Cell-Demanded Liberation of VEGF ₁₂₁ From Fibrin Implants Induces Local and Controlled Blood Vessel Growth

Abstract

Abstract-Although vascular endothelial growth factor (VEGF) has been described as a potent angiogenic stimulus, its application in therapy remains difficult: blood vessels formed by exposure to VEGF tend to be malformed and leaky. In nature, the principal form of VEGF possesses a binding site for ECM components that maintain it in the immobilized state until released by local cellular enzymatic activity. In this study, we present an engineered variant form of VEGF, ␣ 2 PI 1-8 -VEGF 121 , that mimics this concept of matrix-binding and cell-mediated release by local cell-associated enzymatic activity, working in the surgically-relevant biological matrix fibrin. We show that matrix-conjugated ␣ 2 PI 1-8 -VEGF 121 is protected from clearance, contrary to native VEGF 121 mixed into fibrin, which was completely released as a passive diffusive burst. Grafting studies on the embryonic chicken chorioallantoic membrane (CAM) and in adult mice were performed to assess and compare the quantity and quality of neovasculature induced in response to fibrin implants formulated with matrix-bound

Preventing hypoxia-induced cell death in beta cells and islets via hydrolytically activated, oxygen-generating biomaterials

“…With low adhesion properties, the PDMS insert can be easily removed once the embedded solid peroxide is expired or the local supplementation of oxygen is no longer desired. Although one potential drawback of this approach is that hypoxia inducible factor pathways that stimulate release of angiogenic growth factors would be suppressed and potentially delay implant vascularization, we anticipate that this effect could be mitigated through the codelivery of proangiogenic factors (13,14). Overall, we have demonstrated the usefulness of our materials to mitigate hypoxia-induced cell death, which would be highly desirable for preserving the viability of the transplanted cells after transplant, particularly for implants for which cell dosage is critical for efficacy, such as in the transplantation of β cells for type 1 diabetes.…”

“…Limiting or eliminating the hypoxic period between implantation and the development of a fully functional, intradevice, vascular network would dramatically reduce hypoxia-induced cell death and permit for more clinically translatable devices. Such methods include prevascularization of the transplant site (12), hastening vascularization through the delivery of growth factors (13,14), incorporation of oxygen carriers within biomaterials (15), or the in situ generation of supplemental oxygen (16)(17)(18)(19). In situ oxygen generation is a highly desirable approach, in that it does not require multiple surgeries and provides supplemental oxygen immediately upon implantation.…”

Intussusceptive angiogenesis: Its emergence, its characteristics, and its significance

“…The opposite is found in avascular tissue overexpressing VEGF, what induces vascular sprouting based on a chemoattractive gradient (Auerbach et al, 2003). Recently published results indicated that, in addition to the amount of the applied (expressed) VEGF, the release modality (slow vs. rapid liberation) is a crucial factor for the onset of angiogenic modality and vascular morphogenesis (Ehrbar et al, 2004).…”

In situ cell manipulation through enzymatic hydrogel photopatterning

“…These signals can be readily modified to have photoreactive groups, which is not the case for full-length proteins. We used recombinant VEGF 121 engineered with an exogenous Q-peptide domain at the N terminus to enable enzymatic crosslinking 25 . On localized uncaging of the tethered caged Kpeptide, hydrogel films were immersed in FXIIIa-containing buffer together with VEGF 121 .…”

“…S9). Using a HUVEC proliferation assay 25 , we compared the mitogenic activity of both PEG-VEGF 121 constructs to native VEGF 121 . At a relatively low (that is, nonsaturating) concentration of 5 ng ml −1 , a significant reduction in the activity was found for nonspecifically coupled PEG-VEGF 121 , in contrast to the site-specifically modified version ( Supplementary Fig.…”