Myocardial energetics in cardiac hypertrophy

Layer myocardial strain is the most heritable echocardiographic trait

AIMS

Myocardial deformation assessed by strain analysis represents a significant advancement in our assessment of cardiac mechanics. However, whether this variable is genetically heritable or whether all/most of its variability is related to environmental factors is currently unknown. We sought to determine the heritability of echocardiographically determined cardiac mechanics indices in a population setting.

METHODS AND RESULTS

A total of 1357 initially healthy subjects (women 51.6%; 48.2 ± 14.1 years) were included in this study from 20-year follow-up after the fourth visit of the longitudinal familial STANISLAS cohort (Lorraine, France). Data were acquired using state-of-the-art cardiac ultrasound equipment, using acquisition and measurement protocols recommended by the EACVI (European Association of Cardiovascular Imaging)/ASE (American Society of Echocardiography)/Industry Task Force. Layer-specific global longitudinal strain (GLS) and global circumferential strain (full-wall, subendocardial, and subepicardial) and conventional structural and functional cardiac parameters and their potential heritability were assessed using restricted maximum likelihood analysis, with genetic relatedness matrix calculated from genome-wide association data. Indices of longitudinal/circumferential myocardial function and left ventricular (LV) ejection fraction had low heritability (ranging from 10% to 20%). Diastolic and standard LV function parameters had moderate heritability (ranging from 20% to 30%) except for end-systolic and end-diastolic volumes (30% and 45%, respectively). In contrast, global longitudinal subendocardial strain (GLSEndo)/global longitudinal subepicardial strain (GLSEpi) ratio had a high level of heritability (65%). Except for GLSEndo/GLSEpi ratio, a large percentage of variance remained unexplained (>50%).

CONCLUSIONS

In our population cohort, GLSEndo/GLSEpi ratio had a high level of heritability, whereas other classical and mechanical LV function parameters did not. Given the increasing recognition of GLSEndo/GLSEpi ratio as an early/sensitive imaging biomarker of systolic dysfunction, our results suggest the possible existence of individual genetic predispositions to myocardial decline.

Postpartum cardiovascular function in patients with hypertensive disorders of pregnancy: a longitudinal study

BACKGROUND

Women with a history of hypertensive disorders of pregnancy are at increased risk of cardiovascular diseases, which are usually mediated by the development of cardiovascular risk factors, such as chronic hypertension, metabolic syndrome, or subclinical myocardial dysfunction. Increasing evidence has been showing that little time elapses between the end of pregnancy and the development of these cardiovascular risk factors.

OBJECTIVE

This study aimed to assess the persistence of hypertension and myocardial dysfunction at 4 months postpartum in a cohort of women with hypertensive disorders of pregnancy, and to compare the echocardiographic parameters between the peripartum and the postpartum period.

STUDY DESIGN

In a longitudinal prospective study, a cohort of women with preterm or term hypertensive disorders of pregnancy and an unmatched group of women with term normotensive pregnancy were recruited. Women with preexisting chronic hypertension (n=29) were included in the hypertensive disorders of pregnancy cohort. All participants underwent 2 cardiovascular assessments: the first was conducted either before or within 1 week of delivery (V1: peripartum assessment), and the second between 3 and 12 months following delivery (V2: postpartum assessment). The cardiovascular evaluation included blood pressure profile, maternal transthoracic echocardiography (left ventricular mass index, relative wall thickness, left atrial volume index, E/A, E/e', peak velocity of tricuspid regurgitation, ejection fraction, and left ventricular global longitudinal strain and twist), and metabolic assessment (fasting glycemia, insulin, lipid profile, and waist measurement). Echocardiographic data were compared between V1 and V2 using paired t test or McNemar test in hypertensive disorders of pregnancy and in the control groups.

RESULTS

Among 260 patients with pregnancies complicated by hypertensive disorders of pregnancy and 33 patients with normotensive pregnancies, 219 (84.2%) and 30 (90.9%) attended postpartum follow-up, respectively. Patients were evaluated at a median of 124 days (interquartile range, 103-145) after delivery. Paired comparisons of echocardiographic findings demonstrated significant improvements in cardiac remodeling rates (left ventricular mass index [g/m2], 63.4±14.4 vs 78.9±16.2; P<.001; relative wall thickness, 0.35±0.1 vs 0.42±0.1; P<.001), most diastolic indices (E/e', 6.3±1.6 vs 7.4±1.9; P<.001), ejection fraction (ejection fraction <55%, 9 [4.1%] vs 28 [13.0%]; P<.001), and global longitudinal strain (-17.3±2.6% vs -16.2±2.4%; P<.001) in the postpartum period compared with the peripartum. The same improvements in cardiac indices were observed in the normotensive group. However, at the postnatal assessment, 153 of 219 (69.9%) had either hypertension (76/219; 34.7%) or an abnormal global longitudinal strain (125/219; 57.1%), 13 of 67 (19.4%) had metabolic syndrome, and 18 of 67 (26.9%) exhibited insulin resistance.

CONCLUSION

Although persistent postpartum cardiovascular impairment was evident in a substantial proportion of patients given that more than two-thirds had either hypertension or myocardial dysfunction postpartum, cardiac modifications because of pregnancy-related overload and hypertension were more pronounced in the peripartum than in the postpartum period.

Recreating the heart's helical structure-function relationship with focused rotary jet spinning

Helical alignments within the heart's musculature have been speculated to be important in achieving physiological pumping efficiencies. Testing this possibility is difficult, however, because it is challenging to reproduce the fine spatial features and complex structures of the heart's musculature using current techniques. Here we report focused rotary jet spinning (FRJS), an additive manufacturing approach that enables rapid fabrication of micro/nanofiber scaffolds with programmable alignments in three-dimensional geometries. Seeding these scaffolds with cardiomyocytes enabled the biofabrication of tissue-engineered ventricles, with helically aligned models displaying more uniform deformations, greater apical shortening, and increased ejection fractions compared with circumferential alignments. The ability of FRJS to control fiber arrangements in three dimensions offers a streamlined approach to fabricating tissues and organs, with this work demonstrating how helical architectures contribute to cardiac performance.

Cardiomyocyte Proliferation from Fetal- to Adult- and from Normal- to Hypertrophy and Failing Hearts

Simple Summary

Death from injury to the heart from a variety of causes remains a major cause of mortality worldwide. The cardiomyocyte, the major contracting cell of the heart, is responsible for pumping blood to the rest of the body. During fetal development, these immature cardiomyocytes are small and rapidly divide to complete development of the heart by birth when they develop structural and functional characteristics of mature cells which prevent further division. All further growth of the heart after birth is due to an increase in the size of cardiomyocytes, hypertrophy. Following the loss of functional cardiomyocytes due to coronary artery occlusion or other causes, the heart is unable to replace the lost cells. One of the significant research goals has been to induce adult cardiomyocytes to reactivate the cell cycle and repair cardiac injury. This review explores the developmental, structural, and functional changes of the growing cardiomyocyte, and particularly the sarcomere, responsible for force generation, from the early fetal period of reproductive cell growth through the neonatal period and on to adulthood, as well as during pathological response to different forms of myocardial diseases or injury. Multiple issues relative to cardiomyocyte cell-cycle regulation in normal or diseased conditions are discussed.

Abstract

The cardiomyocyte undergoes dramatic changes in structure, metabolism, and function from the early fetal stage of hyperplastic cell growth, through birth and the conversion to hypertrophic cell growth, continuing to the adult stage and responding to various forms of stress on the myocardium, often leading to myocardial failure. The fetal cell with incompletely formed sarcomeres and other cellular and extracellular components is actively undergoing mitosis, organelle dispersion, and formation of daughter cells. In the first few days of neonatal life, the heart is able to repair fully from injury, but not after conversion to hypertrophic growth. Structural and metabolic changes occur following conversion to hypertrophic growth which forms a barrier to further cardiomyocyte division, though interstitial components continue dividing to keep pace with cardiac growth. Both intra- and extracellular structural changes occur in the stressed myocardium which together with hemodynamic alterations lead to metabolic and functional alterations of myocardial failure. This review probes some of the questions regarding conditions that regulate normal and pathologic growth of the heart.

CMR-derived myocardial strain analysis differentiates ischemic and dilated cardiomyopathy-a propensity score-matched study

Left ventricular (LV) longitudinal, circumferential, and radial motion can be measured using feature tracking of cardiac magnetic resonance (CMR) images. The aim of our study was to detect differences in LV mechanics between patients with dilated cardiomyopathy (DCM) and ischemic cardiomyopathy (ICM) who were matched using a propensity score-based model. Between April 2017 and October 2019, 1224 patients were included in our CMR registry, among them 141 with ICM and 77 with DCM. Propensity score matching was used to pair patients based on their indexed end-diastolic volume (EDVi), ejection fraction (EF), and septal T1 relaxation time (psmatch2 module L Feature tracking provided six parameters for global longitudinal, circumferential, and radial strain with corresponding strain rates in each group. Strain parameters were compared between matched pairs of ICM and DCM patients using paired t tests. Propensity score matching yielded 72 patients in each group (DCM mean age 58.6 ± 11.6 years, 15 females; ICM mean age 62.6 ± 13.2 years, 11 females, p = 0.084 and 0.44 respectively; LV-EF 32.2 ± 13.5% vs. 33.8 ± 12.1%, p = 0.356; EDVi 127.2 ± 30.7 ml/m2 vs. 121.1 ± 41.8 ml/m2, p = 0.251; native T1 values 1165 ± 58 ms vs. 1167 ± 70 ms, p = 0.862). There was no difference in global longitudinal strain between DCM and ICM patients (- 10.9 ± 5.5% vs. - 11.2 ± 4.7%, p = 0.72), whereas in DCM patients there was a significant reduction in global circumferential strain (- 10.0 ± 4.5% vs. - 12.2 ± 4.7%, p = 0.002) and radial strain (17.1 ± 8.51 vs. 21.2 ± 9.7%, p = 0.039). Our data suggest that ICM and DCM patients have inherently different myocardial mechanics, even if phenotypes are similar. Our data show that GCS is significantly more impaired in DCM patients. This feature may help in more thoroughly characterizing cardiomyopathy patients.

Cardiac mechanics in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is a complex clinical entity associated with significant morbidity and mortality. Common comorbidities including hypertension, coronary artery disease, diabetes, chronic kidney disease, obesity, and increasing age predispose to preclinical diastolic dysfunction that often progresses to frank HFpEF. Clinical HFpEF is typically associated with some degree of diastolic dysfunction, but can occur in the absence of many conventional diastolic dysfunction indices. The exact biologic links between risk factors, structural changes, and clinical manifestations are not clearly apparent. Innovative approaches including deformation imaging have enabled deeper understanding of HFpEF cardiac mechanics beyond conventional metrics. Furthermore, predictive analytics through data-driven platforms have allowed for a deeper understanding of HFpEF phenotypes. This review focuses on the changes in cardiac mechanics that occur through preclinical myocardial dysfunction to clinically apparent HFpEF.

Increased myocardial mass and attenuation of myocardial strain in professional male soccer players and competitive male triathletes

The purpose of this prospective study was to analyze the relationship between ventricular morphology and parameters of cardiac function in two different athletic groups and controls, using feature tracking cardiac magnetic resonance (FT-CMR). Twenty-three professional soccer players (22 ± 4 years), 19 competitive triathletes (28 ± 6 years) and 16 controls (26 ± 3 years) were included in the study. CMR was performed using a 1.5 T scanner. Cardiac chamber volumes, mass and biventricular global myocardial strain were obtained and compared. In comparison to the control subjects, athletes were characterized by a higher cardiac volume (p < 0.0001), higher cardiac mass (p < 0.001), reduced longitudinal strain of the left and right ventricle (p < 0.05 and p < 0.01 respectively) and reduced left ventricular radial strain (p < 0.05). Soccer players revealed higher amounts of left ventricular mass (87 ± 15 vs. 75 ± 13 g/m², p < 0.05) than triathletes. Moreover, they showed a greater decrease in left and right ventricular longitudinal strain (p < 0.05 and p < 0.05) as well as in radial left ventricular strain (p < 0.05) in comparison to triathletes. An increase in left ventricular mass correlated significantly with a decrease in longitudinal (r = 0.47, p < 0.001) and radial (r =  − 0.28, p < 0.05) strain. In athletes, attenuation of strain values is associated with cardiac hypertrophy and differ between soccer players and triathletes. Further studies are needed to investigate whether it is an adaptive or maladaptive change of the heart induced by intense athletic training.

Left ventricular hypertrophy is associated with overexpression of HSP60, TLR2, and TLR4 in the myocardium

Left ventricular hypertrophy is a common adaptive response to increased cardiac workload. Cardiomyocytes growth and increase in contractile force are conditioned by sufficient energy production, which implies appropriate mitochondrial function. The 60 kDa heat shock protein (HSP60) is a chaperone essential for mitochondrial proteostasis, but when translocates from mitochondria, it can also act as a potent inflammatory mediator binding to toll-like receptors (TLRs). In this study, we aimed to compare the expression pattern of HSP60, TLR2, and TLR4 in hypertrophic vs non-hypertrophic, normal human myocardium. We further examined whether HSP60 in situ binds to TLRs in hypertrophic myocardial tissue. In addition, expression of activated downstream targets of TLR 2/4 pathways was also evaluated.For this purpose, immunohistochemical expression analyses were performed on myocardial tissue samples obtained during the autopsy of human subjects in which left ventricular hypertrophy was the only cardiopathological finding and had died from sudden cardiac death, as well as from the subjects without any cardiac pathology, that died by unnatural death (accident or suicide). Double immunofluorescence was used to examine HSP60 translocation, while proximity ligation assay (PLA) was performed to assess HSP60 and TLRs interactions.Hypertrophic myocardium showed significantly higher expression of HSP60, TLR2, and TLR4 compared to normal myocardium. Furthermore, in hypertrophic cardiomyocytes, we found membrane translocation of HSP60 and signs of HSP60/TLR interactions.Conclusion: The obtained data point to an important supportive role of HSP60 in adaptive cardiomyocytes growth, while concomitant induction of TLR2 and TLR4 candidates HSP60-TLRs interactions as an early events during pathogenesis of secondary complications consequently to the left ventricular hypertrophy.

Trimetazidine attenuates pressure overload-induced early cardiac energy dysfunction via regulation of neuropeptide Y system in a rat model of abdominal aortic constriction

Background

Metabolism remodeling has been recognized as an early event following cardiac pressure overload. However, its temporal association with ventricular hypertrophy has not been confirmed. Moreover, whether trimetazidine could favorably affect this process also needs to be determined. The aim of the study was to explore the temporal changes of myocardial metabolism remodeling following pressure-overload induced ventricular hypertrophy and the potential favorable effect of trimetazidine on myocardial metabolism remodeling.

Methods

A rat model of abdominal aortic constriction (AAC)-induced cardiac pressure overload was induced. These rats were grouped as the AAC (no treatment) or TMZ group according to whether oral trimetazidine (TMZ, 40 mg/kg/d, for 5 days) was administered. Changes in cardiac structures were sequentially evaluated via echocardiography. The myocardial ADP/ATP ratio was determined to reflect the metabolic status, and changes in serum neuropeptide Y systems were evaluated.

Results

Myocardial metabolic disorder was acutely induced as evidenced by an increased ADP/ATP ratio within 7 days of AAC before the morphological changes in the myocardium, accompanied by up-regulation of serum oxidative stress markers and expression of fetal genes related to hypertrophy. Moreover, the serum NPY and myocardial NPY-1R, 2R, and 5R levels were increased within the acute phase of AAC-induced cardiac pressure overload. Pretreatment with TMZ could partly attenuate myocardial energy metabolic homeostasis, decrease serum levels of oxidative stress markers, attenuate the induction of hypertrophy-related myocardial fetal genes, inhibit the up-regulation of serum NPY levels, and further increase the myocardial expression of NPY receptors.

Conclusions

Cardiac metabolic remodeling is an early change in the myocardium before the presence of typical morphological ventricular remodeling following cardiac pressure overload, and pretreatment with TMZ may at least partly reverse the acute metabolic disturbance, perhaps via regulation of the NPY system.

Tissue Tracking Technology for Assessing Cardiac Mechanics: Principles, Normal Values, and Clinical Applications

Tissue tracking technologies such as speckle tracking echocardiography and feature tracking cardiac magnetic resonance have enhanced the noninvasive assessment of myocardial deformation in clinical research and clinical practice. The widespread enthusiasm for using tissue tracking techniques in research and clinical practice stems from the ready applicability of these technologies to routine echocardiographic or cardiac magnetic resonance images. The technology is common to both modalities, and derived parameters to describe myocardial mechanics are the similar, albeit with different accuracies. We provide an overview of the normal values and reproducibility of the clinically applicable parameters, together with their clinical validation. The use of these technologies in different clinical scenarios, and the additive value to current imaging diagnostics are discussed.

Endurance training or beta-blockade can partially block the energy metabolism remodeling taking place in experimental chronic left ventricle volume overload

Background

Patients with chronic aortic valve regurgitation (AR) causing left ventricular (LV) volume overload can remain asymptomatic for many years despite having a severely dilated heart. The sudden development of heart failure is not well understood but alterations of myocardial energy metabolism may be contributive. We studied the evolution of LV energy metabolism in experimental AR.

Methods

LV glucose utilization was evaluated in vivo by positron emission tomography (microPET) scanning of 6-month AR rats. Sham-operated or AR rats (n = 10-30 animals/group) were evaluated 3, 6 or 9 months post-surgery. We also tested treatment intervention in order to evaluate their impact on metabolism. AR rats (20 animals) were trained on a treadmill 5 times a week for 9 months and another group of rats received a beta-blockade treatment (carvedilol) for 6 months.

Results

MicroPET revealed an abnormal increase in glucose consumption in the LV free wall of AR rats at 6 months. On the other hand, fatty acid beta-oxidation was significantly reduced compared to sham control rats 6 months post AR induction. A significant decrease in citrate synthase and complex 1 activity suggested that mitochondrial oxidative phosphorylation was also affected maybe as soon as 3 months post-AR.

Moderate intensity endurance training starting 2 weeks post-AR was able to partially normalize the activity of various myocardial enzymes implicated in energy metabolism. The same was true for the AR rats treated with carvedilol (30 mg/kg/d). Responses to these interventions were different at the level of gene expression. We measured mRNA levels of a number of genes implicated in the transport of energy substrates and we observed that training did not reverse the general down-regulation of these genes in AR rats whereas carvedilol normalized the expression of most of them.

Conclusion

This study shows that myocardial energy metabolism remodeling taking place in the dilated left ventricle submitted to severe volume overload from AR can be partially avoided by exercise or beta-blockade in rats.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2261-14-190) contains supplementary material, which is available to authorized users.

A new twist on an old idea part 2: cyclosporine preserves normal mitochondrial but not cardiomyocyte function in mini-swine with compensated heart failure

We recently developed a clinically relevant mini‐swine model of heart failure with preserved ejection fraction (HFpEF), in which diastolic dysfunction was associated with increased mitochondrial permeability transition (MPT). Early diastolic function is ATP and Ca²⁺‐dependent, thus, we hypothesized chronic low doses of cyclosporine (CsA) would preserve mitochondrial function via inhibition of MPT and subsequently maintain normal cardiomyocyte Ca²⁺ handling and contractile characteristics. Left ventricular cardiomyocytes were isolated from aortic‐banded Yucatan mini‐swine divided into three groups; control nonbanded (CON), HFpEF nontreated (HF), and HFpEF treated with CsA (HF‐CsA). CsA mitigated the deterioration of mitochondrial function observed in HF animals, including functional uncoupling of Complex I‐dependent mitochondrial respiration and increased susceptibility to MPT. Attenuation of mitochondrial dysfunction in the HF‐CsA group was not associated with commensurate improvement in cardiomyocyte Ca²⁺ handling or contractility. Ca²⁺ transient amplitude was reduced and transient time to peak and recovery (tau) prolonged in HF and HF‐CsA groups compared to CON. Alterations in Ca²⁺ transient parameters observed in the HF and HF‐CsA groups were associated with decreased cardiomyocyte shortening and shortening rate. Cellular function was consistent with impaired in vivo systolic and diastolic whole heart function. A significant systemic hypertensive response to CsA was observed in HF‐CsA animals, and may have played a role in the accelerated the development of heart failure at both the whole heart and cellular levels. Given the significant detriment to cardiac function observed in response to CsA, our findings suggest chronic CsA treatment is not a viable therapeutic option for HFpEF.

In a recently developed a translational mini‐swine model of heart failure with preserved ejection fraction (HFpEF), we hypothesized inhibiting mitochondrial permeability transition using cyclosporine (CsA) would improve cardiomyocyte function and calcium handling by supporting mitochondrial function. The purpose of this study was to examine the impact of inhibiting cyclophilin D on mitochondrial function and subsequent cardiomyocyte calcium handling using a reduced, nonimmunosuppressive dose of CsA chronically. We found improved mitochondrial function following chronic CsA treatment was not associated with a parallel improvement in cardiomyocyte calcium handling and contractile function, and demonstrate for the first time impaired cardiomyocyte calcium handling and contractile function are present early in the disease process in our HFpEF model.

A new twist on an old idea: a two-dimensional speckle tracking assessment of cyclosporine as a therapeutic alternative for heart failure with preserved ejection fraction

We recently reported that mitochondrial dysfunction, characterized by increased mitochondrial permeability transition (MPT), was present in a translational swine model of heart failure with preserved ejection fraction (HFpEF). Cyclophilin D is a key component of the MPT pore, therefore, the purpose of this study was to test the efficacy of a novel cyclosporine (CsA) dosing scheme as a therapeutic alternative for HFpEF. Computed tomography (CT), two‐dimensional speckle tracking two‐dimensional speckle tracking (2DST), and invasive hemodynamics were used to evaluate cardiac function. CT imaging showed 14 weeks of CsA treatment caused eccentric myocardial remodeling (contrasting concentric remodeling in untreated HF animals) and elevated systemic pressures. 2DST detected left ventricular (LV) mechanics associated with systolic and diastolic dysfunction prior to the onset of significantly increased LV end diastolic pressure including: (1) decreased systolic apical rotation rate, longitudinal displacement, and longitudinal/radial/circumferential strain; (2) decreased early diastolic untwisting and longitudinal strain rate; and (3) increased late diastolic radial/circumferential mitral strain rate. LV mechanics associated with systolic and diastolic impairment was enhanced to a greater extent than seen in untreated HF animals following CsA treatment. In conclusion, CsA treatment accelerated the development of heart failure, including dilatory LV remodeling and impaired systolic and diastolic mechanics. Although our findings do not support CsA as a viable therapy for HFpEF, 2DST was effective in differentiating between progressive gradations of developing HF and detecting diastolic impairment prior to the development of overt diastolic dysfunction.

We recently reported that mitochondrial dysfunction, characterized by increased mitochondrial permeability transition (MPT), was present in a translational swine model of heart failure with preserved ejection fraction (HFpEF). Cyclophilin D is a key component of the MPT pore, therefore, the purpose of this study was to test the efficacy of a novel cyclosporine (CsA) dosing scheme as a therapeutic alternative for HFpEF. CsA treatment accelerated the development of heart failure, including dilatory LV remodeling and impaired systolic and diastolic mechanics. Although our findings do not support CsA as a viable therapy for HFpEF, 2DST was effective in differentiating between progressive gradations of developing HF and detecting diastolic impairment prior to the development of overt diastolic dysfunction.

The rate of ATP export in the extramitochondrial phase via the adenine nucleotide translocator changes in aging in mitochondria isolated from heart left ventricle of either normotensive or spontaneously hypertensive rats

To find out whether and how deficit of cellular energy supply from mitochondria to cytosol occurs in aging and hypertension, we used mitochondria isolated from 5 to 72 week-old heart left ventricle of either normotensive (WKY) or spontaneous hypertensive (SH) rats as a model system. Measurements were made of the rate of ATP appearance outside mitochondria, due to externally added ADP, as an increase of NADPH absorbance which occurs when ATP is produced in the presence of glucose, hexokinase and glucose-6-phosphate dehydrogenase. Such a rate proved to mirror the function of the adenine nucleotide translocator (ANT) rather than other processes linked to the both oxidative and substrate level phosphorylation. The changes in both Ki for atractyloside and Km for ADP suggest the occurrence of modification of the ANT conformation during aging in which the ANT Vmax was found to decrease in normotensive but to increase under spontaneously hypertension in 24 week-old rats with a subsequent decrease in both cases. ANT function, as investigated in the ADP physiological range (20-60μM), is expected to decrease in normotensive, but to increase in hypertensive rats up to 48 weeks. Later a decrease in the ATP rate of export outside mitochondria should occur in both cases.

Impaired subendocardial wall thickening and post-systolic shortening are signs of critical myocardial ischemia in patients with flow-limiting coronary stenosis

BACKGROUND

The early diagnosis of myocardial ischemia is still challenging. The aim of the present study was to determine whether subendocardial hypokinesis and post-systolic contraction could be early markers of myocardial ischemia.

METHODS AND RESULTS

Thirty-one consecutive patients with flow-limiting severe coronary stenosis but without visually abnormal left ventricular wall motion underwent quantitative echocardiography. Myocardial strain was measured using layer-by-layer analysis in severely hypoperfused segments. Radial strain (RS) was measured in the subendocardial, subepicardial, and total wall (innerRS, outerRS, and totalRS, respectively). Circumferential strain (CS) was also measured as 3 separate layers: subendocardial, mid-layer, and subepicardial layers (innerCS, midCS, and outerCS, respectively). Post-systolic shortening (PSS) was defined as the peak strain after end systole, and post-systolic strain index (PSI) was calculated as PSS divided by end-systolic strain. TotalRS was similar between ischemic and normally perfused segments, but innerRS and inner/outer RS ratio were significantly smaller in the ischemic segments than in corresponding segments in healthy subjects. Receiver operating characteristic analysis identified an optimum cut-off for PSI of 0.6. The combined criteria of inner/outer RS ratio <1.0 and PSI >0.6 achieved 95% specificity for the presence of flow-limiting stenosis.

CONCLUSIONS

Combined assessment of both subendocardial contractile impairment and PSS is very useful in identifying a severely hypoperfused left ventricular wall even without visual wall motion abnormality.

The bone mass (BM) and chronic cardiac decompensation (CCD) in an elderly population

This study intended to evaluate the existing correlation between the cardiac compensation and the bone mass, investigating the bone mineral density (BMD) in a population suffering from CCD or chronic heart disease (CHD). We enrolled 171 patients, all over the age of 70, being in the functional N.Y.H.A. Class II (Population A: 85 patients) and in Class III (Population B: 86 patients). All patients underwent an analysis of their cardiac functions using a Doppler echo-cardiographic method measuring the ventricular ejection fraction (VEF), as well as the BMD by means of a computerized bone mineralometric DEXA method, performed in vertebral and femoral measurement sites. Both populations proved to be osteopenic, displaying reduced values of BMD. Higher bone mineral losses were measured in the patients who had more severe cardiac insufficiency. The present data revealed a significant reduction of BMD in the N.Y.H.A. Class III patients, in correlation with the VEF (p<0.001), both in the lumbar vertebral area (p<0.01) and even more in the femoral sites (p<0.001), where a direct correlation exists between BMD and the VEF. On the basis of these findings one can suggest that the actual VEF level has an influence on the bone turnover, reducing the mineral content through various mechanisms of action.

Novel strategy for measuring creatine kinase reaction rate in the in vivo heart

In the heart, the creatine kinase (CK) system plays an important role in the cascade of ATP production, transportation, and utilization. The forward pseudo-first-order rate constant for the CK reaction can be measured noninvasively by the (31)P-magnetic resonance (MR) spectroscopy magnetization saturation transfer (MST) techniques. However, the measurement of MST in the in vivo heart is limited by the lengthy data acquisition time, especially for studies requiring spatial localization. This technical report presents a new method for measuring ATP production rate via CK that can reduce the MST data acquisition time by 82%. This method is validated using an in vivo pig model to evaluate the forward pseudo-first-order rate constant of myocardial CK reaction noninvasively.

Cardiovascular proteomics: past, present, and future

With cardiovascular (CV)-related disorders accounting for the highest mortality rates in the world, affecting the quantity and quality of life of patients and creating an economic burden of prolonged therapeutic intervention, there is great significance in understanding the cellular and molecular alterations that influence the progression of these pathologies. The cellular genotype is regulated by the DNA component, whilst the cellular phenotype is influenced by the protein complement. By improving the understanding of the molecular mechanisms that influence the protein profile, the pathologies that influence the intrinsic functions of the CV system may be detected earlier or managed more efficiently. This is achievable with technologies encompassed by 'proteomics.' Proteomic investigations of CV diseases, including dilated cardiomyopathy (DCM), atherosclerosis, and ischemia/reperfusion (I/R) injury, have identified candidate proteins altered with the pathologic states, complementing past biochemical and physiologic observations. Whilst proteomics is still a relatively new discipline to be applied to the basic scientific investigation of CV diseases, it is emerging as a technique to screen for potential biomarkers in both tissues/cells and biologic fluids (biofluids), as well as to identify the targets of existing therapeutics. By enabling the separation of complex mixtures over numerous dimensions, exploiting the intrinsic properties of proteins, including charge state, molecular mass, and hydrophobicity, in addition to cellular location, the discrete alterations within the cell may be resolved. Proteomics has shown alterations to myofilament proteins including troponin I and myosin light chain, correlating with the reduction in contractility in the myocardium from DCM and I/R. The diverse cell types that coalesce to induce atherosclerotic plaque formation have been investigated both collectively and individually to elucidate the influence of the modifications to single cell types on the developing plaque as a whole. Proteomics has also been used to observe changes to biofluids occurring with these pathologies, a new potential link between basic science and clinical applications. The development of CV proteomics has helped to identify a number of possible protein candidates, and offers the potential to treat and diagnose CV disease more effectively in the future.

Does normothermic normokalemic simultaneous antegrade/retrograde perfusion improve myocardial oxygenation and energy metabolism for hypertrophied hearts?

BACKGROUND

Beating-heart valve surgery appears to be a promising technique for protection of hypertrophied hearts. Normothermic normokalemic simultaneous antegrade/retrograde perfusion (NNSP) may improve myocardial perfusion. However, its effects on myocardial oxygenation and energy metabolism remain unclear. The present study was to determine whether NNSP improved myocardial oxygenation and energy metabolism of hypertrophied hearts relative to normothermic normokalemic antegrade perfusion (NNAP).

METHODS

Twelve hypertrophied pig hearts underwent a protocol consisting of three 20-minute perfusion episodes (10 minutes NNAP and 10 minutes NNSP in a random order) with each conducted at a different blood flow in the left anterior descending coronary artery (LAD [100%, 50%, and 20% of its initial control]). Myocardial oxygenation was assessed using near-infrared spectroscopic imaging. Myocardial energy metabolism was monitored using localized phosphorus-31 magnetic resonance spectroscopy.

RESULTS

With 100% LAD flow, both NNAP and NNSP maintained myocardial oxygenation, adenosine triphosphate, phosphocreatine, and inorganic phosphate at normal levels. When LAD flow was reduced to 50% of its control level, NNSP resulted in a small but significant decrease in myocardial oxygenation and phosphocreatine, whereas those measurements did not change significantly during NNAP. With LAD flow further reduced to 20% of its control level, both NNAP and NNSP caused a substantial decrease in myocardial oxygenation, adenosine triphosphate, and phosphocreatine with an increase in inorganic phosphate. However, the changes were significantly greater during NNSP than during NNAP.

CONCLUSIONS

Normothermic normokalemic simultaneous antegrade/retrograde perfusion did not improve, but slightly impaired myocardial oxygenation and energy metabolism of beating hypertrophied hearts relative to NNAP. Therefore, NNSP for protection of beating hypertrophied hearts during valve surgery should be used with extra caution.

Keeping the heart empty and beating improves preservation of hypertrophied hearts for valve surgery

OBJECTIVE

This study was designed to determine whether keeping the heart empty and beating improved myocardial fluid homeostasis and energy metabolism of hypertrophied pig hearts in comparison with cardioplegic arrest.

METHODS

Twenty piglets underwent a 8-weeks (corrected) ascending aortic banding to induce left ventricular hypertrophy. Isolated hypertrophied hearts were divided into 4 groups (n = 5 in each group). Two groups underwent normothermic normokalemic simultaneous perfusion. The other 2 groups were subjected to normothermic hyperkalemic simultaneous perfusion and used as controls. Intramyocardial hydrostatic pressure was monitored with a microtip pressure transducer. Volumes of intracellular and extracellular compartments and myocardial energy metabolism were monitored by using phosphorus 31 magnetic resonance spectroscopy.

RESULTS

Normothermic normokalemic simultaneous perfusion (NNSP) maintained intramyocardial hydrostatic pressure at a significantly lower level (13.0 +/- 0.6 mm Hg) compared with normothermic hyperkalemic simultaneous perfusion (NHSP) (23.3 +/- 1.2 mm Hg) during a 90-minute preservation. NNSP maintained the normal volume of the intracellular compartment throughout the preservation period, whereas NHSP caused significant enlargement (to 123% +/- 6% of its normal volume) of the intracellular compartment. Expansion of the extracellular compartment during preservation was significantly less in the NNSP group (124% +/- 6%) than in the NHSP group (152% +/- 7%). NNSP maintained normal levels of phosphocreatine and adenosine triphosphate until coronary perfusion flow was reduced to 50% of the initial control level. No decrease in energy metabolites was observed in the NHSP group even when coronary perfusion flow was reduced to 10% of the initial control level.

CONCLUSIONS

Keeping the heart empty and beating improves myocardial fluid homeostasis for hypertrophied hearts relative to cardioplegic arrest. Its ability to maintain energy metabolism depends on the degree of coronary stenosis. This technique may be a promising protective strategy for hypertrophied hearts.

Heart failure: a model of cardiac and skeletal muscle energetic failure

Chronic heart failure (CHF), the new epidemic in cardiology, is characterized by energetic failure of both cardiac and skeletal muscles. The failing heart wastes energy due to anatomical changes that include cavity enlargement, altered geometry, tachycardia, mitral insufficiency and abnormal loading, while skeletal muscle undergoes atrophy. Cardiac and skeletal muscles also have altered high-energy phosphate production and handling in CHF. Nevertheless, there are differences in the phenotype of myocardial and skeletal muscle myopathy in CHF: cardiomyocytes have a lower mitochondrial oxidative capacity, abnormal substrate utilisation and intracellular signalling but a maintained oxidative profile; in skeletal muscle, by contrast, mitochondrial failure is less clear, and there is altered microvascular reactivity, fibre type shifts and abnormalities in the enzymatic systems involved in energy distribution. Underlying these phenotypic abnormalities are changes in gene regulation in both cardiac and skeletal muscle cells. Here, we review the latest advances in cardiac and skeletal muscle energetic research and argue that energetic failure could be taken as a unifying mechanism leading to contractile failure, ultimately resulting in skeletal muscle energetic failure, exertional fatigue and death.

Mitochondrial creatine kinase in human health and disease

Mitochondrial creatine kinase (MtCK), together with cytosolic creatine kinase isoenzymes and the highly diffusible CK reaction product, phosphocreatine, provide a temporal and spatial energy buffer to maintain cellular energy homeostasis. Mitochondrial proteolipid complexes containing MtCK form microcompartments that are involved in channeling energy in form of phosphocreatine rather than ATP into the cytosol. Under situations of compromised cellular energy state, which are often linked to ischemia, oxidative stress and calcium overload, two characteristics of mitochondrial creatine kinase are particularly relevant: its exquisite susceptibility to oxidative modifications and the compensatory up-regulation of its gene expression, in some cases leading to accumulation of crystalline MtCK inclusion bodies in mitochondria that are the clinical hallmarks for mitochondrial cytopathies. Both of these events may either impair or reinforce, respectively, the functions of mitochondrial MtCK complexes in cellular energy supply and protection of mitochondria form the so-called permeability transition leading to apoptosis or necrosis.

Mitochondrial contact sites: Their role in energy metabolism and apoptosis

The energy metabolism of the failing heart is characterised by a 30% decrease of the total adenine nucleotides content and what may be more important by a 60% loss of creatine and creatine phosphate [J.S. Ingwall, R.G. Weiss, Is the failing heart energy starved? On using chemical energy to support cardiac function, Circ. Res. 95 (2004) 35-145]. Besides the effect of these changes on the energy supply, failing heart is known to be more vulnerable to Ca2+ overload and apoptosis-inducing processes. Recent studies have pointed to the critical role of mitochondrial contact sites in controlling both the mitochondrial energy metabolism and Ca2+ homeostasis. This review focuses on the structure and function of protein complexes in mitochondrial contact sites and their regulatory role in the cellular bioenergetics, intra- and extra-mitochondrial Ca2+ levels, and release of apoptosis-inducing factors. Firstly, we review the compositions of different contact sites following by the discussion of experimental data obtained with isolated and reconstituted voltage-dependent anion channel-adenine nucleotide translocase complexes and consequences of the complex disassembling. Furthermore, we describe experiments involving the complex-stabilizing conditions in vitro and in intact cells. At the end, we discuss unsolved problems and opportunities for clinical application of the complex-stabilizing factors.

Genome-wide expression dynamics during mouse embryonic development reveal similarities to Drosophila development

Gene transcription mediates many vital aspects of mammalian embryonic development. A comprehensive characterization and analysis of the dynamics of gene transcription in the embryo is therefore likely to provide significant insights into the basic mechanisms of this process. We used microarrays to map transcription in the mouse embryo in the important period from embryonic day 8 (e8.0) to postnatal day 1 (p1) during which the bulk of the differentiation and development of organ systems takes place. Analysis of these expression profiles revealed distinct patterns of gene expression which correlate with the differentiation of organs including the nervous system, liver, skin, lungs, and digestive system, among others. Statistical analysis of the data based on Gene Ontology (GO) group annotation showed that specific temporal sequence patterns in gene class utilization across development are very similar to patterns seen during the embryonic development of Drosophila, suggesting conservation of the temporal progression of these processes across 550 million years of evolution. The temporal profiles of gene expression and activation of processes revealed here provide intriguing insights into the mechanisms of mammalian development, embryogenesis, and organogenesis, as well as into the evolution of developmental processes.

Acute toxicity of doxorubicin on isolated perfused heart: response of kinases regulating energy supply

Doxorubicin (DXR) is a widely used and efficient anticancer drug. However, its application is limited by the risk of severe cardiotoxicity. Impairment of cardiac high-energy phosphate homeostasis is an important manifestation of both acute and chronic DXR cardiotoxic action. Using the Langendorff model of the perfused rat heart, we characterized the acute effects of 1-h perfusion with 2 or 20 microM DXR on two key kinases in cardiac energy metabolism, creatine kinase (CK) and AMP-activated protein kinase (AMPK), and related them to functional responses of the perfused heart and structural integrity of the contractile apparatus as well as drug accumulation in cardiomyocytes. DXR-induced changes in CK were dependent on the isoenzyme, with a shift in protein levels of cytosolic isoenzymes from muscle-type CK to brain-type CK, and a destabilization of octamers of the mitochondrial isoenzyme (sarcometric mitochondrial CK) accompanied by drug accumulation in mitochondria. Interestingly, DXR rapidly reduced the protein level and phosphorylation of AMPK as well as phosphorylation of its target, acetyl-CoA-carboxylase. AMPK was strongly affected already at 2 microM DXR, even before substantial cardiac dysfunction occurred. Impairment of CK isoenzymes was mostly moderate but became significant at 20 microM DXR. Only at 2 microM DXR did upregulation of brain-type CK compensate for inactivation of other isoenzymes. These results suggest that an impairment of kinase systems regulating cellular energy homeostasis is involved in the development of DXR cardiotoxicity.

Genetic manipulation of calcium-handling proteins in cardiac myocytes. II. Mathematical modeling studies

We developed a mathematical model specific to rat ventricular myocytes that includes electrophysiological representation, ionic homeostasis, force production, and sarcomere movement. We used this model to interpret, analyze, and compare two genetic manipulations that have been shown to increase myocyte relaxation rates, parvalbumin (Parv) de novo expression, and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2a) overexpression. The model was used to seek mechanistic insights into 1) the relative contribution of two mechanisms by which SERCA2a overexpression modifies Ca2+ sequestration, i.e., more pumps and an increase in the SERCA2a-to-phospholamban ratio, 2) the mechanisms behind postrest potentiation and how Parv and SERCA2a influence this response, and 3) why Parv myocytes retain their fast kinetics when endogenous SERCA2a is partially impaired by thapsigargin (a condition used to mimic diastolic dysfunction). The model was also utilized to predict whether Parv metal-binding characteristics might be modified to improve diastolic and systolic functions and whether Parv or SERCA2a might affect diastolic Ca2+ levels and myocyte energetics. One outcome of the model was to demonstrate a higher peak and total ATP consumption in SERCA2a myocytes and more even distribution of ATP throughout the cardiac cycle in Parv myocytes. This may have implications for failing hearts that are energetically compromised.

Energy metabolism in heart failure

Heart failure (HF) is a syndrome resulting from the inability of the cardiac pump to meet the energy requirements of the body. Despite intensive work, the pathogenesis of the cardiac intracellular abnormalities that result from HF remains incompletely understood. Factors that lead to abnormal contraction and relaxation in the failing heart include metabolic pathway abnormalities that result in decreased energy production, energy transfer and energy utilization. Heart failure also affects the periphery. Patients suffering from heart failure always complain of early muscular fatigue and exercise intolerance. This is linked in part to intrinsic alterations of skeletal muscle, among which decreases in the mitochondrial ATP production and in the transfer of energy through the phosphotransfer kinases play an important role. Alterations in energy metabolism that affect both cardiac and skeletal muscles argue for a generalized metabolic myopathy in heart failure. Recent evidence shows that decreased expression of mitochondrial transcription factors and mitochondrial proteins are involved in mechanisms causing the energy starvation in heart failure. This review will focus on energy metabolism alterations in long-term chronic heart failure with only a few references to compensated hypertrophy when necessary. It will briefly describe the energy metabolism of normal heart and skeletal muscles and their alterations in chronic heart failure. It is beyond the scope of this review to address the metabolic switches occurring in compensated hypertrophy; readers could refer to well-documented reviews on this subject.

Proteomics of heart disease

Heart diseases resulting in heart failure are among the leading causes of morbidity and mortality in developed countries. The underlying molecular causes of cardiac dysfunction in most heart diseases are still largely unknown, but are likely to result from underlying alterations in gene and protein expression. Proteomics now allows us to examine global alterations in protein expression in the diseased heart and will provide new insights into cellular mechanisms involved in cardiac dysfunction and should also result in the generation of new diagnostic and therapeutic markers. In this article we review the current status of proteomic technologies and describe how these are being applied to studies of human heart disease.

Measuring in-vivo metabolism using nuclear magnetic resonance

PURPOSE OF REVIEW

This review introduces physiologists and clinical investigators to an ever-widening array of nuclear magnetic resonance applications. In particular, it highlights a multiple tracer technique that provides a comprehensive picture of metabolic processes within human liver.

RECENT FINDINGS

Magnetic resonance spectroscopy is an important technique for studying metabolism in the brain, liver, heart and skeletal muscle. One fundamental advantage is that the studies are inherently noninvasive, so time-dependent information can be obtained. For example, 31P nuclear magnetic resonance investigations indicate that greater maximal oxygen uptake and oxidative capacity in trained athletes can be partially attributed to adaptations enhancing the rates at which phosphocreatine and inorganic phosphate recover during stress. In-vivo measurements of lipids and glycogen by 1H and 13C spectroscopy demonstrate that accumulation of intracellular lipids and impaired rates of glycogen synthesis contribute to insulin resistance and type 2 diabetes mellitus. Similar techniques can be used to analyze blood and urine samples obtained during administration of 2H or 13C tracers to yield information that cannot be easily obtained by mass spectrometry. Additional information available from nuclear magnetic resonance yields a comprehensive picture of liver metabolic pathways from a single clinical study.

SUMMARY

A variety of magnetic resonance spectroscopy protocols have been validated and exploited for clinical studies, but relatively few investigators are comfortable with technical aspects of these protocols and utilize them for clinical research. Increased interaction between spectroscopists and other investigators is needed if the potential of nuclear magnetic resonance for studying in-vivo metabolism is to be fully realized.

The adenine nucleotide translocator: regulation and function during myocardial development and hypertrophy

1. The present review focuses on the adenine nucleotide translocator (ANT), which facilitates exchange of cytosolic ADP for mitochondrial ATP. This protein serves a central role in regulating cellular oxidative capacity. 2. The ANT, a nuclear-encoded mitochondrial protein, is developmentally regulated and, thus, accumulates within the mitochondrial membrane during maturation. 3. Accumulation of ANT parallels changes in kinetics of myocardial respiration determined from 31P magnetic resonance spectroscopy studies. 4. Thyroid hormone modulates developmental transitions in ANT content, as well as respiratory control patterns. These transitions are linked to quantitative ANT changes, not to alterations in functionality at individual exchanger sites. 5. Developmental programming for ANT and parallel alterations in oxidative phosphorylation kinetics are relevant to the heart, which exhibits remodelling in response to pathological processes. Maladaptive hearts exhibiting ANT deficits demonstrate ADP-dependent respiratory kinetics similar to the newborn heart. Thus, ANT deficits and alterations in mitochondrial respiratory function may contribute to the pathogenesis of myocardial remodelling and heart failure.