Oxidative stress in dry age-related macular degeneration and exfoliation syndrome

Unveiling the therapeutic potential and mechanisms of stanniocalcin-1 in retinal degeneration

Retinal degeneration (RD) is a group of ocular diseases characterized by progressive photoreceptor apoptosis and visual impairment. Mitochondrial malfunction, excessive oxidative stress, and chronic activation of neuroglia collectively contribute to the development of RD. Currently, there is a lack of efficacious therapeutic interventions for RD. Stanniocalcin-1 (STC-1) is a promising candidate molecule to decelerate photoreceptor cell death. STC-1 is a secreted calcium/phosphorus regulatory protein that exerts diverse protective effects. Accumulating evidence suggests that STC-1 protects retinal cells from ischemic injury, oxidative stress, and excessive apoptosis through enhancing the expression of uncoupling protein-2 (UCP-2). Furthermore, STC-1 exerts its antiinflammatory effects by inhibiting the activation of microglia and macrophages, as well as the synthesis and secretion of proinflammatory cytokines, such as TNF-α, IL-1, and IL-6. By employing these mechanisms, STC-1 effectively shields the retinal photoreceptors and optic nerve, thereby slowing down the progression of RD. We summarize the STC-1-mediated therapeutic effects on the degenerating retina, with a particular focus on its underlying mechanisms. These findings highlight that STC-1 may act as a versatile molecule to treat degenerative retinopathy. Further research on STC-1 is imperative to establish optimal protocols for its clinical use.

Protection effect of lutein-loaded Pickering emulsion prepared via ultrasound-assisted Maillard reaction conjugates on dry age-related macular degeneration

Age-related macular degeneration (AMD) is a prominent cause of vision loss among the elderly, and the treatment options for dry AMD (dAMD) are severely limited. Lutein has a favorable effect on the treatment of dAMD. Algae oil, rich in docosahexaenoic acid (DHA), is considered an effective intervention for eye diseases. In this study, casein-mannose conjugates were prepared to form algal oil-in-water Pickering emulsions by ultrasound-assisted Maillard reaction. As the ultrasound time increased from 0 to 25 min, the droplet size decreased to 648.2 ± 21.18 nm, which substantially improved the stability of the Pickering emulsions. The retention of lutein in the Pickering emulsions under ultrasonic treatment for 20 min was significantly improved under different conditions. The simulated gastrointestinal digestion revealed that ultrasound-assisted Pickering emulsions are an effective method for improving the bioaccessibility of lutein (19.76%-53.34%). In vivo studies elucidated that the lutein-loaded Pickering emulsions could effectively alleviate retinal thinning induced by sodium iodate (NaIO3) in mice with dAMD. Mechanistically, lutein-loaded Pickering emulsions significantly reduced oxidative stress by decreasing the MDA level, increasing the SOD production, and reducing the retinal ROS production. These findings explored the protective effects of lutein-loaded Pickering emulsions on dAMD and offered promising prospects for the nutritional intervention of dAMD.

Crosstalk between Oxidative Stress and Aging in Neurodegeneration Disorders

The world population is aging rapidly, and increasing lifespan exacerbates the burden of age-related health issues. On the other hand, premature aging has begun to be a problem, with increasing numbers of younger people suffering aging-related symptoms. Advanced aging is caused by a combination of factors: lifestyle, diet, external and internal factors, as well as oxidative stress (OS). Although OS is the most researched aging factor, it is also the least understood. OS is important not only in relation to aging but also due to its strong impact on neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimer's disease (AD), and Parkinson's disease (PD). In this review, we will discuss the aging process in relation to OS, the function of OS in neurodegenerative disorders, and prospective therapeutics capable of relieving neurodegenerative symptoms associated with the pro-oxidative condition.

Biomacromolecular Profile in Human Primary Retinal Pigment Epithelial Cells-A Study of Oxidative Stress and Autophagy by Synchrotron-Based FTIR Microspectroscopy

Synchrotron radiation-based Fourier Transform Infrared (SR-FTIR) microspectroscopy is a non-destructive and chemically sensitive technique for the rapid detection of changes in the different components of the cell's biomacromolecular profile. Reactive oxygen species and oxidative stress may cause damage to the DNA, RNA, and proteins in the retinal pigment epithelium (RPE), which can further lead to age-related macular degeneration (AMD) and visual loss in the elderly. In this study, human primary RPEs (hRPEs) were used to study AMD pathogenesis by using an established in vitro cellular model of the disease. Autophagy-a mechanism of intracellular degradation, which is altered during AMD, was studied in the hRPEs by using the autophagy inducer rapamycin and treated with the autophagy inhibitor bafilomycin A1. In addition, oxidative stress was induced by the hydrogen peroxide (H₂O₂) treatment of hRPEs. By using SR-FTIR microspectroscopy and multivariate analyses, the changes in the phosphate groups of nucleic acids, Amide I and II of the proteins, the carbonyl groups, and the lipid status in the hRPEs showed a significantly different pattern under oxidative stress/autophagy induction and inhibition. This biomolecular fingerprint can be evaluated in future drug discovery studies affecting autophagy and oxidative stress in AMD.

Emerging roles of oxidative stress in the pathogenesis of pseudoexfoliation syndrome (Review)

Pseudoexfoliation syndrome (PEXS) is a systemic disease caused by defects in the extracellular matrix (ECM) remodelling process leading to the chronic deposition of extracellular, fibrillary, white flaky pseudoexfoliation material (PEXM) throughout the body. Specifically, PEXM deposits on the lens capsule cause open-angle glaucoma, cataracts and blindness in patients with PEXS. Several gene single nucleotide polymorphisms are linked to the development of PEXS in humans, including lysyl oxidase-like 1 gene, clusterin and fibulin-5. The exact reason for the PEXM generation and its resulting pathogenesis is not well understood. However, defective ECM remodelling and oxidative stress (OS) have been hypothesized as significant events leading to the PEXM. Specifically, the link between OS and PEXS has been well studied, although the investigation is still ongoing. The present review explored recent advances in various aspects of PEXS and the involvement of OS in the eye for PEXS development.

Protective Effect of Ribes nigrum Extract against Blue Light-Induced Retinal Degeneration In Vitro and In Vivo

Although blackcurrant has several health benefits, such as antioxidant and anti-inflammatory properties, its effects on the retina remain unclear. In this study, we investigated the efficacy of black currant extract (BCE) in an in vitro and in vivo model of dry age-related macular degeneration (AMD) induced by blue light. Dry macular degeneration is characterized by the abnormal accumulation of lipofuscin (e.g., N-retinylidene-N-retinylethanolamine, A2E) in the retina. Blue light (BL) significantly decreased the viability of A2E-laden human retinal pigment epithelial cells (ARPE-19). However, BCE treatment protected ARPE-19 cells from A2E and BL. A2E, which is oxidized by blue light, generates reactive oxygen species in RPE cells. Treatment with BCE significantly decreased (80.8%) reactive oxygen species levels induced by A2E and BL in a concentration-dependent manner. BCE inhibited A2E accumulation in ARPE-19 cells and significantly downregulated the expression of genes increased by A2E and BL in ARPE-19 cells. In vivo, oral administration of BCE (25–100 mg/kg) ameliorated ocular lesions of BL-induced retinal damage in a mouse model and rescued the thickness of the whole retina, photoreceptor segment layer, outer nuclear layer, and inner nuclear layer. The decrease in the number of nuclei in the outer nuclear layer induced by BL was also rescued by BCE. Additionally, BCE administration rescued (40.0%) the BL-induced reduction in the expression level of superoxide dismutase 1. Taken together, our results suggest that BCE may have preventive and therapeutic effects on dry AMD through its antioxidant activity and inhibition of lipofuscin accumulation in the retina.

The Role of Vessel Density as Measured by Optical Coherence Tomography Angiography in the Evaluation of Pseudoexfoliative Glaucoma: A Review of the Literature

INTRODUCTION

To review the existing literature about the optical coherence tomography angiography (OCTA) findings regarding peripapillary and macular vessel density (VD) in patients with pseudoexfoliative glaucoma (PXG).

METHODS

A comprehensive search of the PubMed database was conducted to include articles up to November 1, 2021, using an appropriate search algorithm. The retrieved articles were assessed for eligibility and filtered manually to exclude duplicates, while articles and book chapters cited in the reference lists of the eligible articles obtained by this method were reviewed so as not to miss any relevant studies.

RESULTS

There is consistency among the studies published so far that a significant decrease in peripapillary VD exists in eyes with PXG compared to controls, and macular VD has also been reported to be significantly lower in PXG eyes than controls. However, the existing literature remains controversial regarding OCTA findings in eyes with PXG compared to those with primary open-angle glaucoma (POAG). Several studies have found that peripapillary VD and macular VD were significantly lower in PXG than POAG, while other studies reported no significant difference.

CONCLUSIONS

Eyes with PXG were found to present decreased peripapillary and macular VD compared to control eyes, suggesting that a vascular component, including optic nerve hypoperfusion, may be implicated in the pathogenesis of PXG.

Pseudoexfoliation syndrome: The critical role of the extracellular matrix in pathogenesis and treatment

Pseudoexfoliation syndrome (PEXS) is an age-related condition manifesting mainly in ocular tissues. PEXS is manifested through excess aggregation of fibrillary extracellular material at the anterior part of the eye that consists of a plethora of biomolecules, such as different proteoglycans (PGs) and glycosaminoglycans. PEXS is often linked to increased intraocular pressure, and can also lead to pseudoexfoliation glaucoma with very poor prognosis. Various stimuli are known to affect PEXS, including oxidation stress (OS), UV radiation and osmotic pressure. OS, is prominently involved on the progression of the syndrome as it promotes fibrogenesis, possibly via the induction of transforming growth factor-β (TGF-β) and other biomolecular effectors. In addition, PEXS initiation is tightly connected with the dysregulation of extracellular matrix (ECM) homeostasis since aberrant expression of ECM molecules is linked to both the accumulation and low degradation of pseudoexfoliation material. This article aims at uncovering the crucial role of various ECM effectors such as lysyl oxidase-like proteins, matrix metalloproteinases, and TGF-β1, as well as the biochemical pathways involved in the development and the progression of the PEXS.

The Protective Effects of n-Butylidenephthalide on Retinal Ganglion Cells during Ischemic Injury

Clinically, acute ischemic symptoms in the eyes are one of the main causes of vision loss, with the associated inflammatory response and oxidative stress being the key factors that cause injury. Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common type of ischemic optic neuropathy (ION); however, there are still no effective or safe treatment options to date. In this study, we investigated the neuroprotective effects of n-butylidenephthalide (BP) treatment in an experimental NAION rodent model (rAION). BP (10 mg/kg) or PBS (control group) were administered on seven consecutive days in the rAION model. Rats were evaluated for visual function by flash visual evoked potentials (FVEPs) at 4 weeks after NAION induction. The retina and optic nerve were removed for histological examination after the rats were euthanized. The molecular machinery of BP treatment in the rAION model was analyzed using Western blotting. We discovered that BP effectively improves retinal ganglion cell survival rates by preventing apoptotic processes after AION induction and reducing the inflammatory response through which blood-borne macrophages infiltrate the optic nerve. In addition, BP significantly preserved the integrity of the myelin sheath in the rAION model, demonstrating that BP can prevent the development of demyelination. Our immunoblotting results revealed the molecular mechanism through which BP mitigates the neuroinflammatory response through inhibition of the NF-κB signaling pathway. Taken together, these results demonstrate that BP can be used as an exceptional neuroprotective agent for ischemic injury.

Temporary Upregulation of Nrf2 by Naringenin Alleviates Oxidative Damage in the Retina and ARPE-19 Cells

Dry age-related macular degeneration (dAMD) is a chronic degenerative ophthalmopathy that leads to serious burden of visual impairment. Antioxidation in retinal pigment epithelium (RPE) cells is considered as a potential treatment for dAMD. Our previous studies have showed that naringenin (NAR) protects RPE cells from oxidative damage partly through SIRT1-mediated antioxidation. In this study, we tested the hypothesis that the Nrf2 signaling is another protective mechanism of NAR on dAMD. NaIO₃-induced mouse retinopathy and ARPE-19 cell injury models were established. Immunochemical staining, immunofluorescence, and western blotting were performed to detect the protein expressions of Nrf2 and HO-1. In addition, ML385 (activity inhibitor of Nrf2) and zinc protoporphyrin (ZnPP, activity inhibitor of HO-1) were applied to explore the effect of NaIO₃ or NAR. The results showed that NAR increased the protein expressions of Nrf2 and HO-1 in the retinas in mice exposed to NaIO₃ at the early stage. NAR treatment also resulted in a stronger activation of Nrf2 at the early stage in NaIO₃-treated ARPE-19 cells. Moreover, inhibition of HO-1 by ZnPP weakened the cytoprotective effect of NAR. The constitutive accumulation and activation of Nrf2 induced by NaIO₃ led to the death of RPE cells. However, NAR decreased the protein expressions of Nrf2 and HO-1 towards normal level in the mouse retinas and ARPE-19 cells exposed to NaIO₃ at the late stage. Our findings indicate that NAR protects RPE cells from oxidative damage via activating the Nrf2 signaling pathway.

Catalpol Protects ARPE-19 Cells against Oxidative Stress via Activation of the Keap1/Nrf2/ARE Pathway

Oxidative damage to retinal pigment epithelial (RPE) has been identified as one of the major regulatory factors in the pathogenesis of age-related macular degeneration (AMD). Catalpol is an iridoid glucoside compound that has been found to possess potential antioxidant activity. In the present study, we aimed to investigate the protective effect of catalpol on RPE cells under oxidative stress and to elucidate the potential molecular mechanism involved. We found that catalpol significantly attenuated hydrogen peroxide (H₂O₂)-induced cytotoxicity, G0/G1 phase cell cycle arrest, and apoptosis in RPE cells. The overproduction of reactive oxygen species (ROS) and malondialdehyde (MDA) stimulated by oxidative stress and the corresponding reductions in antioxidant glutathione (GSH) and superoxide dismutase (SOD) levels were largely reversed by catalpol pretreatment. Moreover, catalpol pretreatment markedly activated the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and its downstream antioxidant enzymes, catalase (CAT), heme oxygenase-1 (HO-1), and NADPH dehydrogenase (NQO1). It also increased the expression levels of cyclin E, Bcl-2, cyclin A, and cyclin-dependent kinase 2 (CDK2) and decreased the expression levels of Bax, Fas, cleaved PARP, p-p53, and p21 cleaved caspase-3, 8, and 9. The oxidative stress-induced formation of the Keap1/Nrf2 complex in the cytoplasm was significantly blocked by catalpol pretreatment. These results indicate that catalpol protected RPE cells from oxidative stress through a mechanism involving the activation of the Keap1/Nrf2/ARE pathways and the inactivation of oxidative stress-mediated pathways of apoptosis.

Sodium Iodate-Induced Degeneration Results in Local Complement Changes and Inflammatory Processes in Murine Retina

Age-related macular degeneration (AMD), one of the leading causes of blindness worldwide, causes personal suffering and high socioeconomic costs. While there has been progress in the treatments for the neovascular form of AMD, no therapy is yet available for the more common dry form, also known as geographic atrophy. We analysed the retinal tissue in a mouse model of retinal degeneration caused by sodium iodate (NaIO3)-induced retinal pigment epithelium (RPE) atrophy to understand the underlying pathology. RNA sequencing (RNA-seq), qRT-PCR, Western blot, immunohistochemistry of the retinas and multiplex ELISA of the mouse serum were applied to find the pathways involved in the degeneration. NaIO3 caused patchy RPE loss and thinning of the photoreceptor layer. This was accompanied by the increased retinal expression of complement components c1s, c3, c4, cfb and cfh. C1s, C3, CFH and CFB were complement proteins, with enhanced deposition at day 3. C4 was upregulated in retinal degeneration at day 10. Consistently, the transcript levels of proinflammatory ccl-2, -3, -5, il-1β, il-33 and tgf-β were increased in the retinas of NaIO3 mice, but vegf-a mRNA was reduced. Macrophages, microglia and gliotic Müller cells could be a cellular source for local retinal inflammatory changes in the NaIO3 retina. Systemic complement and cytokines/chemokines remained unaltered in this model of NaIO3-dependent retinal degeneration. In conclusion, systemically administered NaIO3 promotes degenerative and inflammatory processes in the retina, which can mimic the hallmarks of geographic atrophy.

Correlation of the intronic LOXL1 polymorphism rs11638944 with pseudoexfoliation syndrome and glaucoma in a Greek population

BACKGROUND

The purpose of this study is the development and validation of a novel and robust genotyping method for a new lysyl oxidase-like 1 (LOXL1) intronic polymorphism (rs11638944, C > G) and the investigation of its potential association with pseudoexfoliation syndrome (PXS) and pseudoexfoliation glaucoma (PXG) in a Greek population.

MATERIAL AND METHODS

242 DNA samples from 49 PXS, 64 PXG, 50 primary open-angle glaucoma (POAG) patients and 79 healthy age-matched controls were analyzed. Novel methodologies were developed and optimized, in order to genotype the intronic LOXL1 polymorphism: a) a real-time qPCR and melting curve analysis in the Light Cycler platform for rapid and cost-effective analysis and, b) a conventional PCR-RFLP method for analysis of a small number of samples. In selected samples, validity was checked with the reference DNA Sequencing method.

RESULTS

The real-time qPCR methodology was reliable, demonstrating good efficiency, reproducibility, accuracy in genotyping (100% concordance with the PCR-RFLP method and DNA Sequencing), with good allele discrimination (Tm = 53.26°C for C allele, Tm = 61.83°C for G allele, ΔTm = 8.57°C). The results were characterized by Hardy-Weinberg equilibrium in all groups. An increase from 18% in healthy controls to 61% in PXS patients was detected for the G/G homozygote thus, the C allele is protective for PXS with OR = 0.22 (95%CI: 0.11-0.42, p < .0001). Moreover, an increase from 18% in healthy controls to 70% in PXG patients was detected for the G/G homozygote thus, the C allele is protective for PXG with OR = 0.13 (95%CI: 0.06-0.25, p < .0001).

CONCLUSIONS

A statistically significant association was verified for the intronic LOXL1 polymorphism rs11638944 and PXS/PXG in a Greek population.

Leukemia inhibitory factor protects photoreceptor cone cells against oxidative damage through activating JAK/STAT3 signaling

Background

The present study aimed to investigate the protective role of leukemia inhibitory factor (LIF) against oxidative damage in photoreceptor cone cells.

Methods

In vivo, dark-adapted mice were injected with LIF or phosphate-buffered saline (PBS) intravitreously prior to being exposed to 5,000 lux bright light to determine the protective effect of LIF against light damage in cone cells. Oxidative damage to cone cells was analyzed using electroretinograms, immunostaining, Western blotting and reverse transcription quantitative polymerase chain reaction (RT-qPCR). In vitro, 661W cells were pretreated with 5 ng/mL of LIF with or without 50 µM of signal transducer and activator of transcription 3 (STAT3) inhibitor S3I201 for 1 h prior to treatment with 1 mM H₂O₂; cell survival, apoptosis, the oxidative stress index, and the activation of STAT3, extracellular signal-regulated kinase (ERK1/2), and AKT were subsequently determined.

Results

In vivo, light induction damaged the function and morphology of cone cells, and LIF was observed to protect cone cells from this light damage. Moreover, the activation of the Janus tyrosine kinase (JAK)/STAT3 signaling pathway and the subsequent changes in apoptosis and proliferation-related genes were found to be involved in the protective effect of LIF against light-induced retinal damage. In the H₂O₂-induced 661W cell model, H₂O₂ increased cellular apoptosis rates, the expression levels of Bcl-2–associated X-protein (BAX) and cleaved caspase 3, reactive oxygen species (ROS) production, and malondialdehyde content, while decreasing the cell viability, and Bcl-2, superoxide dismutase, catalase, and glutathione peroxidase activity. LIF was observed to block these events; however, the administration of the STAT3 inhibitor S3I201 reversed the beneficial effects of LIF on H₂O₂-triggered apoptosis and ROS production.

Conclusions

In conclusion, the present study suggested that LIF may relieve oxidative damage in cone cells through suppressing apoptosis and oxidative stress by targeting the STAT3 signaling pathway.

Naringenin protects RPE cells from NaIO3-induced oxidative damage in vivo and in vitro through up-regulation of SIRT1

BACKGROUND

Dry age-related macular degeneration (dAMD) leads to serious burden of visual impairment and there is no definitive treatment. Previous studies have showed that naringenin (NAR) significantly increased electroretinography (ERG) c-wave in sodium iodate (NaIO₃)-treated rats and viability of NaIO₃-treated ARPE-19 cells. But the underlying mechanism is still unknown.

PURPOSE

We tested the hypothesis that anti-oxidation mediated by Sirtuin 1 (SIRT1) was important to the protective effect of NAR on dAMD.

STUDY DESIGN/METHODS

NaIO₃-induced mice retinopathy and ARPE-19 cells injury models were established. In vivo, the protective effect of NAR eye drops on retina was evaluated by flash ERG (FERG) recording and histopathological examination. In vitro, viability of ARPE-19 cells, and the levels of lactic dehydrogenase (LDH), reactive oxygen species (ROS) and carbonyl protein were detected. Protein expression of SIRT1 was analyzed by immunochemical staining, immunofluorescence and western blotting.

RESULTS

NAR eye drops improved retinal function and morphology and normalized the protein expression of SIRT1 in mice exposed to NaIO₃. NAR promoted the survival of ARPE-19 cells in a concentration-dependent manner. NAR up-regulated SIRT1 protein expression, and decreased levels of ROS and carbonyl protein. Moreover, EX527, a selective inhibitor of SIRT1, abolished the effects of NAR on the cell viability and ROS. In addition, SRT1720, a selective agonist of SIRT1, improved the viability of cells and suppressed the production of ROS.

CONCLUSION

Our findings indicate that SIRT1-mediated anti-oxidation contributes to the protective effect of NAR eye drops on dAMD.

Cholesterol Regulation in Age-Related Macular Degeneration: A Framework for Mathematical Modelling of Drusen Biogenesis

In age-related macular degeneration (AMD), there is, in common with many other age-related diseases, the need to distinguish between changes in the ageing eye that lead to disease and those changes that are considered part of a healthy, ageing eye. Various studies investigating the multitude of mechanisms involved in the aetiology of AMD exist within the field of ophthalmology and related medical fields, yet many aspects of it remain poorly understood and only a limited number of therapies are available. A recent study relates drusen's topographically cellular characteristics to the neural retina's metabolic needs and associated cholesterol involvement within the retina. In particular, there is a need to fully understand the maintenance of cholesterol homeostasis in the retina to prevent normal ageing processes from being perturbed towards maculopathy. Here, we present an extensive review of the clinical and physiological features of the ageing retina, as well as mechanisms implicated in pathology, synthesised from a vast body of the published literature. We use this novel synthesis to construct a comprehensive process schematic, encompassing all key species and physiological processes such as nutrients, waste and lipoprotein management. We are therefore able to express these processes in a mathematical language via a comprehensive modelling framework, comprising a set of twenty-three equations spanning three distinct biological compartments. This very general modelling framework may now be adapted to more focused studies on individual mechanisms, processes or components underlying of the many facets of AMD. As an example of such a focused application, we conclude this article with a one-compartment, four-species model of the retinal pigment epithelium, which considers the parametric conditions under which either cholesterol homeostasis or unregulated accumulation of cholesterol may obtain in the ageing eye.

Single and repeated low-dose UVB radiation exposures affect the visual system

The visual system is an important biological indicator of effects induced by ultraviolet (UV) radiation. However, research has extensively investigated the effects of high-dose UV radiation in a single exposure, thus, the differential of this work was to investigate the effects of UVB radiation in low doses in single and repeated exposure. Therefore, we investigated the effects of repeated exposure to environmental UVB doses (0.09 J/cm²) on the retina and optic lobes of the crab Neohelice granulata. We evaluated the reactive oxygen species (ROS) concentration, antioxidant capacity against peroxyl radicals (ACAP) levels, catalase (CAT) and glutathione S-transferase (GST) activities and lipoperoxidation (LPO) levels and performed histological analysis. The crabs were exposed to UVB radiation for 1 or 60 days, while the control group was exposed to visible light. In the retina region, increases in ROS concentration and CAT and GST activities after the single exposure were observed. After 60 days of exposure, we observed an increase in ACAP levels. In the optic lobes, we observed an increase in GST activity and a decrease in LPO levels after the single exposure. However, we observed an increase in ROS concentration after 60 days of exposure. Moreover, after 60 days of exposure, infiltrating hemocytes in the retina and disorganization in neuron cell bodies of the external medulla were observed. In this sense, single and repeated exposure to low doses of UVB radiation induced changes in oxidative status and inflammatory process in the visual system of the crab Neohelice granulata.

Ultra-small-size Astragaloside-IV loaded lipid nanocapsules eye drops for the effective management of dry age-related macular degeneration

Background Age-related macular degeneration (AMD) is a major cause of severe visual loss in elderly people. The treatments for dry AMD (dAMD) are severely limited so far. In this work, we aim to develop an eye drop to protect retinal functions against oxidative stress and apoptosis for improving dAMD management. Methods Astragaloside-IV (ASIV) was prepared into phospholipid complex and loaded into three sizes (20, 50 and 90 nm) of ASIV lipid nanocapsules (ASIV-LNCs). The penetration and distribution of LNCs were investigated. DAMD mice model was induced by NaIO₃, and therapeutic effect was evaluated by electroretinography (ERG), histological examination, apoptosis and ROS detection. Results The ocular penetration and pharmacokinetic studies corroborated the feasibility of the LNCs to reach the fundus, and ultra-small-size LNCs (ASIV-LNCs-20) had the best delivery effect. ASIV-LNCs-20 was able to decrease ROS production and reduce the apoptosis rate from 5.12% to 0.533%. ERG and H&E staining results confirmed ASIV-LNCs-20 had a good protective effect on the morphology and function of the retina. Conclusions These results suggest that ASIV-LNCs can be a promising therapy approach for dAMD, and this research also offers new possibilities for further applications of LNCs as a drug delivery system for other eye diseases. Abbreviations AMD: Age-related macular degeneration;AREDS Age-related eye disease study; ASIV: Astragaloside-IV;AUC: Area under the concentration-time curve; dAMD: Dry age-related macular degeneration; DHE: Dihydroethidium; DL: Drug Loading; DLS: Dynamic light scattering; DSC: Differential scanning calorimetry; EE: Entrapment efficiency; ELSD: Evaporative light scattering detector; ERG: Electroretinographic; H&E: Hematoxylin and Eosin; I.S.: Internal standard; LB: Langmuir-Blodgett; LNCs: Lipid nanocapsules; MCT: Medium-chain triacylglycerol; ONL: Outer nuclear layer; OPL: Outer plexiform layer; PDI: Polydispersity index; PR: Photoreceptor;ROS: Reactive oxygen species; RPE: Retinal pigment epithelium; TEM: Transmission electron microscope; wAMD: Wet age-related macular degeneration.

Recent advances in risk factors associated with ocular exfoliation syndrome

Exfoliation syndrome is generally considered a progressive age-related systemic disorder of the extracellular matrix, which is clinically characterized through the observation of flaky white aggregates on ocular tissues. Exfoliation syndrome is directly linked to exfoliative glaucoma in elderly patients, where it is known as the most common identifiable cause of open-angle glaucoma. Despite the identification of various risk factors associated with exfoliation syndrome, the exact pathogenesis of this syndrome has not been fully elucidated. There is a growing number of genome-wide association studies in different populations around the world to identify genetic factors underlying exfoliation syndrome. Besides variants in LOXL1 and CACNA1A genes, new loci have been recently identified which are believed to be associated with exfoliation syndrome. Among different genetic factors, functional variants might help to better understand mechanisms underlying this systemic disorder. Besides genetic factors, epigenetic regulation of different gene expression patterns has been thought to play a role in its pathogenesis. Other factors have been also considered to be involved in the development of exfoliation syndrome at cellular organelles level where mitochondrial impairment and autophagy dysfunction have been suggested in relation to exfoliation syndrome. This review addresses the most recent findings on genetic factors as well as cellular and molecular mechanisms involved in both the development and progression of exfoliation syndrome.

A Solid Dispersion of Quercetin Shows Enhanced Nrf2 Activation and Protective Effects against Oxidative Injury in a Mouse Model of Dry Age-Related Macular Degeneration

Age-related macular degeneration (AMD) represents a major reason for blindness in the elderly population. Oxidative stress is a predominant factor in the pathology of AMD. We previously evaluated the effects of phospholipid complex of quercetin (Q-PC) on oxidative injury in ARPE-19 cells, but the underlying mechanisms are not fully understood. Herein, the solid dispersion of quercetin-PC (Q-SD) was prepared with solubility being 235.54 μg/mL in water and 2.3×10⁴ μg/mL in chloroform, which were significantly higher than that of quercetin (QT) and Q-PC. Q-SD also exhibited a considerably higher dissolution rate than QT and Q-PC. Additionally, Q-SD had Cmax of 4.143 μg/mL and AUC of 12.015 μg·h/mL in rats, suggesting better bioavailability than QT and Q-PC. Then, a mouse model of dry AMD (Nrf2 wild-type (WT) and Nrf2 knockout (KO)) was established for evaluating the effects of Q-SD in vivo. Q-SD more potently reduced retinal pigment epithelium sediments and Bruch's membrane thickness than QT and Q-PC at 200 mg/kg in Nrf2 WT mice and did not work in Nrf2 KO mice at the same dosage. Additionally, Q-SD significantly decreased ROS and MDA contents and restored SOD, GSH-PX, and CAT activities of serum and retinal tissues in Nrf2 WT mice, but not in Nrf2 KO mice. Furthermore, Q-SD more potently increased Nrf2 mRNA expression and stimulated its nuclear translocation in retinal tissues of Nrf2 WT mice. Q-SD significantly increased the expression of Nrf2 target genes HO-1, HQO-1, and GCL of retinal tissues in Nrf2 WT mice, not in Nrf2 KO mice. Altogether, Q-SD had improved physicochemical and pharmacokinetic properties compared to QT and Q-PC and exhibited more potent protective effects on retina oxidative injury in vivo. These effects were associated with activation of Nrf2 signaling and upregulation of antioxidant enzymes.

Light-induced Nrf2-/- mice as atrophic age-related macular degeneration model and treatment with nanoceria laden injectable hydrogel

Elevated oxidative stress and associated reactive oxygen species (ROS) accumulation are hallmarks in the induction and progression of age-related macular degeneration (AMD). By exposing nuclear factor erythroid 2-related factor (Nrf2) knockout (Nrf2-/-) mice to mild white light, we were able to generate a new dry-AMD like murine model to the study. This animal model developed phenotypes of photoreceptor degeneration, retinal function impairment, ROS accumulation, and inflammation reaction in a relatively shorter time. In the treatment of this animal model we utilized an antioxidative and water soluble nanoparticle known as glycol chitosan coated cerium oxide nanoparticles (GCCNP). The delivery of GCCNP protected retina against progressive retinal oxidative damage. Further combination of GCCNP with alginate-gelatin based injectable hydrogel provided synergistic antioxidant effects and achieved a more rapid recovery of the retinal pigment epithelium and photoreceptor cells. This combined treatment technique has the potential to translate into a clinical intervention for the treatment of AMD.

Cone photoreceptor macular function and recovery after photostress in early non-exudative age-related macular degeneration

Purpose

To identify parameters from cone function and recovery after photostress that detect functional deficits in early non-exudative age-related macular degeneration (AMD) and to determine the repeatability of these parameters.

Methods

Cone-mediated visual function recovery after photostress was examined in three groups of subjects: young normal subjects (ages 20–29; N=8), older normal subjects (ages 50–90; N=9), and early non-exudative AMD subjects (ages 50–90; N=12). Eight AMD and four normal subjects were retested 1 year after the initial evaluation. Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity (VA) and parameters of cone function (baseline cone sensitivity and cone recovery half-life following photobleach) were measured and compared between AMD and normal subjects. Short-term repeatability was assessed for each subject’s initial evaluation. Long-term repeatability was assessed by comparing outcomes from the initial evaluation and 1-year follow-up.

Results

The mean baseline cone threshold was significantly worse in subjects with early AMD compared to older normal subjects (−1.80±0.04 vs −1.57±0.06 log cd/m²p=0.0027). Moreover, the baseline cone threshold parameter exhibited good short-term (intraclass correlation coefficient [ICC]=0.88) and long-term (ICC=0.85) repeatability in all subjects. The cone intercept parameter and ETDRS VA were not significantly different between AMD and older normal subject groups. Cone recovery half-life was significantly different between older normal and AMD subject groups (p=0.041). Neither ETDRS VA nor cone function parameters were significantly different for any group at the 1-year follow-up.

Conclusion

The baseline cone threshold shows potential as a novel parameter to assess visual dysfunction in early AMD. This outcome consistently detected deficits in AMD subjects, and differentiated them from age-matched controls with high test–retest repeatability.

Lipocalin 2 Plays an Important Role in Regulating Inflammation in Retinal Degeneration

It has become increasingly important to understand how retinal inflammation is regulated because inflammation plays a role in retinal degenerative diseases. Lipocalin 2 (LCN2), an acute stress response protein with multiple innate immune functions, is increased in ATP-binding cassette subfamily A member 4 (Abca4) ^-/- retinol dehydrogenase 8 (Rdh8) ^-/- double-knockout mice, an animal model for Stargardt disease and age-related macular degeneration (AMD). To examine roles of LCN2 in retinal inflammation and degeneration, Lcn2^-/-Abca4^-/-Rdh8^-/- triple-knockout mice were generated. Exacerbated inflammation following light exposure was observed in Lcn2^-/-Abca4^-/-Rdh8^-/- mice as compared with Abca4^-/-Rdh8^-/- mice, with upregulation of proinflammatory genes and microglial activation. RNA array analyses revealed an increase in immune response molecules such as Ccl8, Ccl2, and Cxcl10 To further probe a possible regulatory role for LCN2 in retinal inflammation, we examined the in vitro effects of LCN2 on NF-κB signaling in human retinal pigmented epithelial (RPE) cells differentiated from induced pluripotent stem cells derived from healthy donors. We found that LCN2 induced expression of antioxidant enzymes heme oxygenase 1 and superoxide dismutase 2 in these RPE cells and could inhibit the cytotoxic effects of H₂O₂ and LPS. ELISA revealed increased LCN2 levels in plasma of patients with Stargardt disease, retinitis pigmentosa, and age-related macular degeneration as compared with healthy controls. Finally, overexpression of LCN2 in RPE cells displayed protection from cell death. Overall these results suggest that LCN2 is involved in prosurvival responses during cell stress and plays an important role in regulating inflammation during retinal degeneration.

Protective Effects of Memantine on Hydroquinone-Treated Human Retinal Pigment Epithelium Cells and Human Retinal Müller Cells

PURPOSE

Memantine (MEM) acts on the glutamatergic system by blocking N-methyl-d-aspartate (NMDA) glutamate receptors. The role that MEM plays in protecting retinal cells is unknown. Hydroquinone (HQ) is one of the cytotoxic components in cigarette smoke. In the present study, we tested whether pretreatment with MEM could protect against the cytotoxic effects of HQ on human retinal pigment epithelium cells (ARPE-19) and human retinal Müller cells (MIO-M1) in vitro.

METHODS

Cells were plated, pretreated for 6 h with 30 μM of MEM, and then exposed for 24 h to 200, 100, 50, and 25 μM of HQ while MEM was still present. Cell viability (CV), reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm), and lactate dehydrogenase (LDH) release assays were performed.

RESULTS

HQ-treated cells showed a dose-dependent decrease in CV and ΔΨm, but an increase in ROS production and LDH levels in both cell lines. MEM pretreatment reversed the CV in 50, 100, and 200 μM doses in ARPE-19 cells and at all HQ concentrations in MIO-M1 cells compared to HQ-treated cultures. ROS production was reversed in all HQ concentrations in both cell lines. ΔΨm was significantly increased after MEM pretreatment only in 50 μM HQ concentration for both cell lines. LDH levels were decreased at 50 and 25 μM HQ in ARPE-19 and MIO-M1 cells, respectively.

CONCLUSION

HQ-induced toxicity is concentration dependent in ARPE-19 and MIO-M1 cultures. MEM exerts protective effects against HQ-induced toxicity on human retinal pigment epithelial and Müller cells in vitro.

Artemisinin Protects Retinal Neuronal Cells against Oxidative Stress and Restores Rat Retinal Physiological Function from Light Exposed Damage

Oxidative stress plays a key role in the pathogenesis of age-related macular degeneration (AMD), a leading cause of severe visual loss and blindness in the aging population which lacks any effective treatments currently. In this study, artemisinin, a well-known antimalarial drug was found to suppress hydrogen peroxide (H₂O₂)-induced cell death in retinal neuronal RGC-5 cells. Artemisinin, in the therapeutically relevant dosage, concentration-dependently attenuated the accumulation of intracellular reactive oxygen species (ROS), increased mitochondrial membrane potential and decreased cell apoptosis in RGC-5 cells induced by H₂O₂. Western blot analysis showed that artemisinin upregulated the phosphorylation of p38 and extracellular signal-regulated kinases1/2 (ERK1/2) and reversed the inhibitory effect of H₂O₂ on the phosphorylation of these two kinases. Moreover, protective effect of artemisinin was blocked by the p38 kinase inhibitor PD169316 or ERK1/2 kinase pathway inhibitor PD98059, respectively. In contrast, c-Jun N-terminal kinase inhibitor and rapamycin had no effect in the protective effect of artemisinin. Taken together, these results demonstrated that artemisinin promoted the survival of RGC-5 cells from H₂O₂ toxicity via the activation of the p38 and ERK1/2 pathways. Interestingly, intravitreous injection of artimisinin, concentration-dependently reversed light exposed-damage (a dry AMD animal model) of rat retinal physiological function detected by flash electroretinogram. These results indicate that artemisinin can protect retinal neuronal functions from H₂O₂-induced damage in vitro and in vivo and suggest the potential application of artemisinin as a new drug in the treatment of retinal disorders like AMD.

Comparison of cytokine profiles in the aqueous humor of eyes with pseudoexfoliation syndrome and glaucoma

PURPOSE

To compare the cyto- and chemokine profiles in the aqueous humor of PEXS eyes in the absence or presence of secondary glaucoma with or without luxation of the intraocular lens (IOL).

METHODS

Samples of aqueous humor were collected intraoperatively from 20 healthy controls and from 73 eyes with PEX-syndrome, which was manifested in the absence of any other local or systemic desease. The latter group was sub-devided into eyes with an early form of PEX-syndrome in the absence of complications (PEX, n = 33), those with a late form of PEX-syndrome and glaucoma (PEXG, n = 30), and those with a late form of PEX-syndrome with luxation of the IOL that required surgery (PEXL, n = 10). The samples were analyzed in parallel after storage at -80°C. The levels of 40 cytokines were simultaneously quantified using the Bio-Plex® multiplex beads system. The inter-group data were statistically compared using the Kruskal-Wallis test (p ≤ 0.01).

RESULTS

PEX and PEXG were comparable in their cytokine profiles for all 40 cytokines, whereas the cytokine profile in PEXL-eyes revealed higher levels of all but 5 cytokines (CXCL13, CCL27, IL-2, CCL3, CCL20; p ≤ 0.01). This latter finding is indicative of a non-specific inflammatory reaction in the context of IOL-luxation. The concentrations of 6 cytokines lay below the detection limit in all groups.

CONCLUSIONS

The local up-regulation of 85% of the detectable cytokines in the aqueous humor of PEXL-eyes may be linked either with a progression of the disease or a breakdown of the antero-posterior barrier in the context of IOL-luxation.

Investigation of associations of ARMS2, CD14, and TLR4 gene polymorphisms with wet age-related macular degeneration in a Greek population

Background

Age-related macular degeneration (AMD) is a multifactorial degenerative ocular disease that leads to loss of central vision. Functional gene polymorphisms have already been associated with the disease (for example, ARMS2 A69S, rs10490924).

Aim

The goal of our study was to verify the correlation of the aforementioned ARMS2 variation with the disease, to examine, for the first time, the role of the CD14 C260T variation (rs2569190), and to investigate the association of two TLR4 polymorphisms (Asp299Gly or rs4986790 and Thr399Ile or rs4986791) in a Greek population with the wet form of AMD.

Patients and methods

Genomic DNAs were isolated from blood samples of 103 healthy controls and 120 Greek patients with wet AMD who were age- and sex-matched, and all of whom were clinically evaluated. For the genotyping of all selected polymorphisms, polymerase chain reaction–restriction fragment length polymorphism analysis was performed.

Results and conclusions

This study confirmed the association between the ARMS2 variation and AMD, detecting the T risk allele in a significantly higher frequency in the patient group, compared with the control subjects (45% vs 29.13%, P<0.001, odds ratio [OR] 1.99, confidence interval 1.34–2.95). For the CD14 polymorphism, no statistically significant correlation was observed. As for the TLR4 polymorphisms, the percentage of heterozygotes increased from 2.9% to 11.7% in the patient population for Asp299Gly and from 1.9% to 10% for the Thr399Ile polymorphism (ORs 4.40 [P=0.01] and 5.61 [P=0.0088], respectively). Although our ARMS2 and CD14 results provided definite conclusions, the role of innate immunity TLR4 gene awaits further investigation in larger AMD populations with more clinical data collected on past microbial infections.

Isoforms of TGF-β in the aqueous humor of patients with pseudoexfoliation syndrome and a possible association with the long-term stability of the capsular bag after cataract surgery

BACKGROUND

Pseudoexfoliation syndrome (PEXS) may go along with capsular bag shrinkage and luxation. In the present study, we focus on an association of isoforms of TGF-β with capsular bag luxation.

METHODS

Aqueous humor was collected intraoperatively from 20 healthy controls and from 73 otherwise healthy patients with PEXS [PEXS without complications (PEX, n = 33), late PEXS with glaucoma (PEXG, n = 30) and with IOL and capsular bag luxation (PEXL, n = 10)]. The concentrations of TGF-β1, TGF-β2 and TGF-β3 were compared using the Bio-Plex® multiplex beads system based on the non-parametric Kruskal-Wallis H test (p < 0.01).

RESULTS

Concentrations of TGF-β 1, TGF-β 2 and TGF-β 3 were higher in the sub-groups PEX and PEXG than in controls (TGF-β 1; p = 0.009 and 0.0005; TGF-β 2; p = 0.002 and 0.005 and TGF-β 3; 0.0005 and 0.0005; respectively), whereas for TGF β2, no significant difference between controls and PEXL was revealed (p = 1.0). TGF-β2 concentrations were elevated in a similar degree in early PEX and PEXG, but not in PEXL compared to controls (p = 0.002). The concentrations of of TGF-β 1 and TGF-β 3 increased in parallel with the progression of disease. The levels of TGF-β 3, however, did not attain pathophysiological levels (>100 pg/ml) in any group.

CONCLUSIONS

A stage-dependent increase in the concentrations of TGF-β1 and TGF-β3, but not of TGF-β2, accords to the shrinkage of the capsular bag. This could increase the tension on the zonular fibers and contribute to luxation of the capsular bag.

One protein, multiple pathologies: multifaceted involvement of amyloid β in neurodegenerative disorders of the brain and retina

Accumulation of amyloid β (Aβ) and its aggregates in the ageing central nervous system is regarded synonymous to Alzheimer's disease (AD) pathology. Despite unquestionable advances in mechanistic and diagnostic aspects of the disease understanding, the primary cause of Aβ accumulation as well as its in vivo roles remains elusive; nonetheless, the majority of the efforts to address pathological mechanisms for therapeutic development are focused towards moderating Aβ accumulation in the brain. More recently, Aβ deposition has been identified in the eye and is linked with distinct age-related diseases including age-related macular degeneration, glaucoma as well as AD. Awareness of the Aβ accumulation in these markedly different degenerative disorders has led to an increasing body of work exploring overlapping mechanisms, a prospective biomarker role for Aβ and the potential to use retina as a model for brain related neurodegenerative disorders. Here, we present an integrated view of current understanding of the retinal Aβ deposition discussing the accumulation mechanisms, anticipated impacts and outlining ameliorative approaches that can be extrapolated to the retina for potential therapeutic benefits. Further longitudinal investigations in humans and animal models will determine retinal Aβ association as a potential pathognomonic, diagnostic or prognostic biomarker.

Clearance of autophagy-associated dying retinal pigment epithelial cells - a possible source for inflammation in age-related macular degeneration

Retinal pigment epithelial (RPE) cells can undergo different forms of cell death, including autophagy-associated cell death during age-related macular degeneration (AMD). Failure of macrophages or dendritic cells (DCs) to engulf the different dying cells in the retina may result in the accumulation of debris and progression of AMD. ARPE-19 and primary human RPE cells undergo autophagy-associated cell death upon serum depletion and oxidative stress induced by hydrogen peroxide (H₂O₂). Autophagy was revealed by elevated light-chain-3 II (LC3-II) expression and electron microscopy, while autophagic flux was confirmed by blocking the autophago-lysosomal fusion using chloroquine (CQ) in these cells. The autophagy-associated dying RPE cells were engulfed by human macrophages, DCs and living RPE cells in an increasing and time-dependent manner. Inhibition of autophagy by 3-methyladenine (3-MA) decreased the engulfment of the autophagy-associated dying cells by macrophages, whereas sorting out the GFP-LC3-positive/autophagic cell population or treatment by the glucocorticoid triamcinolone (TC) enhanced it. Increased amounts of IL-6 and IL-8 were released when autophagy-associated dying RPEs were engulfed by macrophages. Our data suggest that cells undergoing autophagy-associated cell death engage in clearance mechanisms guided by professional and non-professional phagocytes, which is accompanied by inflammation as part of an in vitro modeling of AMD pathogenesis.

Protective effect of alpha-mangostin against oxidative stress induced-retinal cell death

It is known that oxidative stress plays a pivotal role in age-related macular degeneration (AMD) pathogenesis. Alpha-mangostin is the main xanthone purified from mangosteen known as anti-oxidative properties. The aim of the study was to test the protective effect of alpha-mangostin against oxidative stress both in retina of light-damaged mice model and in hydrogen peroxide (H2O2)-stressed RPE cells. We observed that alpha-mangostin significantly inhibited light-induced degeneration of photoreceptors and 200 μM H2O2-induced apoptosis of RPE cells. 200 μM H2O2-induced generation of reactive oxygen species (ROS) and light-induced generation of malondialdehyde (MDA) were suppressed by alpha-mangostin. Alpha-mangostin stimulation resulted in an increase of superoxide dismutase (SOD) activity, glutathione peroxidase (GPX) activity and glutathione (GSH) content both in vivo and vitro. Furthermore, the mechanism of retinal protection against oxidative stress by alpha-mangostin involves accumulation and the nuclear translocation of the NF-E2-related factor (Nrf2) along with up-regulation the expression of heme oxygenas-1 (HO-1). Meanwhile, alpha-mangostin can activate the expression of PKC-δ and down-regulate the expression of mitogen-activated protein kinases (MAPKs), including ERK1/2, JNK, P38. The results suggest that alpha-mangostin could be a new approach to suspend the onset and development of AMD.

Brimonidine Can Prevent In Vitro Hydroquinone Damage on Retinal Pigment Epithelium Cells and Retinal Müller Cells

PURPOSE

Brimonidine is a selective alpha-2 adrenergic agonist used to reduce intraocular pressure and it has been shown to have some neuroprotective effects. Hydroquinone (HQ) is a toxicant present in cigarette smoke, and other sources. In this study, we investigated the cyto-protective effects in vitro of Brimonidine on human retinal pigment epithelium cells (ARPE-19) and human retinal Müller cells (MIO-M1) that had been treated with HQ.

METHODS

Cells were pretreated for 6 h with different doses of Brimonidine tartrate 0.1% (1/2×, 1×, 5×, 10×), followed by a 24-h exposure to 100 μM of HQ, while the Brimonidine was still present. Assays were used to measure cell viability, mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS) production, and lactate dehydrogenase (LDH) release.

RESULTS

Brimonidine increased the cell viability at all concentrations studied in both cell lines studied. ΔΨm also improved at all Brimonidine doses in ARPE-19 cells and in the 5× and 10× dosages MIO-M1 cells. The ROS levels decreased at 1×, 5×, and 10× doses of Brimonidine in ARPE-19 but only at 10× on MIO-M1 cells. The 10×-Brimonidine ARPE-19 cells had decreased LDH release, but no LDH changes were observed on MIO-M1 cells.

CONCLUSION

HQ-induced toxicity is mediated through mitochondrial damaging, oxidative stress-related and necrosis-related pathways; Brimonidine significantly prevented the mitochondrial damaging and oxidative stress-related effects but had little effect on blocking the necrosis component of HQ-toxicity. Brimonidine protective effects differ between the different retinal cell types and high concentrations of Brimonidine (10×) have minimal damaging effects on human retinal cells.

Biophysical chemistry of the ageing eye lens

This review examines both recent and historical literature related to the biophysical chemistry of the proteins in the ageing eye, with a particular focus on cataract development. The lens is a vital component of the eye, acting as an optical focusing device to form clear images on the retina. The lens maintains the necessary high transparency and refractive index by expressing crystallin proteins in high concentration and eliminating all large cellular structures that may cause light scattering. This has the consequence of eliminating lens fibre cell metabolism and results in mature lens fibre cells having no mechanism for protein expression and a complete absence of protein recycling or turnover. As a result, the crystallins are some of the oldest proteins in the human body. Lack of protein repair or recycling means the lens tends to accumulate damage with age in the form of protein post-translational modifications. The crystallins can be subject to a wide range of age-related changes, including isomerisation, deamidation and racemisation. Many of these modification are highly correlated with cataract formation and represent a biochemical mechanism for age-related blindness.

Oxidative stress to the cornea, changes in corneal optical properties, and advances in treatment of corneal oxidative injuries

Oxidative stress is involved in many ocular diseases and injuries. The imbalance between oxidants and antioxidants in favour of oxidants (oxidative stress) leads to the damage and may be highly involved in ocular aging processes. The anterior eye segment and mainly the cornea are directly exposed to noxae of external environment, such as air pollution, radiation, cigarette smoke, vapors or gases from household cleaning products, chemical burns from splashes of industrial chemicals, and danger from potential oxidative damage evoked by them. Oxidative stress may initiate or develop ocular injury resulting in decreased visual acuity or even vision loss. The role of oxidative stress in the pathogenesis of ocular diseases with particular attention to oxidative stress in the cornea and changes in corneal optical properties are discussed. Advances in the treatment of corneal oxidative injuries or diseases are shown.