Amiodarone reversibly decreases sodium-iodide symporter mRNA expression at therapeutic concentrations and induces antioxidant responses at supraphysiological concentrations in cultured human thyroid follicles

Risks of Iodine Excess

Iodine is a micronutrient that is required for thyroid hormone synthesis. The iodide cycle in thyroid hormone synthesis consists of a series of transport, oxidation, organification, and binding/coupling steps in thyroid follicular cells. Common sources of iodine include the consumption of an iodine-rich diet or iodine fortified foods, the administration of amiodarone, iodine-containing supplements, or iodinated contrast media, and other miscellaneous sources. Methods to assess population iodine status include the measurement of urinary iodine concentrations, blood thyroglobulin levels, prevalence of elevated neonatal TSH levels, and thyroid volume. Although excessive iodine intake or exposure is generally well tolerated, an acute iodine load may result in thyroid dysfunction (hypothyroidism or hyperthyroidism) in certain susceptible individuals due to the failure to escape from the Wolff-Chaikoff effect and to the Jod-Basedow phenomenon, respectively. In this review, we discuss the associations between excessive iodine intake or exposure, with particular focus on iodinated contrast media as a common source of excess iodine in healthcare settings, and risks of incident thyroid dysfunction. We also summarize the risks of iodine excess in vulnerable populations and review current guidelines regarding the screening and monitoring of iodinated contrast-induced thyroid dysfunction. Finally, we discuss the long-term potential nonthyroidal health risks associated with iodine excess and suggest the need for more data to define safe upper limits for iodine intake, particularly in high-risk populations.

Inverse Association between Metformin and Amiodarone-Associated Extracardiac Adverse Events

Background: The association between metformin and amiodarone-induced adverse events was examined using spontaneous adverse event database. Additionally, the association between other antidiabetic drugs and amiodarone-induced adverse events were also examined. Methods: A total of 6,153,696 reports from the first quarter of 2004 through the fourth quarter of 2015 were downloaded from the US Food and Drug Administration adverse event reporting system. Reporting odds ratio (ROR) and information component (IC) were used to detect associations between antidiabetic drugs and amiodarone-associated adverse events. Additionally, subset data analysis was performed to investigate whether the use of antidiabetic drugs further increased or decreased the risk of adverse events in patients receiving amiodarone therapy. Next, the RORs were adjusted for coadministered antidiabetic drugs using logistic regression analysis. Results: By whole dataset analysis, significant inverse associations were found between metformin and interstitial lung disease (ROR 0.84, 95% confidence interval [CI] 0.79-0.90; IC -0.24, 95% CI -0.33 to -0.15). In the subset data analysis, metformin (ROR 0.62, 95%CI 0.43-0.89; IC -0.63, 95%CI -1.14 to -0.11), sulfonylureas (ROR 0.53, 95%CI 0.32-0.85; IC -0.85, 95%CI -1.53 to -0.17), and dipeptidyl peptidase-4 (DPP-4) inhibitors (ROR 0.25, 95%CI 0.08-0.78; IC -1.66, 95%CI -3.08 to -0.23) were inversely associated with hyperthyroidism. Additionally, metformin (ROR 0.43, 95%CI 0.33-0.57; IC -1.09, 95%CI -1.49 to -0.69), sulfonylureas (ROR 0.64, 95%CI 0.48-0.86; IC -0.59, 95%CI -1.00 to -0.17), and DPP-4 inhibitors (ROR 0.47, 95%CI 0.27-0.81; IC -0.99, 95%CI -1.76 to -0.22) were inversely associated with interstitial lung disease. In the logistic regression analyses, DPP-4 inhibitors (adjusted ROR 0.32, 95% CI 0.10-1.00) and metformin (adjusted ROR 0.46, 95% CI 0.34-0.62) were inversely associated with amiodarone-associated hyperthyroidism and interstitial lung disease, respectively. Conclusion: Metformin is a candidate drug to reduce the risk of amiodarone-induced hyperthyroidism and interstitial lung disease.

2018 European Thyroid Association (ETA) Guidelines for the Management of Amiodarone-Associated Thyroid Dysfunction

Treatment with amiodarone is associated with changes in thyroid function tests, but also with thyroid dysfunction (amiodarone-induced hypothyroidism, AIH, and amiodarone-induced thyrotoxicosis, AIT). Both AIH and AIT may develop in apparently normal thyroid glands or in the presence of underlying thyroid abnormalities. AIH does not require amiodarone withdrawal, and is treated with levothyroxine replacement if overt, whereas subclinical forms may be followed without treatment. Two main types of AIT are recognized: type 1 AIT (AIT 1), a form of iodine-induced hyperthyroidism occurring in nodular goitres or latent Graves disease, and type 2 AIT (AIT 2), resulting from destructive thyroiditis in a normal thyroid gland. Mixed/indefinite forms exist due to both pathogenic mechanisms. AIT 1 is best treated with thionamides that may be combined for a few weeks with sodium perchlorate to make the thyroid gland more sensitive to thionamides. AIT 2 is treated with oral glucocorticoids. Once euthyroidism has been restored, AIT 2 patients are followed up without treatment, whereas AIT 1 patients should be treated with thyroidectomy or radioiodine. Mixed/indefinite forms of AIT are treated with thionamides. Oral glucocorticoids can be added from the beginning if a precise diagnosis is uncertain, or after a few weeks if response to thionamides alone is poor. The decision to continue or to stop amiodarone in AIT should be individualized in relation to cardiovascular risk stratification and taken jointly by specialist cardiologists and endocrinologists. In the presence of rapidly deteriorating cardiac conditions, emergency thyroidectomy may be required for all forms of AIT.

The Pathology of Hyperthyroidism

This article reviews those pathologic lesions which are associated with clinical and/or biochemical hyperthyroidism. Beginning with the descriptive pathology of classical Graves' disease and the less common toxic nodular goiter and hyper-functioning thyroid nodules, this paper describes the effects of non-thyroidal hormones, glandular function (including pituitary and hypothalamic lesions), ectopic production of thyroid stimulating proteins by non-thyroidal neoplasms, exogenous drug reactions causing hyper-function and finally conditions associated with a mechanic- destructive cause of hyperthyroidism.

Risk factors for amiodarone-induced thyroid dysfunction in Japan

Background

Amiodarone is associated with a number of significant adverse effects, including elevated transaminase levels, pulmonary fibrosis, arrhythmia, and thyroid dysfunction. Although thyroid dysfunction is considered to be a common and potentially serious adverse effect of amiodarone therapy, the exact pathogenesis remains unknown because of its complex manifestations. Therefore, the prevalence of, and risk factors for, amiodarone-induced thyroid dysfunction in Japanese patients were investigated in the present study.

Methods

A retrospective analysis of patients treated with amiodarone between January 2012 and December 2013 was performed. A total of 317 patients with euthyroidism, or subclinical hyperthyroidism or hypothyroidism, were enrolled in this study.

Results

After being treated with amiodarone, 30 (9.5%) and 60 patients (18.9%) developed amiodarone-induced hyperthyroidism and amiodarone-induced hypothyroidism, respectively. Ten (33.3%) patients with amiodarone-induced hyperthyroidism and 40 (66.6%) with amiodarone-induced hypothyroidism were diagnosed within two years of the initiation of amiodarone therapy. Dilated cardiomyopathy (DCM) [Adjusted odds ratio (OR) 3.30 (95% confidence interval (CI): 1.26–8.90)], and cardiac sarcoidosis [Adjusted OR 6.47 (95% CI: 1.60–25.77)] were identified as predictors of amiodarone-induced hyperthyroidism. The baseline free thyroxine (T4) level [Adjusted OR 0.13 (95% CI: 0.03–0.68)], and thyroid-stimulating hormone (TSH) level [Adjusted OR1.47 (95% CI: 1.26–1.74)] were identified as predictors of amiodarone-induced hypothyroidism.

Conclusion

DCM and cardiac sarcoidosis were identified as risk factors for amiodarone-induced hyperthyroidism. Risk factors for amiodarone-induced hypothyroidism included higher baseline TSH level and lower baseline free T4 level, suggesting that subclinical hypothyroidism may be a potential risk factor for the development of amiodarone-induced hypothyroidism.

Endoplasmic reticulum stress as a novel mechanism in amiodarone-induced destructive thyroiditis

CONTEXT

Amiodarone (AMIO) is one of the most effective antiarrhythmic drugs available; however, its use is limited by a serious side effect profile, including thyroiditis. The mechanisms underlying AMIO thyroid toxicity have been elusive; thus, identification of novel approaches in order to prevent thyroiditis is essential in patients treated with AMIO.

OBJECTIVE

Our aim was to evaluate whether AMIO treatment could induce endoplasmic reticulum (ER) stress in human thyroid cells and the possible implications of this effect in AMIO-induced destructive thyroiditis.

RESULTS

Here we report that AMIO, but not iodine, significantly induced the expression of ER stress markers including Ig heavy chain-binding protein (BiP), phosphoeukaryotic translation initiation factor 2α (eIF2α), CCAAT/enhancer-binding protein homologous protein (CHOP) and spliced X-box binding protein-1 (XBP-1) in human thyroid ML-1 cells and human primary thyrocytes. In both experimental systems AMIO down-regulated thyroglobulin (Tg) protein but had little effect on Tg mRNA levels, suggesting a mechanism involving Tg protein degradation. Indeed, pretreatment with the specific proteasome inhibitor MG132 reversed AMIO-induced down-regulation of Tg protein levels, confirming a proteasome-dependent degradation of Tg protein. Corroborating our findings, pretreatment of ML-1 cells and human primary thyrocytes with the chemical chaperone 4-phenylbutyric acid completely prevented the effect of AMIO on both ER stress induction and Tg down-regulation.

CONCLUSIONS

We identified ER stress as a novel mechanism contributing to AMIO-induced destructive thyroiditis. Our data establish that AMIO-induced ER stress impairs Tg expression via proteasome activation, providing a valuable therapeutic avenue for the treatment of AMIO-induced destructive thyroiditis.

Iodine-induced thyroid dysfunction

PURPOSE OF REVIEW

To summarize the mechanisms of iodine-induced hypothyroidism and hyperthyroidism, identify the risk factors for thyroid dysfunction following an iodine load, and summarize the major sources of excess iodine exposure.

RECENT FINDINGS

Excess iodine is generally well tolerated, but individuals with underlying thyroid disease or other risk factors may be susceptible to iodine-induced thyroid dysfunction following acute or chronic exposure. Sources of increased iodine exposure include the global public health efforts of iodine supplementation, the escalating use of iodinated contrast radiologic studies, amiodarone administration in vulnerable patients, excess seaweed consumption, and various miscellaneous sources.

SUMMARY

Iodine-induced thyroid dysfunction may be subclinical or overt. Recognition of the association between iodine excess and iodine-induced hypothyroidism or hyperthyroidism is important in the differential diagnosis of patients who present without a known cause of thyroid dysfunction.

Amiodarone and the thyroid: a 2012 update

Amiodarone-induced thyroid dysfunction occurs in 15-20% of amiodarone-treated patients. Amiodarone-induced hypothyroidism (AIH) does not pose relevant problems, is easily controlled by L-thyroxine replacement, and does not require amiodarone withdrawal. Most frequently AIH develops in patients with chronic autoimmune thyroiditis. Amiodarone- induced thyrotoxicosis (AIT) is most frequently due to destructive thyroiditis (type 2 AIT) causing discharge of thyroid hormones from the damaged, but otherwise substantially normal gland. Less frequently AIT is a form of hyperthyroidism (type 1 AIT) caused by the iodine load in a diseased gland (nodular goiter, Graves' disease). A clearcut differentiation between the two main forms is not always possible, despite recent diagnostic advances. As a matter of fact, mixed or indefinite forms do exist, contributed to by both thyroid damage and increased thyroid hormone synthesis. Treatment of type 1 (and mixed forms) AIT is based on the use of thionamides, a short course of potassium perchlorate and, if treatment is not rapidly effective, oral glucocorticoids. Glucocorticoids are the first-line treatment for type 2 AIT. Amiodarone should be discontinued, if feasible from a cardiac standpoint. Continuation of amiodarone has recently been associated with a delayed restoration of euthyroidism and a higher chance of recurrence after glucocorticoid withdrawal. Whether amiodarone treatment can be safely reinstituted after restoration of euthyroidism is still unknown. In rare cases of AIT resistance to standard treatments, or when a rapid restoration of euthyroidism is advisable, total thyroidectomy represents a valid alternative. Radioiodine treatment is usually not feasible due to the low thyroidal iodine uptake.

Amiodarone and thyroid

Assessment of TSH and TPO-Ab before starting amiodarone (AM) treatment is recommended. The usefulness of periodic TSH measurement every 6 months during AM treatment is limited by the often sudden explosive onset of AIT, and the spontaneous return of a suppressed TSH to normal values in half of the cases. AM-induced hypothyroidism develops rather early after starting treatment, preferentially in iodine-sufficient areas and in females with TPO-Ab; it is due to failure to escape from the Wolff-Chaikoff effect, resulting in preserved radioiodine uptake. AM-induced thyrotoxicosis (AIT) occurs at any time during treatment, preferentially in iodine-deficient regions and in males. AIT can be classified in type 1 (iodide-induced thyrotoxicosis, best treated by potassium perchlorate in combination with thionamides and discontinuation of AM) and type 2 (destructive thyrotoxicosis, best treated by prednisone; discontinuation of AM may not be necessary). AIT is associated with a higher rate of major adverse cardiovascular events (especially of ventricular arrhythmias). Uncertainty continues to exist with respect to the feasibility of continuation of AM despite AIT, the appropriate methods to distinguish between AIT type 1 and 2 as well as the advantages of AIT classification into subtypes in view of possible mixed cases, and the best policy when AM needs to be restarted.

Association of polymorphism at position 49 in exon 1 of the cytotoxic T-lymphocyte-associated factor 4 gene with Graves' disease refractory to medical treatment, but not with amiodarone-associated thyroid dysfunction

BACKGROUND

Recently, the G allele of the cytotoxic T-lymphocyte-associated factor 4 (CTLA-4) exon 1 single-nucleotide polymorphism (CTLA-4 A/G(49)) has been identified as the most informative marker in patients with Graves' disease. Patients with the G/G genotype are refractory to medical treatment and frequently relapse after discontinuation of antithyroid drugs. Therefore, we analyzed CTLA-4 A/G(49) in patients who had been treated with (131)I. Further, a preliminary report has suggested that amiodarone-associated thyroid dysfunction (AATD) has a relationship with human leukocyte antigen (HLA) class I and class II.

METHOD

CTLA-4 genotypes in exon 1 (A/G(49)) and CT60 were analyzed in 415 Japanese patients with Graves' disease and 65 patients with AATD.

RESULTS

The frequencies of the G alleles and G/G genotype at the both polymorphisms were significantly higher in Graves' patients compared with normal subjects. Compared with CT60, the frequencies of the G alleles and G/G genotypes at the A/G(49) were more significantly higher in patients with persistently positive thyrotropin receptor antibody despite >5 years of antithyroid drug therapy, compared with those whose thyrotropin receptor antibody became negative in <5 years (p < 0.0001). Consequently, the frequencies of the G/G genotype and G allele at the A/G(49) were also significantly higher in patients with Graves' disease who received (131)I therapy (p < 0.05). However, there was no significant difference in the A/G polymorphisms in the 65 patients with AATD.

CONCLUSIONS

The G/G genotype in exon 1 (A/G(49)) is frequently expressed in Graves' disease patients who are refractory to antithyroid drug treatment. Therefore, the G/G genotype in A/G(49) would be a useful predictor of Graves' patients who are suitable for radioiodine therapy. Although the number of analyzed patients was small, our preliminary data suggest that the CTLA-4 gene polymorphisms might be unassociated with AATD.

Stimulating parathyroid cell proliferation and PTH release with phosphate in organ cultures obtained from patients with primary and secondary hyperparathyroidism for a prolonged period

The pathogenesis of primary hyperparathyroidism (I degrees -HPT) and secondary hyperparathyroidism (II degrees -HPT) remains to be elucidated. To characterize their pathophysiology, we investigated the effects of calcium and phosphate on cell proliferation and PTH release in an organ culture of parathyroid tissues. Dissected parathyroid tissues obtained from patients with I degrees -HPT (adenoma) or II degrees -HPT (nodular hyperplasia) were precultured on a collagen-coated membrane for 1-4 week. After changing the medium for one containing various concentrations of phosphate, PTH release and [(3)H]thymidine incorporation were studied. In contrast to dispersed parathyroid cells cultured in a monolayer, calcium decreased PTH release in a concentration-dependent manner in parathyroid tissues. Furthermore, when parathyroid tissues obtained from II degrees -HPT were precultured for 1-4 weeks, PTH release and parathyroid cell proliferation were significantly increased in high-phosphate medium. These phosphate effects were also observed to a lesser extent in parathyroid tissues obtained from I degrees -HPT, but there was no significant difference between I degrees -HPT and II degrees -HPT. Microarray analyses revealed that mRNA levels of PTH, CaSR, and VDR were well preserved, and several growth factors (e.g. TGF-beta1-induced protein) were abundantly expressed in II degrees -HPT. Using organ cultures of hyperparathyroid tissues, in which PTH release and CaSR are well preserved for a prolonged period, we have demonstrated that phosphate stimulates parathyroid cell proliferation not only in II degrees -HPT but also in I degrees -HPT. Although the mechanism responsible for phosphate-induced cell proliferation remains to be elucidated, our in vitro findings suggest that both parathyroid tissues preserve to some extent a physiological response system to hyperphosphatemia as observed in normal parathyroid cells.

Differential diagnosis and appropriate treatment of four thyrotoxic patients with Graves' disease required to take amiodarone due to life-threatening arrhythmia

We report the treatment of four thyrotoxic patients. Two were cases of type I amiodarone-induced thyrotoxicosis (AIT) treated with methimazole. The third Graves' disease patient, who became hypothyroid 25 years after subtotal thyroidectomy, developed type II AIT. Furthermore, one case with heart failure and ventricular tachycardia, who developed an adverse reaction to antithyroid agents and was prescribed amiodarone, underwent total thyroidectomy. The clinical course was uneventful, and the patient is doing well. Since amiodarone contains a large amount of iodine, it is frequently difficult to make a differential diagnosis. Surgical treatment of Graves' disease patients is recommended when immediate control of hyperthyroidism and heart failure is required.