Cardiac contractile dysfunction in Lep/Lep obesity is accompanied by NADPH oxidase activation, oxidative modification of sarco(endo)plasmic reticulum Ca2+-ATPase and myosin heavy chain isozyme switch

SERCA2a dysfunction in the pathophysiology of heart failure with preserved ejection fraction: a direct role is yet to be established

With rising incidence, mortality and limited therapeutic options, heart failure with preserved ejection fraction (HFpEF) remains one of the most important topics in cardiovascular medicine today. Characterised by left ventricular diastolic dysfunction partially due to impaired Ca2+ homeostasis, one ion channel in particular, SarcoEndoplasmic Reticulum Ca2+-ATPase (SERCA2a), may play a significant role in its pathophysiology. A better understanding of the complex mechanisms interplaying to contribute to SERCA2a dysfunction will help develop treatments targeting it and thus address the growing clinical challenge HFpEF poses. This review examines the conflicting evidence present for changes in SERCA2a expression and activity in HFpEF, explores potential underlying mechanisms, and finally evaluates the drug and gene therapy trials targeting SERCA2a in heart failure. Recent positive results from trials involving widely used anti-diabetic agents such as sodium-glucose co-transporter protein 2 inhibitors (SGLT2i) and glucagon-like peptide-1 (GLP-1) agonists offer advancement in HFpEF management. The potential interplay between these agents and SERCA2a regulation presents a novel angle that could open new avenues for modulating diastolic function; however, the mechanistic research in this emerging field is limited. Overall, the direct role of SERCA2a dysfunction in HFpEF remains undetermined, highlighting the need for well-designed pre-clinical studies and robust clinical trials.

Inhibition of ER stress using tauroursodeoxycholic acid rescues obesity-evoked cardiac remodeling and contractile anomalies through regulation of ferroptosis

Interrupted ER homeostasis contributes to the etiology of obesity cardiomyopathy although it remains elusive how ER stress evokes cardiac anomalies in obesity. Our study evaluated the impact of ER stress inhibition on cardiac anomalies in obesity. Lean and ob/ob obese mice received chemical ER chaperone tauroursodeoxycholic acid (TUDCA, 50 mg/kg/d, p.o.) for 35 days prior to evaluation of glucose sensitivity, echocardiographic, myocardial geometric, cardiomyocyte mechanical and subcellular Ca2+ property, mitochondrial integrity, oxidative stress, apoptosis, and ferroptosis. Intracellular Ca2+ governing domains including sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) were monitored by45Ca2+uptake and immunoblotting. Our results noted that TUDCA alleviated myocardial remodeling (fibrosis, hypertrophy, enlarged LVESD), echocardiographic anomalies (compromised fractional shortening and ejection fraction), cardiomyocyte contractile dysfunction (amplitude and velocity of cell shortening, relengthening time) and intracellular Ca2+ anomalies (compromised subcellular Ca2+ release, clearance and SERCA function), mitochondrial damage (collapsed membrane potential, downregulated mitochondrial elements and ultrastructural alteration), ER stress (GRP78, eIF2α and ATF4), oxidative stress, apoptosis and ferroptosis [downregulated SLC7A11, GPx4 and upregulated transferrin receptor (TFRC)] without affecting global glucose sensitivity and serum Fe2+ in obese mice. Obesity-evoked change in HSP90, phospholamban and Na+-Ca2+ exchanger was spared by the chemical ER chaperone. Moreover, in vitro results noted that TUDCA, PERK inhibitor GSK2606414, TFRC neutralizing antibody and ferroptosis inhibitor LIP1 mitigated palmitic acid-elicited changes in lipid peroxidation and mechanical function. Our findings favored a role for ferroptosis in obesity cardiomyopathy downstream of ER stress.

Metallothionein Alleviates Glutathione Depletion-Induced Oxidative Cardiomyopathy through CISD1-Dependent Regulation of Ferroptosis in Murine Hearts

This study was designed to discern the effect of heavy scavenger metallothionein on glutathione (GSH) deprivation-evoked cardiac anomalies and mechanisms involved with an emphasis on ferroptosis. Wild-type and cardiac metallothionein transgenic mice received GSH synthase inhibitor buthionine sulfoximine (BSO; 30 mmol/L in drinking water) for 14 days before assessment of myocardial morphology and function. BSO evoked cardiac remodeling and contractile anomalies, including cardiac hypertrophy, interstitial fibrosis, enlarged left ventricular chambers, deranged ejection fraction, fraction shortening, cardiomyocyte contractile capacity, intracellular Ca2+ handling, sarcoplasmic reticulum Ca2+ reuptake, loss of mitochondrial integrity (mitochondrial swelling, loss of aconitase activity), mitochondrial energy deficit, carbonyl damage, lipid peroxidation, ferroptosis, and apoptosis. Metallothionein itself did not affect myocardial morphology and function, although it mitigated BSO-provoked myocardial anomalies, loss of mitochondrial integrity and energy, and ferroptosis. Immunoblotting revealed down-regulated sarco(endo)plasmic reticulum Ca2+-ATPase 2a, glutathione peroxidase 4, ferroptosis-suppressing CDGSH iron-sulfur domain 1 (CISD1), and mitochondrial regulating glycogen synthase kinase-3β phosphorylation with elevated p53, myosin heavy chain-β isozyme, IκB phosphorylation, and solute carrier family 7 member 11 (SLC7A11) as well as unchanged SLC39A1, SLC1A5, and ferroptosis-suppressing protein 1 following BSO challenge, all of which, except glutamine transporter SLC7A11 and p53, were abrogated by metallothionein. Inhibition of CISD1 using pioglitazone nullified GSH-offered benefit against BSO-induced cardiomyocyte ferroptosis and contractile and intracellular Ca2+ derangement. Taken together, these findings support a regulatory modality for CISD1 in the impedance of ferroptosis in metallothionein-offered protection against GSH depletion-evoked cardiac aberration.

Effect of exercise on improving myocardial mitochondrial function in decreasing diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is a significant cause of heart failure in patients with diabetes, and its pathogenesis is closely related to myocardial mitochondrial injury and functional disability. Studies have shown that the development of diabetic cardiomyopathy is related to disorders in mitochondrial metabolic substrates, changes in mitochondrial dynamics, an imbalance in mitochondrial Ca2+ regulation, defects in the regulation of microRNAs, and mitochondrial oxidative stress. Physical activity may play a role in resistance to the development of diabetic cardiomyopathy by improving myocardial mitochondrial biogenesis, the level of autophagy and dynamic changes in fusion and division; enhancing the ability to cope with oxidative stress; and optimising the metabolic substrates of the myocardium. This paper puts forward a new idea for further understanding the specific mitochondrial mechanism of the occurrence and development of diabetic cardiomyopathy and clarifying the role of exercise-mediated myocardial mitochondrial changes in the prevention and treatment of diabetic cardiomyopathy. This is expected to provide a new theoretical basis for exercise to reduce diabetic cardiomyopathy symptoms.

Common mechanisms underlying diabetic vascular complications: focus on the interaction of metabolic disorders, immuno-inflammation, and endothelial dysfunction

Diabetic vascular complications (DVCs), including macro- and micro- angiopathy, account for a high percentage of mortality in patients with diabetes mellitus (DM). Endothelial dysfunction is the initial and role step for the pathogenesis of DVCs. Hyperglycemia and lipid metabolism disorders contribute to endothelial dysfunction via direct injury of metabolism products, crosstalk between immunity and inflammation, as well as related interaction network. Although physiological and phenotypic differences support their specified changes in different targeted organs, there are still several common mechanisms underlying DVCs. Also, inhibitors of these common mechanisms may decrease the incidence of DVCs effectively. Thus, this review may provide new insights into the possible measures for the secondary prevention of DM. And we discussed the current limitations of those present preventive measures in DVCs research. Video Abstract.

Oxidative stress in early metabolic syndrome impairs cardiac RyR2 and SERCA2a activity and modifies the interplay of these proteins during Ca2+ waves

We investigated how oxidative stress (OS) alters Ca2+ handling in ventricular myocytes in early metabolic syndrome (MetS) in sucrose-fed rats. The effects of N-acetyl cysteine (NAC) or dl-Dithiothreitol (DTT) on systolic Ca2+ transients (SCaTs), diastolic Ca2+ sparks (CaS) and Ca2+ waves (CaW), recorded by confocal techniques, and L-type Ca2+ current (ICa), assessed by whole-cell patch clamp, were evaluated in MetS and Control cells. MetS myocytes exhibited decreased SCaTs and CaS frequency but unaffected CaW propagation. In Control cells, NAC/DTT reduced RyR2/SERCA2a activity blunting SCaTs, CaS frequency and CaW propagation, suggesting that basal ROS optimised Ca2+ signalling by maintaining RyR2/SERCA2a function and that these proteins facilitate CaW propagation. Conversely, NAC/DTT in MetS recovered RyR2/SERCA2a function, improving SCaTs and CaS frequency, but unexpectedly decreasing CaW propagation. We hypothesised that OS decreases RyR2/SERCA2a activity at early MetS, and while decreased SERCA2a favours CaW propagation, diminished RyR2 restrains it.

Interplay between obesity and aging on myocardial geometry and function: Role of leptin-STAT3-stress signaling

BACKGROUND

Uncorrected obesity facilitates premature aging and cardiovascular anomalies. This study examined the interaction between obesity and aging on cardiac remodeling and contractile function.

METHODS

Cardiac echocardiographic geometry, function, morphology, intracellular Ca²⁺ handling, oxidative stress (DHE fluorescence), STAT3 and stress signaling were evaluated in young (3-mo) and old (12- and 18-mo) lean and leptin deficient ob/ob obese mice. Cardiomyocytes from young and old lean and ob/ob mice were treated with leptin (1 nM) for 4 h in vitro prior to assessment of mechanical and biochemical properties. High fat diet (45% calorie from fat) and the leptin receptor mutant db/db obese mice at young and old age were evaluated for comparison.

RESULTS

Our results displayed reduced survival in ob/ob mice. Obesity but less likely older age dampened echocardiographic, geometric, cardiomyocyte function and intracellular Ca²⁺ properties, elevated O₂^- and p^47phox NADPH oxidase levels with a more pronounced geometric change at older age. Immunoblot analysis revealed elevated p^47phox NADPH oxidase and dampened phosphorylation of STAT3, with a more pronounced response in old ob/ob mice, the effects were restored by leptin. Obesity and aging inhibited phosphorylation of Akt, eNOS, AMPK, and p38 while promoting phosphorylation of JNK and IκB. Leptin reconciled cardiomyocyte dysfunction, O₂^- yield, p^47phox upregulation, STAT3 dephosphorylation and stress signaling in ob/ob mice although its action on stress signaling cascades were lost at old age. High fat diet-induced and db/db obesity displayed aging-associated cardiomyocyte anomalies reminiscent of ob/ob model albeit lost leptin response.

CONCLUSIONS

Our data suggest disparate age-associated obesity response in cardiac remodeling and contractile dysfunction due to phosphorylation of Akt, eNOS and stress signaling-related oxidative stress.

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.

Energy substrate metabolism and oxidative stress in metabolic cardiomyopathy

Metabolic cardiomyopathy is an emerging cause of heart failure in patients with obesity, insulin resistance, and diabetes. It is characterized by impaired myocardial metabolic flexibility, intramyocardial triglyceride accumulation, and lipotoxic damage in association with structural and functional alterations of the heart, unrelated to hypertension, coronary artery disease, and other cardiovascular diseases. Oxidative stress plays an important role in the development and progression of metabolic cardiomyopathy. Mitochondria are the most significant sources of reactive oxygen species (ROS) in cardiomyocytes. Disturbances in myocardial substrate metabolism induce mitochondrial adaptation and dysfunction, manifested as a mismatch between mitochondrial fatty acid oxidation and the electron transport chain (ETC) activity, which facilitates ROS production within the ETC components. In addition, non-ETC sources of mitochondrial ROS, such as β-oxidation of fatty acids, may also produce a considerable quantity of ROS in metabolic cardiomyopathy. Augmented ROS production in cardiomyocytes can induce a variety of effects, including the programming of myocardial energy substrate metabolism, modulation of metabolic inflammation, redox modification of ion channels and transporters, and cardiomyocyte apoptosis, ultimately leading to the structural and functional alterations of the heart. Based on the above mechanistic views, the present review summarizes the current understanding of the mechanisms underlying metabolic cardiomyopathy, focusing on the role of oxidative stress.

Heart failure with preserved ejection fraction (HFpEF) in type 2 diabetes mellitus: from pathophysiology to therapeutics

Type 2 diabetes mellitus (T2DM or T2D) is a devastating metabolic abnormality featured by insulin resistance, hyperglycemia, and hyperlipidemia. T2D provokes unique metabolic changes and compromises cardiovascular geometry and function. Meanwhile, T2D increases the overall risk for heart failure (HF) and acts independent of classical risk factors including coronary artery disease, hypertension, and valvular heart diseases. The incidence of HF is extremely high in patients with T2D and is manifested as HF with preserved, reduced, and midrange ejection fraction (HFpEF, HFrEF, and HFmrEF, respectively), all of which significantly worsen the prognosis for T2D. HFpEF is seen in approximately half of the HF cases and is defined as a heterogenous syndrome with discrete phenotypes, particularly in close association with metabolic syndrome. Nonetheless, management of HFpEF in T2D remains unclear, largely due to the poorly defined pathophysiology behind HFpEF. Here, in this review, we will summarize findings from multiple preclinical and clinical studies as well as recent clinical trials, mainly focusing on the pathophysiology, potential mechanisms, and therapies of HFpEF in T2D.

Surgically Metabolic Resection of Pericardial Fat to Ameliorate Myocardial Mitochondrial Dysfunction in Acute Myocardial Infarction Obese Rats

BACKGROUND

Pericardial fat (PF) is highly associated with cardiovascular disease but the effectiveness of surgical resection of PF is still unknown for myocardial mitochondrial structure and function in acute myocardial infarction (AMI) with obesity. The aim of this study was to demonstrate the difference in myocardial mitochondrial structure and function between obese AMI with additionally resected PF and those without resected PF.

METHODS

Obese rats with 12-week high fat diet (45 kcal% fat, n = 21) were randomly assigned into 3 groups: obese control, obese AMI and obese AMI with additionally resected PF. One week after developing AMI and additional resection of PF, echocardiogram, myocardial mitochondrial histomorphology, oxidative phosphorylation system (OXPHOS), anti-oxidative enzyme and sarcoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) in the non-infarcted area were assessed between these groups.

RESULTS

There was significant improvement of systolic function in AMI with PF resection compared with the AMI group in the echocardiogram. Even though the electron microscopic morphology for the mitochondria seems to be similar between the AMI with PF resection and AMI groups, there was an improved expression of PGC-1α and responsive OXPHOS including NDUFB3, NDUFB5 and SDHB are associated with the ATP levels in the AMI with PF resection compared with those in the AMI group. In addition, the expression levels of antioxidant enzymes (MnSOD) and SERCA2 were improved in the AMI with PF resection compared with those in the AMI group.

CONCLUSION

Surgical resection of PF might ameliorate myocardial mitochondria dysfunction in obese AMI.

Ca2+ mishandling and mitochondrial dysfunction: a converging road to prediabetic and diabetic cardiomyopathy

Diabetic cardiomyopathy is defined as the myocardial dysfunction that suffers patients with diabetes mellitus (DM) in the absence of hypertension and structural heart diseases such as valvular or coronary artery dysfunctions. Since the impact of DM on cardiac function is rather silent and slow, early stages of diabetic cardiomyopathy, known as prediabetes, are poorly recognized, and, on many occasions, cardiac illness is diagnosed only after a severe degree of dysfunction was reached. Therefore, exploration and recognition of the initial pathophysiological mechanisms that lead to cardiac dysfunction in diabetic cardiomyopathy are of vital importance for an on-time diagnosis and treatment of the malady. Among the complex and intricate mechanisms involved in diabetic cardiomyopathy, Ca2+ mishandling and mitochondrial dysfunction have been described as pivotal early processes. In the present review, we will focus on these two processes and the molecular pathway that relates these two alterations to the earlier stages and the development of diabetic cardiomyopathy.

Signaling Pathways Related to Oxidative Stress in Diabetic Cardiomyopathy

Diabetes is a chronic metabolic disease that is increasing in prevalence and causes many complications. Diabetic cardiomyopathy (DCM) is a complication of diabetes that is associated with high mortality, but it is not well defined. Nevertheless, it is generally accepted that DCM refers to a clinical disease that occurs in patients with diabetes and involves ventricular dysfunction, in the absence of other cardiovascular diseases, such as coronary atherosclerotic heart disease, hypertension, or valvular heart disease. However, it is currently uncertain whether the pathogenesis of DCM is directly attributable to metabolic dysfunction or secondary to diabetic microangiopathy. Oxidative stress (OS) is considered to be a key component of its pathogenesis. The production of reactive oxygen species (ROS) in cardiomyocytes is a vicious circle, resulting in further production of ROS, mitochondrial DNA damage, lipid peroxidation, and the post-translational modification of proteins, as well as inflammation, cardiac hypertrophy and fibrosis, ultimately leading to cell death and cardiac dysfunction. ROS have been shown to affect various signaling pathways involved in the development of DCM. For instance, OS causes metabolic disorders by affecting the regulation of PPARα, AMPK/mTOR, and SIRT3/FOXO3a. Furthermore, OS participates in inflammation mediated by the NF-κB pathway, NLRP3 inflammasome, and the TLR4 pathway. OS also promotes TGF-β-, Rho-ROCK-, and Notch-mediated cardiac remodeling, and is involved in the regulation of calcium homeostasis, which impairs ATP production and causes ROS overproduction. In this review, we summarize the signaling pathways that link OS to DCM, with the intention of identifying appropriate targets and new antioxidant therapies for DCM.

Consumption of a high-fat-high-sucrose diet partly diminishes mechanical and structural adaptations of cardiac muscle following resistance training

[Purpose]

The purpose of this study was to investigate the effects of a high-fat high-sucrose (HFHS) diet on previously reported adaptations of cardiac morphological and contractile properties to resistance training.

[Methods]

Twelve-week-old rats participated in 12-weeks of resistance exercise training and consumed an HFHS diet. Echocardiography and skinned cardiac muscle fiber bundle testing were performed to determine the structural and mechanical adaptations.

[Results]

Compared to chow-fed sedentary animals, both HFHS- and chow-fed resistance-trained animals had thicker left ventricular walls. Isolated trabecular fiber bundles from chow-fed resistance-trained animals had greater force output, shortening velocities, and calcium sensitivities than those of chow-fed sedentary controls. However, trabeculae from the HFHS resistance-trained animals had greater force output but no change in unloaded shortening velocity or calcium sensitivity than those of the chow-fed sedentary group animals.

[Conclusion]

Resistance exercise training led to positive structural and mechanical adaptations of the heart, which were partly offset by the HFHS diet.

Therapeutic potential of targeting oxidative stress in diabetic cardiomyopathy

Even in the absence of coronary artery disease and hypertension, diabetes mellitus (DM) may increase the risk for heart failure development. This risk evolves from functional and structural alterations induced by diabetes in the heart, a cardiac entity termed diabetic cardiomyopathy (DbCM). Oxidative stress, defined as the imbalance of reactive oxygen species (ROS) has been increasingly proposed to contribute to the development of DbCM. There are several sources of ROS production including the mitochondria, NAD(P)H oxidase, xanthine oxidase, and uncoupled nitric oxide synthase. Overproduction of ROS in DbCM is thought to be counterbalanced by elevated antioxidant defense enzymes such as catalase and superoxide dismutase. Excess ROS in the cardiomyocyte results in further ROS production, mitochondrial DNA damage, lipid peroxidation, post-translational modifications of proteins and ultimately cell death and cardiac dysfunction. Furthermore, ROS modulates transcription factors responsible for expression of antioxidant enzymes. Lastly, evidence exists that several pharmacological agents may convey cardiovascular benefit by antioxidant mechanisms. As such, increasing our understanding of the pathways that lead to increased ROS production and impaired antioxidant defense may enable the development of therapeutic strategies against the progression of DbCM. Herein, we review the current knowledge about causes and consequences of ROS in DbCM, as well as the therapeutic potential and strategies of targeting oxidative stress in the diabetic heart.

Obesity cardiomyopathy: evidence, mechanisms, and therapeutic implications

The prevalence of heart failure is on the rise and imposes a major health threat, in part, due to the rapidly increased prevalence of overweight and obesity. To this point, epidemiological, clinical, and experimental evidence supports the existence of a unique disease entity termed “obesity cardiomyopathy,” which develops independent of hypertension, coronary heart disease, and other heart diseases. Our contemporary review evaluates the evidence for this pathological condition, examines putative responsible mechanisms, and discusses therapeutic options for this disorder. Clinical findings have consolidated the presence of left ventricular dysfunction in obesity. Experimental investigations have uncovered pathophysiological changes in myocardial structure and function in genetically predisposed and diet-induced obesity. Indeed, contemporary evidence consolidates a wide array of cellular and molecular mechanisms underlying the etiology of obesity cardiomyopathy including adipose tissue dysfunction, systemic inflammation, metabolic disturbances (insulin resistance, abnormal glucose transport, spillover of free fatty acids, lipotoxicity, and amino acid derangement), altered intracellular especially mitochondrial Ca²⁺ homeostasis, oxidative stress, autophagy/mitophagy defect, myocardial fibrosis, dampened coronary flow reserve, coronary microvascular disease (microangiopathy), and endothelial impairment. Given the important role of obesity in the increased risk of heart failure, especially that with preserved systolic function and the recent rises in COVID-19-associated cardiovascular mortality, this review should provide compelling evidence for the presence of obesity cardiomyopathy, independent of various comorbid conditions, underlying mechanisms, and offer new insights into potential therapeutic approaches (pharmacological and lifestyle modification) for the clinical management of obesity cardiomyopathy.

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.

Diabetes-induced changes in cardiac voltage-gated ion channels

Diabetes mellitus affects the heart through various mechanisms such as microvascular defects, metabolic abnormalities, autonomic dysfunction and incompatible immune response. Furthermore, it can also cause functional and structural changes in the myocardium by a disease known as diabetic cardiomyopathy (DCM) in the absence of coronary artery disease. As DCM progresses it causes electrical remodeling of the heart, left ventricular dysfunction and heart failure. Electrophysiological changes in the diabetic heart contribute significantly to the incidence of arrhythmias and sudden cardiac death in diabetes mellitus patients. In recent studies, significant changes in repolarizing K⁺ currents, Na⁺ currents and L-type Ca²⁺ currents along with impaired Ca²⁺ homeostasis and defective contractile function have been identified in the diabetic heart. In addition, insulin levels and other trophic factors change significantly to maintain the ionic channel expression in diabetic patients. There are many diagnostic tools and management options for DCM, but it is difficult to detect its development and to effectively prevent its progress. In this review, diabetes-associated alterations in voltage-sensitive cardiac ion channels are comprehensively assessed to understand their potential role in the pathophysiology and pathogenesis of DCM.

Role of AMP-activated protein kinase on cardio-metabolic abnormalities in the development of diabetic cardiomyopathy: A molecular landscape

Cardiovascular complications associated with diabetes mellitus remains a leading cause of morbidity and mortality across the world. Diabetic cardiomyopathy is a descriptive pathology that in absence of co-morbidities such as hypertension, dyslipidemia initially characterized by cardiac stiffness, myocardial fibrosis, ventricular hypertrophy, and remodeling. These abnormalities further contribute to diastolic dysfunctions followed by systolic dysfunctions and eventually results in clinical heart failure (HF). The clinical outcomes associated with HF are considerably worse in patients with diabetes. The complexity of the pathogenesis and clinical features of diabetic cardiomyopathy raises serious questions in developing a therapeutic strategy to manage cardio-metabolic abnormalities. Despite extensive research in the past decade the compelling approaches to manage and treat diabetic cardiomyopathy are limited. AMP-Activated Protein Kinase (AMPK), a serine-threonine kinase, often referred to as cellular "metabolic master switch". During the development and progression of diabetic cardiomyopathy, a plethora of evidence demonstrate the beneficial role of AMPK on cardio-metabolic abnormalities including altered substrate utilization, impaired cardiac insulin metabolic signaling, mitochondrial dysfunction and oxidative stress, myocardial inflammation, increased accumulation of advanced glycation end-products, impaired cardiac calcium handling, maladaptive activation of the renin-angiotensin-aldosterone system, endoplasmic reticulum stress, myocardial fibrosis, ventricular hypertrophy, cardiac apoptosis, and impaired autophagy. Therefore, in this review, we have summarized the findings from pre-clinical and clinical studies and provided a collective overview of the pathophysiological mechanism and the regulatory role of AMPK on cardio-metabolic abnormalities during the development of diabetic cardiomyopathy.

Phospholamban and sarcolipin prevent thermal inactivation of sarco(endo)plasmic reticulum Ca2+-ATPases

Na+-K+-ATPase from mice lacking the γ subunit exhibits decreased thermal stability. Phospholamban (PLN) and sarcolipin (SLN) are small homologous proteins that regulate sarco(endo)plasmic reticulum Ca2+-ATPases (SERCAs) with properties similar to the γ subunit, through physical interactions with SERCAs. Here, we tested the hypothesis that PLN and SLN may protect against thermal inactivation of SERCAs. HEK-293 cells were co-transfected with different combinations of cDNAs encoding SERCA2a, PLN, a PLN mutant (N34A) that cannot bind to SERCA2a, and SLN. One-half of the cells were heat stressed at 40°C for 1 h (HS), and one-half were maintained at 37°C (CTL) before harvesting the cells and isolating microsomes. Compared with CTL, maximal SERCA activity was reduced by 25-35% following HS in cells that expressed either SERCA2a alone or SERCA2a and mutant PLN (N34A) whereas no change in maximal SERCA2a activity was observed in cells that co-expressed SERCA2a and either PLN or SLN following HS. Increases in SERCA2a carbonyl group content and nitrotyrosine levels that were detected following HS in cells that expressed SERCA2a alone were prevented in cells co-expressing SERCA2a with PLN or SLN, whereas co-expression of SERCA2a with mutant PLN (N34A) only prevented carbonyl group formation. In other experiments using knock-out mice, we found that thermal inactivation of SERCA was increased in cardiac left ventricle samples from Pln-null mice and in diaphragm samples from Sln-null mice, compared with WT littermates. Our results show that both PLN and SLN form a protective interaction with SERCA pumps during HS, preventing nitrosylation and oxidation of SERCA and thus preserving its maximal activity.

Mechanical function of cardiac fibre bundles is partly protected by exercise in response to diet-induced obesity in rats

Decrements in contractile function resulting from obesity are thought to be major reasons for the link between obesity and cardiovascular disease, while exercise has been shown to improve cardiac muscle contractile function. The purpose of this study was to evaluate cardiac contractile properties following obesity induction and the potential protective effect of exercise. Twelve-week-old rats (n = 30) were organized into either a chow diet or a high-fat, high-sucrose (HFHS) diet group. Following 12 weeks of obesity induction the HFHS group animals were stratified and grouped into sedentary (HFHS+Sed) and exercise (HFHS+Ex) groups for an additional 12 weeks. Following 24 weeks of diet intervention, with 12 weeks of aerobic exercise (25 m/min, 30 min/day, 5 days/week) for the HFHS+Ex group, skinned cardiac fibre bundle testing was used to evaluate cardiac contractile properties. Body fat and mass were significantly greater in the HFHS-fed animals compared with the chow controls (p < 0.043). Hearts from rats in the HFHS+Sed group had significantly greater mass (p < 0.03), significantly slower maximum shortening velocity (p = 0.001), and tended to have lower calcium sensitivity (p = 0.077) and a lower proportion of α-myosin heavy chain composition (p = 0.074) than the sedentary chow animals. However, 12 weeks of moderate aerobic exercise partially prevented these decrements in contractile properties. Novelty Cardiac muscle from animals exposed to an obesogenic diet for 24 weeks had impaired contractile properties compared with controls. Obesity-induced impairment of contractile properties of the heart were partially prevented by a 12-week aerobic exercise regime.

Basic Mechanisms of Diabetic Heart Disease

Diabetes mellitus predisposes affected individuals to a significant spectrum of cardiovascular complications, one of the most debilitating in terms of prognosis is heart failure. Indeed, the increasing global prevalence of diabetes mellitus and an aging population has given rise to an epidemic of diabetes mellitus-induced heart failure. Despite the significant research attention this phenomenon, termed diabetic cardiomyopathy, has received over several decades, understanding of the full spectrum of potential contributing mechanisms, and their relative contribution to this heart failure phenotype in the specific context of diabetes mellitus, has not yet been fully resolved. Key recent preclinical discoveries that comprise the current state-of-the-art understanding of the basic mechanisms of the complex phenotype, that is, the diabetic heart, form the basis of this review. Abnormalities in each of cardiac metabolism, physiological and pathophysiological signaling, and the mitochondrial compartment, in addition to oxidative stress, inflammation, myocardial cell death pathways, and neurohumoral mechanisms, are addressed. Further, the interactions between each of these contributing mechanisms and how they align to the functional, morphological, and structural impairments that characterize the diabetic heart are considered in light of the clinical context: from the disease burden, its current management in the clinic, and where the knowledge gaps remain. The need for continued interrogation of these mechanisms (both known and those yet to be identified) is essential to not only decipher the how and why of diabetes mellitus-induced heart failure but also to facilitate improved inroads into the clinical management of this pervasive clinical challenge.

Reduction of oxidative stress improves insulin signaling in cardiac tissue of obese mice

Objective

To evaluate the effects of oxidative stress on insulin signaling in cardiac tissue of obese mice.

Methods

Thirty Swiss mice were equally divided (n=10) into three groups: Control Group, Obese Group, and Obese Group Treated with N-acetylcysteine. After obesity and insulin resistance were established, the obese mice were treated with N-acetylcysteine at a dose of 50mg/kg daily for 15 days via oral gavage.

Results

Higher blood glucose levels and nitrite and carbonyl contents, and lower protein levels of glutathione peroxidase and phosphorylated protein kinase B were observed in the obese group when compared with their respective control. On the other hand, treatment with N-acetylcysteine was effective in reducing blood glucose levels and nitrite and carbonyl contents, and significantly increased protein levels of glutathione peroxidase and phosphorylated protein kinase B compared to the Obese Group.

Conclusion

Obesity and/or a high-lipid diet may result in oxidative stress and insulin resistance in the heart tissue of obese mice, and the use of N-acetylcysteine as a methodological and therapeutic strategy suggested there is a relation between them.

Mechanical adaptations of skinned cardiac muscle in response to dietary-induced obesity during adolescence in rats

Childhood obesity is a major risk factor for heart disease during adulthood, independent of adulthood behaviours. Therefore, it seems that childhood obesity leads to partly irreversible decrements in cardiac function. Little is known about how obesity during maturation affects the mechanical properties of the heart. The purpose of this study was to evaluate contractile properties in developing hearts from animals with dietary-induced obesity (high-fat high-sucrose diet). We hypothesized that obesity induced during adolescence results in decrements in cardiac contractile function. Three-week-old rats (n = 16) were randomized into control (chow) or dietary-induced obesity (high-fat high-sucrose diet) groups. Following 14 weeks on the diet, skinned cardiac trabeculae fibre bundle testing was performed to evaluate active and passive force, maximum shortening velocity, and calcium sensitivity. Rats in the high-fat high-sucrose diet group had significantly larger body mass and total body fat percentage. There were no differences in maximal active or passive properties of hearts between groups. Hearts from the high-fat high-sucrose diet rats had significantly slower maximum shortening velocities and lower calcium sensitivity than controls. Decreased shortening velocity and calcium sensitivity in hearts of obese animals may constitute increased risk of cardiac disease in adulthood. Novelty Cardiac muscle from animals exposed to an obesogenic diet during development had lower shortening velocity and calcium sensitivity than those from animals fed a chow diet. These alterations in mechanical function may be a mechanism for the increased risk of cardiac disease observed in adulthood.

Insulin-like growth factor-1 short-period therapy improves cardiomyopathy stimulating cardiac progenitor cells survival in obese mice

BACKGROUND AND AIMS

Cardiovascular diseases are the main cause of mortality in obesity. Despite advanced understanding, the mechanisms that regulate cardiac progenitor cells (CPC) survival in pathological conditions are not clear. Low IGF-1 plasma levels are correlated to obesity, cardiomyopathy and CPC death, so this work aimed to investigate IGF-1 therapeutic potential on cardiomyopathy and its relationship with the survival, proliferation and differentiation of CPC in Western diet-induced obesity.

METHODS AND RESULTS

Male Swiss mice were divided into control group (CG, n = 8), fed with standard diet; and obese group (OG, n = 16), fed with Western diet, for 12 weeks. At 11th week, OG was subdivided to receive a daily subcutaneous injection of human recombinant IGF-1 (100 μg.Kg^-1) for seven consecutive days (OG + IGF1, n = 8). Results showed that IGF-1 therapy improved the metabolic parameters negatively impacted by western diet in OG, reaching levels similar to CG. OG + IGF-1 also demonstrated restored heart energetic metabolism, fibrosis resolution, decreased apoptosis level, restored cardiac gap junctions and intracellular calcium balance. Cardiomyopathy improvement was accompanied by increased CPC survival, proliferation and newly cardiomyocytes formation related to increased pAkt/Akt ratio.

CONCLUSION

These results suggest that only one week of IGF-1 therapy has cardioprotective effects through Akt pathway upregulation, ensuring CPC survival and differentiation, contributing to heart failure rescue.

Heart Failure in Type 2 Diabetes Mellitus

Patients with diabetes mellitus have >2× the risk for developing heart failure (HF; HF with reduced ejection fraction and HF with preserved ejection fraction). Cardiovascular outcomes, hospitalization, and prognosis are worse for patients with diabetes mellitus relative to those without. Beyond the structural and functional changes that characterize diabetic cardiomyopathy, a complex underlying, and interrelated pathophysiology exists. Despite the success of many commonly used antihyperglycemic therapies to lower hyperglycemia in type 2 diabetes mellitus the high prevalence of HF persists. This, therefore, raises the possibility that additional factors beyond glycemia might contribute to the increased HF risk in diabetes mellitus. This review summarizes the state of knowledge about the impact of existing antihyperglycemic therapies on HF and discusses potential mechanisms for beneficial or deleterious effects. Second, we review currently approved pharmacological therapies for HF and review evidence that addresses their efficacy in the context of diabetes mellitus. Dysregulation of many cellular mechanisms in multiple models of diabetic cardiomyopathy and in human hearts have been described. These include oxidative stress, inflammation, endoplasmic reticulum stress, aberrant insulin signaling, accumulation of advanced glycated end-products, altered autophagy, changes in myocardial substrate metabolism and mitochondrial bioenergetics, lipotoxicity, and altered signal transduction such as GRK (g-protein receptor kinase) signaling, renin angiotensin aldosterone signaling and β-2 adrenergic receptor signaling. These pathophysiological pathways might be amenable to pharmacological therapy to reduce the risk of HF in the context of type 2 diabetes mellitus. Successful targeting of these pathways could alter the prognosis and risk of HF beyond what is currently achieved using existing antihyperglycemic and HF therapeutics.

Molecular Dysfunction and Phenotypic Derangement in Diabetic Cardiomyopathy

The high incidence and poor prognosis of heart failure (HF) patients affected with diabetes (DM) is in part related to a specific cardiac remodeling currently recognized as diabetic cardiomyopathy (DCM). This cardiac frame occurs regardless of the presence of coronary artery diseases (CAD) and it can account for 15–20% of the total diabetic population. The pathogenesis of DCM remains controversial, and several molecular and cellular alterations including myocardial hypertrophy, interstitial fibrosis, oxidative stress and vascular inflammation, have been postulated. The main cardio-vascular alterations associated with hyperglycemia comprise endothelial dysfunction, adverse effects of circulating free fatty acids (FFA) and increased systemic inflammation. High glucose concentrations lead to a loss of mitochondrial networks, increased reactive oxygen species (ROS), endothelial nitric oxide synthase (eNOS) activation and a reduction in cGMP production related to protein kinase G (PKG) activity. Current mechanisms enhance the collagen deposition with subsequent increased myocardial stiffness. Several concerns regarding the exact role of DCM in HF development such as having an appearance as either dilated or as a concentric phenotype and whether diabetes could be considered a causal factor or a comorbidity in HF, remain to be clarified. In this review, we sought to explain the different DCM subtypes and the underlying pathophysiological mechanisms. Therefore, the traditional and new molecular and signal alterations and their relationship with macroscopic structural abnormalities are described.

Adipokinome Signatures in Obese Mouse Models Reflect Adipose Tissue Health and Are Associated with Serum Lipid Composition

Adipocyte and hepatic lipid metabolism govern whole-body metabolic homeostasis, whereas a disbalance of de novo lipogenesis (DNL) in fat and liver might lead to obesity, with severe co-morbidities. Nevertheless, some obese people are metabolically healthy, but the “protective” mechanisms are not yet known in detail. Especially, the adipocyte-derived molecular mediators that indicate adipose functionality are poorly understood. We studied transgenic mice (alb-SREBP-1c) with a “healthy” obese phenotype, and obob mice with hyperphagia-induced “sick” obesity to analyze the impact of the tissue-specific DNL on the secreted proteins, i.e., the adipokinome, of the primary adipose cells by label-free proteomics. Compared to the control mice, adipose DNL is reduced in both obese mouse models. In contrast, the hepatic DNL is reduced in obob but elevated in alb-SREBP-1c mice. To investigate the relationship between lipid metabolism and adipokinomes, we formulated the “liver-to-adipose-tissue DNL” ratio. Knowledge-based analyses of these results revealed adipocyte functionality with proteins, which was involved in tissue remodeling or metabolism in the alb-SREBP-1c mice and in the control mice, but mainly in fibrosis in the obob mice. The adipokinome in “healthy” obesity is similar to that in a normal condition, but it differs from that in “sick” obesity, whereas the serum lipid patterns reflect the “liver-to-adipose-tissue DNL” ratio and are associated with the adipokinome signature.

Polyphenol-enriched azuki bean (Vina angularis) extract reduces the oxidative stress and prevents DNA oxidation in the hearts of streptozotocin-induced early diabetic rats

We examined the changes in the heart of rats at the early stages of streptozotocin (STZ)-induced diabetes, and whether azuki bean extract (ABE) could influence these changes. The experimental diabetic rats received 0 or 40 mg/kg of ABE orally for 4 weeks, whereas the control group rats received distilled water. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) and expression of proteins associated with peroxisomal FA β-oxidation as well as oxidative stress markers were examined. The levels of peroxisomal ACOX1 and catalase of the diabetic groups were significantly higher than those in the control group. The levels of p62, phosphorylated-p62 (p-p62) and HO-1 in the STZ group were significantly higher than those in the control group, and the levels of p-p62, HO-1, and 8-OHdG were significantly lower by ABE administration. The STZ-induced early diabetes increases the levels of proteins related to peroxisomal FA β-oxidation and oxidative stress markers in hearts. ABE protects diabetic hearts from oxidative damage.

SGLT2 inhibition with empagliflozin improves coronary microvascular function and cardiac contractility in prediabetic ob/ob-/- mice

BACKGROUND

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) is the first class of anti-diabetes treatment that reduces mortality and risk for hospitalization due to heart failure. In clinical studies it has been shown that SGLT2i's promote a general shift to fasting state metabolism characterized by reduced body weight and blood glucose, increase in glucagon/insulin ratio and modest increase in blood ketone levels. Therefore, we investigated the connection between metabolic changes and cardiovascular function in the ob/ob-/- mice; a rodent model of early diabetes with specific focus on coronary microvascular function. Due to leptin deficiency these mice develop metabolic syndrome/diabetes and hepatic steatosis. They also develop cardiac contractile and microvascular dysfunction and are thus a promising model for translational studies of cardiometabolic diseases. We investigated whether this mouse model responded in a human-like manner to empagliflozin treatment in terms of metabolic parameters and tested the hypothesis that it could exert direct effects on coronary microvascular function and contractile performance.

METHODS

Lean, ob/ob-/- untreated and ob/ob-/- treated with SGLT2i were followed for 10 weeks. Coronary flow velocity reserve (CFVR) and fractional area change (FAC) were monitored with non-invasive Doppler ultrasound imaging. Food intake, urinary glucose excursion and glucose control via HbA1c measurements were followed throughout the study. Liver steatosis was assessed by histology and metabolic parameters determined at the end of the study.

RESULTS

Sodium-glucose cotransporter 2 inhibitors treatment of ob/ob-/- animals resulted in a switch to a more catabolic state as observed in clinical studies: blood cholesterol and HbA1c were decreased whereas glucagon/insulin ratio and ketone levels were increased. SGLT2i treatment reduced liver triglyceride, steatosis and alanine aminotransferase, an indicator for liver dysfunction. L-Arginine/ADMA ratio, a marker for endothelial function was increased. SGLT2i treatment improved both cardiac contractile function and coronary microvascular function as indicated by improvement of FAC and CFVR, respectively.

CONCLUSIONS

Sodium-glucose cotransporter 2 inhibitors treatment of ob/ob-/- mice mimics major clinical findings regarding metabolism and cardiovascular improvements and is thus a useful translational model. We demonstrate that SGLT2 inhibition improves coronary microvascular function and contractile performance, two measures with strong predictive values in humans for CV outcome, alongside with the known metabolic changes in a preclinical model for prediabetes and heart failure.

Of mice and men: models and mechanisms of diabetic cardiomyopathy

Diabetes mellitus increases the risk of heart failure independent of co-existing hypertension and coronary artery disease. Although several molecular mechanisms for the development of diabetic cardiomyopathy have been identified, they are incompletely understood. The pathomechanisms are multifactorial and as a consequence, no causative treatment exists at this time to modulate or reverse the molecular changes contributing to accelerated cardiac dysfunction in diabetic patients. Numerous animal models have been generated, which serve as powerful tools to study the impact of type 1 and type 2 diabetes on the heart. Despite specific limitations of the models generated, they mimic various perturbations observed in the diabetic myocardium and continue to provide important mechanistic insight into the pathogenesis underlying diabetic cardiomyopathy. This article reviews recent studies in both diabetic patients and in these animal models, and discusses novel hypotheses to delineate the increased incidence of heart failure in diabetic patients.

Clinical Impact of Hemorheology on Subclinical Myocardial Injury in Patients with Hypertension

Background

The blood concentration of high-sensitivity cardiac troponin T (hs-cTnT) is a useful biomarker for myocardial injury or the pathogenesis of hypertension. Little is known about the relationship between hemorheology and myocardial injury in patients with hypertension. This cross-sectional study aimed to clarify the clinical impact of hemorheology on subclinical myocardial injury assessed with a microchannel array flow analyzer (MC-FAN) and its impact on hs-cTnT in patients with hypertension.

Methods

A total of 447 outpatients (men: 181; women: 266; mean age: 65 ± 13 years), with no history of cardiovascular disease, including admission for heart failure, who were undergoing treatment for hypertension, were enrolled. Whole blood passage time (WBPT) as a marker of hemorheology was measured with a MC-FAN, and the relationship between hs-cTnT levels and various clinical parameters, including WBPT, was examined.

Results

hs-cTnT levels were detected in 400 patients (89.5%). WBPT was significantly higher in patients with detectable hs-cTnT levels than in those with undetectable hs-cTnT levels (60.5 ± 16.8 s versus 50.2 ± 14.2 s, P < 0.001). In patients with detectable hs-cTnT levels, there was a significant positive correlation between WBPT and hs-cTnT level (r = 0.33; P < 0.001). Multiple regression analysis revealed that WBPT was an independent variable when hs-cTnT was a subordinate factor (β = 0.15; P < 0.01). Receiver-operating characteristic curve analysis indicated that a cutoff value for WBPT of 55.6 s yielded the largest area under the curve (0.744; P < 0.001) for discriminating high hs-cTnT levels as ≥ 0.014 ng/mL.

Conclusion

The results indicate that WBPT is independently associated with hs-cTnT in hypertensive patients with no history of cardiovascular events, suggesting that impairment of hemorheology in small cardiac vessels causes subclinical myocardial injury. In addition, the study suggests that progression of myocardial injury can be prevented by maintaining WBPT at approximately ≤ 55 s.

The Falconoid Luteolin Mitigates the Myocardial Inflammatory Response Induced by High-Carbohydrate/High-Fat Diet in Wistar Rats

Luteolin is a major component of many medicinal plants and traditional medicines. The current study aims at testing its protective effect against high-carbohydrate/high-fat (HCHF) diet-induced cardiac dysfunction in rats. Male Wistar rats were divided into six groups as follows: control group that received standard rat chow, group received HCHF diet (~ 30% carbohydrate and 42% fat) daily for 16 weeks, and four groups received HCHF diet concurrently with luteolin (10, 25, 50 or 100 mg/kg; 10% w/v suspension in 0.9% NaCl) daily from the first week by oral gavage. Body weight was measured weekly. At the end of the study, histopathological examinations of stained heart sections were carried out. Lipid profile, oxidative stress, and cardiac function biomarkers were measured. Furthermore, neurohumoral mediators and inflammatory cytokines (TNF-α, IL-18) were assigned. Results showed a significant improvement in cardiac function, tissue integrity, and a decrease in the compensatory neurohumoral mediators by luteolin 50 and 100 mg/kg. In addition, a significant (P < 0.05) decrease in collagen deposition, fibrosis percentage, lipid peroxidation, and inflammatory cells (macrophages and lymphocytes) infiltration was observed. Tested doses of luteolin decreased lipid peroxidation and elevated the endogenous antioxidant biomarkers (reduced glutathione and superoxide dismutase) significantly (P < 0.05). Finally, luteolin decreased TNF-α and IL-18 (P < 0.001) in a dose-dependent manner. It can be concluded that luteolin has a cardioprotective effect against HCHF diet-induced myocardial inflammation through antioxidant anti-inflammatory mechanisms.

Molecular mechanism of lipid-induced cardiac insulin resistance and contractile dysfunction

Long-chain fatty acids are the main cardiac substrates from which ATP is generated continually to serve the high energy demand and sustain the normal function of the heart. Under healthy conditions, fatty acid β-oxidation produces 50-70% of the energy demands with the remainder largely accounted for by glucose. Chronically increased dietary lipid supply often leads to excess lipid accumulation in the heart, which is linked to a variety of maladaptive phenomena, such as insulin resistance, cardiac hypertrophy and contractile dysfunction. CD36, the predominant cardiac fatty acid transporter, has a key role in setting the heart on a road to contractile dysfunction upon the onset of chronic lipid oversupply by translocating to the cell surface and opening the cellular 'doors' for fatty acids. The sequence of events after the CD36-mediated myocellular lipid accumulation is less understood, but in general it has been accepted that the excessively imported lipids cause insulin resistance, which in turn leads to contractile dysfunction. There are several gaps of knowledge in this proposed order of events which this review aims to discuss. First, the molecular mechanisms underlying lipid-induced insulin resistance are not yet completely disclosed. Specifically, several mediators have been proposed, such as diacylglycerols, ceramides, peroxisome proliferator-activated receptors (PPAR), inflammatory kinases and reactive oxygen species (ROS), but their relative contributions to the onset of insulin resistance and their putatively synergistic actions are topics of controversy. Second, there are also pieces of evidence that lipids can induce contractile dysfunction independently of insulin resistance. Perhaps, a more integrative view is needed, in which several lipid-induced pathways operate synergistically or in parallel to induce contractile dysfunction. Unraveling of these processes is expected to be important in designing effective therapeutic strategies to protect the lipid-overloaded heart.

Diabetes-related cardiomyopathy: The sweet story of glucose overload from epidemiology to cellular pathways

Type 2 diabetes (T2D) is a major risk factor for heart failure (HF). Although the number of cases of myocardial infarction in the T2D population has been reduced by 25% over the last 10 years, the incidence of HF is continuously increasing, making it the most worrying diabetes complication. This strongly reinforces the urgent need for innovative therapeutic interventions to prevent cardiac dysfunction in T2D patients. To this end, epidemiological, imaging and animal studies have aimed to highlight the mechanisms involved in the development of diabetic cardiomyopathy. Epidemiological observations clearly show that hyperglycaemia correlates with severity of cardiac dysfunction and mortality in T2D patients. Both animal and cellular studies have demonstrated that, in the context of diabetes, the heart loses its ability to utilize glucose, therefore leading to glucose overload in cardiomyocytes that, in turn, promotes oxidative stress, accumulation of advanced glycation end-products (AGEs) and chronic activation of the hexosamine pathway. These have all been found to activate apoptosis and to alter heart contractility, calcium signalling and mitochondrial function. Although, in the past, tight glycaemic control has failed to improve cardiac function in T2D patients, recent clinical trials have reported cardiovascular benefit with hypoglycaemic antidiabetic drugs of the SGLT2-inhibitor family. This review, based on clinical evidence from mechanistic studies as well as several large clinical trials, covers 15 years of research, and strongly supports the idea that hyperglycaemia and glucose overload play a central role in the pathophysiology of diabetic cardiomyopathy.

Efficacy of the Reactive Oxygen Metabolite Test as a Predictor of Initial Heart Failure Hospitalization in Elderly Patients With Chronic Heart Failure

Background

The reactive oxygen metabolites (d-ROMs) test has recently been explored as a novel marker of oxidative stress in vivo and used in clinical settings. Conversely, data regarding the utility of the d-ROMs test as a predictor of patients with chronic heart failure (CHF) are limited. This prospective study aims to elucidate the efficacy of the d-ROMs test as a predictor of initial heart failure (HF) hospitalization in elderly patients with CHF.

Methods

A total of 428 elderly outpatients with CHF with no history of HF hospitalization (108 males, 320 females; mean age, 75 ± 7 years) were enrolled. Based on the median value of d-ROMs test levels (303 U.CARR), the patients were divided into the following two groups: group L (low d-ROMs test levels) and group H (high d-ROMs test levels). The utility of the d-ROMs test as a predictor of initial HF hospitalization was evaluated.

Results

During the 88.1-month follow-up period, 58 HF cases were hospitalized (group L, 17 cases; group H, 41 cases; P < 0.001, log-rank test). Multivariate Cox regression analyses revealed that group H exhibited a significantly higher risk for HF hospitalization than did group L (hazard ratio (HR), 2.35; 95% confidence interval (CI), 1.37 - 4.43; P < 0.01). Furthermore, the HR (vs. group L with low brain natriuretic peptide (BNP) levels (< 200 pg/mL), HR, 9.18; 95% CI, 4.78 - 22.94; P < 0.001) for the incidence of HF hospitalization increased in group H with high BNP levels (≥ 200 pg/mL).

Conclusions

The present study demonstrates that high d-ROMs test levels predict initial HF hospitalization in elderly patients with CHF. In addition, the predictive value for the incidence of HF hospitalization increases by using a combination of two biomarkers as d-ROMs test and BNP levels.

Clinical Significance of Skin Autofluorescence in Patients With Type 2 Diabetes Mellitus With Chronic Heart Failure

Background

Recent clinical studies have shown that skin autofluorescence (AF) levels are significantly associated with diabetic complications. In contrast, data regarding the relationships between skin AF and chronic heart failure (CHF) are limited. The aim of this study was to clarify the clinical significance of skin AF in patients with type 2 diabetes mellitus (DM) with CHF.

Methods

This cross-sectional study enrolled 257 outpatients with type 2 DM with CHF who were treated medically (96 men and 161 women; mean age, 79 ± 7 years). Associations between skin AF and various clinical parameters were examined.

Results

Incidence of skin AF in patients with a history of hospitalization due to HF was significantly higher than in those without a history of hospitalization due to HF (3.0 ± 0.5 AU vs. 2.7 ± 0.5 AU, respectively, P < 0.001). Significant positive correlations were found between skin AF and various clinical parameters, such as E/e′ as a maker of left ventricular diastolic function (r = 0.30, P < 0.001), high-sensitivity cardiac troponin T levels as a marker of myocardial injury (r = 0.45, P < 0.001), reactive oxygen metabolite levels as an oxidative stress marker (r = 0.31, P < 0.001), and cardio-ankle vascular index as a marker of arterial function (r = 0.38, P < 0.001). Furthermore, multiple regression analyses showed that these clinical parameters (E/e′ (β = 0.25, P < 0.001)), high-sensitivity cardiac troponin T levels (β = 0.30, P < 0.001), cardio-ankle vascular index (β = 0.21, P < 0.001), reactive oxygen metabolite levels (β = 0.15, P < 0.01), and a history of hospitalization due to HF (β = 0.23, P < 0.001) were independent variables when skin AF was used as a subordinate factor.

Conclusion

The findings of this study showed that skin AF may be a determining factor for prognosis in patients with type 2 DM with CHF. Further investigations in a large prospective study, including intervention therapies, are required to validate the results of this study.

Molecular mechanism of diabetic cardiomyopathy and modulation of microRNA function by synthetic oligonucleotides

Diabetic cardiomyopathy (DCM) is a chronic complication in individuals with diabetes and is characterized by ventricular dilation and hypertrophy, diastolic dysfunction, decreased or preserved systolic function and reduced ejection fraction eventually resulting in heart failure. Despite being well characterized, the fundamental mechanisms leading to DCM are still elusive. Recent studies identified the involvement of small non-coding small RNA molecules such as microRNAs (miRs) playing a key role in the etiology of DCM. Therefore, miRs associated with DCM represents a new class of targets for the development of mechanistic therapeutics, which may yield marked benefits compared to other therapeutic approaches. Indeed, few miRs currently under active clinical investigation, with many expressing cautious optimism that miRs based therapies will succeed in the coming years. The major caution in using miRs based therapy is the need to improve the stability and specificity following systemic injection, which can be achieved through chemical and structural modification. In this review, we first discuss the established role of miRs in DCM and the advances in miRs based therapeutic strategies for the prevention/treatment of DCM. We next discuss the currently employed chemical modification of miR oligonucleotides and their utility in therapies specifically focusing on the DCM. Finally, we summarize the commonly used delivery system and approaches for assessment of miRNA modulation and potential off-target effects.

Association of Hemorheology With High-Sensitivity Cardiac Troponin T Levels in Patients With Type 2 Diabetes Mellitus Assessed by Microchannel Array Flow Analyzer

Background

Recent studies on high-sensitivity cardiac troponin T (hs-cTnT) and whole blood passage time (WBPT), estimated by hemorheology assessed with the microchannel array flow analyzer (MC-FAN), have revealed the significance of cardiovascular risk factors. However, there are no known reports on the relationship between these two clinical parameters. This cross-sectional study aimed to clarify the associations between WBPT and hs-cTnT levels in patients with type 2 diabetes mellitus from the perspective of subclinical myocardial injury or the primary prevention of cardiovascular events.

Methods

A total of 301 outpatients (men, 116; women, 185; mean age, 65 ± 11 years), with no history of cardiovascular diseases, undergoing treatment for diabetes mellitus were enrolled. Hs-cTnT levels and WBPT were measured using a commercial device, and the relationship between hs-cTnT levels and various clinical parameters, including WBPT, was examined.

Results

Hs-cTnT levels were detected in 261 (86.7%) patients. WBPT was significantly higher in patients with detectable hs-cTnT levels than in those with undetectable hs-cTnT levels (64 ± 18 s vs. 51 ± 13 s, P < 0.001). In patients with detectable hs-cTnT levels, there was a significantly positive correlation between WBPT and hs-cTnT levels (r = 0.40; P < 0.001). Furthermore, multiple regression analysis revealed that WBPT (β = 0.24; P < 0.001) was an independent variable when hs-cTnT was a subordinate factor. Conversely, patients with high (≥ 70 s; odds ratio, 5.3 (95% CI, 1.6 - 16.1); P < 0.01) and median (50.2 - 69.8 s; odds ratio, 3.8 (95% CI, 1.2 - 12.4); P < 0.05) WBPT had a significantly higher risk for high hs-cTnT levels (≥ 0.014 ng/mL) than those with low WBPT (≤ 50.0 s).

Conclusions

The results of this study indicated independent associations of hemorheology with hs-cTnT in patients with type 2 diabetes mellitus assessed by MC-FAN. We suggest that an increase in hs-cTnT levels can be prevented by maintaining WBPT at ≤ 50.0 s.

New Insights into the Immunobiology of Mononuclear Phagocytic Cells and Their Relevance to the Pathogenesis of Cardiovascular Diseases

Macrophages are the primary immune cells that reside within the myocardium, suggesting that these mononuclear phagocytes are essential in the orchestration of cardiac immunity and homeostasis. Independent of the nature of the injury, the heart triggers leukocyte activation and recruitment. However, inflammation is harmful to this vital terminally differentiated organ with extremely poor regenerative capacity. As such, cardiac tissue has evolved particular strategies to increase the stress tolerance and minimize the impact of inflammation. In this sense, growing evidences show that mononuclear phagocytic cells are particularly dynamic during cardiac inflammation or infection and would actively participate in tissue repair and functional recovery. They respond to soluble mediators such as metabolites or cytokines, which play central roles in the timing of the intrinsic cardiac stress response. During myocardial infarction two distinct phases of monocyte influx have been identified. Upon infarction, the heart modulates its chemokine expression profile that sequentially and actively recruits inflammatory monocytes, first, and healing monocytes, later. In the same way, a sudden switch from inflammatory macrophages (with microbicidal effectors) toward anti-inflammatory macrophages occurs within the myocardium very shortly after infection with Trypanosoma cruzi, the causal agent of Chagas cardiomyopathy. While in sterile injury, healing response is necessary to stop tissue damage; during an intracellular infection, the anti-inflammatory milieu in infected hearts would promote microbial persistence. The balance of mononuclear phagocytic cells seems to be also dynamic in atherosclerosis influencing plaque initiation and fate. This review summarizes the participation of mononuclear phagocyte system in cardiovascular diseases, keeping in mind that the immune system evolved to promote the reestablishment of tissue homeostasis following infection/injury, and that the effects of different mediators could modulate the magnitude and quality of the immune response. The knowledge of the effects triggered by diverse mediators would serve to identify new therapeutic targets in different cardiovascular pathologies.

Activation of IGF-1 receptors and Akt signaling by systemic hyperinsulinemia contributes to cardiac hypertrophy but does not regulate cardiac autophagy in obese diabetic mice

Autophagy plays an important role in the maintenance of normal heart function. However, the role of autophagy in the inulin resistant and diabetic heart is not well understood. Furthermore, the upstream signaling and the downstream targets involved in cardiac autophagy regulation during obesity and type 2 diabetes mellitus (T2DM) are not fully elucidated. The aim of this study was to measure autophagic flux and to dissect the upstream and downstream signaling involved in cardiac autophagy regulation in the hearts of obese T2DM mice. Our study demonstrated that cardiac autophagic flux is suppressed in the heart of obese diabetic (ob/ob) mice due to impaired autophagosome formation. We showed that suppression of autophagy was due to sustained activation of mTOR as we could restore cardiac autophagy by inhibiting mTOR. Moreover, the novel finding of this study is that while IGF-1 receptor-mediated Akt activation contributes to cardiac hypertrophy, it is not involved in mTOR activation and autophagy suppression in obesity and T2DM. In contrast, inhibition of ERK signaling abolished mTOR activation and restored autophagy in the heart of obese diabetic (ob/ob) mice. The study identifies mechanisms regulating cardiac autophagy in obesity and T2DM that are mediated by ERK/mTOR but are distinct from Akt. The findings are of significant importance as they demonstrate for the first time the contribution of IGF-1 receptors (IGF-1R) and Akt signaling in cardiac hypertrophy but not in cardiac autophagy regulation in obesity and T2DM.

Clinical impact of skin autofluorescence on high-sensitivity troponin T in hypertensive patients

Background

Recent studies have reported the importance of high-sensitivity troponin T (hs-cTnT) or skin autofluorescence (AF) as a cardiovascular risk factor. However, little is known about the relationship between these two markers. The aim of this study was to clarify the clinical impact of skin AF on hs-cTnT in hypertensive patients, from the perspective of primary prevention of cardiovascular events.

Methods

In total, 457 outpatients on treatment for hypertension [182 men and 275 women; mean (± SD) age, 67 ± 13 y] and with no history of cardiovascular events were enrolled. Hs-cTnT levels and skin AF were measured using commercial devices, and relationships between hs-cTnT levels and various clinical parameters including skin AF were examined.

Results

Hs-cTnT was detected in 405 (88.6%) patients. Skin AF was significantly higher in patients with detectable hs-cTnT than in those without detectable hs-cTnT [2.6 ± 0.5 arbitrary units (AU) vs. 2.2 ± 0.5 AU, respectively, p < 0.001]. In patients with detectable hs-cTnT, there was a significantly positive correlation between skin AF and Log-hs-cTnT (r = 0.41, p < 0.001). Furthermore, multiple regression analysis revealed that skin AF was the strongest variable associated with Log-hs-cTnT as a subordinate factor (β = 0.30, p < 0.001).

Conclusions

The results of this study indicate that skin AF is an important determining factor for hs-cTnT elevation in hypertensive patients with no history of cardiovascular events.

Obesity and hypertension

Obesity and in particular the excessive visceral fat distribution is accompanied by several alterations at hormonal, inflammatory and endothelial level. These alterations induce a stimulation of several other mechanisms that contribute to the hypertensive state and on the other side to increase the cardiovascular morbidity. In these chapter we will examine the main mechanisms of obesity and obesity-related hypertension and in particular the role of sympathetic nervous system, the alterations of the renal function and at the microvascular level. We will also depict the role of insulin resistance as factor stimulating and potentiating the other mechanisms. The second part will be focalized on the major target organ damage linked with obesity and obesity-related hypertension. We will finally describe the management and treatment of obesity and the antihypertensive drug therapies more effective in hypertensive obeses.

Arterial Velocity Pulse Index as a Novel Marker of Atherosclerosis Using Pulse Wave Analysis on High Sensitivity Troponin T in Hypertensive Patients

Background

The arterial velocity pulse index (AVI) is explored as a novel marker of atherosclerosis using pulse wave analysis in clinical settings. Recent clinical studies have reported that the level of high-sensitivity troponin T (hs-cTnT) is an important biomarker in hypertensive patients. The aim of this study was to clarify the impact of AVI on hs-cTnT in these patients.

Methods

This study enrolled 455 hypertensive outpatients (181 males and 274 females; mean age, 65 ± 11 years (mean ± standard deviation)) without a history of cardiovascular events. AVI and hs-cTnT levels were measured using a commercial device, and relations among various clinical parameters, including AVI and hs-cTnT, were examined.

Results

Hs-cTnT was detected in 405 patients (89.0%). AVI was significantly higher in patients with detectable hs-cTnT than in those without (28 ± 7 vs. 24 ± 8, respectively, P < 0.001). In patients with detectable hs-cTnT, there was a significant positive correlation between AVI and hs-cTnT (r = 0.42, P < 0.001). Furthermore, multiple regression analyses revealed that AVI was an independent variable when hs-cTnT was used as a subordinate factor. On the other hand, hs-cTnT age, Cornell electrocardiographic voltage, height, urinary albumin excretion, pulse rate, and derivatives of reactive oxygen metabolites test were independent variables when AVI was used as a subordinate factor.

Conclusion

The results of this study indicate that AVI reflects features of arterial wave reflection and is an important factor for hs-cTnT elevation in hypertensive patients.

Nanothermometry Measure of Muscle Efficiency

Despite recent advances in thermometry, determination of temperature at the nanometer scale in single molecules to live cells remains a challenge that holds great promise in disease detection among others. In the present study, we use a new approach to nanometer scale thermometry with a spatial and thermal resolution of 80 nm and 1 mK respectively, by directly associating 2 nm cadmium telluride quantum dots (CdTe QDs) to the subject under study. The 2 nm CdTe QDs physically adhered to bovine cardiac and rabbit skeletal muscle myosin, enabling the determination of heat released when ATP is hydrolyzed by both myosin motors. Greater heat loss reflects less work performed by the motor, hence decreased efficiency. Surprisingly, we found rabbit skeletal myosin to be more efficient than bovine cardiac. We have further extended this approach to demonstrate the gain in efficiency of Drosophila melanogaster skeletal muscle overexpressing the PGC-1α homologue spargel, a known mediator of improved exercise performance in humans. Our results establish a novel approach to determine muscle efficiency with promise for early diagnosis and treatment of various metabolic disorders including cancer.

Insights into the role of maladaptive hexosamine biosynthesis and O-GlcNAcylation in development of diabetic cardiac complications

Diabetes mellitus significantly increases the risk of heart failure, independent of coronary artery disease. The mechanisms implicated in the development of diabetic heart disease, commonly termed diabetic cardiomyopathy, are complex, but much of the impact of diabetes on the heart can be attributed to impaired glucose handling. It has been shown that the maladaptive nutrient-sensing hexosamine biosynthesis pathway (HBP) contributes to diabetic complications in many non-cardiac tissues. Glucose metabolism by the HBP leads to enzymatically-regulated, O-linked attachment of a sugar moiety molecule, β-N-acetylglucosamine (O-GlcNAc), to proteins, affecting their biological activity (similar to phosphorylation). In normal physiology, transient activation of HBP/O-GlcNAc mechanisms is an adaptive, protective means to enhance cell survival; interventions that acutely suppress this pathway decrease tolerance to stress. Conversely, chronic dysregulation of HBP/O-GlcNAc mechanisms has been shown to be detrimental in certain pathological settings, including diabetes and cancer. Most of our understanding of the impact of sustained maladaptive HBP and O-GlcNAc protein modifications has been derived from adipose tissue, skeletal muscle and other non-cardiac tissues, as a contributing mechanism to insulin resistance and progression of diabetic complications. However, the long-term consequences of persistent activation of cardiac HBP and O-GlcNAc are not well-understood; therefore, the goal of this timely review is to highlight current understanding of the role of the HBP pathway in development of diabetic cardiomyopathy.

Regular treadmill exercise inhibits mitochondrial accumulation of cholesterol and oxysterols during myocardial ischemia-reperfusion in wild-type and ob/ob mice

Mitochondria play a central role in the irreversible damages induced to the heart by a prolonged period of ischemia followed by reperfusion. We previously demonstrated that (1) myocardial ischemia-reperfusion induces mitochondrial accumulation of cholesterol and oxysterols that are deleterious for the organelle; (2) inhibition of cholesterol and oxysterol accumulation prevents mitochondrial injury at reperfusion; (3) exercise is cardioprotective and remains efficient in the presence of co-morbidities such as obesity. The aim of this study was to investigate whether regular exercise limits mitochondrial cholesterol and oxysterol accumulation in wild-type and obese mice. Wild-type C57BL/6J and obese (ob/ob) mice were assigned to sedentary conditions or regular treadmill exercise and submitted to 30min of coronary artery occlusion followed by 15min of reperfusion. Regular exercise improved oxidative phosphorylation, restored the antioxidant capacity of the heart by increasing the expression of SOD1 and catalase and reduced the mitochondrial generation of oxysterols in wild-type as well as in ob/ob mice. In wild-type animals, exercise limited the production of oxysterols. In ob/ob mice, despite hypercholesterolemia, chronic exercise abolished the mitochondrial accumulation of cholesterol and concomitantly reduced the generation of 7α-hydroxycholesterol, 7-ketocholesterol and cholesterol-5α,6α-epoxide. In conclusion, regular exercise prevents the mitochondrial accumulation of cholesterol and oxysterols which occurs during early reperfusion of an ischemic myocardium in mice. This effect is observed in normo and hypercholesterolemic animals. It may be partly responsible for the antioxidant properties of regular exercise and contribute to its cardioprotective effect in obese conditions.