Group 2 Innate Lymphoid Cells Protect Mice from Abdominal Aortic Aneurysm Formation via IL5 and Eosinophils

Development of abdominal aortic aneurysms (AAA) enhances lesion group-2 innate lymphoid cell (ILC2) accumulation and blood IL5. ILC2 deficiency in Rora^fl/fl Il7r^Cre/+ mice or induced ILC2 depletion in Icos^fl-DTR-fl/+ Cd4^Cre/+ mice expedites AAA growth, increases lesion inflammation, but leads to systemic IL5 and eosinophil (EOS) deficiency. Mechanistic studies show that ILC2 protect mice from AAA formation via IL5 and EOS. IL5 or ILC2 from wild-type (WT) mice, but not ILC2 from Il5^-/- mice induces EOS differentiation in bone-marrow cells from Rora^fl/fl Il7r^Cre/+ mice. IL5, IL13, and EOS or ILC2 from WT mice, but not ILC2 from Il5^-/- and Il13^-/- mice block SMC apoptosis and promote SMC proliferation. EOS but not ILC2 from WT or Il5^-/- mice block endothelial cell (EC) adhesion molecule expression, angiogenesis, dendritic cell differentiation, and Ly6C^hi monocyte polarization. Reconstitution of WT EOS and ILC2 but not Il5^-/- ILC2 slows AAA growth in Rora^fl/fl Il7r^Cre/+ mice by increasing systemic EOS. Besides regulating SMC pathobiology, ILC2 play an indirect role in AAA protection via the IL5 and EOS mechanism.

Hexarelin attenuates abdominal aortic aneurysm formation by inhibiting SMC phenotype switch and inflammasome activation

Hexarelin, a synthetic growth hormone-releasing peptide, is shown to be protective in cardiovascular diseases such as myocardial infraction and atherosclerosis. However, the functional role of hexarelin in abdominal aortic aneurysm (AAA) remains undefined. The present study determined the effect of hexarelin administration (200 μg/kg twice per day) in a mouse model of elastase-induced abdominal aortic aneurysm. Echocardiography and in situ pictures showed hexarelin decreased infrarenal aorta diameter. Histology staining showed elastin degradation was improved in hexarelin-treated group. Hexarelin rescued smooth muscle cell contractile phenotype with increased α-SMA and decreased MMP2. Furthermore, hexarelin inhibited inflammatory cell infiltration, NLRP3 inflammasome activation and IL-18 production. Particularly, hexarelin suppressed NF-κB signaling pathway which is a key initiator of inflammatory response. These results demonstrated that hexarelin attenuated AAA development by inhibiting SMC phenotype switch and NF-κB signaling mediated inflammatory response.

Paeonol Ameliorates Abdominal Aortic Aneurysm Progression by the NF-κB Pathway

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by localized progressive dilatation. Currently, paeonol has been shown to possess anti-inflammatory and protective cardiovascular properties. Our study aimed to investigate the potential influences of paeonol on AAA progression.

METHODS

Experimental AAAs were created in C57BL/6J mice by intra-aortic infusion of porcine pancreatic elastase, and then intragastrically administered paeonol (20 mg/kg/day) for 14 days. The effects of paeonol on experimental AAA were measured by ultrasound imaging, histopathology, and western blot analyses.

RESULTS

Paeonol treatment limited the enlargement of the aneurysmal diameter and alleviated the depletion of elastic fibers and vascular smooth muscle cells (VSMCs). Furthermore, the infiltration of CD68+ macrophages and CD8+ lymphocytes was obviously attenuated after paeonol administration, along with mural neoangiogenesis. Western blot results showed that paeonol inhibited the expression of matrix metalloproteinase (MMP) and the NF-κB pathway activation.

CONCLUSIONS

Paeonol might prevent experimental AAA progression by inhibiting the NF-κB pathway, which suggests that it is a potential drug for AAA.

Surgical strategy of IgG4-related inflammatory abdominal aortic aneurysm with preoperative steroid therapy: A case report

Immunoglobulin G4 (IgG4)-related disease, characterized by high serum IgG4 concentrations and IgG4-positive plasma cell infiltration, often presents as an inflammatory aneurysm. We herein report the case of a 78 year-old man, presenting with elevated inflammatory markers and IgG4 concentrations, who was diagnosed with IgG4-related inflammatory abdominal aortic aneurysm with dense perianeurysmal fibrosis. Before the surgical intervention, steroid therapy was administered to resolve his perianeurysmal inflammatory fibrosis. Half a year after the initiation of steroid therapy, there was an improvement in serum inflammatory markers and IgG4 concentrations, and the perianeurysmal fibrosis had regressed. Thus, we performed a surgical intervention including resection of the aneurysm and interposition with a prosthetic graft. Histopathological examination demonstrated few IgG4-positive plasma cells were distributed in the adventitia, which was suspected to be associated with the preoperative steroid therapy. This case study suggests preoperative steroid therapy is a useful therapeutic strategy for IgG4-related abdominal aortic aneurysm because it allows the use of open surgical procedures with reduced surgical risk.

Association of Differential Leukocyte Count With Incident Abdominal Aortic Aneurysm Over 22.5 Years: The ARIC Study

OBJECTIVE: Leukocytes contribute to the development of abdominal aortic aneurysm (AAA). We evaluated whether associations of differential leukocyte counts with AAA persist after accounting for traditional risk factors of AAA. APPROACH AND RESULTS: Among 11 217 adults from the Atherosclerosis Risk in Communities Study, we evaluated associations of differential leukocyte counts at baseline (1987–1989) with incident AAAs over a median follow-up of 22.5 years, using Cox proportional hazards regression. Each differential leukocyte count was categorized into 5 groups—below normal, tertiles within the normal range, and above normal, with the first tertile serving as the referent. We identified 377 incident AAAs through 2011, using hospital discharge diagnoses, linked Medicare records, or death certificates. At baseline, higher neutrophil, monocyte, and eosinophil counts were associated with higher risk of AAA, independent of smoking, other differential leukocyte counts, and other traditional risk factors. The association with incident AAA was the strongest for above normal neutrophil count, with an adjusted hazard ratio (95% CI) of 2.17 (1.29–3.64). Below normal neutrophil, lymphocyte, eosinophil and basophil counts were associated with higher risk of AAA with adjusted hazard ratio (95% CI) between 1.86 (1.04–3.35) and 1.62 (1.10–2.39). CONCLUSIONS: Higher neutrophil, monocyte, and eosinophil counts in midlife are associated with higher risk of AAA, even after accounting for traditional risk factors such as smoking, obesity, and atherosclerosis. This suggests the need to identify nontraditional risk factors and treatment strategies to mitigate the residual risk of AAA conferred by midlife inflammation. Whether immunosuppression is associated with higher risk of AAA needs further investigation.

NSun2 regulates aneurysm formation by promoting autotaxin expression and T cell recruitment

Abdominal aortic aneurysm (AAA) is characterized by inflammatory cell infiltration and aggravated by hyperhomocysteinemia (HHcy). It is unknown whether the homocysteine (Hcy)-activated RNA methyltransferase NOP2/Sun domain family member 2 (NSun2) is associated with AAA. Here, we found that NSun2 deficiency significantly attenuated elastase-induced and HHcy-aggravated murine AAA with decreased T cell infiltration in the vessel walls. T cell labeling and adoptive transfer experiments confirmed that NSun2 deficiency inhibited the chemotaxis of vessels to T cells. RNA sequencing of endothelial cells showed that Hcy induced the accumulation of various metabolic enzymes of the phospholipid PC-LPC-LPA metabolic pathway, especially autotaxin (ATX). In the elastase-induced mouse model of AAA, ATX was specifically expressed in the endothelium and the plasma ATX concentration was upregulated and even higher in the HHcy group, which were decreased dramatically by NSun2 knockdown. In vitro Transwell experiments showed that ATX dose-dependently promoted T cell migration. HHcy may upregulate endothelial ATX expression and secretion and in turn recruit T cells into the vessel walls to induce vascular inflammation and consequently accelerate the pathogenesis of AAA. Mechanistically, secreted ATX interacted with T cells by binding to integrin α4, which subsequently activated downstream FAK/Src-RhoA signaling pathways and then induced T cell chemokinesis and adhesion. ATX overexpression in the vessel walls reversed the inhibited development of AAA in the NSun2-deficient mice. Therefore, NSun2 mediates the development of HHcy-aggravated AAA primarily by increasing endothelial ATX expression, secretion and T cell migration, which is a novel mechanism for HHcy-aggravated vascular inflammation and pathogenesis of AAA.

Ex vivo expansion of regulatory T cells from abdominal aortic aneurysm patients inhibits aneurysm in humanized murine model

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease. Studies of human aneurysm tissue demonstrate dense inflammatory cell infiltrates with CD4+ T cells predominating. Regulatory T cells (Tregs) play an important role in inhibiting pro-inflammatory T cell proliferation, therefore, limiting collateral tissue destruction. The aim of this study was to investigate whether ex vivo augmentation of human Tregs attenuates aneurysm formation in humanized murine model of AAA.

METHODS

Circulating Treg population in AAA patients and age- and gender-matched controls were determined by real-time polymerase chain reaction and flow cytometry. To create humanized murine model of AAA, irradiated Rag1-deficient (Rag1-/-) mice, without mature T lymphocytes, at 7 weeks of age were given 5 × 106 of human CD4+ T cells intraperitoneally. Then the mice underwent CaCl2 aneurysm induction. Aortic diameters were measured before and at 6 weeks after aneurysm induction. Aortic tissue was collected for histology and protein extraction. Verhoeff-Van Gieson stain was used for staining elastic fiber. CD4+ T cells in the aortic tissue were detected by immunohistochemical staining.

RESULTS

In human peripheral blood mononuclear cells, the proportion of Tregs are decreased in AAA patients compared with matched control patients with significant vascular disease. We first validated the role of Tregs in the CaCl2 model of AAA. To determine the role of human T cells in AAA formation, Rag1-/- mice, resistant to CaCl2-aneurysm induction, were transplanted with human CD4+ T cells. Human CD4+ T cells were able to drive aneurysm formation in Rag1-/- mice. We show that ex vivo augmentation of human Tregs by interleukin-2 resulted in decreased aneurysm progression.

CONCLUSIONS

These data suggest that the ex vivo expansion of human Tregs may be a potential therapeutic strategy for inhibiting progression of AAA.

Deficiency of immunoglobulin E protects mice from experimental abdominal aortic aneurysms

Allergic asthma with high plasma IgE levels is a significant risk factor of human abdominal aortic aneurysm (AAA). This study tests a direct role of IgE in angiotensin-II (Ang-II) perfusion- and peri-aortic CaCl2 injury-induced AAA in mice. In both models, IgE-deficiency in Apoe-/- Ige-/- mice blunts AAA growth and reduces lesion accumulation of macrophages, CD4+ and CD8+ T cells, and lesion MHC class-II expression, CD31+ microvessel growth, and media smooth muscle cell loss, compared with those from Apoe-/- control mice. Real time-PCR reveals significant reductions in expression of neutrophil chemoattractants MIP-2α and CXCL5 in AAA lesions or macrophages from Apoe-/- Ige-/- mice, along with reduced lesion Ly6G+ neutrophil accumulation. Consistent with reduced lesion inflammatory cell accumulation, we find significant reductions of plasma and AAA lesion IL6 expression in Apoe-/- Ige-/- mice. Immunofluorescent staining and FACS analysis show that AAA lesion neutrophils express FcεR1. Mechanistic study demonstrates that IgE induces neutrophil FcεR1 expression, activates MAPK signaling, and promotes IL6 production. This study supports a direct role of IgE in AAA by promoting lesion chemokine expression, inflammatory cell accumulation, MAPK signaling, and cytokine expression. IgE inhibition may represent a novel therapeutic approach in AAA management.

Dipeptidyl peptidase-4 is increased in the abdominal aortic aneurysm vessel wall and is associated with aneurysm disease processes

BACKGROUND

Abdominal aortic aneurysm (AAA) is a potentially life-threatening disease, and until today there is no other treatment available than surgical intervention. Dipeptidyl peptidase-4 (DPP4)-inhibitors, used clinically to treat type 2 diabetes, have in murine models been shown to attenuate aneurysm formation and decrease aortic wall matrix degradation, inflammation and apoptosis. Our aim was to investigate if DPP4 is present, active and differentially expressed in human AAA.

METHODS AND RESULTS

DPP4 gene expression was elevated in both media and adventitia of AAA tissue compared with control tissue, as measured by microarrays and qPCR, with consistent findings in external data. The plasma activity of DPP4 was however lower in male patients with AAA compared with age- and gender-matched controls, independently of comorbidity or medication. Immunohistochemical double staining revealed co-localization of DPP4 with cells positive for CD68, CD4 and -8, CD20, and SMA. Gene set enrichment analysis demonstrated that expression of DPP4 in AAA tissue correlated with expression of biological processes related to B- and T-cells, extracellular matrix turnover, peptidase activity, oxidative stress and angiogenesis whereas it correlated negatively with muscle-/actin-related processes.

CONCLUSION

DPP4 is upregulated in both media and adventitia of human AAA and correlates with aneurysm pathophysiological processes. These results support previous murine mechanistic studies and implicate DPP4 as a target in AAA disease.

Clonally expanded alpha-chain T-cell receptor (TCR) transcripts are present in aneurysmal lesions of patients with Abdominal Aortic Aneurysm (AAA)

Abdominal aortic aneurysm (AAA) is a life-threatening immunological disease responsible for 1 to 2% of all deaths in 65 year old or older individuals. Although mononuclear cell infiltrates have been demonstrated in AAA lesions and autoimmunity may be responsible for the initiation and account for the propagation of the disease, the information available about the pathogenesis of AAA is limited. To examine whether AAA lesions from patients with AAA contain clonally expanded α-chain TCR transcripts, we amplified by the non-palindromic adaptor-PCR (NPA-PCR)/Vα-specific PCR and/or the Vα-specific PCR these α-chain TCR transcripts. The amplified transcripts were cloned and sequenced. Substantial proportions of identical α-chain TCR transcripts were identified in AAA lesions of 4 of 5 patients, demonstrating that clonally expanded T cells are present in these AAA lesions. These results were statistically significant by the bimodal distribution. Three of 5 of these patients were typed by DNA-based HLA-typing and all three expressed DRB1 alleles containing the DRβGln70 amino acid residue that has been demonstrated to be associated with AAA. All three patients exhibited clonally expanded T cells in AAA lesions. Four of the 5 patients with AAA who exhibited clonal expansions of α-chain TCR transcripts, also exhibited clonal expansions of β-chain TCR transcripts in AAA lesions, as we have demonstrated previously (J Immunol 192:4897, 2014). αβ TCR-expressing T cells infiltrating AAA lesions contain T-cell clones which have undergone proliferation and clonal expansion in vivo in response to as yet unidentified specific antigens that may be self or nonself. These results provide additional evidence supporting the hypothesis that AAA is a specific antigen-driven T-cell autoimmune disease.

IL (Interleukin)-33 Suppresses Abdominal Aortic Aneurysm by Enhancing Regulatory T-Cell Expansion and Activity

Objective- Inflammation occurs during the progression of abdominal aortic aneurysm (AAA). IL (interleukin)-33 is a pleiotropic cytokine with multiple immunomodulatory effects, yet its role in AAA remains unknown. Approach and Results- Immunoblot, immunohistochemistry, and immunofluorescent staining revealed increased IL-33 expression in adventitia fibroblasts from mouse AAA lesions. Daily intraperitoneal administration of recombinant IL-33 or transgenic IL-33 expression ameliorated periaorta CaPO4 injury- and aortic elastase exposure-induced AAA in mice, as demonstrated by blunted aortic expansion, reduced aortic wall elastica fragmentation, enhanced AAA lesion collagen deposition, attenuated T-cell and macrophage infiltration, reduced inflammatory cytokine production, skewed M2 macrophage polarization, and reduced lesion MMP (matrix metalloproteinase) expression and cell apoptosis. Flow cytometry analysis, immunostaining, and immunoblot analysis showed that exogenous IL-33 increased CD4+Foxp3+ regulatory T cells in spleens, blood, and aortas in periaorta CaPO4-treated mice. Yet, ST2 deficiency muted these IL-33 activities. Regulatory T cells from IL-33-treated mice also showed significantly stronger activities in suppressing smooth muscle cell inflammatory cytokine and chemokine expression, macrophage MMP expression, and in increasing M2 macrophage polarization than those from vehicle-treated mice. In contrast, IL-33 failed to prevent AAA and lost its beneficial activities in CaPO4-treated mice after selective depletion of regulatory T cells. Conclusions- Together, this study established a role of IL-33 in protecting mice from AAA formation by enhancing ST2-dependent aortic and systemic regulatory T-cell expansion and their immunosuppressive activities.

Characterization of CD4+ T Cell Subsets in Patients with Abdominal Aortic Aneurysms

BACKGROUND

The mediators produced by CD4+ T lymphocytes are involved in the pathogenesis of aneurysmal lesions in abdominal aortic aneurysm (AAA) patients. The aim of this study was to identify and characterize the CD4+ T cell subsets involved in human AAA.

METHODS

The CD4+ T cell subsets in 30 human aneurysmal lesions were determined using flow cytometry (FC) and immunohistochemistry (IHC). The peripheral blood mononuclear cells (PBMCs) from patients with AAA were also analyzed by FC and compared with control subjects.

RESULTS

Human aneurysmal lesions contained IFN-γ, IL-12p35, IL-4, IL-23p19, IL-17R, and IL-22 positive cells. PBMCs from AAA patients had higher expression levels of IFN-γ, TNF-α, IL-4, and IL-22 when compared to controls.

CONCLUSIONS

Our results show the presence of TH1, TH2, TH17, and TH22 subsets in aneurysmal lesions of AAA patients and suggest that these cells may be mainly activated in situ, where they can induce tissue degradation and contribute to the pathogenesis of AAA.

Analysis of host Toll-like receptor 3 and RIG-I-like receptor gene expression in patients with abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a vascular disease relatively common in the elderly population. Although some events that contribute to the development and progression of AAA are known, there are limited data examining the association of Toll-like receptor 3 (TLR3) and RIG-I-like receptor expression with the pathogenesis of AAAs. In this study, we investigated the gene and protein expression of TLR3 and RIG-I-like receptors (RIG-I and MDA5) in aortic wall and blood of AAA patients and examined the relationship between their expression and immune response.

METHODS

Total RNA was extracted from aortic wall tissues and blood samples collected from 20 patients with AAA and blood samples of 17 healthy volunteers without aortic aneurysm. To evaluate the DDX58 (RIG-I), IFIH1 (MDA5), and TLR3 gene expression level, quantitative real-time polymerase chain reaction was used. Extracellular cytokine and pattern recognition receptor levels were quantified by enzyme-linked immunosorbent assays.

RESULTS

TLR3, RIG-I, and MDA5 were constitutively expressed in both aortic tissues and blood samples from AAA patients and healthy volunteers. In patients with AAA, higher TLR3 expression in aortic tissues than in blood was found (P = .004). The DDX58 messenger RNA expression was higher in blood of patients with AAA compared with healthy subjects (P = .021). A significantly higher level of plasma interleukin 4 was noticed in patients with AAA than in healthy individuals (P = .008).

CONCLUSIONS

This study suggests that RIG-I and TLR3 seem to be important factors in the pathogenesis of AAA.

Diabetes Reduces Severity of Aortic Aneurysms Depending on the Presence of Cell Division Autoantigen 1 (CDA1)

Diabetes is a negative risk factor for aortic aneurysm, but the underlying explanation for this phenomenon is unknown. We have previously demonstrated that cell division autoantigen 1 (CDA1), which enhances transforming growth factor-β signaling, is upregulated in diabetes. We hypothesized that CDA1 plays a key role in conferring the protective effect of diabetes against aortic aneurysms. Male wild-type, CDA1 knockout (KO), apolipoprotein E (ApoE) KO, and CDA1/ApoE double-KO (dKO) mice were rendered diabetic. Whereas aneurysms were not observed in diabetic ApoE KO and wild-type mice, 40% of diabetic dKO mice developed aortic aneurysms. These aneurysms were associated with attenuated aortic transforming growth factor-β signaling, reduced expression of various collagens, and increased aortic macrophage infiltration and matrix metalloproteinase 12 expression. In the well-characterized model of angiotensin II-induced aneurysm formation, concomitant diabetes reduced fatal aortic rupture and attenuated suprarenal aortic expansion, changes not seen in dKO mice. Furthermore, aortic CDA1 expression was downregulated ∼70% within biopsies from human abdominal aortic aneurysms. The identification that diabetes is associated with upregulation of vascular CDA1 and that CDA1 deletion in diabetic mice promotes aneurysm formation provides evidence that CDA1 plays a role in diabetes to reduce susceptibility to aneurysm formation.

TSG-6 is highly expressed in human abdominal aortic aneurysms

BACKGROUND

The formation of abdominal aortic aneurysms (AAA) is characterized by a dominance of proinflammatory forces that result in smooth muscle cell apoptosis, extracellular matrix degradation, and progressive diameter expansion. Additional defects in the antiinflammatory response may also play a role but have yet to be fully characterized. TSG-6 (TNF-stimulated gene-6) is a potent antiinflammatory protein involved in extracellular matrix stabilization and cell migration active in many pathological conditions. Here, we describe its role in AAA formation.

METHODS

Blood and/or aortic tissue samples were collected from organ donors, subjects undergoing elective AAA screening, and open surgical AAA repair. Aortic specimens collected were preserved for IHC or immediately assayed after tissue homogenization. Protein concentrations in tissue and plasma were assayed by ELISA. All immune cell populations were assayed using FACS. In vitro, macrophage polarization from monocytes was performed with young, healthy donor PBMCs.

RESULTS

TSG-6 was found to be abnormally elevated in both the plasma and aortic wall of patients with AAA compared with healthy and risk-factor matched non-AAA donors. We observed the highest tissue concentration of TSG-6 in the less-diseased proximal and distal shoulders compared with the central aspect of the aneurysm. IHC localized most TSG-6 to the tunica media with minor expression in the tunica adventitia of the aortic wall. Higher concentrations of both M1 and M2 macrophages where also observed, however M1/M2 ratios were unchanged from healthy controls. We observed no difference in M1/M2 ratios in the peripheral blood of risk-factor matched non-AAA and AAA patients. Interesting, TSG-6 inhibited the polarization of the antiinflammatory M2 phenotype in vitro.

CONCLUSIONS

AAA formation results from an imbalance of inflammatory forces causing aortic wall infiltration of mononuclear cells leading to the vessel breakdown. In the AAA condition, we report an elevation of TSG-6 expression in both the aortic wall and the peripheral circulation.

Deficiency of γδT cells protects against abdominal aortic aneurysms by regulating phosphoinositide 3-kinase/AKT signaling

OBJECTIVE

It is known that T lymphocytes are activated in human abdominal aortic aneurysms (AAAs). γδT cells, as a subset of T cells, play a role in many inflammation-related diseases. However, whether γδT cells participate in the formation of AAA remains unknown. In this study, we explored the role of γδT cells in AAA lesions.

METHODS AND RESULTS

Using the porcine pancreatic elastase-induced AAA model, we found that knock out of γδT cells significantly attenuated AAA formation. To elucidate how γδT cells contribute to AAA, microarray analysis was performed, which found that the phosphoinositide 3-kinase/AKT signaling pathway was activated in elastase-perfused γδT knockout (γδT KO) mice. By studying differentially expressed genes involved in phosphoinositide 3-kinase signaling, we found that proliferation-related genes (Sos1, Mtor, Myc) were upregulated whereas apoptosis-related genes (Pten, Bcl1, Bad) were downregulated in elastase-perfused γδT KO mice. Furthermore, histopathologic analysis showed increased PCNA⁺ and decreased TUNEL⁺ cells in elastase-perfused γδT KO mice compared with wild-type mice. In addition, inflammatory cytokines including interleukin-1β, Mcp-1, and tumor necrosis factor-α were downregulated in the aneurysm tissues of elastase-perfused γδT KO mice.

CONCLUSIONS

These data reveal a pathogenic role of γδT cells in the experimental AAA model, likely through mechanisms regulating cell proliferation and mediating inflammatory response. Thus, targeting of γδT cells may offer a potential therapeutic method for aortic aneurysms.

The pivotal role of matrix metalloproteinases in the development of human abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) represent a chronic degenerative condition and impart the risk of a life-threatening episode of rupture. Chronic inflammation and destructive remodeling of the extracellular matrix of the aortic wall constitute trademarks of this entity. Multiple studies have implicated a group of locally produced matrix endopeptidases-the matrix metalloproteinases (MMPs)-as the main culprits of this process. For this reason, extensive research on the Identification of the role of these enzymes, as well as possible alternative pharmacological treatments of AAAs, has taken place during the last few years. The exact role of the several members of the group of metalloproteinases has already been discovered, and conservative therapeutic strategies oriented towards these agents have been suggested, but a Definite treatment plan is still a controversial topic. The possible role of a genetic predisposition to AAAs is another crucial topic that remains to be determined, as it would render the confrontation of this condition much more efficient.

Biological Responses to Endovascular Treatment of Abdominal Aortic Aneurysms

Purpose:

To review the findings of two studies investigating the apparent differences in inflammatory responses demonstrated in patients undergoing endovascular as opposed to classic surgical treatment of abdominal aortic aneurysms (AAAs).

Methods:

The clinical course of seven patients treated with an endoluminal procedure (AAA-E) and seven patients undergoing conventional surgery (AAA-C) were compared (all men; ages 52 to 80 years). Blood samples were taken pre-, intra-, and postoperatively for up to 7 days. Inflammatory responses were assessed from measurement of interleukins (IL)-1 β, IL-6, IL-8, and tumor necrosis factor (TNF-α); complement proteins C1q, C4, C5a, and terminal complement complexes, C5b-C9; and C-reactive proteins. Granulocyte and monocyte surface adhesion molecule expression was determined indirectly using a panel of monoclonal antibodies against CD11a, CD11b, CD11c, CD18, and L-selectin in donor white blood cells exposed to patient plasma.

Results:

In six of the AAA-E patients, blood pressure decreases were recorded during the introduction of the device. Elevated body temperature was sustained for 2 to 5 days postoperatively in the AAA-E group. IL-6 levels were significantly higher in AAA-C patients (p < 0.0005), while TNF-α release was recorded in the AAA-E group only. CD11b, CD11c, and CD18 molecules on both granulocytes and monocytes were significantly upregulated 60 minutes after the endovascular procedure compared to conventional surgery.

Conclusions:

Endovascular aortic aneurysm repair apparently induces a significant inflammatory response, mainly involving TNF-α release, which differs from open AAA repair. These inflammatory responses, which may be related to the observed intraprocedural blood pressure decreases, could be caused by cell activation arising from intra-aneurysmal device manipulation.

Background differences in baseline and stimulated MMP levels influence abdominal aortic aneurysm susceptibility

OBJECTIVE

Evidence has demonstrated profound influence of genetic background on cardiovascular phenotypes. Murine models in Marfan syndrome (MFS) have shown that genetic background-related variations affect thoracic aortic aneurysm formation, rupture, and lifespan of mice. MFS mice with C57Bl/6 genetic background are less susceptible to aneurysm formation compared to the 129/SvEv genetic background. In this study, we hypothesize that susceptibility to abdominal aortic aneurysm (AAA) will be increased in 129/SvEv mice versus C57Bl/6 mice. We tested this hypothesis by assessing differences in aneurysm size, tissue properties, immune response, and MMP expression.

METHODS

Mice of C57Bl/6 or 129/SvEv background underwent AAA induction by periaortic application of CaCl2. Baseline aortic diameters, tissue properties and MMP levels were measured. After aneurysm induction, diameters, MMP expression, and immune response (macrophage infiltration and bone marrow transplantation) were measured.

RESULTS

Aneurysms were larger in 129/SvEv mice than C57Bl/6 mice (83.0% ± 13.6 increase compared to 57.8% ± 6.4). The aorta was stiffer in the 129/SvEv mice compared to C57Bl/6 mice (952.5 kPa ± 93.6 versus 621.4 kPa ± 84.2). Baseline MMP-2 and post-aneurysm MMP-2 and -9 levels were higher in 129/SvEv aortas compared to C57Bl/6 aortas. Elastic lamella disruption/fragmentation and macrophage infiltration were increased in 129/SvEv mice. Myelogenous cell reversal by bone marrow transplantation did not affect aneurysm size.

CONCLUSIONS

These data demonstrate that 129/SvEv mice are more susceptible to AAA compared to C57Bl/6 mice. Intrinsic properties of the aorta between the two strains of mice, including baseline expression of MMP-2, influence susceptibility to AAA.

Immunohistochemical analysis of the natural killer cell cytotoxicity pathway in human abdominal aortic aneurysms

Our previous analysis using genome-wide microarray expression data revealed extreme overrepresentation of immune related genes belonging the Natural Killer (NK) Cell Mediated Cytotoxicity pathway (hsa04650) in human abdominal aortic aneurysm (AAA). We followed up the microarray studies by immunohistochemical analyses using antibodies against nine members of the NK pathway (VAV1, VAV3, PLCG1, PLCG2, HCST, TYROBP, PTK2B, TNFA, and GZMB) and aortic tissue samples from AAA repair operations (n = 6) and control aortae (n = 8) from age-, sex- and ethnicity-matched donors from autopsies. The results confirmed the microarray results. Two different members of the NK pathway, HCST and GRZB, which act at different steps in the NK-pathway, were actively transcribed and translated into proteins in the same cells in the AAA tissue demonstrated by double staining. Furthermore, double staining with antibodies against CD68 or CD8 together with HCST, TYROBP, PTK2B or PLCG2 revealed that CD68 and CD8 positive cells expressed proteins of the NK-pathway but were not the only inflammatory cells involved in the NK-pathway in the AAA tissue. The results provide strong evidence that the NK Cell Mediated Cytotoxicity Pathway is activated in human AAA and valuable insight for future studies to dissect the pathogenesis of human AAA.

Inflammatory micro-environmental cues of human atherothrombotic arteries confer to vascular smooth muscle cells the capacity to trigger lymphoid neogenesis

BACKGROUND

Experimental atherosclerosis is characterized by the formation of tertiary lymphoid structures (TLOs) within the adventitial layer, which involves the chemokine-expressing aortic smooth muscle cells (SMCs). TLOs have also been described around human atherothrombotic arteries but the mechanisms of their formation remain poorly investigated. Herein, we tested whether human vascular SMCs play the role of chemokine-expressing cells that would trigger the formation of TLOs in atherothrombotic arteries.

RESULTS

We first characterized, by flow cytometry and immunofluorescence analysis, the prevalence and cell composition of TLOs in human abdominal aneurysms of the aorta (AAAs), an evolutive form of atherothrombosis. Chemotaxis experiments revealed that the conditioned medium from AAA tissues recruited significantly more B and T lymphocytes than the conditioned medium from control (N-AAA) tissues. This was associated with an increase in the concentration of CXCL13, CXCL16, CCL19, CCL20, and CCL21 chemokines in the conditioned medium from AAA tissues. Immunofluorescence analysis of AAA cryosections revealed that α-SMA-positive SMCs were the main contributors to the chemokine production. These results were confirmed by RT-qPCR assays where we found that primary vascular SMCs from AAA tissues expressed significantly more chemokines than SMCs from N-AAA. Finally, in vitro experiments demonstrated that the inflammatory cytokines found to be increased in the conditioned medium from AAA were able to trigger the production of chemokines by primary SMCs.

CONCLUSION

Together, these results suggest that human vascular SMCs in atherothrombotic arteries, in response to inflammatory signals, are converted into chemokine-expressing cells that trigger the recruitment of immune cells and the formation of aortic TLOs.

[Individual selection of immunocorrector in surgical treatment of obliterating atherosclerosis of the aorta and its branches]

The method for individual selection of immunocorrector in surgical treatment of patients, suffering obliterating atherosclerosis of abdominal aorta and its branches, was proposed. There were examined 69 patients, suffering affection of abdominal aorta and its branches. Inhibition of phagocytic function of neutrophils was observed; on background of activation of the oxygen-dependent metabolism; decompensation of the phagocytic cells function, not depending from the disease stage present. Introduction of the proposed method for the immunocorrector selection secures rising of the diagnosis accuracy and the immunotherapy efficacy.

Monocyte chemoattractant protein-1 (MCP-1) regulates macrophage cytotoxicity in abdominal aortic aneurysm

Aims

In abdominal aortic aneurysm (AAA), macrophages are detected in the proximity of aortic smooth muscle cells (SMCs). We have previously demonstrated in a murine model of AAA that apoptotic SMCs attract monocytes and other leukocytes by producing MCP-1. Here we tested whether infiltrating macrophages also directly contribute to SMC apoptosis.

Methods and Results

Using a SMC/RAW264.7 macrophage co-culture system, we demonstrated that MCP-1-primed RAWs caused a significantly higher level of apoptosis in SMCs as compared to control macrophages. Next, we detected an enhanced Fas ligand (FasL) mRNA level and membrane FasL protein expression in MCP-1-primed RAWs. Neutralizing FasL blocked SMC apoptosis in the co-culture. In situ proximity ligation assay showed that SMCs exposed to primed macrophages contained higher levels of receptor interacting protein-1 (RIP1)/Caspase 8 containing cell death complexes. Silencing RIP1 conferred apoptosis resistance to SMCs. In the mouse elastase injury model of aneurysm, aneurysm induction increased the level of RIP1/Caspase 8 containing complexes in medial SMCs. Moreover, TUNEL-positive SMCs in aneurysmal tissues were frequently surrounded by CD68⁺/FasL⁺ macrophages. Conversely, elastase-treated arteries from MCP-1 knockout mice display a reduction of both macrophage infiltration and FasL expression, which was accompanied by diminished apoptosis of SMCs.

Conclusion

Our data suggest that MCP-1-primed macrophages are more cytotoxic. MCP-1 appears to modulate macrophage cytotoxicity by increasing the level of membrane bound FasL. Thus, we showed that MCP-1-primed macrophages kill SMCs through a FasL/Fas-Caspase8-RIP1 mediated mechanism.

Angiotensin-induced abdominal aortic aneurysms in hypercholesterolemic mice: role of serum cholesterol and temporal effects of exposure

Objective

Understanding variations in size and pattern of development of angiotensin II (Ang II)-induced abdominal aortic aneurysms (AAA) may inform translational research strategies. Thus, we sought insight into the temporal evolution of AAA in apolipoprotein (apo)E^−/− mice.

Approach

A cohort of mice underwent a 4-week pump-mediated infusion of saline (n = 23) or 1500 ng/kg/min of Ang II (n = 85) and AAA development was tracked via in vivo ultrasound imaging. We adjusted for hemodynamic covariates in the regression models for AAA occurrence in relation to time.

Results

The overall effect of time was statistically significant (p<0.001). Compared to day 7 of AngII infusion, there was no decrease in the log odds of AAA occurrence by day 14 (−0.234, p = 0.65), but compared to day 21 and 28, the log odds decreased by 9.07 (p<0.001) and 2.35 (p = 0.04), respectively. Hemodynamic parameters were not predictive of change in aortic diameter (Δ) (SBP, p = 0.66; DBP, p = 0.66). Mean total cholesterol (TC) was higher among mice with large versus small AAA (601 vs. 422 mg/ml, p<0.0001), and the difference was due to LDL. AngII exposure was associated with 0.43 mm (95% CI, 0.27 to 0.61, p<0.0001) increase in aortic diameter; and a 100 mg/dl increase in mean final cholesterol level was associated with a 12% (95% CI, 5.68 to 18.23, p<0.0001) increase in aortic diameter. Baseline cholesterol was not associated with change in aortic diameter (p = 0.86).

Conclusions

These are the first formal estimates of a consistent pattern of Ang II-induced AAA development. The odds of AAA occurrence diminish after the second week of Ang II infusion, and TC is independently associated with AAA size.

β-Carotene Attenuates Angiotensin II-Induced Aortic Aneurysm by Alleviating Macrophage Recruitment in Apoe(-/-) Mice

Abdominal aortic aneurysm (AAA) is a common chronic degenerative disease characterized by progressive aortic dilation and rupture. The mechanisms underlying the role of α-tocopherol and β-carotene on AAA have not been comprehensively assessed. We investigated if α-tocopherol and β-carotene supplementation could attenuate AAA, and studied the underlying mechanisms utilized by the antioxidants to alleviate AAA. Four-months-old Apoe^−/− mice were used in the induction of aneurysm by infusion of angiotensin II (Ang II), and were orally administered with α-tocopherol and β-carotene enriched diet for 60 days. Significant increase of LDL, cholesterol, triglycerides and circulating inflammatory cells was observed in the Ang II-treated animals, and gene expression studies showed that ICAM-1, VCAM-1, MCP-1, M-CSF, MMP-2, MMP-9 and MMP-12 were upregulated in the aorta of aneurysm-induced mice. Extensive plaques, aneurysm and diffusion of inflammatory cells into the tunica intima were also noticed. The size of aorta was significantly (P = 0.0002) increased (2.24±0.20 mm) in the aneurysm-induced animals as compared to control mice (1.17±0.06 mm). Interestingly, β-carotene dramatically controlled the diffusion of macrophages into the aortic tunica intima, and circulation. It also dissolved the formation of atheromatous plaque. Further, β-carotene significantly decreased the aortic diameter (1.33±0.12 mm) in the aneurysm-induced mice (β-carotene, P = 0.0002). It also downregulated ICAM-1, VCAM-1, MCP-1, M-CSF, MMP-2, MMP-9, MMP-12, PPAR-α and PPAR-γ following treatment. Hence, dietary supplementation of β-carotene may have a protective function against Ang II-induced AAA by ameliorating macrophage recruitment in Apoe^−/− mice.

CD14 directs adventitial macrophage precursor recruitment: role in early abdominal aortic aneurysm formation

Background

Recruitment of macrophage precursors to the adventitia plays a key role in the pathogenesis of abdominal aortic aneurysms (AAAs), but molecular mechanisms remain undefined. The innate immune signaling molecule CD14 was reported to be upregulated in adventitial macrophages in a murine model of AAA and in monocytes cocultured with aortic adventitial fibroblasts (AoAf) in vitro, concurrent with increased interleukin‐6 (IL‐6) expression. We hypothesized that CD14 plays a crucial role in adventitial macrophage precursor recruitment early during AAA formation.

Methods and Results

CD14^−/− mice were resistant to AAA formation induced by 2 different AAA induction models: aortic elastase infusion and systemic angiotensin II (AngII) infusion. CD14 gene deletion led to reduced aortic macrophage infiltration and diminished elastin degradation. Adventitial monocyte binding to AngII‐infused aorta in vitro was dependent on CD14, and incubation of human acute monocytic leukemia cell line‐1 (THP‐1) monocytes with IL‐6 or conditioned medium from perivascular adipose tissue (PVAT) upregulated CD14 expression. Conditioned medium from AoAf and PVAT induced CD14‐dependent monocyte chemotaxis, which was potentiated by IL‐6. CD14 expression in aorta and plasma CD14 levels were increased in AAA patients compared with controls.

Conclusions

These findings link CD14 innate immune signaling via a novel IL‐6 amplification loop to adventitial macrophage precursor recruitment in the pathogenesis of AAA.

A clinical evaluation of statin pleiotropy: statins selectively and dose-dependently reduce vascular inflammation

Statins are thought to reduce vascular inflammation through lipid independent mechanisms. Evaluation of such an effect in atherosclerotic disease is complicated by simultaneous effects on lipid metabolism. Abdominal aortic aneurysms (AAA) are part of the atherosclerotic spectrum of diseases. Unlike atherosclerotic occlusive disease, AAA is not lipid driven, thus allowing direct evaluation of putative anti-inflammatory effects. The anti-inflammatory potency of increasing doses (0, 20 or 40 mg/day) simvastatin or atorvastatin was evaluated in 63 patients that were at least 6 weeks on statin therapy and who underwent open AAA repair. A comprehensive analysis using immunohistochemistry, mRNA and protein analyses was applied on aortic wall samples collected during surgery. The effect of statins on AAA growth was analyzed in a separate prospective study in incorporating 142 patients. Both statins equally effectively and dose-dependently reduced aortic wall expression of NFκB regulated mediators (i.e. IL-6 (P<0.001) and MCP-1 (P<0.001)); shifted macrophage polarization towards a M2 phenotype (P<0.0003); selectively reduced macrophage-related markers such as cathepsin K and S (P<0.009 and 0.0027 respectively), and ALOX5 (P<0.0009), and reduced vascular wall NFκB activity (40 mg/day group, P<0.016). No effect was found on other cell types. Evaluation of the clinical efficacy of statins to reduce AAA progression did not indicate an effect of statins on aneurysm growth (P<0.337). Hence, in the context of AAA the clinical relevance of statins pleiotropy appears minimal.

Performance of a modified rabbit model of abdominal aortic aneurysm induced by topical application of porcine elastase: 5-month follow-up study

OBJECTIVES

To modify the method for creating an abdominal aortic aneurysm in rabbits, and to study its performance.

MATERIALS AND METHODS

A total of 24 New Zealand white rabbits were induced topically with 10 μl of porcine elastase (0, 0.1, 5 and 10 units μl(-1)) to define the optimal concentration (groups A-D). Twelve aneurysms were induced with 10 units μl(-1) of 10 μl elastase to serve as a follow-up group (group E) to serve as a follow-up. A 1.5-cm aortic segment was isolated and induced with elastase solution for 30 min.

RESULTS

All animals in groups D and E developed AAA by day 5. Aneurysms in Group E were stable over 100 days. Partial destruction to disappearance of elastic lamellae and smooth muscle cells (SMCs) was seen in elastase-treated animals by day 5. Regenerated elastin and proliferated SMCs were present in group E. Matrix metalloproteinases 2 and 9 and RAM11 showed strong expression in group D, but expression decreased in group E after day 15.

CONCLUSIONS

The rabbit AAA model induced via topical application of porcine elastase at 10 units μl(-1) for 30 min appears easy and simple, with shorter induction and more rapid aortic dilation. The model is stable over 100 days and is useful to study the formation and progress of AAAs.

Interleukin-5 is a potential mediator of angiotensin II-induced aneurysm formation in apolipoprotein E knockout mice

BACKGROUND

The aim of this study was to evaluate alterations in Th1 and Th2 cytokines during experimental abdominal aortic aneurysm (AAA) formation.

METHODS

AAAs were induced in apolipoprotein E null mice by infusing angiotensin II (Ang II, 1000 ng/kg/min). Aortic homogenates were assessed at 0, 7, 14, and 28 d (n = 11/time point) for select Th1 and Th2 cytokines by ELISA. Additional mice had co-administration of anti-IgG (n = 20) or anti-IL-5 (n = 20) and were assessed at 28 d for AAA. Aortic homogenates were assessed for MMP-2 and MMP-9 expression. Mouse aortic SMC (MASMC) and peritoneal-derived macrophages were treated with IL-5 (0-40 ng/mL), and cell extracts and media (0-48 h) were assessed for MMP-2 and MMP-9 expression.

RESULTS

Ang II infusion was associated with a 3.4-fold (P < 0.01) and 3.6-fold (P < 0.01) increase in IL-5 and IL-10 (respectively), and a 0.6-fold reduction in IL-6, by 7 d. Anti-IL-5, but not anti-IgG, ameliorated Ang II-induced AAA formation. Up-regulation of MMP-2 and MMP-9 was observed in aneurysmal aortas, but not in the aortas obtained from mice treated with anti-IL-5. IL-5 stimulation of MASMC increased MMP-2 and MMP-9 mRNA (2.1-fold and 2.7-fold, respectively, P < 0.01) and protein (1.6-fold and 1.9-fold, respectively, P < 0.01) by 24 h. IL-5 stimulation of macrophages did not alter MMP expression.

CONCLUSIONS

Ang II induces increased Th2 cytokines IL-5 and IL-10 early in the course of experimental AAA formation, and inhibition of IL-5 prevents AAA formation suggesting an important role. While IL-5 is capable of up-regulating MMP-2 and MMP-9 expression in MASMC, investigations into alternate roles in AAA formation is warranted.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Resveratrol counteracts systemic and local inflammation involved in early abdominal aortic aneurysm development

BACKGROUND

Monocyte activation, macrophage infiltration, vascular oxidative stress and matrix proteolysis are inflammatory key steps contributing to abdominal aortic aneurysm (AAA) development. A phenotypical and functional heterogeneity is recognizable in monocytes by the differential expression of surface molecules: CD62L- subset corresponds to activated monocytes, while CD143/ACE surface expression increases during their differentiation into macrophages. In this work, Resveratrol, which is an antioxidant polyphenol with vasoprotective properties, has been evaluated for its potential to limit aneurysm development and monocyte-dependent inflammatory response in a model of elastase-induced AAA.

METHODS

Male Sprague-Dawley rats received Resveratrol (10 mg/kg/die) (Rsv group, n=15) or vehicle (ethanol) alone (Et-OH group, n=15) continuously from 7 d before until 14 d after the AAA induction with elastase; five littermates were used as untreated control group (Ctr group, n=5). At the end of treatment, CD143 and CD62L monocyte expression was analyzed by flow cytometry, serum antioxidant capacity was evaluated using the TRAP method and circulating TNFα, and MMP-9 were measured with ELISA and gel zymography, respectively. Aortas were subjected to histology and immunohistochemistry for morphological analysis, macrophage infiltration, and MMP-9, TNFα, and VEGF expression.

RESULTS

Resveratrol counteracted the CD62L-monocyte subset expansion, CD143 monocyte expression, and circulating levels of MMP-9 activity and TNFα associated to AAA induction. Similarly, treatment with Resveratrol significantly attenuated AAA expansion, vessel wall macrophage infiltration and MMP-9, VEGF, and TNFα expression, compared with AAA from Et-OH group.

CONCLUSIONS

Resveratrol limited the monocyte-dependent inflammatory response, macrophage differentiation and aortic lumen enlargement in elastase-induced AAA. These data suggest that Resveratrol might be tested in selected patients with small AAA to modulate the early systemic and local inflammatory response associated to AAA progression.

Endovascular aneurysm repair reverses the increased titer and the inflammatory activity of interleukin-1α in the serum of patients with abdominal aortic aneurysm

OBJECTIVE

To examine serum cytokine/chemokine profiles before and 6 months after endovascular repair (EVAR) of abdominal aortic aneurysm (AAA) and to determine whether they correlate with serum inflammatory activity using an in vitro model of leukocyte recruitment.

METHODS

Serum IL-1-α, IL-1β, IL-4, IL-6, IL-8, IL-10, IFN-γ, IP-10, MCP-1, TNF-α, and TNF-β were measured using a cytometry-based immunoassay. To test patient serum for direct inflammatory activity, human endothelial cells (EC) were stimulated with 30% patient serum for 24 hours. To test patient serum for the ability to prime EC for inflammatory responses, EC were incubated with 30% patient serum for 24 hours, followed by stimulation with low-dose (5 U/mL) TNF for 4 hours. Under both regimens of stimulation, the degree of EC activation was assessed by assaying neutrophil recruitment in a flow-based model.

RESULTS

Only IL-1α (67.9 ± 10.4 pg/mL vs 41.9 ± 7.4 pg/mL) and IL-8 (51.5 ± 5.1 vs 32.6 ± 4.7 pg/mL) changed significantly after surgery. Patient serum alone was unable to activate EC. However, serum from both time points could prime EC responses to low-dose TNF. Thus, after priming with preoperative serum, EC stimulated with TNF could recruit 76.7 ± 12.0 neutrophils/mm(2) into the subendothelial cell space. Post-EVAR serum was significantly less effective (44.4 ± 10.2 neutrophils/mm(2)). This reduction in neutrophil recruitment correlated with reduced IL-1α in post-EVAR serum. The addition of a neutralizing antibody against IL-1α to pre-EVAR serum inhibited EC priming and neutrophil recruitment, strongly implying that this cytokine was the priming agent.

CONCLUSION

EVAR reduces serum IL-1α and its inflammatory activity in patient serum. IL-1α is, therefore, implicated in the molecular pathology of AAAs and may have potential as a clinically useful biomarker.

Porphyromonas gingivalis participates in pathogenesis of human abdominal aortic aneurysm by neutrophil activation. Proof of concept in rats

Background

Abdominal Aortic Aneurysms (AAAs) represent a particular form of atherothrombosis where neutrophil proteolytic activity plays a major role. We postulated that neutrophil recruitment and activation participating in AAA growth may originate in part from repeated episodes of periodontal bacteremia.

Methods and Findings

Our results show that neutrophil activation in human AAA was associated with Neutrophil Extracellular Trap (NET) formation in the IntraLuminal Thrombus, leading to the release of cell-free DNA. Human AAA samples were shown to contain bacterial DNA with high frequency (11/16), and in particular that of Porphyromonas gingivalis (Pg), the most prevalent pathogen involved in chronic periodontitis, a common form of periodontal disease. Both DNA reflecting the presence of NETs and antibodies to Pg were found to be increased in plasma of patients with AAA. Using a rat model of AAA, we demonstrated that repeated injection of Pg fostered aneurysm development, associated with pathological characteristics similar to those observed in humans, such as the persistence of a neutrophil-rich luminal thrombus, not observed in saline-injected rats in which a healing process was observed.

Conclusions

Thus, the control of periodontal disease may represent a therapeutic target to limit human AAA progression.

Aneurysm and Helicobacter pylori relationship: the seropositivity of CagA, VacA and other antigens of Helicobacter pylori in abdominal and ascending aortic aneurysms

Helicobacter pylori is thought to be related to atherosclerosis and aneurysm development. We aimed to detect virulance factors of H. pylori and examine the potential etiopathogenetic relationship between aortic aneurysm and H. pylori, 58 abdominal aortic aneurysm (AAA) and 38 ascending aortic aneurysm (AsAA) cases and 57 Healty control group (HCG) were included. We investigated H. pylori IgG by ELISA and virulance factors by Western-Blot (WB) method. No difference was found between AAA (67.24%), AsAA (73.68%) and HCG (57.89%) for H. pylori IgG (p > 0.05). A significant difference was found between AsAA (78.95%) and HCG (57.89%) for H.pylori IgG (p < 0.05) by ELISA and a significant difference was found only between AsAA (100%) and HCG (37.5%) for H. pylori IgG in the 45-55 age group by WB. A statistically significant difference was found between AAA and AsAA for VacA and CagA + VacA and CagA + VacA + UreA antigens and also a significant difference was found between AsAA and HCG for CagA + UreA antigens (p < 0.05). Finally, we suggest that H. pylori VacA has a more important role than CagA in the development of two aneurysms especially in ruptured AAA. New extended studies detecting H. pylori DNA are needed to detect the aetiopathogenesis between aneurysm types and H. pylori.

Cystatin C deficiency promotes inflammation in angiotensin II-induced abdominal aortic aneurisms in atherosclerotic mice

An imbalance between cysteinyl cathepsins and their principal endogenous inhibitor cystatin C (CystC) may favor proteolysis in the pathogenesis of human abdominal aortic aneurysms (AAA), yet a direct role of CystC in AAA remains unproven. This study used CystC and apolipoprotein E (ApoE) compound mutant (CystC(-/-)ApoE(-/-)) mice to examine directly the role of cysteine protease/protease inhibitor imbalance in AAA formation in angiotensin II-induced AAA. CystC-deficiency increased lumenal diameter and lesion size compared with control mice. CystC(-/-) ApoE(-/-) lesions also demonstrated enhanced inflammatory cell accumulation, more severe elastin fragmentation, and fewer smooth muscle cells in the tunica media. Macrophage content, measured as percent positive area (23.2 +/- 1.4% versus 11.2 +/- 1.4%; P = 0.0003) and number of the CD4(+) T cells (ninefold; P = 0.048), increased significantly in CystC(-/-)ApoE(-/-) lesions. CystC deficiency increased cathepsin activity (5.5 fold; P = 0.001) in AAA, yielding greater elastin degradation and proangiogenic laminin-5 gamma2 peptide production, which may account for increased microvascularization in CystC(-/-)ApoE(-/-) compared with ApoE(-/-) lesions. Increased leukocyte adhesion molecule VCAM-1 expression and leukocyte proliferation might also promote inflammation in CystC-deficient AAA. These data indicate that CystC contributes to experimental AAA pathogenesis and that enhanced cysteine protease activity, due to the lack of CystC, favors inflammation in AAA lesions induced in atherosclerotic mice by promoting microvascularization and smooth muscle cell apoptosis as well as leukocytes adhesion and proliferation.

Perigraft hemorrhage after abdominal aortic aneurysm repair in a heart transplant patient

Spontaneous perigraft hemorrhage can occur years after a successful aortic aneurysm repair. Such hemorrhage can result, in part, from inadequate graft healing. Herein, we describe the case of a heart transplant recipient who underwent an abdominal aortic aneurysm repair that was complicated by an acute perigraft leak 6 weeks later. Apparently, suppression of the patient's immune system impaired proper healing of the graft-aortic anastomosis site. In patients who have a compromised immune system, an additional 4-0 polypropylene pledgeted suture line should be placed for reinforcement during abdominal aortic aneurysm repair. Postoperatively, patients who are given immunosuppressive therapy should undergo careful, long-term monitoring.

Gender differences in abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) comprise the tenth leading cause of death in Caucasian males 65 to 74 years of age and accounted for nearly 16,000 deaths overall in 2000. Therefore, understanding the pathophysiology of AAAs is an important undertaking. Clinically, multiple risk factors are associated with the development of AAAs, including increasing age, positive smoking history, and hypertension. Male gender is also a well-established risk factor for the development of an AAA, with a 4:1 male to female ratio. The reason for this gender disparity is unknown. The pathogenesis of AAAs formation is complex and multifactorial. Histologically, AAAs are characterized by early chemokine-driven leukocyte infiltration into the aortic wall. Subsequent destruction of elastin and collagen in the media and adventitia ensues owing to excessive local production of matrix-degrading enzymes and is accompanied by smooth muscle cell loss and thinning of the aortic wall. At present, no medical therapies are available to treat patients with aortic aneurysms, using only the crude measurement of aortic diameter as a threshold for which patients must undergo life-threatening and costly surgery. Defining the early mechanisms underlying gender-related differences in AAA formation is critical as understanding differences in disease patterns based on gender may allow us to develop new translational approaches to the prevention and treatment of patients with aortic aneurysms.

Basic research studies to understand aneurysm disease

Abdominal aortic aneurysm (AAA) is a complex multifactorial disease with life-threatening implications. Aneurysms typically have no signs or symptoms, and rupture of AAA has a high mortality rate. Multiple environmental and genetic risk factors are involved in aneurysm formation and progression making it a complicated disease to study. Little is understood about the mechanisms in disease initiation, thus there are currently no therapeutic approaches to prevent AAA, leaving patients with surgery as their only option. Ongoing research into the genetic components of AAA using a candidate gene approach has been overall unsuccessful. A more promising approach to study complex diseases involves genome-wide techniques such as DNA linkage analysis, genetic association studies and microarray expression profiling. Furthermore, studies involving inhibition of AAA progression, rather than formation, have a potentially promising outcome. Targeting biological pathways in AAA pathogenesis may benefit patients by slowing the growth and possibly preventing the rupture of AAA. Critical pathways involved in AAA pathogenesis include immunological processes, such as T-cell and natural killer cell pathways, oxidative stress, depletion of vascular smooth muscle cells through the process of apoptosis and the destruction of the extracellular matrix by matrix metalloproteinases.

Deletion of CCR2 but not CCR5 or CXCR3 inhibits aortic aneurysm formation

BACKGROUND

Microscopic analysis of abdominal aortic aneurysms (AAAs) demonstrates an abundance of infiltrating leukocytes. The chemokine receptors CCR2, CCR5, and CXCR3 are associated with pathways implicated previously in aneurysm pathogenesis. We hypothesized that genetic deletions of CCR2, CCR5, and CXCR3 would limit leukocyte infiltration and aneurysm formation in a mouse model of AAA.

METHODS

CCR2(-/-), CCR5(-/-), CXCR3(-/-), and control mice of the same genetic background were subject to periaortic application of calcium chloride. Aortic diameters were measured before aneurysm induction and at harvest 6 weeks later. Diameters were compared using the Mann-Whitney test. Aortas were stained with H&E and trichrome for histologic analysis. Aortic MMP-2 and MMP-9 activities were measured using zymography.

RESULTS

Aneurysm formation was attenuated in CCR2(-/-) mice with the final mean aortic diameter less than that of the control mice (P < .01). Histology revealed preservation of the lamellar architecture and decreased inflammatory cells. Aortic MMP-2 and MMP-9 levels were decreased in CCR2(-/-) mice. CCR5(-/-) and CXCR3(-/-) mice demonstrated no protection from aneurysm formation, which was corroborated by the tissue histology showing similar inflammatory cell infiltration and elastin degradation.

CONCLUSIONS

The CCR2 receptor is involved directly in AAA formation, whereas the CCR5 and CXCR3 receptors are not.

The role of the adventitia in vascular inflammation

Traditional concepts of vascular inflammation are considered "inside-out" responses centered on the monocyte adhesion and lipid oxidation hypotheses. These mechanisms likely operate in concert, holding the central tenet that the inflammatory response is initiated at the luminal surface. However, growing evidence supports a new paradigm of an "outside-in" hypothesis, in which vascular inflammation is initiated in the adventitia and progresses inward toward the intima. Hallmarks of the outside-in hypothesis include population of the adventitia with exogenous cell types, including monocytes, macrophages, and lymphocytes, the phenotypic switch of adventitial fibroblasts into migratory myofibroblasts, and increased vasa vasorum neovascularization. The resident and migrating cells deposit collagen and matrix components, respond to and upregulate inflammatory chemokines and/or antigens, and regulate the local redox state of the adventitia. B cells and T cells generate local humoral immune responses against local antigen presentation by foam cells and antigen presenting cells. These events result in increased local expression of cytokines and growth factors, evoking an inflammatory response that propagates inward toward the intima. Ultimately, it appears that the basic mechanisms of cellular activation and migration in vascular inflammation are highly conserved across a variety of cardiovascular disease states and that major inflammatory events begin in the adventitia.

Systemic Inflammation and Repair of Abdominal Aortic Aneurysm

BACKGROUND

Inflammation is integral to the pathogenesis of abdominal aortic aneurysm (AAA). This study examines preoperative biomarkers of systemic inflammation in patients undergoing open repair of intact and ruptured AAA.

METHODS

One-hundred twelve patients were entered into a prospective observational study. Preoperative POSSUM physiology score, C-reactive protein (CRP), white blood count (WBC), platelet count, fibrinogen, and albumin were recorded and related to clinical variables using univariate analysis.

RESULTS

Sixty-one patients with a ruptured AAA, 39 with an asymptomatic intact AAA, and 12 with an acutely symptomatic intact AAA underwent attempted repair. There were two inflammatory asymptomatic aneurysms and one inflammatory ruptured aneurysm. No patient had clinical evidence of coexistent inflammatory disease. Patients with a symptomatic intact AAA had a significantly greater level of CRP and fibrinogen, higher WBC, and lower serum albumin, than those with an asymptomatic intact AAA. Patients with a ruptured aneurysm had a significantly greater level of CRP, higher WBC, and lower serum albumin than those with an asymptomatic intact aneurysm. Patients with a symptomatic intact AAA had a significantly higher CRP level, but lower WBC, than those with a ruptured AAA. There was no difference in CRP level, WBC, or serum albumin between survivors and non-survivors of attempted repair of asymptomatic, symptomatic and ruptured AAA.

CONCLUSIONS

Acutely symptomatic and ruptured AAAs are associated with an early elevation in systemic inflammatory biomarkers. This early activation of the inflammatory response might influence perioperative outcome.

Interferon-beta attenuates angiotensin II-accelerated atherosclerosis and vascular remodeling in apolipoprotein E deficient mice

Atherosclerotic vascular disease is an inflammatory disease. Interferon-beta (IFN-beta) is an important immune modulator. However, the role of IFN-beta in atherosclerotic vascular disease is still not clear. The present study is designed to determine the effects of IFN-beta on atherosclerosis, abdominal aortic aneurysm (AAA) formation and proliferative vascular remodeling in apolipoprotein E (apoE) deficient mice. Six-month-old male apoE deficient mice fed a normal chow underwent ligation of the common left carotid artery, and were randomly assigned to receive either vehicle or angiotensin II (Ang II, 1.4 mg/kg daily) via a subcutaneously implanted osmotic infusion pump. The animals were further assigned to groups that were subjected to subcutaneous injection of vehicle or murine IFN-beta (10 MIU/kg, daily). Ang II increased atherosclerotic area in the non-ligated carotid artery and aortic arch, induced AAA, and exacerbated ligation-induced adventitial proliferation and neointimal hyperplasia characterized by smooth muscle cell (SMC) proliferation and macrophage infiltration in the ligated carotid artery. Co-treatment with IFN-beta, had no effects by itself, significantly attenuated Ang II-accelerated increase in the areas of neointima, adventitia, SMC and macrophage in the ligated carotid artery and suppressed Ang II-exacerbated atherosclerosis, but did not affect Ang II-induced AAA formation. These data indicate that IFN-beta can play a prominent anti-atherosclerosis, anti-inflammation, and anti-proliferation role of vasculoprotection.

The soluble forms of CD28, CD86 and CTLA-4 constitute possible immunological markers in patients with abdominal aortic aneurysm

OBJECTIVE

The T cell co-stimulatory factors CD28 and CTLA-4 and their ligands CD80 and CD86 occur as receptors on T cells and antigen-presenting cells and also in soluble forms in the circulation. We determined the levels of soluble co-stimulatory molecules in patients with abdominal aortic aneurysm (AAA) and normal individuals. We further correlated these soluble co-stimulatory molecules to other clinical parameters of importance such as age of the patient, presence of hypertension, size of the aneurysm and levels of matrix metalloproteinases-9 and C-reactive protein.

DESIGN, SETTING, SUBJECTS

This case-control study was designed to quantify the circulating levels of soluble co-stimulatory molecules by an in-house enzyme linked immunosorbent assay. A total of 314 subjects participated in the study including 100 patients and 214 normal controls. The statistical analysis was performed by Mann-Whitney test and Spearman's correlation rank test.

RESULTS

Our results show increased plasma levels of sCD28, sCD86 (P = 0.0001) and decreased plasma levels of sCTLA-4 (P = 0.0018) in the patients compared with normal individuals. The levels of these factors were not related to the age of the patient, size of aneurysm or levels of C-reactive protein in plasma. There was, however, a significant inverse relationship between the concentrations of sCTLA-4 and sCD80 with matrix metalloproteinase-9.

CONCLUSIONS

We suggest that soluble co-stimulatory molecules serve as biomarkers for the estimation of immune activation in AAA patients.

Topological determinants and consequences of adventitial responses to arterial wall injury

Arteries are composed of 3 concentric tissue layers which exhibit different structures and properties. Because arterial injury is generally initiated at the interface with circulating blood, most studies performed to unravel the mechanisms involved in injury-induced arterial responses have focused on the innermost layer (intima) rather than on the outermost adventitial layer. In the present review, we focus on the involvement of the adventitia in response to various types of arterial injury leading to vascular remodeling. Physiologically, soluble vascular mediators are centrifugally conveyed by mass transport toward the adventitia. Moreover, in pathological conditions, neomediators and antigens can be generated within the arterial wall, whose outward conveyance triggers different patterns of local adventitial response. Adventitial angiogenesis, immunoinflammation, and fibrosis sequentially interact and their net balance defines the participation of the adventitial response in arterial pathology. In the present review we discuss 4 pathological entities in which the adventitial response to arterial wall injury participates in arterial wall remodeling. Hence, the adventitial adaptive immune response predominates in chronic rejection. Inflammatory phagocytic cell recruitment and initiation of a shift from innate to adaptive immunity characterize the adventitial response to products of proteolysis in abdominal aortic aneurysm. Adventitial sprouting of neovessels, leading to intraplaque hemorrhages, predominates in atherothrombosis. Adventitial fibrosis characterizes the response to mechanical stress and is responsible for the constrictive remodeling of arterial segments and initiating interstitial fibrosis in perivascular tissues. These adventitial events, therefore, have an impact not only on the vessel wall biology but also on the surrounding tissue.

Pathogenesis of thoracic and abdominal aortic aneurysms

The major disease processes affecting the aorta are aortic aneurysms and dissections. Aneurysms are usually described in terms of their anatomic location, with thoracic aortic aneurysms (TAAs) involving the ascending and descending aorta in the thoracic cavity and abdominal aortic aneurysms (AAAs) involving the infrarenal abdominal aorta. Both thoracic and abdominal aortas are elastic arteries, and share similarities in their physical structures and cellular components. However, thoracic and abdominal aortas differ in their biochemical properties and the origin of their vascular smooth muscle cells (VSMCs). These similarities and differences between thoracic and abdominal aortas provide the basis for the various pathologic mechanisms observed in this disease. This review focuses on the comparison of the pathologic mechanisms involved in TAA and AAA.

Abdominal aortic aneurysm is a specific antigen-driven T cell disease

To determine whether monoclonal/oligoclonal T cells are present in abdominal aortic aneurysm (AAA) lesions, we amplified beta-chain T cell receptor (TCR) transcripts from these lesions by the nonpalindromic adaptor (NPA)-polymerase chain reaction (PCR)/V-beta-specific PCR followed by cloning and sequencing. Sequence analysis revealed the presence of substantial proportions of identical beta-chain TCR transcripts in AAA lesions in 9 of 10 patients examined, strongly suggesting the presence of oligoclonal populations of alphabeta TCR+ T cells. We have also shown the presence of oligoclonal populations of gammadelta TCR+ T cells in AAA lesions. Sequence analysis after appropriate PCR amplification and cloning revealed the presence of substantial proportions of identical VgammaI and VgammaII TCR transcripts in 15 of 15 patients examined, and of Vdelta1 and Vdelta2 TCR transcripts in 12 of 12 patients. These clonal expansions were very strong. All these clonal expansions were statistically significant by the binomial distribution. In other studies, we determined that mononuclear cells infiltrating AAA lesions express early- (CD69), intermediate- (CD25, CD38), and late- (CD45RO, HLA class II) activation antigens. These findings suggest that active ongoing inflammation is present in the aortic wall of patients with AAA. These results demonstrate that oligoclonal alphabeta TCR+ and gammadelta TCR+T cells are present in AAA lesions. These oligoclonal T cells have been clonally expanded in vivo in response to yet unidentified antigens. Although the antigenic specificity of these T cells remains to be determined, these T cells may play a significant role in the initiation and/or the propagation of the AAA. It appears that AAA is a specific antigen-driven T cell disease.