Creatine kinase adenosine triphosphate and phosphocreatine energy supply in a single kindred of patients with hypertrophic cardiomyopathy

Human cardiac metabolism

The heart is the most metabolically active organ in the human body, and cardiac metabolism has been studied for decades. However, the bulk of studies have focused on animal models. The objective of this review is to summarize specifically what is known about cardiac metabolism in humans. Techniques available to study human cardiac metabolism are first discussed, followed by a review of human cardiac metabolism in health and in heart failure. Mechanistic insights, where available, are reviewed, and the evidence for the contribution of metabolic insufficiency to heart failure, as well as past and current attempts at metabolism-based therapies, is also discussed.

Allele-specific dysregulation of lipid and energy metabolism in early-stage hypertrophic cardiomyopathy

Introduction

Hypertrophic cardiomyopathy (HCM) results from pathogenic variants in sarcomeric protein genes that increase myocyte energy demand and lead to cardiac hypertrophy. However, it is unknown whether a common metabolic trait underlies cardiac phenotype at the early disease stage. To address this question and define cardiac biochemical pathology in early-stage HCM, we studied two HCM mouse models that express pathogenic variants in cardiac troponin T (Tnt2) or myosin heavy chain (Myh6) genes, and have marked differences in cardiac imaging phenotype, mitochondrial function at early disease stage.

Methods

We used a combination of echocardiography, transcriptomics, mass spectrometry-based untargeted metabolomics (GC-TOF, HILIC, CSH-QTOF), and computational modeling (CardioNet) to examine cardiac structural and metabolic remodeling at early disease stage (5 weeks of age) in R92W-TnT+/- and R403Q-MyHC+/- mutant mice. Data from mutants was compared with respective littermate controls (WT).

Results

Allele-specific differences in cardiac phenotype, gene expression and metabolites were observed at early disease stage. LV diastolic dysfunction was prominent in TnT mutants. Differentially-expressed genes in TnT mutant hearts were predominantly enriched in the Krebs cycle, respiratory electron transport, and branched-chain amino acid metabolism, whereas MyHC mutants were enriched in mitochondrial biogenesis, calcium homeostasis, and liver-X-receptor signaling. Both mutant hearts demonstrated significant alterations in levels of purine nucleosides, trisaccharides, dicarboxylic acids, acylcarnitines, phosphatidylethanolamines, phosphatidylinositols, ceramides and triglycerides; 40.4 % of lipids and 24.7 % of metabolites were significantly different in TnT mutants, whereas 10.4 % of lipids and 5.8 % of metabolites were significantly different in MyHC mutants. Both mutant hearts had a lower abundance of unsaturated long-chain acyl-carnitines (18:1, 18:2, 20:1), but only TnT mutants showed enrichment of FA18:0 in ceramide and cardiolipin species. CardioNet predicted impaired energy substrate metabolism and greater phospholipid remodeling in TnT mutants than in MyHC mutants.

Conclusions

Our systems biology approach revealed marked differences in metabolic remodeling in R92W-TnT and R403Q-MyHC mutant hearts, with TnT mutants showing greater derangements than MyHC mutants, at early disease stage. Changes in cardiolipin composition in TnT mutants could contribute to impairment of energy metabolism and diastolic dysfunction observed in this study, and predispose to energetic stress, ventricular arrhythmias under high workloads such as exercise.

Modeling cardiomyocyte signaling and metabolism predicts genotype-to-phenotype mechanisms in hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (HCM) is a significant precursor of heart failure and sudden cardiac death, primarily caused by mutations in sarcomeric and structural proteins. Despite the extensive research on the HCM genotype, the complex and context-specific nature of many signaling and metabolic pathways linking the HCM genotype to phenotype has hindered therapeutic advancements for patients. Here, we have developed a computational model of HCM encompassing cardiomyocyte signaling and metabolic networks and their associated interactions. Utilizing a stochastic logic-based ODE approach, we linked cardiomyocyte signaling to the metabolic network through a gene regulatory network and post-translational modifications. We validated the model against published data on activities of signaling species in the HCM context and transcriptomes of two HCM mouse models (i.e., R403Q-αMyHC and R92W-TnT). Our model predicts that HCM mutation induces changes in metabolic functions such as ATP synthase deficiency and a transition from fatty acids to carbohydrate metabolism. The model indicated major shifts in glutamine-related metabolism and increased apoptosis after HCM-induced ATP synthase deficiency. We predicted that the transcription factors STAT, SRF, GATA4, TP53, and FoxO are the key regulators of cardiomyocyte hypertrophy and apoptosis in HCM in alignment with experiments. Moreover, we identified shared (e.g., activation of PGC1α by AMPK, and FHL1 by titin) and context-specific mechanisms (e.g., regulation of Ca2+ sensitivity by titin in HCM patients) that may control genotype-to-phenotype transition in HCM across different species or mutations. We also predicted potential combination drug targets for HCM (e.g., mavacamten plus ROS inhibitors) preventing or reversing HCM phenotype (i.e., hypertrophic growth, apoptosis, and metabolic remodeling) in cardiomyocytes. This study provides new insights into mechanisms linking genotype to phenotype in familial hypertrophic cardiomyopathy and offers a framework for assessing new treatments and exploring variations in HCM experimental models.

Single-nucleus RNA/ATAC-seq in early-stage HCM models predicts SWI/SNF-activation in mutant-myocytes, and allele-specific differences in fibroblasts

Hypertrophic cardiomyopathy (HCM) is associated with phenotypic variability. To gain insights into transcriptional regulation of cardiac phenotype, single-nucleus linked RNA-/ATAC-seq was performed in 5-week-old control mouse-hearts (WT) and two HCM-models (R92W-TnT, R403Q-MyHC) that exhibit differences in heart size/function and fibrosis; mutant data was compared to WT. Analysis of 23,304 nuclei from mutant hearts, and 17,669 nuclei from WT, revealed similar dysregulation of gene expression, activation of AP-1 TFs (FOS, JUN) and the SWI/SNF complex in both mutant ventricular-myocytes. In contrast, marked differences were observed between mutants, for gene expression/TF enrichment, in fibroblasts, macrophages, endothelial cells. Cellchat predicted activation of pro-hypertrophic IGF-signaling in both mutant ventricular-myocytes, and profibrotic TGFβ-signaling only in mutant-TnT fibroblasts. In summary, our bioinformatics analyses suggest that activation of IGF-signaling, AP-1 TFs and the SWI/SNF chromatin remodeler complex promotes myocyte hypertrophy in early-stage HCM. Selective activation of TGFβ-signaling in mutant-TnT fibroblasts contributes to genotype-specific differences in cardiac fibrosis.

Maintaining energy provision in the heart: the creatine kinase system in ischaemia-reperfusion injury and chronic heart failure

The non-stop provision of chemical energy is of critical importance to normal cardiac function, requiring the rapid turnover of ATP to power both relaxation and contraction. Central to this is the creatine kinase (CK) phosphagen system, which buffers local ATP levels to optimise the energy available from ATP hydrolysis, to stimulate energy production via the mitochondria and to smooth out mismatches between energy supply and demand. In this review, we discuss the changes that occur in high-energy phosphate metabolism (i.e., in ATP and phosphocreatine) during ischaemia and reperfusion, which represents an acute crisis of energy provision. Evidence is presented from preclinical models that augmentation of the CK system can reduce ischaemia-reperfusion injury and improve functional recovery. Energetic impairment is also a hallmark of chronic heart failure, in particular, down-regulation of the CK system and loss of adenine nucleotides, which may contribute to pathophysiology by limiting ATP supply. Herein, we discuss the evidence for this hypothesis based on preclinical studies and in patients using magnetic resonance spectroscopy. We conclude that the correlative evidence linking impaired energetics to cardiac dysfunction is compelling; however, causal evidence from loss-of-function models remains equivocal. Nevertheless, proof-of-principle studies suggest that augmentation of CK activity is a therapeutic target to improve cardiac function and remodelling in the failing heart. Further work is necessary to translate these findings to the clinic, in particular, a better understanding of the mechanisms by which the CK system is regulated in disease.

Lipid metabolism drives allele-specific early-stage hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) results from pathogenic variants in sarcomeric protein genes, that increase myocyte energy demand and lead to cardiac hypertrophy. But it is unknown whether a common metabolic trait underlies the cardiac phenotype at early disease stage. This study characterized two HCM mouse models (R92W-TnT, R403Q-MyHC) that demonstrate differences in mitochondrial function at early disease stage. Using a combination of cardiac phenotyping, transcriptomics, mass spectrometry-based metabolomics and computational modeling, we discovered allele-specific differences in cardiac structure/function and metabolic changes. TnT-mutant hearts had impaired energy substrate metabolism and increased phospholipid remodeling compared to MyHC-mutants. TnT-mutants showed increased incorporation of saturated fatty acid residues into ceramides, cardiolipin, and increased lipid peroxidation, that could underlie allele-specific differences in mitochondrial function and cardiomyopathy.

Cardiac 31P MR spectroscopy: development of the past five decades and future vision-will it be of diagnostic use in clinics?

In the past five decades, the use of the magnetic resonance (MR) technique for cardiovascular diseases has engendered much attention and raised the opportunity that the technique could be useful for clinical applications. MR has two arrows in its quiver: One is magnetic resonance imaging (MRI), and the other is magnetic resonance spectroscopy (MRS). Non-invasively, highly advanced MRI provides unique and profound information about the anatomical changes of the heart. Excellently developed MRS provides irreplaceable and insightful evidence of the real-time biochemistry of cardiac metabolism of underpinning diseases. Compared to MRI, which has already been successfully applied in routine clinical practice, MRS still has a long way to travel to be incorporated into routine diagnostics. Considering the exceptional potential of ³¹P MRS to measure the real-time metabolic changes of energetic molecules qualitatively and quantitatively, how far its powerful technique should be waited before a successful transition from "bench-to-bedside" is enticing. The present review highlights the seminal studies on the chronological development of cardiac ³¹P MRS in the past five decades and the future vision and challenges to incorporating it for routine diagnostics of cardiovascular disease.

Phosphorus Magnetic Resonance Spectroscopy (31P MRS) and Cardiovascular Disease: The Importance of Energy

Background and Objectives: The heart is the organ with the highest metabolic demand in the body, and it relies on high ATP turnover and efficient energy substrate utilisation in order to function normally. The derangement of myocardial energetics may lead to abnormalities in cardiac metabolism, which herald the symptoms of heart failure (HF). In addition, phosphorus magnetic resonance spectroscopy (³¹P MRS) is the only available non-invasive method that allows clinicians and researchers to evaluate the myocardial metabolic state in vivo. This review summarises the importance of myocardial energetics and provides a systematic review of all the available research studies utilising ³¹P MRS to evaluate patients with a range of cardiac pathologies. Materials and Methods: We have performed a systematic review of all available studies that used ³¹P MRS for the investigation of myocardial energetics in cardiovascular disease. Results: A systematic search of the Medline database, the Cochrane library, and Web of Science yielded 1092 results, out of which 62 studies were included in the systematic review. The ³¹P MRS has been used in numerous studies and has demonstrated that impaired myocardial energetics is often the beginning of pathological processes in several cardiac pathologies. Conclusions: The ³¹P MRS has become a valuable tool in the understanding of myocardial metabolic changes and their impact on the diagnosis, risk stratification, and prognosis of patients with cardiovascular diseases.

How cytoskeletal proteins regulate mitochondrial energetics in cell physiology and diseases

Mitochondria are ubiquitous organelles that play a pivotal role in the supply of energy through the production of adenosine triphosphate in all eukaryotic cells. The importance of mitochondria in cells is demonstrated in the poor survival outcomes observed in patients with defects in mitochondrial gene or RNA expression. Studies have identified that mitochondria are influenced by the cell's cytoskeletal environment. This is evident in pathological conditions such as cardiomyopathy where the cytoskeleton is in disarray and leads to alterations in mitochondrial oxygen consumption and electron transport. In cancer, reorganization of the actin cytoskeleton is critical for trans-differentiation of epithelial-like cells into motile mesenchymal-like cells that promotes cancer progression. The cytoskeleton is critical to the shape and elongation of neurons, facilitating communication during development and nerve signalling. Although it is recognized that cytoskeletal proteins physically tether mitochondria, it is not well understood how cytoskeletal proteins alter mitochondrial function. Since end-stage disease frequently involves poor energy production, understanding the role of the cytoskeleton in the progression of chronic pathology may enable the development of therapeutics to improve energy production and consumption and slow disease progression.

This article is part of the theme issue ‘The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease’.

Altered contractility in mutation-specific hypertrophic cardiomyopathy: A mechano-energetic in silico study with pharmacological insights

Introduction: Mavacamten (MAVA), Blebbistatin (BLEB), and Omecamtiv mecarbil (OM) are promising drugs directly targeting sarcomere dynamics, with demonstrated efficacy against hypertrophic cardiomyopathy (HCM) in (pre)clinical trials. However, the molecular mechanism affecting cardiac contractility regulation, and the diseased cell mechano-energetics are not fully understood yet. Methods: We present a new metabolite-sensitive computational model of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) electromechanics to investigate the pathology of R403Q HCM mutation and the effect of MAVA, BLEB, and OM on the cell mechano-energetics. Results: We offer a mechano-energetic HCM calibration of the model, capturing the prolonged contractile relaxation due to R403Q mutation (∼33%), without assuming any further modifications such as an additional Ca²⁺ flux to the thin filaments. The HCM model variant correctly predicts the negligible alteration in ATPase activity in R403Q HCM condition compared to normal hiPSC-CMs. The simulated inotropic effects of MAVA, OM, and BLEB, along with the ATPase activities in the control and HCM model variant agree with in vitro results from different labs. The proposed model recapitulates the tension-Ca²⁺ relationship and action potential duration change due to 1 µM OM and 5 µM BLEB, consistently with in vitro data. Finally, our model replicates the experimental dose-dependent effect of OM and BLEB on the normalized isometric tension. Conclusion: This work is a step toward deep-phenotyping the mutation-specific HCM pathophysiology, manifesting as altered interfilament kinetics. Accordingly, the modeling efforts lend original insights into the MAVA, BLEB, and OM contributions to a new interfilament balance resulting in a cardioprotective effect.

Efficient Correction of a Hypertrophic Cardiomyopathy Mutation by ABEmax-NG

[Figure: see text].

LC-MS Based Metabolomics Study of the Effects of EGCG on A549 Cells

(−)-Epigallocatechin-3-gallate (EGCG) is the main bioactive catechin in green tea. The antitumor activity of EGCG has been confirmed in various types of cancer, including lung cancer. However, the precise underlying mechanisms are still largely unclear. In the present study, we investigated the metabolite changes in A549 cells induced by EGCG in vitro utilizing liquid chromatography-mass spectrometry (LC-MS)-based metabolomics. The result revealed 33 differentially expressed metabolites between untreated and 80 μM EGCG-treated A549 cells. The altered metabolites were involved in the metabolism of glucose, amino acid, nucleotide, glutathione, and vitamin. Two markedly altered pathways, including glycine, serine and threonine metabolism and alanine, aspartate and glutamate metabolism, were identified by MetaboAnalyst 5.0 metabolic pathway analysis. These results may provide potential clues for the intramolecular mechanisms of EGCG’s effect on A549 cells. Our study may contribute to future molecular mechanistic studies of EGCG and the therapeutic application of EGCG in cancer management.

Measuring Myocardial Energetics with Cardiovascular Magnetic Resonance Spectroscopy

The heart has the highest energy demands per gram of any organ in the body and energy metabolism fuels normal contractile function. Metabolic inflexibility and impairment of myocardial energetics occur with several common cardiac diseases, including ischemia and heart failure. This review explores several decades of innovation in cardiac magnetic resonance spectroscopy modalities and their use to noninvasively identify and quantify metabolic derangements in the normal, failing, and diseased heart. The implications of this noninvasive modality for predicting significant clinical outcomes and guiding future investigation and therapies to improve patient care are discussed.

Genetic study of pediatric hypertrophic cardiomyopathy in Egypt

Paediatric cardiomyopathy is a progressive and often lethal disorder and the most common cause of heart failure in children. Despite their severe outcomes, their genetic etiology is still poorly characterised. The current study aimed at uncovering the genetic background of idiopathic primary hypertrophic cardiomyopathy in a cohort of Egyptian children using targeted next-generation sequencing. The study included 24 patients (15 males and 9 females) presented to the cardiomyopathy clinic of Cairo University Children's Hospital with a median age of 2.75 (0.5-14) years. Consanguinity was positive in 62.5% of patients. A family history of hypertrophic cardiomyopathy was present in 20.8% of patients. Ten rare variants were detected in eight patients; two pathogenic variants (8.3%) in MBPC3 and MYH7, and eight variants of uncertain significance in MYBPC3, TTN, VCL, MYL2, CSRP3, and RBM20.Here, we report on the first national study in Egypt that analysed sarcomeric and non-sarcomeric variants in a cohort of idiopathic paediatric hypertrophic cardiomyopathy patients using next-generation sequencing. The current pilot study suggests that paediatric hypertrophic cardiomyopathy in Egypt might have a particular genetic background, especially with the high burden of consanguinity. Including the genetic testing in the routine diagnostic service is important for a better understanding of the pathophysiology of the disease, proper patient management, and at-risk detection. Genome-wide tests (whole exome/genome sequencing) might be better than the targeted sequencing approach to test primary hypertrophic cardiomyopathy patients in addition to its ability for the identification of novel genetic causes.

Preventative therapeutic approaches for hypertrophic cardiomyopathy

Sarcomeric gene mutations are associated with the development of hypertrophic cardiomyopathy (HCM). Current drug therapeutics for HCM patients are effective in relieving symptoms, but do not prevent or reverse disease progression. Moreover, due to heterogeneity in the clinical manifestations of the disease, patients experience variable outcomes in response to therapeutics. Mechanistically, alterations in calcium handling, sarcomeric disorganization, energy metabolism and contractility participate in HCM disease progression. While some similarities exist, each mutation appears to lead to mutation‐specific pathophysiology. Furthermore, these alterations may precede or proceed development of the pathology. This review assesses the efficacy of HCM therapeutics from studies performed in animal models of HCM and human clinical trials. Evidence suggests that a preventative rather than corrective therapeutic approach may be more efficacious in the treatment of HCM. In addition, a clear understanding of mutation‐specific mechanisms may assist in informing the most effective therapeutic mode of action.

Mitochondrial Energetics and Ca2+-Activated ATPase in Obstructive Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common genetic disease of the myocardium associated to mutations in sarcomeric genes, but the link between genotype and phenotype remains poorly understood. Magnetic resonance spectroscopy studies have demonstrated impaired cardiac energetics in patients with HCM, and altered mitochondria were described in biopsies, but little is known about possible perturbations of mitochondrial function and adenosine triphosphate (ATP) production/consumption. The aim of this study was to investigate possible abnormalities in mitochondrial enzymes generating/scavenging reactive oxygen species, and changes in the Ca²⁺-activated ATPases in myocardial tissue from patients with obstructive HCM undergoing surgical myectomy compared to unused donor hearts (CTRL). Methods and Results: Both the amount and activity of mitochondrial Complex I (nicotinamide adenine dinucleotide -reduced form, NADH, dehydrogenase) were upregulated in HCM vs. CTRL, whilst the activity of Complex V (ATP synthase) was not reduced and ATP levels were significantly higher in HCM vs. CTRL. Antioxidant Mn-activated superoxide dismutase (SOD2) and (m)-aconitase activities were increased in HCM vs. CTRL. The Cu/Zn-activated superoxide dismutase (SOD1) amount and mtDNA copy number were unaltered in HCM. Total Ca²⁺-activated ATPase activity and absolute amount were not different HCM vs. CTRL, but the ratio between ATPase sarcoplasmic/endoplasmic reticulum Ca²⁺ transporting type 2 (ATP2A2) and type 1 (ATP2A1), ATP2A2/ATP2A1, was increased in HCM in favor of the slow isoform (ATP2A2). Conclusion: HCM is characterized by mitochondrial Complex I hyperactivity and preserved Ca²⁺-activated ATPase activity with a partial switch towards slow ATP2A2. This data may give insight into the abnormal cellular energetics observed in HCM cardiomyopathy but other studies would need to be performed to confirm the observations described here.

Myocardial Energetics in Obesity: Enhanced ATP Delivery Through Creatine Kinase With Blunted Stress Response

BACKGROUND

Obesity is strongly associated with exercise intolerance and the development of heart failure. Whereas myocardial energetics and diastolic function are impaired in obesity, systolic function is usually preserved. This suggests that the rate of ATP delivery is maintained, but this has never been explored in human obesity. We hypothesized that ATP transfer rate through creatine kinase (CK) (k_f^CKrest) would be increased, compensating for depleted energy stores (phosphocreatine/ATP), but potentially limiting greater ATP delivery during increased workload. We hypothesized that these changes would normalize with weight loss.

METHODS

We recruited 80 volunteers (35 controls [body mass index 24±3 kg/m²], 45 obese [body mass index 35±5 kg/m²]) without coexisting cardiovascular disease. Participants underwent body composition analysis, magnetic resonance imaging of abdominal, liver, and myocardial fat content, left ventricular function, and ³¹P magnetic resonance spectroscopy to assess phosphocreatine/ATP and CK kinetics, at rest and during dobutamine stress. Obese volunteers were assigned to a dietary weight loss intervention, before reexamination.

RESULTS

At rest, although myocardial phosphocreatine/ATP was 14% lower in obesity (1.9±0.3 versus 2.2±0.2, P<0.001), k_f^Ckrest was 33% higher (0.23±0.07 s^-1 versus 0.16±0.08 s^-1, P=0.002), yielding no difference in overall resting ATP delivery (obese 2.5±0.9 µmol·g^-1·s^-1 versus control 2.2±1.1 µmol·g^-1·s^-1, P=0.232). In controls, increasing cardiac workload led to an increase in both k_f^CK (+86%, P<0.001) and ATP delivery (+80%, P<0.001). However, in obesity, similar stress led to no significant increase in either k_f^CK (P=0.117) or ATP delivery (P=0.608). This was accompanied by reduced systolic augmentation (absolute increase in left ventricular ejection fraction, obese +16±7% versus control +21±4%, P=0.031). Successful weight loss (-11±5% body weight) was associated with improvement of these energetic changes such that there was no significant difference in comparison with controls.

CONCLUSIONS

In the obese resting heart, the myocardial CK reaction rate is increased, maintaining ATP delivery despite reduced phosphocreatine/ATP. During increased workload, although the nonobese heart increases ATP delivery through CK, the obese heart does not; this is associated with reduced systolic augmentation and exercise tolerance. Weight loss reverses these energetic changes. This highlights myocardial energy delivery through CK as a potential therapeutic target to improve symptoms in obesity-related heart disease, and a fascinating modifiable pathway involved in the progression to heart failure, as well.

Differences in microRNA-29 and Pro-fibrotic Gene Expression in Mouse and Human Hypertrophic Cardiomyopathy

Background: Hypertrophic cardiomyopathy (HCM) is characterized by myocyte hypertrophy and fibrosis. Studies in two mouse models (R92W-TnT/R403Q-MyHC) at early HCM stage revealed upregulation of endothelin (ET1) signaling in both mutants, but TGFβ signaling only in TnT mutants. Dysregulation of miR-29 expression has been implicated in cardiac fibrosis. But it is unknown whether expression of miR-29a/b/c and profibrotic genes is commonly regulated in mouse and human HCM.

Methods: In order to understand mechanisms underlying fibrosis in HCM, and examine similarities/differences in expression of miR-29a/b/c and several profibrotic genes in mouse and human HCM, we performed parallel studies in rat cardiac myocyte/fibroblast cultures, examined gene expression in two mouse models of (non-obstructive) HCM (R92W-TnT, R403Q-MyHC)/controls at early (5 weeks) and established (24 weeks) disease stage, and analyzed publicly available mRNA/miRNA expression data from obstructive-HCM patients undergoing septal myectomy/controls (unused donor hearts).

Results: Myocyte cultures: ET1 increased superoxide/H₂O₂, stimulated TGFβ expression/secretion, and suppressed miR-29a expression in myocytes. The effect of ET1 on miR-29 and TGFβ expression/secretion was antagonized by N-acetyl-cysteine, a reactive oxygen species scavenger. Fibroblast cultures: ET1 had no effect on pro-fibrotic gene expression in fibroblasts. TGFβ1/TGFβ2 suppressed miR-29a and increased collagen expression, which was abolished by miR-29a overexpression. Mouse and human HCM: Expression of miR-29a/b/c was lower, and TGFB1/collagen gene expression was higher in TnT mutant-LV at 5 and 24 weeks; no difference was observed in expression of these genes in MyHC mutant-LV and in human myectomy tissue. TGFB2 expression was higher in LV of both mutant mice and human myectomy tissue. ACE2, a negative regulator of the renin-angiotensin-aldosterone system, was the most upregulated transcript in human myectomy tissue. Pathway analysis predicted upregulation of the anti-hypertrophic/anti-fibrotic liver X receptor/retinoid X receptor (LXR/RXR) pathway only in human myectomy tissue.

Conclusions: Our in vitro studies suggest that activation of ET1 signaling in cardiac myocytes increases reactive oxygen species and stimulates TGFβ secretion, which downregulates miR-29a and increases collagen in fibroblasts, thus contributing to fibrosis. Our gene expression studies in mouse and human HCM reveal allele-specific differences in miR-29 family/profibrotic gene expression in mouse HCM, and activation of anti-hypertrophic/anti-fibrotic genes and pathways in human HCM.

Neural-network classification of cardiac disease from 31P cardiovascular magnetic resonance spectroscopy measures of creatine kinase energy metabolism

BACKGROUND

The heart's energy demand per gram of tissue is the body's highest and creatine kinase (CK) metabolism, its primary energy reserve, is compromised in common heart diseases. Here, neural-network analysis is used to test whether noninvasive phosphorus (31P) cardiovascular magnetic resonance spectroscopy (CMRS) measurements of cardiac adenosine triphosphate (ATP) energy, phosphocreatine (PCr), the first-order CK reaction rate kf, and the rate of ATP synthesis through CK (CK flux), can predict specific human heart disease and clinical severity.

METHODS

The data comprised the extant 178 complete sets of PCr and ATP concentrations, kf, and CK flux data from human CMRS studies performed on clinical 1.5 and 3 Tesla scanners. Healthy subjects and patients with nonischemic cardiomyopathy, dilated (DCM) or hypertrophic disease, New York Heart Association (NYHA) class I-IV heart failure (HF), or with anterior myocardial infarction are included. Three-layer neural-networks were created to classify disease and to differentiate DCM, hypertrophy and clinical NYHA class in HF patients using leave-one-out training. Network performance was assessed using 'confusion matrices' and 'area-under-the-curve' (AUC) analyses of 'receiver operating curves'. Possible methodological bias and network imbalance were tested by segregating 1.5 and 3 Tesla data, and by data augmentation by random interpolation of nearest neighbors, respectively.

RESULTS

The network differentiated healthy, HF and non-HF cardiac disease with an overall accuracy of 84% and AUC > 90% for each category using the four CK metabolic parameters, alone. HF patients with DCM, hypertrophy, and different NYHA severity were differentiated with ~ 80% overall accuracy independent of CMRS methodology.

CONCLUSIONS

While sample-size was limited in some sub-classes, a neural network classifier applied to noninvasive cardiac 31P CMRS data, could serve as a metabolic biomarker for common disease types and HF severity with clinically-relevant accuracy. Moreover, the network's ability to individually classify disease and HF severity using CK metabolism alone, implies an intimate relationship between CK metabolism and disease, with subtle underlying phenotypic differences that enable their differentiation.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00181259.

Hypertrophic Cardiomyopathy: A Vicious Cycle Triggered by Sarcomere Mutations and Secondary Disease Hits

Significance: Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by left ventricular hypertrophy, diastolic dysfunction, and myocardial disarray. Disease onset occurs between 20 and 50 years of age, thus affecting patients in the prime of their life. HCM is caused by mutations in sarcomere proteins, the contractile building blocks of the heart. Despite increased knowledge of causal mutations, the exact path from genetic defect leading to cardiomyopathy is complex and involves additional disease hits. Recent Advances: Laboratory-based studies indicate that HCM development not only depends on the primary sarcomere impairment caused by the mutation but also on secondary disease-related alterations in the heart. Here we propose a vicious mutation-induced disease cycle, in which a mutation-induced energy depletion alters cellular metabolism with increased mitochondrial work, which triggers secondary disease modifiers that will worsen disease and ultimately lead to end-stage HCM. Critical Issues: Evidence shows excessive cellular reactive oxygen species (ROS) in HCM patients and HCM animal models. Oxidative stress markers are increased in the heart (oxidized proteins, DNA, and lipids) and serum of HCM patients. In addition, increased mitochondrial ROS production and changes in endogenous antioxidants are reported in HCM. Mutant sarcomeric protein may drive excessive levels of cardiac ROS via changes in cardiac efficiency and metabolism, mitochondrial activation and/or dysfunction, impaired protein quality control, and microvascular dysfunction. Future Directions: Interventions restoring metabolism, mitochondrial function, and improved ROS balance may be promising therapeutic approaches. We discuss the effects of current HCM pharmacological therapies and potential future therapies to prevent and reverse HCM. Antioxid. Redox Signal. 31, 318-358.

Energetic drain driving hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common form of hereditary cardiomyopathy and is mainly caused by mutations of genes encoding cardiac sarcomeric proteins. HCM is characterized by hypertrophy of the left ventricle, frequently involving the septum, that is not explained solely by loading conditions. HCM has a heterogeneous clinical profile, but diastolic dysfunction and ventricular arrhythmias represent two dominant features of the disease. Preclinical evidence indicates that the enhanced Calcium (Ca²⁺ ) sensitivity of the myofilaments plays a key role in the pathophysiology of HCM. Notably, this is not always a direct consequence of sarcomeric mutations, but can also result from secondary mutation-driven alterations. Here, we review experimental and clinical evidence indicating that increased myofilament Ca²⁺ sensitivity lies upstream of numerous cellular derangements which potentially contribute to the progression of HCM toward heart failure and sudden cardiac death.

A novel traditional Chinese medicine ameliorates fatigue-induced cardiac hypertrophy and dysfunction via regulation of energy metabolism

Prolonged exercise and exercise training can adversely affect cardiac function in some individuals. QiShenYiQi Pills (QSYQ), which are a compound Chinese medicine, have been previously shown to improve pressure overload-induced cardiac hypertrophy. We hypothesized that QSYQ can ameliorate as well the fatigue-induced cardiac hypertrophy. This study was to test this hypothesis and underlying mechanism with a focus on its role in energy regulation. Male Sprague-Dawley rats were used to establish exercise adaptation and fatigue model on a motorized rodent treadmill. Echocardiographic analysis and heart function test were performed to assess heart systolic function. Food-intake weight/body weight and heart weight/body weight were assessed, and hematoxylin and eosin staining and immunofluorescence staining of myocardium sections were performed. ATP synthase expression and activity and ATP, ADP, and AMP levels were assessed using Western blot and ELISA. Expression of proteins related to energy metabolism and IGF-1R signaling was determined using Western blot. QSYQ attenuated the food-intake weight/body weight decrease, improved myocardial structure and heart function, and restored the expression and distribution of myocardial connexin 43 after fatigue, concomitant with an increased ATP production and a restoration of metabolism-related protein expression. QSYQ upgraded the expression of IGF-1R, P-AMPK/AMPK, peroxisome proliferator-activated receptor-γ coactivator-1α, nuclear respiratory factor-1, P-phosphatidylinositol 3-kinase (PI3K)/PI3K, and P-Akt/Akt thereby attenuated the dysregulation of IGF-1R signaling after fatigue. QSYQ relieved fatigue-induced cardiac hypertrophy and enhanced heart function, which is correlated with its potential to improve energy metabolism by regulating IGF-1R signaling. NEW & NOTEWORTHY Prolonged exercise may impact some people leading to pathological cardiac hypertrophy. This study using an animal model of fatigue-induced cardiac hypertrophy provides evidence showing the potential of QiShenYiQi Pills, a novel traditional Chinese medicine, to prevent the cardiac adaptive hypertrophy from development to pathological hypertrophy and demonstrates that this effect is correlated with its capacity for regulating energy metabolism through interacting with insulin-like growth factor-1 receptor.

Impaired calcium handling and mitochondrial metabolic dysfunction as early markers of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a primary myocardial disorder, characterised by myocyte remodeling, disorganisation of sarcomeric proteins, impaired energy metabolism and altered cardiac contractility. Gene mutations encoding cardiac contractile proteins account for 60% of HCM aetiology. Current drug therapy including L-type calcium channel antagonists, are used to manage symptoms in patients with overt HCM, but no treatment exists that can reverse or prevent the cardiomyopathy. Design of effective drug therapy will require a clear understanding of the early pathophysiological mechanisms of the disease. Numerous studies have investigated specific aspects of HCM pathophysiology. This review brings these findings together, in order to develop a holistic understanding of the early pathophysiological mechanisms of the disease. We focus on gene mutations in cardiac myosin binding protein-C, β-cardiac myosin heavy chain, cardiac troponin I, and cardiac troponin T, that comprise the majority of all HCM sarcomeric gene mutations. We find that although some similarities exist, each mutation leads to mutation-specific alterations in calcium handling, myofilament calcium sensitivity and mitochondrial metabolic function. This may contribute to the observed clinical phenotypic variability in sarcomeric-related HCM. An understanding of early mutation-specific mechanisms of the disease may provide useful markers of disease progression, and inform therapeutic design.

Heterogeneous Pulmonary Response After Tracheal Occlusion: Clues to Fetal Lung Growth

BACKGROUND

Understanding inconsistent clinical outcomes in infants with severe congenital diaphragmatic hernia (CDH) after tracheal occlusion (TO) is a crucial step for advancing neonatal care. The objective of this study is to explore the heterogeneous airspace morphometry and the metabolic landscape changes in fetal lungs after TO.

METHODS

Fetal lungs on days 1 and 4 after TO were examined using mass spectrometry-based metabolomics, fluorescence lifetime imaging microscopy (FLIM), the number of airspaces, and tissue-to-airspace ratio (TAR).

RESULTS

Two morphometric areas were identified in TO lungs compared with controls (more small airspaces at day 1 and a higher number of enlarged airspaces at day 4). Global metabolomics analysis revealed a significant upregulation of glycolysis and a suppression of the tricarboxylic acid cycle in day 4 TO lungs compared with day 1 TO lungs. In addition, there was a significant increase in polyamines involved in cell growth and proliferation. Locally, FLIM analysis on day 1 TO lungs demonstrated two types of heterogeneous zones-similar to control and with increased oxidative phosphorylation. FLIM on day 4 TO lungs demonstrated appearance of zones with enlarged airspaces and a metabolic shift toward glycolysis, accompanied by a decrease in the FLIM "lipid-surfactant" signal.

CONCLUSIONS

In normal fetal lungs, we report a novel temporal pattern of varied morphometric and metabolic changes. Initially, there is formation of zones with small airspaces, followed by airspace enlargement over time. Metabolically day 1 TO lungs have zones with increased oxidative phosphorylation, whereas day 4 TO lungs have a shift toward glycolysis in the enlarged airspaces. Based on our observations, we speculate that the "best responders" to tracheal occlusion should have bigger lungs with small airspaces and normal surfactant production.

Myocardial adaptation after surgical therapy differs for aortic valve stenosis and hypertrophic obstructive cardiomyopathy

Surgical therapies in aortic valve stenosis (AVS) and hypertrophic obstructive cardiomyopathy (HOCM) aim to relief intraventricular pressure overload and improve clinical outcome. It is currently unknown to what extent myocardial adaptation concurs with restoration of intraventricular pressures, and whether this is similar in both patient groups. The aim of this study was to investigate changes in myocardial adaptation after surgical therapies for AVS and HOCM. Ten AVS and ten HOCM patients were enrolled and underwent cardiac magnetic resonance cine imaging and myocardial tagging prior to, and 4 months after aortic valve replacement (AVR) and septal myectomy, respectively. Global left ventricular (LV) analyses were derived from cine images. Circumferential strain was assessed from myocardial tagging images at the septal and lateral wall of the mid ventricle. Pressure gradients significantly decreased in both AVS and HOCM after surgery (p < 0.01), with a concomitant decrease in left atrial volume (p < 0.05) suggesting lower diastolic filling pressures. Also, LV volumes, mass and septal wall thickness decreased in both, but to a larger extent in AVS than in HOCM patients. AVR improved wall thickening (p < 0.05) and did not change systolic strain rate. Myectomy did not affect wall thickening and reduced septal systolic strain rate (p = 0.03). Both AVR and myectomy induced positive structural remodeling in line with a reduction of pressure overload. A concomitant recovery in systolic function however was found in AVR only. The systolic functional deterioration in HOCM patients seems to be inherent to myectomy and the ongoing and irreversible disease.

INDUCED PLURIPOTENT STEM CELLS FOR MODELLING ENERGETIC ALTERATIONS IN HYPERTROPHIC CARDIOMYOPATHY

Hypertrophic cardiomyopathy (HCM) is one of the most commonly inherited cardiac disorders that manifests with increased ventricular wall thickening, cardiomyocyte hypertrophy, disarrayed myofibers and interstitial fibrosis. The major pathophysiological features include, diastolic dysfunction, obstruction of the left ventricular outflow tract and cardiac arrhythmias. Mutations in genes that encode mostly for sarcomeric proteins have been associated with HCM but, despite the abundant research conducted to decipher the molecular mechanisms underlying the disease, it remains unclear as to how a primary defect in the sarcomere could lead to secondary phenotypes such as cellular hypertrophy. Mounting evidence suggests energy deficiency could be an important contributor of disease pathogenesis as well. Various animal models of HCM have been generated for gaining deeper insight into disease pathogenesis, however species variation between animals and humans, as well as the limited availability of human myocardial samples, has encouraged researchers to seek alternative 'humanized' models. Using induced pluripotent stem cells (iPSCs), human cardiomyocytes (CMs) have been generated from patients with HCM for investigating disease mechanisms. While these HCM-iPSC models demonstrate most of the phenotypic traits, it is important to ascertain if they recapitulate all pathophysiological features, especially that of energy deficiency. In this review we discuss the currently established HCM-iPSC models with emphasis on altered energetics.

Stress Myocardial Blood Flow Heterogeneity Is a Positron Emission Tomography Biomarker of Ventricular Arrhythmias in Patients With Hypertrophic Cardiomyopathy

Patients with hypertrophic cardiomyopathy (HC) are at increased risk of sudden cardiac death. Abnormalities in myocardial blood flow (MBF) detected by positron emission tomography (PET) are common in HC, but a PET marker that identifies patients at risk of sudden cardiac death is lacking. We hypothesized that disparities in regional myocardial perfusion detected by PET would identify patients with HC at risk of ventricular arrhythmias. To test this hypothesis, we quantified global and regional MBFs by ¹³NH₃-PET at rest and at stress, and developed a heterogeneity index to assess MBF heterogeneity in 133 symptomatic patients with HC. The MBF heterogeneity index was computed by dividing the highest by the lowest regional MBF value, at rest and after vasodilator stress, in each patient. High stress MBF heterogeneity was defined as an index of ≧1.85. Patients with HC were stratified by the presence or the absence of ventricular arrhythmias, defined as sustained ventricular tachycardia (VT) and/or nonsustained VT, during follow-up. We found that global and regional MBFs at rest and stress were similar in patients with HC with or without ventricular arrhythmias. Variability in regional stress MBF was observed in both groups, but the stress MBF heterogeneity index was significantly higher in patients with HC who developed ventricular arrhythmias (1.82 ± 0.77 vs 1.49 ± 0.25, p <0.001). A stress MBF heterogeneity index of ≧1.85 was an independent predictor of both sustained VT (hazard ratio 16.1, 95% confidence interval 3.2 to 80.3) and all-VT (sustained-VT + nonsustained VT: hazard ratio 3.7, 95% confidence interval 1.4 to 9.7). High heterogeneity of stress MBF, reflected by an MBF heterogeneity index of ≥1.85, is a PET biomarker for ventricular arrhythmias in symptomatic patients with HC.

Allele-specific differences in transcriptome, miRNome, and mitochondrial function in two hypertrophic cardiomyopathy mouse models

Hypertrophic cardiomyopathy (HCM) stems from mutations in sarcomeric proteins that elicit distinct biophysical sequelae, which in turn may yield radically different intracellular signaling and molecular pathologic profiles. These signaling events remain largely unaddressed by clinical trials that have selected patients based on clinical HCM diagnosis, irrespective of genotype. In this study, we determined how two mouse models of HCM differ, with respect to cellular/mitochondrial function and molecular biosignatures, at an early stage of disease. We show that hearts from young R92W-TnT and R403Q-αMyHC mutation-bearing mice differ in their transcriptome, miRNome, intracellular redox environment, mitochondrial antioxidant defense mechanisms, and susceptibility to mitochondrial permeability transition pore opening. Pathway analysis of mRNA-sequencing data and microRNA profiles indicate that R92W-TnT mutants exhibit a biosignature consistent with activation of profibrotic TGF-β signaling. Our results suggest that the oxidative environment and mitochondrial impairment in young R92W-TnT mice promote activation of TGF-β signaling that foreshadows a pernicious phenotype in young individuals. Of the two mutations, R92W-TnT is more likely to benefit from anti-TGF-β signaling effects conferred by angiotensin receptor blockers and may be responsive to mitochondrial antioxidant strategies in the early stage of disease. Molecular and functional profiling may therefore serve as aids to guide precision therapy for HCM.

Decreased ATP production and myocardial contractile reserve in metabolic heart disease

Metabolic syndrome is a cluster of obesity-related metabolic abnormalities that lead to metabolic heart disease (MHD) with left ventricular pump dysfunction. Although MHD is thought to be associated with myocardial energetic deficiency, two key questions have not been answered. First, it is not known whether there is a sufficient energy deficit to contribute to pump dysfunction. Second, the basis for the energy deficit is not clear. To address these questions, mice were fed a high fat, high sucrose (HFHS) 'Western' diet to recapitulate the MHD phenotype. In isolated beating hearts, we used 31P NMR spectroscopy with magnetization transfer to determine a) the concentrations of high energy phosphates ([ATP], [ADP], [PCr]), b) the free energy of ATP hydrolysis (∆G~ATP), c) the rate of ATP production and d) flux through the creatine kinase (CK) reaction. At the lowest workload, the diastolic pressure-volume relationship was shifted upward in HFHS hearts, indicative of diastolic dysfunction, whereas systolic function was preserved. At this workload, the rate of ATP synthesis was decreased in HFHS hearts, and was associated with decreases in both [PCr] and ∆G~ATP. Higher work demands unmasked the inability of HFHS hearts to increase systolic function and led to a further decrease in ∆G~ATP to a level that is not sufficient to maintain normal function of sarcoplasmic Ca2+-ATPase (SERCA). While [ATP] was preserved at all work demands in HFHS hearts, the progressive increase in [ADP] led to a decrease in ∆G~ATP with increased work demands. Surprisingly, CK flux, CK activity and total creatine were normal in HFHS hearts. These findings differ from dilated cardiomyopathy, in which the energetic deficiency is associated with decreases in CK flux, CK activity and total creatine. Thus, in HFHS-fed mice with MHD there is a distinct metabolic phenotype of the heart characterized by a decrease in ATP production that leads to a functionally-important energetic deficiency and an elevation of [ADP], with preservation of CK flux.

Rest and Stress Longitudinal Systolic Left Ventricular Mechanics in Hypertrophic Cardiomyopathy: Implications for Prognostication

BACKGROUND

Exercise intolerance is the most common symptom in hypertrophic cardiomyopathy (HCM). We examined whether inability to augment myocardial mechanics during exercise would influence functional performance and clinical outcomes in HCM.

METHODS

Ninety-five HCM patients (32 nonobstructive, 32 labile-obstructive, 31 obstructive) and 26 controls of similar age and gender distribution were recruited prospectively. They underwent rest and treadmill stress strain echocardiography, and 61 of them underwent magnetic resonance imaging. Mechanical reserve (MRES) was defined as percent change in systolic strain rate (SR) immediately postexercise.

RESULTS

Global strain and SR were significantly lower in HCM patients at rest (strain: nonobstructive, -15.6 ± 3.0; labile-obstructive, -15.9 ± 3.0; obstructive, -13.8 ± 2.9; control, -17.7% ± 2.1%, P < .001; SR: nonobstructive, -0.92 ± 0.20; labile-obstructive, -0.94 ± 0.17; obstructive, -0.85 ± 0.18; control, -1.04 ± 0.14 s^-1, P = .002); and immediately postexercise (strain: nonobstructive, -15.6 ± 3.0; labile-obstructive, -17.6 ± 3.6; obstructive, -15.6 ± 3.6; control, -19.2 ± 3.1%; P = .001; SR: nonobstructive, -1.41 ± 0.37; labile-obstructive, -1.64 ± 0.38; obstructive, -1.32 ± 0.29; control, -1.82 ± 0.29 s^-1, P < .001). MRES was lower in nonobstructive and obstructive compared with labile-obstructive and controls (51% ± 29%, 54% ± 31%, 78% ± 38%, 77% ± 30%, P = .001, respectively). Postexercise SR and MRES were associated with exercise capacity (r = 0.47 and 0.42, P < .001 both, respectively). When adjusted for age, gender, body mass index, E/e', and resting peak instantaneous systolic gradient, postexercise SR best predicted exercise capacity (r = 0.74, P = .003). Postexercise SR was correlated with extent of late gadolinium enhancement (r = 0.34, P = .03). By Cox regression, exercise SR and MRES predicted ventricular tachycardia/ventricular fibrillation (VT/VF) even after adjustment for age, gender, family history of sudden cardiac death, septum ≥ 3 cm and abnormal blood pressure response (P = .04 and P = .046, respectively).

CONCLUSIONS

Nonobstructive and obstructive patients have reduced MRES compared with labile-obstructive and controls. Postexercise SR correlates with LGE and exercise capacity. Exercise SR and MRES predict VT/VF.

Metabolic heterogeneity of idiopathic pulmonary fibrosis: a metabolomic study

Introduction

Idiopathic pulmonary fibrosis (IPF) is a chronic and fatal disease of unknown cause characterised by progressive fibrotic formation in lung tissue. We hypothesise that disrupted metabolic pathways in IPF contribute to disease pathogenesis.

Methods

Metabolomics of human IPF was performed using mass spectroscopy (IPF lung=8; donor lung=8). Gene expression of key metabolic enzymes was measured using microarrays. Of the 108 metabolites whose levels were found altered, 48 were significantly increased, whereas 60 were significantly decreased in IPF samples compared with normal controls.

Results

Specific metabolic pathways mediating the IPF remodelling were found with a downregulated sphingolipid metabolic pathway but an upregulated arginine pathway in IPF. In addition, disrupted glycolysis, mitochondrial beta-oxidation and tricarboxylic acid cycle, altered bile acid, haem and glutamate/aspartate metabolism were found in IPF samples compared with control.

Conclusions

Our results show alterations in metabolic pathways for energy consumption during lung structural remodelling, which may contribute to IPF pathogenesis. We believe that this is the first report of simultaneously and systemically measuring changes of metabolites involving nine metabolic pathways in human severe IPF lungs. The measurement of the metabolites may serve in the future diagnosis and prognosis of IPF.

Linking myofilaments to sudden cardiac death: recent advances

The major goal of this focused review is to highlight some of the recent advances and remaining open questions about how a mutation in a myofilament protein leads to an increased risk for sudden cardiac death (SCD). The link between myofilaments and SCD has been known for over 25 years, but identifying mutation carriers at risk for SCD is still a challenge and currently the only effective prevention is implantation of a defibrillator (ICD). In addition to recognized risk factors, other contributing factors need to be considered and assessed, e.g. 'microvascular dysfunction', to calibrate individual risk more accurately. Similarly, improving our understanding about the underlying mechanisms of SCD in patients with sarcomeric mutations will also allow us to design new and less invasive treatment options that will minimize risk and hopefully make implantation of an ICD unnecessary.

Creatine kinase rate constant in the human heart measured with 3D-localization at 7 tesla

PURPOSE

We present a new Bloch-Siegert four Angle Saturation Transfer (BOAST) method for measuring the creatine kinase (CK) first-order effective rate constant k_f in human myocardium at 7 tesla (T). BOAST combines a variant of the four-angle saturation transfer (FAST) method using amplitude-modulated radiofrequency pulses, phosphorus Bloch-Siegert B1+-mapping to determine the per-voxel flip angles, and nonlinear fitting to Bloch simulations for postprocessing.

METHODS

Optimal flip angles and repetition time parameters were determined from Monte Carlo simulations. BOAST was validated in the calf muscle of two volunteers at 3T and 7T. The myocardial CK forward rate constant was then measured in 10 volunteers at 7T in 82 min (after ¹ H localization).

RESULTS

BOAST kfCK values were 0.281 ± 0.002 s^-1 in the calf and 0.35 ± 0.05 s^-1 in myocardium. These are consistent with literature values from lower fields. Using a literature values for adenosine triphosphate concentration, we computed CK flux values of 4.55 ± 1.52 mmol kg^-1 s^-1 . The sensitive volume for BOAST depends on the B₁ inhomogeneity of the transmit coil.

CONCLUSION

BOAST enables measurement of the CK rate constant in the human heart at 7T, with spatial localization in three dimensions to 5.6 mL voxels, using a 10-cm loop coil. Magn Reson Med 78:20-32, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Clinical Genetic Testing for the Cardiomyopathies and Arrhythmias: A Systematic Framework for Establishing Clinical Validity and Addressing Genotypic and Phenotypic Heterogeneity

Advances in DNA sequencing have made large, diagnostic gene panels affordable and efficient. Broad adoption of such panels has begun to deliver on the promises of personalized medicine, but has also brought new challenges such as the presence of unexpected results, or results of uncertain clinical significance. Genetic analysis of inherited cardiac conditions is particularly challenging due to the extensive genetic heterogeneity underlying cardiac phenotypes, and the overlapping, variable, and incompletely penetrant nature of their clinical presentations. The design of effective diagnostic tests and the effective use of the results depend on a clear understanding of the relationship between each gene and each considered condition. To address these issues, we developed simple, systematic approaches to three fundamental challenges: (1) evaluating the strength of the evidence suggesting that a particular condition is caused by pathogenic variants in a particular gene, (2) evaluating whether unusual genotype/phenotype observations represent a plausible expansion of clinical phenotype associated with a gene, and (3) establishing a molecular diagnostic strategy to capture overlapping clinical presentations. These approaches focus on the systematic evaluation of the pathogenicity of variants identified in clinically affected individuals, and the natural history of disease in those individuals. Here, we applied these approaches to the evaluation of more than 100 genes reported to be associated with inherited cardiomyopathies and arrhythmias including hypertrophic cardiomyopathy, dilated cardiomyopathy, arrhythmogenic right ventricular dysplasia or cardiomyopathy, long QT syndrome, short QT syndrome, Brugada, and catecholaminergic polymorphic ventricular tachycardia, and to a set of related syndromes such as Noonan Syndrome and Fabry disease. These approaches provide a framework for delivering meaningful and accurate genetic test results to individuals with hereditary cardiac conditions.

MRS: a noninvasive window into cardiac metabolism

A well-functioning heart requires a constant supply of a balanced mixture of nutrients to be used for the production of adequate amounts of adenosine triphosphate, which is the main energy source for most cellular functions. Defects in cardiac energy metabolism are linked to several myocardial disorders. MRS can be used to study in vivo changes in cardiac metabolism noninvasively. MR techniques allow repeated measurements, so that disease progression and the response to treatment or to a lifestyle intervention can be monitored. It has also been shown that MRS can predict clinical heart failure and death. This article focuses on in vivo MRS to assess cardiac metabolism in humans and experimental animals, as experimental animals are often used to investigate the mechanisms underlying the development of metabolic diseases. Various MR techniques, such as cardiac (31) P-MRS, (1) H-MRS, hyperpolarized (13) C-MRS and Dixon MRI, are described. A short overview of current and emerging applications is given. Cardiac MRS is a promising technique for the investigation of the relationship between cardiac metabolism and cardiac disease. However, further optimization of scan time and signal-to-noise ratio is required before broad clinical application. In this respect, the ongoing development of advanced shimming algorithms, radiofrequency pulses, pulse sequences, (multichannel) detection coils, the use of hyperpolarized nuclei and scanning at higher magnetic field strengths offer future perspective for clinical applications of MRS.

Hypertrophic cardiomyopathy: a heart in need of an energy bar?

Hypertrophic cardiomyopathy (HCM) has been recently recognized as the most common inherited cardiovascular disorder, affecting 1 in 500 adults worldwide. HCM is characterized by myocyte hypertrophy resulting in thickening of the ventricular wall, myocyte disarray, interstitial and/or replacement fibrosis, decreased ventricular cavity volume and diastolic dysfunction. HCM is also the most common cause of sudden death in the young. A large proportion of patients diagnosed with HCM have mutations in sarcomeric proteins. However, it is unclear how these mutations lead to the cardiac phenotype, which is variable even in patients carrying the same causal mutation. Abnormalities in calcium cycling, oxidative stress, mitochondrial dysfunction and energetic deficiency have been described constituting the basis of therapies in experimental models of HCM and HCM patients. This review focuses on evidence supporting the role of cellular metabolism and mitochondria in HCM.