Oxidants, antioxidants and mitochondrial function in non-proliferative diabetic retinopathy

Abstract

Background: Diabetic retinopathy (DR) is a preventable cause of visual disability. The aims of the present study were to investigate levels and behavior oxidative stress markers and mitochondrial function in non-proliferative DR (NPDR) and to establish the correlation between the severity of NPDR and markers of oxidative stress and mitochondrial function.

Methods: In a transverse analysis, type 2 diabetes mellitus (T2DM) patients with mild, moderate and severe non-proliferative DR (NPDR) were evaluated for markers of oxidative stress (i.e. products of lipid peroxidation (LPO) and nitric oxide (NO) catabolites) and antioxidant activity (i.e. total antioxidant capacity (TAC), catalase, and glutathione peroxidase (GPx) activity of erythrocytes). Mitochondrial function was also determined as the fluidity of the submitochondrial particles of platelets and the hydrolytic activity of F0 /F1 -ATPase.

Results: Levels of LPO and NO were significantly increased in T2DM patients with severe NPDR (3.19 ± 0.05 μmol/mL and 45.62 ± 1.27 pmol/mL, respectively; P < 0.007 and P < 0.0001 vs levels in health volunteers, respectively), suggesting the presence of oxidative stress. TAC had significant decrease levels with minimum peak in severe retinopathy with 7.98 ± 0.48 mEq/mL (P < 0.0001). In contrast with TAC, erythrocyte catalase and GPx activity was increased in patients with severe NPDR (139.4 ± 4.4 and 117.13 ± 14.84 U/mg, respectively; P < 0.0001 vs healthy volunteers for both), suggesting an imbalance between oxidants and antioxidants. The fluidity of membrane submitochondrial particles decreased significantly in T2DM patients with mild, moderate, or severe NPDR compared with that in healthy volunteers (P < 0.0001 for all). Furthermore, there was a significant increase in the hydrolytic activity of the F0 /F1 -ATPase in T2DM patients with mild NPDR (265.07 ± 29.55 nmol/PO4 ; P < 0.0001 vs healthy volunteers), suggesting increased catabolism.

Conclusions: Patients with NPDR exhibit oxidative deregulation with decreased membrane fluidity of submitochondrial particles and increased systemic catabolism (mitochondrial dysfunction) with the potential for generalized systemic damage in T2DM.

Keywords: diabetes mellitus; diabetic retinopathy; membrane fluidity; nitrosative stress; oxidative stress; 糖尿病，糖尿病视网膜病变，膜流动性，硝化应激，氧化应激.

© 2013 The Authors. Journal of Diabetes published by Ruijin Hospital, Shanghai Jiaotong University School of Medicine and Wiley Publishing Asia Pty Ltd.

Figures

Fig 1

Oxidants (a,b) and antioxidants (c–e) in type 2 diabetes mellitus patients with mild, moderate, or severe non-proliferative diabetic retinopathy (NPDR). (a) Products of lipid peroxidation (LPO), given as malondialdehyde (MDA) and 4-hydroxyalkenals (4HDA), were highest in patients with severe NPDR (3.29 ± 0.05 μmol/L; P < 0.017 compared with control), as were levels of (b) nitric oxide (NO) catabolites (45.62 ± 1.27 pmol/mL; P < 0.0001 compared with control). (c) Total antioxidant capacity (TAC) was significantly decreased in all three groups of NPDR, with the greatest decrease seen in patients with severe NPDR (7.98 ± 0.48 mEq/mL; P < 0.0001 compared with control). (d,e) Erythrocyte catalase and glutathione peroxidase (GPx) activity was higher in patients with NPDR, with maximum catalase activity seen in patients with mild retinopathy (142 ± 6 U/mg protein; P < 0.0001 compared with control), whereas GPx activity was highest in those with severe retinopathy (117 ± 15 U/min/mg protein; P < 0.0001 compared with control). Data are the mean ± SE. *P < 0.05 compared with healthy volunteers.

Fig 2

Mitochondrial function in type 2 diabetes mellitus patients with mild, moderate, or severe non-proliferative diabetic retinopathy (NPDR). (a) The fluorescence ratio of the excimer (Ie) to monomer (Im) decreased significantly in patients with NPDR, with the greatest decrease seen in patients with mild retinopathy (Ie/Im 0.12 ± 0.01; P < 0.0001 compared with control). (b) Significant increases were seen in the hydrolytic activity of F0/F1-ATPase in all three groups of NPDR, with the greatest increase seen in patients with mild retinopathy (300 ± 38 nmol PO4; P < 0.0001 compared with control). This could mean lower ATP synthesis with excessive production of cellular catabolism. Data are the mean ± SE. *P < 0.05 compared with healthy volunteers.

Fig 3

Results of Spearman's correlation tests. Significant positive correlations were found between (a) the products of lipid peroxidation (LPO) and nitric oxide (NO), as well as between (b) LPO and diminished total antioxidant capacity (TAC; P < 0.010). In addition, significant positive correlations were found between (c) LPO and uric acid (P < 0.025), (d) increased catalase and glutathione peroxidase (GPx) activity (P < 0.007), and (e) increased NOx levels and TAC (P < 0.010). We can assume that there is oxidant, antioxidant, and mitochondrial dysregulation in chronic type 2 diabetes mellitus.