Dexamethasone protects retinal ganglion cells but not Müller glia against hyperglycemia in vitro

Switching to an Intravitreal Dexamethasone Implant after Intravitreal Anti-VEGF Therapy for Diabetic Macular Edema: A Review

Among working-age people, diabetic retinopathy and diabetic macular edema are currently considered the main causes of blindness. Nowadays, intravitreal injections are widely acknowledged as a significant milestone in ophthalmology, especially for the treatment of several retinal diseases, including diabetic macular edema. In particular, anti-vascular endothelial growth factor (VEGF) agents are typically the first line of treatment; however, monthly injections are required, at least, during the loading dosage. Notably, an intravitreal 0.7 mg dexamethasone (DEX) implant (Ozurdex®, AbbVie Inc., North Chicago, IL, USA) is considered a legitimate substitute treatment for diabetic eyes that have not responded to anti-VEGF treatment. In fact, clinical trials and real-life studies have demonstrated the effectiveness and safety of an intravitreal DEX implant in treating such conditions over a period of three to six months. For this reason, wisely selecting diabetic patients might be crucial to decreasing the load of injections in clinics and hospitals. The purpose of this review is to analyze the available scientific literature to highlight the benefits, efficacy, and clinical criteria for choosing whether to switch from intravitreal anti-VEGF therapy to an intravitreal DEX implant in diabetic macular edema.

Evaluating the protective effects of dexamethasone and electrospun mesh combination on primary human mixed retinal cells under hyperglycemic stress

Chronic inflammation is a leading cause of neurodegeneration and vision loss in hyperglycemia-associated conditions such as diabetic retinopathy. Corticosteroid injections are widely used for treatment but suffer from limitations such as rapid drug clearance, short drug half-lives and frequent administration. While drug release from biomaterial carriers can overcome these shortcomings, evaluating the combined effects of corticosteroids and polymeric matrices under hyperglycemic stress is an important step towards aiding translation. In this study, we investigated the effects of dexamethasone (DEX) and electrospun mesh combination on primary human mixed retinal cells under normal and hyperglycemic culture conditions. DEX-incorporated poly(lactide-co-glycolide) (PLGA) meshes were prepared and characterized for architecture, chemistry, drug distribution and in vitro release. The meshes exhibited cumulative in vitro drug release of 39.5 % over 2 months at a near constant rate. Under normal culture conditions, DEX-PLGA meshes promoted significantly higher viability of mixed retinal cells than the control groups but without adverse phenotypic activation. Under hyperglycemic conditions, DEX supplementation resulted in higher viability than the control, although the highest viability was achieved only when DEX was added to cells cultured on PLGA fibers. The combination of DEX and PLGA fibers also promoted higher mRNA expression of the antioxidant GSH under hyperglycemia. Importantly, the largest reduction in the production of pro-inflammatory cytokines viz., MMP-9, IL-6, IL-8 and VEGF-R1 was observed for the DEX and PLGA combination. Our study reveals a combined effect of DEX and electrospun fibers in combating hyperglycemia-driven pro-inflammatory responses, which can aid the development of DEX-loaded electrospun implants for diabetes-driven retinal conditions.

Müller glial cells located in the peripheral retina are more susceptible to high pressure: implications for glaucoma

BACKGROUND

Glaucoma, a progressive neurodegenerative disease, is a leading cause of irreversible vision loss worldwide. This study aims to elucidate the critical role of Müller glia (MG) in the context of retinal ganglion cell (RGC) death, particularly focusing on the influence of peripheral MG sensitivity to high pressure (HP).

METHODS

Co-cultures of porcine RGCs with MG were isolated from both the central and peripheral regions of pig retinas and subjected to both normal and HP conditions. Mass spectrometry analysis of the MG-conditioned medium was conducted to identify the proteins released by MG under all conditions.

RESULTS

Peripheral MG were found to secrete a higher quantity of neuroprotective factors, effectively promoting RGC survival under normal physiological conditions. However, under HP conditions, co-cultures with peripheral MG exhibited impaired RGC survival. Moreover, under HP conditions, peripheral MG significantly upregulated the secretion of proteins associated with apoptosis, oxidative stress, and inflammation.

CONCLUSIONS

This study provides robust evidence suggesting the involvement of MG in RGC death in glaucoma, thus paving the way for future therapeutic investigations.

Role of inflammatory cells in pathophysiology and management of diabetic retinopathy

Diabetic retinopathy (DR) is a sight-threatening complication of diabetes mellitus. Several inflammatory cells and proteins, including macrophages and microglia, cytokines, and vascular endothelial growth factors, are found to play a significant role in the development and progression of DR. Inflammatory cells play a significant role in the earliest changes seen in DR including the breakdown of the blood retinal barrier leading to leakage of blood into the retina. They also have an important role in the pathogenesis of more advanced stage of proliferative diabetic retinopathy, leading to neovascularization, vitreous hemorrhage, and tractional retinal detachment. In this review, we examine the function of numerous inflammatory cells involved in the pathogenesis, progression, and role as a potential therapeutic target in DR. Additionally, we explore the role of inflammation following treatment of DR.

Surgical Outcomes of Modified CO2 Laser-assisted Sclerectomy for Uveitic Glaucoma

PURPOSE

To evaluate the clinical safety and efficacy of modified CO₂ laser-assisted sclerectomy surgery (CLASS) in patients with uveitic glaucoma (UG) using primary open-angle glaucoma (POAG) patients for a comparison.

METHODS

This retrospective study included UG and POAG patients from the modified CLASS Study Group database. Intraocular pressure (IOP) and the number of glaucoma medications were compared between groups by the Wilcoxon test. The Kaplan-Meier method was used for survival analysis; complete success was defined as 5≤ IOP≤18 mmHg and a ≥ 20% reduction in IOP from baseline without medication.

RESULTS

Twenty-three and 25 eyes in UG and POAG groups were included. At the 12-month visit in both groups, the mean IOP and mean number of IOP-lowering medications were significantly reduced compared to baseline, with complete success rates of 60.9% and 64.0% in the UG and POAG groups (P = .859).

CONCLUSIONS

Modified CLASS yields similar outcomes for patients with UG and POAG.

Individualized, Additively Manufactured Drug-Releasing External Ear Canal Implant for Prevention of Postoperative Restenosis: Development, In Vitro Testing, and Proof of Concept in an Individual Curative Trial

Postoperative restenosis in patients with external ear canal (EEC) atresia or stenosis is a common complication following canaloplasty. Our aim in this study was to explore the feasibility of using a three dimensionally (3D)-printed, patient-individualized, drug ((dexamethasone (DEX)), and ciprofloxacin (cipro))-releasing external ear canal implant (EECI) as a postoperative stent after canaloplasty. We designed and pre-clinically tested this novel implant for drug release (by high-performance liquid chromatography), biocompatibility (by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay), bio-efficacy (by the TNF-α (tumor necrosis factor-alpha)-reduction test (DEX) and inhibition zone test (for cipro)), and microbial contamination (formation of turbidity or sediments in culture medium). The EECI was implanted for the first time to one patient with a history of congenital EEC atresia and state after three canaloplasties due to EEC restenosis. The preclinical tests revealed no cytotoxic effect of the used materials; an antibacterial effect was verified against the bacteria Staphylococcus aureus and Pseudomonas aeruginosa, and the tested UV-irradiated EECI showed no microbiological contamination. Based on the test results, the combination of silicone with 1% DEX and 0.3% cipro was chosen to treat the patient. The EECI was implantable into the EEC; the postoperative follow-up visits revealed no otogenic symptoms or infections and the EECI was explanted three months postoperatively. Even at 12 months postoperatively, the EEC showed good epithelialization and patency. Here, we report the first ever clinical application of an individualized, drug-releasing, mechanically flexible implant and suggest that our novel EECI represents a safe and effective method for postoperatively stenting the reconstructed EEC.

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.

High glucose concentrations induce oxidative stress by inhibiting Nrf2 expression in rat Müller retinal cells in vitro

Diabetic retinopathy (DR) is a complication of diabetes. Several studies have implicated oxidative stress as a fundamental factor in the progression of the disease. The nuclear factor erythroid-2-related factor 2 (Nrf2) is one of the main regulators of redox homeostasis. Glia Müller cells (MC) maintain the structural and functional stability of the retina. The objective of this study was to evaluate the effect of high glucose concentrations on reactive oxygen species (ROS) production and Nrf2 expression levels in rat MC. MC were incubated with normal (NG; 5 mM) or high glucose (HG; 25 mM) for different times. Incubation with HG increased ROS levels from 12 to 48 h but did not affect cell viability. However, exposure to 3 h of HG caused a transient decrease Nrf2 levels. At that time, we also observed a decrease in the mRNA expression of Nrf2 target genes, glutathione levels, and catalase activity, all of which increased significantly beyond initial levels after 48 h of incubation. HG exposure leads to an increase in the p65 subunit of nuclear factor-κB (NF-kB) levels, and its target genes. These results suggest that high glucose concentrations lead to alteration of the redox regulatory capacity of Nrf2 mediated by NF-kB regulation.

Novel biomarkers and therapeutic approaches for diabetic retinopathy and nephropathy: Recent progress and future perspectives

The global burden due to microvascular complications in patients with diabetes mellitus persists and even increases alarmingly, the intervention and management are now encountering many difficulties and challenges. This paper reviews the recent advancement and progress in novel biomarkers, artificial intelligence technology, therapeutic agents and approaches of diabetic retinopathy and nephropathy, providing more insights into the management of microvascular complications.

Epigenetic alterations associated with dexamethasone sodium phosphate through DNMT and TET in RPE cells

PURPOSE

To elucidate the mechanism behind epigenetic alteration associated with dexamethasone (DEX) sodium phosphate treatment.

METHODS

We performed enzyme-linked immunosorbent assay to quantify changes in global DNA methylation and hydroxymethylation, quantitative real-time PCR (qRT-PCR) of the DNA methylation- and hydroxymethylation-related gene, in vitro DNA methyltransferase (DNMT) enzymatic activity assays with purified DNMTs, and DNA hydroxymethylation pattern with super-resolution imaging.

RESULTS

We identified global DNA hypomethylation and hyper-hydroxymethylation upon DEX treatment, associated with aberrant mRNA expression levels of DNMT and ten-eleven translocation (TET) proteins. Additionally, DEX exposure could directly hinder DNMT activities.

CONCLUSIONS

We showed that DEX-induced epigenetic alterations are linked to aberrant DNMT and TET expression, potentially through an essential role of DNMT.

The Effect of Plasma Rich in Growth Factors on Microglial Migration, Macroglial Gliosis and Proliferation, and Neuronal Survival

Plasma rich in growth factors (PRGF) is a subtype of platelet-rich plasma that has being employed in the clinic due to its capacity to accelerate tissue regeneration. Autologous PRGF has been used in ophthalmology to repair a range of retinal pathologies with some efficiency. In the present study, we have explored the role of PRGF and its effect on microglial motility, as well as its possible pro-inflammatory effects. Organotypic cultures from adult pig retinas were used to test the effect of the PRGF obtained from human as well as pig blood. Microglial migration, as well as gliosis, proliferation and the survival of retinal ganglion cells (RGCs) were analyzed by immunohistochemistry. The cytokines present in these PRGFs were analyzed by multiplex ELISA. In addition, we set out to determine if blocking some of the inflammatory components of PRGF alter its effect on microglial migration. In organotypic cultures, PRGF induces microglial migration to the outer nuclear layers as a sign of inflammation. This phenomenon could be due to the presence of several cytokines in PRGF that were quantified here, such as the major pro-inflammatory cytokines IL-1β, IL-6 and TNFα. Heterologous PRGF (human) and longer periods of cultured (3 days) induced more microglia migration than autologous porcine PRGF. Moreover, the migratory effect of microglia was partially mitigated by: 1) heat inactivation of the PRGF; 2) the presence of dexamethasone; or 3) anti-cytokine factors. Furthermore, PRGF seems not to affect gliosis, proliferation or RGC survival in organotypic cultures of adult porcine retinas. PRGF can trigger an inflammatory response as witnessed by the activation of microglial migration in the retina. This can be prevented by using autologous PRGF or if this is not possible due to autoimmune diseases, by mitigating its inflammatory effect. In addition, PRGF does not increase either the proliferation rate of microglial cells or the survival of neurons. We cannot discard the possible positive effect of microglial cells on retinal function. Further studies should be performed to warrant the use of PRGF on the nervous system.

The innate immune system in diabetic retinopathy

The prevalence of diabetes has been rising steadily in the past half-century, along with the burden of its associated complications, including diabetic retinopathy (DR). DR is currently the most common cause of vision loss in working-age adults in the United States. Historically, DR has been diagnosed and classified clinically based on what is visible by fundoscopy; that is vasculature alterations. However, recent technological advances have confirmed pathology of the neuroretina prior to any detectable vascular changes. These, coupled with molecular studies, and the positive impact of anti-inflammatory therapeutics in DR patients have highlighted the central involvement of the innate immune system. Reminiscent of the systemic impact of diabetes, immune dysregulation has become increasingly identified as a key element of the pathophysiology of DR by interfering with normal homeostatic systems. This review uses the growing body of literature across various model systems to demonstrate the clear involvement of all three pillars of the immune system: immune-competent cells, mediators, and the complement system. It also demonstrates how the relative contribution of each of these requires more extensive analysis, including in human tissues over the continuum of disease progression. Finally, although this review demonstrates how the complex interactions of the immune system pose many more questions than answers, the intimately connected nature of the three pillars of the immune system may also point to possible new targets to reverse or even halt reverse retinopathy.

Microfluidic and Microscale Assays to Examine Regenerative Strategies in the Neuro Retina

Bioengineering systems have transformed scientific knowledge of cellular behaviors in the nervous system (NS) and pioneered innovative, regenerative therapies to treat adult neural disorders. Microscale systems with characteristic lengths of single to hundreds of microns have examined the development and specialized behaviors of numerous neuromuscular and neurosensory components of the NS. The visual system is comprised of the eye sensory organ and its connecting pathways to the visual cortex. Significant vision loss arises from dysfunction in the retina, the photosensitive tissue at the eye posterior that achieves phototransduction of light to form images in the brain. Retinal regenerative medicine has embraced microfluidic technologies to manipulate stem-like cells for transplantation therapies, where de/differentiated cells are introduced within adult tissue to replace dysfunctional or damaged neurons. Microfluidic systems coupled with stem cell biology and biomaterials have produced exciting advances to restore vision. The current article reviews contemporary microfluidic technologies and microfluidics-enhanced bioassays, developed to interrogate cellular responses to adult retinal cues. The focus is on applications of microfluidics and microscale assays within mammalian sensory retina, or neuro retina, comprised of five types of retinal neurons (photoreceptors, horizontal, bipolar, amacrine, retinal ganglion) and one neuroglia (Müller), but excludes the non-sensory, retinal pigmented epithelium.

Comparative lipidomic analysis of mammalian retinal ganglion cells and Müller glia in situ and in vitro using High-Resolution Imaging Mass Spectrometry

In order to better understand retinal physiology, alterations to which underlie some ocular diseases, we set out to establish the lipid signature of two fundamental cell types in the retina, Müller Glia and Retinal Ganglion Cells (RGCs). Moreover, we compared the lipid signature of these cells in sections (in situ), as well as after culturing the cells and isolating their cell membranes (in vitro). The lipidome of Müller glia and RGCs was analyzed in porcine retinal sections using Matrix Assisted Laser Desorption Ionization Imaging Mass Spectrometry (MALDI-IMS). Isolated membranes, as well as whole cells from primary cell cultures of RGCs and Müller glia, were printed onto glass slides using a non-contact microarrayer (Nano Plotter), and a LTQ-Orbitrap XL analyzer was used to scan the samples in negative ion mode, thereafter identifying the RGCs and Müller cells immunohistochemically. The spectra acquired were aligned and normalized against the total ion current, and a statistical analysis was carried out to select the lipids specific to each cell type in the retinal sections and microarrays. The peaks of interest were identified by MS/MS analysis. A cluster analysis of the MS spectra obtained from the retinal sections identified regions containing RGCs and Müller glia, as confirmed by immunohistochemistry in the same sections. The relative density of certain lipids differed significantly (p-value ≤ 0.05) between the areas containing Müller glia and RGCs. Likewise, different densities of lipids were evident between the RGC and Müller glia cultures in vitro. Finally, a comparative analysis of the lipid profiles in the retinal sections and microarrays identified six peaks that corresponded to a collection of 10 lipids characteristic of retinal cells. These lipids were identified by MS/MS. The analyses performed on the RGC layer of the retina, on RGCs in culture and using cell membrane microarrays of RGCs indicate that the lipid composition of the retina detected in sections is preserved in primary cell cultures. Specific lipid species were found in RGCs and Müller glia, allowing both cell types to be identified by a lipid fingerprint. Further studies into these specific lipids and of their behavior in pathological conditions may well help identify novel therapeutic targets for ocular diseases.

Mechanisms behind Retinal Ganglion Cell Loss in Diabetes and Therapeutic Approach

Diabetes produces several changes in the body triggered by high glycemia. Some of these changes include altered metabolism, structural changes in blood vessels and chronic inflammation. The eye and particularly the retinal ganglion cells (RGCs) are not spared, and the changes eventually lead to cell loss and visual function impairment. Understanding the mechanisms resulting in RGC damage and loss from diabetic retinopathy is essential to find an effective treatment. This review focuses mainly on the signaling pathways and molecules involved in RGC loss and the potential therapeutic approaches for the prevention of this cell death. Throughout the manuscript it became evident that multiple factors of different kind are responsible for RGC damage. This shows that new therapeutic agents targeting several factors at the same time are needed. Alpha-1 antitrypsin as an anti-inflammatory agent may become a suitable option for the treatment of RGC loss because of its beneficial interaction with several signaling pathways involved in RGC injury and inflammation. In conclusion, alpha-1 antitrypsin may become a potential therapeutic agent for the treatment of RGC loss and processes behind diabetic retinopathy.

Neuroprotective Strategies for Retinal Ganglion Cell Degeneration: Current Status and Challenges Ahead

The retinal ganglion cells (RGCs) are the output cells of the retina into the brain. In mammals, these cells are not able to regenerate their axons after optic nerve injury, leaving the patients with optic neuropathies with permanent visual loss. An effective RGCs-directed therapy could provide a beneficial effect to prevent the progression of the disease. Axonal injury leads to the functional loss of RGCs and subsequently induces neuronal death, and axonal regeneration would be essential to restore the neuronal connectivity, and to reestablish the function of the visual system. The manipulation of several intrinsic and extrinsic factors has been proposed in order to stimulate axonal regeneration and functional repairing of axonal connections in the visual pathway. However, there is a missing point in the process since, until now, there is no therapeutic strategy directed to promote axonal regeneration of RGCs as a therapeutic approach for optic neuropathies.

The mito-QC Reporter for Quantitative Mitophagy Assessment in Primary Retinal Ganglion Cells and Experimental Glaucoma Models

Mitochondrial damage plays a prominent role in glaucoma. The only way cells can degrade whole mitochondria is via autophagy, in a process called mitophagy. Thus, studying mitophagy in the context of glaucoma is essential to understand the disease. Up to date limited tools are available for analyzing mitophagy in vivo. We have taken advantage of the mito-QC reporter, a recently generated mouse model that allows an accurate mitophagy assessment to fill this gap. We used primary RGCs and retinal explants derived from mito-QC mice to quantify mitophagy activation in vitro and ex vivo. We also analyzed mitophagy in retinal ganglion cells (RGCs), in vivo, using different mitophagy inducers, as well as after optic nerve crush (ONC) in mice, a commonly used surgical procedure to model glaucoma. Using mito-QC reporter we quantified mitophagy induced by several known inducers in primary RGCs in vitro, ex vivo and in vivo. We also found that RGCs were rescued from some glaucoma relevant stress factors by incubation with the iron chelator deferiprone (DFP). Thus, the mito-QC reporter-based model is a valuable tool for accurately analyzing mitophagy in the context of glaucoma.

Optimization of a Method to Isolate and Culture Adult Porcine, Rats and Mice Müller Glia in Order to Study Retinal Diseases

Müller cells are the predominant glial elements in the retina, extending vertically across this structure, and they fulfill a wealth support roles that are critical for neurons. Alterations to the behavior and phenotype of Müller glia are often seen in animal models of retinal degeneration and in retinal tissue from patients with a variety of retinal disorders. Thus, elucidating the mechanisms underlying the development of retinal diseases would help better understand the cellular processes involved in such pathological changes. Studies into Müller cell activity in vitro have been hindered by the difficulty in obtaining pure cell populations and the tendency of these cells to rapidly differentiate in culture. Most protocols currently used to isolate Müller glia use neonatal or embryonic tissue but here, we report an optimized protocol that facilitates the reliable and straightforward isolation and culture of Müller cells from adult pigs, rats and mice. The protocol described here provides an efficient method for the rapid isolation of adult mammalian Müller cells, which represents a reliable platform to study therapeutic targets and to test the effects of drugs that might combat retinal diseases.