Sustained delivery of FGF-1 increases vascular density in comparison to bolus administration

The use of growth factors for the therapeutic stimulation of neovascularization in regenerative medicine has been extensively investigated, but the inability to control their temporal delivery may limit clinical success. A strategy that delivers continuous therapeutic concentrations of growth factors may increase the protein's efficacy. The present study investigates the ability of sustained delivery of fibroblast growth factor-1 (FGF-1), to induce neovascularization in vivo. Alginate microbeads were synthesized to release active FGF-1 for three weeks. Microbeads loaded with FGF-1 (total amount 150 ng) were implanted into a surgically created omentum pouch in rats and were compared to control empty microbead implants and a single bolus injection of 150 ng of FGF-1 with empty microbead implant. Animals were sacrificed at either 3 or 6 weeks post implantation and omenta were analyzed for vascular density and mural cell interactions. Vascular area for bolus FGF-1 and FGF-1 loaded microbeads was higher than control at 3 weeks. At 6 weeks, vascular density in the group with FGF-1 loaded microbeads was significantly higher than the group with bolus administration of FGF-1, primarily due to an increase in the number of vessels less than 20 µm in diameter. Vascular density in omenta of the group receiving the bolus FGF-1 returned to control levels by 6 weeks. Staining for smooth muscle actin showed that 50% of vessels had associated mural cells. There was a trend of increased mural cell staining at 6 weeks for the FGF-1 loaded beads compared to bolus FGF-1 and control levels. Results in these studies suggest that sustained release of FGF-1 increases the duration of the vascular response in contrast to a bolus injection of FGF-1.