Antimyeloperoxidase antibodies and adverse reactions to clozapine

Drug-induced anti-neutrophil cytoplasmic antibody-associated vasculitis

OBJECTIVE

In recent years, an increasing number of drugs have been proved to be associated with the induction of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This article reviews the latest research progress on drug-induced AAV.

DATA SOURCES

We conducted a comprehensive and detailed search of the PubMed database. The search terms mainly included drug-induced, ANCA, and vasculitis.

STUDY SELECTION

We summarized the original articles and reviews on drug-induced AAV in recent years. The extracted information included the definition, epidemiology, associated drugs, pathogenesis, clinical features, diagnosis, treatment, and prognosis of drug-induced AAV. We also focused on the differences between drug-induced AAV and primary vasculitis.

RESULTS

The offending drugs leading to drug-induced AAV are almost from pharmacologic categories and we need to be vigilant when using these drugs. The pathogenesis of drug-induced AAV might be multifactorial. The formation of neutrophil extracellular traps is an important mechanism for the development of drug-induced AAV. The clinical features of drug-induced AAV are similar to those of primary AAV. Understanding the difference between drug-induced AAV and primary AAV is helpful to identify drug-induced AAV. Stopping the offending drug at once after diagnosis may be sufficient for those patients with mild symptoms. Immunosuppressive therapy should only be used in patients with vital organs involvement.

CONCLUSIONS

Patients with drug-induced AAV usually have a good prognosis if they stop using the offending drug immediately. Recent advances in research on AAV are expected to help us better understand the pathogenesis of drug-induced AAV.

Clozapine-induced antineutrophil cytoplasmic antibody-associated vasculitis: a case report

Clozapine is the most effective antipsychotic medication for refractory schizophrenia, but it has many possible serious side effects, including antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). However, the rare case reports available have not presented sufficient characteristic features of drug-induced AAV. Herein, we report a case of a 48-year-old Japanese woman with schizophrenia who presented with fever, arthralgia, myalgia and skin rash after 2 years of clozapine treatment. Her C-reactive protein (CRP) level increased, myeloperoxidase ANCA was positive and skin biopsy revealed leukocytoclastic vasculitis. Initially, steroid administration achieved remission, but her symptoms and high CRP levels relapsed every time the steroid dosage was tapered down. Upon discontinuation of clozapine, her symptoms and elevated CRP level immediately improved and the steroid was successfully tapered and discontinued. This outcome suggested that clozapine was the main cause of AAV.

More than 25 years of genetic studies of clozapine-induced agranulocytosis

Clozapine is one of the most effective atypical antipsychotic drugs prescribed to patients with treatment-resistant schizophrenia. Approximately 1% of patients experience potential life-threatening adverse effects in the form of agranulocytosis, greatly hindering its applicability in clinical practice. The etiology of clozapine-induced agranulocytosis (CIA) remains unclear, but is thought to be a heritable trait. We reviewed the genetic studies of CIA published thus far. One recurrent finding from early candidate gene study to more recent genome-wide analysis is that of the involvement of human leukocyte antigen locus. We conclude that CIA is most likely a complex, polygenic trait, which may hamper efforts to the development of a genetic predictor test with clinical relevance. To decipher the genetic architecture of CIA, it is necessary to apply more rigorous standards of phenotyping and study much larger sample sizes.

Metabolic basis of benzene toxicity

Potential metabolic mechanisms underlying the haemopoietic toxicity of benzene include bioactivation of phenolic metabolites of benzene by peroxidases in bone marrow and ring opening reactions to generate muconate derivatives. Peroxidase-mediated activation of phenolic metabolites of benzene generates reactive quinones which can be detoxified by NAD(P)H:quinone acceptor oxidoreductase (NQO1). The major peroxidase enzyme in bone marrow is myeloperoxidase (MPO) and potential target cells for phenolic metabolites of benzene were characterized in bone marrow stroma on the basis of high MPO:NQO1 ratios. MPO was found to be expressed at the level of myeloid progenitor cells in both murine (lineage negative cells) and human (CD34+ cells) systems. This suggests that progenitor cells may be relevant targets of phenolic metabolites of benzene resulting in aberrant haemopoiesis. A polymorphism in NQO1 is also described which leads to a complete lack of NQO1 activity. The toxicological significance of this polymorphism with respect to benzene toxicity is under investigation.

Drug-induced diffuse alveolar hemorrhage syndromes and vasculitis

Current and past drug intake is essential in the evaluation of a patient who has DAH. Simple treatments, such as reversal of a coagulation defect or withdrawal of the drug, can reverse a life-threatening situation. DAO may result in DAH, and depending on the severity of the drug withdrawl, will not be adequate and corticosteroid therapy is recommended.

Structure toxicity relationships--how useful are they in predicting toxicities of new drugs?

This chapter provides just a few newer examples of structural moieties found in drugs that have been associated with reactive metabolite formation and toxicities. For a discussion of several other structures in drugs that undergo metabolic activation to reactive intermediates, the reader is directed to previous volumes in this series and other chapters in this book, as well as a previous condensed review (Nelson, 1982). Since that review, some new knowledge allows us to better predict that some structural moieties are more likely than others to form drug reactive metabolites that may be involved in causing toxic effects in humans. For example, most aniline-, thiophene-, and nitroaromatic-containing drugs have had a relatively high incidence of adverse effects, and it would be prudent in the drug discovery process to avoid these substructures if possible. However, as illustrated by the case of olanzapine, these structures may be important for potent activity, and could therefore be beneficial in some cases. The glitazones represent a new class of drugs with a unique thiazolidinedione structure. This raises two important points. First, it demonstrates how limited our knowledge base is in regard to structure toxicity relationships when new structures are introduced. Our approaches must be very empirical and are far from quantitative for the reasons outlined in the introduction. Secondly, the glitazones point out the importance of benefit/risk considerations. This was a new structural class of drugs with a unique spectrum of action that is very beneficial in the treatment of a major disease. Despite some suspected risk of toxicity, based on early trials, troglitazone was approved for use with careful monitoring. This author believes that was the right decision, as was the decision to withdraw the drug when the risk became unacceptable, especially with the introduction of safer alternatives. If this were just another NSAID (e.g., bromfenac), there would be little reason for approval. In summary, as I pointed out previously (Nelson, 1982), with our limited knowledge of structure toxicity relationships, we can only make reasonable judgments as to risk assessment of a new drug in humans, and hope that we neither release a dangerous chemical entity nor, as importantly, abort an effective one.

Drug-induced vasculitis

DIV is a relatively common cause of inflammatory vasculitis. Drugs from almost every pharmacologic class have been implicated in causing vasculitis in sporadic cases. The level of certainty and quality of evidence for these associations between specific agents and vasculitis vary greatly. The clinical manifestations of DIV range from single organ involvement (most commonly, skin) to life-threatening multiorgan disease. The recently described subset of cases of DIV associated with positive tests for ANCA are an interesting subset of DIV. The diagnosis of DIV is usually one of exclusion. The treatment of DIV is dependent on the severity of disease activity but should always include withdrawal of the suspected drug. If no agent can be implicated, as many drugs as feasible should be discontinued. The necessity of prescribing glucocorticoids or immunosuppressive agents depends on the disease severity and other case-specific information. Increasing understanding of the pathophysiologic characteristics of all inflammatory vasculitides should lead to better diagnostic and therapeutic approaches to DIV.

Autoantibodies Associated with Rheumatic Diseases

The identification of circulating autoantibodies contributes to the correct diagnosis as well as to the follow-up of rheumatic diseases. Some autoantibodies are even included in diagnostic and classification criteria for these types of autoimmune diseases. There are several relatively specific screening and identification methods for the measurement of autoantibodies available. The type of assay crucially influences the diagnostic value of the parameters. In general, routine laboratories should prefer enzyme immunoassays (ELISA) using well characterized antigens, although ELISA tests tend to produce more false-positive and true weakly positive results, which reduce their positive predictive value. Therefore one should be aware that laboratory results can only be properly interpreted when there is a correlation with the clinical situation and when the limitations of the technologies used for autoantibody identification have been taken into consideration. A diagnostic algorithm consisting of screening and identification steps should be established by each laboratory in order to create a rational, evidence-based and cost-effective basis for the diagnosis of rheumatic diseases.

Immunological principles of adverse drug reactions: the initiation and propagation of immune responses elicited by drug treatment

Adverse drug reactions account for between 2 to 5% of all hospital admissions and can prevent the administration of an otherwise effective therapeutic agent. Hypersensitivity or immune-mediated reactions, although less common, tend to be proportionately more serious. There is convincing evidence to implicate the immune system in the pathogenesis of hypersensitivity reactions. Our understanding of the way in which the immune system recognises drugs is based on the hapten hypothesis; the onset of hypersensitivity involves drug bioactivation, covalent binding to proteins, followed by uptake, antigen processing and T cell proliferation. Central to this hypothesis is the critical role of drug metabolism, with the balance between metabolic bioactivation and detoxification being one important component of individual susceptibility. The purpose of this review is to classify drug hypersensitivity reactions in terms of their clinical presentation, and also to consider recent advances in our understanding of the chemical, biochemical and, in particular, cellular immunological mechanisms of hypersensitivity. The following topics are reviewed: (i) drug disposition and cellular metabolism; (ii) mechanisms of antigen processing and presentation; (iii) the role of cytokines and co-stimulatory molecules in the induction and maintenance of a polarised immune response; and (iv) the application of the hapten hypothesis, danger hypothesis and serial triggering model to drug hypersensitivity. A greater understanding of the mechanism(s) of hypersensitivity may identify novel therapeutic strategies and help to combat one of the more severe forms of adverse reactions to drugs.

Evaluation of antineutrophil cytoplasmic antibody seroconversion induced by minocycline, sulfasalazine, or penicillamine

OBJECTIVE

Case reports have suggested that minocycline, sulfasalazine, and penicillamine are associated with antineutrophil cytoplasmic antibody (ANCA)-positive vasculitis. This study evaluated ANCA seroconversion due to these agents in serum samples prospectively collected in randomized, double-blind, controlled trials.

METHODS

The sources of study sera were 3 clinical trials: 1) a 48-week trial of minocycline for early rheumatoid arthritis, with 64 patients receiving minocycline compared with 68 receiving placebo; 2) a 37-week trial of sulfasalazine for rheumatoid arthritis, with 51 receiving sulfasalazine compared with 38 receiving placebo; and 3) a 104-week trial of penicillamine for early systemic sclerosis, with 15 undergoing high-dose penicillamine treatment versus 12 receiving low-dose penicillamine. ANCA were measured in the baseline and study-end serum samples by indirect immunofluorescence (IIF) for perinuclear ANCA (pANCA) and cytoplasmic ANCA (cANCA) patterns, and by antigen-specific enzyme-linked immunosorbent assay (ELISA) for antibodies to myeloperoxidase (anti-MPO) and proteinase 3 (anti-PR3). Laboratory personnel were blinded to the group identity of the samples. ANCA results were interpreted using an ANCA scoring system that combines the results of IIF and ELISA testing.

RESULTS

No patient in any of the active study drug groups demonstrated ANCA seroconversion according to the final interpretation of the combined IIF and ELISA results. Twelve of the 248 patients (5%) were positive for anti-MPO with pANCA at baseline. No subject was positive for anti-PR3 with cANCA. There were no findings suggestive of vasculitis in any of these patients.

CONCLUSION

From our study results, there was no suggestion of ANCA seroconversion induced by minocycline, sulfasalazine, or penicillamine. However, these findings do not rule out the possibility of rare, sporadic cases of either ANCA seroconversion or true drug-induced vasculitis with these drugs.

Diffuse alveolar hemorrhage and pulmonary capillaritis due to propylthiouracil

Propylthiouracil (PTU) has recently been observed to be associated with antineutrophil cytoplasmic antibody (ANCA)-positive small vessel vasculitis, resulting in crescentic glomerulonephritis and, infrequently, diffuse alveolar hemorrhage (DAH). We describe a case of a 23-year-old pregnant woman who developed a perinuclear ANCA and antimyeloperoxidase-positive small vessel vasculitis manifesting as DAH and crescentic glomerulonephritis after she began taking PTU. An open lung biopsy was consistent with pulmonary capillaritis. She responded to corticosteroid therapy and discontinuation of PTU. DAH can be caused by pulmonary capillaritis, bland hemorrhage, or diffuse alveolar damage. To our knowledge, this represents the first documentation of an underlying pulmonary capillaritis in a case of PTU-induced DAH.

Tumor Necrosis Factor Constellation Polymorphism and Clozapine-Induced Agranulocytosis in Two Different Ethnic Groups

Genes of the major histocompatibility complex (MHC) are associated with susceptibility to different immune and nonimmune mediated diseases. We had reported that the drug adverse reaction, clozapine-induced agranulocytosis (CA), is associated with different HLA types and HSP70 variants in Ashkenazi Jewish and non-Jewish patients, suggesting that a gene within the MHC region is associated with CA. This study was designed to find common genetic markers for this disorder in both ethnic groups. The tumor necrosis factor (TNF ) microsatellites d3 and b4 were found in higher frequencies in both Jewish and nonJewish patients: 51 of 66 (77%) and 48 of 66 (57%), respectively. Comparisons of these frequencies with those of controls, 28 of 66 (42%) and 18 of 66 (27%), were statistically significant (corrected P value = .001 for the d3 allele and .0005 for the b4 allele). On the other hand, the TNF microsatellite b5 was underrepresented in the group of patients, 9 of 66 (14%), when compared with the control subjects, 43 of 66 (65%) (corrected P value = .0005), probably related to protection from CA. Our results show a strong association of some genetic variants of the TNF loci with susceptibility to CA in two different ethnic groups suggesting involvement of TNF and/or associated gene(s) products in the pathogenesis of this hematologic-drug adverse reaction.

Mechanism of clozapine-induced agranulocytosis : current status of research and implications for drug development

Clozapine is an atypical antipsychotic agent that has several advantages over conventional antipsychotics, not least of which is its superior efficacy. However, the high risk of agranulocytosis (0.8% of patients) associated with clozapine therapy has resulted in restricted indications for its use.The mechanism of clozapine-induced agranulocytosis is not clear. The target cells affected are the myeloid precursors, although the mature neutrophil may also be targeted simultaneously. There is no convincing evidence of direct toxicity of the parent compound or its stable metabolites (demethyl-clozapine and clozapine N-oxide). Clozapine is also metabolised by liver microsomes, peripheral blood neutrophils and their bone marrow precursors to a chemically reactive intermediate that has been postulated to be a nitrenium ion. This toxic metabolite has been shown to covalently bind to neutrophil proteins, suggesting that it may be involved in the pathogenesis of the toxicity. However, it is not clear how toxicity is mediated. The nitrenium ion may bind to essential cellular proteins and disrupt neutrophil function or, alternatively, it may act as a hapten and initiate an immune reaction resulting in immune-mediated destruction of the neutrophil. Indirect evidence exists to support both mechanisms, although clear direct evidence is still lacking. The role of cytokines and apoptosis in the pathogenesis of the agranulocytosis is unclear.The reason why only approximately 1% of individuals who are treated with clozapine are affected by agranulocytosis has not been elucidated. Evidence exists to implicate both the major histocompatibility complex antigens and heat shock protein variants in determining individual susceptibility, although more patients of different ethnic backgrounds need to be studied.The ultimate aim of research into clozapine-induced agranulocytosis should be to either prospectively predict which individuals are going to develop agranulocytosis and/or to develop analogues that retain efficacy but are not toxic. The former is complicated by the fact that predisposition may be multifactorial, and thus prediction may require multiple tests that may be of statistical but not absolute validity. The latter depends on identifying the mechanism of toxicity and the chemical characteristics of clozapine that are responsible for the toxicity. This knowledge may allow rational design of new analogues that do not cause agranulocytosis.

Antibodies to myeloperoxidase in propylthiouracil-induced autoimmune disease in the cat

Cats are known to develop a lupus-like syndrome similar to that observed in humans when treated with propylthiouracil. We have previously demonstrated that propylthiouracil and other drugs associated with lupus are oxidized in the presence of myeloperoxidase to reactive intermediates. We postulated that these reactive metabolites could modify myeloperoxidase resulting in anti-myeloperoxidase antibodies and possibly be responsible for the lupus-like syndrome. Five cats were treated with propylthiouracil and 2 developed the lupus-like syndrome as well as anti-myeloperoxidase antibodies. These appeared to correlate better with disease than antinuclear antibodies. The antibodies were true autoantibodies because the myeloperoxidase used to detect the antibodies did not require treatment with propylthiouracil. In a subsequent study in which the cat food contained a higher level of taurine, none of the animals developed the autoimmune syndrome. It is possible that diet also plays an important role in the development of such adverse reactions.

Free radical scavenging enzyme activity and related trace metals in clozapine-induced agranulocytosis: a pilot study

We hypothesized that patients who had experienced clozapine-induced agranulocytosis would have abnormalities in their free radical scavenging enzyme activity (FRESA) and levels of related trace metals. We therefore measured FRESA profiles and related trace metals in four groups: post-clozapine agranulocytosis (POST CLOZ AGRAN) (N = 9); clozapine no agranulocytosis (CLOZ NO AGRAN) (N = 12); West Coast controls (WC CONTROLS) (N = 14); and Long Island Jewish Medical Center controls (LIJ CONTROLS) (N = 12). Glutathione peroxidase (GSH-Px, P1) levels in plasma were slowest in the POST CLOZ AGRAN group (34.3 +/- 6.9 IU/dl [standard deviation; SD]; p < 0.002); red blood cell glutathione peroxidase (GSH-Px, RBC) was highest in the WC CONTROLS (38.7 +/- 4.7 IU/g hemoglobin [Hgb]; p < 0.008); and selenium (SE) levels in plasma were lower in both the POST CLOZ AGRAN group (111.6 +/- 14.7 ng/ml) and the CLOZ NO AGRAN group(115.0 +/- 17.8) than in the WC CONTROLS (142.5 +/- 18.3; p < 0.0006). SE was also lower in the POST CLOZ AGRAN group than in the LIJ CONTROLS (129.1 +/- 21.6; p < 0.04). The presence of at least one of the following: (1) GSH-Px, P1 < 37.6 IU/dl; (2) GSH-Px, RBC < 31.0 IU/g Hgb; or (3) SE < 112.4 ng/ml, distinguished POST CLOZ AGRAN subjects from the WC CONTROLS, but not from the LIJ CONTROLS. Data from this cross-sectional pilot study suggest that abnormalities in the body's antioxidant defense system may be involved in the pathogenesis of clozapine-associated agranulocytosis. If confirmed in large-scale, prospective studies, these preliminary findings have potential clinical application in the screening and prophylaxis of clozapine agranulocytosis.

ANCA and associated diseases: immunodiagnostic and pathogenetic aspects

The past decade has seen an explosion of data on the new group of autoantibodies known collectively as ANCA (anti-neutrophil cytoplasmic antibodies). ANCA are specific for granule proteins of granulocytes and monocytes and induce distinct fluorescence patterns, e.g. the cytoplasmic (classic) cANCA and the perinuclear pANCA. cANCA is induced by antibodies directed against Proteinase 3 (PR3; PR3-ANCA) in about 90% of all ANCA-positive sera, and pANCA is induced by antibodies against myeloperoxidase (MPO; MPO-ANCA) in about 40%. A further staining pattern, which does not have a clear cut association with a distinct granule protein, is sometimes seen in chronic inflammatory bowel diseases. PR3-ANCA are serological markers for Wegener's granulomatosis (WG) and MPO-ANCA are associated with certain subtypes of primary vasculitides. Evidence exists that both the autoantigen and ANCA participate in the pathogenesis of at least the group of 'ANCA-associated vasculitides'.