Clinical implications of anti-cardiac immunity in dilated cardiomyopathy

An autoantibody identifies arrhythmogenic right ventricular cardiomyopathy and participates in its pathogenesis

Aims

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by right ventricular myocardial replacement and life-threatening ventricular arrhythmias. Desmosomal gene mutations are sometimes identified, but clinical and genetic diagnosis remains challenging. Desmosomal skin disorders can be caused by desmosomal gene mutations or autoantibodies. We sought to determine if anti-desmosome antibodies are present in subjects with ARVC.

Methods and results

We evaluated ARVC subjects and controls for antibodies to cardiac desmosomal cadherin proteins. Desmoglein-2 (DSG2), desmocollin-2, and N-cadherin proteins on western blots were exposed to sera, in primary and validation cohorts of subjects and controls, as well as the naturally occurring Boxer dog model of ARVC. We identified anti-DSG2 antibodies in 12/12 and 25/25 definite ARVC cohorts and 7/8 borderline subjects. Antibody was absent in 11/12, faint in 1/12, and absent in 20/20 of two control cohorts. Anti-DSG2 antibodies were present in 10/10 Boxer dogs with ARVC, and absent in 18/18 without. In humans, the level of anti-DSG2 antibodies correlated with the burden of premature ventricular contractions (r = 0.70), and antibodies caused gap junction dysfunction, a common feature of ARVC, in vitro. Anti-DSG2 antibodies were present in ARVC subjects regardless of whether an underlying mutation was identified, or which mutation was present. A disease-specific DSG2 epitope was identified.

Conclusion

Anti-DSG2 antibodies are a sensitive and specific biomarker for ARVC. The development of autoimmunity as a result of target-related mutations is unique. Anti-DSG2 antibodies likely explain the cardiac inflammation that is frequently identified in ARVC and may represent a new therapeutic target.

Cardiac myosin-Th17 responses promote heart failure in human myocarditis

In human myocarditis and its sequela dilated cardiomyopathy (DCM), the mechanisms and immune phenotype governing disease and subsequent heart failure are not known. Here, we identified a Th17 cell immunophenotype of human myocarditis/DCM with elevated CD4⁺IL17⁺ T cells and Th17-promoting cytokines IL-6, TGF-β, and IL-23 as well as GM-CSF-secreting CD4⁺ T cells. The Th17 phenotype was linked with the effects of cardiac myosin on CD14⁺ monocytes, TLR2, and heart failure. Persistent heart failure was associated with high percentages of IL-17-producing T cells and IL-17-promoting cytokines, and the myocarditis/DCM phenotype included significantly low percentages of FOXP3⁺ Tregs, which may contribute to disease severity. We demonstrate a potentially novel mechanism in human myocarditis/DCM in which TLR2 peptide ligands from human cardiac myosin stimulated exaggerated Th17-related cytokines including TGF-β, IL-6, and IL-23 from myocarditic CD14⁺ monocytes in vitro, and an anti-TLR2 antibody abrogated the cytokine response. Our translational study explains how an immune phenotype may be initiated by cardiac myosin TLR ligand stimulation of monocytes to generate Th17-promoting cytokines and development of pathogenic Th17 cells in human myocarditis and heart failure, and provides a rationale for targeting IL-17A as a therapeutic option.

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.

Effects of protein A immunoadsorption in patients with chronic dilated cardiomyopathy

OBJECTIVES

The objective of this study was to investigate functional effects of immunoadsorption (IA) in patients with chronic nonfamilial dilated cardiomyopathy (DCM) regarding clinical and humoral markers of heart failure.

BACKGROUND

IA has been shown to induce early hemodynamic improvement in patients with nonfamilial dilated cardiomyopathy (DCM).

METHODS

We performed IA using protein A agarose columns on five consecutive days in 51 patients with chronic DCM, congestive heart failure of NYHA class ≥ II, left ventricular ejection fraction ≤50%, and mean time since initial diagnosis of 5.0 ± 5.8 years.

RESULTS

Immediately after IA, immunoglobulin G (IgG) decreased by 89.4% and IgG3 by 66.7% (both P < 0.0001). Median NT-pro BNP was reduced from 1230.0 ng L(-1) at baseline to 829.0 ng L(-1) after 6 months (P < 0.0001). Also mean left ventricular ejection fraction (LVEF) was significantly improved (26.3% ± 9.4% to 28.7% ± 11.4% after 6 months, P = 0.016) and LVEF improved ≥5% (absolute) in 21 of 51 (41.2%) patients. After 6 months, bicycle spiroergometry showed a significant increase in exercise capacity from 82.0 ± 30.8 Watts to 93.1 ± 34.3 Watts (P = 0.008) while VO2max rose from 15.0 ± 4.1 to 16.4 ± 4.8 mL min(-1) kg(-1) (P = 0.01).

CONCLUSIONS

In this study, on heart failure patients with nonfamilial DCM, IA therapy significantly improved clinical and humoral markers of heart failure severity. These promising results may be due to the selected study population, with a shorter disease duration and the higher amount of IgG 3 reduction. Future blinded prospective multicenter studies are necessary to identify those patients that benefit most.

Effects of protein A immunoadsorption in patients with advanced chronic dilated cardiomyopathy

OBJECTIVES

The objective of this study was to investigate functional effects of immunoadsorption (IA) in severely limited study patients with chronic nonfamilial dilated cardiomyopathy (DCM), and to analyze the prevalence of Troponin I (TNI) autoantibodies.

BACKGROUND

Immunoadsorption (IA) has been shown to induce early hemodynamic improvement in patients with nonfamilial DCM.

METHODS

We performed IA using Immunosorba columns on five consecutive days in 27 patients with chronic DCM, congestive heart failure of NYHA class >or=II, left ventricular ejection fraction below 40%, and mean time since initial diagnosis of 7.2 +/- 6.8 years.

RESULTS

Immediately after IA, IgG decreased by 87.7% and IgG3 by 58.5%. Median NT-pro BNP was reduced from 1740.0 ng/L at baseline to 1504.0 ng/L after 6 months (P = 0.004). Mean left ventricular ejection fraction (LVEF) was not significantly improved overall (24.1 +/- 7.8% to 25.4 +/- 10.4% after 6 months, P = 0.38), but LVEF improved >or=5% (absolute) in 9 of 27 (33%) patients. Bicycle spiroergometry showed a significant increase in exercise capacity from 73.7 +/- 29.4 Watts to 88.8 +/- 31.1 Watts (P = 0.003) after 6 months while VO2max rose from 13.7 +/- 3.8 to 14.9 +/- 3.0 mL/min kg after 6 months (P = 0.09). Subgroup analysis revealed a higher NT-pro BNP reduction in patients with shorter disease duration (P = 0.03) and without TNI autoantibodies at baseline (P = 0.05). All 9 patients with an absolute increase of LVEF of >or=5.0% were diabetic (P = 0.0001).

CONCLUSIONS

In this study, on severely limited heart failure patients with nonfamilial DCM, IA therapy moderately improved markers of heart failure severity in a limited subgroup of patients. This may be due to the selected study population with end-stage heart failure patients and the lower reduction of IgG3 compared to previous studies. Future blinded multicenter studies are necessary to identify those patients that benefit most.

Consequences of unlocking the cardiac myosin molecule in human myocarditis and cardiomyopathies

Myocarditis, often initiated by viral infection, may progress to autoimmune inflammatory heart disease, dilated cardiomyopathy and heart failure. Although cardiac myosin is a dominant autoantigen in animal models of myocarditis and is released from the heart during viral myocarditis, the characterization, role and significance of anti-cardiac myosin autoantibodies is poorly defined. In our study, we define the human cardiac myosin epitopes in human myocarditis and cardiomyopathies and establish a mechanism to explain how anti-cardiac myosin autoantibodies may contribute to heart disease. We show that autoantibodies to cardiac myosin in sera from myocarditis and dilated cardiomyopathies in humans targeted primarily epitopes in the S2 hinge region of cardiac myosin. In addition, anti-cardiac myosin antibodies in sera or purified IgG from myocarditis and cardiomyopathy targeted the beta-adrenergic receptor and induced antibody-mediated cAMP-dependent protein kinase A (PKA) cell signaling activity in heart cells. Antibody-mediated PKA activity in sera was abrogated by absorption with anti-human IgG. Antibody-mediated cell signaling of PKA was blocked by antigen-specific inhibition by human cardiac myosin or the beta-adrenergic receptor but not the alpha adrenergic receptor or bovine serum albumin. Propranolol, a beta blocker and inhibitor of the beta-adrenergic receptor pathway also blocked the antibody-mediated signaling of the beta-adrenergic receptor and PKA. The data suggest that IgG antibody against human cardiac myosin reacts with the beta-adrenergic receptor and triggers PKA signaling in heart cells. In summary, we have identified a new class of crossreactive autoantibodies against human cardiac myosin and the beta-adrenergic receptor in the heart. In addition, we have defined disease specific peptide epitopes in the human cardiac myosin rod S2 region in human myocarditis and cardiomyopathy as well as a mechanistic role of autoantibody in the pathogenesis of disease.