Experimental Models of Glaucoma: A Powerful Translational Tool for the Future Development of New Therapies for Glaucoma in Humans-A Review of the Literature

Effect of ophthalmic preparation of methyldopa on induced ocular hypertension in rabbits

Glaucoma is a type of ocular disorder with multifaceted etiologies characterized by progressive optic nerve damage and ultimately loss of visual field. This study aimed to evaluate the possible intraocular pressure (IOP) lowering effect of an ophthalmic preparation of methyldopa (MD) in corticosteroid-induced ocular hypertension in rabbits. Forty New Zealand white male rabbits were assigned to the experiment and then randomly divided into five groups (n = 8). Ocular hypertension was induced by weekly subconjunctival injection of betamethasone suspension in both eyes. Animal groups included the control (healthy) group, which received the ophthalmic vehicle only; the standard (timolol) group, which received 0.5% timolol eye drops (ED); and the MD groups, which received 0.5%, 1%, and 2% of methyldopa ophthalmic preparation. Treatments were applied to the right eye twice daily for 7 days, whereas the left eye served as a control and was given only distilled water. IOP was recorded and ocular reflexes were observed. Weekly subconjunctival injections of betamethasone resulted in a significant elevation in the IOP (P ≤ 0.001) that was reduced after treatments with timolol 0.5% and MD at different concentrations. Timolol showed the highest reduction (P ≤ 0.001) in the mean IOP with a 30% reduction. MD showed a concentration-dependent reduction with the highest reduction (P ≤ 0.01) observed at 2% compared to the induced/distilled water (DW) eyes and no significant difference compared to the timolol 0.5% (P ≥ 0.05) with a 24.2% reduction in the mean IOP. Methyldopa managed to reduce the IOP in the chronic model of glaucoma, making MD a promising addition to the anti-glaucoma medications.

Inhibition of cGMP-Signalling Rescues Retinal Ganglion Cells From Axotomy-Induced Degeneration

The axons of retinal ganglion cells (RGCs) form the optic nerve, which relays visual information to the brain. RGC degeneration is the root cause of a variety of blinding diseases linked to optic nerve damage, including glaucoma, the second leading cause of blindness worldwide. The underlying cellular mechanisms of RGC degeneration are largely unclear; yet, they have been connected to excessive production of the signalling molecule nitric oxide (NO) by nitric oxide synthase (NOS). NO activates soluble guanylate cyclase (sGC), which subsequently produces the second messenger cyclic guanosine monophosphate (cGMP). This, in turn, activates protein kinase G (PKG), which can phosphorylate downstream protein targets. To study the role of NO/cGMP/PKG signalling in RGC degeneration, we used organotypic retinal explant cultures in which the optic nerve had been severed. We assessed the activity of NOS, RGC death and survival at different times after optic nerve transection. While NOS activity was high right after optic nerve transection, significant RGC loss occurred with a 24-48-h delay. We then treated retinal explants with inhibitors selectively targeting either NOS, sGC, PKG, or Kv1.3 and Kv1.6 voltage-gated potassium channels. While all four treatments reduced RGC death, the PKG inhibitor CN238 and the Kv-channel blocker Margatoxin (MrgX) showed the most pronounced rescue effects. Our results confirm an involvement of NO/cGMP/PKG signalling in RGC degeneration, highlight the potential of PKG and Kv1-channel targeting drugs for treatment development, and further suggest organotypic retinal explant cultures as a useful model for investigations into optic nerve damage.

Protective effects of different exercise modalities on oxidative stress in animal models of high intraocular pressure and diabetes

High intraocular pressure (HIOP) and high glucose levels are associated with oxidative stress. Although physical exercise protects against oxidative damage, its specific impact on eye health remains unclear. Thus, this study aimed to assess the impact of physical exercise on the oxidative status of whole eyes in male Swiss mice subjected to HIOP model and cafeteria diet (CD). In experiment one, mice were divided into sedentary, aerobic, and strength (four-week physical exercise) groups and subjected to an HIOP/ischemia model. In experiment two, mice were submitted to CD and voluntary physical exercise for 18 weeks, according to the following groups: sedentary control, sedentary CD, exercise control, and exercise CD. Experiment one revealed elevated 2',7'-dichlorodihydrofluorescein (DCFH) levels in aerobic group, which decreased in all groups after ischemia. Nitrite levels were decreased on strength than in sedentary group. The superoxide dismutase (SOD) activity did not change in all treatments. Although catalase (CAT) activity increased in aerobic and strength groups, and after ischemia in all groups. In experiment two, the sedentary CD group presented higher body weight than the other groups. DCFH levels were increased in the exercise control and reduced in the exercise CD compared with the other groups. CAT activity and sulfhydryl groups were decreased, while protein carbonylation was increased in the sedentary CD group compared with the other groups. Thus, these results suggested that physical exercise promoted antioxidant effects on eyes exposed to an HIOP model and CD.

From Preformulative Design to in Vivo Tests: A Complex Path of Requisites and Studies for Nanoparticle Ocular Application. Part 2: In Vitro, Ex Vivo, and In Vivo Studies

The incidence of ocular pathologies is constantly increasing, as is the interest of the researchers in developing new strategies to ameliorate the treatment of these conditions. Nowadays, drug delivery systems are considered among the most relevant approaches due to their applicability in the treatment of a great variety of inner and outer eye pathologies through painless topical administrations. The design of such nanocarriers requires a deep study of many aspects related to the administration route but also a consideration of the authorities and pharmacopeial requirements, in order to achieve a clinical outcome. On such bases, the scope of this review is to describe the path of the analyses that could be performed on nanoparticles, along with the assessment of their applicability for ophthalmic treatments. Preformulation studies, physicochemical and technological characterization, and preliminary noncellular in vitro studies have been described in part 1 of this review. Herein, first the in vitro cellular assays are described; subsequently, nonocular organotypic tests and ex vivo studies are reported, as to present the various analyses to which the formulations can be subjected before in vivo studies, described in the last part. In each step, the models that could be used are presented and compared, highlighting the pros and cons. Moreover, their reliability and eventual acceptance by regulatory agencies are discussed. Hence, this review provides an overview of the most relevant assays applicable for nanocarriers intended for ophthalmic administration to guide researchers in the experimental decision process.

Phytochemical Composition and Toxicological Screening of Anise Myrtle and Lemon Myrtle Using Zebrafish Larvae

Plants are an immense source of drugs, and 50% of modern pharmacopeia has a plant origin. With increasing life expectancy in humans, many age-related degenerative diseases converge on oxidative cellular stress pathways. This provides an opportunity to develop broad treatments by targeting the cause of common pathologic cell degeneration. Toxicological effects can be readily assessed in a live animal model system to establish potential fauna for clinical use. Here, we characterized and evaluated the antioxidant potential and toxicological effects of anise myrtle (Syzygium anisatum) and lemon myrtle (Backhousia citriodora) leaves. Using zebrafish larvae, a model for high-throughput pre-clinical in vivo toxicology screening, we identified safe levels of extract exposures for development of future therapeutics. The antioxidant capacity and toxicity were very similar in these two myrtles. The LC50-96h for anise myrtle was 284 mg/L, and for lemon myrtle, it was 270 mg/L. These measurements are comparable to ongoing studies we are performing using the same criteria in zebrafish, which allow for robust testing and prioritization of natural fauna for drug development.

The Prodrug DHED Delivers 17β-Estradiol into the Retina for Protection of Retinal Ganglion Cells and Preservation of Visual Function in an Animal Model of Glaucoma

We report a three-pronged phenotypic evaluation of the bioprecursor prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED) that selectively produces 17β-estradiol (E2) in the retina after topical administration and halts glaucomatous neurodegeneration in a male rat model of the disease. Ocular hypertension (OHT) was induced by hyperosmotic saline injection into an episcleral vein of the eye. Animals received daily DHED eye drops for 12 weeks. Deterioration of visual acuity and contrast sensitivity by OHT in these animals were markedly prevented by the DHED-derived E2 with concomitant preservation of retinal ganglion cells and their axons. In addition, we utilized targeted retina proteomics and a previously established panel of proteins as preclinical biomarkers in the context of OHT-induced neurodegeneration as a characteristic process of the disease. The prodrug treatment provided retina-targeted remediation against the glaucomatous dysregulations of these surrogate endpoints without increasing circulating E2 levels. Collectively, the demonstrated significant neuroprotective effect by the DHED-derived E2 in the selected animal model of glaucoma supports the translational potential of our presented ocular neuroprotective approach owing to its inherent therapeutic safety and efficacy.

Age-related changes of intraocular pressure in Dutch belted rabbits

This study investigated intraocular pressure (IOP) in Dutch belted rabbits using two different tonometers, rebound tonometry (TonoVet Plus; TVP) and a Tonopen (Tono-Pen AVIA Vet; TPA). Post-pubescent male Dutch belted rabbits aged 36 weeks (n = 10 animals) were used in the study. IOP measurements were conducted every 2 weeks for 22 weeks using TVP and TPA on both eyes of each rabbit. The average IOP measurements were compared by the paired Student's t-test. Pairwise Pearson's correlation coefficients and Bland-Altman statistics were used. The overall mean IOP measured with TPA was significantly higher than that with TVP (23.5 ± 4.9 vs. 21.8 ± 2.4 mmHg for the right eyes; P = 0.045, and 23.0 ± 4.7 vs. 21.5 ± 2.4 mmHg for the left eyes; P = 0.047). Both tonometers tended to show increased IOP readings with age, and positive correlations between IOP and age were observed with both TPA (r = 0.95, P < 0.001 for right eyes; r = 0.95, P < 0.001 for left eyes) and TVP (r = 0.91, P < 0.001 for right eyes; r = 0.64, P = 0.024 for left eyes). The average bias calculated by subtracting TPA from TVP was - 1.60 (95% confidence intervals - 1.927, - 1.281) mmHg. IOP in post-pubescent Dutch belted rabbits tended to increase with age throughout the 22 week study.

A review of using Traditional Chinese Medicine in the management of glaucoma and cataract

Traditional Chinese Medicine has a long history in ophthalmology in China. Over 250 kinds of Traditional Chinese Medicine have been recorded in ancient books for the management of eye diseases, which may provide an alternative or supplement to current ocular therapies. However, the core holistic philosophy of Traditional Chinese Medicine that makes it attractive can also hinder its understanding from a scientific perspective - in particular, determining true cause and effect. This review focused on how Traditional Chinese Medicine could be applied to two prevalent ocular diseases, glaucoma, and cataract. The literature on preclinical and clinical studies in both English and Chinese on the use of Traditional Chinese Medicine to treat these two diseases was reviewed. The pharmacological effects, safety profile, and drug-herb interaction of selected herbal formulas were also investigated. Finally, key considerations for conducting future Traditional Chinese Medicine studies are discussed.

Novel ancestry-specific primary open-angle glaucoma loci and shared biology with vascular mechanisms and cell proliferation

Primary open-angle glaucoma (POAG), a leading cause of irreversible blindness globally, shows disparity in prevalence and manifestations across ancestries. We perform meta-analysis across 15 biobanks (of the Global Biobank Meta-analysis Initiative) (n = 1,487,441: cases = 26,848) and merge with previous multi-ancestry studies, with the combined dataset representing the largest and most diverse POAG study to date (n = 1,478,037: cases = 46,325) and identify 17 novel significant loci, 5 of which were ancestry specific. Gene-enrichment and transcriptome-wide association analyses implicate vascular and cancer genes, a fifth of which are primary ciliary related. We perform an extensive statistical analysis of SIX6 and CDKN2B-AS1 loci in human GTEx data and across large electronic health records showing interaction between SIX6 gene and causal variants in the chr9p21.3 locus, with expression effect on CDKN2A/B. Our results suggest that some POAG risk variants may be ancestry specific, sex specific, or both, and support the contribution of genes involved in programmed cell death in POAG pathogenesis.

The visual field-testing maze and vision maze: Feasible techniques to evaluate visual field loss in animals

Visual field loss due to glaucoma is a severe and concerning problem, leading to limited visual range and poor quality vision. The progression of this loss begins with a para-central arcuate scotoma which eventually advances to a ring scotoma and constricted visual fields in later stages. Currently, no animal model is available for screening this pattern of vision loss. However, we have successfully developed two mazes to evaluate visual field loss - the visual field-testing maze (VFTZ) for peripheral vision loss and the vision maze (VM) for central vision loss. Our studies involved inducing glaucoma in Wistar and Sprague Dawley rats using lipopolysaccharide (LPS) and testing them in VFTZ and VM. We used Latanoprost and dorzolamide eye drops as standard drug candidates during the study. We evaluated the animals for intraocular pressure, retinal vasculature imaging, and anxiety using tonometry, ophthalmoscopy, and light and dark model techniques. Furthermore, we quantified the antioxidant parameters of the retina using UV spectroscopy. Our findings showed that animals with peripheral visual field loss in VFTZ took significantly more time to reach the goal and spent more time within the maze compared to normal or drug-treated animals (P < 0.001). Additionally, animals with compromised central visual field in VM spent more time in a particular arm and changed arms less frequently (P < 0.001) compared to normal or drug-treated animals. Moreover, we observed that glaucomatous rats exhibited elevated anxiety levels and impaired performance in the mazes, emphasizing the impact of vision loss on anxiety. Finally, the antioxidant and ATPase alterations in the retinal layers verified the glaucomatous changes in the experimental animals. Based on our remarkable findings, we strongly recommend the use of VFTZ and VM to evaluate visual field loss in animals.

Real-Time Imaging of Single Retinal Cell Apoptosis in a Non-Human Primate Ocular Hypertension Model

Purpose

To evaluate the feasibility of using DARC (detection of apoptosing retinal cells) technology as a biomarker for preclinical assessment of glaucomatous damage in a non-human primate (NHP) model of ocular hypertension (OHT).

Methods

Elevated intraocular pressure (IOP) was induced by applying a laser to the trabecular meshwork in each eye of NHPs. Changes in DARC counts in the retina, identified as fluorescent-tagged annexin V (ANX776)-positive cells, were evaluated together with optic nerve damage, assessed using spectral domain-optical coherence tomography. The pharmacokinetic properties of ANX776 in both healthy and OHT model monkeys were also examined.

Results

Sustained elevation of IOP and subsequent thinning of the retinal nerve fiber layer thickness (RNFLT) around the optic nerve head were confirmed in the OHT model. Increases in DARC counts were also detected after IOP elevation. We identified a statistically significant relationship between cumulative DARC counts and reductions in RNFLT both globally and in each peripapillary sector. Intravenous administration of ANX776 increased blood annexin V in a dose-dependent manner, which was subsequently eliminated.

Conclusions

This study revealed that DARC technology can effectively assess glaucomatous damage in an NHP OHT model. We obtained the fundamental data that could serve as a reference for developing preclinical models to evaluate the pharmacodynamics of neuroprotective agents using DARC technology in NHP OHT models.

Translational Relevance

Our basic data in a monkey OHT model could be useful for future preclinical studies using DARC technology to estimate the pharmacodynamic response of neuroprotective agents.

[Continuous Optimisation of Experimental Models - an Example from Glaucoma Research]

BACKGROUND

There is a great demand for suitable models to test novel surgical and therapeutic approaches in glaucoma therapy. To address this need and to provide further alternatives to in vivo animal models, we aimed at modifying an established in vitro porcine eye perfusion model.

METHODS

Two weaknesses of the previously established porcine anterior segment model include media leakage during perfusion and setup disintegration due to mechanical instability. To overcome these, we slightly modified the previously used custom-made perfusion dishes and incorporated new components into the model setup. To prevent fluid leakage, we secured the anterior segments more firmly to the perfusion trays using a compression ring, steel screws, and nuts. Customised mounts were used to stabilise the perfusion dish and pressure transducer as a single unit. The mounts were made of polylactide (PLA) and printed using a 3D printer.

RESULTS

The use of steel screws and nuts allowed tighter clamping of the anterior segments and prevented medium leakage. Our PLA custom mounts stabilised the entire assembly and facilitated handling during experiments and improved comparability between tested eyes. They also prevented accidental detachment of the pressure transducers, which resulted in more stable pressure curves. Our PLA mounts tolerated incubation temperatures of up to 37 °C and disinfection with enzymatic detergents and 70% ethanol without showing signs of deformation or degradation after four months of regular usage.

CONCLUSION

Modifications introduced to an established in vitro perfusion model improved its efficacy and reproducibility. Our adjusted model is an example of how many models can be optimised through critical analysis, thereby saving resources and providing reliable results in the long run.

Proteomics-Based Identification of Retinal Protein Networks Impacted by Elevated Intraocular Pressure in the Hypertonic Saline Injection Model of Experimental Glaucoma

Elevated intraocular pressure is considered a major cause of glaucomatous retinal neurodegeneration. To facilitate a better understanding of the underlying molecular processes and mechanisms, we report a study focusing on alterations of the retina proteome by induced ocular hypertension in a rat model of the disease. Glaucomatous processes were modeled through sclerosing the aqueous outflow routes of the eyes by hypertonic saline injections into an episcleral vein. Mass spectrometry-based quantitative retina proteomics using a label-free shotgun methodology identified over 200 proteins significantly affected by ocular hypertension. Various facets of glaucomatous pathophysiology were revealed through the organization of the findings into protein interaction networks and by pathway analyses. Concentrating on retinal neurodegeneration as a characteristic process of the disease, elevated intraocular pressure-induced alterations in the expression of selected proteins were verified by targeted proteomics based on nanoflow liquid chromatography coupled with nano-electrospray ionization tandem mass spectrometry using the parallel reaction monitoring method of data acquisition. Acquired raw data are shared through deposition to the ProteomeXchange Consortium (PXD042729), making a retina proteomics dataset on the selected animal model of glaucoma available for the first time.

Exploring the current use of animal models in glaucoma drug discovery: where are we in 2023?

INTRODUCTION

Animal models are widely used in glaucoma-related research. Since the elevated intraocular pressure (IOP) is a major risk factor underlying the disease pathogenesis, animal models with high IOP are commonly used. However, models are also used to represent the clinical context of glaucomatous changes developing despite a normal IOP.

AREAS COVERED

Herein, the authors discuss the various factors that contribute to the quality of studies using animal models based on the evaluation of studies published in 2022. The factors affecting the quality of studies using animal models, such as the animal species, age, and sex, are discussed, along with various methods and outcomes of studies involving different animal models of glaucoma.

EXPERT OPINION

Translating animal research data to clinical applications remains challenging. Our observations in this review clearly indicate that many studies lack scientific robustness not only in their experiment conduct but also in data analysis, interpretation, and presentation. In this context, ensuring the internal validity of animal studies is the first step in quality assurance. External validity, however, is more challenging, and steps should be taken to satisfy external validity at least to some extent.

Biochemical-molecular-genetic biomarkers in the tear film, aqueous humor, and blood of primary open-angle glaucoma patients

Introduction

Glaucoma is a chronic neurodegenerative disease, which is the leading cause of irreversible blindness worldwide. As a response to high intraocular pressure, the clinical and molecular glaucoma biomarkers indicate the biological state of the visual system. Classical and uncovering novel biomarkers of glaucoma development and progression, follow-up, and monitoring the response to treatment are key objectives to improve vision outcomes. While the glaucoma imaging field has successfully validated biomarkers of disease progression, there is still a considerable need for developing new biomarkers of early glaucoma, that is, at the preclinical and initial glaucoma stages. Outstanding clinical trials and animal-model study designs, innovative technology, and analytical approaches in bioinformatics are essential tools to successfully uncover novel glaucoma biomarkers with a high potential for translation into clinical practice.

Methods

To better understand the clinical and biochemical-molecular-genetic glaucoma pathogenesis, we conducted an analytical, observational, and case-comparative/control study in 358 primary open-angle glaucoma (POAG) patients and 226 comparative-control individuals (CG) to collect tears, aqueous humor, and blood samples to be processed for identifying POAG biomarkers by exploring several biological pathways, such as inflammation, neurotransmitter/neurotrophin alteration, oxidative stress, gene expression, miRNAs fingerprint and its biological targets, and vascular endothelial dysfunction, Statistics were done by using the IBM SPSS 25.0 program. Differences were considered statistically significant when p ≤ 0.05.

Results

Mean age of the POAG patients was 70.03 ± 9.23 years, and 70.62 ± 7.89 years in the CG. Malondialdehyde (MDA), nitric oxide (NO), interleuquin (IL)-6, endothelin-1 (ET-1), and 5 hydroxyindolacetic acid (5-HIAA), displayed significantly higher levels in the POAG patients vs. the CG (p < 0.001). Total antioxidant capacity (TAC), brain derived neurotrophic factor (BDNF), 5-hydroxy tryptamine (5-HT), solute carrier family 23-nucleobase transporters-member 2 (SLC23A2) gene, and the glutathione peroxidase 4 (GPX4) gene, showed significantly lower levelsin the POAG patients than in the CG (p < 0.001). The miRNAs that differentially expressed in tear samples of the POAG patients respect to the CG were the hsa miR-26b-5p (involved in cell proliferation and apoptosis), hsa miR-152-3p (regulator of cell proliferation, and extracellular matrix expression), hsa miR-30e-5p (regulator of autophagy and apoptosis), and hsa miR-151a-3p (regulator of myoblast proliferation).

Discussion

We are incredibly enthusiastic gathering as much information as possible on POAG biomarkers to learn how the above information can be used to better steer the diagnosis and therapy of glaucoma to prevent blindness in the predictable future. In fact, we may suggest that the design and development of blended biomarkers is a more appropriate solution in ophthalmological practice for early diagnosis and to predict therapeutic response in the POAG patients.

Scar formation in the presence of mitomycin C and the anti-fibrotic antibody in a rabbit model of glaucoma microsurgery: A pilot study

Purpose

This study aimed to evaluate the utility of a rationally engineered antibody that directly blocks collagen fibrillogenesis to reduce scar tissue formation associated with subconjunctival glaucoma surgery.

Material and methods

Fourteen eyes of 7 adult rabbits underwent glaucoma filtering surgery using XEN 45 Gel Stent. The rabbits' eyes were divided randomly into three treatment groups: (i) treated with the antibody, (ii) treated with mitomycin C, and (iii) treated with the antibody and mitomycin C. Following surgeries, the intraocular pressure and bleb appearance were evaluated in vivo. The rabbits were sacrificed 8 weeks after the surgery, and their eyes were harvested and processed for tissue analysis. Subsequently, tissue samples were analyzed microscopically for fibrotic tissue and cellular markers of inflammation. Moreover, the collagen-rich fibrotic tissue formed around the stents was analyzed using quantitative histology and infrared spectroscopy. The outcomes of this study were analyzed using the ANOVA test.

Results

This study demonstrated no significant differences in intraocular pressure, bleb appearance, or presence of complications such as bleb leak among the treatment groups. In contrast, we observed significant differences among the subpopulations of collagen fibrils formed within scar neo-tissue. Based on the spectroscopic analyses, we determined that the relative content of mature collagen cross-links in the antibody-treated group was significantly reduced compared to other groups.

Conclusions

Direct blocking of collagen fibrillogenesis with the anti-collagen antibody offers potentially beneficial effects that may reduce the negative impact of the subconjunctival scarring associated with glaucoma filtering surgery.

Reverse translation of artificial intelligence in glaucoma: Connecting basic science with clinical applications

Artificial intelligence (AI) has been approved for biomedical research in diverse areas from bedside clinical studies to benchtop basic scientific research. For ophthalmic research, in particular glaucoma, AI applications are rapidly growing for potential clinical translation given the vast data available and the introduction of federated learning. Conversely, AI for basic science remains limited despite its useful power in providing mechanistic insight. In this perspective, we discuss recent progress, opportunities, and challenges in the application of AI in glaucoma for scientific discoveries. Specifically, we focus on the research paradigm of reverse translation, in which clinical data are first used for patient-centered hypothesis generation followed by transitioning into basic science studies for hypothesis validation. We elaborate on several distinctive areas of research opportunities for reverse translation of AI in glaucoma including disease risk and progression prediction, pathology characterization, and sub-phenotype identification. We conclude with current challenges and future opportunities for AI research in basic science for glaucoma such as inter-species diversity, AI model generalizability and explainability, as well as AI applications using advanced ocular imaging and genomic data.

Effect of Polydeoxyribonucleotide (PDRN) Treatment on Corneal Wound Healing in Zebrafish (Danio rerio)

This study aimed to develop a corneal epithelial injury model in zebrafish (Danio rerio) and investigate the effectiveness of polydeoxyribonucleotide (PDRN) treatment on in vivo corneal epithelial regeneration and wound healing. Chemical injury to zebrafish cornea was produced by placing a small cotton swab containing 3% acetic acid solution. PDRN treatment was performed by immersing corneal-injured zebrafish in water containing PDRN (2 mg/mL) for 10 min at 0, 24, 48, and 72 h post-injury (hpi). The level of corneal healing was evaluated by fluorescein staining, histological examination, transcriptional profiling, and immunoblotting techniques. Fluorescein staining results demonstrate that PDRN treatment significantly (p < 0.05) reduced the wounded area of the zebrafish eye at 48 and 72 hpi, suggesting that PDRN may accelerate the corneal re-epithelialization. Histopathological evaluation revealed that injured corneal epithelial cells were re-organized at 72 hpi upon PDRN treatment with increased goblet cell density and size. Moreover, transcriptional analysis results demonstrate that PDRN treatment induced the mRNA expression of adora2ab (6.3-fold), pax6a (7.8-fold), pax6b (29.3-fold), klf4 (7.3-fold), and muc2.1 (5.0-fold) after the first treatment. Besides, tnf-α (2.0-fold) and heat-shock proteins (hsp70; 2.8-fold and hsp90ab1; 1.6-fold) have modulated the gene expression following the PDRN treatment. Immunoblotting results convincingly confirmed the modulation of Mmp-9, Hsp70, and Tnf-α expression levels upon PDRN treatment. Overall, our corneal injury model in zebrafish allows for understanding the morphological and molecular events of corneal epithelial healing, and ophthalmic responses for PDRN treatment following acid injury in zebrafish.

Morphological Aspects and Microscopic Analyses of Fibrous Tunic and Uveal Components in Bovine Eye

This study aimed to reveal the anatomical features of the bovine eye by scanning electron and light microscopic methods. For this purpose, a total of 40 eyes were evaluated. Gross and microscopic characteristics of the cornea, sclera, ciliary body, choroid, iris, and lens were determined. Bowman's and Descemet's membranes of the cornea were quite dense and prominent. Collagen lamellae of the cornea were wavy in the periphery and more parallel to the basal and metachromatic fibroblasts were noted. Three to four ciliary plicae merged to form ciliary processes. The presence of prominent intermediate bands connecting the ciliary plicae was determined. The zonular fibrils merged and attached to the lens in the form of thick zonular bands. A dense corpora nigra was present at the rectangular pupillary border of the iris. Tapetum fibrosum, consisting of polygonal tapetal cells, was in blue-yellow-green color and covered most of the choroid. A complex drainage system consisting of trabecular meshwork, angular aqueous plexus, ciliary sinus, and scleral venous vessels localized in a fairly wide iridocorneal angle was identified. Identifying structural features of the bovine eye is very important and useful for pathological evaluations, understanding species-specific physiological mechanisms and for operative interventions of ruminant species.

Comprehensive spectral libraries for various rabbit eye tissue proteomes

Rabbits have been widely used for studying ocular physiology and pathology due to their relatively large eye size and similar structures with human eyes. Various rabbit ocular disease models, such as dry eye, age-related macular degeneration, and glaucoma, have been established. Despite the growing application of proteomics in vision research using rabbit ocular models, there is no spectral assay library for rabbit eye proteome publicly available. Here, we generated spectral assay libraries for rabbit eye compartments, including conjunctiva, cornea, iris, retina, sclera, vitreous humor, and tears using fractionated samples and ion mobility separation enabling deep proteome coverage. The rabbit eye spectral assay library includes 9,830 protein groups and 113,593 peptides. We present the data as a freely available community resource for proteomic studies in the vision field. Instrument data and spectral libraries are available via ProteomeXchange with identifier PXD031194.

Measurement(s)	database type spectral library
Technology Type(s)	ion mobility spectrometry-mass spectrometry
Sample Characteristic - Organism	Oryctolagus cuniculus
Sample Characteristic - Environment	eye
Sample Characteristic - Location	United States of America

Treatment of Glaucoma with Natural Products and Their Mechanism of Action: An Update

Glaucoma is one of the leading causes of irreversible blindness. It is generally caused by increased intraocular pressure, which results in damage of the optic nerve and retinal ganglion cells, ultimately leading to visual field dysfunction. However, even with the use of intraocular pressure-lowering eye drops, the disease still progresses in some patients. In addition to mechanical and vascular dysfunctions of the eye, oxidative stress, neuroinflammation and excitotoxicity have also been implicated in the pathogenesis of glaucoma. Hence, the use of natural products with antioxidant and anti-inflammatory properties may represent an alternative approach for glaucoma treatment. The present review highlights recent preclinical and clinical studies on various natural products shown to possess neuroprotective properties for retinal ganglion cells, which thereby may be effective in the treatment of glaucoma. Intraocular pressure can be reduced by baicalein, forskolin, marijuana, ginsenoside, resveratrol and hesperidin. Alternatively, Ginkgo biloba, Lycium barbarum, Diospyros kaki, Tripterygium wilfordii, saffron, curcumin, caffeine, anthocyanin, coenzyme Q10 and vitamins B3 and D have shown neuroprotective effects on retinal ganglion cells via various mechanisms, especially antioxidant, anti-inflammatory and anti-apoptosis mechanisms. Extensive studies are still required in the future to ensure natural products' efficacy and safety to serve as an alternative therapy for glaucoma.

Primary Human Trabecular Meshwork Model for Pseudoexfoliation

The lack of an animal model or an in vitro model limits experimental options for studying temporal molecular events in pseudoexfoliation syndrome (PXF), an age related fibrillopathy causing trabecular meshwork damage and glaucoma. Our goal was to create a workable in vitro model of PXF using primary human TM (HTM) cell lines simulating human disease. Primary HTM cells harvested from healthy donors (n = 3), were exposed to various concentrations (5 ng/mL, 10 ng/mL, 15 ng/mL) of transforming growth factor-beta1 (TGF-β1) for different time points. Morphological change of epithelial–mesenchymal transition (EMT) was analyzed by direct microscopic visualization and immunoblotting for EMT markers. Expression of pro-fibrotic markers were analyzed by quantitative RT-PCR and immunoblotting. Cell viability and death in treated cells was analyzed using FACS and MTT assay. Protein complex and amyloid aggregate formation was analyzed by Immunofluorescence of oligomer11 and amyloid beta fibrils. Effect of these changes with pharmacological inhibitors of canonical and non-canonical TGF pathway was done to analyze the pathway involved. The expression of pro-fibrotic markers was markedly upregulated at 10 ng/mL of TGF-β1 exposure at 48–72 h of exposure with associated EMT changes at the same time point. Protein aggregates were seen maximally at these time points that were found to be localized around the nucleus and in the extracellular matrix (ECM). EMT and pro-fibrotic expression was differentially regulated by different canonical and non-canonical pathways suggesting complex regulatory mechanisms. This in vitro model using HTM cells simulated the main characteristics of human disease in PXF like pro-fibrotic gene expression, EMT, and aggregate formation.

Fundamental Biomaterial Considerations in the Development of a 3D Model Representative of Primary Open Angle Glaucoma

Glaucoma is a leading cause of irreversible blindness globally, with primary open angle glaucoma (POAG) being the most common subset. Raised intraocular pressure is an important risk factor for POAG and is caused by a reduction in aqueous humour (AqH) outflow due to dysfunctional cellular and matrix dynamics in the eye’s main drainage site, the trabecular meshwork (TM) and Schlemm’s canal (SC). The TM/SC are highly specialised tissues that regulate AqH outflow; however, their exact mechanisms of AqH outflow control are still not fully understood. Emulating physiologically relevant 3D TM/S in vitro models poses challenges to accurately mimic the complex biophysical and biochemical cues that take place in healthy and glaucomatous TM/SC in vivo. With development of such models still in its infancy, there is a clear need for more well-defined approaches that will accurately contrast the two central regions that become dysfunctional in POAG; the juxtacanalicular tissue (JCT) region of the TM and inner wall endothelia of the Schlemm’s canal (eSC). This review will discuss the unique biological and biomechanical characteristics that are thought to influence AqH outflow and POAG progression. Further consideration into fundamental biomaterial attributes for the formation of a biomimetic POAG/AqH outflow model will also be explored for future success in pre-clinical drug discovery and disease translation.

Effects of a New Combination of Natural Extracts on Glaucoma-Related Retinal Degeneration

BACKGROUND

Glaucoma is currently the leading cause of irreversible blindness; it is a neuropathy characterized by structural alterations of the optic nerve, leading to visual impairments. The aim of this work is to develop a new oral formulation able to counteract the early changes connected to glaucomatous degeneration. The composition is based on gastrodin and vitamin D3 combined with vitamin C, blackcurrant, and lycopene.

METHODS

Cells and tissues of the retina were used to study biological mechanisms involved in glaucoma, to slow down the progression of the disease. Experiments mimicking the conditions of glaucoma were carried out to examine the etiology of retinal degeneration.

RESULTS

Our results show a significant ability to restore glaucoma-induced damage, by counteracting ROS production and promoting cell survival by inhibiting apoptosis. These effects were confirmed by the intracellular mechanism that was activated following administration of the compound, either before or after the glaucoma induction. In particular, the main results were obtained as a preventive action of glaucoma, showing a beneficial action on all selected markers, both on cells and on eyecup preparations. It is therefore possible to hypothesize both the preventive and therapeutic use of this formulation, in the presence of risk factors, and due to its ability to inhibit the apoptotic cycle and to stimulate cell survival mechanisms, respectively.

CONCLUSION

This formulation has exhibited an active role in the prevention or restoration of glaucoma damage for the first time.

A Fair Assessment of Evaluation Tools for the Murine Microbead Occlusion Model of Glaucoma

Despite being one of the most studied eye diseases, clinical translation of glaucoma research is hampered, at least in part, by the lack of validated preclinical models and readouts. The most popular experimental glaucoma model is the murine microbead occlusion model, yet the observed mild phenotype, mixed success rate, and weak reproducibility urge for an expansion of available readout tools. For this purpose, we evaluated various measures that reflect early onset glaucomatous changes in the murine microbead occlusion model. Anterior chamber depth measurements and scotopic threshold response recordings were identified as an outstanding set of tools to assess the model’s success rate and to chart glaucomatous damage (or neuroprotection in future studies), respectively. Both are easy-to-measure, in vivo tools with a fast acquisition time and high translatability to the clinic and can be used, whenever judged beneficial, in combination with the more conventional measures in present-day glaucoma research (i.e., intraocular pressure measurements and post-mortem histological analyses). Furthermore, we highlighted the use of dendritic arbor analysis as an alternative histological readout for retinal ganglion cell density counts.

Relationship between retinal capillary vessel density of OCT angiography and intraocular pressure in pig

The purpose of this study was to evaluate density change in the retinal capillary plexus during intra ocular pressure (IOP) elevation in vitrectomized pigs’ eyes using optical coherence tomography angiography (OCTA). Eight eyes of eight micro pigs received vitrectomy and the IOP was controlled from 15 mmHg (baseline) to 105 mmHg in 15 mmHg increments using a vented-gas forced-infusion system, and then decreased back to normal IOP (recovery state). The spectral-domain OCTA device was set to scan an area of 8.8 × 4.4 mm (30° × 15°) above the optic nerve head for each IOP. The relative vessel density (rVAD) compared to baseline was determined for the total retinal blood flow (RBF) which included major retinal artery and venous vessels, radial peripapillary capillaries (RPCs), superficial (SVP), intermediate (IVP), and deep vascular plexus (DVP). The mean rVAD was 0.890 in RBF, 0.826 in RPCs, 0.817 in SVP, 0.819 in IVP, and 0.794 in DVP at 30 mmHg. While the rVAD of RBF and RPCs decreased to 0.504 and 0.541 at 45 mmHg, the SVP, IVP, and DVP decreased to 0.433, 0.359, and 0.345, respectively. When IOP was normalized, the rVAD was recovered in all layers and the VAD of RBF, IVP, and DVP were higher than baseline (P = 0.040, 0.019, and 0.019, respectively). Retinal capillary density deterioration in each layer was found from 30 mmHg using an OCTA system which showed excellent depth-resolved segmentation of retinal capillary layers even at higher IOPs. Reduction in VAD showed full recovery after IOP normalization.

Oxidative Stress and the Role of NADPH Oxidase in Glaucoma

Glaucoma is characterised by loss of retinal ganglion cells, and their axons and many pathophysiological processes are postulated to be involved. It is increasingly understood that not one pathway underlies glaucoma aetiology, but rather they occur as a continuum that ultimately results in the apoptosis of retinal ganglion cells. Oxidative stress is recognised as an important mechanism of cell death in many neurodegenerative diseases, including glaucoma. NADPH oxidase (NOX) are enzymes that are widely expressed in vascular and non-vascular cells, and they are unique in that they primarily produce reactive oxygen species (ROS). There is mounting evidence that NOX are an important source of ROS and oxidative stress in glaucoma and other retinal diseases. This review aims to provide a perspective on the complex role of oxidative stress in glaucoma, in particular how NOX expression may influence glaucoma pathogenesis as illustrated by different experimental models of glaucoma and highlights potential therapeutic targets that may offer a novel treatment option to glaucoma patients.

A 3D Model of Human Trabecular Meshwork for the Research Study of Glaucoma

Glaucoma is a multifactorial syndrome in which the development of pro-apoptotic signals are the causes for retinal ganglion cell (RGC) loss. Most of the research progress in the glaucoma field have been based on experimentally inducible glaucoma animal models, which provided results about RGC loss after either the crash of the optic nerve or IOP elevation. In addition, there are genetically modified mouse models (DBA/2J), which make the study of hereditary forms of glaucoma possible. However, these approaches have not been able to identify all the molecular mechanisms characterizing glaucoma, possibly due to the disadvantages and limits related to the use of animals. In fact, the results obtained with small animals (i.e., rodents), which are the most commonly used, are often not aligned with human conditions due to their low degree of similarity with the human eye anatomy. Although the results obtained from non-human primates are in line with human conditions, they are little used for the study of glaucoma and its outcomes at cellular level due to their costs and their poor ease of handling. In this regard, according to at least two of the 3Rs principles, there is a need for reliable human-based in vitro models to better clarify the mechanisms involved in disease progression, and possibly to broaden the scope of the results so far obtained with animal models. The proper selection of an in vitro model with a "closer to in vivo" microenvironment and structure, for instance, allows for the identification of the biomarkers involved in the early stages of glaucoma and contributes to the development of new therapeutic approaches. This review summarizes the most recent findings in the glaucoma field through the use of human two- and three-dimensional cultures. In particular, it focuses on the role of the scaffold and the use of bioreactors in preserving the physiological relevance of in vivo conditions of the human trabecular meshwork cells in three-dimensional cultures. Moreover, data from these studies also highlight the pivotal role of oxidative stress in promoting the production of trabecular meshwork-derived pro-apoptotic signals, which are one of the first marks of trabecular meshwork damage. The resulting loss of barrier function, increase of intraocular pressure, as well the promotion of neuroinflammation and neurodegeneration are listed as the main features of glaucoma. Therefore, a better understanding of the first molecular events, which trigger the glaucoma cascade, allows the identification of new targets for an early neuroprotective therapeutic approach.

Glaucoma and Antioxidants: Review and Update

Glaucoma is a neurodegenerative disease characterised by the progressive degeneration of retinal ganglion cells. Oxidative stress has been related to the cell death in this disease. Theoretically, this deleterious consequence can be reduced by antioxidants substances. The aim of this review is to assemble the studies published in relation to antioxidant supplementation and its effects on glaucoma and to offer the reader an update on this field. With this purpose, we have included studies in animal models of glaucoma and clinical trials. Although there are variable results, supplementation with antioxidants in glaucoma may be a promising therapy in glaucoma.

A Dietary Combination of Forskolin with Homotaurine, Spearmint and B Vitamins Protects Injured Retinal Ganglion Cells in a Rodent Model of Hypertensive Glaucoma

There is indication that nutritional supplements protect retinal cells from degeneration. In a previous study, we demonstrated that dietary supplementation with an association of forskolin, homotaurine, spearmint extract and B vitamins efficiently counteracts retinal dysfunction associated with retinal ganglion cell (RGC) death caused by optic nerve crush. We extended our investigation on the efficacy of dietary supplementation with the use of a mouse model in which RGC degeneration depends as closely as possible on intraocular pressure (IOP) elevation. In this model, injecting the anterior chamber of the eye with methylcellulose (MCE) causes IOP elevation leading to RGC dysfunction. The MCE model was characterized in terms of IOP elevation, retinal dysfunction as determined by electrophysiological recordings, RGC loss as determined by brain-specific homeobox/POU domain protein 3A immunoreactivity and dysregulated levels of inflammatory and apoptotic markers. Except for IOP elevation, dysfunctional retinal parameters were all recovered by dietary supplementation indicating the involvement of non-IOP-related neuroprotective mechanisms of action. Our hypothesis is that the diet supplement may be used to counteract the inflammatory processes triggered by glial cell activation, thus leading to spared RGC loss and the preservation of visual dysfunction. In this respect, the present compound may be viewed as a potential remedy to be added to the currently approved drug therapies for improving RGC protection.

Protective Efficacy of a Dietary Supplement Based on Forskolin, Homotaurine, Spearmint Extract, and Group B Vitamins in a Mouse Model of Optic Nerve Injury

Glaucoma is a multifactorial blinding disease with a major inflammatory component ultimately leading to apoptotic retinal ganglion cell (RGC) death. Pharmacological treatments lowering intraocular pressure can help slow or prevent vision loss although the damage caused by glaucoma cannot be reversed. Recently, nutritional approaches have been evaluated for their efficacy in preventing degenerative events in the retina although mechanisms underlying their effectiveness remain to be elucidated. Here, we evaluated the efficacy of a diet supplement consisting of forskolin, homotaurine, spearmint extract, and vitamins of the B group in counteracting retinal dysfunction in a mouse model of optic nerve crush (ONC) used as an in vivo model of glaucoma. After demonstrating that ONC did not affect retinal vasculature by fluorescein angiography, we determined the effect of the diet supplement on the photopic negative response (PhNR) whose amplitude is strictly related to RGC integrity and is therefore drastically reduced in concomitance with RGC death. We found that the diet supplementation prevents the reduction of PhNR amplitude (p < 0.001) and concomitantly counteracts RGC death, as in supplemented mice, RGC number assessed immunohistochemically is significantly higher than that in non-supplemented animals (p < 0.01). Major determinants of the protective efficacy of the compound are due to a reduction of ONC-associated cytokine secretion leading to decreased levels of apoptotic markers that in supplemented mice are significantly lower than in non-supplemented animals (p < 0.001), ultimately causing RGC survival and ameliorated visual dysfunction. Overall, our data suggest that the above association of compounds plays a neuroprotective role in this mouse model of glaucoma thus offering a new perspective in inflammation-associated neurodegenerative diseases of the inner retina.