bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pressure and Angiotensin II Influence the Mechanical Properties of Aortic Valves
Authors: Myles Valtresa , Liao Jun , Warnock James N. 
Published: July 2012

AbstractElevated cyclic pressure and angiotensin II (Ang II) both promote aortic valve collagen synthesis, an early hallmark of aortic sclerosis. In the current study, it was hypothesized that the increased collagen production induced by either elevated pressure or Ang II would increase tissue stiffness.
Porcine aortic valve leaflets were randomly assigned to four groups; leaflets in group 1 were treated with 10-6M Ang II, leaflets in group 2 were exposed to 80 or 120 mmHg cyclic pressure, leaflets in group 3 were treated with Ang II and exposed to cyclic pressure and leaflets in group 4 were the control. Biaxial testing was performed after 24 and 48 hours on 10mm x 10mm samples of tissue dissected from the central region of the leaflets. Four fiducial markers arranged in an approximately 4 mm x 4 mm square were placed in the center of the extracted portion of the leaflets to track tissue strain. A membrane tension (force/unit length) was applied along each axis and increased slowly from a pre-stress tension of ~0.5 N/m to a peak tension of 60 N/m. The samples were preconditioned for ten contiguous cycles, following an equibiaxial protocol of TCC:TRR = 60:60 N/m, where TCC and TRR are the tensions applied in the circumferential and radial directions, respectively. Tissue extensibility was characterized by maximum stretch along the circumferential direction (λcc) and maximum stretch along the radial direction (λrr), at an equibiaxial tension of 60 N/m. Leaflet stiffness was greater in the circumferential direction than in the radial direction, which is consistent with previous studies. The peak stretches of native valves were calculated as 1.05±0.02 and 1.40±0.02 in the circumferential and radial directions, respectively. There was no significant difference in the stiffness of native valves compared to those exposed to 0mmHg(-Ang II) or 80mmHg(-Ang II) for 24 or 48 hours. Elevated pressure increased stiffness in both directions after 24 and 48 hours. After 24 and 48 hours Ang II significantly increased stiffness in the radial direction. The combination of Ang II and elevated pressure increased stiffness in radial direction after 24 and 48 hours. Increased stiffness may be due to remodeling of the ECM. Excessive collagen production is known to hinder valve function, eventually resulting in aortic stenosis. In conclusion, the results of the present study demonstrated that both elevated pressure and Ang II play a role in the increased stiffness of aortic valve leaflets.
Adaptation of the Mitral Valve to Chronic Ischemic Left Ventricular Failure in Swine
Authors: McIver Bryant V. , Hussain Samiya , Thourani Vinod , Padala Muralidhar 
Published: July 2012

AbstractMitral valve leaflets in patients with chronic heart failure are severely stiffened, larger and fibrotic; though the mechanisms underlying such biological remodeling are currently unknown. Chronic tethering of the valve leaflets by the enlarged left ventricle, and the presence of mitral regurgitation (MR), is hypothesized to trigger fibrotic pathways that induce such remodeling. In this study, we sought to develop a large animal model of chronic ischemic left ventricular failure in which moderate leaflet tethering and MR can be repeatedly induced, and the remodeling of the mitral valve can be assessed in vivo using echocardiography. Inferior wall myocardial infarction (IMI) was induced in 16 farm swine (30-35kg) using a percutaneous transfemoral approach. Coronary angiography was performed to selectively identify the marginal branches of the left circumflex artery perfusing the inferior left ventricular (LV) wall and the posterior papillary muscle (PPM), and then these regions were infarcted using a 2 mm balloon catheter and injection of 100% ethyl alcohol into the corresponding branch. Transthoracic 2D echocardiography (TTE) of the left heart was performed pre and post-IMI in all animals, at 4 weeks and at 8 weeks. MR percentage (MR jet/left atrial area), mitral leaflet length and thickness, and mitral annular geometry were measured. Leaflet length and thickness were measured at end diastole to assure measurements were taken in the maximal unloaded state. All animals survived the procedure without complications (0% mortality). At baseline, the swine had mild MR (10.7±8%) which significantly increased to 26.6±9% immediately post-op (p<0.05), declined slightly to 23.8±7.8% at 4 weeks, and increased to 32.2±13.9% at 8 weeks. Mitral annular diameter increased from 2.7±0.5 cm pre-op, to 3.1±0.5 cm post-op (p<0.05), then to 3.8±0.4 cm (p<0.005) and 3.9±0.6 cm (p<0.005), at 4 and 8 weeks, respectively. Posterior leaflet length was 1.8±0.2 cm pre-op, and then stabilized at 1.9±0.2 cm post-op, at 4 weeks, and at 8 weeks. Anterior leaflet length was 2.3±0.3 cm at baseline and increased with the increase in MR, to 2.5±0.4 cm post-op, 2.8±0.5 cm at 4 weeks (p<0.05), and 3.2±0.2 cm at 8 weeks (p<0.001). Posterior leaflet thickness increased from 0.36±0.05 cm at baseline, to 0.37±0.07 cm post-op, and then to 0.4±0.05 cm and 0.41±0.03 cm at 4 weeks and 8 weeks, respectively. Anterior leaflet thickness was 0.4±0.05 cm at baseline and post-operatively, and 0.47±0.03 cm (p<0.01) and 0.45±0.07 cm at 4 weeks and 8 weeks, respectively. Changes in mitral leaflet geometry correspond with changes in the mitral valvular apparatus after IMI in a chronic swine model. As the mitral annulus increases in diameter, significant lengthening is seen from the anterior leaflet, while the posterior leaflet remains relatively static and tethered. The anterior leaflet thickens by 4 weeks, while the posterior leaflet remains stable.
Distensibility of Decellularized and Glutaraldehyde-Preserved Aortic Full Roots as Evaluated by Computed Tomography
Authors: Honge Jesper L. , Mads B Kronborg Mads B Kronborg , Bottcher Morter , Norgaard Bjarne L , Hasenkam J Michael , Sten L Nielsen Sten L Nielsen 
Published: July 2012

AbstractThe aortic root is a dynamic structure and its distensibility is considered an important factor in native and prosthetic heart valve function. Glutaraldehyde-preserved (GLUT) valves have limited durability possibly due to increased tissue stiffening. Decellularized deoxycholic acid-treated (DOA) valves exhibit excellent long-term performance in the pulmonary position in humans possibly due to preservation of valve tissue distensibility. We investigated aortic distensibility in DOA (n=8) and GLUT (n=3) aortic root prostheses in 60 kg pigs 2 weeks after orthotopic implantation. Five pigs served as controls. Using a dual source computed tomography scanner (Somatom Flash, Siemens Medical Solution, Forcheim, Germany) the cross sectional area at the level of Sinus of Valsalva (SoV), sino-tubular junction (STJ), and ascending aorta (AA), respectively, was measured in both diastole and systole. Distensibility was defined as the change in area from diastole (RR 95%) to systole (RR 15%). For assessment of the prosthetic- independent aortic distensibility we performed the same measurements in the descending aorta (AD) in all animals. Data were analyzed using students t-test and reported as a mean±SD.
Native aortic distensibility was significant larger at the level of SoV (15.8%±4.9), STJ (46.7%±10.3), and AA (40.6%±9.0), compared with both DOA and GLUT aortic roots (p<0.05). No difference in distensibility between the DOA and GLUT aortic roots were observed: 8.8%±2.4 vs 6.2%±5.5 (SoV), 11.7%±3.0 vs 10.0%±7.1 (STJ), 14.9%±6.1 vs 11.8±1.7 (AA), and 15.6±1.5 vs 15.5±1.8 (DA) , respectively (p>0.05). There was no difference in mean distensibility between the three groups in the decending aorta. This is the first study to evaluate in-vivo distensibility of aortic root prostheses in vivo. Aortic root distensibility is reduced following implantation of DOA or GLUT prosthetic aortic valves. No difference was observed between DOA and GLUT valves. Long-term follow-up is needed in order to verify any changes in bioprosthetic aortic root distensibility over time.
The Role of Integrins on the Regulation of Contractility in Mitral Valve
Authors: Zamani Marzieh , Sarathchandra Padmini , Latif Najma , Yacoub Magdi H. , Chester Adrian H. 
Published: July 2012

AbstractThe mechanical properties of heart valves are modulated by the contractile response of valve interstitial cells (VICs). It is unknown how the contractile responses of VICs are translated to the extra cellular matrix to alter the stiffness of the valve tissue. We have studied the signalling mechanisms of integrin subunits and specifically α2β1 integrin, a predominant collagen binding molecule, in mediating the contractility of porcine mitral valve tissue and cells.
The expression of integrins was analysed by immunostaining of cells. The contractility of porcine mitral VICs in the presence and absence of a α2β1 integrin blocking antibody and the effect of different signalling inhibitors was analysed in a collagen gel. The effect of modulators of contractility was determined on mitral valve tissue incubated in organ baths which challenged with endothelin-1 (10-10-10-7M) following 24 hours incubation with α2β1 integrin blocking antibody. Immunohistochemistry confirmed positive staining for α2β1 integrin and the expression of α1, α2, α3 and β1 in the VICs. The α2β1 blocking antibody was able to significantly reduce the contraction of collagen gels from 63.6±7.8 to 23.4±4.3 % (p<0.001) of control (no cells in gel). PF573228, the inhibitor of focal adhesion kinase, caused a reduction of gel contraction by 30% of the control. The maximum contractile response of cusp tissue to ET-1 maintained under isometric conditions in tissue baths was significantly reduced from 9.5±5.0 to 3.0±2.5mN/g (p<0.001) wet weight by the presence of the α2β1 integrin blocking antibody. These results demonstrate a role for α2β1 integrin in linking the contractile response of valve cells to the extra cellular matrix and highlight further the complex interactions between the cells and the extra cellular matrix of the valve.
The Congenital Bicuspid Aortic Valve can Experience High Frequency Unsteady Shear Stresses on its Leaflet Surface
Authors: Yap Choon Hwai , Saikrishnan Neelakantan , Tamilselvan Gowthami , Vasilyev Nikolai , Yoganathan Ajit P. 
Published: July 2012

AbstractBicuspid aortic valve (BAV) is a common congenital malformation affecting 1-2% of the population and is highly correlated to early calcification of the valve leaflets. Two widely held hypothesis for this correlation are (1) altered shape of the BAV results in altered fluid mechanical environment, leading to pro-calcification biology responses, and (2) inherent genetic defects results in pre-disposition of the tissues to calcify. In the current study, we tested the first hypothesis with porcine valve models in an in vitro flow loop. One BAV model and one tricuspid aortic valve (TAV) model were constructed using healthy porcine AV leaflets and tested in a physiological pulsatile flow loop. Fluid velocities near the center of the aortic surface of the valve leaflets were measured with Laser Doppler Velocimetry at a spatial resolution of 89 microns, and ensemble average shear stresses were calculated at various time points in the cardiac cycle. Unsteadiness of flow near the valve leaflets was quantified with variance analysis and power spectral analysis. Particle Image Velocimetry was used to visualize flow fields downstream of the valves and in the sinuses. The leaflets of the BAV model experienced shear stresses on the aortic surface with magnitudes similar to that of the TAV. However, flow near the BAV leaflets had high frequency unsteadiness components, especially during mid- to late- systole, and had high cycle-to-cycle magnitude variability, indicating that shear stresses will have similar unsteadiness and magnitude variability. These are most likely due to the stenosis in the BAV and the skewed forward flow, which collided with the aorta wall. In conclusion, our study indicated that some BAVs could experience high frequency unsteadiness and cycle-to-cycle magnitude variability on the valve leaflets because of its geometry. We speculate that, together with genetic factors, such adverse mechanical force environment could play a role in causing early calcification in the BAV leaflets.
Shear- and Side-dependent microRNAs and Messenger RNAs in Aortic Valvular Endothelium
Authors: Holliday-Ankeny Casey J. , Ankeny Randall F. , Ferdous Zannatul , Nerem Robert M. , Jo Hanjoong 
Published: July 2012

AbstractAortic valve (AV) disease is a major cause of cardiovascular-linked deaths globally. In addition, AV disease is a strong risk factor for additional cardiovascular events; however, the mechanism by which it initiates and progresses is not well-understood. We hypothesize that low and oscillatory flow is present on the fibrosa side of the AV and stimulates ECs to differentially regulate microRNA (miRNA) and mRNAs and influence AV disease progression. This hypothesis was tested employing both in vitro and in vivo approaches, high throughput microarray and pathway analyses, as well as a variety of functional assays. First, we isolated and characterized side-dependent, human aortic valvular endothelial cells (HAVECs) isolated from transplant recipient AVs. We found that HAVECs express both endothelial cell markers (VE-Cadherin, vWF, and PECAM) as well as smooth muscle cell markers (SMA and basic calponin). Further, HAVECs align in the direction of the flow as well as uptake acetylated LDL. Using microarray analysis on sheared, side-specific HAVECs, we identified side- and shear-induced changes in miRNA and mRNA expression profiles. More specifically, we identified over 1000 shear-responsive mRNAs which showed robust validation (93% of those tested). We then used Ingenuity Pathway Analysis to identify key miRNAs, including those with many relationships to other genes (for example, thrombospondin and IκB) and those that are members of over-represented pathways and processes (for example, sulfur metabolism). Furthermore, we validated five shear-sensitive miRNAs: miR-139-3p, miR-148a, miR-187, miR-192, and miR-486-5p and one side-dependent miRNA, miR-370. To prioritize these miRNAs, we performed in silico analysis to group these key miRNAs by cellular functions related to AV disease (including tissue remodeling, inflammation, and calcification). Additional miRNAs of interest (including miR-7 and miR-506) were determined through analysis of overrepresented miRNA binding sequences in the shear-sensitive mRNA array. Next, to compare our in vitro HAVEC results in vivo, we developed a method to isolate endothelial-enriched, side-dependent total RNA and identify and validate side-dependent (fibrosa vs. ventricularis) miRNAs in porcine aortic valvular endothelium. From this analysis, we discovered and validated eight side-dependent miRNAs in porcine endothelial-enriched AV RNA, including one miRNA previously identified in vitro, miR-486-5p, as well as a shear-responsive miRNA cluster, miR-199a/214. Through microarray studies and in silico analysis, we have prioritized key miRNAs which may serve as master regulators of AV disease. Better understanding of AV biology and disease in terms of gene-regulation under different hemodynamic conditions will facilitate the design of a tissue-engineered valve and provide alternative treatment options.
Modeling Flow-Responsive Gene Regulation In Native Valve Tissue
Authors: Siyahian Arpi , Chalajour Fariba , Ma Xiaoyuan , Hanley Frank L. , Riemer R. Kirk 
Published: July 2012

AbstractA variety of approaches to heart valve tissue engineering are underway by many groups of investigators. We believe that a thorough understanding of the biophysical and biomolecular interactions that mediate normal leaflet homeostasis will inform improved approaches to the engineering of truly regenerative heart valve grafts. However, our understanding of the fundamental biology of normal valve tissue is still quite limited. This informational gap has led us to develop an ex vivo system for long-term valve culture in order to study the mechanobiology of native tissue. Using this system, we have cultured trileaflet rat heart valves with and without flow-induced valve cycling. We report here the preliminary findings about the effects of both ex vivo culture and of valve cycling on pulmonary leaflet cell gene expression following 7 days of flow culture. Expression of leaflet mRNA was queried using Affymetrix whole genome microarrays and the results analyzed using GeneSpring, EXPLAIN and MetaCore (GeneGO) software. Our analysis revealed 2147 genes whose expression was altered under flow conditions, and 1918 genes under static conditions. 1501 genes were common to both conditions. The effects of culture on gene expression affected multiple pathways, but the most active gene groups involved pathways for cytoskeletal remodeling, development, and cell adhesion. The genes involved in these pathways were altered in both culture conditions. Changes in cytoskeletal and ECM remodeling genes were more prominent in the static condition, while those involved in VEGF signaling were seen under flow condition. Our previously reported histological analyses of cultured rat pulmonary valve leaflet tissue revealed that flow promotes the maintenance of tissue integrity while the lack of flow leads to extracellular matrix remodeling and fibrinoid tissue formation. These gene expression analyses confirm the expected role of flow in maintaining leaflet tissue integrity as evidenced by its induction of VEGF signaling genes, while the lack of flow induces changes in genes involved in extracellular matrix and cytoskeletal remodeling.
Computational Structural Biomechanical Models to Guide Tissue Engineered Heart Valve Leaflet Fabrication
Authors: D'Amore Antonio , Bayoumi Ahmed S. , Amoroso Nicholas , Wagner William R. , Mayer John , Sacks Michael S. 
Published: July 2012

AbstractA computational structural deterministic modeling strategy has been developed and experimentally validated to (1) assist tissue engineering scaffold fabrication, and as a consequence to improve in vivo scaffolds performances, and (2) provide a better understanding of cellular mechanical and metabolic response to local micro-structural deformations of the extracellular matrix (ECM). Image analysis software was developed and tested on electrospun poly (ester urethane) urea (PEUU) scaffolds, collagen gels, decellularized tissues. The algorithm analyzed SEM and multi-photon images (maximum imaging penetration depth: 160 µm) providing a full 3D characterization of engineered constructs morphology (n ≥ 6). The detected material topologies were adopted to generate statistically equivalent scaffold biomechanical models minimizing the difference between the real material and network model architectural features. The mechanical response at the macro scale was fully characterized by stress control biaxial tests (n ≥ 6). The experimental biaxial response was used to calibrate a Finite Element Model able to predict, for a given material topology, the mechanical response at both organ (cm), cells (100 µm) and fiber (1 µm) levels. Scaffold networks models were imported in Abaqus, Yeoh strain energy with incompressibility hypothesis and t2d2h elements were adopted. Stress vs. strain prediction was produced for four different scaffold groups: isotropic ES-PEUU, anisotropic ES-PEUU, Vascular Smooth Muscle Cells integrated PEUU, Polystyrene micro-spheres integrated (10 µm diameter) proving the flexibility of the modeling approach. At mesoscopic level nuclear aspect ratio vs. strain curve for the rat VSMCs embedded into the scaffold was produced and compared with previous experimental findings. At the microscopic level the single fiber initial shear modulus was quantified from the strain energy function material parameters, and compared with Atomic Force Microscopy measurements on single PEUU fibers. The developed generalist modeling approach bridges scaffold fabrication parameters, micro architecture, and organ level - cell level mechanical response.
Inflammation Drives Endothelial-to-Mesenchymal Transition and Interstitial Calcification in 3D in Vitro Culture
Authors: Richards Jennifer , Farrar Emily , Mahler Gretchen , Butcher Jonathan 
Published: July 2012

AbstractCalcific aortic stenosis is a serious pathology that accounts for 43% of those suffering from heart valve disease. Valve disease initially presents with inflammation and endothelial dysfunction, which can lead to an endothelial-to-mesenchymal (EndMT) shift in the endothelial layer of the valve. It is not yet well understood how valve endothelial cells (VEC) regulate valve interstitial cells (VIC) in inflammatory or osteogenic environments. We here present a 3D culture system that models cellular responses and interactions when exposed to different environmental conditions. Porcine aortic VEC and/or VIC were cultured in mechanically constrained 3D type I collagen hydrogels for up to 14 days. Early disease studies introduced different dosages of TNFα to VEC on gel surfaces for up to 48 hours. EndMT was assessed via real time PCR and cell invasion within the matrix. Apoptosis and proliferation in VEC via TUNEL and anti-BrdU IHC staining were also evaluated in early inflammatory conditions. Later early-stage disease studies introduced osteogenic and inflammatory environments to 3D VIC/VEC gels through the addition of osteogenic differentiation factors into the culture media (OGM), or 30 ng/ml TNFα. Calcium deposition within the matrix was measured via Alizarin Red staining. Real time PCR was used to evaluate the expression of calcification-related genes such as osteocalcin and runx-2.
Early inflammatory conditions as induced by addition of TNFα for 48 hours stimulated EndMT-like VEC activation, including matrix invasion and upregulation of αSMA and snail. Addition of TNFα increases VEC proliferation in a dose dependent manner. TNFα does not significantly increase apoptosis, even at the highest dosage levels. VIC gels cultured in OGM for 14 days significantly calcified and expressed osteocalcin and runx-2. Co-culture with VEC inhibited both matrix calcium deposition and osteoblastic differentiation. When 30 ng/ml TNFα was added to VIC 3D cultures, TNFa induced increased matrix calcium deposition in 14 days, which was then mitigated by co-culture with VEC. The inhibitory effect of VEC on VIC calcification in OGM was blocked when TNFα was introduced to the culture. These results demonstrate that inflammatory microenvironments induce calcification in valve interstitial cells. There is a protective role for the valve endothelium in VIC calcification, which could be inhibited by EndMT induced by the inflammatory conditions found in diseased valves. We found that apoptosis is not a driving factor in inflammatory activation of VEC or osteogenic differentiation of VIC. Targeting TNFα and EndMT signaling could be important therapeutic strategies. More generally, targeting VEC is a promising approach for early treatment of valve disease. This co-culture 3D system is a powerful tool to elucidate mechanisms of valve disease.