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      Oxidative Stress: Implications for the Development of Diabetic Retinopathy and Antioxidant Therapeutic Perspectives

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      Oxidative Medicine and Cellular Longevity
      Hindawi Publishing Corporation

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          Abstract

          In recent decades, localized tissue oxidative stress has been implicated as a key component in the development of diabetic retinopathy (DR). Increasing evidence shows that oxidative stress caused by diabetes-induced metabolic abnormalities is the most common mechanism associated with the pathogenesis of DR for both type 1 and type 2 diabetes. Increase in intracellular reactive oxygen species (ROS) concentrations results in the activation of several mechanisms involved in the pathogenesis of DR. In particular, damage or dysfunction caused by oxidative stress still persists even after glycemia has been normalized. Despite considerable evidence showing the beneficial effects of antioxidants in preventing the development of retinopathy, results from large-scale clinical trials on classic antioxidants are somewhat ambiguous. Scavenging reactive radicals may not be the most ideal antioxidant strategy in DR. Advances in understanding the function of ROS in the development of DR can lead to the development of new therapeutic strategies based on the mechanisms of ROS generation and scavenging. Increasing amounts of data have demonstrated the promising prospect of antioxidant therapy and its beneficial effects in vision protection. Therefore, new strategies that utilize antioxidants as additive therapy should be implemented in the treatment of DR.

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          Effect of fenofibrate on the need for laser treatment for diabetic retinopathy (FIELD study): a randomised controlled trial.

          Laser treatment for diabetic retinopathy is often associated with visual field reduction and other ocular side-effects. Our aim was to assess whether long-term lipid-lowering therapy with fenofibrate could reduce the progression of retinopathy and the need for laser treatment in patients with type 2 diabetes mellitus. The Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study was a multinational randomised trial of 9795 patients aged 50-75 years with type 2 diabetes mellitus. Eligible patients were randomly assigned to receive fenofibrate 200 mg/day (n=4895) or matching placebo (n=4900). At each clinic visit, information concerning laser treatment for diabetic retinopathy-a prespecified tertiary endpoint of the main study-was gathered. Adjudication by ophthalmologists masked to treatment allocation defined instances of laser treatment for macular oedema, proliferative retinopathy, or other eye conditions. In a substudy of 1012 patients, standardised retinal photography was done and photographs graded with Early Treatment Diabetic Retinopathy Study (ETDRS) criteria to determine the cumulative incidence of diabetic retinopathy and its component lesions. Analyses were by intention to treat. This study is registered as an International Standard Randomised Controlled Trial, number ISRCTN64783481. Laser treatment was needed more frequently in participants with poorer glycaemic or blood pressure control than in those with good control of these factors, and in those with a greater burden of clinical microvascular disease, but the need for such treatment was not affected by plasma lipid concentrations. The requirement for first laser treatment for all retinopathy was significantly lower in the fenofibrate group than in the placebo group (164 [3.4%] patients on fenofibrate vs 238 [4.9%] on placebo; hazard ratio [HR] 0.69, 95% CI 0.56-0.84; p=0.0002; absolute risk reduction 1.5% [0.7-2.3]). In the ophthalmology substudy, the primary endpoint of 2-step progression of retinopathy grade did not differ significantly between the two groups overall (46 [9.6%] patients on fenofibrate vs 57 [12.3%] on placebo; p=0.19) or in the subset of patients without pre-existing retinopathy (43 [11.4%] vs 43 [11.7%]; p=0.87). By contrast, in patients with pre-existing retinopathy, significantly fewer patients on fenofibrate had a 2-step progression than did those on placebo (three [3.1%] patients vs 14 [14.6%]; p=0.004). An exploratory composite endpoint of 2-step progression of retinopathy grade, macular oedema, or laser treatments was significantly lower in the fenofibrate group than in the placebo group (HR 0.66, 95% CI 0.47-0.94; p=0.022). Treatment with fenofibrate in individuals with type 2 diabetes mellitus reduces the need for laser treatment for diabetic retinopathy, although the mechanism of this effect does not seem to be related to plasma concentrations of lipids.
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            Retinopathy and nephropathy in patients with type 1 diabetes four years after a trial of intensive therapy. The Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Research Group.

            Among patients with type 1 diabetes mellitus, intensive therapy (with the aim of achieving near-normal blood glucose and glycosylated hemoglobin concentrations [hemoglobin A1c]) markedly reduces the risk of microvascular complications as compared with conventional therapy. To assess whether these benefits persist, we compared the effects of former and intensive conventional therapy on the recurrence and severity of retinopathy and nephropathy for four years after the end of the Diabetes Control and Complications Trial (DCCT). At the end of the DCCT, the patients in the conventional-therapy group were offered intensive therapy, and the care of all patients was transferred to their own physicians. Retinopathy was evaluated on the basis of centrally graded fundus photographs in 1208 patients during the fourth year after the DCCT ended, and nephropathy was evaluated on the basis of urine specimens obtained from 1302 patients during the third or fourth year, approximately half of whom were from each treatment group. The difference in the median glycosylated hemoglobin values between the conventional-therapy and intensive-therapy groups during the 6.5 years of the DCCT (average, 9.1 percent and 7.2 percent, respectively) narrowed during follow-up (median during 4 years, 8.2 percent and 7.9 percent, respectively, P<0.001). Nevertheless, the proportion of patients who had worsening retinopathy, including proliferative retinopathy, macular edema, and the need for laser therapy, was lower in the intensive-therapy group than in the conventional-therapy group (odds reduction, 72 percent to 87 percent, P<0.001). The proportion of patients with an increase in urinary albumin excretion was significantly lower in the intensive-therapy group. The reduction in the risk of progressive retinopathy and nephropathy resulting from intensive therapy in patients with type 1 diabetes persists for at least four years, despite increasing hyperglycemia.
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              Intensified multifactorial intervention in patients with type 2 diabetes mellitus and microalbuminuria: the Steno type 2 randomised study.

              In type 2 diabetes mellitus the aetiology of long-term complications is multifactorial. We carried out a randomised trial of stepwise intensive treatment or standard treatment of risk factors in patients with microalbuminuria. In this open, parallel trial patients were allocated standard treatment (n=80) or intensive treatment (n=80). Standard treatment followed Danish guidelines. Intensive treatment was a stepwise implementation of behaviour modification, pharmacological therapy targeting hyperglycaemia, hypertension, dyslipidaemia, and microalbuminuria. The primary endpoint was the development of nephropathy (median albumin excretion rate >300 mg per 24 h in at least one of the two-yearly examinations). Secondary endpoints were the incidence or progression of diabetic retinopathy and neuropathy. The mean age was 55.1 years (SD 7.2) and patients were followed up for 3.8 years (0.3). Patients in the intensive group had significantly lower rates of progression to nephropathy (odds ratio 0.27 [95% CI 0-10-0.75]), progression of retinopathy (0.45 [0.21-0.95]), and progression of autonomic neuropathy (0.32 [0.12-0.78]) than those in the standard group. Intensified multifactorial intervention in patients with type 2 diabetes and microalbuminuria slows progression to nephropathy, and progression of retinopathy and autonomic neuropathy. However, further studies are needed to establish the effect of intensified multifactorial treatment on macrovascular complications and mortality.
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                Author and article information

                Journal
                Oxid Med Cell Longev
                Oxid Med Cell Longev
                OMCL
                Oxidative Medicine and Cellular Longevity
                Hindawi Publishing Corporation
                1942-0900
                1942-0994
                2014
                10 August 2014
                : 2014
                : 752387
                Affiliations
                Department of Ophthalmology, Second Xiangya Hospital, Central South University, 139 Middle Renmin Road, Changsha 410011, China
                Author notes

                Academic Editor: Ersin Fadillioglu

                Author information
                http://orcid.org/0000-0002-0031-6561
                Article
                10.1155/2014/752387
                4142742
                25180070
                41cd4ac8-2ab3-433a-a761-42b18e8e9eb9
                Copyright © 2014 Ying Wu et al.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 13 April 2014
                : 11 July 2014
                Categories
                Review Article

                Molecular medicine
                Molecular medicine

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