Left ventricular diastolic dysfunction and myocardial stiffness in diabetic mice is attenuated by inhibition of dipeptidyl peptidase 4

Metabolic Flexibility of the Heart: The Role of Fatty Acid Metabolism in Health, Heart Failure, and Cardiometabolic Diseases

This comprehensive review explores the critical role of fatty acid (FA) metabolism in cardiac diseases, particularly heart failure (HF), and the implications for therapeutic strategies. The heart's reliance on ATP, primarily sourced from mitochondrial oxidative metabolism, underscores the significance of metabolic flexibility, with fatty acid oxidation (FAO) being a dominant source. In HF, metabolic shifts occur with an altered FA uptake and FAO, impacting mitochondrial function and contributing to disease progression. Conditions like obesity and diabetes also lead to metabolic disturbances, resulting in cardiomyopathy marked by an over-reliance on FAO, mitochondrial dysfunction, and lipotoxicity. Therapeutic approaches targeting FA metabolism in cardiac diseases have evolved, focusing on inhibiting or stimulating FAO to optimize cardiac energetics. Strategies include using CPT1A inhibitors, using PPARα agonists, and enhancing mitochondrial biogenesis and function. However, the effectiveness varies, reflecting the complexity of metabolic remodeling in HF. Hence, treatment strategies should be individualized, considering that cardiac energy metabolism is intricate and tightly regulated. The therapeutic aim is to optimize overall metabolic function, recognizing the pivotal role of FAs and the need for further research to develop effective therapies, with promising new approaches targeting mitochondrial oxidative metabolism and FAO that improve cardiac function.

Mapping the cellular and molecular landscape of cardiac non-myocytes in murine diabetic cardiomyopathy

Diabetes is associated with a significantly elevated risk of heart failure. However, despite extensive efforts to characterize the phenotype of the diabetic heart, the molecular and cellular protagonists that underpin cardiac pathological remodeling in diabetes remain unclear, with a notable paucity of data regarding the impact of diabetes on non-myocytes within the heart. Here we aimed to define key differences in cardiac non-myocytes between spontaneously type-2 diabetic (db/db) and healthy control (db/h) mouse hearts. Single-cell transcriptomic analysis revealed a concerted diabetes-induced cellular response contributing to cardiac remodeling. These included cell-specific activation of gene programs relating to fibroblast hyperplasia and cell migration, and dysregulation of pathways involving vascular homeostasis and protein folding. This work offers a new perspective for understanding the cellular mediators of diabetes-induced cardiac pathology, and pathways that may be targeted to address the cardiac complications associated with diabetes.

Searching for Effective Treatments in HFpEF: Implications for Modeling the Disease in Rodents

BACKGROUND

While the prevalence of heart failure with preserved ejection fraction (HFpEF) has increased over the last two decades, there still remains a lack of effective treatment. A key therapeutic challenge is posed by the absence of animal models that accurately replicate the complexities of HFpEF. The present review summarizes the effects of a wide spectrum of therapeutic agents on HF.

METHODS

Two online databases were searched for studies; in total, 194 experimental protocols were analyzed following the PRISMA protocol.

RESULTS

A diverse range of models has been proposed for studying therapeutic interventions for HFpEF, with most being based on pressure overload and systemic hypertension. They have been used to evaluate more than 150 different substances including ARNIs, ARBs, HMGR inhibitors, SGLT-2 inhibitors and incretins. Existing preclinical studies have primarily focused on LV diastolic performance, and this has been significantly improved by a wide spectrum of candidate therapeutic agents. Few experiments have investigated the normalization of pulmonary congestion, exercise capacity, animal mortality, or certain molecular hallmarks of heart disease.

CONCLUSIONS

The development of comprehensive preclinical HFpEF models, with multi-organ system phenotyping and physiologic stress-based functional testing, is needed for more successful translation of preclinical research to clinical trials.

The effect of exenatide (a GLP-1 analogue) and sitagliptin (a DPP-4 inhibitor) on asymmetric dimethylarginine (ADMA) metabolism and selected biomarkers of cardiac fibrosis in rats with fructose-induced metabolic syndrome

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis, is a risk factor for endothelial dysfunction, a common pathophysiological denominator for both atherogenesis and cardiac fibrosis. We aimed to investigate whether the cardioprotective and antifibrotic effects of incretin drugs, exenatide and sitagliptin, may be associated with their ability to affect circulating and cardiac ADMA metabolism. Normal and fructose-fed rats were treated with sitagliptin (5.0/10 mg/kg) or exenatide (5/10 µg/kg) for 4 weeks. The following methods were used: LC-MS/MS, ELISA, Real-Time-PCR, colorimetry, IHC and H&E staining, PCA and OPLS-DA projections. Eight-week fructose feeding resulted in an increase in plasma ADMA and a decrease in NO concentration. Exenatide administration into fructose-fed rats reduced the plasma ADMA level and increased NO level. In the heart of these animals exenatide administration increased NO and PRMT1 level, reduced TGF-ß1, α-SMA levels and COL1A1 expression. In the exenatide treated rats renal DDAH activity positively correlated with plasma NO level and negatively with plasma ADMA level and cardiac α-SMA concentration. Sitagliptin treatment of fructose-fed rats increased plasma NO concentration, reduced circulating SDMA level, increased renal DDAH activity and reduced myocardial DDAH activity. Both drugs attenuated the myocardial immunoexpression of Smad2/3/P and perivascular fibrosis. In the metabolic syndrome condition both sitagliptin and exenatide positively modulated cardiac fibrotic remodeling and circulating level of endogenous NOS inhibitors but had no effects on ADMA levels in the myocardium.

Multi-omic analysis of the cardiac cellulome defines a vascular contribution to cardiac diastolic dysfunction in obese female mice

Coronary microvascular dysfunction (CMD) is associated with cardiac dysfunction and predictive of cardiac mortality in obesity, especially in females. Clinical data further support that CMD associates with development of heart failure with preserved ejection fraction and that mineralocorticoid receptor (MR) antagonism may be more efficacious in obese female, versus male, HFpEF patients. Accordingly, we examined the impact of smooth muscle cell (SMC)-specific MR deletion on obesity-associated coronary and cardiac diastolic dysfunction in female mice. Obesity was induced in female mice via western diet (WD) feeding alongside littermates fed standard diet. Global MR blockade with spironolactone prevented coronary and cardiac dysfunction in obese females and specific deletion of SMC-MR was sufficient to prevent obesity-associated coronary and cardiac diastolic dysfunction. Cardiac gene expression profiling suggested reduced cardiac inflammation in WD-fed mice with SMC-MR deletion independent of blood pressure, aortic stiffening, and cardiac hypertrophy. Further mechanistic studies utilizing single-cell RNA sequencing of non-cardiomyocyte cell populations revealed novel impacts of SMC-MR deletion on the cardiac cellulome in obese mice. Specifically, WD feeding induced inflammatory gene signatures in non-myocyte populations including B/T cells, macrophages, and endothelium as well as increased coronary VCAM-1 protein expression, independent of cardiac fibrosis, that was prevented by SMC-MR deletion. Further, SMC-MR deletion induced a basal reduction in cardiac mast cells and prevented WD-induced cardiac pro-inflammatory chemokine expression and leukocyte recruitment. These data reveal a central role for SMC-MR signaling in obesity-associated coronary and cardiac dysfunction, thus supporting the emerging paradigm of a vascular origin of cardiac dysfunction in obesity.

In Search of the Holy Grail: Stem Cell Therapy as a Novel Treatment of Heart Failure with Preserved Ejection Fraction

Heart failure, a leading cause of hospitalizations and deaths, is a major clinical problem. In recent years, the increasing incidence of heart failure with preserved ejection fraction (HFpEF) has been observed. Despite extensive research, there is no efficient treatment for HFpEF available. However, a growing body of evidence suggests stem cell transplantation, due to its immunomodulatory effect, may decrease fibrosis and improve microcirculation and therefore, could be the first etiology-based therapy of the disease. In this review, we explain the complex pathogenesis of HFpEF, delineate the beneficial effects of stem cells in cardiovascular therapy, and summarize the current knowledge concerning cell therapy in diastolic dysfunction. Furthermore, we identify outstanding knowledge gaps that may indicate directions for future clinical studies.

Diabetes disturbs functional adaptation of the remote myocardium after ischemia/reperfusion

Diabetes mellitus type 2 is associated with adverse clinical outcome after myocardial infarction. To better understand the underlying causes we here investigated sarcomere protein function and its calcium-dependent regulation in the non-ischemic remote myocardium (RM) of diabetic mice (db/db) after transient occlusion of the left anterior descending coronary artery. Before and 24 h after surgery db/db and non-diabetic db/+ underwent magnetic resonance imaging followed by histological and biochemical analyses of heart tissue. Intracellular calcium transients and sarcomere function were measured in isolated cardiomyocytes. Active and passive force generation was assessed in skinned fibers and papillary muscle preparations. Before ischemia and reperfusion (I/R), beat-to-beat calcium cycling was depressed in diabetic cardiomyocytes. Nevertheless, contractile function was preserved owing to increased myofilament calcium sensitivity and higher responsiveness of myocardial force production to β-adrenergic stimulation in db/db compared to db/+. In addition, protein kinase C activity was elevated in db/db hearts leading to strong phosphorylation of the titin PEVK region and increased titin-based tension of myofilaments. I/R impaired the function of whole hearts and RM sarcomeres in db/db to a larger extent than in non-diabetic db/+, and we identified several reasons. First, the amplitude and the kinetics of cardiomyocyte calcium transients were further reduced in the RM of db/db. Underlying causes involved altered expression of calcium regulatory proteins. Diabetes and I/R additively reduced phospholamban S16-phosphorylation by 80% (P < 000.1) leading to strong inhibition of the calcium ATPase SERCA2a. Second, titin stiffening was only observed in the RM of db/+, but not in the RM of db/db. Finally, db/db myofilament calcium sensitivity and force generation upon β-adrenergic stimulation were no longer enhanced over db/+ in the RM. The findings demonstrate that impaired cardiomyocyte calcium cycling of db/db hearts is compensated by increased myofilament calcium sensitivity and increased titin-based stiffness prior to I/R. In contrast, sarcomere function of the RM 24 h after I/R is poor because both these compensatory mechanisms fail and myocyte calcium handling is further depressed.

Chronic high-rate pacing induces heart failure with preserved ejection fraction-like phenotype in Ossabaw swine

The lack of pre-clinical large animal models of heart failure with preserved ejection fraction (HFpEF) remains a growing, yet unmet obstacle to improving understanding of this complex condition. We examined whether chronic cardiometabolic stress in Ossabaw swine, which possess a genetic propensity for obesity and cardiovascular complications, produces an HFpEF-like phenotype. Swine were fed standard chow (lean; n = 13) or an excess calorie, high-fat, high-fructose diet (obese; n = 16) for ~ 18 weeks with lean (n = 5) and obese (n = 8) swine subjected to right ventricular pacing (180 beats/min for ~ 4 weeks) to induce heart failure (HF). Baseline blood pressure, heart rate, LV end-diastolic volume, and ejection fraction were similar between groups. High-rate pacing increased LV end-diastolic pressure from ~ 11 ± 1 mmHg in lean and obese swine to ~ 26 ± 2 mmHg in lean HF and obese HF swine. Regression analyses revealed an upward shift in LV diastolic pressure vs. diastolic volume in paced swine that was associated with an ~ twofold increase in myocardial fibrosis and an ~ 50% reduction in myocardial capillary density. Hemodynamic responses to graded hemorrhage revealed an ~ 40% decrease in the chronotropic response to reductions in blood pressure in lean HF and obese HF swine without appreciable changes in myocardial oxygen delivery or transmural perfusion. These findings support that high-rate ventricular pacing of lean and obese Ossabaw swine initiates underlying cardiac remodeling accompanied by elevated LV filling pressures with normal ejection fraction. This distinct pre-clinical tool provides a unique platform for further mechanistic and therapeutic studies of this highly complex syndrome.

Diabetes-induced chronic heart failure is due to defects in calcium transporting and regulatory contractile proteins: cellular and molecular evidence

Heart failure (HF) is a major deteriorating disease of the myocardium due to weak myocardial muscles. As such, the heart is unable to pump blood efficiently around the body to meet its constant demand. HF is a major global health problem with more than 7 million deaths annually worldwide, with some patients dying suddenly due to sudden cardiac death (SCD). There are several risk factors which are associated with HF and SCD which can negatively affect the heart synergistically. One major risk factor is diabetes mellitus (DM) which can cause an elevation in blood glucose level or hyperglycaemia (HG) which, in turn, has an insulting effect on the myocardium. This review attempted to explain the subcellular, cellular and molecular mechanisms and to a lesser extent, the genetic factors associated with the development of diabetes- induced cardiomyopathy due to the HG which can subsequently lead to chronic heart failure (CHF) and SCD. The study first explained the structure and function of the myocardium and then focussed mainly on the excitation-contraction coupling (ECC) processes highlighting the defects of calcium transporting (SERCA, NCX, RyR and connexin) and contractile regulatory (myosin, actin, titin and troponin) proteins. The study also highlighted new therapies and those under development, as well as preventative strategies to either treat or prevent diabetic cardiomyopathy (DCM). It is postulated that prevention is better than cure.

Genomic, Proteomic, and Metabolic Comparisons of Small Animal Models of Heart Failure With Preserved Ejection Fraction: A Tale of Mice, Rats, and Cats

Heart failure with preserved ejection fraction (HFpEF) remains a medical anomaly that baffles researchers and physicians alike. The overall phenotypical changes of diastolic function and left ventricular hypertrophy observed in HFpEF are definable; however, the metabolic and molecular alterations that ultimately produce these changes are not well established. Comorbidities such as obesity, hypertension, and diabetes, as well as general aging, play crucial roles in its development and progression. Various animal models have recently been developed to better understand the pathophysiological and metabolic developments in HFpEF and to illuminate novel avenues for pharmacotherapy. These models include multi‐hit rodents and feline aortic constriction animals. Recently, genomic, proteomic, and metabolomic approaches have been used to define altered signaling pathways in the heart associated with HFpEF, including those involved in inflammation, cGMP‐related, Ca²⁺ handling, mitochondrial respiration, and the unfolded protein response in endoplasmic reticulum stress. This article aims to present an overview of what has been learnt by these studies, focusing mainly on the findings in common while highlighting unresolved issues. The knowledge gained from these research models will not simply be of benefit for treating HFpEF but will undoubtedly provide new insights into the mechanisms by which the heart deals with external stresses and how the processes involved can fail.

Current Understanding of Molecular Pathophysiology of Heart Failure With Preserved Ejection Fraction

Heart Failure (HF) is the most common cause of hospitalization in the Western societies. HF is a heterogeneous and complex syndrome that may result from any dysfunction of systolic or diastolic capacity. Abnormal diastolic left ventricular function with impaired relaxation and increased diastolic stiffness is characteristic of heart failure with preserved ejection fraction (HFpEF). HFpEF accounts for more than 50% of all cases of HF. The prevalence increases with age: from around 1% for those aged &lt;55 years to &gt;10% in those aged 70 years or over. Nearly 50% of HF patients have HFrEF and the other 50% have HFpEF/HFmrEF, mainly based on studies in hospitalized patients. The ESC Long-Term Registry, in the outpatient setting, reports that 60% have HFrEF, 24% have HFmrEF, and 16% have HFpEF. To some extent, more than 50% of HF patients are female. HFpEF is closely associated with co-morbidities, age, and gender. Epidemiological evidence suggests that HFpEF is highly represented in older obese women and proposed as ‘obese female HFpEF phenotype’. While HFrEF phenotype is more a male phenotype. In addition, metabolic abnormalities and hemodynamic perturbations in obese HFpEF patients appear to have a greater impact in women then in men (Sorimachi et al., European J of Heart Fail, 2022, 22). To date, numerous clinical trials of HFpEF treatments have produced disappointing results. This outcome suggests that a “one size fits all” approach to HFpEF may be inappropriate and supports the use of tailored, personalized therapeutic strategies with specific treatments for distinct HFpEF phenotypes. The most important mediators of diastolic stiffness are the cardiomyocytes, endothelial cells, and extracellular matrix (ECM). The complex physiological signal transduction networks that respond to the dual challenges of inflammatory and oxidative stress are major factors that promote the development of HFpEF pathologies. These signalling networks contribute to the development of the diseases. Inhibition and/or attenuation of these signalling networks also delays the onset of disease. In this review, we discuss the molecular mechanisms associated with the physiological responses to inflammation and oxidative stress and emphasize the nature of the contribution of most important cells to the development of HFpEF via increased inflammation and oxidative stress.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

Ca2+/calmodulin-dependent protein kinase II and protein kinase G oxidation contributes to impaired sarcomeric proteins in hypertrophy model

Aims

Volume overload (VO) induced hypertrophy is one of the hallmarks to the development of heart diseases. Understanding the compensatory mechanisms involved in this process might help preventing the disease progression.

Methods and results

Therefore, the present study used 2 months old Wistar rats, which underwent an aortocaval fistula to develop VO‐induced hypertrophy. The animals were subdivided into four different groups, two sham operated animals served as age‐matched controls and two groups with aortocaval fistula. Echocardiography was performed prior termination after 4‐ and 8‐month. Functional and molecular changes of several sarcomeric proteins and their signalling pathways involved in the regulation and modulation of cardiomyocyte function were investigated.

Results

The model was characterized with preserved ejection fraction in all groups and with elevated heart/body weight ratio, left/right ventricular and atrial weight at 4‐ and 8‐month, which indicates VO‐induced hypertrophy. In addition, 8‐months groups showed increased left ventricular internal diameter during diastole, RV internal diameter, stroke volume and velocity‐time index compared with their age‐matched controls. These changes were accompanied by increased Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness in 8‐month VO rats compared with other groups. The altered cardiomyocyte mechanics was associated with phosphorylation deficit of sarcomeric proteins cardiac troponin I, myosin binding protein C and titin, also accompanied with impaired signalling pathways involved in phosphorylation of these sarcomeric proteins in 8‐month VO rats compared with age‐matched control group. Impaired protein phosphorylation status and dysregulated signalling pathways were associated with significant alterations in the oxidative status of both kinases CaMKII and PKG explaining by this the elevated Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness and perhaps the development of hypertrophy.

Conclusions

Our findings showed VO‐induced cardiomyocyte dysfunction via deranged phosphorylation of myofilament proteins and signalling pathways due to increased oxidative state of CaMKII and PKG and this might contribute to the development of hypertrophy.

Cardiac mechanisms of the beneficial effects of SGLT2 inhibitors in heart failure: Evidence for potential off-target effects

Sodium glucose cotransporter 2 inhibitors (SGLT2i) constitute a promising drug treatment for heart failure patients with either preserved or reduced ejection fraction. Whereas SGLT2i were originally developed to target SGLT2 in the kidney to facilitate glucosuria in diabetic patients, it is becoming increasingly clear that these drugs also have important effects outside of the kidney. In this review we summarize the literature on cardiac effects of SGLT2i, focussing on pro-inflammatory and oxidative stress processes, ion transport mechanisms controlling sodium and calcium homeostasis and metabolic/mitochondrial pathways. These mechanisms are particularly important as disturbances in these pathways result in endothelial dysfunction, diastolic dysfunction, cardiac stiffness, and cardiac arrhythmias that together contribute to heart failure. We review the findings that support the concept that SGLT2i directly and beneficially interfere with inflammation, oxidative stress, ionic homeostasis, and metabolism within the cardiac cell. However, given the very low levels of SGLT2 in cardiac cells, the evidence suggests that SGLT2-independent effects of this class of drugs likely occurs via off-target effects in the myocardium. Thus, while there is still much to be understood about the various factors which determine how SGLT2i affect cardiac cells, much of the research clearly demonstrates that direct cardiac effects of these SGLT2i exist, albeit mediated via SGLT2-independent pathways, and these pathways may play a role in explaining the beneficial effects of SGLT2 inhibitors in heart failure.

Impact of Syndecan-2-Selected Mesenchymal Stromal Cells on the Early Onset of Diabetic Cardiomyopathy in Diabetic db/db Mice

Background: Mesenchymal stromal cells (MSCs) are an attractive cell type for cell therapy given their immunomodulatory, anti-fibrotic, and endothelial-protective features. The heparin sulfate proteoglycan, syndecan-2/CD362, has been identified as a functional marker for MSC isolation, allowing one to obtain a homogeneous cell product that meets regulatory requirements for clinical use. We previously assessed the impact of wild-type (WT), CD362^-, and CD362⁺ MSCs on local changes in protein distribution in left ventricular (LV) tissue and on LV function in an experimental model of early-onset diabetic cardiomyopathy. The present study aimed to further explore their impact on mechanisms underlying diastolic dysfunction in this model. Materials: For this purpose, 1 × 10⁶ WT, CD362^-, or CD362⁺ MSCs were intravenously (i.v.) injected into 20-week-old diabetic BKS.Cg-m+/+Lepr^db/BomTac, i.e., db/db mice. Control animals (db+/db) were injected with the equivalent volume of phosphate-buffered saline (PBS) alone. After 4 weeks, mice were sacrificed for further analysis. Results: Treatment with all three MSC populations had no impact on blood glucose levels in db/db mice. WT, CD362^-, and CD362⁺ MSC application restored LV nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) levels in db/db mice, which correlated with a reduction in cardiomyocyte stiffness. Furthermore, all stromal cells were able to increase arteriole density in db/db mice. The effect of CD362⁺ MSCs on NO and cGMP levels, cardiomyocyte stiffness, and arteriole density was less pronounced than in mice treated with WT or CD362^- MSCs. Analysis of collagen I and III protein expression revealed that fibrosis had not yet developed at this stage of experimental diabetic cardiomyopathy. All MSCs reduced the number of cardiac CD3⁺ and CD68⁺ cells in db/db mice, whereas only splenocytes from CD362^-- and CD362⁺-db/db mice exhibited a lower pro-fibrotic potential compared to splenocytes from db/db mice. Conclusion: CD362⁺ MSC application decreased cardiomyocyte stiffness, increased myocardial NO and cGMP levels, and increased arteriole density, although to a lesser extent than WT and CD362^- MSCs in an experimental model of early-onset diabetic cardiomyopathy without cardiac fibrosis. These findings suggest that the degree in improvement of cardiomyocyte stiffness following CD362⁺ MSC application was insufficient to improve diastolic function.

Cardiac Energy Metabolism in Heart Failure

Alterations in cardiac energy metabolism contribute to the severity of heart failure. However, the energy metabolic changes that occur in heart failure are complex and are dependent not only on the severity and type of heart failure present but also on the co-existence of common comorbidities such as obesity and type 2 diabetes. The failing heart faces an energy deficit, primarily because of a decrease in mitochondrial oxidative capacity. This is partly compensated for by an increase in ATP production from glycolysis. The relative contribution of the different fuels for mitochondrial ATP production also changes, including a decrease in glucose and amino acid oxidation, and an increase in ketone oxidation. The oxidation of fatty acids by the heart increases or decreases, depending on the type of heart failure. For instance, in heart failure associated with diabetes and obesity, myocardial fatty acid oxidation increases, while in heart failure associated with hypertension or ischemia, myocardial fatty acid oxidation decreases. Combined, these energy metabolic changes result in the failing heart becoming less efficient (ie, a decrease in cardiac work/O₂ consumed). The alterations in both glycolysis and mitochondrial oxidative metabolism in the failing heart are due to both transcriptional changes in key enzymes involved in these metabolic pathways, as well as alterations in NAD redox state (NAD⁺ and nicotinamide adenine dinucleotide levels) and metabolite signaling that contribute to posttranslational epigenetic changes in the control of expression of genes encoding energy metabolic enzymes. Alterations in the fate of glucose, beyond flux through glycolysis or glucose oxidation, also contribute to the pathology of heart failure. Of importance, pharmacological targeting of the energy metabolic pathways has emerged as a novel therapeutic approach to improving cardiac efficiency, decreasing the energy deficit and improving cardiac function in the failing heart.

Low-intensity pulsed ultrasound ameliorates cardiac diastolic dysfunction in mice: a possible novel therapy for heart failure with preserved left ventricular ejection fraction

AIMS

Heart failure with preserved left ventricular ejection fraction (HFpEF) is a serious health problem worldwide, as no effective therapy is yet available. We have previously demonstrated that our low-intensity pulsed ultrasound (LIPUS) therapy is effective and safe for angina and dementia. In this study, we aimed to examine whether the LIPUS therapy also ameliorates cardiac diastolic dysfunction in mice.

METHODS AND RESULTS

Twelve-week-old obese diabetic mice (db/db) and their control littermates (db/+) were treated with either the LIPUS therapy [1.875 MHz, 32 cycles, Ispta (spatial peak temporal average intensity) 117-162 mW/cm2, 0.25 W/cm2] or placebo procedure two times a week for 4 weeks. At 20-week-old, transthoracic echocardiography and invasive haemodynamic analysis showed that cardiac diastolic function parameters, such as e', E/e', end-diastolic pressure-volume relationship, Tau, and dP/dt min, were all deteriorated in placebo-treated db/db mice compared with db/+ mice, while systolic function was preserved. Importantly, these cardiac diastolic function parameters were significantly ameliorated in the LIPUS-treated db/db mice. We also measured the force (F) and intracellular Ca2+ ([Ca2+]i) in trabeculae dissected from ventricles. We found that relaxation time and [Ca2+]i decay (Tau) were prolonged during electrically stimulated twitch contractions in db/db mice, both of which were significantly ameliorated in the LIPUS-treated db/db mice, indicating that the LIPUS therapy also improves relaxation properties at tissue level. Functionally, exercise capacity was also improved in the LIPUS-treated db/db mice. Histologically, db/db mice displayed progressed cardiomyocyte hypertrophy and myocardial interstitial fibrosis, while those changes were significantly suppressed in the LIPUS-treated db/db mice. Mechanistically, western blot showed that the endothelial nitric oxide synthase (eNOS)-nitric oxide (NO)-cGMP-protein kinase G (PKG) pathway and Ca2+-handling molecules were up-regulated in the LIPUS-treated heart.

CONCLUSIONS

These results indicate that the LIPUS therapy ameliorates cardiac diastolic dysfunction in db/db mice through improvement of eNOS-NO-cGMP-PKG pathway and cardiomyocyte Ca2+-handling system, suggesting its potential usefulness for the treatment of HFpEF patients.

Concurrent diabetes and heart failure: interplay and novel therapeutic approaches

Diabetes mellitus increases the risk of developing heart failure, and the co-existence of both diseases worsens cardiovascular outcomes, hospitalization and the progression of heart failure. Despite current advancements on therapeutic strategies to manage hyperglycemia, the likelihood of developing diabetes-induced heart failure is still significant, especially with the accelerating global prevalence of diabetes and an ageing population. This raises the likelihood of other contributing mechanisms beyond hyperglycemia in predisposing diabetic patients to cardiovascular disease risk. There has been considerable interest in understanding the alterations in cardiac structure and function in the diabetic patients, collectively termed as "diabetic cardiomyopathy". However, the factors that contribute to the development of diabetic cardiomyopathies is not fully understood. This review summarizes the main characteristics of diabetic cardiomyopathies, and the basic mechanisms that contribute to its occurrence. This includes perturbations in insulin resistance, fuel preference, reactive oxygen species generation, inflammation, cell death pathways, neurohormonal mechanisms, advanced glycated end-products accumulation, lipotoxicity, glucotoxicity, and posttranslational modifications in the heart of the diabetic. This review also discusses the impact of antihyperglycemic therapies on the development of heart failure, as well as how current heart failure therapies influence glycemic control in diabetic patients. We also highlight the current knowledge gaps in understanding how diabetes induces heart failure.

Application of Animal Models in Diabetic Cardiomyopathy

Diabetic heart disease is a growing and important public health risk. Apart from the risk of coronary artery disease or hypertension, diabetes mellitus (DM) is a well-known risk factor for heart failure in the form of diabetic cardiomyopathy (DiaCM). Currently, DiaCM is defined as myocardial dysfunction in patients with DM in the absence of coronary artery disease and hypertension. The underlying pathomechanism of DiaCM is partially understood, but accumulating evidence suggests that metabolic derangements, oxidative stress, increased myocardial fibrosis and hypertrophy, inflammation, enhanced apoptosis, impaired intracellular calcium handling, activation of the renin-angiotensin-aldosterone system, mitochondrial dysfunction, and dysregulation of microRNAs, among other factors, are involved. Numerous animal models have been used to investigate the pathomechanisms of DiaCM. Despite some limitations, animal models for DiaCM have greatly advanced our understanding of pathomechanisms and have helped in the development of successful disease management strategies. In this review, we summarize the current pathomechanisms of DiaCM and provide animal models for DiaCM according to its pathomechanisms, which may contribute to broadening our understanding of the underlying mechanisms and facilitating the identification of possible new therapeutic targets.

Linagliptin prevents left ventricular stiffening by reducing titin cleavage and hypophosphorylation

The metabolic syndrome (MetS) is an escalating problem worldwide, causing left ventricular stiffening, an early characteristic of diastolic dysfunction for which no treatment exists. As diastolic dysfunction and stiffening in MetS patients are associated with increased circulating dipeptidyl peptidase-4 (DPP-4) levels, we investigated whether the clinically approved DPP-4 inhibitor linagliptin reduces left ventricular stiffness in MetS-induced cardiac disease. Sixteen-week-old obese ZSF1 rats, displaying the MetS and left ventricular stiffness, received linagliptin-supplemented or placebo diet for four weeks. Linagliptin significantly reduced obesity, hyperlipidaemia, and hyperglycaemia and improved left ventricular relaxation. This improved relaxation was related to decreased cardiac fibrosis and cardiomyocyte passive stiffness (Fpassive ). The reduced Fpassive was the result of titin isoform switching from the stiff N2B to the more flexible N2BA and increased phosphorylation of total titin and specifically its N2Bus region (S4080 and S3391). Importantly, DPP-4 directly cleaved titin in vitro, resulting in an increased Fpassive , which was prevented by simultaneous administration of linagliptin. In conclusion, linagliptin improves left ventricular stiffness in obese ZSF1 rats by preventing direct DPP4-mediated titin cleavage, as well as by modulating both titin isoform levels and phosphorylation. Reducing left ventricular stiffness by administering linagliptin might prevent MetS-induced early diastolic dysfunction in human.

MALDI-IMS as a Tool to Determine the Myocardial Response to Syndecan-2-Selected Mesenchymal Stromal Cell Application in an Experimental Model of Diabetic Cardiomyopathy

PURPOSE

Mesenchymal stromal cells (MSC) are an attractive tool for treatment of diabetic cardiomyopathy. Syndecan-2/CD362 has been identified as a functional marker for MSC isolation. Imaging mass spectrometry (IMS) allows for the characterization of therapeutic responses in the left ventricle. This study aims to investigate whether IMS can assess the therapeutic effect of CD362⁺ -selected MSC on early onset experimental diabetic cardiomyopathy.

EXPERIMENTAL DESIGN

1 × 10⁶ wild type (WT), CD362^- , or CD362⁺ MSC are intravenously injected into db/db mice. Four weeks later, mice are hemodynamically characterized and subsequently sacrificed for IMS combined with bottom-up mass spectrometry, and isoform and phosphorylation analyses of cardiac titin.

RESULTS

Overall alterations of the cardiac proteome signatures, especially titin, are observed in db/db compared to control mice. Interestingly, only CD362⁺ MSC can overcome the reduced titin intensity distribution and shifts the isoform ratio toward the more compliant N2BA form. In contrast, WT and CD362^- MSCs improve all-titin phosphorylation and protein kinase G activity, which is reflected in an improvement in diastolic performance.

CONCLUSIONS AND CLINICAL RELEVANCE

IMS enables the characterization of differences in titin intensity distribution following MSC application. However, further analysis of titin phosphorylation is needed to allow for the assessment of the therapeutic efficacy of MSC.

Cardiac cGMP Signaling in Health and Disease: Location, Location, Location

3',5'-Cyclic guanosine monophosphate (cGMP) is a ubiquitous second messenger, which critically regulates cardiac pump function and protects from the development of cardiac hypertrophy by acting in various subcellular microdomains. Although clinical studies testing the potential of cGMP elevating drugs in patients suffering from cardiac disease showed promising results, deeper insight into the local actions of these drugs at the subcellular level are indispensable to inspire novel therapeutic strategies. Detailed information on the spatio-temporal dynamics of cGMP production and degradation can be provided by the use of fluorescent biosensors that are capable of monitoring this second messenger at different locations inside the cell with high temporal and spatial resolution. In this review, we will summarize how these emerging new tools have improved our understanding of cardiac cGMP signaling in health and disease, and attempt to anticipate future challenges in the field.

Repurposing Antidiabetic Drugs for Cardiovascular Disease

Metabolic diseases and diabetes represent an increasing global challenge for human health care. As associated with a strongly elevated risk of developing atherosclerosis, kidney failure and death from myocardial infarction or stroke, the treatment of diabetes requires a more effective approach than lowering blood glucose levels. This review summarizes the evidence for the cardioprotective benefits induced by antidiabetic agents, including sodium-glucose cotransporter 2 inhibitor (SGLT2i) and glucagon-like peptide-1 receptor agonist (GLP1-RA), along with sometimes conversely discussed effects of dipeptidyl peptidase-4 inhibitor (DPP4i) and metformin in patients with high cardiovascular risk with or without type 2 diabetes. Moreover, the proposed mechanisms of the different drugs are described based on the results of preclinical studies. Recent cardiovascular outcome trials unexpectedly confirmed a beneficial effect of GLP-1RA and SGLT2i in type 2 diabetes patients with high cardiovascular risk and with standard care, which was independent of glycaemic control. These results triggered a plethora of studies to clarify the underlying mechanisms and the relevance of these effects. Taken together, the available data strongly highlight the potential of repurposing the original antidiabetics GLP1-RA and SGLT2i to improve cardiovascular outcome even in non-diabetic patients with cardiovascular diseases.

Important Roles of Endothelium-Dependent Hyperpolarization in Coronary Microcirculation and Cardiac Diastolic Function in Mice

Endothelium-dependent hyperpolarization (EDH) factor is one of endothelium-derived relaxing factors and plays important roles especially in microvessels. We have previously demonstrated that endothelium-derived hydrogen peroxide (H2O2) is an EDH factor produced by all types of nitric oxide synthases (NOSs), including endothelial NOS (eNOS), neuronal NOS (nNOS), and inducible NOS. Recent studies have suggested the association between coronary microvascular dysfunction and cardiac diastolic dysfunction. However, the role of EDH in this issue remains to be fully elucidated. We thus examined whether EDH plays an important role in coronary microcirculation and if so, whether endothelial dysfunction, especially impaired EDH, is involved in the pathogenesis of cardiac diastolic dysfunction in mice. Using a Langendorff-perfused heart experiment, we examined the increase in coronary flow in response to bradykinin in the presence of indomethacin and N-nitro-L-arginine (EDH condition) in wild-type, eNOS-knockout (KO), and nNOS/eNOS-double-KO mice. Compared with wild-type mice, EDH-mediated relaxations were increased in eNOS-KO mice but were significantly reduced in n/eNOS-KO mice. Catalase, a specific H2O2 scavenger, markedly inhibited EDH-mediated relaxations in all 3 genotypes, indicating compensatory roles of nNOS-derived H2O2 as an EDH factor in coronary microcirculation. Although both eNOS-KO and n/eNOS-KO mice exhibited similar extents of cardiac morphological changes, only n/eNOS-KO mice exhibited cardiac diastolic dysfunction. The expression of oxidized protein kinase G I-α (PKGIα) in the heart was significantly increased in eNOS-KO mice compared with n/eNOS-KO mice. These results indicate that EDH/H2O2 plays important roles in maintaining coronary microcirculation and cardiac diastolic function through oxidative PKGIα activation.

Mechanisms of diabetic cardiomyopathy and potential therapeutic strategies: preclinical and clinical evidence

The pathogenesis and clinical features of diabetic cardiomyopathy have been well-studied in the past decade, but effective approaches to prevent and treat this disease are limited. Diabetic cardiomyopathy occurs as a result of the dysregulated glucose and lipid metabolism associated with diabetes mellitus, which leads to increased oxidative stress and the activation of multiple inflammatory pathways that mediate cellular and extracellular injury, pathological cardiac remodelling, and diastolic and systolic dysfunction. Preclinical studies in animal models of diabetes have identified multiple intracellular pathways involved in the pathogenesis of diabetic cardiomyopathy and potential cardioprotective strategies to prevent and treat the disease, including antifibrotic agents, anti-inflammatory agents and antioxidants. Some of these interventions have been tested in clinical trials and have shown favourable initial results. In this Review, we discuss the mechanisms underlying the development of diabetic cardiomyopathy and heart failure in type 1 and type 2 diabetes mellitus, and we summarize the evidence from preclinical and clinical studies that might provide guidance for the development of targeted strategies. We also highlight some of the novel pharmacological therapeutic strategies for the treatment and prevention of diabetic cardiomyopathy.

Cellular, mitochondrial and molecular alterations associate with early left ventricular diastolic dysfunction in a porcine model of diabetic metabolic derangement

The prevalence of diabetic metabolic derangement (DMetD) has increased dramatically over the last decades. Although there is increasing evidence that DMetD is associated with cardiac dysfunction, the early DMetD-induced myocardial alterations remain incompletely understood. Here, we studied early DMetD-related cardiac changes in a clinically relevant large animal model. DMetD was established in adult male Göttingen miniswine by streptozotocin injections and a high-fat, high-sugar diet, while control animals remained on normal pig chow. Five months later left ventricular (LV) function was assessed by echocardiography and hemodynamic measurements, followed by comprehensive biochemical, molecular and histological analyses. Robust DMetD developed, evidenced by hyperglycemia, hypercholesterolemia and hypertriglyceridemia. DMetD resulted in altered LV nitroso-redox balance, increased superoxide production—principally due to endothelial nitric oxide synthase (eNOS) uncoupling—reduced nitric oxide (NO) production, alterations in myocardial gene-expression—particularly genes related to glucose and fatty acid metabolism—and mitochondrial dysfunction. These abnormalities were accompanied by increased passive force of isolated cardiomyocytes, and impaired LV diastolic function, evidenced by reduced LV peak untwist velocity and increased E/e′. However, LV weight, volume, collagen content, and cardiomyocyte cross-sectional area were unchanged at this stage of DMetD. In conclusion, DMetD, in a clinically relevant large-animal model results in myocardial oxidative stress, eNOS uncoupling and reduced NO production, together with an altered metabolic gene expression profile and mitochondrial dysfunction. These molecular alterations are associated with stiffening of the cardiomyocytes and early diastolic dysfunction before any structural cardiac remodeling occurs. Therapies should be directed to ameliorate these early DMetD-induced myocardial changes to prevent the development of overt cardiac failure.

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.

The molecular mechanisms associated with the physiological responses to inflammation and oxidative stress in cardiovascular diseases

The complex physiological signal transduction networks that respond to the dual challenges of inflammatory and oxidative stress are major factors that promote the development of cardiovascular pathologies. These signaling networks contribute to the development of age-related diseases, suggesting crosstalk between the development of aging and cardiovascular disease. Inhibition and/or attenuation of these signaling networks also delays the onset of disease. Therefore, a concept of targeting the signaling networks that are involved in inflammation and oxidative stress may represent a novel treatment paradigm for many types of heart disease. In this review, we discuss the molecular mechanisms associated with the physiological responses to inflammation and oxidative stress especially in heart failure with preserved ejection fraction and emphasize the nature of the crosstalk of these signaling processes as well as possible therapeutic implications for cardiovascular medicine.

Enhanced Cardiomyocyte Function in Hypertensive Rats With Diastolic Dysfunction and Human Heart Failure Patients After Acute Treatment With Soluble Guanylyl Cyclase (sGC) Activator

Aims

Our aim was to investigate the effect of nitric oxide (NO)-independent activation of soluble guanylyl cyclase (sGC) on cardiomyocyte function in a hypertensive animal model with diastolic dysfunction and in biopsies from human heart failure with preserved ejection fraction (HFpEF).

Methods

Dahl salt-sensitive (DSS) rats and control rats were fed a high-salt diet for 10 weeks and then acutely treated in vivo with the sGC activator BAY 58-2667 (cinaciguat) for 30 min. Single skinned cardiomyocyte passive stiffness (F_passive) was determined in rats and human myocardium biopsies before and after acute treatment. Titin phosphorylation, activation of the NO/sGC/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) cascade, as well as hypertrophic pathways including NO/sGC/cGMP/PKG, PKA, calcium–calmodulin kinase II (CaMKII), extracellular signal-regulated kinase 2 (ERK2), and PKC were assessed. In addition, we explored the contribution of pro-inflammatory cytokines and oxidative stress levels to the modulation of cardiomyocyte function. Immunohistochemistry and electron microscopy were used to assess the translocation of sGC and connexin 43 proteins in the rat model before and after treatment.

Results

High cardiomyocyte F_passive was found in rats and human myocardial biopsies compared to control groups, which was attributed to hypophosphorylation of total titin and to deranged site-specific phosphorylation of elastic titin regions. This was accompanied by lower levels of PKG and PKA activity, along with dysregulation of hypertrophic pathway markers such as CaMKII, PKC, and ERK2. Furthermore, DSS rats and human myocardium biopsies showed higher pro-inflammatory cytokines and oxidative stress compared to controls. DSS animals benefited from treatment with the sGC activator, as F_passive, titin phosphorylation, PKG and the hypertrophic pathway kinases, pro-inflammatory cytokines, and oxidative stress markers all significantly improved to the level observed in controls. Immunohistochemistry and electron microscopy revealed a translocation of sGC protein toward the intercalated disc and t-tubuli following treatment in both control and DSS samples. This translocation was confirmed by staining for the gap junction protein connexin 43 at the intercalated disk. DSS rats showed a disrupted connexin 43 pattern, and sGC activator was able to partially reduce disruption and increase expression of connexin 43. In human HFpEF biopsies, the high F_passive, reduced titin phosphorylation, dysregulation of the NO–sGC–cGMP–PKG pathway and PKA activity level, and activity of kinases involved in hypertrophic pathways CaMKII, PKC, and ERK2 were all significantly improved by sGC treatment and accompanied by a reduction in pro-inflammatory cytokines and oxidative stress markers.

Conclusion

Our data show that sGC activator improves cardiomyocyte function, reduces inflammation and oxidative stress, improves sGC–PKG signaling, and normalizes hypertrophic kinases, indicating that it is a potential treatment option for HFpEF patients and perhaps also for cases with increased hypertrophic signaling.

Phosphodiesterase 9a Inhibition in Mouse Models of Diastolic Dysfunction

BACKGROUND

Low myocardial cGMP-PKG (cyclic guanosine monophosphate-protein kinase G) activity has been associated with increased cardiomyocyte diastolic stiffness in heart failure with preserved ejection fraction. Cyclic guanosine monophosphate is mainly hydrolyzed by PDE (phosphodiesterases) 5a and 9a. Importantly, PDE9a expression has been reported to be upregulated in human heart failure with preserved ejection fraction myocardium and chronic administration of a PDE9a inhibitor reverses preestablished cardiac hypertrophy and systolic dysfunction in mice subjected to transverse aortic constriction (TAC). We hypothesized that inhibiting PDE9a activity ameliorates diastolic dysfunction.

METHODS

To examine the effect of chronic PDE9a inhibition, 2 diastolic dysfunction mouse models were studied: (1) TAC-deoxycorticosterone acetate and (2) Lepr^db/db. PDE9a inhibitor (5 and 8 mg/kg per day) was administered to the mice via subcutaneously implanted osmotic minipumps for 28 days. The effect of acute PDE9a inhibition was investigated in intact cardiomyocytes isolated from TAC-deoxycorticosterone acetate mice. Atrial natriuretic peptide together with PDE9a inhibitor were administered to the isolated intact cardiomyocytes through the cell perfusate.

RESULTS

For acute inhibition, no cellular stiffness reduction was found, whereas chronic PDE9a inhibition resulted in reduced left ventricular chamber stiffness in TAC-deoxycorticosterone acetate, but not in Lepr^db/db mice. Passive cardiomyocyte stiffness was reduced by chronic PDE9a inhibition, with no differences in myocardial fibrosis or cardiac morphometry. PDE9a inhibition increased the ventricular-arterial coupling ratio, reflecting impaired systolic function.

CONCLUSIONS

Chronic PDE9a inhibition lowers left ventricular chamber stiffness in TAC-deoxycorticosterone acetate mice. However, the usefulness of PDE9a inhibition to treat high-diastolic stiffness may be limited as the required PDE9a inhibitor dose also impairs systolic function, observed as a decline in ventricular-arterial coordination, in this model.

Modulation of Titin-Based Stiffness in Hypertrophic Cardiomyopathy via Protein Kinase D

The giant protein titin performs structure-preserving functions in the sarcomere and is important for the passive stiffness (F_passive) of cardiomyocytes. Protein kinase D (PKD) enzymes play crucial roles in regulating myocardial contraction, hypertrophy, and remodeling. PKD phosphorylates myofilament proteins, but it is not known whether the giant protein titin is also a PKD substrate. Here, we aimed to determine whether PKD phosphorylates titin and thereby modulates cardiomyocyte F_passive in normal and failing myocardium. The phosphorylation of titin was assessed in cardiomyocyte-specific PKD knock-out mice (cKO) and human hearts using immunoblotting with a phosphoserine/threonine and a phosphosite-specific titin antibody. PKD-dependent site-specific titin phosphorylation in vivo was quantified by mass spectrometry using stable isotope labeling by amino acids in cell culture (SILAC) of SILAC-labeled mouse heart protein lysates that were mixed with lysates isolated from hearts of either wild-type control (WT) or cKO mice. F_passive of single permeabilized cardiomyocytes was recorded before and after PKD and HSP27 administration. All-titin phosphorylation was reduced in cKO compared to WT hearts. Multiple conserved PKD-dependent phosphosites were identified within the Z-disk, A-band and M-band regions of titin by quantitative mass spectrometry, and many PKD-dependent phosphosites detected in the elastic titin I-band region were significantly decreased in cKO. Analysis of titin site-specific phosphorylation showed unaltered or upregulated phosphorylation in cKO compared to matched WT hearts. F_passive was elevated in cKO compared to WT cardiomyocytes and PKD administration lowered F_passive of WT and cKO cardiomyocytes. Cardiomyocytes from hypertrophic cardiomyopathy (HCM) patients showed higher F_passive compared to control hearts and significantly lower F_passive after PKD treatment. In addition, we found higher phosphorylation at CaMKII-dependent titin sites in HCM compared to control hearts. Expression and phosphorylation of HSP27, a substrate of PKD, were elevated in HCM hearts, which was associated with increased PKD expression and phosphorylation. The relocalization of HSP27 in HCM away from the sarcomeric Z-disk and I-band suggested that HSP27 failed to exert its protective action on titin extensibility. This protection could, however, be restored by administration of HSP27, which significantly reduced F_passive in HCM cardiomyocytes. These findings establish a previously unknown role for PKDin regulating diastolic passive properties of healthy and diseased hearts.

Effects of sitagliptin on exercise capacity and hemodynamics in patients with type 2 diabetes mellitus and coronary artery disease

Sitagliptin attenuates left ventricular (LV) dysfunction and may improve oxygen uptake in animals. The effects of sitagliptin on oxygen uptake (VO₂) and exercise hemodynamics have been unclear in patients with type 2 diabetes mellitus (T2DM) and coronary artery disease (CAD). Thirty patients with T2DM and CAD were randomized into a sitagliptin (50 mg/day) or voglibose (0.6 mg/day) group. Patients underwent maximal cardiopulmonary exercise testing. VO₂ and hemodynamics were evaluated at rest, anaerobic threshold and peak exercise. Resting LV diastolic function (E', peak early diastolic mitral annular velocity) and geometry were evaluated by echocardiography, and endothelial function by reactive hyperemia peripheral arterial tonometry. A total of 24 patients (69 ± 9 years) completed 6 months of intervention. Peak VO₂ in the sitagliptin and voglibose groups (25.3 ± 7.3 vs. 24.0 ± 7.4, 22.7 ± 4.8 vs. 22.1 ± 5.2 ml/kg/min) was slightly decreased after 6 months (time effect p = 0.051; group × time effect p = 0.49). No effects were observed on LV ejection fraction, E', or reactive hyperemia index in either group. Heart rate during exercise was unaffected in both groups. Systolic blood pressure was unchanged by sitagliptin at rest and during exercise, but slightly lowered by voglibose at anaerobic threshold and peak exercise. In patients with T2DM and CAD, sitagliptin had little effect on resting LV and arterial function, exercise capacity, or exercise hemodynamics. Further studies need to be conducted with more patients as the number of the patients in this study was limited.

Sitagliptin Protects Cardiac Function by Reducing Nitroxidative Stress and Promoting Autophagy in Zucker Diabetic Fatty (ZDF) Rats

PURPOSE

The purpose of the study is to identify potential mechanisms involved in the cardiac protective effects of sitagliptin in Zucker diabetic fatty (ZDF) rats.

METHODS AND RESULTS

Male non-diabetic lean Zucker rats (Lean) and ZDF rats treated with saline (ZDF) or sitagliptin (ZDF + sita) were used in this study. The blood pressure and lipid profiles were increased significantly in ZDF rats compared with Lean rats. ZDF + sitagliptin rats had decreased systolic blood pressure compared with ZDF rats. Sitagliptin treatment decreased total cholesterol (TC), triglycerides (TGs), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) levels. Ejection fraction (EF) and fractional shortening (FS) were decreased in ZDF rats, which improved with sitagliptin from 59.8% ± 3.0 and 34.5% ± 3.1 to 66.9% ± 3.4 and 40.9% ± 4.2, respectively. Moreover, the nitroxidative stress level was increased while autophagy levels were decreased in ZDF rats, which was reversed by the administration of sitagliptin. Treatment with sitagliptin or FeTMPyP improved the autophagy level in high-glucose cultured H9c2 cells by increasing autolysosome numbers from 15 ± 4 to 21 ± 3 and 22 ± 3, respectively. We detected a positive correlation between DPP-4 activity and 3-nitrotyrosine levels (r = 0.3903; P < 0.01), a negative correlation between Beclin-1 levels and DPP-4 activity (r = - 0.3335; P < 0.01), and a negative correlation between 3-nitrotyrosine and Beclin-1 levels (r = - 0.3794; P < 0.01) in coronary heart disease patients.

CONCLUSIONS

Sitagliptin alleviates diabetes-induced cardiac injury by reducing nitroxidative stress and promoting autophagy. This study indicates a novel target pathway for the treatment of cardiovascular complications in type 2 diabetes mellitus.

Posttranslational modifications of titin from cardiac muscle: how, where, and what for?

Titin is a giant elastic protein expressed in the contractile units of striated muscle cells, including the sarcomeres of cardiomyocytes. The last decade has seen enormous progress in our understanding of how titin molecular elasticity is modulated in a dynamic manner to help cardiac sarcomeres adjust to the varying hemodynamic demands on the heart. Crucial events mediating the rapid modulation of cardiac titin stiffness are post‐translational modifications (PTMs) of titin. In this review, we first recollect what is known from earlier and recent work on the molecular mechanisms of titin extensibility and force generation. The main goal then is to provide a comprehensive overview of current insight into the relationship between titin PTMs and cardiomyocyte stiffness, notably the effect of oxidation and phosphorylation of titin spring segments on titin stiffness. A synopsis is given of which type of oxidative titin modification can cause which effect on titin stiffness. A large part of the review then covers the mechanically relevant phosphorylation sites in titin, their location along the elastic segment, and the protein kinases and phosphatases known to target these sites. We also include a detailed coverage of the complex changes in phosphorylation at specific titin residues, which have been reported in both animal models of heart disease and in human heart failure, and their correlation with titin‐based stiffness alterations. Knowledge of the relationship between titin PTMs and titin elasticity can be exploited in the search for therapeutic approaches aimed at softening the pathologically stiffened myocardium in heart failure patients.

Empagliflozin directly improves diastolic function in human heart failure

AIMS

Empagliflozin, a clinically used oral antidiabetic drug that inhibits the sodium-dependent glucose co-transporter 2, has recently been evaluated for its cardiovascular safety. Surprisingly, empagliflozin reduced mortality and hospitalization for heart failure (HF) compared to placebo. However, the underlying mechanisms remain unclear. Therefore, our study aims to investigate whether empagliflozin may cause direct pleiotropic effects on the myocardium.

METHODS AND RESULTS

In order to assess possible direct myocardial effects of empagliflozin, we performed contractility experiments with in toto-isolated human systolic end-stage HF ventricular trabeculae. Empagliflozin significantly reduced diastolic tension, whereas systolic force was not changed. These results were confirmed in murine myocardium from diabetic and non-diabetic mice, suggesting independent effects from diabetic conditions. In human HF cardiomyocytes, empagliflozin did not influence calcium transient amplitude or diastolic calcium level. The mechanisms underlying the improved diastolic function were further elucidated by studying myocardial fibres from patients and rats with diastolic HF (HF with preserved ejection fraction, HFpEF). Empagliflozin beneficially reduced myofilament passive stiffness by enhancing phosphorylation levels of myofilament regulatory proteins. Intravenous injection of empagliflozin in anaesthetized HFpEF rats significantly improved diastolic function measured by echocardiography, while systolic contractility was unaffected.

CONCLUSION

Empagliflozin causes direct pleiotropic effects on the myocardium by improving diastolic stiffness and hence diastolic function. These effects were independent of diabetic conditions. Since pharmacological therapy of diastolic dysfunction and HF is an unmet need, our results provide a rationale for new translational studies and might also contribute to the understanding of the EMPA-REG OUTCOME trial.

Isolated perfused working hearts provide valuable additional information during phenotypic assessment of the diabetic mouse heart

Although murine models for studying the development of cardiac dysfunction in diabetes mellitus are well established, their reported cardiac phenotypes vary. These reported divergences may, in addition to the severity of different models, also be linked to the methods used for cardiac functional assessment. In the present study, we examined the functional changes using conventional transthoracic echocardiography (in vivo) and isolated heart perfusion techniques (ex vivo), in hearts from two mouse models; one with an overt type 2 diabetes (the db/db mouse) and one with a prediabetic state, where obesity was induced by a high-fat diet (HFD). Analysis of left ventricular function in the isolated working hearts from HFD-fed mice, suggested that these hearts develop diastolic dysfunction with preserved systolic function. Accordingly, in vivo examination demonstrated maintained systolic function, but we did not find parameters of diastolic function to be altered. In db/db mice, ex vivo working hearts showed both diastolic and systolic dysfunction. Although in vivo functional assessment revealed signs of diastolic dysfunction, the hearts did not display reduced systolic function. The contrasting results between ex vivo and in vivo function could be due to systemic changes that may sustain in vivo function, or a lack of sensitivity using conventional transthoracic echocardiography. Thus, this study demonstrates that the isolated perfused working heart preparation provides unique additional information related to the development of cardiomyopathy, which might otherwise go unnoticed when only using conventional echocardiographic assessment.

Pathophysiological Mapping of Experimental Heart Failure: Left and Right Ventricular Remodeling in Transverse Aortic Constriction Is Temporally, Kinetically and Structurally Distinct

A growing proportion of heart failure (HF) patients present with impairments in both ventricles. Experimental pressure-overload (i.e., transverse aortic constriction, TAC) induces left ventricle (LV) hypertrophy and failure, as well as right ventricle (RV) dysfunction. However, little is known about the coordinated progression of biventricular dysfunction that occurs in TAC. Here we investigated the time course of systolic and diastolic function in both the LV and RV concurrently to improve our understanding of the chronology of events in TAC. Hemodynamic, histological, and morphometric assessments were obtained from the LV and RV at 2, 4, 9, and 18 weeks post-surgery. Results: Systolic pressures peaked in both ventricles at 4 weeks, thereafter steadily declining in the LV, while remaining elevated in the RV. The LV and RV followed different structural and functional timelines, suggesting the patterns in one ventricle are independent from the opposing ventricle. RV hypertrophy/fibrosis and pulmonary arterial remodeling confirmed a progressive right-sided pathology. We further identified both compensation and decompensation in the LV with persistent concentric hypertrophy in both phases. Finally, diastolic impairments in both ventricles manifested as an intricate progression of multiple parameters that were not in agreement until overt systolic failure was evident. Conclusion: We establish pulmonary hypertension was secondary to LV dysfunction, confirming TAC is a model of type II pulmonary hypertension. This study also challenges some common assumptions in experimental HF (e.g., the relationship between fibrosis and filling pressure) while addressing a knowledge gap with respect to temporality of RV remodeling in pressure-overload.

Diabetes-Induced Cardiomyocyte Passive Stiffening Is Caused by Impaired Insulin-Dependent Titin Modification and Can Be Modulated by Neuregulin-1

RATIONALE

Increased titin-dependent cardiomyocyte tension is a hallmark of heart failure with preserved ejection fraction associated with type-2 diabetes mellitus. However, the insulin-related signaling pathways that modify titin-based cardiomyocyte tension, thereby contributing to modulation of diastolic function, are largely unknown.

OBJECTIVE

We aimed to determine how impaired insulin signaling affects titin expression and phosphorylation and thus increases passive cardiomyocyte tension, and whether metformin or neuregulin-1 (NRG-1) can correct disturbed titin modifications and increased titin-based stiffness.

METHODS AND RESULTS

We used cardiac biopsies from human diabetic (n=23) and nondiabetic patients (n=19), cultured rat cardiomyocytes, left ventricular tissue from apolipoprotein E-deficient mice with streptozotocin-induced diabetes mellitus (n=12-22), and ZSF1 (obese diabetic Zucker fatty/spontaneously hypertensive heart failure F1 hybrid) rats (n=5-6) and analyzed insulin-dependent signaling pathways that modulate titin phosphorylation. Titin-based passive tension was measured using permeabilized cardiomyocytes. In human diabetic hearts, we detected titin hypophosphorylation at S4099 and hyperphosphorylation at S11878, suggesting altered activity of protein kinases; cardiomyocyte passive tension was significantly increased. When applied to cultured cardiomyocytes, insulin and metformin increased titin phosphorylation at S4010, S4099, and S11878 via enhanced ERK1/2 (extracellular signal regulated kinase 1/2) and PKCα (protein kinase Cα) activity; NRG-1 application enhanced ERK1/2 activity but reduced PKCα activity. In apolipoprotein E-deficient mice, chronic treatment of streptozotocin-induced diabetes mellitus with NRG-1 corrected titin phosphorylation via increased PKG (protein kinase G) and ERK1/2 activity and reduced PKCα activity, which reversed the diabetes mellitus-associated changes in titin-based passive tension. Acute application of NRG-1 to obese ZSF1 rats with type-2 diabetes mellitus reduced end-diastolic pressure.

CONCLUSIONS

Mechanistically, we found that impaired cGMP-PKG signaling and elevated PKCα activity are key modulators of titin-based cardiomyocyte stiffening in diabetic hearts. We conclude that by restoring normal kinase activities of PKG, ERK1/2, and PKCα, and by reducing cardiomyocyte passive tension, chronic NRG-1 application is a promising approach to modulate titin properties in heart failure with preserved ejection fraction associated with type-2 diabetes mellitus.

Effect of Sitagliptin on Coronary Flow Reserve Assessed by Magnetic Resonance Imaging in Type 2 Diabetic Patients With Coronary Artery Disease

BACKGROUND

The present study was conducted to assess the cardiovascular effects of dipeptidyl peptidase-4 inhibitors (DPP4i) on coronary flow reserve (CFR), left ventricular (LV) function and endothelial function of the peripheral artery by comparison with those of α-glucosidase inhibitors (αGI) in patients with type 2 diabetes mellitus (T2DM) and coronary artery disease (CAD).Methods and Results:We randomly assigned 30 patients with T2DM and CAD to receive either sitagliptin or voglibose, and 28 patients (age 69±9 years, 75% male, hemoglobin A1c [HbA1c] 6.62±0.48%) completed the study (14 in each group). CFR and LV function, assessed by cardiac magnetic resonance imaging, and endothelial function, assessed by reactive hyperemia peripheral arterial tonometry (RH-PAT), were measured at baseline and 24 weeks after treatment. Clinical and laboratory parameters, including HbA1c level, plasma active glucagon-like peptide-1 concentrations, and biomarkers of inflammation, were unchanged in both groups after 24 weeks of treatment. CFR were unchanged in both the αGI group (3.01±0.98 at baseline and 3.06±0.8 after treatment, P=NS) and the DPP4i group (4.29±2.04 at baseline and 3.63±1.31 after treatment, P=NS), with no interaction effect. LV functional parameters and the reactive hyperemia index also remained unchanged after the 24-week treatment.

CONCLUSIONS

DPP4i did not improve CFR, LV function or endothelial function of the peripheral artery in patients with relatively well-controlled T2DM and CAD.

Murine Models of Heart Failure with Preserved Ejection Fraction: a "Fishing Expedition"

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of HF in the presence of a normal left ventricular (LV) ejection fraction (EF). Despite accounting for up to 50% of all clinical presentations of HF, the mechanisms implicated in HFpEF are poorly understood, thus precluding effective therapy. The pathophysiological heterogeneity in the HFpEF phenotype also contributes to this disease and likely to the absence of evidence-based therapies. Limited access to human samples and imperfect animal models that completely recapitulate the human HFpEF phenotype have impeded our understanding of the mechanistic underpinnings that exist in this disease. Aging and comorbidities such as atrial fibrillation, hypertension, diabetes and obesity, pulmonary hypertension and renal dysfunction are highly associated with HFpEF. Yet, the relationship and contribution between them remains ill-defined. This review discusses some of the distinctive clinical features of HFpEF in association with these comorbidities and highlights the advantages and disadvantage of commonly used murine models, used to study the HFpEF phenotype.

Sitagliptin reduces inflammation, fibrosis and preserves diastolic function in a rat model of heart failure with preserved ejection fraction

BACKGROUND AND PURPOSE

Heart failure with preserved ejection fraction (HFpEF) is a systemic syndrome driven by co-morbidities, and its pathophysiology is poorly understood. Several studies suggesting that dipeptidyl peptidase 4 (DPP4) might be involved in the pathophysiology of heart failure have prompted experimental and clinical investigations of DPP4 inhibitors in the cardiovascular system. Here we have investigated whether the DPP4 inhibitor sitagliptin affected the progression of HFpEF independently of its effects on glycaemia.

EXPERIMENTAL APPROACH

Seven-week-old Dahl salt-sensitive rats were fed a high-salt diet for 5 weeks to induce hypertension. Then the rats continued with the high-salt diet and were treated with either sitagliptin (10 mg·kg-1 ) or vehicle for the following 8 weeks. Blood pressure and cardiac function were measured in vivo. Histochemical and molecular biology analyses of myocardium were used to assay cytokines, fibrotic markers, DPP4 and glucagon-like peptide-1 (GLP-1)/GLP-1 receptor.

KEY RESULTS

Treatment with sitagliptin attenuated diastolic dysfunction, reduced mortality and reduced cardiac DPP4 activity, along with increased circulating GLP-1 and myocardial expression of GLP-1 receptors. Myocardial levels of pro-inflammatory cytokines (TNF-α, IL-6 and CCL2) were reduced. Sitagliptin treatment decreased the levels of endothelial NOS monomer, responsible for generation of ROS, while the amount of NO-producing dimeric form increased. Markers of oxidative and nitrosative stress were decreased. Moreover, increased collagen deposition and activation of pro-fibrotic signalling, inducing elevated myocardial stiffness, were attenuated by sitagliptin treatment.

CONCLUSIONS AND IMPLICATIONS

Sitagliptin positively modulated active relaxation and passive diastolic compliance by decreasing inflammation-related endothelial dysfunction and fibrosis, associated with HFpEF.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Heart failure with preserved ejection fraction: current management and future strategies : Expert opinion on the behalf of the Nucleus of the "Heart Failure Working Group" of the German Society of Cardiology (DKG)

About 50% of all patients suffering from heart failure (HF) exhibit a reduced ejection fraction (EF ≤ 40%), termed HFrEF. The others may be classified into HF with midrange EF (HFmrEF 40-50%) or preserved ejection fraction (HFpEF, EF ≥ 50%). Presentation and pathophysiology of HFpEF is heterogeneous and its management remains a challenge since evidence of therapeutic benefits on outcome is scarce. Up to now, there are no therapies improving survival in patients with HFpEF. Thus, the treatment targets symptom relief, quality of life and reduction of cardiac decompensations by controlling fluid retention and managing risk factors and comorbidities. As such, renin-angiotensin-aldosterone inhibitors, diuretics, calcium channel blockers (CBB) and beta-blockers, diet and exercise recommendations are still important in HFpEF, although these interventions are not proven to reduce mortality in large randomized controlled trials. Recently, numerous new treatment targets have been identified, which are further investigated in studies using, e.g. soluble guanylate cyclase stimulators, inorganic nitrates, the angiotensin receptor neprilysin inhibitor LCZ 696, and SGLT2 inhibitors. In addition, several devices such as the CardioMEMS, interatrial septal devices (IASD), cardiac contractility modulation (CCM), renal denervation, and baroreflex activation therapy (BAT) were investigated in different forms of HFpEF populations and some of them have the potency to offer new hopes for patients suffering from HFpEF. On the basic research field side, lot of new disease-modifying strategies are under development including anti-inflammatory drugs, mitochondrial-targeted antioxidants, new anti-fibrotic and microRNA-guided interventions are under investigation and showed already promising results. This review addresses available data of current best clinical practice and management approaches based on expert experiences and summarizes novel approaches towards HFpEF.

New Antihyperglycemic Drugs and Heart Failure: Synopsis of Basic and Clinical Data

The assessment of the cardiovascular safety profile of any newly developed antihyperglycemic drug is mandatory before registration, as a meta-analysis raised alarm describing a significant increase in myocardial infarction with the thiazolidinedione rosiglitazone. The first results from completed cardiovascular outcome trials are already available: TECOS, SAVOR-TIMI, and EXAMINE investigated dipeptidyl peptidase 4 (DPP-4) inhibitors, ELIXA, LEADER, and SUSTAIN-6 investigated glucagon-like peptide 1 (GLP-1) receptor agonists, and EMPA-REG OUTCOME and CANVAS investigated sodium-dependent glucose transporter 2 (SGLT-2) inhibitors. LEADER, SUSTAIN-6, EMPA-REG OUTCOME, and CANVAS showed potential beneficial results, while the SAVOR-TIMI trial had an increased rate of hospitalization for heart failure. Meanwhile, the same drugs are investigated in preclinical experiments mainly using various animal models, which aim to find interactions and elucidate the underlying downstream mechanisms between the antihyperglycemic drugs and the cardiovascular system. Yet the direct link for observed effects, especially for DPP-4 and SGLT-2 inhibitors, is still unknown. Further inquiry into these mechanisms is crucial for the interpretation of the clinical trials' outcome and, vice versa, the clinical trials provide hints for an involvement of the cardiovascular system. The synopsis of preclinical and clinical data is essential for a detailed understanding of benefits and risks of new antihyperglycemic drugs.

Tampering with springs: phosphorylation of titin affecting the mechanical function of cardiomyocytes

Reversible post-translational modifications of various cardiac proteins regulate the mechanical properties of the cardiomyocytes and thus modulate the contractile performance of the heart. The giant protein titin forms a continuous filament network in the sarcomeres of striated muscle cells, where it determines passive tension development and modulates active contraction. These mechanical properties of titin are altered through post-translational modifications, particularly phosphorylation. Titin contains hundreds of potential phosphorylation sites, the functional relevance of which is only beginning to emerge. Here, we provide a state-of-the-art summary of the phosphorylation sites in titin, with a particular focus on the elastic titin spring segment. We discuss how phosphorylation at specific amino acids can reduce or increase the stretch-induced spring force of titin, depending on where the spring region is phosphorylated. We also review which protein kinases phosphorylate titin and how this phosphorylation affects titin-based passive tension in cardiomyocytes. A comprehensive overview is provided of studies that have measured altered titin phosphorylation and titin-based passive tension in myocardial samples from human heart failure patients and animal models of heart disease. As our understanding of the broader implications of phosphorylation in titin progresses, this knowledge could be used to design targeted interventions aimed at reducing pathologically increased titin stiffness in patients with stiff hearts.

Complex Energy Metabolic Changes in Heart Failure With Preserved Ejection Fraction and Heart Failure With Reduced Ejection Fraction

Alterations in cardiac energy metabolism contribute to the severity of heart failure. However, the energy metabolic changes that occur in heart failure are complex, and are dependent not only on the severity and type of heart failure present, but also on the coexistence of common comorbidities such as obesity and type 2 diabetes. In this article we review the cardiac energy metabolic changes that occur in heart failure. An emphasis is made on distinguishing the differences in cardiac energy metabolism between heart failure with preserved ejection fraction (HFpEF) and heart failure with reduced ejection fraction (HFrEF) and in clarifying the common misconceptions surrounding the fate of fatty acids and glucose in the failing heart. The major key points from this article are: (1) mitochondrial oxidative capacity is reduced in HFpEF and HFrEF; (2) fatty acid oxidation is increased in HFpEF and reduced in HFrEF (however, oxidative metabolism of fatty acids in HFrEF still exceeds that of glucose); (3) glucose oxidation is decreased in HFpEF and HFrEF; (4) there is an uncoupling between glucose uptake and oxidation in HFpEF and HFrEF, resulting in an increased rate of glycolysis; (5) ketone body oxidation is increased in HFrEF, which might further reduce fatty acid and glucose oxidation; and finally, (6) branched chain amino acid oxidation is impaired in HFrEF. The understanding of these changes in cardiac energy metabolism in heart failure are essential to allow the development of metabolic modulators in the treatment of heart failure.