Repetitive coxsackievirus infection induces cardiac dilatation in post-myocarditic mice

The knowns and unknowns of cardiac autoimmunity in viral myocarditis

Myocarditis can result from various infectious and non-infectious causes that can lead to dilated cardiomyopathy (DCM) and heart failure. Among the infectious causes, viruses are commonly suspected. But the challenge is our inability to demonstrate infectious viral particles during clinical presentations, partly because by that point, the viruses would have damaged the tissues and be cleared by the immune system. Therefore, viral signatures such as viral nucleic acids and virus-reactive antibodies may be the only readouts pointing to viruses as potential primary triggers of DCM. Thus, it becomes hard to explain persistent inflammatory infiltrates that might occur in individuals affected with chronic myocarditis/DCM manifesting myocardial dysfunctions. In these circumstances, autoimmunity is suspected, and antibodies to various autoantigens have been demonstrated, suggesting that immune therapies to suppress the autoimmune responses may be necessary. From this perspective, we endeavoured to determine whether or not the known viral causes are associated with development of autoimmune responses to cardiac antigens that include both cardiotropic and non-cardiotropic viruses. If so, what their nature and significance are in developing chronic myocarditis resulting from viruses as primary triggers.

Ivabradine Treatment Reduces Cardiomyocyte Apoptosis in a Murine Model of Chronic Viral Myocarditis

This study was designed to explore the effects of ivabradine on cardiomyocyte apoptosis in a murine model of chronic viral myocarditis (CVMC). Mice were inoculated intraperitoneally with Coxsackievirus B3 at days 1, 14, and 28, respectively. On day 42, the mice were gavaged with ivabradine for 30 days until the 72nd day. The heart of infected mice was dilated and a large number of interstitial fibroblasts infiltrated into the myocardium on day 42. Compared with the untreated CVMC mice, mice treated with ivabradine showed a significant reduction in heart rate and less impairment of left ventricular function on day 72. The positive apoptosis of myocardial cells in the untreated CVMC group was significantly higher than that of the normal group and was significantly reduced after treatment with ivabradine. The expression levels of Bax and Caspase-3 in the untreated CVMC group were significantly higher than those of the normal group and were apparently reduced in the ivabradine-treated group versus the untreated CVMC group. Bcl-2 showed a high expression in the normal group and low expression in the untreated CVMC group, but its expression level in the ivabradine-treated group were higher than that of the untreated CVMC group. These results indicate that ivabradine could attenuate the expression of Caspase-3 by downregulation of Bax and upregulation of Bcl-2 to prevent the deterioration of cardiac function resulting from ventricular myocyte loss by cardiomyocyte apoptosis.

Phenylthiomethyl Ketone-Based Fragments Show Selective and Irreversible Inhibition of Enteroviral 3C Proteases

Lead structure discovery mainly focuses on the identification of noncovalently binding ligands. Covalent linkage, however, is an essential binding mechanism for a multitude of successfully marketed drugs, although discovered by serendipity in most cases. We present a concept for the design of fragments covalently binding to proteases. Covalent linkage enables fragment binding unrelated to affinity to shallow protein binding sites and at the same time allows differentiated targeted hit verification and binding location verification through mass spectrometry. We describe a systematic and rational computational approach for the identification of covalently binding fragments from compound collections inhibiting enteroviral 3C protease, a target with high therapeutic potential. By implementing reactive groups potentially forming covalent bonds as a chemical feature in our 3D pharmacophore methodology, covalent binders were discovered by high-throughput virtual screening. We present careful experimental validation of the virtual hits using enzymatic assays and mass spectrometry unraveling a novel, previously unknown irreversible inhibition of the 3C protease by phenylthiomethyl ketone-based fragments. Subsequent synthetic optimization through fragment growing and reactivity analysis against catalytic and noncatalytic cysteines revealed specific irreversible 3C protease inhibition.

Coxsackievirus B3 Induces Autophagic Response in Cardiac Myocytes in vivo

Viral myocarditis is a common disease that contributes to dilated cardiomyopathy or heart failure. Coxsackievirus B (CVB) is one of the major causative pathogens of viral myocarditis. Previous studies have shown that autophagy is exploited to promote CVB replication in cell lines. To study whether cardiac myocytes respond to CVB infection in a similar way, viral myocarditis was established by the inoculation of 3-week-old BALB/c mice with CVB3. Electron microscopic observation showed that autophagosome-like vesicles were induced in the cardiac myocytes of mice infected by CVB3 at 3, 5, and 7 days after viral infection. The lipidated microtubule-associated protein 1 light chain 3 (LC3), LC3-II, was also significantly increased in both myocardium and the cardiac myocytes extracted from the ventricles of mice infected with CVB3. The increased LC3-II coincided with high level of viral RNA and proteins in both myocardium and isolated cardiac myocytes. Moreover, viral protein synthesis was significantly decreased in primary cardiac myocytes by the treatment with 3-methyladenine, an inhibitor of autophagy. The expression and the phosphorylation of extracellular signal regulated kinase (ERK) were also increased in both myocardium and in the isolated cardiac myocytes of the virus-infected mice, while the interplay of ERK with autophagic response remains to be studied. This study demonstrated that cardiac myocytes respond to CVB3 infection by increased formation of autophagosomes in vivo, which might be exploited for viral replication.

Coxsackievirus B3 infection leads to the generation of cardiac myosin heavy chain-α-reactive CD4 T cells in A/J mice

Enteroviruses like coxsackievirus B3 (CVB3) are common suspects in myocarditis/dilated cardiomyopathy patients. Autoimmunity has been proposed as an underlying mechanism, but direct evidence of its role is lacking. To delineate autoimmune response in CVB3 myocarditis, we used IA(k) dextramers for cardiac myosin heavy chain (Myhc)-α 334-352. We have demonstrated that myocarditis-susceptible A/J mice infected with CVB3 generate Myhc-α-reactive CD4 T cells and such a repertoire was absent in naïve mice as measured by proliferative response to Myhc-α 334-352 and IA(k) dextramer staining. We also detected Myhc-α 334-352 dextramer(+) cells in the hearts of CVB3-infected mice. The autoreactive T cell repertoire derived from infected mice contained a high frequency of interleukin-17-producing cells capable of inducing myocarditis in naïve recipients. The data suggest that CVB3, a bona fide pathogen of cardiovascular system that primarily infects the heart can lead to the secondary generation of autoreactive T cells and contribute to cardiac pathology.

A NADH dehydrogenase ubiquinone flavoprotein is decreased in patients with dilated cardiomyopathy

BACKGROUND

It is known that patients with myocarditis of unknown etiology and with dilated cardiomyopathy show a high incidence of serum autoantibodies (M7) directed against mitochondrial flavoproteins. The tissue concentration of mitochondrial flavoproteins in the myocardium obtained from patients with dilated cardiomyopathy (DCM) was examined to further investigate the immunopathological mechanism of cardiomyopathy.

METHODS AND RESULTS

Myocardial tissue specimens were obtained from patients who underwent cardiac catheterization and a subendomyocardial biopsy for the diagnosis of cardiomyopathy. All samples were analyzed by Western blotting. NADH dehydrogenase ubiquinone flavoprotein (NDUFV1) production in the myocardium decreased significantly with DCM, in comparison to fumarate hydratase and flavoprotein SDHA. There was a significant negative-correlation between the left ventricular end-diastolic dimension and NDUFV1 production (R(2)=0.291, p value<0.05).

CONCLUSION

NDUFV1 may be involved in the pathogenesis of DCM. A defect of mitochondrial NDUFV1 may reduce complex I, which produces most of the superoxide, which is then scavenged by the mitochondrial enzyme Mn-superoxide dismutase to produce H(2)O(2). Exploring the nature of the candidate protein found in the myocardium in this study will provide further insight into the immunological mechanism of DCM.

Cardiac protective effect of Astragalus on viral myocarditis mice: comparison with Perindopril

In clinical practice, Astragali Radix (Astragalus), the root of Astragalus membranaceus Bunge, has been widely applied to treat patients with viral diseases, including viral myocarditis in China. The present study was designed to evaluate the protective effects of Astragalus on the function of sarcoplasmic reticulum calcium ATPase (SERCA2) activity and endothelin system at acute and chronic periods of myocarditis mice induced by CVB(3) infection. Astragalus feeding (2.2 mg/kg/day) could significantly increase the survival rate, alleviate pathological alterations and serum cardiac troponin I (cTnI), as well as restore impaired SERCA activity at the acute stage. Low affinity and capacity of ETR were reversed with Astragalus after the first CVB(3) inoculation up to 7 days and after the second virus inoculation up to 150 days. In the meantime, the contents of cardiac ET-1 and ANP were reduced. Comparison the myocarditis mice treated with Perindopril (0.44 mg/kg/day), an ACE inhibitor, shows that Astragalus achieved a similar effect on survival rate, SERCA2 and ET system. These results indicated that the beneficial effects of Astragalus and Perindopril for treating viral myocarditis might be partly mediated by preserving the functions of SERCA 2 activity and ET system.

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.

Immunomodulatory effect of pentoxifylline in suppressing experimental autoimmune myocarditis

Although a recent clinical study reported the beneficial effects of pentoxifylline (PTX), a phosphodiesterase inhibitor, on both symptoms and cardiac function in dilated cardiomyopathy (DCM), the precise mechanism of the drug has not been delineated. This study examined the efficacy of PTX in the treatment of experimental autoimmune myocarditis (EAM), as a model of the autoimmune mechanism involved in DCM. Oral PTX, or saline as control, was administered to Lewis rats at 150mg/kg body weight per day bid daily from 5 days before immunization with cardiac myosin until death on Day 21. Histological examination of the hearts showed PTX significantly reduced the severity of EAM. mRNA expression of tumor necrosis factor (TNF)-alpha, interleukin (IL)-4, IL-6, and IL-10 was significantly reduced in peripheral blood mononuclear cells, but expression of IL-4 and IL-6 was upregulated in heart tissue. PTX in vitro could suppress T cell proliferation and inhibit TNF-alpha and interferon-gamma production. In conclusion, the immunomodulatory effects of PTX had a significant therapeutic result in EAM. This is the first report to describe such an effect of PTX in a specific animal model for DCM.

Molecular Aspects of Myocarditis

Myocarditis is an acquired form inflammatory heart muscle disease, manifested as acute and chronic conditions. While many etiologies have been reported, the most common cause of this disease is infection, primarily viral. Typically, the specific causative agent(s) and mechanism(s) are elusive. Over the past several years, various new findings have added to our understanding of myocarditis. These include the identification of adenoviruses as important causative agents, a new receptor protein likely to play an important role in the virulence of certain agents affecting the myocardium, and the effect of viruses on the cardiac cytoskeleton. This report reviews the current understanding of myocarditis, proposes a hypothesis about the long-term sequelae, and suggests possible new therapeutic strategies.