Geofrey De Visscher

The remodeling of cardiovascular bioprostheses under influence of stem cell homing signal pathways

Optimizing current heart valve replacement strategies by creating living prostheses is a necessity to alleviate complications with current bioprosthetic devices such as calcification and degeneration. Regenerative medicine, mostly in vitro tissue engineering, is the forerunner of this optimization search, yet here we show the functionality of an in vivo alternative making use of 2 homing axes for stem cells. In rats we studied the signaling pathways of stem cells on implanted bioprosthetic tissue (photooxidized bovine pericardium (POP)), by gene and protein expression analysis. We found that SDF-1alpha/CXCR4 and FN/VLA4 homing axes play a role. When we implanted vascular grafts impregnated with SDF-1alpha and/or FN as carotid artery interpositions, primitive cells were attracted from the circulation. Next, bioprosthetic heart valves, constructed from POP impregnated with SDF-1alpha and/or FN, were implanted in pulmonary position. As shown by CD90, CD34 and CD117 immunofluorescent staining they became completely recellularized after 5 months, had a normal function and biomechanical properties and specifically the combination of SDF-1alpha and FN had an optimal valve-cell phenotype.

Functional and biomechanical evaluation of a completely recellularized stentless pulmonary bioprosthesis in sheep

OBJECTIVE In a previous study we showed that recellularization of a stentless bioprosthetic valve is stimulated 1 month after implantation in the pulmonary position, when its matrix (acellular photo-oxidized bovine pericardium) was preseeded by intraperitoneal implantation during a 3-day period. METHODS The present study reports on the functional and biomechanical properties of such valves (n = 19) in sheep up to 5 months after implantation. Similar valves (n = 20) that were not intraperitoneally preseeded served as controls. RESULTS Recellularization was partial in control valves and excessive in preseeded valves: 66% versus 223% of cellularity of native valves, respectively (P < .05). The valves were endothelialized and contained interstitial cells depositing new matrix (collagens and elastin). However, phenotyping revealed an increased proportion of cells with contractile properties (30%-40% alpha smooth muscle actin+) in both groups. Intraperitoneally seeded valves had thicker and shorter leaflets that were associated with mildly increased peak gradients and regurgitation. Characterization of the matrix properties revealed a gradually degrading matrix (+/-25% loss of collagen organization at 5 months) and a concomitant alteration of its biomechanical properties, that is, decreased strength, stiffness, and maximum force. However, overall valve function remained intact, and the biomechanical properties of the whole valves were superior to that of the native valves. CONCLUSION The ectopic in vivo seeding paradigm provides full recellularization. However, the volume fraction of the cellular phenotypes is not optimal, resulting in inadequate remodeling of the valves.

Gene expression study of monocytes/macrophages during early foreign body reaction and identification of potential precursors of myofibroblasts.

Foreign body reaction (FBR), initiated by adherence of macrophages to biomaterials, is associated with several complications. Searching for mechanisms potentially useful to overcome these complications, we have established the signaling role of monocytes/macrophages in the development of FBR and the presence of CD34+ cells that potentially differentiate into myofibroblasts. Therefore, CD68+ cells were in vitro activated with fibrinogen and also purified from the FBR after 3 days of implantation in rats. Gene expression profiles showed a switch from monocytes and macrophages attracted by fibrinogen to activated macrophages and eventually wound-healing macrophages. The immature FBR also contained a subpopulation of CD34+ cells, which could be differentiated into myofibroblasts. This study showed that macrophages are the clear driving force of FBR, dependent on milieu, and myofibroblast deposition and differentiation.

Trilogy Pericardial Valve : Hemodynamic Performance and Calcification in Adolescent Sheep

BACKGROUND We assessed the hemodynamic performance and calcification potential of a new design of bovine pericardial valve, the Trilogy valve (Arbor Surgical Technologies Inc, Irvine, CA). We compared this new valve with the Perimount valve (Edwards Lifesciences, Irvine, CA) in a randomized prospective study in adolescent sheep. METHODS Nine Trilogy valves (size 21) and six Perimount valves (size 23 or 25) were implanted in the mitral position in adolescent sheep and studied during five months. Hemodynamic measurements were performed at one week, three months, and five months using transthoracic echocardiography. Valve calcification was assessed by X-ray and calcium content was measured by atomic absorption spectrometry after five months implantation in sheep. Tissues were also evaluated histologically (Von Kossa staining). RESULTS The nine Trilogy valves had lower peak velocity, peak gradient, and mean gradient compared with the six Perimount valves. These 21-mm Trilogy valves had similar deceleration time and effective orifice area compared with the 23- and 25-mm Perimount valves. Calcification of the Trilogy valves was significantly lower than Perimount valves (p < 0.01), particularly in the commissural (p < 0.01) and free margin regions (p < 0.03). In all parameters assessed, the Trilogy valves exhibited less variation valve-to-valve compared with Perimount valves. CONCLUSIONS These findings demonstrate that a valve designed to reduce stress in the tissue, improve leaflet kinematics, with advanced antimineralization treatment, can exhibit superior calcification resistance in the mitral position of adolescent sheep. The trilobal geometry and independent leaflet suspension design, combined with an advanced tissue treatment, appears to be a promising breakthrough in the effort to develop a more durable and hemodynamically efficient bioprosthetic valve.

Selection of an immunohistochemical panel for cardiovascular research in sheep.

Large animal research, often required as a final phase before commencing clinical trials for devices, has generally been hampered by the lack of appropriate tools to compare it with either initial small animal tests or to later evaluation in humans. Setting out to tissue engineer heart valves, we were particularly struck by the limited availability of immunohistochemical markers for sheep tissue, despite sheep being the FDA-approved animal for heart valve testing. This paper, therefore, aims to compile the available knowledge and extend the marker list with antibodies cross-reacting with sheep tissue. Thirty-seven antibodies attributed to 1 of these classes were found to be useful: (1) endothelium, (2) mesenchymal cells, myofibroblasts, and smooth muscle cells, (3) immune response, (4) primitive cells, (5) extracellular matrix, and (6) miscellaneous. Twelve had already been used in sheep tissue, but to our knowledge, the remaining 25 have not been described for use in sheep. From this result, we can conclude that the immunohistochemical panel for sheep has been extensively expanded with respect to cardiovascular research.