The Effect Of Intermittent High Glucose On Oxidative Stress And Inflammatory Injury In Human Retinal Pigment Epithelial Cells

Objective: The diabetic retinopathy (DR) is one of the common chronic microvascular complications of diabetes, it is also a blinding disease, the pathogenesis underlying retinopathy is complicated and yet not well clarified, the cytotoxicity of high glucose is one of the most important reasons. In the past years, people paid more attention on constant high glucose, both in the clinical research and the fundamental research. Recently, the study for the mechanisms of diabetes developed gradually, people come to realize the importance of intermittent high glucose. Recent studies showed that the diabetic complications not only associated with the constant high glucose, but also associated with the intermittent high glucose. More and more studies proved that the intermittent high glucose can cause more serious damages than the constant high glucose, but the pathogenesis is not clear. Lots of studies showed that the intermittent high glucose caused heavier oxidative stress and inflammatory reaction. People have focused on the damages of intermittent high glucose, there are plenty of studies about the influences of intermittent high glucose on the diabetic complications, but few studies are about the effect of intermittent high glucose on the diabetic retinopathy. Our study is to compare the effects of intermittent and constant high glucose on the oxidative stress and inflammatory injury in Human Retinal Pigment Epithelial cells (HRPE), and to explore the pathogenic pathways of intermittent high glucose which accelerated the diabetic retinopathy. Through this study we can provide theoretical and experimental foundation for the diabetic retinopathy.Methods: Human retinal pigment epithelial cells were cultured, and were randomly divided into four groups: normal glucose control group (5.5mmol/L glucose, NG), constant high glucose group (33mmol/L glucose, HG),intermittent high glucose group (33mmol/l glucose for three hours, at an interval of two hours of 5.5mmol/L glucose, such intermittent exposure was repeated three times a day and the cells were exposed to 33mmol/L glucose in the night, IHG) and high mannitol group(33mmol/L mannitol, MG). They were exposed to experimental conditions for 72 hours. The activity of the total superoxide (T-SOD) and the levels of malondialdehyde (MDA), glutathione (GSH), intercellular cell adhesion molecule-1 (ICAM-1) in supernatant were measured in 24 hours, 48 hours, and 72 hours.Results: 1 After 24 hours, 48 hours and 72 hours, compared with normal glucose group, the activity of T-SOD in high glucose group and intermittent high glucose both decreased (P<0.01, respectively) at any moment, especially the intermittent high glucose group, when compared with the constant high glucose group, the intermittent high glucose group significantly decreased (P <0.01, respectively).2 After 24 hours, 48 hours and 72 hours, compared with normal glucose group, the level of GSH in high glucose group and intermittent high glucose both decreased (P<0.01,respectively) at any moment, especially the intermittent high glucose group, when compared with the constant high glucose group, the intermittent high glucose group significantly decreased (P<0.01, respectively).3 After 24 hours, 48 hours and 72 hours, compared with normal glucose group ,the level of MDA in high glucose group and intermittent high glucose both increased (P<0.01,respectively) at any moment, especially the intermittent high glucose group, when compared with the constant high glucose group, the intermittent high glucose group significantly increased(P<0.01, respectively).4 After 24 hours, 48 hours and 72 hours, compared with normal glucose group, the level of ICAM-1 in high glucose group and intermittent high glucose both increased (P<0.01, respectively) at any moment, especially the intermittent high glucose group, when compared with the constant high glucose group, the intermittent high glucose group significantly increased (24h P<0.01, 48h P<0.01, 72h P<0.05, respectively). 5 After 24 hours, 48 hours and 72 hours, compared with normal glucose group , there were no significant difference for each index between mannitol group and normal glucose group (P>0.05) at any moment .Compared with constant high glucose group and intermittent high glucose, the mannitol group is significantly different from them (P <0.01,respectively).Conclusions: Both the constant high glucose and the intermittent high glucose damaged the human retinal pigment epithelial cells, they made the levels of MDA and ICAM-1increased, the levels of SOD and GSH decreased. Compared with the constant high glucose, the intermittent high glucose caused more dramatic changes. Intermittent high glucose caused a more serious oxidative stress and inflammatory injury to HRPE cells. Intermittent high glucose may be one of the most important risk factors of diabetic retinopathy.