Vascular endothelial growth factor enhances angiotensin II-induced aneurysm formation in apolipoprotein E-deficient mice

Aortic aneurysms: current pathogenesis and therapeutic targets

Aortic aneurysm is a chronic disease characterized by localized expansion of the aorta, including the ascending aorta, arch, descending aorta, and abdominal aorta. Although aortic aneurysms are generally asymptomatic, they can threaten human health by sudden death due to aortic rupture. Aortic aneurysms are estimated to lead to 150,000 ~ 200,000 deaths per year worldwide. Currently, there are no effective drugs to prevent the growth or rupture of aortic aneurysms; surgical repair or endovascular repair is the only option for treating this condition. The pathogenic mechanisms and therapeutic targets for aortic aneurysms have been examined over the past decade; however, there are unknown pathogenic mechanisms involved in cellular heterogeneity and plasticity, the complexity of the transforming growth factor-β signaling pathway, inflammation, cell death, intramural neovascularization, and intercellular communication. This review summarizes the latest research findings and current pathogenic mechanisms of aortic aneurysms, which may enhance our understanding of aortic aneurysms.

The protective effects of pirfenidone in preventing abdominal aortic aneurysm formation

Vascular endothelial growth factor (VEGF)-mediated angiogenesis participates in the initiation and progression of abdominal aortic aneurysm (AAA). Pirfenidone is a compound that has anti-inflammatory and antioxidant properties and suppresses angiogenesis. Pirfenidone targets the extracellular matrix (ECM) and has therapeutic effects on fibrotic diseases. Therefore, we speculated that pirfenidone might have meaningful therapeutic effects in AAA, and the current study was designed to investigate this capacity. An AAA model was constructed in mice using a long-term injection of angiotensin II (Ang II), followed by a 28-day administration of 200 mg/kg/day pirfenidone. Increased maximal external diameter of the abdominal artery, promoted levels of VEGF-A and its receptor VEGF-R2, upregulated matrix metallopeptidases (MMP)-2 and MMP-9, and elevated release of pro-inflammatory cytokines were observed in AAA mice, which were extremely repressed by 200 mg/kg pirfenidone. Human aortic endothelial cells (HAECs) were stimulated with Ang II for 1 day, in the presence or absence of pirfenidone (100 nM). Elevated expression of VEGF-A and VEGF-R2, facilitated proliferation, increased tube formation ability, and upregulated MMP-2 and MMP-9 were observed in Ang II-stimulated HAECs, all of which were significantly rescued by 100 nM pirfenidone. Finally, the elevated levels of myeloid differentiation primary response 88 and phosphorylated nuclear factor-kappa-B subunit p65 observed in Ang II-stimulated HAECs were repressed by pirfenidone. Collectively, pirfenidone alleviated AAA by inhibiting ECM degradation and ameliorating endothelial dysfunction.

Therapeutic Potential of Targeting Prokineticin Receptors in Diseases

The prokineticins (PKs) were discovered approximately 20 years ago as small peptides inducing gut contractility. Today, they are established as angiogenic, anorectic, and proinflammatory cytokines, chemokines, hormones, and neuropeptides involved in variety of physiologic and pathophysiological pathways. Their altered expression or mutations implicated in several diseases make them a potential biomarker. Their G-protein coupled receptors, PKR1 and PKR2, have divergent roles that can be therapeutic target for treatment of cardiovascular, metabolic, and neural diseases as well as pain and cancer. This article reviews and summarizes our current knowledge of PK family functions from development of heart and brain to regulation of homeostasis in health and diseases. Finally, the review summarizes the established roles of the endogenous peptides, synthetic peptides and the selective ligands of PKR1 and PKR2, and nonpeptide orthostatic and allosteric modulator of the receptors in preclinical disease models. The present review emphasizes the ambiguous aspects and gaps in our knowledge of functions of PKR ligands and elucidates future perspectives for PK research. SIGNIFICANCE STATEMENT: This review provides an in-depth view of the prokineticin family and PK receptors that can be active without their endogenous ligand and exhibits "constitutive" activity in diseases. Their non- peptide ligands display promising effects in several preclinical disease models. PKs can be the diagnostic biomarker of several diseases. A thorough understanding of the role of prokineticin family and their receptor types in health and diseases is critical to develop novel therapeutic strategies with safety concerns.

Administration of anti-inflammatory M2 macrophages suppresses progression of angiotensin II-induced aortic aneurysm in mice

Aortic aneurysm (AA) is a vascular disorder characterized pathologically by inflammatory cell invasion and extracellular matrix (ECM) degradation. It is known that regulation of the balance between pro-inflammatory M1 macrophages (M1Ms) and anti-inflammatory M2 macrophages (M2Ms) plays a pivotal role in AA stabilization. We investigated the effects of M2M administration in an apolipoprotein E-deficient (apoE^-/-) mouse model in which AA was induced by angiotensin II (ATII) infusion. Mice received intraperitoneal administration of 1 million M2Ms 4 weeks after ATII infusion. Compared with a control group that was administered saline, the M2M group exhibited reduced AA expansion; decreased expression levels of interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α), and monocyte chemoattractant protein-1 (MCP-1); and a lower M1M/M2M ratio. Moreover, the M2M group exhibited upregulation of anti-inflammatory factors, including IL-4 and IL-10. PKH26-labeled M2Ms accounted for 6.5% of cells in the aneurysmal site and co-expressed CD206. Taken together, intraperitoneal administration of M2Ms inhibited AA expansion by reducing the inflammatory reaction via regulating the M1M/M2M ratio. This study shows that M2M administration might be useful for the treatment of AA.

miR-424/322 protects against abdominal aortic aneurysm formation by modulating the Smad2/3/runt-related transcription factor 2 axis

Rupture of abdominal aortic aneurysms (AAAs) is one of the leading causes of sudden death in the elderly population. The osteogenic transcription factor runt-related gene (RUNX) encodes multifunctional mediators of intracellular signal transduction pathways in vascular remodeling and inflammation. We aimed to evaluate the roles of RUNX2 and its putative downstream target miR-424/322 in the modulation of several AAA progression-related key molecules, such as matrix metalloproteinases and vascular endothelial growth factor. In the GEO database, we found that male patients with AAAs had higher RUNX2 expression than did control patients. Several risk factors for aneurysm induced the overexpression of MMPs through RUNX2 transactivation, and this was dependent on Smad2/3 upregulation in human aortic smooth muscle cells. miR-424 was overexpressed through RUNX2 after angiotensin II (AngII) challenge. The administration of siRUNX2 and miR-424 mimics attenuated the activation of the Smad/RUNX2 axis and the overexpression of several AAA progression-related molecules in vitro. Compared to their littermates, miR-322 KO mice were susceptible to AngII-induced AAA, whereas the silencing of RUNX2 and the administration of exogenous miR-322 mimics ameliorated the AngII-induced AAA in ApoE KO mice. Overall, we established the roles of the Smad/RUNX2/miR-424/322 axis in AAA pathogenesis. We demonstrated the therapeutic potentials of miR-424/322 mimics and RUNX2 inhibitor for AAA progression.

Treatment with the Prolyl Hydroxylase Inhibitor JNJ Promotes Abdominal Aortic Aneurysm Progression in Diabetic Mice

OBJECTIVE

Prolyl hydroxylase domain containing proteins (PHD) rigorously regulate intracellular hypoxia inducible factor-1 (HIF-1) protein expression and activity. Diabetes impairs PHD activity and attenuates abdominal aortic aneurysm (AAA) progression. The extent to which dysregulated PHD activity contributes to diabetes mediated AAA suppression remains undetermined.

METHODS

AAAs were induced in diabetic and non-diabetic male C57BL/6J mice via intra-aortic elastase infusion. A PHD inhibitor (JNJ-42041935, aka "JNJ", 150 mmol/kg) or vehicle alone was administered daily starting one day prior to AAA induction for 14 days. Influences on AAA progression was assessed via ultrasonography and histopathology. Expression of aortic HIF-1α, three of its target genes and macrophage derived mediators were assayed via quantitative reverse transcription polymerase chain reaction. Aneurysmal sections from AAA patients with and without diabetes (two patients in each group) were immunostained for HIF-1α and vascular endothelial growth factor (VEGF)-A.

RESULTS

Expression of HIF-1α target genes (erythropoietin, VEGF-A, and glucose transporter-1) was reduced by 45% - 95% in experimental diabetic aortas. Diameter enlargement was similarly limited, as were mural elastin degradation, leukocyte infiltration, and neo-angiogenesis (reduced capillary density and length) on histopathology. Pre-treatment with JNJ prior to AAA initiation augmented aortic HIF-1α target gene expression and aneurysm progression in diabetic mice, along with macrophage VEGF-A and matrix metalloproteinase 2 mRNA expression. No differences were noted in HIF-1α or VEGF-A expression on aortic immunohistochemical staining of human aortic tissue as a function of diabetes status.

CONCLUSION

Small molecule PHD inhibitor treatment reduces or offsets impairment of experimental AAA progression in hyperglycemic mice, highlighting the potential contribution of dysregulated PHD activity to diabetes mediated aneurysm suppression.

Importance of NLRP3 Inflammasome in Abdominal Aortic Aneurysms

Abdominal aortic aneurysm (AAA) is a chronic inflammatory degenerative aortic disease, which particularly affects older people. Nucleotide-binding oligomerization domain-like receptor family protein 3 (NLRP3) inflammasome is a multi-protein complex and mediates inflammatory responses by activating caspase 1 for processing premature interleukin (IL)-1β and IL-18. In this review, we first summarize the principle of NLRP3 inflammasome activation and the functionally distinct classes of small molecule NLRP3 inflammasome inhibitors. Next, we provide a comprehensive literature review on the expression of NLRP3 inflammasome effector mediators (IL-1β and IL-18) and components (caspase 1, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and NLRP3) in clinical and experimental AAAs. Finally, we discuss the influence of genetic deficiency or pharmacological inhibition of individual effector mediators and components of NLRP3 inflammasome on experimental AAAs. Accumulating clinical and experimental evidence suggests that NLRP3 inflammasome may be a promise therapeutic target for developing pharmacological strategies for clinical AAA management.

Aortic Aneurysm Natural Progression is Not Influenced by Concomitant Malignancy and Chemotherapy

BACKGROUND

Aortic aneurysms occur concomitantly with malignancy in approximately 1.0-17.0% of patients. There is little published information regarding the effects of subsequent oncological therapies on aortic aneurysm growth. The aim of this study was to determine the effects of chemoradiation therapies on the natural progression of small abdominal aortic aneurysm (AAA), thoracic aortic aneurysm, and thoracoabdominal aortic aneurysm.

METHODS

Patients with aortic aneurysms with and without malignancy between 2005 and 2017 were identified within institutional databases using Current Procedural Terminology and International Classification of Disease codes. Inclusion criteria included complete chemotherapy documentation, a minimum of 3 multiplanar axial/coronal imaging or ultrasonography before, during, and after receiving therapy or 2 studies for patients without malignancy. Propensity matching, Cox and linear regression, and Kaplan-Meier survival analyses were performed.

RESULTS

A total of 159 (172 aneurysms) patients with malignancy and 127 (149 aneurysms) patients without malignancy were included. Average patient demographics were 74.4 ± 9.8-years-old, Caucasian (66.8%), male (70.3%), with hypertension (71.1%), current smoking (24.5%), coronary atherosclerotic disease (26.2%), and AAA (71.0%). The most common malignancy was lung cancer (48.4%) with most chemotherapy regimens including a platinum-based alkylating agent and concurrent antimetabolite (56.0%). The overall median follow-up time was 28.2 (range 3.1-174.4) months. Aortic aneurysms in patients without malignancy grew to larger sizes (4.43 ± 0.96 vs. 4.14 ± 1.00, P = 0.008) with similar median growth rates (0.12 vs. 0.12 cm/year, P = 0.090), had more atypical morphologic features (14.1% vs. 0.6%, P < 0.001), more frequently underwent repair (22.1% vs. 8.7%, P = 0.001), and more frequently required emergency repair for rupture (5.4% vs. 0.0%, P = 0.087). Cox regression identified initial aortic size ≥4.0 cm (hazard ratio [HR] 3.028), AAA (HR 2.146), chronic aortic findings (3.589), and the use of topoisomerase inhibitors (HR 2.694). Linear regression demonstrated increased growth rates predicted by antimetabolite chemotherapy (β 0.170), initial aortic size (β 0.086), and abdominal aortic location (β 0.139, all P < 0.002).

CONCLUSIONS

Small aortic aneurysms with concomitant malignancies are discovered at smaller initial sizes, grow at similar rates, require fewer interventions, and have fewer ruptures and acute dissections than patients without malignancy. Antimetabolite therapies modestly accelerate aneurysmal growth, and patients receiving topoisomerase inhibitors may require earlier repair. Patients with concomitant disease can be confidently treated according to standard institutional aneurysm surveillance protocols. Overall, we recommend treatment of the malignancy before small aortic aneurysm repair as these aneurysms behave similarly to those in patients without malignancy.

Quercetin Downregulates Cyclooxygenase-2 Expression and HIF-1α/VEGF Signaling-Related Angiogenesis in a Mouse Model of Abdominal Aortic Aneurysm

Objective

Abdominal aortic aneurysm (AAA) development has been characterized by increased expression of vascular endothelial growth factor (VEGF), which contributes to angiogenesis via cyclooxygenase-2 (COX-2). Quercetin, one of the most common and well-researched flavonoids and abundant in vegetables and fruits, has beneficial effects in inhibiting angiogenesis. This study investigated the antiangiogenic effects of quercetin on experimental aneurysms.

Methods

We utilized the in vivo AAA mouse model induced by the periaortic application of CaCl₂ to examine the effectiveness of quercetin in blocking angiogenesis. Quercetin was administered at 60 mg/kg once daily on the day of the AAA induction and then continued for 6 weeks. Celecoxib, a selective COX-2 inhibitor, was used as the positive control.

Results

Our results demonstrated that quercetin significantly attenuated aneurysm growth in AAA mice and medial neovascularization. Accordingly, quercetin decreased the expression of proangiogenic mediators, including VEGF-A, intercellular adhesion molecule-1, vascular cell adhesion molecule 1, and vascular endothelial cadherin. Quercetin treatment also inhibited the expression of COX-2 and hypoxia-inducible factor 1α (HIF-1α). It was also found that quercetin-3-glucuronide, a major quercetin metabolite, downregulated the expression of COX-2, HIF-1α, VEGF-A, and matrix metalloproteinase activities in aortic vascular smooth muscle cells isolated from AAA mice.

Conclusion

Quercetin attenuates neovascularization during AAA growth, and this effect is mediated via the inhibition of COX-2, which decreases HIF-1α/VEGF signaling-related angiogenesis.

The protein Deleted in Breast Cancer-1 (DBC1) regulates vascular response and formation of aortic dissection during Angiotensin II infusion

Cardiovascular diseases are among the main causes of morbimortality in the adult population. Among them, hypertension is a leading cause for stroke, heart disease and kidney failure. Also, as a result of arterial wall weakness, hypertension can lead to the development of dissecting aortic aneurysms, a rare but often fatal condition if not readily treated. In this work, we investigated the role of DBC1 in the regulation of vascular function in an ANGII-induced hypertension mouse model. We found that WT and DBC1 KO mice developed hypertension in response to ANGII infusion. However, DBC1 KO mice showed increased susceptibility to develop aortic dissections. The effect was accompanied by upregulation of vascular remodeling factors, including MMP9 and also VEGF. Consistent with this, we found decreased collagen deposition and elastic fiber fragmentation, suggesting that increased expression of MMPs in DBC1 KO mice weakens the arterial wall, promoting the formation of aortic dissections during treatment with ANGII. Finally, DBC1 KO mice had reduced cell proliferation in the intima-media layer in response to ANGII, paralleled with an impairment to increase wall thickness in response to hypertension. Furthermore, VSMC purified from DBC1 KO mice showed impaired capacity to leave quiescence, confirming the in vivo results. Altogether, our results show for the first time that DBC1 regulates vascular response and function during hypertension and protects against vascular injury. This work also brings novel insights into the molecular mechanisms of the development of aortic dissections.

Genome-Wide Expression Profiling Unveils Autoimmune Response Signatures in the Perivascular Adipose Tissue of Abdominal Aortic Aneurysm

Objective- Perivascular adipose tissue (PVAT) is thought to play a role in vascular homeostasis and in the pathogenesis of large vessel diseases, including abdominal aortic aneurysm (AAA). Herein, we tested the hypothesis that locally restricted transcriptional profiles characterize PVAT surrounding AAA, indicating specific dysfunctions associated with the disease. Approach and Results- Using a paired sample design to limit the effects of interindividual variation, we performed a microarray-based investigation of the PVAT transcriptome in 30 patients with AAA, comparing the adipose layer of the dilated abdominal aorta with that of the not-dilated aortic neck in each patient. Furthermore, we used a state-of-the-art data mining procedure to remove the effect of confounders produced by high-throughput gene expression techniques. We found substantial differences in PVAT gene expression clearly distinguishing the dilated from the not-dilated aorta, which increased in number and magnitude with increasing AAA diameter. Comparisons with other adipose depots (omental or subcutaneous fat) confirmed that gene expression changes are locally restricted. We dissected putative mechanisms associated with AAA PVAT dysfunction through a functional enrichment network analysis: both innate and adaptive immune-response genes along with genes related to cell-death pathways, metabolic processes of collagen, sphingolipids, aminoglycans, and extracellular matrix degradation were strongly overrepresented in PVAT of AAA compared with PVAT of the not-dilated aorta. Conclusions- Our results support a possible function of PVAT in AAA pathogenesis and suggest that AAA is an immunologic disease with an underlying autoimmune component. Interfering with these disease-specific pathways would clarify their precise role in AAA pathogenesis.

Inhibition of VEGF (Vascular Endothelial Growth Factor)-A or its Receptor Activity Suppresses Experimental Aneurysm Progression in the Aortic Elastase Infusion Model

OBJECTIVE

We examined the pathogenic significance of VEGF (vascular endothelial growth factor)-A in experimental abdominal aortic aneurysms (AAAs) and the translational value of pharmacological VEGF-A or its receptor inhibition in aneurysm suppression. Approaches and Results: AAAs were created in male C57BL/6J mice via intra-aortic elastase infusion. Soluble VEGFR (VEGF receptor)-2 extracellular ligand-binding domain (delivered in Ad [adenovirus]-VEGFR-2), anti-VEGF-A mAb (monoclonal antibody), and sunitinib were used to sequester VEGF-A, neutralize VEGF-A, and inhibit receptor tyrosine kinase activity, respectively. Influences on AAAs were assessed using ultrasonography and histopathology. In vitro transwell migration and quantitative reverse transcription polymerase chain reaction assays were used to assess myeloid cell chemotaxis and mRNA expression, respectively. Abundant VEGF-A mRNA and VEGF-A-positive cells were present in aneurysmal aortae. Sequestration of VEGF-A by Ad-VEGFR-2 prevented AAA formation, with attenuation of medial elastolysis and smooth muscle depletion, mural angiogenesis and monocyte/macrophage infiltration. Treatment with anti-VEGF-A mAb prevented AAA formation without affecting further progression of established AAAs. Sunitinib therapy substantially mitigated both AAA formation and further progression of established AAAs, attenuated aneurysmal aortic MMP2 (matrix metalloproteinase) and MMP9 protein expression, inhibited inflammatory monocyte and neutrophil chemotaxis to VEGF-A, and reduced MMP2, MMP9, and VEGF-A mRNA expression in macrophages and smooth muscle cells in vitro. Additionally, sunitinib treatment reduced circulating monocytes in aneurysmal mice.

CONCLUSIONS

VEGF-A and its receptors contribute to experimental AAA formation by suppressing mural angiogenesis, MMP and VEGF-A production, myeloid cell chemotaxis, and circulating monocytes. Pharmacological inhibition of receptor tyrosine kinases by sunitinib or related compounds may provide novel opportunities for clinical aneurysm suppression.

Acute blood pressure elevation associated with biological therapies for cancer: a focus on VEGF signaling pathway inhibitors

INTRODUCTION

Treatment with biological agents interfering with mechanisms of angiogenesis, such as vascular endothelial growth factor (VEGF) signaling pathway (VSP) inhibitors, was associated with an enhanced risk of acute and severe blood pressure (BP) increase and development of hypertensive emergencies. Areas covered: The present article will review the scientific literature reporting hypertensive emergencies as a complication of biological treatment with VSP inhibitors. Hypertensive emergency is a life-threatening condition characterized by very high BP values (>180/110 mmHg) associated with acute organ damage. The exact mechanism of action is still incompletely clarified. Endothelial dysfunction following reduced bioavailability of nitric oxide has been hypothesized to play an important role in promoting hypertension and the occurrence of acute organ damage. Expert opinion: Prevention, prompt recognition and treatment of hypertensive emergencies associated with treatment with VSP-inhibitors are essential to reduce the risk of adverse events. Not infrequently, the occurrence of hypertensive emergency led to VSP treatment discontinuation, with potential negative consequences on patient overall survival. The present review aims at providing detailed knowledge for the clinician regarding this specific issue, which could be of high impact in usual clinical practice, given the increasing burden of indications to treatment with biological agents targeted to the VEGF pathway.

Cerebral Aneurysms Differ in Patients with Hysterectomies

OBJECTIVE

Female sex is a well-known risk factor for aneurysm formation. Although the role of the ovaries and estrogen in aneurysm development has been supported, other organ-hormone pairs unique between sexes also may be implicated. In this study, we aimed to determine whether intracranial aneurysms microsurgically clipped in patients with previous hysterectomies exhibit any unique aneurysm characteristics from those without hysterectomies.

METHODS

Solitary aneurysms microsurgically treated by the senior author (M.T.L.) were included from a database of patients treated between January 2010 and April 2013 at a tertiary academic medical center. Only female patients and patients equal or older in age to the youngest patient in the hysterectomy group were included in the control group. Patient and aneurysm characteristics were compared using the χ² test for categorical variables and the independent t test analysis for continuous variables.

RESULTS

A total 233 patients were included in the study. Forty-three patients (19%) had undergone a previous hysterectomy; none had oophorectomies recorded. No difference in mean age (P = 0.89), hypertension (P = 0.38), alcohol use (P = 0.87), tobacco use (P = 0.22), or aneurysm location (P = 1) existed. However, patients in the hysterectomy group more often presented in a good neurologic condition before surgery (88% vs. 74%, P = 0.04) and had fewer large aneurysms (8% vs. 24%, P = 0.03). Also, fewer presented with a ruptured aneurysm (28%) then the nonhysterectomy group (51%) (P = 0.004).

CONCLUSIONS

Female patients with a surgical history of a hysterectomy have a lower rate of large aneurysms, present in better neurologic condition, and are less likely to present with a ruptured aneurysm than females without a hysterectomy.

Inhibition or deletion of angiotensin II type 1 receptor suppresses elastase-induced experimental abdominal aortic aneurysms

OBJECTIVE

Angiotensin (Ang) II type 1 receptor (AT1) activation is essential for the development of exogenous Ang II-induced abdominal aortic aneurysms (AAAs) in hyperlipidemic animals. Experimental data derived from this modeling system, however, provide limited insight into the role of endogenous Ang II in aneurysm pathogenesis. Consequently, the potential translational value of AT1 inhibition in clinical AAA disease management remains incompletely understood on the basis of the existing literature.

METHODS

AAAs were created in wild-type (WT) and AT1a knockout (KO) mice by intra-aortic infusion of porcine pancreatic elastase (PPE). WT mice were treated with the AT1 receptor antagonist telmisartan, 10 mg/kg/d in chow, or the peroxisome proliferator-activated receptor γ (PPARγ) antagonist GW9662, 3 mg/kg/d through oral gavage, beginning 1 week before or 3 days after PPE infusion. Influences on aneurysm progression as well as mechanistic insights into AT1-mediated pathogenic processes were determined using noninvasive ultrasound imaging, histopathology, aortic gene expression profiling, and flow cytometric analysis.

RESULTS

After PPE infusion, aortic enlargement was almost completely abrogated in AT1a KO mice compared with WT mice. As defined by a ≥50% increase in aortic diameter, no PPE-infused, AT1a KO mouse actually developed an AAA. On histologic evaluation, medial smooth muscle cellularity and elastic lamellae were preserved in AT1a KO mice compared with WT mice, with marked attenuation of mural angiogenesis and leukocyte infiltration. In WT mice, telmisartan administration effectively suppressed aneurysm pathogenesis after PPE infusion as well, regardless of whether treatment was initiated before or after aneurysm creation or continued for a limited or extended time. Telmisartan treatment was associated with reduced messenger RNA levels for CCL5 and matrix metalloproteinases 2 and 9 in aneurysmal aortae, with no apparent effect on PPARγ-regulated gene expression. Administration of the PPARγ antagonist GW9662 failed to "rescue" the aneurysm phenotype in telmisartan-treated, PPE-infused WT mice. Neither effector T-cell differentiation nor regulatory T-cell cellularity was affected by telmisartan treatment status.

CONCLUSIONS

Telmisartan effectively suppresses the progression of elastase-induced AAAs without apparent effect on PPARγ activation or T-cell differentiation. These findings reinforce the critical importance of endogenous AT1 activation in experimental AAA pathogenesis and reinforce the translational potential of AT1 inhibition in medical aneurysm disease management.

Angiopoietin-2 attenuates angiotensin II-induced aortic aneurysm and atherosclerosis in apolipoprotein E-deficient mice

Angiogenesis and inflammation are implicated in aortic aneurysm and atherosclerosis and regulated by angiopoietin-2 (Angpt2). The effect of Angpt2 administration on experimental aortic aneurysm and atherosclerosis was examined. Six-month-old male apolipoprotein E deficient (ApoE^-/-) mice were infused with angiotensin II (AngII) and administered subcutaneous human Fc-protein (control) or recombinant Angpt2 (rAngpt2) over 14 days. Administration of rAngpt2 significantly inhibited AngII-induced aortic dilatation and rupture of the suprarenal aorta (SRA), and development of atherosclerosis within the aortic arch. These effects were blood pressure and plasma lipoprotein independent and associated with Tie2 activation and down-regulation of monocyte chemotactic protein-1 (MCP-1) within the SRA. Plasma concentrations of MCP-1 and interleukin-6 were significantly lower in mice receiving rAngpt2. Immunostaining for the monocyte/macrophage marker MOMA-2 and the angiogenesis marker CD31 within the SRA were less in mice receiving rAngpt2 than controls. The percentage of inflammatory (Ly6C^hi) monocytes within the bone marrow was increased while that in peripheral blood was decreased by rAngpt2 administration. In conclusion, administration of rAngpt2 attenuated angiotensin II-induced aortic aneurysm and atherosclerosis in ApoE^-/- mice associated with reduced aortic inflammation and angiogenesis. Up-regulation of Angpt2 may have potential therapeutic value in patients with aortic aneurysm and atherosclerosis.

Inhibition of hypoxia inducible factor-1α attenuates abdominal aortic aneurysm progression through the down-regulation of matrix metalloproteinases

Hypoxia inducible factor-1α (HIF-1α) pathway is associated with many vascular diseases, including atherosclerosis, arterial aneurysms, pulmonary hypertension and chronic venous diseases. Significant HIF-1α expression could be found at the rupture edge at human abdominal aortic aneurysm (AAA) tissues. While our initial in vitro experiments had shown that deferoxamine (DFO) could attenuate angiotensin II (AngII) induced endothelial activations; we unexpectedly found that DFO augmented the severity of AngII-induced AAA, at least partly through increased accumulation of HIF-1α. The findings promoted us to test whether aneurysmal prone factors could up-regulate the expression of MMP-2 and MMP-9 through aberrantly increased HIF-1α and promote AAA development. AngII induced AAA in hyperlipidemic mice model was used. DFO, as a prolyl hydroxylase inhibitor, stabilized HIF-1α and augmented MMPs activities. Aneurysmal-prone factors induced HIF-1α can cause overexpression of MMP-2 and MMP-9 and promote aneurysmal progression. Pharmacological HIF-1α inhibitors, digoxin and 2-ME could ameliorate AngII induced AAA in vivo. HIF-1α is pivotal for the development of AAA. Our study provides a rationale for using HIF-1α inhibitors as an adjunctive medical therapy in addition to current cardiovascular risk-reducing regimens.

Unbiased Profile of MicroRNA Expression in Ascending Aortic Aneurysm Tissue Appoints Molecular Pathways Contributing to the Pathology

BACKGROUND

Complex etiopathogenesis of ascending aortic aneurysm suggests contribution of epigenetic mechanisms in its development. Several studies appointed microRNAs (miRs) as essential epigenetic factors in various human diseases; however, little is known about their role in ascending aortic aneurysm. Therefore, the aim of this study was to perform unbiased molecular screening of miRs expression in aneurysmal tissue and establish their functions on a transcriptional level.

METHODS

Samples of ascending aortic tissue were obtained from 15 patients, and total RNA was isolated separately from aneurysmal and unaffected aortic tissue obtained from the same patient. Expression of the complete panel of human miRs was assessed by quantitative real-time polymerase chain reaction. Using bioinformatic tools, 13 genes were selected that were putatively regulated by overexpressed miRs. Expression level of transcripts were evaluated by quantitative real-time polymerase chain reaction and correlated with their targeting miRs.

RESULTS

Overexpression of 10 miRs distinguished aneurysmal tissue from the unchanged one. These miRs were involved in cell senescence (miR-191-5p), maintenance of vascular integrity (miR-126-3p and miR-374-5p), nitric oxide-dependent vascular relaxation (miR-21-5p), smooth muscle differentiation, and contractility (miR-145- 3p, miR-29c-3p, miR-133a-3p, miR-186-5p, miR-143-3p, and miR-24-3p), and correlated with abundance of its miR targets.

CONCLUSIONS

Altered expression of particular miRs selectively in the affected tissue indicate their role as factors that trigger pathways of aneurysmal transformation. Limited reparative properties due to overexpression of miR-191 may play a crucial role for aneurysm enlargement, whereas nitric oxide-dependent relaxation of vascular smooth muscle mediated by miR-21 offers an attractive explanation of the aneurysm's initiation, and is confirmed in experimental conditions.

Chemokine (C-X-C motif) receptor 4 blockade by AMD3100 inhibits experimental abdominal aortic aneurysm expansion through anti-inflammatory effects

OBJECTIVE

Inflammation plays a critical role in the development of abdominal aortic aneurysms (AAAs). Because stromal cell-derived factor 1 (SDF-1) is known for its ability to attract inflammatory cells, we investigated whether SDF-1/chemokine (C-X-C motif) receptor 4 (CXCR4) axis is expressed in aneurysmal aortic wall and plays a role in AAA physiopathology and asked whether its blockade modulates AAA formation and expansion.

APPROACH AND RESULTS

Quantitative real-time polymerase chain reaction analysis showed that SDF-1α and CXCR4 mRNA levels are increased in both human and CaCl2-induced mouse AAA wall and are positively correlated to the aortic diameter in mice. ELISA quantification and immunostaining demonstrated that, in mice, aortic SDF-1α is rapidly induced during AAA formation, first by apoptotic vascular smooth muscle cells in the injured media and then by adventitial macrophages once AAA is fully established. Using green fluorescent protein-positive (GFP(+/-)) bone marrow transplantation experiments, we demonstrated that aortic SDF-1 overexpression is implicated in the recruitment of bone marrow-derived macrophages within the AAA wall. Furthermore, in mice, blockade of CXCR4 by AMD3100 decreases the infiltration of adventitial macrophages, inhibits AAA formation, and prevents aortic wall destruction. AMD3100 reduces the mRNA levels of MMP-12 and MMP-14 as well as that of inflammatory effectors MCP-1, MIP-1β, MIP-2α, RANTES, IL-1β, IL-6, TNF-α, and E-selectin. Finally, AMD3100 stabilizes the diameter of formed, expanding AAAs in 2 experimental models.

CONCLUSIONS

SDF-1/CXCR4 axis is upregulated in human and mouse AAAs. Blockade of CXCR4 with AMD3100 suppresses AAA formation and progression in two rodent models. Blockade of SDF-1/CXCR4 axis may represent a new strategy to limit progression of small human AAAs.

Rapamycin limits the growth of established experimental abdominal aortic aneurysms

OBJECTIVES

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease affecting 4-8% of men older than 60 years. No pharmacologic strategies limit disease progression, aneurysm rupture, or aneurysm-related death. We examined the ability of rapamycin to limit the progression of established experimental AAAs.

METHODS

AAAs were created in 10-12-week-old male C57BL/6J mice via the porcine pancreatic elastase (PPE) infusion method. Beginning 4 days after PPE infusion, mice were treated with rapamycin (5 mg/kg/day) or an equal volume of vehicle for 10 days. AAA progression was monitored by serial ultrasound examination. Aortae were harvested for histological analyses at sacrifice.

RESULTS

Three days after PPE infusion, prior to vehicle or rapamycin treatment, aneurysms were enlarging at an equal rate between groups. In the rapamycin group, treatment reduced aortic enlargement by 38%, and 53% at 3 and 10 days, respectively. On histological analysis, medial elastin and smooth muscle cell populations were relatively preserved in the rapamycin group. Rapamycin treatment also reduced mural macrophage density and neoangiogenesis.

CONCLUSION

Rapamycin limits the progression of established experimental aneurysms, increasing the translational potential of mechanistic target of rapamycin-related AAA inhibition strategies.

Potential role for anti-angiogenic therapy in abdominal aortic aneurysms

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a condition that mainly affects elderly men. At present, there is no effective medical therapy that can retard aneurysm growth or prevent aneurysm rupture. There is evidence that angiogenesis within the wall of an aortic aneurysm may play key roles in aneurysm progression as well as rupture. The use of anti-angiogenic therapy as potential medical therapy in AAA is a promising strategy but has never been studied in detail.

DESIGN

This paper discusses the basic mechanisms of angiogenesis, the role played by angiogenesis in aortic aneurysms and the potential therapeutic role of anti-angiogenic drugs against aneurysm expansion or rupture.

RESULTS

Angiogenesis is a multi-step process which is fundamental for growth and differentiation of various tissues within a multi-cellular organism. Hypoxia and inflammation are key stimuli for activation of neoangiogenesis. Investigations in both human tissues and animal models of AAA have shown that angiogenesis is a pathological hallmark of AAA and appears to play a role in the development and progression of the condition. Pre-clinical studies have shown that anti-angiogenic drugs can potentially be effective in reducing the intensity of aneurysm formation, suggesting that such drugs may potentially be useful as novel drug therapy for AAA in humans.

CONCLUSION

Current evidence suggests that angiogenesis contributes to the destructive processes within aneurysmal aortic wall. As novel drug therapy for aortic aneurysms (for use in humans) is still eluding researchers, anti-angiogenic pathway appears to be an attractive approach.

Reestablishment of the Endothelial Lining by Endothelial Cell Therapy Stabilizes Experimental Abdominal Aortic Aneurysms

Background—

Loss of the endothelium and its replacement by a thick thrombus are structural features of human abdominal aortic aneurysms (AAAs). In AAAs, the relationship between aortic diameter expansion, the presence of thrombus, and the lack of endothelial cells (ECs) remains unexplored. We hypothesized that reendothelialization by cell therapy would modulate aortic wall destruction and ultimately stabilize AAAs. We evaluated the impact of local seeding of rat aortic ECs or peripheral blood–derived outgrowth ECs on AAA evolution.

Methods and Results—

Rat aortic ECs (n=30) or serum-free medium (controls; n=29) were seeded endovascularly immediately (day 0) or 14 days after surgery in the rat xenograft model. Rat aortic EC seeding prevented AAA formation and stabilized formed AAAs at 28 days (diameter increase at day 0+28, 51±6% versus 83±6%; day 14+28, −1±4% versus 22±6% in rat aortic ECs and controls, respectively; P <0.01). This stabilizing effect was associated with the reestablishment of the endothelial lining, the suspension of proteolysis, and the reconstitution of new aortic wall rich in smooth muscle cells and extracellular matrix. Transplanted rat aortic ECs did not participate directly in aortic wall repair but exerted their healing properties through paracrine mechanisms involving the upregulation of endothelium-derived stabilizing factors and the recruitment of resident vascular cells. In rats, the transplantation of outgrowth ECs (n=7) significantly reduced by 30% the progression of AAAs and restored the abluminal endothelium at 28 days compared with controls (n=9).

Conclusion—

Our study demonstrates the potential of restoring the endothelial lining to control AAA dynamics and designates ECs as an efficient therapy to stop AAA expansion.

Molecular imaging of experimental abdominal aortic aneurysms

Current laboratory research in the field of abdominal aortic aneurysm (AAA) disease often utilizes small animal experimental models induced by genetic manipulation or chemical application. This has led to the use and development of multiple high-resolution molecular imaging modalities capable of tracking disease progression, quantifying the role of inflammation, and evaluating the effects of potential therapeutics. In vivo imaging reduces the number of research animals used, provides molecular and cellular information, and allows for longitudinal studies, a necessity when tracking vessel expansion in a single animal. This review outlines developments of both established and emerging molecular imaging techniques used to study AAA disease. Beyond the typical modalities used for anatomical imaging, which include ultrasound (US) and computed tomography (CT), previous molecular imaging efforts have used magnetic resonance (MR), near-infrared fluorescence (NIRF), bioluminescence, single-photon emission computed tomography (SPECT), and positron emission tomography (PET). Mouse and rat AAA models will hopefully provide insight into potential disease mechanisms, and the development of advanced molecular imaging techniques, if clinically useful, may have translational potential. These efforts could help improve the management of aneurysms and better evaluate the therapeutic potential of new treatments for human AAA disease.

Peptide inhibitor of CXCL4-CCL5 heterodimer formation, MKEY, inhibits experimental aortic aneurysm initiation and progression

OBJECTIVE

Macrophages are critical contributors to abdominal aortic aneurysm (AAA) disease. We examined the ability of MKEY, a peptide inhibitor of CXCL4-CCL5 interaction, to influence AAA progression in murine models.

APPROACH AND RESULTS

AAAs were created in 10-week-old male C57BL/6J mice by transient infrarenal aortic porcine pancreatic elastase infusion. Mice were treated with MKEY via intravenous injection either (1) before porcine pancreatic elastase infusion or (2) after aneurysm initiation. Immunostaining demonstrated CCL5 and CCR5 expression on aneurysmal aortae and mural monocytes/macrophages, respectively. MKEY treatment partially inhibited migration of adaptively transferred leukocytes into aneurysmal aortae in recipient mice. Although all vehicle-pretreated mice developed AAAs, aneurysms formed in only 60% (3/5) and 14% (1/7) of mice pretreated with MKEY at 10 and 20 mg/kg, respectively. MKEY pretreatment reduced aortic diameter enlargement, preserved medial elastin fibers and smooth muscle cells, and attenuated mural macrophage infiltration, angiogenesis, and aortic metalloproteinase 2 and 9 expression after porcine pancreatic elastase infusion. MKEY initiated after porcine pancreatic elastase infusion also stabilized or reduced enlargement of existing AAAs. Finally, MKEY treatment was effective in limiting AAA formation after angiotensin II infusion in apolipoprotein E-deficient mice.

CONCLUSIONS

MKEY suppresses AAA formation and progression in 2 complementary experimental models. Peptide inhibition of CXCL4-CCL5 interactions may represent a viable translational strategy to limit progression of human AAA disease.

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.

Involvement of the renin-angiotensin system in abdominal and thoracic aortic aneurysms

Aortic aneurysms are relatively common maladies that may lead to the devastating consequence of aortic rupture. AAAs (abdominal aortic aneurysms) and TAAs (thoracic aortic aneurysms) are two common forms of aneurysmal diseases in humans that appear to have distinct pathologies and mechanisms. Despite this divergence, there are numerous and consistent demonstrations that overactivation of the RAS (renin-angiotensin system) promotes both AAAs and TAAs in animal models. For example, in mice, both AAAs and TAAs are formed during infusion of AngII (angiotensin II), the major bioactive peptide in the RAS. There are many proposed mechanisms by which the RAS initiates and perpetuates aortic aneurysms, including effects of AngII on a diverse array of cell types and mediators. These experimental findings are complemented in humans by genetic association studies and retrospective analyses of clinical data that generally support a role of the RAS in both AAAs and TAAs. Given the lack of a validated pharmacological therapy for any form of aortic aneurysm, there is a pressing need to determine whether the consistent findings on the role of the RAS in animal models are translatable to humans afflicted with these diseases. The present review compiles the recent literature that has shown the RAS as a critical component in the pathogenesis of aortic aneurysms.

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

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

Resveratrol counteracts systemic and local inflammation involved in early abdominal aortic aneurysm development

BACKGROUND

Monocyte activation, macrophage infiltration, vascular oxidative stress and matrix proteolysis are inflammatory key steps contributing to abdominal aortic aneurysm (AAA) development. A phenotypical and functional heterogeneity is recognizable in monocytes by the differential expression of surface molecules: CD62L- subset corresponds to activated monocytes, while CD143/ACE surface expression increases during their differentiation into macrophages. In this work, Resveratrol, which is an antioxidant polyphenol with vasoprotective properties, has been evaluated for its potential to limit aneurysm development and monocyte-dependent inflammatory response in a model of elastase-induced AAA.

METHODS

Male Sprague-Dawley rats received Resveratrol (10 mg/kg/die) (Rsv group, n=15) or vehicle (ethanol) alone (Et-OH group, n=15) continuously from 7 d before until 14 d after the AAA induction with elastase; five littermates were used as untreated control group (Ctr group, n=5). At the end of treatment, CD143 and CD62L monocyte expression was analyzed by flow cytometry, serum antioxidant capacity was evaluated using the TRAP method and circulating TNFα, and MMP-9 were measured with ELISA and gel zymography, respectively. Aortas were subjected to histology and immunohistochemistry for morphological analysis, macrophage infiltration, and MMP-9, TNFα, and VEGF expression.

RESULTS

Resveratrol counteracted the CD62L-monocyte subset expansion, CD143 monocyte expression, and circulating levels of MMP-9 activity and TNFα associated to AAA induction. Similarly, treatment with Resveratrol significantly attenuated AAA expansion, vessel wall macrophage infiltration and MMP-9, VEGF, and TNFα expression, compared with AAA from Et-OH group.

CONCLUSIONS

Resveratrol limited the monocyte-dependent inflammatory response, macrophage differentiation and aortic lumen enlargement in elastase-induced AAA. These data suggest that Resveratrol might be tested in selected patients with small AAA to modulate the early systemic and local inflammatory response associated to AAA progression.

Role of vascular endothelial growth factor-A in development of abdominal aortic aneurysm

AIMS

Increased angiogenesis, chronic inflammation, and extracellular matrix degradation are the major pathological features of abdominal aortic aneurysm (AAA). We sought to elucidate the role of vascular endothelial growth factor (VEGF)-A, a potent angiogenic and proinflammatory factor, in the development of AAA.

METHODS AND RESULTS

Human AAA samples showed increased VEGF-A expression, neovascularization, and macrophage infiltration compared with normal aortic walls. AAA was induced in mice by periaortic application of CaCl(2). AAA mice were treated with soluble VEGF-A receptor (sFlt)-1 or phosphate-buffered saline and sacrificed 6 weeks after the operation. Treatment with sFlt-1 resulted in reduced aneurysm size, restored wavy structure of the elastic lamellae, reduced Mac-2(+) monocytes/macrophages, CD3(+) T-lymphocytes, and CD31(+) vessels, and attenuated matrix metalloproteinase (MMP)-2 and 9 activity in periaortic tissue of AAA. Increased aortic mRNA expression of monocyte chemotactic protein-1, tumour necrosis factor-α, and intercellular adhesion molecule-1 in AAA was attenuated by sFlt-1 treatment.

CONCLUSION

VEGF-A was overexpressed in the aortic wall of human and experimental AAA. Treatment with sFlt-1 inhibited AAA development in mice, in association with reduced neoangiogenesis, infiltration of inflammatory cells, MMP activity, and extracellular matrix degradation. These findings suggest a crucial role of VEGF-A in the development of AAA.