OBJECTIVE—Neutrophils promote experimental abdominal aortic aneurysm (AAA) formation via a mechanism that is independent from MMPs (matrix metalloproteinases). Recently, we reported a dominant role ...of IL (interleukin)-1β in the formation of murine experimental AAAs. Here, the hypothesis that IL-1β–induced neutrophil extracellular trap formation (NETosis) promotes AAA was tested.
APPROACH AND RESULTS—NETs were identified through colocalized staining of neutrophil, Cit-H3 (citrullinated histone H3), and DNA, using immunohistochemistry. NETs were detected in human AAAs and were colocalized with IL-1β. In vitro, IL-1RA attenuated IL-1β–induced NETosis in human neutrophils. Mechanistically, IL-1β treatment of isolated neutrophils induced nuclear localization of ceramide synthase 6 and synthesis of C16-ceramide, which was inhibited by IL-1RA or fumonicin B1, an inhibitor of ceramide synthesis. Furthermore, IL-1RA or fumonicin B1 attenuated IL1-β–induced NETosis. In an experimental model of murine AAA, NETs were detected at a very early stage–day 3 of aneurysm induction. IL-1β–knockout mice demonstrated significantly lower infiltration of neutrophils to aorta and were protected from AAA. Adoptive transfer of wild-type neutrophils promoted AAA formation in IL-1β–knockout mice. Moreover, treatment of wild-type mice with Cl-amidine, an inhibitor NETosis, significantly attenuated AAA formation, whereas, treatment with deoxyribonuclease, a DNA digesting enzyme, had no effect on AAA formation.
CONCLUSIONS—Altogether, the results suggest a dominant role of IL-1β–induced NETosis in AAA formation.
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Arterial walls can be regarded as composite materials consisting of collagen fibers embedded in an elastic matrix and smooth muscle cells. Remodeling of the structural proteins has ...been shown to play a significant role in the mechanical behavior of walls during pathogenesis of abdominal aortic aneurysms (AAA). In this study, we systematically studied the change in the microstructure, histology and mechanics to link them to AAA disease progression. We performed biaxial extension tests, second-harmonic generation imaging and histology on 15 samples from the anterior part of AAA walls harvested during open aneurysm surgery. Structural data were gained by fitting to a bivariate von Mises distribution and yielded the mean fiber direction and in- and out-of-plane fiber dispersions of collagen. Mechanical and structural data were fitted to a recently proposed material model. Additionally, the mechanical data were used to derive collagen recruitment points in the obtained stress-stretch curves. We derived 14 parameters from histology such as smooth muscle cell-, elastin-, and abluminal adipocyte content. In total, 22 parameters were obtained and statistically evaluated. Based on the collagen recruitment points we were able to define three different stages of disease progression. Significant differences in elastin content, collagen orientation and adipocyte contents were discovered. Nerves entrapped inside AAA walls pointed towards a significant deposition of newly formed collagen abluminally, which we propose as neo-adventitia formation. We were able to discriminate two types of remodeled walls with a high collagen content – potentially safe and possibly vulnerable walls with a high adipocyte content inside the wall and significant amounts of inflammation. The study yielded a hypothesis for disease progression, derived from the systematic comparison of mechanical, microstructural and histological changes in AAAs.
Remodeling of the structural proteins plays an important role in the mechanical behavior of walls during pathogenesis of abdominal aortic aneurysms (AAA). We analyzed changes in the microstructure, histology and biomechanics of 15 samples from the anterior part of AAA walls and, for the first time, linked the results to three different stages of disease progression. We identified significant differences in elastin content, collagen orientation, adipocyte contents, and also a deposition of newly formed collagen forming a neoadventitia. We could discriminate two types of remodeled walls: (i) potentially safe and (ii) possibly vulnerable associated with inflammation and a high amount of adipocytes.
Aortic disease is a significant cause of death in developed countries. The most common forms of aortic disease are aneurysm, dissection, atherosclerotic occlusion and ageing-induced stiffening. The ...microstructure of the aortic tissue has been studied with great interest, because alteration of the quantity and/or architecture of the connective fibres (elastin and collagen) within the aortic wall, which directly imparts elasticity and strength, can lead to the mechanical and functional changes associated with these conditions. This review article summarizes the state of the art with respect to characterization of connective fibre microstructure in the wall of the human aorta in ageing and disease, with emphasis on the ascending thoracic aorta and abdominal aorta where the most common forms of aortic disease tend to occur.
Human abdominal aortic aneurysm (AAA) pathophysiology is not yet completely understood. In conductance arteries, the insoluble extracellular matrix, synthesized by vascular smooth muscle cells, ...assumes the function of withstanding the intraluminal arterial blood pressure. Progressive loss of this function through extracellular matrix proteolysis is a main feature of AAAs. As most patients are now treated via endovascular approaches, surgical AAA specimens have become rare. Animal models provide valuable complementary insights into AAA pathophysiology. Current experimental AAA models involve induction of intraluminal dilation (nondissecting AAAs) or a contained intramural rupture (dissecting models). Although the ideal model should reproduce the histological characteristics and natural history of the human disease, none of the currently available animal models perfectly do so. Experimental models try to represent the main pathophysiological determinants of AAAsgenetic or acquired defects in extracellular matrix, loss of vascular smooth muscle cells, and innate or adaptive immune response. Nevertheless, most models are characterized by aneurysmal stabilization and healing after a few weeks because of cessation of the initial stimulus. Recent studies have focused on ways to optimize existing models to allow continuous aneurysmal growth. This review aims to discuss the relevance and recent advances of current animal AAA models.
VISUAL OVERVIEW—An online visual overview is available for this article.
IMPORTANCE: Abdominal aortic aneurysms affect more than 3% of US older adults. OBJECTIVE: To test whether doxycycline reduces the growth of abdominal aortic aneurysm over 2 years as measured by ...maximum transverse diameter. DESIGN, SETTING, AND PARTICIPANTS: Parallel, 2-group, randomized clinical trial that was conducted at 22 US clinical centers between May 2013 and January 2017, and enrolled patients 50 years or older with small (3.5-5.0 cm for men, 3.5-4.5 cm for women) infrarenal aneurysms. The final date of follow-up was July 31, 2018. INTERVENTIONS: Patients were randomized to receive twice daily for 2 years doxycycline 100 mg orally (as capsules) (n = 133) or placebo (n = 128). MAIN OUTCOMES AND MEASURES: The primary outcome was change in abdominal aortic aneurysm maximum transverse diameter measured from CT images at baseline and follow-up at 2 years. Patients were assigned ranks based on the maximum transverse diameter (measured or imputed) of the aorta and also if they underwent aneurysm repair or died. The ranks were converted to scores having a normal distribution to facilitate the primary analysis (“normal scores”). RESULTS: Of 261 patients randomized, no follow-up CT scans were obtained on 7 (3%), leaving a final analysis set of 129 patients assigned to doxycycline and 125 to placebo (mean SD age, 71.0 years 7.4 years, 35 women 14%). The outcome normal scores used in the primary analysis were based on maximum transverse diameter (measured or imputed) in 113 patients (88%) in the doxycycline group and 112 patients (90%) in the placebo group; aneurysm repair in 13 (10%) and 9 (7%), and death in 3 (2%) and 4 (3%), respectively. The primary outcome, normal scores reflecting change in aortic diameter, did not differ significantly between the 2 groups, mean change in normal scores, 0.0262 vs −0.0258 (1-sided P = .71). Mean (SD) baseline maximum transverse diameter was 4.3 cm (0.4 cm) for doxycycline and 4.3 cm (0.4 cm) for placebo. At the 2-year follow-up, the change in measured maximum transverse diameter was 0.36 cm (95% CI, 0.31 to 0.40 cm) for 96 patients in the doxycycline group vs 0.36 cm (95% CI, 0.30 to 0.41 cm) for 101 patients in the placebo group (difference, 0.0; 95% CI, −0.07 to 0.07 cm; 2-sided P = .93). No patients were withdrawn from the study because of adverse effects. Joint pain occurred in 84 of 129 patients (65%) with doxycycline and 79 of 125 (63%) with placebo. CONCLUSIONS AND RELEVANCE: Among patients with small infrarenal abdominal aortic aneurysms, doxycycline compared with placebo did not significantly reduce aneurysm growth at 2 years. These findings do not support the use of doxycycline for reducing the growth of small abdominal aortic aneurysms. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01756833
OBJECTIVE—Current experimental models of abdominal aortic aneurysm (AAA) do not accurately reproduce the major features of human AAA. We hypothesized that blockade of TGFβ (transforming growth ...factor-β) activity—a guardian of vascular integrity and immune homeostasis—would impair vascular healing in models of nondissecting AAA and would lead to sustained aneurysmal growth until rupture.
APPROACH AND RESULTS—Here, we test this hypothesis in the elastase-induced AAA model in mice. We analyze AAA development and progression using ultrasound in vivo, synchrotron-based ultrahigh resolution imaging ex vivo, and a combination of biological, histological, and flow cytometry-based cellular and molecular approaches in vitro. Systemic blockade of TGFβ using a monoclonal antibody induces a transition from a self-contained aortic dilatation to a model of sustained aneurysmal growth, associated with the formation of an intraluminal thrombus. AAA growth is associated with wall disruption but no medial dissection and culminates in fatal transmural aortic wall rupture. TGFβ blockade enhances leukocyte infiltration both in the aortic wall and the intraluminal thrombus and aggravates extracellular matrix degradation. Early blockade of IL-1β or monocyte-dependent responses substantially limits AAA severity. However, blockade of IL-1β after disease initiation has no effect on AAA progression to rupture.
CONCLUSIONS—Endogenous TGFβ activity is required for the healing of AAA. TGFβ blockade may be harnessed to generate new models of AAA with better relevance to the human disease. We expect that the new models will improve our understanding of the pathophysiology of AAA and will be useful in the identification of new therapeutic targets.
Abstract Objective This review describes ongoing efforts to develop a medical therapy to limit abdominal aortic aneurysm (AAA) growth. Methods Data from animal model studies, human investigations, ...and clinical trials are described. Results Studies in rodent models and human samples have suggested a number of potential targets for slowing or halting AAA growth. A number of clinical trials are now examining the value of medications targeting some of the pathways identified. These trials have a number of challenges, including identifying medications safe to use in older patients with multiple comorbidities, developing accurate outcome assessments, and minimizing the dropout of patients during the trials. Three recent trials have reported no benefit of the antibiotic doxycycline, a mast cell inhibitor, an angiotensin-converting enzyme inhibitor, or a calcium channel blocker in limiting AAA growth. A number of other trials examining angiotensin receptor blockers, cyclosporine, and an antiplatelet agent are currently underway. Conclusions Further refinement of drug discovery pathways and testing paradigms are likely needed to develop effective nonsurgical therapies for AAA.
Renovascular hypertension (RVH) associated with renal artery and abdominal aortic narrowings is the third most common cause of pediatric hypertension. Untreated children may experience major ...cardiopulmonary complications, stroke, renal failure, and death. The impetus of this study was to describe the increasingly complex surgical practice for such patients with an emphasis on anatomic phenotype and contemporary outcomes after surgical management as a means of identifying those factors responsible for persistent or recurrent hypertension necessitating reoperation.
A retrospective analysis was performed of consecutive pediatric patients with RVH undergoing open surgical procedures at the University of Michigan from 1991 to 2017. Anatomic phenotype and patient risk factors were analyzed to predict outcomes of blood pressure control and the need for secondary operations using ordered and binomial logistic multinomial regression models, respectively.
There were 169 children (76 girls, 93 boys) who underwent primary index operations at a median age of 8.3 years; 31 children (18%) had neurofibromatosis type 1, 76 (45%) had abdominal aortic coarctations, and 28 (17%) had a single functioning kidney. Before treatment at the University of Michigan, 51 children experienced failed previous open operations (15) or endovascular interventions (36) for RVH at other institutions. Primary surgical interventions (342) included main renal artery (136) and segmental renal artery (10) aortic reimplantation, renal artery bypass (55), segmental renal artery embolization (10), renal artery patch angioplasty (8), resection with reanastomosis (4), and partial or total nephrectomy (25). Non-renal artery procedures included patch aortoplasty (32), aortoaortic bypass (32), and splanchnic arterial revascularization (30). Nine patients required reoperation in the early postoperative period. During a mean follow-up of 49 months, secondary interventions were required in 35 children (21%), including both open surgical (37) and endovascular (14) interventions. Remedial intervention to preserve primary renal artery patency or a nephrectomy if such was impossible was required in 22 children (13%). The remaining secondary procedures were performed to treat previously untreated disease that became clinically evident during follow-up. Age at operation and abdominal aortic coarctation were independent predictors for reoperation. The overall experience revealed hypertension to be cured in 74 children (44%), improved in 78 (46%), and unchanged in 17 (10%). Children undergoing remedial operations were less likely (33%) to be cured of hypertension. There was no perioperative death or renal insufficiency requiring dialysis after either primary or secondary interventions.
Contemporary surgical treatment of pediatric RVH provides a sustainable overall benefit to 90% of children. Interventions in the very young (<3 years) and concurrent abdominal aortic coarctation increase the likelihood of reoperation. Patients undergoing remedial surgery after earlier operative failures are less likely to be cured of hypertension. Judicious postoperative surveillance is imperative in children surgically treated for RVH.
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OBJECTIVE—Increasing evidence suggests that contractile dysfunction in smooth muscle cells (SMCs) plays a critical role in aortic biomechanical dysfunction and aortic aneurysm and dissection (AAD) ...development. However, the mechanisms underlying SMC contractile dysfunction in sporadic AAD are poorly understood. In this study, we examined the role of the NLRP3 (nucleotide oligomerization domain–like receptor family, pyrin domain containing 3)–caspase-1 inflammasome, a key inflammatory cascade, in SMC contractile dysfunction in AAD.
APPROACH AND RESULTS—We observed significant SMC contractile protein degradation in aortas from patients with sporadic thoracic AAD. The contractile protein degradation was associated with activation of the NLRP3–caspase-1 inflammasome cascade. In SMCs, caspase-1 bound and directly cleaved and degraded contractile proteins, leading to contractile dysfunction. Furthermore, Nlrp3 or caspase-1 deficiency in mice significantly reduced angiotensin II–induced contractile protein degradation, biomechanical dysfunction, and AAD formation in both thoracic and abdominal aortas. Finally, blocking this cascade with the inflammasome inhibitor, glyburide (an antidiabetic medication), reduced angiotensin II–induced AAD formation.
CONCLUSIONS—Inflammasome-caspase-1–mediated degradation of SMC contractile proteins may contribute to aortic biomechanical dysfunction and AAD development. This cascade may be a therapeutic target in AAD formation. In addition, glyburide may have protective effects against AAD development.
RATIONALE:Matrix metalloproteinases (MMPs)–mediated extracellular matrix destruction is the major cause of development and progression of abdominal aortic aneurysms. Systemic treatments of MMP ...inhibitors have shown effectiveness in animal models, but it did not translate to clinical success either because of low doses used or systemic side effects of MMP inhibitors. We propose a targeted nanoparticle (NP)–based delivery of MMP inhibitor at low doses to the abdominal aortic aneurysms site. Such therapy will be an attractive option for preventing expansion of aneurysms in patients without systemic side effects.
OBJECTIVE:Our previous study showed that poly(D,L-lactide) NPs conjugated with an antielastin antibody could be targeted to the site of an aneurysm in a rat model of abdominal aortic aneurysms. In the study reported here, we tested whether such targeted NPs could deliver the MMP inhibitor batimastat (BB-94) to the site of an aneurysm and prevent aneurysmal growth.
METHODS AND RESULTS:Poly(D,L-lactide) NPs were loaded with BB-94 and conjugated with an elastin antibody. Intravenous injections of elastin antibody–conjugated BB-94-loaded NPs targeted the site of aneurysms and delivered BB-94 in a calcium chloride injury-induced abdominal aortic aneurysms in rats. Such targeted delivery inhibited MMP activity, elastin degradation, calcification, and aneurysmal development in the aorta (269% expansion in control versus 40% elastin antibody–conjugated BB-94-loaded NPs) at a low dose of BB-94. The systemic administration of BB-94 alone at the same dose was ineffective in producing MMP inhibition.
CONCLUSIONS:Targeted delivery of MMP inhibitors using NPs may be an attractive strategy to inhibit aneurysmal progression.
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