The thyroid gland and the process of aging; what is new?

Triiodothyronine enhances various forms of kidney-specific Klotho protein and suppresses the Wnt/β-catenin pathway: Insights from in-vitro, in-vivo and in-silico investigations

Age-related diseases are intricately linked to the molecular processes underlying aging, with the decline of the antiaging protein Klotho being a key factor. Investigating these processes is crucial for developing therapeutic strategies. The age-associated reduction in Klotho expression, coupled with a decline in the endocrine hormone triiodothyronine (T3), prompted a detailed exploration of their potential interplay. Our research, conducted through both in-vitro and in-vivo studies on BALB/c mice, unveiled a significant capacity of T3 to upregulate various forms of Klotho via ATF-3/p-c-Jun transcription factor. This effect was particularly noteworthy in aged individuals, where Klotho expression had waned compared to their younger counterparts. Importantly, T3 demonstrated a promising therapeutic impact in rejuvenating Klotho expression in this context. Further investigations elucidated the molecular mechanisms underlying T3's impact on aging-related pathways. In-vitro and in-vivo experiments established T3's ability to downregulate the Wnt/β-Catenin pathway by enhancing Klotho expression. In-silico analyses provided insights into Klotho's intricate role, showing its capacity to inhibit Wnt ligands such as Wnt3 and Wnt8a, consequently disrupting their interaction with the Wnt receptor. Additionally, T3 was found to downregulate kidney-specific GSK-3β expression through the augmentation of Klotho expression. The study also highlighted T3's role in maintaining calcium and phosphate homeostasis via Klotho. This comprehensive investigation not only sheds light on the intricate mechanisms governing aging processes but also presents promising avenues for therapeutic interventions targeting the Wnt/β-Catenin pathway implicated in various age-associated diseases.

Associations between Differential Aging and Lifestyle, Environment, Current, and Future Health Conditions: Findings from Canadian Longitudinal Study on Aging

INTRODUCTION

An aging population will bring a pressing challenge for the healthcare system. Insights into promoting healthy longevity can be gained by quantifying the biological aging process and understanding the roles of modifiable lifestyle and environmental factors, and chronic disease conditions.

METHODS

We developed a biological age (BioAge) index by applying multiple state-of-art machine learning models based on easily accessible blood test data from the Canadian Longitudinal Study of Aging (CLSA). The BioAge gap, which is the difference between BioAge index and chronological age, was used to quantify the differential aging, i.e., the difference between biological and chronological age, of the CLSA participants. We further investigated the associations between the BioAge gap and lifestyle, environmental factors, and current and future health conditions.

RESULTS

BioAge gap had strong associations with existing adverse health conditions (e.g., cancers, cardiovascular diseases, diabetes, and kidney diseases) and future disease onset (e.g., Parkinson's disease, diabetes, and kidney diseases). We identified that frequent consumption of processed meat, pork, beef, and chicken, poor outcomes in nutritional risk screening, cigarette smoking, exposure to passive smoking are associated with positive BioAge gap ("older" BioAge than expected). We also identified several modifiable factors, including eating fruits, legumes, vegetables, related to negative BioAge gap ("younger" BioAge than expected).

CONCLUSIONS

Our study shows that a BioAge index based on easily accessible blood tests has the potential to quantify the differential biological aging process that can be associated with current and future adverse health events. The identified risk and protective factors for differential aging indicated by BioAge gap are informative for future research and guidelines to promote healthy longevity.

Identification of crucial genes involved in thyroid cancer development

BACKGROUND

A malignancy of the endocrine system, one of the most common types, is thyroid cancer. It is proven that children who receive radiation treatment for leukemia or lymphoma are at a heightened risk of thyroid cancer due to low-dose radiation exposure throughout childhood. Several factors can increase the risk of thyroid cancer (ThyCa), such as chromosomal and genetic mutations, iodine intake, TSH levels, autoimmune thyroid disorders, estrogen, obesity, lifestyle changes, and environmental contaminants.

OBJECTIVES

The study aimed to identify a specific gene as an essential candidate for thyroid cancer progression. We might be able to focus on developing a better understanding of how thyroid cancer is inherited.

METHODS

The review article uses electronic databases such as PubMed, Google Scholar, Ovid MEDLINE, Embase, and Cochrane Central. The most frequently associated genes with thyroid cancer found on PubMed were BAX, XRCC1, XRCC3, XPO5, IL-10, BRAF, RET, and K-RAS. To perform an electronic literature search, genes derived from DisGeNET: a database of gene-disease associations, including PRKAR1A, BRAF, RET, NRAS, and KRAS, are used.

CONCLUSION

Examining the genetics of thyroid cancer explicitly emphasizes the primary genes associated with the pathophysiology of young and older people with thyroid cancer. Developing such gene investigations at the beginning of the thyroid cancer development process can identify better outcomes and the most aggressive thyroid cancers.

The Etiology of Abnormal TSH in Veterans Cared by a VA Medical Center - One High Serum Thyrotropin is Associated with Higher 5-Years Mortality

Objective

By analyzing the etiology of abnormal TSH in randomly selected veteran patients, we set our heart on improving future clinical care/management of the clinical/subclinical hyper- and hypothyroidism in the aging veteran population.

Methods

A total of 1100 patients' charts in alphabetical order were selected. Excluded cases of insufficient information, 897 patients' charts were reviewed and analyzed for causes of abnormal TSH. Among them, 602 for the cause of low TSH (below 0.55 uU/mL) and 295 for high TSH (above 4.78 uU/mL) were reviewed retrospectively.

Findings

Among the 1100 patients selected, 680 (61.8%) were 60 y or older (female=44, 6.8%); 420 were under 60 y (female=80, 19.0%); significantly more female patients were found in the younger age group (P<0.001). After excluding patients with insufficient data, the most common cause of suppressed TSH is iodine-induced, CT iodinated contrast and betadine use caused 35.0% in the older group (n=126) compared to 23.6% in the younger group(n=57) (P = 0.027). The significant difference is that older veterans received more contrast CTs (P < 0.05 compared to the younger group). In both age groups with concurrent FT4 study, we found four high FT4 among 90 studies, 4.4% overt hyperthyroidism. The second most common cause of suppressed TSH is due to thyroid hormone (TH) replacement in the older group (119 patients, 33.1%) with age > 60y, significantly more frequent compared to the younger group, P<0.001. There is significantly more overt hyperthyroidism, 27.8/%, than the iodine-load induced suppression of TSH, P<0.001, due to 17 patients on TSH suppression therapy after total thyroidectomy for thyroid cancer. Among the 295 patients with elevated TSH, the most common cause of high TSH was due to hypothyroidism on T4 replacement: a total of 128 (59.3%) in the older group (N=216) is, similar to 47 (59.5%) in the younger group (N=79). In both age groups, there were 139 patients with concomitant FT4 measurement; 17 overt hypothyroidism were found, 12.2%. No significant difference is seen in the two age groups. The next most common causes of elevated TSH are CT contrast infusion, 23 (10.6%) in the older group and 7 (8.9%) in the younger group. We find high TSH is associated with a higher death rate of 101/238 (42.4%) in a 5-year follow-up (from 2016 to 2021), as compared to low TSH of 68/238 (28.6%), in the older age group, p<0.03； both were significantly higher than the age- and sex-matched general US population, 19.7%, P<0.01.

Conclusion

Even though most, ~ 90%, were subclinical, the suppressed and elevated TSH are associated with severe consequences in CV/CNS and immune-suppression complications in aging veterans. Therefore, cautious use (and more frequent check of TSH) of TH replacement and CT contrast in aging veterans is recommended. The alarming increase in 5 years death rate in older patients with elevated TSH deserves further study.

[Regional Differences in Thyroid Function Parameters: A Comparison of European Cohort Studies]

AIM OF THE STUDY

The aim of the project was to investigate regional differences in thyroid stimulating hormone (TSH), and free thyroxine (fT4) concentrations and iodine status in comparable German and European cohort studies.

METHODS

Sex- and age-stratified TSH, fT4, and urine iodine concentrations of thyroid-healthy participants (age group 45-75 years) of the HNR (Heinz Nixdorf Recall) Study in the Ruhr region of Germany, the southern German KORA (Cooperative Health Research in the Augsburg Region) and northeastern German SHIP (Study of Health in Pomerania) studies, as well as the Norwegian HUNT (Nord-Trøndelag Health) study (age group 40-79 years), the English EPIC (European Prospective Investigation of Cancer)-Norfolk study, and the Dutch Rotterdam study were compared. The TSH reference range for the HNR study population was calculated and compared to the KORA and SHIP studies.

RESULTS

Regional differences showed a stronger influence on TSH and fT4 concentrations than sex and age of the subjects in the 45- to 75-year age group. The estimated difference in medians, as measured by the HNR study, was lowest in the SHIP study, -0.47 (95% CI: -0.53; -0.41) for men and -0.41 (-0.53; -0.41) for women. The Rotterdam study had the highest difference in medians for both men and women (men: 0.56 with 0.44; 0.68 and women: 0.62 with 0.46; 0.78). The lowest median TSH concentrations, across all age categories considered, were seen in the German cohorts.

CONCLUSIONS

Comparison of thyroid function parameters and iodine in elderly subjects between six comparable cohort studies from Germany and Europe showed a significant influence of region, which exceeded the sex and age dependence of the parameters.

Single Cell Analysis of Human Thyroid Reveals the Transcriptional Signatures of Aging

The thyroid gland plays a critical role in the maintenance of whole-body metabolism. However, aging frequently impairs homeostatic maintenance by thyroid hormones due to increased prevalence of subclinical hypothyroidism associated with mitochondrial dysfunction, inflammation, and fibrosis. To understand the specific aging-related changes of endocrine function in thyroid epithelial cells, we performed single-cell RNA sequencing (RNA-seq) of 54 726 cells derived from pathologically normal thyroid tissues from 7 patients who underwent thyroidectomy. Thyroid endocrine epithelial cells were clustered into 5 distinct subpopulations, and a subset of cells was found to be particularly vulnerable with aging, showing functional deterioration associated with the expression of metallothionein (MT) and major histocompatibility complex class II genes. We further validated that increased expression of MT family genes are highly correlated with thyroid gland aging in bulk RNAseq datasets. This study provides evidence that aging induces specific transcriptomic changes across multiple cell populations in the human thyroid gland.

The landscape of expression and alternative splicing variation across human traits

Understanding the consequences of individual transcriptome variation is fundamental to deciphering human biology and disease. We implement a statistical framework to quantify the contributions of 21 individual traits as drivers of gene expression and alternative splicing variation across 46 human tissues and 781 individuals from the Genotype-Tissue Expression project. We demonstrate that ancestry, sex, age, and BMI make additive and tissue-specific contributions to expression variability, whereas interactions are rare. Variation in splicing is dominated by ancestry and is under genetic control in most tissues, with ribosomal proteins showing a strong enrichment of tissue-shared splicing events. Our analyses reveal a systemic contribution of types 1 and 2 diabetes to tissue transcriptome variation with the strongest signal in the nerve, where histopathology image analysis identifies novel genes related to diabetic neuropathy. Our multi-tissue and multi-trait approach provides an extensive characterization of the main drivers of human transcriptome variation in health and disease.

Exploring the Importance of Corticalization Occurring in Alveolar Bone Surrounding a Dental Implant

Several measures describing the transformation of trabecular bone to cortical bone on the basis of analysis of intraoral radiographs are known (including bone index or corticalization index, CI). At the same time, it has been noted that after functional loading of dental implants such transformations occur in the bone directly adjacent to the fixture. Intuitively, it seems that this is a process conducive to the long-term maintenance of dental implants and certainly necessary when immediate loading is applied. The authors examined the relationship of implant design features to marginal bone loss (MBL) and the intensity of corticalization over a 10-year period of functional loading. This study is a general description of the phenomenon of peri-implant bone corticalization and an attempt to interpret this phenomenon to achieve success of implant treatment in the long term. Corticalization significantly increased over the first 5-year functional loading (CI from 200 ± 146 initially to 282 ± 182, p < 0.001) and maintained a high level (CI = 261 ± 168) in the 10-year study relative to the reference bone (149 ± 178). MBL significantly increased throughout the follow-up period—5 years: 0.83 ± 1.26 mm (p < 0.001), 10 years: 1.48 ± 2.01 mm (p < 0.001). MBL and radiographic bone structure (CI) were evaluated in relation to intraosseous implant design features and prosthetic work performed. In the scope of the study, it can be concluded that the phenomenon of peri-implant jawbone corticalization seems an unfavorable condition for the future fate of bone-anchored implants, but it requires further research to fully explain the significance of this phenomenon.

Thyroid Dysfunction: An Alternate Plausibility in Perimenopausal Women!

Introduction

Perimenopause phase of a woman's life is featured by decline in the ovarian activity, predisposing her to several health consequences. The signs and symptoms of thyroid disorders simulate those of menopausal features which may go unnoticed and can cause untoward complications in these women.

Aims and Objective

The primary objective is to screen women of perimenopausal age for thyroid disorders. The secondary objective is to examine the variations in thyroid hormone levels in these women with advancing age.

Materials and Methods

One hundred and forty-eight apparently healthy women between the age group of 46 and 55 years were study subjects. They were divided into, Group I which constituted women between 46 and 50 years and Group II consisted of women between 51 and 55 years. Thyroid profile comprising serum thyroid-stimulating hormone (TSH), serum total triiodothyronine (T3), and serum total thyroxine (T4) were estimated for all the women recruited in the study.

Results

Subclinical hypothyroidism (SCH) and overt hypothyroidism (OH) were detected in 22 and 8 women who constituted 14.9% and 5.4%, respectively, of the total women populace. In Group I, it was noted that 17.1% and 1.8% of women were suffering from SCH and OH, respectively. In Group II, while 8.1% of the women had SCH, 16.2% of women had progressed to OH. TSH levels were significantly higher (P = 0.002) in women of Group II than in Group I, suggesting increase in TSH levels with advancing age.

Conclusion

Screening of perimenopausal women for thyroid disorders will assure timely detection and proper management which will aid in reducing the morbidity and associated complications.

The Less We Eat, the Longer We Live: Can Caloric Restriction Help Us Become Centenarians?

Striving for longevity is neither a recent human desire nor a novel scientific field. The first article on this topic was published in 1838, when the average human life expectancy was approximately 40 years. Although nowadays people on average live almost as twice as long, we still (and perhaps more than ever) look for new ways to extend our lifespan. During this seemingly endless journey of discovering efficient methods to prolong life, humans were enthusiastic regarding several approaches, one of which is caloric restriction (CR). Where does CR, initially considered universally beneficial for extending both lifespan and health span, stand today? Does a lifelong decrease in food consumption represent one of the secrets of centenarians’ long and healthy life? Do we still believe that if we eat less, we will live longer? This review aims to summarize the current literature on CR as a potential life-prolonging intervention in humans and discusses metabolic pathways that underlie this effect.

Association of thyroid function with insulin resistance: data from two population-based studies

OBJECTIVE

Thyroid dysfunction is associated with relevant disturbances in glucose metabolism. Moreover, thyroid function undergoes important changes with ageing. The objective of this study was to investigate the association of thyroid function with insulin resistance with particular consideration of possible age-related effect modifications.

DESIGN

A sample of 4193 participants from two independent epidemiological studies, the Study of Health in Pomerania-TREND-0 and the Berlin Aging Study II, was included in this cross-sectional analysis.

METHODS

Insulin resistance was estimated by homeostasis model of insulin resistance (HOMA-IR) and the insulin sensitivity index (ISI). Associations of thyroid biomarkers (thyroid-stimulating hormone, free thyroxine, and free triiodothyronine (fT3)) with parameters of glucose metabolism were analysed by regression models adjusted for age, sex, smoking status, and study site.

RESULTS

A higher fT3 was significantly associated with higher fasting glucose and higher fasting and 2-h postload insulin levels, a higher HOMA-IR, and lower ISI. A higher fT3 was also associated with a higher risk for impaired fasting glucose (RR 1.09, 95 CI 1.02; 1.18; P = 0.017). Many of these associations between thyroid markers and parameters of glucose metabolism were significant in young and middle-aged participants but not in older individuals.

CONCLUSIONS

The main finding of this study was a consistent association of fT3 with almost all markers of insulin resistance. However, this effect seems to be wearing off in higher age highlighting a potential age-related modification of the interaction between thyroid function and glucose metabolism. Further studies are needed to clarify causal relationships.

Effect of Subclinical Hypothyroidism on the Association between Hemoglobin A1c and Reduced Renal Function: A Prospective Study

Subclinical hypothyroidism (SCH) was reported to be associated with accelerating endothelial dysfunction, which is recognized as one of the upstream mechanisms that leads to glomerular injury (lower glomerular filtration rate (GFR)). SCH was also reported to be associated with hyperglycemia, which is associated with higher hemoglobin A1c (HbA1c) levels and induces endothelial dysfunction. Therefore, SCH status could influence the association between HbA1c and reduced eGFR. To clarify those associations, we conducted a prospective study of 1580 Japanese individuals who participated in an annual health check-up in 2014 with 2.8 years of follow-up. All participants had free triiodothyronine (T3) and free thyroxine (T4) levels in the normal range. Among study participants, 88 were diagnosed as having SCH. Even though no significant correlation was observed between HbA1c and annual change in estimated GFR among participants without SCH (multi-adjusted standardized parameter estimate (β) = 0.03, p = 0.250), a significant inverse association was observed among participants with SCH (β = −0.26, p = 0.014). When those analyses were performed among participants who were not taking glucose lowering medication, the observed associations were essentially the same: β = 0.03, p = 0.266 for participants without SCH and β = −0.32, p = 0.006 for participants with SCH, respectively. Therefore, SCH status could influence the association between HbA1c and renal function.

Association between dietary onion intake and subclinical hypothyroidism in adults: a population-based study from an iodine-replete area

PURPOSE

The protective effect of onion against thyroid hypofunction has been reported in animal studies. However, in humans, the association between onion consumption and subclinical hypothyroidism (SCH) are unclear. The study sought to explore the association between habitual onion intake and SCH among adult population from an iodine-replete area.

METHODS

A cross-sectional study (6515 men and 5290 women) was performed in Tianjin, China. Frequency of onion consumption was assessed using a valid self-administered food frequency questionnaire. Serum free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) were determined by chemiluminescence immunoassay. SCH was diagnosed with TSH > 4.78 mIU/L. Multiple logistic regression was used to evaluate the association of onion intake with SCH.

RESULTS

The prevalence of SCH was 2.56% in men and 7.18% in women, respectively. In women, the fully adjusted odds ratios [95% confidence interval (CI)] of having SCH across increasing frequency of onion intake were 1.00 (reference) for <1 time/week, 0.99 (0.73, 1.34) for 1-3 times/week, 0.74 (0.53, 1.03) for 4-6 times/week, and 0.67 (0.47, 0.97) for ≥7 times/week (P for trend <0.01). However, we observed no significant association between onion intake and SCH in men. Stratified analyses suggested a potential effect modification by age: the odds ratios (95% CI) across extreme quartiles was 0.37 (0.17, 0.80) in <40 women and 1.11 (0.51, 2.47) in >60 women.

CONCLUSIONS

Frequent consumption of onion is inversely associated with SCH in adult women from an iodine-replete area. Further studies are needed to explore the casual relationship. TRIAL REGISTRATION WEBSITE: https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000031137.

Association between thyroid-stimulating hormone (TSH) and proteinuria in relation to thyroid cyst in a euthyroid general population

Background

High normal levels of thyroid-stimulating hormone (TSH) have been reported to be associated with chronic kidney disease (CKD) among euthyroid individuals. However, there has been only limited research on the association between TSH and proteinuria, a major risk factor for the progression of renal disease.

Methods

A cross-sectional study of 1595 euthyroid individuals was conducted. All participants were within the normal range for free triiodothyronine (T3), free thyroxine (T4), and TSH. Analyses were stratified by thyroid cyst status to test the hypothesis that the absence of thyroid cysts, an indicator of latent thyroid damage, is associated with declining ability to synthesis thyroid hormone.

Results

For participants with thyroid cysts, a significant inverse association between TSH and proteinuria was observed (adjusted odds ratio (95% confidence intervals) of log-transformed TSH for proteinuria 0.40 (0.18, 0.89)). In participants without thyroid cysts, a significant positive association between those two factors was observed (2.06 (1.09, 3.90)).

Conclusions

Among euthyroid individuals in the general population, being in the normal range of TSH was found to have an ambivalent association with proteinuria. Thyroid cyst status could be an effect modifier for those associations.

Comparison of Incidental Thyroid Nodules Between Early Breast Cancer Patients and Healthy Controls: Higher Incidence and Thyroid Imaging Reporting and Data System (TI-RADS) Score of Patients with Cancer

Background: Breast and thyroid cancers remain among the most common malignancies in women. In previous studies, the co-occurrence of thyroid and breast cancers has been reported. Objectives: The aim of this study was to evaluate and compare the risk and incidence of incidental thyroid nodules (ITNs) between patients with breast cancer and healthy controls, based on the Thyroid Imaging Reporting and Data System (TI-RADS). Methods: This case-control study was conducted on 140 patients with breast cancer and 140 cancer-free women in a similar age range. Thyroid ultrasonography (US) was performed before the onset of treatment. The risk stratification of thyroid nodules was based on the TI-RADS. Results: The mean age of the participants was not significantly different between the case (43.35 ± 7.85 years) and control (42.11 ± 3.69 years) groups (P = 0.094). Invasive ductal carcinoma was the most frequent type of breast cancer in the patients. Normal thyroid US findings were significantly less frequent in patients with breast cancer (35.7%) compared to the healthy controls (76.4%) (P = 0.001). On the other hand, thyroid nodules were more frequent in the patients and associated with a higher risk of malignancy (i.e., high TI-RADS scores) compared to healthy women (P = 0.001 and P = 0.001, respectively). Besides, patients with breast cancer showed more thyroid abnormalities in the US examinations. Conclusions: A higher frequency of ITN, with an elevated TI-RADS score, which raised the suspicion of malignancy, was seen in patients with breast cancer. Overall, patients with breast cancer may benefit from a regular thyroid US examination.

Higher Prevalence of Non-thyroidal-Illness Syndrome in Elderly Male Patients With Active Helicobacter pylori Infection

Objective: It is currently unclear whether the Helicobacter pylori (H. pylori) infection leads to associated alterations in thyroid functions and thyroidal illnesses. This study aims to analyse this relationship in an elderly male cohort over a five-year period.

Design: A case retrospective study.

Methods: A longitudinal study was designed to collect subjects (≥65 years old) receiving both a thyroid examination and H. pylori infection status determined by ¹³C-urea breath test in 2013 at our unit. Subjects were followed every 1 to 2 years until December 2017 for laboratory results, visits to outpatient clinics/emergency departments etc. Blood tests and thyroid ultrasonography were performed to determine thyroid function and morphology.

Results: 356 male subjects with mean age 78.5 ± 9.8 years were included. Active H. pylori infection was positive in 88 subjects (24.7%). Thyroid function tests and ultrasonography showed similar patterns between H. pylori positive and negative groups. Non-thyroidal-illness syndrome (NTIS) was diagnosed in 30/210 (14%) patients who experienced acute illnesses and hospitalization over five-year follow-up. Notably, NTIS demonstrated significantly higher prevalence in the H. pylori positive group compared to the negative group (17.1 vs. 5.6%, P = 0.001). Multivariate analysis showed that when age, APACHE II score and hemoglobin levels were adjusted, H. pylori status still has significant interrelationship with NTIS (OR = 3.497, P = 0.003).

Conclusions: There is a positive association between chronic active H. pylori infection and NTIS prevalence in this elderly male cohort. Further studies are needed to elucidate the role of H. pylori infection on NTIS in elderly male patients.

Association between thyroid cysts and hypertension by atherosclerosis status: a cross-sectional study

Our recent studies indicate that thyroid cysts have clinical implications. Thyroid cysts could have a positive effect on the supply of thyroid hormones. Both hyperthyroidism and hypothyroidism cause hypertension. Hypothyroidism, but not hyperthyroidism, is a risk factor for atherosclerosis. Therefore, thyroid cysts could be associated with hypertension, and atherosclerosis might influence the association between thyroid cysts and hypertension. To evaluate the clinical significance of thyroid cysts, a cross-sectional study was conducted with 1801 Japanese aged 40–74 years. Thyroid cysts were significantly positively associated with hypertension in participants without atherosclerosis. However, there was a significant inverse association in those with atherosclerosis. The potential confounding factor adjusted odd ratios and 95% confidence intervals (95% CIs) were 1.49 (95% CI 1.17–1.90) for participants without atherosclerosis and 0.49 (95% CI 0.24–0.98) for those with atherosclerosis. The present study demonstrates that thyroid cysts have clinical implications because thyroid cysts support thyroid hormone activity. Our findings provide sufficient evidence to develop a risk assessment for hypertension for the general population, even though further research is required.

HbA1c is inversely associated with thyroid cysts in a euthyroid population: A cross-sectional study

Anti-thyroid peroxidase antibody (TPO-Ab) is revealed to be inversely associated with thyroid cysts among euthyroid population. TPO-Ab causes autoimmune thyroiditis by bolstering thyroid inflammation. Therefore, at least partly, absence of thyroid cysts could indicate latent thyroid damage. Since participants with subclinical hypothyroidism are reported to have higher HbA1c than normal healthy controls, HbA1c could be inversely associated with thyroid cysts through a mechanism reflecting latent thyroid damage. To investigate the association between HbA1c and thyroid cysts among a euthyroid population, a cross-sectional study was conducted on 1,724 Japanese individuals who were within the normal range of thyroid function [i.e., normal range of free triiodothyronine (T3) and free thyroxine (T4)] and aged 40–74 years. Among this study population, 564 were diagnosed with thyroid cysts. Independently of thyroid related hormones [thyroid stimulating hormone (TSH), free T3, and free T4] and known cardiovascular risk factors, HbA1c was found to be significantly inversely associated with the presence of thyroid cysts. This association remained significant even after this analysis was limited to participants within a normal range of TSH. The fully adjusted odds ratios (ORs) of thyroid cysts for 1 standard deviation (SD) increment of HbA1c were 0.84 (0.74, 0.95) for total participants and 0.80 (0.70, 0.92) for participants within a normal range of TSH. Among participants with normal thyroid function, HbA1c was inversely associated with the presence of thyroid cysts. The absence of thyroid cysts and higher levels of HbA1c could indicate the latent functional damage of the thyroid.

Thyroid disorders in elderly: A comprehensive review

The approach to management of thyroid disorders in the elderly differs from that for younger individuals: it considers frailty of the population, coexisting medical illness and medications, clearance rate of medications and drug-drug interactions along with target organ sensitivity to the treatment. We present a comprehensive review of literature for the clinical presentation, pathophysiology, diagnostic evaluation, and management of thyroid disorders in the elderly.

The Role of Thyroid Hormone in Neuronal Protection

Thyroid hormone is essential for brain development and brain function in the adult. During development, thyroid hormone acts in a spatial and temporal-specific manner to regulate the expression of genes essential for normal neural cell differentiation, migration, and myelination. In the adult brain, thyroid hormone is important for maintaining normal brain function. Thyroid hormone excess, hyperthyroidism, and thyroid hormone deficiency, hypothyroidism, are associated with disordered brain function, including depression, memory loss, impaired cognitive function, irritability, and anxiety. Adequate thyroid hormone levels are required for normal brain function. Thyroid hormone acts through a cascade of signaling components: activation and inactivation by deiodinase enzymes, thyroid hormone membrane transporters, and nuclear thyroid hormone receptors. Additionally, the hypothalamic-pituitary-thyroid axis, with negative feedback of thyroid hormone on thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH) secretion, regulates serum thyroid hormone levels in a narrow range. Animal and human studies have shown both systemic and local reduction in thyroid hormone availability in neurologic disease and after brain trauma. Treatment with thyroid hormone and selective thyroid hormone analogs has resulted in a reduction in injury and improved recovery. This article will describe the thyroid hormone signal transduction pathway in the brain and the role of thyroid hormone in the aging brain, neurologic diseases, and the protective role when administered after traumatic brain injury. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.

Aging and the hypothalamic-pituitary-thyroid axis

The world's population is increasingly aging, this noted particularly in the Western world where there are ever greater numbers of centenarians and those over 85 years. Given the immense importance of the thyroid gland for optimal health and the fact that morphological and functional changes in the hypothalamic-pituitary-thyroid (HPT) axis take place as a natural adaptation to the aging process, a clear distinction must be made in older individuals between these and the onset of disease. However, this is problematic since, frequently, subtle differences exist between them, making diagnosis a challenging task, especially as concerns subclinical disease. The newly emerging interdisciplinary field of geroscience offers the prospect of being used as a platform to investigate the effect of disrupted HPT function on functional capacity and cognitive ability among the aged, as well as the risk or onset of age-associated diseases, thus enhancing healthspan and lifespan. Because optimal functioning of the thyroid gland is a prerequisite for longevity as well as for mental and physical wellbeing, this review summarizes the recent scientific data regarding HPT and aging while discussing alternative and personalized treatment approaches to maintaining a healthy thyroid as a means to ensuring a long, active, and healthy life.

Different Relationships Between Thyrotropin and Muscle Strength According to Sex and Age in Euthyroid Koreans (The 6th Korea National Health and Nutritional Examination Survey 2014-2015)

Background: Changes in muscle mass and strength can be caused by multiple endocrine factors, including thyroid dysfunction. However, the relationship between thyroid function and muscle strength in euthyroid individuals is not clear. In the present study, we investigated the relationship between thyroid function and handgrip strength (HGS) in euthyroid Koreans, especially according to sex and age. Methods: This was a population-based, cross-sectional study from the 6th Korea National Health and Nutrition Examination Survey including 2894 Koreans (1487 men and 1407 women) aged ≥19 years. Serum thyrotropin (TSH) and free thyroxine (fT4) levels were measured. HGS was measured using a digital grip strength dynamometer. Results: Serum TSH level, but not serum fT4 level, was significantly associated with HGS in men, but neither TSH nor fT4 level was associated with HGS in women. Serum TSH showed a negative association with HGS in men aged <65 years (n = 1376; β = -0.566, p = 0.008), but a positive association in men aged ≥65 years (n = 111; β = 1.158, p = 0.010) after adjusting for confounders. HGS decreased as TSH tertile increased in men aged <65 years (p for trend = 0.010), but increased with TSH tertile in men aged ≥65 years (p for trend = 0.009) after adjusting for confounders. Odds ratios (ORs) for the lowest quartile of HGS increased in the highest tertile of TSH among men aged <65 years (OR = 1.657 [95% confidence interval {CI} 1.099-2.500], p = 0.006) and decreased in the highest tertile of TSH among men aged ≥65 years (OR = 0.176 [CI 0.032-0.966], p = 0.034) after adjusting for confounders. Conclusions: In euthyroid Koreans, serum TSH levels were significantly associated with HGS only in men and this relationship was found to depend significantly on age. These findings suggest that age has a distinct influence on the effect of even subtle change of thyroid function on muscle strength in men.

Reinterpreting patterns of variation in human thyroid function: An evolutionary ecology perspective

Two hundred million people worldwide experience some form of thyroid disorder, with women being especially at risk. However, why human thyroid function varies between populations, individuals, and across the lifespan has attracted little research to date. This limits our ability to evaluate the conditions under which patterns of variation in thyroid function are best understood as 'normal' or 'pathological'. In this review, we aim to spark interest in research aimed at understanding the causes of variation in thyroid phenotypes. We start by assessing the biomedical literature on thyroid imbalance to discuss the validity of existing reference intervals for diagnosis and treatment across individuals and populations. We then propose an evolutionary ecological framework for understanding the phylogenetic, genetic, ecological, developmental, and physiological causes of normal variation in thyroid function. We build on this approach to suggest testable predictions for how environmental challenges interact with individual circumstances to influence the onset of thyroid disorders. We propose that dietary changes, ecological disruptions of co-evolutionary processes during pregnancy and with pathogens, emerging infections, and exacerbated stress responses can contribute to explaining the onset of thyroid diseases. For patients to receive the best personalized care, research into the causes of thyroid variation at multiple levels is needed.

Associations between thyroid-stimulating hormone and hypertension according to thyroid cyst status in the general population: a cross-sectional study

Background

The absence of thyroid cysts may indicate latent thyroid damage, as demonstrated in our previous study. However, the association between the absence of thyroid cysts and latent functional damage of the thyroid is unknown. At low thyroid hormone productivity, which may be associated with latent functional damage of the thyroid, the association between thyroid-stimulating hormone (TSH) and hypertension might be enhanced. Therefore, we evaluated the association between TSH level and hypertension stratified by thyroid cyst status.

Methods

We conducted a cross-sectional study of 1724 euthyroid Japanese individuals aged 40–74 years who participated in an annual health checkup in 2014.

Results

In the study population, 564 and 686 participants had thyroid cysts and hypertension, respectively. A significant positive association was observed between TSH and hypertension in subjects without a thyroid cyst but not in subjects with thyroid cysts. There was a significant positive association between hypertension and TSH in subjects without a thyroid cyst (odds ratio [OR] 1.27; 95% confidence intervals [CI] 1.01, 1.61) but not in subjects with thyroid cysts (OR 0.79; CI 0.57, 1.09) in the model fully adjusted for known confounding factors. The correlation between the TSH and free triiodothyronine (fee T3) levels (simple correlation coefficient [r] = − 0.13, p < 0.01) was stronger in the subjects without thyroid cysts than in those with thyroid cysts (r = − 0.03, p = 0.525).

Conclusions

TSH is positively associated with hypertension only in individuals without thyroid cysts. The correlation between the TSH and free T3 levels was stronger in the subjects without thyroid cysts than in those with thyroid cysts. Therefore, the absence of thyroid cysts could be related to the association between TSH level and hypertension, possibly by indicating that the subjects without thyroid cysts had limited thyroid hormone reserves. Therefore, the absence of thyroid cysts could indicate the latent functional damage of the thyroid.

Thyroid hormones in diabetes, cancer, and aging

Thyroid function is central in the control of physiological and pathophysiological processes. Studies in animal models and human research have determined that thyroid hormones modulate cellular processes relevant for aging and for the majority of age‐related diseases. While several studies have associated mild reductions on thyroid hormone function with exceptional longevity in animals and humans, alterations in thyroid hormones are serious medical conditions associated with unhealthy aging and premature death. Moreover, both hyperthyroidism and hypothyroidism have been associated with the development of certain types of diabetes and cancers, indicating a great complexity of the molecular mechanisms controlled by thyroid hormones. In this review, we describe the latest findings in thyroid hormone research in the field of aging, diabetes, and cancer, with a special focus on hepatocellular carcinomas. While aging studies indicate that the direct modulation of thyroid hormones is not a viable strategy to promote healthy aging or longevity and the development of thyromimetics is challenging due to inefficacy and potential toxicity, we argue that interventions based on the use of modulators of thyroid hormone function might provide therapeutic benefit in certain types of diabetes and cancers.

Anti-thyroid peroxidase antibody and subclinical hypothyroidism in relation to hypertension and thyroid cysts

Hypertension frequently occurs in subclinical hypothyroidism (SCH). By bolstering thyroid inflammation, anti-peroxidase antibody (TPO-Ab) causes autoimmune thyroiditis, which is one of the most common causes of SCH. Since the absence of thyroid cysts is associated with TPO-Ab (+) based on the indication of latent thyroid damage, we explored the potential mechanism underlying the association among TPO-Ab, SCH, hypertension, and thyroid cysts. A cross-sectional study of 1,483 Japanese aged 40–74 years was conducted. Thyroid cysts were defined as those having a maximum diameter of ≥ 2.0 mm, containing no solid component. TPO-Ab (+) was positively associated with SCH with hypertension (adjusted odds ratio [OR] and 95% confidence interval [CI], 2.62 [1.40, 4.89]) but not with SCH without hypertension (0.84 [0.37, 1.89]), respectively. Moreover, among participants without thyroid cysts, SCH was positively associated with hypertension (2.15 [1.23, 3.76]) but not among participants with thyroid cysts (0.58 [0.16, 2.16]), respectively. TPO-Ab was positively associated with SCH with hypertension, but not with SCH without hypertension. In addition, status of thyroid cysts might act as a determinant factor on the association between SCH and hypertension. These findings are efficient tools to clarify the background mechanism that underlies SCH.

Association Between Exposure to Ambient Air Pollution and Thyroid Function in Korean Adults

CONTEXT

Although a significant relationship has been reported between air pollution and thyroid function in limited samples or regions, few studies have addressed this association in the general population.

OBJECTIVE

Using a nationwide sample of Korean adults, we investigated the association between exposure to air pollution and thyroid function, and whether this association differed between subgroups stratified according to age or body mass index (BMI).

METHODS

We included 4704 adults in the final analysis and used each person's annual average exposure to 4 air pollutants, namely, particulate matter with an aerodynamic diameter less than or equal to 10 μm (PM10), nitrogen dioxide (NO2), sulfur dioxide, and carbon monoxide (CO). We measured serum thyrotropin (TSH) and free thyroxine (FT4) concentrations as indicators of thyroid function according to age and BMI.

RESULTS

The annual average exposure to NO2 and CO was significantly associated with an elevated TSH and reduced FT4 concentration after adjusting for possible confounding factors (all P < .05). In men, in addition to these 2 pollutants, PM10 exposure was positively associated with TSH level (P = .03). Age-stratified analysis showed stronger effects of NO2 and CO exposure in older than in younger adults. Exposure to these air pollutants was related to serum TSH and FT4 concentrations in people with overweight or obesity but not in those of normal weight.

CONCLUSIONS

This study provides the first evidence that air pollution exposure is linked to thyroid function in the general population and that this association may be stronger in older or overweight or obese adults.

Hypothyroidism Treatment Among Older Adults: Evidence from a Claims Database

INTRODUCTION

Hypothyroidism is a common but often unrecognized condition associated with significant morbidity in the older adult population. This study characterizes a large population of older adults diagnosed with hypothyroidism and examines concordance of their treatment with recommendations from expert bodies, e.g., the American Thyroid Association and American Association of Clinical Endocrinologists.

METHODS

Individuals seen in general and/or specialty practices who were age ≥ 65 years and diagnosed with hypothyroidism were included in this observational, retrospective cohort study using a large US claims database. Analyses describe the population and examine the prevalence of hypothyroidism, treatment with levothyroxine and, among those treated, whether TSH laboratory values are within a guideline-recommended target range.

RESULTS

Prevalence of hypothyroidism in this older adult population increased from 5.62% to 8.24% over the 2007-2015 period. Among older adults diagnosed with hypothyroidism (N = 4025), a substantial proportion (28.0%) did not receive levothyroxine therapy, and, of those who were receiving such therapy (N = 2899), 32.9% did not have evidence of being monitored to determine whether the dosage was appropriate. Moreover, the laboratory results of those who were treated suggest that a significant proportion (17.4%) had a TSH level above the recommended target range, while TSH levels for a smaller proportion (3.7%) were below target.

CONCLUSIONS

Many older adults diagnosed with hypothyroidism may not have received medical care complying with clinical practice guidelines. Results of this study reveal a number of areas to target to potentially improve the treatment of older adults with hypothyroidism.

Thyroid Function and Sarcopenia: Results from the ELSA-Brasil Study

OBJECTIVES

We aimed to investigate the association of subclinical thyroid disease and thyroid hormone levels with sarcopenia and its defining components in community-dwelling middle-aged and older adults without overt thyroid dysfunction.

DESIGN

Cross-sectional study.

SETTING

Active and retired employees from public institutions located in six Brazilian cities.

PARTICIPANTS

A total of 6974 participants from the ELSA-Brasil study's second wave, aged 50 years and older, without overt thyroid dysfunction and with complete data for exposure, outcome, and covariates.

METHODS

Serum levels of thyrotropin (TSH), free thyroxine, and free triiodothyronine (FT3) were measured and divided in quintiles for the analyses. Participants were classified with euthyroidism, subclinical hypothyroidism, and subclinical hyperthyroidism. Muscle mass was assessed by bioelectrical impedance analysis and muscle strength by handgrip strength. Sarcopenia was defined according to the Foundation for the National Institutes of Health criteria. Possible confounders included sociodemographic characteristics, clinical conditions, and lifestyle. Analyses were performed separately for middle-aged and older adults (≥65 y).

RESULTS

The frequencies of sarcopenia, low muscle mass, low muscle strength, subclinical hypothyroidism, and subclinical hyperthyroidism were 1.5%, 20.8%, 3.8%, 9.1%, and .9%, respectively. Subclinical thyroid dysfunction was not associated with sarcopenia and its defining components. Among older adults, TSH had a U-shaped association with sarcopenia and low muscle strength. The odds ratios (ORs) (95% confidence intervals [CIs]) for the associations of the first, second, fourth, and fifth quintile with sarcopenia, respectively, were 5.18 (1.47-18.28), 6.28 (1.82-21.73), 4.12 (1.15-14.76), and 4.81 (1.35-17.10), and with low muscle strength was (OR (95% CI) for the first, second, and fifth quintiles, respectively: 1.43 (1.16-5.07), 2.07 (1.24-4.70), and 2.18 (1.03-4.60). Additionally, FT3 had a negative association with muscle mass in both age strata.

CONCLUSION

Subtle thyroid hormone alterations are associated with sarcopenia or its defining components in middle-aged and older adults without overt thyroid dysfunction. J Am Geriatr Soc 68:1545-1553, 2020.

Murine single-cell RNA-seq reveals cell-identity- and tissue-specific trajectories of aging

Aging is a pleiotropic process affecting many aspects of mammalian physiology. Mammals are composed of distinct cell type identities and tissue environments, but the influence of these cell identities and environments on the trajectory of aging in individual cells remains unclear. Here, we performed single-cell RNA-seq on >50,000 individual cells across three tissues in young and old mice to allow for direct comparison of aging phenotypes across cell types. We found transcriptional features of aging common across many cell types, as well as features of aging unique to each type. Leveraging matrix factorization and optimal transport methods, we found that both cell identities and tissue environments exert influence on the trajectory and magnitude of aging, with cell identity influence predominating. These results suggest that aging manifests with unique directionality and magnitude across the diverse cell identities in mammals.

Aging Is Associated with Low Thyroid State and Organ-Specific Sensitivity to Thyroxine

Background: Serum thyroid state in older adults correlates with extended longevity. We hypothesized that age impacts not only systemic but also organ-specific thyroid state and response to thyroxine (T4). Methods: Young (3 months) and old (23 months) male mice were analyzed at baseline and after acute T4 challenge. Age effects on circulating thyrotropin (TSH) and thyroid hormone (TH) concentrations, transcript expression in the pituitary and thyroid were compared with organ-specific responses characterized by hepatic and cardiac content of TH and TH metabolites and expression of TH-target genes, as well as hepatic deiodinase 1 activity. Results: Circulating TH concentrations and hepatic and cardiac TH content were lower in old versus young mice. After injection with T4, conversion of T4 to triiodothyronine was decreased in old mice while TH transport in liver and heart was not affected. Organ-specific TH response was augmented in old mice in liver but not heart, indicating age- and tissue-specific sensitivity to TH. A compensatory increase of thyroid stimulating hormone subunit beta expression in the pituitary and increased serum TSH concentrations, but reduced expression of thyroid differentiation markers were found in old mice. Conclusions: We suggest that a reduced activity of the aged thyroid is responsible for the systemic low TH state in old mice. Further, divergent TH metabolism and tissue response in liver and heart occur after T4 treatment in an aged organism. These rodent data are in agreement with a much narrower window for T4 substitution in the older adults to avoid overtreatment.

Micronutrients, iodine status and concentrations of thyroid hormones: a systematic review

Context

The metabolism of thyroid hormones, which are essential for normal development, involves many proteins and enzymes. It requires iodine as a key component but is also influenced by several other micronutrients, including selenium, zinc, iron, and vitamin A.

Objective

This systematic review was designed to investigate the effect of micronutrient status and supplementation on iodine status and thyroid hormone concentrations.

Data Sources

Using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines, electronic databases were searched from their inception to April 2016.

Study Selection

Human studies published in English and reporting data on micronutrient status and iodine status and/or thyroid hormone concentrations were included. Studies that examined the effect of micronutrient supplementation on iodine status and/or thyroid hormone concentrations were also included.

Data Extraction

A predesigned and piloted data extraction form was used to compile data from individual studies.

Results

A total of 57 studies were included: 20 intervention studies and 37 observational studies. Although observational evidence suggests that concentrations of selenium, zinc, and iron are positively associated with iodine status, data from randomized controlled trials fail to confirm this relationship.

Conclusions

Further studies are needed to provide greater understanding of the role of micronutrient status in iodine nutrition and thyroid function to ascertain the public health implications for populations worldwide.

Inadequate control of thyroid hormones sensitizes to hepatocarcinogenesis and unhealthy aging

An inverse correlation between thyroid hormone levels and longevity has been reported in several species and reduced thyroid hormone levels have been proposed as a biomarker for healthy aging and metabolic fitness. However, hypothyroidism is a medical condition associated with compromised health and reduced life expectancy. Herein, we show, using wild-type and the Pax8 ablated model of hypothyroidism in mice, that hyperthyroidism and severe hypothyroidism are associated with an overall unhealthy status and shorter lifespan. Mild hypothyroid Pax8 +/- mice were heavier and displayed insulin resistance, hepatic steatosis and increased prevalence of liver cancer yet had normal lifespan. These pathophysiological conditions were precipitated by hepatic mitochondrial dysfunction and oxidative damage accumulation. These findings indicate that individuals carrying mutations on PAX8 may be susceptible to develop liver cancer and/or diabetes and raise concerns regarding the development of interventions aiming to modulate thyroid hormones to promote healthy aging or lifespan in mammals.

Parasitism Elicits a Stress Response That Allocates Resources for Immune Function in South American Fur Seals (Arctocephalus australis)

Parasites can cause chronic stress in some animal species, and this type of stress response has been associated with adverse consequences for the host. In order to know whether parasitism elicited a stress response associated with decreased host fitness, hookworm (Uncinaria sp.) infection was studied in a colony of South American fur seals (Arctocephalus australis) in which hookworms infect nearly all pups born in a reproductive season. A parasite-free group was generated by treating a subset of pups with an antiparasitic drug before they developed patent hookworm infection. Stress and metabolic hormones, energy balance, and humoral and cellular immune parameters were measured in this group and hookworm-infected pups. Hookworms elicited a marked increase in plasma cortisol levels in fur seal pups. These hookworm-infected pups were able to maintain constant glucose levels, despite losing body mass over the course of infection potentially because of increased protein catabolism. Infected pups were able to mount an effective immune response against the parasite and eliminated hookworms from the intestine, recovering partial body mass lost as a result of hookworm infection at the end of the study period. As shown in previous studies, adequate glucose levels are critical for proper T lymphocyte reactivity, and it is possible that, through activation of a stress response, energy can be readily available for immune response against the parasite contributing to early recovery from infection. Although there are potential fitness costs to mounting a sustained stress response, these could also be adaptive and promote survival during critical life-history stages.

The prognostic value of total T3 after acute cerebral infarction is age-dependent: a retrospective study on 768 patients

BACKGROUND

Serum triiodothyronine (T3) concentration was reported to be associated with the prognosis after acute ischemic stroke. The aim of this study was to evaluate the effect of age on the prognostic value of thyroid-related hormones after an acute ischemic stroke.

METHODS

This was a retrospective study involving the review of 1072 ischemic stroke patients who had been consecutively admitted to the hospital within 72 h of symptom onset. Total triiodothyronine (T3), total thyroxine (T4), free T3, free T4, and thyroid-stimulating hormone (TSH) were assessed to determine their values for predicting functional outcome at the first follow-up clinic visits, which usually occurred 2 to 4 weeks after discharge from the hospital.

RESULTS

A total of 768 patients were finally included in the study and divided into two age groups: a younger group (age < 65 years) and an older group (age ≥ 65 years). On univariate analysis, four factors-lower total T3, free T3 concentrations, higher scores on the National Institute of Health Stroke Scale (NIHSS) and the presence of atrial fibrillation-were associated with poor functional outcomes in both groups. In addition, older age, female gender, higher free T4, and lower TSH levels were also associated with poor function in the older group. On multiple logistic regression analysis, higher NIHSS scores (odds ratio [OR] =1.95; 95% confidence interval [CI], 1.66-2.30; P ≤ .001) and lower total T3 concentrations (OR = 0.06; 95% CI, 0.01-0.68; P = .024) remained independently associated with poor functional outcome in the older group. However, the independent association with poor function of lower total T3 was not confirmed in the younger group.

CONCLUSIONS

The prognostic value of low total T3 is age-associated and more meaningful in an older population.

Metabolic Plasticity of Astrocytes and Aging of the Brain

As part of the blood-brain-barrier, astrocytes are ideally positioned between cerebral vasculature and neuronal synapses to mediate nutrient uptake from the systemic circulation. In addition, astrocytes have a robust enzymatic capacity of glycolysis, glycogenesis and lipid metabolism, managing nutrient support in the brain parenchyma for neuronal consumption. Here, we review the plasticity of astrocyte energy metabolism under physiologic and pathologic conditions, highlighting age-dependent brain dysfunctions. In astrocytes, glycolysis and glycogenesis are regulated by noradrenaline and insulin, respectively, while mitochondrial ATP production and fatty acid oxidation are influenced by the thyroid hormone. These regulations are essential for maintaining normal brain activities, and impairments of these processes may lead to neurodegeneration and cognitive decline. Metabolic plasticity is also associated with (re)activation of astrocytes, a process associated with pathologic events. It is likely that the recently described neurodegenerative and neuroprotective subpopulations of reactive astrocytes metabolize distinct energy substrates, and that this preference is supposed to explain some of their impacts on pathologic processes. Importantly, physiologic and pathologic properties of astrocytic metabolic plasticity bear translational potential in defining new potential diagnostic biomarkers and novel therapeutic targets to mitigate neurodegeneration and age-related brain dysfunctions.

Overt and Subclinical Hypothyroidism in the Elderly: When to Treat?

Hypothyroidism is characterized by increased thyrotropin (TSH) levels and reduced free thyroid hormone fractions while, subclinical hypothyroidism (sHT) by elevated serum TSH in the face of normal thyroid hormones. The high frequency of hypothyroidism among the general population in Western Countries made levothyroxine (LT4) one of the 10 most prescribed drugs. However, circulating TSH has been demonstrated to increase with aging, regardless the existence of an actual thyroid disease. Thus, when confronting an increase in circulating TSH levels in the elderly, especially in the oldest old, it is important to carry an appropriate diagnostic path, comprehensive of clinical picture as well as laboratory and imaging techniques. In the current review, we summarize the recommendations for a correct diagnostic workup and therapeutic approach to older people with elevated TSH value, with special attention to the presence of frailty, comorbidities, and poly-therapy. The treatment of choice for hypothyroid patients is hormone replacement with LT₄ but, it is important to consider multiple factors before commencing the therapy, from the age dependent TSH increase to the presence of an actual thyroid disease and comorbidities. When treatment is necessary, a tailored therapy should be chosen, considering poly-pharmacy and frailty. A careful follow-up and treatment re-assessment should be always considered to avoid the risk of over-treatment. It is important to stress the need of educating the patient for a correct administration of LT₄, particularly when poly-therapy is in place, and the importance of a tailored therapeutic approach and follow-up, to avoid overtreatment.

β-Arrestin Based Receptor Signaling Paradigms: Potential Therapeutic Targets for Complex Age-Related Disorders

G protein coupled receptors (GPCRs) were first characterized as signal transducers that elicit downstream effects through modulation of guanine (G) nucleotide-binding proteins. The pharmacotherapeutic exploitation of this signaling paradigm has created a drug-based field covering nearly 50% of the current pharmacopeia. Since the groundbreaking discoveries of the late 1990s to the present day, it is now clear however that GPCRs can also generate productive signaling cascades through the modulation of β-arrestin functionality. β-Arrestins were first thought to only regulate receptor desensitization and internalization - exemplified by the action of visual arrestin with respect to rhodopsin desensitization. Nearly 20 years ago, it was found that rather than controlling GPCR signal termination, productive β-arrestin dependent GPCR signaling paradigms were highly dependent on multi-protein complex formation and generated long-lasting cellular effects, in contrast to G protein signaling which is transient and functions through soluble second messenger systems. β-Arrestin signaling was then first shown to activate mitogen activated protein kinase signaling in a G protein-independent manner and eventually initiate protein transcription - thus controlling expression patterns of downstream proteins. While the possibility of developing β-arrestin biased or functionally selective ligands is now being investigated, no additional research has been performed on its possible contextual specificity in treating age-related disorders. The ability of β-arrestin-dependent signaling to control complex and multidimensional protein expression patterns makes this therapeutic strategy feasible, as treating complex age-related disorders will likely require therapeutics that can exert network-level efficacy profiles. It is our understanding that therapeutically targeting G protein-independent effectors such as β-arrestin will aid in the development of precision medicines with tailored efficacy profiles for disease/age-specific contextualities.

Applications for non-invasive thyroid hormone measurements in mammalian ecology, growth, and maintenance

Thyroid hormones (THs) play a pivotal role in the regulation of metabolic activity throughout all life stages. Cross-talk with other hormone systems permits THs to coordinate metabolic changes as well as modifications in growth and maintenance in response to changing environmental conditions. The scope of this review is to explain the relevant basics of TH endocrinology, highlight pertinent topics that have been investigated so far, and offer guidance on measuring THs in non-invasively collected matrices. The first part of the review provides an overview of TH biochemistry, which is necessary to understand and interpret the findings of existing studies and to apply non-invasive TH monitoring. The second part focuses on the role of THs in mammalian ecology, and the third part highlights the role of THs in growth and maintenance. The fourth part deals with the advantages and difficulties of measuring THs in non-invasively collected samples. This review concludes with a summary that considers future directions in the study of THs.

An extremely high dietary iodide supply forestalls severe hypothyroidism in Na+/I- symporter (NIS) knockout mice

The sodium/iodide symporter (NIS) mediates active iodide (I⁻) accumulation in the thyroid, the first step in thyroid hormone (TH) biosynthesis. Mutations in the SLC5A5 gene encoding NIS that result in a non-functional protein lead to congenital hypothyroidism due to I⁻ transport defect (ITD). ITD is a rare autosomal disorder that, if not treated promptly in infancy, can cause mental retardation, as the TH decrease results in improper development of the nervous system. However, in some patients, hypothyroidism has been ameliorated by unusually large amounts of dietary I⁻. Here we report the first NIS knockout (KO) mouse model, obtained by targeting exons 6 and 7 of the Slc5a5 gene. In NIS KO mice, in the thyroid, stomach, and salivary gland, NIS is absent, and hence there is no active accumulation of the NIS substrate pertechnetate (^99mTcO₄⁻). NIS KO mice showed undetectable serum T₄ and very low serum T₃ levels when fed a diet supplying the minimum I⁻ requirement for rodents. These hypothyroid mice displayed oxidative stress in the thyroid, but not in the brown adipose tissue or liver. Feeding the mice a high-I⁻ diet partially rescued TH biosynthesis, demonstrating that, at high I⁻ concentrations, I⁻ enters the thyroid through routes other than NIS.

Ultrasonographic assessment of thyroid volume in oldest-old individuals

Objective

The aim of this study was to describe the relationship between thyroid volume and age, gender, anthropometric characteristics, and echogenicity in oldest-old subjects in an iodine-sufficient area.

Subjects and methods

The study included 81 independent elderly individuals aged ≥ 80 years (65 [80.2%] women). We determined these individuals' anthropometric characteristics, body mass index (BMI), and lean body mass, as well as thyroid volume and echogenicity by ultrasonography.

Results

We observed that octogenarians and nonagenarians had different profiles of thyroid echogenicity. The volume of the thyroid was smaller in nonagenarians than octogenarians (p = 0.012, r = 0.176), and subjects aged 80-89 years had more often hypoechoic glands than those aged ≥ 90 years (p = 0.01 versus 0.602).

Conclusion

The identification of ultrasonographic differences in oldest-old individuals will contribute to establishing preclinical markers, such as echogenicity, to identify individuals at risk of developing autoimmune thyroid disease. Future prospective studies should identify if 80-89-year-old individuals with hypoechoic glands progress to hypothyroidism, and if the absence of changes in echogenicity (i.e. a normal thyroid parenchyma) would have a positive impact on longevity among nonagenarians.

Thyroid Function and Cancer Risk: The Rotterdam Study

CONTEXT

In vitro and in vivo experiments have assigned both oncosuppressive and oncogenic properties to thyroid hormones. Population-based studies have found inconclusive results.

OBJECTIVE

We aimed to prospectively assess the relation between thyroid function and incident cancer in a population-based setting.

DESIGN, SETTING, AND PARTICIPANTS

The current study is a prospective population-based cohort study including 10 318 participants for whom baseline measurements of free T₄ (FT₄) and/or TSH were available.

MAIN OUTCOME MEASURES

Cox proportional hazards models were used to assess hazard ratios (HRs) of any solid non-skin cancer, as well as lung, breast, prostate, and gastrointestinal cancer specifically.

RESULTS

Higher FT₄ levels were associated with a higher risk of any solid cancer (HR, 1.42; 95% confidence interval [CI], 1.12-1.79), lung cancer (HR, 2.33; 95% CI, 1.39-3.92) and breast (HR, 1.77; 95% CI, 1.10-2.84) cancer. The risk estimates were similar after exclusion of thyroid-altering medication, but the association lost significance for breast cancer. Compared with the lowest FT₄ tertile, the highest tertile was associated with a 1.13-fold increased risk of any solid, 1.79-fold increased risk of lung, and 1.14-fold increased risk of breast cancer (P for trend <.05 for all). For TSH levels we found no associations with cancer risk. There was no differential effect of sex or age on the association between thyroid function and cancer risk.

CONCLUSIONS

Higher FT₄ levels are significantly associated with an increased risk of any solid, lung, and breast cancer. Further research should elucidate the underlying pathophysiological mechanisms.

Melatonin alleviates hyperthyroidism induced oxidative stress and neuronal cell death in hippocampus of aged female golden hamster, Mesocricetus auratus

Oxidative stress is a well known phenomenon under hyperthyroid condition that induces various physiological and neural problems with a higher prevalence in females. We, therefore investigated the antioxidant potential of melatonin (Mel) on hyperthyroidism-induced oxidative stress and neuronal cell death in the hippocampus region of brain (cognition and memory centre) of aged female golden hamster, Mesocricetus auratus. Aged female hamsters were randomly divided into four experimental groups (n=7); group-I: control, group-II: Melatonin (5mgkg(-1)day(-1), i.p., for one week), group-III: Hyperthyroid (100μg kg(-1)day(-1), i.p., for two weeks) and group-IV- Hyper+Mel. Hormonal profiles (thyroid and melatonin), activity of antioxidant enzymes (SOD, CAT and GPX), lipid peroxidation level (TBARS) and the specific apoptotic markers (Bax/Bcl-2 ratio and Caspase-3) expression were evaluated. A significant increase in the profile of total thyroid hormone (tT3 and tT4) in hyperthyroidic group as compared to control while tT3 significantly decreased in melatonin treated hyperthyroidic group. However, Mel level significantly decreased in hyperthyroidic group but increased in melatonin treated hyperthyroidic group. Further, the number of immune-positive cells for thyroid hormone receptor-alpha (TR-α) decreased in the hippocampus of hyperthyroidic group and increased in melatonin treated hyperthyroidic group. Profiles of antioxidant enzymes showed a significant decrease in hyperthyroidic group with a simultaneous increase in lipid peroxidation (TBARS). Melatonin treatment to hyperthyroidic group lead to decreased TBARS level with a concomitant increase in antioxidant enzyme activity. Moreover, increased expression of Bax/Bcl-2 ratio and Caspase-3, in hyperthyroidic group had elevated neuronal cell death in hippocampal area and melatonin treatment reduced its expression in hyperthyroidic group. Our findings thus indicate that melatonin reduced the hyperthyroidism-induced oxidative stress and neuronal cell death in the hippocampus region of brain, suggesting a novel therapeutic approach of melatonin for management of cognition and memory function in females under hyperthyroid condition.

MECHANISMS IN ENDOCRINOLOGY: Impact of isolated TSH levels in and out of normal range on different tissues

Routine treatment of thyroid cancer (TC) includes long-term suppression of TSH. The necessity of this treatment in low- and intermediate-risk patients as well as the extent of TSH suppression is currently under discussion. A literature search was performed to illustrate the role of TSH in extrathyroidal cells and to identify potential reasons for different effects of exogenously suppressed and endogenously low TSH levels. Although adverse effects of subnormal and supranormal TSH blood levels on heart and brain have not been consistently found, studies show a clear negative effect of suppressed TSH levels on bone mineral density. Experimental data also support an important role of TSH in the immune system. The ability of levothyroxine (l-T4) to regulate TSH levels and triiodothyronine levels in a physiological manner is limited. Reduction of circadian changes in TSH levels, decrease of thyroid hormone-binding proteins, prevention of potential compensatory increases of TSH levels (e.g., in old age), and unresponsiveness of TSH-producing cells to TRH on l-T4 treatment might cause adverse effects of suppressed TSH levels. In view of the adverse effects of aggressive TSH suppression, achieving the suggested levels of TSH between 0.9 and 1 mU/l in the treatment of low-to-intermediate risk TC patients appears justified.