Nitrosative Stress in Retinal Pathologies: Review

Diabetic retinopathy: New concepts of screening, monitoring, and interventions

The science of diabetes care has progressed to provide a better understanding of the oxidative and inflammatory lesions and pathophysiology of the neurovascular unit within the retina (and brain) that occur early in diabetes, even prediabetes. Screening for retinal structural abnormalities, has traditionally been performed by fundus examination or color fundus photography; however, these imaging techniques detect the disease only when there are sufficient lesions, predominantly hemorrhagic, that are recognized to occur late in the disease process after significant neuronal apoptosis and atrophy, as well as microvascular occlusion with alterations in vision. Thus, interventions have been primarily oriented toward the later-detected stages, and clinical trials, while demonstrating a slowing of the disease progression, demonstrate minimal visual improvement and modest reduction in the continued loss over prolonged periods. Similarly, vision measurement utilizing charts detects only problems of visual function late, as the process begins most often parafoveally with increasing number and progressive expansion, including into the fovea. While visual acuity has long been used to define endpoints of visual function for such trials, current methods reviewed herein are found to be imprecise. We review improved methods of testing visual function and newer imaging techniques with the recommendation that these must be utilized to discover and evaluate the injury earlier in the disease process, even in the prediabetic state. This would allow earlier therapy with ocular as well as systemic pharmacologic treatments that lower the and neuro-inflammatory processes within eye and brain. This also may include newer, micropulsed laser therapy that, if applied during the earlier cascade, should result in improved and often normalized retinal function without the adverse treatment effects of standard photocoagulation therapy.

Nitric Oxide Binding Geometry in Heme-Proteins: Relevance for Signal Transduction

Nitric oxide (NO) synthesis, signaling, and scavenging is associated to relevant physiological and pathological events. In all tissues and organs, NO levels and related functions are regulated at different levels, with heme proteins playing pivotal roles. Here, we focus on the structural changes related to the different binding modes of NO to heme-Fe(II), as well as the modulatory effects of this diatomic messenger on heme-protein functions. Specifically, the ability of heme proteins to bind NO at either the distal or proximal side of the heme and the transient interchanging of the binding site is reported. This sheds light on the regulation of O2 supply to tissues with high metabolic activity, such as the retina, where a precise regulation of blood flow is necessary to meet the demand of nutrients.

Protective Effect of Probiotics against Pseudomonas aeruginosa Infection of Human Corneal Epithelial Cells

Probiotic therapy needs consideration as an alternative strategy to prevent and possibly treat corneal infection. This study aimed to assess the preventive effect of Lactobacillus reuteri and Bifidobacterium longum subsp. infantis on reducing the infection of human corneal epithelial (HCE) cells caused by Pseudomonas aeruginosa. The probiotics' preventive effect against infection was evaluated in cell monolayers pretreated with each probiotic 1 h and 24 h prior to P. aeruginosa challenge followed by 1 h and 24 h of growth in combination. Cell adhesion, cytotoxicity, anti-inflammatory, and antinitrosative activities were evaluated. L. reuteri and B. longum adhered to HCE cells, preserved occludin tight junctions' integrity, and increased mucin production on a SkinEthicTM HCE model. Pretreatment with L. reuteri or B. longum significantly protected HCE cells from infection at 24 h, increasing cell viability at 110% (110.51 ± 5.15; p ≤ 0.05) and 137% (137.55 ± 11.97; p ≤ 0.05), respectively. Each probiotic showed anti-inflammatory and antinitrosative activities, reducing TNF-α level (p ≤ 0.001) and NOx amount (p ≤ 0.001) and reestablishing IL-10 level (p ≤ 0.001). In conclusion, this study demonstrated that L. reuteri and B. longum exert protective effects in the context of corneal infection caused by P. aeruginosa by restoring cell viability and modulating inflammatory cytokine release.

Role of mitophagy in ocular neurodegeneration

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

Nitric oxide: an old drug but with new horizons in ophthalmology-a narrative review

Background and Objective

Based on basic knowledge and prior research on nitric oxide (NO), the potential of NO for treating eye diseases is reviewed, and the possibility of NO-based eye drops in clinical practice and the future potential of NO in ophthalmology are discussed.

Methods

A PubMed search was performed for English-language original reports and reviews using the following key words: nitric oxide, eye, ocular, and drug.

Key Content and Findings

NO is synthesized in the human body by NO synthase (NOS) from L-arginine or through enzyme-dependent reduction of dietary nitrate. Three types of NOS (eNOS, nNOS, and iNOS) are abundantly expressed in the eye under normal physiologic or pathologic conditions. The biological effect of NO in the eye is dose dependent. Low intraocular NO concentrations, produced by eNOS or nNOS, have various cellular effects, including vasodilation, intraocular pressure (IOP) regulation, and neuroprotection. iNOS induced under pathologic ocular conditions produces high NO concentrations in the local environment and mediates tissue inflammation, ocular cell apoptosis, and neurodegeneration. In particular, increased iNOS has been reported in glaucoma and retinal ischemic or degenerative diseases. NO plays a vital role in ocular injury. NO can facilitate ocular surface wound healing while eradicating pathogens such as bacteria and Acanthamoeba in chemical burns or infectious keratitis. Furthermore, NO has antifibrotic activity via the cyclic guanosine monophosphate (cGMP) signaling pathway. NO causes smooth muscle relaxation, which can be used to inhibit myopia progression in children. NO can be a stem cell modulator and may help in treating ocular stem cell disorders.

Conclusions

Because of its diverse biologic effects, NO can be a key player in regulating ocular inflammation in various ocular diseases, aiding ocular surface wound healing, controlling IOP in glaucoma, alleviating retinal disease, and suppressing myopia progression. Although there remain limitations to the effective use of highly unstable state, gaseous NO, the role of NO in the field of ophthalmology can be greatly expanded through the development of novel NO donors and effective delivery platforms.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

Toxic External Exposure Leading to Ocular Surface Injury

The surface of the eye is directly exposed to the external environment, protected only by a thin tear film, and may therefore be damaged by contact with ambient particulate matter, liquids, aerosols, or vapors. In the workplace or home, the eye is subject to accidental or incidental exposure to cleaning products and pesticides. Organic matter may enter the eye and cause infection. Ocular surface damage can trigger a range of symptoms such as itch, discharge, hyperemia, photophobia, blurred vision, and foreign body sensation. Toxin exposure can be assessed clinically in multiple ways, including via measurement of tear production, slit-lamp examination, corneal staining, and conjunctival staining. At the cellular level, environmental toxins can cause oxidative damage, apoptosis of corneal and conjunctival cells, cell senescence, and impaired motility. Outcomes range from transient and reversible with complete healing to severe and sight-compromising structural changes. Classically, evaluation of tolerance and safety was carried out using live animal testing; however, new in vitro and computer-based, in silico modes are superseding the gold standard Draize test. This review examines how environmental features such as pollutants, temperature, and seasonality affect the ocular surface. Chemical burns to the eye are considered, and approaches to protect the ocular surface are detailed.

Effects of Resveratrol on Vascular Function in Retinal Ischemia-Reperfusion Injury

Ischemia-reperfusion (I/R) events are involved in the development of various ocular pathologies, e.g., retinal artery or vein occlusion. We tested the hypothesis that resveratrol is protective against I/R injury in the murine retina. Intraocular pressure (IOP) was elevated in anaesthetized mice to 110 mm Hg for 45 min via a micropipette placed in the anterior chamber to induce ocular ischemia. In the fellow eye, which served as control, IOP was kept at a physiological level. One group received resveratrol (30 mg/kg/day p.o. once daily) starting one day before the I/R event, whereas the other group of mice received vehicle solution only. On day eight after the I/R event, mice were sacrificed and retinal wholemounts were prepared and immuno-stained using a Brn3a antibody to quantify retinal ganglion cells. Reactivity of retinal arterioles was measured in retinal vascular preparations using video microscopy. Reactive oxygen species (ROS) and nitrogen species (RNS) were quantified in ocular cryosections by dihydroethidium and anti-3-nitrotyrosine staining, respectively. Moreover, hypoxic, redox and nitric oxide synthase gene expression was quantified in retinal explants by PCR. I/R significantly diminished retinal ganglion cell number in vehicle-treated mice. Conversely, only a negligible reduction in retinal ganglion cell number was observed in resveratrol-treated mice following I/R. Endothelial function and autoregulation were markedly reduced, which was accompanied by increased ROS and RNS in retinal blood vessels of vehicle-exposed mice following I/R, whereas resveratrol preserved vascular endothelial function and autoregulation and blunted ROS and RNS formation. Moreover, resveratrol reduced I/R-induced mRNA expression for the prooxidant enzyme, nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2). Our data provide evidence that resveratrol protects from I/R-induced retinal ganglion cell loss and endothelial dysfunction in the murine retina by reducing nitro-oxidative stress possibly via suppression of NOX2 upregulation.

Nitrite Reductase Activity of Ferrous Nitrobindins: A Comparative Study

Nitrobindins (Nbs) are all-β-barrel heme proteins spanning from bacteria to Homo sapiens. They inactivate reactive nitrogen species by sequestering NO, converting NO to HNO2, and promoting peroxynitrite isomerization to NO3−. Here, the nitrite reductase activity of Nb(II) from Mycobacterium tuberculosis (Mt-Nb(II)), Arabidopsis thaliana (At-Nb(II)), Danio rerio (Dr-Nb(II)), and Homo sapiens (Hs-Nb(II)) is reported. This activity is crucial for the in vivo production of NO, and thus for the regulation of blood pressure, being of the utmost importance for the blood supply to poorly oxygenated tissues, such as the eye retina. At pH 7.3 and 20.0 °C, the values of the second-order rate constants (i.e., kon) for the reduction of NO2− to NO and the concomitant formation of nitrosylated Mt-Nb(II), At-Nb(II), Dr-Nb(II), and Hs-Nb(II) (Nb(II)-NO) were 7.6 M−1 s−1, 9.3 M−1 s−1, 1.4 × 101 M−1 s−1, and 5.8 M−1 s−1, respectively. The values of kon increased linearly with decreasing pH, thus indicating that the NO2−-based conversion of Nb(II) to Nb(II)-NO requires the involvement of one proton. These results represent the first evidence for the NO2 reductase activity of Nbs(II), strongly supporting the view that Nbs are involved in NO metabolism. Interestingly, the nitrite reductase reactivity of all-β-barrel Nbs and of all-α-helical globins (e.g., myoglobin) was very similar despite the very different three-dimensional fold; however, differences between all-α-helical globins and all-β-barrel Nbs suggest that nitrite reductase activity appears to be controlled by distal steric barriers, even though a more complex regulatory mechanism can be also envisaged.

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.

The Balancing of Peroxynitrite Detoxification between Ferric Heme-Proteins and CO2: The Case of Zebrafish Nitrobindin

Nitrobindins (Nbs) are all-β-barrel heme proteins and are present in prokaryotes and eukaryotes. Although their function(s) is still obscure, Nbs trap NO and inactivate peroxynitrite. Here, the kinetics of peroxynitrite scavenging by ferric Danio rerio Nb (Dr-Nb(III)) in the absence and presence of CO₂ is reported. The Dr-Nb(III)-catalyzed scavenging of peroxynitrite is facilitated by a low pH, indicating that the heme protein interacts preferentially with peroxynitrous acid, leading to the formation of nitrate (~91%) and nitrite (~9%). The physiological levels of CO₂ dramatically facilitate the spontaneous decay of peroxynitrite, overwhelming the scavenging activity of Dr-Nb(III). The effect of Dr-Nb(III) on the peroxynitrite-induced nitration of L-tyrosine was also investigated. Dr-Nb(III) inhibits the peroxynitrite-mediated nitration of free L-tyrosine, while, in the presence of CO₂, Dr-Nb(III) does not impair nitro-L-tyrosine formation. The comparative analysis of the present results with data reported in the literature indicates that, to act as efficient peroxynitrite scavengers in vivo, i.e., in the presence of physiological levels of CO₂, the ferric heme protein concentration must be higher than 10⁻⁴ M. Thus, only the circulating ferric hemoglobin levels appear to be high enough to efficiently compete with CO₂/HCO₃⁻ in peroxynitrite inactivation. The present results are of the utmost importance for tissues, like the eye retina in fish, where blood circulation is critical for adaptation to diving conditions.

Oxidative Stress Implication in Retinal Diseases-A Review

Oxidative stress (OS) refers to an imbalance between free radicals (FRs), namely highly reactive molecules normally generated in our body by several pathways, and intrinsic antioxidant capacity. When FR levels overwhelm intrinsic antioxidant defenses, OS occurs, inducing a series of downstream chemical reactions. Both reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced by numerous chemical reactions that take place in tissues and organs and are then eliminated by antioxidant molecules. In particular, the scientific literature focuses more on ROS participation in the pathogenesis of diseases than on the role played by RNS. By its very nature, the eye is highly exposed to ultraviolet radiation (UVR), which is directly responsible for increased OS. In this review, we aimed to focus on the retinal damage caused by ROS/RNS and the related retinal pathologies. A deeper understanding of the role of oxidative and nitrosative stress in retinal damage is needed in order to develop targeted therapeutic interventions to slow these pathologies.

Pump proton inhibitors display anti-tumour potential in glioma

OBJECTIVES

Glioma is one of the most aggressive brain tumours with poor overall survival despite advanced technology in surgical resection, chemotherapy and radiation. Progression and recurrence are the hinge causes of low survival. Our aim is to explain the concrete mechanism in the proliferation and progression of tumours based on tumour microenvironment (TME). The main purpose is to illustrate the mechanism of proton pump inhibitors (PPIs) in affecting acidity, hypoxia, oxidative stress, inflammatory response and autophagy based on the TME to induce apoptosis and enhance the sensitivity of chemoradiotherapy.

FINDINGS

TME is the main medium for tumour growth and progression. Acidity, hypoxia, inflammatory response, autophagy, angiogenesis and so on are the main causes of tumour progress. PPIs, as a common clinical drug to inhibit gastric acid secretion, have the advantages of fast onset, long action time and small adverse reactions. Nowadays, several kinds of literature highlight the potential of PPIs in inhibiting tumour progression. However, long-term use of PPIs alone also has obvious side effects. Therefore, till now, how to apply PPIs to promote the effect of radio-chemotherapy and find the concrete dose and concentration of combined use are novel challenges.

CONCLUSIONS

PPIs display the potential in enhancing the sensitivity of chemoradiotherapy to defend against glioma based on TME. In the clinic, it is also necessary to explore specific concentrations and dosages in synthetic applications.

Kinins and Their Receptors as Potential Therapeutic Targets in Retinal Pathologies

The kallikrein-kinin system (KKS) contributes to retinal inflammation and neovascularization, notably in diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Bradykinin type 1 (B1R) and type 2 (B2R) receptors are G-protein-coupled receptors that sense and mediate the effects of kinins. While B2R is constitutively expressed and regulates a plethora of physiological processes, B1R is almost undetectable under physiological conditions and contributes to pathological inflammation. Several KKS components (kininogens, tissue and plasma kallikreins, and kinin receptors) are overexpressed in human and animal models of retinal diseases, and their inhibition, particularly B1R, reduces inflammation and pathological neovascularization. In this review, we provide an overview of the KKS with emphasis on kinin receptors in the healthy retina and their detrimental roles in DR and AMD. We highlight the crosstalk between the KKS and the renin–angiotensin system (RAS), which is known to be detrimental in ocular pathologies. Targeting the KKS, particularly the B1R, is a promising therapy in retinal diseases, and B1R may represent an effector of the detrimental effects of RAS (Ang II-AT1R).

Sex and Age-Related Differences in Neuroinflammation and Apoptosis in Balb/c Mice Retina Involve Resolvin D1

(1) Background: The pro-resolving lipid mediator Resolvin D1 (RvD1) has already shown protective effects in animal models of diabetic retinopathy. This study aimed to investigate the retinal levels of RvD1 in aged (24 months) and younger (3 months) Balb/c mice, along with the activation of macro- and microglia, apoptosis, and neuroinflammation. (2) Methods: Retinas from male and female mice were used for immunohistochemistry, immunofluorescence, transmission electron microscopy, Western blotting, and enzyme-linked immunosorbent assays. (3) Results: Endogenous retinal levels of RvD1 were reduced in aged mice. While RvD1 levels were similar in younger males and females, they were markedly decreased in aged males but less reduced in aged females. Both aged males and females showed a significant increase in retinal microglia activation compared to younger mice, with a more marked reactivity in aged males than in aged females. The same trend was shown by astrocyte activation, neuroinflammation, apoptosis, and nitrosative stress, in line with the microglia and Müller cell hypertrophy evidenced in aged retinas by electron microscopy. (4) Conclusions: Aged mice had sex-related differences in neuroinflammation and apoptosis and low retinal levels of endogenous RvD1.

Nitric Oxide Interaction with the Eye

Nitric oxide (NO) is acknowledged as a vital intercellular messenger in multiple systems in the body. Medicine has focused on its functions and therapeutic applications for decades, especially in cardiovascular and nervous systems, and its role in immunological responses. This review was composed to demonstrate the prevalence of NO in components of the ocular system, including corneal cells and multiple cells in the retina. It discussed NO's assistance during the immune, inflammation and wound-healing processes. NO is identified as a vascular endothelial relaxant that can alter the choroidal blood flow and prompt or suppress vascular changes in age-related macular degeneration and diabetes, as well as the blood supply to the optic nerve, possibly influencing the progression of glaucoma. It will provide a deeper understanding of the role of NO in ocular homeostasis, the delicate balance between overproduction or underproduction and the effect on the processes from aqueous outflow and subsequent intraocular pressure to axial elongation and the development of myopia. This review also recognized the research and investigation of therapies being developed to target the NO complex and treat various ocular diseases.

Spinach Methanolic Extract Attenuates the Retinal Degeneration in Diabetic Rats

It has been suggested that spinach methanolic extract (SME) inhibits the formation of advanced glycation end products (AGEs), which are increased during diabetes progression, so it is important to know if SME has beneficial effects in the diabetic retina. In this study, in vitro assays showed that SME inhibits glycation, carbonyl groups formation, and reduced-thiol groups depletion in bovine serum albumin incubated either reducing sugars or methylglyoxal. The SME effect in retinas of streptozotocin-induced diabetic rats (STZ) was also studied (n = 10) in the normoglycemic group, STZ, STZ rats treated with SME, and STZ rats treated with aminoguanidine (anti-AGEs reference group) during 12 weeks. The retina was sectioned and immunostained for Nε-carboxymethyl lysine (CML), receptor RAGE, NADPH-Nox4, inducible nitric oxide synthase (iNOS), 3-nitrotyrosine (NT), nuclear NF-κB, vascular endothelial growth factor (VEGF), glial fibrillary acidic protein (GFAP), S100B protein, and TUNEL assay. Lipid peroxidation was determined in the whole retina by malondialdehyde (MDA) levels. The results showed that in the diabetic retina, SME reduced the CML-RAGE co-localization, oxidative stress (NOX4, iNOS, NT, MDA), inflammation (NF-κB, VEGF, S100B, GFAP), and apoptosis (p < 0.05). Therefore, SME could attenuate the retinal degeneration by inhibition of CML-RAGE interaction.

Oxidative and Nitrosative Stress in Age-Related Macular Degeneration: A Review of Their Role in Different Stages of Disease

Although the exact pathogenetic mechanisms leading to age-related macular degeneration (AMD) have not been clearly identified, oxidative damage in the retina and choroid due to an imbalance between local oxidants/anti-oxidant systems leading to chronic inflammation could represent the trigger event. Different in vitro and in vivo models have demonstrated the involvement of reactive oxygen species generated in a highly oxidative environment in the development of drusen and retinal pigment epithelium (RPE) changes in the initial pathologic processes of AMD; moreover, recent evidence has highlighted the possible association of oxidative stress and neovascular AMD. Nitric oxide (NO), which is known to play a key role in retinal physiological processes and in the regulation of choroidal blood flow, under pathologic conditions could lead to RPE/photoreceptor degeneration due to the generation of peroxynitrite, a potentially cytotoxic tyrosine-nitrating molecule. Furthermore, the altered expression of the different isoforms of NO synthases could be involved in choroidal microvascular changes leading to neovascularization. The purpose of this review was to investigate the different pathways activated by oxidative/nitrosative stress in the pathogenesis of AMD, focusing on the mechanisms leading to neovascularization and on the possible protective role of anti-vascular endothelial growth factor agents in this context.

Impaired TRPV4-eNOS signaling in trabecular meshwork elevates intraocular pressure in glaucoma

Primary Open Angle Glaucoma (POAG) is the most common form of glaucoma that leads to irreversible vision loss. Dysfunction of trabecular meshwork (TM) tissue, a major regulator of aqueous humor (AH) outflow resistance, is associated with intraocular pressure (IOP) elevation in POAG. However, the underlying pathological mechanisms of TM dysfunction in POAG remain elusive. In this regard, transient receptor potential vanilloid 4 (TRPV4) cation channels are known to be important Ca2+ entry pathways in multiple cell types. Here, we provide direct evidence supporting Ca2+ entry through TRPV4 channels in human TM cells and show that TRPV4 channels in TM cells can be activated by increased fluid flow/shear stress. TM-specific TRPV4 channel knockout in mice elevated IOP, supporting a crucial role for TRPV4 channels in IOP regulation. Pharmacological activation of TRPV4 channels in mouse eyes also improved AH outflow facility and lowered IOP. Importantly, TRPV4 channels activated endothelial nitric oxide synthase (eNOS) in TM cells, and loss of eNOS abrogated TRPV4-induced lowering of IOP. Remarkably, TRPV4-eNOS signaling was significantly more pronounced in TM cells compared to Schlemm's canal cells. Furthermore, glaucomatous human TM cells show impaired activity of TRPV4 channels and disrupted TRPV4-eNOS signaling. Flow/shear stress activation of TRPV4 channels and subsequent NO release were also impaired in glaucomatous primary human TM cells. Together, our studies demonstrate a central role for TRPV4-eNOS signaling in IOP regulation. Our results also provide evidence that impaired TRPV4 channel activity in TM cells contributes to TM dysfunction and elevated IOP in glaucoma.

Retinal damage in a new model of hyperglycemia induced by high-sucrose diets

Loss of retinal neurons may precede clinical signs of diabetic retinopathy (DR). We studied for the first time the effects of hyperglycemia on the visual system of the fruit fly Drosophila melanogaster to characterize a model for glucose-induced retinal neurodegeneration, thus complementing more traditional vertebrate systems. Adult flies were fed with increased high-sucrose regimens which did not modify the locomotion ability, muscle phenotype and mobility after 10 days. The increased availability of dietary sucrose induced hyperglycemia and phosphorylation of Akt in fat tissue, without significant effects on adult growth and viability, consistent with the early phase of insulin signaling and a low impact on the overall metabolic profile of flies at short term. Noteworthy, high-sucrose diets significantly decreased Drosophila responsiveness to the light as a consequence of vision defects. Hyperglycemia did not alter the gross anatomical architecture of the external eye phenotype although a progressive damage of photosensitive units was observed. Appreciable levels of cleaved caspase 3 and nitrotyrosine were detected in the internal retina network as well as punctate staining of Light-Chain 3 and p62, and accumulated autophagosomes, indicating apoptotic features, peroxynitrite formation and autophagy turnover defects. In summary, our results in Drosophila support the view that hyperglycemia induced by high-sucrose diets lead to eye defects, apoptosis/autophagy dysregulation, oxidative stress, and visual dysfunctions which are evolutionarily conserved, thus offering a meaningful opportunity of using a simple in vivo model to study the pathophysiology of neuroretinal alterations that develop in patients at the early stages of DR.

Gradual Increase in Environmental Light Intensity Induces Oxidative Stress and Inflammation and Accelerates Retinal Neurodegeneration

Purpose

Retinitis pigmentosa (RP) is a blinding neurodegenerative disease of the retina that can be affected by many factors. The present study aimed to analyze the effect of different environmental light intensities in rd10 mice retina.

Methods

C57BL/6J and rd10 mice were bred and housed under three different environmental light intensities: scotopic (5 lux), mesopic (50 lux), and photopic (300 lux). Visual function was studied using electroretinography and optomotor testing. The structural and morphological integrity of the retinas was evaluated by optical coherence tomography imaging and immunohistochemistry. Additionally, inflammatory processes and oxidative stress markers were analyzed by flow cytometry and western blotting.

Results

When the environmental light intensity was higher, retinal function decreased in rd10 mice and was accompanied by light-dependent photoreceptor loss, followed by morphological alterations, and synaptic connectivity loss. Moreover, light-dependent retinal degeneration was accompanied by an increased number of inflammatory cells, which became more activated and phagocytic, and by an exacerbated reactive gliosis. Furthermore, light-dependent increment in oxidative stress markers in rd10 mice retina pointed to a possible mechanism for light-induced photoreceptor degeneration.

Conclusions

An increase in rd10 mice housing light intensity accelerates retinal degeneration, activating cell death, oxidative stress pathways, and inflammatory cells. Lighting intensity is a key factor in the progression of retinal degeneration, and standardized lighting conditions are advisable for proper analysis and interpretation of experimental results from RP animal models, and specifically from rd10 mice. Also, it can be hypothesized that light protection could be an option to slow down retinal degeneration in some cases of RP.

An allosteric interleukin-1 receptor modulator mitigates inflammation and photoreceptor toxicity in a model of retinal degeneration

BACKGROUND

Inflammation and particularly interleukin-1β (IL-1β), a pro-inflammatory cytokine highly secreted by activated immune cells during early AMD pathological events, contribute significantly to retinal neurodegeneration. Here, we identify specific cell types that generate IL-1β and harbor the IL-1 receptor (IL-1R) and pharmacologically validate IL-1β's contribution to neuro-retinal degeneration using the IL-1R allosteric modulator composed of the amino acid sequence rytvela (as well as the orthosteric antagonist, Kineret) in a model of blue light-induced retinal degeneration.

METHODS

Mice were exposed to blue light for 6 h and sacrificed 3 days later. Mice were intraperitoneally injected with rytvela, Kineret, or vehicle twice daily for 3 days. The inflammatory markers F4/80, NLRP3, caspase-1, and IL-1β were assessed in the retinas. Single-cell RNA sequencing was used to determine the cell-specific expression patterns of retinal Il1b and Il1r1. Macrophage-induced photoreceptor death was assessed ex vivo using retinal explants co-cultured with LPS-activated bone marrow-derived macrophages. Photoreceptor cell death was evaluated by the TUNEL assay. Retinal function was assessed by flash electroretinography.

RESULTS

Blue light markedly increased the mononuclear phagocyte recruitment and levels of inflammatory markers associated with photoreceptor death. Co-localization of NLRP3, caspase-1, and IL-1β with F4/80⁺ mononuclear phagocytes was clearly detected in the subretinal space, suggesting that these inflammatory cells are the main source of IL-1β. Single-cell RNA sequencing confirmed the immune-specific expression of Il1b and notably perivascular macrophages in light-challenged mice, while Il1r1 expression was found primarily in astrocytes, bipolar, and vascular cells. Retinal explants co-cultured with LPS/ATP-activated bone marrow-derived macrophages displayed a high number of TUNEL-positive photoreceptors, which was abrogated by rytvela treatment. IL-1R antagonism significantly mitigated the inflammatory response triggered in vivo by blue light exposure, and rytvela was superior to Kineret in preserving photoreceptor density and retinal function.

CONCLUSION

These findings substantiate the importance of IL-1β in neuro-retinal degeneration and revealed specific sources of Il1b from perivascular MPs, with its receptor Ilr1 being separately expressed on surrounding neuro-vascular and astroglial cells. They also validate the efficacy of rytvela-induced IL-1R modulation in suppressing detrimental inflammatory responses and preserving photoreceptor density and function in these conditions, reinforcing the rationale for clinical translation.

Ex-Vivo Trans-Corneal and Trans-Scleral Diffusion Studies with Ocular Formulations of Glutathione as an Antioxidant Treatment for Ocular Diseases

Exposure to sunlight and contact with atmospheric oxygen makes the eye particularly susceptible to oxidative stress, which can potentially produce cellular damage. In physiological conditions, there are several antioxidant defense mechanisms within the eye. Glutathione (GSH) is the most important antioxidant in the eye; GSH deficit has been linked to several ocular pathologies. The aim of this study was to explore the potential for newly developed formulations allowing controlled delivery of antioxidants such as GSH and vitamin C (Vit C) directly to the eye. We have investigated the stability of antioxidants in aqueous solution and assessed ex-vivo the diffusion of GSH through two ocular membranes, namely cornea and sclera, either in solution or included in a semisolid insert. We have also carried out the hen’s egg-chlorioallantoic membrane test (HET-CAM) to evaluate the ocular irritancy of the different antioxidant solutions. Our results showed that GSH is stable for up to 30 days at 4 °C in darkness and it is not an irritant to the eye. The diffusion studies revealed that the manufactured formulation, a semisolid insert containing GSH, could deliver this tripeptide directly to the eye in a sustained manner.

Relationship between Oxidative Stress Biomarkers and Visual Field Progression in Patients with Primary Angle Closure Glaucoma

Purpose

To investigate the serum changes of oxidative stress markers and the relationship between these factors and visual field (VF) progression in patients with primary angle closure glaucoma (PACG).

Methods

A case-control and a prospective cohort study. A total of 94 patients with PACG and 89 normal controls were enrolled. Furthermore, 94 PACG subjects were followed up for at least two years (once every six months). All participants were evaluated for serum levels of superoxide dismutase (SOD), total antioxidant status (TAS), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), glutathione peroxidase, glutathione reductase, and detailed eye and systematic examination. Binary logistic regression analysis and Cox regression analysis were performed.

Results

The serum levels of SOD and TAS in the PACG group were significantly lower than those in the control group (p < 0.001). Meanwhile, PACG subjects had significantly higher levels of MDA and H₂O₂ than the normal control subjects (p < 0.001). Serum levels of TAS (OR = 0.773, 95%CI = 0.349 − 0.714, p < 0.001), SOD (OR = 0.975, 95%CI = 0.955 − 0.995, p < 0.001), MDA (OR = 1.155, 95%CI = 1.080 − 1.235, p < 0.001), and H₂O₂ (OR = 1.216, 95%CI = 1.142 − 1.295, p < 0.001) were independent risk/protective factors for PACG. TAS levels (HR = 0.041, 95%CI = 0.008–0.218, p < 0.001), SOD levels (HR = 0.983, 95%CI = 0.971–0.994, p = 0.003), and MDA levels (HR = 1.010, 95%CI = 1.001–1.018, p = 0.015) at baseline were associated with visual field progression. Kaplan–Meier curves reveal that patients with TAS < 0.95/SOD < 143/MDA > 12 had a significantly higher percentage of PACG progression (p < 0.05).

Conclusions

Decreased levels of TAS and SOD as well as increased levels of MDA at baseline were associated with VF progression in patients with PACG. These findings suggest that oxidative stress was involved in the onset and development of PACG.

Metformin Protects ARPE-19 Cells from Glyoxal-Induced Oxidative Stress

The protective effects and mechanisms of metformin against oxidative stress were evaluated both in vivo and in vitro. ARPE-19 cells comprised the normal group, the glyoxal-treated group (0.5 mM glyoxal), and the glyoxal+metformin group (0.5 mM glyoxal and 0.1 mM metformin). In the in vitro model, differences in cell viability, ROS production, NO products, cellular apoptosis, and the expressions of phospho-AMPKα, total-AMPKα, Sirt1, Nrf2, TXNIP, ZO-1, and Occludin were assessed. In the glyoxal-treated group, cell viability and NO production were decreased, while ROS production and cell apoptosis were increased (p < 0.05), compared with the control group. These changes were prevented by metformin treatment. Protein expressions of phospho-AMPKα, Sirt1, TXNIP, ZO-1, and Occludin, but not Nrf2, were decreased significantly in the glyoxal-treated group compared to normal controls. Metformin treatment significantly increased the above protein expressions and slightly increased TXNIP expression. Immunofluorescence showed that metformin prevented the glyoxal-induced, disorganized tight junctions in ARPE-19 cells. To confirm metformin's protection, Sprague-Dawley rats were injected intravenously with sodium iodate (SI) to induce oxidative stress in the retinal pigment epithelium (RPE). Metformin was then delivered intraperitoneally or intravitreally. One day and three days after SI and metformin treatments, the RPE-Bruch's membrane-choriocapillaris complex was isolated and immune-stained with ZO-1 antibodies. The morphology of the RPE showed enlarged cellular bodies and disorganized ZO-1 staining in SI-treated rats. Metformin treatment prevented these changes. The results indicated that metformin maintained the barrier functions of RPE cells both in vivo and in vitro. Metformin exerted its protection against oxidative stress possibly via activating AMPK/Sirt1 and increasing TXNIP. Metformin has been proposed as a candidate drug for age-related macular degeneration (AMD) by both preclinical and clinical studies. The cellular and animal models used in this study might be useful for the interpretation of the molecular mechanisms involved in the drug activity.

Technical brief: Direct, real-time electrochemical measurement of nitric oxide in ex vivo cultured human corneoscleral segments

Chronic elevation of intraocular pressure (IOP) is a major risk factor associated with primary open angle glaucoma (POAG), a common form of progressive optic neuropathy that can lead to debilitating loss of vision. Recent studies have identified the role of nitric oxide (NO) in the regulation of IOP, and as a result, several therapeutic ventures are currently targeting enhancement of NO signaling in the eye. Although a low level of NO is important for ocular physiology, excess exogenous NO can be detrimental. Therefore, the ability to directly measure NO in real time is essential for determining the role of NO signaling in glaucomatous pathophysiology. Historically, NO activity in human tissues has been determined by indirect methods that measure levels of NO metabolites (nitrate/nitrite) or downstream components of the NO signaling pathway (cGMP). In this proof-of-concept work, we assess the feasibility of direct, real-time measurement of NO in ex vivo cultured human corneoscleral segments using electrochemistry. A NO-selective electrode (ISO-NOPF200) paired to a free radical analyzer (TBR1025) was placed on the trabecular meshwork (TM) rim for real-time measurement of NO released from cells. Exogenous NO produced within cells was measured after treatment of corneoscleral segments with esterase-dependent NO-donor O2-acetoxymethylated diazeniumdiolate (DETA-NONOate/AM; 20 μM) and latanoprostene bunod (5-20 μM). A fluorescent NO-binding dye DAF-FM (4-Amino-5-methylamino- 2',7'-difluorofluorescein diacetate) was used for validation. A linear relationship was observed between the electric currents measured by the NO-sensing electrode and the NO standard concentrations, establishing a robust calibration curve. Treatment of ex vivo cultured human donor corneoscleral segments with DETA-NONOate/AM and latanoprostene bunod led to a significant increase in NO production compared with vehicle-treated controls, as detected electrochemically. Furthermore, the DAF-FM fluorescence intensity was higher in outflow pathway tissues of corneoscleral segments treated with DETA-NONOate/AM and latanoprostene bunod compared with vehicle-treated controls. In conclusion, these results demonstrate that NO-sensing electrodes can be used to directly measure NO levels in real time from the tissues of the outflow pathway.

Microglia Contribution to the Regulation of the Retinal and Choroidal Vasculature in Age-Related Macular Degeneration

The retina is a highly metabolically active tissue with high-level consumption of nutrients and oxygen. This high metabolic demand requires a properly developed and maintained vascular system. The retina is nourished by two systems: the central retinal artery that supplies the inner retina and the choriocapillaris that supplies the outer retina and retinal pigment epithelium (RPE). Pathological neovascularization, characterized by endothelial cell proliferation and new vessel formation, is a common hallmark in several retinal degenerative diseases, including age-related macular degeneration (AMD). A limited number of studies have suggested that microglia, the resident immune cells of the retina, have an important role not only in the pathology but also in the formation and physiology of the retinal vascular system. Here, we review the current knowledge on microglial interaction with the retinal vascular system under physiological and pathological conditions. To do so, we first highlight the role of microglial cells in the formation and maintenance of the retinal vasculature system. Thereafter, we discuss the molecular signaling mechanisms through which microglial cells contribute to the alterations in retinal and choroidal vasculatures and to the neovascularization in AMD.