Attenuated Superoxide Dismutase Induction in Retinal Cells in Response to Intermittent High Versus Continuous High Glucose

High glucose, particularly in oscillating conditions, produces an increase in oxidative stress and has been shown to result in an increase in diabetic complications, retinopathy in particular. The hypothesis of this work was that chronic exposure to intermittent high glucose results in an attenuated induction of an antioxidant response as compared to continuous high glucose exposure in isolated retinal cells In this work, human retinal pericytes and ARPE-19 cells were exposed to 5 mM or 30 mM continuous high glucose or to 5 mM oscillating daily with 30 mM glucose for 14 days. Levels of antioxidant proteins and activity and levels of reactive species protein adducts were measured. We demonstrate that the induction of total cellular superoxide dismutase (SOD) activity in isolated retinal pericytes and ARPE-19 cells is significantly attenuated in response to oscillating glucose as compared to continuous high glucose. We also show that a marker of nitrosative stress, 3-nitrotyrosine and a general marker of oxidized proteins, OxyBlo^TM, were significantly increased in both cell types exposed to intermittent high glucose as compared to continuous high glucose. Finally, we show that levels of nitrated MnSOD were increased in response to intermittent high versus continuous high glucose and that the addition of a reactive nitrogen species scavenger to oscillating glucose resulted in significantly increased levels of SOD activity. In conclusion, our results demonstrate for the first time a link between intermittent high glucose and a decreased induction of an antioxidant response of SOD.