Dynamic contrast-enhanced MRI to quantify VEGF-enhanced tissue-engineered bladder graft neovascularization: pilot study.

Tissue engineered organs require an immediately perfused vascular tree. Currently, neovascularization assessment requires animal sacrifice and graft harvest. In this pilot study we assess whether neovascularization of an engineered urinary bladder construct is enhanced with vascular-derived endothelial growth factor (VEGF) and assessable non-invasively with dynamic contrast-enhanced MRI (DCE-MRI). Rabbit bladder acellular matrix was hybridized with hyaluronic acid (ACM-HA), fortified with one of three concentrations (0 ng, 10 ng, or 20 ng per gram of tissue) of vascular-derived endothelial growth factor (VEGF), and grafted onto bladders in nine rabbits (3 per VEGF concentration). At 1, 2 and 3 weeks, one rabbit from each VEGF group underwent DCE-MRI and graft harvest. Microvasculature was quantified with scrial optical transverse sectioning of CD31 stained whole mounts using PCl software. Masson trichrome and H&E staining were used to assess cellular proliferation and fibrosis. There was a significant difference in mean microvascular area (MVA) between the 10 and 20 ng VEGF groups (230187 vs 477894 microm2, P=0.014) but not between the 0 and 10 ng groups (210497 microm2, P=0.21). Gadolinium uptake increased with MVA and correlated with it on linear regression analysis (Pearson's correlation coefficient r=0.71). At three weeks, stromal cellularity was greatest, and fibrosis was least, in the high VEGF group. This preliminary work demonstrates improved neovascularization of bladder constructs with VEGF fortification of ACM-HA and the feasibility of MRI as a non-invasive method to assume angiogenesis in tissue engineered constructs.