Thyroid hormone activation in human vascular smooth muscle cells: expression of type II iodothyronine deiodinase

Energy availability modulates regional blood flow via estrogen-independent pathways in regularly menstruating young women

PURPOSE

This study aimed to investigate the impact of short-term low energy availability (LEA) on vascular function in young, regularly menstruating women.

METHODS

Participants were 19 women, aged 22.9 ± 4.2 years, with body mass index 18-30 kg·m2. They were divided into two groups and completed two conditions in a crossover design: a 3-day control condition (CON) with an energy availability of 45 kcals·kgFFM-1·day-1 and a 3-day LEA condition of 15 kcals·kgFFM-1 day-1. Assessments were conducted during the early follicular phase of the menstrual cycle. Outcome measures included forearm blood flow (FBF), heart rate, blood pressure, arterial stiffness, resting energy expenditure (REE), metabolic blood markers and body composition.

RESULTS

Significant time-by-condition interactions were found for resting FBF (p = .004), REE (p = .042), triiodothyronine (p = .006), β-hydroxybutyrate (p = .002) and body mass (p < .001). Resting FBF was 1.43 ± 1.01 and 1.31 ± 0.61 (arbitrary units) at pre and post, respectively, in LEA and 1.52 ± 0.7 and 1.76 ± 0.57 at pre and post in CON. The LEA condition led to a decrease in triiodothyronine (pre: 1.54 ± 0.28, post: 1.29 ± 0.27 ng ml-1), REE (pre: 1588 ± 165, post: 1487 ± 160 kcals day-1) and body mass (pre: 61.4 ± 7.5, post: 59.6 ± 7.3 kg). Changes in resting FBF were significantly correlated with changes in REE in the LEA condition (r = 0.53; p = 0.02).

CONCLUSION

Short-term LEA modifies regional blood flow and this might contribute to the observed decreased in REE. Findings emphasize the need for careful management of energy availability in populations at risk of LEA.

Analysis of correlative factors of female coronary slow-flow phenomenon: A retrospective study

The coronary slow-flow phenomenon (CSFP) is a manifestation of coronary artery disease wherein coronary angiography reveals no apparent stenosis; however, there is a delay in blood flow perfusion. Given its increased occurrence in male patients, with the majority of subjects in previous studies being male, this study aimed to explore whether distinct risk factors are present in female patients with CSFP. This single-center retrospective study focused on female patients diagnosed with CSFP by using coronary angiography. Eligible patients meeting the predefined inclusion and exclusion criteria were divided into the study group (presenting with CSFP) and control group (displaying normal epicardial coronary arteries). Comparative analyses of clinical and diagnostic data were performed. Ninety-two patients with CSFP and an equal number of controls were enrolled in this study. Patients with CSFP exhibited a higher prevalence of smokers (P = .017) and a heightened incidence of diabetes mellitus (DM) (P = .007). Significantly elevated levels of total cholesterol (TC) (P = .034) and free fatty acids (FFA) (P = .016) were observed in the CSFP group compared to those in the control group. Additionally, patients with CSFP displayed lower levels of apolipoprotein E (ApoE) (P = .092), free thyroxine (FT4) (P = .001), and total thyroxine (TT4) (P = .025). Logistic regression analysis indicated that smoking (P = .019), FFA (P < .001), ApoE (P = .015), and FT4 (P < .001) were independent risk factors for CSFP, accounting for confounding factors. Additionally, the area under the ROC curve (AUC) of the combined effect of smoking, ApoE, FT4, and FFA on CSFP was 0.793 (95% CI: 0.729-0.857, P < .01). In addition to the established risk factors for smoking, diabetes, and hyperlipidemia, female patients with CSFP exhibited significant differences in apoE, FFA, FT4, and TT4 levels compared to the control group. Smoking, FFA, and FT4 levels emerged as independent risk factors for CSFP.

Thyroid Disorders and Peripheral Arterial Disease

Hypothyroidism and hyperthyroidism, both overt and subclinical, are associated with increased risk of cardiovascular morbidity and mortality. The association between thyroid-stimulating hormone levels and cardiovascular risk has been demonstrated in large epidemiological studies and meta-analyses and is now considered a U-shaped curve. Several pathophysiological mechanisms linking thyroid and cardiovascular disease are known; however, specific clinical complications of peripheral arterial disease as endpoints of clinical trials have not been adequately investigated. The potential mechanisms linking hypothyroidism and peripheral arterial disease are endothelial dysfunction, blood pressure changes, dyslipidemia, and low-grade systemic inflammation. The potential mechanisms linking hyperthyroidism and peripheral arterial disease are hyperdynamic circulation, elevated systolic blood pressure, hypercoagulability, and possibly increased arterial inflammation.

Exploring the Potential of Olfactory Receptor Circulating RNA Measurement for Preeclampsia Prediction and Its Linkage to Mild Gestational Hypothyroidism

Gestational hypothyroidism may lead to preeclampsia development. However, this pathophysiological is unknown. We expect to find a shared mechanism by comparing hypothyroidism and preeclampsia. From our transcriptome data, we recognized olfactory receptors as that fingerprint. The reduction of taste and smell in hypothyroid patients has been known for a long time. Therefore, we decided to look to the olfactory receptors and aimed to identify genes capable of predicting preeclampsia (PEC). Methods: An Ion Proton Sequencer (Thermo Fisher Scientific, Waltham, MA, USA) was used to construct the transcriptome databases. RStudio with packages Limma v.3.50.0, GEOquery v.2.62.2, and umap v.0.2.8.8 were used to analyze the differentially expressed genes in GSE149440 from the Gene Expression Omnibus (GEO). The 7500 Real-Time PCR System (Applied Biosystems, Foster City, CA, USA) was used for RT-qPCR amplification of OR6X1 and OR4E2. Results: Our transcriptomic datasets analysis revealed 25.08% and 26.75% downregulated olfactory receptor (ORs) in mild nontreated gestational hypothyroidism (GHT) and PEC, respectively. In the GSE149440 GEO dataset, we found OR5H1, OR5T3, OR51A7, OR51B6, OR10J5, OR6C6, and OR2AG2 as predictors of early-onset PEC. We also evaluate two chosen biomarkers' responses to levothyroxine. The RT-qPCR demonstrated a difference in OR6X1 and OR4E2 expression between GHT and healthy pregnancy (p < 0.05). Those genes presented a negative correlation with TSH (r: -0.51, p < 0.05; and r: -0.44, p < 0.05), a strong positive correlation with each other (r: 0.89; p < 0.01) and the levothyroxine-treated group had no difference from the healthy one. We conclude that ORs could be used as biomarkers at the beginning of gestation, and the downregulated ORs found in GHT may be improved with levothyroxine treatment.

Prenatal hypothyroidism diminished exogenous NO-mediated diastolic effects in fetal rat thoracic aorta smooth muscle via increased oxidative stress

Maternal hypothyroidism is an important problem of modern healthcare and is reported to increase the risk of cardiovascular diseases in the offspring later in life. However, it is unclear whether hypothyroidism during pregnancy causes vascular damage in the fetal period. We established the prenatal hypothyroidism rat model and collected the fetuses at the 21th day of gestation (GD21). Thyroid hormone concentrations in maternal and offspring blood serum were assessed by enzyme-linked immunosorbent assay (ELISA). The thoracic aortas of the fetuses were isolated for microvessel functional testing and histochemical stainings. qPCR and Western blot were performed to access mRNA and protein expression. We found that the concentrations of thyroid hormones in the serum of pregnant rats and fetuses were significantly suppressed at GD21. The responses of the fetal thoracic aortas to SNP were significantly attenuated in the PTU group. However, no statistical difference was found between the two groups when treated with either inhibitor (ODQ) or activator (BAY58-2667) of sGC. The production of O₂^-• in the arterial wall was significantly increased in hypothyroid fetuses. Moreover, the level of NADPH oxidase (NOX) was increased, while superoxide dismutase 2 (SOD2) was down-regulated in the PTU group, ultimately contributing to the increased production of superoxide. Additionally, decreased SNP-mediated vasodilation found in fetal vessels was improved by either NOX inhibitor (Apocynin) or SOD mimic (Tempol). These results indicate that increased oxidative stress is probably the cause of the diminished diastolic effect of exogenous NO in the thoracic artery of prenatal hypothyroidism exposed fetuses.

Hypothyroidism and Risk of Cardiovascular Disease

Thyroid hormones (TH) have a significant impact on cellular oxidative metabolism. Besides that, they maintain vascular homeostasis by positive effects on endothelial and vascular smooth muscle cells. Subclinical (SCH) and clinical (CH) hypothyroidism influences target organs by changing their morphology and function and impaired blood and oxygen supply induced by accelerated atherosclerosis. The increased risk of acceleration and extension of atherosclerosis in patients with SCH and CH could be explained by dyslipidemia, diastolic hypertension, increased arterial stiffness, endothelial dysfunction, and altered blood coagulation. Instability of atherosclerotic plaque in hypothyroidism could cause excessive activity of the elements of innate immunity, which are characterized by: the significant presence of macrophages in atherosclerotic plaques, increased nuclear factor kappa B (NFkB) expression, and elevated levels of tumor necrosis factor α (TNF-α) and matrix metalloproteinase (MMP) 9, with reduced interstitial collagen, which all together creates inflammation milieu resulted in plaque rupture. Optimal substitution by levothyroxine (LT4) restores biochemical euthyroidism. In postmenopausal women and elderly patients with hypothyroidism and associated vascular comorbidity, excessive LT4 substitution could lead to atrial rhythm disorders and osteoporosis. Therefore, it is of interest to maintain thyroid-stimulating hormone (TSH) levels in the reference range, thus eliminating the deleterious effects of lower or higher TSH levels on the cardiovascular system. This review summarizes the recent literature on subclinical and clinical hypothyroidism and atherosclerotic cardiovascular disease and discusses the effects of LT4 replacement therapy on restoring biochemical euthyroidism and atherosclerosis processes.

Meta-analysis on the association between thyroid hormone disorders and arterial stiffness

Context

Aortic stiffness is an emerging predictor of cardiovascular morbidity and mortality. Current data about the effect of subclinical and overt thyroid hormone disorders on aortic stiffness are often conflicting.

Objective

Primary outcome was to investigate if subclinical and overt thyroid hormone disorders were associated with aortic stiffness. Secondary outcome was to identify disease effect modifiers.

Methods

Data sources were PubMed, Google Scholar, SCOPUS, Web of Sciences, and the Cochrane Library. Eligible studies included reports of pulse wave velocity (PWV), which is the gold standard method for measuring aortic stiffness, in patients with subclinical and overt thyroid disorders. Two investigators independently identified eligible studies and extracted data. Pooled mean difference was the summary effect measure. Data were presented in forest plots with outlier and influential case diagnostics. Univariate meta-regression analysis was used to identify effect modifiers.

Results

Eleven observational studies were selected, including 1239 patients with subclinical hypothyroidism, 81 patients with overt hypothyroidism, 338 patients with thyrotoxicosis, and 12 715 controls. PWV was significantly higher in subclinical (P < .001) and overt hypothyroidism (P < .001), as well as in patients with thyrotoxicosis (P = .027) compared with controls. Age was an effect modifier in hypothyroid patients.

Conclusion

This study shows that both overt and subclinical hypothyroidism as well as thyrotoxicosis were associated with an increase of aortic stiffness. The impact of treatment of these conditions on aortic stiffness should be assessed in clinical trials.

Region-specific effects of antenatal/early postnatal hypothyroidism on endothelial NO-pathway activity in systemic circulation

Background

Antenatal/early postnatal hypothyroidism weakens NO-mediated anticontractile influence of endothelium in coronary arteries of adult rats, but it remains unclear whether this occurs in other vascular regions. We hypothesized that developmental thyroid deficiency is followed by region-specific changes in the endothelial NO-pathway activity in systemic vasculature. To explore this, we estimated the effects of antenatal/early postnatal hypothyroidism on NO-pathway activity and its potential local control mechanisms in rat mesenteric and skeletal muscle (sural) arteries.

Methods

Dams were treated with 6-propyl-2-thiouracil (PTU) in drinking water (0.0007%) during pregnancy and 2 weeks postpartum; control (CON) females received PTU-free water. Adult offspring (10–12-weeks) arteries were studied by wire myography, qPCR, and Western blotting.

Results

Endothelium removal or inhibition of NO-synthase with L-NNA augmented contractile responses to α₁-adrenoceptor agonist methoxamine. In PTU compared to CON group, these effects were stronger in sural arteries, but did not differ in mesenteric arteries. The responses of both arteries to NO-donor DEA/NO were similar in CON and PTU rats. mRNA contents of deiodinase 2 and thyroid hormone receptor α were similar in mesenteric arteries of two groups but were elevated in sural arteries of PTU group compared to CON. The abundance of eNOS protein was higher in sural arteries of PTU compared to CON rats.

Conclusion

Antenatal/early postnatal hypothyroidism is followed by an increase in NO-mediated anticontractile influence in sural, but not in mesenteric arteries of adult animals. The diversity of hypothyroidism effects may be due to different alterations of local T3 synthesis/reception in different vascular beds.

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Antenatal hypothyroidism increases anticontractile NO-effect in sural arteries.

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Antenatal hypothyroidism doesn't change anticontractile effect in mesenteric arteries.

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Diverse hypothyroidism effects may be due to the differences in local T3 signaling.

Impaired sensitivity to thyroid hormones and carotid plaque in patients with coronary heart disease: A RCSCD-TCM study in China

CONTEXT

Previous studies on the association between thyroid function and carotid plaque have shown contradictory results, which may be attributable to the sensitivity to thyroid hormone indices. This study aimed to analyze the association between thyroid hormone sensitivity and risk of carotid plaque in patients with coronary heart disease (CHD) and further explore this association according to sex, age, smoking, and drinking status.

METHODS

This large-scale, multi-center, retrospective, cross-sectional study included 6679 patients with CHD (age 35-75). Central sensitivity to thyroid hormone was evaluated by the thyroid feedback quantile-based index (TFQI), parametric thyroid feedback quantile-based index (PTFQI), thyroid-stimulating hormone index (TSHI), and thyrotroph thyroxine resistance index (TT4RI). Peripheral sensitivity to thyroid hormone was assessed by free triiodothyronine/free thyroxine (FT3/FT4) ratio. Taking no carotid plaque as a reference, this study used logistic regression to analyze the association between central and peripheral thyroid hormone sensitivity and carotid plaque in patients with CHD.

RESULTS

Of the 6679 patients with CHD, 4843 (72.50%) had carotid plaque. In the multi-adjusted models, the TFQI (odds ratio [OR]: 1.50; 95% confidence interval [CI]: 1.26-1.78; P < 0.001), PTFQI (OR: 1.76; 95% CI: 1.46-2.12; P < 0.001), TSHI (OR: 1.21; 95% CI: 1.10-1.33; P < 0.001), and TT4RI (OR: 1.00; 95% CI: 1.00-1.01; P = 0.003) were positively associated with the risk of carotid plaque. Compared with that in females and people > 60 years, the OR value for carotid plaque was higher in males and people ≤ 60 years. Similarly, smokers and drinkers had higher OR values for carotid plaque than non-smokers and non-drinkers. Conversely, FT3/FT4 ratio (OR: 0.75; 95% CI: 0.70-0.81; P < 0.001) was negatively associated with carotid plaque, and the OR value for carotid plaque was lower in males, patients ≤ 60 years, smokers, and drinkers.

CONCLUSION

This study showed that thyroid hormone sensitivity is significantly associated with carotid plaque in patients with CHD. This association is more significant in males, patients ≤ 60 years, smokers, and drinkers.

Deiodinases and the Three Types of Thyroid Hormone Deiodination Reactions

Thyroid hormone (TH) signaling is strictly regulated by iodothyronine deiodinase activity, which both preserves the circulating levels of the biologically active triiodothyronine (T3) and regulates TH homeostasis at the local level, in a cell- and time-dependent manner. Three deiodinases have been identified-namely iodothyronine deiodinase 1 (DIO1), DIO2, and DIO3-that differ in their catalytic properties and tissue distribution. The deiodinases represent a dynamic system that changes in the different stages of life according to their functions and roles in various cell types and tissues. Deiodinase activity at the tissue level permits cell-targeted fine regulation of TH homeostasis, mediating the activation (DIO1 and DIO2) and inactivation (DIO3) of THs. Deiodinase homeostasis is the driving force that leads T3-target cells towards customized TH signaling, which takes into account both the hormonal circulating levels and the tissue-specific response. This review analyzes the complex role of deiodinases in physiological and pathological contexts, exploring new challenges and opportunities deriving from a deeper knowledge of the dynamics underlying their roles and functions.

Autoimmune diseases in patients undergoing percutaneous coronary intervention: A risk factor for in-stent restenosis?

BACKGROUND AND AIMS

Despite the relation between autoimmune diseases and increased atherosclerotic risk is established, the influence of autoimmune disorders on in-stent restenosis (ISR) after percutaneous coronary intervention (PCI) is only partly known. ISR is an aberrant reparative process mainly characterized by an increased number of vascular smooth muscle cells and excessive deposition of extracellular proteoglycans and type III collagen. Chronic inflammation, always present in autoimmune diseases, modulates the endothelial response to PCI. Aim of this review is to resume the current evidence on the association between ISR and autoimmune diseases, focusing on pathogenic mechanisms and therapeutic targets.

METHODS

We conducted a comprehensive review of the literature on the relationship between ISR and insulin-dependent diabetes mellitus (IDDM), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), antiphospholipid-antibodies syndrome (APS), inflammatory bowel diseases (IBD), and Hashimoto's thyroiditis (HT).

RESULTS

Patients affected with IDDM, RA, SLE, APS, IBD and HT proved to face higher rates of ISR compared to the general population. The endothelial dysfunction seems the principal common pathogenic pathway for ISR and is attributed to both the immune system disorder and the systemic inflammation. Some evidence suggested that methotrexate and anti-tumor necrosis factor treatments can be effective in reducing ISR, while antibodies against vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 showed to reduce neointimal hyperplasia in animal models.

CONCLUSIONS

Autoimmune diseases are a risk factor for ISR. The study of the potential cardiovascular benefits of the current therapies, mainly anti-inflammatory drugs, and the pursuit of innovative treatments appear of paramount interest.

FMD and CIMT: Surrogate Markers of Atherosclerosis in Subclinical and Overt Hypothyroidism in Sub Himalyan Region

INTRODUCTION

Hypothyroidism increases the risk of atherosclerosis. Carotid intima-media thickness (CIMT) and flow-mediated dilation (FMD) have been used as a noninvasive method to detect atherosclerosis. But the literature is scarce on patients with subclinical hypothyroidism. Such a study was not done in our region, so we conducted this study at a tertiary care center to compare CIMT and FMD among subclinical and overt hypothyroid patients and to analyze the risk of atherosclerosis.

METHODS

We evaluated 68 patients aged 18-50 years, with newly diagnosed hypothyroidism. We divided them into overt and subclinical hypothyroidism groups and compared the findings. All analyses were performed by the computerized SPSS 17.0. The results were noted as means ± SD and percentage. Student's t-test was used to compare continuous variables, and the Chi-square test was used to compare differences.

RESULTS

The total number of patients with dyslipidemia in the subclinical hypothyroidism (SCH) group was 22 (45.83%) and in the overt hypothyroidism (OH) group was 26 (54.16%) with a P- value of 0.009. The mean FMD% in subclinical hypothyroidism patients was 6.9816 ± 3.4224 and in overt hypothyroidism patients was 5.3670 ± 2.7278 (P = 0.03). The mean CIMT was 0.5009 ± 0.0732, CIMT in the SCH group was 0.5082 ± 0.0672 and in the OH group was 0.5305 ± 0.0799 (P = 0.2).

CONCLUSION

The outcome of this study specifies that hypothyroidism is associated with endothelial dysfunction as established by impaired FMD, and it may be the first marker of atherosclerosis appearing before any structural evidence like CIMT. We can speculate that there is a link between subclinical hypothyroidism and atherosclerosis, and thyroxine replacement in SCH may help to prevent the progression of atherosclerosis.

Thyroid Dysfunction and Atherosclerosis: A Systematic Review

BACKGROUND/AIM

Thyroid dysfunction, both hypo- and hyperthyroidism, has been associated with cardiovascular disease. The aim of this study was to evaluate the association between thyroid dysfunction and atherosclerosis measured mostly by carotid intima-media thickness, as well as discuss whether L-T4 replacement is able to reverse or slow down the progression of atherosclerosis.

MATERIALS AND METHODS

The review was conducted according the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. We performed on PubMed a literature search from May 2004 to January 2020, using the search terms 'subclinical hypothyroidism' or 'thyroid disorders' and 'carotid artery', 'carotid intima-media thickness (IMT)', 'levothyroxine', and 'atherosclerosis'.

RESULTS

Twenty-six studies were eligible and included in the analysis. Overall, the studies encompassed a total of 36.434 patients included in this review. Most studies indicated a proportional correlation between IMT and thyroid dysfunction. Levothyroxine (L-T4) replacement led to significant decrease of IMT after 1 year in most studies.

CONCLUSION

Most studies have concluded that thyroid dysfunction is associated with arterial wall remodeling and, thus, with increased cardiovascular risk. However, the exact mechanistic background of pathological structural changes in the arterial wall is still unsettled. Large randomized controlled studies are required to definitively address the extent to which T4 replacement therapy might benefit patients with subclinical thyroid disorders.

Association between high normal-range thyrotropin concentration and carotid intima-media thickness in euthyroid premenopausal, perimenopausal and postmenopausal women

OBJECTIVE

There are currently no established cutoff levels for thyrotropin (TSH) within the reference intervals associated with carotid atherosclerosis to prevent the onset of cardiovascular diseases. The present study aimed to determine the TSH cutoff level associated with carotid maximum intima-media thickness (max IMT) in euthyroid premenopausal, perimenopausal and postmenopausal women.

STUDY DESIGN

We conducted a cross-sectional study of 468 euthyroid women who had not been treated for or diagnosed with cardiovascular diseases and/or metabolic disorders among 1221 Japanese women who participated in a comprehensive medical examination at the Hidaka Hospital, Japan. Participants' weight, blood pressure, plasma glucose, serum lipoprotein, free thyroxine and TSH were measured and an interview about menstruation was conducted. Carotid ultrasonography was performed to determine max IMT.

RESULTS

Max IMT significantly increased stepwise as menopausal status progressed (p < 0.001). Serum TSH levels were significantly higher in participants with carotid plaques, defined as max IMT ≥1.1 mm (p = 0.038), and were independently associated with the presence of carotid plaque using multivariate logistic regression analysis (β =1.218, p = 0.036). In postmenopausal women, significantly higher carotid max IMT values were observed in women with serum TSH ≥2.5 μIU/mL compared with women with concentrations <2.5 μIU/mL (p = 0.018) without elevated total cholesterol and low-density lipoprotein cholesterol concentrations. These differences were not observed in premenopausal women.

CONCLUSIONS

Laboratory finding of serum TSH concentration ≥2.5 μIU/mL may be useful to assess risk of atherosclerosis, especially in postmenopausal women.

Bipolar limbic expression of auto-immune thyroid targets: thyroglobulin and thyroid-stimulating hormone receptor

The associations between thyroid auto-immunity and neuro-psychiatric disorders are well-documented. However, there exists limited literature specifically linking auto-immune thyroid disease (AITD) to bipolar disorder (BD). Thus, we investigated the likely association between Hashimoto's disease and BD through the extra-thyroidal localisation of thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in limbic regions of normal and bipolar human adult brain. Further, we hypothesised that changes in thyroid expression in bipolar limbic cortex may contribute to mood dysregulation associated with BD. Immuno-chemistry and in-situ PCR were used to localise TSH-R/TG within the amygdala, cingulate gyrus and frontal cortex of normal (n = 5) and bipolar (n = 5) brains. Reverse-transcriptase qPCR provided fold-change differences in TSH-R gene expression. The results demonstrated reduced thyroid protein expression in bipolar limbic regions; these novel results correlate with other neuro-imaging reports that describe reduced cortico-limbic tissue volumes and neuro-physiological activity during BD. We also demonstrated TG-like proteins exclusive to bipolar amygdala neurons, and which relates to previous neuro-imaging studies of amygdala hyperactivity and enhanced emotional sensitivity in BD. Indeed, reduced TSH-R/TG in limbic regions may predispose to, or bear relevance in the pathophysiology of mood dysregulation and symptoms of BD. Further, we attribute mood dysregulation in BD to limbic-derived TSH-R, which probably provides potential targets for thyroid auto-immune factors during Hashimoto's disease. Consequently, this may lead to inactivated and/or damaged neurons. The neuro-pathology of diminished neuronal functioning or neuronal atrophy suggests a novel neuro-degeneration mechanism in BD.

Paradigms of Dynamic Control of Thyroid Hormone Signaling

Thyroid hormone (TH) molecules enter cells via membrane transporters and, depending on the cell type, can be activated (i.e., T4 to T3 conversion) or inactivated (i.e., T3 to 3,3'-diiodo-l-thyronine or T4 to reverse T3 conversion). These reactions are catalyzed by the deiodinases. The biologically active hormone, T3, eventually binds to intracellular TH receptors (TRs), TRα and TRβ, and initiate TH signaling, that is, regulation of target genes and other metabolic pathways. At least three families of transmembrane transporters, MCT, OATP, and LAT, facilitate the entry of TH into cells, which follow the gradient of free hormone between the extracellular fluid and the cytoplasm. Inactivation or marked downregulation of TH transporters can dampen TH signaling. At the same time, dynamic modifications in the expression or activity of TRs and transcriptional coregulators can affect positively or negatively the intensity of TH signaling. However, the deiodinases are the element that provides greatest amplitude in dynamic control of TH signaling. Cells that express the activating deiodinase DIO2 can rapidly enhance TH signaling due to intracellular buildup of T3. In contrast, TH signaling is dampened in cells that express the inactivating deiodinase DIO3. This explains how THs can regulate pathways in development, metabolism, and growth, despite rather stable levels in the circulation. As a consequence, TH signaling is unique for each cell (tissue or organ), depending on circulating TH levels and on the exclusive blend of transporters, deiodinases, and TRs present in each cell. In this review we explore the key mechanisms underlying customization of TH signaling during development, in health and in disease states.

TRα inhibits arterial renin-angiotensin system expression and prevents cholesterol accumulation in vascular smooth muscle cells

OBJECTIVES

The tissue renin-angiotensin system (tRAS) plays a key role in the maintenance of cellular homeostasis but is also implicated in atherosclerosis. Thyroid hormone (TH) contributes, via genomic effects, to control of tRAS gene expression in the arterial wall and vascular smooth muscle cells (VSMCs). We investigated the specific functions of TH receptors-α and -β (TRα and TRβ) on tRAS gene expression in the aorta and VSMCs, and the potential protective effect of TRα against atherosclerosis.

MATERIAL AND METHODS

Using aorta and cultured aortic VSMCs from TRα and TRβ deficient mice, tRAS gene expression was analyzed by determining mRNA levels on real-time PCR. Gene regulation under cholesterol loading mimicking atherosclerosis conditions was also examined in VSMCs in vitro.

RESULTS

TRα deletion significantly increased expression of angiotensinogen (AGT) and angiotensin II receptor type 1 subtype a (AT₁R_a) at transcriptional level in aorta, a tissue with high TRα expression level. TRα activity thus seems to be required for maintenance of physiological levels of AGTand AT₁R_aexpression in the arterial wall. In addition, during cholesterol loading, TRα deletion significantly increased cholesterol content in VSMCs, with a weaker decrease in AGTexpression.

CONCLUSION

TRα seems to have an inhibitory impact on AGTand AT₁R_aexpression, and loss of TRα function in TRα^0/0 mice increases tRAS expression in the aortic wall. More importantly, TRα deletion significantly increases VSMC cholesterol content. Our results are consistent with a protective role of TRα against atherosclerosis.

Specification and Diversification of Pericytes and Smooth Muscle Cells from Mesenchymoangioblasts

Elucidating the pathways that lead to vasculogenic cells, and being able to identify their progenitors and lineage-restricted cells, is critical to the establishment of human pluripotent stem cell (hPSC) models for vascular diseases and development of vascular therapies. Here, we find that mesoderm-derived pericytes (PCs) and smooth muscle cells (SMCs) originate from a clonal mesenchymal progenitor mesenchymoangioblast (MB). In clonogenic cultures, MBs differentiate into primitive PDGFRβ⁺ CD271⁺CD73⁻ mesenchymal progenitors, which give rise to proliferative PCs, SMCs, and mesenchymal stem/stromal cells. MB-derived PCs can be further specified to CD274⁺ capillary and DLK1⁺ arteriolar PCs with a proinflammatory and contractile phenotype, respectively. SMC maturation was induced using a MEK inhibitor. Establishing the vasculogenic lineage tree, along with identification of stage- and lineage-specific markers, provides a platform for interrogating the molecular mechanisms that regulate vasculogenic cell specification and diversification and manufacturing well-defined mural cell populations for vascular engineering and cellular therapies from hPSCs.

Kumar et al. find that mesodermal pericytes and smooth muscle cells in human pluripotent stem cell cultures originate from a common endothelial and mesenchymal cell precursor, the mesenchymoangioblast. They show how different lineages of mural cells are specified from mesenchymoangioblasts and define stage- and lineage-specific markers for vasculogenic cells.

Lack of Association Between Subclinical Hypothyroidism and Carotid-Femoral Pulse Wave Velocity in a Cross-Sectional Analysis of the ELSA-Brasil

BACKGROUND

There is little available data on carotid-femoral pulse wave velocity (cf-PWV) in subjects with subclinical hypothyroidism (SCH). We aimed to analyze the association between SCH and cf-PWV using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

METHODS

We included subjects with normal thyroid function (thyrotropin (TSH): 0.4-4.0 mIU/l, and normal free thyroxine (FT4: 0.8-1.9ng/dl) and SCH (TSH > 4.0 mIU/l and normal FT4) evaluated for cf-PWV in a cross-sectional analysis. We excluded individuals using medications that interfere in thyroid function, antihypertensives, or diuretics, and subjects with chronic kidney disease or previous cardiovascular disease. Generalized linear and logistic regression models evaluated cf-PWV as a dependent variable and SCH as an independent variable, adjusted for cardiovascular risk factors.

RESULTS

Of 8,341 subjects (52.3% women), 7,878 (94.4%) were euthyroid and 463 (5.6%) showed SCH. The median age was 50 years (interquartile range: 44-56). The groups differed by age, sex, body mass index, glomerular filtration rate, and C-reactive protein. SCH was not associated with cf-PWV in the full-adjusted linear model (β = -0.039; P = 0.562) and with cf-PWV >75^th percentile in the full-adjusted logistic model (odds ratio = 0.94; 95% confidence interval = 0.72-1.22).

CONCLUSION

In a large sample, SCH was not associated with increased cf-PWV.

Arterial Stiffness and Central Hemodynamics in Thyroidectomized Patients on Long-Term Substitution Therapy with Levothyroxine

BACKGROUND

Long-term levothyroxine (LT4) therapy targeting thyrotropin (TSH) suppression in hypothyroid patients treated for thyroid cancer has been associated with increased arterial stiffness and increased cardiovascular mortality. However, most patients with hypothyroidism receive LT4 therapy targeting TSH in the reference range. The long-term vascular effects of this strategy have never been evaluated.

METHODS

Arterial stiffness and central hemodynamics were studied in 30 thyroidectomized patients (Mage = 54.5 ± 10.2 years; 80% female) on long-term (median = 11 years; range 3-41 years) LT4 replacement therapy targeting TSH in the reference range and 30 sex- and age-matched controls. Arterial stiffness was evaluated by carotid-femoral pulse wave velocity (PWV) and central hemodynamics by pulse wave analysis using the SphygmoCor system.

RESULTS

TSH levels were comparable in patients and controls (median = 1.99 × 10(3) IU/L [range 0.24-5.64 × 10(3) IU/L] vs. median = 2.13 × 10(3) IU/L [range 0.59-5.63 × 10(3) IU/L]; p = 0.69), but patients had higher plasma thyroxine and lower plasma triiodothyronine levels than controls (median = 108 nmol/L [range 84-149 nmol/L] vs. 86 nmol/L [range 59-141 nmol/L]; p < 0.001 and median = 1.49 nmol/L [range 1.00-2.37 nmol/L] vs. 1.62 nmol/L [range 1.18-2.09 nmol/L]; p = 0.04, respectively). PWV was not significantly higher in patients compared to controls (8.2 ± 1.9 vs. 7.9 ± 1.9 m/s, p = 0.69). Similarly, no group differences were observed in central systolic/diastolic blood pressure (120 ± 16 mmHg vs. 119 ± 12 mmHg, p = 0.77; and 80 ± 11 mmHg vs. 80 ± 10 mmHg, p = 0.98, respectively), the augmentation index (28 ± 13% vs. 29 ± 8%, p = 0.72), or the pulse pressure amplification ratio (129 ± 17% vs. 124 ± 13%, p = 0.18).

CONCLUSION

Despite subtle differences in plasma levels of thyroid hormones, long-term LT4 replacement therapy targeting TSH in the reference range does not seem to cause adverse effects on arterial stiffness and central hemodynamics.

Thyroid hormone receptor-α deletion decreases heart function and exercise performance in apolipoprotein E-deficient mice

The deletion of thyroid hormone receptor-α (TRα) in atherosclerosis-prone apolipoprotein E-deficient (ApoE(-/-)) mice (ApoE(-/-)TRα(0/0)) accelerates the formation of atherosclerotic plaques without aggravation of hypercholesterolemia. To evaluate other predisposition risk factors to atherosclerosis in this model, we studied blood pressure (BP) and cardiac and vascular functions, as well as exercise tolerance in young adult ApoE(-/-)TRα(0/0) mice before the development of atherosclerotic plaques. Telemetric BP recorded for 4 consecutive days showed that the spontaneous systolic BP was slightly decreased in ApoE(-/-)TRα(0/0) compared with ApoE(-/-) mice associated with a reduced locomotor activity. The percentage of animals that completed endurance (57% vs. 89%) and maximal running (0% vs. 89% at 46 cm/s speed in ApoE(-/-)TRα(0/0) and ApoE(-/-) mice, respectively) tests was lower in ApoE(-/-)TRα(0/0) mice. Moreover, during the maximal running test, both maximal running speed and running distance were significantly reduced in ApoE(-/-)TRα(0/0) mice, associated with a blunted BP response to exercise. Transthoracic echocardiography revealed a decreased interventricular septum thickness and an increased end-systolic left ventricular volume in ApoE(-/-)TRα(0/0) mice. Accordingly, left ventricular fractional shortening, ejection fraction, and stroke volume were all significantly decreased in ApoE(-/-)TRα(0/0) mice with a concomitant blunted cardiac output. No interstrain difference was observed in vascular reactivity, except that ApoE(-/-)TRα(0/0) mice exhibited an enhanced acetylcholine-induced relaxation in mesenteric and distal femoral arteries. In conclusion, the deletion of TRα in ApoE(-/-) mice alters cardiac structure and contractility; both could contribute to blunted BP response to physical exercise and impaired exercise performance.

Thyroid Hormone and Vascular Remodeling

Both hyperthyroidism and hypothyroidism affect the cardiovascular system. Hypothyroidism is known to be associated with enhanced atherosclerosis and ischemic heart diseases. The accelerated atherosclerosis in the hypothyroid state has been traditionally ascribed to atherogenic lipid profile, diastolic hypertension, and impaired endothelial function. However, recent studies indicate that thyroid hormone has direct anti-atherosclerotic effects, such as production of nitric oxide and suppression of smooth muscle cell proliferation. These data suggest that thyroid hormone inhibits atherogenesis through direct effects on the vasculature as well as modification of risk factors for atherosclerosis. This review summarizes the basic and clinical studies on the role of thyroid hormone in vascular remodeling. The possible application of thyroid hormone mimetics to the therapy of hypercholesterolemia and atherosclerosis is also discussed.

Type 2 Iodothyronine Deiodinase Activity Is Required for Rapid Stimulation of PI3K by Thyroxine in Human Umbilical Vein Endothelial Cells

Thyroid hormones (THs) exert a number of physiological effects on the cardiovascular system. Some of the nongenomic actions of T3 are achieved by cross coupling the TH receptor (TR) with the phosphatidylinositol 3-kinase (PI3K)/protein kinase Akt (Akt) pathway. We observed that both T3 and T4 rapidly stimulated Akt phosphorylation and Ras-related C3 botulinum toxin substrate 1 (Rac1) activation, which resulted in cell migration, in a PI3K-dependent manner in human umbilical vein endothelial cells (HUVECs). We identified the expression of type 2 iodothyronine deiodinase (D2), which converts T4 to T3, and TRα1 in HUVECs. D2 activity was significantly stimulated by (Bu)2cAMP in HUVECs. The blockade of D2 activity through transfection of small interfering RNA (siRNA) specific to D2 as well as by addition of iopanoic acid, a potent D2 inhibitor, abolished Akt phosphorylation, Rac activation, and cell migration induced by T4 but not by T3. The inhibition of TRα1 expression by the transfection of siRNA for TRα1 canceled Akt phosphorylation, Rac activation, and cell migration induced by T3 and T4. These findings suggest that conversion of T4 to T3 by D2 is required for TRα1/PI3K-mediated nongenomic actions of T4 in HUVECs, including stimulation of Akt phosphorylation and Rac activation, which result in cell migration.

Thyroid Hormone Signaling in Male Mouse Skeletal Muscle Is Largely Independent of D2 in Myocytes

The type 2 deiodinase (D2) activates the prohormone T4 to T3. D2 is expressed in skeletal muscle (SKM), and its global inactivation (GLOB-D2KO mice) reportedly leads to skeletal muscle hypothyroidism and impaired differentiation. Here floxed Dio2 mice were crossed with mice expressing Cre-recombinase under the myosin light chain 1f (cre-MLC) to disrupt D2 expression in the late developmental stages of skeletal myocytes (SKM-D2KO). This led to a loss of approximately 50% in D2 activity in neonatal and adult SKM-D2KO skeletal muscle and about 75% in isolated SKM-D2KO myocytes. To test the impact of Dio2 disruption, we measured soleus T3 content and found it to be normal. We also looked at the expression of T3-responsive genes in skeletal muscle, ie, myosin heavy chain I, α-actin, myosin light chain, tropomyosin, and serca 1 and 2, which was preserved in neonatal SKM-D2KO hindlimb muscles, at a time that coincides with a peak of D2 activity in control animals. In adult soleus the baseline level of D2 activity was about 6-fold lower, and in the SKM-D2KO soleus, the expression of only one of five T3-responsive genes was reduced. Despite this, adult SKM-D2KO animals performed indistinguishably from controls on a treadmill test, running for approximately 16 minutes and reached a speed of about 23 m/min; muscle strength was about 0.3 mN/m·g body weight in SKM-D2KO and control ankle muscles. In conclusion, there are multiple sources of D2 in the mouse SKM, and its role is limited in postnatal skeletal muscle fibers.

Hypothyroidism Is Associated With Coronary Endothelial Dysfunction in Women

BACKGROUND

Hypothyroidism is associated with an increased risk of coronary artery disease, beyond that which can be explained by its association with conventional cardiovascular risk factors. Coronary endothelial dysfunction precedes atherosclerosis, has been linked to adverse cardiovascular events, and may account for some of the increased risk in patients with hypothyroidism. The aim of this study was to determine whether there is an association between epicardial and microvascular coronary endothelial dysfunction and hypothyroidism.

METHODS AND RESULTS

In 1388 patients (mean age 50.5 [12.3] years, 34% male) presenting with stable chest pain to Mayo Clinic, Rochester, MN for diagnostic coronary angiography, and who were found to have nonobstructive coronary artery disease (<40% stenosis), we invasively assessed coronary artery endothelial-dependent microvascular and epicardial function by evaluating changes in coronary blood flow (% Δ CBF Ach) and diameter (% Δ CAD Ach), respectively, in response to intracoronary infusions of acetylcholine. Patients were divided into 2 groups: hypothyroidism, defined as a documented history of hypothyroidism or a thyroid-stimulating hormone (TSH) >10.0 mU/mL, n=188, and euthyroidism, defined as an absence of a history of hypothyroidism in the clinical record and/or 0.3<TSH≤10.0 mU/mL, n=1200. Subjects with a history of hypothyroidism had a significantly lower % Δ CBF Ach (48.26 [80.66] versus 64.58 [128.30]) compared to patients with euthyroidism, while the % Δ CAD Ach did not vary significantly between groups. After adjusting for covariates, females with hypothyroidism still had a significantly lower % Δ CBF Ach (estimated difference in % Δ CBF Ach [SE]: -16.79 [8.18]).

CONCLUSIONS

Hypothyroidism in women is associated with microvascular endothelial dysfunction, even after adjusting for confounders, and may explain some of the increased risk of cardiovascular disease in these patients.

The Impact of Subclinical Hypothyroidism or Thyroid Autoimmunity on Coronary Vasospasm in Patients without Associated Cardiovascular Risk Factors

Background and Objectives

Subclinical hypothyroidism is associated with endothelial dysfunction and impaired coronary flow reserve. However, the effect of subclinical hypothyroidism or thyroid autoimmunity on variant angina has yet to be determined.

Subjects and Methods

Among 385 consecutive patients without associated cardiovascular risk factors who underwent coronary angiography with the ergonovine provocation test (EPT), 165 had a positive EPT {EPT(+)} and 220 had a negative EPT {EPT(-)}. The relationship between coronary artery spasm and the presence of subclinical thyroid dysfunction as well as serum thyroid peroxidase autoantibody (TPO Ab) was evaluated.

Results

The proportion of patients with subclinical hypothyroidism among those who were EPT(+) was significantly higher than that in those who were EPT(-) (18% vs. 11%, p=0.001). However, there was no significant difference in the proportion of patients with subclinical hyperthyroidism between the groups. Moreover, EPT(+) patients showed significantly more positive TPO Ab (33% vs. 14%, p<0.001) than those with EPT(-). There was a positive correlation between EPT(+) and TPO positivity (r=0.226, p<0.001), subclinical hypothyroidism (r=0.112, p=0.033), and body mass index (r=0.123, p=0.018). Binary logistic regression analysis revealed that the significant predictors of EPT(+) were body mass index {adjusted odds ratio (OR)=1.042, 95% confidence interval (CI)=1.005-1.080}, presence of subclinical hypothyroidism (OR=3.047, 95% CI=1.083-8.572), TPO Ab titer (OR=1.028, 95% CI=1.015-1.041), and the presence of TPO Ab (OR=4.904, 95% CI=1.544-15.567).

Conclusion

Subclinical hypothyroidism and the presence of TPO Ab are significantly associated with coronary vasospasm in patients without cardiovascular risk factors.

Thyroid hormone attenuates vascular calcification induced by vitamin D3 plus nicotine in rats

Thyroid hormones (THs) including thyroxine (T4) and triiodothyronine (T3) play critical roles in bone remodeling. However, the role and mechanism of THs in vascular calcification (VC) have been unclear. To explore the pathophysiological roles of T3 on VC, we investigated the changes in plasma and aortas of THs concentrations and the effect of T3 on rat VC induced by vitamin D3 plus nicotine (VDN). VDN-treated rat showed decreased plasma T3 content, increased vascular calcium deposition, and alkaline phosphatase (ALP) activity. Administration of T3 (0.2 mg/kg body weight IP) for 10 days greatly reduced vascular calcium deposition and ALP activity in calcified rat aortas when compared with controls. Concurrently, the loss of smooth muscle lineage markers α-actin and SM22a was restored, and the increased bone-associated molecules, such as runt-related transcription factor2 (Runx2), Osterix, and osteopontin (OPN) levels in calcified aorta, were reduced by administration of T3. The suppression of klotho in calcified rat aorta was restored by T3. Methimazole (400 mg/L) blocked the beneficial effect of T3 on VC. These results suggested that T3 can inhibit VC development.

Association of thyroid-stimulating hormone and cardiovascular risk factors

Thyroid hormone plays an important role in regulating the lipid and glucose metabolism. Previously, much attention has been drawn to define the pathophysiological relationship between thyroid dysfunction and the incidence of cardiovascular diseases (CVDs). While the conditions of overt hypothyroidism and subclinical hypothyroidism were both emphasized, the association between CVD risks and the deregulated circulating thyroid-stimulating hormone (TSH) level remains to be elucidated. Nevertheless, multiple TSH-mediated physiological adaptations, including alteration of the serum lipids, body mass index, blood pressure and insulin sensitivity, have led to the difficulty of clearly examining the association between the TSH level and CVD prevalence. The current review aims to 1) summarize the evidence for the role of thyroid dysfunction and TSH abnormality in CVD pathogenesis and 2) explore the possible underlying molecular mechanisms of TSH-mediated cardiovascular pathology in hopes of providing better therapeutic strategies for the patients with deregulated TSH.

Defending plasma T3 is a biological priority

Triiodothyronine (T3), the active form of thyroid hormone is produced predominantly outside the thyroid parenchyma secondary to peripheral tissue deiodination of thyroxine (T4), with <20% being secreted directly from the thyroid. In healthy individuals, plasma T3 is regulated by the negative feedback loop of the hypothalamus-pituitary-thyroid axis and by homoeostatic changes in deiodinase expression. Therefore, with the exception of a minimal circadian rhythmicity, serum T3 levels are stable over long periods of time. Studies in rodents indicate that different levels of genetic disruption of the feedback mechanism and deiodinase system are met with increase in serum T4 and thyroid-stimulating hormone (TSH) levels, while serum T3 levels remain stable. These findings have focused attention on serum T3 levels in patients with thyroid disease, with important clinical implications affecting therapeutic goals and choice of therapy for patients with hypothyroidism. Although monotherapy with levothyroxine is the standard of care for hypothyroidism, not all patients normalize serum T3 levels with many advocating for combination therapy with levothyroxine and liothyronine. The latter could be relevant for a significant number of patients that remain symptomatic on monotherapy with levothyroxine, despite normalization of serum TSH levels.

A novel mechanism for the inhibition of type 2 iodothyronine deiodinase by tumor necrosis factor α: involvement of proteasomal degradation

Thyroxine (T₄) needs to be converted to 3,5,3'-triiodothyronine (T₃) by iodothyronine deiodinase to exert its biological activity. Recent studies revealed the presence of type 2 iodothyronine deiodinase (D2) in human thyroid tissue, human skeletal muscle and other tissues, suggesting that D2 is involved in maintaining plasma T₃ level in human. Tumor necrosis factor α (TNFα) is an inflammatory cytokine of which production is elevated in patients with nonthyroidal illness. Although several lines of evidence suggest the causal role of TNFα in nonthyroidal illness, detailed nature of the effect of TNFα on D2 remains unclear. In the present study, we identified D2 activity and D2 mRNA in TCO-1 cells, which were derived from human anaplastic thyroid carcinoma, and studied the mechanisms involved in the regulation of D2 expression by TNFα. The characteristics of the deiodinating activity in TCO-1 cells were compatible with those of D2 and Northern analysis demonstrated that D2 mRNA was expressed in TCO-1cells. D2 activity and D2 mRNA expression were rapidly increased by dibutyryl cAMP ((Bu)₂cAMP). TNFα showed an inhibitory effect on (Bu)₂cAMP-stimulated D2 activity in spite of little effect on (Bu)₂cAMP-stimulated D2 mRNA expression. MG132, a proteasome inhibitor abolished TNFα suppression of D2 activity whereas BAY11-7082 or 6-amino-4-(4-phenoxyphenylethylamino) quinazoline, inhibitors of nuclear factor-κB (NF-κB) failed to attenuate the effect of TNFα on D2 activity. These data suggest that a posttranslational mechanism through proteasomal degradation but not NF-κB activation is involved in the suppression of D2 by TNFα.

Emerging role of angiotensin type 2 receptor (AT2R)/Akt/NO pathway in vascular smooth muscle cell in the hyperthyroidism

Hyperthyroidism is characterized by increased vascular relaxation and decreased vascular contraction and is associated with augmented levels of triiodothyronine (T3) that contribute to the diminished systemic vascular resistance found in this condition. T3 leads to augmented NO production via PI3K/Akt signaling pathway, which in turn causes vascular smooth muscle cell (VSMC) relaxation; however, the underlying mechanisms involved remain largely unknown. Evidence from human and animal studies demonstrates that the renin-angiotensin system (RAS) plays a crucial role in vascular function and also mediates some of cardiovascular effects found during hyperthyroidism. Thus, in this study, we hypothesized that type 2 angiotensin II receptor (AT2R), a key component of RAS vasodilatory actions, mediates T3 induced-decreased vascular contraction. Marked induction of AT2R expression was observed in aortas from T3-induced hyperthyroid rats (Hyper). These vessels showed decreased protein levels of the contractile apparatus: α-actin, calponin and phosphorylated myosin light chain (p-MLC). Vascular reactivity studies showed that denuded aortic rings from Hyper rats exhibited decreased maximal contractile response to angiotensin II (AngII), which was attenuated in aortic rings pre-incubated with an AT2R blocker. Further study showed that cultured VSMC stimulated with T3 (0.1 µmol/L) for 24 hours had increased AT2R gene and protein expression. Augmented NO levels and decreased p-MLC levels were found in VSMC stimulated with T3, both of which were reversed by a PI3K/Akt inhibitor and AT2R blocker. These findings indicate for the first time that the AT2R/Akt/NO pathway contributes to decreased contractile responses in rat aorta, promoted by T3, and this mechanism is independent from the endothelium.

Thyroid hormone and cardiovascular system: from basic concepts to clinical application

Experimental and clinical findings strongly support the concept that thyroid hormone (TH) plays a fundamental role in the cardiovascular (CV) homeostasis. CV diseases represent a major public health care and economic problem being one of the principal causes of morbidity, mortality and hospitalization. In particular, chronic heart failure (HF) is one of the most common reasons for general practitioners consultations in people >65-70 years old. TH derangement may have a key role in the evolution process of HF. In HF, the main and earlier alteration of the thyroid function is referred to as "low-T3" syndrome characterized by the reduction in serum total T3 and free T3 with normal levels of thyroxine (T4) and thyrotropin (TSH). This syndrome may affect till one-third of advanced HF patients. The main goal of this mini-review is to examine the main pathophysiological and clinical links between an altered thyroid metabolism and CV diseases, namely HF during progression of disease from organ specific to systemic disorder.

Noninvasive indicators of atherosclerosis in subclinical hypothyroidism

INTRODUCTION

Cardiovascular system is rich in thyroid hormone receptors and is one of the major sites of action for thyroid hormones. However, the effect of subclinical hypothyroidism (SCH) on atherosclerosis has not been cleared yet.

MATERIALS AND METHODS

SCH is defined as high thyroid-stimulating hormone (TSH) levels in the presence of normal serum T4 and T3 levels. A total of 32 patients with SCH and 29 controls were included in the study. Carotid intima-media thickness, flow-mediated dilatation, and aortic distensibility were compared between the groups.

RESULTS

FMD was lower in patients with SCH than in controls. GTN-induced vasodilatation was similar in the patients with SCH and controls. There was no statistically significant difference between the patients with SCH and controls with respect to CIMT and aortic distensibility.

CONCLUSION

SCH is associated with endothelial dysfunction as established by FMD. Inconsistent results of CIMT and aortic stiffness can be explained by these parameters being measures of structural changes whereas FMD is a dynamic measure that reflects the impact of both acute and chronic influences on endothelial function.

The contribution of thyroid dysfunction on cardiovascular disease in patients with chronic kidney disease

Accelerated atherosclerosis and arterial stiffness are the two leading causes of increased cardiovascular disease in patients with chronic kidney disease. Dysfunctional thyroid hormone metabolism has been suggested to play a role in atherosclerosis and arterial stiffness. Changes in cardiac contractility and output, myocardial oxygen demand, systemic and peripheral vascular resistance, blood pressure and lipid profile, increased inflammatory burden and endothelial dysfunction may be responsible for thyroid hormone-related cardiovascular disease. This article focuses on the mechanistic insights of this association and provides a concise review of the current literature.

Statins and downstream inhibitors of the isoprenylation pathway increase type 2 iodothyronine deiodinase activity

The type 2 iodothyronine selenodeiodinase (D2) is a critical determinant of local thyroid signaling, converting T(4) to the active form T(3) at the cytoplasmic face of the endoplasmic reticulum, thus supplying the nucleus with T(3) without immediately affecting circulating thyroid hormone levels. Although inhibitors of the cholesterol synthesis/isoprenylation pathway, such as hydroxy-methyl-glutaryl-coenzyme A reductase inhibitors (statins) have been to shown to down-regulate selenoproteins via interruption of normal selenocysteine incorporation, little is known about the effect of statins on D2. Here, we report that statins and prenyl transferase inhibitors actually increase D2 activity in cells with endogenous D2 expression. Although we confirmed that lovastatin (LVS) decreases the activity of transiently expressed D2 in HEK-293 cells, the prenyl transferase inhibitors increase activity in this system as well. LVS treatment increases endogenous Dio2 mRNA in MSTO-211H cells but does not alter transiently expressed Dio2 mRNA in HEK-293 cells. The prenyl transferase inhibitors do not increase Dio2 mRNA in either system, indicating that a posttranscriptional mechanism must exist. Cotreatment with LVS or the prenyl transferase inhibitors with the proteasome inhibitor MG-132 did not lead to additive increases in D2 activity, indirectly implicating the ubiquitin-proteasomal system in the mechanism. Finally, C57BL/6J mice treated with LVS or farnesyl transferase inhibitor-277 for 24 h exhibited increased D2 activity in their brown adipose tissue. These data indicate that statins and downstream inhibitors of the isoprenylation pathway may increase thyroid signaling via stimulation of D2 activity.

Thyroid hormone receptor-α and vascular function

Thyroid hormone (TH) treatment exerts beneficial effects on the cardiovascular system: it lowers cholesterol and LDL levels and enhances cardiac contractile function. However, little is known about the effect of TH on vascular function or the functional role of TH receptors (TRs) in the regulation of vascular tone. We have investigated the contribution of TRs to vascular contractility in the heart. Among different TR subtype-specific knockout (KO) mice, vascular contraction was significantly enhanced in coronary arteries isolated from TRα KO compared with wild-type mice, while chronic TH treatment significantly attenuated coronary vascular contraction. We found that TRα is the predominant TR in mouse coronary smooth muscle cells (SMCs). Coronary SMCs isolated from TRα KO mice exhibited a significant decrease in K(+) channel activity, whereas TH treatment increased K(+) channel activity in a dose-dependent manner. These data suggest that TRα in SMCs has prominent effects on regulation of vascular tone and TH treatment helps decrease coronary vascular tone by increasing K(+) channel activity through TRα in SMCs.

Endothelial dysfunction and subclinical hypothyroidism: a brief review

Subclinical hypothyroidism (SH) is characterized by normal serum free T4 and free T3 levels and increased serum TSH levels. The relationship between SH and cardiovascular diseases has been one of the most popular topics recently. There is still some controversy concerning the cardiovascular impact of SH and management protocols. The vast majority of the studies published so far, suggests that SH accelerates endothelial dysfunction through traditional effects on risk factors that promote atherosclerosis and nontraditional effects on vasculature. In particular, SH is associated with increased of LDL-cholesterol, diastolic blood pressure, and markers of chronic inflammation (C reactive protein) and simultaneously reduces the bioavailability of nitric oxide to blood vessels and increases the expression of angiotensin receptor. Furthermore, replacement therapy seems to improve all these aspects.

Thyroid hormone and cardiac disease: from basic concepts to clinical application

Nature's models of regeneration provide substantial evidence that a natural healing process may exist in the heart. Analogies existing between the damaged myocardium and the developing heart strongly indicate that regulatory factors which drive embryonic heart development may also control aspects of heart regeneration. In this context, thyroid hormone (TH) which is critical in heart maturation during development appears to have a reparative role in adult life. Thus, changes in TH -thyroid hormone receptor (TR) homeostasis are shown to govern the return of the damaged myocardium to the fetal phenotype. Accordingly, thyroid hormone treatment preferentially rebuilds the injured myocardium by reactivating developmental gene programming. Clinical data provide further support to this experimental evidence and changes in TH levels and in particular a reduction of biologically active triiodothyronine (T3) in plasma after myocardial infarction or during evolution of heart failure, are strongly correlated with patients morbidity and mortality. The potential of TH to regenerate a diseased heart has now been testing in patients with acute myocardial infarction in a phase II, randomized, double blind, placebo-controlled study (the THiRST study).

Hyperthyrotropinemia in relation to endothelial dysfunction in obese adolescents

SUMMARY

BACKGROUND

It has been shown that isolated elevation of thyroid stimulating hormone (hyperthyrotropinemia) is quite frequent in obese adolescents, but it is not clear whether this condition entails an increased risk related to body mass index (BMI).

AIM

The aim of the current study was to investigate the relationship between hyperthyrotropinemia and endothelial dysfunction and other cardiovascular risk factors in obese adolescents.

METHODS

Seventeen obese adolescents with hyperthyrotropinemia (TSH ≥ 4.2 μUI/ml) (group 1), 21 obese adolescents with normal thyroid stimulating hormone (TSH) level (group 2) and 10 age- and sex-matched healthy lean controls were included in the study. Fasting blood glucose (FBG), lipid profile, insulin resistance (HOMA-IR) and thyroid hormones were determined. All participants were subjected to ultrasound recording of brachial artery diameter at rest and after reactive hyperemia (FMD) for assessment of endothelial function.

RESULTS

BMI and free triiodothyronine (fT3) levels were higher in obese adolescents with hyperthyrotropinemia (group 1) than in those with normal TSH (group 2) (p < 0.05), but there were no significant differences between the two groups in other metabolic parameters (lipid profile and HOMA-IR). The FMD was significantly low in obese adolescents (groups 1 and 2) relative to controls (3.4 ± 18% in group 1 and 3.6 ± 2.2% in group 2 vs. 10.4 ± 3.1% in control subjects), but there was no statistical difference between obese adolescents with hyperthyrotropinemia (group 1) and those with normal TSH (group 2). There were positive correlations between TSH and BMI (p = 0.03) and between fT3 and BMI (p = 0.04), but no correlation between TSH and lipid profile, HOMA-IR or FMD.

CONCLUSIONS

Hyperthyrotropinemia is not related to endothelial dysfunction or metabolic risk factors in obese adolescents.

Hypothyroidism and hypertension

Hypothyroidism has been recognized as a cause of secondary hypertension. Previous studies on the prevalence of hypertension in subjects with hypothyroidism have demonstrated elevated blood pressure values. Increased peripheral vascular resistance and low cardiac output has been suggested to be the possible link between hypothyroidism and diastolic hypertension. The hypothyroid population is characterized by significant volume changes, initiating a volume-dependent, low plasma renin activity mechanism of blood pressure elevation. This article summarizes previous studies on the impact of hypothyroidism on blood pressure and early atherosclerotic process.

Type 2 iodothyronine deiodinase is expressed in human preadipocytes

BACKGROUND

Type 2 iodothyronine deiodinase (D2) is an enzyme that catalyzes the production of triiodothyronine (T3) from thyroxine (T4) and plays a critical role in providing the local intracellular T3. Although D2 is highly expressed in brown adipose tissue, it was thought that D2 is hardly expressed in white adipose tissue. In the present study, we examined whether D2 is expressed in human preadipocytes, using human mesenteric and subcutaneous preadipocytes (HMPA and HSCPA, respectively).

METHODS

HMPA and HSCPA were purchased and cultured in the preadipocyte medium containing 10% fetal bovine serum. We measured D2 activity and mRNA level in HMPA and HSCPA incubated with or without dibutyryl cyclic adenosine monophosphate [(Bu)₂cAMP].

RESULTS

D2 activity and mRNA were detectable in human HMPA and HSCPA. The apparent Michaelis-Menten constant (K(m)) value for T4 in HMPA was 2.1 ± 0.2 nM, and the maximum velocity (V(max)) value was 333.3 ± 28.0 femtomols of I⁻ released/mg protein/hour, respectively. On the other hand, the apparent K(m) value for T4 in HSCPA was 2.0 ± 0.2 nM and the V(max) value was 91.2 ± 8.7 femtomols of I⁻ released/mg protein/hour, respectively. D2 activities in HMPA and HSCPA incubated with 1 mM (Bu)₂cAMP for 24 hours were 7-fold (HMPA) and 3-fold (HSCPA) higher than those without (Bu)₂cAMP, respectively. D2 mRNA levels in HMPA and HSCPA incubated with 1 mM (Bu)₂cAMP for 3 hours were 10-fold (HMPA) and 5-fold (HSCPA) higher than those without (Bu)₂cAMP, respectively.

CONCLUSIONS

In the present study, we have clearly demonstrated that D2 activity and mRNA are present in the human preadipocytes from both mesenteric and subcutaneous adipose tissue. Our experiments are the first ones that identify human preadipocytes as one of the sources of T3 production.

[Thyroid diseases and hypertension]

Thyroid hormones have several well-recognized effects on the vasculature and heart, resulting in characteristic cardiovascular changes in thyroid disease, including an increase in blood pressure. In hyperthyroidism reduced systemic vascular resistance and increased blood volume lead to an enhanced preload, which, in association with reduced afterload, improved contractility, as well as increased beta-adrenergic activity, results in isolated systolic hypertension based on enhanced stroke volume and cardiac output. In contrast, hypothyroidism causes increased systemic vascular resistance in association with decreased arterial compliance resulting in elevated diastolic blood pressure. Therefore in the evaluation of arterial hypertension secondary hypertension based on thyroid disease should always be considered, especially given the fact that blood pressure changes in the course of thyroid dysfunction are usually reversible upon adequate treatment of hypo- or hyperthyroidism.

Assessment of low-density lipoprotein oxidation, paraoxonase activity, and arterial distensibility in epileptic children who were treated with anti-epileptic drugs

OBJECTIVE

Studies show that anti-epileptic drugs increase oxidative stress. Thus, low-density lipoprotein oxidation increases and atherogenesis is induced. Paraoxonase-associated high-density lipoprotein protects low-density lipoprotein and high-density lipoprotein oxidation. The effects of anti-epileptic drugs on paraoxonase activity has not been investigated yet. The aim of this study is to investigate the effect of anti-epileptic drugs on paraoxonase activity, lipid profiles, folat, vitamin B12, homocysteine, thyroid hormones, apolipoprotein A-1, total anti-oxidant capacity, malondialdehyd, nitric oxide, and oxidised low-density lipoprotein. The association with carotid-femoral pulse wave velocity and current biochemical parameters had been searched for assessing the effects of anti-epileptic drugs on the vascular system.

PATIENTS AND METHODS

We recruited 59 epileptic patients treated with anti-epileptic drugs and 23 controls (group IV) at least 6 months ago. The epileptic group was divided into three groups by receiving anti-epileptic drugs as follows: group I: carbamazepine, group II: valproic acid, and group III: carbamazepine and valproic acid. Arterial distensibility was assessed with the Complior device.

RESULTS

There was no difference between the current biochemical parameters in epileptic children. Serum-free T4 was decreased, when compared with group IV. Thyroid-stimulating hormone was increased in group II, compared with group IV. The carotid-femoral pulse wave velocity was increased in group III, compared with group IV. The carotid-femoral pulse wave velocity was correlated with thyroid-stimulating hormone and valproic acid levels.

CONCLUSIONS

Anti-epileptic drugs may induce atherogenesis by affecting the thyroid hormones. According to the current data, the effects of thyroid hormones on vascular system may be independent of other biochemical markers. Epileptic patients using anti-epileptic drugs must be followed closely for arterial stiffness, and also for the development and progression of atherosclerosis.

Ontogenetic profile of the expression of thyroid hormone receptors in rat and human corpora cavernosa of the penis

Introduction

In the last few years, various studies have underlined a correlation between thyroid function and male sexual function, hypothesizing a direct action of thyroid hormones on the penis.

Aim

To study the spatiotemporal distribution of mRNA for the thyroid hormone nuclear receptors (TR) α1, α2 and β in the penis and smooth muscle cells (SMCs) of the corpora cavernosa of rats and humans during development.

Methods

We used several molecular biology techniques to study the TR expression in whole tissues or primary cultures from human and rodent penile tissues of different ages.

Main Outcome Measure

We measured our data by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) amplification, Northern blot and immunohistochemistry.

Results

We found that TRα1 and TRα2 are both expressed in the penis and in SMCs during ontogenesis without development-dependent changes. However, in the rodent model, TRβ shows an increase from 3 to 6 days post natum (dpn) to 20 dpn, remaining high in adulthood. The same expression profile was observed in humans. While the expression of TRβ is strictly regulated by development, TRα1 is the principal isoform present in corpora cavernosa, suggesting its importance in SMC function. These results have been confirmed by immunohistochemistry localization in SMCs and endothelial cells of the corpora cavernosa.

Conclusions

The presence of TRs in the penis provides the biological basis for the direct action of thyroid hormones on this organ. Given this evidence, physicians would be advised to investigate sexual function in men with thyroid disorders. Carosa E, Di Sante S, Rossi S, Castri A, D'Adamo F, Gravina GL, Ronchi P, Kostrouch Z, Dolci S, Lenzi A, and Jannini EA. Ontogenetic profile of the expression of thyroid hormone receptors in rat and human corpora cavernosa of the penis. J Sex Med 2010;7:1381–1390.

Thyroid hormone stimulates NO production via activation of the PI3K/Akt pathway in vascular myocytes

AIMS

Thyroid hormone (TH) rapidly relaxes vascular smooth muscle cells (VSMCs). However, the mechanisms involved in this effect remain unclear. We hypothesize that TH-induced rapid vascular relaxation is mediated by VSMC-derived nitric oxide (NO) production and is associated with the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signalling pathway.

METHODS AND RESULTS

NO levels were determined using a NO-specific fluorescent dye (DAF-2) and nitrite (NO2-) levels. Expression of NO synthase (NOS) isoforms and proteins of the PI3K/Akt pathway was determined by both western blotting and immunocytochemistry. Myosin light chain (MLC) phosphorylation levels were also investigated by western blotting. Exposure of cultured VSMCs from rat thoracic aortas to triiodothyronine (T3) resulted in a significant decrease of MLC phosphorylation levels. T3 also induced a rapid increase in Akt phosphorylation and increased NO production in a dose-dependent manner (0.001-1 microM). VSMCs stimulated with T3 for 30 min showed an increase in the expression of all three NOS isoforms and augmented NO production, effects that were prevented by inhibitors of PI3K. Vascular reactivity studies showed that vessels treated with T3 displayed a decreased response to phenylephrine, which was reversed by NOS inhibition. These data suggest that T3 treatment induces greater generation of NO both in aorta and VSMCs and that this phenomenon is endothelium independent. In addition, these findings show for the first time that the PI3K/Akt signalling pathway is involved in T3-induced NO production by VSMCs, which occurs with expressive participation of inducible and neuronal NOS.

CONCLUSION

Our data strongly indicate that T3 causes NO-dependent rapid relaxation of VSMC and that this effect is mediated by the PI3K/Akt signalling pathway.

Impact of thyroid function and polymorphisms in the type 2 deiodinase on blood pressure: the Rotterdam Study and the Rotterdam Scan Study

INTRODUCTION

Thyroid function and genetic variation in the hypothalamus-pituitary-thyroid axis have been implicated in blood pressure regulation and susceptibility to hypertension. However studies conducted thus far were small with controversial results.

OBJECTIVE

To examine whether serum thyroid parameters and polymorphisms in the type 2 deiodinase and the TSH receptor are associated with blood pressure and the presence of hypertension in two large cohorts of elderly subjects.

DESIGN AND PARTICIPANTS

We studied a random sample of 1444 subjects of the Rotterdam study, and 997 subjects of the Rotterdam Scan study, two population-based cohort studies among elderly individuals aged 55-90 years. Outcome measurements Data on blood pressure and hypertension were obtained, and serum thyroid parameters, D2-Thr92Ala, D2-ORFa-Gly3Asp and TSHR-Asp727Glu polymorphisms were determined.

RESULTS

In contrast to previous findings, no consistent and/or significant associations were found between serum TSH and FT4 and blood pressure in both cohorts. In addition, the D2-Thr92Ala, D2-ORFa-Gly3Asp and TSHR-Asp727Glu polymorphisms were not associated with blood pressure or the risk of hypertension.

CONCLUSIONS

In two large populations of elderly subjects, neither serum thyroid parameters nor polymorphisms in the type 2 deiodinase and the TSH receptor, were associated with blood pressure or the presence of hypertension. Our data suggest that thyroid function is not an important determinant of hypertension in elderly Dutch subjects.

Thyroid hormone activation in vascular smooth muscle cells is negatively regulated by glucocorticoid

BACKGROUND

Type 2 iodothyronine deiodinase (D2) catalyzes the production of triiodothyronine from thyroxine. D2 is present in rat aorta media, and there is a circadian variation in the D2 expression. In rat aorta media, the D2 activity exhibited the maximal value at 1200 hour and low value between 1800 and 2400 hour. To understand the mechanisms that induce the circadian variation in the D2 expression, we examined the effects of glucocorticoid on the D2 activity and mRNA in rat aorta media and cultured vascular smooth muscle cells (VSMCs).

METHODS

The effects of intrinsic and extrinsic glucocorticoid on the D2 activity and mRNA in rat aorta media were studied using metyrapone, a corticosterone synthesis inhibitor, and dexamethasone (DEX). Further, the effects of DEX on D2 expression were studied using the cultured rat VSMCs.

RESULTS

The trough values of D2 activity and mRNA at 2100 hour were increased by the treatment with metyrapone. On the other hand, the peak values of D2 activity and mRNA were decreased by the treatment with DEX. D2 activity and mRNA in cultured rat VSMCs were increased by the addition of 10(-3) M dibutyryl cyclic adenosine monophosphate [(Bu)(2)cAMP]. The increments were reduced by coincubation with 10(-6) M DEX.

CONCLUSIONS

These results suggest that glucocorticoids might directly suppress the D2 expression in rat VSMCs induced by a cAMP-dependent mechanism.