Diabetic Retinopathy - Treatment

Antioxidants - updated: 15 March 2008

TOZAL Study: an open case control study of an oral antioxidant and omega-3 supplement for dry AMD

BMC Ophthalmol. 2007 Feb 26;7:3

Cangemi FE.

BACKGROUND: The primary objective of this prospective study was to measure the change from baseline in visual function--Best-Corrected Visual Acuity (BCVA) via the Early Treatment Diabetic Retinopathy Study (ETDRS) chart, contrast sensitivity, central 10 degree visual fields and retinal imaging (angiograms and photographs) at 6 months in subjects with atrophic (dry) age-related macular degeneration treated with a targeted nutritional supplement. METHODS: 37 mixed gender patients with a mean age of 76.3 +/- 7.8 years were enrolled at 5 independent study sites and received standard of care with a novel formulation of a nutritional supplement. Results were compared to a placebo cohort constructed from the literature that was matched for inclusion and exclusion criteria. A paired t-test was used to test a null hypothesis and a two-sided alpha level of 0.05 was used to determine statistical significance. RESULTS: 76.7% of subjects receiving the nutritional supplement demonstrated stabilization or improvement of BCVA at 6 months. Subjects gained an average of 0.0541 logMAR or one-half of a line of visual acuity (VA) over the 6-month period. There was a statistically significant improvement in VA from baseline with P = .045. The results provide strong evidence that the treatment being studied produces an improvement in VA. CONCLUSION: Treatment with this unique nutritional supplement increased VA above the expected baseline decrease in the majority of patients in this population with dry macular degeneration. The results of the TOZAL study agree with the LAST and CARMIS studies and are predictive for positive visual acuity outcomes in the AREDS II trial. However, patients will likely require supplementation for longer than 6 months to effect changes in additional visual parameters.

Publication Types:

• open case control study

Abnormalities of retinal metabolism in diabetes and experimental galactosemia. VII. Effect of long-term administration of antioxidants on the development of retinopathy

Diabetes. 2001 Aug;50(8):1938-42

Kowluru RA, Tang J, Kern TS.

Antioxidants were administered to diabetic rats and experimentally galactosemic rats to evaluate the ability of these agents to inhibit the development of diabetic retinopathy. Alloxan diabetic rats and nondiabetic rats that were fed 30% galactose randomly received standard diets or the diets supplemented with ascorbic acid and alpha-tocopherol (vitamins C+E diet) or a more comprehensive mixture of antioxidants (multi-antioxidant diet), including Trolox, alpha-tocopherol, N-acetyl cysteine, ascorbic acid, beta-carotene, and selenium. Diabetes or galactose feeding of at least 12 months resulted in pericyte loss, acellular capillaries, and basement membrane thickening. Compared with diabetic controls, the development of acellular capillaries was inhibited by 50% (P < 0.05) in diabetic rats that received supplemental vitamins C+E, and the number of pericyte ghosts tended to be reduced. The vitamins C+E supplement had no beneficial effect in galactosemic rats, but these rats consumed only approximately half as much of the antioxidants as the diabetic rats. The multi-antioxidant diet significantly inhibited ( approximately 55-65%) formation of both pericyte ghosts and acellular capillaries in diabetic rats and galactosemic rats (P < 0.05 vs. controls), without affecting the severity of hyperglycemia. Parameters of retinal oxidative stress, protein kinase C activity, and nitric oxides remained elevated for at least 1 year of hyperglycemia, and these abnormalities were normalized by multi-antioxidant therapy. Thus, long-term administration of antioxidants can inhibit the development of the early stages of diabetic retinopathy, and the mechanism by which this action occurs warrants further investigation. Supplementation with antioxidants can offer an achievable and inexpensive adjunct therapy to help inhibit the development of retinopathy in diabetes.

Publication Types:

• Animal Study

A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8

Arch Ophthalmol. 2001 Oct;119(10):1417-36

Age-Related Eye Disease Study Research Group.

BACKGROUND: Observational and experimental data suggest that antioxidant and/or zinc supplements may delay progression of age-related macular degeneration (AMD) and vision loss. OBJECTIVE: To evaluate the effect of high-dose vitamins C and E, beta carotene, and zinc supplements on AMD progression and visual acuity. DESIGN: The Age-Related Eye Disease Study, an 11-center double-masked clinical trial, enrolled participants in an AMD trial if they had extensive small drusen, intermediate drusen, large drusen, noncentral geographic atrophy, or pigment abnormalities in 1 or both eyes, or advanced AMD or vision loss due to AMD in 1 eye. At least 1 eye had best-corrected visual acuity of 20/32 or better. Participants were randomly assigned to receive daily oral tablets containing: (1) antioxidants (vitamin C, 500 mg; vitamin E, 400 IU; and beta carotene, 15 mg); (2) zinc, 80 mg, as zinc oxide and copper, 2 mg, as cupric oxide; (3) antioxidants plus zinc; or (4) placebo. MAIN OUTCOME MEASURES: (1) Photographic assessment of progression to or treatment for advanced AMD and (2) at least moderate visual acuity loss from baseline (> or =15 letters). Primary analyses used repeated-measures logistic regression with a significance level of.01, unadjusted for covariates. Serum level measurements, medical histories, and mortality rates were used for safety monitoring. RESULTS: Average follow-up of the 3640 enrolled study participants, aged 55-80 years, was 6.3 years, with 2.4% lost to follow-up. Comparison with placebo demonstrated a statistically significant odds reduction for the development of advanced AMD with antioxidants plus zinc (odds ratio [OR], 0.72; 99% confidence interval [CI], 0.52-0.98). The ORs for zinc alone and antioxidants alone are 0.75 (99% CI, 0.55-1.03) and 0.80 (99% CI, 0.59-1.09), respectively. Participants with extensive small drusen, nonextensive intermediate size drusen, or pigment abnormalities had only a 1.3% 5-year probability of progression to advanced AMD. Odds reduction estimates increased when these 1063 participants were excluded (antioxidants plus zinc: OR, 0.66; 99% CI, 0.47-0.91; zinc: OR, 0.71; 99% CI, 0.52-0.99; antioxidants: OR, 0.76; 99% CI, 0.55-1.05). Both zinc and antioxidants plus zinc significantly reduced the odds of developing advanced AMD in this higher-risk group. The only statistically significant reduction in rates of at least moderate visual acuity loss occurred in persons assigned to receive antioxidants plus zinc (OR, 0.73; 99% CI, 0.54-0.99). No statistically significant serious adverse effect was associated with any of the formulations. CONCLUSIONS: Persons older than 55 years should have dilated eye examinations to determine their risk of developing advanced AMD. Those with extensive intermediate size drusen, at least 1 large druse, noncentral geographic atrophy in 1 or both eyes, or advanced AMD or vision loss due to AMD in 1 eye, and without contraindications such as smoking, should consider taking a supplement of antioxidants plus zinc such as that used in this study.

Publication Types:

• Placebo Controlled

Diabetes-induced activation of caspase-3 in retina: effect of antioxidant therapy

Free Radic Res. 2002 Sep;36(9):993-

Kowluru RA, Koppolu P.

Apoptosis of retinal endothelial cells and pericytes is postulated to contribute to the development of retinopathy in diabetes. The goal of this study is to investigate diabetes-induced activation of retinal caspase-3, an apoptosis executer enzyme, in retina, and examine the effects of antioxidants on the activation. Caspase-3 activation was determined in the retina of alloxan diabetic rats (2-14 months duration) and in the isolated retinal capillary cells (endothelial cells and pericytes) by measuring cleavage of caspase-3 specific fluorescent substrate, and cleavage of caspase-3 holoenzyme and poly (ADP ribosyl) polymerase. Effect of antioxidants on the activation of caspase-3 was determined by feeding a group of diabetic rats diet supplemented with a comprehensive mixture of antioxidants, including Trolox, alpha-tocopherol, N-acetyl cysteine, ascorbic acid, beta-carotene and selenium for 2-14 months, and also under in vitro conditions by incubating isolated retinal capillary cells with antioxidants with wide range of actions. Caspase-3 was activated in the rat retina at 14 months of diabetes (P < 0.05 vs. normal), but not at 2 months of diabetes, and administration of antioxidants for the entire duration inhibited this activation. In the isolated retinal capillary cells incubated in 25 mM glucose medium, caspase-3 activity was increased by 50% compared to the cells incubated in 5 mM glucose (P < 0.02), and antioxidants or caspase-3 inhibitor inhibited this increase. Our results suggest that increased oxidative stress in diabetes is involved in the activation of retinal caspase-3 and apoptosis of endothelial cells and pericytes. Antioxidants might be inhibiting the development of diabetic retinopathy by inhibiting microvascular apoptosis.

Abnormalities of retinal metabolism in diabetes or experimental galactosemia. III. Effects of antioxidants

Diabetes. 1996 Sep;45(9):1233-7

Kowluru RA, Kern TS, Engerman RL, Armstrong D.

Effects of antioxidants on hyperglycemia-induced alterations of retinal metabolism were evaluated in rats diabetic or experimentally galactosemic for 2 months. Oxidative stress was estimated by measuring lipid peroxides (measured as thiobarbituric acid reactive substances [TBARS]) in retina and plasma. Erythrocyte osmotic fragility, another measure of oxidative stress, also was determined in the same groups of rats. In diabetic rats, TBARS were elevated by 74% in retina and 87% in plasma. In galactose-fed rats, TBARS were significantly elevated in retina (P < 0.05), but were normal in plasma. The administration of supplemental dietary ascorbic acid and alpha-tocopherol acetate for 2 months prevented the elevation of retinal TBARS and the decrease of Na(+)-K(+)-ATPase and calcium ATPase activities in retinas of diabetic animals without having any beneficial effect on plasma TBARS. In galactosemic rats, these antioxidants had a partial beneficial effect on the activity of retinal Na(+)-K(+)-ATPase, but failed to have any effect on calcium ATPase. The beneficial effects of antioxidants in diabetes and experimental galactosemia were not caused by the amelioration of hyperglycemia or retinal polyol accumulation. Erythrocyte osmotic fragility was increased by more than twofold in diabetes, but was normal in experimental galactosemia, and antioxidants prevented diabetes-induced increases in erythrocyte osmotic fragility-Diabetes-induced increased oxidative stress and subnormal ATPase activities in the retina can be inhibited by dietary supplementation with antioxidants.

Publication Types:

• Animal Study

Diabetes mellitus--a free radical-associated disease. Results of adjuvant antioxidant supplementation

Z Gesamte Inn Med. 1993 May;48(5):223-32

Kähler W, Kuklinski B, Rühlmann C, Plötz C.

Our investigations carried out in patients with diabetes mellitus revealed oxidative stress loads. The study presented here was to clarify whether a therapy with antioxidants can contribute to an improvement of prognosis. 80 patients affected with a long term diabetic late syndrome were randomised and arranged to 4 groups of n = 20 each. In contrast to a control group these patients received 600 mg of alpha lipoic acid or 100 micrograms of selenium (sodium selenite) daily or 1200 IE of D-alpha-tocopherol respectively for a time of 3 months. In comparison with the control group all groups treated in an antioxidative way showed significantly diminished serum concentrations of thiobarbituric acid reactive substances and of urinary albumin excretion rates. The symptoms of distal symmetric neuropathy measured according to the thermo- and vibration sensitivity also improved in a highly significant manner. The results prove that oxidative stress plays a promoting role in developing of long term diabetic late complications and that a therapy with adjuvant antioxidants may lead to a regression of diabetic late complications.

Significant photoreceptor rescue by treatment with a combination of antioxidants in an animal model for retinal degeneration

Neuroscience. 2007 Mar 30;145(3):1120-9. Epub 2007 Feb 9

Sanz MM, Johnson LE, Ahuja S, Ekström PA, Romero J, van Veen T.

The purpose of this study was to investigate the presence of oxidative DNA damage in the photoreceptors of the rd1 mouse, an animal model for retinitis pigmentosa, and to determine if antioxidants could delay the progress of photoreceptor cell death. Retinas of rd1 mice and congenic wild type controls were examined for DNA oxidation and fragmentation. To study the rescue effect of antioxidants on retinal degeneration, rd1 retinas were studied in vitro and in vivo using lutein, zeaxanthin, alpha lipoic acid and reduced l-glutathione. For the in vitro studies, antioxidants were added to the culture medium. For the in vivo studies, postnatal day (PN3) pups of rd1 mice were fed antioxidants either individually or in combination and control rd1 animals received vehicle alone. Histological evaluation was performed using hematoxylin/eosin and avidin staining, as well as terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Many of the rd1 rod photoreceptors at PN11 displayed oxidative DNA damage and TUNEL positive reaction which co-localized in a subset of rod photoreceptors. Avidin-labeled rod photoreceptors were more abundant than the TUNEL positive photoreceptors of the rd1 mouse, indicating that oxidative DNA damage precedes fragmentation. The number of TUNEL positive and avidin positive cells was considerably decreased upon treatment with the combination of the antioxidants. Rescue of rd1 photoreceptors was significant at PN18 and PN17, respectively, in the in vitro and in vivo studies. In conclusion individual antioxidants had no significant rescue effect but the combination slowed down the rd1 rod photoreceptor degeneration, indicating an additive or synergistic effect.

Publication Types:

• Animal Study

Effects of antioxidant treatment on normal and diabetic rat retinal enzyme activities

J Ocul Pharmacol Ther. 2005 Feb;21(1):28-35

Dene BA, Maritim AC, Sanders RA, Watkins JB 3rd.

Diabetes mellitus is characterized by hyperglycemia and, in chronic disease, by microvascular pathologies, especially in the kidney, peripheral nerve, and eye. Although hyperglycemia can be controlled with insulin and/or antihyperglycemic medications, diabetic retinopathy continues to be the leading cause of blindness in the United States. Because increased oxidative stress may be a cause of retinopathy, this study examined the hypothesis that administration of exogenous antioxidants can restore a more balanced oxidative condition. Normal and 30-day streptozotocin-induced diabetic Sprague-Dawley rats received daily intraperitoneal doses (10 mg/kg) of beta-carotene, alpha-lipoic, and Pycnogenol individually or in combinations for 14 days, after which retinae were dissected and fractionated for the assay of activities of glutathione reductase, glutathione peroxidase, gamma-glutamyl transferase, and superoxide dismutase. In normal rats, treatment with antioxidant combinations led to a decrease in gamma-glutamyl transferase activity; beta-carotene plus pycnogenol treatment decreased the activity of both glutathione-related enzymes. Decreased retinal gamma-glutamyl transferase activity of diabetic rats was normalized by the administration of pycnogenol alone or in combination with beta-carotene. In diabetic rats, retinal glutathione reductase activity increased after treatment with beta-carotene alone or with pycnogenol. Treatment with pycnogenol and alpha-lipoic acid alone or in combination decreased the activity of glutathione peroxidase, while this activity was increased after treatment with a combination of all antioxidants. Elevated activity of superoxide dismutase in diabetic retina was normalized by treatment with alpha-lipoic acid and with pycnogenol and beta-carotene in combination, but not with all three together. Antioxidants can access the retina and, once there, can alter antioxidant enzyme activities. In both normal and diabetic rats, combinations of antioxidants have different effects on retinal antioxidant enzyme activities than do individual antioxidants.

Increased oxidative stress in diabetes regulates activation of a small molecular weight G-protein, H-Ras, in the retina

Mol Vis. 2007 Apr 19;13:602-10.

Kowluru V, Kowluru RA.

PURPOSE: Increased superoxide levels are implicated in the pathogenesis of diabetic retinopathy. We have shown that functional activation of a small molecular weight G-protein, H-Ras, is one of the signaling steps involved in glucose-induced apoptosis of retinal capillary cells. The goal of this study was to elucidate the mechanism(s) by which oxidative stress could result in the activation of H-Ras in diabetes. METHODS: Experiments were performed in isolated retinal endothelial cells that were treated with H(2)O(2), or the cells in which glucose-induced superoxide accumulation was inhibited either by superoxide dismutase mimetic (MnTBAP) or by overexpressing mitochondrial superoxide dismutase (MnSOD). The in vitro experiments were complemented with in vivo experiments using the retina from mice overexpressing MnSOD. RESULTS: H(2)O(2) activated H-Ras and its downstream signaling pathway, including Raf-1 and phosphorylation of p38 (p-p38) MAP kinase. Inhibition of superoxide significantly attenuated glucose-induced activation of H-Ras, Raf-1 and p-p38 MAP kinase. Overexpression of MnSOD in mice prevented diabetes-induced activation of both H-Ras and p-p38 MAP kinase. CONCLUSIONS: Our results clearly indicate that the activation of H-Ras and its downstream signaling pathway in the retina and its vasculature could be under the control of superoxide, and H-Ras activation in diabetes can be prevented by inhibiting superoxide accumulation.

Publication Types:

• Vitro

Antioxidant enzymes and diabetic retinopathy

Ann N Y Acad Sci. 2007 Apr;1100:199-2

Yildirim Z, Uçgun NI, Kiliç N, Gürsel E, Sepici-Dinçel A.

The aim of this study was to discuss the serum copper (Cu), zinc (Zn), nitric oxide (NO), glutathione (GSH), advanced oxidation protein products (AOPP) levels, and superoxide dismutase (SOD) activities with diabetic retinopathy severity. Twenty-five patients with proliferative diabetic retinopathy (PDR group 1), 25 patients with nonproliferative diabetic retinopathy (NPDR group 2), and 25 nondiabetic controls (control group) were included in the study. Patients who had macrovascular complications of diabetes (coronary arterial disease, periferic vascular disease) were excluded. The major finding of our study was that we did not observe any differences between group 1 and 2, which we aimed to discuss the severity of diabetic retinopathy. As the levels of SOD and Zn were not different between the groups, statistically significant differences were observed for GSH, NO, and Cu levels when compared to control group. AOPP levels were statistically increased in group 1 compared to control group. It can be suggested that hyperglycemia in DM is associated with accelerated nonenzymatic glycation and oxidative stress.