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Objective: Evaluate the mechanical and matrix effects on abdominal aortic aneurysms (AAA) during the initial aortic dilation and after prolonged exposure to beta-aminopropionitrile (BAPN) in a topical elastase AAA model. Methods: Abdominal aortae of C57/BL6 mice were exposed to topical elastase with or without BAPN in the drinking water starting 4 days before elastase exposure. For the standard AAA model, animals were harvested at 2 weeks after active elastase (STD2) or heat-inactivated elastase (SHAM2). For the enhanced elastase model, BAPN treatment continued for either 4 days (ENH2b) or until harvest (ENH2) at 2 weeks; BAPN was continued until harvest at 8 weeks in one group (ENH8). Each group underwent assessment of aortic diameter, mechanical testing (tangent modulus and ultimate tensile strength [UTS]), and quantification of insoluble elastin and bulk collagen in both the elastase exposed aorta as well as the descending thoracic aorta. Results: BAPN treatment did not increase aortic dilation compared with the standard model after 2 weeks (ENH2, 1.65 ± 0.23 mm; ENH2b, 1.49 ± 0.39 mm; STD2, 1.67 ± 0.29 mm; and SHAM2, 0.73 ± 0.10 mm), but did result in increased dilation after 8 weeks (4.3 ± 2.0 mm; P = .005). After 2 weeks, compared with the standard model, continuous therapy with BAPN did not have an effect on UTS (24.84 ± 7.62 N/cm2; 18.05 ± 4.95 N/cm2), tangent modulus (32.60 ± 9.83 N/cm2; 26.13 ± 9.10 N/cm2), elastin (7.41 ± 2.43%; 7.37 ± 4.00%), or collagen (4.25 ± 0.79%; 5.86 ± 1.19%) content. The brief treatment, EHN2b, resulted in increased aortic collagen content compared with STD2 (7.55 ± 2.48%; P = .006) and an increase in UTS compared with ENH2 (35.18 ± 18.60 N/cm2; P = .03). The ENH8 group had the lowest tangent modulus (3.71 ± 3.10 N/cm2; P = .005) compared with all aortas harvested at 2 weeks and a lower UTS (2.18 ± 2.18 N/cm2) compared with both the STD2 (24.84 ± 7.62 N/cm2; P = .008) and ENH2b (35.18 ± 18.60 N/cm2; P = .001) groups. No differences in the mechanical properties or matrix protein concentrations were associated with abdominal elastase exposure or BAPN treatment for the thoracic aorta. The tangent modulus was higher in the STD2 group (32.60 ± 9.83 N/cm2; P = .0456) vs the SHAM2 group (17.99 ± 5.76 N/cm2), and the UTS was lower in the ENH2 group (18.05 ± 4.95 N/cm2; P = .0292) compared with the ENH2b group (35.18 ± 18.60 N/cm2). The ENH8 group had the lowest tangent modulus (3.71 ± 3.10 N/cm2; P = .005) compared with all aortas harvested at 2 weeks and a lower UTS (2.18 ± 2.18 N/cm2) compared with both the STD2 (24.84 ± 7.62 N/cm2; P = .008) and ENH2b (35.18 ± 18.60 N/cm2; P = .001) groups. Abdominal aortic elastin in the STD2 group (7.41 ± 2.43%; P = .035) was lower compared with the SHAM2 group (15.29 ± 7.66%). Aortic collagen was lower in the STD2 group (4.25 ± 0.79%; P = .007) compared with the SHAM2 group (12.44 ± 6.02%) and higher for the ENH2b (7.55 ± 2.48%; P = .006) compared with the STD2 group. Conclusions: Enhancing an elastase AAA model with BAPN does not affect the initial (2-week) dilation phase substantially, either mechanically or by altering the matrix content. Late mechanical and matrix effects of prolonged BAPN treatment are limited to the elastase-exposed segment of the aorta. Clinical Relevance: This paper explores the use of short- and long-term exposure to beta-aminopropionitrile to create an enhanced topical elastase abdominal aortic aneurysm model in mice. Readouts of aneurysm severity included loss of mechanical stability and vascular extracellular matrix composition reminiscent of what is seen in the course of human disease. Additionally, we show that the thoracic aorta, unlike the findings below the renal arteries, is not damaged in our animal model.
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OBJECTIVE: We created a finite element model to predict the probability of dissection based on imaging-derived aortic stiffness and investigated the link between stiffness and wall tensile stress using our model. METHODS: Transthoracic echocardiogram measurements were used to calculate aortic diameter change over the cardiac cycle. Aortic stiffness index was subsequently calculated based on diameter change and blood pressure. A series of logistic models were developed to predict the binary outcome of aortic dissection using 1 or more series of predictor parameters such as aortic stiffness index or patient characteristics. Finite element analysis was performed on a subset of diameter-matched patients exhibiting patient-specific material properties. RESULTS: Transthoracic echocardiogram scans of patients with type A aortic dissection (n = 22) exhibited elevated baseline aortic stiffness index when compared with aneurysmal patients' scans with tricuspid aortic valve (n = 83, P < .001) and bicuspid aortic valve (n = 80, P < .001). Aortic stiffness index proved an excellent discriminator for a future dissection event (area under the curve, 0.9337, odds ratio, 2.896). From the parametric finite element study, we found a correlation between peak longitudinal wall tensile stress and stiffness index (ρ = .6268, P < .001, n = 28 pooled). CONCLUSIONS: Noninvasive transthoracic echocardiogram-derived aortic stiffness measurements may serve as an impactful metric toward predicting aortic dissection or quantifying dissection risk. A correlation between longitudinal stress and stiffness establishes an evidence-based link between a noninvasive stiffness parameter and stress state of the aorta with clinically apparent dissection events.
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OBJECTIVE: To assess ascending aortic distensibility and build geometry and distensibility-based patient-specific stress distribution maps in patients sustaining type A aortic dissection (TAAD) using predissection noninvasive imaging. METHODS: Review of charts from patients undergoing surgical repair of TAAD (n = 351) led to the selection of a subset population (n = 7) with 2 or more predissection computed tomography angiography scans and echocardiograms at least 1 year before dissection. Ascending aortic wall biomechanical properties (aortic strain, distensibility, and stiffness) were compared with age- and size-matched nondissected nonaneurysmal controls. Patient-specific aortic strain served as an input in aortic geometry-based simulated 3-dimensional reconstructions to generate longitudinal and circumferential wall stress maps. Inspection of perioperative dissection scans and intraoperative visual examination confirmed primary tear locations. RESULTS: Predissection echocardiography revealed ascending aortas of patients sustaining TAAD to exhibit decreased aortic wall strain (14.50 ± 1.13% vs 8.49 ± 1.08%; P < .01), decreased distensibility (4.26 ± 0.44 vs 2.39 ± 0.33 10-6 cm2·dyne-1; P < .01), increased stiffness (3.84 ± 0.24 vs 7.48 ± 1.05; P < .001), and increased longitudinal wall stress (246 ± 22 vs 172 ± 37 kPa; P < .01). There was no significant difference in circumferential wall stress. Predissection computed tomography angiography models revealed overlap between regions of increased longitudinal wall stress and primary tear sites. CONCLUSIONS: Using predissection imaging, we identified increased stiffness and longitudinal wall stress in ascending aortas of patients with dissection. Patient-specific imaging-derived biomechanical property maps like these may be instrumental toward designing better prediction models of aortic dissection potential.
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Aorta/patologia , Dissecção Aórtica/etiologia , Rigidez Vascular , Aorta/fisiopatologia , Angiografia por Tomografia Computadorizada , Ecocardiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Fatores de Risco , Estresse FisiológicoRESUMO
OBJECTIVE: Tissue-engineered vascular grafts containing adipose-derived mesenchymal stem cells offer an alternative to small-diameter vascular grafts currently used in cardiac and lower-extremity revascularization procedures. Adipose-derived, mesenchymal stem cell-infused, tissue-engineered vascular grafts have been shown to promote remodeling and vascular homeostasis in vivo and offer a possible treatment solution for those with cardiovascular disease. Unfortunately, the time needed to cultivate adipose-derived mesenchymal stem cells remains a large hurdle for tissue-engineered vascular grafts as a treatment option. The purpose of this study was to determine if stromal vascular fraction (known to contain progenitor cells) seeded tissue-engineered vascular grafts would remain patent in vivo and remodel, allowing for a "same-day" process for tissue-engineered vascular graft fabrication and implantation. METHODS: Stromal vascular fraction, obtained from adult human adipose tissue, was seeded within 4 hours after acquisition from the patient onto poly(ester urethane)urea bilayered scaffolds using a customized rotational vacuum seeding device. Constructs were then surgically implanted as abdominal aortic interposition grafts in Lewis rats. RESULTS: Findings revealed patency in 5 of 7 implanted scaffolds at 8 weeks, along with neotissue formation and remodeling occurring in patent tissue-engineered vascular grafts. Patency was documented using angiography and gross inspection, and remodeling and vascular components were detected using immunofluorescent chemistry. CONCLUSIONS: A "same-day" cell-seeded, tissue-engineered vascular graft can remain patent after implantation in vivo, with neotissue formation and remodeling occurring by 8 weeks.
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Tecido Adiposo/citologia , Aorta Abdominal/cirurgia , Bioprótese , Implante de Prótese Vascular/instrumentação , Prótese Vascular , Transplante de Células-Tronco/instrumentação , Células Estromais/fisiologia , Células Estromais/transplante , Engenharia Tecidual/métodos , Alicerces Teciduais , Adulto , Animais , Aorta Abdominal/metabolismo , Aorta Abdominal/patologia , Aorta Abdominal/fisiopatologia , Biomarcadores/metabolismo , Células Cultivadas , Estudos de Viabilidade , Feminino , Humanos , Pessoa de Meia-Idade , Neointima , Fenótipo , Desenho de Prótese , Ratos Endogâmicos Lew , Células Estromais/metabolismo , Fatores de Tempo , Transplante Heterólogo , Grau de Desobstrução Vascular , Remodelação Vascular , Fluxo de TrabalhoRESUMO
OBJECTIVE: One of the rate-limiting barriers within the field of vascular tissue engineering is the lengthy fabrication time associated with expanding appropriate cell types in culture. One particularly attractive cell type for this purpose is the adipose-derived mesenchymal stem cell (AD-MSC), which is abundant and easily harvested from liposuction procedures. Even this cell type has its drawbacks, however, including the required culture period for expansion, which could pose risks of cellular transformation or contamination. Eliminating culture entirely would be ideal to avoid these concerns. In this study, we used the raw population of cells obtained after digestion of human liposuction aspirates, known as the stromal vascular fraction (SVF), as an abundant, culture-free cell source for tissue-engineered vascular grafts (TEVGs). METHODS: SVF cells and donor-paired cultured AD-MSCs were first assessed for their abilities to differentiate into vascular smooth muscle cells (SMCs) after angiotensin II stimulation and to secrete factors (eg, conditioned media) that promote SMC migration. Next, both cell types were incorporated into TEVG scaffolds, implanted as an aortic graft in a Lewis rat model, and assessed for their patency and composition. RESULTS: In general, the human SVF cells were able to perform the same functions as AD-MSCs isolated from the same donor by culture expansion. Specifically, cells within the SVF performed two important functions; namely, they were able to differentiate into SMCs (SVF calponin expression: 16.4% ± 7.7% vs AD-MSC: 19.9%% ± 1.7%) and could secrete promigratory factors (SVF migration rate relative to control: 3.1 ± 0.3 vs AD-MSC: 2.5 ± 0.5). The SVF cells were also capable of being seeded within biodegradable, elastomeric, porous scaffolds that, when implanted in vivo for 8 weeks, generated patent TEVGs (SVF: 83% patency vs AD-MSC: 100% patency) populated with primary vascular components (eg, SMCs, endothelial cells, collagen, and elastin). CONCLUSIONS: Human adipose tissue can be used as a culture-free cell source to create TEVGs, laying the groundwork for the rapid production of cell-seeded grafts.
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Tecido Adiposo/irrigação sanguínea , Bioprótese , Implante de Prótese Vascular/instrumentação , Prótese Vascular , Músculo Liso Vascular/transplante , Miócitos de Músculo Liso/transplante , Células Estromais/transplante , Engenharia Tecidual/métodos , Adulto , Angiotensina II/farmacologia , Animais , Aorta Abdominal/metabolismo , Aorta Abdominal/patologia , Aorta Abdominal/cirurgia , Implante de Prótese Vascular/métodos , Diferenciação Celular , Movimento Celular , Separação Celular , Células Cultivadas , Feminino , Humanos , Lipectomia , Transplante de Células-Tronco Mesenquimais , Células-Tronco Mesenquimais/efeitos dos fármacos , Células-Tronco Mesenquimais/metabolismo , Músculo Liso Vascular/efeitos dos fármacos , Músculo Liso Vascular/metabolismo , Miócitos de Músculo Liso/efeitos dos fármacos , Miócitos de Músculo Liso/metabolismo , Fenótipo , Ratos Endogâmicos Lew , Células Estromais/efeitos dos fármacos , Células Estromais/metabolismo , Fatores de Tempo , Alicerces TeciduaisRESUMO
Current commercial tensile testing systems use spring-loaded or other compression-based grips to clamp materials in place posing a problem for very soft or delicate materials that cannot withstand this mechanical clamping force. In order to perform uniaxial tensile tests on soft tissues or materials, we have created a novel vacuum-assisted anchor (VAA). Fibrin gels were subjected to uniaxial extension, and the testing data was used to determine material mechanical properties. Utilizing the VAA, we achieved successful tensile breaks of soft fibrin gels while finding statistically significant differences between the mechanical properties of gels fabricated at two different fibrinogen concentrations.
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OBJECTIVE: Ascending thoracic aortic aneurysm (ATAA) in patients with bicuspid aortic valve (BAV) commonly dilate asymmetrically compared with patients with tricuspid aortic valve (TAV). This discrepancy in aneurysm geometry led us to hypothesize that microarchitectural differences underlie the observed asymmetric dilatation pattern. The purpose of this study was to characterize the microarchitectural distinctions of the extracellular matrix of the 2 phenotypes with a focus on the proportion of radially oriented elastin and collagen fibers in different circumferential aortic regions. METHODS: Aortic tissue rings were obtained just distal to the sinotubular junction from patients with BAV or TAV undergoing elective aneurysm repair. They were sectioned into three circumferentially based regions according to adjacent aortic sinus segment (left coronary sinus [L], right coronary sinus [R], or noncoronary sinus [N]). Multiphoton microscopy was used to quantify and characterize the number of radially oriented elastin and collagen fibers. RESULTS: There were fewer radially oriented fibers in medial region N and medial-intimal region R of BAV-ATAAs when compared with TAV-ATAAs (medial region N, amplitude of angular undulation of elastin = 10.67° ± 1.35° vs 15.58° ± 1.91°; P = .041; medial-intimal region R, amplitude of angular undulation of elastin = 9.83° ± 0.83° vs 14.72° ± 1.64°; P = .015). Conversely, fibers became more radially oriented in the medial-intimal region L of BAV-ATAA when compared with TAV-ATAA (amplitude of angular undulation of collagen = 18.67° ± 0.95° vs 14.56° ± 1.37°; P = .041). CONCLUSIONS: The differential pattern of fiber orientation noted between L and N-R regions help explain the unique pattern of greater curvature dilatation of BAV-ATAA. The distinctions noted in matrix microarchitecture may form the basis of differing aneurysm geometries and aortic wall integrities in ATAAs arising in these different valve morphologies.
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Aorta Torácica/patologia , Aneurisma da Aorta Torácica/etiologia , Valva Aórtica/anormalidades , Matriz Extracelular/ultraestrutura , Doenças das Valvas Cardíacas/complicações , Adulto , Idoso , Idoso de 80 Anos ou mais , Aorta Torácica/fisiopatologia , Aneurisma da Aorta Torácica/diagnóstico , Aneurisma da Aorta Torácica/fisiopatologia , Doença da Válvula Aórtica Bicúspide , Elasticidade , Feminino , Doenças das Valvas Cardíacas/diagnóstico , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
OBJECTIVE: Little is known about the etiologic factors that lead to the occurrence of intraluminal thrombus (ILT) during abdominal aortic aneurysm (AAA) development. Recent work has suggested that macrophages may play an important role in progression of a number of other vascular diseases, including atherosclerosis; however, whether these cells are present within the ILT of a progressing AAA is unknown. The purpose of this work was to define the presence, phenotype, and spatial distribution of macrophages within the ILT excised from six patients. We hypothesized that the ILT contains a population of activated macrophages with a distinct, nonclassical phenotypic profile. METHODS: ILT samples were examined using histologic staining and immunofluorescent labeling for multiple markers of activated macrophages (cluster of differentiation [CD]45, CD68, human leukocyte antigen-DR, matrix metalloproteinase 9) and the additional markers α-smooth muscle actin, CD34, CD105, fetal liver kinase-1, and collagen I and III. RESULTS: Histologic staining revealed a distinct laminar organization of collagen within the shoulder region of the ILT lumen and a spatially heterogeneous cell composition within the ILT. Most of the cellular constituents of the ILT were in the luminal region and predominantly expressed markers of activated macrophages but also concurrently expressed α-smooth muscle actin, CD105, and synthesized collagen I and III. CONCLUSIONS: This report presents evidence for the presence of a distinct macrophage population within the luminal region of AAA ILT. These cells express a set of markers indicative of a unique population of activated macrophages. The exact contributions of these previously unrecognized cells to ILT formation and AAA pathobiology remains unknown.