elastin and Bicuspid-Aortic-Valve-Disease

The lattice Boltzmann method (LBM) has been increasingly used as a stand-alone CFD solver in various biomechanical applications. This study proposes a new fluid-structure interaction (FSI) co-modeling framework for the hemodynamic-structural analysis of compliant aortic valves. Toward that goal, two commercial software packages are integrated using the lattice Boltzmann (LBM) and finite element (FE) methods. The suitability of the LBM-FE hemodynamic FSI is examined in modeling healthy tricuspid and bicuspid aortic valves (TAV and BAV), respectively. In addition, a multi-scale structural approach that has been employed explicitly recognizes the heterogeneous leaflet tissues and differentiates between the collagen fiber network (CFN) embedded within the elastin matrix of the leaflets. The CFN multi-scale tissue model is inspired by monitoring the distribution of the collagen in 15 porcine leaflets. Different simulations have been examined, and structural stresses and resulting hemodynamics are analyzed. We found that LBM-FE FSI approach can produce good predictions for the flow and structural behaviors of TAV and BAV and correlates well with those reported in the literature. The multi-scale heterogeneous CFN tissue structural model enhances our understanding of the mechanical roles of the CFN and the elastin matrix behaviors. The importance of LBM-FE FSI also emerges in its ability to resolve local hemodynamic and structural behaviors. In particular, the diastolic fluctuating velocity phenomenon near the leaflets is explicitly predicted, providing vital information on the flow transient nature. The full closure of the contacting leaflets in BAV is also demonstrated. Accordingly, good structural kinematics and deformations are captured for the entire cardiac cycle.

Topics: Animals; Aortic Valve; Bicuspid Aortic Valve Disease; Collagen; Elastin; Hemodynamics; Models, Cardiovascular; Swine

This study aims to identify the clinical utility of targeted-genetic sequencing in a cohort of patients with TAA and establish a new method for regional histological characterisation of TAA disease.. Fifty-four patients undergoing surgery for proximal TAA were recruited.. connective tissue disease, bicuspid aortic valves, redo surgery. All patients underwent next generation sequencing (NGS) using a custom gene panel containing 63 genes previously associated with TAA on Illumina MiSeqor NextSeq550 platforms. Explanted TAA tissue was obtained en-bloc from 34/54 patients, and complete circumferential strips of TAA tissue processed into whole slides which were subsequently digitalised. Computational pathology methods were employed to quantify elastin, cellularity and collagen in six equally divided regions across the whole aneurysm circumference.. Of 54 patients, clearly pathogenic or potentially pathogenic variants were found in 7.4%: namely LOX, PRKG1, TGFBR1 and SMAD3 genes. 55% had at least one variant of unknown significance (VUS) and seven of the VUSs were in genes with a strong disease association (category A) genes, whilst 15 were from moderate risk (category B) genes. Elastin and collagen abundance displayed high regional variation throughout the aneurysm circumference. In patients with <60% total elastin, the loss of elastin was more significant on the outer curve (38.0% vs 47.4%, p = 0.0094). The presence of VUS, higher pulse wave velocity and advancing age were predictors of elastin loss (regression analysis: p < 0.05).. These findings demonstrate the heterogeneity of TAA disease microstructure and the potential link between histological appearance and clinical factors, including genetic variation.

Topics: Aortic Aneurysm, Thoracic; Bicuspid Aortic Valve Disease; Collagen; Elastin; Humans; Pulse Wave Analysis

Bicuspid aortic valve (BAV) may be complicated by aortic aneurysms and dissection. This study aimed to evaluate the prognostic efficacy of markers from cardiac imaging, as well as genetic and new biomarkers, to early predict aortic complications.. We re-evaluated after a mean time of 48 ± 11 months 47 BAV patients who had undergone previous echocardiography for evaluation of aortic stiffness and 2D aortic longitudinal strain (LS) (by speckle-tracking analysis), and who had given a blood sample for the assessment of a single-nucleotide polymorphism of elastin gene (ELN rs2 071307) and quantification of elastin soluble fragments (ESF). Surgical treatment of aortic aneurysm/dissection was the primary endpoint, and an aortic dimension increase (of one or more aortic segments) ≥1 mm/year was the secondary endpoint. Nine patients underwent surgical treatment of ascending aorta (AA) aneurysms. Out of the 38 patients who did not need surgical intervention, 16 showed an increase of aortic root and/or AA dimension ≥1 mm/year. At multivariate Cox regression analysis, an impaired AA LS was an independent predictor of aortic surgery [P = 0.04; hazard ratio (HR) 0.961; 95% confidence interval (CI) 0.924-0.984] and aortic dilatation (P = 0.007; HR 0.960; 95% CI 0.932-0.989). An increased quantity of ESF was correlated (P = 0.015) with the primary endpoint at univariate Cox regression analysis but it did not keep statistical significance at multivariate analysis.. In BAV patients, impairment of elastic properties of the AA, as assessed by 2D LS, is an effective predictor of aortic complications.

Topics: Aortic Valve; Bicuspid Aortic Valve Disease; Elastin; Heart Valve Diseases; Humans; Prognosis

Medial degeneration is a common histopathological finding in aortopathy and is considered a mechanism for dilatation. We investigated if medial degeneration is specific for sporadic thoracic aortic aneurysms versus nondilated aortas. Specimens were graded by pathologists, blinded to the clinical diagnosis, according to consensus histopathological criteria. The extent of medial degeneration by qualitative (semi-quantitative) assessment was not specific for aneurysmal compared to nondilated aortas. In contrast, blinded quantitative assessment of elastin amount and medial cell number distinguished aortic aneurysms and referent specimens, albeit with marked overlap in results. Specifically, the medial fraction of elastin decreased from dilution rather than loss of protein as cross-sectional amount was maintained while the cross-sectional number, though not density, of smooth muscle cells increased in proportion to expansion of the media. Furthermore, elastic lamellae did not thin and interlamellar distance did not diminish as expected for lumen dilatation, implying a net gain of lamellar elastin and intralamellar cells or extracellular matrix during aneurysmal wall remodeling. These findings support the concepts that: (1) medial degeneration need not induce aortic aneurysms, (2) adaptive responses to altered mechanical stresses increase medial tissue, and (3) greater turnover, not loss, of mural cells and extracellular matrix associates with aortic dilatation.

Topics: Adaptation, Physiological; Adult; Aged; Aorta; Aortic Aneurysm, Thoracic; Bicuspid Aortic Valve Disease; Cell Count; Comorbidity; Elastin; Extracellular Matrix; Female; Humans; Male; Middle Aged; Myocytes, Smooth Muscle; Single-Blind Method; Staining and Labeling; Tunica Media; Vascular Remodeling

To explore the micromechanical, biochemical, and microstructural differences between bicuspid aortic valve aneurysm (BAV-A) and tricuspid aortic valve idiopathic degenerative aneurysm (DA), compared with normal aorta.. Aortic tissue was obtained from patients undergoing aneurysmal repair surgery (BAV-A; n = 15 and DA; n = 15). Control tissue was obtained from aortic punch biopsies during coronary artery bypass graft surgery (n = 9). Nanoindentation was used to determine the elastic modulus on the medial layer. Glycosaminoglycan, collagen, and elastin levels were measured using biochemical assays. Verhoeff Van Gieson-stained cross-sections were imaged for elastin microstructural quantification.. The elastic modulus was more than 20% greater for BAV-A relative to control and DA (signifying a loss of compliance). No significance difference between control and DA were observed. Collagen levels for BAV-A (36.9 ± 7.4 μg/mg) and DA (49.9 ± 10.9 μg/mg) were greater compared with the control (30.2 ± 13.1 μg/mg). Glycosaminoglycan and elastin levels were not significant between the groups. Elastin segments were uniform throughout the control. Aneurysmal tissues had less elastin segments close to the intima and adventitia layers. Both BAV-A and DA had elastin segments compacted in the media; however, elastin segments were highly fragmented in DA.. BAV-A has a greater loss of aortic wall compliance relative to DA and the control. Although elastin levels were equal for all groups, spatial distribution of elastin provided a unique profile of matrix degradation for BAV-A. Elastin compaction within the media of BAV-A may have resulted from the altered hemodynamic pressure against the wall, which could explain for the stiffness of the tissue.

Topics: Aged; Aorta, Thoracic; Aortic Aneurysm, Thoracic; Bicuspid Aortic Valve Disease; Biopsy; Collagen; Disease Progression; Echocardiography; Elastin; Female; Glycosaminoglycans; Humans; Male; Middle Aged

Ascending aorta aneurysms (AsAA) are associated with a degeneration of the aortic wall tissue, which leads to changes in tissue mechanical properties. Risk factors for the development of the AsAA disease are recognized in patient age and gender, valve type, hypertension, diabetes mellitus, smoking history, and a prior diagnosis of Marfan syndrome. The present study aims to assess how such clinico-pathological factors can affect the mechanical properties of human dilated ascending aorta. Specimens of AsAA are excised from 68 patients who underwent elective AsAA surgical repair and stretched until rupture during the execution of uniaxial tensile tests. Experimental stress-stretch curves are used to determine tissue mechanical properties (stress and stretch at failure point and at transition point, low and high elastic modulus). Data are divided into groups according to region (anterior vs posterior), direction (circumferential vs longitudinal), and then according to age (young vs old), gender (male vs female), valve type (tricuspid aortic valve, TAV, vs bicuspid aortic valve, BAV), and presence of hypertension, diabetes mellitus, and/or Marfan syndrome (yes/no). Moreover, data are grouped according to the critical value of body mass index (BMI), maximum AsAA diameter, and aortic stiffness index (ASI), respectively. Finally, a non-parametric statistical analysis is performed to find possible significant differences and correlations between mechanical properties and clinico-pathological data. Our results confirm the anisotropy and heterogeneity of the AsAA tissue and highlight that ageing and hypertension make the AsAA tissue weaker and less extensible, whereas the valve type affects the tissue strength with higher values in BAV than in TAV patients. No effects of gender, critical BMI, critical maximum AsAA diameter, critical ASI, smoking status, and presence of diabetes mellitus, and Marfan syndrome are evidenced.

Topics: Aged; Anisotropy; Aorta; Aortic Aneurysm, Thoracic; Aortic Valve; Bicuspid Aortic Valve Disease; Biomechanical Phenomena; Body Mass Index; Body Weight; Collagen; Diabetes Mellitus; Elastin; Female; Heart Valve Diseases; Humans; Hypertension; Male; Marfan Syndrome; Middle Aged; Models, Statistical; Risk Factors; Stress, Mechanical; Tensile Strength; Vascular Stiffness

Bicuspid aortic valve (BAV) is associated with aortic wall alterations. We aimed to detect any correlation between aortic elasticity and genetic and biomolecular patterns of elastin.. Forty-nine BAV patients (mean age: 38 ± 17.05) were prospectively enrolled. A blood sample was drawn for analysis of a single nucleotide polymorphism of elastin gene (ELN rs2071307) responsible for misfolding of elastin, and for the amount of elastin soluble fragments (ESF) in the plasma. Aortic dimensions and elastic properties were determined by echocardiography, aortic stiffness (AS) by M-mode analysis, and longitudinal strain (LS) of the ascending aorta (AA) by speckle-tracking echocardiography; values of aortic strain were compared with 45 age-matched subjects (mean age: 33 ± 9.67) with tricuspid aortic valve (TAV). BAV patients had greater aortic dimensions [Valsalva sinus (P = 0.004), sinotubular junction (P = 0.013), AA (P < 0.001)] and stiffness (P = 0.002) but lower LS (P = 0.04) than those with TAV. Results from comparisons of mutated genotype patients (AA, n = 10) with heterozygous (GA, n = 21) and wild-types ones (GG, n = 16) revealed that the presence of mutation was associated with increased ESF (P = 0.010 GG vs. GA; P = 0.035 GA vs. AA), larger AA (P = 0.019 GG vs. GA; P = 0.001 GG vs. AA), and lower LS (P = 0.032 GG vs. AA). Patients with a dilated AA showed greater ESF (P < 0.001), greater AS (P = 0.007), and lower LS of the AA (P = 0.002) than those with a normal AA. The same parameters were not significantly different comparing patients with moderate or severe aortic valve disease and patients with less than moderate valve disease.. Our results show a close correlation between genetic and biomolecular patterns of elastin and mechanical properties of the aorta in patients with BAV.

Topics: Adult; Aortic Valve; Aortic Valve Insufficiency; Bicuspid Aortic Valve Disease; Case-Control Studies; Echocardiography; Elastin; Female; Gene Expression Regulation; Genotype; Heart Defects, Congenital; Heart Valve Diseases; Humans; Image Interpretation, Computer-Assisted; Male; Middle Aged; Prospective Studies; Reference Values; Young Adult

Suspected genetic causes for extracellular matrix (ECM) dysregulation in the ascending aorta in patients with bicuspid aortic valves (BAV) have influenced strategies and thresholds for surgical resection of BAV aortopathy. Using 4-dimensional (4D) flow cardiac magnetic resonance imaging (CMR), we have documented increased regional wall shear stress (WSS) in the ascending aorta of BAV patients.. This study assessed the relationship between WSS and regional aortic tissue remodeling in BAV patients to determine the influence of regional WSS on the expression of ECM dysregulation.. BAV patients (n = 20) undergoing ascending aortic resection underwent pre-operative 4D flow CMR to regionally map WSS. Paired aortic wall samples (i.e., within-patient samples obtained from regions of elevated and normal WSS) were collected and compared for medial elastin degeneration by histology and ECM regulation by protein expression.. Regions of increased WSS showed greater medial elastin degradation compared to adjacent areas with normal WSS: decreased total elastin (p = 0.01) with thinner fibers (p = 0.00007) that were farther apart (p = 0.001). Multiplex protein analyses of ECM regulatory molecules revealed an increase in transforming growth factor β-1 (p = 0.04), matrix metalloproteinase (MMP)-1 (p = 0.03), MMP-2 (p = 0.06), MMP-3 (p = 0.02), and tissue inhibitor of metalloproteinase-1 (p = 0.04) in elevated WSS regions, indicating ECM dysregulation in regions of high WSS.. Regions of increased WSS correspond with ECM dysregulation and elastic fiber degeneration in the ascending aorta of BAV patients, implicating valve-related hemodynamics as a contributing factor in the development of aortopathy. Further study to validate the use of 4D flow CMR as a noninvasive biomarker of disease progression and its ability to individualize resection strategies is warranted.

Topics: Adult; Aorta; Aortic Valve; Bicuspid Aortic Valve Disease; Case-Control Studies; Elastin; Female; Heart Valve Diseases; Hemodynamics; Humans; Magnetic Resonance Imaging; Male; Matrix Metalloproteinases; Middle Aged; Stress, Mechanical; Tissue Inhibitor of Metalloproteinases

Patients with bicuspid aortic valves (BAV) are predisposed to developing ascending thoracic aortic aneurysms (TAA) at an earlier age than patients who develop degenerative TAAs and have a tricuspid aortic valve (TAV). The hypothesis tested is that BAV-associated aortopathy is mediated by a mechanism of matrix remodeling that is distinct from that seen in TAAs of patients with tricuspid aortic valves.. Aortic specimens were collected during ascending aortic replacement, aortic valve replacement, and heart transplants from nonaneurysmal (NA) donors and recipients. Matrix architecture of the aortic media was assessed qualitatively using multiphoton microscopy followed by quantification of collagen and elastin fiber orientation. α-Elastin was determined and matrix maturity was assessed by quantifying immature and mature collagen and lysyl oxidase (Lox) expression and activity in aortic specimens. Matrix metalloproteinase-2/9 activity was quantified in aortic smooth muscle cells.. Elastin and collagen fibers were more highly aligned in BAV-NA and BAV-TAA cases than in TAV-TAA cases, whereas TAV-TAA cases were more disorganized than TAV-NA cases. α-Elastin content was unchanged. Immature collagen was reduced in BAV-NA and BAV-TAA cases when compared with TAV-NA and TAV-TAA cases. Mature collagen was elevated in TAV-TAA cases compared with TAV-NA and BAV-TAA cases. There was a trend toward elevated Lox gene expression and activity and matrix metalloproteinase-2/9 activity for TAV-TAA, BAV-NA, and BAV-TAA specimens.. The highly aligned matrix architecture in patients with BAVs indicates that wall remodeling is distinct from TAV-TAA. Altered matrix architecture and reduced collagen maturity suggest that the effector molecules mediating the remodeling of TAAs are different in BAV and TAV cases.

Topics: Adult; Aged; Aorta, Thoracic; Aortic Diseases; Aortic Valve; Bicuspid Aortic Valve Disease; Biomarkers; Collagen; Elastin; Female; Heart Valve Diseases; Humans; Male; Matrix Metalloproteinase 2; Matrix Metalloproteinase 9; Middle Aged; Protein-Lysine 6-Oxidase; Tunica Media

The bicuspid aortic valve (AV) is the most common cardiac congenital anomaly and has been found to be a significant risk factor for developing calcific AV disease. However, the mechanisms of disease development remain unclear. In this study we quantified the structure of human normal and bicuspid leaflets in the early disease stage. From these individual leaflet maps average fiber structure maps were generated using a novel spline based technique. Interestingly, we found statistically different and consistent regional structures between the normal and bicuspid valves. The regularity in the observed microstructure was a surprising finding, especially for the pathological BAV leaflets and is an essential cornerstone of any predictive mathematical models of valve disease. In contrast, we determined that isolated valve interstitial cells from BAV leaflets show the same in vitro calcification pathways as those from the normal AV leaflets. This result suggests the VICs are not intrinsically different when isolated, and that external features, such as abnormal microstructure and altered flow may be the primary contributors in the accelerated calcification experienced by BAV patients.

Topics: Aged; Aortic Valve; Bicuspid Aortic Valve Disease; Collagen; Elastin; Female; Heart Valve Diseases; Humans; Imaging, Three-Dimensional; Male; Middle Aged; Proteoglycans

An aortic aneurysm is characterized by widening of the aortic lumen diameter with adverse remodelling of the vascular extracellular matrix. A thoracic aortic aneurysm (TAA) is highly prevalent in patients with a bicuspid aortic valve (BAV). We investigated the structural remodelling in the aneurysmal ascending aorta in correlation to molecular alterations in male versus female BAV-TAA patients. Aneurysmal aortic samples (diameter >4.4 cm) from male and female patients were compared to non-aneurysmal non-BAV samples. The diameter of the aneurysmal aorta was smaller in females but comparable to that of male patients when normalized to body mass index. Disorganized elastin fibres and reduced elastin protein were found in samples from males and females with BAV-TAA. However, disarrayed collagen fibres and reduced protein were detected only in aortas from males with BAV-TAA. Elastin and collagen I messenger RNA (mRNA) levels were comparable in the BAV-TAA and control groups of both genders, suggesting post-translation degradation. Total elastase activity was elevated similarly in both genders. The activity of MT1-MMP, a potent collagenase, was increased more in aortic samples from males than females with BAV-TAA samples. MMP8 and MMP13 were lower whereas MMP2 was higher in female compared to samples from male BAV-TAA group. TIMP3 and TIMP4 decreased similarly in both genders, while TIMP2 increased in the female BAV-TAA group. Lower smooth muscle cell density in the medial layer of aortas from males with BAV-TAA samples corresponded to the increased caspase-3 cleavage compared to that of females.. We report a gender-dependent MMP/TIMP axis, collagen remodelling and smooth muscle cell (SMC) survival in the BAV-TAA aorta. The elevated TIMP2 could protect against the collagenolytic activity of MT1-MMP, leading to reduced collagen disarray and degradation in female BAV.. More collagen degradation/disarray and smooth muscle cell loss in male BAV-TAA patients. Similar elastin degradation/disarray in the aneurysmal aorta of both genders. Reduced collagen and elastin in BAV-TAA due to enhanced degradation, not reduced synthesis. Elevated TIMP2 in female BAV-TAA aortas protects against collagen degradation by MT1-MMP.

Topics: Aorta; Aortic Aneurysm, Thoracic; Aortic Valve; Bicuspid Aortic Valve Disease; Caspase 3; Collagen; Elastin; Extracellular Matrix; Female; Heart Valve Diseases; Humans; Male; Matrix Metalloproteinase 14; Middle Aged; Proteolysis; Sex Factors; Tissue Inhibitor of Metalloproteinase-2

Thoracic aortic aneurism (TAA) develops as a result of complex series of events that dynamically alter the structure and composition of the aortic vascular extracellular matrix (ECM). The main elements that alter the composition of aortic wall are smooth muscle cells (SMC). The purpose of the present work was to study alteration of smooth muscle cell functions derived from the patients with TAA and from healthy donors. As it is supposed that TAA associated with bicuspid aortic valve (BAV) and with tricuspid aortic valve (TAV) differ in their pathogenesis, we compared the SMC and tissues samples from BAV-, TAV-patients and healthy donors. We compared TAA patients' derived tissues and SMC to healthy donors' ones in several parameters: SMC growth, migration and apoptotic dynamics; metalloproteinase MMP2 and MMP9 activity (zymography) and elastin, collagen and fibrillin content (Western blot) in both tissue samples and cultured SMC. Proliferation ability of both BAV and TAV SMC was decreased comparing to donors cells; migration ability in scratch tests was increased in TAV-derived SMC comparing to donor cells. BAV-cells migration ability was not changed comparing to donor-SMC. Elastin content was decreased in TAA SMC comparing to donor cells whereas the content of fibrillin and collagen was not altered. At the same time elastin and collagen protein level was significantly higher in tissue samples of TAA patients comparing to donor-derived samples. SMS proliferation and migration ability is differently affected in TAV and BAV-associated TAA that supports the idea of different nature of these two groups of TAA. Also our data show that SMC functional properties are altered in TAA patients and these alterations could play a significant role in the disease pathogenesis.

Topics: Aorta; Aortic Aneurysm, Thoracic; Aortic Valve; Apoptosis; Bicuspid Aortic Valve Disease; Biomarkers; Case-Control Studies; Cell Movement; Cell Proliferation; Collagen; Elastin; Fibrillins; Heart Valve Diseases; Humans; Matrix Metalloproteinase 2; Matrix Metalloproteinase 9; Microfilament Proteins; Myocytes, Smooth Muscle; Tricuspid Atresia