Bioengineering Suprachoroidal Pro-Angiogenic VEGF/bFGF Implants for Induction of Subretinal Neovascularization in the Rabbit

Abstract

Abstract: : Purpose: To evaluate the potential for induction of subretinal neovascularization by sustained-release VEGF/bFGF Hydron polymeric implants in the rabbit. Methods: A total of 6 New Zealand white albinos and 20 Dutch belt pigmented rabbits were utilized; 3 eyes (2 pigmented & 1 albino) received blank non-biodegradable Hydron pellets as negative controls. Rabbits were divided into groups that received either bFGF (n=3), VEGF (n=7) or bFGF + VEGF (n=10) via suprachoroidal implantation (inferior to the optic nerve) of pellets containing the growth factor(s) (GF). Surgery was performed under general anesthesia. Follow-up exams were performed under sedation. Pupil dilation was achieved with both topical myfrin (2.5%) and mydriacyl (1%). Animals were sacrificed at 3 or 4 weeks after implantation. Fluorescein angiography (FA) was performed at 2 and 4 weeks. Upon enucleation, eyes were dissected at the area of implantation. Tissues were then fixed in formalin and embedded in paraffin for serial sectioning. General morphology of cells and tissues was examined at the light microscopic level using H & E and PAS staining. Immunoperoxidase staining was performed with an antibody to CD-31 for labeling endothelial cells. Results: No retinal detachments were observed after pellet implantation. Controls exhibited what appeared to be a mild foreign-body reaction to the blank pellets in the suprachoroidal space. In the groups that received growth factors, fluorescein leakage was observed at 2 and 4 weeks. Histological examination revealed various degrees of sub-retinal and suprachoroidal neovascularization, pigment cell dispersion, fibrous metaplasia, and areas of focal degeneration and/or hypertrophy of the RPE. An inflammatory response was occasionally seen at the site of implantation. Positive immunostaining by the endothelial marker CD-31 was found in areas adjacent to the RPE and in peri-retinal vasculature. Conclusion: This preliminary study demonstrated evidence that suprachoroidally implanted Hydron pellents may be a viable delivery system for growth factor stimulation of subretinal neovascularization. However, the data is limited to a short time course. Introducing vascular-specific growth factors with this methodology at longer time points with continued FA monitoring could provide further mechanistic insight and reveal new strategies for studying models of AMD and other forms of ocular neovascular diseases.

Keywords: age-related macular degeneration • animal model • growth factors/growth factor receptors