Immunosuppressive effects of antithyroid drugs

Hyperthyroidism in the personalized medicine era: the rise of mathematical optimization

Thyroid over-activity or hyperthyroidism constitutes a significant morbidity afflicting the world. The current medical practice of dose titration of anti-thyroid drug (ATD) treatment for hyperthyroidism is relatively archaic, being based on arbitrary and time-consuming trending of thyroid function that requires multiple clinic monitoring visits before an optimal dose is found. This prompts a re-examination into more deterministic and efficient treatment approaches in the present personalized medicine era. Our research project seeks to develop a personalized medicine model that facilitates optimal drug dosing via the titration regimen. We analysed 49 patients' data consisting of drug dosage, time period and serum free thyroxine (FT4). Ordinary differential equation modelling was applied to describe the dynamic behaviour of FT4 concentration. With each patient's data, an optimization model was developed to determine parameters of synthesis rate, decay rate and IC₅₀. We derived the closed-form time- and dose-dependent solution which allowed explicit estimates of personalized predicted FT4. Our equation system involving time, drug dosage and FT4 can be solved for any variable provided the values of the other two are known. Compared against actual FT4 data within a tolerance, we demonstrated the feasibility of predicting the FT4 subsequent to any prescribed dose of ATD with favourable accuracy using the initial three to five patient-visits' data respectively. This proposed mathematical model may assist clinicians in rapid determination of optimal ATD doses within allowable prescription limits to achieve any desired FT4 within a specified treatment period to accelerate the attainment of euthyroid targets.

Methimazole interferes with the progression of experimental autoimmune myocarditis in rats

In order to ascertain whether methimazole, a drug commonly used for the treatment of hyperthyroidism, interferes with the progression of autoimmune-mediated myocardial injury, we investigated the effect of methimazole on experimental autoimmune myocarditis (EAM) in rats. EAM was induced by immunization with porcine cardiac myosin. Methimazole administration markedly slowed the body weight growth in both normal and EAM rats, but did not induce morphologic change of cardiac tissue in normal rats. In EAM rats, macroscopic examination revealed discoloration of the cardiac surface, and histopathological examination by light microscopy showed extensive myocardial necrosis, infiltration by inflammatory cells and myocardial fibrosis. In the EAM rats treated with methimazole, the discolored areas on the cardiac surface were markedly diminished in size, and the myocardial necrosis, cellular infiltration and fibrosis were significantly less severe. To identify the mechanism responsible of this effect, we investigated the change of regulatory lymphocyte subsets in peripheral blood using an immunofluorescence technique with a flow cytometer. A decrease in the helper/suppressor T cell ratio as a result of the increased proportion of suppressor T cells and a decrease in the proportion of B cells were observed in normal rats after methimazole administration, and similar findings were made in the EAM rats treated with methimazole. These results indicate that methimazole interferes with the progression of EAM, and immunosuppression may, at least in part, be involved in the inhibitory effect of methimazole on EAM in rats.

Thyroid autoimmune disease: demonstration of thyroid antigen-specific B cells and recombination-activating gene expression in chemokine-containing active intrathyroidal germinal centers

Autoimmune thyroid disease--Hashimoto thyroiditis and Graves' disease--patients produce high levels of thyroid autoantibodies and contain lymphoid tissue that resembles secondary lymphoid follicles (LFs). We compared the specificity, structure, and function of tonsil and lymph node LFs with those of the intrathyroidal LFs to assess the latter's capability to contribute to autoimmune response. Thyroglobulin and thyroperoxidase binding to LFs indicated that most intrathyroidal LFs were committed to response to thyroid self-antigens and were associated to higher levels of antibodies to thyroglobulin, thyroperoxidase, and thyroid-stimulating hormone receptor. Intrathyroidal LFs were microanatomically very similar to canonical LFs, ie, they had well-developed germinal centers with mantle, light, and dark zones and each of these zones contained B and T lymphocytes, follicular dendritic and interdigitating dendritic cells with typical phenotypes. Careful assessment of proliferation (Ki67) and apoptosis (terminal dUTP nick-end labeling) indicators and of the occurrence of secondary immunoglobulin gene rearrangements (RAG1 and RAG2) confirmed the parallelism. Unexpected high levels of RAG expression suggested that receptor revision occurs in intrathyroidal LFs and may contribute to generate high-affinity thyroid autoantibodies. Well-formed high endothelial venules and a congruent pattern of adhesion molecules and chemokine expression in intrathyroidal LFs were also detected. These data suggest that ectopic intrathyroidal LFs contain all of the elements needed to drive the autoimmune response and also that their microenvironment may favor the expansion and perpetuation of autoimmune response.

Fas ligand expression in thyroid follicular cells from patients with thionamide-treated Graves' disease

Thionamides are used in the treatment of Graves' disease (GD) and act mainly by inhibiting the organification of iodide, but also lower the levels of thyroid autoantibodies, sometimes leading to long-term remission. Fas ligand (FasL) induces apoptosis of susceptible cells by cross-linking its own receptor, Fas. While Fas is present in a wide variety of normal tissues, FasL expression is limited mainly to cells of the immune system, where it acts as an effector molecule of cell-mediated cytotoxicity, and to the placenta, brain, eye, and testis where it presumably contributes to their immune-privileged status by eliminating infiltrating lymphocytes. We examined immunohistochemically the presence of FasL in thyroid tissue from 15 glands of thionamide-treated GD patients and in 8 normal thyroid control specimens. We also investigated the presence of FasL in thionamide-treated thyrocytes in vitro and their ability to induce Fas-mediated apoptosis in lymphocytes. We found that FasL expression was very weak to undetectable in normal thyroid tissue and cultured thyrocytes, whereas it was strong in thionamide-treated GD glands and cultured thyrocytes. Methimazole-treated thyrocytes induced FasL-dependent apoptosis in cocultured lymphocytes, whereas methimazole treatment of lymphocytes grown in the absence of thyrocytes had no such effect. We conclude that FasL is highly expressed in follicular cells of thyroid glands obtained from thionamide-treated Graves' patients and may contribute to the immunomodulatory effect of thionamides in this disease.

ULTRASONOGRAPHIC AND DOPPLER STUDY OF THE THYROID GLAND IN GRAVES' DISEASE BEFORE AND AFTER TREATMENT WITH ANTITHYROID DRUGS

OBJECTIVE

To determine the effects of medical treatment on the thyroid gland, peripheral circulation, and laboratory findings in patients with Graves' disease.

METHODS

Twenty patients with Graves' disease were treated with either carbimazole and propranolol (group I) or carbimazole only (group II). Serum free thyroxine (FT(4)), thyroid-stimulating hormone (TSH), and thyrotropin-binding inhibitory immunoglobulins (TBII) were estimated before and after 6 weeks of treatment. Duplex Doppler ultrasonographic examination of the thyroid, inferior thyroid artery (ITA), and common carotid artery (CCA) was performed before and after 2, 4, and 6 weeks of therapy.

RESULTS

Serum FT(4) and TBII decreased after treatment in both groups, whereas serum TSH increased in group I only. The volume of the thyroid gland and parenchymal blood velocity were increased in these patients and diminished only with addition of propranolol to carbimazole. A diffuse hypoechogenic pattern in the thyroid gland and increased ITA blood flow and peak velocity were observed in all patients and persisted throughout treatment. The mean CCA peak blood velocity was accelerated in Graves' disease and diminished after 6 weeks of therapy in both groups, whereas increased CCA blood flow diminished only in group I.

CONCLUSION

A 6-week period of therapy with carbimazole and propranolol has no effect on the diffuse low echogenic pattern in the thyroid gland and the accelerated ITA blood flow in Graves' disease. The addition of propranolol is associated with early decrements in thyroid volume, parenchymal vascularity, and CCA blood flow as well as early recovery of TSH suppression, but it has no additional effect on thyroid hormone secretion or TBII levels.

[Amiodarone-induced thyrotoxicosis cured by thyroidectomy]

We report a case of amiodarone-induced thyrotoxicosis, diagnosed with a systematic laboratory investigation in a 64-year-old patient, for haematuria. Despite the interruption of amiodarone, hyperthyroidism and a goiter occurred. Conventional therapy betablockers, antithyroid agents, prednisone, potassium perchlorate) did not result in any clinical improvement. The development of a malignant thyrotoxicosis with neurologic disturbances and acute respiratory insufficiency required mechanical ventilation and a subtotal thyroidectomy. The patient's status improved progressively and he was discharged without sequelae. The respective roles of medical therapy and thyroidectomy in amiodarone-induced thyrotoxicosis are discussed.

A Clinical Guide to the Management of Graves’ Disease with Radioactive Iodine

More than 50 years have passed since radioactive iodine (RAI) was initially demonstrated as a therapeutic modality for the treatment of Graves' Disease. Today, more than a million patients have been treated with RAI. RAI is considered safe and highly effective. Its side-effect profile, ease of administration, and relative cost make RAI the treatment of choice for Graves' Disease of thyroidologists in this country. Questions continue to be raised as to which patients will benefit most from RAI therapy. Marked differences still exist between the practice preferences of thyroidologists as to whom, when, and how to treat with RAI. Factors that influence patient selection for RAI include age, the presence of pre-existing ophthalmopathy, lifestyle, history of previous treatment failure, and goiter size. Treatment goals, dosimetry, use of thionamides prior to therapy, safety recommendations following therapy, and prophylactic therapy with glucocorticoids for patients with ophthalmopathy highlight are some of the controversial issues facing the endocrinologist treating Graves' Disease with RAI. This symposium article reviews the current management of Graves' Disease with RAI.

The Pathogenesis of Graves’ Disease

We have hypothesized over many years that Graves' disease (GD) and the other autoimmune thyroid diseases (AITD) are each due to antigen-specific defects in suppressor (regulatory) T lymphocyte function. There have been several reports dealing with the role of regulatory T lymphocyte subsets, ie., that will prevent autoimmune disease in these and other organ-specific autoimmune diseases. In AITD, suppressor T cells have been shown to be less well activated by relevant antigen, but are normally activated by irrelevant antigen; suppressor T cells from normal persons react equally well to both. In GD, these cells have been shown to be inadequately activated by TSH receptor antigen, but are normally activated by irrelevant autoantigen. This reduction is partial only, and insufficient itself to precipitate the autoimmune disease; further insults from the environment are necessary to further reduce generalized regulatory cell activity, adding to the genetically induced specific regulatory cell dysfunction, which appears in turn to be due to a specific defect in the presentation of a specific antigen. This, in turn, may relate to abnormalities of the genes responsible for antigen presentation. The end result is activation of appropriate helper and effector T cells, the stimulation by these of appropriate B lymphocytes, and the concurrent production of cytokines. These events lead to functional changes within the target cell which itself will express Class II antigens, heat shock proteins, and intercellular adhesion molecules, all of which amplify the immune response. Moreover, the activation of helper T lymphocytes by specific antigen depends on the availability of normal amounts of antigen being presented to them by antigen-presenting cells. Thus, there is no need to invoke any primary abnormality or infection of the thyroid cell, or any cross-reacting antigen of microorganismic origin to initiate this process. What is required is an abnormality of antigen-presentation such that regulatory cells are not properly activated, plus some additive environmental disturbance acting on the immune system. GD specifically results from the production by B lymphocytes of an antibody directed against the TSH receptor which stimulates the thyrocyte in a manner similar to TSH, but for a much longer interval. There are also antibodies to the thyrotrophin (TSH) receptor which block the action of TSH. Thyroid stimulating antibody is typical of GD and is detectable in about 95% of cases, but is also seen in destructive thyroiditis transiently. It tends to decline with antithyoid drug therapy, and rises further (for several months) after 131 I treatment. It may slowly decline after subtotal thyroidectomy. It also declines in the third trimester of pregnancy but sometimes is sufficiently high to cause foetal and neonatal passive transfer GD. It tends to rebound in the mother after delivery and may result in postpartum GD. The blocking antibody may cause atrophic thyroiditis and hypothyroidism. Antimicrosomal antibody has now been shown to be antithyroperoxidase. It correlates moderately well with thyroid dysfunction in Hashimoto's thyroiditis (HT) and GD, while antithyroglobulin is of much less value. Graves' ophthalmopathy is still not well understood, and its precise relationship to Graves' hyperthyroidism has yet to be worked out. However the retroorbital fibroblast is now emerging as the most likely target cell, with retroorbital muscle involvement possibly secondary. A recent observation of a genomic point mutation on the TSH receptor on fibroblasts from patients with Graves' ophthalmopathy but not normal persons raises interesting possibilities.

Age-related therapeutic response to antithyroid drug in patients with hyperthyroid Graves' disease

OBJECTIVE

To determine whether there is an age-related difference in the therapeutic response to antithyroid drugs in hyperthyroid Graves' disease.

DESIGN

Retrospective analysis of treatment duration and recurrence rate.

PATIENTS

Two hundred and twenty-two patients who have triiodothyronine-suppressible thyroids within 4 years of methimazole treatment.

MEASUREMENTS

Serum thyroid hormone levels, serum thyrotropin receptor antibody titer, and thyroidal radioiodine uptake.

MAIN RESULTS

A longer period of methimazole treatment was needed to normalize serum thyroid hormone levels and to restore normal thyroidal triiodothyronine suppressibility in young than in aged patients. There was an average 10-month lag between normalization of thyrotropin receptor antibody titer and restoration of thyroidal triiodothyronine suppressibility in both young and aged patients. Recurrence after discontinuation of methimazole was more frequent in young than in aged patients.

CONCLUSIONS

Aged patients with hyperthyroid Graves' disease show a more favorable response to antithyroid drugs than young counterparts.

The incidence of recurrence and hypothyroidism following treatment with antithyroid drugs, surgery or radioiodine in all patients with thyrotoxicosis in Malmö during the period 1970-1974

The incidence of recurrence and of hypothyroidism was determined in all new patients treated for thyrotoxicosis during the period 1970-1974 in an unselected, well-defined urban population. A total of 309 patients were followed up for a median time period of 108 (1-192) months. There was a cumulative incidence of 51% recurrence in patients who were treated with antithyroid drugs for Graves' thyrotoxicosis, whereas after surgery or radioiodine treatment there were few recurrences, but 32% and 78% cumulative incidences of hypothyroidism. There were no recurrences after surgery or radioiodine treatment in patients with toxic multinodular goitre or solitary toxic adenoma, but 29% and 40% cumulative incidences of hypothyroidism following radioiodine treatment. Late hypothyroidism occurred after surgery for Graves' thyrotoxicosis, and in all groups treated with radioiodine. Thus it is advisable that all patients with Graves' thyrotoxicosis, regardless of treatment, and all patients with toxic multinodular goitre or solitary toxic adenoma treated with radioiodine, should be followed up for many years, and probably for life.

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.

Pregnancy and autoimmune thyroid disease

Immunological and endocrine changes related to pregnancy influence the course and development of autoimmune thyroid disease (AITD). Conversely, the presence of AITD can affect both the mother and her child-both in utero and in the neonatal period. The successful management of AITD in pregnancy requires a knowledge of the differential placental transfer of various hormones, antibodies, and drugs.

The thyroid stimulating hormone receptor in human disease

The initial step in the action of thyrotropin (TSH) is its binding to the TSH receptor. TSH receptor antibodies are detected in up to 90% of patients with Graves' disease. Serial measurements of TSH receptor antibodies in patients with Graves' hyperthyroidism are helpful in predicting relapse. The TSH receptor was purified using affinity chromatography on wheat germ lectin agarose and TSH-agarose. Using an immunoblotting technique to characterize the TSH receptor, it was found to be an oligomeric glycoprotein consisting of three noncovalently bound subunits of Mr approximately 70,000, approximately 50,000 and approximately 35,000 which on reduction yield a single subunit of Mr approximately 25,000.

DQA2 U allele: a genetic marker for relapse of Graves' disease

The association of HLA-DR3 with Graves' disease in Caucasoids is well established but its significance is unclear and its clinical value as a predictive parameter for relapse after a course of antithyroid drug therapy is controversial. We have further investigated the predictive value at the genomic level in 51 patients with Graves' disease who were treated with a 6-month course of carbimazole and followed up for 2 years. Using DNA-restriction fragment length polymorphism (DNA-RFLP) allogenotyping, (i) complete concordance of HLA-DR assignment was observed between serological and DNA-RFLP analysis of all but one of 51 patients with Graves' disease; (ii) the DR beta 17(1)-DQ alpha 2-DQ beta 2a (a DNA-RFLP allogenotype of the classical Northern European haplotype of HLA-B8 DR3) was significantly (corrected P = Pcorr less than 0.02) associated with Graves' disease particularly in patients who relapsed (Pcorr less than 0.005); (iii) HLA-DR3 was highly associated with DQA2 U allele (chi 2 = 18.53, d.f.2, P less than 0.0005); (iv) a strong correlation between the DQA2 U allele and the outcome of the disease was observed. Relapse occurred in 91% (10/11) of the patients who were homozygous for the DQA2 U allele whilst only 65% (15/23) and 41% (7/17) of patients who were hetero or homo-zygous for the DQA2 L allele (DQA2 U/L and DQA2 L/L) relapsed within the same period of follow-up (chi 2 = 7.18, d.f.2, P less than 0.05). Though the relapse rate in patients with the DQA2 U/U genotype was not significantly higher than the relapse rate in patients with the DQA2 U/L genotype, it was significantly higher than the relapse rate in patients with DQA2 L/L genotype (P less than 0.0001) with a relative risk of 14.3.

Lack of effect of methimazole on thyrocyte cell-surface antigen expression

The nature of the immunosuppressive effect of antithyroid drugs has been a subject of controversy. It has been claimed that these agents exert a direct effect on the immune system, although we and others have suggested that the drugs affect the thyroid cells primarily with consequent reduced thyrocyte-immunocyte signalling. This may occur from reduced thyroid hormone production and/or reduced antigen presentation by the thyrocytes to local T lymphocytes. Using a cytotoxicity assay system, with chromium-51 labelling, monoclonal antibodies against thyroperoxidase (TPO) and HLA-DR, and complement, we have measured the expression of TPO and HLA-DR on cultured normal human thyroid cells; we have also measured thyroglobulin (Tg) release by radioimmunoassay into the medium of the cultured cells. The thyroid cells were stimulated with TSH or thyrotropin binding inhibitory immunoglobulin (TBII) for 48 hours before measuring for TPO induction, and with interferon gamma (IFN-gamma) (with or without TSH or TBII) for thyrocyte HLA-DR expression. A dosage of 1.6 milliunits per ml of TSH resulted in a significant increase in TPO expression on thyrocytes when compared with control unstimulated thyroid cells (p less than 0.001). The concentrations of Tg released into the medium with TSH or TBII were also significantly higher than those of the control thyrocytes. IFN-gamma at 200 units per ml induced HLA-DR expression, but did not induce thyrocyte TPO expression, or Tg release. Addition of the antithyroid drug, methimazole (MMI), at different concentrations, in addition to the other stimulators, IFN-gamma, TSH, or TBII, did not result in any inhibition of TPO, Tg release, or HLA-DR expression on the thyroid cells. It would thus appear that the pathways for stimulation for the expression of TPO and HLA-DR appear to be different. Finally, MMI does not cause its immunosuppressive effect by any reduction of thyroid antigen expression or release.

Complement component C9 in Graves' disease

C9, the terminal component of complement, is the key part of the membrane attack complex formed as a result of complement activation; it has also been reported to be an acute phase protein. Its potential role in Graves' disease has been studied by measuring plasma C9 concentrations using an automated two-site immunoradiometric assay employing monoclonal antibodies, whose binding to thyroid tissue has also been investigated. The plasma C9 concentration in patients with hyperthyroid Graves' disease (86.3 +/- 21.6 mg/l, mean +/- SD; n = 49) was significantly increased (P less than 0.001) compared with normal subjects (60.4 +/- 13.4 mg/l; n = 48). In contrast, the plasma concentration of C-reactive protein, a marker of the acute phase response, was not significantly different between the two groups. The plasma C9 concentration in patients with hyperthyroid Graves' disease decreased significantly (P less than 0.01) after treatment with antithyroid drugs (carbimazole or methimazole; n = 14), but not after radioactive iodine (131I) treatment (n = 18). Immunohistochemical staining demonstrated that monoclonal antibody to C9 bound to the basement membranes of thyroid follicular cells of Graves' thyroid tissue but not to normal thyroid tissue. Radiolabelled monoclonal antibody to C9 bound to membrane fragments prepared from thyroid glands from two patients with Graves' disease. We conclude that C9, and by implication the membrane attack complex, may be involved in the pathogenesis of Graves' disease.