EVAR and OPEN treatment of abdominal aortic aneurysm: What is the role of MMP-9 in the follow-up?

Biomarkers in EndoVascular Aneurysm Repair (EVAR) and Abdominal Aortic Aneurysm: Pathophysiology and Clinical Implications

Circulating biomarkers have been recently investigated among patients undergoing endovascular aortic aneurysm repair (EVAR) for abdominal aortic aneurysm (AAA). Considering the plethora of small descriptive studies reporting potential associations between biomarkers and clinical outcomes, this review aims to summarize the current literature considering both the treated disease (post EVAR) and the untreated disease (AAA before EVAR). All studies describing outcomes of tissue biomarkers in patients undergoing EVAR and in patients with AAA were included, and references were checked for additional sources. In the EVAR scenario, circulating interleukin-6 (IL-6) is a marker of inflammatory reaction which might predict postoperative morbidity; cystatin C is a promising early marker of post-procedural acute kidney injury; plasma matrix metalloproteinase-9 (MMP-9) concentration after 3 months from EVAR might help in detecting post-procedural endoleak. This review also summarizes the current gaps in knowledge and future direction of this field of research. Among markers used in patients with AAA, galectin and granzyme appear to be promising and should be carefully investigated even in the EVAR setting. Larger prospective trials are required to establish and evaluate prognostic models with highest values with these markers.

LOXL4 Abrogation Does Not Exaggerate Angiotensin II-Induced Thoracic or Abdominal Aortic Aneurysm in Mice

It has been shown that thoracic aortic aneurysm and dissection (TAAD) could be a Mendelian trait caused by a single gene mutation. The LOX gene mutation leads to the development of human TAAD. The LOXL4 gene is a member of the lysyl oxidase gene family. We identified seven variants in the LOXL4 gene in 219 unrelated patients with TAAD by whole-exome sequencing (WES). To further investigate whether LOXL4 is a candidate causative gene for human TAAD, a Loxl4 knockout mouse was generated, and the mutant mice were treated by subcutaneous infusion of angiotensin II. We found that abrogation of Loxl4 did not induce a more severe thoracic or abdominal aortic aneurysm compared with the wild-type C57BL/6J mice. Our results suggest that LOXL4 may not play a major role in the development of angiotensin II-induced aortic aneurysm. The functional study using this animal model system is important for the evaluation of candidate genes of TAAD identified by WES.

Calprotectin and Receptor for Advanced Glycation End Products as a Potential Biomarker in Abdominal Aortic Aneurysm

Experiments conducted in recent years on animals and research works worldwide show a linkage between calprotectin and occurrence and development of the abdominal aortic aneurysm (AAA). Additionally, a correlation between the level of the receptor for advanced glycation end products (RAGE) and the diameter of the abdominal aorta was found. The purpose of this study was to investigate whether calprotectin and the RAGE plasma level may be a biomarker of human AAA occurrence. We determined two groups of research participants: a group of 32 patients aged 53–88 undergoing primary endovascular aneurysm repair and a control group of 43 volunteers aged 59–82 without the AAA. All the patients from the study group had their blood samples drawn in order to determine the level of calprotectin and RAGE in plasma. The second follow-up examination was carried out after three months. The concentration of calprotectin and RAGE in plasma was determined with the use of the immunoenzymatic method (ELISA). The study showed that patients with the AAA had significantly higher mean calprotectin and RAGE plasma levels (p = 0.0001 and p = 0.0002, respectively) as compared to the control group. After the AAA repair operations, the level of concentration of the calprotectin decreased significantly (p = 0.0002). So far, no studies on the connection between the increase of the calprotectin and RAGE in the patient’s plasma with the AAA have been published. Calprotectin may be a promising biomarker related to the occurrence of AAA. Larger studies are needed to fully elucidate and confirm the role of calprotectin in the development and progression of the aneurysm.

Let-7f: A New Potential Circulating Biomarker Identified by miRNA Profiling of Cells Isolated from Human Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a progressive vascular disease responsible for 1–4% of the deaths in elderly men. This study aimed to characterize specific microRNA (miRNA) expression in aneurysmal smooth muscle cells (SMCs) and macrophages in order to identify circulating miRNAs associated with AAA. We screened 850 miRNAs in aneurysmal SMCs, M1 and M2 macrophages, and in control SMCs isolated by micro-dissection from aortic biopsies using microarray analysis. In all, 92 miRNAs were detected and 10 miRNAs were selected for validation by qRT-PCR in isolated cells (n = 5), whole control and aneurysmal aorta biopsies (n = 13), and plasma from patients (n = 24) undergoing AAA (over 50 mm) repair matched to patients (n = 18) with peripheral arterial disease (PAD) with atherosclerosis but not AAA. Seven miRNAs were modulated similarly in all aneurysmal cells. The Let-7f was downregulated in aneurysmal cells compared to control SMCs with a significant lower expression in M1 compared to M2 macrophages (0.1 fold, p = 0.03), correlated with a significant downregulation in whole aneurysmal aorta compared to control aorta (0.2 fold, p = 0.03). Significant levels of circulating let-7f (p = 0.048) were found in AAA patients compared to PAD patients with no significant correlation with aortic diameter (R² = 0.03). Our study underlines the utility of profiling isolated aneurysmal cells to identify other miRNAs for which the modulation of expression might be masked when the whole aorta is used. The results highlight let-7f as a new potential biomarker for AAA.

Effect of Cyclic Stretch on Vascular Endothelial Cells and Abdominal Aortic Aneurysm (AAA): Role in the Inflammatory Response

Abdominal aortic aneurysm (AAA) is a focal dilatation of the aorta, caused by both genetic and environmental factors. Although vascular endothelium plays a key role in AAA progression, the biological mechanisms underlying the mechanical stress involvement are only partially understood. In this study, we developed an in vitro model to characterize the role of mechanical stress as a potential trigger of endothelial deregulation in terms of inflammatory response bridging between endothelial cells (ECs), inflammatory cells, and matrix remodeling. In AAA patients, data revealed different degrees of calcification, inversely correlated with wall stretching and also with inflammation and extracellular matrix degradation. In order to study the role of mechanical stimulation, endothelial cell line (EA.hy926) has been cultured in healthy (10% strain) and pathological (5% strain) dynamic conditions using a bioreactor. In presence of tumor necrosis factor alpha (TNF-α), high levels of matrix metalloproteinase-9 (MMP-9) expression and inflammation are obtained, while mechanical stimulation significantly counteracts the TNF-α effects. Moreover, physiological deformation also plays a significant role in the control of the oxidative stress. Overall our findings indicate that, due to wall calcification, in AAA there is a significant change in terms of decreased wall stretching.