Extensive In Vivo Angiogenesis Following Controlled Release of Human Vascular Endothelial Cell Growth Factor: Implications for Tissue Engineering and Wound Healing

Abstract

Vascular endothelial cell growth factor (VEGF) has strong stimulating effects on vascularization. Though very potent, VEGF is rapidly degraded due to its short half-life and when administrated by uncontrolled and nonspecific methods; however, its systemic administration in large doses can cause harmful side effects. Controlled release technology would allow delivering desired levels of bioactive VEGF within extended periods and permit examination of the in vivo effects of the compound in a broader way. The objective of this study was to determine the in vitro release behavior of VEGF from calcium alginate microspheres and the potency of this controlled release system in promoting localized neovascularization at the subcutaneous site of the rat model. In vitro release of human VEGF165 (2 and 4 microg/cm3 microsphere) was studied for 3 weeks under static conditions at 25 degrees C, and daily hormone release was measured using a competitive enzyme immunoassay. Following an uncontrolled release within the first 4 days, a quite constant zero-order VEGF release of 50 to 90 and 70 to 120 ng/day was achieved from 2 and 4 microg/cm3 polymer loaded microspheres respectively. In vivo angiogenesis was studied for a period of 8 weeks and evaluated using immunoperoidase staining and histopathological measurements. In vivo studies with rats (n = 24) showed a considerable level of capillary network formation at the epigastric groin fascia of VEGF microsphere-implanted rats starting from the first week. The most extensive neovascularization was observed in the group with 3 week postimplanted 4 microg VEGF containing microspheres; this level of vascularization was quite similar after 8 weeks. While the control group showed no evidence of angiogenesis, the difference in VEGF-induced neovascularization is statistically significant (p < 0.03). Immunostaining of the specimens showed a strong relationship between the release of human VEGF and neovascularization. The controlled VEGF release system described here promotes vigorous angiogenesis and has applicability for tissue engineering and wound healing studies.

Fibrin Gel-Immobilized VEGF and bFGF Efficiently Stimulate Angiogenesis in the AV Loop Model

“…The axial type of vascularization allows vascularization and subsequent transfer of biomaterials independent of local conditions at the recipient site (27). The use of angiogenic factors may shorten the period between implantation and vascularization of matrices (7,8).…”

“…Vascularization from the periphery toward the center, which was defined as "extrinsic vascularisation" by Cassell and coworkers (6), and vascularization from a vascular axis radiating from the center toward the periphery, which represents an outgrowth from within, called "intrinsic vascularization." Angiogenic factors may be used to shorten the time period between implantation and vascularization of matrices (7,8). The most extensively tested angioinductive growth factors in animal models are basic fibrobast growth factor (bFGF) and vascular endothelial growth factor (VEGF).…”

Vascularization of Engineered Tissues: Approaches to Promote Angiogenesis in Biomaterials

“…Tight control over particle composition, size, wettability, and degradation profile allows regulated release kinetics of many drugs. For example, VEGF loaded in calcium alginate microparticles promoted formation of extensive capillary beds in local regions of implantation in rats [85]. These microparticles can also be incorporated into scaffolds to ensure more localized release of the growth factors.…”

Nanoprecipitated catestatin released from pharmacologically active microcarriers (PAMs) exerts pro-survival effects on MSC

“…The later phases may be critical for tissue repair and regeneration and a continuous slow release of a therapeutic peptide (e.g. 430 VEGF and CST) released by microspheres transporting cells on their 3D functionalized surface may be beneficial for tissue engineering strategies (Elçin et al, 2001;Madonna et al, 2015). However, this needs to be ascertained in vivo for CST, and it should be ascertained whether other conditions, such as fibronectin coating, may affect the release of the active peptide.…”