Eales' disease: increased oxidation and peroxidation products of membrane constituents chiefly lipids and decreased antioxidant enzymes and reduced glutathione in vitreous

Oxidative Stress Implication in Retinal Diseases-A Review

Oxidative stress (OS) refers to an imbalance between free radicals (FRs), namely highly reactive molecules normally generated in our body by several pathways, and intrinsic antioxidant capacity. When FR levels overwhelm intrinsic antioxidant defenses, OS occurs, inducing a series of downstream chemical reactions. Both reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced by numerous chemical reactions that take place in tissues and organs and are then eliminated by antioxidant molecules. In particular, the scientific literature focuses more on ROS participation in the pathogenesis of diseases than on the role played by RNS. By its very nature, the eye is highly exposed to ultraviolet radiation (UVR), which is directly responsible for increased OS. In this review, we aimed to focus on the retinal damage caused by ROS/RNS and the related retinal pathologies. A deeper understanding of the role of oxidative and nitrosative stress in retinal damage is needed in order to develop targeted therapeutic interventions to slow these pathologies.

Gender differences in albumin and ascorbic acid in the vitreous antioxidant system

Ascorbic acid is present at high concentrations in the vitreous and plays a central role in vitreous redox chemistry. Albumin is the main protein in the vitreous with antioxidant properties and occurs in different oxidation states, which can be used as redox indicators, but have not been studied in the vitreous. This study, therefore, addressed the vitreous redox state of cysteine-34 of albumin in relation to the ascorbic acid content, which has been suggested to exert a main function in detoxifying reactive oxygen in the vitreous. A total of 58 vitreous samples obtained from patients undergoing vitrectomy were analyzed for (i) human mercaptalbumin (HMA), the reduced thiol form; (ii) human non-mercaptalbumin1 (HNA1), a reversible oxidative modification with a disulfide at cysteine-34; and (iii) human non-mercaptalbumin2 (HNA2), a non-reversibly (highly) oxidized form of albumin; as well as (iv) ascorbic acid concentrations, to study possible relations. In addition, blood samples were taken to compare albumin redox state between plasma and the vitreous. Vitreous albumin showed greater variability in the redox state of cysteine-34 and a shift to the oxidized fractions compared to plasma albumin (P < 0.001). A strong positive relation was observed between the vitreous ascorbic acid concentrations and the reversibly oxidized form, HNA1 (P < 0.001), and a negative relation with the reduced form, HMA. Positive relations between ascorbic acid and HNA1 in the vitreous were stronger in men than in women. In contrast to HMA and HNA1, there was a distinct gender difference noted for the irreversibly oxidized form, HNA2. While males showed a positive relation between the vitreous ascorbic acid concentrations and HNA2, there was no correlation found with HNA2 in females. Our results support the view that ascorbic acid, by decreasing either directly or indirectly the concentrations of molecular oxygen, generates hydrogen peroxide, and that thiols, including HMA, are acting as antioxidants. This study for the first time provides evidence that vitreous albumin can be used as a marker molecule for the appearance of reactive oxygen species in the vitreous of patients undergoing vitrectomy. Moreover, it can be shown that there are gender differences in vitreous ascorbic acid and albumin concentrations as well as in oxidation state of vitreous albumin.

Vitreous Antioxidants, Degeneration, and Vitreo-Retinopathy: Exploring the Links

The transparent vitreous body, which occupies about 80% of the eye’s volume, is laden with numerous enzymatic and non-enzymatic antioxidants that could protect the eye from oxidative stress and disease. Aging is associated with degeneration of vitreous structure as well as a reduction in its antioxidant capacity. A growing body of evidence suggests these age-related changes may be the precursor of numerous oxidative stress-induced vitreo-retinopathies, including vision degrading myodesopsia, the clinically significant entoptic phenomena that can result from advanced vitreous degeneration. Adequate intravitreal antioxidant levels may be protective against vitreous degeneration, possibly preventing and even improving vision degrading myodesopsia as well as mitigating various other vitreo-retinopathies. The present article is, therefore, a review of the different antioxidant molecules within vitreous and the inter-relationships between vitreous antioxidant capacity and degeneration.

Lens glutathione homeostasis: Discrepancies and gaps in knowledge standing in the way of novel therapeutic approaches

Cataract is the major cause of blindness worldwide. The WHO has estimated around 20 million people have bilateral blindness from cataract, and that number is expected to reach 50 million in 2050. The cataract surgery is currently the main treatment approach, though often associated with complications, such as Posterior Capsule Opacification (PCO)-also known as secondary cataract. The lens is an avascular ocular structure equipped with an unusually high level of glutathione (GSH), which plays a vital role in maintaining lens transparency by regulating lenticular redox state. The lens epithelium and outer cortex are thought to be responsible for providing the majority of lens GSH via GSH de novo synthesis, assisted by a continuous supply of constituent amino acids from the aqueous humor, as well as extracellular GSH recycling from the gamma-glutamyl cycle. However, when de novo synthesis is impaired, in the presence of low GSH levels, as in the aging human lens, compensatory mechanisms exist, suggesting that the lens is able to uptake GSH from the surrounding ocular tissues. However, these uptake mechanisms, and the GSH source and its origin, are largely unknown. The lens nucleus does not have the ability to synthesize its own GSH and fully relies on transport from the outer cortex by yet unknown mechanisms. Understanding how aging reduces GSH levels, particularly in the lens nucleus, how it is associated with age-related nuclear cataract (ARNC), and how the lens compensates for GSH loss via external uptake should be a major research priority. The intent of this review, which is dedicated to the memory of David C. Beebe, is to summarize our current understanding of lens GSH homeostasis and highlight discrepancies and gaps in knowledge that stand in the way of pharmacologically minimizing the impact of declining GSH content in the prevention of age-related cataract.

Increased homocysteine, homocysteine-thiolactone, protein homocysteinylation and oxidative stress in the circulation of patients with Eales' disease

BACKGROUND

Eales' disease (ED) is an idiopathic retinal vascular disorder. It presents with inflammation and neovascularization in the retina. Adult men, aged between 15 and 40 years are more susceptible than women. Homocysteine has been implicated in other ocular diseases including age-related macular degeneration (ARMD), central retinal vein occlusion (CRVO) and optic neuropathy. The present study investigates the role of homocysteine in ED.

METHODS

Forty male subjects, 20 with ED and 20 healthy controls, were recruited to the study. Their blood samples were used to measure thiobarbituric acid reactive substances (TBARS), glutathione (GSH), homocysteine, homocysteine-thiolactone, extent of homocysteine conjugation with proteins and plasma copper concentration.

RESULTS

In the ED group, plasma homocysteine (18.6 ± 1.77 µmol/L, P < 0.001) and homocysteine-thiolactone (45.3 ± 6.8 nmol/L, P < 0.0001) concentrations were significantly higher compared to homocysteine (11.2 ± 0.64 µmol/L) and homocysteine-thiolactone (7.1 ± 0.94 nmol/L) concentrations in control subjects. TBARS (P < 0.011) and protein homocysteinylation (P < 0.030) were higher in the ED group while GSH (5.9 ± 0.44 µmol/L, P < 0.01) and copper (6.6 ± 0.42 µmol/L, P < 0.001) were lower compared to GSH (8.1 ± 0.41 µmol/L) and copper (15.4 ± 0.73 µmol/L) concentrations in control subjects.

CONCLUSIONS

Increased homocysteine, and its metabolite thiolactone, is associated with the functional impairment of protein due to homocysteinylation in ED.

Antioxidant supplementation improves platelet membrane fluidity in idiopathic retinal periphlebitis (Eales' disease)

PURPOSE

Oxidative damage to cellular membranes plays an important role in the pathobiology of tissue injury. Retinal photoreceptors and platelets are an easy target of oxidants because of high proportion of polyunsaturated fatty acids. A tertiary-care center-based prospective study was undertaken to study the effect of antioxidant supplementation over membrane fluidity in platelets in idiopathic retinal periphlebitis (Eales' disease) for the first time.

METHODS

Assay of thiobarbituric acid reactive substances (TBARS) levels was done following a standard protocol and membrane fluidity in platelets was estimated using a fluorescent probe, 1,6-diphenyl-1,3,5-hexatrience, in 15 cases and 12 healthy controls. Prednisolone (1 mg/kg) in a weekly tapering dose for 6 weeks and a commercially available antioxidant preparation [lutein 3.2 mg (containing zeaxanthin 256 mcg), L-glutathione 5 mg, vitamin E 15 IU, vitamin C 150 mg, zinc 40 mg, copper 2 mg, selenium 40 mcg, and manganese 5 mg] was administered once a day for 3 months to all the cases. Pre- and postantioxidant supplementation platelet TBARS and membrane fluidity levels were assessed in all the cases.

RESULTS

Significant increase was observed in TBARS levels in the cases when compared with controls (P = 0.01). Platelet fluorescence polarization was significantly higher in cases, indicating decreased membrane fluidity, when compared with controls (P = 0.005). Antioxidant supplementation led to marked decrease in TBARS levels (P = 0.01) and improved levels of platelet membrane fluidity (P = 0.001).

CONCLUSION

Antioxidant supplementation leads to significant decrease in oxidative stress and a significant improvement in platelet membrane fluidity, thereby helping to prevent retinal photoreceptor dysfunction.

Increase in Fe3+/Fe2+ ratio and iron-induced oxidative stress in Eales disease and presence of ferrous iron in circulating transferrin

Eales disease was shown to be associated with oxidant stress and weak antioxidant defense. Total iron, ferrous iron, thiobarbituric acid reactive substances (TBARS), and ceruloplasmin were estimated in the blood samples of patients with inflammation, perivasculitis, and venous insufficiency. Levels of ferric iron were determined from the difference in those of total iron and ferrous iron. All biochemical parameters were estimated in age and sex-matched controls. Fe3+/Fe2+ ratio was greater in patients with Eales disease than in normal controls. Similar increase in TBARS and ceruloplasmin levels were noted. The patients were treated with prednisone and vitamins E and C, then Fe3+/Fe2+ ratios and TBARS decreased progressively; the active state of the disease was reduced to 16%. So Fe3+/Fe2+ ratio in addition to TBARS levels could be considered an index of the active state of the disease. Circulating transferrin in blood did contain ferrous iron. Binding of ferrous iron to transferrin was confirmed by estimating iron-binding capacity using ferrous ammonium sulphate.

Contaminants-induced oxidative damage on the carp Cyprinus carpio collected from the upper Yellow River, China

The Yellow River, the second largest river in China, is the most important resource of water supply in North China. In the last 40 years, even in the upper Yellow River, with the development of industry and agriculture, more and more contaminants have been discharged into this river and greatly polluted the water. Although a routine chemical component analysis has been performed, little is known about the real toxic effects of the polluted water on organisms at environmental level. To explore whether the pollutants induced oxidative stress and damage to aquatic organisms, malondialdehyde (MDA) level and activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) in hepatopancreas, kidney and intestine of the field-collected carp Cyprinus carpio from a mixed polluted (Lanzhou Region, LZR) and a relatively unpolluted (Liujiaxia Region, LJXR) sites of the upper Yellow River were measured. The results showed that when the values of LZR compared with those of LJXR, SOD and GST activities increased and GPx activity decreased significantly in all the three organs (P < 0.05-0.01); CAT activity decreased but MDA level increased significantly (P < 0.05-0.01) only in kidney and intestine. In conclusion, the results of this study suggest that the pollutants can induce obvious oxidative damage in the carp, and the SOD, GST and GPx might be better indicators for the oxidative damage in aquatic organisms.

Decreased platelet membrane fluidity in retinal periphlebitis in Eales' disease

PURPOSE

Oxidative damage to cellular membranes plays an important role in the pathobiology of tissue injury. Free radical-induced peroxidation of membrane lipid and protein is associated with alterations in cellular, morphological, biochemical, and physical dynamics, which are related to the mobility of lipid molecules. Retinal photoreceptors and platelets have been shown to be an easy target of oxidants because of their high proportion of polyunsaturated fatty acids. This study was undertaken, for the first time, to investigate membrane fluidity in the platelets of patients with Eales' disease.

METHODS

Assays of malonaldialdehyde levels and the enzymes superoxide dismutase and catalase and fluorescence polarization, for estimating membrane fluidity, were carried out on platelets from 20 patients with Eales' disease (stage 1 characterized by periphlebitis of small (1a) and large (1b) caliber vessels with superficial retinal hemorrhages) and 15 healthy controls.

RESULTS

A significant increase was observed in the malonaldialdehyde levels. A significant decrease in the activity of superoxide dismutase and catalase was also observed. Platelet fluorescence polarization was significantly higher in the patients, indicating decreased membrane fluidity compared to controls (p<0.01).

CONCLUSION

A decrease in platelet membrane fluidity occurs as a result of oxidative stress in retinal periphlebitis in Eales' disease. The decreased membrane fluidity suggests alterations in the physiological events, which may result in alterations in the functioning of retinal photoreceptors.

Response time and safety profile of pulsed oral methotrexate therapy in idiopathic retinal periphlebitis

PURPOSE

To evaluate the response time and safety profile of low-dose oral methotrexate pulsed therapy in idiopathic retinal periphlebitis (Eales' disease).

METHODS

A tertiary care center-based prospective interventional study, based on visual acuity grading, was undertaken. Twenty-one consecutive patients with idiopathic retinal periphlebitis were administered 12.5 mg methotrexate as a single oral dose, once per week for 12 weeks (cumulative dose = 150 mg). Each patient was assessed for change in visual acuity grades. Time of first therapeutic response was also noted. Drug safety was monitored by laboratory tests that included twice-weekly white blood cells and differential counts, twice-weekly platelet counts, and monthly liver function tests.

RESULTS

Twenty-one eyes were assessed. Mean follow-up period was 6 months. All showed improvement in visual acuity grades. An excellent visual outcome (6/6 or better) was achieved in 18 (69%) eyes. Time of first therapeutic response varied from 2 to 6 weeks with a majority of eyes (80%) showing response by 4 weeks (median = 3 weeks). All the side effects of methotrexate were mild or moderate in severity and rapidly reversible on dose reduction or discontinuation. No patient had any constitutional symptoms severe enough to necessitate cessation of therapy.

CONCLUSIONS

Low dose oral methotrexate pulse therapy (at a dose of 12.5 mg/week) is clinically effective within 4 weeks, and is associated with an acceptable safety profile.

Protective effect of polyethylene glycol-superoxide dismutase on leukocyte dynamics in rat retinal microcirculation under lipid hydroperoxide-induced oxidative stress

The levels of lipid hydroperoxide (LHPs) in vitreous are elevated in a variety of retinal disorders. Recently, we have shown that increased levels of LHPs in the vitreous enhanced leukocyte-endothelium interaction in the retina, which should contribute to the initial disturbance of the retinal microcirculation. Based upon the previous work, the purpose of the present study was to investigate the effect of polyethylene glycol-superoxide dismutase (PEG-SOD), one of the important enzyme antioxidants, on leukocyte-endothelial interaction in the retinal microcirculation under LHP-induced oxidative stress. Male Brown-Norway rats weighing approximately 250 g were used. LHP(18:2) was made from linoleic acid (LA) with lipoxygenase and 10 microg of LHP dissolved in 5 microl of sodium borate buffer (SBB, 0.02 m) was slowly injected into the vitreous using a 33-gauge needle. PEG-SOD (5000 units/kg) was given intravenously 5 min before LHP injection. At 2, 4, 6, 12, 24 and 48 hr after the vitreous injections, we evaluated the number of rolling leukocytes along the major retinal veins and the number of leukocytes that accumulated in the retinal microvasculature with acridine orange digital fluorography. In LHP-treated rats, leukocyte rolling along the major retinal veins was maximal at 6 hr after LHP injection. The number of rolling leukocytes in the PEG-SOD-treated rats was decreased to 5.5% of those in the LHP-treated rats at 6 hr after LHP injection (P<0.01). No rolling leukocytes were observed in either control or vehicle-treated eyes. The number of accumulated leukocytes in LHP-treated eyes started to increase at 12 hr, and peaked at 24 hr which was significantly higher than in both control and vehicle-treated eyes (P<0.01). The number of accumulated leukocytes in the PEG-SOD-treated rats was reduced by 88.0% at 24 hr (P<0.01). Intravenous injection of PEG-SOD significantly inhibited the leukocyte rolling and its accumulation under LHP-induced oxidative stress. These results suggest that PEG-SOD might attenuate various retinal microcirculatory disorders associated with LHP.

A comparative study of epiretinal membranes associated with Eales' disease: a clinicopathologic evaluation

AIM

To study the histopathologic features and clinical correlation of epiretinal membranes (ERM) obtained from patients of Eales' disease and compare with other vasoproliferative disorders.

METHODS

Retrospective analysis of epiretinal membranes submitted for histological evaluation between January 1995 and June 2001, from the patients of diabetic retinopathy and vascular occlusions (Group 1; vaso-occlusive disorders) and of Eales' disease (Group 2; vasoinflammatory disorders). Demographics, pre and postoperative visual acuity, and anatomic and histologic characteristics of membranes were studied. Histopathologic features and clinical outcomes were correlated between the groups. The results were analysed statistically by Student's t-test, Fisher's exact test and Kruskal-Wallis test.

RESULTS

This study consisted of 42 patients, 24 in Group 1 and 18 in Group 2. Patients in Group 2 (33.0+/-9.2 years) were significantly younger than the patients in Group 1 (49.9+/-7.6 years) (P< or =0.0001). Final visual acuity of >20/400 was attained in 79.2% (19/24) patients in Group 1 and 83.3% (15/18) in Group 2 (P=1.0). Inflammatory membranes were significantly associated with presumed Eales' disease (94.4 vs 0%) (P< or =0.0001) and fibrovascular membranes with Group 1 (70.8% vs 33.3%) (P=0.028). Mast cells and eosinophils were observed as special features in epiretinal membranes of patients with Eales' disease.

CONCLUSIONS

Histological features of ERM in Eales' disease are comparable to other vasoproliferative disorders except for features of inflammation. Presence of mast cells and eosinophils in epiretinal membranes of Eales' disease needs further investigation.

A new staging system for idiopathic retinal periphlebitis

PURPOSE

To develop and standardize a universally acceptable new staging system for idiopathic retinal periphlebitis (Eales disease).

METHODS

A new staging system was established and standardized based on standard terminology and features. Idiopathic retinal periphlebitis was classified as peripheral and central types. Peripheral disease consisted of four stages. Stage 1 is periphlebitis of small (1a) and large (1b) caliber vessels with superficial retinal hemorrhages. Stage 2a denotes capillary nonperfusion and 2b neovascularization elsewhere/of the disc. Stage 3a is classified as fibrovascular proliferation and 3b vitreous hemorrhage. Stage 4a is traction/combined rhegmatogenous retinal detachment whereas 4b is rubeosis iridis, neovascular glaucoma, complicated cataract, and optic atrophy. A total of 253 cases of idiopathic retinal periphlebitis (mean age, 24.7 +/- 4.7 years, all male) presenting at this tertiary care center were classified prospectively according to the new staging system, by two independent observers (interobserver correlation = 0.7).

RESULTS

The new staging system was consistent, simple, and easy to recall. Peripheral and central types of idiopathic retinal periphlebitis were found in 94.07% and 5.93% of cases, respectively. The new staging system also defined the severity of the disease. Vitreous hemorrhage was found to be the commonest presenting feature (51.68%), whereas traction/combined rhegmatogenous detachment was found in 5.88% of cases.

CONCLUSIONS

The new staging system is useful in classifying and assessing the severity of disease. Management strategy can also be defined according to the stage of the disease. It is designed to promote the use of standard assessment with applications to clinical management and research.

Involvement of oxidative and nitrosative stress in promoting retinal vasculitis in patients with Eales' disease

OBJECTIVES

Eales' disease (ED) is an idiopathic retinal vasculitis condition, which affects retina of young adult males. The histopathological hallmark in ED is the adhesion of leukocytes to the endothelium and the infiltration of these cells into the retinal parenchyma. Phagocyte generated free radicals have been implicated in mediating tissue damage associated with various inflammatory vasculopathies. In the present study, we have investigated the possible role of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in causing retinal tissue damage in ED.

DESIGN AND METHODS

35 patients with ED and 20 healthy control subjects were included in the study. Monocytes (MC) were separated from peripheral blood of the respective study participants. Inducible nitric oxide synthase (iNOS) protein expression was assessed using Western blot and 3 nitrotyrosine (3NTYR) by reversed phase high performance liquid chromatography (RP HPLC). Thiobarbituric acid reactive substances (TBARS) were determined by measuring malondialdehyde (MDA) formed. Superoxide dismutase (SOD) activity was assayed based on the ability of SOD to inhibit auto-oxidation of epinephrine. Iron, copper and zinc content were determined using Atomic Absorption Spectrophotometer. Immunolocalization of iNOS and 3NTYR was performed on the surgically excised epiretinal membranes (ERM) from patients with ED.

RESULTS

There was a significant increase in the expression of iNOS, as well as 3NTYR accumulation, diminished SOD activity, elevated lipid peroxides, iron, copper and decreased zinc content in the MC of patients with ED when compared with healthy control subjects. The elevated levels of ROS and RNS products correlated with diminished antioxidant status in patients with ED. Strong immunoreactivity for iNOS and 3NTYR was observed in inflammatory cells and endothelial cells in ERM obtained from patients with ED.

CONCLUSIONS

Our findings from this study clearly reveal the involvement of RNS and ROS in the development of retinal vasculitis in ED. Based on our present study and earlier studies we confirm the role of free radicals in mediating retinal tissue damage in ED. Hence we believe selective inhibition of iNOS or supplementation with antioxidants vitamin E and C might be beneficial in controlling retinal vasculitis in patients with ED.

Eales disease--an update

Eales disease, first described by Henry Eales in 1880, remains an enigma. The disease, observed more commonly in the Indian subcontinent than in the rest of the world, occurs in young healthy adult males, initially presenting as retinal periphlebitis and later as retinal ischemia that may lead to vascular alterations and neovascularization. Recurrent vitreous hemorrhage with or without retinal detachment is the common sequelae. In recent years, immunological, molecular biological, and biochemical studies have indicated the role of human leukocyte antigen, retinal autoimmunity, mycobacterium tuberculosis genome, and free radical mediated damage in the etiopathogenesis of this disease. However, its etiology appears to be multifactorial. The management depends on the stage of the disease and consists of medical treatment with oral corticosteroids in the active inflammatory stage and laser photocoagulation in the advanced retinal ischemia and neovascularization stages. The results of vitreoretinal surgery have been found to be satisfactory in case of vitreous hemorrhage with or without retinal detachment.

Purification and characterization of a novel 88 kDa protein from serum and vitreous of patients with Eales' disease

Eales' disease is a perivasculitis that affects the peripheral retina of young adults and results in recurrent vitreous hemorrhage. Although increased oxidative stress and decreased antioxidant defense have been reported to be associated with Eales' disease, the exact cause for the disease and its pathogenesis are not known. Here is reported the identification, purification and characterization of a new protein from the serum and vitreous of patients with Eales' disease. This protein was purified using preparative electrophoresis and HPLC. The purified protein had a retention time of 9.2 min in RP HPLC. Its molecular weight as determined by gel permeation chromatography was 88 kDa hence, it was termed as 88 kDa protein. Alcian blue and Schiffs staining revealed 88 kDa protein to be a glycoprotein. Proteins purified from both serum and vitreous exhibited anti lipid peroxidation effect on erythrocyte when added during in vitro assay of thiobarbuteric acid reactive substances (TBARS). In addition to this property the protein also has Fe(2+)sequestering effect. The anti TBARS activity of 88 kDa protein was completely inhibited by 0.1 m M concentration of parachlromercuric benzoate (PCMB) and 5,5' dithiobis(2-nitrobenzoic acid) DTNB. The total thiol content (cysteine) of the purified 88 kDa protein was found to be 8% by mass. Eighty eight kDa protein from both the sources namely vitreous and serum are immunologically identical when studied using polyclonal antibodies raised in goat against purified serum protein. The N terminal sequence of 88 kDa protein by automated Edman's degradation chemistry is A D D P N S L S P S A F A E A L A L L R D S X L A R F V. The protein and DNA data base search revealed no match to 88 kDa protein and hence this was considered as unique protein. Further knowledge on the in vivo function of 88 kDa protein is very important to understand its role in the pathogenesis of Eales' disease.