Biochemistry and molecular regulation of matrix macromolecules in abdominal aortic aneurysms

A Novel Method for the Rat Model of Abdominal Aortic Aneurysm Induced by Retroperitoneal Implantation of an Osmotic Pump System With Lipopolysaccharide

BACKGROUND

Few methods can cocurrently mimic the pathological characteristics and nature history of human abdominal aortic aneurysms (AAAs), especially for the exist of the self-healing tendency of rodents. This study tested a novel method for the AAA rat model induced by retroperitoneal implantation of an osmotic pump system with lipopolysaccharide (LPS) based on the hypothesis that chronic inflammation of perivascular adipose tissue directly influenced the development and progression of AAAs.

METHODS

20 male Sprague-Dawley rats (10-month-old) fed with the Paigen diet were randomly divided into 4 groups: the blank group ×2, the sham group ×4, the empty capsule group ×4, and the LPS capsule group ×10. The LPS capsule group received implantations of the ALZET® osmotic pump capsule with LPS (3.6 μg/day) parallel to the abdominal aorta through a retroperitoneal approach. Two weeks later, 6 rats were randomly selected from the LPS capsule group to form the anti-inflammatory group and received implantations of another osmotic pump capsule with interleukin (IL)-10 (75 ng/day) through the same approach. The changes in abdominal aortic diameter were observed by ultrasound every 2 weeks, and samples were harvested for histopathologic and immunohistochemical analysis 6 weeks later.

RESULTS

Within the 6 weeks after modeling, the LPS capsule group showed sustained and significant aortic dilatation (P < 0.01), while the anti-inflammatory group showed a rapid and obvious shrinkage 2 weeks after the IL-10 osmotic pump capsule implantation (P < 0.01). The LPS capsule group presented excellent pathological mimicking of human AAAs and showed severe medial degeneration with the least elastic content among the 5 groups at the end of the sixth week (P < 0.05). Notably, the anti-inflammatory group showed perfect medial preservation with the most elastic content (P < 0.05) and the highest elastin/collagen ratio (P < 0.01) at the end of the study. Matrix metalloproteinases (MMP) 2 and 9 and toll-like receptor 2 showed strong expression in the LPS capsule group at the end of the sixth week, which was significantly higher than that in the blank group and sham group. Interestingly, the anti-inflammatory group showed a slightly higher MMP9 expression than the LPS capsule group though there was no statistical difference between them.

CONCLUSIONS

This novel method for the rat AAA model induced by retroperitoneal implantation of an osmotic pump capsule with LPS can concurrently mimic the histological characteristics and natural history of human AAAs. Further studies were needed to improve the osmotic pump system.

Oxidative Stress and the Pathogenesis of Aortic Aneurysms

Aortic aneurysms are responsible for significant morbidity and mortality. Despite their clinical significance, there remain critical knowledge gaps in the pathogenesis of aneurysm disease and the mechanisms involved in aortic rupture. Recent studies have drawn attention to the role of reactive oxygen species (ROS) and their down-stream effectors in chronic cardiovascular diseases and specifically in the pathogenesis of aortic aneurysm formation. This review will discuss current mechanisms of ROS in mediating aortic aneurysms, the failure of endogenous antioxidant systems in chronic vascular diseases, and their relation to the development of aortic aneurysms.

A Novel Model of Tobacco Smoke-Mediated Aortic Injury

OBJECTIVE

Tobacco smoke exposure is a major risk factor for aortic aneurysm development. However, the initial aortic response to tobacco smoke, preceding aneurysm formation, is not well understood. We sought to create a model to determine the effect of solubilized tobacco smoke (STS) on the thoracic and abdominal aorta of mice as well as on cultured human aortic smooth muscle cells (HASMCs).

METHODS

Tobacco smoke was solubilized and delivered to mice via implanted osmotic minipumps. Twenty male C57BL/6 mice received STS or vehicle infusion. The descending thoracic, suprarenal abdominal, and infrarenal abdominal segments of the aorta were assessed for elastic lamellar damage, smooth muscle cell phenotype, and infiltration of inflammatory cells. Cultured HASMCs grown in media containing STS were compared to cells grown in standard media in order to verify our in vivo findings.

RESULTS

Tobacco smoke solution caused significantly more breaks in the elastic lamellae of the thoracic and abdominal aorta compared to control solution (P< .0001) without inciting an inflammatory infiltrate. Elastin breaks occurred more frequently in the abdominal aorta than the thoracic aorta (P < .01). Exposure to STS-induced aortic microdissections and downregulation of α-smooth muscle actin (α-SMA) by vascular smooth muscle cells (VSMCs). Treatment of cultured HASMCs with STS confirmed the decrease in α-SMA expression.

CONCLUSION

Delivery of STS via osmotic minipumps appears to be a promising model for investigating the early aortic response to tobacco smoke exposure. The initial effect of tobacco smoke exposure on the aorta is elastic lamellar damage and downregulation of (α-SMA) expression by VSMCs. Elastic lamellar damage occurs more frequently in the abdominal aorta than the thoracic aorta and does not seem to be mediated by the presence of macrophages or other inflammatory cells.

The Short-term Predictive Value of Vessel Wall Stiffness on Abdominal Aortic Aneurysm Growth

BACKGROUND

Abdominal aortic aneurysm (AAA) surveillance programs are currently based solely on AAA diameter. The diameter criterion alone, however, seems inadequate as small AAAs comprise 5-10 % of ruptured AAAs as well as some large AAAs never rupture. Aneurysm wall stiffness has been suggested to predict rupture and growth; this study aimed to investigate the prognostic value of AAA vessel wall stiffness for growth on prospectively collected data.

METHODS

Analysis was based on data from a randomised, placebo-controlled, multicentre trial investigating mast-cell-inhibitors to halt aneurysm growth (the AORTA trial). Systolic and diastolic AAA diameter was determined in 326 patients using electrocardiogram-gated ultrasound (US). Stiffness was calculated at baseline and after 1 year.

RESULTS

Maximum AAA diameter increased from 44.1 mm to 46.5 mm during the study period. Aneurysm growth after 1 year was not predicted by baseline stiffness (-0.003 mm/U; 95 % CI: -0.007 to 0.001 mm/U; P = 0.15). Throughout the study period, stiffness remained unchanged (8.3 U; 95 % CI: -2.5 to 19.1 U; P = 0.13) and without significant correlation to aneurysm growth (R: 0.053; P = 0.38).

CONCLUSIONS

Following a rigorous US protocol, this study could not confirm AAA vessel wall stiffness as a predictor of aneurysm growth in a 1-year follow-up design. The need for new and subtle methods to complement diameter for improved AAA risk assessment is warranted.

Role of Noncoding RNAs in the Pathogenesis of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a local dilatation of the abdominal aortic vessel wall and is among the most challenging cardiovascular diseases as without urgent surgical intervention, ruptured AAA has a mortality rate of >80%. Most patients present acutely after aneurysm rupture or dissection from a previously asymptomatic condition and are managed by either surgery or endovascular repair. Patients usually are old and have other concurrent diseases and conditions, such as diabetes mellitus, obesity, and hypercholesterolemia making surgical intervention more difficult. Collectively, these issues have driven the search for alternative methods of diagnosing, monitoring, and treating AAA using therapeutics and less invasive approaches. Noncoding RNAs-short noncoding RNAs (microRNAs) and long-noncoding RNAs-are emerging as new fundamental regulators of gene expression. Researchers and clinicians are aiming at targeting these microRNAs and long noncoding RNAs and exploit their potential as clinical biomarkers and new therapeutic targets for AAAs. While the role of miRNAs in AAA is established, studies on long-noncoding RNAs are only beginning to emerge, suggesting their important yet unexplored role in vascular physiology and disease. Here, we review the role of noncoding RNAs and their target genes focusing on their role in AAA. We also discuss the animal models used for mechanistic understanding of AAA. Furthermore, we discuss the potential role of microRNAs and long noncoding RNAs as clinical biomarkers and therapeutics.

Radical polymerization-crosslinking method for improving extracellular matrix stability in bioprosthetic heart valves with reduced potential for calcification and inflammatory response

In recent years, the number of heart valve replacements has multiplied with valve diseases because of aging populations and the surge in rheumatic heart disease in young people. Among them, bioprosthetic heart valves (BHVs) have become increasingly popular. Transcatheter aortic valve implantation (TAVI) valve as an emerging BHV has been increasingly applied to patients. However, the current commercially used BHVs treated with glutaraldehyde (Glut) still face the problem of durability. BHVs derived from Glut-treated xenogenetic tissues would undergo structural degeneration and calcification sometimes even as short as less than 10 years. This issue has already become a big challenge considering more and more young patients at the age of 50-60 s are receiving the BHV replacement. In our study, an approach that is totally different from the previous techniques named by us as the radical polymerization-crosslinking (RPC) method was developed to improve extracellular matrix stability, prevent calcification, and reduce inflammatory response in BHVs. The porcine pericardium (PP) tissue was decellularized, functionalized with methacryloyl groups, and subsequently crosslinked by radical polymerization. We found that high-density RPC treatment remarkably improved the stability of collagen and elastin of PP, enhanced its endothelialization potential, and provided reliable biomechanical performance as compared to Glut treatment. The in vivo rat model also confirmed the increased componential stability and the reduced inflammatory response of RPC-treated PP. Moreover, the RPC-treated PP showed better in vivo anticalcification potential than Glut-treated PP. STATEMENT OF SIGNIFICANCE: Bioprosthetic heart valves (BHVs) manufactured from glutaraldehyde (Glut)-treated xenogeneic tissues have been used to treat valve-related diseases for several decades. However, the durability of BHVs remains unresolved and becomes more pronounced particularly in younger patients. Although a number of new alternative methods for Glut crosslinking have been proposed, their overall performance is still far from ready to use in humans. In this study, radical polymerization was investigated for crosslinking the porcine pericardium (PP). This treatment was found to have advantages compared to Glut-treated PP in terms of stability, biocompatibility, and anticalcification potential with the hope of addressing the needs of more robust biomaterials for the fabrication of BHVs.

Preliminary analysis of proteome alterations in non-aneurysmal, internal mammary artery tissue from patients with abdominal aortic aneurysms

Objective

The pathogenesis of abdominal aortic aneurysms (AAA) involves a disturbed balance of breakdown and buildup of arterial proteins. We envision that individuals with AAA carry generalized arterial protein alterations either because of effects of genetically or environmental AAA risk factors or because of compensatory changes due to signaling molecules released from the affected aneurysmal tissue.

Approach

Protein extraction and quantitative proteome analysis by LC-MS/MS (liquid chromatography-mass spectrometry) was done on individual samples from the internal mammary artery from 11 individuals with AAA and 33 sex- and age-matched controls without AAA. Samples were selected from a biobank of leftover internal mammary arterial tissue gathered at coronary by-pass operations.

Results

We identified and quantitated 877 proteins, of which 44 were differentially expressed between the two groups (nominal p-values without correction for multiple testing). Some proteins related to the extracellular matrix displayed altered concentrations in the AAA group, particularly among elastin-related molecules [elastin, microfibrillar-associated protein 4 (MFAP4), lysyl oxidase]. In addition, several histones e.g. (e.g. HIST1H1E, HIST1H2BB) and other vascular cell proteins (e.g. versican, type VI collagen) were altered.

Conclusions

Our results support the notion that generalized alterations occur in the arterial tree in patients with AAA. Elastin-related proteins and histones seem to be part of such changes, however these preliminary results require replication in an independent set of specimens and validation by functional studies.

Molecular targets in aortic aneurysm for establishing novel management paradigms

Aortic aneurysm (AA) is a lethal disease and presents a large challenge for surgeons in the clinic. Although surgical management remains the major choice of AA, operative mortality remains high. With advances in understanding of the mechanisms of AAs, molecular targets, such as matrix metalloproteinases (MMPs), D-dimer, and inflammation markers, including C-reactive protein, interleukins and phagocytes, are important in the pathology of development of AA. These markers may become important for improving the diagnostic quality and provide more therapeutic choices for treatment of AA. Although these new markers require long-term trials before they can be translated into the clinic, they can still be helpful in determining new directions. The main aim of this review is to discuss the current findings of molecular targets in progression of AA and discuss the potential application of these new targets for managing this disease.

Matrix Metalloproteinases in the Aneurysm Wall of Patients Treated with Low-Dose Doxycycline

The purpose of this study was to determine the effect of low-dose doxycycline on matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP)-1 expression in the wall of abdominal aortic aneurysms.

A double-blind, randomized study was conducted of patients treated with doxycycline (100 mg/d orally) or placebo for 1 month prior to surgery. MMP-2, -3, and -9 (zymogen and activity); MMP-1, -2, -3, -7, -9, -11, -12, and -14; and TIMP-1 (messenger ribonucleic acid [mRNA]) were measured in the aneurysm wall.

No differences were found between the treatment and placebo groups in zymogen levels of MMP-2, -3, or -9 or in the free or total activities of MMP-2 and -9. Treatment with doxycycline also had no effect on the concentration of any mRNA measured. No relationship was found between the number of tablets taken and MMP or TIMP protein, mRNA, or activity levels in the aneurysm wall.

Low-dose doxycycline treatment does not alter the expression or activity of metalloproteinases or their inhibitor, TIMP-1, in the aneurysm wall.

Micro-RNAs in abdominal aortic aneurysms: insights from animal models and relevance to human disease

Abdominal aortic aneurysm (AAA) is a major health concern and may be associated with high rates of mortality linked to acute complications. Diagnosis and treatment are, respectively, based on imaging and surgical techniques. Drug-based therapies are still mostly ineffective, which highlight a real unmet need. Major pathophysiological mechanisms leading to aneurysm formation involve inflammatory processes, degradation of the extracellular matrix, and loss of smooth muscle cells. However, the precise cellular and molecular pathways are still poorly understood. Recently, microRNAs have emerged as major intracellular players in a wide range of biological processes, and their stability in extracellular medium within microvesicles has led to propose them as mediators of intercellular crosstalk and as potential biomarkers and therapeutic targets in a variety of disease settings. To date, several studies have been performed to address the involvement of micro-RNAs (miRs) in aneurysm formation and complications. Here, we discuss the roles and implications of miRs in animal models and their relevance to human AAA.

Low wall stress in the popliteal artery: Other mechanisms responsible for the predilection of aneurysmal dilatation?

The popliteal artery (PA) is, after aorta, the most common site for aneurysm formation. Why the PA is more susceptible than other peripheral muscular arteries is unknown. We hypothesized that the wall composition, which in turn affects wall properties, as well as the circumferential wall stress (WS) imposed on the arterial wall, might differ compared to other muscular arteries. The aim was to study the WS of the PA in healthy subjects with the adjacent, muscular, common femoral artery (CFA) as a comparison. Ninety-four healthy subjects were included in this study (45 males, aged 10-78 years and 49 females, aged 10-83 years). The diameter and intima-media thickness (IMT) in the PA and CFA were investigated with ultrasound. Together with blood pressure the WS was defined according to the law of Laplace adjusted for IMT. The diameter increased with age in both PA and CFA (p<0.001), with males having a larger diameter than females (p<0.001). IMT increased with age in both PA and CFA (p<0.001), with higher IMT values in males only in PA (p<0.001). The calculated WS was unchanged with age in both arteries, but lower in PA than in CFA in both sexes (p<0.001). In conclusion, this study shows that the PA and CFA WS is maintained during aging, probably due to a compensatory remodelling response with an increase in arterial wall thickness. However, the stress imposed on the PA wall is quite low, indicating that mechanisms other than WS contribute to the process of pathological arterial dilatation in the PA.

Factors affecting the postoperative mortality in the ruptured abdominal aortic aneurysm

Background

Although patients with a ruptured abdominal aortic aneurysm (RAAA) often reach the hospital alive, the perioperative mortality is still very high. We retrospectively reviewed thirty patients who underwent repair of RAAA to identify the factors affecting postoperative mortality in a single hospital.

Materials and Methods

Between September 2007 and May 2011, thirty patients with RAAA underwent emergent surgery (n=27) or endovascular aneurysm repair (n=3). Their medical records were retrospectively reviewed regarding three categories: 1) preoperative patient status: age, gender, vital signs, serum creatinine, blood urea nitrogen, hematocrit, and hemoglobin level: 2) aneurysmal status: size, type, and rupture status; and 3) operative factors: interval time to operating room, operative duration, and amount of perioperative transfusion.

Results

The 30-day postoperative mortality rate was 13.3% (4/30); later mortality was 3.3% (1/30). On multivariate analysis, the initial diastolic blood pressure (BP), interval time to operating room and amount of preoperative packed cell transfusion were statistically significantly linked with postoperative mortality (p<0.05).

Conclusion

In this study, preoperative diastolic BP, preoperative packed cell transfusion amount and interval time between arrival and entry to operating room were significantly associated with postoperative mortality. It is important to prevent hemorrhage as quickly as possible.

Mast cell tryptase deficiency attenuates mouse abdominal aortic aneurysm formation

RATIONALE

Mast cells (MCs) contribute to the formation of abdominal aortic aneurysms (AAAs) by producing biologically active mediators. Tryptase is the most abundant MC granule protein and participates in MC activation, protease maturation, leukocyte recruitment, and angiogenesis-all processes critical to AAA pathogenesis.

OBJECTIVE

To test the hypothesis that tryptase participates directly in AAA formation.

METHODS AND RESULTS

Immunohistochemistry demonstrated enhanced tryptase staining in media and adventitia of human and mouse AAA lesions. Serum tryptase levels correlated significantly with the annual expansion rate of AAA before (r = 0.30, P = 0.003) and after (r = 0.29, P = 0.005) adjustment for common AAA risk factors in a patient follow-up study, and associated with risks for later surgical repair or overall mortality before (P = 0.009, P = 0.065) and after (P = 0.004, P = 0.001) the adjustment. Using MC protease-6-deficient mice (Mcpt6(-/-)) and aortic elastase perfusion-induced experimental AAAs, we proved a direct role of this tryptase in AAA pathogenesis. Whereas all wild-type (WT) mice developed AAA at 14 or 56 days postperfusion, Mcpt6(-/-) mice were fully protected. AAA lesions from Mcpt6(-/-) mice had fewer inflammatory and apoptotic cells, and lower chemokine levels, than did those from WT mice. MC from WT mice restored reduced AAA lesions and lesion inflammatory cell content in MC-deficient Kit(W-sh/W-sh) mice, but those prepared from Mcpt6(-/-) mice did not. Mechanistic studies demonstrated that tryptase deficiency affected endothelial cell (EC) chemokine and cytokine expression, monocyte transmigration, smooth-muscle cell apoptosis, and MC and AAA lesion cysteinyl cathepsin expression and activities.

CONCLUSIONS

This study establishes the direct participation of MC tryptase in the pathogenesis of experimental AAAs, and suggests that levels of this protease can serve as a novel biomarker for abdominal aortic expansion.

Integrins and extracellular matrix in mechanotransduction

Integrins bind extracellular matrix fibrils and associate with intracellular actin filaments through a variety of cytoskeletal linker proteins to mechanically connect intracellular and extracellular structures. Each component of the linkage from the cytoskeleton through the integrin-mediated adhesions to the extracellular matrix therefore transmits forces that may derive from both intracellular, myosin-generated contractile forces and forces from outside the cell. These forces activate a wide range of signaling pathways and genetic programs to control cell survival, fate, and behavior. Additionally, cells sense the physical properties of their surrounding environment through forces exerted on integrin-mediated adhesions. This article first summarizes current knowledge about regulation of cell function by mechanical forces acting through integrin-mediated adhesions and then discusses models for mechanotransduction and sensing of environmental forces.

Recent advances in the application of computational mechanics to the diagnosis and treatment of cardiovascular disease

During the last 30 years, research into the pathogenesis and progression of cardiovascular disease has had to employ a multidisciplinary approach involving a wide range of subject areas, from molecular and cell biology to computational mechanics and experimental solid and fluid mechanics. In general, research was driven by the need to provide answers to questions of critical importance for disease management. Ongoing improvements in the spatial resolution of medical imaging equipment coupled to an exponential growth in the capacity, flexibility and speed of computational techniques have provided a valuable opportunity for numerical simulations and complex experimental techniques to make a contribution to improving the diagnosis and clinical management of many forms of cardiovascular disease. This paper contains a review of recent progress in the numerical simulation of cardiovascular mechanics, focusing on three particular areas: patient-specific modeling and the optimization of surgery in pediatric cardiology, evaluating the risk of rupture in aortic aneurysms, and noninvasive characterization of intraventricular flow in the management of heart failure.

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.

Reduced aortic wall stress in diabetes mellitus

OBJECTIVE

Most risk factors are similar for abdominal aortic aneurysm (AAA) and atherosclerosis, e.g. smoking, male gender, age, high blood pressure, hyperlipidemia. Diabetes mellitus however, is a risk factor for atherosclerosis, but diabetic patients seldom develop AAA. The reason for this discrepancy is unknown. Increased aortic wall stress seems to be an etiologic factor in the formation, growth and rupture of AAA in man. The aim of our study was to study the wall stress in the abdominal aorta in diabetic patients compared with healthy controls.

METHODS

39 patients with diabetes mellitus and 46 age - and sex matched healthy subjects were examined with B-mode ultrasound to determine the lumen diameter (LD) and intima-media thickness (IMT) in the abdominal aorta (AA) and the common carotid artery (CCA). Diastolic blood pressure (DBP) was measured non-invasively in the brachial artery. LaPlace law was used to calculate circumferential wall stress.

RESULTS

Age, DBP, and LD in the abdominal aorta were not significantly different in the diabetic patients compared to controls. IMT in the AA was larger in the diabetic patients, 0.89+/-0.17 vs 0.73+/-0.11 mm (p<.001). Accordingly aortic wall stress was reduced in the diabetics, 7.8+/-1.7 x 10(5) vs 9.7+/-1.9 x 10(5)dynes/cm(2) (p<.001).

CONCLUSIONS

Wall stress in the abdominal aorta is reduced in diabetes mellitus. This is mainly due to a thicker aortic wall compared to healthy controls. The reduced aortic wall stress coincides with the fact that epidemiological studies have shown a decreased risk of aneurysm development in diabetic patients.

Smoking status and common carotid artery intima-medial thickness among middle-aged men and women based on ultrasound measurement: a cohort study

Background

Cigarette smoking is an established causal factor for atherosclerosis. However, the smoking effect on different echogenic components of carotid arterial wall measured by ultrasound is not well elucidated.

Methods

Middle-aged men and women who had IMT measurement ≥ 0.7 mm at baseline and follow-up were included (N = 413, age 40–60 years at baseline in 1995). Intima-media thickness of common carotid artery (CCA-IMT) and its components (echogenic and echolucent layers) were measured at baseline and in the follow-up examination 3 years later. IMT and its components were compared across current, former and never smokers. Individual growth models were used to examine how smoking status was related to the baseline and progression of overall IMT and IMT components.

Results

For both men and women, current smoking was associated with thicker echogenic layer than never smokers; former smokers exhibited thinner echogenic layer than current smokers after adjustment for cigarette pack-years. Among women, current smoking was also associated with a thinned echolucent layer that resulted in a non-significant overall association of current smoking with IMT for women.

Conclusion

Cigarette smoking is associated with carotid artery morphological changes and the association is sex-dependent. The atherogenic effect of smoking appears to be partly reversible among former smokers. IMT measurement alone may not be adequate to detect carotid atherosclerosis associated with cigarette smoking among middle-age women.

Abdominal aortic aneurysm is associated with high serum levels of tenascin-X and decreased aneurysmal tissue tenascin-X

BACKGROUND

Tenascin-X is a large extracellular matrix protein that is abundantly expressed in several connective tissues. A 140-kDa C-terminal fragment of tenascin-X is present in human serum. Complete deficiency of tenascin-X is associated with Ehlers-Danlos syndrome, and these patients show major connective tissue alterations in their skin, as well as blood vessel fragility. In this study, we investigated whether tenascin-X is present in normal human aorta and abdominal aortic aneurysm (AAA) tissues and whether an association exists between serum tenascin-X levels and AAA.

METHODS AND RESULTS

Five normal aortas and 5 AAA tissues were immunostained for tenascin-X and elastin. Tenascin-X was present throughout the entire aorta and was especially abundant near the elastic lamellae, whereas tenascin-X expression was strongly decreased in AAA tissue. Measurement of tenascin-X serum concentration by enzyme-linked immunosorbent assay (ELISA) in 87 AAA patients and 86 controls demonstrated an increasing risk for AAA with increasing tenascin-X serum concentrations. After adjustment for established risk factors, tenascin-X serum concentrations in the highest quartile were associated with a 5-fold increase in risk of AAA (odds ratio, 5.3; 95% confidence interval, 2.0 to 13.8).

CONCLUSIONS

Tenascin-X expression is markedly decreased in AAA tissue, and AAA is associated with high serum concentrations of tenascin-X.

Renewal of mural thrombus releases plasma markers and is involved in aortic abdominal aneurysm evolution

Human abdominal aortic aneurysm (AAA) expansion has been linked to the presence of a mural thrombus. Here we explored the mechanism of the continual luminal renewal of this thrombus and its ability to release biological markers potentially detectable in plasma. We also explored the ability of platelet inhibition to pacify the thrombus and to limit aneurysm progression in an experimental model. Blood samples and mural thrombi were collected in 20 AAA patients. In parallel, segments of sodium dodecyl sulfate-decellularized guinea pig aorta were xenografted onto the abdominal aorta of 30 rats to induce aneurysms. Fifteen rats received abciximab treatment and fifteen received irrelevant immunoglobulins. Procoagulant activity and platelet activation markers (microparticles, sP-selectin, sGPV, sCD40L) were increased threefold to fivefold in eluates from the luminal thrombus layer compared to other layers. All these markers were increased twofold to fivefold in patients' plasma compared to matched controls (P < 0.005). In the rat model, abciximab reduced both thrombus area and aneurysmal enlargement (P < 0.05). Platelet aggregation is probably responsible for the renewal of the thrombus in AAA. The luminal thrombus released markers of platelet activation that could easily be detected in plasma. Platelet inhibition limited aortic aneurysm expansion in a rat model, providing new therapeutic perspectives in the prevention of AAA enlargement.

Age-related increase in wall stress of the human abdominal aorta: an in vivo study

BACKGROUND

The regulation of wall stress in the abdominal aorta (AA) of humans might be of specific interest, because the AA is the most common site for aneurysm formation in which wall stress seems to be an important pathophysiological factor. We studied the age-related changes in wall stress of the AA in healthy subjects, with the common carotid artery (CCA) as a comparison.

METHODS

A total of 111 healthy subjects were examined with B-mode ultrasonography to determine the lumen diameter and intima-media thickness (IMT) in the AA and the CCA.

RESULTS

Aortic IMT was affected by age in men and by both age and lumen diameter in women. Carotid IMT was affected by age and pulse pressure in both men and women. Wall stress was higher in the AA than in the CCA (P < .001), and men had higher wall stress than women in both the AA (P < .001) and the CCA (P < .05). Furthermore, wall stress was constant during life in the CCA of men and women and in the AA of women. In the male aorta, however, wall stress increased with age (P < 0.01).

CONCLUSIONS

Arterial diameters increase with age, and a compensatory thickening of the arterial wall prevents the circumferential wall stress from increasing. However, this compensatory response is insufficient in the male AA and results in an increase in stress with age. These findings might explain the propensity for aneurysms to develop in the AA of men.

Hyperplastic Cellular Remodeling of the Media in Ascending Thoracic Aortic Aneurysms

Background— Progressive medial degeneration and atrophy is thought to be a cause of ascending thoracic aortic aneurysms in the elderly. Extensive apoptosis of vascular smooth muscle cells (VSMCs) has been demonstrated in the media of abdominal aortic aneurysms. We investigated whether medial atrophy from loss of VSMCs occurs in primary ascending thoracic aortic aneurysms.

Methods and Results— Morphometric analysis of 28 nonaneurysmal ascending thoracic aortas and 29 ascending thoracic aortic aneurysms was performed by directly measuring the thickness of their vascular layers and by indirectly calculating the area of their vascular compartments. The cellular and matrix composition of the media was assessed at the structural, protein, and transcript levels. Despite thinning of the media secondary to vascular dilatation, there was an overall increase in the medial area of aneurysms. VSMC density was preserved, implying cellular hyperplasia as a result of the increased medial mass. There was decreased expression of matrix proteins, despite sustained synthesis of these molecules, which was associated with evidence of increased matrix degradation. The remodeling and expansion of the media was most evident in comparisons between nonaneurysmal aortas versus smaller aneurysms and did not evolve further in larger aneurysms.

Conclusions— The mechanisms for luminal enlargement in thoracic and abdominal aortic aneurysms differ significantly with regard to the survival of VSMCs and atrophy of the media but share common pathophysiology involving degeneration of the matrix. Hyperplastic cellular remodeling of the media in ascending thoracic aortic aneurysms may be an initial adaptive response to minimize increased wall stress resulting from vascular dilatation.

Transmural inflammation by interferon-gamma-producing T cells correlates with outward vascular remodeling and intimal expansion of ascending thoracic aortic aneurysms

Arterial pathology manifests as aneurysmal or obstructive disease depending on changes in lumen size due to vascular remodeling (change in vessel external diameter) and/or intimal expansion. Recent clinical and experimental observations in abdominal aortic aneurysms have led to the emerging dogma that Th2-dominant immune responses result in expansive vascular remodeling and luminal ectasia, whereas Th1 immune responses cause intimal hyperplasia and luminal stenosis. We tested this hypothesis by descriptive analyses of 31 non-aneurysmal and 29 aneurysmal ascending thoracic aortic specimens. Approximately half the aneurysms were distinguished by transmural inflammation. The remaining aneurysms and all the non-aneurysmal aortas had a similar leukocytic infiltrate that spared the inner media. Aneurysm tissue had increased expression of the prototypical Th1 cytokine, interferon (IFN)-gamma, and undetectable Th2 cytokines. Specimens with inner media infiltration displayed robust production of IFN-gamma, induction of the IFN-gamma-inducible chemokines IP-10 and Mig, and recruitment of lymphocytes bearing their cognate receptor CXCR3. Transmural inflammation and IFN-gamma production were associated with increased aortic external diameter, intimal thickening, preserved vascular smooth muscle cell density, and decreased matrix proteins. Th1, but not Th2, immune responses have a positive correlation with both outward vascular remodeling and intimal expansion of ascending thoracic aortic aneurysms.

Abdominal aortic aneurysm

Abdominal aortic aneurysms cause 1.3% of all deaths among men aged 65-85 years in developed countries. These aneurysms are typically asymptomatic until the catastrophic event of rupture. Repair of large or symptomatic aneurysms by open surgery or endovascular repair is recommended, whereas repair of small abdominal aortic aneurysms does not provide a significant benefit. Abdominal aortic aneurysm is linked to the degradation of the elastic media of the atheromatous aorta. An inflammatory cell infiltrate, neovascularisation, and production and activation of various proteases and cytokines contribute to the development of this disorder, although the underlying mechanisms are unknown. In this Seminar, we aim to provide an updated review of the pathophysiology, current and new diagnostic procedures, assessment, and treatment of abdominal aortic aneurysm to provide family practitioners with a working knowledge of this disorder.

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.

Near-Infrared Spectrometry of Abdominal Aortic Aneurysm in the ApoE-/- Mouse

Abdominal aortic aneurysms (AAAs) occur in 5-7% of people over age 60 in the United States. Early intervention in the disease process could have a significant impact on the incidence of complications and on patient survival, but identifying incipient aneurysms can be difficult. ApoE knockout mice develop AAAs following infusion of angiotensin II (AngII) by osmotic minipump into the subcutaneous space of mice at doses ranging from 500 to 1000 ng kg(-1) min(-1) for 7-28 days. These mice are used as models of AAA development. This study tested the hypothesis that near-IR spectrometry and PCR can determine AngII dose (SEE = 26 ng kg(-1) min(-1), SEP = 37 ng kg(-1) min(-1), r2 = 0.99) and collagen/elastin (C/E) ratio (SEE = 0.38, SEP = 0.39, r2 = 0.85) in mouse aortas.

Basic fibroblast growth factor decreases elastin gene transcription in aortic smooth muscle cells

The extracellular matrix (ECM) protein elastin plays an essential role in the cardiovascular system by imparting elasticity to blood vessel wall. In this study, we examined the effect of basic fibroblast growth factor (bFGF) on the expression of elastin in aortic smooth muscle cells (SMC) to gain insight into events associated with cardiovascular diseases. The results show that bFGF treatment of SMC causes a significant decrease in elastin mRNA and secreted tropoelastin levels. Nuclear run-on analyses demonstrate that the downregulation is due to a decrease in the level of elastin gene transcription. Transient transfections of SMC with wild-type and mutated elastin gene promoter/chloramphenicol acetyl transferase (CAT) constructs show that a previously identified activator protein-1-cAMP response element (AP1/CRE) (-564 to -558-bp) within the elastin promoter mediates the bFGF-dependent downregulation of elastin gene transcription in SMC. Addition of bFGF to SMC activates the extracellular signal-regulated kinases 1/2 (ERK1/2) resulting in their translocation into the nucleus and subsequent induction of Fra-1. The addition of PD-98059, an inhibitor of ERK1/2 kinase, abrogates the bFGF-dependent decrease of elastin mRNA in SMC. The described inhibitory effect of bFGF on elastin gene expression in SMC may significantly contribute to the inefficient repair of elastin in early stages of vascular wall injury.

Familial abdominal aortic aneurysm: a systematic review of a genetic background

BACKGROUND

Familial clustering of the abdominal aortic aneurysm (AAA) is clear, 12-19% of AAA patients have one or more first-degree relatives with an aneurysm and 4-19% is detected with ultrasound screening.

OBJECTIVES

To review the genetic background of AAA. DESIGN, METHODS AND MATERIALS: Computer searches of the MEDLINE, EMBASE, SUMsearch database and the Cochrane Library and searched reference lists of English language articles concerning the genetics of AAA, candidate gene approach and linkage analysis.

RESULTS

Brothers of AAA patients are at high risk to develop an AAA. The candidate gene approach was performed to detect defects in one of the components of the connective tissue, i.e. type I and III collagen, elastin and fibrillin, the inflammatory cell-derived matrix metalloproteinase, there inhibitors, auto-immune components and components related to atherosclerosis.

CONCLUSION

These studies give us insight in the pathology but do not lead to the specific genetic factor(s) responsible for (familial) AAA. Considering the supposed autosomal dominant inheritance, a gene mutation in one of the structural proteins of the connective tissue is expected. In the future, linkage analysis may resolve the genetic background of AAA.

Response of plasma matrix metalloproteinase-9 to conventional abdominal aortic aneurysm repair or endovascular exclusion: implications for endoleak

PURPOSE

Matrix metalloproteinases are enzymes capable of breaking down all of the components of the extracellular matrix and have been implicated in the development of aneurysm formation. Because matrix metalloproteinase-9 (MMP-9) levels are elevated in aortic aneurysmal tissue and in that patient plasma, we hypothesized that plasma MMP-9 levels should decrease significantly after conventional and endovascular infrarenal abdominal aortic aneurysm (AAA) repair but that plasma MMP-9 levels would remain elevated in patients with endoleaks.

METHODS

A sandwich enzyme-linked immunosorbent assay was used to measure plasma levels of MMP-9 in patients with AAA who underwent conventional (n = 26; mean age, 71.5 years) and endovascular (n = 25; mean age, 76.4 years) AAA repair. Levels were drawn before surgery and at 1 month and 3 months after surgery. Eight patients for endovascular repair had endoleaks identified on postoperative computed axial tomographic scans.

RESULTS

No correlation existed between preoperative plasma MMP-9 levels when compared with age, gender, or aneurysm diameter. No significant difference in preoperative plasma MMP-9 levels or AAA diameter was identified between patients with conventional repair compared with endovascular repair. Of the 51 patients, 33 had follow-up samples available for analysis. A significant increase in mean plasma MMP-9 levels was noted 1 month (149.5 +/- 40.1 ng/mL) after conventional AAA repair compared with preoperative levels (83.9 +/- 26.1 ng/mL; P <.05) and remained elevated 3 months after surgery (129.8 +/- 56.6 ng/mL). In those patients who underwent endovascular aneurysm exclusion without endoleak, a significant decrease in mean plasma MMP-9 levels was noted at 3 months (27.4 +/- 5.2 ng/mL) when compared with preoperative values (60.8 +/- 8.8 ng/mL; P <.01). In contrast, patients with endoleak after endovascular exclusion did not have a significant decrease in plasma MMP-9 levels at 3 months.

CONCLUSION

Plasma MMP-9 levels remain elevated for as much as 3 months after conventional AAA repair, whereas successful endovascular exclusion of an AAA results in decreased plasma MMP-9 levels by 3 months. MMP-9 may have clinical value as an enzymatic marker for endoleak after endovascular AAA exclusion.

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.

The relationship between abdominal aortic aneurysm distensibility and serum markers of elastin and collagen metabolism

BACKGROUND

abdominal aortic aneurysm (AAA) distensibility may be an independent predictor of growth and rupture, possibly because it reflects changes in aortic wall structure and composition.

AIM

to determine whether AAA distensibility is related to circulating markers of elastin and collagen metabolism.

METHODS

sixty-two male patients of median age (IQR) 68 (65-72) years with asymptomatic AAA of median (IQR) diameter 42 (37-45) mm were prospectively studied. Pressure-strain elastic modulus (Ep) and stiffness (beta) were measured using an ultrasonic echo-tracker (Diamove). Serum elastin peptides (SEP), plasma elastin-alpha1-antitrypsin complex (E-AT), procollagen III-N-terminal propeptide (PIIINP) were measured by enzyme-linked immunoassay.

RESULTS

age and smoking adjusted Ep and beta were significantly inversely related to SEP (r=-0.33 and r=-0.31 respectively, both p<0.02) and E-AT (r=-0.27 and r=-0.27 respectively, both p<0.05) both of which indicate elastolysis. By contrast, there was a significant positive correlation between PIIINP, indicative of increased collagen turn-over, and both Ep and beta (both r=0.45, p<0.01 unadjusted correlations).

CONCLUSION

increased elastolysis is associated with increased AAA wall distensibility; whereas increased collagen turn-over is associated with reduced distensibility.

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.

Cystatin C deficiency in human atherosclerosis and aortic aneurysms

The pathogenesis of atherosclerosis and abdominal aortic aneurysm involves breakdown of the elastic laminae. Elastolytic cysteine proteases, including cathepsins S and K, are overexpressed at sites of arterial elastin damage, but whether endogenous local inhibitors counterbalance these proteases is unknown. We show here that, whereas cystatin C is normally expressed in vascular wall smooth muscle cells (SMCs), this cysteine protease inhibitor is severely reduced in both atherosclerotic and aneurysmal aortic lesions. Furthermore, increased abdominal aortic diameter among 122 patients screened by ultrasonography correlated inversely with serum cystatin C levels. In vitro, cytokine-stimulated vascular SMCs secrete cathepsins, whose elastolytic activity could be blocked when cystatin C secretion was induced by treatment with TGF-beta(1). The findings highlight a potentially important role for imbalance between cysteine proteases and cystatin C in arterial wall remodeling and establish that cystatin C deficiency occurs in vascular disease.

Suppression of experimental abdominal aortic aneurysms by systemic treatment with a hydroxamate-based matrix metalloproteinase inhibitor (RS 132908)

BACKGROUND

Abdominal aortic aneurysms (AAAs) are associated with chronic inflammation, disruption of medial elastin, and increased local production of elastolytic matrix metalloproteinases (MMPs). The purpose of this study was to investigate how treatment with a hydroxamate-based MMP antagonist (RS 132908) might affect the development of experimental AAAs.

METHODS

Male Wistar rats underwent intraluminal perfusion of the abdominal aorta with 50 units of porcine pancreatic elastase followed by treatment for 14 days with RS 132908 (100 mg/kg/day subcutaneously; n = 8) or with vehicle alone (n = 6). The external aortic diameter (AD) was measured in millimeters before elastase perfusion and at death, with AAA defined as an increase in AD (DeltaAD) of at least 100%. Aortic wall elastin and collagen concentrations were measured with assays for desmosine and hydroxyproline, and fixed aortic tissues were examined by light microscopy.

RESULTS

AAAs developed in all vehicle-treated rats, with a mean AD (+/- SE) that increased from 1.60 +/- 0.03 mm before perfusion to 5.98 +/- 1.02 mm on day 14 (DeltaAD = 276.4 +/- 67.7%). AAAs developed in only five of eight animals (62.5%) after MMP inhibition, with a mean AD that increased from 1.56 +/- 0.05 mm to 3.59 +/- 0.34 mm (DeltaAD = 128.1 +/- 18.7%; P <.05, vs vehicle). The overall inhibition of aortic dilatation attributable to RS 132908 was 53.6 +/- 6.8%. Aortic wall desmosine fell by 85.4% in the vehicle-treated rats (1210.6 +/- 87.8 pmol/sample to 176.7 +/- 33.4 pmol/sample; P <.05) but only by 65.6% in the animals treated with RS 312908 (416.2 +/- 120.5 pmol/sample). In contrast, hydroxyproline was not significantly affected by either elastase perfusion or drug treatment. Microscopic examination revealed the preservation of pericellular elastin and a greater degree of fibrocollagenous wall thickening after MMP inhibition, with no detectable difference in the extent of inflammation.

CONCLUSIONS

Systemic MMP inhibition suppresses aneurysmal dilatation in the elastase-induced rodent model of AAA. Consistent with its direct inhibitory effect on various MMPs, RS 132908 promotes the preservation of aortic elastin and appears to enhance a profibrotic response within the aortic wall. Hydroxamate-based MMP antagonists may therefore be useful in the development of pharmacologic approaches to the suppression of AAAs.

Reduced capacity to inhibit elastase in abdominal aortic aneurysm

BACKGROUND

Loss of elastin in the aortic wall is an early event in abdominal aortic aneurysm (AAA). An imbalance in the protease-antiprotease system is proposed to be one of the factors that promote connective tissue destruction. We hypothesize that plasma from AAA patients will have a reduced inhibitory capacity in comparison to normal controls.

MATERIALS AND METHODS

Using an assay we developed, plasma (10 microliters), collected from AAA patients (n = 14) and normal controls (n = 13), was added to the elastase inhibition assay containing succinylated elastin substrate. The reaction was initiated with 13.9 units porcine pancreatic elastase (PPE). Elastase activity in the presence and absence of plasma was compared. Plasma elastase was also determined using the Merck PMN-elastase kit.

RESULTS

The relative activity of exogenous elastase (%) in the presence of AAA plasma (n = 14, mean age 73.4 years +/- 1.7 SEM) was 42.59% +/- 4.3 SEM, while that in the presence of control plasma (n = 13, mean age 73.9 years +/- 2.1 SEM) was 10.23% +/- 2.1 SEM (P < 0.0001). Analysis of plasma elastase (microgram/L) indicated that there was no significant difference between normal (n = 9, 207.33 microgram/L +/- 58.67 SEM) and AAA (n = 9, 145.34 microgram/L +/- 29.54 SEM) (P = 0.359).

CONCLUSION

There is a significant reduction in the plasma inhibitory capacity of elastase in AAA patients in comparison to normal controls, though plasma elastase level was not significantly different. The data presented here give experimental evidence to the protease-antiprotease imbalance in AAA patient plasma and may lead to the development of a measurable parameter to monitor AAA.