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The microfibril-elastin fiber system, an important constituent of the extracellular matrix, was studied in the rat left atrioventricular valve to investigate the interrelationship of oxytalan, elaunin and elastic fibers in left atrioventricular valve morphology. The elastin fibers forms continuous bundles observed along the length of the valve in atrial and ventricular layers and oriented parallel to endothelium. The elaunin and oxytalan fibers are distributed in the thickest fiber bundles along the length of the valve. The thinner fibers which radiated towards both the atrial and spongiosa layers, either as isolated or arborescent fiber bundles were identified as oxytalan fibers. With transmission electron microscopy elastic fibers were seen mainly in the atrial layer. The spongiosa layer was composed of elaunin and oxytalan fibers and ventricular layer showed elaunin fibers arranged in continuous bundles parallel to the endothelium. Both fibrillin and elastin were seen and identified by immunocytochemistry with colloidal gold in the left atrioventricular valve spongiosa and atrial layers. These observations allow us to suggest that the microfibril-elastin fiber system plays a role in the mechanical protection and maintenance of the integrity of the rat left atrioventricular valve.

Fue estudiado el sistema de fibras microfibrillas-elastina, un componente importante de la matriz extracelular, en la valva atrioventricular izquierda de rata, con la finalidad de investigar la interrelación de oxitalán, elaunin y fibras elásticas en la morfología de dicha valva. Las fibras de elastina forman paquetes continuos a lo largo de la valva en las capas atriales y ventriculares, orientadas paralelamente al endotelio. Las fibras de elaunin y oxitalán se distribuyen en haces de fibras más gruesas a lo largo de la valva. Las fibras más delgadas, las cuales se irradiaban hacia las capas atrial y esponjosa, ya sea como haces de fibras aisladas o arborescentes, fueron identificadas como fibras oxitalán. En la capa atrial a través de microscopía electrónica de transmisión se observaron principalmente fibras elásticas. La capa esponjosa estaba compuesta por fibras de elaunin y oxitalán; la capa ventricular mostró fibras de elaunin dispuestas en haces continuos paralelos al endotelio. Tanto fibrilina y elastina se observaron e identificaron por inmunocitoquímica con oro coloidal en las capas esponjosa y atrial de la valva atrioventricular izquierda. Estas observaciones nos permiten sugerir que el sistema de fibras de elastina-microfibrillas tienen participación en la protección mecánica y la mantención de la integridad de la valva atrioventricular izquierda en la rata.

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Human cardiac valve allografts (HVAs) suffer injuries during the cryopreservation period. Here, we described structural, ultrastructural and functional damages suffered by HVAs after an increment of their cryostorage temperature (100 degree C). Two experimental groups of pulmonary and aortic HVAs were compared: cryopreserved (HVAcryo) and cryopreserved with temperature changes (HVAΔT). Transmission electron microscopy (TEM) was used to analyze valve fibroblasts and extracellular matrix morphology. Total collagen amount was estimated using two different methods and fibroblast viability was assessed measuring their oxygen consumption rate. Porcine heart grafts valves were used to set the techniques. Disorganized collagen network was seen in HVAΔT by TEM. Fibroblasts showed damages in the cellular membrane and many secretor vesicles. Mitochondria and chromatin were also altered. HVAΔT had less amount of collagen and fibroblasts showed an oxygen consumption rate markedly diminished compared to HVAcryo. The increment of 100 degree C suffered by HVAs caused damages that made them unsuitable for clinical purposes.

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The 'biomimetic' approach to tissue engineering usually involves the use of a bioreactor mimicking physiological parameters whilst supplying nutrients to the developing tissue. Here we present a new heart valve bioreactor, having as its centrepiece a ventricular assist device (VAD), which exposes the cell-scaffold constructs to a wider array of mechanical forces. The pump of the VAD has two chambers: a blood and a pneumatic chamber, separated by an elastic membrane. Pulsatile air-pressure is generated by a piston-type actuator and delivered to the pneumatic chamber, ejecting the fluid in the blood chamber. Subsequently, applied vacuum to the pneumatic chamber causes the blood chamber to fill. A mechanical heart valve was placed in the VAD's inflow position. The tissue engineered (TE) valve was placed in the outflow position. The VAD was coupled in series with a Windkessel compliance chamber, variable throttle and reservoir, connected by silicone tubings. The reservoir sat on an elevated platform, allowing adjustment of ventricular preload between 0 and 11 mmHg. To allow for sterile gaseous exchange between the circuit interior and exterior, a 0.2 µm filter was placed at the reservoir. Pressure and flow were registered downstream of the TE valve. The circuit was filled with culture medium and fitted in a standard 5% CO(2) incubator set at 37 °C. Pressure and flow waveforms were similar to those obtained under physiological conditions for the pulmonary circulation. The 'cardiomimetic' approach presented here represents a new perspective to conventional biomimetic approaches in TE, with potential advantages.

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Type XVIII collagen is a multidomain protein that contains cleavable C-terminal NC1 and endostatin fragments, which have been shown to either induce or inhibit cell migration. Endostatin is being intensely studied because of its anti-angiogenic activity. Three variants of type XVIII collagen have been reported to be distributed in epithelial and endothelial basement membranes in a tissue-specific manner. The single gene encoding collagen XVIII is on chromosome 21 within the region associated with the congenital heart disease phenotype observed in Down's syndrome. In this study, we investigated the expression pattern of collagen XVIII in embryonic mouse hearts during formation of the atrioventricular (AV) valves. We found that collagen XVIII is localized not only in various basement membranes but is also highly expressed throughout the connective tissue core of the endocardial cushions and forming AV valve leaflets. It was closely associated with the epithelial-mesenchymal transformation of endothelial cells into mesenchymal cushion tissue cells and was localized around these cells as they migrated into the cardiac jelly to form the initial connective tissue elements of the valve leaflets. However, after embryonic day 17.5 collagen XVIII expression decreased rapidly in the connective tissue and thereafter remained detectable only in the basement membranes of the endothelial layer covering the leaflets. The staining pattern observed within the AV endocardial cushions suggests that collagen XVIII may have a role in cardiac valve morphogenesis. These results may help us to better understand normal heart development and the aberrant mechanisms that cause cardiac malformations in Down's syndrome.

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The mucopolysaccharidoses (MPS) are lysosomal storage diseases in which a specific enzyme defect causes glycosaminoglycans storage in tissues. The authors present a necropsy case of a 10 years old boy with clinical and laboratorial diagnosis of MPS. The necropsy revealed thickening of meninges, cardiac valves and hepatomegaly. The microscopical examination of the brain showed finely vacuolated histiocytes around blood vessels and meninges. Systemic deposits of vacuolated histiocytes in cardiac valves and liver were also detected. The ultrastructural examination of the brain, liver and spleen showed filamentous material accumulated in vacuolated histiocytes and hepatocytes and features neuronal storage disease.

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As mucopolissacaridoses (MPS) sao doencas de acumulo lisossomal em que ocorre defeito enzimatico especifico com consequente acumulo de glicosaminoglicanos nos tecidos. Os autores relatam o caso de necropsia de paciente do sexo masculino, com 10 anos de idade, com diagnostico clinico e laboratorial de MPS. O exame de necropsia revelou espessamento acentuado de meninges e das valvas cardiacas e hepatomegalia. O exame microscopico do encefalo evidenciou acumulo de histiocitos espumosos ao redor dos vasos e nas meninges, assim como neuronios contendo material citoplasmatico condizente com gangliosideo. Alteracoes sistemicas como acumulo de histiocitos espumosos em valvas cardiacas e figado foram evidenciados. O exame ultra-estrutural do encefalo, figado e baco demonstrouacumulo de material grumoso no interior de vacuolos em histiocitos e hepatocitos, alem de acumulo de gangliosideo nos neuronios.

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Os estudaram através de corts histológicos e técnica das linhas de fenda os elementos da valva atrioventricular direita, para determinar diferenças morfológicas entre os folhetos considerados ou näo como cúspides. Foram utilizados 10 coraçöes de cadáveres humanos, de indivíduos e de ambos os sexos, provenientes do Serviço de Verificaçäo de Obitos da Escola Paulista de Medicina. As cúspides foram submetidas à técnica habitual para Microscopia Optica Comum. A técnica das linhas de fenda foi realizada com pequena agulha cilíndrica de ponta cônica, imersa em nanquim. Os locais de puncturas foram: superfície atrial, nódulo da cúspide atrioventricular, comissura, cúspide comissural e outras cúspides eventuais. Os resultados mostraram que a disposiçäo das linhas de fenda estariam relacionadas com as inserçöes das cordas tendíneas, e a força resultante que estas exercem sogre as cúspides. Histologicamente, näo há diferenças enquanto a orientaçäo e concentraçäo das fibras colágenas entre as cúspides habituais, comissurais e outras cuspides eventuais

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Se realizaron estudios de ultraestructura con microscopía convencional y electrónica en 7 válvulas de porcino. Cinco de las prótesis habían sido sometidas a más de 24 meses de conservación en glutaraldehído. Las dos restantes habían sido descartadas en la evaluación final por presentar áreas de diferente tinción en el examen de control final. El examen microscópico reveló en las cinco primeras válvulas las alteraciones típicas secundarias al manipuleo durante la elaboración de las mismas (pérdida parcial del endotelio), con preservación de la estructura en las restantes capas. Las dos válvulas restantes presentaban degeneración fibrosa y lipomatosa por patología propia del cerdo. Se concluye que tiempos prolongados de preservación en glutaral dehído no ocasiona modificaciones ulteriores a las ya observadas en una válvula recientemente confeccionada. Se destaca la importancia de los procesos de elaboración y controles de las prótesis, particularmente el examen con magnificación óptica para detectar alteraciones degenerativas propias del animal

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