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

Hemoglobin homeostasis in abdominal aortic aneurysm: diagnostic and prognostic potential of hemoglobin/heme and scavenger molecules

BACKGROUND

There is increasing evidence implicating hemoglobin/heme and their scavengers in oxidative stress-mediated pathologies, but information is limited in abdominal aortic aneurysm (AAA).

METHODS AND RESULTS

In this case-control study, we assessed heme/heme-related markers in 142 men with AAA and 279 men with a normal aortic diameter consecutively recruited from an ultrasound screening program in Sweden. Enzyme-linked immunosorbent assays (ELISAs) were used to measure heme oxygenase-1 (HO-1) and hemopexin (Hpx) plasma levels, colorimetric assays for cell-free heme and whole blood hemoglobin (Hb) levels, and droplet digital PCR (ddPCR) and real-time PCR to determine haptoglobin (Hp) (pheno)type and genotype, respectively. Hpx and heme plasma levels at baseline were elevated, while HO-1 levels were lower in men with AAA (p < 0.001) and were significantly associated with AAA prevalence independently of potential confounders. A combination of heme and HO-1 showed the best diagnostic potential based on the area under the curve (AUC): 0.76, sensitivity: 80%, specificity: 48%. Additionally, when previously described inflammatory biomarker interleukin-6 (IL-6), was added to our model it significantly improved the diagnostic value (AUC: 0.87, sensitivity: 80%, specificity: 79%) compared to IL-6 alone (AUC: 0.73, sensitivity: 80%, specificity: 49%). Finally, Hb (positively) and Hpx (negatively) levels at baseline were associated with AAA growth rate (mm/year), and their combination showed the best prognostic value for discriminating fast and slow-growing AAA (AUC: 0.76, sensitivity: 80%, specificity: 62%).

CONCLUSIONS

This study reports the distinct disruption of heme and related markers in both the development and progression of AAA, underscoring their potential in aiding risk stratification and therapeutic strategies.

Factors predicting acute kidney injury in patients after abdominal aortic aneurysm repair

INTRODUCTION

Postoperative acute kidney injury (AKI) is one of the most frequent complications in abdominal aortic aneurysm (AAA) patients after open and endovascular aortic aneurysm repair. AKI decreases the efficiency of kidney function, allowing accumulation of waste products in the body, and an imbalance of water, acid and electrolytes in the body. As a result, the functioning of various organs throughout the body is affected. These effects may raise the cost of treatment, length of stay, and mortality rate.

OBJECTIVE

This study aims to examine the predictive factors of AKI - preoperative of estimated glomerular filtration rate (eGFR), preoperative of hemoglobin level, types of abdominal aortic aneurysms repair, and intraoperative of cardiac arrhythmias - after open and endovascular aortic repair among AAA patients within 72 h.

METHODS

This is a retrospective study of 196 patients with AAA after elective open and endovascular aortic aneurysm repair within the first 72 h who met the inclusion criteria recruited from a tertiary care hospital in Bangkok, Thailand. Postoperative AKI after elective open and endovascular aortic repair among AAA patients is defined by the 2012 Kidney Disease Improving Global Outcomes (KDIGO) Clinical Practice Guidelines.

RESULTS

A total of 196 AAA patients, 75.5% were male with an average age of 75.12 years (SD = 8.45). Endovascular aortic aneurysm repair was used more frequently than open aortic aneurysm repair (64.8% vs 35.2%) and 37.2% of the AAA patients had intraoperative cardiac arrhythmias. The occurrence of AKI among the AAA patients after abdominal aortic aneurysm repair within 72 h was 54.1%. The AKI rate of EVAR patients was 69.8% while the AKI rate for OAR patients was 30.2%. The preoperative estimated glomerular filtration rate (eGFR) and hemoglobin level were found to jointly predict AKI and explain 32.2% of the variance (Nagelkerke R2 = 0.322, p < .05). However, the type of abdominal aortic aneurysms repair and intraoperative cardiac arrhythmias did not correlate with the incidence of AKI in AAA repair patients. The predictive factors for AKI among AAA patients after aortic aneurysm repair were preoperative eGFR < 60 mL/min/1.73 m2 (OR = 4.436, 95% CI: 2.202-8.928, p < .001) and preoperative hemoglobin level between 8.1-10.0 g/dL (OR = 4.496, 95% CI: 1.831-11.040, p = .001).

CONCLUSION

Preoperative eGFR < 60 mL/min/1.73 m2 and preoperative hemoglobin level between 8.1-10.0 g/dL were the predictive factors for AKI among AAA patients after both open and endovascular AAA repair. Therefore, healthcare providers should be aware of and monitor signs of AKI after surgery in AAA patients, especially those undergoing EVAR with lower eGFR and hemoglobin levels.

Ganglioside GM3 Protects Against Abdominal Aortic Aneurysm by Suppressing Ferroptosis

BACKGROUND

Abdominal aortic aneurysm (AAA) is a potentially life-threatening vascular condition, but approved medical therapies to prevent AAA progression and rupture are currently lacking. Sphingolipid metabolism disorders are associated with the occurrence and development of AAA. It has been discovered that ganglioside GM3, a sialic acid-containing type of glycosphingolipid, plays a protective role in atherosclerosis, which is an important risk factor for AAA; however, the potential contribution of GM3 to AAA development has not been investigated.

METHODS

We performed a metabolomics study to evaluated GM3 level in plasma of human patients with AAA. We profiled GM3 synthase (ST3GAL5) expression in the mouse model of aneurysm and human AAA tissues through Western blotting and immunofluorescence staining. RNA sequencing, affinity purification and mass spectrometry, proteomic analysis, surface plasmon resonance analysis, and functional studies were used to dissect the molecular mechanism of GM3-regulating ferroptosis. We conditionally deleted and overexpressed St3gal5 in smooth muscle cells (SMCs) in vivo to investigate its role in AAA.

RESULTS

We found significantly reduced plasma levels of GM3 in human patients with AAA. GM3 content and ST3GAL5 expression were decreased in abdominal aortic vascular SMCs in patients with AAA and an AAA mouse model. RNA sequencing analysis showed that ST3GAL5 silencing in human aortic SMCs induced ferroptosis. We showed that GM3 interacted directly with the extracellular domain of TFR1 (transferrin receptor 1), a cell membrane protein critical for cellular iron uptake, and disrupted its interaction with holo-transferrin. SMC-specific St3gal5 knockout exacerbated iron accumulation at lesion sites and significantly promoted AAA development in mice, whereas GM3 supplementation suppressed lipid peroxidation, reduced iron deposition in aortic vascular SMCs, and markedly decreased AAA incidence.

CONCLUSIONS

Together, these results suggest that GM3 dysregulation promotes ferroptosis of vascular SMCs in AAA. Furthermore, GM3 may constitute a new therapeutic target for AAA.

Protective Role for Smooth Muscle Cell Hepcidin in Abdominal Aortic Aneurysm

BACKGROUND

Hepcidin is a liver-derived hormone that controls systemic iron homeostasis, by inhibiting the iron exporter ferroportin in the gut and spleen, respective sites of iron absorption and recycling. Hepcidin is also expressed ectopically in the context of cardiovascular disease. However, the precise role of ectopic hepcidin in underlying pathophysiology is unknown. In patients with abdominal aortic aneurysm (AAA), hepcidin is markedly induced in smooth muscle cells (SMCs) of the aneurysm wall and inversely correlated with the expression of LCN2 (lipocalin-2), a protein implicated in AAA pathology. In addition, plasma hepcidin levels were inversely correlated with aneurysm growth, suggesting hepcidin has a potential disease-modifying role.

METHODS

To probe the role of SMC-derived hepcidin in the setting of AAA, we applied AngII (Angiotensin-II)-induced AAA model to mice harbouring an inducible, SMC-specific deletion of hepcidin. To determine whether SMC-derived hepcidin acted cell-autonomously, we also used mice harboring an inducible SMC-specific knock-in of hepcidin-resistant ferroportinC326Y. The involvement of LCN2 was established using a LCN2-neutralizing antibody.

RESULTS

Mice with SMC-specific deletion of hepcidin or knock-in of hepcidin-resistant ferroportinC326Y had a heightened AAA phenotype compared with controls. In both models, SMCs exhibited raised ferroportin expression and reduced iron retention, accompanied by failure to suppress LCN2, impaired autophagy in SMCs, and greater aortic neutrophil infiltration. Pretreatment with LCN2-neutralizing antibody restored autophagy, reduced neutrophil infiltration, and prevented the heightened AAA phenotype. Finally, plasma hepcidin levels were consistently lower in mice with SMC-specific deletion of hepcidin than in controls, indicating that SMC-derived hepcidin contributes to the circulating pool in AAA.

CONCLUSIONS

Hepcidin elevation in SMCs plays a protective role in the setting of AAA. These findings are the first demonstration of a protective rather than deleterious role for hepcidin in cardiovascular disease. They highlight the need to further explore the prognostic and therapeutic value of hepcidin outside disorders of iron homeostasis.

Conductance Artery Wall Layers and Their Respective Roles in the Clearance Functions

Evolutionary organization of the arterial wall into layers occurred concomitantly with the emergence of a highly muscularized, pressurized arterial system that facilitates outward hydraulic conductance and mass transport of soluble substances across the arterial wall. Although colliding circulating cells disperse potential energy within the arterial wall, the different layers counteract this effect: (1) the endothelium ensures a partial barrier function; (2) the media comprises smooth muscle cells capable of endocytosis/phagocytosis; (3) the outer adventitia and perivascular adipocytic tissue are the final receptacles of convected substances. While the endothelium forms a physical and a biochemical barrier, the medial layer is avascular, relying on the specific permeability properties of the endothelium for metabolic support. Different components of the media interact with convected molecules: medial smooth muscle cells take up numerous molecules via scavenger receptors and are capable of phagocytosis of macro/micro particles. The outer layers-the highly microvascularized innervated adventitia and perivascular adipose tissue-are also involved in the clearance functions of the media: the adventitia is the seat of immune response development, inward angiogenesis, macromolecular lymphatic drainage, and neuronal stimulation. Consequently, the clearance functions of the arterial wall are physiologically essential, but also may favor the development of arterial wall pathologies. This review describes how the walls of large conductance arteries have acquired physiological clearance functions, how this is determined by the attributes of the endothelial barrier, governed by endocytic and phagocytic capacities of smooth muscle cells, impacting adventitial functions, and the role of these clearance functions in arterial wall diseases.

Malondialdehyde-modified HDL particles elicit a specific IgG response in abdominal aortic aneurysm

High Density Lipoprotein (HDL) plays a protective role in abdominal aortic aneurysm (AAA); however, recent findings suggest that oxidative modifications could lead to dysfunctional HDL in AAA. This study aimed at testing the effect of oxidized HDL on aortic lesions and humoral immune responses in a mouse model of AAA induced by elastase, and evaluating whether antibodies against modified HDL can be found in AAA patients. HDL particles were oxidized with malondialdehyde (HDL-MDA) and the changes were studied by biochemical and proteomics approaches. Experimental AAA was induced in mice by elastase perfusion and then mice were treated with HDL-MDA, HDL or vehicle for 14 days. Aortic lesions were studied by histomorphometric analysis. Levels of anti-HDL-MDA IgG antibodies were measured by an in-house immunoassay in the mouse model, in human tissue-supernatants and in plasma samples from the VIVA cohort. HDL oxidation with MDA was confirmed by enhanced susceptibility to diene formation. Proteomics demonstrated the presence of MDA adducts on Lysine residues of HDL proteins, mainly ApoA-I. MDA-modification of HDL abrogated the protective effect of HDL on cultured endothelial cells as well as on AAA dilation in mice. Exposure to HDL-MDA elicited an anti-HDL-MDA IgG response in mice. Anti-HDL-MDA were also detected in tissue-conditioned media from AAA patients, mainly in intraluminal thrombus. Higher plasma levels of anti-HDL-MDA IgG antibodies were found in AAA patients compared to controls. Anti-HDL-MDA levels were associated with smoking and were independent predictors of overall mortality in AAA patients. Overall, MDA-oxidized HDL trigger a specific humoral immune response in mice. Besides, antibodies against HDL-MDA can be detected in tissue and plasma of AAA patients, suggesting its potential use as surrogate stable biomarkers of oxidative stress in AAA.

Neutrophils as Regulators and Biomarkers of Cardiovascular Inflammation in the Context of Abdominal Aortic Aneurysms

Neutrophils represent up to 70% of circulating leukocytes in healthy humans and combat infection mostly by phagocytosis, degranulation and NETosis. It has been reported that neutrophils are centrally involved in abdominal aortic aneurysm (AAA) pathogenesis. The natural course of AAA is growth and rupture, if left undiagnosed or untreated. The rupture of AAA has a very high mortality and is currently among the leading causes of death worldwide. The use of noninvasive cardiovascular imaging techniques for patient screening, surveillance and postoperative follow-up is well established and recommended by the current guidelines. Neutrophil-derived biomarkers may offer clinical value to the monitoring and prognosis of AAA patients, allowing for potential early therapeutic intervention. Numerous promising biomarkers have been studied. In this review, we discuss neutrophils and neutrophil-derived molecules as regulators and biomarkers of AAA, and our aim was to specifically highlight diagnostic and prognostic markers. Neutrophil-derived biomarkers may potentially, in the future, assist in determining AAA presence, predict size, expansion rate, rupture risk, and postoperative outcome once validated in highly warranted future prospective clinical studies.

Erythropoietin promotes abdominal aortic aneurysms in mice through angiogenesis and inflammatory infiltration

Abdominal aortic aneurysm (AAA) is a potentially fatal vascular disease, but the underlying mechanisms remain unknown. Here, we tested the hypothesis that erythropoietin (EPO) may promote the formation of AAA. We found that EPO dose-dependently promoted the formation of AAA in both Apoe ^-/- (66.7%) and wild-type (WT) (60%) mice receiving a high dose of EPO. EPO monoclonal antibodies given to Apoe ^-/- mice receiving angiotensin II (AngII) stimulation resulted in a markedly lower incidence of AAA (from 86.7 to 20%, P < 0.001), and EPO receptor (EPOR) knockdown in Epor ^+/- Apoe ^-/- mice substantially reduced the incidence of AAA compared to Apoe ^-/- mice after AngII stimulation (from 86.7 to 45.5%, P < 0.05), further supporting the finding that EPO is a contributor to AAA formation. EPO-induced AAA resulted in increased microvessels, phagocyte infiltration, and matrix metalloproteinase secretion, as well as reduced collagen and smooth muscle cells (SMCs). Experiments in vitro and ex vivo demonstrated that EPO induced proliferation, migration, and tube formation of endothelial cells via the JAK2/STAT5 signaling pathway. In humans, serum EPO concentrations were higher in patients with AAA than in healthy individuals and correlated with the size of the AAA, suggesting a potential link between EPO and the severity of AAA in humans. In conclusion, we found that EPO promotes the formation of AAA in both Apoe ^-/- and WT mice by enhancing angiogenesis, inflammation, collagen degradation, and apoptosis of SMCs and that EPO/EPOR signaling is essential for AngII-induced AAA. The association between EPO and AAA in humans warrants further study.

Colocalization of Erythrocytes and Vascular Calcification in Human Atherosclerosis: A Systematic Histomorphometric Analysis

Background  Intimal calcification typically develops in advanced atherosclerosis, and microcalcification may promote plaque progression and instability. Conversely, intraplaque hemorrhage and erythrocyte extravasation may stimulate osteoblastic differentiation and intralesional calcium phosphate deposition. The presence of erythrocytes and their main cellular components (membranes, hemoglobin, and iron) and colocalization with calcification has never been systematically studied. Methods and Results  We examined three types of diseased vascular tissue specimens, namely, degenerative aortic valve stenosis ( n  = 46), atherosclerotic carotid artery plaques ( n  = 9), and abdominal aortic aneurysms ( n  = 14). Biomaterial was obtained from symptomatic patients undergoing elective aortic valve replacement, carotid artery endatherectomy, or aortic aneurysm repair, respectively. Serial sections were stained using Masson-Goldner trichrome, Alizarin red S, and Perl's iron stain to visualize erythrocytes, extracelluar matrix and osteoid, calcium phosphate deposition, or the presence of iron and hemosiderin, respectively. Immunohistochemistry was employed to detect erythrocyte membranes (CD235a), hemoglobin or the hemoglobin scavenger receptor (CD163), endothelial cells (CD31), myofibroblasts (SMA), mesenchymal cells (osteopontin), or osteoblasts (periostin). Our analyses revealed a varying degree of intraplaque hemorrhage and that the majority of extravasated erythrocytes were lysed. Osteoid and calcifications also were frequently present, and erythrocyte membranes were significantly more prevalent in areas with calcification. Areas with extravasated erythrocytes frequently contained CD163-positive cells, although calcification also occurred in areas without CD163 immunosignals. Conclusion  Our findings underline the presence of extravasated erythrocytes and their membranes in different types of vascular lesions, and their association with areas of calcification suggests an active role of erythrocytes in vascular disease processes.

Iron deficiency promotes aortic medial degeneration via destructing cytoskeleton of vascular smooth muscle cells

BACKGROUND

Aortic dissection (AD) and aortic aneurysm (AA) are critical illnesses with an unclear pathogenetic mechanism that seriously threaten human life. Aortic medial degeneration (AMD) is the main pathological feature of AD and AA. Diseases of iron metabolism can cause a variety of physiological dysfunctions. In this study, we aimed to clarify the state of iron metabolism in patients with AD and AA, and to explore the effect of iron metabolism on AMD.

METHODS

A total of 200 patients with AD or AA, and 60 patients with hypertension were included in the study. Blood samples were drawn immediately when patients were admitted to the hospital. Aortic specimens from patients with Stanford type A AD were obtained at the time of surgery. The status of iron metabolism in the circulation and the aortic wall was analyzed. In addition, apolipoprotein E knockout mice were fed chow with a different iron content, and angiotensin II (Ang II) was used to induce AMD. Furthermore, transferrin receptor 1 knockout (TFR1-/-) mice were used to study the effects of iron deficiency (ID) on aortic development, to observe the effects of different iron metabolism status on the formation of AMD in mice, and to explore the cytoskeleton of vascular smooth muscle cells (VSMCs) under different iron metabolism.

RESULTS

Patients with AMD were iron deficient. ID is associated with the development of AMD in hypertensive patients. Iron-deficient feeding combined with Ang II pumping promoted the formation of AMD and significantly shortened the survival time of mice. ID significantly impaired the cytoskeleton of VSMCs.

CONCLUSIONS

Our results highlighted that ID was associated with the formation of AMD in patients with hypertension. In this study, we identified a novel mechanism behind VSMCs dysfunction that was induced by ID, thereby suggesting iron homeostasis as a future precaution in patients with hypertension based on its important role in the maintenance of VSMC function.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Red Blood Cells and Hemoglobin in Human Atherosclerosis and Related Arterial Diseases

As the main particulate component of the circulating blood, RBCs play major roles in physiological hemodynamics and impact all arterial wall pathologies. RBCs are the main determinant of blood viscosity, defining the frictional forces exerted by the blood on the arterial wall. This function is used in phylogeny and ontogeny of the cardiovascular (CV) system, allowing the acquisition of vasomotricity adapted to local metabolic demands, and systemic arterial pressure after birth. In pathology, RBCs collide with the arterial wall, inducing both local retention of their membranous lipids and local hemolysis, releasing heme-Fe⁺⁺ with a high toxicity for arterial cells: endothelial and smooth muscle cells (SMCs) cardiomyocytes, neurons, etc. Specifically, overloading of cells by Fe⁺⁺ promotes cell death. This local hemolysis is an event associated with early and advanced stages of human atherosclerosis. Similarly, the permanent renewal of mural RBC clotting is the major support of oxidation in abdominal aortic aneurysm. In parallel, calcifications promote intramural hemorrhages, and hemorrhages promote an osteoblastic phenotypic shift of arterial wall cells. Different plasma or tissue systems are able, at least in part, to limit this injury by acting at the different levels of this system.

Intravenous Iron in a Prehabilitation Program for Older Surgical Patients: Prospective Cohort Study

BACKGROUND

Older patients often have iron deficiency anemia before surgery, which can be effectively treated with intravenous iron supplementation (IVIS). Anemia and blood transfusions are associated with an increased risk of delirium. The aim of this research was to assess the effectiveness and safety of using IVIS in a prehabilitation program.

MATERIAL AND METHODS

Patients ≥70 y who underwent abdominal surgery between November 2015 and June 2018 were included in this single-center prospective cohort study. All patients were prehabilitated; however, only anemic patients received a single dose of 1000 mg intravenous iron (ferric carboxymaltose) to increase preoperative hemoglobin levels (IVIS group). Nonanemic patients received standard care (SC). The hemoglobin levels (primary outcome) were assessed at the outpatient clinic visit, at admission, and at discharge. Secondary outcomes were postoperative delirium, postoperative anemia, blood transfusion, complications other than delirium, and length of hospital stay. All outcomes were compared between the IVIS group and SC group.

RESULTS

Of all patients (n = 248), 97 anemic patients received IVIS (39%). Of the anemic patients, 50 patients (52%) had iron deficiency. Initial differences in hemoglobin concentrations between the IVIS group and SC group at T1 and T2 (7.2 versus 8.8; P < 0.001 and 7.4 versus 8.6; P = 0.023, respectively) were no longer present at discharge (6.6 versus 7.2; P = 0.35). No statistically significant differences were observed for all secondary outcomes between the IVIS group and the SC group. No infusion-related adverse events occurred.

CONCLUSIONS

Adding IVIS to prehabilitation programs is safe and diminishes differences in these concentrations between preoperatively anemic and nonanemic patients. IVIS may be worthwhile as an additional component of prehabilitation programs. Results merit further investigation.

Red Cell Distribution Width is Associated with Future Incidence of Abdominal Aortic Aneurysm in a Population-Based Cohort Study

Red cell distribution width (RDW) has been suggested to have a predictive potential for several cardiovascular diseases, but its association with abdominal aortic aneurysm (AAA) is unknown. We examined whether RDW is associated with the risk of AAA among 27,260 individuals from the population-based Malmö Diet and Cancer Study cohort. Data of baseline characteristics were collected during 1991–1996. Cox regression was used to estimate hazard ratios (HR) with 95% confidence intervals (CI) for AAA across quartiles of RDW. During a median follow-up of 21.7 years, 491 subjects developed AAA. After adjustment for other confounding factors, participants in the highest quartile of RDW experienced 61% increased risk of AAA as compared to those with the lowest quartile (HR = 1.61, CI = 1.20, 2.12). RDW showed similar relationship with severe (i.e. ruptured or surgically repaired) AAA or non-severe AAA (adjusted HR 1.58 and 1.60, respectively). The observed association between RDW and AAA risk was significant in current smokers (adjusted HR = 1.68, CI = 1.18, 2.38) but not in former smokers (adjusted HR = 1.13, CI = 0.72, 1.79), or never-smokers (adjusted HR = 1.77, CI = 0.74, 4.22). Elevated RDW is associated with increased future incidence of AAA, however the causal and pathophysiological mechanisms remain to be explored.

APOA1 oxidation is associated to dysfunctional high-density lipoproteins in human abdominal aortic aneurysm

Background

High-density lipoproteins (HDL) are a complex mixture of lipids and proteins with vasculoprotective properties. However, HDL components could suffer post-translational modifications (PTMs) under pathological conditions, leading to dysfunctional HDL. We studied whether HDL are modified in abdominal aortic aneurysm (AAA) and the effect on HDL functionality.

Methods

HDL were isolated by ultracentrifugation from AAA tissue (HDL-T) and from plasma of healthy volunteers and then incubated with AAA tissue-conditioned medium (HDL-AAA CM). PTMs from these particles were characterized using Comet-PTM. The ability of HDL-AAA CM for promoting cholesterol efflux was determined ex vivo and in vivo by using J774A.1 [³H]cholesterol-labeled mouse macrophages and after injecting [³H]cholesterol-labeled mouse macrophages and HDL into the peritoneal cavity of wild-type C57BL/6 mice, respectively. Trp50 and Trp108 oxidized forms of APOA1 in HDL incubated with conditioned-medium of activated neutrophils and in plasma of AAA patients and controls were measured by targeted parallel reaction monitoring.

Findings

Oxidation was the most prevalent PTM in apolipoproteins, particularly in APOA1. Trp50 and Trp108 in APOA1 were the residues most clearly affected by oxidation in HDL-T and in HDL-AAA CM, when compared to their controls. In addition, cholesterol efflux was decreased in macrophages incubated with HDL-AAA CM in vitro and a decreased macrophage-to-serum reverse cholesterol transport was also observed in mice injected with HDL-AAA CM. Finally, both oxidized Trp50 and Trp108 forms of APOA1 were increased in HDL incubated with conditioned-medium of activated neutrophils and in plasma of AAA patients in relation to controls.

Interpretation

Oxidative modifications of HDL present in AAA tissue and plasma were closely associated with the loss of vasculoprotective properties of HDL in AAA.

Fund

MINECO, ISCiii-FEDER, CIBERDEM, CIBERCV and LA CAIXA.

Abdominal aortic aneurysms

An abdominal aortic aneurysm (AAA) is a localized dilatation of the infrarenal aorta. AAA is a multifactorial disease, and genetic and environmental factors play a part; smoking, male sex and a positive family history are the most important risk factors, and AAA is most common in men >65 years of age. AAA results from changes in the aortic wall structure, including thinning of the media and adventitia due to the loss of vascular smooth muscle cells and degradation of the extracellular matrix. If the mechanical stress of the blood pressure acting on the wall exceeds the wall strength, the AAA ruptures, causing life-threatening intra-abdominal haemorrhage - the mortality for patients with ruptured AAA is 65-85%. Although AAAs of any size can rupture, the risk of rupture increases with diameter. Intact AAAs are typically asymptomatic, and in settings where screening programmes with ultrasonography are not implemented, most cases are diagnosed incidentally. Modern functional imaging techniques (PET, CT and MRI) may help to assess rupture risk. Elective repair of AAA with open surgery or endovascular aortic repair (EVAR) should be considered to prevent AAA rupture, although the morbidity and mortality associated with both techniques remain non-negligible.

ApoA-I/HDL-C levels are inversely associated with abdominal aortic aneurysm progression

Abdominal aortic aneurysm (AAA) evolution is unpredictable, and there is no therapy except surgery for patients with an aortic size > 5 cm (large AAA). We aimed to identify new potential biomarkers that could facilitate prognosis and treatment of patients with AAA. A differential quantitative proteomic analysis of plasma proteins was performed in AAA patients at different stages of evolution [small AAA (aortic size=3�5cm) vs large AAA] using iTRAQ labelling, highthroughput nano-LC-MS/MS and a novel multi-layered statistical model. Among the proteins identified, ApoA-I was decreased in patients with large AAA compared to those with small AAA. These results were validated by ELISA on plasma samples from small (n=90) and large AAA (n=26) patients (150 ± 3 vs 133 ± 5 mg/dl, respectively, p< 0.001). ApoA-I levels strongly correlated with HDL-Cholesterol (HDL-C) concentration (r=0.9, p< 0.001) and showed a negative correlation with aortic size (r=-0.4, p< 0.01) and thrombus volume (r=-0.3, p< 0.01), which remained significant after adjusting for traditional risk factors. In a prospective study, HDL-C independently predicted aneurysmal growth rate in multiple linear regression analysis (n=122, p=0.008) and was inversely associated with need for surgical repair (Adjusted hazard ratio: 0.18, 95 % confidence interval: 0.04�0.74, p=0.018). In a nation-wide Danish registry, we found lower mean HDL-C concentration in large AAA patients (n=6,560) compared with patients with aorto-iliac occlusive disease (n=23,496) (0.89 ± 2.99 vs 1.59 ± 5.74 mmol/l, p< 0.001). Finally, reduced mean aortic AAA diameter was observed in AngII-infused mice treated with ApoA-I mimetic peptide compared with saline-injected controls. In conclusion, ApoAI/ HDL-C systemic levels are negatively associated with AAA evolution. Therapies targeting HDL functionality could halt AAA formation.

Oxidative Stress in Human Atherothrombosis: Sources, Markers and Therapeutic Targets

Atherothrombosis remains one of the main causes of morbidity and mortality worldwide. The underlying pathology is a chronic pathological vascular remodeling of the arterial wall involving several pathways, including oxidative stress. Cellular and animal studies have provided compelling evidence of the direct role of oxidative stress in atherothrombosis, but such a relationship is not clearly established in humans and, to date, clinical trials on the possible beneficial effects of antioxidant therapy have provided equivocal results. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is one of the main sources of reactive oxygen species (ROS) in human atherothrombosis. Moreover, leukocyte-derived myeloperoxidase (MPO) and red blood cell-derived iron could be involved in the oxidative modification of lipids/lipoproteins (LDL/HDL) in the arterial wall. Interestingly, oxidized lipoproteins, and antioxidants, have been analyzed as potential markers of oxidative stress in the plasma of patients with atherothrombosis. In this review, we will revise sources of ROS, focusing on NADPH oxidase, but also on MPO and iron. We will also discuss the impact of these oxidative systems on LDL and HDL, as well as the value of these modified lipoproteins as circulating markers of oxidative stress in atherothrombosis. We will finish by reviewing some antioxidant systems and compounds as therapeutic strategies to prevent pathological vascular remodeling.

Preoperative Predictors of Long-Term Mortality after Elective Endovascular Aneurysm Repair for Abdominal Aortic Aneurysm

OBJECTIVE

This study aimed to clarify long-term mortality and its predictors in patients with abdominal aortic aneurysm (AAA) who underwent endovascular aneurysm repair (EVAR).

MATERIALS AND METHODS

Patients with AAA who underwent elective EVAR at Tokyo Medical and Dental University hospital between 2008 and 2011 were reviewed. The patients' data were retrospectively collected from medical records.

RESULTS

Sixty-four patients were identified for this study. In long-term follow-up, the survival rate was significantly lower in patients with high preoperative C-reactive protein (CRP) levels. Patients with obstructive lung disease (FEV1/FVC <70%) or anemia tended to have a poorer prognosis but the association was not statistically significant. Age, concurrent hyperlipidemia, and blood pressure levels were not predictors of mortality rates.

DISCUSSION

High CRP level, COPD, and anemia reflect inflammation, which is associated with the pathogenesis of AAA. These inflammatory markers are predictors of long-term mortality after EVAR for AAA as well as for other diseases.

CONCLUSIONS

A high preoperative CRP level was a predictor of increased long-term mortality in patients with AAA who underwent EVAR. No specific leading causes of death were identified for this increase in the mortality rate.

Prevalent cardiac, renal and cardiorenal damage in patients with advanced abdominal aortic aneurysms

Chronic kidney disease (CKD), cardiac damage (CD) and the combination of the two are associated with increased morbidity and death in patients admitted to vascular surgery units. We assessed the prevalence of cardiac and renal damage and cardiorenal syndrome (CRS) in 563 patients with abdominal aortic aneurysms (AAA) who underwent cardiac screening before either an endovascular procedure (EVAR) or open surgery (OS) for aneurysm repair. CD was defined by ≥stage B as per the ACC/AHA classification of congestive heart failure (CHF), while CKD was defined by estimated GFR <60 mL/min/1.73 m(2) (CKD-EPI). Anemia [World Health Organization (WHO) guidelines] and iron deficiency (ID) (criteria for CHF patients) were also calculated. AAA patients were stratified into the following groups: CD, CKD, CRS or none of these conditions [no risk factors (NoRF)]. The prevalence of isolated cardiac and renal structural damage, of combined cardiorenal damage and of ID was 24.1, 15.0, 20.6 and 23.4 %, respectively. The frequency of anemia (mostly unrecognized) among the groups increased from NoRF (12.8 %)/CKD (19 %)/CD (25 %) up to CRS (38.8 %). This large-scale observational study provides clues for the increased CD/CKD risk profiles of unselected AAA patients, and underlines the need for better identification of ID/anemia and for appropriate treatment of CKD and CD before these patients undergo EVAR/OS.

Multimodality imaging assessment of the deleterious role of the intraluminal thrombus on the growth of abdominal aortic aneurysm in a rat model

OBJECTIVES

To evaluate imaging changes occurring in a rat model of elastase-induced abdominal aortic aneurysm (AAA), with emphasis on the intraluminal thrombus (ILT) occurrence.

METHODS

The post-induction growth of the AAA diameter was characterized using ultrasound in 22 rats. ILT was reported on 13 rats that underwent 14 magnetic resonance imaging (MRI) 2-18 days post-surgery, and on 10 rats that underwent 18 fluoro-deoxyglucose (FDG) positron emission tomography (PET)/microcomputed tomography examinations 2-27 days post-surgery. Logistic regressions were used to establish the evolution with time of AAA length, diameter, ILT thickness, volume, stratification, MRI and FDG PET signalling properties, and histological assessment of inflammatory infiltrates.

RESULTS

All of the following significantly increased with time post-induction (p < 0.001): AAA length, AAA diameter, ILT maximal thickness, ILT volume, ILT iron content and related MRI signalling changes, quantitative uptake on FDG PET, and the magnitude of inflammatory infiltrates on histology. However, the aneurysm growth peak followed occurrence of ILT approximately 6 days after elastase infusion.

CONCLUSION

Our model emphasizes that occurrence of ILT precedes AAA peak growth. Aneurysm growth is associated with increasing levels of iron, signalling properties changes in both MRI and FDG PET, relating to its biological activities.

KEY POINTS

• ILT occurrence in AAA is associated with increasing FDG uptake and growth. • MRI signalling changes in ILT reflect activities such as haemorrhage and RBC trapping. • Monitoring ILT activities using MRI may require no exogenous contrast agent.

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.

Aortic Iron Overload With Oxidative Stress and Inflammation in Human and Murine Abdominal Aortic Aneurysm

Objective—

Although iron is an essential element for maintaining physiological function, excess iron leads to tissue damage caused by oxidative stress and inflammation. Oxidative stress and inflammation play critical roles for the development of abdominal aortic aneurysm (AAA). However, it has not been investigated whether iron plays a role in AAA formation through oxidative stress and inflammation. We, therefore, examined whether iron is involved in the pathophysiology of AAA formation using human AAA walls and murine AAA models.

Approach and Results—

Human aortic walls were collected from 53 patients who underwent cardiovascular surgery (non-AAA=34; AAA=19). Murine AAA was induced by infusion of angiotensin II to apolipoprotein E knockout mice. Iron was accumulated in human and murine AAA walls compared with non-AAA walls. Immunohistochemistry showed that both 8-hydroxy-2′-deoxyguanosine and CD68-positive areas were increased in AAA walls compared with non-AAA walls. The extent of iron accumulated area positively correlated with that of 8-hydroxy-2′-deoxyguanosine expression area and macrophage infiltration area in human and murine AAA walls. We next investigated the effects of dietary iron restriction on AAA formation in mice. Iron restriction reduced the incidence of AAA formation with attenuation of oxidative stress and inflammation. Aortic expression of transferrin receptor 1, intracellular iron transport protein, was increased in human and murine AAA walls, and transferrin receptor 1–positive area was similar to areas where iron accumulated and F4/80 were positive.

Conclusions—

Iron is involved in the pathophysiology of AAA formation with oxidative stress and inflammation. Dietary iron restriction could be a new therapeutic strategy for AAA progression.

Novel biomarkers of abdominal aortic aneurysm disease: identifying gaps and dispelling misperceptions

Abdominal aortic aneurysm (AAA) is a prevalent and potentially life-threatening disease. Early detection by screening programs and subsequent surveillance has been shown to be effective at reducing the risk of mortality due to aneurysm rupture. The aim of this review is to summarize the developments in the literature concerning the latest biomarkers (from 2008 to date) and their potential screening and therapeutic values. Our search included human studies in English and found numerous novel biomarkers under research, which were categorized in 6 groups. Most of these studies are either experimental or hampered by their low numbers of patients. We concluded that currently no specific laboratory markers allow screeing for the disease and monitoring its progression or the results of treatment. Further studies and studies in larger patient groups are required in order to validate biomarkers as cost-effective tools in the AAA disease.