Characterization of anti-myocardial autoantibodies in Japanese patients with dilated cardiomyopathy

Immunoadsorption therapy for dilated cardiomyopathy using tryptophan column-A prospective, multicenter, randomized, within-patient and parallel-group comparative study to evaluate efficacy and safety

Over the past few decades, several cardiac autoantibodies have been reported in sera from patients with dilated cardiomyopathy (DCM). Immunoadsorption (IA) therapy is one of the therapeutic tools to remove such autoantibodies. The objective of this study was to investigate functional effects of IA therapy using a tryptophan column in severe DCM patients. Of 49 patients enrolled, 44 were randomized from 10 sites in Japan. IA therapy was conducted in 40 patients with DCM (refractory to standard therapy for heart failure, New York Heart Association [NYHA] class III/IV, left ventricular ejection fraction [LVEF] <30%). Mean echocardiographic LVEF was significantly improved (23.8 ± 1.3% to 25.9 ± 1.3%, P = 0.0015). However, mean radionuclide LVEF over 3 months of IA therapy was not significantly improved (20.8 ± 1.1% to 21.9 ± 1%, P = 0.0605). The cardiothoracic ratio was also significantly decreased (P = 0.0010). NYHA functional class (P < 0.0001), subjective symptoms assessed by a quality of life questionnaire (P = 0.0022), maximum oxygen consumption (P = 0.0074), and 6‐minute walk distance (P = 0.0050) were improved after IA therapy. Subgroup analysis revealed improvement of echocardiographic LVEF in patients with higher baseline autoantibody scores but not in those with lower scores. IA therapy improved subjective symptoms and exercise capacity in patients with refractory heart failure resulting from DCM. Favorable effect on cardiac function was noted in patients with higher autoantibody scores. J. Clin. Apheresis 31:535–544, 2016. © 2015 Wiley Periodicals, Inc.

Animal models of cardiac disease and stem cell therapy

Animal models that mimic cardiovascular diseases are indispensable tools for understanding the mechanisms underlying the diseases at the cellular and molecular level. This review focuses on various methods in preclinical research to create small animal models of cardiac diseases, such as myocardial infarction, dilated cardiomyopathy, heart failure, myocarditis and cardiac hypertrophy, and the related stem cell treatment for these diseases.

Autoimmune mechanisms underlying dilated cardiomyopathy

Autoimmune abnormalities, as well as viral infection and genetic abnormalities, appear to be major predisposing factors for dilated cardiomyopathy (DCM). Abnormalities of cell-mediated immunity are mainly involved in the onset of cardiomyopathy secondary to myocarditis. However, various antimyocardial antibodies are detected in the serum of patients with DCM. The appearance of these antibodies was considered to be an epiphenomenon associated with myocyte injury resulting from myocarditis, but recent findings have suggested that at least some of them are directly related to the pathophysiology of DCM. In particular, an autoantibody targeting the beta1-adrenergic receptor that exhibits an agonist-like effect is related to the persistent myocardial damage resulting in DCM and provides substrates for fatal ventricular arrhythmias. In addition, an antibody for the muscarinic M2 receptor is related to atrial fibrillation, an antibody targeting Na-K-ATPase is closely related to sudden cardiac death as a result of fatal ventricular arrhythmias, and an autoantibody for troponin I increases the L-type calcium current and is related to the myocardial damage. Based on these findings, immunoadsorption therapy was developed to remove such autoantibodies in patients with refractory heart failure as a result of DCM.

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.

Characterization of pathogenic T cells and autoantibodies in C-protein-induced autoimmune polymyositis

Although autoimmune processes may take place in human polymyositis, little is known with regard to its pathogenesis due to the lack of appropriate animal models. In the present study, we developed experimental autoimmune myositis (EAM) in Lewis rats by immunization with recombinant skeletal C-protein and examined the role of pathogenic T cells and autoantibodies. Using recombinant proteins and synthetic peptides, we demonstrated that skeletal C-protein Fragment 2 (SC2) has the strongest myositis-inducing ability and that myositis-inducing epitope(s) reside within the residues 334-363 of SC2 (SC2P3). However, immunization with SC2P3 induced only mild EAM compared with SC2 immunization. Characterization of T cells and antisera revealed that SC2P3 and SC2P7 contain the B cell epitope, while the T cell epitope resides in SC2P5. Furthermore, anti-SC2, but not anti-SC2P3, antisera contained antibodies against the conformational epitope(s) in the SC2 molecule. However, SC2P3 or SC2P5 immunization plus anti-SC2 antibody transfer aggravated the disease only slightly. These findings suggest that C-protein-induced EAM is formed by activation of C-protein-specific T cells along with antibodies against conformational epitopes in C-protein but that there are undetermined factors related to the disease progression. Further analysis of C-protein-induced EAM will provide useful information to elucidate the pathomechanisms of human polymyositis.

B-cell epitope spreading is a critical step for the switch from C-protein-induced myocarditis to dilated cardiomyopathy

Repeated inflammation in the heart is one of the initiation factors of dilated cardiomyopathy (DCM). In a previous study, we established a new animal model for DCM by immunization of rats with recombinant cardiac C-protein fragment 2 (CC2). The present study examined factors involved in the development of DCM. Analysis using overlapping peptides revealed that the major carditogenic epitope resides only in the residue 615-647 [CC2 peptide 12 (CC2P12)]. However, immunization with CC2P12 induced moderate inflammation without subsequent DCM. CDR3 spectratyping analysis of the T-cell repertoire demonstrated that Vbeta4-positive T cells were preferentially expanded in both CC2- and CC2P12-immunized rats. Although there was no significant difference in the T-cell characteristics, examinations of the B-cell epitope revealed that marked epitope spreading occurred in CC2-immunized but not CC2P12-immunized rats from 4 weeks after immunization. Consistent with this finding, immunization with CC2P12 and simultaneous transfer of anti-peptide antisera induced significantly more severe inflammation and fibrosis than CC2P12 immunization alone. However, the transfer of the antisera without CC2P12 immunization did not induce any pathology. These findings suggest that T-cell activation and B-cell epitope spreading in the CC2 molecule is a key step for the switch from myocarditis to the development of DCM.

Identification of autoantibodies with the corresponding antigen for repetitive coxsackievirus infection-induced cardiomyopathy

BACKGROUND

The hypothesis that viral myocarditis causes an autoimmune response and subsequent dilated cardiomyopathy is controversial. To further investigate the autoimmune mechanism of cardiac dilatation and dysfunction after repeated episodes of viral myocarditis, the cardiac autoantigens induced by repetitive coxsackievirus B3 (CVB3) infection were examined.

METHODS AND RESULTS

Male inbred A/J mice were inoculated intraperitoneally with CVB3 at 3 and 40 weeks of age. At 8 weeks after the second inoculation, the mortality of the repetitive CVB3 group was significantly increased compared with that of the control group, and was associated with a significant reduction in fractional shortening and marked left ventricular dilatation without inflammatory cell infiltration. The cardiac antigens in the repetitive CVB3 infection were identified by 2-dimensional electrophoresis and subsequent liquid chromatography/tandem mass spectrometry (LC-MS/MS) using the serum at 2 weeks after the second inoculation. LC-MS/MS and immunohistochemistry demonstrated alpha-cardiac actin and heat shock protein 60 (HSP60) as cardiac near-surface antigens induced by the repetitive CVB3 infection. Immunoelectron microscopy disclosed the selective localization of anti-IgM antibody on the membrane of the myocytes in the repetitive CVB3 group.

CONCLUSIONS

IgM antibodies against alpha-cardiac actin and HSP60, which were induced by repetitive CVB3 infection, may play an important role in the pathophysiology of the subsequent cardiac dysfunction and dilatation.

Autoantibodies produced against sarcolemmal Na-K-ATPase: possible upstream targets of arrhythmias and sudden death in patients with dilated cardiomyopathy

OBJECTIVES

We sought to test the hypothesis that autoantibodies (Abs) produced against sarcolemmal Na-K-ATPase play a role in the development of ventricular tachycardia (VT) and cardiac sudden death in patients with dilated cardiomyopathy (DCM).

BACKGROUND

Autoimmunity is one of the mechanisms of pathogenesis of DCM as well as virus infection and genetic predisposition.

METHODS

One hundred patients with DCM and age-matched control subjects (CTL) were screened for Abs produced against Na-K-ATPase by using enzyme-linked immunosorbent assay.

RESULTS

Abs were detected in 26 DCM and 2 CTL patients. Na-K-ATPase activity in the presence of patient IgG was lower in DCM with Abs than without Abs, but there was no difference between two groups in CTL. Western blots showed that Abs recognized the alpha subunit of Na-K-ATPase, and 3H-ouabain bindings in the presence of patient IgG showed that dissociation constant was higher in DCM with Abs than without Abs. No difference existed between subjects with regard to age, gender, New York Heart Association functional class, cardiac function, or neurohormone levels, except for plasma norepinephrine, which was higher in patients with Abs than without Abs. VTs were more common in patients with Abs than without Abs, and multiple logistic regression analysis demonstrated that the presence of Abs, but not plasma norepinephrine, was an independent predictor for the occurrence of VT. Cardiac sudden death was independently predicted by the presence of Abs, as well as poor systolic function.

CONCLUSION

We conclude that there are Abs produced against sarcolemmal Na-K-ATPase in patients with DCM and that Abs could be responsible for the electrical instability in some cases.