Water soluble antioxidants in mammalian aqueous humor: interaction with UV B and hydrogen peroxide

The effect of hyperbaric oxygen therapy on corneal endothelial structure and anterior segment parameters

PURPOSE

To assess the effect of hyperbaric oxygen therapy (HBOT) on corneal endothelial structure and anterior segment parameters in healthy eyes.

METHODS

17 eyes of 17 patients who were scheduled to receive HBOT for other than ophthalmologic indications were investigated in this prospective study. Central corneal thickness (CCT) and corneal endothelial properties were evaluated using a specular microscope. Endothelial cell density (ECD), average cell area (AVG), coefficient of variation in cell size (CV), percentage of hexagonal cells (HEX), CCT, intraocular pressure (IOP), spherical equivalent (SE), axial length (AL) and anterior chamber depth (ACD) values were measured before the HBOT, after the 1st session, and after the 20th session of therapy.

RESULTS

47% of the patients (n = 8) received HBOT because of avascular necrosis, 35% (n = 6) due to sudden hearing loss, 12% (n = 2) for diabetic foot, and 6% (n = 1) for wound infection. The mean IOP was 14,80 mmHg before HBOT, 14,20 mmHg after the 1st session, and 13,73 mmHg after the 20th session. The mean ACD was 3,38 mm before HBOT, 3,34 mm after the 1st session, and 3,16 mm after the 20th session. Although the mean IOP and ACD decreased after HBOT sessions, it was not statistically significant (p > 0.05). A significant reduction was observed in SE values after 20 sessions of HBOT compared to the values measured before HBOT (p = 0,009). The mean ECD was 2572,53 ± 261,51 cells/mm2 before HBOT, 2554,47 ± 236,13 after the 1st session, and 2563,13 ± 226,92 after the 20th session. When the corneal properties measured before and after HBOT sessions were compared, no significant difference was found in terms of CCT, ECD, AVG, CV, and HEX (p > 0.05).

CONCLUSION

We observed no significant change in CCT, corneal endothelial layer properties, and anterior segment morphology after the 1st session, and after the 20th session of HBOT. Although HBOT reduced IOP and ACD, it was not statistically significant. HBOT may lead to a significant decrease in SE values after the 20th session.

Antioxidant Nutraceutical Strategies in the Prevention of Oxidative Stress Related Eye Diseases

This review aims to discuss the delicate balance between the physiological production of reactive oxygen species and the role of antioxidant nutraceutical molecules in managing radicals in the complex anatomical structure of the eye. Many molecules and enzymes with reducing and antioxidant potential are present in different parts of the eye. Some of these, such as glutathione, N-acetylcysteine, α-lipoic acid, coenzyme Q10, and enzymatic antioxidants, are endogenously produced by the body. Others, such as plant-derived polyphenols and carotenoids, vitamins B2, C, and E, zinc and selenium, and omega-3 polyunsaturated fatty acids, must be obtained through the diet and are considered essential nutrients. When the equilibrium between the production of reactive oxygen species and their scavenging is disrupted, radical generation overwhelms the endogenous antioxidant arsenal, leading to oxidative stress-related eye disorders and aging. Therefore, the roles of antioxidants contained in dietary supplements in preventing oxidative stress-based ocular dysfunctions are also discussed. However, the results of studies investigating the efficacy of antioxidant supplementation have been mixed or inconclusive, indicating a need for future research to highlight the potential of antioxidant molecules and to develop new preventive nutritional strategies.

Oxidative Stress in Optic Neuropathies

Increasing evidence indicates that changes in the redox system may contribute to the pathogenesis of multiple optic neuropathies. Optic neuropathies are characterized by the neurodegeneration of the inner-most retinal neurons, the retinal ganglion cells (RGCs), and their axons, which form the optic nerve. Often, optic neuropathies are asymptomatic until advanced stages, when visual impairment or blindness is unavoidable despite existing treatments. In this review, we describe systemic and, whenever possible, ocular redox dysregulations observed in patients with glaucoma, ischemic optic neuropathy, optic neuritis, hereditary optic neuropathies (i.e., Leber's hereditary optic neuropathy and autosomal dominant optic atrophy), nutritional and toxic optic neuropathies, and optic disc drusen. We discuss aspects related to anti/oxidative stress biomarkers that need further investigation and features related to study design that should be optimized to generate more valuable and comparable results. Understanding the role of oxidative stress in optic neuropathies can serve to develop therapeutic strategies directed at the redox system to arrest the neurodegenerative processes in the retina and RGCs and ultimately prevent vision loss.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Importance of the Use of Oxidative Stress Biomarkers and Inflammatory Profile in Aqueous and Vitreous Humor in Diabetic Retinopathy

Diabetic retinopathy is one of the leading causes of visual impairment and morbidity worldwide, being the number one cause of blindness in people between 27 and 75 years old. It is estimated that ~191 million people will be diagnosed with this microvascular complication by 2030. Its pathogenesis is due to alterations in the retinal microvasculature as a result of a high concentration of glucose in the blood for a long time which generates numerous molecular changes like oxidative stress. Therefore, this narrative review aims to approach various biomarkers associated with the development of diabetic retinopathy. Focusing on the molecules showing promise as detection tools, among them we consider markers of oxidative stress (TAC, LPO, MDA, 4-HNE, SOD, GPx, and catalase), inflammation (IL-6, IL-1ß, IL-8, IL-10, IL-17A, TNF-α, and MMPs), apoptosis (NF-kB, cyt-c, and caspases), and recently those that have to do with epigenetic modifications, their measurement in different biological matrices obtained from the eye, including importance, obtaining process, handling, and storage of these matrices in order to have the ability to detect the disease in its early stages.

Extracellular Vesicles Mediate Anti-Oxidative Response-In Vitro Study in the Ocular Drainage System

The importance of extracellular vesicles (EVs) as signaling mediators has been emphasized for several pathways with only limited data regarding their role as protective messages during oxidative stress (OS). The ocular drainage system is unique by being continuously exposed to OS and having a one-way flow of the aqueous humor carrying EVs taking role in glaucoma disease. Here, we aimed to examine the ability of EVs derived from the non-pigmented ciliary epithelium (NPCE)—the aqueous humor producing cells exposed to OS—to deliver protecting messages to the trabecular meshwork (TM)—the aqueous humor draining cells—a process with significance to the pathophysiology of glaucoma disease. EVs extracted from media of NPCE cells exposed to non-lethal OS and their unstressed control were incubated with TM cells. The effects of EVs derived from oxidative stressed cells on the activation of the nuclear factor erythroid 2-related factor 2-Kelch-like ECH-associated protein 1 (Nrf2-Keap1), a major OS pathway, and of the Wnt pathway, known for its role in primary open-angle glaucoma, were evaluated. EVs derived from oxidized NPCE cells significantly protected TM cells from direct OS. The TM cells uptake of EVs from oxidized NPCE and their cytosolic Nrf2 levels were significantly higher at 8 h post-exposure. EVs derived from oxidized NPCE cells significantly attenuated Wnt protein expression in TM cells and activated major antioxidant genes as measured by qRT-PCR. TM cells exposed to EVs derived from oxidized NPCE cells exhibited significantly lower OS and higher super oxide dismutase and catalase activity. Finally, we were able to show that carbonylated proteins and products of oxidized protein are presented in significantly higher levels in EVs derived from oxidized NPCE cells, supporting their suggested role in the signaling process. We hypothesize that these findings may have implications beyond understanding the pathophysiology of glaucoma disease and that transmitting signals that activate the antioxidant system in target cells represent a broad response common to many tissues communication.

The Association between Dietary Vitamin A and C Intakes and Cataract: Data from Korea National Health and Nutrition Examination Survey 2012

Oxidative stress in eye lens is one of the main causes of the cataract. Dietary antioxidants including vitamin A and C are therefore known to be associated with the risk of the disease. However, evidences are still lacking in Koreans. This study aimed to examine whether dietary vitamin A and C levels are associated with the cataract, using data of Korea National Health and Nutrition Examination Survey 2012. A total of 3,344 individuals (599 cases and 2,745 controls) were analyzed in the study. Dietary data was classified into 3 groups following Dietary Reference Intakes for Koreans 2015: 1) ≤ estimated average requirements (EAR), 2) EAR-recommended nutrient intake (RNI), and 3) ≥ RNI. Findings suggested normal subjects (controls) had better vitamin A and C nutritional status. Vitamin A and C intakes of normal subjects were significantly higher than those of cataract cases (p < 0.001, respectively). Ratio of subjects who consumed vitamin A and C lower than EAR was higher in cataract cases compared to normal subjects (p < 0.001, respectively). These antioxidant intake levels predicted that having lower level of vitamins lower than EAR increased the odd ratios (ORs) for cataract [for vitamin A: OR, 1.89; 95% confidence interval (CI), 1.55–2.31 and for vitamin C: OR, 2.06; 95% CI, 1.69–2.51]. However, such associations were not retained, when the subjects’ demographic and lifestyle factor were adjusted. In conclusion, vitamin A and C showed a protective effect against cataract. However, subjects' life style and demographic factors nullified the association. More studies are required to verify the true association between dietary antioxidants and risk of cataract in Koreans.

Detection of small molecule concentration gradients in ocular tissues and humours

The eye is an elegant organ consisting of a number of tissues and fluids with specialised functions that together allow it to effectively transmit and transduce light input to the brain for visual perception. One key determinant of this integrated function is the spatial relationship of ocular tissues. Biomolecular distributions within the main ocular tissues cornea, lens, and retina have been studied extensively in isolation, yet the potential for metabolic communication between ocular tissues via the ocular humours has been difficult to visualise. To address this limitation, the current study presents a method to map spatial distributions of metabolites and small molecules in whole eyes, including ocular humours. Using a tape-transfer system and freeze-drying, the spatial distribution of ocular small molecules was investigated in mouse, rat, fish (black bream), and rabbit eyes using negative ion mode MALDI imaging mass spectrometry. Full-scan imaging was used for discovery experiments, while MS/MS imaging for identification and localisation was also demonstrated. In all eyes, metabolites such as glutathione and phospholipids were localised in the main ocular tissues. In addition, in rodent eyes, major metabolites were distributed relatively uniformly in ocular humours. In contrast, both uniform and spatially defined ocular metabolite distributions were observed in the black bream eye. Tissue and ocular humour distributions were reproducible, as demonstrated by the three-dimensional analysis of a mouse eye, and able to be captured with high spatial resolution analysis. The presented method could be used to further investigate the role of inter-tissue metabolism in ocular health, and to support the development of therapeutics to treat major ocular diseases.

Mechanisms and Treatment of Light-Induced Retinal Degeneration-Associated Inflammation: Insights from Biochemical Profiling of the Aqueous Humor

Ocular inflammation contributes to the pathogenesis of blind-causing retinal degenerative diseases, such as age-related macular degeneration (AMD) or photic maculopathy. Here, we report on inflammatory mechanisms that are associated with retinal degeneration induced by bright visible light, which were revealed while using a rabbit model. Histologically and electrophysiologically noticeable degeneration of the retina is preceded and accompanied by oxidative stress and inflammation, as evidenced by granulocyte infiltration and edema in this tissue, as well as the upregulation of total protein, pro-inflammatory cytokines, and oxidative stress markers in aqueous humor (AH). Consistently, quantitative lipidomic studies of AH elucidated increase in the concentration of arachidonic (AA) and docosahexaenoic (DHA) acids and lyso-platelet activating factor (lyso-PAF), together with pronounced oxidative and inflammatory alterations in content of lipid mediators oxylipins. These alterations include long-term elevation of prostaglandins, which are synthesized from AA via cyclooxygenase-dependent pathways, as well as a short burst of linoleic acid derivatives that can be produced by both enzymatic and non-enzymatic free radical-dependent mechanisms. The upregulation of all oxylipins is inhibited by the premedication of the eyes while using mitochondria-targeted antioxidant SkQ1, whereas the accumulation of prostaglandins and lyso-PAF can be specifically suppressed by topical treatment with cyclooxygenase inhibitor Nepafenac. Interestingly, the most prominent antioxidant and anti-inflammatory benefits and overall retinal protective effects are achieved by simultaneous administrating of both drugs indicating their synergistic action. Taken together, these findings provide a rationale for using a combination of mitochondria-targeted antioxidant and cyclooxygenase inhibitor for the treatment of inflammatory components of retinal degenerative diseases.

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.

Analysis of pharmaceuticals and small molecules in aqueous humor

Aqueous humor (AH) is a transparent fluid found in the anterior chamber of the eye. The circulating AH nourishes the cornea and lens and removes the metabolic waste moving through the ocular chambers and drains from the eye to the venous blood. Analysis of drugs in AH is necessary to evaluate their pharmacokinetics parameters, which may be crucial to avoid potential adverse effects. Analysis of endogenous components of AH may help to understand its physiology as well as changes evoked by pathological situation. This review describes analytical methods used for determination of pharmaceuticals and small endogenous molecules in AH, focusing on sample preparation procedures and analytical techniques. Studies on human and animal samples are included. After inspection and filtering of records found in PubMed about 100 research papers were selected to review. In these articles AH samples of human and rabbit origin were studied most often. Sample evaporation and reconstitution in smaller solvent volume was the most popular method for analyte pre-concentration. Acetonitrile, methanol or mixture of both solvents were used most often for protein precipitation.

Structure and Misfolding of the Flexible Tripartite Coiled-Coil Domain of Glaucoma-Associated Myocilin

Glaucoma-associated myocilin is a member of the olfactomedins, a protein family involved in neuronal development and human diseases. Molecular studies of the myocilin N-terminal coiled coil demonstrate a unique tripartite architecture: a Y-shaped parallel dimer-of-dimers with distinct tetramer and dimer regions. The structure of the dimeric C-terminal 7-heptad repeats elucidates an unexpected repeat pattern involving inter-strand stabilization by oppositely charged residues. Molecular dynamics simulations reveal an alternate accessible conformation in which the terminal inter-strand disulfide limits the extent of unfolding and results in a kinked configuration. By inference, full-length myocilin is also branched, with two pairs of C-terminal olfactomedin domains. Selected variants within the N-terminal region alter the apparent quaternary structure of myocilin but do so without compromising stability or causing aggregation. In addition to increasing our structural knowledge of naturally occurring extracellular coiled coils and biomedically important olfactomedins, this work broadens the scope of protein misfolding in the pathogenesis of myocilin-associated glaucoma.

Neuroprotection in Glaucoma: Old and New Promising Treatments

Glaucoma is a major global cause of blindness, but the molecular mechanisms responsible for the neurodegenerative damage are not clear. Undoubtedly, the high intraocular pressure (IOP) and the secondary ischemic and mechanical damage of the optic nerve have a crucial role in retinal ganglion cell (RGC) death. Several studies specifically analyzed the events that lead to nerve fiber layer thinning, showing the importance of both intra- and extracellular factors. In parallel, many neuroprotective substances have been tested for their efficacy and safety in hindering the negative effects that lead to RGC death. New formulations of these compounds, also suitable for chronic oral administration, are likely to be used in clinical practice in the future along with conventional therapies, in order to control the progression of the visual impairment due to primary open-angle glaucoma (POAG). This review illustrates some of these old and new promising agents for the adjuvant treatment of POAG, with particular emphasis on forskolin and melatonin.

Gallic acid grafting effect on delivery performance and antiglaucoma efficacy of antioxidant-functionalized intracameral pilocarpine carriers

Functionalization of therapeutic carrier biomaterials can potentially provide additional benefits in drug delivery for disease treatment. Given that this modification determines final therapeutic efficacy of drug carriers, here, we investigate systematically the role of grafting amount of antioxidant gallic acid (GA) onto GN in situ gelling copolymers made of biodegradable gelatin and thermo-responsive poly(N-isopropylacrylamide) for intracameral delivery of pilocarpine in antiglaucoma treatment. As expected, increasing redox reaction time increased total antioxidant activities and free radical scavenging abilities of synthesized carrier biomaterials. The hydrophilic nature of antioxidant molecules strongly affected physicochemical properties of carrier materials with varying GA grafting amounts, thereby dictating in vitro release behaviors and mechanisms of pilocarpine. In vitro oxidative stress challenges revealed that biocompatible carriers with high GA content alleviated lens epithelial cell damage and reduced reactive oxygen species. Intraocular pressure and pupil diameter in glaucomatous rabbits showed correlations with GA-mediated release of pilocarpine. Additionally, enhanced pharmacological treatment effects prevented corneal endothelial cell loss during disease progression. Increasing GA content increased total antioxidant level and decreased nitrite level in the aqueous humor, suggesting a much improved antioxidant status in glaucomatous eyes. This work significantly highlights the dependence of physicochemical properties, drug release behaviors, and bioactivities on intrinsic antioxidant capacities of therapeutic carrier biomaterials for glaucoma treatment.

STATEMENT OF SIGNIFICANCE

Development of injectable biodegradable polymer depots and functionalization of carrier biomaterials with antioxidant can potentially provide benefits such as improved bioavailability, controlled release pattern, and increased therapeutic effect in intracameral pilocarpine administration for glaucoma treatment. For the first time, this study demonstrated that the biodegradable in situ gelling copolymers can incorporate different levels of antioxidant gallic acid to tailor the structure-property-function relationship of the intracameral drug delivery system. The systematic evaluation fully verified the dependence of phase transition, degradation behavior, drug release mechanism, and antiglaucoma efficacy on intrinsic antioxidant capacities of carrier biomaterials. The report highlights the significant role of grafting amount of gallic acid in optimizing performance of antioxidant-functionalized polymer therapeutics as new drug delivery platforms in disease treatment.

Looking into aqueous humor through metabolomics spectacles - exploring its metabolic characteristics in relation to myopia

Aqueous humor is the transparent fluid found in the anterior chamber of the eye that provides the metabolic requirements to the avascular tissues surrounding it. Despite the fact that metabolomics could be a powerful tool in the characterization of this biofluid and in revealing metabolic signatures of common ocular diseases such as myopia, it has never to our knowledge previously been applied in humans. In this research a novel method for the analysis of aqueous humor is presented to show its application in the characterization of this biofluid using CE-MS. The method was extended to a dual platform method (CE-MS and LC-MS) in order to compare samples from patients with different severities of myopia in order to explore the disease from the metabolic phenotype point of view. With this method, a profound knowledge of the metabolites present in human aqueous humor has been obtained: over 40 metabolites were reproducibly and simultaneously identified from a low volume of sample by CE-MS, including among others, a vast number of amino acids and derivatives. When this method was extended to study groups of patients with high or low myopia in both CE-MS and LC-MS, it has been possible to identify over 20 significantly different metabolite and lipid signatures that distinguish patients based on the severity of myopia. Among these, the most notable higher abundant metabolites in high myopia were aminooctanoic acid, arginine, citrulline and sphinganine while features of low myopia were aminoundecanoic acid, dihydro-retinoic acid and cysteinylglycine disulfide. This dual platform approach offered complementarity such that different metabolites were detected in each technique. Together the experiments presented provide a whelm of valuable information about human aqueous humor and myopia, proving the utility of non-targeted metabolomics for the first time in analyzing this type of sample and the metabolic phenotype of this disease.

Anti-glaucoma potential of Heliotropium indicum Linn in experimentally-induced glaucoma

Background

Heliotropium indicum is used as a traditional remedy for hypertension in Ghana. The aim of the study was to evaluate the anti-glaucoma potential of an aqueous whole plant extract of H. indicum to manage experimentally-induced glaucoma.

Methods

The percentage change in intraocular pressure (IOP), after inducing acute glaucoma (15 mLkg⁻¹ of 5 % dextrose, i.v.), in New Zealand White rabbits pretreated with Heliotropium indicum aqueous extract (HIE) (30–300 mgkg⁻¹), acetazolamide (5 mgkg⁻¹), and normal saline (10 mLkg⁻¹) per os were measured. IOPs were also monitored in chronic glaucoma in rabbits (induced by 1 % prednisolone acetate drops, 12 hourly for 21 days) after treatments with the same doses of HIE, acetazolamide, and normal saline for 2 weeks. The anti-oxidant property of the extract was assessed by assaying for glutathione levels in the aqueous humour. Glutamate concentration in the vitreous humour was also determined using ELISA technique. Histopathological assessment of the ciliary bodies was made.

Results

The extract significantly reduced intraocular pressure (p ≤ 0.05–0.001) in acute and chronic glaucoma, preserved glutathione levels and glutamate concentration (p ≤ 0.01–0.001). Histological assessment of the ciliary body showed a decrease in inflammatory infiltration in the extract and acetazolamide-treated group compared with the normal saline-treated group.

Conclusion

The aqueous whole plant extract of Heliotropium indicum has ocular hypotensive, anti-oxidant and possible neuro-protective effects, which therefore underscore its plausible utility as an anti-glaucoma drug with further investigation.

Formation constants of copper(i) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye

Speciation modelling incorporating redox equilibria provides a plausible explanation for copper deposition in the human eye associated with Wilson's disease.

Protective Effects of Verapamil against H2O2-Induced Apoptosis in Human Lens Epithelial Cells

Verapamil is used in the treatment of hypertension, angina pectoris, and atrial fibrillation. Recently, several studies have demonstrated that verapamil increased the optic nerve head blood flow and improved the retrobulbar circulation. All these show that verapamil is potentially useful for ophthalmic treatment. Thus, the aim of this study is to investigate whether verapamil could protect human lens epithelial cell (HLEC) from oxidative stress induced by H₂O₂ and the cellular mechanism underlying this protective function. The viability of HLEC was determined by the MTT assay and apoptotic cell death was analyzed by Hoechst 33258 staining. Moreover, Caspase-3 expression was detected by immunocytochemistry and flow cytometry analysis. We also detected Caspase-3 mRNA expression by reverse-transcription-polymerase chain reaction and the GSH content in cell culture. The results showed that oxidative stress produced significant cell apoptotic death and it was reduced by previous treatment with the verapamil. Verapamil was effective in reducing HLEC death mainly through reducing the expression level of apoptosis-related proteins, caspase-3, and increasing glutathione content. Therefore, it was suggested that verapamil was effective in reducing HLEC apoptosis induced by H₂O₂.

Polarized human embryonic stem cell-derived retinal pigment epithelial cell monolayers have higher resistance to oxidative stress-induced cell death than nonpolarized cultures

Oxidative stress-mediated injury to the retinal pigment epithelium (RPE) is a major factor involved in the pathogenesis of age-related macular degeneration (AMD), the leading cause of blindness in the elderly. Human embryonic stem cell (hESC)-derived RPE cells are currently being evaluated for their potential for cell therapy in AMD patients through subretinal injection of cells in suspension and subretinal placement as a polarized monolayer. To gain an understanding of how transplanted RPE cells will respond to the highly oxidatively stressed environment of an AMD patient eye, we compared the survival of polarized and nonpolarized RPE cultures following oxidative stress treatment. Polarized, nonpolarized/confluent, nonpolarized/subconfluent hESC-RPE cells were treated with H2O2. Terminal deoxynucleotidyl transferase dUTP nick end labeling stains revealed the highest amount of cell death in subconfluent hESC-RPE cells and little cell death in polarized hESC-RPE cells with H2O2 treatment. There were higher levels of proapoptotic factors (phosphorylated p38, phosphorylated c-Jun NH2-terminal kinase, Bax, and cleaved caspase 3 fragments) in treated nonpolarized RPE-particularly subconfluent cells-relative to polarized cells. On the other hand, polarized RPE cells had constitutively higher levels of cell survival and antiapoptotic signaling factors such as p-Akt and Bcl-2, as well as antioxidants superoxide dismutase 1 and catalase relative to nonpolarized cells, that possibly contributed to polarized cells' higher tolerance to oxidative stress compared with nonpolarized RPE cells. Subconfluent cells were particularly sensitive to oxidative stress-induced apoptosis. These results suggest that implantation of polarized hESC-RPE monolayers for treating AMD patients with geographic atrophy should have better survival than injections of hESC-RPE cells in suspension.

Toward the practical implementation of eye-related bioavailability prediction models

The development and registration of reformulated ophthalmic products (OPs) requires eye-related bioavailability (BA) assessments. Common BA algorithms associated with other routes of application, such as the oral route, cannot be easily applied to eye-related BA testing. Here, we provide an analysis of the current literature and suggestions for further directions in the development of high-capacity, cost-effective, and highly predictive nonclinical models of eye-related drug BA. One, or a combination of these models, has the potential for routine use in research laboratories and/or the pharmaceutical industry to overcome various obstacles in reformulated OP development and registration.

Ultrathin chitosan-poly(ethylene glycol) hydrogel films for corneal tissue engineering

Due to the high demand for donor corneas and their low supply, autologous corneal endothelial cell (CEC) culture and transplantation for treatment of corneal endothelial dysfunction would be highly desirable. Many studies have shown the possibility of culturing CECs in vitro, but lack potential robust substrates for transplantation into the cornea. In this study, we investigate the properties of novel ultrathin chitosan-poly(ethylene glycol) (PEG) hydrogel films (CPHFs) for corneal tissue engineering applications. Cross-linking of chitosan films with diepoxy-PEG and cystamine was employed to prepare ~50 μm (hydrated) hydrogel films. Through variation of the PEG content (1.5-5.9 wt.%) it was possible to tailor the CPHFs to have tensile strains and ultimate stresses identical to or greater than those of human corneal tissue while retaining similar tensile moduli. Light transmission measurements in the visible spectrum (400-700 nm) revealed that the films were >95% optically transparent, above that of the human cornea (maximum ~90%), whilst in vitro degradation studies with lysozyme revealed that the CPHFs maintained the biodegradable characteristics of chitosan. Cell culture studies demonstrated the ability of the CPHFs to support the attachment and proliferation of sheep CECs. Ex vivo surgical trials on ovine eyes demonstrated that the CPHFs displayed excellent characteristics for physical manipulation and implantation purposes. The ultrathin CPHFs display desirable mechanical, optical and degradation properties whilst allowing attachment and proliferation of ovine CECs, and as such are attractive candidates for the regeneration and transplantation of CECs, as well as other corneal tissue engineering applications.

Oxidative stress and potential applications of free radical scavengers in glaucoma

Glaucoma is the leading cause of irreversible blindness in industrialized countries and comprises a group of diseases characterized by progressive optic nerve degeneration. Glaucoma is commonly associated with elevated intraocular pressure due to impaired outflow of aqueous humor resulting from abnormalities within the drainage system of the anterior chamber angle (open-angle glaucoma) or impaired access of aqueous humor to the drainage system (angle-closure glaucoma). Oxidative injury and altered antioxidant defense mechanisms in glaucoma appear to play a role in the pathophysiology of glaucomatous neurodegeneration that is characterized by death of retinal ganglion cells. Oxidative protein modifications occurring in glaucoma serve as immunostimulatory signals and alter neurosupportive and immunoregulatory functions of glial cells. Initiation of the apoptotic cascade observed in glaucomatous retinopathy can involve oxidant mechanisms and different agents have been shown to be neuroprotective. This review focuses on the molecular mechanisms of oxidant injury and summarizes studies that have investigated novel free radical scavengers in the treatment of glaucomatous neurodegeneration.

Edible seaweed, Eisenia bicyclis, protects retinal ganglion cells death caused by oxidative stress

The purpose of the present study was to determine whether edible seaweed, Eisenia bicyclis, is effective in blunting the negative influence of N-methyl-D-aspartate (NMDA) on rat retinas and of oxidative stress-induced transformed retinal ganglion cell (RGC-5 cell line) death. The ethanol extract of E. bicyclis (EEEB) significantly attenuated the negative insult of L: -buthionine-(S,R)-sulfoximine plus glutamate on RGC-5 cells. Treatment of the RGC-5 cells with EEEB reduced the reactive oxygen species and recovered the reduced glutathione level caused by various radical species such as H(2)O(2), OH·, or O(2)·(-). Moreover, EEEB inhibited lipid peroxidation on rat brain homogenates caused by sodium nitroprusside. Applying NMDA to the retina affected the thickness of the inner plexiform layer (IPL) and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) produced a positive effect on ganglion cells. Importantly, EEEB protected the thinning of IPL and increased TUNEL positive cells in the ganglion cell layer (GCL). Five phlorotannin derivatives were isolated using chromatographic methods and liquid chromatography-mass spectroscopy analysis which has been known as an antioxidant. In conclusion, EEEB has a neuroprotective effect in vitro and in vivo. Furthermore, the major constituents of this extract, phlorotannins, could possibly be active compounds due to their antioxidative potency.

Circulating total glutathione in normal tension glaucoma patients: comparison with normal control subjects

PURPOSE

Oxidative stress plays a critical role in the pathogenesis of glaucoma. Glutathione is a major antioxidant molecule present in intracellular or extracellular space. Herein, we aimed to examine circulating glutathione level in normal tension glaucoma (NTG), which comprises the largest proportion of glaucoma disease in the Korean population.

METHODS

Nineteen NTG patients (NTG group) and 30 age- and gender-matched normal control subjects (control group) were included. Antecubital venous puncture was performed between 8 and 10 o'clock in the morning to obtain a 4 mL venous blood sample. Total glutathione level was measured by the spectrophotometric method at 412 nm. Correlation of total glutathione level with mean deviation and pattern standard deviation from the Humphrey visual field test was analyzed in the NTG group.

RESULTS

Total glutathione level in circulating blood was 524.02 ± 231.09 nmol and 586.06 ± 156.08 nmol in the NTG group and the control group, respectively. The difference between these values was not statistically significant (p = 0.121, F = 2.212). Age had no significant effect on circulating total glutathione level in either the NTG group (p = 0.171, r = -0.328) or the control group (p = 0.380, r = -0.166). In the NTG group, circulating total glutathione level had no significant relationship with mean deviation (p = 0.226, F = 1.636) and pattern standard deviation (p = 0.200, F = 1.766) after correcting for age and gender.

CONCLUSIONS

In NTG patients, circulating total glutathione levels were not different compared to those of normal subjects.

Antioxidant defenses in the ocular surface

The human eye is subjected constantly to oxidative stress due to daily exposure to sunlight, high metabolic activities, and oxygen tension. Reactive oxygen species generated from environmental insults and pathological conditions render the human eye particularly vulnerable to oxidative damage. The ocular surface composed of the tear film, the cornea, and the aqueous humor forms the first physical and biochemical barrier of the eye and plays a pivotal role in combating free radicals. These ocular compartments are enriched in certain antioxidants in the form of metabolic enzymes or small molecules. Such an antioxidant defense system in the ocular surface is essential for the maintenance of redox homeostasis in the eye and protection against oxidative damage. Herein, we review the properties and functions of key constituent antioxidants of the ocular surface.

Ultraviolet radiation: cellular antioxidant response and the role of ocular aldehyde dehydrogenase enzymes

Solar ultraviolet radiation (UVR) exposes the human eye to near constant oxidative stress. Evidence suggests that UVR is the most important environmental insult leading to the development of a variety of ophthalmoheliosis disorders. UVR-induced reactive oxygen species (ROS) are highly reactive with DNA, proteins, and cellular membranes, resulting in cellular and tissue damage. Antioxidant defense systems present in ocular tissues function to combat ROS and protect the eye from oxidative damage. Important enzymatic antioxidants are the superoxide dismutases, catalase, glutathione peroxidases, glutathione reductase, and members of the aldehyde dehydrogenase (ALDH) superfamily. Glutathione, ascorbic and uric acids, α-tocopherol, nicotinamide-adenine dinucleotide phosphate, and ferritin serve as small molecule, nonenzymatic antioxidants. Ocular tissues have high levels of these antioxidants, which are essential for the maintenance of reduction-oxidation homeostasis in the eye and protection against oxidative damage. ALDH1A1 and ALDH3A1, present abundantly in the cornea and lens, have been shown to have unique roles in the defense against UVR and the downstream effects of oxidative stress. This review presents the properties and functions of ocular antioxidants that play critical roles in the cellular response to UVR exposure, including a focused discussion of the unique roles that the ALDH1A1 and ALDH3A1 enzymes have as multifunctional ocular antioxidants.

Selenium and pseudoexfoliation syndrome

PURPOSE

To investigate the levels of selenium (Se), an essential trace element, in aqueous humor, conjunctival specimens, and serum of patients with pseudoexfoliation (PEX) syndrome and control subjects; and to determine the role of Se in the development and pathogenesis of PEX syndrome.

DESIGN

A prospective case-control study.

METHODS

Twenty-seven cataract patients with PEX syndrome and 20 age-matched cataract patients without PEX syndrome were enrolled in this institutional study. Patients with ophthalmic conditions other than PEX and conditions that may influence Se levels were excluded. During cataract surgeries, aqueous humor, conjunctival specimens, and serum were collected in both groups. Selenium levels of all samples were measured by using atomic absorption spectrophotometer.

RESULTS

The mean Se levels in aqueous humor of patients with PEX syndrome (50.96 ± 23.79 μg/L) were significantly lower than the control group (77.85 ± 19.21 μg/L) (P < .001). The mean Se levels in conjunctival specimens of patients with PEX syndrome (4.04 ± 1.44 μg/mg) were significantly lower than the control group (7.19 ± 2.00 μg/mg) (P < .001), as well. The mean Se levels in serum of patients with PEX syndrome (115.25 ± 25.20 μg/L) were lower than the control group (124.25 ± 14.40 μg/L), but this was not statistically significant (P = .325).

CONCLUSION

Reduced levels of Se in aqueous humor, conjunctival specimens, and serum of patients with PEX may support the role of impairment in antioxidant defense system in the pathogenesis of PEX syndrome.

Protective effect of Coenzyme Q(10) against oxidative damage in human lens epithelial cells by novel ocular drug carriers

The evaluation of N-trimethyl chitosan (TMC)-coated liposomes containing Coenzyme Q(10) as potential ophthalmic drug delivery system was carried out. Firstly, transcorneal permeation studies were conducted at 34°C using a side-by-side diffusion apparatus. The transport process of the fluorescent marker, rhodamine B, across the corneal epithelium was visualized with confocal laser scanning microscopy. Secondly, the human lens epithelial cells (HLECs) were cultured without or with Coenzyme Q(10) followed by addition of H(2)O(2). The cell viability and apoptosis were evaluated. The permeability coefficient for rhodamine B with TMC-coated liposomes increased more than two times in comparison with the value obtained for solution as control, from (0.42±0.018)×10(5)cms(-1) to (1.31±0.030)×10(5)cms(-1). Confocal laser scanning microscopy revealed that a TMC coating enhanced the transepithelial transport, dependent on the TMC concentration and contacting time. Coenzyme Q(10) elevated the cell viability and reduced the oxidative damage with the decreased percentage of apoptotic cells in a positive concentration-dependent manner. The ATP content of liposome-treated cells was increased about 2-fold compared with that of H(2)O(2)-treated cells. Together, our findings demonstrate that with the enhanced permeation effect of the TMC coating, Coenzyme Q(10)-loaded TMC-coated liposomes appear to be a promising ophthalmic drug delivery carrier with an efficacy in protecting HLECs against H(2)O(2)-induced oxidative damage.

Oxidative stress markers in patients with primary open-angle glaucoma

PURPOSE

To investigate the levels of antioxidant enzymes catalase (CAT), glutathione peroxidase (GPO), superoxide dismutase (SOD), and malondialdehyde (MDA) in human eyes with primary open-angle glaucoma (POAG) and to correlate their concentrations with severity of glaucoma.

DESIGN

A prospective cases control study.

PATIENTS AND METHODS

Thirty patients with primary open-angle glaucoma and twenty-five patients with senile cataracts of matched age and gender were included in the study prospectively. Aqueous humor samples were obtained by paracentesis at the time of elective surgery for glaucomatous and cataractous patients. Aqueous humor were analyzed for CAT, GPO, SOD, and MDA status.

RESULTS

GPO, SOD, and MDA enzyme levels revealed a high significant increase in aqueous humor of POAG patients with respect to the comparative group of cataract patients (P < 0.001). No significant difference in the activity of CAT enzyme in aqueous humor of POAG and cataract patient (P = 0.201). Significant correlation was found between the MDA enzyme level and severe visual field loss (P < 0.001) in POAG patients.

CONCLUSION

Increased levels of aqueous humor GPO, SOD, and MDA may be associated with POAG. In addition, they may be useful antioxidant enzyme levels in aqueous humor of POAG patients as a result of glaucoma disease and not a cause.

Molecular complexity of primary open angle glaucoma: current concepts

Glaucoma is a group of heterogeneous optic neuropathies with complex genetic basis. Among the three principle subtypes of glaucoma, primary open angle glaucoma (POAG) occurs most frequently. Till date, 25 loci have been found to be linked to POAG. However, only three underlying genes (Myocilin, Optineurin and WDR36) have been identified. In addition, at least 30 other genes have been reported to be associated with POAG. Despite strong genetic influence in POAG pathogenesis, only a small part of the disease can be explained in terms of genetic aberration. Current concepts of glaucoma pathogenesis suggest it to be a neurodegenerative disorder which is triggered by different factors including mechanical stress due to intra-ocular pressure, reduced blood flow to retina, reperfusion injury, oxidative stress, glutamate excitotoxicity, and aberrant immune response. Here we present a mechanistic overview of potential pathways and crosstalk between them operating in POAG pathogenesis.

Lactate dehydrogenase and oxidative stress activity in primary open-angle glaucoma aqueous humour

Lactate dehydrogenase (LDH) and lactate are some of the hypoxy biochemical parameters. Extracellular activity of this enzyme increases under the condition of oxidative stress, since the cell integrity can be disrupted during the lipid peroxidation process. Subsequently that leads to the increase level of the lactic acid and lactic acid salts. The objective of this investigation is establishing the level of LDH, LDH1 (HBDH) and the lactate concentration in aqueous humour in patients with primary open-angle glaucoma. Biochemical analysis have been made by enzymatic-colometric method (lactate) and UV-kinetic method (LDH and HBDH) in aqueous humour of 30 patients (42 eyes) with primary open-angle glaucoma (POAG) and 30 patients (40 eyes) with cataract (the control group). The increased values of lactate and the activity of LDH and HBDH enzyme in aqueous humour of POAG patients in correlation with the control group are the results not only of oxidative stress but also of hypoxy and the mitochondry oxidative function (p<0,001). The increased activity of the examined biochemical parameters in the aqueous humour of the POAG patients points to the fact that other mechanisms, besides IOP, have a role in glaucoma pathogenesis.

Determination of uric acid concentrations in human tear fluid, aqueous humour and serum

PURPOSE

The aim of this investigation was to assess and compare levels of uric acid in human tear fluid, aqueous humour and serum in cataract patients in order to obtain information about uric acid-dependent antioxidative status.

METHODS

Reflex tear fluid, aqueous humour and serum were obtained from 103 cataract patients (52 women, 51 men). Uric acid was determined by a reversed phase chromatographic method with electrochemical detection. The Randox test was used to measure the contribution of uric acid to the total antioxidative status (TAS) of these body fluids.

RESULTS

Mean concentrations of uric acid were 20 +/- 8 microg/ml in tear fluid, 18 +/- 6 microg/ml in aqueous humour and 58 +/- 15 microg/ml in serum. Significantly less uric acid was found in tear fluid (p < 0.01) and aqueous humour (p < 0.01) in female cataract patients compared with male cataract patients. There was a significant positive correlation between uric acid content in tear fluid, aqueous humour and serum, respectively (p < 0.01). The contribution of uric acid to TAS (Randox test) amounted to 38% in tear fluid, 10% in aqueous humour and 37% in serum.

CONCLUSIONS

Uric acid was found in comparable amounts in tear fluid and aqueous humour, but these were two- to threefold lower than in serum. Female cataract patients had lower uric acid values in tear fluid and aqueous humour compared with male cataract patients. Uric acid is an important antioxidant, as proven by its contribution to TAS as determined by the Randox test. The precise role of uric acid in the antioxidative reactions in tear fluid and aqueous humour is still under debate.

Oxidative stress in diseases of the human cornea

Intense exposure to light, robust metabolic activity, and high oxygen tension render the human eye particularly vulnerable to oxidative damage and the list of ophthalmological disorders implicating reactive oxygen and nitrogen species is rapidly expanding. Here, we review the roles of oxidative stress in the etiopathogeneses and pathophysiology of diseases of the human cornea including pterygium, keratoconus, trauma and chemical injury, and a host of inflammatory, metabolic, degenerative, and iatrogenic conditions. Data from animal and tissue culture experimentation germane to these conditions are also adduced.

Cataract: Window for systemic disorders

Cataract is the leading cause of visual handicap throughout the world, and almost all elderly individuals develop lens opacities. Epidemiological studies have shown that nuclear cataracts in young adults are associated with higher mortality. Many cataractogenic stressors induce endoplasmic reticulum (ER) stress, which in turn induces the unfolded protein response (UPR). The UPR can damage or kill a wide range of cell types and may be involved in many human diseases. We hypothesize that a cataract can be considered a window that can indicate the presence of systemic disorders. This is important because cataract is easily detected during a routine ocular examination. The slightest opacity in any region of the lenses, especially in younger patients, may be a sign of systemic disorders. Earlier detection of systemic disorders can save the lives of patients. If our hypothesis is correct, then elimination of known ER/cataractogenic stressors from individuals with cataracts should be the one of the first steps for treatments of the systemic disorders. We discuss the potential risk factors and beneficial effects of removal of such risk factors in patients with early cataracts. All patients with cataract should be referred for comprehensive medical examination.

Glaucomatous outflow pathway and oxidative stress

Oxidative free radicals and reactive oxygen species (ROS) are able to affect the cellularity of the human trabecular meshwork (HTM). These findings suggest that intraocular pressure increase, which characterises most glaucomas, is related to oxidative degenerative processes affecting the HTM and specifically its endothelial cells. Much evidence indicates that in this region ROS play a fundamental pathogenic role by reducing local antioxidant activities, inducing outflow resistance and exacerbating the activities of superoxide dismutase and glutathione peroxidase in glaucomatous eyes. Furthermore, hydrogen peroxide induces rearrangement of HTM cells and compromises their integrity. Glaucomatous subjects might have a genetic predisposition rendering them more susceptible to ROS-induced damage. A fairly significant correlation between oxidative DNA damage in the HTM and intraocular pressure increase and visual field defects in glaucomatous patients has been demonstrated. Thus, oxidative stress may play a significant role during glaucoma course initially damaging HTM cells, then contributing to the alteration of the homeostasis between NO and endothelins, and finally through its possible involvement in ganglional cell death. On the whole, these findings support the hypothesis that oxidative damage is an important step in the pathogenesis of primary open-angle glaucoma, and might be a relevant target for both prevention and therapy.

Ascorbate in the rat lens: dependence on dietary intake

PURPOSE

To establish a method for sample preparation to measure ascorbate in whole lenses and to investigate whether lens ascorbate concentration is dependent on dietary ascorbate intake.

METHODS

Four groups of 3 young Sprague-Dawley rats each were fed chow containing L-ascorbate, either 0.0, 5.7, 57.0 or 114.0 mmol/kg for a duration of 4 weeks. Thereafter, each rat was sacrificed. The lens was extracted, photographed, and lens wet weight was measured. The lens was homogenized in 1.0 ml of 0.25% metaphosphoric acid, the homogenate was centrifuged and the supernatant ultrafiltered. The filtrate was injected into an ion exchange, reversed-phase Polypore H HPLC column equipped with a 254-nm ultraviolet detector. Samples were calibrated against an L-ascorbate standard. Polynomial regression analysis was performed on the data.

RESULTS

All lenses were devoid of cataract. A 95% confidence interval for baseline content of ascorbate without any dietary intake was estimated to be 0.16+/-0.01 micromol/g wet weight of lens. The lens ascorbate concentration increased linearly with dietary ascorbate intake with an increased rate, estimated as a 95% confidence interval of 0.33+/-0.18 (micromol ascorbate) (g lens)-1)(mol ascorbate)-1 (kg chow) with r2=0.62.

CONCLUSION

Lens ascorbate concentration linearly increases with dietary ascorbate intake without cataract development in the rat. The currently presented method for sample preparation to measure the whole-lens content of ascorbate is applicable.

Ascorbate in the guinea pig lens: dependence on drinking water supplementation

PURPOSE

To investigate whether lens ascorbate concentration can be elevated with drinking water supplementation.

METHODS

Pigmented guinea pigs received drinking water supplemented with L-ascorbate, concentration 0.00, 2.84, 5.68 or 8.52 mm for a duration of 4 weeks. In addition, the chow fed to all animals contained 125 mmol L-ascorbate per kg of chow. At the end of the supplementation period, the guinea pigs were killed. Each lens was extracted. The lens was processed and ascorbate concentration was measured using high performance liquid chromatography (HPLC) with 254 nm ultraviolet radiation detection. The data were analysed with regression.

RESULTS

At the end of the test period, all lenses were devoid of cataract as observed by slit-lamp examination. All lenses contained a detectable concentration of ascorbate. Estimated 95% confidence intervals for mean animal-averaged lens ascorbate concentrations (micromol/g wet weight of whole lens) per group were 0.51 +/- 0.04 (0.00 mm; n = 6), 0.70 +/- 0.18 (2.84 mm; n = 6), 0.71 +/- 0.11 (5.68 mm; n = 5), and 0.71 +/- 0.06 (8.52 mm; n = 6). Animal-averaged lens ascorbate concentration [Asc(lens)] (micromol/g wet weight lens) increased with ascorbate supplementation in drinking water [Asc(water)] (M), in agreement with the model: [Asc(lens)] = A - Be(-kAsc(water)].

CONCLUSION

Lens ascorbate concentration increases with drinking water supplementation in the guinea pig without cataract development. The currently presented method for measurement of whole lens ascorbate content is suitable.