bluuebunny/crossref_metadata_2025_split huggingface dataset:
AlphaGal Residue in Xenograft Heart Valve Bioprostheses and Tissue Engineered Construct
Authors: Naso Filippo , Gandaglia Alessandro , Comacchio Giovanni , Spina Michele , Gerosa Gino 
Published: July 2012

AbstractThe glutaraldehyde (GA) fixed heart valve bioprostheses (HVB) fail in the long term due to dystrophic degeneration. To avoid GA treatment, xenogenic tissues have been processed by detergent-based decellularization procedures (DBDP). However a complete immunogeneic tolerance by the host is not granted. Degenerative inflammatory process seems to be triggered by the persistent presence of reactive xenogeneic residual, specifically by the alpha-Gal antigen. Through the use of an ELISA assay we assessed and quantified the content of such xenoantigen in different commercial bioprosthetic heart valves and compare to that present in the native and decellularized tissues used for their manufacture. Four models of pericardial and two of porcine HVBs were investigated for the alpha-Gal content. Untreated porcine aortic leaflets (UPAL) were assessed before and after 3 different detergent-based decellularization procedure: TRICOL (Triton X100 and Sodium Cholate), DOC (Sodium Deoxycholate) and DOC-SDS (Sodium Deoxycholate and Sodium Dodecyl Sulfate). Moreover the total amount of alpha-Gal epitopes in native bovine pericardium (NBP) was determined. All the specimens react with the M86 primary monoclonal antibody and the exposed alpha-Gal epitopes is determined by an indirect ELISA assay. For each sample, the amount of alpha-Gal was expressed as numbers of epitopes *10e11 each 10 mg of wet tissue. The amount of alpha-Gal xenoantigen in pericardial HVB (1.5 ± 0.18 *10e11, n=15) was three and half times less with respect to NBP (5.1 ± 0.21 *10e11, n=9). In a model of porcine HVB the xenoantigen was not detected, in the second one the absolute value (1.37 ± 0.25 *10e11, n=9) was similar to that of the pericardial HVB and half of UPAL (2.5 ± 0.31 *10e11, n=9). DOC and DOC-SDS treatments leave on the tissue the 40% (1.02 ± 0.1 *10e11) of the epitopes originally present in the native cusps. TRICOL has proven to be able to eliminate all the alpha-Gal antigen. HVBs GA-treatment do not prevent the binding of resident alpha-Gal antigens with M86 antibodies. The investigated HVBs exhibited a non negligible amount of reactive epitopes accounting to 29.3% of those exposed by native pericardial tissue and 55% for the porcine one. Probably, the pericardial simpler structure allow a better action of the GA, which is able to ensure a greater, but non complete epitope masking. In one model of porcine HVB the alpha-Gal was not found. Regarding the different DBDPs, the removal of cell components is not a sufficient condition to ensure the elimination of the alpha-Gal epitopes. Up to date the TRICOL seems to be the only method capable of producing an alpha-Gal tissue free.
The Cellular and Extracellular Matrix Structure of Human Pericardium for Heart Valve Tissue Engineering
Authors: Schornik David , Straka Frantisek , Jaroslav Masin Jaroslav Masin , Filova Elena F , Burdikova Zuzana , Mirejovsky Tomas , Lodererova Alena , Chlup Hynek , Horny Lukas , Pirk Jan , Bacakova Lucie 
Published: July 2012

AbstractThe objective of our study was to compare the histological structure and cellular organization of autologous human pericardium to that of the human aortic heart valve. Collagen, elastin and glycosaminoglycans are responsible for the mechanical properties of aortic heart valve leaflets. Aortic valve leaflets are composed primarily of collagen representing 50% of total extracellular matrix (ECM). The main collagen types in the aortic heart valve are collagen I (74% of total collagen) and collagen III (24% of total collagen). Elastin represents 13% and is responsible for the elastic properties of the valve leaflet. Collagen has a specific architecture that endows heart valve tissue with the ability to withstand circulatory forces over the course of a lifetime. Its fiber orientation, density and cell associations are very important for this purpose. Normal aortic heart valves were obtained during heart transplantation and compared to autologous human pericardium before and after dynamic conditioning using classical histological assessment, immunohistochemical analysis and confocal microscopy. The architecture of pericardial tissue is very similar to that of the normal aortic heart valve possessing well organized collagen fibers with embedded pericardial interstitial cells (PICs) forming a three dimensional network. Instead of the trilaminar histological organization present in the aortic heart valve, the pericardium possesses one layer whose densely packed collagen bundles closely resemble that of the lamina fibrosa of the native aortic heart valve by confocal microscopy. Elastin fibers are evenly distributed throughout the entire thickness of the pericardium in comparison to the specialized elastin containing layer in the lamina ventricularis of the aortic heart valve. PICs are also evenly distributed throughout the pericardium. In the inner pericardial layer facing the heart these cells have a more spindle-like shape similar to that of valvular interstitial cells (VICs) in the lamina fibrosa, while in the outer part of the pericardium these cells have a more spread-out cytoplasmic morphology interacting with more loosely distributed collagen bundles. Like in the aortic heart valve, PICs show cell-cell interactions in addition to cell-matrix interactions. Our study confirmed similarities in the cellular and ECM organization of human pericardium and the native aortic heart valve. It may be concluded that human autologous pericardium may be a favorable tissue for heart valve replacement. Autologous pericardial tissue may also avoid a negative immune system response that could adversely affect recipient graft uptake and downstream ECM remodeling events.
Mitral Valve Mechanics Following Posterior Leaflet Patch Augmentation
Authors: Rasmussen Ann Q. , Rahmani Azadeh , Honge Jesper L. , Ostli Bjørn , Levine Robert A. , Hagège Albert , Nygaard Hans , Hasenkam J. Michael , Nielsen Sten L. , Jensen Morten O. 
Published: July 2012

AbstractAttention towards optimization of mitral valve repair methods is increasing. Patch augmentation strategy is used to treat functional ischemic mitral regurgitation (FIMR) and hypertrophic cardiomyopathy. When used to extend the anterior leaflet, the procedure decreases the forces exerted on the secondary chordae. The purpose of this study was therefore to investigate the force balance changes following patch augmentation of the posterior leaflet, with particular attention to the secondary chordae tendineae emanating from the posterior papillary muscle (PPM) in an FIMR simulated valve. Twelve mitral valves were obtained from 80kg pigs. An in vitro test setup simulating the left ventricle was used to hold the valves with a papillary muscle positioning system. Water pressure within the ventricular chamber was regulated manually in order to simulate different static pressures during valve closure. An oval shaped porcine pericardial patch measuring 17x29mm was introduced into the posterior leaflet approximately 2mm from the annulus and extending circumferentially from the middle of P2 to the end of the P3 scallop. In order to simulate a healthy valve, retraction of the patch was performed using sutures, which were then released to simulate patch repair. Data were acquired with and without PPM displacement to simulate the effect from one of the main contributors of FIMR, before and after patch augmentation, giving four simulation scenarios. The PPM was displaced 12mm posteriorly and 5mm apically. Dedicated miniature transducers were used to record the forces exerted on the secondary chordae tendineae. Three-way ANOVA was used to analyze the measurements.
The effect of displacing the posterior papillary muscle (p < .010) and implementing patch augmentation (p<.004) are significant and independent of each other. The overall effect of displacing the PPM induced tethering on the secondary chordae tendineae from the PPM to the posterior leaflet resulting in a force increase of 28.2 %. The overall effect of implementing the patch augmentation into the posterior leaflet induced a decrease in force of 24.8 % for the healthy and PPM displaced simulations together. The repairing effect of the patch augmentation is found by comparing the specific scenarios. A 40 % increase is induced by displacing the PPM and a 31 % decrease is found by implementing the patch augmentation, leaving the repaired tethering force a mere 9 % higher than that of the healthy measurements. Posterior leaflet patch augmentation significantly reduced the forces exerted onto the secondary chordae tendineae from the PPM in both healthy and PPM displaced valves. As changes in chordal tension leads to redistribution of the total stress exerted on the valve, patch augmentation may have adverse long term influence on mitral.
The Way to a New Generation of Bio-Prostheses
Authors: Waldow Thomas , Plötze Katrin , König Matthias , Matschke Klaus 
Published: July 2012

AbstractDiseases of heart valves often make a prosthetic replacement therapy necessary. Long term goal is the development of artificial leaflet material with defining properties of mechanical prostheses (i.e. durability) with complete biocompatibility without the need for any anticoagulation therapy whatsoever. In order to achieve this aim, objective efforts are being made to use a new material that is still in the process of development. It is a film-like tissue, made of pure carbon in the form of carbon-nanotubes, which are characterized by their excellent mechanical properties (tensile strength 65GPa in comparison to steel with 0.6Gpa). The woven material has also a very small mesh width, which can be influenced by the spinning method. Due to the nature of this material, which is associated with a high surface energy, there is a need for adaptions for the use in vivo according to the requirements. Plasma Enhanced Chemical Vapor Deposition PECVD has proven to be the appropriate method for such a functionalization. It is possible to deposit amorphous hydrocarbon coatings below 60°C and in a thickness range from a few nanometers up to several microns, while at the same time providing a very low Young's modulus that ensures to withstand mechanical stress. In addition, this method allows to influence regional properties e.g. by incorporating silicon into the matrix to prevent adhesion of thrombocytes and/or to add nitrogen to give the ability to endothelial cell growing. The first project step is to evaluate in high resolution and accuracy the parameter characteristic of native valves and prostheses. Therefore the elastic modulus, flexibility, extension, expansion, banding stress, banding elasticity, banding rigidity, reversed banding strength, cantilever load, surface tension, surface structure, surface tension and intensity of surface loading are under investigation. A mix of physical, chemical and visual analysis methods are used. The parameter characteristic of the nanotube material has to match these results. In cases of mismatch a technical adjustment, e.g. during weaving or coating, is possible. At least two big advantages of this new composite material exist: The possibility to produce a compound material with regional different main characteristics by using a two-phase coating process. And on the other hand the abandonment of exogenous substances during the production process and so the material has a distinct advantage over those currently used Teflon fabrics.
The role of the epigenetic factor in valvulogenesis in zebrafish in vivo
Authors: Kang Hae Jin , Gharib Morteza 
Published: July 2012

AbstractIn this study, we focused on wall shear stress as an epigenetic factor to initiate valve formation. Fast or oscillatory flow is induced in an embryonic zebrafish vessel to mimic the flow in atrioventricular canal (AVC). By creating an environment similar to AVC in non-cardiac region in vivo, we propose to seek a better understanding of the mechanisms associated with the induction of valvulogenesis signaling pathways. Polydimethylsiloxane is injected at the vessel wall of embryonic zebrafish, creating fast or oscillatory flow, therefore modulating local wall shear stress (WSS). Particle image velocimetry (PIV) technique is used to measure blood flow velocity. Whole mount in situ hybridization is performed to detect kruppel-like factor 2a (klf2a) expression. Klf2a is used as a marker gene since it responds to shear stress and is crucial for valve formation. Using PIV, WSS is calculated. In situ hybridization showed klf2a expression in the vessel as a result of either high WSS or oscillatory WSS. Klf2a is not expressed in the vessel during normal embryonic development. With a new gel injection technique, local WSS in the zebrafish vessel has changed, inducing expression of klf2a, an important gene for the initiation of valve formation. Expression of different genes such as TGF-β family that are involved in valve formation will be studied further to establish an innovative model to explore valvulogenesis in vivo.
Calcification of Aortic Valve leaflets is Shear Dependent and Side-specific
Authors: Rathan Swetha , Anita Rajamani Anita Rajamani , Gorti Harika , Arjunon Sivakkumar , Jo Hanjoong , Yoganathan Ajit 
Published: July 2012

AbstractAortic valve (AV) sclerosis is a degenerative disease and is one of the leading causes of mortality in elderly population. AV experiences various mechanical stimuli such as pressure, shear and flexure with differing magnitudes on either sides of AV (fibrosa and ventricularis) with fibrosa side facing more dynamic environment. Normal hemodynamic conditions constantly renew and remodel the valve, whereas altered mechanical loading such as hypertension and altered shear stress can cause tissue inflammation that leads to calcification, preferentially on fibrosa side. AV calcification progressively leads to sclerosis and ultimately results in valve failure. However, the molecular and cellular processes that lead to inflammation and calcification are not very well understood. To understand the role of mechanics and underlying molecular mechanisms behind this preferential calcification, aortic side and ventricularis side of fresh porcine AVs were exposed to different shear stress patterns using an ex vivo cone and plate viscometer for 72 hours. Osteogenic medium was used to accelerate the calcification process ex vivo. To investigate the effect of shear stress magnitudes on fibrosa side, sine waveforms of amplitudes 5, 10 and 25 dynes/cm2 at a frequency of 1 Hz were used. To investigate the effects of shear stress frequency on fibrosa side, sine waveforms of 1 and 2 Hz at 10dynes/cm2 were used. Following exposure to shear, calcium levels of the samples were quantified using calcium Arsenazo assay. Von Kossa stain for mineralization was also done. Fresh porcine AVs were used as controls. Results indicated that low magnitude shear stress, 5 dyne/cm2 at 1 Hz elicited significant calcium levels on fibrosa side compared to other magnitudes and frequencies. To investigate if the oscillatory nature or the low magnitude was responsible for this high calcium response, fibrosa side was exposed to steady 5 dyne/cm2 under same experimental conditions as above. However, calcium levels at steady 5dyne/cm2 were comparable to fresh AV levels and thus non-significant. This result indicated that the magnitude in combination with the oscillatory nature of the sine 5dyne/cm2 triggered significant calcification levels on the fibrosa side of the AV leaflets. To test the side-specificity of this response, ventricularis side was also exposed to 5 dyne/cm2 under same experimental conditions as above. It is interesting to note that calcium levels on ventricularis side were not significant compared to that on the fibrosa side. This result further indicated that the expression of significant calcium levels in response to the low oscillatory shear is indeed side-specific. Thus our results suggest that the calcification of the AV leaflets is shear-dependent and side-specific. Shear dependent calcification in AV also suggests mechanobiological similarities with the atherosclerosis of blood vessels.
Gelatin and Decorin are Suitable Candidates for Application in Tissue-Engineered Matrices - an Immunological In Vitro Study
Authors: Bayrak Alexandra , Ibold Bettina , Hinderer Svenja , Schenke-Layland Katja , Stock Ulrich A. , Seifert Martina 
Published: July 2012

AbstractInflammatory and immune-mediated responses to extracellular matrix proteins (ECMp) or biomaterials mainly determine the acceptance of tissue-engineered scaffolds like heart valve grafts. Therefore, we focused on detailed analysis of those responses induced either by the single ECMp gelatin and the proteoglycan decorin or by electrospun scaffolds composed of both proteins. Proliferation assays were performed to analyze response of T cell subsets by flow cytometry. Therefore, human peripheral blood mononuclear cells (PBMCs) were co-cultured with bovine decorin, porcine gelatin or with electrospun scaffolds generated of poly-ε-caprolacton (PCL) with either gelatin alone or in combination with decorin under low-dose anti-CD3 treatment for 5 days. Moreover, monocyte-derived immature dendritic cells (DC) were co-cultured with decorin and gelatin to determine maturation effects by specific surface markers and flow cytometric analysis compared to a Lipopolysaccharride (LPS) stimulated control. Supernatants of both T cell and DC cultures were analyzed for the pro-inflammatory cytokines IFNγ, TNFα and IL-6 by cytometric bead arrays or ELISA. Additionally, complement activation by decorin and gelatin was screened by incubation with pooled human serum and measuring induced C5a release by standard ELISA. In general, a slight reduction of the T cell subset proliferation compared to the anti-CD3 stimulated positive control in CFSE-based assays could be demonstrated for bovine decorin and porcine gelatin. Both electrospun scaffold types did not alter the proliferation response. Additionally, neither decorin nor gelatin induced a distinct proinflammatory cytokine secretion of IFNγ and TNFα relative to the control. The overall high secretion level of IL-6 was not affected by both proteins and electrospun scaffolds. Remarkably, a trend for reduced IFNγ and TNFα release could be observed for both scaffold types. Moreover, the surface marker expression pattern of DC revealed that decorin as well as gelatin were not able to induce DC maturation due to low expression levels for CD83 and fairly low TNFα secretion when compared to the LPS control. Analyzing complement activating capacities of both ECMp as part of the first line innate immune response, decorin as well as gelatin did not induce enhanced C5a release compared to controls. The results presented here illustrate the important role of evaluating complex immune responses to single ECMp as well as to electrospun scaffolds to facilitate an efficient selection of immunological inert tissue-engineered matrices for their future application as heart valve substitutes. Thus, gelatin as well as decorin are promising candidates for tissue engineering scaffolds as seen by their low immunogeneic properties as single ECMp or as part of electrospun blends.
A New Approach to Heart Valve Tissue Engineering Based on the Modification of Human Pericardial Tissue
Authors: Straka Frantisek , Schornik David , Masin Jaroslav , Filova Elena , Burdikova Zuzana , Mirejovsky Tomas , Honsova Eva , Lodererova Alena , Chlup Hynek , Horny Lukas , Vesely Jan , Pirk Jan , Bacakova Lucie 
Published: July 2012

AbstractThe main problem of currently used xenogeneic biological heart valves is the development of degenerative changes leading to valve failure. Reoperation is required in approximately 65% of patients at 15 years after implantation. The challenge of heart valve tissue engineering is to create a new type of biological prosthesis for clinical use. The aim of our study is to construct a living autologous human pericardial heart valve that will have optimal mechanical properties and a similar histological structure as the normal aortic heart valve. Three leaflet heart valve constructs made from human pericardium were attached onto a plastic holder and cultured under dynamic conditions for up to four weeks. After this time conditioned pericardial samples were compared to control unconditioned pericardial samples from the same patient and to that of the normal aortic heart valve. Histological, immunohistochemical and biomechanical assessments were performed. Pericardial interstitial cells (PICs) are able to respond to mechanical stresses by proliferating and differentiating into an active (myofibroblast-like) phenotype and are able to produce new extracellurar matrix (ECM). A threefold increase in PIC number and a twofold increase in smooth muscle actin (SMA) positive cells was observed after dynamic conditioning. These measurements were statistically significant (p<0.001). The histological structure of conditioned pericardium is very similar to the normal aortic heart valve and dynamic conditioning was shown to be important for PIC activation. Uniaxial tensile tests were performed to compare the mechanical properties of conditioned pericardium with the native aortic heart valve. Our results indicate that the secant elastic modulus of pericardium before and after conditioning (13.1 ± 8.3 Mpa) is comparable to the native aortic heart valve. Autologous human pericardium mimics the natural structure of the normal aortic heart valve and has similar mechanical properties. PICs are activated to an active VIC-like phenotype by mechanical conditioning. Our pericardial heart valve construct also possesses optimal hemodynamic properties by echocardiographic measurements similar to the healthy aortic heart valve.

Acknowledgements: Supported by the Grant Agency of the Ministry of Health of the Czech Republic (project No. NT 11270.
Derivatives of the Triaminoguanidinium Ion, 1. Synthesis, Crystal and Molecular Structures of 1,2,3-Tris(benzylamino)guanidinium Salts
Authors: Bucher Nicolas , Szabo Jan , Oppel Iris M. , Maas Gerhard 
Published: July 2012

Abstract
Triaminoguanidinium chloride was transformed into 1,2,3-tris(benzylamino)guanidinium chloride (3-Cl) in two steps. Anion exchange allowed the preparation of further salts 3-X. The crystal and molecular structures of 3-Cl, 3-I, 3-CF3COO and 3-CF3SO3 were determined. It was found that both the conformation of the cation and the nature of the anion determines the packing in the solid state. Interestingly, three different conformations of the cation were observed in the crystals.