Aortic Wall Inflammation Predicts Abdominal Aortic Aneurysm Expansion, Rupture, and Need for Surgical Repair

Depletion of CD11c+ dendritic cells in apolipoprotein E-deficient mice limits angiotensin II-induced abdominal aortic aneurysm formation and growth

OBJECTIVE

The role of chronic inflammation in abdominal aortic aneurysm (AAA) is controversial. CD11c+ antigen-presenting cells (APCs) (dendritic cells (DCs)) have been reported in human AAA samples but their role is unclear. The effect of conditional depletion of CD11c+ cells on experimental AAA was investigated in the angiotensin II (AngII)-infused apolipoprotein E-deficient (ApoE-/-) mouse model.

APPROACH

CD11c-diphtheria toxin (DT or D.tox) receptor (DTR), ovalbumin (OVA) fragment aa 140-386, and enhanced green fluorescent protein (eGFP)-ApoE-/- (CD11c.DOG.ApoE-/-) mice were generated and CD11c+ cell depletion achieved with D.tox injections (8 ng/g body weight, i.p., every-other-day). AAA formation and growth were assessed by measurement of supra-renal aortic (SRA) diameter in vivo by serial ultrasound and by morphometry assessment of harvested aortas at the end of the study.

RESULTS

Depletion of CD11c+ cells by administration of D.tox on alternative days was shown to reduce the maximum diameter of AAAs induced by 28 days AngII infusion compared with controls (D.tox, 1.58 ± 0.03 mm vs Vehicle control, 1.81 ± 0.06 mm, P<0.001). CD11c+ depletion commencing after AAA establishment by 14 days of AngII infusion, was also shown to lead to smaller AAAs than controls after a further 14 days (D.tox, 1.54 ± 0.04 mm vs Vehicle control, 1.80 ± 0.03 mm, P<0.001). Flow cytometry revealed significantly lower numbers of circulating CD44hi CD62Llo effector CD4 T cells, CD44hi CD62Llo effector CD8 T cells and B220+ B cells in CD11c+ cell-depleted mice versus controls. CD11c+ depletion attenuated SRA matrix degradation indicated by decreased neutrophil elastase activity (P=0.014), lower elastin degradation score (P=0.012) and higher collagen content (P=0.002).

CONCLUSION

CD11c+ cell-depletion inhibited experimental AAA development and growth associated with down-regulation of circulating effector T cells and attenuated matrix degradation. The findings suggest involvement of autoreactive immune cells in AAA pathogenesis.

Red Cell Distribution Width is Associated with Future Incidence of Abdominal Aortic Aneurysm in a Population-Based Cohort Study

Red cell distribution width (RDW) has been suggested to have a predictive potential for several cardiovascular diseases, but its association with abdominal aortic aneurysm (AAA) is unknown. We examined whether RDW is associated with the risk of AAA among 27,260 individuals from the population-based Malmö Diet and Cancer Study cohort. Data of baseline characteristics were collected during 1991–1996. Cox regression was used to estimate hazard ratios (HR) with 95% confidence intervals (CI) for AAA across quartiles of RDW. During a median follow-up of 21.7 years, 491 subjects developed AAA. After adjustment for other confounding factors, participants in the highest quartile of RDW experienced 61% increased risk of AAA as compared to those with the lowest quartile (HR = 1.61, CI = 1.20, 2.12). RDW showed similar relationship with severe (i.e. ruptured or surgically repaired) AAA or non-severe AAA (adjusted HR 1.58 and 1.60, respectively). The observed association between RDW and AAA risk was significant in current smokers (adjusted HR = 1.68, CI = 1.18, 2.38) but not in former smokers (adjusted HR = 1.13, CI = 0.72, 1.79), or never-smokers (adjusted HR = 1.77, CI = 0.74, 4.22). Elevated RDW is associated with increased future incidence of AAA, however the causal and pathophysiological mechanisms remain to be explored.

CCR2 Positron Emission Tomography for the Assessment of Abdominal Aortic Aneurysm Inflammation and Rupture Prediction

BACKGROUND

The monocyte chemoattractant protein-1/CCR2 (chemokine receptor 2) axis plays an important role in abdominal aortic aneurysm (AAA) pathogenesis, with effects on disease progression and anatomic stability. We assessed the expression of CCR2 in a rodent model and human tissues, using a targeted positron emission tomography radiotracer (64Cu-DOTA-ECL1i).

METHODS

AAAs were generated in Sprague-Dawley rats by exposing the infrarenal, intraluminal aorta to PPE (porcine pancreatic elastase) under pressure to induce aneurysmal degeneration. Heat-inactivated PPE was used to generate a sham operative control. Rat AAA rupture was stimulated by the administration of β-aminopropionitrile, a lysyl oxidase inhibitor. Biodistribution was performed in wild-type rats at 1 hour post tail vein injection of 64Cu-DOTA-ECL1i. Dynamic positron emission tomography/computed tomography imaging was performed in rats to determine the in vivo distribution of radiotracer.

RESULTS

Biodistribution showed fast renal clearance. The localization of radiotracer uptake in AAA was verified with high-resolution computed tomography. At day 7 post-AAA induction, the radiotracer uptake (standardized uptake value [SUV]=0.91±0.25) was approximately twice that of sham-controls (SUV=0.47±0.10; P<0.01). At 14 days post-AAA induction, radiotracer uptake by either group did not significantly change (AAA SUV=0.86±0.17 and sham-control SUV=0.46±0.10), independent of variations in aortic diameter. Competitive CCR2 receptor blocking significantly decreased AAA uptake (SUV=0.42±0.09). Tracer uptake in AAAs that subsequently ruptured (SUV=1.31±0.14; P<0.005) demonstrated uptake nearly twice that of nonruptured AAAs (SUV=0.73±0.11). Histopathologic characterization of rat and human AAA tissues obtained from surgery revealed increased expression of CCR2 that was co-localized with CD68+ macrophages. Ex vivo autoradiography demonstrated specific binding of 64Cu-DOTA-ECL1i to CCR2 in both rat and human aortic tissues.

CONCLUSIONS

CCR2 positron emission tomography is a promising new biomarker for the noninvasive assessment of AAA inflammation that may aid in associated rupture prediction.

Cellular signaling in Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAAs) are highly lethal cardiovascular diseases without effective medications. However, the molecular and signaling mechanisms remain unclear. A series of pathological cellular processes have been shown to contribute to AAA formation, including vascular extracellular matrix remodeling, inflammatory and immune responses, oxidative stress, and dysfunction of vascular smooth muscle cells. Each cellular process involves complex cellular signaling, such as NF-κB, MAPK, TGFβ, Notch and inflammasome signaling. In this review, we discuss how cellular signaling networks function in various cellular processes during the pathogenesis and progression of AAA. Understanding the interaction of cellular signaling networks with AAA pathogenesis as well as the crosstalk of different signaling pathways is essential for the development of novel therapeutic approaches to and personalized treatments of AAA diseases.

Imaging inflammation after myocardial infarction: implications for prognosis and therapeutic guidance

Inflammation after myocardial infarction (MI) has been in the focus of cardiovascular research for several years as it influences the remodeling process of the ischemic heart and thereby critically determines the clinical outcome of the patient. Today, it is well appreciated that inflammation is a crucial necessity for the initiation of the natural wound healing process; however, excessive inflammation can have detrimental effects and might result in adverse ventricular remodeling which is associated with an increased risk of heart failure. Newly emerged imaging techniques facilitate the non-invasive assessment of immune cell infiltration into the ischemic myocardium and can provide greater insight into the underlying complex and dynamic repair mechanisms. Molecular imaging of inflammation in the context of MI may help with stratification of patients at high risk of adverse ventricular remodeling post-MI which may be of diagnostic, therapeutic, and prognostic value. Novel radiopharmaceuticals may additionally provide a way to combine patient monitoring and therapy. In spite of great advances in recent years in the field of imaging sciences, clinicians still need to overcome some obstacles to a wider implementation of inflammation imaging post-MI. This review focuses on inflammation as a molecular imaging target and its potential implication in prognosis and therapeutic guidance.

Ferumoxytol-enhanced three-dimensional magnetic resonance imaging of carotid atheroma- a feasibility and temporal dependence study

Ferumoxytol is an ultrasmall super paramagnetic particles of iron oxide (USPIO) agent recently used for magnetic resonance (MR) vascular imaging. Other USPIOs have been previously used for assessing inflammation within atheroma. We aim to assess feasibility of ferumoxytol in imaging carotid atheroma (with histological assessment); and the optimum MR imaging time to detect maximum quantitative signal change post-ferumoxytol infusion. Ten patients with carotid artery disease underwent high-resolution MR imaging of their carotid arteries on a 1.5 T MR system. MR imaging was performed before and at 24, 48, 72 and 96 hrs post ferumoxytol infusion. Optimal ferumoxytol uptake time was evaluated by quantitative relaxometry maps indicating the difference in T₂* (ΔT₂*) and T₂ (ΔT₂) between baseline and post-Ferumoxytol MR imaging using 3D DANTE MEFGRE qT₂*w and iMSDE black-blood qT₂w sequences respectively. 20 patients in total (10 symptomatic and 10 with asymptomatic carotid artery disease) had ferumoxytol-enhanced MR imaging at the optimal imaging window. 69 carotid MR imaging studies were completed. Ferumoxytol uptake (determined by a decrease in ΔT₂* and ΔT₂) was identified in all carotid plaques (symptomatic and asymptomatic). Maximum quantitative decrease in ΔT₂* (10.4 [3.5-16.2] ms, p < 0.001) and ΔT₂ (13.4 [6.₂-18.9] ms; p = 0.001) was found on carotid MR imaging at 48 hrs following the ferumoxytol infusion. Ferumoxytol uptake by carotid plaques was assessed by histopathological analysis of excised atheroma. Ferumoxytol-enhanced MR imaging using quantitative 3D MR pulse sequences allows assessment of inflammation within carotid atheroma in symptomatic and asymptomatic patients. The optimum MR imaging time for carotid atheroma is 48 hrs after its administration.

Concurrent Molecular Magnetic Resonance Imaging of Inflammatory Activity and Extracellular Matrix Degradation for the Prediction of Aneurysm Rupture

BACKGROUND

Molecular magnetic resonance imaging is a promising modality for the characterization of abdominal aortic aneurysms (AAAs). The combination of different molecular imaging biomarkers may improve the assessment of the risk of rupture. This study investigates the feasibility of imaging inflammatory activity and extracellular matrix degradation by concurrent dual-probe molecular magnetic resonance imaging in an AAA mouse model.

METHODS

Osmotic minipumps with a continuous infusion of Ang II (angiotensin II; 1000 ng/[kg·min]) to induce AAAs were implanted in apolipoprotein-deficient mice (N=58). Animals were assigned to 2 groups. In group 1 (longitudinal group, n=13), imaging was performed once after 1 week with a clinical dose of a macrophage-specific iron oxide-based probe (ferumoxytol, 4 mgFe/kg, surrogate marker for inflammatory activity) and an elastin-specific gadolinium-based probe (0.2 mmol/kg, surrogate marker for extracellular matrix degradation). Animals were then monitored with death as end point. In group 2 (week-by-week-group), imaging with both probes was performed after 1, 2, 3, and 4 weeks (n=9 per group). Both probes were evaluated in 1 magnetic resonance session.

RESULTS

The combined assessment of inflammatory activity and extracellular matrix degradation was the strongest predictor of AAA rupture (sensitivity 100%; specificity 89%; area under the curve, 0.99). Information from each single probe alone resulted in lower predictive accuracy. In vivo measurements for the elastin- and iron oxide-probe were in good agreement with ex vivo histopathology (Prussian blue-stain: R²=0.96, P<0.001; Elastica van Giesson stain: R²=0.79, P<0.001). Contrast-to-noise ratio measurements for the iron oxide and elastin-probe were in good agreement with inductively coupled mass spectroscopy ( R²=0.88, R²=0.75, P<0.001) and laser ablation coupled to inductively coupled plasma-mass spectrometry.

CONCLUSIONS

This study demonstrates the potential of the concurrent assessment of inflammatory activity and extracellular matrix degradation by dual-probe molecular magnetic resonance imaging in an AAA mouse model. Based on the combined information from both molecular probes, the rupture of AAAs could reliably be predicted.

Intraluminal Thrombus Predicts Rapid Growth of Abdominal Aortic Aneurysms

Background Intraluminal thrombus (ILT) within abdominal aortic aneurysms (AAAs) may be a potential marker for subsequent aneurysm growth. Purpose To investigate the role of ILT in AAA progression as assessed with CT and MRI. Materials and Methods This was a retrospective study, with patient data included from January 2004 to December 2018 at a Veteran Affairs medical center. Male patients with AAA who underwent contrast material-enhanced CT at baseline and CT or black-blood MRI at follow-up (minimal follow-up duration of 6 months) were included. The maximal AAA diameter was measured with multiplanar reconstruction, and the annual growth rate of aneurysms was calculated. Uni- and multivariable linear regression analyses were used to determine the relationship between demographic and imaging factors and aneurysm growth. Results A total of 225 patients (mean age, 72 years ± 9 [standard deviation]) were followed for a mean of 3.3 years ± 2.5. A total of 207 patients were followed up with CT, and 18 were followed up with MRI. At baseline, the median size of the AAA was 3.8 cm (interquartile range [IQR], 3.3-4.3 cm); 127 of 225 patients (54.7%) had ILT. When compared with AAAs without ILT, AAAs with ILT had larger baseline diameters (median, 4.1 cm [IQR, 3.6-4.8 cm] vs 3.4 cm [IQR, 3.2-3.9 cm]; P < .001) and faster growth rates (median, 2.0 mm/y [IQR, 1.3-3.2 mm/y] vs 1.0 mm/y [IQR, 0.4-1.8 mm/y]; P < .001). Small AAAs (size range, 3-4 cm) with ILT grew 1.9-fold faster than did those without ILT (median, 1.5 mm/y [IQR, 0.9-2.7 mm/y] vs 0.8 mm/y [IQR, 0.3-1.5 mm/y]; P < .001). Medium AAAs (size range, 4-5 cm) with ILT had 1.2-fold faster growth than did those without ILT (median growth, 2.1 mm/y [IQR, 1.4, 3.7 mm/y] vs 1.8 mm/y [IQR, 0.9, 2.0 mm/y]; P = .06). In multivariable analysis, baseline diameter and ILT were independently positively related to aneurysm growth rate (standardized regression coefficient, 0.43 [P < .001] and 0.15 [P = .02], respectively). Conclusion Both maximal cross-sectional aneurysm diameter and the presence of intraluminal thrombus are independent predictors of abdominal aortic aneurysm growth. © RSNA, 2020 Online supplemental material is available for this article.

The application of computational modeling for risk prediction in type B aortic dissection

OBJECTIVE

New tools are urgently needed to help with surgical decision-making in type B aortic dissection (TBAD) that is uncomplicated at the time of initial presentation. This narrative review aims to answer the clinical question, Can computational modeling be used to predict risk in acute and chronic Stanford TBAD?

METHODS

The review (PROSPERO 2018 CRD42018104472) focused on risk prediction in TBAD. A comprehensive search of the Ovid MEDLINE database, using terms related to computational modeling and aortic dissection, was conducted to find studies of any form published between 1998 and 2018. Cohort studies, case series, and case reports of adults (older than 18 years) with computed tomography or magnetic resonance imaging diagnosis of TBAD were included. Computational modeling was applied in all selected studies.

RESULTS

There were 37 studies about computational modeling of TBAD identified from the search, and the findings were synthesized into a narrative review. Computational modeling can produce numerically calculated values of stresses, pressures, and flow velocities that are difficult to measure in vivo. Hemodynamic parameters-high or low wall shear stress, high pressure gradient between lumens during the cardiac cycle, and high false lumen flow rate-have been linked to the pathogenesis of branch malperfusion and aneurysm formation by numerous studies. Considering the major outcomes of end-organ failure, aortic rupture, and stabilization and remodeling, hypotheses have been generated about inter-relationships of measurable parameters in computational models with observable anatomic and pathologic changes, resulting in specific clinical outcomes.

CONCLUSIONS

There is consistency in study findings about computational modeling in TBAD, although a limited number of patients have been analyzed using various techniques. The mechanistic patterns of association found in this narrative review should be investigated in larger cohort prospective studies to further refine our understanding. It highlights the importance of patient-specific computational hemodynamic parameters in clinical decision-making algorithms. The current challenge is to develop and to test a risk assessment method that can be used by clinicians for TBAD.

On the Relative Impact of Intraluminal Thrombus Heterogeneity on Abdominal Aortic Aneurysm Mechanics

Intraluminal thrombus (ILT) is present in the majority of abdominal aortic aneurysms (AAA) of a size warranting consideration for surgical or endovascular intervention. The rupture risk of AAAs is thought to be related to the balance of vessel wall strength and the mechanical stress caused by systemic blood pressure. Previous finite element analyses of AAAs have shown that ILT can reduce and homogenize aneurysm wall stress. These works have largely considered ILT to be homogeneous in mechanical character or have idealized a stiffness distribution through the thrombus thickness. In this work, we use magnetic resonance imaging (MRI) to delineate the heterogeneous composition of ILT in 7 AAAs and perform patient-specific finite element analysis under multiple conditions of ILT layer stiffness disparity. We find that explicit incorporation of ILT heterogeneity in the finite element analysis is unlikely to substantially alter major stress analysis predictions regarding aneurysm rupture risk in comparison to models assuming a homogenous thrombus, provided that the maximal ILT stiffness is the same between models. Our results also show that under a homogeneous ILT assumption, the choice of ILT stiffness from values common in the literature can result in significantly larger variations in stress predictions compared to the effects of thrombus heterogeneity.

Discovery of crucial cytokines associated with abdominal aortic aneurysm formation by protein array analysis

As a common disease, abdominal aortic aneurysm (AAA) features permanently progressively dilated abdominal aorta. Various cytokines are implicated in AAA pathogenesis. Clarification of involved cytokines combined with functional analysis may provide new insights into AAA pathogenesis. Using a mouse model, this study analyzed the cytokine profiles in AAA. Cytokines were measured in AAA tissues of saline control or angiotensin II-treated ApoE−/− mice using an antibody array of 200 cytokines, cytokine receptors, and related proteins. Statistical analysis revealed that 21 of 200 proteins were differentially expressed in AAA. These differentially expressed proteins were subjected to function and pathway enrichment analysis, which revealed that leukocyte migration and positive regulation of cell adhesion were the most significant biological processes. Specific signaling pathways, including Janus kinase/signal transducers and activators of transcription and cytokine–cytokine receptor interaction, were prominent in Kyoto encyclopedia of genes and genomes pathway enrichment analysis. Importantly, our data identified cytokines which had not previously been illustrated in AAA pathogenic pathways. Bivariate correlation analysis between these cytokines and protease activity showed that granulocyte colony-stimulating factor (G-CSF), macrophage inflammatory protein 1 g, cardiotrophin 1, milk fat globule-EGF factor 8 protein, interleukin 33, and periostin were positively correlated with matrix metalloprotease 1 (MMP-1), MMP-9, cathepsin B, and cathepsin L. G-CSF was positively correlated with cathepsin L. In conclusion, these results demonstrate that cytokine profile is significantly altered in AAA, and that the newly identified crucial cytokines may function potentially in AAA pathogenesis.

Impact statement

Various cytokines are known contributors to abdominal aortic aneurysm (AAA) pathologic processes, but the mechanisms underlying the pathogenesis remains unclear. We illustrated the altered cytokine profiles in AAA by high throughput antibody array of 200 cytokines, cytokine receptors and related proteins, as well as bioinformatics analysis of differentially expressed proteins in lesion tissues from AAA mice infused with angiotensin II. Functional analyses of differentially expressed cytokines showed clustering on cell migration and adhesion processes. More importantly, crucial cytokines whose association with AAA formation had not been established were identified. Significant correlations were found between these cytokines and protease activity. This study identifies several crucial markers for further researches on the molecular basis of AAA.

Plasma Desmosine and Abdominal Aortic Aneurysm Disease

Background

It is recognized that factors beyond aortic size are important in predicting outcome in abdominal aortic aneurysm (AAA) disease. AAA is characterized by the breakdown of elastin within the aortic tunica media, leading to aortic dilatation and rupture. The aim of this study was to investigate the association of plasma desmosine (pDES), an elastin‐specific degradation product, with disease severity and clinical outcome in patients with AAA.

Methods and Results

We measured pDES and serum biomarker concentrations in 507 patients with AAAs (94% men; mean age, 72.4±6.1 years; mean AAA diameter, 48±8 mm) and 162 control subjects (100% men; mean age, 71.5±4.4 years) from 2 observational cohort studies. In the longitudinal cohort study (n=239), we explored the incremental prognostic value of pDES on AAA events. pDES was higher in patients with AAA compared with control subjects (mean±SD: 0.46±0.22 versus 0.33±0.16 ng/mL; P<0.001) and had the strongest correlation with AAA diameter (r=0.39; P<0.0001) of any serum biomarker. After adjustment for baseline AAA diameter, pDES was associated with an AAA event (hazard ratio, 2.03 per SD increase [95% CI, 1.02–4.02]; P=0.044). In addition to AAA diameter, pDES provided incremental improvement in risk stratification (continuous net reclassification improvement, 34.4% [95% CI, −10.8% to 57.5%; P=0.09]; integrated discrimination improvement, 0.04 [95% CI, 0.00–0.15; P=0.050]).

Conclusions

pDES concentrations predict disease severity and clinical outcomes in patients with AAA.

Clinical Trial Registration

http://www.isrctn.com. Unique identifier: ISRCTN76413758.

Takayasu Arteritis with Dyslipidemia Increases Risk of Aneurysm

Low-density lipoprotein cholesterol (LDL-C) has been associated with the occurrence of abdominal aortic aneurysm. However, whether LDL-C elevation associated with aneurysms in large vessel vasculitis is unknown. The aim of this study is to investigate the clinical and laboratory features of Takayasu arteritis (TAK) and explore the risk factors that associated with aneurysm in these patients. This retrospective study compared the clinical manifestations, laboratory parameters, and imaging results of 103 TAK patients with or without aneurysms and analyzed the risk factors of aneurysm formation. 20.4% of TAK patients were found to have aneurysms. The LDL-C levels was higher in the aneurysm group than in the non-aneurysm group (2.9 ± 0.9 mmol/l vs. 2.4 ± 0.9 mmol/l, p = 0.032). Elevated serum LDL-C levels increased the risk of aneurysm by 5.8-fold (p = 0.021, odds ratio [OR] = 5.767, 95% confidence interval [CI]: 1.302-25.543), and the cutoff value of level of serum LDL-C was 3.08 mmol/l. The risk of aneurysm was 4.2-fold higher in patients with disease duration >5 years (p = 0.042, OR = 4.237, 95% CI: 1.055-17.023), and 2.9-fold higher when an elevated erythrocyte sedimentation rate was present (p = 0.077, OR = 2.851, 95% CI: 0.891-9.115). In this study, elevated LDL-C levels increased the risk of developing aneurysms in patients with TAK.

Systems Approach to Study Associations between OxLDL and Abdominal Aortic Aneurysms

Although abdominal aortic aneurysm (AAA) is a common vascular disease and is associated with high mortality, the full pathogenesis of AAA remains unknown to researchers. Abdominal aortic aneurysms and atherosclerosis are strongly related. Currently, it is more often suggested that development of AAA is not a result of atherosclerosis, however, individual factors can act independently or synergistically with atherosclerosis. One of such factors is low-density lipoprotein (LDL) and its oxidized form (oxLDL). It is known that oxLDL plays an important role in the pathogenesis of atherosclerosis, thus, we decided to examine oxLDL impact on the development of AAA by creating two models using Petri-nets. The first, full model, contains subprocess of LDL oxidation and all subprocesses in which it participates, while the second, reduced model, does not contain them. The analysis of such models can be based on t-invariants. They correspond to subprocesses which do not change the state of the modeled system. Moreover, the knockout analysis has been used to estimate how crucial a selected transition (representing elementary subprocess) is, based on the number of excluded subprocesses as a result of its knockout. The results of the analysis of our models show that oxLDL affects 55.84% of subprocesses related to AAA development, but the analysis of the nets based on knockouts and simulation has shown that the influence of oxLDL on enlargement and rupture of AAA is negligible.

18F-Sodium Fluoride Uptake in Abdominal Aortic Aneurysms: The SoFIA3 Study

Background

Fluorine-18–sodium fluoride (¹⁸F-NaF) uptake is a marker of active vascular calcification associated with high-risk atherosclerotic plaque.

Objectives

In patients with abdominal aortic aneurysm (AAA), the authors assessed whether ¹⁸F-NaF positron emission tomography (PET) and computed tomography (CT) predicts AAA growth and clinical outcomes.

Methods

In prospective case-control (n = 20 per group) and longitudinal cohort (n = 72) studies, patients with AAA (aortic diameter >40 mm) and control subjects (aortic diameter <30 mm) underwent abdominal ultrasound, ¹⁸F-NaF PET-CT, CT angiography, and calcium scoring. Clinical endpoints were aneurysm expansion and the composite of AAA repair or rupture.

Results

Fluorine-18-NaF uptake was increased in AAA compared with nonaneurysmal regions within the same aorta (p = 0.004) and aortas of control subjects (p = 0.023). Histology and micro-PET-CT demonstrated that ¹⁸F-NaF uptake localized to areas of aneurysm disease and active calcification. In 72 patients within the longitudinal cohort study (mean age 73 ± 7 years, 85% men, baseline aneurysm diameter 48.8 ± 7.7 mm), there were 19 aneurysm repairs (26.4%) and 3 ruptures (4.2%) after 510 ± 196 days. Aneurysms in the highest tertile of ¹⁸F-NaF uptake expanded 2.5× more rapidly than those in the lowest tertile (3.10 [interquartile range (IQR): 2.34 to 5.92 mm/year] vs. 1.24 [IQR: 0.52 to 2.92 mm/year]; p = 0.008) and were nearly 3× as likely to experience AAA repair or rupture (15.3% vs. 5.6%; log-rank p = 0.043).

Conclusions

Fluorine-18-NaF PET-CT is a novel and promising approach to the identification of disease activity in patients with AAA and is an additive predictor of aneurysm growth and future clinical events. (Sodium Fluoride Imaging of Abdominal Aortic Aneurysms [SoFIA³]; NCT02229006; Magnetic Resonance Imaging [MRI] for Abdominal Aortic Aneurysms to Predict Rupture or Surgery: The MA3RS Trial; ISRCTN76413758)

Molecular Imaging in Ischemic Heart Disease

Purpose of Review

The purpose of this paper is to review current and new modalities to image key biological processes in ischemic heart disease and after myocardial infarction non-invasively.

Recent Findings

New imaging targets have been developed to detect and quantify myocardial damage after ischemia. Although positron emission tomography (PET) has been leading the development of new probes in the past, continuous improvements of magnetic resonance imaging (MRI) together with the development of new novel MRI contrast agents opens new research avenues including the combination of both PET and MRI to obtain anatomic, functional, and molecular information simultaneously, which is not possible from a single imaging session.

Summary

This review summarizes the state of art of non-invasive molecular imaging of the myocardium during ischemia and after myocardial infarction using PET and MRI. We also describe the different contrast agents that have been developed to image the different phases of cardiac healing and the biological processes associated with each of those phases. Importantly, here we focus on imaging of inflammation as it is the key biological process that orchestrates clearance of dead cells, tissue remodeling, cardiac repair, and future outcome. We also focus on clinical translation of some of the novel contrast agents that have been tested in patients and discuss the need for larger, multi-center patient studies to fully validate the applicability of new imaging probes.

n-3 PUFAs improve erythrocyte fatty acid profile in patients with small AAA: a randomized controlled trial

Abdominal aortic aneurysm (AAA) is an important cause of death in older adults, which has no current drug therapy. Inflammation and abnormal redox status are believed to be key pathogenic mechanisms for AAA. In light of evidence correlating inflammation with aberrant fatty acid profiles, this study compared erythrocyte fatty acid content in 43 AAA patients (diameter 3.0-4.5 cm) and 52 healthy controls. In addition, the effect of omega-3 PUFA (n-3 PUFA) supplementation on erythrocyte fatty acid content was examined in a cohort of 30 AAA patients as part of a 12 week randomized placebo-controlled clinical trial. Blood analyses identified associations between AAA and decreased linoleic acid (LA), and AAA and increased Δ6-desaturase activity and biosynthesis of arachidonic acid (AA) from LA. Omega-3 PUFA supplementation (1.5 g DHA + 0.3 g EPA/day) decreased red blood cell distribution width (14.8 ± 0.4% to 13.8 ± 0.2%; P = 0.003) and levels of pro-inflammatory n-6 PUFAs (AA, 12.46 ± 0.23% to 10.14 ± 0.3%, P < 0.001; adrenic acid, 2.12 ± 0.13% to 1.23 ± 0.09%; P < 0.001). In addition, Δ-4 desaturase activity increased (DHA/docosapentaenoic acid ratio, 1.85 ± 0.14 to 3.93 ± 0.17; P < 0.001) and elongase 2/5 activity decreased (adrenic acid/AA ratio, 0.17 ± 0.01 to 0.12 ± 0.01; P < 0.01) following supplementation. The findings suggest that n-3 PUFAs improve fatty acid profiles and ameliorate factors associated with inflammation in AAA patients.

Spontaneous perforation of small intestine followed by rupture of the cystic artery: the natural history of Vascular Ehlers-Danlos Syndrome

Vascular Ehlers-Danlos Syndrome (VEDS) is a rare autosomal dominant disorder caused by mutations in the COL3A1 or COL1A1 genes. Its mortality is secondary to sudden and spontaneous rupture of arteries or hollow organs. The genotype influences the distribution of arterial pathology with aneurysms of intra-abdominal visceral arteries being relatively uncommon. We describe the case of a young man with probable VEDS who died of a spontaneous rupture and dissection of the cystic artery. The patient initially presented with abdominal pain due to an unrecognized spontaneous perforation of the small intestine complicated by sepsis. We postulate that inflammatory mediators may have triggered the arterial rupture due to remodeling and weakening of vessel walls. The phenotype of the patient’s vascular damage included bilateral spontaneous carotid-cavernous sinus fistulae and dissection with pseudoaneurysm formation of large- and medium-sized arteries, predominantly the abdominal aorta and its branches. The autopsy uncovered a long history of vascular events that may have been asymptomatic. These findings along with a positive family history supported the VEDS diagnosis. Loeys-Dietz, Marfan, and familial thoracic aortic aneurysm and dissection syndromes were ruled out based on the absence of arterial tortuosity, eye abnormalities, bone overgrowth, and the distribution of vascular damage among other features. Interestingly, microscopic examination of the hippocampus revealed a focus of neuronal heterotopia, commonly associated with epilepsy; however, the patient had no history of seizures. The natural course of VEDS involves the rupture and dissection of arteries that, if unrecognized, can lead to a rapid death after bleeding into free spaces.

MRI Relaxometry for Quantitative Analysis of USPIO Uptake in Cerebral Small Vessel Disease

A protocol for evaluating ultrasmall superparamagnetic particles of iron oxide (USPIO) uptake and elimination in cerebral small vessel disease patients was developed and piloted. B₁-insensitive R₁ measurement was evaluated in vitro. Twelve participants with history of minor stroke were scanned at 3-T MRI including structural imaging, and R₁ and R₂* mapping. Participants were scanned (i) before and (ii) after USPIO (ferumoxytol) infusion, and again at (iii) 24–30 h and (iv) one month. Absolute and blood-normalised changes in R₁ and R₂* were measured in white matter (WM), deep grey matter (GM), white matter hyperintensity (WMH) and stroke lesion regions. R₁ measurements were accurate across a wide range of values. R₁ (p < 0.05) and R₂* (p < 0.01) mapping detected increases in relaxation rate in all tissues immediately post-USPIO and at 24–30 h. R₂* returned to baseline at one month. Blood-normalised R₁ and R₂* changes post-infusion and at 24–30 h were similar, and were greater in GM versus WM (p < 0.001). Narrower distributions were seen with R₂* than for R₁ mapping. R₁ and R₂* changes were correlated at 24–30 h (p < 0.01). MRI relaxometry permits quantitative evaluation of USPIO uptake; R₂* appears to be more sensitive to USPIO than R₁. Our data are explained by intravascular uptake alone, yielding estimates of cerebral blood volume, and did not support parenchymal uptake. Ferumoxytol appears to be eliminated at 1 month. The approach should be valuable in future studies to quantify both blood-pool USPIO and parenchymal uptake associated with inflammatory cells or blood-brain barrier leak.

Imaging aortic wall inflammation

Inflammation affects the aortic wall through complex pathways that alter its biomechanical structure and cellular composition. Inflammatory processes that predominantly affect the intima cause occlusive disease whereas medial inflammation and degeneration cause aneurysm formation.

Aortic inflammatory pathways share common metabolic features that can be localized by smart contrast agents and radiolabelled positron emission tomography (PET) tracers. ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) is a non-specific marker of metabolism and has been widely used to study aortic inflammation in various diseased aortic states. Although useful in detecting disease, ¹⁸F-FDG has yet to demonstrate a reliable link between vessel wall disease and clinical progression.

¹⁸F-Sodium fluoride (¹⁸F-NaF) is a promising biological tracer that detects microcalcification related to active disease and cellular necrosis within the vessel wall. ¹⁸F-NaF shows a high affinity to bind to diseased arterial tissue irrespective of the underlying inflammatory process. In abdominal aortic aneurysms, ¹⁸F-NaF PET/CT predicts increased rates of growth and important clinical end-points, such as rupture or the requirement for repair.

Much work remains to be done to bridge the gap between detecting aortic inflammation in at-risk individuals and predicting adverse clinical events. Novel radiotracers may hold the key to improve our understanding of vessel wall biology and how this relates to patients. Combined with established clinical and morphological assessment techniques, PET imaging promises to improve disease detection and clinical risk stratification.

Anatomic predictors for late mortality after standard endovascular aneurysm repair

OBJECTIVE

Abdominal aortic aneurysm (AAA) management involves a decision process that takes into account anatomic characteristics, surgical risks, patients' preferences, and expected survival. Whereas larger AAA diameter has been associated with increased mortality after both standard endovascular aneurysm repair (EVAR) and open repair, it is unclear whether survival after EVAR is influenced by other anatomic characteristics. The purpose of this study was to determine the importance of baseline anatomic features on survival after EVAR.

METHODS

All patients treated at a tertiary teaching center with EVAR for intact standard infrarenal AAA from 2000 to 2014 were included. The civil data registry was queried to determine survival status; causes of death were obtained from death certificates. The primary study end point was to determine the impact of baseline morphologic features on all-cause and cardiovascular mortality after EVAR.

RESULTS

This study included 404 EVAR patients (12.1% women; mean age, 73 years) with a median follow-up of 5.8 years (interquartile range, 3.1-7.4 years). The 5- and 10-year overall survival rates for the entire population after EVAR were 70% (95% confidence interval [CI], 66%-75%) and 43% (95% CI, 37%-50%), respectively. Only AAA diameter >70 mm (hazard ratio [HR], 1.75; 95% CI, 1.20-3.56) was identified as an independent anatomic predictor of all-cause mortality. Death due to cardiovascular causes occurred in 60 (38.5%) patients. Aneurysm-related mortality was responsible for six of the cardiovascular-related deaths. In multivariable analysis, both neck diameter ≥30 mm (HR, 2.16; 95% CI, 1.05-4.43) and AAA diameter >70 mm (HR, 2.45; 95% CI, 1.34-4.46) were identified as independent morphologic risk factors for cardiovascular mortality, whereas >25% circumferential neck thrombus (HR, 0.32; 95% CI, 0.13-0.77) was protective.

CONCLUSIONS

This study suggests that patients with AAA diameters >70 mm are at increased risk of all-cause and cardiovascular mortality. In addition, patients with infrarenal neck diameters ≥30 mm have a greater risk of cardiovascular mortality, although AAA-related deaths were not more frequent in this group of patients. Consequently, a more aggressive management of cardiovascular medical comorbidities may be warranted to improve survival after standard EVAR in these patients.

Adherence to the Dietary Approaches to Stop Hypertension Dietary Pattern and Risk of Abdominal Aortic Aneurysm: Results From the ARIC Study

Background The role of a healthy dietary pattern in the prevention of abdominal aortic aneurysms ( AAA ) is unknown. We aimed to evaluate the relationship between adherence to a Dietary Approaches To Stop Hypertension-style dietary pattern and the risk of incident AAA s. Methods and Results Dietary intake was assessed via a 66-item food frequency questionnaire at baseline (1987-1989) and at visit 3 (1993-1995) in 13 496 participants enrolled in the ARIC (Atherosclerosis Risk in Communities) study without clinical AAA (mean age, 54 years). A dietary scoring index based on food times was constructed to assess self-reported adherence to a dietary approaches to stop hypertension-style dietary pattern. Participants were followed for incident clinical AAA s using hospital discharge diagnoses, Medicare inpatient and outpatient diagnoses, or death certificates through December 31, 2011. Cox proportional hazards models with covariate adjustment were used to estimate hazard ratios with 95% confidence intervals. During a median follow-up of 23 years, there were 517 incident AAA cases. Individuals with a Dietary Approaches To Stop Hypertension-style diet score in the highest quintile had a 40% lower risk of hospitalization for AAA than those in the lowest quintile (hazard ratioQ5 vs Q1: 0.60; 95% confidence intervals: 0.44, 0.83; Ptrend=0.002). In detailed analyses, higher consumption of fruits, vegetables, whole grains, low-fat dairy, and nuts and legumes was related to a lower risk for AAA . Conclusions Greater adherence to a Dietary Approaches To Stop Hypertension-style dietary pattern was associated with lower risk for AAA . Higher consumption of fruits, vegetables, whole grains, low-fat dairy as well as nuts and legumes may help to decrease the burden of AAA s.

Risk Factor Analyses of Abdominal Aortic Aneurysms Growth in Japanese Patients

BACKGROUND

This study aimed to retrospectively demonstrate the growth rate (mm/year) of abdominal aortic aneurysm (AAA) diameters (ADs) and to analyze risk factors for AAA expansion.

METHODS

We retrospectively investigated the clinical data of 319 patients with AAAs who were followed up as outpatients for >2 years after their initial visit and who underwent computed tomography >4 times.

RESULTS

The mean follow-up period was 3.7 ± 1.5 years. The annual average growth rates according to varying ADs were as follows: 1.9 ± 0.8 (AD 30-34 mm), 2.6 ± 1.2 (AD 35-39 mm), 2.8 ± 1.1 (AD 40-44 mm), 3.1 ± 1.3 (AD 45-49 mm), 3.4 ± 1.6 (AD 50-54 mm), and 3.5 ± 1.4 mm (AD ≥55 mm). Factors associated with AAA expansion were smoking (P = 0.017), hypertension (P < 0.001), and ADs (P < 0.001). In the subgroup analysis, data regarding growth rates of ≥3 mm were extracted, and a statistically significant difference between smoking status and ADs of ≥40 mm was observed.

CONCLUSIONS

Factors associated with AAA expansion in Japanese patients included smoking, hypertension, and ADs, and a statistically significant difference was observed between smoking status and ADs of ≥40 mm.

Ultrasmall superparamagnetic iron oxide nanoparticle uptake as noninvasive marker of aortic wall inflammation on MRI: proof of concept study

OBJECTIVE:

Radiation therapy for cancer can lead to atherosclerosis by inducing inflammatory changes in the vascular wall. It is difficult to quantitatively measure inflammation on CT and MRI studies. The purpose of this study was to assess the use of ferumoxytol, an ultrasmall superparamagnetic iron oxide nanoparticle, as a noninvasive marker of vessel wall inflammation secondary to radiation therapy in pancreatic cancer patients in comparison with healthy volunteers.

METHODS:

MRI of upper abdomen (T₁, T₂, multi echo T₂* weighted imaging) was performed on 3 T magnet before and 48 h after intravenous administration of ferumoxytol in pancreatic cancer patients who underwent radiation therapy (n = 8) and in healthy volunteers (n = 8). R₂* value was obtained by drawing regions of interest outlining the aortic wall directly on the T₂* medic image and subsequently transposed to the R₂* image using Amira software (v. 5.3.2, FEI, Bordeaux, France). The change in R₂* values was analyzed by student's t-test.

RESULTS:

The average change in R₂* value of the pancreatic cancer patients was determined to be 216.1 ms^-1. The average change R₂* value of the control patients was determined to be 54.6 ms^-1. Thus, pancreatic cancer patients following radiation therapy had a greater uptake of ferumoxytol (p = 0.0082) in their aortic wall as compared to healthy controls.

CONCLUSION:

This proof of concept study suggests that greater uptake of ferumoxytol in the aortic wall in cancer patients without visible atherosclerosis may be the expression of increased inflammation.

ADVANCES IN KNOWLEDGE:

Ultrasmall superparamagnetic iron oxide enhanced MRI can offer an imaging biomarker for quantitative estimation of aortic inflammation preceding atherosclerosis.

Abdominal Aortic Aneurysms Growth Is Associated With High Concentrations of Plasma Proteins in the Intraluminal Thrombus and Diseased Arterial Tissue

Objective—

Porosity of the intraluminal thrombus (ILT) is believed to convey biologically active components from the bloodstream toward the aneurismal wall. Accumulation of molecules in the abdominal aortic aneurysmatic tissue may influence vascular protein turnover and regulate abdominal aortic aneurysm growth. We sought to identify proteins with concentrations in the ILT and the abdominal aortic aneurysm wall which associate with aneurysmal expansion rate.

Approach and Results—

Proteomic analysis by liquid chromatography tandem-mass spectrometry of separated wall and ILT samples was correlated with preoperative aneurysmal growth rate in 24 individuals operated electively for infrarenal abdominal aortic aneurysm. The median preoperative growth rate was 3.8 mm/y (interquartile range, 3) and the mean observational time was 3.3±1.7 years. Plasma components dominated the group of proteins with tissue concentrations, which correlate positively with growth rates ( P <0.001, Fisher exact test, both in the ILT and the wall). In contrast, in the wall and thrombus samples, ECM (extracellular matrix) proteins were significantly more prevalent in the group of proteins with negative correlations to growth rates ( P <0.05, Fisher exact test). Similarly, a long series of proteins, related to cellular functions correlated negatively to growth rates.

Conclusions—

When the preoperative aneurysmatic growth rate has been high, the concentration of many plasma proteins residing in the ILT and the aneurysmatic tissue is also high, compatible with the hypothesis of increased tissue porosity and accumulation of plasma components as a driver of aneurysm expansion. Moreover, many matrix and cellular proteins which are found in high concentrations in slower-growing aneurysms provides new knowledge about potential treatment targets.

On the optimization of low-cost FDM 3D printers for accurate replication of patient-specific abdominal aortic aneurysm geometry

BACKGROUND

There is a potential for direct model manufacturing of abdominal aortic aneurysm (AAA) using 3D printing technique for generating flexible semi-transparent prototypes. A patient-specific AAA model was manufactured using fused deposition modelling (FDM) 3D printing technology. A flexible, semi-transparent thermoplastic polyurethane (TPU), called Cheetah Water (produced by Ninjatek, USA), was used as the flexible, transparent material for model manufacture with a hydrophilic support structure 3D printed with polyvinyl alcohol (PVA). Printing parameters were investigated to evaluate their effect on 3D-printing precision and transparency of the final model. ISO standard tear resistance tests were carried out on Ninjatek Cheetah specimens for a comparison of tear strength with silicone rubbers.

RESULTS

It was found that an increase in printing speed decreased printing accuracy, whilst using an infill percentage of 100% and printing nozzle temperature of 255 °C produced the most transparent results. The model had fair transparency, allowing external inspection of model inserts such as stent grafts, and good flexibility with an overall discrepancy between CAD and physical model average wall thicknesses of 0.05 mm (2.5% thicker than the CAD model). The tear resistance test found Ninjatek Cheetah TPU to have an average tear resistance of 83 kN/m, higher than any of the silicone rubbers used in previous AAA model manufacture. The model had lower cost (4.50 GBP per model), shorter manufacturing time (25 h 3 min) and an acceptable level of accuracy (2.61% error) compared to other methods.

CONCLUSIONS

It was concluded that the model would be of use in endovascular aneurysm repair planning and education, particularly for practicing placement of hooked or barbed stents, due to the model's balance of flexibility, transparency, robustness and cost-effectiveness.

Epigenetic Regulation of Vascular Aging and Age-Related Vascular Diseases

Vascular aging refers to the structural and functional defects that occur in the aorta during the aging process and is characterized by increased vascular cell senescence, vascular dyshomeostasis, and vascular remodeling. Vascular aging is a major risk factor for vascular diseases. However, the current understanding of the biological process of vascular aging and age-related diseases is insufficient. Epigenetic regulation can influence gene expression independently of the gene sequence and mainly includes DNA methylation, histone modifications, and RNA-based gene regulation. Epigenetic regulation plays important roles in many physiological and pathophysiological processes and may explain some gaps in our knowledge regarding the interaction between genes and diseases. In this review, we summarize recent advances in the understanding of the epigenetic regulation of vascular aging and age-related diseases in terms of vascular cell senescence, vascular dyshomeostasis, and vascular remodeling. Moreover, the possibility of targeting epigenetic regulation to delay vascular aging and treat age-related vascular diseases is also discussed.

Exploring the Biological and Mechanical Properties of Abdominal Aortic Aneurysms Using USPIO MRI and Peak Tissue Stress: A Combined Clinical and Finite Element Study

Inflammation detected through the uptake of ultrasmall superparamagnetic particles of iron oxide (USPIO) on magnetic resonance imaging (MRI) and finite element (FE) modelling of tissue stress both hold potential in the assessment of abdominal aortic aneurysm (AAA) rupture risk. This study aimed to examine the spatial relationship between these two biomarkers. Patients (n = 50) > 40 years with AAA maximum diameters > = 40 mm underwent USPIO-enhanced MRI and computed tomography angiogram (CTA). USPIO uptake was compared with wall stress predictions from CTA-based patient-specific FE models of each aneurysm. Elevated stress was commonly observed in areas vulnerable to rupture (e.g. posterior wall and shoulder). Only 16% of aneurysms exhibited co-localisation of elevated stress and mural USPIO enhancement. Globally, no correlation was observed between stress and other measures of USPIO uptake (i.e. mean or peak). It is suggested that cellular inflammation and stress may represent different but complimentary aspects of AAA disease progression.