Thyroid hormones regulate cardiac repolarization and QT-interval related gene expression in hiPSC cardiomyocytes

Prolongation of cardiac repolarization (QT interval) represents a dangerous and potentially life-threatening electrical event affecting the heart. Thyroid hormones (THs) are critical for cardiac development and heart function. However, little is known about THs influence on ventricular repolarization and controversial effects on QT prolongation are reported. Human iPSC-derived cardiomyocytes (hiPSC-CMs) and multielectrode array (MEA) systems were used to investigate the influence of 3,3′,5-triiodo-l-Thyronine (T3) and 3,3′,5,5′-tetraiodo-l-Thyronine (T4) on corrected Field Potential Duration (FPDc), the in vitro analog of QT interval, and on local extracellular Action Potential Duration (APD). Treatment with high THs doses induces a significant prolongation of both FPDc and APD, with the strongest increase reached after 24 h exposure. Preincubation with reverse T3 (rT3), a specific antagonist for nuclear TH receptor binding, significantly reduces T3 effects on FPDc, suggesting a TRs-mediated transcriptional mechanism. RNA-seq analysis showed significant deregulation in genes involved in cardiac repolarization pathways, including several QT-interval related genes. In conclusion, long-time administration of high THs doses induces FPDc prolongation in hiPSC-CMs probably through the modulation of genes linked to QT-interval regulation. These results open the way to investigate new potential diagnostic biomarkers and specific targeted therapies for cardiac repolarization dysfunctions.

PSVI-17 Dissimilarities in thyroid profiles and pregnancy rates in dairy cows with different polymorphic variants of the DIO1 gene

Thyroid hormones are implicated in regulation of the reproductive function in cattle. In turn, thyroid metabolism is determined by the activity of different types deiodinases. Our research was aimed to compare post-insemination thyroid profiles and pregnancy rates in dairy cows with different SNP genotypes in the deiodinase gene of the first type (DIO1). Thirty lactating Russian Black Pied cows were synchronized using the Ovsynch protocol and artificially inseminated (AI). Blood samples from the cows were collected on Days 0, 7, 14, 21, and 33 after AI. Hormonal levels in the serum were measured by ELISA. Pregnancy was confirmed by progesterone concentrations and ultrasonography. Genetic variants for the DIO1 gene were tested by RT-PCR and polymorphism at position 13149 (NC_037330) was found. The occurrence frequency of cows with genotypes CC, CG, and GG was 43.3, 33.3, and 23.3 %, respectively. A proportion of pregnant cows in the CC group was higher than in the CG group (84.6 vs. 40.0%, P < 0.05) and tended to be higher than in the GG group (42.9%). The concentration of triiodothyronine (T3) in the blood of CC animals did not change during the studied period, whereas that in CG animals decreased between Days 0 and 14 (from 1.60±0.21 to 1.10±0.22 nmol/L, P < 0.05). Concurrently, the T3 concentration on Day 0 was 1.4 times lower (P < 0.05) in the CC group than in the CG group. Furthermore, the level of reverse T3 on Day 7 in the GG group was 1.3 times higher (P < 0.05) than in the CC or CG groups. Thus, cows with DIO1 gene CC genotype have a higher reproductive ability than cows with CG or GG genotypes, which may be due to peculiarities of thyroid profiles during the first two weeks of pregnancy. The study was supported by Russian Ministry of Science and Higher Education (0445-2021-0004).

Inherited Selenocysteine Transfer RNA Mutation: Clinical and Hormonal Evaluation of 2 Patients

<b><i>Introduction:</i></b> Iodothyronine deiodinases are selenoproteins with the amino acid selenocysteine (Sec) introduced into the position of a TGA stop codon by a complex machinery involving tRNA^[Ser]Sec when a cis-acting Sec-insertion sequence element is present in the 3′ end of the mRNA. Recently, a variant in the <i>TRU-TCA1-1</i> gene encoding for tRNA^[Ser]Sec was reported, which resulted in reduced expression of stress-related selenoproteins. The proband presented with multisystem symptoms, euthyroid hyperthyroxinemia, and selenium deficiency. Here, we describe 2 new members of a family harboring the same tRNA^[Ser]Sec variant. <b><i>Case Presentation:</i></b> A 13-year-old patient was seen for Hashimoto’s disease with high FT3 (4.6 pg/mL, normal range 2–4.2 pg/mL) and normal FT4 and TSH concentrations. He had no clinical complaints. During a 6-year clinical and hormonal follow-up, the index patient was not treated, FT3 decreased, FT4 increased, and serum TSH stayed in the normal range resulting in a euthyroid hyperthyroxinemia. Reverse T3 concentration was significantly increased at the last visit (19 years and 4 months). At the last evaluation, the total selenium level was low (91 μg/L, normal range 95–125). DNA sequencing identified a germinal homozygous variant (C65G) in the <i>TRU-TCA1-1</i> gene. During follow-up, no additional clinical symptom was observed in the absence of any treatment. The same germinal tRNA^[Ser]Sec variant was identified at heterozygous state in his father, who had normal thyroid function tests except a moderately increased reverse T3 concentration, with increased total selenium (143 μg/L) level. In both patients, the expression of stress-related selenoprotein GPX3 was in the low-normal range (168 and 180 IU/L, respectively, normal range: 150–558 IU/L). We did not find any significant biological abnormalities evocative of other selenoprotein deficiencies. <b><i>Discussion/Conclusion:</i></b> We report on 2 members of a family with a variant in the <i>TRU-TCA1-1</i> gene encoding for tRNA^[Ser]Sec. Our study suggests that this tRNA^[Ser]Sec variant is not exclusively causative of disruption in selenoprotein synthesis.

Reverse T3 Level and T3 to Reverse T3 Ratio in Dried Blood Spot Samples at Birth May Facilitate Early Diagnosis of MCT8 Deficiency

Background: Monocarboxylate transporter 8 (MCT8) deficiency is an X- chromosome-linked neurodevelopmental disorder resulting from impaired thyroid hormone transporter across cell membrane. The diagnosis of MCT8 deficiency is typically delayed owing to the late appearance of signs and symptoms as well as inability of standard biomarkers of neonatal screening to make an early diagnosis. Here, we report for the first time the ability to identify MCT8 deficiency at birth using dried blood spot (DBS) samples. Methods: We measured T3, T4, and reverse T3 (rT3) levels in DBS samples obtained at birth in healthy neonates (n = 42) and neonates with genetically confirmed diagnosis of MCT8 deficiency (n = 6). T3, rT3 and T4 levels were measured in 8 mm diameter DBS samples using liquid chromatography-tandem mass spectrometry. Results: Mean ± SD level of T3 tended to be higher in the MCT8 group than that in healthy neonates (0.941 ± 0.183 ng/mL vs. 0.742 ± 0.195 ng/mL, p = 0.0525). More importantly rT3 level in the MCT8 group was significantly lower than that in healthy neonates (0.317 ± 0.065 ng/mL vs. 0.768 ± 0.196 ng/mL, p &lt; 0.0001) and the T3/rT3 ratio in the MCT8 group was significantly higher (3.04 ± 0.67 vs. 1.01 ± 0.34, p &lt; 0.0001) with no overlap of values. T4 was lower in the MCT8 group than in healthy babies (93.4 ± 22.4 ng/mL vs. 156.7 ± 35.9 ng/mL, p &lt; 0.0005) and the T3/T4 ratio of the MCT8 deficient group was higher (0.0105 ± 0.0029 vs. 0.0051 ± 0.0010, p&lt; 0.0001). Conclusion: rT3 and T3/rT3 ratio measured in the DBS obtained from neonates can serve as biomarkers for diagnosis of MCT8 deficiency at birth.

Factitious Total Triiodothyronine(T3) Elevation in a Euthyroid Patient With Paraproteinemia

Background: We report a rare case of a patient treated with levothyroxine for hypothyroidism who also had paraproteinemia and was found to have a clinically inconsistent elevation of T3 by RIA. Clinical Case: A 72 Year old African American female with a history of hypothyroidism and IgG kappa Multiple Myeloma (MM) was admitted to the hospital for altered mental status. Her hypothyroidism had been well controlled for years on a stable dose of levothyroxine 0.075mg daily. Review of systems were negative pertinent to thyroid dysfunction. Family history: negative for thyroid disease. On physical exam, an elderly female clinically euthyroid without palpable thyromegaly but was confused and disoriented. Initial Vital signs: BP 117/67, HR 62, RR 14, T 98, SpO2 99% on room air. BMI 19. EKG: normal sinus rhythm, CXR: normal, TSH: 6.27 (0.55-4.78 uIU/mL), total T3: &gt;600 (60-181ng/dL), total T4: 4.5 (3.2-12.6 ug/dL), FT4: 1.22 (0.89-1.76 ng/dL), hemoglobin: 6.6 (12-16 g/dL), hematocrit: 20.9 (38-47 %), Na: 132 (136-145 mmol/L), K: 4.0 (3.5-5.1 mmol/L), Cl: 104 (98-10/ mmol/L), BUN: 45 (20-31 mmol/L), creatinine: 2.8 (0.6-1.0 mg/dL), total protein: 10.1 (5.7-8.2 g/dL), albumin: 1.8 (3.4- 5.0 g/dL), A:G ratio: 0.22 (0.60-1.50 mmol/L). Serum protein electrophoresis revealed Gamma Globulin 5.8 (0.8-1.7 g/dL), Kappa 9270 mg/L (3.3 -19.4 mg/L) Lambda 9.3 (5.7-26.3mg/L), K/L 996.7 (0.26 -1.65), B2 - macroglobulin: 17.9 (ref: &lt;or= 2.51mg/L) which is consistent with an M- spike migrating in the gamma globulin region. Serum TPO, TG, TSI antibodies were negative. Further testing again reported Total T3 &gt;600 with normal reverse T3 21(8-25 ng/dL). Conclusion: Rare cases of factitious elevations of thyroid hormone have been reported in patients with elevated abnormal IgG or IgA proteins having high binding affinity for thyroid hormone.[1] This hypothyroid patient was clinically and biochemically euthyroid except for a dramatic but clinically inconsistent elevated total T3. She also had multiple myeloma with paraproteinemia (IgG Kappa M spike). The few cases reported to date have shown factitious elevation of either or both total T4 and total T3. In our case the factitious elevation was limited to total T3. We alert clinicians to be aware of factitious elevation of thyroid hormones due to high affinity binding to immunoglobulins. In our case this caused spurious elevation of total T3, but not total T4, in a patient with multiple myeloma and an IgG kappa M spike paraprotein. Reference: 1: Marianna Antonopoulou, Arnold Silverberg, “Spurious T3 Thyrotoxicosis Unmasking Multiple Myeloma”, Case Reports in Endocrinology, vol. 2013, Article ID 739302, 3 pages, 2013. https://doi.org/10.1155/2013/739302

Reverse T3 in Patients With Hypothyroidism, Helpful or a Waste of Time?

Background: Reverse T3 (rT3) is a biologically inactive form of T3 that is created by peripheral 5 deiodination of T4 by type 1 and type 3 deiodinases and may block T3 binding to the thyroid hormone receptor. As about 15% of patients on L-T4 replacement with a normalized TSH report continued fatigue and other hypothyroid symptoms, efforts are needed to understand why this occurs and how it can be corrected. Decades ago, endocrinologists realized that in severe illnesses, rT3 is often high and T3 is often low and termed this “sick euthyroid syndrome”. However, more recently, alternative doctors, including functional medicine doctors, have argued that high rT3 is detrimental and can block T3 from binding to the thyroid hormone receptor. Without peer-reviewed publications, these functional medicine doctors rely heavily on rT3 levels to treat patients that may have no other laboratory findings of hypothyroidism and often prescribe them L-T3-only preparations to try to lower the rT3. Also poorly characterized in the literature are the effects of hypercortisolism and hypopituitarism, both of which should modulate the expression of deiodinases to increase rT3. Hypotheses: 1) Patient rT3 levels will vary significantly with the type of thyroid medication taken. 2) Patient rT3 levels will be clinically significant in the management of patients on thyroid medications. 3) Hypercortisolism and hypopituitarism will increase rT3 levels. Methods: The most recent rT3 measurements were analyzed from 621 patients currently being managed by TCF. The upper limit of normal for rT3 at either Quest or LabCorp, which is usually 24.1 ng/dL was used as a cut-off for a high result and below 9.2 ng/dL as the low cut-off. Results: Elevate rT3 levels was seen in 3% of patients of patients not on thyroid replacement (5/143), seen in 8% of patients (17/203) taking desiccated thyroid. It was more prevalent in patients taking desiccated thyroid with synthetic T3 (27%, 7/26) or T4 (15%, 16/104) and was seen in 15% of patients (9/58) taking synthetic T4 alone. Changes were made to the amount or type of medications in 199 patients. Levels of rT3 levels were outside the normal range in 27% of these patients (54/199), being above normal range in 16% of these patients (32/199). Hypercortisolism was seen in 37 patients, 36 from Cushing’s disease, however above normal rT3 was seen in only 2 patients. Hypopituitarism was diagnosed in 22 patients, only one had above normal rT3 levels because they couldn’t afford their growth hormone replacement. Conclusion: Measuring rT3 may be helpful in patients who are already on thyroid treatments, and is of greater importance in patients taking synthetic preparations. It is not recommended in patients who are not taking thyroid medicine (even if experiencing hypercortisolism) or in patients with hypopituitarism that are taking adequate hormone replacement.

Physiological Role and Use of Thyroid Hormone Metabolites - Potential Utility in COVID-19 Patients

Thyroxine and triiodothyronine (T3) are classical thyroid hormones and with relatively well-understood actions. In contrast, the physiological role of thyroid hormone metabolites, also circulating in the blood, is less well characterized. These molecules, namely, reverse triiodothyronine, 3,5-diiodothyronine, 3-iodothyronamine, tetraiodoacetic acid and triiodoacetic acid, mediate both agonistic (thyromimetic) and antagonistic actions additional to the effects of the classical thyroid hormones. Here, we provide an overview of the main factors influencing thyroid hormone action, and then go on to describe the main effects of the metabolites and their potential use in medicine. One section addresses thyroid hormone levels in corona virus disease 19 (COVID-19). It appears that i) the more potently-acting molecules T3 and triiodoacetic acid have shorter half-lives than the less potent antagonists 3-iodothyronamine and tetraiodoacetic acid; ii) reverse T3 and 3,5-diiodothyronine may serve as indicators for metabolic dysregulation and disease, and iii) Nanotetrac may be a promising candidate for treating cancer, and resmetirom and VK2809 for steatohepatitis. Further, the use of L-T3 in the treatment of severely ill COVID-19 patients is critically discussed.

Association between albuminuria and thyroid function in patients with chronic kidney disease

Purpose The relationship between proteinuria and thyroid function remains controversial in patients with chronic kidney disease (CKD). We prospectively investigated the association between kidney and thyroid function in thyroid antibody-negative patients through all CKD stages. Methods We enrolled 184 nondialysis patients (mean age: 63.1 ± 16.9 years) without previous thyroid disease or thyroid-specific antibodies. Kidney function was assessed by estimating the glomerular filtration rate (eGFR) classified according KDIGO (CKD G1–5). Kidney damage was assessed by albuminuria (albumin-to-creatinine ratio, ACR) and classified as mild, moderate, or severe (ACR1: <300, ACR2: 300–3000, and ACR3: 3000 mg/g). To evaluate thyroid function, TSH, T4, fT4, T3, fT3, reverse T3 (rT3), and thyroxine-binding globulin (TBG) were measured. Results rT3 concentrations correlated negatively with albuminuria (r = −0.286, p < 0.001) and were significantly lower in patients with severe albuminuria than in those with mild or moderate albuminuria (ACR3: 0.28 vs. ACR2: 0.32 vs. ACR1: 0.36 nmol/l, p < 0.001). The severity of albuminuria revealed no impact on TSH, fT4, T3, fT3, and TBG. EGFR correlated with increasing T4, fT4, T3, fT3, and TBG (T4: r = 0.289, p < 0.01; fT4: r = 0.196, p < 0.01; T3: r = 0.408, p < 0.01; fT3: r = 0.390, p < 0.01) but not with rT3. Conclusions In thyroid antibody-negative patients presenting advanced CKD (stages 4 and 5), even severe kidney protein loss failed to influence thyroid hormone status. However, albuminuria severity correlated negatively with rT3, which was significantly lower in patients with albuminuria in the nephrotic range.