New technologies to probe the global output of the normal and cancer genomes have recently reached widespread use. The resulting genomewide gene expression profiles, e.g, a gene expression measurement per gene and per tissue sample, remain challenging to analyze and interpret, but have already provided new insights into the pathophysiology of cancer and towards personalized care. In vitro cell culture-based experimental models are used to elucidate cancer onset and progression because experimentation in humans is difficult practically and ethically unacceptable, and because they provide simplified, reproducible and controlled systems to test hypotheses. The thyroid tumors and their in vitro experimental models are particularly suited to compare the molecular phenotypes of experimental models and tumors. From one type of cell, the thyrocyte, at least five distinct benign and malignant tumors can arise. In addition, many immortalized tumor-derived cell lines and primary cultures models of these cells exist. This thesis has focused on the bioinformatic comparison of these in vitro models to the in vivo tumors, from the point of view of their gene expression profiles, to gain insight into the pathogenesis of thyroid tumors, and of tumors in general. In a first study, we showed that primary cultures of freshly isolated normal thyroid cells where proliferation and differentiation through the TSHR/cAMP pathway was chronically activated experimentally resemble specifically the autonomous thyroid adenomas, a type of benign thyroid tumor, and provide insight into a general mechanism of tumor progression: the suppression of negative feedbacks that normally restrain excessive cell division. Subsequently, we found that immortalized thyroid tumor-derived cell lines have converged to a common phenotype regardless of their tumor subtype of origin. A TSHR/cAMP thyroid cell differentiation signature, derived from data obtained for the first study, was used to show that the cell lines were dedifferentiated. Accordingly, we showed that the cell lines resemble most the phenotype of the more dedifferentiated, clinically aggressive anaplastic thyroid cancers. Finally, using large databases of gene expression profiles publicly available, we extended the comparison of cell lines and tumors to cancers of five other organs: breast, colon, kidney, ovary and lung. We discuss the correct use of these models and advance an hypothesis regarding the nature of the state to which these cells have converged: they could represent a surviving subpopulation of tumors cells, cancer stem cells, capable of initiating and maintaining tumor growth. As other technologies designed to perturb the genome in experimental models are emerging, careful characterization and validation of the experimental models are needed to extrapolate the results in vivo. Although many differences exist between the experimental models and their in vivo disease counterparts, focusing on the similarities could provide a path to design successful therapeutic interventions more systematically.

New technologies to probe the global output of the normal and cancer genomes have recently reached widespread use. The resulting genomewide gene expression profiles, e.g, a gene expression measurement per gene and per tissue sample, remain challenging to analyze and interpret, but have already provided new insights into the pathophysiology of cancer and towards personalized care. In vitro cell culture-based experimental models are used to elucidate cancer onset and progression because experimentation in humans is difficult practically and ethically unacceptable, and because they provide simplified, reproducible and controlled systems to test hypotheses. The thyroid tumors and their in vitro experimental models are particularly suited to compare the molecular phenotypes of experimental models and tumors. From one type of cell, the thyrocyte, at least five distinct benign and malignant tumors can arise. In addition, many immortalized tumor-derived cell lines and primary cultures models of these cells exist. This thesis has focused on the bioinformatic comparison of these in vitro models to the in vivo tumors, from the point of view of their gene expression profiles, to gain insight into the pathogenesis of thyroid tumors, and of tumors in general. In a first study, we showed that primary cultures of freshly isolated normal thyroid cells where proliferation and differentiation through the TSHR/cAMP pathway was chronically activated experimentally resemble specifically the autonomous thyroid adenomas, a type of benign thyroid tumor, and provide insight into a general mechanism of tumor progression: the suppression of negative feedbacks that normally restrain excessive cell division. Subsequently, we found that immortalized thyroid tumor-derived cell lines have converged to a common phenotype regardless of their tumor subtype of origin. A TSHR/cAMP thyroid cell differentiation signature, derived from data obtained for the first study, was used to show that the cell lines were dedifferentiated. Accordingly, we showed that the cell lines resemble most the phenotype of the more dedifferentiated, clinically aggressive anaplastic thyroid cancers. Finally, using large databases of gene expression profiles publicly available, we extended the comparison of cell lines and tumors to cancers of five other organs: breast, colon, kidney, ovary and lung. We discuss the correct use of these models and advance an hypothesis regarding the nature of the state to which these cells have converged: they could represent a surviving subpopulation of tumors cells, cancer stem cells, capable of initiating and maintaining tumor growth. As other technologies designed to perturb the genome in experimental models are emerging, careful characterization and validation of the experimental models are needed to extrapolate the results in vivo.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 3 uppsatser.

The endocrine system is vulnerable to a range of chemicals in the environment. Endocrine disrupting chemicals (EDCs) are exogenous agents that can induce responses on the endocrine system because of their hormone-like activity and toxicity. Specific to this study are thyroid disrupting chemicals (TDCs), these are EDCs that specifically disrupt the thyroid hormone signalling pathway, and this may result in adverse health effects. Thyroid hormones play a crucial part in metabolism, growth, maintenance of brain function and fertility; hence disruption of the thyroid signalling axis implicates human health. We are exposed to TDCs regularly, and studies have shown an association between TDC exposure and neurobehavioural disorders, reproductive abnormalities and obesity. There is a lack of data associated to thyroid hormone receptor activity in surface and drinking water. Hence, the potential human health risks posed by thyroid disruption may therefore be underestimated. The aim of the study was to optimise and validate the GH3.TRE.Luc reporter gene bioassay that can measure thyroid hormone receptor mediated activity and cytotoxicity in drinking and source water, with relevance to water monitoring. The GH3.TRE.Luc reporter gene bioassay was established, optimized and validated to detect thyroid hormone receptor activity. The luciferace assay was used to test for metabolic activity and the resazurine cell proliferation assay was used to assess cell viability. The assay was applied to compounds with agonistic and antagonistic properties; triidothyronine (T3), thyroxine (T4), triac, tetrac, amiodarone, sodium arsenite, pentachlorophenol (PCP), ethylene thiourea, 2,2,4,4-tetrahydroxybenzophenone (THBP) and methimazole. It was also applied to environmental and drinking water samples from the Global Water Research Coalition (GWRC). Finally, the assay was applied to 48 water samples from a water treatment plant in South Africa, collected over a period of 12 months. Every month, four samples were collected. Two samples were source water samples, with one going into the treatment plant and coming out as 2 distribution pipelines (drinking water). For optimisation and validation, the dose response curves obtained for T3, T4, tetrac and triac (agonists) were comparable to literature. Antagonistic behaviour was seen in sodium arsenite, amiodarone, PCP and methimazole. Spiked water samples from the GWRC showed thyroid hormone receptor activity. Sixteen of the 48 water samples collected from the water treatment plant were positive for thyroid hormone disruptor activity. Highest activity was seen in the winter season, accounting for seasonal variations. High TDCs activity reported in the source water may be due to activities occurring near the dam. The water treatment plant seemed effective for only one of the distribution pipelines, and not the other. This study confirms that GH3.TRE.Luc Reporter Gene Bioassay is a sensitive and effective tool to identify and quantify TDC activity in pure chemicals and in complex environmental mixtures present in water. Further monitoring of water sources for TDCs is recommended to ensure water quality and safety. / Dissertation (MSc)--University of Pretoria, 2017. / School of Health Systems and Public Health (SHSPH) / MSc / Unrestricted

Orientadores: Denise Engelbrecht Zantut-Wittmann, José Vassallo, Patrícia Sabino Matos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-18T16:27:46Z (GMT). No. of bitstreams: 1 Maia_FredericoFernandesRibeiro_M.pdf: 3526510 bytes, checksum: 65aa0cfcc1c703f9021864119260a326 (MD5) Previous issue date: 2011 / Resumo: Introdução: A punção aspirativa por agulha fina (PAAF) permanece como o procedimento de referência na avaliação dos nódulos de tireóide. No entanto, em cerca de 10 a 30% dos casos, o diagnóstico citológico é indeterminado. Alguns estudos recentes buscam estabelecer modelos de predição de risco para malignidade no nódulo de tireóide, correlacionando fatores de risco, como idade, sexo, nódulo solitário, níveis de hormônio estimulador da tireóide (TSH), auto-imunidade tireoidiana, nódulos frios e aspectos ultrassonográficos, entre outros. No entanto, os resultados são discordantes, carecendo de novos estudos sobre o tema. Objetivos: Avaliar os parâmetros clínicos, laboratoriais, de ultra-sonografia (US), cintilografia e cito-patologia em nódulos de tireóide, incluindo nódulos de citologia indeterminada, e investigar o papel destes fatores como preditores de malignidade em nódulos de tireóide com resultados citológicos inicialmente benignos submetidos à repetição criteriosa da PAAF. Métodos: Cento e quarenta e três pacientes tratados cirurgicamente em um único centro hospitalar, sendo confirmadas pela histologia que 65% (93) apresentavam nódulos de tireóide benignos e 35%, lesões malignas (50). Todas as citologias foram revisadas por patologista experiente na área e pelo autor, sendo reclassificadas prospectivamente pelo sistema de Bethesda. As variáveis clínicas, laboratoriais, cintilográficas, ultrassonográficas e cito-patológicas foram definidas com base na literatura consensual e comparadas retrospectivamente, definindo-se os marcadores de risco de malignidade após análise de regressão multivariada. Dentre os 143 casos, em 80 estabeleceu-se o diagnóstico de citologia indeterminada, sendo pesquisados os preditores clínicos, ultrassonográficos e variáveis citológicas apontadas pela classificação de Bethesda. Dentre o total dos 143 nódulos, avaliamos a evolução de 35 deles que apresentaram resultados citológicos inicialmente benignos e foram submetidos à PAAF de repetição guiada por US (PAAF-US). Resultados: Entre os grupos de pacientes com diagnóstico histológico de nódulos benignos e malignos, não houve diferença significativa quanto ao sexo, função tireoidiana avaliada por níveis séricos de TSH e T4L, doença auto-imune da tireóide, e padrão cintilográfico, incluindo os nódulos com citologia indeterminada e o grupo de nódulos com citologia inicial benigna. O modelo obtido após análise de regressão multivariada evidenciou como fatores preditivos de malignidade em nódulo de tireóide a idade do paciente acima de 38,5 anos (determinado pela análise da curva ROC), o diâmetro do nódulo (> 2 cm), presença de microcalcificações e irregularidade da borda ao ultra-som, exibindo acurácia de 81,7%. A comparação entre os achados de US mostrou diferenças em relação às características suspeitas de malignidade (microcalcificações, fluxo central, irregularidade da borda e hipoecogenicidade). A prevalência de malignidade nos nódulos com citologia indeterminada (n=80) foi de 25% (20/80). A análise de regressão multivariada mostrou irregularidade da borda ao ultra-som e citologia categoria IV de Bethesda como variáveis significativas para prever a malignidade em nódulos de tireóide com citologia indeterminada, proporcionando 76,9% de acurácia. Quanto aos pacientes com nódulos apresentando citologia inicial benigna e submetidos à repetição da PAAF, obtivemos 10 casos malignos (28,5%) (G1) e 25 nódulos que mantiveram diagnóstico de benignidade (G2) à histologia final. Dentre o total de 35 pacientes, a PAAF de repetição resultou em 28 citologias indeterminadas durante o seguimento, sendo que 23 (82,1%) foram identificadas até a 3ª PAAF-US. O intervalo entre a 1ª e 3ª PAAF-US foi de 13 meses (mediana). A análise dos dados obtidos pelos laudos do estudo ultrassonográfico mostrou diferença significativa entre as características suspeitas no G1: microcalcificações, irregularidade da borda, fluxo central, hipoecogenicidade, em relação ao G2. Conclusões: Verificamos maior risco de carcinoma em nódulos de tireóide de pacientes com idade acima de 39 anos e US com características suspeitas de malignidade. O estudo de ultra-som e resultado categoria IV de Bethesda à citologia mostraram alta acurácia para predição de malignidade em nódulos com citologia indeterminada. Em nódulos com citologia inicial benigna, seguidos ambulatorialmente, observou-se maior taxa de malignidade na presença de US suspeito inicial, indicando que a repetição da PAAF-US por até duas vezes, em um período médio de 13 meses após a 1ª punção pode elevar a taxa de diagnóstico. Estes resultados podem ser usados para orientar a tomada de decisões cirúrgicas com maior propriedade / Abstract: Background: Althout fine-needle aspiration cytology (FNAC) is considering the gold standard for evaluating thyroid nodules, in about 10-30% of the cases, cytology is indeterminate. Some studies in literature showed different models of prediction for thyroid nodule malignancy, including age, gender, solitary nodule, thyrotropin (TSH) levels, thyroid auto-immunity, cold nodules and suspect ultrasound aspects. However, the adequate predictor model for clinical application and surgical guidance for thyroid nodule management is not well established in medical literature. Objectives: This study aimed to evaluate clinical, laboratory, ultrasound (US) and scintigraphyc parameters in thyroid nodule. This study still aimed to investigate the role of these predictors to determine malignancy in thyroid nodules with indeterminate cytology and nodules with initially benign cytological result at 1st presentation. Methods: This study enrolled 143 patients surgically treated in a single center, 65% (93) of benign thyroid nodule vs. 35% (50) malignant lesions at final histology (1998 to 2008). The clinical, laboratory, scintigraphyc and US features were retrospectively compared and a predictor model was designed after multivariate analysis to predict malignancy in this group. 80/143 selected cases of indeterminate cytology were prospective studied and re-classified by Bethesda System. The clinical, scintigraphyc, sonographic and cytological classification (Bethesda) variables were analyzed in this specific group. At finally, we studied 35/143 nodules with initially benign cytological result who underwent serious ultrasound guided re-biopsy [fine-needle aspiration cytology (FNAC-US)]. Results: Between the benign and malignant nodules groups, there were no differences in gender, serum TSH and FT4 levels, thyroid auto-antibodies, thyroid dysfunction and scintigraphyc result, including indeterminate cytology group and the specific group of thyroid nodules with initially benign cytology result. Sonographic study showed differences between the presences of suspected characteristics of nodule in the group of malignant lesions: microcalcifications, central flow, border irregularity and hypoechogenicity. The model obtained after multivariate analysis, showed age (>39yrs), border irregularity, microcalcifications and nodule size as factors predictive of malignancy, featuring 81.7% of accuracy. In the specific group of indeterminate cytology, there was a 25% prevalence of malignancy (20/80). The model obtained after multivariate analysis demonstrated border irregularity by US and category IV of Bethesda as significant variables to predict malignancy in indeterminate thyroid nodules (76.9% of accuracy). By means of surgery, malignancy histology results were confirmed in 10 (28.5%) cases (G1) vs. 25 (71.5%) benign nodules (G2) in the group of nodules with initially cytological result. Of the 28/35 indeterminate FNAC result during the follow up, 23 (82.1%) was identified until the 3rd FNAC-US. The interval between 1st and 3rd re-biopsy was 13 months (median). Sonographic studies showed malignant suspected US features in G1: microcalcifications, central flow, hypoechogenicity and border irregularity. Conclusions: This study confirmed significantly increased risk for malignancy in patients over 39 years and suspects US features. The ultrasound study and category IV of Bethesda were correlated to malignancy in thyroid nodules with indeterminate cytology. This study demonstrated malignancy rate in thyroid nodules with first benign cytologic result and suspicious US features of malignancy and suggests repeating FNAC-US in this group of nodules for at least two times (until the 3rd FNAC) in about 13 months horizon. These findings can be used to guide surgical decision making / Mestrado / Clinica Medica / Mestre em Clinica Medica

Thyroid nodules represent a very common pathology. Using modern high-resolution ultrasound, nodules could be found in up to 68 % of patients. The most important task is the diagnosis of thyroid cancer which represents only about 5-15 % of nodules, however the incidence is still growing. Even with the use of a fine needle aspiration biopsy, it is not always possible to decide on the biological nature of the nodule. A significant proportion of such patients have to undergo thyroid surgery for diagnostic reason. Thyroid surgery is associated with risks to the patient and financial costs to the health-care system. In recent decades, the efforts to improve non-invasive diagnostics of thyroid nodules have been made. The thyroid elastography and thyroid autoimmunity are among the examined risk parameters. Using real-time strain elastography, thyroid carcinomas elasticity has been significantly reduced compared to benign thyroid nodules in our group of patients. The elastography of thyroid nodules can be used as a suitable complement to conventional sonographic examination. In our work, the combination of both methods (conventional ultrasound and elastography) increased the negative predictive value compared to both methods individually. The results of our work further indicate that, in case of absence of...

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The impact of the increasing incidence of thyroid cancer presents an interesting case study in public health policy and resource allocation. During the last three decades, thyroid cancer cases have increased by more than 400%. As an illness that affects the lives of hundreds of thousands each year, the human and economic costs will be magnified in the next decade. It is estimated that approximately 13-67% of people will have thyroid nodules during their life of which approximately 5% will be malignant. The standard treatment, a thyroidectomy frequently followed by radioactive 131 iodine treatment, accordingly would seem to be a likely future event for an increasing percentage of the population. Despite the magnitude of the increase, there has been no increase in age-adjusted mortality rates. This raises the question whether treatment is effective or warranted for many of these patients. Although there is almost no reliable data on its economic impact, its prevalence makes it likely that it is becoming one of the more expensive diseases in our health care system. Despite the pressing issue of its growth, thyroid cancer is one of the least studied and least funded cancers in the United States.

Thyroxine is the main secretory hormone of thyroid gland and it is produced in thyroglobulin by thyroid peroxidase/hydrogen peroxide/iodide system. After biosynthesis and secretion of thyroxine, it undergoes multiple metabolic reactions. The most important metabolic pathway is the stepwise deiodination from the inner ring or outer ring. Removal of one of the outer ring or phenolic ring iodines of biologically less active T4, leads to the formation of 3,5,3'-triiodothyronine or T3, a compound which is biologically more active. On the other hand, removal of one of the inner ring or tyrosyl ring iodines gives 3,3',5'-triiodothyronine (3,3',5'-T3 or rT3) which is a biologically inactive thyroid hormone. Three enzymes involved in this activation and inactivation pathway of thyroid hormones are known as iodothyronine deiodinases (IDs), which are dimeric integral-membrane selenoproteins. Depending upon the sequence and substrate specificity, three iodothyronine deiodinase enzymes have been identified, iodothyronine deiodinase-1 (ID-1), iodothyronine deiodinase-2 (ID-2) and iodothyronine deiodinase-3 (ID-3). ID-1 can catalyze both inner ring and outer ring deiodination of thyroid hormones whereas, ID-2 is selective to the outer ring deiodination. The type-1 and -2 deiodinases (ID-1 and ID-2) produces the biologically active hormone 3,5,3′-triiodothyronine (T3). These two enzymes also convert 3,3′,5′-triiodothyronine (reverse T3 or rT3) to 3,3′-diiodothyronine (3,3′-T2) by outer-ring deiodination (Scheme 1). The type-3 deiodinase (ID-3) catalyzes the convertion of T4 to rT3 by an inner-ring deiodination pathway. Apart from deiodination, there are several alternate pathways of thyroid hormone metabolism, which include sulfate conjugation and glucoronidation of the phenolic hydroxyl group of iodothyronines, the oxidative deamination and decarboxylation of the alanine side chain to form thyroacetic acid and thyronamines, respectively. Glucoronidation and sulfate conjugation changes the physico-chemical properties of iodothyronines dramatically. This thesis consists of five chapters. The first chapter provides a general introduction of biosynthesis of thyroid hormones and followed by deiodination by three iodothyronine deiodinase enzyme. This chapter also provides an overview of thyroid hormone transport and different transport proteins and their mode of binding with thyroid hormones. Apart from this, this chapter also provides a brief overview on other thyroid hormone metabolites. In the second chapter of the thesis, initial attempts in the development of different iodothyronine deiodinase mimics have been discussed. Goto et al have shown that the sterically hindered selenol 1 converts the thyroxine derivative 3 (N¬butyrylthyroxine methyl ester) to the corresponding triiodo derivative 4 by an outer-ring deiodination (Scheme 2). Although the reaction was carried out in organic solvent and a relatively higher temperature (50 °C) and longer reaction time (7 days) were required for about 65% deiodination, this study also provides an experimental evidence for the formation of selenenyl iodide (2) in the deiodination of a thyroxine derivative by an organoselenol. However, only one iodine was removed from the outer ring of 3, no inner ring deiodination was detected (Scheme 2). Interestingly, when compound 5 was treated with selenol 1 under similar conditions, no deiodination was observed (Scheme 3). This leads to assumption that presence of free phenolic hydroxyl group is important for the deiodinase activity. Based on this experimental observation, they proposed a mechanism which involves an enol¬keto tautomerism of the phenolic hydroxyl group. In the case of thyroxine, the outer-ring can undergo enol-keto tautomerism, whereas due to lack of free hydroxyl group, the inner ring cannot undergo similar kind of tautomerism. The enol-keto tautomerism probably makes the outer ring iodines more reactive than the inner ring iodines of thyroxine. We have developed tthe first chemmical modell for the inneer ring deioddination of TT4 and T3 by type 33 deiodinase . We have shown that naphthyl-baseed selenol 6 bearing a thhiol group in the cloose proximitty to the sellenium act aas an excelleent model foor ID-3 by selectively deiodinatting T4 andd T3 to prodduce rT3 annd 3,3'-T2, rrespectively,, under physiological relevant conditions. When 2 equuivalent of ccompound 66 was emplooyed in the assay, an almost quuantitative cconversion oof T4 to rT3 was observeed within 300 hours and there was no indicaation of the fformation off T3 or 3,3'-TT2. When the selenol group was repplaced with a thiol group in compouund 7, the ddeiodinase activity wwas decreassed. On thee other handd, when thee thiol groupp was replaaced with selenol mmoiety in commpound 8, thhe deiodinasse activity drramatically iincreased wiithout any change iin the selecttivity. Comppounds 10 and 11 havving N-methhylamino grooup were found too be more aactive than the correspponding unssubstituted ccompounds 7 and 8, respectively. However, introduction of a secondary amine adjacent to the selenol moiety into the compound 9 significantly reduces the deiodinase activity. In the third chapter synthesis, deiodinase activity and mechanism of deiodination of a series of peri-substituted naphthalene derivatives is discussed. Iodobenzene was used as halogen bond donor for the DFT calculations. From the orbital analysis it is observed that there is perfect orbital symmetry match between the HOMO of compound 8 (selenolate form) and LUMO of iodobenzene. When the selenolate form of 1-selenonaphthol interacts with iodobenzene, a halogen bonded adduct is formed. The negative charge on the selenium center decreases as it donates electron pair to the σ* orbital of C–I bond in iodobenzene and as a consequence the positive charge on the iodine center decreases (Figure 1). Addition of iodobenzene to 1-selenonaphthol led to a significant downfield shift in 77Se NMR spectrum of 1-selenonaphthol and with an increase in the concentration of iodobenzene, more downfield shift in the signal was observed. Figure 1. The charges obtained from Natural Bond Orbital (NBO) analysis for the selenolate form of (a) 1-selenonaphthol (b) iodobenzene, (c) halogen-bonded adduct On the basis of experimental end theoretical data, a mechanism for the deiodination of T4 by compound 8 is proposed. According to the mechanism, the initial interaction of one of the selenol moieties with an iodine leads to the formation of halogen bond. The transfer of electron density from selenium to the σ* orbital of the C−I bond generates a σ-hole or partial positive charge on the selenium atom, which facilitates an interaction between the halogen bonded selenium atom and the free selenol (selenolate) moiety (intermediate 12). The selenium−selenium interaction (chalcogen bond) strengthens the halogen bond, leading to a heterolytic cleavage of the C−I bond. The protonation of the resulting carbanion leads to the formation of rT3. On the other hand, the formation of an Se−Se bond produces the diselenide 13 with elimination of iodide as HI. The reductive cleavage of the Se−Se bond in compound 13 regenerates the diselenol 8 (Figure 2). In the fourth chapter deiodination of sulfated thyroid hormones is discussed. Sulfate conjugation is an important step in in the irreversible inactivation of thyroid hormones. Sulfate conjugation of the phenolic hydroxyl group stimulates the inner ring deiodination of T4 and T3 but it blocks the outer ring deiodination of T4 by ID-1. The thyroxine sulfate (T4S) undergoes faster deiodination as compared to the parent thyroid hormone T4. Only ID-1 catalyzes the deiodination of sulfated thyroid hormones. In contrast, ID-2 and ID-3 do not accept T4S and/or T3S as substrate. We have shown that iodothyronine sulfates can be readily deiodinated by synthetic deiodinase model compound 8 and its derivatives. In contrast to the inner ring-selective deiodination of T4, the synthetic compounds loses the selectivity and mediate both inner and outer-ring deiodination of T4S and outer ring deiodination of rT3S. From this study, we have also proposed that the enol-keto tautomerism is probably not required for the outer ring deiodination and the strength of halogen bonding controls the regioselective deiodination by model compounds. In the fifth chapter, the mechanism of inhibition of iodothyronine deiodinases by PTU and IAA is discussed with the help of model compounds. In the model study, it has been observed that compound 8 does not form a stable Se-I intermediate (14), which is essential for the formation of Se-S covalent bond with PTU. As a consequence, the deiodination of T4 by compound 8 is not inhibited by PTU. This study supports the proposal that ID-3 does not follow a ping-pong bi-substrate pathway for deiodination and may not form a stable E-Se-I intermediate, which is responsible for the insensitivity of ID-3 towards PTU. The biphenyl based diselenol 15 reacts with IAA and iodoacetamide to form the corresponding carboxymethylated product 17. On the other hand, compound 8 does not undergo the expected carboxymethylation by IAA and iodoacetamide, but they readily deiodinate both IAA and iodoacetamide. Based on this model study, a possible model is proposed for the insensitivity of ID-3 towards IAA. Iopanoic acid (18) is a well known radiocontrast agent and is used as adjunctive therapy with PTU and CBZ for the treatment of thyrotoxicosis.[9] We show in this chapter that iopanoic acid undergoes monodeiodination by compound 8 under physiological relevant conditions. The deiodinated products (19 and 20) from iopanoic acid are characterized by NMR spectroscopy and single crystal X-ray crystallography. It is observed that after monodeiodination, the strength of halogen bonding decreases and therefore, the monodeiodinated products do not undergo further deiodination.

Thyroid hormone is a master regulator of growth and development in all vertebrates. Thus, disruption of its synthesis and activity can lead to profound consequences. Past decade studies on thyroid function tests have established an efficient guideline for monitoring thyroid diseases, yet a significant proportion of healthcare providers do not defer to it in their practice. The aim of this study is to assess provider practices in the diagnosis and treatment of primary hypothyroidism due to autoimmunity at Boston Children's Hospital (CHB) for a primarily pediatric patient population. Commonly known as Hashimoto's thyroiditis (HT), this is the most common thyroid disease in the world as well as the most common manifestation of human autoimmune endocrine disease. Through CHB's bioinformatics institute, a rich data set was collected to assess the manner in which healthcare providers utilized relevant thyroid function tests (TFTs). This work assessed and confirmed the superior sensitivity of thyroid peroxidase autoantibodies (TPO) relative to thyroglobulin antibodies (TgAb) for diagnosing HT in children. We also verified proper utilization of thyroid stimulating hormone tests to monitor HT but concluded that there is a low utilization efficiency with regards to measurements of thyroid hormones (thyroxine and triiodothyronine). Based upon the observation of unnecessary monetary loss caused by improper TFTs utilization, it can be concluded that reflex testing at CHB may improve provider practices' efficiency for HT monitoring.