The effect of methimazole on the immune system is unlikely to operate directly on T lymphocytes

Antithyroid Drugs

The thionamide drugs, i.e. carbimazole and its metabolite methimazole (MMI), and propylthiouracil (PTU) have extensively been used in the management of various forms of hyperthyroidism over the past eight decades. This review aims to summarize different aspects of these outstanding medications. Thionamides have shown their own acceptable efficacy and even safety profiles in treatment of hyperthyroidism, especially GD in both children and adults and also during pregnancy and lactation. Of the antithyroid drugs (ATDs) available, MMI is the preferred choice in most situations taking into account its better efficacy and less adverse effects accompanied by once-daily dose prescription because of a long half-life and similar cost. Considering the more severe teratogenic effects of MMI, PTU would be the selected ATD for treatment of hyperthyroidism during pre-pregnancy months and the first 16 weeks of gestation. Recent studies have confirmed the efficacy and safety of long-term MMI therapy with low maintenance doses for GD and toxic multinodular goiter. Despite the long-term history of ATD use, there is still ongoing debate regarding their pharmacology and diverse mechanisms of action, viz. their immunomodulatory effects, and mechanisms and susceptibility factors to their adverse reactions.

Predicting relapse of Graves' disease following treatment with antithyroid drugs

The aim of the present study was to monitor long term antithyroid drug treatments and to identify prognostic factors for Graves' disease (GD). A total of 306 patients with GD who were referred to the Endocrinology Clinic at Weifang People's Hospital (Weifang, China) between August 2005 and June 2009 and treated with methimazole were included in the present study. Following treatment, patients were divided into non-remission, including recurrence and constant treatment subgroups, and remission groups. Various prognosis factors were analyzed and compared, including: Patient age, gender, size of thyroid prior to and following treatment, thyroid hormone levels, disease relapse, hypothyroidism and drug side-effects, and states of thyrotropin suppression were observed at 3, 6 and 12 months post-treatment. Sixty-five patients (21.2%) were male, and 241 patients (78.8%) were female. The mean age was 42±11 years, and the follow-up was 31.5±6.8 months. Following long-term treatment, 141 patients (46%) demonstrated remission of hyperthyroidism with a mean duration of 18.7±1.9 months. The average age at diagnosis was 45.6±10.3 years in the remission group, as compared with 36.4±8.8 years in the non-remission group (t=3.152; P=0.002). Free thyroxine (FT)3 levels were demonstrated to be 25.2±8.9 and 18.7±9.4 pmol/l in the non-remission and remission groups, respectively (t=3.326, P=0.001). The FT3/FT4 ratio and thyrotrophin receptor antibody (TRAb) levels were both significantly higher in the non-remission group (t=3.331, 3.389, P=0.001), as compared with the remission group. Logistic regression analysis demonstrated that elevated thyroid size, FT3/FT4 ratio and TRAb at diagnosis were associated with poor outcomes. The ratio of continued thyrotropin suppression in the recurrent subgroup was significantly increased, as compared with the remission group (P=0.001), as thyroid function reached euthyroid state at 3, 6 and 12 months post-treatment. Patients with GD exhibiting large thyroids, high pre-mediation TRAb levels and elevated FT3/FT4 ratios responded less markedly to antithyroid drug treatments, as compared with patients not exhibiting these prognostic factors. Furthermore, patients with large thyroids, post-medication ophthalmopathy and continued thyrotropin suppression demonstrated higher rates of recurrence.

Effect of the inhibition of triiodothyronine (T3) production by thiamazole on the T3 and serotonin content of immune cells

Triiodothyronine (T3) and serotonin are present in the cells of immune system (blood, peritoneal and thymic lymphocytes, monocytes and granulocytes of the blood and peritoneal fluid, mast cells). In the present experiments the effect of thiamazole, an antithyroid drug was studied on the content of these two hormones in immune cells after one and two weeks of continuous treatment (by drinking water, containing 30 mg/100 ml thiamazole, ad libitum) in adult male rats, using flow cytometric and confocal microscopic analysis. In thymic lymphocytes both hormone contents significantly increased in both time points. A significant decrease of T3 was observed in peritoneal monocytes and granulocytes also in both time points, in peritoneal mast cells after one week and in blood lymphocytes after two weeks. Serotonin content in addition to the elevated thymic values (in both measurements) was significantly reduced in blood lymphocytes after two weeks. Confocal microscopy demonstrated heterogeneous cell populations with disparate hormone content and mostly diffuse localization The experiments call attention to the presence of T3 in the immune cells and to its variable concentration under the effect of a thyrostatic drug as well, as to the T3-serotonin relationship in the cells of the immune system.

Provirus load in patients with human T-cell leukemia virus type 1 uveitis correlates with precedent Graves' disease and disease activities

We previously demonstrated the increased provirus load in the peripheral blood of patients with human T-cell leukemia virus type 1 (HTLV-1) uveitis (HU). To delineate the relevance of the increased provirus load to clinical and immunologic parameters, we studied the correlation between them. Seventy-nine HU patients (24 male and 55 female) were included in the study, with their informed consent. Plasma samples and genomic DNA of the peripheral blood mononuclear cells were isolated and the provirus load was estimated by semi-quantitative polymerase chain reaction of the gag region sequence. Serum levels of anti-HTLV-1 antibodies and soluble IL-2R were determined by electrochemiluminescence immuno assay and by ELISA, respectively. Disease activities were assessed and graded 0 to 4 according to the evaluation system. Recurrence of the disease during the follow-up period was diagnosed ophthalmologically. The provirus load was significantly higher in the HU patients after Graves' disease (GD) than in those without GD (P<0.05). It correlated with disease activities assessed in terms of vitreous inflammation and interval to recurrence (both P<0.05). In the HU patients without GD, it correlated with the serum levels of soluble IL-2 receptor (P<0.01), and nearly with those of HTLV-1 antibody (P=0.063). These correlations were not found in the HU patients after GD under methimazole treatment. The results suggested a direct involvement of HTLV-1-infected cells in the pathogenesis of uveitis, and raise the possibility that hyperthyroidism may contribute to the clonal expansion of HTLV-1-infected cells.

Evidence that the immunosuppressive effects of antithyroid drugs are mediated through actions on the thyroid cell, modulating thyrocyte-immunocyte signaling: a review

The mechanism of action of the immunosuppressive effects of antithyroid drugs has remained a matter of controversy, despite our earlier contention that such effects in vivo were indirect, i.e., it was our view that the drugs were acting on the thyroid cells, reducing their hormone production and other activities, with a consequent reduction in thyrocyte-immunocyte signaling. The reduction in the activation of CD4+ cells, the increased number and activation of CD8+ (and CD8+CDIIb+) cells, and the reduction of soluble interleukin-2 receptors, thought once to be direct effects of the medication, are now shown to be due to amelioration of the hyperthyroidism. Thus the reduction in thyroid hormone production induced by the drugs is central to these actions. In addition, the iodination of thyroglobulin is inhibited by these agents, which may affect antigen presentation by the thyrocyte. Furthermore, there is now evidence that the thionamides interfere with thyrocyte expression of Class I antigen, interleukin-1, interleukin-6, prostaglandin E2, and heat shock protein. The expression of thyrocyte Class II antigen is probably not inhibited by these drugs, although one group has shown that lectin-stimulated thyrocyte Class II expression is diminished by this treatment; this group postulated that this effect might be mediated by reduced interferon-gamma production by T lymphocytes, but in vitro experiments do not corroborate this proposal. In any event, the actions as described, of the antithyroid drugs on the thyroid cells, would certainly suffice to explain the diminution of thyroid antibodies (including thyroid stimulating antibody), the reduced immunological response, and the increased remission rate in Graves' disease, without the need to invoke a direct immunosuppressive effect.

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.

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.

Has the use of antithyroid drugs for Graves' disease become obsolete?

In spite of an experience of almost 50 years of use of antithyroid drugs and radioiodine for the treatment of Graves' disease, the rationale for choice is often obscure. Early reports of high remission rates during thiourea therapy were followed by less optimistic ones, which along with other factors may have fueled the current major shift toward use of radioiodine. This review examines whether or not the use of antithyroid drugs indeed may have become obsolete. The intrathyroidal and extrathyroidal mechanisms of action of the drugs are reviewed with emphasis on their potential immunosuppressive effects. The latter may involve a direct effect on thyroid follicular cells, a direct suppression of TSH receptor antibody formation, or indirect effects mediated via heat shock proteins, oxygen free radicals, and the immune system. Potential factors associated with success or failure with antithyroid drug therapy are discussed, such as the effects of dose and duration of treatment, iodine milieu, and concomitant L-thyroxine therapy. The risks inherent to radioiodine therapy are only briefly described with emphasis on the possible aggravation by radioiodine of preexistent ophthalmopathy. The reader must decide whether the evidence marshalled convincingly indicates that the use of the thiourea compounds should be abandoned. The author thinks not, and is optimistic that imminent discovery of the yet elusive and enigmatic pathogenesis of Graves' disease will permit new and innovative treatment or more effective use of currently available therapies.