Decellularized Allogeneic Heart Valves Demonstrate Self-Regeneration Potential after a Long-Term Preclinical Evaluation

Abstract

Tissue-engineered heart valves are proposed as novel viable replacements granting longer durability and growth potential. However, they require extensive in vitro cell-conditioning in bioreactor before implantation. Here, the propensity of non-preconditioned decellularized heart valves to spontaneous in body self-regeneration was investigated in a large animal model. Decellularized porcine aortic valves were evaluated for right ventricular outflow tract (RVOT) reconstruction in Vietnamese Pigs (n = 11) with 6 (n = 5) and 15 (n = 6) follow-up months. Repositioned native valves (n = 2 for each time) were considered as control. Tissue and cell components from explanted valves were investigated by histology, immunohistochemistry, electron microscopy, and gene expression. Most substitutes constantly demonstrated in vivo adequate hemodynamic performances and ex vivo progressive repopulation during the 15 implantation months without signs of calcifications, fibrosis and/or thrombosis, as revealed by histological, immunohistochemical, ultrastructural, metabolic and transcriptomic profiles. Colonizing cells displayed native-like phenotypes and actively synthesized novel extracellular matrix elements, as collagen and elastin fibers. New mature blood vessels, i.e. capillaries and vasa vasorum, were identified in repopulated valves especially in the medial and adventitial tunicae of regenerated arterial walls. Such findings correlated to the up-regulated vascular gene transcription. Neoinnervation hallmarks were appreciated at histological and ultrastructural levels. Macrophage populations with reparative M2 phenotype were highly represented in repopulated valves. Indeed, no aspects of adverse/immune reaction were revealed in immunohistochemical and transcriptomic patterns. Among differentiated elements, several cells were identified expressing typical stem cell markers of embryonic, hematopoietic, neural and mesenchymal lineages in significantly higher number and specific topographic distribution in respect to control valves. Following the longest follow-up ever realized in preclinical models, non-preconditioned decellularized allogeneic valves offer suitable microenvironment for in vivo cell homing and tissue remodeling. Manufactured with simple, timesaving and cost-effective procedures, these promising valve replacements hold promise to become an effective alternative, especially for pediatric patients.

Decellularized aortic conduits: could their cryopreservation affect post-implantation outcomes? A morpho-functional study on porcine homografts

“…From our previous experience [19][20][21], spontaneous tissue-guided regeneration of acellular scaffolds from native heart valves proved to be an appealing technique for a straight-forward and functional clinical application. Previous studies utilize as animal model the juvenile sheep and more recently also the elderly sheep [24][25][26].…”

“…AVCs from both groups were implanted in 12-month-old VPs (54.3 ± 2.5 and 69.0 ± 3.7 kg for females and males, respectively) using beating heart cardiopulmonary bypass. Surgical procedure and postoperative management were performed as previously described [19][20][21].…”

“…AVCs were explanted under general anesthesia 15 months after implantation, and animals were euthanized with Tanax [20]. Both D and DC AVCs were excised under aseptic conditions, examined macroscopically, and documented photographically.…”

“…In fact, it provides a suitable preservation of the texture of native valve interstitium and hemodynamic performance [15][16][17], with concurrent removal of the xenoantigen galactose-α-1,3-galactose (alpha-gal) [18]. In addition, TRICOL-treated porcine aortic valve conduits (AVCs) were shown to exhibit physiological performance for up to 15 months after implantation in Vietnamese Pigs (VPs) as well as permissivity to repopulation by recipient's cells and tissue remodeling capability, as revealed by ex vivo morphological analyses [19,20].…”

Nanopatterned acellular valve conduits drive the commitment of blood-derived multipotent cells

“…4,15 In contrast, sodium cholate-and deoxycholate-based methods are useful to achieve fully nude matrices, with high in vitro and/or in vivo repopulation potentialities. [16][17][18][19] Recently, the development of decellularized xenografts or homografts with self-regeneration potential is considered as an attractive option to obtain novel viable replacements granting longer durability and avoiding the extensive in vitro cell conditioning. Various studies have already reported in situ recellularization of decellularized xenografts and homografts in animal models highlighting variable success rate in dependence on the adopted decellularization method or used graft typology (xenograft or homograft).…”