed by perchlorate and generally in the same direction. three specific transporter genes, AQP1, NIS, & SLC22A3 were changed by both treatments, indicating that the membrane specific changes were similar. Iodine-deficiency primarily caused changes in retinol and calcium signaling pathways and perchlorate primarily caused changes related to the accumulation of extracellular matrix proteins. This study provides evidence that perchlorate, at least at this dose level, changes more genes and changes different genes compared to iodine deficiency.

24