Review
Epicardial adipose tissue: emerging physiological, pathophysiological and clinical features

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Epicardial adipose tissue is an unusual visceral fat depot with anatomical and functional contiguity to the myocardium and coronary arteries. Under physiological conditions, epicardial adipose tissue displays biochemical, mechanical and thermogenic cardioprotective properties. Under pathological circumstances, epicardial fat can locally affect the heart and coronary arteries through vasocrine or paracrine secretion of proinflammatory cytokines. What influences this equilibrium remains unclear. Improved local vascularization, weight loss, and targeted pharmaceutical interventions could help to return epicardial fat to its physiological role. This review focuses on the emerging physiological and pathophysiological aspects of the epicardial fat and its numerous and innovative clinical applications. Particular emphasis is placed on the paracrine/endocrine properties of epicardial fat and its role in the development and progression of atherosclerosis.

Section snippets

Anatomy of epicardial adipose tissue

The adipose tissue of the heart consists of epicardial fat (Table 1), located between the myocardium and visceral pericardium, and the pericardial fat, situated outside the visceral pericardium and on the external surface of the parietal pericardium 1, 2, 3, 4, 5, 6, 7, 8. Epicardial and pericardial fat are embryologically different. The epicardium comprises a population of mesothelial cells that migrate onto the surface of the heart from the area of the septum transversum 1, 2, 3, 4.

Epicardial adipose tissue and myocardial metabolism

Epicardial fat is not merely a passive lipid-storage unit, but is actively involved in lipid and energy homeostasis (Table 2) 1, 2, 3, 4. The principal difference between epicardial adipose tissue and other visceral fat depots is its greater capacity for release and uptake free fatty acids (FFAs) and a lower rate of glucose utilization. Indeed, FFA synthesis and rates of incorporation and breakdown are significantly higher in epicardial fat than other fat depots [17]. Higher rates of lipolysis

Epicardial adipose tissue as brown fat

Brown adipose tissue generates heat in response to cold temperatures and activation of the autonomic nervous system [20]. However, the presence and role of brown fat in humans is unclear. Very recently, expression of uncoupling protein-1 (UCP-1), a marker of brown fat, has been reported in human epicardial fat [21]. UCP-1 expression was significantly higher in human epicardial fat than in other fat depots, therefore suggesting that epicardial fat might function in the same way as brown fat to

Epicardial adipose tissue as an endocrine and paracrine organ

Human epicardial fat is a metabolically active organ and a source of several bioactive molecules (Table 3) that might substantially influence the myocardium and coronary arteries 1, 10, 23, 24, 25, 26, 27, 28. Two major mechanisms of interaction between the myocardium and the epicardial fat (i.e. paracrine and vasocrine) (Figure 2), have been suggested [3]. Paracrine release of cytokines from periadventitial epicardial fat could traverse the coronary wall by outside-to-inside diffusion. Given

Imaging of epicardial adipose tissue

Epicardial fat can be easily detected and measured by imaging. Ultrasound provides a simple and readily available assessment, whereas multi-detector computed tomography (MDCT) or cardiac magnetic-resonance imaging (MRI) allow an accurate but more expensive and cumbersome measurement. Overall, objective and reproducible measurement of epicardial fat is certainly a promising tool in both the clinical and research setting. Epicardial fat thickness was first visualized and measured with

Concluding remarks

Epicardial fat is a heart fat depot with unique anatomical and functional characteristics. Epicardial adipocytes are smaller in size than those of other fat depots, and with different fatty acid composition, higher rates of FFA synthesis, uptake and release, and lower rates of glucose utilization. Epicardial fat is also a source of several bioactive molecules and, given its anatomical proximity to the heart, it is thought to interact locally with the coronary arteries and the myocardium through

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