Oxidative stress and glaucoma: injury in the anterior segment of the eye

Paeoniflorin alleviates TGF-β2-mediated extracellular matrix remodeling and oxidative stress in human trabecular meshwork cells

BACKGROUND

The multifunctional profibrotic cytokine transforming growth factor-beta2 (TGF-β2) is implicated in the pathophysiology of primary open angle glaucoma. Paeoniflorin (PAE) is a monoterpene glycoside with multiple pharmacological efficacies, such as antioxidant, anti-fibrotic, and anti-inflammatory properties. Studies have demonstrated that paeoniflorin protects human corneal epithelial cells, retinal pigment epithelial cells, and retinal microglia from damage. Here, the biological role of PAE in TGF-β2-dependent remodeling of the extracellular matrix (ECM) within the trabecular meshwork (TM) microenvironment.

METHODS

Primary or transformed (GTM3) human TM (HTM) cells conditioned in serum-free media were incubated with TGF-β2 (5 ng/mL). PAE (300 μM) was added to serum-starved confluent cultures of HTM cells for 2 h, followed by incubation with TGF-β2 for 22 h. SB-431542, a TGF-β receptor inhibitor (10 μM), was used as a positive control. The levels of intracellular ROS were evaluated by CellROX green dye. Western blotting was used to measure the levels of TGF-β2/Smad2/3 signaling-related molecules. Collagen 1α1, collagen 4α1, and connective tissue growth factor (CTGF) expression was evaluated by RT-qPCR. Immunofluorescence assay was conducted to measure collagen I/IV expression in HTM cells. Phalloidin staining assay was conducted for evaluating F-actin stress fiber formation in the cells.

RESULTS

PAE attenuated TGF-β2-induced oxidative stress and suppressed TGF-β2-induced Smad2/3 signaling in primary or transformed HTM cells. Additionally, PAE repressed TGF-β2-induced upregulation of collagen 1α1, collagen 4α1, and CTGF expression and reduced TGF-β2-mediated collagen I/IV expression and of F-actin stress fiber formation in primary or transformed HTM cells.

CONCLUSION

PAE alleviates TGF-β2-induced ECM deposition and oxidative stress in HTM cells through inactivation of Smad2/3 signaling.

Role of mitophagy in ocular neurodegeneration

Neurons in the central nervous system are among the most metabolically active cells in the body, characterized by high oxygen consumption utilizing glucose both aerobically and anaerobically. Neurons have an abundance of mitochondria which generate adequate ATP to keep up with the high metabolic demand. One consequence of the oxidative phosphorylation mechanism of ATP synthesis, is the generation of reactive oxygen species which produces cellular injury as well as damage to mitochondria. Mitochondria respond to injury by fusion which serves to ameliorate the damage through genetic complementation. Mitochondria also undergo fission to meet an increased energy demand. Loss of mitochondria is also compensated by increased biogenesis to generate new mitochondria. Damaged mitochondria are removed by mitophagy, an autophagic process, in which damaged mitochondria are surrounded by a membrane to form an autophagosome which ultimately fuses with the lysosome resulting in degradation of faulty mitochondria. Dysregulation of mitophagy has been reported in several central nervous system disorders, including, Alzheimer's disease and Parkinson's disease. Recent studies point to aberrant mitophagy in ocular neurodegenerative disorders which could be an important contributor to the disease etiology/pathology. This review article highlights some of the recent findings that point to dysregulation of mitophagy and it's underlying mechanisms in ocular neurodegenerative diseases, including, glaucoma, age-related macular degeneration and diabetic retinopathy.

Biochemical-molecular-genetic biomarkers in the tear film, aqueous humor, and blood of primary open-angle glaucoma patients

Introduction

Glaucoma is a chronic neurodegenerative disease, which is the leading cause of irreversible blindness worldwide. As a response to high intraocular pressure, the clinical and molecular glaucoma biomarkers indicate the biological state of the visual system. Classical and uncovering novel biomarkers of glaucoma development and progression, follow-up, and monitoring the response to treatment are key objectives to improve vision outcomes. While the glaucoma imaging field has successfully validated biomarkers of disease progression, there is still a considerable need for developing new biomarkers of early glaucoma, that is, at the preclinical and initial glaucoma stages. Outstanding clinical trials and animal-model study designs, innovative technology, and analytical approaches in bioinformatics are essential tools to successfully uncover novel glaucoma biomarkers with a high potential for translation into clinical practice.

Methods

To better understand the clinical and biochemical-molecular-genetic glaucoma pathogenesis, we conducted an analytical, observational, and case-comparative/control study in 358 primary open-angle glaucoma (POAG) patients and 226 comparative-control individuals (CG) to collect tears, aqueous humor, and blood samples to be processed for identifying POAG biomarkers by exploring several biological pathways, such as inflammation, neurotransmitter/neurotrophin alteration, oxidative stress, gene expression, miRNAs fingerprint and its biological targets, and vascular endothelial dysfunction, Statistics were done by using the IBM SPSS 25.0 program. Differences were considered statistically significant when p ≤ 0.05.

Results

Mean age of the POAG patients was 70.03 ± 9.23 years, and 70.62 ± 7.89 years in the CG. Malondialdehyde (MDA), nitric oxide (NO), interleuquin (IL)-6, endothelin-1 (ET-1), and 5 hydroxyindolacetic acid (5-HIAA), displayed significantly higher levels in the POAG patients vs. the CG (p < 0.001). Total antioxidant capacity (TAC), brain derived neurotrophic factor (BDNF), 5-hydroxy tryptamine (5-HT), solute carrier family 23-nucleobase transporters-member 2 (SLC23A2) gene, and the glutathione peroxidase 4 (GPX4) gene, showed significantly lower levelsin the POAG patients than in the CG (p < 0.001). The miRNAs that differentially expressed in tear samples of the POAG patients respect to the CG were the hsa miR-26b-5p (involved in cell proliferation and apoptosis), hsa miR-152-3p (regulator of cell proliferation, and extracellular matrix expression), hsa miR-30e-5p (regulator of autophagy and apoptosis), and hsa miR-151a-3p (regulator of myoblast proliferation).

Discussion

We are incredibly enthusiastic gathering as much information as possible on POAG biomarkers to learn how the above information can be used to better steer the diagnosis and therapy of glaucoma to prevent blindness in the predictable future. In fact, we may suggest that the design and development of blended biomarkers is a more appropriate solution in ophthalmological practice for early diagnosis and to predict therapeutic response in the POAG patients.

Mitochondrial Open Reading Frame of the 12S rRNA Type-c: Potential Therapeutic Candidate in Retinal Diseases

Mitochondrial open reading frame of the 12S rRNA type-c (MOTS-c) is the most unearthed peptide encoded by mitochondrial DNA (mtDNA). It is an important regulator of the nuclear genome during times of stress because it promotes an adaptive stress response to maintain cellular homeostasis. Identifying MOTS-c specific binding partners may aid in deciphering the complex web of mitochondrial and nuclear-encoded signals. Mitochondrial damage and dysfunction have been linked to aging and the accelerated cell death associated with many types of retinal degenerations. Furthermore, research on MOTS-c ability to revive oxidatively stressed RPE cells has revealed a significant protective role for the molecule. Evidence suggests that senescent cells play a role in the development of age-related retinal disorders. This review examines the links between MOTS-c, mitochondria, and age-related diseases of the retina. Moreover, the untapped potential of MOTS-c as a treatment for glaucoma, diabetic retinopathy, and age-related macular degeneration is reviewed.

Caveolin-1 in vascular health and glaucoma: A critical vascular regulator and potential therapeutic target

Caveolin-1 (Cav-1) is an integral scaffolding membrane protein found in most cell types. Cav-1 has been found to contribute significantly to ocular function, with mutations of Cav-1 being associated with a genetic risk of glaucoma development. Raised intraocular pressure (IOP) is a major modifiable risk factor for glaucoma. Cav-1 may be involved in both IOP-dependent and independent mechanisms involving vascular dysregulation. Systemic vascular diseases including hypertension, diabetes and hyperlipidaemia, have been shown to be associated with glaucoma development. Cav-1 is closely interlinked with endothelial nitric oxide synthase pathways that mediate vascular function and prevent cardiovascular diseases. Endothelial nitric oxide synthase and endothelin-1 are key vasoactive molecules expressed in retinal blood vessels that function to autoregulate ocular blood flow (OBF). Disruptions in the homeostasis of OBF have led to a growing concept of impaired neurovascular coupling in glaucoma. The imbalance between perfusion and neuronal stimulation arising from Cav-1 depletion may result in relative ischemia of the optic nerve head and glaucomatous injury. OBF is also governed by circadian variation in IOP and systemic blood pressure (BP). Cav-1 has been shown to influence central BP variability and other circadian rhythms such as the diurnal phagolysosomal digestion of photoreceptor fragments and toxic substrates to maintain ocular health. Overall, the vast implications of Cav-1 on various ocular mechanisms leading to glaucoma suggest a potential for new therapeutics to enhance Cav-1 expression, which has seen success in other neurodegenerative diseases.

[The effect of antioxidant therapy on some pathogenetic factors of primary open-angle glaucoma]

In patients with glaucoma, one of the main initiating mechanisms that triggers the chain of events is disruption of the universal mechanism for regulating vascular tone due to endothelial dysfunction (ED). The main manifestation of ED is an imbalance of vasoconstrictor and vasodilator endothelial mediators, which inconsistency triggers the mechanisms of adaptive distress leading to the progression of morphological destruction, dyslipidemia, acceleration of atherogenesis, development of hemodynamic and hydrodynamic disorders. The drug Mexidol has a wide range of pharmacological activity and affects the main pathogenetic links of primary open-angle glaucoma (POAG).

PURPOSE

The study analyzes the vascular remodulation, antioxidant and antihypoxic effects of the drug Mexidol in patients with PAOG.

MATERIAL AND METHODS

The study included 78 patients with POAG of the early (n=43) and advanced stage (n=35) with average age of 67.8±1.5 years. The main study group consisted of 47 patients who received Mexidol in addition to local hypotensive treatment; 31 patients comprised the control group. In the comparison groups, the degree of ED was determined by the results of reactive hyperemia test, patients' blood plasma was analyzed for levels of stable nitric oxide metabolite (nitrite NO2-) and endothelin-1 (ET-1). General assessment of oxidative stress was carried out by high-performance liquid chromatography. Functional activity of the retina was studied using an electroretinograph and static computer perimetry performed according to the standard technique.

RESULTS

The following changes are observed in patients of the main group using Mexidol: the index of oscillatory potentials significantly increases, peak latency decreases, perimeter indices show positive trends, vascular endothelial function improves according to reactive hyperemia test, concentration of vasoconstrictor mediator ET-1 in blood plasma decreases and of nitrite (NO2-) increases moderately, the coefficient of bioeffective vasotonic activity decreases, the level of glutathione peroxidase increases (p<0.05 compared to the baseline value), the level of malonyldialdehyde decreases, lipid metabolism improves (reduction in total cholesterol, low-density lipoprotein-cholesterol, triglycerides, decrease in the Atherogenic Index compared to the initial level).

CONCLUSIONS

The drug Mexidol proved to be an effective endothelial protector, a powerful antioxidant and antihypoxant, contributed to deceleration of atherogenesis in patients with POAG.

RAGE and its ligand amyloid beta promote retinal ganglion cell loss following ischemia-reperfusion injury

Introduction

Glaucoma is a progressive neurodegenerative disease associated with age. Accumulation of amyloid-beta (Aß) proteins in the ganglion cell layer (GCL) and subsequent retinal ganglion cell (RGC) loss is an established pathological hallmark of the disease. The mechanism through which Aß provokes RGC loss remains unclear. The receptor for the advanced glycation end product (RAGE), and its ligand Aß, have been shown to mediate neuronal loss via internalizing Aß within the neurons. In this study, we investigated whether the RAGE-Aß axis plays a role in RGC loss in experimental glaucoma.

Methods

Retinal ischemia was induced by an acute elevation of intraocular pressure in RAGE^-/- and wild-type (WT) control mice. In a subset of animals, oligomeric Aß was injected directly into the vitreous of both strains. RGC loss was assessed using histology and biochemical assays. Baseline and terminal positive scotopic threshold (pSTR) were also recorded.

Results

Retinal ischemia resulted in 1.9-fold higher RGC loss in WT mice compared to RAGE^-/- mice (36 ± 3% p < 0.0001 vs. 19 ± 2%, p = 0.004). Intravitreal injection of oligomeric Aß resulted in 2.3-fold greater RGC loss in WT mice compared to RAGE^-/- mice, 7-days post-injection (55 ± 4% p = 0.008 vs. 24 ± 2%, p = 0.02). We also found a significant decline in the positive scotopic threshold response (pSTR) amplitude of WT mice compared to RAGE^-/- (36 ± 3% vs. 16 ± 6%).

Discussion

RAGE^-/- mice are protected against RGC loss following retinal ischemia. Intravitreal injection of oligomeric Aß accelerated RGC loss in WT mice but not RAGE^-/-. A co-localization of RAGE and Aß, suggests that RAGE-Aß binding may contribute to RGC loss.

Multiomics analysis reveals the mechanical stress-dependent changes in trabecular meshwork cytoskeletal-extracellular matrix interactions

Trabecular meshwork (TM) tissue is subjected to constant mechanical stress due to the ocular pulse created by the cardiac cycle. This brings about alterations in the membrane lipids and associated cell-cell adhesion and cell-extracellular matrix (ECM) interactions, triggering intracellular signaling responses to counter mechanical insults. A loss of such response can lead to elevated intraocular pressure (IOP), a major risk factor for primary open-angle glaucoma. This study is aimed to understand the changes in signaling responses by TM subjected to mechanical stretch. We utilized multiomics to perform an unbiased mRNA sequencing to identify changes in transcripts, mass spectrometry- (MS-) based quantitative proteomics for protein changes, and multiple reaction monitoring (MRM) profiling-based MS and high-performance liquid chromatography (HPLC-) based MS to characterize the lipid changes. We performed pathway analysis to obtain an integrated map of TM response to mechanical stretch. The human TM cells subjected to mechanical stretch demonstrated an upregulation of protein quality control, oxidative damage response, pro-autophagic signal, induction of anti-apoptotic, and survival signaling. We propose that mechanical stretch-induced lipid signaling via increased ceramide and sphingomyelin potentially contributes to increased TM stiffness through actin-cytoskeleton reorganization and profibrotic response. Interestingly, increased phospholipids and diacylglycerol due to mechanical stretch potentially enable cell membrane remodeling and changes in signaling pathways to alter cellular contractility. Overall, we propose the mechanistic interplay of macromolecules to bring about a concerted cellular response in TM cells to achieve mechanotransduction and IOP regulation when TM cells undergo mechanical stretch.

Evaluation of Topical and Subconjunctival Injection of Hyaluronic Acid-Coated Nanoparticles for Drug Delivery to Posterior Eye

Posterior eye diseases, such as age-related macular degeneration and diabetic retinopathy, are difficult to treat due to ineffective drug delivery to affected areas. Intravitreal injection is the primary method for posterior eye drug delivery; however, it is usually accompanied by complications. Therefore, an effective and non-invasive method is required. Self-assembling nanoparticles (NPs) made from gelatin-epigallocatechin gallate (EGCG) were synthesized (GE) and surface-decorated with hyaluronic acid (HA) for drug delivery to the retinal/choroidal area. Different HA concentrations were used to prepare NPs with negative (GEH-) or positive (GEH+) surface charges. The size/zeta potential and morphology of the NPs were characterized by a dynamic light scattering (DLS) system and transmission electron microscope (TEM). The size/zeta potential of GEH+ NPs was 253.4 nm and 9.2 mV. The GEH- NPs were 390.0 nm and -35.9 mV, respectively. The cytotoxicity was tested by adult human retinal pigment epithelial cells (ARPE-19), with the results revealing that variant NPs were non-toxicity at 0.2-50 µg/mL of EGCG, and that the highest amount of GEH+ NPs was accumulated in cells examined by flowcytometry. Topical delivery (eye drops) and subconjunctival injection (SCI) methods were used to evaluate the efficiency of NP delivery to the posterior eyes in a mouse model. Whole eyeball cryosections were used to trace the location of fluorescent NPs in the eyes. The area of fluorescent signal obtained in the posterior eyes treated with GEH+ NPs in both methods (eye drops: 6.89% and SCI: 14.55%) was the greatest when compared with other groups, especially higher than free dye solution (2.79%). In summary, GEH+ NPs can be transported to the retina by eye drops and SCI; in particular, eye drops are a noninvasive method. Furthermore, GEH+ NPs, characterized by a positive surface and HA decoration, could facilitate drug delivery to the posterior eye as a useful drug carrier.

Development of a HPLC-MS/MS method for assessment of thiol redox status in human tear fluids

Oxidative stress is reported to be part of the pathology of many ocular diseases. For the diagnosis of ocular diseases, tear fluid has unique advantages. Although numerous analytical methods exist for the measurement of different types of biomolecules in tear fluid, few have been reported for comprehensive understanding of oxidative stress-related thiol redox signaling. In this study, a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed to determine a panel of twelve metabolites that systematically covered several thiol metabolic pathways. With optimization of MS/MS parameters and HPLC mobile phases, this method was sensitive (LOQ as low as 0.01 ng/ml), accurate (80-125% spike recovery) and precise (<10% RSD). This LC-MS/MS method combined with a simple tear fluid collection with Schirmer test strip followed by ultrafiltration allowed the high-throughput analysis for efficient determination of metabolites associated with thiol redox signaling in human tear fluids. The method was then applied to a small cohort of tear fluids obtained from healthy individuals. The method presented here provides a new technique to facilitate future work aiming to determine the complex thiol redox signaling in tear fluids for accurate assessment and diagnosis of ocular diseases.

Homeostatic alterations related to total antioxidant capacity, elemental concentrations and isotopic compositions in aqueous humor of glaucoma patients

Glaucoma is a multifactorial eye disease, characterized by progressive optic neurodegeneration. Elevation of the intraocular pressure is the main risk factor for glaucoma and is a consequence of an imbalance in the aqueous humor hydrodynamics, the physiology of which is influenced by the homeostatic equilibrium of essential elements, oxidative stress, and antioxidants. The aim of this work was to study local alterations in glaucomatous patients from two different, but connected, points of view: (i) the total antioxidant capacity (as an indicator of oxidative damage) and (ii) the concentration of mineral elements and their isotopic composition. Such objective was pursued using aqueous humor from patients diagnosed with pseudoexfoliation glaucoma (PEXG, n = 17) and primary open-angle glaucoma (POAG, n = 5) and age-matched control subjects (n = 16). The total antioxidant capacity (TAC) was examined in both aqueous humor and 60 serum samples (n = 20 controls, n = 20 for PEXG, and n = 20 for POAG), both showing higher TAC for the glaucoma population. The concentrations of the essential mineral elements (Cu, Fe, Mg, Na, P, and Zn) and the isotopic compositions of Cu and Zn were determined in aqueous humor using single-collector and multi-collector inductively coupled plasma–mass spectrometry, respectively. Significant differences were established for Mg and P levels when comparing the results for glaucomatous patients with those for the control population (p < 0.01 and p < 0.05 for Mg and P respectively, ANOVA and Kruskal-Wallis). The Zn isotopic composition was significantly shifted from that for the control population for PEXG patients. A significant difference in the isotopic composition of Zn was also established between the PEXG and POAG glaucoma cohorts.

Current Perspective of Hydrogen Sulfide as a Novel Gaseous Modulator of Oxidative Stress in Glaucoma

Glaucoma is a group of diseases characterized by the progressive loss of retinal ganglion cells and their axons. Elevated intraocular pressure (IOP) is the main clinical manifestation of glaucoma. Despite being in the focus of the studies for decades, the characteristic and the exact pathology of neurodegeneration in glaucoma remains unclear. Oxidative stress is believed to be one of the main risk factors in neurodegeneration, especially its damage to the retinal ganglion cells. Hydrogen sulfide (H₂S), the recently recognized gas signaling molecule, plays a pivotal role in the nervous system, vascular system, and immune system. It has also shown properties in regulating oxidative stress through different pathways in vivo. In this review, we summarize the distribution and the properties of H₂S within the eye with an emphasis on its role in modulating oxidative stress in glaucoma.

MiR-137 promotes cell growth and inhibits extracellular matrix protein expression in H2O2-induced human trabecular meshwork cells by targeting Src

Glaucoma is a progressive optic neuropathy in more than 25 % of cases in patients with permanent blindness. The microRNA is implicated in modulating the cellular function of the trabecular meshwork (TM). The aim of this study is to investigate the role of miR-137 in glaucoma and illustrate the potential molecular mechanisms. We show that miR-137 was down-regulated in H₂O₂-induced human trabecular meshwork cells (HTMCs), and overexpression of miR-137 attenuated H₂O₂-induced cell growth inhibition, apoptosis and elevated extracellular matrix (ECM) protein expression. In addition, miR-137 blocked the activation of YAP/TAZ by directly targeting src. Overexpression of src or activation of the YAP/TAZ pathway partly abrogated the effects of miR-137 on H₂O₂-induced cell viability and apoptosis and dampened the inhibition effect on ECM protein expression. In conclusion, miR-137 promotes cell growth and inhibits extracellular matrix protein expression in H₂O₂-induced human trabecular meshwork cells via the YAP/TAZ pathway by targeting src. Hence, miR-137 might be used as a novel therapeutic target to treat glaucoma.

TGF-β2 Promotes Oxidative Stress in Human Trabecular Meshwork Cells by Selectively Enhancing NADPH Oxidase 4 Expression

Purpose

The multifunctional profibrotic cytokine TGF-β2 is implicated in the pathophysiology of primary open angle glaucoma (POAG). While the underlying cause of POAG remains unclear, TGF-β2 dependent remodeling of the extracellular matrix (ECM) within the trabecular meshwork (TM) microenvironment is considered an early pathologic consequence associated with impaired aqueous humor (AH) outflow and elevated IOP. Mitochondrial-targeted antioxidants have been recently shown by our group to markedly attenuate TGF-β2 profibrotic responses, strongly implicating oxidative stress as a key facilitator of TGF-β2 signaling in human TM cells. In this study, we determined the mechanism by which oxidative stress facilitates TGF-β2 profibrotic responses in cultured primary human TM cells.

Methods

Semiconfluent cultures of primary or transformed human TM cells were conditioned overnight in serum-free media and subsequently challenged without or with TGF-β2 (5 ng/mL). Relative changes in the mRNA content of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) isoforms, connective tissue growth factor (CTGF), collagen 1α1 and 4α1 isoforms or relative changes in the protein content of Nox4, phospho- and total-Smad2 and -Smad3, collagens I and IV were determined in the absence or presence of GKT137831, a Nox1-Nox4 dual enzyme inhibitor, and quantified by real-time qPCR or by immunoblot, respectively. Relative in situ changes in collagens I and IV and in alpha smooth muscle actin (αSMA) were semiquantified by immunocytochemistry, whereas relative changes in filamentous actin stress fiber formation was semiquantified by phalloidin staining.

Results

Quiescent primary human TM cells cultured in the presence of TGF-β2 exhibited a marked selective increase in endogenous Nox4 mRNA and Nox4 protein expression. Actinomycin D prevented TGF-β2 mediated increases in Nox4 mRNA expression. TM cells reverse transfected with siRNA against Smad3 prevented TGF-β2 mediated increases in Nox4 mRNA expression. Pre-incubating TM cells with GKT137831 attenuated TGF-β2 mediated increases in intracellular reactive oxygen species (ROS), in COL1A1, COL4A1, and CTGF mRNA expression, in Smad3 protein phosphorylation, in collagens I, collagens IV, and αSMA protein expression, and in filamentous actin stress fiber formation.

Conclusions

TGF-β2 promotes oxidative stress in primary human TM cells by selectively increasing expression of NADPH oxidase 4. Dysregulation of redox equilibrium by induction of NADPH oxidase 4 expression appears to be a key early event involved in the pathologic profibrotic responses elicited by TGF-β2 canonical signaling, including ECM remodeling, filamentous actin stress fiber formation, and αSMA expression. Selective inhibition of Nox4 expression/activation, in combination with mitochondrial-targeted antioxidants, represents a novel strategy by which to slow the progression of TGF-β2 elicited profibrotic responses within the TM.

Evaluation of serum and aqueous humor klotho levels in pseudoexfoliation syndrome, pseudoexfoliation and primary open-angle glaucoma

PURPOSE

The aim of our study was to compare klotho in the serum and aqueous humor of patients with primary open-angle glaucoma (POAG), pseudoexfoliation glaucoma (PEXG) and pseudoexfoliation syndrome (PEX).

MATERIALS AND METHODS

18 POAG, 20 PEXG, 19 PEX and 20 control patients were included in our study. Aqueous humor and serum samples were collected at the time of cataract surgery. Samples were collected using enzyme-linked immunosorbent assay to evaluate the levels of Klotho protein.

RESULTS

Klotho levels in the serum and aqueous humor of PEXG patients (34.45 ± 3.59, 0.20 ± 0.15 ng/ml), PEX (35.85 ± 4.26, 0.23 ± 0.20 ng/ml) patients and POAG patients (35.99 ± 3.73, 0.25 ± 0.20 ng/ml) were significantly lower than control group (40.14 ± 3.85, 0.53 ± 0.39 ng/ml) (PEXG, P < 0.001, P < 0.001; PEX, P = 0.002, P = 0.003; POAG, P = 0.006, P = 0.003, respectively). Both serum and aqueous levels of klotho in the PEXG and PEX patients were lower than POAG patients, but the difference did not reach statistical significance (PEXG & POAG P = 0.149, P = 0.696), (PEX & POAG P = 0.845, P = 0.775).

CONCLUSION

Klotho levels in the serum and aqueous humor decreased in PEX, PEXG and POAG groups compared to control group, but the reduction was most significant in PEXG group.

Gadd45α affects retinal ganglion cell injury in chronic ocular hypertension rats by regulating p38MAPK pathway

OBJECTIVE

To investigate the impact and the mechanism of Gadd45α mediating p38MAPK pathway on the retinal ganglion cells (RGCs) injury in chronic ocular hypertension (COH) rats.

METHODS

COH model in rats were established and intraocular pressure (IOP) was tested. Retrograde labeling was used for counting RGCs and TUNEL staining was performed for RGCs apoptosis. Western Blotting was conducted to examine the expression of Gadd45α and p38MAPK pathway. Besides, RGC-5 cells cultured in vitro were treated with H₂O₂. Cell viability was detected by CCK-8, ROS level tested by DCFH-DA assay, and cell apoptosis examined by flow cytometry.

RESULTS

COH rats had increased expression of Gadd45α and p-p38/p38 protein 1-4 weeks after surgery. Rats in COH group enhanced obviously in IOP, RGC apoptosis rate and the protein expression of Gadd45α, p-p38/p38, Bax/Bcl-2 and cleaved caspase-3, but declined appreciably in RGC counting. However, the above indicators of COH rats were effectively improved by Gadd45α shRNA treatment. Additionally, RGC-5 cells in H₂O₂ group reduced in cell viability and went up in ROS level and apoptosis rate. The H₂O₂-induced RGC-5 cells treated with Gadd45α shRNA were improved apparently in those indicators, and cells treated with pcDNA Gadd45α showed an opposite trend. Moreover, p38 MAPK inhibitor SB203580 can effectively reverse the damage of pcDNA Gadd45α from H₂O₂-induced RGC-5 cells.

CONCLUSION

Silencing Gadd45α can reduce the RGC damage in COH rats by inhibiting p38MAPK pathway and such a protective role may be associated with the suppression of RGC apoptosis and the mitigation of oxidative stress.

Relationship between Periodontitis and Glaucoma: A Cross-Sectional Study

The objective of this cross-sectional study was to evaluate the association between periodontitis and glaucoma. This prospective cohort study used epidemiological data from the Korean Genome and Epidemiology Study performed between 2004 and 2016. Among 173,209 participants, 9572 patients with periodontitis and 115,332 controls (nonperiodontitis) were selected. We analysed the history of glaucoma in periodontitis and control participants. The participants were interviewed regarding their history of hypertension, diabetes mellitus, hyperlipidaemia, periodontitis, glaucoma, smoking, and alcohol consumption by trained interviewers. A logistic regression model was created to analyse the odds ratio of having a history of glaucoma among patients with periodontitis. Two-tailed analyses using chi-square and independent t-tests were used for statistical analysis. The adjusted odds ratio of periodontitis as a risk factor for glaucoma was 3.44 (95% confidence interval = 2.99–3.97, $p<0.001$ ). This study demonstrated that glaucoma was associated with periodontitis.

Can Polyphenols in Eye Drops Be Useful for Trabecular Protection from Oxidative Damage?

Polyphenols, with anti-oxidant properties, counteract oxidative stress effects. Increasing evidence has found oxidative stressto be the main risk factor for trabecular meshwork (TM) damage, leading to high-tension glaucoma. Topical anti-oxidants could represent a new target for glaucoma treatment. Our aim is to investigate the protective mechanisms on a human TM culture of a patented polyphenol and fatty acid (iTRAB^®)formulation in response to oxidative stress using an advanced invitromodel consisting of 3D-human TM cells, embedded in a natural hydrogel, and a milli-scaled multi-organ device model for constantdynamic conditions. The 3D-human TM cells(3D-HTMCs) were treated daily with 500 µM H₂O₂or 500 µM H₂O₂and 0.15% iTRAB^®(m/v) for 72 h, and molecular differences in the intracellular reactive oxygen species (iROS), state of the cells, activation of the apoptosis pathway and NF-kB and the expression ofinflammatory and fibrotic markers wereanalyzed at different time-points.Concomitant exposure significantly reduced iROS and restored TM viability, iTRAB^® having a significant inhibitory effect on the apoptotic pathway, activation of NF-κB, induction of pro-inflammatory (IL-1α, IL-1ß and TNFα) and pro-fibrotic (TGFβ) cytokines and the matrix metalloproteinase expressions. It is clear that this specific anti-oxidant provides a valid TM protection, suggesting iTRAB^® could be an adjuvant therapy in primary open-angle glaucoma (POAG).

Insights into the regulatory molecules involved in glaucoma pathogenesis

Glaucoma is an important cause of irreversible blindness, characterized by optic nerve anomalies. Increased intraocular pressure (IOP) and aging are major risk factors. Retinal ganglion cells and trabecular meshwork cells are certainly involved in the etiology of glaucoma. Glaucoma is usually a complex disease, and various genes and functions may contribute to its etiology. Among these may be genes that encode regulatory molecules. In this review, regulatory molecules including 18 transcription factors (TFs), 195 microRNAs (miRNAs), 106 long noncoding RNAs (lncRNAs), and two circular RNAs (circRNAs) that are reasonable candidates for having roles in glaucoma pathogenesis are described. The targets of the regulators are reported. Glaucoma-related features including apoptosis, stress responses, immune functions, ECM properties, IOP, and eye development are affected by the targeted genes. The targeted genes that are frequently targeted by multiple regulators most often affect apoptosis and the related features of cell death and cell survival. BCL2, CDKN1A, and TP53 are among the frequent targets of three types of glaucoma-relevant regulators, TFs, miRNAs, and lncRNAs. TP53 was itself identified as a glaucoma-relevant TF. Several of the glaucoma-relevant TFs are themselves among frequent targets of regulatory molecules, which is consistent with existence of a complex network involved in glaucoma pathogenesis.

Mitochondrial Markers in Aging and Primary Open-Angle Glaucoma

This review focuses on recent progress in understanding the role of mitochondrial markers in the context of mitochondrial dysfunction in glaucoma and discussing new therapeutic approaches to modulate mitochondrial function and potentially lead to improved outcomes in glaucoma.

Common aspects between glaucoma and brain neurodegeneration

Neurodegeneration can be defined as progressive cell damage to nervous system cells, and more specifically to neurons, which involves morphologic alterations and progressive loss of function until cell death. Glaucoma exhibits many aspects of neurodegenerative disease. This review examines the pathogenesis of glaucoma, comparing it with that of Alzheimer's disease (AD) and Parkinson's disease (PD), highlighting their common features. Indeed, in all three diseases there are not only the same types of pathogenic events, but also similarities of temporal cadences that determine neuronal damage. All three age-related illnesses have oxidative damage and mitochondrial dysfunction as the first pathogenic steps. The consequence of these alterations is the death of visual neurons in glaucoma, cognitive neurons in AD and regulatory motor neurons (substantia nigra) in PD. The study of these common pathogenic events (oxidative stress, mitochondrial dysfunction, protein degradation, apoptosis and autophagy) leads us to consider common therapeutic strategies for the treatment and prevention of these diseases. Also, examination of the genetic aspects of the pathways involved in neurodegenerative processes plays a key role in shedding light on the details of pathogenesis and can suggest new treatments. This review discusses the common molecular aspects involved in these three oxidative-stress and age-related diseases.

Rho-kinase (ROCK) Inhibitors - A Neuroprotective Therapeutic Paradigm with a Focus on Ocular Utility

BACKGROUND

Glaucoma is a progressive optic neuropathy causing visual impairment and Retinal Ganglionic Cells (RGCs) death gradually posing a need for neuroprotective strategies to minimize the loss of RGCs and visual field. It is recognized as a multifactorial disease, Intraocular Pressure (IOP) being the foremost risk factor. ROCK inhibitors have been probed for various possible indications, such as myocardial ischemia, hypertension, kidney diseases. Their role in neuroprotection and neuronal regeneration has been suggested to be of value in the treatment of neurological diseases, like spinal-cord injury, Alzheimer's disease and multiple sclerosis but recently Rho-associated Kinase inhibitors have been recognized as potential antiglaucoma agents.

EVIDENCE SYNTHESIS

Rho-Kinase is a serine/threonine kinase with a kinase domain which is constitutively active and is involved in the regulation of smooth muscle contraction and stress fibre formation. Two isoforms of Rho-Kinase, ROCK-I (ROCK β) and ROCK-II (ROCK α) have been identified. ROCK II plays a pathophysiological role in glaucoma and hence the inhibitors of ROCK may be beneficial to ameliorate the vision loss. These inhibitors decrease the intraocular pressure in the glaucomatous eye by increasing the aqueous humour outflow through the trabecular meshwork pathway. They also act as anti-scarring agents and hence prevent post-operative scarring after the glaucoma filtration surgery. Their major role involves axon regeneration by increasing the optic nerve blood flow which may be useful in treating the damaged optic neurons. These drugs act directly on the neurons in the central visual pathway, interrupting the RGC apoptosis and therefore serve as a novel pharmacological approach for glaucoma neuroprotection.

CONCLUSION

Based on the results of high-throughput screening, several Rho kinase inhibitors have been designed and developed comprising of diverse scaffolds exhibiting Rho kinase inhibitory activity from micromolar to subnanomolar ranges. This diversity in the scaffolds with inhibitory potential against the kinase and their SAR development will be intricated in the present review. Ripasudil is the only Rho kinase inhibitor marketed to date for the treatment of glaucoma. Another ROCK inhibitor AR-13324 has recently passed the clinical trials whereas AMA0076, K115, PG324, Y39983 and RKI-983 are still under trials. In view of this, a detailed and updated account of ROCK II inhibitors as the next generation therapeutic agents for glaucoma will be discussed in this review.

Mitochondrial Dysfunction as a Novel Target for Neuroprotective Nutraceuticals in Ocular Diseases

The eyes require a rich oxygen and nutrient supply; hence, the high-energy demand of the visual system makes it sensitive to oxidative stress. Excessive free radicals result in mitochondrial dysfunction and lead to retinal neurodegeneration, as an early stage of retinal metabolic disorders. Retinal cells are vulnerable because of their coordinated interaction and intricate neural networks. Nutraceuticals are believed to target multiple pathways and have shown neuroprotective benefits by scavenging free radicals and promoting mitochondrial gene expression. Furthermore, encouraging results demonstrate that nutraceuticals improve the organization of retinal cells and visual functions. This review discusses the mitochondrial impairments of retinal cells and the mechanisms underlying the neuroprotective effects of nutraceuticals. However, some unsolved problems still exist between laboratory study and clinical therapy. Poor bioavailability and bioaccessibility strongly limit their development. A new delivery system and improved formulation may offer promise for health care applications.

Protection of human retinal pigment epithelial cells from oxidative damage using cysteine prodrugs

Age-related macular degeneration (AMD) is one of the major causes of vision loss in the elderly in most developed countries. Among other causes, oxidative stress in the retinal pigment epithelium (RPE) has been hypothesized to be a major driving force of AMD pathology. Oxidative stress could be treated by antioxidant administration into the RPE cells. However, to achieve high in-vivo efficacy of an antioxidant, it is imperative that the agent be able to penetrate the tissues and cells. Evidence suggests that lipophilicity governs cellular penetrance. Out of many antioxidant candidates, N-acetyl-L-cysteine (a prodrug of L-cysteine) (NAC) is a potent antioxidant as the bioavailability of the parent drug, L-cysteine, determines the production of glutathione; the universal antioxidant that regulates ROS. To increase the lipophilicity, four ester derivatives of N-acetylcysteine: N-acetylcysteine methyl ester, N-acetylcysteine ethyl ester, N-acetylcysteine propyl ester, and N-acetylcysteine butyl ester were synthesized. To mimic in vitro AMD conditions, hydroquinone, a component of cigarette smoke, was used as the oxidative insult. Cytosolic and mitochondrial protection against oxidative stress were tested using cytosolic and mitochondrial specific assays. The results provide evidence that these lipophilic cysteine prodrugs provide increased protection against oxidative stress in human RPE cells compared with NAC.

iNOS-inhibitor driven neuroprotection in a porcine retina organ culture model

Nitrite oxide plays an important role in the pathogenesis of various retinal diseases, especially when hypoxic processes are involved. This degeneration can be simulated by incubating porcine retinal explants with CoCl₂. Here, the therapeutic potential of iNOS‐inhibitor 1400W was evaluated. Degeneration through CoCl₂ and treatment with the 1400W were applied simultaneously to porcine retinae explants. Three groups were compared: control, CoCl₂, and CoCl₂ + iNOS‐inhibitor (1400W). At days 4 and 8, retinal ganglion cells (RGCs), bipolar, and amacrine cells were analysed. Furthermore, the influence on the glia cells and different stress markers were evaluated. Treatment with CoCl₂ resulted in a significant loss of RGCs already after 4 days, which was counteracted by the iNOS‐inhibitor. Expression of HIF‐1α and its downstream targets confirmed the effective treatment with 1400W. After 8 days, the CoCl₂ group displayed a significant loss in amacrine cells and also a drastic reduction in bipolar cells was observed, which was prevented by 1400W. The decrease in microglia could not be prevented by the inhibitor. CoCl₂ induces strong degeneration in porcine retinae by mimicking hypoxia, damaging certain retinal cell types. Treatment with the iNOS‐inhibitor counteracted these effects to some extent, by preventing loss of retinal ganglion and bipolar cells. Hence, this inhibitor seems to be a very promising treatment for retinal diseases.

Effect of an oral supplementation with a formula containing R-lipoic acid in glaucoma patients

OBJECTIVE

To analyse the safety and effectiveness of the oral administration of a commercialised supplement containing R-alpha lipoic acid, taurine, vitamins C and E, lutein, zeaxanthin, zinc, copper and docosahexaenoic acid, in patients with primary open angle glaucoma (POAG), and in control subjects.

MATERIAL AND METHODS

A prospective study of cases and controls was carried out, including 30 participants of both genders that were divided into: POAG Group (n=15) and a control group (CG; n=15), assigned to the oral intake of NuaDHA preparations Vision® (1 pill/day)+NuaDHA 1000 (2 pills/day) for 6 months. Participants were interviewed, ophthalmologically examined, and peripheral blood was taken for routine analysis and the determination of the pro-oxidant (malondialdehyde) and total antioxidant status. Statistical analysis was performed using the SPSS 22.0 program.

RESULTS

After 6 months of supplementation, there was a significant increase in the plasma total antioxidant status (1.073±0.090mM vs 1.276±0.107mM, P=.028), along with a parallel decrease in malondialdehyde (7.066±1.070μM vs 2.771±0.462μM, P=.005) in the POAG group. The malondialdehyde also decreased in the control group (6.17±1.336 vs. 2.51±0.391, P=.028). The Schirmer test improved (20-30%) and the subjective dry eye signs/symptoms noticeably decreased in the POAG group versus the CG.

CONCLUSIONS

Formulations containing antioxidant vitamins, R-alpha lipoic acid and docosahexaenoic acid, administered for 6 consecutive months, counteracted the oxidative stress by further stabilising the morphological/functional parameters of both the ocular surface and the glaucoma, without presenting with adverse effects or intolerances.

The Potential Role of Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) in Glaucoma: A Review

Nuclear factor erythroid 2-related factor 2 (Nrf2) acts as a regulator of many biological processes and plays an essential role in preventing oxidation, inflammation, and fibrosis. In the past 20 years, there has been increasing research on the role of Nrf2 and oxidative stress in human glaucoma, including the roles of inflammation, trabecular meshwork cells, retinal ganglion cells, Tenon's capsule, antioxidants, fibrosis, and noncoding RNAs. Studies have shown that the upregulation of Nrf2 can reduce damage from oxidative stress in the trabecular meshwork cells and the retinal ganglion cells, reduce fibrosis in Tenon's capsule fibroblasts, which may reduce the progression of fibrosis after surgery for glaucoma. The regulatory roles of Nrf2, microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and exogenous compounds on trabecular meshwork cells (TMCs) and retinal ganglion cells have also been studied. The use of Nrf2 agonists, including noncoding RNAs, control the expression of Nrf2 through signaling pathways that continue to be investigated to identify effective treatments to improve clinical outcome following surgery for glaucoma. This review of publications between 1999 and 2019 aims to focus on the potential mechanisms of Nrf2 in the occurrence and development of glaucoma and the prognosis following surgical treatment. Also, several factors that induce the expression of Nrf2 in trabecular meshwork cells, retinal ganglion cells, and human Tenon's capsule fibroblasts are discussed.

Identification of genes involved in glaucoma pathogenesis using combined network analysis and empirical studies

Glaucoma is a leading cause of blindness. We aimed in this study to identify genes that may make subtle and cumulative contributions to glaucoma pathogenesis. To this end, we identified molecular interactions and pathways that include transcription factors (TFs) FOXC1, PITX2, PAX6 and NFKB1 and various microRNAs including miR-204 known to have relevance to trabecular meshwork (TM) functions and/or glaucoma. TM tissue is involved in glaucoma pathogenesis. In-house microarray transcriptome results and data sources were used to identify target genes of the regulatory molecules. Bioinformatics analyses were done to filter TM and glaucoma relevant genes. These were submitted to network-creating softwares to define interactions, pathways and a network that would include the genes. The network was stringently scrutinized and minimized, then expanded by addition of microarray data and data on TF and microRNA-binding sites. Selected features of the network were confirmed by empirical studies such as dual luciferase assays, real-time PCR and western blot experiments and apoptosis assays. MYOC, WDR36, LTPBP2, RHOA, CYP1B1, OPA1, SPARC, MEIS2, PLEKHG5, RGS5, BBS5, ALDH1A1, NOMO2, CXCL6, FMNL2, ADAMTS5, CLOCK and DKK1 were among the genes included in the final network. Pathways identified included those that affect ECM properties, IOP, ciliary body functions, retinal ganglion cell viability, apoptosis, focal adhesion and oxidative stress response. The identification of many genes potentially involved in glaucoma pathology is consistent with its being a complex disease. The inclusion of several known glaucoma-related genes validates the approach used.

Mitochondrial-Targeted Antioxidants Attenuate TGF-β2 Signaling in Human Trabecular Meshwork Cells

Purpose

POAG is a progressive optic neuropathy that is currently the leading cause of irreversible blindness worldwide. While the underlying cause of POAG remains unclear, TGF-β2-dependent remodeling of the extracellular matrix (ECM) within the trabecular meshwork (TM) microenvironment is considered an early pathologic consequence associated with impaired aqueous humor (AH) outflow and elevated IOP. Early studies have also demonstrated markedly elevated levels of oxidative stress markers in AH from POAG patients along with altered expression of antioxidant defenses. Here, using cultured primary or transformed human TM cells, we investigated the role oxidative stress plays at regulating TGF-β2-mediated remodeling of the ECM.

Methods

Primary or transformed (GTM3) human TM cells conditioned in serum-free media were incubated in the absence or presence of TGF-β2 and relative changes in intracellular reactive oxygen species (ROS) were measured using oxidation-sensitive fluorogenic dyes CellROX green or 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate (carboxy-H2DCFDA). TGF-β2-mediated changes in the content of connective tissue growth factor (CTGF) and collagen types 1α1 (COL1A1) and 4α1 (COL4A1) mRNA or collagens I and IV isoform proteins were determined in the absence or presence of mitochondrial-targeted antioxidants (XJB-5-131 or MitoQ) and quantified by quantitative PCR or by immunoblot and immunocytochemistry. Smad-dependent canonic signaling was determined by immunoblot, whereas Smad-dependent transcriptional activity was quantified using a Smad2/3-responsive SBE-luciferase reporter assay.

Results

Primary or transformed human TM cells cultured in the presence of TGF-β2 (5 ng/mL; 2 hours) exhibited marked increases in CellROX or fluorescein fluorescence. Consistent with previous reports, challenging cultured human TM cells with TGF-β2 elicited measurable increases in regulated Smad2/3 signaling as well as increases in CTGF, COL1A1, and COL4A1 mRNA and collagen protein content. Pretreating human TM cells with mitochondrial-targeted antioxidants XJB-5-131 (10 μM) or MitoQ (10 nM) attenuated TGF-β2-mediated changes in Smad-dependent transcriptional activity.

Conclusions

The multifunctional profibrotic cytokine TGF-β2 elicits a marked increase in oxidative stress in human TM cells. Mitochondrial-targeted antioxidants attenuate TGF-β2-mediated changes in Smad-dependent transcriptional activity, including marked reductions in CTGF and collagen isoform gene and protein expression. These findings suggest that mitochondrial-targeted antioxidants, when delivered directly to the TM, exhibit potential as a novel strategy by which to slow the progression of TGF-β2-mediated remodeling of the ECM within the TM.

Intraocular Oxygen and Antioxidant Status: New Insights on the Effect of Vitrectomy and Glaucoma Pathogenesis

PURPOSE

The purpose of this study was to investigate correlations of partial pressure of oxygen (pO₂) in the ocular anterior segment of human eyes and aqueous humor antioxidant levels of ascorbate (AsA) and total reactive antioxidant potential (TRAP) with glaucoma and vitreous status.

METHODS

This prospective, cross-sectional study stratified patients (n = 288 eyes) by lens and vitreous status and the presence of primary open-angle glaucoma for statistical analyses. Intraocular pO₂ concentrations were measured using a fiberoptic probe in patients at the beginning of planned glaucoma and/or cataract surgery. Aqueous humor specimens were obtained for antioxidant analysis of AsA and TRAP.

RESULTS

Following prior pars plana vitrectomy, pO₂ levels were significantly higher than in the reference group of cataract surgery in the anterior chamber angle (16.2 ± 5.0 vs. 13.0 ± 3.9 mm Hg; P = .0171) and in the posterior chamber (7.6 ± 3.1 vs. 3.9 ± 2.7 mm Hg; P < .0001). AsA and TRAP levels were significantly lower (1.1 ± 0.4 vs. 1.4 ± 0.5 mM, respectively; 403.3 ±116.5 vs. 479.0 ± 146.7 Trolox units, respectively; P = .004 and P = .024, respectively) in patients after vitrectomy. In patients with an intact vitreous, neither pO₂ nor antioxidant status correlated with lens status or glaucoma.

CONCLUSIONS

Increased pO₂ and antioxidant depletion following vitrectomy suggests an alteration of the intraocular oxidant-antioxidant balance. Our study links physiologic factors such as increased pO₂ in the anterior chamber angle and the posterior chamber to decreased antioxidant levels in aqueous humor following vitrectomy. Oxidative stress/damage to the trabecular meshwork in such post-vitrectomy cases may contribute to intraocular pressure elevation and increased risk of glaucoma. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Non-Synonymous variants in premelanosome protein (PMEL) cause ocular pigment dispersion and pigmentary glaucoma

Pigmentary glaucoma (PG) is a common glaucoma subtype that results from release of pigment from the iris, called pigment dispersion syndrome (PDS), and its deposition throughout the anterior chamber of the eye. Although PG has a substantial heritable component, no causative genes have yet been identified. We used whole exome sequencing of two independent pedigrees to identify two premelanosome protein (PMEL) variants associated with heritable PDS/PG. PMEL encodes a key component of the melanosome, the organelle essential for melanin synthesis, storage and transport. Targeted screening of PMEL in three independent cohorts (n = 394) identified seven additional PDS/PG-associated non-synonymous variants. Five of the nine variants exhibited defective processing of the PMEL protein. In addition, analysis of PDS/PG-associated PMEL variants expressed in HeLa cells revealed structural changes to pseudomelanosomes indicating altered amyloid fibril formation in five of the nine variants. Introduction of 11-base pair deletions to the homologous pmela in zebrafish by the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 method caused profound pigmentation defects and enlarged anterior segments in the eye, further supporting PMEL's role in ocular pigmentation and function. Taken together, these data support a model in which missense PMEL variants represent dominant negative mutations that impair the ability of PMEL to form functional amyloid fibrils. While PMEL mutations have previously been shown to cause pigmentation and ocular defects in animals, this research is the first report of mutations in PMEL causing human disease.

Possible role of differentially expressing novel protein markers (ligatin and fibulin-7) in human aqueous humor and trabecular meshwork tissue in glaucoma progression

The pathological mechanism underlying glaucoma has always been a complex aspect of this permanently blinding disease but proteomic studies have been helpful in elucidating it to a great extent in several studies. This study was designed to evaluate the expression and to get an idea about the function of two novel markers (ligatin and fibulin-7) identified in human aqueous humor (hAH) in relation to glaucomatous progression. A significant increase in the protein content of glaucomatous hAH compared to that of non-glaucomatous controls (NG-Ctrls) was observed. Ligatin, fibulin-7, and its proteolysis were revealed in hAH of primary open angle glaucoma (POAG), primary angle closure glaucoma (PACG) and NG-Ctrls. Quantification confirmed no significant difference in expression of ligatin, whereas fibulin-7 was significantly (P < 0.05) low in hAH of PACG in comparison to NG-Ctrls and POAG. Importantly the immunohistochemical assay for both indicated their possible involvement in the maintenance of the appropriate structure of TM in vivo. Since oxidative stress is a major contributor to glaucomatous pathogenesis, in vitro analysis of nuclear and cytoplasmic fractions indicated intracellular changes in localization and expression of ligatin upon oxidative insult of human trabecular meshwork (TM) cells. While no such changes were found for fibulin-7 expression. This was also corroborated with the immunocytochemical assay. Though a study with a small sample size, this is the first report which confirms the presence of ligatin and fibulin-7 in hAH, quantified their differential expression, and indicated the possibility of their involvement in the maintenance of the TM structure.

Cell Autonomous Neuroprotection by the Mitochondrial Uncoupling Protein 2 in a Mouse Model of Glaucoma

Glaucoma is a group of disorders associated with retinal ganglion cell (RGC) degeneration and death. There is a clear contribution of mitochondrial dysfunction and oxidative stress toward glaucomatous RGC death. Mitochondrial uncoupling protein 2 (Ucp2) is a well-known regulator of oxidative stress that increases cell survival in acute models of oxidative damage. The impact of Ucp2 on cell survival during sub-acute and chronic neurodegenerative conditions, however, is not yet clear. Herein, we test the hypothesis that increased Ucp2 expression will improve RGC survival in a mouse model of glaucoma. We show that increasing RGC but not glial Ucp2 expression in transgenic animals decreases glaucomatous RGC death, but also that the PPAR-γ agonist rosiglitazone (RSG), an endogenous transcriptional activator of Ucp2, does not significantly alter RGC loss during glaucoma. Together, these data support a model whereby increased Ucp2 expression mediates neuroprotection during a long-term oxidative stressor, but that transcriptional activation alone is insufficient to elicit a neuroprotective effect, motivating further research in to the post-transcriptional regulation of Ucp2.

Health Benefits of Polyphenols and Carotenoids in Age-Related Eye Diseases

Oxidative stress and inflammation play a critical role in the initiation and progression of age-related ocular abnormalities as cataract, glaucoma, diabetic retinopathy, and macular degeneration. Therefore, phytochemicals with proven antioxidant and anti-inflammatory activities, such as carotenoids and polyphenols, could be of benefit in these diseases. We searched PubMed and Web of Science databases for original studies investigating the benefits of different carotenoids and polyphenols in age-related ophthalmic diseases. Our results showed that several polyphenols (such as anthocyanins, Ginkgo biloba, quercetin, and resveratrol) and carotenoids (such as lutein, zeaxanthin, and mezoxanthin) have shown significant preventive and therapeutic benefits against the aforementioned conditions. The involved mechanisms in these findings include mitigating the production of reactive oxygen species, inhibiting the tumor necrosis factor-α and vascular endothelial growth factor pathways, suppressing p53-dependent apoptosis, and suppressing the production of inflammatory markers, such as interleukin- (IL-) 8, IL-6, IL-1a, and endothelial leucocyte adhesion molecule-1. Consumption of products containing these phytochemicals may be protective against these diseases; however, adequate human data are lacking. This review discusses the role and mechanisms of polyphenols and carotenoids and their possible synergistic effects on the prevention and treatment of age-related eye diseases that are induced or augmented by oxidative stress and inflammation.

Sulforaphane Attenuates H₂O₂-induced Oxidant Stress in Human Trabecular Meshwork Cells (HTMCs) via the Phosphatidylinositol 3-Kinase (PI3K)/Serine/Threonine Kinase (Akt)-Mediated Factor-E2-Related Factor 2 (Nrf2) Signaling Activation

Background

The aim of this study was to investigate whether and how sulforaphane (SFN), a novel promising nuclear factor-E2-related factor 2 (Nrf2) activator, exerted antioxidative stress through activating Nrf2 signaling.

Material/Methods

Cultured human trabecular meshwork cells (HTMCs) were treated with SFN for 6 hours after establishing the oxidative stress model by hydrogen peroxide (H₂O₂). The cell viability, the level of intercellular reactive oxygen species (ROS), and the apoptosis rate were observed using various kits. In addition, the gene and protein expression of Nrf2 and the phase II antioxidative enzymes were determined by performing qRT-PCR and western blotting.

Results

In H₂O₂-treated HTMCs, SFN protected HTMCs from oxidative stress damage and decreased the intracellular ROS accumulation, thus inhibiting cell apoptosis. SFN also increased the gene and protein expression of phase II antioxidative enzymes such as NAD(P)H: quinone oxidoreductase 1 (NQO-1), heme oxygenase-1 (HO-1), glutamate-cysteine ligase catalytic subunit (GCLC), and glutamate-cysteine ligase modifier subunit (GCLM) by Nrf2-dependent pathway. Furthermore, investigations of the pathway showed that HTMCs pretreated with LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3K), downregulated the expression of phase II antioxidative enzymes, partly.

Conclusions

These results indicated a novel application for SFN in attenuating H₂O₂-induced oxidative stress in HTMCs through activating PI3K/Akt/Nrf2 signaling pathway.

Substances of Interest That Support Glaucoma Therapy

Glaucoma is a multifactorial disease in which pro-apoptotic signals are directed to retinal ganglion cells. During this disease the conventional outflow pathway becomes malfunctioning. Aqueous humour builds up in the anterior chamber, leading to increased intraocular pressure. Both of these events are related to functional impairment. The knowledge of molecular mechanisms allows us to better understand the usefulness of substances that can support anti-glaucoma therapy. The goal of glaucoma therapy is not simply to lower intraocular pressure; it should also be to facilitate the survival of retinal ganglion cells, as these constitute the real target tissue in this disease, in which the visual pathway is progressively compromised. Indeed, an endothelial dysfunction syndrome affecting the endothelial cells of the trabecular meshwork occurs in both normal-tension glaucoma and high-tension glaucoma. Some substances, such as polyunsaturated fatty acids, can counteract the damage due to the molecular mechanisms - whether ischemic, oxidative, inflammatory or other - that underlie the pathogenesis of glaucoma. In this review, we consider some molecules, such as polyphenols, that can contribute, not only theoretically, to neuroprotection but which are also able to counteract the metabolic pathways that lead to glaucomatous damage. Ginkgo biloba extract, for instance, improves the blood supply to peripheral districts, including the optic nerve and retina and exerts a neuro-protective action by inhibiting apoptosis. Polyunsaturated fatty acids can protect the endothelium and polyphenols exert an anti-inflammatory action through the down-regulation of cytokines such as TNF-α and IL-6. All these substances can aid anti-glaucoma therapy by providing metabolic support for the cells involved in glaucomatous injury. Indeed, it is known that the food we eat is able to change our gene expression.

Progressive retinal ganglion cell loss in primary open-angle glaucoma is associated with temperature circadian rhythm phase delay and compromised sleep

Advanced primary open-angle glaucoma (POAG) is characterized by progressive retinal ganglion cell complex (RGCC) damage that may cause subsequent disruption of the circadian rhythms. Therefore, we evaluated circadian body temperature (BT) rhythm and sleep characteristics of 115 individuals (38 men and 77 women) diagnosed with POAG. GLV (global loss volume; %), a measure of RGCC damage, was estimated by high-definition optical coherence tomography, and RGC functional ability was assessed by pattern electroretinogram amplitude (PERGA). Depending on dynamics of POAG progression criteria, two groups were formed that were distinctively different in GLV: Stable POAG group (S-POAG; GLV = 5.95 ± 1.84, n = 65) and Progressive POAG group (P-POAG; GLV = 24.27 ± 5.09, n = 50). S-POAG and P-POAG groups were not different in mean age (67.61 ± 7.56 versus 69.98 ± 8.15) or body mass index (24.66 ± 3.03 versus 24.77 ± 2.90). All subjects performed 21 around-the-clock BT self-measurements during a 72-h period and kept activity/sleep diaries. Results showed pronounced disruption of circadian physiology in POAG and its progression with increasing severity of the disease. The daily mean of BT was unusually low, compared to age-matched controls. Moreover, our results revealed distinctive features of BT circadian rhythm alterations in POAG development and POAG progression. S-POAG is associated with lowered BT circadian rhythm robustness and inter-daily phase stability compared to controls. In the P-POAG group, the mean phase of the circadian BT rhythm was delayed by about 5 h and phases were highly scattered among individual patients, which led to reduced group mean amplitude. Circadian amplitudes of individuals were not different between the groups. Altogether, these results suggest that the body clock still works in POAG patients, but its entrainment to the 24-h environment is compromised. Probably because of the internal desynchronization, bedtime is delayed, and sleep duration is accordingly shortened by about 55 min in P-POAG compared to S-POAG patients. In the entire POAG cohort (both groups), later sleep phase and shorter mean sleep duration correlate with the delayed BT phase (r = 0.215; p = 0.021 and r = 0.322; p = 0.0004, respectively). An RGCC GLV of 15% apparently constitutes a threshold above which a delay of the circadian BT rhythm and a shortening of sleep duration occur.

Visual Defects and Ageing

Many diseases are related to age, among these neurodegeneration is particularly important. Alzheimer's disease Parkinson's and Glaucoma have many common pathogenic events including oxidative damage, Mitochondrial dysfunction, endothelial alterations and changes in the visual field. These are well known in the case of glaucoma, less in the case of neurodegeneration of the brain. Many other molecular aspects are common, such as the role of endoplasmic reticulum autophagy and neuronal apoptosis while others have been neglected due to lack of space such as inflammatory cytokine or miRNA. Moreover, the loss of specific neuronal populations, the induction of similar mechanisms of cell injury and the deposition of protein aggregates in specific anatomical areas are very similar events between these diseases. Intracellular and/or extracellular accumulation of protein aggregates is a key feature of many neurodegenerative disorders. The existence of abnormal protein aggregates has been documented in the RGCs of glaucomatous patients such as the anomalous Tau protein or the β-amyloid accumulations. Intra-cell catabolic processes also appear to be common in both glaucoma and neurodegeneration. They also help us to understand how the basis between these diseases is common and how the visual aspects can be a serious problem for those who are affected.

Effect of Myricetin on Primary Open-angle Glaucoma

Background

Primary open angle glaucoma (POAG) is the most common form of glaucoma, with a multifactorial etiology that results in retinal ganglion cell death and loss of vision. In this study, we assessed the effects of myricetin on the trabecular meshwork cells in POAG.

Methods

In the in-vivo model, glaucoma was induced in Sprague-Dawley rats by injecting hyaluronic acid into the anterior chamber of the eye (every week for six-weeks). Treatment group rats were administered myricetin (25, 50 or 100 mg/ kg body weight via oral gavage) each day for of six weeks.

Results

POAG TM cells exposed to myricetin (25, 50 or 100 μM) exhibited significantly lowered reactive oxidative species (ROS) levels and lipid peroxidation products. The expressions of transforming growth factors (TGFβ1/β2), vascular endothelial growth factor, and senescence markers (senescence associated-β-galactosidase, cyclin-dependent kinase inhibitors-p16 and p21) were substantially down-regulated in POAG TM cells exposed to myricetin. Myricetin effectively prevented IOP elevation in glaucoma-induced rats and decreased inflammatory cytokines (IL-1α, IL-1β, IL-6, Il-8, TNF-α) in the aqueous humor and POAG TM cells of glaucoma-induced rats.

Conclusion

The observations of the study illustrate the protective effects of myricetin in glaucomatous TM cells.

Functional role of peroxiredoxin 6 in the eye

Peroxiredoxin 6 (Prdx6) is the only mammalian 1-Cys member of the Prdx family, a group of enzymes which share the ability to reduce peroxides. In addition to its peroxidase function, Prdx6 also demonstrates phospholipase A₂ and lysophosphatidylcholine acyl transferase (LPCAT) activities. These enzymatic activities play an important role in regenerating oxidized membrane phospholipids and maintaining an appropriate balance of intracellular reactive oxygen species. Development of clinical pathologies, including those within the eye, have been linked to dysregulation of Prdx6 function. Interplay between external stressors like exposure to UV light, transforming growth factor β (TGF-β), and hyperglycemia in conjunction with diminished Prdx6 levels and loss of redox balance is associated with cellular changes in a variety of ophthalmic pathologies including cataracts, glaucoma, and retinal degeneration. Many of these cellular abnormalities can be rescued through supplementation with exogenous Prdx6. Additionally, corneal endothelial cells have been found to express high levels of Prdx6 in the plasma membrane. These findings highlight the importance of Prdx6 as an essential regulator of oxidative stress in the eye.

Treatment merits of Latanoprost/Thymoquinone - Encapsulated liposome for glaucomatus rabbits

Elevation of the intraocular pressure (IOP) is recognized as a risk factor for glaucoma development. Latanoprost (LAT) is a prostaglandin analog used to reduce the (IOP). Thymoquinone (TQ) is a major bioactive ingredient of Nigella sativa. The aim of this study was to develop novel liposomal drug carriers for ocular delivery of LAT, TQ and a mixture of them to investigate their IOP lowering efficacy upon subconjunctival injection in glaucoma-induced rabbit's eye. The aim of the present work extends also to study the effect of the different liposome formulations on the aqueous humor oxidative stress. Liposome samples were prepared using thin film hydration method. The physiochemical properties of the prepared drugs were characterized. The IOP was recorded for 70 rabbits using Schiotz-tonometer. Malondialdehyde (MDA), reduced glutathione (GSH), catalase (CAT) activities and total antioxidant activity of the aqueous humor were estimated. Fourier transform infrared and differential scanning calorimetric studies confirmed the interaction between the drug and the vesicles, which resulted in high drug encapsulation efficiency ≥88%. The size of the prepared liposomes was less than 10 μm which make them suitable in ophthalmic applications. The sustained effect was achieved by liposome samples of Lip (LAT) and Lip (LAT + TQ) which were able to reduce the IOP significantly up to 84 h. Morever, the treatment of glaucomatous rabbits with liposome formulations containing TQ in their preparation [Lip (TQ) and Lip (LAT + TQ)] greatly improved the ocular tissue-induced histopathological lesions. None of the prepared liposome formulations succeeded to improve the glaucoma-induced oxidative stress damage.

Ultraviolet radiation oxidative stress affects eye health

In the eye, ultraviolet radiation (UVR) is not known to contribute to visual perception but to mainly damage multiple structures. UVR carries higher energy than visible light and high dose exposure to UVR causes direct cellular damage, which has an important role in the development of cancer. This review provides an overview on the most recent knowledge on the role of UVR in oxidative stress (OS) in relation to noncancer ocular pathologies: various corneal pathologies, cataract, glaucoma and age-related macular degeneration. Possible OS signaling streams and mechanisms in the aging eye are discussed. Excessive exposure to UVR through live may seriously contribute to increase in OS of various eye tissues and thus lead to the advancement of serious ocular pathologies. Children are especially vulnerable to UVR because of their larger pupils and more transparent ocular media: up to 80% of a person's lifetime exposure to UVR is reached before the age of 18. Therefore, efficient everyday protection of the sensitive tissues of the eye by wearing of sunglasses, clear UVR-blocking spectacles or contact lenses should be considered from early age on. Many initiatives are taken worldwide to inform and raise the population's awareness about these possible UVR hazards to the eye.

LTBP2 knockdown and oxidative stress affect glaucoma features including TGFβ pathways, ECM genes expression and apoptosis in trabecular meshwork cells

Glaucoma is the leading cause of irreversible blindness worldwide. Although the etiology of glaucoma is incompletely understood, it is known that the extracellular matrix (ECM) of the trabecular meshwork, oxidative stress, TGFβ signaling pathways, and apoptosis are important components of glaucoma pathogenesis. These components appear to be interrelated, but knowledge on their interactions remains incomplete. Relevant to this gap in knowledge, LTBP2, glaucoma causing gene, may also be related to the mentioned components of glaucoma pathogenesis because of its putative roles in TGFβ signaling and ECM functions. This background prompted us to further query interactions among some molecules and pathways thought to be important in glaucoma etiology, with emphasis on oxidative stress and LTBP2. To this end, effects of LTBP2 siRNA knockdown, oxidative stress induction, TGFβ2 and gremlin exposures on canonical TGFβ and BMP signaling pathways, expression of ECM related genes, and apoptosis were assayed in primary human trabecular meshwork cell cultures. We found that oxidative stress induction and LTBP2 knockdown both affected all the processes queried, and that their affects paralleled one another. We suggest that effects of both oxidative stress and LTBP2 knockdown on the ECM and apoptosis may be mediated by TGFβ and BMP signaling pathway activation.

A Multi-Locus Genetic Risk Score for Primary Open-Angle Glaucoma (POAG) Variants Is Associated with POAG Risk in a Mediterranean Population: Inverse Correlations with Plasma Vitamin C and E Concentrations

Primary open-angle glaucoma (POAG) is a leading cause of blindness worldwide. The genetics of POAG are complex, and population-specific effects have been reported. Although many polymorphisms associated with POAG risk have been reported, few studies have analyzed their additive effects. We investigated, in a southern European Mediterranean population, the association between relevant POAG polymorphisms, identified by initial genome-wide association studies (GWASs) and POAG risk, both separately and as an aggregated multi-locus genetic risk score (GRS). Also, bearing in mind that oxidative stress is a factor increasingly recognized in the pathogenesis of POAG, we analyzed the potential association of the GRS with plasma concentrations of antioxidant vitamins (C and E). We carried out a case–control study including 391 POAG cases and 383 healthy controls, and analyzed four genetic polymorphisms (rs4656461-TMCO1, rs4236601-CAV1/CAV2, rs2157719-CDKN2B-AS1 and rs3088440-CDKN2A). An unweighted GRS including the four non-linked polymorphisms was constructed. A strong association between the GRS and POAG risk was found. When three categories of the GRS were considered, subjects in the top category of the GRS were 2.92 (95% confidence interval (CI): 1.79–4.77) times more likely to have POAG compared with participants in the bottom category (p < 0.001). Moreover, the GRS was inversely correlated with plasma vitamin C (p = 0.002) and vitamin E (p = 0.001) concentrations, even after additional adjustment for POAG status. In conclusion, we have found a strong association between the GRS and POAG risk in this Mediterranean population. While the additional correlation found between GRS and low levels of vitamins C and E does not indicated a causal relationship, it does suggest the need for new and deeper research into the effects of oxidative stress as a potential mechanism for those associations.

HES1 promotes extracellular matrix protein expression and inhibits proliferation and migration in human trabecular meshwork cells under oxidative stress

Glaucoma is the leading cause of irreversible blindness. The most prevalent form of glaucoma is primary open-angle glaucoma (POAG). Oxidative stress is one of the major pathogenic factors of the POAG, and can elicit molecular and functional changes in trabecular meshwork cells, causing increased aqueous humor outflow resistance and elevated intraocular pressure. However, the regulatory mechanisms underlying oxidative stress-induced cell phenotypic changes remain elusive. Herein, we exposed primary human trabecular meshwork cells to the oxidative stress induced by 300 μM H₂O₂ for 2 h, and found significantly up-regulated expression of extracellular matrix proteins and a transcription factor, hairy and enhancer of split-1 (HES1). The cell functions, including migration and proliferation, were impaired by the oxidative stress. Furthermore, HES1 shRNA abrogated the extracellular matrix protein up-regulation and rescued the functional defects caused by the oxidative stress; conversely, HES1 overexpression resulted in the molecular and functional changes similar to those induced by H₂O₂. These results suggest that HES1 promotes extracellular matrix protein expression and inhibits proliferative and migratory functions in the trabecular meshwork cells under oxidative stress, thereby providing a novel pathogenic mechanism underlying and a potential therapeutic target to the POAG.