Secretory products from epicardial adipose tissue of patients with type 2 diabetes mellitus induce cardiomyocyte dysfunction

Is echocardiographic epicardial fat thickness increased in patients with coronary artery disease? A systematic review and meta-analysis

Background

The relation of epicardial fat thickness (EFT) to coronary artery disease (CAD) has recently been reported in multiple studies. Echocardiography is a safe and relatively inexpensive and accessible approach to assess regional EFT, which can be performed easily in many centers.

Objective

To determine the association between echocardiographic EFT and the presence or the absence of CAD.

Methods

This was a systematic review and meta-analysis conducted on literature available in electronic databases up to March 2018. The articles measuring EFT by echocardiography in the right ventricular (RV) free wall were included in the study. The quality of the enrolled items was assessed using the Methodological Index for Non-Randomized Studies (MINORS) checklist. The analyses were performed using the Comprehensive Meta-Analysis version 2 software. Cochran’s Q test and I² index were used to evaluate heterogeneity.

Results

This meta-analysis was performed on 13 studies involving 2,436 patients (1,622 with CAD, and 814 without CAD). The maximum EFT reported by echocardiography was 12.9±2.7 mm in the CAD group and 8.4±2.5 mm in the non-CAD group. The minimum EFT reported by echocardiography was 2.2±1.8 mm in the CAD group and 1.8±1.4 mm in the non-CAD group. The heterogeneity was found among the researched studies (I²=91.8%, p=0.000, Q-value=146.43, df [Q] =12) using the random effect model. The patients with CAD had a significantly higher echocardiographic EFT than those without CAD (SMD=1.03, 95% CI= 0.70–1.37, p=0.000).

Conclusion

According to the findings of this meta-analysis, the echocardiographic EFT in the subjects with CAD was significantly higher than that of those without CAD. The measurement of echocardiographic EFT seems to be an acceptable strategy for risk stratification of heart diseases considering ease of use, cost-effectiveness and non-exposure characteristics, compared to other imaging interventions.

Epicardial adipose tissue feeding and overfeeding the heart

Epicardial adipose tissue is a particular visceral fat depot with unique anatomic, biomolecular, and genetic features. Epicardial fat displays both physiological and pathological properties. Epicardial fat expresses genes and secretes cytokines actively involved in the thermogenesis and regulation of lipid and glucose metabolism of the adjacent myocardium. A disequilibrium between epicardial fat feeding and overfeeding the myocardium with free fatty acids leads to intramyocardial fat infiltration causing organ damage and clinical consequences. The upregulation of epicardial fat proinflammatory and lipogenic genes contributes to the fat build up in the proximal coronary arteries. Epicardial fat is a measurable and modifiable risk factor that can serve as a novel and additional tool for cardiovascular risk stratification. Pharmacologically targeting epicardial fat with drugs such as glucagon peptide-like 1 analogs or sodium glucose transport 2 inhibitors reduces the epicardial fat burden and induces beneficial cardiometabolic effects. Assessment and manipulation of epicardial fat transcriptome might open new avenues in the prevention of cardiometabolic diseases.

Epicardial adipose tissue as a metabolic transducer: role in heart failure and coronary artery disease

Obesity and diabetes are strongly associated with metabolic and cardiovascular disorders including dyslipidemia, coronary artery disease, hypertension, and heart failure. Adipose tissue is identified as a complex endocrine organ, which by exerting a wide array of regulatory functions at the cellular, tissue and systemic levels can have profound effects on the cardiovascular system. Different terms including "epicardial," "pericardial," and "paracardial" have been used to describe adipose tissue deposits surrounding the heart. Epicardial adipose tissue (EAT) is a unique and multifaceted fat depot with local and systemic effects. The functional and anatomic proximity of EAT to the myocardium enables endocrine, paracrine, and vasocrine effects on the heart. EAT displays a large secretosome, which regulates physiological and pathophysiological processes in the heart. Perivascular adipose tissue (PVAT) secretes adipose-derived relaxing factor, which is a "cocktail" of cytokines, adipokines, microRNAs, and cellular mediators, with a potent effect on paracrine regulation of vascular tone, vascular smooth muscle cell proliferation, migration, atherosclerosis-susceptibility, and restenosis. Although there are various physiological functions of the EAT and PVAT, a phenotypic transformation can lead to a major pathogenic role in various cardiovascular diseases. The equilibrium between the physiological and pathophysiological properties of EAT is very delicate and susceptible to the influences of intrinsic and extrinsic factors. Various adipokines secreted from EAT and PVAT have a profound effect on the myocardium and coronary arteries; targeting these adipokines could be an important therapeutic approach to counteract cardiovascular disease.

Increased activin A levels in prediabetes and association with carotid intima-media thickness: a cross-sectional analysis from I-Lan Longitudinal Aging Study

Activin A and its binding protein follistatin may be crucial in glucose homeostasis, as multifunctional proteins mediating inflammatory and anti-inflammatory effects. However, clinical data on the activin A level in prediabetes, and the association between the circulating activin A level and carotid intima-media thickness (cIMT), are lacking. We aimed to investigate activin A and follistatin levels and their associations with cIMT. In total, 470 inhabitants of I-Lan county (235 men; mean age 69 ± 9 years) with measurements of serum activin A and follistatin levels were included. Patients with prediabetes and diabetes had significantly increased activin A concentrations compared with those in the normal glycemic group (both p < 0.001). A multivariable logistic regression model demonstrated that the circulating activin A level was associated with prediabetes and diabetes independently of other risk factors. Moreover, the circulating activin A levels were associated positively with cIMT in prediabetes (r_s = 0.264, p = 0.001). In conclusion, activin A level, but not follistatin, was elevated independent of demographic variables with borderline significance and was correlated positively with cIMT in prediabetes. Activin A and follistatin levels were elevated in diabetes. In addition, elevated activin A was an independent risk factor for prediabetes and diabetes.

Mechanisms and Drug Development in Atrial Fibrillation

Atrial fibrillation is a highly prevalent cardiac arrhythmia and the most important cause of embolic stroke. Although genetic studies have identified an increasing assembly of AF-related genes, the impact of these genetic discoveries is yet to be realized. In addition, despite more than a century of research and speculation, the molecular and cellular mechanisms underlying AF have not been established, and therapy for AF, particularly persistent AF, remains suboptimal. Current antiarrhythmic drugs are associated with a significant rate of adverse events, particularly proarrhythmia, which may explain why many highly symptomatic AF patients are not receiving any rhythm control therapy. This review focuses on recent advances in AF research, including its epidemiology, genetics, and pathophysiological mechanisms. We then discuss the status of antiarrhythmic drug therapy for AF today, reviewing molecular mechanisms, and the possible clinical use of some of the new atrial-selective antifibrillatory agents, as well as drugs that target atrial remodeling, inflammation and fibrosis, which are being tested as upstream therapies to prevent AF perpetuation. Altogether, the objective is to highlight the magnitude and endemic dimension of AF, which requires a significant effort to develop new and effective antiarrhythmic drugs, but also improve AF prevention and treatment of risk factors that are associated with AF complications.

Potentiation of Insulin Signaling Contributes to Heart Failure in Type 2 Diabetes: A Hypothesis Supported by Both Mechanistic Studies and Clinical Trials

The heightened risk of heart failure in type 2 diabetes cannot be explained by the occurrence of clinically overt myocardial ischemic events or hyperglycemia. Experimentally, insulin exerts detrimental effects on the heart, vasculature, kidneys, and adipose tissue that can lead to heart failure. In both randomized clinical trials and observational studies, antihyperglycemic drugs that act through insulin signaling (i.e., sulfonylureas, thiazolidinediones, and incretins) increase the risk or worsen the clinical course of heart failure, whereas drugs that ameliorate hyperinsulinemia and do not signal through insulin (i.e., metformin and sodium-glucose cotransporter 2 inhibitors) reduce the risk of heart failure.

Interplay between epicardial adipose tissue, metabolic and cardiovascular diseases

Cardiovascular disease is the primary cause of death in obese and diabetic patients. In these groups of patients, the alterations of epicardial adipose tissue (EAT) contribute to both vascular and myocardial dysfunction. Therefore, it is of clinical interest to determine the mechanisms by which EAT influences cardiovascular disease. Two key factors contribute to the tight intercommunication among EAT, coronary arteries and myocardium. One is the close anatomical proximity between these tissues. The other is the capacity of EAT to secrete cytokines and other molecules with paracrine and vasocrine effects on the cardiovascular system. Epidemiological studies have demonstrated that EAT thickness is associated with not only metabolic syndrome but also atherosclerosis and heart failure. The evaluation of EAT using imaging modalities, although effective, presents several disadvantages including radiation exposure, limited availability and elevated costs. Therefore, there is a clinical interest in EAT as a source of new biomarkers of cardiovascular and endocrine alterations. In this review, we revise the mechanisms involved in the protective and pathological role of EAT and present the molecules released by EAT with greater potential to become biomarkers of cardiometabolic alterations.

Dobutamine Stress Echocardiography Unmasks Early Left Ventricular Dysfunction in Asymptomatic Patients with Uncomplicated Type 2 Diabetes: A Comprehensive Two-Dimensional Speckle-Tracking Imaging Study

BACKGROUND

Discrepancies are present in the literature on resting myocardial mechanics in patients with uncomplicated type 2 diabetes mellitus (T2DM). Data are noticeably sparse regarding circumferential function and torsional mechanics. Resting deformation imaging may not be sensitive enough to detect subtle dysfunctions. The aim of this study was thus to comprehensively evaluate myocardial mechanics in patients with T2DM at rest and to investigate whether dobutamine stress echocardiography could unmask functional alterations that would remain otherwise subtle at rest.

METHODS

Forty-four patients with T2DM and 35 healthy control subjects of similar age and sex were prospectively recruited. After conventional echocardiography, myocardial mechanics was evaluated at rest and during low-dose dobutamine stress echocardiography (target heart rate, 110 beats/min).

RESULTS

Patients with T2DM presented with altered global diastolic function but preserved systolic function. Deformation imaging indexes were similar between groups at rest, but significant differences were noticed under dobutamine infusion for longitudinal strain (-21.2 ± 2.4% vs -24.2 ± 2.5%, P < .001), circumferential strain (apex, -32.3 ± 5.3% vs -36.3 ± 5.3%, P = .002; papillary muscle, -25.6 ± 3.2% vs -28.0 ± 3.6%, P = .001; base, -23.2 ± 3.6% vs -25.3 ± 3.8%, P = .03), apical (11.2 ± 4.4° vs 14.1 ± 6.3°, P = .020) and basal (-12.2 ± 3.3° vs -14.3 ± 3.9°, P = .021) rotation, and twist (21.9 ± 5.9° vs 26.8 ± 8.3°, P = .007). Multivariate analysis identified epicardial fat, dyslipidemia, and fasting glycaemia as significant contributors to the changes from rest to dobutamine.

CONCLUSIONS

These findings demonstrate the usefulness of dobutamine stress echocardiography in establishing impairments in myocardial mechanics in patients with uncomplicated T2DM. Systemic metabolic disturbances and epicardial fat act as the main contributors to the blunted response to dobutamine stress in these patients.

Effects of dapagliflozin on human epicardial adipose tissue: modulation of insulin resistance, inflammatory chemokine production, and differentiation ability

AIMS

In patients with cardiovascular disease, epicardial adipose tissue (EAT) is characterized by insulin resistance, high pro-inflammatory chemokines, and low differentiation ability. As dapagliflozin reduces body fat and cardiovascular events in diabetic patients, we would like to know its effect on EAT and subcutaneous adipose tissue (SAT).

METHODS AND RESULTS

Adipose samples were obtained from 52 patients undergoing heart surgery. Sodium-glucose cotransporter 2 (SGLT2) expression was determined by real-time polymerase chain reaction (n = 20), western blot, and immunohistochemistry. Fat explants (n = 21) were treated with dapagliflozin and/or insulin and glucose transporters expression measured. Glucose, free fatty acid, and adipokine levels (by array) were measured in the EAT secretomes, which were then tested on human coronary endothelial cells using wound healing assays. Glucose uptake was also measured using the fluorescent glucose analogue (6NBDG) in differentiated stromal vascular cells (SVCs) from the fat pads (n = 11). Finally, dapagliflozin-induced adipocyte differentiation was assessed from the levels of fat droplets (AdipoRed staining) and of perilipin. SGLT2 was expressed in EAT. Dapagliflozin increased glucose uptake (20.95 ± 4.4 mg/dL vs. 12.97 ± 4.1 mg/dL; P < 0.001) and glucose transporter type 4 (2.09 ± 0.3 fold change; P < 0.01) in EAT. Moreover, dapagliflozin reduced the secretion levels of chemokines and benefited wound healing in endothelial cells (0.21 ± 0.05 vs. 0.38 ± 0.08 open wound; P < 0.05). Finally, chronic treatment with dapagliflozin improved the differentiation of SVC, confirmed by AdipoRed staining [539 ± 142 arbitrary units (a.u.) vs. 473 ± 136 a.u.; P < 0.01] and perilipin expression levels (121 ± 10 vs. 84 ± 11 a.u.).

CONCLUSIONS

Dapagliflozin increased glucose uptake, reduced the secretion of pro-inflammatory chemokines (with a beneficial effect on the healing of human coronary artery endothelial cells), and improved the differentiation of EAT cells. These results suggest a new protective pathway for this drug on EAT from patients with cardiovascular disease.

Functional characterization of the Ucp1-associated oxidative phenotype of human epicardial adipose tissue

Brown fat presence and metabolic activity has been associated with lower body mass index, higher insulin sensitivity and better cardiometabolic profile in humans. We, and others, have previously reported the presence of Ucp1, a marker of brown adipocytes, in human epicardial adipose tissue (eAT). Characterization of the metabolic activity and associated physiological relevance of Ucp1 within eAT, however, is still awaited. Here, we validate the presence of Ucp1 within human eAT and its ‘beige’ nature. Using in-vitro analytical approaches, we further characterize its thermogenic potential and demonstrate that human eAT is capable of undergoing enhanced uncoupling respiration upon stimulation. Direct biopsy gene expression analysis reveals a negative association between thermogenic markers and oxidative stress-related genes in this depot. Consistently, isoproterenol (Iso) stimulation of eAT leads to a downregulation of secreted proteins included in the GO terms ‘cell redox homeostasis’ and ‘protein folding’. In addition, cardiac endothelial cells exhibit a downregulation in the expression of adhesion markers upon treatment with Iso-stimulated eAT derived conditioned media. Overall, these observations suggest that Ucp1- associated metabolic activity plays a significant role in local tissue homeostasis within eAT and can plausibly alter its communication with neighboring cells of the cardiovascular system.

Joint statement of the European Association for the Study of Obesity and the European Society of Hypertension: obesity and heart failure

Obese individuals are more likely to develop heart failure. Yet, once heart failure is established, the impact of overweight and obesity on prognosis and survival is unclear. The purpose of this joint scientific statement of the European Association for the Study of Obesity and the European Society of Hypertension is to provide an overview on the current scientific literature on obesity and heart failure in terms of prognosis, mechanisms, and clinical management implications. Moreover, the document identifies open questions that ought to be addressed. The need for more tailored weight management recommendations in heart failure will be emphasized and, in line with the emerging evidence, aims to distinguish between primary disease and secondary outcome prevention. In the primary prevention of heart failure, it appears prudent advising obese individuals to lose or achieve a healthy body weight, especially in those with risk factors such as hypertension or type 2 diabetes. However, there is no evidence from clinical trials to guide weight management in overweight or obese patients with established heart failure. Prospective clinical trials are strongly encouraged.

Investigating interactions between epicardial adipose tissue and cardiac myocytes: what can we learn from different approaches?

Heart disease is a major cause of morbidity and mortality throughout the world. Some cardiovascular conditions can be modulated by lifestyle factors such as increased exercise or a healthier diet, but many require surgical or pharmacological interventions for their management. More targeted and less invasive therapies would be beneficial. Recently, it has become apparent that epicardial adipose tissue plays an important role in normal and pathological cardiac function, and it is now the focus of considerable research. Epicardial adipose tissue can be studied by imaging of various kinds, and these approaches have yielded much useful information. However, at a molecular level, it is more difficult to study as it is relatively scarce in animal models and, for practical and ethical reasons, not always available in sufficient quantities from patients. What is needed is a robust model system in which the interactions between epicardial adipocytes and cardiac myocytes can be studied, and physiologically relevant manipulations performed. There are drawbacks to conventional culture methods, not least the difficulty of culturing both cardiac myocytes and adipocytes, each of which has special requirements. We discuss the benefits of a three-dimensional co-culture model in which in vivo interactions can be replicated.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Association Between 25-Hydroxyvitamin D and Epicardial Adipose Tissue in Chinese Non-Obese Patients with Type 2 Diabetes

Background

Epicardial adipose tissue (EAT) is recognized as a useful indicator for type 2 diabetes mellitus (T2DM) and obesity. However, studies on the association between vitamin D status and EAT thickness in type 2 diabetes (T2D) are limited. In this study, we aimed to evaluate the association of vitamin D (Calcifediol) status and EAT thickness (EATT) in Chinese non-obese patients with T2D.

Material/Methods

A cross-sectional study was performed among 167 non-obese T2D Chinese patients and 82 non-diabetic patients, who are age- and gender-matched during the winter months. EATT was evaluated by two-dimensional transthoracic echocardiography. Serum 25-hydroxyvitamin D [25(OH)D, Calcifediol] was examined in the diabetic patients and in the control group.

Results

The concentration of 25(OH)D was 32.00 nmol/l (19.30–53.70 nmol/l) among diabetic patients. Most (93.4%) of the diabetic patients had hypovitaminosis D. We confirmed a clear negative association between 25(OH)D level and EATT in non-obese T2D patients (p=0.01). EATT was significantly correlated with 25(OH)D level (p=0.001) and HOMA-IR (p=0.001). Results of multivariate logistic regression analysis demonstrated increased EATT, which was remarkably associated with 25(OH)D levels (p=0.039), systolic blood pressure (SBP) (p=0.013), HOMA-IR (p=0.030), and waist circumference (p<0.001) in T2D patients after adjusting for the confounding factors.

Conclusions

Increased EATT was found in Chinese non-obese T2D patients. 25(OH)D and HOMA-IR were independently associated with increased EATT after adjusting for multiple confounders.

Role of Epicardial Adipose Tissue in Health and Disease: A Matter of Fat?

Epicardial adipose tissue (EAT) is a small but very biologically active ectopic fat depot that surrounds the heart. Given its rapid metabolism, thermogenic capacity, unique transcriptome, secretory profile, and simply measurability, epicardial fat has drawn increasing attention among researchers attempting to elucidate its putative role in health and cardiovascular diseases. The cellular crosstalk between epicardial adipocytes and cells of the vascular wall or myocytes is high and suggests a local role for this tissue. The balance between protective and proinflammatory/profibrotic cytokines, chemokines, and adipokines released by EAT seem to be a key element in atherogenesis and could represent a future therapeutic target. EAT amount has been found to predict clinical coronary outcomes. EAT can also modulate cardiac structure and function. Its amount has been associated with atrial fibrillation, coronary artery disease, and sleep apnea syndrome. Conversely, a beiging fat profile of EAT has been identified. In this review, we describe the current state of knowledge regarding the anatomy, physiology and pathophysiological role of EAT, and the factors more globally leading to ectopic fat development. We will also highlight the most recent findings on the origin of this ectopic tissue, and its association with cardiac diseases. © 2017 American Physiological Society. Compr Physiol 7:1051-1082, 2017.

Impact of the cardiovascular system-associated adipose tissue on atherosclerotic pathology

Cardiac obesity makes an important contribution to the pathogenesis of cardiovascular disease. One of the important pathways of this contribution is the inflammatory process that takes place in the adipose tissue. In this review, we consider the role of the cardiovascular system-associated fat in atherosclerotic cardiovascular pathology and a non-atherosclerotic cause of coronary artery disease, such as atrial fibrillation. Cardiovascular system-associated fat not only serves as the energy store, but also releases adipokines that control local and systemic metabolism, heart/vascular function and vessel tone, and a number of vasodilating and anti-inflammatory substances. Adipokine appears to play an important protective role in cardiovascular system. Under chronic inflammation conditions, the repertoire of signaling molecules secreted by cardiac fat can be altered, leading to a higher amount of pro-inflammatory messengers, vasoconstrictors, profibrotic modulators. This further aggravates cardiovascular inflammation and leads to hypertension, induction of the pathological tissue remodeling and cardiac fibrosis. Contemporary imaging techniques showed that epicardial fat thickness correlates with the visceral fat mass, which is an established risk factor and predictor of cardiovascular disease in obese subjects. However, this correlation is no longer present after adjustment for other covariates. Nevertheless, recent studies showed that pericardial fat volume and epicardial fat thickness can probably serve as a better indicator for atrial fibrillation.

Omentin treatment of epicardial fat improves its anti-inflammatory activity and paracrine benefit on smooth muscle cells

OBJECTIVE

Epicardial adipose tissue (EAT) in coronary artery disease is insulin resistant and has a proinflammatory profile. This study examined the regulation of EAT by exogenous omentin and its consequence on vascular cells.

METHODS

Stromal vascular cells (SC) of EAT and subcutaneous adipose tissue (SAT) from patients who underwent heart surgery were cultured and exposed to adipogenic factors with or without omentin. Proinflammatory cytokine regulation by omentin was analyzed in SC and mature adipocytes. Glucose uptake by EAT and SAT explants was determined after insulin, omentin, or combined treatment. Human vascular cells were exposed to secretomes of SC, with and without omentin treatment. Migration of smooth muscle cells and expression of adhesion molecules were determined by wound healing or real-time polymerase chain reaction, respectively.

RESULTS

Omentin treatment raised adipogenesis-induced adiponectin levels on SC of EAT and reduced TNF-α expression levels (0.58 ± 0.14-fold change; P = 0.034) in mature adipocytes. Omentin improved the insulin activity of EAT and SAT explants from cardiovascular disease patients. Finally, secretomes of SC under omentin treatment reduced the migration of smooth muscle cells.

CONCLUSIONS

Exogenous omentin might support a cardioprotective role through its effect on EAT regarding glucose uptake, anti-inflammatory response, and its paracrine role on smooth muscle cells.

Plasminogen Activator Inhibitor-1 and Pericardial Fat in Individuals with Type 2 Diabetes Mellitus

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) is implicated in the pathophysiology of cardiovascular disease (CVD) and increased in individuals with type 2 diabetes mellitus (T2DM). Adipose tissue produces PAI-1, and pericardial fat is a CVD risk factor. We sought to determine the relationship between PAI-1 and pericardial fat in males and females with well-controlled T2DM.

METHODS

The study population consisted of 32 males and 19 females, aged 35-70 years with T2DM, without clinical evidence of CVD or other active medical problems except for hypertension. Subjects were studied under good cardiometabolic control. Study procedures included fasting blood work and cardiovascular imaging. Cardiac magnetic resonance imaging of the heart was used to identify and quantify pericardial fat from the bifurcation of the pulmonary trunk to the last slice containing cardiac tissue.

RESULTS

PAI-1 was positively correlated with pericardial fat (β = 0.72, r = 0.72, P < 0.001) as well as with homeostatic model assessment of insulin resistance (r = 0.31, P = 0.03) and serum triglycerides (r = 0.27, P = 0.05). In a multivariable regression model, controlling for insulin sensitivity, triglycerides, and body mass index, pericardial fat was independently associated with PAI-1 (β = 0.80, P < 0.001).

CONCLUSIONS

PAI-1 is positively associated with pericardial fat in individuals with T2DM.

Atrial Fibrillation: Epidemiology, Pathophysiology, and Clinical Outcomes

The past 3 decades have been characterized by an exponential growth in knowledge and advances in the clinical treatment of atrial fibrillation (AF). It is now known that AF genesis requires a vulnerable atrial substrate and that the formation and composition of this substrate may vary depending on comorbid conditions, genetics, sex, and other factors. Population-based studies have identified numerous factors that modify the atrial substrate and increase AF susceptibility. To date, genetic studies have reported 17 independent signals for AF at 14 genomic regions. Studies have established that advanced age, male sex, and European ancestry are prominent AF risk factors. Other modifiable risk factors include sedentary lifestyle, smoking, obesity, diabetes mellitus, obstructive sleep apnea, and elevated blood pressure predispose to AF, and each factor has been shown to induce structural and electric remodeling of the atria. Both heart failure and myocardial infarction increase risk of AF and vice versa creating a feed-forward loop that increases mortality. Other cardiovascular outcomes attributed to AF, including stroke and thromboembolism, are well established, and epidemiology studies have championed therapeutics that mitigate these adverse outcomes. However, the role of anticoagulation for preventing dementia attributed to AF is less established. Our review is a comprehensive examination of the epidemiological data associating unmodifiable and modifiable risk factors for AF and of the pathophysiological evidence supporting the mechanistic link between each risk factor and AF genesis. Our review also critically examines the epidemiological data on clinical outcomes attributed to AF and summarizes current evidence linking each outcome with AF.

Transcriptome analysis reveals potential mechanisms underlying differential heart development in fast- and slow-growing broilers under heat stress

BACKGROUND

Modern fast-growing broilers are susceptible to heart failure under heat stress because their relatively small hearts cannot meet increased need of blood pumping. To improve the cardiac tolerance to heat stress in modern broilers through breeding, we need to find the important genes and pathways that contribute to imbalanced cardiac development and frequent occurrence of heat-related heart dysfunction. Two broiler lines - Ross 708 and Illinois - were included in this study as a fast-growing model and a slow-growing model respectively. Each broiler line was separated to two groups at 21 days posthatch. One group was subjected to heat stress treatment in the range of 35-37 °C for 8 h per day, and the other was kept in thermoneutral condition. Body and heart weights were measured at 42 days posthatch, and gene expression in left ventricles were compared between treatments and broiler lines through RNA-seq analysis.

RESULTS

Body weight and normalized heart weight were significantly reduced by heat stress only in Ross broilers. RNA-seq results of 44 genes were validated using Biomark assay. A total of 325 differentially expressed (DE) genes were detected between heat stress and thermoneutral in Ross 708 birds, but only 3 in Illinois broilers. Ingenuity pathway analysis (IPA) predicted dramatic changes in multiple cellular activities especially downregulation of cell cycle. Comparison between two lines showed that cell cycle activity is higher in Ross than Illinois in thermoneutral condition but is decreased under heat stress. Among the significant pathways (P < 0.01) listed for different comparisons, "Mitotic Roles of Polo-like Kinases" is always ranked first.

CONCLUSIONS

The increased susceptibility of modern broilers to cardiac dysfunction under heat stress compared to slow-growing broilers could be due to diminished heart capacity related to reduction in relative heart size. The smaller relative heart size in Ross heat stress group than in Ross thermoneutral group is suggested by the transcriptome analysis to be caused by decreased cell cycle activity and increased apoptosis. The DE genes in RNA-seq analysis and significant pathways in IPA provides potential targets for breeding of heat-tolerant broilers with optimized heart function.

The role of epicardial adipose tissue in cardiac biology: classic concepts and emerging roles

Classic concepts about the role of epicardial adipose tissue (EpAT) in heart physiology include its role in cardiac metabolism, mechanical protection of coronaries, innervation and possibly cryoprotection of the heart too. Nevertheless, recent evidence has revealed that epicardial adipose tissue regulates multiple aspects of cardiac biology including myocardial redox state, intracellular Ca²⁺ cycling, the electrophysiological and contractile properties of cardiomyocytes, cardiac fibrosis as well as coronary atherosclerosis progression. Moreover, it is now understood that the communication between EpAT and the heart is regulated by complex bidirectional pathways, since not only do adipokines regulate cardiac function, but also the heart affects EpAT biology via paracrine 'reverse' signalling. Such complex interactions as well as epicardial fat accumulation as a consequence of cardiac disease and epicardium to adipocyte differentiation should be taken into account by the clinical studies investigating EpAT as a risk marker and its potential as a therapeutic target against cardiovascular disease. Further in-depth exploration of the molecular mechanisms regulating the cross-talk between the heart and EpAT is expected to enhance our understanding regarding the role of the latter in cardiac physiology and relevant disease mechanisms.

Secretory products from epicardial adipose tissue from patients with type 2 diabetes impair mitochondrial β-oxidation in cardiomyocytes via activation of the cardiac renin-angiotensin system and induction of miR-208a

Secretory products from epicardial adipose tissue (EAT) from patients with type 2 diabetes (T2D) impair cardiomyocyte function. These changes associate with alterations in miRNA expression, including the induction of miR-208a. Recent studies suggest that activation of the cardiac-specific renin-angiotensin system (RAS) may affect cardiac energy metabolism via induction of miR-208a. This study investigated whether cardiomyocyte dysfunction induced by conditioned media (CM) from EAT-T2D involves activation of the RAS/miR-208a pathway. Therefore, primary adult rat cardiomyocytes were incubated with CM generated from EAT biopsies from patients with T2D and without T2D (ND). Exposing cardiomyocytes to CM-EAT-T2D reduced sarcomere shortening and increased miR-208a expression versus cells exposed to CM-EAT-ND or control medium. The angiotensin II receptor type 1 (AGTR1) antagonist losartan reversed these effects. Accordingly, incubation with angiotensin II (Ang II) reduced sarcomere shortening, and lowered palmitate-induced mitochondrial respiration and carnitine palmitoyltransferase 1c (CPT1c) expression in cardiomyocytes. Locked-nucleic-acid-mediated inhibition of miR-208a function reversed the detrimental effects induced by Ang II. Interestingly, Ang II levels in CM-EAT-T2D were increased by 2.6-fold after culture with cardiomyocytes. The paracrine activation of the cardiac-specific RAS by CM-EAT-T2D was corroborated by increases in the expression of AGTR1 and renin, as well as a reduction in angiotensin-converting enzyme 2 levels. Collectively, these data show that secretory products from EAT-T2D impair cardiomyocyte contractile function and mitochondrial β-oxidation via activation of the cardiac-specific RAS system and induction of miR-208a, and suggest that alterations in the secretory profile of EAT may contribute to the development of diabetes-related heart disease.

Effects of lifestyle intervention on left ventricular regional myocardial function in metabolic syndrome patients from the RESOLVE randomized trial

AIMS

The purpose of our study was to determine the effect of lifestyle intervention on left ventricular (LV) regional myocardial function in patients with metabolic syndrome (MetS) and investigate the relationships of the changes in myocardial function to changes in epicardial adipose tissue (EAT), inflammatory profile and MetS components.

METHODS

Eighty-seven MetS patients were enrolled in a 6month lifestyle intervention program based on dietary management and increased physical activity, and compared with 44 aged and sex-matched healthy controls. MetS individuals were allocated to different groups randomized (computer-generated randomization) on exercise modalities (high-intensity dominant resistance or aerobic training, and moderate-intensity of both modes). EAT was measured by transthoracic echocardiography and LV longitudinal strains and strain rates were obtained using vector velocity imaging. Blood chemistry allowed assessments of adipocytokines (TNF-α: tumor necrosis factor α, PAI active: active plasminogen activator inhibitor-1 and adiponectin) and glucose tolerance markers.

RESULTS

Regardless of exercise training modalities, lifestyle intervention improved significantly LV strains and strain rates (p<0.001) as well as metabolic and inflammatory profiles. Stepwise multiple regression analyses revealed EAT (β=0.73, p<0.01), log adiponectin (β=-0.13, p<0.05) and log TNF-α (β=0.15, p<0.05) as independent predictors of LV longitudinal strain (R(2)=0.74, p<0.001) while myocardial function improvement consecutive to lifestyle intervention was explained by EAT changes only (R(2)=0.54, p<0.001).

CONCLUSION

The mechanisms through which regional myocardial function is impaired in MetS and improved consecutive to intervention involved EAT, possibly via paracrine effects of adipocytokines. EAT should be considered as a future therapeutic target of interest in the treatment of metabolic-related cardiac diseases.

The Abundance of Epicardial Adipose Tissue Surrounding Left Atrium Is Associated With the Occurrence of Stroke in Patients With Atrial Fibrillation

Epicardial adipose tissue (EAT) is positively associated with risk factors for cardiovascular disease, but the role of EAT in the development of atrial fibrillation (AF)-related stroke and its association with the anatomical and functional remodeling of the left atrium (LA) have not been elucidated.This was a comparative cross-sectional study. Twenty-seven patients with paroxysmal or persistent AF and cardioembolic stroke were selected and compared with 68 age- and sex-matched AF patients without stroke. In addition, 20 controls without a history of AF or stroke were included. The periatrial EAT and the structural and functional properties of the LA and left ventricle were evaluated using contrast-enhanced 64-slice multidetector computed tomography during sinus rhythm. Total EAT around the LA was significantly increased across the groups (control vs AF vs AF-related stroke, P < 0.001). The volumes of the LA and the LA appendage (LAA) were also significantly increased across the 3 groups (P < 0.001 for each). The emptying fraction of the LA and LAA and the booster-pump function of the LA and LAA were all reduced across the 3 groups (P < 0.001 for all). In addition, the Hounsfield unit (HU) ratio of the LAA to the ascending aorta (LAA/AA) was also decreased in patients with stroke (P < 0.001). Furthermore, EAT had a negative correlation with the dynamic function of the LA, LAA, and the HU ratio. After a multivariate analysis, increased EAT (P < 0.001) was shown to be independently associated with the occurrence of AF-related stroke.Periatrial EAT was increased and was correlated with atrial dysfunction in patients with AF-related stroke. Hence, EAT assessment may potentially offer an incremental value for grading the risk of cardioembolic stroke in patients with AF.

Pericardial- Rather than Intramyocardial Fat Is Independently Associated with Left Ventricular Systolic Heart Function in Metabolically Healthy Humans

Background

Obesity is a major risk factor to develop heart failure, in part due to possible lipotoxic effects of increased intramyocardial (MYCL) and/or local or paracrine effects of pericardial (PERI) lipid accumulation. Recent evidence suggests that MYCL is highly dynamic and might rather be a surrogate marker for disturbed energy metabolism than the underlying cause of cardiac dysfunction. On the other hand, PERI might contribute directly by mechanic and paracrine effects. Therefore, we hypothesized that PERI rather than MYCL is associated with myocardial function.

Methods

To avoid potential confounding of metabolic disease 31 metabolically healthy subjects (age: 29±10yrs; BMI: 23±3kg/m²) were investigated using ¹H-magnetic resonance spectroscopy and imaging. MYCL and PERI, as well as systolic and diastolic left ventricular heart function were assessed. Additionally, anthropometric data and parameters of glucose and lipid metabolism were analyzed. Correlation analysis was performed using Pearson’s correlation coefficient. Linear regression model was used to show individual effects of PERI and MYCL on myocardial functional parameters.

Results

Correlation analysis with parameters of systolic heart function revealed significant associations for PERI (Stroke Volume (SV): R = -0.513 p = 0.001; CardiacIndex (CI): R = -0.442 p = 0.014), but not for MYCL (SV: R = -0.233; p = 0.207; CI: R = -0.130; p = 0.484). No significant correlations were found for E/A ratio as a parameter of diastolic heart function. In multiple regression analysis CI was negatively predicted by PERI, whereas no impact of MYCL was observed in direct comparison.

Conclusions

Cardiac fat depots impact left ventricular heart function in a metabolically healthy population. Direct comparison of different lipid stores revealed that PERI is a more important predictor than MYCL for altered myocardial function.

Mutual Regulation of Epicardial Adipose Tissue and Myocardial Redox State by PPAR-γ/Adiponectin Signalling

RATIONALE

Adiponectin has anti-inflammatory effects in experimental models, but its role in the regulation of myocardial redox state in humans is unknown. Although adiponectin is released from epicardial adipose tissue (EpAT), it is unclear whether it exerts any paracrine effects on the human myocardium.

OBJECTIVE

To explore the cross talk between EpAT-derived adiponectin and myocardial redox state in the human heart.

METHODS AND RESULTS

EpAT and atrial myocardium were obtained from 306 patients undergoing coronary artery bypass grafting. Functional genetic polymorphisms that increase ADIPOQ expression (encoding adiponectin) led to reduced myocardial nicotinamide adenine dinucleotide phosphate oxidase-derived O2 (-), whereas circulating adiponectin and ADIPOQ expression in EpAT were associated with elevated myocardial O2 (-). In human atrial tissue, we demonstrated that adiponectin suppresses myocardial nicotinamide adenine dinucleotide phosphate oxidase activity, by preventing AMP kinase-mediated translocation of Rac1 and p47(phox) from the cytosol to the membranes. Induction of O2 (-) production in H9C2 cardiac myocytes led to the release of a transferable factor able to induce peroxisome proliferator-activated receptor-γ-mediated upregulation of ADIPOQ expression in cocultured EpAT. Using a NOX2 transgenic mouse and a pig model of rapid atrial pacing, we found that oxidation products (such as 4-hydroxynonenal) released from the heart trigger peroxisome proliferator-activated receptor-γ-mediated upregulation of ADIPOQ in EpAT.

CONCLUSIONS

We demonstrate for the first time in humans that adiponectin directly decreases myocardial nicotinamide adenine dinucleotide phosphate oxidase activity via endocrine or paracrine effects. Adiponectin expression in EpAT is controlled by paracrine effects of oxidation products released from the heart. These effects constitute a novel defense mechanism of the heart against myocardial oxidative stress.

Cardiac adipose tissue and atrial fibrillation: the perils of adiposity

The amount of adipose tissue that accumulates around the atria is associated with the risk, persistence, and severity of atrial fibrillation (AF). A strong body of clinical and experimental evidence indicates that this relationship is not an epiphenomenon but is the result of complex crosstalk between the adipose tissue and the neighbouring atrial myocardium. For instance, epicardial adipose tissue is a major source of adipokines, inflammatory cytokines, or reactive oxidative species, which can contribute to the fibrotic remodelling of the atrial myocardium. Fibro-fatty infiltrations of the subepicardium could also contribute to the functional disorganization of the atrial myocardium. The observation that obesity is associated with distinct structural and functional remodelling of the atria has opened new perspectives of treating AF substrate with aggressive risk factor management. Advances in cardiac imaging should lead to an improved ability to visualize myocardial fat depositions and to localize AF substrates.

Cardiomyocyte Antihypertrophic Effect of Adipose Tissue Conditioned Medium from Rats and Its Abrogation by Obesity is Mediated by the Leptin to Adiponectin Ratio

White adipocytes are known to function as endocrine organs by secreting a plethora of bioactive adipokines which can regulate cardiac function including the development of hypertrophy. We determined whether adipose tissue conditioned medium (ATCM) generated from the epididymal regions of normal rats can affect the hypertrophic response of cultured rat ventricular myocytes to endothelin-1 (ET-1) administration. Myocytes were treated with ET-1 (10 nM) for 24 hours in the absence or presence of increasing ATCM concentrations. ATCM supressed the hypertrophic response to ET-1 in a concentration-dependent manner, an effect enhanced by the leptin receptor antagonist and attenuated by an antibody against the adiponectin AdipoR1 receptor. Antihypertrophic effects were also observed with ATCM generated from perirenal-derived adipose tissue. However, this effect was absent in ATCM from adipose tissue harvested from corpulent JCR:LA-cp rats. Detailed analyses of adipokine content in ATCM from normal and corpulent rats revealed no differences in the majority of products assayed, although a significant increase in leptin concentrations concomitant with decreased adiponectin levels was observed, resulting in a 11 fold increase in the leptin to adiponectin ratio in ATCM from JCR:LA-cp. The antihypertrophic effect of ATCM was associated with increased phosphorylation of AMP-activated protein kinase (AMPK), an effect abrogated by the AdipoR1 antibody. Moreover, the antihypertrophic effect of ATCM was mimicked by an AMPK activator. There was no effect of ET-1 on mitogen-activated protein kinase (MAPK) activities 24 hour after its addition either in the presence or absence of ATCM. Our study suggests that adipose tissue from healthy subjects exerts antihypertrophic effects via an adiponectin–dependent pathway which is impaired in obesity, most likely due to adipocyte remodelling resulting in enhanced leptin and reduced adiponectin levels.

Integrative miRNA and whole-genome analyses of epicardial adipose tissue in patients with coronary atherosclerosis

BACKGROUND

Epicardial adipose tissue (EAT) is an atypical fat depot surrounding the heart with a putative role in the development of atherosclerosis.

METHODS AND RESULTS

We profiled genes and miRNAs in perivascular EAT and subcutaneous adipose tissue (SAT) of metabolically healthy patients without coronary artery disease (CAD) vs. metabolic patients with CAD. Compared with SAT, a specific tuning of miRNAs and genes points to EAT as a tissue characterized by a metabolically active and pro-inflammatory profile. Then, we depicted both miRNA and gene signatures of EAT in CAD, featuring a down-regulation of genes involved in lipid metabolism, mitochondrial function, nuclear receptor transcriptional activity, and an up-regulation of those involved in antigen presentation, chemokine signalling, and inflammation. Finally, we identified miR-103-3p as candidate modulator of CCL13 in EAT, and a potential biomarker role for the chemokine CCL13 in CAD.

CONCLUSION

EAT in CAD is characterized by changes in the regulation of metabolism and inflammation with miR-103-3p/CCL13 pair as novel putative actors in EAT function and CAD.

Differential behaviour of epicardial adipose tissue-secretomes with high and low orosomucoid levels from patients with cardiovascular disease in H9C2 cells

Epicardial adipose tissue releases orosomucoid (ORM), an acute phase protein with multiple modulatory and protective properties. We aimed to identify the effect of EAT-supernatants according to their ORM levels on H9C2 cells. H9C2 were cultured with EAT-secretomes or ORM protein itself on a Real-Time Cell Analyser. Secretome proteins identification was performed by LC-mass spectrometry according to their ORM levels. Two of them were validated by ELISA in EAT-supernatants from 42 patients. ORM effect on H9C2 and neonatal rat cardiomyocytes apoptosis under hypoxia with or without fatty acid treatment was determined by Annexin-V flow cytometry measurement. Caspase-3 expression levels were determined by western blot in H9C2. Our results showed a differential effect of EAT-secretomes according their ORM levels. Although additional secreted proteins can contribute to their beneficial effects, ORM reduced hypoxia-induced apoptosis through caspase-3 inhibition. Our data showed the cardioprotective role of ORM and suggest that its quantification on EAT secretomes might help us to find new secreted factors with a cardioprotective role.

Thermogenic potential and physiological relevance of human epicardial adipose tissue

Epicardial adipose tissue is a unique fat depot around the heart that shares a close anatomic proximity and vascular supply with the myocardium and coronary arteries. Its accumulation around the heart, measured using various imaging modalities, has been associated with the onset and progression of coronary artery disease in humans. Epicardial adipose tissue is also the only fat depot around the heart that is known to express uncoupling protein 1 at both mRNA and protein levels in the detectable range. Recent advances have further indicated that human epicardial fat exhibits beige fat-like features. Here we provide an overview of the physiological and pathophysiological relevance of human epicardial fat, and further discuss whether its thermogenic properties can serve as a target for the therapeutic management of coronary heart disease in humans.

Local and systemic effects of the multifaceted epicardial adipose tissue depot

Epicardial adipose tissue is a unique and multifaceted fat depot with local and systemic effects. This tissue is distinguished from other visceral fat depots by a number of anatomical and metabolic features, such as increased fatty acid metabolism and a unique transcriptome enriched in genes that are associated with inflammation and endothelial function. Epicardial fat and the heart share an unobstructed microcirculation, which suggests these tissues might interact. Under normal physiological conditions, epicardial fat has metabolic, thermogenic (similar to brown fat) and mechanical (cardioprotective) characteristics. Development of pathological conditions might drive the phenotype of epicardial fat such that it becomes harmful to the myocardium and the coronary arteries. The equilibrium between protective and detrimental effects of this tissue is fragile. Expression of the epicardial-fat-specific transcriptome is downregulated in the presence of severe and advanced coronary artery disease. Improved local vascularization, weight loss and targeted medications can restore the protective physiological functions of epicardial fat. Measurements of epicardial fat have several important applications in the clinical setting: accurate measurement of its thickness or volume is correlated with visceral adiposity, coronary artery disease, the metabolic syndrome, fatty liver disease and cardiac changes. On account of this simple clinical assessment, epicardial fat is a reliable marker of cardiovascular risk and an appealing surrogate for assessing the efficacy of drugs that modulate adipose tissues.

Ischemia and reperfusion related myocardial inflammation: A network of cells and mediators targeting the cardiomyocyte

Occlusion of a coronary artery if maintained for longer period of time results in damage of the cardiac tissue. However, restoration of blood flow to previously ischemic tissue can itself induce further cardiac damage, a phenomenon known as myocardial reperfusion injury. Cardiac homoeostasis is supported by a network of direct and indirect interactions between cardiomyocytes and resident cell types such as fibroblasts, adipocytes, and endothelial cells or invading blood cells. This review will discuss the role of the cellular interplay in ischemia-reperfusion injury from a cardiomyocyte-centered view, although we are aware that other cellular interactions are equally important. We will try to work out currently unresolved questions and potential future directions in the field.

Impaired adipogenesis and insulin resistance in epicardial fat-mesenchymal cells from patients with cardiovascular disease

The thickness of epicardial adipose tissue (EAT), which is an inflammatory source for coronary artery disease (CAD), correlates with insulin resistance. One trigger factor is impaired adipogenesis. Here, our aim was to clarify the underlying mechanisms of insulin resistance on EAT-mesenchymal cells (MC). EAT and subcutaneous adipose tissue (SAT) were collected from 19 patients who were undergoing heart surgery. Their dedifferentiated adipocytes (DAs) and/or MCs were cultured. After the induction of adipogenesis or stimulation with insulin, the expression of adipokines was analyzed using real-time polymerase chain reaction (PCR). Colorimetric assays were performed to measure glucose levels and proliferation rate. Proteins modifications were detected via the proteomic approach and Western blot. Our results showed lower adipogenic ability in EAT-MCs than in SAT-MCs. Maximum adiponectin levels were reached within 28-35 days of exposure to adipogenic inducers. Moreover, the adipogenesis profile in EAT-MCs was dependent on the patients' clinical characteristics. The low adipogenic ability of EAT-MCs might be associated with an insulin-resistant state because chronic insulin treatment reduced the inflammatory cytokine expression levels, improved the glucose consumption, and increased the post-translational modifications (PTMs) of the glycolytic enzyme phosphoglycerate mutase 1 (PGAM1). We found lower adipogenic ability in EAT-MCs than in SAT-MCs. This lower ability level was dependent on gender and the presence of diabetes, obesity, and CAD. Low adipogenesis ability and insulin resistance in EAT-MCs might shed light on the association between EAT dysfunction and cardiovascular disease.

Age-related different relationships between ectopic adipose tissues and measures of central obesity in sedentary subjects

Accumulation of fat at ectopic sites has been gaining attention as pivotal contributor of insulin resistance, metabolic syndrome and related cardiovascular complications. Intermuscular adipose tissue (IMAT), located between skeletal muscle bundles and beneath muscle fascia, has been linked to physical inactivity, ageing and body mass index, but little is known about its relationship with the other AT compartments, in particular with increasing age. To address this issue, erector spinae IMAT, epicardial (EAT), intraabdominal (IAAT) and abdominal subcutaneous adipose tissue (SAT) were simultaneously measured by Magnetic Resonance Imaging (MRI) and related to waist circumference measurements and age in 32 sedentary subjects without cardiovascular disease (18 men; 14 women; mean age 48.5±14 years). Fasting glucose, triglycerides and HDL-cholesterol were also assessed. We observed that, after dividing individuals according to age (≤ or >50 years), IMAT and EAT depots were significantly more expanded in older subjects (63.2±8.3 years) than in the younger ones (38.4±5.2 years) (p<0.001). Overall, both IMAT and EAT showed stronger positive associations with increasing age (β = 0.63 and 0.67, respectively, p<0.001 for both) than with waist circumference (β = 0.55 and 0.49, respectively, p<0.01 for both) after adjusting for gender. In addition, the gender-adjusted associations of IMAT and EAT with waist circumference and IAAT were significant in individuals ≤50 years only (p<0.05 for all) and not in the older ones. In contrast, no age-related differences were seen in the relationships of IAAT and SAT with waist circumference. Finally, serum triglycerides levels turned out not to be independently related with ectopic IMAT and EAT. In conclusion, the expansion of IMAT and EAT in sedentary subjects is more strongly related to age than waist circumference, and a positive association of these ectopic depots with waist circumference and IAAT amount can be postulated in younger individuals only.

Epicardial adipose tissue in endocrine and metabolic diseases

Epicardial adipose tissue has recently emerged as new risk factor and active player in metabolic and cardiovascular diseases. Albeit its physiological and pathological roles are not completely understood, a body of evidence indicates that epicardial adipose tissue is a fat depot with peculiar and unique features. Epicardial fat is able to synthesize, produce, and secrete bioactive molecules which are then transported into the adjacent myocardium through vasocrine and/or paracrine pathways. Based on these evidences, epicardial adipose tissue can be considered an endocrine organ. Epicardial fat is also thought to provide direct heating to the myocardium and protect the heart during unfavorable hemodynamic conditions, such as ischemia or hypoxia. Epicardial fat has been suggested to play an independent role in the development and progression of obesity- and diabetes-related cardiac abnormalities. Clinically, the thickness of epicardial fat can be easily and accurately measured. Epicardial fat thickness can serve as marker of visceral adiposity and visceral fat changes during weight loss interventions and treatments with drugs targeting the fat. The potential of modulating the epicardial fat with targeted pharmacological agents can open new avenues in the pharmacotherapy of endocrine and metabolic diseases. This review article will provide Endocrine's reader with a focus on epicardial adipose tissue in endocrinology. Novel, established, but also speculative findings on epicardial fat will be discussed from the unexplored perspective of both clinical and basic Endocrinologist.

Impact of diabetes mellitus on myocardial lipid deposition: an autopsy study

Lipid accumulation in the cardiac parenchyma has historically been known as fatty heart. Myocardial lipotoxicity and cardiac steatosis have been shown to be involved in the pathogenesis of obesity and diabetic mellitus (DM). Mutated adipose triglyceride lipase (ATGL), a key catalytic enzyme of triglyceride, has been found to cause human triglyceride deposit cardiomyovasculopathy (TGCV). Nevertheless, the significance of fatty heart in the disease process is still unclear. Here, we investigated myocardial lipid deposition (LD) in 73 autopsy cases. Nile blue staining revealed seven cases (9.5%) showing LD with elevated tissue triglyceride content, all of which suffered from DM. Immunohistochemically, ATGL expression was preserved in all tested cases. Rates of myocardial infarction and heart failure were higher in LD/DM cases than in non-LD cases. Semi-quantitative histological analysis revealed no significant differences in the degree of myocardial hypertrophy, myofibrillar loss, fibrosis, small vascular disease, inflammation or fat invasion between LD/DM and non-LD cases. However, more severe histological damage was seen in DM cases than in non-DM cases. Our data suggest that DM is a major risk for fatty heart with myocardial LD based on recent autopsy cases.

Epicardial adipose tissue and atrial fibrillation

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia in clinical practice. AF is often associated with profound functional and structural alterations of the atrial myocardium that compose its substrate. Recently, a relationship between the thickness of epicardial adipose tissue (EAT) and the incidence and severity of AF has been reported. Adipose tissue is a biologically active organ regulating the metabolism of neighbouring organs. It is also a major source of cytokines. In the heart, EAT is contiguous with the myocardium without fascia boundaries resulting in paracrine effects through the release of adipokines. Indeed, Activin A, which is produced in abundance by EAT during heart failure or diabetes, shows a marked fibrotic effect on the atrial myocardium. The infiltration of adipocytes into the atrial myocardium could also disorganize the depolarization wave front favouring micro re-entry circuits and local conduction block. Finally, EAT contains progenitor cells in abundance and therefore could be a source of myofibroblasts producing extracellular matrix. The study on the role played by adipose tissue in the pathogenesis of AF is just starting and is highly likely to uncover new biomarkers and therapeutic targets for AF.

Epicardial fat and vascular risk: a narrative review

PURPOSE OF REVIEW

We comment on the associations between epicardial adiposity and cardiovascular disease (CVD) and associated risk factors. The effects of lifestyle measures and CVD drugs on cardiac adipose tissue are also discussed.

RECENT FINDINGS

Epicardial adipose tissue exerts cardioprotective properties; however, in cases of pathological enlargement, epicardial fat can lead to myocardial inflammation and dysfunction as well as left ventricular hypertrophy and coronary artery disease (CAD) due to paracrine actions that include increased production of reactive oxygen species, atherogenic and inflammatory cytokines. Cardiac adiposity is associated with CAD, obesity, type 2 diabetes, metabolic syndrome, nonalcoholic fatty liver disease, and chronic kidney disease, as well as with CVD risk factors such as lipids, hypertension, obesity markers, and carotid atherosclerosis.

SUMMARY

Due to its anatomical and functional proximity to the coronary circulation, epicardial adipose tissue may represent an even more direct CVD risk marker than central adiposity. Lifestyle measures and certain drugs may affect its thickness, although there are limited data currently available. The clinical implications of epicardial fat in daily practice remain to be established in future studies.

Activation of AKT by O-linked N-acetylglucosamine induces vascular calcification in diabetes mellitus

RATIONALE

Vascular calcification is a serious cardiovascular complication that contributes to the increased morbidity and mortality of patients with diabetes mellitus. Hyperglycemia, a hallmark of diabetes mellitus, is associated with increased vascular calcification and increased modification of proteins by O-linked N-acetylglucosamine (O-GlcNAcylation).

OBJECTIVE

We sought to determine the role of protein O-GlcNAcylation in regulating vascular calcification and the underlying mechanisms.

METHODS AND RESULTS

Low-dose streptozotocin-induced diabetic mice exhibited increased aortic O-GlcNAcylation and vascular calcification, which was also associated with impaired aortic compliance in mice. Elevation of O-GlcNAcylation by administration of Thiamet-G, a potent inhibitor for O-GlcNAcase that removes O-GlcNAcylation, further accelerated vascular calcification and worsened aortic compliance of diabetic mice in vivo. Increased O-GlcNAcylation, either by Thiamet-G or O-GlcNAcase knockdown, promoted calcification of primary mouse vascular smooth muscle cells. Increased O-GlcNAcylation in diabetic arteries or in the O-GlcNAcase knockdown vascular smooth muscle cell upregulated expression of the osteogenic transcription factor Runx2 and enhanced activation of AKT. O-GlcNAcylation of AKT at two new sites, T430 and T479, promoted AKT phosphorylation, which in turn enhanced vascular smooth muscle cell calcification. Site-directed mutation of AKT at T430 and T479 decreased O-GlcNAcylation, inhibited phosphorylation of AKT at S473 and binding of mammalian target of rapamycin complex 2 to AKT, and subsequently blocked Runx2 transactivity and vascular smooth muscle cell calcification.

CONCLUSIONS

O-GlcNAcylation of AKT at 2 new sites enhanced AKT phosphorylation and activation, thus promoting vascular calcification. Our studies have identified a novel causative effect of O-GlcNAcylation in regulating vascular calcification in diabetes mellitus and uncovered a key molecular mechanism underlying O-GlcNAcylation-mediated activation of AKT.