Iodothyronine deiodinase (DIO) (DIO)

Iodothyronine deiodinases are a family of three selenoprotein enzymes (DIO1, DIO2, and DIO3) that play a pivotal role in the peripheral metabolism and regulation of thyroid hormones (Bianco et al., 2002, Endocrine Reviews). These enzymes catalyze the removal of iodine atoms from the outer or inner rings of iodothyronines, thereby activating or inactivating them (Gereben et al., 2008, Endocrine Reviews). Specifically, DIO1 and DIO2 convert the precursor thyroxine (T4) into the biologically active triiodothyronine (T3), while DIO3 serves as the primary inactivator, converting T4 to reverse T3 (rT3) and T3 to T2 (StatPearls, 2023). This local control allows tissues to tailor thyroid hormone signaling independently of circulating levels, which is essential for normal development and metabolic homeostasis (UniProt P49221). Clinically, these enzymes are targets for treating hyperthyroidism; for instance, propylthiouracil inhibits DIO1 to rapidly decrease T3 production during a thyroid storm (PubMed, PMID: 29494050). Dysregulation of deiodinase activity is associated with various conditions, including non-thyroidal illness syndrome and certain types of tumors that cause consumptive hypothyroidism (NIH, 2022). Furthermore, certain drugs like amiodarone can interfere with these enzymes, leading to complex thyroid dysfunction (PubMed, PMID: 30107158). Understanding the tissue-specific expression and regulation of these enzymes is crucial for managing thyroid-related pathologies and optimizing hormone replacement therapies.

Other names

DeiodinaseThyroid hormone deiodinaseSelenocysteine-containing deiodinaseIodothyronine 5'-deiodinaseIodothyronine 5-deiodinaseThyroxine 5'-deiodinaseType 1 iodothyronine deiodinaseType 2 iodothyronine deiodinaseType 3 iodothyronine deiodinaseDIO1DIO2DIO3

The primary mechanism of action for drugs targeting iodothyronine deiodinases involves the inhibition of the 5'-deiodination process, which prevents the conversion of the prohormone thyroxine (T4) into the more metabolically active triiodothyronine (T3) (StatPearls, 2023). For example, propylthiouracil (PTU) acts as an uncompetitive inhibitor of DIO1 by reacting with the enzyme-sulfenyl iodide intermediate (Bianco et al., 2002, Endocrine Reviews). Other agents, such as iodinated contrast media (e.g., iopanoic acid), competitively inhibit the enzyme's access to the substrate, thereby lowering systemic T3 levels in thyrotoxic states (PubMed, PMID: 29494050).