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OBJECTIVE A unique clinical course was observed in a patient with resistance to thyroid hormone β (RTHβ) caused by a variant of the THRB gene leading to the replacement of glycine with arginine in codon 347 (p.G347R). He presented with the syndrome of inappropriate secretion of thyrotropin (TSH) (free T4 [fT4]: 32.43 pmol/L, TSH: 4.67 mIU/L), but slowly developed progressive hypothyroidism (fT4: 8.37 pmol/L, TSH: 100.90 mIU/L) that resolved after suspending bezafibrate (BZ) treatment (fT4: 32.18 pmol/L, TSH: 7.14 mIU/L). This study clinically and experimentally evaluated this interesting phenomenon. METHODS A retrospective cohort analysis of non-RTHβ patients was performed at Kyoto University Hospital. Data before BZ treatment were compared to the first data after treatment. Using reporter assays of iodothyronine deiodinases (DIO1, DIO2, DIO3) in HEK293T cells, we performed functional analyses of mutant thyroid hormone receptor β with p.G347R (G347R TRβ). Mice with G347R TRβ were generated by hydrodynamic gene delivery. RESULTS In non-RTHβ patients (n = 7), BZ treatment did not change serum free T3 and TSH but significantly increased fT4 (p = .008). BZ administration increased DIO3 reporter activity in the context of G347R TRβ, whereas did not change DIO1 and DIO2 reporter activity. In the livers of mice with G347R TRβ, BZ administration increased reverse T3 content, which corresponded to an increase in Dio3 messenger RNA. CONCLUSIONS While hypothyroidism associated with BZ treatment did not occur in non-RTHβ patients, it was observed in a patient with RTHβ due to the p.G347R variant. Liver DIO3 upregulation might involve this hypothyroidism.

Aims/Introduction Type 2 diabetes mellitus is a group of metabolism abnormalities in carbohydrates and energy. Our aim was to investigate resting energy expenditure (REE) and blood glucose changes after biliary diversion in mice with diabetes. Materials and Methods Male mice with diabetes were randomly divided into biliary diversion and sham groups. REE was detected by indirect calorimetry, the levels of fasting blood glucose, total bile acids and triiodothyronine were analyzed. After mice were killed, the weight amount of brown adipose tissue (BAT) and gastrocnemius was measured, and the expression level of G protein‐coupled bile acid receptor and type 2 iodothyronine deiodinase in BAT and gastrocnemius were examined. Results The two groups of mice were pair‐fed, the bodyweights (P, Biliary diversion increased resting energy expenditure in mice with diabetes. Total bile acids increased after biliary diversion. G protein‐coupled bile acid receptor highly expressed in adipose tissue and gastrocnemius after surgery.

Thyroid hormones (THs) are key players in the endocrine system and play pivotal roles in carbohydrate and fat metabolism, protein synthesis, overall growth, and brain development. The thyroid gland predominantly produces thyroxine or 3,5,3â�²,5â�²-tetraiodothyronine (T4) as a prohormone; three isoforms of a mammalian selenoenzymeâ��iodothyronine deiodinase (DIO1, DIO2 and DIO3)â��catalyze the regioselective deiodination of T4 to produce biologically active and inactive metabolites. Whereas DIO1 catalyzes both 5- and 5â�²-deiodination of T4, DIO2 and DIO3 selectively mediate 5- and 5â�²-deiodination, respectively. In this review we discuss the regioselective deiodination of THs in the presence of organochalcogen compounds. Naphthalene-based compounds containing sulfur and/or selenium at the peri positions mediate regioselective 5-deiodination of THs, detailed mechanistic studies having revealed that the heterolytic cleavage of the Câ��I bond is facilitated by the formation of cooperative Se/Sâ� â� â� I halogen bonds and Se/Sâ� â� â� Se chalcogen bonds. We also discuss the biomimetic deiodination of several TH metabolites, including sulfated THs, iodothyronamines, and iodotyrosines. A brief discussion on the dehalogenation of halogenated nucleosides and nucleobases in the presence of organochalcogen compounds is also included. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Polychlorinated biphenyl (PCB) flame retardants are persistent pollutants and inhibit neurodevelopment, particularly in the early stages of life. Halogen bonding (XB) to the iodothyronine deiodinases (Dios) that modulate thyroid hormones (THs) is a potential mechanism for endocrine disruption. Cl⋯Se XB interactions of PCBs with SeMe(−), a small model of the Dio active site selenocysteine, are compared with previous results on polybrominated diphenylethers (PBDEs) and THs using density functional theory. PCBs generally display weaker XB interactions compared to PBDEs and THs, consistent with the dependence of XB strength on the size of the halogen (I > Br > Cl). PCBs also do not meet a proposed energy threshold necessary for substrates to undergo dehalogenation, suggesting they may behave as competitive inhibitors to Dio in addition to other mechanisms of endocrine disruption. XB interactions in PCBs are position-dependent, with ortho interactions slightly more favorable than meta and para interactions, suggesting that PCBs may have a greater effect on certain classes of Dio. Flexibility of PCBs around the biphenyl C-C bond is limited by ortho substitutions relative to the biphenyl linkage, which may contribute to the ability to inhibit Dio and other TH-related proteins.

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.

The glass eel stage of the American Eel Anguilla rostrata marks the onset of the catadromous migration into estuarine or freshwater habitats, and the endocrine mechanisms underlying this habitat selection are still not well understood. Using a candidate genes approach, the aim of this study was to test for different patterns of gene expression related to (1) salinity preferences and/or (2) capture site to predict physiological differences between migratory behaviors. We performed analyses revealing the expression of genes coding for key hormonal factors or their receptors on glass eel‐stage American Eels collected at the mouths of three rivers on the east coast of Canada (Grande‐Riviere‐Blanche, St. Lawrence estuary; Riviere‐Saint‐Jean, Gaspe Peninsula; and the Mersey River, Nova Scotia); eels from the three systems displayed different salinity preferences (brackish water/salt water/freshwater) under laboratory conditions. Transcripts from genes coding for prolactin (PRL), thyroid‐stimulating hormone β subunit, type‐2 iodothyronine deiodinase (DIO‐2), thyroid hormone receptors αa and αb (THRαa and THRαb), growth hormone (GH), insulin‐like growth factor 1 (IGF‐1), and their respective receptors (GH‐R1 and IGF‐1R) were all detected in glass eels. No differences in the expression patterns were detected pertaining to salinity preference, but strong differences were found among rivers. Riviere‐Saint‐Jean glass eels, which were the longest and the least pigmented among the three rivers, were characterized by the highest expression of PRL, DIO‐2, and THRαb. Those from Grande‐Riviere‐Blanche showed an increase in IGF‐1R. Glass eels captured from these two rivers also exhibited the highest expression of GH and GH‐R1. Overall, these results confirm gene × environment interactions at the gene expression level when glass eels settle into their continental habitat. As such, our results also support the concept of the presence of different ecotypes in the Atlantic Canadian coast and in the estuary and Gulf of St. Lawrence.

This paper deals with as ystematic density func- tional theory (DFT) study aiming to unravel the mechanism of the thyroxine (T4) conversion into 3,3',5-triiodothyronine (rT3) by using different bio-inspired naphthyl-based models, which are able to reproduce the catalytic functions of the type-3 deiodinase ID-3. Such naphthalenes, having two sele- nols, two thiols, an da selenol-thiol pair in peri positions, which were previously synthesized and tested in their deio- dinase activity, are able to remove iodine selectively from the inner ring of T4 to produce rT3. Calculation sw ere per- formed including also an imidazole ring that, mimicking the role of the His residue, plays an essential role deprotonating the selenol/thiol moiety .F or all the used complexes, the cal- culated potential energ ys urfaces show that the reaction proceeds via an intermediate, characterized by the presence of aX ¢ I ¢ C( X =Se, S) halogen bond, whose transformation into as ubsequent intermediate in which the C¢ Ib ond is de- finitively cleaved and the incipien tX ¢ Ib ond is formed repre- sents the rate-determining step of the whole process. The calculated trend in the barrier heights of the corresponding transition states allows us to rationalize the experimentally observed superior deiodinas ea ctivity of the naphthyl-based compound with two selenol groups. The role of the peri in- teractions between chalcogen atoms appears to be less prominen ti nd etermining the deiodination activity.

This study investigated the gene transcription and activities of iodothyronine deiodinases in the hepatic cell line of grass carp (Ctenopharyngodon idella) exposed in vitro to 1, 10, 100, and 1000 μg /L microcystin-LR (MC-LR) for either 24 or 48 h. The cell viabilities were not significantly affected by MC-LR exposure. The mRNA expressions of type I iodothyronine deiodinase (ID1) and type Ⅱ iodothyronine deiodinase (ID2) reduced after the exposure to MC-LR. However, MC-LR exposure led to the increase in the mRNA expression of type Ⅲ iodothyronine deiodinase (ID3). Moreover, significant ID1 and ID2 activities decline were also observed in the hepatic cell line of grass carp exposed to MC-LR, and the activity of ID3 increased significantly in the MC-LR treated groups. The results suggested that MC-LR could alter the gene transcription or activities of IDs in the hepatic cell line of grass carp.

During amphibian metamorphosis, a series of dynamic changes occur in a predetermined order. Hind limb morphogenesis begins in response to low levels of thyroid hormone (TH) in early prometamorphosis, but tail muscle cell death is delayed until climax, when TH levels are high. It takes about 20 days for tadpoles to grow from early prometamorphosis to climax. To study the molecular basis of the timing of tissue-specific transformations, we introduced thyroid hormone receptor (TR) expression constructs into tail muscle cells of Xenopus tadpoles. The TR-transfected tail muscle cells died upon exposure to a low level of thyroxine (T4). This cell death was suggested to be mediated by type 2 iodothyronine deiodinase (D2) that converts T4 to T3-the more active form of TH. D2 mRNA was induced in the TR-overexpressing cells by low levels of TH. D2 promoter contains a TH-response element (TRE) with a lower affinity for TR. These results show that the TR transfection confers the ability to respond to physiological concentrations of TH at early prometamorphosis to tail muscle cells through D2 activity and promotes TH signaling. We propose the positive feedback loop model to amplify the cell's ability to respond to low levels of T4.

A solid-phase liquid chromatography tandem mass spectrometry (SPE LC-MS/MS) method was developed to determine thyroid hormones and their metabolites in tissue samples. The separation was achieved using reversed-phase ultra-performance liquid chromatography (UPLC); the mass spectrometric detection was achieved by positive electrospray ionization and multiple reaction monitoring. Prior to the UPLC separation a sample cleanup with a cation exchange was performed. 13 C6 labeled internal standards were used for the thyroid hormones and their metabolites. The method was linear over a range from 0.23 to 90nmol/L for thyroxine and from 0.23 to 9nmol/L for the metabolites. The lower limit of quanti- fication ranged from 0.98 to 1.73pg on column. Intra- and total assay variation were

Background: Fetal alcohol spectrum disorder (FASD) is a leading cause of nongenetic mental retardation and other neurodevelopmental deficits. Earlier diagnosis of FASD would greatly improve prognosis for individuals and families affected by this disorder. Here, we identify candidate placental biomarkers in an animal model of FASD that recapitulates many aspects of human FASD. Methods: Pregnant Sprague-Dawley (SD) females were assigned to 1 of 3 diet groups on gestation day 8 (G8): Ethanol (E), Pair-fed (PF) or Control (C). E dams received ethanol-containing liquid diet and PF dams received isocaloric liquid diet in an amount that matched the paired E dam’s diet consumption the previous day. Control dams received laboratory chow and water ad libitum. Whole placentae from individual fetuses were collected on gestational day 21 (G21) for analyses. Western blotting and quantitative real-time RT-PCR were used to measure protein and mRNA levels of placental iodothyronine deiodinase III (Dio3), thyroid hormone receptor α1 (TRα1), and glucocorticoid receptor (GR). Placental mRNA levels of insulin-like growth factor 2 (Igf-2), pleckstrin homology-like domain family A member 2 (Phlda2), and cyclin-dependent kinase inhibitor 1C (Cdkn1c) were also measured. Results: Placental protein and mRNA levels from ethanol (E)-consuming dams showed the following changes: increased Dio3, decreased TRα1, and decreased GR compared to both C and PF dams. Placental mRNA levels of intrauterine growth restriction (IUGR) markers Igf-2, Phlda2, and Cdkn1c were altered similarly in PF and E dams. Conclusions: We propose the specific pattern of increased Dio3 and decreased TRα1 and GR protein levels in the placenta as selective biomarker for intrauterine alcohol exposure.

Thyroxine (T4), the main secretory hormone of the thyroid gland, is produced on thyroglobulin by thyroid peroxidase (TPO)/H(2)O(2)/iodide system and deiodinated to its active form (T3) by a selenocysteine-containing enzyme, iodothyronine deiodinase (ID). The activation of thyroid-stimulating hormone (TSH) receptor by auto-antibodies leads to 'hyperthyroidism', a life-threatening disease which is treated by antithyroid drugs such as 6-propyl-2-thiouracil (PTU) and methimazole (MMI). The present review describes the biological activities of a number of S/Se derivatives bearing the methimazole pharmacophore. It is shown that the isosteric substitutions in the existing drugs lead to compounds that can effectively and reversibly inhibit the heme-containing lactoperoxidase (LPO). In contrast to methimazole, the selenium analogue, MSeI, does not interfere with the enzyme directly, but it inhibits LPO by reducing the H(2)O(2) that is required for the oxidation of the Fe-center in LPO. These studies reveal that the degradation of the intracellular H(2)O(2) by the Se analogues of antithyroid drugs may be beneficial to the thyroid gland, as these compounds may act as antioxidants and protect thyroid cells from oxidative damage. Because the drugs with an action essentially on H(2)O(2) can reversibly inhibit the thyroid peroxidase, such drugs could be of great importance in the treatment of hyperthyroidism.

Background information. There are significant indications that amphibians require TH (thyroid hormones) prior to their involvement in the regulation of metamorphosis and before the development of a functional thyroid. Results. In order to investigate the potential role for TH in pre-metamorphic Xenopus tropicalis we have cloned cDNAs for, and analysed the expression of, TPO (thyroid peroxidase), 5′DII (type II iodothyronine deiodinase) and 5DIII (type III iodothyronine deiodinase), enzymes involved in TH metabolism. Zygotic expression of TPO was detected in neurula stage embryos. Expression was observed in the notochord and later in the thyroid. The notochord was also a common site of expression for 5′DII and 5DIII. Other sites of 5′DII expression are the otic vesicles, retina, liver, blood-forming region, branchial arches and brain. 5DIII is also expressed in the brain, retina, liver, developing pro-nephros, blood-forming region and branchial arches. Embryos exposed to the TPO inhibitor methimazole showed a distinctive dose-dependent phenotype of a crimped notochord and shortened axis, together with alterations in 125I− uptake. Conclusions. These data suggest a novel extrathyroidal role for TH during early development, and support the proposal that embryos require thyroid signalling for normal development prior to metamorphosis.

Summary Objective Type I iodothyronine deiodinase (D1) catalyses the 5′ monodeiodination of T4 and is highly expressed in normal human thyroid gland. We have investigated D1 expression in a series of benign and malignant differentiated thyroid neoplasias. Design Surgically isolated thyroid tumour fragments were used. D1 expression was determined by reverse transcription polymerase chain reaction (RT-PCR) and enzymatic assay. Patients Tumours and adjacent normal tissues were obtained from 28 unselected patients (papillary carcinoma, n = 14; follicular adenoma, n = 7; follicular carcinoma, n = 6; anaplastic carcinoma, n = 1). Measurements D1 mRNA levels were determined using specific primers for the human D1 gene and enzymatic assays were performed using T4 as substrate. Results In papillary thyroid carcinoma (PTC), D1 mRNA and activity levels were decreased compared with the surrounding tissue (0·25 ± 0·24 vs. 1·09 ± 0·54 arbitrary units (AU), P

Over the past three decades, selenium has been intensively investigated as an antioxidant trace element. It is widely distributed throughout the body, but is particularly well maintained in the brain, even upon prolonged dietary selenium deficiency. Changes in selenium concentration in blood and brain have been reported in Alzheimer's disease and brain tumors. The functions of selenium are believed to be carried out by selenoproteins, in which selenium is specifically incorporated as the amino acid, selenocysteine. Several selenoproteins are expressed in brain, but many questions remain about their roles in neuronal function. Glutathione peroxidase has been localized in glial cells, and its expression is increased surrounding the damaged area in Parkinson's disease and occlusive cerebrovascular disease, consistent with its protective role against oxidative damage. Selenoprotein P has been reported to possess antioxidant activities and the ability to promote neuronal cell survival. Recent studies in cell culture and gene knockout models support a function for selenoprotein P in delivery of selenium to the brain. mRNAs for other selenoproteins, including selenoprotein W, thioredoxin reductases, 15-kDa selenoprotein and type 2 iodothyronine deiodinase, are also detected in the brain. Future research directions will surely unravel the important functions of this class of proteins in the brain.

Selenium is an integral component of the enzymes glutathione peroxidase (GPx) and iodothyronine deiodinases. Although selenium nutrition could conceivably affect thyroid function in infants, children and adolescents, available data suggest that the effect of selenium deficiency on thyroid function is relatively modest. In patients with isolated selenium deficiency (such as patients with phenylketonuria receiving a low-protein diet), peripheral thyroid hormone metabolism is impaired but there are no changes in thyrotropin (TSH) or clinical signs of hypothyroidism, suggesting that these patients are euthyroid. Selenium supplementation may be advisable to optimize tissue GPx activity and prevent potential oxidative stress damage. In areas where combined selenium and iodine deficiencies are present (such as endemic goiter areas in Central Africa), selenium deficiency may be responsible for the destruction of the thyroid gland in myxoedematous cretins but may also play a protective role by mitigating fetal hypothyroidism. In these areas, selenium supplementation should only be advocated at the same time or after iodine supplementation. In patients with absent or decreased production of thyroid hormones and who rely solely on deiodination of exogenous L-thyroxine for generation of the active triiodothyronine (such as patients with congenital hypothyroidism), selenium supplementation may optimize thyroid hormone feedback at the pituitary level and decrease stimulation of the residual thyroid tissue.

The 24-h patterns of tissue thyroid hormone concentrations and type II 5'- and type III 5-iodothyronine deiodinase (5'D-II and 5D-III, respectively) activities were determined at 4-h intervals in different brain regions of male euthyroid rats entrained to a regular 12-h light/12-h dark cycle (lights on at 6:00 a.m.). Activity of 5'D-II, which catalyzes the intracellular conversion of thyroxine (T4) to 3,3',5-triiodo-L-thyronine (T3) in the CNS, and the tissue concentrations of both T4 and T3 exhibited significant daily variations in all brain regions examined. Periodic regression analysis revealed significant circadian rhythms with amplitudes ranging from 9 to 23% (for T3) and from 15 to 40% (for T4 and 5'D-II) of the daily mean value. 5'D-II activity showed a marked nocturnal increase (1.3-2.1-fold vs. daytime basal value), with a maximum at the end of the dark period and a minimum between noon and 4:00 p.m. 5D-III did not exhibit circadian patterns of variation in any of the brain tissues investigated. Our results disclose circadian rhythms of 5'D-II activity and thyroid hormone concentrations in discrete brain regions of rats entrained to a regular 12:12-h light-dark cycle and reveal that, in the rat CNS, T3 biosynthesis is activated during the dark phase of the photoperiod. For all parameters under investigation, the patterns of variation observed were in part regionally specific, indicating that different regulatory mechanisms may be involved in generating the observed rhythms.

The effects of different kinds of acute stressor on thyroid hormone concentrations and deiodinase activities were investigated in four brain regions (frontal cortex, amygdala, hypothalamus, and cerebellum) and in the pituitaries and livers of adult male rats. Five groups of rats were killed after each of the following stressors: (a) an intraperitoneal injection of saline, (b) intragastric intubation, (c) and (d) two different forms of handling, being grasped as for intraperitoneal injection and being moved from one cage to another, and (e) a 2-h period spent in a slowly rotating drum. Two other groups were placed in the rotating drums for 10 and 19 h (sleep deprivation experiment), respectively. All stressors induced significant (in some cases up to 200%) increases in the activity of type II 5'-iodothyronine deiodinase, which catalyzes the deiodination of the prohormone L-thyroxine (T 4 ) to the active metabolite 3,3',5-triiodo-L-thyronine (T 3 ). As a consequence, the tissue concentrations of T 4 fell, and those of T 3 rose (sometimes by up to 300%). However, these changes were limited to selected areas of the brain that were specific for each stressor and were not seen in all brain regions investigated in any group. No clear-cut effects of stress were seen on the activities of the type III 5-iodothyronine deiodinase isoenzyme, which catalyzes the inactivation of T 3 , on liver or serum thyroid hormone concentrations or on liver of brain type I 5'-iodothyronine deiodinase activities. In summary, our results show that even mild and very brief stress can induce marked increases in T 3 concentrations specifically in brain but not in liver or blood. Thus, contrary to common opinion, thyroid hormones may play an important physiological role in stress reactions, at least in tissues that contain type II 5'-iodothyronine deiodinase, such as brain and pituitary.

Summary objective Thyroid hormones (THs) perform essential roles in pituitary function. They regulate anterior pituitary hormone secretion and are also key determinants of pituitary cell proliferation and differentiation. The critical role of deiodinase enzymes, which serve as prereceptor regulators of TH action, remains largely unexplored. Three deiodinase enzymes metabolize active and inactive THs and thereby determine tissue concentrations of the biologically active ligand, tri-iodothyronine (T3). We hypothesized that aberrant expression of deiodinase enzymes and/or altered enzyme activity in pituitary tumours may change tissue concentrations of THs and influence their growth and secretory characteristics. study design and patients We studied 105 pituitary tumours and 10 normal pituitaries for expression of deiodinase enzyme mRNAs encoding types 1 (D1), 2 (D2) and 3 (D3) using real-time RT-PCR. Enzyme activity data from 20 pituitary samples were also obtained. results Pituitary tumours expressed significantly increased D3 mRNA (6·5-fold, P

The development of the brain is critically dependent on an adequate supply of iodine. Iodine is an integral part of thyroid hormone, which acts on brain development by regulating the expression of target genes. The active thyroid hormone, T3, is generated in part in the thyroid gland, but about 80% of T3 in brain is formed locally from T4 deiodination mainly by the action of a specific iodothyronine deiodinase. This enzyme is highly expressed in astrocytes, which take up T4 from the blood and deliver T3 for neuronal use. In the target cells T3 binds to nuclear receptors which are transcription factors. The T3 receptors are expressed in the brain before fetal thyroid gland function and may be activated by maternal thyroid hormone during midgestation. Although a group of thyroid hormone target genes has been identified in recent years, many basic questions of thyroid hormone action in the brain remain to be elucidated.

The method is also applied to the synthesis of aureusidin (VIb), an inhibitor of iodothyronine deiodinase.

The type III iodothyronine deiodinase (ID-III) catalyzes the inner ring deiodination and, thus, the inactivation of the thyroid hormones T4 and T3. ID-III activity in rat brain, rat placenta and embryonic chicken liver is inhibited by the affinity label N-bromoacetyl-T3, (BrAcT3) with an affinity similar to that of T3. Reaction of rat brain and placenta microsomes with BrAc[125I]T3 resulted in the extensive labeling of a 32 kDa protein (p32). However, p32 was also prominently labeled in fetal rat liver microsomes which have no ID-III activity. Labeling of p32 was not influenced by 100 μM substrate analogs or inhibitors of ID-III, some of which completely inhibit ID-III activity at 1 μ. BrAc[125I]T3, labeling of embryonic chicken liver microsomes did not reveal p32 or another protein possibly related to ID-III. In contrast to previous suggestions, it is unlikely that p32 represents ID-III or a subunit thereof.

Crystal structure determination and AM1 molecular orbital calculations were performed on the flavone, 3′,5′ — dibromo — 3 — methyl — 6,4′ — dihydroxyflavone (EMD21388), crystallized as a (1:2) triphenylphosphine oxide (TPPO) co-crystal complex. This is also the first structural report of a 2∶1 TPPO co-crystal complex with a flavone. The calculated molecular structure is in good agreement with the observed crystallographic conformation which shows that the angle between the benzopyrone and phenyl rings,θ, [C(3)-C(2)-C(1′)-C(6′)] is 49.1(8)°, compared with the geometry-optimized minimum energy angle of 46.0°. The barrier to rotation in this system is about 3.5 kcal/mol. Biochemical data for EMD 21388 show it is the most potent inhibitor of the enzyme iodothyronine deiodinase and is the strongest competitor for the binding of thyroxine to its serum transport protein transthyretin. This analysis reveals that the flavone can adopt a conformation that has structural homology with the thyroid hormone.

To better understand, and in the extension mimic, the action of the three selenium-containing iodothyronine deiodinases, o,o'-diiodophenols were reacted under acidic conditions with sodium hydrogen ...

The influence of 2 different routes of amiodarone (AMIO) administration, oral gavage (OG) and subcutaneous injection (SC), on the density of cardiac beta-adrenoceptors (Bmax), hepatic type I 5' iodothyronine deiodinase (5' DI) and thyroid hormone serum concentrations was studied. Compared with respective control values, AMIO treatment (50 mg/kg per day, 7 days) via both OG and SC routes significantly lowered Bmax (OG: 14.6 +/- 1.92 vs 18.2 +/- 1.03 fmol/mg and SC: 16.6 +/- 2.34 vs 19.1 +/- 2.05 fmol/mg) and 5' DI activity (from 409 to 85 and 340 to 47 fmol I-/mg per min, respectively). The SC route induced a fall in thyroid secretion and a generalized hypothyroidism (decreased serum FT4 and FT3, inhibition of body weight gain. The OG route did not modify thyroid secretion. These results demonstrated that the effects on cardiac beta-receptor density in the SC group might be due to the generalized hypothyroidism and that AMIO produced its specific cardiac effects only after oral route medication, suggesting that the oral route is the best choice for studying AMIO cardiac effects on beta-receptor density.

The importance of selenium as an essential trace element is now well recognized. In proteins, the redox-active selenium moiety is incorporated as selenocysteine (Sec), the 21st amino acid. In mammals, selenium exerts its redox activities through several selenocysteine-containing enzymes, which include glutathione peroxidase (GPx), iodothyronine deiodinase (ID), and thioredoxin reductase (TrxR). Although these enzymes have Sec in their active sites, they catalyze completely different reactions and their substrate specificity and cofactor or co-substrate systems are significantly different. The antioxidant enzyme GPx uses the tripeptide glutathione (GSH) for the catalytic reduction of hydrogen peroxide and organic peroxides, whereas the larger and more advanced mammalian TrxRs have cysteine moieties in different subunits and prefer to utilize these internal cysteines as thiol cofactors for their catalytic activity. On the other hand, the nature of in vivo cofactor for the deiodinating enzyme ID is not known, although the use of thiols as reducing agents has been well-documented. Recent studies suggest that molecular recognition and effective binding of the thiol cofactors at the active site of the selenoenzymes and their mimics play crucial roles in the catalytic activity. The aim of this perspective is to present an overview of the thiol cofactor systems used by different selenoenzymes and their mimics.

Thyroxine (T4), the main secretory hormone of the thyroid gland, is produced on thyroglobulin by thyroid peroxidase $(TPO)/H_2O_2/$iodide system and deiodinated to its active form (T3) by a selenocysteine-containing enzyme, iodothyronine deiodinase (ID). The activation of thyroid - timulating hormone (TSH) receptor by auto-antibodies leads to 'hyperthyroidism', a life-threatening disease which is treated by antithyroid drugs such as 6-propyl-2-thiouracil PTU) and methimazole (MMI). The present review describes the biological activities of a number of S/Se derivatives bearing the methimazole pharmacophore. It is shown that the isosteric substitutions in the existing drugs lead to compounds that can effectively and reversibly inhibit the heme-containing lactoperoxidase (LPO). In contrast to methimazole, the selenium analogue, MSeI, does not interfere with the enzyme directly, but it inhibits LPO by reducing the $H_2O_2$ that is required for the oxidation of the Fe-center in LPO. These studies reveal that the degradation of the intracellular $H2_O_2$ by the Se analogues of antithyroid drugs may be beneficial to the thyroid gland, as these compounds may act as antioxidants and protect thyroid cells from oxidative damage. Because the drugs with an action essentially on $H_2O_2$ can reversibly inhibit the thyroid peroxidase, such drugs could be of great importance in the treatment of hyperthyroidism.

Direct reaction of 6-n-propyl-2-thiouracil (PTU), a widely used anti-thyroid drug against hyperthyroidism (Graves' disease), or 5-chloro-2-mercaptobenzothiazole (CMBZTH) with iodine in a molar ratio of 1: 1 resulted in the formation of the charge-transfer (CT) complexes [(PTU)12] (1) or [(CMBZT)12] (2). All reactions were carried out in dichloromethane and water solutions. Compounds 1 and 2 were characterized by elemental analyses, FT-Raman, FT-IR, UV/Vis and H-1 NMR spectroscopy. The crystal structures of both complexes were determined by X-ray diffraction at 120(l) K (1) and 293(2) K (2). The charge-transfer nature of the bonds in the adducts 1 and 2 was verified by the lengthening of the I-I bond lengths as compared to the S-I bond lengths and by the characteristic CT bands observed in the UV spectra of the complexes. Compound 1 [(C7H10N2OS)I-2] [monoclinic with space group P2(1)/c and a = 9.8501(7), b = 10.3101(7), c = 12.0287(8) Angstrom, beta = 99.707(6)degrees, Z = 4] consists of a propylthiouracil ligand bonded with an iodine atom through sulfur. Extended intermolecular N-(HO)-O-... contacts link the molecules forming a supramolecular assembly. Compound 2 {(C7H4ClNS2)I-2} {orthorhombic, space group P2(1)2(1)2(1), a = 4.1650(10), b = 9.691(2), c = 28.471(6) Angstrom, Z = 41 consists of a 5-chloro-2-mercaptobenzothiazole ligand bonded with an iodine atom through sulfur. An extended intermolecular linkage via (IH)-H-...-N bonds leads to the formation of an extended structure. Attempts to draw conclusions on the behavior of a thioamide - when used as an anti-thyroidal drug - towards iodine have been made. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003). European Journal of Inorganic Chemistry

Enzyme mimetic studies on the crucial intermediate (E-SeI) of the iodothyronine deiodinase cycle have been carried out by using an areneselenenyl iodide stabilized by intramolecular Se···N interactions. Treatment of this compound with aromatic thiols and thiobenzoxazole in the presence of NEt(3) affords areneselenenyl sulfides that are stable towards disproportionation reactions. The structures of three of the areneselenenyl sulfides were determined by X-ray crystallography. In one case, in the absence of NEt 3 , a diselenide can be formed rather than the selenenyl sulfide. The areneselenenyl iodide also reacts with a related selenol to produce the corresponding diselenide, and this reaction is found to be much faster than that with thiols. The high reactivity of the selenenyl iodide with the selenol suggests that a reduced selenol group (R'-SeH) may react with the E-SeI intermediate to produce a diselenide (E-Se-Se-R') without any thiol cosubstrate. The intermediacy of selenenyl sulfides during the reduction of selenenyl iodide by thiols and its possible relevance to the iodothyronine deiodinase catalytic cycle is also described.

Several 6-anilino-2-thiouracils were synthesized and tested for their ability to inhibit the inner-ring iodothyronine deiodinase from human placenta. The p-ethyl and p-n-butyl analogues were strongly inhibitory to the enzyme and were much more effective than the standard deiodinase inhibitor, 6-propyl-2-thiouracil. The degree of inhibition caused by 6-(p-n-butylanilino)-2-thiouracil was, moreover, unaffected by high concentrations of reducing agent in the enzyme assay. Attempts to prepare 3-alkyl derivatives via S-debenzylation of 2-benzylthio intermediates led to rearrangement to, for example, 3-methyl-5-benzyl-6-amino-2-thiouracil. This compound also strongly inhibited the deiodinase reaction. Preliminary results suggest that these compounds are useful to study in vitro and in vivo metabolism of thyroid hormones and may be clinically useful to enhance the availability of active thyroid hormones to certain organs.