Tissue-engineered heart valve leaflets: does cell origin affect outcome?

Abstract

Background: We previously reported the successful creation of tissue-engineered valve leaflet constructs and the implantation of these autologous tissue leaflets in the pulmonary valve position in a lamb model. The optimal cell origin for creating these valve leaflets remains unclear. This study was designed to compare dermal with arterial wall myofibroblasts as the cells of origin for the leaflet constructs.

Methods and results: Mixed cell populations of endothelial cells and fibroblasts were isolated from ovine femoral arteries or subdermis and then expanded in vitro. A synthetic biodegradable polymer scaffold was then seeded with the cultured cells. The tissue scaffold was composed of a polyglactin woven mesh sandwiched between two nonwoven polyglycolic acid mesh sheets, which measured 3x3 cm in size and 3.2 mm in thickness. The cell-seeded polymer construct was implanted to replace one pulmonary valve leaflet in the same juvenile animal from which the cells had originally been obtained. Using cardiopulmonary bypass, the right posterior leaflet of the pulmonary valve was completely resected and replaced with an autologous engineered valve leaflet. In group D (n=5), the cells were obtained from subdermis, and in group A (n=4), they were obtained from the arterial wall. Eight to 10 weeks after leaflet implantation, the animals were killed, and the implanted valve leaflets were examined histologically, biochemically, and biomechanically. The dimensions of each tissue-engineered leaflet (TEL) were compared with those of the two remaining native valve leaflets to obtain a growth index. A 4-hydroxyproline assay was performed to evaluate collagen content. Leaflet tensile strength was evaluated in vitro by using a Vitrodyne V-1000 mechanical tester. Factor VIII and elastin stains were performed to histologically assess the presence of endothelial cells and elastin, respectively. In all animals, the TEL persisted in the pulmonary valve position after 8 to 10 weeks, and all polyglycolic acid polymer had been degraded. Group A leaflets had a higher growth index (0.86+/-0.11) than group D (0.41+/-0.08) (P<.05). Macroscopically, the group D leaflets appeared thicker and contracted. Histologically, elastic fibers were more abundant in group A than in group D. Total collagen content and biomechanical testing showed no differences between groups. Leaflets from both groups had positive staining for factor VIII on the surface, confirming growth of endothelial cells to cover the TEL.

Conclusions: Autologous TEL derived from vascular fibroblasts seem to develop functionally and morphologically like the native valve leaflets in the pulmonary circulation. Use of arterial myofibroblasts for the creation of TEL seems preferable to dermal fibroblasts with current tissue culture conditions.