Simultaneous Identification of Major Thyroid Hormones by a Nickel Immobilized Biological Nanopore.

Thyroid hormones (THs) are a variety of iodine-containing hormones that demonstrate critical physiological impacts on cellular activities. The assessment of thyroid function and the diagnosis of thyroid disorders require accurate measurement of TH levels. However, largely due to their structural similarities, the simultaneous discrimination of different THs is challenging. Nanopores, single-molecule sensors with a high resolution, are suitable for this task. In this paper, a hetero-octameric Mycobacterium smegmatis porin A (MspA) nanopore containing a single nickel ion immobilized to the pore constriction has enabled simultaneous identification of five representative THs including l-thyroxine (T4), 3,3',5-triiodo-l-thyronine (T3), 3,3',5'-triiodo-l-thyronine (rT3), 3,5-diiodo-l-thyronine (3,5-T2) and 3,3'-diiodo-l-thyronine (3,3'-T2). To automate event classification and avoid human bias, a machine learning algorithm was also developed, reporting an accuracy of 99.0%. This sensing strategy is also applied in the analysis of TH in a real human serum environment, suggesting its potential use in a clinical diagnosis.

Thyroid hormone profile in preeclampsia patients: a case control study.

Objective: Preeclamptic women are reported to have a higher incidence of thyroid dysfunction that correlates with the severity of preeclampsia. The aim of this study was to assess thyroid hormone profiles in in pregnant women with preeclampsia and gestational hypertension and the risk for thyroid dysfunction.Methods: In this study, age-matched pregnant females in the second trimester of pregnancy, diagnosed with preeclampsia (PE), gestational hypertension (GH), as cases, and apparently healthy normotensive (NT) pregnant woman as controls were recruited. Blood samples were drawn for the assessment of thyroid hormone (TSH, FT3 and FT4) levels and thyroid dysfunction.Results: Out of the total of 133 pregnant women recruited for this study, sub-clinical hypothyroidism was the only thyroid dysfunction common to all study groups, with a prevalence of 3.3% in both PE and NT groups, and 4.3% in the GH group. 1% of women in the PE group had sub-clinical hyperthyroidism, compared to 3.3% in the NT group. Although TSH and FT3 were elevated in normotensives, mean differences between the three groups were not statistically significant. However, mean FT4 levels in the GH group (12.99 ± 1.24) and PE group (12.33 ± 2.26), when compared to the control group (11.55 ± 1.94), were significantly higher (p < 0.05).Conclusion: Undiagnosed subclinical hypothyroidism was found in all the categories of pregnant women studied, which if uncontrolled, could increase the risk of pregnancy-related complications, especially in pregnant women with preeclampsia and gestational hypertension.

A Simple Substitution on Thyroid Hormones Remarkably Alters the Regioselectivity of Deiodination by a Deiodinase Mimic.

The regioselective deiodinations of L-thyroxine (T4) play key roles in the thyroid hormone homeostasis. These reactions are catalyzed by three isoforms of the selenoenzymes, iodothyronine deiodinases (Dio1, Dio2 and Dio3), which are highly homologous in nature. Dio1 mediates 5'- or 5-deiodinations of T4 to produce T3 and rT3, respectively. In contrast, Dio2 and Dio3 are selective to 5'- or 5-deiodination to produce T3 and rT3, respectively. Understanding of the regioselectivity of deiodination at the molecular level is important as abnormal levels of thyroid hormone have been implicated in various clinical conditions, such as hypoxia, myocardial infarction, neuronal ischemia and cancer. In this paper, we report that the electronic properties of the iodine atoms in thyroxine (T4) can be modulated through a simple substitution in the 4'-phenolic moiety. This leads to the change in the regioselectivity of deiodination by different small molecule mimics of Dio enzymes. By using this chemical approach, we also show that the substitution of a strong electron withdrawing group facilitates the removal of all four iodine atoms in the T4 derivative. Theoretical investigations on the hydrogen bonded adducts of T4 with imidazole indicate that the charge on the iodine atoms depend on the nature of hydrogen bond between the -OH group of T4 and the imidazole moiety. While the imidazole can act as either hydrogen bond acceptor (HBA) or hydrogen bond donor (HBD), the protonated imidazole acts exclusively as HBD in T4-imidazole complex. These studies support the earlier observations that the histidine residue at the active sites of the deiodinases play an important role not only in the substrate binding, but also in altering the regioselectivity of the deiodination reactions.

Cryo-EM structure of native human thyroglobulin.

The thyroglobulin (TG) protein is essential to thyroid hormone synthesis, plays a vital role in the regulation of metabolism, development and growth and serves as intraglandular iodine storage. Its architecture is conserved among vertebrates. Synthesis of triiodothyronine (T3) and thyroxine (T4) hormones depends on the conformation, iodination and post-translational modification of TG. Although structural information is available on recombinant and deglycosylated endogenous human thyroglobulin (hTG) from patients with goiters, the structure of native, fully glycosylated hTG remained unknown. Here, we present the cryo-electron microscopy structure of native and fully glycosylated hTG from healthy thyroid glands to 3.2 Å resolution. The structure provides detailed information on hormonogenic and glycosylation sites. We employ liquid chromatography-mass spectrometry (LC-MS) to validate these findings as well as other post-translational modifications and proteolytic cleavage sites. Our results offer insights into thyroid hormonogenesis of native hTG and provide a fundamental understanding of clinically relevant mutations.

Mass spectrometry in the diagnosis of thyroid disease and in the study of thyroid hormone metabolism.

The importance of thyroid hormones in the regulation of development, growth, and energy metabolism is well known. Over the last decades, mass spectrometry has been extensively used to investigate thyroid hormone metabolism and to discover and characterize new molecules involved in thyroid hormones production, such as thyrotropin-releasing hormone. In the earlier period, the quantification methods, usually based on gas chromatography-mass spectrometry, were complicated and time consuming. They were mainly focused on basic research, and were not suitable for clinical diagnostics on a routine basis. The development of the modern mass spectrometers, mainly coupled to liquid chromatography, enabled simpler sample preparation procedures, and the accurate quantification of thyroid hormones, of their precursors, and of their metabolites in biological fluids, tissues, and cells became feasible. Nowadays, molecules of physiological and pathological interest can be assayed also for diagnostic purposes on a routine basis, and mass spectrometry is slowly entering the clinical laboratory. This review takes stock of the advancements in the field of thyroid metabolism that were carried out with mass spectrometry, with special focus on the use of this technique for the quantification of molecules involved in thyroid diseases.

Role of PKM2-Mediated Immunometabolic Reprogramming on Development of Cytokine Storm.

The cytokine storm is a marker of severity of various diseases and increased mortality. The altered metabolic profile and energy generation of immune cells affects their activation, exacerbating the cytokine storm. Currently, the emerging field of immunometabolism has highlighted the importance of specific metabolic pathways in immune regulation. The glycolytic enzyme pyruvate kinase M2 (PKM2) is a key regulator of immunometabolism and bridges metabolic and inflammatory dysfunction. This enzyme changes its conformation thus walks in different fields including metabolism and inflammation and associates with various transcription factors. This review summarizes the vital role of PKM2 in mediating immunometabolic reprogramming and its role in inducing cytokine storm, with a focus on providing references for further understanding of its pathological functions and for proposing new targets for the treatment of related diseases.

Diphenyl-Methane Based Thyromimetic Inhibitors for Transthyretin Amyloidosis.

Thyromimetics, whose physicochemical characteristics are analog to thyroid hormones (THs) and their derivatives, are promising candidates as novel therapeutics for neurodegenerative and metabolic pathologies. In particular, sobetirome (GC-1), one of the initial halogen-free thyromimetics, and newly synthesized IS25 and TG68, with optimized ADME-Tox profile, have recently attracted attention owing to their superior therapeutic benefits, selectivity, and enhanced permeability. Here, we further explored the functional capabilities of these thyromimetics to inhibit transthyretin (TTR) amyloidosis. TTR is a homotetrameric transporter protein for THs, yet it is also responsible for severe amyloid fibril formation, which is facilitated by tetramer dissociation into non-native monomers. By combining nuclear magnetic resonance (NMR) spectroscopy, computational simulation, and biochemical assays, we found that GC-1 and newly designed diphenyl-methane-based thyromimetics, namely IS25 and TG68, are TTR stabilizers and efficient suppressors of TTR aggregation. Based on these observations, we propose the novel potential of thyromimetics as a multi-functional therapeutic molecule for TTR-related pathologies, including neurodegenerative diseases.

Comprehensive analyses of the cysteine thiol oxidation of PKM2 reveal the effects of multiple oxidation on cellular oxidative stress response.

Redox regulation of proteins via cysteine residue oxidation is involved in the control of various cellular signal pathways. Pyruvate kinase M2 (PKM2), a rate-limiting enzyme in glycolysis, is critical for the metabolic shift from glycolysis to the pentose phosphate pathway under oxidative stress in cancer cell growth. The PKM2 tetramer is required for optimal pyruvate kinase (PK) activity, whereas the inhibition of inter-subunit interaction of PKM2 induced by Cys358 oxidation has reduced PK activity. In the present study, we identified three oxidation-sensitive cysteine residues (Cys358, Cys423 and Cys424) responsible for four oxidation forms via the thiol oxidant diamide and/or hydrogen peroxide (H2O2). Possibly due to obstruction of the dimer-dimer interface, H2O2-induced sulfenylation (-SOH) and diamide-induced modification at Cys424 inhibited tetramer formation and PK activity. Cys423 is responsible for intermolecular disulfide bonds with heterologous proteins via diamide. Additionally, intramolecular polysulphide linkage (-Sn-, n ≧ 3) between Cys358 and an unidentified PKM2 Cys could be induced by diamide. We observed that cells expressing the oxidation-resistant PKM2 (PKM2C358,424A) produced more intracellular reactive oxygen species (ROS) and exhibited greater sensitivity to ROS-generating reagents and ROS-inducible anti-cancer drugs compared with cells expressing wild-type PKM2. These results highlight the possibility that PKM2 inhibition via Cys358 and Cys424 oxidation contributes to eliminating excess ROS and oxidative stress.

Therapeutic applications of thyroid hormone analogues.

Cellular thyroid hormone homeostasis requires adequate function of: (1) thyroid hormone transporter proteins at the plasma membrane, (2) deiodinating enzymes and (3) nuclear thyroid hormone receptors (TRs). Defects in any of these processes give rise to distinct disease entities, collectively called thyroid hormone signaling disorders. Thyroid hormone analogues hold therapeutic potential in thyroid hormone signaling disorders by bypassing defective transporters or binding to mutant TRs. This review will focus on the application of analogues in thyroid hormone signaling disorders, particularly monocarboxylate transporter (MCT)8 deficiency, and resistance to thyroid hormone due to mutations in TRß (RTHß).

Theoretical study on endocrine disrupting effects of polychlorinated dibenzo-p-dioxins using molecular docking simulation.

Polychlorinated dibenzo-p-dioxins (PCDDs) are hypothesized to exert their toxic effects in wildlife and humans via endocrine disruption. However, very scanty information is available on the underlying molecular interactions that trigger this disruption. In this study, molecular docking simulation was used to predict the susceptibility of 12 nuclear receptors to disruption via PCDD bindings. Findings revealed that androgen (AR and AR an), estrogen (ER α and ER ß), glucocorticoid (GR) and thyroid hormone (TR α and TR ß) receptors are the most probable protein targets that bind to PCDDs. Further molecular docking analyses showed that PCDD molecules mimic the modes of interaction observed for the co-crystallized ligands of the affected receptors, resulting in the formation of ligand-receptor complexes that were stabilized through electrostatic, van der Waals, pi-effect and hydrophobic interactions with 18, 17, 17, 16, 18, eight and four amino acid residues in the active sites of AR, AR an, ER α, ER ß, GR, TR α and TR ß respectively. The commonalities of these interacting amino acid residues with those utilized by dihydrotestosterone in AR, bicalutamide in AR an, 17ß-estradiol in ER α, 17ß-estradiol in ER ß, cortisol in GR, thyromimetic GC-1 in TR α and thyromimetic GC-1 in TR ß are 86%, 74%, 94%, 80%, 82%, 50% and 43% respectively. The results obtained in this study provide supporting evidence that PCDD molecules may interfere with the endocrine system via binding interactions with some vital amino acid residues in the binding pockets of AR, ERs, GRs and TRs.

Physicochemical Properties of Zwitterionic Drugs in Therapy.

In solution, amphoteric compounds exist in anionic, uncharged, zwitterionic and cationic forms. The importance of zwitterionic drugs is currently under-represented in the literature. Herein, the acid-base parameters, lipophilicity and solubility of such compounds are discussed to deepen the molecular-level understanding of their pharmacokinetic and pharmacodynamic behaviour. Our recent studies show there are many drug molecules, including thyroid hormones and 5-hydroxytryptophan, the precursor of the neurotransmitter serotonin, for which the contribution of the zwitterionic microspecies to the overall lipophilicity exceeds that of the uncharged one, which is of higher individual lipophilicity, but occurs in much lower concentration. The second part of the minireview highlights the most important zwitterionic compounds in therapy, grouped into therapeutic classes. The importance of the charge of the molecules is emphasized in their binding to the target molecules.

The cysteine residue at 424th of pyruvate kinase M2 is crucial for tetramerization and responsiveness to oxidative stress.

Alternative splicing of the pyruvate kinase M (PKM) pre-mRNA generates two isoforms, PKM1 and PKM2. PKM catalyzes the conversion of phosphoenol-pyruvate to pyruvate in glycolytic pathway. PKM1 exist as a stable tetramer that is at an active enzyme state, while PKM2 is in equilibrium among monomer, dimer and tetramer under the regulation of its allosteric activators. Many cancer cells show the feature of higher glucose uptake and lactate production in spite of oxygen availability, which is known as the Warburg effect. PKM2 is upregulated in most cancer types and the inactive PKM2 lead to the cancer metabolism. In addition, dimeric PKM2 induces its nuclear translocation through posttranslational modification and acts as a transcriptional co-activator for the expression of oncogenes. Therefore, it is important to elucidate mechanisms for modulation of an active or inactive state of PKM2, namely the tetramer-to-dimer-transition. The definitive difference between PKM1 and PKM2 is to constitutively form tetramer or not in the cytoplasm, which is ascribed to 22 amino acids derived from exon 9 (PKM1) or exon 10 (PKM2). In this study, we generated 22 different PKM1-mimetic point mutants of PKM2, and demonstrated that replacement of cysteine424 residue of PKM2 with leucine424 conserved in PKM1 (C424L) promote its tetramerization. PKM2(C424L) formed a tetramer without allosteric activator, and escaped the inhibitory effects by oxidative stress, like PKM1. Our findings intensely suggest that C424 or L424 determines the different catalytic and modulatory properties between PKM splicing isoforms.

Halogen bonding for molecular recognition: new developments in materials and biological sciences.

Two decades ago, halogen bonding attracted considerable attention as a new type of non-covalent interaction and has now emerged as an important supramolecular tool for crystal engineering, demonstrating its ability to self-assemble low affinity entities. Specific features of halogen bonds have been subsequently harnessed in biological and material sciences to give rise to elegant functional systems with a wide range of applications. In this highlight, we focused on new concepts in polymer science, electrochemistry, electronic and sensing materials. Recent findings on the use of halogenated compounds for transmembrane transport are also discussed, together with a short summary of the current understanding of the nature of the halogen bond, in the light of modern computational tools and energy decomposition.

The hypothalamic-pituitary-gonadal axis and thyroid hormone regulation interact to influence seasonal breeding in green anole lizards (Anolis carolinensis).

Reproductive physiology and behavior is mainly regulated by the hypothalamus-pituitary-gonad (HPG) axis, although abnormal thyroid hormone (TH) levels alter HPG axis activity. Seasonally breeding animals, such as green anole lizards (Anolis carolinensis), undergo drastic hormonal and behavioral changes between breeding and non-breeding seasons, with increased sex steroid hormones, larger gonads and increased reproductive behaviors during the breeding compared to non-breeding seasons. Relatively less is known regarding the regulation of gonadal TH in seasonal reproduction. We examined whether the gonadal expression of enzymes involved in TH activation are altered in concert with seasonal reproduction. Type 2 deiodinase (Dio2) mRNA, the TH activating enzyme, was upregulated in breeding compared to non-breeding testes, while type 3 deiodinase (Dio3) mRNA, the TH deactivating enzyme, was upregulated in breeding ovaries. To study the association between the HPG axis and local activation of TH, we manipulated the HPG axis during the non-breeding season by subcutaneously injecting luteinizing hormone (LH) and follicle stimulating hormone (FSH) in male lizards. We found that acute LH and FSH injections induced many aspects of breeding, with increased testes size and testosterone levels. Surprisingly, Dio3 was upregulated in the testes after LH and FSH injections, while Dio2 mRNA levels were unchanged. These results suggest that there might be different roles for local TH activation in developing and maintaining fully mature and functional gonads. Our findings continue to support the role for TH in regulating reproduction.

Biochemical and structural insights into how amino acids regulate pyruvate kinase muscle isoform 2.

Pyruvate kinase muscle isoform 2 (PKM2) is a key glycolytic enzyme involved in ATP generation and critical for cancer metabolism. PKM2 is expressed in many human cancers and is regulated by complex mechanisms that promote tumor growth and proliferation. Therefore, it is considered an attractive therapeutic target for modulating tumor metabolism. Various stimuli allosterically regulate PKM2 by cycling it between highly active and less active states. Several small molecules activate PKM2 by binding to its intersubunit interface. Serine and cysteine serve as an activator and inhibitor of PKM2, respectively, by binding to its amino acid (AA)-binding pocket, which therefore represents a potential druggable site. Despite binding similarly to PKM2, how cysteine and serine differentially regulate this enzyme remains elusive. Using kinetic analyses, fluorescence binding, X-ray crystallography, and gel filtration experiments with asparagine, aspartate, and valine as PKM2 ligands, we examined whether the differences in the side-chain polarity of these AAs trigger distinct allosteric responses in PKM2. We found that Asn (polar) and Asp (charged) activate PKM2 and that Val (hydrophobic) inhibits it. The results also indicate that both Asn and Asp can restore the activity of Val-inhibited PKM2. AA-bound crystal structures of PKM2 displayed distinctive interactions within the binding pocket, causing unique allosteric effects in the enzyme. These structure-function analyses of AA-mediated PKM2 regulation shed light on the chemical requirements in the development of mechanism-based small-molecule modulators targeting the AA-binding pocket of PKM2 and provide broader insights into the regulatory mechanisms of complex allosteric enzymes.

Thyroid Hormone Analogues: An Update.

The development of thyroid hormone (TH) analogues was prompted by the attempt to exploit the effects of TH on lipid metabolism, avoiding cardiac thyrotoxicosis. Analysis of the relative distribution of the α and ß subtypes of nuclear TH receptors (TRα and TRß) showed that TRα and TRß are responsible for cardiac and metabolic responses, respectively. Therefore, analogues with TRß selectivity were developed, and four different compounds have been used in clinical trials: GC-1 (sobetirome), KB-2115 (eprotirome), MB07344/VK2809, and MGL-3196 (resmetirom). Each of these compounds was able to reduce low-density lipoprotein cholesterol, but a phase 3 trial with eprotirome was interrupted because of a significant increase in liver enzymes and the contemporary report of cartilage side effects in animals. As a consequence, the other projects were terminated as well. However, in recent years, TRß agonists have raised new interest for the treatment of nonalcoholic fatty liver disease (NAFLD). After obtaining excellent results in experimental models, clinical trials have been started with MGL-3196 and VK2809, and the initial reports are encouraging. Sobetirome turned out to be effective also in experimental models of demyelinating disease. Aside TRß agonists, TH analogues include some TH metabolites that are biologically active on their own, and their synthetic analogues. 3,5,3'-triiodothyroacetic acid has already found clinical use in the treatment of some cases of TH resistance due to TRß mutations, and interesting results have recently been reported in patients with the Allan-Herndon-Dudley syndrome, a rare disease caused by mutations in the TH transporter MCT8. 3,5-diiodothyronine (T2) has been used with success in rat models of dyslipidemia and NAFLD, but the outcome of a clinical trial with a synthetic T2 analogue was disappointing. 3-iodothyronamine (T1AM) is the last entry in the group of active TH metabolites. Promising results have been obtained in animal models of neurological injury induced by ß-amyloid or by convulsive agents, but no clinical data are available so far.

Thyroid Hormones, Glucocorticoids, Insulin, and Bone.

Several endocrine systems have important effects on bone tissue. Thyroid hormones are essential for normal growth and development. Excess of these hormones will result in clinically significant changes that may require intervention. Glucocorticoids also have a marked effect on bone metabolism by several pathways. Their endogenous or exogenous excess will induce pathological processes that might elevate the risk of fractures. Insulin and the carbohydrate metabolism elicit a physiological effect on bone; however, the lack of insulin (type 1 diabetes) or insulin resistance (type 2 diabetes) have deleterious influence on bone tissue.

Halogen Bonding Interactions of Polychlorinated Biphenyls and the Potential for Thyroid Disruption.

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 (Dio) 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 for substrates to undergo dehalogenation, suggesting they may behave as competitive inhibitors of 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.

Cancer-associated mutations in human pyruvate kinase M2 impair enzyme activity.

Mammalian pyruvate kinase catalyzes the final step of glycolysis, and its M2 isoform (PKM2) is widely expressed in proliferative tissues. Mutations in PKM2 are found in some human cancers; however, the effects of these mutations on enzyme activity and regulation are unknown. Here, we characterized five cancer-associated PKM2 mutations, occurring at various locations on the enzyme, with respect to substrate kinetics and activation by the allosteric activator fructose-1,6-bisphosphate (FBP). The mutants exhibit reduced maximal velocity, reduced substrate affinity, and/or altered activation by FBP. The kinetic parameters of five additional PKM2 mutants that have been used to study enzyme function or regulation also demonstrate the deleterious effects of mutations on PKM2 function. Our findings indicate that PKM2 is sensitive to many amino acid changes and support the hypothesis that decreased PKM2 activity is selected for in rapidly proliferating cells.

Halogen Bonding in Biomimetic Deiodination of Thyroid Hormones and their Metabolites and Dehalogenation of Halogenated Nucleosides.

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 3,5,3',5'-tetraiodothyronine (T4) as a prohormone; three isoforms of a mammalian selenoenzyme-iodothyronine deiodinase (DIO1, DIO2 and DIO3)-catalyze the regioselective deiodination of T4 to produce biologically active and inactive metabolites. Whereas DIO1 catalyzes both 5- and 5'-deiodination of T4, DIO2 and DIO3 selectively mediate 5- and 5'-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 C-I bond is facilitated by the formation of cooperative Se/S⋅⋅⋅I halogen bonds and Se/S⋅⋅⋅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.