Hypoxia-ischemia and retinal ganglion cell damage

Molecular Mechanisms of Vitamin E in Ocular Neurodegenerative Disorders: An Update on the Emerging Evidence and Therapeutic Implications

Vitamin E is renowned for its potent antioxidant properties, crucial for shielding cells against oxidative stress and damage. Deficiency in this vitamin can lead to various health issues, including neurodegenerative diseases, due to its pivotal role in preserving cell membrane integrity and combating cellular oxidative damage. While its importance for overall health, including neurodegeneration, is acknowledged, the specific correlation between vitamin E deficiency and distinct ocular neurodegenerative disorders need to be further explored. This review delves into the molecular mechanisms of vitamin E in ocular neurodegenerative disorders; diabetic retinopathy, age-related macular degeneration, glaucoma, and cataracts, and emphasising the therapeutic implications drawn from existing evidence. Relationship between vitamin E and ocular neurodegenerative disorders is widely researched on, with its primary protective mechanisms attributed to its antioxidant and anti-inflammatory properties. However, studies on the supplementation of vitamin E among human subjects present mixed results, suggesting its complexities and variability depending on factors such as the specific disorder, disease stage, genetic differences, and form of vitamin E utilized. In conclusion, while vitamin E holds promise in mitigating ocular neurodegeneration through its antioxidant and anti-inflammatory properties, its supplementation's efficacy remains nuanced and context dependent. More research works are essential to elucidate its precise role and therapeutic potential in combating various ocular neurodegenerative disorders.

SIRT4 Protects Retina Against Excitotoxic Injury by Promoting OPA1-Mediated Müller Glial Cell Mitochondrial Fusion and GLAST Expression

Purpose

This study aimed to investigate the role of SIRT4 in retinal protection, specifically its ability to mitigate excitotoxic damage to Müller glial cells through the regulation of mitochondrial dynamics and glutamate transporters (GLASTs).

Methods

A model of retinal excitatory neurotoxicity was established in mice. Proteins related to mitochondrial dynamics, GLAST, and SIRT4 were analyzed on days 0, 1, 3, and 5 following toxic injury. The influence of SIRT4 on mitochondrial dynamics-related proteins and GLAST was examined by inducing SIRT4 overexpression through intraperitoneal injection of resveratrol or by using SIRT4 knockout (KO) mice. Additionally, the effects of upregulating and downregulating SIRT4 expression in rat Müller glial cell lines (rMC-1) were explored via lentiviral vector transfection to assess changes in mitochondrial morphology and GLAST expression.

Results

After excitotoxic injury to the mouse retina, the retinal thickness and structure were disrupted, the number of retinal ganglion cells (RGCs) decreased, and Müller glial cells were activated by day 1. The levels of OPA1, GLAST, and SIRT4 proteins peaked on the first day after injury and then gradually decreased, indicating a synchronized dynamic trend. The upregulation of SIRT4 expression promoted OPA1 and GLAST protein expression, thereby alleviating retinal excitotoxic injury. Furthermore, the upregulation of SIRT4 expression promoted mitochondrial fusion and increased GLAST expression in rMC-1 cells, reducing cellular excitotoxic damage. Conversely, downregulation of SIRT4 had the opposite effect.

Conclusions

SIRT4 plays a significant role in mitigating excitotoxic damage in the retina, modulating Müller glial cell injury by regulating mitochondrial dynamics and glutamate transporter expression, ultimately influencing retinal health.

Transplantation of derivative retinal organoids from chemically induced pluripotent stem cells restored visual function

As an emerging type of pluripotent stem cells, chemically induced pluripotent stem cells (CiPSCs) avoid the risks of genomic disintegration by exogenous DNAs from viruses or plasmids, providing a safer stem cell source. To verify CiPSCs' capacity to differentiate into retinal organoids (ROs), we induced CiPSCs from mouse embryonic fibroblasts by defined small-molecule compounds and successfully differentiated the CiPSCs into three-dimensional ROs, in which all major retinal cell types and retinal genes were in concordance with those in vivo. We transplanted retinal photoreceptors from ROs into the subretinal space of retinal degeneration mouse models and the cells could integrate into the host retina, establish synaptic connections, and significantly improve the visual functions of the murine models. This proof-of-concept study for the first time demonstrated that CiPSCs could differentiate into ROs with a full spectrum of retinal cell types, and provided new insights into chemical approach-based retinal regeneration for degenerative diseases.

Short-term effects of sunlight exposure on fundus blood flow perfusion in children: a randomised controlled trial

AIM

To evaluate the short-term effects of different sunlight exposure on fundus blood flow perfusion (BFP) after near work.

METHODS

In this parallel randomised controlled trial, 81 students aged 7-15 with spherical equivalent refraction between -2.00 and +3.00 diopters were randomly assigned to either a low-illuminance (4k lux) group (N=40) or high-illuminance (10k lux) (N=41). Following 1 hour indoor reading, participants had sunlight exposure matching their group's intensity for 15 minutes. BFPs in the superficial retina, deep retina and choroid were measured at four time points: pre-reading, post-reading, 5th-minute and 15th-minute sunlight exposure.

RESULTS

Within the initial 5 minutes of sunlight exposure, the 10k lux group showed a tendency for decreased BFP, particularly in the choroid (superficial retina: -0.2, 95% CI -0.9 to 0.5; deep retina: -0.1, 95% CI -0.6 to 0.4; choroid: -0.4, 95% CI -0.8 to 0.0), while the 4k lux group exhibited an increase (superficial retina: 0.7, 95% CI 0.1 to 1.3; deep retina: 0.3, 95% CI -0.2 to 0.8; choroid: 0.1, 95% CI -0.2 to 0.5). From 5 to 15 minutes, BFP decreased in both groups. At the 5th-minute mark, the 10k lux group exhibited a greater decrease in choroid (10k -0.4 vs 4k 0.1, p=0.051). No significant difference was observed after 15 minutes of exposure.

CONCLUSION

Higher illuminance sunlight exposure can restore fundus BFP more rapidly than lower; however, duration remains pivotal. To prevent myopia, continuous sunlight exposure for over 15 minutes is recommended to aid in reinstating the fundus BFP increased by near work.

TRIAL REGISTRATION NUMBER

NCT05594732.

Characteristics of optical coherence tomography in patients with iron deficiency anemia : a systematic review and meta-analysis

OBJECTIVE

The primary objective of this systematic review and meta-analysis was to assess the association between iron deficiency anemia (IDA) and retinal changes via optical coherence tomography (OCT).

METHODS

The search was conducted in MEDLINE, Scopus, Embase, Web of Science, and Google Scholar until February 1, 2024. Two independent researchers included the articles based on the inclusion and exclusion criteria. Data regarding the study design, patient characteristics, number of patients with and without IDA, mean and SD of the retinal nerve fiber layer (RNFL), C/D ratio, foveal avascular zone (FAZ) area and perimeter, foveal density and superficial and deep capillary plexus (SCP and DCP) vascular density (VD) were collected. STATA version 17.0 was used to compute pooled measures of the standardized mean difference. I2 and chi-square tests were used to assess heterogeneity between studies.

RESULTS

We found 1378 nonduplicate studies, 35 of which were potentially relevant. 19 articles met the inclusion criteria and were included in the review. The meta-analysis confirmed that there was a statistically significant association between IDA and RNFL thickness reduction (SMD = -0.76, 95% CI: -1.09 to -0.44 ; p-value = 0.001, I2 = 86.88%), FAZ area (SMD =-0.35, 95% CI: -0.67 to -0.02; p value = 0.04, I2 = 59.76%) and SCP VD (SMD = -1.12, 95% CI: -1.85 to -0.39; p-value = 0.001, I2 = 83.15%). The associations between IDA and the C/D ratio (SMD = 0.07, 95% CI: -0.13 to 0.28; p value = 0.49, I2 = 0.0%) and DCP VD (SMD = -0.30, 95% CI: -0.89 to 0.29; ,p-value = 0.32 ,I2 = 77.20%) were not significant. There was no considerable publication bias.

CONCLUSION

The results of this meta-analysis demonstrated that, compared with healthy controls, individuals with IDA presented a thinner RNFL, a smaller FAZ, and lower SCP and DCP vascular densities. However, further studies are needed to reach more conclusive results.

FK962 protects retinal ganglion cell under hypoxia/reoxygenation: Possible involvement of glial cell line-derived neurotrophic factor signaling pathway

Loss of retinal ganglion cells (RGCs) is the cause of visual impairment and blindness in glaucoma. Previously, our studies showed that FK962 (N-[1-acetylpiperidin-4-yl]-4-fluorobenzamide) promoted neurite elongation in rat RGCs and trigeminal ganglion (TG) cells. In TG cells, glial cell line-derived neurotrophic factor (GDNF) is known to be involved in the mechanism. The purpose of the present study is to investigate whether, 1) FK962 shows an RGC-protective effect under hypoxia/reoxygenation (H/R) and 2) GDNF is involved in the neuroprotective mechanism of FK962. Rat primary retinal cells were cultured under 24-h hypoxia/24-h reoxygenation conditions, with or without FK962, recombinant GDNF, GDNF antibody and RET receptor tyrosine kinase inhibitor, GSK3179106. Cells were co-immunostained with RBPMS and Neurofilament 200 as a RGC marker, and the number of survived RGCs was counted. Results showed H/R treatment decreased the number of survived RGCs. FK962 promoted RGC survival under H/R by a bell-shaped dose response, with the highest RGC-protective effect of 10-8 M. The protective effect was the same level with 10-12 M exogenous GDNF. Addition of GDNF antibody or GSK3179106 counteracted the neuroprotective effect of FK962. From these results, it is suggested that FK962 ameliorates RGC death under H/R, possibly via a GDNF signaling pathway.

Longitudinal evaluation of morphological, functional and vascular alterations in a rat model of experimental glaucoma

Glaucoma, the leading cause of irreversible blindness worldwide, is a neurodegenerative disease characterized by chronic axonal damages and progressive loss of retinal ganglion cells, with increased intraocular pressure (IOP) as the primary risk factor. While current treatments focus solely on reducing IOP, understanding glaucoma through experimental models is essential for developing new therapeutic strategies and biomarkers for early diagnosis. Our research group developed an ocular hypertension rat model based on limbal plexus cautery, which provides significant glaucomatous neurodegeneration up to four weeks after injury. We evaluated long-term morphological, functional, and vascular alterations in this model. Our results showed that transient ocular hypertension, lasting approximately one week, can lead to progressive increase in optic nerve cupping and retinal ganglion cells loss. Remarkably, the pressure insult caused several vascular changes, such as arteriolar and venular thinning, and permanent choroidal vascular swelling. This study provides evidence of the longitudinal effects of a pressure insult on retinal structure and function using clinical modalities and techniques. The multifactorial changes reported in this model resemble the complex retinal ganglion cell degeneration found in glaucoma patients, and therefore may also provide a unique tool for the development of novel interventions to either halt or slow down disease progression.

Characteristics of the radial peripapillary capillary network in patients with COVID-19 based on optical coherence tomography angiography: A literature review

PURPOSE

This review aimed to evaluate the significance of assessing radial peripheral capillary (RPC) network parameters by optical coherence tomography angiography (OCTA) in patients with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection confirmed by polymerase chain reaction.

METHODS

A literature search was conducted in the PubMed database to select high-quality reviews and original articles on the use of OCTA for visualizing the RPC network and calculating RPC parameters.

RESULTS

The study revealed that systemic hypoxia, hypercoagulable state, and inflammation affect the RPC network in patients with coronavirus disease 2019 (COVID-19). Reduced RPC parameters were observed early in the course of SARS-CoV-2 infection and after several months of follow-up. Additionally, there was a correlation between reduced RPC parameters and subsequent thinning of the retinal nerve fiber layer.

CONCLUSIONS

The OCTA examination of the retina and optic disc should be considered in patients with a history of COVID-19 to assess the impact of systemic hypoxia and inflammation on ocular function. Follow-up assessment of these patients is also necessary to understand the potential consequences of ischemia affecting the optic nerve, retina, and choroid.

Effects of Acute High-Altitude Exposure on Morphology and Function of Retinal Ganglion Cell in Mice

Purpose

High altitude retinopathy (HAR) is a retinal functional disorder caused by inadequate adaptation after exposure to high altitude. However, the cellular and molecular mechanisms underlying retinal dysfunction remain elusive. Retinal ganglion cell (RGC) injury is the most important pathological basis for most retinal and optic nerve diseases. Studies focusing on RGC injury after high-altitude exposure (HAE) are scanty. Therefore, the present study sought to explore both functional and morphological alterations of RGCs after HAE.

Methods

A mouse model of acute hypobaric hypoxia was established by mimicking the conditions of a high altitude of 5000 m. After HAE for 2, 4, 6, 10, 24, and 72 hours, the functional and morphological alterations of RGCs were assessed using retinal hematoxylin and eosin (H&E) sections, retinal whole mounts, transmission electron microscopy (TEM), and the photopic negative response (PhNR) of the electroretinogram.

Results

Compared with the control group, the thickness of the ganglion cell layer and retinal nerve fiber layer increased significantly, RGC loss remained significant, and the amplitudes of a-wave, b-wave, and PhNR were significantly reduced after HAE. In addition, RGCs and their axons exhibited an abnormal ultrastructure after HAE, including nuclear membrane abnormalities, uneven distribution of chromatin in the nucleus, decreased cytoplasmic electron density, widening and vacuolization of the gap between axons, loosening and disorder of myelin sheath structure, widening of the gap between myelin sheath and axon membrane, decreased axoplasmic density, unclear microtubule and nerve fiber structure, and abnormal mitochondrial structure (mostly swollen, with widened membrane gaps and reduced cristae and vacuolization).

Conclusions

The study findings confirm that the morphology and function of RGCs are damaged after HAE. These findings lay the foundation for further study of the specific molecular mechanisms of HAR and promote the effective prevention.

Agonism of β3-Adrenoceptors Inhibits Pathological Retinal Angiogenesis in the Model of Oxygen-Induced Retinopathy

Purpose

In response to hypoxia, sympathetic fibers to the retina activate β-adrenoceptors (β-ARs) that play an important role in the regulation of vascular and neuronal functions. We investigated the role of β3-AR using the mouse model of oxygen-induced retinopathy (OIR).

Methods

Mouse pups were exposed to 75% oxygen at postnatal day 7 (PD7) followed by a return to room air at PD12. The β3-AR preferential agonist BRL37344 was subcutaneously administered once daily at different times after the return to room air. At PD17, the OIR mice underwent flash and pattern electroretinogram. After sacrifice, retinal wholemounts were used for vessel staining or immunohistochemistry for astrocytes, Müller cells, or retinal ganglion cells (RGCs). In retinal homogenates, the levels of markers associated with neovascularization (NV), the blood-retinal barrier (BRB), or astrocytes were determined by western blot, and quantitative reverse-transcription polymerase chain reaction was used to assess β3-AR messenger. Administration of the β3-AR antagonist SR59230A was performed to verify BRL37344 selectivity.

Results

β3-AR expression is upregulated in response to hypoxia, but its increase is prevented by BRL37344, which counteracts NV by inhibiting the pro-angiogenic pathway, activating the anti-angiogenic pathway, recovering BRB-associated markers, triggering nitric oxide production, and favoring revascularization of the central retina through recovered density of astrocytes that ultimately counteracts NV in the midperiphery. Vasculature rescue prevents dysfunctional retinal activity and counteracts OIR-associated retinal ganglion cell loss.

Conclusions

β3-AR has emerged as a crucial intermediary in hypoxia-dependent NV, suggesting a role of β3-AR agonists in the treatment of proliferative retinopathies.

Nitrate and Nitrite Exposure Induces Visual Impairments in Adult Zebrafish

Nitrate and nitrite have emerged as increasingly common environmental pollutants, posing significant risks to various forms of life within ecosystems. To understand their impact on the visual system of zebrafish, adult zebrafish were exposed to environmentally relevant concentrations of nitrate (10 mg/L) and nitrite (1 mg/L) for 7 days. Visual behaviors were examined using optomotor and avoidance response. The eyeballs of the zebrafish were collected for H&E staining, IHC, and qPCR. Exposure decreased visual behavior and the thickness of most retinal layers. Exposure decreased expression of pax6a, pax6b, gpx1a, and bcl2a. Exposure increased expression of esr1, esr1a, esr2b, cyp19a1b, sod1a, nos2a, casps3, and tp53, and increased retinal brain aromatase expression by IHC. Collectively, our findings demonstrate that nitrate and nitrite exposure negatively impacted the visual system of adult zebrafish, highlighting the potential hazards of these environmental pollutants on aquatic organisms.

Higher vitamin B6 dietary consumption is associated with a lower risk of glaucoma among United States adults

Objective

Although numerous studies have substantiated the neuroprotective effects of vitamin B6 on the optic nerve and its enhancement of visual function, comprehensive data delineating the correlation between vitamin B6 and glaucoma at a national demographic scale remain insufficient. This study is designed to explore the link between the dietary consumption of vitamin B6 and glaucoma.

Methods

This study included 3,850 individuals aged 40 and older from the National Health and Nutrition Examination Survey (NHANES), spanning 2005-2008. Dietary consumption of vitamin B6 was calculated from the average of two 24-h dietary recall interviews. Glaucoma was diagnosed in accordance with the established Rotterdam criteria. To evaluate the relationship between vitamin B6 dietary consumption and the risk of glaucoma, we employed Restricted Cubic Splines and weighted multivariable logistic regression analysis. We employed stratified and three other sensitivity analyses to confirm the robustness of our results, and conducted a preliminary exploration of the potential association between vitamin B6 supplement consumption and glaucoma risk.

Results

After adjusting for covariates, we found a significant inverse correlation between dietary consumption of vitamin B6 and glaucoma risk (p non-linearity = 0.18; p for trend = 0.02). Stratified analysis and three other sensitivity analyses revealed stability in the outcomes (all p for interaction>0.05). Compared to the lowest quartile of consumption (≤1.23 mg/day), individuals in the highest quartile of vitamin B6 consumption (>2.34 mg/day) experienced a 75% reduction in glaucoma risk (OR = 0.25, 95% CI 0.07-0.92). However, the effect of vitamin B6 supplements on glaucoma was inconclusive.

Conclusion

A diet high in vitamin B6 inversely correlates with glaucoma risk, suggesting that increasing dietary intake of vitamin B6 could be a viable preventative strategy against glaucoma among adults in the United States.

Aetiology, Diagnosis and Treatment of Arterial Occlusions of the Retina-A Narrative Review

Arterial occlusions of the retina are potentially sight-threatening diseases which often result in profound visual loss. The aim of this narrative review is to provide an overview of the aetiology, discuss major risk factors, describe the management and systemic assessments and evaluate existing therapies. For this review, an extensive literature search in PubMed was performed. Emboli from the heart or the carotid arteries can cause ophthalmic artery occlusion (OAO), central retinal artery occlusion (CRAO) and branch retinal artery occlusion (BRAO). Most patients with arterial occlusions have vascular risk factors such as arterial hypertension, hyperhomocysteinaemia, carotid stenosis and atrial fibrillation, which also increase the risk of cerebral stroke and myocardial infarction. Therapies such as ocular massage, thrombolysis and anterior chamber paracentesis have been suggested but are still equivocal. However, it is evident that retinal artery occlusion should be immediately treated and accompanied by interdisciplinary collaboration, since early diagnosis and the proper treatment of possible risk factors are important to reduce the risk of further damage, recurrences, other vascular diseases and mortality.

siRNA Mediated Downregulation of RhoA Expression Reduces Oxidative Induced Apoptosis in Retinal Ganglion Cells

BACKGROUNDS

Glaucoma is the second leading cause of blindness. Apoptosis of retinal ganglion cells (RGCs) is an important mechanism of glaucomatous optic injury. Rho kinase expression is significantly increased in apoptotic RGCs. This study aimed to investigate the role of RhoA, a Rho GTPase, on the survival of RGCs and further to explore its potential therapeutic applications.

METHODS

RGCs were treated with siRhoA for 24 hours in vitro. Knockdown of RhoA was confirmed with quantitative RT-PCR. Oxidative stress was induced by treating the RGCs with 200 μM of H2O2 for 1 hour, and apoptosis of RGCs was quantified with TUNEL assay in situ, and with flow cytometry. The mRNA expression levels of RhoA, Nogo receptor, caspase 3 and Bcl-2 were evaluated by quantitative RT-PCR, and the protein levels of RhoA, ROCK1, ROCK2, Nogo receptor, caspase 3 and Bcl-2 were evaluated by Western blot. We found siRhoA treatment efficiently downregulated the expression of RhoA in RGCs and protected against H2O2-induced injury in RGCs in vitro. Apoptosis of RGC cells under oxidative stress was quantified in situ using TUNEL assay and confirmed with flow cytometry (FCM).

RESULTS

With the knockdown of RhoA, the expression of ROCK1, ROCK2, Nogo Receptor, Casepase-3 were decreased, while the expression of Bcl-2 was increased in both mRNA and protein level. Our data indicated that siRhoA prevented H2O2-induced apoptosis in RGC cells by modulating the RhoA/ROCK pathway.

CONCLUSION

The results suggested that siRhoA may exert potentially effective neuroprotection for RGCs by reducing injury.

Introducing Dynamicity: Engineering Stress Relaxation Into Hydrogels Via Thiol-Ene Modified Alginate for Mechanobiological in vitro Modeling of the Cornea

Developing biomaterials for corneal repair and regeneration is crucial for maintaining clear vision. The cornea, a specialized tissue, relies on corneal keratocytes, that respond to their mechanical environment. Altering stiffness affects keratocyte behavior, but static stiffness alone cannot capture the dynamic properties of in vivo tissue. This study proposes that the cornea exhibits time-dependent mechanical properties, similar to other tissues, and aims to replicate these properties in potential therapeutic matrices. First, the cornea's stress relaxation properties are investigated using nanoindentation, revealing 15% relaxation within 10 seconds. Hydrogel dynamicity is then modulated using a specially formulated alginate-PEG and alginate-norbornene mixture. The tuning of the hydrogel's dynamicity is achieved through a photoinitiated norbornene-norbornene dimerization reaction, resulting in relaxation times ranging from 30 seconds to 10 minutes. Human primary corneal keratocytes are cultured on these hydrogels, demonstrating reduced αSMA (alpha smooth muscle actin) expression and increased filopodia formation on slower relaxing hydrogels, resembling their native phenotype. This in vitro model can enable the optimization of stress relaxation for various cell types, including corneal keratocytes, to control tissue formation. Combining stress relaxation optimization with stiffness assessment provides a more accurate tool for studying cell behavior and reduces mechanical mismatch with native tissues in implanted constructs.

Addressing retinal hypoxia: pathophysiology, therapeutic innovations, and future prospects

Retinal hypoxia stands as a pivotal yet often underappreciated factor in the etiology and progression of many retinal disorders such as glaucoma, hypertensive retinopathy, diabetic retinopathy, retinal vein occlusions, and retinal artery occlusions. Current treatment methodologies fail to directly address the underlying pathophysiology of hypoxia and aim to improve ischemia through alternative methods. In this review, we discuss the critical role of retinal hypoxia in the pathogenesis of various retinal diseases and highlight the need for innovative therapeutic strategies that address the root cause of these conditions. As our understanding of retinal hypoxia continues to evolve, the emergence of new technologies holds the promise of more effective treatments, offering hope to patients at risk of vision loss.

The ganglion cell complex damage in coronary artery disease

PURPOSE

This study aims to investigate the correlation between macular thickness, retinal nerve fiber layer thickness, ganglion cell complex thickness, and Gensini scores in patients who have undergone coronary angiography, using spectral-domain optical coherence tomography.

METHODS

We retrospectively evaluated optical coherence tomography results from patients who had undergone coronary angiography between January 2019 and January 2021 due to coronary artery disease, with angiography performed within one month of the optical coherence tomography examination. Based on their Gensini scores, patients were classified into two groups: mild coronary artery disease (Gensini score ≤ 20, Group 1) and severe coronary artery disease (Gensini score > 20, Group 2).

RESULTS

Group 1 comprised 28 patients with an average age of 61.3 ± 10.2, while Group 2 consisted of 25 patients with an average age of 65.4 ± 9.6. While there was no statistically significant difference found in retinal nerve fiber layer and macular thickness between the groups, the ganglion cell complex thickness was significantly thinner in Group 2 in the inner superior temporal (112.55 ± 34.12 µm vs. 99.68 ± 37.81 µm, p = 0.026), inner superior nasal (121.14 ± 32.92 µm vs. 108.36±24.53 µm, p = 0.012), inner inferior nasal (120.81 ± 32.34 µm vs. 108.45 ± 12.53 µm, p = 0.048), and superior (99.11 ± 25.91 µm vs. 88.77 ± 16.75 µm, p = 0.020) regions. Furthermore, a significant negative correlation was observed between the Gensini score and the ganglion cell complex thickness in both the inner superior nasal and superior regions.

CONCLUSION

Compared to patients with mild coronary artery disease, those with severe disease exhibited a significant decrease in ganglion cell complex thickness in the superior and inner superior nasal regions.

Accelerated progression of diabetic retinopathy following severe COVID-19 infection

PURPOSE

The impact of SARS-CoV-2 infection on pre-existing retinal pathology is currently unknown.

OBSERVATIONS

We present a unique case of rapidly progressing diabetic retinopathy (DR) following severe COVID-19 infection requiring supplemental oxygen and subsequent long-COVID.

CONCLUSIONS AND IMPORTANCE

Following infection with SARS-CoV-2, the associated acute and possible long-term hypoxia has the potential to affect the retina and accelerate the natural course of diabetic retinopathy.

Retinal ganglion cell-inner plexiform layer, white matter hyperintensities, and their interaction with cognition in older adults

Purpose

We explored the interaction of optical coherence tomography (OCT) parameters and white matter hyperintensities with cognitive measures in our older adult cohort.

Methods

This observational study enrolled participants who underwent a comprehensive neuropsychological battery, structural 3-T brain magnetic resonance imaging (MRI), visual acuity examination, and OCT imaging. Cerebral small vessel disease (CSVD) markers were read on MR images; lacune, cerebral microbleeds (CMB), white matter hyperintensities (WMH), and enlarged perivascular spaces (EPVS), were defined according to the STRIVE standards. Retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thicknesses (μm) were measured on the OCT tool.

Results

Older adults with cognitive impairment (CI) showed lower RNFL (p = 0.001), GCIPL (p = 0.009) thicknesses, and lower hippocampal volume (p = 0.004) when compared to non-cognitively impaired (NCI). RNFL (p = 0.006) and GCIPL thicknesses (p = 0.032) correlated with MoCA scores. GCIPL thickness (p = 0.037), total WMH (p = 0.003), PWMH (p = 0.041), and DWMH (p = 0.001) correlated with hippocampal volume in our older adults after adjusting for covariates. With hippocampal volume as the outcome, a significant interaction (p < 0.05) between GCIPL and PWMH and total WMH was observed in our older adults.

Conclusion

Both GCIPL thinning and higher WMH burden (especially PWMH) are associated with hippocampal volume and older adults with both pathologies are more susceptible to subclinical cognitive decline.

A simplified protocol to induce hypoxia in a standard incubator: A focus on retinal cells

Hypoxia chambers have traditionally been used to induce hypoxia in cell cultures. Cellular responses to hypoxia can also be mimicked with the use of chemicals such as cobalt chloride (CoCl2), which stabilizes hypoxia-inducible factor alpha-subunit proteins. In studies of ocular cells using primary cells and cell lines, such as Müller glial cell (MGC) lines, photoreceptor cell lines, retinal pigment epithelial (RPE) cell lines and retinoblastoma cell lines oxygen levels employed in hypoxia chambers range typically between 0.2% and 5% oxygen. For chemical induction of hypoxic response in these cells, the CoCl2 concentrations used typically range from 100 to 600 μM. Here, we describe simplified protocols for stabilizing cellular hypoxia-inducible factor-1α (HIF-1α) in cell culture using either a hypoxia chamber or CoCl2. In addition, we also provide a detailed methodology to confirm hypoxia induction by the assessment of protein levels of HIF-1α, which accumulates in response to hypoxic conditions. Furthermore, we provide a summary of conditions applied in previous studies of ocular cells.

A hypothermia mimetic molecule (zr17-2) reduces ganglion cell death, gliosis, and electroretinogram distortion in male rats subjected to perinatal asphyxia

Introduction: Perinatal asphyxia (PA) represents a major problem in perinatology and may cause visual losses, including blindness. We, and others, have shown that hypothermia prevents retinal symptoms associated to PA. In the present work, we evaluate whether a hypothermia mimetic small molecule, zr17-2, has similar effects in the context of PA. Methods: Four experimental groups were studied in male rats: Naturally born rats as controls (CTL), naturally born rats injected s.c. with 50 µL of 330 nmols/L zr17-2 (ZR), animals that were exposed to PA for 20 min at 37°C (PA), and rats that were exposed to PA and injected with zr17-2 (PA-ZR). Forty-five days after treatment, animals were subjected to electroretinography. In addition, morphological techniques (TUNEL, H&E, multiple immunofluorescence) were applied to the retinas. Results: A reduction in the amplitude of the a- and b-wave and oscillatory potentials (OP) of the electroretinogram (ERG) was detected in PA animals. Treatment with zr17-2 resulted in a significant amelioration of these parameters (p < 0.01). In PA animals, a large number of apoptotic cells was found in the GCL. This number was significantly reduced by treatment with the small molecule (p < 0.0001). In a similar way, the thickness of the inner retina and the intensity of GFAP immunoreactivity (gliosis) increased in PA retinas (p < 0.0001). These parameters were corrected by the administration of zr17-2 (p < 0.0001). Furthermore, injection of the small molecule in the absence of PA did not modify the ERG nor the morphological parameters studied, suggesting a lack of toxicity. Discussion: In conclusion, our results indicate that a single s.c. injection of zr17-2 in asphyctic neonates may provide a novel and efficacious method to prevent the visual sequelae of PA.

Optical coherence tomography angiography characteristics of retinochoroidal and optic nerve head microcirculation in cryptogenic organizing pneumonia

BACKGROUND

To assess retinochoroidal and optic nerve head microcirculation alterations in cryptogenic organizing pneumonia.

METHODS

Thirty cryptogenic organizing pneumonia patients in the resolution phase (group 1, 30 right eyes) and 33 healthy subjects (group 2, 33 right eyes) were compared. Patients had 40 mg/day corticosteroids for 8-10 days, and a pulmonary function test, which revealed only minimally restrictive ventilation features. After gathering demographic data, a comprehensive ophthalmological exam and optical coherence tomography angiography were performed three months following maximum disease resolution with corticosteroid therapy RESULTS: Groups 1 and 2 had mean ages of 54.37±14.87 and 49.61±12.36 years, respectively (P = 0.171). Despite the lack of statistical significance, superficial and deep capillary plexus vessel densities in all macular regions were lower in group 1, as were foveal avascular zone parameters (P>0.05). However, the outer retinal and choriocapillaris flows increased significantly in group 1, especially in select areas (P<0.001, for both). There were no significant differences in whole image (P = 0.346), inside disk (P = 0.438), or peripapillary (P = 0.185) optic nerve head vessel densities between the two groups; however, nasal (P<0.001) and inferior quadrant (P = 0.006) vessel densities differed significantly. Global retinal nerve fiber layer thickness did not differ significantly between groups 1 and 2 (112.83±14.71 versus 111.45±12.74 µm, respectively; P = 0.692). Group 1, however, had significantly higher superior, nasal, and inferior quadrant, and significantly lower temporal quadrant retinal nerve fiber layer thickness (P<0.001, for all).

CONCLUSIONS

Concerning the impact of probable cryptogenic organizing pneumonia-induced hypoxia on ocular tissues, optical coherence tomography angiography assessments of retinochoroidal and optic nerve head microcirculation could be employed as a biomarker for cerebral microcirculation.

Inhibition of NOX4 with GLX351322 alleviates acute ocular hypertension-induced retinal inflammation and injury by suppressing ROS mediated redox-sensitive factors activation

Reactive oxygen species (ROS) overproduction plays an essential role in the etiology of ischemic/hypoxic retinopathy caused by acute glaucoma. NADPH oxidase (NOX) 4 was discovered as one of the main sources of ROS in glaucoma. However, the role and potential mechanisms of NOX4 in acute glaucoma have not been fully elucidated. Therefore, the current study aims to investigate the NOX4 inhibitor GLX351322 that targets NOX4 inhibition in acute ocular hypertension (AOH)-induced retinal ischemia/hypoxia injury in mice. Herein, NOX4 was highly expressed in AOH retinas, particularly the retinal ganglion cell layer (GCL). Importantly, the NOX4 inhibitor GLX351322 reduced ROS overproduction, inhibited inflammatory factor release, suppressed glial cell activation and hyperplasia, inhibited leukocyte infiltration, reduced retinal cell senescence and apoptosis in damaged areas, reduced retinal degeneration and improved retinal function. This neuroprotective effect is at least partially associated with mediated redox-sensitive factor (HIF-1α, NF-κB, and MAPKs) pathways by NOX4-derived ROS overproduction. These results suggest that inhibition of NOX4 with GLX351322 attenuated AOH-induced retinal inflammation, cellular senescence, and apoptosis by inhibiting the activation of the redox-sensitive factor pathway mediated by ROS overproduction, thereby protecting retinal structure and function. Targeted inhibition of NOX4 is expected to be a new idea in the treatment of acute glaucoma.

Prevention and Treatment of Retinal Vein Occlusion: The Role of Diet-A Review

Retinal vein occlusion (RVO) is the second most common retinal disorder. In comparison to diabetic retinopathy or age-related macular degeneration, RVO is usually an unexpected event that carries a greater psychological impact. There is strong evidence to suggest that cardiovascular diseases are the most common risk factors in this pathology and it has long been known that a higher consumption of fish, nuts, fruits, and vegetables has a protective effect against these types of conditions. In the last several years, interest in plant-based diets has grown in both the general population and in the scientific community, to the point to which it has become one of the main dietary patterns adopted in Western countries. The aim of this review is to investigate the potential impact of macro- and micronutrients on retinal vein occlusion.

State of the Art of Pharmacological Activators of p53 in Ocular Malignancies

The pivotal role of p53 in the regulation of a vast array of cellular functions has been the subject of extensive research. The biological activity of p53 is not strictly limited to cell cycle arrest but also includes the regulation of homeostasis, DNA repair, apoptosis, and senescence. Thus, mutations in the p53 gene with loss of function represent one of the major mechanisms for cancer development. As expected, due to its key role, p53 is expressed throughout the human body including the eye. Specifically, altered p53 signaling pathways have been implicated in the development of conjunctival and corneal tumors, retinoblastoma, uveal melanoma, and intraocular melanoma. As non-selective cancer chemotherapies as well as ionizing radiation can be associated with either poor efficacy or dose-limiting toxicities in the eye, reconstitution of the p53 signaling pathway currently represents an attractive target for cancer therapy. The present review discusses the role of p53 in the pathogenesis of these ocular tumors and outlines the various pharmacological activators of p53 that are currently under investigation for the treatment of ocular malignancies.

Inhibition of high-voltage-activated calcium currents by acute hypoxia in cultured retinal ganglion cells

Hypoxia is a common factor of numerous ocular diseases that lead to dysfunctions and loss of retinal ganglion cells (RGCs) with subsequent vision loss. High-voltage-activated calcium channels are the main source of calcium entry into neurons. Their activity plays a central role in different signaling processes in health and diseases, such as enzyme activation, gene transcription, synaptic transmission, or the onset of cell death. This study aims to establish and evaluate the initial effect of the early stage of acute hypoxia on somatic HVA calcium currents in cultured RGCs. HVA calcium currents were recorded in RGCs using the whole-cell patch-clamp technique in the voltage-clamp mode. The fast local superfusion was used for a brief (up to 270 s) application of the hypoxic solution (pO₂ < 5 mmHg). The switch from normoxic to hypoxic solutions and vice versa was less than 1 s. The HVA calcium channel activity was inhibited by acute hypoxia in 79% of RGCs (30 of 38 RGCs) in a strong voltage-dependent manner. The level of inhibition was independent of the duration of hypoxia or repeated applications. The hypoxia-induced inhibition of calcium currents had a strong correlation with the duration of hypoxia and showed the transition from reversible to irreversible at 75 s of hypoxia and longer. The results obtained are the first demonstration of the phenomena of HVA calcium current inhibition by acute hypoxia in RGCs and provide a conceptual framework for further research.

Increased peripapillary capillaries in patients with acute leukemia by using optical coherence tomography angiography

PURPOSE

To evaluate the radial peripapillary capillary vessel density (RPC-VD) and thickness of the retinal nerve fiber layer (RNFL) in acute leukemia (AL) and the associations of these characteristics with blood laboratory parameters.

METHODS

A cross-sectional study was performed at the Ophthalmology Department of the Sun Yat-sen Memorial Hospital from February 2019 to April 2022. Sixty eyes of 30 patients diagnosed with AL and sixty eyes of 30 matched healthy controls were included. Optical coherence tomography angiography (OCTA) in the 4.5-mm Angio Disc scan mode and the Ganglion cell complex scan mode were performed for all participants. Correlation analyses were used to examine the associations of RPC-VD and RNFL with blood laboratory parameters.

RESULTS

Patients in the AL group had significantly increased RPC-VD in the whole-image (51.42±0.35 vs. 49.52±0.36) and peripapillary fields (53.90±0.43 vs. 51.17±0.50) compared with people in the control group (all P<0.001), while no difference was found for RPC-VD in the inside optic disc fields in the two groups. The RNFL in the AL group was significantly thicker than that in the control group (131.10±3.89 μm vs. 115.03±2.22 μm, P<0.05). Complete blood count (CBC) parameters, including red blood cells, hemoglobin and hematocrit, had a significant negative correlation with RPC-VD and RNFL (all P <0.05).

CONCLUSION

An increased RPC-VD and a thicker RNFL are evidence of fundus changes in patients with early-stage AL, and these metrics may be related to decreases in red blood cells, hemoglobin and hematocrit.

Retinal tissue and microvasculature loss in COVID-19 infection

This cross-sectional study aimed to investigate the hypothesis that permanent capillary damage may underlie the long-term COVID-19 sequela by quantifying the retinal vessel integrity. Participants were divided into three subgroups; Normal controls who had not been affected by COVID-19, mild COVID-19 cases who received out-patient care, and severe COVID-19 cases requiring intensive care unit (ICU) admission and respiratory support. Patients with systemic conditions that may affect the retinal vasculature before the diagnosis of COVID-19 infection were excluded. Participants underwent comprehensive ophthalmologic examination and retinal imaging obtained from Spectral-Domain Optical Coherence Tomography (SD-OCT), and vessel density using OCT Angiography. Sixty-one eyes from 31 individuals were studied. Retinal volume was significantly decreased in the outer 3 mm of the macula in the severe COVID-19 group (p = 0.02). Total retinal vessel density was significantly lower in the severe COVID-19 group compared to the normal and mild COVID-19 groups (p = 0.004 and 0.0057, respectively). The intermediate and deep capillary plexuses in the severe COVID-19 group were significantly lower compared to other groups (p < 0.05). Retinal tissue and microvascular loss may be a biomarker of COVID-19 severity. Further monitoring of the retina in COVID-19-recovered patients may help further understand the COVID-19 sequela.

Non-prophylactic resveratrol-mediated protection of neurite integrity under chronic hypoxia is associated with reduction of Cav1.2 channel expression and calcium overloading

Cellular hypoxia is a major cause of oxidative stress, culminating in neuronal damage in neurodegenerative diseases. Numerous ex vivo studies have implicated that hypoxia episodes leading to disruption of Ca²⁺ homeostasis and redox status contribute to the progression of various neuropathologies and cell death. Isolation and maintenance of primary cell culture being cost-intensive, the details of the time course relationship between Ca²⁺ overload, L-type Ca²⁺ channel function, and neurite retraction under chronic and long-term hypoxia remain undefined. In order to explore the effect of oxidative stress and Ca²⁺ overload on neurite length, first, we developed a 5-day-long neurite outgrowth model using N2a cell line. Second, we propose a chronic hypoxia model to investigate the modulation of the L-type Ca²⁺ channel (Cav1.2) and oxidative resistance gene (OXR1) expression level during the process of neurite retraction and neuronal damage over 32 h. Thirdly, we developed a framework for quantitative analysis of cytosolic Ca²⁺, superoxide formation, neurite length, and constriction formation in individual cells using live imaging that provides an understanding of molecular targets. Our findings suggest that an increase in cytosolic Ca²⁺ is a feature of an early phase of hypoxic stress. Further, we demonstrate that augmentation in the L-type channel leads to amplification in Ca²⁺ overload, ROS accumulation, and a reduction in neurite length during the late phase of hypoxic stress. Next, we demonstrated that non-prophylactic treatment of resveratrol leads to the reduction of calcium overloading under chronic hypoxia via lowering of L-type channel expression. Finally, we demonstrate that resveratrol-mediated reduction of Cav1.2 channel and STAT3 expression are associated with retention of neurite integrity. The proposed in vitro model assumes significance in the context of drug designing and testing that demands monitoring of neurite length and constriction formations by imaging before animal testing.

Factors That Can Prolong Ocular Treatment Duration in Age-Related Macular Degeneration

Intravitreal injections of anti-vascular endothelial growth factor (VEGF) agents are used to treat wet age-related macular degeneration (wAMD); however, they are associated with a considerable treatment burden and poor real-world outcomes. The molecular size and charge of anti-VEGF agents influence drug pharmacokinetics in the vitreous and peak drug efficacy. This article reviews the established and novel strategies to prolong drug action, in the vitreal cavity, and thus reduce dosing frequency. Increased ocular residency can be attained by increasing drug size as with large molecules, such as KSI-301; adding polyethylene glycol to pegcetacoplan (APL-2) or avacincaptad pegol to increase molecular size; or binding to other targets that increase molecular size, such as vitreal albumin in the case of BI-X. Faricimab is a bispecific antibody in which the fragment crystallizable portion is engineered to prolong ocular residency and reduce systemic exposure. Conversely, small VEGF-binding molecules, such as brolucizumab, can be administered at higher clinical doses, with the potential for prolonged clinical activity versus larger molecules. Other important considerations include sustained drug delivery routes, such as the ranibizumab port delivery system or subconjunctival or suprachoroidal injection. More effective and longer-lasting treatments are needed for wAMD to prolong drug action and reduce dosing frequency. Several strategies are under investigation and the prevention of vision loss in patients with AMD or other retinal diseases may be attainable in the near future.

Isozyme-specific histone deacetylase 1/2 inhibitor K560 attenuates oxidative stress-induced retinal cell death

Oxidative stress-induced damage is an underlying mechanism in the pathogenesis of age-related retinal diseases. Here, we examined the effects of K560, a potential candidate drug for the treatment of these diseases, on oxidative stress-induced retinal cell death. K560 is a novel isozyme-specific inhibitor of histone deacetylase 1 and 2 (HDAC1/2). Histone acetylation in retinal lysates and dissociated retinal cells was detected with a western blot analysis and cell-based enzyme-linked immunosorbent assay (ELISA), respectively. The viability of mouse retinal cells was measured with an alamarBlue assay. We used immunohistochemistry for RNA binding protein with multiple splicing (RBPMS) to visualize the retinal ganglion cells (RGCs) of mice. An ELISA analysis indicated that histone acetylation was enhanced in dissociated mouse retinal cells treated with K560. The cell viability assay indicated that K560 attenuated both exogenous hydrogen peroxide-induced and endogenous oxidative stress-induced cell death in dissociated retinal cells. Western blot analysis indicated that intravitreal K560 administration enhanced the acetylation of histones H3 and H4 in mouse retinal lysates. To examine the effect of K560 on oxidative stress-induced RGC death, we performed whole-mount immunohistochemistry for RBPMS on retinas dissected from eyes treated with K560 or vehicle on day one, and K560 or vehicle and NMDA on day two. Quantification of RBPMS-immunopositive cells indicated that K560 attenuated NMDA-induced RGC death. Taken together, our findings suggest that administration of a HDAC1/2-specific inhibitor K560 may be effective in the treatment of oxidative stress-mediated retinal degeneration and have less cytotoxicity than other known HDAC inhibitors, which are known to target a wide range of HDAC family members.

Impact of obstructive sleep apnea on the expression of inflammatory mediators in diabetic macular edema

PURPOSE

To determine differences in inflammatory markers expressed in diabetic macular edema (DME) patients with and without obstructive sleep apnea (OSA).

METHODS

This was a prospective, cross-sectional study. Patients with treatment naive DME were enrolled in the study. They were stratified into 2 groups based on Apnea Hypopnea Index (AHI) from overnight polysomnography: OSA + (AHI ≥ 15) and OSA - (AHI<15). Multiplex immunoassay was performed for aqueous and serum cytokines including VEGF, placental growth factor (PGF), ICAM, IL2, IL3, IL6, IL8, IL10, IL17, vascular cell adhesion molecule-1 (VCAM1), monocyte attractant protein-1 (MCP1), epidermal growth factor (EGF) and platelet derived growth factor (PDGF). Statistical significance was defined as p < 0.004 using Bonferroni correction.

RESULTS

32 DME positive patients were enrolled in the study; of which 17 patients were OSA + and 15 OSA-. The OSA + cohort had significantly higher levels of serum EGF (p = 0.003), and trended towards higher levels of most serum cytokines including ICAM and IL6. OSA- cohort had significantly higher levels of aqueous IL17 compared to the OSA + cohort (2.97 ± 1.7 vs. 1.4 ± 0.46 pg/mL, p = 0.004). There were no significant differences in other aqueous cytokines.

CONCLUSIONS

OSA + group trended towards higher levels of most serum inflammatory markers, suggesting a greater pro-inflammatory state. However, they did not have significantly greater level of aqueous cytokines.

Continuous Hypoxia Reduces Retinal Ganglion Cell Degeneration in a Mouse Model of Mitochondrial Optic Neuropathy

Purpose

To test whether continuous hypoxia is neuroprotective to retinal ganglion cells (RGCs) in a mouse model of mitochondrial optic neuropathy.

Methods

RGC degeneration was assessed in genetically modified mice in which the floxed gene for the complex I subunit NDUFS4 is deleted from RGCs using Vlgut2-driven Cre recombinase. Beginning at postnatal day 25 (P25), Vglut2-Cre;ndufs4loxP/loxP mice and control littermates were housed under hypoxia (11% oxygen) or kept under normoxia (21% oxygen). Survival of RGC somas and axons was assessed at P60 and P90 via histological analysis of retinal flatmounts and optic nerve cross-sections, respectively. Retinal tissue was also assessed for gliosis and neuroinflammation using western blot and immunofluorescence.

Results

Consistent with our previous characterization of this model, at least one-third of RGCs had degenerated by P60 in Vglut2-Cre;ndufs4loxP/loxP mice remaining under normoxia. However, continuous hypoxia resulted in complete rescue of RGC somas and axons at this time point, with normal axonal myelination observed on electron microscopy. Though only partial, hypoxia-mediated rescue of complex I-deficient RGC somas and axons remained significant at P90. Hypoxia prevented reactive gliosis at P60, but the retinal accumulation of Iba1+ mononuclear phagocytic cells was not substantially reduced.

Conclusions

Continuous hypoxia achieved dramatic rescue of early RGC degeneration in mice with severe mitochondrial dysfunction. Although complete rescue was not durable to P90, our observations suggest that investigating the mechanisms underlying hypoxia-mediated neuroprotection of RGCs may identify useful therapeutic strategies for optic neuropathies resulting from less profound mitochondrial impairment, such as Leber hereditary optic neuropathy.

More than meets the eye: The role of microglia in healthy and diseased retina

Microglia are the main resident immune cells of the nervous system and as such they are involved in multiple roles ranging from tissue homeostasis to response to insults and circuit refinement. While most knowledge about microglia comes from brain studies, some mechanisms have been confirmed for microglia cells in the retina, the light-sensing compartment of the eye responsible for initial processing of visual information. However, several key pieces of this puzzle are still unaccounted for, as the characterization of retinal microglia has long been hindered by the reduced population size within the retina as well as the previous lack of technologies enabling single-cell analyses. Accumulating evidence indicates that the same cell type may harbor a high degree of transcriptional, morphological and functional differences depending on its location within the central nervous system. Thus, studying the roles and signatures adopted specifically by microglia in the retina has become increasingly important. Here, we review the current understanding of retinal microglia cells in physiology and in disease, with particular emphasis on newly discovered mechanisms and future research directions.

Peptains block retinal ganglion cell death in animal models of ocular hypertension: implications for neuroprotection in glaucoma

Ocular hypertension is a significant risk factor for vision loss in glaucoma due to the death of retinal ganglion cells (RGCs). This study investigated the effects of the antiapoptotic peptides peptain-1 and peptain-3a on RGC death in vitro in rat primary RGCs and in mouse models of ocular hypertension. Apoptosis was induced in primary rat RGCs by trophic factor deprivation for 48 h in the presence or absence of peptains. The effects of intravitreally injected peptains on RGC death were investigated in mice subjected to retinal ischemic/reperfusion (I/R) injury and elevated intraocular pressure (IOP). I/R injury was induced in mice by elevating the IOP to 120 mm Hg for 1 h, followed by rapid reperfusion. Ocular hypertension was induced in mice by injecting microbeads (MB) or silicone oil (SO) into the anterior chamber of the eye. Retinal flatmounts were immunostained with RGC and activated glial markers. Effects on anterograde axonal transport were determined by intravitreal injection of cholera toxin-B. Peptain-1 and peptain-3a inhibited neurotrophic factor deprivation-mediated RGC apoptosis by 29% and 35%, respectively. I/R injury caused 52% RGC loss, but peptain-1 and peptain-3a restricted RGC loss to 13% and 16%, respectively. MB and SO injections resulted in 31% and 36% loss in RGCs following 6 weeks and 4 weeks of IOP elevation, respectively. Peptain-1 and peptain-3a inhibited RGC death; the loss was only 4% and 12% in MB-injected eyes and 16% and 15% in SO-injected eyes, respectively. Anterograde transport was defective in eyes with ocular hypertension, but this defect was substantially ameliorated in peptain-injected eyes. Peptains suppressed ocular hypertension-mediated retinal glial activation. In summary, our results showed that peptains block RGC somal and axonal damage and neuroinflammation in animal models of glaucoma. We propose that peptains have the potential to be developed as therapeutics against neurodegeneration in glaucoma.

Caffeine and Its Neuroprotective Role in Ischemic Events: A Mechanism Dependent on Adenosine Receptors

Ischemia is characterized by a transient, insufficient, or permanent interruption of blood flow to a tissue, which leads to an inadequate glucose and oxygen supply. The nervous tissue is highly active, and it closely depends on glucose and oxygen to satisfy its metabolic demand. Therefore, ischemic conditions promote cell death and lead to a secondary wave of cell damage that progressively spreads to the neighborhood areas, called penumbra. Brain ischemia is one of the main causes of deaths and summed with retinal ischemia comprises one of the principal reasons of disability. Although several studies have been performed to investigate the mechanisms of damage to find protective/preventive interventions, an effective treatment does not exist yet. Adenosine is a well-described neuromodulator in the central nervous system (CNS), and acts through four subtypes of G-protein-coupled receptors. Adenosine receptors, especially A1 and A2A receptors, are the main targets of caffeine in daily consumption doses. Accordingly, caffeine has been greatly studied in the context of CNS pathologies. In fact, adenosine system, as well as caffeine, is involved in neuroprotection effects in different pathological situations. Therefore, the present review focuses on the role of adenosine/caffeine in CNS, brain and retina, ischemic events.

Changes of retinal ganglion cell complex after vitrectomy in rhegmatogenous retinal detachment patients and its correlation with inflammatory blood biomarkers

Purpose

To compare retinal ganglion cell complex (GCC) parameters between rhegmatogenous retinal detachment (RRD) eyes and normal contralateral eyes after vitrectomy and to evaluate their correlation with inflammatory blood markers.

Methods

We investigated 25 eyes that underwent vitrectomy due to RRD. Venous blood samples were collected from all participants before 08:00 a.m. on the second day of admission after a 12-hour fast for blood counts. The differences of retinal structure between RRD and contralateral eyes were compared 1 week postoperatively.

Results

Focal loss volume (FLV) (2.009 ± 1.286)% was significantly increased compared with the contralateral eyes (p <  0.001). Monocyte-to-high-density lipoprotein was significantly positively correlated with GCC thickness parameters, and negatively correlated with FLV and global loss volume (GLV). Postoperative best-corrected visual acuity was negatively correlated with GLV (p = 0.039, R² = 0.172).

Conclusion

Retinal ganglion cells (RGCs) loss might present early postoperatively in RRD eyes, and was associated with systemic inflammation. RGCs loss might affect postoperative vision.

Curcumin and Wnt/β‑catenin signaling in exudative age‑related macular degeneration (Review)

Curcumin is a natural product widely used due to its pharmacological effects. Nevertheless, only a limited number of studies concerning the effects of curcumin on exudative age‑related macular degeneration (AMD) is currently available. Since ophthalmic diseases, including exudative AMD, have a marked impact on public health, the prevention and therapy of ophthalmic disorders remain of increasing concern. Exudative AMD is characterized by choroidal neovascularization (CNV) invading the subretinal space, ultimately enhancing exudation and hemorrhaging. The exudative AMD subtype corresponds to 10 to 15% of cases of macular degeneration; however, the occurrence of this subtype has been reported as the major cause of vision loss and blindness, with the occurrence of CNV being responsible for 80% of the cases with vision loss. In CNV increased expression of VEGF has been observed, stimulated by the overactivation of Wnt/β‑catenin signaling pathway. The stimulation of the Wnt/β‑catenin signaling pathway is responsible for the activation of several cellular mechanisms, simultaneously enhancing inflammation, oxidative stress and angiogenesis in numerous diseases, including ophthalmic disorders. Some studies have previously demonstrated the possible advantage of the use of curcumin for the inhibition of Wnt/β‑catenin signaling. In the present review article, the different mechanisms of curcumin are described concerning its effects on oxidative stress, inflammation and angiogenesis in exudative AMD, by interacting with Wnt/β‑catenin signaling.

Statins Inhibit the Gliosis of MIO-M1, a Müller Glial Cell Line Induced by TRPV4 Activation

We characterized Müller cell gliosis induced by the activation of transient receptor potential vanilloid-type 4 (TRPV4) and assessed whether statins could modulate the gliosis. The human Müller cell line, MIO-M1, was used to analyze the gliosis caused by glaucomatous stimulation. To induce Müller gliosis in MIO-M1 cells, GSK101 was used to activate TRPV4, and Müller gliosis was evaluated by analyzing vimentin, nestin, and glial fibrillary acidic protein (GFAP) expression. The expression level of TNF-α was determined by ELISA. To evaluate the GSK101 activation of the NF-κB pathway, p65 phosphorylation was measured by Western blotting, and the nuclear translocation of p65 and IκBα phosphorylation were assessed by immunostaining. To assess the effect of statins on MIO-M1 gliosis, cells were pretreated for 24 h with statins before GSK101 treatment. Vimentin, nestin, and GFAP expression were upregulated by GSK101, while statins effectively inhibited them. The expression of TNF-α was increased by GSK101. The phosphorylation and nuclear translocation of p65 and IκBα phosphorylation, which occurs prior to p65 activation, were induced. Statins suppressed the GSK101-mediated phosphorylation of IκBα and p65 translocation. Statins can mitigate gliosis in the human Müller cell line. Because TRPV4 activation in Müller cells reflects glaucoma pathophysiology, statins may have the potential to prevent RGC death.

Retinal Glutamate Neurotransmission: From Physiology to Pathophysiological Mechanisms of Retinal Ganglion Cell Degeneration

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

Case of unilateral anaemic retinopathy unmasking colorectal carcinoma

Anaemic retinopathy presents commonly with bilateral retinal haemorrhages and soft exudates. Unilateral optic disc oedema in these patients has rarely been mentioned. We report a case of an atypical presentation of anaemic retinopathy with recurrent unilateral optic disc oedema and retinal haemorrhages secondary to iron deficiency anaemia from a newly diagnosed colorectal adenocarcinoma.A man in his 70s with multiple ischaemic risk factors was referred for unilateral optic disc oedema associated with a few retinal haemorrhages. Initial diagnosis was that of impending central retinal vein occlusion. The optic disc oedema initially resolved but recurred 8 months later with worsening unilateral disc oedema, 'coin-shaped' retinal haemorrhages, Roth's spots and venous tortuosity. Full blood count showed microcytic hypochromic anaemia secondary to iron deficiency and colonoscopy revealed colorectal adenocarcinoma. The patient received blood transfusions, oral iron replacement and underwent surgical resection of the tumour. The anaemia resolved, and the fundus findings resolved as well.

Morphology and Vessel Density of the Macula in Preterm Children Using Optical Coherence Tomography Angiography

Background: Retinal morphology changes may be associated with prematurity and can lead to visual impairment. Optical coherence tomography angiography may contribute to understanding the pathomechanism of structural and vascular retinal impairment in premature children. The aim of this study was to assess an influence of prematurity, neonatal clinical characteristics, and a history of retinopathy of prematurity (ROP) on the morphology and retinal vascularity of macula in children. Methods: A case−control study of 123 preterm children and 86 full-term children was performed. The age of the subjects was 10.45 years (IQR: 8.12−12.77), while the age of the control group was 11.78 years (IQR: 8.81−13.79). Optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA, angio-OCT) were performed using RTVueXR Avanti (Optovue, Fremont, CA, USA). Ganglion cell complex (GCC), foveal thickness (FT), parafoveal thickness (PFT), size of foveal avascular zone (FAZ) in superficial plexus, superficial capillary vessel density (sVD), deep capillary vessel density (dVD), central choroidal thickness (CCT), and presence of macular hypoplasia were analyzed. The association between OCT/angio-OCT results and clinical characteristics including the degree of ROP and therapy requirements was assessed in preterm infants. Results: Foveal morphology was affected in preterm children with high incidence of foveal hypoplasia (24.77%). GCC was thinner in preterm children compared to controls: avgGG 93 μm vs. 100 μm, p < 0.001. No associations between GCC and gestational age (R = −0.085; p = 0.228) and birth weight (R = −0.054; p = 0.446) were found. FAZ in preterm group was smaller than in controls (0.13 ± 0.09 vs. 0.22 ± 0.09; p < 0.001). FAZ area correlated with gestational age (R = 0.456; p < 0.001) and birth weight (R = 0.472; p < 0.001). Deep vessel density in the fovea was higher in preterm children than in control group (p < 0.001). PFT was significantly lower in preterm children compared to control group. However, increased thickness in the fovea was noted in preterm children (p < 0.001). FT was inversely correlated with gestational age (R = −0.562; p < 0.001) and birth weight (R = −0.508, p < 0.001). CCT was lower in preterm children (312 μm vs. 337.5 μm, p < 0.001) Parameters of GCC and FT were higher in patients with ROP required treatment compared to patients without ROP and spontaneously regressed retinopathy. FAZ was smaller in patients with retinopathy than in preterm children without ROP. Conclusion: Prematurity has a significant negative impact on GCC, macular morphology, and vascularization. In premature children, decreased FAZ, increased FT, and vessel density were strongly associated with gestational age, birth weight, Apgar score, ROP stage, and treatment requirement. Optical coherence tomography angiography is a useful tool for detecting retinal changes in premature children.

Aqueous humor proteomic analysis of acute angle-closure glaucoma with visual field loss

Background

Acute angle-closure glaucoma (AACG) is an ophthalmic emergency that occurs over the course of hours or days and may cause irreversible blindness if not treated immediately. In most cases, optic nerve damage is the cause of visual field (VF) loss in AACG. There has been no reliable biomarker found to evaluate optic nerve damage to date. Aqueous humor (AH) proteome analysis might reveal the proteomic alterations in AACG and provide helpful clues in the search for an AH biomarker of optic nerve damage and VF loss.

Methods

In this study, we used the AH proteome to explore the functions of differentially expressed proteins (DEPs) during disease progression. The AH proteins from the early-stage group and late-stage group were extracted and analyzed by the data-independent acquisition (DIA) method. The DEPs functions were annotated, and parallel reaction monitoring (PRM) was used to validate the key DEPs.

Results

A total of 87 DEPs were found. Gene Ontology analysis showed that most DEPs were enriched in immunology, hemodynamics, and apoptosis. Ingenuity pathway analysis found that vascular endothelial growth factor (VEGF) signaling, the production of reactive oxygen species (ROS) in macrophages, and the nuclear factor erythroid 2-related factor 2 (NRF2)-mediated oxidative stress response were active pathways in the late stage of AACG. The mechanism of retinal ganglion cell (RGC) death was hypothesized on the basis of DEP functional analysis. A total of 20 DEPs were validated by using PRM, and prostaglandin-H2 D-isomerase was found to have the potential to evaluate optic nerve damage.

Conclusions

This study showed that AH proteomic analysis could reveal the proteomic alterations in the pathogenesis of VF loss in AACG and help to provide objective protein biomarkers to evaluate VF loss. These findings will benefit the application of the AH proteome to clinical research.

Investigation on the expression regulation of RIPK1/RIPK3 in the retinal ganglion cells (RGCs) cultured in high glucose

Diabetic retinopathy (DR) represents the most typical complication of type 2 diabetes mellitus and one of the most primary oculopathy causing blindness. However, the mechanism of DR remains unknown. RIPK1/RIPK3, as homologous serine/threonine kinases, are key elements in mediating necroptosis and may have functions in DR development. To clarify the relationship between DR and RIPK1/RIPK3, this study established a model of apoptosis using high-glucose induced RGCs, which were treated with 7.5, 19.5, and 35 mM D-glucose for 12, 24, and 48 h, respectively. Subsequently, the expression of RIPK1/RIPK3 was determined and the protective effect of necrostatin-1 on RGCs injury induced by high glucose was explored. The results demonstrated that the expression of RIPK1 and RIPK3 in the cells was increased markedly following 12 h treatment with 19.5 mM D-glucose. Additionally, following an addition of 100 μM necrostatin-1 in 19.5 mM D-glucose medium for RGCs treatment 12 h, the protein expression of RIPK1 and RIPK3 was decreased markedly, and the number of Nissl bodies in cells was increased substantially. The findings of the present study indicated that high glucose could induce the expression of RIPK1/RIPK3, and necrostatin-1 could effectively protect RGCs from D-glucose-induced cell necrosis.

Adaptation of mammals to hypoxia

Oxygen plays a pivotal role in the metabolism and activities of mammals. However, oxygen is restricted in some environments-subterranean burrow systems or habitats at high altitude or deep in the ocean-and this could exert hypoxic stresses such as oxidative damage on organisms living in these environments. In order to cope with these stresses, organisms have evolved specific strategies to adapt to hypoxia, including changes in physiology, gene expression regulation, and genetic mutations. Here, we review how mammals have adapted to the three high-altitude plateaus of the world, the limited oxygen dissolved in deep water habitats, and underground tunnels, with the aim of better understanding the adaptation of mammals to hypoxia.

Assessment of retinal oxygen metabolism, visual function, thickness and degeneration markers after variable ischemia/reperfusion in rats

After total retinal ischemia induced experimentally by ophthalmic vessel occlusion followed by reperfusion, studies have reported alterations in retinal oxygen metabolism (MO₂), delivery (DO₂), and extraction fraction (OEF), as well as visual dysfunction and cell loss. In the current study, under variable durations of ischemia/reperfusion, changes in these oxygen metrics, visual function, retinal thickness, and degeneration markers (gliosis and apoptosis) were assessed and related. Additionally, the prognostic value of MO₂ for predicting visual function and retinal thickness outcomes was reported. Sixty-one rats were divided into 5 groups of ischemia duration (0 [sham], 60, 90, 120, or 180 min) and 2 reperfusion durations (1 h, 7 days). Phosphorescence lifetime and blood flow imaging, electroretinography, and optical coherence tomography were performed. MO₂ reduction was related to visual dysfunction, retinal thinning, increased gliosis and apoptosis after 7-days reperfusion. Impairment in MO₂ after 1-h reperfusion predicted visual function and retinal thickness outcomes after 7-days reperfusion. Since MO₂ can be measured in humans, findings from analogous studies may find value in the clinical setting.

An Innovative In Vitro Open-Angle Glaucoma Model (IVOM) Shows Changes Induced by Increased Ocular Pressure and Oxidative Stress

Primary Open-Angle Glaucoma (POAG) is a neurodegenerative disease, and its clinical outcomes lead to visual field constriction and blindness. POAG's etiology is very complex and its pathogenesis is mainly explained through both mechanical and vascular theories. The trabecular meshwork (TM), the most sensitive tissue of the eye anterior segment to oxidative stress (OS), is the main tissue involved in early-stage POAG, characterized by an increase in pressure. Preclinical assessments of neuroprotective drugs on animal models have not always shown correspondence with human clinical studies. In addition, intra-ocular pressure management after a glaucoma diagnosis does not always prevent blindness. Recently, we have been developing an innovative in vitro 3Dadvanced human trabecular cell model on a millifluidicplatform as a tool to improve glaucoma studies. Herein, we analyze the effects of prolonged increased pressure alone and, in association with OS, on such in vitro platform. Moreover, we verify whethersuch damaged TM triggers apoptosis on neuron-like cells. The preliminary results show that TM cells are less sensitive to pressure elevation than OS, and OS-damaging effects were worsened by the pressure increase. The stressed TM releases harmful signals, which increase apoptosis stimuli on neuron-like cells, suggesting its pivotal role in the glaucoma cascade.

Possible antiapoptotic and neuroprotective effects of magnesium sulphate on retina in a preterm hypoxic-ischemic rat model

Background/aim

The effects of systemic magnesium sulfate (MgSO4) on retina in preterm hypoxic-ischemic (HI) rat model are not known. Our aim was to investigate the effects of MgSO4 on retinal ganglion cell (RGC) count, retinal ganglion cell (RGC) apoptotic index, retinal vascular endothelial growth factor receptor-2 (VEGFR-2), and glial fibrillary acidic protein (GFAP) expressions in preterm HI rat model.

Materials and methods

Fifteen, postnatal day (PND) 7 rat pups were divided into 3 groups: 1. Sham-operated group, 2. HI group, and 3. MgSO4-treated HI group. The second and third groups underwent ischemia followed by exposure to hypoxia for 2 h (Vannucci model). The first and second groups received intraperitoneal saline and the third group received intraperitoneal MgSO4. On PND 10, eyes of the pups were evaluated for RGC count, apoptotic index, VEGFR-2, and GFAP expressions.

Results

In both HI and MgSO4-treated HI group, the mean total RGC counts were found to be significantly decreased. However, the mean total RGC count in the MgSO4-treated HI group was significantly higher than that of the HI group. The mean apoptotic index was found to be significantly increased in the HI group. Retinal VEGFR-2 and GFAP expressions were found to be significantly higher in the HI group.

Conclusions

Magnesium sulfate preconditioning and treatment in preterm HI rat model might diminish apoptosis, relatively preserve RGCs, and reduce retinal VEGFR-2 and GFAP expressions.

Enhanced Physiological Stress Response in Patients with Normal Tension Glaucoma during Hypoxia

Purpose

To investigate whether patients with normal tension glaucoma (NTG) show an enhanced stress response to reduced oxygen supply compared to age-matched healthy controls, measured by serum adrenaline and endothelin-1 (ET-1) levels and changes in distal finger temperature.

Methods

A thorough clinical characterization of patients with NTG and age-matched controls was performed prior to inclusion in the study. Twelve patients with NTG and eleven healthy controls met the inclusion criteria and were enrolled in the study. All subjects underwent a two-day investigation. Participants were randomly exposed to either hypoxia or normoxia during the first visit. Hypoxia or normoxia was induced for two hours through a tightly fitting face mask. In addition, the peripheral circulation was assessed with a thermographic camera. Blood samples were obtained before, during, and after hypoxia or normoxia to evaluate systemic stress molecules such as catecholamines and ET-1 levels.

Results

In patients with NTG, reduced oxygen supply induced an increase in peripheral blood adrenaline (p < 0.05) and a decrease during recovery (p < 0.01). A difference in distal finger temperature was shown in patients with NTG under hypoxia compared to normoxia (exposure: p < 0.05; recovery: p < 0.05). Hypoxia induced an increase in peripheral blood ET-1 levels in both groups (NTG: p < 0.01; controls: p < 0.05).

Conclusion

Patients with NTG had an enhanced physiological stress response as a consequence of hypoxia compared with age-matched controls. Although more studies are needed, the present study supports the involvement of vascular risk factors in the pathophysiology of NTG.