Role of plasma proteins in the binding, distribution and metabolism of the thyroid hormones

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Case report: Impact of hyperthyroidism on psychotic symptoms in schizophrenia comorbid with Graves' disease

Introduction

Auditory hallucinations are the most common type of hallucinations observed in schizophrenia; however, visual hallucinations are not uncommon. In Graves' disease, depression, hypomania, and psychosis can occur. While the association between Graves' disease and psychosis has been explored, understanding of the specific impact of thyroid dysfunction severity on psychiatric symptom severity is limited. Here, we present a case report of a patient with schizophrenia comorbid with Graves' disease whose psychotic symptoms were impacted by hyperthyroidism.

Case

The patient was a 32-year-old Japanese woman who presented with auditory and visual hallucinations, agitation, and pressured speech. The patient was diagnosed with schizophrenia comorbid with Graves' disease and thyroid storm. The patient's psychotic symptoms were found to be associated with fluctuations in thyroid hormone levels, and visual hallucinations were observed only during thyroid storms. Treatment involved dexamethasone, potassium iodide, bisoprolol fumarate, and methimazole for thyrotoxicosis, and a blonanserin transdermal patch, paliperidone, and paliperidone palmitate for psychotic symptoms. The patient's auditory and visual hallucinations improved with antipsychotic treatment and decreased thyroid hormone levels.

Conclusion

This case highlights the importance of monitoring thyroid function in patients with schizophrenia, particularly those with comorbid Graves' disease. The correlation between psychiatric symptoms and thyroid hormone levels was demonstrated on an individual level over time, with symptoms worsening as thyroid hormone levels increased. Additionally, our case suggests that abnormally high thyroid hormone levels may trigger visual hallucinations in individuals with schizophrenia. Further studies are needed to elucidate the underlying mechanisms and potential treatment implications of this association.

Identification of Mutations in the Thyroxine-Binding Globulin (TBG) Gene in Patients with TBG Deficiency in Korea

BACKGRUOUND

Thyroxine-binding globulin (TBG) is a major transporter protein for thyroid hormones. The serpin family A member 7 (SERPINA7) gene codes for TBG, and mutations of the SERPINA7 gene result in TBG deficiency. Although more than 40 mutations have been reported in several countries, only a few studies of TBG deficiency and SERPINA7 gene mutation have been performed in Korea. The aim of this study is to review the clinical presentations and laboratory findings of patients with TBG deficiency and to investigate the types of SERPINA7 gene mutation.

METHODS

Five unrelated Korean adults with TBG deficiency attending endocrinology clinic underwent SERPINA7 gene sequencing. Four patients harbored a SERPINA7 gene mutation. Serum thyroid hormones, anti-microsomal antibodies, and TBG were measured. Genomic DNA was extracted from whole blood. All exons and intron-exon boundaries of the TBG gene were amplified and sequencing was performed.

RESULTS

Two patients were heterozygous females, and the other two were hemizygous males. One heterozygous female had coexisting hypothyroidism. The other heterozygous female was erroneously prescribed levothyroxine at a local clinic. One hemizygous male harbored a novel mutation, p.Phe269Cysfs*18, which caused TBG partial deficiency. Three patients had the p.Leu372Phefs*23 mutation, which is known as TBG-complete deficiency Japan (TBG-CDJ) and was also presented in previous mutation analyses in Korea.

CONCLUSION

This study presents four patients diagnosed with TBG deficiency and provides the results of SERPINA7 gene sequencing. One novel mutation, p.Phe269Cysfs*18, causing TBD-partial deficiency and three cases of TBG-CDJ were demonstrated. It is necessary to identify TBG deficiency to prevent improper treatment. Also, sequencing of the SERPINA7 gene would provide valuable information about the TBG variants in Korea.

Organophosphate esters cause thyroid dysfunction via multiple signaling pathways in zebrafish brain

Organophosphate esters (OPEs) are widespread in various environmental media, and can disrupt thyroid endocrine signaling pathways. Mechanisms by which OPEs disrupt thyroid hormone (TH) signal transduction are not fully understood. Here, we present in vivo-in vitro-in silico evidence establishing OPEs as environmental THs competitively entering the brain to inhibit growth of zebrafish via multiple signaling pathways. OPEs can bind to transthyretin (TTR) and thyroxine-binding globulin, thereby affecting the transport of TH in the blood, and to the brain by TTR through the blood-brain barrier. When GH3 cells were exposed to OPEs, cell proliferation was significantly inhibited given that OPEs are competitive inhibitors of TH. Cresyl diphenyl phosphate was shown to be an effective antagonist of TH. Chronic exposure to OPEs significantly inhibited the growth of zebrafish by interfering with thyroperoxidase and thyroglobulin to inhibit TH synthesis. Based on comparisons of modulations of gene expression with the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases, signaling pathways related to thyroid endocrine functions, such as receptor-ligand binding and regulation of hormone levels, were identified as being affected by exposure to OPEs. Effects were also associated with the biosynthesis and metabolism of lipids, and neuroactive ligand-receptor interactions. These findings provide a comprehensive understanding of the mechanisms by which OPEs disrupt thyroid pathways in zebrafish.

Binding Characteristics of Thyroid Hormone Distributor Proteins to Thyroid Hormone Metabolites

Background: In contrast to the thyroid hormones (THs) 3,3',5-triiodothyronine (T3) and 3,3',5,5'-tetraiodothyronine (thyroxine or T4), the binding characteristics of the thyroid hormone distributor proteins (THDP), thyroxine-binding globulin (TBG), albumin, and transthyretin in relation to TH metabolites are mostly lacking. In this study, we determined the distribution and binding affinity of TH metabolites to THDP, which is important for adequate interpretation of TH metabolite concentrations. Methods: Distribution of ¹²⁵I-3,3'-diiodothyronine (3,3'-T2), -T3, -3,3',5'-triiodothyronine (rT3), -3,3',5-triiodothyroacetic acid (TA3), and -3,3',5,5'-tetraiodothyroacetic acid (TA4) to TBG, transthyretin, and albumin was determined by agar gel electrophoresis. The rank order of affinity (IC₅₀) of TBG and transthyretin to thyronine (T0), 3-monoiodothyronine (3-T1), 3,5-diiodothyronine (3,5-T2), 3,3'-T2, T3, rT3, T4, TA3, and TA4 was determined with a radioligand, competitive binding assay. In healthy subjects, associations of serum TBG, transthyretin, and albumin with TH and its metabolites were analyzed using multiple linear regression models, adjusted for sex and age. Results: While T3 and T4 are predominantly bound to TBG, we demonstrated that the predominant THDP of 3,3'-T2 and rT3 is albumin, of TA3 is transthyretin and albumin, and of TA4 is transthyretin. With the radioligand binding assay, we showed that the rank order of affinity was T4>TA4 = rT3>T3>TA3 = 3,3'-T2 > 3-T1 = 3,5-T2>T0 for TBG (IC₅₀-range: 0.36 nM to >100 μM) and TA4>T4 = TA3>rT3>T3 > 3,3'-T2 > 3-T1 > 3,5-T2>T0 for transthyretin (IC₅₀-range: 0.94 nM to >100 μM). TBG, transthyretin, and albumin were not associated with T0, 3-T1, 3,3'-T2, rT3, and TA4. Conclusions: Differences in serum TBG, transthyretin, and albumin concentrations within the reference interval do not influence serum concentrations of T0, 3-T1, 3,3'-T2, rT3, and TA4. Distribution of TH metabolites between THDP differs from T4 and T3, which predominantly bind to TBG. The results from our study have potential clinical importance for adequate interpretation of TH metabolism in (patho)physiology.

A U-shaped association between serum albumin with total triiodothyronine in adults

BACKGROUND

Thyroid dysfunction is a common thyroid disorder in our life and its symptoms are non-specific, therefore the diagnosis of thyroid dysfunction is important for patients. Albumin (ALB) can carry thyroid hormones to their sites of action as a way to achieve rapid delivery of thyroid hormones to the tissues. The purpose of this study was to investigate the relationship between serum ALB levels and total triiodothyronine (TT3) in adults.

METHODS

Data from the 2007-2012 National Health and Nutrition Examination Survey (NHANES) were used to examine the association between ALB and TT3 using multivariate logistic regression models. Fitting smoothed curves and generalized weighted models were also used.

RESULTS

The analysis included a total of 7933 participants that we found an independent positive relationship between ALB and TT3 among participants [0.006 (0.003, 0.009)]. In men, there was a significant positive correlation between ALB and TT3, whereas in women ALB and TT3 suggested a significant negative correlation. Moreover, our study revealed that the independent association between the levels of ALB and TT3 was significant in Non-Hispanic White, but not in Non-Hispanic Black. Notably, we found a U-shaped association between ALB and serum TT3 in total participants (inflection point for ALB: 41 g/L) and females after adjusted covariates (inflection point for ALB: 46 g/L).

CONCLUSIONS

We found a U-shaped relationship between serum ALB and TT3 with infection point at 41 g/L for ALB, which may provide a reference for future screening in adults with thyroid dysfunction.

A Correlational Analysis of Phthalate Exposure and Thyroid Hormone Levels in Common Bottlenose Dolphins (Tursiops truncatus) from Sarasota Bay, Florida (2010–2019)

Simple Summary

Phthalate exposure is prevalent in common bottlenose dolphins sampled from Sarasota Bay, Florida. With evidence of potential adverse effects as identified in human and laboratory studies, there is a concern for bottlenose dolphin health. This study investigated potential correlations between serum hormone levels and urinary phthalate metabolite concentrations to begin to understand whether health effects would be expected in dolphins. We observed a positive relationship between free thyroxine and mono(2-ethylhexyl) phthalate (MEHP) for both adult female and male dolphins, suggesting potential associations with normal thyroid production.

Abstract

Phthalates are chemical esters used to enhance desirable properties of plastics, personal care, and cleaning products. Phthalates have shown ubiquitous environmental contamination due to their abundant use and propensity to leach from products to which they are added. Following exposure, phthalates are rapidly metabolized and excreted through urine. Common bottlenose dolphins (Tursiops truncatus) sampled from Sarasota Bay, Florida, have demonstrated prevalent di(2-ethylhexyl) phthalate (DEHP) exposure indicated by detectable urinary mono(2-ethylhexyl) phthalate (MEHP) concentrations. Widespread exposure is concerning due to evidence of endocrine disruption from human and laboratory studies. To better understand how phthalate exposure may impact dolphin health, correlations between relevant hormone levels and detectable urinary MEHP concentrations were examined. Hormone concentrations measured via blood serum samples included triiodothyronine (T3), total thyroxine (T4), and free thyroxine (FT4). Urinary MEHP concentrations were detected in 56% of sampled individuals (n = 50; mean = 8.13 ng/mL; s.d. = 15.99 ng/mL). Adult female and male FT4 was significantly correlated with urinary MEHP concentrations (adult female Kendall’s tau = 0.36, p = 0.04; adult male Kendall’s tau = 0.42, p = 0.02). Evidence from this study suggests DEHP exposure may be impacting thyroid hormone homeostasis. Cumulative effects of other stressors and resultant endocrine impacts are unknown. Further research is warranted to understand potential health implications associated with this relationship.

Gaps in the knowledge of thyroid hormones and placental biology

Thyroid hormones (THs) are required for the growth and development of the foetus, stimulating anabolism and oxygen consumption from the early stages of pregnancy to the period of foetal differentiation close to delivery. Maternal changes in the hypothalamic–pituitary thyroid axis are also well known. In contrast, several open questions remain regarding the relationships between the placenta and the maternal and foetal TH systems. The exact mechanism by which the placenta participates in regulating the TH concentration in the foetus and mother and the role of TH in the placenta are still poorly studied. In this review, we aim to summarize the available data in the area and highlight significant gaps in our understanding of the ontogeny and cell-specific localization of TH transporters, TH receptors and TH metabolic enzymes in the placenta in both human and rodent models. Significant deficiencies also exist in knowledge of the contribution of genomic and nongenomic effects of TH on the placenta and finally how the placenta reacts during pregnancy when the mother has thyroid disease. By addressing these key knowledge gaps, improved pregnancy outcomes and management of women with thyroid alterations may be possible.

Quantification of triiodothyronine and thyroxine in rat serum using liquid chromatography tandem mass spectrometry

Thyroid hormones act on almost every tissue in the body to promote catabolism in cells and are important for regulating many biological processes. Accurate quantification of endogenous thyroid hormones has become essential for clinical and non-clinical applications in the development of new drugs according to the OECD Guideline (2018). However, there are difficulties in quantitative analysis of thyroid hormones because no analyte-free biological matrices are available for analysis of endogenous substances. In this study, surrogate matrix and surrogate analyte methods were compared and validated to quantify endogenous triiodothyronine (T₃) and thyroxine (T₄) in rat serum using LC-MS/MS. Separation of analytes was performed using an Xbridge™ C18 (2.1 × 50 mm, 2.5 μm) column. In the surrogate matrix, 3,3'5-triiodo- l-thyronine-¹³C₆ (cT₃) and l-thyroxine-¹³C₆ (cT₄) were used as the internal standard (IS), and in the surrogate analyte, l-3,3'-diiodothyronine-¹³C₆ (cT₂) was used as the IS. The mobile phases consisted of 0.1 % acetic acid in purified water (A) and 0.1 % acetic acid in acetonitrile (B). Both analytical methods were suitable for selectivity, matrix effect, carryover, lower limit of quantification, linearity, accuracy, precision, recovery, stability and parallelism. The surrogate matrix method was more accurate than using the surrogate analyte method, including evaluation of parallelism at low concentrations. Additionally, the surrogate matrix is cost-effective for T₃ and T₄ analysis in biological samples because it consists only of deionized water. However, surrogate analytes difficult to evaluate parallelism by obtaining response factors for mass spectrometric signal differences between the actual and surrogate analytes. Therefore, the results of this study indicate that it is more cost-effective to use the surrogate matrix method for endogenous thyroid hormone, T₃ and T₄, analysis in biological samples.

Partial thyroxine-binding globulin deficiency in a family with coding region mutations in the TBG gene

PURPOSE

T4-binding globulin (TBG) is the main thyroid hormone (TH) transporter present in human serum. Inherited thyroxine-binding globulin (TBG) deficiency is caused by mutations in the TBG (SERPINA7) gene, which is located on the X chromosome. This study was performed to report and evaluate coding region mutations in TBG gene for partial thyroxine-binding globulin deficiency.

METHODS

A pedigree spanning four generations is described in this study. The proband is a female with partial TBG deficiency. All members of this pedigree underwent thyroid function tests, while Sanger sequencing was used to identify the TBG gene mutations. Bioinformatics databases were used to evaluate the deleterious effects of the mutation(s). Two hundred and seven unrelated individuals were used to evaluate the thyroid function of individuals with different TBG mutations. A one-way ANOVA was used to analyze the impact of the TBG mutations on thyroid function.

RESULTS

TBG gene sequencing results revealed that the proband had a novel mutation in codon 27 leading to alanine to valine substitution (p.A27V). This mutation was associated with lower serum T4 levels (p < 0.0001) when compared to the groups that did not carry the mutation. The previously reported p.L283F mutation was also found in the proband. The hemizygous p.L283F individuals presenting with lower T4 serum and TBG levels (p < 0.001) when compared to wildtype males and females. Both mutations were deleterious upon SIFT and PolyPhen-2 evaluation.

CONCLUSION

Associated with partial thyroxine-binding globulin deficiency, this study reports a novel p.A27V mutation in the TBG gene.

Structural studies on the endocrine-disrupting role of polybrominated diphenyl ethers (PBDEs) in thyroid diseases

Polybrominated diphenyl ethers (PBDEs) are synthetic brominated flame retardants with extensive applications in daily-life consumer products. However, PBDEs have become ubiquitous environmental contaminants due to their leach-out capability. The hazardous human health effects and endocrine-disrupting activity of PBDEs have led many governmental organizations to impose ban on their manufacture, causing their gradual phase out from commercial products. However, PBDEs and their metabolites are still being detected from biological and environmental samples owing to their persistence and bioaccumulation. The PDBE metabolites in these samples are present in concentrations often higher and even with higher toxic potential than parent PBDEs. The two commonly detected environmental PBDE congeners, 2,2',4,4'-tetra-bromodiphenyl ether (BDE-47) and 2,2',4,4',5-penta-bromodiphenyl ether (BDE-99), and their HO- and MeO- metabolites were considered in this study for their potential disrupting activity on thyroid hormone transport. Specifically, the study involved structural binding characterization of BDE-47 and BDE-99 including their two HO- and two MeO- metabolites with thyroxine-binding globulin (TBG), which is the main thyroid hormone transport protein in blood. The results showed that the binding pattern and molecular interactions of above two PBDEs and their metabolites exhibited overall similarity to native ligand, thyroxine in dock score, binding energy, and amino acid interactions with TBG. The BDE-99 and its metabolites were predicted to have stronger binding to TBG than BDE-47 with the metabolite 5-MeO-BDE-99 showing equal binding affinity to that of thyroxine. It is concluded that BDE-47 and BDE-99 and their metabolites have the potential to disrupt thyroid hormone transport and interfere in thyroid function.

Endocrine disruption: Molecular interactions of environmental bisphenol contaminants with thyroid hormone receptor and thyroxine-binding globulin

Many bisphenol A (BPA) analogs have been commercially used recently, such as 2,2-bis(4-hydroxyphenyl)butane (BPB), 4,4′-ethylidenebisphenol, 4,4′-methylenediphenol (BPF), 4,4′-(1,4-phenylenediisopropylidene)bisphenol (BPP), 4,4′-dihydroxydiphenyl sulfone (BPS), 4,4′-cyclohexylidenebisphenol (BPZ), 4,4′-(hexafluoroisopropylidene)diphenol (BPAF), 4,4′-(1-phenylethylidene)bisphenol (BPAP), and 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane (TMBPA), to circumvent adverse effects of BPA. However, their increasing use is also contaminating the environment, which is a potential cause of concern for human health. Thyroid hormone transport and signaling are potential targets for endocrine-disrupting activity of BPA analogs. Thyroxine-binding globulin (TBG) is the major carrier protein for thyroxine (T4) and triiodothyronine (T3) in blood. Thyroid hormones exert their action through thyroid hormone receptors (TRα and TRβ). This report presents the thyroid-disrupting potential of indicated nine BPA analogs from structure-based studies with TBG and TRα. Each BPA analog formed important polar and hydrophobic interactions with a number of residues of TBG and TRα. Majority of TBG residues (77–100%) and TRα residues (70–91%) interacting with BPA analogs were common with those of native ligands T4 and T3, respectively. Majority of BPA analogs interacted with TBG forming a salt bridge interaction at Lys-270. The hydrogen-bonding interaction of T3 with TRα at His-381 was also shared by majority of analogs. The binding energy for BPP, BPB, BPZ, BPAP, and TMBPA with both proteins was closer to binding energy of respective native ligands. The similarity in structural binding characteristics suggested potential disrupting activity of thyroid hormone signaling and transport.

Molecular interactions of thyroxine binding globulin and thyroid hormone receptor with estrogenic compounds 4-nonylphenol, 4-tert-octylphenol and bisphenol A metabolite (MBP)

AIM

Endocrine disruption due to environmental chemical contaminants is a global human health issue. The aim of present study was to investigate the structural binding aspects of possible interference of commonly detected environmental contaminants on thyroid function.

MATERIAL AND METHODS

Three compounds, 4-tert-octylphenol (4-tert-OP), 4-nonylphenol (4-NP), and 4-methyl-2,4-bis(4-hydroxypentyl)pent-1-ene (MBP) were subjected to induced fit docking (IFD) against thyroxine binding globulin (TBG) and thyroid hormone receptor (THR). Structural analysis included molecular interactions of the amino acid residues and binding energy estimation between the ligands and the target proteins.

KEY RESULTS

All the ligands were successfully placed in the ligand binding pocket of TBG and THR using induced fit docking (IFD). The IFD results revealed high percentage of commonality in interacting amino acid residues between the aforementioned compounds and the native ligand for both TBG and THR. The results of our study further revealed that all the compounds have the potential to interfere with thyroid transport and signaling. However, MBP showed higher binding affinity for both TBG and THR, suggesting higher thyroid disruptive potential as compared to 4-t-OP and 4-NP. Furthermore, our results also suggest that the reported disruptive effects of BPA could actually be exerted through its metabolite; MBP.

SIGNIFICANCE

This work implies that all the three compounds 4-NP, 4-t-OP and especially MBP have the potential to interfere with thyroid hormone transport and signaling. This potentially leads to disruption of thyroid hormone function.

Clinical recognition and evaluation of patients with inherited serum thyroid hormone-binding protein mutations

There are three important thyroid hormone-binding proteins in human serum, thyroxine-binding globulin, transthyretin, and albumin. Genetic variation in these proteins can lead to altered thyroid hormone binding and abnormalities in serum tests of thyroid hormone. Importantly, patients harboring these mutations are euthyroid; thus, the recognition of these conditions is crucial to prevent unnecessary repeated testing and treatment. This article provides an updated overview of serum thyroid hormone transport biology and reviews the underlying genetic alterations, clinical presentation, and appropriate evaluation of patients with suspected mutations in serum thyroid hormone-binding proteins.

Thyroid hormones and menstrual cycle function in a longitudinal cohort of premenopausal women

BACKGROUND

Previous studies have reported that hyperthyroid and hypothyroid women experience menstrual irregularities more often compared with euthyroid women, but reasons for this are not well-understood and studies on thyroid hormones among euthyroid women are lacking. In a prospective cohort study of euthyroid women, this study characterised the relationship between thyroid hormone concentrations and prospectively collected menstrual function outcomes.

METHODS

Between 2004-2014, 86 euthyroid premenopausal women not lactating or taking hormonal medications participated in a study measuring menstrual function. Serum thyroid hormones were measured before the menstrual function study began. Women then collected first morning urine voids and completed daily bleeding diaries every day for three cycles. Urinary oestrogen and progesterone metabolites (estrone 3-glucuronide (E₁ 3G) and pregnanediol 3-glucuronide (Pd3G)) and follicle-stimulating hormone were measured and adjusted for creatinine (Cr).

RESULTS

Total thyroxine (T₄ ) concentrations were positively associated with Pd3G and E₁ 3G. Women with higher (vs lower) T₄ had greater luteal phase maximum Pd3G (Pd3G = 11.7 μg/mg Cr for women with high T₄ vs Pd3G = 9.5 and 8.1 μg/mg Cr for women with medium and low T₄ , respectively) and greater follicular phase maximum E₁ 3G (E₁ 3G = 41.7 ng/mg Cr for women with high T₄ vs E₁ 3G = 34.3 and 33.7 ng/mg Cr for women with medium and low T₄ , respectively).

CONCLUSIONS

Circulating thyroid hormone concentrations were associated with subtle differences in menstrual cycle function outcomes, particularly sex steroid hormone levels in healthy women. Results contribute to the understanding of the relationship between thyroid function and the menstrual cycle, and may have implications for fertility and chronic disease.

Directional thyroid hormone distribution via the blood stream to target sites

Thyroid hormones are bound to three major serum transport proteins, thyroxin-binding globulin (TBG), transthyretin (TTR) and human serum albumin (HSA). TBG has the strongest affinity for thyroid hormones, TTR is also found in the cerebrospinal fluid and HSA is the most abundant protein in plasma. Combination defects of either a high affinity TTR or HSA variant do not compensate TBG deficiency, underscoring the dominant role of TBG among the thyroid hormone transport proteins. On the other hand, coexistence of raised affinity TTR and HSA variants causes an augmented hyperthyroxinemia. Variations in thyroid hormone transport proteins may alter thyroid function tests to mimic hypo- or hyperthyroidism. As affected individuals are clinically euthyroid and do not require treatment, identification of thyroid hormone transport protein defects is important to avoid unnecessary diagnostic and therapeutic interventions. Mammals share the multilayered system of thyroid hormone binding proteins with humans. Some of them, especially carnivores, do not express TBG. In dogs, this defect has been shown to be caused by a defective hepatocyte nuclear factor-1 binding site in the TBG promoter, preventing TBG synthesis in the liver. The major endogenous thyroid hormone metabolite 3-iodothyronamine (3-T1AM) exerts marked cryogenic, metabolic, cardiac and central nervous system actions. It is bound to apolipoproteinB-100 (ApoB100), possibly facilitating its cellular uptake via interaction with the low density lipoprotein-receptor. This review summarizes the handling of hydrophobic charged thyroid hormone signaling molecules and their metabolite 3-T1AM in aqueous body fluids and the advantages and limits of their serum distributor proteins.

MANAGEMENT OF ENDOCRINE DISEASE: Isolated maternal hypothyroxinemia during pregnancy: knowns and unknowns

Isolated maternal hypothyroxinemia (IMH) during pregnancy is defined as a low maternal T₄ in the absence of TSH elevation. As IMH is common, with a prevalence of 1-2% in iodine-sufficient populations, and early research has suggested adverse effects on fetal neurodevelopment, it has been the focus of many studies in the last decade. In the current review, we first discuss the significance of IMH based on data from animal models and recent discoveries regarding the role of thyroid hormone on neurodevelopment. We address issues surrounding the definition and prevalence of this entity and discuss new insights into the etiologies, clinical consequences and management of IMH. A number of large cohort studies have investigated the effects of IMH on the risk of various pregnancy complications and child neurodevelopment. We review these studies in detail and describe their limitations. We discuss the available research on management of IMH, including two recent randomized controlled trials (RCTs). Finally, we delineate the remaining uncertainties in this field and emphasize the need for a sufficiently powered, placebo-controlled RCT on the treatment of IMH early in the first trimester of pregnancy.

Circulating 3-T1AM and 3,5-T2 in Critically Ill Patients: A Cross-Sectional Observational Study

BACKGROUND

Critical illness is hallmarked by low circulating thyroxine (T4) and triiodothyronine (T3) concentrations, in the presence of elevated reverse T3 (rT3) and low-normal thyrotropin (TSH), referred to as nonthyroidal illness (NTI). Thyroid hormone (TH) metabolism is substantially increased during NTI, in part explained by enhanced deiodinase 3 (D3) activity. T4- and T3-sulfate concentrations are elevated, due to suppressed D1 activity in the presence of unaltered sulfotransferase activity, and 3,3'-diiodothyronine (3,3'-T2) concentrations are normal. To elucidate further the driving forces behind increased TH metabolism during NTI, two other potential T4 metabolites-3,5-diiodothyronine (3,5-T2) and 3-iodothyronamine (3-T1AM)-were measured and related to their potential TH precursors.

METHODS

Morning blood samples were collected cross-sectionally from 83 critically ill patients on a University Hospital intensive care unit and from 38 demographically matched healthy volunteers. Serum TH and binding proteins were quantified with commercial assays, and 3,5-T2 and 3-T1AM with in-house developed immunoassays.

RESULTS

Critically ill patients revealed, besides the NTI, a median 44% lower serum 3-T1AM concentration (p < 0.0001) and a 30% higher serum 3,5-T2 concentration (p = 0.01) than healthy volunteers did. Non-survivors and patients diagnosed with sepsis upon admission to the intensive-care unit had significantly higher 3,5-T2 (p ≤ 0.01) but comparable 3-T1AM (p > 0.2) concentrations than other patients did. Multivariable linear regression analysis adjusted for potential precursors revealed that the reduced serum 3-T1AM was positively correlated with the low serum T3 (p < 0.001) but unrelated to serum T4 or rT3. The elevated 3,5-T2 concentration did not independently correlate with TH.

CONCLUSIONS

Increased TH metabolism during NTI could not be explained by increased conversion to 3-T1AM, as circulating 3-T1AM was suppressed in proportion to the concomitantly low T3 concentrations. Increased conversion of T4 and/or T3 to 3,5-T2 could be possible, as serum 3,5-T2 concentrations were elevated. Whether 3-T1AM or 3,5-T2 plays a functional role during critical illness needs further investigation.

Analytical Application of Flow Immunosensor in Detection of Thyroxine and Triiodothyronine in Serum

In this study, an immunosensor based on kinetic exclusion analysis (KinExA) was used for thyroxine (T4) and triiodothyronine (T3) estimation. A KinExA™ 3200 instrument was used for this analysis, which is an automated flow fluorimeter designed to separate free unbound antibody binding sites in reaction mixtures of antibody, antigen, and antibody-antigen complex. A T3-BSA- and T4-BSA-coated polymethyl methacrylate (PMMA) bead microcolumn is generated inside the flow cell of the instrument. A sample mixture containing T3 and T4 with their respective monoclonal antibodies and their complexes are drawn past the microbead column. The unbound T3 or T4 monoclonal antibody binding sites are captured by their respective T3 and T4 antigens coated on the PMMA beads as bovine serum albumin conjugates. Fluorescently labeled secondary antibodies bind to the T3 or T4 antigen-antibody complex to generate fluorescence intensity for analysis. The limit of detection for the T3 and T4 assays was found to be 0.06 and 1.9 ng mL^-1 with acceptable precision values. The convenience of the automated KinExA format may be valuable in medical diagnostic laboratories.

Estimating Margin of Exposure to Thyroid Peroxidase Inhibitors Using High-Throughput in vitro Data, High-Throughput Exposure Modeling, and Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling

Some pharmaceuticals and environmental chemicals bind the thyroid peroxidase (TPO) enzyme and disrupt thyroid hormone production. The potential for TPO inhibition is a function of both the binding affinity and concentration of the chemical within the thyroid gland. The former can be determined through in vitro assays, and the latter is influenced by pharmacokinetic properties, along with environmental exposure levels. In this study, a physiologically based pharmacokinetic (PBPK) model was integrated with a pharmacodynamic (PD) model to establish internal doses capable of inhibiting TPO in relation to external exposure levels predicted through exposure modeling. The PBPK/PD model was evaluated using published serum or thyroid gland chemical concentrations or circulating thyroxine (T4) and triiodothyronine (T3) hormone levels measured in rats and humans. After evaluation, the model was used to estimate human equivalent intake doses resulting in reduction of T4 and T3 levels by 10% (ED10) for 6 chemicals of varying TPO-inhibiting potencies. These chemicals were methimazole, 6-propylthiouracil, resorcinol, benzophenone-2, 2-mercaptobenzothiazole, and triclosan. Margin of exposure values were estimated for these chemicals using the ED10 and predicted population exposure levels for females of child-bearing age. The modeling approach presented here revealed that examining hazard or exposure alone when prioritizing chemicals for risk assessment may be insufficient, and that consideration of pharmacokinetic properties is warranted. This approach also provides a mechanism for integrating in vitro data, pharmacokinetic properties, and exposure levels predicted through high-throughput means when interpreting adverse outcome pathways based on biological responses.

Inherited defects of thyroxine-binding proteins

Thyroid hormones (TH) are bound to three major serum transport proteins, thyroxine-binding globulin (TBG), transthyretin (TTR) and human serum albumin (HSA). TBG has the strongest affinity for TH, whereas HSA is the most abundant protein in plasma. Individuals harboring genetic variations in TH transport proteins present with altered thyroid function tests, but are clinically euthyroid and do not require treatment. Clinical awareness and early recognition of these conditions are important to prevent unnecessary therapy with possible untoward effects. This review summarizes the gene, molecular structure and properties of these TH transport proteins and provides an overview of their inherited abnormalities, clinical presentation, genetic background and pathophysiologic mechanisms.

Long term exposure to organochlorine pesticides and thyroid function in children from Cidade dos Meninos, Rio de Janeiro, Brazil

A pesticide factory in Cidade dos Meninos village, Duque de Caxias County, Rio de Janeiro, Brazil, ended its activity in 1961, leading to widespread contamination of the environment by several organochlorine pesticides. The aim of this study was to investigate the effects of chronic exposure to organochlorine pesticides on thyroid hormone levels in children residing in Cidade dos Meninos. In a population-based survey carried out between 2003 and 2004, serum concentration of 19 pesticides and levels of free thyroxine (T4), total triiodothyronine (T3) and thyroid-stimulating hormone (TSH) were determined in 193 children younger than 15 years old. Multivariate linear regression was conducted to examine thyroid hormone levels according to quintiles of organochlorine exposure, controlling for age, gender and serum lipid content. Free T4 and TSH levels were within reference values (0.7-1.8 ng/dl and 0.35-5.5 mU/l), whereas total T3 was above the reference range (80-180 ng/dl) in 28% of children. More than 60% of the children had detectable levels of most organochlorine pesticides. With the exception of heptachlor and methoxychlor, total T3 levels showed a significant increasing linear trend regardless of pesticide type to which children were exposed. Free T4 levels were positively and significantly associated only with exposure to p,p'-DDD, endosulfan 1, and dieldrin. No significant trend was found for TSH. Data showed that exposure of children to organochlorine pesticides produced a significant increase in serum total T3 concentrations. The clinical implications of such a total T3 elevation and subsequent development are uncertain and warrant the need for health monitoring of these children.

Thyroid axis function and dysfunction in critical illness

Acutely ill patients typically present with low circulating T3 and increased reverse T3. When illness is severe and prolonged, also pulsatile TSH secretion and circulating T4 levels are low. This constellation of changes within the thyroid axis is referred to as the low T3 syndrome or non-thyroidal illness syndrome (NTI), and comprises both peripheral and central alterations in the thyroid axis. Acute alterations are dominated by changes in thyroid hormone binding, in thyroid hormone uptake by the cell and in the activity of the type-1 and type-3 deiodinase enzymes. Prolonged critical illness is associated with a neuroendocrine dysfunction characterized by suppressed hypothalamic thyrotropin-releasing hormone (TRH) expression, resulting in reduced stimulation of the thyrotropes whereby thyroidal hormone release is impaired. During prolonged critical illness, several tissue responses could be interpreted as compensatory to low thyroid hormone availability, such as increased expression of monocarboxylate transporters, upregulation of type 2 deiodinase activity and increased sensitivity at the receptor level. Whether the low T3 syndrome should be treated and which compound should be used remains to be further studied.

The interpretation of the serum protein-bound iodine: A review

The effects of physiological and environmental factors, of thyroid and non-thyroid diseases, and of drugs on the serum protein-bound iodine are described and discussed.

Transthyretin and familial amyloidotic polyneuropathy

Familial amyloidotic polyneuropathy (FAP) is an inherited autosomal dominant disease that is commonly caused by accumulation of deposits of transthyretin (TTR) amyloid around peripheral nerves. The only effective treatment for FAP is liver transplantation. However, recent studies on TTR aggregation provide clues to the mechanism of the molecular pathogenesis of FAP and suggest new avenues for therapeutic intervention. It is increasingly recognized that there are common features of a number of protein-misfolding diseases that can lead to neurodegeneration. As for other amyloidogenic proteins, the most toxic forms of aggregated TTR are likely to be the low-molecular-mass diffusible species, and there is increasing evidence that this toxicity is mediated by disturbances in calcium homeostasis. This article reviews what is already known about the mechanism of TTR aggregation in FAP and describes how recent discoveries in other areas of amyloid research, particularly Alzheimer's disease, provide clues to the molecular pathogenesis of FAP.

Effect of conjugated equine estrogens and tamoxifen administration on thyroid gland histomorphology of the rat

OBJECTIVE

The aim of this study was to evaluate the action of the conjugated equine estrogens and tamoxifen on the morphology of thyroid gland in ovariectomized (OVx) rats.

METHODS

Conjugated equine estrogens (CEE), clinically used as estrogen therapy, is a complex formulation containing multiple estrogens that decrease menopausal symptoms. Thirty ovariectomized rats were randomly divided into 3 treatment groups: GI, vehicle (propylene glycol); GII, CEE 200 microg/kg per day; and GIII, tamoxifen 1 mg/kg per day. Another group of 10 rats with intact ovaries (GIV) was included, treated with the vehicle, and sacrificed during estrous. All animals were treated by gavage for 50 days, after which they were sacrificed. Blood samples were collected, and the thyroid was removed for morphological analysis and PCNA evaluation through immunohistochemical study.

RESULTS

The thyroid follicular cell height was increased in animals treated with CEE (14.90 +/- 0.20 microm), with TAM (14.90 +/- 0.10 microm), and in rats with intact ovaries (15.10 +/- 0.50 microm) in comparison to that of the vehicle group (9.90 +/- 0.20 microm) (P < 0.001). The follicular area was larger in the CEE (2,225 +/- 51 microm2) and TAM (2,127 +/- 67 microm2) groups compared to that of the vehicle group (5,016 +/- 53 microm2). The levels of T4 and T3 in rats treated with CEE, with Tamoxifen and in rats with intact ovaries, were higher than those those in the vehicle group (P < 0.001). The PCNA index in the vehicle group was lower than in other groups.

CONCLUSION

Our data suggest that estrogen and tamoxifen administration has a proliferative effect on the thyroid.

Exaggerated TSH responses to TRH in patients with goiter and 'normal' basal TSH levels

BACKGROUND/AIM

The availability of sensitive thyrotropin (TSH) assays decreased the diagnostic value of thyrotropin-releasing hormone stimulation tests (TRH-ST) in subclinical hypothyroidism. In this study we aimed to evaluate the relation between basal and stimulated serum TSH levels on TRH-ST and to determine the prevalence of patients with normal basal serum TSH and exaggerated TSH responses.

METHODS

179 patients (117 girls, 123 pubertal) with a median age of 12 (2.7-21.4) years who presented with goiter were enrolled and evaluated for their pubertal stage, height, thyroid autoimmunity, ultrasonography, thyroid function, and TRH-ST. Serum TSH concentrations were determined by sensitive assays. At TRH-ST, a peak serum TSH level >25 mIU/l was considered as an exaggerated response.

RESULTS

30 (17%) patients had an exaggerated TSH response. In patients with serum TSH levels between 2 and 4.68 mIU/l (upper half the normal range), an exaggerated TSH response was observed in 19.5%. A positive correlation between basal and TRH-stimulated TSH levels was determined (r = 0.536, p < 0.01). In patients with an exaggerated TSH response, 23 had normal (discordant) and 7 had high basal TSH levels (concordant). The mean basal serum TSH level was lower in the discordant group compared to the concordant group (p < 0.01).

CONCLUSION

Basal serum TSH levels might not be sufficient for diagnosing subclinical hypothyroidism. Stimulated TSH levels on TRH-ST are valuable, especially when serum TSH concentrations are in the upper half of the normal range.

Thyroid hormone alteration in pre-eclamptic women

This study sought a possible relationship between pre-eclampsia and thyroid profile. In a case-control setting, total thyroxine (T4), total tri-iodothyronine (T3), free T4, free T3, thyroxine binding globulin (TBG) and thyrotropin (TSH) levels in 39 pre-eclamptic patients were measured and compared with the levels in 42 healthy controls. We examined possible variations with regard to the severity of pre-eclampsia by dividing cases into mild (n = 17) and severe (n = 22) subgroups. Patients with mild pre-eclampsia showed significantly increased free T4 and TSH levels compared to healthy controls. In severe cases, TSH level was higher, but free T3 and free T4 levels were significantly lower than in controls. Other tests returned non-significant differences between the groups. Our findings suggest that primary hypofunctioning of the thyroid can accompany mild pre-eclampsia and possibly contribute to the pathogenesis. Elevated levels of free thyroid hormones in severe cases, however, may have reflected a preceding thyroid disorder.

The hypothalamic-pituitary-thyroid axis and the female reproductive system

Increasing evidence derived from experimental and clinical studies suggests that the hypothalamic-pituitary-thyroid axis (HPT) and the hypothalamic-pituitary-ovarian axis (HPO) are physiologically related and act together as a unified system in a number of pathological conditions. The suggestion that specific thyroid hormone receptors at the ovarian level might regulate reproductive function, as well as the suggested influence of estrogens at the higher levels of the HPT axis, seems to integrate the reciprocal relationship of these two major endocrine axes. Both hyper- and hypothyroidism may result in menstrual disturbances. In hyperthyroidism the most common manifestation is simple oligomenorrhea. Anovulatory cycles are very common. Increased bleeding may also occur, but it is rare. Hypothyroidism in girls can cause alterations in the pubertal process; this is usually a delay, but occasionally it can result in pseudo-precocious puberty. In mature women hypothyroidism usually is associated with abnormal menstrual cycles characterized mainly by polymenorrhea, especially anovulatory cycles, and an increase in fetal wastage.

Characterization of the thyroxine-binding site of thyroxine-binding globulin by site-directed mutagenesis

The principal transport protein for T4 in human blood, thyroxine-binding globulin (TBG), binds T4 with an exceptionally high affinity (Ka = 10(10) M(-1)). Its homology to the superfamily of the serpins has recently been used in the design of chimeric proteins, providing experimental evidence that an eight-stranded beta-barrel domain encompasses the ligand-binding site. We have now characterized the T4 binding site by site-directed mutagenesis. Sequence alignment of TBG from several species revealed a phylogenetically highly conserved stretch of amino acids comprising strands 2B and 3B of the beta-barrel motif. Mutations within this region (Val228Glu, Cys234Trp, Thr235Trp, Thr235Gln, Lys253Ala, and Lys253Asp), designed to impose steric hindrance or restriction of its mobility, had no significant influence on T4 binding. However, binding affinity was 20-fold reduced by introduction of an N-linked glycosylation site at the turn between strands 2B and 3B (Leu246Thr) without compromising the proper folding of this mutant as assessed by immunological methods. In most other serpins, this glycosylation site is highly conserved and has been shown to be crucial for cortisol binding of corticosteroid-binding globulin, the only other member of the serpins with a transport function. The ligand-binding site could thus be located to a highly aromatic environment deep within the beta-barrel. The importance of the binding site's aromatic character was investigated by exchanging phenylalanines with alanines. Indeed, these experiments revealed that substitution of Phe249 in the middle of strand 3B completely abolished T4 binding, while the substitution of several other phenylalanines had no effect.

The presence of transthyretin in rat ependymal cells is due to endocytosis and not synthesis

The presence and synthesis of transthyretin, a major carrier protein of thyroxine in rat cerebrospinal fluid, was investigated in choroid plexus epithelial cells and ependymal cells by immunocytochemistry, in situ hybridization, and analysis by Northern and Western blot using a specific oligonucleotide probe and a specific polyclonal antibody to transthyretin. Choroid plexus epithelial cells expressed transthyretin at high levels in developing rat cerebral hemispheres and in cultured cells. These cells secreted transthyretin into the cerebrospinal fluid. In the developing rat brain transthyretin was present in the cytoplasm of ependymal cells, in vesicles in contact with the apical membrane and in cilia. In ependymal cell cultures this protein was particularly abundant in the cilia of these cells. In contrast, ependymal cells did not synthesize transthyretin. It is postulated that transthyretin is transported to ependymal cells from the cerebrospinal fluid by endocytosis.

Evidence of free and bound leptin in human circulation. Studies in lean and obese subjects and during short-term fasting

Little is known about leptin's interaction with other circulating proteins which could be important for its biological effects. Sephadex G-100 gel filtration elution profiles of 125I-leptin-serum complex demonstrated 125I-leptin eluting in significant proportion associated with macromolecules. The 125I-leptin binding to circulating macromolecules was specific, reversible, and displaceable with unlabeled leptin (ED50: 0.73 +/- 0.09 nM, mean +/- SEM, n = 3). Several putative leptin binding proteins were detected by leptin-affinity chromatography of which either 80- or 100-kD proteins could be the soluble leptin receptor as approximately 10% of the bound 125I-leptin was immunoprecipitable with leptin receptor antibodies. Significantly higher (P < 0.001) proportions of total leptin circulate in the bound form in lean (46.5 +/- 6.6%) compared with obese (21.4 +/- 3.4%) subjects. In lean subjects with 21% or less body fat, 60-98% of the total leptin was in the bound form. Short-term fasting significantly decreased basal leptin levels in three lean (P < 0.0005) and three obese (P < 0.005) subjects while refeeding restored it to basal levels. The effects of fasting on free leptin levels were more pronounced in lean subjects (basal vs. 24-h fasting: 19.6 +/- 1.9 vs. 1.3 +/- 0.4 ng/ml) compared with those in obese subjects (28.3 +/- 9.8 vs. 14.7 +/- 5.3). No significant (P > 0.05) decrease was observed in bound leptin in either group. These studies suggest that in obese individuals the majority of leptin circulates in free form, presumably bioactive protein, and thus obese subjects are resistant to free leptin. In lean subjects with relatively low adipose tissue, the majority of circulating leptin is in the bound form and thus may not be available to brain receptors for its inhibitory effects on food intake both under normal and food deprivation states.

Familial dysalbuminaemic hyperthyroxinaemia and inherited partial TBG deficiency: first report

BACKGROUND

Abnormalities of the serum thyroid hormone binding proteins are not uncommon but, when properly assessed, they do not present diagnostic difficulties. In contrast, the presence of two inherited defects of thyroid hormone transport, of the type presented in the family described here, may cause a major problem in diagnosis and has not been described previously.

METHODS

All conventional thyroid function tests were carried out. In addition, thyroid hormone binding to serum proteins was assessed by agarose gel electrophoresis, and thyroxine binding globulin by immunoassays and by immunodiffusion. The affinity of TBG for thyroxine and its maximal binding capacity were assessed by Scatchard analysis.

RESULTS

Tests carried out on 22 members of the family revealed familial dysalbuminaemic hyperthyroxinaemia in 10 family subjects. All five living siblings of the propositus had familial dysalbuminaemic hyperthyroxinaemia and two tested transmitted this trait to their children and grandchildren. This was not the case with the propositus. Partial thyroxine binding globulin deficiency only, inherited presumably from the propositus' mother, was found in two family members. Both thyroxine binding globulin deficiency and familial dysalbuminaemic hyperthyroxinaemia were detected in the propositus and in his male nephew, masking the typical laboratory abnormalities associated with each of these defects.

CONCLUSIONS

Coexistence of two inherited defects of thyroid hormone transport proteins produce atypical thyroid function test abnormalities, which can be misinterpreted as thyroid hormone dysfunction.

Thyroid hormone autoantibodies and their implications for free thyroid hormone measurement

Thyroid hormone autoantibodies (THAA) disrupt the equilibrium between thyroid hormones and their binding proteins. This may lead to spurious estimations of free thyroxine (FT4) and triiodothyronine (FT3) by radioimmunoassay (RIA). In the present study we highlight the importance of THAA by examining the frequency of THAA in consecutive sera sent to a routine district hospital laboratory. Over a period of six months, sera were collected from 200 consecutive hypothyroid, 200 hyperthyroid and seven patients whose clinical and biochemical thyroid status were contradictory. A further 200 patients with non-thyroid autoimmune conditions, 20 patients with insulin autoantibodies and 100 healthy blood transfusion donors were studied. In all sera, both effects of antigen removal on THAA detection and where THAA were found, the effect of their removal on FT4, were examined. The frequencies of THAA amongst hypothyroid, hyperthyroid and non-thyroid autoimmune conditions were 7%, 1.5% and 7.5% respectively, whilst no THAA were found in insulin autoantibody positive patients and 100 blood transfusion donors. However, THAA frequency was highest in those patients whose biochemical thyroid status was widely inappropriate to clinical state (5/7 = 64%). Sera stripped of thyroid hormones prior to THAA detection had significantly higher antibody activity than unstripped sera (p = 0.0027 and p = 0.0123 for T3 and T4 binding respectively). Free thyroxine levels measured by the Amerlex-M RIA kit after antibody removal fell in all 21 THAA positive sera tested. The correlation coefficient between antibody activity in serum with percentage fall in FT4 was 0.79 (Spearman's Rank Correlation Test).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma catecholamines and postural hypotension in familial amyloidotic polyneuropathy of the Portuguese type

Plasma adrenaline and noradrenaline levels were measured while supine and following head-up tilt to 45 degrees, in both normal controls and in patients with familial amyloidotic polyneuropathy of the Portuguese type. In nine patients systolic blood pressure fell by less than 15 mmHg, while in seven patients it fell by more than 15 mmHg. Plasma noradrenaline rose during tilt in the majority of patients, as in the controls. There was no correlation between levels of catecholamines and fall in blood pressure on head-up tilt. The data excludes widespread sympatho-neural failure as a cause for postural hypotension in familial amyloidotic polyneuropathy of the Portuguese type. The results are compatible with either segmental/patchy sympathetic denervation or dysfunction of the receptor/effector mechanisms in target organs such as the heart and blood vessels.

Human c-erb A protein expressed in Escherichia coli: changes in hydrophobicity upon thyroid hormone binding

The human c-erb A beta gene sequence was inserted in an Escherichia coli expression vector plasmid. The E. coli cells transformed with this plasmid produced proteins with molecular masses of 52 and 50 kDa. These products bound 3,5,3'-triiodo-L-thyronine (T3) with an affinity constant of 4.3 x 10(9) liter/mol. The order of affinity for iodothyronine analogs was triiodothyroacetic acid greater than T3 greater than 3,5,3'-triiodo-D-thyronine greater than L-thyroxine. Affinity labeling experiments showed that the 50 kDa protein was covalently labeled with [125I]T3, and this was competed by triiodothyroacetic acid, T3, and L-thyroxine (from potent to weaker competitor). The c-erb A protein bound to calf thymus DNA-cellulose and the binding was inhibited by 0.3 M KCl or 10 mM pyridoxal 5'-phosphate. Aqueous two-phase partitioning studies showed that the c-erb A product became less hydrophobic upon T3 or triiodothyroacetic acid binding. The same finding was obtained when T3 bound to partially purified rat liver nuclear thyroid hormone receptor. However, thyroxine binding globulin became more hydrophobic upon T3 binding. Since the T3 molecule partitioned preferentially into the upper polyethylene glycol-rich phase, the alteration of partitioning behavior of thyroxine binding globulin was explained by a simple additive effect of T3. In contrast, the alteration of partitioning behavior of the c-erb A product or receptor reflected a conformational transition upon T3 binding. The c-erb A protein expressed in E. coli showed various characteristics similar to classical thyroid hormone receptor and may be useful in studying the structure and function of the thyroid hormone receptor.

Characterization of the latent transforming growth factor beta complex in bone

Transforming growth factor beta (TGF-beta) is a 25 kD multifunctional polypeptide with pronounced effects on the proliferation and differentiation of a variety of cells in vitro. TGF-beta is a potent regulator of the activity of cells with the osteoblast phenotype and of isolated osteoclasts. It is released in increased amounts by bone cultures stimulated to resorb. Organ cultures of neonatal mouse calvaria produce TGF-beta as an inert large-molecular-weight complex that must be dissociated to release biologically active TGF-beta (5-8 ng/ml). We have shown recently that stimulated isolated avian osteoclasts release active TGF-beta from this bone-derived biologically latent form. In this report we have characterized this bone latent form of TGF-beta. Only small amounts of active TGF-beta (less than 0.5 ng/ml) and no free binding protein are detectable in conditioned medium from bone cultures. Active TGF-beta can be detected in acid-treated calvarial conditioned media in which none or only minute amounts could previously be detected. Following incubation at 37 degrees C, this activated TGF-beta gradually loses activity. Cross-linking studies using 125I-labeled TGF-beta show that this loss of activity is due to TGF-beta binding to a protein of approximately 300 kD. The TGF-beta latent complex accumulates in a linear manner and is stable in the presence of serum and the protease trypsin. Increases in temperature and pH extremes dissociate the complex to release active TGF-beta. Decreases in pH result in an exponential increase in TGF-beta activity. Significant activation of the latent TGF-beta was detectable at pH values as high as 4 and 5. Since the osteoclastic microenvironment is acidic during bone resorption, these data suggest that this acidic microenvironment may regulate TGF-beta activity by releasing active TGF-beta from its latent complex.

Cerebrospinal fluid transthyretin in the neonate and blood-cerebrospinal fluid barrier permeability

We measured transthyretin levels in the cerebrospinal fluid (CSF) of newborn infants, older children, patients with viral and bacterial meningitis, and adults with increased CSF protein levels. Neonatal CSF transthyretin levels are elevated disproportionately in comparison to levels in the other groups. We conclude that increased levels of transthyretin in the CSF of neonates are not explained by increased permeability of the blood-CSF barrier.

Increased serum cortisol binding in chronic active hepatitis

PURPOSE

A high serum cortisol concentration, apparently due to increased cortisol-binding globulin (CBG), was found in a patient (index case) with chronic active hepatitis (CAH). We therefore performed further studies to determine whether increased cortisol binding is generally associated with CAH.

PATIENTS AND METHODS

Serum samples were obtained from 15 hospitalized patients with long-term liver function test elevations but no evidence of cirrhosis, 15 normal subjects without a history of hepatitis, four healthy pregnant women, and 10 alcoholic patients with stigmata of cirrhosis. Serum cortisol binding was measured by an adaptation of a previously described charcoal uptake method. Thyroxine-binding globulin (TBG) and sex hormone-binding globulin were determined by radioimmunoassays.

RESULTS AND CONCLUSION

Charcoal uptake of 125I cortisol from sera of normal subjects and additional patients with CAH revealed that increased serum cortisol binding by a saturable site, presumably CBG, was associated with CAH. Cortisol binding was significantly correlated with immunoassayable TBG, suggesting that in CAH, similar mechanisms may be responsible for increasing the serum concentrations of CBG and TBG.