Aminoterminal propeptide of type III procollagen and matrix metalloproteinases-2 and -9 failed to serve as serum markers for abdominal aortic aneurysm

Changes in endocan and dermatan sulfate are associated with biomechanical properties of abdominal aortic wall during aneurysm expansion and rupture

BACKGROUND AND AIMS

The study aimed to assess the potential of proteoglycans (PG) and collagens as serological biomarkers in the abdominal aortic aneurysm (AAA). Furthermore, we investigated the underlying mechano-biological interactions and signaling pathways.

METHODS

Tissue and serum samples from patients with ruptured AAA (rAAA, n=29), elective AAA (eAAA, n=78), and healthy individuals (n=8) were evaluated by histology, immunohistochemistry and Enzyme-linked Immunosorbent Assay (ELISA), mechanical properties were assessed by tensile tests. Regulatory pathways were determined by membrane-based sandwich immunoassay.

RESULTS

In AAA samples, collagen type I and III (Col1, Col3), chondroitin sulfate (CS), and dermatan sulfate (DS) were significantly increased compared to controls (3.0-, 3.2-, 1.3-, and 53-fold; p<0.01). Col1 and endocan were also elevated in the serum of AAA patients (3.6- and 6.0-fold; p<0.01), while DS was significantly decreased (2.5-fold; p<0.01). Histological scoring showed increased total PGs and focal accumulation in rAAA compared to eAAA. Tissue β-stiffness was higher in rAAA compared to eAAA (2.0-fold, p=0.02). Serum Col1 correlated with maximum tensile force and failure tension (r=0.448 and 0.333; p<0.01 and =0.02), tissue endocan correlated with α-stiffness (r=0.340; p<0.01). Signaling pathways in AAA were associated with ECM synthesis and VSMC proliferation. In particular, Src family kinases, PDGF- and EGF-related proteins seem to be involved.

CONCLUSIONS

Our findings reveal a structural association between collagen and PGs and their response to changes in mechanical loads in AAA. Particularly Col1 and endocan reflect the mechano-biological conditions of the aortic wall also in the patient's serum and might serve for AAA risk stratification.

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.

Serum matrix metalloproteinase-9 is a valuable biomarker for identification of abdominal and thoracic aortic aneurysm: a case-control study

Background

Matrix metalloproteinase-9 (MMP9) has been reported to play a key role in the pathogenesis of aortic aneurysm. However, few studies have assessed serum MMP9 levels in both abdominal aortic aneurysm (AAA) and thoracic aortic aneurysm (TAA). In this study, we investigated the serum levels of MMP9 in aortic aneurysm to evaluate its predictive and diagnostic efficacy for AAA and TAA, and explored the association of MMP9 with circulating laboratory markers.

Methods

A total of 296 subjects were enrolled, including 105 AAA patients, 79 TAA patients and 112 healthy controls. The levels of serum MMP9 were detected by enzyme-linked immunosorbent assay (ELISA).

Results

Compared to control group, both AAA and TAA patients had higher serum MMP9 levels in the overall comparison and subgroup analysis based on subjects aged<65 years, either male or female, hypertension, non-diabetes and non-hyperlipidemia (all P<0.05). Moreover, MMP9 levels were significantly higher in TAA group than those in AAA group in the total comparison, and this discrepancy was also found in the non-diabetes, non-hyperlipidemia and aortic diameter ≥ 5.5 cm subgroup analysis. Serum MMP9 levels were influenced by age and hypertension. There was a positive association of serum MMP9 with CRP (r = 0.33, P < 0.001) and Hcy (r = 0.199, P = 0.033). Multiple logistic analyses showed that serum MMP9 was an independent risk factor for AAA and TAA. Based on receiver operating characteristic (ROC) analysis, the area under the curve (AUC) of MMP9 for predicting TAA was 0.83 with 70% sensitivity and 91% specificity, while the AUC of MMP9 to detect AAA was 0.69 and the sensitivity and specificity were 50% and 88%.

Conclusions

Serum MMP9 was closely related to the existence of aortic aneurysms and could be a valuable marker for the discrimination of aortic aneurysm, especially for TAA.

Dilating Vascular Diseases: Pathophysiology and Clinical Aspects

Atherosclerotic disease of the vessels is a significant problem affecting mortality and morbidity all over the world. However, dilatation of the vessels either in the arterial system or in the venous territory is another vessel disease. Varicocele, pelvic, and peripheral varicose veins and hemorrhoids are aneurysms of the venous vascular regions and have been defined as dilating venous disease, recently. Coronary artery ectasia, intracranial aneurysm, and abdominal aortic aneurysm are examples of arterial dilating vascular diseases. Mostly, they have been defined as variants of atherosclerosis. Although there are some similarities in terms of pathogenesis, they are distinct from atherosclerotic disease of the vessels. In addition, pathophysiological and histological similarities and clinical coexistence of these diseases have been demonstrated both in the arterial and in the venous system. This situation underlies the thought that dilatation of the vessels in any vascular territory should be considered as a systemic vessel wall disease rather than being a local disease of any vessel. These patients should be evaluated for other dilating vascular diseases in a systematic manner.

Abdominal Aortic Aneurysm: Evolving Controversies and Uncertainties

Abdominal aortic aneurysm (AAA) is defined as a permanent dilatation of the abdominal aorta that exceeds 3 cm. Most AAAs arise in the portion of abdominal aorta distal to the renal arteries and are defined as infrarenal. Most AAAs are totally asymptomatic until catastrophic rupture. The strongest predictor of AAA rupture is the diameter. Surgery is indicated to prevent rupture when the risk of rupture exceeds the risk of surgery. In this review, we aim to analyze this disease comprehensively, starting from an epidemiological perspective, exploring etiology and pathophysiology, and concluding with surgical controversies. We will pursue these goals by addressing eight specific questions regarding AAA: (1) Is the incidence of AAA increasing? (2) Are ultrasound screening programs for AAA effective? (3) What causes AAA: Genes versus environment? (4) Animal models: Are they really relevant? (5) What pathophysiology leads to AAA? (6) Indications for AAA surgery: Are surgeons over-eager to operate? (7) Elective AAA repair: Open or endovascular? (8) Emergency AAA repair: Open or endovascular?

Matrix Metalloproteinases, Vascular Remodeling, and Vascular Disease

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that degrade various proteins in the extracellular matrix (ECM). Typically, MMPs have a propeptide sequence, a catalytic metalloproteinase domain with catalytic zinc, a hinge region or linker peptide, and a hemopexin domain. MMPs are commonly classified on the basis of their substrates and the organization of their structural domains into collagenases, gelatinases, stromelysins, matrilysins, membrane-type (MT)-MMPs, and other MMPs. MMPs are secreted by many cells including fibroblasts, vascular smooth muscle (VSM), and leukocytes. MMPs are regulated at the level of mRNA expression and by activation through removal of the propeptide domain from their latent zymogen form. MMPs are often secreted in an inactive proMMP form, which is cleaved to the active form by various proteinases including other MMPs. MMPs degrade various protein substrates in ECM including collagen and elastin. MMPs could also influence endothelial cell function as well as VSM cell migration, proliferation, Ca²⁺ signaling, and contraction. MMPs play a role in vascular tissue remodeling during various biological processes such as angiogenesis, embryogenesis, morphogenesis, and wound repair. Alterations in specific MMPs could influence arterial remodeling and lead to various pathological disorders such as hypertension, preeclampsia, atherosclerosis, aneurysm formation, as well as excessive venous dilation and lower extremity venous disease. MMPs are often regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs), and the MMP/TIMP ratio often determines the extent of ECM protein degradation and tissue remodeling. MMPs may serve as biomarkers and potential therapeutic targets for certain vascular disorders.

Matrix Metalloproteinase Inhibitors as Investigational and Therapeutic Tools in Unrestrained Tissue Remodeling and Pathological Disorders

Matrix metalloproteinases (MMPs) are zinc-dependent proteolytic enzymes that degrade various proteins in the extracellular matrix (ECM). MMPs may also regulate the activity of membrane receptors and postreceptor signaling mechanisms and thereby affect cell function. The MMP family includes collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and other MMPs. Inactive proMMPs are cleaved by other MMPs or proteases into active MMPs, which interact with various protein substrates in ECM and cell surface. MMPs regulate important biological processes such as vascular remodeling and angiogenesis and may be involved in the pathogenesis of cardiovascular disorders such as hypertension, atherosclerosis, and aneurysm. The role of MMPs is often assessed by measuring their mRNA expression, protein levels, and proteolytic activity using gel zymography. MMP inhibitors are also used to assess the role of MMPs in different biological processes and pathological conditions. MMP activity is regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs), and the MMP/TIMP balance could determine the net MMP activity, ECM turnover, and tissue remodeling. Also, several synthetic MMP inhibitors have been developed. Synthetic MMP inhibitors include a large number of zinc-binding globulins (ZBGs), in addition to non-ZBGs and mechanism-based inhibitors. MMP inhibitors have been proposed as potential tools in the management of osteoarthritis, cancer, and cardiovascular disorders. However, most MMP inhibitors have broad-spectrum actions on multiple MMPs and could cause undesirable musculoskeletal side effects. Currently, doxycycline is the only MMP inhibitor approved by the Food and Drug Administration. New generation biological and synthetic MMP inhibitors may show greater MMP specificity and fewer side effects and could be useful in targeting specific MMPs, reducing unrestrained tissue remodeling, and the management of MMP-related pathological disorders.

EVAR and OPEN treatment of abdominal aortic aneurysm: What is the role of MMP-9 in the follow-up?

INTRODUCTION

The aim of our study is to verify the role of metalloproteinases in endovascular repair (EVAR) and OPEN surgery treatment for abdominal aortic aneurysm (AAA). Postoperatively, these enzymes could represent an important biomarker to adapt diagnostic tests and further investigations during follow-up.

MATERIAL AND METHOD

From 2004 to 2008, 55 patients were considered with AAA. Of these, 33 patients (mean age: 70.1 years), (mean AAA diameter: 5.4cm) were treated with OPEN surgery (group A) and 22 (mean age: 74.1 years) (mean AAA diameter: 5.1cm) were treated with EVAR. In 17 of them, there were no signs of endoleak (group B1), while in 5 patients, a presence of endoleak (group B2) was detected. Plasma samples were collected in order to determine MMP-9 activity. Enzyme immunoassay was performed preoperatively at 1, 3, 6 and 12 months. Patients treated conventionally were clinically examined after 1 and 12 months by ultrasound. Patients undergoing EVAR treatment were clinically examined by CT scan after 1, 3, 6 and 12 months. The analysis was done by assessing the interaction over time of the MMP-9 value in B1 and B2 groups.

RESULTS

The average values observed for MMP-9 were preoperatively and at 1, 3, 6 and 12 months, respectively: in group A 150.8ng/mL (SD=30.5), 252.5ng/mL (SD=25.2), 315.4ng/mL (SD=22.7), 295.3ng/mL (SD=26.8), 210.7ng/mL (SD=30.2); in group B1 105ng/mL (SD=10.8), 125.6ng/mL (SD=18), 85.8ng/mL (SD=19.9), 95ng/mL (SD=20.2), 80.4ng/mL (SD=15.6); in group B2 149ng/mL (29.2), 375.4ng/mL (SD=40.2), 215ng/mL (SD=35.9), 180ng/mL (SD=20.2), 175ng/mL (SD=33.4). The MMP-9 level was higher in group B2 compared to group B1 (P=0.01), suggesting a correlation with the presence of the endoleak.

CONCLUSIONS

This preliminary study shows that MMP-9 may be a biomarker of the presence of endoleak. Other further investigations and larger series are needed to show that metalloproteases could play a role in the follow-up of EVAR treated patients.

Circulating tetrahydrobiopterin as a novel biomarker for abdominal aortic aneurysm

Rupture of abdominal aortic aneurysm (AAA) is unpredictable and lethal. A clinically valid biomarker to monitor the disease has not been available. Based on our recent discoveries that uncoupled endothelial nitric oxide synthase (eNOS)/tetrahydrobiopterin deficiency plays a causal role in various models of AAA, the present study examined the relationship between circulating and tissue levels of tetrahydrobiopterin (H4B) in angiotensin II-infused hyperphenylalaninemia (hph-1) and apoE null mice. For apoE null mice, tissue and plasma H4B levels decreased time dependently, to 2.69 ± 0.15 and 1.99 ± 0.06 pmol/mg, respectively (from 4.86 ± 0.32 and 3.31 ± 0.13 pmol/mg at baseline) by week 3, when aneurysms developed. For hph-1 mice, tissue and plasma H4B levels decreased significantly to 1.02 ± 0.10 and 0.98 ± 0.09 pmol/mg, respectively (from 1.84 ± 0.18 and 1.48 ± 0.12 pmol/mg at baseline), by week 1, when aneurysms developed. Oral folic acid administration, which has been shown to improve aortic H4B levels to completely prevent or markedly decrease the incidence of AAA, significantly increased tissue and plasma H4B levels in both animal models starting at week 1. The two H4B measurements at all conditions showed significant linear correlation, suggesting that plasma H4B accurately predicts its tissue levels when H4B is either reduced or enhanced. Together, these data demonstrate that H4B levels decrease with AAA development and increase with folic acid treatment in two different murine models of AAA and that plasma H4B levels accurately reflect H4B levels in the tissue, suggesting that circulating H4B levels may be used clinically as a novel and powerful biomarker for the development and response to treatment of AAA.

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.

Cysteine protease cathepsins and matrix metalloproteinases in the development of abdominal aortic aneurysms

Both cysteine protease cathepsins and matrix metalloproteinases are implicated in the pathogenesis of abdominal aortic aneurysms (AAAs) in humans and animals. Blood and aortic tissues from humans or animals with AAAs contain much higher levels of these proteases, and often lower levels of their endogenous inhibitors, than do blood and aortic tissues from healthy subjects. Protease- and protease inhibitor-deficient mice and synthetic protease inhibitors have affirmed that cysteinyl cathepsins and matrix metalloproteinases both participate directly in AAA development in several experimental model systems. Here, we summarize our current understanding of how proteases contribute to the pathogenesis of AAA, and discuss whether proteases or their inhibitors may serve as diagnostic biomarkers or potential therapeutic targets for this common human arterial disease.

Matrix metalloproteinase inhibitors as investigative tools in the pathogenesis and management of vascular disease

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade various components of the extracellular matrix (ECM). MMPs could also regulate the activity of several non-ECM bioactive substrates and consequently affect different cellular functions. Members of the MMPs family include collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and others. Pro-MMPs are cleaved into active MMPs, which in turn act on various substrates in the ECM and on the cell surface. MMPs play an important role in the regulation of numerous physiological processes including vascular remodeling and angiogenesis. MMPs may also be involved in vascular diseases such as hypertension, atherosclerosis, aortic aneurysm, and varicose veins. MMPs also play a role in the hemodynamic and vascular changes associated with pregnancy and preeclampsia. The role of MMPs is commonly assessed by measuring their gene expression, protein amount, and proteolytic activity using gel zymography. Because there are no specific activators of MMPs, MMP inhibitors are often used to investigate the role of MMPs in different physiologic processes and in the pathogenesis of specific diseases. MMP inhibitors include endogenous tissue inhibitors (TIMPs) and pharmacological inhibitors such as zinc chelators, doxycycline, and marimastat. MMP inhibitors have been evaluated as diagnostic and therapeutic tools in cancer, autoimmune disease, and cardiovascular disease. Although several MMP inhibitors have been synthesized and tested both experimentally and clinically, only one MMP inhibitor, i.e., doxycycline, is currently approved by the Food and Drug Administration. This is mainly due to the undesirable side effects of MMP inhibitors especially on the musculoskeletal system. While most experimental and clinical trials of MMP inhibitors have not demonstrated significant benefits, some trials still showed promising results. With the advent of new genetic and pharmacological tools, disease-specific MMP inhibitors with fewer undesirable effects are being developed and could be useful in the management of vascular disease.

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.

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.

Apoptotic cell death and rupture of abdominal aortic aneurysm

The abdominal aortic aneurysm (AAA) development and expansion is characterized by an extracellular matrix degradation and widespread inflammation. In contrast, the processes that characterize the AAA rupture are not completely understood. The results obtained in animal and clinical studies have shown the importance of inflammation, proteolysis, and antioxidant mechanisms in the aortic degeneration and formation of AAA. We hypothesize that the rupture of the AAA could have a similar pathway like an atherosclerotic plaque rupture, and in both the cases the apoptotic cell death of smooth muscle cells could play a significant role. If the apoptotic cell death significantly contributes to the expansion and rupture of aneurysm, the hypothesis is that aggressive medical antiapoptotic treatment with high doses of appropriate drugs could decrease the apoptotic index of smooth muscle cells, reduce the aneurysm expansion and prevent rupture.

Differential effect of 17-beta-estradiol on smooth muscle cell and aortic explant MMP2

OBJECTIVE

The present investigation tested the hypothesis that intrinsic gender-related differences exist in rat aortic smooth muscle cell matrix metalloproteinase 2 (MMP2).

METHODS

This investigation comprised 3 sets of experiments. Experiment I: Adult male and female rat aortic smooth muscle cells (RASMCs) at passages 4-8 were stimulated in serum-free media for 48 h with interleukin(IL)1beta at doses encountered in human abdominal aortic aneurysms (2 ng/mL). Messenger RNA was extracted from the RASMCs, and gene expression of MMP2 and tissue inhibitor of metalloproteinase 2 (TIMP2), a major MMP2 inhibitor, was measured by real-time polymerase chain reaction. MMP2 protein levels in conditioned media were measured by Western blotting, and MMP2 and TIMP2 activity quantified by standard and reverse gelatin zymography. Experiment II: Male and female RASMCs were incubated for 48 h in Dulbecco's modified Eagler's medium containing IL-1beta and 17-beta-estradiol at doses from 1x10(-10) to 1x10(-6) molar. MMP2 activity in the conditioned media was then determined. Experiment III: Male rats underwent sustained 17-beta-estradiol exposure for 21 d using extended-release, subcutaneously implanted pellets prior to sacrifice and aortic explantation. Aortas from males, females, and estradiol-treated males were stimulated with IL-1beta for 48-h, and MMP2 activity in the conditioned media was determined.

RESULTS

Experiment I: MMP2 gene expression was 3-fold higher in male compared with female IL-1beta stimulated RASMCs (P<0.0001). MMP2:TIMP2 gene expression ratio was 7.5-fold greater in male versus female RASMCs. MMP2 protein levels were 3-fold higher (2.68 versus 0.96 o.d./mg total protein, P=0.003) in male versus female RASMCs. Gelatinolytic activity was more than 6-fold higher (15,010 versus 2,472 o.d./mg total protein, P=0.002) in male versus female RASMCs. Experiment II: MMP2 activity in male and female RASMCs was not altered by a wide range of 17-beta-estradiol concentrations. Experiment III: When pretreated with 17-beta-estradiol, MMP2 activity in the media of male rat whole-aortic explants decreased 2-fold (P=0.002). This post-17-beta-estradiol treatment male level was not different than baseline female aortic explant MMP2 levels.

CONCLUSIONS

MMP2 is higher in male RASMCs compared to female RASMCs. Exogenous 17-beta-estradiol did not alter MMP2 activity in vitro, but in vivo 17-beta-estradiol exposure greatly decreased male aortic MMP2 production to levels seen in the female aorta. Gender differences in MMP2 are speculated to be associated with phenotypic differences in human abdominal aortic aneurysm formation.

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

BACKGROUND

The maximal diameter of abdominal aortic aneurysms (AAAs) is the dominating indication for repair. However half of the AAAs repaired would never have ruptured if left unrepaired, although small AAAs occasionally rupture. Earlier surgery may be associated with a lower mortality. More precise indicators for surgery are warranted. This systematic review identifies potential systemic biomarkers for AAA rupture or expansion.

METHODS

MEDLINE/PubMed and EMBASE (from 1985 trough May 2007) were searched with the medical subject heading abdominal aortic aneurysm and keywords "size", "progression" or "growth" or "expansion rate" or "rupture" on the basis of MESH tree and as a text search restricted to English, German, French and Italian. In addition, reference lists were studied and manual searches performed. Observational studies investigating the association of circulating biomarkers with AAA rupture, expansion or size were selected.

DATA EXTRACTION

Two reviewers (SU and GU) independently extracted the following data: year of publication, study characteristics, duration of follow-up, circulating biomarker, AAA expansion rate or size or rupture.

RESULTS

699 papers were identified. After exclusion of thoracic aneurysms and cardiac studies (n=118), surgical or medical treatment studies (n=179), case reports and animal studies (n=87), as well as reviews or letters (n=66), 249 articles were selected. Also excluded were 230 papers that did not report AAA size, expansion rate or rupture. 39 papers were included. Several potential biomarkers were identified. The strongest association with AAA was obtained with serum elastin peptides (SEP) and plasmin-antiplasmin (PAP) complexes. Matrix-degrading metalloproteinase 9 (MMP9) and interferon-gamma (IFN-gamma) could have clinical potential while many putative biomarkers showed poor association.

CONCLUSIONS

Several circulating agents in peripheral blood may predict AAA size, expansion rate or rupture. Few of them have clinical potential for future use. Confirmative studies and development of multivariate models are needed, together with continuing search for new biomarkers using the discovery based sciences within proteomics and/or genomics.

Abdominal aortic aneurysm: pathogenesis and implications for management

Abdominal aortic aneurysm (AAA) affects approximately 5% of elderly men and is responsible for a significant number of deaths in Western Countries. At present surgery by open or endovascular means is the only widely used therapy for this condition. In this review we examine the risk factors, serum, and genetic associations of AAA. Epidemiology studies suggest that smoking cessation and control of cholesterol and blood pressure should reduce the number of patients developing AAA. Natural history studies suggest that smoking cessation should reduce the rate of progression of AAA. Clear level 1 evidence for drug treatments of AAA are presently lacking; however, animal and human in vitro studies suggest that medication targeted at reducing inflammation and proteolysis are most likely to be beneficial, with limited data to support the use of statins, Angiotensin II inhibitors, and macrolides. Work has commenced in understanding which patients, identified by clinical, serum, and genotype, are more at risk of AAA progression and thus should be selected out for aggressive treatment. Well designed large multicenter randomized controlled trials are required to examine the medical treatment of AAA.

RECS1 is a negative regulator of matrix metalloproteinase-9 production and aged RECS1 knockout mice are prone to aortic dilation

BACKGROUND

RECS1 is a mechanical stress responsive gene and RECS1 knockout (KO) mice (older than 14 months) are prone to cystic medial degeneration (CMD). The present study was designed to assess whether RECS1 KO mice have altered gelatinase (matrix metalloproteinase (MMP)-2 and MMP-9) levels and whether they are prone to aortic dilation.

METHODS AND RESULTS

Aortic and plasma gelatinase levels in RECS1 KO and wild-type (WT) mice were assessed by gelatin zymography and Western blot analysis. Pro-MMP-9 (in the aorta), neutrophil gelatinase-associated lipocalin/MMP-9 complex (NGAL-MMP-9, in plasma), and active-MMP-9 protein levels were more abundant in KO mice throughout adulthood compared with WT mice. Aortic MMP-2, aortic MMP-9, and plasma MMP-9 activation increased with age, even though the aortic pro-MMP-9, plasma NGAL-MMP-9, aortic and plasma pro-MMP-2 production decreased: this was true both for the WT and KO animals. Aortic pro-MMP-2, aortic active-MMP-2, and plasma pro-MMP-2 protein levels were higher in the aged KO mice, but they were lower in the young KO mice than those in WT mice. Thoracic aortic dilation was observed only in the aged KO mice. In situ zymographic experiments confirmed that the increased aortic gelatinase activities were associated with CMD and aortic dilation observed in the aged KO mice.

CONCLUSIONS

RECS1 negatively regulates aortic MMP-9 production and knocking out RECS1 induces susceptibility to aortic dilation as well as CMD in the aged mice. The present study suggests that RECS1 plays protective roles in vascular remodeling. We speculate that inhibiting unfavorable deposition and extracellular matrix degradation are both important for prevention and treatment of aneurysms.

Activated protein C-protein C inhibitor complex: A new biological marker for aortic aneurysms

OBJECTIVE

The concentration of the complex between activated protein C (APC) and protein C inhibitor (PCI) is a measure of thrombin generation. We studied whether it can provide information useful for the diagnosis and treatment of arterial vascular disease.

METHODS

Blood was obtained from 429 vascular patients admitted consecutively during September 2004 to March 2005. The APC-PCI complex was measured by using a sandwich immunofluorometric method. The patients were divided into cohorts according to the planned treatment and compared with a control group of healthy individuals.

RESULTS

The APC-PCI complex concentration varied from 0.08 to 2.50 microg/L. In the cohort of patients with aortic aneurysms (n = 78), the median APC-PCI value was 0.45 (10th to 90th percentile, 0.24-1.47), and values were clearly increased compared with all other cohorts (P < .0001). Patients with carotid disease (n = 73) yielded a median of 0.22 (10th to 90th percentile, 0.15-0.48). The median for claudicants (n = 74) was 0.26 microg/L (10th to 90th percentile, 0.15-0.75), which was higher than in those (n = 97) with critical ischemia (0.20; 10th to 90th percentile, 0.13-0.36; P < .0023). The cohort with other forms of atherosclerotic disease (n = 40) had a median of 0.23 (10th to 90th percentile, 0.14-0.42), whereas the value for a cohort of 21 patients with venous disease was 0.19 (10th to 90th percentile, 0.10-0.34). The median was 0.15 (10th to 90th percentile, 0.10-0.23) for the control group (n = 121).

CONCLUSIONS

Patients with atherosclerosis had an increased APC-PCI concentration that corresponded to increased generation of thrombin. Patients with aortic aneurysm had a threefold higher median concentration than the control group. We suggest that this remarkable increase is caused by the local activation of coagulation, and we surmise that APC-PCI measurements can be used as a screening tool to identify patients with aortic aneurysms.

Abdominal aortic aneurysms: an underestimated type of immune-mediated large vessel arteritis?

PURPOSE OF REVIEW

To review recent studies on the immune-mediated pathogenesis of abdominal aortic aneurysms, opening a wide field for possible new therapeutic approaches.

RECENT FINDINGS

Immune-mediated processes including involvement of neutrophils, interferon-gamma producing T cells and proinflammatory cytokines play an important role especially in the initiation of abdominal aortic aneurysm disease. C-reactive protein was associated with aneurysm size and is possibly produced by the aneurysmal tissue itself. From the clinical perspective, both inflammatory and noninflammatory abdominal aortic aneurysms are associated with various autoimmune diseases. Preliminary data of F-FDG positron emission tomography imaging of abdominal aortic aneurysms suggest focal uptake of F-FDG within the aneurysm wall in patients with either large, rapidly expanding or symptomatic aneurysms that are prone to rupture. Thus basic research findings and clinical research focusing on the underlying immune-mediated mechanisms of abdominal aortic aneurysms will likely pave the way for new medical therapies in the future. In animal models the effects of rapamycin as an immunosuppressive agent, modulation of estrogen receptors by tamoxifen as well as gene therapy using decoy oligonucleotides binding to the transcription factor ets has already proved helpful in decreasing aneurysm expansion rates.

SUMMARY

Pathophysiological, immunogenetical and interventional studies support the concept of abdominal aortic aneurysm as an immune-mediated process, which will help to identify more laboratory and imaging signs of development in the future. Further research will now assess the possible benefit of antiinflammatory therapeutic approaches, especially in patients with small abdominal aortic aneurysms.