Functional importance of connective tissue repair during the development of experimental abdominal aortic aneurysms

The role of transcription factors in the pathogenesis and therapeutic targeting of vascular diseases

Transcription factors (TFs) constitute an essential component of epigenetic regulation. They contribute to the progression of vascular diseases by regulating epigenetic gene expression in several vascular diseases. Recently, numerous regulatory mechanisms related to vascular pathology, ranging from general TFs that are continuously activated to histiocyte-specific TFs that are activated under specific circumstances, have been studied. TFs participate in the progression of vascular-related diseases by epigenetically regulating vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). The Krüppel-like family (KLF) TF family is widely recognized as the foremost regulator of vascular diseases. KLF11 prevents aneurysm progression by inhibiting the apoptosis of VSMCs and enhancing their contractile function. The presence of KLF4, another crucial member, suppresses the progression of atherosclerosis (AS) and pulmonary hypertension by attenuating the formation of VSMCs-derived foam cells, ameliorating endothelial dysfunction, and inducing vasodilatory effects. However, the mechanism underlying the regulation of the progression of vascular-related diseases by TFs has remained elusive. The present study categorized the TFs involved in vascular diseases and their regulatory mechanisms to shed light on the potential pathogenesis of vascular diseases, and provide novel insights into their diagnosis and treatment.

Novel pharmacological approaches in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a severe vascular disease and a major public health issue with an unmet medical need for therapy. This disease is featured by a progressive dilation of the abdominal aorta, boosted by atherosclerosis, ageing, and smoking as major risk factors. Aneurysm growth increases the risk of aortic rupture, a life-threatening emergency with high mortality rates. Despite the increasing progress in our knowledge about the etiopathology of AAA, an effective pharmacological treatment against this disorder remains elusive and surgical repair is still the unique available therapeutic approach for high-risk patients. Meanwhile, there is no medical alternative for patients with small aneurysms but close surveillance. Clinical trials assessing the efficacy of antihypertensive agents, statins, doxycycline, or anti-platelet drugs, among others, failed to demonstrate a clear benefit limiting AAA growth, while data from ongoing clinical trials addressing the benefit of metformin on aneurysm progression are eagerly awaited. Recent preclinical studies have postulated new therapeutic targets and pharmacological strategies paving the way for the implementation of future clinical studies exploring these novel therapeutic strategies. This review summarises some of the most relevant clinical and preclinical studies in search of new therapeutic approaches for AAA.

Targeting lysyl-oxidase (LOX) may facilitate intramural periarterial drainage for the treatment of Alzheimer's disease

Alzheimer's disease is the commonest form of dementia. It is likely that a lack of clearance of amyloid beta (Aβ) results in its accumulation in the parenchyma as Aβ oligomers and insoluble plaques, and within the walls of blood vessels as cerebral amyloid angiopathy (CAA). The drainage of Aβ along the basement membranes of blood vessels as intramural periarterial drainage (IPAD), could be improved if the driving force behind IPAD could be augmented, therefore reducing Aβ accumulation. There are alterations in the composition of the vascular basement membrane in Alzheimer's disease. Lysyl oxidase (LOX) is an enzyme involved in the remodelling of the extracellular matrix and its expression and function is altered in various disease states. The expression of LOX is increased in Alzheimer's disease, but it is unclear whether this is a contributory factor in the impairment of IPAD in Alzheimer's disease. The pharmacological inhibition of LOX may be a strategy to improve IPAD and reduce the accumulation of Aβ in the parenchyma and within the walls of blood vessels.

Imaging of Dysfunctional Elastogenesis in Atherosclerosis Using an Improved Gadolinium-Based Tetrameric MRI Probe Targeted to Tropoelastin

Dysfunctional elastin turnover plays a major role in the progression of atherosclerotic plaques. Failure of tropoelastin cross-linking into mature elastin leads to the accumulation of tropoelastin within the growing plaque, increasing its instability. Here we present Gd₄-TESMA, an MRI contrast agent specifically designed for molecular imaging of tropoelastin within plaques. Gd₄-TESMA is a tetrameric probe composed of a tropoelastin-binding peptide (the VVGS-peptide) conjugated with four Gd(III)-DOTA-monoamide chelates. It shows a relaxivity per molecule of 34.0 ± 0.8 mM^-1 s^-1 (20 MHz, 298 K, pH 7.2), a good binding affinity to tropoelastin (K_D = 41 ± 12 μM), and a serum half-life longer than 2 h. Gd₄-TESMA accumulates specifically in atherosclerotic plaques in the ApoE^-/- murine model of plaque progression, with 2 h persistence of contrast enhancement. As compared to the monomeric counterpart (Gd-TESMA), the tetrameric Gd₄-TESMA probe shows a clear advantage regarding both sensitivity and imaging time window, allowing for a better characterization of atherosclerotic plaques.

Moderate aerobic exercise prevents matrix degradation and death in a mouse model of aortic dissection and aneurysm

Thoracic aortic aneurysm and dissection (TAAD) is a deadly disease characterized by intimal disruption induced by hemodynamic forces of the circulation. The effect of exercise in patients with TAAD is largely unknown. β-Aminopropionitrile (BAPN) is an irreversible inhibitor of lysyl oxidase that induces TAAD in mice. The objective of this study was to investigate the effect of aerobic exercise on BAPN-induced TAAD. Upon weaning, mice were given either BAPN-containing water or standard drinking water and subjected to either conventional cage activity (BAPN-CONV) or forced treadmill exercise (BAPN-EX) for up to 26 wk. Mortality was 23.5% (20/85) for BAPN-CONV mice versus 0% (0/22) for BAPN-EX mice (hazard ratio 3.8; P = 0.01). BAPN induced significant elastic lamina fragmentation and intimal-medial thickening compared with BAPN-untreated controls, and aneurysms were identified in 50% (5/10) of mice that underwent contrast-enhanced CT scanning. Exercise significantly decreased BAPN-induced wall thickening, calculated circumferential wall tension, and lumen diameter, with 0% (0/5) of BAPN-EX demonstrating chronic aortic aneurysm formation on CT scan. Expression of selected genes relevant to vascular diseases was analyzed by qRT-PCR. Notably, exercise normalized BAPN-induced increases in TGF-β pathway-related genes Cd109, Smad4, and Tgfβr1; inflammation-related genes Vcam1, Bcl2a1, Ccr2, Pparg, Il1r1, Il1r1, Itgb2, and Itgax; and vascular injury- and response-related genes Mmp3, Fn1, and Vwf. Additionally, exercise significantly increased elastin expression in BAPN-treated animals compared with controls. This study suggests that moderate aerobic exercise may be safe and effective in preventing the most devastating outcomes in TAAD.NEW & NOTEWORTHY Moderate aerobic exercise was shown to significantly reduce mortality, extracellular matrix degradation, and thoracic aortic aneurysm and dissection formation associated with lysyl oxidase inhibition in a mouse model. Gene expression suggested a reversal of TGF-β, inflammation, and extracellular matrix remodeling pathway dysregulation, along with augmented elastogenesis with exercise.

Is there an immunogenomic difference between thoracic and abdominal aortic aneurysms?

BACKGROUND AND AIM

Aortic aneurysms most commonly occur in the infra-renal and proximal thoracic regions. While generally asymptomatic, progressive aneurysmal dilation can become rapidly lethal when dissection or ruptures occurs, highlighting the need for more robust screening. Abdominal aortic aneurysm (AAA) is more prevalent compared to thoracic aortic aneurysm (TAA). The true incidence of TAA is underreported due to the absence of population screening and the silent nature of TAA. To achieve the optimum survival rate in aortic aneurysms, knowledge of natural course, genetic association, and surgical results are needed to be applied with adequate medical treatment and careful selection of patients for operation. The purpose of this paper is to provide a comprehensive review of the literature on natural history, immunology, and genetic differences between thoracic and AAAs.

METHOD

The literature was collected from OVID, SCOPUS, and PubMed.

RESULTS

(1) AAA expands faster than TAA. AAA expands at approximately 0.3-0.45 cm annually, depending on various factors (advancing age, diameter of aorta, smoking etc.). TAA expands up to 0.3 cm annually in a non-bicuspid aortic valve patient. (2) An increase in Matrix metallopeptidase 1, 2, 9, 12, 14 led to degrading extracellular matrix of the aortic vessel wall. This significantly contributed to the pathogenesis in AAA, whereas overactive Transforming growth factor-beta played a major role in the pathogenesis of TAA.

CONCLUSION

In the future, genetic testing may be the gold standard for tackling the geneticheterogeneity of aneurysms, therefore, identifying at-risk individuals developing TAA andAAA earlier.

Molecular MR Contrast Agents

Molecular magnetic resonance (MR) imaging utilizes molecular probes to provide added biochemical or cellular information to what can already be achieved with anatomical and functional MR imaging. This review provides an overview of molecular MR and focuses specifically on molecular MR contrast agents that provide contrast by shortening the T1 time. We describe the requirements for a successful molecular MR contrast agent and the challenges for clinical translation. The review highlights work from the last 5 years and places an emphasis on new contrast agents that have been validated in multiple preclinical models. Applications of molecular MR include imaging of inflammation, fibrosis, fibrogenesis, thromboembolic disease, and cancers. Molecular MR is positioned to move beyond detection of disease to the quantitative staging of disease and measurement of treatment response.

Prevention of CaCl2-induced aortic inflammation and subsequent aneurysm formation by the CCL3-CCR5 axis

Inflammatory mediators such as cytokines and chemokines are crucially involved in the development of abdominal aortic aneurysm (AAA). Here we report that CaCl2 application into abdominal aorta induces AAA with intra-aortic infiltration of macrophages as well as enhanced expression of chemokine (C-C motif) ligand 3 (CCL3) and MMP-9. Moreover, infiltrating macrophages express C-C chemokine receptor 5 (CCR5, a specific receptor for CCL3) and MMP-9. Both Ccl3-/- mice and Ccr5-/- but not Ccr1-/- mice exhibit exaggerated CaCl2-inducced AAA with augmented macrophage infiltration and MMP-9 expression. Similar observations are also obtained on an angiotensin II-induced AAA model. Immunoneutralization of CCL3 mimics the phenotypes observed in CaCl2-treated Ccl3-/- mice. On the contrary, CCL3 treatment attenuates CaCl2-induced AAA in both wild-type and Ccl3-/- mice. Consistently, we find that the CCL3-CCR5 axis suppresses PMA-induced enhancement of MMP-9 expression in macrophages. Thus, CCL3 can be effective to prevent the development of CaCl2-induced AAA by suppressing MMP-9 expression.

Tropoelastin: an in vivo imaging marker of dysfunctional matrix turnover during abdominal aortic dilation

Aims

Dysfunctional matrix turnover is present at sites of abdominal aortic aneurysm (AAA) and leads to the accumulation of monomeric tropoelastin rather than cross-linked elastin. We used a gadolinium-based tropoelastin-specific magnetic resonance contrast agent (Gd-TESMA) to test whether quantifying regional tropoelastin turnover correlates with aortic expansion in a murine model. The binding of Gd-TESMA to excised human AAA was also assessed.

Methods and results

We utilized the angiotensin II (Ang II)-infused apolipoprotein E gene knockout (ApoE^-/-) murine model of aortic dilation and performed in vivo imaging of tropoelastin by administering Gd-TESMA followed by late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) and T₁ mapping at 3 T, with subsequent ex vivo validation. In a cross-sectional study (n = 66; control = 11, infused = 55) we found that Gd-TESMA enhanced MRI was elevated and confined to dilated aortic segments (control: _LGE=0.13 ± 0.04 mm², control _R1= 1.1 ± 0.05 s^-1 vs. dilated _LGE=1.0 ± 0.4 mm², dilated _R1 =2.4 ± 0.9 s^-1) and was greater in segments with medium (8.0 ± 3.8 mm³) and large (10.4 ± 4.1 mm³) compared to small (3.6 ± 2.1 mm³) vessel volume. Furthermore, a proof-of-principle longitudinal study (n = 19) using Gd-TESMA enhanced MRI demonstrated a greater proportion of tropoelastin: elastin expression in dilating compared to non-dilating aortas, which correlated with the rate of aortic expansion. Treatment with pravastatin and aspirin (n = 10) did not reduce tropoelastin turnover (0.87 ± 0.3 mm² vs. 1.0 ± 0.44 mm²) or aortic dilation (4.86 ± 2.44 mm³ vs. 4.0 ± 3.6 mm³). Importantly, Gd-TESMA-enhanced MRI identified accumulation of tropoelastin in excised human aneurysmal tissue (n = 4), which was confirmed histologically.

Conclusion

Tropoelastin MRI identifies dysfunctional matrix remodelling that is specifically expressed in regions of aortic aneurysm or dissection and correlates with the development and rate of aortic expansion. Thus, it may provide an additive imaging marker to the serial assessment of luminal diameter for surveillance of patients at risk of or with established aortopathy.

Immunological therapeutics in acute aortic syndrome

Acute aortic syndrome is a group of interlinked conditions with common presenting symptoms, including aortic dissection, penetrating atherosclerotic ulcer, and intramural hematoma. Pharmacological management of acute aortic syndrome is a growing area, with key themes to address the underlying inflammatory pathways believed to be the cause. Research into interleukins, matrix metalloproteinases, and granulocyte macrophage colony-stimulating factor are just some of the many immunological properties being investigated and translated into medical therapies. Stem cell experiments may indicate further advances in the pathologies of acute aortic syndrome. The study of pharmacogenomics to improve treatment across different genomes is also a novel area outlined in this paper.

Current Status and Perspectives on Pharmacologic Therapy for Abdominal Aortic Aneurysm

Background:

Abdominal aortic aneurysm (AAA), a common disease involving the segmen-tal expansion and rupture of the aorta, has a high mortality rate. Therapeutic options for AAA are cur-rently limited to surgical repair to prevent catastrophic rupture. Non-surgical approaches, particularly pharmacotherapy, are lacking for the treatment of AAA.

Objective:

We review both basic and clinical studies and discuss the current challenges to developing medical therapy that reduces AAA progression.

Results:

Studies using animal models of AAA progression and human AAA explant cultures have identified several potential targets for preventing AAA growth. However, no clinical studies have con-vincingly confirmed the efficacy of any pharmacologic treatment against the growth of AAA. Thus, there is as yet no strong recommendation regarding pharmacotherapy to reduce the risk of AAA pro-gression and rupture.

Conclusion:

This review identifies concerns that need to be addressed for the field to progress and dis-cusses the challenges that must be overcome in order to develop effective pharmacotherapy to reduce AAA progression in the future.

Emerging Roles of Lysyl Oxidases in the Cardiovascular System: New Concepts and Therapeutic Challenges

Lysyl oxidases (LOX and LOX-likes (LOXLs) isoenzymes) belong to a family of copper-dependent enzymes classically involved in the covalent cross-linking of collagen and elastin, a pivotal process that ensures extracellular matrix (ECM) stability and provides the tensile and elastic characteristics of connective tissues. Besides this structural role, in the last years, novel biological properties have been attributed to these enzymes, which can critically influence cardiovascular function. LOX and LOXLs control cell proliferation, migration, adhesion, differentiation, oxidative stress, and transcriptional regulation and, thereby, their dysregulation has been linked to a myriad of cardiovascular pathologies. Lysyl oxidase could modulate virtually all stages of the atherosclerotic process, from endothelial dysfunction and plaque progression to calcification and rupture of advanced and complicated plaques, and contributes to vascular stiffness in hypertension. The alteration of LOX/LOXLs expression underlies the development of other vascular pathologies characterized by a destructive remodeling of the ECM, such as aneurysm and artery dissections, and contributes to the adverse myocardial remodeling and dysfunction in hypertension, myocardial infarction, and obesity. This review examines the most recent advances in the study of LOX and LOXLs biology and their pathophysiological role in cardiovascular diseases with special emphasis on their potential as therapeutic targets.

Alterations in phenotype and gene expression of adult human aneurysmal smooth muscle cells by exogenous nitric oxide

Abdominal aortic aneurysms (AAA) are characterized by matrix remodeling, elastin degradation, absence of nitric oxide (NO) signaling, and inflammation, influencing smooth muscle cell (SMC) phenotype and gene expression. Little is known about the biomolecular release and intrinsic biomechanics of human AAA-SMCs. NO delivery could be an attractive therapeutic strategy to restore lost functionality of AAA-SMCs by inhibiting inflammation and cell stiffening. We aim to establish the differences in phenotype and gene expression of adult human AAA-SMCs from healthy SMCs. Based on our previous study which showed benefits of optimal NO dosage delivered via S-Nitrosoglutathione (GSNO) to healthy aortic SMCs, we tested whether such benefits would occur in AAA-SMCs. The mRNA expression of three genes involved in matrix degradation (ACE, ADAMTS5 and ADAMTS8) was significantly downregulated in AAA-SMCs. Total protein and glycosaminoglycans synthesis were higher in AAA-SMCs than healthy-SMCs (p < 0.05 for AAA-vs. healthy- SMC cultures) and was enhanced by GSNO and 3D cultures (p < 0.05 for 3D vs. 2D cultures; p < 0.05 for GSNO vs. non-GSNO cases). Elastin gene expression, synthesis and deposition, desmosine crosslinker levels, and lysyl oxidase (LOX) functional activity were lower, while cell proliferation, iNOS, LOX and fibrillin-1 gene expressions were higher in AAA-SMCs (p < 0.05 between respective cases), with differential benefits from GSNO exposure. GSNO and 3D cultures reduced MMPs -2, -9, and increased TIMP-1 release in AAA-SMC cultures (p < 0.05 for GSNO vs. non-GSNO cultures). AAA-SMCs were inherently stiffer and had smoother surface than healthy SMCs (p < 0.01 in both cases), but GSNO reduced stiffness (~25%; p < 0.01) and increased roughness (p < 0.05) of both cell types. In conclusion, exogenously-delivered NO offers an attractive strategy by providing therapeutic benefits to AAA-SMCs.

Abdominal aortic aneurysms

An abdominal aortic aneurysm (AAA) is a localized dilatation of the infrarenal aorta. AAA is a multifactorial disease, and genetic and environmental factors play a part; smoking, male sex and a positive family history are the most important risk factors, and AAA is most common in men >65 years of age. AAA results from changes in the aortic wall structure, including thinning of the media and adventitia due to the loss of vascular smooth muscle cells and degradation of the extracellular matrix. If the mechanical stress of the blood pressure acting on the wall exceeds the wall strength, the AAA ruptures, causing life-threatening intra-abdominal haemorrhage - the mortality for patients with ruptured AAA is 65-85%. Although AAAs of any size can rupture, the risk of rupture increases with diameter. Intact AAAs are typically asymptomatic, and in settings where screening programmes with ultrasonography are not implemented, most cases are diagnosed incidentally. Modern functional imaging techniques (PET, CT and MRI) may help to assess rupture risk. Elective repair of AAA with open surgery or endovascular aortic repair (EVAR) should be considered to prevent AAA rupture, although the morbidity and mortality associated with both techniques remain non-negligible.

Tropoelastin: A novel marker for plaque progression and instability

Background

Elastolysis and ineffective elastogenesis favor the accumulation of tropoelastin, rather than cross-linked elastin, in atherosclerotic plaques. We developed gadolinium-labeled tropoelastin-specific magnetic resonance contrast agents (Gd-TESMAs) for tropoelastin imaging in animal models.

Methods and Results

Two peptides, VVGSPSAQDEASPLS and YPDHVQYTHY were selected to target tropoelastin. In vitro binding, relaxivity, and biodistribution experiments enabled characterization of the probes and selecting the best candidate for in vivo MRI. MRI was performed in atherosclerotic apolipoprotein E-deficient (ApoE^-/-) mice and New Zealand white rabbits with stable and rupture-prone plaques using Gd-TESMA. Additionally, human carotid endarterectomy specimens were imaged ex vivo. The VVGSPSAQDEASPLS-based probe discriminated between tropoelastin and cross-linked elastin (64±7% vs 1±2%, P=0.001), had high in vitro relaxivity in solution (r_1-free=11.7±0.6mM^-1s^-1, r_{1-bound to tropoelastin} = 44±1mM^-1s^-1) and favorable pharmacokinetics. In vivo mice vascular enhancement (4wks=0.13±0.007mm², 8wks=0.22±0.01mm², 12wks=0.33±0.01mm², P<0.001) and R₁ relaxation rate (4wks=0.90±0.01 s^-1, 8wks=1.40±0.03 s^-1, 12wks=1.87±0.04s^-1, P<0.001) increased with atherosclerosis progression after Gd-TESMA injection. Conversely, statin-treated (0.13±0.01mm², R₁ =1.37±0.03s^-1) and control (0.10±0.005mm², R₁ =0.87±0.05s^-1) mice showed less enhancement. Rupture-prone rabbit plaques had higher R₁ relaxation rate compared with stale plaques (R₁=2.26±0.1s^-1vs R₁=1.43±0.02s^-1, P=0.001), after administration of Gd-TESMA that allowed detection of rupture-prone plaques with high sensitivity (84.4%) and specificity (92.3%). Increased vascular R₁ relaxation rate was observed in carotid endarterectomy plaques after soaking (R_1pre= 1.1±0.26 s^-1 vs R_1post= 3.0±0.1s^-1, P=0.01). Ex vivo analyses confirmed the MRI findings and showed uptake of the contrast agent to be specific for tropoelastin.

Conclusions

MRI of tropoelastin provides a novel biomarker for atherosclerotic plaque progression and instability.

Quantitative Micro-CT Analysis of Aortopathy in a Mouse Model of β-aminopropionitrile-induced Aortic Aneurysm and Dissection

Aortic aneurysm and dissection is associated with significant morbidity and mortality in the population and can be highly lethal. While animal models of aortic disease exist, in vivo imaging of the vasculature has been limited. In recent years, micro-computerized tomography (micro-CT) has emerged as a preferred modality for imaging both large and small vessels both in vivo and ex vivo. In conjunction with a method of vascular casting, we have successfully used micro-CT to characterize the frequency and distribution of aortic pathology in β-aminopropionitrile-treated C57/Bl6 mice. Technical limitations of this method include variations in the quality of the perfusion introduced by poor animal preparation, the application of proper methodologies for vessel size quantification, and the non-survivability of this procedure. This article details a methodology for the intravascular perfusion of a lead-based radiopaque silicone rubber for the quantitative characterization of aortopathy in a mouse model of aneurysm and dissection. In addition to visualizing aortic pathology, this method may be used for examining other vascular beds in vivo or vascular beds removed post-mortem.

In Vivo Molecular Characterization of Abdominal Aortic Aneurysms Using Fibrin-Specific Magnetic Resonance Imaging

BACKGROUND

The incidence of abdominal aortic aneurysms (AAAs) will significantly increase during the next decade. Novel biomarkers, besides diameter, are needed for a better characterization of aneurysms and the estimation of the risk of rupture. Fibrin is a key protein in the formation of focal hematoma associated with the dissection of the aortic wall and the development of larger thrombi during the progression of AAAs. This study evaluated the potential of a fibrin-specific magnetic resonance (MR) probe for the in vivo characterization of the different stages of AAAs.

METHODS AND RESULTS

AAAs spontaneously developed in ApoE-/- mice following the infusion of angiotensin-II (Ang-II, 1 μg/kg-1·per minute). An established fibrin-specific molecular MR probe (EP2104R, 10 μmol/kg-1) was administered after 1 to 4 weeks following Ang-II infusion (n=8 per group). All imaging experiments were performed on a clinical 3T Achieva MR system with a microscopy coil (Philips Healthcare, Netherlands). The development of AAA-associated fibrin-rich hematoma and thrombi was assessed. The high signal generated by the fibrin probe enabled high-resolution MR imaging for an accurate assessment and quantification of the relative fibrin composition of focal hematoma and thrombi. Contrast-to-noise-ratios (CNRs) and R1-relaxation rates following the administration of the fibrin probe were in good agreement with ex vivo immunohistomorphometry (R2=0.83 and 0.85) and gadolinium concentrations determined by inductively coupled plasma mass spectroscopy (R2=0.78 and 0.72).

CONCLUSIONS

The fibrin-specific molecular MR probe allowed the delineation and quantification of changes in fibrin content in early and advanced AAAs. Fibrin MRI could provide a novel in vivo biomarker to improve the risk stratification of patients with aortic aneurysms.

In Vivo High-Frequency Ultrasound for the Characterization of Thrombi Associated with Aortic Aneurysms in an Experimental Mouse Model

The development of abdominal aortic aneurysm (AAA) associated thrombi plays an important role during the onset and progression of AAAs. The aim of this study was to evaluate the potential of high-frequency ultrasound for characterization of AAA associated thrombi in an apolipoprotein-E-deficient mouse-model. Ultrasound measurements were performed using a high-resolution ultrasound system (Vevo770, FUJIFILM VisualSonics, Inc., Toronto, ON, Canada) with a 30 MHz linear-array transducer (RMV707 B). Magnetic resonance imaging with a 3 Tesla scanner (Achieva MR system, Philips Healthcare, Best, The Netherlands) and a single-loop microscopy coil was performed as a reference standard. All stages of aneurysm development were evaluated by histologic analyses. The "signal-thrombus-matrix" to "signal-blood" ratio on high-frequency ultrasound measurements showed a strong correlation (R² = 0.81, p <0.05) with the state of extracellular matrix remodeling. Furthermore, size measurements derived from the high-frequency ultrasound correlated well with magnetic resonance imaging and histology. This study demonstrated that high-frequency ultrasound enables the reliable in vivo quantification of extracellular matrix remodeling at various stages of thrombus development, based on the thrombus echogenicity.

A novel reproducible model of aortic aneurysm rupture

INTRODUCTION

Given the unknown biologic antecedents before aortic aneurysm rupture, the purpose of this study was to establish a reproducible model of aortic aneurysm rupture.

METHODS

We fed 7-week-old apolipoprotein E deficient mice a high-fat diet for 4 weeks and osmotic infusion pumps containing Angiotensin II were implanted. Angiotensin II was delivered continuously for 4 weeks at either 1,000 ng/kg/min (n = 25) or 2,000 ng/kg/min (n = 29). A third group (n = 14) were given Angiotensin II at 2,000 ng/kg/min and 0.2% β-aminopropionitrile dissolved in drinking water. Surviving mice were killed 28 days after pump placement, aortic diameters were measured, and molecular analyses were performed.

RESULTS

Survival at 28 days was significantly different among groups with 80% survival in the 1,000 ng/kg/min group, 52% in the 2,000 ng/kg/min group, and only 14% in the Angiotensin II/β-aminopropionitrile group (P = .0001). Concordantly, rupture rates were statistically different among groups (8% versus 38% versus 79%, P < .0001). Rates of abdominal aortic aneurysm were 48%, 55%, and 93%, respectively, with statistically higher rates in the Angiotensin II/β-aminopropionitrile group compared with both the 1,000 ng and 2,000 ng Angiotensin II groups (P = .006 and P = .0165, respectively). Rates of thoracic aortic aneurysm formation were 12%, 52%, and 79% in the 3 groups with a statistically higher rate in the Angiotensin II/β-aminopropionitrile group compared with 1,000 ng group (P < .0001).

CONCLUSIONS

A reproducible model of aortic aneurysm rupture was developed with a high incidence of abdominal and thoracic aortic aneurysm. This model should enable further studies investigating the pathogenesis of aortic rupture, as well as allow for targeted strategies to prevent human aortic aneurysm rupture.

A novel chronic advanced stage abdominal aortic aneurysm murine model

OBJECTIVE

The purpose of this study was to establish a reliable, chronic model of abdominal aortic aneurysm (AAA).

METHODS

Wild-type 8-week-old C56BL/6 male mice (n = 120) were equally divided into three groups: (1) BAPN group: 0.2% 3-aminopropionitrile fumarate salt (BAPN) drinking water was provided to mice 2 days before surgery until the end of study. Sham aneurysm induction surgery was performed using 5 μL of heat deactivated elastase. (2) Elastase group: mice were given regular drinking water without BAPN. During aneurysm induction surgery, 5 μL of the active form of elastase (10.3 mg protein/mL, 5.9 U/mg protein) was applied on top of the infrarenal abdominal aorta adventitia for 5 minutes. (3) BAPN+elastase group: mice were given BAPN drinking water and the active form of elastase application, as above. On postoperative days 7, 14, 21, 28, and 100, aortic samples were collected for histology, cytokine array, and gelatin zymography after aortic diameter measurement.

RESULTS

Compared with the elastase group, the BAPN+elastase group had a higher AAA formation rate (93% vs 65%; P < .01) with more advanced AAAs (25 of 42 vs 1 of 40 for stage II and III; P < .001). Aneurysms from the BAPN+elastase group demonstrated persistent long-term growth (221.5% ± 36.6%, 285.8% ± 78.6%, and 801% ± 160% on days 21, 28, and 100, respectively; P < .001), with considerable thrombus formation (54%) and rupture (31%) at the advanced stages of AAA development. Cytokine levels (pro-matrix metalloproteinase 9, interleukin-1β, interleukin-6, chemokine [C-C motif] ligand 5, triggering receptor expressed on myeloid cells 1, monocyte chemotactic protein 1, and tissue inhibitor of metalloproteinase 1) in the BAPN+elastase group were higher than in the elastase group on day 7. After day 7, cytokine levels returned to baseline, with the exception of elevated matrix metalloproteinase 2 activity. By histology, CD3-positive T cells in the BAPN+elastase group were elevated on days 28 and 100.

CONCLUSIONS

A combination of oral BAPN administration and periaortic elastase application induced a chronic, advanced-stage AAA with characteristics of persistent aneurysm growth, thrombus formation, and spontaneous rupture. Future studies should use this model, especially for examining tissue remodeling during the late stages of aneurysm development.

Translational Relevance and Recent Advances of Animal Models of Abdominal Aortic Aneurysm

Human abdominal aortic aneurysm (AAA) pathophysiology is not yet completely understood. In conductance arteries, the insoluble extracellular matrix, synthesized by vascular smooth muscle cells, assumes the function of withstanding the intraluminal arterial blood pressure. Progressive loss of this function through extracellular matrix proteolysis is a main feature of AAAs. As most patients are now treated via endovascular approaches, surgical AAA specimens have become rare. Animal models provide valuable complementary insights into AAA pathophysiology. Current experimental AAA models involve induction of intraluminal dilation (nondissecting AAAs) or a contained intramural rupture (dissecting models). Although the ideal model should reproduce the histological characteristics and natural history of the human disease, none of the currently available animal models perfectly do so. Experimental models try to represent the main pathophysiological determinants of AAAs: genetic or acquired defects in extracellular matrix, loss of vascular smooth muscle cells, and innate or adaptive immune response. Nevertheless, most models are characterized by aneurysmal stabilization and healing after a few weeks because of cessation of the initial stimulus. Recent studies have focused on ways to optimize existing models to allow continuous aneurysmal growth. This review aims to discuss the relevance and recent advances of current animal AAA models.

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Inhibition of Receptor-Interacting Protein Kinase 1 with Necrostatin-1s ameliorates disease progression in elastase-induced mouse abdominal aortic aneurysm model

Abdominal aortic aneurysm (AAA) is a common aortic disease with a progressive nature. There is no approved pharmacological treatment to effectively slow aneurysm growth or prevent rupture. Necroptosis is a form of programmed necrosis that is regulated by receptor-interacting protein kinases (RIPs). We have recently demonstrated that the lack of RIP3 in mice prevented aneurysm formation. The goal of the current study is to test whether perturbing necroptosis affects progression of existing aneurysm using the RIP1 inhibitors Necrostatin-1 (Nec-1) and an optimized form of Nec-1, 7-Cl-O-Nec-1 (Nec-1s). Seven days after aneurysm induction by elastase perfusion, mice were randomly administered DMSO, Nec-1 (3.2 mg/kg/day) and Nec-1s (1.6 mg/kg/day) via intraperitoneal injection. Upon sacrifice on day 14 postaneurysm induction, the aortic expansion in the Nec-1s group (64.12 ± 4.80%) was significantly smaller than that of the DMSO group (172.80 ± 13.68%) (P < 0.05). The mean aortic diameter of Nec-1 treated mice appeared to be smaller (121.60 ± 10.40%) than the DMSO group, though the difference was not statistically significant (P = 0.1). Histologically, the aortic structure of Nec-1s-treated mice appeared normal, with continuous and organized elastin laminae and abundant αActin-expressing SMCs. Moreover, Nect-1s treatment diminished macrophage infiltration and MMP9 accumulation and increased aortic levels of tropoelastin and lysyl oxidase. Together, our data suggest that pharmacological inhibition of necroptosis with Nec-1s stabilizes pre-existing aneurysms by diminishing inflammation and promoting connective tissue repair.

Fourier Transform Infrared Spectroscopic Imaging-Derived Collagen Content and Maturity Correlates with Stress in the Aortic Wall of Abdominal Aortic Aneurysm Patients

Abdominal aortic aneurysm (AAA) is a degenerative disease of the aorta characterized by severe disruption of the structural integrity of the aortic wall and its major molecular constituents. From the early stages of disease, elastin in the aorta becomes highly degraded and is replaced by collagen. Questions persist as to the contribution of collagen content, quality and maturity to the potential for rupture. Here, using our recently developed Fourier transform infrared imaging spectroscopy (FT-IRIS) method, we quantified collagen content and maturity in the wall of AAA tissues in pairs of specimens with different wall stresses. CT scans of AAAs from 12 patients were used to create finite element models to estimate stress in different regions of tissue. Each patient underwent elective repair of the AAA, and two segments of the AAA tissues from anatomic regions more proximal or distal with different wall stresses were evaluated by histology and FT-IRIS after excision. For each patient, collagen content was generally greater in the tissue location with lower wall stress, which corresponded to the more distal anatomic regions. The wall stress/collagen ratio was greater in the higher stress region compared to the lower stress region (1.01 ± 1.09 vs. 0.55 ± 0.084, p = 0.02). The higher stress region also corresponded to the location with reduced intraluminal thrombus thickness. Further, collagen maturity tended to decrease with increased collagen content (p = 0.068, R = 0.38). Together, these results suggest that an increase in less mature collagen content in AAA patients does not effectively compensate for the loss of elastin in the aortic wall, and results in a reduced capability to endure wall stresses.

Expression of Integrin •5•1 and the Relationship to Collagen and Elastin Content in Human Suprarenal and Infrarenal Aortas

The infrarenal aorta is especially prone to the development of aneurysm, suggesting an intrinsic structural and molecular difference in different parts of the aorta. Previous study from this laboratory has implicated a potential role of integrin a5b1 in maintaining aortic integrity. The aim of this study was to investigate the expression of integrin a5b1 and the relationship to collagen and elastin content between 2 different aortic segments. In this study, the variation of smooth muscle cells and the localization of integrin a5b1 in the suprarenal and infrarenal aorta tissues removed from organ donors were studied immunohistochemically. The biochemical analysis for matrix proteins and integrin a5b1 protein was done by Western Blot on the corresponding tissues. All interested protein content was normalized to the smooth muscle a-actin protein. No significant difference of smooth muscle cells density between the 2 segments of aortas was observed. Integrin a5b1 was localized in the outer layer of all aortic media. The authors found that the ratio of collagen/elastin in infrarenal aortas was significantly increased 2-fold because elastin content in infrarenal aortas decreased 49% as compared with suprarenal aortas. Integrin a5b1 content relative to its specific ligand — collagen—did not differ between these 2 different aortic segments. These results suggest that the infrarenal aorta differed biochemically from the suprarenal aorta. A decrease in infrarenal elastin without a corresponding decrease in collagen and integrin a5b1 may affect the compliance and integrity of the distal aorta. These intrinsic anatomic differences may be important in the susceptibility of the infrarenal aortas to aneurysm formation.

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

OBJECTIVE

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Association of polymorphisms of the receptor for advanced glycation end products gene and susceptibility to sporadic abdominal aortic aneurysm

Accumulating evidence has suggested that receptor for advanced glycation end products (RAGE) is involved in the development and progression of human abdominal aortic aneurysms (AAAs). However, the association between RAGE gene polymorphisms and AAA has not yet been determined. The present study was aimed at analyzing the potential association between the RAGE gene polymorphisms and AAAs. A cohort of 381 patients and 436 age-matched healthy controls were genotyped to detect the three RAGE polymorphisms (-374 T/A, -429 T/C, and G82S) using SNaPshot. Our study demonstrated a significant difference in the genotype and allele frequencies of the RAGE G82S polymorphism between the AAA patients and the controls. Further stratification by gender and smoking status revealed that the presence of the RAGE 82S allele confers a higher risk for developing AAA in men and smokers. Moreover, AAA patients with the variant 82S allele of RAGE presented with reduced serum soluble RAGE (sRAGE) production, and this decrease was more significant in men and smokers with AAA. Our study provides preliminary evidence that the 82S allele of RAGE is a risk factor for AAA. This new piece of knowledge regarding RAGE may be clinically important for the prevention and therapy of AAAs.

Interference of doxycycline pretreatment in a model of abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysm (AAA) is characterized by chronic inflammation and degradation of the extracellular matrix, mediated by matrix metalloproteinases (MMPs). Doxycycline has been reported to control the progression of AAA by regulation of MMP. We hypothesized that doxycycline pretreatment in a rat model of AAA would cause reduction in gelatinolytic activity of MMP-2 and -9 and the inflammatory response in the wall of an aneurysm, consequently decreasing the formation and development of AAAs.

METHODS

Male Wistar rats were divided into the following four groups: aneurysm (A); control (C); aneurysm+doxycycline (A+D) and control+doxycycline (C+D), with 24 animals per group subdivided into n=6 animals at different time points [1, 3, 7, and 15 days postsurgery (dps)]. The (A) and (A+D) groups simultaneously received the injury and extrinsic stenosis of the aortic wall. The (C) and (C+D) groups received sham operation. The treated animals received doxycycline via gavage (30 mg/kg/day) from 48 h before surgery until the end of experiment. At 1, 3, 7, and 15 dps, the animals were euthanized, and the aortas were collected for morphological analyses, immunohistochemistry, and zymography.

RESULTS

The animals from the (A) group developed AAAs. However, the animals treated with doxycycline showed a 85% decrease in AAA development, which was associated with a large reduction in gelatinolytic activity of MMP-2 and -9, and decreased inflammatory response (P<.05).

CONCLUSIONS

These results suggest that pretreatment with doxycycline before surgery inhibited the activity of MMP-2 and -9, as well as the inflammatory response, and may play an important role in the prevention of the development of AAAs.

Mesenchymal stem cells for treatment of aortic aneurysms

An aortic aneurysm (AA) is a silent but life-threatening disease that involves rupture. It occurs mainly in aging and severe atherosclerotic damage of the aortic wall. Even though surgical intervention is effective to prevent rupture, surgery for the thoracic and thoraco-abdominal aorta is an invasive procedure with high mortality and morbidity. Therefore, an alternative strategy for treatment of AA is required. Recently, the molecular pathology of AA has been clarified. AA is caused by an imbalance between the synthesis and degradation of extracellular matrices in the aortic wall. Chronic inflammation enhances the degradation of matrices directly and indirectly, making control of the chronic inflammation crucial for aneurysmal development. Meanwhile, mesenchymal stem cells (MSCs) are known to be obtained from an adult population and to differentiate into various types of cells. In addition, MSCs have not only the potential anti-inflammatory and immunosuppressive properties but also can be recruited into damaged tissue. MSCs have been widely used as a source for cell therapy to treat various diseases involving graft-versus-host disease, stroke, myocardial infarction, and chronic inflammatory disease such as Crohn’s disease clinically. Therefore, administration of MSCs might be available to treat AA using anti-inflammatory and immnosuppressive properties. This review provides a summary of several studies on “Cell Therapy for Aortic Aneurysm” including our recent data, and we also discuss the possibility of this kind of treatment.

In vivo assessment of aortic aneurysm wall integrity using elastin-specific molecular magnetic resonance imaging

BACKGROUND

The incidence of abdominal aortic aneurysms (AAAs) has increased during the last decades. However, there is still controversy about the management of medium-sized AAAs. Therefore, novel biomarkers, besides aneurysmal diameter, are needed to assess aortic wall integrity and risk of rupture. Elastin is the key protein for maintaining aortic wall tensile strength and stability. The progressive breakdown of structural proteins, in particular, medial elastin, is responsible for the inability of the aortic wall to withstand intraluminal hemodynamic forces. Here, we evaluate the usefulness of elastin-specific molecular MRI for the in vivo characterization of AAAs.

METHODS AND RESULTS

To induce AAAs, ApoE(-/-) mice were infused with angiotensin-II. An elastin-specific magnetic resonance molecular imaging agent (ESMA) was administered after 1, 2, 3, and 4 weeks of angiotensin-II infusion to assess elastin composition of the aorta (n=8 per group). The high signal provided by ESMA allowed for imaging with high spatial resolution, resulting in an accurate assessment of ruptured elastic laminae and the compensatory expression of elastic fibers. In vivo contrast-to-noise ratios and R1-relaxation rates after ESMA administration were in good agreement with ex vivo histomorphometry (Elastica van Gieson stain) and gadolinium concentrations determined by inductively coupled plasma mass spectroscopy. Electron microscopy confirmed colocalization of ESMA with elastic fibers.

CONCLUSIONS

Changes in elastin content could be readily delineated and quantified at different stages of AAAs by elastin-specific molecular magnetic resonance imaging. ESMA-MRI offers potential for the noninvasive detection of the aortic rupture site prior to dilation of the aorta and the subsequent in vivo monitoring of compensatory repair processes during the progression of AAAs.

Elasto-regenerative properties of polyphenols

Abdominal aortic aneurysms (AAA) are progressive dilatations of infra-renal aorta causing structural weakening rendering the aorta prone to rupture. AAA can be potentially stabilized by inhibiting inflammatory enzymes such as matrix metalloproteinases (MMP); however, active regression of AAA is not possible without new elastic fiber regeneration. Here we report the elastogenic benefit of direct delivery of polyphenols such as pentagalloyl glucose (PGG), epigallocatechin gallate (EGCG), and catechin, to smooth muscle cells obtained either from healthy or from aneurysmal rat aorta. Addition of 10 μg/ml PGG and ECGC induce elastin synthesis, organization, and crosslinking while catechin does not. Our results indicate that polyphenols bind to monomeric tropoelastin and enhance coacervation, aid in crosslinking of elastin by increasing lysyl oxidase (LOX) synthesis, and by blocking MMP-2 activity. Thus, polyphenol treatments leads to increased mature elastin fibers synthesis without increasing the production of intracellular tropoelastin.

Nanoparticles for localized delivery of hyaluronan oligomers towards regenerative repair of elastic matrix

Abdominal aortic aneurysms (AAAs) are rupture-prone progressive dilations of the infrarenal aorta due to a loss of elastic matrix that lead to weakening of the aortic wall. Therapies to coax biomimetic regenerative repair of the elastic matrix by resident, diseased vascular cells may thus be useful to slow, arrest or regress AAA growth. Hyaluronan oligomers (HA-o) have been shown to induce elastic matrix synthesis by healthy and aneurysmal rat aortic smooth muscle cells (SMCs) in vitro but only via exogenous dosing, which potentially has side-effects and limitations to in vivo delivery towards therapy. In this paper, we describe the development of HA-o loaded poly(lactide-co-glycolide) nanoparticles (NPs) for targeted, controlled and sustained delivery of HA-o towards the elastogenic induction of aneurysmal rat aortic SMCs. These NPs were able to deliver HA-o over an extended period (>30 days) at previously determined elastogenic doses (0.2-20 μg ml(-1)). HA-o released from the NPs led to dose-dependent increases in elastic matrix synthesis, and the recruitment and activity of lysyl oxidase, the enzyme which cross-links elastin precursor molecules into mature fibers/matrix. Therefore, we were able to successfully develop a nanoparticle-based system for controlled and sustained HA-o delivery for the in vitro elastogenic induction of aneurysmal rat aortic smooth muscle cells.

Advanced glycation end products suppress lysyl oxidase and induce bone collagen degradation in a rat model of renal osteodystrophy

Renal osteodystrophy (ROD) is a major problem in patients with renal insufficiency. The present study was designed to elucidate the role of bone collagen changes and osteoblast differentiation in a rat model of ROD pathogenesis induced by adenine. Typical characteristics of renal failure, including increased serum urea nitrogen, creatinine, inorganic phosphorus, and intact parathyroid hormone levels, and decreased serum calcium and 1,25(OH)2D3 levels, were observed in adenine-induced rats. Micro-computed tomography analysis of the femur in adenine-induced rats showed decreased bone mineral density and osteoporotic changes, confirmed by the three-point bending test. The cancellous bone histomorphometric parameters of the tibia showed increased osteoblast number, decreased osteoclast surface with peritrabecular fibrosis, and increased osteoid tissue, indicating a severe mineralization disorder similar to clinical ROD. Scanning and transmission electron microscopy revealed irregular alignment and increased diameter of bone collagen fibrils in adenine-induced rats. Protein expression analysis showed greater accumulation of advanced glycation end products (AGEs) in peritrabecular osteoblasts of adenine-induced rats than in the controls. In contrast, suppressed expression of runt-related transcription factor 2, alkaline phosphatase, secreted phosphoprotein 1 (Spp1), and lysyl oxidase (Lox) mRNA levels, particularly the amount of active LOX protein, were observed. In in-vitro experiments, mineralizing MC3T3-E1 osteoblastic cells stimulated with AGE-modified bovine serum albumin had attenuated the expression of Spp1 mRNA levels and active LOX protein, with a decrease in extracellular nodules of mineralization. These observations provide clues to ROD pathogenesis, as they indicate that the suppression of osteoblast differentiation and decreased active LOX protein associated with accumulation of AGEs in osteoblasts caused structural abnormalities of bone collagen fibrils and a severe mineralization disorder, leading to bone fragility.

Perspectives on stem cell-based elastic matrix regenerative therapies for abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are potentially fatal conditions that are characterized by decreased flexibility of the aortic wall due to proteolytic loss of the structural matrix. This leads to their gradual weakening and ultimate rupture. Drug-based inhibition of proteolytic enzymes may provide a nonsurgical treatment alternative for growing AAAs, although it might at best be sufficient to slow their growth. Regenerative repair of disrupted elastic matrix is required if regression of AAAs to a healthy state is to be achieved. Terminally differentiated adult and diseased vascular cells are poorly capable of affecting such regenerative repair. In this context, stem cells and their smooth muscle cell-like derivatives may represent alternate cell sources for regenerative AAA cell therapies. This article examines the pros and cons of using different autologous stem cell sources for AAA therapy, the requirements they must fulfill to provide therapeutic benefit, and the current progress toward characterizing the cells' ability to synthesize elastin, assemble elastic matrix structures, and influence the regenerative potential of diseased vascular cell types. The article also provides a detailed perspective on the limitations, uncertainties, and challenges that will need to be overcome or circumvented to translate current strategies for stem cell use into clinically viable AAA therapies. These therapies will provide a much needed nonsurgical treatment option for the rapidly growing, high-risk, and vulnerable elderly demographic.

Efficacy and mechanism of angiotensin II receptor blocker treatment in experimental abdominal aortic aneurysms

Background

Despite the importance of the renin-angiotensin (Ang) system in abdominal aortic aneurysm (AAA) pathogenesis, strategies targeting this system to prevent clinical aneurysm progression remain controversial and unproven. We compared the relative efficacy of two Ang II type 1 receptor blockers, telmisartan and irbesartan, in limiting experimental AAAs in distinct mouse models of aneurysm disease.

Methodology/Principal Findings

AAAs were induced using either 1) Ang II subcutaneous infusion (1000 ng/kg/min) for 28 days in male ApoE^−/− mice, or 2) transient intra-aortic porcine pancreatic elastase infusion in male C57BL/6 mice. One week prior to AAA creation, mice started to daily receive irbesartan (50 mg/kg), telmisartan (10 mg/kg), fluvastatin (40 mg/kg), bosentan (100 mg/kg), doxycycline (100 mg/kg) or vehicle alone. Efficacy was determined via serial in vivo aortic diameter measurements, histopathology and gene expression analysis at sacrifice. Aortic aneurysms developed in 67% of Ang II-infused ApoE^−/− mice fed with standard chow and water alone (n = 15), and 40% died of rupture. Strikingly, no telmisartan-treated mouse developed an AAA (n = 14). Both telmisartan and irbesartan limited aneurysm enlargement, medial elastolysis, smooth muscle attenuation, macrophage infiltration, adventitial neocapillary formation, and the expression of proteinases and proinflammatory mediators. Doxycycline, fluvastatin and bosentan did not influence aneurysm progression. Telmisartan was also highly effective in intra-aortic porcine pancreatic elastase infusion-induced AAAs, a second AAA model that did not require exogenous Ang II infusion.

Conclusion/Significance

Telmisartan suppresses experimental aneurysms in a model-independent manner and may prove valuable in limiting clinical disease progression.

Recent advances in pharmacotherapy development for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease causing segmental expansion and rupture of the aorta with a high mortality rate. The lack of nonsurgical treatment represents a large and unmet need in terms of pharmacotherapy. Advances in AAA research revealed that activation of inflammatory signaling pathways through proinflammatory mediators shifts the balance of extracellular matrix (ECM) metabolism toward tissue degradation. This idea is supported by experimental evidence in animal models that pharmacologic intervention at each pathological step can prevent AAA development. Previously, we identified c-Jun N-terminal kinase (JNK), a pro-inflammatory signaling molecule, as a therapeutic target for AAA. Abnormal activation of JNK in AAA tissue regulates multiple pathological processes in a coordinated manner. Pharmacologic inhibition of JNK tips the ECM balance back towards repair rather than degradation. Interventions targeting signaling molecules such as JNK in order to manipulate multiple pathological processes may be an ideal therapeutic strategy for AAA. Furthermore, the development of biomarkers as well as appropriate drug delivery systems is essential to produce clinically practical pharmacotherapy for AAA.

Induced elastic matrix deposition within three-dimensional collagen scaffolds

The structural stability of a cyclically distending elastic artery and the healthy functioning of vascular smooth muscle cells (SMCs) within are maintained by the presence of an intact elastic matrix and its principal protein, elastin. The accelerated degradation of the elastic matrix, which occurs in several vascular diseases, coupled with the poor ability of adult SMCs to regenerate lost elastin, can therefore adversely impact vascular homeostasis. Similarly, efforts to tissue engineer elastic matrix structures are constrained by our inability to induce adult cells to synthesize tropoelastin precursors and to crosslink them into architectural mimics of native elastic matrices, especially within engineered constructs where SMCs/fibroblasts primarily deposit collagen in abundance. In this study, we have shown that transforming growth factor-beta1 (TGF-β1) and hyaluronan oligomers (HA-o) synergistically enhance elastic matrix deposition by adult rat aortic SMCs (RASMCs) seeded within nonelastogenic, statically loaded three-dimensional gels, composed of nonelastogenic type-I collagen. While there was no substantial increase in production of tropoelastin within experimental cases compared to the nonadditive control cultures over 3 weeks, we observed significant increases in matrix elastin deposition; soluble matrix elastin in constructs that received the lowest doses of TGF-β1 with respective doses of HA-o, and insoluble matrix at the highest doses that corresponded with elevated lysyl-oxidase protein quantities. However, despite elastogenic induction, overall matrix yields remained poor in all experimental cases. At all provided doses, the factors reduced the production of matrix metalloproteinases (MMP)-9, especially the active enzyme, though MMP-2 levels were lowered only in constructs cultured with the higher doses of TGF-β1. Immuno-fluorescence showed elastic fibers within the collagen constructs to be discontinuous, except at the edges of the constructs. Von Kossa staining revealed no calcific deposits in any of the cases. This study confirms the benefits of utilizing TGF-β1 and HA-o in inducing matrix elastin synthesis by adult RASMCs over nonadditive controls, within a collagenous environment, that is not inherently conducive to elastogenesis.

Lysyl oxidase G473A polymorphism is associated with increased risk of coronary artery diseases

Lysyl oxidase (LOX) plays a crucial role in the maintenance of extracellular matrix stability and could participate in vascular remodeling associated with cardiovascular diseases. A novel polymorphism in the LOX gene, G473A (rs1800449), was identified. The objective of this study was to investigate the association between LOX G473A polymorphism and susceptibility to coronary artery diseases (CADs) in Chinese population. The LOX variant G473A was detected by polymerase chain reaction-restriction fragment length polymorphism in 656 CAD cases and 718 age-matched controls. Frequencies of LOX 473 AA genotype and A allele were significantly higher in patients with CAD than in controls (odds ratio = 1.93, 95% confidence interval 1.26-2.95, p = 0.002; and odds ratio = 1.38, 95% confidence interval 1.15-1.67, p = 0.001). Our data suggest that the G473A polymorphism of LOX gene is associated with increased susceptibility to CAD.

A doxycycline loaded, controlled-release, biodegradable fiber for the treatment of aortic aneurysms

The pathogenesis of aortic aneurysm (AA) is characterized by degradation of extracellular matrix with increased matrix metalloproteinases (MMPs) and inflammatory reaction. Doxycycline (DOXY) has been reported to control the extension of AA by regulation of MMP. However, systemic administration may cause adverse side effects. In this study, we demonstrated the possibility of local administration of DOXY controlled-release biodegradable fiber (DCRBF) for AA in mice. DCRBF was fabricated by biodegradable polymer (polylactic acid; PLA) mixed with DOXY using an electrospinning technique. DCRBF was cocultured with SMCs, macrophages and aortic tissue, and placed on an abdominal aortic aneurysm which induced apolipoprotein E-deficient mice. We evaluated gene and protein expression of proteases, elastin and inflammatory markers. In the presence of DCRBF, MMP-12 was significantly decreased, TGF-β1 and Lox were significantly increased in SMC gene expression, MMP-9 and -12 significantly decreased gene expression of macrophages. The DCRBF preserved elastin content and decreased MMP-2 and -9 in aortic tissue. In addition, IGF-1 and TIMP-1 were significantly increased and IL-6 and TNF-α were significantly decreased with DCRBF in vivo. In conclusion, our results suggested that local administration of DCRBF may become a promising alternative therapeutic strategy for AA.

Differential regulation of MMP-2 in the gastrohepatic ligament of the gastroesophageal junction

INTRODUCTION

Ligamentous attachments maintain the normal anatomic position of the gastroesophageal (GE) junction. Failure of these elastic ligaments through an alteration in collagen synthesis, deposition, and metabolism may be a primary etiology of hiatal hernia formation. Differential expression of zinc-dependent matrix metalloproteinases (MMPs) is largely responsible for collagen remodeling. The purpose of this study was to survey baseline levels of MMPs in supporting ligaments of the GE junction from patients without hiatal hernia.

METHODS

Following an institutional review board-approved protocol, plasma and tissue biopsies of the gastrohepatic ligament (GHL), gastrophrenic ligament (GPL), and phrenoesophageal ligament (PEL) were obtained in six patients without a hiatal hernia during laparoscopic anterior esophageal myotomy for achalasia. Total protein extracts from tissue biopsies were analyzed for elastases MMP-2, -9, and -12 and collagenases MMP-1, -3, -7, -8, and -13 using a multiplex profiling kit (R&D Systems, Minneapolis, MN). Data are reported as mean +/- standard deviation. Statistical significance (p < 0.05) was determined using Tukey's test and analysis of variance.

RESULTS

In control patients without hiatal hernias, increased levels of MMP-2 (p < 0.02) were detected in the GHL compared with the GPL and PEL, respectively. Tissue levels of MMP-1, -12, and -13 were not detectable.

CONCLUSIONS

Gelatinase-A (MMP-2) is present in the GHL and plasma of control patients. The GHL may provide the primary GE junction supporting ligament to compare tissue from patients with type I (sliding) and type III (paraesophageal) hiatal hernias to examine the role of altered collagen metabolism in hiatal hernia formation.

Anti-receptor for advanced glycation end products therapies as novel treatment for abdominal aortic aneurysm

OBJECTIVE

Rupture of abdominal aortic aneurysms (AAA) is a devastating event potentially preventable by therapies that inhibit growth of small aneurysms. Receptor of advanced glycation end products (RAGE) has been implicated in age related diseases including atherosclerosis and Alzheimer. Consequently, we explored whether RAGE may also contribute to the formation of AAAs.

RESULTS

Implicating a role for RAGE in AAA, we found the expression of RAGE and its ligand AGE were highly elevated in human aneurysm specimens as compared with normal aortic tissue. In a mouse model of AAA, RAGE gene deletion (knockout) dramatically reduced the incidence of AAA to 1/3 of control (AAAs in 75.0% of controls vs. 25.0% knockouts). Moreover, aortic diameter was markedly reduced in RAGE knockout animals versus controls. As to mechanism, we found that RAGE was coexpressed in AAA macrophages with MMP-9, a promoter of matrix degradation, which is known to induce AAA. In vitro, AGE induced the production of MMP-9 in macrophages in a dose-dependent manner while blocking RAGE signaling with a soluble AGE inhibitor prevented MMP-9 expression. In vivo, RAGE gene deficiency eliminated MMP-9 activity that was prevalent in aneurismal wall of the wild-type mice.

CONCLUSIONS

RAGE promotes the development of AAA by inducing MMP-9 expression. Blocking RAGE in a mouse aneurysm model has a dramatic inhibitory effect on the formation of aneurysms. These data suggest that larger animal and eventually human trials should be designed to test oral RAGE inhibitors and their potential to prevent progression of small aneurysms.

Lysyl oxidase resolves inflammation by reducing monocyte chemoattractant protein-1 in abdominal aortic aneurysm

Lysyl oxidase (LOX) is an enzyme critical for the stability of extracellular matrix and also known to have diverse biological functions. Little is known, however, about the role of LOX in regulating inflammation. Here we demonstrate that LOX suppresses secretion of monocyte chemoattractant protein-1 (MCP-1) in cultured vascular smooth muscle cells. Furthermore, enhancement of LOX activity reduces MCP-1 in a mouse model of abdominal aortic aneurysm (AAA), thereby preventing macrophage infiltration and AAA progression. These findings suggest that LOX has a novel function in resolving inflammation by reducing MCP-1 in AAA.

Upregulation of protein kinase cdelta in vascular smooth muscle cells promotes inflammation in abdominal aortic aneurysm

BACKGROUND

The development of abdominal aortic aneurysms (AAAs) involves a complex interplay of extracellular matrix degradation, inflammation, and apoptosis. We have previously shown that protein kinase Cdelta (PKCdelta) plays a critical role in vascular smooth muscle cell (vSMC) apoptosis in the setting of oxidative stresses. Here, we show that PKCdelta is also involved in the signaling that draws inflammatory cells to aneurismal tissue.

MATERIALS AND METHODS

Immunostaining for monocyte chemotactic factor (MCP)-1 and PKCdelta was performed on paraffin-fixed arterial sections. Enzyme-linked immunosorbent assay to detect MCP-1 produced by vSMCs was performed on media from cultured rat A10 cells after cytokine induction with or without the PKCdelta-specific inhibitor rottlerin. Migration of isolated lymphocytes was evaluated in response to media from activated A10 cells.

RESULTS

Human AAAs show widespread and elevated expression of PKCdelta that is not seen in normal aortic tissues. Cytokine stimulation of cultured vSMCs induced vigorous production of the key chemotactant MCP-1, the expression of which was PKCdelta dependent. Stimulated vSMCs were capable of inducing the migration of leukocytes, and this effect was also dependent on PKCdelta activity. Staining of human AAA tissue for MCP-1 showed an expression pattern that was identical to that of PKCdelta and smooth muscle specific alpha-actin.

CONCLUSIONS

PKCdelta is widely expressed in human AAA vessel walls and mediates MCP-1 expression by vSMCs, which could contribute to the inflammatory process. These findings, coupled with earlier studies of PKCdelta, suggest that PKCdelta plays a central role in the pathogenesis of AAAs and may be a potential target for future therapies.

Osteitis fibrosa is mediated by Platelet-Derived Growth Factor-A via a phosphoinositide 3-kinase-dependent signaling pathway in a rat model for chronic hyperparathyroidism

Abnormal secretion of PTH by the parathyroid glands contributes to a variety of common skeletal disorders. Prior studies implicate platelet-derived growth factor-A (PDGF-A) as an important mediator of selective PTH actions on bone. The present studies used targeted gene profiling and small-molecule antagonists directed against candidate gene products to elucidate the roles of specific PTH-regulated genes and signaling pathways. A group of 29 genes in rats continuously infused with PTH and cotreated with the PDGF receptor antagonist trapidil were differentially expressed compared with PTH treatment alone. Several of the identified genes were functionally clustered as regulators of fibroblast differentiation and extracellular matrix modeling, including the matrix cross-linking enzyme lysyl oxidase (LOX). Treatment with beta-aminopropionitrile, an irreversible inhibitor of LOX activity, dramatically reduced diffuse mineralization but had no effect on PTH-induced fibrosis. In contrast, the receptor tyrosine kinase inhibitor Gleevec and the phosphoinositide 3-kinase inhibitor wortmannin each reduced bone marrow fibrosis. In summary, the present studies support the hypotheses that PTH-induced bone marrow fibrosis is mediated by PDGF-A via a phosphoinositide 3-kinase-dependent signaling pathway and that increased LOX gene expression plays a key role in abnormal mineralization, a hallmark of chronic hyperparathyroidism.

Regulation of lysyl oxidase in vascular cells: lysyl oxidase as a new player in cardiovascular diseases

Lysyl oxidase (LOX) plays a crucial role in the maintenance of extracellular matrix stability and could participate in vascular remodelling associated with cardiovascular diseases. Evidence from in vitro and in vivo studies shows that LOX downregulation is associated with the endothelial dysfunction characteristic of earlier stages of the atherosclerotic process. Conversely, upregulation of this enzyme in vascular cells could induce neointimal thickening in atherosclerosis and restenosis. In fact, LOX is chemotactic for vascular smooth muscle cells and monocytes, is modulated by proliferative stimulus in these cells, and could control other cellular processes such as gene expression and cell transformation. Furthermore, it is conceivable that LOX downregulation could underlie plaque instability and contribute to the destructive remodelling that takes place during aneurysm development. Overall, LOX could play a key role in vascular homeostasis and, hence, it emerges as a new player in cardiovascular diseases. This review addresses the experimental evidence related to the role of LOX in vascular disorders and the potential benefits of controlling its expression and function.

Lysyl oxidase (LOX) down-regulation by TNFalpha: a new mechanism underlying TNFalpha-induced endothelial dysfunction

OBJECTIVE

TNFalpha is a pro-inflammatory cytokine that induces endothelial dysfunction and promotes atherosclerosis progression. Down-regulation of lysyl oxidase (LOX), a key enzyme in extracellular matrix maturation, by pro-atherogenic risk factors such as LDL and homocysteine, is associated with an impairment of endothelial barrier function. Our hypothesis is that the inflammatory cytokine TNFalpha could also modulate LOX expression/function in endothelial cells.

METHODS

The study was carried out in human umbilical vein endothelial cells (HUVEC), porcine aortic endothelial cells (PAEC) and bovine aortic endothelial cells (BAEC). LOX mRNA levels were analysed by real-time PCR and LOX activity was assessed by a high sensitive fluorescent assay. Promoter activity was determined by transient transfection using a luciferase reporter system.

RESULTS

TNFalpha decreases LOX mRNA levels in endothelial cells in a dose- and time-dependent manner. The effect of TNFalpha was observed at low concentrations (0.1-1 ng/mL) and was maximal at 2.5 ng/mL (after 21 h). In transfection assays, TNFalpha reduced LOX transcriptional activity to a similar extent than LOX mRNA. Furthermore, TNFalpha decreases endothelial LOX enzymatic activity. By using both TNF receptor (TNFR) agonist and blocking antibodies we determined the involvement of TNFR2 on LOX down-regulation. Moreover, while TNFR-associated factor-2 (TRAF-2) did not mediate signalling events leading to LOX inhibition, PKC inhibitors counteracted the TNFalpha-induced decrease of LOX mRNA levels. Finally, TNFalpha administration significantly reduced vascular LOX expression in rat aorta.

CONCLUSIONS

Endothelial dysfunction induced by TNFalpha is associated with a decrease of LOX expression/activity. Thus, LOX seems to be involved in the impairment of endothelial function triggered by different pathological conditions.

Effect of smoking on abdominal aortic aneurysms: novel insights through murine models

Abdominal aortic aneurysm is a poorly understood and fatal disease. The etiology of the disease is believed to be multifactorial. Of all the recognized clinical associations, none has a greater impact on the incidence and progression of the disease than exposure to tobacco smoke. Novel murine models developed over the past several years present the opportunity to investigate the mechanism of this critical clinical relationship.

Turning back the clock: regression of abdominal aortic aneurysms via pharmacotherapy

Abdominal aortic aneurysm (AAA) is a common disease that causes progressive expansion and rupture of the aorta with high mortality. There is a large and unmet need for nonsurgical treatment for AAA. Research has shown that an intricate network of inflammatory cells and interstitial cells contributes to the formation of AAA by producing pro-inflammatory mediators that activate enzymes to degrade the extracellular matrix (ECM) and impair ECM biosynthesis. Pharmacological agents such as statins and angiotensin-converting enzyme inhibitors may promote tissue stabilization in AAA by diminishing pro-inflammatory signaling and normalizing metabolism of the ECM. Our recent experiments in animal models demonstrate that inhibition of c-Jun N terminal kinase (JNK) inhibits multiple pathological processes and causes regression of established AAA. Thus, emerging evidence indicates that pharmacological intervention targeting pro-inflammatory signaling and abnormal ECM metabolism is a promising strategy for treatment of AAA.