ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 P701

Thyronamines are isozyme specific substrates of deiodinases

Susanne Piehl1, Thomas Heberer2, Gabor Balizs2, Thomas Scanlan3, René Smits4, Beate Koksch4 & Josef Köhrle1


1Institut für Experimentelle Endokrinologie und Endokrinologisches Forschungszentrum der Charité EnForCé, Charité – Universitätsmedizin Berlin, Berlin, Germany; 2Federal Institute for Risk Assessment, Berlin, Germany; 3Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon, USA; 4Department of Chemistry and Biochemistry – Organic Chemistry, Free University of Berlin, Berlin, Germany.


3-iodothyronamine (3-T1AM) and thyronamine (T0AM) are novel endogenous signaling molecules that exhibit great structural similarity to thyroid hormones but apparently antagonize classical thyroid hormone (T3) actions. Their proposed biosynthesis from thyroid hormones would require decarboxylation and more or less extensive deiodination. Deiodinases (Dio1, Dio2 and Dio3) catalyze the removal of iodine from their substrates. Since a role of deiodinases in thyronamine biosynthesis requires their ability to accept thyronamines as substrates, we investigated whether thyronamines are converted by deiodinases.

Thyronamines were incubated with isozyme specific deiodinase preparations. Deiodination products were analyzed using a newly established method applying liquid chromatography and tandem mass spectrometry (LC-MS/MS). Phenolic ring deiodinations of 3,3′,5′-triiodothyronamine (rT3AM), 3′,5′-diiodothyronamine (3′,5′-T2AM), 3,3′-diiodothyronamine (3,3′-T2AM) as well as tyrosyl ring deiodinations of 3,5,3′-triiodothyronamine (T3AM) and 3,5-diiodothyronamine (3,5-T2AM) were observed with Dio1. These reactions were completely inhibited by the Dio1 specific inhibitor 6n-propyl-2-thiouracil (PTU). Dio2 containing preparations also deiodinated rT3AM and 3′,5′-T2AM at the phenolic rings but in a PTU-insensitive fashion. All thyronamines with tyrosyl ring iodine atoms were 5(3)-deiodinated by Dio3 containing preparations. In functional competition assays, the newly identified thyronamine substrates inhibited an established iodothyronine deiodination reaction. By contrast, thyronamines which had been excluded as deiodinase substrates in LC-MS/MS experiments, failed to show any effect in the competition assays, thus verifying the former results.

These data support a role for deiodinases in thyronamine biosynthesis and contribute to confining the biosynthetic pathways for 3-T1AM and T0AM.

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