Diabetic Retinopathy - Pathology

Oxidative Stress - updated: 15 March 2008

Role of mitochondrial superoxide dismutase in the development of diabetic retinopathy

Invest Ophthalmol Vis Sci. 2006 Apr;47(4):1594-9

Kowluru RA, Atasi L, Ho YS.

PURPOSE: Apoptosis of retinal capillary cells is an early event in the pathogenesis of retinopathy in diabetes, and oxidative stress has been linked to accelerated apoptosis of retinal capillary cells. Mitochondria are the major endogenous source of superoxide, and superoxide is considered to be a causal link between elevated glucose and the major biochemical pathways postulated to be involved in the development of vascular complications in diabetes. The purpose of the present study is to determine the role of mitochondrial superoxide dismutase (MnSOD) in the development of diabetic retinopathy. METHODS: The effect of overexpression of MnSOD on glucose-induced endothelial cell oxidative stress, nitrosative stress, and apoptosis was determined by using bovine retinal endothelial cells. Furthermore, the effect of diabetes in rats (11 months' duration) on the activity and the mRNA expression of retinal MnSOD were also determined. RESULTS: MnSOD activity in the nontransfected control retinal endothelial cells was 20% compared with the total SOD activity and was increased to 60% in the MnSOD-transfected cells. MnSOD overexpression prevented a glucose-induced increase in oxidative stress (8-hydroxy guanosine levels), nitrosative stress (nitrotyrosine formation), and apoptosis of retinal endothelial cells. MnSOD enzyme activity and its mRNA were decreased significantly in the retina obtained from the diabetic rats, and these abnormalities were prevented by long-term lipoic acid therapy. CONCLUSIONS: The results of this study suggest a protective role for MnSOD in retinal capillary cell death and, ultimately, in the pathogenesis of retinopathy in diabetes. Understanding the role of MnSOD to modify the course of retinopathy could elucidate important molecular targets for future pharmacological interventions.

Does oxidant stress play a role in diabetic retinopathy?

Indian J Ophthalmol. 1995 Mar;43(1):17-21

Rema M, Mohan V, Bhaskar A, Shanmugasundaram KR.

The role of oxidant stress in the causation of chronic tissue damage is being increasingly recognized. Oxidant stress is usually countered by abundant supply of antioxidants. If concomitant antioxidant deficiency occurs, oxidant stress may produce tissue damage. We took up a study on antioxidant status in non-insulin dependent diabetes mellitus (NIDDM) patients with and without retinopathy and compared them with a control non-diabetic group. The levels of superoxide dismutase (SOD) were significantly reduced in all diabetic patients, i.e., those with and without retinopathy. However, the lowest levels were found in the diabetic patients with retinopathy. Vitamin E and vitamin C levels were also markedly lower in the diabetic patients. There was a paradoxical rise in the catalase and glutathione peroxidase (GPx) in the diabetic patients with retinopathy. This may be a compensatory mechanism by the body to prevent tissue damage by increasing the levels of the two alternative antioxidant enzymes.

Are free radical reactions increased in the diabetic eye?

Antioxid Redox Signal. 2007 Mar;9(3):367-73

Yamato M, Matsumoto S, Ura K, Yamada K, Naganuma T, Inoguchi T, Watanabe T, Utsumi H.

Reactive oxygen species (ROS) are thought to play a significant role in the development of diabetic retinopathy; however, no direct evidence supports ROS generation in vivo. This study used in vivo electron spin resonance (ESR) spectroscopy with a surface resonator to detect local free radical reactions. The ESR signal decay of carbamoyl-PROXYL was enhanced in the eyes of streptozotocin (STZ)-induced diabetic mice. This enhanced signal decay was suppressed by the administration of SOD or the pretreatment with aminoguanidine. We demonstrate, for the first time, specific free radical reactions in the eyes of mice with STZ-induced diabetes.

Publication Types:

• Animal Study

Oxidative damage in the retinal mitochondria of diabetic mice: possible protection by superoxide dismutase

Invest Ophthalmol Vis Sci. 2007 Aug;48(8):3805-11

Kanwar M, Chan PS, Kern TS, Kowluru RA.

PURPOSE: Superoxide levels are elevated in the retina in patients with diabetes, and cytochrome c is released from the mitochondria. The purpose of this study was to elucidate the mechanism involved in the oxidative damage of retinal mitochondria in diabetes and to determine whether mitochondrial superoxide dismutase (MnSOD) provides protection. METHODS: Effects of diabetes were investigated on superoxide and GSH levels, electron transport complexes I and III, and membrane permeability in the isolated mitochondria prepared from the retinas of streptozotocin diabetic mice. To investigate the effect of MnSOD, retinal mitochondrial oxidative stress and electron transport complexes were determined in mice overexpressing MnSOD (MnSOD-Tg). Histopathology was evaluated in trypsin-digested retina. RESULTS: Retinal mitochondria had twofold increase in superoxide levels in nontransgenic (wild-type [WT]) diabetic mice compared with WT nondiabetic mice. In the same retina, diabetes decreased mitochondrial GSH levels by 40% and complex III activity by approximately 20%, and it increased mitochondrial membrane permeability (swelling) by more than twofold; however, complex I activity was not affected. Overexpression of MnSOD inhibited diabetes-induced increases in mitochondrial superoxide levels and membrane permeability and the decrease in complex III activity. GSH values, however, were not statistically different in WT and MnSOD-Tg diabetic mice. In contrast to the diabetes-induced increase in the number of degenerate (acellular) capillaries in WT diabetic mice, the numbers of acellular capillaries in MnSOD-Tg nondiabetic and diabetic mice were similar to those in WT nondiabetic mice. CONCLUSIONS: Retinal mitochondria experience increased oxidative damage in diabetes, and complex III is one of the sources of increased superoxide. MnSOD protects the retina from diabetes-induced abnormalities in the mitochondria and prevents vascular histopathology, strongly implicating the role for MnSOD in the pathogenesis of retinopathy in diabetes.

Abnormalities of retinal metabolism in diabetes or experimental galactosemia. IV. Antioxidant defense system

Free Radic Biol Med. 1997;22(4):587-92

Kowluru RA, Kern TS, Engerman RL.

Activities of enzymes that protect the retina from reactive oxygen species were investigated in experimentally diabetic rats and experimentally galactosemic rats, two animal models known to develop vascular lesions consistent with diabetic retinopathy. Diabetes or experimental galactosemia of 2 months duration significantly decreased the activities of glutathione reductase and glutathione peroxidase in the retina while having no effect on the glutathione synthesizing enzymes glutathione synthetase and gamma-glutamyl cysteine synthetase. Activities of two other important antioxidant defense enzymes-superoxide dismutase (SOD) and catalase-also were decreased (by more than 25%) in retinas of diabetic rats and galactosemic rats. Administration of supplemental antioxidants, vitamins C and E, for the 2 months prevented the diabetes-induced impairment of antioxidant defense system in the retina. In experimentally galactosemic rats, the supplemental antioxidants were not as effective: SOD activity was normalized, but the enzymes of the glutathione redox cycle were only partly restored, and the subnormal catalase activity was unaffected. Diabetes or experimental galactosemia results in significant impairment of the antioxidant defense system in the retina, and exogenous antioxidant supplementation can help alleviate the subnormal activities of antioxidant defense enzymes.

Publication Types:

• Animal Study

Blood antioxidant parameters in patients with diabetic retinopathy

Int J Mol Med. 2004 Sep;14(3):433-7

Siemianowicz K, Gminski J, Telega A, Wójcik A, Posielezna B, Grabowska-Bochenek R, Francuz T.

It has been postulated that enhanced generation of reactive oxygen species (ROS) may take part in a pathogenesis of diabetic microvascular complication - retinopathy. There are two types of diabetic retinopathy, non-proliferative (simplex) and proliferative. ROS are anihilated by an intracelluar enzymatic system composed mainly of glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT). Beta-carotene, tocopherols and ascorbic acid are major components of serum antioxidants. All serum antioxidants are usually measured together as total antioxidant status (TAS). Erythrocyte activities of GPx, SOD, CAT and TAS were measured in diabetic patients without retinopathy, with non-proliferative and proliferative retinopathy. Obtained results were correlated with a period of diabetic history and a period of insulin treatment. SOD was significantly elevated in diabetics with non-proliferative retinopathy compared to patients without retinopathy. TAS was significantly lower in patients with proliferative retinopathy than in diabetics not developing retinopathy. Only CAT was significantly negatively correlated with the period of insulin treatment. This significant negative correlation was also observed in a subgroup of patients with proliferative retinopathy.

Oxidative protein damage in human diabetic eye: evidence of a retinal participation

Eur J Clin Invest. 1997 Feb;27(2):141-7

Altomare E, Grattagliano I, Vendemaile G, Micelli-Ferrari T, Signorile A, Cardia L.

Considerable evidence indicates that the maintenance of protein redox status is of fundamental importance for cell function, whereas structural changes in proteins are considered to be among the molecular mechanisms leading to diabetic complications. In this study, protein redox status and antioxidant activity were investigated in the lens and vitreous of diabetic and nondiabetic subjects. A significantly lower content of sulphydryl proteins was found in lens and vitreous of diabetic patients than in those of non-diabetic and control subjects. Moreover, an increased formation of protein-bound free sulphydryls and carbonyl proteins, indices of oxidative damage to proteins, was noted in diabetic patients. All these parameters were shown to be altered particularly when diabetes was complicated with retinal alterations. In addition, glutathione peroxidase activity and ascorbic acid levels, known to exert important antioxidant functions in the eye compartment, were found to be significantly decreased in the lens of diabetic patients, especially in the presence of retinal damage. This study indicates an alteration of protein redox status in subjects affected by diabetes mellitus; lens and vitreous proteins were found to be oxidized to a greater extent in the presence of retinal disease, together with a marked decrease of eye antioxidant systems. These results suggest that oxidative events are involved in the onset of diabetic eye complications, in which the decrease in free radical scavengers was shown to be associated with the oxidation of vitreous and lens proteins. Protein oxidation may, therefore, represent an important mechanism in the onset of eye complications in diabetic patients.

Publication Types:

• Review