Persistence of viral genome into late stages of murine myocarditis detected by polymerase chain reaction

Myocarditis and pericarditis in children

Myocarditis and pericarditis are rare but important causes of pediatric chest pain. The diagnostic criteria, clinical course, causes, and treatment of myocarditis is reviewed. There is particular attention to the relationship of myocarditis with dilated cardiomyopathy. Supportive therapy remains the standard of care for pump dysfunction. The identification and treatment of pericarditis with associated large pericardial effusion can be lifesaving. This article reviews the important clinical features that might lead the clinician to diagnose either myocarditis or pericarditis and thus separate the few patients with either of these conditions from the legions of children with noncardiac chest pain.

Myocarditis

Viruses are the most common cause of myocarditis in economically advanced countries.

Enteroviruses and adenoviruses are the most common etiologic agents.

Viral myocarditis is a triphasic process. Phase 1 is the period of active viral replication in the myocardium during which the symptoms of myocardial damage range from none to cardiogenic shock. If the disease process continues, it enters phase 2, which is characterized by autoimmunity triggered by viral and myocardial proteins. Heart failure often appears for the first time in phase 2. Phase 3, dilated cardiomyopathy, is the end result in some patients. Diagnostic procedures and treatment should be tailored to the phase of disease.

Viral myocarditis is a significant cause of dilated cardiomyopathy, as proved by the frequent presence of viral genomic material in the myocardium, and by improvement in ventricular function by immunomodulatory therapy.

Myocarditis of any etiology usually presents with heart failure, but the second most common presentation is ventricular arrhythmia. As a result, myocarditis is one of the most common causes of sudden death in young people and others without preexisting structural heart disease.

Myocarditis can be definitively diagnosed by endomyocardial biopsy. However, it is clear that existing criteria for the histologic diagnosis need to be refined, and that a variety of molecular markers in the myocardium and the circulation can be used to establish the diagnosis.

Treatment of myocarditis has been generally disappointing. Accurate staging of the disease will undoubtedly improve treatment in the future. It is clear that immunosuppression and immunomodulation are effective in some patients, especially during phase 2, but may not be as useful in phases 1 and 3. Since myocarditis is often selflimited, bridging and recovery therapy with circulatory assistance may be effective. Prevention by immunization or receptor blocking strategies is under development.

Giant cell myocarditis is an unusually fulminant form of the disease that progresses rapidly to heart failure or sudden death. Rapid onset of disease in young people, especially those with other autoimmune manifestations, accompanied by heart failure or ventricular arrhythmias, suggests giant cell myocarditis.

Peripartum cardiomyopathy in economically developed countries is usually the result of myocarditis.

Detection of Coxsackievirus B3 RNA in mouse myocarditis by nested polymerase chain reaction

BACKGROUND

A majority of cases of viral myocarditis are associated with group B Coxsackieviruses (CVB) and the persistence of these viruses in the myocardium is associated with the progression of acute myocarditis to chronic dilated cardiomyopathy. A highly sensitive nested polymerase chain reaction (NPCR) is required to study the mechanisms of viral persistence in the myocardium.

OBJECTIVES

To develop an enterovirus group-specific NPCR system, to compare it to the reverse-transcription PCR (RT-PCR) plus Southern hybridisation and to investigate the dynamics of viral RNA in a murine model of myocarditis induced by CVB3.

STUDY DESIGN

Primers corresponding to the conserved sequences in the 5'-nontranslated region of enteroviruses were designed to ensure a broad specificity. The specificity of PCR products was confirmed by Southern hybridisation. The sensitivity of RT-PCR or NPCR was assessed using reconstructed infected muscle samples. The myocardial samples of the SWR murine model of CVB3-myocarditis were collected from day 1 to 30 after infection. The presence of viral RNA was detected by the RT-PCR or NPCR and infectious virus was isolated by cell culture.

RESULTS

Both RT-PCR and NPCR could detect all 11 representative enteroviruses. The NPCR could detect as few as 0.01 plaque forming unit of virus, 100 times more sensitive than the RT-PCR. Virus was isolated from the myocardium in acute phase, but was no longer recoverable after 9 days. Viral RNA was detected by the NPCR technique throughout the studied period.

CONCLUSIONS

An enterovirus group-specific NPCR system was developed and was much more sensitive than the RT-PCR technique. It can replace the Southern hybridisation of RT-PCR products. The presence of viral RNA in the myocardium after acute phase indicates a possibility of CVB3 shifting to persistent infection in the SWR mice.

Myocardial remodeling in viral heart disease: possible interactions between inflammatory mediators and MMP-TIMP system

Matrix metalloproteinases (MMP), a family of proteases, are involved in the degradation of extracellular matrix proteins and hence in the determination of interstitial architecture. In the heart, MMPs have been found to play a significant role in the development of myocardial remodeling and congestive heart failure. Tissue inhibitors of matrix metalloproteinases (TIMPs) represent a family of proteins which are known to regulate the expression and activity of MMPs. TIMPs are endogenous physiological inhibitors of MMPs and their concomitant downregulation in heart failure suggests the existence of a critical balance between MMPs and TIMPs in the normal maintenance of myocardial interstitial homeostasis. In addition, cytokines regulate expression of both MMPs and TIMPs besides eliciting a direct effect on myocardial cell function. Therefore, myocardial inflammation may also contribute to the development of cardiac remodeling along with other stimuli like mechanical stress and humoral factors. Viral myocarditis, a predisposing factor for dilated cardiomyopathy, is a condition in which extent of intramyocardial inflammation is thought to determine the progression of disease. Inflammatory events in the heart following viral infection are speculated to be responsible for the transition of myocarditis to dilated cardiomyopathy. In viral myocarditis and other inflammatory heart diseases, the inflammatory cells and their battery of cytokines may also alter the myocardial MMP-TIMP system and eventually lead to dilation of the heart and ventricular dysfunction. The objective of this review is to present an overall picture of the inflammatory phase in viral myocarditis and discuss the possible interactions between inflammation and myocardial MMP profiles which may lead to the evolution of dilated cardiomyopathy.

Dissecting mechanisms of innate and acquired immunity in myocarditis

Inflammation underlies the pathogenesis of some of the most common cardiovascular diseases. Myocarditis is a relevant clinical cause of heart failure, but also provides an excellent laboratory model to study the mechanisms of inflammation leading to heart failure. The availability of different inbred mouse strains for inducing myocarditis using viral or myosin as triggers provides an excellent platform for investigation. The recent use of genetically manipulated mouse models of transgenic overexpression or knockout or knockin targets have provided opportunity to pinpoint specific pathways underlying myocarditis. These pathways include the involvement of both innate and acquired immunity, as well as the role of viral receptors in disease phenotype. These different models also permit the evaluation of therapeutic strategies of candidates for clinical development.

An approach to the treatment of pediatric myocarditis

The newest treatment strategies for pediatric myocarditis have evolved from an understanding of the pathophysiology of myocyte damage. Although the initial stages of viral myocarditis apparently result from the direct cytopathic effects on the atrial and ventricular myocardium, later stages of progressive decompensation result from immune-mediated myocyte destruction common to many forms of myocarditis. Despite advances in the understanding of the role of genetics, immunologic mechanisms, and infectious causes of myocarditis, supportive therapy continues to remain the cornerstone of treatment. Presently, therapies include supportive management with anticongestive agents, antiviral medications, and therapies that attempt to interrupt the immunologic cascade. Clinical studies have yet to provide convincing evidence that the use of immunosuppressants and gamma-globulin favorably alters the outcome for pediatric patients with acute myocarditis. Ventricular assist devices and heart transplantation remain as treatment options for all pediatric patients with severe myocarditis resistant to all other therapies. Although this review will focus on viral myocarditis, the supportive strategies and surgical treatment options apply to most forms of cardiomyopathy.

Diagnosis and management of pediatric myocarditis

Myocarditis is an insidious inflammatory disorder of the myocardium. As a clinical entity, it has been recognized for two centuries, but it defies traditional diagnostic tests. A greater understanding of the immune response underlying the pathobiology of the disorder can lead to a more rational therapeutic approach. The presentation, course and therapeutic options appear to be different in the pediatric compared with the adult population. An understanding of the difference between fulminant and acute progressive myocarditis has led to successful treatment strategies. A variety of new therapies are available, including antiviral agents, immunosuppression, and modulation of the biological response to inflammation. The specific question for patients with myocarditis is whether regimens designed to reduce or eliminate inflammation can provide clinical benefits compared with conventional heart failure therapy. This review highlights pathological mechanisms, modalities of diagnosis, and novel therapies which may improve outcomes.

Porcine encephalomyocarditis virus persists in pig myocardium and infects human myocardial cells

Recent advances toward using pig tissues in human transplantation have made it necessary to determine the risk of transmitting zoonotic viruses from pigs to humans or vice versa. We investigated the suitability of the porcine encephalomyocarditis virus (EMCV) model for such studies by determining its ability to persist in pigs, escape detection by routine serological methods, and infect human cells. Intraperitoneal inoculation of 5-week-old pigs with EMCV-30, a strain isolated from commercial pigs, resulted in acute cellular degeneration, infiltration of lymphocytes, and apoptosis in myocardium in 13 of 15 (86.7%) pigs during the acute phase of disease (3 to 21 days postinfection), followed by less-severe lymphocytic infiltration and apoptosis in 5 of 10 (50%) pigs during the chronic phase of the disease (day 45 to 90 postinfection). In the brain, lymphocytic infiltration, neuronal degeneration, and gliosis were observed in 26 to 33% of pigs in the acute phase of disease whereas perivascular cuffing was the predominant feature during chronic disease. EMCV antigens and RNA were demonstrated in the myocardium and brain during the chronic phase of disease. Analysis of 100 commercial pigs that were negative for EMCV antibodies identified two pig hearts positive for EMCV RNA. Porcine EMCV productively infected primary human cardiomyocytes as demonstrated by immunostaining using a monoclonal antibody specific for EMCV RNA polymerase, which is expressed only in productively infected cells, and by a one-step growth curve that showed production of 100 to 1,000 PFU of virus per cell within 6 h. The findings that porcine EMCV can persist in pig myocardium and can infect human myocardial cells make it an important infectious agent to screen for in pig-to-human cardiac transplants and a good model for xenozoonosis.

Diagnosis and treatment of pediatric viral myocarditis

Acute myocarditis is characterized by the rapid development of life-threatening congestive heart failure and arrhythmias. Although the initial stages of this disorder apparently result from direct cytopathic effects on the atrial and ventricular myocardium, later stages of progressive decompensation may result from immune-mediated myocyte destruction. There has been recent improvement in understanding the role of this immunologic cascade. As a result, treatment now begins earlier in the course of the disease and can target both the virus and the immune response. Our ability to implement mechanical support in children as a bridge to transplant or recovery, even in children presenting in the final stages of their disease, has led to an improved outcome regarding morbidity and mortality.

Molecular screening by polymerase chain reaction detects panleukopenia virus DNA in formalin-fixed hearts from cats with idiopathic cardiomyopathy and myocarditis

Viral myocarditis has been suggested as an etiology for cardiomyopathy in several mammalian species. Myocarditis and idiopathic cardiomyopathy have been reported in the domestic cat, although a viral etiology has not been demonstrated. Because of the continuing interest in the potential relationship between viral myocarditis and cardiomyopathy, we evaluated hearts from cats with spontaneous, idiopathic cardiomyopathy for viral genomic material within myocytes by polymerase chain reaction, and for the presence of myocarditis by light microscopy. Thirty-one (31) formalin-fixed hearts from domestic cats who died of idiopathic cardiomyopathy were randomly selected from pathology archives. Seventeen (17) formalin-fixed hearts from healthy cats were similarly selected as normal controls. The polymerase chain reaction (PCR) was used to evaluate myocardial tissue for the presence of viral genome from feline panleukopenia virus, herpes virus, calici virus, and corona virus. Hearts were examined using light microscopy for histologic evidence of myocarditis according to the Dallas criteria. Panleukopenia virus was identified by PCR in 10 of 31 cats with cardiomyopathy but in none of the controls. Neither cardiomyopathic or control cats tested positive by PCR for herpes virus, calici virus, and corona virus. Myocarditis was detected by histologic examination in 18 of 31 cardiomyopathic cats and in none of 17 control cats. Myocarditis and or feline panleukopenia virus genome was detected in felines with idiopathic hypertrophic, dilated, and restrictive cardiomyopathy, suggesting a possible role of viral infection and inflammation in the pathogenesis of cardiomyopathy in this species.

Repetitive coxsackievirus infection induces cardiac dilatation in post-myocarditic mice

The relation between mycarditis and dilated cardiomyopathy (DCM) is controversial. To clarify the pathogenic mechanism of these diseases, the present study examined the effect of repetitive inoculation with coxsackievirus B3 (CVB3) in post-myocarditic mice. Inbred 3-week-old A/J mice were inoculated intraperitoneally with CVB3 (Nancy strain; 2x10(4) plaque-forming units) and reinfected in the same manner with CVB3 at 40 weeks (3W+/40W+). All mice were killed at 42 weeks old. The weight of the hearts of the 3W+/40W+ group were significantly increased compared with those of the 3W-/40W+ group, and both the heart weight/body weight and lung weight/body weight ratios of the 3W+/40W+ group were also significantly increased over those of the 3W-/40W- group, although the levels of serum neutralizing antibody titers were significantly increased in the 3W+/40W+ group over the level of the other groups. No increase in inflammatory cell infiltration or fibrosis progression was observed in the 3W+/40W+ group relative to the 3W+/40W- group, but the second inoculation resulted in a significant left ventricular dilatation and in left and right ventricular free wall thinning (3.31+/-0.20 mm vs 2.61+/-0.19 mm, p<0.05; 0.54+/-0.09 mm vs 0.72+/-0.16 mm, p<0.05, respectively). The sarcomere length was also significantly increased in the 3W+/40W+ group compared with that of the other groups, as determined by electron microscopy. Degenerative or necrotic areas in the infected hearts were not stained with anti-mouse IgG antibody, but were stained, only in 3W+/40W+ mice, with anti-mouse IgM antibody. The concentrations of TNF-alpha in the hearts of the 3W+/40W+ group were increased significantly over those of the 3W+/40W- group. Repetitive CVB3 infection produced cardiac dilatation without inflammatory cell infiltration in post- myocarditic mice. Autoimmunity mediated by the circulation of certain antibodies (eg, antibodies against the CVB3 genome or a CVB3-related protein) may be part of the pathogenic mechanism for this phenomenon. Thus, repetitive virus infection might contribute to the pathogenesis of cardiac dilatation.

Technical report: Part 2. Basic requirements for designing optimal PCR primers

Designing optimal polymerase chain reaction (PCR) primer sequences is one of the critical factors for successful PCR with sensitive, specific, and assay-to-assay reproducible results. In this review, all the requirements of PCR primer sequences are summarized, such as location, size of amplicon, length of primers, nucleotide composition, Tm, 3' terminal hybridization strength and frequency, hairpin formation energy, primer-to-primer interaction, specificity, and location of mismatches to sequences of cross-hybridization. The report also discusses how to explore these various types of information for more advanced PCR applications, which include nested PCR, multiplex PCR, competitive PCR, long PCR, point mutation detection, degenerate primers, and PCR cloning.

Favorable left ventricular remodeling following large myocardial infarction by exercise training. Effect on ventricular morphology and gene expression

Continued adverse remodeling of myocardium after infarction may lead to progressive ventricular dilation and heart failure. We tested the hypothesis that exercise training in a healed myocardial infarction-dysfunction rat model can favorably modify the adverse effects of ventricular remodeling including attenuation of abnormal myosin gene expression. Sprague-Dawley rats were subjected to either proximal LAD ligation or sham operation. At 5 wk after the operation, animals were randomly assigned to sedentary conditions or 6 wk of graduated swim training, creating four experimental groups: infarct sedentary (IS), infarct exercise (IE), sham sedentary (SS), and sham exercise (SE). At 11 wk all rats were sacrificed and analyzed. Compared to sedentary infarct controls, exercise training attenuated left ventricular (LV) dilation and allowed more hypertrophy of the non infarct wall. The exercise-trained hearts also showed a reduction in the estimated peak wall tension. Northern blot analysis showed an increase in beta-myosin heavy chain expression in the hearts of the sedentary infarction group soon after infarction when compared to sham controls. However, with exercise training, there was a significant attenuation of the beta-myosin heavy chain expression in the myocardium. Exercise training in a model of left ventricular dysfunction after healed myocardial infarction can improve the adverse remodeling process by attenuating ventricular dilation and reducing wall tension. The abnormal beta-myosin expression was also attenuated in the exercise trained group. This is evidence that abnormal gene expression following severe myocardial infarction dysfunction can be favorably modified by an intervention.

Persistence of virus and viral genome in myocardium after coxsackievirus B3-induced murine myocarditis

Following infection with Coxsackievirus B3 (CVB3), A-strain mice develop ongoing myocarditis that persists after the virus ceases to be cultivatable from heart tissue. We studied the natural history of this virus-induced but apparently autoimmune inflammation by means of in situ hybridization (ISH) and by polymerase chain reaction (PCR). Both ISH and culture allowed detection of virus up to 2 weeks post-infection in virtually all heart tissues. In contrast, PCR revealed the presence of viral genome for a substantially longer period of time, i.e. at least 34 days after CVB3 infection. Similarly, the majority of mice showed myocardial inflammation at this time point. However, the persistence of virus did not correlate with ongoing myocarditis, and vice versa. Most mice with ongoing myocarditis produced heart myosin autoantibodies, most probably as a result of tissue damage. The lack of correlation between presence of ongoing inflammation and persistence of virus supports our previous view that the late phase of CVB3-induced myocarditis is mediated by autoimmunological mechanisms.

Viral infection and the pathogenesis of dilated cardiomyopathy

Long-term follow-up studies of patients with suspected viral myocarditis reveal progression to dilated cardiomyopathy (DCM) in a significant number of cases. Thus, an underlying viral etiology has been hypothesized in the pathogenesis of ongoing heart disease that leads to DCM. Recent application of molecular biology in clinical diagnosis has strengthened this hypothesis. By use of probe hybridization and polymerase chain reaction, enteroviral RNA has been detected in the myocardium of patients at all stages of the disease process: myocarditis, chronic heart disease, and DCM. Experimental murine models of enterovirus-induced heart disease provide a framework for examining the pathogenic mechanisms. Viral cytotoxicity, immunological responses, viral RNA persistence, and spasm of the coronary microvasculature are all implicated in the ongoing disease process. Abnormal cardiac function and heart failure are attributed to the pathological changes that occur.

Quantitation of enteroviral RNA by competitive polymerase chain reaction

The polymerase chain reaction (PCR) is a new diagnostic technique for the detection of enteroviral infection; however, it currently provides only qualitative results. The aim of this study was to adapt PCR for the accurate quantitation of enteroviral RNA in clinical specimens. For this purpose, we designed a standard RNA which was homologous to sequences at the 5' end of the coxsackie B3 enterovirus genome but contained a single-base-pair mutation which created a novel internal restriction site. Serial dilutions of this standard template RNA were mixed with a fixed concentration of coxsackie B3 enterovirus RNA. The viral and standard templates were reversed transcribed to cDNA and coamplified by PCR, and a comparison of the radioactive PCR products was made. Since the templates were both present in a single reaction tube and competed for the same primers, the ratio of products remained proportional throughout the amplification process. By this approach, a fourfold-difference in viral titer was clearly distinguishable. Moreover, we were able to accurately quantitate as few as 15 50% tissue culture infectious doses, which reflects common clinical viral titers. This study lays the foundation for quantitation of enteroviral RNA in clinical specimens and establishes a technique that can readily be applied to the diagnosis of enteroviral infection.

WIN 54954 treatment of mice infected with a diabetogenic strain of group B coxsackievirus

The therapeutic efficacy of an experimental antiviral agent, WIN 54954, was evaluated in a mouse model in which infection by coxsackievirus B4 (CVB4) strain E2 was followed by diabetes mellitus. Male CD1 mice (age, 5 weeks) were inoculated with 10(4) PFU of CVB4. WIN 54954 was administered orally via gavage tube in a dose of either 5 or 50 mg/kg of body weight per day. Treatment was initiated on the day of inoculation and was continued for 10 days. Control animals received the xanthan gum carrier only. At 3 days postinoculation (p.i.), the mean titer of virus in the pancreas was found to be significantly lower in both the high-dose (P < 0.001) and low-dose (P < 0.05) treatment groups compared with that in the controls. Furthermore, islet histologic abnormalities were significantly less common in the high-dose group (P < 0.02) than in the controls. At 7 weeks p.i., both fasting and 1-h postprandial glucose levels in blood were significantly lower for both the high-dose (P < 0.001) and the low-dose (P < 0.01) treatment groups than in controls. The proportion of mice with persistent viral RNA in the pancreas at this time, as detected by polymerase chain reaction, was significantly reduced in the high-dose treatment group (4 of 11 mice) compared with that in the controls (7 of 8 mice). When mice received 50 mg of WIN 54954 per kg daily beginning at either 48 or 72 h postinoculation, the titers in the pancreas were again significantly reduced at 3 days p.i. compared with those in the controls (P < 0.01 and P < 0.05, respectively). Thus, WIN 54954 effectively reduces virus replication and islet histologic changes acutely and decreases, at 7 weeks, both the metabolic alteration associated with diabetes mellitus and the incidence of detectable viral RNA in the pancreas.