Animal Models Used to Explore Abdominal Aortic Aneurysms: A Systematic Review

Porphyromonas gingivalis GroEL accelerates abdominal aortic aneurysm formation by matrix metalloproteinase-2 SUMOylation in vascular smooth muscle cells: A novel finding for the activation of MMP-2

Infection is a known cause of abdominal aortic aneurysm (AAA), and matrix metalloproteases-2 (MMP-2) secreted by vascular smooth muscle cells (SMCs) plays a key role in the structural disruption of the middle layer of the arteries during AAA progression. The periodontal pathogen Porphyromonas gingivalis is highly associated with the progression of periodontitis. GroEL protein of periodontal pathogens is an important virulence factor that can invade the body through either the bloodstream or digestive tract and is associated with numerous systemic diseases. Although P. gingivalis aggravates AAA by increasing the expression of MMP-2 in animal studies, the molecular mechanism through which P. gingivalis regulates the expression of MMP-2 is still unknown and requires further investigation. In this study, we first confirmed through animal experiments that P. gingivalis GroEL promotes MMP-2 secretion from vascular SMCs, thereby aggravating Ang II-induced aortic remodeling and AAA formation. In addition, rat vascular SMCs and A7r5 cells were used to investigate the underlying mechanisms in vitro. The results demonstrated that GroEL can promote the interaction between the K639 site of MMP-2 and SUMO-1, leading to MMP-2 SUMOylation, which inhibits the reoccurrence of non-K639-mediated monoubiquitylation. Hence, the monoubiquitylation-mediated lysosomal degradation of MMP-2 is inhibited, consequently promoting MMP-2 stability and production. SUMOylation may facilitate intra-endoplasmic reticulum (ER) and Golgi trafficking of MMP-2, thereby enhancing its transport capacity. In conclusion, this is the first report demonstrating the presence of a novel posttranslational modification, SUMOylation, in the MMP family, suggesting that P. gingivalis GroEL may exacerbate AAA formation by increasing MMP-2 production through SUMOylation in vascular SMCs. This study also provides a novel perspective on the role of SUMOylation in MMP-2-induced systemic diseases.

The effect of edoxaban on apoptosis in an abdominal aortic aneurysm model in rats

Background

This study aimed to evaluate the effects of edoxaban, which is used in venous thrombosis, systemic embolism, and stroke, on an aortic aneurysm model and to demonstrate the pharmacokinetic and molecular effects of edoxaban through the induction of apoptosis.

Methods

In this double-blind experimental study, 21 Wistar albino male rats (mean weight: 290 g; range, 280 to 300 g) were divided into three groups: the sham group (n=7), the abdominal aortic aneurysm (AAA) group (n=7), and the AAA-edoxaban group (n=7). Edoxaban 10 mg/kg was given to the AAA-edoxaban group by oral gavage daily for 30 days. At the end of 30 days, the aneurysmal aorta was surgically removed and histologically examined. The abdominal aorta was surgically exposed and wrapped with a calcium chloride (0.5 mol/L) sponge for 10 min.

Results

Immunohistochemically, aortic sections were marked with caspase-3 and caspase-9 antibodies. It was observed that the pathways that trigger apoptosis (caspase-3 and caspase-9; p <0.004 and p <0.005, respectively) were significantly reduced in the AAA-edoxaban group compared to the AAA group. In the AAA-edoxaban group, it was observed that the expansion in aortic diameter and the deterioration in the elastic fibril structure in the aortic aneurysm were decreased as a result of edoxaban treatment. Edoxaban treatment was observed to reduce cell death in both the tunica intima and tunica media.

Conclusion

This study provided strong evidence of the protective effect of edoxaban on aortic aneurysm-related vascular damage by reducing apoptosis and mitophagy.

Establishment of Mouse Models of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a chronic vascular disease that commonly affects elderly individuals but has recently increased in younger populations. As the aneurysm grows, it can cause compression symptoms such as abdominal pain, rupture, and bleeding, which are absent in the early stages. Once an AAA ruptures and causes bleeding, the mortality rate is alarmingly high. Currently, the pathogenesis for AAA is unknown, and therapeutic options are limited, necessitating improvement in treatment efficacy. An essential research method for studying the processes and potential treatment of AAA is establishing animal models using mice. The present study provides a detailed overview of the widely used AAA mouse animal models and their construction strategies, advantages, disadvantages, scope of applications, and prospects.

Aortic Uptake of 18F-NaF and 18F-FDG and Calcification Predict the Development of Abdominal Aortic Aneurysms and Is Attenuated by Drug Therapy

BACKGROUND

Abdominal aortic aneurysms expand over time and increase the risk of fatal ruptures. To predict expansion, the isolated assessment of 18F-fluorodeoxyglucose (FDG) and sodium fluoride (NaF) uptake or calcification volume in aneurysms has been investigated with variability in results. We systematically evaluated whether 18F-FDG and 18F-NaF uptake was predictive of abdominal aortic aneurysm expansion.

METHODS

Seventy-four male Sprague-Dawley rat abdominal aortic aneurysm models were imaged using positron emission tomography-computed tomography with 18F-FDG and 18F-NaF at 1, 2, 4, 6, and 8 weeks after CaCl2 or saline stimulation. In the 1-week cohort (n=25), the correlation between 18F-FDG or 18F-NaF uptake and pathological markers was investigated. In the time course cohort (n=49), animals received either atorvastatin, losartan, aldactone, or risedronate to assess the effect of these drugs, and the relationship between aortic size and sequential 18F-FDG and 18F-NaF uptake or calcification volume was examined.

RESULTS

In the 1-week cohort, the maximum standard unit value of 18F-FDG and 18F-NaF uptake correlated with CD68- (r=0.82; P=0.001) and von Kossa staining-positive areas (r=0.89; P<0.001), respectively. In the time course cohort, 18F-FDG and 18F-NaF uptake changed in a time-dependent manner and drugs attenuated this uptake. Specifically, 18F-FDG showed high uptake at weeks 1 and 2, whereas a high 18F-NaF uptake was noted throughout the study period. Atorvastatin and risedronate showed a decreased and increased aortic size, respectively. The final aortic area correlated well with 18F-FDG and 18F-NaF uptake and calcification volume, especially at 1 and 2 weeks (18F-NaF [1 week]: r=0.61, 18F-FDG [2 weeks]: r=0.51, calcification volume [1 week]: r=0.59; P<0.001). Multiple linear regression analysis showed that the combination of these factors predicted the final aortic size, with 18F-NaF uptake at 1 week being the strongest predictor.

CONCLUSIONS

The uptake of 18F-NaF and 18F-FDG and the calcification volume at appropriate times correlated with the development of abdominal aortic aneurysms, with 18F-NaF uptake being the strongest predictor.

Tea polyphenol nanoparticles enable targeted siRNA delivery and multi-bioactive therapy for abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a life-threatening vascular disease, while there is a lack of pharmaceutical interventions to halt AAA progression presently. To address the multifaceted pathology of AAA, this work develops a novel multifunctional gene delivery system to simultaneously deliver two siRNAs targeting MMP-2 and MMP-9. The system (TPNs-siRNA), formed through the oxidative polymerization and self-assembly of epigallocatechin gallate (EGCG), efficiently encapsulates siRNAs during self-assembly. TPNs-siRNA safeguards siRNAs from biological degradation, facilitates intracellular siRNA transfection, promotes lysosomal escape, and releases siRNAs to silence MMP-2 and MMP-9. Additionally, TPNs, serving as a multi-bioactive material, mitigates oxidative stress and inflammation, fosters M1-to-M2 repolarization of macrophages, and inhibits cell calcification and apoptosis. In experiments with AAA mice, TPNs-siRNA accumulated and persisted in aneurysmal tissue after intravenous delivery, demonstrating that TPNs-siRNA can be significantly distributed in macrophages and VSMCs relevant to AAA pathogenesis. Leveraging the carrier's intrinsic multi-bioactive properties, the targeted siRNA delivery by TPNs exhibits a synergistic effect for enhanced AAA therapy. Furthermore, TPNs-siRNA is gradually metabolized and excreted from the body, resulting in excellent biocompatibility. Consequently, TPNs emerges as a promising multi-bioactive nanotherapy and a targeted delivery nanocarrier for effective AAA therapy.

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.

Epigenetic modifications in abdominal aortic aneurysms: from basic to clinical

Abdominal Aortic Aneurysm (AAA) is a disease characterized by localized dilation of the abdominal aorta, involving multiple factors in its occurrence and development, ultimately leading to vessel rupture and severe bleeding. AAA has a high mortality rate, and there is a lack of targeted therapeutic drugs. Epigenetic regulation plays a crucial role in AAA, and the treatment of AAA in the epigenetic field may involve a series of related genes and pathways. Abnormal expression of these genes may be a key factor in the occurrence of the disease and could potentially serve as promising therapeutic targets. Understanding the epigenetic regulation of AAA is of significant importance in revealing the mechanisms underlying the disease and identifying new therapeutic targets. This knowledge can contribute to offering AAA patients better clinical treatment options beyond surgery. This review systematically explores various aspects of epigenetic regulation in AAA, including DNA methylation, histone modification, non-coding RNA, and RNA modification. The analysis of the roles of these regulatory mechanisms, along with the identification of relevant genes and pathways associated with AAA, is discussed comprehensively. Additionally, a comprehensive discussion is provided on existing treatment strategies and prospects for epigenetics-based treatments, offering insights for future clinical interventions.

IRF5 governs macrophage adventitial infiltration to fuel abdominal aortic aneurysm formation

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by the expansion of the aortic wall. One of the most significant features is the infiltration of macrophages in the adventitia, which drives vasculature remodeling. The role of macrophage-derived interferon regulatory factor 5 (IRF5) in macrophage infiltration and AAA formation remains unknown. RNA sequencing of AAA adventitia identified Irf5 as the top significantly increased transcription factor that is predominantly expressed in macrophages. Global and myeloid cell-specific deficiency of Irf5 reduced AAA progression, with a marked reduction in macrophage infiltration. Further cellular investigations indicated that IRF5 promotes macrophage migration by direct regulation of downstream phosphoinositide 3-kinase γ (PI3Kγ, Pik3cg). Pik3cg ablation hindered AAA progression, and myeloid cell-specific salvage of Pik3cg restored AAA progression and macrophage infiltration derived from Irf5 deficiency. Finally, we found that IRF5 and PI3Kγ expression in the adventitia is significantly increased in patients with AAA. These findings reveal that the IRF5-dependent regulation of PI3Kγ is essential for AAA formation.

Vasculoprotective Potential of Baicalein in Angiotensin II-Infused Abdominal Aortic Aneurysms through Inhibiting Inflammation and Oxidative Stress

Aortic wall inflammation, abnormal oxidative stress and progressive degradation of extracellular matrix proteins are the main characteristics of abdominal aortic aneurysms (AAAs). The nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome dysregulation plays a crucial role in aortic damage and disease progression. The first aim of this study was to examine the effect of baicalein (5,6,7-trihydroxy-2-phenyl-4H-1-benzopyran-4-one) on AAA formation in apolipoprotein E-deficient (ApoE-/-) mice. The second aim was to define whether baicalein attenuates aberrant vascular smooth muscle cell (VSMC) proliferation and inflammation in VSMC culture. For male ApoE-/- mice, a clinically relevant AAA model was randomly divided into four groups: saline infusion, baicalein intraperitoneal injection, Angiotensin II (Ang II) infusion and Ang II + baicalein. Twenty-seven days of treatment with baicalein markedly decreased Ang II-infused AAA incidence and aortic diameter, reduced collagen-fiber formation, preserved elastic structure and density and prevented smooth muscle cell contractile protein degradation. Baicalein inhibited rat VSMC proliferation and migration following the stimulation of VSMC cultures with Ang II while blocking the Ang II-inducible cell cycle progression from G0/G1 to the S phase in the synchronized cells. Cal-520 AM staining showed that baicalein decreased cellular calcium in Ang II-induced VSMCs; furthermore, a Western blot assay indicated that baicalein inhibited the expression of PCNA and significantly lowered levels of phospho-Akt and phospho-ERK, along with an increase in baicalein concentration in Ang II-induced VSMCs. Immunofluorescence staining showed that baicalein pretreatment reduced NF-κB nuclear translocation in Ang II-induced VSMCs and furthered the protein expressions of NLRP3 while ASC and caspase-1 were suppressed in a dose-dependent manner. Baicalein pretreatment upregulated Nrf2/HO-1 signaling in Ang II-induced VSMCs. Thus, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) staining showed that its reactive oxygen species (ROS) production decreased, along with the baicalein pretreatment. Our overall results indicate that baicalein could have therapeutic potential in preventing aneurysm development.

Quantitative Magnetic Resonance Imaging to Assess Progression and Rupture Risk of Aortic Aneurysms: A Scoping Review

PURPOSE

In current practice, the diameter of an aortic aneurysm is utilized to estimate the rupture risk and decide upon timing of elective repair, although it is known to be imprecise and not patient-specific. Quantitative magnetic resonance imaging (MRI) enables the visualization of several biomarkers that provide information about processes within the aneurysm and may therefore facilitate patient-specific risk stratification. We performed a scoping review of the literature on quantitative MRI techniques to assess aortic aneurysm progression and rupture risk, summarized these findings, and identified knowledge gaps.

METHODS

Literature concerning primary research was of interest and the medical databases PubMed, Scopus, Embase, and Cochrane were systematically searched. This study used the PRISMA protocol extension for scoping reviews. Articles published between January 2010 and February 2023 involving animals and/or humans were included. Data were extracted by 2 authors using a predefined charting method.

RESULTS

A total of 1641 articles were identified, of which 21 were included in the scoping review. Quantitative MRI-derived biomarkers were categorized into hemodynamic (8 studies), wall (5 studies) and molecular biomarkers (8 studies). Fifteen studies included patients and/or healthy human subjects. Animal models were investigated in the other 6 studies. A cross-sectional study design was the most common, whereas 5 animal studies had a longitudinal component and 2 studies including patients had a prospective design. A promising hemodynamic biomarker is wall shear stress (WSS), which is estimated based on 4D-flow MRI. Molecular biomarkers enable the assessment of inflammatory and wall deterioration processes. The ADAMTS4-specific molecular magnetic resonance (MR) probe showed potential to predict abdominal aortic aneurysm (AAA) formation and rupture in a murine model. Wall biomarkers assessed using dynamic contrast-enhanced (DCE) MRI showed great potential for assessing AAA progression independent of the maximum diameter.

CONCLUSION

This scoping review provides an overview of quantitative MRI techniques studied and the biomarkers derived from them to assess aortic aneurysm progression and rupture risk. Longitudinal studies are needed to validate the causal relationships between the identified biomarkers and aneurysm growth, rupture, or repair. In the future, quantitative MRI could play an important role in the personalized risk assessment of aortic aneurysm rupture.

CLINICAL IMPACT

The currently used maximum aneurysm diameter fails to accurately assess the multifactorial pathology of an aortic aneurysm and precisely predicts rupture in a patient-specific manner. Quantitative magnetic resonance imaging (MRI) enables the detection of various quantitative parameters involved in aneurysm progression and subsequent rupture. This scoping review provides an overview of the studied quantitative MRI techniques, the biomarkers derived from them, and recommendations for future research needed for the implementation of these biomarkers. Ultimately, quantitative MRI could facilitate personalized risk assessment for patients with aortic aneurysms, thereby reducing untimely repairs and improving rupture prevention.

Vascular Ultrasound for In Vivo Assessment of Arterial Pathologies in a Murine Model of Atherosclerosis and Aortic Aneurysm

Vascular diseases like atherosclerosis and abdominal aortic aneurysm (AAA) are common pathologies in the western world, promoting various potentially fatal conditions. Here, we evaluate high-resolution (HR) ultrasound in mouse models of atherosclerosis and AAA as a useful tool for noninvasive monitoring of early vascular changes in vivo. We used Apolipoprotein E-deficient (ApoE-/-) mice as an atherosclerosis model and induced AAA development by the implementation of Angiotensin II-releasing osmotic minipumps. HR ultrasound of the carotid artery or the abdominal aorta was performed to monitor vascular remodeling in vivo. Images were analyzed by speckle tracking algorithms and correlated to histological analyses and subsequent automated collagen quantification. Consistent changes were observed via ultrasound in both models: Global radial strain (GRS) was notably reduced in the AAA model (23.8 ± 2.8% vs. 12.5 ± 2.5%, p = 0.01) and in the atherosclerotic mice (20.6 ± 1.3% vs. 15.8 ± 0.9%, p = 0.02). In mice with AAA, vessel distensibility was significantly reduced, whereas intima-media thickness was increased in atherosclerotic mice. The area and collagen content of the tunica media were increased in diseased arteries of both models as measured by automated image analysis of Picrosirius Red-stained aortic sections. Correlation analysis revealed a strong correlation of multiple parameters, predicting early vascular damage in HR ultrasound and histological examinations. In conclusion, our findings underscore the potential of HR ultrasound in effectively tracing early alterations in arterial wall properties in murine models of atherosclerosis and AAA.

CD73 deficiency does not aggravate angiotensin II-induced aortic inflammation in mice

Vascular inflammation plays a key role in the development of aortic diseases. A potential novel target for treatment might be CD73, an ecto-5'-nucleotidase that generates anti-inflammatory adenosine in the extracellular space. Here, we investigated whether a lack of CD73 results in enhanced aortic inflammation. To this end, angiotensin II was infused into wildtype and CD73-/- mice over 10 days. Before and after infusion, mice were analyzed using magnetic resonance imaging, ultrasound, flow cytometry, and histology. The impact of age and gender was investigated using female and male mice of three and six months of age, respectively. Angiotensin II infusion led to increased immune cell infiltration in both genotypes' aortae, but depletion of CD73 had no impact on immune cell recruitment. These findings were not modified by age or sex. No substantial difference in morphological or functional characteristics could be detected between wildtype and CD73-/- mice. Interestingly, the expression of CD73 on neutrophils decreased significantly in wildtype mice during treatment. In summary, we have found no evidence that CD73 deficiency affects the onset of aortic inflammation. However, as CD73 expression decreased during disease induction, an increase in CD73 by pharmaceutical intervention might result in lower vascular inflammation and less vascular disease.

Nicotine Administration Augments Abdominal Aortic Aneurysm Progression in Rats

Inflammation and elastin degradation are key hallmarks in the pathogenesis of abdominal aortic aneurysms (AAAs). It has been acknowledged that activation of alpha7 nicotinic acetylcholine receptors (α7nAChRs) attenuates inflammation, termed the cholinergic anti-inflammatory pathway (CAP). Thus, we hypothesize that low-dose nicotine impairs the progression of elastase-induced AAAs in rats by exerting anti-inflammatory and anti-oxidative stress properties. Male Sprague-Dawley rats underwent surgical AAA induction with intraluminal elastase infusion. We compared vehicle rats with rats treated with nicotine (1.25 mg/kg/day), and aneurysm progression was monitored by weekly ultrasound images for 28 days. Nicotine treatment significantly promoted AAA progression (p = 0.031). Additionally, gelatin zymography demonstrated that nicotine significantly reduced pro-matrix metalloproteinase (pro-MMP) 2 (p = 0.029) and MMP9 (p = 0.030) activity in aneurysmal tissue. No significant difference was found in the elastin content or the score of elastin degradation between the groups. Neither infiltrating neutrophils nor macrophages, nor aneurysmal messenger RNA (mRNA) levels of pro- or anti-inflammatory cytokines, differed between the vehicle and nicotine groups. Finally, no difference in mRNA levels of markers for anti-oxidative stress or the vascular smooth muscle cells' contractile phenotype was observed. However, proteomics analyses of non-aneurysmal abdominal aortas revealed that nicotine decreased myristoylated alanine-rich C-kinase substrate and proteins, in ontology terms, inflammatory response and reactive oxygen species, and in contradiction to augmented AAAs. In conclusion, nicotine at a dose of 1.25 mg/kg/day augments AAA expansion in this elastase AAA model. These results do not support the use of low-dose nicotine administration for the prevention of AAA progression.

Mouse Abdominal Aortic Aneurysm Model Induced by Periarterial Incubation of Papain

For decades, numerous experimental animal models have been developed to examine the pathophysiologic mechanisms and potential treatments for abdominal aortic aneurysms (AAAs) in diverse species with varying chemical or surgical approaches. This study aimed to create an AAA mouse model by the periarterial incubation with papain, which can mimic human AAA with advantages such as simplicity, convenience, and high efficiency. Eighty C57BL/6J male mice were randomly assigned to 1 of the 4 groups: papain (1.0 or 2.0 mg), porcine pancreatic elastase, and phosphate-buffered solution. The aortic segment was wrapped for 20 minutes, and the diameter was measured using ultrasound preoperatively and postoperative days 7 and 14. Then, the mice were killed for histomorphometric and immunohistochemical analyses. According to ultrasound measurements and histomorphometric analyses, on postoperative day 7, 65% of mice in the 1.0-mg papain group and 60% of mice in the 2.0-mg papain group developed AAA. In both papain groups, 100% of mice developed AAA, and 65% of mice in the porcine pancreatic elastase group developed AAA on postoperative day 14. Furthermore, hematoxylin/eosin, elastin van Gieson, and Masson staining of tissues from the papain group revealed thickened media and intimal hyperplasia, collagen sediments, and elastin destruction, indicating that AAA histochemical alteration was similar to that of humans. In addition, the immunohistochemical analysis was conducted to detect infiltrated inflammatory cells, such as macrophages and leukocytes, in the aortic wall and hyperplasic adventitia. The expression of matrix metalloproteinase 2 and 9 was significantly upregulated in papain and human AAA tissues. Periarterial incubation with 1.0 mg of papain for 20 minutes can successfully create an experimental AAA model in mice for 14 days, which can be used to explore the mechanism and treatment of human AAA.

Murine model of elastase-induced proximal thoracic aortic aneurysm through a midline incision in the anterior neck

Objective

This study was performed to develop a murine model of elastase-induced proximal thoracic aortic aneurysms (PTAAs).

Methods

The ascending thoracic aorta and aortic arch of adult C57BL/6J male mice were exposed through a midline incision in the anterior neck, followed by peri-adventitial elastase or saline application. The maximal ascending thoracic aorta diameter was measured with high-resolution micro-ultrasound. Twenty-eight days after the operation, the aortas were harvested and analyzed by histopathological examination and qualitative polymerase chain reaction to determine the basic characteristics of the aneurysmal lesions.

Results

Fourteen days after the operation, the dilation rate (mean ± standard error) in the 10-min elastase application group (n = 10, 71.44 ± 10.45%) or 5-min application group (n = 9, 42.67 ± 3.72%) were significantly higher than that in the saline application group (n = 9, 7.37 ± 0.94%, P < 0.001 for both). Histopathological examination revealed aortic wall thickening, degradation of elastin fibers, loss of smooth muscle cells, more vasa vasorum, enhanced extracellular matrix degradation, augmented collagen synthesis, upregulated apoptosis and proliferation capacity of smooth muscle cells, and increased macrophages and CD4⁺ T cells infiltration in the PTAA lesions. Qualitative analyses indicated higher expression of the proinflammatory markers, matrix metalloproteinase-2 and -9 as well as Collagen III, Collagen I in the PTAAs than in the controls.

Conclusion

We established a novel in vivo mouse model of PTAAs through a midline incision in the anterior neck by peri-adventitial application of elastase. This model may facilitate research into the pathogenesis of PTAA formation and the treatment strategy for this devastating disease.

Host-Derived Cytotoxic Agents in Chronic Inflammation and Disease Progression

At inflammatory sites, cytotoxic agents are released and generated from invading immune cells and damaged tissue cells. The further fate of the inflammation highly depends on the presence of antagonizing principles that are able to inactivate these host-derived cytotoxic agents. As long as the affected tissues are well equipped with ready-to-use protective mechanisms, no damage by cytotoxic agents occurs and resolution of inflammation is initiated. However, long-lasting and severe immune responses can be associated with the decline, exhaustion, or inactivation of selected antagonizing principles. Hence, cytotoxic agents are only partially inactivated and contribute to damage of yet-unperturbed cells. Consequently, a chronic inflammatory process results. In this vicious circle of permanent cell destruction, not only novel cytotoxic elements but also novel alarmins and antigens are liberated from affected cells. In severe cases, very low protection leads to organ failure, sepsis, and septic shock. In this review, the major classes of host-derived cytotoxic agents (reactive species, oxidized heme proteins and free heme, transition metal ions, serine proteases, matrix metalloproteases, and pro-inflammatory peptides), their corresponding protective principles, and resulting implications on the pathogenesis of diseases are highlighted.

Single-cell transcriptome in silico analysis reveals conserved regulatory programs in macrophages/monocytes of abdominal aortic aneurysm from multiple mouse models and human

Abdominal aortic aneurysm (AAA) is a life-threatening disease and there is currently a lack of effective treatment to prevent it rupturing. ScRNA-seq studies of AAA are still lacking. In the study, we analyzed the published AAA scRNA-seq datasets from the mouse elastase-induced model, CaCl₂ treatment model, Ang II-induced model and human by using bioinformatic approaches and in silico analysis. A total of 26 cell clusters were obtained and 11 cell types were identified from multiple mouse AAA models. Also, the proportion of Mφ/Mo increased in the AAA group and Mφ/Mo was divided into seven subtypes. There were significant differences in transcriptional regulation patterns of Mφ/Mo in different AAA models. The enrichment pathways of upregulated or downregulated genes from Mφ/Mo in the three mouse datasets were different. The actived regulons of Mφ/Mo had strong specificity and the repressed regulons showed high consistency. The co-upregulated genes as well as actived regulons and co-downregulated genes as well as repressed regulons were closely correlated and formed regulatory networks. Mφ/Mo from human AAA dataset was divided into five subtypes. The proportion of three macrophage subpopulations increased but the proportion of two monocyte subpopulations decreased. In the AAA group, the upregulated or downregulated genes of Mφ/Mo were enriched in different pathways. After further analyzing the genes in Mφ/Mo of both mouse and human scRNA-seq datasets, two genes were upregulated in the four datasets, IL-1B and THBS1. In conclusion, in silico analysis of scRNA-seq revealed that Mφ/Mo and their regulatory related genes as well as interaction networks played an important role in the pathogenesis of AAA.

Animal models and animal-free innovations for cardiovascular research: current status and routes to be explored. Consensus document of the ESC Working Group on Myocardial Function and the ESC Working Group on Cellular Biology of the Heart

Cardiovascular diseases represent a major cause of morbidity and mortality, necessitating research to improve diagnostics, and to discover and test novel preventive and curative therapies, all of which warrant experimental models that recapitulate human disease. The translation of basic science results to clinical practice is a challenging task, in particular for complex conditions such as cardiovascular diseases, which often result from multiple risk factors and comorbidities. This difficulty might lead some individuals to question the value of animal research, citing the translational 'valley of death', which largely reflects the fact that studies in rodents are difficult to translate to humans. This is also influenced by the fact that new, human-derived in vitro models can recapitulate aspects of disease processes. However, it would be a mistake to think that animal models do not represent a vital step in the translational pathway as they do provide important pathophysiological insights into disease mechanisms particularly on an organ and systemic level. While stem cell-derived human models have the potential to become key in testing toxicity and effectiveness of new drugs, we need to be realistic, and carefully validate all new human-like disease models. In this position paper, we highlight recent advances in trying to reduce the number of animals for cardiovascular research ranging from stem cell-derived models to in situ modelling of heart properties, bioinformatic models based on large datasets, and state-of-the-art animal models, which show clinically relevant characteristics observed in patients with a cardiovascular disease. We aim to provide a guide to help researchers in their experimental design to translate bench findings to clinical routine taking the replacement, reduction, and refinement (3R) as a guiding concept.

A Multi-Bioactive Nanomicelle-Based "One Stone for Multiple Birds" Strategy for Precision Therapy of Abdominal Aortic Aneurysms

Abdominal aortic aneurysm (AAA) remains a lethal aortic disease in the elderly. Currently, no effective drugs can be clinically applied to prevent the development of AAA. Herein, a "one stone for multiple birds" strategy for AAA therapy is reported. As a proof of concept, three bioactive conjugates are designed and synthesized, which can assemble into nanomicelles. Cellularly, these nanomicelles significantly inhibit migration and activation of inflammatory cells as well as protect vascular smooth muscle cells (VSMCs) from induced oxidative stress, calcification and apoptosis, with the best effect for nanomicelles (TPTN) derived from a conjugate defined as TPT. After intravenous delivery, TPTN efficiently accumulates in the aneurysmal tissue of AAA rats, showing notable distribution in neutrophils, macrophages and VSMCs, all relevant to AAA pathogenesis. Whereas three examined nanomicelles effectively delay expansion of AAA in rats, TPTN most potently prevents AAA growth by simultaneously normalizing the pro-inflammatory microenvironment and regulating multiple pathological cells. TPTN is effective even at 0.2 mg kg^-1 . Besides, TPTN can function as a bioactive nanoplatform for site-specifically delivering and triggerably releasing anti-aneurysmal drugs, affording synergistic therapeutic effects. Consequently, TPTN is a promising multi-bioactive nanotherapy and bioresponsive targeting delivery nanocarrier for effective therapy of AAA and other inflammatory vascular diseases.

Artificial intelligence assisted compositional analyses of human abdominal aortic aneurysms ex vivo

Quantification of histological information from excised human abdominal aortic aneurysm (AAA) specimens may provide essential information on the degree of infiltration of inflammatory cells in different regions of the AAA. Such information will support mechanistic insight in AAA pathology and can be linked to clinical measures for further development of AAA treatment regimens. We hypothesize that artificial intelligence can support high throughput analyses of histological sections of excised human AAA. We present an analysis framework based on supervised machine learning. We used TensorFlow and QuPath to determine the overall architecture of the AAA: thrombus, arterial wall, and adventitial loose connective tissue. Within the wall and adventitial zones, the content of collagen, elastin, and specific inflammatory cells was quantified. A deep neural network (DNN) was trained on manually annotated, Weigert stained, tissue sections (14 patients) and validated on images from two other patients. Finally, we applied the method on 95 new patient samples. The DNN was able to segment the sections according to the overall wall architecture with Jaccard coefficients after 65 epocs of 92% for the training and 88% for the validation data set, respectively. Precision and recall both reached 92%. The zone areas were highly variable between patients, as were the outputs on total cell count and elastin/collagen fiber content. The number of specific cells or stained area per zone was deterministically determined. However, combining the masks based on the Weigert stainings, with images of immunostained serial sections requires addition of landmark recognition to the analysis path. The combination of digital pathology, the DNN we developed, and landmark registration will provide a strong tool for future analyses of the histology of excised human AAA. In combination with biomechanical testing and microstructurally motivated mathematical models of AAA remodeling, the method has the potential to be a strong tool to provide mechanistic insight in the disease. In combination with each patients’ demographic and clinical profile, the method can be an interesting tool to in supportof a better treatment regime for the patients.

The molecular mechanism of Ang II induced-AAA models based on proteomics analysis in ApoE-/- and CD57BL/6J mice

Apolipoprotein knockout (ApoE^-/-) and CD57BL/6J mouse models of angiotensin II (Ang II)-induced abdominal aortic aneurysm (AAA) are commonly used in AAA research. However, the similarities and differences in the molecular mechanisms of AAA in these two genotypes have not been reported. In our study, we analyzed proteomics data from ApoE^-/- and CD57BL/6J mouse models of Ang II-induced AAA and control mice by LC-MS/MS. Gene set enrichment analysis (GSEA) of differentially abundance proteins (DAPs) in the ApoE^-/- or CD57BL/6J mouse groups was performed in R software, and infiltration of immune cells in groups was assessed. DAP that showed the same trend in abundance in ApoE^-/- and CD57BL/6J mice (S-DAP) were identified and subjected to GO enrichment, KEGG pathway, and connectivity map (CMap) analyses. The protein-protein interaction (PPI) network of the S-DAP was drawn, the key S-DAP were identified by MCODE, and the transcription factors (TFs) of crucial S-DAP were predicted by iRegulon in Cytoscape. Male ApoE^-/- and CD57BL/6J mouse models of Ang II-induced AAA are commonly used in AAA research, and extracellular matrix organization is associated with AAA in both of these models. However, there are some differences between the mechanisms underlying AAA in these two genotypes, and these differences need to be considered when studying AAA and selecting models. SIGNIFICANCE: Our research provided the first insight into the similarity and differential mechanisms of Ang II infused AAA models using ApoE^-/- and CD57BL/6J mice. This study might provide the some advises for the selection of Ang II infused AAA models for further AAA researches.

Identifying novel mechanisms of abdominal aortic aneurysm via unbiased proteomics and systems biology

Background

Abdominal aortic aneurysm (AAA), characterized by a continued expansion of the aorta, leads to rupture if not surgically repaired. Mice aid the study of disease progression and its underlying mechanisms since sequential studies of aneurysm development are not feasible in humans. The present study used unbiased proteomics and systems biology to understand the molecular relationship between the mouse models of AAA and the human disease.

Methods and results

Aortic tissues of developing and established aneurysms produced by either angiotensin II (AngII) infusion in Apoe -/- and Ldlr -/- mice or intraluminal elastase incubation in wildtype C57BL/6J mice were examined. Aortas were dissected free and separated into eight anatomical segments for proteomics in comparison to their appropriate controls. High-dimensional proteome cluster analyses identified site-specific protein signatures in the suprarenal segment for AngII-infused mice (159 for Apoe -/- and 158 for Ldlr -/-) and the infrarenal segment for elastase-incubated mice (173). Network analysis revealed a predominance of inflammatory and coagulation factors in developing aneurysms, and a predominance of fibrosis-related pathways in established aneurysms for both models. To further substantiate our discovery platform, proteomics was performed on human infrarenal aortic aneurysm tissues as well as aortic tissue collected from age-matched controls. Protein processing and inflammatory pathways, particularly neutrophil-associated inflammation, dominated the proteome of the human aneurysm abdominal tissue. Aneurysmal tissue from both mouse and human had inflammation, coagulation, and protein processing signatures, but differed in the prevalence of neutrophil-associated pathways, and erythrocyte and oxidative stress-dominated networks in the human aneurysms.

Conclusions

Identifying changes unique to each mouse model will help to contextualize model-specific findings. Focusing on shared proteins between mouse experimental models or between mouse and human tissues may help to better understand the mechanisms for AAA and establish molecular bases for novel therapies.

FOS gene associated immune infiltration signature in perivascular adipose tissues of abdominal aortic aneurysm

Abdominal aortic aneurysms (AAA) are pathological dilations in local aortic wall. The inflammatory infiltrates of the perivascular adipose tissue (PAT) surrounding AAAs were associated with AAAs and have been shown to contribute vascular pathology. However, the mechanism by which PAT inflammation contributes to vascular pathology in AAA remains to be clarified. This study aimed to explore the association between immune cell infiltration and key gene expression profile in PAT of AAA. For that, a gene expression dataset of human dilated perivascular adipose tissue (dPAT), non-dilated perivascular adipose tissue (ndPAT), subcutaneous abdominal fat (SAF) and omental-visceral fat (OVF) samples, as well as another microarray dataset of the abdominal perivascular adipose tissue in peripheral artery disease patients were downloaded from GEO database for analysis in this study. The CIBERSORT algorithm, weighted gene co-expression network analysis (WGCNA) and LASSO algorithm were used for the identification of immune infiltration, immune-related genes and the development of diagnostic signature. Our data discovered a significant higher proportion of activated mast cells and follicular helper T (Tfh) cells in dPAT than ndPAT, OVT and SAF samples. Moreover, AP-1 family members (FOS, FOSB, ATF3, JUN and JUNB) were found to compose the hub genes of purple module in WGCNA. Among them, FOS gene acts as a higher efficient marker to discriminate dPAT from ndPAT, OVT and SAF in AAA. Meanwhile, the expression profiles of the AP-1 family members are all significantly positive correlated with activated mast cell, plasma cell and Tfh cell infiltration in dPAT of AAA. Therefore, in the PAT surrounding AAA, the signature of inflammatory infiltration might be represented by a FOS-dominated cell network consist of activated mast cell, plasma cell and Tfh cell. Given the complicated etiology of AAA, our results are likely to shed new light on the pathophysiologic mechanism of AAA influenced by the local dPAT.

Peptide Amphiphile Supramolecular Nanofibers Designed to Target Abdominal Aortic Aneurysms

An abdominal aortic aneurysm (AAA) is a localized dilation of the aorta located in the abdomen that poses a severe risk of death when ruptured. The cause of AAA is not fully understood, but degradation of medial elastin due to elastolytic matrix metalloproteinases is a key step leading to aortic dilation. Current therapeutic interventions are limited to surgical repair to prevent catastrophic rupture. Here, we report the development of injectable supramolecular nanofibers using peptide amphiphile molecules designed to localize to AAA by targeting fragmented elastin, matrix metalloproteinase 2 (MMP-2), and membrane type 1 matrix metalloproteinase. We designed four targeting peptide sequences from X-ray crystallographic data and incorporated them into PA molecules via solid phase peptide synthesis. After coassembling targeted and diluent PAs at different molar ratios, we assessed their ability to form nanofibers using transmission electron microscopy and to localize to AAA in male and female Sprague-Dawley rats using light sheet fluorescence microscopy. We found that three formulations of the PA nanofibers were able to localize to AAA tissue, but the MMP-2 targeting PA substantially outperformed the other nanofibers. Additionally, we demonstrated that the MMP-2 targeting PA nanofibers had an optimal dose of 5 mg (∼12 mg/kg). Our results show that there was not a significant difference in targeting between male and female Sprague-Dawley rats. Given the ability of the MMP-2 targeting PA nanofiber to localize to AAA tissue, future studies will investigate potential diagnostic and targeted drug delivery applications for AAA.

Disintegrin and Metalloproteinases (ADAMs [A Disintegrin and Metalloproteinase] and ADAMTSs [ADAMs With a Thrombospondin Motif]) in Aortic Aneurysm

Aortic aneurysm is a complex pathology that can be lethal if not detected in time. Although several molecular mechanisms and pathways have been identified to be involved in aortic aneurysm development and growth, the current lack of an effective pharmacological treatment highlights the need for a more thorough understanding of the factors that regulate the remodeling of the aortic wall in response to triggers that lead to aneurysm formation. This task is further complicated by the regional heterogeneity of the aorta and that thoracic and abdominal aortic aneurysm are distinct pathologies with different risk factors and distinct course of progression. ADAMs (a disintegrin and metalloproteinases) and ADAMTS (ADAMs with a thrombospondin motif) are proteinases that share similarities with other proteinases but possess unique and diverse properties that place them in a category of their own. In this review, we discuss what is known on how ADAMs and ADAMTSs are altered in abdominal aortic aneurysm and thoracic aortic aneurysm in patients, in different animal models, and their role in regulating the function of different vascular and inflammatory cell types. A full understanding of the role of ADAMs and ADAMTSs in aortic aneurysm will help reveal a more complete understanding of the underlying mechanism driving aneurysm formation, which will help towards developing an effective treatment in preventing or limiting the growth of aortic aneurysm.

Cycloastragenol Inhibits Experimental Abdominal Aortic Aneurysm Progression

The pathogenesis of abdominal aortic aneurysm involves vascular inflammation and elastin degradation. Astragalusradix contains cycloastragenol, which is known to be anti-inflammatory and to protect against elastin degradation. We hypothesized that cycloastragenol supplementation inhibits abdominal aortic aneurysm progression. Abdominal aortic aneurysm was induced in male rats by intraluminal elastase infusion in the infrarenal aorta and treated daily with cycloastragenol (125 mg/kg/day). Aortic expansion was followed weekly by ultrasound for 28 days. Changes in aneurysmal wall composition were analyzed by mRNA levels, histology, zymography and explorative proteomic analyses. At day 28, mean aneurysm diameter was 37% lower in the cycloastragenol group (p < 0.0001). In aneurysm cross sections, elastin content was insignificantly higher in the cycloastragenol group (10.5% ± 5.9% vs. 19.9% ± 16.8%, p = 0.20), with more preserved elastin lamellae structures (p = 0.0003) and without microcalcifications. Aneurysmal matrix metalloprotease-2 activity was reduced by the treatment (p = 0.022). Messenger RNA levels of inflammatory- and anti-oxidative markers did not differ between groups. Explorative proteomic analysis showed no difference in protein levels when adjusting for multiple testing. Among proteins displaying nominal regulation were fibulin-5 (p = 0.02), aquaporin-1 (p = 0.02) and prostacyclin synthase (p = 0.007). Cycloastragenol inhibits experimental abdominal aortic aneurysm progression. The suggested underlying mechanisms involve decreased matrix metalloprotease-2 activity and preservation of elastin and reduced calcification, thus, cycloastragenol could be considered for trial in abdominal aortic aneurysm patients.

Experimental aortic aneurysm severity and growth depend on topical elastase concentration and lysyl oxidase inhibition

Abdominal aortic aneurysm (AAA) formation and expansion is highly complex and multifactorial, and the improvement of animal models is an important step to enhance our understanding of AAA pathophysiology. In this study, we explore our ability to influence aneurysm growth in a topical elastase plus β-Aminopropionitrile (BAPN) mouse model by varying elastase concentration and by altering the cross-linking capability of the tissue. To do so, we assess both chronic and acute effects of elastase concentration using volumetric ultrasound. Our results suggest that the applied elastase concentration affects initial elastin degradation, as well as long-term vessel expansion. Additionally, we assessed the effects of BAPN by (1) removing it to restore the cross-linking capability of tissue after aneurysm formation and (2) adding it to animals with stable aneurysms to interrupt cross-linking. These results demonstrate that, even after aneurysm formation, lysyl oxidase inhibition remains necessary for continued expansion. Removing BAPN reduces the aneurysm growth rate to near zero, resulting in a stable aneurysm. In contrast, adding BAPN causes a stable aneurysm to expand. Altogether, these results demonstrate the ability of elastase concentration and BAPN to modulate aneurysm growth rate and severity. The findings open several new areas of investigation in a murine model that mimics many aspects of human AAA.

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.

Effects of hypercholesterolism on expansion of abdominal aortic aneurysm in rat model

Background

Inflammation is recognized as a critical process in expansion of abdominal aortic aneurysm (AAA). A relationship between effects of cholesterol and statin in this process have been suggested, but remain untested. Therefore, current study aimed to examine the effects of hypercholesterolism on expansion of AAA in a rat model.

Methods

A total of 16 male rats were divided into 4 groups as follows: group I, normocholesterol diet and saline infusion, group II, normocholesterol diet and porcine pancreatic elastase (PPE) infusion, group III, hypercholesterol diet and PPE infusion, and group IV, hypercholesterol diet, PPE infusion and statin administration. At the 3rd week, saline was infused intraluminally in group I and PPE in groups II-IV to induce AAA. At the 5th week, blood and aortic tissue were obtained from each rat for evaluation of lipid profiles, aortic diameters (ADs), and characteristics of stains.

Results

Post-procedural aortic diameter (AD3) and AD3/pre-procedural aortic diameter (AD1) were significantly different among four groups (P = 0.042, P = 0.028, respectively). AD3 was significantly larger in group II than group I, and group III than group IV (P = 0.012, P = 0.043, respectively). AD3/AD1 was significantly higher in group II than group I, and group III than group II (P = 0.008, P = 0.030, respectively). Group III showed the highest cellularity for inflammatory cells.

Conclusions

Though larger experimental and clinical studies are necessary, authors suggest that hypercholesterolism can aggravate expansion of AAA, and that statin therapy can reduce it. Therefore, monitoring for hypercholesterolism and instituting statin therapy may be helpful to suppress expansion of AAA.

Translating mouse models of abdominal aortic aneurysm to the translational needs of vascular surgery

Introduction

Abdominal aortic aneurysm (AAA) is a condition that has considerable socioeconomic impact and an eventual rupture is associated with high mortality and morbidity. Despite decades of research, surgical repair remains the treatment of choice and no medical therapy is currently available. Animal models and, in particular, murine models, of AAA are a vital tool for experimental in vivo research. However, each of the different models has individual limitations and provide only partial mimicry of human disease. This narrative review addresses the translational potential of the available mouse models, highlighting unanswered questions from a clinical perspective. It is based on a thorough presentation of the available literature and more than a decade of personal experience, with most of the available models in experimental and translational AAA research.

Results

From all the models published, only the four inducible models, namely the angiotensin II model (AngII), the porcine pancreatic elastase perfusion model (PPE), the external periadventitial elastase application (ePPE), and the CaCl₂ model have been widely used by different independent research groups. Although the angiotensin II model provides features of dissection and aneurysm formation, the PPE model shows reliable features of human AAA, especially beyond day 7 after induction, but remains technically challenging. The translational value of ePPE as a model and the combination with β-aminopropionitrile to induce rupture and intraluminal thrombus formation is promising, but warrants further mechanistic insights. Finally, the external CaCl₂ application is known to produce inflammatory vascular wall thickening. Unmet translational research questions include the origin of AAA development, monitoring aneurysm growth, gender issues, and novel surgical therapies as well as novel nonsurgical therapies.

Conclusion

New imaging techniques, experimental therapeutic alternatives, and endovascular treatment options provide a plethora of research topics to strengthen the individual features of currently available mouse models, creating the possibility of shedding new light on translational research questions.

Systems toxicology study reveals reduced impact of heated tobacco product aerosol extract relative to cigarette smoke on premature aging and exacerbation effects in aged aortic cells in vitro

Aging and smoking are major risk factors for cardiovascular diseases (CVD). Our in vitro study compared, in the context of aging, the effects of the aerosol of Tobacco Heating System 2.2 (THS; an electrically heated tobacco product) and 3R4F reference cigarette smoke (CS) on processes that contribute to vascular pathomechanisms leading to CVD. Young and old human aortic smooth muscle cells (HAoSMC) were exposed to various concentrations of aqueous extracts (AE) from 3R4F CS [0.014-0.22 puffs/mL] or THS aerosol [0.11-1.76 puffs/mL] for 24 h. Key markers were measured by high-content imaging, transcriptomics profiling and multianalyte profiling. In our study, in vitro aging increased senescence, DNA damage, and inflammation and decreased proliferation in the HAoSMCs. At higher concentrations of 3R4F AE, young HAoSMCs behaved similarly to aged cells, while old HAoSMCs showed additional DNA damage and apoptosis effects. At 3R4F AE concentrations with the maximum effect, the THS AE showed no significant effect in young or old HAoSMCs. It required an approximately ten-fold higher concentration of THS AE to induce effects similar to those observed with 3R4F. These effects were independent of nicotine, which did not show a significant effect on HAoSMCs at any tested concentration. Our results show that 3R4F AE accelerates aging in young HAoSMCs and exacerbates the aging effect in old HAoSMCs in vitro, consistent with CS-related contributions to the risk of CVD. Relative to 3R4F AE, the THS AE showed a significantly reduced impact on HAoSMCs, suggesting its lower risk for vascular SMC-associated pathomechanisms leading to CVD.

Smoking and the Pathophysiology of Peripheral Artery Disease

Smoking is one of the most important preventable factors causing peripheral artery disease (PAD). The purpose of this review is to comprehensively analyze and summarize the pathogenesis and clinical characteristics of smoking in PAD based on existing clinical, in vivo, and in vitro studies. Extensive searches and literature reviews have shown that a large amount of data exists on the pathological process underlying the effects of cigarette smoke and its components on PAD through various mechanisms. Cigarette smoke extracts (CSE) induce endothelial cell dysfunction, smooth muscle cell remodeling and macrophage phenotypic transformation through multiple molecular mechanisms. These pathological changes are the molecular basis for the occurrence and development of peripheral vascular diseases. With few discussions on the topic, we will summarize recent insights into the effect of smoking on regulating PAD through multiple pathways and its possible pathogenic mechanism.

The role of dipeptidyl peptidase-IV in abdominal aortic aneurysm pathogenesis: A systematic review

Abdominal aortic aneurysm (AAA) is an important vascular disease carrying significant mortality implications due to the risk of aneurysm rupture. Current management relies exclusively on surgical repair as there is no effective medical therapy. A key element of AAA pathogenesis is the chronic inflammation mediated by inflammatory cells releasing proteases, including the enzyme dipeptidyl peptidase IV (DPP-IV). This review sought to recapitulate available evidence on the involvement of DPP-IV in AAA development. Further, we assessed the experimental use of currently available DPP-IV inhibitors for AAA management in murine models. Embase, Medline, PubMed, and Web of Science databases were utilised to access the relevant studies. The review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). A narrative synthesis approach was used. Sixty-four studies were identified from the searched databases; a final 11 were included in the analysis. DPP-IV was reported to be significantly increased in both AAA tissue and plasma of patients and correlated with AAA growth. DPP-IV inhibitors (sitagliptin, vildagliptin, alogliptin, and teneligliptin) were all shown to attenuate AAA formation in murine models by reducing monocyte differentiation, the release of reactive oxygen species (ROS), and metalloproteinases (MMP-2 and MMP-9). DPP-IV seems to play a role in AAA pathogenesis by propagating the inflammatory microenvironment. This is supported by observations of decreased AAA formation and reduction in macrophage infiltration, ROS, matrix MMPs, and interleukins following the use of DPP-IV inhibitors in murine models. There is an existing translational gap from preclinical observations to clinical trials in this important and novel mechanism of AAA pathogenesis. This prior literature highlights the need for further research on molecular targets involved in AAA formation.

Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) Use in Animal Trauma Models

BACKGROUND

Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) was developed to prevent traumatic exsanguination. We aim to identify the outcomes in animal models with 1) partial versus complete REBOA occlusion and 2) zone 1 versus 2 placements.

METHODS

The PRISMA guidelines were followed. We conducted a search of PubMed, EMBASE and Google Scholar for REBOA studies in animal trauma models using the following search terms: "REBOA trauma", "REBOA outcomes" "REBOA complications". SYRCLE's RoB Tool was utilized for the risk of bias and study quality assessment.

RESULTS

Our search yielded 14 RCTs for inclusion. Eleven studies directly investigated partial REBOA versus total aortic occlusion. Overall, partial REBOA techniques were associated with similar attainment of proximal MAP but with significantly less ischemic burden. Significant mortality benefit with partial occlusion was observed in three studies. Survival time post-occlusion also was improved with zone 3 placement versus zone 1 (100% versus 33%; P < 0.01).

CONCLUSIONS

There appears to be a fine balance between desired proximal arterial pressure and time of occlusion for overall survival and subsequent risk of distal ischemia. Many "partial occlusion" techniques may be superior in attaining such balance over prolonged REBOA inflation where no distal flow is allowed. Tailored zone 3 placement may offer significant mortality and morbidity advantages compared to sustained total occlusion and indiscriminate zone 1 placement strategies. As clear conclusions regarding REBOA are unlikely to be established in animal models, larger randomized investigations utilizing human subjects are needed to describe optimal REBOA technique and applicability in greater detail.

Current pharmacological management of aortic aneurysm

ABSTRACT

Aortic aneurysm (AA) remains one of the primary causes of death worldwide. Of the major treatments, prophylactic operative repair is used for AA to avoid potential aortic dissection (AD) or rupture. To halt the development of AA and alleviate its progression into AD, pharmacological treatment has been investigated for years. Currently, β-adrenergic blocking agents, losartan, irbesartan, angiotensin-converting-enzyme inhibitors, statins, antiplatelet agents, doxycycline, and metformin have been investigated as potential candidates for preventing AA progression. However, the paradox between preclinical successes and clinical failures still exists, with no medical therapy currently available for ideally negating the disease progression. This review describes the current drugs used for pharmacological management of AA and their individual potential mechanisms. Preclinical models for drug screening and evaluation are also discussed to gain a better understanding of the underlying pathophysiology and ultimately find new therapeutic targets for AA.

Single-cell RNA sequencing reveals the cellular heterogeneity of aneurysmal infrarenal abdominal aorta

AIMS

The artery contains numerous cell types which contribute to multiple vascular diseases. However, the heterogeneity and cellular responses of these vascular cells during abdominal aortic aneurysm (AAA) progression have not been well characterized.

METHODS AND RESULTS

Single-cell RNA sequencing was performed on the infrarenal abdominal aortas (IAAs) from C57BL/6J mice at Days 7 and 14 post-sham or peri-adventitial elastase-induced AAA. Unbiased clustering analysis of the transcriptional profiles from >4500 aortic cells identified 17 clusters representing nine-cell lineages, encompassing vascular smooth muscle cells (VSMCs), fibroblasts, endothelial cells, immune cells (macrophages, T cells, B cells, and dendritic cells), and two types of rare cells, including neural cells and erythrocyte cells. Seurat clustering analysis identified four smooth muscle cell (SMC) subpopulations and five monocyte/macrophage subpopulations, with distinct transcriptional profiles. During AAA progression, three major SMC subpopulations were proportionally decreased, whereas the small subpopulation was increased, accompanied with down-regulation of SMC contractile markers and up-regulation of pro-inflammatory genes. Another AAA-associated cellular response is immune cell expansion, particularly monocytes/macrophages. Elastase exposure induced significant expansion and activation of aortic resident macrophages, blood-derived monocytes and inflammatory macrophages. We also identified increased blood-derived reparative macrophages expressing anti-inflammatory cytokines suggesting that resolution of inflammation and vascular repair also persist during AAA progression.

CONCLUSION

Our data identify AAA disease-relevant transcriptional signatures of vascular cells in the IAA. Furthermore, we characterize the heterogeneity and cellular responses of VSMCs and monocytes/macrophages during AAA progression, which provide insights into their function and the regulation of AAA onset and progression.

Inhibition of macrophage histone demethylase JMJD3 protects against abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a life-threatening disease for which there is a lack of effective therapy preventing aortic rupture. During AAA formation, pathological vascular remodeling is driven by macrophage infiltration, and the mechanisms regulating macrophage-mediated inflammation remain undefined. Recent evidence suggests that an epigenetic enzyme, JMJD3, plays a critical role in establishing macrophage phenotype. Using single-cell RNA sequencing of human AAA tissues, we identified increased JMJD3 in aortic monocyte/macrophages resulting in up-regulation of an inflammatory immune response. Mechanistically, we report that interferon-β regulates Jmjd3 expression via JAK/STAT and that JMJD3 induces NF-κB–mediated inflammatory gene transcription in infiltrating aortic macrophages. In vivo targeted inhibition of JMJD3 with myeloid-specific genetic depletion (JMJD3^f/fLyz2^Cre+) or pharmacological inhibition in the elastase or angiotensin II–induced AAA model preserved the repressive H3K27me3 on inflammatory gene promoters and markedly reduced AAA expansion and attenuated macrophage-mediated inflammation. Together, our findings suggest that cell-specific pharmacologic therapy targeting JMJD3 may be an effective intervention for AAA expansion.

Vinpocetine protects against the development of experimental abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA), commonly occurring in the aged population, is a degenerative disease that dilate and weaken infrarenal aorta due to progressive degeneration of aortic wall integrity. Vinpocetine, a derivative of alkaloid vincamine, has long been used for cerebrovascular disorders and cognitive impairment in the aged population. Recent studies have indicated that vinpocetine antagonizes occlusive vascular disorders such as intimal hyperplasia and atherosclerosis. However, its role in vascular degenerative disease AAA remains unexplored. Herein, we determined the effect of vinpocetine on the formation of AAA as well as the intervention of pre-existing moderate AAA. AAA was induced by periaortic elastase application in C57BL/6J mice. Systemic vinpocetine treatment was applied daily via intraperitoneal injection. We showed that vinpocetine pre-treatment remarkably attenuated aneurysmal dilation assessed by diameter and volume. More importantly, vinpocetine also significantly suppressed the progression of pre-existing moderate AAA in a post-intervention model. Vinpocetine improved multiple cellular and molecular changes associated with AAA, such as elastin degradation, media smooth muscle cell depletion, collagen fibers remodeling and macrophage infiltration in aneurysmal tissues. Vinpocetine potently suppressed tumor necrosis factor-α-induced nuclear factor kappa-light-chain-enhancer of activated B cells activation and proinflammatory mediator expression in primary cultured macrophages in vitro, as well as in the aorta wall in vivo, suggesting vinpocetine conferred anti-AAA effect at least partially via the inhibition of inflammation. Taken together, our findings reveal a novel role of vinpocetine in AAA formation, development and progression. Given the excellent safety profile of vinpocetine, the present study suggests vinpocetine may be a novel therapeutic agent for AAA prevention and treatment.

A Dual Role of Heme Oxygenase-1 in Angiotensin II-Induced Abdominal Aortic Aneurysm in the Normolipidemic Mice

Abdominal aortic aneurysm (AAA) bears a high risk of rupture and sudden death of the patient. The pathogenic mechanisms of AAA remain elusive, and surgical intervention represents the only treatment option. Heme oxygenase-1 (HO-1), a heme degrading enzyme, is induced in AAA, both in mice and humans. HO-1 was reported to mitigate AAA development in an angiotensin II (AngII)-induced model of AAA in hyperlipidemic ApoE^-/- mice. Since the role of hyperlipidaemia in the pathogenesis of AAA remains controversial, we aimed to evaluate the significance of HO-1 in the development and progression of AAA in normolipidemic animals. The experiments were performed in HO-1-deficient mice and their wild-type counterparts. We demonstrated in non-hypercholesterolemic mice that the high-dose of AngII leads to the efficient formation of AAA, which is attenuated by HO-1 deficiency. Yet, if formed, they are significantly more prone to rupture upon HO-1 shortage. Differential susceptibility to AAA formation does not rely on enhanced inflammatory response or oxidative stress. AAA-resistant mice are characterized by an increase in regulators of aortic remodeling and angiotensin receptor-2 expression, significant medial thickening, and delayed blood pressure elevation in response to AngII. To conclude, we unveil a dual role of HO-1 deficiency in AAA in normolipidemic mice, where it protects against AAA development, but exacerbates the state of formed AAA.

P-Selectin Glycoprotein Ligand-1 Deficiency Protects Against Aortic Aneurysm Formation Induced by DOCA Plus Salt

PURPOSE

P-selectin glycoprotein ligand-1 (PSGL-1) acts as a crucial regulator for the inflammatory cells infiltration by mediating the adhesion of leukocytes. However, the role of PSGL-1 in aortic aneurysm remains elusive. Here, we investigated the role of PSGL-1 in aortic aneurysm (AA) development.

METHODS

We first detected PSGL-1 expression in samples from aortic aneurysm patients and mouse AA models via western blotting, immunofluorescence, and flow cytometry, and then we used global PSGL-1 knockout mice and their wild type controls to establish an aortic aneurysm model induced by deoxycorticosterone acetate (DOCA) plus high salt (HS). The incidence, fatality rates, and the pathological changes of aortic aneurysm were analyzed in each group. The inflammation, adhesion molecules expression, and PSGL-1 mediated leukocyte-endothelial adhesion and their underlying mechanisms were explored further.

RESULTS

Increased PSGL-1 levels were observed in human and mouse aortic aneurysm, and on leukocytes of mice treated with DOCA+HS. PSGL-1 deficiency reduced the incidence and severity of aortic aneurysm significantly, as well as decreased elastin fragmentation, collagen accumulation, and smooth muscle cells degeneration. Mechanistically, the protective effect of PSGL-1 inhibition was mediated by the reduced adhesion molecules, and the subsequently reduced leukocyte-endothelial adhesion through the NF-κB pathway, which finally led to reduced inflammatory cells infiltration and decreased inflammatory factors expression.

CONCLUSION

PSGL-1 deficiency is protective against inflammatory cells migration and recruitment in the condition of AA through attenuation of leukocyte-endothelial adhesion. Inhibition of PSGL-1 may be a potential therapeutic target for the prevention and treatment of human AA.

CTRP13 Mitigates Abdominal Aortic Aneurysm Formation via NAMPT1

Abdominal aortic aneurysm (AAA) is a life-threatening cardiovascular disease characterized by localized dilation of the abdominal aorta. C1q/tumor necrosis factor (TNF)-related protein-13 (CTRP13) is a secreted adipokine that plays important roles in the cardiovascular system. However, the functional role of CTRP13 in the formation and development of AAA has yet to be explored. In this study, we determined that serum CTRP13 levels were significantly downregulated in blood samples from patients with AAA and in rodent AAA models induced by Angiotensin II (Ang II) in ApoE^-/- mice or by CaCl₂ in C57BL/6J mice. Using two distinct murine models of AAA, CTRP13 was shown to effectively reduce the incidence and severity of AAA in conjunction with reduced aortic macrophage infiltration, expression of proinflammatory cytokines (interleukin-6 [IL-6], TNF-α, and monocyte chemoattractant protein 1 [MCP-1]), and vascular smooth muscle cell (SMC) apoptosis. Mechanistically, nicotinamide phosphoribosyl-transferase 1 (NAMPT1) was identified as a new target of CTRP13. The decreased in vivo and in vitro expression of NAMPT1 was markedly reversed by CTRP13 supplementation in a ubiquitination-proteasome-dependent manner. NAMPT1 knockdown further blocked the beneficial effects of CTRP13 on vascular inflammation and SMC apoptosis. Overall, our study reveals that CTRP13 management may be an effective treatment for preventing AAA formation.

Associations of global DNA methylation and homocysteine levels with abdominal aortic aneurysm: A cohort study from a population-based screening program in Sweden

Abdominal aortic aneurysm (AAA) is a life-threatening condition with a mortality rate of over 80%. Persistent smoking, which is a risk factor for AAA, has lasting effects on DNA methylation. Moreover, a plasma-amino acid, homocysteine, previously implicated in vascular diseases, including aneurysms, has well-established biological association with methylation. In the present study, we aimed to determine the global DNA methylation, homocysteine levels and their association with AAA and its growth. Enzyme-linked immunosorbent assay (ELISA) was used to quantify global DNA methylation in whole blood-DNA samples and diagnostic enzymatic assay quantified plasma homocysteine, from 65-year old men with (n = 116) and without AAA (n = 230) diagnosed at ultrasound screening. We found significantly higher global DNA methylation (p < .001) and homocysteine levels (p < .001) in men with AAA compared to those without AAA, and direct linear associations with baseline aortic diameter. On multivariable regression analysis, global DNA methylation (odds ratio [OR]: 1.8; 95% confidence interval [CI]: 1.1-2.9) and homocysteine levels (OR: 1.1; 95% CI:1.0-1.1) were positively associated with AAA, independent of smoking, medication use, and major co-morbidities. However, we did not find any significant association between DNA methylation or homocysteine levels with AAA growth during follow-up. We found that global DNA methylation and homocysteine levels are higher in men with AAA but are not associated with AAA growth. This indicates that different pathways and mechanisms may be involved in initiation and progression of AAA. More studies are needed to understand the precise role of DNA methylation, homocysteine and their interplay in AAA pathophysiology.

The C57Bl/6J mouse strain is more susceptible to angiotensin II-induced aortic aneurysm formation than C57Bl/6N

BACKGROUND AND AIMS

Genetic variations between C57Bl/6 mouse substrains are highly relevant to the investigation of cardiovascular disease. We here assessed whether these variations have an impact on the incidence of abdominal aortic aneurysms (AAA) in C57Bl/6J and 6 N mice.

METHODS

AAA were induced by subcutaneous infusion of 1500 ng/kg*min Angiotensin-II for four weeks in six-month-old male CB57Bl/6J and 6N mice. Aortic smooth muscle cells (VSMC) were isolated from untreated animals for in vitro analysis.

RESULTS

C57Bl/6J mice are more susceptible to AAA formation (76.5% vs. 7.1%, p = 0.0002). C57Bl/6J VSMC expressed more pro-inflammatory molecules such as Nlrp3, Aim2 and NF-κB. Additionally, these cells presented significantly higher levels of NADP/NADPH and oxidative DNA modifications, as indicated by 8-OHdG-staining, compared to C57Bl/6N VSMC.

CONCLUSIONS

In contrast to previous reports, we present evidence that six-month-old C57BL/6J, but not C57BL/6N mice develop AAA. In accordance with the deficiency of nicotinamide-nucleotide-transhydrogenase (Nnt), C57BL/6J VSMC displayed increased oxidative stress, oxidative DNA damage and a stronger inflammatory phenotype than C57BL/6N VSMC.

Profiling of Histone Modifications Reveals Epigenomic Dynamics During Abdominal Aortic Aneurysm Formation in Mouse Models

Introduction: Abdominal aortic aneurysms (AAA) are characterized by localized inflammation, extracellular matrix degradation, and apoptosis of smooth muscle cells, which together lead to progressive and irreversible aortic dilation. Major risk factors for AAA include smoking and aging, both of which prominently alter gene expression via epigenetic mechanisms, including histone methylation (me) and acetylation (ac).However, little is known about epigenomic dynamics during AAA formation. Here, we profiled histone modification patterns in aortic tissues during AAA formation in two distinct mouse models; (1) angiotensin II (AngII) infusion in low density lipoprotein receptor (LDLR) knockout (KO) mice, and (2) calcium chloride (CaCl₂) application in wild type mice.

Methods and Results: AAA formed in both models, in conjunction with enhanced macrophage infiltration, elastin degradation and matrix metalloproteinases expression as evaluated by immunohistochemistry. To investigate the histone modification patterns during AAA formation, total histone proteins were extracted from AAA tissues, and histone H3 modifications were quantified using profiling kits. Intriguingly, we observed dynamic changes in histone H3 modifications of lysine (K) residues at different time points during AAA formation. In mature aneurysmal tissues at 3 weeks after AngII infusion, we detected reduced K4/K27/K36 monomethylation, K9 trimethylation K9, and K9/K56 acetylation (<70%), and increased K4 trimethylation (>130%). Conversely, in CaCl₂-induced AAA, K4/K9/K27/K36/K79 monomethylation and K9/K18/K56 acetylation were reduced in AAA tissues, whereas K27 di-/tri-methylation and K14 acetylation were upregulated. Interestingly, K4/K27/K36 monomethylation, K9 trimethylation, and K9/K56 acetylation were commonly downregulated in both animal models, while no H3 modifications were uniformly upregulated. Western blot of AAA tissues confirmed markedly reduced levels of key H3 modifications, including H3K4me1, H3K9me3, and H3K56ac. Furthermore, pathway enrichment analysis using an integrative bioinformatics approach identified specific molecular pathways, including endocytosis, exon guidance and focal adhesion signaling, that may potentially be linked to these histone H3 modifications during AAA formation.

Conclusions: Dynamic modifications of histone H3 occur during AAA formation in both animal models. We identified 6 discreet H3 modifications that are consistently downregulated in both models, suggesting a possible role in AAA pathobiology. Identifying the functional mechanisms may facilitate development of novel strategies for AAA prevention or treatment.

Nano-Biomaterials for the Delivery of Therapeutic and Monitoring Cues for Aortic Diseases

The aorta is the largest artery in the body, so any diseases or conditions which could cause damage to the aorta would put patients at considerable and life-threatening risk. In the management of aortic diseases, the major treatments include drug therapy, endovascular treatment, and surgical treatment, which are of great danger or with a poor prognosis. The delivery of nano-biomaterials provides a potential development trend and an emerging field where we could monitor patients’ conditions and responses to the nanotherapeutics. One of the putative applications of nanotechnology is ultrasensitive monitoring of cardiovascular markers by detecting and identifying aneurysms. Moreover, the use of nanosystems for targeted drug delivery can minimize the systemic side effects and enhance drug positioning and efficacy compared to conventional drug therapies. This review shows some examples of utilizing nano-biomaterials in in vitro organ and cell culture experiments and explains some developing technologies in delivering and monitoring regenerative therapeutics.

Nucleolar stress induces a senescence-like phenotype in smooth muscle cells and promotes development of vascular degeneration

Senescence of smooth muscle cells (SMCs) has a crucial role in the pathogenesis of abdominal aortic aneurysm (AAA), a disease of vascular degeneration. Perturbation of cellular ribosomal DNA (rDNA) transcription triggers nucleolar stress response. Previously we demonstrated that induction of nucleolar stress in SMCs elicited cell cycle arrest via the ataxia-telangiectasia mutated (ATM)/ATM- and Rad3-related (ATR)-p53 axis. However, the specific roles of nucleolar stress in vascular degeneration remain unexplored. In the present study, we demonstrated for the first time that in both human and animal AAA tissues, there were non-coordinated changes in the expression of RNA polymerase I machinery components, including a downregulation of transcription initiation factor-IA (TIF-IA). Genetic deletion of TIF-IA in SMCs in mice (smTIF-IA^-/-) caused spontaneous aneurysm-like lesions in the aorta. In vitro, induction of nucleolar stress triggered a non-canonical DNA damage response, leading to p53 phosphorylation and a senescence-like phenotype in SMCs. In human AAA tissues, there was increased nucleolar stress in medial cells, accompanied by localized DNA damage response within the nucleolar compartment. Our data suggest that perturbed rDNA transcription and induction of nucleolar stress contribute to the pathogenesis of AAA. Moreover, smTIF-IA^-/- mice may be a novel animal model for studying spontaneous AAA-like vascular degenerations.

Prevention of Progression of Aortic Aneurysm by Peptide Vaccine Against Ang II (Angiotensin II) in a Rat Model

There is no proven medical therapy to inhibit the progression of abdominal aortic aneurysm (AAA) in the clinical setting. To develop a novel therapeutic approach for the treatment of AAA, we focused on vaccination targeting Ang II (angiotensin II) and assessed the effect of an Ang II peptide vaccine on the progression of AAA using a rat model. Ang II peptide was conjugated with KLH (keyhole limpet hemocyanin) carrier protein to induce a sufficient immune response. Male rats were subcutaneously immunized with Ang II-KLH with an adjuvant on days 0, 14, and 28. Aortic dilatation was induced by intraluminal incubation with elastase on day 35. Treatment with Ang II vaccine successfully induced the production of a high titer of anti-Ang II antibodies. Immunization with Ang II vaccine resulted in a significant reduction in expansion of the aortic diameter compared with control rats, without a blood pressure-lowering effect. Four weeks after operation, the increase in Ang II in the aneurysm wall was significantly inhibited by treatment with Ang II vaccine. Inhibition of Ang II action led to suppression of the inflammatory response in the AAA wall through attenuation of the NFκB (nuclear factor kappa B) and c-jun N-terminal kinase signaling cascades. Treatment with Ang II vaccine inhibited accumulation of macrophages in the AAA wall. In addition, expression of TNF-α (tumor necrosis factor alpha) and activation of MMP (matrix metalloproteinase)-2 and MMP-9 were also inhibited by treatment with Ang II vaccine, resulting in protection against the destruction of elastic fibers. This vaccine therapy could become a potent therapeutic option to treat patients with AAA.

Simultaneous molecular MRI of extracellular matrix collagen and inflammatory activity to predict abdominal aortic aneurysm rupture

Abdominal aortic aneurysm (AAA) is a life-threatening vascular disease with an up to 80% mortality in case of rupture. Current biomarkers fail to account for size-independent risk of rupture. By combining the information of different molecular probes, multi-target molecular MRI holds the potential to enable individual characterization of AAA. In this experimental study, we aimed to examine the feasibility of simultaneous imaging of extracellular collagen and inflammation for size-independent prediction of risk of rupture in murine AAA. The study design consisted of: (1) A outcome-based longitudinal study with imaging performed once after one week with follow-up and death as the end-point for assessment of rupture risk. (2) A week-by-week study for the characterization of AAA development with imaging after 1, 2, 3 and 4 weeks. For both studies, the animals were administered a type 1 collagen-targeted gadolinium-based probe (surrogate marker for extracellular matrix (ECM) remodeling) and an iron oxide-based probe (surrogate marker for inflammatory activity), in one imaging session. In vivo measurements of collagen and iron oxide probes showed a significant correlation with ex vivo histology (p < 0.001) and also corresponded well to inductively-coupled plasma-mass spectrometry and laser-ablation inductively-coupled plasma mass spectrometry. Combined evaluation of collagen-related ECM remodeling and inflammatory activity was the most accurate predictor for AAA rupture (sensitivity 80%, specificity 100%, area under the curve 0.85), being superior to information from the individual probes alone. Our study supports the feasibility of a simultaneous assessment of collagen-related extracellular matrix remodeling and inflammatory activity in a murine model of AAA.

Mouse models for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) rupture is estimated to cause 200,000 deaths each year. Currently, the only treatment for AAA is surgical repair; however, this is only indicated for large asymptomatic, symptomatic or ruptured aneurysms, is not always durable, and is associated with a risk of serious perioperative complications. As a result, patients with small asymptomatic aneurysms or who are otherwise unfit for surgery are treated conservatively, but up to 70% of small aneurysms continue to grow, increasing the risk of rupture. There is thus an urgent need to develop drug therapies effective at slowing AAA growth. This review describes the commonly used mouse models for AAA. Recent research in these models highlights key roles for pathways involved in inflammation and cell turnover in AAA pathogenesis. There is also evidence for long non-coding RNAs and thrombosis in aneurysm pathology. Further well-designed research in clinically relevant models is expected to be translated into effective AAA drugs.

Hyperlipidemia does not affect development of elastase-induced abdominal aortic aneurysm in mice

BACKGROUND AND AIMS

Hyperlipidemia is a suggested risk factor for abdominal aortic aneurysm (AAA). However, whether hyperlipidemia is causally involved in AAA progression remains elusive. Here, we tested the hypothesis that hyperlipidemia aggravates AAA formation in the widely used porcine pancreatic elastase (PPE) model of AAA in mice with varying levels of plasma lipids.

METHODS

Prior to PPE-surgery, 8-week-old male C57BL/6J mice (n = 32) received 1·10¹¹ viral genomes of rAAV8-D377Y-mPcsk9 or control rAAV8 via the tail vein. Mice were fed either western type diet or regular chow. At baseline and during the 28 days following PPE-surgery, mice underwent weekly ultrasonic assessment of AAA progression. Experiments were repeated using Apolipoprotein E knockout (ApoE^-/-) mice (n = 7) and wildtype C57BL/6J mice (n = 5).

RESULTS

At sacrifice, maximal intergroup plasma cholesterol and non-HDL/HDL ratio differences were >5-fold and >20-fold, respectively. AAA diameters expanded to 150% of baseline, but no intergroup differences were detected. This was verified in an independent experiment comparing 8-week-old male ApoE^-/- mice with wildtype mice. Histological evaluation of experimental AAA lesions revealed accumulated lipid in neointimal and medial layers, and analysis of human AAA lesions (n = 5) obtained from open repair showed medial lipid deposition.

CONCLUSIONS

In summary, we find that lipid deposition in the aortic wall is a feature of PPE-induced AAA in mice as well as human AAA lesions. Despite, our data do not support the hypothesis that hyperlipidemia contributes to AAA progression.