Changes in blood antioxidants and several lipid peroxidation products in women with age-related macular degeneration

The Role of Glutathione in Age-Related Macular Degeneration (AMD)

Age-related macular degeneration (AMD) is a chronic disease that usually develops in older people. Pathogenetic changes in this disease include anatomical and functional complexes. Harmful factors damage the retina and macula. These changes may lead to partial or total loss of vision. The disease can occur in two clinical forms: dry (the progression is slow and gentle) and exudative (wet-progression is acute and severe), which usually starts in the dry form; however, the coexistence of both forms is possible. The etiology of AMD is not fully understood, and the precise mechanisms of the development of this illness are still unknown. Extensive genetic studies have shown that AMD is a multi-factorial disease and that genetic determinants, along with external and internal environmental and metabolic-functional factors, are important risk factors. This article reviews the role of glutathione (GSH) enzymes engaged in maintaining the reduced form and polymorphism in glutathione S-transferase theta-1 (GSTT1) and glutathione S-transferase mu-1 (GSTM1) in the development of AMD. We only chose papers that confirmed the influence of the parameters on the development of AMD. Because GSH is the most important antioxidant in the eye, it is important to know the influence of the enzymes and genetic background to ensure an optimal level of glutathione concentration. Numerous studies have been conducted on how the glutathione system works till today. This paper presents the current state of knowledge about the changes in GSH, GST, GR, and GPx in AMD. GST studies clearly show increased activity in ill people, but for GPx, the results relating to activity are not so clear. Depending on the research, the results also suggest higher and lower GPx activity in patients with AMD. The analysis of polymorphisms in GST genes confirmed that mutations lead to weaker antioxidant barriers and may contribute to the development of AMD; unfortunately, a meta-analysis and some research did not confirm that connection. Unspecific results of many of the parameters that make up the glutathione system show many unknowns. It is so important to conduct further research to understand the exact mechanism of defense functions of glutathione against oxidative stress in the human eye.

Effects of vitamin E and pinoline on retinal lipid peroxidation

BACKGROUND

Pinoline is a pineal indoleamine naturally found in the retina. This study compared the effects of pinoline and vitamin E on the copper (I)-induced retinal lipid peroxidation (LPO).

METHODS

Porcine retinal homogenates were mixed with 120 micro M copper (I) solution. The mixtures were co-incubated with various concentrations of pinoline or trolox (water-soluble vitamin E analogue) at 37 degrees Centigrade for 60 minutes. The amounts of malondialdehyde (MDA) and protein were assayed to quantify the LPO.

RESULTS

Copper (I) ions significantly increased the MDA concentration in the retinal homogenates (p < 0.0007). Both pinoline and trolox significantly suppressed MDA in a dose-dependent manner (p < 0.0001) and their effects were significantly different (p = 0.004). The concentrations that inhibited 50 per cent of LPO were 0.24 mM and 0.68 mM for pinoline and trolox, respectively.

DISCUSSION

Pinoline suppressed the LPO at a potency of 2.8 times compared with trolox. The results support an anti-oxidative role for pinoline in the retina. Further study is required to characterise the pharmacological potency of pinoline in vivo.

SLC7A11 Reduces Laser-Induced Choroidal Neovascularization by Inhibiting RPE Ferroptosis and VEGF Production

In age-related macular degeneration (AMD), one of the principal sources of vascular endothelial growth factor (VEGF) is retinal pigment epithelium (RPE) cells under hypoxia or oxidative stress. Solute carrier family 7 member 11 (SLC7A11), a key component of cystine/glutamate transporter, regulates the level of cellular lipid peroxidation, and restrains ferroptosis. In our study, we assessed the role of SLC7A11 in laser-induced choroidal neovascularization (CNV) and explored the underlying mechanism. We established a mouse model of CNV to detect the expression level of SLC7A11 and VEGF during disease progression. We found the expression of the SLC7A11 protein in RPE cells peaked at 3 days after laser treatment, which was correlated with the expression of VEGF. Intraperitoneal injection of SLC7A11 inhibitor expanded the area of CNV. We examined functional proteins related to oxidative stress and Fe²⁺ and found laser-induced ferroptosis accompanied by increased Fe²⁺ content and GPX4 expression in the RPE-choroidal complex after laser treatment. We verified the expression of SLC7A11 in the ARPE19 cell line and the effects of its inhibitors on cell viability and lipid peroxidation in vitro. Application of SLC7A11 inhibitor and SLC7A11 knockdown increased the level of lipid peroxidation and reduced the cell viability of ARPE19 which can be rescued by ferroptosis inhibitors ferrostatin-1 (Fer-1) and liproxstatin-1 (Lip-1). Conversely, SLC7A11 overexpression induced resistance to erastin or RSL3-induced ferroptosis. Moreover, we tested the possible regulatory transcription factor NF-E2-related factor 2 (NRF2) of SLC7A11 by Western blot. Knock-down of NRF2 decreased the expression of SLC7A11. Our study suggests that SLC7A11 plays a key role in the laser-induced CNV model by protecting RPE cells from ferroptosis. SLC7A11 provides a new therapeutic target for neovascular AMD patients.

Determination of Oxidative Stress Markers in the Aqueous Humor and Corneal Tissues of Patients With Congenital Hereditary Endothelial Dystrophy

PURPOSE

The aim of this study is to determine the presence of oxidative stress markers in the aqueous humor (AH) and corneal tissues of patients with congenital hereditary endothelial dystrophy (CHED).

METHODS

Interventional prospective study was undertaken to quantify levels of ascorbic acid and glutathione in the AH of patients with CHED. AH was collected from patients undergoing keratoplasty and levels of ascorbic acid and glutathione were determined using biochemical assays and measured spectrophotometrically. AH collected from pediatric patients with cataract were used as control. Corneal sections of patients who underwent penetrating keratoplasty were obtained, and presence of glutathione peroxidase 1, catalase, and superoxide dismutase was determined by immunohistochemistry. Tissue sections obtained from cadaveric corneas unsuitable for clinical transplant were used as control.

RESULTS

Significantly increased ascorbic acid levels were determined in patients with CHED (605.6 ± 158.9 μM) compared with those in controls (190.5 ± 74.72 μM). However, a trend toward reduced level of glutathione was detected in patients with CHED compared with that in the controls. Increased glutathione peroxidase 1 staining and reduced expression of catalase was detected in corneal tissues of patients with CHED compared with those in control corneal tissues. There was no apparent changes observed in the expression of superoxide dismutase in the corneal sections obtained from patients with CHED.

CONCLUSIONS

To the best of our knowledge, this is the first study to determine the levels of ascorbic acid and glutathione in AH of patients with CHED. Our data suggest the presence of oxidative stress in CHED that might be responsible for the pathological changes in patients with CHED.

Oxidative stress biomarkers in Fabry disease: is there a room for them?

BACKGROUND

Fabry disease (FD) is an X-linked lysosomal storage disorder, caused by deficient activity of the alpha-galactosidase A enzyme leading to progressive and multisystemic accumulation of globotriaosylceramide. Recent data point toward oxidative stress signalling which could play an important role in both pathophysiology and disease progression.

METHODS

We have examined oxidative stress biomarkers [Advanced Oxidation Protein Products (AOPP), Ferric Reducing Antioxidant Power (FRAP), thiolic groups] in blood samples from 60 patients and 77 healthy controls.

RESULTS

AOPP levels were higher in patients than in controls (p < 0.00001) and patients presented decreased levels of antioxidant defences (FRAP and thiols) with respect to controls (p < 0.00001). In a small group of eight treatment-naïve subjects with FD-related mutations, we found altered levels of oxidative stress parameters and incipient signs of organ damage despite normal lyso-Gb3 levels.

CONCLUSIONS

Oxidative stress occurs in FD in both treated and naïve patients, highlighting the need of further research in oxidative stress-targeted therapies. Furthermore, we found that oxidative stress biomarkers may represent early markers of disease in treatment-naïve patients with a potential role in helping interpretation of FD-related mutations and time to treatment decision.

Kinsenoside Ameliorates Oxidative Stress-Induced RPE Cell Apoptosis and Inhibits Angiogenesis via Erk/p38/NF-κB/VEGF Signaling

The pathological superoxidative condition that retinal pigment epithelium (RPE) cells experience contributed to the advancement of age-related macular degeneration (AMD), which was accompanied by significant neovascularization. Therefore, the discovery of novel pharmacological candidates to ameliorate oxidative damage (H₂O₂) against RPE cells and inhibit the following angiogenesis simultaneously is urgently needed. Herein, we found that kinsenoside (Kin), an active component derived from Anoectochilus roxburghii, was able to protect RPE cells effectively and attenuate subsequent angiogenesis. In this study, H₂O₂-induced oxidative injury reduced RPE cell viability and increased cell apoptosis, which was significantly rescued by the treatment with Kin. Compared with H₂O₂ alone, Kin decreased the levels of Bax and increased the production of Bcl-2 in RPE cells. H₂O₂-stimulated VEGF up-regulation was inhibited by Kin treatment. Human umbilical vein endothelial cell (HUVEC) neovascularization induced by conditioned medium (CM) from H₂O₂-stimulated RPE cells was attenuated by treatment with Kin, VEGF antagonist, NF-κB, Erk-MAPK, and p38-MAPK inhibitors. Additionally, H₂O₂-activated phosphorylated expression of IκBα, p65, Erk, and p38 in RPE cells was inhibited by treatment with Kin. Taken together, Kin protected RPE from apoptosis against oxidative stress while simultaneously decreasing apoptosis-related neovascularization. This could be ascribed to the inhibition of Erk/p38/NF-κB signaling by Kin that contributed to the resulting decreased VEGF expression in H₂O₂-treated RPE cells.

Role of macrophage migration inhibitory factor (MIF) in the effects of oxidative stress on human retinal pigment epithelial cells

Proliferative vitreoretinopathy (PVR) is the major cause of treatment failure in individuals who undergo surgery for retinal detachment. The epithelial-mesenchymal transition (EMT) in retinal pigment epithelium (RPE) cells contributes to the pathogenesis of PVR. Oxidative stress is thought to play a role in the progression of retinal diseases including PVR. We have now examined the effects of oxidative stress on the EMT and related processes in the human RPE cell line. We found that H₂ O₂ induced the contraction of RPE cells in a three-dimensional collagen gel. Analysis of a cytokine array revealed that H₂ O₂ specifically increased the release of macrophage migration inhibitory factor (MIF) from RPE cells. Reverse transcription-polymerase chain reaction and immunoblot analyses showed that H₂ O₂ increased the expression of MIF in RPE cells. Immunoblot and immunofluorescence analyses revealed that H₂ O₂ upregulated the expression of α-SMA and vimentin and downregulated that of ZO-1 and N-cadherin. Consistent with these observations, the transepithelial electrical resistance of cell was reduced by exposure to H₂ O₂ . The effects of oxidative stress on EMT-related and junctional protein expression as well as on transepithelial electrical resistance were inhibited by antibodies to MIF, but they were not mimicked by treatment with recombinant MIF. Finally, analysis with a profiling array for mitogen-activated protein kinase signalling revealed that H₂ O₂ specifically induced the phosphorylation of p38 mitogen-activated protein kinase. Our results thus suggest that MIF may play a role in induction of the EMT and related processes by oxidative stress in RPE cells and that it might thereby contribute to the pathogenesis of PVR. Proliferative vitreoretinopathy is a major complication of rhegmatogenous retinal detachment, and both oxidative stress and induction of the EMT in RPE cells are thought to contribute to the pathogenesis of this condition. We have now examined the effects of oxidative stress on the EMT and related processes in the human RPE cell line ARPE19. Our results thus implicate MIF in induction of the EMT and related processes by oxidative stress in RPE cells and the regulated expression of EMT markers. They further suggest that MIF may play an important role in the pathogenesis of PVR.

A chimeric Cfh transgene leads to increased retinal oxidative stress, inflammation, and accumulation of activated subretinal microglia in mice

PURPOSE

Variants of complement factor H (Cfh) affecting short consensus repeats (SCRs) 6 to 8 increase the risk of age-related macular degeneration. Our aim was to explore the effect of expressing a Cfh variant on the in vivo susceptibility of the retina and RPE to oxidative stress and inflammation, using chimeric Cfh transgenic mice (chCfhTg).

METHODS

The chCfhTg and age-matched C57BL/6J (B6) mice were subjected to oxidative stress by either normal aging, or by exposure to a combination of oral hydroquinone (0.8% HQ) and increased light. Eyes were collected for immunohistochemistry of RPE-choroid flat mounts and of retinal sections, ELISA, electron microscopy, and RPE/microglia gene expression analysis.

RESULTS

Aging mice to 2 years led to an increased accumulation of basal laminar deposits, subretinal microglia/macrophages (MG/MΦ) staining for CD16 and for malondialdehyde (MDA), and MDA-modified proteins in the retina in chCfhTg compared to B6 mice. The chCfhTg mice maintained on HQ diet and increased light showed greater deposition of basal laminar deposits, more accumulation of fundus spots suggestive of MG/MΦ, and increased deposition of C3d in the sub-RPE space, compared to controls. In addition, chCfhTg mice demonstrated upregulation of NLRP3, IP-10, CD68, and TREM-2 in the RNA isolates from RPE/MG/MΦ.

CONCLUSIONS

Expression of a Cfh transgene introducing a variant in SCRs 6 to 8 was sufficient to lead to increased retinal/RPE susceptibility to oxidative stress, a proinflammatory MG/MΦ phenotype, and a proinflammatory RPE/MG/MΦ gene expression profile in a transgenic mouse model. Our data suggest that altered interactions of Cfh with MDA-modified proteins may be relevant in explaining the effects of the Cfh variant.

Oxidative stress sensitizes retinal pigmented epithelial (RPE) cells to complement-mediated injury in a natural antibody-, lectin pathway-, and phospholipid epitope-dependent manner

Uncontrolled activation of the alternative complement pathway (AP) is thought to be associated with age-related macular degeneration. Previously, we have shown that in retinal pigmented epithelial (RPE) monolayers, oxidative stress reduced complement inhibition on the cell surface, resulting in sublytic complement activation and loss of transepithelial resistance (TER), but the potential ligand and pathway involved are unknown. ARPE-19 cells were grown as monolayers on transwell plates, and sublytic complement activation was induced with H2O2 and normal human serum. TER deteriorated rapidly in H2O2-exposed monolayers upon adding normal human serum. Although the effect required AP activation, AP was not sufficient, because elimination of MASP, but not C1q, prevented TER reduction. Reconstitution experiments to unravel essential components of the lectin pathway (LP) showed that both ficolin and mannan-binding lectin can activate the LP through natural IgM antibodies (IgM-C2) that recognize phospholipid cell surface modifications on oxidatively stressed RPE cells. The same epitopes were found on human primary embryonic RPE monolayers. Likewise, mouse laser-induced choroidal neovascularization, an injury that involves LP activation, could be increased in antibody-deficient rag1(-/-) mice using the phospholipid-specific IgM-C2. In summary, using a combination of depletion and reconstitution strategies, we have shown that the LP is required to initiate the complement cascade following natural antibody recognition of neoepitopes, which is then further amplified by the AP. LP activation is triggered by IgM bound to phospholipids. Taken together, we have defined novel mechanisms of complement activation in oxidatively stressed RPE, linking molecular events involved in age-related macular degeneration, including the presence of natural antibodies and neoepitopes.

Animal models of age related macular degeneration

Age related macular degeneration (AMD) is the leading cause of vision loss of those over the age of 65 in the industrialized world. The prevalence and need to develop effective treatments for AMD has lead to the development of multiple animal models. AMD is a complex and heterogeneous disease that involves the interaction of both genetic and environmental factors with the unique anatomy of the human macula. Models in mice, rats, rabbits, pigs and non-human primates have recreated many of the histological features of AMD and provided much insight into the underlying pathological mechanisms of this disease. In spite of the large number of models developed, no one model yet recapitulates all of the features of human AMD. However, these models have helped reveal the roles of chronic oxidative damage, inflammation and immune dysregulation, and lipid metabolism in the development of AMD. Models for induced choroidal neovascularization have served as the backbone for testing new therapies. This article will review the diversity of animal models that exist for AMD as well as their strengths and limitations.

Changes in blood oxidative and antioxidant parameters in a group of Chinese patients with age-related macular degeneration

OBJECTIVE

To measure the oxidative and antioxidant biochemical parameters in the serum of Chinese patients with age-related macular degeneration (AMD) and in a similar age control group from the same area.

DESIGN

A case-control study.

PARTICIPANTS

56 AMD patients ( 21 early dry, 13 geographic atrophy and 22 wet form) and 34 normal subjects, similar for age and sex were studied.

MEASUREMENTS

Both groups completed a questionnaire about demographic characters and dieatry habit, and the levels of serum lipid peroxidation (malondialdehyde, MDA) and antioxidants parameters (vitamin C and E, the activities of superoxide dismutase--SOD, total antioxidant capacity--TAC ) were determined.

RESULTS

There was a significantly higher frequency of daily intake of fruit and legumes in controls than in AMD patients. There was a significantly increased serum MDA levels and SOD activities, and significantly decreased serum vitamin C and total antioxidant capacity in AMD patients as compared to controls. The intensity of lipid peroxidation was higher with the progression of AMD. There was not difference in serum vitamin E levels between AMD patients and controls.

CONCLUSION

Oxido-reduction disturbance may be involved in the pathogenesis of AMD. There is a significantly decreased antioxidant capacity in AMD patients.

Induction of phase 2 antioxidant enzymes by broccoli sulforaphane: perspectives in maintaining the antioxidant activity of vitamins a, C, and e

Consumption of fruits and vegetables is recognized as an important part of a healthy diet. Increased consumption of cruciferous vegetables in particular has been associated with a decreased risk of several degenerative and chronic diseases, including cardiovascular disease and certain cancers. Members of the cruciferous vegetable family, which includes broccoli, Brussels sprouts, cauliflower, and cabbage, accumulate significant concentrations of glucosinolates, which are metabolized in vivo to biologically active isothiocyanates (ITCs). The ITC sulforaphane, which is derived from glucoraphanin, has garnered particular interest as an indirect antioxidant due to its extraordinary ability to induce expression of several enzymes via the KEAP1/Nrf2/ARE pathway. Nrf2/ARE gene products are typically characterized as Phase II detoxification enzymes and/or antioxidant (AO) enzymes. Over the last decade, human clinical studies have begun to provide in vivo evidence of both Phase II and AO enzyme induction by SF. Many AO enzymes are redox cycling enzymes that maintain redox homeostasis and activity of free radical scavengers such as vitamins A, C, and E. In this review, we present the existing evidence for induction of PII and AO enzymes by SF, the interactions of SF-induced AO enzymes and proposed maintenance of the essential vitamins A, C, and E, and, finally, the current view of genotypic effects on ITC metabolism and AO enzyme induction and function.

p53, oxidative stress, and aging

Mammalian aging is associated with elevated levels of oxidative damage of DNA, proteins, and lipids as a result of unbalanced prooxidant and antioxidant activities. Accumulating evidence indicates that oxidative stress is a major physiological inducer of aging. p53, the guardian of the genome that is important for cellular responses to oxidative stresses, might be a key coordinator of oxidative stress and aging. In response to low levels of oxidative stresses, p53 exhibits antioxidant activities to eliminate oxidative stress and ensure cell survival; in response to high levels of oxidative stresses, p53 exhibits pro-oxidative activities that further increase the levels of stresses, leading to cell death. p53 accomplishes these context-dependent roles by regulating the expression of a panel of genes involved in cellular responses to oxidative stresses and by modulating other pathways important for oxidative stress responses. The mechanism that switches p53 function from antioxidant to prooxidant remains unclear, but could account for the findings that increased p53 activities have been linked to both accelerated aging and increased life span in mice. Therefore, a balance of p53 antioxidant and prooxidant activities in response to oxidative stresses could be important for longevity by suppressing the accumulation of oxidative stresses and DNA damage.

Serum superoxide dismutase and malondialdehyde levels in a group of Chinese patients with age-related macular degeneration

BACKGROUND AND AIMS

The aim of this study was to investigate superoxide dismutase (SOD) activity together with malondialdehyde (MDA) levels in a group of Chinese patients with age-related macular degeneration (AMD).

METHODS

Serum SOD activity and MDA levels were analysed in 56 AMD patients with subtypes (early dry, geographic atrophy, and wet) and 34 healthy controls matched with age and sex.

RESULTS

Serum MDA levels were significantly higher in AMD (3.68 ± 1.06 nmol/mL) than in controls (2.83 ± 0.43 nmol/mL; p=0.000), and was significantly higher in wet AMD (3.79 ± 0.79 nmol/mL) than in early dry AMD (3.26 ± 0.99 nmol/mL; p=0.038). Serum SOD activity was significantly higher in AMD (87.12 ± 13.22 U/mL) than in controls (79.91 ± 11.80 U/mL; p=0.012), and slightly higher in wet AMD (89.52 ± 16.25 U/mL) than in GA (83.62 ± 9.75 U/mL; p=0.275) and early dry AMD (81.64 ± 18.90 U/mL; p=0.093). There was a positive correlation between serum MDA levels and SOD activities in AMD patients and controls (r=0.320, p=0.002).

CONCLUSIONS

The observed increase in SOD activity in our study may be related to increased MDA levels, as a compensatory regulation in response to oxidative stress in AMD patients. The present data also demonstrate that oxido-reduction disturbance may be hypothesized in the pathogenesis of AMD.

The redox state of human serum albumin in eye diseases with and without complications

PURPOSE

To investigate the redox state of human serum albumin concerning cysteine-34 as a possible systemic redox marker in patients with different eye diseases with and without complications and with consideration of possible effects of age.

METHODS

Cataract (CAT), glaucoma, age-related macular degeneration (AMD), diabetes mellitus (DM), diabetic retinopathy and hypertension were the pathologies investigated. Albumin redox state concerning cysteine-34 was measured by high-performance liquid chromatography with fluorescence detection. The separation gives three fractions: the fully reduced form containing a thiol group, the disulphide form and a higher oxidized form. Statistical analysis was done by Student's t-test, analysis of variance and stepwise regression analysis.

RESULTS

Albumin as a systemic marker for oxidative stress was shifted to a more oxidized state by DM. An even stronger shift to the oxidized form was observed in patients with proliferative diabetic retinopathy. Notably, these effects were independent from age. In contrast, CAT and AMD had no influence on serum albumin redox state.

CONCLUSION

Serum albumin is not shifted to more oxidized forms by localized oxidative stress, but it is in systemic diseases like DM.

The role of lipid peroxidation products and oxidative stress in activation of the canonical wingless-type MMTV integration site (WNT) pathway in a rat model of diabetic retinopathy

AIMS/HYPOTHESIS

Our recent studies suggest that activation of the wingless-type MMTV integration site (WNT) pathway plays pathogenic roles in diabetic retinopathy and age-related macular degeneration. Here we investigated the causative role of oxidative stress in retinal WNT pathway activation in an experimental model of diabetes.

METHODS

Cultured retinal pigment epithelial cells and retinal capillary endothelial cells were treated with a lipid peroxidation product, 4-hydroxynonenal (HNE), and an antioxidant, N-acetyl-cysteine (NAC). In vivo, rats with streptozotocin-induced diabetes were treated by NAC for 8 weeks. Activation of the canonical WNT pathway was measured by TOPFLASH assay and by western blot analysis of WNT pathway components and a WNT target gene, Ctgf. Oxidative stress in the retina was evaluated by immunostaining of HNE and 3-nitrotyrosine.

RESULTS

Levels of phosphorylated and total LDL receptor-related protein (LRP)6, and cytosolic β-catenin, as well as transcriptional activity of T cell factor (TCF)/β-catenin were significantly increased by HNE. The production of connective tissue growth factor (CTGF) was also upregulated by HNE. NAC blocked the WNT pathway activation induced by HNE. Furthermore, LRP6 stability was increased by HNE and decreased by NAC. Retinal levels of HNE and 3-nitrotyrosine were significantly increased in diabetic rats, compared with those in non-diabetic rats. In the same diabetic rat retinas, levels of LRP6, cytosolic β-catenin and CTGF were significantly increased. NAC treatment reduced HNE and 3-nitrotyrosine levels and attenuated the upregulation of LRP6, β-catenin and CTGF in diabetic rat retina.

CONCLUSIONS/INTERPRETATION

Lipid peroxidation products activate the canonical WNT pathway through oxidative stress, which plays an important role in the development of retinal diseases.

Iron prochelator BSIH protects retinal pigment epithelial cells against cell death induced by hydrogen peroxide

Dysregulation of localized iron homeostasis is implicated in several degenerative diseases, including Parkinson's, Alzheimer's, and age-related macular degeneration, wherein iron-mediated oxidative stress is hypothesized to contribute to cell death. Inhibiting toxic iron without altering normal metal-dependent processes presents significant challenges for standard small molecule chelating agents. We previously introduced BSIH (isonicotinic acid [2-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-benzylidene]-hydrazide) prochelators that are converted by hydrogen peroxide into SIH (salicylaldehyde isonicotinoyl hydrazone) chelating agents that inhibit iron-catalyzed hydroxyl radical generation. Here, we show that BSIH protects a cultured cell model for retinal pigment epithelium against cell death induced by hydrogen peroxide. BSIH is more stable than SIH in cell culture medium and is more protective during long-term experiments. Repetitive exposure of cells to BSIH is nontoxic, whereas SIH and desferrioxamine induce cell death after repeated exposure. Combined, our results indicate that cell protection by BSIH involves iron sequestration that occurs only when the cells are stressed by hydrogen peroxide. These findings suggest that prochelators discriminate toxic iron from healthy iron and are promising candidates for neuro- and retinal protection.

Plasma homocysteine and total thiol content in patients with exudative age-related macular degeneration

PURPOSE

Exudative age-related macular degeneration (ARMD) is one of the debilitating ocular complications, which results in permanent blindness. Elevated homocysteine (Hcys) levels have been associated in the development of several vascular diseases. Vascular and oxidative stress theories have been implicated for the development of choroidal neovascularization in exudative ARMD. The aim of the present study was to investigate the possible role of plasma Hcys and thiol content (tSH) as a risk factor for the development of exudative ARMD.

METHOD

A total of 16 patients with exudative ARMD and 20 age-matched controls were recruited for the study. Plasma Hcys levels were analysed using Reverse Phase High Performance Liquid Chromatography. Plasma glutathione (GSH) content was determined using o-phthalaldehyde (OPA) derivatization and subsequent detection by fluorimeter. Plasma tSH levels were determined by using thiol-specific reagent dithionitrobenzoic acid (DTNB) spectrophotometrically.

RESULTS

Plasma Hcys levels in exudative ARMD were elevated three-fold (18+/-5.0 microM) when compared to healthy controls (6.7+/-1.8 microM). There was a two-fold decrease in the GSH and tSH in exudative ARMD when compared with controls. Negative correlation was observed between diminished tSH and Hcys levels (r=-0.4837, P=0.05). Similarly plasma Hcys levels negatively correlated with GSH content (r=-0.6620, P<0.05).

CONCLUSION

Results from our present study revealed that there is an elevated Hcys level and diminished thiol pool content in exudative ARMD that are significant.

Serum paraoxonase 1 activity and lipid peroxidation levels in patients with age-related macular degeneration

Our objective was to investigate antioxidant paraoxonase 1 (PON1) activity together with malondialdehyde (MDA) levels to evaluate oxidative stress in patients with age-related macular degeneration (AMD), an important cause of blindness in the elderly population. Serum PON1 activity and MDA levels were analyzed in 37 patients with AMD and compared with 29 healthy controls using a spectrophotometric method. Serum MDA levels were significantly higher in the patient group (2.76 +/- 1.28 nmol/ml) than controls (1.00 +/- 0.36 nmol/ml; p < 0.001), whereas PON1 activity was lower in the patient group (132.27 +/- 63.39 U/l) than controls (312.13 +/- 136.23 U/l; p < 0.001). There was a negative correlation between MDA and PON1 levels (r = -0.470, p < 0.001). We conclude that the observed increase in MDA levels may be related to decreased PON1 activity; the present data also demonstrated that an obvious negative correlation between PON1 activity and MDA levels exists in patients with AMD. PON1 is also an antioxidant agent, therefore effective antioxidant therapy to inhibit lipid peroxidation is necessary and agents to increase PON1 activity may be a therapeutic option in AMD.

Biochemical properties of purified human retinol dehydrogenase 12 (RDH12): catalytic efficiency toward retinoids and C9 aldehydes and effects of cellular retinol-binding protein type I (CRBPI) and cellular retinaldehyde-binding protein (CRALBP) on the oxidation and reduction of retinoids

Retinol dehydrogenase 12 (RDH12) is a novel member of the short-chain dehydrogenase/reductase superfamily of proteins that was recently linked to Leber's congenital amaurosis 3 (LCA). We report the first biochemical characterization of purified human RDH12 and analysis of its expression in human tissues. RDH12 exhibits approximately 2000-fold lower K(m) values for NADP(+) and NADPH than for NAD(+) and NADH and recognizes both retinoids and lipid peroxidation products (C(9) aldehydes) as substrates. The k(cat) values of RDH12 for retinaldehydes and C(9) aldehydes are similar, but the K(m) values are, in general, lower for retinoids. The enzyme exhibits the highest catalytic efficiency for all-trans-retinal (k(cat)/K(m) approximately 900 min(-)(1) microM(-)(1)), followed by 11-cis-retinal (450 min(-)(1) mM(-)(1)) and 9-cis-retinal (100 min(-)(1) mM(-)(1)). Analysis of RDH12 activity toward retinoids in the presence of cellular retinol-binding protein (CRBP) type I or cellular retinaldehyde-binding protein (CRALBP) suggests that RDH12 utilizes the unbound forms of all-trans- and 11-cis-retinoids. As a result, the widely expressed CRBPI, which binds all-trans-retinol with much higher affinity than all-trans-retinaldehyde, restricts the oxidation of all-trans-retinol by RDH12, but has little effect on the reduction of all-trans-retinaldehyde, and CRALBP inhibits the reduction of 11-cis-retinal stronger than the oxidation of 11-cis-retinol, in accord with its higher affinity for 11-cis-retinal. Together, the tissue distribution of RDH12 and its catalytic properties suggest that, in most tissues, RDH12 primarily contributes to the reduction of all-trans-retinaldehyde; however, at saturating concentrations of peroxidic aldehydes in the cells undergoing oxidative stress, for example, photoreceptors, RDH12 might also play a role in detoxification of lipid peroxidation products.

Resveratrol reduces oxidation and proliferation of human retinal pigment epithelial cells via extracellular signal-regulated kinase inhibition

Epidemiological evidence suggests that moderate wine consumption and antioxidant-rich diets may protect against age-related macular degeneration (AMD), the leading cause of vision loss among the elderly. Development of AMD and other retinal diseases, such as proliferative vitreoretinopathy (PVR), is associated with oxidative stress in the retinal pigment epithelium (RPE), a cell layer responsible for maintaining the health of the retina by providing structural and nutritional support. We hypothesize that resveratrol, a red wine polyphenol, may be responsible, in part, for the health benefits of moderate red wine consumption on retinal disease. To test this hypothesis, the antioxidant and antiproliferative effects of resveratrol were examined in a human RPE cell line (designated ARPE-19). Cell proliferation was determined using the bromodeoxyuridine (BrdU) assay, intracellular oxidation was assessed by dichlorofluorescein fluorescence, and activation of the mitogen-activated protein kinase (MAPK) cascade was measured by immunoblotting. Treatment with 50 and 100 micromol/L resveratrol significantly reduced proliferation of RPE cells by 10% and 25%, respectively (P<0.05). This reduction in proliferation was not associated with resveratrol-induced cytotoxicity. Resveratrol (100 micromol/L) inhibited basal and H2O2-induced intracellular oxidation and protected RPE cells from H2O2-induced cell death. The observed reduction in cell proliferation was associated with inhibition of mitogen activated protein kinase/ERK (MEK) and extracellular signal-regulated kinase (ERK 1/2) activities at concentrations of resveratrol as low as 5 micromol/L. These results suggest that resveratrol can reduce oxidative stress and hyperproliferation of the RPE.

Enhanced expression of glutathione-S-transferase A1-1 protects against oxidative stress in human retinal pigment epithelial cells

Glutathione-S-transferases (GSTs) play an important role in protection mechanisms against oxidative stress. We sought to determine whether over-expression of human GSTA1-1 in RPE cells is able to attenuate H(2)O(2)-induced oxidative stress. SV40-transformed human fetal RPE cells were stably transfected with pRC/hGSTA1-1 vector which carries a full-length of human GSTA1-1 cDNA. The control RPE cells were either non-transfected or transfected with control vector pRC. Expression of hGSTA1-1 protein in these cells was confirmed by Western blot and immunocytochemical analyses. The protective effects of hGSTA1-1 on cell viability and mitochondrial DNA (mtDNA) damage caused by H(2)O(2) were examined with MTT assay and quantitative PCR (QPCR), respectively. The hGSTA1-1 transfected RPE cells exhibited a similar morphology and growth rate as control RPE cells. Immunocytochemical analysis showed robust expression hGSTA1-1 in hGSTA1-1 transfected cells versus background staining in control cells. Western blotting of protein extracts from cells transfected with hGSTA1-1 revealed a 26 kDa protein band which corresponds to the size of recombinant mature hGSTA1-1. The active GST present in the hGSTA1-1 transfected cells was approximately three times higher than in control cells. The MTT assay showed a significantly greater viability of hGSTA1-1 cells in response to H(2)O(2) (100 and 200 microm) compared to control cells (p<0.05). QPCR indicated that mtDNA damage was significantly decreased in hGSTA1-1 cells than in control cells (p<0.05). Human GSTA1-1 transfection protect against RPE cell death and mtDNA damage caused by H(2)O(2), suggesting an important role of GST in protection against oxidative stress in RPE cells.

Induction of phase 2 genes by sulforaphane protects retinal pigment epithelial cells against photooxidative damage

The retinal pigment epithelial cell (RPE cell) layer protects the photoreceptors of the retina against oxidative stress. The decline of this capacity is believed to be a major factor in the impairment of vision in age-related macular degeneration. Exposure of human adult RPE cells to UV light at predominantly 320-400 nm (UVA light) in the presence of all-trans-retinaldehyde results in photooxidative cytotoxicity. Significant protection of RPE cells was obtained by prior treatment with phase 2 gene inducers, such as the isothiocyanate sulforaphane or a bis-2-hydroxybenzylideneacetone Michael reaction acceptor. The degree of protection was correlated with the potencies of these inducers in elevating cytoprotective glutathione levels and activities of NAD(P)H:quinone oxidoreductase. In embryonic fibroblasts derived from mice in which the genes for the transcription factor Nrf2, the repressor Keap1, or both Nrf2 and Keap1 were disrupted, the magnitude of resistance to photooxidative damage paralleled the basal levels of glutathione and NAD(P)H:quinone oxidoreductase in each cell type. Demonstration of protection of RPE cells against photooxidative damage by induction of phase 2 proteins may shed light on the role of oxidative injury in ocular disease. Moreover, the finding that dietary inducers provide indirect antioxidant protection suggests novel strategies for preventing chronic degenerative diseases, such as age-related macular degeneration.