Endothelialization of Cardiac Valve Bioprostheses

Abstract

The main disadvantage of implanted xenograft valves used in cardiac surgery is their poor clinical long-term result, due to early tissue degeneration. In order to improve the performance of such glutaraldehyde fixed bioprostheses, a biological coating with viable endothelial cells was suggested. Therefore, glutaraldehyde preserved bovine pericard patches, as well as commercially available xenograft valves, were lined using human venous endothelial cells or microvascular cells from the subcutaneous fat tissue. Before cells were transplanted into their new environment, grafts were treated with an amino acid solution in order to neutralize the cytotoxic effect of free aldehydes, and precoated with fibronectinheparin and basic fibroblast growth factor (bFGF) or endothelial cell growth supplement (ECGS) in order to enhance cell proliferation. Coated specimens were kept in culture conditions for a further seven days. Proliferation of transplanted cells was verified by an increase of activation following ³H-thymidine incorporation, while the maintained metabolic cell activity was demonstrated via Prostacycline (PGI₂) measurement. Morphology was evaluated by means of scanning electron microscopy (SEM). As evaluated by the β-Counter, 7 ng/ml bFGF (288,727 ± 39,668 counts on day 4) substantially enhanced cell proliferation after seeding, opposed to the stimulation with 30,000 ng/ml ECGS (91,924 ± 1129 counts on day 4), (p<0.001). The PGI₂ release of transplanted cells was stimulated with 25 μM Na arachidonic acid by the factor 2.6 ± 0.3 and inhibited with 5 mM acetylsalecylic acid by the factor 0.7 + 0.2 on day 4 when compared with the basic level. After seven days of cultivation, SEM observation revealed that specimens stimulated with bFGF showed areas of confluent coated leaflets with an even distribution of cell layer. We therefore conclude that proliferation of transplanted cells is most favorable when stimulated with bFGF and that a special treatment of GA preserved cardiac valve bioprostheses allows a vital biological coating with human endothelial cells.