Congenital Hypothyroidism in Two Sudanese Families Harboring a Novel Iodotyrosine Deiodinase Mutation (IYD R279C).

Background: Congenital hypothyroidism due to defects in iodotyrosine deiodinase has variable phenotypes and can present as hypothyroid or with normal thyroid testing. Methods: Whole exome sequencing was performed in individuals from two families originating from different regions of Sudan. Mass spectrometry of urine and serum iodotyrosines was performed on subjects from both families. Results: A novel iodotyrosine deiodinase (IYD) mutation (c.835C>T; R279C) was identified in individuals from two Sudanese families inherited as autosomal recessive. The mutation was identified by multiple in silica analyses to likely be detrimental. Serum and urine monoiodotyrosine (MIT) and diiodotyrosine (DIT) were markedly elevated in the homozygous subjects. Conclusion: Measurement of serum and urine DIT and MIT was more sensitive than that of urine iodine or serum thyroid function tests to determine the effect of the IYD mutation.

Identification of natural product 3, 5-diiodotyrosine as APOBEC3B inhibitor to prevent somatic mutation accumulation and cancer progression.

BACKGROUND: The development of cancer is largely dependent on the accumulation of somatic mutations, indicating the potential to develop cancer chemoprevention agents targeting mutation drivers. However, ideal cancer chemoprevention agents that can effectively inhibit the mutation drivers have not been identified yet. METHODS: The somatic mutation signatures and expression analyses of APOBEC3B were performed in patient with pan-cancer. The computer-aided screening and skeleton-based searching were performed to identify natural products that can inhibit the activity of APOBEC3B. 4-nitroquinoline-1-oxide (4-NQO)-induced spontaneous esophageal squamous cell carcinoma (ESCC) and azoxymethane/dextran sulfate sodium (AOM/DSS)-induced spontaneous colon cancer mouse models were conducted to investigate the influences of APOBEC3B inhibitor on the prevention of somatic mutation accumulation and cancer progression. RESULTS: Here, we discovered that the cytidine deaminase APOBEC3B correlated somatic mutations were widely observed in a variety of cancers, and its overexpression indicated poor survival. SMC247 (3, 5-diiodotyrosine), as a source of kelp iodine without side effects, could strongly bind APOBEC3B (KD=65 nM) and effectively inhibit its deaminase activity (IC50=1.69 µM). Interestingly, 3, 5-diiodotyrosine could significantly reduce the clusters of mutations, prevent the precancerous lesion progression, and prolong the survival in 4-NQO-induced spontaneous ESCC and AOM/DSS-induced spontaneous colon cancer mouse models. Furthermore, 3, 5-diiodotyrosine could reduce colitis, increase the proportion and function of T lymphocytes via IL-15 in tumor microenvironment. The synergistic cancer prevention effects were observed when 3, 5-diiodotyrosine combined with PD-1/PD-L1 blockade. CONCLUSIONS: This is the first prove-of-concept study to elucidate that the natural product 3, 5-diiodotyrosine could prevent somatic mutation accumulation and cancer progression through inhibiting the enzymatic activity of APOBEC3B. In addition, 3, 5-diiodotyrosine could reduce the colitis and increase the infiltration and function of T lymphocytes via IL-15 in tumor microenvironment. 3, 5-diiodotyrosine combined with PD-1/PD-L1 blockade could elicit synergistic cancer prevention effects, indicating a novel strategy for both prevent the somatic mutation accumulation and the immune-suppressive microenvironment exacerbation.

Determination of 3-monoiodotyrosine and 3,5-diiodotyrosine in newborn urine and dried urine spots by isotope dilution tandem mass spectrometry.

High levels of 3-mono- and 3,5-diiodotyrosine (MIT and DIT, respectively) in urine have been related to iodotyrosine dehalogenase 1 deficiency, a type of congenital hypothyroidism. However, the determination of MIT and DIT in urine is not included in newborn screening programs performed in clinical laboratories to detect inborn errors of metabolism. We report here on the development of an analytical method for the determination of MIT and DIT in newborn urine and dried urine spots (DUS) by Liquid Chromatography Isotope Dilution tandem Mass Spectrometry (LC-IDMSMS). The development included the synthesis of 15N-monoiodotyrosine and 13C2-diiodotyrosine through the iodination of 15N-tyrosine and 13C2-tyrosine, respectively, using bis(pyridine)iodonium(I) tetrafluoroborate (IPy2BF4). Both labelled analogues were added at the beginning of the sample preparation procedure and used to develop both single- and double-spike LC-IDMS methods for the determination of MIT and DIT. The developed double spike methodology was able to quantify and correct possible MIT ↔ DIT interconversions throughout the sample preparation, which was observed for concentrated urine samples but not for DUS. Suppression matrix effects on the absolute signals of MIT and DIT were observed in urine samples but did not affect the IDMS results as recoveries on urine samples at different dilution factors could be considered quantitative. Method detection limits were 0.018 and 0.046 ng g-1 (limits of quantification 0.06 and 0.15 ng g-1) by single-spike IDMS, for MIT and DIT, respectively, in the analysis of urine samples and 0.07 and 0.05 ng g-1 (limits of quantification 0.23 and 0.17 ng g-1) for MIT and DIT, respectively, in the analysis of DUS. No significant differences were obtained for MIT concentrations in the analysis of the same newborn samples stored as liquid urine or DUS when the results were corrected for the creatinine content. Finally, 36 DUS samples from healthy newborns were analyzed and MIT was detected in all samples at low ng mg-1creatinine levels.

Serum diiodotyrosine - a biomarker to differentiate destructive thyroiditis from Graves' disease.

OBJECTIVE: Conventional diagnostic methods are limited in their ability to differentiate destructive thyroiditis from Graves' disease. We hypothesised that serum diiodotyrosine (DIT) and monoiodotyrosine (MIT) levels could be biomarkers for differentiating destructive thyroiditis from Graves' disease. DESIGN: Patients with destructive thyroiditis (n = 13) and Graves' disease (n = 22) were enrolled in this cross-sectional study. METHODS: We assayed the serum DIT and MIT levels using liquid chromatography-tandem mass spectrometry. A receiver operating characteristic (ROC) curve analysis was used to determine the sensitivity and specificity of the serum DIT and MIT levels as biomarkers for differentiating destructive thyroiditis from Graves' disease. RESULTS: The serum DIT and MIT levels were significantly higher in patients with destructive thyroiditis than in those with Graves' disease. The ROC curve analysis showed that the serum DIT levels (≥359.9 pg/mL) differentiated destructive thyroiditis from Graves' disease, significantly, with 100.0% sensitivity and 95.5% specificity (P < 0.001). The diagnostic accuracy of the serum MIT levels (≥119.4 pg/mL) was not as high as that of the serum DIT levels (sensitivity, 84.6%; specificity, 77.3%; P = 0.001). CONCLUSIONS: The serum DIT levels may serve as a novel diagnostic biomarker for differentiating destructive thyroiditis from Graves' disease.

Environmental photochemical fate and UVC degradation of sodium levothyroxine in aqueous medium.

The synthetic hormone sodium levothyroxine (LTX) is one of the most prescribed drugs in the world and the most effective in hypothyroidism treatment. The presence of LTX in the environment has become a matter of major concern due to the widespread use of this hormone and by the fact that it is only partially removed in conventional water and sewage treatment plants. However, information regarding the photochemical fate of this hormone in environmental or engineered systems is scarce in the literature. In this work, the sunlight-driven direct and indirect LTX degradation was investigated by determining the photolysis quantum yield, ΦLTX = 3.80 (± 0.02) × 10-5, as well as the second-order kinetic constants of the reactions with hydroxyl radicals, kLTX,•OH = 1.50 (± 0.01) × 1010 L mol-1 s-1 and singlet oxygen, kLTX,1O2 = 1.47 (± 0.66) × 108 L mol-1 s-1. Mathematical simulations indicate that LTX photodegradation is favored in shallow, nitrite-rich, and dissolved organic matter (DOM)-poor environments, with LTX half-life times varying from less than 10 days to about 80 days. LTX removals of 85 and 95% were achieved by UVC photolysis and UVC/H2O2 after 120 min, respectively. Three transformation products, triiodothyronine, diiodothyronine, and diiodotyrosine, were identified during LTX degradation by the UVC-based processes studied. The results herein regarding photo-induced kinetics coupled with environmental fate simulations may help evaluate LTX persistence and also the design of water and wastewater treatment processes.

Thyroid hormone binding motifs and iodination pattern of thyroglobulin.

A phylogenetically conserved 5-residue thyroid hormone (TH)- binding motif was originally found in a few TH plasma carriers and, more recently, in all known plasma and cell-associated proteins interacting with TH as well as in proteins involved in iodide uptake. Minor variations of the motif were found, depending on the particular class of those proteins. Since thyroglobulin (Tg) is the protein matrix for TH synthesis starting from iodination of a selected number of tyrosines (to form first monoiodotyrosine (MIT) and diiodotyrosine (DIT) and then T3 and T4), we hypothesized that by searching the presence of perfect or imperfect versions of that motif in two Tg species (human and murine) in which the iodinated tyrosines and pattern of iodotyrosine/iodothyronine formation are known, we could have found relevant explanations. Explanations, which are not furnished by the simple possession of tyrosine-iodination motifs and sequence of the iodination motif, concern why only some (but not other) tyrosine residues in one species are iodinated and why they have a particular iodination pattern. In this bioinformatics study, we provide such explanations.

Reversibly Switchable, pH-Dependent Peptide Ligand Binding via 3,5-Diiodotyrosine Substitutions.

Cell type-specific targeting ligands utilized in drug delivery applications typically recognize receptors that are overexpressed on the cells of interest. Nonetheless, these receptors may also be expressed, to varying extents, on off-target cells, contributing to unintended side effects. For the selectivity profile of targeting ligands in cancer therapy to be improved, stimuli-responsive masking of these ligands with acid-, redox-, or enzyme-cleavable molecules has been reported, whereby the targeting ligands are exposed in specific environments, e.g., acidic tumor hypoxia. One possible drawback of these systems lies in their one-time, permanent trigger, which enables the "demasked" ligands to bind off-target cells if released back into the systemic circulation. A promising strategy to address the aforementioned problem is to design ligands that show selective binding based on ionization state, which may be microenvironment-dependent. In this study, we report a systematic strategy to engineer low pH-selective targeting peptides using an M2 macrophage-targeting peptide (M2pep) as an example. 3,5-Diiodotyrosine mutagenesis into native tyrosine residues of M2pep confers pH-dependent binding behavior specific to acidic environment (pH 6) when the amino acid is protonated into the native tyrosine-like state. At physiological pH of 7.4, the hydroxyl group of 3,5-diiodotyrosine on the peptide is deprotonated leading to interruption of the peptide native binding property. Our engineered pH-responsive M2pep (Ac-Y-Î-Î) binds target M2 macrophages more selectively at pH 6 than at pH 7.4. In addition, 3,5-diiodotyrosine substitutions also improve serum stability of the peptide. Finally, we demonstrate pH-dependent reversibility in target binding via a postbinding peptide elution study. The strategy presented here should be applicable for engineering pH-dependent functionality of other targeting peptides with potential applications in physiology-dependent in vivo targeting applications (e.g., targeting hypoxic tumor/inflammation) or in in vitro receptor identification.

[The study of the metabolism of iodotyrosines included in the iodized milk protein in rats].

In the course of evolution in animals and humans, a complex and effective system for providing the body with iodine in the form of various organic and inorganic compounds was developed. The metabolism of inorganic iodine has been studied quite well, in contrast to the mechanism of assimilation of its organic compounds. Among the latter, iodotyrosines, which are part of iodinated milk proteins, are of particular interest. To distinguish the peculiarities of the biotransformation of iodotyrosines in the animals' organism, their concentration and the concentration of tyrosine in blood plasma of rats after single administration of iodinated milk proteins were determined. For comparison, in parallel a group of animals received potassium iodide. The tested preparations were administered intragastrically with a probe in the form of aqueous solutions at a dose equivalent to 30 µg iodine per 1 kg of body weight. The level of mono- and diiodotyrosine in rat blood plasma was determined by HPLC with a mass spectrometer detector. The tyrosine content was determined on an automatic amino acid analyzer. The registration of the indices was carried out before the administration and 1, 4 and 24 hours after the administration of the substances. In the course of the conducted studies it was found that when iodinated milk proteins are once administered, a significant increase in the concentrations of monoiodotyrosine and diiodotyrosine is observed. The maximum level of iodinated amino acids, exceeding the control values by more than 6 fold, was recorded 4 hours after the ingestion of iodine-containing organic compounds into the body. At the same time interval, an increase in the concentration of tyrosine was observed in one of the experimental groups receiving iodinated milk protein. The simultaneous presence of tyrosine and its iodinated derivatives in blood plasma may indicate that monoiodotyrosine and diiodotyrosine are capable of being absorbed into the systemic bloodstream without metabolic transformations in the liver. Under introduction of potassium iodide, an increase in blood plasma concentration of monoiodotyrosine by 35% compared to the control was observed only after 24 hours, which may be a consequence of the activation of the thyroid gland due to the intake of an increased amount of iodine.

Rapid Identification of Unknown Organic Iodine in Small-Volume Complex Biological Samples Based on Nanospray Mass Spectrometry Coupled with in-Tube Solid Phase Microextraction.

A new method for rapid screening of unknown organic iodine (OI) in small-volume complex biological samples was developed using in-tube solid phase microextraction (SPME) nanospray mass spectrometry (MS). The method proposed a new identification scheme for OI based on nanospray high-resolution mass spectrometry (HR-MS). The mass ranges of OI ions were confirmed using the t-MS2 scan mode first; then, the possible precursor ions of OI were selected and identified orderly in full MS/ddMS2 and t-MS2 scan modes. Besides, in-tube SPME was used for the pretreatment of small-volume biological samples, and it was the first time in-tube SPME combined with nanospray MS for OI identification. The whole analysis procedure took only 8 min and consumed 50 µL per sample. Using the new method, six kinds of OI added to urine and an unknown OI C12H23O11I in human milk were successfully identified. Moreover, the proposed identification scheme is also suitable for other ambient mass spectrometry (AMS) to determine unknown compounds with characteristic fragment ions.

Effects of 3,5-Diiodotyrosine and Potassium Iodide on Thyroid Function and Oxidative Stress in Iodine-Excess Wistar Rats.

The objective of this study was to investigate the effects of organic iodine (3,5-diiodotyrosine, DIT) and inorganic iodine (potassium iodine, KI) on thyroid function and oxidative stress in iodine-excess Wistar rats. Seventy-two Wistar rats were randomly divided into eight groups: normal control (NC), thyroid tablet-induced hyperthyroidism model (HM), low DIT (L-DIT), medium DIT (M-DIT), high DIT (H-DIT), low KI (L-KI), medium KI (M-KI), and high KI (H-KI). All rats were fed ad libitum for 30 days. Morphological changes in the thyroid, absolute and relative weights of the thyroid, thyroid function markers free triiodothyronine (FT3) and free thyroxine (FT4), urinary iodine level, and oxidative stress indicators were measured. Compared to the HM groups, the FT3 and FT4 levels decreased in the L-DIT groups; the thyroid weight and thyroid weight/body weight values decreased markedly in the L-DIT and M-DIT groups; serum superoxide dismutase/malondialdehyde increased markedly; glutathione peroxidase activity increased markedly in the L-DIT groups; and malondialdehyde levels decreased significantly in the M-DIT groups. However, the FT3 and FT4 levels decreased and glutathione peroxidase levels increased significantly in the DIT groups compared to their corresponding KI groups. Additionally, urinary iodine levels increased significantly in both DIT and KI groups, while the highest urinary iodine excretion was showed in the DIT groups among groups. When the addition of iodine with the same doses in iodine-excess rats, although neither DIT nor KI normalized iodine levels in the iodine-excess rats, the DIT did less damage than did KI to thyroid follicular cells. Therefore, DIT rather than KI had a protective effect by balancing the antioxidant system when exposed to supraphysiological iodine. These suggest that DIT may be used as a new alternative iodized salt in the universal salt iodization to avoid the potential damage of surplus KI.

In silico investigation of potential TRAF6 inhibitor from traditional Chinese medicine against cancers.

It has been indicated that tumor necrosis factor receptor-associated factor-6 (TRAF6) will upregulate the expression of hypoxia-inducible factor-1α (HIF-1α) and promote tumor angiogenesis. TRAF6 proteins can be treated as drug target proteins for a differentiation therapy against cancers. As structural disordered disposition in the protein may induce the side-effect and reduce the occupancy for ligand to bind with target protein, PONDR-Fit protocol was performed to predict the disordered disposition in TRAF6 protein before virtual screening. TCM compounds from the TCM Database@Taiwan were employed for virtual screening to identify potent compounds as lead compounds of TRAF6 inhibitor. After virtual screening, the MD simulation was performed to validate the stability of interactions between TRAF6 proteins and each ligand. The top TCM compounds, tryptophan, diiodotyrosine, and saussureamine C, extracted from Saussurea lappa Clarke, Bos taurus domesticus Gmelin, and Lycium chinense Mill., have higher binding affinities with target protein in docking simulation. However, the docking pose of TRAF6 protein with tryptophan is not stable under dynamic condition. For the other two TCM candidates, diiodotyrosine and saussureamine C maintain the similar docking poses under dynamic conditions. Hence, we propose the TCM compounds, diiodotyrosine and saussureamine C, as potential candidates as lead compounds for further study in drug development process with the TRAF6 protein against cancer.

[Thyroid hormones and their precursors. II. Species-specific properties]. / Pajzsmirigyhormonok és eloanyagaik. II. Részecske-specifikus tulajdonságok.

This paper surveys the species-specific physico-chemical parameters (basicity and lipophilicity) and related biological functions of thyroid hormones (thyroxine, liothyronine and reverse liothyronine) and their biological precursors (tyrosine, monoiodotyrosine and diiodotyrosine). The protonation macroconstants were determined by 1H NMR-pH titrations while the microconstants were determined by a multimodal spectroscopic-deductive methodology using auxiliary derivatives of reduced complexity. Our results show that the different number and/or position of iodine are the key factors to influence the phenolate basicity. The ionization state of the phenolate site is crucial in the biosynthesis and protein binding of thyroid hormones. The role of the protonation state in the receptor binding was investigated by an in silico docking method. Microspecies of thyroid hormones were docked to the thyroid hormone receptor isoforms. Our results quantitate at the molecular level how the ionization stage and the charge distribution influence the protein binding. The anionic form of the carboxyl group is essential for the protein binding, whereas the protonated form of the amino group loosens it. The protonation state of the phenolate plays a role of secondary importance in the receptor binding. The combined results of docking and microspeciation studies show that microspecies of the highest concentration at the pH of blood are not the strongest binding ones. The site-specific lipophilicity of our investigated molecules was determined with the measurement of distribution coefficients at different pH using carboxymethyl- and O-methyl-derivatives to mimic the partition of some of the individual microspecies. Correction factors were determined and introduced. Our data show that the iodinated aromatic ring system is the definitive structural element that fundamentally determines the lipophilicity of thyroid hormones, whereas the protonation state of the aliphatic part is essential in receptor binding. The membrane transport of thyroid hormones can be well interpreted in terms of the site-specific lipophilicity. At physiological pH these biomolecules are strongly amphipathic due to the lipophilic aromatic rings and hydrophilic amino acid side chains which can well be the reason why thyroid hormones cannot cross membranes by passive diffusion and they even become constituents of biological membranes. The site-specific physico-chemical characterization of the thyroid hormones is of fundamental importance to understand their (patho) physiological behavior and also, to influence the therapeutic properties of their drug candidate derivatives at the molecular level.

Towards the pre-clinical diagnosis of hypothyroidism caused by iodotyrosine deiodinase (DEHAL1) defects.

DEHAL1 (also named IYD) is the thyroidal enzyme that deiodinates mono- and diiodotyrosines (MIT, DIT) and recycles iodine, a scarce element in the environment, for the efficient synthesis of thyroid hormone. Failure of this enzyme leads to the iodotyrosine deiodinase deficiency (ITDD), characterized by hypothyroidism, compressive goiter and variable mental retardation, whose diagnostic hallmark is the elevation of iodotyrosines in serum and urine. However, the specific diagnosis of this type of hypothyroidism is not routinely performed, due to technical and practical difficulties in iodotyrosine determinations. A handful of mutations in the DEHAL1 gene have been identified as the molecular basis for the ITDD. Patients harboring DEHAL1 defects so far described all belong to consanguineous families, and psychomotor deficits were present in some affected individuals. This is probably due to the lack of biochemical expression of the disease at the beginning of life, which causes ITDD being undetected in screening programs for congenital hypothyroidism, as currently performed. This worrying feature calls for efforts to improve pre-clinical detection of iodotyrosine deiodinase deficiency during the neonatal time. Such a challenge poses questions of patho-physiological (natural history of the disease, environmental factors influencing its expression) epidemiological (prevalence of ITDD) and technical nature (development of optimal methodology for safe detection of pre-clinical ITDD), which will be addressed in this review.

Iodotyrosine deiodinase: a unique flavoprotein present in organisms of diverse phyla.

Iodide is required for thyroid hormone synthesis in mammals and other vertebrates. The role of both iodide and iodinated tyrosine derivatives is currently unknown in lower organisms, yet the presence of a key enzyme in iodide conservation, iodotyrosine deiodinase (IYD), is suggested by genomic data from a wide range of multicellular organisms as well as some bacteria. A representative set of these genes has now been expressed, and the resulting enzymes all catalyze reductive deiodination of diiodotyrosine with kcat/Km values within a single order of magnitude. This implies a physiological presence of iodotyrosines (or related halotyrosines) and a physiological role for their turnover. At least for Metazoa, IYD should provide a new marker for tracing the evolutionary development of iodinated amino acids as regulatory signals through the tree of life.

Ultrasound-assisted enzymatic hydrolysis for iodinated amino acid extraction from edible seaweed before reversed-phase high performance liquid chromatography-inductively coupled plasma-mass spectrometry.

The combination of reverse phase high performance liquid chromatography (RP-HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) was used for the determination of monoiodotyrosine (MIT) and diiodotyrosine (DIT) in edible seaweed. A sample pre-treatment based on ultrasound assisted enzymatic hydrolysis was optimized for the extraction of these iodinated amino acids. Pancreatin was selected as the most adequate type of enzyme, and parameters affecting the extraction efficiency (pH, temperature, mass of enzyme and extraction time) were evaluated by univariate approaches. In addition, extractable inorganic iodine (iodide) was also quantified by anion exchange high performance liquid chromatography (AE-HPLC) coupled with ICP-MS. The proposed procedure offered limits of detection of 1.1 and 4.3ngg(-1) for MIT and DIT, respectively. Total iodine contents in seaweed, as well as total iodine in enzymatic digests were measured by ICP-MS after microwave assisted alkaline digestion with tetramethylamonium hydroxide (TMAH) for total iodine assessment, and also by treating the pancreatin extracts (extractable total iodine assessment). The optimized procedure was successfully applied to five different types of edible seaweed. The highest total iodine content, and also the highest iodide levels, was found in the brown seaweed Kombu (6646±45µgg(-1)). Regarding iodinated amino acids, Nori (a red seaweed) was by far the one with the highest amount of both species (42±3 and 0.41±0.024µgg(-1) for MIT and DIT, respectively). In general, MIT concentrations were much higher than the amounts of DIT, which suggests that iodine from iodinated proteins in seaweed is most likely bound in the form of MIT residues.

[Thyroid hormones and their precursors I. Biochemical properties]. / Pajzsmirigyhormonok és eloanyagaik I. Biokémiai tulajdonságok.

This paper and the following one (see the next issue of Acta Pharmaceutica Hungarica) survey the biological roles and the related site-specific physico-chemical parameters (basicity and lipophilicity) of the presently known thyroid hormones (thyroxine, liothyronine and reverse liothyronine) and their biological precursors (monoiodotyrosine and diiodotyrosine). Here the literature of the thyroid hormone biochemistry, biosynthesis, plasma- and membrane transport is summarized, focusing on the pH-dependent processes. Biosyntheses of the thyroid hormones take place by oxidative coupling of two iodotyrosine residues catalyzed by thyreoperoxidase in thyreoglobulin. The protonation state of the precursors, especially that of the phenolic OH is crucial for the biosynthesis, since anionic iodotyrosine residues can only be coupled in the thyroid hormone biosyntheses. In the blood more than 99% of the circulating thyroid hormone is bound to plasma proteins among which the thyroxine-binding globulin and transthyretin are crucial. The amphiphilic character of the hormones is assumed to be the reason why their membrane transport is an energy-dependent, transport-mediated process, in which the organic anion transporter family, mainly OATP1C1, and the amino acid transporters, such as MCT8 play important roles. Liothyronine is the biologically active hormone; it binds the thyroid hormone receptor, a type of nuclear receptor. There are two major thyroid hormone receptor (TR) isoforms, alfa (TRalpha) and beta (TRbeta). The activation of the TRalpha is associated with modifications in cardiac behavior, while activation of the TRbeta is associated with increasing metabolic rates, resulting in weight loss and reduction of blood plasma lipid levels. The affinity of the thyroid hormones for different proteins depends on the ionization state of the ligands. The site-specific physico-chemical characterization of the thyroid hormones is of fundamental importance to understand their (patho)physiological behavior and also, to influence their therapeutic properties at the molecular level.

Species-specific lipophilicity of thyroid hormones and their precursors in view of their membrane transport properties.

A total of 30 species-specific partition coefficients of three thyroid hormones (thyroxine, liothyronine, reverse liothyronine) and their two biological precursors (monoiodotyrosine, diiodotyrosine) are presented. The molecules were studied using combined methods of microspeciation and lipophilicity. Microspeciation was carried out by (1)H NMR-pH and UV-pH titration techniques on the title compounds and their auxiliary derivatives of reduced complexity. Partition of some of the individual microspecies was mimicked by model compounds of the closest possible similarity, then correction factors were determined and introduced. Our data show that the iodinated aromatic ring system is the definitive structural element that fundamentally determines the lipophilicity of thyroid hormones, whereas the protonation state of the aliphatic part plays a role of secondary importance. On the other hand, the lipophilicity of the precursors is highly influenced by the protonation state due to the relative lack of overwhelmingly lipophilic moieties. The different logp values of the positional isomers liothyronine and reverse liothyronine represent the importance of steric and electronic factors in lipophilicity. Our investigations provided clear indication that overall partition, the best membrane transport - predicting physico-chemical parameter depends collectively on the site-specific basicity and species-specific partition coefficient. At physiological pH these biomolecules are strongly amphipathic due to the lipophilic aromatic rings and hydrophilic amino acid side chains which can well be the reason why thyroid hormones cannot cross membranes by passive diffusion and they are constituents of biological membranes. The lipophilicity profile of thyroid hormones and their precursors are calculated and depicted in terms of species-specific lipophilicities over the entire pH range.

Differentiation of enantiomeric drugs by iodo-substituted L-amino acid references under electrospray ionization mass spectrometric conditions.

RATIONALE: In chiral differentiation by mass spectrometry, use of a single reference that differentiates various classes of compounds including drugs is ideal, but so far there are no such reports in the literature. We have successfully used iodo-substituted amino acids for the chiral differentiation of ten enantiomeric pairs of drugs. METHODS: To achieve the chiral differentiation, the trimeric Cu complex ion consisting of two chiral reference molecules and an analyte molecule was generated under positive ion electrospray ionization (ESI) conditions and subsequently subjected for collision- induced dissociation (CID) experiments using an LCQ ion trap mass spectrometer. The spectra were recorded under identical experimental conditions for both the enantiomers, and were averages of 30 scans. Cooks' kinetic method and chiral recognition ratio method (CR method) were used to arrive at the R(chiral) /CR values, respectively. RESULTS: The R(chiral) or CR values of the studied drugs are higher for 3,5-diiodo-L-tyrosine as the reference, than for 4-iodo-L-phenylalanine, except for isoproterenol and atenolol. Both the references show the same selectivity (R- or S-selectivity) towards all the studied drugs. With 3,5-diiodo-L-tyrosine as the reference, an R(chiral) value of 12.75 is obtained for DOPA and this is the highest reported value in the literature till now. The suitability of the current method in measuring enantiomeric excess is also demonstrated for DOPA. CONCLUSIONS: The use of 4-iodo-L-phenylalanine or 3,5-diiodo-L-tyrosine as a chiral reference for the chiral differentiation of ten enantiomeric pairs of pharmaceutically important drugs has been demonstrated. The chiral differentiation of pregabalin, tenofovir and pramipexole is reported for the first time. This study shows that it is possible to develop a single chiral reference compound for the differentiation of a group of chiral drugs having some similarities.

Development of anion-exchange/reversed-phase high performance liquid chromatography-inductively coupled plasma-mass spectrometry methods for the speciation of bio-available iodine and bromine from edible seaweed.

Anion exchange high performance liquid chromatography hyphenated with inductively coupled plasma-mass spectrometry has been novelly applied to assess inorganic (iodide and iodate) and organic (3-iodotyrosine - MIT, and 3,5-diiodotyrosine - DIT) iodine species in a single chromatographic run. The optimized operating conditions (Dionex IonPac AS7, gradient elution with 175 mM ammonium nitrate plus 15% (v/v) methanol, pH 3.8, as a mobile phase and flow rates within the 0.5-1.5 mL min(-1) range) have also been used to perform inorganic bromine speciation analysis (bromide and bromate). The developed method has been applied for determining the bio-available contents of iodine and bromine species in dialyzates from edible seaweed. Reverse phase high performance liquid chromatography (Zorbax Eclipse XDB-C8, gradient elution with 0.2% (m/m) acetic acid, and 0.2% (m/m) acetic acid in methanol, as mobile phases, and a constant flow rate of 0.75 mL min(-1)) also hyphenated with inductively coupled plasma-mass spectrometry was used to confirm the presence of organic iodine species (MIT and DIT) in the dialyzates. The verification of the presence of iodinated amino acids (MIT and DIT) in the extracts was also performed by reverse phase high performance liquid chromatography-electrospray ionization-mass spectrometry (LTQ Orbitrap). The developed methods have provided good repeatability (RSD values lower than 10% for both anion exchange and reverse phase separations) and analytical recoveries within the 90-105% range for all cases. The in vitro bio-availability method consisted of a simulated gastric and an intestinal digestion/dialysis (10 kDa molecular weight cut-off - MWCO) two-stage procedure. Iodide and MIT were the main bio-available species quantified, whereas bromide was the major bromine species found in the extracts.

Expression pattern of iodotyrosine dehalogenase 1 (DEHAL1) during chick ontogeny.

The iodotyrosine dehalogenase1 (DEHAL1) enzyme is a transmembrane protein that belongs to the nitroreductase family and shows a highly conserved N-terminal domain. DEHAL1 is present in the liver, kidney and thyroid of mammals. DEHAL1 is known to act on diiodotyrosine (DIT) and monoiodotyrosine (MIT), and is involved in iodine recycling in relation to thyroglobulin. Here, we show the distribution of DEHAL1 during gastrulation to neurulation in developing chick. Immunocytochemistry using an anti-serum directed against the N-terminal domain (met(27)-trp(180) fragment) of human DEHAL1 revealed labelled cells in the embryonic ectoderm, embryonic endoderm, neural plate and in the yolk platelets of the chick embryo at gastrulation stage. Distinct DEHAL1 positive cells were located in the presumptive head ectoderm, presumptive neural crest, head mesenchymal cells and in the dorsal, lateral and ventral parts of neural tube during neurulation. Some cells located at the margin of the developing notochord and somites were also DEHAL1-positive. While the functional significance of this observation is not known, it is likely that DEHAL1 might serve as an agent that regulates cell specific deiodination of MIT and DIT before the onset of thyroidal secretion. The presence of DEHAL1 in different components of the chick embryo suggests its involvement in iodine turnover prior to the formation of functional thyroid.