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BackgroundThere is growing evidence that, in addition to the reproductive system, the hypothalamic–pituitary–thyroid axis is a target of endocrine-disrupting compounds (EDCs). However, this is not reflected adequately in current screening and assessment procedures for endocrine activity that to date determine only general parameters of thyroid function.Objective and MethodsWe used several in vitro and ex vivo assays in an attempt to identify suitable biomarkers for antithyroid action testing a selected panel of putative EDCs.ResultsIn vitro we detected stimulation or inhibition of iodide uptake into FRTL-5 rat thyroid cells, inhibition of thyroid hormone binding to transthyretin, agonistic or antagonistic effects in a thyroid hormone receptor–dependent reporter assay, and inhibition of thyroid peroxidase using a novel assay system based on human recombinant thyroperoxidase that might be suitable for routine screening for potential EDCs. In rats, chronic application of several EDCs led to changes in thyroid morphology, alterations of thyrotropin and thyroid hormone serum levels as well as alterations in peripheral thyroid hormone–regulated end points such as malic enzyme and type I 5′-deiodinase activity.ConclusionsAs the effects of EDCs do not reflect classic mechanisms of hormone-dependent regulation and feedback, we believe multitarget and multimodal actions of EDCs affect the hypothalamic–pituitary–thyroid axis. These complex effects require a diverse approach for screening, evaluation, and risk assessment of potential antithyroid compounds. This approach involves novel in vitro or cell-based screening assays in order to assess thyroid hormone synthesis, transport, metabolism, and action as well as in vivo assays to measure thyroid hormone–regulated tissue-specific and developmental end points in animals.

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Important enzymes for thyroid hormone metabolism, antioxidative defense, and intracellular redox control contain selenocysteine (Sec) in their active centers. Expression of these selenoproteins is tightly controlled, and a sex-specific phenotype is observed on disturbance of selenium (Se) transport in mice. Therefore, we analyzed Se concentrations and expression levels of several selenoproteins including type I iodothyronine deiodinase (Dio1) and glutathione peroxidase (GPx) isozymes in male and female mice. On regular lab chow, serum Se levels were comparable, but serum GPx3 activity was higher in females than males (1.3-fold). Selenoprotein P (SePP) mRNA levels were higher in livers (1.3-fold) and lower in kidneys (to 31%) in female compared with male mice. Orchidectomy alleviated the sex-specific differences in SePP mRNA amounts, indicating modulatory effects of androgens on SePP expression. Female mice expressed higher levels of Dio1 mRNA in kidney (2.6-fold) and liver (1.4-fold) in comparison with male mice. This sexual dimorphic expression of Dio1 mRNA was paralleled by increased Dio1 activity in female kidney (1.8-fold) but not in liver in which males expressed higher Dio1 activity (2.8-fold). Interestingly, Se deficiency decreased Dio1 activity more effectively in males than females, and resulting hepatic enzyme levels were then comparable between the sexes. At the same time, the sex-specific difference of Dio1 activity widened in kidney. Orchidectomy or estradiol treatment of ovariectomized females impacted stronger on renal than hepatic Dio1 expression. Thus, we conclude that Se-dependent posttranscriptional mechanisms are operational that affect either translational efficiency or Dio1 stability in a sex- and tissue-specific manner.

Culture medium of mesenchymal stromal cells (MSCs) is usually supplemented with either human platelet lysate (HPL) or fetal calf serum (FCS). Many studies have demonstrated that proliferation and cellular morphology are affected by these supplements – it is therefore important to determine if they favor outgrowth of different subpopulations and thereby impact on the heterogeneous composition of MSCs. We have isolated and expanded human bone marrow-derived MSCs in parallel with HPL or FCS and demonstrated that HPL significantly increases proliferation and leads to dramatic differences in cellular morphology. Remarkably, global DNA-methylation profiles did not reveal any significant differences. Even at the transcriptomic level, there were only moderate changes in pairwise comparison. Furthermore, the effects on proliferation, cytoskeletal organization, and focal adhesions were reversible by interchanging to opposite culture conditions. These results indicate that cultivation of MSCs with HPL or FCS has no systematic bias for specific cell types.