Nonhuman Primate Models for Diabetic Ocular Neovascularization Using AAV2-Mediated Overexpression of Vascular Endothelial Growth Factor

Abstract

Neovascularization leads to blindness in numerous ocular diseases, including diabetic retinopathy, agerelated macular degeneration, retinopathy of prematurity, and sickle cell disease. More effective and stable treatments for ocular neovascularization are needed, yet there are major limitations in the present animal models. To develop primate models of diabetic retinopathy and choroidal neovascularization, rhesus monkeys were injected subretinally or intravitreally with an adeno-associated virus (AAV)-2 vector carrying the cDNA encoding human vascular endothelial growth factor (VEGF). Overexpression of VEGF was measured by intraocular fluid sampling over time. Neovascularization was evaluated by ophthalmoscopy through angiography, optical coherence tomography, and ultimately histopathology. Overexpression of VEGF through AAV2 results in rapid development of features of diabetic retinopathy or macular edema, depending on the targeted cell type/mode of production of VEGF and diffusion of VEGF. Nonhuman primate models will be useful in testing long-term safety and efficacy of novel therapeutic agents for blinding neovascular diseases. Diabetes 54:1141-1149, 2005 D iabetic retinopathy is the most common microvascular complication of diabetes, resulting in blindness for Ͼ10,000 people with diabetes per year. Chronic diabetes can also result in macular edema, neovascular glaucoma, and neovascularization of the optic disc. There are other conditions in which such pathology can develop, including retinopathy of prematurity, sickle cell retinopathy, and retinal vein occlusion.Diabetic ocular neovascularization and related conditions are leading causes of blindness around the world.Current treatment options for retinal neovascularization are limited to interventional (1-3) or surgical (4,5) procedures. These treatments are often suboptimal, as they are only suitable for a subset of patients, may stabilize vision loss for only a limited time, and can, themselves, destroy functioning retina. In addition, recurrence of neovascularization is frequent.Therefore, a number of experimental antiangiogenic therapies have evolved over the last couple of years (rev. in 6). Their aim is to inhibit vessel growth by blocking angiogenic factors like vascular endothelial growth factor (VEGF) using antibodies (7,8), interference RNA (9), or chimeric or soluble VEGF receptor proteins (10,11). Alternatively, they try to induce antiangiogenic activity using enzyme inhibitors (12), fungus-derived antiangiogenic agents (13), or viral vector-mediated delivery of a range of compounds including pigment epithelium-derived factor (14,15), tissue inhibitor of metalloproteinases-3, endostatin, or angiostatin (16).Even though some of these experimental therapies have been moved to human clinical trials already, the lack of large animal models for ocular neovascularization prevents thorough testing of these substances beforehand. In addition, the paucity of available rodent animal models makes it difficult to select the most appropriate targets for anti...

Long-term global retinal microvascular changes in a transgenic vascular endothelial growth factor mouse model

“…The vascular changes in trVEGF029 differ from two other models in which VEGF was upregulated via a transgene or via intravitreal or subretinal injection of a recombinant adeno-associated virus carrying the gene encoding VEGF (AAV.VEGF) [21,35] with high protein levels leading to severe neovascularisation, an immune reaction and photoreceptor destruction [21,36]. In comparison, moderate VEGF expression in another model induced by AAV.VEGF gene transfer also produced a mild phenotype with features similar to trVEGF029 and with no immune reaction elicited [37].…”

Gene Therapies for Neovascular Age-Related Macular Degeneration

“…The four main biological effects of VEGF, as determined by Ferrara and Gerber (2001), are increase in vascular permeability, growth and proliferation of vascular endothelial cells, migration of vascular endothelial cells, and survival of immature endothelial cells by preventing apoptosis. The role of VEGF in inducing retinal neovascularization and vascular leakage has been confirmed in several animal models using ocular gene delivery of VEGF (Yu et al 1999;Rakoczy et al 2003;Lebherz et al 2005;Julien et al 2008). Since the original study in rhesus monkeys (Ryan 1979), laser rupture of Bruch's membrane has become a common technique to induce CNV in different animal species.…”

Ocular Vascular Endothelial Heterogeneity

“…Rodents and other mammals injected systemically with streptozotocin develop a diabetic syndrome that is characterized by the vascular changes also observed in patients with background diabetic retinopathy [55]. Intravitreal injection of adenoviral vector encoding VEGF may induce iris and inner retinal neovascularization in the eyes of rhesus monkeys [56]. Very recently, Zhang et al [57] presented a rat model of retinal vein -central or branch -occlusion, which was adapted from other published animal models.…”