Topological determinants and consequences of adventitial responses to arterial wall injury

From tissue iron retention to low systemic haemoglobin levels, new pathophysiological biomarkers of human abdominal aortic aneurysm

Iron deposits are observed in tissue of abdominal aortic aneurysm (AAA) patients, although the underlying mechanisms are not completely elucidated. Therefore we explored circulating markers of iron metabolism in AAA patients, and tested if they could serve as biomarkers of AAA. Increased red blood cell (RBC)-borne iron retention and transferrin, transferrin receptor and ferritin expression was observed in AAA tissue compared to control aorta (immunohistochemistry and western blot). In contrast, decreased circulating iron, transferrin, mean corpuscular haemoglobin concentration (MCHC) and haemoglobin concentration, along with circulating RBC count, were observed in AAA patients (aortic diameter >3 cm, n=114) compared to controls (aortic diameter <3 cm, n=88) (ELISA), whereas hepcidin concentrations were increased in AAA subjects (MS/MS assay). Moreover, iron, transferrin and haemoglobin levels were negatively, and hepcidin positively, correlated with aortic diameter in AAA patients. The association of low haemoglobin with AAA presence or aortic diameter was independent of specific risk factors. Moreover, MCHC negatively correlated with thrombus area in another cohort of AAA patients (aortic diameter 3–5 cm, n=357). We found that anaemia was significantly more prevalent in AAA patients (aortic diameter >5 cm, n=8,912) compared to those in patients with atherosclerotic aorto-iliac occlusive disease (n=17,737) [adjusted odds ratio=1.77 (95% confidence interval: 1.61;1.93)]. Finally, the mortality risk among AAA patients with anaemia was increased by almost 30% [adjusted hazard ratio: 1.29 (95% confidence interval: 1.16;1.44)] as compared to AAA subjects without anaemia. In conclusion, local iron retention and altered iron recycling associated to high hepcidin and low transferrin systemic concentrations could lead to reduced circulating haemoglobin levels in AAA patients. Low haemoglobin levels are independently associated to AAA presence and clinical outcome.

High-density lipoprotein therapy inhibits Porphyromonas gingivalis-induced abdominal aortic aneurysm progression

Clinical and experimental studies have highlighted the potential implication of periondontal bacteria contamination in the pathogenesis of abdominal aortic aneurysms (AAA). In addition to their role in reverse cholesterol transport, high-density lipoproteins (HDLs) display multiple functions, including anti-inflammatory and lipopolysaccharide scavenging properties. Low plasma levels of HDL-cholesterol have been reported in AAA patients. We tested the effect of a HDL therapy in Sprague-Dawley rat model of AAA, obtained by intraluminal elastase infusion followed by repeated injections of Porphyromonas gingivalis (Pg). HDLs, isolated by ultracentrifugation of plasma from healthy human volunteers, were co-injected intravenously (10 mg/kg) with Pg (1.107 Colony Forming Unit) one, eight and 15 days after elastase perfusion. Rats were sacrificed one week after the last injection. Our results show that Pg injections promote the formation of a persistent neutrophil-rich thrombus associated with increased aortic diameter in this AAA model. HDLs significantly reduced the increased AAA diameter induced by Pg. Histology showed the onset of a healing process in the Pg/HDL group. HDL injections also reduced neutrophil activation in Pg-injected rats associated with decreased cytokine levels in conditioned media and plasma. Scintigraphic analysis showed an intense uptake of 99mTc-HDL by the AAA suggesting that HDLs could exert their beneficial effect by acting directly on the thrombus components. HDL supplementation may therefore constitute a new therapeutic tool for AAA treatment.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Clearance of plasmin-PN-1 complexes by vascular smooth muscle cells in human aneurysm of the ascending aorta

Plasminogen is a circulating zymogen which enters the arterial wall by radial, transmural hydraulic conductance, where it is converted to plasmin by tissue plasminogen activator t-PA on an activation platform involving S100A4 on the vascular smooth muscle cell (vSMC) membrane. Plasmin is involved in the progression of human thoracic aneurysm of the ascending aorta (TAA). vSMCs protect the TAA wall from plasmin-induced proteolytic injury by expressing high levels of antiproteases. Protease nexin-1 (PN-1) is a tissue antiprotease belonging to the serpin superfamily, expressed in the vascular wall, and is able to form a covalent complex with plasmin. LDL receptor-related protein-1 (LRP-1) is a scavenger receptor implicated in protease-antiprotease complex internalization. In this study, we investigated whether PN-1 and LRP-1 are involved in the inhibition and clearance of plasminogen by the SMCs of human TAA. We demonstrated an overexpression of S100A4, PN-1, and LRP-1 in the medial layer of human TAA. Plasminogen activation taking place in the media of TAA was revealed by immunohistochemical staining and plasmin activity analyses. We showed by cell biology studies that plasmin-PN-1 complexes are internalized via LRP-1 in vSMCs from healthy and TAA media. Thus, two complementary mechanisms are involved in the protective role of PN-1 in human TAA: one involving plasmin inhibition and the other involving tissue clearance of plasmin-PN1 complexes via the scavenger receptor LRP-1.

Cell Based Therapeutic Approach in Vascular Surgery: Application and Review

Multipotent stem cells - such as mesenchymal stem/stromal cells and stem cells derived from different sources like vascular wall are intensely studied to try to rapidly translate their discovered features from bench to bedside. Vascular wall resident stem cells recruitment, differentiation, survival, proliferation, growth factor production, and signaling pathways transduced were analyzed. We studied biological properties of vascular resident stem cells and explored the relationship from several factors as Matrix Metalloproteinases (MMPs) and regulations of biological, translational and clinical features of these cells. In this review we described a translational and clinical approach to Adult Vascular Wall Resident Multipotent Vascular Stem Cells (VW-SCs) and reported their involvement in alternative clinical approach as cells based therapy in vascular disease like arterial aneurysms or peripheral arterial obstructive disease.

Is Vascular Amyloidosis Intertwined with Arterial Aging, Hypertension and Atherosclerosis?

Vascular amyloidosis (VA) is a component of aging, but both VA and aging move forward together. Although, not all age-related molecules are involved with VA, some molecules are involved in a crosstalk between both of them. However, the cellular mechanism by which, vascular cells are phenotypically shifted to arterial remodeling, is not only involved in aging but also linked to VA. Additionally, patients with hypertension and atherosclerosis are susceptible to VA, while amyloidosis alone may provide fertile soil for the initiation and progression of subsequent hypertension and atherosclerosis. It is known that hypertension, atherosclerosis and amyloidosis can be viewed as accelerated aging. This review summarizes the available experimental and clinical evidence to help the reader to understand the advance and underlying mechanisms for VA involvement in and interaction with aging. Taken together, it is clear that VA, hypertension and atherosclerosis are closely intertwined with arterial aging as equal partners.

CYLD Deubiquitinates Nicotinamide Adenine Dinucleotide Phosphate Oxidase 4 Contributing to Adventitial Remodeling

OBJECTIVE

Transdifferentiation of adventitial fibroblasts (AFs) into myofibroblasts plays a critical role during the vascular remodeling that occurs during atherosclerosis, restenosis, and aortic aneurysm. The ubiquitination/deubiquitination regulatory system is essential for the quality control of proteins. The involvement of ubiquitination/deubiquitination during AF transdifferentiation remains largely unknown. In this study, we determined the role of cylindromatosis (CYLD), a deubiquitinase, in the process of AF differentiation and activation in vitro and in vivo.

APPROACH AND RESULTS

Transforming growth factor-β1 and homocysteine, 2 known inducers of AF transdifferentiation, greatly upregulated CYLD expression in a time- and dose-dependent manner. The silencing of CYLD significantly inhibited AF transdifferentiation and activation as evidenced by the expression of contractile proteins, the production of the proinflammatory cytokines MCP-1 (monocyte chemotactic protein 1) and IL-6 (interleukin-6), the deposition of extracellular matrix, and cell migration. We further asked whether CYLD mediates AF activation via the regulation of nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) as it is an essential factor during AF transdifferentiation. Indeed, the silencing of CYLD repressed transforming growth factor-β1-induced and homocysteine-induced Nox4 upregulation and reactive oxygen species production, whereas Nox4 overexpression greatly rescued the inhibitory effect on AF activation by CYLD silencing. Most interestingly, transforming growth factor-β1 and homocysteine repressed Nox4 ubiquitination and prolonged the half-life of Nox4. Moreover, Nox4 was deubiquitinated via a direct interaction with the ubiquitin-specific protease domain of CYLD. In accordance, hyperhomocysteinemia significantly increased adventitial CYLD and Nox4 expression, promoted AF transdifferentiation, and aggravated CaPO₄-induced abdominal aortic aneurysm in mice. These effects were abolished in CYLD^-/- mice.

CONCLUSIONS

CYLD contributes to the transdifferentiation of AFs via deubiquitinating Nox4 and may play a role in vascular remodeling.

Tracking Adventitial Fibroblast Contribution to Disease: A Review of Current Methods to Identify Resident Fibroblasts

Cells present in the adventitia, or outermost layer of the blood vessel, contribute to the progression of vascular diseases, such as atherosclerosis, hypertension, and aortic dissection. The adventitial fibroblast of the aorta is the prototypic perivascular fibroblast, but the adventitia is composed of multiple distinct cell populations. Therefore, methods for uniquely identifying the fibroblast are critical for a better understanding of how these cells contribute to disease processes. A popular method for distinguishing adventitial cell types relies on the use of genetic tools in the mouse to trace and manipulate these cells. Because lineage tracing relying on Cre-recombinase expressing mice is used more frequently in studies of vascular disease, it is important to outline the advantages and limitations of these genetic tools. The purpose of this article is to provide an overview of the various genetic tools available in the mouse for the study of resident adventitial fibroblasts.

Leptin induces osteoblast differentiation of human valvular interstitial cells via the Akt and ERK pathways

AIMS

Calcific aortic valve disease (CAVD) affects 2-6% of the population over 65 years, and age, gender, smoking, overweight, dyslipidemia, diabetes contribute to the development of this disease. CAVD results, in part, from the osteoblast differentiation of human valvular interstitial cells (VICs). This study aims to elucidate the effects of leptin on osteoblast phenotype of VICs and the signalling pathways involved.

METHODS

Patients who underwent aortic valve replacement for CAVD (n = 43) were included in this study. Patients with coronary artery disease (CAD) without CAVD (n = 129) were used as controls.

RESULTS

Patients with CAVD had higher serum leptin concentrations than CAD patients (p = 0.002). Leptin was found in calcific aortic valves, with higher concentrations in calcified versus non-calcified zones (p = 0.01). Chronic leptin stimulation of human VICs enhanced alkaline phosphatase (ALP) activity and ALP, BMP-2 and RUNX2 expression and decreased osteopontin expression. Moreover, inhibiting Akt or ERK during leptin stimulation lowered the expression of osteoblast markers in VIC.

CONCLUSIONS

Taken together, these findings indicate that leptin plays a critical role in CAVD development by promoting osteoblast differentiation of human aortic VICs in an Akt- and ERK-dependent manner. This study highlights the role of leptin in CAVD development, and further studies are needed to determine whether reducing circulating leptin levels or blocking leptin actions on VICs is efficient to slow CAVD progression.

Angiogenesis in the atherosclerotic plaque

Atherosclerosis is a multifocal alteration of the vascular wall of medium and large arteries characterized by a local accumulation of cholesterol and non-resolving inflammation. Atherothrombotic complications are the leading cause of disability and mortality in western countries. Neovascularization in atherosclerotic lesions plays a major role in plaque growth and instability. The angiogenic process is mediated by classical angiogenic factors and by additional factors specific to atherosclerotic angiogenesis. In addition to its role in plaque progression, neovascularization may take part in plaque destabilization and thromboembolic events. Anti-angiogenic agents are effective to reduce atherosclerosis progression in various animal models. However, clinical trials with anti-angiogenic drugs, mainly anti-VEGF/VEGFR, used in anti-cancer therapy show cardiovascular adverse effects, and require additional investigations.

The association of obesity and obesity-related conditions with carotid extra-medial thickness in children and adolescents

BACKGROUND

Carotid extra-medial thickness (EMT) and carotid intima-media thickness (cIMT) provide information concerning vascular changes.

OBJECTIVES

In this study, we aimed to evaluate the association between carotid EMT and obesity and its metabolic complications in children.

METHODS

The study included 38 obese subjects and 30 age-matched and sex-matched healthy controls aged between 7 and 17 years. For all subjects, complete blood count, fasting blood glucose, serum insulin, aspartate aminotransferase, alanine aminotransferase, HDL cholesterol, total cholesterol and triglyceride levels were measured. The carotid EMT and cIMT were measured by an expert radiologist in all patients.

RESULTS

Body mass index (BMI) (28.8 ± 3 vs. 18.1 ± 2.2, p < 0.001), total cholesterol (167.9 ± 34.8 mg dL^-1 vs. 150.5 ± 28.1 mg dL^-1 , p = 0.029), homeostatic model assessment of insulin resistance (HOMA-IR) (4.3 vs. 1.7, p < 0.001), cIMT (0.51 ± 0.08 mm vs. 0.45 ± 0.06 mm, p < 0.001) and carotid EMT (0.74 ± 0.11 mm vs. 0.64 ± 0.1 mm, p < 0.001) were significantly higher in obese subjects than in controls, while HDL cholesterol (41.6 ± 6.5 mg dL^-1 vs. 49.5 ± 7.5 mg dL^-1 , p < 0.001) was lower in obesity group. Among the obese subjects, the HOMA-IR values (4.7 vs. 3.6, p = 0.027), cIMT (0.54 ± 0.07 mm vs. 0.49 ± 0.07 mm, p = 0.039) and carotid EMT (0.79 ± 0.1 mm vs. 0.7 ± 0.1 mm, p = 0.013) were significantly higher in post-pubertal children compared with prepubertal children. BMI, cut-off values of HOMA-IR and cIMT were significantly associated with increased carotid EMT (p < 0.001, p = 0.023 and p < 0.001, respectively). The only independent risk factor affecting carotid EMT was BMI (p < 0.001).

CONCLUSION

We have found that carotid EMT is associated with cIMT, obesity and insulin resistance and the assessment of carotid EMT may provide additional information concerning early vascular disease.

Nano- and microstructured materials for in vitro studies of the physiology of vascular cells

The extracellular environment of vascular cells in vivo is complex in its chemical composition, physical properties, and architecture. Consequently, it has been a great challenge to study vascular cell responses in vitro, either to understand their interaction with their native environment or to investigate their interaction with artificial structures such as implant surfaces. New procedures and techniques from materials science to fabricate bio-scaffolds and surfaces have enabled novel studies of vascular cell responses under well-defined, controllable culture conditions. These advancements are paving the way for a deeper understanding of vascular cell biology and materials-cell interaction. Here, we review previous work focusing on the interaction of vascular smooth muscle cells (SMCs) and endothelial cells (ECs) with materials having micro- and nanostructured surfaces. We summarize fabrication techniques for surface topographies, materials, geometries, biochemical functionalization, and mechanical properties of such materials. Furthermore, various studies on vascular cell behavior and their biological responses to micro- and nanostructured surfaces are reviewed. Emphasis is given to studies of cell morphology and motility, cell proliferation, the cytoskeleton and cell-matrix adhesions, and signal transduction pathways of vascular cells. We finalize with a short outlook on potential interesting future studies.

Artery Tertiary Lymphoid Organs: Powerhouses of Atherosclerosis Immunity

Artery tertiary lymphoid organs (ATLOs) are atherosclerosis-associated lymphoid aggregates with varying degrees of complexity ranging from small T/B-cell clusters to well-structured lymph node-like though unencapsulated lymphoid tissues. ATLOs arise in the connective tissue that surrounds diseased arteries, i.e., the adventitia. ATLOs have been identified in aged atherosclerosis-prone hyperlipidemic apolipoprotein E-deficient (ApoE-/-) mice: they are organized into distinct immune cell compartments, including separate T-cell areas, activated B-cell follicles, and plasma cell niches. Analyses of ATLO immune cell subsets indicate antigen-specific T- and B-cell immune reactions within the atherosclerotic arterial wall adventitia. Moreover, ATLOs harbor innate immune cells, including a large component of inflammatory macrophages, B-1 cells, and an aberrant set of antigen-presenting cells. There is marked neoangiogenesis, irregular lymphangiogenesis, neoformation of high endothelial venules, and de novo synthesis of lymph node-like conduits. Molecular mechanisms of ATLO formation remain to be identified though media vascular smooth muscle cells may adopt features of lymphoid tissue organizer-like cells by expressing lymphorganogenic chemokines, i.e., CXCL13 and CCL21. Although these data are consistent with the view that ATLOs participate in primary T- and B-cell responses against elusive atherosclerosis-specific autoantigens, their specific protective or disease-promoting roles remain to be identified. In this review, we discuss what is currently known about ATLOs and their potential impact on atherosclerosis and make attempts to define challenges ahead.

Peristrut microhemorrhages: a possible cause of in-stent neoatherosclerosis?

BACKGROUND

In-stent neoatherosclerosis is characterized by the delayed appearance of markers of atheroma in the subintima, but the pathophysiology underlying this new disease entity remains unclear.

METHODS AND RESULTS

We collected 20 human coronary artery stents by removal from explanted hearts. The mean duration of stent implantation was 34 months. In all samples, neoatherosclerosis was detected, particularly in peristrut areas. It consisted of foam cells and cholesterol clefts, with or without calcification, associated with neovascularization. Iron and glycophorin-A were present in peristrut areas, as well as autofluorescent ceroids. Moreover, in response to neoatherosclerosis, tertiary lymphoid organs (tissue lymphoid clusters) often developed in the adventitia. Some of these features could be reproduced in an experimental carotid stenting model in rabbits fed a high-cholesterol diet. Foam cells were present in all samples, and peristrut red blood cells (RBCs) were also detected, as shown by iron deposits and Bandeiraea simplicifiola isolectin-B4 staining of RBC membranes. Finally, in silico models were used to evaluate the compliance mismatch between the rigid struts and the distensible arterial wall using finite element analysis. They show that stenting approximately doubles the local von Mises stress in the intimal layer.

CONCLUSIONS

We show here that stent implantation both in human and in rabbit arteries is characterized by local peristrut microhemorrhages and finally by both cholesterol accumulation and oxidation, triggering together in-stent neoatherosclerosis. Our data indicate that these processes are likely initiated by an increased mechanical stress due to the compliance mismatch between the rigid stent and the soft wall.

Chronic adventitial inflammation, vasa vasorum expansion, and 5-lipoxygenase up-regulation in irradiated arteries from cancer survivors

Radiation-induced cardiovascular disease is an emerging problem in a steadily increasing population of survivors of cancer. However, the underlying biology is poorly described, and the late onset, which occurs several years after exposure, precludes adequate investigations in animal and cell culture models. We investigated the role of the 5-lipoxygenase (5-LO)/leukotriene pathway in radiation-induced vascular changes. Use of paired samples of irradiated arteries and nonirradiated internal control arteries from the same patient that were harvested during surgery for cancer reconstruction ≤10 yr after radiotherapy provides a unique human model of chronic radiation–induced vascular changes. Immunohistochemical stainings and perioperative inspection revealed an adventitial inflammatory response, with vasa vasorum expansion and chronic infiltration of CD68⁺ macrophages. These macrophages stained positive for the leukotriene-forming enzyme 5-LO. Messenger RNA levels of 5-LO and leukotriene B₄ receptor 1 were increased in irradiated arterial segments compared with control vessels. These results point to targeting the 5-LO/leukotriene pathway as a therapeutic adjunct to prevent late adverse vascular effects of radiotherapy.—Halle, M., Christersdottir, T., Bäck, M. Chronic adventitial inflammation, vasa vasorum expansion, and 5-lipoxygenase up-regulation in irradiated arteries from cancer survivors.

Pathology of coronary atherosclerosis and thrombosis

The process of early atherosclerotic plaque progression is characterized by the development of pathologic intimal thickening (PIT) with lipid pool that may transform into the necrotic core to form fibroatheroma, where infiltration of foamy macrophages plays a crucial role. The expansion of the necrotic core is also attributable to intraplaque hemorrhage. Thin-cap fibroatheroma (TCFA) is characterized by a relatively large necrotic core with an overlying thin fibrous cap measuring <65 µm typically containing numerous macrophages, and is considered to be the precursor lesion of plaque rupture which is the most common cause of coronary thrombosis. The second common cause of acute thrombosis is plaque erosion, while calcified nodules is known to be the least frequent cause of coronary thrombosis. Coronary thrombosis can occur without symptoms to form healed lesions, which contributes to an increase in plaque burden and luminal narrowing. The process of plaque progression is generally accompanied by the progression of calcification. An understanding of the histomorphological characteristics of coronary plaques should provide important insights into the pathogenesis, diagnosis, and treatment of atherosclerotic coronary disease for both basic and clinical researchers as well as for clinicians.

Carotid extramedial thickness is associated with local arterial stiffness in children

OBJECTIVES

Experimental evidence suggests that structural changes to the arterial adventitia may be a key vascular determinant of early arterial stiffening, although this has not been directly studied. Accordingly, we hypothesized that in young children, in whom this relationship would not be altered by atheroma, carotid extramedial thickness (EMT), a measure that incorporates the thickness of the arterial adventitia, perivascular tissues and the internal jugular venous wall, would be associated with localized arterial stiffness of the same arterial region.

METHODS

We studied 248 healthy prepubescent children (aged 8 years). Carotid diameter and carotid EMT were measured by high-resolution ultrasound. Carotid blood pressure was derived from brachial blood pressure and carotid tonometry. Three measures of localized arterial stiffness (β stiffness index, distensibility coefficient and incremental modulus of elasticity) were calculated for the common carotid artery. Results were adjusted for heart rate and DBP, two important hemodynamic determinants of arterial stiffness.

RESULTS

Carotid EMT was associated with all three measures of arterial stiffness (β stiffness index: standardized β = 0.121, P = 0.03; distensibility coefficient: standardized β = -0.121, P = 0.05; incremental modulus of elasticity: standardized β = 0.140, P = 0.02). These associations remained significant after adjustment for potential confounders such as sex, height, waist circumference, BMI and body surface area.

CONCLUSION

Carotid EMT is associated with the stiffness of the same arterial segment in children, suggesting that the arterial adventitia may be involved in early changes in arterial stiffness during childhood.

Uptake of Plasmin-PN-1 Complexes in Early Human Atheroma

Zymogens are delivered to the arterial wall by radial transmural convection. Plasminogen can be activated within the arterial wall to produce plasmin, which is involved in evolution of the atherosclerotic plaque. Vascular smooth muscle cells (vSMCs) protect the vessels from proteolytic injury due to atherosclerosis development by highly expressing endocytic LDL receptor-related protein-1 (LRP-1), and by producing anti-proteases, such as Protease Nexin-1 (PN-1). PN-1 is able to form covalent complexes with plasmin. We hypothesized that plasmin-PN-1 complexes could be internalized via LRP-1 by vSMCs during the early stages of human atheroma. LRP-1 is also responsible for the capture of aggregated LDL in human atheroma. Plasmin activity and immunohistochemical analyses of early human atheroma showed that the plasminergic system is activated within the arterial wall, where intimal foam cells, including vSMCs and platelets, are the major sites of PN-1 accumulation. Both PN-1 and LRP-1 are overexpressed in early atheroma at both messenger and protein levels. Cell biology studies demonstrated an increased expression of PN-1 and tissue plasminogen activator by vSMCs in response to LDL. Plasmin-PN-1 complexes are internalized via LRP-1 in vSMCs, whereas plasmin alone is not. Tissue PN-1 interacts with plasmin in early human atheroma via two complementary mechanisms: plasmin inhibition and tissue uptake of plasmin-PN-1 complexes via LRP-1 in vSMCs. Despite this potential protective effect, plasminogen activation by vSMCs remains abnormally elevated in the intima in early stages of human atheroma.

Multidimensional Contribution of Matrix Metalloproteinases to Atherosclerotic Plaque Vulnerability: Multiple Mechanisms of Inhibition to Promote Stability

The prevalence of atherosclerotic disease continues to increase, and despite significant reductions in major cardiovascular events with current medical interventions, an additional therapeutic window exists. Atherosclerotic plaque growth is a complex integration of cholesterol penetration, inflammatory cell infiltration, vascular smooth muscle cell (VSMC) migration, and neovascular invasion. A family of matrix-degrading proteases, the matrix metalloproteinases (MMPs), contributes to all phases of vascular remodeling. The contribution of specific MMPs to endothelial cell integrity and VSMC migration in atherosclerotic lesion initiation and progression has been confirmed by the increased expression of these proteases in plasma and plaque specimens. Endogenous blockade of MMPs by the tissue inhibitors of metalloproteinases (TIMPs) may attenuate proteolysis in some regions, but the progression of matrix degeneration suggests that MMPs predominate in atherosclerotic plaque, precipitating vulnerability. Plaque neovascularization also contributes to instability and, coupling the known role of MMPs in angiogenesis to that of atherosclerotic plaque growth, interest in targeting MMPs to facilitate plaque stabilization continues to accumulate. This article aims to review the contributions of MMPs and TIMPs to atherosclerotic plaque expansion, neovascularization, and rupture vulnerability with an interest in promoting targeted therapies to improve plaque stabilization and decrease the risk of major cardiovascular events.

Neutrophil Gelatinase Associated Lipocalin (NGAL) as a Biomarker. Does It Apply in Abdominal Aortic Aneurysms? A Review of Literature

Neutrophil gelatinase associated lipocalin (NGAL) as a protein derived from neutrophils has recently been the field of investigation in a wide range of diseases (renal disease, coronary artery disease, etc). The MEDLINE/PubMed database was searched for publications with the medical subject heading "NGAL" and keywords "Abdominal aortic aneurysm (AAA)," "biomarker," and "growth". We restricted our search to date. In this review, we included 38 articles and abstracts that were accessible and available in English. An effort to further explain the role of NGAL within AAA has been made. NGAL seems to be a hopeful marker for the pathogenesis and the progression of abdominal aortic aneurysms (AAAs), which has significant morbidity and mortality rates.

A Methodology for Concomitant Isolation of Intimal and Adventitial Endothelial Cells from the Human Thoracic Aorta

BACKGROUND

Aortic diseases are diverse and involve a multiplicity of biological systems in the vascular wall. Aortic dissection, which is usually preceded by aortic aneurysm, is a leading cause of morbidity and mortality in modern societies. Although the endothelium is now known to play an important role in vascular diseases, its contribution to aneurysmal aortic lesions remains largely unknown. The aim of this study was to define a reliable methodology for the isolation of aortic intimal and adventitial endothelial cells in order to throw light on issues relevant to endothelial cell biology in aneurysmal diseases.

METHODOLOGY/PRINCIPAL FINDINGS

We set up protocols to isolate endothelial cells from both the intima and the adventitia of human aneurysmal aortic vessel segments. Throughout the procedure, analysis of cell morphology and endothelial markers allowed us to select an endothelial fraction which after two rounds of expansion yielded a population of >90% pure endothelial cells. These cells have the features and functionalities of freshly isolated cells and can be used for biochemical studies. The technique was successfully used for aortic vessel segments of 20 patients and 3 healthy donors.

CONCLUSIONS/SIGNIFICANCE

This simple and highly reproducible method allows the simultaneous preparation of reasonably pure primary cultures of intimal and adventitial human endothelial cells, thus providing a reliable source for investigating their biology and involvement in both thoracic aneurysms and other aortic diseases.

Hemoglobin induces monocyte recruitment and CD163-macrophage polarization in abdominal aortic aneurysm

BACKGROUND

Increased hemoglobin (Hb) accumulation was reported in abdominal aortic aneurysms (AAAs). CD163 is a macrophage receptor involved in tissue Hb clearance, however its role in AAA has not been reported. We investigated the role of Hb on monocyte recruitment and differentiation towards CD163 expressing macrophages ex vivo, in vitro and in human AAA.

METHODS AND RESULTS

CD163 mRNA and protein expression was significantly higher in human AAA (n=7) vs. healthy wall (n=6). CD163 was predominantly found in adventitia of AAA, coinciding with areas rich in hemosiderin and adjacent to neoangiogenic microvessels. Dual CD14/CD163 expression was observed in recently infiltrated monocytes surrounding microvessels. A higher release of soluble CD163 was observed in the conditioned medium from AAA (AAA-CM, n=10), mainly in the adventitial layer. Similar to Hb, AAA-CM induced CD163-dependent monocyte chemotaxis, especially on circulating monocytes from AAA patients. Hb or AAA-CM promoted differentiation towards CD163(high)/HLA-DR(low)-expressing macrophages, with enhanced Hb uptake, increased anti-inflammatory IL-10 secretion and decreased pro-inflammatory IL-12p40 release. All these effects were partially suppressed when Hb was removed from AAA-CM. Separate analysis on circulating monocytes reported increased percentage of pre-infiltrating CD14(++)CD16(+) monocytes in patients with AAA (n=21), as compared to controls (n=14). A significant increase in CD163 expression in CD14(++)CD16(+) monocyte subpopulation was observed in AAA patients.

CONCLUSIONS

The presence of Hb in the adventitial AAA-wall promotes the migration and differentiation of activated circulating monocytes in AAA patients, explaining the existence of a protective CD163-macrophage phenotype that could take up the Hb present in the AAA-wall, avoiding its injurious effects.

Adventitial Tertiary Lymphoid Organs as Potential Source of MicroRNA Biomarkers for Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is an inflammatory disease associated with marked changes in the cellular composition of the aortic wall. This study aims to identify microRNA (miRNA) expression in aneurysmal inflammatory cells isolated by laser microdissection from human tissue samples. The distribution of inflammatory cells (neutrophils, B and T lymphocytes, mast cells) was evaluated in human AAA biopsies. We observed in half of the samples that adventitial tertiary lymphoid organs (ATLOs) with a thickness from 0.5 to 2 mm were located exclusively in the adventitia. Out of the 850 miRNA that were screened by microarray in isolated ATLOs (n = 2), 164 miRNAs were detected in ATLOs. The three miRNAs (miR-15a-3p, miR-30a-5p and miR-489-3p) with the highest expression levels were chosen and their expression quantified by RT-PCR in isolated ATLOs (n = 4), M1 (n = 2) and M2 macrophages (n = 2) and entire aneurysmal biopsies (n = 3). Except for the miR-30a-5p, a similar modulation was found in ATLOs and the two subtypes of macrophages. The modulated miRNAs were then evaluated in the plasma of AAA patients for their potential as AAA biomarkers. Our data emphasize the potential of miR-15a-3p and miR-30a-5p as biomarkers of AAA but also as triggers of ATLO evolution. Further investigations will be required to evaluate their targets in order to better understand AAA pathophysiology.

Adult vascular wall resident multipotent vascular stem cells, matrix metalloproteinases, and arterial aneurysms

Evidences have shown the presence of multipotent stem cells (SCs) at sites of arterial aneurysms: they can differentiate into smooth muscle cells (SMCs) and are activated after residing in a quiescent state in the vascular wall. Recent studies have implicated the role of matrix metalloproteinases in the pathogenesis of arterial aneurysms: in fact the increased synthesis of MMPs by arterial SMCs is thought to be a pivotal mechanism in aneurysm formation. The factors and signaling pathways involved in regulating wall resident SC recruitment, survival, proliferation, growth factor production, and differentiation may be also related to selective expression of different MMPs. This review explores the relationship between adult vascular wall resident multipotent vascular SCs, MMPs, and arterial aneurysms.

Contribution of neovascularization and intraplaque haemorrhage to atherosclerotic plaque progression and instability

Atherosclerosis is a continuous pathological process that starts early in life and progresses frequently to unstable plaques. Plaque rupture leads to deleterious consequences such as acute coronary syndrome, stroke and atherothrombosis. The vulnerable lesion has several structural and functional hallmarks that distinguish it from the stable plaque. The unstable plaque has large necrotic core (over 40% plaque volume) composed of cholesterol crystals, cholesterol esters, oxidized lipids, fibrin, erythrocytes and their remnants (haeme, iron, haemoglobin), and dying macrophages. The fibrous cap is thin, depleted of smooth muscle cells and collagen, and is infiltrated with proinflammatory cells. In unstable lesion, formation of neomicrovessels is increased. These neovessels have weak integrity and leak thereby leading to recurrent haemorrhages. Haemorrhages deliver erythrocytes to the necrotic core where they degrade promoting inflammation and oxidative stress. Inflammatory cells mostly presented by monocytes/macrophages, neutrophils and mast cells extravagate from bleeding neovessels and infiltrate adventitia where they support chronic inflammation. Plaque destabilization is an evolutionary process that could start at early atherosclerotic stages and whose progression is influenced by many factors including neovascularization, intraplaque haemorrhages, formation of cholesterol crystals, inflammation, oxidative stress and intraplaque protease activity.

Variability and uncertainty of 18F-FDG PET imaging protocols for assessing inflammation in atherosclerosis: suggestions for improvement

PET with (18)F-FDG shows promise for the evaluation of metabolic activities in atherosclerotic plaques. Although recommendations regarding the acquisition and measurement protocols to be used for (18)F-FDG PET imaging of atherosclerosis inflammation have been published, there is no consensus regarding the most appropriate protocols, and the image reconstruction approach has been especially overlooked. Given the small size of the targeted lesions, the reconstruction and measurement methods might strongly affect the results. We determined the differences in results due to the protocol variability and identified means of increasing the measurement reliability.

METHODS

An extensive literature search was performed to characterize the variability in atherosclerosis imaging and quantification protocols. Highly realistic simulations of atherosclerotic carotid lesions based on real patient data were designed to determine how the acquisition and processing protocol parameters affected the measured values.

RESULTS

In 49 articles, we identified 53 different acquisition protocols, 51 reconstruction protocols, and 46 quantification methods to characterize atherosclerotic lesions from (18)F-FDG PET images. The most important parameters affecting the measurement accuracy were the number of iterations used for reconstruction and the postfiltering applied to the reconstructed images, which could together make the measured standardized uptake values (SUVs) vary by a factor greater than 3. Image sampling, acquisition duration, and metrics used for the measurements also affected the results to a lesser extent (SUV varying by a factor of 1.3 at most). For an acceptable SUV variability, the lowest bias in SUV was observed using an 8-min acquisition per bed position; ordered-subset expectation maximization reconstruction with at least 120 maximum likelihood expectation maximization equivalent iterations, including a point spread function model using a 1 mm(3) voxel size; and no postfiltering. Because of the partial-volume effect, measurement bias remained greater than 60%. The use and limitations of the target-to-blood activity ratio metrics are also presented and discussed.

CONCLUSION

(18)F-FDG PET protocol harmonization is needed in atherosclerosis imaging. Optimized protocols can significantly reduce the measurement errors in wall activity estimates, but PET systems with higher spatial resolution and advanced partial-volume corrections will be required to accurately assess plaque inflammation from (18)F-FDG PET.

Inflammatory micro-environmental cues of human atherothrombotic arteries confer to vascular smooth muscle cells the capacity to trigger lymphoid neogenesis

BACKGROUND

Experimental atherosclerosis is characterized by the formation of tertiary lymphoid structures (TLOs) within the adventitial layer, which involves the chemokine-expressing aortic smooth muscle cells (SMCs). TLOs have also been described around human atherothrombotic arteries but the mechanisms of their formation remain poorly investigated. Herein, we tested whether human vascular SMCs play the role of chemokine-expressing cells that would trigger the formation of TLOs in atherothrombotic arteries.

RESULTS

We first characterized, by flow cytometry and immunofluorescence analysis, the prevalence and cell composition of TLOs in human abdominal aneurysms of the aorta (AAAs), an evolutive form of atherothrombosis. Chemotaxis experiments revealed that the conditioned medium from AAA tissues recruited significantly more B and T lymphocytes than the conditioned medium from control (N-AAA) tissues. This was associated with an increase in the concentration of CXCL13, CXCL16, CCL19, CCL20, and CCL21 chemokines in the conditioned medium from AAA tissues. Immunofluorescence analysis of AAA cryosections revealed that α-SMA-positive SMCs were the main contributors to the chemokine production. These results were confirmed by RT-qPCR assays where we found that primary vascular SMCs from AAA tissues expressed significantly more chemokines than SMCs from N-AAA. Finally, in vitro experiments demonstrated that the inflammatory cytokines found to be increased in the conditioned medium from AAA were able to trigger the production of chemokines by primary SMCs.

CONCLUSION

Together, these results suggest that human vascular SMCs in atherothrombotic arteries, in response to inflammatory signals, are converted into chemokine-expressing cells that trigger the recruitment of immune cells and the formation of aortic TLOs.

Hyperhomocysteinemia accelerates collagen accumulation in the adventitia of balloon-injured rat carotid arteries via angiotensin II type 1 receptor

Recent studies suggest that hyperhomocysteinemia (HHcy) increases collagen type I accumulation in rat vascular adventitia after balloon injury and that Angiotensin II (Ang II) induces collagen synthesis in vascular adventitial fibroblasts. Reports also indicate that Ang II type1 receptor (AT1R) activation, mediated by homocysteine (Hcy) may contribute to collagen type 1 expression in mouse aortic endothelial cells. However, little is known about the possible mechanisms behind the relationship between Hcy and AT1R in adventitial remodeling. Thus, we investigated whether HHcy induces collagen accumulation via activation of AT1R in the adventitia. Male Sprague-Dawley (SD) rats were randomly divided into a control group and a 1% l-methionine-induced HHcy group. Balloon injury was performed after 12 experimental weeks and animals were sacrificed at 7, 14, and 28 days after injury. Collagen deposition and AT1R expression was measured with Western blot. Serum Hcy, adventitial collagen, and AT1R levels were higher in the HHcy group compared with the control group. Hcy time-dependently induced collagen type 1 and AT1R expression, with the highest induction observed at 48 h. Also, we observed that the AT1R blocker, valsartan, attenuated collagen type 1 and AT1R expression. HHcy exacerbates adventitial remodeling after balloon injury, and the underling mechanisms may be related to AT1R activity.

Deficiency of Long Pentraxin PTX3 Promoted Neointimal Hyperplasia after Vascular Injury

AIM

Pentraxin 3 (PTX3) is a novel marker for the primary local activation of innate immunity and inflammatory responses. Although clinical and experimental evidence suggests that PTX3 is associated with atherosclerosis, the relationship between PTX3 and vascular remodeling after wall injury remains to be determined. We investigated the effects of PTX3 on neointimal hyperplasia following wire vascular injury.

METHODS

PTX3 systemic knockout (PTX3-KO) mice and wild-type littermate (WT) mice were subjected to wire-mediated endovascular injury. At four weeks after wire-mediated injury, the areas of neointimal and medial hyperplasia were evaluated.

RESULTS

The PTX3-KO mice exhibited higher hyperplasia/media ratios than the WT mice after wire injury, and the degree of Mac-3-positive macrophage accumulation was significantly higher in the PTX3-KO mice than in the WT mice. Furthermore, the PTX3-KO mice showed a much greater increase in the number of PCNA-stained cells in the vascular wall than that observed in the WT mice.

CONCLUSIONS

A deficiency of PTX3 results in deteriorated neointimal hyperplasia after vascular injury via the effects of macrophage accumulation and vascular smooth muscle cell proliferation and migration.

Tumor necrosis factor-like weak inducer of apoptosis or Fn14 deficiency reduce elastase perfusion-induced aortic abdominal aneurysm in mice

Background

Abdominal aortic aneurysm (AAA) involves leukocyte recruitment, inflammatory cytokine production, vascular cell apoptosis, neovascularization, and vascular remodeling, all of which contribute to aortic dilatation. Tumor necrosis factor‐like weak inducer of apoptosis (TWEAK) is a cytokine implicated in proinflammatory responses, angiogenesis, and matrix degradation but its role in AAA formation is currently unknown.

Methods and Results

Experimental AAA with aortic elastase perfusion in mice was induced in wild‐type (WT), TWEAK deficient (TWEAK KO), or Fn14‐deficient (Fn14 KO) mice. TWEAK or Fn14 KO deficiency reduced aortic expansion, lesion macrophages, CD3⁺ T cells, neutrophils, CD31⁺ microvessels, CCL2 and CCL5 chemokines expression, and MMP activity after 14 days postperfusion. TWEAK and Fn14 KO mice also showed a reduced loss of medial vascular smooth muscle cells (VSMC) that was related to a reduced number of apoptotic cells in these animals compared with WT mice. Aortas from WT animals present a higher disruption of the elastic layer and MMP activity than those from TWEAK or Fn14 KO mice, indicating a diminished vascular remodeling in KO animals. In vitro experiments unveiled that TWEAK induces CCL5 secretion and MMP‐9 activation in both VSMC and bone marrow‐derived macrophages, and decrease VSMC viability, effects dependent on Fn14.

Conclusions

TWEAK/Fn14 axis participates in AAA formation by promoting lesion inflammatory cell accumulation, angiogenesis, matrix‐degrading protease expression, and vascular remodeling. Blocking TWEAK/Fn14 interaction could be a new target for the treatment of AAA.

Artery Tertiary Lymphoid Organs Contribute to Innate and Adaptive Immune Responses in Advanced Mouse Atherosclerosis

Tertiary lymphoid organs emerge in tissues in response to nonresolving inflammation. Recent research characterized artery tertiary lymphoid organs in the aorta adventitia of aged apolipoprotein E–deficient mice. The atherosclerosis-associated lymphocyte aggregates are organized into distinct compartments, including separate T-cell areas harboring conventional, monocyte-derived, lymphoid, and plasmacytoid dendritic cells, as well as activated T-cell effectors and memory cells; B-cell follicles containing follicular dendritic cells in activated germinal centers; and peripheral niches of plasma cells. Artery tertiary lymphoid organs show marked neoangiogenesis, aberrant lymphangiogenesis, and extensive induction of high endothelial venules. Moreover, newly formed lymph node–like conduits connect the external lamina with high endothelial venules in T-cell areas and also extend into germinal centers. Mouse artery tertiary lymphoid organs recruit large numbers of naïve T cells and harbor lymphocyte subsets with opposing activities, including CD4 + and CD8 + effector and memory T cells, natural and induced CD4 + regulatory T cells, and memory B cells at different stages of differentiation. These data suggest that artery tertiary lymphoid organs participate in primary immune responses and organize T- and B-cell autoimmune responses in advanced atherosclerosis. In this review, we discuss the novel concept that pro- and antiatherogenic immune responses toward unknown arterial wall–derived autoantigens may be organized by artery tertiary lymphoid organs and that disruption of the balance between pro- and antiatherogenic immune cell subsets may trigger clinically overt atherosclerosis.

Pathology of human plaque vulnerability: mechanisms and consequences of intraplaque haemorrhages

Atherothrombotic diseases are still major causes of inability and mortality and fighting atherothrombosis remains a public health priority. The involvement of repeated intraplaque haemorrhages (IPH) in the evolution of atherothrombotic lesions towards complications was proposed as early as 1936. This important topic has been recently revisited and reviewed. Histological observations have been corroborated by magnetic resonance imaging (MRI) of human carotid atheroma, identifying IPH as the main determinant of plaque evolution towards rupture. Beside the intimal integration of asymptomatic luminal coagulum, inward sprouting of neovessels from the adventitia towards the plaque, is one source of IPH in human atheroma. We recently described that directed neo-angiogenesis from the adventitia towards the plaque, across the media, is initiated by lipid mediators generated by the plaque on the luminal side, outwardly convected to the medial VSMCs. Subsequent stimulation of VSMC PPAR-γ receptors induces VEGF expression which causes centripetal sprouting of adventitial vessels. However, this neovascularization is considered to be immature and highly susceptible to leakage. The main cellular components of IPH are Red Blood Cells (RBCs), which with their haemoglobin content and their cell membrane components, particularly enriched in unesterified cholesterol, participate in both the oxidative process and cholesterol accumulation. The presence of iron, glycophorin A and ceroids provides evidence of RBCs. IPH also convey blood leukocytes and platelets and are sites prone to weak pathogen contamination. Therefore prevention and treatment of the biological consequences of IPH pave the way to innovative preventive strategies and improved therapeutic options in human atherothrombotic diseases.

Deciphering the stromal and hematopoietic cell network of the adventitia from non-aneurysmal and aneurysmal human aorta

Aneurysm is associated to a complex remodeling of arteries that affects all their layers. Although events taking place in the intima and the media have received a particular attention, molecular and cellular events taking place in the adventitia have started to be deciphered only recently. In this study, we have precisely described the composition and distribution of stromal and hematopoietic cells in human arterial adventitia, both at steady state and in the setting of aortic aneurysm. Using polychromatic immunofluorescent and flow cytometry analyses, we observed that unlike the medial layer (which comprises mostly macrophages and T cells among leukocytes), the adventitia comprises a much greater variety of leukocytes. We observed an altered balance in macrophages subsets in favor of M2-like macrophages, an increased proliferation of macrophages, a greater number of all stromal cells in aneurysmal aortas. We also confirmed that in this pathological setting, adventitia comprised blood vessels and arterial tertiary lymphoid organs (ATLOs), which contained also M-DC8⁺ dendritic cells (slanDCs) that could participate in the induction of T-cell responses. Finally, we showed that lymphatic vessels can be detected in aneurysmal adventitia, the functionality of which will have to be evaluated in future studies. All together, these observations provide an integrative outlook of the stromal and hematopoietic cell network of the human adventitia both at steady state and in the context of aneurysm.

Tgfbr2 disruption in postnatal smooth muscle impairs aortic wall homeostasis

TGF-β is essential for vascular development; however, excess TGF-β signaling promotes thoracic aortic aneurysm and dissection in multiple disorders, including Marfan syndrome. Since the pathology of TGF-β overactivity manifests primarily within the arterial media, it is widely assumed that suppression of TGF-β signaling in vascular smooth muscle cells will ameliorate aortic disease. We tested this hypothesis by conditional inactivation of Tgfbr2, which encodes the TGF-β type II receptor, in smooth muscle cells of postweanling mice. Surprisingly, the thoracic aorta rapidly thickened, dilated, and dissected in these animals. Tgfbr2 disruption predictably decreased canonical Smad signaling, but unexpectedly increased MAPK signaling. Type II receptor-independent effects of TGF-β and pathological responses by nonrecombined smooth muscle cells were excluded by serologic neutralization. Aortic disease was caused by a perturbed contractile apparatus in medial cells and growth factor production by adventitial cells, both of which resulted in maladaptive paracrine interactions between the vessel wall compartments. Treatment with rapamycin restored a quiescent smooth muscle phenotype and prevented dissection. Tgfbr2 disruption in smooth muscle cells also accelerated aneurysm growth in a murine model of Marfan syndrome. Our data indicate that basal TGF-β signaling in smooth muscle promotes postnatal aortic wall homeostasis and impedes disease progression.

Fluid Mechanics, Arterial Disease, and Gene Expression

This review places modern research developments in vascular mechanobiology in the context of hemodynamic phenomena in the cardiovascular system and the discrete localization of vascular disease. The modern origins of this field are traced, beginning in the 1960s when associations between flow characteristics, particularly blood flow-induced wall shear stress, and the localization of atherosclerotic plaques were uncovered, and continuing to fluid shear stress effects on the vascular lining endothelial) cells (ECs), including their effects on EC morphology, biochemical production, and gene expression. The earliest single-gene studies and genome-wide analyses are considered. The final section moves from the ECs lining the vessel wall to the smooth muscle cells and fibroblasts within the wall that are fluid me chanically activated by interstitial flow that imposes shear stresses on their surfaces comparable with those of flowing blood on EC surfaces. Interstitial flow stimulates biochemical production and gene expression, much like blood flow on ECs.

M1 macrophages act as LTβR-independent lymphoid tissue inducer cells during atherosclerosis-related lymphoid neogenesis

AIMS

The goal of this study was to characterize the role of inflammatory macrophages in the induction of the vascular smooth muscle cell (VSMC)-mediated formation of aortic tertiary lymphoid organs (TLOs).

METHODS AND RESULTS

Mouse bone marrow-derived M1 macrophages acted as lymphoid tissue inducer cells. Indeed, they expressed high levels of tumour necrosis factor (TNF)-α and membrane-bound lymphotoxin (LT)-α, two inducing cytokines that triggered expression of the chemokines CCL19, CCL20, and CXCL16, as did M1 supernatant. The blockade of LTβR signalling with LTβR-Ig had no effect, whereas that of TNFR1/2 signalling reduced chemokine expression by VSMCs in both wild-type (WT) and LTβR KO mice, demonstrating that LTβR signalling is dispensable for the M1-inducing effect. This effect was corroborated by the development of TLOs observed in LTβR KO->apolipoprotein E knockout (ApoE KO) aortic segments after orthotopic transplantation. Furthermore, treatment of ApoE KO mice with anti-TNF-α antibody decreased the number and incidence of aortic TLOs. Finally, lymphoid nodules composed of T and B cells formed in in vivo-implanted scaffolds seeded with VSMCs previously stimulated ex vivo by M1-conditioned medium.

CONCLUSIONS

These results are the first to identify M1 macrophages as inducer cells that trigger the expression of chemokines by VSMCs independently of LTβR signalling. We propose that the dialogue between macrophages and VSMCs-established across the vascular wall-contributes to the formation of aortic TLOs.

Multifactorial relationship between 18F-fluoro-deoxy-glucose positron emission tomography signaling and biomechanical properties in unruptured aortic aneurysms

BACKGROUND

The relationship between biomechanical properties and biological activities in aortic aneurysms was investigated with finite element simulations and 18F-fluoro-deoxy-glucose (18F-FDG) positron emission tomography.

METHODS AND RESULTS

The study included 53 patients (45 men) with aortic aneurysms, 47 infrarenal (abdominal aortic) and 6 thoracic (thoracic aortic), who had ≥1 18F-FDG positron emission tomography/computed tomography. During a 30-month period, more clinical events occurred in patients with increased 18F-FDG uptake on their last examination than in those without (5 of 18 [28%] versus 2 of 35 [6%]; P=0.03). Wall stress and stress/strength index computed by finite element simulations and 18F-FDG uptake were evaluated in a total of 68 examinations. Twenty-five (38%) examinations demonstrated ≥1 aneurysm wall area of increased 18F-FDG uptake. The mean number of these areas per examination was 1.6 (18 of 11) in thoracic aortic aneurysms versus 0.25 (14 of 57) in abdominal aortic aneurysms, whereas the mean number of increased uptake areas colocalizing with highest wall stress and stress/strength index areas was 0.55 (6 of 11) and 0.02 (1 of 57), respectively. Quantitatively, 18F-FDG positron emission tomographic uptake correlated positively with both wall stress and stress/strength index (P<0.05). 18F-FDG uptake was particularly high in subjects with personal history of angina pectoris and familial aneurysm.

CONCLUSIONS

Increased 18F-FDG positron emission tomographic uptake in aortic aneurysms is strongly related to aneurysm location, wall stress as derived by finite element simulations, and patient risk factors such as acquired and inherited susceptibilities.

Opposite associations of plasma homoarginine and ornithine with arginine in healthy children and adolescents

Homoarginine, a non-proteinogenic amino acid, is formed when lysine replaces ornithine in reactions catalyzed by hepatic urea cycle enzymes or lysine substitutes for glycine as a substrate of renal arginine:glycine amidinotransferase. Decreased circulating homoarginine and elevated ornithine, a downstream product of arginase, predict adverse cardiovascular outcome. Our aim was to investigate correlates of plasma homoarginine and ornithine and their relations with carotid vascular structure in 40 healthy children and adolescents aged 3–18 years without coexistent diseases or subclinical carotid atherosclerosis. Homoarginine, ornithine, arginine, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) were measured by liquid chromatography-tandem mass spectrometry with stable isotope-labeled internal standards. Intima-media thickness (IMT) and extra-medial thickness (EMT) of common carotid arteries were estimated by B-mode ultrasound. Homoarginine correlated with arginine (r = 0.43, p = 0.005), age (r = 0.42, p = 0.007) and, weakly, with an increased arginine-to-ornithine ratio, a putative measure of lower arginase activity (r = 0.31, p = 0.048). Ornithine correlated inversely with arginine (r = −0.64, p < 0.001). IMT, EMT or their sum were unrelated to any of the biochemical parameters (p > 0.12). Thus, opposite associations of plasma homoarginine and ornithine with arginine may partially result from possible involvement of arginase, an enzyme controlling homoarginine degradation and ornithine synthesis from arginine. Age-dependency of homoarginine levels can reflect developmental changes in homoarginine metabolism. However, neither homoarginine nor ornithine appears to be associated with carotid vascular structure in healthy children and adolescents.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Biochemomechanics of intraluminal thrombus in abdominal aortic aneurysms

Most computational models of abdominal aortic aneurysms address either the hemodynamics within the lesion or the mechanics of the wall. More recently, however, some models have appropriately begun to account for the evolving mechanics of the wall in response to the changing hemodynamic loads. Collectively, this large body of work has provided tremendous insight into this life-threatening condition and has provided important guidance for current research. Nevertheless, there has yet to be a comprehensive model that addresses the mechanobiology, biochemistry, and biomechanics of thrombus-laden abdominal aortic aneurysms. That is, there is a pressing need to include effects of the hemodynamics on both the development of the nearly ubiquitous intraluminal thrombus and the evolving mechanics of the wall, which depends in part on biochemical effects of the adjacent thrombus. Indeed, there is increasing evidence that intraluminal thrombus in abdominal aortic aneurysms is biologically active and should not be treated as homogeneous inert material. In this review paper, we bring together diverse findings from the literature to encourage next generation models that account for the biochemomechanics of growth and remodeling in patient-specific, thrombus-laden abdominal aortic aneurysms.

Impaired high-density lipoprotein anti-oxidant capacity in human abdominal aortic aneurysm

AIMS

Abdominal aortic aneurysm (AAA) is a particular form of atherothrombotic disease characterized by the dilation of the aortic wall and the presence of an intraluminal thrombus (ILT). The objective of the present study was to evaluate the pro-oxidant properties of the ILT and to characterize the anti-oxidant capacity of high-density lipoproteins (HDLs).

METHODS AND RESULTS

Our results show that ILT, adventitia, and plasma from AAA patients contained high concentrations of lipid and protein oxidation products. Mediators produced within or released by the thrombus and the adventitia were shown to induce reactive oxygen species (ROS) production by cultured aortic smooth muscle cells (AoSMCs) and to trigger the onset of apoptosis (an increase in mitochondrial membrane potential). Iron chelation limited these effects. Both concentration and functionality of HDLs were altered in AAA patients. Plasma levels of Apo A-I were lower, and small HDL subclasses were decreased in AAA patients. Circulating HDLs in AAA patients displayed an impaired capacity to inhibit copper-induced low-density lipoprotein oxidation and AoSMC ROS production. Western blot analyses of HDLs demonstrated that myeloperoxidase is associated with HDL particles in AAA patients.

CONCLUSION

ILT and adventitia are a source of pro-oxidant products, in particular haemoglobin, which may impact on the wall stability/rupture in AAA. In addition, HDLs from AAA patients exhibit an impaired anti-oxidant activity. In this context, restoring HDL functionality may represent a new therapeutic option in AAA.

Adventitial stem cells in vein grafts display multilineage potential that contributes to neointimal formation

OBJECTIVE

This study was designed to carry out the characterization of stem cells within the adventitia and to elucidate their functional role in the pathogenesis of vein graft atherosclerosis.

APPROACH AND RESULTS

A mouse vein graft model was used to investigate the functional role of adventitial stem/progenitor cells on atherosclerosis. The adventitia of vein grafts underwent significant remodeling during early stages of vessel grafting and displayed markedly heterogeneous cell compositions. Immunofluorescence staining indicated a significant number of stem cell antigen-1-positive cells that were closely located to vasa vasorum. In vitro clonogenic assays demonstrated 1% to 11% of growing rates from adventitial cell cultures, most of which could be differentiated into smooth muscle cells (SMCs). These stem cell antigen-1-positive cells also displayed a potential to differentiate into adipogenic, osteogenic, or chondrogenic lineages in vitro. In light of the proatherogenic roles of SMCs in atherosclerosis, we focused on the functional roles of progenitor-SMC differentiation, in which we subsequently demonstrated that it was driven by direct interaction of the integrin/collagen IV axis. The ex vivo bioreactor system revealed the migratory capacity of stem cell antigen-1-positive progenitor cells into the vessel wall in response to stromal cell-derived factor-1. Stem cell antigen-1-positive cells that were applied to the outer layer of vein grafts showed enhanced atherosclerosis in apolipoprotein E-deficient mice, which contributed to ≈ 30% of neointimal SMCs.

CONCLUSIONS

We demonstrate that during pathological conditions in vein grafting, the adventitia harbors stem/progenitor cells that can actively participate in the pathogenesis of vascular disease via differentiation into SMCs.

New Insights Into Aortic Diseases: A Report From the Third International Meeting on Aortic Diseases (IMAD3)

The current state of research and treatment on aortic diseases was discussed in the "3rd International Meeting on Aortic Diseases" (IMAD3) held on October 4-6, 2012, in Liège, Belgium. The 3-day meeting covered a wide range of topics related to thoracic aortic aneurysms and dissections, abdominal aortic aneurysms, and valvular diseases. It brought together clinicians and basic scientists and provided an excellent opportunity to discuss future collaborative research projects for genetic, genomics, and biomarker studies, as well as clinical trials. Although great progress has been made in the past few years, there are still a large number of unsolved questions about aortic diseases. Obtaining answers to the key questions will require innovative, interdisciplinary approaches that integrate information from epidemiological, genetic, molecular biology, and bioengineering studies on humans and animal models. It is more evident than ever that multicenter collaborations are needed to accomplish these goals.

Pathophysiology of atherosclerosis plaque progression

Atherosclerotic plaque rupture with luminal thrombosis is the most common mechanism responsible for the majority of acute coronary syndromes and sudden coronary death. The precursor lesion of plaque rupture is thought to be a thin cap fibroatheroma (TCFA) or "vulnerable plaque". TCFA is characterised by a necrotic core with an overlying thin fibrous cap (≤65 μm) that is infiltrated by macrophages and T-lymphocytes. Intraplaque haemorrhage is a major contributor to the enlargement of the necrotic core. Haemorrhage is thought to occur from leaky vasa vasorum that invades the intima from the adventitia as the intima enlarges. The early atherosclerotic plaque progression from pathologic intimal thickening (PIT) to a fibroatheroma is thought to be the result of macrophage infiltration. PIT is characterised by the presence of lipid pools which consist of proteoglycan with lipid insudation. The conversion of the lipid pool to a necrotic core is poorly understood but is thought to occur as a result of macrophage infiltration which releases matrix metalloproteinase (MMPs) along with macrophage apoptosis that leads to the formation of a acellular necrotic core. The fibroatheroma has a thick fibrous cap that begins to thin over time through macrophage MMP release and apoptotic death of smooth muscle cells converting the fibroatheroma into a TCFA. Other causes of thrombosis include plaque erosion which is less frequent than plaque rupture but is a common cause of thrombosis in young individuals especially women <50 years of age. The underlying lesion morphology in plaque erosion consists of PIT or a thick cap fibroatheroma. Calcified nodule is the least frequent cause of thrombosis, which occurs in older individuals with heavily calcified and tortious arteries.