Proteolysis of the abdominal aortic aneurysm wall and the association with rupture

Sex-based outcomes in surgical repair of acute type A aortic dissection: A meta-analysis and meta-regression

OBJECTIVE

Epidemiologic variation with respect to sex has been established in aortic dissection. However, current literature on sex-based outcomes in patients with aortic dissection is conflicting. In this study we aimed to compare perioperative outcomes according to sex in patients treated surgically for acute type A aortic dissection.

METHODS

PubMed/MEDLINE, Embase, and Web of Science were searched for studies that reported sex-based differences in postoperative outcomes among patients with acute type A aortic dissection. The primary outcome was in-hospital/30-day mortality, and secondary outcomes included postoperative stroke, renal failure requiring dialysis, and reoperation for bleeding. Data were aggregated using the random effects model as pooled risk ratio (RR). Meta-regression was applied to identify sources of heterogeneity between studies.

RESULTS

Nine of 1022 studies were included for final analysis comprising 3338 female and 5979 male participants. Compared with male sex, female sex was associated with similar in-hospital/30-day mortality (RR, 1.04; 95% CI, 0.85-1.28; P = .67), postoperative stroke risk (RR, 1.07; 95% CI, 0.91-1.25; P = .43), and postoperative risk of acute renal failure requiring dialysis (RR, 0.84; 95% CI, 0.59-1.19; P = .32). A decreased risk of reoperation for bleeding (RR, 0.84; 95% CI, 0.75-0.94; P < .01) was observed in female participants. Meta-regression analysis indicated that differences in preoperative shock were a source of heterogeneity in the sex difference in in-hospital/30-day mortality across studies.

CONCLUSIONS

Among patients treated surgically for acute type A aortic dissection, female sex was not associated with increased risk of short-term mortality nor with major postoperative complications. Male sex was associated with a greater risk of postoperative bleeding.

MiR-30c-1-3p targets matrix metalloproteinase 9 involved in the rupture of abdominal aortic aneurysms

Abstract

Abdominal aortic aneurysm (AAA) can be fatal if ruptured, but there is no predictive biomarker. Our aim was to evaluate the prognostic potential of microRNAs (miRNAs/miRs) in an AAA mouse model and patients with unruptured AAA (URAAA) and ruptured AAA (RAAA). Among the 64 miRNAs differentially expressed in mice with AAA compared to control, miR-30c-1-3p, miR-432-3p, miR-3154, and miR-379-5p had high homology with human miRNAs. MiR-30c-1-3p plasma levels were significantly lower in patients with RAAA than in those with URAAA or control and tended to negatively correlate with the maximum aortic diameter (r =  −0.3153, P = 0.06109). MiR-30c-1-3p targeted matrix metalloproteinase (MMP)-9 mRNA through the coding region and downregulated its expression in vitro. MMP-9 plasma concentrations were significantly higher in the RAAA group than in the URAAA group (P < 0.001) and were negatively associated with miR-30c-1-3p levels (r =  −0.3671, P = 0.01981) and positively–with the maximal aortic diameter (r = 0.6251, P < 0.0001). The optimal cutoff values for MMP-9 expression and the maximal aortic diameter were 461.08 ng/ml and 55.95 mm, with areas under the curve of 0.816 and 0.844, respectively. Our results indicate that plasma levels of miR-30c-1-3p and MMP-9 may be candidate biomarkers of AAA progression.

Key messages

Downregulation of miR-30c-1-3p expression and upregulation of its potential target MMP-9 are predictors of the devastation of AAA.

Downregulation of miR-30c-1-3p expression and its downstream impact on MMP-9 have a potential on predicting the development and rupture of AAA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-022-02230-2.

Evaluation of Prognosis and Risk of Death by Neutrophil/Lymphocyte Ratio, C-Reactive Protein/Albumin Ratio and Plasma D-Dimer in Patients with Pulmonary Thromboembolism

Objective

To investigate the relationship between neutrophil/lymphocyte ratio, C-reactive protein/albumin ratio, plasma D-dimer and prognosis in patients with pulmonary thromboembolism, and to evaluate the risk of death.

Methods

We retrospectively analyzed peripheral hematology and coagulation-related indicators of 362 pulmonary thromboembolism patients and 32 normal people, and the differences between the patients and control group and between good and poor prognosis groups were compared. And we analyzed and compared separate detection and combined detection of neutrophil/lymphocyte ratio, C-reactive protein/albumin ratio and D-dimer on the efficiency of risk of death in patients.

Results

① Neutrophil/lymphocyte ratio of pulmonary thromboembolism patients was 8.96±1.94, significantly higher than that of control group 1.76±0.53 (t=2.4281, P<0.05). C-reactive protein/albumin ratio was 2.13±2.08, significantly higher than 0.03±0.01 in control group (t=20.7736, P<0.01). D-dimer was 9.69±8.61mg/L, significantly higher than 0.20±0.11mg/L in control group (t=3.0066, P<0.01). ② Hemoglobin, lymphocyte, albumin and lymphocyte/monocyte ratio in patients with good prognosis were significantly lower than those in poor prognosis group, while white blood cell, C-creative protein, neutrophil, C-reactive protein/albumin ratio, neutrophil/lymphocyte ratio and D-dimer were significantly lower than those in poor prognosis group (P all <0.05). ③ Regression analysis showed that neutrophil/lymphocyte ratio (P=0.007), C-reactive protein/albumin ratio (P=0.010) and D-dimer (P=0.003) were independent prognostic factors for pulmonary thromboembolism. ④ In assessing the risk of death of patients, D-dimer alone had the highest sensitivity (93.1%), and C-reactive protein/albumin ratio alone had the highest specificity (68.8%). The combined detection of these three indicators had higher sensitivity (86.2%) and higher specificity (67.6%) at the same time. ⑤ The area under receiver operating characteristic curve for combined detection of neutrophil/lymphocyte ratio, C-reactive protein/albumin ratio and D-dimer was the largest (up to 0.821).

Conclusion

Patients with pulmonary thromboembolism highly expressed in neutrophil/lymphocyte ratio, C-reactive protein/albumin ratio and D-dimer. The combined detection of these three indicators can improve the assessment efficacy of the risk of death in patients with pulmonary thromboembolism.

Fcγ receptor activation mediates vascular inflammation and abdominal aortic aneurysm development

BACKGROUND

Abdominal aortic aneurysm (AAA), a degenerative vascular pathology characterized by permanent dilation of the aorta, is considered a chronic inflammatory disease involving innate/adaptive immunity. However, the functional role of antibody-dependent immune response against antigens present in the damaged vessel remains unresolved. We hypothesized that engagement of immunoglobulin G (IgG) Fc receptors (FcγR) by immune complexes (IC) in the aortic wall contributes to AAA development. We therefore evaluated FcγR expression in AAA lesions and analysed whether inhibition of FcγR signaling molecules (γ-chain and Syk kinase) influences AAA formation in mice.

METHODS

FcγR gene/protein expression was assessed in human and mouse AAA tissues. Experimental AAA was induced by aortic elastase perfusion in wild-type (WT) mice and γ-chain knockout (γKO) mice (devoid of activating FcγR) in combination with macrophage adoptive transfer or Syk inhibitor treatment. To verify the mechanisms of FcγR in vitro, vascular smooth muscle cells (VSMC) and macrophages were stimulated with IgG IC.

RESULTS

FcγR overexpression was detected in adventitia and media layers of human and mouse AAA. Elastase-perfused γKO mice exhibited a decrease in AAA incidence, aortic dilation, elastin degradation, and VSMC loss. This was associated with (1) reduced infiltrating leukocytes and immune deposits in AAA lesions, (2) inflammatory genes and metalloproteinases downregulation, (3) redox balance restoration, and (4) converse phenotype of anti-inflammatory macrophage M2 and contractile VSMC. Adoptive transfer of FcγR-expressing macrophages aggravated aneurysm in γKO mice. In vitro, FcγR deficiency attenuated inflammatory gene expression, oxidative stress, and phenotypic switch triggered by IC. Additionally, Syk inhibition prevented IC-mediated cell responses, reduced inflammation, and mitigated AAA formation.

CONCLUSION

Our findings provide insight into the role and mechanisms mediating IgG-FcγR-associated inflammation and aortic wall injury in AAA, which might represent therapeutic targets against AAA disease.

LncRNA H19 regulates smooth muscle cell functions and participates in the development of aortic dissection through sponging miR-193b-3p

BACKGROUND

Multiple studies showed that long-chain noncoding RNA H19 (LncRNA H19) is high-expressed in human and mouse abdominal aortic aneurysms (AAAs). We speculated that it plays an important role in arterial disease, and therefore studied the role and mechanism of H19 in aortic dissection (AD).

METHODS

The expressions of related genes in human aortic smooth muscle cells (HASMCs) induced by platelet-derived growth factor BB (PDGF-BB) or in the aortic tissue of AD patients/mice were identified by Western blot and quantitative real-time polymerase chain reaction. The targeting relationship between H19 and miR-193b-3p was predicted and verified by bioinformatics analysis, dual luciferase assay, RNA pull-down assay, RNA immunoprecipitation (RIP), and Pearson correlation coefficient. The H19 and miR-193b-3p effects on the biological functions of tissues and cells were examined by MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide, thiazolyl blue tetrazolium bromide) assay, wound-healing assay, and Hematoxylin-Eosin (HE) staining.

RESULTS

LncRNA H19 was abnormally high-expressed in thoracic aorta tissues of AD patients, and it could competitively bind to and inhibit miR-193b-3p. In the PDGF-BB group, the expressions of H19, matrix metallopeptidase (MMP) 2 (MMP-2) and MMP-9 were up-regulated and the expressions of miR-193b-3p, α-SMA, and SM22α were down-regulated; moreover, the proliferation and migration rate of HASMCs were increased. However, H19 silencing reversed the regulation of PDGF-BB on HASMCs. More interestingly, miR-193b-3p inhibitor could partially reverse the effect of H19 silencing. In addition, the above results were verified by animal experiments, showing that shH19 and up-regulated miR-193b-3p could significantly reduce the thoracic aorta pathological damage in AD mice.

CONCLUSION

LncRNA H19 regulated smooth muscle cell function by sponging miR-193b-3p and it participated in the development of AD.

Tissue-specific relaxin-2 is differentially associated with the presence/size of an arterial aneurysm and the severity of atherosclerotic disease in humans

Circulating or tissue-related biomarkers are of clinical value for risk stratification in patients with abdominal aortic aneurysms. Relaxin-2 (RL2) has been linked to the presence and size of arterial aneurysms, and to the extent of atherosclerosis in human subjects. Here, we assessed the expression levels of RL2 in aneurysmal (AA, n = 16) and atherosclerotic (ATH, n = 22) arteries, and established the correlation between RL2 levels and the presence/size of AA and the clinical severity of atherosclerosis. The expression levels of metalloproteinases (MMPs) and endothelial nitric oxide synthetase (eNOS) were also detected for correlations with different phenotypes of atherosclerosis and AA. Temporal artery biopsy specimens (n = 6) and abdominal aortic tissues harvested from accident victims during autopsy (n = 10) were used as controls. Quantitative tissue biomarker analysis revealed that tissue-specific RL2 was increased in patients with larger or symptomatic AA compared to subjects with atherosclerotic disease and healthy controls. In situ RL2 levels were proportional to the size and the severity of aneurysmatic disease, and were substantially elevated in patients with symptomatic aneurysm of any diameter or asymptomatic aneurysm of a diameter >350% of that of the normal artery. In contrast, tissue RL2 was inversely associated with the clinical severity of atherosclerotic lesions. Correlation between RL2 and MMP2 was different between ATH1 and ATH2, depending on atherosclerosis grade. Overall, tissue RL2 is differentially associated with discrete phenotypes of arterial disease and might exert multipotent biological effects on vascular wall integrity and remodeling in human subjects.

Targeted Gold Nanoparticles as an Indicator of Mechanical Damage in an Elastase Model of Aortic Aneurysm

Elastin is a key structural protein and its pathological degradation deterministic in aortic aneurysm (AA) outcomes. Unfortunately, using current diagnostic and clinical surveillance techniques the integrity of the elastic fiber network can only be assessed invasively. To address this, we employed fragmented elastin-targeting gold nanoparticles (EL-AuNPs) as a diagnostic tool for the evaluation of unruptured AAs. Electron dense EL-AuNPs were visualized within AAs using micro-computed tomography (micro-CT) and the corresponding Gold-to-Tissue volume ratios quantified. The Gold-to-Tissue volume ratios correlated strongly with the concentration (0, 0.5, or 10 U/mL) of infused porcine pancreatic elastase and therefore the degree of elastin damage. Hyperspectral mapping confirmed the spatial targeting of the EL-AuNPs to the sites of damaged elastin. Nonparametric Spearman's rank correlation indicated that the micro-CT-based Gold-to-Tissue volume ratios had a strong correlation with loaded (ρ = 0.867, p-val = 0.015) and unloaded (ρ = 0.830, p-val = 0.005) vessel diameter, percent dilation (ρ = 0.976, p-val = 0.015), circumferential stress (ρ = 0.673, p-val = 0.007), loaded (ρ = - 0.673, p-val = 0.017) and unloaded (ρ = - 0.697, p-val = 0.031) wall thicknesses, circumferential stretch (ρ = - 0.7234, p-val = 0.018), and lumen area compliance (ρ = - 0.831, p-val = 0.003). Likewise, in terms of axial force and axial stress vs. stretch, the post-elastase vessels were stiffer. Collectively, these findings suggest that, when combined with CT imaging, EL-AuNPs can be used as a powerful tool in the non-destructive estimation of mechanical and geometric features of AAs.

Expression of MMP-2, MMP-9, and NGAL in Tissue and Serum of Patients with Vascular Aneurysms and Their Modulation by Statin Treatment: A Pilot Study

BACKGROUND

Matrix metalloproteinases (MMPs) are involved in vascular wall degradation, and drugs able to modulate MMP activity can be used to prevent or treat aneurysmal disease. In this study, we evaluated the effects of statins on MMP-2, MMP-9, and neutrophil gelatinase-associated lipocalin (NGAL) in both plasma and tissue in patients with aneurysmal disease.

METHODS

We performed a prospective, single-blind, multicenter, control group clinical drug trial on 184 patients of both sexes >18 years old with a diagnosis of arterial aneurysmal disease. Enrolled patients were divided into two groups: Group I under statin treatment and Group II not taking statins. In addition, 122 patients without aneurysmal disease and under statin treatment were enrolled as a control group (Group III). The expression of MMPs and NGAL in plasma was evaluated using ELISA, while their expression in endothelial tissues was evaluated using Western blot.

RESULTS

The ELISA test revealed greater plasma levels (p < 0.01) of MMPs and NGAL in Groups I and II vs. Group III. Western blot analysis showed higher expression (p < 0.01) of MMPs and NGAL in Group II vs. Group I, and this increase was significantly higher (p < 0.01) in patients treated with low potency statins compared to high potency ones.

CONCLUSIONS

MMPs and NGAL seem to play a major role in the development of aneurysms, and their modulation by statins suggests that these drugs could be used to prevent arterial aneurysmal disease.

Pathogenic mechanisms and the potential of drug therapies for aortic aneurysm

Aortic aneurysm is a permanent focal dilation of the aorta. It is usually an asymptomatic disease but can lead to sudden death due to aortic rupture. Aortic aneurysm-related mortalities are estimated at ∼200,000 deaths per year worldwide. Because no pharmacological treatment has been found to be effective so far, surgical repair remains the only treatment for aortic aneurysm. Aortic aneurysm results from changes in the aortic wall structure due to loss of smooth muscle cells and degradation of the extracellular matrix and can form in different regions of the aorta. Research over the past decade has identified novel contributors to aneurysm formation and progression. The present review provides an overview of cellular and noncellular factors as well as enzymes that process extracellular matrix and regulate cellular functions (e.g., matrix metalloproteinases, granzymes, and cathepsins) in the context of aneurysm pathogenesis. An update of clinical trials focusing on therapeutic strategies to slow abdominal aortic aneurysm growth and efforts underway to develop effective pharmacological treatments is also provided.

The Relationship between the Concentration of Cathepsin A, D, and E and the Concentration of Copper and Zinc, and the Size of the Aneurysmal Enlargement in the Wall of the Abdominal Aortic Aneurysm

BACKGROUND

Despite advances in diagnostics and treatment, aortic aneurysms are an important clinical problem, mainly due to the accompanying complications that may lead to direct loss of life, also the number of diagnosed and operated aneurysms is constantly increasing. The aim of this study is to determine the relationship between the concentration of lysosomal peptidases cathepsin A, D, and E in the wall of the abdominal aortic aneurysm and the concentration of copper and zinc, and the size of the aneurysm widening in the wall of the abdominal aortic aneurysm.

METHODS

The study included 27 patients with abdominal aortic aneurysm from the Department of Vascular Surgery and Transplantation of the University Clinical Hospital in Bialystok. The research material was the wall of the abdominal aortic aneurysm collected intraoperatively. The control material consisted of fragments of the abdominal aorta obtained from organ donors for transplantation. The concentration of cathepsin A, D, and E was determined using enzyme-linked immunosorbent assays. Concentrations of copper and zinc were determined by flame atomic absorption spectrometry after prior mineralization of the samples. All patients were interviewed and asked about basic demographic data, comorbidities, and risk factors for cardiovascular disease to which they were exposed in the past. The statistical analysis was performed using Statistica 10 statistical package. Mann-Whitney U-tests were used and also Spearman's r correlation assuming a significance level of P < 0.05.

RESULTS

The concentration of cathepsin A, D, and E was higher in the aortic wall altered by the aneurysm than in the wall of the control aorta (P < 0.05). The analysis of the data showed that there was a positive correlation between the concentration of cathepsin A and D and the width of the aneurysmal widening (r = 0.699 and 0.750, respectively). There was no correlation between cathepsin E concentration and aneurysm width.

CONCLUSIONS

The higher contents of cathepsin A, D, and E in the wall of the aortic aneurysm than in the normal aortic wall, as well as a positive correlation between the concentration of cathepsin A and D and the width of the aneurysmal widening, allow to assume the participation of these enzymes in the pathogenesis of the aneurysm.

Platelet Inhibitors Reduce Rupture in a Mouse Model of Established Abdominal Aortic Aneurysm

OBJECTIVE

Rupture of abdominal aortic aneurysms causes a high morbidity and mortality in the elderly population. Platelet-rich thrombi form on the surface of aneurysms and may contribute to disease progression. In this study, we used a pharmacological approach to examine a role of platelets in established aneurysms induced by angiotensin II infusion into hypercholesterolemic mice.

APPROACH AND RESULTS

Administration of the platelet inhibitors aspirin or clopidogrel bisulfate to established abdominal aortic aneurysms dramatically reduced rupture. These platelet inhibitors reduced abdominal aortic platelet and macrophage recruitment resulting in decreased active matrix metalloproteinase-2 and matrix metalloproteinase-9. Platelet inhibitors also resulted in reduced plasma concentrations of platelet factor 4, cytokines, and components of the plasminogen activation system in mice. To determine the validity of these findings in human subjects, a cohort of aneurysm patients were retrospectively analyzed using developed and validated algorithms in the electronic medical record database at Vanderbilt University. Similar to mice, administration of aspirin or P2Y12 inhibitors was associated with reduced death among patients with abdominal aortic aneurysm.

CONCLUSIONS

These results suggest that platelets contribute to abdominal aortic aneurysm progression and rupture.

Gene expression study in positron emission tomography-positive abdominal aortic aneurysms identifies CCL18 as a potential biomarker for rupture risk

Rupture of abdominal aortic aneurysm (AAA) is a cause of significant mortality and morbidity in aging populations. Uptake of 18-fluorodeoxyglucose (FDG) detected by positron emission tomography (PET) is observed in the wall of 12% of AAA (A+), with most of them being symptomatic. We previously showed that the metabolically active areas displayed adventitial inflammation, medial degeneration and molecular alterations prefacing wall rupture. The aim of this study was to identify new factors predictive of rupture. Transcriptomic analyses were performed in the media and adventitia layers from three types of samples: AAA with-out FDG uptake (A0) and with FDG uptake (A+), both at the positive spot (A+(Pos)) and at a paired distant negative site (A+(Neg)) of the same aneurysm. Follow-up studies included reverse-transcriptase-polymerase chain reaction (RT-PCR), immunohistochemical staining and enzyme-linked immunosorbent assay (ELISA). A large number of genes, including matrix metalloproteinases, collagens and cytokines as well as genes involved in osteochondral development, were differentially expressed in the A+(Pos) compared with A+(Neg). Moreover, a series of genes (notably CCL18) was differentially expressed both in the A+(Neg) and A+(Pos) compared with the A0. A significant increase of CCL18 was also found at the protein level in the aortic wall and in peripheral blood of A+ patients compared with A0. In conclusion, new factors, including CCL18, involved in the progression of AAA and, potentially, in their rupture were identified by a genome-wide analysis of PET-positive and -negative human aortic tissue samples. Further work is needed to study their role in AAA destabilization and weakening.

Increased 18F-FDG uptake is predictive of rupture in a novel rat abdominal aortic aneurysm rupture model

OBJECTIVE

To determine whether F-fluorodeoxyglucose (F-FDG) micro-positron emission tomography (micro-PET) can predict abdominal aortic aneurysm (AAA) rupture.

BACKGROUND

An infrarenal AAA model is needed to study inflammatory mechanisms that drive rupture. F-FDG PET can detect vascular inflammation in animal models and patients.

METHODS

After exposing Sprague-Dawley rats to intra-aortic porcine pancreatic elastase (PPE) (12 U/mL), AAA rupture was induced by daily, subcutaneous, β-aminopropionitrile (BAPN, 300 mg/kg, N = 24) administration. Negative control AAA animals (N = 15) underwent daily saline subcutaneous injection after PPE exposure. BAPN-exposed animals that did not rupture served as positive controls [nonruptured AAA (NRAAA) 14d, N = 9]. Rupture was witnessed using radiotelemetry. Maximum standard uptakes for F-FDG micro-PET studies were determined. Aortic wall PAI-1, uPA, and tPA concentrations were determined by western blot analyses. Interleukin (IL)-1β, IL-6, IL-10, and MIP-2 were determined by Bio-Plex bead array. Neutrophil and macrophage populations per high-power field were quantified. Matrix metalloproteinase (MMP) activities were determined by zymography.

RESULTS

When comparing ruptured AAA (RAAA) to NRAAA 14d animals, increased focal F-FDG uptakes were detected at subsequent sites of rupture (P = 0.03). PAI-1 expression was significantly less in RAAA tissue (P = 0.01), with comparable uPA and decreased tPA levels (P = 0.02). IL-1β (P = 0.04), IL-6 (P = 0.001), IL-10 (P = 0.04), and MIP-2 (P = 0.02) expression, neutrophil (P = 0.02) and macrophage presence (P = 0.002), and MMP9 (P < 0.0001) activity were increased in RAAA tissue.

CONCLUSIONS

With this AAA rupture model, increased prerupture F-FDG uptake on micro-PET imaging was associated with increased inflammation in the ruptured AAA wall. F-FDG PET imaging may be used to monitor inflammatory changes before AAA rupture.

Differences in Elastin and Elastolytic Enzymes between Men and Women with Abdominal Aortic Aneurysm

BACKGROUND

Abdominal aortic aneurysms (AAAs) in women differ in some important aspects from those in men. The lower prevalence rate, higher rupture rate and potentially increased growth rate in women with AAA suggest gender to be of importance for aneurysm development and progression. The aim of the study was to analyze wall properties with respect to synthesis and destruction of elastin in men and women with AAA, with and without an intraluminal thrombus.

METHODS

Patient characteristics and aneurysm wall biopsies were collected from all women (n = 14) treated with open repair for AAA, 2008-2012, and men with similar aneurysm diameter and similar age (n = 23) treated during the same time period. The expressions of elastin, matrix metalloproteinase (MMP)-2 and -9, and cathepsin K were quantified by immunohistochemistry, Western blot, and gene expression analysis on the aneurysm wall.

RESULTS

The protein expression of elastin was less in women than in men in the non-thrombus-covered aneurysm wall. In addition, the protein and mRNA expressions of MMP-9 were higher in women (-0.83 versus 0.09, P = 0.041). There was no difference in elastin and elastolytic enzymes between men and women in the thrombus-covered aneurysm wall.

CONCLUSION

Less elastin in the non-thrombus-covered aneurysm wall in women than that in men, and the simultaneous higher level of MMP-9, suggest differences in the elastolytic process in AAA between the sexes.

Meta-analysis and meta-regression analysis of biomarkers for abdominal aortic aneurysm

Background

Many studies have investigated the systemic and local expression of biomarkers in patients with abdominal aortic aneurysm (AAA). The natural history of AAA varies between patients, and predictors of the presence and diameter of AAA have not been determined consistently. The aim of this study was to perform a systematic review, meta-analysis and meta-regression of studies comparing biomarkers in patients with and without AAA, with the aim of summarizing the association of identified markers with both AAA presence and size.

Methods and results

Literature review identified 106 studies suitable for inclusion. Meta-analysis demonstrated a significant difference between matrix metalloproteinase (MMP) 9, tissue inhibitor of matrix metalloproteinase 1, interleukin (IL) 6, C-reactive protein (CRP), α1-antitrypsin, triglycerides, lipoprotein(a), apolipoprotein A and high-density lipoprotein in patients with and without AAA. Although meta-analysis was not possible for MMP-2 in aortic tissue, tumour necrosis factor α, osteoprotegerin, osteopontin, interferon γ, intercellular cell adhesion molecule 1 and vascular cell adhesion molecule 1, systematic review suggested an increase in these biomarkers in patients with AAA. Meta-regression analysis identified a significant positive linear correlation between aortic diameter and CRP level.

Conclusion

A wide variety of biomarkers are dysregulated in patients with AAA, but their clinical value is yet to be established. Future research should focus on the most relevant biomarkers of AAA, and how they could be used clinically.

Influence of cardiovascular risk factors on levels of matrix metalloproteinases 2 and 9 in human abdominal aortic aneurysms

OBJECTIVE

To evaluate the influence of cardiovascular risk factors on levels of matrix metalloproteinases (MMP) 2 and 9 in human abdominal aortic aneurysms (AAA).

METHODS

Aortic samples were collected from patients who underwent AAA repair (n = 89). Patients were stratified according to the maximum transverse aorta diameter: small diameter (<55 mm), moderate diameter (55-69.9 mm) and large diameter (≥70 mm). Aortic walls were studied using real-time PCR and immunohistochemistry. MMP-2, MMP-9, α-actin, CD45, and CD68 transcript levels were determined relative to β-actin. Quantitative data were expressed as median (IQ-range).

RESULTS

No differences were found in MMP-2 expression between the patient groups, which was mainly associated with vascular smooth muscle cells (VSMC); however, MMP-9 displayed the maximum level in the moderate-diameter group, associated with infiltrating macrophages. Current smoking (CS) and renal insufficiency (RI) significantly increased local levels of MMP-2 (CS 349.5 [219.5-414.1] vs. no-CS 184.4 [100.0-320.5]; p < .008; RI 286.8 [189.6-410.8] vs. no-RI 177.3 [99.3-326.9]; p = .047). Nevertheless, after stepwise linear regression analysis only CS remained as an independent variable predicting local levels of MMP-2 (p = .002). No risk factors influenced local levels of MMP-9.

CONCLUSIONS

The results show that local levels of MMP-2, an important factor for AAA development, were increased in current smoking AAA patients. MMP-2 was mainly associated with VSMC. It is suggested that MMP-2 could contribute significantly to the increased AAA growth rate observed in current smoking patients. These findings support inclusion of smokers in screening for aneurysmal disease, and emphasize the need for more aggressive monitoring of aneurysmal disease outside the surgical range in patients who smoke at the time of diagnosis and in those who continue to smoke during follow-up.

Matrix metalloproteinase levels in chronic thoracic aortic dissection

BACKGROUND

Imbalance between matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) can lead to aortic wall failure. We hypothesized that patients with aneurysms resulting from chronic descending thoracic aortic dissection have elevated tissue and plasma levels of specific MMPs and decreased tissue levels of TIMPs.

MATERIALS AND METHODS

Aortic tissue was obtained from 25 patients who required surgical repair of descending thoracic aortic aneurysm due to chronic aortic dissection and from 17 organ-donor controls without aortic disease. Tissue levels of MMP-1, -2, -3, -9, -12, and -13 and TIMP-1 and -2 were measured by colorimetric activity assay or enzyme-linked immunosorbent assay and confirmed by Western blot and immunohistochemistry. Blood obtained from the 25 patients and 15 controls without aortic diseases was used to compare plasma levels of MMP-3, -9, and -12.

RESULTS

Total MMP-1, total MMP-9, and active MMP-9 levels were higher and total MMP-2 levels were lower in dissection tissue than in control tissue. Additionally, the MMP-9 to TIMP-1 and active to total MMP-2 ratios were higher and the MMP-2 to TIMP-2 ratio was lower in dissection tissue. Furthermore, patients had higher plasma active to total MMP-9 ratios than the controls. Age and hypertension were associated with increased MMP levels.

CONCLUSIONS

Increased levels of several MMPs and increased MMP to TIMP ratios in aortic tissue from patients suggest an environment that favors proteolysis, which may promote progressive extracellular matrix destruction and medial degeneration after aortic dissection. An elevated active to total MMP-9 ratio in plasma may be a biomarker for end-stage aneurysm development in patients with chronic thoracic aortic disease.

IL-6 regulates extracellular matrix remodeling associated with aortic dilation in a fibrillin-1 hypomorphic mgR/mgR mouse model of severe Marfan syndrome

Background

Development of thoracic aortic aneurysms is the most significant clinical phenotype in patients with Marfan syndrome. An inflammatory response has been described in advanced stages of the disease. Because the hallmark of vascular inflammation is local interleukin‐6 (IL‐6) secretion, we explored the role of this proinflammatory cytokine in the formation of aortic aneurysms and rupture in hypomorphic fibrillin‐deficient mice (mgR/mgR).

Methods and Results

MgR/mgR mice developed ascending aortic aneurysms with significant dilation of the ascending aorta by 12 weeks (2.7±0.1 and 1.3±0.1 for mgR/mgR versus wild‐type mice, respectively; P<0.001). IL‐6 signaling was increased in mgR/mgR aortas measured by increases in IL‐6 and SOCS3 mRNA transcripts (P<0.05) and in cytokine secretion of IL‐6, MCP‐1, and GM‐CSF (P<0.05). To investigate the role of IL‐6 signaling, we generated mgR homozygous mice with IL‐6 deficiency (DKO). The extracellular matrix of mgR/mgR mice showed significant disruption of elastin and the presence of dysregulated collagen deposition in the medial‐adventitial border by second harmonic generation multiphoton autofluorescence microscopy. DKO mice exhibited less elastin and collagen degeneration than mgR/mgR mice, which was associated with decreased activity of matrix metalloproteinase‐9 and had significantly reduced aortic dilation (1.0±0.1 versus 1.6±0.2 mm change from baseline, DKO versus mgR/mgR, P<0.05) that did not affect rupture and survival.

Conclusion

Activation of IL‐6‐STAT3 signaling contributes to aneurysmal dilation in mgR/mgR mice through increased MMP‐9 activity, aggravating extracellular matrix degradation.

Development of abdominal aortic aneurysm is decreased in mice with plasma phospholipid transfer protein deficiency

Plasma phospholipid transfer protein (PLTP) increases the circulating levels of proatherogenic lipoproteins, accelerates blood coagulation, and modulates inflammation. The role of PLTP in the development of abdominal aortic aneurysm (AAA) was investigated by using either a combination of mechanical and elastase injury at one site of mouse aorta (elastase model) or continuous infusion of angiotensin II in hyperlipidemic ApoE-knockout mice (Ang II model). With the elastase model, complete PLTP deficiency was associated with a significantly lower incidence and a lesser degree of AAA expansion. With the Ang II model, findings were consistent with those in the elastase model, with a lower severity grade in PLTP-deficient mice, an intermediate phenotype in PLTP-deficient heterozygotes, and a blunted effect of the PLTP-deficient trait when restricted to bone marrow-derived immune cells. The protective effect of whole-body PLTP deficiency in AAA was illustrated further by a lesser degree of adventitia expansion, reduced elastin degradation, fewer recruited macrophages, and less smooth muscle cell depletion in PLTP-deficient than in wild-type mice, as evident from comparative microscopic analysis of aorta sections. Finally, cumulative evidence supports the association of PLTP deficiency with reduced expression and activity levels of matrix metalloproteinases, known to degrade elastin and collagen. We conclude that PLTP can play a significant role in the pathophysiology of AAA.

Matrix metalloproteinase-9 genotype as a potential genetic marker for abdominal aortic aneurysm

BACKGROUND

Degradation of extracellular matrix support in the large abdominal arteries contribute to abnormal dilation of aorta, leading to abdominal aortic aneurysms, and matrix metalloproteinase-9 (MMP-9) is the predominant enzyme targeting elastin and collagen present in the walls of the abdominal aorta. Previous studies have suggested a potential association between MMP-9 genotype and abdominal aortic aneurysm, but these studies have been limited only to the p-1562 and (CA) dinucleotide repeat microsatellite polymorphisms in the promoter region of the MMP-9 gene. We determined the functional alterations caused by 15 MMP-9 single-nucleotide polymorphisms (SNPs) reported to be relatively abundant in the human genome through Western blots, gelatinase, and promoter-reporter assays and incorporated this information to perform a logistic-regression analysis of MMP-9 SNPs in 336 human abdominal aortic aneurysm cases and controls.

METHODS AND RESULTS

Significant functional alterations were observed for 6 exon SNPs and 4 promoter SNPs. Genotype analysis of frequency-matched (age, sex, history of hypertension, hypercholesterolemia, and smoking) cases and controls revealed significant genetic heterogeneity exceeding 20% observed for 6 SNPs in our population of mostly white subjects from Northern Wisconsin. A step-wise logistic-regression analysis with 6 functional SNPs, where weakly contributing confounds were eliminated using Akaike information criteria, gave a final 2 SNP (D165N and p-2502) model with an overall odds ratio of 2.45 (95% confidence interval, 1.06-5.70).

CONCLUSIONS

The combined approach of direct experimental confirmation of the functional alterations of MMP-9 SNPs and logistic-regression analysis revealed significant association between MMP-9 genotype and abdominal aortic aneurysm.

Turnover of fibrillar collagen in soft biological tissue with application to the expansion of abdominal aortic aneurysms

A better understanding of the inherent properties of vascular tissue to adapt to its mechanical environment is crucial to improve the predictability of biomechanical simulations. Fibrillar collagen in the vascular wall plays a central role in tissue adaptation owing to its relatively short lifetime. Pathological alterations of collagen turnover may fail to result in homeostasis and could be responsible for abdominal aortic aneurysm (AAA) growth at later stages of the disease. For this reason our previously reported multiscale constitutive framework (Martufi, G. & Gasser, T. C. 2011 J. Biomech. 44, 2544-2550 (doi:10.1016/j.jbiomech.2011.07.015)) has been enriched by a collagen turnover model. Specifically, the framework's collagen fibril level allowed a sound integration of vascular wall biology, and the impact of collagen turnover on the macroscopic properties of AAAs was studied. To this end, model parameters were taken from the literature and/or estimated from clinical follow-up data of AAAs (on average 50.7 mm-large). Likewise, the in vivo stretch of the AAA wall was set, such that 10 per cent of collagen fibres were engaged. Results showed that the stretch spectrum, at which collagen fibrils are deposed, is the most influential parameter, i.e. it determines whether the vascular geometry grows, shrinks or remains stable over time. Most importantly, collagen turnover also had a remarkable impact on the macroscopic stress field. It avoided high stress gradients across the vessel wall, thus predicted a physiologically reasonable stress field. Although the constitutive model could be successfully calibrated to match the growth of small AAAs, a rigorous validation against experimental data is crucial to further explore the model's descriptive and predictive capabilities.

Combined stimulation with cyclic stretching and hypoxia increases production of matrix metalloproteinase-9 and cytokines by macrophages

Macrophages in the vessel wall of advanced abdominal aortic aneurysms (AAAs) are subjected to cyclic stretching and hypoxia because of pulsatile blood flow and intraluminal thrombi, respectively. It is possible that these conditions induce abnormal changes in macrophage functions, such as increased production of matrix metalloproteinase-2 (MMP-2), MMP-9, and inflammatory cytokines, leading to weakening of the aortic wall through excessive extracellular matrix disruption. Here we show the effects of cyclic stretching and hypoxia on the production of MMP-9 and inflammatory cytokines by macrophages. Gelatin zymography revealed that MMP-9 production by macrophages was significantly increased by 5% and 10% cyclic stretching under hypoxia (2.2% O(2)). Using enzyme-linked immunosorbent assay, we also evaluated the production of 12 different inflammatory cytokines and found that there was a tendency toward higher expressions of interleukin-8 and tumor necrosis factor-α by macrophages subjected to 10% cyclic stretching under normoxia and hypoxia. Next, we evaluated apoptosis of smooth muscle cells (SMCs) in medium conditioned by macrophages cultured under the 2 conditions described above. SMC apoptosis increased significantly when exposed to media harvested from macrophages subjected to 10% cyclic stretching under normoxia and hypoxia. On the basis of these results, we believe that macrophages produce cytokines that induce SMC apoptosis. Our results suggest that the combination of cyclic stretching and hypoxia stimulates MMP-9 and cytokine production in macrophages, which may result in weakening of AAA walls.

Effect of statin therapy on serum activity of proteinases and cytokines in patients with abdominal aortic aneurysm

Background and aims:

Metalloproteinases (MMPs) are considered to be key enzymes in the pathogenesis of abdominal aortic aneurysms (AAA), with elevated levels in diseased aorta and in patient sera. Statins seem to exert an inhibitory effect on MMP activity in the aortic wall. No data exist on the effect of statins on serum activity of MMPs and inflammatory cytokines (interleukins, IL).

Methods:

The serum activities of MMP2 and MMP9, osteoprotegerin (OPG), and IL6 and IL10 in 63 patients undergoing elective infrarenal aneurysm repair were measured on the day before surgery. Levels were correlated to statin therapy and aneurysm diameter.

Results:

There was no significant difference between the two groups in the activity of circulating levels of MMP2/9, OPG, and IL6/10 in patients with infrarenal aortic aneurysm. IL6 levels in patients with AAA larger than 6 cm were significantly elevated; differences in serum activities of MMP2/9, OPG, and IL10 were not related to AAA diameter.

Conclusion:

Serum activities of MMP2/9, OPG, and IL6/10 are not correlated to statin therapy; IL6 levels are higher in patients with large aneurysms. Hence the effect of statin therapy in the treatment of aneurismal disease remains to be elucidated.

Plasma matrix metalloproteinase levels do not predict tissue levels in abdominal aortic aneurysms suitable for elective repair

The role of matrix metalloproteinases (MMPs) in abdominal aortic aneurysm (AAA) pathogenesis is well described. However, a clear role for the MMPs in disease prediction has not been established. The aim of this study was to determine if circulating levels of MMPs correlated with AAA diameter and with MMP concentrations within the aneurysm wall. Preoperative plasma samples and intraoperative infrarenal AAA sac biopsies were taken in a standard fashion from 31 patients undergoing elective repair.The concentrations of MMP-1, MMP-2, MMP-3, MMP-9, tissue inhibitor of matrix metalloproteinase (TIMP)-1, and TIMP-2 were quantified in plasma and aneurysm wall homogenates using enzyme-linked immunosorbent assay. Comparison used the Spearman correlation. There were no correlations between the paired plasma and aneurysm wall concentrations for any MMP or TIMP. Correlation between MMP-9 levels in the aneurysm wall and aneurysm diameter was negative (r = -.42, p = .019). Other correlations between plasma and tissue levels with aneurysm diameter were nonsignificant.

Pravastatin increases the expression of the tissue inhibitor of matrix metalloproteinase-1 and the oncogeneBaxin human aortic abdominal aneurysms

The effect of pravastatin on matrix metalloproteinase-9 (MMP-9) and the level of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 was studied in explants of human abdominal aortic aneurysm (AAA) obtained from 13 patients. The effect of pravastatin on the apoptotic status of human AAA explants was also examined. Total MMP-9 content did not differ in human AAA explants incubated in vitro in the presence or absence of pravastatin (10−6mol/L) for 48 h. TIMP-1 levels were significantly increased in pravastatin-incubated AAA explants, but TIMP-2 production was not modified by pravastatin. Western blot experiments showed that, whereas Bax expression was increased in pravastatin-incubated AAA explants, the expression of Bcl-2 was not modified. On the other hand, the ratio of the expression of Bax to Bcl-2, an apoptotic index, was not modified by pravastatin. In the human AAA explants, the increase in Bax expression, but not the increase in TIMP-1 expression elicited by pravastatin, was reversed by l-mevalonate, a downstream HMG-CoA reductase metabolite, suggesting that the expression of Bax and TIMP-1 followed HMG-CoA reductase-dependent and -independent pathways, respectively. In conclusion, pravastatin increases both TIMP-1 and Bax expression in human AAA explants without changes in either MMP-9 activity or the apoptotic status.

Increased 18F-fluorodeoxyglucose uptake in abdominal aortic aneurysms in positron emission/computed tomography is associated with inflammation, aortic wall instability, and acute symptoms

OBJECTIVE

With the established computed tomographic (CT)- morphologic parameters, only the relative, but not the individual rupture risk of abdominal aortic aneurysm (AAA), can be determined. So far, increased aortic 18F-fluorodeoxyglucose (FDG) metabolism measured by positron emission tomography (PET) has been reported in AAA with increased rupture risk. The aim of the study was to analyze the histopathologic changes in AAA wall correlated with increased FDG uptake for further implications on aortic wall stability and AAA rupture risk.

METHODS

Fifteen patients with asymptomatic (n = 12) and symptomatic (n = 3) AAA underwent FDG-PET/CT, followed by open AAA repair. FDG-PET/CT was used for precise localization of maximum FDG uptake, and the maximum standard uptake values (SUV(max)) were calculated. Biopsies of the AAA wall were operatively collected from areas with maximum FDG uptake, immunohistologically stained, and semiquantitatively analyzed for inflammatory infiltrates, vascular smooth muscle cells (VSMC), matrix metalloproteinase (MMP)-2 and -9 expression, as well as for elastin and collagenous fibers.

RESULTS

Symptomatic AAA showed significantly increased FDG uptake compared with asymptomatic AAA (SUV(max), 3.5 +/- 0.6 vs 7.5 +/- 3; P < .001). Thus, increased FDG uptake was correlated with higher densities of inflammatory infiltrates (r = +0.87, P < .01) and macrophage and T-cell infiltrations (r = +0.95, P < .01 and r = +0.66, P < .05), with higher MMP-9 expressions (r = +0.86; P < .01), and with reduction of collagen fiber (r = -0.76; P < .01) and VSMCs (r = -0.71; P < .01). Consecutive correlations were found for total inflammatory infiltrates, T lymphocytes, and macrophages with MMP-9 expression (r = +0.79, +0.79 and +0.74; P < .01). Moreover, MMP-9 expression was correlated with decreasing collagen fiber content (r = -0.53, P < .05) and VSMC density (r = -0.57, P < .05).

CONCLUSIONS

Maximum aortic FDG uptake correlated significantly with inflammation, followed by increased MMP expression and histopathologic characteristics of aneurysm wall instability and clinical symptoms. Therefore, FDG-PET/CT might be a new diagnostic technique to study AAA disease in vivo and may contribute to improve prediction of individual AAA rupture risk.

Gender-specific differences in aortic sinus curvature during aging: an anatomical and computational study

INTRODUCTION

Our goal was to investigate the potential impact of aortic sinus wall curvature on the risk for type A aortic dissection.

METHODS

We measured the curvature and carried out histological tests of the aortic noncoronary sinus in 46 patients who did not die from cardiac disease. Based on observed curvature values, we investigated the mechanical stress in the aortic root using finite element analysis.

RESULTS

Sinus curvature was found to experience a more than fourfold increase with age in males and reached the higher, age-independent values measured in females by age 65. The histological tests revealed that degenerative alterations did not significantly increase with aging in either gender, although fibrosis did in older women. Finite element analysis illustrated that the risk for a circumferential tear to occur was smallest when sinus curvature was highest.

CONCLUSIONS

We established significant gender-specific disparities in the aortic root during aging: while aortic sinus curvature was high in females throughout their lives, it experienced a more than fourfold increase in the lifetime of males, matching values in females only by age 65. Our mechanical analyses confirmed the overall potential protective role of higher sinus wall curvature with respect to type A aortic dissection, and geometry alone could not account for the known gender difference in aortic dissection prevalence.

Long-term doxycycline is more effective than atenolol to prevent thoracic aortic aneurysm in marfan syndrome through the inhibition of matrix metalloproteinase-2 and -9

Beta-blockers, eg, atenolol, are the cornerstone therapy for thoracic aortic aneurysm (TAA) in patients with Marfan syndrome; however, continued aortic dilatation has been reported. We have demonstrated that matrix metalloproteinase (MMP)-2 and -9 were upregulated during progression of TAA in Marfan syndrome, accompanied with degenerated elastic fibers and vasomotor dysfunction. We hypothesized that doxycycline, a nonspecific inhibitor of MMPs, would ameliorate TAA by attenuating elastic fiber degeneration and improving vasomotor function. A well-characterized mouse model of Marfan syndrome (Fbn1(C1039G/+)) was used. Mice were untreated (n=40), given doxycycline (0.24 g/L, n=30), or given atenolol (0.5 g/L, n=30) in drinking water at 6 weeks of age. The Fbn1(+/+) mice served as control (n=40). At 3, 6, and 9 months, aortic segments from the ascending, arch, and descending portions were used to obtain the "average" value of the whole thoracic aorta. TAA was prevented in the doxycycline group, whereas mild aneurysm was evident in the atenolol group. Doxycycline improved elastic fiber integrity, normalized aortic stiffness, and prevented vessel weakening. The impairment of vasocontraction and endothelium-dependent relaxation in the untreated and atenolol groups were improved by doxycycline. The upregulation of transforming growth factor-beta in the Marfan aorta was suppressed by doxycycline. Doxycycline augmented expression ratios of tissue inhibitors of MMP to MMPs. Intraperitoneally injected neutralizing antibodies against MMP-2 and -9 yielded similar effects to doxycycline. We concluded that long-term treatment with doxycycline, through the inhibition of MMP-2 and -9, is more effective than atenolol in preventing TAA in Marfan syndrome by preserving elastic fiber integrity, normalizing vasomotor function, and reducing transforming growth factor-beta activation.

Can local secretion of prostaglandin E2, thromboxane B2, and interleukin-6 play a role in ruptured abdominal aortic aneurysm?

BACKGROUND

Our laboratory has previously shown that the levels of secreted prostaglandin E(2) (PGE(2)), Thromboxane B(2) (TxB(2)), and interleukin-6 (IL-6) by aortic explant cultures were high in patients with ruptured abdominal aortic aneurysm (AAA). In the present study, we sought to examine the secretory levels of these inflammatory mediators in aortic explant cultured from a group of AAAs rupturing at a certain size and a group that did not rupture at that size. It was thought that such a comparison might reveal the contribution of those inflammatory mediators to the risk of AAA rupture.

MATERIALS AND METHODS

All subjects had abdominal computed tomography (CT) scans to determine the size of the aneurysm, and surgical aortic tissue was collected from both nonruptured AAAs (18 with a mean size of 6 + 0.5 cm [range: 5-7 cm] and 12 with a mean size of 8 + 0.1 cm [range: 7.01-10 cm]) and ruptured AAAs (10 with a mean size of 5.8 + 0.3 cm [range: 5-7 cm] and 10 with a mean size of 7.8 + 0.1 cm [range: 7.01-10 cm]). Aortic explant cultures from different sizes of aneurysms were immediately established and the culture media were collected 72 h later.

RESULTS

The levels of PGE(2), TxB(2), and IL-6 secreted in the cultured medium were quantified by specific enzyme-linked immunosorbent assays (ELISA). The secretary levels of PGE(2), TxB(2), and IL-6 were significantly higher in ruptured AAAs than in nonruptured AAAs of similar diameter. However, there was no correlation between these three inflammatory mediators and the size of AAA.

CONCLUSIONS

This study shows that these inflammatory mediators may play a role in the progression toward rupture but may not be responsible for the expansion of AAA.

Elevated plasma MMP1 and MMP9 are associated with abdominal aortic aneurysm rupture

BACKGROUND

The role of matrix metalloproteinases (MMPs) in abdominal aortic aneurysm (AAA) formation is well established. However the changes in plasma MMP levels with AAA rupture have not been reported. The aim of this study was to determine circulating levels of MMPs in non-ruptured and ruptured AAA immediately prior to open repair.

METHODS

Concentrations of MMPs and their endogenous tissue inhibitors (TIMPs) were quantified using ELISA in pre-operative plasma samples from non-ruptured and ruptured AAA.

RESULTS

MMP1 and MMP9 were elevated in the plasma of ruptured AAA versus non-ruptured AAA. A four-fold elevation in pre-operative plasma MMP9 was associated with non-survival at 30 days from rupture surgery compared with those surviving for greater than 30 days.

CONCLUSION

In conclusion, these findings support the role of MMPs in AAA pathogenesis. Elevation of MMP9 was associated with ruptured aneurysm related 30-day mortality and may represent a survival indicator in this group.

Novel insight into the pathobiology of abdominal aortic aneurysm and potential future treatment concepts

The patient with abdominal aortic aneurysm (AAA) commonly is a nondiabetic, white man with a history of smoking. Moreover, AAA represents a leading cause of death in elderly men in Western countries. The purpose of this manuscript is to review current evidence as to the pathobiology of AAA as well as potential future drug targets to prevent progression of AAA.

Role of matrix metalloproteinase inhibitors in preventing abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a significant health problem in the United States, with approximately 30,000 repair operations annually. Treatment of AAA is associated with more than 150,000 hospital admissions per year. The development of AAA is characterized by destruction of the elastic media of the aortic wall. A large body of evidence suggests that a group of enzymes called matrix metalloproteinases (MMPs) plays a significant role in the destruction of extracellular matrix in the aortic wall. MMP inhibition has, therefore, been viewed as an alternative pharmacotherapeutic approach to slow down the development and progression of small AAAs, thus reducing the need for surgical intervention.

Effects of tissue inhibitor of metalloproteinase 2 deficiency on aneurysm formation

OBJECTIVE

Matrix metalloproteinase (MMP)-2 has been shown to play a pivotal role in aortic aneurysm formation. Its activation requires formation of a trimolecular complex of MMP-2, tissue inhibitor of metalloproteinase-2 (TIMP-2), and membrane type 1 (MT1)-MMP, which is attached to the cell surface. At higher concentrations, TIMP-2 becomes an inhibitor of MMP-2. Thus, TIMP-2 could both augment and inhibit matrix degradation. This study was undertaken to define the net effect of TIMP-2 on matrix destruction and aneurysm formation.

METHODS

The abdominal aortas of wild-type and TIMP-2-deficient (TIMP-2 -/-) mice were exposed to 0.25 mol/L CaCl2 or 0.9% NaCl for 15 minutes after laparotomy. Aortic diameters were measured before treatment and 6 weeks after aneurysm induction. In addition, aortic tissues were studied for MMP-2 activation by zymography, and matrix structure was studied by connective tissue staining.

RESULTS

The aortic diameter increased in both wild-type and TIMP-2-/- mice. The increase in the TIMP-2 -/- mice was significantly smaller after CaCl2 treatment (51% +/- 3%) compared with the diameter of wild-type mice (67% +/- 4%). Connective staining of aortic sections from the CaCl2-treated mice revealed disruption and fragmentation of the medial elastic lamellae in both wild-type and TIMP-2 -/- mice. Zymographic analysis showed that active MMP-2 levels were decreased in TIMP-2 -/- aortas compared with wild-type mice.

CONCLUSIONS

Targeted deletion of TIMP-2 results in attenuation of aneurysm development. Despite its name as an inhibitor of MMPs, TIMP-2 promotes aortic enlargement in vivo, presumably through its role as a cofactor in the activation of MMP-2.

CLINICAL RELEVANCE

Abdominal aortic aneurysmal (AAA) disease is a potentially fatal disorder that screening studies have detected in 2% to 9% of the general population. Medical therapy designed to inhibit the progression of small aneurysms includes control of hypertension and smoking cessation; neither of these measures is of proven benefit. Effective and directed medical treatments for small AAAs await elucidation of key etiologic factors. Understanding precisely which molecules mediate AAA development, and blocking the activity of these molecules, could lead to important new therapies. Through our research, we have found that tissue inhibitor of metalloproteinase (TIMP)-2 has a role in this process in an experimental model of aortic aneurysms. We believe that TIMP-2 promotes aortic enlargement in vivo by activating matrix metalloproteinase 2.

A single nucleotide polymorphism in the matrix metalloproteinase 9 gene (-8202A/G) is associated with thoracic aortic aneurysms and thoracic aortic dissection

OBJECTIVE

Matrix metalloproteinase 9 plays an important role in the maintenance of the aortic extracellular matrix. Genetic variations that affect protease expression or activity might contribute to thoracic aortic disease. The purpose of this study was to determine whether 3 single nucleotide polymorphisms in the matrix metalloproteinase 9 gene are associated with thoracic aortic aneurysms and dissection.

METHODS

Genomic DNA was isolated from blood or aortic tissue from 28 patients with degenerative thoracic aortic aneurysms, 60 patients with thoracic aortic dissection, and 111 control patients. The frequency distributions of 3 matrix metalloproteinase 9 single nucleotide polymorphisms (-8202A/G, IVS4+3G/T, and 2003A/G [Q668R]) were determined by using genotyping accomplished with a real-time detection system. Associations between polymorphisms and disease were estimated with odds ratios and their 95% confidence intervals.

RESULTS

The frequency of the -8202G allele was significantly higher in patients with thoracic aortic aneurysms and aortic dissection (0.52 and 0.56, respectively) than in control subjects (0.36, P < .001). Patients with thoracic aortic aneurysms or dissection were nearly 5 times more likely than control subjects to have the G allele (adjusted odds ratio, 4.87; 95% confidence interval, 2.04-11.64). There were no significant associations between the IVS4+3G/T or 2003A/G polymorphisms and thoracic aortic disease.

CONCLUSIONS

The matrix metalloproteinase 9 -8202A/G polymorphism is associated with thoracic aortic aneurysms and dissection. Further studies are warranted to elucidate the functional role of the -8202A/G variant in matrix metalloproteinase 9 expression.

Biomechanical properties of ruptured versus electively repaired abdominal aortic aneurysm wall tissue

OBJECTIVE

The purpose of this study was to evaluate and compare the biomechanical properties of abdominal aortic aneurysm (AAA) wall tissue from patients who experienced AAA rupture with that of those who received elective repair.

METHODS

Rectangular, circumferentially oriented AAA wall specimens (approximately 2.5 cm x 7 mm) were obtained fresh from the operating room from patients undergoing surgical repair. The width and thickness were measured for each specimen by using a laser micrometer before testing to failure with a uniaxial tensile testing system. The force and deformation applied to each specimen were measured continuously during testing, and the data were converted to stress and stretch ratio. The tensile strength was taken as the peak stress obtained before specimen failure, and the distensibility was taken as the stretch ratio at failure. The maximum tangential modulus and average modulus were also computed according to the peak and average slope of the stress-stretch ratio curve.

RESULTS

Twenty-six specimens were obtained from 16 patients (aged 73 +/- 3 years [mean +/- SEM]) undergoing elective repair of their AAA (diameter, 7.0 +/- 0.5 cm). Thirteen specimens were resected from nine patients (aged 73 +/- 3 years; P = not significant in comparison to the electively repaired AAAs) during repair of their ruptured AAA (diameter, 7.8 +/- 0.6 cm; P = not significant). A significant difference was noted in wall thickness between ruptured and elective AAAs: 3.6 +/- 0.3 mm vs 2.5 +/- 0.1 mm, respectively (P < .001). The tensile strength of the ruptured tissue was found to be lower than that for the electively repaired tissue (54 +/- 6 N/cm2 vs 82 +/- 9.0 N/cm2; P = .04). Considering all specimens, no significant correlation was noted between tensile strength and diameter (R = -0.10; P = .55). Tensile strength, however, had a significant negative correlation with wall thickness (R = -0.42; P < .05) and a significant positive correlation with the tissue maximum tangential modulus (R = 0.76; P < .05).

CONCLUSIONS

Our data suggest that AAA rupture is associated with aortic wall weakening, but not with wall stiffening. A widely accepted indicator for risk of aneurysm rupture is the maximum transverse diameter. Our results suggest that AAA wall strength, in large aneurysms, is not related to the maximum transverse diameter. Rather, wall thickness or stiffness may be a better predictor of rupture for large AAAs.

An overview of matrix metalloproteinases in the pathogenesis and treatment of abdominal aortic aneurysms

Recent basic and clinical research has established a link between the pathogenesis of abdominal aortic aneurysms (AAA) and matrix metalloproteinases (MMP). The discovery of the influence of MMPs on in vitro and in vivo aneurysm development has yielded promising information that may eventually decode the pathogenetic factors affecting the initiation and growth rate of AAAs. In this review, an analysis of MMPs involved in AAA disease is presented, including the data from recent research studies and planned clinical drug trails designed to retard the AAA growth by inhibiting MMP activity.

Matrix Metalloproteinase-8 and -9 Are Increased at the Site of Abdominal Aortic Aneurysm Rupture

Background— Abdominal aortic aneurysm (AAA) expansion is characterized by extracellular matrix degradation and widespread inflammation. In contrast, the processes that characterize AAA rupture are not well understood. The aim of this study was to investigate the proteolytic and cellular activity of ruptured AAA, focusing on matrix metalloproteinases (MMPs) and their inhibitors (TIMPs).

Methods and Results— Anterior aneurysm wall biopsies were taken from 55 nonruptured and 21 ruptured AAAs. A further biopsy from the site of rupture was taken from 12 of the ruptured AAAs. MMP-1, -2, -3, -8, -9, and -13, as well as TIMP-1 and -2, were quantified in each biopsy with ELISA. A comparison of anterior aneurysm biopsies showed no difference in MMP or TIMP concentrations between nonruptured and ruptured AAA. In a comparison of ruptured AAA biopsies, MMP-8 and -9 levels were significantly elevated in the 12 rupture site biopsies compared with their 12 paired anterior wall biopsies, whereas other MMPs and TIMPs showed no difference (MMP-8, P <0.001; MMP-9, P =0.01). MMP-8 and -9 expression was mediated by native mesenchymal cells and was independent of the inflammatory infiltrate.

Conclusions— A localized increase in MMP-8 and –9, mediated by native mesenchymal cells, presents a potential pathway for collagen breakdown and AAA rupture.

A failure of matrix metalloproteinase inhibition in the prevention of rat intracranial aneurysm formation

We tested the hypothesis that nonspecific matrix metalloproteinase (MMP) inhibition with doxycycline would decrease the incidence of intracranial aneurysm formation in a rat aneurysm model. We performed common carotid artery ligation on 96 Long-Evans rats. A treatment group of 48 animals was chosen at random to receive oral doxycycline (3 mg/kg) in addition to standard rat chow, and the control group of 48 animals received standard rat chow only. The major circle of Willis arteries was dissected at 1 year following carotid ligation, and the proportions of animals with aneurysms were compared between groups using Fisher's exact test. Four animals given oral doxycycline and ten control animals expired before 1 year. Of the examined animals, eight saccular intracranial aneurysms were found in 8 of 45 animals which had received doxycycline (17.8%) and seven saccular intracranial aneurysms were found in 7 of 37 control animals (18.9%). There was no significant difference in aneurysm formation between the doxycycline-treated and control groups (P=0.894). Nonspecific MMP inhibition with doxycycline is not effective in preventing intracranial aneurysm formation in a rat model.

Inhibition of ets, an essential transcription factor for angiogenesis, to prevent the development of abdominal aortic aneurysm in a rat model

The pathophysiology of abdominal aortic aneurysms (AAA) is considered to be complicated. As matrix degradation contributes to the progression of AAA, the destruction and degradation of elastin fibers caused by an increase in matrix metalloproteinases (MMPs) plays a pivotal role in the development of AAA. Although ets, an essential transcription factor for angiogenesis, regulates MMPs, the role of ets in the development of AAA has not yet been clarified. Thus, we evaluated the role of ets in a rat AAA model using a decoy strategy. Transfection of ODN into AAA was performed by transient aortic perfusion of elastase and by wrapping the AAA in a delivery sheet containing decoy ODN. The inhibitory effect of ets decoy ODN on ets binding activity was confirmed by gel mobility shift assay. MMPs expression was decreased in the aorta transfected with ets decoy ODN as compared to scrambled decoy ODN. Also, ultrasound study demonstrated that elastase-induced aneurismal dilation was significantly suppressed by transfection of ets decoy ODN at 4 weeks after treatment as compared to scrambled decoy ODN. Moreover, the destruction of elastin fibers was inhibited in the aorta transfected with ets decoy ODN, accompanied by a reduction of MMPs expression. An inhibitory effect of decoy ODN on MMP expression was confirmed by ex vivo experiments showing that transfection of decoy ODN into an organ culture of human aorta resulted in significant inhibition of the secretion of both MMP-1 and MMP-9. Here, we demonstrated that ets may play a pivotal role in the progression of AAA through the activation of MMPs in a rat model. Ets might be a potential target to develop pharmacotherapy/gene therapy to treat AAA through the inhibition of MMPs.

HMG-CoA reductase inhibitors (statins) decrease MMP-3 and MMP-9 concentrations in abdominal aortic aneurysms

BACKGROUND

An imbalance in matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) are implicated in AAA formation. 3-Hydroxy-3-methylglutaryl coenzyme-A reductase inhibitors (statins) are known to reduce MMP levels. The aim of this study was to investigate the in vivo effect of statins on MMP levels in AAA.

METHODS

Infra-renal aortic biopsies were obtained from the anterior sac of 63 patients undergoing asymptomatic repair. Seventeen patients were taking a statin pre-operatively, while 46 were not. The concentrations of MMP-1, -2, -3, -8, -9, -13, TIMP-1 and TIMP-2 were quantified using ELISA.

RESULTS

There was no difference in the concentration of MMP-1, -2, -8, -13, TIMP-1 or -2 in patients taking versus not taking a statin pre-operatively. In contrast levels of MMP-9 and MMP-3 were significantly lower in patients taking a statin.

CONCLUSIONS

These data demonstrate that statins decrease MMP-9 and MMP-3 levels and represent a potential pharmacotherapy in established AAA.

Heterogeneity of tensile strength and matrix metalloproteinase activity in the wall of abdominal aortic aneurysms

PURPOSE

To measure the tensile strength of the aneurysm wall and the matrix metalloproteinase (MMP) activity in similar samples of aortic tissue.

METHODS

Detailed mechanical testing was conducted on 124 standardized specimens of aneurysm wall harvested from 24 patients undergoing elective aneurysm repair. The intrasac pressure required to cause aneurysm rupture was calculated based upon the Law of Laplace. In addition, MMP-2 and 9 were assayed from these specimens. Sixty specimens of nonaneurysmal aorta from 6 cadaveric organ donors served as controls. Intrasubject and intersubject variations were analyzed.

RESULTS

In the aneurysm specimens, the Young's modulus was 1.80x10(6) N/m(2), the load at break was 6.36 N, the strain at break was 0.30, the ultimate strength was 0.53x10(6) N/ m(2), and the MMP activity was 312 for MMP-2 and 460 for MMP-9. In the controls, the circumferential measurements were a Young's modulus of 1.82x10(6) N/m(2), a load at break of 5.43 N, strain at break of 0.29, ultimate strength of 0.61x10(6) N/m(2), and MMP activity of 395 for MMP-2 and 2019 for MMP-9. Longitudinal measurements in controls were a Young's modulus of 1.38x10(6) N/m(2), a load at break of 11.39 N, a strain at break of 0.33, and ultimate strength of 1.30x10(6) N/m(2). Intra and intersubject variation of all parameters was very high. Based upon the lowest measured tensile strength for each aneurysm, the intrasac pressure required to cause rupture varied from 142 to 982 mmHg.

CONCLUSIONS

Localized "hot spots" of MMP hyperactivity could lead to focal weakening of the aneurysm wall and rupture at relatively low levels of intraluminal pressure. These data suggest that tensile strength of the sac is just as important as intrasac tension in determining the risk of rupture. Moreover, these observations may explain why some small aneurysms rupture and larger aneurysms do not. Assessment of rupture risk based on computation or measurement of wall stress may be subject to error and inaccuracy due to variations in wall tensile strength.

Decreased plasminogen activator inhibitor-1 levels in coronary artery aneurysmatic patients

BACKGROUND

Matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of arterial aneurysms through increased proteolysis of extracellular matrix proteins. Increased proteolysis due to elevated matrix degrading enzyme activity in the arterial wall may act as a susceptibility factor for the development of coronary aneurysms. Plasmin strongly stimulates pro-MMP enzyme conversion to the active form. Plasmin hyperactivity due to decreased plasminogen activator inhibitor-1 (PAI-1) may cause MMP over activity and coronary aneurysms. The aim of this study was to investigate the association between PAI-1 and presence of coronary aneurysms.

METHODS

Twenty-three patients with aneurysmal coronary artery disease and stable angina were enrolled into study (Group 1). Twenty-two patients without coronary aneurysm were selected as a control group (Group 2). PAI-1 was measured in peripheral venous blood.

RESULTS

The plasma PAI-1 level was lower in the coronary artery aneurysmatic patients compared to the control group (8.41 +/- 4.28 vs. 13.32 +/- 10.05 ng/ml, p = 0.037). Serum C-reactive protein (CRP) values were not significantly different between groups (3.83 +/- 1.08 vs. 4.01 +/- 1.35 mg/l, p >0.05).

CONCLUSION

Increased matrix degrading enzyme activity can cause arterial wall destruction through increased proteolysis of extracellular matrix proteins. Unregulated plasmin hyperactivity due to decreased inhibition by PAI-1 may play an important role in coronary aneurysm formation.