Cardiomyocyte apoptosis in experimental coxsackievirus B3 myocarditis

Infectious factors in myocarditis: a comprehensive review of common and rare pathogens

BACKGROUND

Myocarditis is a significant health threat today, with infectious agents being the most common cause. Accurate diagnosis of the etiology of infectious myocarditis is crucial for effective treatment.

MAIN BODY

Infectious myocarditis can be caused by viruses, prokaryotes, parasites, and fungi. Viral infections are typically the primary cause. However, some rare opportunistic pathogens can also damage heart muscle cells in patients with immunodeficiencies, neoplasms and those who have undergone heart surgery.

CONCLUSIONS

This article reviews research on common and rare pathogens of infectious myocarditis, emphasizing the complexity of its etiology, with the aim of helping clinicians make an accurate diagnosis of infectious myocarditis.

Investigating the virulence of coxsackievirus B6 strains and antiviral treatments in a neonatal murine model

Coxsackievirus B6 (CVB6), a member of the human enterovirus family, is associated with severe diseases such as myocarditis in children. However, to date, only a limited number of CVB6 strains have been identified, and their characterization in animal models has been lacking. To address this gap, in this study, a neonatal murine model of CVB6 infection was established to compare the replication and virulence of three infectious-clone-derived CVB6 strains in vivo. The results showed that following challenge with a lethal dose of CVB6 strains, the neonatal mice rapidly exhibited a series of clinical signs, such as weight loss, limb paralysis, and death. For the two high-virulence CVB6 strains, histological examination revealed myocyte necrosis in skeletal and cardiac muscle, and immunohistochemistry confirmed the expression of CVB6 viral protein in these tissues. Real-time PCR assay also revealed higher viral loads in the skeletal and cardiac muscle than in other tissues at different time points post infection. Furthermore, the protective effect of passive immunization with antisera and a neutralizing monoclonal antibody against CVB6 infection was evaluated in the neonatal mouse model. This study should provide insights into the pathogenesis of CVB6 and facilitate further research in the development of vaccines and antivirals against CVBs.

COVID-19-Induced Myocarditis: Pathophysiological Roles of ACE2 and Toll-like Receptors

The clinical manifestations of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection responsible for coronavirus disease 2019 (COVID-19) commonly include dyspnoea and fatigue, and they primarily involve the lungs. However, extra-pulmonary organ dysfunctions, particularly affecting the cardiovascular system, have also been observed following COVID-19 infection. In this context, several cardiac complications have been reported, including hypertension, thromboembolism, arrythmia and heart failure, with myocardial injury and myocarditis being the most frequent. These secondary myocardial inflammatory responses appear to be associated with a poorer disease course and increased mortality in patients with severe COVID-19. In addition, numerous episodes of myocarditis have been reported as a complication of COVID-19 mRNA vaccinations, especially in young adult males. Changes in the cell surface expression of angiotensin-converting enzyme 2 (ACE2) and direct injury to cardiomyocytes resulting from exaggerated immune responses to COVID-19 are just some of the mechanisms that may explain the pathogenesis of COVID-19-induced myocarditis. Here, we review the pathophysiological mechanisms underlying myocarditis associated with COVID-19 infection, with a particular focus on the involvement of ACE2 and Toll-like receptors (TLRs).

In Vitro Model Systems of Coxsackievirus B3-Induced Myocarditis: Comparison of Commonly Used Cell Lines and Characterization of CVB3-Infected iCell® Cardiomyocytes

Coxsackievirus B3 (CVB3) belongs to the enteroviruses, which are a well-known cause of acute and chronic myocarditis, primarily infecting cardiac myocytes. As primary human cardiomyocytes are difficult to obtain, viral myocarditis is quite frequently studied in vitro in different non-cardiac and cardiac-like cell lines. Recently, cardiomyocytes that have been differentiated from human-induced pluripotent stem cells have been described as a new model system to study CVB3 infection. Here, we compared iCell^® Cardiomyocytes with other cell lines that are commonly used to study CVB3 infection regarding their susceptibility and patterns of infection and the mode of cell death. iCell^® Cardiomyocytes, HeLa cells, HL-1 cells and H9c2 cells were infected with CVB3 (Nancy strain). The viral load, CVB3 RNA genome localization, VP1 expression (including the intracellular localization), cellular morphology and the expression of cell death markers were compared. The various cell lines clearly differed in their permissiveness to CVB3 infection, patterns of infection, viral load, and mode of cell death. When studying the mode of cell death of CVB3-infected iCell^® Cardiomyocytes in more detail, especially regarding the necroptosis key players RIPK1 and RIPK3, we found that RIPK1 is cleaved during CVB3 infection. iCell^® Cardiomyocytes represent well the natural host of CVB3 in the heart and are thus the most appropriate model system to study molecular mechanisms of CVB3-induced myocarditis in vitro. Doubts are raised about the suitability of commonly used cell lines such as HeLa cells, HL-1 cells and H9c2 cells to evaluate molecular pathways and processes occurring in vivo in enteroviral myocarditis.

Inhibition of Calpain Alleviates Apoptosis in Coxsackievirus B3-induced Acute Virus Myocarditis Through Suppressing Endoplasmic Reticulum Stress

Virus myocarditis (VMC) is a common cardiovascular disease and a major cause of sudden death in young adults. However, there is still a lack of effective treatments. Our previous studies found that calpain activation was involved in VMC pathogenesis. This study aims to explore the underlying mechanisms further. Neonatal rat cardiomyocytes (NRCMs) and transgenic mice overexpressing calpastatin (Tg-CAST), the endogenous calpain inhibitor, were used to establish VMC model. Hematoxylin and eosin and Masson staining revealed inflammatory cell infiltration and fibrosis. An ELISA array detected myocardial injury. Cardiac function was measured using echocardiography. CVB3 replication was assessed by capsid protein VP1. Apoptosis was measured by TUNEL staining, flow cytometry, and western blot. The endoplasmic reticulum (ER) stress-related proteins were detected by western blot. Our data showed that CVB3 infection resulted in cardiac injury, as evidenced by increased inflammatory responses and fibrosis, which induced myocardial apoptosis. Inhibiting calpain, both by PD150606 and calpastatin overexpression, could attenuate these effects. Furthermore, ER stress was activated during CVB3 infection. However, calpain inhibition could downregulate some ER stress-associated protein levels such as GRP78, pancreatic ER kinase-like ER kinase (PERK), and inositol-requiring enzyme-1α (IRE-1α), and ER stress-related apoptotic factors, during CVB3 infection. In conclusion, calpain inhibition attenuated CVB3-induced myocarditis by suppressing ER stress, thereby inhibiting cardiomyocyte apoptosis.

The protection effects of survivin in the cell model of CVB3-induced viral myocarditis

Viral myocarditis (VMC) is a widely studied but poorly understood inflammatory cardiomyopathy which mainly affects children and young adults and results in adverse outcomes. Cardiomyocyte apoptosis was reported important in the progress of coxsackievirus B3 (CVB3)-induced VMC and the blocking of this process may contribute to the therapeutic effect towards VMC. Therefore, this study was designed to explore whether survivin, one of the strongest antiapoptotic proteins, can protect cardiomyocytes from apoptosis in VMC and to discover its related mechanisms. Here, the cultured neonatal mouse cardiomyocytes (NMCs) were exposed to CVB3 to establish the cell model of VMC and the results of Western Blot showed that the protein expression of survivin in CVB3-infected NMCs varied at different post-infection time. Lentivirus was next used to examine the function of survivin in CVB3-infected NMCs. TUNEL assay demonstrated that the overexpression of survivin interrupted CVB3-induced apoptosis. It was next examined whether caspase-3 and -9 were involved in the antiapoptotic pathway initiated by survivin via Western Blot. The results showed a reverse relationship between the protein expression of survivin and that of cleaved caspase-3 and cleaved caspase-9, suggesting that survivin may attenuate apoptosis through restraining the activity of caspase-3 and -9. Moreover, the supernatant fluid of cultured NMCs was extracted to detect the quantitation of released lactate dehydrogenase (LDH) and a sharp decrease was discovered in the survivin-overexpressed group compared to the CVB3-infected group, indicating a protective role of survivin in the cell model of CVB3-induced myocarditis. This study demonstrated that survivin was triggered by CVB3 infection in NMCs and survivin executed its antiapoptotic effects via caspase-3- and caspase-9-dependent signaling pathway.

Inhibition of microRNA-15 protects H9c2 cells against CVB3-induced myocardial injury by targeting NLRX1 to regulate the NLRP3 inflammasome

Background

Viral myocarditis (VMC) is a type of cardiac inflammation that is generally caused by coxsackievirus B3 (CVB3) infection. Several MicroRNAs (miRNAs) are known to play crucial roles in VMC pathogenesis. MiR-15 is reportedly associated with myocardial injury, inflammatory responses and viral infection. Whether miR-15 affects the occurrence and development of VMC remains largely unknown. The roles of miR-15 and their underlying mechanisms in CVB3-stimulated H9c2 cells were assessed in this study.

Methods

We infected H9c2 cells with CVB3 to establish a VMC cellular model. We then determined the effects of miR-15 inhibition on three cardiomyocyte injury markers: lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB) and cardiac troponin-I (cTn-I). The impact on CVB3-induced cell apoptosis and pro-inflammatory cytokines was also investigated. The effects of miR-15 inhibition on NLRP3 inflammasome activation were also assessed. The target relationship between miR-15 and NOD-like receptor X1 (NLRX1) was determined using a luciferase reporter assay.

Results

MiR-15 expression was significantly upregulated in H9c2 cells after CVB3 infection. Inhibition of miR-15 significantly decreased the CVB3-induced levels of LDH, CK-MB and cTn-I. It also elevated cell viability, reduced CVB3-induced cell apoptosis and decreased the generation of the interleukins IL-1β, IL-6 and IL-18. Furthermore, we determined that miR-15 inhibition suppressed NLRP3 inflammasome activation by downregulating NLRP3 and caspase-1 p20 expression. We found a direct target relationship between miR-15 and NLRX1. Additionally, inhibition of NLRX1 reversed the protective effects of miR-15 inhibition against CVB3-induced myocardial cell injury by regulating the NLRP3 inflammasome.

Conclusion

Our results indicate that miR-15 inhibition alleviates CVB3-induced myocardial inflammation and cell injury. This may be partially due to NLRX1-mediated NLRP3 inflammasome inactivation.

Activation of CaMKII via ER-stress mediates coxsackievirus B3-induced cardiomyocyte apoptosis

Cardiomyocyte apoptosis contributes to the development of coxsackievirus B3 (CVB3)-induced myocarditis, but the mechanism for the apoptosis by CVB3 infection remains unclear. Here, we showed that CVB3-induced endoplasmic reticulum (ER) stress response and apoptosis in cultured H9c2 cardiomyocytes. We found that Ca²⁺ -calmodulin-dependent kinase II (CaMKII) was activated by ER stress-dependent intracellular Ca²⁺ overload in the CVB3-infected H9c2 cardiomyocytes. Treatment with an inhibitor of ER stress, 4-phenylbutyric acid (4-PBA), attenuated intracellular Ca²⁺ accumulation indirectly and reduced CaMKII activity. Inhibition of CaMKII with pharmacological inhibitor (KN-93) or short hairpin RNA reduced CVB3-induced H9c2 apoptosis and repressed cytochrome c release from mitochondria to cytoplasm; whereas overexpression of the activated mutant of CaMKII (CaMKII-T287D) enhanced CVB3-induced H9c2 apoptosis and mitochondrial cytochrome c release, which could be alleviated by blocking of mitochondrial Ca²⁺ uniporter or mitochondrial permeability transition pore. Further in vivo investigation revealed that blocking of CaMKII with KN-93 prevented cardiomyocytes apoptosis and improved cardiac contractile function in CVB3-infected mouse heart. Collectively, these findings provide a novel evidence that CaMKII plays a vital role in the promotion of CVB3-induced cardiomyocyte apoptosis, which links ER stress and mitochondrial Ca²⁺ uptake.

Hydrogen sulfide-mediated regulation of cell death signaling ameliorates adverse cardiac remodeling and diabetic cardiomyopathy

The death of cardiomyocytes is a precursor for the cascade of hypertrophic and fibrotic remodeling that leads to cardiomyopathy. In diabetes mellitus (DM), the metabolic environment of hyperglycemia, hyperlipidemia, and oxidative stress causes cardiomyocyte cell death, leading to diabetic cardiomyopathy (DMCM), an independent cause of heart failure. Understanding the roles of the cell death signaling pathways involved in the development of cardiomyopathies is crucial to the discovery of novel targeted therapeutics and biomarkers for DMCM. Recent evidence suggests that hydrogen sulfide (H2S), an endogenous gaseous molecule, has cardioprotective effects against cell death. However, very little is known about signaling by which H2S and its downstream targets regulate myocardial cell death in the DM heart. This review focuses on H2S in the signaling of apoptotic, autophagic, necroptotic, and pyroptotic cell death in DMCM and other cardiomyopathies, abnormalities in H2S synthesis in DM, and potential H2S-based therapeutic strategies to mitigate myocardial cell death to ameliorate DMCM.

Myocarditis in Humans and in Experimental Animal Models

Myocarditis is defined as an inflammation of the cardiac muscle. In humans, various infectious and non-infectious triggers induce myocarditis with a broad spectrum of histological presentations and clinical symptoms of the disease. Myocarditis often resolves spontaneously, but some patients develop heart failure and require organ transplantation. The need to understand cellular and molecular mechanisms of inflammatory heart diseases led to the development of mouse models for experimental myocarditis. It has been shown that pathogenic agents inducing myocarditis in humans can often trigger the disease in mice. Due to multiple etiologies of inflammatory heart diseases in humans, a number of different experimental approaches have been developed to induce myocarditis in mice. Accordingly, experimental myocarditis in mice can be induced by infection with cardiotropic agents, such as coxsackievirus B3 and protozoan parasite Trypanosoma cruzi or by activating autoimmune responses against heart-specific antigens. In certain models, myocarditis is followed by the phenotype of dilated cardiomyopathy and the end stage of heart failure. This review describes the most commonly used mouse models of experimental myocarditis with a focus on the role of the innate and adaptive immune systems in induction and progression of the disease. The review discusses also advantages and limitations of individual mouse models in the context of the clinical manifestation and the course of the disease in humans. Finally, animal-free alternatives in myocarditis research are outlined.

Nicotinic Agonist Inhibits Cardiomyocyte Apoptosis in CVB3-Induced Myocarditis via α3β4-nAChR/PI3K/Akt-Dependent Survivin Upregulation

Background

Cardiomyocyte apoptosis is critical for the development of coxsackievirus B3- (CVB3-) induced myocarditis, which is a common cardiac disease that may result in heart failure or even sudden death. Previous studies have associated CVB3-induced apoptosis with the downregulation of antiapoptotic proteins. Here, attempts were made to examine whether nicotinic acetylcholine receptors (nAChRs), especially α3β4-nAChRs, were a novel therapeutic antiapoptotic target via the activation of survivin, a strong antiapoptotic protein, in viral myocarditis (VMC).

Methods and Results

In the present study, we demonstrated that nAChRs, α3β4-nAChR subunits in particular, were present and upregulated in CVB3-infected neonatal rat cardiomyocytes (NRC) and H9c2 cells by RT-qPCR. The function of α3β4-nAChRs was next examined using its specific blocker α-CTX AuIB in vitro. The results of the TUNEL assay and western blot experiments showed that the block of α3β4-nAChRs abrogated nicotine-mediated protection of NRC from CVB3-induced apoptosis, and this effect displayed a substantial correlation with the protein expressions of pAkt, survivin, and Cleaved Caspase-3. Hence, the involvement of the PI3K/Akt pathway was further verified by LY294002, a selective inhibitor of PI3K. As a result, nicotine-mediated induction of pAkt and survivin was abolished by LY294002; meanwhile, apoptotic NRC were increased accompanied by an increase of Cleaved Caspase-3 expression. Regarding CVB3-infected BALB/c mice, the α-CTX AuIB- and LY294002-treated groups had a lower survival rate, deteriorative ventricular systolic function, and more severe inflammation than the nicotine-treated group and the modulation of pAkt, survivin, and Cleaved Caspase-3 protein expressions was similar to that in CVB3-infected NRC. In addition, we found that a nicotinic agonist reduced CVB3 replication in a dose-dependent manner in vitro, which indicates that nAChR activation may serve as a possible protection mechanism of CVB3-induced myocarditis.

Conclusions

Our study demonstrated that α3β4-nAChR subunits are essential in the nicotine-mediated antiapoptotic effect of protecting cardiomyocytes from CVB3-induced apoptosis in vivo and in vitro. This protection correlated with the PI3K/Akt pathway and the inducement of the antiapoptotic protein survivin. A combination of these mechanisms serves as a novel protective response to treat viral myocarditis.

Melatonin Ameliorates Coxsackievirus B3-Induced Myocarditis by Regulating Apoptosis and Autophagy

Current therapeutics options for viral myocarditis are unsatisfactory. Melatonin (MLT), a hormone secreted by the pineal gland and other organs, has protective effects on ischemic heart injury. However, the potential therapeutic effect of MLT on viral myocarditis is unknown. In this study, we investigated the protective effect of MLT on viral myocarditis in a mouse model of myocarditis infected with coxsackievirus B3 (CVB3) and explored the probable mechanisms. Mice with CVB3-induced myocarditis displayed inflammatory cell infiltration and interstitial edema. MLT treatment significantly ameliorated the myocardial injuries. In addition, the rate of autophagy changed, although apoptosis was inhibited in mouse hearts following treatment with MLT. These results suggest that MLT has a strong therapeutic effect on acute viral myocarditis, which is associated with changes in autophagy and apoptosis in the heart. Thus, MLT could be a promising novel therapeutic approach against viral myocarditis.

The cytotoxicity of coxsackievirus B3 is associated with a blockage of autophagic flux mediated by reduced syntaxin 17 expression

Coxsackievirus B3 (CVB3) is an important human pathogen linked to cardiac arrhythmias and acute heart failure. CVB3 infection has been reported to induce the formation of autophagosomes that support the viral replication in host cells. Interestingly, our study shows that the accumulation of autophagosomes during CVB3 infection is caused by a blockage of autophagosome–lysosome fusion rather than the induction of autophagosome biogenesis. Moreover, CVB3 decreases the transcription and translation of syntaxin 17 (STX17), a SNARE (soluble N-ethylmaleimide-sensitive factor activating protein receptor) protein involved in autophagosome–lysosome fusion. Overexpression of STX17 restored the autophagic flux, alleviated the virus-induced lysosomal dysfunction, and decreased the apoptosis induced by CVB3 infection in HeLa cells. Taken together, our results suggest that CVB3 infection impairs the autophagic flux by blocking autophagosome–lysosome fusion. These findings thus point to potential new therapeutic strategies targeting STX17 or autophagosome–lysosome fusion for treating CVB3-associated diseases.

Nilotinib induces ER stress and cell death in H9c2 cells

Tyrosine kinases inhibitors (TKi) represent a relatively novel class of anticancer drugs that target cellular pathways overexpressed in certain types of malignancies, such as chronic myeloid leukaemia (CML). Nilotinib, ponatinib and imatinib exhibit cardiotoxic and vascular effects. In this study, we focused on possible cardiotoxicity of nilotinib using H9c2 cells as a suitable cell model. We studied role of endoplasmic reticulum (ER) stress and apoptosis in nilotinib toxicity using a complex approach. Nilotinib impaired mitochondrial function and induced formation of ROS under clinically relevant concentrations. In addition, ability of nilotinib to induce ER stress has been shown. These events result in apoptotic cell death. All these mechanisms contribute to cytotoxic effect of the drug. In addition, involvement of ER stress in nilotinib toxicity may be important in co-treatment with pharmaceuticals affecting ER and ER stress, e.g. beta-blockers or sartans, and should be further investigated.

Profiling Subcellular Protein Phosphatase Responses to Coxsackievirus B3 Infection of Cardiomyocytes

Cellular responses to stimuli involve dynamic and localized changes in protein kinases and phosphatases. Here, we report a generalized functional assay for high-throughput profiling of multiple protein phosphatases with subcellular resolution and apply it to analyze coxsackievirus B3 (CVB3) infection counteracted by interferon signaling. Using on-plate cell fractionation optimized for adherent cells, we isolate protein extracts containing active endogenous phosphatases from cell membranes, the cytoplasm, and the nucleus. The extracts contain all major classes of protein phosphatases and catalyze dephosphorylation of plate-bound phosphosubstrates in a microtiter format, with cellular activity quantified at the end point by phosphospecific ELISA. The platform is optimized for six phosphosubstrates (ERK2, JNK1, p38α, MK2, CREB, and STAT1) and measures specific activities from extracts of fewer than 50,000 cells. The assay was exploited to examine viral and antiviral signaling in AC16 cardiomyocytes, which we show can be engineered to serve as susceptible and permissive hosts for CVB3. Phosphatase responses were profiled in these cells by completing a full-factorial experiment for CVB3 infection and type I/II interferon signaling. Over 850 functional measurements revealed several independent, subcellular changes in specific phosphatase activities. During CVB3 infection, we found that type I interferon signaling increases subcellular JNK1 phosphatase activity, inhibiting nuclear JNK1 activity that otherwise promotes viral protein synthesis in the infected host cell. Our assay provides a high-throughput way to capture perturbations in important negative regulators of intracellular signal-transduction networks.

Tanshinone IIA promotes the proliferation of WB-F344 hepatic oval cells via Wnt/β-catenin signaling

Tanshinone IIA (TSA) is a widely used traditional Chinese medicine, which has been demonstrated to protect damaged liver cells and is currently administered in the treatment of liver fibrosis. Liver precursor cells, also termed oval cells, are key in the repair of liver tissues following injury. However, whether TSA improves the function of liver cells and protects the liver from injury by enhancing the growth and proliferation of hepatic oval cells remains to be elucidated. In the present study, low to moderate concentrations of TSA were observed to stimulate proliferation, did not induce apoptosis in WB-F344 rat hepatic oval cells and the increased expression levels of β-catenin. WB-F344 cells were treated with various concentrations of TSA (0-80 µg/ml) for 24, 48, 72 and 96 h. Cell proliferation was measured using a Cell Counting kit-8 (CCK-8) assay, a 5-ethynyl-2'-deoxyuridine assay and a carboxyfluorescein diacetate succinimidyl ester (CFSE) assay. The CCK-8 assay demonstrated that treatment of WB-F344 cells with 20-40 µg/ml TSA for up to 72 h significantly increased proliferation. Similar results were observed in the subsequent EdU and CFSE assays. Furthermore, a terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay demonstrated that 20-40 µg/ml TSA treatment for up to 96 h did not induce apoptosis of the WB-F344 cells. Notably, the results of western blot, immunofluorescence and reverse transcription-quantitative polymerase chain reaction analyses demonstrated that treatment of the WB-F344 cells with 20-40 µg/ml TSA for up to 72 h significantly increased the expression levels of β-catenin. These data indicated that TSA at concentrations between 20 and 40 µg/ml may induce WB-F344 cell proliferation by activating the canonical Wnt signaling pathway. The results of the present study suggest that TSA may be a useful natural agent to enhance repair and regeneration of the injured liver, and improve liver regeneration following orthotopic liver transplantation.

Involvement of Endoplasmic Reticulum Stress-Mediated C/EBP Homologous Protein Activation in Coxsackievirus B3-Induced Acute Viral Myocarditis

BACKGROUND

This study tested the hypothesis whether endoplasmic reticulum (ER) stress/C/EBP homologous protein (CHOP) signaling is linked with coxsackievirus B3 (CVB3)-induced acute viral myocarditis (AVMC) in vivo.

METHODS AND RESULTS

AVMC was induced by intraperitoneal injection of 1000 tissue culture infectious dose (TCID50) of CVB3 virus in mice. In AVMC mouse hearts (n=11), ER stress and CHOP were significantly activated, and were linked to the induction of proapoptotic signaling including reduction of Bcl-2, activation of Bax and caspase 3, compared with the controls (n=10), whereas these could be markedly blocked by ER stress inhibitor tauroursodeoxycholic acid administration (n=11). Moreover, chemical inhibition of ER stress significantly attenuated cardiomyocytes apoptosis, and prevented cardiac troponin I elevation, ameliorated cardiac dysfunction assessed by both hemodynamic and echocardiographic analysis, reduced viral replication, and increased survival rate after CVB3 inoculation. We further discovered that genetic ablation of CHOP (n=10) suppressed cardiac Bcl-2/Bax ratio reduction and caspase 3 activation, and prevented cardiomyotes apoptosis in vivo, compared with wild-type receiving CVB3 inoculation (n=10). Strikingly, CHOP deficiency exhibited dramatic protective effects on cardiac damage, cardiac dysfunction, viral replication, and promoted survival in CVB3-caused AVMC.

CONCLUSIONS

Our data imply the involvement of ER stress/CHOP signaling in CVB3-induced AVMC via proapoptotic pathways, and provide a novel strategy for AVMC treatment.

Antiviral and myocyte protective effects of IL-28A in coxsackievirus B3-induced myocarditis

OBJECTIVE

This study aimed to investigate whether interleukin-28A (IL-28A) plays a role in murine myocarditis induced by coxsackievirus B3 (CVB3), and to explore its possible mechanism involved.

METHODS

Male BALB/c mice both infected and not infected by CVB3 were randomly divided into four groups (n=40), untreated or treated with different doses of IL-28A for 4 days, and then sacrificed on days 4 and 7 post-infection. The heart samples were collected for histopathologic examination. Cardiac viral load was determined by a plaque assay. Additionally, immunoblot analysis, TUNEL assay, and immunohistochemistry were performed to examine the expression of signal transducer, activator of transcription 1 and 2 (STAT1 and STAT2), CVB3-induced apoptosis and the expression of Bcl-2, BAX and Caspase-3.

RESULTS

Compared to uninfected mice, the CVB3 infected mice exhibited higher mortality rate (p<0.001), apparent inflammation and myocardial lesion (p<0.01), and higher cardiac viral load (p<0.01). After CVB3 infection, IL-28A treated mice presented no death (p<0.001), reduced inflammation and myocardial lesion (p<0.01), and lower viral load (p<0.01) compared to untreated mice. Besides, treatment with IL-28A markedly increased the expressions of STAT1 and STAT2, and inhibited CVB3-induced apoptosis in myocardial cells with increased ratio of Bcl-2/BAX.

CONCLUSION

The antiviral and myocyte protective effects of IL-28A in CVB3-induced myocarditis are regulated by STAT1 and STAT2.

Myocardial apoptosis and SIDS

Apoptosis mediates cardiac damage in severe forms of myocarditis. In fatal myocarditis, large amounts of cardiomyocytes show apoptotic DNA fragmentation, while in human controls, few apoptotic cardiomyocytes are found. In the present study the frequency of apoptosis in 88 SIDS cases (category 1b according to the San Diego Classification) and 15 control cases was investigated. In every case myocardial samples from 8 standard locations were collected. Detection of apoptotic cardiomyocytes was performed by TUNEL method. Furthermore the myocardial tissue was stained with HE and immunohistochemical methods (LCA, CD68, CD45-R0). More than 90% of the slides did not contain apoptotic cardiomyocytes at all. The detection rate of apoptotic cardiomyocytes was almost equal in control group (26.7%) and SIDS group (23.86%). A quantification of apoptotic cardiomyocytes per mm(2) revealed no significant difference between both groups either. Altogether there is no evidence for a higher rate of apoptosis in SIDS.

Human induced pluripotent stem cell-derived cardiomyocytes as an in vitro model for coxsackievirus B3-induced myocarditis and antiviral drug screening platform

RATIONALE

Viral myocarditis is a life-threatening illness that may lead to heart failure or cardiac arrhythmias. A major causative agent for viral myocarditis is the B3 strain of coxsackievirus, a positive-sense RNA enterovirus. However, human cardiac tissues are difficult to procure in sufficient enough quantities for studying the mechanisms of cardiac-specific viral infection.

OBJECTIVE

This study examined whether human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) could be used to model the pathogenic processes of coxsackievirus-induced viral myocarditis and to screen antiviral therapeutics for efficacy.

METHODS AND RESULTS

hiPSC-CMs were infected with a luciferase-expressing coxsackievirus B3 strain (CVB3-Luc). Brightfield microscopy, immunofluorescence, and calcium imaging were used to characterize virally infected hiPSC-CMs for alterations in cellular morphology and calcium handling. Viral proliferation in hiPSC-CMs was quantified using bioluminescence imaging. Antiviral compounds including interferonβ1, ribavirin, pyrrolidine dithiocarbamate, and fluoxetine were tested for their capacity to abrogate CVB3-Luc proliferation in hiPSC-CMs in vitro. The ability of these compounds to reduce CVB3-Luc proliferation in hiPSC-CMs was consistent with reported drug effects in previous studies. Mechanistic analyses via gene expression profiling of hiPSC-CMs infected with CVB3-Luc revealed an activation of viral RNA and protein clearance pathways after interferonβ1 treatment.

CONCLUSIONS

This study demonstrates that hiPSC-CMs express the coxsackievirus and adenovirus receptor, are susceptible to coxsackievirus infection, and can be used to predict antiviral drug efficacy. Our results suggest that the hiPSC-CM/CVB3-Luc assay is a sensitive platform that can screen novel antiviral therapeutics for their effectiveness in a high-throughput fashion.

Coxsackievirus A16 infection induces neural cell and non-neural cell apoptosis in vitro

Coxsackievirus A16 (CA16) is one of the main causative pathogens of hand, foot and mouth disease (HFMD). Viral replication typically results in host cell apoptosis. Although CA16 infection has been reported to induce apoptosis in the human rhabdomyosarcoma (RD) cell line, it remains unclear whether CA16 induces apoptosis in diverse cell types, especially neural cells which have important clinical significance. In the current study, CA16 infection was found to induce similar apoptotic responses in both neural cells and non-neural cells in vitro, including nuclear fragmentation, DNA fragmentation and phosphatidylserine translocation. CA16 generally is not known to lead to serious neurological symptoms in vivo. In order to further clarify the correlation between clinical symptoms and cell apoptosis, two CA16 strains from patients with different clinical features were investigated. The results showed that both CA16 strains with or without neurological symptoms in infected patients led to neural and muscle cell apoptosis. Furthermore, mechanistic studies showed that CA16 infection induced apoptosis through the same mechanism in both neural and non-neural cells, namely via activation of both the mitochondrial (intrinsic) pathway-related caspase 9 protein and the Fas death receptor (extrinsic) pathway-related caspase 8 protein. Understanding the mechanisms by which CA16 infection induces apoptosis in both neural and non-neural cells will facilitate a better understanding of CA16 pathogenesis.

Cardiac-specific overexpression of melanoma differentiation-associated gene-5 protects mice from lethal viral myocarditis

BACKGROUND

Viral myocarditis is among the most common causes of heart failure in children and young adults. The RNA helicase melanoma differentiation-associated gene-5 (MDA5) is critical for host antiviral responses against members of the Picornaviridae family, such as encephalomyocarditis virus (EMCV). MDA5-knockout mice are highly susceptible to EMCV infection and develop significant myocardial injury and left ventricular dysfunction. However, the mechanisms by which MDA5 signaling within cardiac myocytes contributes to the host response against viral infection have not been defined.

METHODS AND RESULTS

We generated cardiac-specific MDA5 transgenic (alpha-myosin heavy chain [αMHC]-MDA5) mice. These mice showed increased baseline cardiac expression of antiviral cytokines and increased cellular infiltration but no alterations in cardiac function and structure. αMHC-MDA5 mice were less susceptible to EMCV infection and had a significantly lower cardiac viral load compared with littermate control mice. The severity of myocarditis, prevalence of cardiac myocyte apoptosis, and cleavage of caspase 3 after EMCV infection were attenuated in αMHC-MDA5 mice. Furthermore, αMHC-MDA5 mice were protected against EMCV-induced myocardial dysfunction.

CONCLUSIONS

Our data suggest that myocardial MDA5 may be a key molecule in protecting the heart from direct viral injury and myocardial dysfunction.

Comparison of effects of ivabradine versus carvedilol in murine model with the Coxsackievirus B3-induced viral myocarditis

BACKGROUND

Elevated heart rate is associated with increased cardiovascular morbidity. The selective I(f) current inhibitor ivabradine reduces heart rate without affecting cardiac contractility, and has been shown to be cardioprotective in the failing heart. Ivabradine also exerts some of its beneficial effects by decreasing cardiac proinflammatory cytokines and inhibiting peroxidants and collagen accumulation in atherosclerosis or congestive heart failure. However, the effects of ivabradine in the setting of acute viral myocarditis and on the cytokines, oxidative stress and cardiomyocyte apoptosis have not been investigated.

METHODOLOGY/PRINCIPAL FINDINGS

The study was designed to compare the effects of ivabradine and carvedilol in acute viral myocarditis. In a coxsackievirus B3 murine myocarditis model (Balb/c), effects of ivabradine and carvedilol (a nonselective β-adrenoceptor antagonist) on myocardial histopathological changes, cardiac function, plasma noradrenaline, cytokine levels, cardiomyocyte apoptosis, malondialdehyde and superoxide dismutase contents were studied. Both ivabradine and carvedilol similarly and significantly reduced heart rate, attenuated myocardial lesions and improved the impairment of left ventricular function. In addition, ivabradine treatment as well as carvedilol treatment showed significant effects on altered myocardial cytokines with a decrease in the amount of plasma noradrenaline. The increased myocardial MCP-1, IL-6, and TNF-α. in the infected mice was significantly attenuated in the ivabradine treatment group. Only carvedilol had significant anti-oxidative and anti-apoptoic effects in coxsackievirus B3-infected mice.

CONCLUSIONS/SIGNIFICANCE

These results show that the protective effects of heart rate reduction with ivabradine and carvedilol observed in the acute phase of coxsackievirus B3 murine myocarditis may be due not only to the heart rate reduction itself but also to the downregulation of inflammatory cytokines.

A model for cardiomyocyte cell death: insights into mechanisms of oncosis

It is now known that there are at least two basic patterns of cell injury progressing to cell death: cell injury with swelling, known as oncosis, and cell injury with shrinkage, known as apoptosis. Both types of cell death are "programmed" in the sense that the genetic information and many of the enzymes and other factors pre-exist in the cell. Previous investigation has pointed to cardiomyocyte ischemic injury evolving as the oncotic pattern of injury, although apoptosis has also been implicated. This study was designed, using a unique cell model system, to gain insight into the molecular events of anticancer agent-induced cardiomyocyte injury. Cardiomyocytes exposed for 2 h to 1.5 μg/ml sanguinarine consistently displayed the morphology of apoptosis in over 80% of cells, whereas a higher dose of 25 μg/ml at 2 h yielded the pattern of oncosis in over 90% of cells. Microarray analysis revealed altered expression of 2514 probes in sanguinarine-induced oncosis and 1643 probes in apoptosis at a level of significance of p<0.001. Some of the inductions such as perforin were found to be higher than 11-fold in oncosis. When perforin was blocked by perforin-specific siRNA we found a reduction in oncotic cell death. These results strengthen the notion that oncosis is not representative of nonspecific necrosis, but constitutes a genetically controlled form of "programmed cell death"; and also that oncosis might represent a pathogenetic mechanism of cardiomyocyte injury. This is also the first demonstration of the involvement of perforin in cardiomyocyte oncosis.

Oxidative stress and heart failure in altered thyroid States

Increased or reduced action of thyroid hormone on certain molecular pathways in the heart and vasculature causes relevant cardiovascular derangements. It is well established that hyperthyroidism induces a hyperdynamic cardiovascular state, which is associated with a faster heart rate, enhanced left ventricular systolic and diastolic function whereas hypothyroidism is characterized by the opposite changes. Hyperthyroidism and hypothyroidism represent opposite clinical conditions, albeit not mirror images. Recent experimental and clinical studies have suggested the involvement of ROS tissue damage under altered thyroid status. Altered-thyroid state-linked changes in heart modify their susceptibility to oxidants and the extent of the oxidative damage they suffer following oxidative challenge. Chronic increase in the cellular levels of ROS can lead to a catastrophic cycle of DNA damage, mitochondrial dysfunction, further ROS generation and cellular injury. Thus, these cellular events might play an important role in the development and progression of myocardial remodeling and heart failure in altered thyroid states (hypo- and hyper-thyroidism). The present review aims at elucidating the various signaling pathways mediated via ROS and their modulation under altered thyroid state and the possibility of antioxidant therapy.

Viral and host factors that contribute to pathogenicity of enterovirus 71

The single-stranded RNA virus enterovirus 71 (EV71), which belongs to the Picornaviridae family, has caused epidemics worldwide, particularly in the Asia–Pacific region. Most EV71 infections result in mild clinical symptoms, including herpangina and hand, foot and mouth disease. However, serious pathological complications have also been reported, especially for young children. The mechanisms of EV71 disease progression remain unclear. The pathogenesis of adverse clinical outcomes may relate to many factors, including cell tropism, cell death and host immune responses. This article reviews the recent advances in the identification of factors determining EV71 cell tropism, the associated mechanisms of viral infection-induced cell death and the interplay between EV71 and immunity.

Modulation of endoplasmic reticulum stress and cardiomyocyte apoptosis by mulberry leaf diet in experimental autoimmune myocarditis rats

Mulberry is commonly used as silkworm diet and an alternative medicine in Japan and China, has recently reported to contain many antioxidative flavanoid compounds and having the free radical scavenging effects. Antioxidants reduce cardiac oxidative stress and attenuate cardiac dysfunction in animals with pacing-induced congestive heart failure. Hence we investigated the cardioprotective effect of mulberry leaf powder in rats with experimental autoimmune myocarditis. Eight-week-old Lewis rats immunized with cardiac myosin were fed with either normal chow or a diet containing 5% mulberry leaf powder and were examined on day 21. ML significantly decreased oxidative stress, myocyte apoptosis, cellular infiltration, cardiac fibrosis, mast cell density, myocardial levels of sarco/endo-plasmic reticulum Ca²⁺ ATPase2, p22^phox, receptor for advanced glycation end products, phospho-p38 mitogen activated protein kinase, phospho-c-Jun NH₂-terminal protein kinase, glucose regulated protein78, caspase12 and osteopontin levels in EAM rats. These results may suggest that mulberry diet can preserve the cardiac function in experimental autoimmune myocarditis by modulating oxidative stress induced MAPK activation and further afford protection against endoplasmic reticulum stress mediated apoptosis.

Experimental SSM-CVB3 infection in macaques

OBJECTIVE

To evaluate the pathogenicity of SSM-CVB3 in a macaque model.

METHODS

The clinical symptoms of macaques were recorded; hematological, biochemical and histopathological evaluations were completed; viral titers and neutralization titers (NT-titers) in sera were tested; and the mRNA levels of SSM-CVB3, coxsackievirus and adenovirus receptor (CAR) and decay accelerating factor (DAF) were determined.

RESULTS

After SSM-CVB3 infection, the macaques showed a lack of activity, a poor appetite, a higher body temperature, and severe diarrhea. The macaques also developed hematuria and albuminuria at 4 to 10 days post-inoculation. Virus titers (5.1-6.5 LogTCID(50)/mL) were higher at 6 to 10 days post-inoculation, and NT-titers (6.5-7.3 Log2) reached plateaus at 8 to 14 days post-inoculation. The infected macaques developed serious anemia with decreased RBC and WBC, but the percentages of LYM were increased. The levels of CK, CK-MB, AST and ALT in the sera were 84-169 U/L, 87.6-271.1 U/L, 43-87 U/L and 43-82 U/L, respectively, and all of those were higher than normal. Histological analysis showed obvious cardiac, hepatic and renal damages in the infected macaques and the mRNA contents of SSM-CVB3, CAR and DAF in the heart, liver and kidneys of infected macaques were higher (P<0.05).

CONCLUSION

This was the first report on experimental SSM-CVB3 infections in macaques with serious hepatic and renal damage, except for myocarditis. The information obtained from this study suggests that the SSM-CVB3 strain and this macaque model could be used for studying CVB3-induced cardiac, hepatic or renal diseases.

Viral myocarditis: potential defense mechanisms within the cardiomyocyte against virus infection

Virus infection can inflict significant damage on cardiomyocytes through direct injury and secondary immune reactions, leading to myocarditis and dilated cardiomyopathy. While viral myocarditis or cardiomyopathy is a complication of systemic infection of cardiotropic viruses, most individuals infected with the viruses do not develop significant cardiac disease. However, some individuals proceed to develop severe virus-mediated heart disease. Recent studies have shown that viral infection of cardiomyocytes is required for the development of myocarditis and subsequent cardiomyopathy. This suggests that viral infection of cardiomyocytes can be an important step that determines the pathogenesis of viral myocarditis during systemic infection. Accordingly, this article focuses on potential defense mechanisms within the cardiomyocyte against virus infection. Understanding of the cardiomyocyte defense against invading viruses may give us novel insights into the pathophysiology of viral myocarditis, and enable us to develop innovative strategies of diagnosis and treatment for this challenging clinical entity.

Coxsackievirus B3 infection activates the unfolded protein response and induces apoptosis through downregulation of p58IPK and activation of CHOP and SREBP1

Cardiomyocyte apoptosis is a hallmark of coxsackievirus B3 (CVB3)-induced myocarditis. We used cardiomyocytes and HeLa cells to explore the cellular response to CVB3 infection, with a focus on pathways leading to apoptosis. CVB3 infection triggered endoplasmic reticulum (ER) stress and differentially regulated the three arms of the unfolded protein response (UPR) initiated by the proximal ER stress sensors ATF6a (activating transcription factor 6a), IRE1-XBP1 (X box binding protein 1), and PERK (PKR-like ER protein kinase). Upon CVB3 infection, glucose-regulated protein 78 expression was upregulated, and in turn ATF6a and XBP1 were activated via protein cleavage and mRNA splicing, respectively. UPR activity was further confirmed by the enhanced expression of UPR target genes ERdj4 and EDEM1. Surprisingly, another UPR-associated gene, p58(IPK), which often is upregulated during infections with other types of viruses, was downregulated at both mRNA and protein levels after CVB3 infection. These findings were observed similarly for uninfected Tet-On HeLa cells induced to overexpress ATF6a or XBP1. In exploring potential connections between the three UPR pathways, we found that the ATF6a-induced downregulation of p58(IPK) was associated with the activation of PKR (PERK) and the phosphorylation of eIF2alpha, suggesting that p58(IPK), a negative regulator of PERK and PKR, mediates cross-talk between the ATF6a/IRE1-XBP1 and PERK arms. Finally, we found that CVB3 infection eventually produced the induction of the proapoptoic transcription factor CHOP and the activation of SREBP1 and caspase-12. Taken together, these data suggest that CVB3 infection activates UPR pathways and induces ER stress-mediated apoptosis through the suppression of P58(IPK) and induction/activation of CHOP, SREBP1, and caspase-12.

The heart-protective mechanism of Qishaowuwei formula on murine viral myocarditis induced by CVB3

AIM OF STUDY

The heart-protective effect and mechanism of Qishaowuwei formula (QSW), a Traditional Chinese Medicine formula composed of Radix Astragali, Radix Paeoniae Rubra and Fructus Schisandrae was investigated on murine model of viral myocarditis (VMC) induced by Coxsackievirus B3 (CVB3).

MATERIALS AND METHODS

Mice were randomly divided into infected control group, QSW high dose group, QSW medium dose group, QSW low dose group and Vitamin C plus Ribavirin treatment group. 50 mice were included in each group. The day of virus inoculation was defined as day 0 and the drug treatment continued once a day for 14 days. Mice were sacrificed on days 3, 7, 14, 21 postinoculation (p.i.). The histopathological changes of myocardium, CVB3 RNA copies in the myocardium, cardiomycytic apoptosis, the serum level of superoxide dismutase (SOD) and maleic dialdehyde (MDA) and the phenotype of T lymphocytes subsets in peripheral blood was analyzed.

RESULTS

QSW treatment significantly increase the survival rate (p<0.05) in VMC model. Histopathology and flow cytometry inspection revealed low ratio of cardiomyocytes necrosis and apoptosis in QSW treated mice with dose dependent manner. The cardiomyocytic ultra-structure observed by transmission electron microscope also supported the above results. The ameliorated tissue damage was consistent with reduced CVB3 copy numbers detected by real-time PCR in the myocardium of QSW treated mice. The antioxidant effect of QSW was proved by elevated activity of SOD and reduced level of MDA in the serum. Furthermore, the disturbed balance of CD4+ and CD8+ subsets in peripheral blood was restored.

CONCLUSION

These results demonstrated QSW had potent protective effect against CVB3-induced heart injury and this effect might be mediated by its inhibition on viral replication, antioxidant activity and immunoregulation mechanism.

Anti-perforin neutralizing antibody reduces myocardial injury in viral myocarditis

AIM

To investigate the role of anti-perforin neutralizing antibody in viral myocarditis.

METHODS

We divided 45 Balb/c mice randomly into 3 groups, a normal control group, a control group inoculated with coxsackie virus B3, and a group inoculated with anti-perforin neutralizing antibody. The second group was inoculated with 0.15 milliliters coxsackie virus B3, and the third group additionally with 0.1 milligrams/kilogram anti-perforin neutralizing antibody at time points of 6 hours and 3 days after infection. Histopathology was performed using haematoxylin and eosin, with apoptosis examined by the terminal transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick, end-labeling method, or Tunel. The expression of caspase-3 in myocardium was investigated by immunohistochemistry and reverse-transcription polymerase chain reaction.

RESULTS

The pathologic score, myocardial viral titers, average percentages of apoptotic cardiomyocytes, expression of active caspase-3 protein and messenger ribonucleic acid in the myocardium of the mice receiving anti-PFP neutralizing antibody therapy were all significantly reduced when compared to values from the group inoculated with coxsackie virus B3. The rates of expression of Caspase-3 and myocardial apoptosis were positively correlated with the scores for myocardial pathology.

CONCLUSION

Our results suggest that anti- perforin neutralizing antibody can reduce the myocardial damage by blocking the perforin/granzyme pathway, and downregulating the expression of messenger ribonucleic acid and protein of Caspase-3. These approaches may offer promising novel therapeutic strategies for the clinical treatment of viral myocarditis.

Apoptosis in patients with acute myocarditis

Acute myocarditis is an acute inflammatory syndrome characterized by acute myocardial damage and dysfunction followed by a variable recovery over time with some patients progressing toward severe dilated cardiomyopathy. Cardiomyocyte apoptosis, a key pathologic feature of heart failure, may play a critical role in functional recovery in patients with acute myocarditis. The aim of the study was to investigate whether apoptosis predicts functional recovery in patients with acute myocarditis. Sixteen patients with biopsy-documented acute myocarditis were followed for 1 year with serial transthoracic echocardiography. Functional recovery was defined as 12-month left ventricular ejection fraction >40%. Cardiomyocyte apoptosis, leukocyte infiltration, and cell proliferation was assessed in all samples. A group of cases in which the diagnosis of acute myocarditis was made after death was also selected for comparison, and morphologically normal hearts from patients who died from a noncardiac cause were selected as controls. Six patients (38%) had functional recovery at 12 months, whereas 10 (62%) did not. The 2 groups had similar characteristics except for lower baseline left ventricular ejection fraction in the group with functional recovery. Apoptotic rate was found to be significantly higher in patients with acute myocarditis than in control hearts, and, unexpectedly, patients with functional recovery had significantly higher apoptotic rates than patients without recovery (3.2% vs 0.5%, p = 0.001). None of the patients with apoptotic rates below the median had functional recovery versus 86% of patients with apoptotic rates above the median (p <0.001). In conclusion, higher rates of cardiomyocyte apoptosis in patients with acute myocarditis are associated with functional recovery at 1 year.

Effects of levosimendan in experimental acute coxsackievirus myocarditis

BACKGROUND

Acute heart failure is a potentially fatal manifestation of viral myocarditis. Development of myocardial damage in myocarditis involves cardiomyocyte apoptosis. Levosimendan is a novel calcium sensitizing inotropic agent with anti-apoptotic properties. We studied the feasibility of inotropic treatment with levosimendan and its effects on apoptosis in experimental acute heart failure caused by coxsackievirus myocarditis.

MATERIALS AND METHODS

Adolescent BALB/c mice were infected with myocarditic Woodruff variant of coxsackievirus B3 (2 x 10(4) plaque-forming units). Mice were randomized into those receiving levosimendan 0.33 mg kg(-1) (total dose 1 mg kg(-1) day(-1)) (n = 20) or vehicle (n = 19) given orally by gauge three times a day for 7 days after infection. Left ventricular function was evaluated by transthoracic echocardiography and the mice were euthanized on day 7. Histopathology, amount of virus in the heart (virus titration assay) and cardiomyocyte apoptosis (TUNEL assay) were studied. Uninfected untreated control mice were also studied.

RESULTS

Infection resulted in histopathologically severe myocarditis and significant impairment of left ventricular function. Levosimendan treatment significantly improved ventricular function (fractional shortening 0.32 +/- 0.04 vs. 0.23 +/- 0.05, P = 0.005; contractility 0.60 +/- 0.12 vs. 0.39 +/- 0.14, P = 0.007 and myocardial performance index 0.36 +/- 0.06 vs. 0.62 +/- 0.15, P < 0.0001) compared with vehicle. Levosimendan also reduced cardiomyocyte apoptosis (0.26 +/- 0.08% vs. 0.44 +/- 0.15% in vehicle, P = 0.008), but did not have an effect on areas of myocardial necrosis or inflammation, or the amount of virus in the heart. Levosimendan treatment did not affect mortality (total mortality 63%). CONCLUSIONS; Levosimendan improves ventricular function and inhibits cardiomyocyte apoptosis; therefore, it is suggested as a potentially feasible therapy in acute heart failure caused by viral myocarditis.

Phyllaemblicin B inhibits Coxsackie virus B3 induced apoptosis and myocarditis

Coxsackie virus B3 (CVB3) is believed to be a major contributor to viral myocarditis since virus-associated apoptosis plays a role in the pathogenesis of experimental myocarditis. In this study, we investigated the in vitro and in vivo antiviral activities of Phyllaemblicin B, the main ellagitannin compound isolated from Phyllanthus emblica, a Chinese herb medicine, against CVB3. Herein we report that Phyllaemblicin B inhibited CVB3-mediated cytopathic effects on HeLa cells with an IC(50) value of 7.75+/-0.15microg/mL. In an in vivo assay, treatment with 12mgkg(-1)d(-1) Phyllaemblicin B reduced cardiac CVB3 titers, decreased the activities of LDH and CK in murine serum, and alleviated pathological damages of cardiac muscle in myocarditic mice. Moreover, Phyllaemblicin B clearly inhibited CVB3-associated apoptosis effects both in vitro and in vivo. These results show that Phyllaemblicin B exerts significant antiviral activities against CVB3. Therefore, Phyllaemblicin B may represent a potential therapeutic agent for viral myocarditis.

Development of troponin autoantibodies in experimental coxsackievirus B3 myocarditis

BACKGROUND

Autoantibodies against various endogenous proteins are found in myocarditis. Troponin autoantibodies are detected in patients with chronic dilated cardiomyopathy, but their presence in myocarditis remains unknown. We set out to study the presence of troponin autoantibodies in experimental viral myocarditis.

MATERIALS AND METHODS

BALB/c mice infected with coxsackievirus B3 Nancy strain were followed-up at days 1-7 and 2, 4, 8 and 12 weeks after infection. Levels of circulating cardiac troponin I and circulating troponin autoantibodies were measured. Transthoracic echocardiography was performed. Myocarditis was histopathologically graded and cardiomyocyte apoptosis was quantified (TUNEL).

RESULTS

Histopathologically relatively mild acute myocarditis followed by persistent cardiomyocyte damage was observed. Rate of cardiomyocyte apoptosis was the highest on day 5 (0.16 +/- 0.01% vs. 0.03 +/- 0.01% in controls, P < 0.001). Circulating troponin I levels were increased to day 5 (45.2 +/- 6.5 ng mL(-1), P < 0.005 vs. controls). Troponin autoantibodies were detected from 2 weeks after infection (20% of animals had autoantibodies at 2 weeks, 60% at 4 and 8 weeks and 20% at 12 weeks, P < 0.05 vs. controls). Fractional shortening remained decreased after acute myocarditis (0.36 +/- 0.02 at 4 weeks, 0.30 +/- 0.02 at 8 and 12 weeks vs. 0.41 +/- 0.01 before infection, P < 0.01) parallel to development of troponin autoantibodies.

CONCLUSION

Troponin autoantibodies are formed in experimental virus induced myocarditis following troponin I release and cardiomyocyte apoptosis. The definite role of these autoantibodies remains to be further characterized.

Cardiac cell-specific apoptotic and cytokine responses to reovirus infection: determinants of myocarditic phenotype

BACKGROUND

The pathophysiologic mechanisms underlying viral myocarditis are not well defined. As a result, effective treatments do not exist and viral myocarditis remains a potentially lethal infection of the heart.

METHODS AND RESULTS

We used cultured rat cardiac myocytes and fibroblasts to investigate apoptosis and cytokine production in response to infection by myocarditic vs. non-myocarditic strains of reovirus. Myocarditic reovirus strain 8B and non-myocarditic strain DB188 replicate comparably in each cardiac cell type. However, strain 8B and related myocarditic reoviruses preferentially increase apoptosis of myocytes relative to fibroblasts, whereas DB188 and nonmyocarditic strains preferentially increase fibroblast apoptosis. Infection of cardiac fibroblasts with the nonmyocarditic strain DB188 elicits substantial increases in a panel of cytokines compared to fibroblasts infected with strain 8B or mock-infected controls. Analysis of culture supernatants using cytometric bead arrays revealed that DB188 enhanced release of interleukin (IL)-1beta, IL-4, IL-6, IL-10, IL-12(p70), GRO-KC, tumor necrosis factor-alpha, and MCP-1 relative to 8B or mock-infected controls (all P < .05).

CONCLUSION

We hypothesize that differential cytokine production and cell-specific apoptosis are important determinants of myocarditic potential of reoviral strains. Therapies that target the beneficial effects of cytokines in limiting cytopathic damage may offer an effective and novel treatment approach to viral myocarditis.

Apoptosis in animal models of virus-induced disease

Apoptosis is associated with virus-induced human diseases of the central nervous system, heart and liver, and causes substantial morbidity and mortality. Although virus-induced apoptosis is well characterized in individual cells in cell culture, virus-induced apoptosis in vivo and the role of apoptosis in virus-induced disease is not well established. This review focuses on animal models of virus-induced diseases of the central nervous system, heart and liver that provide insights into the role of apoptosis in pathogenesis, the pathways involved and the potential therapeutic implications.

The effects of NK4 on viral myocarditis mice

NK4 may be a promising agent to inhibit tumor invasion and metastasis. To observe the effects of NK4 on the cardiovascular system with pathological injury and to discuss the mechanism, we established an experimental model of viral myocarditis (VCM) by coxsackievirus B3 infection in Balb/c mice on Day 0 and administered NK4 twice daily to the VCM and control mice from Day 20 to Day 45. We then evaluated the cardiac function by means of ultrasonic inspection. Hepatocyte growth factor, TNF (tumor necrosis factor)-alpha, and angiotensin II levels in the myocardial tissue were measured with enzyme-linked immunosorbent assay. Myocardium histopathology was examined with hematoxylin and eosin stain. Collagen deposition of the myocardium was detected through Masson staining. Microvessel staining with the RECA antibody and apoptosis detection with terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling were performed in the myocardium. The changes in MMP3 (matrix metalloproteinase 3), MMP9, TIMP1 (tissue inhibitor of metalloproteinase 1), and TGF (transforming growth factor)-beta1 expression in the myocardium were measured by reverse-transcriptase polymerase chain reaction. We found that NK4 intervention increased TGF-beta and angiotensin II expression, suppressed MMPs, improved the activities of TIMPs, and then promoted collagen deposition in the myocardium. NK4 intervention also decreased the microvessels' density and increased the apoptotic cell count in the myocardia of VCM mice. However, we did not observe the obvious changes in the myocardia of control mice after NK4 intervention. These data suggest that NK4 made negative impacts on the restoration of cardiac function and the recovery from VCM in the experimental mice.

Novel therapeutic targets in viral myocarditis

Viral myocarditis is an elusive infection of the heart that is currently without an effective or definitive treatment. Viral myocarditis has a complex disease progression that can be divided into early, middle and late phases. Direct cytopathic injury, apoptosis, activation of the innate and adaptive immune system and cardiac remodeling have all been implicated in the pathogenesis of viral myocarditis. Novel treatment approaches are evolving at a rapid pace. The purpose of this review is to provide an update on current research focused on identifying potential treatment options for viral myocarditis.

Molecular biology and pathogenesis of viral myocarditis

Myocarditis is a cardiac disease associated with inflammation and injury of the myocardium. Several viruses have been associated with myocarditis in humans. However, coxsackievirus B3 is still considered the dominant etiological agent. The observed pathology in viral myocarditis is a result of cooperation or teamwork between viral processes and host immune responses at various stages of disease. Both innate and adaptive immune responses are crucial determinants of the severity of myocardial damage, and contribute to the development of chronic myocarditis and dilated cardiomyopathy following acute viral myocarditis. Advances in genomics and proteomics, and in the use of informatics and biostatistics, are allowing unbiased initial evaluations that can be the basis for testable hypotheses about virus pathogenesis and new therapies.