Aminoterminal propeptide of type III procollagen in the follow-up of patients with abdominal aortic aneurysms

Plasma complement component C2: a potential biomarker for predicting abdominal aortic aneurysm related complications

Blood-based adjunctive measures that can reliably predict abdominal aortic aneurysm (AAA)-related complications hold promise for mitigating the AAA disease burden. In this pilot study, we sought to evaluate the prognostic performance of complement factors in predicting AAA-related clinical outcomes. We recruited consecutive AAA patients (n = 75) and non-AAA patients (n = 75) presenting to St. Michael's Hospital. Plasma levels of complement proteins were assessed at baseline, as well as prospectively measured regularly over a period of 2 years. The primary outcome was the incidence of rapidly progressing AAA (i.e. aortic expansion), defined as change in AAA diameter by either 0.5 cm in 6 months, or 1 cm in 12 months. Secondary outcomes included incidence of major adverse aortic events (MAAE) and major adverse cardiovascular events (MACE). All study outcomes (AAA diameter, MACE and MAAE) were obtained during follow-up. Multivariable adjusted Cox regression analyses were performed to assess the prognostic value of plasma C2 levels in patients with AAA regarding rapid aortic expansion and MAAE and MACE. Event-free survival rates of both groups were also compared. Compared to non-AAA patients, patients with AAA demonstrated significantly higher plasma concentrations of C1q, C4, Factor B, Factor H and Factor D, and significantly lower plasma concentrations of C2, C3, and C4b (p = 0.001). After a median of 24 months from initial baseline measurements, C2 was determined as the strongest predictor of rapid aortic expansion (HR 0.10, p = 0.040), MAAE (HR 0.09, p = 0.001) and MACE (HR 0.14, p = 0.011). Based on the data from the survival analysis, higher levels of C2 at admission in patients with AAA predicted greater risk for rapid aortic expansion and MAAE (not MACE). Plasma C2 has the potential to be a biomarker for predicting rapid aortic expansion, MAAE, and the eventual need for an aortic intervention in AAA patients.

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.

Circulating Biomarkers for the Prediction of Abdominal Aortic Aneurysm Growth

BACKGROUND

Abdominal aortic aneurysm represents a distinct group of vascular lesions, in terms of surveillance and treatment. Screening and follow-up of patients via duplex ultrasound has been well established and proposed by current guidelines. However, serum circulating biomarkers could earn a position in individualized patient surveillance, especially in cases of aggressive AAA growth rates. A systematic review was conducted to assess the correlation of AAA expansion rates with serum circulating biomarkers.

METHODS

A data search of English medical literature was conducted, using PubMed, EMBASE, and CENTRAL, until 7 March 2021, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statement (PRISMA) guidelines. Studies reporting on humans, on abdominal aortic aneurysm growth rates and on serum circulating biomarkers were included. No statistical analysis was conducted.

RESULTS

A total of 25 studies with 4753 patients were included. Studies were divided in two broad categories: Those reporting on clinically applicable (8 studies) and those reporting on experimental (17 studies) biomarkers. Twenty-three out of 25 studies used duplex ultrasound (DUS) for following patients. Amongst clinically applicable biomarkers, D-dimers, LDL-C, HDL-C, TC, ApoB, and HbA1c were found to bear the most significant association with AAA growth rates. In terms of the experimental biomarkers, PIIINP, osteopontin, tPA, osteopontin, haptoglobin polymorphisms, insulin-like growth factor I, thioredoxin, neutrophil extracellular traps (NETs), and genetic factors, as polymorphisms and microRNAs were positively correlated with increased AAA expansion rates.

CONCLUSION

In the presence of future robust data, specific serum biomarkers could potentially form the basis of an individualized surveillance strategy of patients presenting with increased AAA growth rates.

Hypovolemic shock induced by a large chest wall hematoma caused by a single rib fracture in an elderly patient

Displaced rib fractures can injure intercostal vessels leading to chest wall hematomas. As the bleeding occurs within the vessel, compression of the vessel wall helps in preventing further bleeding. Therefore, chest wall hematomas rarely result in shock. A thin 78-year-old man transferred to the emergency department with complaints of left dorsal pain due to an injury. He had a history of hypertension and aorta dissection. He arrived at the ED in a state of shock and presented with a large left dorsal wall mass. Subsequent imaging using computed tomography angiography revealed a large hyperdense hematoma at the left dorsal-flank wall along with rib fracture (11th intercostal artery). Moreover, a large fusiform aneurysm was detected from the abdominal aorta to the iliac arteries. Extravasation of the contrast agent was detected at the branch of the 11th intercostal artery, and hence, embolization was performed. The dermis, which comprises collagen and elastin fibers, plays an important role in vessel compression to prevent bleeding. The aortic media also comprises collagen and elastin fibers. Cell turnover, loss of collagen, and excessive elastolysis are associated with the formation of abdominal aortic aneurysms. The systemic degeneration of connecting tissue (collagen and elastin fiber) appears to be progress in patients with an aortic aneurysms and history of aortic dissection compared with other healthy older individuals. Physicians should be cognizant of the potential unexpected large hematoma complications if a risk of systemic connecting tissue degradation exists, as seen in patients with aortic aneurysm or aortic dissection.

Matrix Metalloproteinase in Abdominal Aortic Aneurysm and Aortic Dissection

Abdominal Aortic Aneurysm (AAA) affects 4–5% of men over 65, and Aortic Dissection (AD) is a life-threatening aortic pathology associated with high morbidity and mortality. Initiators of AAA and AD include smoking and arterial hypertension, whilst key pathophysiological features of AAA and AD include chronic inflammation, hypoxia, and large modifications to the extra cellular matrix (ECM). As it stands, only surgical methods are available for preventing aortic rupture in patients, which often presents difficulties for recovery. No pharmacological treatment is available, as such researchers are attempting to understand the cellular and molecular pathophysiology of AAA and AD. Upregulation of matrix metalloproteinase (MMPs), particularly MMP-2 and MMP-9, has been identified as a key event occurring during aneurysmal growth. As such, several animal models of AAA and AD have been used to investigate the therapeutic potential of suppressing MMP-2 and MMP-9 activity as well as modulating the activity of other MMPs, and TIMPs involved in the pathology. Whilst several studies have offered promising results, targeted delivery of MMP inhibition still needs to be developed in order to avoid surgery in high risk patients.

PARP-1 (Poly[ADP-Ribose] Polymerase 1) Inhibition Protects From Ang II (Angiotensin II)-Induced Abdominal Aortic Aneurysm in Mice

Abdominal aortic aneurysm (AAA) is a common vascular degenerative disease. PARP-1 (poly[ADP-ribose] polymerase 1) is a nuclear enzyme, which plays a critical role in vascular diseases. We hypothesized that PARP-1 inhibition might have protective effects on AAA. In vivo, Ang II (angiotensin II) was continuously infused by a micropump for 28 days to induce AAA in mice. In vitro, aortic endothelial cells and smooth muscle cells were stimulated by Ang II for 24 hours. Ang II infusion increased PARP-1 expression and activity and successfully induced AAA formation partly with a hemorrhage in ApoE^-/- mice. Genetic deletion of PARP-1 markedly reduced the AAA incidence, abdominal aortic diameter, macrophage infiltration, ICAM-1 (intercellular adhesion molecule 1) and VCAM-1 (vascular adhesion molecule 1) expression, and MMP (matrix metalloproteinase) expression, as well as MMP activity; but increased smooth muscle cells content and collagens expression in AAA. PARP-1 inhibition by PJ-34 also exerted a protective effect on AAA in mice. In aortic endothelial cells, Ang II-induced oxidative stress and DNA damage, resulting in increased PARP-1 expression and activity. Compared with the control, Ang II increased TNF-α (tumor necrosis factor α) and IL-6 (interleukin-6) secretions, ICAM-1 expression and THP-1 (human acute monocytic leukemia cell line) cells adhesion, while PARP-1 inhibition by siRNA reduced the inflammatory response probably through inhibition of the phosphorylation of ERK (extracellular signal-regulated kinase), NF-κB (nuclear factor-κB), and Akt signaling pathways. In smooth muscle cells, Ang II promoted cell migration, proliferation, and apoptosis, reduced collagens expression, but increased MMPs expression, while PARP-1 deletion alleviated these effects partly by reducing NF-κB-targeted MMP-9 expression. PARP-1 inhibition might be a feasible strategy for the treatment of AAA.

Systematic Review of Circulating, Biomechanical, and Genetic Markers for the Prediction of Abdominal Aortic Aneurysm Growth and Rupture

BACKGROUND

The natural course of abdominal aortic aneurysms (AAA) is growth and rupture if left untreated. Numerous markers have been investigated; however, none are broadly acknowledged. Our aim was to identify potential prognostic markers for AAA growth and rupture.

METHODS AND RESULTS

Potential circulating, biomechanical, and genetic markers were studied. A comprehensive search was conducted in PubMed, Embase, and Cochrane Library in February 2017, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Study selection, data extraction, and methodological quality assessment were conducted by 2 independent researchers. Plausibility of markers was based on the amount of publications regarding the marker (more than 3), pooled sample size (more than 100), bias risk and statistical significance of the studies. Eighty-two studies were included, which examined circulating (n=40), biomechanical (n=27), and genetic markers (n=7) and combinations of markers (n=8). Factors with an increased expansion risk included: AAA diameter (9 studies; n=1938; low bias risk), chlamydophila pneumonia (4 studies; n=311; medium bias risk), S-elastin peptides (3 studies; n=205; medium bias risk), fluorodeoxyglucose uptake (3 studies; n=104; medium bias risk), and intraluminal thrombus size (5 studies; n=758; medium bias risk). Factors with an increased rupture risk rupture included: peak wall stress (9 studies; n=579; medium bias risk) and AAA diameter (8 studies; n=354; medium bias risk). No meta-analysis was conducted because of clinical and methodological heterogeneity.

CONCLUSIONS

We identified 5 potential markers with a prognostic value for AAA growth and 2 for rupture. While interpreting these data, one must realize that conclusions are based on small sample sizes and clinical and methodological heterogeneity. Prospective and methodological consonant studies are strongly urged to further study these potential markers.

Non-coding RNAs in aneurysmal aortopathy

Aortic aneurysms represent a major public health burden, and currently have no medical treatment options. The pathophysiology behind these aneurysms is complex and variable, depending on location and underlying cause, and generally involves progressive dysfunction of all elements of the aortic wall. Changes in smooth muscle behavior, endothelial signaling, extracellular matrix remodeling, and to a variable extent inflammatory signaling and cells, all contribute to the dilation of the aorta, ultimately resulting in high mortality and morbidity events including dissection and rupture. A large number of researchers have identified non-coding RNAs as crucial regulators of aortic aneurysm development, both in humans and in animal models. While most work to-date has focused on microRNAs, intriguing information has also begun to emerge regarding the role of long-non-coding RNAs. This review summarizes the currently available data regarding the involvement of non-coding RNAs in aneurysmal aortopathies. Going forward, these represent key potential therapeutic targets that might be leveraged in the future to slow or prevent aortic aneurysm formation, progression and rupture.

Surrogate Markers of Abdominal Aortic Aneurysm Progression

The natural course of many abdominal aortic aneurysms (AAA) is to gradually expand and eventually rupture and monitoring the disease progression is essential to their management. In this publication, we review surrogate markers of AAA progression. AAA diameter remains the most widely used and important marker of AAA growth. Standardized reporting of reproducible methods of measuring AAA diameter is essential. Newer imaging assessments, such as volume measurements, biomechanical analyses, and functional and molecular imaging, as well as circulating biomarkers, have potential to add important information about AAA progression. Currently, however, there is insufficient evidence to recommend their routine use in clinical practice.

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.

Ruptured abdominal aortic aneurysm diagnosed through non-contrast MRI

Rupture of an aneurysm is a rare complication although it is considered a common cause of death. Some of these patients present with the classic triad of symptoms such as abdominal pain, pulsatile abdominal mass and shock. Most symptoms are misleading and will only present as vague abdominal pain. Here we describe one such patient with an unusual presentation of a misleading abdominal mass which was eventually diagnosed as a ruptured abdominal aortic aneurysm after an emergency MRI.

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

OBJECTIVE

Patients with abdominal aortic aneurysms have lower concentrations of high-density lipoproteins (HDLs), leading us to investigate whether increasing plasma HDLs could influence aneurysm formation.

METHODS AND RESULTS

Using the angiotensin II-induced hypercholesterolemic and the CaCl(2)-induced normocholesterolemic mouse model of AAA, we investigated the hypothesis that elevation of HDLs inhibits AAA. HDLs elevated before or at the time of AAA induction reduced AAA formation in both models but had no effect on early ruptures. Analysis of protein lysates from specific aortic segments demonstrated site-specific effects of HDLs on early signal transduction and cellular attrition. We found that HDLs reduced extracellular signal related kinases 1/2 activation in the suprarenal segment, while having no effect on p38 mitogen-associated protein kinase activation in any aortic segment and inhibiting c-Jun N-terminal kinase activation in all aortic segments. In addition, HDL elevation inhibited angiotensin II-induced apoptosis while inducing autophagy in the suprarenal segment of the aorta. Using Illumina gene array profiling we investigated the ability of HDL to modulate basal suprarenal aortic gene expression.

CONCLUSIONS

Increasing plasma HDLs inhibit experimental AAA formation, independent of hypercholesterolemia via reduced extracellular signal related kinases 1/2 activation and alteration of the balance of cellular attrition. HDLs modulate genes involved in matrix remodelling, cell migration, and proliferation.

Plasma cathepsin S and cystatin C levels and risk of abdominal aortic aneurysm: a randomized population-based study

BACKGROUND

Human abdominal aortic aneurysm (AAA) lesions contain high levels of cathepsin S (CatS), but are deficient in its inhibitor, cystatin C. Whether plasma CatS and cystatin C levels are also altered in AAA patients remains unknown.

METHODS AND RESULTS

Plasma samples were collected from 476 male AAA patients and 200 age-matched male controls to determine CatS and cystatin C levels by ELISA. Student's t test demonstrated higher plasma levels of total, active, and pro-CatS in AAA patients than in controls (P<0.001). ROC curve analysis confirmed higher plasma total, active, and pro-CatS levels in AAA patients than in controls (P<0.001). Logistic regression suggested that plasma total (odds ratio [OR] = 1.332), active (OR = 1.21), and pro-CatS (OR = 1.25) levels were independent AAA risk factors that associated positively with AAA (P<0.001). Plasma cystatin C levels associated significantly, but negatively, with AAA (OR = 0.356, P<0.001). Univariate correlation demonstrated that plasma total and active CatS levels correlated positively with body-mass index, diastolic blood pressure, and aortic diameter, but negatively with the lowest ankle-brachial index (ABI). Plasma cystatin C levels also correlated negatively with the lowest ABI. Multivariate linear regression showed that plasma total, active, and pro-CatS levels correlated positively with aortic diameter and negatively with the lowest ABI, whereas plasma cystatin C levels correlated negatively with aortic diameter and the lowest ABI, after adjusting for common AAA risk factors.

CONCLUSIONS

Correlation of plasma CatS and cystatin C with aortic diameter and the lowest ABI suggest these serological parameters as biomarkers for human peripheral arterial diseases and AAA.

Deficiency of interleukin-1 receptor antagonist promotes spontaneous femoral artery aneurysm formation in mice

Femoral artery aneurysms (FAAs) are very rare, and their natural history is not well understood. In this study, we sought to analyze the pathogenesis of inflammatory FAAs in interleukin-1 receptor antagonist-deficient (IL-1Ra(-/-)) B6 mice. Systolic arterial pressures and plasma lipid levels of IL-1Ra(-/-) mice and wild-type (WT) mice did not differ significantly. However, IL-1Ra(-/-) mice spontaneously developed fusiform FAAs. Real-time PCR of 9-month-old IL-1Ra(-/-) mice revealed significantly increased mRNA levels of IL-1β (6.6-fold), tumor necrosis factor-α (TNF-α) (12.4-fold), and matrix metalloproteinase-9 (6.0-fold) compared with WT mice. Histological analysis revealed numerous inflammatory cells around the FAAs in IL-1Ra(-/-) mice, and elastin staining showed destruction of both the internal and external elastic lamina in IL-1Ra(-/-) mice. Afterward, macrophage function was studied. After lipopolysaccharide (1 μg/mL) stimulation, IL-1Ra-deficient macrophages produced much higher levels of TNF-α than those from WT mice. Finally, we performed bone marrow cell transplantation. FAAs with many inflammatory cells in the adventitia were detected in several WT mice that received bone marrow cells from IL-1Ra(-/-) mice (44%), but not from WT mice (0%). Our study is the first to demonstrate that IL-1Ra deficiency in inflammatory cells disrupts immune system homeostasis and induces inflammatory FAAs in IL-1Ra(-/-) B6 mice. We believe that these mice will provide much information about the natural history and management of FAAs.

Differential roles of endothelin-1 in angiotensin II-induced atherosclerosis and aortic aneurysms in apolipoprotein E-null mice

Because both endothelin-1 (ET-1) and angiotensin II (AngII) are independent mediators of arterial remodeling, we sought to determine the role of ET receptor inhibition in AngII-accelerated atherosclerosis and aortic aneurysm formation. We administered saline or AngII and/or bosentan, an endothelin receptor antagonist (ERA) for 7, 14, or 28 days to 6-week- and 6-month-old apolipoprotein E-knockout mice. AngII treatment increased aortic atherosclerosis, which was reduced by ERA. ET-1 immunostaining was localized to macrophage-rich regions in aneurysmal vessels. ERA did not prevent AngII-induced aneurysm formation but instead may have increased aneurysm incidence. In AngII-treated animals with aneurysms, ERA had a profound effect on the non-aneurysmal thoracic aorta via increasing wall thickness, collagen/elastin ratio, wall stiffness, and viscous responses. These observations were confirmed in acute in vitro collagen sheet production models in which ERA inhibited AngII's dose-dependent effect on collagen type 1 α 1 (COL1A1) gene transcription. However, chronic treatment reduced matrix metalloproteinase 2 mRNA expression but enhanced COL3A1, tissue inhibitor of metalloproteinase 1 (TIMP-1), and TIMP-2 mRNA expressions. These data confirm a role for the ET system in AngII-accelerated atherosclerosis but suggest that ERA therapy is not protective against the formation of AngII-induced aneurysms and can paradoxically stimulate a chronic arterial matrix remodeling response.

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.

Elevation of ADAM10, ADAM17, MMP-2 and MMP-9 expression with media degeneration features CaCl2-induced thoracic aortic aneurysm in a rat model

PURPOSE

This study was designed to establish a rat model of thoracic aortic aneurysm (TAA) by calcium chloride (CaCl(2))-induced arterial injury and to explore the potential role of a disintegrin and metalloproteinase (ADAM), matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs) in TAA formation.

METHODS

Thoracic aorta of male Sprague-Dawley rats was exposed to 0.5M CaCl(2) or normal saline (NaCl). After 12weeks, animals were euthanized, and CaCl(2)-treated, CaCl(2)-untreated (n=12) and NaCl-treated aortic segments (n=12) were collected for histological and molecular assessments. MMP-TIMP and ADAM mRNAs were semi-quantitatively analyzed and protein expressions were determined by immunohistochemistry.

RESULTS

Despite similar external diameters among CaCl(2)-treated, non-CaCl(2)-treated and NaCl-treated segments, aneurymal alteration (n=6, 50%), media degeneration with regional disruption, fragmentation of elastic fiber, and increased collagen deposition (n=12, 100%) were demonstrated in CaCl(2)-treated segments. MMP-2, MMP-9, ADAM-10 and ADAM-17 mRNA levels were increased in CaCl(2)-treated segments (all p<0.01), with trends of elevation in CaCl(2)-untreated segments, as compared with NaCl-treated segments. Immunohistochemistry displayed significantly increased expressions of MMP-2, MMP-9, ADAM-10 and ADAM-17 (all p<0.01) in intima and media for CaCl(2)-treated segments. TIMP mRNA and tissue levels did not differ obviously among the three aortic segments.

CONCLUSION

This study establishes a TAA model by periarterial CaCl(2) exposure in rats, and demonstrates a significant elevation of expression of MMP-2, MMP-9, ADAM10 and ADAM17 in the pathogenesis of vascular remodeling.

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.

Does size matter? Clinical applications of scaling cardiac size and function for body size

Extensive evidence is available that cardiovascular structure and function, along with other biological properties that span the range of organism size and speciation, scale with body size. Although appreciation of such factors is commonplace in pediatrics, cardiovascular measurements in the adult population, with similarly wide variation in body size, are rarely corrected for body size. In this review, we describe the critical role of body size measurements in cardiovascular medicine. Using examples, we illustrate the confounding effects of body size. Current cardiovascular scaling practices are reviewed, as are limitations and alternative relationships between body and cardiovascular dimensions. The experimental evidence, theoretical basis, and clinical application of scaling of various functional parameters are presented. Appropriately scaled parameters aid diagnostic and therapeutic decision making in specific disease states such as hypertrophic cardiomyopathy and congestive heart failure. Large-scale studies in clinical populations are needed to define normative relationships for this purpose. Lack of appropriate consideration of body size in the evaluation of cardiovascular structure and function may adversely affect recognition and treatment of cardiovascular disease states in the adult patient.

Vascular Remodeling in Transplant Vasculopathy

As therapeutic strategies to prevent acute rejection progressively improve, transplant vasculopathy (TV) constitutes the single most important limitation for long-term functioning of solid organ allografts. In TV, allograft arteries characteristically develop severe, diffuse intimal hyperplastic lesions that eventually compromise luminal flow and cause ischemic graft failure. Traditional immunosuppressive strategies that check acute allograft rejection do not prevent TV; indeed 50% of transplant recipients will have significant disease within five years of organ transplantation, and 90% will have significant TV a decade after their surgery. TV can involve the entire length of the transplanted arterial bed, including penetrating intraorgan arterioles. Indeed, the luminal narrowing of such penetrating vessels may be the most functionally significant because arterioles represent the major contributors to tissue vascular resistance. Because of the diffuseness of TV involvement in the allograft vascular bed, the only currently definitive therapy requires re-transplantation. Nevertheless, as we better understand the pathogenesis and critical mediators of these lesions, pharmacological advances can be anticipated. Other articles in this thematic review series focus on the specifics of the inciting injury, the cytokines and chemokines that drive TV development, and the nature of the recruited cells in TV lesions, as well as the pathogenic similarities between TV and other vascular lesions such as atherosclerosis. This review focuses on the mechanisms of vascular wall remodeling in TV, including the intimal accumulation of smooth muscle-like cells and associated extracellular matrix, medial smooth muscle cell degeneration, and adventitial fibrosis. A brief overview highlights the aneurysmal changes that can accrue when vessel wall inflammation has a cytokine profile distinct from the typical proinflammatory interferon-gamma-dominated milieu.

Pathogenesis of thoracic and abdominal aortic aneurysms

The major disease processes affecting the aorta are aortic aneurysms and dissections. Aneurysms are usually described in terms of their anatomic location, with thoracic aortic aneurysms (TAAs) involving the ascending and descending aorta in the thoracic cavity and abdominal aortic aneurysms (AAAs) involving the infrarenal abdominal aorta. Both thoracic and abdominal aortas are elastic arteries, and share similarities in their physical structures and cellular components. However, thoracic and abdominal aortas differ in their biochemical properties and the origin of their vascular smooth muscle cells (VSMCs). These similarities and differences between thoracic and abdominal aortas provide the basis for the various pathologic mechanisms observed in this disease. This review focuses on the comparison of the pathologic mechanisms involved in TAA and AAA.

Pharmacological targets in the treatment of abdominal aortic aneurysms

The natural history of an abdominal aortic aneurysm (AAA) is of progressive aortic wall degeneration occurring over the course of many years, ultimately, culminating in loss of structural integrity and fatal aortic rupture. Although surgical exclusion of an aneurysm can effectively prevent aortic rupture in large aneurysms, small aneurysms are generally completely asymptomatic and are very unlikely to rupture. Further, AAA can be easily diagnosed with noninvasive testing; thus, small aneurysms present an excellent opportunity for disease-modifying pharmacological intervention. Research over the past two decades has defined many of the mechanisms which result in aortic matrix degeneration in both human tissue and particularly within animal models. This has resulted in the identification of several potential targets for pharmacological intervention. Drugs directed at inhibition of the inflammatory process and matrix degrading enzymes have been successful in multiple animal models, and early evidence now suggests that disease modification with some of these agents may be successful in slowing AAA growth in humans as well. The future of AAA therapy, however, may belong to agents which can induce aneurysm regression and to delivery methods which specifically target affected arterial tissue.

Inflammation and cellular immune responses in abdominal aortic aneurysms

Expansion and rupture of abdominal aortic aneurysms (AAA) result in high morbidity and mortality rates. Like stenotic atherosclerotic lesions, AAA accumulate inflammatory cells, but usually exhibit much more extensive medial damage. Leukocyte recruitment and expression of pro-inflammatory Th1 cytokines typically characterize early atherogenesis of any kind, and modulation of inflammatory mediators mutes atheroma formation in mice. However, the mechanistic differences between stenotic and aneurysmal manifestations of atherosclerosis remain unexplained. We recently showed that aortic allografts deficient in interferon-gamma (IFN-gamma) signaling developed AAA correlating with skewed Th2 cytokine environments, suggesting important regulatory roles for Th1/Th2 cytokine balance in modulating matrix remodeling and important implications for the pathophysiology of aortic aneurysm and atherosclerosis. Further probing of their distinct aspects of immune and inflammatory responses in vascular diseases should continue to shed new light on the pathophysiologic mechanisms that give rise to aneurysmal versus occlusive manifestations and atherosclerosis.

Circulating biomarkers of extracellular matrix remodeling and risk of atherosclerotic events

PURPOSE OF REVIEW

Disturbances of the synthesis and breakdown of the extracellular matrix of arterial walls have emerged as key features of the atherosclerotic process. Altered levels of circulating extracellular matrix markers have frequently been observed in relation to manifestations of atherosclerotic disease and its risk factors.

RECENT FINDINGS

Research has been focused on the matrix-degrading metalloproteinases, their tissue inhibitors, and procollagen peptides. The most promising matrix metalloproteinase is matrix metalloproteinase-9, which has been observed to predict rapid coronary artery narrowing, ischemic heart disease incidence, abdominal aortic aneurysm expansion, worse outcome in stroke patients, and cardiovascular death. The use of tissue inhibitors of metalloproteinases for prognostication is uncertain thus far. The procollagen marker with most prognostic potential is the marker for type III collagen turnover rate, the N-terminal propeptide PIIINP, higher levels of which predict an adverse outcome after a myocardial infarction and in chronic heart failure, and portend abdominal aortic aneurysm expansion and risk of rupture. Also, the marker for type I collagen synthesis, the C-terminal propeptide PICP, predicts adverse outcomes following myocardial infarction and in chronic heart failure. Extracellular matrix remodeling is also a promising therapeutic target, being favorably affected by several conventional cardiovascular drugs and select dietary interventions. Synthetic matrix metalloproteinase inhibitors are also under development.

SUMMARY

Circulating matrix markers have emerged as candidate biomarkers for predicting risk of subsequent atherosclerotic events. Future large longitudinal observational and intervention studies will determine the role of matrix biomarkers in diagnosis and prognostication, and as targets for intervention in cardiovascular diseases.

Application of real-time RT-PCR to quantifying gene expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases in human abdominal aortic aneurysm

BACKGROUND

The relative expression levels of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), key regulators in remodeling of extracellular matrix, are considered to play a pivotal role in the development of abdominal aortic aneurysm (AAA). However, few data exist regarding quantitative assessment of their expression in clinical settings.

METHODS

In 22 patients with AAA who underwent graft replacement, tissue samples of the AAA and non-dilated aorta were obtained. Using a real-time RT-PCR method that enabled quantitative measurement of mRNA levels in small tissue samples, we determined gene expression levels of MMPs and TIMPs relative to that of glutaraldehyde 3-phosphate dehydrogenase in each sample.

RESULTS

The expression levels of the MMP-1 and -3 genes were significantly augmented in AAA compared with non-dilated regions (4.48 +/- 2.01 versus 0.26 +/- 0.12, P < 0.01 and 1.89 +/- 1.00 versus 5.01 +/- 0.97, P < 0.05, respectively). Although genes for TIMP-1, -2 and -3 tended to be upregulated in AAA, relative expression levels of MMP-1 to TIMP-1, MMP-1 to TIMP-2, MMP-1 to TIMP-3, and MMP-3 to TIMP-2 were still higher in AAA than in non-dilated regions (1.12 +/- 0.63 versus 0.10 +/- 0.03, 4.13 +/- 1.12 versus 0.43 +/- 0.11, 1.61 +/- 0.59 versus 0.14 +/- 0.03, and 7.81 +/- 1.60 versus 2.56 +/- 0.76, respectively, P < 0.05).

CONCLUSION

These results demonstrate that the present real-time RT-PCR method is reliable for the determination of mRNA levels in small samples of vascular tissue and that disproportional expression of both MMP-1 and MMP-3 relative to TIMPs relates pathologically to the evolution of AAA.

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

OBJECTIVES

Matrix-metalloproteinase (MMP)-2 and -9 and aminoterminal propeptide of type III collagen (NIIINP) have been reported to be elevated in patients with abdominal aortic aneurysm (AAA). The aim of our study was to test NIIINP, MMP-2 and -9 as potential serum markers for AAA in a large population group at risk for AAA.

METHODS

Fifty-five to 70 year old men were screened for AAA by abdominal ultrasound. Simultaneously, blood samples were taken and the patients were interviewed for known risk factors for AAA. Patients with a dilatation of the infrarenal aorta of > or =25mm (Group 1, n=76) were compared to randomly assigned patients with normal aortic diameters (Group 2, n=83). A third group consisted of patients scheduled for operation of AAA (n=19).

RESULTS

A total of 987 men were investigated with ultrasound. Seventy-six (7.7%) had an aortic dilatation > or =25mm. Aortic dilatation was correlated with age (P=0.0001). However, serum levels of NIIINP and MMP 2 were not different between the three groups of patients. For MMP-9 there was a weak inverse correlation with lower serum levels in patients with aortic dilatation (P=0.043).

CONCLUSIONS

Both MMP-2 and -9 and NIIINP failed to show relevance as serum markers for aortic dilatation. Our results are, therefore, in contradiction to previous published results. AAAs cannot be diagnosed with a simple blood test.

Relationship between Hemostatic Markers and Circulating Biochemical Markers of Collagen Metabolism in Patients with Aortic Aneurysm

Our objective was to determine the relationship between plasma levels of hemostatic molecular markers--D-dimer and thrombin-antithrombin III complex (TAT)--and circulating biochemical markers of collagen metabolism--aminoterminal propeptide of type III procollagen (PIIIP) and carboxyterminal propeptide of type I procollagen (PICP)--in patients with aortic aneurysm. The subjects were 43 patients with aortic aneurysm (AA; mean age 71 years) and 26 age-matched controls (mean age 75 years). The mean D-dimer, TAT and PIIIP levels were higher in the patients than in the controls (p < 0.0001, 0.0001 and 0.012, respectively), while the mean PICP level was similar to that in the controls. Increased D-dimer had a significant correlation with PIIIP (r = 0.412, p = 0.006) and PICP (r = 0.342, p = 0.0246), while TAT correlated with PIIIP (r = 0.3194, p = 0.0374), but not with PICP. There was also a significant correlation (r = 0.306, p = 0.0463) between PIIIP and PICP. As shown by the significant positive correlations among D-dimer, TAT and PIIIP, accelerated fibrinolysis and thrombogenesis induce an increase of collagen degradation and procollagen synthesis in atherosclerotic lesions. These findings show that D-dimer and TAT, especially the former, may be useful markers to monitor the progression and predict the prognosis of AA.

Prospects for the medical management of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a chronic degenerative disease with life-threatening implications. While AAAs are thought to arise through a localized form of arterial wall injury superimposed on various predisposing factors, their natural history is one of progressive structural deterioration, gradual expansion, and eventual rupture. Pathologic processes contributing to the changes observed in AAAs include chronic inflammation, destructive remodeling of the extracellular matrix, and depletion of vascular smooth muscle cells. These changes result in progressive aortic dilatation accompanied by alterations in vessel geometry, redistribution of hemodynamic wall stresses, and diminished tensile strength. As outlined in this review, better understanding of the biological mechanisms underlying these changes will allow design of novel therapeutic strategies to suppress the process of aneurysmal degeneration.

Increased amount of type III pN-collagen in AAA when compared with AOD

OBJECTIVE

the extent of the processing of type III procollagen to type III collagen was determined in nine human abdominal aortic aneurysms (AAA), and compared with ten samples of aortoiliac occlusive disease (AOD).

METHODS

the aminoterminal propeptide (PIIINP) and telopeptide (IIINTP) of type III procollagen and collagen, respectively, were immunologically measured in the soluble and insoluble fractions of the extracellular matrix. The assay for PIIINP in the insoluble matrix was further validated.

RESULTS

the insoluble matrices of AAAs contained at least 12 times more incompletely processed type III pN-collagen than AOD specimens (0.74% and 0.061%, respectively). Also, the soluble extracts of AAAs tended to contain more non-processed type III pN-collagen than free, properly cleaved aminoterminal propeptide.

CONCLUSIONS

the larger amount of type III pN-collagen suggests an alteration in the metabolism of type III collagen in AAAs. This may partially explain the decreased tensile strength of the aortic tissue.

Serum levels of elastin-derived peptides in patients with ruptured and asymptomatic abdominal aortic aneurysms

OBJECTIVE

to determine whether serum elastin-derived peptides (S-EDP), are lower in patients with ruptured abdominal aortic aneurysms (rAAA) than asymptomatic (aAAA).

MATERIALS AND METHODS

serum samples were collected preoperatively from 45 consecutive patients with aAAA and 15 haemodynamically stable patients with rAAA. S-EDP (ng/ml) was measured by a competitive enzyme-linked immunosorbent assay (ELISA).

RESULTS

S-EDP (mean +/- s.d.) was significantly lower in patients with rAAA (31.6 ng/ml +/- 6.8) than in patients with aAAA (39.4 ng/ml +/- 8.0 p=0.001).

CONCLUSION

patients with rAAA had significantly lower levels of S-EDP than patients with aAAA. The possibility that S-EDP can be used to identify patients at increased risk of rupture requires further investigation.

Increased amount of type III pN-collagen in human abdominal aortic aneurysms: evidence for impaired type III collagen fibrillogenesis

PURPOSE

This study aimed to characterize the distribution of structural domains of type I and III collagens in the wall of abdominal aortic aneurysms (AAAs), by the use of undilated atherosclerotic aortas (aortoiliac occlusive disease [AOD]) and healthy abdominal aortas as controls.

METHODS

Immunohistochemical staining was applied with antibodies for the aminoterminal propeptides of type I (PINP) and type III (PIIINP) procollagens, which represent newly synthesized type I and III pN-collagens. In addition, an antibody against the aminoterminal telopeptide of type III collagen (IIINTP) was used as a means of detecting maturely cross-linked type III collagen fibrils.

RESULTS

The newly synthesized type III procollagen detected by means of PIIINP staining was concentrated in the media in aneurysmal aortas, whereas type I pN-collagen was localized in the intima in both AAAs and AODs. The healthy aortas showed no immunoreactivity for either PIIINP or PINP. The cross-linked type III collagen, detected by means of IIINTP staining, stained transmurally in all study groups, but appeared more abundant in the media in AAAs.

CONCLUSION

Our results strongly suggest that the metabolism of type III collagen is enhanced in AAAs. Intensive type III pN-collagen staining was present mainly in the media layer in AAAs, suggesting a role of type III collagen in aneurysm formation, whereas type I pN-collagen was present in the intima in both AAAs and AODs, suggesting that type I collagen synthesis is a fibroproliferative response related to the atherosclerotic process. The increased type III pN-collagen in AAAs may result in impaired fibril formation and, thus, in decreased tensile strength of aneurysmal tissue.

Elevated plasma levels of matrix metalloproteinase-9 in patients with abdominal aortic aneurysms: a circulating marker of degenerative aneurysm disease

PURPOSE

Matrix metalloproteinase-9 (MMP-9) is abundantly expressed in abdominal aortic aneurysms (AAAs), where it plays a pivotal role in connective tissue destruction. Elevated plasma concentrations of MMP-9 (MMP-9PL) also have been reported in patients with AAAs, but it is unclear if this can distinguish patients with AAAs from those with atherosclerotic occlusive disease (AOD). The purpose of this study was to further define the utility of elevated MMP-9PL levels in the diagnosis and evaluation of AAAs, and to examine if changes in MMP-9PL can be used as a functional biomarker of degenerative aneurysm disease.

MATERIALS AND METHODS

Peripheral venous blood was obtained from 25 patients with AAAs, 15 patients with AOD, and five normal control subjects. MMP-9PL levels were determined by an enzyme-linked immunosorbent assay. In four patients undergoing open AAA repair, MMP-9PL levels were directly compared with the amount of MMP-9 produced in aortic tissue. Six additional patients undergoing operative AAA repair were followed for 3-10 months to determine how treatment affected elevated MMP-9PL concentrations.

RESULTS

Mean (+/- SE) MMP-9PL was 36.1 +/- 7.7 ng/mL in normal control subjects, 54.7 +/- 10.5 ng/mL in patients with AOD, and 99.4 +/- 17.4 ng/mL in patients with AAAs (P < .05 versus normal control subjects and patients with AOD). Elevated MMP-9PL levels (> 87.8 ng/mL) were found in 12 of 25 (48%) patients with AAA but in only one of 15 (7%) patients with AOD (P < .05). MMP-9PL levels did not correlate significantly with either age, gender, or aneurysm diameter, although there was a trend toward the highest values in male patients with large AAAs. Production of MMP-9 in aneurysm tissues paralleled MMP-9PL levels, and elevated MMP-9PL levels decreased by 92.7% +/- 3.2% after surgical AAA repair.

CONCLUSIONS

Elevated MMP-9PL levels were observed in approximately one half of patients with AAAs and less than 10% of those with AOD (positive predictive value of 92.3%), but normal MMP-9PL levels had limited utility in excluding the presence of an aortic aneurysm (negative predictive value, 52%). MMP-9PL levels in patients with AAAs appeared to directly reflect the amount of MMP-9 produced within aneurysm tissue, and MMP-9PL levels decreased substantially after aneurysm repair. Measures of circulating MMP-9 may provide a biologically relevant marker of connective tissue metabolism in patients with AAAs.

Activity of matrix metalloproteinase-2 and -9 in abdominal aortic aneurysms. Relation to size and rupture

OBJECTIVES

to investigate the activity of matrix metalloproteinase (MMP)-2 and -9 in asymptomatic abdominal aortic aneurysms (aAAAs) and ruptured abdominal aortic aneurysms (rAAAs).

DESIGN

cross-sectional study.

MATERIALS AND METHODS

MMP-2 and MMP-9 activity was estimated in biopsies from the anterior wall of 60 AAAs using gelatin zymography. There were 20 medium-sized (diameter 5<7 cm) aAAAs, 20 large (>57 cm) aAAAs and 20 rAAAs. MMP activity was quantified using a laser densitometer and expressed as arbitrary units (au).

RESULTS

mean (SEM) MMP-9 activity was significantly lower in large aAAAs (1190 au +/-247) than in rAAAs (2647 au +/-498, p<0.05). There was no difference in MMP-2 activity.

CONCLUSION

High MMP-9 activity in the AAA wall is associated with rupture.

Circulating biochemical marker levels of collagen metabolism are abnormal in patients with abdominal aortic aneurysm

Changes in extracellular matrix composition induced by abnormal collagen metabolism in the aortic wall may be an important factor in the progression of aortic structural changes. The authors have measured several types of biochemical marker for collagen metabolism in plasma: carboxyterminal propeptide of type Icollagen (PICP) for a pure collagen synthesis marker, matrix metalloproteinase-1 (MMP-1) for a degradation marker of collagen matrix, and tissue inhibitors of metalloproteinase-1 (TIMP-1) as a native inhibitor of MMP-1. Subjects of this study were 17 patients with abdominal aortic aneurysm (AAA), 14 patients with atherosclerosis obliterans (ASO), and 22 age/sex-matched healthy controls (HC). Blood samples were drawn from a forearm vein and measured by radioimmunoassay or enzyme-linked immunosorbent assay. Plasma concentrations of PICP in patients with AAA were significantly decreased compared to those in HC patients (82.0 +/- 16.4 vs 111.3 +/- 40.3 ng/mL; p < 0.01), but those in patients with ASO (105.4 +/- 55.4 ng/mL) were comparable to control concentrations. Although no differences in plasma concentrations of MMP-1 were observed among the three subject groups (HC, 20.0 +/- 5.6 ng/mL; ASO, 21.4 +/- 13.8 ng/mL; AAA, 24.5 +/- 11.7 ng/mL; NS), MMP-1/PICP ratio as an index of collagen degradation to collagen neosynthesis in AAA was significantly elevated compared to HC (0.32 +/- 0.18 vs 0.20 +/- 0.08; p < 0.01). Plasma concentrations of TIMP-1 in patients with AAA (293.8 +/- 61.2 ng/mL) or ASO (327.6 +/- 54.9 ng/mL) were significantly higher than in HC (227.3 +/- 60.2 ng/mL; both p < 0.01). In conclusion, these data suggest that although a compensatory mechanism such as increased TIMP-1 may be activated, collagen neosynthesis may decrease with relatively increased collagen degradation in patients with AAA.