Administration of the cyclic peptide COR-1 in humans (phase I study): ex vivo measurements of anti-β1-adrenergic receptor antibody neutralization and of immune parameters

Autoantibodies and Cardiomyopathy: Focus on Beta-1 Adrenergic Receptor Autoantibodies

ABSTRACT

Antibody response to self-antigens leads to autoimmune response that plays a determinant role in cardiovascular disease outcomes including dilated cardiomyopathy (DCM). Although the origins of the self-reactive endogenous autoantibodies are not well-characterized, it is believed to be triggered by tissue injury or dysregulated humoral response. Autoantibodies that recognize G protein-coupled receptors are considered consequential because they act as modulators of downstream receptor signaling displaying a wide range of unique pharmacological properties. These wide range of pharmacological properties exhibited by autoantibodies has cellular consequences that is associated with progression of disease including DCM. Increase in autoantibodies recognizing beta-1 adrenergic receptor (β1AR), a G protein-coupled receptor critical for cardiac function, is observed in patients with DCM. Cellular and animal model studies have indicated pathological roles for the β1AR autoantibodies but less is understood about the molecular basis of their modulatory effects. Despite the recognition that β1AR autoantibodies could mediate deleterious outcomes, emerging evidence suggests that not all β1AR autoantibodies are deleterious. Recent clinical studies show that β1AR autoantibodies belonging to the IgG3 subclass is associated with beneficial cardiac outcomes in patients. This suggests that our understanding on the roles the β1AR autoantibodies play in mediating outcomes is not well-understood. Technological advances including structural determinants of antibody binding could provide insights on the modulatory capabilities of β1AR autoantibodies in turn, reflecting their diversity in mediating β1AR signaling response. In this study, we discuss the significance of the diversity in signaling and its implications in pathology.

Reappraising the role of inflammation in heart failure

The observation that heart failure with reduced ejection fraction is associated with elevated circulating levels of pro-inflammatory cytokines opened a new area of research that has revealed a potentially important role for the immune system in the pathogenesis of heart failure. However, until the publication in 2019 of the CANTOS trial findings on heart failure outcomes, all attempts to target inflammation in the heart failure setting in phase III clinical trials resulted in neutral effects or worsening of clinical outcomes. This lack of positive results in turn prompted questions on whether inflammation is a cause or consequence of heart failure. This Review summarizes the latest developments in our understanding of the role of the innate and adaptive immune systems in the pathogenesis of heart failure, and highlights the results of phase III clinical trials of therapies targeting inflammatory processes in the heart failure setting, such as anti-inflammatory and immunomodulatory strategies. The most recent of these studies, the CANTOS trial, raises the exciting possibility that, in the foreseeable future, we might be able to identify those patients with heart failure who have a cardio-inflammatory phenotype and will thus benefit from therapies targeting inflammation.

β1-Adrenoreceptor Autoantibodies in Heart Failure: Physiology and Therapeutic Implications

Antibodies that activate the β₁-AR (β₁-adrenoreceptor) can induce heart failure in animal models. These antibodies are often found in patients with heart failure secondary to varying etiologies. Their binding to the β₁ receptor leads to prolonged receptor activation with subsequent induction of cellular dysfunction, apoptosis, and arrhythmias. β-blocker therapy while highly effective for heart failure, may not be sufficient treatment for patients who have β₁ receptor autoantibodies. Removal of these autoantibodies by immunoadsorption has been shown to improve heart failure in small studies. However, immunoadsorption is costly, time consuming, and carries potential risks. An alternative to immunoadsorption is neutralization of autoantibodies through the intravenous application of small soluble molecules, such as peptides or aptamers, which specifically target and neutralize β₁-AR autoantibodies. Peptides may induce immunogenicity. Animal as well as early phase human studies with aptamers have not shown safety concerns to date and have demonstrated effectiveness in reducing autoantibody levels. Novel aptamers have the potential advantage of having a wide spectrum of action, neutralizing a variety of known circulating G-protein coupled receptor autoantibodies. These aptamers, therefore, have the potential to be novel therapeutic option for patients with heart failure who have positive for β₁-AR autoantibodies. However, clinical outcomes trials are needed to assess the clinical utility of this novel approach to treat heart failure.

Cyclic peptide RD808 reduces myocardial injury induced by β1-adrenoreceptor autoantibodies

Autoantibodies against the second extracellular loop of β₁-adrenergic receptor (β₁-AA) have been shown to be involved in the development of cardiovascular diseases. Recently, there has been considerable interest in strategies to remove these autoantibodies, particularly therapeutic peptides to neutralize β₁-AA. Researchers are investigating the roles of cyclic peptides that mimic the structure of relevant epitopes on the β₁-AR-EC_II in a number of immune-mediated diseases. Here, we used a cyclic peptide, namely, RD808, to neutralize β₁-AA, consequently alleviating β₁-AA-induced myocardial injury. We investigated the protective effects of RD808 on the myocardium both in vitro and in vivo. RD808 was found to increase the survival rate of cardiomyocytes; furthermore, it decreased myocardial necrosis and apoptosis and improved the cardiac function of BalB/c mice in a β₁-AA transfer model. In vitro and in vivo experiments showed that myocardial autophagy was increased in the presence of RD808, which might contribute to its cardioprotective effects. Our findings indicate that RD808 reduced myocardial injury induced by β₁-AA.

Cyclopeptide COR-1 to treat beta1-adrenergic receptor antibody-induced heart failure

RATIONALE

Despite advances in pharmacotherapy, heart failure still incurs significant morbidity and mortality. Stimulating antibodies directed against the secondextracellular loop of the human ß1-adrenergic receptor (anti-ß1EC2) cause myocyte damage and heart failure in rats. This receptor domain is 100% homologous between rats and humans.

OBJECTIVE

ß1EC2-mimicking cyclopeptides (25-meric) markedly improved the development and/or course of anti-ß1EC2-mediated cardiomyopathy. Further developments should be investigated.

METHODS AND RESULTS

The shortened 18-meric cyclic peptide COR-1, in which one of the two disulphide bonds was removed to enable reproducible GMP production, can also be used to treat cardiomyopathic rats. Echocardiography, catheterization and histopathology of the rat hearts revealed that monthly intravenous administrations of COR-1 almost fully reversed the cardiomyopathic phenotype within 6 months at doses of 1 to 4 mg/kg body weight. Administration of COR-1 resulted in markedly reduced anti-ß1EC2-expressing memory B lymphocytes in the spleen despite continued antigenic boosts, but did not significantly decrease overall peripheral anti-ß1EC2 titers. COR-1 did not induce any anti-ß1EC2 or other immune response in naïve rats (corresponding to findings in healthy human volunteers). It did not cause any toxic side effects in GLP studies in dogs, rats or mice, and the "no observed adverse effect level" (NOAEL) exceeded the therapeutic doses by 100-fold.

CONCLUSION

The second generation immunomodulating epitope-mimicking cyclopeptide COR-1 (also termed JNJ-5442840) offers promise to treat immune-mediated cardiac diseases.

Follicular B Cells Promote Atherosclerosis via T Cell–Mediated Differentiation Into Plasma Cells and Secreting Pathogenic Immunoglobulin G

Objective—

B cells promote or protect development of atherosclerosis. In this study, we examined the role of MHCII (major histocompatibility II), CD40 (cluster of differentiation 40), and Blimp-1 (B-lymphocyte–induced maturation protein) expression by follicular B (FO B) cells in development of atherosclerosis together with the effects of IgG purified from atherosclerotic mice.

Approach and Results—

Using mixed chimeric Ldlr −/− mice whose B cells are deficient in MHCII or CD40, we demonstrate that these molecules are critical for the proatherogenic actions of FO B cells. During development of atherosclerosis, these deficiencies affected T–B cell interactions, germinal center B cells, plasma cells, and IgG. As FO B cells differentiating into plasma cells require Blimp-1, we also assessed its role in the development of atherosclerosis. Blimp-1-deficient B cells greatly attenuated atherosclerosis and immunoglobulin—including IgG production, preventing IgG accumulation in atherosclerotic lesions; Blimp-1 deletion also attenuated lesion proinflammatory cytokines, apoptotic cell numbers, and necrotic core. To determine the importance of IgG for atherosclerosis, we purified IgG from atherosclerotic mice. Their transfer but not IgG from nonatherosclerotic mice into Ldlr −/− mice whose B cells are Blimp-1-deficient increased atherosclerosis; transfer was associated with IgG accumulating in atherosclerotic lesions, increased lesion inflammatory cytokines, apoptotic cell numbers, and necrotic core size.

Conclusions—

The mechanism by which FO B cells promote atherosclerosis is highly dependent on their expression of MHCII, CD40, and Blimp-1. FO B cell differentiation into IgG-producing plasma cells also is critical for their proatherogenic actions. Targeting B–T cell interactions and pathogenic IgG may provide novel therapeutic strategies to prevent atherosclerosis and its adverse cardiovascular complications.

Opposing roles of B lymphocyte subsets in atherosclerosis

Atherosclerosis is initiated by cholesterol entry into arteries that triggers chronic immune-inflammatory lesions in the vessels. Early lesions are clinically insignificant but advanced complex lesions and vulnerable rupture prone lesions impact on quality of life and can be life threatening. Rupture of vulnerable atherosclerotic lesions initiates thrombotic occlusion of vital arteries precipitating heart attacks and strokes that remain major killers globally despite therapeutic use of statins to lower blood cholesterol levels. Conventional B2 cells are proatherogenic whereas peritoneal Bla cells are atheroprotective. Depletion of B2 cells by administration of mAb to CD20 or to BAFF receptor or in BAFF receptor-deficient mice ameliorates atherosclerosis. B2 cells may promote atherosclerosis by production of IgG, secretion of proinflammatory cytokine TNFα and activation of CD4 T cells. Together these B2 cell mechanisms contribute to generation of rupture-prone vulnerable atherosclerotic plaques characterised by large necrotic cores. In contrast, peritoneal Bla cells protect against atherosclerosis by secretion of natural IgM that scavenges apoptotic cells and oxidised LDL and reduces necrotic cores in atherosclerotic lesions. These atheroprotective effects can be further increased by stimulating Bla cells by administration of apoptotic cells, liposomes of phosphatidylserine abundant on surfaces of apoptotic cell, by mAb to TIM1, a phosphatidylserine receptor expressed by B1a cells and by TLR4-MyD88 activation. Experimental studies of atherosclerosis in mouse models indicate that reductions in atherogenic B2 cells and/or activation of atheroprotective B1a cells protects against atherosclerosis development, findings which have potential for clinical translation to reduce risks of deaths from heart attacks and strokes.

Role of Adaptive Immunity in the Development and Progression of Heart Failure: New Evidence

Heart failure (HF) is considered the endpoint of a variety of cardiac diseases, which are the leading cause of death in adults and considered a growing pandemic worldwide. Independent of the initial form of cardiac injury, there is evidence linking the involvement of the immune system. In HF there is evidence of the participation of T_H1, and T_H17 cells, which account for sustained pathological chronic inflammation, cell migration, and the induction of specific pathological phenotypes of mononuclear cells. Of equal or even higher relevance are the B lymphocyte activation mechanisms that include production of pro-inflammatory cytokines, chemokines, and cardiac autoantibodies with or without activation of the complement proteins. Both of these unbalanced T- and B-cell pathways of the adaptive immune system are associated with cardiomyocyte death and tissue remodeling by fibrosis leading to a dysfunctional heart. At this time, therapy with neutralizing antibodies and the use of anti-cytokine immunomodulators to counteract the immune system effects have reached a plateau of mixed results in clinical trials. Nevertheless, recent evidence showed promising results in animal models that suggest that modulation of the adaptive immune system cells more than some of their effector molecules could have benefits in HF patients. This review summarizes the role of the adaptive immunity cells in HF, considering the sustained activation of adaptive immune system as a potential contributor to disease progression in humans and experimental models where its regulation provides a new therapeutic target.

Myocardial Recovery in Patients With Systolic Heart Failure and Autoantibodies Against β1-Adrenergic Receptors

BACKGROUND

Among various cardiac autoantibodies (AAbs), those recognizing the β₁-adrenergic receptor (β₁AR) demonstrate agonist-like effects and induce myocardial damage that can be reversed by β-blockers and immunoglobulin G3 (IgG3) immunoadsorption.

OBJECTIVES

The goal of this study was to investigate the role of β₁AR-AAbs belonging to the IgG3 subclass in patients with recent-onset cardiomyopathy.

METHODS

Peripheral blood samples were drawn at enrollment in patients with recent-onset cardiomyopathy (left ventricular ejection fraction [LVEF] ≤0.40; <6 months). The presence of IgG and IgG3-β₁AR-AAb was determined, and echocardiograms were assessed, at baseline and 6 months. Patients were followed up for ≤48 months.

RESULTS

Among the 353 patients who had blood samples adequate for the analysis, 62 (18%) were positive for IgG3-β₁AR-AAbs (IgG3 group), 58 (16%) were positive for IgG but not IgG3 (non-IgG3 group), and the remaining were negative. There were no significant differences in baseline systolic blood pressure, heart rate, or LVEF among the groups at baseline. Left ventricular end-diastolic and end-systolic diameters were significantly larger in the non-IgG3 group compared with the other groups (left ventricular end-diastolic diameter, p < 0.01; left ventricular end-systolic diameter, p = 0.03). At 6 months, LVEF was significantly higher in the IgG3 group (p = 0.007). Multiple regression analysis showed that IgG3-β₁AR-AAb was an independent predictor of LVEF at 6 months and change in LVEF over 6 months, even after multivariable adjustment (LVEF at 6 months, β = 0.20, p = 0.01; change in LVEF, β = 0.20, p = 0.008). In patients with high New York Heart Association functional class (III or IV) at baseline, the IgG3 group had a lower incidence of the composite endpoint of all-cause death, cardiac transplantation, and hospitalization due to heart failure, whereas the non-IgG3 group had the highest incidence of the composite endpoint.

CONCLUSIONS

IgG3-β₁AR-AAbs were associated with more favorable myocardial recovery in patients with recent-onset cardiomyopathy.

Cyclic Peptides for Effective Treatment in a Long-Term Model of Graves Disease and Orbitopathy in Female Mice

A model for human Graves disease in mice was used to compare several treatment approaches. The mice received regular adenovirus (Ad) thyroid-stimulating hormone receptor (TSHR) A subunit immunizations (injections every 4 weeks). The generation of anti-TSHR antibodies, enlarged thyroid sizes (goiter), elevated serum thyroxine levels, retro-orbital fibrosis, and cardiac involvement (tachycardia and hypertrophy) were consistently observed over 9 months. Treatment of established disease in these mice using cyclic peptides that mimic one of the cylindrical loops of the TSHR leucine-rich repeat domain improved or cured all investigated parameters after six consecutive monthly injections. The first significant beneficial effects were observed 3 to 4 months after starting these therapies. In immunologically naïve mice, administration of any of the cyclic peptides did not induce any immune response. In contrast, monthly injections of the full antigenic TSHR A domain as fusion protein with immunoglobulin G crystallizable fragment induced clinical signs of allergy in Ad-TSHR-immunized mice and anti-TSHR antibodies in naïve control mice. In conclusion, cyclic peptides resolved many clinical findings in a mouse model of established Graves disease and orbitopathy. In contrast to blocking TSHR by allosteric modulation, the approach does not incur a direct receptor antagonism, which might offer a favorable side effect profile.

Review of Mouse Models of Graves' Disease and Orbitopathy-Novel Treatment by Induction of Tolerance

Various approaches have been used to model human Graves' disease in mice, including transfected fibroblasts, and plasmid or adenoviral immunisations with the extracellular A subunit of the human thyrotropin receptor (TSHR). Some of these models were only observed for a short time period or were self-limiting. A long-term model for human Graves' disease was established in mice using continuing immunisations (4-weekly injections) with recombinant adenovirus expressing TSHR. Generation of TSHR binding cAMP-stimulatory antibodies, thyroid enlargement and alterations, elevated serum thyroxin levels, tachycardia and cardiac hypertrophy were maintained for at least 9 months in all Ad-TSHR-immunised mice. Here, we show that these mice suffer from orbitopathy, which was detected by serial orbital sectioning and histomorphometry. Attempts to treat established Graves' disease in preclinical mouse model studies have included small molecule allosteric antagonists and specific antagonist antibodies which were isolated from hypothyroid patients. In addition, novel peptides have been conceived which mimic the cylindrical loops of the TSHR leucine-rich repeat domain, in order to re-establish tolerance toward the antigen. Here, we show preliminary results that one set of these peptides improves or even cures all signs and symptoms of Graves' disease in mice after six consecutive monthly injections. First beneficial effects were observed 3-4 months after starting these therapies. In immunologically naïve mice, administration of the peptides did not induce any immune response.

MRI Assessment of Cardiomyopathy Induced by β1-Adrenoreceptor Autoantibodies and Protection Through β3-Adrenoreceptor Overexpression

The cardiopathogenic role of autoantibodies (aabs) directed against β1-adrenoreceptors (β1-AR) is well established. In mouse models, they cause progressive dilated cardiomyopathy (DCM) whose characterization with echocardiography requires prolonged protocols with numerous animals, complicating the evaluation of new treatments. Here, we report on the characterization of β1-aabs-induced DCM in mice using 11.7T MRI. C57BL/6J mice (n = 10 per group) were immunized against the β1-AR and left ventricular (LV) systolic function was assessed at 10, 18 and 27 weeks. Increase in LV mass/tibial length ratio was detected as the first modification at 10 weeks together with dilation of cavities, thereby outperforming echocardiography. Significant impairment in diastolic index was also observed in immunized animals before the onset of systolic dysfunction. Morphometric and histological measurements confirmed these observations. The same protocol performed on β3-AR-overexpressing mice and wild-type littermates (n = 8–12 per group) showed that transgenic animals were protected with reduced LV/TL ratio compared to wild-type animals and maintenance of the diastolic index. This study demonstrates that MRI allows a precocious detection of the subtle myocardial dysfunction induced by β1-aabs and that β3-AR stimulation blunts the development of β1-aabs-induced DCM, thereby paving the way for the use of β3AR-stimulating drugs to treat this autoimmune cardiomyopathy.

Cardiomyopathy - An approach to the autoimmune background

Autoimmunity is increasingly accepted as the origin or amplifier of various diseases. In contrast to classic autoantibodies (AABs), which induce immune responses resulting in the destruction of the affected tissue, an additional class of AABs is directed against G-protein-coupled receptors (GPCRs; GPCR-AABs). GPCR-AABs functionally affect their related GPCRs for activation of receptor mediated signal cascades. Diseases which are characterized by the presence of GPCR-AABs with evidence for disease-specific pathogenic activity could be named "functional autoantibody disease". We briefly summarize here the historical view on autoimmunity in cardiomyopathy, followed by an approach to the mechanistic autoimmunity background. Furthermore, autoantibodies with outstanding importance for cardiomyopathies as a functional autoantibody disease, such as GPCR-AABs, and mainly those directed against the beta1-adrenergic and muscarinic 2 receptor autoantibodies, are introduced. Anti-cardiac myosin and anti-cardiac troponin autoantibodies, as further potential players in autoimmune cardiomyopathy, are additionally taken into account. The basic view on the autoantibodies, their related receptor interactions and pathogenic consequences are presented. Focused specifically on GPCR-AABs, "pros and cons" of assays such as indirect assays (functional changes of cell preparations are monitored after GPCR-AAB receptor binding) and direct assays based on the ELISA technologies (GPCR epitope mimics for GPCR-AAB binding) are critically discussed. Last but not least, treatment strategies for "functional autoantibody disease", such as for GPCR-AAB removal (therapeutic plasma exchange, immunoadsorption) and in vivo GPCR-AAB attack such as intravenous IgG treatment (IVIG), B-cell depletion and GPCR-AAB binding and neutralization, are critically reflected with respect to their patient benefits.

Pharmacokinetics and Safety of Single Intravenous Doses of JNJ-54452840, an Anti-β1-Adrenergic Receptor Antibody Cyclopeptide, in Healthy Male Japanese and Caucasian Participants

AIM

To evaluate the pharmacokinetics and safety of single intravenous doses of JNJ-54452840 infused over 1 minute in healthy male Japanese and Caucasian participants. JNJ-54452840 is a novel peptide for the treatment of chronic heart failure, with a proposed mechanism of action of binding interference and decreased production of anti-β1-adrenergic receptor (anti-β1-AR) antibodies, which stimulate the cardiac β1-AR.

METHODS

In this randomized, single-centre, double-blind, placebo-controlled, four-way crossover study, 32 male Japanese and Caucasian participants (16 in each group) received single intravenous doses of JNJ-54452840 20, 80 and 240 mg, and placebo, each separated by a ≥7-day washout period. Pharmacokinetics and safety were assessed predose and at specified timepoints for 24 h. Anti-β1-AR antibodies were monitored.

RESULTS

The mean JNJ-54452840 maximum observed plasma concentration (C max) and area under the concentration-time curve from time zero to infinity with extrapolation of the terminal phase (AUCinf) values increased linearly with dose, with rapid elimination in both groups. Dose proportionality criteria were not met between the 20 and 240 mg doses for both study cohorts. The median time to reach C max (T max) ranged from 1 to 5 minutes. The mean total systemic clearance after intravenous administration (CL), volume of distribution at steady state (V ss), mean residence time (MRT) and terminal half-life (T ½) values were similar for both groups. The mean T ½ values ranged from 5.9 to 26.1 min in a dose-dependent manner. The overall prevalence of antibodies was 9.4 % at baseline; antibodies not present at baseline developed in five Caucasians (15.6 %) but not in Japanese participants. One participant in each group experienced a serious thromboembolic event (pulmonary embolism, ischaemic stroke).

CONCLUSION

JNJ-54452840 demonstrated similar pharmacokinetics in both groups. JNJ-54452840 was possibly immunogenic, and two participants reported thromboembolic serious adverse events. The relationship between these events and antibody formation is not known.

A standardised FACS assay based on native, receptor transfected cells for the clinical diagnosis and monitoring of β1-adrenergic receptor autoantibodies in human heart disease

BACKGROUND

Autoantibodies against β1-adrenergic receptors (β1AR) that stimulate cardiac cAMP-production play a causal role in the pathogenesis of human heart failure. Patients can be subjected to specific therapies, if the presence of potentially cardio-noxious β1AR-autoantibodies is reliably diagnosed. This requires assessment of IgG-interactions with the native β1AR because β1AR-autoantibodies target a conformational epitope inadequately presented by denatured receptors or linear peptides. Here, we report on a standardised diagnostic procedure for the assessment of β1AR-autoantibodies in heart failure patients, which is based on IgG-binding to native human β1AR.

METHODS

Good laboratory practice (GLP)-conform measurement of β1AR-autoantibodies was based on flow-cytometric quantification of differential IgG-binding to native HT1080 cells overexpressing biofluorescent human β1AR or not. Receptor-specific IgG-binding was derived from IgG-related median fluorescence of β1AR-positive cells corrected for background staining of β1AR-negative cells admixed to each measurement. The slope of IgG binding at two different concentrations was used as measure for the titre/avidity of β1AR-autoantibodies.

RESULTS

Sensitivity and specificity of the novel procedure for high β1AR-autoantibody levels in dilated cardiomyopathy patients (n=40, NYHA class III-IV) relative to n=40 matched healthy subjects was >90%. It was similar to functional assays considered the gold standard and vastly superior to existing screening-procedures employing fixed cells or linear receptor-peptides as auto-antigenic targets. Inter-assay scatter was 7%-15% and linear dilution recovery was within ±10% of expected values throughout.

CONCLUSIONS

The novel assay possibly provides a tool to determine true prevalence and clinical impact of β1AR-autoantibodies. Furthermore, it may serve as companion diagnostic for therapies specifically directed at β1AR-autoantibodies.

Chronic Heart Failure and Inflammation

As a greater proportion of patients survive their initial cardiac insult, medical systems worldwide are being faced with an ever-growing need to understand the mechanisms behind the pathogenesis of chronic heart failure (HF). There is a wealth of information about the role of inflammatory cells and pathways during acute injury and the reparative processes that are subsequently activated. We discuss the different causes that lead to chronic HF development and how the sum of initial inflammatory and reparative responses only sets the trajectory for disease progression. Unfortunately, comparatively little is known about the contribution of the immune system once the trajectory has been set, and chronic HF has been established—which clinically represents the majority of patients. It is known that chronic HF is associated with circulating inflammatory cytokines that can predict clinical outcomes, yet the causative role inflammation plays in disease progression is not well defined, and the majority of clinical trials that target aspects of inflammation in patients with chronic HF have largely been negative. This review will present what is currently known about inflammation in chronic HF in both humans and animal models as a means to highlight the gap in our knowledge base that requires further examination.

Emerging pharmacologic targets and treatments for myocarditis

Myocarditis is a heterogeneous group of disorders defined by inflammation of the heart muscle. The primary clinical manifestations of myocarditis are heart failure and sudden death in children and young adults. Numerous interventions have been investigated for the treatment of myocarditis, including broad spectrum alteration of the immune response and antiviral treatments; however, success has been limited. Since the myocarditis treatment trials in the 1990s there has been an improved understanding of disease progression and new facets of the immune response have been discovered. This new information provides fresh opportunities to develop therapeutics to treat myocarditis. This review analyzes previous pharmacologic approaches including immunosuppression, high dose intravenous immunoglobulin treatment, immunoadsorption and antiviral treatments, and looks forward toward recently identified immune factors that can be exploited as targets for new treatments. Such strategies include bolstering beneficial regulatory T cells or mitigating the detrimental Th17 T cells which can drive autoimmunity in the heart. The surging interest of the application of humanized monoclonal antibodies makes targeting deleterious arms of the immune response like Th17 cells a tangible goal in the near future. Promising constituents of herbal remedies have also been identified that may hold potential as new pharmacological treatments for myocarditis, however, significant work remains to elucidate the pharmacokinetics and side-effects of these compounds. Finally, advances in our understanding of the function of Matrix Metalloproteinases yield another target for altering disease progression given their role in the development of fibrosis during Dilated Cardiomyopathy. In bringing to light the various new targets and treatments available since the last myocarditis treatment trials, the aim of this review is to explore the new treatments that are possible in new myocarditis treatment trials.

A peptidomimetic inhibitor suppresses the inducibility of β1-adrenergic autoantibody-mediated cardiac arrhythmias in the rabbit

PURPOSE

Previous studies demonstrated that burst pacing and subthreshold infusion of acetylcholine in β1-adrenergic receptor (β1AR)-immunized rabbits induced sustained sinus tachycardia. The aim of this study was to examine the anti-arrhythmogenic effect of a newly designed retro-inverso (RI) peptidomimetic inhibitor that specifically targets the β1AR antibodies in the rabbit.

METHODS

Six New Zealand white rabbits were immunized with a β1AR second extracellular loop peptide to produce sympathomimetic β1AR antibodies. A catheter-based electrophysiological study was performed on anesthetized rabbits before and after immunization and subsequent treatment with the RI peptide inhibitor. Each rabbit served as its own control.

RESULTS

No sustained arrhythmias were induced at preimmune baseline. At 6 weeks after immunization, there was a marked increase in induced sustained tachyarrhythmias, predominantly sinus tachycardia, which was largely suppressed by the RI peptide. The atrial effective refractory period was shortened significantly in immunized rabbits compared to their preimmune state. The RI peptide reversed and prolonged this shortening. β1AR antibody levels were negatively correlated with the atrial effective refractory period. Postimmune sera-induced β1AR activation in transfected cells in vitro was also blocked by the RI peptide.

CONCLUSIONS

β1AR-activating autoantibodies are associated with reduction of the atrial effective refractory period and facilitate arrhythmia induction in this model. The RI peptide reversal may have important therapeutic implications in subjects who harbor these autoantibodies.

Inherited cardiomyopathies--Novel therapies

Cardiomyopathies arising due to a single gene defect represent various pathways that evoke adverse remodeling and cardiac dysfunction. While the gene therapy approach is slowly evolving and has not yet reached clinical "prime time" and gene correction approaches are applicable at the bench but not at the bedside, major advances are being made with molecular and drug therapies. This review summarizes the contemporary drugs introduced or being tested to help manage these unique disorders bearing a major impact on the quality of life and survival of the affected individuals. The restoration of the RNA reading frame facilitates the expression of partly functional protein to salvage or alleviate the disease phenotype. Chaperones are used to prevent the degradation of abnormal but still functional proteins, while other molecules are given for pathogen silencing, to prevent aggregation or to enhance clearance of protein deposits. The absence of protein may be managed by viral gene delivery or protein therapy. Enzyme replacement therapy is already a clinical reality for a series of metabolic diseases. The progress in molecular biology, based on the knowledge of the gene defect, helps generate small molecules and pharmaceuticals targeting the key events occurring in the malfunctioning element of the sick organ. Cumulatively, these tools augment the existing armamentarium of phenotype oriented symptomatic and evidence-based therapies for patients with inherited cardiomyopathies.

Targeting of anti-citrullinated protein/peptide antibodies in rheumatoid arthritis using peptides mimicking endogenously citrullinated fibrinogen antigens

INTRODUCTION

We have previously identified endogenously citrullinated peptides derived from fibrinogen in rheumatoid arthritis (RA) synovial tissues. In this study, we have investigated the auto-antigenicity of four of those citrullinated peptides, and explored their feasibility to target anti-citrullinated protein/peptide antibodies (ACPA).

METHODS

The autoantigenic potential of the fibrinogen peptides was investigated by screening 927 serum samples from the Epidemiological Investigation of RA (EIRA) cohort on a peptide microarray based on the ImmunoCAP ISAC® system. In order to assay for ACPA blocking, two independent pools of purified ACPA were incubated with the respective targeting peptide prior to binding to cyclic citrullinated peptide (CCP)2 using the CCPlus® ELISA kit.

RESULTS

Two peptides derived from the fibrinogen α chain, Arg573Cit (563-583) and Arg591Cit (580-600), referred to as Cit573 and Cit591, and two peptides from the fibrinogen β chain, Arg72Cit (62-81) and Arg74Cit (62-81) (Cit72 and Cit74), displayed 65%, 15%, 35%, and 53% of immune reactivity among CCP2-positive RA sera, respectively. In CCP2-negative RA sera, a positive reactivity was detected in 5% (Cit573), 6% (Cit591), 8% (Cit72), and 4% (Cit74). In the competition assay, Cit573 and Cit591 peptides reduced ACPA binding to CCP2 by a maximum of 84% and 63% respectively. An additive effect was observed when these peptides were combined. In contrast, Cit74 and Cit72 were less effective. Cyclization of the peptide structure containing Cit573 significantly increased the blocking efficiency.

CONCLUSIONS

Here we demonstrate extensive autoantibody reactivity against in vivo citrullinated fibrinogen epitopes, and further show the potential use of these peptides for antagonizing ACPA.

Innate immunity and the failing heart: the cytokine hypothesis revisited

Elevated levels of inflammatory mediators have been identified in patients with heart failure, including heart failure with reduced and preserved ejection fraction, as well as acute decompensated heart failure. Moreover, experimental studies have shown repeatedly that activation of inflammation in the heart provokes left ventricular remodeling and left ventricular dysfunction. Nonetheless, phase III clinical trials that have attempted to antagonize inflammatory mediators have been negative with respect to the primary end points of the trials, and in some patients, resulted in worsening heart failure or death. The following review will discuss how recent developments in the field of innate immunity have advanced our understanding of the role of inflammation in the pathogenesis of heart failure and will discuss the negative outcomes of the existing clinical trials in light of this new information.

Novel retro-inverso peptide inhibitor reverses angiotensin receptor autoantibody-induced hypertension in the rabbit

Activating autoantibodies to the angiotensin II type 1 receptor (AT1R) have been implicated in hypertensive disorders. We investigated whether AT1R antibodies produced in immunized rabbits will activate AT1R and contribute to hypertension by a direct contractile effect on the vasculature and whether they can be blocked by a novel decoy peptide. A multiple antigenic peptide containing the AT1R epitope AFHYESQ, which is the receptor-binding epitope of AT1R-activating autoantibodies, was used to immunize 6 rabbits. AT1R antibody activity was analyzed in AT1R-transfected cells, and their contractile effects were assayed using isolated perfused rat cremaster resistance arterioles. A retro-inverso D-amino acid epitope-mimetic peptide was tested for AT1R antibody inhibition in vitro and in vivo. All immunized animals produced high AT1R antibody titers and developed elevated blood pressure. No changes in measured blood chemistry values were observed after immunization. Rabbit anti-AT1R sera induced significant AT1R activation in transfected cells and vasoconstriction in the arteriole assay, both of which were blocked by losartan and the retro-inverso D-amino acid peptide. A single intravenous bolus injection of the retro-inverso d-amino acid peptide (1 mg/kg) into immunized rabbits dropped the mean arterial pressure from 122±11 to 82±6 mm Hg. Rabbit anti-AT1R sera partially suppressed angiotensin II-induced contraction of isolated rat cremaster arterioles, and the pressor response to angiotensin II infusion was attenuated in immunized animals. In conclusion, AT1R-activating autoantibodies and the retro-inverso d-amino acid peptide, respectively, have important etiologic and therapeutic implications in hypertensive subjects who harbor these autoantibodies.

Discoveries in peripartum cardiomyopathy

The past decade has seen remarkable gains for outcomes in peripartum cardiomyopathy (PPCM), one of the leading causes of maternal mortality and morbidity in the USA and many other countries, including the high-incidence areas of Haiti and South Africa. This review article emphasizes the importance of continuing the process of increasing awareness of PPCM and presents details of this evolving picture, including important discoveries that point the way to full recovery for almost all PPCM subjects. In addition, new interventions will be highlighted, which may facilitate recovery. Numerous studies have demonstrated that when the diagnosis of PPCM is made with LVEF > 0.30, the probability is that recovery to LVEF ≥ 0.50 will occur in the overwhelming majority of subjects. PPCM patients diagnosed with severely depressed systolic function (LVEF < 0.30) and a remodeled left ventricle with greater dilatation (LVEDd ≥ 60mm) are least likely to reach the outcome recovery goals. These are the patients with the greatest need for newer interventional strategies.

Monoclonal anti-β1-adrenergic receptor antibodies activate G protein signaling in the absence of β-arrestin recruitment

Thermostabilized G protein-coupled receptors used as antigens for in vivo immunization have resulted in the generation of functional agonistic anti-β1-adrenergic (β1AR) receptor monoclonal antibodies (mAbs). The focus of this study was to examine the pharmacology of these antibodies to evaluate their mechanistic activity at β1AR. Immunization with the β1AR stabilized receptor yielded five stable hybridoma clones, four of which expressed functional IgG, as determined in cell-based assays used to evaluate cAMP stimulation. The antibodies bind diverse epitopes associated with low nanomolar agonist activity at β1AR, and they appeared to show some degree of biased signaling as they were inactive in an assay measuring signaling through β-arrestin. In vitro characterization also verified different antibody receptor interactions reflecting the different epitopes on the extracellular surface of β1AR to which the mAbs bind. The anti-β1AR mAbs only demonstrated agonist activity when in dimeric antibody format, but not as the monomeric Fab format, suggesting that agonist activation may be mediated through promoting receptor dimerization. Finally, we have also shown that at least one of these antibodies exhibits in vivo functional activity at a therapeutically-relevant dose producing an increase in heart rate consistent with β1AR agonism.

The patent situation concerning the treatment of diseases associated with autoantibodies directed against G-protein-coupled receptors

Agonist-like autoantibodies against receptors of the G-protein-coupled signal cascade have been identified as the pathogenic principle for a variety of diseases, especially those of the heart and vascular system. Consequently, the elimination or neutralization of such autoantibodies is an advised goal for causal therapeutic intervention. This article provides a short, noncomplete overview about remarkable developmental strategies and technical solutions for the therapy of diseases, associated with G-protein-coupled receptor autoantibodies. According to the immunoglobulin nature of the therapeutic target, several strategies are possible, such as the use of the autoantibody epitope sequences as competitors or binding molecules for specific autoantibody-elimination by apheresis. Complete immunoglobulin elimination, as is currently being tested in autoantibody-positive cardiomyopathy patients, would be a nonspecific solution as would the use of immunosuppressant agents. The use of autoantibody-binding molecules on an aptamer basis for neutralization or elimination is a newly developed specific therapeutic option.

Agonistic autoantibodies directed against G-protein-coupled receptors and their relationship to cardiovascular diseases

Agonistic autoantibodies (AABs) against G-protein-coupled receptor (GPCR) are present mainly in diseases of the cardiovascular system or in diseases associated with cardiovascular disturbances. The increasing knowledge about the role of autoantibodies against G-protein-coupled receptor (GPCR-AABs) as pathogenic drivers, the resulting development of strategies aimed at their removal or neutralization, and the evidenced patient benefit associated with such therapies have created the need for a summary of GPCR-AAB-associated diseases. Here, we summarize the present knowledge about GPCR-AABs in cardiovascular diseases. The identity of the GPCR-AABs and their prevalence in each of several specific cardiovascular diseases are documented. The structure of GPCR is also briefly discussed. Using this information, differences between classic agonists and GPCR-AABs in their GPCR binding and activation are presented and the resulting pathogenic consequences are discussed. Furthermore, treatment strategies that are currently under study, most of which are aimed at the removal and in vivo neutralization of GPCR-AABs, are indicated and their patient benefits discussed. In this context, immunoadsorption using peptides/proteins or aptamers as binders are introduced. The use of peptides or aptamers for in vivo neutralization of GPCR-AABs is also described. Particular attention is given to the GPCR-AABs directed against the adrenergic beta1-, beta2-, and α1-receptor as well as the muscarinic receptor M2, angiotensin II-angiotensin receptor type I, endothelin1 receptor type A, angiotensin (1-7) Mas-receptor, and 5-hydroxytryptamine receptor 4. Among the diseases associated with GPCR-AABs, special focus is given to idiopathic dilated cardiomyopathy, Chagas' cardiomyopathy, malignant and pulmonary hypertension, and kidney diseases. Relationships of GPCR-AABs are indicated to glaucoma, peripartum cardiomyopathy, myocarditis, pericarditis, preeclampsia, Alzheimer's disease, Sjörgren's syndrome, and metabolic syndrome after cancer chemotherapy.

Peripartum cardiomyopathy: A puzzle closer to solution

Peripartum cardiomyopathy (PPCM) represents new heart failure in a previously heart-healthy peripartum patient. It is necessary to rule out all other known causes of heart failure before accepting a diagnosis of PPCM. The modern era for PPCM in the United States and beyond began with the report of the National Institutes of Health PPCM Workshop in 2000, clarifying all then-currently known aspects of the disease. Since then, hundreds of publications have appeared, an indication of how devastating this disease can be to young mothers and their families and the urgent desire to find solutions for its cause and better treatment. The purpose of this review is to highlight the important advances that have brought us nearer to the solution of this puzzle, focusing on what we have learned about PPCM since 2000; and what still remains unanswered. Despite many improvements in outcome, we still do not know the actual triggers that initiate the pathological process; but realize that cardiac angiogenic imbalances resulting from complex pregnancy-related immune system and hormonal changes play a key role.

How can we cure a heart "in flame"? A translational view on inflammation in heart failure

The prevalence of chronic heart failure is still increasing making it a major health issue in the 21st century. Tremendous evidence has emerged over the past decades that heart failure is associated with a wide array of mechanisms subsumed under the term “inflammation”. Based on the great success of immuno-suppressive treatments in auto-immunity and transplantation, clinical trials were launched targeting inflammatory mediators in patients with chronic heart failure. However, they widely lacked positive outcomes. The failure of the initial study program directed against tumor necrosis factor-α led to the search for alternative therapeutic targets involving a broader spectrum of mechanisms besides cytokines. We here provide an overview of the current knowledge on immune activation in chronic heart failure of different etiologies, summarize clinical studies in the field, address unresolved key questions, and highlight some promising novel therapeutic targets for clinical trials from a translational basic science and clinical perspective.

Targeting anti-beta-1-adrenergic receptor antibodies for dilated cardiomyopathy

Anti-beta-1-adrenergic receptor antibodies (anti-β1AR Abs) have long been implicated in the pathogenesis of dilated cardiomyopathy (DCM). It is believed that these autoantibodies bind to and constitutively stimulate the β1AR to promote pathological cardiac remodelling and β1AR desensitization and downregulation. The prevalence of anti-β1AR Abs in patients with DCM ranges from 26% to 60%, and the presence of these autoantibodies correlates with a poor prognosis. Several small studies have shown improvements in functional status, haemodynamics, and biomarkers of heart failure upon removal or neutralization of these antibodies from the sera of affected patients. Traditionally, removal of anti-β1AR Abs required immunoadsorption therapy with apheresis columns directed against human immunoglobulins (Igs) and subsequent i.v. Ig infusion, thereby essentially performing a plasma exchange transfusion. However, recent advances have allowed the development of small peptides and nucleotide sequences that specifically target and neutralize anti-β1AR Abs, providing a hopeful avenue for future drug development to treat DCM. Herein, we briefly review the clinical literature of therapy directed against anti-β1AR Abs and highlight the opportunity for further research and development in this area.

Impact of human autoantibodies on β1-adrenergic receptor conformation, activity, and internalization

Aims

Autoantibodies against second extracellular loops of β₁-adrenergic receptors frequent in dilated cardiomyopathy confer myocardial dysfunction presumably via cAMP stimulation. Here, we investigate the autoantibody impact on receptor conformation and function.

Methods and results

IgG was prepared from patients with dilated cardiomyopathy, matched healthy donors (10 each) or commercial IgG preparations (2). IgG binding to β₁-adrenergic receptor peptides was detected in 5 of 10 patients and 2 of 10 controls. IgG colocalization with the native receptor was detected in 8 of 10 patients and 1 of 10 controls (10 of 10 patients and 7 of 10 controls at >30 mg IgG/L). All IgGs exhibiting receptor colocalization triggered changes in receptor conformation (determined with fluorescent sensors) not stringently correlated to cAMP stimulation, suggesting the induction of more or less active receptor conformations. Receptor-activating IgG was detected in 8 of 10 patients but only 1 of 10 controls. In addition, IgG from 8 of 10 patients and 3 of 10 controls attenuated receptor internalization (measured by total internal reflection fluorescence microscopy). IgG-inducing inactive receptor conformations had no effect on subsequent cAMP stimulation by isoproterenol. IgG-inducing active receptor conformations dampened or augmented subsequent cAMP stimulation by isoproterenol, depending on whether receptor internalization was attenuated or not. Corresponding IgG effects on the basal beating rate and chronotropic isoproterenol response of embryonic human cardiomyocytes were observed.

Conclusions

(i) Autoantibodies trigger conformation changes in the β₁-adrenergic receptor molecule. (ii) Some also attenuate receptor internalization. (iii) Combinations thereof increase the basal beating rate of cardiomyocytes and optionally entail dampening of their chronotropic catecholamine responses. (iv) The latter effects seem specific for patient autoantibodies, which also have higher levels.

Detection of anti-β1-AR autoantibodies in heart failure by a cell-based competition ELISA

RATIONALE

Autoantibodies directed against the second extracellular loop of the cardiac β1-adrenergic receptor (β1-AR) are thought to contribute to the pathogenesis of dilated cardiomyopathy (DCM) and Chagas heart disease. Various approaches have been used to detect such autoantibodies; however, the reported prevalence varies largely, depending on the detection method used.

OBJECTIVE

We analyzed sera from 167 DCM patients (ejection fraction<45%) and from 110 age-matched volunteers who did not report any heart disease themselves, with an often used simple peptide-ELISA approach, and compared it with a novel whole cell-based ELISA, using cells expressing the full transgene for the human β1-AR. Additionally, 35 patients with hypertensive heart disease with preserved ejection fraction were investigated.

METHODS AND RESULTS

The novel assay was designed according to the currently most reliable anti-TSH receptor antibody-ELISA used to diagnose Graves disease ("third-generation assay") and also detects the target antibodies by competition with a specific monoclonal anti-β1-AR antibody (β1-AR MAb) directed against the functionally relevant β1-AR epitope. Anti-β1-AR antibodies were detected in ≈60% of DCM patients and in ≈8% of healthy volunteers using the same cutoff values. The prevalence of these antibodies was 17% in patients with hypertensive heart disease. Anti-β1-AR antibody titers (defined as inhibition of β1-AR MAb-binding) were no longer detected after depleting sera from IgG antibodies by protein G adsorption. In contrast, a previously used ELISA conducted with a linear 26-meric peptide derived from the second extracellular β1-AR loop yielded a high number of false-positive results precluding any specific identification of DCM patients.

CONCLUSIONS

We established a simple and efficient screening assay detecting disease-relevant β1-AR autoantibodies in patient sera yielding a high reproducibility also in high throughput screening. The assay was validated according to "good laboratory practice" and can serve as a companion biodiagnostic assay for the development and evaluation of antibody-directed therapies in antibody-positive heart failure.