Modulation of Vascular Reactivity by Perivascular Adipose Tissue (PVAT)

Purpose of Review

In this review, we discuss the role of perivascular adipose tissue (PVAT) in the modulation of vascular contractility and arterial pressure, focusing on the role of the renin-angiotensin-aldosterone system and oxidative stress/inflammation.

Recent Findings

PVAT possesses a relevant endocrine-paracrine activity, which may be altered in several pathophysiological and clinical conditions. During the last two decades, it has been shown that PVAT may modulate vascular reactivity. It has also been previously demonstrated that inflammation in adipose tissue may be implicated in vascular dysfunction. In particular, adipocytes secrete a number of adipokines with various functions, as well as several vasoactive factors, together with components of the renin-angiotensin system which may act at local or at systemic level. It has been shown that the anti-contractile effect of PVAT is lost in obesity, probably as a consequence of the development of adipocyte hypertrophy, inflammation, and oxidative stress.

Summary

Adipose tissue dysfunction is interrelated with inflammation and oxidative stress, thus contributing to endothelial dysfunction observed in several pathological and clinical conditions such as obesity and hypertension. Decreased local adiponectin level, macrophage recruitment and infiltration, and activation of renin-angiotensin-aldosterone system could play an important role in this regard.

     

Adipose Tissue and Bone

There is extensive clinical evidence that fat mass and bone mass are related to one another, and there are many laboratory and animal studies that explore the mechanisms of these relationships. However, there are a number of methodological issues that complicate the interpretation of both types of studies, and these need to be borne in mind as the studies reviewed in this volume are considered. These issues are reviewed in this introduction.     

血管旁脂肪组织与心血管疾病的关系

血管旁脂肪组织与血管在组织学上密切相关,近期研究表明它不只是惰性的能量储存器官,还是个活跃的内分泌器官,可分泌血管活性因子调节血管张力,并释放炎性因子等参与血管炎症、内皮损伤,从而与高血压、动脉粥样硬化等心血管疾病有密切的关系。现就血管旁脂肪组织参与高血压、动脉粥样硬化的机制作一综述。     

The Procoagulant Activity of Adipose Tissue

Homogenates of several rat and human adipose tissues contain procoagulant activity mainly due to the presence of tissue thromboplastin. Intravenous injections in rats of the active fraction from such homogenates cause the accumulation of ⁵¹Cr-labelled platelets and ¹²⁵I-labelled fibrin in the lungs. The effect of phospholipase C and of specific antibodies against tissue thromboplastin on this procoagulant activity of adipose tissue has been studied in vitro and in vivo.     

Visceral Adipose Tissue and Cardiovascular Disease Risk

Adipose tissue has been recognized as an endocrine organ. Cytokines released from adipose tissue not only influence lipid metabolism, they also affect multiple organ systems such as the immune and nervous systems, and of interest in this review, the cardiovascular system. While there are multiple depots of adipose tissue, visceral adipose tissue appears to be the most metabolically active. This fat depot has been linked to dysfunction of the vascular endothelium with the subsequent development of atherosclerosis and incident cardiovascular events. In this regard and within the last two years, several studies have examined the effect of visceral adipose tissue on subclinical and clinical CVD outcomes. This review highlights these findings and focuses on the associations between visceral adipose tissue and ethnicity, risk factors, vascular changes, clinical effects and cardiovascular disease outcomes.     

Gender and Sex Differences in Adipose Tissue

Purpose of Review

As the ongoing epidemic of adult and childhood obesity grows, it puts a greater burden on individuals and the healthcare system due to increased prevalence of obesity-associated diseases. An important area that has gained much attention recently is the sex and gender difference related to obesity and associated complications. Basic science and clinical studies have now improved our understanding of obesity and have discovered adipose tissue biology to be key in metabolism.

Recent Findings

There is evidence related to the sex dichotomy in obesity in a variety of areas including adipocyte function, sex hormone effects, genetics, and metabolic inflammation leading to critical differences in adipose tissue biology.

Summary

The sex and gender difference in adipose tissue is a factor that should be considered when studying an individuals’ risk for obesity and metabolic dysfunction. This understanding is important for strategizing treatment and prevention measures.

     

Adipose Tissue as Regulator of Vascular Tone

Adipokines secreted by visceral, subcutaneous, and perivascular adipocytes are involved in the regulation of vascular tone by acting as circulatory hormones (leptin, adiponectin, omentin, visfatin, angiotensin II, resistin, tumor necrosis factor-α, interleukin-6, apelin) and/or via local paracrine factors (perivascular adipocyte-derived relaxing and contractile factors). Vascular tone regulation by adipokines is compromised in obesitas and obesity-related disorders. Hypoxia created in growing adipose tissue dysregulates synthesis of vasoactive adipokines in favor of harmful proinflammatory adipokines, while the levels of the cardioprotective adipokines adiponectin and omentin decrease. Considering the potential of the role of adipokines in obesity-related vascular diseases, strategies to counter these diseases by targeting the adipokines are discussed.     

Visceral Adipose Tissue Accumulation and Residual Cardiovascular Risk

Purpose of the Review

Low-grade systemic inflammation increases residual cardiovascular risk. The pathogenesis of low-grade systemic inflammation is not well understood.

Recent Findings

Visceral adipose tissue accumulates when the subcutaneous adipose tissue can no longer store excess nutrients. Visceral adipose tissue inflammation initially facilitates storage of nutrients but with time become maladaptive and responsible for low-grade systemic inflammation. Control of low-grade systemic inflammation requires reversal of visceral adipose tissue accumulation with intense and sustained aerobic exercise or bariatric surgery. Alternatively, pharmacologic inhibition of the inflammatory signaling pathway may be considered.

Summary

Reversal visceral adipose tissue accumulation lowers residual cardiovascular risk.

     

Increased Epicardial Adipose Tissue Thickness as a Predictor for Hypertension: A Cross‐Sectional Observational Study

The aim of the study was to determine whether epicardial adipose tissue thickness (EAT), a new cardiometabolic risk factor, is associated with essential hypertension. The sample included 127 asymptomatic patients with one or more cardiovascular risk factors consecutively referred for cardiac computed tomography angiography. Data were collected retrospectively and compared between hypertensive (n=39) and normotensive (n=88) patients. The hypertensive patients had a significantly higher mean EAT thickness than the normotensive group (2.81±1.6 mm vs 2.07±1.43 mm; P=.011) and a significantly elevated mean coronary artery calcium score (316.8±512.6 vs 108.73±215; P=.0257). The odds ratio for a patient with tissue thickness ≥2.4 mm having hypertension was 1.396 (95% confidence interval, 1.033–1.922). Factors independently associated with hypertension were body mass index, low‐density lipoprotein, and age. A model score was developed using the logistic regression coefficients for calculation of individual risk. Hypertensive patients have significantly higher than normal EAT thickness. Epicardial adipose tissue thickness may serve as a risk indicator for hypertension and cardiovascular morbidity.     

High Visceral Adipose Tissue to Subcutaneous Adipose Tissue Ratio as a Predictor of Mortality in Acute Respiratory Distress Syndrome

Background

We aimed to further determine the relationship between the areas of visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and the ratio of VAT to SAT (VAT/SAT) with the outcomes of acute respiratory distress syndrome (ARDS) patients.

Adipose Tissue Dysfunction in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disorder among premenopausal women. In addition to infertility, PCOS is associated with insulin resistance, features of the metabolic syndrome, and an increased risk for diabetes. Similar to individuals with metabolic syndrome, many women with PCOS manifest abdominal obesity, suggesting adipose tissue dysfunction. The adipose tissue of women with PCOS is characterized by hypertrophic adipocytes and impairments in lipolysis and insulin action. The expression and secretion of a wide variety of adipokines implicated in insulin resistance, including adiponectin and others, are also altered in PCOS. Collectively, the available data indicate that adipose tissue dysfunction plays a central role in the metabolic abnormalities observed in PCOS. Whether these abnormalities are primary or secondary to hyperandrogenism or other abnormalities in PCOS is not yet known.