PURPOSE. Retinal ischemia/reperfusion (I/R) injury results in the generation of reactive oxygen species (ROS). The aim of this study was to investigate whether delivery of the manganese superoxide dismutase gene (SOD2) or the catalase gene (CAT) could rescue the retinal vascular damage induced by I/R in mice. METHODS. I/R injury to the retina was induced in mice by elevating intraocular pressure for 2 hours, and reperfusion was established immediately afterward. One eye of each mouse was pretreated with plasmids encoding manganese superoxide dismutase or catalase complexed with cationic liposomes and delivered by intravitreous injection 48 hours before initiation of the procedure. Superoxide ion, hydrogen peroxide, and 4-hydroxynonenal (4-HNE) protein modifications were measured by fluorescence staining, immunohistochemistry, and Western blot analysis 1 day after the I/R injury. At 7 days after injury, retinal vascular cell apoptosis and acellular capillaries were quantitated. RESULTS. Superoxide ion, hydrogen peroxide, and 4-HNE protein modifications increased at 24 hours after I/R injury. Administration of plasmids encoding SOD2 or CAT significantly reduced levels of superoxide ion, hydrogen peroxide, and 4-HNE. Retinal vascular cell apoptosis and acellular capillary numbers increased greatly by 7 days after the injury. Ϫ in retinal I/R injury was proven either directly by electron paramagnetic resonance or indirectly by showing diminished damage after administration of antioxidant drugs such as EGB 761 extracted from Ginkgo biloba, vitamin E, mannitol, catalase, and several other compounds. 2-6 The importance of ⅐ O 2 Ϫ is also indicated by the fact that a manganese superoxide dismutase mimetic and transgenic manganese superoxide dismutase inhibited I/R-induced retinal injury and diabetes-induced oxidative stress. 6 -8 Superoxide dismutase catalyzes the dismutation of ⅐ O 2 Ϫ to O 2 and the less reactive species, H 2 O 2 . Catalase is a potent scavenger of H 2 O 2 and provides another means of inhibiting oxidant stress. It prevents the formation of the more toxic hydroxyl radical (HO ⅐ ) resulting from the reaction of H 2 O 2 and ferrous ions. Thus, the production of catalase provides additional antioxidative protection during I/R. The delivery of SOD and catalase proteins has successfully prevented retinal I/R injury in rabbits. 8 A recent report showed that retinal ischemia and reperfusion cause capillary degeneration similar to diabetes. 6,10 demonstrated that transgenic mice that express elevated levels of manganese superoxide dismutase have higher antioxidant capacity and are protected from damage to the retinal vasculature (formation of acellular blood vessels) as a result of streptozotocin-induced diabetes. Berkowitz et al. 11 have recently shown that transgenic expression of SOD1, which encodes the cytoplasmic Cu/Zn superoxide dismutase, also protects retinal vasculature in the same diabetes model. However, overexpression of Cu/Zn superoxide dismutase caused retinal degeneration independent of diabetes. 11 The purpose of the present study was to assess the efficacy of manganese superoxide dismutase and catalase gene transfer on I/R-induced retinal capillary injury in mice. We investigated the effect of I/R injury on superoxide and hydrogen peroxide levels, apoptosis of retinal vascular cells, number of acellular capillaries, and levels of 4-hydroxynonenal (4-HNE) protein modifications. We also determined whether increased expression of superoxide dismutase and catalase protected against capillary injury. Our studies show that in this model there is an increase in capillary degeneration, superoxide radical and hydrogen peroxide production and 4-HNE in the retinas. Transfer of superoxide dismutase or catalase genes protected the retinal capillaries from ROS elevation and from I/R-induced injury
