Inner Ring Deiodination Research Articles

THU230 Consumptive Hypothyroidism Secondary To Hemangioma

Abstract Disclosure: R. Thirunagari: None. D. Taha: None. Background: Peripheral Hypothyroidism also known as consumptive hypothyroidism has been rarely described in association with vascular tumors such as hemangiomas. It is due to excessive production of type 3 iodothyronine deiodinase (D3) enzyme by the hemangioma leading to increased rate of deiodination of T4 and T3 to inactive forms. Clinical case: We report a 4-year-old girl who was diagnosed with consumptive hypothyroidism at the age of 2 months. She was born at full term via scheduled C-section. Mother has hypothyroidism. She was admitted to NICU for respiratory distress and needed oxygen supplementation. She had a large hemangioma covering most of her back on exam. An ultrasound of the head/neck soft tissue showed an ill-defined lobular heterogeneous mass measuring 3.4 x 1.2 x 4.5 cm, markedly hypervascular with both arterial and venous flow likely consistent with hemangioma. At follow up plastic surgery clinic she had respiratory distress which necessitated readmission to the NICU for further workup and possible initiation of Propranolol. An abdominal ultrasound showed enlargement of the right adrenal and on further dedicated ultrasound a right suprarenal lobulated mass as well as intrathoracic soft tissue mass were found. MRI of the abdomen and thorax, revealed multiple large bilateral paraspinal masses throughout the thoracic and lower cervical spine(largest measuring 3.3 x 7 x 15 cm AP) invading the neural foramen at multiple levels, and causing mass effect on the spinal cord which is displaced to the left. There was mass effect on adjacent vascular structures without significant vascular compromise. Biopsy was consistent with hemangioma. Thyroid Newborn screening result was normal. Thyroid evaluation done at 3 months age revealed, free T4 level of 1.04 ng/dL and TSH level of 11.3 µIU/mL. She was started on Levothyroxine 50 mcg daily. Reverse T3 was elevated at 139.2 ng/dl (reference range 13-107 ng/dl) 2 weeks after treatment initiation. She was initiated on propranolol and was followed up by plastic surgery and oncology. She had a very good response to Propranolol. Follow up MRI at 4 years shows almost complete resolution of the mass. She continues to be on Levothyroxine but is requiring smaller dose. Conclusion: Infantile hemangiomas can express high levels of type 3 iodothyronine deiodinase (D3), an enzyme that catalyzes the inner-ring deiodination of T4 to reverse T3 (rT3) and of T3 to 3,3'-diiiodothyronine (T2), both of which are biologically inactive. The hypothyroidism is a result of degeneration of thyroid hormones at rates that exceed the synthetic capacity of the infant's thyroid gland. Our case illustrates the importance of closely monitoring thyroid function tests in infants with large hemangiomas even if newborn thyroid screening result is normal. Some infants may require higher Levothyroxine doses than usual. Hypothyroidism usually resolves after resolution of the mass. Presentation: Thursday, June 15, 2023

The role of the halogen bond in iodothyronine deiodinase: Dependence on chalcogen substitution in naphthyl-based mimetics.

The effects on the activity of thyroxine (T4) due to the chalcogen replacement in a series of peri-substituted naphthalenes mimicking the catalytic function of deiodinase enzymes are computationally examined using density functional theory. In particular, T4 inner-ring deiodination pathways assisted by naphthyl-based models bearing two tellurols and a tellurol-thiol pair in peri-position are explored and compared with the analogous energy profiles for the naphthalene mimic having two selenols. The presence of a halogen bond (XB) in the intermediate formed in the first step and involved in the rate-determining step of the reaction is assumed to facilitate the process increasing the rate of the reaction. The rate-determining step calculated energy barrier heights allow rationalizing the experimentally observed superior catalytic activity of tellurium containing mimics. Charge displacement analysis is used to ascertain the presence and the role of the electron density charge transfer occurring in the rate-determining step of the reaction, suggesting the incipient formation or presence of a XB interaction. © 2019 Wiley Periodicals, Inc.

Govindasamy Mugesh

Angewandte Chemie International EditionVolume 58, Issue 3 p. 662-662 Author ProfileFree Access Govindasamy Mugesh First published: 30 August 2018 https://doi.org/10.1002/anie.201809460Citations: 2AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract “When I was eighteen I wanted to be a farmer. The natural talent I would like to be gifted with is the ability to learn new languages quickly …” Find out more about Govindasamy Mugesh in his Author Profile. Govindasamy Mugesh The author presented on this page has recently published his 10th article since 2010 in Angewandte Chemie: “Remarkable Effect of Halogen Substitution on the Membrane Transport of Fluorescent Molecules in Living Cells”: H. Ungati, V. Govindaraj, G. Mugesh, Angew. Chem. Int. Ed. 2018, 57, 8989; Angew. Chem. 2018, 130, 9127. The work of G. Mugesh has been featured on the cover of Angewandte Chemie: “Chemistry and Biology in the Biosynthesis and Action of Thyroid Hormones”: S. Mondal, K. Raja, U. Schweizer, G. Mugesh, Angew. Chem. Int. Ed. 2016, 55, 7606; Angew. Chem. 2016, 128, 7734. Date of birth: May 29, 1970 Position: Professor, Indian Institute of Science, Bangalore E-mail: mugesh@iisc.ac.in Homepage: http://ipc.iisc.ac.in/gm.php ORCID: 0000-0002-5389-5309 Education: 1993 MSc, Bharathidasan University, Tiruchirappalli 1998 PhD with Prof. Harkesh B. Singh, Indian Institute of Technology, Bombay 2000–2001 Postdoctoral fellow with Prof. W.-W. du Mont, Technische Universität Braunschweig 2001–2002 Postdoctoral fellow with Prof. K. C. Nicolaou, The Scripps Research Institute, La Jolla Awards: 2011 CRSI Bronze Medal; 2011 AstraZeneca Excellence in Chemistry Award; 2012 Shanti Swarup Bhatnagar Prize; 2015 JC Bose Fellowship, Science and Engineering Research Board; 2017 National Prize for Research on Interfaces of Chemistry and Biology; Current research interests: Artificial enzymes; cellular redox regulation; ferroptosis; fluorescent probes; nitric oxide signaling; thyroid hormones Hobbies: Watching movies, cooking, driving When I was eighteen I wanted to be a farmer. The natural talent I would like to be gifted with is the ability to learn new languages quickly. The biggest challenge facing scientists is too many irrelevant and misleading research problems. My motto is work hard with dedication, serve people, and do not expect anything in return. Looking back over my career, I am satisfied! My favorite saying is “great minds discuss ideas; average minds discuss events; weak minds discuss people”. My favorite time of day is 10.30 am when I take a break and go with my colleagues to the Faculty Club on our beautiful campus for a cup of tea. I advise my students to be honest and help others. My favorite molecule is thyroxine, a simple molecule with amazing functions in the human body. My favorite composer is Isai Gnani Ilaiyaraaja, one of the greatest Indian composers, who wrote music for our every emotion in life. My favorite book is Thirukkural—a 2000-year-old classic Tamil work on ethics, which consists of 1 330 couplets (Kurals), dealing with all aspects of Aram (virtue), Poruḷ (wealth), and Inbam (love). My 5 top papers: 1“An antioxidant nanozyme that uncovers the cytoprotective potential of vanadia nanowires”: A. A. Vernekar, D. Sinha, S. Srivastava, P. U. Paramasivam, P. D'Silva, G. Mugesh, Nature Commun. 2014, 5, 5301. (Turning potentially cytotoxic vanadium into a cytoprotective redox modulator in human cells.) 2“A Chemical Model for the Inner-Ring Deiodination of Thyroxine by Iodothyronine Deiodinase”: D. Manna, G. Mugesh, Angew. Chem. Int. Ed. 2010, 49, 9246– 9249; Angew. Chem. 2010, 122, 9432. (Highlights the importance of two biological trace elements, selenium and iodine, in thyroid hormone activation and metabolism.) 3“Antibiotic Resistance: Mono- and Dinuclear Zinc Complexes as Metallo-β-Lactamase Mimics”: A. Tamilselvi, M. Nethaji, G. Mugesh, Chem. Eur. J. 2006, 12, 7797. (The key role played by metal ions in bacterial drug resistance and inactivation of β-lactam antibiotics.) 4“Biomimetic Studies on Anti-Thyroid Drugs and Thyroid Hormone Synthesis”: G. Roy, M. Nethaji, G. Mugesh, J. Am. Chem. Soc. 2004, 126, 2712. (My first paper as an independent researcher. Selenomethimazole can exert its anti-thyroid action by a mechanism different from that of the sulfur analogue.) 5“Synthesis and Structural Characterization of Monomeric Selenolato Complexes of Zinc, Cadmium, and Mercury”: G. Mugesh, H. B. Singh, R. P. Patel, R. J. Butcher, Inorg. Chem. 1998, 37, 2663. (My first ever publication. An intramolecular coordination strategy to prevent the polymerization that is generally observed for Group 12 metal chalcogenolate complexes.) Citing Literature Volume58, Issue3January 14, 2019Pages 662-662 ReferencesRelatedInformation

The variable region of iodothyronine deiodinases directs their catalytic properties and subcellular localization

The stereospecific removal of iodine from thyroid hormones is an essential first step for T3 action and is catalyzed by three different deiodinases: D2 and D3 remove iodine only from the outer or inner ring, respectively, whereas D1 catalyzes both pathways. We used in silico predictions from vertebrate deiodinase sequences to identify two domains: the N-terminal variable region (VR) containing the transmembrane, hinge and linker domains, and the conserved or globular region (CR). Given the high sequence and structural identity of the CR among paralogs as well as of the VR among orthologs but not paralogs, we hypothesized that both the catalytic properties and the subcellular localization rely on the VR. We used shark D2 and D3 as templates to build the chimeric enzymes D2VR/D3CR and D3VR/D2CR. Biochemical characterization revealed that D3VR/D2CR has inner-ring deiodination activity and T3 as preferred substrate, whereas D2VR/D3CR showed no deiodinating activity. Also, D2VR/D3CR and D3VR/D2CR reside in the endoplasmic reticulum and plasmatic membrane, respectively, as do their D2 and D3 wild-type counterparts. We conclude that the VR determines the subcellular localization and is critical in defining the catalytic properties and activity of thyroid hormone deiodinases.

Halogen Bonding Controls the Regioselectivity of the Deiodination of Thyroid Hormones and their Sulfate Analogues

The type 1 iodothyronine deiodinase (1D-1) in liver and kidney converts the L-thyroxine (T4), a prohormone, by outer-ring (5') deiodination to biologically active 3,3',5-triiodothyronine (T3) or by inner-ring (5) deiodination to inactive 3,3',5'-triiodothronine (rT3). Sulfate conjugation is an important step in the irreversible inactivation of thyroid hormones. While sulfate conjugation of the phenolic hydroxyl group stimulates the 5-deiodination of T4 and T3, it blocks the 5'-deiodination of T4. We show that thyroxine sulfate (T4S) undergoes faster deiodination as compared to the parent thyroid hormone T4 by synthetic selenium compounds. It is also shown that ID-3 mimics, which are remarkably selective to the inner-ring deiodination of T4 and T3, changes the selectivity completely when T4S is used as a substrate. From the theoretical investigations, it is observed that the strength of halogen bonding increases upon sulfate conjugation, which leads to a change in the regioselectivity of ID-3 mimics towards the deiodination of T4S. It has been shown that these mimics perform both the 5'- and 5-ring deiodinations by an identical mechanism.

COMPARATIVE ASPECTS OF MATURATION AND CONTROL OF THYROID HORMONE DEIODINATION DURING DEVELOPMENT

ABSTRACT In all vertebrates the main secretory product of the thyroid gland is thyroxine (T4). The rate of its conversion to the active triiodothyronine (T3) or to the inactive reverse T3 (rT3) can be regulated in the peripheral tissues by deiodination. Probably all vertebrates are capable of both outer and inner ring deiodination (ORD and IRD), catalyzed by deiodinases. Most of these enzymes are related to one of the three mammalian deiodinase types, but the abundance and tissue localization can differ substantially among vertebrate groups. During ontogeny high plasma levels of T3 occur around the period of birth in mammals, of hatching in birds, and of metamorphosis in amphibians. This T3 increase seems to be not only the result of increased T3 production (ORD), but also in considerable degree of decreased T3 degradation (IRD). In fish, birds, and mammals growth hormone can increase plasma T3 levels. In chickens this effect is obtained not by increasing the amount of active hepatic T3-producing (type I)...

Regioselective Deiodination of Thyroxine by Iodothyronine Deiodinase Mimics: An Unusual Mechanistic Pathway Involving Cooperative Chalcogen and Halogen Bonding

Iodothyronine deiodinases (IDs) are mammalian selenoenzymes that catalyze the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (rT3) by the outer- and inner-ring deiodination pathways, respectively. These enzymes also catalyze further deiodination of T3 and rT3 to produce a variety of di- and monoiodo derivatives. In this paper, the deiodinase activity of a series of peri-substituted naphthalenes having different amino groups is described. These compounds remove iodine selectively from the inner-ring of T4 and T3 to produce rT3 and 3,3'-diiodothyronine (3,3'-T2), respectively. The naphthyl-based compounds having two selenols in the peri-positions exhibit much higher deiodinase activity than those having two thiols or a thiol-selenol pair. Mechanistic investigations reveal that the formation of a halogen bond between the iodine and chalcogen (S or Se) and the peri-interaction between two chalcogen atoms (chalcogen bond) are important for the deiodination reactions. Although the formation of a halogen bond leads to elongation of the C-I bond, the chalcogen bond facilitates the transfer of more electron density to the C-I σ* orbitals, leading to a complete cleavage of the C-I bond. The higher activity of amino-substituted selenium compounds can be ascribed to the deprotonation of thiol/selenol moiety by the amino group, which not only increases the strength of halogen bond but also facilitates the chalcogen-chalcogen interactions.

Deiodination of Thyroid Hormones by Iodothyronine Deiodinase Mimics: Does an Increase in the Reactivity Alter the Regioselectivity?

Organoselenium compounds as functional mimics of iodothyronine deiodinase are described. The naphthyl-based compounds having two selenol groups are remarkably efficient in the inner-ring deiodination of thyroxine. The introduction of a basic amino group in close proximity to one of the selenol moieties enhances the deiodination. This study suggests that an increase in the nucleophilic reactivity of the conserved Cys residue at the active site of deiodinases is very important for effective deiodination.

Tissue-specific effects of mutations in the thyroid hormone transporter MCT8

hyroid hormone (TH) is important for the development of different tissues, in particular the brain, as well as for the regulation of the metabolic activities of the tissues and thermogenesis throughout life. Most TH actions are initiated by bind-ing of the active hormone 3,3’,5-triiodothyronine (T3) to its nuclear receptor. This induces an alteration in proteins associated with the transcription initiation complex, resulting in the stimulation or suppression of the expression of TH responsive genes. The biological activity of TH is thus determined by the intracellular T3 concentra-tion, which is only indirectly dependent on the function of the thyroid gland which secretes predominantly the prohormone thyroxine (3,3’,5,5’-tetraiodothyronine, T4). In many target tissues, T3 availability is regulated in a paracrine manner, where T3 sup-ply to target cells is derived from T4 to T3 conversion in neighbouring cells. Brain and cochlea are examples of tissues with paracrine regulation of TH action. In other tissues, such as the pituitary and brown adipose tissue (BAT), T3 may be produced from T4 di-rectly in its target cells, representing an autocrine mechanism of TH action (Figure 1). In yet other tissues such as the liver and the kidneys, intracellular T3 is in rapid exchan-ge with circulating T3. This could be regarded as an endocrine action of T3, although it is still largely derived from peripheral conversion of T4 even in these same tissues.In contrast to the activation of T4 by enzymatic outer ring deiodination (ORD) to T3, TH is inactivated by inner ring deiodination (IRD), which converts T4 to 3,3’,5’-triiodothyronine (reverse T3, rT3) and T3 to 3,3’-diiodothyronine (T2) (1). Three iodothyronine deiodinases (D1-3) are involved in these different deiodination reactions (1). D1 is expressed in liver, kidneys and thyroid and has both ORD and IRD activity. It is thought to contribute importantly to production of serum T3, in particular in eu- and hyperthyroid conditions. D2 has only ORD activity and is ex-pressed in brain, pituitary, BAT, thyroid and skeletal muscle. It is essential for local production of T3 in brain, pituitary and BAT, but the enzyme in thyroid and muscle may also be an important site for production of serum T3 in eu- and hypothyroid subjects. D3 is highly expressed in different fetal tissues, placenta and pregnant ute-rus, and also in adult brain and skin. It has only IRD activity and thus catalyzes the inactivation of TH. Together with D2, D3 has a crucial role in the region-specific and time-dependent regulation of T3 in the developing brain. The deiodinases are homo-logous selenoprotein embedded in the membrane of the endoplasmic reticulum or the plasma membrane, such that the active sites are located in the cytoplasm (1).TH metabolism and action are intracellular processes that require transport of io-dothyronines across the cell membrane. This does not take place by passive diffu-sion but requires the involvement of specific transporters (2). A number of multi--specific transporters have been identified which are also capable of transporting TH.

Regulation of thyroid hormone bioactivity by deiodinases; from invertebrates to humans

Event Abstract Back to Event Regulation of thyroid hormone bioactivity by deiodinases; from invertebrates to humans Theo J. Visser1* 1 Erasmus University Medical Center, Internal Medicine, Netherlands In most species, the thyroid largely secretes the prohormone T4 and a small amount of the bioactive hormone T3. Most T3 is generated by outer ring deiodination (ORD) of T4. T4 is inactivated by inner ring deiodination (IRD) to rT3, and T3 by IRD to 3,3’-T2. In mammals, 3 deiodinases are involved in these processes. D1 is highly expressed in liver and kidneys and has both ORD and IRD activities. It is important for production of serum T3. D2 has only ORD activity; it is highly expressed in brain, pituitary and brown adipose tissue, where it plays an important role in local T3 production. D3 has only IRD activity and is highly expressed in fetal tissues (e.g. brain), placenta and pregnant uterus, and in adult brain and skin. With D2, D3 is crucial for local regulation of thyroid hormone (TH) bioactivity in the brain, and thus for brain development. In all vertebrates, the deiodinases are homologous selenoproteins, containing a selenocysteine (Sec) residue in the active center. Most fish have 2 closely related D3 genes, D3a and D3b, the purpose of which is unknown. In addition to deiodination, TH is metabolized by conjugation with glucuronic acid or sulfate and by side chain modification. The latter produces, among others, the acetic acid metabolites Tetrac (TA4) and Triac (TA3). Interestingly, TA3 has equal or even higher affinity for the T3 receptors TRα and TRβ, respectively. TH is essential for metamorphosis in different species, including fish, amphibians and invertebrates such as ascidians and amphioxus. We have recently characterized a deiodinase from Branchiostoma floridae, with remarkable properties. Firstly, this deiodinase, termed bfDy, is not a selenoprotein but features a Cys residue instead of Sec. Secondly, this enzyme does not act on iodothyronines but specifically catalyzes the IRD of TA3 and TA4. This is interesting as the TH receptor of B. floridae is activated by TA3 but not by T3. This suggests that TA3 may be the primordial bioactive TH. Keywords: amphioxus, deiodinase, Iodothyronines, Selenoprotein, Thyroid hormone, Triac Conference: NASCE 2011: The inaugural meeting of the North American Society for Comparative Endocrinology, Ann Arbor, United States, 13 Jul - 16 Jul, 2011. Presentation Type: Invited Symposium Topic: Thyroid Citation: Visser TJ (2011). Regulation of thyroid hormone bioactivity by deiodinases; from invertebrates to humans. Front. Endocrinol. Conference Abstract: NASCE 2011: The inaugural meeting of the North American Society for Comparative Endocrinology. doi: 10.3389/conf.fendo.2011.04.00051 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 08 Jul 2011; Published Online: 09 Aug 2011. * Correspondence: Prof. Theo J Visser, Erasmus University Medical Center, Internal Medicine, Rotterdam, 3015 GE, Netherlands, t.j.visser@erasmusmc.nl Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Theo J Visser Google Theo J Visser Google Scholar Theo J Visser PubMed Theo J Visser Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Regulation of iodothyronine deiodinases and sodium iodide symporter mRNA expression by perchlorate in larvae and adult Chinese rare minnow (Gobiocypris rarus)

Perchlorate is a widespread contaminant in the aquatic environment. In the present work, the expressions of deiodinase enzymes (d1, d2, and d3) and sodium iodide symporter (nis) genes were determined after larval and adult rare minnow (Gobiocypris rarus) exposed to 5 and 50μg/L perchlorate for 21days. The results showed that deflation of swim bladder development was observed in larvae at 50μg/L perchlorate treatment. An up-regulation of the d2 and nis mRNA levels were observed in the larve and in brain of adults. Meanwhile the expressions of d3 mRNA levels were significantly down-regulated in the liver. These results indicate the changes in d2, nis, and d3 mRNA expression brings about increased outer-ring deiodination, idodine uptake, and a further decrease of inner-ring deiodination, respectively reflecting auto-regulation of hypothalamic-pituitary-thyroid (HPT) axis in adult after perchlorate exposure. The larval fish development could be affected by perchlorate at environmentally relevant concentrations.

WHERE IS THE DEIODINASE SELECTIVITY FOR ORD OR IRD LOCATED? A STRUCTURE-FUNCTION APPROACH

WHERE IS THE DEIODINASE SELECTIVITY FOR ORD OR IRD LOCATED? A STRUCTURE-FUNCTION APPROACH

A Chemical Model for the Inner‐Ring Deiodination of Thyroxine by Iodothyronine Deiodinase

The I of the beholder: The presented chemical model for the inner-ring deiodination of thyroxine (T4) and 3,5,3′-triiodothyronine (T3) by iodothyronine deiodinase (see scheme) highlights the importance of an in-built thiol group in proximity to the selenium atom. The effective removal of iodine in the case of T4 indicates that an enol–keto tautomerism is not required for deiodination.

Effects of selenium and iodine deficiency on type I, type II and type III iodothyronine deiodinases and circulating thyroid hormones in the rat.

The effects of nutritional selenium (Se) deficiency over a period of three generations and of a combined selenium and iodine deficiency on hepatic and cerebrocortical iodothyronine deiodinases and on circulating thyroid hormone levels were examined in the rat. Se deficiency strongly decreased hepatic type I iodothyronine 5'- and 5-deiodinase to 6-13% of that in controls. Iodine depletion had only a marginal decreasing effect on the type I activity. Cerebrocortical type II 5'-deiodinase was decreased in Se-deficient, iodine-replete rats. Its 5-6-fold elevation in iodine-deficient rats was not reversed by additional selenium deficiency. Cortex type III 5-deiodinase was modestly decreased in all groups with insufficient trace element supply. Long-term Se deficiency has only limited effects on serum T4 and T3 levels. Two months of iodine deficiency decreased serum T4 to less than 10% of that in controls, but did not significantly affect serum T3 levels. The strong decrease of hepatic outer- and inner-ring deiodination of T4 in Se deficiency obviously reflects the reduced tissue concentration of the type I deiodinase which was recently identified as a selenoenzyme. The maintenance of increased cerebrocortical type II deiodinase in iodine-depleted animals irrespective of adequate or deficient selenium supply suggests that the type II isoenzyme does not contain selenium in its catalytic site. Further studies are necessary to clarify whether the weak, but repeatedly confirmed decrease of cortex type III deiodinase is the direct effect of Se deficiency or the indirect consequence of the multilevel change in thyroid hormone metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Deiodination and Cellular Proliferation: Parallels between Development, Differentiation, Tumorigenesis, and Now Regeneration

Deiodination and Cellular Proliferation: Parallels between Development, Differentiation, Tumorigenesis, and Now Regeneration

Seasonal changes in channel catfish thyroid hormones reflect increased magnitude of daily thyroid hormone cycles

Channel catfish ( Ictalurus punctatus) in pond culture, sampled once per day, have been reported to exhibit significant seasonal cycles in the thyroid hormones thyroxine (T 4) and 3,5,3′-triiodothyronine (T 3), rising from levels generally below 2 ng/ml in January to above 8 ng/ml in July. To determine if daily thyroid hormone cycles underlie these seasonal changes, we blood sampled groups of 20 catfish (10 males and 10 females) in the morning (approx. 1 h after sunrise), midday, and evening (approx. 1.5 h before sunset) on January 9, April 4, and July 29. From January to July, pond temperatures rose from 7 ° to 32 °, associated with significant ( p < 0.05) increases in mean fish weight (from 477 to 1052 g) and in monthly mean food consumption (from 34 to 474.7 g/kg fish). On all three dates, significantly ( p < 0.05) greater levels of both hormones (except T 3 in April) were found in midday and evening compared to morning samples. In January, the daily change was small (from morning to midday, mean T 3 rose from 2.2 to 3.6 ng/ml and mean T 4 from 2.3 to 4.8 ng/ml), whereas in July it was considerably greater (from morning to evening, mean T 3 rose from 7.2 to 17.8 ng/ml, and T 4 from 9.0 to 22.4 ng/ml). No significant differences were found between midday and evening levels, or between males and females. Additionally, no seasonal phase-shifting of cycles was apparent. A subset of animals was examined to evaluate the potential contribution of peripheral mechanisms in generating these seasonal and daily cycles. Whereas we observed only minor changes in thyroid hormone binding to plasma proteins during any single day, a significant seasonal increase in the ratio of free T 4:free T 3 indices (from a mean of 1.3–1.5 in January to 2.0–2.1 in July) indicated enhanced T 3 binding by plasma proteins in July. Furthermore, in vitro hepatic T 4 and T 3 deiodination activities showed across dates no significant change in T 4 outer-ring deiodination to produce T 3 (ranging from a mean of 53.1 to 70.1 pmol T 4 deiodinated/h/mg microsomal protein), but a significant ( p < 0.05) decrease in T 4 inner-ring deiodination to degrade T 4 to 3,3′5′-triiodothyronine (from a mean in January of 2.4 to 0.65 pmol T 4 deiodinated /h/mg protein in April) and a significant ( p < 0.05) decrease in T 3 inner-ring deiodination to degrade T 3 to 3,3′-diiodothyronine (from a mean in January of 115.5 to 3.1 pmol T 4 deiodinated/h/mg protein in July). These results demonstrate that channel catfish under conditions of natural temperature and photoperiod exhibit robust daily cycles in total plasma T 4 and T 3 similar in magnitude to those reported for other fish species held under controlled laboratory conditions. These cycles maintain a similar phase throughout the year, indicating that apparent seasonal increases in thyroid hormones are not due to phase-shifting of daily cycles. However, seasonal studies sampling fish only in the morning would underestimate the magnitude of the annual changes in blood thyroid hormones. Thyroidal status, as judged from total plasma T 4 and T 3 levels in the afternoon, is greatest in July, coinciding with the postspawning peak in food consumption and growth. Enhanced T 3 plasma protein binding and a shift from predominantly hepatic inner-ring deiodination in winter to outer-ring deiodination in summer suggest that peripheral mechanisms contribute to the generation of these seasonal changes.

Biochemical Mechanisms of Thyroid Hormone Deiodination

Deiodination is the foremost pathway of thyroid hormone metabolism not only in quantitative terms but also because thyroxine (T(4)) is activated by outer ring deiodination (ORD) to 3,3',5-triiodothyronine (T(3)), whereas both T(4) and T(3) are inactivated by inner ring deiodination (IRD) to 3,3',5-triiodothyronine and 3,3'-diiodothyronine, respectively. These reactions are catalyzed by three iodothyronine deiodinases, D1-3. Although they are homologous selenoproteins, they differ in important respects such as catalysis of ORD and/or IRD, deiodination of sulfated iodothyronines, inhibition by the thyrostatic drug propylthiouracil, and regulation during fetal and neonatal development, by thyroid state, and during illness. In this review we will briefly discuss recent developments in these different areas. These have resulted in the emerging view that the biological activity of thyroid hormone is regulated locally by tissue-specific regulation of the different deiodinases.

Expression of recombinant membrane-bound type I iodothyronine deiodinase in yeast

The bioactivity of thyroid hormone is determined to a large extent by the monodeiodination of the prohormone thyroxine (T4) by the hepatic selenoenzyme type I iodothyronine deiodinase (D1), i.e. by outer ring deiodination (ORD) to the active hormone triiodothyronine (T3) or by inner ring deiodination (IRD) to the inactive metabolite reverse T3 (rT3). Since D1 is a membrane-bound protein with an N-terminal membrane-spanning domain, the enzyme is very difficult to purify in an active state. This study was undertaken in order to develop a heterologous (over)-expression system that would eventually allow the production of large amounts of purified active D1 protein. We have expressed a mutant rat D1 protein, in which the selenocysteine residue in the core catalytic center was replaced by cysteine (D1 Cys) in yeast cells (Saccharomyces cerevisiae). After yeast cell fractionation, kinetic analysis was performed with dithiothreitol as reducing cofactor. ORD activity was associated with membrane fractions, while no activity could be detected in the cytosolic fraction. The D1 Cys protein displayed a tenfold increase in Km (2 microM) for rT3 as compared with native D1 protein in rat liver microsomes. The D1 protein content is about 65 pmol/mg microsomal protein, as compared with about 3 pmol/mg in rat liver microsomal fraction. SDS-PAGE analysis of N-bromoacetyl-[125I]T3 affinity-labeled D1 protein showed several labeled protein isoforms with apparent molecular masses between 27 and 32 kDa. Immunoblot analysis with a specific D1 antiserum confirmed the observed D1 protein heterogeneity. Site-directed mutagenesis of several potential N-linked glycosylation sites, phosphorylation sites and a unique myristoylation site established that D1 heterogeneity is not caused by N-linked glycosylation, but probably by a combination of O-linked glycosylation and phosphorylation. Deletion of the endoplasmic reticulum (ER)-signal sequence and the membrane-spanning domain (amino acid residue 2-35), did not result in the production of a soluble D1 enzyme. Although this mutated D1 protein is inactive, the fact that it is still membrane bound indicates the existence of additional membrane attachment site(s) or membrane-spanning domains. Overall, our studies indicate that yeast cells provide a useful system for the expression of relatively high levels of D1 protein which could be used for further structure-function analysis.

The effects of 17β-estradiol injections on thyroid hormone deiodination pathways in liver and other tissues of female and male rainbow trout (Oncorhynchus mykiss) at different stages of sexual maturity

The effects of two intraperitoneal injections of 17β-estradiol (E2) over 7 days were studied on thyroid hormone plasma levels and on activities of thyroxine (T4), 3,5,3'-triiodothyronine (T3), and 3,3',5'-triiodothyronine (rT3) outer-ring deiodination (ORD) and inner-ring deiodination (IRD) pathways in various tissues of female and male rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). E2 administered to adult females and males at different stages of sexual maturity increased liver mass, depressed plasma T3 levels with no change in plasma T4 levels, and severely decreased liver T4ORD activity. E2 also modestly depressed hepatic rT3ORD activity, but only at low substrate levels, and had no consistent effect on the hepatic IRD pathways. There were no E2-induced changes in brain, gill, or heart deiodination, but E2 increased kidney T3IRD activity. In contrast, an all-female stock of trout with rudimentary ovaries responded to E2 with an increase in liver mass but without change in plasma T4 and T3 levels or liver and brain deiodination activities. In conclusion, the decrease in plasma T3 levels in both male and female adult E2-injected trout may be due to both decreased hepatic T3 production and increased renal T3 degradation. However, thyroidal responses to E2 depend on physiological/developmental state and were absent in a highly immature all-female trout stock.

Thyroid function in growth-hormone-transgenic coho salmon (Oncorhynchus kisutch)

We measured growth rate, plasma thyroxine (T4) and 3,5,3'-triiodothyronine (T3) concentrations, and liver and whole-brain T4 and T3 deiodination activities in yearling non-transgenic coho salmon, Oncorhynchus kisutch (Walbaum, 1792), fed a satiation ration (NTS) and in growth-hormone (GH)-transgenic salmon fed for 63 d with either a satiation ration (TS) or pair-fed the satiation ration consumed by NTS fish (TNT). Daily feed intake and specific growth rate for TS fish were significantly enhanced and approximately double those for TNT and NTS fish. There were no differences among groups in plasma T4 concentration or liver T4 outer-ring deiodination activity, but for both TS and TNT fish, plasma T3 concentrations were higher and liver T4 and T3 inner-ring deiodination activities were lower than for NTS fish. Whole-brain deiodination activities did not differ between TS and NTS fish. We conclude that the elevated plasma T3 concentrations of GH-transgenic salmon neither are driven by elevated plasma T4 concentrations nor are they the result of increased hepatic conversion of T4 to T3 by outer-ring deiodination. Instead they can be explained, at least in part, by reduced hepatic degradation of T3 to 3,3'-diiodothyronine by inner-ring deiodination. These changes in T4 and T3 metabolism are tightly linked to the GH-transgenic state and not to food intake or growth rate.