Translational Preclinical Pharmacologic Disease Models for Ophthalmic Drug Development

Assessment of Brain-Derived Neurotrophic Factor on Retinal Structure and Visual Function in Rodent Models of Optic Nerve Crush

The effects of brain-derived neurotrophic factor (BDNF) on retinal ganglion cell (RGC) survival and visual function were assessed in rat and mouse models of optic nerve (ON) crush. ONs were crushed on Day 1, followed by intravitreal injections of a vehicle or BDNF on Days 1 and 8. The spatial frequency threshold was measured using optokinetic tracking on Days 7 and 14. On Day 15, ganglion cell complex (GCC) thickness was quantified using optical coherence tomography. Furthermore, all eyes were enucleated for immunohistochemical analysis of the surviving RGC somas and axons. BDNF significantly reduced the RGC soma in mice and increased GCC thickness in intact eyes, with apparent axonal swelling in both species. It displayed significantly greater RGC soma survival in eyes with ON injury, with moderately thicker axonal bundles in both species and a thicker GCC in rats. Visual function was significantly reduced in all ON-crushed animals, regardless of BDNF treatment. Thus, we obtained a comprehensive analysis of the structural and functional impact of BDNF in intact and ON-crushed eyes in two rodent models. Our results provide a foundation for further BDNF evaluation and the design of preclinical studies on neuroprotectants using BDNF as a reference positive control.

A Clinical, Pharmacological, and Formulation Evaluation of Melatonin in the Treatment of Ocular Disorders-A Systematic Review

Melatonin's cytoprotective properties may have therapeutic implications in treating ocular diseases like glaucoma and age-related macular degeneration. Literature data suggest that melatonin could potentially protect ocular tissues by decreasing the production of free radicals and pro-inflammatory mediators. This study aims to summarize the screened articles on melatonin's clinical, pharmacological, and formulation evaluation in treating ocular disorders. The identification of relevant studies on the topic in focus was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines. The studies were searched in the following databases and web search engines: Pubmed, Scopus, Science Direct, Web of Science, Reaxys, Google Scholar, Google Patents, Espacenet, and Patentscope. The search time interval was 2013-2023, with the following keywords: melatonin AND ocular OR ophthalmic AND formulation OR insert AND disease. Our key conclusion was that using melatonin-loaded nano-delivery systems enabled the improved permeation of the molecule into intraocular tissues and assured controlled release profiles. Although preclinical studies have demonstrated the efficacy of developed formulations, a considerable gap has been observed in the clinical translation of the results. To overcome this failure, revising the preclinical experimental phase might be useful by selecting endpoints close to clinical ones.

Medicinal Plants Used for Eye Conditions in Mexico-A Review

Medicinal plants have been historically significant for treating common human diseases in Mexico. Although some ethnobotanical research exists, limited ethnomedicinal data has documented medicinal plants employed for eye health. This review focuses on ethnomedicinal information and preclinical and clinical studies regarding medicinal plants used in Mexico for treating symptoms associated with eye conditions. An electronic database search was conducted by consulting scientific articles, books about Mexican herbal medicine, and academic theses. This work recorded 69 plant species belonging to 26 plant families, especially plants from the Crassulaceae family, which are used as remedies for irritation and infections in the eye. Eight of these medicinal plants have been the subject of preclinical studies using ocular models, and one medicinal plant has been tested in clinical trials. The evidence of pharmacological effects indicates the promising therapeutic potential of these medicinal plants for developing new treatments for eye conditions. However, toxicological studies are necessary to ensure safe application to the eye, particularly as traditional medicine continues to be relied upon worldwide. In addition, this review highlights the need to perform ethnobotanical and phytochemical studies in Mexico regarding the medicinal flora used as remedies for eye conditions.

Generation of a 3D Outer Blood-Retinal Barrier with Advanced Choriocapillaris and Its Application in Diabetic Retinopathy in a Microphysiological System

The outer blood-retinal barrier (oBRB) provides an optimal environment for the function of the photoreceptor by regulating the exchange of molecules between subretinal space and the choriocapillaris, and its dysfunction could impair the photoreceptor's function and vision. The existing in vitro models have limitations in reproducing the barrier function or physiological characteristics of oBRB and choriocapillaris. Here, we engineered a microphysiological system-based oBRB-choriocapillaris model that simultaneously incorporates the desired physiological characteristics and is simple to fabricate. First, we generated microvascular networks to mimic choriocapillaris and investigated the role of fibroblasts in vasculogenesis. By adding retinal pigment epithelial cells to one side of blood vessels formed with endothelial cells and fibroblasts and optimizing their culture medium conditions, we established an oBRB-choriocapillaris model. To verify the physiological similarity of our oBRB-choriocapillaris model, we identified the polarization and expression of the tight junction of the retinal pigment epithelium, Bruch's membrane, and the fenestral diaphragm of choriocapillaris. Finally, we tried to recapitulate the diabetes mellitus environment in our model with hyperglycemia and diabetes-related cytokines. This induced a decrease in tight junction integrity, loss of barrier function, and shrinkage of blood vessels, similar to the in vivo pathological changes observed in the oBRB and choriocapillaris. The oBRB-choriocapillaris model developed using a microphysiological system is expected to offer a valuable in vitro platform for retinal and choroidal vascular diseases in preclinical applications.

The Bovine Ex Vivo Retina: A Versatile Model for Retinal Neuroscience

Purpose

The isolated ex vivo retina is the standard model in retinal physiology and neuroscience. During isolation, the retina is peeled from the retinal pigment epithelium (RPE), which plays a key role in the visual cycle. Here we introduce the choroid-attached bovine retina as an in vivo-like model for retinal physiology. We find that-in the bovine eye-the choroid and retina can be peeled from the sclera as a single thin sheet. Importantly, the retina remains tightly associated with the RPE, which is sandwiched between the retina and the choroid. Furthermore, bovine tissue is readily available and cheap, and there are no ethical concerns related to the use of animals solely for research purposes.

Methods

We combine multi-electrode array and single-cell patch-clamp recordings to characterize light responses in the choroid-attached bovine ex vivo retina.

Results

We demonstrate robust and consistent light responses in choroid-attached preparations. Importantly, light responses adapt to different levels of background illumination and rapidly recover from photobleaching. The choroid-attached retina is also thin enough to permit targeted electrophysiological recording from individual retinal neurons using standard differential interference contrast microscopy. We also characterize light responses and membrane properties of bovine retinal ganglion cells and compare data obtained from bovine and murine retinas.

Conclusions

The choroid-attached retinal model retains the advantages of the isolated retina but with an intact visual cycle and represents a useful tool to elucidate retinal physiology.

Donkey Colostrum and Milk: How Dietary Probiotics Can Affect Metabolomic Profile, Alkaline Sphingomyelinase and Alkaline Phosphatase Activity

Positive results on animal health, feed efficiency, and milk's nutritional content have been obtained after oral administration of probiotics. The aim of the present study was therefore to evaluate the effect of dietary supplementation with high numbers of multispecies probiotic formulations on the milk metabolomic profiles of alkaline sphingomyelinase (alk-SMase) and alkaline phosphatase (ALP) in donkeys. Twenty animals were randomly allocated to receive either a normal diet (group B) or a supplemented diet (group A). Colostrum and milk samples were obtained within 48 h, at 15 days (supplementation start), and at 45 days after parturition. Different metabolomic profiles were observed between colostrum and milk, as were the concentrations of 12 metabolites that changed following 30 days of probiotic supplementation. Alk-SMase activity was found to be higher in donkey colostrum (vs. milk at 15 days); this enzyme, together with ALP, increased in milk after 30 days of probiotic supplementation. The results of the present study provide new insight into the complex changes in donkey colostrum and milk composition in the first 45 days of lactation and how the milk metabolome can be modulated by probiotic supplementation.

Development of In Vitro Dry Eye Models to Study Proliferative and Anti-Inflammatory Effects of Allogeneic Serum Eye Drops

This study aimed to develop valid in vitro models for preclinical evaluation of proliferative and anti-inflammatory effects of human allogeneic serum eye drops for dry eye disease (DED) treatment. A DED wound healing model was developed by analyzing the influence of coating and serum concentrations on human corneal epithelial (HCE-T) wound closure. Further, intralaboratory variance, freeze-thaw cycle effects, donor variability and stability assays were conducted. Interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα) were used to induce the gene expression of matrix metalloproteinase 9 (MMP9), cyclooxygenase 2 (COX2), transforming growth factor-β (TGFβ) and IL-1β. MMP9 induction was optimized using a design-of-experiments (DoE) approach and applied to examine serum under static and dynamic conditions. MMP9 protein expression was analyzed by ELISA. The DED wound healing model detected proliferative effects of serum down to 1% with a small intralaboratory variance. Serum stability was shown over six months, donor variance could be detected, and freeze-thaw cycle effects did not affect wound closure. Serum decreased MMP9 expression on the gene and protein levels. The induction method was successfully optimized using DoE modeling and transferred to a dynamic setting mimicking tear film fluidics. The DED wound healing and inflammatory DED model present useful in vitro models for the preclinical evaluation of allogeneic serum eye drops without the use of animal experiments.

Modulation of ocular surface desiccation in a murine model by histatin-5 application

PURPOSE

To determine the efficacy of Histatin-5 (Hst5) peptide treatment in ameliorating dry eye disease (DED) phenotype in an in-vivo mouse model of scopolamine and desiccating stress (SDS) dry eye.

METHODS

SDS was induced in female C57BL/6 mice by subcutaneous injections of scopolamine hydrobromide and exposure to low relative humidity and forced air draft for five days. Mouse eyes were topically treated with synthetic Hst5 peptide or balanced salt solution (BSS) twice a day for four days. Control mice were not exposed to SDS induction and did not receive any treatments. Oregon green dextran (OGD) staining was used to evaluate corneal permeability. Histologically, staining with periodic acid schiff (PAS), immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), were used to quantify the number of goblet cells (GC), CD45+ immune cells and apoptotic cells respectively in formalin fixed paraffin embedded (FFPE) mouse whole eye sections.

RESULTS

Compared to treatment with BSS, Hst5 treatment significantly lowered corneal epithelial permeability, prevented conjunctival epithelial GC loss, decreased conjunctival CD45+ immune cell infiltration and reduced conjunctival epithelial cell apoptosis.

CONCLUSIONS

Hst5 peptide topical treatment significantly improves the clinical parameters observed in SDS experimental model of DED. This is the first report of the efficacy of Hst5 treatment of dry eye phenotype, and potential novel treatment for DED in the clinic. Hst5 represents a new class of efficacious therapeutic agents, demonstrating pro-epithelial and anti-inflammatory activities at the ocular surface.

Nicotinamide Mononucleotide Prevents Retinal Dysfunction in a Mouse Model of Retinal Ischemia/Reperfusion Injury

Retinal ischemia/reperfusion (I/R) injury can cause severe vision impairment. Retinal I/R injury is associated with pathological increases in reactive oxygen species and inflammation, resulting in retinal neuronal cell death. To date, effective therapies have not been developed. Nicotinamide mononucleotide (NMN), a key nicotinamide adenine dinucleotide (NAD+) intermediate, has been shown to exert neuroprotection for retinal diseases. However, it remains unclear whether NMN can prevent retinal I/R injury. Thus, we aimed to determine whether NMN therapy is useful for retinal I/R injury-induced retinal degeneration. One day after NMN intraperitoneal (IP) injection, adult mice were subjected to retinal I/R injury. Then, the mice were injected with NMN once every day for three days. Electroretinography and immunohistochemistry were used to measure retinal functional alterations and retinal inflammation, respectively. The protective effect of NMN administration was further examined using a retinal cell line, 661W, under CoCl2-induced oxidative stress conditions. NMN IP injection significantly suppressed retinal functional damage, as well as inflammation. NMN treatment showed protective effects against oxidative stress-induced cell death. The antioxidant pathway (Nrf2 and Hmox-1) was activated by NMN treatment. In conclusion, NMN could be a promising preventive neuroprotective drug for ischemic retinopathy.

Zebrafish (Danio rerio) Is an Economical and Efficient Animal Model for Screening Potential Anti-cataract Compounds

Purpose

To develop a zebrafish cataract model for screening potential anti-cataract compounds.

Methods

Living zebrafish were anesthetized and exposed to ultraviolet-C (UV-C) irradiation at a dosage of 3250 mJ/cm2/d until they developed severe cataracts. These cataracts were graded based on photographs analyzed with ImageQuant TL version 7.0. Fish with severe cataracts were used to evaluate a range of compounds for cataract treatment, including the previously demonstrated hit compound lanosterol. For the initial evaluation, fish were divided into four groups: no treatment, balanced salt solution, β-cyclodextrin (β-CD), and lanosterol dissolved in β-CD. The treatments were performed for 10 days, and the clarity of lenses was evaluated. To assess the persistence of treatment, fish were treated with β-CD and lanosterol dissolved in β-CD for seven consecutive days followed by monitoring for three days without treatment.

Results

The average time for zebrafish to develop severe cataracts using the present UV-C irradiation protocol was 7.8 days (range 4-15 days). Both study designs required only another 10 days to determine the effect of hit compounds. The total experimental period could be completed within one month, and the entire experiment was economical.

Conclusions

We could assay a large number of hit compounds at a reasonable cost and within a short time using this newly developed zebrafish cataract model. These assays may allow development of an efficient platform for screening potential anti-cataract compounds.

Translational Relevance

The results may facilitate the development of ani-cataract medication for humans after further experiments and investigations.

Treatment and prevention of pathological mitochondrial dysfunction in retinal degeneration and in photoreceptor injury

Pathological deterioration of mitochondrial function is increasingly linked with multiple degenerative illnesses as a mediator of a wide range of neurologic and age-related chronic diseases, including those of genetic origin. Several of these diseases are rare, typically defined in the United States as an illness affecting fewer than 200,000 people in the U.S. population, or about one in 1600 individuals. Vision impairment due to mitochondrial dysfunction in the eye is a prominent feature evident in numerous primary mitochondrial diseases and is common to the pathophysiology of many of the familiar ophthalmic disorders, including age-related macular degeneration, diabetic retinopathy, glaucoma and retinopathy of prematurity - a collection of syndromes, diseases and disorders with significant unmet medical needs. Focusing on metabolic mitochondrial pathway mechanisms, including the possible roles of cuproptosis and ferroptosis in retinal mitochondrial dysfunction, we shed light on the potential of α-lipoyl-L-carnitine in treating eye diseases. α-Lipoyl-L-carnitine is a bioavailable mitochondria-targeting lipoic acid prodrug that has shown potential in protecting against retinal degeneration and photoreceptor cell loss in ophthalmic indications.

A new non-human primate model of desiccating stress-induced dry eye disease

Dry eye disease (DED), a multifactorial ocular surface disease, is estimated to affect up to 34% of individuals over 50 years old. Although numerous animal models, including rodents and rabbits, have been developed to mimic the pathophysiologic mechanisms involved in dry eye, there is a lack of non-human primate (NHP) models, critical for translational drug studies. Here, we developed a novel desiccating stress-induced dry eye disease model using Rhesus macaque monkeys. The monkeys were housed in a controlled environment room for 21 to 36 days under humidity, temperature, and airflow regulation. Following desiccating stress, NHPs demonstrated clinical symptoms similar to those of humans, as shown by increased corneal fluorescein staining (CFS) and decreased tear-film breakup time (TFBUT). Moreover, corticosteroid treatment significantly reduced CFS scoring, restored TFBUT, and prevented upregulation of tear proinflammatory cytokines as observed in dry eye patients following steroid treatment. The close resemblance of clinical symptoms and treatment responses to those of human DED patients provides great translational value to the NHP model, which could serve as a clinically relevant animal model to study the efficacy of new potential treatments for DED.

Translating pharmacology models effectively to predict therapeutic benefit

Many in vitro and in vivo models are used in pharmacological research to evaluate the role of targeted proteins in a disease. Understanding the translational relevance and limitation of these models for analyzing the disposition, pharmacokinetic/pharmacodynamic (PK/PD) profile, mechanism, and efficacy of a drug, is essential when selecting the most appropriate model of the disease of interest and predicting clinically efficacious doses of the investigational drug. Here, we review selected animal models used in ophthalmology, infectious diseases, oncology, autoimmune diseases, and neuroscience. Each area has specific challenges around translatability and determination of an efficacious dose: new patient-specific dosing methods could help overcome these limitations.

Validation of a preclinical dry eye model in New Zealand white rabbits during and following topical instillation of 1% ophthalmic atropine sulfate

BACKGROUND

The objective of this study was to validate an animal model for dry eye during and after the administration of 1% ophthalmic atropine sulfate (OAS) in New Zealand white (NZW) rabbits.

METHODS

OAS (1%) was applied three times per day to 30 eyes of 15 healthy NZW rabbits. Sacrifice, enucleation, and lacrimal gland removal took place on days 15, 21, and 30 (OAS group). A second group (n = 5) was used as control. Clinical evaluations took place on days 3, 10, 15, 18, 21, 24 and 30. The primary endpoints were: Schirmer I test, tear break-up time (TBUT), and corneal fluorescein staining. As secondary endpoints, clinical changes including intraocular pressure, and histopathology were evaluated.

RESULTS

While OAS was administered, the Schirmer I test showed a statistically significant reduction for OAS group versus control (p < 0.001), and versus basal production (p < 0.001). TBUT showed statistically significant differences between groups (days 3 and 10; p = 0.001) and versus basal values (day 3; p < 0.001). Fluorescein staining showed a statistically significant difference (day 3; p = 0.001). The most frequent clinical finding was conjunctival hyperemia (76.9% OAS vs. 20% control). For histopathology, all OAS subjects presented some degree of inflammation (86.7% minimal; 13.3% mild) whereas the control presented only 30% minimal inflammation. Goblet cell density showed no difference.

CONCLUSIONS

The effectiveness of the OAS dry eye model in NZW rabbits as reported in previous studies was confirmed, provided that the application of the drug is maintained throughout the intervention; it is not a viable model after OAS administration is suspended.

Intravitreal Administration of rhNGF Enhances Regenerative Processes in a Zebrafish Model of Retinal Degeneration

Nerve growth factor (NGF) is the best characterized neurotrophin, and it is known to play an important role in ocular homeostasis. Here, we demonstrated the expression of NGF receptors in adult zebrafish retina and optimized a light-induced retina degeneration (LID) zebrafish model that mimics human cone-rod disorders, demonstrating that intravitreal (IV) administration of rhNGF can boost zebrafish retinal regeneration in this model. Adult zebrafish retinae exposed to 60 h of light irradiation (60 h LID) displayed evident reduction of outer nuclear layer (ONL) thickness and cell number with presence of apoptotic cells. Retinal histologic evaluation at different time points showed that IV therapeutic injection of rhNGF resulted in an increase of ONL thickness and cell number at late time points after damage (14 and 21 days post injury), ultimately accelerating retinal tissue recovery by driving retinal cell proliferation. At a molecular level, rhNGF activated the ERK1/2 pathway and enhanced the regenerative potential of Müller glia gfap- and vim-expressing cells by stimulating at early time points the expression of the photoreceptor regeneration factor Drgal1-L2. Our results demonstrate the highly conserved nature of NGF canonical pathway in zebrafish and thus support the use of zebrafish models for testing new compounds with potential retinal regenerative properties. Moreover, the pro-regenerative effects of IV-injected NGF that we observed pave the way to further studies aimed at evaluating its effects also in mammals, in order to expedite the development of novel rhNGF-based therapeutic approaches for ophthalmological disorders.

Importance of Nonhuman Primates as a Model System for Gene Therapy Development in Ophthalmology

Gene therapy is a treatment concept that uses, in most cases, viral vectors to deliver a therapeutic transgene to target cells. Although the idea of gene therapy dates back over 50 years ago, due to the complexity of the treatment concept, it took until the last decade for the responsible agencies like FDA and EMA to recommend the first gene therapy products for clinical use. The development of these therapies relies on molecular engineering of specifically designed vectors and models to test the effectiveness and safety of the treatment. Despite an increasing effort to find effective surrogates, animal models are still irreplaceable in gene therapy development. Rodents are important for exploring pathways and disease mechanisms and identifying potential treatment targets. However, only the primate eye resembles the human eye to a degree where most structures are nearly identical. Some research questions can therefore only be answered using a nonhuman primate (NHP) model. In this review, we want to summarize these key features and highlight the importance of the NHP model for gene therapy development in ophthalmology.

Discovering the Potential of Natural Antioxidants in Age-Related Macular Degeneration: A Review

Age-related macular degeneration (AMD) is a multifactorial disease associated with anatomical changes in the inner retina. Despite tremendous advances in clinical care, there is currently no cure for AMD. This review aims to evaluate the published literature on the therapeutic roles of natural antioxidants in AMD. A literature search of PubMed, Web of Science and Google Scholar for peer-reviewed articles published between 1 January 2011 and 31 October 2021 was undertaken. A total of 82 preclinical and 18 clinical studies were eligible for inclusion in this review. We identified active compounds, carotenoids, extracts and polysaccharides, flavonoids, formulations, vitamins and whole foods with potential therapeutic roles in AMD. We evaluated the integral cellular signaling pathways including the activation of antioxidant pathways and angiogenesis pathways orchestrating their mode of action. In conclusion, we examined the therapeutic roles of natural antioxidants in AMD which warrant further study for application in clinical practice. Our current understanding is that natural antioxidants have the potential to improve or halt the progression of AMD, and tailoring therapeutics to the specific disease stages may be the key to preventing irreversible vision loss.

Management and control of intraocular pressure applying macitentan hydrogel film formulation: improved effect of surfactant and cosurfactant system

BACKGROUND

Macitentan blocks endothelin receptors in order to control the pulmonary arterial hypertension (PAH). Oral administration of macitentan is associated with painful urination and troubled breathing.

OBJECTIVES

Formulated macitentan hydrogel film was used for examining the control of intraocular pressure, and the effect of surfactant and cosurfactant was studied.

METHODS

Macitentan ocular film formulation has been prepared in hydroxypropyl methylcellulose (HPMC) matrix system using different surfactant/co-surfactant system, and intraocular pressure was monitored on normotensive rabbit eyes after application in the cul-de-sac.

RESULTS

The solid state characterization of the film indicated amorphisation of macitentan and no issues regarding major incompatibility was observed. Combination of surfactant, co-surfactant and hydrophilic co-solvent systems in the said films markedly improved the drug release and mucosal tissue permeation. Presence of PEG and Transcutol significantly improved ex vivo corneal permeation of MP and MT respectively compared to other films. Transcutol (MT) exhibited greatest difference among the formulations by improving the vesicular bilayer fluidity and reducing the mucosal tissue barrier facilitating the transcorneal diffusion. A combination of diffusion and erosion control behavior was observed in drug release and corneal permeation of the films due to the balanced liquid penetration and polymeric chain relaxation rate. MP and MT films were used for further in vivo studies to achieve possible effective and prolonged control of intraocular pressure. In vivo study has revealed the reduction in intraocular pressure upto about 23 % when tested on normotensive rabbit model. The films has managed to lower the IOP upto 3 h.

CONCLUSION

Developed macitentan hydrogel film containing Transcutol (MT) could have a high potential for the control and management of ocular hypertension after topical application.

Establishment of the New Zealand white rabbit animal model of fatty keratopathy associated with corneal neovascularization

The term fatty keratopathy is used to describe the phenomenon of fat deposition caused by corneal neovascularization, which will severely affect the eye's beauty and vision. The purpose of this study was to establish a New Zealand white rabbit animal model of fatty keratopathy, that is, the establishment of an animal model of fatty keratopathy. The goal was achieved by the combination of a corneal neovascularization animal model and a hyperlipidemia animal model. Two groups were created according to the experimental sequence. The first group initially induced a corneal neovascularization pattern and later induced a hyperlipidemia pattern, and the second group followed the opposite sequence. The results of the two groups showed that all the significant crystalline deposits of the cornea were visible. So the animal models of fatty keratopathy were successfully established in both groups.

Therapeutic Drugs and Devices for Tackling Ocular Hypertension and Glaucoma, and Need for Neuroprotection and Cytoprotective Therapies

Damage to the optic nerve and the death of associated retinal ganglion cells (RGCs) by elevated intraocular pressure (IOP), also known as glaucoma, is responsible for visual impairment and blindness in millions of people worldwide. The ocular hypertension (OHT) and the deleterious mechanical forces it exerts at the back of the eye, at the level of the optic nerve head/optic disc and lamina cribosa, is the only modifiable risk factor associated with glaucoma that can be treated. The elevated IOP occurs due to the inability of accumulated aqueous humor (AQH) to egress from the anterior chamber of the eye due to occlusion of the major outflow pathway, the trabecular meshwork (TM) and Schlemm’s canal (SC). Several different classes of pharmaceutical agents, surgical techniques and implantable devices have been developed to lower and control IOP. First-line drugs to promote AQH outflow via the uveoscleral outflow pathway include FP-receptor prostaglandin (PG) agonists (e.g., latanoprost, travoprost and tafluprost) and a novel non-PG EP2-receptor agonist (omidenepag isopropyl, Eybelis^®). TM/SC outflow enhancing drugs are also effective ocular hypotensive agents (e.g., rho kinase inhibitors like ripasudil and netarsudil; and latanoprostene bunod, a conjugate of a nitric oxide donor and latanoprost). One of the most effective anterior chamber AQH microshunt devices is the Preserflo^® microshunt which can lower IOP down to 10–13 mmHg. Other IOP-lowering drugs and devices on the horizon will be also discussed. Additionally, since elevated IOP is only one of many risk factors for development of glaucomatous optic neuropathy, a treatise of the role of inflammatory neurodegeneration of the optic nerve and retinal ganglion cells and appropriate neuroprotective strategies to mitigate this disease will also be reviewed and discussed.

Looking for In Vitro Models for Retinal Diseases

Retina is a layered structure of the eye, composed of different cellular components working together to produce a complex visual output. Because of its important role in visual function, retinal pathologies commonly represent the main causes of visual injury and blindness in the industrialized world. It is important to develop in vitro models of retinal diseases to use them in first screenings before translating in in vivo experiments and clinics. For this reason, it is important to develop bidimensional (2D) models that are more suitable for drug screening and toxicological studies and tridimensional (3D) models, which can replicate physiological conditions, for investigating pathological mechanisms leading to visual loss. This review provides an overview of the most common retinal diseases, relating to in vivo models, with a specific focus on alternative 2D and 3D in vitro models that can replicate the different cellular and matrix components of retinal layers, as well as injury insults that induce retinal disease and loss of the visual function.

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.

Features of Retinal Neurogenesis as a Key Factor of Age-Related Neurodegeneration: Myth or Reality?

Age-related macular degeneration (AMD) is a complex multifactorial neurodegenerative disease that constitutes the most common cause of irreversible blindness in the elderly in the developed countries. Incomplete knowledge about its pathogenesis prevents the search for effective methods of prevention and treatment of AMD, primarily of its "dry" type which is by far the most common (90% of all AMD cases). In the recent years, AMD has become "younger": late stages of the disease are now detected in relatively young people. It is known that AMD pathogenesis-according to the age-related structural and functional changes in the retina-is linked with inflammation, hypoxia, oxidative stress, mitochondrial dysfunction, and an impairment of neurotrophic support, but the mechanisms that trigger the conversion of normal age-related changes to the pathological process as well as the reason for early AMD development remain unclear. In the adult mammalian retina, de novo neurogenesis is very limited. Therefore, the structural and functional features that arise during its maturation and formation can exert long-term effects on further ontogenesis of this tissue. The aim of this review was to discuss possible contributions of the changes/disturbances in retinal neurogenesis to the early development of AMD.

The Emerging Role of Topical Ocular Drugs to Target the Posterior Eye

The prevalence of chronic fundus diseases is increasing with the aging of the general population. The treatment of these intraocular diseases relies on invasive drug delivery because of the globular structure and multiple barriers of the eye. Frequent intraocular injections bring heavy burdens to the medical care system and patients. The use of topical drugs to treat retinal diseases has always been an attractive solution. The fast development of new materials and technologies brings the possibility to develop innovative topical formulations. This article reviews anatomical and physiological barriers of the eye which affect the bioavailability of topical drugs. In addition, we summarize innovative topical formulations which enhance the permeability of drugs through the ocular surface and/or extend the drug retention time in the eye. This article also reviews the differences of eyes between different laboratory animals to address the translational challenges of preclinical models. The fast development of in vitro eye models may provide more tools to increase the clinical translationality of topical formulations for intraocular diseases. Clinical successes of topical formulations rely on continuous and collaborative efforts between different disciplines.

Deep Learning Model for Pathogen Classification Using Feature Fusion and Data Augmentation

Background:

Bacterial pathogens are deadly for animals and humans. The ease of their dissemination, coupled with their high capacity for ailment and death in infected individuals, makes them a threat to society.

Objective:

Due to high similarity among genera and species of pathogens, it is sometimes difficult for microbiologists to differentiate between them. Their automatic classification using deep-learning models can help in reliable, and accurate outcomes.

Method:

Deep-learning models, namely; AlexNet, GoogleNet, ResNet101, and InceptionV3 are used with numerous variations including training model from scratch, fine-tuning without pre-trained weights, fine-tuning along with freezing weights of initial layers, fine-tuning along with adjusting weights of all layers and augmenting the dataset by random translation and reflection. Moreover, as the dataset is small, fine-tuning and data augmentation strategies are applied to avoid overfitting and produce a generalized model. A merged feature vector is produced using two best-performing models and accuracy is calculated by xgboost algorithm on the feature vector by applying cross-validation.

Results:

Fine-tuned models where augmentation is applied produces the best results. Out of these, two-best-performing deep models i.e. (ResNet101, and InceptionV3) selected for feature fusion, produced a similar validation accuracy of 95.83 with a loss of 0.0213 and 0.1066, and a testing accuracy of 97.92 and 93.75, respectively. The proposed model used xgboost to attained a classification accuracy of 98.17% by using 35-folds cross-validation.

Conclusion:

The automatic classification using these models can help experts in the correct identification of pathogens. Consequently, they can help in controlling epidemics and thereby minimizing the socio-economic impact on the community.

Pharmacokinetics of intravitreal macromolecules: Scaling between rats and rabbits

Rats are widely used to study ocular drug responses, whereas rabbits are the most widely used preclinical model of ocular pharmacokinetics. Despite their wide use in evaluation of intravitreally injected drugs, translational information about pharmacokinetics and dose scaling between rats and rabbits is missing. In this study, we investigated intravitreal pharmacokinetics in rats and rabbits using non-invasive ocular fluorophotometry. Fluorescein and fluorescently labeled molecules (dextrans) with different molecular weights (376 Da, 10, 150 and 500 kDa), were injected into the vitreous of rabbits and rats. Intravitreal concentrations of the compounds were determined and pharmacokinetic parameters were calculated. Overall, the elimination half-lives of the macromolecules in rat vitreous were 5-6 times shorter than in rabbits, and the half-lives were prolonged at increasing molecular weights. The apparent volumes of distribution for tested compounds in rats and rabbits were in the range of the anatomical vitreal volumes. In both species, anterior route of elimination was predominant for the dextrans, whereas fluorescein was mainly eliminated via posterior route. Rabbit-to-rat ratios for intravitreal clearance were in the range of 2 to 5 for dextrans. Therefore, 2-5 times higher doses are needed for similar drug exposure in rabbits than in rats. Also, the shorter half-lives of macromolecules in the rat vitreous must be taken into account in translation to rabbit and human studies. The scaling factors presented herein will augment translational drug development for eye diseases.

Stable oxime-crosslinked hyaluronan-based hydrogel as a biomimetic vitreous substitute

Vitreous substitutes are clinically used to maintain retinal apposition and preserve retinal function; yet the most used substitutes are gases and oils which have disadvantages including strict face-down positioning post-surgery and the need for subsequent surgical removal, respectively. We have engineered a vitreous substitute comprised of a novel hyaluronan-oxime crosslinked hydrogel. Hyaluronan, which is naturally abundant in the vitreous of the eye, is chemically modified to crosslink with poly(ethylene glycol)-tetraoxyamine via oxime chemistry to produce a vitreous substitute that has similar physical properties to the native vitreous including refractive index, density and transparency. The oxime hydrogel is cytocompatible in vitro with photoreceptors from mouse retinal explants and biocompatible in rabbit eyes as determined by histology of the inner nuclear layer and photoreceptors in the outer nuclear layer. The ocular pressure in the rabbit eyes was consistent over 56 d, demonstrating limited to no swelling. Our vitreous substitute was stable in vivo over 28 d after which it began to degrade, with approximately 50% loss by day 56. We confirmed that the implanted hydrogel did not impact retina function using electroretinography over 90 days versus eyes injected with balanced saline solution. This new oxime hydrogel provides a significant improvement over the status quo as a vitreous substitute.

PDGF Receptor Alpha Signaling Is Key for Müller Cell Homeostasis Functions

Müller cells, the major retinal macroglia, are key to maintaining vascular integrity as well as retinal fluid and ion homeostasis. Although platelet derived growth factor (PDGF) receptor expression in Müller glia has been reported earlier, their actual role for Müller cell function and intimate interaction with cells of the retinal neurovascular unit remains unclear. To close this gap of knowledge, Müller cell-specific PDGF receptor alpha (PDGFRα) knockout (KO) mice were generated, characterized, and subjected to a model of choroidal neovascularization (CNV). PDGFRα-deficient Müller cells could not counterbalance hypoosmotic stress as efficiently as their wildtype counterparts. In wildtypes, the PDGFRα ligand PDGF-BB prevented Müller cell swelling induced by the administration of barium ions. This effect could be blocked by the PDGFR family inhibitor AC710. PDGF-BB could not restore the capability of an efficient volume regulation in PDGFRα KO Müller cells. Additionally, PDGFRα KO mice displayed reduced rod and cone-driven light responses. Altogether, these findings suggest that Müller glial PDGFRα is central for retinal functions under physiological conditions. In contrast, Müller cell-specific PDGFRα KO resulted in less vascular leakage and smaller lesion areas in the CNV model. Of note, the effect size was comparable to pharmacological blockade of PDGF signaling alone or in combination with anti-vascular endothelial growth factor (VEGF) therapy—a treatment regimen currently being tested in clinical trials. These data imply that targeting PDGF to treat retinal neovascular diseases may have short-term beneficial effects, but may elicit unwarranted side effects given the putative negative effects on Müller cell homeostatic functions potentially interfering with a long-term positive outcome.

Quantification of Drugs in Distinctly Separated Ocular Substructures of Albino and Pigmented Rats

The rat is a commonly used species in ocular drug research. Detailed methods of separating rat ocular tissues have not been described in literature. To understand the intraocular drug distribution, we developed a robust method for the separation of individual anterior and posterior substructures of pigmented Brown Norway (BN) and albino Wistar Han (WH) rat eyes, followed by quantification of drug concentration in these substructures. A short formalin incubation, which did not interfere with drug quantification, enabled the preservation of individual tissue sections while minimizing cross-tissue contamination, as demonstrated by histological analysis. Following oral administration, we applied the tissue separation method, in order to determine the ocular concentrations of dexamethasone and levofloxacin, as well as two in-house molecules BI 113823 and BI 1026706, compounds differing in their melanin binding. The inter-individual variability in tissue partitioning coefficients (Kp) was low, demonstrating the reproducibility of the separation method. Kp values of individual tissues varied up to 100-fold in WH and up to 46,000-fold in BN rats highlighting the importance of measuring concentration directly from the ocular tissue of interest. Additionally, clear differences were observed in the BN rat tissue partitioning compared to the WH rat. Overall, the developed method enables a reliable determination of small molecule drug concentrations in ocular tissues to support ocular drug research and development.

Williams G, Brocchini S, Awwad S. Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

An eye on the dog as the scientist's best friend for translational research in ophthalmology: Focus on the ocular surface

Preclinical animal studies provide valuable opportunities to better understand human diseases and contribute to major advances in medicine. This review provides a comprehensive overview of ocular parameters in humans and selected animals, with a focus on the ocular surface, detailing species differences in ocular surface anatomy, physiology, tear film dynamics and tear film composition. We describe major pitfalls that tremendously limit the translational potential of traditional laboratory animals (i.e., rabbits, mice, and rats) in ophthalmic research, and highlight the benefits of integrating companion dogs with clinical analogues to human diseases into preclinical pharmacology studies. This One Health approach can help accelerate and improve the framework in which ophthalmic research is translated to the human clinic. Studies can be conducted in canine subjects with naturally occurring or noninvasively induced ocular surface disorders (e.g., dry eye disease, conjunctivitis), reviewed herein, and tear fluid can be easily retrieved from canine eyes for various bioanalytical purposes. In this review, we discuss common tear collection methods, including capillary tubes and Schirmer tear strips, and provide guidelines for tear sampling and extraction to improve the reliability of analyte quantification (drugs, proteins, others).

A Systematic Review on Transplantation Studies of the Retinal Pigment Epithelium in Animal Models

The retinal pigment epithelium (RPE) and the adjacent light-sensitive photoreceptors form a single functional unit lining the back of the eye. Both cell layers are essential for normal vision. RPE degeneration is usually followed by photoreceptor degeneration and vice versa. There are currently almost no effective therapies available for RPE disorders such as Stargardt disease, specific types of retinitis pigmentosa, and age-related macular degeneration. RPE replacement for these disorders, especially in later stages of the disease, may be one of the most promising future therapies. There is, however, no consensus regarding the optimal RPE source, delivery strategy, or the optimal experimental host in which to test RPE replacement therapy. Multiple RPE sources, delivery methods, and recipient animal models have been investigated, with variable results. So far, a systematic evaluation of the (variables influencing) efficacy of experimental RPE replacement parameters is lacking. Here we investigate the effect of RPE transplantation on vision and vision-based behavior in animal models of retinal degenerated diseases. In addition, we aim to explore the effect of RPE source used for transplantation, the method of intervention, and the animal model which is used.

METHODS

In this study, we systematically identified all publications concerning transplantation of RPE in experimental animal models targeting the improvement of vision (e.g., outcome measurements related to the morphology or function of the eye). A variety of characteristics, such as species, gender, and age of the animals but also cell type, number of cells, and other intervention characteristics were extracted from all studies. A risk of bias analysis was performed as well. Subsequently, all references describing one of the following outcomes were analyzed in depth in this systematic review: a-, b-, and c-wave amplitudes, vision-based, thickness analyses based on optical coherence tomography (OCT) data, and transplant survival based on scanning laser ophthalmoscopy (SLO) data. Meta-analyses were performed on the a- and b-wave amplitudes from electroretinography (ERG) data as well as data from vision-based behavioral assays.

RESULTS

original research articles met the inclusion criteria after two screening rounds. Overall, most studies were categorized as unclear regarding the risk of bias, because many experimental details were poorly reported. Twenty-three studies reporting one or more of the outcome measures of interest were eligible for either descriptive (thickness analyses based on OCT data; n = 2) or meta-analyses. RPE transplantation significantly increased ERG a-wave (Hedges' g 1.181 (0.471-1.892), n = 6) and b-wave (Hedges' g 1.734 (1.295-2.172), n = 42) amplitudes and improved vision-based behavior (Hedges' g 1.018 (0.826-1.209), n = 96). Subgroup analyses revealed a significantly increased effect of the use of young and adolescent animals compared to adult animals. Moreover, transplanting more cells (in the range of 105 versus in the range of 104) resulted in a significantly increased effect on vision-based behavior as well. The origin of cells mattered as well. A significantly increased effect was found on vision-based behavior when using ARPE-19 and OpRegen® RPE.

CONCLUSIONS

This systematic review shows that RPE transplantation in animal models for retinal degeneration significantly increases a- and b- wave amplitudes and improves vision-related behavior. These effects appear to be more pronounced in young animals, when the number of transplanted cells is larger and when ARPE-19 and OpRegen® RPE cells are used. We further emphasize that there is an urgent need for improving the reporting and methodological quality of animal experiments, to make such studies more comparable.

Effect of ocular hypertension on the pattern of retinal ganglion cell subtype loss in a mouse model of early-onset glaucoma

Glaucoma is a neurodegenerative disease with elevated intraocular pressure as one of the major risk factors. Glaucoma leads to irreversible loss of vision and its progression involves optic nerve head cupping, axonal degeneration, retinal ganglion cell (RGC) loss, and visual field defects. Despite its high global prevalence, glaucoma still remains a major neurodegenerative disease. Introduction of mouse models of experimental glaucoma has become integral to glaucoma research due to well-studied genetics as well as ease of manipulations. Many established inherent and inducible mouse models of glaucoma are used to study the molecular and physiological progression of the disease. One such model of spontaneous mutation is the nee model, which is caused by mutation of the Sh3pxd2b gene. In both humans and mice, mutations disrupting function of the SH3PXD2B adaptor protein cause a developmental syndrome including secondary congenital glaucoma. The purpose of this study was to characterize the early onset nee glaucoma phenotype on the C57BL/6J background and to evaluate the pattern of RGC loss and axonal degeneration in specific RGC subtypes. We found that the B6.Sh3pxd2b^nee mutant animals exhibit glaucoma phenotypes of elevated intraocular pressure, RGC loss and axonal degeneration. Moreover, the non-image forming RGCs survived longer than the On-Off direction selective RGCs (DSGC), and the axonal death in these RGCs was independent of their respective RGC subtype. In conclusion, through this study we characterized an experimental model of early onset glaucoma on a C57BL/6J background exhibiting key glaucoma phenotypes. In addition, we describe that RGC death has subtype-specific sensitivities and follows a specific pattern of cell death under glaucomatous conditions.