Comparison of catalase, glutathione peroxidase and malondialdehyde levels in tears among diabetic patients with and without diabetic retinopathy

BACKGROUND: Various studies suggest that oxidative stress has a role in the etiology of diabetes mellitus (DM) and its complications. Detection of antioxidant enzymes and malondialdehyde (MDA) level in ocular fluid may provide the possible biomarkers for monitoring the progression of diabetic retinopathy (DR). The aim of this study was to compare catalase, glutathione peroxidase (GPx) and MDA levels in tears among diabetic patients with and without DR.

METHODS: A cross-sectional study was conducted among type 2 DM patients. The patients were divided into three groups: no DR, non-proliferative DR (NPDR) and proliferative DR (PDR). Tears samples were collected using Schirmer strips for measurement of catalase, GPx and MDA.

RESULTS: A total of 171 patients were recruited in this study (no DR, 58 patients; NPDR, 57 patients; PDR, 56 patients). There was significant difference in the mean level of GPx in tears between the three groups (no DR, 658.08 ± 115.70 U/L; NPDR, 653.78 ± 87.90 U/L; PDR, 605.31 ± 107.47 U/L, respectively) before and after adjustment for covariates (p = 0.013 and p = 0.001, respectively). Bonferroni post-hoc analysis showed PDR group had significantly lower mean GPx level than in no DR (p=0.001) and NPDR (p=0.037) after adjustment for covariates. There was no significant difference of mean catalase and MDA in the tears between the three groups before and after adjustment for covariates.

CONCLUSION: This study demonstrated that diabetic patient with DR is associated with low level of GPx in tears, suggesting that this antioxidant enzyme is a potential biomarker for predicting the presence of DR.