Leptin-induced suppression of cardiomyocyte contraction is amplified by ceramide

From Beats to Metabolism: the Heart at the Core of Interorgan Metabolic Cross Talk

The heart, once considered a mere blood pump, is now recognized as a multifunctional metabolic and endocrine organ. Its function is tightly regulated by various metabolic processes, at the same time it serves as an endocrine organ, secreting bioactive molecules that impact systemic metabolism. In recent years, research has shed light on the intricate interplay between the heart and other metabolic organs, such as adipose tissue, liver, and skeletal muscle. The metabolic flexibility of the heart and its ability to switch between different energy substrates play a crucial role in maintaining cardiac function and overall metabolic homeostasis. Gaining a comprehensive understanding of how metabolic disorders disrupt cardiac metabolism is crucial, as it plays a pivotal role in the development and progression of cardiac diseases. The emerging understanding of the heart as a metabolic and endocrine organ highlights its essential contribution to whole body metabolic regulation and offers new insights into the pathogenesis of metabolic diseases, such as obesity, diabetes, and cardiovascular disorders. In this review, we provide an in-depth exploration of the heart's metabolic and endocrine functions, emphasizing its role in systemic metabolism and the interplay between the heart and other metabolic organs. Furthermore, emerging evidence suggests a correlation between heart disease and other conditions such as aging and cancer, indicating that the metabolic dysfunction observed in these conditions may share common underlying mechanisms. By unraveling the complex mechanisms underlying cardiac metabolism, we aim to contribute to the development of novel therapeutic strategies for metabolic diseases and improve overall cardiovascular health.

Mathematical Modelling of Leptin-Induced Effects on Electrophysiological Properties of Rat Cardiomyocytes and Cardiac Arrhythmias

Elevated plasma leptin levels, or hyperleptinemia, have been demonstrated to correlate with metabolic syndrome markers, including obesity, and may be an independent risk factor for the development of cardiovascular disease. In this paper, we use cardiac models to study possible effects of hyperleptinemia on the electrophysiological properties of cardiomyocytes and cardiac arrhythmias. We modified the parameters of an improved Gattoni 2016 model of rat ventricular cardiomyocytes to simulate experimental data for the leptin effects on ionic currents. We used four model variants to investigate the effects of leptin-induced parameter modification at the cellular level and in 2D tissue. In all models, leptin was found to increase the duration of the action potential. In some cases, we observed a dramatic change in the shape of the action potential from triangular, characteristic of rat cardiomyocytes, to a spike-and-dome, indicating predisposition to arrhythmias. In all 2D tissue models, leptin increased the period of cardiac arrhythmia caused by a spiral wave and enhanced dynamic instability, manifesting as increased meandering, onset of hypermeandering, and even spiral wave breakup. The leptin-modified cellular models developed can be used in subsequent research in rat heart anatomy models.

The Acute Effects of Leptin on the Contractility of Isolated Rat Atrial and Ventricular Cardiomyocytes

Leptin is a pleiotropic peptide playing an important role in the regulation of cardiac functions. It is not clear whether leptin directly modulates the mechanical function of atrial cardiomyocytes. We compared the acute effects of leptin on the characteristics of mechanically non-loaded sarcomere shortening and cytosolic Ca2+ concentration ([Ca2+]i) transients in single rat atrial and ventricular cardiomyocytes. We also studied the functional properties of myosin obtained from cardiomyocytes using an in vitro motility assay and assessed the sarcomeric protein phosphorylation. Single cardiomyocytes were exposed to 5, 20, and 60 nM leptin for 60 min. In ventricular cardiomyocytes, 60 nM leptin depressed sarcomere shortening amplitude and decreased the rates of shortening and relaxation. These effects were accompanied by a decrease in the phosphorylation of cMyBP-C, an increase in Tpm phosphorylation, and a slowdown of the sliding velocity of thin filaments over myosin in the in vitro motility assay. In contrast, in atrial cardiomyocytes, the phosphorylation of cMyBP-C and TnI increased, and the characteristics of sarcomere shortening did not change. Leptin had no effect on the characteristics of [Ca2+]i transients in ventricular cardiomyocytes, while 5 nM leptin prolonged [Ca2+]i transients in atrial cardiomyocytes. Thus, leptin-induced changes in contractility of ventricular cardiomyocytes may be attributed to the direct effects of leptin on cross-bridge kinetics and sarcomeric protein properties rather than changes in [Ca2+]i. We also suggest that the observed differences between atrial and ventricular cardiomyocytes may be associated with the peculiarities of the expression of leptin receptors, as well as signaling pathways in the atrial and ventricular myocardium.

Emerging Roles of Ceramide in Cardiovascular Diseases

Ceramide is a core molecule of sphingolipid metabolism that causes selective insulin resistance and dyslipidemia. Research on its involvement in cardiovascular diseases has grown rapidly. In resting cells, ceramide levels are extremely low, while they rapidly accumulate upon encountering external stimuli. Recently, the regulation of ceramide levels under pathological conditions, including myocardial infarction, hypertension, and atherosclerosis, has drawn great attention. Increased ceramide levels are strongly associated with adverse cardiovascular risks and events while inhibiting the synthesis of ceramide or accelerating its degradation improves a variety of cardiovascular diseases. In this article, we summarize the role of ceramide in cardiovascular disease, investigate the possible application of ceramide as a new diagnostic biomarker and a therapeutic target for cardiovascular disorders, and highlight the remaining problems.

Role of Ceramides in the Molecular Pathogenesis and Potential Therapeutic Strategies of Cardiometabolic Diseases: What we Know so Far

Ceramides represent a class of biologically active lipids that are involved in orchestrating vital signal transduction pathways responsible for regulating cellular differentiation and proliferation. However, accumulating clinical evidence have shown that ceramides are playing a detrimental role in the pathogenesis of several diseases including cardiovascular disease, type II diabetes and obesity, collectively referred to as cardiometabolic disease. Therefore, it has become necessary to study in depth the role of ceramides in the pathophysiology of such diseases, aiming to tailor more efficient treatment regimens. Furthermore, understanding the contribution of ceramides to the pathological molecular mechanisms of those interrelated conditions may improve not only the therapeutic but also the diagnostic and preventive approaches of the preceding hazardous events. Hence, the purpose of this article is to review currently available evidence on the role of ceramides as a common factor in the pathological mechanisms of cardiometabolic diseases as well as the mechanism of action of the latest ceramides-targeted therapies.

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.

The Role of Ceramides in Diabetes and Cardiovascular Disease Regulation of Ceramides by Adipokines

Metabolic dysfunction is intertwined with the pathophysiology of both diabetes and cardiovascular disease. Recently, one particular lipid class has been shown to influence the development and sustainment of these diseases: ceramides. As a subtype of sphingolipids, these species are particularly central to many sphingolipid pathways. Increased levels of ceramides are known to correlate with impaired cardiovascular and metabolic health. Furthermore, the interaction between ceramides and adipokines, most notably adiponectin and leptin, appears to play a role in the pathophysiology of these conditions. Adiponectin appears to counteract the detrimental effects of elevated ceramides, largely through activation of the ceramidase activity of its receptors. Elevated ceramides appear to worsen leptin resistance, which is an important phenomenon in the pathophysiology of obesity and metabolic syndrome.

Circulating Ceramide: A New Cardiometabolic Biomarker in Patients With Comorbid Acute Coronary Syndrome and Type 2 Diabetes Mellitus

Aims

This study investigated the association of circulating ceramides in patients with comorbid acute coronary syndrome and type 2 diabetes mellitus (ACS-DM).

Methods

A total of 761 patients with coronary heart disease who were admitted to the Department of Cardiology at the Chinese PLA General Hospital from March to August 2018 were enrolled in this study. Of these 761 patients, 282 were diagnosed with acute coronary syndrome (ACS). We selected 65 patients with ACS-DM (ACS-DM group; mean age 64.88 years; 38 men) and 65 patients with ACS but without any comorbidities (ACS group; mean age 64.68 years; 38 men); the two groups were matched by age and sex. We determined four circulating ceramides in 130 plasma samples: Cer(d18:1/16:0), Cer(d18:1/18:0), Cer(d18:1/24:1), and Cer(d18:1/24:0). The ceramides in plasma samples from patients with ACS and those from patients with ACS-DM were compared. Pearson correlation coefficients between individual ceramides and traditional cardiovascular risk factors for the whole study population were calculated. Multiple logistic regression models were used to evaluate the relativity between the ceramide and ACS-DM.

Results

Compared with the ACS group, the levels of Cer(d18:1/16:0), Cer(d18:1/18:0), and Cer(d18:1/24:1) and their ratios to Cer(d18:1/24:0) were higher in the ACS-DM group and Cer(d18:1/24:0) was lower in the ACS-DM group (P < 0.05). Correlation analysis demonstrated mild-to-moderate correlations of ceramide and traditional cardiovascular risk factors. There were relatively strong correlations of Cer(d18:1/18:0) and Cer(d18:1/24:1) with C-reactive protein, blood lipids, fasting blood glucose, and glycated hemoglobin A₁c. In multiple logistic regression models, Cer(d18:1/18:0) [odds ratio (OR) 2.396; 95% confidence interval (CI) 1.103–5.205; P = 0.027], Cer(d18:1/24:1) (OR 2.826; 95% CI 1.158–6.896; P = 0.023), Cer(d18:1/18:0)/Cer(d18:1/24:0) (OR 2.242; 95% CI 1.103–4.555; P = 0.026), and Cer(d18:1/24:1)/Cer(d18:1/24:0) (OR 2.673; 95% CI 1.225–5.836; P = 0.014) were positively correlated with ACS-DM, and Cer(d18:1/24:0) (OR 0.200; 95% CI 0.051–0.778; P = 0.020) was negatively correlated with ACS-DM.

Conclusion

Circulating ceramides are positively correlated with the risk of ACS-DM comorbidity. These results give a new insight into the pathogenesis of ACS-DM comorbidity and could provide new options for risk estimation.

Adipokines and the cardiovascular system: mechanisms mediating health and disease

This review focuses on the role of adipokines in the maintenance of a healthy cardiovascular system, and the mechanisms by which these factors mediate the development of cardiovascular disease in obesity. Adipocytes are the major cell type comprising the adipose tissue. These cells secrete numerous factors, termed adipokines, into the blood, including adiponectin, leptin, resistin, chemerin, omentin, vaspin, and visfatin. Adipose tissue is a highly vascularised endocrine organ, and different adipose depots have distinct adipokine secretion profiles, which are altered with obesity. The ability of many adipokines to stimulate angiogenesis is crucial for adipose tissue expansion; however, excessive blood vessel growth is deleterious. As well, some adipokines induce inflammation, which promotes cardiovascular disease progression. We discuss how these 7 aforementioned adipokines act upon the various cardiovascular cell types (endothelial progenitor cells, endothelial cells, vascular smooth muscle cells, pericytes, cardiomyocytes, and cardiac fibroblasts), the direct effects of these actions, and their overall impact on the cardiovascular system. These were chosen, as these adipokines are secreted predominantly from adipocytes and have known effects on cardiovascular cells.

Adipose tissue and ceramide biosynthesis in the pathogenesis of obesity

Although obesity is a complex metabolic disorder often associated with insulin resistance, hyperinsulinemia and Type 2 diabetes, as well as with accelerated atherosclerosis, the molecular changes in obesity that promote these disorders are not completely understood. Several mechanisms have been proposed to explain how increased adipose tissue mass affects whole body insulin resistance and cardiovascular risk. One theory is that increased adipose derived inflammatory cytokines induces a chronic inflammatory state that not only increases cardiovascular risk, but also antagonizes insulin signaling and mitochondrial function and thereby impair glucose hemostasis. Another suggests that lipid accumulation in nonadipose tissues not suited for fat storage leads to the buildup of bioactive lipids that inhibit insulin signaling and metabolism. Recent evidence demonstrates that sphingolipid metabolism is dysregulated in obesity and specific sphingolipids may provide a common pathway that link excess nutrients and inflammation to increased metabolic and cardiovascular risk. This chapter will focus primarily on the expression and regulation of adipose and plasma ceramide biosynthesis in obesity and, its potential contribution to the pathogenesis of obesity and the metabolic syndrome.

Leptin signaling and obesity: cardiovascular consequences

Leptin, among the best known hormone markers for obesity, exerts pleiotropic actions on multiple organ systems. In this review, we summarize major leptin signaling pathways, namely Janus-activated kinase/signal transducers and activators of transcription and mitogen-activated protein kinase, including possible mechanisms of leptin resistance in obesity. The effects of leptin on the cardiovascular system are discussed in detail, including its contributions to hypertension, atherosclerosis, depressed myocardial contractile function, fatty acid metabolism, hypertrophic remodeling, and reduction of ischemic/reperfusion injury. The overall goal is to summarize current understanding of how altered leptin signaling in obesity contributes to obesity-related cardiovascular disease.