Elevation of plasma high-density lipoproteins inhibits development of experimental abdominal aortic aneurysms

Restoring Vascular Smooth Muscle Cell Mitochondrial Function Attenuates Abdominal Aortic Aneurysm in Mice

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex vascular pathology without pharmaceutical interventions. This study aimed to evaluate whether restoring vascular smooth muscle cell (VSMC) mitochondrial function could prevent AAA development.

METHODS

Ang II (angiotensin II)-induced AAA was established in Ldlr-deficient mice, and the gene expression profiles in abdominal aortic tissues exhibiting varying degrees of severity were analyzed. Synthetic high-density lipoprotein (sHDL) formulated with Apoa1 mimetic peptide and phospholipids was evaluated for the protective effects on VSMC mitochondria. The therapeutic efficacy of sHDL was further investigated in Ang II-infusion and PPE (porcine pancreatic elastase)-induced AAA models.

RESULTS

VSMC mitochondrial damage intensified gradually during AAA development, which was confirmed in distinct AAA animal models and human tissues. sHDL accumulated in the aneurysmatic lesions and restored mitochondrial DNA levels and the expression of genes related to oxidative phosphorylation following Ang II infusion. In mouse primary VSMCs, sHDL maintained mitochondrial homeostasis by suppressing the upregulation of DRP1 (dynamin-related protein 1), a protein involved in mitochondrial fission, reducing the generation of reactive oxygen species, preventing the loss of mitochondrial membrane potential, and preserving mitochondrial respiratory capacity. Administration of sHDL decreased Ang II-induced AAA incidence (control versus treatment, 76% versus 40%; P<0.05) and maximum aortic diameters. The protective effects of sHDL were further validated in the PPE model, with reductions observed in maximum aortic diameters and aortic mitochondrial DNA loss. Post-Ang II infusion, administration of sHDL improved VSMC mitochondrial function and suppressed aneurysm growth in Apoe-deficient mice. Human AAA is characterized by mitochondrial dysfunction, and liver-derived HDL (high-density lipoprotein) components play a pivotal role in regulating gene expression in aortic tissues.

CONCLUSIONS

VSMC mitochondrial damage is a pivotal factor in the development of AAA. The utilization of sHDL nanoparticles represents a promising novel therapeutic approach for AAA, aimed at restoring VSMC mitochondrial function.

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.

Admission LDL-C and long-term mortality in patients with acute aortic dissection: a survival analysis in China

BACKGROUND

The level of blood lipid is closely related to prognosis in cardiovascular diseases. This study aims to analyze the effect of serum low-density lipoprotein cholesterol (LDL-C) levels on the long-term mortality in acute aortic dissection (AAD). A lower admission LDL-C level is associated with an increased risk of long-term mortality in AAD.

METHODS

We analyzed the data of 284 patients with AAD admitted to the First Affiliated Hospital of Shantou University Medical College from February 2016 to September 2019. Patients were followed up post-discharge. All patients were divided into either an LDL-C low-level group or an LDL-C high-level group according to the optimal cut-off point obtained by the receiver operating characteristic (ROC) curve. The endpoint outcome was long-term mortality in AAD. A survival analysis and Cox proportional hazards model were used.

RESULTS

According to the Youden index, the optimal cut-off point for LDL-C was 2.755 mmol/L. The Kaplan-Meier survival analysis curves showed that the long-term mortality of the LDL-C low-level group (<2.755 mmol/L) was significantly higher than that of the LDL-C high-level group (≥2.755 mmol/L) (log-rank χ2=13.912, P<0.001). After multivariate Cox regression analysis, LDL-C <2.755 mmol/L was still significantly associated with long-term mortality in AAD (HR=3.287, 95% CI: 1.637-6.600, P=0.001). In addition, cystatin C was also an independent risk factor for the long-term prognosis of AAD (HR=1.253, 95% CI: 1.057-1.486, P=0.009).

CONCLUSIONS

A lower admission LDL-C level may be associated with an increased risk of long-term mortality in AAD.

Macrophage Cholesterol Efflux Downregulation Is Not Associated with Abdominal Aortic Aneurysm (AAA) Progression

Recent studies have raised the possibility of a role for lipoproteins, including high-density lipoprotein cholesterol (HDLc), in abdominal aortic aneurysm (AAA). The study was conducted in plasmas from 39 large size AAA patients (aortic diameter > 50 mm), 81 small/medium size AAA patients (aortic diameter between 30 and 50 mm) and 38 control subjects (aortic diameter < 30 mm). We evaluated the potential of HDL-mediated macrophage cholesterol efflux (MCE) to predict AAA growth and/or the need for surgery. MCE was impaired in the large aortic diameter AAA group as compared with that in the small/medium size AAA group and the control group. However, no significant difference in HDL-mediated MCE capacity was observed in 3 different progression subgroups (classified according to growth rate < 1 mm per year, between 1 and 5 mm per year or >5 mm per year) in patients with small/medium size AAA. Moreover, no correlation was found between MCE capacity and the aneurysm growth rate. A multivariate Cox regression analysis revealed a significant association between lower MCE capacity with the need for surgery in all AAA patients. Nevertheless, the significance was lost when only small/medium size AAA patients were included. Our results suggest that MCE, a major HDL functional activity, is not involved in AAA progression.

IgG Anti-High Density Lipoprotein Antibodies Are Elevated in Abdominal Aortic Aneurysm and Associated with Lipid Profile and Clinical Features

High-density lipoproteins cholesterol (HDLc) levels are decreased in abdominal aortic aneurysm (AAA), which is hallmarked by autoimmunity and lipid aortic deposits. To investigate whether IgG anti-HDL antibodies were present in AAA and their potential association with clinical features, IgG anti-HDL and total IgG along with HDLc plasma levels were measured in 488 AAA patients and 184 controls from the Viborg Vascular (VIVA) study, and in tissue-conditioned media from AAA intraluminal thrombus and media layer samples compared to control aortas. Higher IgG anti-HDL levels were found in AAA compared to controls, even after correcting for total IgG, and after adjusting for potential confounders. IgG anti-HDL levels were correlated with aortic diameter in univariate and adjusted multivariate analyses. IgG anti-HDL antibodies were negatively associated with HDLc levels before and after correcting for potential confounders. Increased anti-HDL antibodies were identified in tissue-conditioned media from AAA samples compared to healthy aortas, with higher levels being observed in the media layer. In conclusion, increased IgG anti-HDL levels (both in plasma and in tissue) are linked to AAA, associated with aortic diameter and HDLc levels. These data suggest a potential immune response against HDL in AAA and support an emerging role of anti-HDL antibodies in AAA.

Impaired HDL (High-Density Lipoprotein)-Mediated Macrophage Cholesterol Efflux in Patients With Abdominal Aortic Aneurysm-Brief Report

Objective- The ability of HDL (high-density lipoprotein) to promote macrophage cholesterol efflux is considered the main HDL cardioprotective function. Abdominal aortic aneurysm (AAA) is usually characterized by cholesterol accumulation and macrophage infiltration in the aortic wall. Here, we aim to evaluate the composition of circulating HDL particles and their potential for promoting macrophage cholesterol efflux in AAA subjects. Approach and Results- First, we randomly selected AAA and control subjects from Spain. The AAA patients in the Spanish cohort showed lower plasma apoA-I levels concomitantly associated with low levels of plasma HDL cholesterol and the amount of preβ-HDL particles. We determined macrophage cholesterol efflux to apoB-depleted plasma, which contains mature HDL, preβ-HDL particles and HDL regulatory proteins. ApoB-depleted plasma from AAA patients displayed an impaired ability to promote macrophage cholesterol efflux. Next, we replicated the experiments with AAA and control subjects derived from Danish cohort. Danish AAA patients also showed lower apoA-I levels and a defective HDL-mediated macrophage cholesterol efflux. Conclusions- AAA patients show impaired HDL-facilitated cholesterol removal from macrophages, which could be mechanistically linked to AAA.

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.

The synthetic glycolipid-based TLR4 antagonist FP7 negatively regulates in vitro and in vivo haematopoietic and non-haematopoietic vascular TLR4 signalling

TLRs, including TLR4, have been shown to play a crucial role in cardiovascular inflammatory-based diseases. The main goal of this study was to determine the potential of FP7, a synthetic glycolipid active as a TLR4 antagonist, to modulate haematopoietic and non-haematopoietic vascular TLR4 pro-inflammatory signalling. HUVEC, human THP-1 monocytes, THP-1-derived macrophages, mouse RAW-264.7 macrophages and Angiotensin II-infused apolipoprotein E-deficient mice were in vitro and in vivo models, respectively. Western blotting, Ab array and ELISA approaches were used to explore the effect of FP7 on TLR4 functional activity in response to bacterial LPS (in vitro) and endogenous ligands of sterile inflammation (in vitro and in vivo). Following activation of TLR4, in vitro and in vivo data revealed that FP7 inhibited p38 MAPK and p65 NF-kB phosphorylation associated with down-regulation of a number of TLR4-dependent pro-inflammatory proteins. In addition to inhibition of LPS-induced TLR4 signalling, FP7 negatively regulated TLR4 activation in response to ligands of sterile inflammation (hydroperoxide-rich oxidised LDL, in vitro and Angiotensin II infusion, in vivo). These results demonstrate the ability of FP7 to negatively regulate in vitro and in vivo haematopoietic and non-haematopoietic vascular TLR4 signalling both in humans and mice, suggesting the potential therapeutic use of this TLR4 antagonist for pharmacological intervention of vascular inflammatory diseases.

High-Density Lipoprotein Is Associated with Progression of Intracranial Aneurysms

BACKGROUND

We tested the hypothesis that high-density lipoprotein (HDL) is associated with intracranial aneurysm growth and rupture.

METHODS

We used an observational cohort study design. Age, sex, admission systolic blood pressure (SBP), diabetes, hypertension, coronary artery disease, aneurysmal rupture, apolipoprotein (APO)-A1, APO-B, HDL, low-density lipoprotein, triglycerides, cholesterol, and aneurysm location and size were recorded. Aneurysms <8 mm were categorized as small.

RESULTS

The data from 581 patients with intracranial aneurysms were analyzed. The predictive factors for small size of aneurysms were female sex (odds ratio [OR], 0.630; 95% confidence interval [CI], 0.428-0.927; P = 0.019) and higher HDL (OR, 0.327; 95% CI, 0.159-0.672; P = 0.0002). In the subgroup of male patients, lower HDL was the only risk factor for large size (P = 0.015). The predictors of aneurysmal rupture were small size (OR, 0.875; 95% CI, 0.842-0.910; P = 0.000), higher HDL (OR, 3.716; 95% CI, 1.623-8.509; P = 0.002), no coronary artery disease (OR, 4.736; 95% CI, 1.528-14.681; P = 0.007), lower APO-A1 (OR, 0.202; 95% CI, 0.064-0.641; P = 0.007), and higher admission SBP (OR, 1.024; 95% CI, 1.015-1.032; P = 0.000). An HDL/aneurysm size ratio >0.31 was associated with a 46.2-fold increased likelihood of aneurysmal rupture (OR, 46.214; 95% CI, 13.386-159.548; P = 0.002).

CONCLUSIONS

The HDL level was inversely associated with intracranial aneurysm growth, especially in men. Higher HDL levels and small aneurysm size contributed to a greater risk of aneurysmal rupture. An HDL/size ratio >0.31 was a valuable predictor of intracranial rupture.

Lipid-Lowering Agents and High HDL (High-Density Lipoprotein) Are Inversely Associated With Intracranial Aneurysm Rupture

BACKGROUND AND PURPOSE

Growing evidence from experimental animal models and clinical studies suggests the protective effect of statin use against rupture of intracranial aneurysms; however, results from large studies detailing the relationship between intracranial aneurysm rupture and total cholesterol, HDL (high-density lipoprotein), LDL (low-density lipoprotein), and lipid-lowering agent use are lacking.

METHODS

The medical records of 4701 patients with 6411 intracranial aneurysms diagnosed at the Massachusetts General Hospital and the Brigham and Women's Hospital between 1990 and 2016 were reviewed and analyzed. Patients were separated into ruptured and nonruptured groups. Univariable and multivariable logistic regression analyses were performed to determine the effects of lipids (total cholesterol, LDL, and HDL) and lipid-lowering medications on intracranial aneurysm rupture risk. Propensity score weighting was used to account for differences in baseline characteristics of the cohorts.

RESULTS

Lipid-lowering agent use was significantly inversely associated with rupture status (odds ratio, 0.58; 95% confidence interval, 0.47-0.71). In a subgroup analysis of complete cases that includes both lipid-lowering agent use and lipid values, higher HDL levels (odds ratio, 0.95; 95% confidence interval, 0.93-0.98) and lipid-lowering agent use (odds ratio, 0.41; 95% confidence interval, 0.23-0.73) were both significantly and inversely associated with rupture status, whereas total cholesterol and LDL levels were not significant. A monotonic exposure-response curve between HDL levels and risk of aneurysmal rupture was obtained.

CONCLUSIONS

Higher HDL values and the use of lipid-lowering agents are significantly inversely associated with ruptured intracranial aneurysms.

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.

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.

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.

High density lipoproteins are modulators of protease activity: Implications in inflammation, complement activation, and atherothrombosis

High density lipoproteins (HDL) represent a compositionally diverse population of particles in the circulation, containing a wide variety of lipids and proteins. Gene ontology functional analysis of the 96 commonly identified HDL binding proteins reveals that almost half of these proteins are either proteases or have known roles in protease regulation. Here, we discuss the activities of some of these proteins in regard to their roles in regulating proteases involved in inflammation, coagulation, and complement activation, particularly in the context of atherosclerosis. The overall goal of this review is to discuss potential functional roles of HDL in protease regulatory pathways based on current literature and known functions of HDL binding proteins and to promote the consideration of HDL as a global modulator of proteolytic equilibrium.

Increased Expression of Lamin A/C Correlate with Regions of High Wall Stress in Abdominal Aortic Aneurysms

BACKGROUND

Since aortic diameter is the most -significant risk factor for rupture, we sought to identify stress-dependent changes in gene expression to illuminate novel molecular processes in aneurysm rupture.

MATERIALS AND METHODS

We constructed finite element maps of abdominal computerized tomography scans (CTs) of seven abdominal aortic aneurysm (AAA) patients to map wall stress. Paired biopsies from high- and low-stress areas were collected at surgery using vascular landmarks as coordinates. Differential gene expression was evaluated by Illumina Array analysis, using the whole genome DNA-mediated, annealing, selection, extension, and ligation (DASL) gene chip (n = 3 paired samples).

RESULTS

The sole significant candidate from this analysis, Lamin A/C, was validated at the protein level, using western blotting. Lamin A/C expression in the inferior mesenteric vein (IMV) of AAA patients was compared to a control group and in aortic smooth muscle cells in culture in response to physiological pulsatile stretch. -Areas of high wall stress (n = 7) correlate to those -regions which have the thinnest walls [778 µm (585-1120 µm)] in comparison to areas of lowest wall stress [1620 µm (962-2919 µm)]. Induced expression of Lamin A/C -correlated with areas of high wall stress from AAAs but was not significantly induced in the IMV from AAA patients compared to controls (n = 16). Stress-induced expression of Lamin A/C was mimicked by exposing aortic smooth muscle cells to prolonged pulsatile stretch.

CONCLUSION

Lamin A/C protein is specifically increased in areas of high wall stress in AAA from patients, but is not increased on other vascular beds of aneurysm patients, suggesting that its elevation may be a compensatory response to the pathobiology leading to aneurysms.

Associations of ApoAI and ApoB-containing lipoproteins with AngII-induced abdominal aortic aneurysms in mice

OBJECTIVE

Dyslipidemia is implicated in abdominal aortic aneurysms (AAAs) in humans and angiotensin (Ang) II-infused mice. This study determined effects of major lipoprotein classes on AngII-induced AAAs using multiple mouse strains with dietary and pharmacological manipulations.

APPROACH AND RESULTS

Western diet had minor effects on plasma cholesterol concentrations and the low incidence of AngII-induced AAAs in C57BL/6J mice. Low incidence of AAAs in this strain was not attributed to protection from high-density lipoprotein, because apolipoprotein (apo) AI deficiency did not increase AngII-induced AAAs. ApoAI deletion also failed to alter AAA occurrence in hypercholesterolemic mice. Low-density lipoprotein receptor-/- mice fed normal diet had low incidence of AngII-induced AAAs. Western diet feeding of this strain provoked pronounced hypercholesterolemia because of increased apoB-containing lipoproteins with attendant increases of atherosclerosis in both sexes, but AAAs only in male mice. ApoE-deficient mice fed normal diet were modestly hypercholesterolemic, whereas this strain fed Western diet was severely hypercholesterolemic because of increased apoB-containing lipoprotein concentrations. The latter augmented atherosclerosis, but did not change the high incidence of AAAs in this strain. To determine whether reductions in apoB-containing lipoproteins influenced AngII-induced AAAs, ezetimibe was administered at a dose that partially reduced plasma cholesterol concentrations to ApoE-deficient mice fed Western diet. This decreased atherosclerosis, but not AAAs. This ezetimibe dose in ApoE-deficient mice fed normal diet significantly decreased plasma apoB-containing lipoprotein concentrations and reduced AngII-induced AAAs.

CONCLUSIONS

ApoB-containing lipoproteins contribute to augmentation of AngII-induced AAA in male mice. However, unlike atherosclerosis, AAA occurrence was not correlated with increases in plasma apoB-containing lipoprotein concentrations.

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.

Effects of long-term chloroquine administration on the natural history of aortic aneurysms in mice

Autophagy regulates cellular homeostasis and integrates the cellular pro-survival machinery. We investigated the role of autophagy in the natural history of murine abdominal aortic aneurysms (AAA). ApoE(-/-) mice were implanted with saline- or angiotensin II (Ang-II)-filled miniosmotic pumps then treated with either the autophagy inhibitor chloroquine (CQ; 50 mg·(kg body mass)(-1)·day(-1), by intraperitoneal injection) or saline. Ang-II-elicited aneurysmal expansion of the suprarenal aorta coupled with thrombus formation were apparent 8 weeks later. CQ had no impact on the incidence (50% for Ang-II compared with 46.2% for Ang-II + CQ; P = NS) and categorical distribution of aneurysms. The markedly reduced survival rate observed with Ang-II (57.1% for Ang-II compared with 100% for saline; P < 0.05) was unaffected by CQ (61.5% for Ang-II + CQ; P = NS compared with Ang-II). CQ did not affect the mean maximum suprarenal aortic diameter (1.91 ± 0.19 mm for Ang-II compared with 1.97 ± 0.21 mm for Ang-II + CQ; P = NS). Elastin fragmentation, collagen accumulation, and smooth muscle attrition, which were higher in Ang-II-treated mice, were unaffected by CQ treatment. Long-term CQ administration does not affect the natural history and prognosis of experimental AAA, suggesting that global loss of autophagy is unlikely to be a causal factor in the development of aortic aneurysms. Manipulation of autophagy as a mechanism to reduce AAA may need re-evaluation.

A peptide antagonist of thrombospondin-1 promotes abdominal aortic aneurysm progression in the angiotensin II-infused apolipoprotein-E-deficient mouse

OBJECTIVE

Interaction of the activating sequence in thrombospondin-1 (TSP-1) with the conserved sequence (leucine-serine-lysine-leucine [LSKL]) in the latency-associated peptide region of latent transforming growth factor (TGF)-β complex is important in regulating TGF-β1 activity. We aimed to assess the effect of blocking peptide LSKL on the progression of pre-established abdominal aortic aneurysm in angiotensin II-infused apolipoprotein E-deficient (ApoE(-/-)) mice.

APPROACH AND RESULTS

Abdominal aortic aneurysm was established in 3-month-old male ApoE(-/-) mice with subcutaneous infusion of angiotensin II for 28 days. After this, mice received LSKL peptide or control SLLK (serine-leucine-leucine-lysine) peptide (4 mg/kg) via daily intraperitoneal injection for an additional 2 weeks. Administration of LSKL peptide promoted larger suprarenal aortic diameter, as determined by ultrasound and morphometric analysis, and stimulated more severe atherosclerosis within the aortic arch. In addition, mice receiving LSKL peptide exhibited elevated circulating proinflammatory cytokine levels and greater inflammatory cells within the suprarenal aorta compared with controls. Mice receiving LSKL peptide showed low plasma TGF-β1 activity and low levels of aortic tissue phosphorylated to total Smad2/3. Aortic gene expression of TGF-β receptor 1 (TGFBRI) and receptor 2 (TGFBRII), but not TGF-β1 and thrombospondin-1, were lower in mice receiving LSKL peptide than controls. LSKL peptide administration was associated with greater aortic elastin fragmentation and lower expression and activity of the TGF-β1-target gene lysyl oxidase like 1 (LOXL1).

CONCLUSIONS

Attenuation of thrombospondin-1-directed activation of TGF-β1 promotes abdominal aortic aneurysm and atherosclerosis progression in the angiotensin II-infused ApoE(-/-) mouse model.

SEPP1 gene variants and abdominal aortic aneurysm: gene association in relation to metabolic risk factors and peripheral arterial disease coexistence

An inadequate selenium level is supposed to be a risk factor for cardiovascular diseases. However little is known about variation of the genes encoding selenium-containing proteins that would confirm the causality in these diseases. The aim of this study was to analyze the relationships between two functional variants of selenoprotein P gene (SEPP1 rs3877899G>A, rs7579G>A) and the occurrence of abdominal aortic aneurysm (AAA) and aortoiliac occlusive disease (AIOD), as well as their metabolic risk factors. In AAA, the rs3877899A allele was associated with higher systolic blood (P < .003) and pulse pressure (P < .003) values (recessive model), and with coexistence of peripheral arterial disease (PAD; carriers: P = .033). The other SEPP1 variants were associated with BMI values and influenced the risk of aortic diseases, depending on body weight. The strongest associations in the case-control analysis was found between the presence of the rs3877899G-rs7579G haplotype and development of AAA in overweight and obese subjects (OR = 1.80, 95%CI = 1.16-2.79, P = .008). The higher BMI values were correlated with lower age of AAA patients and larger size of aneurysm. Our results suggests the potential role of the selenoprotein P in pathogenesis of AAA. Future studies should consider the role of the rs3877899G-rs7579G haplotype as a risk factor for aggressive-growing AAAs.

Angiotensin II induces region-specific medial disruption during evolution of ascending aortic aneurysms

Angiotensin II (Ang II) promotes development of ascending aortic aneurysms (AAs), but progression of this pathology is undefined. We evaluated factors potentially involved in progression, and determined the temporal sequence of tissue changes during development of Ang II-induced ascending AAs. Ang II infusion into C57BL/6J mice promoted rapid expansion of the ascending aorta, with significant increases within 5 days, as determined by both in vivo ultrasonography and ex vivo sequential acquisition of tissues. Rates of expansion were not significantly different in LDL receptor-null mice fed a saturated fat-enriched diet, demonstrating a lack of effect of hypercholesterolemia. Augmenting systolic blood pressure with norepinephrine infusion had no significant effect on ascending aortic expansion. Pathological changes observed within 5 days of Ang II infusion included increased medial thickness and intramural hemorrhage characterized by erythrocyte extravasation in outer lamellar layers of the media. Intramedial hemorrhage was not observed after prolonged Ang II infusion, although partial medial disruption was present. Elastin fragmentation and transmural medial breaks of the ascending aorta were observed with continued Ang II infusion, which were restricted to anterior aspects. CD45(+) cells accumulated in adventitia but were minimal in media. Similar pathology was observed in tissues obtained from patients with ascending AAs. In conclusion, Ang II promotes ascending AAs through region-specific changes that are independent of hypercholesterolemia or systolic blood pressure.

Influence of apolipoprotein E, age and aortic site on calcium phosphate induced abdominal aortic aneurysm in mice

OBJECTIVE

To assess relevant features of abdominal aortic aneurysms (AAA) induced by calcium phosphate within a mouse model. Specifically we investigated: (1) whether apolipoprotein E deficiency and older age promoted AAA formation, and (2) whether the local application of calcium phosphate affected the size of distant aortic segments.

METHODS

AAA was induced by application of calcium phosphate to the infra-renal aortas of 3 and 7 month old male mice. AAA induction was assessed by calculating expansion of the infra-renal aortic diameter over 1-4 weeks. Aortic samples were assessed to quantify calcification, macrophages infiltration, elastic lamellar degradation and apoptosis. Blood pressure was measured by the tail cuff method, and plasma concentrations of total cholesterol, low density lipoprotein and very low density lipoprotein cholesterol, and pro-inflammatory cytokines were measured using commercially available kits. The maximum diameters of the aortic arch, thoracic and supra-renal aorta at sacrifice were measured by morphometry and the mean maximal diameter of these three aortic segments was calculated.

RESULTS

The median expansion of the infra-renal aorta 2 weeks after AAA induction was significantly greater in apolipoprotein E deficient (ApoE(-/-)) mice than in age- and gender-matched wild type controls [275.8% (IQR 193.8%-348.5%) versus 94.7% (IQR 47.8%-163.4%), P = 0.02]. The greater aortic expansion in ApoE(-/-) mice was associated with aortic calcification, macrophage infiltration, elastic lamellar degradation and apoptosis of cells in the media and adventitia. The plasma low density lipoprotein/very low density lipoprotein cholesterol concentrations 2 weeks after AAA induction were positively correlated with the expansion of the infra-renal aorta induced by calcium phosphate. The median expansion of the infra-renal aorta 2 weeks after AAA induction was similar in 3 and 7 month old wild type mice. The local administration of calcium phosphate was associated with an increase in the mean maximal diameter of distant aortic segments, but not associated with changes in the concentrations of pro-inflammatory markers in either the plasma or the spleen.

CONCLUSION

This study suggests that apolipoprotein E deficiency, but not age, predisposes to AAA induced within the calcium phosphate model. Increased AAA expansion in ApoE(-/-) mice was associated with calcification, macrophage infiltration, elastic lamellar degradation, and cell apoptosis. Local application of calcium phosphate also promoted dilation of distant aortic segments.

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.

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.