In vitro effects of natural phytoestrogens on sodium/iodide symporter mediated thyroid iodide uptake by using a differentiated TSH-dependent cell line

Abstract Soy food health effects are due to isoflavone (ISF) components functioning as phytoestrogens similar to natural estrogen. Epidemiological data suggest a role of estrogens in pathogenesis of thyroid diseases explaining their prevalence in women. Aim of this study was to determine in vitro effects of isoflavones, soybean extract and Cimicifuga extract on iodide uptake, a crucial step in thyroid hormone biosynthesis, by using a differentiated TSH-dependent cell line (FRTL5). Estradiol didn’t influence iodide uptake and sodium-iodide symporter (NIS) mRNA expression in FRTL-5 cells. None of analyzed glycoside or aglycone isoflavone determined a significant inhibition of iodide uptake, while both isoflavone rich and triterpene rich extracts determined a significant reduction of iodide uptake at the higher doses. While soybean and Cimicifuga extracts inhibited iodide uptake at high doses, none of analyzed isoflavone exerted this effect. These elevated doses, however, are never reached in the blood following intake of food supplements.