Active immunization of combined beta1-adrenoceptor and M2-muscarinic receptor peptides induces cardiac hypertrophy in rabbits

β1 Adrenergic Receptor Autoantibodies and IgG Subclasses: Current Status and Unsolved Issues

A wide range of anti-myocardial autoantibodies have been reported since the 1970s. Among them, autoantibodies against the β1-adrenergic receptor (β1AR-AAb) have been the most thoroughly investigated, especially in dilated cardiomyopathy (DCM). Β1AR-Aabs have agonist effects inducing desensitization of β1AR, cardiomyocyte apoptosis, and sustained calcium influx which lead to cardiac dysfunction and arrhythmias. Β1AR-Aab has been reported to be detected in approximately 40% of patients with DCM, and the presence of the antibody has been associated with worse clinical outcomes. The removal of anti-myocardial autoantibodies including β1AR-AAb by immunoadsorption is beneficial for the improvement of cardiac function for DCM patients. However, several studies have suggested that its efficacy depended on the removal of AAbs belonging to the IgG3 subclass, not total IgG. IgG subclasses differ in the structure of the Fc region, suggesting that the mechanism of action of β1AR-AAb differs depending on the IgG subclasses. Our previous clinical research demonstrated that the patients with β1AR-AAb better responded to β-blocker therapy, but the following studies found that its response also differed among IgG subclasses. Further studies are needed to elucidate the possible pathogenic role of IgG subclasses of β1AR-AAbs in DCM, and the broad spectrum of cardiovascular diseases including HF with preserved ejection fraction.

M2 muscarinic autoantibodies and thyroid hormone promote susceptibility to atrial fibrillation and sinus tachycardia in an autoimmune rabbit model

NEW FINDINGS

What is the central question of this study? Do autoantibodies to the M2 muscarinic receptor (M2R-AAbs) have the potential to facilitate specific sustained tachyarrhythmias in the presence of thyroxine (T4 ) in rabbits? What is the main finding and its importance? The M2R-AAb and T4 jointly destabilized the electrophysiological properties, thus promoting the occurrence of atrial and sinus tachyarrhythmias in rabbits. These findings provide a practical basis for understanding the pathophysiological role of M2R-AAb alone and with T4 in arrhythmia induction and might provide an innovative option for treatment of Graves' disease with rhythm disturbance.

ABSTRACT

Activating autoantibodies toward the β1/2 -adrenergic receptors (β1/2AR-AAbs) and M2 muscarinic receptor (M2R-AAbs) are present in a high proportion of patients with Graves' disease. We previously demonstrated that β1/2AR-AAbs with or without the presence of M2R-AAbs in combination with excessive thyroxine (T4 ) increased the induction of sustained tachyarrhythmias in an autoimmune rabbit model. However, the separate role of M2R-AAbs and their interaction with T4 are not clear. The aim of this study was to investigate the impact of M2R-AAbs and T4 on the induction of cardiac arrhythmias in a similar rabbit model. Ten New Zealand White rabbits were randomly divided into two groups. In group A (n = 6), the rabbits were immunized with the second extracellular loop peptide of M2R and subjected to 2 weeks of T4 treatment. In group B (n = 4), the rabbits were treated only with T4 for 2 weeks. After induction of general anaesthesia, rabbits were subjected to an electrophysiological study at 0 (pre-immune), 6 (post-immune) and 8 weeks (post-immune+T4 treatment) in group A and at 0 (baseline) and 8 weeks (T4 treatment) in group B. Each rabbit served as its own control. In group A, high levels and activity of M2R-AAbs were detected in all immunized animals. Thyroxine in combination with immunization significantly increased induction of sustained sinus tachycardia and atrial fibrillation in comparison to the pre-immune state. In group B, T4 predominantly induced sustained sinus tachycardia. This study demonstrated that M2R-AAbs and T4 jointly increased the susceptibility to both sinus and atrial tachyarrhythmias. The data supported the pathophysiological role of M2R-AAbs in hyperthyroidism-associated supraventricular tachyarrhythmias.

Elevated β1-Adrenergic Receptor Autoantibody Levels Increase Atrial Fibrillation Susceptibility by Promoting Atrial Fibrosis

Objective

Beta 1-adrenergic receptor autoantibodies (β1ARAbs) have been identified as a pathogenic factor in atrial fibrillation (AF), but the underlying pathogenetic mechanism is not well understood. We assessed the hypothesis that elevated β1ARAb levels increase AF susceptibility by promoting atrial fibrosis.

Methods

A total of 70 patients with paroxysmal AF were continuously recruited. The serum levels of β1ARAb and circulating fibrosis biomarkers were analyzed by ELISA. Linear regression was used to examine the correlations of β1ARAb levels with left atrial diameter (LAD) and circulating fibrosis biomarker levels. Furthermore, we established a rabbit β1ARAb overexpression model. We conducted electrophysiological studies and multielectrode array recordings to evaluate the atrial effective refractory period (AERP), AF inducibility and electrical conduction. AF was defined as irregular, rapid atrial beats > 500 bpm for > 1000 ms. Echocardiography, hematoxylin and eosin staining, Masson's trichrome staining, and picrosirius red staining were performed to evaluate changes in atrial structure and detect fibrosis. Western blotting and PCR were used to detect alterations in the protein and mRNA expression of TGF-β1, collagen I and collagen III.

Results

Patients with a LAD ≥ 40 mm had higher β1ARAb levels than patients with a smaller LAD (8.87 ± 3.16 vs. 6.75 ± 1.34 ng/mL, P = 0.005). β1ARAb levels were positively correlated with LAD and circulating biomarker levels (all P < 0.05). Compared with the control group, the rabbits in the immune group showed the following: (1) enhanced heart rate, shortened AERP (70.00 ± 5.49 vs. 96.46 ± 3.27 ms, P < 0.001), increased AF inducibility (55% vs. 0%, P < 0.001), decreased conduction velocity and increased conduction heterogeneity; (2) enlarged LAD and elevated systolic dysfunction; (3) significant fibrosis in the left atrium identified by Masson's trichrome staining (15.17 ± 3.46 vs. 4.92 ± 1.72%, P < 0.001) and picrosirius red staining (16.76 ± 6.40 vs. 4.85 ± 0.40%, P < 0.001); and (4) increased expression levels of TGF-β1, collagen I and collagen III.

Conclusion

Our clinical and experiential studies showed that β1ARAbs participate in the development of AF and that the potential mechanism is related to the promotion of atrial fibrosis.

Doberman pinschers present autoimmunity associated with functional autoantibodies: A model to study the autoimmune background of human dilated cardiomyopathy

Background

Autoimmunity associated with autoantibodies against the β1-adrenergic receptor (β1-AAB) is increasingly accepted as the driver of human dilated cardiomyopathy (DCM). Unfortunately, there is a lack of animal models to extend the knowledge about β1-AAB autoimmunity in DCM and to develop appropriate treatment strategies.

Objectives

To introduce an animal model, we investigated the β1-AAB associated autoimmunity in Doberman Pinscher (DP) with dilated cardiomyopathy, which has similarities to human DCM.

Materials and methods

Eighty-seven DP with cardiomyopathy in terms of pathological ECG and echocardiography (DoCM) and 31 dogs (at enrollment) without DoCM (controls) were analyzed for serum activity of β1-AAB with a bioassay that records the chronotropic response of spontaneously beating cultured neonatal rat cardiomyocytes to the DP’s IgG. To locate the receptor binding site of β1-AAB and the autoantibody’s sensitivity to inhibition, competing experiments with related blockers were performed with the bioassay. In controls that developed DoCM during follow-up, β1-AAB were analyzed during progress.

Results

Fifty-nine (67.8%) DoCM dogs and 19 (61.3%) controls were β1-AAB positive. Of the controls that developed DoCM, 8 were β1-AAB positive (p = 0.044 vs. dogs remaining in the control group); their β1-AAB activity increased with the cardiomyopathy progress (p<0.02). To supplement DoCM group with the 9 animals which developed cardiomyopathy in the follow up, a more pronounced β1-AAB positivity became visible in the DoCM group (p = 0.066).

Total and cardiac mortality were higher in β1-AAB positive DP (p = 0.002; p = 0037). The dogs’ β1-AAB recognized a specific epitope on the second extracellular receptor and were sensitive to inhibition by drugs already successfully tested to inhibit the corresponding human autoantibody.

Conclusions

Doberman Pinschers presented β1-AAB associated autoimmunity, similar as in the pathogenesis of human DCM. Consequently, DP could compensate the lack of animal models for the investigation of β1-AAB autoimmunity in human DCM.

Autoantibody profiling on a plasmonic nano-gold chip for the early detection of hypertensive heart disease

The role of autoimmunity in cardiovascular (CV) diseases has been increasingly recognized. Autoimmunity is most commonly examined by the levels of circulating autoantibodies in clinical practices. Measurement of autoantibodies remains, however, challenging because of the deficiency of reproducible, sensitive, and standardized assays. The lack of multiplexed assays also limits the potential to identify a CV-specific autoantibody profile. To overcome these challenges, we developed a nanotechnology-based plasmonic gold chip for autoantibody profiling. This approach allowed simultaneous detection of 10 CV autoantibodies targeting the structural myocardial proteins, the neurohormonal regulatory proteins, the vascular proteins, and the proteins associated with apoptosis and coagulation. Autoantibodies were measured in four groups of participants across the continuum of hypertensive heart diseases. We observed higher levels of all 10 CV autoantibodies in hypertensive subjects (n = 77) compared with healthy participants (n = 30), and the autoantibodies investigated were related to each other, forming a highly linked network. In addition, we established that autoantibodies to troponin I, annexin-A5, and beta 1-adrenegic receptor best discriminated hypertensive subjects with adverse left ventricular (LV) remodeling or dysfunction (n = 49) from hypertensive subjects with normal LV structure and function (n = 28). By further linking these three significant CV autoantibodies to the innate and growth factors, we revealed a positive but weak association between autoantibodies to troponin I and proinflammatory cytokine IL-18. Overall, we demonstrated that this platform can be used to evaluate autoantibody profiles in hypertensive subjects at risk for heart failure.

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.

Aptamer BC 007 - A broad spectrum neutralizer of pathogenic autoantibodies against G-protein-coupled receptors

The effect of autoantibodies on G-protein coupled receptors in the pathogenesis of diseases, especially of the heart and vascular system, is an increasingly accepted fact today. Dilated cardiomyopathy (DCM) is the most intensively investigated pathological situation of these. With DCM, autoantibodies against the β1-adrenoceptor and the muscarinic M2-receptor have been found in high percentage of investigated patients. Immunoadsorption for autoantibody removal has already shown a long-term beneficial therapeutic effect, but has remained limited in its application because of the complexity of this method. A new easy applicable treatment strategy has, therefore, been discovered. Because of intra- and inter-loop epitope variability of the β1-adrenoceptor specific autoantibodies and also the occurrence of further autoantibodies of this class such as the ones against the β2- and α1-adrenoceptor, the ETA-, proteinase activated-, and the AT1-receptors in different pathological situations, this newly discovered broad-spectrum neutralizer of all these autoantibodies - aptamer BC 007 - is under development. The binding and neutralizing effect was investigated applying a bioassay of spontaneously beating neonatal rat cardiomyocytes and enzyme-linked immunosorbent assay (ELISA) - technology. The usefulness of aptamer BC 007 to specify column technology for the removal of serum autoantibodies was also demonstrated. The presented data suggest that aptamer BC 007 might be an appropriate molecule candidate to support future research about the meaning of G-protein-coupled receptor autoantibodies.

β1-Adrenergic and M2 Muscarinic Autoantibodies and Thyroid Hormone Facilitate Induction of Atrial Fibrillation in Male Rabbits

Activating autoantibodies to the β1-adrenergic and M2 muscarinic receptors are present in a very high percentage of patients with Graves' disease and atrial fibrillation (AF). The objective of this study was to develop a reproducible animal model and thereby to examine the impact of these endocrine-like autoantibodies alone and with thyroid hormone on induction of thyroid-associated atrial tachyarrhythmias. Five New Zealand white rabbits were coimmunized with peptides from the second extracellular loops of the β1-adrenergic and M2 muscarinic receptors to produce both sympathomimetic and parasympathomimetic antibodies. A catheter-based electrophysiological study was performed on anesthetized rabbits before and after immunization and subsequent treatment with thyroid hormone. Antibody expression facilitated the induction of sustained sinus, junctional and atrial tachycardias, but not AF. Addition of excessive thyroid hormone resulted in induced sustained AF in all animals. AF induction was blocked acutely by the neutralization of these antibodies with immunogenic peptides despite continued hyperthyroidism. The measured atrial effective refractory period as one parameter of AF propensity shortened significantly after immunization and was acutely reversed by peptide neutralization. No further decrease in the effective refractory period was observed after the addition of thyroid hormone, suggesting other cardiac effects of thyroid hormone may contribute to its role in AF induction. This study demonstrates autonomic autoantibodies and thyroid hormone potentiate the vulnerability of the heart to AF, which can be reversed by decoy peptide therapy. These data help fulfill Witebsky's postulates for an increased autoimmune/endocrine basis for Graves' hyperthyroidism and AF.

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.

Neutralization of pathogenic beta1-receptor autoantibodies by aptamers in vivo: the first successful proof of principle in spontaneously hypertensive rats

Autoantibodies (AABs) against the second extracellular loop of the beta1-receptor (beta1(II)-AABs) are found as a pathogenic driver in patients with idiopathic dilated cardiomyopathy, Chagas cardiomyopathy, peripartum cardiomyopathy, and myocarditis, and have been increasingly seen as a treatment target. We recently identified an aptamer (single short DNA strand) that specifically binds and neutralizes beta1(II)-AABs. Via application of this aptamer, a new treatment strategy for diseases associated with the cardio-pathogenic beta1(II)-AABs could be developed. Spontaneously hypertensive rats (SHR) positive for beta1(II)-AABs were treated five times at weekly intervals (bolus application of 2 mg/kg body weight followed by an infusion of the same amount over 20 min). SHR responded to aptamer treatment with a strong reduction in the cardio-pathogenic beta1(II)-AABs. The AABs did not substantially return within the study period. No signs for aptamer toxicity were observed by visual examination of the heart, liver, and kidney, or by measurement of plasma CK, ALT, and creatinine. The aptamer's potential for beta1(II)-AAB neutralization and consequently for cardiomyopathy treatment has been shown for the first time in vivo.

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.

Aptamer binding and neutralization of β1-adrenoceptor autoantibodies: basics and a vision of its future in cardiomyopathy treatment

Autoantibodies directed against the second extracellular receptor loop of the β(1) receptor (β(1)-ECII-AABs) that belong to the superfamily of G protein-coupled receptors have been frequently found in patients with idiopathic dilated cardiomyopathy, Chagas' cardiomyopathy, and peripartum cardiomyopathy and have been clearly evidenced to be related to disease pathogenesis. Consequently, specific proteins or peptides used as binders in immunoapheresis or as in vivo neutralizers of β(1)-ECII-AABs have been suggested for patient treatment. Aptamers, which are target specifically selected short single- or double-stranded RNA or DNA sequences, are a recently introduced new molecule class applicable to bind and neutralize diverse molecule species, including antibodies. This article reviews selection technologies and characteristics of aptamers with respect to a single-stranded DNA aptamer recently identified as having a very high affinity against β(1)-ECII-AABs. The potential of this aptamer for the elimination of β(1)-ECII-AABs and in vivo neutralization is critically analyzed in view of its potential for future use in cardiomyopathy treatment.

Drug-like actions of autoantibodies against receptors of the autonomous nervous system and their impact on human heart function

Antibodies against cholinergic and adrenergic receptors (adrenoceptors) are frequent in serum of patients with chronic heart failure. Their prevalence is associated with Chagas' disease, idiopathic dilated cardiomyopathy (DCM), and ischaemic heart disease. Among the epitopes targeted are first and second extracellular loops of the β-adrenergic (β-adrenoceptor) and M2 muscarinic receptor. β₁-adrenoceptor autoantibodies affect radioligand binding and cardiomyocyte function similar to agonists. Corresponding rodent immunizations induce symptoms compatible with chronic heart failure that are reversible upon removal of the antibodies, transferable via the serum and abrogated by adrenergic antagonists. In DCM patients, prevalence and stimulatory efficacy of β₁-adrenoceptor autoantibodies are correlated to the decline in cardiac function, ventricular arrhythmia and higher incidence of cardiac death. In conclusion, such autoantibodies seem to cause or promote chronic human left ventricular dysfunction by acting on their receptor targets in a drug-like fashion. However, the pharmacology of this interaction is poorly understood. It is unclear how the autoantibodies trigger changes in receptor activity and second messenger coupling and how that is related to the pathogenesis and severity of the associated diseases. Here, we summarize the available evidence regarding these issues and discuss these findings in the light of recent knowledge about the conformational activation of the human β₂-adrenoceptor and the properties of bona fide cardiopathogenic autoantibodies derived from immune-adsorption therapy of DCM patients. These considerations might contribute to the conception of therapy regimen aimed at counteracting or neutralizing cardiopathogenic receptor autoantibodies.

The diagnostic and clinical significance of anti-muscarinic receptor autoantibodies

The role of autoimmunity in cardiovascular diseases has become one of the focal points of research studies. Autoimmune response and autoreactive autoantibodies have been found in dilated cardiomyopathy, heart failure, rheumatic fever, myocarditis, atherosclerosis, and other diseases. Autoantibodies may appear due to tissue injury and exposure of autoantigens, in addition to molecular mimicry and cross-reactivity with antigens found in infectious agents in predisposed individuals. In the early 1990s, autoantibodies reacting with the M2 muscarinic receptor were found in patients with dilated cardiomyopathy and subsequently, in patients with Chagas heart disease and arrhythmic disorders. Immunization of animals with the corresponding antigen triggered cardiac abnormalities also appearing in dilated cardiomyopathy of humans. It has been suggested that antibodies against M2 muscarinic receptors play a role in the pathogenesis of cardiac diseases and may also alter the electrophysiological properties of cardiac tissue. Herein, we review the current knowledge of antibodies against M2 muscarinic receptors and the possible use of a targeted therapy against these autoantibodies.

Opposing cardiac effects of autoantibody activation of β-adrenergic and M2 muscarinic receptors in cardiac-related diseases

BACKGROUND

Activating autoantibodies to β-adrenergic receptors (AAβ1/2AR) and M2 muscarinic receptors (AAM2R) have been reported in several cardiac diseases and may have pathophysiologic relevance. However, the interactions and relative effects of AAβ1AR, AAβ2AR and AAM2R on contractile function have not been characterized.

METHODS

The inotropic effects of IgG from 18 selected patients with cardiomyopathy and/or atrial tachyarrhythmias positive by ELISA for antibodies to β1/2AR were studied using an isolated canine Purkinje fiber contractility assay. M2R-blockade was tested using atropine while selective β1AR and β2AR blockade used CGP-20712A and ICI-118551 respectively.

RESULTS

Fifteen of the 18 anti-β1/2AR ELISA-positive samples demonstrated evidence for negative inotropic muscarinic effects which were blocked using atropine. Atropine failed to uncover a positive inotropic response in 2 of the 18 IgG samples (false positive ELISA for AAβAR). In the remaining 16 AAβAR true-positive subjects, the β1AR-induced increase in contractility (concurrent M2/β2 blockade) was augmented to 140.5±12.2% of baseline compared to 127.4±7.2% of baseline with M2 blockade (atropine) only (p<0.001, n=16). The β2AR-induced increase in contractility (concurrent M2/β1 blockade) was only 114.5±4.3% of baseline (p<0.001, n=16). Combined M2 and β1/β2 blockade eliminated any increase in contractility.

CONCLUSIONS

The inherently positive inotropic effect of AAβ1AR was negatively modulated by AAM2R and AAβ2AR. These opposing effects of receptor-activating autoantibodies may alter cardiac performance and influence clinical outcome depending on their receptor type and relative contractile activity.

[Synthesis and properties of a new conformational antigen modeling an extracellular region of beta(1)-adrenoreceptor]

Two fragments corresponding to the 125-133 and 206-218 sequences of a molecule of the beta(1) adrenoreceptor (autoantibodies to this protein are often found in patients with dilated cardiomyopathy) were synthesized by the solid phase method with the use of Fmoc technology. Two new conformational antigens were prepared by directed (regioselective) and undirected (spontaneous) formation of intramolecular and intermolecular disulfide bridges between the corresponding cysteine residues of the synthesized peptides. One of these antigens consisted of a mixture of disulfide isomers, and another antigen was an isomer with a natural arrangement of S-S bridges. Immunosorbents were obtained by immobilization of the synthesizes antigens on the bromocyanogenactivated sepharose and applied to the removal of autoantibodies in a beta(1)-adrenoreceptor from the blood plasma of patients. We demonstrated that the sorbents on the basis of the conformational antigens were more effective in comparison with those containing linear peptide precursors.

Transfer of immune components from rabbit autoimmune cardiomyopathy into severe combined immunodeficiency (SCID) mice induces cardiomyopathic changes

BACKGROUND

Growing evidence suggests that autoimmune mechanism plays an important role in the pathogenesis of cardiomyopathy. The purpose of this study was to investigate whether passive transfer of IgG and/or lymphocytes from rabbits with autoimmune cardiomyopathy is able to reproduce cardiomyopathic changes in severe combined immunodeficiency (SCID) mice.

METHODS AND RESULTS

SCID mice were injected intraperitoneally with IgG and/or peripheral blood lymphocytes (PBL) from either rabbits immunized with both beta1-adrenoceptor peptide and M2-muscarinic receptor peptide (beta1+M2 group) or rabbits with adjuvant (N group). Thirty five SCID mice were divided into seven groups; N-IgG, N-PBL, N-IgG & PBL, (beta1+M2)-IgG, (beta1+M2)-PBL, (beta1+M2)-IgG & PBL and control groups. Heart weight in three (beta1+M2) groups were significantly increased. All mice in three (beta1+M2) groups showed high titer of rabbit anti-beta1 adrenoceptor autoantibodies, and 4 mice in the (beta1+M2)-PBL group and 3 mice in the (beta1+M2)-IgG & PBL group showed a significant increase in titer of rabbit anti-M2-muscarinic receptor autoantibodies. Focal infiltration of inflammatory cells in the myocardium was observed in the (beta1+M2)-IgG & PBL group. In the (beta1+M2)-PBL group and (beta1+M2)-IgG & PBL group, cardiomyocyte diameters were significantly increased. Some myocytes of the (beta1+M2)-IgG & PBL group exhibited intracellular edema, clumps of Z-band and increased numbers of mitochondria by using electron microscopy.

CONCLUSION

Transfer of IgG and PBL from rabbits immunized with combined beta1 and M2 peptides was able to reproduce the early stage of cardiomyopathic changes in SCID mice.

Throat infection, neck and chest pain and cardiac response: a persistent infection-related clinical syndrome

Dizziness, chest discomfort, chest depression and dyspnea are a group of symptoms that are common complaints in clinical practice. Patients with these symptoms are usually informed that while neurosis consequent to coronary heart disease is excluded nonetheless they remain unhealthy with no rational explanation or treatment. 165 cases of these symptoms and 85 control subjects were reviewed and underwent further medical history inquiry, routine EKG test and cardiac ultrasound examination. Thirty-five patients received coronary artery angiography to exclude coronary heart disease. Serum myocardial autoantibodies against beta(1)-adrenoceptor, alpha-myosin heavy chain, M(2)-muscarinic receptor and adenine-nucleotide translocator were tested, and inflammatory cytokines and high sensitivity C-reaction protein were measured and lymphocyte subclass was assayed by flow cytometry. All patients had a complex of four symptoms or tetralogy: (1) persistent throat or upper respiratory tract infection, (2) neck pain, (3) chest pain and (4) chest depression or dyspnea, some of them with anxiety. Anti-myocardial autoantibodies (AMCAs) were present in all patients vs. 8% in controls. TNF-alpha, IL-1 and IL-6 were significantly higher in patients than in controls (P<0.01). CD3(+) and CD4-CD8(+) lymphocytes were significantly higher and CD56(+) lymphocytes lower in patients than those in controls (P<0.01). The ratio of serum pathogen antibodies positive against Coxsackie virus-B, cytomegalovirus, Mycoplasma pneumoniae and Chlamydia pneumoniae were all markedly higher in patients. These data led to identification of a persistent respiratory infection-related clinical syndrome, including persistent throat infection, neck spinal lesion, rib cartilage inflammation, symptoms of cardiac depression and dyspnea with or without anxiety.

Anti-beta1-adrenergic receptor autoantibodies in patients with chronic Chagas heart disease

Chronic Chagas heart disease (cChHD), a chronic manifestation of the Trypanosoma cruzi infection, is characterized by high antibody levels against the C-terminal region of the ribosomal P proteins (i.e. peptide R13, EEEDDDMGFGLFD) which bears similarity with the second extracellular loop of beta1-adrenergic receptor (beta1-AR, peptide H26R HWWRAESDEARRCYNDPKCCDFVTNR). Because it has not been demonstrated clearly that IgGs from cChHD patients bind to native human beta1-AR, the aim of this study was to investigate further the physical interaction between cChHD IgGs and the human beta1-AR. Immunofluorescence assays demonstrated the binding of these antibodies to the receptor expressed on stably transfected cells, together with a beta1-AR agonist-like effect. In addition, immunoadsorption of the serum samples from cChHD patients with a commercially available matrix, containing peptides representing the first and the second extracellular loop of the beta1-AR, completely abolished reactivity against the H26R peptide and the physiological response to the receptor. The follow-up of this specificity after in vitro immunoadsorption procedures suggests that this treatment might be used to diminish significantly the serum levels of anti-beta1-AR antibodies in patients with Chagas heart disease.

Phenotype of early cardiomyopathic changes induced by active immunization of rats with a synthetic peptide corresponding to the second extracellular loop of the human beta-adrenergic receptor

In the failing human heart, due to idiopathic dilated cardiomyopathy, it has been suggested that the beta1-adrenergic receptor (beta1AR) is a potential pathogenic autoantigen. The aim of the present study was to investigate whether immunization of rats with a synthetic peptide corresponding to the second extracellular loop of the beta1AR (beta1AR EC(II)) was able to induce the early stage of cardiomyopathy and also to investigate immunological and receptor functional parameters at a transcriptional level to permit insights into the autoimmune mechanism in cardiomyopathy. Eleven Whistar Fur rats were immunized with a beta1AR EC(II) peptide (H26R) once a month during 12 months and seven control rats were injected with vehicle according to the same procedure used for the immunized group. Cardiac function, beta1AR autoantibodies and their functional effects on cardiomyocytes were analysed. beta1AR receptor signalling, immunological and cardiomyocyte stretch markers were determined on transcriptional level. In H26R immunized rats, beta1AR autoantibodies were shown to be present and functionally active, cardiac functions in terms of fractional shortening were decreased and beta1-adrenergic receptor kinase (GRK2) mRNA were increased compared with the control group. These data have shown that immunization of rats with a putative antigenic peptide was able to induce an early stage phenotype of cardiomyopathy in the form of cardiac dysfunction and up-regulation of GRK2 as the first step in the desensitization process of the beta1AR, implying the pathological importance of the beta1AR autoantibody.

Effects on heart rate of an anti-M2 acetylcholine receptor immune response in mice

Autoantibodies in vitro modulating the M2 acetylcholine receptor (M2ACh-R) were observed in patients with idiopathic dilated cardiomyopathy (IDC) or Chagas' cardiomyopathy (ChC). We investigated the in vivo consequences on heart rate of such antibodies in mice immunized with a peptide derived from the second extracellular loop of the M2ACh-R compared with mice immunized with an irrelevant peptide. Sera of mice immunized with the M2ACh-R-derived peptide recognized the M2ACh-R on immunoblots and enhanced agonist activity of carbachol toward the M2AChR transfected in CHO cells. In vivo, no difference could be shown in heart rate or heart rate variability between the two groups of mice. The decrease in heart rate induced by carbachol was more pronounced, however, in the M2ACh-R immunized mice. The increase in heart rate induced by atropine, gallamine, and isoproterenol was significantly attenuated in the M2ACh-R immunized mice. Analysis of heart rate variability further argued for an increased parasympathetic response to different drugs in the M2ACh-R immunized mice. Antibodies raised against the M2AChR can behave as positive M2AChR allosteric modulators in vivo. They might be protective in boosting the activity of the parasympathetic drive to the heart, especially in patients with a high sympathetic tone.

Cardiac remodeling after long-term stimulation by antibodies against the alpha1-adrenergic receptor in rats

Although autoantibodies against the alpha1-adrenergic receptor which had been found in hypertensive patients had agonist-like activity as phenylephrine, the effects of these antibodies on cardiac remodeling have not been known. In this paper, the models with agonist-like activity of antibodies to alpha1-adrenergic receptor were made by immunized Wistar rats using synthesized peptides of alpha1A-adrenergic receptor and raised for 1 year, and the excited antibodies against the alpha1-adrenergic receptor which could elevate the free Ca2+ in isolated adult rat cardiomyocytes had been existed throughout the experiments after immunization. In immunized rats, despite that systolic blood pressure (SBP) had no difference with normal control, the hypertrophy of heart and cardiomyocytes was observed, the collagen deposition in heart interstitium increased, and c-jun expression and matrix metalloproteinase (MMP)-2 mRNA expression and activity in heart had increased. The results suggested that antibodies against the alpha1-adrenergic receptor could induce cardiac remodeling and maybe play a particular role in hypertension.

Prevention of experimental autoimmune cardiomyopathy in rabbits by receptor blockers

We investigated the effects of beta1-adrenoceptor blockade and M2-muscarinic receptor antagonist in rabbits which have developed dilated cardiomyopathy-like changes after immunization with the peptides from the second extracellular loop of human beta1-adrenoceptor (beta1-peptide) and M2-muscarinic receptor (M2-peptide). Ten rabbits, which were immunized with beta1-peptide once a month for one year, were treated with bisoprolol and 10 rabbits, which were immunized with M2-peptide, were treated with otenzepad. Although both groups treated with receptor blockade or antagonist showed an increased titer of anti-beta1-adrenoceptor or anti-M2-muscarinic receptor antibodies, myocardial damages were markedly less than those in beta1-peptide- or M2-peptide-immunized rabbits. This study indicates that anti-beta1-adrenoceptor and anti-M2-muscarinic receptor antibodies are of pathogenic importance in the development of human dilated cardiomyopathy, and that beta-adrenoceptor blockade, bisoprolol, and M2-muscarinic receptor antagonist, otenzepad, might be clinically useful for treatment of dilated cardiomyopathy.

A monoclonal antibody against the immunodominant epitope of the ribosomal P2beta protein of Trypanosoma cruzi interacts with the human beta 1-adrenergic receptor

Monoclonal antibodies were raised against a recombinant ribosomal P2beta protein of Trypanosoma cruzi. One of these reacted with the C terminus of this protein (peptide R13, EEEDDDMGFGLFD) and epitope mapping confirmed that this epitope was the same as the one defined by the serum of immunized mice, and similar to the previously described chronic Chagas' heart disease (cChHD) anti-P epitope. Western blotting showed that the monoclonal antibody recognized the parasite ribosomal P proteins, as well as the human ribosomal P proteins. Electron microscopy showed that it stained different structures in parasite and human cells. Interestingly, surface plasmon resonance measurements indicated that the affinity for the parasite ribosomal P protein epitope (R13) was five times higher than for its human counterpart (peptide H13, EESDDDMGFGLFD). Since the human epitope contained an acidic region (EESDD) similar to the AESDE peptide recognized by cChHD patients in the second extra-cellular loop of the human beta1-adrenergic receptor, the biological activity of the antibody was assessed on neonatal rat cardiomyocytes in culture. The monoclonal antibody had an agonist-like effect. These results, together with the fact that the monoclonal reacted in Western blots with the different isoforms of the heart beta1-adrenergic receptor, confirm the possible pathogenic role of antibodies against the parasite ribosomal P protein based on their cross-reaction with the human beta1-adrenergic receptor.

Induction of cardiomyopathy in severe combined immunodeficiency mice by transfer of lymphocytes from patients with idiopathic dilated cardiomyopathy

Growing evidence suggests that autoimmune mechanisms play an important role in the pathogenesis of idiopathic dilated cardiomyopathy (DCM). The aim of the study was to evaluate the effects of transfer of lymphocytes from patients with DCM into severe combined immunodeficiency (SCID) mice on the heart structure and function. Thirty CB-17 SCID (6-8 weeks old) mice were used and divided into 3 groups (n = 10). Mice were injected intraperitoneally with up to 25 x 10(6) peripheral blood lymphocytes (PBL) from either patients with DCM which contain human autoantibodies against cardiac beta1-adrenergic receptors and M2-muscarinic receptors (DCM group) or PBL from healthy controls (control-H group). Ten mice did not receive any injections and were used as baseline controls (control-N group). Echocardiography and morphological studies were performed seventy five days after the transfer. Results showed that in DCM group, left ventricle dimensions (LVD) in diastole were increased (4.2 +/- 0.1mm) as compared to both control-H group (3.8 +/- 0.1mm) and control-N group (3.6 +/- 0.1 mm) (p < 0.01). Further, there was a trend for increased LVD in systole. Fractional shortening was not different between groups. Histological evaluation revealed accumulation of human lymphocytes in the capillaries and scarce infiltration of the lymphocytes in the hearts from DCM group. Diffuse fibrosis was significant increased in DCM mice as compared to mice receiving PBL from normal subjects (2.2 +/- 0.3% vs. 0.8 +/- 0.1%, p < 0.01). In conclusion, transfer of the PBL from the patients with DCM was able to induce early stage of heart dilatation in SCID mice. These data provide for the first time the direct evidence supporting that the autoimmune mechanism is important in the pathogenesis of human DCM.