Comparison of the stage-dependent mitochondrial changes in response to pressure overload between the diseased right and left ventricle in the rat

The right ventricle (RV) differs developmentally, anatomically and functionally from the left ventricle (LV). Therefore, characteristics of LV adaptation to chronic pressure overload cannot easily be extrapolated to the RV. Mitochondrial abnormalities are considered a crucial contributor in heart failure (HF), but have never been compared directly between RV and LV tissues and cardiomyocytes. To identify ventricle-specific mitochondrial molecular and functional signatures, we established rat models with two slowly developing disease stages (compensated and decompensated) in response to pulmonary artery banding (PAB) or ascending aortic banding (AOB). Genome-wide transcriptomic and proteomic analyses were used to identify differentially expressed mitochondrial genes and proteins and were accompanied by a detailed characterization of mitochondrial function and morphology. Two clearly distinguishable disease stages, which culminated in a comparable systolic impairment of the respective ventricle, were observed. Mitochondrial respiration was similarly impaired at the decompensated stage, while respiratory chain activity or mitochondrial biogenesis were more severely deteriorated in the failing LV. Bioinformatics analyses of the RNA-seq. and proteomic data sets identified specifically deregulated mitochondrial components and pathways. Although the top regulated mitochondrial genes and proteins differed between the RV and LV, the overall changes in tissue and cardiomyocyte gene expression were highly similar. In conclusion, mitochondrial dysfuntion contributes to disease progression in right and left heart failure. Ventricle-specific differences in mitochondrial gene and protein expression are mostly related to the extent of observed changes, suggesting that despite developmental, anatomical and functional differences mitochondrial adaptations to chronic pressure overload are comparable in both ventricles.

Exercise Hemodynamics and Mitochondrial Oxidative Capacity in Disease Stages of Wild-Type Transthyretin Amyloid Cardiomyopathy

BACKGROUND

Wild-type transthyretin amyloid (ATTRwt) cardiomyopathy is increasingly recognized in the development of heart failure. The link between cardiac performance, hemodynamics, and mitochondrial function in disease stages of ATTRwt has not previously been studied but may provide new insights into the pathophysiology and clinical performance of the patients.

METHODS AND RESULTS

The study investigated 47 patients diagnosed with ATTRwt at Aarhus University Hospital, Denmark. Patients were stratified according to the disease stages of the National Amyloidosis Centre (NAC) as NAC I with low levels of NT-proBNP (N-terminal pro-B-type natriuretic peptide) (NAC I-L, n=14), NAC I with high levels NT-proBNP (NAC I-H, n=20), and NAC II-III (n=13). Exercise testing with simultaneous right heart catheterization was performed in all patients. Endomyocardial biopsies were collected from the patients and the mitochondrial oxidative phosphorylation capacity was assessed. All NAC disease groups, even in the NAC I-L group, a significant abnormal increase in biventricular filling pressures were noted during exercise while the filling pressures was normal or near normal at rest. The inotropic response to exercise was reduced with diminished increase in cardiac output which was significantly more pronounced in the NAC I-H (Diff. -2.4, 95% CI (-4.2: -0.7), P=0.00) and the NAC II-III group (Diff: -3.1 L/min, 95% CI (-5.2: -1.1), P=0.00) compared with the NAC I-L group. The pulmonary artery wedge pressure to cardiac output ratio at peak exercise was significantly different between NAC I-L and NAC II-III (Diff: 1.6 mm Hg*min/L, 95% CI (0.01:3.3, P=0.04)). Patients with ATTRwt had a reduced oxidative phosphorylation capacity which correlated to left ventricular mass but not to cardiac output capacity.

CONCLUSIONS

An abnormal restrictive left ventricle and right ventricle response to exercise was demonstrated, even present in patients with early-stage ATTRwt. In more advanced disease stages a progressive impairment of the pressure-flow relationship was noted. The myocyte energetics is deranged but not associated to the contractile reserve or restrictive filling characteristics in ATTRwt.

Macrophages in cardiovascular diseases: molecular mechanisms and therapeutic targets

The immune response holds a pivotal role in cardiovascular disease development. As multifunctional cells of the innate immune system, macrophages play an essential role in initial inflammatory response that occurs following cardiovascular injury, thereby inducing subsequent damage while also facilitating recovery. Meanwhile, the diverse phenotypes and phenotypic alterations of macrophages strongly associate with distinct types and severity of cardiovascular diseases, including coronary heart disease, valvular disease, myocarditis, cardiomyopathy, heart failure, atherosclerosis and aneurysm, which underscores the importance of investigating macrophage regulatory mechanisms within the context of specific diseases. Besides, recent strides in single-cell sequencing technologies have revealed macrophage heterogeneity, cell-cell interactions, and downstream mechanisms of therapeutic targets at a higher resolution, which brings new perspectives into macrophage-mediated mechanisms and potential therapeutic targets in cardiovascular diseases. Remarkably, myocardial fibrosis, a prevalent characteristic in most cardiac diseases, remains a formidable clinical challenge, necessitating a profound investigation into the impact of macrophages on myocardial fibrosis within the context of cardiac diseases. In this review, we systematically summarize the diverse phenotypic and functional plasticity of macrophages in regulatory mechanisms of cardiovascular diseases and unprecedented insights introduced by single-cell sequencing technologies, with a focus on different causes and characteristics of diseases, especially the relationship between inflammation and fibrosis in cardiac diseases (myocardial infarction, pressure overload, myocarditis, dilated cardiomyopathy, diabetic cardiomyopathy and cardiac aging) and the relationship between inflammation and vascular injury in vascular diseases (atherosclerosis and aneurysm). Finally, we also highlight the preclinical/clinical macrophage targeting strategies and translational implications.

Inferring mitochondrial and cytosolic metabolism by coupling isotope tracing and deconvolution

The inability to inspect metabolic activities within distinct subcellular compartments has been a major barrier to our understanding of eukaryotic cell metabolism. Previous work addressed this challenge by analyzing metabolism in isolated organelles, which grossly bias metabolic activity. Here, we describe a method for inferring physiological metabolic fluxes and metabolite concentrations in mitochondria and cytosol based on isotope tracing experiments performed with intact cells. This is made possible by computational deconvolution of metabolite isotopic labeling patterns and concentrations into cytosolic and mitochondrial counterparts, coupled with metabolic and thermodynamic modelling. Our approach lowers the uncertainty regarding compartmentalized fluxes and concentrations by one and three orders of magnitude compared to existing modelling approaches, respectively. We derive a quantitative view of mitochondrial and cytosolic metabolic activities in central carbon metabolism across cultured cell lines without performing cell fractionation, finding major variability in compartmentalized malate-aspartate shuttle fluxes. We expect our approach for inferring metabolism at a subcellular resolution to be instrumental for a variety of studies of metabolic dysfunction in human disease and for bioengineering.

Metabolomic Profiles, Ideal Cardiovascular Health, and Risk of Heart Failure and Atrial Fibrillation: Insights From the Framingham Heart Study

Background The American Heart Association's framework "ideal cardiovascular health" (CVH) focuses on modifiable risk factors to reduce cardiovascular disease (CVD). Metabolomics provides important pathobiological insights into risk factors and CVD development. We hypothesized that metabolomic signatures associate with CVH status, and that metabolites, at least partially, mediate the association of CVH score with atrial fibrillation (AF) and heart failure (HF). Methods and Results We studied 3056 adults in the FHS (Framingham Heart Study) cohort to evaluate CVH score and incident outcomes of AF and HF. Metabolomics data were available in 2059 participants; mediation analysis was performed to evaluate the mediation of metabolites in the association of CVH score and incident AF and HF. In the smaller cohort (mean age, 54 years; 53% women), CVH score was associated with 144 metabolites, with 64 metabolites shared across key cardiometabolic components (body mass index, blood pressure, and fasting blood glucose) of the CVH score. In mediation analyses, 3 metabolites (glycerol, cholesterol ester 16:1, and phosphatidylcholine 32:1) mediated the association of CVH score with incident AF. Seven metabolites (glycerol, isocitrate, asparagine, glutamine, indole-3-proprionate, phosphatidylcholine C36:4, and lysophosphatidylcholine 18:2), partly mediated the association between CVH score and incident HF in multivariable-adjusted models. Conclusions Most metabolites that associated with CVH score were shared the most among 3 cardiometabolic components. Three main pathways: (1) alanine, glutamine, and glutamate metabolism; (2) citric acid cycle metabolism; and (3) glycerolipid metabolism mediated CVH score with HF. Metabolomics provides insights into how ideal CVH status contributes to the development of AF and HF.

PCr/ATP ratios and mitochondrial function in the heart. A comparative study in humans

Cardiac energy status, measured as phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio with 31P-Magnetic Resonance Spectroscopy (31P-MRS) in vivo, is a prognostic factor in heart failure and is lowered in cardiometabolic disease. It has been suggested that, as oxidative phosphorylation is the major contributor to ATP synthesis, PCr/ATP ratio might be a reflection of cardiac mitochondrial function. The objective of the study was to investigate whether PCr/ATP ratios can be used as in vivo marker for cardiac mitochondrial function. We enrolled thirty-eight patients scheduled for open-heart surgery in this study. Cardiac 31P-MRS was performed before surgery. Tissue from the right atrial appendage was obtained during surgery for high-resolution respirometry for the assessment of mitochondrial function. There was no correlation between the PCr/ATP ratio and ADP-stimulated respiration rates (octanoylcarnitine R² < 0.005, p = 0.74; pyruvate R² < 0.025, p = 0.41) nor with maximally uncoupled respiration (octanoylcarnitine R² = 0.005, p = 0.71; pyruvate R² = 0.040, p = 0.26). PCr/ATP ratio did correlate with indexed LV end systolic mass. As no direct correlation between cardiac energy status (PCr/ATP) and mitochondrial function in the heart was found, the study suggests that mitochondrial function might not the only determinant of cardiac energy status. Interpretation should be done in the right context in cardiac metabolic studies.

Targeting Mitochondrial Metabolism to Save the Failing Heart

Despite considerable progress in treating cardiac disorders, the prevalence of heart failure (HF) keeps growing, making it a global medical and economic burden. HF is characterized by profound metabolic remodeling, which mostly occurs in the mitochondria. Although it is well established that the failing heart is energy-deficient, the role of mitochondria in the pathophysiology of HF extends beyond the energetic aspects. Changes in substrate oxidation, tricarboxylic acid cycle and the respiratory chain have emerged as key players in regulating myocardial energy homeostasis, Ca²⁺ handling, oxidative stress and inflammation. This work aims to highlight metabolic alterations in the mitochondria and their far-reaching effects on the pathophysiology of HF. Based on this knowledge, we will also discuss potential metabolic approaches to improve cardiac function.

Cardiac Metabolism in Heart Failure and Implications for Uremic Cardiomyopathy

Chronic kidney disease is associated with an increased risk for the development and progression of cardiovascular disorders including hypertension, dyslipidemia, and coronary artery disease. Chronic kidney disease may also affect the myocardium through complex systemic changes, resulting in structural remodeling such as hypertrophy and fibrosis, as well as impairments in both diastolic and systolic function. These cardiac changes in the setting of chronic kidney disease define a specific cardiomyopathic phenotype known as uremic cardiomyopathy. Cardiac function is tightly linked to its metabolism, and research over the past 3 decades has revealed significant metabolic remodeling in the myocardium during the development of heart failure. Because the concept of uremic cardiomyopathy has only been recognized in recent years, there are limited data on metabolism in the uremic heart. Nonetheless, recent findings suggest overlapping mechanisms with heart failure. This work reviews key features of metabolic remodeling in the failing heart in the general population and extends this to patients with chronic kidney disease. The knowledge of similarities and differences in cardiac metabolism between heart failure and uremic cardiomyopathy may help identify new targets for mechanistic and therapeutic research on uremic cardiomyopathy.

Inefficient Batteries in Heart Failure: Metabolic Bottlenecks Disrupting the Mitochondrial Ecosystem

Mitochondrial abnormalities have long been described in the setting of cardiomyopathies and heart failure (HF), yet the mechanisms of mitochondrial dysfunction in cardiac pathophysiology remain poorly understood. Many studies have described HF as an energy-deprived state characterized by a decline in adenosine triphosphate production, largely driven by impaired oxidative phosphorylation. However, impairments in oxidative phosphorylation extend beyond a simple decline in adenosine triphosphate production and, in fact, reflect pervasive metabolic aberrations that cannot be fully appreciated from the isolated, often siloed, interrogation of individual aspects of mitochondrial function. With the application of broader and deeper examinations into mitochondrial and metabolic systems, recent data suggest that HF with preserved ejection fraction is likely metabolically disparate from HF with reduced ejection fraction. In our review, we introduce the concept of the mitochondrial ecosystem, comprising intricate systems of metabolic pathways and dynamic changes in mitochondrial networks and subcellular locations. The mitochondrial ecosystem exists in a delicate balance, and perturbations in one component often have a ripple effect, influencing both upstream and downstream cellular pathways with effects enhanced by mitochondrial genetic variation. Expanding and deepening our vantage of the mitochondrial ecosystem in HF is critical to identifying consistent metabolic perturbations to develop therapeutics aimed at preventing and improving outcomes in HF.

Cellular Bioenergetics: Experimental Evidence for Alcohol-induced Adaptations

At-risk alcohol use is associated with multisystemic effects and end-organ injury, and significantly contributes to global health burden. Several alcohol-mediated mechanisms have been identified, with bioenergetic maladaptation gaining credence as an underlying pathophysiological mechanism contributing to cellular injury. This evidence-based review focuses on the current knowledge of alcohol-induced bioenergetic adaptations in metabolically active tissues: liver, cardiac and skeletal muscle, pancreas, and brain. Alcohol metabolism itself significantly interferes with bioenergetic pathways in tissues, particularly the liver. Alcohol decreases states of respiration in the electron transport chain, and activity and expression of respiratory complexes, with a net effect to decrease ATP content. In addition, alcohol dysregulates major metabolic pathways, including glycolysis, the tricarboxylic acid cycle, and fatty acid oxidation. These bioenergetic alterations are influenced by alcohol-mediated changes in mitochondrial morphology, biogenesis, and dynamics. The review highlights similarities and differences in bioenergetic adaptations according to tissue type, pattern of (acute vs. chronic) alcohol use, and energy substrate availability. The compromised bioenergetics synergizes with other critical pathophysiological mechanisms, including increased oxidative stress and accelerates cellular dysfunction, promoting senescence, programmed cell death, and end-organ injury.

Reversible Thiol Oxidation Increases Mitochondrial Electron Transport Complex Enzyme Activity but Not Respiration in Cardiomyocytes from Patients with End-Stage Heart Failure

Cardiomyocyte dysfunction in patients with end-stage heart failure with reduced ejection fraction (HFrEF) stems from mitochondrial dysfunction, which contributes to an energetic crisis. Mitochondrial dysfunction reportedly relates to increased markers of oxidative stress, but the impact of reversible thiol oxidation on myocardial mitochondrial function in patients with HFrEF has not been investigated. In the present study, we assessed mitochondrial function in ventricular biopsies from patients with end-stage HFrEF in the presence and absence of the thiol-reducing agent dithiothreitol (DTT). Isolated mitochondria exposed to DTT had increased enzyme activity of complexes I (p = 0.009) and III (p = 0.018) of the electron transport system, while complexes II (p = 0.630) and IV (p = 0.926) showed no changes. However, increased enzyme activity did not carry over to measurements of mitochondrial respiration in permeabilized bundles. Oxidative phosphorylation conductance (p = 0.439), maximal respiration (p = 0.312), and ADP sensitivity (p = 0.514) were unchanged by 5 mM DTT treatment. These results indicate that mitochondrial function can be modulated through reversible thiol oxidation, but other components of mitochondrial energy transfer are rate limiting in end-stage HFrEF. Optimal therapies to normalize cardiac mitochondrial respiration in patients with end-stage HFrEF may benefit from interventions to reverse thiol oxidation, which limits complex I and III activities.

Understanding How Heart Metabolic Derangement Shows Differential Stage Specificity for Heart Failure with Preserved and Reduced Ejection Fraction

Heart failure (HF) is a clinical condition defined by structural and functional abnormalities in the heart that gradually result in reduced cardiac output (HFrEF) and/or increased cardiac pressures at rest and under stress (HFpEF). The presence of asymptomatic individuals hampers HF identification, resulting in delays in recognizing patients until heart dysfunction is manifested, thus increasing the chance of poor prognosis. Given the recent advances in metabolomics, in this review we dissect the main alterations occurring in the metabolic pathways behind the decrease in cardiac function caused by HF. Indeed, relevant preclinical and clinical research has been conducted on the metabolite connections and differences between HFpEF and HFrEF. Despite these promising results, it is crucial to note that, in addition to identifying single markers and reliable threshold levels within the healthy population, the introduction of composite panels would strongly help in the identification of those individuals with an increased HF risk. That said, additional research in the field is required to overcome the current drawbacks and shed light on the pathophysiological changes that lead to HF. Finally, greater collaborative data sharing, as well as standardization of procedures and approaches, would enhance this research field to fulfil its potential.

Traditional Chinese medicine enhances myocardial metabolism during heart failure

The prognosis of various cardiovascular diseases eventually leads to heart failure (HF). An energy metabolism disorder of cardiomyocytes is important in explaining the molecular basis of HF; this will aid global research regarding treatment options for HF from the perspective of myocardial metabolism. There are many drugs to improve myocardial metabolism for the treatment of HF, including angiotensin receptor blocker-neprilysin inhibitor (ARNi) and sodium glucose cotransporter 2 (SGLT-2) inhibitors. Although Western medicine has made considerable progress in HF therapy, the morbidity and mortality of the disease remain high. Therefore, HF has attracted attention from researchers worldwide. In recent years, the application of traditional Chinese medicine (TCM) in HF treatment has been gradually accepted, and many studies have investigated the mechanism whereby TCM improves myocardial metabolism; the TCMs studied include Danshen yin, Fufang Danshen dripping pill, and Shenmai injection. This enables the clinical application of TCM in the treatment of HF by improving myocardial metabolism. We systematically reviewed the efficacy of TCM for improving myocardial metabolism during HF as well as the pharmacological effects of active TCM ingredients on the cardiovascular system and the potential mechanisms underlying their ability to improve myocardial metabolism. The results indicate that TCM may serve as a complementary and alternative approach for the prevention of HF. However, further rigorously designed randomized controlled trials are warranted to assess the effect of TCM on long-term hard endpoints in patients with cardiovascular disease.

Impairment of Multiple Mitochondrial Energy Metabolism Pathways in the Heart of Chagas Disease Cardiomyopathy Patients

Chagas disease cardiomyopathy (CCC) is an inflammatory dilated cardiomyopathy occurring in 30% of the 6 million infected with the protozoan Trypanosoma cruzi in Latin America. Survival is significantly lower in CCC than ischemic (IC) and idiopathic dilated cardiomyopathy (DCM). Previous studies disclosed a selective decrease in mitochondrial ATP synthase alpha expression and creatine kinase activity in CCC myocardium as compared to IDC and IC, as well as decreased in vivo myocardial ATP production. Aiming to identify additional constraints in energy metabolism specific to CCC, we performed a proteomic study in myocardial tissue samples from CCC, IC and DCM obtained at transplantation, in comparison with control myocardial tissue samples from organ donors. Left ventricle free wall myocardial samples were subject to two-dimensional electrophoresis with fluorescent labeling (2D-DIGE) and protein identification by mass spectrometry. We found altered expression of proteins related to mitochondrial energy metabolism, cardiac remodeling, and oxidative stress in the 3 patient groups. Pathways analysis of proteins differentially expressed in CCC disclosed mitochondrial dysfunction, fatty acid metabolism and transmembrane potential of mitochondria. CCC patients’ myocardium displayed reduced expression of 22 mitochondrial proteins belonging to energy metabolism pathways, as compared to 17 in DCM and 3 in IC. Significantly, 6 beta-oxidation enzymes were reduced in CCC, while only 2 of them were down-regulated in DCM and 1 in IC. We also observed that the cytokine IFN-gamma, previously described with increased levels in CCC, reduces mitochondrial membrane potential in cardiomyocytes. Results suggest a major reduction of mitochondrial energy metabolism and mitochondrial dysfunction in CCC myocardium which may be in part linked to IFN-gamma. This may partially explain the worse prognosis of CCC as compared to DCM or IC.

Co-Polarized [1-13C]Pyruvate and [1,3-13C2]Acetoacetate Provide a Simultaneous View of Cytosolic and Mitochondrial Redox in a Single Experiment

Cellular redox is intricately linked to energy production and normal cell function. Although the redox states of mitochondria and cytosol are connected by shuttle mechanisms, the redox state of mitochondria may differ from redox in the cytosol in response to stress. However, detecting these differences in functioning tissues is difficult. Here, we employed ¹³C magnetic resonance spectroscopy (MRS) and co-polarized [1-¹³C]pyruvate and [1,3-¹³C₂]acetoacetate ([1,3-¹³C₂]AcAc) to monitor production of hyperpolarized (HP) lactate and β-hydroxybutyrate as indicators of cytosolic and mitochondrial redox, respectively. Isolated rat hearts were examined under normoxic conditions, during low-flow ischemia, and after pretreatment with either aminooxyacetate (AOA) or rotenone. All interventions were associated with an increase in [P_i]/[ATP] measured by ³¹P NMR. In well-oxygenated untreated hearts, rapid conversion of HP [1-¹³C]pyruvate to [1-¹³C]lactate and [1,3-¹³C₂]AcAc to [1,3-¹³C₂]β-hydroxybutyrate ([1,3-¹³C₂]β-HB) was readily detected. A significant increase in HP [1,3-¹³C₂]β-HB but not [1-¹³C]lactate was observed in rotenone-treated and ischemic hearts, consistent with an increase in mitochondrial NADH but not cytosolic NADH. AOA treatments did not alter the productions of HP [1-¹³C]lactate or [1,3-¹³C₂]β-HB. This study demonstrates that biomarkers of mitochondrial and cytosolic redox may be detected simultaneously in functioning tissues using co-polarized [1-¹³C]pyruvate and [1,3-¹³C₂]AcAc and ¹³C MRS and that changes in mitochondrial redox may precede changes in cytosolic redox.

Metabolic Remodeling and Implicated Calcium and Signal Transduction Pathways in the Pathogenesis of Heart Failure

The heart is an organ with high-energy demands in which the mitochondria are most abundant. They are considered the powerhouse of the cell and occupy a central role in cellular metabolism. The intermyofibrillar mitochondria constitute the majority of the three-mitochondrial subpopulations in the heart. They are also considered to be the most important in terms of their ability to participate in calcium and cellular signaling, which are critical for the regulation of mitochondrial function and adenosine triphosphate (ATP) production. This is because they are located in very close proximity with the endoplasmic reticulum (ER), and for the presence of tethering complexes enabling interorganelle crosstalk via calcium signaling. Calcium is an important second messenger that regulates mitochondrial function. It promotes ATP production and cellular survival under physiological changes in cardiac energetic demand. This is accomplished in concert with signaling pathways that regulate both calcium cycling and mitochondrial function. Perturbations in mitochondrial homeostasis and metabolic remodeling occupy a central role in the pathogenesis of heart failure. In this review we will discuss perturbations in ER-mitochondrial crosstalk and touch on important signaling pathways and molecular mechanisms involved in the dysregulation of calcium homeostasis and mitochondrial function in heart failure.

Human myocardial mitochondrial oxidative capacity is impaired in mild acute heart transplant rejection

Aims

Acute cellular rejection (ACR) following heart transplantation (HTX) is associated with long‐term graft loss and increased mortality. Disturbed mitochondrial bioenergetics have been identified as pathophysiological drivers in heart failure, but their role in ACR remains unclear. We aimed to prove functional disturbances of myocardial bioenergetics in human heart transplant recipients with mild ACR by assessing myocardial mitochondrial respiration using high‐resolution respirometry, digital image analysis of myocardial inflammatory cell infiltration, and clinical assessment of HTX patients. We hypothesized that (i) mild ACR is associated with impaired myocardial mitochondrial respiration and (ii) myocardial inflammation, systemic oxidative stress, and myocardial oedema relate to impaired mitochondrial respiration and myocardial dysfunction.

Methods and results

We classified 35 HTX recipients undergoing endomyocardial biopsy according International Society for Heart and Lung Transplantation criteria to have no (0R) or mild (1R) ACR. Additionally, we quantified immune cell infiltration by immunohistochemistry and digital image analysis. We analysed mitochondrial substrate utilization in myocardial fibres by high‐resolution respirometry and performed cardiovascular magnetic resonance (CMR). ACR (1R) was diagnosed in 12 patients (34%), while the remaining 23 patients revealed no signs of ACR (0R). Underlying cardiomyopathies (dilated cardiomyopathy 50% vs. 65%; P = 0.77), comorbidities (type 2 diabetes mellitus: 50% vs. 35%, P = 0.57; chronic kidney disease stage 5: 8% vs. 9%, P > 0.99; arterial hypertension: 59% vs. 30%, P = 0.35), medications (tacrolimus: 100% vs. 91%, P = 0.54; mycophenolate mofetil: 92% vs. 91%, P > 0.99; prednisolone: 92% vs. 96%, P > 0.99) and time post‐transplantation (21.5 ± 26.0 months vs. 29.4 ± 26.4 months, P = 0.40) were similar between groups. Mitochondrial respiration was reduced by 40% in ACR (1R) compared with ACR (0R) (77.8 ± 23.0 vs. 128.0 ± 33.0; P < 0.0001). Quantitative assessment of myocardial CD3⁺‐lymphocyte infiltration identified ACR (1R) with a cut‐off of >14 CD3⁺‐lymphocytes/mm² (100% sensitivity, 82% specificity; P < 0.0001). Myocardial CD3⁺ infiltration (r = −0.41, P < 0.05), systemic oxidative stress (thiobarbituric acid reactive substances; r = −0.42, P < 0.01) and myocardial oedema depicted by global CMR derived T2 time (r = −0.62, P < 0.01) correlated with lower oxidative capacity and overt cardiac dysfunction (global longitudinal strain; r = −0.63, P < 0.01).

Conclusions

Mild ACR with inflammatory cell infiltration associates with impaired mitochondrial bioenergetics in cardiomyocytes. Our findings may help to identify novel checkpoints in cardiac immune metabolism as potential therapeutic targets in post‐transplant care.

Cardiac hypoxic resistance and decreasing lactate during maximum apnea in elite breath hold divers

Breath-hold divers (BHD) enduring apnea for more than 4 min are characterized by resistance to release of reactive oxygen species, reduced sensitivity to hypoxia, and low mitochondrial oxygen consumption in their skeletal muscles similar to northern elephant seals. The muscles and myocardium of harbor seals also exhibit metabolic adaptations including increased cardiac lactate-dehydrogenase-activity, exceeding their hypoxic limit. We hypothesized that the myocardium of BHD possesses similar adaptive mechanisms. During maximum apnea ¹⁵O-H₂O-PET/CT (n = 6) revealed no myocardial perfusion deficits but increased myocardial blood flow (MBF). Cardiac MRI determined blood oxygen level dependence oxygenation (n = 8) after 4 min of apnea was unaltered compared to rest, whereas cine-MRI demonstrated increased left ventricular wall thickness (LVWT). Arterial blood gases were collected after warm-up and maximum apnea in a pool. At the end of the maximum pool apnea (5 min), arterial saturation decreased to 52%, and lactate decreased 20%. Our findings contrast with previous MR studies of BHD, that reported elevated cardiac troponins and decreased myocardial perfusion after 4 min of apnea. In conclusion, we demonstrated for the first time with ¹⁵O-H₂O-PET/CT and MRI in elite BHD during maximum apnea, that MBF and LVWT increases while lactate decreases, indicating anaerobic/fat-based cardiac-metabolism similar to diving mammals.

Depleted Myocardial Coenzyme Q10 in Cavalier King Charles Spaniels with Congestive Heart Failure Due to Myxomatous Mitral Valve Disease

Congestive heart failure (CHF) has been associated with depleted myocardial coenzyme Q10 (Q10) concentrations in human patients. The aim of this study was to investigate associations between myocardial Q10 concentrations and myxomatous mitral valve disease (MMVD) severity in dogs. Furthermore, citrate synthase (CS) activity was analysed to determine if a reduction in myocardial Q10 was associated with mitochondrial depletion in the myocardium. Thirty Cavalier King Charles spaniels (CKCS) in MMVD stages B1 (n = 11), B2 (n = 5) and C (n = 14) according to the American College of Veterinary Internal Medicine (ACVIM) guidelines and 10 control (CON) dogs of other breeds were included. Myocardial Q10 concentration was analysed in left ventricular tissue samples using HPLC-ECD. CKCS with congestive heart failure (CHF; group C) had significantly reduced Q10 concentrations (median, 1.54 µg/mg; IQR, 1.36–1.94), compared to B1 (2.76 µg/mg; 2.10–4.81, p < 0.0018), B2 (3.85 µg/mg; 3.13–4.46, p < 0.0054) and CON dogs (2.8 µg/mg; 1.64–4.88, p < 0.0089). CS activity was comparable between disease groups. In conclusion, dogs with CHF due to MMVD had reduced myocardial Q10 concentrations. Studies evaluating antioxidant defense mechanisms as a therapeutic target for treatment of CHF in dogs are warranted.

Cancer-induced Cardiac Atrophy Adversely Affects Myocardial Redox State and Mitochondrial Oxidative Characteristics

Cachexia presents in 80% of advanced cancer patients; however, cardiac atrophy in cachectic patients receives little attention. This cardiomyopathy contributes to increased occurrence of adverse cardiac events compared to age-matched population norms. Research on cardiac atrophy has focused on remodeling; however, alterations in metabolic properties may be a primary contributor.

PURPOSE

Determine how cancer-induced cardiac atrophy alters mitochondrial turnover, mitochondrial mRNA translation machinery and in-vitro oxidative characteristics.

METHODS

Lewis lung carcinoma (LLC) tumors were implanted in C57BL6/J mice and grown for 28days to induce cardiac atrophy. Endogenous metabolic species, and markers of mitochondrial function were assessed. H9c2 cardiomyocytes were cultured in LLC-conditioned media with(out) the antioxidant MitoTempo. Cells were analyzed for ROS, oxidative capacity, and hypoxic resistance.

RESULTS

LLC heart weights were ~10% lower than controls. LLC hearts demonstrated ~15% lower optical redox ratio (FAD/FAD+NADH) compared to PBS controls. When compared to PBS, LLC hearts showed ~50% greater COX-IV and VDAC, attributed to ~50% lower mitophagy markers. mt-mRNA translation machinery was elevated similarly to markers of mitochondrial content. mitochondrial DNA-encoded Cytb was ~30% lower in LLC hearts. ROS scavengers GPx-3 and GPx-7 were ~50% lower in LLC hearts. Treatment of cardiomyocytes with LLC-conditioned media resulted in higher ROS (25%), lower oxygen consumption rates (10% at basal, 75% at maximal), and greater susceptibility to hypoxia (~25%) -- which was reversed by MitoTempo.

CONCLUSION

These results substantiate metabolic cardiotoxic effects attributable to tumor-associated factors and provide insight into interactions between mitochondrial mRNA translation, ROS mitigation, oxidative capacity and hypoxia resistance.

Natural Antioxidant Control of Neuropathic Pain-Exploring the Role of Mitochondrial SIRT3 Pathway

Neuropathic pain is a chronic painful disease. Data have shown that reactive oxygen species (ROS) are implicated in chronic pain. Particularly, the enhanced ROS production alters the mitochondrial genome and proteome through the accumulation of lipid peroxidation products, such as 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA). Sirtuin 3 (SIRT3) is a mitochondrial protein and its activity can reduce ROS levels by modulating key antioxidant enzymes, such as manganese superoxide dismutase (MnSOD). Here, we evaluated the role of SIRT3 in the maintenance of basal levels of ROS in a model of chronic constriction injury (CCI) of the sciatic nerve and the protective effects of a natural antioxidant, the bergamot polyphenolic fraction (BPF). Rats were exposed to CCI of the sciatic nerve in the presence or absence of BPF (25–75 mg/kg). Level of acetylation, post-translational modulation on cysteine residues of proteins by HNE and SIRT3 activation, were detected in the spinal cord through western blotting, WES methodology and enzymatic assays. Our results reported that SIRT3 carbonylation and therefore its inactivation contributes to mitochondrial MnSOD hyperacetylation during CCI induced neuropathic pain in rats. In particular, we have demonstrated a close relation between oxidative stress, hyperalgesia, allodynia and sirtuins inactivation reverted by BPF administration.

Impaired Myocardial Energetics Causes Mechanical Dysfunction in Decompensated Failing Hearts

Cardiac mechanical function is supported by ATP hydrolysis, which provides the chemical-free energy to drive the molecular processes underlying cardiac pumping. Physiological rates of myocardial ATP consumption require the heart to resynthesize its entire ATP pool several times per minute. In the failing heart, cardiomyocyte metabolic dysfunction leads to a reduction in the capacity for ATP synthesis and associated free energy to drive cellular processes. Yet it remains unclear if and how metabolic/energetic dysfunction that occurs during heart failure affects mechanical function of the heart. We hypothesize that changes in phosphate metabolite concentrations (ATP, ADP, inorganic phosphate) that are associated with decompensation and failure have direct roles in impeding contractile function of the myocardium in heart failure, contributing to the whole-body phenotype. To test this hypothesis, a transverse aortic constriction (TAC) rat model of pressure overload, hypertrophy, and decompensation was used to assess relationships between metrics of whole-organ pump function and myocardial energetic state. A multiscale computational model of cardiac mechanoenergetic coupling was used to identify and quantify the contribution of metabolic dysfunction to observed mechanical dysfunction. Results show an overall reduction in capacity for oxidative ATP synthesis fueled by either fatty acid or carbohydrate substrates as well as a reduction in total levels of adenine nucleotides and creatine in myocardium from TAC animals compared to sham-operated controls. Changes in phosphate metabolite levels in the TAC rats are correlated with impaired mechanical function, consistent with the overall hypothesis. Furthermore, computational analysis of myocardial metabolism and contractile dynamics predicts that increased levels of inorganic phosphate in TAC compared to control animals kinetically impair the myosin ATPase crossbridge cycle in decompensated hypertrophy/heart failure.

Pharmacokinetics of Repeated Oral Dosing with Coenzyme Q10 in Cavalier King Charles Spaniels with Myxomatous Mitral Valve Disease

Coenzyme Q10 (Q10) is a mitochondrial cofactor and an antioxidant with the potential to combat oxidative stress in heart failure. This study aims to determine the pharmacokinetics of repeated oral dosing of Q10 in Cavalier King Charles Spaniels (CKCS) with spontaneous myxomatous mitral valve disease (MMVD) and to evaluate echocardiographic parameters, circulating cardiac biomarkers, and quality of life (QoL) after treatment. The study is a randomized, placebo-controlled, single-blinded crossover study. Nineteen CKCS with MMVD were randomized to receive 100 mg Q10 (ubiquinone) bi-daily for three weeks, then placebo (or in reverse order). Clinical examination, blood sampling, echocardiography, and QoL assessment were performed before and after each treatment phase. Q10 plasma concentrations were determined in plasma using a validated high-performance liquid chromatography method using electrochemical detection (HPLC-ECD). Eighteen CKCS were included in the analyses. Total plasma concentration of Q10 increased significantly (p < 0.0001) from baseline (median, 0.92 µg/mL; interquartile range (IQR), 0.70-1.26) to after treatment (median, 3.51 µg/mL; IQR, 2.30-6.88). Thirteen dogs reached the threshold of a total plasma Q10 concentration of ≥2.0 µg/mL. The average half-life (T_1/2) of Q10 was 2.95 days (IQR, 1.75-4.02). No significant differences were observed in clinical MMVD severity, and the owner perceived QoL between Q10 and placebo treatment. The solubilized Q10 formulation was well-tolerated in the dogs. Individual variation in plasma concentrations was observed following oral treatment. A long-term placebo-controlled trial is warranted in dogs with MMVD to determine long-term efficacy on the clinical severity of MMVD.

The association between left ventricular mass index and serum sirtuin 3 level in patients with hypertension

Objectives

Sirtuin 3 (SIRT3) can protect cardiomyocytes from oxidative stress-mediated cell damage and prevent cardiac hypertrophy development. The aim of this study was to evaluate whether a relationship existed between left ventricular mass index (LVMI) and serum SIRT3 levels in patients with hypertension.

Patients and methods

This study was conducted as a cross-sectional study of 83 patients between April 2018 and October 2018. The LVMI of all patients was calculated using the formula of the American Echocardiography Association and patients were divided into two groups according to results (increased LVMI and normal LVMI).

Results

Increased LVMI was determined in 37.3% of patients, whereas 62.7% had normal LVMI. There was no significant difference between serum SIRT3 levels between those with increased LVMI and normal LVMI (5.8 versus 5.4 ng/ml; P = 0.914). Serum pro-brain natriuretic peptide levels (69 versus 41 ng/ml; P = 0.019) were found to be higher in patients with increased LVMI than in those with normal LVMI. A positive correlation between SIRT3 levels and Sm (myocardial systolic) velocity was also determined (r = 0.338; P = 0.002).

Conclusion

The serum levels of SIRT3, a molecule which has been proposed to have protective properties against myocardial hypertrophy, were not found to be correlated with LVMI values; however, SIRT3 levels were found to be correlated with Sm velocity, which is accepted to be an indicator of myocardial early diastolic dysfunction.

Mitochondrial reactive oxygen species generation in blood cells is associated with disease severity and exercise intolerance in heart failure patients

Systemic oxidative stress plays a key role in the development of chronic heart failure (CHF). We tested the hypothesis that mitochondrial reactive oxygen species (ROS) generation in circulating peripheral blood mononuclear cells (PBMCs) contributes to CHF progression. A total of 31 patients who had a history of hospital admission due to worsening HF were enrolled and grouped as having either mild CHF defined as New York Heart Association (NYHA) functional class I-II or moderate-to-severe CHF defined as NYHA functional class III. ROS levels in PBMC mitochondria were significantly increased in CHF patients with NYHA functional class III compared to those with NYHA functional class I-II, accompanied by impaired mitochondrial respiratory capacity in PBMCs. ROS generation in PBMC mitochondria was positively correlated with urinary 8-hydroxydeoxyguanosine, a systemic oxidative stress marker, in CHF patients. Importantly, mitochondrial ROS generation in PBMCs was directly correlated with plasma levels of B-type natriuretic peptide, a biomarker for severity of HF, and inversely correlated with peak oxygen uptake, a parameter of exercise capacity, in CHF patients. The study showed that ROS generation in PBMC mitochondria was higher in patients with advanced CHF, and it was associated with disease severity and exercise intolerance in CHF patients.

Metabolic Coordination of Physiological and Pathological Cardiac Remodeling

Metabolic pathways integrate to support tissue homeostasis and to prompt changes in cell phenotype. In particular, the heart consumes relatively large amounts of substrate not only to regenerate ATP for contraction but also to sustain biosynthetic reactions for replacement of cellular building blocks. Metabolic pathways also control intracellular redox state, and metabolic intermediates and end products provide signals that prompt changes in enzymatic activity and gene expression. Mounting evidence suggests that the changes in cardiac metabolism that occur during development, exercise, and pregnancy as well as with pathological stress (eg, myocardial infarction, pressure overload) are causative in cardiac remodeling. Metabolism-mediated changes in gene expression, metabolite signaling, and the channeling of glucose-derived carbon toward anabolic pathways seem critical for physiological growth of the heart, and metabolic inefficiency and loss of coordinated anabolic activity are emerging as proximal causes of pathological remodeling. This review integrates knowledge of different forms of cardiac remodeling to develop general models of how relationships between catabolic and anabolic glucose metabolism may fortify cardiac health or promote (mal)adaptive myocardial remodeling. Adoption of conceptual frameworks based in relational biology may enable further understanding of how metabolism regulates cardiac structure and function.

Mitochondrial mRNA translation initiation contributes to oxidative metabolism in the myocardia of aged, obese mice

Being both advanced in age and obese each contribute to cardiac hypertrophy in a unique manner. Electron transport complexes I and IV are implicated in deficient electron transport during cardiomyopathies and contain the majority of protein subunits that are transcribed and translated by machinery localized within the mitochondria.

PURPOSE

To assess myocardial mt-mRNA translation factors in relation to mitochondrial content and mtDNA-encoded protein using a mouse model of aged obesity and to test the relationship of mt-mRNA translation initiation factor 2 (mtIF2) to oxidative capacity and the cellular oxidation-reduction (redox) state in cardiomyocytes.

METHODS

Male C56BL/6 J mice fed lean or high fat diet were aged to either ~3 months or ~22 months, the heart was excised and analyzed using immunoblot and qPCR to assess differences in mitochondrial mRNA translation machinery. Using H9c2 cardiomyocytes, mtIF2 was knocked-down and oxidative metabolic characteristics assessed including oxidation/reduction state, bioenergetic flux, and hypoxic resistance was tested.

RESULTS

Aged, obese mouse hearts were ~40% larger than young, lean controls and contained ~50% less mtIF2 protein alongside ~25-50% lower content of Cytb, a protein encoded by mtDNA. Reducing the level of mtIF2 by shRNA is associated with ~15-20% lower content of OXPHOS complex I and IV, ~30% lower optical redox ratio, ~40% oxygen reserve capacity, and ~20% less cell survival following hypoxia.

CONCLUSION

We present evidence of altered mt-mRNA translation during cardiac hypertrophy in aged obesity. We build on these results by demonstrating the necessity of mtIF2 in maintaining oxidative characteristics of cardiac muscle cells.

Mitochondrial dysfunction in adults after out-of-hospital cardiac arrest

BACKGROUND

While preclinical studies suggest that mitochondria play a pivotal role in ischaemia-reperfusion injury, the knowledge of mitochondrial function in human out-of-hospital cardiac arrest remains scarce. The present study sought to compare oxidative phosphorylation capacity in skeletal muscle biopsies from out-of-hospital cardiac arrest patients to healthy controls.

METHODS

This was a substudy of a randomised trial comparing targeted temperature management at 33°C versus 36°C for out-of-hospital cardiac arrest patients. Skeletal muscle biopsies were obtained from adult resuscitated comatose out-of-hospital cardiac arrest patients 28 hours after initiation of targeted temperature management, i.e. at target temperature prior to rewarming, and from age-matched healthy controls. Mitochondrial function was analysed by high-resolution respirometry. Maximal sustained respiration through complex I, maximal coupled respiration through complex I and complex II and maximal electron transport system capacity was compared.

RESULTS

A total of 20 out-of-hospital cardiac arrest patients and 21 controls were included in the analysis. We found no difference in mitochondrial function between temperature allocations. We found no difference in complex I sustained respiration between out-of-hospital cardiac arrest and controls (23 (18-26) vs. 22 (19-26) pmol O₂/mg/s, P=0.76), whereas coupled complex I and complex II respiration was significantly lower in out-of-hospital cardiac arrest patients versus controls (53 (42-59) vs. 64 (54-68) pmol O₂/mg/s, P=0.01). Furthermore, electron transport system capacity was lower in out-of-hospital cardiac arrest versus controls (63 (51-69) vs. 73 (66-78) pmol O₂/mg/s, P=0.005).

CONCLUSIONS

Mitochondrial oxidative phosphorylation capacity in skeletal muscle biopsies was reduced in out-of-hospital cardiac arrest patients undergoing targeted temperature management compared to age-matched, healthy controls. The role of mitochondria as risk markers and potential targets for post-resuscitation care remains unknown.

Impaired mitochondrial oxidative phosphorylation capacity in epicardial adipose tissue is associated with decreased concentration of adiponectin and severity of coronary atherosclerosis

Epicardial adipose tissue (EAT), a source of adipokines, is metabolically active, but the role of EAT mitochondria in coronary artery disease (CAD) has not been established. We investigated the association between EAT mitochondrial respiratory capacity, adiponectin concentration in the EAT, and coronary atherosclerosis. EAT samples were obtained from 25 patients who underwent elective cardiac surgery. Based on the coronary angiographycal findings, the patients were divided into two groups; coronary artery disease (CAD; n = 14) and non-CAD (n = 11) groups. The mitochondrial respiratory capacities including oxidative phosphorylation (OXPHOS) capacity with non-fatty acid (complex I and complex I + II-linked) substrates and fatty acids in the EAT were significantly lowered in CAD patients. The EAT mitochondrial OXPHOS capacities had a close and inverse correlation with the severity of coronary artery stenosis evaluated by the Gensini score. Intriguingly, the protein level of adiponectin, an anti-atherogenic adipokine, in the EAT was significantly reduced in CAD patients, and it was positively correlated with the mitochondrial OXPHOS capacities in the EAT and inversely correlated with the Gensini score. Our study showed that impaired mitochondrial OXPHOS capacity in the EAT was closely linked to decreased concentration of adiponectin in the EAT and severity of coronary atherosclerosis.

High-resolution respirometry in human endomyocardial biopsies shows reduced ventricular oxidative capacity related to heart failure

The lifetime risk of developing heart failure is approximately 20%, and survival rates remain poor. Myocardial mitochondrial function has been suggested to play a pivotal role in heart failure pathophysiology. Human studies on ex vivo mitochondrial function have mostly been limited to atrial tissue obtained during open heart surgery and have provided contradictory results. This study aimed at measuring myocardial mitochondrial function in transcatheter ventricular endomyocardial biopsies and assessing the relationship between oxidative capacity and heart function. We enrolled 40 heart failure patients undergoing ventricular assist device surgery or heart transplantation (34 males, age 57 ± 11 years, body mass index 26.6 ± 4.8 kg/m²) and 29 heart transplant recipients of comparable age and body mass index with normal left ventricular function undergoing surveillance biopsies (23 males, 57 ± 12 years, body mass index 26.2 ± 4.1 kg/m²). High-resolution respirometry was established in the myocardium to measure oxidative capacity ex vivo. The mitochondrial oxidative capacity was 90% higher in ventricular compared to atrial tissues (n = 11, p < 0.01) of explanted hearts. Respiration rates were comparable in ventricular samples of heart failure patients obtained during open heart surgery by standard tissue preparation or ex vivo endomyocardial biopsy (r = 0.9988, p < 0.0001, n = 8), and the mitochondrial oxidative capacity in samples from these patients remained stable for 8 h when stored in either of two common preservation buffers. The oxidative capacity was 44% lower in heart failure than in transplant recipients (67 ± 3 vs. 97 ± 5 pmol/[s mg], p < 0.0001) and correlated positively with heart function (r = 0.49, p < 0.01). High-resolution respirometry of ventricular tissue is feasible in transcatheter biopsies, facilitating clinical studies on myocardial mitochondrial function in patients not undergoing heart surgery.

The capacity of mitochondria in heart muscle cells to use oxygen to produce energy correlates with cardiac function. Julia Szendroedi at Heinrich-Heine University, Düsseldorf, Germany, and colleagues have established a technique to reliably evaluate mitochondrial energy metabolism in patients with or recovering from heart failure. They showed that the mitochondrial oxidative capacity of cells in the lower heart chambers (ventricles) was significantly higher than in the upper heart chambers (atria). Moreover, they found that mitochondrial oxidative capacity was reduced by 44% in heart muscle biopsies from patients with heart failure compared with biopsies from heart transplant recipients with normal ventricular function. Stimulating the respiration rate of mitochondria in ventricular heart cells could be a promising strategy for improving cardiac function.

Macrophages in Heart Failure with Reduced versus Preserved Ejection Fraction

There is a growing number of individuals living with heart failure (HF) with reduced ejection fraction (HFrEF) or preserved ejection fraction (HFpEF). Long-term prognosis remains poor in both cases, especially in HFpEF, which is rising in incidence and lacks effective therapeutics. In both HFrEF and HFpEF, there is evidence that elevated inflammatory biomarkers, implicating innate immune cells such as macrophages, are associated with worsened clinical outcomes. Macrophage subsets are active in both inflammatory and reparative processes, yet our understanding of the causative roles for these cells in HF development and progression is incomplete. Here, we discuss recent findings interrogating the role of macrophages in inflammation and its resolution in the context of HF, with a specific focus on HFrEF versus HFpEF.

Emerging role of SIRT3 in endothelial metabolism, angiogenesis, and cardiovascular disease

Sirtuin 3 (SIRT3) a mitochondrial enzyme that plays an important role in energy homeostasis, cardiac remodeling, and heart failure (HF). The expression of SIRT3 declines with advanced age, cardiovascular, and metabolic diseases. Accumulating evidence suggests that SIRT3 plays a critical role in protecting the heart from cardiac hypertrophy, cardiac dysfunction associated with HF, and in the protection of cardiac cells from stress-mediated cell death. Clinical studies have demonstrated that HF with preserved ejection fraction (HFpEF) in patients present with abnormalities in coronary microcirculation related to endothelial dysfunction and coronary microvascular rarefaction. Although SIRT3-mediated regulation of mitochondrial homeostasis and heart function has been intensively investigated, the effect of SIRT3 on endothelial cell (EC) glycolytic metabolism and microvascular function has not been well studied. ECs utilize glycolysis for generating ATP rather than oxidative phosphorylation to maintain their normal functions and promote angiogenesis and EC-cardiomyocyte interactions. Emerging evidence indicates that SIRT3 is involved in the regulation of endothelial metabolism and angiogenesis and thus affects the development of cardiovascular diseases associated with aging. This review will discuss the current knowledge of SIRT3 and its functional role on endothelial metabolism, cardiac function, and cardiovascular diseases.

The effect of oxygen in Sirt3-mediated myocardial protection: a proof-of-concept study in cultured cardiomyoblasts

Sirtuin 3 is a nicotinamide adenine dinucleotide dependent mitochondrial deacetylase that governs mitochondrial metabolism and oxidative defense. The demise in myocardial function following myocardial ischemia has been associated with mitochondrial dysfunction. Sirt3 maintains myocardial contractile function and protects from cardiac hypertrophy. The role of Sirt3 in ischemia is controversial. Our objective was to understand, under what circumstances Sirt3 is protective in different facets of ischemia, using an in vitro proof-of-concept approach based on simulated ischemia in cultured cardiomyoblasts. Cultured H9c2 cardiomyoblasts were subjected to hypoxia and/or serum deprivation, the combination of which we refer to as simulated ischemia. Apoptosis, as assessed by Annexin V staining in life-cell imaging and propidium-iodide inclusion in flow cytometry, was enhanced following simulated ischemia. Interestingly, serum deprivation was a stronger trigger of apoptosis than hypoxia. Knockdown of Sirt3 further increased apoptosis upon serum deprivation, whereas no such effect occurred upon additional hypoxia. Similarly, only upon serum deprivation but not upon simulated ischemia, silencing of Sirt3 led to a deterioration of mitochondrial function in extracellular flux analysis. In the absence of oxygen these Sirt3-dependent effects were abolished. These data indicate, that Sirt3-mediated myocardial protection is oxygen-dependent. Thus, mitochondrial respiration takes center-stage in Sirt3-dependent prevention of stress-induced myocardial damage.

Increased skeletal muscle mitochondrial free radical production in peripheral arterial disease despite preserved mitochondrial respiratory capacity

NEW FINDINGS

What is the central question of this study? What is the degree to which skeletal muscle mitochondria-derived reactive oxygen species (ROS) production is linked to impaired skeletal muscle function in patients with early-stage peripheral arterial disease (PAD) and what is the impact on mitochondrial respiratory capacity? What is the main finding and its importance? This is the first study to document increased mitochondria-derived reactive oxygen species production associated with elevated intramuscular oxidative stress, despite preserved mitochondrial respiratory function, in patients with PAD. Furthermore, systemic inflammation, mitochondria-derived ROS production and skeletal muscle oxidative stress were strongly correlated to disease severity, as indicated by ankle-brachial index, in patients with PAD.

ABSTRACT

Skeletal muscle mitochondrial dysfunction, which is not fully explained by disease-related arterial occlusion, has been implicated in the pathophysiology of peripheral arterial disease (PAD). Therefore, this study comprehensively assessed mitochondrial respiratory function in biopsies from the gastrocnemius of 10 patients with PAD (Fontaine Stage II) and 12 healthy controls (HC). Intramuscular and systemic inflammation, mitochondria-derived reactive oxygen species (ROS) production, and oxidative stress were also assessed to better understand the mechanisms responsible for the proposed PAD-induced mitochondrial dysfunction. Interestingly, mitochondrial respiratory capacity, assessed as complex I (CI) and complex II (CII)-driven State 3 respiration, measured separately and in combination (State 3 CI+II), revealed no difference between the patients with PAD and the HC. However, mitochondria-derived ROS production was significantly elevated in PAD (HC: 1.0 ± 0.9; PAD: 4.3 ± 1.0 AU (mg tissue)^-1 ). Furthermore, patients with PAD exhibited significantly greater concentrations of the pro-inflammatory markers tumour necrosis factor α in plasma (HC: 0.9 ± 0.4; PAD: 2.0 ± 0.3 pg ml^-1 ) and interleukin 6 in both plasma (HC: 2.3 ± 0.4; PAD: 4.3 ± 0.5 pg ml^-1 ) and muscle (∼75% greater). Intramuscular oxidative stress, assessed by protein carbonyls and 4-hydroxynonenal, was significantly greater in PAD compared to HC. Ankle brachial index was significantly correlated with intramuscular inflammation, oxidative stress and mitochondria-derived ROS production. Thus, elevated intramuscular inflammation, oxidative stress and mitochondria-derived ROS production are likely to contribute to the pathophysiology of the skeletal muscle dysfunction associated with PAD, even in the presence of preserved mitochondrial respiratory function in this population.

l-Carnitine and heart disease

Cardiovascular disease (CVD) is a key cause of deaths worldwide, comprising 15-17% of healthcare expenditure in developed countries. Current records estimate an annual global average of 30 million cardiac dysfunction cases, with a predicted escalation by two-three folds for the next 20-30years. Although β-blockers and angiotensin-converting-enzymes are commonly prescribed to control CVD risk, hepatotoxicity and hematological changes are frequent adverse events associated with these drugs. Search for alternatives identified endogenous cofactor l-carnitine, which is capable of promoting mitochondrial β-oxidation towards a balanced cardiac energy metabolism. l-Carnitine facilitates transport of long-chain fatty acids into the mitochondrial matrix, triggering cardioprotective effects through reduced oxidative stress, inflammation and necrosis of cardiac myocytes. Additionally, l-carnitine regulates calcium influx, endothelial integrity, intracellular enzyme release and membrane phospholipid content for sustained cellular homeostasis. Carnitine depletion, characterized by reduced expression of "organic cation transporter-2" gene, is a metabolic and autosomal recessive disorder that also frequently associates with CVD. Hence, exogenous carnitine administration through dietary and intravenous routes serves as a suitable protective strategy against ventricular dysfunction, ischemia-reperfusion injury, cardiac arrhythmia and toxic myocardial injury that prominently mark CVD. Additionally, carnitine reduces hypertension, hyperlipidemia, diabetic ketoacidosis, hyperglycemia, insulin-dependent diabetes mellitus, insulin resistance, obesity, etc. that enhance cardiovascular pathology. These favorable effects of l-carnitine have been evident in infants, juvenile, young, adult and aged patients of sudden and chronic heart failure as well. This review describes the mechanism of action, metabolism and pharmacokinetics of l-carnitine. It specifically emphasizes upon the beneficial role of l-carnitine in cardiomyopathy.

Mitochondrial Function in Non-ischemic Heart Failure

Provision for the continuous demand for energy from the beating heart relies heavily on efficient mitochondrial activity. Non-ischemic cardiomyopathy in which oxygen supply is not limiting results from etiologies such as pressure overload. It is associated with progressive development of metabolic stress culminating in energy depletion and heart failure. The mitochondria from the ventricular walls undergoing non-ischemic cardiomyopathy are subjected to long periods of adaptation to support the changing metabolic milieu, which has been described as mal-adaptation since it ultimately results in loss of cardiac contractile function. While the chronicity of exposure to metabolic stressors, co-morbidities and thereby adaptive changes in mitochondria maybe different between ischemic and non-ischemic heart failure, the resulting pathology is very similar, especially in late stage heart failure. Understanding of the mitochondrial changes in early-stage heart failure may guide the development of mitochondrial-targeted therapeutic options to prevent progression of non-ischemic heart failure. This chapter reviews findings of mitochondrial functional changes in animal models and humans with non-ischemic heart failure. While most animal models of non-ischemic heart failure exhibit cardiac mitochondrial dysfunction, studies in humans have been inconsistent despite confirmed reduction in ATP production. This chapter also reviews the possibility of impairment of substrate supply processes upstream of the mitochondria in heart failure, and discusses potential metabolism-targeted therapeutic options.

The ‘Goldilocks zone’ of fatty acid metabolism; to ensure that the relationship with cardiac function is just right

Fatty acids (FA) are the main fuel used by the healthy heart to power contraction, supplying 60–70% of the ATP required. FA generate more ATP per carbon molecule than glucose, but require more oxygen to produce the ATP, making them a more energy dense but less oxygen efficient fuel compared with glucose. The pathways involved in myocardial FA metabolism are regulated at various subcellular levels, and can be divided into sarcolemmal FA uptake, cytosolic activation and storage, mitochondrial uptake and β-oxidation. An understanding of the critical involvement of each of these steps has been amassed from genetic mouse models, where forcing the heart to metabolize too much or too little fat was accompanied by cardiac contractile dysfunction and hypertrophy. In cardiac pathologies, such as heart disease and diabetes, aberrations in FA metabolism occur concomitantly with changes in cardiac function. In heart failure, FA oxidation is decreased, correlating with systolic dysfunction and hypertrophy. In contrast, in type 2 diabetes, FA oxidation and triglyceride storage are increased, and correlate with diastolic dysfunction and insulin resistance. Therefore, too much FA metabolism is as detrimental as too little FA metabolism in these settings. Therapeutic compounds that rebalance FA metabolism may provide a mechanism to improve cardiac function in disease. Just like Goldilocks and her porridge, the heart needs to maintain FA metabolism in a zone that is ‘just right’ to support contractile function.

Lack of effect of prolonged treatment with liraglutide on cardiac remodeling in rats after acute myocardial infarction

Following the acute phase of a myocardial infarction, a set of structural and functional changes evolves in the myocardium, collectively referred to as cardiac remodeling. This complex set of processes, including interstitial fibrosis, inflammation, myocyte hypertrophy and apoptosis may progress to heart failure. Analogs of the incretin hormone glucagon-like peptide 1 (GLP-1) have shown some promise as cardioprotective agents. We hypothesized that a long-acting GLP-1 analog liraglutide would ameliorate cardiac remodeling over the course of 4 weeks in a rat model of non-reperfused myocardial infarction. In 134 male Sprague Dawley rats myocardial infarctions were induced by ligation of the left anterior descending coronary artery. Rats were randomized to either subcutaneous injection of placebo or 0.3mg liraglutide once daily. Cardiac magnetic resonance imaging was performed after 4 weeks. Histology of the infarcted and remote non-infarcted myocardium, selected molecular remodeling markers and mitochondrial respiration in fibers of remote non-infarcted myocardium were analyzed. Left ventricular end diastolic volume increased in the infarcted hearts by 62% (from 0.58±0.03mL to 0.95±0.07mL, P<0.05) compared to sham operated hearts and left ventricle ejection fraction decreased by 37% (63±1%-40±3%, P<0.05). Increased interstitial fibrosis and phosphorylation of p38 Mitogen Activated Protein Kinase were observed in the non-infarct regions. Mitochondrial fatty acid oxidation was impaired. Liraglutide did not affect any of these alterations. Four-week treatment with liraglutide did not affect cardiac remodeling following a non-reperfused myocardial infarction, as assessed by cardiac magnetic resonance imaging, histological and molecular analysis and measurements of mitochondrial respiration.

Metabolic remodeling in hypertrophied and failing myocardium: a review

The energy starvation hypothesis proposes that maladaptive metabolic remodeling antedates, initiates, and maintains adverse contractile dysfunction in heart failure (HF). Better understanding of the cardiac metabolic phenotype and metabolic signaling could help identify the role metabolic remodeling plays within HF and the conditions known to transition toward HF, including "pathological" hypertrophy. In this review, we discuss metabolic phenotype and metabolic signaling in the contexts of pathological hypertrophy and HF. We discuss the significance of alterations in energy supply (substrate utilization, oxidative capacity, and phosphotransfer) and energy sensing using observations from human and animal disease models and models of manipulated energy supply/sensing. We aim to provide ways of thinking about metabolic remodeling that center around metabolic flexibility, capacity (reserve), and efficiency rather than around particular substrate preferences or transcriptomic profiles. We show that maladaptive metabolic remodeling takes multiple forms across multiple energy-handling domains. We suggest that lack of metabolic flexibility and reserve (substrate, oxidative, and phosphotransfer) represents a final common denominator ultimately compromising efficiency and contractile reserve in stressful contexts.

Mitochondria and ageing: role in heart, skeletal muscle and adipose tissue

Age is the most important risk factor for most diseases. Mitochondria play a central role in bioenergetics and metabolism. In addition, several lines of evidence indicate the impact of mitochondria in lifespan determination and ageing. The best-known hypothesis to explain ageing is the free radical theory, which proposes that cells, organs, and organisms age because they accumulate reactive oxygen species (ROS) damage over time. Mitochondria play a central role as the principle source of intracellular ROS, which are mainly formed at the level of complex I and III of the respiratory chain. Dysfunctional mitochondria generating less ATP have been observed in various aged organs. Mitochondrial dysfunction comprises different features including reduced mitochondrial content, altered mitochondrial morphology, reduced activity of the complexes of the electron transport chain, opening of the mitochondrial permeability transition pore, and increased ROS formation. Furthermore, abnormalities in mitochondrial quality control or defects in mitochondrial dynamics have also been linked to senescence. Among the tissues affected by mitochondrial dysfunction are those with a high-energy demand and thus high mitochondrial content. Therefore, the present review focuses on the impact of mitochondria in the ageing process of heart and skeletal muscle. In this article, we review different aspects of mitochondrial dysfunction and discuss potential therapeutic strategies to improve mitochondrial function. Finally, novel aspects of adipose tissue biology and their involvement in the ageing process are discussed.

A fast method for high resolution oxymetry study of skeletal muscle mitochondrial respiratory chain complexes

High resolution oxymetry study (HROS) of skeletal muscle usually requires 90-120 min preparative phase (dissection, permeabilization and washing). This work reports on the suitability of a rapid muscle preparation which by-passes this long preparation. For a few seconds only, muscle biopsy from pigs is submitted to gentle homogenization at 8000 rotations per minute using an ultra-dispersor apparatus. Subsequent HROS is performed using FCCP instead of ADP, compounds crossing and not plasma membrane, respectively. This simplified procedure compares favorably with classical (permeabilized fibers) HROS in terms of respiratory chain complex activities. Mitochondria from cells undergoing ultradispersion were functionally preserved as attested by relative inefficacy of added cytochrome C (not crossing intact mitochondrial outer membrane) to stimulate mitochondrial respiration. Responsiveness of respiration to ADP (in the absence of FCCP) suggested that these intact mitochondria were outside cells disrupted by ultradispersion or within cells permeated by this procedure.

Inflammation and metabolic cardiomyopathy

Excessive feeding is associated with an increase in the incidence of chronic metabolic diseases, such as obesity, insulin resistance, and type 2 diabetes. Metabolic disturbance induces chronic low-grade inflammation in metabolically-important organs, such as the liver and adipose tissue. Many of the inflammatory signalling pathways are directly triggered by nutrients. The pro-inflammatory mediators in adipocytes and macrophages infiltrating adipose tissue promote both local and systemic pro-inflammatory status. Metabolic cardiomyopathy is a chronic metabolic disease characterized by structural and functional alterations and interstitial fibrosis without coronary artery disease or hypertension. In the early stage of metabolic cardiomyopathy, metabolic disturbance is not accompanied by substantial changes in myocardial structure and cardiac function. However, metabolic disturbance induces subcellular low-grade inflammation in the heart, and in turn, subcellular component abnormalities, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, and impaired calcium handling, leading to impaired myocardial relaxation. In the advanced stage, the vicious cycle of subcellular component abnormalities, inflammatory cell infiltration, and neurohumoral activation induces cardiomyocyte injury and death, and cardiac fibrosis, resulting in impairment of both diastolic and systolic functions. This review discusses some recent advances in understanding involvement of inflammation in metabolic cardiomyopathy.

Pre-ischaemic mitochondrial substrate constraint by inhibition of malate-aspartate shuttle preserves mitochondrial function after ischaemia-reperfusion

KEY POINTS

Pre-ischaemic administration of aminooxiacetate (AOA), an inhibitor of the malate-aspartate shuttle (MAS), provides cardioprotection against ischaemia-reperfusion injury. The underlying mechanism remains unknown. We examined whether transient inhibition of the MAS during ischaemia and early reperfusion by AOA treatment could prevent mitochondrial damage at later reperfusion. The AOA treatment preserved mitochondrial respiratory capacity with reduced mitochondrial oxidative stress during late reperfusion to the same extent as ischaemic preconditioning (IPC). However, AOA treatment, but not IPC, reduced the myocardial interstitial concentration of tricarboxylic acid cycle intermediates at the onset of reperfusion. The results obtained in the present study demonstrate that metabolic regulation by inhibition of the MAS at the onset of reperfusion may be beneficial for the preservation of mitochondrial function during late reperfusion in an IR-injured heart.

ABSTRACT

Mitochondrial dysfunction plays a central role in ischaemia-reperfusion (IR) injury. Pre-ischaemic administration of aminooxyacetate (AOA), an inhibitor of the malate-aspartate shuttle (MAS), provides cardioprotection against IR injury, although the underlying mechanism remains unknown. We hypothesized that a transient inhibition of the MAS during ischaemia and early reperfusion could preserve mitochondrial function at later phase of reperfusion in the IR-injured heart to the same extent as ischaemic preconditioning (IPC), which is a well-validated cardioprotective strategy against IR injury. In the present study, we show that pre-ischaemic administration of AOA preserved mitochondrial complex I-linked state 3 respiration and fatty acid oxidation during late reperfusion in IR-injured isolated rat hearts. AOA treatment also attenuated the excessive emission of mitochondrial reactive oxygen species during state 3 with complex I-linked substrates during late reperfusion, which was consistent with reduced oxidative damage in the IR-injured heart. As a result, AOA treatment reduced infarct size after reperfusion. These protective effects of MAS inhibition on the mitochondria were similar to those of IPC. Intriguingly, the protection of mitochondrial function by AOA treatment appears to be different from that of IPC because AOA treatment, but not IPC, downregulated myocardial tricarboxilic acid (TCA)-cycle intermediates at the onset of reperfusion. MAS inhibition thus preserved mitochondrial respiratory capacity and decreased mitochondrial oxidative stress during late reperfusion in the IR-injured heart, at least in part, via metabolic regulation of TCA cycle intermediates in the mitochondria at the onset of reperfusion.

SIRT3 in Cardiac Physiology and Disease

Functional defects in mitochondrial biology causally contribute to various human diseases, including cardiovascular disease. Impairment in oxidative phosphorylation, mitochondrial oxidative stress, and increased opening of the mitochondrial permeability transition pore add to the underlying mechanisms of heart failure or myocardial ischemia–reperfusion (IR) injury. Recent evidence demonstrated that the mitochondrial NAD⁺-dependent deacetylase sirtuin 3 (SIRT3) may regulate these mitochondrial functions by reversible protein lysine deacetylation. Loss of function studies demonstrated a role of impaired SIRT3 activity in the pathogenesis of myocardial IR injury as well as in the development of cardiac hypertrophy and the transition into heart failure. Gain of function studies and treatment approaches increasing mitochondrial NAD⁺ availability that ameliorate these cardiac pathologies have led to the proposal that activation of SIRT3 may represent a promising therapeutic strategy to improve mitochondrial derangements in various cardiac pathologies. In the current review, we will present and discuss the available literature on the role of SIRT3 in cardiac physiology and disease.

Mitochondrial complex I dysfunction and altered NAD(P)H kinetics in rat myocardium in cardiac right ventricular hypertrophy and failure

AIMS

In cardiac hypertrophy (CH) and heart failure (HF), alterations occur in mitochondrial enzyme content and activities but the origin and implications of these changes for mitochondrial function need to be resolved.

METHODS AND RESULTS

Right ventricular CH or HF was induced by monocrotaline injection, which causes pulmonary artery hypertension, in rats. Results were compared with saline injection (CON). NAD(P)H and FAD autofluorescence were recorded in thin intact cardiac trabeculae during transitions in stimulation frequency, to assess mitochondrial complex I and complex II function, respectively. Oxygen consumption, mitochondrial morphology, protein content, and enzymatic activity were assessed. NAD(P)H autofluorescence upon an increase in stimulation frequency showed a rapid decline followed by a slow recovery. FAD autofluorescence followed a similar time course, but in opposite direction. The amplitude of the early rapid change in NAD(P)H autofluorescence was severely depressed in CH and HF compared with CON. The rapid changes in FAD autofluorescence in CH and HF were reduced to a lesser extent. Complex I-coupled respiration showed an ∼3.5-fold reduction in CH and HF; complex II-coupled respiration was depressed two-fold in HF. Western blot analyses revealed modest reductions in complex I protein content in CH and HF and in complex I activity in supercomplexes in HF. Mitochondrial volume density was similar, but mitochondrial remodelling was evident from changes in ultrastructure and fusion/fission indices in CH and HF.

CONCLUSION

These results suggest that the alterations in mitochondrial function observed in right ventricular CH and HF can be mainly attributed to complex I dysfunction.

Mitochondrial function in heart failure: The impact of ischemic and non-ischemic etiology

BACKGROUND

Although cardiac mitochondrial dysfunction is associated with heart failure (HF), this is a complex syndrome with two predominant etiologies, ischemic HF (iHF) and non-ischemic HF (niHF), and the exact impact of mitochondrial dysfunction in these two distinct forms of HF is unknown.

METHODS AND RESULTS

To determine the impact of HF etiology on mitochondrial function, respiration was measured in permeabilized cardiac muscle fibers from patients with iHF (n=17), niHF (n=18), and healthy donor hearts (HdH). Oxidative phosphorylation capacity (OXPHOS), assessed as state 3 respiration, fell progressively from HdH to niHF, to iHF (Complex I+II: 54±1; 34±4; 27±3pmol·s(-1)·mg(-1)) as did citrate synthase activity (CSA: 206±18; 129±6; 82±6nmol·mg(-1)·min(-1)). Although still significantly lower than HdH, normalization of OXPHOS by CSA negated the difference in mass specific OXPHOS between iHF and niHF. Interestingly, Complex I state 2 respiration increased progressively from HdH, to niHF, to iHF, whether or not normalized for CSA (0.6±0.2; 1.1±0.3; 2.3±0.3; pmol·mg(-1)·CSA), such that the respiratory control ratio (RCR), fell in the same manner across groups. Finally, both the total free radical levels (60±6; 46±4AU) and level of mitochondrial derived superoxide (1.0±0.2; 0.7±0.1AU) were greater in iHF compared to niHF, respectively.

CONCLUSIONS

Thus, the HF-related attenuation in OXPHOS actually appears to be independent of etiology when the lower mitochondrial content of iHF is taken into account. However, these findings provide evidence of deleterious intrinsic mitochondrial changes in iHF, compared to niHF, including greater proton leak, attenuated OXPHOS efficiency, and augmented free radical levels.

Assessment of Mitochondrial Dysfunction and Monoamine Oxidase Contribution to Oxidative Stress in Human Diabetic Hearts

Mitochondria-related oxidative stress is a pathomechanism causally linked to coronary heart disease (CHD) and diabetes mellitus (DM). Recently, mitochondrial monoamine oxidases (MAOs) have emerged as novel sources of oxidative stress in the cardiovascular system and experimental diabetes. The present study was purported to assess the mitochondrial impairment and the contribution of MAOs-related oxidative stress to the cardiovascular dysfunction in coronary patients with/without DM. Right atrial appendages were obtained from 75 patients randomized into 3 groups: (1) Control (CTRL), valvular patients without CHD; (2) CHD, patients with confirmed CHD; and (3) CHD-DM, patients with CHD and DM. Mitochondrial respiration was measured by high-resolution respirometry and MAOs expression was evaluated by RT-PCR and immunohistochemistry. Hydrogen peroxide (H₂O₂) emission was assessed by confocal microscopy and spectrophotometrically. The impairment of mitochondrial respiration was substrate-independent in CHD-DM group. MAOs expression was comparable among the groups, with the predominance of MAO-B isoform but no significant differences regarding oxidative stress were detected by either method. Incubation of atrial samples with MAOs inhibitors significantly reduced the H₂O₂ in all groups. In conclusion, abnormal mitochondrial respiration occurs in CHD and is more severe in DM and MAOs contribute to oxidative stress in human diseased hearts with/without DM.

Mitochondrial structure and function are not different between nonfailing donor and end-stage failing human hearts

During human heart failure, the balance of cardiac energy use switches from predominantly fatty acids (FAs) to glucose. We hypothesized that this substrate shift was the result of mitochondrial degeneration; therefore, we examined mitochondrial oxidation and ultrastructure in the failing human heart by using respirometry, transmission electron microscopy, and gene expression studies of demographically matched donor and failing human heart left ventricular (LV) tissues. Surprisingly, respiratory capacities for failing LV isolated mitochondria (n = 9) were not significantly diminished compared with donor LV isolated mitochondria (n = 7) for glycolysis (pyruvate + malate)- or FA (palmitoylcarnitine)-derived substrates, and mitochondrial densities, assessed via citrate synthase activity, were consistent between groups. Transmission electron microscopy images also showed no ultrastructural remodeling for failing vs. donor mitochondria; however, the fraction of lipid droplets (LDs) in direct contact with a mitochondrion was reduced, and the average distance between an LD and its nearest neighboring mitochondrion was increased. Analysis of FA processing gene expression between donor and failing LVs revealed 0.64-fold reduced transcript levels for the mitochondrial-LD tether, perilipin 5, in the failing myocardium (P = 0.003). Thus, reduced FA use in heart failure may result from improper delivery, potentially via decreased perilipin 5 expression and mitochondrial-LD tethering, and not from intrinsic mitochondrial dysfunction.-Holzem, K. M., Vinnakota, K. C., Ravikumar, V. K., Madden, E. J., Ewald, G. A., Dikranian, K., Beard, D. A., Efimov, I. R. Mitochondrial structure and function are not different between nonfailing donor and end-stage failing human hearts.