Inflammation In Abdominal Aortic Aneurysm Research Articles

HMGB2 Deficiency Mitigates Abdominal Aortic Aneurysm by Suppressing Ang-II-Caused Ferroptosis and Inflammation via NF-κβ Pathway.

Ferroptosis is a new form of cell death, which is closely related to the occurrence of many diseases. Our work focused on the mechanism by which HMGB2 regulate ferroptosis and inflammation in abdominal aortic aneurysm (AAA). Reverse transcription-quantitative polymerase chain reaction and western blot were utilized to assess HMGB2 levels. CCK-8 and flow cytometry assays were utilized to measure cell viability and apoptosis. We detected reactive oxygen species generation, Fe2+ level, and ferroptosis-related protein levels in Ang-II-treated VSMCs, which were typical characteristics of ferroptosis. Finally, the mice model of AAA was established to verify the function of HMGB2 in vivo. Increased HMGB2 level was observed in Ang-II-treated VSMCs and Ang-II-induced mice model. HMGB2 depletion accelerated viability and impeded apoptosis in Ang-II-irritatived VSMCs. Moreover, HMGB2 deficiency neutralized the increase of ROS in VSMCs caused by Ang-II. HMGB2 silencing considerably weakened Ang-II-caused VSMC ferroptosis, as revealed by the decrease of Fe2+ level and ACSL4 and COX2 levels and the increase in GPX4 and FTH1 levels. Furthermore, the mitigation effects of shHMGB2 on Ang-II-induced VSMC damage could be counteracted by erastin, a ferroptosis agonist. Mechanically, HMGB2 depletion inactivated the NF-κβ signaling in Ang-II-treated VSMCs. Our work demonstrated that inhibition of HMGB2-regulated ferroptosis and inflammation to protect against AAA via NF-κβ signaling, suggesting that HMGB2 may be a potent therapeutic agent for AAA.

Dysregulations of Key Regulators of Angiogenesis and Inflammation in Abdominal Aortic Aneurysm.

Abdominal aortic aneurysm (AAA) is a chronic vascular disease caused by localized weakening and broadening of the abdominal aorta. AAA is a clearly underdiagnosed disease and is burdened with a high mortality rate (65-85%) from AAA rupture. Studies indicate that abnormal regulation of angiogenesis and inflammation contributes to progression and onset of this disease; however, dysregulations in the molecular pathways associated with this disease are not yet fully explained. Therefore, in our study, we aimed to identify dysregulations in the key regulators of angiogenesis and inflammation in patients with AAA in peripheral blood mononuclear cells (using qPCR) and plasma samples (using ELISA). Expression levels of ANGPT1, CXCL8, PDGFA, TGFB1, VEGFB, and VEGFC and plasma levels of TGF-alpha, TGF-beta 1, VEGF-A, and VEGF-C were found to be significantly altered in the AAA group compared to the control subjects without AAA. Associations between analyzed factors and risk factors or biochemical parameters were also explored. Any of the analyzed factors was associated with the size of the aneurysm. The presented study identified dysregulations in key angiogenesis- and inflammation-related factors potentially involved in AAA formation, giving new insight into the molecular pathways involved in the development of this disease and providing candidates for biomarkers that could serve as diagnostic or therapeutic targets.

LncRNA MIR503HG Targets miR-191-5p/PLCD1 Axis and Negatively Modulates Apoptosis, Extracellular Matrix Disruption, and Inflammation in Abdominal Aortic Aneurysm.

As the most prevalent subtype of aortic aneurysm, abdominal aortic aneurysm (AAA) features the apoptosis, extracellular matrix (ECM) disruption, and inflammation response of vascular smooth muscle cells (VSMCs). Noncoding RNAs (ncRNAs) are crucial factors in AAA progression, while the investigations have not been fully explained. miR-191-5p upregulation is found in aortic aneurysm. However, its role in AAA has not been addressed. This research purposed to excavate the possible and associated molecular axis of miR-191-5p in AAA. In our study, miR-191-5p level was detected to be high in the tissues from AAA patients in comparison with the control group. After miR-191-5p expression was enhanced, cell viability was repressed, cell apoptosis was boosted, and ECM disruption and the inflammation response were fortified. Furthermore, the relationship among MIR503HG, miR-191-5p, and phospholipase C delta 1 (PLCD1) in VSMCs was disclosed via mechanism assays. Decreased MIR503HG lacked the inhibition on miR-191-5p targeting PLCD1, resulting in downregulation of PLCD1, which facilitated the progression of AAA. Thus, targeting MIR503HG/miR-191-5p/PLCD1 pathway will provide an additional method for the cure of AAA patients.

Abstract 278: Ccr2 Inhibition Impacts Abdominal Aortic Aneurysm Rupture In Rodents

Background: There is growing evidence that monocyte chemoattractant protein (MCP-1) / C-C chemokine receptor type 2 (CCR2) axis crucially affects the initiation and progression of abdominal aortic aneurysm (AAA). We hypothesize that inhibition of CCR2 may prevent AAA inflammation and rupture. Methods: 40 Male and 49 female Sprague-Dawley rats underwent intraluminal infrarenal abdominal aortic exposure to elastase to induce AAA. Rats received daily β-aminopropionitrile to promote AAA rupture. On post-operative day 3 (POD3), a treatment group (15 males, 17 females) received daily oral gavage of a CCR2 inhibitor (CCR2i; RS-504393), and a control group (25 males, 32 females) received no CCR2i. On POD6, both groups underwent PET/CT with a CCR2 targeting radiotracer 64 Cu-DOTA-ECL1i. In addition, AAA tissue cytokine/chemokine arrays were evaluated. Incidence of AAA rupture was evaluated in the remaining surviving rats until POD14 (Figure 1A). Results: Compared with controls, the incidence of AAA rupture was reduced in treated male AAA rats (0% vs 56%, p <0.001; and tended to decreased in treated female AAA rats (18% vs 42%, p =0.09;). PET/CT demonstrated that male and female treatment groups had significantly decreased 64 Cu-DOTA-ECL1i uptake in AAAs ( p= 0.02 for male AAAs , p <0.001 for females, Figure 1B). All cytokines, including MCP-1, RANTES, IL-17A, IL-18, IL-1B, IL-6, IL-10, except TNF-a were significantly reduced in the male treatment group compared to control group ( p <0.05; Figure 1C). Interestingly, in the female treatment group, IL-1B was significantly decreased ( p <0.05), and RANTES was significantly increased ( p <0.05). Conclusion: In rats, CCR2 appears to be a promising theranostic biomarker for AAAs. CCR2i can greatly impact AAA tissue inflammation and reduces the incidence of AAA rupture. Differences between male and female rats suggest that CCR2 signaling may be different in AAA between sexes and highlights future avenues of further investigation.

Scale down and optimized automated production of [68Ga]68Ga-DOTA-ECL1i PET tracer targeting CCR2 expression

BackgroundRecently it has been identified a short peptide that showed allosteric antagonism against C–C motif chemokine receptor 2 (CCR2) expressed on inflammatory monocyte and macrophages. A 7-d-amino acid peptidic CCR2 inhibitor called extracellular loop 1 inverso (ECL1i), d(LGTFLKC) has been identified and labeled to obtain a new probe for positron emission tomography in pulmonary fibrosis, heart injury, abdominal aortic aneurysm inflammation, atherosclerosis, head and neck cancer. Our goal was to develop, optimize and validate an automated synthesis method for [68Ga]68Ga-DOTA-ECL1i to make it available for a broader community. The synthesis of [68Ga]68Ga-DOTA-ECL1i was done using the Scintomics GRP® module with the already estabilished synthesis template for [68Ga]68Ga-DOTATOC/[68Ga]68Ga-PSMA. The radiopharmaceutical production was optimized scaling down the amount of DOTA-ECL1i (from 50 to 10 μg), evaluating synthesis efficiency and relevant quality control parameters in accordance with the European Pharmacopeia.ResultsBest results were yielded with 20 μg DOTA-ECL1i and then the process validation was carried out by producing three different batches on three different days obtaining an optimal radiochemical yield (66.69%) as well as radiochemical purity (100%) and molar activity (45.41 GBq/µmol).Conclusions[68Ga]68Ga-DOTA-ECL1i was successfully synthesized and it is, thus, available for multi-dose application in clinical settings.

ADAR1 Non-Editing Function in Macrophage Activation and Abdominal Aortic Aneurysm.

Macrophage activation plays a critical role in abdominal aortic aneurysm (AAA) development. However, molecular mechanisms controlling macrophage activation and vascular inflammation in AAA remain largely unknown. The objective of the study was to identify novel mechanisms underlying adenosine deaminase acting on RNA (ADAR1) function in macrophage activation and AAA formation. Aortic transplantation was conducted to determine the importance of nonvascular ADAR1 in AAA development/dissection. Ang II (Angiotensin II) infusion of ApoE-/- mouse model combined with macrophage-specific knockout of ADAR1 was used to study ADAR1 macrophage-specific role in AAA formation/dissection. The relevance of macrophage ADAR1 to human AAA was examined using human aneurysm specimens. Moreover, a novel humanized AAA model was established to test the role of human macrophages in aneurysm formation in human arteries. Allograft transplantation of wild-type abdominal aortas to ADAR1+/- recipient mice significantly attenuated AAA formation, suggesting that nonvascular ADAR1 is essential for AAA development. ADAR1 deficiency in hematopoietic cells decreased the prevalence and severity of AAA while inhibited macrophage infiltration and aorta wall inflammation. ADAR1 deletion blocked the classic macrophage activation, diminished NF-κB (nuclear factor kappa B) signaling, and enhanced the expression of a number of anti-inflammatory microRNAs. Mechanistically, ADAR1 interacted with Drosha to promote its degradation, which attenuated Drosha-DGCR8 (DiGeorge syndrome critical region 8) interaction, and consequently inhibited pri- to pre-microRNA processing of microRNAs targeting IKKβ, resulting in an increased IKKβ (inhibitor of nuclear factor kappa-B) expression and enhanced NF-κB signaling. Significantly, ADAR1 was induced in macrophages and interacted with Drosha in human AAA lesions. Reconstitution of ADAR1-deficient, but not the wild type, human monocytes to immunodeficient mice blocked the aneurysm formation in transplanted human arteries. Macrophage ADAR1 promotes aneurysm formation in both mouse and human arteries through a novel mechanism, that is, Drosha protein degradation, which inhibits the processing of microRNAs targeting NF-kB signaling and thus elicits macrophage-mediated vascular inflammation in AAA.

Role of Extracellular Matrix and Inflammation in Abdominal Aortic Aneurysm.

Abdominal aortic aneurysm (AAA) is one of the most dangerous cardiovascular diseases, occurring mainly in men over the age of 55 years. As it is asymptomatic, patients are diagnosed very late, usually when they suffer pain in the abdominal cavity. The late detection of AAA contributes to the high mortality rate. Many environmental, genetic, and molecular factors contribute to the development and subsequent rupture of AAA. Inflammation, apoptosis of smooth muscle cells, and degradation of the extracellular matrix in the AAA wall are believed to be the major molecular processes underlying AAA formation. Until now, no pharmacological treatment has been implemented to prevent the formation of AAA or to cure the disease. Therefore, it is important that patients are diagnosed at a very early stage of the disease. Biomarkers contribute to the assessment of the concentration level, which will help to determine the level and rate of AAA development. The potential biomarkers today include homocysteine, cathepsins, osteopontin, and osteoprotegerin. In this review, we describe the major aspects of molecular processes that take place in the aortic wall during AAA formation. In addition, biomarkers, the monitoring of which will contribute to the prompt diagnosis of AAA patients over the age of 55 years, are described.

B Cell–Activating Factor Antagonism Attenuates the Growth of Experimental Abdominal Aortic Aneurysm

B cell-activating factor (BAFF), part of a tumor necrosis factor family of cytokines, was recently identified as a regulator of atherosclerosis; however, its role in aortic aneurysm has not been determined. Here, the study examined the effect of selective BAFF antagonism using an anti-BAFF antibody (blocks binding of BAFF to receptors BAFF receptor 3, transmembrane activator and CAML interactor, and B-cell maturation antigen) and mBaffR-mFc (blocks binding of BAFF to BAFF receptor 3) on a murine model of abdominal aortic aneurysm (AAA). In a prevention strategy, the antagonists were injected before the induction of AAA, and in an intervention strategy, the antagonists were injected after the induction of AAA. Both strategies attenuated the formation of AAA. In the intervention group, BAFF antagonism depleted most of the mature B-cell subsets in spleen and circulation, leading to enhanced resolution of inflammation in AAA as indicated by decreased infiltration of B cells and proinflammatory macrophages and a reduced number of apoptotic cells. In AAA tissues, B cells and macrophages were found in close contact. Invitro, B cells, irrespective of treatment with BAFF, impaired the efferocytosis activity of macrophages, suggesting a direct innate role of B cells on macrophage function. Altogether, BAFF antagonism affects survival of the mature B cells, promotes resolution of inflammation in the aorta, and attenuates the growth of AAA in mice.

JMJD3 Influences Macrophage-Mediated Inflammation in Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAAs) are characterized by inflammatory macrophage (Mφ) infiltration and pathologic vascular remodeling. The mechanisms regulating Mφ polarization during AAA development remain unknown. There is increasing evidence that epigenetic enzymes, specifically the histone demethylase JMJD3, direct Mφ polarization. The purpose of this study was to investigate whether JMJD3-mediated epigenetic modifications regulate Mφ inflammation and drive AAA formation. Single-cell RNA sequencing was conducted on human AAA and age-matched atherosclerotic control tissue samples. In addition, the angiotensin (Ang) II-induced AAA model was used to gain mechanistic insight. Briefly, after 4 weeks of high-fat diet, mice were infused with AngII or saline to induce AAAs. AAA maximum diameters were quantified and Mφs were sorted. Messenger RNA abundance of inflammatory cytokines and Jmjd3 were determined by quantitative polymerase chain reaction; levels of histone 3 lysine 27 trimethylation (H3K27me3) on gene promoters were determined by chromatin immunoprecipitation. Statistical significance was determined using Student t-test or analysis of variance. Single-cell RNA sequencing analysis of human AAAs and age-matched atherosclerotic controls demonstrated a significant upregulation of Jmjd3 and inflammatory cytokine expression in monocyte and Mφ subsets within AAA tissue. Congruently, AAA tissue- and bone marrow-derived Mφs from AngII-induced AAAs displayed marked upregulation of Jmjd3 and increased messenger RNA abundance of inflammatory genes (interleukins 1β, 12, and 23) during AAA development (P < .05). To determine the mechanistic impact of JMJD3 on Mφ polarization, histone methylation was evaluated on monocyte-macrophages and demonstrated decreased levels of the repressive histone methylation mark H3K27me3 on inflammatory gene promoters in AngII-induced AAAs compared with controls. In vitro inhibition of JMJD3 using short interfering RNA significantly reduced Mφ inflammatory cytokine expression (P < .05). These Results suggest an important role for JMJD3 in regulating macrophage-mediated inflammation and identify a potential target for the treatment of chronic inflammation in human AAAs.

Ex vivo magnetic particle imaging of vascular inflammation in abdominal aortic aneurysm in a murine model

Abdominal aortic aneurysms (AAAs) are currently one of the leading causes of death in developed countries. Inflammation is crucial in the disease progression, having a substantial impact on various determinants in AAAs development. Magnetic particle imaging (MPI) is an innovative imaging modality, enabling the highly sensitive detection of magnetic nanoparticles (MNPs), suitable as surrogate marker for molecular targeting of vascular inflammation. For this study, Apolipoprotein E-deficient-mice underwent surgical implantation of osmotic minipumps with constant Angiotensin II infusion. After 3 and 4 weeks respectively, in-vivo-magnetic resonance imaging (MRI), ex-vivo-MPI and ex-vivo-magnetic particle spectroscopy (MPS) were performed. The results were validated by histological analysis, immunohistology and laser ablation-inductively coupled plasma-mass spectrometry. MR-angiography enabled the visualization of aneurysmal development and dilatation in the experimental group. A close correlation (R = 0.87) with histological area assessment was measured. Ex-vivo-MPS revealed abundant iron deposits in AAA samples and ex-vivo histopathology measurements were in good agreement (R = 0.76). Ex-vivo-MPI and MPS results correlated greatly (R = 0.99). CD68-immunohistology stain and Perls’-Prussian-Blue-stain confirmed the colocalization of macrophages and MNPs. This study demonstrates the feasibility of ex-vivo-MPI for detecting inflammation in AAA. The quantitative ability for mapping MNPs establishes MPI as a promising tool for monitoring inflammatory progression in AAA in an experimental setting.

Kallistatin correlates with inflammation in abdominal aortic aneurysm and suppresses its formation in mice.

Kallistatin (KS), encoded by SERPINA4, was suggested to play a protective role in many cardiovascular diseases. However, its role in the pathogenesis of abdominal aortic aneurysm (AAA) remains unclear. The aim of this study was to examine the potential association of KS with AAA pathogenesis. We examined KS (SERPINA4) expression in human AAA by PCR, immunohistochemistry, western blotting, and enzyme-linked immunosorbent assay (ELISA) and analyzed correlations between kallistain and clinical data. We then analyzed the effect of recombinant KS on AAA formation and the Wingless (Wnt) signaling pathway in a mouse AAA model developed by angiotensin II (AngII) infusion to apolipoprotein E-deficient (ApoE-/-) mice. In AAA tissue samples, KS was significantly increased compared with samples from the control group (P<0.001, P<0.001, respectively). Clinically, decreased SERPINA4 expression in AAA tissue samples represented an increased rate of iliac artery aneurysm [odds ratio (OR): 0.017; P=0.040]. And decreased plasma KS level represented a high risk for rupture (OR: 0.837; P=0.034). KS inhibited AAA formation and blocked the Wnt signaling pathway in AngII-infused ApoE-/- mice. The present study demonstrates that aberrant changes in KS expression occur in AAA. KS plays an important anti-inflammatory role and showed important clinical correlations in AAA. Decreased KS (SERPINA4) level is a risk factor of AAA rupture. Our pre-clinical animal experiments indicate that treatment with recombination KS suppresses AngII-induced aortic aneurysm formation and might be a new target for the drug therapy of AAA.

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

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

Quantification of Plasma Markers of Nets in Patients with Abdominal Aortic Aneurysm

Introduction: Neutrophil extracellular traps (NETs) are highly prothrombotic networks released by neutrophils upon activation in response to an inflammatory stimulus (1) in a process called NETosis. NETs are composed of different molecules such as DNA, nucleosomes and granule proteins like myeloperoxidase and calprotectin. The relationship between abdominal aortic aneurysm (AAA) and NETs has been previously suggested. Accordingly, our aim was to quantify plasma markers of NETs in AAA patients to evaluate their use as biomarkers. Methods: Plasma samples were obtained from 78 subjects: 40 AAA patients, 19 healthy volunteers and 19 patients with severe atherosclerosis (carotid stenosis) without evidence of AAA. Four NETs' markers were quantified in all samples: DNA was quantified with PicoGreen, whereas nucleosomes, myeloperoxidase and calprotectin were quantified with commercial immunoassays. Differences between groups were compared with a student t test and p< 0.05 was considered significant. Results: Differences in plasma calprotectin levels were observed between AAA patients and healthy volunteers (1095 ± 72.5 vs 742.7 ± 56.3 ng/ml) (p=0.0028; 95% Confidence Interval (CI) [126.7, 577.2]). Differences were also observed between AAA patients and severe atherosclerotic patients (740.4 ± 87.8 ng/ml) (p=0.0051; 95%CI [110.9, 597.6]), although no differences between atherosclerotic patients and healthy volunteers (p=0.98). Other markers of NETs (DNA, myeloperoxidase and nucleosomes) rendered no differences in AAA patients when compared to healthy volunteers or atherosclerotic patients. Conclusion: In the present study we have observed an increased level of plasma calprotectin in AAA patients. Accordingly, calprotectin has been previously related with inflammatory and thrombotic diseases in humans, and its relationship with AAA has been suggested in animal models (2). When validated in an independent cohort, calprotectin could be a promising biomarker of inflammation in AAA. This protein is secreted mostly by neutrophils, thus arising once more the relevance of this type of cells in AAA development. Further studies are needed to elucidate the role of calprotectin in the development and progression of AAA. Disclosure: Nothing to disclose

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

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. 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. 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). 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.

T Cells Are Dominant Population in Human Abdominal Aortic Aneurysms and Their Infiltration in the Perivascular Tissue Correlates With Disease Severity.

Abdominal Aortic Aneurysm (AAA) is a major cause of cardiovascular mortality. Adverse changes in vascular phenotype act in concert with chronic inflammation to promote AAA progression. Perivascular adipose tissue (PVAT) helps maintain vascular homeostasis but when inflamed and dysfunctional, can also promote vascular pathology. Previous studies suggested that PVAT may be an important site of vascular inflammation in AAA; however, a detailed assessment of leukocyte populations in human AAA, their anatomic location in the vessel wall and correlation to AAA size remain undefined. Accordingly, we performed in depth immunophenotyping of cells infiltrating the pathologically altered perivascular tissue (PVT) and vessel wall in AAA samples at the site of maximal dilatation (n = 51 patients). Flow cytometry revealed that T cells, rather than macrophages, are the major leukocyte subset in AAA and that their greatest accumulations occur in PVT. Both CD4+ and CD8+ T cell populations are highly activated in both compartments, with CD4+ T cells displaying the highest activation status within the AAA wall. Finally, we observed a positive relationship between T cell infiltration in PVT and AAA wall. Interestingly, only PVT T cell infiltration was strongly related to tertiles of AAA size. In summary, this study highlights an important role for PVT as a reservoir of T lymphocytes and potentially as a key site in modulating the underlying inflammation in AAA.

Allogeneic Mesenchymal Stem Cells Induce Regulatory T Cells and Suppress Aneurysm Inflammation: Interim Results of the Phase 1 ARREST Trial

We have previously shown that patients with abdominal aortic aneurysm (AAA) have decreased number and diminished immune suppressive function of regulatory type 1 T cells (Tr1) and increased numbers of activated effector Th17 cells. The objective of this clinical trial was to assess the efficacy of allogeneic mesenchymal stem cells (MSCs) in inducing Tr1 cells and suppressing AAA inflammation. The AneuRysm Repression with mEsenchymal STem cells (ARREST) trial is a blinded, placebo-controlled phase 1 study in which patients with small AAA (30- to 50-mm diameter) are randomized to intravenous infusion of placebo (plasmalyte A), 1 million MSCs/kg, and 3 million MSCs/kg (n = 12/group). Blood samples are collected at baseline and at days 3, 7, 14, 28, and 60 and yearly. The primary end point is change in the ratio of Tr1:Th17 cells at 14 days after treatment using flow cytometry. Secondary end points are changes in FoxP3+ T-regulatory cells, myeloid-derived suppressor cells, microRNA profiles, serum cytokine levels, changes in AAA inflammation as measured by 18-fluorodeoxyglucose positron emission tomography/computed tomography, and changes in aneurysm diameter and volume at years 1 to 5. Twenty-one patients have been enrolled to date. There have been no treatment-related adverse events, and one patient withdrew after discovery of an occult pulmonary malignant neoplasm on baseline positron emission tomography/computed tomography. At day 14, the ratio of Tr1:Th17 cells increased by 20.3 ± 1.3-fold from baseline for the high-dose MSC group (n = 7) compared with 4.3 ±-fold for the low-dose group (n = 7; P < .01) and −10 .6± 2.3-fold for the placebo group (n = 7; P = .001; Fig). There was a decrease in 18-fluorodeoxyglucose uptake as measured by standard uptake values by 5.6% ±1.3% in the combined MSC group (n = 7) compared with an increase in standard uptake values of 4.1% ± 1.0% in the placebo group (n = 4; P < .05). Although the sample size was too small for statistical comparison, the average increase in maximal transverse diameter of AAA at 12 months after treatment was −1.6 ± 0.6 mm in the combined MSC group (n = 4 ) and 4.3 ± 0.9 mm in the placebo group. The results of the ARREST trial demonstrate a significant increase in Tr1 cells concurrent with a decrease in cytotoxic effector Th17 cells in an MSC dose-dependent fashion, achieving the primary end point. Preliminary data suggest that aneurysm inflammation and expansion are decreased with MSC treatment.

Inflammasome activity in leucocytes decreases with abdominal aortic aneurysm progression.

Abdominal aortic aneurysms (AAAs) are characterized by chronic inflammatory cell infiltration. The present extended immunohistochemistry study aimed to characterize inflammation in AAA and aortic control samples. In specific, the composition of the infiltrating immune cells and the expression of five inflammasome components in these immune cells were evaluated, in order to characterize their role in AAA development. A total of 104 biopsies from 48 AAA patients and 40 healthy specimens from organ donors were evaluated for their grade of inflammation. Infiltrating leukocytes were characterized by specific markers (CD3, CD20 and CD68), intramural localization and inflammasome protein expression [NLR family pyrin domain containing 3 (NLRP3), absent in melanoma 2 (AIM2), apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), Caspase-1 and Caspase-5]. Macrophages, B and T lymphocytes were detected to a similar extent in grade 1, 2 and 3 AAA specimens, whereas in control samples, B and T lymphocytes were rarely observed in grade 1 lesions. Expression frequencies of NLRP3, AIM2 and Caspase-5 were significantly higher in grade 1 lesions of AAA samples compared with grade 1 lesions in control samples. Finally, AIM2, ASC, and Caspase-5 displayed significantly lower expression frequencies in grade 3 compared with grade 2 AAA specimens, and all inflammasome components were less frequently detected in grade 3 than in grade 1 lesions of AAA. This indicates that inflammasome activities decrease with AAA progression in infiltrating leukocytes. No statistically significant association was found for grade 2 and grade 3 lesions and total leukocyte count, C-reactive protein levels, maximal aortic diameter, plasma cholesterol level or biomechanical parameters (derived from finite element analysis) of the respective patients. Overall, the aortic wall of AAA contained lymphocytes and macrophages with different states of activity. The present data suggested that therapeutic inhibition of specific inflammasome components might counteract AAA development and progression.

Serum Calprotectin as a Novel Biomarker in Abdominal Aortic Aneurysm Pathogenesis and Progression: Preliminary Data from Experimental Model in Rats.

Abdominal aortic aneurysm (AAA) formation is associated with by inflammation and matrix degradation. This study tested the hypothesis that calprotectin, a novel biomarker for inflammation, as well as established biomarkers such as C-reactive protein (CRP) and matrix metalloproteinase- 9 (MMP-9) could also be indicative inflammatory biomarkers during AAA pathogenesis and progression. We also evaluated the correlation of serum soluble Receptor for Advanced Glycation End Products (sRAGE) with AAA diameter and serum calprotectin levels. Rat abdominal aortas were perfused with porcine pancreatic elastase (AAA Group) or saline (Control Group) and studied on post-perfusion days 7 and 14 (n=11 per treatment group). Aneurysm was defined as a dilatation of the aorta above 150% of its original diameter. Laparotomy was performed on days 0 (T0), 7 (T7) and 14 (T14) for aortic diameter measurement. At the same time intervals, we measured the serum levels of calprotectin, CRP, sRAGE and MMP-9. All animals developed AAA and no rupture occurred. MMP-9 in AAA group at T14 (p<0.05 compared with T7 and p<0.005 compared with T0) and calprotectin in AAA group at T14 (p<0.001 compared with T7 and T0) continued to significantly increase at all times. Serum sRAGE was significantly lower in the AAA group compared with the control group and within AAA group at all time points (p<0.001). On the other hand, the highest levels of CRP were identified at T7 in both groups. Calprotectin concentrations in AAA group were significantly higher compared with controls at T7 and T14 (p<0.001 and p<0.001, respectively). Aortic diameter was significantly correlated with MMP-9 and calprotectin serum concentrations at all time points (r=0.51, p<0.001; r=0.728, p<0.001 respectively). Serum sRAGE levels were significantly correlated with aortic diameter at all time points (r=-0.48, p<0.001) and serum calprotectin levels (r=-0.22, p<0.001). This is the first evaluation of calprotectin as an AAA inflammation biomarker. It seems to be a promising marker related to AAA natural history. Further experimental and large human studies are needed to fully elucidate the role of calprotectin in the development and progression of AAAs.

MiR-195 suppresses abdominal aortic aneurysm through the TNF-α/NF-κB and VEGF/PI3K/Akt pathway.

In the present study, the function of microRNA (miR)‑195 on abdominal aortic aneurysm (AAA) andits possible mechanism were investigated. Reverse transcription‑quantitative polymerase chain reaction analysis was used to detect the expression of miR‑195 in patients with AAA. The expression levels of miR‑195 in patients with AAA were effectively increased. The present study also used miR‑195 mimics to increase the expression of miR‑195, and ELISA kits and western blot analysis were used to analyze the levels of interleukin (IL)‑1β and IL‑6, and the protein expression levels of matrix metalloproteinase (MMP)‑2, MMP‑9, tumor necrosis factor (TNF)‑α, nuclear factor (NF)‑κB, vascular endothelial growth factor (VEGF), phosphoinositide 3‑kinase (PI3K) and phosphorylated (p‑)Akt. The overexpression of miR‑195 promoted the levels of IL‑1β and IL‑6, induced the protein expression of MMP‑2 and MMP‑9, upregulated the protein expression ofTNF‑α and NF‑κB, and suppressed the protein expression levels of VEGF, PI3K and p‑Akt in angiotensin II‑vascular smooth muscle cells. In addition, TNF‑α promoted the pre‑inflammatory effect of miR‑195 on the protein expression levels of TNF‑α and NF‑κB, levels of IL‑1β and IL‑6, and protein expression levels of MMP‑2 and MMP‑9 in the angiotensin II‑vascular smooth muscle cells. Suppression of PI3K promoted the pre‑inflammatory effect of miR‑195 on the protein expression of PI3K, p‑Akt and VEGF, the levels of IL‑1β and IL‑6, and the protein expression of MMP‑2 and MMP‑9 in angiotensin II‑vascular smooth muscle cells. Combined, these results suggested that miR‑195 suppressed AAA inflammation through the TNF‑α/NF‑κB and VEGF/PI3K/Akt pathways.

Down-regulation of Fibulin-5 is associated with aortic dilation: role of inflammation and epigenetics.

Destructive remodelling of extracellular matrix (ECM) and inflammation lead to dilation and ultimately abdominal aortic aneurysm (AAA). Fibulin-5 (FBLN5) mediates cell-ECM interactions and elastic fibre assembly and is critical for ECM remodelling. We aimed to characterize FBLN5 regulation in human AAA and analyse the underlying mechanisms. FBLN5 expression was significantly decreased in human aneurysmatic aortas compared with healthy vessels. Local FBLN5 knockdown promoted aortic dilation and enhanced vascular expression of inflammatory markers in Ang II-infused C57BL/6J mice. Inflammatory stimuli down-regulated FBLN5 expression and transcriptional activity in human aortic vascular smooth muscle cells (VSMC). Further, aortic FBLN5 expression was reduced in LPS-challenged mice. A SOX response element was critical for FBLN5 promoter activity. The SOX9 expression pattern in human AAA parallels that of FBLN5, and like FBLN5, it was reduced in TNFα-stimulated VSMC. Interestingly, SOX9 over-expression prevented the cytokine-mediated reduction of FBLN5 expression and transcription. The inhibition of Class I histone deacetylases (HDACs) by MS-275 or gene silencing attenuated the inflammation-mediated decrease of FBLN5 expression in VSMC and in the vascular wall. Consistently, HDAC inhibition counteracted the reduction of SOX9 expression induced by inflammatory stimuli and prevented the TNFα-mediated decrease in the binding of SOX9 to FBLN5 promoter normalizing FBLN5 expression. We evidence the deregulation of FBLN5 in human AAA and identify a SOX9/HDAC-dependent mechanism involved in the down-regulation of FBLN5 by inflammation. HDAC inhibitors or pharmacological approaches that aimed to preserve FBLN5 could be useful to prevent the disorganization of ECM induced by inflammation in AAA.