Will the real plaque vasculature please stand up? Why we need to distinguish the vasa plaquorum from the vasa vasorum

Progression of Arterial Vasa Vasorum from Regulator of Arterial Homeostasis to Promoter of Atherogenesis

The vasa vasorum (vessels of vessels) are a dynamic microvascular system uniquely distributed to maintain physiological homeostasis of the artery wall by supplying nutrients and oxygen to the outer layers of the artery wall, adventitia, and perivascular adipose tissue, and in large arteries, to the outer portion of the medial layer. Vasa vasorum endothelium and contractile mural cells regulate direct access of bioactive cells and factors present in both the systemic circulation and the arterial perivascular adipose tissue and adventitia to the artery wall. Experimental and human data show that proatherogenic factors and cells gain direct access to the artery wall via the vasa vasorum and may initiate, promote, and destabilize the plaque. Activation and growth of vasa vasorum occur in all blood vessel layers primarily by angiogenesis, producing fragile and permeable new microvessels that may cause plaque hemorrhage and fibrous cap rupture. Ironically, invasive therapies, such as angioplasty and coronary artery bypass grafting, injure the vasa vasorum, leading to treatment failures. The vasa vasorum function both as a master integrator of arterial homeostasis and, once perturbed or injured, as a promotor of atherogenesis. Future studies need to be directed at establishing reliable in vivo and in vitro models to investigate the cellular and molecular regulation of the function and dysfunction of the arterial vasa vasorum.

Excessive Adventitial and Perivascular Vascularisation Correlates with Vascular Inflammation and Intimal Hyperplasia

Albeit multiple studies demonstrated that vasa vasorum (VV) have a crucial importance in vascular pathology, the informative markers and metrics of vascular inflammation defining the development of intimal hyperplasia (IH) have been vaguely studied. Here, we employed two rat models (balloon injury of the abdominal aorta and the same intervention optionally complemented with intravenous injections of calciprotein particles) and a clinical scenario (arterial and venous conduits for coronary artery bypass graft (CABG) surgery) to investigate the pathophysiological interconnections among VV, myeloperoxidase-positive (MPO⁺) clusters, and IH. We found that the amounts of VV and MPO⁺ clusters were strongly correlated; further, MPO⁺ clusters density was significantly associated with balloon-induced IH and increased at calciprotein particle-provoked endothelial dysfunction. Likewise, number and density of VV correlated with IH in bypass grafts for CABG surgery at the pre-intervention stage and were higher in venous conduits which more frequently suffered from IH as compared with arterial grafts. Collectively, our results underline the pathophysiological importance of excessive VV upon the vascular injury or at the exposure to cardiovascular risk factors, highlight MPO⁺ clusters as an informative marker of adventitial and perivascular inflammation, and propose another mechanistic explanation of a higher long-term patency of arterial grafts upon the CABG surgery.

Backscattered Scanning Electron Microscopy Approach for Assessment of Microvessels under Conditions of Normal Microanatomy and Pathological Neovascularization

We evaluated the efficiency of an original method for studying of the microvascular bed under conditions of normal microanatomy and pathological neovascularization. The blood vessels, tissues surrounding the stent in the pulmonary artery and subcutaneously implanted titanium nickelide plate, atherosclerotic plaque, and vascular stent with restenosis were examined. The specimens were fixed in formalin and stained in OsO₄, embedded into fresh epoxy resin, grinded, polished, and counterstained with uranyl acetate and lead citrate. Numerous vasa vasorum were found in all native vessels. Around the pulmonary artery stent and metal plates, numerous newly formed vessels of small diameter were seen. The intensity of neovascularization in atherosclerosis and carotid stent restenosis differed significantly. Our technique can be successfully used for evaluation of the microvascular bed.

Quest for the Vulnerable Atheroma: Carotid Stenosis and Diametric Strain--A Feasibility Study

The Bernoulli effect may result in eruption of a vulnerable carotid atheroma, causing a stroke. We measured electrocardiography (ECG)-registered QRS intra-stenotic blood velocity and atheroma strain dynamics in carotid artery walls using ultrasonic tissue Doppler methods, providing displacement and time resolutions of 0.1 μm and 3.7 ms. Of 22 arteries, 1 had a peak systolic velocity (PSV) >280 cm/s, 4 had PSVs between 165 and 280 cm/s and 17 had PSVs <165 cm/s. Eight arteries with PSVs <65 cm/s and 4 of 9 with PSVs between 65 and 165 cm/s had normal systolic diametric expansion (0% and 7%) and corresponding systolic wall thinning. The remaining 10 arteries had abnormal systolic strain dynamics, 2 with diametric reduction (>-0.05 mm), 2 with extreme wall expansion (>0.1 mm), 2 with extreme wall thinning (>-0.1 mm) and 4 with combinations. Decreases in systolic diameter and/or extreme systolic arterial wall thickening may indicate imminent atheroma rupture.

Ultrastructure and histogenesis of the acral calcified angioleiomyoma

We studied the ultrastructure, immunohistochemistry, and histogenesis of the acral calcified angioleiomyoma, observing three concentric zones: (a) pseudocapsular, thin, with spindle-shaped stromal cells (SCs), presenting scarce organelles and expressing CD34, (b) muscular, forming a ring, with smooth muscle cells of heterogenous phenotype (mainly in quantity and thickness of filaments, and in expression of h-caldesmon, αSMA, and desmin), and (c) central, extensive, calcified (spicular and/or star-shaped calcium deposits around collagen fibers), with pericytic involutive vasculature. The intratumoral vessels were thick (several layers of perivascular cells, with a continuum of phenotypes, resembling myopericytoma vessels) and thin (slit-like channels), without adventitial SCs or elastic material. The extratumoral vessels showed adventitial SCs (which contribute to form the tumor pseudocapsule), hyperplasia of the media and intima layers, and/or occlusion of the lumen by a wide, homogenous fibrotic central zone. Histogenetically, the collagenous matrix may act as a mineralization substrate and the calcifying modified pericytes as inductors; intratumoral vessels may originate from the peritumoral vessels or from the vessel where the tumor develops; and extratumoral vessel modifications, mimicking tumor features, concur with a minor repetitive trauma pathogenesis.

Red blood cell, hemoglobin and heme in the progression of atherosclerosis

For decades plaque neovascularization was considered as an innocent feature of advanced atherosclerotic lesions, but nowadays growing evidence suggest that this process triggers plaque progression and vulnerability. Neovascularization is induced mostly by hypoxia, but the involvement of oxidative stress is also established. Because of inappropriate angiogenesis, neovessels are leaky and prone to rupture, leading to the extravasation of red blood cells (RBCs) within the plaque. RBCs, in the highly oxidative environment of the atherosclerotic lesions, tend to lyse quickly. Both RBC membrane and the released hemoglobin (Hb) possess atherogenic activities. Cholesterol content of RBC membrane contributes to lipid deposition and lipid core expansion upon intraplaque hemorrhage. Cell-free Hb is prone to oxidation, and the oxidation products possess pro-oxidant and pro-inflammatory activities. Defense and adaptation mechanisms evolved to cope with the deleterious effects of cell free Hb and heme. These rely on plasma proteins haptoglobin (Hp) and hemopexin (Hx) with the ability to scavenge and eliminate free Hb and heme form the circulation. The protective strategy is completed with the cellular heme oxygenase-1/ferritin system that becomes activated when Hp and Hx fail to control free Hb and heme-mediated stress. These protective molecules have pharmacological potential in diverse pathologies including atherosclerosis.

Biomechanical factors in the biology of aortic wall and aortic valve diseases

The biomechanical factors that result from the haemodynamic load on the cardiovascular system are a common denominator of several vascular pathologies. Thickening and calcification of the aortic valve will lead to reduced opening and the development of left ventricular outflow obstruction, referred to as aortic valve stenosis. The most common pathology of the aorta is the formation of an aneurysm, morphologically defined as a progressive dilatation of a vessel segment by more than 50% of its normal diameter. The aortic valve is exposed to both haemodynamic forces and structural leaflet deformation as it opens and closes with each heartbeat to assure unidirectional flow from the left ventricle to the aorta. The arterial pressure is translated into tension-dominated mechanical wall stress in the aorta. In addition, stress and strain are related through the aortic stiffness. Furthermore, blood flow over the valvular and vascular endothelial layer induces wall shear stress. Several pathophysiological processes of aortic valve stenosis and aortic aneurysms, such as macromolecule transport, gene expression alterations, cell death pathways, calcification, inflammation, and neoangiogenesis directly depend on biomechanical factors.

Microvessel density but not neoangiogenesis is associated with 18F-FDG uptake in human atherosclerotic carotid plaques

INTRODUCTION

The vulnerable atherosclerotic lesion exhibits the proliferation of neovessels and inflammation. The imaging modality 2-deoxy-2-[(18)F]fluoro-D: -glucose positron emission tomography ((18)FDG-PET) is considered for the identification of vulnerable plaques.

PURPOSE

The purpose of this study was to compare the gene expression of neoangiogenesis and vulnerability-associated genes with (18)FDG uptake in patients undergoing carotid endarterectomy.

PROCEDURES

Human atherosclerotic carotid artery plaques from symptomatic patients were used for gene expression analysis by quantitative PCR of vascular endothelial growth factor (VEGF) and integrin α(V) and integrin β(3) subunits, genes essential during neoangiogenesis. We also evaluated the gene expression of CD34, a measure of microvessel density (MVD), as well as CD68, MMP-9, and cathepsin K, genes of major importance in plaque vulnerability. Gene expression analysis was compared with (18)FDG-PET.

RESULTS

VEGF and integrin α(V)β(3) gene expression did not correlate with (18)FDG uptake, whereas CD34 gene expression exhibited an inverse correlation with (18)FDG uptake. Additionally, we established that markers of vulnerability were correlated with (18)FDG uptake.

CONCLUSIONS

Neoangiogenesis is not associated with (18)FDG uptake, whereas MVD and markers of vulnerability correlate with (18)FDG uptake. The absence of correlation between markers of neoangiogenesis and (18)FDG uptake suggests a temporal separation between the process of neoangiogenesis and inflammatory activity.

Nonproteolytic properties of murine alternatively spliced tissue factor: implications for integrin-mediated signaling in murine models

This study was performed to determine whether murine alternatively spliced tissue factor (masTF) acts analogously to human alternatively spliced tissue factor (hasTF) in promoting neovascularization via integrin ligation. Immunohistochemical evaluation of a spontaneous murine pancreatic ductal adenocarcinoma model revealed increased levels of masTF and murine full-length tissue factor (mflTF) in tumor lesions compared with benign pancreas; furthermore, masTF colocalized with mflTF in spontaneous aortic plaques of Ldlr(-/-) mice, indicating that masTF is likely involved in atherogenesis and tumorigenesis. Recombinant masTF was used to perform in vitro and ex vivo studies examining its integrin-mediated biologic activity. Murine endothelial cells (ECs) rapidly adhered to masTF in a β3-dependent fashion. Using adult and embryonic murine ECs, masTF potentiated cell migration in transwell assays. Scratch assays were performed using murine and primary human ECs; the effects of masTF and hasTF were comparable in murine ECs, but in human ECs, the effects of hasTF were more pronounced. In aortic sprouting assays, the potency of masTF-triggered vessel growth was undistinguishable from that observed with hasTF. The proangiogenic effects of masTF were found to be Ccl2-mediated, yet independent of vascular endothelial growth factor. In murine ECs, masTF and hasTF upregulated genes involved in inflammatory responses; murine and human ECs stimulated with masTF and hasTF exhibited increased interaction with murine monocytic cells under orbital shear. We propose that masTF is a functional homolog of hasTF, exerting some of its key effects via β3 integrins. Our findings have implications for the development of murine models to examine the interplay between blood coagulation, atherosclerosis and cancer.