The role of perivascular adipose tissue in obesity-induced vascular dysfunction

Weight Loss and Hypertension in Obese Subjects

Arterial hypertension is strongly related to overweight and obesity. In obese subjects, several mechanisms may lead to hypertension such as insulin and leptin resistance, perivascular adipose tissue dysfunction, renal impairment, renin-angiotensin-aldosterone-system activation and sympathetic nervous system activity. Weight loss (WL) seems to have positive effects on blood pressure (BP). The aim of this review was to explain the mechanisms linking obesity and hypertension and to evaluate the main studies assessing the effect of WL on BP. We analysed studies published in the last 10 years (13 studies either interventional or observational) showing the effect of WL on BP. Different WL strategies were taken into account-diet and lifestyle modification, pharmacological intervention and bariatric surgery. Although a positive effect of WL could be identified in each study, the main difference seems to be the magnitude and the durability of BP reduction over time. Nevertheless, further follow-up data are needed: there is still a lack of evidence about long term effects of WL on hypertension. Hence, given the significant results obtained in several recent studies, weight management should always be pursued in obese patients with hypertension.

The role of perivascular adipose tissue in the development of cardiovascular diseases. The importance of diagnosis for assessing the risk stratification of cardiovascular diseases

Obesity is closely associated with metabolic and cardiovascular diseases, including dyslipidemia, coronary artery disease, hypertension, and heart failure. Adipose tissue (AT) is identified as a complex endocrine organ, with a wide range of regulatory functions at the cellular, tissue and systemic levels. Various terms, including paracardiac, epicardial and pericardial, are used to describe the fatty deposits surrounding the heart. Among all the fat depots, perivascular AT (PVAT) is of great biological significance for the cardiovascular system due to its anatomical proximity to the vessels. Recent studies have shown the presence of a complex, bidirectional paracrine and vasocardial signaling system between the vascular wall and PVAT. In the review, we will discuss the biological role of PVAT in both the physiological state and cardiovascular pathology, emphasizing its dual proatherogenic and antiatherogenic role. Let us consider PVAT as a target for various therapeutic agents in cardiovascular diseases. We will also analyze data on the role of non-invasive techniques as a diagnostic tool for assessing coronary artery inflammation.

Rab27a Regulates Human Perivascular Adipose Progenitor Cell Differentiation

PURPOSE

Perivascular adipose tissue (PVAT) surrounds blood vessels and regulates vascular tone through paracrine secretion of cytokines. During conditions promoting cardiometabolic dysfunction, such as obesity, cytokine secretion is altered towards a proinflammatory and proatherogenic profile. Despite the clinical implications for cardiovascular disease, studies addressing the biology of human PVAT remain limited. We are interested in characterizing the resident adipose progenitor cells (APCs) because of their potential role in PVAT expansion during obesity. We also focused on proteins regulating paracrine interactions, including the small GTPase Rab27a, which regulates protein trafficking and secretion.

METHODS

PVAT from the ascending aorta was collected from patients with severe cardiovascular disease undergoing coronary artery bypass grafting (CABG). Freshly-isolated PVAT was digested and APC expanded in culture for characterizing progenitor markers, evaluating adipogenic potential and assessing the function(s) of Rab27a.

RESULTS

Using flow cytometry, RT-PCR, and immunoblot, we characterized APC from human PVAT as negative for CD45 and CD31 and expressing CD73, CD105, and CD140A. These APCs differentiate into multilocular, UCP1-producing adipocytes in vitro. Rab27a was detected in interstitial cells of human PVAT in vivo and along F-actin tracks of PVAT-APC in vitro. Knockdown of Rab27a using siRNA in PVAT-APC prior to induction resulted in a marked reduction in lipid accumulation and reduced expression of adipogenic differentiation markers.

CONCLUSIONS

PVAT-APC from CABG donors express common adipocyte progenitor markers and differentiate into UCP1-containing adipocytes. Rab27a has an endogenous role in promoting the maturation of adipocytes from human PVAT-derived APC.

Perivascular Adipose Tissue: the Sixth Man of the Cardiovascular System

Perivascular adipose tissue (PVAT) refers to the local aggregate of adipose tissue surrounding the vascular tree, exhibiting phenotypes from white to brown and beige adipocytes. Although PVAT has long been regarded as simply a structural unit providing mechanical support to vasculature, it is now gaining reputation as an integral endocrine/paracrine component, in addition to the well-established modulator endothelium, in regulating vascular tone. Since the discovery of anti-contractile effect of PVAT in 1991, the use of multiple rodent models of reduced amounts of PVAT has revealed its regulatory role in vascular remodeling and cardiovascular implications, including atherosclerosis. PVAT does not only release PVAT-derived relaxing factors (PVRFs) to activate multiple subsets of endothelial and vascular smooth muscle potassium channels and anti-inflammatory signals in the vasculature, but it does also provide an interface for neuron-adipocyte interactions in the vascular wall to regulate arterial vascular tone. In this review, we outline our current understanding towards PVAT and attempt to provide hints about future studies that can sharpen the therapeutic potential of PVAT against cardiovascular diseases and their complications.

Resveratrol and Vascular Function

Resveratrol increases the production of nitric oxide (NO) in endothelial cells by upregulating the expression of endothelial NO synthase (eNOS), stimulating eNOS enzymatic activity, and preventing eNOS uncoupling. At the same time, resveratrol inhibits the synthesis of endothelin-1 and reduces oxidative stress in both endothelial cells and smooth muscle cells. Pathological stimuli-induced smooth muscle cell proliferation, vascular remodeling, and arterial stiffness can be ameliorated by resveratrol as well. In addition, resveratrol also modulates immune cell function, inhibition of immune cell infiltration into the vascular wall, and improves the function of perivascular adipose tissue. All these mechanisms contribute to the protective effects of resveratrol on vascular function and blood pressure in vivo. Sirtuin 1, AMP-activated protein kinase, and estrogen receptors represent the major molecules mediating the vascular effects of resveratrol.

GLP-1-based therapies to boost autophagy in cardiometabolic patients: From experimental evidence to clinical trials

Obesity has many deleterious effects on the cardiovascular system, mediated by changes in insulin sensitivity, dyslipidaemia, oxidative stress and inflammation. Current therapies mainly focus on caloric intake suppression and bariatric surgery, however the efficacy of these approaches remains elusive as most patients regain their body weight within the next 5 years. A better understanding of the pathophysiology of obesity is of paramount importance for the development of new therapeutic strategies to prevent vascular complications. Autophagy has emerged as key self-degrading process responsible for the maintenance of cellular homeostasis. Defects in autophagy homeostasis are implicated in metabolic disorders, including obesity, insulin resistance, diabetes mellitus and atherosclerosis. Most importantly, autophagy regulates animal lifespan. Albeit ample preclinical evidence supports the therapeutic promise of autophagy modulators for the treatment of obesity and metabolic diseases, the clinical efficacy of pharmacological modulation of autophagy remains to be proven. Recent work has shown that GLP-1-based therapeutic approaches may positively affect autophagy in perivascular adipose tissue, thus improving obesity-related endothelial dysfunction. In the present review we discuss current evidence on the role of autophagy in obesity, with a specific focus on DPP-4 inhibitors (DPP-4i) and GLP-1 receptor agonists (GLP-1 RA) as modulators of this process. Experimental evidence on GLP-1-based approaches is critically discussed in light of recent clinical trials with DPP-4i and GLP-1 RA.

Oxidative Stress and Oral Mucosal Diseases: An Overview

BACKGROUND

Reactive oxygen species (ROS) and free radicals are physiologically produced during cellular metabolism. When their balance is disrupted in favor of ROS, a condition called oxidative stress occurs. Oxidative stress represents a widespread phenomenon involved in several pathological conditions. The aim of the present review was to report current knowledge on oxidative stress related to oral mucosal diseases.

MATERIALS AND METHODS

Articles from 2000 to 2018 were selected for relevance, validity and quality, from results obtained in PubMed, MEDLINE and Google Scholar using the following search terms: oxidative stress and oral lichen, oral pemphigus, aphthous stomatitis, oral leukoplakia, oral cancer, oral squamous cell carcinoma and oral carcinoma. All articles were independently screened for eligibility by the authors.

RESULTS

This narrative review integrates extensive information from all relevant published studies focusing on oxidative stress in oral mucosal diseases. We outline the pathogenetic function of oxidative stress in the most frequent inflammatory, potentially malignant and malignant diseases of the oral mucosa and provide detailed findings from human research.

CONCLUSION

Although variability in findings between individual studies exists, it justifies the conclusion that oxidative stress is a significant process in the oral mucosal diseases pathogenesis.

Obesity and cardiovascular disease: revisiting an old relationship

A wealth of clinical and epidemiological evidence has linked obesity to a broad spectrum of cardiovascular diseases (CVD) including coronary heart disease, heart failure, hypertension, stroke, atrial fibrillation and sudden cardiac death. Obesity can increase CVD morbidity and mortality directly and indirectly. Direct effects are mediated by obesity-induced structural and functional adaptations of the cardiovascular system to accommodate excess body weight, as well as by adipokine effects on inflammation and vascular homeostasis. Indirect effects are mediated by co-existing CVD risk factors such as insulin resistance, hyperglycemia, hypertension and dyslipidemia. Adipose tissue (AT) quality and functionality are more relevant aspects for cardiometabolic risk than its total amount. The consequences of maladaptive AT expansion in obesity are local and systemic: the local include inflammation, hypoxia, dysregulated adipokine secretion and impaired mitochondrial function; the systemic comprise insulin resistance, abnormal glucose/lipid metabolism, hypertension, a pro-inflammatory and pro-thrombotic state and endothelial dysfunction, all of which provide linking mechanisms for the association between obesity and CVD. The present narrative review summarizes the major pathophysiological links between obesity and CVD (traditional and novel concepts), analyses the heterogeneity of obesity-related cardiometabolic consequences, and provides an overview of the cardiovascular impact of weight loss interventions.

Muscle Insulin Resistance and the Inflamed Microvasculature: Fire from Within

Insulin is a vascular hormone and regulates vascular tone and reactivity. Muscle is a major insulin target that is responsible for the majority of insulin-stimulated glucose use. Evidence confirms that muscle microvasculature is an important insulin action site and critically regulates insulin delivery to muscle and action on myocytes, thereby affecting insulin-mediated glucose disposal. Insulin via activation of its signaling cascade in the endothelial cells increases muscle microvascular perfusion, which leads to an expansion of the endothelial exchange surface area. Insulin’s microvascular actions closely couple with its metabolic actions in muscle and blockade of insulin-mediated microvascular perfusion reduces insulin-stimulated muscle glucose disposal. Type 2 diabetes is associated with chronic low-grade inflammation, which engenders both metabolic and microvascular insulin resistance through endocrine, autocrine and paracrine actions of multiple pro-inflammatory factors. Here, we review the crucial role of muscle microvasculature in the regulation of insulin action in muscle and how inflammation in the muscle microvasculature affects insulin’s microvascular actions as well as metabolic actions. We propose that microvascular insulin resistance induced by inflammation is an early event in the development of metabolic insulin resistance and eventually type 2 diabetes and its related cardiovascular complications, and thus is a potential therapeutic target for the prevention or treatment of obesity and diabetes.

Influence of Age on Anticontractile Effect of Perivascular Adipose Tissue in Normotensive and Hypertensive Rats

Perivascular adipose tissue (PVAT) and its vasomodulatory effects play an important role in the physiology and pathophysiology of blood vessels. Alterations in PVAT associated with reduction in its anticontractile influence are proven to contribute to vascular dysfunction in hypertension. The aim of this study was to examine whether the changes in PVAT properties could participate in progression of vascular abnormalities in developing spontaneously hypertensive rats (SHR). Normotensive Wistar-Kyoto (WKY) rats and SHR, both in 5th and in 12th week of age, were used. Systolic blood pressure was similar between WKY rats and SHR in 5th week of age; however, in 12th week, it was significantly increased in SHR comparing to WKY rats. The amount of retroperitoneal fat was higher in WKY rats in both age groups, whereas body weight was higher in WKY rats only in 12th week, when compared to age-matched SHR. From isolated superior mesenteric arteries, two ring preparations were prepared for isometric tension recording, one with PVAT intact and other with PVAT removed. In WKY rats as well as in SHR, arterial contractile responses to noradrenaline, applied cumulatively on rings, were significantly inhibited in the presence of intact PVAT. In both age groups, anticontractile effect of PVAT was higher in WKY rats than in SHR. Neurogenic contractions, induced by electrical stimulation of perivascular sympathoadrenergic nerves, were significantly attenuated in the presence of PVAT in WKY mesenteric arteries from both age groups; however, in arteries from SHR, intact PVAT had no influence on this type of contractile responses. The results suggest that in SHR impairment of anticontractile effect of PVAT precedes hypertension and might contribute to its development.

New Therapeutic Implications of Endothelial Nitric Oxide Synthase (eNOS) Function/Dysfunction in Cardiovascular Disease

The Global Burden of Disease Study identified cardiovascular risk factors as leading causes of global deaths and life years lost. Endothelial dysfunction represents a pathomechanism that is associated with most of these risk factors and stressors, and represents an early (subclinical) marker/predictor of atherosclerosis. Oxidative stress is a trigger of endothelial dysfunction and it is a hall-mark of cardiovascular diseases and of the risk factors/stressors that are responsible for their initiation. Endothelial function is largely based on endothelial nitric oxide synthase (eNOS) function and activity. Likewise, oxidative stress can lead to the loss of eNOS activity or even “uncoupling” of the enzyme by adverse regulation of well-defined “redox switches” in eNOS itself or up-/down-stream signaling molecules. Of note, not only eNOS function and activity in the endothelium are essential for vascular integrity and homeostasis, but also eNOS in perivascular adipose tissue plays an important role for these processes. Accordingly, eNOS protein represents an attractive therapeutic target that, so far, was not pharmacologically exploited. With our present work, we want to provide an overview on recent advances and future therapeutic strategies that could be used to target eNOS activity and function in cardiovascular (and other) diseases, including life style changes and epigenetic modulations. We highlight the redox-regulatory mechanisms in eNOS function and up- and down-stream signaling pathways (e.g., tetrahydrobiopterin metabolism and soluble guanylyl cyclase/cGMP pathway) and their potential pharmacological exploitation.

Coronary artery hypoxic vasorelaxation is augmented by perivascular adipose tissue through a mechanism involving hydrogen sulphide and cystathionine-β-synthase

AIM

Hypoxia causes vasodilatation of coronary arteries which protects the heart from ischaemic damage through mechanisms including the generation of hydrogen sulphide (H₂ S), but the influence of the perivascular adipose tissue (PVAT) and myocardium is incompletely understood. This study aimed to determine whether PVAT and the myocardium modulate the coronary artery hypoxic response and whether this involves hydrogen sulphide.

METHODS

Porcine left circumflex coronary arteries were prepared as cleaned segments and with PVAT intact, myocardium intact or both PVAT and myocardium intact, and contractility investigated using isometric tension recording. Immunoblotting was used to measure levels of H₂ S-synthesizing enzymes: cystathionine-β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (MPST).

RESULTS

All three H₂ S-synthesizing enzymes were detected in the artery and myocardium, but only CBS and MPST were detected in PVAT. Hypoxia elicited a biphasic response in cleaned artery segments consisting of transient contraction followed by prolonged relaxation. In arteries with PVAT intact, hypoxic contraction was attenuated and relaxation augmented. In arteries with myocardium intact, hypoxic contraction was attenuated, but relaxation was unaffected. In replacement experiments, replacement of dissected PVAT and myocardium attenuated artery contraction and augmented relaxation to hypoxia, mimicking the effect of in situ PVAT and indicating involvement of a diffusible factor(s). In arteries with intact PVAT, augmentation of hypoxic relaxation was reversed by amino-oxyacetate (CBS inhibitor), but not DL-propargylglycine (CSE inhibitor) or aspartate (inhibits MPST pathway).

CONCLUSION

PVAT augments hypoxic relaxation of coronary arteries through a mechanism involving H₂ S and CBS, pointing to an important role in regulation of coronary blood flow during hypoxia.

Increased endothelin-1-mediated vasoconstrictor tone in human obesity: effects of gut hormones

The heavy impact of obesity on the development and progression of cardiovascular disease has sparked sustained efforts to uncover the mechanisms linking excess adiposity to vascular dysfunction. Impaired vasodilator reactivity has been recognized as an early hemodynamic abnormality in obese patients, but also increased vasoconstrictor tone importantly contributes to their vascular damage. In particular, upregulation of the endothelin (ET)-1 system, consistently reported in these patients, might accelerate atherosclerosis and its complication, given the pro-inflammatory and mitogenic properties of ET-1. In recent years, a number of gut hormones, in addition to their role as modulators of food intake, energy balance, glucose and lipid metabolism, and insulin secretion and action, have demonstrated favorable vascular actions. They increase the bioavailability of vasodilator mediators like nitric oxide, but they have also been shown to inhibit the ET-1 system. These features make gut hormones promising tools for targeting both the metabolic and cardiovascular complications of obesity, a view supported by recent large-scale clinical trials indicating that novel drugs for type 2 diabetes with cardiovascular potential may translate into clinically significant advantages. Therefore, there is real hope that better understanding of the properties of gut-derived substances might provide more effective therapies for the obesity-related cardiometabolic syndrome.

Perivascular adipose tissue (PVAT) in atherosclerosis: a double-edged sword

Perivascular adipose tissue (PVAT), the adipose tissue that surrounds most of the vasculature, has emerged as an active component of the blood vessel wall regulating vascular homeostasis and affecting the pathogenesis of atherosclerosis. Although PVAT characteristics resemble both brown and white adipose tissues, recent evidence suggests that PVAT develops from its own distinct precursors implying a closer link between PVAT and vascular system. Under physiological conditions, PVAT has potent anti-atherogenic properties mediated by its ability to secrete various biologically active factors that induce non-shivering thermogenesis and metabolize fatty acids. In contrast, under pathological conditions (mainly obesity), PVAT becomes dysfunctional, loses its thermogenic capacity and secretes pro-inflammatory adipokines that induce endothelial dysfunction and infiltration of inflammatory cells, promoting atherosclerosis development. Since PVAT plays crucial roles in regulating key steps of atherosclerosis development, it may constitute a novel therapeutic target for the prevention and treatment of atherosclerosis. Here, we review the current literature regarding the roles of PVAT in the pathogenesis of atherosclerosis.

Effect of perivascular adipose tissue on arterial adrenergic contractions in normotensive and hypertensive rats with high fructose intake

The aim of this study was to investigate the effect of high fructose intake associated with moderate increase in adiposity on rat arterial adrenergic responses and their modulation by perivascular adipose tissue (PVAT). After eight-week-lasting substitution of drinking water with 10 % fructose solution in adult normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), their systolic blood pressure, plasma triglycerides, and relative liver weight were elevated when compared to their respective control groups. Moreover, in SHR, body weight and relative heart weight were increased after treatment with fructose. In superior mesenteric arteries, PVAT exerted inhibitory influence on adrenergic contractile responses and this effect was markedly stronger in control WKY than in SHR. In fructose-administered WKY, arterial adrenergic contractions were substantially reduced in comparison with the control group; this was caused mainly by enhancement of anticontractile action of PVAT. The diminution of the mesenteric arterial contractions was not observed after fructose treatment in SHR. We conclude that the increase in body adiposity due to fructose overfeeding in rats might have prehypertensive effect. However, in WKY it might cause PVAT-dependent and independent reduction in arterial contractile responses to adrenergic stimuli, which could attenuate the pathological elevation in vascular tone.

Influence of the periprostatic adipose tissue in obesity-associated mouse urethral dysfunction and oxidative stress: Effect of resveratrol treatment

Obese mice display overactive bladder (OAB) associated with impaired urethra smooth muscle (USM) function. In this study, we evaluated the role of the adipose tissue surrounding the urethra and prostate in obese mice (here referred as periprostatic adipose tissue; PPAT) to the USM dysfunction. Male C57BL6/JUnib mice fed with either a standard-chow or high-fat diet to induce obesity were used. In PPAT, histological analysis, and qPCR analysis for gp91phox, tumor necrosis factor-α (TNF-α) and superoxide dismutase (SOD) were conducted. In USM, concentration-response curves to contractile and relaxing agents, as well as measurements of reactive-oxygen species and nitric oxide (NO) levels were performed. The higher PPAT area in obese mice was accompanied by augmented gp91phox (NOX2) and TNF-α expressions, together with decreased SOD1 expression. In USM of obese group, the contractile responses to phenylephrine and vasopressin were increased, whereas the relaxations induced with glyceryl trinitrate were reduced. The reactive-oxygen species and NO levels in USM of obese mice were increased and decreased, respectively. A higher SOD expression was also detected in obese group whilst no changes in the gp91phox levels were observed. We next evaluated the effects of the antioxidant resveratrol (100 mg/kg/day, two-weeks, PO) in the functional alterations and NO levels of obese mice. Resveratrol treatment in obese mice reversed both the functional USM dysfunction and the reduced NO production. Our data show that PPAT exerts a local inflammatory response and increases oxidative stress that lead to urethral dysfunction. Resveratrol could be an auxiliary option to prevent obesity-associated urethral dysfunction.

Immunometabolic Regulation of Vascular Redox State: The Role of Adipose Tissue

SIGNIFICANCE

Vascular oxidative stress plays a crucial role in atherogenesis and cardiovascular disease (CVD). Recent evidence suggests that vascular redox state is under the control of complex pathophysiological mechanisms, ranging from inflammation to obesity and insulin resistance (IR). Recent Advances: Adipose tissue (AT) is now recognized as a dynamic endocrine and paracrine organ that secretes several bioactive molecules, called adipokines. AT has recently been shown to regulate vascular redox state in both an endocrine and a paracrine manner through the secretion of adipokines, therefore providing a mechanistic link for the association between obesity, IR, inflammation, and vascular disease. Importantly, AT behaves as a sensor of cardiovascular oxidative stress, modifying its secretory profile in response to cardiovascular oxidative injury.

CRITICAL ISSUES

The present article presents an up-to-date review of the association between AT and vascular oxidative stress. We focus on the effects of individual adipokines on modulating reactive oxygen species production and scavenging in the vascular wall. In addition, we highlight how inflammation, obesity, and IR alter the biology and secretome of AT leading to a more pro-oxidant phenotype with a particular focus on the local regulatory mechanisms of perivascular AT driven by vascular oxidation.

FUTURE DIRECTIONS

The complex and dynamic biology of AT, as well as its importance in the regulation of vascular redox state, provides numerous opportunities for the development of novel, targeted treatments in the management of CVD. Therapeutic modulation of AT biology could improve vascular redox state affecting vascular disease pathogenesis. Antioxid. Redox Signal. 29, 313-336.

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.

Molecular mechanisms regulating perivascular adipose tissue - potential pharmacological targets?

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.

Anti-Inflammatory Effects of Melatonin in Obesity and Hypertension

PURPOSE OF REVIEW

Here, we review the known relations between hypertension and obesity to inflammation and postulate the endogenous protective effect of melatonin and its potential as a therapeutic agent. We will describe the multiple effects of melatonin on blood pressure, adiposity, body weight, and focus on mitochondrial-related anti-inflammatory and antioxidant protective effects.

RECENT FINDINGS

Hypertension and obesity are usually associated with systemic and tissular inflammation. The progressive affection of target-organs involves multiple mediators of inflammation, most of them redundant, which make anti-inflammatory strategies ineffective. Melatonin reduces blood pressure, body weight, and inflammation. The mechanisms of action of this ancient molecule of protection involve multiple levels of action, from subcellular to intercellular. Mitochondria is a key inflammatory element in vascular and adipose tissue and a potential pharmacological target. Melatonin protects against mitochondrial dysfunction. Melatonin reduces blood pressure and adipose tissue dysfunction by multiple anti-inflammatory/antioxidant actions and provides potent protection against mitochondria-mediated injury in hypertension and obesity. This inexpensive and multitarget molecule has great therapeutic potential against both epidemic diseases.

Suppression of gut dysbiosis reverses Western diet-induced vascular dysfunction

Vascular dysfunction represents a critical preclinical step in the development of cardiovascular disease. We examined the role of the gut microbiota in the development of obesity-related vascular dysfunction. Male C57BL/6J mice were fed either a standard diet (SD) ( n = 12) or Western diet (WD) ( n = 24) for 5 mo, after which time WD mice were randomized to receive either unsupplemented drinking water or water containing a broad-spectrum antibiotic cocktail (WD + Abx) ( n = 12/group) for 2 mo. Seven months of WD caused gut dysbiosis, increased arterial stiffness (SD 412.0 ± 6.0 vs. WD 458.3 ± 9.0 cm/s, P < 0.05) and endothelial dysfunction (28% decrease in max dilation, P < 0.05), and reduced l-NAME-inhibited dilation. Vascular dysfunction was accompanied by significant increases in circulating LPS-binding protein (LBP) (SD 5.26 ± 0.23 vs. WD 11 ± 0.86 µg/ml, P < 0.05) and interleukin-6 (IL-6) (SD 3.27 ± 0.25 vs. WD 7.09 ± 1.07 pg/ml, P < 0.05); aortic expression of phosphorylated nuclear factor-κB (p-NF-κB) ( P < 0.05); and perivascular adipose expression of NADPH oxidase subunit p67phox ( P < 0.05). Impairments in vascular function correlated with reductions in Bifidobacterium spp. Antibiotic treatment successfully abrogated the gut microbiota and reversed WD-induced arterial stiffness and endothelial dysfunction. These improvements were accompanied by significant reductions in LBP, IL-6, p-NF-κB, and advanced glycation end products (AGEs), and were independent from changes in body weight and glucose tolerance. These results indicate that gut dysbiosis contributes to the development of WD-induced vascular dysfunction, and identify the gut microbiota as a novel therapeutic target for obesity-related vascular abnormalities.

Increased O-GlcNAcylation of Endothelial Nitric Oxide Synthase Compromises the Anti-contractile Properties of Perivascular Adipose Tissue in Metabolic Syndrome

Under physiological conditions, the perivascular adipose tissue (PVAT) negatively modulates vascular contractility. This property is lost in experimental and human obesity and in the metabolic syndrome, indicating that changes in PVAT function may contribute to vascular dysfunction associated with increased body weight and hyperglycemia. The O-linked β-N-acetylglucosamine (O-GlcNAc) modification of proteins (O-GlcNAcylation) is a unique posttranslational process that integrates glucose metabolism with intracellular protein activity. Increased flux of glucose through the hexosamine biosynthetic pathway and the consequent increase in tissue-specific O-GlcNAc modification of proteins have been linked to multiple facets of vascular dysfunction in diabetes and other pathological conditions. We hypothesized that chronic consumption of glucose, a condition that progresses to metabolic syndrome, leads to increased O-GlcNAc modification of proteins in the PVAT, decreasing its anti-contractile effects. Therefore, the current study was devised to determine whether a high-sugar diet increases O-GlcNAcylation in the PVAT and how increased O-GlcNAc interferes with PVAT vasorelaxant function. To assess molecular mechanisms by which O-GlcNAc contributes to PVAT dysfunction, thoracic aortas surrounded by PVAT were isolated from Wistar rats fed either a control or high sugar diet, for 10 and 12 weeks. Rats chronically fed a high sugar diet exhibited metabolic syndrome features, increased O-GlcNAcylated-proteins in the PVAT and loss of PVAT anti-contractile effect. PVAT from high sugar diet-fed rats for 12 weeks exhibited decreased NO formation, reduced expression of endothelial nitric oxide synthase (eNOS) and increased O-GlcNAcylation of eNOS. High sugar diet also decreased OGA activity and increased superoxide anion generation in the PVAT. Visceral adipose tissue samples from hyperglycemic patients showed increased levels of O-GlcNAc-modified proteins, increased ROS generation and decreased OGA activity. These data indicate that O-GlcNAcylation contributes to metabolic syndrome-induced PVAT dysfunction and that O-GlcNAcylation of eNOS may be targeted in the development of novel therapies for vascular dysfunction in conditions associated with hyperglycemia.

Perivascular Adipose Tissue as a Relevant Fat Depot for Cardiovascular Risk in Obesity

Obesity is associated with increased risk of premature death, morbidity, and mortality from several cardiovascular diseases (CVDs), including stroke, coronary heart disease (CHD), myocardial infarction, and congestive heart failure. However, this is not a straightforward relationship. Although several studies have substantiated that obesity confers an independent and additive risk of all-cause and cardiovascular death, there is significant variability in these associations, with some lean individuals developing diseases and others remaining healthy despite severe obesity, the so-called metabolically healthy obese. Part of this variability has been attributed to the heterogeneity in both the distribution of body fat and the intrinsic properties of adipose tissue depots, including developmental origin, adipogenic and proliferative capacity, glucose and lipid metabolism, hormonal control, thermogenic ability, and vascularization. In obesity, these depot-specific differences translate into specific fat distribution patterns, which are closely associated with differential cardiometabolic risks. The adventitial fat layer, also known as perivascular adipose tissue (PVAT), is of major importance. Similar to the visceral adipose tissue, PVAT has a pathophysiological role in CVDs. PVAT influences vascular homeostasis by releasing numerous vasoactive factors, cytokines, and adipokines, which can readily target the underlying smooth muscle cell layers, regulating the vascular tone, distribution of blood flow, as well as angiogenesis, inflammatory processes, and redox status. In this review, we summarize the current knowledge and discuss the role of PVAT within the scope of adipose tissue as a major contributing factor to obesity-associated cardiovascular risk. Relevant clinical studies documenting the relationship between PVAT dysfunction and CVD with a focus on potential mechanisms by which PVAT contributes to obesity-related CVDs are pointed out.

Neck adipose tissue - tying ties in metabolic disorders

Upper body adipose tissue accumulation has been associated with clustering of metabolic disorders and increased cardiovascular risk. Neck circumference (NC) indicated that subcutaneous adipose tissue (SAT) in that region is an independent pathogenic depot that might account for the additional risk missed by visceral adipose tissue (VAT). Neck adipose tissue (NAT) is not only one more ectopic depot but has several particular features that might modulate its metabolic role. Besides a controversial impact on obstructive apnea syndrome, neck fat encompasses carotid arteries as an important perivascular adipose tissue (PVAT) depot. With dysfunctional changes in obesity, physiologic vascular regulation is lost and inflammatory signals accelerate atherogenesis. Unexpected was the discovery of brown and beige adipocytes in the neck of human adults. When stimulated, brown adipose tissue (BAT) dissipates energy through thermogenesis and it is associated with other favorable metabolic effects. Moreover, the neck is the region where the browning mechanism was disclosed. With this unique plastic nature, NAT revealed multiple ties, challenging dynamics and potential new therapeutic targets that might have significant implications on metabolic outcomes and vascular risk.

Favorable Vascular Actions of Angiotensin-(1-7) in Human Obesity

Obese patients have vascular dysfunction related to impaired insulin-stimulated vasodilation and increased endothelin-1-mediated vasoconstriction. In contrast to the harmful vascular actions of angiotensin (Ang) II, the angiotensin-converting enzyme 2 product Ang-(1-7) has shown to exert cardiovascular and metabolic benefits in experimental models through stimulation of the Mas receptor. We, therefore, examined the effects of exogenous Ang-(1-7) on vasodilator tone and endothelin-1-dependent vasoconstriction in obese patients. Intra-arterial infusion of Ang-(1-7) (10 nmol/min) resulted in significant increase in unstimulated forearm flow (P=0.03), an effect that was not affected by the Mas receptor antagonist A779 (10 nmol/min; P>0.05). In the absence of hyperinsulinemia, however, forearm flow responses to graded doses of acetylcholine and sodium nitroprusside were not different during Ang-(1-7) administration compared with saline (both P>0.05). During infusion of regular insulin (0.15 mU/kg per minute), by contrast, endothelium-dependent vasodilator response to acetylcholine was significantly enhanced by Ang-(1-7) (P=0.04 versus saline), whereas endothelium-independent response to sodium nitroprusside was not modified (P=0.91). Finally, Ang-(1-7) decreased the vasodilator response to endothelin A receptor blockade (BQ-123; 10 nmol/min) compared with saline (6±1% versus 93±17%; P<0.001); nitric oxide inhibition by l-N-monomethylarginine (4 µmol/min) during concurrent endothelin A antagonism resulted in similar vasoconstriction in the absence or presence of Ang-(1-7 Ang-(1-7) (P=0.69). Our findings indicate that in obese patients Ang-(1-7) has favorable effects not only to improve insulin-stimulated endothelium-dependent vasodilation but also to blunt endothelin-1-dependent vasoconstrictor tone. These findings provide support for targeting Ang-(1-7) to counteract the hemodynamic abnormalities of human obesity.

Effects of aging and exercise training on the dynamics of vasoconstriction in skeletal muscle resistance vessels

It is unknown whether aging or exercise training affect the dynamics of arteriolar vasoconstriction.

PURPOSE

We hypothesized that old age will slow, and exercise training will speed, the dynamics of skeletal muscle arteriolar vasoconstriction in resistance vessels of aged rats.

METHOD

Young (6 month old) and aged (24 month old) male Fischer-344 rats were assigned to sedentary (Sed: n = 6/age group) or exercise-trained (ET: n = 5 aged and 6 young; via treadmill running for 10-12 weeks) groups. After completion of training, arterioles from the red portion of the gastrocnemius muscle were removed, cannulated, and exposed to 10^-4 M norepinephrine (NE) or 20 mM caffeine. Changes in luminal diameter were recorded for analysis of constrictor dynamics.

RESULT

Old age blunted all kinetic parameters (i.e., time delay, time constant) resulting in vasoconstriction taking ~3 times as long to reach a steady state (SS) versus younger counterparts for NE (aged-sed: 15.6 ± 6.0 versus young-sed: 4.6 ± 0.5 s; P < 0.05) with a similar time course to caffeine. Exercise training resulted in a similar time to SS between age groups for NE (aged-ET: 6.8 ± 1.6 versus young-ET: 7.0 ± 0.6 s) and caffeine (aged-ET: 7.8 ± 0.6 versus young-ET: 8.6 ± 1.0 s).

CONCLUSION

The results of this study demonstrate that aging blunts the rate of vasoconstriction in skeletal muscle resistance vessels to the sympathetic neurotransmitter NE due, in part, to an attenuated rate of contraction from intracellular calcium release. Further, exercise training speeds the dynamics of constriction to both NE and caffeine with old age.

Restoration of perivascular adipose tissue function in diet-induced obese mice without changing bodyweight

Background and Purpose

We have recently shown that a reduced function of endothelial nitric oxide synthase (eNOS) in the perivascular adipose tissue (PVAT) contributes crucially to obesity‐induced vascular dysfunction in mice. The current study was conducted to test the hypothesis that vascular dysfunction in obesity can be reversed by in vivo improvement of PVAT eNOS activity.

Experimental Approach

Male C57BL/6J mice were fed a high‐fat diet (HFD) for 22 weeks to induce obesity. During the last 4 weeks of HFD feeding, the obese mice were treated p.o. with the standardized Crataegus extract WS® 1442, which has been shown previously to improve eNOS activity.

Key Results

Diet‐induced obesity in mice markedly reduced the vasodilator response of thoracic aorta to acetylcholine in wire myograph experiments. Strikingly, this vascular dysfunction was only evident in PVAT‐containing aorta but not in PVAT‐free aorta. In vivo treatment of obese mice with WS® 1442 had no effect on body weight or epididymal fat mass, but completely restored the vascular function of PVAT‐containing aorta. Feeding a HFD led to a reduced phosphorylation and an enhanced acetylation of PVAT eNOS, both effects were reversed by WS® 1442 treatment.

Conclusion and Implications

PVAT plays a key role in vascular dysfunction in diet‐induced obese mice. Not obesity itself, but a PVAT dysfunction is responsible for obesity‐induced vascular disorders. Improving PVAT function by pharmacological means (e.g. with WS® 1442) can ameliorate vascular function even without reducing body weight or fat mass.

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

Functional Characterization of Preadipocytes Derived from Human Periaortic Adipose Tissue

Adipose tissue can affect the metabolic control of the cardiovascular system, and its anatomic location can affect the vascular function differently. In this study, biochemical and phenotypical characteristics of adipose tissue from periaortic fat were evaluated. Periaortic and subcutaneous adipose tissues were obtained from areas surrounding the ascending aorta and sternotomy incision, respectively. Adipose tissues were collected from patients undergoing myocardial revascularization or mitral valve replacement surgery. Morphological studies with hematoxylin/eosin and immunohistochemical assay were performed in situ to quantify adipokine expression. To analyze adipogenic capacity, adipokine expression, and the levels of thermogenic proteins, adipocyte precursor cells were isolated from periaortic and subcutaneous adipose tissues and induced to differentiation. The precursors of adipocytes from the periaortic tissue accumulated less triglycerides than those from the subcutaneous tissue after differentiation and were smaller than those from subcutaneous adipose tissue. The levels of proteins involved in thermogenesis and energy expenditure increased significantly in periaortic adipose tissue. Additionally, the expression levels of adipokines that affect carbohydrate metabolism, such as FGF21, increased significantly in mature adipocytes induced from periaortic adipose tissue. These results demonstrate that precursors of periaortic adipose tissue in humans may affect cardiovascular events and might serve as a target for preventing vascular diseases.

The role of perivascular adipose tissue in obesity-induced vascular dysfunction

Under physiological conditions, perivascular adipose tissue (PVAT) attenuates agonist‐induced vasoconstriction by releasing vasoactive molecules including hydrogen peroxide, angiotensin 1–7, adiponectin, methyl palmitate, hydrogen sulfide, NO and leptin. This anticontractile effect of PVAT is lost under conditions of obesity. The central mechanism underlying this PVAT dysfunction in obesity is likely to be an ‘obesity triad’ (consisting of PVAT hypoxia, inflammation and oxidative stress) that leads to the impairment of PVAT‐derived vasoregulators. The production of hydrogen sulfide, NO and adiponectin by PVAT is reduced in obesity, whereas the vasodilator response to leptin is impaired (vascular leptin resistance). Strikingly, the vasodilator response to acetylcholine is reduced only in PVAT‐containing, but not in PVAT‐free thoracic aorta isolated from diet‐induced obese mice, indicating a unique role for PVAT in obesity‐induced vascular dysfunction. Furthermore, PVAT dysfunction has also been observed in small arteries isolated from the gluteal/visceral fat biopsy samples of obese individuals. Therefore, PVAT may represent a new therapeutic target for vascular complications in obesity. A number of approaches are currently being tested under experimental conditions. Potential therapeutic strategies improving PVAT function include body weight reduction, enhancing PVAT hydrogen sulfide release (e.g. rosiglitazone, atorvastatin and cannabinoid CB₁ receptor agonists) and NO production (e.g. arginase inhibitors), inhibition of the renin–angiotensin–aldosterone system, inhibition of inflammation with melatonin or cytokine antagonists, activators of AMP‐activated kinase (e.g. metformin, resveratrol and diosgenin) and adiponectin releasers or expression enhancers.

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