Dolph Houben

107 Neoangiogenensis, transplant viability and molecular analysis of bone VCA 5 Neo-angiogenesis markers We examined the biological effect of different genes associated with neo-angiogenesis. Endothelial growth factor-like 6 ( EGFL6 ), which is a member of the epidermal growth factor (EGF) repeat superfamily, promotes endothelial cell migration and angiogenesis by activation of extracellular signal-regulated kinase. In bone , EGFL6 mediates cross-talk between endothelial cells and osteoblasts by this mechanism [15, 18] . Hypoxia-inducible factor 1 alpha ( HIF1A ) is a master regulator of cellular response to hypoxia in tissues. Vascular endothelial growth factor A ( VEGFA ) is one of the most important growth factors for regulation neo-angiogenesis. Cluster differentiation-34 ( CD34 ) is a transmembrane protein on the vascular associated tissue and hence higher expression of CD34 may correlate with increased presence of vascular tissue. A biologically and statistically significant (p=0.03) increase in the expression of EFGL6 was found for the patent AV-bundle group (Fig. 4). In addition, a trend towards higher expression of HIF1A was found for the implementation of an AV-bundle (p=0.07). VEGFA and CD34 were expressed in all groups with no median significant difference between the groups. Thus, the implementation of an AV-bundle seems to have a positive biological effect on neo-angiogenesis markers ( EGFL6/ HIF1A ) measured by gene expression analyses (Fig. 4). Discussion The ideal reconstructive method for large bone defects is one that functions immediately and is biologically equivalent to the missing bone segment. It should provide immediate strength, permit stable internal fixation, heal promptly and remain viable to resist infection, while resisting late structural failure by active bone remodeling. Transplantation of living allogenic bone is a potential candidate for such a ‘perfect’ solution—but only if the appreciable risks of long-term immunosuppression can be avoided. We have sought to replace the allogenic bone nutrient blood supply with an autogenous neoangiogenic blood supply to allow survival with only short-term immunosuppression. This has shown promise in prior small animal studies from our laboratory- but required a large animal study before consideration of this methodology in clinical practice. This porcine orthotopic tibial defect model was developed for this purpose. Our study which reports results at 20 weeks after transplantation surgery provides further insights into the potential future clinical utility of our method for bone vascularization. In long bones, approximately 70% of the bone is vascularized by longitudinal endosteal blood supply and the remaining 30% is provided by periosteal blood supply [7, 19] . A vascularized bone autograft, such as the fibular free bone flap will maintain blood flow long-term, while a bone VCA pedicle will thrombose without sustained immunosuppression [1, 2, 4, 20] . This study advances previous work based on small experimental models by evaluating a novel method of VCA transplantation that requires neither systemic drug immunosuppression nor induction of donor-specific tolerance. Instead, surgically-induced autogenous neo-angiogenesis maintains VCA viability long-term [1, 2, 4, 5] .