Increased serum total antioxidant status and decreased urinary 8-hydroxy-2'-deoxyguanosine levels in patients with normal-tension glaucoma

Cholesterol and oxysterols in retinal neuron-glia interactions: relevance for glaucoma

Cholesterol is an essential component of cellular membranes, crucial for maintaining their structural and functional integrity. It is especially important for nervous tissues, including the retina, which rely on high amounts of plasma membranes for the transmission of the nervous signal. While cholesterol is by far the most abundant sterol, the retina also contains cholesterol precursors and metabolites, especially oxysterols, which are bioactive molecules. Cholesterol lack or excess is deleterious and some oxysterols are known for their effect on neuron survival. Cholesterol homeostasis must therefore be maintained. Retinal glial cells, especially Müller cells, the principal glial cells of the vertebrate retina, provide mechanical, nutritional, and metabolic support for the neighboring neurons. Several pieces of evidence indicate that Müller cells are major actors of cholesterol homeostasis in the retina, as it is known for other glial cells in the brain. This process is based on a close cooperation with neurons, and sterols can be signaling molecules participating in glia-neuron interactions. While some implication of cholesterol in age-related macular degeneration is now recognized, based on epidemiological and laboratory data, evidence for its role in glaucoma is still scarce. The association between cholesterolemia and glaucoma is controversial, but experimental data suggest that sterols could take part in the pathological processes. It has been demonstrated that Müller glial cells are implicated in the development of glaucoma through an ambivalent reactive retinal gliosis process. The early steps contribute to maintaining retinal homeostasis and favor the survival of ganglion cells, which are targeted during glaucoma. If gliosis persists, dysregulation of the neuroprotective functions, cytotoxic effects of gliotic Müller cells and disruption of glia-neuron interactions lead to an acceleration of ganglion cell death. Sterols could play a role in the glial cell response to glaucomatous injury. This represents an understudied but attractive topic to better understand glaucoma and conceive novel preventive or curative strategies. The present review describes the current knowledge on i) sterol metabolism in retinal glial cells, ii) the potential role of cholesterol in glaucoma, and iii) the possible relationships between cholesterol and oxysterols, glial cells and glaucoma. Focus is put on glia-neuron interactions.

Association between dietary antioxidant indices and glaucoma in the National Health and Nutrition Examination Survey

OBJECTIVE

To explore the relationship between dietary antioxidant indices (DAI) and glaucoma using the data from the 2005 to 2008 National Health and Nutrition Examination Survey (NHANES).

METHODS

Our study comprised participants who completed the NHANES dietary intake interview and visual health questionnaire at age 40 or older. The intakes of the vitamins A, C, and E as well as of zinc, selenium, and magnesium were used to generate the DAI, which represents the overall antioxidant qualities. The self-report method for glaucoma diagnosis (ever been told by an eye doctor) was used. Survey logistic regression analyses were employed to investigate the association between DAI and glaucoma.

RESULTS

A total of 6,128 participants were included in our study. The unadjusted model's findings revealed a negative correlation between dietary antioxidant indices and self-reported glaucoma [0.93 (0.90, 0.96), p < 0.0001]. For every unit increase in dietary antioxidant indices, the risks of self-reported glaucoma in model 1 (adjusted for age, sex, race, marital status and PIR) decreased by 5% [0.95 (0.90, 0.99), p = 0.02]. After adjusting all the covariates (model 2), the risks of self-reported glaucoma decreased by 6% [0.94 (0.90, 0.99), p = 0.02] for each unit increase of dietary antioxidant indices. After converting DAI into classified variables (tertile), the same trend was found (p = 0.001).

CONCLUSION

In this analysis of the NHANES database, we found higher dietary antioxidant indices were associated with lower risk of glaucoma.

Is the clinical course of non-arteritic ischemic optic neuropathy associated with oxidative damage and the dynamics of the antioxidant response?

PURPOSE

Oxidative stress is known to be a decisive factor in the wide etiopathogenesis of optic neuropathy. This study aimed to comprehensively evaluate the interaction of optic neuropathy's clinical course with systemic oxidative damage and antioxidant response dynamics in a large series.

METHODS

This case-controlled clinical study included 33 non-arteritic anterior ischemic optic neuropathy (NAION) patients and 32 healthy individuals. Extensive systemic oxidation profiles were statistically compared between the two groups, and correlations between the clinical and biochemical data in the study group were analyzed.

RESULTS

Vitamin E and malondialdehyde (MDA) levels were significantly higher in the study group. Significant correlations were observed in the analyses between clinical findings and oxidative stress parameters. Correlations between vitamin E and intraocular pressure (IOP), between B12 and cup-to-disk ratio (c/d), between antioxidant glutathione and superoxide dismutase (SOD) enzyme systems, and between uric acid (UA) and age were found to be very significant. As significant correlations were found in either clinical and biochemical data or in oxidative stress parameters, correlations between vitamin E and cholesterol, MDA were found to be very significant.

CONCLUSIONS

This study not only supplies significant information regarding oxidative damage and antioxidant response in NAION, but also points out the specific interactions of neuromodulators, like vitamin E, in intracellular signaling pathways and regulation mechanisms. A better reading of these connections may help improve diagnosis, follow-ups and treatment criteria and strategies.

Regulatory mechanisms of retinal ganglion cell death in normal tension glaucoma and potential therapies

Normal tension glaucoma (NTG) is a multifactorial optic neuropathy characterized by normal intraocular pressure, progressive retinal ganglion cell (RGC) death, and glaucomatous visual field loss. Recent studies have described the mechanisms underlying the pathogenesis of NTG. In addition to controlling intraocular pressure, neuroprotection and reduction of RGC degeneration may be beneficial therapies for NTG. In this review, we summarized the main regulatory mechanisms of RGC death in NTG, including autophagy, glutamate neurotoxicity, oxidative stress, neuroinflammation, immunity, and vasoconstriction. Autophagy can be induced by retinal hypoxia and axonal damage. In this process, ischemia can cause mutations of optineurin and activate the nuclear factor-kappa B pathway. Glutamate neurotoxicity is induced by the over-stimulation of N-methyl-D-aspartate membrane receptors by glutamate, which occurs in RGCs and induces progressive glaucomatous optic neuropathy. Oxidative stress also participates in NTG-related glaucomatous optic neuropathy. It impairs the mitochondrial and DNA function of RGCs through the apoptosis signal-regulating kinase-JUN N-terminal kinase pathway. Moreover, it increases inflammation and the immune response of RGCs. Endothelin 1 causes endothelial dysfunction and impairment of ocular blood flow, promoting vasospasm and glaucomatous optic neuropathy, as a result of NTG. In conclusion, we discussed research progress on potential options for the protection of RGCs, including TANK binding kinase 1 inhibitors regulating autophagy, N-methyl-D-aspartate receptor antagonists inhibiting glutamate toxicity, ASK1 inhibitors regulating mitochondrial function, and antioxidants inhibiting oxidative stress. In NTG, RGC death is regulated by a network of mechanisms, while various potential targets protect RGCs. Collectively, these findings provide insight into the pathogenesis of NTG and potential therapeutic strategies.

Cholesterol and glaucoma: a systematic review and meta-analysis

PURPOSE

Intraocular pressure is the main risk factor for glaucoma; however, additional risk factors may also matter. This systematic review and meta-analysis were conducted to summarize the evidence regarding the association of cholesterol parameters (total cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) levels) and glaucoma.

METHODS

Four electronic databases were searched for all publications containing 'glaucoma' and one of various forms of 'cholesterol' or 'lipoprotein'. Two independent reviewers screened abstracts and potentially full texts of identified articles for eligibility. Risk of bias was assessed with the Newcastle-Ottawa Scale. A random-effects meta-analysis was used to investigate the differences in total cholesterol, LDL and HDL levels between patients with and without glaucoma.

RESULTS

Overall, 29 observational studies were included in the systematic review and 26 reported quantitative information to investigate differences in cholesterol parameters between patients with glaucoma (N = 7196) and patients without glaucoma (N = 350 441). Patients with glaucoma had significantly higher total cholesterol levels than patients without glaucoma (Mean Difference (MD) 7.9 mg/dl, 95% CI 3.3 to 12.5, p = 0.001) and lower mean HDL levels (MD -2.0 mg/dl, 95% CI: -3.1 to -0.9, p = 0.001). Patients with glaucoma had higher mean LDL levels than patients without glaucoma, albeit not statistically significant (MD 6.1 mg/dl, 95% CI: -4.3 to 16.4, p = 0.251).

CONCLUSION

This systematic review and meta-analysis of observational studies found an association of glaucoma and high total cholesterol and low HDL levels, respectively. Although this supports the hypothesis that lipid levels pose an additional risk for glaucoma development, heterogeneity was substantial and causality cannot be presumed from identified observational studies.

Role of Oxidative Stress in Ocular Diseases Associated with Retinal Ganglion Cells Degeneration

Ocular diseases associated with retinal ganglion cell (RGC) degeneration is the most common neurodegenerative disorder that causes irreversible blindness worldwide. It is characterized by visual field defects and progressive optic nerve atrophy. The underlying pathophysiology and mechanisms of RGC degeneration in several ocular diseases remain largely unknown. RGCs are a population of central nervous system neurons, with their soma located in the retina and long axons that extend through the optic nerve to form distal terminals and connections in the brain. Because of this unique cytoarchitecture and highly compartmentalized energy demand, RGCs are highly mitochondrial-dependent for adenosine triphosphate (ATP) production. Recently, oxidative stress and mitochondrial dysfunction have been found to be the principal mechanisms in RGC degeneration as well as in other neurodegenerative disorders. Here, we review the role of oxidative stress in several ocular diseases associated with RGC degenerations, including glaucoma, hereditary optic atrophy, inflammatory optic neuritis, ischemic optic neuropathy, traumatic optic neuropathy, and drug toxicity. We also review experimental approaches using cell and animal models for research on the underlying mechanisms of RGC degeneration. Lastly, we discuss the application of antioxidants as a potential future therapy for the ocular diseases associated with RGC degenerations.

From Oxidative Stress to Inflammation in the Posterior Ocular Diseases: Diagnosis and Treatment

Most irreversible blindness observed with glaucoma and retina-related ocular diseases, including age-related macular degeneration and diabetic retinopathy, have their origin in the posterior segment of the eye, making their physiopathology both complex and interconnected. In addition to the age factor, these diseases share the same mechanism disorder based essentially on oxidative stress. In this context, the imbalance between the production of reactive oxygen species (ROS) mainly by mitochondria and their elimination by protective mechanisms leads to chronic inflammation. Oxidative stress and inflammation share a close pathophysiological process, appearing simultaneously and suggesting a relationship between both mechanisms. The biochemical end point of these two biological alarming systems is the release of different biomarkers that can be used in the diagnosis. Furthermore, oxidative stress, initiating in the vulnerable tissue of the posterior segment, is closely related to mitochondrial dysfunction, apoptosis, autophagy dysfunction, and inflammation, which are involved in each disease progression. In this review, we have analyzed (1) the oxidative stress and inflammatory processes in the back of the eye, (2) the importance of biomarkers, detected in systemic or ocular fluids, for the diagnosis of eye diseases based on recent studies, and (3) the treatment of posterior ocular diseases, based on long-term clinical studies.

Neuroprotection in Glaucoma: NAD+/NADH Redox State as a Potential Biomarker and Therapeutic Target

Glaucoma is the leading cause of irreversible blindness worldwide. Its prevalence and incidence increase exponentially with age and the level of intraocular pressure (IOP). IOP reduction is currently the only therapeutic modality shown to slow glaucoma progression. However, patients still lose vision despite best treatment, suggesting that other factors confer susceptibility. Several studies indicate that mitochondrial function may underlie both susceptibility and resistance to developing glaucoma. Mitochondria meet high energy demand, in the form of ATP, that is required for the maintenance of optimum retinal ganglion cell (RGC) function. Reduced nicotinamide adenine dinucleotide (NAD⁺) levels have been closely correlated to mitochondrial dysfunction and have been implicated in several neurodegenerative diseases including glaucoma. NAD⁺ is at the centre of various metabolic reactions culminating in ATP production—essential for RGC function. In this review we present various pathways that influence the NAD⁺(H) redox state, affecting mitochondrial function and making RGCs susceptible to degeneration. Such disruptions of the NAD⁺(H) redox state are generalised and not solely induced in RGCs because of high IOP. This places the NAD⁺(H) redox state as a potential systemic biomarker for glaucoma susceptibility and progression; a hypothesis which may be tested in clinical trials and then translated to clinical practice.

Neuroinflammatory Mechanisms of Mitochondrial Dysfunction and Neurodegeneration in Glaucoma

The exact mechanism of retinal ganglion cell loss in the pathogenesis of glaucoma is yet to be understood. Mitochondrial damage-associated molecular patterns (DAMPs) resulting from mitochondrial dysfunction have been linked to Leber's hereditary optic neuropathy and autosomal dominant optic atrophy, as well as to brain neurodegenerative diseases. Recent evidence shows that, in conditions where mitochondria are damaged, a sustained inflammatory response and downstream pathological inflammation may ensue. Mitochondrial damage has been linked to the accumulation of age-related mitochondrial DNA mutations and mitochondrial dysfunction, possibly through aberrant reactive oxygen species production and defective mitophagy. The present review focuses on how mitochondrial dysfunction may overwhelm the ability of neurons and glial cells to adequately maintain homeostasis and how mitochondria-derived DAMPs trigger the immune system and induce neurodegeneration.

Effect of Ubiquinol on Glaucomatous Neurodegeneration and Oxidative Stress: Studies for Retinal Ganglion Cell Survival and/or Visual Function

Oxidative stress is one of major causal factors in glaucomatous neurodegeneration. Ubiquinol promotes retinal ganglion cell (RGC) survival against glaucomatous insults such as oxidative stress. Here we investigated the effect of ubiquinol on RGC survival and/or visual function in mouse models of glaucoma and oxidative stress. DBA/2J and age-matched DBA/2J-Gpnmb+ (D2-Gpnmb+), which do not develop intraocular pressure elevation, or C57BL/6J mice were fed with ubiquinol (1%) or control diet daily for 5 or 2 months. We assessed RGC survival by Brn3a immunohistochemistry and measured expression levels of active and total BAX, peroxisome proliferator-activated receptor-gamma coactivator 1α, transcription factor A (TFAM) and oxidative phosphorylation (OXPHOS) complex protein. Following induction of oxidative stress by paraquat injection, we also assessed visual function. In glaucomatous retina, ubiquinol supplementation significantly promoted RGC survival, blocked BAX activation and increased TFAM and OXPHOS complex II protein expression. Also, ubiquinol supplementation ameliorated oxidative stress-induced visual dysfunction. These findings indicate that ubiquinol promotes RGC survival by increasing TFAM expression and OXPHOS complex II activity in glaucomatous neurodegeneration, and that ubiquinol enhances RGC survival and preserves visual function against oxidative stress. We propose that ubiquinol has a therapeutic potential for treating oxidative stress-associated glaucomatous neurodegeneration.

Increased Antioxidant Capacity and Pro-Homeostatic Lipid Mediators in Ocular Hypertension-A Human Experimental Model

The main risk factor for primary open-angle glaucoma (POAG) is increased intraocular pressure (IOP). It is of interest that about half of the patients have an IOP within the normal range (normal-tension glaucoma, NTG). Additionally, there is a group of patients with a high IOP but no glaucomatous neurodegeneration (ocular hypertension, OHT). Therefore, risk factors other than IOP are involved in the pathogenesis of glaucoma. Since the retina has a very high oxygen-demand, decreased autoregulation and a fluctuating oxygen supply to the retina have been linked to glaucomatous neurodegeneration. To assess the significance of these mechanisms, we have utilized a human experimental model, in which we stress participants with a fluctuating oxygen supply. Levels of oxidative stress molecules, antioxidants, and lipid mediators were measured in the plasma. Patients with NTG, OHT, and control subjects were found to have similar levels of oxidative stress markers. In contrast, patients with OHT had a higher level of total antioxidant capacity (TAC) and pro-homeostatic lipid mediators. Thus, we suggest that OHT patients manage fluctuating oxygen levels more efficiently and, thus, are less susceptible to glaucomatous neurodegenerations, due to enhanced systemic antioxidant protection.

Elevated Plasma Level of 8-Hydroxy-2'-deoxyguanosine Is Associated with Primary Open-Angle Glaucoma

Purpose

To determine the association between plasma 8-hydroxy-2′-deoxyguanosine (8-OHdG) levels, a marker for oxidative DNA damage, and patients with primary open-angle glaucoma (POAG) or its clinical phenotypes. Furthermore, we also examined the utility of plasma 8-OHdG as a potential biomarker in POAG.

Materials and Methods

In a retrospective case-control study, plasma samples were obtained from 50 POAG cases and 45 glaucoma-free controls matched for age, sex, and ethnicity. 8-OHdG levels were measured in duplicate using an enzyme-linked immunosorbent assay (ELISA) on an automated ELISA analyzer.

Results

There was no significant difference in age, sex, and systemic disease distribution between POAG cases and controls. Both mean and median 8-OHdG levels were significantly elevated in POAG cases and male subjects. The area under the receiver operating characteristic (ROC) curve value for plasma 8-OHdG was 0.653 (95% confidence interval = 0.54–0.76, p = 0.010). The cutoff values based on quartile distribution and ROC curve analysis showed that elevated plasma 8-OHdG significantly increased the risk of POAG by more than 4-folds. Plasma 8-OHdG had a sensitivity of 78% and specificity of 53%. In logistic regression analysis, 8-OHdG showed a significant effect on POAG outcome (p = 0.016) independent of age, sex, smoking, and systemic diseases. However, no significant correlation was observed between 8-OHdG and specific clinical markers of glaucoma such as intraocular pressure (p = 0.699), cup/disc ratio (p = 0.213), and the number of antiglaucoma medications (p = 0.603).

Conclusion

The study shows that there is a significant association between elevated plasma 8-OHdG and POAG, supporting the role of systemic oxidative stress-induced DNA damage in POAG pathogenesis. However, with a high rate of false-positivity, plasma 8-OHdG may lack the ability to serve as a potential biomarker in POAG. Further studies in a much larger cohort are needed to confirm these findings.

Hyperlipidemia, Blood Lipid Level, and the Risk of Glaucoma: A Meta-Analysis

Purpose

Previous studies reported that hyperlipidemia and blood lipid levels were associated with glaucoma, ocular hypertension (OHT), and intraocular pressure (IOP). However, studies aimed at investigating this association have yielded conflicting results. Therefore, to shed light on these inconclusive findings, we performed multiple distinct meta-analyses to clarify the association of hyperlipidemia and blood lipid levels with glaucoma, OHT, and IOP.

Methods

A systematic literature search from Embase, Web of Science, and PubMed was performed to identify relevant studies. To assess the association between hyperlipidemia and glaucoma, we used the pooled odds ratio (OR) with 95% confidence interval (CI). When we assessed the association between blood lipid levels and IOP levels, the pooled mean difference in IOP associated with a 10 mg/dL increase in the blood lipid level was estimated. The pooled difference in IOP was also estimated between patients with and without hyperlipidemia. All the papers that assessed the correlation between hyperlipidemia and glaucoma, between blood lipid levels and IOP levels, and between hyperlipidemia and IOP were included in this meta-analysis.

Results

We detected a marked association between hyperlipidemia and glaucoma (OR = 1.37; 95% CI = 1.16-1.61), with significant heterogeneity among studies. However, hyperlipidemia was not significantly associated with glaucoma in our analysis of only cross-sectional studies, studies that reported only on hypercholesterolemia patients, studies that were conducted only in North America and Europe, or studies in which normal-tension glaucoma (NTG) patients were included only in the subgroup analyses. The pooled results showed that an increase of 10 mg/dL in blood triglyceride levels would increase the IOP by 0.016 mm Hg (95% CI = 0.009-0.024), with evident heterogeneity between studies (P < 0.001; I2 = 92.0%). The pooled results showed that the blood total cholesterol and low-density lipoprotein-cholesterol (LDL-c) level both had a significant association with IOP. When compared to the patients with nonhyperlipidemia, those with hyperlipidemia had a significantly higher IOP of 0.51 mm Hg (95% CI = 0.18-0.83) (P = 0.001 for heterogeneity; I2 = 81.6%).

Conclusions

The evidence suggests that hyperlipidemia is significantly associated with an increased risk of glaucoma and that hyperlipidemia and the increased blood lipid levels are associated with increased IOP.

The Association of Oxidative Stress Status with Open-Angle Glaucoma and Exfoliation Glaucoma: A Systematic Review and Meta-Analysis

Purpose

To systematically evaluate the associations between oxidative stress status and different types of glaucoma.

Design

Systematic review and meta-analysis.

Methods

We searched PubMed, EMBASE, and the Web of Science for randomized controlled trials written in the English language between January 1, 1990, and November 30, 2016. A random effects model was used to estimate oxidative stress status along with weighted mean differences and 95% confidence intervals (CIs). A funnel plot analysis and Egger's test were performed to assess potential publication bias.

Main outcome measures

Oxidative stress status was abnormal and different in patients with OAG (open-angle glaucoma) and EXG (exfoliation glaucoma).

Results

Blood TAS (total antioxidant status) was lower in the OAG group than in the control group, with a mean difference of 0.580 mmol/L (p < 0.0001, 95% CI = −0.668 to −0.492). The aqueous humor SOD (superoxide dismutase), GPX (glutathione peroxidase), and CAT (catalase) levels were higher in the OAG group than in the control group, with mean differences of 17.989 U/mL (p < 0.0001, 95% CI = 14.579–21.298), 12.441 U/mL (p < 0.0001, 95% CI = 10.423–14.459), and 1.229 fmol/mL (p=0.042, 95% CI = 0.043–2.414), respectively. Blood TAS was lower in the EXG group than in the control group, with a mean difference of 0.262 mmol/L (p < 0.0001, 95% CI = −0.393 to −0.132). However, there were no differences in blood TOS and aqueous humor TOS between the EXG group and the control group.

Conclusions

This meta-analysis indicates that OAG patients had a lower TAS in the blood and higher levels of SOD, GPX, and CAT in the aqueous humor, while EXG patients only had a decreased TAS in the blood.

Triglycerides and Open Angle Glaucoma - A Meta-analysis with meta-regression

Although intraocular pressure is the main the risk factor for the development of glaucoma, other risk factors such as vascular dysfunction might play an additional pathogenic role. Hypertriglyceridemia, which may lead to vascular dysfunction, has been implicated in the development of glaucoma. The objective of this meta-analysis was to investigate the association of triglyceride levels with the risk of glaucoma in case-control studies. Seventeen case-control studies were included investigating the difference in triglyceride levels in patients with glaucoma (N = 1 391) compared to subjects without glaucoma (N = 25 575). In random effects meta-analysis, the pooled mean triglyceride level across all studies and patients with and without glaucoma was 132.9 mg/dL (95%CI: 124.0-141.7). Patients with glaucoma had significantly higher mean triglyceride levels than patients without glaucoma (absolute difference = 14.2 mg/dL, 95%CI: 5.8-22.5, p < 0.0001). A considerable amount of heterogeneity of included studies was observed (I2 = 66.2%, heterogeneity χ2 = 47.4 on 16 degrees of freedom, p < 0.0001). In conclusion, this meta-analysis of case-control studies found that patients with glaucoma had higher mean triglyceride levels than patients without glaucoma. This finding is consistent with the concept that hypertriglyceridemia represents an additional risk factor for glaucoma. Whether this association is causal and/or might be modified by glaucoma medications remains to be investigated.

Topical Coenzyme Q10 demonstrates mitochondrial-mediated neuroprotection in a rodent model of ocular hypertension

Coenzyme Q10 (CoQ10) is a mitochondrial-targeted antioxidant with known neuroprotective activity. Its ocular effects when co-solubilised with α-tocopherol polyethylene glycol succinate (TPGS) were evaluated. In vitro studies confirmed that CoQ10 was significantly protective in different retinal ganglion cell (RGC) models. In vivo studies in Adult Dark Agouti (DA) rats with unilateral surgically-induced ocular hypertension (OHT) treated with either CoQ10/TPGS micelles or TPGS vehicle twice daily for three weeks were performed, following which retinal cell health was assessed in vivo using DARC (Detection of Apoptotic Retinal Cells) and post-mortem with Brn3a histological assessment on whole retinal mounts. CoQ10/TPGS showed a significant neuroprotective effect compared to control with DARC (p<0.05) and Brn3 (p<0.01). Topical CoQ10 appears an effective therapy preventing RGC apoptosis and loss in glaucoma-related models.

Preventing, treating, and predicting barbering: A fundamental role for biomarkers of oxidative stress in a mouse model of Trichotillomania

Barbering, where a “barber” mouse plucks hair from its cagemates or itself, is both a spontaneously occurring abnormal behavior in mice and a well validated model of Trichotillomania (TTM). N-Acetylcysteine, (NAC) a cysteine derived food additive, is remarkably effective in treating TTM patients, but its mechanism of action is unknown. Reactive Oxygen Species (ROS), also known as free radicals, form as a natural byproduct of the normal metabolism of oxygen. Under normal circumstances, cells are able to defend themselves against ROS damage with antioxidant pathways. NAC is the precursor to the main antioxidant produced to defend the brain. Therefore, we hypothesized that barbering is a disease of oxidative stress, whereby ROS and/or a failure of antioxidant defenses leads to neuronal damage that induces barbering in susceptible animals. We tested this hypothesis in 32 female C57BL/6J mice by treating half with 1g/kg BW/day of NAC in their diet, and testing for protection against developing barbering behavior and curing of barbering behavior, and simultaneously testing for a panel of biomarkers of oxidative stress. NAC reduced the chance that mice would be barbers, and this effect did not differ between healthy (i.e. prevention) and affected animals (i.e. cure). Barbering animals had elevated urinary antioxidant capacity, indicative of oxidative stress, at all timepoints. Additionally, after treatment the risk of barbering increased with decreasing hydroxy-2′-deoxyguanosine (8-OHdG) levels, and with increasing glutathione (GSH) and oxidized glutathione (GSSG) levels, further indicating that barbering mice were under oxidative stress regardless of treatment with NAC. We did not find compelling evidence that urinary total antioxidant capacity, or urinary 8-OHdG, could predict response to NAC treatment. We conclude that NAC is effective in preventing and/or curing barbering at least in part by promoting GSH synthesis, thereby preventing oxidative damage.

Antioxidant Treatment Limits Neuroinflammation in Experimental Glaucoma

Purpose

Besides primary neurotoxicity, oxidative stress may compromise the glial immune regulation and shift the immune homeostasis toward neurodegenerative inflammation in glaucoma. We tested this hypothesis through the analysis of neuroinflammatory and neurodegenerative outcomes in mouse glaucoma using two experimental paradigms of decreased or increased oxidative stress.

Methods

The first experimental paradigm tested the effects of Tempol, a multifunctional antioxidant, given through osmotic mini-pumps for drug delivery by constant infusion. Following a 6-week treatment period after microbead/viscoelastic injection-induced ocular hypertension, retina and optic nerve samples were analyzed for markers of oxidative stress and cytokine profiles using specific bioassays. We also analyzed a redox-sensitive transcriptional regulator of neuroinflammation, namely NF-κB. The second paradigm included a similar analysis of the effects of overloaded oxidative stress on retina and optic nerve inflammation in mice knockout for a major antioxidant enzyme (SOD1^−/−).

Results

Increased antioxidant capacity and decreased protein carbonyls and HNE adducts with Tempol treatment verified the drug delivery and biological function. Among a range of cytokines measured, proinflammatory cytokines, including IL-1, IL-2, IFN-γ, and TNF-α, exhibited more than 2-fold decreased titers in Tempol-treated ocular hypertensive eyes. Antioxidant treatment also resulted in a prominent decrease in NF-κB activation in the ocular hypertensive retina and optic nerve. Although pharmacological treatment limiting the oxidative stress resulted in decreased neuroinflammation, ocular hypertension–induced neuroinflammatory responses were increased in SOD1^−/− mice with defective antioxidant response.

Conclusions

These findings support the oxidative stress–related mechanisms of neuroinflammation and the potential of antioxidant treatment as an immunomodulation strategy for neuroprotection in glaucoma.

Early remodelling of the extracellular matrix proteins tenascin-C and phosphacan in retina and optic nerve of an experimental autoimmune glaucoma model

Glaucoma is characterized by the loss of retinal ganglion cells (RGCs) and optic nerve fibres. Previous studies noted fewer RGCs after immunization with ocular antigens at 28 days. It is known that changes in extracellular matrix (ECM) components conduct retina and optic nerve degeneration. Here, we focused on the remodelling of tenascin‐C and phosphacan/receptor protein tyrosine phosphatase β/ζ in an autoimmune glaucoma model. Rats were immunized with optic nerve homogenate (ONA) or S100B protein (S100). Controls received sodium chloride (Co). After 14 days, no changes in RGC number were noted in all groups. An increase in GFAPmRNA expression was observed in the S100 group, whereas no alterations were noted via immunohistochemistry in both groups. Extracellular matrix remodelling was analyzed after 3, 7, 14 and 28 days. Tenascin‐C and 473HD immunoreactivity in retinae and optic nerves was unaltered in both immunized groups at 3 days. At 7 days, tenascin‐C staining increased in both tissues in the ONA group. Also, in the optic nerves of the S100 group, an intense tenascin‐C staining could be shown. In the retina, an increased tenascin‐C expression was also observed in ONA animals via Western blot. 473HD immunoreactivity was elevated in the ONA group in both tissues and in the S100 optic nerves at 7 days. At 14 days, tenascin‐C and 473HD immunoreactivity was up‐regulated in the ONA retinae, whereas phosphacan expression was up‐regulated in both groups. We conclude that remodelling of tenascin‐C and phosphacan occurred shortly after immunization, already before RGC loss. We assume that both ECM molecules represent early indicators of neurodegeneration.

Association between systemic oxidative stress and visual field damage in open-angle glaucoma

Local and systemic oxidative stress in intraocular pressure (IOP) elevation and optic nerve damage may be involved in the pathogenesis of glaucoma. We reported previously that a lower level of systemic antioxidative capacity is associated with IOP elevation in open-angle glaucoma (OAG). We assessed the correlation between the visual field sensitivity value, i.e., mean deviation (MD), and systemic levels of prooxidants and antioxidants by analyzing the blood biochemistry in 202 patients with glaucoma. Serum levels of lipid peroxides, ferric-reducing activity, and thiol antioxidant activity were measured using the diacron reactive oxygen metabolite (dROM), biological antioxidant potential (BAP), and sulfhydryl (SH) tests, respectively, using a free-radical analyzer. Univariate and multivariate analyses suggested a positive correlation between MD and BAP (R = 0.005 and P = 0.0442 by a multiple regression model adjusted for seven demographic parameters), but no significant associations between the MD and the dROM (R = 0.002 and P = 0.8556) and SH tests (R = −0.001 and P = 0.8280). Use of more antiglaucoma medication and primary OAG rather than normal tension glaucoma also were associated significantly with worse visual field damage. This large and comprehensive assessment of the association between systemic redox status and visual field damage in OAG suggests that lower systemic antioxidant capacity measured by ferric-reducing activity is associated with more severe visual field damage in OAG that partly explained its roles in IOP elevation.

Correlation between Systemic Oxidative Stress and Intraocular Pressure Level

BACKGROUND

The involvement of local and systemic oxidative stress in intraocular pressure (IOP) elevation and optic nerve damage has been hypothesized in the pathogenesis of glaucoma. We reported previously that the level of systemic antioxidative capacity is lower in patients with open-angle glaucoma than controls without glaucoma. Here, we assessed the correlation between IOP and systemic levels of prooxidants and antioxidants by analyzing the blood biochemistry in patients with glaucoma.

METHODS

Peripheral blood samples were collected from Japanese patients with primary open-angle glaucoma (n = 206), exfoliation syndrome (n = 199), and controls (n = 126). Serum levels of lipid peroxides, ferric-reducing activity, and thiol antioxidant activity were measured by diacron reactive oxygen metabolite (dROM), biological antioxidant potential (BAP), and sulfhydryl (SH) tests, respectively, using a free radical analyzer. To test the possible effect of oxidative stress on IOP levels, the patients were classified into one of four groups (Q1, Q2, Q3, and Q4, with Q1 having the lowest IOP) based on the quartile value of IOP. For this classification, the known highest IOP value in both the right and left eyes was regarded as each subject's IOP. For comparisons among the IOP groups, the differences were calculated using one-way analysis of variance followed by post-hoc unpaired t-tests. To adjust for differences in demographic characteristic distributions, the dROM, BAP, and SH test values were compared among the IOP groups using multiple logistic regression analysis; the odds ratio (OR) of each variable was calculated with the Q1 group as the reference.

RESULTS

The dROM and the SH levels did not differ significantly (p = 0.6704 and p = 0.6376, respectively) among the four IOP groups. The BAP levels differed significantly (p = 0.0115) among the four IOP groups; the value was significantly lower in the Q4 group (1,932 μmol/L) compared with the Q1 (2,023 μmol/L, p = 0.0042) and Q2 (2,003 μmol/L, p = 0.0302) groups and significantly lower in the Q3 group (1,948 μmol/L) than the Q1 (p = 0.0174) group. After adjustment for differences in various demographic characteristics, lower BAP values were significantly associated with the classification into higher IOP groups (Q3 group, p = 0.0261 and OR = 0.06/range; Q4 group, p = 0.0018 and OR = 0.04/range). The dROM and SH values did not reach significance in any comparisons.

CONCLUSIONS

Lower systemic antioxidant capacity measured by ferric-reducing activity is involved in the pathogenesis of open-angle glaucoma via its roles in IOP elevation.

Effects of feeding polyphenol-rich winery wastes on digestibility, nitrogen utilization, ruminal fermentation, antioxidant status and oxidative stress in wethers

Four wethers were used in a 4 × 4 Latin square design experiment to evaluate the availability of two types of winery wastes, winery sediment and grape pomace, as ruminant feeds possessing antioxidant activities. Each wether was assigned to one of the following four treatments: (i) 75 g/kg winery sediment (WS) on a dry matter (DM) basis; (ii) 166 g/kg DM winery grape pomace (WP); (iii) control diet (CD; 17 g/kg DM soybean meal);and (iv) only tall fescue hay (TFH; no additive). Winery sediment and grape pomace had high levels of polyphenols and of radical scavenging activities. Feeding with winery sediment and grape pomace did not negatively affect the intake, but it depressed crude protein (CP) digestibility compared with CD (P = 0.052 and P < 0.01 for WS and WP, respectively). Polyphenols in winery wastes decreased ruminal ammonia production (P = 0.089 and P < 0.05), likely due to their inhibitive effect on microbial activities in the rumen. The addition of winery sediment and grape pomace decreased urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG; an index of oxidative damages) excretion per day (P < 0.05 and P = 0.059). The results indicated that winery sediment and grape pomace could alter nitrogen metabolism and/or act as new antioxidants for ruminants.

Total antioxidant level is correlated with intra-ocular pressure in patients with primary angle closure glaucoma

Background

To evaluate total antioxidant status (TAS) in the plasma of primary angle closure glaucoma (PACG) patients and to compare it to that of the control group. Additionally, we aim to investigate the association of various PACG clinical indices with TAS level.

Methods

Plasma samples were obtained from 139 PACG patients and 149 glaucoma-free controls of matching age, sex, and ethnicity. TAS in all samples was determined by spectrophotometric and enzyme-linked immunosorbent assay methods. We studied the possible association of the TAS level with various clinical indices relevant to PACG.

Results

The mean (±SD) total antioxidant (TAS) value was almost similar in patients 1 (±0.22) compared to controls 0.97 (±0.43); p = 0.345. Among cases, mean TAS concentration showed a statistically significant lower pattern among subjects with glaucoma onset at the age of ≤ 50 years (p = 0.037) and female subjects (p = 0.014) as well as having a family history of glaucoma (p = 0.010). Interestingly, a statistically significant inverse correlation was detected between TAS concentration and intra ocular pressure (IOP), (R = -0.14, p = 0.037).

Conclusions

The inverse correlation of TAS level with IOP, highlights TAS potential role as a predictive-marker for PACG-severity.

Decreased total antioxidants in patients with primary open angle glaucoma

PURPOSE

To evaluate total antioxidant status (TAS) in the plasma of primary open angle glaucoma (POAG) patients and to compare it to that of the control group. Additionally, we aim to investigate the association of various POAG clinical indices with TAS level.

MATERIALS AND METHODS

Plasma samples were obtained from 139 POAG patients and 148 glaucoma-free controls of matching age, sex, and ethnicity. TAS in all samples was determined by spectrophotometric and enzyme-linked immunosorbent assay methods.We studied the possible association of the TAS level with various clinical indices relevant to POAG.

RESULTS

The mean (±SD) total antioxidant (TAS) value was lower among patients: 0.47 (±0.32), than controls: 0.97 (±0.43) and this difference was statistically significant (p<0.0001). TAS concentration was not significantly associated neither with the level of intraocular pressure, nor with number of anti-glaucoma medications (p = 0.532 and 0.084 respectively). However, TAS level shows a trend towards reduction with increased severity of glaucoma presented in a reversed significant association with cup/disc ratio (p = 0.043).

CONCLUSIONS

Our findings provide evidence that TAS decreases in the plasma of POAG patients and that it may play a role in POAG pathogenesis. Association of TAS level with increased cup-to-disc ratio highlights TAS potential role as a predictive-marker for POAG-severity.

Coenzyme Q10 inhibits glutamate excitotoxicity and oxidative stress-mediated mitochondrial alteration in a mouse model of glaucoma

PURPOSE

To test whether a diet supplemented with coenzyme Q10 (CoQ10) ameliorates glutamate excitotoxicity and oxidative stress-mediated retinal ganglion cell (RGC) degeneration by preventing mitochondrial alterations in the retina of glaucomatous DBA/2J mice.

METHODS

Preglaucomatous DBA/2J and age-matched control DBA/2J-Gpnmb(+) mice were fed with CoQ10 (1%) or a control diet daily for 6 months. The RGC survival and axon preservation were measured by Brn3a and neurofilament immunohistochemistry and by conventional transmission electron microscopy. Glial fibrillary acidic protein (GFAP), superoxide dismutase-2 (SOD2), heme oxygenase-1 (HO1), N-methyl-d-aspartate receptor (NR) 1 and 2A, and Bax and phosphorylated Bad (pBad) protein expression was measured by Western blot analysis. Apoptotic cell death was assessed by TUNEL staining. Mitochondrial DNA (mtDNA) content and mitochondrial transcription factor A (Tfam)/oxidative phosphorylation (OXPHOS) complex IV protein expression were measured by real-time PCR and Western blot analysis.

RESULTS

Coenzyme Q10 promoted RGC survival by approximately 29% and preserved the axons in the optic nerve head (ONH), as well as inhibited astroglial activation by decreasing GFAP expression in the retina and ONH of glaucomatous DBA/2J mice. Intriguingly, CoQ10 significantly blocked the upregulation of NR1 and NR2A, as well as of SOD2 and HO1 protein expression in the retina of glaucomatous DBA/2J mice. In addition, CoQ10 significantly prevented apoptotic cell death by decreasing Bax protein expression or by increasing pBad protein expression. More importantly, CoQ10 preserved mtDNA content and Tfam/OXPHOS complex IV protein expression in the retina of glaucomatous DBA/2J mice.

CONCLUSIONS

Our findings suggest that CoQ10 may be a promising therapeutic strategy for ameliorating glutamate excitotoxicity and oxidative stress in glaucomatous neurodegeneration.

Increased urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG)/creatinine level is associated with the progression of normal-tension glaucoma

PURPOSE

The objective of this study was to investigate the association between systemic oxidative stress and visual field defect progression in normal-tension glaucoma (NTG).

PATIENTS AND METHODS

The subjects were 40 consecutive patients with NTG who were admitted to Keio University Hospital for 24-h intraocular pressure (IOP) evaluation; all subjects underwent six or more visual field tests in either eye and were followed up for >5 years. Spot samples of morning urine were collected during admission from all participants to determine the levels of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) by ELISA kit. A linear regression line was calculated with the least squares method. Those subjects whose regression lines were negative and the p value <0.05 were classified as progressive, while all others were defined as non-progressive. Urinary 8-OHdG/creatinine level was compared between the two groups. Adjusted odds ratio and 95% confidence intervals for the progression were estimated with logistic regression models.

RESULTS

Seventeen subjects showed visual field defect progression (age: 59.9 ± 9.5 years, untreated IOP in the right eye: 15.8 ± 2.1 mmHg), and 23 subjects showed no progression (age: 57.4 ± 10.4 years, untreated IOP in the right eye: 16.0 ± 2.6 mmHg). Urinary 8-OHdG/creatinine level was significantly higher in the progressive group than in the non-progressive group (progressive group: 9.0 ± 2.4 ng/mg creatinine, non-progressive group: 7.3 ± 1.8 ng/mg creatinine, p = 0.02). Multivariable analysis revealed that higher urinary 8-OHdG/creatinine level was a significant risk factor for the progression (odds ratio 1.54, 95% confidence interval 1.03-2.29).

CONCLUSIONS

Increased urinary 8-OHdG/creatinine was associated with glaucomatous visual field progression in subjects with NTG.

Status of systemic oxidative stresses in patients with primary open-angle glaucoma and pseudoexfoliation syndrome

Background

The involvement of local and systemic oxidative stress in intraocular pressure (IOP) elevation and optic nerve damage has been hypothesized in the pathogenesis of glaucoma. To test this, we measured the systemic levels of prooxidants and antioxidants by analyzing the blood biochemistry in patients with glaucoma.

Methods

Peripheral blood samples were collected from Japanese patients with primary open-angle glaucoma (PG) (n = 206), exfoliation syndrome (EX) (n = 199), and controls (n = 126). Plasma levels of lipid peroxides, ferric-reducing activity, and thiol antioxidant activity were measured by diacron reactive oxygen metabolites (dROM), biological antioxidant potential (BAP), and sulfhydryl (SH) tests, respectively, using a free radical analyzer.

Results

In the PG, EX, and control groups, the mean ± standard deviation values were 355±63, 357±69, and 348±56 (U. Carr), respectively, for dROM; 1,951±282, 1,969±252, and 2,033±252 (µmol/L), respectively, for BAP (µmol/L); and 614±98, 584±91, and 617±99 (µmol/L), respectively, for SH. The differences in the BAP values were significant between the PG and control groups (p = 0.0062), for SH between the EX and control groups (p = 0.0017), and for SH between the PG and EX groups (p = 0.0026). After adjustment for differences in age and sex among groups using multiple regression analysis, lower BAP values were correlated significantly with PG (p = 0.0155) and EX (p = 0.0049). Higher dROM values with and without glaucoma were correlated with female gender, and lower SH values with older age. There were no significant differences between the higher (≥21 mmHg) and lower (<21 mmHg) baseline IOPs in the PG group or between the presence or absence of glaucoma in the EX group.

Conclusions

Lower systemic antioxidant capacity that measured by ferric-reducing activity is involved in the pathogenesis of PG and EX.

Oxidative stress and mitochondrial dysfunction in glaucoma

Mitochondrial dysfunction increases reactive oxygen species (ROS) production and when this overwhelms the cellular antioxidant defences, oxidative stress ensues. Oxidative stress is recognized as a common pathologic pathway in many neurodegenerative diseases. Recent reports have also demonstrated oxidative stress in ocular tissues derived from experimental glaucoma models and clinical samples. There is also accumulating evidence pointing to mitochondrial dysfunction being present in some glaucoma patients. Thus oxidative stress from mitochondrial dysfunction may also play a causal role in glaucoma. The mechanisms by which oxidative stress may induce retinal ganglion cell loss in glaucoma are not fully understood but could include direct neurotoxic effects from ROS or indirect damage from oxidative stress-induced dysfunction of glial cells. This review will consider the evidence for the presence of oxidative stress in glaucoma; the mechanisms by which oxidative stress may contribute to disease pathogenesis; and also consider therapeutic approaches that target oxidative stress as a means of protecting against optic nerve degeneration.