Leptin attenuates cardiac apoptosis after chronic ischaemic injury

Therapeutic Efficacy of Interferon-Gamma and Hypoxia-Primed Mesenchymal Stromal Cells and Their Extracellular Vesicles: Underlying Mechanisms and Potentials in Clinical Translation

Multipotent mesenchymal stromal cells (MSCs) hold promises for cell therapy and tissue engineering due to their self-renewal and differentiation abilities, along with immunomodulatory properties and trophic factor secretion. Extracellular vesicles (EVs) from MSCs offer similar therapeutic effects. However, MSCs are heterogeneous and lead to variable outcomes. In vitro priming enhances MSC performance, improving immunomodulation, angiogenesis, proliferation, and tissue regeneration. Various stimuli, such as cytokines, growth factors, and oxygen tension, can prime MSCs. Two classical priming methods, interferon-gamma (IFN-γ) and hypoxia, enhance MSC immunomodulation, although standardized protocols are lacking. This review discusses priming protocols, highlighting the most commonly used concentrations and durations, along with mechanisms and in vivo therapeutics effects of primed MSCs and their EVs. The feasibility of up-scaling their production was also discussed. The review concluded that priming with IFN-γ or hypoxia (alone or in combination with other factors) boosted the immunomodulation capability of MSCs and their EVs, primarily via the JAK/STAT and PI3K/AKT and Leptin/JAK/STAT and TGF-β/Smad signalling pathways, respectively. Incorporating priming in MSC and EV production enables translation into cell-based or cell-free therapies for various disorders.

Prospects of potential adipokines as therapeutic agents in obesity-linked atherogenic dyslipidemia and insulin resistance

BACKGROUND

In normal circumstances, AT secretes anti-inflammatory adipokines (AAKs) which regulates lipid metabolism, insulin sensitivity, vascular hemostasis, and angiogenesis. However, during obesity AT dysfunction occurs and leads to microvascular imbalance and secretes several pro-inflammatory adipokines (PAKs), thereby favoring atherogenic dyslipidemia and insulin resistance. Literature suggests decreased levels of circulating AAKs and increased levels of PAKs in obesity-linked disorders. Importantly, AAKs have been reported to play a vital role in obesity-linked metabolic disorders mainly insulin resistance, type-2 diabetes mellitus and coronary heart diseases. Interestingly, AAKs counteract the microvascular imbalance in AT and exert cardioprotection via several signaling pathways such as PI3-AKT/PKB pathway. Although literature reviews have presented a number of investigations detailing specific pathways involved in obesity-linked disorders, literature concerning AT dysfunction and AAKs remains sketchy. In view of the above, in the present contribution an effort has been made to provide an insight on the AT dysfunction and role of AAKs in modulating the obesity and obesity-linked atherogenesis and insulin resistance.

MAIN BODY

"Obesity-linked insulin resistance", "obesity-linked cardiometabolic disease", "anti-inflammatory adipokines", "pro-inflammatory adipokines", "adipose tissue dysfunction" and "obesity-linked microvascular dysfunction" are the keywords used for searching article. Google scholar, Google, Pubmed and Scopus were used as search engines for the articles.

CONCLUSIONS

This review offers an overview on the pathophysiology of obesity, management of obesity-linked disorders, and areas in need of attention such as novel therapeutic adipokines and their possible future perspectives as therapeutic agents.

Cardiac ischemia modulates white adipose tissue in a depot-specific manner

The incidence of heart failure after myocardial infarction (MI) remains high and the underlying causes are incompletely understood. The crosstalk between heart and adipose tissue and stimulated lipolysis has been identified as potential driver of heart failure. Lipolysis is also activated acutely in response to MI. However, the role in the post-ischemic remodeling process and the contribution of different depots of adipose tissue is unclear. Here, we employ a mouse model of 60 min cardiac ischemia and reperfusion (I/R) to monitor morphology, cellular infiltrates and gene expression of visceral and subcutaneous white adipose tissue depots (VAT and SAT) for up to 28 days post ischemia. We found that in SAT but not VAT, adipocyte size gradually decreased over the course of reperfusion and that these changes were associated with upregulation of UCP1 protein, indicating white adipocyte conversion to the so-called ‘brown-in-white’ phenotype. While this phenomenon is generally associated with beneficial metabolic consequences, its role in the context of MI is unknown. We further measured decreased lipogenesis in SAT together with enhanced infiltration of MAC-2+ macrophages. Finally, quantitative PCR analysis revealed transient downregulation of the adipokines adiponectin, leptin and resistin in SAT. While adiponectin and leptin have been shown to be cardioprotective, the role of resistin after MI needs further investigation. Importantly, all significant changes were identified in SAT, while VAT was largely unaffected by MI. We conclude that targeted interference with lipolysis in SAT may be a promising approach to promote cardiac healing after ischemia.

Leptin Gene Protects Against Cold Stress in Antarctic Toothfish

Leptin is a cytokine-like peptide, predominantly biosynthesized in adipose tissue, which plays an important role in regulating food intake, energy balance and reproduction in mammals. However, how it may have been modified to enable life in the chronic cold is unclear. Here, we identified a leptin-a gene (lepa) in the cold-adapted and neutrally buoyant Antarctic toothfish Dissostichus mawsoni that encodes a polypeptide carrying four α-helices and two cysteine residues forming in-chain disulfide bonds, structures shared by most vertebrate leptins. Quantitative RT-PCR confirmed that mRNA levels of the leptin-a gene of D. mawsoni (DM-lepa) were highest in muscle, followed by kidney and liver; detection levels were low in the gill, brain, intestine, and ovary tissues. Compared with leptin-a genes of fishes living in warmer waters, DM-lepa underwent rapid evolution and was subjected to positive selection. Over-expression of DM-lepa in the zebrafish cell line ZFL resulted in signal accumulation in the cytoplasm and significantly increased cell proliferation both at the normal culture temperature and under cold treatment. DM-lepa over-expression also reduced apoptosis under low-temperature stress and activated the STAT3 signaling pathway, in turn upregulating the anti-apoptotic proteins bcl2l1, bcl2a, myca and mdm2 while downregulating the pro-apoptotic baxa, p53 and caspase-3. These results demonstrate that DM-lepa, through STAT3 signaling, plays a protective role in cold stress by preventing apoptotic damage. Our study reveals a new role of lepa in polar fish.

Hyperleptinemia results in systemic inflammation and the exacerbation of ischemia-reperfusion myocardial injury

Aim

Hyperleptinemia potentiates the effects of many atherogenic factors, such as inflammation, platelet aggregation, migration, hypertrophy, proliferation of vascular smooth muscle cells, and endothelial cell dysfunction. The present study analysed the effects of long-term hyperleptinemia in an in vivo myocardial ischemia-reperfusion model to demonstrate whether the in vivo deleterious effect also affects cardiac structure and function.

Main methods

Rats were subcutaneously administered leptin for 8 days to estimate the involvement of the JAK/STAT pathway. Data from 58 male Wistar rats were included in the final analysis. Myocardial infarction (MI) was modelled by the 30-minute ligation of the main left coronary artery followed by 120-minute reperfusion. Hemodynamic measurements, electrocardiography monitoring, echocardiography, myocardial infarct size and area at risk, blood biochemical parameters, leptin, IL-6, TNF-alpha, FGF-21, and cardiomyocyte morphology were measured. The expression of JAK2, p-JAK2, STAT3, p-STAT3 was assessed by Western Blot analysis. Statistical analyses were performed using IBM SPSS Statistics v.26.

Key findings

Eight-day hyperleptinemia in rats leads to an increase in blood pressure and heart rate, myocardial hypertrophy, impaired LV function, the frequency of ischemic arrhythmias, dyslipidemia, systemic inflammation, and the size of induced myocardial infarction. Significance: The blockade of the JAK/STAT signalling pathway effectively reverses the negative effects of leptin, including increased blood pressure and total cholesterol.

Inflammation in Metabolic Cardiomyopathy

Overlapping pandemics of lifestyle-related diseases pose a substantial threat to cardiovascular health. Apart from coronary artery disease, metabolic disturbances linked to obesity, insulin resistance and diabetes directly compromise myocardial structure and function through independent and shared mechanisms heavily involving inflammatory signals. Accumulating evidence indicates that metabolic dysregulation causes systemic inflammation, which in turn aggravates cardiovascular disease. Indeed, elevated systemic levels of pro-inflammatory cytokines and metabolic substrates induce an inflammatory state in different cardiac cells and lead to subcellular alterations thereby promoting maladaptive myocardial remodeling. At the cellular level, inflammation-induced oxidative stress, mitochondrial dysfunction, impaired calcium handling, and lipotoxicity contribute to cardiomyocyte hypertrophy and dysfunction, extracellular matrix accumulation and microvascular disease. In cardiometabolic patients, myocardial inflammation is maintained by innate immune cell activation mediated by pattern recognition receptors such as Toll-like receptor 4 (TLR4) and downstream activation of the NLRP3 inflammasome and NF-κB-dependent pathways. Chronic low-grade inflammation progressively alters metabolic processes in the heart, leading to a metabolic cardiomyopathy (MC) phenotype and eventually to heart failure with preserved ejection fraction (HFpEF). In accordance with preclinical data, observational studies consistently showed increased inflammatory markers and cardiometabolic features in patients with HFpEF. Future treatment approaches of MC may target inflammatory mediators as they are closely intertwined with cardiac nutrient metabolism. Here, we review current evidence on inflammatory processes involved in the development of MC and provide an overview of nutrient and cytokine-driven pro-inflammatory effects stratified by cell type.

Leptin modulates gene expression in the heart and cardiomyocytes towards mitigating ischemia-induced damage

Leptin, an adipocyte-derived satiety hormone, has been previously linked to cardioprotection. We have shown before that leptin conferred resistance to ischemic damage in the heart in long-lived transgenic αMUPA mice overexpressing leptin compared to the wild type (WT) FVB/N control mice. To better understand the contribution of leptin to the ischemic heart, we measured here the expression of genes encoding leptin and ischemia-related proteins in αMUPA and WT mice in the heart vs adipose tissue after MI. In addition, we investigated gene expression in neonatal rat cardiomyocytes under hypoxia in the absence and presence of exogenously added leptin or a leptin antagonist. We used real time RT-PCR and ELISA or Western blot assays to measure, respectively, mRNA and protein levels. The results have shown that circulating leptin levels and mRNA levels of leptin and heme oxygenase-1 (HO-1) in the heart were elevated in both mouse genotypes after 24 h myocardial infarction (MI), reaching higher values in αMUPA mice. In contrast, leptin gene expression in the adipose tissue was significantly increased only in WT mice, but reaching lower levels compared to the heart. Expression of the proinflammatory genes encoding TNFα and IL-1β was also largely increased after MI in the heart in both mouse types, however reaching considerably lower levels in αMUPA mice indicating a mitigated inflammatory state. In cardiomyocytes, mRNA levels of all aforementioned genes as well as HIF-1α and SOD2 genes were elevated after hypoxia. Pretreatment with exogenous leptin largely reduced the mRNA levels of TNFα and IL-1β after hypoxia, while enhancing expression of all other genes and reducing ROS levels. Pretreating the cells with a leptin antagonist increased solely the levels of leptin mRNA, suggesting a negative regulation of the hormone on the expression of its own gene. Overall, the results have shown that leptin affects expression of genes in cardiomyocytes under hypoxia in a manner that could mitigate inflammation and oxidative stress, suggesting a similar influence by endogenous leptin in αMUPA mice. Furthermore, leptin is likely to function in the ischemic murine heart more effectively in an autocrine compared to paracrine manner. These results suggest that leptin can reduce ischemic damage by modulating gene expression in the heart.

Weight loss normalizes enhanced expression of the oncogene survivin in visceral adipose tissue and blood leukocytes from individuals with obesity

BACKGROUND/OBJECTIVES

Survivin is an oncogene associated with a decrease in apoptosis, an increase in tumor growth, and poor clinical outcome of diverse malignancies. A correlation between obesity, cancer, and survivin is reported in the literature. To date, the impact of weight loss on change in survivin levels is understudied. This study was aimed at: (1) comparing survivin levels in adipose tissue (AT) from lean and obese animal models and evaluating changes after weight loss induced by energy restriction and/or exercise; (2) comparing survivin levels in normal weighted and obese humans and evaluating changes in survivin levels after weight loss induced by a very-low-calorie ketogenic diet (VLCKD) or bariatric surgery in AT and/or blood leukocytes (PBL/PBMCs).

SUBJECTS/METHODS

Survivin expression was evaluated in subcutaneous (SAT) and visceral (VAT) AT derived from animal models of monogenic (Zucker rats) and diet-induced obesity (Sprague Dawley rats and C57BL/6J mice) and after a 4-week weight-loss protocol of energy restriction and/or exercise. Plasma was used to measure the inflammatory status. Survivin expression was also evaluated in PBMCs from patients with obesity and compared with normal weight, in PBLs after VLCKD, and in SAT and/or PBLs after bariatric surgery.

RESULTS

Survivin expression was specifically higher in VAT from obese that lean animals, without differences in SAT. It decreased after weight loss induced by energy restriction and correlated with adiposity and inflammatory markers. In humans, the correlation between being obese and higher levels of survivin was confirmed. In obese subjects, survivin levels were reduced following weight loss after either VLCKD or bariatric surgery. Particularly, a decrease in PBMCs expression (not in SAT one) was found after surgery.

CONCLUSIONS

Weight loss is effective in decreasing survivin levels. Also, PBL/PBMC should be regarded as appropriate mirror of survivin levels in VAT for the identification of an obesity-related protumoral microenvironment.

Mechanisms linking adipose tissue inflammation to cardiac hypertrophy and fibrosis

Adipose tissue is classically recognized as the primary site of lipid storage, but in recent years has garnered appreciation for its broad role as an endocrine organ comprising multiple cell types whose collective secretome, termed as adipokines, is highly interdependent on metabolic homeostasis and inflammatory state. Anatomical location (e.g. visceral, subcutaneous, epicardial etc) and cellular composition of adipose tissue (e.g. white, beige, and brown adipocytes, macrophages etc.) also plays a critical role in determining its response to metabolic state, the resulting secretome, and its potential impact on remote tissues. Compared with other tissues, the heart has an extremely high and constant demand for energy generation, of which most is derived from oxidation of fatty acids. Availability of this fatty acid fuel source is dependent on adipose tissue, but evidence is mounting that adipose tissue plays a much broader role in cardiovascular physiology. In this review, we discuss the impact of the brown, subcutaneous, and visceral white, perivascular (PVAT), and epicardial adipose tissue (EAT) secretome on the development and progression of cardiovascular disease (CVD), with a particular focus on cardiac hypertrophy and fibrosis.

Lactobacillus plantarum And Inulin: Therapeutic Agents to Enhance Cardiac Ob Receptor Expression and Suppress Cardiac Apoptosis in Type 2 Diabetic Rats

BACKGROUND

T2DM may cause increased levels of oxidative stress and cardiac apoptosis through elevated blood glucose. The present study investigated the effects of Lactobacillus plantarum (L. plantarum) as a probiotic strain and inulin as a prebiotic supplement on cardiac oxidative stress and apoptotic markers in type 2 diabetes mellitus (T2DM) rats.

METHODS

A high-fat diet and a low dose of streptozotocin were used to induce type 2 diabetes. The rats were divided into six groups which were supplemented with L. plantarum, inulin, or their combination for 8 weeks.

RESULTS

The results showed improved activity of cardiac antioxidant parameters including total antioxidant capacity (TAC), superoxide dismutase (SOD), and glutathione peroxidase (GPx) (P < 0.001, P < 0.01, and P < 0.01, respectively) and decreased level of cardiac malondialdehyde (MDA) concentration (P < 0.05). These changes were accompanied with increased protein expression of cardiac obesity receptor (Ob-R) (P = 0.05) and reduced apoptotic markers such as tumor necrosis factor-alpha (TNF-α), Fas ligand (FasL), and caspase proteins (P < 0.001, P = 0.003, and P < 0.01, respectively) in T2DM rats after concurrent L. plantarum and inulin supplementation. Moreover, a remarkable correlation of cardiac Ob-R and oxidative stress parameters with cardiac apoptotic markers was observed (P < 0.01).

CONCLUSION

The concurrent use of L. plantarum and inulin seems to be beneficial, as they can lead to decreased heart complications of T2DM via reducing cardiac apoptotic markers.

Systems Network Genomic Analysis Reveals Cardioprotective Effect of MURC/Cavin-4 Deletion Against Ischemia/Reperfusion Injury

Background

Ischemia/reperfusion (I/R) injury is a critical issue in the development of treatment strategies for ischemic heart disease. MURC (muscle‐restricted coiled‐coil protein)/Cavin‐4 (caveolae‐associated protein 4), which is a component of caveolae, is involved in the pathophysiology of dilated cardiomyopathy and cardiac hypertrophy. However, the role of MURC in cardiac I/R injury remains unknown.

Methods and Results

The systems network genomic analysis based on PC‐corr network inference on microarray data between wild‐type and MURC knockout mouse hearts predicted a network of discriminating genes associated with reactive oxygen species. To demonstrate the prediction, we analyzed I/R‐injured mouse hearts. MURC deletion decreased infarct size and preserved heart contraction with reactive oxygen species–related molecule EGR1 (early growth response protein 1) and DDIT4 (DNA‐damage‐inducible transcript 4) suppression in I/R‐injured hearts. Because PC‐corr network inference integrated with a protein–protein interaction network prediction also showed that MURC is involved in the apoptotic pathway, we confirmed the upregulation of STAT3 (signal transducer and activator of transcription 3) and BCL2 (B‐cell lymphoma 2) and the inactivation of caspase 3 in I/R‐injured hearts of MURC knockout mice compared with those of wild‐type mice. STAT3 inhibitor canceled the cardioprotective effect of MURC deletion in I/R‐injured hearts. In cardiomyocytes exposed to hydrogen peroxide, MURC overexpression promoted apoptosis and MURC knockdown inhibited apoptosis. STAT3 inhibitor canceled the antiapoptotic effect of MURC knockdown in cardiomyocytes.

Conclusions

Our findings, obtained by prediction from systems network genomic analysis followed by experimental validation, suggested that MURC modulates cardiac I/R injury through the regulation of reactive oxygen species–induced cell death and STAT3‐meditated antiapoptosis. Functional inhibition of MURC may be effective in reducing cardiac I/R injury.

Leptin increases mitochondrial OPA1 via GSK3-mediated OMA1 ubiquitination to enhance therapeutic effects of mesenchymal stem cell transplantation

Accumulating evidence revealed that mesenchymal stem cells (MSCs) confer cardioprotection against myocardial infarction (MI). However, the poor survival and engraftment rate of the transplanted cells limited their therapeutic efficacy in the heart. The enhanced leptin production associated with hypoxia preconditioning contributed to the improved MSCs survival. Mitochondrial integrity determines the cellular fate. Thus, we aimed to investigate whether leptin can enhance mitochondrial integrity of human MSCs (hMSCs) to protect against various stress. In vivo, transplantation of leptin-overexpressing hMSCs into the infarcted heart resulted in improved cell viability, leading to enhanced angiogenesis and cardiac function. In vitro, pretreatment of hMSCs with recombinant leptin (hMSCs-Lep^pre) displayed improved cell survival against severe ischemic condition (glucose and serum deprivation under hypoxia), which was associated with increased mitochondrial fusion. Subsequently, Optic atrophy 1 (OPA1), a mitochondrial inner membrane protein that regulates fusion and cristae structure, was significantly elevated in the hMSCs-Lep^pre group, and the protection of leptin was abrogated by targeting OPA1 with a selective siRNA. Furthermore, OMA1, a mitochondrial protease that cleaves OPA1, decreased in a leptin-dependent manner. Pretreatment of cells with an inhibitor of the proteasome (MG132), prevented leptin-induced OMA1 degradation, implicating the ubiquitination/proteasome system as a part of the protective leptin pathway. In addition, GSK3 inhibitor (SB216763) was also involved in the degradation of OMA1. In conclusion, in the hostile microenvironment caused by MI, (a) leptin can maintain the mitochondrial integrity and prolong the survival of hMSCs; (b) leptin-mediated mitochondrial integrity requires phosphorylation of GSK3 as a prerequisite for ubiquitination-depended degradation of OMA1 and attenuation of long-OPA1 cleavage. Thus, leptin targeting the GSK3/OMA1/OPA1 signaling pathway can optimize hMSCs therapy for cardiovascular diseases such as MI.

Shenfu Injection attenuates rat myocardial hypertrophy by up-regulating miR-19a-3p expression

Shenfu Injection (SFI) is a classical Chinese medicine used to treat heart failure. Our previous study demonstrated that miRNAs underwent changes in rats with myocardial hypertrophy induced by abdominal aortic constriction. Interestingly, there was a significant change in miR-19a-3p, whose target gene is known to be associated with MEF2 signaling. However, whether and how SFI regulates miR-19a-3p in the treatment of myocardial hypertrophy has not been investigated. The purpose of the present study was to investigate the regulatory effect of SFI on miR-19a-3p in MEF2 signaling in the rat hypertrophic myocardium. We found that the miR-19a-3p expression level was significantly decreased in the hypertrophic myocardium, and MEF2A was the target gene of miR-19a-3p. The protein expressions of MEF2A, β-MHC, BNP and TRPC1 were significantly increased in hypertrophic cardiomyocytes. MiR-19a-3p was up-regulated after SFI treatment, and the protein expressions of these genes were significantly decreased. In addition, miR-19a-3p over-expression in hypertrophic cardiomyocytes could decrease MEF2A mRNA and protein expressions, and anti-miR-19a-3p showed the opposite result. Our study provided substantial evidence that miR-19a-3p played a functional role in MEF2 signaling in myocardial hypertrophy. SFI attenuated cardiomyocyte hypertrophy probably through up-regulating or maintaining the miR-19a-3p levels and regulating the MEF2 signaling pathway.

Beneficial effects of leptin treatment in a setting of cardiac dysfunction induced by transverse aortic constriction in mouse

KEY POINTS

Leptin, is a 16 kDa pleiotropic peptide not only primarily secreted by adipocytes, but also produced by other tissues, including the heart. Controversy exists regarding the adverse and beneficial effects of leptin on the heart We analysed the effect of a non-hypertensive dose of leptin on cardiac function, [Ca²⁺ ]_i handling and cellular electrophysiology, which participate in the genesis of pump failure and related arrhythmias, both in control mice and in mice subjected to chronic pressure-overload by transverse aorta constriction. We find that leptin activates mechanisms that contribute to cardiac dysfunction under physiological conditions. However, after the establishment of pressure overload, an increase in leptin levels has protective cardiac effects with respect to rescuing the cellular heart failure phenotype. These beneficial effects of leptin involve restoration of action potential duration via normalization of transient outward potassium current and sarcoplasmic reticulum Ca²⁺ content via rescue of control sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase levels and ryanodine receptor function modulation, leading to normalization of Ca²⁺ handling parameters.

ABSTRACT

Leptin, is a 16 kDa pleiotropic peptide not only primary secreted by adipocytes, but also produced by other tissues, including the heart. Evidence indicates that leptin may have either adverse or beneficial effects on the heart. To obtain further insights, in the present study, we analysed the effect of leptin treatment on cardiac function, [Ca²⁺ ]_i handling and cellular electrophysiology, which participate in the genesis of pump failure and related arrhythmias, both in control mice and in mice subjected to chronic pressure-overload by transverse aorta constriction (TAC). Three weeks after surgery, animals received either leptin (0.36 mg kg^-1  day^-1 ) or vehicle via osmotic minipumps for 3 weeks. Echocardiographic measurements showed that, although leptin treatment was deleterious on cardiac function in sham, leptin had a cardioprotective effect following TAC. [Ca²⁺ ]_i transient in cardiomyocytes followed similar pattern. Patch clamp experiments showed prolongation of action potential duration (APD) in TAC and leptin-treated sham animals, whereas, following TAC, leptin reduced the APD towards control values. APD variations were associated with decreased transient outward potassium current and Kv4.2 and KChIP2 protein expression. TAC myocytes showed a higher incidence of triggered activities and spontaneous Ca²⁺ waves. These proarrhythmic manifestations, related to Ca²⁺ /calmodulin-dependent protein kinase II and ryanodine receptor phosphorylation, were reduced by leptin. The results of the present study demonstrate that, although leptin treatment was deleterious on cardiac function in control animals, leptin had a cardioprotective effect following TAC, normalizing cardiac function and reducing arrhythmogeneity at the cellular level.

Obesity-Induced Changes in Adipose Tissue Microenvironment and Their Impact on Cardiovascular Disease

Obesity is causally linked with the development of cardiovascular disorders. Accumulating evidence indicates that cardiovascular disease is the collateral damage of obesity-driven adipose tissue dysfunction that promotes a chronic inflammatory state within the organism. Adipose tissues secrete bioactive substances, referred to as adipokines, which largely function as modulators of inflammation. The microenvironment of adipose tissue will affect the adipokine secretome, having actions on remote tissues. Obesity typically leads to the upregulation of proinflammatory adipokines and the downregulation of anti-inflammatory adipokines, thereby contributing to the pathogenesis of cardiovascular diseases. In this review, we focus on the microenvironment of adipose tissue and how it influences cardiovascular disorders, including atherosclerosis and ischemic heart diseases, through the systemic actions of adipokines.

Sex differences in leptin modulate ventilation in heart failure

BACKGROUND

Leptin modulates ventilation and circulating levels are higher in normal women than men.

OBJECTIVES

The aim of this study was to compare exercise ventilation and gas exchange in men and women with heart failure (HF) and their relation to circulating leptin concentration.

METHODS

Consecutive HF patients were studied by cardiopulmonary exercise testing and assay of circulating leptin concentration.

RESULTS

Fifty-seven men and 20 women were similar with respect to age, BMI, NYHA class, left ventricular ejection fraction, and peak oxygen consumption (all p > 0.05). Leptin concentration was lower (10.3 ± 10 vs. 25.3 ± 16 ng/mL; p < 0.01) and peak exercise ventilatory efficiency (V_E/VCO₂) was higher (43 ± 10 vs. 36 ± 5; p < 0.01) in men. Leptin concentration was associated with peak exercise V_E/VCO₂ (b = -0.35; F = 5.6; p = 0.02).

CONCLUSION

Men have significantly lower circulating leptin concentration and increased ventilatory drive during exercise than women with comparable HF. In men with HF, lower leptin concentration may account for an increased ventilatory drive.

Long-Lived αMUPA Mice Show Attenuation of Cardiac Aging and Leptin-Dependent Cardioprotection

αMUPA transgenic mice spontaneously consume less food compared with their wild type (WT) ancestors due to endogenously increased levels of the satiety hormone leptin. αMUPA mice share many benefits with mice under caloric restriction (CR) including an extended life span. To understand mechanisms linked to cardiac aging, we explored the response of αMUPA hearts to ischemic conditions at the age of 6, 18, or 24 months. Mice were subjected to myocardial infarction (MI) in vivo and to ischemia/reperfusion ex vivo. Compared to WT mice, αMUPA showed functional and histological advantages under all experimental conditions. At 24 months, none of the WT mice survived the first ischemic day while αMUPA mice demonstrated 50% survival after 7 ischemic days. Leptin, an adipokine decreasing under CR, was consistently ~60% higher in αMUPA sera at baseline. Leptin levels gradually increased in both genotypes 24h post MI but were doubled in αMUPA. Pretreatment with leptin neutralizing antibodies or with inhibitors of leptin signaling (AG-490 and Wortmannin) abrogated the αMUPA benefits. The antibodies also reduced phosphorylation of the leptin signaling components STAT3 and AKT specifically in the αMUPA myocardium. αMUPA mice did not show elevation in adiponectin, an adipokine previously implicated in CR-induced cardioprotection. WT mice treated for short-term CR exhibited cardioprotection similar to that of αMUPA, however, along with increased adiponectin at baseline. Collectively, the results demonstrate a life-long increased ischemic tolerance in αMUPA mice, indicating the attenuation of cardiac aging. αMUPA cardioprotection is mediated through endogenous leptin, suggesting a protective pathway distinct from that elicited under CR.

Leptin protects rat articular chondrocytes from cytotoxicity induced by TNF-α in the presence of cyclohexamide

OBJECTIVE

Although leptin appears to be an important local and systemic factor influencing cartilage homeostasis, the role of leptin in chondrocyte death is largely unknown. Tumor necrosis factor α (TNF-α) is a pro-inflammatory cytokine that plays a central role in the pathogenesis of articular diseases. This study examines whether leptin modulates TNF-α-induced articular chondrocyte death.

METHODS

Primary rat articular chondrocytes were isolated from knee joint cartilage slices. To induce cell death, the chondrocytes were treated with TNF-α. To examine whether leptin modulates the extent of TNF-α-mediated chondrocyte death, the cells were pretreated with leptin for 3 h before TNF-α treatment followed by viability analysis. To examine the mechanism by which leptin modulates the extent of TNF-α-mediated chondrocyte death, we utilized mitochondrial membrane potential (MMP) measurements, flow cytometry, nuclear morphology observation, co-immunoprecipitation, western blot analysis and confocal microscopy.

RESULTS

We demonstrated that leptin suppresses TNF-α induced chondrocyte death. We further found that apoptosis partially contributes to TNF-α induced chondrocyte death while necroptosis primarily contributes to TNF-α induced chondrocyte death. In addition, we observed that leptin exerts anti-TNF-α toxicity via c-jun N-terminal kinase (JNK) in rat articular chondrocytes.

CONCLUSION

Based on our findings, we suggest that the leptin present in the articular joint fluid protects articular chondrocytes against cumulative mechanical load and detrimental stresses throughout a lifetime, delaying the onset of degenerative changes in chondrocytes. We can further hypothesize that leptin protects articular chondrocytes against destructive stimuli even in the joints of osteoarthritis (OA) patients.

Lean heart: Role of leptin in cardiac hypertrophy and metabolism

Leptin is an adipokine that has been linked with the cardiovascular complications resulting from obesity such as hypertension and heart disease. Obese patients have high levels of circulating leptin due to increased fat mass. Clinical and population studies have correlated high levels of circulating leptin with the development of cardiac hypertrophy in obesity. Leptin has also been demonstrated to increase the growth of cultured cardiomyocytes. However, several animal studies of obese leptin deficient mice have not supported a role for leptin in promoting cardiac hypertrophy so the role of leptin in this pathological process remains unclear. Leptin is also an important hormone in the regulation of cardiac metabolism where it supports oxidation of glucose and fatty acids. In addition, leptin plays a critical role in protecting the heart from excess lipid accumulation and the formation of toxic lipids in obesity a condition known as cardiac lipotoxicity. This paper focuses on the data supporting and refuting leptin’s role in promoting cardiac hypertrophy as well as its important role in the regulation of cardiac metabolism and protection against cardiac lipotoxicity.

Leptin decreases heart rate associated with increased ventricular repolarization via its receptor

Leptin has been proposed to modulate cardiac electrical properties via β-adrenergic receptor activation. The presence of leptin receptors and adipocytes in myocardium raised a question as to whether leptin can directly modulate cardiac electrical properties such as heart rate and QT interval via its receptor. In this work, the role of local direct actions of leptin on heart rate and ventricular repolarization was investigated. We identified the protein expression of leptin receptors at cell surface of sinus node, atrial, and ventricular myocytes isolated from rat heart. Leptin at low doses (0.1-30 μg/kg) decreased resting heart rate; at high doses (150-300 μg/kg), leptin induced a biphasic effect (decrease and then increase) on heart rate. In the presence of high-dose propranolol (30 mg/kg), high-dose leptin only reduced heart rate and sometimes caused sinus pauses and ventricular tachycardia. The leptin-induced inhibition of resting heart rate was fully reversed by leptin antagonist. Leptin also increased heart rate-corrected QT interval (QTc), and leptin antagonist did not. In isolated ventricular myocytes, leptin (0.03-0.3 μg/ml) reversibly increased the action potential duration. These results supported our hypothesis that in addition to indirect pathway via sympathetic tone, leptin can directly decrease heart rate and increase QT interval via its receptor independent of β-adrenergic receptor stimulation. During inhibition of β-adrenergic receptor activity, high concentration of leptin in myocardium can cause deep bradycardia, prolonged QT interval, and ventricular arrhythmias.

Cardiopulmonary Bypass Decreases Activation of the Signal Transducer and Activator of Transcription 3 (STAT3) Pathway in Diabetic Human Myocardium

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with increased myocardial oxidative stress and apoptosis in diabetic patients. A mechanistic understanding of this relationship could have therapeutic value. To establish a possible mechanism, we compared the activation of the cardioprotective signal transducer and activator of transcription 3 (STAT3) pathway between patients with uncontrolled diabetes (UD) and nondiabetic (ND) patients.

METHODS

Right atrial tissue and serum were collected before and after CPB from 80 patients, 39 ND and 41 UD (HbA1c ≥ 6.5), undergoing cardiac operations. The samples were evaluated with Western blotting, immunohistochemistry, and microarray.

RESULTS

On Western blot, leptin levels were significantly increased in ND post-CPB (p < 0.05). Compared with ND, the expression of Janus kinase 2 and phosphorylation (p-) of STAT3 was significantly decreased in UD (p < 0.05). The apoptotic proteins p-Bc12/Bc12 and caspase 3 were significantly increased (p < 0.05), antiapoptotic proteins Mcl-1, Bcl-2, and p-Akt were significantly decreased (p < 0.05) in UD compared with ND. The microarray data suggested significantly increased expression of interleukin-6 R, proapoptotic p-STAT1, caspase 9, and decreased expression of Bc12 and protein inhibitor of activated STAT1 antiapoptotic genes (p = 0.05) in the UD patients. The oxidative stress marker nuclear factor-κB was significantly higher (p < 0.05) in UD patients post-CPB compared with the pre-CPB value, but was decreased, albeit insignificantly, in ND patients post-CPB.

CONCLUSIONS

Compared with ND, UD myocardium demonstrated attenuation of the cardioprotective STAT3 pathway. Identification of this mechanism offers a possible target for therapeutic modulation.

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.

Association of serum leptin with future left ventricular structure and function: The Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND/OBJECTIVES

Earlier studies differ on whether serum leptin is associated with adverse or beneficial cardiac structure. We determined the association between serum leptin with subsequent cardiac structure and function.

METHODS

MESA is a multicenter longitudinal study of Black, White, Hispanic and Asian-American men and women. Cardiac MRI (CMR) was completed 6 to 8 years after leptin was measured. Left ventricular (LV) mass and volumes were indexed to body surface area. Multivariable linear regression models were constructed to assess the associations between leptin and risk factor adjusted (age, race, gender, systolic blood pressure, anti-hypertensive usage, LDL, HDL, hyperlipidemia medication usage, diabetes, diabetic medication usage, chronic kidney disease, alcohol and tobacco use, adiponectin and BMI) CMR variables.

RESULTS

Relative to participants in the lowest quintile of leptin concentration, participants in the highest quintile had a lower risk factor adjusted LV mass (-14 g), LV mass index (-9 g/m(2)), LV end diastolic volume index (LVEDVi) (-7 ml/m(2)), LV end systolic volume index (LVESVi) (-3 ml/m(2)) and stroke volume (-5 ml) (all p≤0.05). On regression analysis, a doubling of leptin concentration was associated with lower LV mass (-2.5 g ± 0.7 g), LV mass index (-1.7 ± 0.3g/m(2)), LVEDVi (-1.5 ± 0.4 ml/m(2)), LVESVi (-0.7 ± 0.2 ml/m(2)) and stroke volume (-1.0 ± 0.5 ml) (all p ≤ 0.05).

CONCLUSIONS

Higher leptin was associated with more favorable subsequent cardiac structure. Further study is needed to assess the prognostic and therapeutic implications of these observations.

Leptin and its cardiovascular effects: Focus on angiogenesis

Leptin is an endocrine hormone synthesized by adipocytes. It plays a key role in the energy homeostasis in central and peripheral tissues and has additional roles are attributed to it, such as the regulation of reproduction, immune function, bone homeostasis, and angiogenesis. The plasma concentration of leptin significantly increases in obese individuals. In the present review, we give an introduction concerning leptin, its receptors, signaling pathways, and its effect on cardiovascular system, especially on angiogenesis.

Leptin signaling is required for augmented therapeutic properties of mesenchymal stem cells conferred by hypoxia preconditioning

Hypoxia preconditioning enhances the therapeutic effect of mesenchymal stem cells (MSCs). However, the mechanism underlying hypoxia-induced augmentation of the protective effect of MSCs on myocardial infarction (MI) is poorly understood. We show that hypoxia-enhanced survival, mobility, and protection of cocultured cardiomyocytes were paralleled by increased expression of leptin and cell surface receptor CXCR4. The enhanced activities were abolished by either knockdown of leptin with a selective shRNA or by genetic deficiency of leptin or its receptor in MSCs derived, respectively, from ob/ob or db/db mice. To characterize the role of leptin in the regulation of MSC functions by hypoxia and its possible contribution to enhanced therapeutic efficacy, cell therapy using MSCs derived from wild-type, ob/ob, or db/db mice was implemented in mouse models of acute MI. Augmented protection by hypoxia pretreatment was only seen with MSCs from wild-type mice. Parameters that were differentially affected by hypoxia pretreatment included MSC engraftment, c-Kit(+) cell recruitment to the infarct, vascular density, infarct size, and long-term contractile function. These data show that leptin signaling is an early and essential step for the enhanced survival, chemotaxis, and therapeutic properties of MSCs conferred by preculture under hypoxia. Leptin may play a physiological role in priming MSCs resident in the bone marrow endosteum for optimal response to systemic signaling molecules and subsequent tissue repair.

Short-term response of metabolic hormones to coronary artery bypass surgery

PURPOSE

To explore the response pattern of plasma adipokine and ghrelin levels to coronary artery bypass graft (CABG) surgery in patients with (on-pump) and without (off-pump) cardiopulmonary bypass (CPB).

MATERIAL/METHODS

Sixteen consecutive patients (age: 62 ± 10 years, male: 10) with obstructive coronary artery disease (CAD) who underwent elective CABG surgery with CPB and intraoperative GIK infusion were selected for on-pump group and 19 CAD patients (age: 63 ± 10 years, male: 16) were included in the off-pump group. Blood samples were taken before, during and after surgery. Intraoperative samples were withdrawn simultaneously for peripheral vein and sinus coronarius (SC). Plasma adipokine concentrations were measured by ELISA, those of ghrelin by RIA kits.

RESULTS

In response to surgical intervention there was an early, transient fall in plasma levels of adiponectin (p<0.0001) and resistin (p=0.002) followed by an increase to approach their initial values. Plasma ghrelin also increased (p=0.045), this increase, however, was confined to the period of GIK supported CPB. Plasma insulin (p=0.003) and resistin (p=0.009) was significantly higher in the peripheral vein than in SC. The perioperative hormone profile of patients without CPB (off-pump) proved to be comparable to that of on-pump patients in spite of the insulin administration and greater oxidative and inflammatory stress.

CONCLUSIONS

Adipose tissue-derived factors appear to mediate the metabolic and vascular changes that occur in patients with CABG surgery. Epicardial adipose tissue is unlikely to have major contribution to the development of CAD as adipokines are not elevated in SC independent of the mode of intervention.

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.

Adipokines: a link between obesity and cardiovascular disease

Obesity is a risk factor for various cardiovascular diseases including hypertension, atherosclerosis, and myocardial infarction. Recent studies aimed at understanding the microenvironment of adipose tissue and its impact on systemic metabolism have shed light on the pathogenesis of obesity-linked cardiovascular diseases. Adipose tissue functions as an endocrine organ by secreting multiple immune-modulatory proteins known as adipokines. Obesity leads to increased expression of pro-inflammatory adipokines and diminished expression of anti-inflammatory adipokines, resulting in the development of a chronic, low-grade inflammatory state. This adipokine imbalance is thought to be a key event in promoting both systemic metabolic dysfunction and cardiovascular disease. This review will focus on the adipose tissue microenvironment and the role of adipokines in modulating systemic inflammatory responses that contribute to cardiovascular disease.

STAT3, a key regulator of cell-to-cell communication in the heart

The signal transducer and activator of transcription 3 (STAT3) is fundamental for physiological homeostasis and stress-induced remodelling of the heart as deregulated STAT3 circuits are sufficient to induce dilated and peripartum cardiomyopathy and adverse remodelling after myocardial infarction. STAT3 activity depends on multiple post-translational modifications (phosphorylation, acetylation, and dimerization). It is regulated by multiple receptor systems, which are coupled to positive and negative feedback loops to ensure physiological and beneficial action. Its intracellular functions are diverse as it acts as a signalling protein, a transcription factor but also participates in mitochondria energy production and protection. STAT3 modulates proliferation, differentiation, survival, oxidative stress, and/or metabolism in cardiomyocytes, fibroblasts, endothelial cells, progenitor cells, and various inflammatory cells. By regulating the secretome of these cardiac cells, STAT3 influences a broad range of intercellular communication systems. It thereby impacts on the communication between cardiomyocytes, the plasticity of the cardiac microenvironment, the vasculature, the extracellular matrix, and the inflammation in response to physiological and pathophysiological stress. Here, we sum up current knowledge on STAT3-mediated intra- and intercellular communication within the heterogeneous cellular network of the myocardium to co-ordinate complex biological processes and discuss STAT3-dependent targets as novel therapeutic concepts to treat various forms of heart disease.

Leptin, a mediator of cardiac damage associated with obesity

Obesity and excess of adipose tissue are associated with the development of cardiovascular risk factors such as diabetes, hypertension, and hyperlipidemia. At the cardiac level, various morphological adaptations in cardiac structure and function occur in obese individuals. Different mechanisms linking obesity to these modifications have been postulated. Adipose tissue and epicardial fat releases a large number of cytokines and bioactive mediators such as leptin. Leptin circulates in proportion to body fat mass, thus serving as a satiety signal and informing central metabolic control centers as to the status of peripheral energy stores. It participates in numerous other functions both peripherally and centrally, as indicated by the wide distribution of leptin and the different isoforms of its receptor in different tissues including the heart. This hormone has distinct effects on the reproductive, cardiovascular, and immune systems; however, its role in the heart could mediate wide physiological effects observed in obese individuals. Oxidative stress is associated with obesity and may be considered to be a unifying mechanism in the development of obesity-related comorbidities. It has been reported that obesity may induce systemic oxidative stress; in turn, oxidative stress is associated with an irregular production of adipokines. We herein review the current knowledge of cardiac effects of leptin and the possible mechanisms that are involved, including oxidative stress that plays a major role in the development of cardiovascular damage.

Importance of leptin signaling and signal transducer and activator of transcription-3 activation in mediating the cardiac hypertrophy associated with obesity

Background

The adipokine leptin and its receptor are expressed in the heart, and leptin has been shown to promote cardiomyocyte hypertrophy in vitro. Obesity is associated with hyperleptinemia and hypothalamic leptin resistance as well as an increased risk to develop cardiac hypertrophy and heart failure. However, the role of cardiac leptin signaling in mediating the cardiomyopathy associated with increased body weight is unclear, in particular, whether it develops subsequently to cardiac leptin resistance or overactivation of hypertrophic signaling pathways via elevated leptin levels.

Methods

The cardiac phenotype of high-fat diet (HFD)-induced obese wildtype (WT) mice was examined and compared to age-matched genetically obese leptin receptor (LepR)-deficient (LepR^db/db) or lean WT mice. To study the role of leptin-mediated STAT3 activation during obesity-induced cardiac remodeling, mice in which tyrosine residue 1138 within LepR had been replaced with a serine (LepR^S1138) were also analyzed.

Results

Obesity was associated with hyperleptinemia and elevated cardiac leptin expression in both diet-induced and genetically obese mice. Enhanced LepR and STAT3 phosphorylation levels were detected in hearts of obese WT mice, but not in those with LepR mutations. Moreover, exogenous leptin continued to induce cardiac STAT3 activation in diet-induced obese mice. Although echocardiography revealed signs of cardiac hypertrophy in all obese mice, the increase in left ventricular (LV) mass and diameter was significantly more pronounced in LepR^S1138 animals. LepR^S1138 mice also exhibited an increased activation of signaling proteins downstream of LepR, including Jak2 (1.8-fold), Src kinase (1.7-fold), protein kinase B (1.3-fold) or C (1.6-fold). Histological analysis of hearts revealed that the inability of leptin to activate STAT3 in LepR^db/db and LepR^S1138 mice was associated with reduced cardiac angiogenesis as well as increased apoptosis and fibrosis.

Conclusions

Our findings suggest that hearts from obese mice continue to respond to elevated circulating or cardiac leptin, which may mediate cardioprotection via LepR-induced STAT3 activation, whereas signals distinct from LepR-Tyr1138 promote cardiac hypertrophy. On the other hand, the presence of cardiac hypertrophy in obese mice with complete LepR signal disruption indicates that additional pathways also play a role.

Use of high-dose erythropoietin for repair after injury: A comparison of outcomes in heart and kidney

CONTEXT

There is a need to define the exact benefits and contraindications of use of high-dose recombinant human erythropoietin (EPO) for its non-hematopoietic function as a cytokine that enhances tissue repair after injury. This review compares the outcomes from use of EPO in the injured heart and kidney, two organs that are thought, traditionally, to have intrinsically-different repair mechanisms.

EVIDENCE ACQUISITIONS

Directory of Open Access Journals (DOAJ), Google Scholar, Pubmed (NLM), LISTA (EBSCO) and Web of Science have been searched.

RESULTS

Ongoing work by us on EPO protection of ischemia-reperfusion-injured kidneys indicated, first, that EPO acutely enhanced kidney repair via anti-apoptotic, pro-regenerative mechanisms, and second, that EPO may promote chronic fibrosis in the long term. Work by others on the ischaemia-injured heart has also indicated that EPO promotes repair. Although myocardial infarcts are made up mostly of necrotic tissue, many publications state EPO is anti-apoptotic in the heart, as well as promoting healing via cell differentiation and stimulation of granulation tissue. In the case of the heart, promotion of fibrosis may be advantageous where an infarct has destroyed a zone of cardiomyocytes, but if EPO stimulates progressive fibrosis in the heart, this may promote cardiac failure.

CONCLUSIONS

A major concern in relation to the use of EPO in a cytoprotective role is its stimulation of long-term inflammation and fibrosis. EPO usage for cytoprotection is undoubtedly advantageous, but it may need to be offset with an anti-inflammatory agent in some organs, like kidney and heart, where progression to chronic fibrosis after acute injury is often recorded.

Investigation into the optimal surgical conditions for coronary artery ligation for establishing a myocardial infarction model in mice

In the present study, the left anterior descending coronary arteries of mice under anesthesia were ligated, and the optimal surgical conditions for coronary artery ligation (CAL) in the establishment of a myocardial infarction (MI) mouse model were investigated. All mice that survived were sacrificed seven days subsequent to the successful surgery. Body weight, blood serum and heart tissues were obtained for further analysis or biochemical and histopathological examinations. The survival rate of the mice following the CAL procedure was 70%. The aspartate aminotransferase (AST), creatine kinase (CK) and lactate dehydrogenase (LDH) concentrations in the serum of the experimental mice were significantly increased compared with those of the control mice, which reflected the enzyme release from the infarcted myocardial cells. Histopathological examination showed different degrees of MI in the heart tissues of the experimental mice. The results indicate that an MI model in mice may be successfully established using CAL under the surgical conditions utilized in the present study. These conditions were cost effective and the results may be replicated by laboratories that are less well-equipped.

A high leucine diet mitigates cardiac injury and improves survival after acute myocardial infarction

OBJECTIVE

Evidence suggests that branched chain amino acids (BCAAs) are beneficial in treating human disease. It is unknown, however, what impact BCAAs have on outcomes in acute myocardial infarction (MI). This study was performed to test the hypothesis that the specific BCAA leucine mitigates cardiac injury and improves survival post-MI.

MATERIALS/METHODS

11-12 week old male C57BL/6 mice were subjected to experimental MI or sham procedure, and provided regular chow (RC; 1.5% leucine) or a high leucine diet (HLD; 5% leucine), and followed for 3½ or 28 days. All mice were studied by echocardiography and cardiac catheterization, and all hearts were collected for histologic measurements of hypertrophy, fibrosis and apoptosis. Inflammation, hypertrophic gene expression, signal transduction, and glucose, palmitate and leucine metabolism were also measured in 3½day hearts.

RESULTS

Except for increased leucine and decreased glucose oxidation, an HLD had no effect on measured outcomes in sham mice. With MI, cardiac structure, function, and survival were significantly improved with an HLD. At 3½days post-MI, an HLD increased cardiac hypertrophic signaling and decreased inflammation. Cardiac leucine oxidation was decreased in RC mice post-MI, but significantly increased with an HLD. These changes in metabolism were accompanied by a significant increase in cardiac ATP content in the HLD group. Finally, at both 3½ and 28 days post-MI, an HLD increased compensatory hypertrophy, and attenuated cardiac fibrosis and apoptosis.

CONCLUSIONS

An HLD increases compensatory hypertrophy, attenuates fibrosis and apoptosis, and positively modulates oxidative metabolism to improve cardiac structure, function, and survival post-MI.

Cardiomyocyte-specific deletion of leptin receptors causes lethal heart failure in Cre-recombinase-mediated cardiotoxicity

Although disruption of leptin signaling is associated with obesity as well as cardiac lipid accumulation and dysfunction, it has been difficult to separate the direct effects of leptin on the heart from those associated with the effects of leptin on body weight and fat mass. Using Cre-loxP recombinase technology, we developed tamoxifen-inducible, cardiomyocyte-specific leptin receptor-deficient mice to assess the role of leptin in regulating cardiac function. Cre recombinase activation in the heart resulted in transient reduction in left ventricular systolic function which recovered to normal levels by day 10. However, when cardiomyocyte leptin receptors were deleted in the setting of Cre recombinase-induced left ventricular dysfunction, irreversible lethal heart failure was observed in less than 10 days in all mice. Heart failure after leptin receptor deletion was associated with marked decreases of cardiac mitochondrial ATP, phosphorylated mammalian target of rapamycin (mTOR), and AMP-activated kinase (pAMPK). Our results demonstrate that specific deletion of cardiomyocyte leptin receptors, in the presence of increased Cre recombinase expression, causes lethal heart failure associated with decreased cardiac energy production. These observations indicate that leptin plays an important role in regulating cardiac function in the setting of cardiac stress caused by Cre-recombinase expression, likely through actions on cardiomyocyte energy metabolism.

Anti-inflammatory and cardioprotective effects of tadalafil in diabetic mice

Background

Insulin resistance impairs nitric oxide (NO) bioavailability and obesity promotes a state of chronic inflammation and damages the vascular endothelium. Phosphodiesterase-5 inhibitors restore NO signaling and may reduce circulating inflammatory markers, and improve metabolic parameters through a number of mechanisms. We hypothesized that daily administration of the PDE-5 inhibitor, tadalafil (TAD) will attenuate inflammation, improve fasting plasma glucose and triglyceride levels, body weight, and reduce infarct size after ischemia/reperfusion injury in obese, diabetic mice.

Methods

Twenty leptin receptor null (db/db) mice underwent treatment with TAD (1 mg/Kg) or 10% DMSO for 28 days. Body weight and fasting plasma glucose levels were determined weekly. Upon completion, hearts were isolated and subjected to 30 min global ischemia followed by 60 min reperfusion in a Langendorff model. Plasma samples were taken for cytokine analysis and fasting triglyceride levels. Infarct size was measured using computer morphometry of tetrazolium stained sections. Additionally, ventricular cardiomyocytes were isolated and subjected to 40 min of simulated ischemia and reoxygenation. Necrosis was determined using trypan blue exclusion and LDH release assay and apoptosis was assessed by TUNEL assay after 1 h or 18 h of reoxygenation, respectively.

Results

Treatment with TAD caused a reduction in infarct size in the diabetic heart (23.2±1.5 vs. 47.8±3.7%, p<0.01, n = 6/group), reduced fasting glucose levels (292±31.8 vs. 511±19.3 mg/dL, p<0.001) and fasting triglycerides (43.3±21 vs. 129.7±29 mg/dL, p<0.05) as compared to DMSO, however body weight was not significantly reduced. Circulating tumor necrosis factor-α and interleukin-1β were reduced after treatment compared to control (257±16.51 vs. 402.3±17.26 and 150.8±12.55 vs. 264±31.85 pg/mL, respectively; P<0.001) Isolated cardiomyocytes from TAD-treated mice showed reduced apoptosis and necrosis.

Conclusion

We have provided the first evidence that TAD therapy ameliorates circulating inflammatory cytokines and chemokines in a diabetic animal model while improving fasting glucose levels and reducing infarct size following ischemia-reperfusion injury in the heart.

Leptin levels predict survival in pulmonary arterial hypertension

Evidence suggests that leptin is involved in relevant processes in the cardiovascular system. Low serum leptin levels have been associated with increased cardiovascular events and mortality in patients with coronary artery, diabetes, or chronic kidney disease. We hypothesized that leptin is increased in pulmonary arterial hypertension (PAH) and provides prognostic information. We correlated leptin levels with clinical data and assessed its association with survival. Sixty-seven patients with PAH and 29 healthy controls were studied. Plasma leptin levels were nonlinearly associated with BMI. Leptin level <15 μg/l was associated with higher mortality in PAH patients, with an adjusted (age, gender, BMI, and smoking status) hazard ratio of 3.8 (95% CI: 1.3-11.2), P=0.016. Similarly, PAH patients with leptin/BMI ratio <0.5 μg * m²/kg * l had worse survival than those with a level >0.5 μg * m²/ kg * l (P=0.046 by log-rank test). Two-year mortality in PAH patients was 24%. A receiver operating characteristic curve using leptin/BMI ratio as the test variable and 2-year mortality as the state variable showed an area under the curve of 0.74 (95% CI: 0.62–0.86). A leptin/BMI ratio cut-off of 0.6 had a high sensitivity (94%) and negative predictive value (96%) for predicting death of any cause at 2 years. In PAH, plasma leptin levels are directly associated with BMI. Lower leptin levels, when adjusted by BMI, are associated with an increased overall mortality and leptin/BMI ratio has high negative predictive value for mortality at 2 years.

Angiotensin-converting enzyme inhibition and food restriction in diabetic mice do not correct the increased sensitivity for ischemia-reperfusion injury

Background

The number of patients with diabetes or the metabolic syndrome reaches epidemic proportions. On top of their diabetic cardiomyopathy, these patients experience frequent and severe cardiac ischemia-reperfusion (IR) insults, which further aggravate their degree of heart failure. Food restriction and angiotensin-converting enzyme inhibition (ACE-I) are standard therapies in these patients but the effects on cardiac IR injury have never been investigated. In this study, we tested the hypothesis that 1° food restriction and 2° ACE-I reduce infarct size and preserve cardiac contractility after IR injury in mouse models of diabetes and the metabolic syndrome.

Methods

C57Bl6/J wild type (WT) mice, leptin deficient ob/ob (model for type II diabetes) and double knock-out (LDLR-/-;ob/ob, further called DKO) mice with combined leptin and LDL-receptor deficiency (model for metabolic syndrome) were used. The effects of 12 weeks food restriction or ACE-I on infarct size and load-independent left ventricular contractility after 30 min regional cardiac ischemia were investigated. Differences between groups were analyzed for statistical significance by Student’s t-test or factorial ANOVA followed by a Fisher’s LSD post hoc test.

Results

Infarct size was larger in ob/ob and DKO versus WT. Twelve weeks of ACE-I improved pre-ischemic left ventricular contractility in ob/ob and DKO. Twelve weeks of food restriction, with a weight reduction of 35-40%, or ACE-I did not reduce the effect of IR.

Conclusion

ACE-I and food restriction do not correct the increased sensitivity for cardiac IR-injury in mouse models of type II diabetes and the metabolic syndrome.

Leptin protects host cells from Entamoeba histolytica cytotoxicity by a STAT3-dependent mechanism

The adipocytokine leptin links nutritional status to immune function. Leptin signaling protects from amebiasis, but the molecular mechanism is not understood. We developed an in vitro model of ameba-host cell interaction to test the hypothesis that leptin prevents ameba-induced apoptosis in host epithelial cells. We demonstrated that activation of mammalian leptin signaling increased cellular resistance to amebic cytotoxicity, including caspase-3 activation. Exogenous expression of the leptin receptor conferred resistance in susceptible cells, and leptin stimulation enhanced protection. A series of leptin receptor signaling mutants showed that resistance to amebic cytotoxicity was dependent on activation of STAT3 but not the Src homology-2 domain-containing tyrosine phosphatase (SHP-2) or STAT5. A common polymorphism in the leptin receptor (Q223R) that increases susceptibility to amebiasis in humans and mice was found to increase susceptibility to amebic cytotoxicity in single cells. The Q223R polymorphism also decreased leptin-dependent STAT3 activation by 21% relative to that of the wild-type (WT) receptor (P = 0.035), consistent with a central role of STAT3 signaling in protection. A subset of genes uniquely regulated by STAT3 in response to leptin was identified. Most notable were the TRIB1 and suppressor of cytokine signaling 3 (SOCS3) genes, which have opposing roles in the regulation of apoptosis. Overall apoptotic genes were highly enriched in this gene set (P < 1E-05), supporting the hypothesis that leptin regulation of host apoptotic genes via STAT3 is responsible for protection. This is the first demonstration of a mammalian signaling pathway that restricts amebic pathogenesis and represents an important advance in our mechanistic understanding of how leptin links nutrition and susceptibility to infection.

Lifestyle Modification with Diet and Exercise in Obese Patients with Heart Failure - A Pilot Study

OBJECTIVE: There is a paucity of data regarding intentional weight loss in obese heart failure patients. This study sought to ascertain the safety and effectiveness of a lifestyle modification program in patients with systolic heart failure and metabolic syndrome. METHODS: Patients (n=20) with systolic heart failure (ejection fraction < 50%) and metabolic syndrome were randomized to standard medical therapy (Control) versus medical therapy and lifestyle modification (Lifestyle) and followed prospectively for 3 months. Lifestyle modification involved a walking program and reduced calorie diet with 2 meal replacement products (Slim Fast®) daily. Patients attended weekly meetings with a dietitian for 12 weeks. Endpoints were obtained at baseline and 3 months and included physical exam, laboratory values, quality of life questionnaire, 6 minute walk, and brachial ultrasound. RESULTS: At 3 months, 5 patients in each group had lost weight. Excluding 1 patient in each group who had increased diuretic dosing, the overall change in weight was -0.84 ± 3.82 and -0.50 ± 3.64 kg (p=0.85) in the control versus lifestyle groups respectively. No significant differences in the defined endpoints were noted. None of the patients had an adverse event that was related to weight loss or exercise. CONCLUSIONS: This study is the first to assess the effects of a comprehensive program of dietary, behavioral, and exercise modifications in this population. Institution of lifestyle modification in patients with systolic heart failure and metabolic syndrome was well tolerated, but did not result in significant weight loss.

Inhibition of cardiac leptin expression after infarction reduces subsequent dysfunction

Leptin is known to exert cardiodepressive effects and to induce left ventricular (LV) remodelling. Nevertheless, the autocrine and/or paracrine activities of this adipokine in the context of post-infarct dysfunction and remodelling have not yet been elucidated. Therefore, we have investigated the evolution of myocardial leptin expression following myocardial infarction (MI) and evaluated the consequences of specific cardiac leptin inhibition on subsequent LV dysfunction. Anaesthetized rats were subjected to temporary coronary occlusion. An antisense oligodesoxynucleotide (AS ODN) directed against leptin mRNA was injected intramyocardially along the border of the infarct 5 days after surgery. Cardiac morphometry and function were monitored by echocardiography over 11 weeks following MI. Production of myocardial leptin and pro-inflammatory cytokines interleukin (IL)-1β and IL-6 were assessed by ELISA. Our results show that (1) cardiac leptin level peaks 7 days after reperfused MI; (2) intramyocardial injection of leptin-AS ODN reduces early IL-1β and IL-6 overexpression and markedly protects contractile function. In conclusion, our findings demonstrate that cardiac leptin expression after MI could contribute to the evolution towards heart failure through autocrine and/or paracrine actions. The detrimental effect of leptin could be mediated by pro-inflammatory cytokines such as IL-1β and IL-6. Our data could constitute the basis of new therapeutic approaches aimed to improve post-MI outcome.

Effects of leptin on lipopolysaccharide-induced myometrial apoptosis in an in vitro human model of chorioamnionitis

OBJECTIVE

This study was aimed at assessing the role of leptin on human myometrium, by studying its receptor expression in pregnant myometrium and the interaction of leptin with inflammation-induced apoptosis.

STUDY DESIGN

Myometrial samples were obtained from women with uncomplicated pregnancies who underwent cesarean delivery at term before labor onset. The effect of leptin on apoptosis was assessed by the incubation of myometrial strips with leptin (10(-10) to 10(-8) mol/L; 48 hours) before lipopolysaccharide treatment (10 μg/mL; 48 hours).

RESULTS

Long and short leptin receptor isoforms were expressed in myometrial cells of pregnant women. Leptin prevented lipopolysaccharide-induced apoptosis, in a concentration-dependent manner, by down-regulating cleaved caspase-3 and BCL2-associated X protein and up-regulating BCL2 expression. This effect was mediated specifically through leptin receptor stimulation, followed by ERK1/2 signaling pathway activation.

CONCLUSION

These results suggest a new potential pathway that is involved in delivery disorders of obese women and propose a role for the leptin-induced inhibition of myometrial apoptosis in the development of such disorders.

ES cells overexpressing microRNA-1 attenuate apoptosis in the injured myocardium

MicroRNAs (miRs) are small, single-stranded, noncoding RNA's involved in post-transcriptional negative gene regulation. Recent investigations have underscored the integral role of miRs in various biological processes including innate immunity, cell-cycle regulation, metabolism, differentiation, and cell death. In the present study, we overexpressed miR-1, a muscle-specific miR, in embryonic stem cells (miR-1-ES cells), transplanted them into the infarcted myocardium, and evaluated their impact on cardiac apoptosis and function. We provide evidence demonstrating reduced apoptosis following transplantation of miR-1-ES cells 4 weeks post-myocardial infarction as compared to respective controls assessed by TUNEL staining and a capsase-3 activity assay. Moreover, we show significant elevation in p-Akt levels and diminished PTEN levels in hearts transplanted with miR-1-ES cells as determined by enzyme-linked immunoassays. Finally, using echocardiography, we reveal mice receiving miR-1-ES cell transplantation post-myocardial infarction had significantly improved fractional shortening and ejection fraction compared with respective controls. Our data suggest transplanted miR-1-ES cells inhibit apoptosis, mediated through the PTEN/Akt pathway, leading to improved cardiac function in the infarcted myocardium.

Stem cells in the diabetic infarcted heart

Diabetes mellitus is one of the leading causes of death, and the majority of these deaths are associated with cardiovascular diseases. Development and progression of myocardial infarction leading to heart failure is much more complex and multifactorial in diabetics compared with non-diabetics. Despite significant advances in pharmacological interventions and surgical techniques, the disease progression leading to diabetic end-stage heart failure remains very high. Recently, cell therapy has gained much attention as an alternative approach to treat various heart diseases. However, transplanted stem cell studies in diabetic animal models are very limited. In this review, we discuss the pathogenesis of the diabetic infarcted heart and the potential of stem cell therapy to repair and regenerate.