Control of human vascular tone by prostanoids derived from perivascular adipose tissue

An Obligatory Role of Perivascular Adipose Tissue in Improved Saphenous Vein Graft Patency in Coronary Artery Bypass Grafting

The gold standard graft for coronary artery bypass grafting (CABG) is the internal thoracic artery (ITA), and the second recommendation is the radial artery. However, complete revascularization with arterial grafts alone is often difficult, and the saphenous vein (SV) is the most commonly used autologous graft for CABG, because it is easier to use without restriction for the length of the graft. On the other hand, the patency of SV grafts (SVGs) is poor compared with that of arterial grafts. The SVG is conventionally harvested as a distended conduit with surrounding tissue removed, a procedure that may cause vascular damage. A no-touch technique of SVG harvesting has been reported to result in improved long-term patency in CABG comparable to that when using the ITA for grafting. Possible reasons for the excellent long-term patency of no-touch SVGs are the physical support provided by preserved surrounding perivascular adipose tissue, preservation of the vascular wall structure including the vasa vasorum, and production of adipocyte-derived factors. In this review, we discuss recent strategies aimed at improving the performance of SVGs, including no-touch harvesting, minimally invasive harvesting and mechanical support using external stents.

Effect of specialized pro-resolving lipid mediators in the regulation of vascular tone and inflammation in human saphenous vein

Specialized pro-resolving lipid mediators (SPMs), derived from polyunsaturated fatty acids are important mediators in the resolution of inflammation. Recent studies have focused on the effects of SPMs in cardiovascular health and diseases. However, little is known about the effect SPMs on human vascular tone. Therefore, in this study it is aimed to investigate the effect of various SPMs including resolvin D- and E-series, maresin-1 (MaR1) and lipoxin-A4 (LxA4) on the vascular tone of human isolated saphenous vein (SV) preparations under inflammatory conditions. In addition, we aimed to evaluate the effects of SPMs on the release of pro-inflammatory mediators, monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-alpha (TNF- α) from human SV. Pretreatment of isolated of human SV with resolvin E1 (RvE1), resolvin D1 (RvD1) and MaR1 (100 nM, 18 h) significantly reduced the contractile responses to thromboxane A2 mimetic, U46619 whereas pretreatment with LxA4 and RvD2 (100 nM, 18 h) had no significant effect on the vascular tone of SV. Moreover, RvE1, RvD1 and MaR1 but not LxA4 and RvD2 (100 nM, 18 h) pretreatment diminished the release of MCP-1 and TNF-α from SV. In conclusion, our findings suggest that pre-treatment with RvE1, RvD1, and MaR1 could have potential benefits in decreasing graft vasospasm and vascular inflammation in SV.

3D Elastomeric Stent Functionalized with Antioxidative and Perivascular Tissue Regenerative Activities Ameliorated PVT Deprivation-Induced Vein Graft Failure

Clinically, arterial injuries are always accompanied with perivascular tissue damage, which may contribute to high failure rate of vein grafts due to intimal hyperplasia and acute thrombosis. In this study, a "perivascular tissue (PVT) deprivation" animal model is constructed to mimic clinical scenarios and identify the contribution of arterial PVT to the success of vein grafts. Proteomics analysis suggests that depriving PVT may exacerbate reactive oxygen species (ROS)-induced endothelial apoptosis by up-regulating inflammation response and oxidative stress. Locally administering metformin on vein grafts through 3D-printed external stent (PGS-PCL) shows antioxidative and anti-inflammatory properties to protect cells from ROS invasion, thereafter decreasing acute thrombosis. Moreover, metformin induce rapid regeneration of perivascular adipose tissue in recipient regions, which improves patency by inhibiting intimal hyperplasia. Proteomics, western blot, and in vitro blocking tests reveal that metformin resists endothelial apoptosis through AMPK/mTOR and NFκB signaling pathways. To conclude, PVT deprivation exacerbates inflammatory response and oxidative stress in vein grafts bridging arterial circulation. Metformin-loaded stent ameliorates "PVT damage" related vein graft failure, and enhances patency of through resisting endothelial apoptosis and regenerating arterial PVAT, offering a promising avenue to improve the success of vein grafts in clinic.

Perivascular Adipose Tissue and Vascular Smooth Muscle Tone: Friends or Foes?

Perivascular adipose tissue (PVAT) is a specialized type of adipose tissue that surrounds most mammalian blood vessels. PVAT is a metabolically active, endocrine organ capable of regulating blood vessel tone, endothelium function, vascular smooth muscle cell growth and proliferation, and contributing critically to cardiovascular disease onset and progression. In the context of vascular tone regulation, under physiological conditions, PVAT exerts a potent anticontractile effect by releasing a plethora of vasoactive substances, including NO, H₂S, H₂O₂, prostacyclin, palmitic acid methyl ester, angiotensin 1-7, adiponectin, leptin, and omentin. However, under certain pathophysiological conditions, PVAT exerts pro-contractile effects by decreasing the production of anticontractile and increasing that of pro-contractile factors, including superoxide anion, angiotensin II, catecholamines, prostaglandins, chemerin, resistin, and visfatin. The present review discusses the regulatory effect of PVAT on vascular tone and the factors involved. In this scenario, dissecting the precise role of PVAT is a prerequisite to the development of PVAT-targeted therapies.

Effect of Carotid Body Denervation on Systemic Endothelial Function in a Diabetic Animal Model

Endothelial dysfunction is an essential intermediary for development of cardiovascular diseases associated with diabetes and hypertension (HT). The carotid body (CB) dysfunction contributes to dysmetabolic states, and the resection of carotid sinus nerve (CSN) prevents and reverts dysmetabolism and HT. Herein, we investigated if CSN denervation ameliorates systemic endothelial dysfunction in an animal model of type 2 diabetes mellitus (T2DM).We used Wistar male rats submitted to HFHSu diet during 25 weeks and the correspondent age-matched controls fed with a standard diet. CSN resection was performed in half of the groups after 14 weeks of diet. In vivo insulin sensitivity, glucose tolerance and blood pressure, ex vivo aortic artery contraction and relaxation and nitric oxide (NO) levels in plasma and aorta, aorta nitric oxide synthase (NOS) isoforms, and PGF2αR levels were evaluated.We demonstrated that, alongside to dysmetabolism and HT reversion, CSN resection restores endothelial function in the aorta and decreases the NO levels in plasma and aorta at the same time that restores normal levels of iNOS in aorta without changing eNOS or PGF2αR levels.These results suggest that the modulation of CB activity can be important for the treatment of HT and endothelial dysfunction related with T2DM.

The biological actions of prostanoids in adipose tissue in physiological and pathophysiological conditions

Adipose tissue has been established as an endocrine organ that plays an important role in maintaining metabolic homeostasis. Adipose tissue releases several bioactive molecules called adipokines. Inflammation, dysregulation of adipokine synthesis, and secretion are observed in obesity and related diseases and cause adipose tissue dysfunction. Prostanoids, belonging to the eicosanoid family of lipid mediators, can be synthesized in adipose tissue and play a critical role in adipose tissue biology. In this review, we summarized the current knowledge regarding the interaction of prostanoids with adipokines, the expression of prostanoid receptors, and prostanoid synthase enzymes in adipose tissues in health and disease. Furthermore, the involvement of prostanoids in the physiological function or dysfunction of adipose tissue including inflammation, lipolysis, adipogenesis, thermogenesis, browning of adipocytes, and vascular tone regulation was also discussed by examining studies using pharmacological approaches or genetically modified animals for prostanoid receptors/synthase enzymes. Overall, the present review provides a perspective on the evidence from literature regarding the biological effects of prostanoids in adipose tissue. Among prostanoids, prostaglandin E2 (PGE₂) is prominent in regards to its substantial role in both adipose tissue physiology and pathophysiology. Targeting prostanoids may serve as a potential therapeutic strategy for preventing or treating obesity and related diseases.

Contribution of RAS, ROS and COX-1-derived prostanoids to the contractile profile of perivascular adipose tissue in cafeteria diet-induced obesity

AIMS

Obesity can lead to the loss of the anticontractile properties of perivascular adipose tissue (PVAT). Given that cafeteria (CAF) diet reflects the variety of highly calorie and easily accessible foods in Western societies, contributing to obesity and metabolic disorders, we sought to investigate the impact of CAF diet on PVAT vasoactive profile and the involvement of renin-angiotensin system, oxidative stress, and cyclooxygenase pathway.

MAIN METHODS

Male Balb/c mice received standard or CAF diet for 4 weeks. Oral glucose tolerance and insulin sensitivity tests were performed, and fasting serum glucose, cholesterol and triglyceride parameters were determined. Vascular reactivity, fluorescence and immunofluorescence analyzes were carried out in intact thoracic aorta in the presence or absence of PVAT.

KEY FINDINGS

CAF diet was effective in inducing obesity and metabolic disorders, as demonstrated by increased body weight gain and adiposity index, hyperlipidemia, hyperglycemia, glucose intolerance and insulin insensitivity. Importantly, CAF diet led to a significant decrease in aortic contractility which was restored in the presence of PVAT, exhibiting therefore a contractile profile. The contractile effect of PVAT was associated with the activation of AT₁ receptor, reactive oxygen species, cyclooxygenase-1, thromboxane A₂ and prostaglandin E₂ receptors.

SIGNIFICANCE

These findings suggest that the contractile profile of PVAT involving the renin-angiotensin system activation, reactive oxygen species and cyclooxygenase-1 metabolites may be a protective compensatory adaptive response during early stage of CAF diet-induced obesity as an attempt to restore the impaired vascular contraction observed in the absence of PVAT, contributing to the maintenance of vascular tone.

Perivascular adipose tissue in autoimmune rheumatic diseases

Perivascular adipose tissue (PVAT) resides at the outermost boundary of the vascular wall, surrounding most conduit blood vessels, except for the cerebral vessels, in humans. A growing body of evidence suggests that inflammation localized within PVAT may contribute to the pathogenesis of cardiovascular disease (CVD). Patients with autoimmune rheumatic diseases (ARDs), e.g., systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), psoriasis, etc., exhibit heightened systemic inflammation and are at increased risk for CVD. Data from clinical studies in patients with ARDs support a linkage between dysfunctional adipose tissue, and PVAT in particular, in disease pathogenesis. Here, we review the data linking PVAT to the pathogenesis of CVD in patients with ARDs, focusing on the role of novel PVAT imaging techniques in defining disease risk and responses to biological therapies.

Endothelial Nitric Oxide Synthase in the Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) is a special type of ectopic fat depot that adheres to most vasculatures. PVAT has been shown to exert anticontractile effects on the blood vessels and confers protective effects against metabolic and cardiovascular diseases. PVAT plays a critical role in vascular homeostasis via secreting adipokine, hormones, and growth factors. Endothelial nitric oxide synthase (eNOS; also known as NOS3 or NOSIII) is well-known for its role in the generation of vasoprotective nitric oxide (NO). eNOS is primarily expressed, but not exclusively, in endothelial cells, while recent studies have identified its expression in both adipocytes and endothelial cells of PVAT. PVAT eNOS is an important player in the protective role of PVAT. Different studies have demonstrated that, under obesity-linked metabolic diseases, PVAT eNOS may be even more important than endothelium eNOS in obesity-induced vascular dysfunction, which may be attributed to certain PVAT eNOS-specific functions. In this review, we summarized the current understanding of eNOS expression in PVAT, its function under both physiological and pathological conditions and listed out a few pharmacological interventions of interest that target eNOS in PVAT.

Comparative study of coronary artery bypass graft materials: reduced contraction and ADMA levels in internal mammary artery versus saphenous vein

BACKGROUND

Vasospasm and atherosclerosis due to low endothelial capacity are the most important causes of coronary artery bypass graft failure observed in internal mammary artery (IMA) and saphenous vein (SV). Vasospasm can be mimicked in in vitro studies by inducing vasoconstriction of graft materials. In the present study, we aimed to compare the vascular contraction induced by several spasmogens including prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2α), phenylephrine (PE), leukotriene C4 (LTC4), LTD4, potassium chloride (KCl), and arachidonic acid between IMA and SV preparations. Furthermore, endothelial capacity, nitrite and asymmetric dimethylarginine (ADMA) levels were compared between two grafts.

METHODS

By using organ bath, contractile responses induced by different spasmogens were compared between IMA and SV preparations derived from patients underwent coronary artery bypass surgery (n=35). The endothelial capacity was determined by acetylcholine (ACh) -induced relaxation in PE-precontracted vessels. Nitrite and ADMA levels were measured in organ culture supernatant of IMA and SV preparations.

RESULTS

Contractile responses induced by PGE2, PGF2α, PE, LTC4, LTD4, KCl and arachidonic acid were significantly lower in IMA preparations versus SV preparations. ACh-induced relaxation was significantly more prominent in IMA than SV preparations. Nitrite levels were greater and ADMA levels were lower in IMA versus SV preparations.

CONCLUSIONS

IMA has reduced capacity to constrict to several vasoconstrictor agents. Furthermore, IMA has greater endothelial capacity associated with higher nitrite levels and lower ADMA levels. Our results support the greater patency rate observed in IMA versus SV preparations.

Vascular reactivity stimulated by TMA and TMAO: Are perivascular adipose tissue and endothelium involved?

Trimethylamine (TMA), formed by intestinal microbiota, and its Flavin-Monooxygenase 3 (FMO3) product Trimethylamine-N-Oxide (TMAO), are potential modulators of host cardiometabolic phenotypes. High circulating levels of TMAO are associated with increased risk for cardiovascular diseases. We hypothesized that TMA/TMAO could directly change the vascular tone. Perivascular adipose tissue (PVAT) helps to regulate vascular homeostasis and may also possess FMO3. Thoracic aorta with(+) or without(-) PVAT, also + or - the endothelium (E), of male Sprague Dawley rats were isolated for measurement of isometric tone in response to TMA/TMAO (1nM-0.5 M). Immunohistochemistry (IHC) studies were done to identify the presence of FMO3. TMA and TMAO elicited concentration-dependent arterial contraction. However, at a maximally achievable concentration (0.2 M), contraction stimulated by TMA was of a greater magnitude (141.5 ± 16% of maximum phenylephrine contraction) than that elicited by TMAO (19.1 ± 4.03%) with PVAT and endothelium intact. When PVAT was preserved, TMAO-induced contraction was extensively reduced the presence (19.1 ± 4.03%) versus absence of E (147.2 ± 20.5%), indicating that the endothelium plays a protective role against TMAO-induced contraction. FMO3 enzyme was present in aortic PVAT, but the FMO3 inhibitor methimazole did not affect contraction stimulated by TMA in aorta + PVAT. However, the l-type calcium channel blocker nifedipine reduced TMA-induced contraction by ∼50% compared to the vehicle. Though a high concentration of these compounds was needed to achieve contraction, the findings that TMA-induced contraction was independent of PVAT and E and mediated by nifedipine-sensitive calcium channels suggest metabolite-induced contraction may be physiologically important.

Saphenous Vein Vasa Vasorum as a Potential Target for Perivascular Fat-Derived Factors

Perivascular adipose tissue (PVAT) is a source of factors affecting vasomotor tone with the potential to play a role in the performance of saphenous vein (SV) bypass grafts. As these factors have been described as having constrictor or relaxant effects, they may be considered either beneficial or detrimental. The close proximity of PVAT to the adventitia provides an environment whereby adipose tissue-derived factors may affect the vasa vasorum, a microvascular network providing the vessel wall with oxygen and nutrients. Since medial ischaemia promotes aspects of graft occlusion the involvement of the PVAT/vasa vasorum axis in vein graft patency should be considered.

Losartan prevents mesenteric vascular bed alterations in high-fat diet fed rats

Dysfunction of perivascular adipose tissue of mesenteric bed participates in the pathophysiology of high blood pressure linked to metabolic syndrome. Thus, it might consider a new therapeutic objective to take account in cardiovascular and metabolic diseases. Besides its antihypertensive effect, there is a growing interest on the pleiotropic actions of losartan, an angiotensin II type 1 (AT₁) receptor antagonist. The aim of the study was to analyze the actions of losartan treatment on adiposity index and prostanoids release from mesenteric vascular bed and its relationship with blood pressure as well as homeostasis model of assessment of insulin resistance (HOMA-IR) in Sprague-Dawley rats under a high-fat (HF) diet for 8 weeks. Four groups were used: control (C), HF diet (HF, 50%, w/w bovine fat), losartan-treated (CL8, 30mg/kg/body weight/day in the drinking water) and losartan-treated HF diet (HFL, both treatments). A high-fat diet incremented systolic blood pressure, HOMA-IR, adiposity of mesenteric vascular bed and the release of vasoconstrictor prostanoids such as thromboxane (TX) B₂ and prostaglandin (PG) F_2α as well as PGE₂, an inflammatory prostanoid in a context of insulin resistance and hypertension. We found a positive correlation between adiposity index and systolic blood pressure. Also, both parameters are positive correlated with the HOMA IR index. Moreover, we also found that these prostanoids release correlate with systolic blood pressure as well as with mesenteric vascular bed adiposity index. Losartan treatment prevented all these alterations and normalized the PGI₂/TXA₂ ratio in high-fat fed rats. We conclude that losartan may play beneficial actions on perivascular adipose tissue alterations and endothelial dysfunction through restoration of normal balance of vasoactive substances in this model.

COVID-19 - Endothelial Axis and Coronary Artery Bypass Graft Patency: a Target for Therapeutic Intervention?

It has been reported that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection induces endothelial inflammation, therefore facilitating the progression of endothelial and vascular dysfunction in coronavirus disease 2019 (COVID-19) patients. Coronary artery bypass grafting (CABG) involves mainly the use of the saphenous vein (SV) and internal mammary artery as graft material in the stenosed coronary arteries. Unfortunately, graft patency of the SV is low due to endothelial dysfunction and inflammation. We propose that SARS-CoV-2 might cause vascular inflammation, endothelial dysfunction, and thrombosis in coronary artery bypass graft vessels by binding angiotensin-converting enzyme 2 receptor. Therefore, in this Special Article, we consider the potential influence of COVID-19 on the patency rates of coronary artery bypass graft vessels, mainly with reference to the SV. Moreover, we discuss the technique of SV graft harvesting and the therapeutic potential of focusing on endothelial dysfunction, vascular inflammation, and thrombosis for protecting coronary artery bypass grafts in COVID-19 infected CABG patients.

Perivascular Adipose Tissue as a Target for Antioxidant Therapy for Cardiovascular Complications

Perivascular adipose tissue (PVAT) is the connective tissue surrounding most of the systemic blood vessels. PVAT is now recognized as an important endocrine tissue that maintains vascular homeostasis. Healthy PVAT has anticontractile, anti-inflammatory, and antioxidative roles. Vascular oxidative stress is an important pathophysiological event in cardiometabolic complications of obesity, type 2 diabetes, and hypertension. Accumulating data from both humans and experimental animal models suggests that PVAT dysfunction is potentially linked to cardiovascular diseases, and associated with augmented vascular inflammation, oxidative stress, and arterial remodeling. Reactive oxygen species produced from PVAT can be originated from mitochondria, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, and uncoupled endothelial nitric oxide synthase. PVAT can also sense vascular paracrine signals and response by secreting vasoactive adipokines. Therefore, PVAT may constitute a novel therapeutic target for the prevention and treatment of cardiovascular diseases. In this review, we summarize recent findings on PVAT functions, ROS production, and oxidative stress in different pathophysiological settings and discuss the potential antioxidant therapies for cardiovascular diseases by targeting PVAT.

Perivascular Adipose Tissue Regulates Vascular Function by Targeting Vascular Smooth Muscle Cells

Adipose tissues are present at multiple locations in the body. Most blood vessels are surrounded with adipose tissue which is referred to as perivascular adipose tissue (PVAT). Similarly to adipose tissues at other locations, PVAT harbors many types of cells which produce and secrete adipokines and other undetermined factors which locally modulate PVAT metabolism and vascular function. Uncoupling protein-1, which is considered as a brown fat marker, is also expressed in PVAT of rodents and humans. Thus, compared with other adipose tissues in the visceral area, PVAT displays brown-like characteristics. PVAT shows a distinct function in the cardiovascular system compared with adipose tissues in other depots which are not adjacent to the vascular tree. Growing and extensive studies have demonstrated that presence of normal PVAT is required to maintain the vasculature in a functional status. However, excessive accumulation of dysfunctional PVAT leads to vascular disorders, partially through alteration of its secretome which, in turn, affects vascular smooth muscle cells and endothelial cells. In this review, we highlight the cross talk between PVAT and vascular smooth muscle cells and its roles in vascular remodeling and blood pressure regulation.

Twenty-Five Years of No-Touch Saphenous Vein Harvesting for Coronary Artery Bypass Grafting: Structural Observations and Impact on Graft Performance

The saphenous vein is the most common conduit used in coronary artery bypass grafting (CABG) yet its failure rate is higher compared to arterial grafts. An improvement in saphenous vein graft performance is therefore a major priority in CABG. No-touch harvesting of the saphenous vein is one of the few interventions that has shown improved patency rates, comparable to that of the left internal thoracic artery. After more than two decades of no-touch research, this technique is now recognized as a Class IIa recommendation in the 2018 European Society of Cardiology and the European Association for Cardio-Thoracic Surgery guidelines on myocardial revascularization. In this review, we describe the structural alterations that occur in conventional versus no-touch saphenous vein grafts and how these changes affect graft patency. In addition, we discuss various strategies aimed at repairing saphenous vein grafts prepared at conventional CABG.

The no-touch saphenous vein is an excellent alternative conduit to the radial artery 8 years after coronary artery bypass grafting: A randomized trial

BACKGROUND

In 2004, a prospective randomized trial demonstrated that after 3 years, saphenous veins (SVs) harvested with a no touch (NT) technique had a greater patency than radial grafts for coronary bypass surgery. Here we report the 8-year follow-up data of this trial.

METHODS

The trial included 108 patients undergoing coronary artery bypass grafting (CABG). Each patient was assigned to receive 1 NT SV and 1 radial artery (RA) graft to either the left or right coronary territory to complement the left internal thoracic artery (LITA). Sequential grafting was common, so overall graft patency as well as the patency of each anastomosis were assessed.

RESULTS

Angiography was performed in 84 patients (78%) at mean of 97 months postoperatively. Graft patency were high and similar for both NT and RA: 86% for NT versus 79% for RA (P = .22). The patency of coronary anastomoses was significantly higher with the NT SV grafts (91% vs 81%; P = .046). The NT grafts also had excellent patency in coronary arteries with <90% stenosis (93% patency) and in coronary arteries of small diameter (87% patency) or with mild calcification (88% patency). Patency for the LITA was 92%.

CONCLUSIONS

NT SV grafts have excellent patency similar to that of RA grafts after 8 years. In addition, NT SV grafts can be used in situations that are not ideal for RA grafts.

Alteration of Pressure-Induced Vasodilation in Aging and Diabetes, a Neuro-Vascular Damage

Skin is constantly subjected to pressure at different levels. Pressure-induced vasodilation (PIV) is one of the response mechanisms to low pressure that maintains the homeostasis of the skin. PIV results from the interaction of primary afferent nerves and vascular endothelium of skin vessels. Thanks to this cutaneous neuro-vascular interaction, the cutaneous blood flow increase allows the maintenance of an optimal level of oxygenation and minimizes the lack of vascularization of the skin tissue under low pressure. It seems to be associated with the cutaneous protection mechanisms to prevent pressure ulcers. In some contexts, where microangiopathy and neuropathy can occur, such as aging and diabetes, PIV is impaired, leading to a dramatic early decrease in local skin blood flow when low pressure is applied. In aging, PIV alteration is due to endothelial dysfunction, essentially from an alteration of the nitric oxide pathway. In the inflamm-aging context, oxidative stress increases leading to endothelial cell and nerve damages. An age-related sensory neuropathy will exacerbate the alteration of PIV during the aging process. In diabetes, non-controlled hyperglycaemia leads to an increase in several pathological biochemical pathways that involve oxidative stress and can affect PIV. Sorbinil, alagebrium and alpha-lipoic acid are able individually to restore PIV through a possible oxidative stress reduction. Candesartan, an angiotensin II type 1 receptor blocker, is also able to restore PIV and prevent pressure ulcer formation. The possibility of preventing pressure ulcer associated to diabetes and/or aging with the restoration of PIV seems to be a promising research path.

The Local Regulation of Vascular Function: From an Inside-Outside to an Outside-Inside Model

Our understanding of the regulation of vascular function, specifically that of vasomotion, has evolved dramatically over the past few decades. The classic conception of a vascular system solely regulated by circulating hormones and sympathetic innervation gave way to a vision of a local regulation. Initially by the so-called, autacoids like prostacyclin, which represented the first endothelium-derived paracrine regulator of smooth muscle. This was the prelude of the EDRF-nitric oxide age that has occupied vascular scientists for nearly 30 years. Endothelial cells revealed to have the ability to generate numerous mediators besides prostacyclin and nitric oxide (NO). The need to classify these substances led to the coining of the terms: endothelium-derived relaxing, hyperpolarizing and contracting factors, which included various prostaglandins, thromboxane A2, endothelin, as well numerous candidates for the hyperpolarizing factor. The opposite layer of the vascular wall, the adventitia, eventually and for a quite short period of time, enjoyed the attention of some vascular physiologists. Adventitial fibroblasts were recognized as paracrine cells to the smooth muscle because of their ability to produce some substances such as superoxide. Remarkably, this took place before our awareness of the functional potential of another adventitial cell, the adipocyte. Possibly, because the perivascular adipose tissue (PVAT) was systematically removed during the experiments as considered a non-vascular artifact tissue, it took quite long to be considered a major source of paracrine substances. These are now being integrated in the vast pool of mediators synthesized by adipocytes, known as adipokines. They include hormones involved in metabolic regulation, like leptin or adiponectin; classic vascular mediators like NO, angiotensin II or catecholamines; and inflammatory mediators or adipocytokines. The first substance studied was an anti-contractile factor named adipose-derived relaxing factor of uncertain chemical nature but possibly, some of the relaxing mediators mentioned above are behind this factor. This manuscript intends to review the vascular regulation from the point of view of the paracrine control exerted by the cells present in the vascular environment, namely, endothelial, adventitial, adipocyte and vascular stromal cells.

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.

Preserved Vasoconstriction and Relaxation of Saphenous Vein Grafts Obtained by a No-Touch Technique for Coronary Artery Bypass Grafting

BACKGROUND

To obtain a saphenous vein graft (SVG) for coronary artery bypass grafting (CABG), the benefit of using a no-touch (NT) technique in vascular function has not been fully investigated. Methods and Results: The pathological and physiological functions of human SVGs with a NT technique to preserve the perivascular adipose tissue (PVAT) and ones obtained by using a conventional (CON) technique removing PVAT, were examined. Immunohistochemistry of the section of SVGs showed that the phosphorylation of endothelial nitric oxide synthase in the endothelium of the NT group was more responsive to vascular endothelial growth factor. A myograph of SVGs showed greater contraction with phenylephrine in the NT group. However, the strong contraction was eliminated in SVGs taken by electrocautery. In the 10 patients whose SVGs were taken without electrocautery, endothelial-dependent relaxation with bradykinin was apparently increased in the CON group more than in the NT group. Smooth muscle relaxation with nitroprusside was higher in the CON group at the lower concentrations; however, the relaxation became greater in the NT group at the high concentrations. Therefore, the effect of neutralizing PVAT-released factors in the both groups was further examined. After medium of NT and CON were exchanged in half, relaxation of SVGs was immediately restored in the NT group.

CONCLUSIONS

The results suggest that the NT technique preserves the functions of vasoconstriction and relaxation. Also, the presence of PVAT-released vasoconstrictive factors was suspected.

Inflammation-linked adaptations in dermal microvascular reactivity accompany the development of obesity and type 2 diabetes

Background/Objectives

The increased prevalence of obesity has prompted great strides in our understanding of specific adipose depots and their involvement in cardio-metabolic health. However, the impact of obesity on dermal white adipose tissue (dWAT) and dermal microvascular functionality remains unclear. This study aimed to investigate the temporal changes that occur in dWAT and dermal microvascular functionality during the development of diet-induced obesity and type 2 diabetes in mice.

Methods

Metabolic phenotyping of a murine model of hypercaloric diet (HCD)-induced obesity and type 2 diabetes was performed at three time points that reflected three distinct stages of disease development; 2 weeks of HCD-overweight-metabolically healthy, 4 weeks of HCD-obese-prediabetic and 12 weeks of HCD-obese-type 2 diabetic mice. Expansion of dWAT was characterized histologically, and changes in dermal microvascular reactivity were assessed in response to pressure and the vasodilators SNP and Ach.

Results

HCD resulted in a progressive expansion of dWAT and increased expression of pro-inflammatory markers (IL1β and COX-2). Impairments in pressure-induced (PIV) and Ach-induced (endothelium-dependent) vasodilation occurred early, in overweight-metabolically healthy mice. Residual vasodilatory responses were NOS-independent but sensitive to COX inhibition. These changes were associated with reductions in NO and adiponectin bioavailability, and rescued by exogenous adiponectin or hyperinsulinemia. Obese-prediabetic mice continued to exhibit impaired Ach-dependent vasodilation but PIV appeared normalized. This normalization coincided with elevated endogenous adiponectin and insulin levels, and was sensitive to NOS, COX and PI3K, inhibition. In obese-type 2 diabetic mice, both Ach-stimulated and pressure-induced vasodilatory responses were increased through enhanced COX-2-dependent prostaglandin response.

Conclusions

We demonstrate that the development of obesity, metabolic dysfunction and type 2 diabetes, in HCD-fed mice, is accompanied by increased dermal adiposity and associated metaflammation in dWAT. Importantly, these temporal changes are also linked to disease stage-specific dermal microvascular reactivity, which may reflect adaptive mechanisms driven by metaflammation.

Renal perivascular adipose tissue: Form and function

Renal sympathetic activity affects blood pressure in part by increasing renovascular resistance via release of norepinephrine (NE) from sympathetic nerves onto renal arteries. Here we test the idea that adipose tissue adjacent to renal blood vessels, i.e. renal perivascular adipose tissue (RPVAT), contains a pool of NE which can be released to alter renal vascular function. RPVAT was obtained from around the main renal artery/vein of the male Sprague Dawley rats. Thoracic aortic PVAT and mesenteric PVAT also were studied as brown-like and white fat comparators respectively. RPVAT was identified as a mix of white and brown adipocytes, because of expression of both brown-like (e.g. uncoupling protein 1) and white adipogenic genes. All PVATs contained NE (ng/g tissue, RPVAT:524 ± 68, TAPVAT:740 ± 16, MPVAT:96 ± 24). NE was visualized specifically in RPVAT adipocytes by immunohistochemistry. The presence of RPVAT (+RPVAT) did not alter the response of isolated renal arteries to NE compared to responses of arteries without RPVAT (-RPVAT). By contrast, the maximum contraction to the sympathomimetic tyramine was ~2× greater in the renal artery +PVAT versus -PVAT. Tyramine-induced contraction in +RPVAT renal arteries was reduced by the α₁-adrenoceptor antagonist prazosin and the NE transporter inhibitor nisoxetine. These results suggest that tyramine caused release of NE from RPVAT. Renal denervation significantly (>50%) reduced NE content of RPVAT but did not modify tyramine-induced contraction of +RPVAT renal arteries. Collectively, these data support the existence of a releasable pool of NE in RPVAT that is independent of renal sympathetic innervation and has the potential to change renal arterial function.

Inflammation in Vein Graft Disease

Bypass surgery is one of the most frequently used strategies to revascularize tissues downstream occlusive atherosclerotic lesions. For venous bypass surgery the great saphenous vein is the most commonly used vessel. Unfortunately, graft efficacy is low due to the development of vascular inflammation, intimal hyperplasia and accelerated atherosclerosis. Moreover, failure of grafts leads to significant adverse outcomes and even mortality. The last couple of decades not much has changed in the treatment of vein graft disease (VGD). However, insight is the cellular and molecular mechanisms of VGD has increased. In this review, we discuss the latest insights on VGD and the role of inflammation in this. We discuss vein graft pathophysiology including hemodynamic changes, the role of vessel wall constitutions and vascular remodeling. We show that profound systemic and local inflammatory responses, including inflammation of the perivascular fat, involve both the innate and adaptive immune system.

Role of Perivascular Adipose Tissue in Health and Disease

Perivascular adipose tissue (PVAT) is cushion of fat tissue surrounding blood vessels, which is phenotypically different from other adipose tissue depots. PVAT is composed of adipocytes and stromal vascular fraction, constituted by different populations of immune cells, endothelial cells, and adipose-derived stromal cells. It expresses and releases an important number of vasoactive factors with paracrine effects on vascular structure and function. In healthy individuals, these factors elicit a net anticontractile and anti-inflammatory paracrine effect aimed at meeting hemodynamic and metabolic demands of specific organs and regions of the body. Pathophysiological situations, such as obesity, diabetes or hypertension, induce changes in its amount and in the expression pattern of vasoactive factors leading to a PVAT dysfunction in which the beneficial paracrine influence of PVAT is shifted to a pro-oxidant, proinflammatory, contractile, and trophic environment leading to functional and structural cardiovascular alterations and cardiovascular disease. Many different PVATs surrounding a variety of blood vessels have been described and exhibit regional differences. Both protective and deleterious influence of PVAT differs regionally depending on the specific vascular bed contributing to variations in the susceptibility of arteries and veins to vascular disease. PVAT therefore, might represent a novel target for pharmacological intervention in cardiovascular disease. © 2018 American Physiological Society. Compr Physiol 8:23-59, 2018.

Comparisons between perivascular adipose tissue and the endothelium in their modulation of vascular tone

The endothelium is an established modulator of vascular tone; however, the recent discovery of the anti-contractile nature of perivascular adipose tissue (PVAT) suggests that the fat, which surrounds many blood vessels, can also modulate vascular tone. Both the endothelium and PVAT secrete vasoactive substances, which regulate vascular function. Many of these factors are common to both the endothelium and PVAT; therefore, this review will highlight the potential shared mechanisms in the modulation of vascular tone. Endothelial dysfunction is a hallmark of many vascular diseases, including hypertension and obesity. Moreover, PVAT dysfunction is now being reported in several cardio-metabolic disorders. Thus, this review will also discuss the mechanistic insights into endothelial and PVAT dysfunction in order to evaluate whether PVAT modulation of vascular contractility is similar to that of the endothelium in health and disease.

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.

Sex differences in the role of phospholipase A2 -dependent arachidonic acid pathway in the perivascular adipose tissue function in pigs

KEY POINTS

The fat surrounding blood vessels (perivascular adipose tissue or PVAT) releases vasoactive compounds that regulate vascular smooth muscle tone. There are sex differences in the regulation of vascular tone, but, to date, no study has investigated whether there are sex differences in the regulation of blood vessel tone by PVAT. This study has identified that the cyclooxygenase products thromboxane and PGF_2α are released from coronary artery PVAT from pigs. Thromboxane appears to mediate the PVAT-induced contraction in arteries from females, whereas PGF_2α appears to mediate the contraction in arteries from males. These sex differences in the role of these prostanoids in the PVAT-induced contraction can be explained by a greater release of thromboxane from PVAT from female animals and greater sensitivity to PGF_2α in the porcine coronary artery from males.

ABSTRACT

Previous studies have demonstrated that perivascular adipose tissue (PVAT) causes vasoconstriction. In this present study, we determined the role of cyclooxygenase-derived prostanoids in this contractile response and determined whether there were any sex differences in the regulation of vascular tone by PVAT. Contractions in isolated segments of coronary arteries were determined using isolated tissue baths and isometric tension recording. Segments were initially cleaned of PVAT, which was then re-added to the tissue bath and changes in tone measured over 1 h. Levels of PGF_2α and thromboxane B₂ (TXB₂ ) were quantified by ELISA, and PGF_2α (FP) and thromboxane A₂ (TP) receptor expression determined by Western blotting. In arteries from both male and female pigs, re-addition of PVAT caused a contraction, which was partially inhibited by the cyclooxygenase inhibitors indomethacin and flurbiprofen. The FP receptor antagonist AL8810 attenuated the PVAT-induced contraction in arteries from males, whereas the TP receptor antagonist GR32191B inhibited the PVAT-induced contraction in arteries from females. Although there was no difference in PGF_2α levels in PVAT between females and males, PGF_2α produced a larger contraction in arteries from males, correlating with a higher FP receptor expression. In contrast, release of TXB₂ from PVAT from females was greater than from males, but there was no difference in the contraction by the TXA₂ agonist U46619, or TP receptor expression in arteries from different sexes. These findings demonstrate clear sex differences in PVAT function in which PGF_2α and TXA₂ antagonists can inhibit the PVAT-induced vasoconstriction in male and female PCAs, respectively.

Prostanoids in the pathophysiology of human coronary artery

Coronary artery disease is one of the leading causes of death in wordwide. There is growing evidence that prostanoids are involved in the physiology and pathophysiology of the human coronary artery by controlling vascular tone, remodelling of the vascular wall or angiogenesis. In this review, the production of prostanoids and the expression of prostanoid receptors in human coronary artery in health or disease are described. In addition, the interactions between sex hormones and prostanoids, their participations in the development of coronary artery diseases have been addressed. Globally, most of the studies performed in human coronary artery preparations have shown that prostacyclin (PGI₂) has beneficial effects by inducing vasodilatation and promoting angiogenesis while reverse effects are confirmed by thromboxane A₂ (TxA₂). More studies are needed to determine the roles of the other prostanoids (PGE₂, PGD₂ and PGF_2α) in vascular functions of the human coronary artery. Finally, in addition to the in vitro data about the human coronary artery, myocardial infarction induced by cyclooxygenase-2 (COX-2) inhibitor and the protective effects of aspirin after coronary artery bypass surgery suggest that prostanoids are key mediators in coronary homeostasis.

Role of PVAT in coronary atherosclerosis and vein graft patency: friend or foe?

Perivascular adipose tissue (PVAT) releases numerous factors and adipokines with paracrine effects on both vascular structure and function. These effects are variable as they depend on regional differences in PVAT among blood vessels and vary with changes in adiposity. There is considerable evidence demonstrating an association between coronary PVAT and the development and progression of coronary artery disease, which is associated with inflammation, oxidative stress, angiogenesis, vascular remodelling and blood clotting. However, PVAT also has a protective role in vascular grafts, especially the no-touch saphenous vein, in patients undergoing coronary artery bypass. This beneficial influence of PVAT involves factors such as adipocyte-derived relaxing factor, nitric oxide (NO), leptin, adiponectin, prostanoids, hydrogen sulphide and neurotransmitters, as well as mechanical protection. This article aims to highlight and compare the dual role of PVAT in the development and progression of coronary atherosclerosis, as well as in increased graft patency. Different deleterious and protective mechanisms of PVAT are also discussed and the inside-outside signalling paradigm of atherosclerosis development re-evaluated. The bidirectional communication between the arterial and venous wall and their surrounding PVAT, where signals originating from the vascular wall or lumen can affect PVAT phenotype, has been shown to be very complex. Moreover, signals from PVAT also influence the structure and function of the vascular wall in a paracrine manner.

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.

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

The paracrine control of vascular motion. A historical perspective

During the last quarter of the past century, the leading role the endocrine and nervous systems had on the regulation of vasomotion, shifted towards a more paracrine-based regulation. This begun with the recognition of endothelial cells as active players of vascular control, when the vessel's intimal layer was identified as the main source of prostacyclin and was followed by the discovery of an endothelium-derived smooth muscle cell relaxing factor (EDRF). The new position acquired by endothelial cells prompted the discovery of other endothelium-derived regulatory products: vasoconstrictors, generally known as EDCFs, endothelin, and other vasodilators with hyperpolarizing properties (EDHFs). While this research was taking place, a quest for the discovery of the nature of EDRF carried back to a research line commenced a decade earlier: the recently found intracellular messenger cGMP and nitrovasodilators. Both were smooth muscle relaxants and appeared to interact in a hormonal fashion. Prejudice against an unconventional gaseous molecule delayed the acceptance that EDRF was nitric oxide (NO). When this happened, a new era of research that exceeded the vascular field commenced. The discovery of the pathway for NO synthesis from L-arginine involved the clever assembling of numerous unrelated observations of different areas of knowledge. The last ten years of research on the paracrine regulation of the vascular wall has shifted to perivascular fat (PVAT), which is beginning to be regarded as the fourth layer of the vascular wall. Starting with the discovery of an adipose-derived relaxing substance (ADRF), the role that different adipokines have on the paracrine control of vasomotion is now filling the research activity of many vascular pharmacology labs, and surprising interactions between the endothelium, PVAT and smooth muscle are being unveiled.

The role of perivascular adipose tissue in vasoconstriction, arterial stiffness, and aneurysm

Since the "rediscovery" of brown adipose tissue in adult humans, significant scientific efforts are being pursued to identify the molecular mechanisms to promote a phenotypic change of white adipocytes into brown-like cells, a process called "browning". It is well documented that white adipose tissue (WAT) mass and factors released from WAT influence the vascular function and positively correlate with cardiac arrest, stroke, and other cardiovascular complications. Similar to other fat depots, perivascular adipose tissue (PVAT) is an active endocrine organ and anatomically surrounds vessels. Both brown-like and white-like PVAT secrete various adipokines, cytokines, and growth factors that either prevent or promote the development of cardiovascular diseases (CVDs) depending on the relative abundance of each type and their bioactivity in the neighboring vasculature. Notably, pathophysiological conditions, such as obesity, hypertension, or diabetes, induce the imbalance of PVAT-derived vasoactive products that promote the infiltration of inflammatory cells. This then triggers derangements in vascular smooth muscle cells and endothelial cell dysfunction, resulting in the development of vascular diseases. In this review, we discuss the recent advances on the contribution of PVAT in CVDs. Specifically, we summarize the current proposed roles of PVAT in relationship with vascular contractility, endothelial dysfunction, neointimal formation, arterial stiffness, and aneurysm.

Intercellular communication lessons in heart failure

Cell-cell or inter-organ communication allows the exchange of information and messages, which is essential for the coordination of cell/organ functions and the maintenance of homeostasis. It has become evident that dynamic interactions of different cell types play a major role in the heart, in particular during the progression of heart failure, a leading cause of mortality worldwide. Heart failure is associated with compensatory structural and functional changes mostly in cardiomyocytes and cardiac fibroblasts, which finally lead to cardiomyocyte hypertrophy and fibrosis. Intercellular communication within the heart is mediated mostly via direct cell-cell interaction or the release of paracrine signalling mediators such as cytokines and chemokines. However, recent studies have focused on the exchange of genetic information via the packaging into vesicles as well as the crosstalk of lipids and other paracrine molecules within the heart and distant organs, such as kidney and adipose tissue, which might all contribute to the pathogenesis of heart failure. In this review, we discuss emerging communication networks and respective underlying mechanisms which could be involved in cardiovascular disease conditions and further emphasize promising therapeutic targets for drug development.

Regional differences in perivascular adipose tissue impacting vascular homeostasis

Perivascular adipose tissue (PVAT) releases several important vasoactive factors with physiological and pathophysiological paracrine effects. A large body of evidence suggests regional phenotypic and functional differences among PVAT depots, depending on the specific vascular bed or different regions in the vascular bed where the PVAT is located. These non-uniform and separate PVATs exert various paracrine effects on vascular structure and function that largely impact disease states, such as endothelial dysfunction, atherosclerosis, or insulin resistance. This emerging view of PVAT function requires considering heterogeneous PVAT as a specialized organ that can differentially regulate vascular function depending on its anatomical location. In this context, the adipose-vascular axis may represent a novel target for pharmacological intervention in vasculopathy in cardiometabolic disorders.

Effect of resveratrol and orchidectomy on the vasorelaxing influence of perivascular adipose tissue

Perivascular adipose tissue (PVAT) releases several adipo(cyto)kines. Some are vasoactive substances that elicit a net beneficial anticontractile effect. Resveratrol and testosterone are known to modulate adipo(cyto)kine release from adipose tissue and could therefore influence the anticontractile effect of PVAT. In vitro tension measurements were performed using thoracic aorta segments with and without adipose tissue from sham-operated or orchidectomized male Swiss mice. Concentration-response curves to norepinephrine (NOR) were constructed in the presence and absence of resveratrol (10 μM, 15 min) or the relaxant effect of resveratrol (10-100 μM) was investigated after inducing tone with NOR (5 μM). Aortas with PVAT displayed significantly attenuated contractions to NOR compared with aortas without PVAT. In aortas without PVAT, resveratrol (10 μM) significantly decreased NOR responses and elicited concentration-dependent (10-100 µM) relaxations. However, in aortas with adherent PVAT, resveratrol (10 μM) neither decreased NOR responses, nor did resveratrol (10-100 µM) induce arterial relaxations. The anticontractile effect of PVAT was less pronounced in the presence of resveratrol and unaltered by orchidectomy. Orchidectomy did not influence contractions induced by NOR. Orchidectomy does not modulate the anticontractile capacity of PVAT, while resveratrol decreases the vasorelaxing influence of PVAT. The positive effects associated with resveratrol addition are neutralized by the presence of PVAT. This is thought to result from a dual effect of resveratrol: (1) inhibition of the influence of vasodilatory adipo(cyto)kines and (2) a direct relaxant effect on the vascular smooth muscle. Overall, the beneficial relaxing effect of resveratrol is lost in mice thoracic aorta surrounded by PVAT.

Perivascular adipose tissue in vascular function and disease: a review of current research and animal models

Perivascular adipose tissue (PVAT), long assumed to be nothing more than vessel-supporting connective tissue, is now understood to be an important, active component of the vasculature, with integral roles in vascular health and disease. PVAT is an adipose tissue with similarities to both brown and white adipose tissue, although recent evidence suggests that PVAT develops from its own precursors. Like other adipose tissue depots, PVAT secretes numerous biologically active substances that can act in both autocrine and paracrine fashion. PVAT has also proven to be involved in vascular inflammation. Although PVAT can support inflammation during atherosclerosis via macrophage accumulation, emerging evidence suggests that PVAT also has antiatherosclerotic properties related to its abilities to induce nonshivering thermogenesis and metabolize fatty acids. We here discuss the accumulated knowledge of PVAT biology and related research on models of hypertension and atherosclerosis.