Potential circulating biomarkers for abdominal aortic aneurysm expansion and rupture--a systematic review

Disease specific biomarkers of abdominal aortic aneurysms detected by surface enhanced laser desorption ionization time of flight mass spectrometry

INTRODUCTION

Biomarkers have the potential to improve the clinical management of patients with AAA.

REPORT

A prospective, proteomics discovery study was undertaken to compare patients with AAA (n = 20) to matched screened controls (n = 19) for plasma protein expression. Surface-Enhanced-Laser-Desorption-Ionization Time of Flight Mass Spectrometry (SELDI ToF MS) coupled with Artificial Neural Networks (ANN) analysis identified six protein related diagnostic biomarker ions with a combined AUC of 0.89.

DISCUSSION

This study discovered a signature plasma protein profile for patients with AAA and demonstrated that mass spectrometric based research for disease specific biomarker of AAA is feasible.

Prediction of asymptomatic abdominal aortic aneurysm expansion by means of rate of variation of C-reactive protein plasma levels

OBJECTIVE

C-reactive protein (CRP) is an independent risk factor for arteriosclerosis, but its role in abdominal aortic aneurysm (AAA) expansion remains not completely verified. There are no data about the prognostic significance of rates of variation of the CRP levels in asymptomatic AAAs. This study investigated the association between plasma CRP levels and AAA diameter and assessed the relationship between the gradient of CRP levels and rates of expansion in asymptomatic AAAs.

METHODS

Plasma levels of high-sensitive CRP (hs-CRP) were measured using a high-sensitivity technique and AAA size was determined by computed tomography in 435 patients with asymptomatic AAAs followed up in our outpatient department.

RESULTS

The median hs-CRP level was 4.23 mg/L. The aorta diameter increased in the four groups of patients determined according to hs-CRP quartiles (35 ± 2, 40 ± 3, 49 ± 4, and 58 ± 5 mm; P = .01). The median rate of CRP level variation per year was 1.4 mg/L. Patients with an elevation >1.4 mg/L had an expansion rate of 4.8 mm vs 3.9 mm in those <1.4 mg/L (P < .01). The multivariate age-adjusted logistic model confirmed initial diameter and variation of CRP level were the only factors associated with expansion, with odds ratios (95% confidence intervals) of 6.3 (3.1-7.5) and 3.4 (2.1-5.6).

CONCLUSIONS

These results confirm a statistical association between AAA diameter and hs-CRP plasma levels. This cohort study corroborates this potential causal association and contributes information about the value of the hs-CRP plasma level gradient as a marker of disease progression and rate of expansion.

Cathepsin L activity is essential to elastase perfusion-induced abdominal aortic aneurysms in mice

OBJECTIVE

The development of abdominal aortic aneurysms (AAA) requires extensive aortic wall matrix degradation. Human AAA lesions express high levels of cathepsin L (CatL), one of the most potent mammalian elastases. Whether this protease participates directly in AAA pathogenesis, however, is unknown.

METHODS AND RESULTS

We generated experimental AAA with aortic elastase perfusion in mice and established an essential role of CatL in AAA formation. After 14 days postperfusion, most wild-type (Ctsl(+/+)) mice developed AAA, but none of the CatL-deficient (Ctsl(-/-)) mice did. AAA lesion macrophage contents, CD4(+) T cell numbers, CD31(+) and laminin-5 angiogenic fragment γ2(+) microvessel numbers, and elastin fragmentation were all significantly lower in Ctsl(-/-) mice than in Ctsl(+/+) mice. While lesions from Ctsl(-/-) mice contained fewer Ki67(+) proliferating cells than did Ctsl(+/+) mice, the absence of CatL did not affect lesion apoptotic cell contents or medial smooth-muscle cell loss significantly. Mechanistic studies indicated that the absence of CatL reduced lesion chemokine monocyte chemotactic protein-1 content, macrophage and T-cell in vitro transmigration, and angiogenesis, and altered the expression and activities of matrix metalloproteinases and other cysteinyl cathepsins in inflammatory cells, vascular cells, and AAA lesions.

CONCLUSION

CatL contributes to AAA formation by promoting lesion inflammatory cell accumulation, angiogenesis, and protease expression.

Discovery of a novel circulating biomarker in patients with abdominal aortic aneurysm: a pilot study using a proteomic approach

Abdominal aortic aneurysm (AAA) is a common condition with high mortality when ruptured. Most clinicians agree that small AAAs are best managed by ultrasonographic surveillance. However, it has been stated in recent reviews that a serum/plasma biomarker that predicts AAA rupture risk would be a powerful tool in stratifying patients with small AAA. Identification of such circulating biomarkers has been to date unsuccessful. In this study, we used a proteomic approach to find new, potential plasma AAA biomarker candidates. Prefractionated plasma samples were analyzed by two-dimensional differential in-gel electrophoresis to identify differentially expressed proteins between four patients with small AAA and four controls without aneurysm. Protein spots that differed significantly between patients and controls were selected and identified by mass spectrometry. Three protein spots had significantly different expression between patients and controls. The most interesting finding was that patients with small AAA had increased levels of the enzyme glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) compared with the controls without aneurysm. In conclusion, by using a proteomic approach, this pilot-study provides evidence of GPI-PLD as a novel potential plasma biomarker for AAA.

Matrix metalloproteinases and descending aortic aneurysms: parity, disparity, and switch

Central to the pathologic changes in developing aortic aneurysms are alterations in the abundance and activity of proteases, of which the most important for aneurysm production comprise the matrix metalloproteinase (MMP) family. In this review, literature demonstrating the role of MMPs in the development of aortic aneurysms is presented, with emphasis on the parity and disparity between the thoracic and abdominal aorta. Furthermore, the role of embryologic cellular origins and evidence of phenotypic switch will be addressed in terms of how this process alters MMP production during aneurysm development.

Differential protein expression in serum of abdominal aortic aneurysm patients - a proteomic approach

OBJECTIVE

The aim of the study is to investigate the differential expression of proteins in serum of abdominal aortic aneurysm (AAA) patients in relation to aneurysm size (D(max)) and progression.

METHODS

Two-dimensional differential in-gel electrophoresis (2D-DIGE) together with tandem mass spectrometry (MS/MS) was used to analyse the serum proteome from patients with small (D(max) 30-54 mm) AAA, either stable (increase D(max) <5 mm year⁻¹; n = 8) or progressive (increase D(max) ≥5 mm year⁻¹; n = 8), and large (D(max) ≥ 55 mm; n = 8) AAA. The identified proteins were quantitatively validated in a larger population (n = 80).

RESULTS

Several proteins were differentially expressed in serum of small stable, small progressive and large AAA. Three validated proteins (immunoglobulin G (IgG), α1-antitrypsin (α1-AT) and Factor XII activity) showed strong correlation with D(max). Size combined with either Factor XII activity or α1-antitrypsin had minimal effect on the prognostic value in predicting aneurysm progression compared with size alone (area under the curve (AUC), 0.85; 95% confidence interval (CI), 0.73-0.97; p < 0.001 and AUC, 0.85; 95% CI, 0.72-0.98; p < 0.001 vs. AUC, 0.83; 95% CI, 0.71-0.96; p < 0.001, respectively).

CONCLUSION

The present study indicates that both Factor XII and α1-antitrypsin are found in increased amounts in the serum of patients with expanding AAA. However, combination of either Factor XII or α1-antitrypsin with aneurysm diameter had little effect on prediction of aneurysm progression versus diameter alone.

Endovascular aneurysm repair reverses the increased titer and the inflammatory activity of interleukin-1α in the serum of patients with abdominal aortic aneurysm

OBJECTIVE

To examine serum cytokine/chemokine profiles before and 6 months after endovascular repair (EVAR) of abdominal aortic aneurysm (AAA) and to determine whether they correlate with serum inflammatory activity using an in vitro model of leukocyte recruitment.

METHODS

Serum IL-1-α, IL-1β, IL-4, IL-6, IL-8, IL-10, IFN-γ, IP-10, MCP-1, TNF-α, and TNF-β were measured using a cytometry-based immunoassay. To test patient serum for direct inflammatory activity, human endothelial cells (EC) were stimulated with 30% patient serum for 24 hours. To test patient serum for the ability to prime EC for inflammatory responses, EC were incubated with 30% patient serum for 24 hours, followed by stimulation with low-dose (5 U/mL) TNF for 4 hours. Under both regimens of stimulation, the degree of EC activation was assessed by assaying neutrophil recruitment in a flow-based model.

RESULTS

Only IL-1α (67.9 ± 10.4 pg/mL vs 41.9 ± 7.4 pg/mL) and IL-8 (51.5 ± 5.1 vs 32.6 ± 4.7 pg/mL) changed significantly after surgery. Patient serum alone was unable to activate EC. However, serum from both time points could prime EC responses to low-dose TNF. Thus, after priming with preoperative serum, EC stimulated with TNF could recruit 76.7 ± 12.0 neutrophils/mm(2) into the subendothelial cell space. Post-EVAR serum was significantly less effective (44.4 ± 10.2 neutrophils/mm(2)). This reduction in neutrophil recruitment correlated with reduced IL-1α in post-EVAR serum. The addition of a neutralizing antibody against IL-1α to pre-EVAR serum inhibited EC priming and neutrophil recruitment, strongly implying that this cytokine was the priming agent.

CONCLUSION

EVAR reduces serum IL-1α and its inflammatory activity in patient serum. IL-1α is, therefore, implicated in the molecular pathology of AAAs and may have potential as a clinically useful biomarker.

Diagnosis and monitoring of abdominal aortic aneurysm: current status and future prospects

Abdominal aortic aneurysm (AAA) remains an important cause of morbidity and mortality in elderly men, and prevalence is predicted to increase in parallel with a global aging population. AAA is commonly asymptomatic, and in the absence of routine screening, diagnosis is usually incidental when imaging to assess unrelated medical complaints. In the absence of approved diagnostic and prognostic markers, AAAs are monitored conservatively via medical imaging until aortic diameter approaches 50-55 mm and surgical repair is performed. There is currently significant interest in identifying molecular markers of diagnostic and prognostic value for AAA. Here we outline the current guidelines for AAA management and discuss modern scientific techniques currently employed to identify improved diagnostic and prognostic markers.

Novel aspects of the pathogenesis of aneurysms of the abdominal aorta in humans

Aneurysm of the abdominal aorta (AAA) is a particular, specifically localized form of atherothrombosis, providing a unique human model of this disease. The pathogenesis of AAA is characterized by a breakdown of the extracellular matrix due to an excessive proteolytic activity, leading to potential arterial wall rupture. The roles of matrix metalloproteinases and plasmin generation in progression of AAA have been demonstrated both in animal models and in clinical studies. In the present review, we highlight recent studies addressing the role of the haemoglobin-rich, intraluminal thrombus and the adventitial response in the development of human AAA. The intraluminal thrombus exerts its pathogenic effect through platelet activation, fibrin formation, binding of plasminogen and its activators, and trapping of erythrocytes and neutrophils, leading to oxidative and proteolytic injury of the arterial wall. These events occur mainly at the intraluminal thrombus-circulating blood interface, and pathological mediators are conveyed outwards, where they promote matrix degradation of the arterial wall. In response, neo-angiogenesis, phagocytosis by mononuclear cells, and a shift from innate to adaptive immunity in the adventitia are observed. Abdominal aortic aneurysm thus represents an accessible spatiotemporal model of human atherothrombotic progression towards clinical events, the study of which should allow further understanding of its pathogenesis and the translation of pathogenic biological activities into diagnostic and therapeutic applications.

Proteomics and pitfalls in the search for potential biomarkers of abdominal aortic aneurysms

Proteomics is evolving as an important research technique in cardiovascular disease. We present exploratory research for a systemic biomarker of abdominal aortic aneurysm (AAA) in serum. Forty patients, 20 with large AAAs and 20 matched controls, were prospectively recruited. Serum was harvested, enriched, and mined for differential protein expression. Difference in gel electrophoresis using a two-dimensional platform, cyanine labeling, and Progenesis SameSpots software identified protein spots with significantly altered intensity. Liquid chromatography mass spectrometry aligned to the Seaquest protein database characterized proteins of interest, and 436 protein spots were demonstrated from the 20 processed gels. Thirteen spots of interest, demonstrating fold change (1.7-4) between the two patient cohorts and consistent significant differential expression (analysis of variance, p </= .003), were picked for identification. Four of 13 spots were identified according to their tandem mass spectra. These were fragments of serum albumin, hemoglobin, and apolipoprotein C-II precursor. Identified spots represented proteins highly abundant in serum, not candidate biomarkers. Issues of variability surrounding serum harvest, processing, enrichment, and the challenge of identifying minimally expressed proteins currently limit this avenue of research. No proteins identified in this study had the biologic plausibility to represent a possible biomarker of aneurysmal disease. The tissue proteome may be a more rewarding approach for preliminary investigation of plausible biomarkers.

In search of blood tests for thoracic aortic diseases

A number of new diagnostic screening tools have been developed for the assessment of acute and chronic diseases of the thoracic aorta. Although standardized blood-based tests capable of detecting individuals at risk for aortic aneurysm and dissection disease are not yet available, our current knowledge is expanding at a rapid rate and the future is very promising. In this review, an update of the contemporary knowledge on blood tests for detecting thoracic aortic diseases in both preclinical and clinical settings is provided, offering the potential to predict adverse aortic events, such as enlargement, rupture, and dissection.

Proteins associated with the size and expansion rate of the abdominal aortic aneurysm wall as identified by proteomic analysis

OBJECTIVES

Identification of biomarkers for the natural history of abdominal aortic aneurysms (AAA) holds the key to non-surgical intervention and improved selection for AAA repair. We aimed to associate the basic proteomic composition of AAA wall tissue with the expansion rate and size in patients with AAA.

METHODS

A proteomic approach was used, consisting of two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and mass spectrometry (MS) to identify differentially expressed proteins in AAA tissue. Relevant protein spots were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Spearman's correlation analysis revealed 16 protein spots were strongly correlated with AAA expansion rate (ρ>±0.75). Nine protein spots were identified. Six protein spots showed correlation with AAA size (ρ>±0.5). Three protein spots were identified: vitronectin with traces of calreticulin, albumin and a spot containing two proteins: collagen α-3(VI) chain and vitamin D binding protein. Interestingly, in our previous study vitronectin was shown to be down-regulated in a ruptured AAA group compared with non-ruptured AAA. Western blot analysis in the present study confirmed a correlation of vitronectin bands with AAA size in aortic aneurysm tissue.

CONCLUSION

A proteomic approach seems valuable, and identified several candidates not previously associated with AAA. Larger studies are required to confirm the potential and clinical role of the identified proteins.

Markers of Proteolysis, Fibrinolysis, and Coagulation in Relation to Size and Growth Rate of Abdominal Aortic Aneurysms

We evaluated whether matrix metalloproteinases (MMPs) 2 and 9, their inhibitors, markers for fibrinolysis, and thrombin activation are associated with diameter and growth of abdominal aortic aneurysms (AAAs). Material and Methods: Matrix metalloproteinases 2 and 9, tissue inhibitor of MMPs (TIMP-1), serpine-1, tPa-serpine-1, and activated protein C— protein C inhibitor (APC-PCI) complex were analyzed in 353 patients with AAA grouped according to AAA size, and 219 gender- and age-matched healthy individuals. Follow-up of AAA growth for up to 7 years was possible in 178 of 353 patients. Results: At baseline, all groups of patients with AAA showed lower levels of MMP-2 and -9, and higher levels of TIMP-1, serpine-1, and t-Pa-serpine-1 than controls. Matrix metalloproteinase 2 correlated inversely and APC-PCI complex correlated directly with AAA diameter. We found no correlations between markers for proteolysis, fibrinolysis, coagulation, and yearly AAA growth. Conclusion: Matrix metalloproteinase 2 is lower and APC-PCI higher in patients with larger AAA, but the relevance of the markers for AAA growth is far from clarified.

Matrix metalloproteinases and peripheral arterial disease

Matrix metalloproteinases (MMPs), a family of enzymes that degrade extracellular matrix, are emerging as important modulators of atherothrombosis. MMPs are produced by inflammatory cells; some of them are also released by activated platelets and play a crucial role in the remodeling processes, leading to atherosclerotic plaque formation, plaque rupture, arterial aneurysm development, and critical limb ischemia. Independent from their matrix degrading activity, MMPs also regulate some cell functions relevant to atherothrombosis, such as platelet activation, neutrophil activation, and vascular reactivity. Plasma levels of some MMPs are increasingly being recognized as a biomarker of atherosclerosis and cardiovascular risk. In peripheral arterial disease, MMPs have been shown to be involved in angiogenesis, arteriogenesis, and the development of arterial calcifications. Increased plasma levels of some MMPs (MMP-2, MMP-9) have been correlated with PAD development and severity. Single nucleotide polymorphisms of the genes encoding for some MMPs have also been associated with the risk of developing peripheral arterial disease and critical limb ischemia. Large prospective observational studies are needed to further demonstrate the role of MMPs in PAD. In perspective, pharmacologic targeting of the expression or activity of MMPs may represent a novel, attractive approach for the treatment of peripheral arterial disease.

Growth rates of small abdominal aortic aneurysms correlate with clinical events

Background

This retrospective analysis of prospectively collected abdominal aortic aneurysm (AAA) screening data aimed to identify predictors of AAA-related events (surgery or death) with a view to better targeting of screening.

Methods

For the interval 1984–2007, data for 1649 subjects with an AAA were collected prospectively as part of the Chichester AAA screening programme. This included serial aortic size measurements, blood pressure, risk factors for arterial disease and concurrent medications. AAA growth rates were adjusted for risk factor confounders using flexible hierarchical modelling. AAA growth distribution was analysed using Silverman's test of multimodality.

Results

Some 1231 subjects met the inclusion criteria of having more than one scan and a surveillance interval of over 3 months. AAA growth showed a bimodal pattern with nearly 50 per cent of all aneurysms never progressing to surgery or rupture. Adjusted annual AAA growth rates of at least 2 mm significantly predicted AAA-related events.

Conclusion

This analysis identified a bimodal growth pattern for AAA, with a significant association between annual AAA growth rate of at least 2 mm and AAA-related events.

High Levels of Endothelin (ET)-1 and Aneurysm Diameter Independently Predict Growth of Stable Abdominal Aortic Aneurysms

The etiology of abdominal aortic aneurysm (AAA) includes inflammation and endothelial dysfunction. To evaluate relations between these mechanisms and AAA growth, endothelin (ET)-1, tumor necrosis factor (TNF)-α, interleukin (IL)-6, and CD40 ligand were related to yearly AAA growth for 2.9 ± 1.6 years (mean ± SD) in 178 patients with conservatively followed AAA. Total number of follow-up years was 491. Abdominal aortic aneurysm diameter increased by 3.3 ± 4.0 mm during the first year and by 4.9 ± 4.4 mm during the first 2 years. Median (range) growth was 2.5 (—1.0 to 30.6) mm/year. When patients with AAA growth above or below median were compared, initial AAA diameter (46.1 ± 5.8 vs 42.0 ± 8.3 mm; P < .0001), age (75 ± 7 vs 72 ± 8 years; P < .029), and initial ET-1 levels (1.31 ± 0.50 vs 1.13 ± 0.49 pg/mL; P < .0177) were higher in patients with growth above median. Endothelin 1 (P = .0230) and initial AAA diameter (P = .0019) predicted AAA growth above median in logistic regression. In conclusion, higher initial levels of ET-1 and initial AAA diameter independently predict AAA growth.

Review of Current Theories for Abdominal Aortic Aneurysm Pathogenesis

Atherosclerotic plaques are a feature of abdominal aortic aneurysms (AAAs). Atherosclerosis and AAA appear to share similar risk factors. These observations have led to the conclusion that AAAs are a consequence of advanced atherosclerosis.

This review explores current theories regarding the pathogenesis of AAA and their implications for treatment.

A systematic literature search was conducted using the search terms abdominal aortic aneurysm, atherosclerosis, pathogenesis, and systemic disease. Articles were categorized according to the association of AAAs with atherosclerosis, arteriomegaly, peripheral aneurysm, systemic expression, genetics, autoimmunity, oxidative stress, and systemic disease. Twenty-nine articles reporting changes in the systemic vasculature associated with AAA and 12 articles examining the shared risk factor hypothesis were identified.

There is insufficient evidence to confirm that AAAs are the result of advanced atherosclerosis. The bulk of evidence points to AAA disease being a systemic disease of the vasculature, with a predetermined genetic susceptibility leading to a phenotype governed by environmental factors.