Abstract 133: HUVECs Support Bone Formation Of ADSC-loaded Osteogenic Matrices In The Rat AV Loop Model

Abstract

Purpose: Large volume bone defects can be challenging for the reconstructive surgeon with regard to donor side morbidity. An elegant strategy to circumvent the limiting donor side morbidity is the generation of bioartificial bone tissue. Bearing in mind that the interplay between angiogenesis and osteogenesis is a crucial prerequisite we set our focus on the microvascular endothelium. The microvascular network does not only support oxygen and nutrition supply but also plays an important role in osteogenic differentiation via heterotypic cell contacts. Using an arteriovenous fistula (AV loop), the surgically induced angiogenesis is a powerful tool to enhance intrinsic vascularization of osteogenic matrices. Due to their easy isolation, expansion and osteogenic differentiation potential adipose derived stem cells (ADSCs) are a promising cell source for bone tissue engineering applications. This study aimed at the generation of bioartificial bone tissue using osteogenic differentiated human ADSCs and human umbilical vein endothelial cells (HUVECs) embedded in a hydroxyapatite matrix vascularized by an AV loop. Methods: An osteogenic composite scaffold was generated using hydroxyapatite granula and fibrin. Four experimental groups were performed. Group A represented the control group without cells. The other groups contained 2 x 106 HUVECs (group B), ADSCs (group C) and both cell types (group D). Intrinsic vascularization was induced using an arteriovenous fistula (AV loop) between the saphenous artery and vein connected with a venous interponat. The osteogenic scaffolds and the AV loop were embedded in a porous titanium chamber, combining extrinsic and intrinsic vascularization, fixed subcutaneously in the hind leg of RNU rats. Explantation and histological analysis of the specimen was performed after 6 weeks. Results: In all experimental groups we were able to prove incipient vascularization of the matrices with newly formed fibrovasculare tissue originating from the AV loop. In all cell containing groups vascularized bone tissue was found with significantly more bone tissue in the ADSC-HUVEC coimplantation group. Interestingly, the cell implantation did not affect the matrix vascularization. Conclusion: For the first time we successfully demonstrated vascularization and human bone tissue formation in the rat AV loop model using ADSCs and/or HUVECs. Moreover, the coimplantation of ADSCs and HUVECs seems to be advantageous compared to the single cell use. Taken together the coimplantation of ADSCs and HUVECs is a promising approach for bone tissue engineering applications.