Heart failure with preserved ejection fraction induces molecular, mitochondrial, histological, and functional alterations in rat respiratory and limb skeletal muscle

Preserved Skeletal Muscle Mitochondrial Function, Redox State, Inflammation and Mass in Obese Mice with Chronic Heart Failure

Background: Skeletal muscle (SM) mitochondrial dysfunction, oxidative stress, inflammation and muscle mass loss may worsen prognosis in chronic heart failure (CHF). Diet-induced obesity may also cause SM mitochondrial dysfunction as well as oxidative stress and inflammation, but obesity per se may be paradoxically associated with high SM mass and mitochondrial adenosine triphosphate (ATP) production, as well as with enhanced survival in CHF. Methods: We investigated interactions between myocardial infarction(MI)-induced CHF and diet-induced obesity (12-wk 60% vs. standard 10% fat) in modulating gastrocnemius muscle (GM) mitochondrial ATP and tissue superoxide generation, oxidized glutathione (GSSG), cytokines and insulin signalling activation in 10-wk-old mice in the following groups: lean sham-operated, lean CHF (LCHF), obese CHF (ObCHF; all n = 8). The metabolic impact of obesity per se was investigated by pair-feeding ObCHF to standard diet with stabilized excess body weight until sacrifice at wk 8 post-MI. Results: Compared to sham, LCHF had low GM mass, paralleled by low mitochondrial ATP production and high mitochondrial reative oxygen species (ROS) production, pro-oxidative redox state, pro-inflammatory cytokine changes and low insulin signaling (p < 0.05). In contrast, excess body weight in pair-fed ObCHF was associated with high GM mass, preserved mitochondrial ATP and mitochondrial ROS production, unaltered redox state, tissue cytokines and insulin signaling (p = non significant vs. Sham, p < 0.05 vs. LCHF) despite higher superoxide generation from non-mitochondrial sources. Conclusions: CHF disrupts skeletal muscle mitochondrial function in lean rodents with low ATP and high mitochondrial ROS production, associated with tissue pro-inflammatory cytokine profile, low insulin signaling and muscle mass loss. Following CHF onset, obesity per se is associated with high skeletal muscle mass and preserved tissue ATP production, mitochondrial ROS production, redox state, cytokines and insulin signaling. These paradoxical and potentially favorable obesity-associated metabolic patterns could contribute to reported obesity-induced survival advantage in CHF.

Effects of Exercise Training on Cardiac Function in Heart Failure with Preserved Ejection Fraction

Nearly half of patients with heart failure in the community have heart failure with preserved ejection fraction (HFpEF). Patients with HFpEF are often elderly and their primary chronic symptom is severe exercise intolerance. Left ventricular diastolic dysfunction is associated with the pathophysiology of HFpEF and is an important contributor to exercise intolerance in HFpEF patients. The effects of exercise training on left ventricular diastolic function in HFpEF patients have been examined in several randomised clinical trials. Meta-analysis of the trials indicates that exercise training can provide clinically relevant improvements in exercise capacity without significant change in left ventricular structure or function in HFpEF patients. Further studies are necessary to elucidate the exact mechanisms of exercise intolerance in HFpEF patients and to develop recommendations regarding the most effective type, intensity, frequency, and duration of training in this group.

Lean Mass Abnormalities in Heart Failure: The Role of Sarcopenia, Sarcopenic Obesity, and Cachexia

The role of body composition in patients with heart failure (HF) has been receiving much attention in the last few years. Particularly, reduced lean mass (LM), the best surrogate for skeletal muscle mass, is independently associated with abnormal cardiorespiratory fitness (CRF) and muscle strength, ultimately leading to reduced quality of life and worse prognosis. While in the past, reduced CRF in patients with HF was thought to result exclusively from cardiac dysfunction leading to reduced cardiac output at peak exercise, current evidence supports the concept that abnormalities in LM may also play a critical role. Abnormalities in the LM body composition compartment are associated with the development of sarcopenia, sarcopenic obesity, and cachexia. Such conditions have been implicated in the pathophysiology and progression of HF. However, identification of such conditions remains challenging, as universal definitions for sarcopenia, sarcopenic obesity, and cachexia are lacking. In this review article, we describe the most common body composition abnormalities related to the LM compartment, including skeletal and respiratory muscle mass abnormalities, and the consequences of such anomalies on CRF and muscle strength in patients with HF. Finally, we discuss the potential nonpharmacologic therapeutic strategies such as exercise training (ie, aerobic exercise and resistance exercise) and dietary interventions (ie, dietary supplementation and dietary patterns) that have been implemented to target body composition, with a focus on HF.

Diaphragm Thickening During Venoarterial Extracorporeal Membrane Oxygenation Weaning: An Observational Prospective Study

OBJECTIVES

The respiratory workload, according to the diaphragm thickening fraction (TF) during sweep gas flow (SGF), decrease during weaning from venoarterial extracorporeal membrane oxygenation (VA ECMO) was evaluated for the present study.

DESIGN

Prospective observational study.

SETTING

Monocentric.

PARTICIPANTS

Patients were included if they were suitable for a first VA ECMO weaning trial and were breathing spontaneously.

INTERVENTIONS

SGF was set for 15 minutes when the TF was measured at 4 L/min, 2 L/min, and 1 L/min, with a 10-minute return to baseline between each step. Mechanical ventilation, when required, was set to pressure-support ventilation mode with 7 cmH₂O (pressure support) and a positive end-expiratory pressure of 0 cmH₂O. Diaphragm ultrasound was used to assess the TF at the end of each step. Demographics, left ventricular ejection fraction (LVEF), and outcome were collected.

MEASUREMENTS AND MAIN RESULTS

Fifteen patients were included. Ten patients were extubated, and five were ventilated. TF values were 6.3% [0-10] at 4 L/min, 13.3% [10-26] at 2 L/min, and 26.7% [22-44] at 1 L/min (analysis of variance: p < 0.001 between 4 L/min and 2 L/min and p = 0.03 between 2 L/min and 1 L/min). TF did not differ whether patients were or were not ventilated or whether they were or were not weaned successfully from ECMO. TF was correlated with LVEF at 1 L/min SGF (Pearson R 0.67 [0.21-0.88]; p = 0.009) and at 2 L/min (R 0.7 [0.27-0.89]; p = 0.005) but not at 4 L/min. SGF mitigated the relationship between LVEF and TF (analysis of covariance: p < 0.005).

CONCLUSIONS

Diaphragm TF was related to the SGF of the venoarterial ECMO settings and LVEF at the time of weaning.

Impact of experimental obesity on diaphragm structure, function, and bioenergetics

Obesity is associated with bioenergetic dysfunction of peripheral muscles; however, little is known regarding the impact of obesity on the diaphragm. We hypothesized that obesity would be associated with diaphragm dysfunction attributable to mitochondrial oxygen consumption and structural and ultrastructural changes. Wistar rat litters were culled to 3 pups to induce early postnatal overfeeding and consequent obesity. Control animals were obtained from unculled litters. From postnatal day 150, diaphragm ultrasound, computed tomography, high-resolution respirometry, immunohistochemical, biomolecular, and ultrastructural histological analyses were performed. The diaphragms of obese animals, compared with those of controls, presented changes in morphology as increased thickening fraction, diaphragm excursion, and diaphragm dome height, as well as increased mitochondrial respiratory capacity coupled to ATP synthesis and maximal respiratory capacity. Fatty acid synthase gene expression was also higher in obese animals, suggesting a source of energy for the respiratory chain. Myosin heavy chain-IIA was increased, indicating shift from glycolytic toward oxidative muscle fiber profile. Diaphragm tissue also exhibited ultrastructural changes, such as compact, round, and swollen mitochondria with fainter cristae and more lysosomal bodies. Dynamin-1 expression in the diaphragm was reduced in obese rats, suggesting decreased mitochondrial fission. Furthermore, gene expressions of peroxisome γ proliferator-activated receptor coactivator-1α and superoxide dismutase-2 were lower in obese animals than in controls, which may indicate a predisposition to oxidative injury. In conclusion, in the obesity model used herein, muscle fiber phenotype was altered in a manner likely associated with increased mitochondrial respiratory capability, suggesting respiratory adaptation to increased metabolic demand.NEW & NOTEWORTHY Obesity has been associated with peripheral muscle dysfunction; however, little is known about its impact on the diaphragm. In the current study, we found high oxygen consumption in diaphragm tissue and changes in muscle fiber phenotypes toward a more oxidative profile in experimental obesity.

Redox Control of Proteolysis During Inactivity-Induced Skeletal Muscle Atrophy

Significance: Skeletal muscles play essential roles in key body functions including breathing, locomotion, and glucose homeostasis; therefore, maintaining healthy skeletal muscles is important. Prolonged periods of muscle inactivity (e.g., bed rest, mechanical ventilation, or limb immobilization) result in skeletal muscle atrophy and weakness. Recent Advances: Disuse skeletal muscle atrophy occurs due to both accelerated proteolysis and decreased protein synthesis with proteolysis playing a leading role in some types of inactivity-induced atrophy. Although all major proteolytic systems are involved in inactivity-induced proteolysis in skeletal muscles, growing evidence indicates that both calpain and autophagy play an important role. Regulation of proteolysis in skeletal muscle is under complex control, but it is established that activation of both calpain and autophagy is directly linked to oxidative stress. Critical Issues: In this review, we highlight the experimental evidence that supports a cause and effect link between reactive oxygen species (ROS) and activation of both calpain and autophagy in skeletal muscle fibers during prolonged inactivity. We also review the sources of oxidant production in muscle fibers during inactivity-induced atrophy, and provide a detailed discussion on how ROS activates both calpain and autophagy during disuse muscle wasting. Future Directions: Future studies are required to delineate the specific mechanisms by which ROS activates both calpain and autophagy in skeletal muscles during prolonged periods of contractile inactivity. This knowledge is essential to develop the most effective strategies to protect against disuse muscle atrophy. Antioxid. Redox Signal. 33, 559-569.

Gain-of-function mutation in SCN11A causes itch and affects neurogenic inflammation and muscle function in Scn11a+/L799P mice

Mutations in the genes encoding for voltage-gated sodium channels cause profound sensory disturbances and other symptoms dependent on the distribution of a particular channel subtype in different organs. Humans with the gain-of-function mutation p.Leu811Pro in SCN11A (encoding for the voltage-gated Nav1.9 channel) exhibit congenital insensitivity to pain, pruritus, self-inflicted injuries, slow healing wounds, muscle weakness, Charcot-like arthropathies, and intestinal dysmotility. As already shown, knock-in mice (Scn11a+/L799P) carrying the orthologous mutation p.Leu799Pro replicate reduced pain sensitivity and show frequent tissue lesions. In the present study we explored whether Scn11a+/L799P mice develop also pruritus, muscle weakness, and changes in gastrointestinal transit time. Furthermore, we analyzed morphological and functional differences in nerves, skeletal muscle, joints and small intestine from Scn11a+/L799P and Scn11a+/+ wild type mice. Compared to Scn11a+/+ mice, Scn11a+/L799P mice showed enhanced scratching bouts before skin lesions developed, indicating pruritus. Scn11a+/L799P mice exhibited reduced grip strength, but no disturbances in motor coordination. Skeletal muscle fiber types and joint architecture were unaltered in Scn11a+/L799P mice. Their gastrointestinal transit time was unaltered. The small intestine from Scn11a+/L799P showed a small shift towards less frequent peristaltic movements. Similar proportions of lumbar dorsal root ganglion neurons from Scn11a+/L799P and Scn11a+/+ mice were calcitonin gene-related peptide (CGRP-) positive, but isolated sciatic nerves from Scn11a+/L799P mice exhibited a significant reduction of the capsaicin-evoked release of CGRP indicating reduced neurogenic inflammation. These data indicate important Nav1.9 channel functions in several organs in both humans and mice. They support the pathophysiological relevance of increased basal activity of Nav1.9 channels for sensory abnormalities (pain and itch) and suggest resulting malfunctions of the motor system and of the gastrointestinal tract. Scn11a+/L799P mice are suitable to investigate the role of Nav1.9, and to explore the pathophysiological changes and mechanisms which develop as a consequence of Nav1.9 hyperactivity.

ZSF1 rat as animal model for HFpEF: Development of reduced diastolic function and skeletal muscle dysfunction

AIMS

The prevalence of heart failure with preserved ejection fraction (HFpEF) is still increasing, and so far, no pharmaceutical treatment has proven to be effective. A key obstacle for testing new pharmaceutical substances is the availability of suitable animal models for HFpEF, which realistically reflect the clinical picture. The aim of the present study was to characterize the development of HFpEF and skeletal muscle (SM) dysfunction in ZSF1 rats over time.

METHODS AND RESULTS

Echocardiography and functional analyses of the SM were performed in 6-, 10-, 15-, 20-, and 32-week-old ZSF1-lean and ZSF1-obese. Furthermore, myocardial and SM tissue was collected for molecular and histological analyses. HFpEF markers were evident as early as 10 weeks of age. Diastolic dysfunction, confirmed by a significant increase in E/e', was detectable at 10 weeks. Increased left ventricular mRNA expression of collagen and BNP was detected in ZSF1-obese animals as early as 15 and 20 weeks, respectively. The loss of muscle force was measurable in the extensor digitorum longus starting at 15 weeks, whereas the soleus muscle function was impaired at Week 32. In addition, at Week 20, markers for aortic valve sclerosis were increased.

CONCLUSIONS

Our measurements confirmed the appearance of HFpEF in ZSF1-obese rats as early as 10 weeks of age, most likely as a result of the pre-existing co-morbidities. In addition, SM function was reduced after the manifestation of HFpEF. In conclusion, the ZSF1 rat may serve as a suitable animal model to study pharmaceutical strategies for the treatment of HFpEF.

Voluntary physical activity counteracts Chronic Heart Failure progression affecting both cardiac function and skeletal muscle in the transgenic Tgαq*44 mouse model

Physical activity is emerging as an alternative nonpharmaceutical strategy to prevent and treat a variety of cardiovascular diseases due to its cardiac and skeletal muscle beneficial effects. Oxidative stress occurs in skeletal muscle of chronic heart failure (CHF) patients with possible impact on muscle function decline. We determined the effect of voluntary‐free wheel running (VFWR) in preventing protein damage in Tgαq*44 transgenic mice (Tg) characterized by a delayed CHF progression. In the early (6 months) and transition (12 months) phase of CHF, VFWR increased the daily mean distance covered by Tg mice eliminating the difference between Tg and WT present before exercise at 12 months of age (WT Pre‐EX 3.62 ± 1.66 vs. Tg Pre‐EX 1.51 ± 1.09 km, P < 0.005; WT Post‐EX 5.72 ± 3.42 vs. Tg Post‐EX 4.17 ± 1.8 km, P > 0.005). This effect was concomitant with an improvement of in vivo cardiac performance [(Cardiac Index (mL/min/cm²): 6 months, untrained‐Tg 0.167 ± 0.005 vs. trained‐Tg 0.21 ± 0.003, P < 0.005; 12 months, untrained‐Tg 0.1 ± 0.009 vs. trained‐Tg 0.133 ± 0.005, P < 0.005]. Such effects were associated with a skeletal muscle antioxidant response effective in preventing oxidative damage induced by CHF at the transition phase (untrained‐Tg 0.438 ± 0.25 vs. trained‐Tg 0.114 ± 0.010, P < 0.05) and with an increased expression of protein control markers (MuRF‐1, untrained‐Tg 1.12 ± 0.29 vs. trained‐Tg 14.14 ± 3.04, P < 0.0001; Atrogin‐1, untrained‐Tg 0.9 ± 0.38 vs. trained‐Tg 7.79 ± 2.03, P < 0.01; Cathepsin L, untrained‐Tg 0.91 ± 0.27 vs. trained‐Tg 2.14 ± 0.55, P < 0.01). At the end‐stage of CHF (14 months), trained‐Tg mice showed a worsening of physical performance (decrease in daily activity and weekly distance and time of activity) compared to trained age‐matched WT in association with oxidative protein damage of a similar level to that of untrained‐Tg mice (untrained‐Tg 0.62 ± 0.24 vs. trained‐Tg 0.64 ± 0.13, P > 0.05). Prolonged voluntary physical activity performed before the onset of CHF end‐stage, appears to be a useful tool to increase cardiac function and to reduce skeletal muscle oxidative damage counteracting physical activity decline.

Endurance exercise training in pulmonary hypertension increases skeletal muscle electron transport chain supercomplex assembly

Pulmonary hypertension is associated with pronounced exercise intolerance (decreased V ċ O₂ max) that can significantly impact quality of life. The cause of exercise intolerance in pulmonary hypertension remains unclear. Mitochondrial supercomplexes are large respiratory assemblies of individual electron transport chain complexes which can promote more efficient respiration. In this study, we examined pulmonary hypertension and exercise-induced changes in skeletal muscle electron transport chain protein expression and supercomplex assembly. Pulmonary arterial hypertension was induced in rats with the Sugen/Hypoxia model (10% FiO₂, three weeks). Pulmonary arterial hypertension and control rats were assigned to an exercise training protocol group or kept sedentary for one month. Cardiac function and V ċ O₂ max were assessed at the beginning and end of exercise training. Red (Type 1—oxidative muscle) and white (Type 2—glycolytic muscle) gastrocnemius were assessed for changes in electron transport chain complex protein expression and supercomplex assembly via SDS- and Blue Native-PAGE. Results showed that pulmonary arterial hypertension caused a significant decrease in V ċ O₂ max via treadmill testing that was improved with exercise (P < 0.01). Decreases in cardiac output and pulmonary acceleration time due to pulmonary arterial hypertension were not improved with exercise. Pulmonary arterial hypertension reduced expression in individual electron transport chain complex protein expression (NDUFB8 (CI), SDHB (CII), Cox IV (CIV), but not UQCRC2 (CIII), or ATP5a (CV)) in red gastrocnemius muscle. Both red gastrocnemius and white gastrocnemius electron transport chain expression was unaffected by exercise. However, non-denaturing Blue Native-PAGE analysis of mitochondrial supercomplexes demonstrated increases with exercise training in pulmonary arterial hypertension in the red gastrocnemius but not white gastrocnemius muscle. Pulmonary arterial hypertension-induced exercise intolerance is improved with exercise and is associated with muscle type specific alteration in mitochondrial supercomplex assembly and expression of mitochondrial electron transport chain proteins.

Osteopontin Promotes Left Ventricular Diastolic Dysfunction Through a Mitochondrial Pathway

BACKGROUND

Patients with chronic kidney disease (CKD) and coincident heart failure with preserved ejection fraction (HFpEF) may constitute a distinct HFpEF phenotype. Osteopontin (OPN) is a biomarker of HFpEF and predictive of disease outcome. We recently reported that OPN blockade reversed hypertension, mitochondrial dysfunction, and kidney failure in Col4a3^-/- mice, a model of human Alport syndrome.

OBJECTIVES

The purpose of this study was to identify potential OPN targets in biopsies of HF patients, healthy control subjects, and human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs), and to characterize the cardiac phenotype of Col4a3^-/- mice, relate this to HFpEF, and investigate possible causative roles for OPN in driving the cardiomyopathy.

METHODS

OGDHL mRNA and protein were quantified in myocardial samples from patients with HFpEF, heart failure with reduced ejection fraction, and donor control subjects. OGDHL expression was quantified in hiPS-CMs treated with or without anti-OPN antibody. Cardiac parameters were evaluated in Col4a3^-/- mice with and without global OPN knockout or AAV9-mediated delivery of 2-oxoglutarate dehydrogenase-like (Ogdhl) to the heart.

RESULTS

OGDHL mRNA and protein displayed abnormal abundances in cardiac biopsies of HFpEF (n = 17) compared with donor control subjects (n = 12; p < 0.01) or heart failure with reduced ejection fraction patients (n = 12; p < 0.05). Blockade of OPN in hiPS-CMs conferred increased OGDHL expression. Col4a3^-/- mice demonstrated cardiomyopathy with similarities to HFpEF, including diastolic dysfunction, cardiac hypertrophy and fibrosis, pulmonary edema, and impaired mitochondrial function. The cardiomyopathy was ameliorated by Opn^-/- coincident with improved renal function and increased expression of Ogdhl. Heart-specific overexpression of Ogdhl in Col4a3^-/- mice also improved cardiac function and cardiomyocyte energy state.

CONCLUSIONS

Col4a3^-/- mice present a model of HFpEF secondary to CKD wherein OPN and OGDHL are intermediates, and possibly therapeutic targets.

Changes in Respiratory Muscle Strength Following Cardiac Rehabilitation for Prognosis in Patients with Heart Failure

Respiratory muscle weakness, frequently observed in patients with heart failure (HF), is reported as a predictor for poor prognosis. Although increased respiratory muscle strength ameliorates exercise tolerance and quality of life in HF patients, the relationship between changes in respiratory muscle strength and patient prognosis remains unclear. A total of 456 patients with HF who continued a 5-month cardiac rehabilitation (CR) were studied. We measured maximal inspiratory pressure (PI_max) at hospital discharge as the baseline and five months thereafter to assess the respiratory muscle strength. Changes in PI_max during the 5-month observation period (⊿PI_max) were examined. We investigated the composite multiple incidence of all-cause death or unplanned readmission after 5-month CR. The relationship between ⊿PI_max and the incidence of clinical events was analyzed. Over a median follow-up of 1.8 years, 221 deaths or readmissions occurred, and their rate of incidence was 4.3/100 person-years. The higher ⊿PI_max was significantly associated with lower incidence of clinical event. In multivariate Poisson regression model after adjustment for clinical confounding factors, ⊿PI_max remained a significant and independent predictor for all-cause death/readmission (adjusted incident rate ratio for ⊿PI_max increase of 10 cmH₂O: 0.77, 95% confidence interval: 0.70–0.86). In conclusion, the changes in respiratory muscle strength independently predict the incidence of clinical events in patients with HF.

Impaired skeletal muscle performance as a consequence of random functional capillary rarefaction can be restored with overload-dependent angiogenesis

KEY POINTS

Loss of skeletal muscle capillaries is thought to contribute to a reduction in exercise tolerance, but the relative contribution of a compromised microcirculation with disease, in isolation of co-morbidities, to impaired muscle function is unknown. We therefore developed a novel method to randomly occlude capillaries in the rat hindlimb to mimic the capillary rarefaction observed in many conditions. We demonstrate that muscle fatigue resistance is closely coupled with functional microvascular density, independent of arterial blood flow, while disturbance of the microcirculation leads to long-term impairment of muscle function if left untreated. Mechanical stretch due to muscle overload causes a restoration of fatigue resistance via angiogenic remodelling. These observations highlight the importance of a healthy microcirculation and suggest that restoring impaired microvascular supply, regardless of disease co-morbidities, will assist recovery of exercise tolerance in a variety of conditions that limit quality of life.

ABSTRACT

To what extent microvascular rarefaction contributes to impaired skeletal muscle function remains unknown. Our understanding of whether pathological changes in the microcirculation can be reversed remains limited by a lack of basic physiological data in otherwise healthy tissue. The principal objectives here were to: (1) quantify the effect of random microvascular rarefaction on limb perfusion and muscle performance, and (2) determine if these changes could be reversed. We developed a novel protocol in rats whereby microspheres injected into the femoral artery allowed a unilateral reduction in functional capillary density in the extensor digitorum longus (EDL), and assessed acute and chronic effects on muscle function. Simultaneous bilateral EDL force and hindlimb blood flow measurements were made during electrical stimulation. Following functional capillary rarefaction there was an acute microsphere dose-dependent reduction in muscle fatigue resistance (P < 0.001), despite preserved femoral artery perfusion. Histological analysis of EDL samples taken from injected animals confirmed a positive correlation between the proportion of functional capillaries and fatigue resistance (P = 0.002). Such impaired performance persisted for at least 2 weeks (P = 0.016). Concomitant mechanical overload improved both perfused capillary density and fatigue resistance (P<0.05), confirming that the capacity for muscle remodelling was retained following chronic distributed ischaemia, and that the impact of capillary rarefaction could be alleviated. These results demonstrate that loss of functional capillaries is detrimental to muscle function, even in otherwise healthy tissue, independent of arterial perfusion. Restoration of muscle performance following a mechanical overload stimulus indicates that angiogenic treatments to alleviate microvascular rarefaction may be key to restoring exercise tolerance.

Divergent skeletal muscle mitochondrial phenotype between male and female patients with chronic heart failure

BACKGROUND

Previous studies in heart failure with reduced ejection fraction (HFrEF) suggest that skeletal muscle mitochondrial impairments are associated with exercise intolerance in men. However, the nature of this relationship in female patients remains to be elucidated. This study aimed to determine the relationship between skeletal muscle mitochondrial impairments and exercise intolerance in male and female patients with HFrEF.

METHODS

Mitochondrial respiration, enzyme activity, and gene expression were examined in pectoralis major biopsies from age-matched male (n = 45) and female (n = 11) patients with HFrEF and healthy-matched male (n = 24) and female (n = 11) controls. Mitochondrial variables were compared between sex and related to peak exercise capacity.

RESULTS

Compared with sex-matched controls, complex I mitochondrial oxygen flux was 17% (P = 0.030) and 29% (P = 0.013) lower in male and female patients with HFrEF, respectively, which correlated to exercise capacity (r = 0.71; P > 0.0001). Female HFrEF patients had a 32% (P = 0.023) lower mitochondrial content compared with controls. However, after adjusting for mitochondrial content, male patients demonstrated lower complex I function by 15% (P = 0.030). Expression of key mitochondrial genes regulating organelle dynamics and maintenance (i.e. optic atrophy 1, peroxisome proliferator-activated receptor γ coactivator-1α, NADH:ubiquinone oxidoreductase core subunit S1/S3, and superoxide dismutase 2) were selectively lower in female HFrEF patients.

CONCLUSIONS

These data provide novel evidence that HFrEF induces divergent sex-specific mitochondrial phenotypes in skeletal muscle that predispose towards exercise intolerance, impacting mitochondrial 'quantity' in female patients and mitochondrial 'quality' in male patients. Therapeutic strategies to improve exercise tolerance in HFrEF should consider targeting sex-specific mitochondrial abnormalities in skeletal muscle.

Sarcopenic Obesity, Insulin Resistance, and Their Implications in Cardiovascular and Metabolic Consequences

The prevalence of sarcopenic obesity is increasing worldwide, particularly amongst aging populations. Insulin resistance is the core mechanism of sarcopenic obesity and is also associated with variable cardiometabolic diseases such as cardiovascular disease, type 2 diabetes mellitus, and non-alcoholic fatty liver disease. Fat accumulation in muscle tissue promotes a proinflammatory cascade and oxidative stress, leading to mitochondrial dysfunction, impaired insulin signaling, and muscle atrophy. To compound the problem, decreased muscle mass aggravates insulin resistance. In addition, the crosstalk between myokines and adipokines leads to negative feedback, which in turn aggravates sarcopenic obesity and insulin resistance. In this review, we focus on the molecular mechanisms linking sarcopenic obesity and insulin resistance with various biological pathways. We also discuss the impact and mechanism of sarcopenic obesity and insulin resistance on cardiometabolic disease.

Mitochondrial Dysfunction in Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome with an increasingly recognized heterogeneity in pathophysiology. Exercise intolerance is the hallmark of HFpEF and appears to be caused by both cardiac and peripheral abnormalities in the arterial tree and skeletal muscle. Mitochondrial abnormalities can significantly contribute to impaired oxygen utilization and the resulting exercise intolerance in HFpEF. We review key aspects of the complex biology of this organelle, the clinical relevance of mitochondrial function, the methods that are currently available to assess mitochondrial function in humans, and the evidence supporting a role for mitochondrial dysfunction in the pathophysiology of HFpEF. We also discuss the role of mitochondrial function as a therapeutic target, some key considerations for the design of early-phase clinical trials using agents that specifically target mitochondrial function to improve symptoms in patients with HFpEF, and ongoing trials with mitochondrial agents in HFpEF.

Prevalence and prognosis of respiratory muscle weakness in heart failure patients with preserved ejection fraction

BACKGROUND

Although respiratory muscle weakness (RMW) is known to predict prognosis in patients with heart failure with reduced ejection fraction (HFrEF), RMW prevalence and its prognosis in those with preserved ejection fraction (HFpEF) remain unknown. We aimed to investigate whether the RMW predicted mortality in HFpEF patients.

METHODS

We conducted a single-centre observational study with consecutive 1023 heart failure patients (445 in HFrEF and 578 in HFpEF). Maximal inspiratory pressure (PI_max) was measured to assess respiratory muscle strength at hospital discharge, and RMW was defined as PI_max <70% of predicted value. Endpoint was all-cause mortality after hospital discharge, and we examined the influence of RMW on the endpoint.

RESULTS

Over a median follow-up of 1.8 years, 134 patients (13.1%) died; of these 53 (11.9%) were in HFrEF and 81 (14.0%) in HFpEF. RMW was evident in 190 (42.7%) HFrEF and 226 (39.1%) HFpEF patients and was independently associated with all-cause mortality in both HFrEF (adjusted hazard ratio [HR]: 2.13, 95% confidence interval [CI]: 1.17-3.88) and HFpEF (adjusted HR: 2.85, 95% CI: 1.74-4.67) patients. Adding RMW to the multivariate logistic regression model significantly increased area under the receiver-operating characteristic curve (AUC) for all-cause mortality in HFpEF (AUC including RMW: 0.78, not including RMW: 0.74, P = 0.026) but not in HFrEF (AUC including RMW: 0.84, not including RMW: 0.82, P = 0.132).

CONCLUSIONS

RMW was observed in 39% of HFpEF patients, which was independently associated with poor prognosis. The additive effect of RMW on prognosis was detected only in HFpEF but not in HFrEF.

Relative Impairments in Hemodynamic Exercise Reserve Parameters in Heart Failure With Preserved Ejection Fraction: A Study-Level Pooled Analysis

OBJECTIVES

The aim of this study was to compare the relative impairment in different exercise hemodynamic reserve parameters in patients with heart failure with preserved ejection fraction (HFpEF) and control patients using a study-level meta-analysis.

BACKGROUND

A cardinal manifestation of chronic HFpEF is severely decreased exercise capacity. Developing effective therapies for exercise intolerance in HFpEF requires optimal understanding of the factors underlying exercise intolerance.

METHODS

Data were included from 17 unique cohorts that measured peak oxygen uptake and hemodynamic or echocardiographic parameters during exercise in patients with HFpEF and control subjects in this meta-analysis. Standardized mean differences (SMDs) in the exercise reserve (exercise - resting) measures of hemodynamic or echocardiographic parameters between the HFpEF and control groups were pooled in a random-effects meta-analysis.

RESULTS

The pooled analysis included 910 patients with HFpEF and 476 control subjects. In pooled analysis, patients with HFpEF had significantly lower peak oxygen uptake (SMD: -2.13; 95% confidence interval [CI]: -2.68 to -1.57). Among hemodynamic exercise reserve parameters, the largest impairment was observed in chronotropic response reserve (change in heart rate from rest to peak exercise; SMD: -1.87; 95% CI: -2.44 to -1.29), followed by exaggerated increase in pulmonary capillary wedge pressure with exercise (SMD: 1.78; 95% CI: 1.46 to 2.09). Significant abnormalities were also observed in the arteriovenous oxygen difference reserve and stroke volume reserve between the HFpEF and control groups.

CONCLUSIONS

The most consistent and severe hemodynamic reserve abnormalities observed in patients with HFpEF were impairment in chronotropic reserve and exaggerated increase in pulmonary capillary wedge pressure with exercise. These may be important targets for therapeutic strategies to improve exercise tolerance in patients with HFpEF.

Towards a personalised approach in exercise-based cardiovascular rehabilitation: How can translational research help? A 'call to action' from the Section on Secondary Prevention and Cardiac Rehabilitation of the European Association of Preventive Cardiology

The benefit of regular physical activity and exercise training for the prevention of cardiovascular and metabolic diseases is undisputed. Many molecular mechanisms mediating exercise effects have been deciphered. Personalised exercise prescription can help patients in achieving their individual greatest benefit from an exercise-based cardiovascular rehabilitation programme. Yet, we still struggle to provide truly personalised exercise prescriptions to our patients. In this position paper, we address novel basic and translational research concepts that can help us understand the principles underlying the inter-individual differences in the response to exercise, and identify early on who would most likely benefit from which exercise intervention. This includes hereditary, non-hereditary and sex-specific concepts. Recent insights have helped us to take on a more holistic view, integrating exercise-mediated molecular mechanisms with those influenced by metabolism and immunity. Unfortunately, while the outline is recognisable, many details are still lacking to turn the understanding of a concept into a roadmap ready to be used in clinical routine. This position paper therefore also investigates perspectives on how the advent of 'big data' and the use of animal models could help unravel inter-individual responses to exercise parameters and thus influence hypothesis-building for translational research in exercise-based cardiovascular rehabilitation.

Small-molecule-mediated chemical knock-down of MuRF1/MuRF2 and attenuation of diaphragm dysfunction in chronic heart failure

BACKGROUND

Chronic heart failure (CHF) leads to diaphragm myopathy that significantly impairs quality of life and worsens prognosis. In this study, we aimed to assess the efficacy of a recently discovered small-molecule inhibitor of MuRF1 in treating CHF-induced diaphragm myopathy and loss of contractile function.

METHODS

Myocardial infarction was induced in mice by ligation of the left anterior descending coronary artery. Sham-operated animals (sham) served as controls. One week post-left anterior descending coronary artery ligation animals were randomized into two groups-one group was fed control rodent chow, whereas the other group was fed a diet containing 0.1% of the compound ID#704946-a recently described MuRF1-interfering small molecule. Echocardiography confirmed development of CHF after 10 weeks. Functional and molecular analysis of the diaphragm was subsequently performed.

RESULTS

Chronic heart failure induced diaphragm fibre atrophy and contractile dysfunction by ~20%, as well as decreased activity of enzymes involved in mitochondrial energy production (P < 0.05). Treatment with compound ID#704946 in CHF mice had beneficial effects on the diaphragm: contractile function was protected, while mitochondrial enzyme activity and up-regulation of the MuRF1 and MuRF2 was attenuated after infarct.

CONCLUSIONS

Our murine CHF model presented with diaphragm fibre atrophy, impaired contractile function, and reduced mitochondrial enzyme activities. Compound ID#704946 rescued from this partially, possibly by targeting MuRF1/MuRF2. However, at this stage of our study, we refrain to claim specific mechanism(s) and targets of compound ID#704946, because the nature of changes after 12 weeks of feeding is likely to be complex and is not necessarily caused by direct mechanistic effects.

[Mechanisms of exercise intolerance in patients with heart failure and preserved ejection fraction. Part II: The role of right heart chambers, vascular system and skeletal muscles]

The main clinical manifestation of heart failure with preserved ejection fraction is poor exercise tolerance. In addi-tion to the dysfunction of the left heart chambers, which were presented in the first part of this review, many other disorders are involved in poor exercise tolerance in such patients: impairments of the right heart, vascular system and skeletal muscle. The second part of this review presents the mechanisms for the development of these disorders, as well as possible ways to correct them.

Muscle Changes During Atrophy

Muscle atrophy typically is a direct effect of protein degradation induced by a diversity of pathophysiologic states such as disuse, immobilization, denervation, aging, sepsis, cachexia, glucocorticoid treatment, hereditary muscular disorders, cancer, diabetes and obesity, kidney and heart failure, and others. Muscle atrophy is defined by changes in the muscles, consisting in shrinkage of myofibers, changes in the types of fiber and myosin isoforms, and a net loss of cytoplasm, organelles and overall a protein loss. Although in the literature there are extensive studies in a range of animal models, the paucity of human data is a reality. This chapter is focused on various aspects of muscle wasting and describes the transitions of myofiber types during the progression of muscle atrophy in several pathological states. Clinical conditions associated with muscle atrophy have been grouped based on the fast-to-slow or slow-to-fast fiber-type shifts. We have also summarized the ultrastructural and histochemical features characteristic for muscle atrophy in clinical and experimental models for aging, cancer, diabetes and obesity, and heart failure and arrhythmia.

Ultrasonographic assessment of organs other than the heart in patients with heart failure

The number of patients with heart failure has been dramatically increasing in Japan in association with aging of the society. This phenomenon is referred to as a heart failure pandemic. The fundamental origin of heart failure is cardiac dysfunction. Echocardiography is widely used to assess cardiac function, as well as to diagnose heart diseases that cause cardiac dysfunction. However, the severity of heart failure is not necessarily correlated with that of cardiac dysfunction. This is partly explained by the fact that heart failure induces dysfunction of organs other than the heart through hemodynamic deterioration and neurohumoral changes. In addition, one of the characteristics of patients with heart failure, particularly elderly patients, is the presence of numerous comorbidities. Symptoms of heart failure are not specific, and assessment of cardiac function, particularly left ventricular diastolic function, has not been established. Thus, ultrasonographic assessment of organs other than the heart helps the diagnosis of heart failure, assessment of the severity of heart failure, and development of our understanding of the pathophysiology in each patient. This review summarizes current knowledge about the usefulness of ultrasonographic assessment of organs other than the heart in heart failure.

Effects of sodium glucose cotransporter type 2 inhibitors on heart failure

Heart failure (HF) is emerging as one of the most common cardiovascular (CV) events in patients with type 2 diabetes (T2D), and the one associated with the worst prognosis. T2D and insulin resistance are strong predictors of incident HF, especially HF with preserved ejection fraction (HFpEF). Recent data suggest that even when all traditional risk factors for ASCVD are well controlled, patients with T2D continue to have a substantially greater risk of developing HF-indicating that traditional risk factor control is insufficient from a HF prevention standpoint, and highlighting the need for novel, more effective strategies for both prevention and treatment of heart failure in patients with T2D. Until recently, medications developed for glucose-lowering had, at best, neutral effect on heart failure outcomes in patients with T2D, while several classes of T2D medications had little data in regards to HF risk, and others actually increased the risk of HF hospitalization. Sodium glucose cotransporter type 2 inhibitors (SGLT-2i) have a novel and unique mechanism of action. By inhibiting sodium and glucose reabsorption in the proximal tubule, SGLT-2i result in a number of downstream effects, including glucosuria, weight loss, osmotic diuresis and natriuresis, which should theoretically be beneficial in HF. Three CVOTs of various SGLT-2i (EMPA-REG OUTCOME, CANVAS and DECLARE-TIMI 58) enrolled markedly different patient populations in terms of ASCVD risk, but have demonstrated robust and consistent benefits in reduction of hospitalization for HF. In a meta-analysis of the three outcomes trials, SGLT-2i significantly reduced the risk of cardiovascular death or hospitalization for HF by 23% and hospitalization for HF by 31%. Although the declines in HF hospitalization with SGLT-2is are impressive, only a small proportion of patients with established HF were enrolled in these trials, and these benefits, therefore, represent primarily a HF prevention signal. Whether this prevention of HF benefit will translate to better outcomes for those patients with established HF (with or without diabetes), and whether it will extend across the spectrum of HF phenotypes (HFrEF and HFpEF) is yet to be determined, and is being actively investigated in several large ongoing trials.

The Effect of Exercise Training on Myocardial and Skeletal Muscle Metabolism by MR Spectroscopy in Rats with Heart Failure

The metabolism and performance of myocardial and skeletal muscle are impaired in heart failure (HF) patients. Exercise training improves the performance and benefits the quality of life in HF patients. The purpose of the present study was to determine the metabolic profiles in myocardial and skeletal muscle in HF and exercise training using MRS, and thus to identify targets for clinical MRS in vivo. After surgically establishing HF in rats, we randomized the rats to exercise training programs of different intensities. After the final training session, rats were sacrificed and tissues from the myocardial and skeletal muscle were extracted. Magnetic resonance spectra were acquired from these extracts, and principal component and metabolic enrichment analysis were used to assess the differences in metabolic profiles. The results indicated that HF affected myocardial metabolism by changing multiple metabolites, whereas it had a limited effect on skeletal muscle metabolism. Moreover, exercise training mainly altered the metabolite distribution in skeletal muscle, indicating regulation of metabolic pathways of taurine and hypotaurine metabolism and carnitine synthesis.

PGC-1α overexpression partially rescues impaired oxidative and contractile pathophysiology following volumetric muscle loss injury

Volumetric muscle loss (VML) injury is characterized by a non-recoverable loss of muscle fibers due to ablative surgery or severe orthopaedic trauma, that results in chronic functional impairments of the soft tissue. Currently, the effects of VML on the oxidative capacity and adaptability of the remaining injured muscle are unclear. A better understanding of this pathophysiology could significantly shape how VML-injured patients and clinicians approach regenerative medicine and rehabilitation following injury. Herein, the data indicated that VML-injured muscle has diminished mitochondrial content and function (i.e., oxidative capacity), loss of mitochondrial network organization, and attenuated oxidative adaptations to exercise. However, forced PGC-1α over-expression rescued the deficits in oxidative capacity and muscle strength. This implicates physiological activation of PGC1-α as a limiting factor in VML-injured muscle's adaptive capacity to exercise and provides a mechanistic target for regenerative rehabilitation approaches to address the skeletal muscle dysfunction.

Exercise Training Improved Longitudinal Intrinsic Left Ventricle Function in Heart Failure with Preserved Ejection Fraction

Exercise improves morbidity, fatality rate, and quality of life in heart failure with low ejection fraction, but fewer data available in heart failure with preserved ejection fraction (HFPEF). The purpose of this study is to test the hypothesis that exercise training might improve the longitudinal intrinsic left ventricular (LV) function in HFPEF patients. This quasi-experimental study had recruited 30 patients with HFPEF. Exercise training program had been performed for a month with a total of 20 times exercise sessions and evaluated every 2 weeks. Echocardiography was performed before sessions, second week and fourth week of exercise training. Six-minute walk tests (6MWTs) and quality-of-life variables using Minnesota living with HF scoring and the 5-item World Health Organization Well-Being Index scoring were measured before and after exercise as well. Left ventricular filling pressure, represented by the ratio of early diastolic mitral flow velocity/early diastolic annular velocity and left atrial volume index, improved during exercise. The longitudinal intrinsic LV function, represented by four-chamber longitudinal strain, augmented during exercise ( p  < 0.001). Aerobic capacity, measured by 6MWT, increased significantly ( p  = 0.001). Quality of life improved significantly during exercise ( p  < 0.001). Exercise training was suggested to improve the longitudinal intrinsic LV function and quality of life in HFPEF. Clinical Trial Registration: ACTRN12614001042639.

Skeletal Muscle Fiber Type in Hypoxia: Adaptation to High-Altitude Exposure and Under Conditions of Pathological Hypoxia

Skeletal muscle is able to modify its size, and its metabolic/contractile properties in response to a variety of stimuli, such as mechanical stress, neuronal activity, metabolic and hormonal influences, and environmental factors. A reduced oxygen availability, called hypoxia, has been proposed to induce metabolic adaptations and loss of mass in skeletal muscle. In addition, several evidences indicate that muscle fiber-type composition could be affected by hypoxia. The main purpose of this review is to explore the adaptation of skeletal muscle fiber-type composition to exposure to high altitude (ambient hypoxia) and under conditions of pathological hypoxia, including chronic obstructive pulmonary disease (COPD), chronic heart failure (CHF) and obstructive sleep apnea syndrome (OSAS). The muscle fiber-type composition of both adult animals and humans is not markedly altered during chronic exposure to high altitude. However, the fast-to-slow fiber-type transition observed in hind limb muscles during post-natal development is impaired in growing rats exposed to severe altitude. A slow-to-fast transition in fiber type is commonly found in lower limb muscles from patients with COPD and CHF, whereas a transition toward a slower fiber-type profile is often found in the diaphragm muscle in these two pathologies. A slow-to-fast transformation in fiber type is generally observed in the upper airway muscles in rodent models of OSAS. The factors potentially responsible for the adaptation of fiber type under these hypoxic conditions are also discussed in this review. The impaired locomotor activity most likely explains the changes in fiber type composition in growing rats exposed to severe altitude. Furthermore, chronic inactivity and muscle deconditioning could result in the slow-to-fast fiber-type conversion in lower limb muscles during COPD and CHF, while the factors responsible for the adaptation of muscle fiber type during OSAS remain hypothetical. Finally, the role played by cellular hypoxia, hypoxia-inducible factor-1 alpha (HIF-1α), and other molecular regulators in the adaptation of muscle fiber-type composition is described in response to high altitude exposure and conditions of pathological hypoxia.

Skeletal Muscle Myopathy in Heart Failure: the Role of Ejection Fraction

PURPOSE OF REVIEW

This review summarizes: (1) the structural and functional features coupled with pathophysiological factors responsible of skeletal muscle myopathy (SMM) in both heart failure with reduced (HFrEF) and preserved (HFpEF) ejection fraction and (2) the role of exercise as treatment of SMM in these HF-related phenotypes.

RECENT FINDINGS

The recent literature showed two main phenotypes of heart failure (HF): (1) HFrEF primarily due to a systolic dysfunction of the left ventricle and (2) HFpEF, mainly related to a diastolic dysfunction. Exercise intolerance is one of most disabling symptoms of HF and it is shown that persists after the normalization of the central hemodynamic impairments by therapy and/or cardiac surgery including heart transplant. A specific skeletal muscle myopathy (SMM) has been defined as one of the main causes of exercise intolerance in HF. The SMM has been well described in the last 20 years in the HFrEF; on the contrary, few studies are available in HFpEF. Recent evidences have revealed that exercise training counteracts HF-related SMM and in turn ameliorates exercise intolerance.

Vascular mitochondrial respiratory function: the impact of advancing age

Little is known about vascular mitochondrial respiratory function and the impact of age. Therefore, skeletal muscle feed arteries were harvested from young (33 ± 7 yr, n = 10), middle-aged (54 ± 5 yr, n = 10), and old (70 ± 7 yr, n = 10) subjects, and mitochondrial respiration as well as citrate synthase (CS) activity were assessed. Complex I (CI) and complex I + II (CI+II) state 3 respiration were greater in young (CI: 10.4 ± 0.8 pmol·s^-1·mg^-1 and CI+II: 12.4 ± 0.8 pmol·s^-1·mg^-1, P < 0.05) than middle-aged (CI: 7 ± 0.6 pmol·s^-1·mg^-1 and CI+II: 8.3 ± 0.5 pmol·s^-1·mg^-1) and old (CI: 7.2 ± 0.4 pmol·s^-1·mg^-1 and CI+II: 7.6 ± 0.5 pmol·s^-1·mg^-1) subjects and, as in the case of complex II (CII) state 3 respiration, were inversely correlated with age [ r = -0.56 (CI), r = -0.7 (CI+II), and r = 0.4 (CII), P < 0.05]. In contrast, state 4 respiration and mitochondria-specific superoxide levels were not different across groups. The respiratory control ratio was greater in young (2.2 ± 0.2, P < 0.05) than middle-aged and old (1.4 ± 0.1 and 1.1 ± 0.1, respectively) subjects and inversely correlated with age ( r = -0.71, P < 0.05). As CS activity was inversely correlated with age ( r = -0.54, P < 0.05), when normalized for mitochondrial content, the age-related differences and relationships with state 3 respiration were ablated. In contrast, mitochondrion-specific state 4 respiration was now lower in young (15 ± 1.4 pmol·s^-1·mg^-1·U CS^-1, P < 0.05) than middle-aged and old (23.4 ± 3.6 and 27.9 ± 3.4 pmol·s^-1·mg^-1·U CS^-1, respectively) subjects and correlated with age ( r = 0.46, P < 0.05). Similarly, superoxide/CS levels were lower in young (0.07 ± 0.01) than old (0.19 ± 0.41) subjects and correlated with age ( r = 0.44, P < 0.05). Therefore, with aging, vascular mitochondrial respiratory function declines, predominantly as a consequence of falling mitochondrial content. However, per mitochondrion, aging likely results in greater mitochondrion-derived oxidative stress, which may contribute to age-related vascular dysfunction. NEW & NOTEWORTHY This study determined, for the first time, that vascular mitochondrial oxidative respiratory capacity, oxidative coupling efficiency, and mitochondrial content fell progressively with advancing age. In terms of single mitochondrion-specific respiration, the age-related differences were completely ablated and the likelihood of free radical production increased progressively with advancing age. This study reveals that vascular mitochondrial respiratory capacity declines with advancing age, as a consequence of falling mitochondrial content, as does oxidative coupling efficiency.

Effects of Endurance Training on Detrimental Structural, Cellular, and Functional Alterations in Skeletal Muscles of Heart Failure With Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is underpinned by detrimental skeletal muscle alterations that contribute to disease severity, yet underlying mechanisms and therapeutic treatments remain poorly established. This study used a nonhuman animal model of HFpEF to better understand whether skeletal muscle abnormalities were (1) fiber-type specific and (2) reversible by various exercise training regimes.

METHODS AND RESULTS

Lean control rats were compared with obese ZSF1 rats at 20 weeks and then 8 weeks after sedentary, high-intensity interval training, or moderate continuous treadmill exercise. Oxidative soleus and glycolytic extensor digitorum longus (EDL) muscles were assessed for fiber size, capillarity, glycolytic metabolism, autophagy, and contractile function. HFpEF reduced fiber size and capillarity by 20%-50% (P < .05) in both soleus and EDL, but these effects were not reversed by endurance training. In contrast, both endurance training regimes in HFpEF attenuated the elevated lactate dehydrogenase activity observed in the soleus. Autophagy was down-regulated in EDL and up-regulated in soleus (P < .05), with no influence of endurance training. HFpEF impaired contractile forces of both muscles by ∼20% (P < .05), and these were not reversed by training.

CONCLUSIONS

Obesity-related HFpEF was associated with detrimental structural, cellular, and functional alterations to both slow-oxidative and fast-glycolytic skeletal muscles that could not be reversed by endurance training.

Endothelial function is disturbed in a hypertensive diabetic animal model of HFpEF: Moderate continuous vs. high intensity interval training

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is associated with endothelial dysfunction, but the molecular mechanisms still remain unclear. Whether exercise training (ET) along with which optimal modality can improve endothelial function is controversial. The present study used a hypertensive, diabetic-driven HFpEF animal model (ZSF1 rats) to determine whether different training modalities (moderate-continuous (MCT) and high-intensity interval training (HIIT)) could reverse endothelial dysfunction and to understand the underlying molecular mechanisms.

METHODS AND RESULTS

The development of HFpEF in ZSF1 obese animals was confirmed by echocardiography and hemodynamic measurements. Thereafter, animals were randomized into following groups: 1) sedentary, 2) 8 weeks of MCT, 3) 8 weeks of HIIT. ZSF1 lean animals served as control. In vitro measurement of endothelial function in aortic rings revealed significantly impaired endothelial-dependent and -independent vasodilation in HFpEF, which was reversed by MCT and HIIT. At the molecular level, the development of endothelial dysfunction was associated with a reduced expression / activation of endothelial nitric oxide synthase (eNOS), an increase in NADPH and activation of c-Jun N-terminal protein kinase (JNK), a reduced collagen I/III ratio and a reduced lining of the vessel wall by endothelial cells. ET primarily decreased NADPH oxidase expression, and JNK activation, elevated collagen I/III ratio while further improving aortic endothelial cell coverage.

CONCLUSIONS

The present study provides evidence that endothelial dysfunction occurs in experimental HFpEF and that ET, independent of the studied training modality, reverses endothelial dysfunction and specific molecular alterations. ET may therefore provide an important therapeutic intervention for HFpEF patients.

Yoga and breathing technique training in patients with heart failure and preserved ejection fraction: study protocol for a randomized clinical trial

Background

Current therapies for heart failure (HF) are followed by strategies to improve quality of life and exercise tolerance, besides reducing morbidity and mortality. Some HF patients present changes in the musculoskeletal system and inspiratory muscle weakness, which may be restored by inspiratory muscle training, thus increasing respiratory muscle strength and endurance, maximal oxygen uptake (VO₂), functional capacity, respiratory responses to exercise, and quality of life. Yoga therapies have been shown to improve quality of life, inflammatory markers, and peak VO₂ mostly in HF patients with a reduced ejection fraction. However, the effect of different yoga breathing techniques in patients showing HF with a preserved ejection fraction (HFpEF) remain to be assessed.

Methods/design

A PROBE (prospective randomized open blinded end-point) parallel-group trial will be conducted at two specialized HF clinics. Adult patients previously diagnosed with HFpEF will be included. After signing informed consent and performing a pre-test intervention, patients will be randomized into three groups and provided with either (1) active yoga breathing techniques; (2) passive yoga breathing techniques (pranayama); or and (3) control (standard pharmacological treatment). Follow-up will last 8 weeks (16 sessions). The post-intervention tests will be performed at the end of the intervention period for analysis of outcomes. Interventions will occur continuously according to patients’ enrollment. The main outcome is respiratory muscular resistance. A total of 33 enrolled patients are expected. The present protocol followed the SPIRIT guidelines and fulfilled the SPIRIT checklist.

Discussion

This trial is probably the first to assess the effects of a non-pharmacological intervention, namely yoga and specific breathing techniques, to improve cardiorespiratory function, autonomic system, and quality of life in patients with HFpEF.

Trial registration

REBEC Identifier: RBR-64mbnx (August 19, 2012).

Clinical Trials Register: NCT03028168. Registered on 16 January 2017).

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2802-5) contains supplementary material, which is available to authorized users.

Regional Adipose Distribution and its Relationship to Exercise Intolerance in Older Obese Patients Who Have Heart Failure With Preserved Ejection Fraction

OBJECTIVES

This study sought to test the hypothesis that older obese patients with heart failure with preserved ejection fraction (HFpEF) have significantly greater abdominal, cardiac, and intermuscular fat than healthy, age-matched controls, out of proportion to total body fat, and that these abnormalities are associated with objective measurements of physical function.

BACKGROUND

Recent studies indicate that excess total body adipose tissue contributes to exercise intolerance in patients with HFpEF. However, the impact of the pattern of regional (abdominal, cardiac, intermuscular) adipose deposition on exercise intolerance in patients with HFpEF is unknown.

METHODS

We measured total body adiposity (using dual-energy x-ray absorptiometry) and regional adiposity (using cardiac magnetic resonance), peak oxygen uptake (Vo₂), 6-min walk distance (6MWD), short physical performance battery (SPPB), and leg press power in 100 older obese patients with HFpEF and 61 healthy controls (HCs) and adjusted for age, sex, race, and body surface area.

RESULTS

Peak Vo₂ (15.7 ± 0.4 ml/kg/min vs. 23.0 ± 0.6 ml/kg/min, respectively; p < 0.001), 6MWD (427 ± 7 m vs. 538 ± 10 m, respectively; p < 0.001), SPPB (10.3 ± 0.2 vs. 10.9 ± 0.2, respectively; p < 0.05), and leg power (117 ± 5 W vs. 152 ± 9 W, respectively; p = 0.004) were significantly lower in patients with HFpEF than HCs. Total fat mass, total percent fat, abdominal subcutaneous fat, intra-abdominal fat, and thigh intermuscular fat were significantly higher, whereas epicardial fat was significantly lower in patients with HFpEF than in HC. After we adjusted for total body fat, intra-abdominal fat remained significantly higher, while epicardial fat remained significantly lower in patients with HFpEF. Abdominal subcutaneous fat, thigh subcutaneous fat, and thigh intermuscular fat:skeletal muscle ratio were inversely associated, whereas epicardial fat was directly associated with peak Vo₂, 6MWD, SPPB, and leg power. Using multiple stepwise regression, we found intra-abdominal fat was the strongest independent predictor of peak Vo₂ and 6MWD.

CONCLUSIONS

In metabolic obese HFpEF, the pattern of regional adipose deposition may have important adverse consequences beyond total body adiposity. Interventions targeting intra-abdominal and intermuscular fat could potentially improve exercise intolerance. (Exercise Intolerance in Elderly Patients With Diastolic Heart Failure [SECRET]; NCT00959660).

Heart failure with preserved ejection fraction and skeletal muscle physiology

Heart failure with preserved ejection fraction (HFpEF) accounts for half of all heart failure in the USA, increases in prevalence with aging, and has no effective therapies. Intriguingly, the pathophysiology of HFpEF has many commonalities with the aged cardiovascular system including reductions in diastolic compliance, chronotropic defects, increased resistance in the peripheral vasculature, and poor energy substrate utilization. Decreased exercise capacity is a cardinal symptom of HFpEF. However, its severity is often out of proportion to changes in cardiac output. This observation has led to studies of muscle function in HFpEF revealing structural, biomechanical, and metabolic changes. These data, while incomplete, support a hypothesis that similar to aging, HFPEF is a systemic process. Understanding the mechanisms leading to exercise intolerance in this condition may lead to strategies to improve morbidity in both HFpEF and aging.

Diaphragm abnormalities in heart failure and aging: mechanisms and integration of cardiovascular and respiratory pathophysiology

Inspiratory function is essential for alveolar ventilation and expulsive behaviors that promote airway clearance (e.g., coughing and sneezing). Current evidence demonstrates that inspiratory dysfunction occurs during healthy aging and is accentuated by chronic heart failure (CHF). This inspiratory dysfunction contributes to key aspects of CHF and aging cardiovascular and pulmonary pathophysiology including: (1) impaired airway clearance and predisposition to pneumonia; (2) inability to sustain ventilation during physical activity; (3) shallow breathing pattern that limits alveolar ventilation and gas exchange; and (4) sympathetic activation that causes cardiac arrhythmias and tissue vasoconstriction. The diaphragm is the primary inspiratory muscle; hence, its neuromuscular integrity is a main determinant of the adequacy of inspiratory function. Mechanistic work within animal and cellular models has revealed specific factors that may be responsible for diaphragm neuromuscular abnormalities in CHF and aging. These include phrenic nerve and neuromuscular junction alterations as well as intrinsic myocyte abnormalities, such as changes in the quantity and quality of contractile proteins, accelerated fiber atrophy, and shifts in fiber type distribution. CHF, aging, or CHF in the presence of aging disturbs the dynamics of circulating factors (e.g., cytokines and angiotensin II) and cell signaling involving sphingolipids, reactive oxygen species, and proteolytic pathways, thus leading to the previously listed abnormalities. Exercise-based rehabilitation combined with pharmacological therapies targeting the pathways reviewed herein hold promise to treat diaphragm abnormalities and inspiratory muscle dysfunction in CHF and aging.

Skeletal muscle alterations in HFrEF vs. HFpEF

PURPOSE OF REVIEW

Severe exercise intolerance and early fatigue are hallmarks of heart failure patients either with a reduced (HFrEF) or a still preserved (HFpEF) ejection fraction. This review, therefore, will provide a contemporary summary of the alterations currently known to occur in the skeletal muscles of both HFrEF and HFpEF, and provide some further directions that will be required if we want to improve our current understanding of this area.

RECENT FINDINGS

Skeletal muscle alterations are well documented for over 20 years in HFrEF, and during the recent years also data are presented that in HFpEF muscular alterations are present. Alterations are ranging from a shift in fiber type and capillarization to an induction of atrophy and modulation of mitochondrial energy supply. In general, the molecular alterations are more severe in the skeletal muscle of HFrEF when compared to HFpEF. The alterations occurring in the skeletal muscle at the molecular level may contribute to exercise intolerance in HFrEF and HFpEF. Nevertheless, the knowledge of changes in the skeletal muscle of HFpEF is still sparsely available and more studies in this HF cohort are clearly warranted.

Exercise Training Reveals Inflexibility of the Diaphragm in an Animal Model of Patients With Obesity-Driven Heart Failure With a Preserved Ejection Fraction

BACKGROUND

Respiratory muscle weakness contributes to exercise intolerance in patients with heart failure with a preserved ejection fraction (HFpEF)-a condition characterized by multiple comorbidities with few proven treatments. We aimed, therefore, to provide novel insight into the underlying diaphragmatic alterations that occur in HFpEF by using an obese cardiometabolic rat model and further assessed whether exercise training performed only after the development of overt HFpEF could reverse impairments.

METHODS AND RESULTS

Obese ZSF1 rats (n=12) were compared with their lean controls (n=8) at 20 weeks, with 3 additional groups of obese ZSF1 rats compared at 28 weeks following 8 weeks of either sedentary behavior (n=13), high-intensity interval training (n=11), or moderate-continuous training (n=11). Obese rats developed an obvious HFpEF phenotype at 20 and 28 weeks. In the diaphragm at 20 weeks, HFpEF induced a shift towards an oxidative phenotype and a fiber hypertrophy paralleled by a lower protein expression in MuRF1 and MuRF2, yet mitochondrial and contractile functional impairments were observed. At 28 weeks, neither the exercise training regimen of high-intensity interval training or moderate-continuous training reversed any of the diaphragm alterations induced by HFpEF.

CONCLUSIONS

This study, using a well-characterized rat model of HFpEF underpinned by multiple comorbidities and exercise intolerance (ie, one that closely resembles the patient phenotype), provides evidence that diaphragm alterations and dysfunction induced in overt HFpEF are not reversed following 8 weeks of aerobic exercise training. As such, whether alternative therapeutic interventions are required to treat respiratory muscle weakness in HFpEF warrants further investigation.

Delayed Repolarization Underlies Ventricular Arrhythmias in Rats With Heart Failure and Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) represents approximately half of heart failure, and its incidence continues to increase. The leading cause of mortality in HFpEF is sudden death, but little is known about the underlying mechanisms.

METHODS

Dahl salt-sensitive rats were fed a high-salt diet (8% NaCl) from 7 weeks of age to induce HFpEF (n=38). Rats fed a normal-salt diet (0.3% NaCl) served as controls (n=13). Echocardiograms were performed to assess systolic and diastolic function from 14 weeks of age. HFpEF-verified and control rats underwent programmed electrical stimulation. Corrected QT interval was measured by surface ECG. The mechanisms of ventricular arrhythmias (VA) were probed by optical mapping, whole-cell patch clamp to measure action potential duration and ionic currents, and quantitative polymerase chain reaction and Western blotting to investigate changes in ion channel expression.

RESULTS

After 7 weeks of a high-salt diet, 31 of 38 rats showed diastolic dysfunction and preserved ejection fraction along with signs of heart failure and hence were diagnosed with HFpEF. Programmed electric stimulation demonstrated increased susceptibility to VA in HFpEF rats (P<0.001 versus controls). The arrhythmogenicity index was increased (P<0.001) and the corrected QT interval on ECG was prolonged (P<0.001) in HFpEF rats. Optical mapping of HFpEF hearts demonstrated prolonged action potentials (P<0.05) and multiple reentry circuits during induced VA. Single-cell recordings of cardiomyocytes isolated from HFpEF rats confirmed a delay of repolarization (P=0.001) and revealed downregulation of transient outward potassium current (I_to; P<0.05). The rapid components of the delayed rectifier potassium current (I_Kr) and the inward rectifier potassium current (I_K1) were also downregulated (P<0.05), but the current densities were much lower than for I_to. In accordance with the reduction of I_to, both Kcnd3 transcript and Kv4.3 protein levels were decreased in HFpEF rat hearts.

CONCLUSIONS

Susceptibility to VA was markedly increased in rats with HFpEF. Underlying abnormalities include QT prolongation, delayed repolarization from downregulation of potassium currents, and multiple reentry circuits during VA. Our findings are consistent with the hypothesis that potassium current downregulation leads to abnormal repolarization in HFpEF, which in turn predisposes to VA and sudden cardiac death.

Respiratory Muscle Training Improves Diaphragm Citrate Synthase Activity and Hemodynamic Function in Rats with Heart Failure

Introduction

Enhanced respiratory muscle strength in patients with heart failure positively alters the clinical trajectory of heart failure. In an experimental model, respiratory muscle training in rats with heart failure has been shown to improve cardiopulmonary function through mechanisms yet to be entirely elucidated.

Objective

The present report aimed to evaluate the respiratory muscle training effects in diaphragm citrate synthase activity and hemodynamic function in rats with heart failure.

Methods

Wistar rats were divided into four experimental groups: sedentary sham (Sed-Sham, n=8), trained sham (RMT-Sham, n=8), sedentary heart failure (Sed-HF, n=7) and trained heart failure (RMT-HF, n=7). The animals were submitted to a RMT protocol performed 30 minutes a day, 5 days/week, for 6 weeks.

Results

In rats with heart failure, respiratory muscle training decreased pulmonary congestion and right ventricular hypertrophy. Deleterious alterations in left ventricular pressures, as well as left ventricular contractility and relaxation, were assuaged by respiratory muscle training in heart failure rats. Citrate synthase activity, which was significantly reduced in heart failure rats, was preserved by respiratory muscle training. Additionally, a negative correlation was found between citrate synthase and left ventricular end diastolic pressure and positive correlation was found between citrate synthase and left ventricular systolic pressure.

Conclusion

Respiratory muscle training produces beneficial adaptations in the diaphragmatic musculature, which is linked to improvements in left ventricular hemodynamics and blood pressure in heart failure rats. The RMT-induced improvements in cardiac architecture and the oxidative capacity of the diaphragm may improve the clinical trajectory of patients with heart failure.

Exercise Training Prevents Diaphragm Contractile Dysfunction in Heart Failure

PURPOSE

Patient studies have demonstrated the efficacy of exercise training in attenuating respiratory muscle weakness in chronic heart failure (HF), yet direct assessment of muscle fiber contractile function together with data on the underlying intracellular mechanisms remains elusive. The present study, therefore, used a mouse model of HF to assess whether exercise training could prevent diaphragm contractile fiber dysfunction by potentially mediating the complex interplay between intracellular oxidative stress and proteolysis.

METHODS

Mice underwent sham operation (n = 10) or a ligation of the left coronary artery and were randomized to sedentary HF (n = 10) or HF with aerobic exercise training (HF + AET; n = 10). Ten weeks later, echocardiography and histological analyses confirmed HF.

RESULTS

In vitro diaphragm fiber bundles demonstrated contractile dysfunction in sedentary HF compared with sham mice that was prevented by AET, with maximal force 21.0 ± 0.7 versus 26.7 ± 1.4 and 25.4 ± 1.4 N·cm, respectively (P < 0.05). Xanthine oxidase enzyme activity and MuRF1 protein expression, markers of oxidative stress and protein degradation, were ~20% and ~70% higher in sedentary HF compared with sham mice (P < 0.05) but were not different when compared with the HF + AET group. Oxidative modifications to numerous contractile proteins (i.e., actin and creatine kinase) and markers of proteolysis (i.e., proteasome and calpain activity) were elevated in sedentary HF compared with HF + AET mice (P < 0.05); however, these indices were not significantly different between sedentary HF and sham mice. Antioxidative enzyme activities were also not different between groups.

CONCLUSION

Our findings demonstrate that AET can protect against diaphragm contractile fiber dysfunction induced by HF, but it remains unclear whether alterations in oxidative stress and/or protein degradation are primarily responsible.

Fatigability, Exercise Intolerance, and Abnormal Skeletal Muscle Energetics in Heart Failure

BACKGROUND

Among central and peripheral factors contributing to exercise intolerance (EI) in heart failure (HF), the extent to which skeletal muscle (SM) energy metabolic abnormalities occur and contribute to EI and increased fatigability in HF patients with reduced or preserved ejection fraction (HFrEF and HFpEF, respectively) are not known. An energetic plantar flexion exercise fatigability test and magnetic resonance spectroscopy were used to probe the mechanistic in vivo relationships among SM high-energy phosphate concentrations, mitochondrial function, and EI in HFrEF and HFpEF patients and in healthy controls.

METHODS AND RESULTS

Resting SM high-energy phosphate concentrations and ATP flux rates were normal in HFrEF and HFpEF patients. Fatigue occurred at similar SM energetic levels in all subjects, consistent with a common SM energetic limit. Importantly, HFrEF New York Heart Association class II-III patients with EI and high fatigability exhibited significantly faster rates of exercise-induced high-energy phosphate decline than did HFrEF patients with low fatigability (New York Heart Association class I), despite similar left ventricular ejection fractions. HFpEF patients exhibited severe EI, the most rapid rates of high-energy phosphate depletion during exercise, and impaired maximal oxidative capacity.

CONCLUSIONS

Symptomatic fatigue during plantar flexion exercise occurs at a common energetic limit in all subjects. HFrEF and HFpEF patients with EI and increased fatigability manifest early, rapid exercise-induced declines in SM high-energy phosphates and reduced oxidative capacity compared with healthy and low-fatigability HF patients, suggesting that SM metabolism is a potentially important target for future HF treatment strategies.