Biomedical subjects

Derek R Boughner

Publications and source records attributed to Derek R Boughner.

9 recordsLinked to original sources

PubMed2006

Radial artery as an autologous cell source for valvular tissue engineering efforts.

To create a viable tissue-engineered aortic valve, it is important to identify suitable autologous cell sources that may be seeded onto a biocompatible scaffold. This study focused on the radial artery (RA) as one possible source, investigated optimal culture conditions, and determined the usefulness of small intestinal submucosa (SIS) as a scaffold for tissue-engineering. Porcine RA cells were cultured on either two-dimensional (2D) 100-mm dishes or three-dimensional (3D) 1-cm(2) SIS sheets, producing cell-scaffold composites (CSCs). Both 2D and 3D cultures were maintained in either Medium 199 (M199) or endothelial growth media (EGM) to determine optimal growth conditions. Cellular phenotype and matrix metalloproteinase (MMP) profiles were determined by immunoblotting of cell lysates and zymography of conditioned media, respectively. Cellular invasion was analyzed immunohistochemically on CSC tissue sections. We show that the RA contains phenotypes consistent with those found in the normal aortic valve. EGM, compared with M199, promotes the invasion and remodeling of SIS by RA cells, which is crucial in the process of replacing the foreign tissue scaffold prior to implantation. To our knowledge, this is the first study to show that the RA is a suitable source for the generation of a tissue-engineered valve.

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PubMed2006

Evaluation of an algorithm for semiautomated segmentation of thin tissue layers in high-frequency ultrasound images.

An algorithm consisting of speckle reduction by median filtering, contrast enhancement using top- and bottom-hat morphological filters, and segmentation with a discrete dynamic contour (DDC) model was implemented for nondestructive measurements of soft tissue layer thickness. Algorithm performance was evaluated by segmenting simulated images of three-layer phantoms and high-frequency (40 MHz) ultrasound images of porcine aortic valve cusps in vitro. The simulations demonstrated the necessity of the median and morphological filtering steps and enabled testing of user-specified parameters of the morphological filters and DDC model. In the experiments, six cusps were imaged in coronary perfusion solution (CPS) then in distilled water to test the algorithm's sensitivity to changes in the dimensions of thin tissue layers. Significant increases in the thickness of the fibrosa, spongiosa, and ventricularis layers, by 53.5% (p < 0.001), 88.5% (p < 0.001), and 35.1% (p = 0.033), respectively, were observed when the specimens were submerged in water. The intraobserver coefficient of variation of repeated thickness estimates ranged from 0.044 for the fibrosa in water to 0.164 for the spongiosa in CPS. Segmentation accuracy and variability depended on the thickness and contrast of the layers, but the modest variability provides confidence in the thickness measurements.

Algorithms↗

PubMed2005

Dermal fibroblasts cultured on small intestinal submucosa: Conditions for the formation of a neotissue.

Small intestinal submucosa (SIS) is a naturally occurring, acellular biomaterial that has been used extensively as a soft tissue replacement, as a scaffold for tissue engineering, and as a substrate for the study of cells in 3D culture. The aim of this study is to define culture parameters that promote neotissue formation with the use of dermal fibroblasts and SIS. SIS sheets were seeded with dermal fibroblasts and cultured for 4 weeks. The resultant cell-scaffold composites (CSCs) were cultured with media alone, media supplemented with ascorbic acid, or fibronectin-pretreated SIS and ascorbic acid. CSCs were analyzed for cellular invasion into the scaffold, the rate of type I collagen production, MMP gelatinolytic activity, thickness, and ultrastructural morphology. CSCs treated with fibronectin and ascorbate showed an increase in Type I collagen production, no change in the MMP gelatinolytic activity, an increase in CSC thickness, and an organized neotissue on the surface of the SIS. Minimal cellular invasion was noted, suggesting that fibroblasts use the SIS as a template for neotissue growth rather than as a scaffold. These results indicate that fibronectin-treated SIS cultured with dermal fibroblasts in the presence of ascorbic acid will promote true neotissue formation for future cardiovascular tissue engineering efforts.

Ascorbic Acid↗

PubMed2005

Development of aortic valve sclerosis in a rabbit model of atherosclerosis: an immunohistochemical and histological study.

BACKGROUND AND AIM OF THE STUDY: It has been suggested that aortic valve sclerosis (AVS) is an atherosclerotic disease process that can proceed to aortic stenosis. The absence of reports studying an animal model of the early stages of this disease has precluded the development of preventive therapeutic strategies. A cholesterol-fed (0.25% cholesterol in chow) rabbit model of atherosclerosis that is characterized by a moderate level of hypercholesterolemia was studied to determine its efficacy as a model of early AVS. Cellular, structural and morphological changes in the aortic valves of these rabbits were studied. METHODS: Twenty rabbits were assigned randomly to four experimental groups: Group 1 received normal chow for 40 weeks; group 2 received 0.25% cholesterol-supplemented chow for 20 weeks; group 3 received 0.25% cholesterol-supplemented chow for 40 weeks; and group 4 received 0.25% cholesterol-supplemented chow for 20 weeks followed by normal chow for an additional 20 weeks. The aortas and aortic valves were analyzed using immunohistochemical and histological methods to detect cellular and structural components of the developing lesions. RESULTS: All rabbits in groups 2, 3 and 4 developed atherosclerotic lesions in their aortas. Aortic valves from these animals demonstrated thickening, lipid deposition, a change in collagen content and organization, a reorganization of elastin, and the presence of both macrophage infiltrate and osteopontin. CONCLUSION: These findings were consistent with the suggestion of a link between atherosclerosis and AVS. Results were also similar to changes reported in human sclerotic aortic valves, suggesting the suitability of this rabbit model of atherosclerosis as a model for AVS.

Animals↗

PubMed2004

Three-dimensional visualization and thickness estimation of aortic valve cusps using high-frequency ultrasound.

High-frequency ultrasound techniques are introduced for three-dimensional imaging and thickness estimation of fresh heart valve cusps. Images of porcine aortic valve specimens were acquired within a 12 x 8 x 8 mm3 volume using a VisualSonics VS40 micro-imaging system operating at a 40 MHz centre frequency. Two image volumes were obtained from each of six left coronary cusps. One volume was acquired with the specimen submerged in distilled water and the second volume was acquired through either Hanks physiologic solution or coronary perfusion solution (CPS). The fibrosa, spongiosa and ventricularis were most readily distinguished when the specimen was imaged in distilled water. Colour thickness maps were computed from B-mode image data, and the mean and standard deviations of the thickness were determined for each cusp. In 11 of 12 trials, the image analysis algorithm yielded valid thickness estimates over greater than 98% of the region examined. Mean thickness estimates obtained with specimens submerged in Hanks solution or CPS ranged from 0.66 to 1.03 mm, and submersion in distilled water increased the mean thickness by 20-40%. This observation suggests that the cusps osmotically absorbed water. Information provided by high-frequency ultrasound is expected be valuable for characterizing the morphological properties of heart valves.

Animals↗

PubMed2003

Smoothelin-positive cells in human and porcine semilunar valves.

Our aim was to further characterize the interstitial cell phenotypes of normal porcine and human semilunar valves, information necessary for the design of bioengineered valves and for the understanding of valve disease processes such as aortic valve sclerosis. Existence of fibroblasts, myofibroblasts, and smooth muscle-like cells within semilunar heart valves has been established. However, the nature of the smooth muscle cell population has been controversial. We used immunochemical and western blotting methods to determine the status of smoothelin and smooth muscle alpha-actin in the valve. Our examination of valve interstitial cells confirmed the presence of terminally differentiated, contractile smooth muscle cells in situ. They were arranged in small bundles of 5-35 cells within the ventricularis or as individual cells scattered throughout the valvular layers in vivo, and were present in cells explanted from the valves in vitro. Colocalization of these proteins in semilunar heart valves was achieved with double-labeling experiments. Protein extraction, followed by coimmunoprecipitation, electrophoresis, and western blotting confirmed the immunochemical analysis and suggested that smooth muscle alpha-actin and smoothelin interact, as has been previously postulated. The presence of contractile smooth muscle within the valve may be an important factor in understanding valve pathology and in the design of tissue engineering efforts.

Animals↗

PubMed2003

Validation of a three-dimensional intravascular ultrasound imaging technique to assess atherosclerotic burden: potential for improved assessment of cardiac allograft coronary artery disease.

BACKGROUND: Serial analysis of intracoronary ultrasound images is limited by difficulty with spatial registration and inability to assess the full extent of vascular disease. Three-dimensional (3D) imaging of coronary arteries can potentially overcome these limitations. OBJECTIVES: To assess the feasibility of using a PC-based 3D rendering technique to assess atherosclerotic burden. METHODS: To define the accuracy of 3D intravascular ultrasound (IVUS) measurements in vitro, six porcine iliac arteries and nine human cadaveric iliac arteries were pressure fixed and imaged with a commercial IVUS system. 3D datasets of the arteries were constructed, and measurements were correlated with histomorphometry. In vivo studies of 53 arterial segments (19 right coronary, 26 anterior descending and eight circumflex) were scanned in 18 patients, one month to nine years post-transplantation and correlated to corresponding angiographic images for the presence of atherosclerosis. RESULTS: Porcine artery length and volume measurements by IVUS showed a high degree of correlation with histomorphometry measurements (r=0.99, P<0.0003 and r=0.99, P<0.0001, respectively). Human arterial length, total artery volume and lumen volume measurements were similarly correlated (r=0.99, P<0.0001, r=0.99, P<0.0001 and r=0.98, P<0.0001, respectively). For plaque volume, r=0.84, P<0.05. In vivo 3D IVUS scans demonstrated atherosclerotic lesions in nine of 18 patients, compared with five detected by angiography alone. CONCLUSIONS: 3D IVUS imaging allows rapid and accurate measurement of arterial length, volume and plaque dimensions in addition to lumenal area and can demonstrate the full extent of atherosclerotic pathology. Because of its superior reproducibility, this technique may be used to assess the progression of coronary artery disease and allow for more accurate evaluation of interventions aimed at preventing or retarding coronary artery disease.

Animals↗

PubMed2002

Aortic valve interstitial cells: an evaluation of cell viability and cell phenotype over time.

BACKGROUND AND AIM OF THE STUDY: In investigating the mechanisms of aortic valve disease processes and to accurately construct tissue-engineered heart valve prostheses, a complete understanding of the native interstitial cell population is required. Previously, autopsy samples have been deemed unsuitable for immunocytochemical studies due to the ischemic time before harvesting. In this study, the viability and phenotypic profile of cells explanted from normal porcine heart valves up to 120 h post mortem was examined. METHODS: The aortic valve leaflets of porcine hearts were excised at 0, 6, 24, 48, 72, 96 and 120 h post mortem; one half of the tissue was used to explant cells, and the other half was fixed in 3.7% formalin for sectioning. Samples taken at each time point were cultured and cell viability was determined using a trypan blue exclusion assay. Immunocytochemical and immunohistochemical analyses, using specific markers for fibroblasts, myofibroblasts and smooth muscle cells, were used to compare cell phenotypes both in vitro and in situ. RESULTS: Absolute numbers of cells obtained from each leaflet decreased significantly over time; however, cell viability in culture was unaffected up to 96 h. At each time point, explanted cell populations expressed similar phenotypes when compared with histological samples prepared from the same valves. CONCLUSION: Porcine aortic valve interstitial cells may be explanted up to and including 96 h post mortem, with no statistically significant change in cell viability in vitro, and with a population that phenotypically resembles aortic valve interstitial cells in situ. These data suggest that human aortic valve interstitial cells may be successfully harvested at autopsy for in vitro studies.

Actins↗

PubMed2002

Mitral valve aneurysm associated with aortic valve endocarditis and regurgitation.

Mitral valve aneurysms are rare complications occurring most commonly in association with aortic valve infective endocarditis. [Decroly 1989, Chua 1990, Northridge 1991, Karalis 1992, Roguin 1996, Mollod 1997, Vilacosta 1997, Cai 1999, Vilacosta 1999, Teskey 1999, Chan 2000, Goh 2000, Marcos- Alberca 2000] While the mechanism of the development of this lesion is unclear, complications such as perforation can occur and lead to significant mitral regurgitation. [Decroly 1989, Karalis 1992, Teskey 1999, Vilacosta 1999]; The case of a 69-year-old male with Streptococcus Sanguis aortic valve endocarditis and associated anterior mitral leaflet aneurysm is presented. Following surgery, tissue pathology of the excised lesion revealed myxomatous degeneration and no active endocarditis or inflammatory cells. This may add support to the hypothesis that physical stress due to severe aortic insufficiency and structural weakening, without infection of the anterior mitral leaflet, can lead to the development of this lesion.

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