The immunosuppressive effect of methimazole on cell-mediated immunity is mediated by its capacity to inhibit peroxidase and to scavenge free oxygen radicals

A single-center analysis of visual outcomes and associated factors after intravenous methylprednisolone treatment for dysthyroid optic neuropathy

BACKGROUND

Dysthyroid optic neuropathy (DON) is a serious threatening vision loss in Graves' ophthalmopathy (GO). Although the European Group on Graves' Ophthalmopathy (EUGOGO) recommend intravenous methylprednisolone therapy for first line treatment, some characteristics predicting the response are still inconclusive.

AIM

To study the efficacy of intravenous pulse methylprednisolone (IVMP) in treating dysthyroid optic neuropathy (DON) and to identify factors predicting poor response to the treatment.

METHODS

All patients diagnosed with DON between January 2010 and December 2021 at Rajavithi Hospital, Thailand, receiving IVMP 1 g/ day for 3 consecutive days were analyzed. The efficacy at 1 week and 3, 6, 12-months in terms of improvement of best corrected visual acuity (BCVA) and proptosis were compiled.

RESULTS

Of the entire 57 DON cases that received IVMP, 50.9% gained at least 0.2 Logarithm of the Minimum Angle of Resolution (logMAR) at 1 week, and the improvement from initial to 1-week BCVA was 0.63 ± 0.63 logMAR (p < 0.001) and the decrease in proptosis was 1.8 ± 1.36 mm (p < 0.001). The remaining 23 orbits underwent orbital decompression and were excluded from the long-term efficacy analysis. In the last 12-months' follow-up time, there was an improvement of BCVA (0.53 ± 0.47 logMAR) and proptosis (0.59 ± 0.66 mm) (both p < 0.001). At last visit, there was an improvement of BCVA (0.2 logMAR) and proptosis (2 mm) in 76.5, and 5.9% respectively. Significant predictive factors of poor treatment response were age ≥ 55 years (odds ratio [OR]: 8.28, 95% confidence interval [CI]: 1.368-50.121, p = 0.021); longer onset duration before treatment (OR: 5.10, 95%CI: 1.061-24.501, p = 0.042); and proptosis at baseline (OR: 9.31, 95%CI: 1.872-46.280, p = 0.006). The strongest risk factor for predicting poor response to IVMP was poor initial visual acuity (OR: 10.26, 95%CI: 1.363-77.234, p = 0.024).

CONCLUSIONS

IVMP is effective for both short- and long-term treatment to improve visual acuity greater than proptosis. Older age, longer disease duration, poor initial visual acuity, and proptotic orbits were identified as risk factors for predicting poor response to IVMP treatment in Thai population. DON patients having those risk factors should be suspected, and treated early with IVMP to preserve their future vision.

Changes of IgG N-Glycosylation in Thyroid Autoimmunity: The Modulatory Effect of Methimazole in Graves' Disease and the Association With the Severity of Inflammation in Hashimoto's Thyroiditis

The N-glycome of immunoglobulin G (IgG), the most abundant glycoprotein in human blood serum, reflects pathological conditions of autoimmunity and is sensitive to medicines applied in disease therapy. Due to the high sensitivity of N-glycosylation, the IgG N-glycan profile may serve as an indicator of an ongoing inflammatory process. The IgG structure and its effector functions are strongly dependent on the composition of N-glycans attached to the Fc fragment, and the binding of antigens is regulated by Fab sugar moieties. Because of the crucial role of N-glycans in IgG function, remodeling of its N-oligosaccharides can induce pathological changes that ultimately contribute to the development of autoimmunity; restoration of their physiological structure is critical to the reduction of disease symptoms. Our recently published data have shown that the pathology of autoimmune thyroid diseases (AITDs), including Hashimoto’s thyroiditis (HT) and Graves’ disease (GD), is accompanied by alterations of the composition of IgG N-glycans. The present study is a more in-depth investigation of IgG glycosylation in both AITDs, designed to determine the relationship between the severity of thyroid inflammation and IgG N-glycan structures in HT, and to assess the impact of immunosuppressive therapy on the N-glycan profile in GD patients. The study material consisted of human serum samples collected from donors with elevated anti-thyroglobulin (Tg) and/or anti-thyroperoxidase (TPO) IgGs without symptoms of hypothyroidism (n=68), HT patients characterized by high autoantibody titers and advanced destruction of the thyroid gland (n=113), GD patients with up-regulated IgG against thyroid-stimulating hormone receptor (TSHR) before (n=62) and after (n=47) stabilization of TSH level as a result of methimazole therapy (study groups), and healthy donors (control group, n=90). IgG was isolated from blood serum using protein G affinity chromatography. N-glycans were released from IgG by PNGase F digestion and analyzed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) after 2-aminobenzamide (2-AB) labeling. UPLC-MS chromatograms were integrated into 25 peaks (GP) in the Waters UNIFI Scientific Information System, and N-glycans were assigned based on the glucose unit values and mass-to-charge ratios (m/z) of the detected ions. The Kruskal-Wallis non-parametric test was used to determine the statistical significance of the results (p<0.05). The obtained results suggest that modifications of IgG sialylation, galactosylation and core-fucosylation are associated with the severity of HT symptoms. Methimazole therapy implemented in GD patients affected the IgG N-glycan profile; as a result, the content of the sialylated and galactosylated oligosaccharides with core fucose differed after treatment. Our results suggest that N-glycosylation of IgG undergoes dynamic changes during the intensification of thyroiditis in HT, and that in GD autoimmunity it is affected significantly by immunosuppressive therapy.

A single-center retrospective study of factors related to the effects of intravenous glucocorticoid therapy in moderate-to-severe and active thyroid-associated ophthalmopathy

BACKGROUND

Intravenous glucocorticoids (ivGC) have been recommended as a first-line treatment of moderate-to-severe and active thyroid-associated ophthalmopathy (TAO). However, not all patients are responsive to ivGC. The identification of potential factors used to predict their efficacy and the selection of suitable patients have both been lacking.

METHODS

It was a single center retrospective study. Potential factors related to the effects of ivGC were analyzed using logistic regression in 90 consecutive patients with moderate-to-severe and active TAO, who received 4.5 g ivGC therapy. Response was defined as the achievement of at least three points of the overall response.

RESULTS

Fifty-two (57.8%) patients showed a positive response to ivGC therapy. Significant correlations were observed between the effects of ivGC and pretreatment clinical activity score (CAS), duration of eye symptoms, and restoration of euthyroidism. The two latter factors were both independent. The duration of eye symptoms was negatively correlated with the effects of ivGC, with an odds ratio (OR) of 0.984 (p = 0.012). Restoration of euthyroidism (OR = 3.282, p = 0.039) and pretreatment CAS (OR = 1.653, p < 0.01) were both positively correlated with the effects of ivGC. The diagnostic accuracy of the duration of eye symptoms was ≤13 months (p = 0.000), with a specificity of 76.9%, and sensitivity of 65.8%. The diagnostic accuracy of the pretreatment CAS was more than 2.5 (p = 0.000), with a specificity of 61.5% and sensitivity of 80.5%. Besides, a multi-variables prediction model were established as well, which was better in the forecasting aspect with an area under curve of 0.784 (p = 0.000).

CONCLUSIONS

The duration of eye symptoms and restoration of euthyroidism are independent factors that are associated with the effects of ivGC. The following practical implications were inferred: firstly, the shorter the duration of eye symptoms, the more favorable the effects of ivGC therapy. Thus, prompt diagnosis and treatment (within 13 months) is important. Secondly, the restoration of euthyroidism improves the efficacy of ivGC. Thirdly, hope the multi-variables prediction model can be applied to clinical therapy in the future.

Low phosphate activates STOP1-ALMT1 to rapidly inhibit root cell elongation

Environmental cues profoundly modulate cell proliferation and cell elongation to inform and direct plant growth and development. External phosphate (Pi) limitation inhibits primary root growth in many plant species. However, the underlying Pi sensory mechanisms are unknown. Here we genetically uncouple two Pi sensing pathways in the root apex of Arabidopsis thaliana. First, the rapid inhibition of cell elongation in the transition zone is controlled by transcription factor STOP1, by its direct target, ALMT1, encoding a malate channel, and by ferroxidase LPR1, which together mediate Fe and peroxidase-dependent cell wall stiffening. Second, during the subsequent slow inhibition of cell proliferation in the apical meristem, which is mediated by LPR1-dependent, but largely STOP1–ALMT1-independent, Fe and callose accumulate in the stem cell niche, leading to meristem reduction. Our work uncovers STOP1 and ALMT1 as a signalling pathway of low Pi availability and exuded malate as an unexpected apoplastic inhibitor of root cell wall expansion.

Low Pi availability inhibits primary root growth, but the sensory mechanisms are not known. Here the authors uncover a signalling pathway regulating Pi-mediated root growth inhibition in Arabidopsis, involving the transcription factor STOP1, its direct target ALMT1, a malate channel, and ferroxidase LPR1.

Adding carbimazole to levothyroxine increases triiodothyronine and improves outcome in patients with primary hypothyroidism: a preliminary study from Egypt

BACKGROUND

Many hypothyroid patients are not tolerant and not satisfied with levothyroxine (LT4). Older studies used large doses of both carbimazole and LT4 for Hashimoto's thyroiditis (HT), because Graves' disease (GD) and HT were considered as very closely related syndromes produced by thyroid autoimmunity.

OBJECTIVE

The aim of the study was to determine the outcome after adding small doses of carbimazole to reduced doses of LT4 for patients with primary hypothyroidism, who are unable to tolerate LT4.

METHODS

The study is a non-randomized, single arm, interventional study. It included 19 female patients diagnosed with primary hypothyroidism who could not tolerate LT4. Subjects were recruited from the outpatient clinic of AL-Azhar University Hospital in Damietta, Egypt from January to March 2015. They were divided into two groups; group 1 included 10 patients with HT and 2 patients with non-specified primary hypothyroidism, and group 2 included 7 patients with subtotal thyroidectomy for GD. All patients received carbimazole (10 mg/day) beside LT4 (25 μg thrice/week) for 10 weeks. Statistical analysis of the data was done by SPSS version 20, using paired-sample t-test, ANOVA, Chi square, and Pearson coefficient test.

RESULTS

There was significant increase in free triiodothyronine (FT3) in addition to significant improvement in depression and LT4 tolerance in the whole population. There was non-significant improvement in TSH in group 1 (p=0.053). Surprisingly, in group 2, in spite of significant increase in TSH (p=0.007) and non-significant decrease in free thyroxine (FT4), there was non-significant increase in FT3. Whether carbimazole improves the pathology of the hypothyroid gland or the peripheral deiodination of T4 to T3 (where the serum and tissue levels of the latter may be responsible for improvement of symptoms) is in need of investigation.

CONCLUSIONS

Adding carbimazole to LT4 improves FT3, LT4 tolerance, and depression in primary hypothyroid female patients. Further studies are required to determine the appropriate doses of this regimen in different cases.

CLINICAL TRIAL REGISTRATION

This study was registered at Thai Clinical Trials Registration center (http://www.clinicaltrials.in.th) with registration ID: TCTR20170123003.

FUNDING

The study received no fund or grant.

Effect of Selenium on HLA-DR Expression of Thyrocytes

Autoimmune thyroid diseases (ATDs) represent the most frequent forms of the organ-specific autoimmune thyroid disorders that result from interaction between genetic and environmental factors. Selenium has been shown to exert a beneficial effect on the autoimmune thyroiditis. In spite of therapeutical effect of selenium on autoimmunity, the mechanism of its action has not been revealed. Objective. To determine whether selenium in vitro thyrocytes cultures are able to influence the HLA-DR molecule expression of human thyrocytes and production of free oxygen radicals. Method. Thyrocytes were prepared from human thyroid gland and cultured in vitro in the presence of interferon-γ and sodium selenite. The expression of HLA-DR molecules induced by interferon-γ in the presence of sodium selenite of various concentration was measured by fluorescence-activated cell sorter. Results. Selenium has a dose-dependent inhibitory effect on the expression of HLA-DR molecules of thyrocytes induced by interferon-γ. This effect of selenium was in the inverse correlation with antioxidative capacity. Conclusion. Beneficial effect of selenium on autoimmune mechanism is a complex mechanism in which the inhibitory effect on HLA-DR molecule expression and antioxidative capacity are involved into therapy of autoimmune thyroiditis.

Prevention of relapse of Graves' disease by treatment with an intrathyroid injection of dexamethasone

INTRODUCTION

Antithyroid drugs are widely used in the treatment of Graves' disease (GD), but the relapse rate is very high after therapy withdrawal. We evaluated the reduction effects of intrathyroid injection of dexamethasone (IID) on the relapse rate of hyperthyroidism in patients with newly diagnosed GD.

PATIENTS AND METHODS

A total of 191 patients with GD completed the study. After 6 months of treatment with methimazole (MMI), the patients were randomly assigned to receive either MMI (96 patients) alone or MMI combined with IID (MMI+IID; 95 patients) treatment for 3 months, followed by continuing a dose of MMI that would maintain euthyroidism for the next 9 months in all of the patients. After withdrawal of the medical therapy, patients were followed for 24 months, and the relapse rate of hyperthyroidism was evaluated.

RESULTS

No statistical difference was observed in the levels of serum FT(4), TSH, or TSH receptor antibodies (TR-Ab), the thyroid volume, or the TR-Ab positive rate between the two groups at month 6. After the next 3 months of treatment with MMI+IID or MMI alone, the levels of TSH increased significantly, and the levels of serum TR-Ab, the TR-Ab positive rate, and thyroid volume decreased significantly in the MMI+IID group compared with the MMI group. Seven patients (7.4%) experienced a relapse of overt hyperthyroidism in the MMI+IID group and 49 patients (51%) in MMI group during the 2-yr follow-up period (P < 0.001).

CONCLUSIONS

MMI+IID treatment is helpful to prevent relapse of hyperthyroidism in GD after medical therapy withdrawal.

Lack of effect of methimazole on dendritic cell (DC) function and DC-induced Graves' hyperthyroidism in mice

In addition to the biochemical inhibition of thyroid hormone synthesis, antithyroid drugs including methimazole (MMI) may have immunosuppressive effect through inhibition of major histocompatibility complex (MHC) class I and II expressions on non-professional (thyrocytes) and professional (macrophages and B cells) antigen presenting cells (APCs). Dendritic cells (DCs) are another professional APCs and very likely play the most important role in the primary immune response. Therefore, we focused in this study on evaluating the effect of MMI on DC function in mice. Bone marrow cells cultured with granulocyte macrophage colony stimulating factor and interleukin (IL)-4 expressed high levels of CD11c and moderate levels of MHC class II, both of which are widely used markers for DCs. In vitro incubation of this DC-containing cell population with 10(- 6)-10(- 4) M MMI for 2 days did not change basal- and maturation signal (adenoviral infection and lipopolysaccharide)-induced levels of the cell surface marker expressions such as MHC class I and II, CD86, CD40 and DEC205, and of proinflammatory cytokine IL-6 release. Further we found that treatment of the DC-containing cell population with MMI did not influence the incidence of Graves' hyperthyroidism and anti-thyrotropin receptor (TSHR) antibody titers in a mouse Graves' model we have recently established with DCs infected with adenovirus expressing the TSHR A subunit. Although we cannot completely exclude immunosuppressive effect of MMI on other immune cells, our data indicate that DCs do not appear to be the primary target for the immunosuppressive effect of MMI.

The balance shift in Th1/Th2 related IL-12/IL-5 cytokines in Graves' disease during methimazole therapy

Th1 and Th2-like cytokines are involved in the pathogenesis of Graves' disease. The shift in balance in IL-12/IL-5 cytokines was applied in judging the immunological events in 74 patients with Graves' disease (50 had ophthalmopathy) during methimazole therapy and in 15 controls. The serum levels of IL-12 and IL-5 were measured with enzyme-linked immunosorbent assay in all Graves' patients. Twelve cases for IL-5 and 20 cases for IL-12 were positive. In Graves' patients only those without ophthalmopathy had higher levels of IL-12 when compared to controls (192.66 +/- 29.19 vs. 85.09 +/- 8.95 pg/ml, P < 0.04). After 2 months of methimazole therapy in Graves' patients without ophthalmopathy an increase in the ratio of IL-12 to IL-5 was also observed as compared to those with eye symptoms (91.78 +/- 34.14 vs. 20.72 +/- 6.36, P < 0.015). Age-related difference in the serum level of IL-5 could be demonstrated between Graves' patients without and those with ophthalmopathy aged < or = 35 years (4.89 +/- 0.57 vs. 50.14 +/- 20.2 pg/ml, P < 0.002). No association was found among the serum levels of IL-5 or IL-12, thyroid hormones and TSH receptor antibodies. The results demonstrated a difference in the balance shift of IL-12/IL-5 between Graves' patients with and without ophthalmopathy. The increased ratio of IL-12 to IL-5 after methimazole therapy could be explained by the elevation of serum IL-12 due to methimazole therapy and the age-related decrease of serum IL-5.

Effects of methimazole on the onset of type 2 diabetes in leptin receptor-deficient rats

We investigated the effects of methimazole, an anti-thyroid drug, on the onset of type 2 diabetes in Zucker diabetic fatty (ZDF) rats. For this, 0.03% methimazole was administered to 7-week-old, pre-diabetic ZDF rats in drinking water for 5 weeks and the animals were sacrificed at 12 weeks of age. Methimazole treatment to ZDF rats significantly reduced blood glucose levels, food intake, body weight, and serum T3 levels. Hepatocytes in ZDF-methi rats were more densely stained with eosin than those in ZDF rats because of low fat accumulation in ZDF-methi hepatocytes. The pancreatic islet in ZDF-methi rats was normal compared to that in ZDF rats. Glucagon, not insulin, immunoreactivity in ZDF-methi rats was significantly higher than that in ZDF-methi rats. These suggest that methimazole treatment may delay the onset of type 2 diabetes in leptin receptor-deficient rats and also suggests that thyroid hormones may be necessary for the onset of diabetes.

[What is the role of allergic sensitization in Graves' disease?]

INTRODUCTION

Recent data supported the presence of T helper 2 dominance in the immune processes of Graves' disease and allergic diseases. A common role of regulatory T cells in the antigen- (or allergen-) specific immune responses was also demonstrated.

AIMS

To study whether allergic events may play a role in the initiation or progression of autoimmune Graves' disease. The occurrence of seasonal allergy may explain the fluctuation in the onset of Graves' disease.

METHODS

The presence of specific IgE levels against inhalative allergens was investigated in 327 patients with thyroid disease (Graves' disease, Hashimoto's thyroiditis, euthyroid goitre). Western blot method was used for the measurement of allergen-specific IgE levels with densitometric evaluation.

RESULTS

Allergic sensitization was found in 88 cases (58%) for Graves' disease, 51 cases (46%) for Hashimoto's thyroiditis and 31 cases (55%) for euthyroid goitre. According to allergens, significant difference was demonstrated by Penicillium notatum, Dermatophagoides farinae, alder - rye (pollens) between Graves' disease (depending ophthalmopathy) and euthyroid goitre. In the four groups based on allergen seasonality, the month of the onset in Graves' disease was associated with the season of early tree and mugwort allergy (P < 0.019 between Graves' disease and Hashimoto's thyroiditis). The number of cases, in whom the onset of Graves' disease in a given month was similar to the month of allergic season, was 17 cases vs 7 cases with Hashimoto's thyroiditis (P < 0.028).

CONCLUSIONS

The allergic sensitization was more frequent in Graves' disease, and the allergic seasonality may explain the fluctuation in the onset of Graves' disease.

Probing the substrate specificity of the ergothioneine transporter with methimazole, hercynine, and organic cations

Recently, we have identified the ergothioneine (ET) transporter ETT (gene symbol SLC22A4). Much interest in human ETT has been generated by case-control studies that suggest an association of polymorphisms in the SLC22A4 gene with susceptibility to chronic inflammatory diseases. ETT was originally designated a multispecific novel organic cation transporter (OCTN1). Here we reinvestigated, based on stably transfected 293 cells and with ET as reference substrate, uptake of quinidine, verapamil, and pyrilamine. ETT from human robustly catalyzed transport of ET (68micfrol/(minmgprotein)), but no transport of organic cations was discernible. With ET as substrate, ETT was relatively resistant to inhibition by selected drugs; the most potent inhibitor was verapamil (K(i)=11micromol/l). The natural compound hercynine and antithyroid drug methimazole are related in structure to ET. However, efficiency of ETT-mediated transport of methimazole (K(i)=7.5mmol/l) was 130-fold lower, and transport of hercynine (K(i)=1.4mmol/l) was 25-fold lower than transport of ET. ETT from mouse, upon expression in 293 cells, catalyzed high affinity, sodium-driven uptake of ET very similar to ETT from human. Additional real-time PCR experiments based on 16 human tissues revealed ETT mRNA levels considerably lower than in bone marrow. Our experiments establish that ETT is highly specific for its physiological substrate ergothioneine. ETT is not a cationic drug transporter, and it does not have high affinity for organic cation inhibitors. Detection of ETT mRNA or protein can therefore be utilized as a specific molecular marker of intracellular ET activity.

Methimazole protects lungs during hepatic ischemia-reperfusion injury in rats: an effect not induced by hypothyroidism

BACKGROUND

Hepatic ischemia-reperfusion injury may lead to remote organ failure with mortal respiratory dysfunction. The aim of the present study was to analyze the possible protective effects of methimazole on lungs after hepatic ischemia-reperfusion injury.

METHODS

Forty male Wistar albino rats were randomized into five groups: a control group, in which bilateral pulmonary lobectomy was done; a hepatic ischemia-reperfusion group, in which bilateral pulmonary lobectomy was done after hepatic ischemia-reperfusion; a thyroidectomy-ischemia-reperfusion group (total thyroidectomy followed by, 7 days later, bilateral pulmonary lobectomy after hepatic ischemia-reperfusion); a methimazole-ischemia-reperfusion group (following methimazole administration for 7 days, bilateral pulmonary lobectomy was done after hepatic ischemia-reperfusion); and a methimazole +L-thyroxine-ischemia-reperfusion group (following methimazole and L-thyroxine administration for 7 days, bilateral pulmonary lobectomy was performed after hepatic ischemia-reperfusion). Pulmonary tissue specimens were evaluated histopathologically and for myeloperoxidase and malondialdehyde levels.

RESULTS

All of the ischemia-reperfusion intervention groups had higher pulmonary injury scoring indices than the control group (P < 0.001). Pulmonary injury index of the ischemia-reperfusion group was higher than that of both the methimazole-supplemented hypothyroid and euthyroid groups (P = 0028; P = 0,038, respectively) and was similar to that of the thyroidectomized group. Pulmonary tissue myeloperoxidase and malondialdehyde levels in the ischemia-reperfusion group were similar with that in the thyroidectomized rats but were significantly higher than that in the control, and both the methimazole-supplemented hypothyroid and euthyroid groups.

CONCLUSION

Methimazole exerts a protective role on lungs during hepatic ischemia-reperfusion injury, which can be attributed to its anti-inflammatory and anti-oxidant effects rather than hypothyroidism alone.

Induction of stimulating thyrotropin receptor antibodies after radioiodine therapy for toxic multinodular goitre and Graves' disease measured with a novel bioassay

BACKGROUND

Radioactive iodine therapy (RaI) in toxic multinodular goitre (TMNG) has been associated with the occurrence of Graves'-like hyperthyroidism. It has been postulated that pre-existing autoimmunity may contribute to this phenomenon.

OBJECTIVE

To study whether RaI induces thyrotropin receptor stimulating antibodies (TSAbs) in the short term in TMNG and whether pre-existing autoimmunity is relevant.

PATIENTS

Thirty-one patients with relapsing Graves' disease and 17 patients with TMNG, all eligible for RaI.

METHODS

Before and 6 weeks after RaI, sera were collected and analysed for the presence of thyroglobulin (Tg), thyroid peroxidase antibodies (TPO-Abs) and thyrotropin receptor binding antibodies (TBIIs). TSAbs were analysed with a novel high-sensitive luciferase-based bioassay based on the JP-26-26 cell line, which constitutively expresses the TSH receptor.

RESULTS

In Graves' disease, RaI did not induce or increase the levels and proportion of patients with measurable levels of any of the antibodies measured, despite a significant increase in Tg. In contrast, in TMNG, RaI induced TBIIs in three TMNG patients, which was accompanied by measurable TSAbs on one occasion.

CONCLUSIONS

We conclude from the present study that induction of TBIIs and TSAbs may occur shortly after RaI in TMNG and that pre-existing autoimmunity may not be a requirement for the induction of TBIIs, as evidenced by the lack of effect of RaI on TBIIs in Graves' disease.

PROLACTIN SECRETION IN HYPOTHYROID ENDOTOXEMIC RATS: INVOLVEMENT OF L-ARGININE AND NITRIC OXIDE SYNTHASE

The identification of nitric oxide (NO) within the hypothalamus and pituitary gland has suggested its role as modulator of the activity on hypothalamic-pituitary axis. Hypothalamic NO synthase (NOS) is known to be regulated by thyroid hormones. We investigated the effects of previous injection of N-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, and L-arginine (L-Arg), the substrate for NO synthesis, on prolactin (PRL) secretion, through the lipopolysaccharide (LPS)-induced inflammatory response in thyroidectomized (TX) rats. TX or sham-operated (N) rats were intraperitoneally (i.p.) injected with L-NAME (10 mg kg) or L-Arg (200 mg kg) or the same volume of vehicle (saline solution) 30 min before endotoxemia-induction with LPS at 250 mug (100 g body weight), i.p.. In N rats, NO increased PRL release in response to endotoxemia, whereas in hypothyroid rats, NO appeared to have the opposite effect. Our data support the hypothesis that NO exerts a modulatory influence on PRL secretion after LPS-induced inflammatory response.

Methimazole-induced hypothyroidism paradoxically decreases homocysteine

Clinical hypothyroidism is associated with hyperhomocysteinemia, whereas the opposite is seen in hyperthyroidism. The effects of mild thyroid dysfunction on homocysteine concentrations are not known. We performed the following study to investigate this. Total homocysteine, vitamins B6 and B12, folate, fibrinogen, plasminogen activator inhibitor type 1, and lipids were measured in 11 subjects at baseline and after methionine loading. Subjects began methimazole (MMI), 40 mg daily, and were restudied during 2 stages of hypothyroidism. Liothyronine was added and subjects were restudied once thyrotropin normalized. Methimazole was stopped and studies were repeated during 2 stages of hyperthyroidism. Data were analyzed using repeated-measures analysis of variance. Post-methionine homocysteine decreased in each hypothyroid study compared with baseline (28.8+/-10.7, 27.5+/-9.9 vs 34.4+/-9.2 micromol/L, respectively). In addition, both fasting and post-methionine homocysteine decreased in the euthyroid/MMI study arm compared with baseline despite equivalent thyrotropin values (fasting, 7.5+/-3.0 vs 8.8+/-3.5 micromol/L, P<.05; and post-methionine, 27.2+/-10.6 vs 34.4+/-9.2 micromol/L, P<.05, respectively). Fasting homocysteine decreased in the first hyperthyroidism study arm compared with baseline (6.6+/-2.3 vs 8.8+/-3.5 micromol/L, P<.05) and post-methionine homocysteine decreased in both hyperthyroid arms compared with baseline (25.2+/-8.1, 24.2+/-10 vs 34.4+/-9.2 micromol/L, P<.05 respectively). In conclusion, mild thyroid dysfunction changes homocysteine metabolism. Unexpectedly, our results suggest a homocysteine-lowering effect of MMI.

Peripheral parameters of oxidative stress in Graves' disease: the effects of methimazole and 131 iodine treatments

BACKGROUND

Increased oxidative stress, with elevated levels of free radicals, together with diminished antioxidation have been described previously in models of hyperthyroidism and in patients with Graves' disease. However, controversial results have been found about the antioxidant status and its response to treatment.

AIM

To evaluate the antioxidant/oxidant balance in active Graves' disease and the effects of treatment with methimazole (MMI) and 131 iodine (131I).

PATIENTS AND METHODS

We studied 69 hyperthyroid (H) patients, 58 female and 11 male, 16-50 years old; total T3: 8 +/- 2 nmol/l, total T4: 264 +/- 65 nmol/l (all mean +/- SD), TSH: 0.1 +/- 0.1 mIU/l, TSH receptor antibody 41 +/- 21%, highest 131Iodine uptake: 67 +/- 16%. As a control group (C), 19 normal adults were studied.

DESIGN

Parameters evaluated were: tert-butyl hydroperoxide initiated chemiluminiscence (CL), superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione peroxidase (GPx) and total reactive antioxidant potential (TRAP).

RESULTS

In patients vs. controls there was an increase in CL levels (6207 +/- 1434 vs. 3000 +/- 851 cpm/mg of haemoglobin, P < 0.001), decrease in SOD (0.4 +/- 0.1 vs. 0.7 +/- 0.2 U/mg prot, P < 0.05; corresponding to 0.15 micro g/ml), CAT (2.8 +/- 0.6 vs. 3.8 +/- 0.7 pmol/mg prot, P < 0.001) and GSH (1.2 +/- 0.4 vs. 2 +/- 0.7 mmol/l erythrocytes, P < 0.05). The decrease in GPx and TRAP did not show significant differences. The parameters were also recorded in 30 patients who became euthyroid after treatment: 20 of them under MMI therapy (2-12 months) and the rest 3-6 months after 131Iodine administration. All the parameters evaluated were normalized after MMI; however, CL levels stayed high after 131I and only CAT and GSH levels returned to normal values.

CONCLUSION

Our results confirm the imbalance of the antioxidant/oxidant status in hyperthyroid patients. MMI treatment was more effective than 131I therapy to improve that balance. We speculate on the benefits of antioxidant therapy administrated together with the habitual treatment of hyperthyroidism, especially in patients after 131I therapy.

Methimazole prevents stress and chemical induced gastropathy in rats

This investigation was undertaken to study the effect of methimazole (MMI) on gastric acid secretion and stress and chemically induced gastric ulcer in rats. Acid secretion studies were undertaken using pylorus-ligated rats pretreated with MMI (10-100 mg/kg, i.p.). The effect of orally administered MMI on water-immersion restraint (WIR) stress, indomethacin and ethanol-induced gastric ulcers was also tested. The level of myeloperoxidase (MPO), non-protein sulfhydryls (NP-SH) and gastric wall mucus was measured in the glandular stomach of rats following ethanol-induced gastric lesions. There was a dose-dependent inhibition of gastric acid secretion and ulcerogen induced gastric lesion formation in the MMI treated rats. Our morphological and histological studies showed a complete prevention of ethanol-induced lesions in the rats treated with high dose (100 mg/kg) of MMI. A significant attenuation of ethanol-induced increase in gastric MPO activity, depletion of NP-SH and reduction of gastric wall mucus was also observed in MMI treated rats. These findings clearly suggest the involvement of endogenous pro-inflammatory agents and oxidative stress in mediating the gastroprotective effect of MMI.

Antithyroid drugs inhibit in vivo HLA-DR expression in thyroid follicular cells in Graves' disease

Antithyroid drugs have been reported to reduce the expression of HLA-DR in thyrocytes in Graves' disease, but only circumstantial evidence has been provided about their in vivo immunologic effects. This present study was designed to examine the in vivo immunologic effect of antithyroid drugs on thyroid follicular cells. The study was conducted on 25 patients who had Graves' disease in remission or in activity and who were or were not receiving treatment (7 in overt thyrotoxicosis, 6 patients in remission, and 12 patients under medication). HLA-DR expression in thyroid biopsies was verified by immunohistochemistry. The follicular cells of all patients in overt thyrotoxicosis expressed HLA-DR whereas those of patients in remission were negative for HLA-DR. HLA-DR was also not expressed in all patients under medication, but this did not correlate with the clinical evolution after thyroid drug withdrawal. In conclusion, antithyroid drugs inhibit follicular cell HLA-DR expression in Graves' disease, when thyrotoxicosis is controlled. This suggests that additional mechanisms not involving HLA-DR play a role in thyroid autoimmune disease.

Role of peroxiredoxins in regulating intracellular hydrogen peroxide and hydrogen peroxide-induced apoptosis in thyroid cells

Peroxiredoxins (Prxs) play an important role in regulating cellular differentiation and proliferation in several types of mammalian cells. One mechanism for this action involves modulation of hydrogen peroxide (H(2)O(2))-mediated cellular responses. This report examines the expression of Prx I and Prx II in thyroid cells and their roles in eliminating H(2)O(2) produced in response to thyrotropin (TSH). Prx I and Prx II are constitutively expressed in FRTL-5 thyroid cells. Prx I expression, but not Prx II expression, is stimulated by exposure to TSH and H(2)O(2). In addition, methimazole induces a high level of Prx I mRNA and protein in these cells. Overexpression of Prx I and Prx II enhances the elimination of H(2)O(2) produced by TSH in FRTL-5 cells. Treatment with 500 micrometer H(2)O(2) causes apoptosis in FRTL-5 cells as evidenced by standard assays of apoptosis (i.e. terminal deoxynucleotidyl transferase deoxyuridine triphosphate-biotin nick end labeling, BAX expression, and poly(ADP-ribose) polymerase cleavage. Overexpression of Prx I and Prx II reduces the amount of H(2)O(2)-induced apoptosis measured by these assays. These results suggest that Prx I and Prx II are involved in the removal of H(2)O(2) in thyroid cells and can protect these cells from undergoing apoptosis. These proteins are likely to be involved in the normal physiological response to TSH-induced production of H(2)O(2) in thyroid cells.

Evidence for carbimazole as an antioxidant?

There is evidence in the literature to support the view that antioxidants are involved in the pathogenesis of Graves disease and that antioxidants may act as free radical scavengers. This study has compared the effects of a 12 month course of conventional Carbimazole therapy on peripheral blood antioxidant levels with those of a 12 month course of a higher dose treatment regime. Fifty seven patients were enrolled into the study. Those in Group 1 (n = 23) received a 12 month course of 60 mg/day Carbimazole. Those in Group 2 (n = 34) received 45 mg/day for the first month, 30 mg/day for the second and 20 mg/day for the remaining 10 months of treatment. T3 was added in both groups after 2-4 months to maintain patients euthyroid. Baseline samples were also obtained from 30 control subjects. Blood samples were taken for the measurement of plasma thiol (PSH), lysate thiol (LSH), superoxide dismutase (SOD) and caeruloplasmin (CP) and for routine thyroid function tests (TT4, TT3 and TSH). In untreated Graves' patients, serum levels of PSH and SOD were reduced and levels of LSH increased compared to controls. Following 2 months high dose Carbimazole therapy there was a significant increase in PSH levels and a significant reduction in CP levels compared to presentation levels. In the more conventional dose Group 2 patients PSH levels also rose significantly during the first 2 months of treatment. Levels for both groups were still significantly lower than the control group. After 12 months high dose Carbimazole therapy PSH levels had decreased so that they no longer differed from untreated levels. LSH and SOD levels still remained abnormal. CP levels continued to fall. Similar findings were obtained in those patients receiving the more conventional course of treatment. At no point was their any significant difference in antioxidant levels between the two treatment groups. The abnormal levels of antioxidants in the serum of untreated Graves' patients confirm their involvement in the pathogenesis of Graves' disease. Carbimazole therapy appeared to have only short term effects on the peripheral blood levels of the antioxidants measured. Carbimazole appeared to act only on the extra cellular markers of antioxidant activity (PSH, CP) although the disease itself had marked intracellular effects (LSH, SOD). These findings suggest that Carbimazole does not act as a free radical scavenger.

Mechanistic analysis of S-(1,2-dichlorovinyl)-L-cysteine-induced cataractogenesis in vitro

Chronic exposure to low concentrations of the nephrotoxic cysteine conjugate S-(1,2-dichlorovinyl)-l-cysteine (DCVC) causes cataracts in mice. This study explored mechanisms of DCVC-induced cataractogenesis using explanted lenses from male Sprague-Dawley rats. Lenses placed in organ culture were exposed to 2.5 microM-1 mM DCVC for 24 hr. DCVC caused concentration and time-dependent changes in biochemical markers of toxicity (lenticular adenosine 5'-triphosphate (ATP) content, mitochondrial reduction of the tetrazolium dye MTT, and glutathione (GSH) content) at concentrations >/=25 microM. Lens clarity was adversely affected at concentrations >/=50 microM. Within 24 hr, 1 mM DCVC altered lens ATP content (-77 +/- 2%), mitochondrial MTT reduction (-40 +/- 3%), and GSH content (-19 +/- 4%) (percent difference from controls, p < 0.05). ATP was the most sensitive index of DCVC exposure in this model, while lens weight was not altered. The role of lenticular DCVC metabolism was investigated using the beta-lyase inhibitor aminooxyacetic acid (AOA) and the flavin monooxygenase (FMO) inhibitor methimazole (MAZ). AOA (1 mM) provided nearly complete protection from changes in biochemical parameters and lens transparency caused by DCVC, while MAZ (1 mM) provided only partial protection. The mitochondrial Ca2+ uniport inhibitor ruthenium red (30 microM) and the poly(ADP ribosyl)transferase inhibitor 3-aminobenzamide (3 mM) were only partially protective, whereas adverse changes in lens transparency and biochemical markers were not prevented by an antioxidant (2 mM dithiothreitol) or nontoxic transport substrates (200 microM probenecid or 10 mm phenylalanine, S-benzyl-L-cysteine or para-aminohippuric acid). Calpain inhibitors E64d (100 microM) and calpain inhibitor II (1 mM) were ineffective in preventing opacity formation caused by DCVC. In a small separate study, DCVC toxicity to explanted lenses from cynomologus monkeys was also ameliorated by coincubation with AOA. These results indicate that opacity formation by DCVC in rodent and primate lenses in vitro is primarily mediated via lenticular beta-lyase metabolism of DCVC to a reactive metabolite. Metabolism of DCVC by FMO and perturbations in mitochondrial calcium (Ca2+) homeostasis and increased poly(ADP-ribosylation) of nuclear proteins may play a limited role in opacity formation in vitro. However, opacity formation does not appear to be the result of oxidative stress or calpain activation. DCVC toxicity to the lens was not blocked with competitive inhibitors of the amino acid and organic anion transporters of DCVC as is found in the kidney.

Effect of TSH and anti-TSH receptor antibodies on the plasma membrane potential of polymorphonuclear granulocytes

Effects of thyrotropin hormone (TSH) and anti-TSH receptor antibodies on the plasma membrane potential of polymorphonuclear granulocytes (PMN) were analyzed by means of flow cytometry. Both TSH and the autoantibody caused a rapid, dose-dependent hyperpolarization of the plasma membrane of PMNs. TSH was also able to mask (revert) the depolarizing effect of a chemotactic peptide, fMLP, on PMNs. No detectable rise in the cytosolic free calcium level accompanied the observed hyperpolarization. Quinine, a blocker of Ca(2+)-activated and voltage-gated K+ channels did not affect the hyperpolarization by TSH and antibodies. Decreasing the [K+] gradient across the plasma membrane by valinomycin, however, blocked the hyperpolarizing effect. Peptide362-376 (derived from the extracellular domain of TSH receptor) also blocked the hyperpolarization induced by both TSH and anti-TSHR antibodies. These data suggest that the observed hyperpolarization is a specific, receptor-mediated early signal during interaction of PMNs with TSH or anti-TSHR antibodies.

Methimazole inhibits peripheral lymphocyte proliferation by inducing S-quiescent phase arrest

The influence of methimazole (MTI) on the mitogenic proliferation of human blood lymphocytes was studied in vitro to evaluate the potential immunomodulatory activity of this antithyroid drug. The effects of the drug on the lymphocyte cell cycle were assessed by multiparametric flow cytometry. Although MTI induced an increase in the number of lymphocytes in the synthesis and G2M compartments, it failed to stimulate proliferation as the cells tended to accumulate in the quiescent S compartment. The effect was dose-dependent over a range from 0.1 to 100 mM. These in vitro results indicate that MTI possesses immunosuppressive activity.

Lymphoproliferative activity of methimazole: free SH group dependency

1. The comparative effects of methimazole (MTI), an antithyroid drug, and its S-methyl derivate (MMTI), were studied in vitro on the lymphoproliferative response to lectin in order to point out the free SH group importance. The cell cycle analysis was performed by flow cytometry after cellular DNA staining by propidium iodide. 2. We showed that MTI enhanced the PHA-induced DNA synthesis phase (P < 0.05 from 1 to 100 microns) whereas MMTI had no significant activity. The free SH group seems to be necessary to the MTI immunomodulatory activity.

Increased serum interleukin-1 beta during treatment of hyperthyroidism with antithyroid drugs

Serum interleukin-1 beta (IL-1 beta) and soluble interleukin-2 receptor (sIL-2R) levels were examined in patients with hyperthyroidism due to Graves' disease (GD) and toxic nodular goitre (TNG) before and during antithyroid drug therapy. A total of 32 patients were studied; 23 patients (14 with GD and nine with TNG) were in a hyperthyroid state (group A) and nine patients (four with GD and five with TNG) were in a euthyroid state, under carbimazole or methimazole treatment (group B). Ten hyperthyroid patients from group A (seven with GD and three with TNG) were also examined while euthyroid on treatment (Subgroup A). Serum was taken from all patients for the measurement of sIL-2R, IL-1 beta, total T4 (TT4), total T3 (TT3) and TSH concentrations. The results were compared with those from 30 normal controls. Serum sIL-2R levels were higher in Group A (671.3 +/- 74.0 U mL-1, mean +/- SE), than in Group B (214.1 +/- 61.8 U mL-1) and controls (149 +/- 14.8 U mL-1), P < 0.001. Similarly, the subgroup of 10 patients had higher levels of sIL-2R during the hyperthyroid phase than while euthyroid (P < 0.001). There was a positive correlation between sIL-2R values and levels of T4 and T3. In contrast, serum IL-1 beta levels were higher in Group B patients (197.5 +/- 39.2 pg mL-1) compared with those in Group A (66.5 +/- 17 pg mL-1, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Sister-chromatid exchanges in lymphocytes from methimazole-induced hypothyroid mice

The inhibitory effect of an antithyroid drug on mouse T lymphocytes was investigated. Inbred C57BL/6 mice were provided with an antithyroid drug, methimazole, for 2, 4 and 6 weeks and the in vitro responses of the lymphocytes were studied. The proliferative responses of T lymphocytes from the spleen of methimazole (MMI)-treated mice significantly (p < 0.05) decreased following concanavalin A stimulation, and the inhibitory effect became prominent with the increased duration of MMI treatment. A concomitant increase in the frequency of induced sister-chromatid exchanges was also observed in these T lymphocytes. When the splenocytes were stimulated with concanavalin A for 24 h, their ability to produce interleukin-2 (IL-2) was significantly decreased (p < 0.05). The results indicated that methimazole interfered with the normal proliferation of T lymphocytes by suppressing the production of IL-2, a cytokine also known as T cell growth factor, as well as inducing a higher incidence of sister-chromatid exchange during cell division.

Effects of antioxidants on the blood-brain barrier and postischemic hyperemia

The role of free oxygen radicals in blood-brain barrier (BBB) disruption and postischemic hyperemia was evaluated in the rabbit model of focal cerebral ischemia-reperfusion. Six groups of rabbits underwent clipping of the anterior cerebral, middle cerebral, and intracranial internal carotid arteries. Cerebral blood flow (CBF) was measured by using radiolabeled microspheres, before, during, and 15 minutes after 1-hour occlusion of these arteries. After 50 minutes of ischemia, Group 1 animals (control) received a placebo. Animals in Groups 2-4 received one of three drugs: catalase at 10 mg/kg, methimazole at 5 mg/kg, or indomethacin at 10 mg/kg. A fifth group received a tungsten-supplemented diet for 14 days before ischemia was induced, and a sixth group was sham operated. Microvascular integrity within the brain was determined by the presence or absence of Evan's Blue (EB)-albumin dye leakage across the BBB and was measured by microspectrofluorometry. In the control group during ischemia, CBF dropped to 14%, 7%, and 11% of preischemic levels in rostral, middle, and caudal sections of the brain, respectively, as characterized by extensive EB-albumin dye leakage through the BBB into the ischemic hemisphere. During early reperfusion, postischemic hyperemia was associated with an increase in CBF of 128%, 123%, and 129% of control in the rostral, middle, and caudal sections of the brain, respectively. In all treated groups and in the group receiving a tungsten-supplemented diet, BBB integrity was protected during reperfusion without inhibition of postischemic hyperemia. This study suggests that early disruption of the BBB to large molecules is mediated by free oxygen radicals, which inhibit rather than cause postischemic hyperemia.

Repressed activity of peritoneal macrophages in methimazole-induced hypothyroid mice

In this study we compared the functions of normal peritoneal macrophages with those from methimazole-induced hypothyroid C57BL/6 mice. Methimazole (MMI) suppressed the expression of the tumor necrosis factor (TNF) gene in peritoneal macrophages (MAM) at both transcriptional and translational levels. The kinetics of TNF synthesis by MAM following in vivo and in vitro lipopolysaccharide (LPS) challenge were different, but both treatments resulted in significant decreases (P < 0.05) in TNF mRNA and protein after 60 min. Similarly, the production of reactive nitrogen and oxygen intermediates by MAM were significantly (P < 0.05) lower compared with control macrophages (CAM). In addition, the serum TNF protein was significantly lower (P < 0.05) in MMI-treated mice following intravenous LPS challenge for 90 min. These data suggested that peritoneal macrophages were inactivated in MMI-induced hypothyroid mice.

Serum ICAM-1 concentrations in patients with psoriasis treated with antithyroid thioureylenes

Serum concentrations of intercellular adhesion molecule-1 (ICAM-1), a marker of early T-cell activation were measured in 14 patients with stable plaque psoriasis who received treatment for 8 weeks with the antithyroid thioureylenes, propylthiouracil (PTU) or methimazole (MMI) which have been previously shown to produce significant improvement in such patients. Baseline serum concentrations of ICAM-1 were significantly higher in the patients with psoriasis compared with normal control volunteers. Following therapy with either PTU (300 mg daily) or MMI (40 mg daily) serum ICAM-1 concentrations did not decline significantly. Since ICAM-1 expression on vascular endothelium increases in active psoriasis, and is postulated to promote T-cell migration to and retention at these sites, it is hypothesized that the beneficial therapeutic effects of thioureylenes in psoriasis occur distal to the events that lead to lymphocyte migration to vascular structures in the dermis.

Expression of tumor necrosis factor and c-fos genes in peritoneal macrophages of hypothyroid mice

It is well documented that hypothyroid patients are more susceptible to microbial infections. In order to study whether this impaired response is due to a decrease in production of antitumor molecules or an impaired ability to transmit information in the macrophage, a hypothyroid animal model was used to study the expression of both tumor necrosis factor gene and c-fos protooncogene in peritoneal macrophages. Inbred mice were rendered hypothyroid by an antithyroid drug, methimazole, and the expression of tumor necrosis factor gene and c-fos protooncogene in peritoneal macrophages were studied. Impairment of c-fos and TNF genes were at both transcriptional and translational levels using northern blot analysis, bioassays, and immunocytochemical staining methods. These results indicate that the reduction in signal transduction and in the production of antitumor molecules may cause the poor defense ability of hypothyroid animals.

The effect of iodine on lipid peroxidation and ultrastructure in the thyroids of BB/Wor rats

There has been recent data suggesting that iodine potentiates lymphocytic thyroiditis (LT) by inciting oxidative stress. However, the mechanism by which iodine induces LT in genetically predisposed animals is unknown. This study was undertaken to examine LT-prone BB/Wor (LT-P) rat thyroids for signs of acute iodine toxicity and oxidative damage before the onset of spontaneous LT. Lipid peroxidation was assessed by the measurement of malonyldialdehyde (MDA) in thyroid homogenates after randomization to a treatment group receiving 0.05% iodide in the drinking water or tap water for 24 hours. Basal MDA levels were higher in LT-prone rat thyroids than Wistar rat thyroids, but iodine treatment did not influence intrathyroidal MDA levels. Electronmicroscopy demonstrated that prolonged treatment with excess iodine, increased the number of apical lysosomes. But there were no ultrastructural changes unique to LT-P rat thyroids. These data suggest that although LT-P rat thyroids may experience subclinical oxidative damage before the onset of histologically demonstrable LT, this activity is not affected by iodine.

Inhibition of metabolic activity of polymorphonuclear granulocytes by thyroid stimulating antibodies

Both thyrocytes and polymorphonuclear granulocytes (PMNs) are known to have on their surface thyrotropin receptor (TSH-R). Anti-TSH-R antibodies having stimulating and blocking effects on thyroid function have been detected in sera of Graves' patients. Thyroid stimulating anti-TSH-R antibodies (TSAb) are involved in the pathomechanism of thyrotoxicosis. The basic question is in this study whether TSAb exerts effects on metabolic activity of PMNs. Immunoglobulin G (IgGs) of 32 patients with thyrotoxicosis had significant inhibitory effect (p less than 0.001) on chemiluminescence of healthy PMNs compared to controls. An inverse correlation was observed between inhibitory effect of IgGs on function of PMNs and TT4 (r = -0.61) in contrast to anti-TSH-receptors antibodies (r = 0.09). TSAbs of eight hyperthyroid patients were measured by determination of cyclic AMP in suspension and slices of porcine thyroid gland. Function of human PMNs separated from healthy donors was determined by luminol-amplified chemiluminescence. Photon-emission of PMNs induced by adherence was significantly lower than that of controls. None of patients' IgGs contained anti-PMNs antibodies or other toxic compounds. It was found an inverse correlation between chemiluminescence of PMNs and capability of TSAb to increase intracellular cAMP in thyroid slices and the thyroid hormone levels of patients with thyrotoxicosis (p = 0.0005). In conclusion, TSH-R on PMNs did not belong to "mute" receptors and metabolic changes in PMNs induced by TSAb might have pathogenetic as well as methodological implications.

Increased level of soluble interleukin-2 receptor in sera of patients with Graves' disease

Soluble interleukin-2 receptor was studied in 20 patients with Graves' disease before and after methimazole treatment. Soluble interleukin-2 receptor level was significantly increased in newly diagnosed Graves' disease compared to controls (667 +/- 270 vs 205 +/- 45 U/ml) (P less than 0.001). In untreated patients' sera the soluble interleukin-2 receptor levels were higher in patients with active ophthalmopathy than in those without eye symptoms. Soluble interleukin-2 receptor levels were normalized in remission induced by methimazole treatment in the majority of patients except those with infiltrative ophthalmopathy. Furthermore, a correlation was found at the hyperthyroid stage of the disease between soluble interleukin-2 receptor level and titre of anti-TSH-receptor antibodies. However, the association with other parameters including anti-eye muscle, anti-thyroid peroxidase, anti-thyroglobulin antibodies was not significant.

Methimazole treatment aggravates low-dose streptozotocin-induced diabetes

Treatment of mice with methimazole was found to modulate diabetes development following low-dose (5 x 40 mg/kg body weight) streptozotocin administration. The administration of 0.2 or 1 mg methimazole per kg body weight for 1-3 weeks significantly enhanced hyperglycemia. The enhancing effect of methimazole was also seen when administration began only after termination of streptozotocin injections. Methimazole treatment did not potentiate diabetes induced by a single high dose of streptozotocin (175 mg/kg). Serum thyroxin levels were not affected due to the short period of thyrostatic treatment. Semiquantitative immunocytochemistry of inflamed islets did not show a stronger influx of immune cells but rather a high activation state of infiltrated macrophages (M1/70 positive). We conclude that methimazole enhances the development of immune-mediated diabetes.

The effect of carbimazole therapy on interleukin 2, interleukin 2 receptors and free radicals

Levels of Interleukin 2 (IL2), IL2 receptors (IL2R) and free radical scavengers were measured in 25 Graves' disease patients prior to and following an 8 week course of Carbimazole therapy in an attempt to understand the mechanism by which the drug acts on the immune system. In untreated Graves' patients IL2R levels were elevated and IL2 levels reduced. Free radical scavengers were also reduced in these patients. Following treatment IL2R levels fell and IL2 levels rose. Levels of the free radical scanvengers also rose. It is not clear whether it is the fall in IL2R levels or the rise in the level of free radical scavengers (implying a reduction in free radical activity) which is responsible for the rise in IL2.

Myeloperoxidase catalysed cooxidative metabolism of methimazole: oxidation of glutathione and NADH by free radical intermediates

The myeloperoxidase catalysed oxidation of methimazole in the presence of NADH or GSH resulted in oxygen uptake suggesting that metabolism proceeded via a one electron mechanism. The GSH was oxidised to GSSG and the thiyl radical could be trapped with DMPO while NADH was oxidized to NAD+. Metabolism proceeded without the inactivation of the enzyme myeloperoxidase. Myeloperoxidase catalyzed oxidation of other substrates which proceed via one electron intermediates; 2,6-dimethylphenol, N,N,N',N'-tetramethyl-phenylenediamine and luminol, were all stimulated by methimazole providing further evidence for a methimazole free radical. The presence of iodide stimulated the oxidation of methimazole but inhibited the oxygen uptake in the presence of GSH or NADH suggesting that metabolism in this case proceeded by a two electron mechanism. In contrast, another S-thioureylene drug, thiourea; did not cause oxygen uptake when oxidised in the presence of GSH or NADH indicating that the myeloperoxidase oxidation of thiourea proceeded primarily by a two electron mechanism. The horseradish peroxidase catalysed one electron oxidation of p'p'-biphenol, and 3,3',5,5'-tetramethylbenzidine was reversibly inhibited by methimazole and thiourea by preventing the accumulation of oxidation products via reductive mechanisms whereas the reversible inhibition of guaiacol and luminol oxidation was the result of competitive inhibition. With p,p'-biphenol, and 3,3',5,5'-tetramethylbenzidine unstable adduct formation could be demonstrated.

Immunomodulatory effect of methimazole on inbred mice

The effects of antithyroid drug, methimazole (MMI, 1-methyl-2-mercaptoimidazole), on the immune system of inbred mice, C57BL/6, were studied. The proliferative response of splenic lymphocytes to concanavalin A (Con A) and allogeneic stimulator cells was reduced when the mice were provided with 0.1% MMI in tap water ad libitum for two to four weeks. The reduction of proliferative response was correlated with a lower frequency of proliferative spleen cells in the MMI-treated mice. The ability to produce macrophage activating factor of these spleen cells and the levels of hemolytic plaque-forming cells were also reduced. However, the mitogenic response of the splenic lymphocytes to lipopolysaccharide (LPS) was enhanced. In order to investigate whether the impaired cell-mediated and humoral immune systems would increase the susceptibility of the MMI-treated animal to the growth of tumor cells, mice were challenged with a lethal dose of Moloney virus-induced T cell lymphoma of C57BL/6 mice (MBL-2). The time required for 50% of the animals to die was reduced from 15 days for the normal mice to 10 days for the MMI-treated mice.

Methimazole blocks Graves' IgG but not interferon-gamma HLA-DR expression by thyroid cells

We have expanded our early observation that a potent Graves' IgG preparation induces HLA-DR expression on thyroid cells, by showing that four randomly-selected Graves' IgG's were also capable of inducing DR antigens on thyroid cells. The effect of Graves' IgG was specific to thyroid cells, as it did not induce MHC Class II molecule expression on endothelial cells whereas interferon-gamma and immune complexes did so. The anti-thyroid drug methimazole was capable of rapidly reducing Graves' IgG-induced DR expression but to a much lesser extent than brought about by interferon-gamma. We conclude that Graves' IgG propagates thyroid-specific autoaggression by continued induction of DR antigens and than an important means whereby methimazole brings about remission is by reducing this induction.

The effect of antithyroid drugs on B and T cell activity in vitro

This study examined the abilities of methimazole, propylthiouracil (PTU) and propranolol to exert an immunosuppressive effect in vitro. Incubation of peripheral blood lymphocytes (PBL) with propranolol showed the drug to have no effect on either B- or T-cell activity. Methimazole or PTU at concentrations of greater than or equal to 10(-5)M resulted in significantly lower amounts of IgG and IgM being released into the culture medium. Both drugs were also found to have a direct effect on T-cell function as they caused the percentage of total and suppressor cells to increase towards normal levels. The three drugs were all found to have some free radical scavenging ability. These ranked PTU greater than methimazole greater than propranolol. These in-vitro findings would suggest that both methimazole and PTU have some direct effect on the immune system. It would seem more likely however that these effects are mediated via interleukin 2 rather than by their ability to act as free radical scavengers.

Depressed natural killer activity in Graves' disease and during antithyroid medication

To investigate the natural killer (NK) cell mediated immunity in Graves' disease (GD) and the effect of antithyroid drugs upon NK cell activity, 51Cr release assay for NK cytotoxicity against K562 cells was examined in patients with GD before and during antithyroid medication and after drug withdrawal. Fifty-eight patients were divided into three groups: the untreated thyrotoxic patients (n = 33), the euthyroid patients under antithyroid treatment (n = 19) and the euthyroid patients after drug withdrawal (n = 6). The results of the three groups were compared to 23, 15 and 5 sex- and age-matched controls, respectively. The data revealed a significant NK dysfunction in the untreated hyperthyroid patients, although the number of the NK cells was not decreased. NK function was normal when patients were no longer taking antithyroid medication and in euthyroid state. However, euthyroid patients under antithyroid medication had markedly depressed NK activity, suggesting an immunosuppressive effect of the antithyroid drugs. This study demonstrated that both the hyperthyroid state and the antithyroid drugs exerted immunosuppressive effects upon the NK cells. Since such an immunosuppressive effect on NK cells might be associated with a decreased immune surveillance against tumour growth, this study implies that a long-term follow up of GD patients treated with antithyroid drugs may be indicated to guard against a possible increased incidence of malignancy.