Penicillamine-induced myasthenia gravis: effects of penicillamine on acetylcholine receptor

Pathomechanisms and Clinical Implications of Myasthenic Syndromes Exacerbated and Induced by Medical Treatments

Myasthenic syndromes are typically characterized by muscle weakness and increased fatigability due to an impaired transmission at the neuromuscular junction (NMJ). Most cases are caused by acquired autoimmune conditions such as myasthenia gravis (MG), typically with antibodies against the acetylcholine receptor (AChR). Different drugs are among the major factors that may complicate pre-existing autoimmune myasthenic conditions by further impairing transmission at the NMJ. Some clinical observations are substantiated by experimental data, indicating that presynaptic, postsynaptic or more complex pathomechanisms at the NMJ may be involved, depending on the individual compound. Most robust data exist for the risks associated with some antibiotics (e.g., aminoglycosides, ketolides, fluoroquinolones) and cardiovascular medications (e.g., class Ia antiarrhythmics, beta blockers). Apart from primarily autoimmune-mediated disorders of the NMJ, de novo myasthenic manifestations may also be triggered by medical treatments that induce an autoimmune reaction. Most notably, there is growing evidence that the immune checkpoint inhibitors (ICI), a modern class of drugs to treat various malignancies, represent a relevant risk factor to develop severe and progressive medication-induced myasthenia via an immune-mediated mechanism. From a clinical perspective, it is of utmost importance for the treating physicians to be aware of such adverse treatment effects and their consequences. In this article, we aim to summarize existing evidence regarding the key molecular and immunological mechanisms as well as the clinical implications of medication-aggravated and medication-induced myasthenic syndromes.

Acetylcholine receptor-alpha subunit expression in myasthenia gravis: a role for the autoantigen in pathogenesis?

Previous studies have shown increased expression of acetylcholine receptor-alpha (AChR-alpha) subunit transcripts in myasthenia gravis (MG) and experimental MG (EAMG), but none examined the functional properties of this overexpression. In this study we examined the mRNA and protein expression of AChR-alpha as well as the pattern of alpha-bungarotoxin labeling in muscle tissue from EAMG mice with varying disease severity. AChR-alpha expression was increased considerably in endplates from mice with severe EAMG, but it was distinct and greatly in excess of alpha-bungarotoxin labeling. This "aberrant expression" occurred in mice with morphologic endplate damage, and the pattern of complement and immunoglobulin deposition in muscle from these mice appeared to mirror the pattern of AChR-alpha expression. The loss of functional AChR in severe MG increases transcription of AChR-alpha mRNA, but the expressed protein is "functionally inert," failing to compensate for loss of AChR. This enhanced expression of AChR may play a role in driving the ongoing autoimmune response. Muscle Nerve 40: 279-286, 2009.

Gold salts, D-penicillamine and allopurinol

Gold salts have been used in the treatment of patients with rheumatoid arthritis since 1927 [1]. After a controlled study, the Empire Rheumatism Council [2], confirmed the effectiveness of gold salts for the treatment of rheumatoid arthritis. Even today, chrysotherapy has remained one of the major therapeutic modalities in the second line treatment of progressive rheumatoid arthritis. Gold salts are also used in the treatment of pemphigus vulgaris [3] and bronchial asthma [4]. Before the introduction of an orally administered gold compound, auranofin (triethylphosphine gold tetra-acetyl glycopyranoside), to clinical use [5-7], parenterally administered gold salts, such as sodium aurothiomalate and gold thioglucose comprised chrysotherapy. The frequency and severity of the side effects for patients treated with parenteral gold versus those given oral gold preparations are significantly different [8-10]. With introduction of newer parental DMARDs, toxicity has been reduced using combination therapy [10a, 10b].

Autoimmune diseases involving nicotinic receptors

The antibody-mediated autoimmune response to alpha1 muscle nicotinic acetylcholine receptors that causes myasthenia gravis is one of the best characterized autoimmune diseases. Antibody-mediated autoimmune responses to neuronal nicotinic receptors are just beginning to be discovered and characterized. One of these causes dysautonomia through antibodies to alpha 3 nicotinic receptors of autonomic ganglia. Another causes pemphigus through antibodies to alpha 9 nicotinic receptors in skin. Other autoimmune responses to nicotinic receptors may be discovered as the many functional roles of nicotinic receptors are revealed.

Thyroid function and immune profile in rheumatoid arthritis. A controlled study

The aim of our study was to determine the prevalence of thyroid dysfunction and autoimmune abnormalities in rheumatoid arthritis (RA) and to further investigate the possible association between D-penicillamine and autoimmune thyroiditis. For this purpose, one hundred and one unselected consecutive patients with RA and 70 age and sex matched controls were studied prospectively. Evaluation included a complete history and physical examination with special attention to symptoms suggestive of thyroid pathology, routine laboratory and serologic immune profile, plus determination of serum levels of thyroxine (T4), triiodothyronine (T3), thyroid stimulating hormone (TSH), antibodies to thyroid peroxidase (AbTPO) and TSH receptor antibodies (TRAB). Serum thyroxine binding globulin (TBG) was measured in all subjects with high thyroid hormone levels, whereas free T3 and T4 concentrations were determined in all individuals with abnormal T3, T4, TSH or TBG. Six patients with hyperhyroidism, 3 with hypothyroidism and 1 with the euthyroid hyperthyroxinemia (EH) syndrome were found, whereas four of the controls had hyperthyroidism. Thirteen patients and 6 controls had high AbTPO levels whereas no one had high TRAB. No association was detected between thyroid abnormalities and any serologic RA finding. Furthermore, no correlation between thyroid dysfunction and elevated AbTPO's was found. A relatively high prevalence of thyroid dysfunction (9,9%) and subclinical autoimmune thyroiditis (12,9%), the latter indicated by elevated AbTPO's, was found in our RA patients. These figures were higher than those in the control group (5,7% and 8,6% respectively), but the difference did not reach statistical significance. Of further interest may be our finding that, despite anecdotal reports blaming D-penicillamine for cases of autoimmune thyroiditis, the incidence of the latter was similar among recipients and nonrecipients of the drug. Similarly, TRAB were not detected in any patient treated with D-penicillamine.

D-penicillamine induced myasthenia gravis in rheumatoid arthritis: an unpredictable common occurrence?

Five patients out of 71 with rheumatoid arthritis (RA), who received D-penicillamine, developed myasthenia gravis (MG) within a two-year period. They all responded promptly to discontinuation of the drug and pyridostigmine administration. None of the patients had anti-Ro(SSA) antibodies or features of Sjögren's syndrome, whereas three of the five had the HLA-DR1 phenotype. The relatively high frequency of MG observed in our population, along with its unpredictability and potentially serious sequelae, necessitates its inclusion in the list of side effects of D-penicillamine routinely discussed with the patient, prior to initiation of the treatment. Full alertness of both the patient and the physician to even minor initial myasthenic symptoms, that dictate immediate discontinuation of the drug, is of obvious importance.

Ocular myasthenia: a protean disorder

Ocular myasthenia is a localized form of myasthenia clinically involving only the extraocular, levator palpebrae superioris, and/or orbicularis oculi muscles. Ocular manifestations can masquerade as a variety of ocular motility disorders, including cranial nerve and gaze palsies. A history of variable and fatiguable muscle weakness suggests this diagnosis, which may be confirmed by the edrophonium (Tensilon) test and acetylcholine receptor antibody titer. Anticholinesterases, corticosteroids and other immunosuppressive agents, and other therapeutic modalities, including thymectomy and plasmapheresis, are used in treatment. As the pathophysiology of myasthenia has been elucidated in recent years, newer treatment strategies have evolved, resulting in a much more favorable prognosis than several decades ago. This review provides historical background, pathophysiology, immuno-genetics, diagnostic testing, and treatment options for ocular myasthenia, as well as a discussion of drug-induced myasthenic syndromes.

Myasthenia gravis: an autoimmune response against the acetylcholine receptor

Myasthenia gravis (MG) is an organ-specific autoimmune disease caused by an antibody-mediated assault on the muscle nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. Binding of antibodies to the AChR leads to loss of functional AChRs and impairs the neuromuscular signal transmission, resulting in muscular weakness. Although a great deal of information on the immunopathological mechanisms involved in AChR destruction exists due to well-characterized animal models, it is not known which etiological factors determine the susceptibility for the disease. This review gives an overview of the literature on the AChR, MG and experimental models for this autoimmune disease.

Augmented IgG anti-acetylcholine receptor response following chronic penicillamine administration

A model of D-penicillamine (DP) induced myasthenia gravis (MG) was developed in which the anti-acetylcholine receptor (anti-AChR) antibody response to AChR challenge was increased in mice chronically treated with DP. To investigate the mechanism of the DP induced increase, IgM and IgG anti-AChR responses to AChR challenge were studied. IgG responses were significantly greater in the DP treated mice than in the control group while IgM responses were not significantly different. This change appeared to be relatively specific for the AChR response because neither serum immunoglobulin levels nor the IgG response to a second antigen (purified protein derivative) were increased by DP treatment. These results suggest that a specific sensitization to AChR occurs during chronic DP treatment.

Autoantibodies in D-penicillamine-induced myasthenia gravis: a comparison with idiopathic myasthenia and rheumatoid arthritis

The distribution of autoantibodies was studied in patients with rheumatoid arthritis (RA) treated by D-penicillamine and who developed myasthenia gravis (MG). The anti-human acetylcholine receptor (AChR) antibodies were specifically associated with clinical symptoms of MG without any difference in the pattern of specificities in idiopathic (id-MG) or in induced MG (DPen-MG). Conversely, anti-nuclear antibodies were elevated in DPen-MG sera compared to id-MG sera (P less than 0.001) but were also compared to patients with RA treated by D-penicillamine (or thiopronine) and who did not develop MG. Anti-denatured DNA antibodies were enhanced in sera from treated patients, whether they had presented or not a MG disease. Anti-histone antibodies were associated with RA. These observations suggest that the immunological imbalance in RA patients, can be increased by a drug treatment which may trigger the appearance of a second autoimmune disease such as MG, where anti-AChR antibodies are associated with anti-nuclear antibodies.

Ocular myasthenia gravis after D-penicillamine administration

A 68-year-old black woman who was put on D-penicillamine therapy (250-500 mg per day, total dose 15 g) for rheumatoid arthritis developed ocular myasthenia gravis. Two weeks after she discontinued D-penicillamine her signs and symptoms cleared with no other treatment. Review of previous cases and possible immunological mechanisms are discussed.

D-penicillamine: chemistry and clinical use in rheumatic disease

The discovery of D-penicillamine and its uses in medicine are reviewed. Chemical-physical properties are discussed, and the molecular structure of D-penicillamine and several of its reaction products are illustrated. Examples of its three main types of biochemical reactions--sulfhydryl-disulfide exchange, thiazolidine formation, and metal chelation are included. Trials of D-penicillamine in RA patients are reviewed critically. The administration of the drug is discussed in detail, including dosages, clinical and laboratory responses, patterns of adverse side effects or toxicity, drug-induced autoimmune diseases, indications and contraindications, and the monitoring and management of patients.

Adverse effects profile of sulfhydryl compounds in man

Many of the adverse reactions produced by penicillamine and other compounds with an active sulfhydryl group form a distinctive pattern when viewed as a class. Alterations in taste perception, mucocutaneous lesions, proteinuria due to immune-complex membranous glomerulopathy, and pemphigus are adverse reactions that have been encountered with all of the compounds discussed herein. Hematologic reactions such as neutropenia and thrombocytopenia occur rarely and with variable frequency. The angiotension converting enzyme inhibitor captopril has an active sulfhydryl group. When it was first given in high doses to patients with severe hypertension, adverse effects similar in pattern to those just outlined were reported. With reduced doses and more careful patient selection, the more serious reactions are no longer found, but disturbances of taste perception, rash, and oral mucosal ulcers are still encountered.

[Myasthenia gravis induced by D-penicillamine in a patient with progressive systemic sclerosis]

The development of autoimmune diseases in some patients treated with D-penicillamine (DPA) suggests that the reported occurrence of a conduction disorder at the neuromuscular junction and the development of a reversible myasthenia gravis in rheumatoid disease, progressive systemic sclerosis or Wilson's disease after the use of DPA are part of a general predisposition for autoimmune disease related to DPA therapy. The case reported is an example. The DPA- induced myasthenia gravis (MG) is similar to the spontaneous MG clinically and electrophysiologically, though ocular signs prevail in the former. Antibodies to acetylcholine receptor have been demonstrated and thymic hyperplasia also has been formed. Regarding the onset of myasthenic manifestations the duration of the treatment with DPA varies from 6 to 10 months. The action of DPA on the neuromuscular junction is different from that occurring in spontaneous MG. The pathogenesis of the DPA induced MG is still obscure. The chemical properties of DPA permit it to react with many proteins and some alteration of proteins may appear, with structural changes in the composition and antigenicity of the collagen fibers. In vitro DPA causes disorder of acetylcholine receptor bridges to alpha, beta, gamma sub-units with reduction of the S-S bridges in the gamma-subunit. This decreases the linkage of high affinity and abolishes its positive cooperative system, reducing the S-S connection in the alpha-unit near the acetylcholine linkage. The interaction between DPA and receptor may induce antigenic alteration in this latter, starting the autoimmune phenomena. The other possibility is the stimulation of prostaglandin E-1 synthesis by DPA may fill the allosteric place of ACh receptor, interfering on the neuromuscular junction.

Myasthenic pseudo-internuclear ophthalmoplegia due to penicillamine

Images

Augmented anti-acetylcholine receptor response following long-term penicillamine administration

Because of the association of D-penicillamine (DP) therapy with myasthenia gravis, we have studied long-term DP treatment in five inbred strains of mice with doses comparable to those used in patients with rheumatoid arthritis. No clinical weakness or anti-acetylcholine receptor (AChR) antibody developed with up to 6 months of treatment, but augmented responses did occur to challenge with purified AChR in adjuvant. Anti-AChR antibody titers in C57BL/6 and C3H/He mice were significantly higher after challenge with AChR in DP-treated than in control mice. Augmented anti-AChR titers were not seen in strain A mice, but after 6 months of DP treatment increased susceptibility developed to the induction of experimental autoimmune myasthenia gravis. Nine weeks after challenge with purified AChR, 10 of 11 mice developed clinical weakness, leading to death in 6. Results of edrophonium testing were positive in 5 of 6 mice, and electrophysiological abnormalities were demonstrated in 3 of the surviving mice. Long-term DP treatment is associated with augmented anti-AChR antibody responses in C3H/He and C57BL/6 mice, and increased susceptibility to experimental autoimmune myasthenia gravis in strain A mice.

Guillain-Barré syndrome and pemphigus foliaceus associated with D-penicillamine therapy

The Guillain-Barré syndrome and pemphigus foliaceus occurred simultaneously in a patient on long-term treatment with D-penicillamine. It is proposed that both conditions may have developed as a result of a disturbance of immunoregulation caused by D-penicillamine.