Low glutathione reductase and peroxidase activity in 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.

Dietary and Lifestyle Factors Modulate the Activity of the Endogenous Antioxidant System in Patients with Age-Related Macular Degeneration: Correlations with Disease Severity

Age-related macular degeneration (AMD) is a common cause of blindness in the elderly population, but the pathogenesis of this disease remains largely unknown. Since oxidative stress is suggested to play a major role in AMD, we aimed to assess the activity levels of components of the antioxidant system in patients with AMD. We also investigated whether lifestyle and dietary factors modulate the activity of these endogenous antioxidants and clinical parameters of disease severity. We recruited 330 patients with AMD (39 with early, 100 with intermediate and 191 with late form of AMD) and 121 controls in this study. At enrolment, patients’ dietary habits and physical activity were assessed, and each study participant underwent a thorough ophthalmologic examination. The activity of several components of the antioxidant system were measured in red blood cells and platelets using both kinetic and spectrophotometric methods. Patients with AMD consumed much lower levels of fatty fish and eggs than the control group (p = 0.008 and p = 0.04, respectively). In the nAMD group, visual acuity (VA) correlated positively with green vegetable consumption (Rs = +0.24, p = 0.004) and omega-3-rich oil intake (Rs = +0.17, p = 0.03). In the AMD group, the total physical activity MET score correlated positively with VA (Rs = +0.17, p = 0.003) and correlated negatively with the severity of AMD (Rs = −0.14, p = 0.01). A multivariate analysis of patients and controls adjusted for age, sex, and smoking status (pack-years) revealed that AMD was an independent variable associated with a lower RBC catalase (β = −0.37, p < 0.001) and higher PLT catalase (β = +0.25, p < 0.001), RBC GPx (β = +0.26, p < 0.001), PLT GPx (β = +0.16, p = 0.001), RBC R-GSSG (β = +0.13, p = 0.009), PLT R-GSSG (β = +0.12, p = 0.02) and RBC GSH transferase (β = +0.23, p < 0.001) activity. The activities of components of the antioxidant system were associated with disease severity and depended on dietary habits. The observed substantial increase in the activity of many critical endogenous antioxidants in patients with AMD further indicates that the required equilibrium in the antioxidant system is disturbed throughout the course of the disease. Our findings explicitly show that a diet rich in green vegetables, fish and omega-3-rich oils, supplemented by physical exercise, is beneficial for patients with AMD, as it might delay disease progression and help retain better visual function.

Inhibiting microRNA-144 potentiates Nrf2-dependent antioxidant signaling in RPE and protects against oxidative stress-induced outer retinal degeneration

The retinal pigment epithelium (RPE) is consistently exposed to high levels of pro-oxidant and inflammatory stimuli. As such, under normal conditions the antioxidant machinery in the RPE cell is one of the most efficient in the entire body. However, antioxidant defense mechanisms are often impacted negatively by the process of aging and/or degenerative disease leaving RPE susceptible to damage which contributes to retinal dysfunction. Thus, understanding better the mechanisms governing antioxidant responses in RPE is critically important. Here, we evaluated the role of the redox sensitive microRNA miR-144 in regulation of antioxidant signaling in human and mouse RPE. In cultured human RPE, miR-144-3p and miR-144-5p expression was upregulated in response to pro-oxidant stimuli. Likewise, overexpression of miR-144-3p and -5p using targeted miR mimics was associated with reduced expression of Nrf2 and downstream antioxidant target genes (NQO1 and GCLC), reduced levels of glutathione and increased RPE cell death. Alternately, some protection was conferred against the above when miR-144-3p and miR-144-5p expression was suppressed using antagomirs. Expression analyses revealed a higher conservation of miR-144-3p expression across species and additionally, the presence of two potential Nrf2 binding sites in the 3p sequence compared to only one in the 5p sequence. Thus, we evaluated the impact of miR-144-3p expression in the retinas of mice in which a robust pro-oxidant environment was generated using sodium iodate (SI). Subretinal injection of miR-144-3p antagomir in SI mice preserved retinal integrity and function, decreased oxidative stress, limited apoptosis and enhanced antioxidant gene expression. Collectively, the present work establishes miR-144 as a potential target for preventing and treating degenerative retinal diseases in which oxidative stress is paramount and RPE is prominently affected (e.g., age-related macular degeneration and diabetic retinopathy).

N-Acetyl-L-cysteine Protects Human Retinal Pigment Epithelial Cells from Oxidative Damage: Implications for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) involves the loss of retinal pigment epithelium (RPE) and photoreceptors and is one of the leading causes of blindness in the elderly. Oxidative damage to proteins, lipids, and DNA has been associated with RPE dysfunction and AMD. In this study, we evaluated oxidative stress in AMD and the efficacy of antioxidant, N-acetyl-L-cysteine (NAC), in protecting RPE from oxidative damage. To test this idea, primary cultures of RPE from human donors with AMD (n = 32) or without AMD (No AMD, n = 21) were examined for expression of NADPH oxidase (NOX) genes, a source of reactive oxygen species (ROS). Additionally, the cells were pretreated with NAC for 2 hours and then treated with either hydrogen peroxide (H₂O₂) or tert-butyl hydroperoxide (t-BHP) to induce cellular oxidation. Twenty-four hours after treatment, ROS production, cell survival, the content of glutathione (GSH) and adenosine triphosphate (ATP), and cellular bioenergetics were measured. We found increased expression of p22phox, a NOX regulator, in AMD cells compared to No AMD cells (p = 0.02). In both AMD and No AMD cells, NAC pretreatment reduced t-BHP-induced ROS production and protected from H₂O₂-induced cell death and ATP depletion. In the absence of oxidation, NAC treatment improved mitochondrial function in both groups (p < 0.01). Conversely, the protective response exhibited by NAC was disease-dependent for some parameters. In the absence of oxidation, NAC significantly reduced ROS production (p < 0.001) and increased GSH content (p = 0.02) only in RPE from AMD donors. Additionally, NAC-mediated protection from H₂O₂-induced GSH depletion (p = 0.04) and mitochondrial dysfunction (p < 0.05) was more pronounced in AMD cells compared with No AMD cells. These results demonstrate the therapeutic benefit of NAC by mitigating oxidative damage in RPE. Additionally, the favorable outcomes observed for AMD RPE support NAC's relevance and the potential therapeutic value in treating AMD.

The Association of Serum Iron-Binding Proteins and the Antioxidant Parameter Levels in Age-Related Macular Degeneration

PURPOSE

Age-related macular degeneration (AMD) is the leading cause of the irreversible central visual loss among the elderly in the developed countries. Iron is considered a potent generator of the oxidative damage whose levels increase with age, potentially exacerbating the age-related diseases. The aim of this study was to assess the serum values of iron, and iron-binding proteins (transferrin, ferritin, and haptoglobin) in patients with AMD along with the parameters of the antioxidant defense: superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase, and total antioxidant status (TAS), in order to analyze the possible impact of iron and iron-binding proteins to the development of oxidative stress in AMD patients, and the association of the selected parameters with the AMD. In addition, the aim was to examine the gender differences and calculate the cutoff points of tested parameters that could be associated with AMD.

MATERIAL AND METHODS

A cross-sectional study included 55 AMD patients aged 71.7 ± 7.36 years and 65 aged-matched control subjects aged 70.25 ± 6.46 years.

RESULTS

Significantly lower ferritin (P = 0.025), SOD (P = 0.026), GPx (P = 0.019), and TAS (P < 0.004) values were found in patients with AMD compared to the controls (P < 0.05). Significant association of GPx < 27 U/gHb (odds ratio [OR]: 1.13; 95% confidence interval [CI] 0.78-2.10; P = 0.049), TAS < 1.25 mmol/L (OR: 5.77; 95% CI 0.98-367.0; P < 0.000), ferritin < 84.8 pg/mL (OR: 2.52; 95% CI 1.37-4.62; P = 0.002), and haptoglobin<1.51 g/L (OR: 1.94; 95% CI 1.05-3.56; P = 0.031) was found with the AMD. According to receiver operating characteristic curve analysis, ferritin concentration <84.8 pg/L, GPx < 27 U/gHb, and TAS < 1.25 mmol/L have sufficient predictive ability for AMD.

CONCLUSION

Significantly reduced capacity of the antioxidant defense system and iron-binding storage proteins (ferritin) found in AMD could have an important role in the development of increase oxidative stress in AMD patients.

Sevoflurane Affects Oxidative Stress and Alters Apoptosis Status in Children and Cultured Neural Stem Cells

Anesthesia-induced neurotoxicity in immature animals has raised concerns about similar effects occurring in young children. Our study investigated two commonly used anesthetics-sevoflurane and propofol-for neurotoxicity in young children. Forty-seven children (aged 12-36 months) undergoing hypospadias repair surgery were randomized to receive sevoflurane (SG, n = 24) or propofol (PG, n = 23) general anesthesia. Venous blood was collected at three different times-immediately after induction, 2 h, and 3 days after surgery. The cellular portion was assessed for antioxidant defense and DNA damage, using enzyme assay kits and qRT-PCR, respectively, while serum was used to treat cultured neural stem cells (NSCs). MTT assay and TUNEL staining were performed, and the mRNA levels of antioxidant enzymes and apoptosis indicators were evaluated by qRT-PCR. Antioxidant defense and apoptosis status in the SG group were significantly higher than in the PG group at 2 h after surgery. Additionally, exposure of NSCs to postoperative serum of the SG group resulted in decreased cell density and viability, increased TUNEL-positive cells, elevated mRNA levels of antioxidant enzymes, and cleaved caspase-3 expression. Our data shows for the first time that in young children, administration of sevoflurane, but not propofol, leads to temporally increased antioxidant defense and apoptosis status as well as damage of NSCs.

Depletion of the Third Complement Component Ameliorates Age-Dependent Oxidative Stress and Positively Modulates Autophagic Activity in Aged Retinas in a Mouse Model

The aim of the study was to investigate the influence of complement component C3 global depletion on the biological structure and function of the aged retina. In vivo morphology (OCT), electrophysiological function (ERG), and the expression of selected oxidative stress-, apoptosis-, and autophagy-related proteins were assessed in retinas of 12-month-old C3-deficient and WT mice. Moreover, global gene expression in retinas was analyzed by RNA arrays. We found that the absence of active C3 was associated with (1) alleviation of the age-dependent decrease in retinal thickness and gradual deterioration of retinal bioelectrical function, (2) significantly higher levels of antioxidant enzymes (catalase and glutathione reductase) and the antiapoptotic survivin and Mcl-1/Bak dimer, (3) lower expression of the cellular oxidative stress marker-4HNE-and decreased activity of proapoptotic caspase-3, (4) ameliorated retinal autophagic activity with localization of ubiquitinated protein conjugates commonly along the retinal pigment epithelium (RPE) layer, and (5) significantly increased expression of several gene sets associated with maintenance of the physiological functions of the neural retina. Our findings shed light on mechanisms of age-related retinal alterations by identifying C3 as a potential therapeutic target for retinal aging.

Systemic and ocular fluid compounds as potential biomarkers in age-related macular degeneration

Biomarkers can help unravel mechanisms of disease and identify new targets for therapy. They can also be useful in clinical practice for monitoring disease progression, evaluation of treatment efficacy, and risk assessment in multifactorial diseases, such as age-related macular degeneration (AMD). AMD is a highly prevalent progressive retinal disorder for which multiple genetic and environmental risk factors have been described, but the exact etiology is not yet fully understood. Many compounds have been evaluated for their association with AMD. We performed an extensive literature review of all compounds measured in serum, plasma, vitreous, aqueous humor, and urine of AMD patients. Over 3600 articles were screened, resulting in more than 100 different compounds analyzed in AMD studies, involved in neovascularization, immunity, lipid metabolism, extracellular matrix, oxidative stress, diet, hormones, and comorbidities (such as kidney disease). For each compound, we provide a short description of its function and discuss the results of the studies in relation to its usefulness as AMD biomarker. In addition, biomarkers identified by hypothesis-free techniques, including metabolomics, proteomics, and epigenomics, are covered. In summary, compounds belonging to the oxidative stress pathway, the complement system, and lipid metabolism are the most promising biomarker candidates for AMD. We hope that this comprehensive survey of the literature on systemic and ocular fluid compounds as potential biomarkers in AMD will provide a stepping stone for future research and possible implementation in clinical practice.

The association of enzymatic and non-enzymatic antioxidant defense parameters with inflammatory markers in patients with exudative form of age-related macular degeneration

There are evidence that oxidative stress and inflammation are involved in the pathogenesis of the age-related macular degeneration (AMD). The aim of this study was to analyze the antioxidant defense parameters and inflammatory markers in patients with exudative form of AMD (eAMD), their mutual correlations and association with the specific forms of AMD. The cross-sectional study, included 75 patients with the eAMD, 31 patients with the early form, and 87 aged-matched control subjects. Significantly lower SOD, TAS and albumin values and higher GR, CRP and IL-6 were found in the eAMD compared to the early form (p<0.05). Significant negative correlations were found between GPx and fibrinogen (r = -0.254), TAS and IL-6 (r = -0.999) and positive correlations between uric acid and CRP (r = 0.292), IL-6 and uric acid (r = 0.398) in the eAMD. A significant association of CRP (OR: 1.16, 95% CI: 1.03-1.32, p = 0.018), fibrinogen (OR: 2.21, 95% CI: 1.14-4.85, p = 0.021), TAS (OR: 7.45, 95% CI: 3.97-14.35, p = 0.0001), albumin (OR: 1.25, 95% CI: 1.11-1.41, p = 0.0001) and uric acid (OR: 1.006, 95% CI: 1.00-1.02, p = 0.003) was found with the eAMD. In conclusion it may be suggested, there is a significant impairment of antioxidant and inflammatory parameter levels in eAMD patients. In addition, significant association exists between the tested inflammatory markers and antioxidant parameters with late-eAMD.

GSTM1 and GSTM5 Genetic Polymorphisms and Expression in Age-Related Macular Degeneration

PURPOSE

Previously, two cytosolic antioxidant enzymes, Glutathione S-transferase Mu 1 (GSTM1) and Mu 5 (GSTM5), were reduced in retinas with age-related macular degeneration (AMD). This study compared genomic copy number variations (gCNV) of these two antioxidant enzymes in AMD versus controls.

METHODS

Genomic copy number (gCN) assays were performed using Taqman Gene Copy Number Assays (Applied Biosystems, Darmstadt, Germany) in technical quadruplicate for both GSTM1 and GSTM5. Peripheral leukocyte RNA levels were compared with controls in technical triplicates. Statistical comparisons were performed in SAS v9.2 (SAS Institute Inc., Cary, NC).

RESULTS

A large percentage of patients in both AMD and age-matched control groups had no copies of GSTM1 (0/0). The mean gCN of GSTM1 was 1.40 (range 0-4) and 1.61 (range 0-5) for AMD and control, respectively (p = 0.29). A greater percentage of control patients had > 3 gCNs of GSTM1 compared with AMD, respectively (15.3% versus 3.0%, p = 0.004). The gCN of GSTM5 was 2 in all samples except one control sample. The relative quantification of GSTM1 and GSTM5 mRNA from peripheral blood leukocytes in patients showed significant differences in relative expression in AMD versus control (p < 0.05). Peripheral blood leukocyte mRNA and gCN were not significantly correlated (p = 0.27).

CONCLUSION

Since high copy numbers of GSTM1 are found more frequently in controls than in AMD, it is possible that high copy number leads to increased retinal antioxidant defense. Genomic polymorphisms of GSTM1 and GSTM5 do not significantly affect the peripheral blood leukocyte mRNA levels.

Association of age-related macular degeneration with erythrocyte antioxidant enzymes activity and serum total antioxidant status

The aim was to estimate association of the oxidative stress with the occurrence of age-related macular degeneration (AMD). The activities of erythrocyte antioxidant enzymes: superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) and additionally serum total antioxidant status (TAS) were used as indicators of the oxidative stress level. 57 AMD patients (32 early and 25 late AMD) and 50 healthy, age and gender matched controls were included. GPx activity (P < 0.001) and serum TAS (P = 0.015) were significantly lower in AMD patients. The difference was not significant for SOD or CAT activities. Significant interaction between GPx and SOD was detected (P = 0.003). At high levels of SOD activity (over 75th percentile), one standard deviation decrease in GPx increases the odds for AMD for six times (OR = 6.22; P < 0.001). ROC analysis revealed that combined values of GPx activity and TAS are significant determinants of AMD status. Accuracy, sensitivity, specificity, and positive and negative predictive values were 75%, 95%, 52%, 69%, and 90%, respectively. The study showed that low GPx activity and TAS are associated with AMD. SOD modulates the association of GPx and AMD. The results suggest that erythrocyte antioxidant enzymes activity and serum TAS could be promising markers for the prediction of AMD.

Oxidative stress and neurodegenerative disorders

Living cells continually generate reactive oxygen species (ROS) through the respiratory chain during energetic metabolism. ROS at low or moderate concentration can play important physiological roles. However, an excessive amount of ROS under oxidative stress would be extremely deleterious. The central nervous system (CNS) is particularly vulnerable to oxidative stress due to its high oxygen consumption, weakly antioxidative systems and the terminal-differentiation characteristic of neurons. Thus, oxidative stress elicits various neurodegenerative diseases. In addition, chemotherapy could result in severe side effects on the CNS and peripheral nervous system (PNS) of cancer patients, and a growing body of evidence demonstrates the involvement of ROS in drug-induced neurotoxicities as well. Therefore, development of antioxidants as neuroprotective drugs is a potentially beneficial strategy for clinical therapy. In this review, we summarize the source, balance maintenance and physiologic functions of ROS, oxidative stress and its toxic mechanisms underlying a number of neurodegenerative diseases, and the possible involvement of ROS in chemotherapy-induced toxicity to the CNS and PNS. We ultimately assess the value for antioxidants as neuroprotective drugs and provide our comments on the unmet needs.

Role of antioxidant enzymes and small molecular weight antioxidants in the pathogenesis of age-related macular degeneration (AMD)

Cells in aerobic condition are constantly exposed to reactive oxygen species (ROS), which may induce damage to biomolecules, including proteins, nucleic acids and lipids. In normal circumstances, the amount of ROS is counterbalanced by cellular antioxidant defence, with its main components—antioxidant enzymes, DNA repair and small molecular weight antioxidants. An imbalance between the production and neutralization of ROS by antioxidant defence is associated with oxidative stress, which plays an important role in the pathogenesis of many age-related and degenerative diseases, including age-related macular degeneration (AMD), affecting the macula—the central part of the retina. The retina is especially prone to oxidative stress due to high oxygen pressure and exposure to UV and blue light promoting ROS generation. Because oxidative stress has an established role in AMD pathogenesis, proper functioning of antioxidant defence may be crucial for the occurrence and progression of this disease. Antioxidant enzymes play a major role in ROS scavenging and changes of their expression or/and activity are reported to be associated with AMD. Therefore, the enzymes in the retina along with their genes may constitute a perspective target in AMD prevention and therapy.

The role of heat stress on the age related protein carbonylation

Since the proteins are involved in many physiological processes in the organisms, modifications of proteins have important outcomes. Protein modifications are classified in several ways and oxidative stress related ones take a wide place. Aging is characterized by the accumulation of oxidized proteins and decreased degradation of these proteins. On the other hand protein turnover is an important regulatory mechanism for the control of protein homeostasis. Heat shock proteins are a highly conserved family of proteins in the various cells and organisms whose expressions are highly inducible during stress conditions. These proteins participate in protein assembly, trafficking, degradation and therefore play important role in protein turnover. Although the entire functions of each heat shock protein are still not completely investigated, these proteins have been implicated in the processes of protection and repair of stress-induced protein damage. This study has focused on the heat stress related carbonylated proteins, as a marker of oxidative protein modification, in young and senescent fibroblasts. The results are discussed with reference to potential involvement of induced heat shock proteins. This article is part of a Special Issue entitled: Protein Modifications.

BIOLOGICAL SIGNIFICANCE

Age-related protein modifications, especially protein carbonylation take a wide place in the literature. In this direction, to highlight the role of heat shock proteins in the oxidative modifications may bring a new aspect to the literature. On the other hand, identified carbonylated proteins in this study confirm the importance of folding process in the mitochondria which will be further analyzed in detail.

Biomarkers of oxidative stress in patients with wet age related macular degeneration

OBJECTIVE

The aim of this study was to analyze biomarkers of oxidative stress in patients with wet age related macular degeneration (AMD).

PARTICIPANTS AND MEASUREMENTS

Case-control study that includes 163 patients with wet AMD (age group of 55-82 years with the mean age of 71 years and 170 age-matched healthy controls in the age group of 55-78 years with the mean age of 71 years. The following parameters were determined: reduced and oxidized Glutathione (GSH/GSSH), protein carbonyl groups, total antioxidant activity in plasma and the activity of endogenous antioxidant enzymes, such as, gluthatione peroxidase, gluthatione reductase and superoxide dismutase.

RESULTS

We observed total antioxidant activity higher in control group (CG) compared with patients with wet AMD (7.1 ± 1.2 μM Trolox vs 5.8 ± 1.1 μM Trolox). Values of superoxide dismutase activity (SOD), gluthatione reductase (GR) and gluthatione peroxidase (GPx) are higher in control group than in patients with wet AMD. According to the GSH/GSSH results, average values were higher in the CG than in patients with wet AMD and data were not significantly different.. Values of protein carbonyl groups were higher in patients with wet AMD than in CG and significant differences were found.

CONCLUSIONS

The finding of the present study suggests that the patients with wet AMD are an altered metabolic state of oxidation-reduction and that it is convenient to give therapeutic interventions with antioxidants. We have demonstrated that systematic oxidative stress, measured by different biomarkers is closely associated with the wet AMD.

DNA methylation is associated with altered gene expression in AMD

PURPOSE

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. Evidence suggests oxidative stress plays a role in the disease. To assess the potential contribution of epigenetic regulation of antioxidant genes relevant to AMD pathogenesis, we evaluated DNA methylation, a tissue-specific genetic modulation that affects gene expression.

METHODS

Using the Infinium HumanMethylation27 Illumina platform, we performed DNA bisulfite sequencing to compare the methylation status in postmortem retina pigment epithelium (RPE)/choroid between patients with AMD and age-matched controls. Gene expression was assessed with the Affymetrix Exon Array. TaqMan gene expression assays were used for relative quantification (RT-PCR) confirmation of the expression array results: Glutathione S-transferase isoform mu1 (GSTM1) and mu5 (GSTM5) promoter methylation was confirmed by CpG island bisulfite pyrosequencing. To assess protein levels and localization, we used Western analysis, immunohistochemistry, and immunofluorescence with murine and human samples.

RESULTS

The mRNA levels of GSTM1 and GSTM5 were significantly reduced in AMD versus age-matched controls in RPE/choroid and neurosensory retina (NSR), which corresponded to hypermethylation of the GSTM1 promoter. mRNA and protein levels were decreased (RPE to a greater extent than NSR) in AMD postmortem samples, irrespective of age. Immunohistochemistry and immunofluorescence confirm the presence of the enzymes in the NSR and RPE.

CONCLUSIONS

Comparison of DNA methylation, together with mRNA levels, revealed significant differences between AMD versus normal retinas. The evidence presented suggests that GSTM1 and GSTM5 undergo epigenetic repression in AMD RPE/choroid, which may increase susceptibility to oxidative stress in AMD retinas.

Transport via SLC5A8 (SMCT1) is obligatory for 2-oxothiazolidine-4-carboxylate to enhance glutathione production in retinal pigment epithelial cells

PURPOSE

To evaluate the role of SLC5A8 in the transport of 2-oxothiazolidine-4-carboxylate (OTC) and to determine whether OTC augments glutathione production in RPE cells, thereby providing protection against oxidative stress.

METHODS

SLC5A8-mediated transport of OTC was monitored in Xenopus laevis oocytes by electrophysiological means. Saturation kinetics, Na(+)-activation kinetics, and inhibition by ibuprofen were analyzed by monitoring OTC-induced currents as a measure of transport activity. Oxidative stress was induced in ARPE-19 cells and primary RPE cells isolated from wild type and Slc5a8(-/-) mouse retinas using H(2)O(2), and the effects of OTC on cell death and intracellular glutathione concentration were examined.

RESULTS

Heterologous expression of human SLC5A8 in X. laevis oocytes induced Na(+)-dependent inward currents in the presence of OTC under voltage-clamp conditions. The transport of OTC via SLC5A8 was saturable, with a K(t) of 104 ± 3 μM. The Na(+)-activation kinetics was sigmoidal with a Hill coefficient of 1.9 ± 0.1, suggesting involvement of two Na(+) in the activation process. Ibuprofen, a blocker of SLC5A8, inhibited SLC5A8-mediated OTC transport; the concentration necessary for half-maximal inhibition was 17 ± 1 μM. OTC increased glutathione levels and protected ARPE-19 and primary RPE cells isolated from wild type mouse retinas from H(2)O(2)-induced cell death. These effects were abolished in primary RPE isolated from Slc5a8(-/-) mouse retinas.

CONCLUSIONS

OTC is a transportable substrate for SLC5A8. OTC augments glutathione production in RPE cells, thereby protecting them from oxidative damage. Transport via SLC5A8 is obligatory for this process.

Oxidation and age-related macular degeneration: insights from molecular biology

Age-related macular degeneration (AMD) is the leading cause of blindness in the developed world. It is a multifactorial disease, and current therapy predominantly limits damage only when it has already occurred. The macula is a source of high metabolic activity, and is therefore exposed to correspondingly high levels of reactive oxygen species (ROS). With age, the balance between production of ROS and local antioxidant levels is shifted, and damage ensues. Systemic ROS and antioxidant levels in AMD reflect these local processes. Genetic studies investigating mutations in antioxidant genes in AMD are inconclusive and further studies are indicated, especially to determine the role of mitochondria. Oral antioxidant supplements could be beneficial, and diet modification may help. Future treatments might either increase antioxidant capacity or reduce the production of ROS, using methods such as genetic manipulation. This article reviews the role of oxidative stress in AMD and the potential therapies that might have a role in preventing the blindness resulting from this disease.

The Clinical Application of Ozonetherapy

The reader may be eager to examine in which diseases ozonetherapy can be proficiently used and she/he will be amazed by the versatility of this complementary approach (Table 9 1). The fact that the medical applications are numerous exposes the ozonetherapist to medical derision because superficial observers or sarcastic sceptics consider ozonetherapy as the modern panacea. This seems so because ozone, like oxygen, is a molecule able to act simultaneously on several blood components with different functions but, as we shall discuss, ozonetherapy is not a panacea. The ozone messengers ROS and LOPs can act either locally or systemically in practically all cells of an organism. In contrast to the dogma that “ozone is always toxic”, three decades of clinical experience, although mostly acquired in private clinics in millions of patients, have shown that ozone can act as a disinfectant, an oxygen donor, an immunomodulator, a paradoxical inducer of antioxidant enzymes, a metabolic enhancer, an inducer of endothelial nitric oxide synthase and possibly an activator of stem cells with consequent neovascularization and tissue reconstruction.

Urinary 6-sulfatoxymelatonin level in age-related macular degeneration patients

PURPOSE

Melatonin is a potent antioxidant and free radical scavenger. It has been reported that serum melatonin level is relevant to certain aging diseases. The purpose of this study was to investigate melatonin levels in age-related macular degeneration (AMD) patients by measurement of 6-sulfatoxymelatonin levels (aMT6s), the major metabolite of melatonin in urine, and compare it with a group of age- and gender-matched controls.

METHODS

The first urine of the morning was collected from 43 AMD patients and 12 controls who did not have AMD. The level of aMT6s in specimens was measured by a commercial 6-sulfatoxymelatonin ELISA kit. The assay was performed by researchers, who were masked to the clinical information. To adjust for variation in the diluteness of urine, urinary creatinine level was measured and aMT6s levels were expressed as aMT6s/creatinine.

RESULTS

The level of urinary aMT6s/creatinine (mean+/-SD) in AMD (6.24+/-3.45 ng aMT6s/mg creatinine) was significantly lower than that of the controls (10.40+/-4.51, p=0.0128). After adjustment for various factors (age, smoking, cancer, and coronary heart disease) that may influence the aMT6s level, the odds-ratio of urinary aMT6s comparing AMD patients to controls was 0.65 (95% confidence interval=0.48-0.88, p=0.0036), indicating that urinary aMT6s level in AMD patients was lower than in controls even after multivariate adjustment.

CONCLUSIONS

Urinary aMT6s level in AMD patients was 40% lower than in age- and gender-matched controls. This difference between AMD patients and controls is present after adjustment for the factors of age, smoking, and histories of cancer and coronary heart disease. The significance of this result and the role of melatonin in the occurrence of AMD require further investigation.

Glutathione-Related Enzymes and the Eye

Glutathione and the related enzymes belong to the defence system protecting the eye against chemical and oxidative stress. This review focuses on GSH and two key enzymes, glutathione reductase and glucose-6-phosphate dehydrogenase in lens, cornea, and retina. Lens contains a high concentration of reduced glutathione, which maintains the thiol groups in the reduced form. These contribute to lens complete transparency as well as to the transparent and refractive properties of the mammalian cornea, which are essential for proper image formation on the retina. In cornea, gluthatione also plays an important role in maintaining normal hydration level, and in protecting cellular membrane integrity. In retina, glutathione is distributed in the different types of retinal cells. Intracellular enzyme, glutathione reductase, involved in reducing the oxidized glutathione has been found at highest activity in human and primate lenses, as compared to other species. Besides the enzymes directly involved in maintaining the normal redox status of the cell, glucose-6-phosphate dehydrogenase which catalyzes the first reaction of the pentose phosphate pathway, plays a key role in protection of the eye against reactive oxygen species. Cornea has a high activity of the pentose phosphate pathway and glucose-6-phosphate dehydrogenase activity. Glycation, the non-enzymic reaction between a free amino group in proteins and a reducing sugar, slowly inactivates gluthathione-related and other enzymes. In addition, glutathione can be also glycated. The presence of glutathione, and of the related enzymes has been also reported in other parts of the eye, such as ciliary body and trabecular meshwork, suggesting that the same enzyme systems are present in all tissues of the eye to generate NADPH and to maintain gluthatione in the reduced form. Changes of glutathione and related enzymes activity in lens, cornea, retina and other eye tissues, occur with ageing, cataract, diabetes, irradiation and administration of some drugs.

Glutathione dysregulation and the etiology and progression of human diseases

Glutathione (GSH) plays an important role in a multitude of cellular processes, including cell differentiation, proliferation, and apoptosis, and as a result, disturbances in GSH homeostasis are implicated in the etiology and/or progression of a number of human diseases, including cancer, diseases of aging, cystic fibrosis, and cardiovascular, inflammatory, immune, metabolic, and neurodegenerative diseases. Owing to the pleiotropic effects of GSH on cell functions, it has been quite difficult to define the role of GSH in the onset and/or the expression of human diseases, although significant progress is being made. GSH levels, turnover rates, and/or oxidation state can be compromised by inherited or acquired defects in the enzymes, transporters, signaling molecules, or transcription factors that are involved in its homeostasis, or from exposure to reactive chemicals or metabolic intermediates. GSH deficiency or a decrease in the GSH/glutathione disulfide ratio manifests itself largely through an increased susceptibility to oxidative stress, and the resulting damage is thought to be involved in diseases, such as cancer, Parkinson's disease, and Alzheimer's disease. In addition, imbalances in GSH levels affect immune system function, and are thought to play a role in the aging process. Just as low intracellular GSH levels decrease cellular antioxidant capacity, elevated GSH levels generally increase antioxidant capacity and resistance to oxidative stress, and this is observed in many cancer cells. The higher GSH levels in some tumor cells are also typically associated with higher levels of GSH-related enzymes and transporters. Although neither the mechanism nor the implications of these changes are well defined, the high GSH content makes cancer cells chemoresistant, which is a major factor that limits drug treatment. The present report highlights and integrates the growing connections between imbalances in GSH homeostasis and a multitude of human diseases.

Decreased serum paraoxonase 1 activity and increased serum homocysteine and malondialdehyde levels in age-related macular degeneration

Age-related macular degeneration (AMD) is one of the most common causes of vision loss. AMD has been classified into two forms: atrophic and exudative forms. The exudative form is associated with choroidal neovascularization of the subretinal macular region, resulting in a sudden loss of central vision. However, the exact cause of AMD remains unknown. Several risk factors have been postulated, including smoking, atherosclerosis, and low levels of antioxidant enzymes. Malondialdehyde (MDA), a lipid peroxidation product, is used as a marker of oxidative stress. Paraoxonase 1 (PON1) metabolizes lipid peroxides and prevents oxidation of low-density lipoprotein. Increased levels of homocysteine may cause vascular endothelial injury by releasing free radicals. The purpose of this study is to investigate the relationships between serum PON1 activity and the serum levels of homocysteine and MDA in AMD. Forty patients with exudative-type AMD (63.3 +/- 5 years) and 40 controls (61+/- 4 years) were assessed in a cross-sectional study. The serum PON1 activity was significantly lower in the patients with AMD than that in the controls (p < 0.001). In contrast, the serum levels of MDA and homocysteine were significantly higher in the patients than those in the controls (p < 0.001, for both). In AMD patients, significant negative correlation was found between PON1 activity and MDA level (r = -0.493, p < 0.05) and between PON1 activity and homocysteine level (r = -0.557, p < 0.05). Increased serum homocysteine and MDA levels may be responsible for the decreased PON1 activity in patients with AMD.

Analysis of age-related carbonylation of human vitreous humor proteins as a tool for forensic diagnosis

Age-related changes of protein carbonylation due to oxidative damage in human vitreous humors were analyzed. The vitreous samples were collected from 51 autopsied bodies (male: 27, 13-87 years-old, female: 24, 18-80 years-old) whose postmortem interval was less than 4 days. Total protein carbonyl content was assessed by colorimetry using 2,4-dinitrophenylhydrazine and particular carbonylated proteins were identified by immunostaining of vitreous proteins resolved by SDS-PAGE and MALDI-TOF MS with peptide mass fingerprinting. No significant correlation was found between total protein carbonyl content and biological age. However, two major proteins, albumin and transferrin, were found to be heavily carbonylated in the samples from individuals age 40 or over. Furthermore, an immunostained cluster of proteins at 50-60 kDa was discernible in the samples of aged individuals, and it was revealed to contain alpha enolase, pigment epithelial differentiating factor, type 2 keratin subunit protein, and S-arrestin. The results of this study suggest that some retinal proteins detected in the vitreous humor sample would be markers of age-related oxidative stress and biological age.

Oxidative damage and age-related functional declines

Most organisms experience progressive declines in physiological function as they age. Since this senescence of function is thought to underlie the decrease in quality of life in addition to the increase in susceptibility to disease and death associated with aging, identifying the mechanisms involved would be highly beneficial. One of the leading mechanistic theories for aging is the oxidative damage hypothesis. A number of studies in a variety of species support a strong link between oxidative damage and life span determination. The role of oxidative damage in functional senescence has also been investigated, albeit not as comprehensively. Here, we review these investigations. Several studies show that the age-related loss of a number of functions is associated with an accrual of oxidative damage in the tissues mediating those functions. Additionally, treatments that increase the accumulation of oxidative damage with age frequently exacerbate functional losses. Moreover, treatments that reduce the accumulation of oxidative damage often attenuate or delay the loss of function associated with aging. These data provide the foundation for a link between oxidative damage and functional senescence, thereby supporting the oxidative damage hypothesis of aging within the context of age-related functional decline.

Microsomal glutathione S-transferase 1 in the retinal pigment epithelium: protection against oxidative stress and a potential role in aging

High oxygen tension, exposure to light, and the biochemical events of vision generate significant oxidative stress in the retina and the retinal pigment epithelium (RPE). Understanding the mechanisms and basis of susceptibility to progressive retinal diseases involving oxidative damage such as age-related macular degeneration (AMD) remains a major challenge. Here microsomal glutathione S-transferase (MGST1) is shown to be a dominant, highly expressed enzyme in bovine and mouse RPE microsomes that displays significant reduction activity toward synthetic peroxides, oxidized RPE lipids, and oxidized retinoids. This enzymatic reduction activity (GPx) can be partially neutralized with a monoclonal anti-MGST1 antibody developed in this study. MGST1-transfected HEK293 cells exhibited greater viability (70 +/- 4% survival) compared with untransfected control cells (46 +/- 4% survival) when challenged with 20 microM H(2)O(2), and greater viability of MGST1-transfected cells following challenge with oxidized docosahexaenoic acid was also observed. Cultured ARPE19 cells transfected with silencing MGST1 siRNAs exhibited lower expression of MGST1 (12% and 26% of the controls) and significantly lower GPx activity (44 +/- 13%) and, thus, were more susceptible to oxidative damage. Immunoblotting revealed that the in vivo expression of MGST1 in mouse RPE decreases 3-4-fold with age, to trace levels in 18-month-old mice. GPx activity in the RPE was also found to be reduced in 12-month-old mice to approximately 67%. These results support an important protective function for MGST1 against oxidative insult in the RPE that decreases with age and suggest that this enzyme may play a role in the development of age-related diseases such as AMD.

Age-related changes in the transcriptional profile of mouse RPE/choroid

To evaluate the age-related changes in gene expression occurring in the complex of retinal pigmented epithelium, Bruch's membrane, and choroid (RPE/choroid), we examined the gene expression profiles of young adult (2 mo) and old (24 mo) male C57BL/6 mice. cDNA probe sets from individual animals were synthesized using total RNA isolated from the RPE/choroid of each animal. Probes were amplified using the Clontech SMART system, radioactively labeled, and hybridized to two different Clontech Atlas mouse cDNA arrays. From each age group, three independent triplicates were hybridized to the arrays. Statistical analyses were performed using the Significance Analysis of Microarrays program (SAM version 1.13; Stanford University). Selected array results were confirmed by semi-quantitative RT-PCR analysis. Of 2,340 genes represented on the arrays, approximately 60% were expressed in young and/or old mouse RPE/choroid. A moderate fraction (12%) of all expressed genes exhibited a statistically significant change in expression with age. Of these 150 genes, all but two, HMG14 and carboxypeptidase E, were upregulated with age. Many of these upregulated genes can be grouped into several broad functional categories: immune response, proteases and protease inhibitors, stress response, and neovascularization. RT-PCR results from six of six genes examined confirmed the differential change in expression with age of these genes. Our study provides likely candidate genes to further study their role in the development of age-related macular degeneration and other aging diseases affecting the RPE/choroid.

Phenotypic change regulates monocyte chemoattractant protein-1 (MCP-1) gene expression in human retinal pigment epithelial cells

We investigated the expression profile of monocyte chemoattractant protein-1 (MCP-1) in human retinal pigment epithelial (RPE) cells under different culture conditions and evaluated the molecular mechanism responsible for MCP-1 gene expression in RPE cells. After cellular confluence, total RNA was extracted and used for RT-PCR. Medium conditioned by RPE was used for ELISA and Western blotting. The result showed that RPE cells cultured on plastic expressed MCP-1 constitutively in the absence of any stimuli. On the other hand, growing human RPE on laminin-coated flasks instead of plastic reduced the production of MCP-1. In the RPE cells cultured on plastic, IkappaB was degraded and A20 protein increased concomitantly. MCP-1 upregulation in RPE cells on plastic was attenuated by the addition of MG-132, a proteasome inhibitor. Also, the addition of pyrolidine dithiocarbonate (PDTC) and hypoxic conditions (0.5% O2) decreased MCP-1 production in these cells. These findings suggested that the expression profile of MCP-1 is regulated by phenotypic alterations of the RPE cells. And the increased MCP-1 expression in RPE cells cultured on plastic is caused via spontaneous activation of NFkappaB induced by susceptibility to oxidative stress.

Induction of vascular endothelial growth factor by 4-hydroxynonenal and its prevention by glutathione precursors in retinal pigment epithelial cells

Although 4-hydroxynonenal, a highly reactive lipid peroxidation product, is implicated in several age-related disorders such as Alzheimer's and Parkinson's diseases, its role in age-related macular degeneration is not known. The purpose of this study was to determine whether 4-hydroxynonenal increases vascular endothelial growth factor (VEGF) expression in human retinal pigment epithelial cells (ARPE-19), a source of VEGF in choroidal neovascularization observed in age-related macular degeneration. In addition, it was the purpose of this study to assess whether glutathione (GSH) and GSH precursors can inhibit the effects of 4-hydroxynonenal. At 1 micro M, 4-hydroxynonenal did not alter cell viability, but elevated VEGF secretion and mRNA expression by 35% (p<0.05) and 1.9-fold (p<0.05), respectively. However, at concentrations 5 microM and above, 4-hydroxynonenal reduced VEGF secretion as well as cell viability. At 1 and 10 microM, 4-hydroxynonenal did not induce apoptosis in ARPE-19 cells. 4-Hydroxynonenal (1 microM) reduced intracellular GSH by 25% (p<0.05) and increased oxidative stress by 50% (p<0.05). GSH precursor pretreatment for 1 h, which increased intracellular GSH levels by 50% (p<0.05), as well as GSH co-treatment, inhibited the VEGF-inductive and cytotoxic effects of 4-hydroxynonenal. Thus, 4-hydroxynonenal (1 microM) induces VEGF expression and secretion in ARPE-19 cells. This effect is likely due to GSH depletion and an associated increase in intracellular oxidative stress, resulting in increased VEGF mRNA levels. 4-Hydroxynonenal-mediated VEGF secretion as well as cytotoxicity can be reversed with GSH precursor pretreatment or GSH co-treatment.

Retinal pigment epithelial acid lipase activity and lipoprotein receptors: effects of dietary omega-3 fatty acids

PURPOSE

To show that fish oil-derived omega-3 polyunsaturated fatty acids, delivered to the retinal pigment epithelium (RPE) by circulating low-density lipoproteins (LDL), enhance already considerable RPE lysosomal acid lipase activity, providing for more efficient hydrolysis of intralysosomal RPE lipids, an effect that may help prevent development of age-related macular degeneration (ARMD).

METHODS

Colorimetric biochemical and histochemical techniques were used to demonstrate RPE acid lipase in situ, in vitro, and after challenge with phagocytic stimuli. Receptor-mediated RPE uptake of fluorescently labeled native, aceto-acetylated, and oxidized LDL was studied in vitro and in vivo. LDL effects on RPE lysosomal enzymes were assessed. Lysosomal enzyme activity was compared in RPE cells from monkeys fed diets rich in fish oil to those from control animals and in cultured RPE cells exposed to sera from these monkeys.

RESULTS

RPE acid lipase activity was substantial and comparable to that of mononuclear phagocytes. Acid lipase activity increased significantly following phagocytic challenge with photoreceptor outer segment (POS) membranes. Receptor-mediated RPE uptake of labeled lipoproteins was determined in vitro. Distinctive uptake of labeled lipoproteins occurred in RPE cells and mononuclear phagocytes in vivo. Native LDL enhanced RPE lysosomal enzyme activity. RPE lysosomal enzymes increased significantly in RPE cells from monkeys fed fish oil-rich diets and in cultured RPE cells exposed to their sera.

CONCLUSIONS

RPE cells contain substantial acid lipase for efficient metabolism of lipids imbibed by POS phagocytosis and LDL uptake. Diets rich in fish oil-derived omega-3 fatty acids, by enhancing acid lipase, may reduce RPE lipofuscin accumulation, RPE oxidative damage, and the development of ARMD.

Plasma malondialdehyde and nitric oxide levels in age related macular degeneration

AIMS

To evaluate alteration of plasma malondialdehyde (MDA) and nitric oxide (NO) levels in patients with exudative age related macular degeneration (ARMD).

METHODS

Plasma nitrite plus nitrate concentrations as an index of plasma NO levels and plasma MDA level as a marker of lipid peroxidation were measured in patients with exudative ARMD and age and sex matched healthy subjects.

RESULTS

Significantly higher MDA and lower NO levels were detected in plasma of patients with ARMD compared with their controls (p=0.01, p=0.001, respectively).

CONCLUSION

The results may support involvement of oxidative damage and vascular theory in the pathogenesis of ARMD as part of the ageing process.

Density-dependent expression of FGF-2 in response to oxidative stress in RPE cells in vitro

PURPOSE

The purpose of this study is to demonstrate the effect of culture density on the steady state mRNA levels of fibroblast growth factor-2 (FGF-2) when retinal pigment epithelial (RPE) cells are subjected to oxidative stress in vitro.

METHODS

Subconfluent and confluent cultures of the established RPE cell line ARPE-19, were treated with increasing concentrations of tert-butyl hydroperoxide (tBH) or hydrogen peroxide (H(2)O(2)). Cell viability was measured using the WST-1 assay, and intracellular reactive oxygen intermediate (ROI) production was quantified by dichlorofluoroscein (DCF) fluorescence. Steady state changes in heme oxygenase-1 (HO-1) and FGF-2 mRNAs were measured by Northern blot analysis.

RESULTS

Confluent cultures of ARPE-19 cells were less susceptible than subconfluent cultures to the toxic effects of the chemical oxidants. The intracellular reactive oxygen intermediate production was higher in subconfluent than confluent cultures with increasing tBH concentration. At nontoxic concentrations of tBH and H(2)O(2), a dose dependent increase in FGF-2 expression was seen as a function of culture density. FGF-2 mRNA expression was induced after tBH treatment in subconfluent, but not confluent cells. On the other hand, FGF-2 mRNA induction was observed after H(2)O( 2) treatment in confluent, but not subconfluent cultures. In contrast, no density dependent induction of HO-1 mRNA was seen after treatment with either tBH or H(2)O(2).

CONCLUSIONS

These results suggest that care should be taken to control for cell density in similar types of in vitro experiments.

Paraoxonase gene polymorphisms and plasma oxidized low-density lipoprotein level as possible risk factors for exudative age-related macular degeneration

PURPOSE

Paraoxonase (E.C.3.1.1.2) is a polymorphic protein shown to prevent low-density lipoprotein oxidation. Our purpose is to evaluate the hypothesis that paraoxonase gene polymorphisms and plasma oxidized low-density lipoprotein level play a role in the occurrence of exudative age-related macular degeneration.

METHODS

We analyzed paraoxonase genotypes (A/B, Gln-Arg192 and L/M, Leu-Met54) and plasma oxidized low-density lipoprotein levels in 72 unrelated Japanese patients with exudative age-related macular degeneration and compared the results with those of 140 age-matched and sex-matched control subjects.

RESULTS

The distribution of paraoxonase 192 and paraoxonase 54 polymorphisms was significantly different between the patients with age-related macular degeneration and control subjects (chi-square = 6.226, P =.0445, and chi-square = 6.863, P =.0323, respectively). The high frequency of the BB genotype at position 192 was observed in the exudative age-related macular degeneration group compared with control subjects (52.8% vs 35.0%, respectively; P =.0127). The high frequency of the LL genotype at position 54 was observed in the patients more than the controls (91.7% vs 77.1%, respectively; P =.0090). The mean (+/- SE) oxidized low-density lipoprotein levels in the patients was significantly higher than in the controls (19.1 +/- 1.0 vs 16.2 +/- 0.6 U/ml, P <.01).

CONCLUSION

These results indicate that the paraoxonase gene polymorphisms may represent a possible genetic risk factor for age-related macular degeneration and that increased plasma oxidized low-density lipoprotein may be involved in the pathogenesis of age-related macular degeneration.

The role of oxidative stress in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blind registration in the developed world, and yet its pathogenesis remains poorly understood. Oxidative stress, which refers to cellular damage caused by reactive oxygen intermediates (ROI), has been implicated in many disease processes, especially age-related disorders. ROIs include free radicals, hydrogen peroxide, and singlet oxygen, and they are often the byproducts of oxygen metabolism. The retina is particularly susceptible to oxidative stress because of its high consumption of oxygen, its high proportion of polyunsaturated fatty acids, and its exposure to visible light. In vitro studies have consistently shown that photochemical retinal injury is attributable to oxidative stress and that the antioxidant vitamins A, C, and E protect against this type of injury. Furthermore, there is strong evidence suggesting that lipofuscin is derived, at least in part, from oxidatively damaged photoreceptor outer segments and that it is itself a photoreactive substance. However, the relationships between dietary and serum levels of the antioxidant vitamins and age-related macular disease are less clear, although a protective effect of high plasma concentrations of alpha-tocopherol has been convincingly demonstrated. Macular pigment is also believed to limit retinal oxidative damage by absorbing incoming blue light and/or quenching ROIs. Many putative risk-factors for AMD have been linked to a lack of macular pigment, including female gender, lens density, tobacco use, light iris color, and reduced visual sensitivity. Moreover, the Eye Disease Case-Control Study found that high plasma levels of lutein and zeaxanthin were associated with reduced risk of neovascular AMD. The concept that AMD can be attributed to cumulative oxidative stress is enticing, but remains unproven. With a view to reducing oxidative damage, the effect of nutritional antioxidant supplements on the onset and natural course of age-related macular disease is currently being evaluated.

An in vitro model of ischemic-like stress in retinal pigmented epithelium cells: protective effects of antioxidants

We have developed a model of in vitro cell oxidative stress in bovine retinal pigment epithelium cells exposed to a ischemia-like condition obtained by interference with glucose utilization through both oxidative phosphorylation and glycolysis. This resulted in a statistically significant decrease of the intracellular ATP levels, which reflects a bioenergetic decline similar to that associated with mitochondrial damage or loss in normal post-mitotic cells aging in vivo. This new model of cellular oxygen stress seems adequate for investigation of the protective action of antioxidants, in agreement with our finding of a statistically significant increase in the ATP levels over the values of the non-treated samples in retinal pigment epithelium cells exposed to the above oxygen stress in medium supplemented with 300 microM vitamin C or 10 mM N-acetylcysteine.

Antioxidant enzymes in the macular retinal pigment epithelium of eyes with neovascular age-related macular degeneration

PURPOSE

To test the hypothesis that neovascular age-related macular degeneration is related to oxidative stress involving the macular retinal pigment epithelium. This study investigated, as a function of age, levels of enzymes that defend tissues against oxidative stress in the macular retinal pigment epithelium of human eyes with this disease.

METHODS

Surgical specimens of macular choroidal neovascular membranes from eyes with age-related macular degeneration and the macular regions of whole donor eyes with neovascular age-related macular degeneration or without evident ocular disease were studied by quantitative electron microscopic immunocytochemistry with colloidal gold-labeled second antibodies. Relative levels in retinal pigment epithelium cell cytoplasm and lysosomes were determined of five enzymes believed to protect cells from oxidative stress, as well as levels of the retinal pigment epithelium marker cytoplasmic retinaldehyde-binding protein, for comparison with the enzymes.

RESULTS

Copper, zinc superoxide dismutase immunoreactivity increased and catalase immunoreactivity decreased with age in cytoplasm and lysosomes from macular retinal pigment epithelium cells of normal eyes and eyes with age-related macular degeneration. Cytoplasmic retinaldehyde-binding protein immunoreactivity showed no significant relationship to age or the presence of neovascular age-related macular degeneration. Glutathione peroxidase immunoreactivity was absent from human retinal pigment epithelium cells. Both heme oxygenase-1 and heme oxygenase-2 had highly significantly greater immunoreactivity in retinal pigment epithelium cell lysosomes than in cytoplasm, differing from the much greater cytoplasmic immunoreactivity of the other proteins studied. This immunoreactivity decreased with age, particularly in the lysosomes of retinal pigment epithelium cells from eyes with neovascular age-related macular degeneration. These decreases were of borderline significance (P = .067 for heme oxygenase-1; P = .12 for heme oxygenase-2) when eyes with age-related macular degeneration were compared with normal eyes by multivariable logistic regression.

CONCLUSIONS

The high heme oxygenase-1 and heme oxygenase-2 lysosomal antigen levels in macular retinal pigment epithelium cells of eyes with neovascular age-related macular degeneration suggest that oxidative stress causes a pathologic upregulation of these enzymes. Increased lysosomal disposal may indicate that the reparative functions of these enzymes are accompanied by deleterious effects, necessitating their rapid removal from the cell. The much higher heme oxygenase-1 and heme oxygenase-2 antigen levels in macular retinal pigment epithelium cells from younger individuals suggest that protective mechanisms against oxidation and, hence, presumably to the development of age-related macular degeneration, decrease with age.

Serum vitamin E levels negatively correlate with severity of age-related macular degeneration

Age-related macular degeneration (AMD) pathogenesis has been related to UV radiation and other factors that may promote increased oxidative damage to the retina. Patients with different AMD grading (n = 25) were compared with an age-matched group of AMD-free subjects (n = 15), both groups older than 60 years. A modification of the AMD grading system is proposed that allows patient grading and not single eye grading. AMD patients showed statistically significant lower serum levels of vitamin E and Zn than AMD-free subjects. Moreover, a negative correlation (Spearman's correlation coefficient r = -0.815, P < 0.001) could be established between AMD grading of both the patients' eyes and serum vitamin E levels. Sun exposure index (SEI) was also compared and found to be significantly higher in the AMD group. The results presented establish the importance of antioxidants in AMD, and set the basis for further studies on adjuvant therapies with antioxidants for AMD. Finally, the results also confirm the pathogenic role of UV radiation in AMD.

Superoxide dismutases in retinal degeneration of WBN/Kob rat

PURPOSE

To examine the relationship between retinal degeneration and superoxide dismutase (SOD) in the degenerative retina of the WBN/Kob rat.

METHODS

The retinas of 4-week-old and 10-month-old WBN/ Kob rats were examined with immunohistochemistry and immunoblotting. Wistar Kyoto rats were used as controls.

RESULTS

Retinal degeneration began 4 weeks after birth. Four-week-old WBN/Kob rats showed no manganese superoxide dismutase (Mn-SOD) immunoreactivity in the photoreceptor inner segments or copper-zinc superoxide dismutase (CuZn-SOD) immunoreactivity in the outer nuclear layer or photoreceptor inner segments. Control 4-week-old Wistar Kyoto rats showed positive immunoreactivities at these sites.

CONCLUSIONS

The retinal degeneration of WBN/Kob rats begins in the outer retina. The lack of SODs in the outer retina may contribute to retinal degeneration in the WBN/Kob rats.

"Oxidative protector" enzymes in the macular retinal pigment epithelium of aging eyes and eyes with age-related macular degeneration

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Extracellular glutathione peroxidase and ascorbic acid in aqueous humor and serum of patients operated on for cataract

Patients operated on for cataract (32 men/75 women, aged 50-93 years) were studied with respect to antioxidative agents in aqueous humor and serum. Extracellular glutathione peroxidase (eGSHPx) was demonstrated in aqueous humor for the first time by a radioimmunoassay, the concentration of eGSHPx being 0.66(0.18) mg/l (mean(S.D.)). The concentration of eGSHPx in serum was 3.81(0.84) mg/l, and its level in aqueous humor was 18(7)% of that level. Serum selenium had positive correlations with both serum eGSHPx (r = 0.34, P < 0.001) and aqueous humor eGSHPx (r = 0.25, P = 0.011). However, there was no relation between the concentrations of eGSHPx in aqueous humor and in serum, suggesting that the maintenance of eGSHPx levels in the two fluids is controlled by different mechanisms beside selenium status. There was an inverse correlation between age and serum eGSHPx but not with aqueous humor eGSHPx. The concentration of ascorbic acid in aqueous humor was 2.04(0.58) mmol/l, and it was closely correlated to the level of ascorbic acid in serum (0.052(0.032) mmol/l), r = 0.58 (P < 0.001). The ratio between the level of ascorbic acid in aqueous humor and that in serum was 39(17). There was no significant difference among patients with nuclear (n = 39), cortical (n = 20), posterior-subcapsular (n = 23) or mixed (n = 23) lens opacity with respect to levels of eGSHPx and ascorbic acid in serum and aqueous humor. Since serum ascorbic acid is related to ascorbic acid intake, its association to aqueous humor ascorbic acid indicates that dietary habits are important for maintaining that level which could play an important role in protecting ocular tissue against oxidative damage. The role of eGSHPx secreted into aqueous humor in the oxidant defence system needs further study.

Red blood cell antioxidant enzymes in age-related macular degeneration

AIMS/BACKGROUND

Oxidative damage has been proposed to be involved in the pathogenesis of age-related macular degeneration (ARMD). The purpose of this study was to evaluate whether red blood cell antioxidant enzyme activity correlates with severity of aging maculopathy in affected individuals.

METHODS

Blood samples were obtained from 54 patients with varying severity of aging maculopathy and 12 similarly aged individuals with normal ophthalmoscopic examination. Macular findings were graded according to a modification of the method described for the Age-Related Eye Disease Study. (AREDS). The activities of superoxide dismutase, catalase, glucose-6-phosphate dehydrogenase, glutathione peroxidase, and glutathione reductase were measured in red blood cells. Haemoglobin content of whole blood was measured, and enzyme activity was determined per mg haemoglobin.

RESULTS

Multiple regression analysis and ordinal logistic regression analysis were performed to determine whether antioxidant enzyme activity was associated with severity of ARMD. No significant association between disease severity of ARMD and antioxidant enzyme activity was identified for any of the enzymes.

CONCLUSION

These results do not provide evidence for a relation between oxidative stress, as measured by antioxidant enzyme activity in red blood cells, and disease severity in ARMD.

Does ozone therapy normalize the cellular redox balance? Implications for therapy of human immunodeficiency virus infection and several other diseases

The role of ozone on earth is controversial, as in the stratosphere it is protective against excessive ultra violet irradiation, and in the troposphere it is toxic for animals and plants. The effectiveness of ozone against pathogens is well recognized and ozone appears to be the best agent for sterilization of water. In spite of this, the use of ozone in medicine has been overlooked or despised, mostly because it has been either misused or used without appropriate controls. Studies carried out in our laboratory have revealed that ozone can display relevant biological effects and that, having defined its therapeutic index, can become an important and reliable drug for the treatment of several diseases. An exciting new aspect is that ozone, being a strong oxidizer, can stimulate the increase of cellular anti-oxidant enzymes, eventually inhibiting the oxidative stress.