Iodine and lithium-induced hypothyroidism. Documentation of synergism

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Trace elements and the thyroid

Trace elements, such as iodine and selenium (Se), are vital to human health and play an essential role in metabolism. They are also important to thyroid metabolism and function, and correlate with thyroid autoimmunity and tumors. Other minerals such as iron (Ir), lithium (Li), copper (Co), zinc (Zn), manganese (Mn), magnesium (Mg), cadmium (Cd), and molybdenum (Mo), may related to thyroid function and disease. Normal thyroid function depends on a variety of trace elements for thyroid hormone synthesis and metabolism. These trace elements interact with each other and are in a dynamic balance. However, this balance may be disturbed by the excess or deficiency of one or more elements, leading to abnormal thyroid function and the promotion of autoimmune thyroid diseases and thyroid tumors.The relationship between trace elements and thyroid disorders is still unclear, and further research is needed to clarify this issue and improve our understanding of how trace elements mediate thyroid function and metabolism. This paper systematically reviewed recently published literature on the relationship between various trace elements and thyroid function to provide a preliminary theoretical basis for future research.

A review of species differences in the control of, and response to, chemical-induced thyroid hormone perturbations leading to thyroid cancer

This review summarises the current state of knowledge regarding the physiology and control of production of thyroid hormones, the effects of chemicals in perturbing their synthesis and release that result in thyroid cancer. It does not consider the potential neurodevelopmental consequences of low thyroid hormones. There are a number of known molecular initiating events (MIEs) that affect thyroid hormone synthesis in mammals and many chemicals are able to activate multiple MIEs simultaneously. AOP analysis of chemical-induced thyroid cancer in rodents has defined the key events that predispose to the development of rodent cancer and many of these will operate in humans under appropriate conditions, if they were exposed to high enough concentrations of the affecting chemicals. There are conditions however that, at the very least, would indicate significant quantitative differences in the sensitivity of humans to these effects, with rodents being considerably more sensitive to thyroid effects by virtue of differences in the biology, transport and control of thyroid hormones in these species as opposed to humans where turnover is appreciably lower and where serum transport of T4/T3 is different to that operating in rodents. There is heated debate around claimed qualitative differences between the rodent and human thyroid physiology, and significant reservations, both scientific and regulatory, still exist in terms of the potential neurodevelopmental consequences of low thyroid hormone levels at critical windows of time. In contrast, the situation for the chemical induction of thyroid cancer, through effects on thyroid hormone production and release, is less ambiguous with both theoretical, and actual data, showing clear dose-related thresholds for the key events predisposing to chemically induced thyroid cancer in rodents. In addition, qualitative differences in transport, and quantitative differences in half life, catabolism and turnover of thyroid hormones, exist that would not operate under normal situations in humans.

Gender differences in thyroid system function: relevance to bipolar disorder and its treatment

OBJECTIVES

Thyroid hormones play a critical role in the functioning of the adult brain, and thyroid diseases impair both mood and cognition. This paper reviews gender differences in thyroid system function that are relevant to the diagnosis and treatment of bipolar disorder.

METHODS

The study comprised a comprehensive literature review of gender differences in thyroid disease that are pertinent to mood disorders.

RESULTS

The prevalence of thyroid disease was found to be much higher in females than males, and to increase with age. The most commonly detected abnormality was subclinical hypothyroidism, which was found to occur in up to 20% of postmenopausal women. Females also had higher rates of thyroid autoimmunity. Individuals at risk for thyroid disease, such as adult females, may have had less ability to compensate for additional challenges to thyroid metabolism, including lithium treatment. Thyroid abnormalities were associated with a poorer response to standard treatments for mood disorders. Females with treatment-resistant mood disorders may have responded better than males to adjunctive therapy with thyroid hormones.

CONCLUSIONS

Disturbances of thyroid system function, which occur commonly in females, may complicate the diagnosis and treatment of mood disorders. In particular, this is clinically relevant during lithium treatment because lithium may impair vital thyroid metabolic pathways secondary to its anti-thyroid activity.

Lithium and other elements in scalp hair of residents of Tokyo Prefecture as investigational predictors of suicide risk

The high suicide rates in Japan and several reports of inverse associations of suicide rates with the levels of lithium (Li) in drinking water prompted determinations of Li along with other elements in samples of scalp hair of 100 male and 100 female residents of Tokyo Prefecture. In more than half of the samples of both genders, Li levels were below the instrumental detection limit or below or the lower limit of the laboratory reference ranges. Among other elements, the concentrations namely of cobalt were also frequently below the laboratory reference range, suggesting that low circulating levels of vitamin B(12) were common in this study population. As vitamin B(12) deficiency is associated with depression and other psychiatric conditions, and there is evidence of interactions between Li and vitamin B(12), Li deficiency as well as suboptimal vitamin B(12) status must be considered as potential suicide risk factors. In view of its established positive effects on mood and brain function, an adequate supply of selenium (Se) is important as well. Although the analytical results suggested that the Se status of the subjects was generally adequate, as seafood was a major dietary source of Se, much of it was actually sequestered by mercury and only a fraction was bio-available. In addition, the hair samples were found to contain not insignificant levels of As, Cd, Ni, and Pb, arising from the adventitious presence of these elements in foods and the environment. As these elements also interact with Se in vivo and are known to adversely affect mood and behavior, in investigational studies, subjects at risk need to be evaluated also with respect to these elements.

Lithium and thyroid

One in 200 people receive lithium for treatment of bipolar disorder. The common clinical side effects of the drug are goitre in up to 40% and hypothyroidism in about 20%. Lithium increases thyroid autoimmunity if present before therapy. Treatment with levothyroxine is effective and lithium therapy should not be stopped. Lithium may cause hyperthyroidism due to thyroiditis or rarely Graves' disease. As lithium inhibits thyroid hormone release from the thyroid gland it can be used as an adjunct therapy in the management of severe hyperthyroidism. It also increases thyroidal radioiodine retention and may be effective in reducing administered activity in hyperthyroidism. There is no clinical benefit of lithium therapy in thyroid cancer. More research is required on the cellular proliferative effects of lithium as well as its impact on the immune system.

Thyrotoxicosis in a patient treated with lithium carbonate for mental disease

In recent years a few cases of hyperthyroidism and several of hypothyroidism which developed during lithium therapy have been described. We give an account of a case of hyperthyroidism, due to painless thyroiditis in a patient on long-term lithium therapy.

A randomized controlled trial to evaluate the adjuvant effect of lithium on radioiodine treatment of hyperthyroidism

OBJECTIVE

To evaluate the role of lithium (Li) as an adjuvant in radioiodine therapy of hyperthyroidism.

METHODS

A randomized controlled trial was carried out on 350 hyperthyroid patients with a mean follow-up period of 32.3 +/- 9.8 months (range, 12-60 months). The patients were randomized into two groups with 175 patients in each group: (1) radioiodine group (controls)-no lithium was given to these patients at any stage of their treatment and (2) radioiodine and lithium group (Li group)-lithium carbonate, 300 mg three times a day, for 3 weeks starting on the day of radioiodine administration. All patients were made euthyroid with antithyroid drugs prior to radioiodine therapy.

RESULTS

Mean age was 41.8 +/- 11.5 years (range, 18-71) in the control group and 41.8 +/- 12.2 years (range, 19-73) in the Li group. Mean first dose and cumulative dose of (131)I were 229 +/- 85 MBq and 326 +/- 204 MBq in controls and 233 +/- 110 MBq and 344 +/- 281 MBq in the Li group. Average number of radioiodine therapy administered was the same (1.4) in both groups. The cure rate (euthyroid plus hypothyroid) after the first dose of radioiodine in the control and the lithium groups was 68.4% and 68.9%, respectively (p = ns). The overall cure rate at the end of the study was also the same in both groups (96.7% and 96.3%, respectively). Even in patients with a rapidly discharging gland or in patients with a large goiter, no significant statistical difference was observed in radioiodine therapy outcome between the two groups. Ten percent of the patients complained of mild to moderate side effects of lithium.

CONCLUSION

The role of lithium as an adjuvant in radioiodine therapy of hyperthyroidism is insignificant.

Review of clinically important drug interactions with lithium

The therapeutic dosage of lithium is close to the toxic level, and drugs reducing the renal clearance of lithium can produce the most serious adverse effects. When used in combination with psychiatric drugs affecting mood, the therapeutic potential of lithium may be enhanced, and earlier concern regarding possible neurotoxic interactions with neuroleptics appear poorly substantiated. A number of specific interactions of low incidence have also been reported which should be borne in mind when new medications are introduced. The ready availability of lithium concentration monitoring in body fluids makes it possible to alter the effects of some potentially interactive drugs that may still need to be given in combination with lithium.

The pathology of autoimmune thyroid disease: a review

Lymphocytic infiltration of the thyroid gland is the pathologic hallmark of autoimmune thyroid disease. Lymphoid cells are seen in the stroma of glands affected by Graves' disease. However, large lymphoid infiltrates are characteristic of that spectrum of diseases conveniently termed chronic lymphocytic thyroiditis. In this review, the pathology of the various subtypes of chronic thyroiditis is enumerated, including recently defined lesions, i.e., painless thyroiditis, thyroiditis associated with interleukin chemotherapy, and peritumor thyroiditis are reviewed. The unifying morphologic characteristics seen in these conditions are discussed.

Iodine and thyroid disease

Iodine is a requisite substrate for the synthesis of the thyroid hormones, the minimum daily requirement being about 50 micrograms. An autoregulatory mechanism within the thyroid serves as the first line of defense against fluctuations in the supply of iodine and also permits escape from the inhibition of hormone synthesis that a very large quantity of iodine induces (Wolff-Chaikoff effect and escape therefrom). Environmental iodine deficiency continues to be a significant public health problem worldwide, compounded in some geographic regions by the presence of other goitrogens in some staple foods. The pathologic consequences of severe iodine deficiency include endemic goiter, endemic cretinism, increased fetal and infant mortality, and an increased prevalence in the community of cognitive and neuromotor disabilities. The implementation of an iodization program prevents endemic cretinism and reduces the frequency of the other pathologic consequences of iodine deficiency. Iodine excess results principally from the use of iodine-containing medicinal preparations or radiographic contrast media. The pathologic consequences of iodine excess will ensue only when thyroid autoregulation is defective, in that escape from the Wolff-Chaikoff effect cannot occur, or when autoregulation is absent. Defective autoregulation characterizes the fetal and neonatal thyroid, Hashimoto's thyroiditis, radioiodine or surgically treated Graves' hyperthyroidism, the thyroid of patients with cystic fibrosis, and the thyroid that has been exposed to weak inhibitors of the organic binding of iodine. In these circumstances, the provision of excess iodine may lead to iodide goiter with or without hypothyroidism. Absent autoregulation may be a feature of longstanding multinodular goiter, and the provision of excess iodine in this circumstance may induce thyrotoxicosis (Jod-Basedow disease). The pathologic consequences of iodine excess will resolve when the source of iodine has been dissipated. In addition to its role in reversing iodine deficiency, iodine is used as adjunctive therapy for hyperthyroidism. By inhibiting the proteolytic release of iodothyronines from thyroglobulin, it induces a prompt slowing of thyroid hormone secretion. This effect is exploited in the treatment of thyrotoxic crisis or severe thyrocardiac disease. Iodine also reduces thyroid cellularity and vascularity and therefore is used in the preparation of the patient for thyroidectomy. Finally, by exploiting the failure of escape from the Wolff-Chaikoff effect, iodine may also be used in the early management of radioiodine-treated Graves' hyperthyroidism.

Review: thyroid function in psychiatric illness

The development of highly sensitive immunometric assays for thyroid-stimulating hormone (TSH) has provided increased understanding of thyroid hormone regulation but, paradoxically, has contributed to a kaleidoscopic complexity of thyroid function test variability in hospitalized patients with nonthyroidal illness (NTI). In primary hypothyroidism, an elevated TSH is the most sensitive chemical index available, although early cases may show a hyperresponse of TSH to thyrotropin-releasing hormone (TRH) stimulation when the TSH is still within the normal range. The ability of the new TSH assays to discriminate between normal and low levels now allows the diagnosis of thyrotoxicosis to be confirmed by a suppressed TSH in the presence of elevated serum thyroxine (T4) and/or triiodothyronine (T3). The TRH stimulation test is virtually obsolete for the diagnosis of thyrotoxicosis but remains of much interest in the investigation of psychiatric syndromes. Approximately 25% of patients with depression have a blunted TSH response (a rise of less than 5 microU/mL) that differs from thyrotoxicosis, wherein the TSH response is suppressed under 1 microU/mL. The cause of the blunted TSH is uncertain but is not due to hyperthyroidism. In contrast, close to 15% may have a TSH hyperresponse to TRH and/or elevated antithyroid antibodies. Thyroid hormone treatment may benefit the depression in some of these cases. In the sick thyroid state of nonthyroidal illness, a low T3 level is the initial manifestation. In more severe cases, the T4 also falls, the free T4 level in this situation is variable, both normal and low levels being reported from different laboratories. A diagnosis of hypothyroidism requiring treatment with thyroid hormone therapy is unlikely unless there is a concomitant lowfree T4 and elevated TSH in a patient who is not in the process of recovery. In acute psychiatric admissions, there is a high frequency of hyperthyroxinemia. The TSH in these cases is generally either normal or high, suggesting central activation of the hypothalamic-pituitary-thyroid axis. In most instances, the thyroid function tests normalize within 2 weeks, and treatment directed toward the thyroid gland is not indicated. Suppressed TSH levels, usually associated with a normal free T4, has also been described in such patients. Finally, various medications utilized in psychiatric practice have diverse effects on thyroid function and can cause diagnostic difficulty. These include lithium, phenytoin sodium, and carbamazepine, and their effects are reviewed.

Effects of low dose oral iodide supplementation on thyroid function in normal men

Previous studies have demonstrated that short-term oral iodide administration, in doses ranging from 1500 micrograms to 250 mg/day, has an inhibitory effect on thyroid hormone secretion in normal men. As iodide intake in the USA may be as high as 800 micrograms/d, we investigated the effects of very low dose iodide supplementation on thyroid function. Thirty normal men aged 22-40 years were randomly assigned to receive 500, 1500, and 4500 micrograms iodide/day for 2 weeks. Blood was obtained on days 1 and 15 for measurement of serum T4, T3, T3-charcoal uptake, TSH, protein-bound iodide (PBI) and total iodide, and 24 h urine samples were collected on these days for measurement of urinary iodide excretion. TRH tests were performed before and at the end of the period of iodide administration. Serum inorganic iodide was calculated by subtracting the PBI from the serum total iodide. We found significant dose-related increases in serum total and inorganic iodide concentrations, as well as urinary iodide excretion. The mean serum T4 concentration and free T4 index values decreased significantly at the 1500 micrograms/day and 4500 micrograms/day doses. No changes in T3-charcoal uptake or serum T3 concentration occurred at any dose. Administration of 500 micrograms iodide/day resulted in a significant increase (P less than 0.005) in the serum TSH response to TRH, and the two larger iodide doses resulted in increases in both basal and TRH-stimulated serum TSH concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

The electrogenic, Na+-dependent I- transport system in plasma membrane vesicles from thyroid glands

Using vesicles from the plasma membrane of hog thyroid, we have characterized its Na+-dependent I- transport system. We have found it to be totally Na+ dependent; K+ cannot substitute and Li+ can partially substitute for Na+; the Na+:I- flux ratio is larger than one; the system is electrogenic, being stimulated by a delta psi negative inside the vesicles. A number of large, lipophilic anions are fully-competitive inhibitors of Na+-dependent I- uptake; the closer their atomic radii are to that of iodine, the smaller their Ki values.

Thyroid gland function and pituitary TSH reserve in patients with cystic fibrosis

In view of the reported enhanced sensitivity to iodide-induced hypothyroidism in patients with cystic fibrosis, studies were carried out to determine the possible mechanism of this abnormality. The intrathyroid organification of iodide, as assessed by the iodide-perchlorate discharge test, was normal in patients with cystic fibrosis, strongly suggesting that an organification defect was not present. The serum TSH response to TRH was not significantly different from the response in normal children and adolescents. Serum T4 concentration was normal whereas that of T3 was decreased in patients with cystic fibrosis, strongly suggesting decreased peripheral conversion of T4 to T3, as commonly occurs in nonthyroid illness. Our findings do not delineate the mechanism whereby patients with cystic fibrosis develop iodide-induced hypothyroidism.

Suppression of thyroid radioiodine uptake by various doses of stable iodide

We studied the effect of various doses of sodium iodide on thyroid radioiodine uptake in euthyroid volunteers by giving single doses of 10, 30, 50, and 100 mg and then daily doses of 10, 15, 30, 50, or 100 mg for 12 days thereafter. All single doses above 10 mg suppressed 24-hour thyroid uptake of 123I to 0.7 to 1.5 per cent. Continued daily administration of 15 mg of iodide or more resulted in values consistently below 2 per cent. A small but statistically significant fall in serum thyroxine (T4) and triiodothyronine (T3) and a rise in serum thyrotropin (TSH) concentrations were observed after eight and 12 days of iodide treatment. These data suggest that the thyroid uptake of radioactive iodine can be markedly suppressed by single-dose administration of 30 mg of stable iodide and that suppression can be maintained with daily doses of at least 15 mg. This study provides guidelines for stable iodide prophylaxis in the event of exposure to radioactive iodine.

Effects of iodides on the hypothalamic-pituitary-thyroid axis in neurological endemic cretinism: evidence for compensated thyroidal failure in adult life

Thyroid function studies, performed after iodide administration to five patients with neurological endemic cretinism, were indicative of hypothyroidism. All five subjects had either a low serum thyroxine (T4) or a high basal thyrotrophin (TSH) level and a clearly exaggerated TSH response to thyrotrophin releasing hormone (TRH). These findings are in sharp contrast with those we have previously described in goitrous patients without cretinism from the same geographical area. One interpretation of our observations is that there is an underlying mild defect in thyroid hormone synthesis in endemic cretinism predisposing to iodine induced hypothyroidism.

No inhibition by Li+ of thyroxine monodeiodination to 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine (reverse triiodothyronine)

The possibility that lithium affects the conversion of thyroxine to 3,5,3"-triiodothyronine and 3,3',5'-triiodothyronine (reverse triiodothyronine) was studied by measurement of the serum concentractions of these parameters in five patients during the first week of lithium therapy. In three patients there was a decrease in serum thyroxine concentration and a slightly less pronounced decrease in that of serum 3,5,3'-triiodothyronine. In two patients, who also received L-tryptophan or flupentixol, no change was noted in the concentrations of these compounds. There was no increase in serum 3,3',5'-triiodothyronine concentration in any of the patients. No systematic change was found in the serum concentrations of thyrotropin or unsaturated thyroid-hormone binding proteins. The results obtained do not support the contention that lithium should inhibit the monodeiodenation of thyroxine to its active and inactive metabolites.

Adverse effects of iodides on thyroid function

The administration of pharmacologic quantities of iodine such as iodides for the treatment of pulmonary disease, organic iodine present in medications and x-ray contrast dyes, and the ingestion of iodine-rich natural foods, may result in goiter, hypothyroidism, or hyperthyroidism, especially in patients with underlying thyroid disease. Medications containing iodide may induce hypothroidism in euthyroid patients with Hashimoto's thyroiditis, 131I or surgically treated Graves' disease, or following hemithyroidectomy for nodules; and they may induce hyperthyroidism in patients with endemic iodine-deficient goiter, autonomous nodules or nontoxic nodular goiter, or in patients recently treated with antithyroid drugs for Graves' disease. Rarely, hypothyroidism or hyperthyroidism may develop in patients with completely normal thyroid function during administration of iodide. The etiology of iodide-induced goiter and hypothyroidism in patients with cystic fibrosis remains obscure. Iodide-induced myxedema may also occur in patients receiving drugs which alter thyroid function, such as lithium, phenazone, and sulfisoxazole. Finally, iodides do have a role in the treatment of hyperthyroidism but their use should probably be restricted to thyroid storm, preoperative preparation of the hyperthyroid patient, and following 131I treatment.