Shared Molecular Mechanisms of Hypertrophic Cardiomyopathy and Its Clinical Presentations: Automated Molecular Mechanisms Extraction Approach

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease with a prevalence of 1 in 500 people and varying clinical presentations. Although there is much research on HCM, underlying molecular mechanisms are poorly understood, and research on the molecular mechanisms of its specific clinical presentations is scarce. Our aim was to explore the molecular mechanisms shared by HCM and its clinical presentations through the automated extraction of molecular mechanisms. Molecular mechanisms were congregated by a query of the INDRA database, which aggregates knowledge from pathway databases and combines it with molecular mechanisms extracted from abstracts and open-access full articles by multiple machine-reading systems. The molecular mechanisms were extracted from 230,072 articles on HCM and 19 HCM clinical presentations, and their intersections were found. Shared molecular mechanisms of HCM and its clinical presentations were represented as networks; the most important elements in the intersections’ networks were found, centrality scores for each element of each network calculated, networks with reduced level of noise generated, and cooperatively working elements detected in each intersection network. The identified shared molecular mechanisms represent possible mechanisms underlying different HCM clinical presentations. Applied methodology produced results consistent with the information in the scientific literature.

Oral batyl alcohol supplementation rescues decreased cardiac conduction in ether phospholipid-deficient mice

Plasmalogens (Pls) are a class of membrane phospholipids which serve a number of essential biological functions. Deficiency of Pls is associated with common disorders such as Alzheimer's disease or ischemic heart disease. A complete lack of Pls due to genetically determined defective biosynthesis gives rise to rhizomelic chondrodysplasia punctata (RCDP), characterized by a number of severe disabling pathologic features and death in early childhood. Frequent cardiac manifestations of RCDP include septal defects, mitral valve prolapse, and patent ductus arteriosus. In a mouse model of RCDP, reduced nerve conduction velocity was partially rescued by dietary oral supplementation of the Pls precursor batyl alcohol (BA). Here, we examine the impact of Pls deficiency on cardiac impulse conduction in a similar mouse model (Gnpat KO). In-vivo electrocardiographic recordings showed that the duration of the QRS complex was significantly longer in Gnpat KO mice than in age- and sex-matched wild-type animals, indicative of reduced cardiac conduction velocity. Oral supplementation of BA for 2 months resulted in normalization of cardiac Pls levels and of the QRS duration in Gnpat KO mice but not in untreated animals. BA treatment had no effect on the QRS duration in age-matched wild-type mice. These data suggest that Pls deficiency is associated with increased ventricular conduction time which can be rescued by oral BA supplementation.

Association Between Genetic Variation in the SCN10A Gene and Cardiac Conduction Abnormalities in Patients With Hypertrophic Cardiomyopathy

Arrhythmias are associated with reduced quality of life and poor prognosis in patients with hypertrophic cardiomyopathy (HCM). Recent genome-wide association studies revealed that a nonsynonymous single nucleotide polymorphism, rs6795970, in the SCN10A gene was associated with the PR interval. We examined whether the PR prolonging allele (A allele) in the SCN10A gene may be associated with cardiac conduction abnormalities in HCM patients.We genotyped the polymorphism in 149 HCM patients. Conduction abnormalities were defined as first-degree heart block, bundle-branch block, and bifascicular heart block. Patients were divided into two groups: group A consisted of 122 patients (82%) without a conduction abnormality; and group B consisted of 27 patients (18%) with one or more cardiac conduction abnormalities. The frequency distribution of the SCN10A genotypes (G/G, G/A, and A/A) among the patients with HCM was 71%, 26%, and 3%, respectively. A cardiac conduction abnormality was documented in 9% with G/G and 40% with G/A or A/A. There was a significant difference in the genotype distribution between the two groups (P = 0.0002). In the dominant A allele model, there was a significant difference in genotypes between the two groups (P < 0.0001). In addition, the A allele remained significant after adjusting for other covariates in a multivariate model (odds ratio = 6.30 [95% confidence interval: 2.24 to 19.09], P = 0.0005).The rs6795970 in the SCN10A gene, which is reported to carry a high risk of heart block, might be associated with cardiac conduction abnormalities in HCM patients.

Atrial and ventricular arrhythmias in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease caused by mutations in genes coding for cardiac sarcomeres. HCM is the most common inherited heart disease, with a prevalence of 0.2%. There are multiple genetic variants that cause pleomorphic clinical attributes and disease characterized by myocardial disarray and myocardial hypertrophy. Patients are at an increased risk of atrial and ventricular arrhythmias. Management of these arrhythmias is complex. Atrial fibrillation is associated with increased mortality and thromboembolism. Ventricular arrhythmias are life threatening and best treated with an implantable defibrillator.

Exercise capacity and paroxysmal atrial fibrillation in patients with hypertrophic cardiomyopathy

Background

Atrial fibrillation (AF) is the most common arrhythmia among patients with hypertrophic cardiomyopathy (HCM). The relationship between paroxysmal AF and exercise capacity in this population is incompletely understood.

Methods

Patients with HCM underwent symptom-limited cardiopulmonary testing with expired gas analysis at Stanford Hospital between October 2006 and October 2012. Baseline demographics, medical histories and resting echocardiograms were obtained for all subjects. Diagnosis of AF was established by review of medical records and baseline ECG. Those with paroxysmal AF were in sinus rhythm at the time of cardiopulmonary testing with expired gas analysis. Exercise intolerance was defined as peak VO2<20 mL/kg/min. We used multivariate logistic regression to evaluate the association between exercise intolerance and paroxysmal AF.

Results

Among the 265 patients recruited, 55 had AF (28 paroxysmal and 27 permanent). Compared with those without AF, subjects with paroxysmal AF were older, more likely to use antiarrhythmic and anticoagulant medications, and had larger left atria. Patients with paroxysmal AF achieved lower peak VO2 (21.9±9.2 mL/kg/min vs 26.9±10.8 mL/kg/min, p=0.02) and were more likely to have exercise intolerance (61% vs 28%, p<0.001) compared with those without AF. After adjustment for age, sex and body mass index (BMI) exercise intolerance remained significantly associated with paroxysmal AF (OR 4.65, 95% CI 1.83 to 11.83, p=0.001).

Conclusions

Patients with HCM and paroxysmal AF demonstrate exercise intolerance despite being in sinus rhythm at the time of exercise testing.

Early progress in epigenetic regulation of endothelin pathway genes

Control of gene transcription is a major regulatory determinant for function of the endothelin pathway. Epigenetic mechanisms act on tissue-specific gene expression during development and in response to physiological stimuli. Most of the limited evidence available on epigenetic regulation of the endothelin pathway focuses on the EDN1 and EDNRB genes. Examination of whole genome databases suggests that both genes are influenced by histone modifications and DNA methylation. This interpretation is supported by studies directed at detecting epigenetic action on the two genes. The clearest illustration of epigenetic factors altering endothelin signalling is DNA methylation-associated EDNRB silencing during tumourigenesis. This review summarizes our current understanding of epigenetic regulation of the endothelin pathway genes. LINKED ARTICLES This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Endothelin-2, the forgotten isoform: emerging role in the cardiovascular system, ovarian development, immunology and cancer

Endothelin-2 [ET-2; also known as vasoactive intestinal contractor (VIC), in rodents] differs from endothelin-1 (ET-1) by only two amino acids, and unlike the third isoform, endothelin-3 (ET-3), it has the same affinity as ET-1 for both ET(A) and ET(B) receptors. It is often assumed that ET-2 would mimic the actions of the more abundant ET-1 and current pharmacological interventions used to inhibit the ET system would also block the actions of ET-2. These assumptions have focused research on ET-1 with ET-2 studied in much less detail. Recent research suggests that our understanding of the ET family requires re-evaluation. Although ET-2 is very similar in structure as well as pharmacology to ET-1, and may co-exist in the same tissue compartments, there is converging evidence for an important and distinct ET-2 pathway. Specifically is has been demonstrated that ET-2 has a key role in ovarian physiology, with ET-2-mediated contraction proposed as a final signal facilitating ovulation. Furthermore, ET-2 may also have a pathophysiological role in heart failure, immunology and cancer. Comparison of ET-2 versus ET-1 mRNA expression suggests this may be accomplished at the level of gene expression but differences may also exist in peptide synthesis by enzymes such as endothelin converting enzymes (ECEs) and chymase, which may allow the two pathways to be distinguished pharmacologically and become separate drug targets. LINKED ARTICLES This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is a myocardial disease characterized by myocardial hypertrophy, disorganization of cardiac myocytes, and fibrosis. Twenty-five percent of patients have a dynamic left ventricular outflow tract gradient caused by the combined effects of rapid ventricular ejection, a narrowed outflow tract, and systolic anterior motion of the mitral valve. Most cases are caused by mutations in genes that encode cardiac sarcomeric proteins. Patients present at all ages with chest pain, dyspnea, palpitations, and syncope. The most important complications of the disease are sudden cardiac death, heart failure, and thromboembolism. The principal aims of management are the alleviation of symptoms and the prevention of sudden death. In patients with substantial left ventricular outflow tract obstruction, interventions that reduce the magnitude of the outflow tract gradient (disopyramide, verapamil, β-blockade, alcohol ablation of the interventricular septum, dual-chamber pacing, and surgery) often improve symptoms. Therapeutic options in patients without left ventricular outflow tract obstruction are more limited. Clinical risk stratification is used to estimate the risk of sudden death and to target effective prophylactic treatment with an implantable cardioverter defibrillator.

Pharmacogenetic interactions between Angiotensin-converting enzyme insertion/deletion polymorphism and response to cibenzoline in patients with hypertrophic obstructive cardiomyopathy

Cibenzoline, a Class I antiarrhythmic agent, can attenuate the left ventricular pressure gradient (LVPG) in patients with hypertrophic obstructive cardiomyopathy (HOCM). An association between the insertion/deletion polymorphism of the angiotensin-converting enzyme (ACE) gene and the progression of left ventricular hypertrophy in patients with hypertrophic cardiomyopathy has been reported. The aim of this study was to investigate the pharmacogenetic interactions between the ACE insertion/deletion polymorphism and the response to cibenzoline in patients with HOCM. Twenty-four patients with HOCM participated in this study. The LVPG and left ventricular function were measured by echocardiography before and 2 hours after administration of a single oral dose of 200 mg cibenzoline. The ACE insertion/deletion polymorphism was genotyped. The frequencies of the genotypes D/D, D/I, and I/I were 16%, 42%, and 42%, respectively. Before administration of cibenzoline, the LVPG was higher in patients with the D allele than in those without it (105 +/- 47 mm Hg versus 64 +/- 24 mm Hg, P = 0.0195). After administration of cibenzoline, the LVPG significantly decreased to 41 +/- 27 mm Hg in those with the D allele (P = 0.0001) and to 33 +/- 24 mm Hg in those without it (P = 0.0003). The LVPG in patients with the D allele was significantly decreased by cibenzoline when compared with patients without the allele (64 +/- 45 mm Hg versus 31 +/- 17 mm Hg, P = 0.038). Patients with HOCM with the ACE D allele had a high LVPG. Cibenzoline was more effective in patients with HOCM with the ACE D allele.

Genetics of atrial fibrillation

Recent studies of atrial fibrillation (AF) have identified mutations in a series of ion channels; however, these mutations appear to be relatively rare causes of AF. A genome-wide association study has identified novel variants on chromosome 4 associated with AF, although the mechanism of action for these variants remains unknown. Ultimately, a greater understanding of the genetics of AF should yield insights into novel pathways, therapeutic targets, and diagnostic testing for this common arrhythmia.

Clinical impact of atrial fibrillation in patients with hypertrophic cardiomyopathy. Results from Kochi RYOMA Study

BACKGROUND

There have been few studies of the clinical features of hypertrophic cardiomyopathy (HCM) in a community-based patient cohort in Japan.

METHODS AND RESULTS

Cardiomyopathy registration was established in Kochi Prefecture and named the Kochi RYOMA (registry of myocardial diseases) study, consisting of 9 hospitals that registered 261 patients with a diagnosis of HCM. At registration, 74 patients (28%) had documented paroxysmal or chronic atrial fibrillation (AF). Although most patients (93%) were in New York Heart Association (NYHA) class I or II, 17 of the 18 patients in NYHA III had AF; 37 of the 74 patients with AF suffered from morbid events (embolism and/or heart failure (HF) admission), and 15 of 19 patients with embolic events had AF prior to or at the time of embolism. Of the 29 patients who had a history of HF admission, 8 had left ventricular systolic dysfunction, and the other 21 patients were hospitalized because of diastolic HF. AF occurred prior to HF in 20 of those 21 patients. Furthermore, 19 of those 20 patients with AF and diastolic HF were hospitalized within 1 year after detection of AF.

CONCLUSIONS

In an unselected regional registry, AF was the major determinant of clinical deteriorations in patients with HCM.

Genetics of atrial fibrillation

Recent studies of AF have identified mutations in a series of ion channels; however, these mutations appear to be relatively rare causes of AF. A genome-wide association study has identified novel variants on chromosome 4 associated with AF, although the mechanism of action for these variants remains unknown. Ultimately, a greater understanding of the genetics of AF should yield insights into novel pathways, therapeutic targets, and diagnostic testing for this common arrhythmia.