Subretinal Injection of AAV2-CMV-hEPO to Diabetic Retina is Protective and Safe

Abstract

Purpose: Erythropoietin (EPO), a hormone known to protect both blood-retinal barrier (BRB) and neurons in early diabetic rat retina, was reported to be beneficial for patients with chronic diabetic macular edema who were unresponsive to current therapies. To maintain a long-term effect and to avoid side effects due to repeated intraocular injections, the efficacy and safety of adeno-associated virus, serotype 2 (AAV2) mediated human EPO expression (AAV2-CMV-hEPO) were studied on experimental diabetic rats after subretinal administration.

Methods: Male Sprague-Dawley (SD) rats, Dark Agouti (DA) rats and C57BL/6 mice were used in this study. Hematocrit (Hct) was measured to prove the erythropoietic function of hEPO after intramuscular injection of the virus. The hEPO concentration was measured by ELISA. Diabetes was induced by intraperitoneal injection of streptozotocin (STZ, 60 mg/kg BW). Electroretinography (ERG) was applied to evaluate the retinal function in different intervals after the virus administration. Two weeks after diabetes onset, the subretinal injection of AAV2-CMV-hEPO or shame buffer (PBS) was performed. Four weeks later, Evans blue permeation (EBP) was determined to test BRB breakdown. Retinal cell apoptosis was measured by TUNEL. Retinal thickness and cell counts were examined under a light microscope. Neovascularization in retina and choroids were evaluated by both fluorescein angiography (FA) and immunostaining for flatmount.

Results: The serum hEPO was elevated 2 weeks after intramuscular injection of AAV2-CMV-hEPO, and Hct began to rise after 4 weeks. In the subretinal injection group, the expression of hEPO in aqueous humor, vitreous and retina follows both a dose- and time- dependent manner. In AAV2-CMV-hEPO treated diabetic group, BRB maintained, and retinal cell apoptosis was significantly reduced. Long-term expression of AAV2-CMV-hEPO did not induce neovascularization. The ERG results also demonstrated that the retinal function was not affected for at least one year after subretinal injection of AAV2-CMV-hEPO.

Conclusions: The present data demonstrate that the gene therapy with AAV2-CMV-hEPO delivered into subretinal space showed the long-term protection of BRB and retinal neurons in experimental diabetic rats. This therapy can safely maintain normal electrophysiologic function and be void of neovascularization formation in retina.

Keywords: 499 diabetic retinopathy • 615 neuroprotection • 503 drug toxicity/drug effects