Effects of green tea polyphenols on iodide-induced autoimmune thyroiditis in nonobese diabetic mice.

Because green tea polyphenols (GTPs) possess anti-inflammatory properties and are effective in inhibiting autoimmune diseases in experimental settings, we examined whether GTPs prevented the development of autoimmune thyroiditis in iodide-treated nonobese diabetic (NOD) mice, an animal model of Hashimoto's thyroiditis (HT). Mice were given 0.05% iodide water or iodide water supplemented with 0.2% GTPs for 8 weeks. GTPs administration led to an enhanced production of interleukin-10 by concanavalin A-stimulated splenocytes but did not interfere with thyroiditis development. Serum thyroxine levels were not influenced by GTPs. Our data suggest that administration of GTPs may not be an effective strategy for the prevention of HT.

Effects of synthetic retinoid Am80 on iodide-induced autoimmune thyroiditis in nonobese diabetic mice.

We examined whether a synthetic retinoid Am80 prevented the development of autoimmune thyroiditis in iodide-treated nonobese diabetic mice, an animal model of Hashimoto's thyroiditis (HT). Am80 (0, 0.1 or 1 mg/kg/day) was orally administered in feed during the 8-week iodide treatment. While iodide ingestion effectively induced thyroiditis, Am80 administration failed to interfere with thyroiditis development and serum anti-thyroglobulin antibody levels regardless of the dose of the retinoid. Splenic T cell numbers, splenocyte proliferation and interferon-γ production were decreased in the Am80-treated mice. Our data suggest that Am80 is not a candidate for use in the prevention of HT.

The sphingosine 1-phosphate receptor modulator FTY720 prevents iodide-induced autoimmune thyroiditis in non-obese diabetic mice.

FTY720 is an immunomodulator that alters migration and homing of lymphocytes via sphingosine 1-phosphate receptors. This compound has been shown to be effective in suppressing autoimmune diseases in experimental and clinical settings. In the present study, we tested whether FTY720 prevented autoimmune thyroiditis in iodide-treated non-obese diabetic (NOD) mice, a model of Hashimoto's thyroiditis (HT) in humans. Mice were given 0.05% iodide water for 8 weeks, and this treatment effectively induced thyroiditis. Iodide-treated mice were injected intraperitoneally with either saline or FTY720 during the iodide treatment. FTY720 clearly suppressed the development of thyroiditis and reduced serum anti-thyroglobulin antibody levels. The number of circulating lymphocytes and spleen cells including CD4(+) T cells, CD8(+) T cells, and CD4(+)Foxp3(+) T cells was decreased in FTY720-treated mice. Our results indicate that FTY720 has immunomodulatory effects on iodide-induced autoimmune thyroiditis in NOD mice and may be a potential candidate for use in the prevention of HT.

Experimental autoimmune thyroiditis in human parvovirus B19 transgenic mice.

Viral infection is implicated as a cause of autoimmune diseases. Whereas its role in Hashimoto's thyroiditis (HT) remains undefined, recent studies suggested a link between human parvovirus B19 (B19) infection and HT. We tested such possibility by using B19 nonstructural protein 1 (NS1) transgenic C57BL/6 mice, which harbor nonpermissive genetic background (H-2(b)). Mice were immunized with either thyroglobulin (Tg) or saline. No thyroiditis developed in saline-treated mice and Tg-immunized males regardless of the presence or absence of NS1. In contrast, thyroiditis was induced by Tg immunization in 25% of transgenic females, but not in wild-type females. However, the thyroiditis incidence in the former did not differ significantly from that of the latter. In addition, intrathyroidal T-cell receptor gene expression was not augmented in Tg-immunized transgenic females. Immunization with Tg led to a comparable increase in serum anti-Tg antibody levels in the wild-type and transgenic mice. Our results indicate that the introduction of B19 NS1 gene into C57BL/6 mice is insufficient to promote the development of autoimmune thyroiditis. Further studies are required, however, before concluding that B19 infection is not involved in HT induction.

Erythrocyte zinc concentration as an indicator to distinguish painless thyroiditis-associated transient hypothyroidism from permanent hypothyroidism.

Red blood cell (RBC) zinc (Zn) concentration reflects a patient's mean thyroid hormone level over the preceding several months. The aim of this study was to examine whether RBC Zn level can be used as an indicator to distinguish painless thyroiditis-associated transient hypothyroidism (TH) from permanent hypothyroidism (PH). RBC Zn level was measured in 30 untreated PH patients with Hashimoto's thyroiditis and 7 untreated TH patients with painless thyroiditis in whom preceding transient thyrotoxicosis had been confirmed. RBC Zn concentration was significantly lower in TH patients than that in PH patients. There was a positive correlation between RBC Zn and serum TSH, and the latter was clearly lower in TH patients than that in PH patients. However, RBC Zn level was again significantly lower in TH patients than PH patients despite of the comparable serum TSH levels in both groups when RBC Zn was evaluated in patients with serum TSH levels of less than 50 mU/L. Thus TH patients could be identified with RBC Zn measurement, allowing us avoidance of unnecessarily prolonged T4 administration to them.

Effects of interleukin-6 blockade on the development of autoimmune thyroiditis in nonobese diabetic mice.

We explored the role of interleukin-6 (IL-6) in the development of autoimmune thyroiditis in nonobese diabetic (NOD) mice, an animal model of Hashimoto's thyroiditis, using anti-mouse IL-6 receptor antibody (MR16-1). Thyroiditis was induced by iodide ingestion or mouse thyroglobulin (Tg) immunization. Mice were injected intraperitoneally with saline, control rat IgG, or MR16-1 (2 or 8 mg). Iodide ingestion did not increase serum IL-6 levels and MR16-1 (2 mg) failed to prevent the development of thyroiditis. In contrast, Tg immunization induced a rapid and significant increase in serum IL-6 levels. While MR16-1 (2 mg) had no effect on Tg-induced thyroiditis, the severity, but not incidence, of thyroiditis was reduced in 8 mg MR16-1-treated mice compared with saline-injected mice. However, thyroiditis development in the 8 mg MR16-1-treated mice was indistinguishable from that in the control IgG-treated mice. MR16-1 (8 mg) did not affect serum anti-Tg antibody levels. These results suggest that IL-6 may play only a minor role in the development of autoimmune thyroiditis in NOD mice.

Autonomously functioning thyroid nodule associated with thyrotoxic periodic paralysis.

Thyrotoxic periodic paralysis (TPP) is mainly associated with Graves' disease but rarely with autonomously functioning thyroid nodule (AFTN). We herein report a case of AFTN associated with TPP in which the latter resolved after (131) I therapy for the former. We analyzed the genes encoding thyrotropin receptor (TSHR), the alpha-subunit of the stimulatory G protein (Gsalpha), calcium channel CACNA1S and potassium channel KCNE3, and found that the patient does not carry the known mutations in these genes. Whereas the pathogenesis of TPP and AFTN remains to be understood, the present case suggests that ion channel defects responsible for familial hypokalemic periodic paralysis may not be associated with TPP, and that mutations in TSHR and Gs alpha genes may be less frequent in AFTN patients in the Japanese population.

Effects of angiotensin II blockade on the development of autoimmune thyroiditis in nonobese diabetic mice.

We evaluated the effects of angiotensin II (Ang II) blockers, losartan, an Ang II receptor blocker, and enalapril, an angiotensin converting enzyme inhibitor, on the development of autoimmune thyroiditis in nonobese diabetic (NOD) mice, an animal model of Hashimoto's thyroiditis (HT). Mice were assigned into three groups, untreated, losartan-treated (30 mg/kg/day), and enalapril-treated (10 mg/kg/day) groups. Thyroiditis was induced by iodide ingestion (experiment 1) or mouse thyroglobulin (Tg) immunization (experiment 2). Both procedures effectively induced thyroiditis. While iodide ingestion failed to induce anti-mouse Tg antibody (TgAb) production, Tg immunization resulted in a significant increase in serum TgAb levels. In both experiments, neither losartan nor enalapril interfered with the development of thyroiditis and TgAb production. These results suggest that Ang II may not be associated with the development of autoimmune thyroiditis in NOD mice. Thus, the Ang II blockade may not have therapeutic potential in HT.

Methylmercury inhibition of type II 5'-deiodinase activity resulting in a decrease in growth hormone production in GH3 cells.

We have recently reported that methylmercury (MeHg) inhibits type II iodothyronine 5'-deiodinase (D2) activity in mouse neuroblastoma NB41A3 cells. In the present study, we determined the biological significance of D2 inhibition by MeHg. GH3 rat pituitary tumor cells were treated with MeHg and D2 activity and production of a thyroid hormone-responsive gene product, growth hormone (GH) were analyzed. MeHg inhibited D2 activity and decreased thyroxine (T4)-induced, but not 3,3',5-triiodothyronine (T3)-induced GH secretion in GH3 cells. Our results suggest that MeHg inhibition of D2 activity might be involved in the inhibition of GH production in GH3 cells. Thus, D2 inhibition could be a novel mechanism involved in MeHg toxicity.

Intrathyroidal persistence of human parvovirus B19 DNA in a patient with Hashimoto's thyroiditis.

Previous studies suggest a role of viral infection in the development of Hashimoto's thyroiditis (HT). Here we report a patient with HT in whom human parvovirus B19 (B19) DNA has been persistently detected in the thyroid regardless of the presence or absence of B19 DNA in peripheral blood mononuclear cells. In contrast to the DNA persistence, however, VP1 capsid protein was not detected in the thyroid by immunohistochemical studies. Thyroid specimens obtained by fine needle aspiration biopsy from two patients with HT and two with Graves' disease were negative for B19 DNA. Thus, whereas a causal link between B19 infection and HT remains to be determined, B19 DNA may persist in the thyroid and B19 infection may facilitate the intrathyroidal inflammatory process in HT patients.

Development of subclinical hyperthyroidism due to Graves' disease in a hypothyroid woman who had undergone hemithyroidectomy for adenomatous goiter and radiotherapy for nasopharyngeal cancer.

A variety of thyroid disorders develop following external radiation to head and neck cancers. Hypothyroidism is the most common clinical consequence of the radiotherapy and lifelong thyroid hormone replacement is required in many cases. Patients who received both hemithyroidectomy and the external radiation to the neck are at especially high risk for permanent hypothyroidism. Here we report an unusual case with radiation-induced hypothyroidism who had undergone hemithyroidectomy for adenomatous goiter 8 years before the radiotherapy for nasopharyngeal cancer and subclinical hyperthyroidism due to Graves' disease developed during thyroxine replacement therapy. Thus subclinical hyperthyroidism due to Graves' disease can develop in patients with radiation-induced hypothyroidism even if they have undergone hemithyroidectomy for thyroid nodules. Therefore careful and periodic evaluation of thyroid function is required even on adequate thyroxine replacement therapy.

Effects of perinatal exposure to low doses of cadmium or methylmercury on thyroid hormone metabolism in metallothionein-deficient mouse neonates.

Perinatal exposure to cadmium (Cd) or methylmercury (MeHg) results in impaired neurodevelopment. Thyroid hormone is essential for normal brain development. However, the issue whether Cd or MeHg, especially at low doses, interrupts thyroid hormone action remains to be investigated. In the present study, effects of perinatal exposure to low levels of Cd or MeHg on thyroid hormone metabolism were examined using metallothionein I and II (MT-I/II) null or wild-type neonatal mice. Dams were exposed to 10 mg/L water of Cd or 5 mg/kg chow of MeHg from gestational day 0 to post-natal day 10 (PND 10). Sera, livers and brains were collected from neonates on PND 10. Iodothyronine deiodinase activities and serum thyroxine (T4) concentrations were measured. MeHg exposure failed to induce changes in serum T4 levels and liver type 1 deiodinase (D1) and brain type 2 deiodinase (D2) activities regardless of the MT genotype. However, exposure to MeHg resulted in a decrease in brain type 3 deiodinase (D3) activity in MT-I/II null and wild-type neonates. In contrast, exposure to Cd resulted in a decrease in serum T4 levels in MT-I/II null neonates. Consistently, brain D2 activity was increased in Cd-exposed MT-I/II null neonates. No significant changes in liver D1 and brain D3 activities were induced by Cd administration. Our study demonstrates that perinatal exposure to low doses of Cd or MeHg can induce changes in brain deiodinase activities in the neonates, suggesting that thyroid hormone metabolism in fetuses and neonates might be a potential target of Cd and MeHg.

Methylmercury inhibits type II 5'-deiodinase activity in NB41A3 neuroblastoma cells.

Methylmercury (MeHg) is a well-known neurotoxicant and prenatal exposure to MeHg results in severe brain damage. Since MeHg has a high affinity for thiol groups, we sought to determine whether MeHg inhibited type II iodothyronine deiodinase (D2) activity, by which prohormone thyroxine (T4) is converted to active thyroid hormone, 3,5,3'-triiodothyronine (T3) in the brain, using NB41A3 mouse neuroblastoma cells. In MeHg-treated cells, D2 activity was inhibited in a dose- and time-dependent manner; relatively low concentrations of MeHg (30 nM) inhibited D2. Kinetic analysis using a double reciplocal plot of D2 activity revealed competitive inhibition by MeHg. DTT protected D2 from MeHg when cells were incubated with both MeHg and DTT or when MeHg was added to the assay buffer containing DTT and cell sonicates from untreated cells. Removal of MeHg from culture medium did not recover D2 activity. These results demonstrate that MeHg inhibited D2 activity in NB41A3 cells and the selenocysteine in the catalytic subunit of D2 may be involved in the inhibitory action of MeHg. Further our results suggest that T3 deficiency due to D2 inhibition in the brain may be involved in the neurotoxicity of MeHg.

Autoinduction of tumor necrosis factor-alpha in FRTL-5 rat thyroid cells.

Tumor necrosis factor-alpha (TNFalpha) may play a role in the development of autoimmune thyroiditis such as Hashimoto's thyroiditis. In the present study, we examined whether TNFalpha induced its own expression in FRTL-5 rat thyroid cells. Lipopolysaccharide (LPS) markedly increased TNFalpha mRNA levels in FRTL-5 cells as assessed by semiquantitative RT-PCR. In addition, LPS-stimulated cells released TNFalpha protein into the culture medium. Similarly, TNFalpha induced its own gene and protein expression in FRTL-5 cells as assessed by RT-PCR and metabolic labeling and immunoprecipitation of TNFalpha. The autoinduction of TNFalpha gene was also observed in TNFalpha-stimulated human thyroid epithelial cells. TNFalpha induction was specific to LPS and TNFalpha since interferon-alpha or amiodarone failed to increase TNFalpha mRNA levels in FRTL-5 cells. Human TNFalpha induced rat TNFalpha gene expression, indicating that type 1 TNF receptor (TNF-R) is involved in the autoinduction. TNFalpha did not increase either type 1 or type 2 TNF-R mRNA levels, suggesting that upregulation of TNF receptors is not involved in the autoinduction of TNFalpha. Although the biological significance of autoinduction of TNFalpha remains unclear, our results suggest that thyroid epithelial cells may participate in the development of autoimmune thyroiditis through production of TNFalpha. Furthermore, inhibition of TNFalpha production in the thyroid may represent a novel approach to mitigating inflammation in autoimmune thyroiditis.

Experimental autoimmune thyroiditis in nonobese diabetic mice lacking interferon regulatory factor-1.

Interferon regulatory factor-1 (IRF-1) is pivotal in the regulation of interferon (IFN)-mediated immune reactions, and studies suggest that IRF-1 is involved in the development of autoimmune diseases. IRF-1+/+, +/-, and -/- nonobese diabetic (NOD) mice were immunized with mouse thyroglobulin (mTg) to determine whether IRF-1 is required in experimental autoimmune thyroiditis (EAT), a murine model for Hashimoto's thyroiditis (HT). IRF-1-deficient mice developed EAT and anti-mTg antibodies comparable to IRF-1+/+ and +/- mice. Whereas both CD4+ and CD8+ T cells were found in thyroids of IRF-1+/+ mice, the latter was not in IRF-1-/- mice. Major histocompatibility complex class II antigen was comparably expressed in thyroids of IRF-1+/+ and -/- mice. Lack of IRF-1 resulted in decreased CD8+ T cell number in the spleen and reduced IFNgamma production by splenocytes. Our results suggest that IRF-1 is not pivotal in EAT in NOD mice.

Artifactually elevated serum-free thyroxine levels measured by equilibrium dialysis in a pregnant woman with familial dysalbuminemic hyperthyroxinemia.

Familial dysalbuminemic hyperthyroxinemia (FDH) is a familial autosomal dominant syndrome caused by abnormal albumin with an increased affinity for thyroxine (T4). Two types of mutations in the albumin gene, replacing the normal arginine 218 with a histidine (R218H) or a proline (R218P), have been reported to cause FDH. Here, we report a pregnant Japanese woman with FDH caused by the mutant albumin R218P. She had extremely elevated total T4 levels but normal TSH. While the majority of T4was bound to albumin, T4 binding to thyroxine-binding globulin (TBG) was progressively increased throughout pregnancy. Her infant also had elevated serum T4 but normal thyrotropin (TSH). The presence of a guanine to cytosine transition in the second nucleotide of codon 218 of the albumin gene, resulting in a substitution of proline for the normal arginine (R218P), was revealed in the proband. Serum free thyroxine (FT4) levels were increased when measured with some commercial kits including equilibrium dialysis followed by radioimmunoassay (RIA) but not when determined by RIA after ultrafiltration of sera. These results indicate an increased T4 binding to TBG during pregnancy in the patients with FDH. Furthermore, our results suggest that normal serum FT4 determined by equilibrium dialysis is not an ultimate standard for the diagnosis of FDH in the patients with the mutant albumin R218P.

Prevention of lymphocytic thyroiditis in iodide-treated non-obese diabetic mice lacking interferon regulatory factor-1.

OBJECTIVE: Interferon regulatory factor-1 (IRF-1) is a critical regulator of interferon-gamma(IFNgamma)-mediated immune responses. To determine whether IRF-1 is involved in the pathogenesis of thyroiditis in animal models, we evaluated the incidence of iodide-induced lymphocytic thyroiditis (LT) in non-obese diabetic (NOD) mice lacking IRF-1 as well as IRF-1 +/+ and +/- mice. DESIGN: IRF-1 +/+, +/- and -/- NOD mice at 6 weeks of age were fed water (group 1) or iodide water (group 2) for 8 weeks. METHODS: Thyroids were examined histopathologically and intrathyroidal lymphocytic infiltration was arbitrarily graded. Serum thyroxine (T(4)) and anti-mouse thyroglobulin antibody (anti-mTgAb) levels were measured. Spleen cell population was analyzed by flow cytometry, and IFNgamma and interleukin-10 produced by splenocytes were measured by enzyme-linked immunosorbent assay. RESULTS: In group 1, only 4.3% of NOD mice developed LT. In contrast, 67.6% of mice in group 2 developed the disease. Iodide treatment induced LT in more than 80% of IRF-1 +/+ and +/- mice. However, no IRF-1 -/- mice in group 2 developed LT. There was no difference in both serum anti-mTgAb and T(4) levels among the three IRF-1 genotypes of NOD mice. Numbers of splenic CD8(+) T cells and IFNgamma production by Concanavalin A-stimulated splenocytes were markedly decreased in IRF-1-deficient NOD mice. CONCLUSIONS: IRF-1 is involved in the development of iodide-induced LT in NOD mice.