Intravenous administration of mesenchymal stem cells prevents angiotensin II-induced aortic aneurysm formation in apolipoprotein E-deficient mouse

Medical treatments for abdominal aortic aneurysm: an overview of clinical trials

INTRODUCTION

Abdominal aortic aneurysm is a progressive, segmental, abdominal aortic dilation associated with a high mortality rate. Abdominal aortic aneurysms with diameters larger than 55 mm are associated with a high risk of rupture, and the most effective treatment options are surgical repair. Close observation and lifestyle adjustments are recommended for smaller abdominal aortic aneurysms with lower rupture risk. The development of medical therapies that limit or prevent the progression, expansion, and eventual rupture of abdominal aortic aneurysms remains an unmet clinical need.

AREAS COVERED

This review provides an overview of completed and ongoing clinical trials examining the efficacies of various drug classes, including antibiotics, antihypertensive drugs, hypolipidemic drugs, hypoglycemic drugs, and other potential therapies for abdominal aortic aneurysms. A search of PubMed, Web of Science, Clinical Trials, and another six clinical trial registries was conducted in January 2024.

EXPERT OPINION

None of the drugs have enough evidence to indicate that they can effectively inhibit the dilation of abdominal aortic aneurysm. More clinical trial data is required to support the efficacy of propranolol. Future research should also explore different drug delivery mechanisms, such as nanoparticles, to elevate drug concentration at the aneurysm wall.

A Single Injection of ADRCs Does Not Prevent AAA Formation in Rats in a Randomized Blinded Design

There is a pressing need for alternative medical treatments for abdominal aortic aneurysms (AAAs). Mesenchymal regenerative cells derived from adipose tissue (ADRCs) have shown potential in modulating the inflammation and immune responses that drive AAA progression. We hypothesized that ADRCs could reduce inflammation and preserve vascular integrity, potentially slowing the progression of AAA. In our study, subcutaneous adipose tissue was harvested from male Sprague Dawley rats, from which ADRCs were isolated. AAA was induced in these rats using intraluminal porcine pancreatic elastase, followed by intravenous administration of either ADRCs (106 cells) or saline (0.1 mL). We monitored the progression of AAA through weekly ultrasound, and the rats were sacrificed on day 28 for histological analysis. Our results showed no significant difference in the inner abdominal aortic diameter at day 28 between the control group (172% ± 73%, n = 17) and the ADRC-treated group (181% ± 75%, n = 15). Histological analyses of AAA cross-sections also revealed no significant difference in the infiltration of neutrophils or macrophages between the two groups. Furthermore, the integrity and content of elastin in the tunica media were similar between groups. These findings indicate that a single injection of ADRCs does not inhibit the development of AAA in rats in a randomized blinded study.

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.

A review of current status of cell-based therapies for aortic aneurysms

An aortic aneurysm (AA) is defined as focal aortic dilation that occurs mainly with older age and with chronic inflammation associated with atherosclerosis. The aneurysmal wall is a complex inflammatory environment characterized by endothelial dysfunction, macrophage activation, vascular smooth muscle cell (VSMC) apoptosis, and the production of proinflammatory molecules and matrix metalloproteases (MMPs) secreted by infiltrated inflammatory cells such as macrophages, T and B cells, dendritic cells, neutrophils, mast cells, and natural killer cells. To date, a considerable number of studies have been conducted on stem cell research, and growing evidence indicates that inflammation and tissue repair can be controlled through the functions of stem/progenitor cells. This review summarizes current cell-based therapies for AA, involving mesenchymal stem cells, VSMCs, multilineage-differentiating stress-enduring cells, and anti-inflammatory M2 macrophages. These cells produce beneficial outcomes in AA treatment by modulating the inflammatory environment, including decreasing the activity of proinflammatory molecules and MMPs, increasing anti-inflammatory molecules, modulating VSMC phenotypes, and preserving elastin. This article also describes detailed studies on pathophysiological mechanisms and the current progress of clinical trials.

MicroRNA-19b-3p dysfunction of mesenchymal stem cell-derived exosomes from patients with abdominal aortic aneurysm impairs therapeutic efficacy

Senescence of vascular smooth muscle cells (VSMCs) contributes to the formation of abdominal aortic aneurysm (AAA). Although mesenchymal stem cell exosomes (MSC-EXO) have been confirmed to restrict the development of AAA, their biological activity depends largely on the physiological state of the MSCs. This study aimed to compare the effects of adipose-derived MSC-EXO from healthy donors (HMEXO) and AAA patients (AMEXO) on senescence of VSMCs in AAA and explore the underlying mechanisms. An ApoE-/- mouse model of AAA was used to investigate the therapeutic effects of HMEXO, AMEXO or miR-19b-3p-AMEXO on AAA development. This in vitro model of AAA was established by treating VSMCs with Ang II (Angiotensin II). The senescence of VSMCs was determined by senescence-associated β-galactosidase (SA-β-gal) staining. The morphology of mitochondria in VSMCs was examined by MitoTracker staining. HMEXO exhibited superior capacity compared with AMEXO to inhibit VSMC senescence and attenuate AAA formation in Ang II-treated ApoE-/- mice. In vitro, both AMEXO and HMEXO inhibited Ang II-induced VSMC senescence via downregulation of mitochondrial fission. Notably, compared with HMEXO, the ability of AMEXO to inhibit VSMC senescence was significantly decreased. miRNA sequencing and the expression of miR-19b-3p was significantly decreased in AMEXO compared with HMEXO. Luciferase assay suggested that MST4 (Mammalian sterile-20-like kinase 4) is a potential target of miR-19b-3p. Mechanistically, miR-19b-3p in HMEXO ameliorated VSMC senescence by inhibiting mitochondrial fission via regulation of the MST4/ERK/Drp1 signaling pathway. Overexpression of miR-19b-3p in AMEXO improved their beneficial effect on AAA formation. Our study reveals that MSC-exosomal miR-19b-3p exerts protective effects against Ang II-induced AAA and VSMC senescence via regulation of the MST4/ERK/Drp1 pathway. The pathological state of AAA patients alters the miRNA components of AMEXO and impairs their therapeutic benefits.

Eicosapentaenoic acid is associated with the attenuation of dysfunctions of mesenchymal stem cells in the abdominal aortic aneurysm wall

Abdominal aortic aneurysm (AAA) is a vascular disease characterized by progressive dilation of the aorta which is reportedly associated with inflammation. Previous studies suggested that eicosapentaenoic acid (EPA) has suppressive effects on AAA development via anti-inflammatory activities. However, relationships between the anti-inflammatory effects and the cells in the AAA wall are poorly understood. In this study, we visualized the distribution of EPA-containing phosphatidylcholine (EPA-PC) in the AAA wall. EPA-PC was not ubiquitously distributed in both animal (hypoperfusion-induced AAA model) and human AAA walls, suggesting the preferential incorporation of EPA into certain cells. In the EPA-PC-high region of both animal and human AAAs, mesenchymal stem cell (MSC) marker positive areas were significantly higher than those in the EPA-PC-low region. Matrix metalloproteinase-positive MSCs were significantly lower in the AAA wall of the animal model which was administered EPA-rich fish oil. These data suggest that EPA is associated with the attenuation of MSC dysfunctions, which result in the suppression of AAA development.

Development of pharmacotherapies for abdominal aortic aneurysms

The cardiovascular field is still searching for a treatment for abdominal aortic aneurysms (AAA). This inflammatory disease often goes undiagnosed until a late stage and associated rupture has a high mortality rate. No pharmacological treatment options are available. Three hallmark factors of AAA pathology include inflammation, extracellular matrix remodeling, and vascular smooth muscle dysfunction. Here we discuss drugs for AAA treatment that have been studied in clinical trials by examining the drug targets and data present for each drug's ability to regulate the aforementioned three hallmark pathways in AAA progression. Historically, drugs that were examined in interventional clinical trials for treatment of AAA were repurposed therapeutics. Novel treatments (biologics, small-molecule compounds etc.) have not been able to reach the clinic, stalling out in pre-clinical studies. Here we discuss the backgrounds of previous investigational drugs in hopes of better informing future development of potential therapeutics. Overall, the highlighted themes discussed here stress the importance of both centralized anti-inflammatory drug targets and rigor of translatability. Exceedingly few murine studies have examined an intervention-based drug treatment in halting further growth of an established AAA despite interventional treatment being the therapeutic approach taken to treat AAA in a clinical setting. Additionally, data suggest that a potentially successful drug target may be a central inflammatory biomarker. Specifically, one that can effectively modulate all three hallmark factors of AAA formation, not just inflammation. It is suggested that inhibiting PGE₂ formation with an mPGES-1 inhibitor is a leading drug target for AAA treatment to this end.

Stem Cell Based Approaches to Modulate the Matrix Milieu in Vascular Disorders

The extracellular matrix (ECM) represents a complex and dynamic framework for cells, characterized by tissue-specific biophysical, mechanical, and biochemical properties. ECM components in vascular tissues provide structural support to vascular cells and modulate their function through interaction with specific cell-surface receptors. ECM–cell interactions, together with neurotransmitters, cytokines, hormones and mechanical forces imposed by blood flow, modulate the structural organization of the vascular wall. Changes in the ECM microenvironment, as in post-injury degradation or remodeling, lead to both altered tissue function and exacerbation of vascular pathologies. Regeneration and repair of the ECM are thus critical toward reinstating vascular homeostasis. The self-renewal and transdifferentiating potential of stem cells (SCs) into other cell lineages represents a potentially useful approach in regenerative medicine, and SC-based approaches hold great promise in the development of novel therapeutics toward ECM repair. Certain adult SCs, including mesenchymal stem cells (MSCs), possess a broader plasticity and differentiation potential, and thus represent a viable option for SC-based therapeutics. However, there are significant challenges to SC therapies including, but not limited to cell processing and scaleup, quality control, phenotypic integrity in a disease milieu in vivo, and inefficient delivery to the site of tissue injury. SC-derived or -inspired strategies as a putative surrogate for conventional cell therapy are thus gaining momentum. In this article, we review current knowledge on the patho-mechanistic roles of ECM components in common vascular disorders and the prospects of developing adult SC based/inspired therapies to modulate the vascular tissue environment and reinstate vessel homeostasis in these disorders.

Molecular Imaging of Aortic Aneurysm and Its Translational Power for Clinical Risk Assessment

Aortic aneurysms (AAs) are dilations of the aorta, that are often fatal upon rupture. Diagnostic radiological techniques such as ultrasound (US), magnetic resonance imaging (MRI), and computed tomography (CT) are currently used in clinical practice for early diagnosis as well as clinical follow-up for preemptive surgery of AA and prevention of rupture. However, the contemporary imaging-based risk prediction of aneurysm enlargement or life-threatening aneurysm-rupture remains limited as these are restricted to visual parameters which fail to provide a personalized risk assessment. Therefore, new insights into early diagnostic approaches to detect AA and therefore to prevent aneurysm-rupture are crucial. Multiple new techniques are developed to obtain a more accurate understanding of the biological processes and pathological alterations at a (micro)structural and molecular level of aortic degeneration. Advanced anatomical imaging combined with molecular imaging, such as molecular MRI, or positron emission tomography (PET)/CT provides novel diagnostic approaches for in vivo visualization of targeted biomarkers. This will aid in the understanding of aortic aneurysm disease pathogenesis and insight into the pathways involved, and will thus facilitate early diagnostic analysis of aneurysmal disease. In this study, we reviewed these molecular imaging modalities and their association with aneurysm growth and/or rupture risk and their limitations. Furthermore, we outline recent pre-clinical and clinical developments in molecular imaging of AA and provide future perspectives based on the advancements made within the field. Within the vastness of pre-clinical markers that have been studied in mice, molecular imaging targets such as elastin/collagen, albumin, matrix metalloproteinases and immune cells demonstrate promising results regarding rupture risk assessment within the pre-clinical setting. Subsequently, these markers hold potential as a future diagnosticum of clinical AA assessment. However currently, clinical translation of molecular imaging is still at the onset. Future human trials are required to assess the effectivity of potentially viable molecular markers with various imaging modalities for clinical rupture risk assessment.

Therapeutic efficacy of mesenchymal stem cells for abdominal aortic aneurysm: a meta-analysis of preclinical studies

Background

Abdominal aortic aneurysm (AAA) is life-threatening, surgical treatment is currently the only clinically available intervention for the disease. Mesenchymal stem cells (MSCs) have presented eligible immunomodulatory and regenerative abilities which showed favorable therapeutic efficacy in various cardiovascular diseases. However, current evidence summarizing the effectiveness of MSCs for AAA is lacking. Thus, a meta-analysis and systematic review was necessary to be performed to assess the therapeutic efficacy of MSCs for AAA in preclinical studies.

Methods

Comprehensive literature search restricted in English was conducted in PubMed, Cochrane Library, EBSCO, EMBASE and Web of Science from inception to Oct 2021. The primary outcomes were parameters about aortic diameter change during MSCs intervention. The secondary outcomes included elastin content and expression level of inflammatory cytokines, matrix metalloproteinases (MMPs) and their inhibitors (TIMPs). Data were extracted and analyzed independently by two authors. The meta package with random effects model was used to calculate the pooled effect size and 95% confidence intervals in R (version 4.0.2).

Results

Meta-analysis of 18 included studies demonstrated that MSCs intervention has significant therapeutic effects on suppressing aortic diameter enlargement compared with the control group (diameter, SMD = − 1.19, 95% CI [− 1.47, − 0.91]; diameter change ratio, SMD = − 1.36, 95% CI [− 1.72, − 1.00]). Subgroup analysis revealed differences between MSCs and control group regarding to cell type, intervention route and cell compatibility. Moreover, the meta-analysis also showed that MSCs intervention had a significant effect on preserving aortic elastin content, reducing MCP-1, TNF-α, IL-6, MMP-2/9 and increasing TIMP-1/2 expression level compared with control group.

Conclusion

Our results suggested that MSC intervention is effective in AAA by suppressing aortic diameter enlargement, reducing elastin degradation, and modulating local immunoinflammatory reactions. These results are important for the systemic application of MSCs as a potential treatment candidate for AAA in further animal experiments and clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02755-w.

Mesenchymal Stem Cells Alter MicroRNA Expression and Attenuate Thoracic Aortic Aneurysm Formation

BACKGROUND

Thoracic aortic aneurysms (TAA) are a progressive disease characterized by inflammation, smooth muscle cell activation and matrix degradation. We hypothesized that mesenchymal stem cells (MSCs) can immunomodulate vascular inflammation and remodeling via altered microRNA (miRNAs) expression profile to attenuate TAA formation.

MATERIALS AND METHODS

C57BL/6 mice underwent topical elastase application to form descending TAAs. Mice were also treated with MSCs on days 1 and 5 and aortas were analyzed on day 14 for aortic diameter. Cytokine array was performed in aortic tissue and total RNA was tagged and hybridized for miRNAs microarray analysis. Immunohistochemistry was performed for elastin degradation and leukocyte infiltration.

RESULTS

Treatment with MSCs significantly attenuated aortic diameter and TAA formation compared to untreated mice. MSC administration also attenuated T-cell, neutrophil and macrophage infiltration and prevented elastic degradation to mitigate vascular remodeling. MSC treatment also attenuated aortic inflammation by decreasing proinflammatory cytokines (CXCL13, IL-27, CXCL12 and RANTES) and upregulating anti-inflammatory interleukin-10 expression in aortic tissue of elastase-treated mice. TAA formation demonstrated activation of specific miRNAs that are associated with aortic inflammation and vascular remodeling. Our results also demonstrated that MSCs modulate a different set of miRNAs that are associated with decrease leukocyte infiltration and vascular inflammation to attenuate the aortic diameter and TAA formation.

CONCLUSIONS

These results indicate that MSCs immunomodulate specific miRNAs that are associated with modulating hallmarks of aortic inflammation and vascular remodeling of aortic aneurysms. Targeted therapies designed using MSCs and miRNAs have the potential to regulate the growth and development of TAAs.

Alternative therapeutic strategy for existing aortic aneurysms using mesenchymal stem cell-derived exosomes

BACKGROUND

Several studies demonstrated the therapeutic potential of mesenchymal stem cell-derived exosomes (MSC-exs) based on their anti-inflammatory properties. The objective was to determine the therapeutic effects of MSC-exs on aortic aneurysms (AAs) caused by atherosclerosis.

RESEARCH DESIGN AND METHODS

Apolipoprotein E knockout mice with AAs induced by angiotensin II were injected with MSC-exs or saline as a control. The change in the diameter of the aorta was measured. The expression of AA-related proteins and the histology of the aortic wall were investigated at 1 week after treatment. MicroRNA and protein profiles of MSC-exs were examined.

RESULTS

MSC-exs significantly attenuated AA progression (2.04 ± 0.20 mm in the saline group and 1.34 ± 0.13 mm in the MSC-ex group, P = 0.004). In the MSC-ex group, the expression of IL-1β, TNF-α and MCP-1 decreased, and expression of IGF-1 and TIMP-2 increased. MSC-ex induced the M2 phenotype in macrophages and suppressed the destruction of the elastic lamellae in the aortic wall. MSC-exs contained high levels of 10 microRNAs that inhibit AA formation and 13 proteins that inhibit inflammation and promote extracellular matrix synthesis.

CONCLUSIONS

MSC-ex might be a novel alternative therapeutic tool for treatment of existing AAs.

peri-Adventitial delivery of smooth muscle cells in porous collagen scaffolds for treatment of experimental abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is associated with the loss of vascular smooth muscle cells (SMCs) within the vessel wall. Direct delivery of therapeutic cells is challenging due to impaired mechanical integrity of the vessel wall. We hypothesized that porous collagen scaffolds can be an effective vehicle for the delivery of human-derived SMCs to the site of AAA. The purpose was to evaluate if the delivery of cell-seeded scaffolds can abrogate progressive expansion in a mouse model of AAA. Collagen scaffolds seeded with either primary human aortic SMCs or induced pluripotent stem cell derived-smooth muscle progenitor cells (iPSC-SMPs) had >80% in vitro cell viability and >75% cell penetrance through the scaffold's depth, while preserving smooth muscle phenotype. The cell-seeded scaffolds were successfully transplanted onto the murine aneurysm peri-adventitia on day 7 following AAA induction using pancreatic porcine elastase infusion. Ultrasound imaging revealed that SMC-seeded scaffolds significantly reduced the aortic diameter by 28 days, compared to scaffolds seeded with iPSC-SMPs or without cells (acellular scaffold), respectively. Bioluminescence imaging demonstrated that both cell-seeded scaffold groups had cellular localization to the aneurysm but a decline in survival with time. Histological analysis revealed that both cell-seeded scaffold groups had more SMC retention and less macrophage invasion into the medial layer of AAA lesions, when compared to the acellular scaffold treatment group. Our data suggest that scaffold-based SMC delivery is feasible and may constitute a platform for cell-based AAA therapy.

Senolytic agents lessen the severity of abdominal aortic aneurysm in aged mice

Age is a major risk factor for abdominal aortic aneurysm (AAA), for which treatment options are limited to surgical intervention for large AAA and watchful waiting for small aneurysms. However, the factors that regulate the expansion of aneurysms are unclear. Development of new therapeutic strategies to prevent or treat small aneurysms awaits a more thorough understanding of the etiology of AAA formation and progression with aging. A variety of structural and functional changes have been reported in aging vasculature, but emerging evidence implicates senescent cells in the formation of AAA through their paracrine effects on vascular wall cell populations. Here we show that aging is associated with transcriptional changes in abdominal aortic tissue consistent with loss of smooth muscle cells, leukocyte adhesion, inflammation, and accumulation of senescent cells in the vascular wall and surrounding perivascular adipose tissue. Furthermore, aged mice demonstrated anatomical and histopathological features of AAA development in response to administration of angiotensin II over 28 days. Importantly, in our study we sought to determine if reducing senescent cells could lessen the severity of AAA in aged mice. We find that pretreatment of aged mice with oral senolytic agents (dasatinib + quercetin) reduced senescent cell abundance in the arterial walls and surrounding tissues and lessened the severity of AAA in response to angiotensin II administration. These data provide important preliminary evidence supporting a role of senescent cells in age-related AAA formation and progression and suggest that strategies to reduce senescent cell burden hold promise to lessen AAA severity.

Pilot Study of Endovascular Delivery of Mesenchymal Stromal Cells in the Aortic Wall in a Pig Model

Abdominal aortic aneurysms (AAAs) have a high mortality. In small-animal models, multipotent mesenchymal stromal cells (MSCs) have shown benefits in attenuating aneurysm formation. However, an optimal cell delivery strategy is lacking. The NOGA system, which targets cell injections in a less-invasive way, has been used for myocardial cell delivery. Here, we assessed the safety and feasibility of the NOGA system for endovascular delivery of MSCs to the aortic wall in an AAA pig model. We induced AAA in 9 pigs by surgery or catheter induction. MSCs were delivered using the NOGA system 6 or 8 weeks after aneurysm induction. We euthanized the pigs and harvested the aorta for histologic analysis 1, 3, and 7 days after cell delivery. During AAA creation, 1 pig died; 8 pigs completed the study without acute adverse events or complications. The cell delivery procedure was safe and feasible. We successfully injected MSCs directly into the aortic wall in a targeted manner. Histologic and immunohistochemical analyses confirmed transmural injections in the aortic wall area of interest and the presence of MSCs. Our study showed the safety and feasibility of endovascular cell delivery to the aortic wall in a pig model.

Therapeutic effect of allogeneic bone marrow-derived mesenchymal stromal cells on aortic aneurysms

We previously reported the effectiveness of autologous mesenchymal stromal cells (MSCs) for the treatment of aortic aneurysm (AA), mediated mainly by these cells' anti-inflammatory properties. In this study, we investigate whether the therapeutic effects of allogeneic MSCs on AA are the same as those of autologous MSCs. To examine the immune response to allogeneic MSCs, C57BL/6 lymphocytes were co-cultured with BALB/c MSCs for 5 days in vitro. Apolipoprotein E-deficient C57BL/6 mice with AA induced by angiotensin II were randomly divided into three groups defined by the following intravenous injections: (i) 0.2 ml of saline (n = 10, group S) as a control, (ii) 1 × 106 autologous MSCs (isolated from C57BL/6, n = 10, group Au) and (iii) 1 × 106 allogeneic MSCs (isolated from BALB/c, n = 10, group Al). Two weeks after injection, aortic diameters were measured, along with enzymatic activities of MMP-2 and MMP-9 and cytokine concentrations in AAs. Neither allogenic (BALB/c) MSCs nor autologous (C57BL/6) MSCs accelerated the proliferation of lymphocytes obtained from C57BL/6. Compared with group S, groups Au and Al had significantly shorter aortic diameters (group S vs Au vs Al; 2.29 vs 1.40 vs 1.36 mm, respectively, p < 0.01), reduced MMP-2 and MMP-9 activities, downregulated IL-6 and MCP-1 and upregulated expression of IGF-1 and TIMP-2. There were no differences in these results between groups Au and Al. Thus, our study suggests that treatment with allogeneic MSCs improves chronic inflammation and reduced aortic dilatation. These effects were equivalent to those of autologous MSCs in established mouse models of AA.

Human Umbilical Cord Mesenchymal Stem Cells Attenuate Abdominal Aortic Aneurysm Progression in Sprague-Dawley Rats: Implication of Vascular Smooth Muscle Cell Phenotypic Modulation

Abdominal aortic aneurysm (AAA) is life-threatening, for which efficient nonsurgical treatment strategy has not been available so far. Several previous studies investigating the therapeutic effect of mesenchymal stem cells (MSCs) in AAA indicated that MSCs could inhibit aneurysmal inflammatory responses and extracellular matrix destruction, and suppress aneurysm occurrence and expansion. Vascular smooth muscle cell (VSMC) phenotypic plasticity is reported to be predisposed in AAA initiation and progression. However, little is known about the effect of MSCs on VSMC phenotypic modulation in AAA. In this study, we investigate the therapeutic efficacy of umbilical cord mesenchymal stem cells (UC-MSCs) in elastase-induced AAA model and evaluate the effect of UC-MSC on VSMC phenotypic regulation. We demonstrate that the intravenous injection of UC-MSC attenuates elastase-induced aneurysmal expansion, reduces elastin degradation and fragmentation, inhibits MMPs and TNF-α expression, and preserves and/or restores VSMC contractile phenotype in AAA. Taken together, these results highlight the therapeutic and VSMC phenotypic modulation effects of UC-MSC in AAA progression, which further indicates the potential of applying UC-MSC as an alternative treatment candidate for AAA.

Mesenchymal stem cell-derived conditioned medium attenuate angiotensin II-induced aortic aneurysm growth by modulating macrophage polarization

Mesenchymal stem cells (MSCs) exhibit therapeutic benefits on aortic aneurysm (AA); however, the molecular mechanisms are not fully understood. The current study aimed to investigate the therapeutic effects and potential mechanisms of murine bone marrow MSC (BM‐MSCs)–derived conditioned medium (MSCs‐CM) on angiotensin II (AngII)‐induced AA in apolipoprotein E‐deficient (apoE^−/−) mice. Murine BM‐MSCs, MSCs‐CM or control medium were intravenously administrated into AngII‐induced AA in apoE^−/− mice. Mice were sacrificed at 2 weeks after injection. BM‐MSCs and MSCs‐CM significantly attenuated matrix metalloproteinase (MMP)‐2 and MMP‐9 expression, aortic elastin degradation and AA growth at the site of AA. These treatments with BM‐MSCs and MSCs‐CM also decreased Ly6c^high monocytes in peripheral blood on day 7 and M1 macrophage infiltration in AA tissues on day 14, whereas they increased M2 macrophages. In addition, BM‐MSCs and MSCs‐CM reduced MCP‐1, IL‐1Ra and IL‐6 expression and increased IL‐10 expression in AA tissues. In vitro, peritoneal macrophages were co‐cultured with BM‐MSCs or fibroblasts as control in a transwell system. The mRNA and protein expression of M2 macrophage markers were evaluated. IL‐6 and IL‐1β were reduced, while IL‐10 was increased in the BM‐MSC systems. The mRNA and protein expression of M2 markers were up‐regulated in the BM‐MSC systems. Furthermore, high concentration of IGF1, VEGF and TGF‐β1 was detected in MSCs‐CM. Our results suggest that MSCs‐CM could prevent AA growth potentially through regulating macrophage polarization. These results may provide a new insight into the mechanisms of BM‐MSCs in the therapy of AA.

Aortic remodelling induced by obstructive apneas is normalized with mesenchymal stem cells infusion

Obstructive sleep apnea syndrome (OSA) promotes aortic dilatation, increased stiffness and accelerated atherosclerosis, but the mechanisms of vascular remodelling are not known. We aimed to assess vascular remodelling, its mechanisms, and the effect of mesenchymal stem cells (MSC) infusions in a clinically relevant rat model of chronic OSA involving recurrent airway obstructions leading thoracic pressure swings and intermittent hypoxia/hypercapnia (OSA-rats). Another group of rats were placed in the same setup without air obstructions (Sham-rats) and were considered controls. Our study demonstrates that chronic, non-invasive repetitive airway obstructions mimicking OSA promote remarkable structural changes of the descending thoracic aorta such as eccentric aortic hypertrophy due to an increased wall thickness and lumen diameter, an increase in the number of elastin fibers which, in contrast, get ruptured, but no changes in tunica media fibrosis. As putative molecular mechanisms of the OSA-induced vascular changes we identified an increase in reactive oxygen species and renin-angiotensin system markers and an imbalance in oxide nitric synthesis. Our results also indicate that MSC infusion blunts the OSA-related vascular changes, most probably due to their anti-inflammatory properties.

Development and growth trends in angiotensin II-induced murine dissecting abdominal aortic aneurysms

Abdominal aortic aneurysms are pathological dilations that can suddenly rupture, causing more than 15,000 deaths in the U.S. annually. Current treatment focuses on observation until an aneurysm's size warrants surgical intervention. Thus, there is a need for therapeutic intervention to inhibit growth of smaller aneurysms. An experimental aneurysm model that infuses angiotensin II into apolipoprotein E‐deficient mice is widely used to investigate underlying pathological mechanisms and potential therapeutics, but this model has two caveats: (1) aneurysms do not always form, and (2) aneurysm severity and growth is inconsistent among animals. Here we use high‐frequency ultrasound to collect data from angiotensin II‐induced aneurysms to develop prediction models of both aneurysm formation and growth. Baseline measurements of aortic diameter, volume/length, and strain were used with animal mass and age in a quadratic discriminant analysis and logistic regression to build two statistical models to predict disease status. Longitudinal ultrasound data were also acquired from mice with aneurysms to quantify aneurysm diameter, circumferential strain, blood flow velocity, aneurysm volume/length, and thrombus and open‐false lumen volumes over 28 days. Measurements taken at aneurysm diagnosis were used with branching artery information to produce a multiple linear regression model to predict final aneurysm volume/length. All three statistical models could be useful in future aneurysm therapeutic studies to better delineate the effects of preventative and suppressive treatments from normal variations in the angiotensin II aneurysm model.

Knockdown of lncRNA PVT1 Inhibits Vascular Smooth Muscle Cell Apoptosis and Extracellular Matrix Disruption in a Murine Abdominal Aortic Aneurysm Model

This study was designed to determine the effects of the long non-coding RNA (lncRNA) plasmacytoma variant translocation 1 (PVT1) on vascular smooth muscle cell (VSMC) apoptosis and extracellular matrix (ECM) disruption in a murine abdominal aortic aneurysm (AAA) model. After injection of PVT1-silencing lentiviruses, AAA was induced in Apolipoprotein E-deficient (ApoE-/-) male mice by angiotensin II (Ang II) infusion for four weeks. After Ang II infusion, mouse serum levels of pro-inflammatory cytokines were analysed, and aortic tissues were isolated for histological, RNA, and protein analysis. Our results also showed that PVT1 expression was significantly upregulated in abdominal aortic tissues from AAA patients compared with that in controls. Additionally, Ang II treatment significantly increased PVT1 expression, both in cultured mouse VSMCs and in AAA murine abdominal aortic tissues. Of note, the effects of Ang II in facilitating cell apoptosis, increasing matrix metalloproteinase (MMP)-2 and MMP-9, reducing tissue inhibitor of MMP (TIMP)-1, and promoting switching from the contractile to synthetic phenotype in cultured VSMCs were enhanced by overexpression of PVT1 but attenuated by knockdown of PVT1. Furthermore, knockdown of PVT1 reversed Ang II-induced AAA-associated alterations in mice, as evidenced by attenuation of aortic diameter dilation, marked adventitial thickening, loss of elastin in the aorta, enhanced aortic cell apoptosis, elevated MMP-2 and MMP-9, reduced TIMP-1, and increased pro-inflammatory cytokines. In conclusion, our findings demonstrate that knockdown of lncRNA PVT1 suppresses VSMC apoptosis, ECM disruption, and serum pro-inflammatory cytokines in a murine Ang II-induced AAA model.

Diverse roles of macrophage polarization in aortic aneurysm: destruction and repair

Aortic aneurysm (AA) is defined as an enlargement of the aorta greater than 1.5 times its normal size. Early diagnosis of AA is challenging and mortality of AA is high. Curative pharmacological treatments for AA are still lacking, highlighting the need for better understanding of the underlying mechanisms of AA progression. Accumulating studies have proven that the polarization state of circulating monocyte-derived macrophages plays a crucial role in regulating the development of AA. Distinct macrophage subtypes display different functions. Several studies targeting macrophage polarization during AA formation and progression showed potential treatment effects. In this review, we focus on the recent advances of research on macrophage polarization in the progression of AA and propose that targeting macrophage polarization could hold great promise for preventing and treating AA.

Pathophisiology of abdominal aortic aneurysm: biomarkers and novel therapeutic targets

Abdominal aortic aneurysm (AAA) is a vascular pathology with a high rate of morbidity and mortality and a prevalence that, in men over 65 years, can reach around 8%. In this disease, usually asymptomatic, there is a progressive dilatation of the vascular wall that can lead to its rupture, a fatal phenomenon in more than 80% of cases. The treatment of patients with asymptomatic aneurysms is limited to periodic monitoring with imaging tests, control of cardiovascular risk factors and treatment with statins and antiplatelet therapy. There is no effective pharmacological treatment capable of limiting AAA progression or avoiding their rupture. At present, the aortic diameter is the only marker of risk of rupture and determines the need for surgical repair when it reaches values greater than 5.5cm. This review addresses the main aspects related to epidemiology, risk factors, diagnosis and clinical management of AAA, exposes the difficulties to have good biomarkers of this pathology and describes the strategies for the identification of new therapeutic targets and biomarkers in AAA.

Human mesenchymal stromal cell-derived extracellular vesicles attenuate aortic aneurysm formation and macrophage activation via microRNA-147

The formation of an abdominal aortic aneurysm (AAA) is characterized by inflammation, macrophage infiltration, and vascular remodeling. In this study, we tested the hypothesis that mesenchymal stromal cell (MSC)-derived extracellular vesicles (EVs) immunomodulate aortic inflammation, to mitigate AAA formation via modulation of microRNA-147. An elastase-treatment model of AAA was used in male C57BL/6 wild-type (WT) mice. Administration of EVs in elastase-treated WT mice caused a significant attenuation of aortic diameter and mitigated proinflammatory cytokines, inflammatory cell infiltration, an increase in smooth muscle cell α-actin expression, and a decrease in elastic fiber disruption, compared with untreated mice. A 10-fold up-regulation of microRNA (miR)-147, a key mediator of macrophage inflammatory responses, was observed in murine aortic tissue in elastase-treated mice compared with controls on d 14. EVs derived from MSCs transfected with miR-147 mimic, but not with miR-147 inhibitor, attenuated aortic diameter, inflammation, and leukocyte infiltration in elastase-treated mice. In vitro studies of human aortic tissue explants and murine-derived CD11b+ macrophages induced proinflammatory cytokines after elastase treatment, and the expression was attenuated by cocultures with EVs transfected with miR-147 mimic, but not with miR-147 inhibitor. Thus, our findings define a critical role of MSC-derived EVs in attenuation of aortic inflammation and macrophage activation via miR-147 during AAA formation.-Spinosa, M., Lu, G., Su, G., Bontha, S. V., Gehrau, R., Salmon, M. D., Smith, J. R., Weiss, M. L., Mas, V. R., Upchurch, G. R., Sharma, A. K. Human mesenchymal stromal cell-derived extracellular vesicles attenuate aortic aneurysm formation and macrophage activation via microRNA-147.

The oral administration of clarithromycin prevents the progression and rupture of aortic aneurysm

OBJECTIVE

The pathogenesis of aortic aneurysm (AA) is associated with chronic inflammation in the aortic wall with increased levels of matrix metalloproteinases (MMPs). Clarithromycin (CAM) has been reported to suppresses MMP activity. In this study, we investigated whether CAM could prevent the formation and rupture of AA.

METHODS

Male apolipoprotein E-deficient mice (28-30 weeks of age) were infused with angiotensin II for 28 days. CAM (100 mg/kg/d) or saline (as a control) was administered orally to the mice every day (CAM group, n = 13; control group, n = 13). After the administration period, the aortic diameter, elastin content, macrophage infiltration, MMP levels, and levels of inflammatory cytokines, including nuclear factor κB (NF-κB), were measured.

RESULTS

The aortic diameter was significantly suppressed in the CAM group (P < .001). No rupture death was observed in the CAM group in contrast to five deaths (38%) in the control group (P < .01). CAM significantly suppressed the degradation of aortic elastin (56.3% vs 16.5%; P < .001) and decreased the infiltration of inflammatory macrophages (0.05 vs 0.16; P < .01). Compared with the controls, the enzymatic activity of MMP-2 and MMP-9 was significantly reduced in the CAM group (MMP-2, 0.15 vs 0.56 [P < .01]; MMP-9, 0.12 vs 0.60 [P < .01]), and the levels of interleukin 1β (346.6 vs 1066.0; P < .05), interleukin 6 (128.4 vs 346.2; P < .05), and phosphorylation of NF-κB were also decreased (0.3 vs 2.0; P < .01).

CONCLUSIONS

CAM suppressed the progression and rupture of AA through the suppression of inflammatory macrophage infiltration, a reduction in MMP-2 and MMP-9 activity, and the inhibition of elastin degradation associated with the suppression of NF-κB phosphorylation.

Emerging role of exosome-mediated intercellular communication in vascular remodeling

Vascular remodeling refers to the alternations of function and structure in vasculature. A complex autocrine/paracrine set of cellular interaction is involved in vascular remodeling. Exosome, a newly identified natural nanocarrier and intercellular messenger, plays a pivotal role in regulating cell-to-cell communication. Exosome emerges as an important mediator in the process of vascular remodeling, showing the most prognostic and therapeutic potent in vascular diseases. Benefiting from exosomal trafficking, the vasculature can not only maintain its function and structure in physiological condition, but also adapt itself in pathological status. In this review, we will represent the roles of exosomes in angiogenesis, endothelial function and cardiac regeneration. In addition, greatly depending on the pathophysiological status of donor cells and peripheral micro-circumstance, the exosomal content could alter, which makes exosomes exhibit pleiotropic effects in vascular diseases. Hence, the diverse effects of exosomes in vascular diseases including atherosclerosis, neointima formation and vascular repair, primary hypertension, pulmonary artery hypertension, and aortic aneurysm will be discussed. Finally, the translational appliances targeting exosomes will be concluded by providing updated applications of engineered exosomes in clinic.

Muse Cells and Aortic Aneurysm

The aorta is a well-organized, multilayered structure comprising several cell types, namely, endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and fibroblasts, as well as an extracellular matrix (ECM), which includes elastic and collagen fibers. Aortic aneurysms (AAs) are defined as progressive enlargements of the aorta that carries an incremental risk of rupture as the diameter increases over time. The destruction of the aortic wall tissue is triggered by atherosclerosis, inflammation, and oxidative stress, leading to the activation of matrix metalloproteinases (MMPs), and inflammatory cytokines and chemokines, resulting in the loss of the structural back bone of VSMCs, ECM, and ECs. To date, cell-based therapy has been applied to animal models using several types of cells, such as VSMCs, ECs, and mesenchymal stem cells (MSCs). Although these cells indeed deliver beneficial outcomes for AAs, particularly by paracrine and immunomodulatory effects, the attenuation of aneurysmal dilation with a robust tissue repair is insufficient. Meanwhile, multilineage-differentiating stress-enduring (Muse) cells are known to be endogenous non-tumorigenic pluripotent-like stem cells that are included as several percent of MSCs. Since Muse cells are pluripotent-like, they have the ability to differentiate into cells representative of all three germ layers from a single cell and to self-renew. Moreover, Muse cells are able to home to the site of damage following simple intravenous injection and repair the tissue by replenishing new functional cells through spontaneous differentiation into tissue-compatible cells. Given these unique properties, Muse cells are expected to provide an efficient therapeutic efficacy for AA by simple intravenous injection. In this chapter, we summarize several studies on Muse cell therapy for AA including our recent data, in comparison with other kinds of cell therapies.

Murine ultrasound-guided transabdominal para-aortic injections of self-assembling type I collagen oligomers

Abdominal aortic aneurysms (AAAs) represent a potentially life-threatening condition that predominantly affects the infrarenal aorta. Several preclinical murine models that mimic the human condition have been developed and are now widely used to investigate AAA pathogenesis. Cell- or pharmaceutical-based therapeutics designed to prevent AAA expansion are currently being evaluated with these animal models, but more minimally invasive strategies for delivery could improve their clinical translation. The purpose of this study was to investigate the use of self-assembling type I collagen oligomers as an injectable therapeutic delivery vehicle in mice. Here we show the success and reliability of a para-aortic, ultrasound-guided technique for injecting quickly-polymerizing collagen oligomer solutions into mice to form a collagen-fibril matrix at body temperature. A commonly used infrarenal mouse AAA model was used to determine the target location of these collagen injections. Ultrasound-guided, closed-abdominal injections supported consistent delivery of collagen to the area surrounding the infrarenal abdominal aorta halfway between the right renal artery and aortic trifurcation into the iliac and tail arteries. This minimally invasive approach yielded outcomes similar to open-abdominal injections into the same region. Histological analysis on tissue removed on day 14 post-operatively showed minimal in vivo degradation of the self-assembled fibrillar collagen and the majority of implants experienced minimal inflammation and cell invasion, further confirming this material's potential as a method for delivering therapeutics. Finally, we showed that the typical length and position of this infrarenal AAA model was statistically similar to the length and targeted location of the injected collagen, increasing its feasibility as a localized therapeutic delivery vehicle. Future preclinical and clinical studies are needed to determine if specific therapeutics incorporated into the self-assembling type I collagen matrix described here can be delivered near the aorta and locally limit AAA expansion.

Human Adipose-Derived Stem Cells Suppress Elastase-Induced Murine Abdominal Aortic Inflammation and Aneurysm Expansion Through Paracrine Factors

Abdominal aortic aneurysm (AAA) is a potentially lethal disease associated with immune activation-induced aortic degradation. We hypothesized that xenotransplantation of human adipose-derived stem cells (hADSCs) would reduce aortic inflammation and attenuate expansion in a murine AAA model. Modulatory effects of ADSCs on immune cell subtypes associated with AAA progression were investigated using human peripheral blood mononuclear cells (hPBMNCs) cocultured with ADSCs. Murine AAA was induced through elastase application to the abdominal aorta in C57BL/6 mice. ADSCs were administered intravenously, and aortic changes were determined by ultrasonography and videomicrometry. Circulating monocytes, aortic neutrophils, CD28- T cells, FoxP3+ regulatory T cells (Tregs), and CD206+ M2 macrophages were assessed at multiple terminal time points. In vitro, ADSCs induced M2 macrophage and Treg phenotypes while inhibiting neutrophil transmigration and lymphocyte activation without cellular contact. Intravenous ADSC delivery reduced aneurysmal expansion starting from day 4 [from baseline: 54.8% (saline) vs. 16.9% (ADSCs), n = 10 at baseline, n = 4 at day 4, p < 0.001], and the therapeutic effect persists through day 14 (from baseline: 64.1% saline vs. 24.6% ADSCs, n = 4, p < 0.01). ADSC administration increased aortic Tregs by 20-fold (n = 5, p < 0.01), while decreasing CD4+CD28- (-28%), CD8+CD28- T cells (-61%), and Ly6G/C+ neutrophils (-43%, n = 5, p < 0.05). Circulating CD115+CXCR1-LY6C+-activated monocytes decreased in the ADSC-treated group by day 7 (-60%, n = 10, p < 0.05), paralleled by an increase in aortic CD206+ M2 macrophages by 2.4-fold (n = 5, p < 0.05). Intravenously injected ADSCs transiently engrafted in the lung on day 1 without aortic engraftment at any time point. In conclusion, ADSCs exhibit pleiotropic immunomodulatory effects in vitro as well as in vivo during the development of AAA. The temporal evolution of these effects systemically as well as in aortic tissue suggests that ADSCs induce a sequence of anti-inflammatory cellular events mediated by paracrine factors, which leads to amelioration of AAA progression.

Strategies to Optimize Adult Stem Cell Therapy for Tissue Regeneration

Stem cell therapy aims to replace damaged or aged cells with healthy functioning cells in congenital defects, tissue injuries, autoimmune disorders, and neurogenic degenerative diseases. Among various types of stem cells, adult stem cells (i.e., tissue-specific stem cells) commit to becoming the functional cells from their tissue of origin. These cells are the most commonly used in cell-based therapy since they do not confer risk of teratomas, do not require fetal stem cell maneuvers and thus are free of ethical concerns, and they confer low immunogenicity (even if allogenous). The goal of this review is to summarize the current state of the art and advances in using stem cell therapy for tissue repair in solid organs. Here we address key factors in cell preparation, such as the source of adult stem cells, optimal cell types for implantation (universal mesenchymal stem cells vs. tissue-specific stem cells, or induced vs. non-induced stem cells), early or late passages of stem cells, stem cells with endogenous or exogenous growth factors, preconditioning of stem cells (hypoxia, growth factors, or conditioned medium), using various controlled release systems to deliver growth factors with hydrogels or microspheres to provide apposite interactions of stem cells and their niche. We also review several approaches of cell delivery that affect the outcomes of cell therapy, including the appropriate routes of cell administration (systemic, intravenous, or intraperitoneal vs. local administration), timing for cell therapy (immediate vs. a few days after injury), single injection of a large number of cells vs. multiple smaller injections, a single site for injection vs. multiple sites and use of rodents vs. larger animal models. Future directions of stem cell-based therapies are also discussed to guide potential clinical applications.

Daidzein attenuates abdominal aortic aneurysm through NF-κB, p38MAPK and TGF-β1 pathways

The current study focuses on the protection of daidzein on nerves, as daidzein was demonstrated to have a protective effect on neurons of the central nervous system in a glutamate excitotoxicity and oxygen/glucose deprivation model. However, the effect of daidzein on the abdominal aortic aneurysm (AAA) remains unclear. The angiotensin II-induced AAA mouse model was utilized in the present study to determine the effect of daidzein on AAA. The results demonstrated that daidzein significantly attenuated incidence of AAA, max aortic aneurysm and mortality in the angiotensin II‑induced AAA mice. Daidzein had an anti‑inflammatory effect by inhibiting tumor necrosis factor α (TNF-α), interleukin 1β (IL‑1β) and nuclear factor κB (NF‑κB) protein expression. In addition, daidzein strongly suppressed the gene expression of cyclooxygenase (COX)‑2, matrix metalloproteinase 2 (MMP‑2), tissue inhibitor of metalloproteinase 1 (TIMP-1), transforming growth factor β1 (TGF‑β1), and inhibited inducible nitric oxide synthase (iNOS) protein expression in angiotensin II‑induced AAA mice. It also inhibited phosphorylation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway. These results demonstrate, to the best of our knowledge for the first time, that the anti‑inflammatory effects and inhibitory mechanism of daidzein attenuates AAA in angiotensin II‑induced mice. Daidzein contains strong anti‑inflammatory activity and affects various mechanism pathways including the NF‑κB, p38MAPK and TGF-β1 pathway.

Ascending Aortic Aneurysm in Angiotensin II-Infused Mice: Formation, Progression, and the Role of Focal Dissections

OBJECTIVE

To understand the anatomy and physiology of ascending aortic aneurysms in angiotensin II-infused ApoE(-/-) mice.

APPROACH AND RESULTS

We combined an extensive in vivo imaging protocol (high-frequency ultrasound and contrast-enhanced microcomputed tomography at baseline and after 3, 10, 18, and 28 days of angiotensin II infusion) with synchrotron-based ultrahigh resolution ex vivo imaging (phase contrast X-ray tomographic microscopy) in n=47 angiotensin II-infused mice and 6 controls. Aortic regurgitation increased significantly over time, as did the luminal volume of the ascending aorta. In the samples that were scanned ex vivo, we observed one or several focal dissections, with the largest located in the outer convex aspect of the ascending aorta. The volume of the dissections moderately correlated to the volume of the aneurysm as measured in vivo (r(2)=0.46). After 3 days of angiotensin II infusion, we found an interlaminar hematoma in 7/12 animals, which could be linked to an intimal tear. There was also a significant increase in single laminar ruptures, which may have facilitated a progressive enlargement of the focal dissections over time. At later time points, the hematoma was resorbed and the medial and adventitial thickness increased. Fatal transmural dissection occurred in 8/47 mice at an early stage of the disease, before adventita remodeling.

CONCLUSIONS

We visualized and quantified the dissections that lead to ascending aortic aneurysms in angiotensin II-infused mice and provided unique insight into the temporal evolution of these lesions.

Imaging of small animal peripheral artery disease models: recent advancements and translational potential

Peripheral artery disease (PAD) is a broad disorder encompassing multiple forms of arterial disease outside of the heart. As such, PAD development is a multifactorial process with a variety of manifestations. For example, aneurysms are pathological expansions of an artery that can lead to rupture, while ischemic atherosclerosis reduces blood flow, increasing the risk of claudication, poor wound healing, limb amputation, and stroke. Current PAD treatment is often ineffective or associated with serious risks, largely because these disorders are commonly undiagnosed or misdiagnosed. Active areas of research are focused on detecting and characterizing deleterious arterial changes at early stages using non-invasive imaging strategies, such as ultrasound, as well as emerging technologies like photoacoustic imaging. Earlier disease detection and characterization could improve interventional strategies, leading to better prognosis in PAD patients. While rodents are being used to investigate PAD pathophysiology, imaging of these animal models has been underutilized. This review focuses on structural and molecular information and disease progression revealed by recent imaging efforts of aortic, cerebral, and peripheral vascular disease models in mice, rats, and rabbits. Effective translation to humans involves better understanding of underlying PAD pathophysiology to develop novel therapeutics and apply non-invasive imaging techniques in the clinic.

Adipose stem cells promote smooth muscle cells to secrete elastin in rat abdominal aortic aneurysm

Background

Abdominal aortic aneurysm (AAA) is a life-threatening disease and its prevalence rate increases with social aging. The degradation of elastic is an important factor in the formation of AAA.

Methods

Adipose derived stem cells (ADSCs) and bone marrow mesenchymal stem cells (BMSCs) were isolated from rats, and identified by Oil red O and alizarin red staining after adipogenesis and osteogenesis induction. In addition, ADSCs were also identified by flow cytometry with CD markers. AAA model in rats was established, and smooth muscle cells (SMCs) were isolated from AAA aortic wall and identified by immunohistochemistry. ADSCs or BMSCs were co-cultured with AAA aortic wall for in vitro experiment, and ADSCs were injected into AAA model for in vivo test. Then orcein staining was used for observing the morphology of elastic fiber, Western blot and real-time PCR were used respectively to detect the protein and gene expression of elastin, gelatinases spectrum analysis was used to detect the activity of matrix metalloproteinase-2 (MMP-2) and MMP-9.

Results

Lots of red lipid droplets were visible by Oil red O staining after adipogenesis induction, and black calcium nodules appeared by alizarin red staining after osteogenesis induction. The results of flow cytometry showed that ADSCs expressed CD44 and CD105, but exhibited negligible expression of CD31 and CD45. SMCs exhibited spindle-like morphology and α-actin protein was positive in cytoplasm. After co-cultured with ADSCs or BMSCs, the elastic fiber recovered normal winding shape, both the gene and protein expression of elastin increased, and the activity of MMP-2 decreased. The in vivo result was similar to that of in vitro.

Conclusions

ADSCs promote the expression of elastin in SMCs and contribute to the reconstruction of elastic fiber, which may provide new ideas for treating AAA.

Rapidly self-renewing human multipotent marrow stromal cells (hMSC) express sialyl Lewis X and actively adhere to arterial endothelium in a chick embryo model system

BACKGROUND

There have been conflicting observations regarding the receptors utilized by human multipotent mesenchymal bone marrow stromal cells (hMSC) to adhere to endothelial cells (EC). To address the discrepancies, we performed experiments with cells prepared with a standardized, low-density protocol preserving a sub-population of small cells that are rapidly self-renewing.

METHODS

Sialyl Lewis X (SLeX) and α4 integrin expression were determined by flow cytometry. Fucosyltransferase expression was determined by quantitative realtime RT-PCR. Cell adhesion assays were carried out with a panel of endothelial cells from arteries, veins and the microvasculature in vitro. In vivo experiments were performed to determine single cell interactions in the chick embryo chorioallantoic membrane (CAM). The CAM is a well-characterized respiratory organ allowing for time-lapse image acquisition of large numbers of cells treated with blocking antibodies against adhesion molecules expressed on hMSC.

RESULTS

hMSC expressed α4 integrin, SLeX and fucosyltransferase 4 and adhered to human EC from arteries, veins and the microvasculature under static conditions in vitro. In vivo, hMSC rolled on and adhered to arterioles in the chick embryo CAM, whereas control melanoma cells embolized. Inhibition of α4 integrin and/or SLeX with blocking antibodies reduced rolling and adhesion in arterioles and increased embolism of hMSC.

CONCLUSIONS

The results demonstrated that rapidly self-renewing hMSC were retained in the CAM because they rolled on and adhered to respiratory arteriolar EC in an α4 integrin- and SLeX-dependent manner. It is therefore important to select cells based on their cell adhesion receptor profile as well as size depending on the intended target of the cell and the injection route.

Nanoparticles and stem cells - has targeted therapy for aneurysms finally arrived?

Until recently, endovascular management of intracranial aneurysms has focused on mechanical and hemodynamic aspects: characterizing aneurysm morphology by angiogram, mechanical obstruction by detachable coils, and flow diversion with endovascular stents. Although now common practice, these interventions only ward off aneurysm rupture. The source of the problem, disease of the vessel wall itself, remains. New imaging technology and treatment modalities, however, are offering great promise to the field. In this review, we outline several new developments in the recent literature and pose potential adaptations toward cerebral aneurysms using them. The incidence, presentation, and contemporary endovascular treatment for aneurysms are first reviewed to lay the groundwork for new adaptations. Nanoparticles, including ultrasmall supraparagmenetic iron oxide particles (USPIOs), are next explored as a novel mechanism of predicting aneurysm wall instability and as an agent themselves for aneurysm occlusion. Cellular transplant grafts, bone marrow-derived stem cells (BM-MSCs), and endothelial progenitor cells (EPCs) are then investigated, with the role of cellular differentiation, chemokine secretion, and integration into the injured vascular wall receiving particular emphasis. Several promising translational papers are next discussed, with review of multiple studies that show benefit in aneurysm treatment and endovascular stenting using these agents as adjuncts. We next adapt these research findings into several potential applications we feel may be promising directions for the aspiring researcher. These new treatments may one day strengthen the arsenal of the endovascular neurosurgeon.

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.

Therapeutic potential of bone marrow-derived mesenchymal stem cells in formed aortic aneurysms of a mouse model

OBJECTIVES

An aortic aneurysm (AA) is caused by atherosclerosis with chronic inflammation. Mesenchymal stem cells (MSCs) have potential anti-inflammatory properties. In this study, we examined whether an already-formed AA can be treated by intravenous injection of bone marrow-derived (BM)-MSCs in a mouse model.

METHODS

AA was induced in apolipoprotein E-deficient mice by angiotensin II-infusion for 28 days through sub-cutaneous osmotic mini-pumps. After that, 1 × 10(6) BM-MSCs (in 0.2 ml saline) or 0.2 ml saline as a control was injected via the tail vein. Mice were sacrificed at 2 (saline group n = 10, BM-MSC group n = 10), 4 (saline group n = 6, BM-MSC group n = 7) or 8 weeks (saline group n = 5, BM-MSC group n = 6) after injection. The aortic tissues of each group were dissected. Aortic diameter, elastin content, matrix metalloproteinase (MMP)-2 and -9 enzymatic activity and cytokine concentrations were measured, as was macrophage infiltration, which was also evaluated histologically.

RESULTS

The incidence of AA in the BM-MSC group was reduced at 2 weeks (BM-MSC 40% vs saline 100%, P < 0.05), and aortic diameter was reduced at 2 and 4 weeks (2 weeks: 1.40 vs 2.29 mm, P < 0.001; 4 weeks: 1.73 vs 2.32 mm, P < 0.05). The enzymatic activities of MMP-2 and -9 were reduced in the BM-MSC group at 2 weeks (active-MMP-2: 0.28 vs 0.45 unit/ml, P < 0.05; active-MMP-9: 0.16 vs 0.34 unit/ml, P < 0.05). Inflammatory cytokines were down-regulated in the BM-MSC group (interleukin-6: 2 weeks: 1475.6 vs 3399.5 pg/ml, P < 0.05; 4 weeks: 2184.7 vs 3712.8 pg/ml, P < 0.05 and monocyte chemotactic protein-1: 2 weeks: 208.0 vs 352.7 pg/ml, P < 0.05) and insulin-like growth factor (IGF)-1 and tissue inhibitor of metalloproteinase (TIMP)-2 were up-regulated in the BM-MSC group at 2 weeks (IGF-1: 4.7 vs 2.0 ng/ml, P < 0.05; TIMP-2: 9.5 vs 4.0 ng/ml, P < 0.001). BM-MSC injection inhibited infiltration of M1 macrophages and preserved the construction of elastin.

CONCLUSIONS

Our results suggest that BM-MSCs might be an effective treatment for AA. Further investigation is necessary to optimize the injected dosage and the frequency of BM-MSCs to prevent a transient effect.