Leptin attenuates cardiac contraction in rat ventricular myocytes. Role of NO

Levocabastine ameliorates cyclophosphamide-induced cardiotoxicity in Swiss albino mice: Targeting TLR4/NF-κB/NLRP3 signaling pathway

Cyclophosphamide (CP), although a potent anti-cancer drug, causes cardiotoxicity as a side effect that limits its use. Hence, a specific medicine that can lower cardiotoxicity and be utilised as an adjuvant in cancer treatment is very much needed. In this light, we intended to assess the protective potential of levocabastine (LEV) on CP-induced cardiotoxicity in Swiss albino mice. Mice were administered LEV (50 and 100 μg/kg, i.p.) daily for 14 days and CP at 200 mg/kg, intraperitoneally once on the 7th day. On the 15th day, mice were weighed, blood withdrawn then sacrificed and hearts were removed to estimate various biochemical and histopathological parameters. CP 200 mg/kg significantly increased cardiac troponin T, LDH, CK-MB, interleukin-1β, IL-6, TNF-α, TBARS, nitrite, and decreased CAT, GSH, and SOD levels, thus, manifested cardiac damage, inflammation, oxidative stress, and nitrative stress, cumulatively causing cardiotoxicity. CP also elevated the expression of various markers including cleaved caspase-3, NF-κB, TLR4, NLRP3, and fibrotic lesions in cardiac tissues, whereas decreased hematological parameters (RBCs, platelets, and Hb) to confirm cardiotoxicity. LEV and fenofibrate (FF) treatment reversed these changes towards normal and showed a significant protective effect against CP. The results showed the protective role of LEV in restoring CP-induced cardiotoxicity in terms of inflammation, apoptosis, oxidative stress, cardiac injury and histopathological damage. Thus, levocabastine can be used as an adjuvant to cyclophosphamide in cancer treatment but a thorough study with various animal cancer models is further needed to establish the fact.

Exploring the Mechanistic Link Between Obesity and Heart Failure

PURPOSE OF REVIEW

Among subtypes of cardiovascular disease, obesity has a potent and unique association with heart failure (HF) that is unexplained by traditional cardiovascular risk mediators. The concomitant rise in the prevalence of obesity and HF necessitates better understanding of their relationship to develop effective prevention and treatment strategies. The purpose of this review is to provide mechanistic insight regarding the link between obesity and HF by elucidating the direct and indirect pathways linking the two conditions.

RECENT FINDINGS

Several direct pathophysiologic mechanisms contribute to HF risk in individuals with excess weight, including hemodynamic alterations, neurohormonal activation, hormonal effects of dysfunctional adipose tissue, ectopic fat deposition with resulting lipotoxicity and microvascular dysfunction. Obesity further predisposes to HF indirectly through causal associations with hypertension, dyslipidemia, and most importantly, diabetes via insulin resistance. Low levels of physical activity and fitness further influence HF risk in the context of obesity. These various processes lead to myocardial injury and cardiac remodeling that are reflected by abnormalities in cardiac biomarkers and cardiac function on myocardial imaging. Understanding and addressing obesity-associated HF is a pressing clinical and public health challenge which can be informed by a deeper understanding of the complex pathways linking these two conditions together.

Assessment of sarcomere shortening and calcium transient in primary human and dog ventricular myocytes

Understanding translation from preclinical observations to clinical findings is important for evaluating the efficacy and safety of novel compounds. Of relevance to cardiac safety is profiling drug effects on cardiomyocyte (CM) sarcomere shortening and intracellular Ca2+ dynamics. Although CM from different animal species have been used to assess such effects, primary human CM isolated from human organ donor heart represent an ideal non-animal alternative approach. We performed a study to evaluate primary human CM and have them compared to freshly isolated dog cardiomyocytes for their basic function and responses to positive inotropes with well-known mechanisms. Our data showed that simultaneous assessment of sarcomere shortening and Ca2+-transient can be performed with both myocytes using the IonOptix system. Amplitude of sarcomere shortening and Ca2+-transient (CaT) were significantly higher in dog compared to human CM in the basic condition (absence of treatment), while longer duration of sarcomere shortening and CaT were observed in human cells. We observed that human and dog CMs have similar pharmacological responses to five inotropes with different mechanisms, including dobutamine and isoproterenol (β-adrenergic stimulation), milrinone (PDE3 inhibition), pimobendan and levosimendan (increase of Ca2+sensitization as well as PDE3 inhibition). In conclusion, our study suggests that myocytes obtained from both human donor hearts and dog hearts can be used to simultaneously assess drug-induced effects on sarcomere shortening and CaT using the IonOptix platform.

Adiposity-associated atrial fibrillation: molecular determinants, mechanisms, and clinical significance

Obesity is an important contributing factor to the pathophysiology of atrial fibrillation (AF) and its complications by causing systemic changes, such as altered haemodynamic, increased sympathetic tone, and low-grade chronic inflammatory state. In addition, adipose tissue is a metabolically active organ that comprises various types of fat deposits with discrete composition and localization that show distinct functions. Fatty tissue differentially affects the evolution of AF, with highly secretory active visceral fat surrounding the heart generally having a more potent influence than the rather inert subcutaneous fat. A variety of proinflammatory, profibrotic, and vasoconstrictive mediators are secreted by adipose tissue, particularly originating from cardiac fat, that promote atrial remodelling and increase the susceptibility to AF. In this review, we address the role of obesity-related factors and in particular specific adipose tissue depots in driving AF risk. We discuss the distinct effects of key secreted adipokines from different adipose tissue depots and their participation in cardiac remodelling. The possible mechanistic basis and molecular determinants of adiposity-related AF are discussed, and finally, we highlight important gaps in current knowledge, areas requiring future investigation, and implications for clinical management.

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.

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.

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.

The Roles and Associated Mechanisms of Adipokines in Development of Metabolic Syndrome

Metabolic syndrome is a cluster of metabolic indicators that increase the risk of diabetes and cardiovascular diseases. Visceral obesity and factors derived from altered adipose tissue, adipokines, play critical roles in the development of metabolic syndrome. Although the adipokines leptin and adiponectin improve insulin sensitivity, others contribute to the development of glucose intolerance, including visfatin, fetuin-A, resistin, and plasminogen activator inhibitor-1 (PAI-1). Leptin and adiponectin increase fatty acid oxidation, prevent foam cell formation, and improve lipid metabolism, while visfatin, fetuin-A, PAI-1, and resistin have pro-atherogenic properties. In this review, we briefly summarize the role of various adipokines in the development of metabolic syndrome, focusing on glucose homeostasis and lipid metabolism.

Ginsenoside Rb1 Protects Against Diabetic Cardiomyopathy by Regulating the Adipocytokine Pathway

PURPOSE

Obesity and diabetes are often accompanied by chronic inflammation and insulin resistance, which lead to complications such as diabetic cardiomyopathy. Ginsenoside Rb1 has been used to treat diabetes and obesity and reduce inflammation as well as risk of heart diseases. However, the role of ginsenoside Rb1 in treating diabetic cardiomyopathy remains unclear.

METHODS

Diabetic mice were administered ginsenoside Rb1 for 12 weeks, and their body weight, body fat, and blood glucose levels as well as and serum insulin, lipids, and adipocytokine levels were assessed. Lipid accumulation, pathological morphology of the adipose tissue, liver, and heart were examined. Western blot and qRT-PCR were performed to investigate the molecular changes in response to ginsenoside Rb1 treatment.

RESULTS

Ginsenoside Rb1 treatment significantly reduced body weight and body fat, attenuated hyperglycemia and hyperlipidemia, and ameliorated insulin resistance and abnormal levels of adipocytokines in diabetic mice. In addition, lipid accumulation and inflammation reduced while the functions of heart improved in the ginsenoside Rb1-treated group. Furthermore, antioxidant function improved in the ginsenoside Rb1-treated diabetic hearts. PCR and Western blotting analyses revealed that the lipid-lowering effect of ginsenoside Rb1 and the resulting improvement of cardiac function could be attributed to the adipocytokine pathway, which promoted energy homeostasis and alleviated cardiac dysfunction.

CONCLUSION

Ginsenoside Rb1 lowered lipid levels in a adipocytokine-mediated manner and attenuated hyperglycemia/hyperlipidemia-induced oxidative stress, hypertrophy, inflammation, fibrosis, and apoptosis in cardiomyocytes.

Between Inflammation and Autophagy: The Role of Leptin-Adiponectin Axis in Cardiac Remodeling

Cardiac remodeling is the process by which the heart adapts to stressful stimuli, such as hypertension and ischemia/reperfusion; it ultimately leads to heart failure upon long-term exposure. Autophagy, a cellular catabolic process that was originally considered as a mechanism of cell death in response to detrimental stimuli, is thought to be one of the main mechanisms that controls cardiac remodeling and induces heart failure. Dysregulation of the adipokines leptin and adiponectin, which plays essential roles in lipid and glucose metabolism, and in the pathophysiology of the neuroendocrine and cardiovascular systems, has been shown to affect the autophagic response in the heart and to contribute to accelerate cardiac remodeling. The obesity-associated protein leptin is a pro-inflammatory, tumor-promoting adipocytokine whose elevated levels in obesity are associated with acute cardiovascular events, and obesity-related hypertension. Adiponectin exerts anti-inflammatory and anti-tumor effects, and its reduced levels in obesity correlate with the pathogenesis of obesity-associated cardiovascular diseases. Leptin- and adiponectin-induced changes in autophagic flux have been linked to cardiac remodeling and heart failure. In this review, we describe the different molecular mechanisms of hyperleptinemia- and hypoadiponectinemia-mediated pathogenesis of cardiac remodeling and the involvement of autophagy in this process. A better understanding of the roles of leptin, adiponectin, and autophagy in cardiac functions and remodeling, and the exact signal transduction pathways by which they contribute to cardiac diseases may well lead to discovery of new therapeutic agents for the treatment of cardiovascular remodeling.

Association of Adiponectin, Leptin and Resistin Plasma Concentrations with Echocardiographic Parameters in Patients with Coronary Artery Disease

The imbalanced network of adipokines may contribute to the development of systemic low-grade inflammation, metabolic diseases and coronary artery disease (CAD). In the last decade, three classic adipokines—adiponectin, leptin and resistin—have been of particular interest in studies of patients with CAD due to their numerous properties in relation to the cardiovascular system. This has directed our attention to the association of adipokines with cardiac structure and function and the development of heart failure (HF), a common end effect of CAD. Thus, the purpose of this study was to analyse the associations of plasma concentrations of adiponectin, leptin and resistin with parameters assessed in the echocardiographic examinations of CAD patients. The presented study enrolled 167 Caucasian patients (133 male; 34 female) with CAD. Anthropometric, echocardiographic and basic biochemical measurements, together with plasma concentrations of adiponectin, leptin and resistin assays, were performed in each patient. Adiponectin concentrations were negatively associated with left ventricular ejection fraction (LVEF) and shortening fraction (LVSF), and positively associated with mitral valve E/A ratio (E/A), left ventricular end-diastolic volume (LVEDV), left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter LVESD, and left atrium diameter (LAD). Resistin concentrations were negatively associated with E/A. Leptin concentrations, although correlated with HF severity assessed by the New York Heart Association (NYHA) Functional Classification, were not independently associated with the echocardiographic parameters of cardiac structure or function. In conclusion, adiponectin and resistin, but not leptin, are associated with the echocardiographic parameters of cardiac remodelling and dysfunction. These associations suggest that adiponectin and resistin might be involved in mechanisms of cardiac remodelling or compensative response. We also suggest the possible benefits of adiponectin and resistin level measurements in the monitoring of patients with CAD.

Leptin as a Key between Obesity and Cardiovascular Disease

Obesity increases the risk of cardiovascular disease through various influencing factors. Leptin, which is predominantly secreted by adipose tissue, regulates satiety homeostasis and energy balance, and influences cardiovascular functions directly and indirectly. Leptin appears to play a role in heart protection in leptin-deficient and leptin-receptor-deficient rodent model experiments. Hyperleptinemia or leptin resistance in human obesity influences the vascular endothelium, cardiovascular structure and functions, inflammation, and sympathetic activity, which may lead to cardiovascular disease. Leptin is involved in many processes, including signal transduction, vascular endothelial function, and cardiac structural remodeling. However, the dual (positive and negative) regulator effect of leptin and its receptor on cardiovascular disease has not been completely understood. The protective role of leptin signaling in cardiovascular disease could be a promising target for cardiovascular disease prevention in obese patients.

Effects of omecamtiv mecarbil on calcium-transients and contractility in a translational canine myocyte model

Omecamtiv mecarbil (OM) is a selective cardiac myosin activator (myotrope), currently in Phase 3 clinical investigation as a novel treatment for heart failure with reduced ejection fraction. OM increases cardiac contractility by enhancing interaction between myosin and actin in a calcium-independent fashion. This study aims to characterize the mechanism of action by evaluating its simultaneous effect on myocyte contractility and calcium-transients (CTs) in healthy canine ventricular myocytes. Left ventricular myocytes were isolated from canines and loaded with Fura-2 AM. With an IonOptix system, contractility parameters including amplitude and duration of sarcomere shortening, contraction and relaxation velocity, and resting sarcomere length were measured. CT parameters including amplitude at systole and diastole, velocity at systole and diastole, and duration at 50% from peak were simultaneously measured. OM was tested at 0.03, 0.1, 0.3, 1, and 3 µmol\L concentrations to simulate therapeutic human plasma exposure levels. OM and isoproterenol (ISO) demonstrated differential effects on CTs and myocyte contractility. OM increased contractility mainly by prolonging duration of contraction while ISO increased contractility mainly by augmenting the amplitude of contraction. ISO increased the amplitude and velocity of CT, shortened duration of CT concurrent with increasing myocyte contraction, while OM did not change the amplitude, velocity, and duration of CT up to 1 µmol\L. Decreases in relaxation velocity and increases in duration were present only at 3 µmol\L. In this translational myocyte model study, therapeutically relevant concentrations of OM increased contractility but did not alter intracellular CTs, a mechanism of action distinct from traditional calcitropes.

NFATc3-dependent expression of miR-153-3p promotes mitochondrial fragmentation in cardiac hypertrophy by impairing mitofusin-1 expression

Mitochondrial dysfunction is involved in the pathogenesis of various cardiovascular disorders. Although mitochondrial dynamics, including changes in mitochondrial fission and fusion, have been implicated in the development of cardiac hypertrophy, the underlying molecular mechanisms remain mostly unknown. Here, we show that NFATc3, miR-153-3p, and mitofusion-1 (Mfn1) constitute a signaling axis that mediates mitochondrial fragmentation and cardiomyocyte hypertrophy.

Methods: Isoprenaline (ISO) was used to stimulate the hypertrophic response and mitochondrial fragmentation in cultured cardiomyocytes and in vivo. We performed immunoblotting, immunofluorescence, and quantitative real-time PCR to validate the function of Mfn1 in cardiomyocyte hypertrophy. Bioinformatic analyses, a luciferase reporter assay, and gain- and loss-of-function studies were used to demonstrate the biological function of miR-153-3p, which regulates mitochondrial fragmentation and hypertrophy by targeting Mfn1. Moreover, ChIP-qPCR and a luciferase reporter assay were performed to identify transcription factor NFATc3 as an upstream regulator to control the expression of miR-153-3p.

Results: Our results show that ISO promoted mitochondrial fission and enhanced the expression of miR-153-3p in cardiomyocytes. Knockdown of miR-153-3p attenuated ISO-induced mitochondrial fission and hypertrophy in cultured primary cardiomyocytes. miR-153-3p suppression inhibited mitochondrial fragmentation in ISO-induced cardiac hypertrophy in a mouse model. We identified direct targeting of Mfn1, a key protein of the mitochondrial fusion process, by miR-153-3p. Also, miR-153-3p promoted ISO-induced mitochondrial fission by suppressing the translation of Mfn1. We further found that NFATc3 activated miR-153-3p expression. Knockdown of NFATc3 inhibited miR-153-3p expression and blocked mitochondrial fission and hypertrophic response in cardiomyocytes.

Conclusions: Our data revealed a novel signaling pathway, involving NFATc3, miR-153-3p, and Mfn1, which could be a therapeutic target for the prevention and treatment of cardiac hypertrophy.

Nerolidol attenuates cyclophosphamide-induced cardiac inflammation, apoptosis and fibrosis in Swiss Albino mice

Incidence and prevalence of cancer is an alarming situation globally. For the treatment of cancer many anticancer drugs have been developed but, unfortunately, their potential cardiotoxic side effects raised serious concerns about their use among clinicians. Cyclophosphamide is a potent anticancer and immunosuppressant drug but its use is limited due to cardiotoxic side effect. Thus, there is a need for the development of certain drug which can reduce cardiotoxicity and can be used as an adjuvant therapy in cancer patients. In this direction we, therefore planned to evaluate nerolidol (NER) for its cardioprotective potential against cyclophosphamide-induced cardiotoxicity in Swiss Albino mice. Animals were divided into 6 groups. Vehicle control; Cyclophosphamide (CP 200); NER 400 per se; NER 200 + CP 200; NER 400 + CP 200; and fenofibrate (FF 80) + CP 200. Dosing was done for 14 days along with a single dose of CP 200 on the 7th day. On 15th day animals were sacrificed and various biochemical parameters pertaining to oxidative stress, nitrative stress, inflammation, apoptosis and fibrosis were estimated in the blood and heart tissues. Histopathological analysis (H & E and Masson's trichrome staining); ultrastructural analysis (transmission electron microscopy) and immunohistochemical analysis were also performed along with mRNA expression and molecular docking to establish the cardioprotective potential of nerolidol. Nerolidol acted as a potent cardioprotective molecule and attenuated CP-induced cardiotoxicity.

Functional Relationship between Leptin and Nitric Oxide in Metabolism

Leptin, the product of the ob gene, was originally described as a satiety factor, playing a crucial role in the control of body weight. Nevertheless, the wide distribution of leptin receptors in peripheral tissues supports that leptin exerts pleiotropic biological effects, consisting of the modulation of numerous processes including thermogenesis, reproduction, angiogenesis, hematopoiesis, osteogenesis, neuroendocrine, and immune functions as well as arterial pressure control. Nitric oxide (NO) is a free radical synthesized from L-arginine by the action of the NO synthase (NOS) enzyme. Three NOS isoforms have been identified: the neuronal NOS (nNOS) and endothelial NOS (eNOS) constitutive isoforms, and the inducible NOS (iNOS). NO mediates multiple biological effects in a variety of physiological systems such as energy balance, blood pressure, reproduction, immune response, or reproduction. Leptin and NO on their own participate in multiple common physiological processes, with a functional relationship between both factors having been identified. The present review describes the functional relationship between leptin and NO in different physiological processes.

In vitro effect of leptin on human cardiac contractility

Leptin, a hormone produced by adipose tissue, has been linked to many regulatory pathways. Its role in the complex relationship between obesity and CVD is not yet clear. The aim of the present study was to evaluate whether leptin interferes directly with cardiac function regulation, altering its contractile force character, and hence contributing to different pathological processes. Muscle samples were obtained from human atrial myocardium. Each trial included two samples from the same patient. They were simultaneously electrically stimulated under sustained perfusion to perform isometric contractions. One sample was treated with a high concentration of human recombinant leptin (1 µg/ml). The other was treated with placebo and served as a control. The exhibited contraction forces (CF) and the contraction duration (CD) after 20 min of treatment were normalised by dividing them by the values before the treatment and reported as a percentage. A total of ten successful trials were conducted. Exposure to leptin did not yield a statistically significant variation in both CF and CF. In the treatment group, CF% measured 108 (95 % CI 91, 125) % and CD% measured 95 (95 % CI 90, 101) % after 20 min. In the control group, CF% measured 105 (90 % CI 84, 126) % and CD% measured 92 (95 % CI 80, 105) % after 20 min. We concluded that leptin does not alter the contractile character of human atrial tissues, even in supraphysiological dosage. These results suggest that leptin does not play a role in short-term cardiac regulation.

Left ventricular diastolic dysfunction without left ventricular hypertrophy in obese children and adolescents: a Tissue Doppler Imaging and Cardiac Troponin I Study

BACKGROUND

Obesity increases the risk for various cardiovascular problems. Increase in body mass index is often an independent risk factor for the development of elevated blood pressure and clustering of various cardiovascular risk factors.

OBJECTIVE

To determine early markers of left ventricular affection in obese patients before the appearance of left ventricular hypertrophy.

METHODS

In this cross-sectional study, we evaluated 42 obese patients and 30 healthy controls. Their ages ranged from 6 to 19 years. Studied children were subjected to anthropometric, lipid profile, and serum Troponin I level measurements. Echocardiographic evaluation performed to assess the left ventricle included left ventricular dimension measurement using motion-mode echocardiography, based on which patients with left ventricular hypertrophy (10 patients) were eliminated, as well as conventional and tissue Doppler imaging.

RESULTS

Tissue Doppler findings in the study groups showed that the ratio of transmitral early diastolic filling velocity to septal peak early diastolic myocardial velocity (E/e') was significantly higher in cases compared with controls [6.9±1.4 versus 9.0±1.6, p (Pearson's coefficient)=0.001, respectively]. The level of cardiac troponin I was significantly higher in cases compared with controls [0.14±0.39 ng/ml versus 0.01±0.01 ng/ml, p (Pearson's coefficient)=0.047, respectively] and there was a significant correlation between troponin I and transmitral early diastolic filling velocity to septal peak early diastolic myocardial velocity ratio (E/e') [R (correlation coefficient)=0.6].

CONCLUSION

Tissue Doppler Imaging and Troponin I evaluation proved useful tools to detect early affection of the left ventricle in obese patients even in the absence of left ventricular hypertrophy.

Sleeve Gastrectomy Decreases Body Weight, Whole-Body Adiposity, and Blood Pressure Even in Aged Diet-Induced Obese Rats

BACKGROUND

Aging and obesity are two conditions associated with increased risk of cardiovascular disease. Our aim was to analyze whether an advanced age affects the beneficial effects of sleeve gastrectomy on weight loss and blood pressure in an experimental model of diet-induced obesity (DIO).

METHODS

Young (6-month-old) and old (18-month-old) male Wistar DIO rats (n = 101) were subjected to surgical (sham operation and sleeve gastrectomy) or dietary interventions (pair-fed to the amount of food eaten by sleeve gastrectomized animals). Systolic (SBP), diastolic (DBP), and mean (MBP) blood pressure values and heart rate (HR) were recorded in conscious, resting animals by non-invasive tail-cuff plethysmography before and 4 weeks after surgical or dietary interventions.

RESULTS

Aging was associated with higher (P < 0.05) body weight and subcutaneous and perirenal fat mass as well as mild cardiac hypertrophy. Sleeve gastrectomy induced a reduction in body weight, whole-body adiposity, and serum total ghrelin in both young and old DIO rats. The younger group achieved a higher excess weight loss than the older group (164 ± 60 vs. 82 ± 17 %, P < 0.05). A significant (P < 0.05) decrease in insulin resistance, SBP, DBP, MBP, and HR without changes in heart weight was observed after sleeve gastrectomy independently of age.

CONCLUSION

Our results provide evidence for the effectiveness of sleeve gastrectomy without increased operative risk in body weight and blood pressure reduction even in aged animals via endocrine changes that go beyond the mere caloric restriction.

C1q/tumor necrosis factor-related protein-3 enhances the contractility of cardiomyocyte by increasing calcium sensitivity

C1q/tumor necrosis factor-related protein-3 (CTRP3) is an adipokine that protects against myocardial infarction-induced cardiac dysfunction through its pro-angiogenic, anti-apoptotic, and anti-fibrotic effects. However, whether CTRP3 can directly affect the systolic and diastolic function of cardiomyocytes remains unknown. Adult rat cardiomyocytes were isolated and loaded with Fura-2AM. The contraction and Ca²⁺ transient data was collected and analyzed by IonOptix system. 1 and 2μg/ml CTRP3 significantly increased the contraction of cardiomyocytes. However, CTRP3 did not alter the diastolic Ca²⁺ content, systolic Ca²⁺ content, Ca²⁺ transient amplitude, and L-type Ca²⁺ channel current. To reveal whether CTRP3 affects the Ca²⁺ sensitivity of cardiomyocytes, the typical phase-plane diagrams of sarcomere length vs. Fura-2 ratio was performed. We observed a left-ward shifting of the late relaxation trajectory after CTRP3 perfusion, as quantified by decreased Ca²⁺ content at 50% sarcomere relaxation, and increased mean gradient (μm/Fura-2 ratio) during 500-600ms (-0.163 vs. -0.279), 500-700ms (-0.159 vs. -0.248), and 500-800ms (-0.148 vs. -0.243). Consistently, the phosphorylation level of cardiac troponin I at Ser23/24 was reduced by CTRP3, which could be eliminated by preincubation of okadaic acid, a type 2A protein phosphatase inhibitor. In summary, CTRP3 increases the contraction of cardiomyocytes by increasing the myofilament Ca²⁺ sensitivity. CTRP3 might be a potential endogenous Ca²⁺ sensitizer that modulates the contractility of cardiomyocytes.

Myofilament function and body mass index

Body mass is reported to influence myocardial performance. Recent studies have emphasised the importance of negative inotropic adipocyte-derived factors and their impact on cardiac contractile function. However, the underlying mechanisms remain unclear. We aimed to determine whether body mass impacts cardiac force development on the level of the contractile apparatus. We examined the influence of body mass index (BMI) (3 groups: group I >25, group II 25-30, group III >30) on the myocardial performance of skinned muscle fibres. Right atrial tissue preparations of 70 patients undergoing aortocoronary bypass operation (CABG, 48 patients, group a) and aortic valve replacement (AVR, 22 patients, group b) were obtained. The fibres were exposed to a gradual increase in the calcium concentration, and the force values were recorded. The statistical analysis was performed using Pearson's correlation (P<0.05 significant). A BMI >30 (group III) was associated with less force (mean force 1.58±0.1 mN, P=0.02, max force 2.24±0.17 mN, P=0.02 vs. group II (mean force 1.8±0.3 mN, P=0.04, max force 2.59±0.2 mN, P=0.03) and group I (mean force 1.8±0.1 mN, P=0,03, max force 2.62±0.3 mN, P=0.03). Dividing the groups in the post-surgical procedure, the impact of BMI on force development in group III was more intense in the CABG group compared to the AVR group: 2.0±0.2 mN vs. 2.4±0.1 mN, P=0.04. In accordance with the literature, a BMI >30 is associated with reduced force capacities. Additionally, the underlying cardiac disease may aggravate the impact of weight on cardiac force. Further studies are needed to evaluate the clinical relevance of this experimental observation and the potential consequences for the treatment of cardiac function.

High plasma leptin levels are associated with impaired diastolic function in patients with coronary artery disease

BACKGROUND AND AIMS

Obese subjects have elevated leptin levels, which have been associated with increased risk of cardiovascular events. Because leptin has direct cellular effects on various tissues, we tested the hypothesis that leptin levels are associated with cardiac structure or function in patients with coronary artery disease (CAD).

METHODS AND RESULTS

The study population consisted of 1 601 CAD patients, of whom 42% had type 2 diabetes mellitus. Plasma leptin was measured in fasted state and an echocardiography performed. Leptin levels were not related to LV dimensions or LV ejection fraction (NS for all), but higher leptin levels were associated with elevated E/E' (9.43 vs. 11.94 in the lowest and the highest leptin quartile, respectively; p=0.018 for trend). Correspondingly, a decreasing trend was observed in E/A (1.15 vs. 1.06; p=0.037). These associations were independent of obesity and other relevant confounding variables.

CONCLUSION

We conclude that elevated plasma leptin levels are associated with impaired left ventricular diastolic function in patients with CAD independently of obesity and other confounding variables. Leptin may be one of the mechanistic links explaining the development of congestive heart failure in obese subjects.

Thymosin β4 Prevents Angiotensin II-Induced Cardiomyocyte Growth by Regulating Wnt/WISP Signaling

Thymosin beta-4 (Tβ4) is a ubiquitous protein with many properties relating to cell proliferation and differentiation that promotes wound healing and modulates inflammatory mediators. However, the role of Tβ4 in cardiomyocyte hypertrophy is currently unknown. The purpose of this study was to determine the cardio-protective effect of Tβ4 in angiotensin II (Ang II)-induced cardiomyocyte growth. Neonatal rat ventricular cardiomyocytes (NRVM) were pretreated with Tβ4 followed by Ang II stimulation. Cell size, hypertrophy marker gene expression and Wnt signaling components, β-catenin, and Wnt-induced secreted protein-1 (WISP-1) were evaluated by quantitative real-time PCR, Western blotting and fluorescent microscopy. Pre-treatment of Tβ4 resulted in reduction of cell size, hypertrophy marker genes and Wnt-associated gene expression, and protein levels; induced by Ang II in cardiomyocyte. WISP-1 was overexpressed in NRVM and, the effect of Tβ4 in Ang II-induced cardiomyocyte growth was evaluated. WISP-1 overexpression promoted cardiomyocytes growth and was reversed by pretreatment with Tβ4. This is the first report which demonstrates that Tβ4 targets Wnt/WISP-1 to protect Ang II-induced cardiomyocyte growth. J. Cell. Physiol. 231: 1737-1744, 2016. © 2015 Wiley Periodicals, Inc.

CTRP3 attenuates post-infarct cardiac fibrosis by targeting Smad3 activation and inhibiting myofibroblast differentiation

C1q/tumor necrosis factor-related protein-3 (CTRP3) is a novel adipokine with modulation effects on metabolism, inflammation, and cardiovascular system. This study aimed to investigate the effect of CTRP3 on cardiac fibrosis and its underlying mechanism. The myocardial expression of CTRP3 was significantly decreased after myocardial infarction (MI). Adenovirus-delivered CTRP3 supplement attenuated myocardial hypertrophy, improved cardiac function, inhibited interstitial fibrosis, and decreased the number of myofibroblasts post-MI. In cultured adult rat cardiac fibroblasts (CFs), CTRP3 attenuated cell proliferation; migration; and the expression of connective tissue growth factor, collagen I, and collagen III induced by transforming growth factor (TGF)-β1. Moreover, CTRP3 inhibited whereas CTRP3 small interfering RNA (siRNA) facilitated the expression of α-SMA and profibrotic molecules induced by TGF-β1. CTRP3 also attenuated TGF-β1-induced Smad3 phosphorylation, nuclear translocation, and interaction with p300. CTRP3 increased the phosphorylation of AMP-activated protein kinase (AMPK) and Akt in both rat hearts and CFs. Adenine 9-β-D-arabinofuranoside (AraA), an AMPK inhibitor, abolished the protective effect of CTRP3 against TGF-β1-induced profibrotic response and Smad3 activation. Taken together, CTRP3 attenuates cardiac fibrosis by inhibiting myofibroblast differentiation and the subsequent extracellular matrix production. AMPK is required for the anti-fibrotic effect of CTRP3 through targeting Smad3 activation and inhibiting myofibroblast differentiation.

KEY MESSAGE

CTRP3 alleviates cardiac fibrosis in a rat post-MI model and in cardiac fibroblasts. CTRP3 inhibits fibroblast-to-myofibroblast differentiation. CTRP3 exerts anti-fibrotic effect through targeting Smad3 activation. AMPK mediates the anti-fibrotic effect of CTRP3 by inhibition of Smad3 activation.

Leptin suppresses non-apoptotic cell death in ischemic rat cardiomyocytes by reduction of iPLA(2) activity

Caspase-independent, non-apoptotic cell death is an important therapeutic target in myocardial ischemia. Leptin, an adipose-derived hormone, is known to exhibit cytoprotective effects on the ischemic heart, but the mechanisms are poorly understood. In this research, we found that pretreatment of leptin strongly suppressed ischemic-augmented nuclear shrinkage and non-apoptotic cell death on cardiomyocytes. Leptin was also shown to significantly inhibit the activity of iPLA2, which is considered to play crucial roles in non-apoptotic cell death, resulting in effective prevention of ischemia-induced myocyte death. These findings provide the first evidence of a protective mechanism of leptin against ischemia-induced non-apoptotic cardiomyocyte death.

C1q/tumor necrosis factor-related protein-6 attenuates post-infarct cardiac fibrosis by targeting RhoA/MRTF-A pathway and inhibiting myofibroblast differentiation

C1q/tumor necrosis factor-related protein-6 (CTRP6) is a newly identified adiponectin paralog with modulation effects on metabolism and inflammation. However, the cardiovascular function of CTRP6 remains unknown. This study aimed to determine its role in cardiac fibrosis and explore the possible mechanism. Myocardial infarction (MI) was induced by left anterior descending coronary artery ligation in rats. CTRP6 was mainly expressed in the cytoplasm of adult rat cardiomyocytes and significantly decreased in the border and infarct zones post-MI. Adenovirus-mediated CTRP6 delivery improved cardiac function, attenuated cardiac hypertrophy, alleviated cardiac fibrosis, and inhibited myofibroblast differentiation as well as the expression of collagen I, collagen III, and connective tissue growth factor post-MI. In cultured adult rat cardiac fibroblasts (CFs), exogenous or cardiomyocyte-secreted CTRP6 inhibited, whereas knockdown of CTRP6 facilitated transforming growth factor-β1 (TGF-β1)-induced expression of α-smooth muscle actin, smooth muscle 22α, and profibrotic molecules. CTRP6 had no effect on CFs proliferation but attenuated CFs migration induced by TGF-β1. CTRP6 increased the phosphorylation of AMP-activated protein kinase (AMPK) and Akt in CFs and post-MI hearts. Pretreatment with adenine 9-β-D-arabinofuranoside (AraA), an AMPK inhibitor, or LY294002, a phosphatidylinositol-3-kinase (PI3 K) inhibitor, abolished the protective effect of CTRP6 on TGF-β1-induced profibrotic response. Furthermore, CTRP6 had no effect on TGF-β1-induced Smad3 phosphorylation and nuclear translocation, whereas significantly decreased TGF-β1-induced RhoA activation and myocardin-related transcription factor-A (MRTF-A) nuclear translocation, and these effects were blocked by AMPK or Akt inhibition. In conclusion, CTRP6 attenuates cardiac fibrosis via inhibiting myofibroblast differentiation. AMPK and Akt activation are responsible for the CTRP6-mediated anti-fibrotic effect by targeting RhoA/MRTF-A pathway.

20 years of leptin: Role of leptin in cardiomyocyte physiology and physiopathology

Since the discovery of leptin in 1994 by Zhang et al., there have been a number of reports showing its implication in the development of a wide range of cardiovascular diseases. However, there exists some controversy about how leptin can induce or preserve cardiovascular function, as different authors have found contradictory results about leptin beneficial or detrimental effects in leptin deficient/resistant murine models and in wild type tissue and cardiomyocytes. Here, we will focus on the main discoveries about the leptin functions at cardiac level within the last two decades, focusing on its role in cardiac metabolism, remodeling and contractile function.

Cardiac NO signalling in the metabolic syndrome

It is well documented that metabolic syndrome (i.e. a group of risk factors, such as abdominal obesity, elevated blood pressure, elevated fasting plasma glucose, high serum triglycerides and low cholesterol level in high-density lipoprotein), which raises the risk for heart disease and diabetes, is associated with increased reactive oxygen and nitrogen species (ROS/RNS) generation. ROS/RNS can modulate cardiac NO signalling and trigger various adaptive changes in NOS and antioxidant enzyme expressions/activities. While initially these changes may represent protective mechanisms in metabolic syndrome, later with more prolonged oxidative, nitrosative and nitrative stress, these are often exhausted, eventually favouring myocardial RNS generation and decreased NO bioavailability. The increased oxidative and nitrative stress also impairs the NO-soluble guanylate cyclase (sGC) signalling pathway, limiting the ability of NO to exert its fundamental signalling roles in the heart. Enhanced ROS/RNS generation in the presence of risk factors also facilitates activation of redox-dependent transcriptional factors such as NF-κB, promoting myocardial expression of various pro-inflammatory mediators, and eventually the development of cardiac dysfunction and remodelling. While the dysregulation of NO signalling may interfere with the therapeutic efficacy of conventional drugs used in the management of metabolic syndrome, the modulation of NO signalling may also be responsible for the therapeutic benefits of already proven or recently developed treatment approaches, such as ACE inhibitors, certain β-blockers, and sGC activators. Better understanding of the above-mentioned pathological processes may ultimately lead to more successful therapeutic approaches to overcome metabolic syndrome and its pathological consequences in cardiac NO signalling.

Adipokines, vascular wall, and cardiovascular disease: a focused overview of the role of adipokines in the pathophysiology of cardiovascular disease

Epidemiological evidence has shown that abdominal obesity is closely associated with the development of cardiovascular (CV) disease, suggesting that it might be considered as an independent CV risk factor. However, the pathophysiological mechanisms responsible for the association between these 2 clinical entities remain largely unknown. Adipocytes are considered able to produce and secrete chemical mediators known as "adipokines" that may exert several biological actions, including those on heart and vessels. Of interest, a different adipokine profile can be observed in the plasma of patients with obesity or metabolic syndrome compared with healthy controls. We consider the main adipokines, focusing on their effects on the vascular wall and analyzing their role in CV pathophysiology.

Mechanisms of adverse cardiometabolic consequences of obesity

Obesity is an epidemic that threatens the health of millions of people worldwide and is a major risk factor for cardiovascular diseases, hypertension, diabetes, and dyslipidemia. There are multiple and complex mechanisms to explain how obesity can cause cardiovascular disease. In recent years, studies have shown some limitations in the way we currently define obesity and assess adiposity. This review focuses on the mechanisms involved in the cardiometabolic consequences of obesity and on the relationship between obesity and cardiovascular comorbidities, and provides a brief review of the latest studies focused on normal weight obesity and the obesity paradox.

Angiotensin II and the ERK pathway mediate the induction of leptin by mechanical cyclic stretch in cultured rat neonatal cardiomyocytes

Mechanical cyclic stretch of cardiomyocytes causes cardiac hypertrophy through cardiac-restricted gene expression. Leptin induces cardiomyocyte hypertrophy in response to myocardial stress. In the present study, we evaluated the expression of leptin under cyclic stretch and its role in regulating genetic transcription in cardiomyocytes. Cultured rat neonatal cardiomyocytes were subjected to cyclic stretch, and the expression levels of leptin, ROS (reactive oxygen species) and AngII (angiotensin II) were evaluated. Signal transduction inhibitors were used to identify the pathway of leptin expression. EMSAs were used to identify the binding of leptin/STAT3 (signal transducer and activator of transcription 3) and luciferase assays were used to identify the transcription of leptin in cardiomyocytes. The study also used an in vivo model of AV (aortocaval) shunt in rats to investigate leptin, ROS and AngII expression. Leptin and leptin receptor levels increased after cyclic stretch with the earlier expression of AngII and ROS. Leptin expression was suppressed by AngII receptor blockers, an ROS scavenger [NAC (N-acetylcysteine)], an ERK (extracellular-signal-regulated kinase) pathway inhibitor (PD98059) and ERK siRNA. Binding of leptin/STAT3 was identified by EMSAs, and luciferase assays confirmed the transcription of leptin in neonatal cardiomyocytes after cyclic stretch. Increased MHC (myosin heavy chain) expression and [3H]-proline incorporation in cardiomyocytes was detected after cyclic stretch, which were inhibited by leptin siRNA and NAC. The in vivo model of AV shunt also demonstrated increased levels of plasma and myocardial leptin, ROS and AngII expression after cyclic stretch. Mechanical cyclic stretch in cardiomyocytes increased leptin expression mediated by the induction of AngII, ROS and the ERK pathway to cause cardiomyocyte hypertrophy. Myocardial hypertrophy can be identified by increased transcriptional activity and an enhanced hypertrophic phenotype of cardiomyocytes.

Lungs, bone marrow, and adipose tissue. A network approach to the pathobiology of chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) often suffer other concomitant disorders, such as cardiovascular diseases and metabolic disorders, that influence significantly (and independently of lung function) their health status and prognosis. Thus, COPD is not a single organ condition, and disturbances of a complex network of interorgan connected responses occur and modulate the natural history of the disease. Here, we propose a novel hypothesis that considers a vascularly connected network with (1) the lungs as the main external sensor of the system and a major source of "danger signals"; (2) the endothelium as an internal sensor of the system (also a potential target tissue); and (3) two key responding elements, bone marrow and adipose tissue, which produce both inflammatory and repair signals. According to the model, the development of COPD, and associated multimorbidities (here we focus on cardiovascular disease as an important example), depend on the manner in which the vascular connected network responds, adapts, or fails to adapt (dictated by the genetic and epigenetic background of the individual) to the inhalation of particles and gases, mainly in cigarette smoke. The caveats and limitations of the hypothesis, as well as the experimental and clinical research needed to test and explore the proposed model, are also briefly discussed.

Increased regional deformation of the left ventricle in normal children with increased body mass index: implications for future cardiovascular health

The prevalence of obesity continues to increase in the developing world. The effects of obesity on the cardiovascular system include changes in systolic and diastolic function. More recently obesity has been linked with impairment of longitudinal myocardial deformation properties in children. We sought to determine the effect of increased body mass index (BMI) on cardiac deformation in a group of children taking part in the population-based Southampton Women's Survey to detect early cardiovascular changes associated with increasing BMI before established obesity. Sixty-eight children at a mean age of 9.4 years old underwent assessment of longitudinal myocardial deformation in the basal septal segment of the left ventricle (LV) using two-dimensional speckle tracking echocardiography. Parameters of afterload and preload, which may influence deformation, were determined from cardiac magnetic resonance imaging. BMI was determined from the child's height and weight at the time of echocardiogram. Greater pediatric BMI was associated with greater longitudinal myocardial deformation or strain in the basal septal segment of the LV (β = 1.6, p < 0.001); however, this was not related to contractility or strain rate in this part of the heart (β = 0.001, p = 0.92). The end-diastolic volume of the LV increased with increasing BMI (β = 3.93, p < 0.01). In young children, regional deformation in the LV increases with increasing BMI, whilst normal contractility is maintained. This effect may be explained by the increased preload of the LV associated with increased somatic growth. The long-term implications of this altered physiology need to be followed-up.

Leptin modulates electrophysiological characteristics and isoproterenol-induced arrhythmogenesis in atrial myocytes

Background

Obesity is an important risk factor for atrial fibrillation (AF). Leptin is an important adipokine. However, it is not clear whether leptin directly modulates the electrophysiological characteristics of atrial myocytes.

Results

Whole cell patch clamp and indo-1 fluorescence were used to record the action potentials (APs) and ionic currents in isolated rabbit left atrial (LA) myocytes incubated with and without (control) leptin (100 nM) for 1 h to investigate the role of leptin on atrial electrophysiology. Leptin-treated LA myocytes (n = 19) had longer 20% of AP duration (28 ± 3 vs. 21 ± 2 ms, p < 0.05), but similar 50% of AP duration (51 ± 4 vs. 50 ± 3 ms, p > 0.05), and 90% of AP duration (89 ± 5 vs. 94 ± 4 ms, p > 0.05), as compared to the control (n = 22). In the presence of isoproterenol (10 nM), leptin-treated LA myocytes (n = 21) showed a lower incidence (19% vs. 54.2%, p < 0.05) of delayed afterdepolarization (DAD) than the control (n = 24). Leptin-treated LA myocytes showed a larger sodium current, but a smaller ultra-rapid delayed rectifier potassium current, and sodium-calcium exchanger current than the control. Leptin-treated and control LA myocytes exhibited a similar late sodium current, inward rectifier potassium current, transient outward current and L-type calcium current. In addition, the leptin-treated LA myocytes (n = 38) exhibited a smaller intracellular Ca²⁺ transient (0.21 ± 0.01 vs. 0.26 ± 0.01 R410/485, p < 0.05) and sarcoplasmic reticulum Ca²⁺ content (0.35 ± 0.02 vs. 0.43 ± 0.03 R410/485, p < 0.05) than the control LA myocytes (n = 42).

Conclusions

Leptin regulates the LA electrophysiological characteristics and attenuates isoproterenol-induced arrhythmogenesis.

Neuroendocrine and cardiac metabolic dysfunction and NLRP3 inflammasome activation in adipose tissue and pancreas following chronic spinal cord injury in the mouse

CVD (cardiovascular disease) represents a leading cause of mortality in chronic SCI (spinal cord injury). Several component risk factors are observed in SCI; however, the underlying mechanisms that contribute to these risks have not been defined. Central and peripheral chronic inflammation is associated with metabolic dysfunction and CVD, including adipokine regulation of neuroendocrine and cardiac function and inflammatory processes initiated by the innate immune response. We use female C57 Bl/6 mice to examine neuroendocrine, cardiac, adipose and pancreatic signaling related to inflammation and metabolic dysfunction in response to experimentally induced chronic SCI. Using immuno-histochemical, -precipitation, and -blotting analysis, we show decreased POMC (proopiomelanocortin) and increased NPY (neuropeptide-Y) expression in the hypothalamic ARC (arcuate nucleus) and PVN (paraventricular nucleus), 1-month post-SCI. Long-form leptin receptor (Ob-Rb), JAK2 (Janus kinase)/STAT3 (signal transducer and activator of transcription 3)/p38 and RhoA/ROCK (Rho-associated kinase) signaling is significantly increased in the heart tissue post-SCI, and we observe the formation and activation of the NLRP3 (NOD-like receptor family, pyrin domain containing 3) inflammasome in VAT (visceral adipose tissue) and pancreas post-SCI. These data demonstrate neuroendocrine signaling peptide alterations, associated with central inflammation and metabolic dysfunction post-SCI, and provide evidence for the peripheral activation of signaling mechanisms involved in cardiac, VAT and pancreatic inflammation and metabolic dysfunction post-SCI. Further understanding of biological mechanisms contributing to SCI-related inflammatory processes and metabolic dysfunction associated with CVD pathology may help to direct therapeutic and rehabilitation countermeasures.

Leptin expression affects metabolic rate in zebrafish embryos (D. rerio)

We used antisense morpholino oligonucleotide technology to knockdown leptin-(A) gene expression in developing zebrafish embryos and measured its effects on metabolic rate and cardiovascular function. Using two indicators of metabolic rate, oxygen consumption was significantly lower in leptin morphants early in development [<48 hours post-fertilization (hpf)], while acid production was significantly lower in morphants later in development (>48 hpf). Oxygen utilization rates in <48 hpf embryos and acid production in 72 hpf embryos could be rescued to that of wildtype embryos by recombinant leptin coinjected with antisense morpholino. Leptin is established to influence metabolic rate in mammals, and these data suggest leptin signaling also influences metabolic rate in fishes.

Cachexia in chronic heart failure: endocrine determinants and treatment perspectives

It is well documented in the current literature that chronic heart failure is often associated with cachexia, defined as involuntary weight loss of 5 % in 12 month or less. Clinical studies unraveled that the presence of cachexia decreases significantly mean survival of the patient. At the molecular level mainly myofibrillar proteins are degraded, although a reduced protein synthesis may also contribute to the loss of muscle mass. Endocrine factors clearly regulate muscle mass and function by influencing the normally precisely controlled balance between protein breakdown and protein synthesis The aim of the present article is to review the knowledge in the field with respect to the role of endocrine factors for the regulation of cachexia in patients with CHF and deduce treatment perspectives.

Role of adipokines in cardiovascular disease

The discovery of leptin in 1994 sparked dramatic new interest in the study of white adipose tissue. It is now recognised to be a metabolically active endocrine organ, producing important chemical messengers - adipokines and cytokines (adipocytokines). The search for new adipocytokines or adipokines gained added fervour with the prospect of the reconciliation between cardiovascular diseases (CVDs), obesity and metabolic syndrome. The role these new chemical messengers play in inflammation, satiety, metabolism and cardiac function has paved the way for new research and theories examining the effects they have on (in this case) CVD. Adipokines are involved in a 'good-bad', yin-yang homoeostatic balance whereby there are substantial benefits: cardioprotection, promoting endothelial function, angiogenesis and reducing hypertension, atherosclerosis and inflammation. The flip side may show contrasting, detrimental effects in aggravating these cardiac parameters.

Pressure mediated hypertrophy and mechanical stretch up-regulate expression of the long form of leptin receptor (ob-Rb) in rat cardiac myocytes

Background

Hyperleptinemia is known to participate in cardiac hypertrophy and hypertension, but the relationship between pressure overload and leptin is poorly understood. We therefore examined the expression of leptin (ob) and the leptin receptor (ob-R) in the pressure-overloaded rat heart. We also examined gene expressions in culture cardiac myocytes to clarify which hypertension-related stimulus induces these genes.

Results

Pressure overload was produced by ligation of the rat abdominal aorta, and ob and ob-R isoform mRNAs were measured using a real-time polymerase chain reaction (PCR). We also measured these gene expressions in neonatal rat cardiac myocytes treated with angiotensin II (ANGII), endothelin-1 (ET-1), or cyclic mechanical stretch. Leptin and the long form of the leptin receptor (ob-Rb) gene were significantly increased 4 weeks after banding, but expression of the short form of the leptin receptor (ob-Ra) was unchanged. ob-Rb protein expression was also detected by immunohistochemistry in hypertrophied cardiac myocytes after banding. Meanwhile, plasma leptin concentrations were not different between the control and banding groups. In cultured myocytes, ANGII and ET-1 increased only ob mRNA expression. However, mechanical stretch activated both ob and ob-Rb mRNA expression in a time-dependent manner, but ob-Ra mRNA was unchanged by any stress.

Conclusions

We first demonstrated that both pressure mediated hypertrophy and mechanical stretch up-regulate ob-Rb gene expression in heart and cardiac myocytes, which are thought to be important for leptin action in cardiac myocytes. These results suggest a new local mechanism by which leptin affects cardiac remodeling in pressure-overloaded hearts.

Leptin and Nitric Oxide Production in Normotensive and Hypertensive Men

OBJECTIVE

Recent findings have shown that leptin, the product of the obesity gene, may actively participate in the regulation of blood pressure and other cardiovascular functions through the nitric oxide (NO)-dependent mechanism.

RESEARCH METHODS AND PROCEDURES

In this study, to test the hypothesis that leptin regulation of NO metabolism is impaired in hypertension, we examined the possible relationship between circulating leptin and plasma NO metabolite level in normotensive (NT) and hypertensive (HT) men.

RESULTS

There were significant correlations between circulating leptin and BMI in both the NT and HT groups (NT: r = 0.64, n = 26, p < 0.01; HT: r = 0.59, n = 22, p < 0.01). The concentration of circulating leptin was similar between the NT and HT men, although the plasma NO metabolite level (nitrite and nitrate) was significantly reduced in the HT men compared with the NT men (NT: 51.0 +/- 4.9 microM, n = 26; HT: 37.1 +/- 2.5 microM, n = 22, p < 0.05). The circulating leptin was significantly correlated with the plasma NO metabolite level in the overall analysis of the NT and HT men (r = 0.35, n = 48, p < 0.05). When the analysis of the correlation for the NT and HT men was performed separately, there was a significant correlation between circulating leptin and plasma NO metabolites in the NT men (r = 0.45, n = 26, p < 0.05) but not in the HT men (r = 0.15, n = 22). The results of this study are consistent with the hypothesis that leptin-related metabolism of NO might be altered in HT men.

Effects of Chronic Nitric Oxide Inhibition on the Renal Excretory Response to Leptin

OBJECTIVE

Previous investigations have demonstrated that leptin promotes natriuresis with a renal tubular effect. However, the mechanisms involved in this response are unclear. The present study was designed to examine the hypothesis that the natriuretic response to leptin in normotensive Sprague-Dawley rats is regulated by nitric oxide (NO).

RESEARCH METHODS AND PROCEDURES

The hemodynamic and renal excretory effects of intravenous bolus administration of pharmacological doses of synthetic murine leptin were examined in groups of control Sprague-Dawley rats (n = 8), Sprague-Dawley rats treated for 4 days with the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) (n = 8), and Sprague-Dawley rats treated for 4 days with L-NAME followed by acute treatment with sodium nitroprusside (n = 8).

RESULTS

In the control group (n = 8), an intravenous bolus of leptin, 400 microg/kg body weight, increased urinary sodium excretion 4- to 6-fold. In the Sprague-Dawley rats chronically administered l-NAME (n = 8), an intravenous bolus of 400 microg/kg of leptin did not increase sodium excretion. Acute sodium nitroprusside infusion to Sprague-Dawley rats chronically treated with L-NAME (n = 8) was associated with partial restoration of the sodium excretory response to leptin administration.

DISCUSSION

Collectively, these results are interpreted to suggest that the natriuretic and diuretic responses to leptin observed in the Sprague-Dawley rat require a functional NO system.

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.

The obesity-related peptide leptin sensitizes cardiac mitochondria to calcium-induced permeability transition pore opening and apoptosis

The obesity-related 16 kDa peptide leptin is synthesized primarily in white adipocytes although its production has been reported in other tissues including the heart. There is emerging evidence that leptin may contribute to cardiac pathology especially that related to myocardial remodelling and heart failure. In view of the importance of mitochondria to these processes, the goal of the present study is to determine the effect of leptin on mitochondria permeability transition pore opening and the potential consequence in terms of development of apoptosis. Experiments were performed using neonatal rat ventricular myocytes exposed to 3.1 nM (50 ng/ml) leptin for 24 hours. Mitochondrial transition pore opening was analyzed as the capacity of mitochondria to retain the dye calcein-AM in presence of 200 µM CaCl2. Leptin significantly increased pore opening although the effect was markedly more pronounced in digitonin-permeabilized myocytes in the presence of calcium with both effects prevented by the transition pore inhibitor sanglifehrin A. These effects were associated with increased apoptosis as evidenced by increased TUNEL staining and caspase 3 activity, both of which were prevented by the transition pore inhibitor sanglifehrin A. Leptin enhanced Stat3 activation whereas a Stat 3 inhibitor peptide prevented leptin-induced mitochondrial transition pore opening as well as the hypertrophic and pro-apoptotic effects of the peptide. Inhibition of the RhoA/ROCK pathway prevented the hypertrophic response to leptin but had no effect on increased pore opening following leptin administration. We conclude that leptin can enhance calcium-mediated, Stat3-dependent pro-apoptotic effects as a result of increased mitochondrial transition pore opening and independently of its hypertrophic actions. Leptin may therefore contribute to mitochondrial dysfunction and the development of apoptosis in the diseased myocardium particularly under conditions of excessive intracellular calcium accumulation.

Alterations in mouse hypothalamic adipokine gene expression and leptin signaling following chronic spinal cord injury and with advanced age

Chronic spinal cord injury (SCI) results in an accelerated trajectory of several cardiovascular disease (CVD) risk factors and related aging characteristics, however the molecular mechanisms that are activated have not been explored. Adipokines and leptin signaling are known to play a critical role in neuro-endocrine regulation of energy metabolism, and are now implicated in central inflammatory processes associated with CVD. Here, we examine hypothalamic adipokine gene expression and leptin signaling in response to chronic spinal cord injury and with advanced age. We demonstrate significant changes in fasting-induced adipose factor (FIAF), resistin (Rstn), long-form leptin receptor (LepRb) and suppressor of cytokine-3 (SOCS3) gene expression following chronic SCI and with advanced age. LepRb and Jak2/stat3 signaling is significantly decreased and the leptin signaling inhibitor SOCS3 is significantly elevated with chronic SCI and advanced age. In addition, we investigate endoplasmic reticulum (ER) stress and activation of the uncoupled protein response (UPR) as a biological hallmark of leptin resistance. We observe the activation of the ER stress/UPR proteins IRE1, PERK, and eIF2alpha, demonstrating leptin resistance in chronic SCI and with advanced age. These findings provide evidence for adipokine-mediated inflammatory responses and leptin resistance as contributing to neuro-endocrine dysfunction and CVD risk following SCI and with advanced age. Understanding the underlying mechanisms contributing to SCI and age related CVD may provide insight that will help direct specific therapeutic interventions.

Automated image analysis of cardiac myocyte Ca2+ dynamics

Intracellular Ca(2+) dynamics act as a key link between the electrical and mechanical activity of the heart. Here we present a method for high-throughput measurement, automated cell segmentation and signal analysis of Ca(2+) transients in isolated adult ventricular myocytes. In addition to increasing experimental throughput ~10-fold compared to conventional approaches, this approach allows the study of individual cell-cell variability and relationships between Ca(2+) signaling and cell morphology.