Editor's Choice - Pharmaceutical Management of Small Abdominal Aortic Aneurysms: A Systematic Review of the Clinical Evidence

Inulin Diet Alleviates Abdominal Aortic Aneurysm by Increasing Akkermansia and Improving Intestinal Barrier

Background/Objectives: Previous studies have shown varying efficacy of high-fiber diets containing different ingredients in abdominal aortic aneurysms (AAAs). This study aimed to identify which high-fiber diet protects against AAA in mice and elucidate the underlying mechanisms. Methods: This study compared inulin, cellulose, and chow diets in terms of their impact on aneurysm enlargement, elastin degradation, matrix metalloproteinase 2 and 9 expressions, CD3+ T cell and CD68+ macrophage infiltration, and macrophage differentiation. It also examined gut microbiota composition, focusing on Akkermansia, and evaluated intestinal barrier function and systemic inflammatory response. Results: The inulin diet, but not the cellulose diet, compared with the chow diet, reduced aneurysm enlargement, elastin degradation, matrix metalloproteinase 2 and 9 expressions, CD3+ T cell and CD68+ macrophage infiltration, and skewed macrophage towards M2 differentiation. The inulin diet enriched Akkermansia in both the small and large intestine. The inulin diet also enhanced the intestinal barrier by augmenting goblet cells, upregulating the gene related to the epithelial barrier and antibacterial peptides in the small intestine, and reducing circulating lipopolysaccharide and interleukin-1β levels. The inulin diet lowered the proportion of Ly6Chi monocytes and C-C chemokine receptor 2 expression on these cells in the bone marrow, reducing aneurysm infiltration. Administering Akkermansia to AAA mice decreased intestinal permeability and mitigated AAA. Conclusions: A diet rich in fermentable fiber inulin, as opposed to cellulose, alleviates AAA in mice. This beneficial effect is attributed to the enhanced presence of Akkermansia bacteria and improvement of the intestinal barrier.

The Justification of Open Surgical Repair for an Abdominal Aortic Aneurysm: A Retrospective Comparison of Outcomes of Endovascular Aneurysm Repair and a Brief Review of the Literature

Background: Abdominal aortic aneurysms (AAAs) are life-threatening conditions that require timely intervention to prevent rupture. Endovascular aneurysm repair (EVAR) is preferred due to faster recovery and lower perioperative risk; however, intraoperative failure and long-term complications highlight the continued significance of open surgical repair (OSR) and the need for improved risk assessment. Methods: This retrospective study analyzed data from 210 patients who underwent EVAR (n = 163) or OSR (n = 47) at a single center. Clinical characteristics, complications, reintervention rates, and 30-day mortality were recorded. EVAR-to-OSR conversion and mortality predictors in AAA treatments were identified. Results: The overall mortality rate was 9.5% (20/210 patients), with 12 patients (7.3%) in the EVAR group and 8 patients (17%) in the OSR group (p = 0.085). Five patients required early and six required late conversion to open surgery. In follow-ups beyond 30 days, the reintervention rate for EVAR was higher (HR: 1.2, 95% CI: 0.4-3.6; p = 0.754). According to the multivariable analysis, rupture (p = 0.045), female sex (p = 0.018), body weight (p = 0.003), and aortic size index (p = 0.019) were significant predictors of mortality, whereas OSR was not (p = 0.212). Conclusions: Treatment optimization requires a balanced approach, integrating both EVAR and OSR based on patient-specific factors. Maintaining expertise in both techniques is essential to ensure the best possible outcomes, and OSR should remain a viable option when clinically indicated.

Protein Drug Targets for Abdominal Aortic Aneurysm and Proteomic Associations Between Modifiable Risk Factors and Abdominal Aortic Aneurysm

BACKGROUND

Abdominal aortic aneurysm (AAA) is a severe aortic disease for which no pharmacological interventions have yet been developed. This investigation focused on identifying protein-based therapeutic targets and assessing how proteins mediate the interplay between modifiable risk factors and AAA development.

METHODS

Causal inferences between plasma proteins and AAA were drawn using 2-sample Mendelian randomization, followed by comprehensive sensitivity testing, colocalization, and replication efforts. Further analyses included database interrogation, single-cell RNA data analysis, enrichment analysis, protein-protein interaction networks, and immunohistochemistry to map the tissue-specific expression of these proteins, their expression within AAA tissues, and their biological roles. Mediation Mendelian randomization was employed to evaluate the mediating effects of AAA-related proteins on the associations between AAA and 3 risk factors: hypertension, smoking, and obesity.

RESULTS

A total of 43 proteins were identified as having causal links to AAA. Colocalization analysis pinpointed 13 proteins with strong evidence of colocalization with AAA. Of these, the causal involvement of 10 proteins was substantiated by external validation data. Consistent evidence for PCSK9 (proprotein convertase subtilisin/kexin type 9), IL6R (interleukin-6R), ECM1 (extracellular matrix protein 1), and ANGPTL4 (angiopoietin-related protein 4) was further validated through tissue immunohistochemistry and blood data. Moreover, Mendelian randomization analysis identified 10 proteins as mediators of the influence of hypertension, smoking, and obesity on AAA development.

CONCLUSIONS

This analysis identifies 4 proteins (PCSK9, IL6R, ECM1, and ANGPTL4) as high-priority therapeutic targets for AAA and emphasizes the intermediary role of plasma proteins in linking hypertension, smoking, obesity, and AAA. Further investigations are needed to clarify the specific roles of these proteins in AAA pathology.

Dimethyl fumarate is repurposed to ameliorate aortic aneurysm and dissection in mice

Aortic aneurysm and dissection pose fatal threats but no effective drug therapies are available. Previous work has been directed to reduce risk factors or target key pathological events, but none of the translational efforts succeeds. Here, we attempt to repurpose dimethyl fumarate (DMF), an FDA-approved immunomodulatory drug for multiple sclerosis, for the treatment of aortic aneurysm and dissection. In three preclinical mouse models of abdominal aortic aneurysm (porcine pancreatic elastase perfusion or CaCl2 incubation) and thoracic aortic aneurysm and dissection (β-Aminopropionitrile feeding), DMF invariably protected mice from aneurysm growth, aortic dissection, rupture and death. Histological H&E and EVG staining demonstrated aortic architecture-preserving effects of DMF. Through transcriptome profiling and the connectivity map (CMap), we showed that DMF restored SRC-FAK signaling in aortic smooth muscle cells and increased collagen I turnover in the tunica media. Our work suggests the potential of DMF being repurposed for aortic aneurysm and dissection, and highlights the importance of SRC-FAK signaling in aortic homeostasis.

Identification of Macrophage-Related Biomarkers for Abdominal Aortic Aneurysm Through Combined Single-Cell Sequencing and Machine Learning

Purpose

The relationship between macrophages and the progression of abdominal aortic aneurysms (AAA) remains unclear, and effective biomarkers are lacking. In this study, we elucidated the mechanism whereby macrophages promote AAA development and identified associated biomarkers, with the goal of developing new targeted therapies and improving patient outcomes.

Patients and Methods

Differential expression analysis, weighted gene co-expression network analysis, and single-cell analysis were used to identify macrophage-related genes in an AAA dataset. Machine learning algorithms identified THBS1, HCLS1, DMXL2, and ZEB2 as key macrophage-related genes upregulated in AAA; these four hub genes were then used to construct a nomogram as an auxiliary tool for clinical diagnosis. Subsequent downstream single-cell and CellChat analyses were conducted to observe the interactions between macrophages and fibroblasts and analyze potential pathways.

Results

Single-cell validation confirmed enhanced THBS1 expression in macrophages in AAA. CellChat analysis revealed enhanced interactions between macrophages and fibroblasts in AAA through THBS1-CD47 signaling. Finally, an analysis of clinical samples from patients with AAA confirmed the high expression of THBS1 and CD47 in AAA and that THBS1 promotes the progression of AAA through the TNF-NFκB signaling pathway. Our findings reveal the THBS1-CD47 signaling pathway as a critical mechanism in macrophage-driven AAA progression, highlighting THBS1's potential as a therapeutic target.

Conclusion

Our findings highlight THBS1 as a potential driver of macrophage-mediated AAA formation and an important biomarker for AAA diagnosis. The study results would help in improving treatment outcomes in patients with AAA. These findings provide a foundation for the development of diagnostic tools and targeted therapies for AAA, potentially improving early detection and patient outcomes.

Comprehensive transcriptomic analysis unveils macrophage-associated genes for establishing an abdominal aortic aneurysm diagnostic model and molecular therapeutic framework

BACKGROUND

Abdominal aortic aneurysm (AAA) is a highly lethal cardiovascular disease. The aim of this research is to identify new biomarkers and therapeutic targets for the treatment of such deadly diseases.

METHODS

Single-sample gene set enrichment analysis (ssGSEA) and CIBERSORT algorithms were used to identify distinct immune cell infiltration types between AAA and normal abdominal aortas. Single-cell RNA sequencing data were used to analyse the hallmark genes of AAA-associated macrophage cell subsets. Six macrophage-related hub genes were identified through weighted gene co-expression network analysis (WGCNA) and validated for expression in clinical samples and AAA mouse models. We screened potential therapeutic drugs for AAA through online Connectivity Map databases (CMap). A network-based approach was used to explore the relationships between the candidate genes and transcription factors (TFs), lncRNAs, and miRNAs. Additionally, we also identified hub genes that can effectively identify AAA and atherosclerosis (AS) through a variety of machine learning algorithms.

RESULTS

We obtained six macrophage hub genes (IL-1B, CXCL1, SOCS3, SLC2A3, G0S2, and CCL3) that can effectively diagnose abdominal aortic aneurysm. The ROC curves and decision curve analysis (DCA) were combined to further confirm the good diagnostic efficacy of the hub genes. Further analysis revealed that the expression of the six hub genes mentioned above was significantly increased in AAA patients and mice. We also constructed TF regulatory networks and competing endogenous RNA networks (ceRNA) to reveal potential mechanisms of disease occurrence. We also obtained two key genes (ZNF652 and UBR5) through a variety of machine learning algorithms, which can effectively distinguish abdominal aortic aneurysm and atherosclerosis.

CONCLUSION

Our findings depict the molecular pharmaceutical network in AAA, providing new ideas for effective diagnosis and treatment of diseases.

Trimethylamine N-oxide promotes abdominal aortic aneurysm by inducing vascular inflammation and vascular smooth muscle cell phenotypic switching

OBJECTIVE

Inflammation and vascular smooth muscle cell (VSMC) phenotypic switching are implicated in the pathogenesis of abdominal aortic aneurysm (AAA). Trimethylamine N-oxide (TMAO) has emerged as a crucial risk factor in cardiovascular diseases, inducing vascular inflammation and calcification. We aimed to evaluate the effect of TMAO on the formation of AAA.

APPROACH AND RESULTS

Here, we showed that TMAO was elevated in plasma from AAA patients compared with nonaneurysmal subjects by liquid chromatography‒mass spectrometry (LC‒MS) detection. Functional studies revealed that increased TMAO induced by feeding a choline-supplemented diet promoted Ang II-induced AAA formation. Immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), and Western blot analyses revealed that TMAO induced macrophage infiltration and inflammatory factor release. Conversely, inhibition of TMAO by supplementation with DMB suppressed AAA formation and the inflammatory response. Molecular studies revealed that TMAO regulated VSMC phenotypic switching. Flow cytometry analyses showed that TMAO induces macrophage M1-type polarization. Furthermore, pharmacological intervention experiments suggested that the nuclear factor-κB (NF-κB) signaling pathway was critical for TMAO to trigger AAA formation.

CONCLUSIONS

TMAO promotes AAA formation by inducing vascular inflammation and VSMC phenotypic switching through activation of the NF-κB signaling pathway. Thus, TMAO is a prospective therapeutic AAA target.

Status of diagnosis and therapy of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are characterized by localized dilation of the abdominal aorta. They are associated with several serious consequences, including compression of adjacent abdominal organs, pain, treatment-related financial expenditure. The main complication of AAA is aortic rupture, which is responsible for about 200,000 deaths per year worldwide. An increasing number of researchers are dedicating their efforts to study AAA, resulting in significant progress in this field. Despite the commendable progress made thus far, there remains a lack of established methods to effectively decelerate the dilation of aneurysms. Therefore, further studies are imperative to expand our understanding and enhance our knowledge concerning AAAs. Although numerous factors are known to be associated with the occurrence and progression of AAA, the exact pathway of development remains unclear. While asymptomatic at most times, AAA features a highly unpredictable disease course, which could culminate in the highly deadly rupture of the aneurysmal aorta. Current guidelines recommend watchful waiting and lifestyle adjustment for smaller, slow-growing aneurysms, while elective/prophylactic surgical repairs including open repair and endovascular aneurysm repair are recommended for larger aneurysms that have grown beyond certain thresholds (55 mm for males and 50 mm for females). The latter is a minimally invasive procedure and is widely believed to be suited for patients with a poor general condition. However, several concerns have recently been raised regarding the postoperative complications and possible loss of associated survival benefits on it. In this review, we aimed to highlight the current status of diagnosis and treatment of AAA by an in-depth analysis of the findings from literatures.

Abdominal Aortic Aneurysms (Etiology, Epidemiology, and Natural History)

Abdominal aortic aneurysm is a potentially lethal condition that is decreasing in frequency as tobacco use declines. The exact etiology remains unknown, but smoking and other perturbations seem to trigger an inflammatory state in the tunica media. Male sex and advanced age are clear demographic risk factors for the development of abdominal aortic aneurysms. The natural history of this disease varies, but screening remains vital as it is rarely diagnosed on physical examination, and elective repair (most commonly done endovascularly) offers significant morbidity and mortality advantages over emergent intervention for aortic rupture.

Identification of a miRSNP Regulatory Axis in Abdominal Aortic Aneurysm by a Network and Pathway-Based Integrative Analysis

Abdominal aortic aneurysm (AAA) refers to local abnormal expansion of the abdominal aorta and mostly occurs in elderly men. MicroRNA (miRNA) is single-stranded RNA consisting of 18-25 nucleotides. It plays a key role in posttranscriptional gene expression and in the regulation of human functions and disease development. miRNA exerts its function mainly through the binding of complementary base pairs to the 3' regulatory region of mRNA transcripts. Therefore, miRNA-related single-nucleotide polymorphisms (miRSNPs) can affect miRNA expression and processing kinetics. miRSNPs can be classified based on their location: miRSNPs within miRNA-producing genes and miRSNPs within miRNA target genes. Increasing evidence indicates that miRSNPs play an important role in the pathogenic kinetics of cardiovascular diseases. The aim of this study was to identify potential miRNAs and integrate them into a miRSNP-based disease-related pathway network, the results of which are of great significance to the interpretation of the potential mechanisms and functions of miRSNPs in the pathogenesis of diseases.

Identification of biomarkers and analysis of infiltrated immune cells in stable and ruptured abdominal aortic aneurysms

Objectives

The mortality rate of abdominal aortic aneurysm (AAA) is extremely high in the older population. This study aimed to identify potential biomarkers of AAA and aortic rupture and analyze infiltration of immune cells in stable and ruptured AAA samples.

Methods

Raw data of GSE47472, GSE57691, and GSE98278 were downloaded. After data processing, the co-expression gene networks were constructed. Gene Ontology and pathway enrichment analysis of AAA- and aortic rupture-related gene modules were conducted using the Database for Annotation, Visualization, and Integrated Discovery. Gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA) were used for further enrichment analysis. The CIBERSORT tool was used to analyze the relative abundance of immune cells in samples. Differentially expressed immune-related genes were analyzed between different samples. Predictive models were constructed via extreme gradient boosting, and hub genes were identified according to feature importance.

Results

Blue and yellow modules were significantly related to AAA, and genes in these modules were associated with the aortic wall and immune response, respectively. In terms of aortic rupture, the most relevant module was significantly enriched in the inflammatory response. The results of GSEA and GSVA suggested that immune cells and the inflammatory response were involved in the development of AAA and aortic rupture. There were significant differences in the infiltration of immune cells and expression levels of immune-related genes among different samples. NFKB1 might be an important transcription factor mediating the inflammatory response of AAA and aortic rupture. After the construction of a predictive model, CD19, SELL, and CCR7 were selected as hub genes for AAA whereas OAS3, IFIT1, and IFI44L were identified as hub genes for aortic rupture.

Conclusion

Weakening of the aortic wall and the immune response both contributed to the development of AAA, and the inflammatory response was closely associated with aortic rupture. The infiltration of immune cells was significantly different between different samples. NFKB1 might be an important transcription factor in AAA and aortic rupture. CD19, SELL, and CCR7 had potential diagnostic value for AAA. OAS3, IFIT1, and IFI44L might be predictive factors for aortic rupture.

Platelet function changes in patients undergoing endovascular aortic aneurysm repair: Review of the literature

Patients with abdominal aortic aneurysm (AAA) have a higher risk of cardiovascular (CV) events, which seems to be associated with disturbed platelet (PLT) function. Endovascular aneurysm repair (EVAR) is an emerging, less-invasive treatment alternative to surgical AAA repair. Both platelet function abnormalities in patients with AAA and the effect of EVAR on platelet function are poorly understood. In this review, we aim to fill the gap regarding the effect of EVAR on PLT function in AAA patients by discussing PLT function disturbances in patients with AAA, PLT function changes after EVAR, evidence from clinical studies regarding PLT function before and after EVAR, and antiplatelet or and antithrombotic treatment in patients undergoing EVAR. The goal of our review is to summarize the contemporary knowledge and initiate further studies to better understand PLT function changes in patients undergoing EVAR, optimize the pharmacotherapy before and after EVAR and further improve outcomes in this group of patients.

Single-Cell Sequencing Analysis and Multiple Machine Learning Methods Identified G0S2 and HPSE as Novel Biomarkers for Abdominal Aortic Aneurysm

Identifying biomarkers for abdominal aortic aneurysms (AAA) is key to understanding their pathogenesis, developing novel targeted therapeutics, and possibly improving patients outcomes and risk of rupture. Here, we identified AAA biomarkers from public databases using single-cell RNA-sequencing, weighted co-expression network (WGCNA), and differential expression analyses. Additionally, we used the multiple machine learning methods to identify biomarkers that differentiated large AAA from small AAA. Biomarkers were validated using GEO datasets. CIBERSORT was used to assess immune cell infiltration into AAA tissues and investigate the relationship between biomarkers and infiltrating immune cells. Therefore, 288 differentially expressed genes (DEGs) were screened for AAA and normal samples. The identified DEGs were mostly related to inflammatory responses, lipids, and atherosclerosis. For the large and small AAA samples, 17 DEGs, mostly related to necroptosis, were screened. As biomarkers for AAA, G0/G1 switch 2 (G0S2) (Area under the curve [AUC] = 0.861, 0.875, and 0.911, in GSE57691, GSE47472, and GSE7284, respectively) and for large AAA, heparinase (HPSE) (AUC = 0.669 and 0.754, in GSE57691 and GSE98278, respectively) were identified and further verified by qRT-PCR. Immune cell infiltration analysis revealed that the AAA process may be mediated by T follicular helper (Tfh) cells and the large AAA process may also be mediated by Tfh cells, M1, and M2 macrophages. Additionally, G0S2 expression was associated with neutrophils, activated and resting mast cells, M0 and M1 macrophages, regulatory T cells (Tregs), resting dendritic cells, and resting CD4 memory T cells. Moreover, HPSE expression was associated with M0 and M1 macrophages, activated and resting mast cells, Tregs, and resting CD4 memory T cells. Additional, G0S2 may be an effective diagnostic biomarker for AAA, whereas HPSE may be used to confer risk of rupture in large AAAs. Immune cells play a role in the onset and progression of AAA, which may improve its diagnosis and treatment.

AAA Revisited: A Comprehensive Review of Risk Factors, Management, and Hallmarks of Pathogenesis

Despite declining incidence and mortality rates in many countries, the abdominal aortic aneurysm (AAA) continues to represent a life-threatening cardiovascular condition with an overall prevalence of about 2-3% in the industrialized world. While the risk of AAA development is considerably higher for men of advanced age with a history of smoking, screening programs serve to detect the often asymptomatic condition and prevent aortic rupture with an associated death rate of up to 80%. This review summarizes the current knowledge on identified risk factors, the multifactorial process of pathogenesis, as well as the latest advances in medical treatment and surgical repair to provide a perspective for AAA management.

Disturbed flow's impact on cellular changes indicative of vascular aneurysm initiation, expansion, and rupture: A pathological and methodological review

Aneurysms are malformations within the arterial vasculature brought on by the structural breakdown of the microarchitecture of the vessel wall, with aneurysms posing serious health risks in the event of their rupture. Blood flow within vessels is generally laminar with high, unidirectional wall shear stressors that modulate vascular endothelial cell functionality and regulate vascular smooth muscle cells. However, altered vascular geometry induced by bifurcations, significant curvature, stenosis, or clinical interventions can alter the flow, generating low stressor disturbed flow patterns. Disturbed flow is associated with altered cellular morphology, upregulated expression of proteins modulating inflammation, decreased regulation of vascular permeability, degraded extracellular matrix, and heightened cellular apoptosis. The understanding of the effects disturbed flow has on the cellular cascades which initiate aneurysms and promote their subsequent growth can further elucidate the nature of this complex pathology. This review summarizes the current knowledge about the disturbed flow and its relation to aneurysm pathology, the methods used to investigate these relations, as well as how such knowledge has impacted clinical treatment methodologies. This information can contribute to the understanding of the development, growth, and rupture of aneurysms and help develop novel research and aneurysmal treatment techniques.

Immune checkpoint programmed death-1 mediates abdominal aortic aneurysm and pseudoaneurysm progression

PURPOSE

The causes and pathogenetic mechanisms underlying abdominal aortic aneurysms (AAAs) and pseudoaneurysms are not fully understood. We hypothesized that inhibiting programmed death-1 (PD-1) can decrease AAA and pseudoaneurysm formation in mouse and rat models.

METHODS

Human AAA samples were examined in conjunction with an adventitial calcium chloride (CaCl2) application mouse model and an aortic patch angioplasty rat model. Single-dose PD-1 antibody (4 mg/kg) or BMS-1 (PD-1 inhibitor-1) (1 mg/kg) was administered by intraperitoneal (IP) or intraluminal injection. In the intramural injection group, PD-1 antibody was injected after CaCl2 incubation. The rats were divided into three groups: (1) the control group was only decellularized without other special treatment, (2) the PD-1 antibody-coated patch group, and (3) the BMS-1 coated patch group. Patches implanted in the rat abdominal aorta were harvested on day 14 after implantation and analyzed.

RESULTS

Immunohistochemical analysis showed PD-1-positive cells, PD-1 and CD3, PD-1 and CD68, and PD-1 and α-actin co-expressed in the human AAA samples. Intraperitoneal (IP) injection or intraluminal injection of PD-1antibody/BMS-1 significantly inhibited AAA progression. PD-1 antibody and BMS-1 were each successfully conjugated to decellularized rat thoracic artery patches, respectively, by hyaluronic acid. Patches coated with either humanized PD-1 antibody or BMS-1 can also inhibit pseudoaneurysm progression and inflammatory cell infiltration.

CONCLUSION

PD-1 pathway inhibition may be a promising therapeutic strategy for inhibiting AAA and pseudoaneurysm progression.

ADAM10 attenuates the development of abdominal aortic aneurysms in a mouse model

An abdominal aortic aneurysm (AAA) is a life-threatening disease associated with a high mortality rate. At present, surgery or minimally invasive interventions are used in clinical treatment, especially for small aneurysms. However, the benefits of surgical repair are not obvious, and AAA ruptures can be prevented by aneurysm therapy to inhibit the growth of small aneurysms. Therefore, evaluating effective drugs to treat small AAAs is urgently required. Chronic inflammation is the main pathological feature of aneurysmal tissues. The aim of the present study was to investigate the protective role and underlying mechanism of ADAM metallopeptidase domain 10 (ADAM10). In the present study, a mouse model of AAA was established via porcine pancreatic elastase perfusion for 5 min per day for 14 days. ADAM10 (6 mg/kg) was injected intraperitoneally following 3 days of porcine pancreatic elastase perfusion in the ADAM10 group and the treatment continued for 10 days. The maximum inner luminal diameters of the infrarenal abdominal aortas were measured using an animal ultrasound system. The levels of high mobility group box 1 (HMGB1) and soluble receptor for advanced glycosylation end products in serum samples were measured by ELISA. Hematoxylin and eosin and elastin van Gieson staining were performed to observe morphology, integrity of the elastin layers and elastin degradation. CD68 expression was detected by immunohistochemical staining. Reverse transcription-quantitative PCR and western blotting were used for detection of mRNA and protein levels. The gelatinolytic activities of MMP-2 and MMP-9 were quantified via gelatin zymography analysis. These results showed that ADAM10 inhibited HMGB1/RAGE/NF-κB signaling and MMP activity in the pathogenesis of pancreatic elastase-induced AAA, which provide insight into the molecular mechanism of AAA and suggested that ADAM10 may be a potential therapeutic target for AAA.

CRP immunodeposition and proteomic analysis in abdominal aortic aneurysm

OBJECTIVE

The molecular mechanisms of the degeneration of the aortic wall in abdominal aortic aneurysm (AAA) are poorly understood. The monomeric form of C-reactive protein (mCRP) is deposited in damaged cardiovascular organs and aggravates the prognosis; however, it is unknown whether mCRP is deposited in the degenerated aorta of abdominal aortic aneurysm (AAA). We investigated whether mCRP is deposited in AAA and examined the associated pathogenic signaling pathways.

METHODS

Twenty-four cases of AAA were analyzed and their histological features were compared according to the level of serum CRP and the degree of mCRP deposition. Proteomic analysis was performed in AAA cases with strong and diffuse CRP immunopositivity (n = 7) and those with weak, focal, and junctional CRP immunopositivity (n = 3).

RESULTS

mCRP was deposited in the aortic specimens of AAA in a characteristic pattern that coincided with the lesion of the diminished elastic layer of the aortic wall. High serum CRP level was associated with stronger mCRP immunopositivity and a larger maximal diameter of aortic aneurysm. Proteomic analysis in AAA showed that multiple proteins were differentially expressed according to mCRP immunopositivity. Also, ingenuity pathway analysis showed that pathways associated with atherosclerosis, acute phase response, complement system, immune system, and coagulation were enriched in AAA cases with high mCRP immunopositivity.

CONCLUSIONS

AAA showed a characteristic deposition of mCRP, and multiple potentially pathologic signaling pathways were upregulated in AAA cases with strong CRP immunopositivity. mCRP and the aforementioned pathological pathways may serve as targets for managing the progression of AAA.

Weighted Gene Co-Expression Network Analysis Reveals Key Genes and Potential Drugs in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a prevalent aortic disease that causes high mortality due to asymptomatic gradual expansion and sudden rupture. The underlying molecular mechanisms and effective pharmaceutical therapy for preventing AAA progression have not been fully identified. In this study, we identified the key modules and hub genes involved in AAA growth from the GSE17901 dataset in the Gene Expression Omnibus (GEO) database through the weighted gene co-expression network analysis (WGCNA). Key genes were further selected and validated in the mouse dataset (GSE12591) and human datasets (GSE7084, GSE47472, and GSE57691). Finally, we predicted drug candidates targeting key genes using the Drug-Gene Interaction database. Overall, we identified key modules enriched in the mitotic cell cycle, GTPase activity, and several metabolic processes. Seven key genes (CCR5, ADCY5, ADCY3, ACACB, LPIN1, ACSL1, UCP3) related to AAA progression were identified. A total of 35 drugs/compounds targeting the key genes were predicted, which may have the potential to prevent AAA progression.

A novel intramural TGF β 1 hydrogel delivery method to decrease murine abdominal aortic aneurysm and rat aortic pseudoaneurysm formation and progression

OBJECTIVES

Aneurysms are generally the result of dilation of all 3 layers of the vessel wall, and pseudoaneurysms are the result of localized extravasation of blood that is contained by surrounding tissue. Since there is still no recommended protocol to decrease aneurysm formation and progression, we hypothesised that intramural delivery of TGF β1 hydrogel can decrease aneurysm and pseudoaneurysm formation and progression.

MATERIALS

Male C57BL/6 J mice (12-14 wk), SD rats (200 g) and pig abdominal aortas were used, and hydrogels were fabricated by the interaction of sodium alginate (SA), hyaluronic acid (HA) and CaCO3.

METHODS

A CaCl2 adventitial incubation model in mice and a decellularized human great saphenous vein patch angioplasty model in rats were used. TGF β1 hydrogel was intramurally delivered after CaCl2 incubation in mice; at day 7, the abdomen in some mice was reopened, and TGF β1 hydrogel was injected intramurally into the aorta. In rats, TGF β1 hydrogel was delivered intramurally after patch angioplasty completion. Tissues were harvested at day 14 and analysed by histology and immunohistochemistry staining. The pig aorta was also intramurally injected with hydrogel.

RESULTS

In mice, rhodamine hydrogel was still found between the medium and adventitia at day 14. In the mouse aneurysm model, there was a thicker wall and smaller amount of elastin breaks in the TGF β1 hydrogel-delivered groups both at day 0 and day 7 after CaCl2 incubation, and there were larger numbers of p-smad2- and TAK1-positive cells in the TGF β1 hydrogel-injected groups. In the rat decellularized human saphenous vein patch pseudoaneurysm model, there was a higher incidence of pseudoaneurysm formation when the patch was decellularized using 3% SDS, and delivery of TGF β1 hydrogel could effectively decrease the formation of pseudoaneurysm formation and increase p-smad2 and TAK1 expression. In pig aortas, hydrogels can be delivered between the medium and adventitia easily and successfully.

CONCLUSIONS

Intramural delivery of TGF β1 hydrogel can effectively decease aneurysm and pseudoaneurysm formation and progression in both mice and rats, and pig aortas can also be successfully intramurally injected with hydrogel. This technique may be a promising drug delivery method and therapeutic choice to decrease aneurysm and pseudoaneurysm formation and progression in the clinic.

A non-coding genetic variant associated with abdominal aortic aneurysm alters ERG gene regulation

Abdominal aortic aneurysm (AAA) is a major cause of sudden death in the elderly. While AAA has some overlapping genetic and environmental risk factors with atherosclerosis, there are substantial differences, and AAA-specific medication is lacking. A recent meta-analysis of genome-wide association studies has identified four novel single-nucleotide polymorphisms (SNPs) specifically associated with AAA. Here, we investigated the gene regulatory function for one of four non-coding SNPs associated with AAA, rs2836411, which is located in an intron of the ERG gene. Rs2836411 resides within a >70 kb super-enhancer that has high levels of H3K27ac and H3K4me1 in vascular endothelial and haematopoietic cell types. Enhancer luciferase assays in cell lines showed that the risk allele significantly alters enhancer activity. The risk allele also correlates with reduced ERG expression in aortic and other vascular tissues. To identify whether rs2836411 directly contacts the promoters of ERG and/or of genes further away, we performed allele-specific circular chromosome conformation capture sequencing. In vascular endothelial cells, which express ERG, the SNP region interacts highly within the super-enhancer, while in vascular smooth muscle cells, which do not express ERG, the interactions are distributed across a wider region that includes neighbouring genes. Furthermore, the risk allele has fewer interactions within the super-enhancer compared to the protective allele. In conclusion, our results indicate that rs2836411 likely affects ERG expression by altering enhancer activity and changing local chromatin interactions. ERG is involved in vascular development, angiogenesis, and inflammation in atherosclerosis; therefore mechanistically, rs2836411 could contribute to AAA by modulating ERG levels.

A Novel Hypothesis: A Role for Follicle Stimulating Hormone in Abdominal Aortic Aneurysm Development in Postmenopausal Women

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta, which can potentially be fatal due to exsanguination following rupture. Although AAA is less prevalent in women, women with AAA have a more severe AAA progression compared to men as reflected by enhanced aneurysm growth rates and a higher rupture risk. Women are diagnosed with AAA at an older age than men, and in line with increased osteoporosis and cardiovascular events, the delayed AAA onset has been attributed to the reduction of the protective effect of oestrogens during the menopausal transition. However, new insights have shown that a high follicle stimulating hormone (FSH) level during menopause may also play a key role in those diseases. In this report we hypothesize that FSH may aggravate AAA development and progression in postmenopausal women via a direct and/or indirect role, promoting aorta pathology. Since FSH receptors (FSHR) are reported on many other cell types than granulosa cells in the ovaries, it is feasible that FSH stimulation of FSHR-bearing cells such as aortic endothelial cells or inflammatory cells, could promote AAA formation directly. Indirectly, AAA progression may be influenced by an FSH-mediated increase in osteoporosis, which is associated with aortic calcification. Also, an FSH-mediated decrease in cholesterol uptake by the liver and an increase in cholesterol biosynthesis will increase the cholesterol level in the circulation, and subsequently promote aortic atherosclerosis and inflammation. Lastly, FSH-induced adipogenesis may lead to obesity-mediated dysfunction of the microvasculature of the aorta and/or modulation of the periaortic adipose tissue. Thus the long term increased plasma FSH levels during the menopausal transition may contribute to enhanced AAA disease in menopausal women and could be a potential novel target for treatment to lower AAA-related events in women.

Involvement of Myeloid Cells and Noncoding RNA in Abdominal Aortic Aneurysm Disease

Significance: Abdominal aortic aneurysm (AAA) is a potentially fatal condition, featuring the possibility of high-mortality rupture. To date, prophylactic surgery by means of open surgical repair or endovascular aortic repair at specific thresholds is considered standard therapy. Both surgical options hold different risk profiles of short- and long-term morbidity and mortality. Targeting early stages of AAA development to decelerate disease progression is desirable. Recent Advances: Understanding the pathomechanisms that initiate formation, maintain growth, and promote rupture of AAA is crucial to developing new medical therapeutic options. Inflammatory cells, in particular macrophages, have been investigated for their contribution to AAA disease for decades, whereas evidence on lymphocytes, mast cells, and neutrophils is sparse. Recently, there has been increasing interest in noncoding RNAs (ncRNAs) and their involvement in disease development, including AAA. Critical Issues: The current evidence on myeloid cells and ncRNAs in AAA largely originates from small animal models, making clinical extrapolation difficult. Although it is feasible to collect surgical human AAA samples, these tissues reflect end-stage disease, preventing examination of critical mechanisms behind early AAA formation. Future Directions: Gaining more insight into how myeloid cells and ncRNAs contribute to AAA disease, particularly in early stages, might suggest nonsurgical AAA treatment options. The utilization of large animal models might be helpful in this context to help bridge translational results to humans.

Genetic and Epigenetic Mechanisms Underlying Vascular Smooth Muscle Cell Phenotypic Modulation in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) refers to the localized dilatation of the infra-renal aorta, in which the diameter exceeds 3.0 cm. Loss of vascular smooth muscle cells, degradation of the extracellular matrix (ECM), vascular inflammation, and oxidative stress are hallmarks of AAA pathogenesis and contribute to the progressive thinning of the media and adventitia of the aortic wall. With increasing AAA diameter, and left untreated, aortic rupture ensues with high mortality. Collective evidence of recent genetic and epigenetic studies has shown that phenotypic modulation of smooth muscle cells (SMCs) towards dedifferentiation and proliferative state, which associate with the ECM remodeling of the vascular wall and accompanied with increased cell senescence and inflammation, is seen in in vitro and in vivo models of the disease. This review critically analyses existing publications on the genetic and epigenetic mechanisms implicated in the complex role of SMCs within the aortic wall in AAA formation and reflects the importance of SMCs plasticity in AAA formation. Although evidence from the wide variety of mouse models is convincing, how this knowledge is applied to human biology needs to be addressed urgently leveraging modern in vitro and in vivo experimental technology.

Background and Proposed Design for a Metformin Abdominal Aortic Aneurysm Suppression Trial

Abdominal aortic aneurysm (AAA) may lead to rupture and death if left untreated. While endovascular or surgical repair is generally recommended for AAA greater than 5–5.5 cm, the vast majority of aneurysms detected by screening modalities are smaller than this threshold. Once discovered, there would be a significant potential benefit in suppressing the growth of these small aneurysms in order to obviate the need for repair and mitigate rupture risk. Patients with diabetes, in particular those taking the oral hypoglycaemic medication metformin, have been shown to have lower incidence, growth rate, and rupture risk of AAA. Metformin therefore represents a widely available, non-toxic, potential inhibitor of AAA growth, but thus far no prospective clinical studies have evaluated this. Here, we present the background, rationale, and design for a randomised, double-blind, placebo-controlled clinical trial of metformin for growth suppression in patients with small AAA.

Lack of an effective drug therapy for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) rupture is a common cause of death in adults. Current AAA treatment is by open surgical or endovascular aneurysm repair. Rodent model and human epidemiology, and genetic and observational studies over the last few decades have highlighted the potential of a number of drug therapies, including medications that lower blood pressure, correct dyslipidaemia, or inhibit thrombosis, inflammation or matrix remodelling, as approaches to managing small AAA. This review summarizes prior AAA pathogenesis data from animal and human studies aimed at identifying targets for the development of drug therapies. The review also systematically assesses past randomized placebo-controlled drug trials in patients with small AAAs. Eleven previously published randomized-controlled clinical trials testing different drug therapies aimed at slowing AAA progression were identified. Five of the trials tested antibiotics and three trials assessed medications that lower blood pressure. Meta-analyses of these trials suggested that neither of these approaches limit AAA growth. Allocation to blood pressure-lowering medication was associated with a small reduction in AAA rupture or repair, compared to placebo (relative risk 0.94, 95% confidence intervals 0.89, 1.00, P = 0.047). Three further trials assessed the effect of a mast cell inhibitor, fibrate or platelet aggregation inhibition and reported no effect on AAA growth or clinical events. Past trials were noted to have a number of design issues, particularly small sample sizes and limited follow-up. Much larger trials are needed to properly test potential therapeutic approaches if a convincingly effective medical therapy for AAA is to be identified.

Spermidine Suppresses Development of Experimental Abdominal Aortic Aneurysms

Background

The protective effects of polyamines on cardiovascular disease have been demonstrated in many studies. However, the roles of spermidine, a natural polyamine, in abdominal aortic aneurysm (AAA) disease have not been studied. In this study, we investigated the influence and potential mechanisms of spermidine treatment on experimental AAA disease.

Methods and Results

Experimental AAAs were induced in 8‐ to 10‐week‐old male C57BL/6J mice by transient intra‐aortic infusion of porcine pancreatic elastase. Spermidine was administered via drinking water at a concentration of 3 mmol/L. Spermidine treatment prevented experimental AAA formation with preservation of medial elastin and smooth muscle cells. In immunostaining, macrophages, T cells, neutrophils, and neovessels were significantly reduced in aorta of spermidine‐treated, as compared with vehicle‐treated elastase‐infused mice. Additionally, flow cytometric analysis showed that spermidine treatment reduced aortic leukocyte infiltration and circulating inflammatory cells. Furthermore, we demonstrated that spermidine treatment promoted autophagy‐related proteins in experimental AAAs using Western blot analysis, immunostaining, and transmission electron microscopic examination. Autophagic function was evaluated for human abdominal aneurysmal and nonaneurysmal adjacent aortae from AAA patients using Western blot analysis and immunohistochemistry. Dysregulated autophagic function, as evidenced by increased SQSTM1/p62 protein and phosphorylated mTOR, was found in aneurysmal, as compared with nonaneurysmal, aortic segments.

Conclusions

Our results suggest that spermidine supplementation limits experimental AAA formation associated with preserved aortic structural integrity, attenuated aortic inflammatory infiltration, reduced circulating inflammatory monocytes, and increased autophagy‐related proteins. These findings suggest that spermidine may be a promising treatment for AAA disease.

Bazedoxifene Attenuates Abdominal Aortic Aneurysm Formation via Downregulation of Interleukin-6/Glycoprotein 130/Signal Transducer and Activator of Transcription 3 Signaling Pathway in Apolipoprotein E-Knockout Mice

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by aortic dilatation and predominantly affects an elderly population. Accumulating evidence suggests that Interleukin-6 (IL-6) and the signal transducer and activator of transcription 3 (STAT3) play an important role in formation of AAAs. However, it remains unclear whether Bazedoxifene (BAZ) could suppress the activation of IL-6/GP130/STAT3 in vascular cells and the formation of AAA. Here we explored the effect of BAZ on AngII-stimulated AAA formation. ApoE^–/– mice infused with AngII for 28 days using osmotic minipumps were treated with placebo or 5mg/kg BAZ. In our results most of the AngII-induced mice developed AAA with exacerbated inflammation, degradation of elastin fibers, STAT3 phosphorylation, and increased expression of matrix metalloproteinases (MMPs). These effects were markedly attenuated by BAZ. Furthermore, BAZ suppressed the stimuli-induced (IL-6 or AngII) expression of P-STAT3, MMP2 and MMP9 in vascular smooth muscle cells (VSMCs). BAZ inhibited wound healing, colony formation and suppressed STAT3 nuclear translocation in vitro. In conclusion, these results indicated that BAZ downregulated IL-6/GP130/STAT3 signaling and interfered with AAA formation induced by AngII in ApoE^–/– mice, which indicates a novel potential strategy for the prevention and therapy of AAA.

Statins Reduce Abdominal Aortic Aneurysm Growth, Rupture, and Perioperative Mortality: A Systematic Review and Meta-Analysis

Background

There are no recognized pharmacological treatments for abdominal aortic aneurysms (AAA), although statins are suggested to be beneficial. We sought to summarize the literature regarding the effects of statins on human AAA growth, rupture, and 30‐day mortality.

Methods and Results

We conducted a systematic review and meta‐analysis of randomized and observational studies using the Cochrane CENTRAL database, MEDLINE, and EMBASE up to June 15, 2018. Review, abstraction, and quality assessment were conducted by 2 independent reviewers, and a third author resolved discrepancies. Pooled mean differences and odds ratios with 95% confidence intervals were calculated using random effects models. Heterogeneity was quantified using the I² statistic, and publication bias was assessed using funnel plots. Our search yielded 911 articles. One case‐control and 21 cohort studies involving 80 428 patients were included. The risk of bias was low to moderate. Statin use was associated with a mean AAA growth rate reduction of 0.82 mm/y (95% confidence interval 0.33, 1.32, P=0.001, I²=86%). Statins were also associated with a lower rupture risk (odds ratio 0.63, 95% confidence interval 0.51, 0.78, P<0.0001, I²=27%), and preoperative statin use was associated with a lower 30‐day mortality following elective AAA repair (odds ratio 0.55, 95% confidence interval 0.36, 0.83, P=0.005, I²=57%).

Conclusions

Statin therapy may be associated with reduction in AAA progression, rupture, and lower rates of perioperative mortality following elective AAA repair. These data argue for widespread statin use in AAA patients.

Clinical Trial Registration

URL: http://www.crd.york.ac.uk. Unique identifier: CRD42017056480.

Current Status and Perspectives on Pharmacologic Therapy for Abdominal Aortic Aneurysm

Background:

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

Objective:

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

Results:

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

Conclusion:

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

A Pilot Study of Protein Microarray for Simultaneous Analysis of 274 Cytokines Between Abdominal Aortic Aneurysm and Normal Aorta

Cytokines play an important role in the pathogenesis of abdominal aortic aneurysm (AAA). We evaluated the cytokine expression profile of large AAA walls using a 274-cytokine protein array. We hypothesized that AAAs are characterized by an inflammatory, chemotactic cytokine profile. We investigated the cytokine expression profile of 12 patients with AAA and 6 nonaneurysmal controls using an antibody-based protein array. The array generated antibodies against homogenized human aortic tissues to validate the cytokines differentially expressed in AAAs and normal aortas. Data were quantified using fluorescent signal intensities and statistically analyzed by the t test. Fifty-nine cytokines were differentially expressed between the AAA and control samples. Of the 35 selected cytokines that had relative expression >1000, 29 were significantly higher and 6 were lower in AAA samples than in controls. They respectively belonged to CC chemokines, CXC chemokines, pro-inflammatory cytokines, growth factors, proteolytic proteins and inhibitors, and cell adhesion cytokines. Our results show that distinct cytokines are involved in AAAs and suggest that the pathways involving these cytokines may be associated with the pathogenesis and development of AAAs. These findings, if confirmed by larger studies, may suggest treatment targets.

Abdominal aortic aneurysms

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

CXCL8 hyper-signaling in the aortic abdominal aneurysm

There are indications for elevated CXCL8 levels in abdominal aortic aneurysm disease (AAA). CXCL8 is concurrently involved in neutrophil-mediated inflammation and angiogenesis, two prominent and distinctive characteristics of AAA. As such we considered an evaluation of a role for CXCL8 in AAA progression relevant. ELISA's, real time PCR and array analysis were used to explore CXCL8 signaling in AAA wall samples. A role for CXCL8 in AAA disease was tested through the oral CXCR1/2 antagonist DF2156A in the elastase model of AAA disease. There is an extreme disparity in aortic wall CXCL8 content between AAA and aortic atherosclerotic disease (median [IQR] aortic wall CXCL8 content: 425 [141-1261] (AAA) vs. 23 [2.8-89] (atherosclerotic aorta) µg/g protein (P < 1 · 10^-14)), and abundant expression of the CXCR1 and 2 receptors in AAA. Array analysis followed by pathway analysis showed that CXCL8 hyper-expression in AAA is followed increased by IL-8 signaling (Z-score for AAA vs. atherosclerotic control: 2.97, p < 0.0001). Interference with CXCL8 signaling through DF2156A fully abrogated AAA formation and prevented matrix degradation in the murine elastase model of AAA disease (p < 0.001). CXCL8-signaling is a prominent and distinctive feature of AAA, interference with the pathway constitutes a promising target for medical stabilization of AAA.

Molecular Fingerprint for Terminal Abdominal Aortic Aneurysm Disease

Background

Clinical decision making in abdominal aortic aneurysms (AAA) relies completely on diameter. At this point, improved decision tools remain an unmet medical need. Our goal was to identify changes at the molecular level specifically leading up to AAA rupture.

Methods and Results

Aortic wall tissue specimens were collected during open elective (eAAA; n=31) or emergency repair of ruptured AAA (rAAA; n=17), and gene expression was investigated using microarrays. Identified candidate genes were validated with quantitative real‐time polymerase chain reaction in an independent sample set (eAAA: n=46; rAAA: n=18). Two gene sets were identified, 1 set containing 5 genes linked to terminal progression, that is, positively associated with progression of larger AAA, and with rupture (HILPDA,ANGPTL4,LOX,SRPX2,FCGBP), and a second set containing 5 genes exclusively upregulated in rAAA (ADAMTS9,STC1,GFPT2,GAL3ST4,CCL4L1). Genes in both sets essentially associated with processes related to impaired tissue remodeling, such as angiogenesis and adipogenesis. In gene expression experiments we were able to show that upregulated gene expression for identified candidate genes is unique for AAA. Functionally, the selected upregulated factors converge at processes coordinated by the canonical HIF‐1α signaling pathway and are highly expressed in fibroblasts but not inflammatory cells of the aneurysmatic wall. Histological quantification of angiogenesis and exploration of the HIF‐1α network in rAAA versus eAAA shows enhanced microvessel density but also clear activation of the HIF‐1α network in rAAA.

Conclusions

Our study shows a specific molecular fingerprint for terminal AAA disease. These changes appear to converge at activation of HIF‐1α signaling in mesenchymal cells. Aspects of this cascade might represent targets for rupture risk assessment.

Adventitial adipogenic degeneration is an unidentified contributor to aortic wall weakening in the abdominal aortic aneurysm

OBJECTIVE

The processes driving human abdominal aortic aneurysm (AAA) progression are not fully understood. Although antiinflammatory and proteolytic strategies effectively quench aneurysm progression in preclinical models, so far all clinical interventions failed. These observations hint at an incomplete understanding of the processes involved in AAA progression and rupture. Interestingly, strong clinical and molecular associations exist between popliteal artery aneurysms (PAAs) and AAAs; however, PAAs have an extremely low propensity to rupture. We thus reasoned that differences between these aneurysms may provide clues toward (auxiliary) processes involved in AAA-related wall debilitation. A better understanding of the pathophysiologic processes driving AAA growth can contribute to pharmaceutical treatments in the future.

METHODS

Aneurysmal wall samples were collected during open elective and emergency repair. Control perirenal aorta was obtained during kidney transplantation, and reference popliteal tissue obtained from the anatomy department. This study incorporates various techniques including (immuno)histochemistry, Western Blot, quantitative polymerase chain reaction, microarray, and cell culture.

RESULTS

Histologic evaluation of AAAs, PAAs, and control aorta shows extensive medial (PAA) and transmural fibrosis (AAA), and reveals abundant adventitial adipocytes aggregates as an exclusive phenomenon of AAAs (P < .001). Quantitative polymerase chain reaction, immunohistochemistry, Western blotting, and microarray analysis showed enrichment of adipogenic mediators (C/EBP family P = .027; KLF5 P < .000; and peroxisome proliferator activated receptor-γ, P = .032) in AAA tissue. In vitro differentiation tests indicated a sharply increased adipogenic potential of AAA adventitial mesenchymal cells (P < .0001). Observed enrichment of adipocyte-related genes and pathways in ruptured AAA (P < .0003) supports an association between the extent of fatty degeneration and rupture.

CONCLUSIONS

This translational study identifies extensive adventitial fatty degeneration as an ignored and distinctive feature of AAA disease. Enrichment of adipocyte genesis and adipocyte-related genes in ruptured AAA point to an association between the extent of fatty degeneration and rupture. This observation may (partly) explain the failure of medical therapy and could provide a lead for pharmaceutical alleviation of AAA progression.

Impact of chronic obstructive pulmonary disease on patients with aortic aneurysms: a nationwide retrospective cohort study in Taiwan

OBJECTIVES

Aortic aneurysm (AA) is a leading cause of death worldwide. Chronic obstructive pulmonary disease (COPD) is a risk factor for AA, and the prognoses of COPD patients with AA who underwent/did not undergo an operation warrant investigation.

DESIGN

A nationwide retrospective cohort study.

SETTING

We included patients with AA older than 18 years who received their first AA diagnosis between 2005 and 2011 in Taiwan.

PARTICIPANTS

This study enrolled 3263 COPD patients with AA before propensity score matching and 2127 COPD patients with AA after propensity score matching.

OUTCOME MEASURES

The main outcomes were all-cause mortality and rehospitalisation for AA or operation. The outcomes of COPD patients with AA and COPD patients without AA during an 8-year follow-up period were examined using Cox proportional hazards models.

RESULTS

In the AA population, patients with COPD showed higher rates of mortality and rehospitalisation than patients without COPD with adjusted HRs of 1.12 (95% CI 1.03 to 1.22) and 1.11 (95% CI 1.01 to 1.23), respectively, after propensity score matching. Analysis of the patients who underwent an operation revealed that the rates of mortality of COPD and non-COPD patients were not significantly different. In contrast, among the patients who did not receive an operation, patients with COPD showed a higher mortality rate than patients without COPD with an adjusted HR of 1.11 (95% CI 1.0 to 1.22).

CONCLUSIONS

The outcomes of COPD patients with AA undergoing an operation were improved, but the mortality rate of non-COPD patients with AA remained high. An effective treatment to reduce mortality in this group warrants further investigation.

Inhibition of endoplasmic reticulum stress signaling pathway: A new mechanism of statins to suppress the development of abdominal aortic aneurysm

Background

Abdominal aortic aneurysm (AAA) is a potentially lethal disease with extremely poor survival rates once the aneurysm ruptures. Statins may exert beneficial effects on the progression of AAA. However, the underlying mechanism is still not known. The purpose of the present study is to investigate whether statin could inhibit AAA formation by inhibiting the endoplasmic reticulum (ER) stress signal pathway.

Methods

A clinically relevant AAA model was induced in Apolipoprotein E-deficient (ApoE^−/−) mice, which were infused with angiotensin II (Ang II) for 28 days. These mice were randomly divided into following 4 groups: saline infusion alone; Ang II infusion alone; Ang II infusion plus Atorvastatin (20mg/kg/d); and Ang II infusion plus Atorvastatin (30mg/kg/d). Besides, another AAA model was induced in C57 mice with extraluminal CaCl₂, which were divided into 3 groups: sham group, CaCl₂-induced AAA group, and CaCl₂-induced AAA plus atorvastatin (20mg/kg/d) group. Then, aortic tissue was excised for further examinations, respectively. In vitro studies, Ang II with or without simvastatin treatment were applied to the vascular smooth muscle cells (VSMCS) and Raw 264.7 cells. The ER stress signal pathway, apoptosis and inflammatory response were evaluated by in vivo and in vitro assays.

Results

We found that higher dose of atorvastatin can effectively suppress the development and progression of AAA induced by Ang II or CaCl₂. Mechanistically, the activation of ER stress and inflammatory response were found involved in Ang II-induced AAA formation. The atorvastatin infusion significantly reduced ER stress signaling proteins, the number of apoptotic cells, and the activation of Caspase12 and Bax in the Ang II-induced ApoE^−/− mice, compared with mice treated by Ang II alone. Furthermore, proinflammatory cytokines such as IL-6, IL-8, IL-1β were all remarkably inhibited after atorvastatin treatment. In vitro, the inhibitory effect of simvastatin on the ER stress signal pathway could be observed in both vascular smooth muscle cells and macrophages, and these inhibitory effects of statin were in a dose-dependent manner. In addition, apoptosis was induced with Ang II treatment. The maximal inhibitory effect of simvastatin on apoptosis was observed at 10 μmol/l.

Conclusions

We conclude that higher dose of statin can effectively suppress the development of AAA, and reduce ER stress, ER stress-associated apoptosis signaling pathways, and inflammatory response. These findings reveal a new mechanism underlying the inhibitory effect of statin on AAA formation/progression.

Abdominal aortic aneurysm and omega-3 polyunsaturated fatty acids: Mechanisms, animal models, and potential treatment

Abdominal aortic aneurysm (AAA) is an inflammatory disease associated with macrophage accumulation in the adventitia, oxidative stress, medial elastin degradation and aortic dilation. Progression of AAA is linked to increased risk of rupture, which carries a high mortality rate. Drug therapies trialled to date lack efficacy and although aneurysm repair is available for patients with large aneurysm, peri-surgical morbidity and mortality have been widely reported. Recent studies using rodent models of AAA suggest that long chain omega-3 polyunsaturated fatty acids (LC n-3 PUFAs) and their metabolites can moderate inflammation and oxidative stress perpetuated by infiltrating macrophages and intervene in the destruction of medial elastin. This review examines evidence from these animal studies and related reports of inhibition of inflammation and arrest of aneurysm development following prophylactic supplementation with LC n-3 PUFAs. The efficacy of LC n-3 PUFAs for management of existing aneurysm is unclear and further investigations involving human clinical trials are warranted.

Molecular Imaging of Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAAs) represent a vascular disease with severe complications. AAAs are currently the overall 10th leading cause of death in western countries and their incidence is rising. Although different diagnostic techniques are currently available in clinical practice, including ultrasound (US), magnetic resonance imaging (MRI), and computed tomography (CT), imaging-based prediction of life-threatening complications such as aneurysm-rupture remains challenging. Molecular imaging provides a novel diagnostic approach for in vivo visualization of biological processes and pathological alterations at a cellular and molecular level. Its overall aim is to improve our understanding of disease pathogenesis and to facilitate novel diagnostic pathways. This review outlines recent preclinical and clinical developments in molecular MRI, positron emission tomography (PET), and single-photon emission computed tomography (SPECT) for imaging of AAAs.

IL-6: A Janus-like factor in abdominal aortic aneurysm disease

BACKGROUND AND AIMS

An abdominal aortic aneurysm (AAA) is part of the atherosclerotic spectrum of diseases. The disease is hallmarked by a comprehensive localized inflammatory response with striking IL-6 hyperexpression. IL-6 is a multifaceted cytokine that, depending on the context, acts as a pro- or anti-inflammatory factor. In this study, we explore a putative role for IL-6 in AAA disease.

METHODS

ELISA's, Western blot analysis, real time PCR and array analysis were used to investigate IL-6 expression and signaling in aneurysm wall samples from patients undergoing elective AAA repair. A role for IL-6 in AAA disease was tested through IL-6 neutralization experiments (neutralizing antibody) in the elastase model of AAA disease.

RESULTS

We confirmed an extreme disparity in aortic wall IL-6 content between AAA and atherosclerotic disease (median [5th-95th percentile] aortic wall IL-6 content: 281.6 [0.0-1820.8] (AAA) vs. 1.9 [0.0-37.8] μg/g protein (atherosclerotic aorta), (p < 0.001). Array analysis followed by pathway analysis showed that IL-6 hyper-expression is followed by increased IL-6 signaling (p < 0.000039), an observation confirmed by higher aneurysm wall pSTAT3 levels, and SOCS1 and SOCS3 mRNA expression, (p < 0.018). Remarkably, preventive IL-6 neutralization i.e. treatment started one day prior to the elastase-induction resulted in >40% 7-day mortality due to aortic rupture. In contrast, delayed IL-6 neutralization (i.e. neutralization started at day 4 after elastase induction) did not result in ruptures, and quenched AAA growth (p < 0.021).

CONCLUSIONS

AAA disease is characterized by increased IL-6 signaling. In the context of the elastase model of AAA disease, IL-6 appears a multi-faceted factor, protective upon acute injury, but negatively involved in the perpetuation of the disease process.

Inflammation as a Predictor of Abdominal Aortic Aneurysm Growth and Rupture: A Systematic Review of Imaging Biomarkers

BACKGROUND

Methods are required to identify abdominal aortic aneurysms (AAAs) at increased risk of rupture. Inflammatory characteristics of AAA can be visualised using advanced imaging techniques and have been proposed as potential predictors of aneurysm progression. The objective of this review was to determine which inflammatory imaging biomarkers are associated with AAA growth and rupture.

METHODS

A systematic review was carried out in accordance with the PRISMA guidelines. The electronic databases of Medline (PubMed), Embase, and the Cochrane Library were searched up to January 1, 2016 for studies to determine the potential association between inflammatory imaging biomarkers and AAA growth or rupture.

RESULTS

Seven studies were included, comprising 202 AAA patients. (18)F-fluoro-deoxy-glucose positron emission tomography ((18)F-FDG PET-CT) was evaluated in six studies. Magnetic resonance imaging with ultrasmall superparamagnetic particles of iron oxide (USPIO-MRI) was evaluated in one study. Two of six (18)F-FDG PET-CT studies reported a significant negative correlation (r=.383, p = .015) or a significant negative association (p = .04). Four of six (18)F-FDG PET-CT studies reported no significant association between (18)F-FDG uptake and AAA growth. The single study investigating USPIO-MRI demonstrated that AAA growth was three times higher in patients with focal USPIO uptake in the AAA wall compared to patients with diffuse or no USPIO uptake in the wall (0.66 vs. 0.24 vs. 0.22 cm/y, p = .020). In the single study relating (18)F-FDG uptake results to AAA rupture, the association was not significant.

CONCLUSIONS

Current evidence shows contradictory associations between (18)F-FDG uptake and AAA growth. Data on the association with rupture are insufficient. Based on the currently available evidence, neither (18)F-FDG PET-CT nor USPIO-MRI can be implemented as growth or rupture prediction tools in daily practice. The heterogeneous results reflect the complex and partially unclear relationship between inflammatory processes and AAA progression.