Role of Oxidative Stress and Severity of Diabetic Retinopathy in Type 1 and Type 2 Diabetes

Background: Diabetic retinopathy (DR) is a sight-threatening complication of diabetes mellitus (DM). Oxidative stress generated on account of hyperglycemic state may lead to retinal abnormalities including DR.

Objectives: The aim of the study was to evaluate the status of antioxidant enzymes; superoxide dismutase (SOD), and catalase (CAT), in different stages of DR severity in subjects with type 1 DM (T1DM) and type 2 DM (T2DM).

Methods: The cross-sectional study enrolled 148 subjects with T1DM (n = 17), T2DM (n = 96), and nondiabetic controls (n = 35). Subjects with DM were divided into 2 subgroups based on DR severity (mild-to-severe nonproliferative DR [NPDR] and proliferative DR [PDR]), and serum glycated hemoglobin (HbA1c), lipid profile, SOD, and CAT were estimated.

Results: Both SOD and CAT levels were lower in diabetic subjects than nondiabetic controls. A significant positive correlation was found between HbA1C level and severity of DR (p < 0.0001). Levels of SOD and CAT varied significantly with DR severity in both diabetic groups at p < 0.05. Furthermore, levels of SOD and CAT were found to decrease significantly (p < 0.001) in DR (+) compared to DR (-) patients. Also, increased levels of HbA1c were significantly associated (p < 0.001) with decreased SOD in both subgroups (NPDR and PDR). DR severity was significantly associated with SOD and CAT in the NPDR and PDR subgroups (p < 0.05).

Conclusion: Oxidative stress and decreased antioxidant defenses are associated with DR progression to its PDR stage.