Dermatomyosite induite par la pravastatine

INTRODUCTION

The toxic myopathy caused by statins (HMG-CoA reductase inhibitors) is well established. Recent reports add to these effects systemic immune diseases including systemic lupus erythematosus, vasculitis, polymyositis or dermatomyositis.

EXEGESIS

We report a case of dermatomyositis in a 69-year-old patient treated with pravastatin [Elisor]. She presented with typical features of dermatomyositis 2 years after she started a treatment with pravastatin. The treatment was discontinued and she slowly improved, with a transient dermocorticosteroid treatment. Eight other patients with dermatomyositis and chronic treatment with HMG-CoA reductase inhibitors are reported in the literature. All of them presented with classical features of dermatomyositis. The discontinuation of the treatment was followed by spontaneous clinical and biological improvement in 3/9 patients. The other patients received high doses of corticosteroids and improved, except one patient who died of respiratory failure (pulmonary fibrosis) despite the adjunction of oral cyclophosphamide [Endoxan]. In these patients, dermatomyositis can be considered as a severe adverse reaction to HMG-CoA reductase inhibitors although a distinct casual link cannot be definitely established.

CONCLUSION

The increasing prescription of statins has led to the parallel increment of reported side-effects, where autoimmune diseases are now described. Among them, our case of dermatomyositis in a patient receiving pravastatin adds to the eight reported cases in the literature and highlights the potential role of statins as triggers of immune systemic diseases.

Molecular model, calcium sensitivity, and disease specificity of a conformational thyroperoxidase B-cell epitope

While studying the humoral mechanisms involved in thyroid autoimmunity, we located a B-cell autoepitope in the extracellular C-terminal region of human thyroperoxidase. Structural modeling showed that this region encompasses both a Sushi-like and an epidermal growth factor-like domain, the flexible arrangement of which was putatively stabilized by calcium. The recombinant peptide was found to contain the previously identified conformational thyroperoxidase autoepitope. The occurrence of a calcium-induced conformational change was confirmed using a recombinant peptide monoclonal antibody, the decrease of which in binding to calcium-saturated thyroperoxidase was reversed by a chelating agent. The disease specificity of recombinant peptide, which was more frequently recognized by Hashimoto's than by Graves' patients, adds to its potential value as a diagnostic and preventive tool in the context of B-cell autoimmunity.

Hydrogen peroxide-induced production of a 40 kDa immunoreactive thyroglobulin fragment in human thyroid cells: the onset of thyroid autoimmunity?

We recently reported that, during in vitro thyroid-hormone synthesis, H(2)O(2) stress cleaved thyroglobulin (Tg) into C-terminal peptides. These peptides were found to contain the immunodominant region of Tg recognized by Tg autoantibodies from patients with an autoimmune thyroid disease. To test the hypothesis that Tg fragmentation is an early upstream initiating event involved in Tg autoimmune response and the consequence of oxidative injuries, we studied the effect of H(2)O(2) stress on human thyroid cells. In culture conditions allowing Tg synthesis and iodine organification by the cells, we found that bolus addition of increasing millimolar doses of H(2)O(2) induced a dose-response appearance of floating cells in the culture medium. These cells apparently resulted from a necrotic process, and they bore iodinated Tg fragments. These fragments were found to be similar to those previously obtained in vitro from purified Tg. In both cases, Tg peptides were recognized by a well-defined monoclonal antibody directed to the immunodominant region of Tg. The smallest immunoreactive Tg peptide had a molecular mass of 40 kDa and entered human thyrocytes more efficiently than the entire Tg. These data suggest that thyrocytes exposed to locally increased H(2)O(2) doses accumulate fragmented Tg for further delivery into surrounding living thyrocytes in the course of an autoimmune response.

A conformational B-cell epitope on the C-terminal end of the extracellular part of human thyroid peroxidase

To investigate the B-cell autoimmune epitopes on human thyroid peroxidase (TPO), we generated proteolytic peptides by enzymatic hydrolysis of TPO in nondenaturing and nonreducing conditions. The hydrolysate was chromatographed on a reverse phase column. We eluted a material immunoreactive with both a TPO monoclonal antibody recognizing a linear epitope (mAb47, amino acid 713-721) and TPO autoantibodies (aAb) from patients. The aAb immunoreactivity, but not that of mAb47, was lost after reduction. Western blots after electrophoresis without reduction showed that the aAb and mAb47 were immunoreactive with a 66-kDa band and that aAb identified a doublet at 20 kDa. For electrophoresis under reducing conditions, the 66-kDa band resolved into two peptides of 40 and 26 kDa, whereas the doublet at 20 kDa remained unchanged. None of these reduced peptides was immunoreactive with aAb, whereas the 40-kDa peptide was immunoreactive with mAb47. The 40-kDa peptide extends from amino acid 549 to 933 of TPO, and its last 192 amino acids overlap the autoimmune 20-kDa peptide. After iodine labeling, the 20-kDa peptide lost its immunoreactivity. We conclude that the C-terminal end of the extracellular part of TPO, which includes all the tyrosine residues of the 20-kDa peptide, contains at least one conformational B-cell epitope involved in autoimmune thyroid diseases.

Multicenter study on TGPO autoantibody prevalence in various thyroid and non-thyroid diseases; relationships with thyroglobulin and thyroperoxidase autoantibody parameters

OBJECTIVE

TGPO autoantibodies (aAbs) that bind simultaneously to thyroglobulin (Tg) and thyroperoxidase (TPO) are present in the serum of patients with autoimmune thyroid diseases (AITD) and have been found to differ from monospecific Tg and TPO aAbs. To obtain further insights on the prevalence defined as the rate of occurrence and significance of TGPO aAbs in a large population, we carried out a collaborative study involving 15 European teams.

METHODS

Serum samples from 3122 patients with various thyroid and non-thyroid diseases and normal subjects were assayed using a novel TGPO aAb detection kit. This test was designed so that TGPO aAbs are trapped between the Tg-coated solid phase and the soluble TPO labeled with a radioiodinated monoclonal antibody.

RESULTS

Only three out of the 220 normal subjects (prevalence of 1.4%) were found to have positive TGPO aAb levels, which were mainly observed in the patients with AITD: the group of patients suffering from Hashimoto's thyroiditis had a TGPO aAb prevalence of 40.5% (n=437 patients), those with Graves' disease, a prevalence of 34.6% (n=645) and those with post-partum thyroiditis, 16.0% (n=243). Among the non-AITD patients with positive TGPO aAb levels, the TGPO aAb prevalence ranged from 20.7% among those with thyroid cancer (n=246) to 0% among those with toxic thyroid nodules (n=47). Among the patients with non-thyroid diseases, the TGPO aAb prevalence ranged from 9.8% in the case of Biermer's pernicious anemia (n=78) to 0% in that of premature ovarian failure (n=44). It is worth noting that the groups showing the highest TGPO aAb prevalence also contained the patients with the highest TGPO aAb titers. Statistical comparisons between the TGPO aAb prevalences in the various groups showed that TGPO aAb could be used as a parameter to distinguish between the groups of Hashimoto's and Graves' patients and between the women with post-partum thyroiditis and the post-partum women with only Tg and/or TPO aAb established during early pregnancy. Unexpectedly, the correlations between TGPO aAbs and Tg and TPO aAbs were found to depend mainly on the assay kit used.

CONCLUSION

High TGPO aAb titers are consistently associated with AITD but the reverse was not found to be true. TGPO aAbs are a potentially useful tool, however, for establishing Hashimoto's diagnosis, and would be worth testing in this respect with a view to using them for routine AITD investigations.

Production of immunoreactive thyroglobulin C-terminal fragments during thyroid hormone synthesis

Here, we studied the fragmentation of the prothyroid hormone, thyroglobulin (Tg), which occurs during thyroid hormone synthesis, a process which involves iodide, thyroperoxidase, and the H2O2-generating system, consisting of glucose and glucose oxidase. Various peptides were found to be immunoreactive to autoantibodies to Tg from patients and monoclonal antibodies directed against the immunodominant region of Tg. The smallest peptide (40 kDa) bore thyroid hormones and was identified at the C-terminal end of the Tg molecule, which shows homologies with acetylcholinesterase. Similar peptides were obtained by performing metal-mediated oxidation of Tg via a Fenton reaction. It was concluded that the oxidative stress induced during hormone synthesis generates free radicals, which, in turn, cleave Tg into immunoreactive peptides.

Thyroglobulin monoclonal antibody cross-reacting with thyroperoxidase induces in syngeneic mice anti-idiotypic monoclonal antibodies with dual autoantigen binding properties. The intertope hypothesis

Autoimmune thyroid diseases are characterized by antibodies (Ab) directed to thyroglobulin (Tg) and thyroperoxidase (TPO). Some of them, TGPO Ab, are Tg Ab with an interspecies idiotype (Id) reacting with TPO. Taking advantage of a carefully studied TGPO monoclonal antibody (mAb), we examined the basis of the hypothesis that TPO Ab would ultimately derive from TGPO Ab through idiotypic induction. We repeatedly immunized naive, syngeneic mice with the TGPO mAb and we derived three novel mAb directed to both Tg and TPO. The most reactive of them, mAb 4F8, was further purified, radiolabeled and its binding properties studied by radioimmunoassay. mAb 4F8 bound to Tg, TPO, the immunogen Ab1 and even to itself, being thus considered as a self-binding Ab2. Competitive binding inhibition experiments demonstrated that Tg, TPO, Ab1 and Ab2 cross-reacted for Ab2 binding to Tg, TPO and Ab1. Fine specificity mapping using panels of specific mAb revealed that Ab1 and Ab2 were similar because they were directed against the same immunodominant regions on Tg and TPO. We propose that unique Id of TGPO Ab resemble dominant epitopes of Tg as well as paratopes of Ab directed against dominant TPO epitopes. This category of Id that we called intertopes may induce TPO-monospecific Ab from TGPO Ab by idiotypically driven somatic mutations.