No abstract

In the venous circulation in severe TR, decellularized valves show superior functional performance compared to Ga-fixed tissue valves. Macroscopic and microscopic analyses suggest preserved structural integrity and advanced endothelial and interstitial repopulation with evidence of less degradation in dTV. © 2014 Wiley Periodicals, Inc.

The present study aimed at developing a small animal transplantation model of accelerated calcifying degeneration, in order to evaluate degenerative in vivo processes in biological heart valves and vascular implants. Male Wistar rats (recipients) with an interventionally induced aortic insufficiency grade II – III (AI; day -14) were fed with a diet containing high-dose vitamin D, cholesterol and calciumphosphate. Aortic conduits of Sprague-Dawley rats (donors) were decellularized according to a detergent-based protocol and infrarenally implanted (day 0) in an end-to-side manner in the recipients (group A; n = 6). Cryopreserved implants served as controls (group B; n = 6). Doppler sonography was conducted at days -14, 0, 28 and 84. Graft explantation, histological and immunohistochemical analyses were performed at days 28 and 84. In all recipients AI grade II – III with subsequent reversed diastolic flow in the abdominal aorta was confirmed. Sonographic competence of the conduit perfusion and overall survival were 100%. After 12 weeks severe calcification of the native aortic media as well as of the aortic conduit implants was observed (vKossa staining), however, in group A diet-induced calcification was significantly lower as compared to group B (p <0.01). Histological evaluation of the conduit implants revealed an intimal hyperplasia, involving α-smooth muscle actin expressing cells, with an increased intima-to-media ratio (p < 0.001) and inflammatory activity (CD3+) in group B versus group A. During the later follow-up, intimal hyperplasia and severe calcification aggravated. After 12 weeks, in opposite to group A explants, all grafts of group B contained Syndecan-3-expressing cells with a chondroid phenotype. Our rapidly calcifying rat transplantation model enables detailed evaluation of native and tissue-engineered aortic conduits, especially in terms of degenerative processes. Compared to cryopreserved grafts, decellularization significantly diminished the calcifying degeneration and intimal hyperplasia of aortic conduit implants. Further work will focus on the characterization of the de novo interstitial repopulation, particularly on the nature of the chondroid cells and their role in graft degeneration.

Strategies that aim at an acceleration of in vivo neoendothelialization and medial repopulation are warranted to increase the integrity and functionality of tissue-engineered cardiovascular implants. Proactive coating of decellularized implants represents a promising approach, however, little is known about the in vivo fate of coated agents over time. Detergent-decellularized aortic rat conduits (n = 24) were coated with covalently Alexa488-labelled (green emission) fibronectin (FN; 50 µg/ml, 24 hours) and implanted in the infrarenal aorta of wildtype Wistar rats (Group A; n = 12). Uncoated implants served as controls (Group B; n = 12). Before implantation and at postoperative day 1 and week 1, 4 and 8, fluorescence-based detection of FN coating was performed. Cellular repopulation was examined by histology and immunohistochemistry. All rats survived without clinical or sonographic signs of lower body malperfusion. Confocal microscopy of the aortic conduits revealed bright green FN fluorescence before and 1 day after implantation on the luminal as well as on the adventitial surface. The signal intensity decreased after 1 week, but was still present after 4 and 8 weeks. Four weeks after the operation, the luminal surface in the perianastomotic regions of Group A was completely neoendothelialized (vWF+) and a myofibroblast hyperplasia (αSMA+) with increased ratio of intima-to-media (I/M) thickness occurred. After 8 weeks I/M was significantly increased in Group A versus Group B (p < 0.01). At the same time point, medial repopulation starting at the adventitial zone was observed in group A, while only marginal repopulation occurred in group B (p < 0.001). In both groups vonKossa staining revealed sparse medial calcification and staining against inflammatory cell markers (CD3 & CD68) was negative. In our standardized rat transplantation model, a biofunctional protein coating of cardiovascular implants in the systemic circulation proved feasible and persistent up to 8 weeks. FN surface coating of aortic conduits induced a significantly increased medial recellularization, originating from the adventitial surface. The role of intimal hyperplasia and the relevance thereof needs further investigation.