Ophthalmic drug discovery

An Antibiotic Nanobomb Constructed from pH-Responsive Chemical Bonds in Metal-Phenolic Network Nanoparticles for Biofilm Eradication and Corneal Ulcer Healing

In the treatment of refractory corneal ulcers caused by Pseudomonas aeruginosa, antibacterial drugs delivery faces the drawbacks of low permeability and short ocular surface retention time. Hence, novel positively-charged modular nanoparticles (NPs) are developed to load tobramycin (TOB) through a one-step self-assembly method based on metal-phenolic network and Schiff base reaction using 3,4,5-trihydroxybenzaldehyde (THBA), ε-poly-ʟ-lysine (EPL), and Cu2+ as matrix components. In vitro antibacterial test demonstrates that THBA-Cu-TOB NPs exhibit efficient instantaneous sterilization owing to the rapid pH responsiveness to bacterial infections. Notably, only 2.6 µg mL-1 TOP is needed to eradicate P. aeruginosa biofilm in the nano-formed THBA-Cu-TOB owing to the greatly enhanced penetration, which is only 1.6% the concentration of free TOB (160 µg mL-1). In animal experiments, THBA-Cu-TOB NPs show significant advantages in ocular surface retention, corneal permeability, rapid sterilization, and inflammation elimination. Based on molecular biology analysis, the toll-like receptor 4 and nuclear factor kappa B signaling pathways are greatly downregulated as well as the reduction of inflammatory cytokines secretions. Such a simple and modular strategy in constructing nano-drug delivery platform offers a new idea for toxicity reduction, physiological barrier penetration, and intelligent drug delivery.

Identification of the novel role of sterol regulatory element binding proteins (SREBPs) in mechanotransduction and intraocular pressure regulation

Trabecular meshwork (TM) cells are contractile and mechanosensitive, and they aid in maintaining intraocular pressure (IOP) homeostasis. Lipids are attributed to modulating TM contractility, with poor mechanistic understanding. In this study using human TM cells, we identify the mechanosensing role of the transcription factors sterol regulatory element binding proteins (SREBPs) involved in lipogenesis. By constitutively activating SREBPs and pharmacologically inactivating SREBPs, we have mechanistically deciphered the attributes of SREBPs in regulating the contractile properties of TM. The pharmacological inhibition of SREBPs by fatostatin and molecular inactivation of SREBPs ex vivo and in vivo, respectively, results in significant IOP lowering. As a proof of concept, fatostatin significantly decreased the SREBPs responsive genes and enzymes involved in lipogenic pathways as well as the levels of the phospholipid, cholesterol, and triglyceride. Further, we show that fatostatin mitigated actin polymerization machinery and stabilization, and decreased ECM synthesis and secretion. We thus postulate that lowering lipogenesis in the TM outflow pathway can hold the key to lowering IOP by modifying the TM biomechanics.

Identification of the novel role of sterol regulatory element binding proteins (SREBPs) in mechanotransduction and intraocular pressure regulation

Trabecular meshwork (TM) cells are highly contractile and mechanosensitive to aid in maintaining intraocular pressure (IOP) homeostasis. Lipids are attributed to modulating TM contractility with poor mechanistic understanding. In this study using human TM cells, we identify the mechanosensing role of the transcription factors sterol regulatory element binding proteins (SREBPs) involved in lipogenesis. By constitutively activating SREBPs and pharmacologically inactivating SREBPs, we have mechanistically deciphered the attributes of SREBPs in regulating the contractile properties of TM. The pharmacological inhibition of SREBPs by fatostatin and molecular inactivation of SREBPs ex vivo and in vivo respectively results in significant IOP lowering. As a proof of concept, fatostatin significantly decreased the SREBPs responsive genes and enzymes involved in lipogenic pathways as well as the levels of the phospholipid, cholesterol, and triglyceride. Further, we show that fatostatin mitigated actin polymerization machinery and stabilization, and decreased ECM synthesis and secretion. We thus postulate that lowering lipogenesis in the TM outflow pathway can hold the key to lowering IOP by modifying the TM biomechanics.

Synopsis

In this study, we show the role of lipogenic transcription factors sterol regulatory element binding proteins (SREBPs) in the regulation of intraocular pressure (IOP). ( Synopsis Figure - Created using Biorender.com ) SREBPs are involved in the sensing of changes in mechanical stress on the trabecular meshwork (TM). SREBPs aid in transducing the mechanical signals to induce actin polymerization and filopodia/lamellipodia formation.SREBPs inactivation lowered genes and enzymes involved in lipogenesis and modified lipid levels in TM.SREBPs activity is a critical regulator of ECM engagement to the matrix sites.Inactivation of SCAP-SREBP pathway lowered IOP via actin relaxation and decreasing ECM production and deposition in TM outflow pathway signifying a novel relationship between SREBP activation status and achieving IOP homeostasis.

Neuroprotective effect of the calcium channel blocker nilvadipine on retinal ganglion cell death in a mouse ocular hypertension model

We investigated whether nilvadipine has a neuroprotective effect on retinal ganglion cells (RGCs) in a mouse model of ocular hypertension (OH) that expresses cyan fluorescein protein (CFP) in RGCs. OH was induced in the right eyes of Thy1-CFP transgenic mice using a laser. Nilvadipine or vehicle treatment began simultaneously with OH modeling and was administered intraperitoneally once daily for 8 weeks. Intraocular pressure (IOP) in both the laser- and non-treated eyes was measured weekly with the microneedle method, and calculations were performed to estimate the pressure insult in each eye. Using a retinal whole mount, the number of RGCs was counted at week 9. Laser-treated eyes showed a significant increase in IOP (p < 0.01), and the pressure insult did not differ between the drug-treated groups. Over time, laser treatment produced a significant decrease in the number of RGCs in the vehicle-treated groups, but this effect was attenuated by nilvadipine treatment. The pressure insult and RGC survival rate were significantly negatively correlated in the vehicle-treated group (y = -0.078 x + 107.8, r = 0.76, p < 0.001), but not in the nilvadipine-treated group (y = -0.015 x + 99.9, r = 0.43, p = 0.128). Nilvadipine was a potent neuroprotective agent for RGCs in our mouse model of OH and may have potential for protection against glaucoma. This model is useful as a screening tool for drugs with retinal protective effects.

Biodegradable silicon nanoneedles for ocular drug delivery

Ocular drug delivery remains a grand challenge due to the complex structure of the eye. Here, we introduce a unique platform of ocular drug delivery through the integration of silicon nanoneedles with a tear-soluble contact lens. The silicon nanoneedles can penetrate into the cornea in a minimally invasive manner and then undergo gradual degradation over the course of months, enabling painless and long-term sustained delivery of ocular drugs. The tear-soluble contact lens can fit a variety of corneal sizes and then quickly dissolve in tear fluid within a minute, enabling an initial burst release of anti-inflammatory drugs. We demonstrated the utility of this platform in effectively treating a chronic ocular disease, such as corneal neovascularization, in a rabbit model without showing a notable side effect over current standard therapies. This platform could also be useful in treating other chronic ocular diseases.

Thermo-sensitivity and erosion of chitosan crosslinked poly[N-isopropylacrylamide-co-(acrylic acid)-co-(methyl methacrylate)] hydrogels for application to the inferior fornix

Thermo-gels based on chitosan crosslinked poly(N-isopropylacrylamide) were developed as alternatives to conventional eye drops for the sustained release of ketotifen fumarate in the treatment of allergic conjunctivitis. The thermo-gelling properties of the base polymer were altered prior to crosslinking with chitosan by incorporation of the hydrophilic and hydrophobic comonomers acrylic acid and methyl methacrylate respectively. Varying amounts of chitosan were incorporated by ionic interaction to produce polyelectrolyte complexes or by carbodiimide chemistry to produce covalently crosslinked networks. The lower critical solution temperature of all the chitosan crosslinked thermo-gels produced was below the surface temperature of the eye. All the chitosan crosslinked thermo-gels were found to have greater than 80% equilibrium water contents following gelation. The method and amount of chitosan incorporation allowed for tailor-ability of material rheologic properties, with full degradation occurring over a one-to-four-day period, and tailorable rates of release of 40-60% of the loaded allergy medication ketotifen fumarate. The chitosan crosslinked thermo-gels were demonstrated to be nontoxic both in vitro and in vivo. It was demonstrated that the synthesized materials could be applied to the inferior fornix of eye, sustaining a multiple day release of ketotifen fumarate, as an alternative to conventional eyedrops. STATEMENT OF SIGNIFICANCE: Topical eyedrops are the main treatment modality for anterior ocular conditions. However, due to the natural clearance mechanisms of the eye, topical eyedrops are well established to be largely ineffective as a method of drug delivery. Herein, we investigate a method of altering thermo-gel properties of an n-isopropylacrylamide based polymer to enable the incorporation of greater amounts of chitosan by different methods of crosslinking. By controlling the synthesis parameters, final material properties can be tailored to impart ideal spreading, retention on the eye, and the rate of degradation and drug release over several days. This work also focuses on studying the rheological properties of the chitosan crosslinked thermo-gels which has not been investigated previously.

Ocular Disease Therapeutics: Design and Delivery of Drugs for Diseases of the Eye

The ocular drug discovery field has evidenced significant advancement in the past decade. The FDA approvals of Rhopressa, Vyzulta, and Roclatan for glaucoma, Brolucizumab for wet age-related macular degeneration (wet AMD), Luxturna for retinitis pigmentosa, Dextenza (0.4 mg dexamethasone intracanalicular insert) for ocular inflammation, ReSure sealant to seal corneal incisions, and Lifitegrast for dry eye represent some of the major developments in the field of ocular therapeutics. A literature survey also indicates that gene therapy, stem cell therapy, and target discovery through genomic research represent significant promise as potential strategies to achieve tissue repair or regeneration and to attain therapeutic benefits in ocular diseases. Overall, the emergence of new technologies coupled with first-in-class entries in ophthalmology are highly anticipated to restructure and boost the future trends in the field of ophthalmic drug discovery. This perspective focuses on various aspects of ocular drug discovery and the recent advances therein. Recent medicinal chemistry campaigns along with a brief overview of the structure-activity relationships of the diverse chemical classes and developments in ocular drug delivery (ODD) are presented.

DNA-Based Hybrid Hydrogels Sustain Water-Insoluble Ophthalmic Therapeutic Delivery against Allergic Conjunctivitis

Clinical need for treating allergic conjunctivitis (AC) is rapidly increasing. However, AC-relevant anti-inflammatory compounds are generally difficult to solubilize in water, thus limiting their therapeutic potential. Solubility-improved eye drop formulations of these compounds have poor bioavailability and a short retention time in ophthalmic tissues. Herein, we report a DNA/poly(lactic-co-glycolicacid) (PLGA) hybrid hydrogel (HDNA) for water-insoluble ophthalmic therapeutic delivery. PLGA pre-encapsulation enables loading of water-insoluble therapeutics. HDNA's porous structure is capable of sustained delivery of therapeutics. Dexamethasone (DEX), with demonstrated activities in attenuating inflammatory symptom in AC, was used as a model system. The designed HDNA hybrid hydrogels significantly improved the DEX accumulation and mediated the gradual DEX release in ophthalmic cells and tissues. Using the HDNA-DEX complexes, potent efficacy in two animal models of AC was acquired. Given this performance, demonstrable biocompatibility, and biodegradability of DNA hydrogel, the HDNA-based ophthalmic therapeutic delivery system enables novel treatment paradigms, which will have widespread applications in the treatment of various eye diseases.

A Controlled Release System for Long-Acting Intravitreal Delivery of Small Molecules

Purpose

The short half lives of small molecules in the vitreous requires frequent repeated intravitreal injections that are impractical for treatment of chronic eye diseases. We sought to develop a method for increasing the intravitreal half-life of small-molecule drugs.

Methods

We adapted a technology for controlled release of drugs from macromolecular carriers for use as a long-acting intravitreal delivery system for small molecules. As a prototype, a small molecule complement factor D inhibitor with an intravitreal half-life of 7 hours was covalently attached to a 4-arm PEG_40kDa by a self-cleaving β-eliminative linker with a cleavage half-life of approximately 1 week.

Results

After intravitreal injection in rabbits, the drug was slowly released in the vitreous, and equilibrated with the retina and choroid. The intravitreal half-life of the intact PEG-drug conjugate in the rabbit was 7 days, and that of the released drug was 3.6 days. We simulated the anticipated pharmacokinetics of the delivery system in human vitreous, and estimated that the half-life of a 4-arm PEG_40kDa conjugate would be approximately 2 weeks, and that of the released drug would be approximately 5 days.

Conclusions

We posit that a linker with a cleavage half life of 2 weeks would confer a half life of approximately 7 days to a released small molecule drug in humans, comparable to the half life of approved intravitreal injected macromolecular drugs.

Translational Relevance

With this technology, a potent small molecule with an appropriate therapeutic window should be administrable by intravitreal injections in the human at once-monthly intervals.

iDrugs and iDevices Discovery Research: Preclinical Assays, Techniques, and Animal Model Studies for Ocular Hypotensives and Neuroprotectants

Discovery ophthalmic research is centered around delineating the molecular and cellular basis of ocular diseases and finding and exploiting molecular and genetic pathways associated with them. From such studies it is possible to determine suitable intervention points to address the disease process and hopefully to discover therapeutics to treat them. An investigational new drug (IND) filing for a new small-molecule drug, peptide, antibody, genetic treatment, or a device with global health authorities requires a number of preclinical studies to provide necessary safety and efficacy data. Specific regulatory elements needed for such IND-enabling studies are beyond the scope of this article. However, to enhance the overall data packages for such entities and permit high-quality foundation-building publications for medical affairs, additional research and development studies are always desirable. This review aims to provide examples of some target localization/verification, ocular drug discovery processes, and mechanistic and portfolio-enhancing exploratory investigations for candidate drugs and devices for the treatment of ocular hypertension and glaucomatous optic neuropathy (neurodegeneration of retinal ganglion cells and their axons). Examples of compound screening assays, use of various technologies and techniques, deployment of animal models, and data obtained from such studies are also presented.

Nanotechnology for Omics-Based Ocular Drug Delivery

Millions of people suffer from ocular diseases that impair vision and can lead to blindness. Advances in genomics and proteomics have revealed a number of different molecular markers specific for different ocular diseases, thereby optimizing the processes of drug development and discovery. Nanotechnology can increase the throughput of data obtained in omics-based studies and allows for more sensitive diagnostic techniques as more efficient drug delivery systems. Biocompatible and biodegradable nanomaterials developed through omics-based research are able to target reported molecular markers for different ocular diseases and offer novel alternatives to conventional drug therapy. In this chapter, the authors review the pathophysiology, current genomic and proteomic information, and current nanomaterial-based therapies of four ocular diseases: glaucoma, uveal melanoma, age-related macular degeneration, and diabetic retinopathy. Omics-based research can be used to elucidate specific genes and proteins and develop novel nanomedicine formulations to prevent, halt, or cure ocular diseases at the transcriptional or translational level.

Nanotechnology for Omics-Based Ocular Drug Delivery

Millions of people suffer from ocular diseases that impair vision and can lead to blindness. Advances in genomics and proteomics have revealed a number of different molecular markers specific for different ocular diseases, thereby optimizing the processes of drug development and discovery. Nanotechnology can increase the throughput of data obtained in omics-based studies and allows for more sensitive diagnostic techniques as more efficient drug delivery systems. Biocompatible and biodegradable nanomaterials developed through omics-based research are able to target reported molecular markers for different ocular diseases and offer novel alternatives to conventional drug therapy. In this chapter, the authors review the pathophysiology, current genomic and proteomic information, and current nanomaterial-based therapies of four ocular diseases: glaucoma, uveal melanoma, age-related macular degeneration, and diabetic retinopathy. Omics-based research can be used to elucidate specific genes and proteins and develop novel nanomedicine formulations to prevent, halt, or cure ocular diseases at the transcriptional or translational level.

Physicochemical properties of core-shell type nanoparticles govern their spatiotemporal biodistribution in the eye

Due to the inherent barrier properties of eye tissues, a major challenge in treating eye diseases is to provide a therapeutic agent to the desired tissue in quantities and durations that are favorable. This study aimed at understanding the influence of physicochemical properties of nanoparticles on their spatiotemporal biodistribution in mouse eye. For this, core-shell nanoparticles with different properties were designed by varying either core or shell and administered as eye-drops to mice. The results demonstrated that all nanoparticles irrespective of type of core or shell followed the conjunctival-scleral pathway. The bioavailability of cores followed the order polylactide-co-glycolide≥polylactide≥polycaprolactone for all tissues and time-points. The bioavailability for all shell types was greater in conjunctiva, sclera, choroid and retina when compared to other eye tissues. Therefore, modulating physicochemical properties of nanoparticles can be used as a design strategy to devise drug carriers that target specific tissues of the eye.

Dexamethasone – PAMAM dendrimer conjugates for retinal delivery: preparation, characterization and in vivo evaluation

Objective

Ocular diseases affecting retina, such as diabetic retinopathy (DR), age-related macular degeneration (AMD) and glaucoma are the major causes of blindness, and their treatment is still a challenge due to the special structure of the eye. The purpose of this study was to prepare a sustained release DEX conjugate formulation with enhanced ocular permeation using poly(amidoamine) (PAMAM) dendrimers and to evaluate the effects of conjugation on DEX release and ocular residence time.

Methods

PAMAM G3.5 and PAMAM G4.5 dendrimers were used to prepare DEX conjugates, and conjugation was confirmed using 1H-NMR. Formulations were evaluated in terms of drug release in the presence of ocular enzymes and cytotoxicity on ARPE19 cell lines. Fluorotron analysis was performed and ocular pharmacokinetic properties of DEX–PAMAM conjugates were studied in Sprague Dawley rats following intravitreal and subconjunctival applications.

Key Findings

The results indicated that DEX–PAMAM conjugates were able to enhance ocular permeability and ocular tissue levels of DEX following subconjunctival injection, and results were encouraging when compared to the literature that has reported DEX getting cleared from vitreous in 3 h.

Conclusion

Current studies are focused on formulation improvement to enhance hydrolysis and clearance time.

N-succinyl chitosan preparation, characterization, properties and biomedical applications: a state of the art review

N-succinyl chitosan (NSC) remains a promising chitosan derivative to develop targeted drug delivery, wound dressings, and tissue engineering systems. All these systems are important in life sciences. NSC is an amphiprotic derivative obtained from the N-acylation of chitosan. NSC exhibits extraordinary biocompatibility, significantly increased aqueous solubility in acidic and basic media without affecting the biological properties, appreciable transfection efficiency, and the ability to stimulate osteogenesis. NSC shows enhanced bioavailability, which highlights its potential applications in the biomedical field. This review briefly introduces chitosan, including its limitations as a biomaterial, and modifications of chitosan with a particular focus on acylation, along with a comprehensive overview of the synthesis, characterization, properties, biodistribution, and toxicological/biopharmaceutical profile of NSC. Furthermore, it extensively surveys current state-of-the-art NSC-based formulations for drug delivery with special emphasis on protein delivery, anti-cancer activity in the colon, as well as nasal and ophthalmic targeted gene/drug delivery. Moreover, it discusses NSC-based biomaterial applications in articular, adipose, and bone tissue engineering. In addition, it describes recent contributions of NSC-based hydrogels in wound dressings along with a brief account of drug delivery in combination with tissue engineering. Finally, it presents potential current challenges and future perspectives of NSC-based formulations in the biomedical field.

A thermo-responsive protein treatment for dry eyes

Millions of Americans suffer from dry eye disease, and there are few effective therapies capable of treating these patients. A decade ago, an abundant protein component of human tears was discovered and named lacritin (Lacrt). Lacrt has prosecretory activity in the lacrimal gland and mitogenic activity at the corneal epithelium. Similar to other proteins placed on the ocular surface, the durability of its effect is limited by rapid tear turnover. Motivated by the rationale that a thermo-responsive coacervate containing Lacrt would have better retention upon administration, we have constructed and tested the activity of a thermo-responsive Lacrt fused to an elastin-like polypeptide (ELP). Inspired from the human tropoelastin protein, ELP protein polymers reversibly phase separate into viscous coacervates above a tunable transition temperature. This fusion construct exhibited the prosecretory function of native Lacrt as illustrated by its ability to stimulate β-hexosaminidase secretion from primary rabbit lacrimal gland acinar cells. It also increased tear secretion from non-obese diabetic (NOD) mice, a model of autoimmune dacryoadenitis, when administered via intra-lacrimal injection. Lacrt ELP fusion proteins undergo temperature-mediated assembly to form a depot inside the lacrimal gland. We propose that these Lacrt ELP fusion proteins represent a potential therapy for dry eye disease and the strategy of ELP-mediated phase separation may have applicability to other diseases of the ocular surface.

FR-190997, a nonpeptide bradykinin B2-receptor partial agonist, is a potent and efficacious intraocular pressure lowering agent in ocular hypertensive cynomolgus monkeys

Preclinical Research FR-190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl) cinnaminoacetyl]-N-methylamino]benzyloxy]-2-methyl-4- (2-pyridylmethoxy) quinoline), a nonpeptide bradykinin (BK) B2-receptor-selective agonist, represents a novel class of ocular hypotensive agents. FR-190997 exhibited a high affinity for the human cloned B2-receptor (Ki = 9.8 nM) and a relatively high potency (EC50 = 155 nM) for mobilizing intracellular Ca(2+) ([Ca(2+)]i) in human ocular cells from nonpigmented ciliary epithelium; trabecular meshwork [h-TM]; ciliary muscle [h-CM] that are involved in regulating intraocular pressure (IOP). Unlike BK, FR-190997 behaved as a partial agonist (Emax = 38-80%) in these cells and its [Ca(2+)]i-mobilizing effects were blocked by the B2-receptor-selective antagonists (HOE-140, Ki = 0.8-7 nM; WIN-64338, Ki = 157-425 nM). FR-190997 stimulated the production of prostaglandins (PGs) in h-CM and h-TM cells (EC50 = 15-19 nM; Emax = 27-33%); an effect that was reduced by the cyclooxygenase-2 inhibitor bromfenac, and by HOE-140. FR-190997 also induced pro-matrix metalloproteinase (MMP)-1 and MMP-3 release from h-CM cells. FR-190997 significantly lowered IOP (37% [P < 0.001] with 30 μg, 24 h post-topical ocular dosing) in ocular hypertensive eyes of conscious Cynomolgus monkeys. This effect was reduced by bromfenac and completely blocked by a B2-antagonist. FR-190997 primarily stimulated uveoslceral outflow (UVSO) of aqueous humor (2.6 to 3.9-fold above baseline). In conclusion, FR-190997 is a B2-receptor selective partial agonist that activates phospholipase C, mobilizes [Ca(2+)]; induces PG and pro-MMP production, and that profoundly lowers IOP by promoting UVSO in ocular hypertensive Cynomolgus monkey eyes.

Endogenous Bioactive Lipids and the Regulation of Conventional Outflow Facility

Perturbation of paracrine signaling within the human conventional outflow pathway influences tissue homeostasis and outflow function. For example, exogenous introduction of the bioactive lipids, sphingosine-1-phosphate, anandamide or prostaglandin F(2α), to conventional outflow tissues alters the rate of drainage of aqueous humor through the trabecular meshwork, and into Schlemm's canal. This review summarizes recent data that characterizes endogenous bioactive lipids, their receptors and associated signaling partners in the conventional outflow tract. We also discuss the potential of targeting such signaling pathways as a strategy for the development of therapeutics to treat ocular hypertension and glaucoma.

Involvement of AP-1 and C/EBPβ in upregulation of endothelin B (ETB) receptor expression in a rodent model of glaucoma

Previous studies showed that the endothelin B receptor (ET_B) expression was upregulated and played a key role in neurodegeneration in rodent models of glaucoma. However, the mechanisms underlying upregulation of ET_B receptor expression remain largely unknown. Using promoter-reporter assays, the 1258 bp upstream the human ET_B promoter region was found to be essential for constitutive expression of ET_B receptor gene in human non-pigmented ciliary epithelial cells (HNPE). The −300 to −1 bp and −1258 to −600 bp upstream promoter regions of the ET_B receptor appeared to be the key binding regions for transcription factors. In addition, the crucial AP-1 binding site located at −615 to −624 bp upstream promoter was confirmed by luciferase assays and CHIP assays which were performed following overexpression of c-Jun in HNPE cells. Overexpression of either c-Jun or C/EBPβ enhanced the ET_B receptor promoter activity, which was reflected in increased mRNA and protein levels of ET_B receptor. Furthermore, knock-down of either c-Jun or C/EBPβ in HNPE cells was significantly correlated to decreased mRNA levels of both ET_B and ET_A receptor. These observations suggest that c-Jun and C/EBPβ are important for regulated expression of the ET_B receptor in HNPE cells. In separate experiments, intraocular pressure (IOP) was elevated in one eye of Brown Norway rats while the corresponding contralateral eye served as control. Two weeks of IOP elevation produced increased expression of c-Jun and C/EBPβ in the retinal ganglion cell (RGC) layer from IOP-elevated eyes. The mRNA levels of c-Jun, ET_A and ET_B receptor were upregulated by 2.2-, 3.1- and 4.4-fold in RGC layers obtained by laser capture microdissection from retinas of eyes with elevated IOP, compared to those from contralateral eyes. Taken together, these data suggest that transcription factor AP-1 plays a key role in elevation of ET_B receptor in a rodent model of ocular hypertension.

The potential of stem cell research for the treatment of neuronal damage in glaucoma

Stem cell research offers a wide variety of approaches for the advancement of our understanding of basic mechanisms of neurodegeneration and tissue regeneration and for the discovery and development of new therapeutic strategies to prevent and restore neuronal cell loss. Similar to most other regions of our central nervous system, degenerative diseases of the retina lead to the loss of neurons, which are not replaced. Recent work in animals has provided proof-of-concept evidence for the restoration of photoreceptor cells by cell transplantation and neuronal cell replacement by regeneration from endogenous cell sources. However, efficient therapeutic prevention of neuronal cell loss has not been achieved. Moreover, successful cell replacement of retinal neurons in humans, including that of ganglion cells, remains a major challenge. Future successes in the discovery and translation of neuroprotective drug and gene therapies and of cell-based regenerative therapies will depend on a better understanding of the underlying disease pathomechanisms. Existing stem cell and cell-reprogramming technologies offer the potential to generate human retina cells, to develop specific human-cell-based retina disease models, and to open up novel therapeutic strategies. Further, we might glean substantial knowledge from species that can or cannot regenerate their neuronal retina, in the search for new therapeutic approaches. Thus, stem cell research will pave the way toward clinical translation. In this review, I address some of the major possibilities presently on offer and speculate about the power of stem cell research to gain further insights into the pathomechanisms of retinal neurodegeneration (with special emphasis on glaucoma) and to advance our therapeutic options.

Ultrasound-enhanced delivery of antibiotics and anti-inflammatory drugs into the eye

Delivery of sufficient amounts of therapeutic drugs into the eye is often a challenging task. In this study, ultrasound application (frequencies of 400 KHz to 1 MHz, intensities of 0.3-1.0 W/cm(2) and exposure duration of 5 min) was investigated to overcome the barrier properties of cornea, which is a typical route for topical administration of ophthalmic drugs. Permeability of ophthalmic drugs, tobramycin and dexamethasone and sodium fluorescein, a drug-mimicking compound, was studied in ultrasound- and sham-treated rabbit corneas in vitro using a standard diffusion cell setup. Light microscopy observations were used to determine ultrasound-induced structural changes in the cornea. For tobramycin, an increase in permeability for ultrasound- and sham-treated corneas was not statistically significant. Increase of 46%-126% and 32%-109% in corneal permeability was observed for sodium fluorescein and dexamethasone, respectively, with statistical significance (p < 0.05) achieved at all treatment parameter combinations (compared with sham treatments) except for 1-MHz ultrasound applications for dexamethasone experiments. This permeability increase was highest at 400 kHz and appeared to be higher at higher intensities applied. Histologic analysis showed structural changes that were limited to epithelial layers of cornea. In summary, ultrasound application provided enhancement of drug delivery, increasing the permeability of the cornea for the anti-inflammatory ocular drug dexamethasone. Future investigations are needed to determine the effectiveness and safety of this application in in vivo long-term survival studies.

Delivery systems and local administration routes for therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.

Extended delivery of an anionic drug by contact lens loaded with a cationic surfactant

Drug eluding contact lenses can be very effective vehicles for ophthalmic drug delivery, but are incapable of releasing drug for more than a few hours. We propose to optimize the interactions of the polymer matrix of the contact lens with the hydrophobic tails of ionic surfactants to adsorb the surfactant molecules on the polymer with high packing and thus create a high surface charge. Ionic drugs can then adsorb on the charged surfactant coated surfaces with high affinity to reduce the transport rates, leading to extended release. Specifically, we show control release of an anionic drug dexamethasone 21-disodium phosphate from poly-hydroxyethyl methacrylate (p-HEMA) contact lenses by utilizing cationic surfactant (cetalkonium chloride). The partition coefficient of the drug increase exponentially with surfactant loading in the gel in at least qualitative agreement with the Debye-Hückel theory. The drug adsorbs on the surfactant covered polymer, and can also diffuse along the surface with diffusivity lower than that for the free drug, leading to a reduction in the effective diffusivity, which is the weighted combination of the free and surface diffusivities. The addition of surfactant did not impact transparency of lenses, and had additional benefits of increase in wettability and significant reduction in protein absorption. With a surfactant loading of about 10%, the drug release duration was increased from about 2 h to 50 h in 1-day ACUVUE(®) contact lenses, proving the viability of using surfactant for increasing drug release durations.

Protection of retinal ganglion cells and retinal vasculature by Lycium barbarum polysaccharides in a mouse model of acute ocular hypertension

Acute ocular hypertension (AOH) is a condition found in acute glaucoma. The purpose of this study is to investigate the protective effect of Lycium barbarum polysaccharides (LBP) and its protective mechanisms in the AOH insult. LBP has been shown to exhibit neuroprotective effect in the chronic ocular hypertension (COH) experiments. AOH mouse model was induced in unilateral eye for one hour by introducing 90 mmHg ocular pressure. The animal was fed with LBP solution (1 mg/kg) or vehicle daily from 7 days before the AOH insult till sacrifice at either day 4 or day 7 post insult. The neuroprotective effects of LBP on retinal ganglion cells (RGCs) and blood-retinal-barrier (BRB) were evaluated. In control AOH retina, loss of RGCs, thinning of IRL thickness, increased IgG leakage, broken tight junctions, and decreased density of retinal blood vessels were observed. However, in LBP-treated AOH retina, there was less loss of RGCs with thinning of IRL thickness, IgG leakage, more continued structure of tight junctions associated with higher level of occludin protein and the recovery of the blood vessel density when compared with vehicle-treated AOH retina. Moreover, we found that LBP provides neuroprotection by down-regulating RAGE, ET-1, Aβ and AGE in the retina, as well as their related signaling pathways, which was related to inhibiting vascular damages and the neuronal degeneration in AOH insults. The present study suggests that LBP could prevent damage to RGCs from AOH-induced ischemic injury; furthermore, through its effects on blood vessel protection, LBP would also be a potential treatment for vascular-related retinopathy.

Ophthalmic drug discovery: novel targets and mechanisms for retinal diseases and glaucoma

Blindness affects 60 million people worldwide. The leading causes of irreversible blindness include age-related macular degeneration, retinal vascular diseases and glaucoma. The unique features of the eye provide both benefits and challenges for drug discovery and delivery. During the past decade, the landscape for ocular drug therapy has substantially changed and our knowledge of the pathogenesis of ophthalmic diseases has grown considerably. Anti-angiogenic drugs have emerged as the most effective form of therapy for age-related macular degeneration and retinal vascular diseases. Lowering intraocular pressure is still the mainstay for glaucoma treatment but neuroprotective drugs represent a promising next-generation therapy. This Review discusses the current state of ocular drug therapy and highlights future therapeutic opportunities.

Effect of Lycium barbarum Polysaccharides on the expression of endothelin-1 and its receptors in an ocular hypertension model of rat glaucoma

Lycium barbarum, a traditional Chinese anti-aging herb, has been shown to protect retinal ganglion cells (RGCs) in a rat chronic ocular hypertension (COH) model. Here, we investigated the expression of endothelin-1 (ET-1), a strong vasoconstrictor, and its receptors, ETA and ETB, in the COH model and assessed the effects of Lycium barbarum on the ET-1 axis. Elevated intraocular pressure (IOP) was induced in the right eye of SD rats using argon laser photocoagulation. (1) The expression of ET-1, ETA and ETB in normal and COH retinas was studied. (2) Some COH rats were fed daily with Lycium barbarum Polysaccharides (LBP) using 1 mg/kg or phosphate-buffered saline (PBS) for 3 weeks (started 1 week before photocoagulation). The effects of LBP on the expression of ET-1 and its receptors, ETA and ETB, in COH retina were evaluated. A semi-quantitative analysis of staining intensity was used to evaluate the expression levels of ET-1, ETA and ETB in retinal vasculature. We found that (1) Under COH condition, the immunoreactivity of ET-1 was increased in retina associated with an increase of ETB receptor immunoreactivity and a decrease of ETA receptor immunoreactivity. (2) After feeding COH rats with LBP, the expression of ET-1 was decreased with an increase of ETA expression and a decrease of ETB expression in the retina, especially in RGCs. (3) By comparing the staining intensity in the vasculature of COH retina in LBP-fed group with PBS-fed group, there was a decrease in the expression of ET-1 and ETA and an increase in ETB. In summary, ET-1 expression was up-regulated in the retina in COH model. LBP could decrease the expression of ET-1 and modulate the expression of its receptors, ETA and ETB, under the condition of COH. The neuroprotective effect of LBP on RGCs might be related to its ability to regulate the ET-1-mediated biological effects on RGCs and retinal vasculature.

The role of calcium-independent phospholipase A2γ in modulation of aqueous humor drainage and Ca2+ sensitization of trabecular meshwork contraction

The contractile and relaxation characteristics of trabecular meshwork (TM) are presumed to influence aqueous humor (AH) drainage and intraocular pressure. The mechanisms underlying regulation of TM cell contractile properties, however, are not well understood. This study investigates the role of calcium-independent phospholipase A(2) (iPLA(2)), which controls eicosanoid synthesis, in regulation of TM cell contraction and AH outflow using mechanism-based isoform specific inhibitors (R)-bromoenol lactone (R-BEL, iPLA(2)γ specific) and (S)-bromoenol lactone (S-BEL, iPLA(2)β specific). Immunohistochemical analysis revealed intense staining for both iPLA(2)β and γ isoforms throughout the TM, juxtacanalicular tissue, and Schlemm's canal of human eye. Inhibition of iPLA(2)γ by R-BEL or small interfering RNA-mediated silencing of iPLA(2)γ expression induced dramatic changes in TM cell morphology, and decreased actin stress fibers, focal adhesions, and myosin light-chain (MLC) phosphorylation. AH outflow facility increased progressively and significantly in enucleated porcine eyes perfused with R-BEL. This response was associated with a significant decrease in TM tissue MLC phosphorylation and alterations in the morphology of aqueous plexi in R-BEL-perfused eyes. In contrast, S-BEL did not affect either of these parameters. Additionally, R-BEL-induced cellular relaxation of the TM was associated with a significant decrease in the levels of active Rho GTPase, phospho-MLC phosphatase, phospho-CPI-17, and arachidonic acid. Taken together, these observations demonstrate that iPLA(2)γ plays a significant and isoform-specific role in regulation of AH outflow facility by altering the contractile characteristics of the TM. The effects of iPLA(2)γ on TM contractile status appear to involve arachidonic acid and Rho GTPase signaling pathways.

1α,25-Dihydroxyvitamin D(3) and its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), suppress intraocular pressure in non-human primates

Ocular hypertension is the greatest known risk factor for glaucoma that affects an estimated 70 million people worldwide. Lowering intraocular pressure (IOP) remains the mainstay of therapy in the management of glaucoma. By means of microarray analysis, we have discovered that 1α,25-dihydroxyvitamin D(3) (1α,25-(OH)(2)D(3)) regulates genes that are known to be involved in the determination of intraocular pressure (IOP). Topical administration of 1α,25-(OH)(2)D(3) or its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), markedly reduces IOP in non-human primates. The reduction in IOP is not the result of reduced aqueous humor formation, while a 35% increase in aqueous humor drainage by 1α,25-(OH)(2)D(3) was found but this increase did not achieve significance. Nevertheless, our results suggest that 1α,25-(OH)(2)D(3), or an analog thereof, may present a new approach to the treatment of glaucoma.

Phoneutria spider toxins block ischemia-induced glutamate release and neuronal death of cell layers of the retina

PURPOSE

To investigate the effect of calcium channel blockers, spider toxins, on cell viability and the glutamate content of ischemic retinal slices.

METHODS

Rat retinal slices were subjected to ischemia via exposure to oxygen-deprived low-glucose medium for 45 minutes. Slices were either treated or not treated with the toxins PhTx3, Tx3-3, and Tx3-4. After oxygen-deprived low-glucose insult, glutamate content and cell viability were assessed in the slices by confocal and optical microscopy.

RESULTS

In the retinal ischemic slices that were treated with PhTx3, Tx3-3, and Tx3-4, confocal imaging showed a decrease in cell death of 79.5 ± 3.1%, 75.5 ± 5.8%, and 61 ± 3.8%, respectively. Neuroprotective effects were also observed 15, 30, 60, and 90 minutes after the onset of the retinal ischemic injury. As a result of the ischemia, glutamate increased from 6.2 ± 1.0 nMol/mg protein to 13.2 ± 1.0 nMol/mg protein and was inhibited by PhTx3, Tx3-3, and Tx3-4 to 8.6 ± 0.7, 8.8 ± 0.9, and 7.4 ± 0.8 nMol/mg protein, respectively. Histologic analysis of the live cells in the outer, inner, and ganglion cell layers of the ischemic slices showed a considerable reduction in cell death by the toxin treatment.

CONCLUSION

Spider toxins reduced glutamate content and cell death of retinal ischemic slices.

Broad spectrum antiangiogenic treatment for ocular neovascular diseases

Pathological neovascularization is a hallmark of late stage neovascular (wet) age-related macular degeneration (AMD) and the leading cause of blindness in people over the age of 50 in the western world. The treatments focus on suppression of choroidal neovascularization (CNV), while current approved therapies are limited to inhibiting vascular endothelial growth factor (VEGF) exclusively. However, this treatment does not address the underlying cause of AMD, and the loss of VEGF's neuroprotective can be a potential side effect. Therapy which targets the key processes in AMD, the pathological neovascularization, vessel leakage and inflammation could bring a major shift in the approach to disease treatment and prevention. In this study we have demonstrated the efficacy of such broad spectrum antiangiogenic therapy on mouse model of AMD.

Molecularly imprinted therapeutic contact lenses

IMPORTANCE OF THE FIELD

There exists a considerable unmet need for more efficacious delivery of ocular therapeutics. Contact lenses have been developed with high loading and controllable sustained release to overcome limited patient compliance and significant ocular transport limitations. This can best be achieved by extending and controlling the residence time of drugs on the eye surface and thereby limiting drug loss by lacrimation, drainage and non-productive absorption.

AREAS COVERED IN THE REVIEW

Within hydrogels, molecular imprinting can be used to create memory for template molecules embedded within a flexible macromolecular network. Control in therapeutic loading and delay of release have been demonstrated with careful attention to the functional monomer/template ratio, the diversity of functional monomers, and the polymer backbone and network structure. Experimental work has also confirmed that macromolecular memory and not structural differences or phenomena are responsible for delayed drug release kinetics compared with non-imprinted systems. A therapeutically relevant amount of drug can be loaded for release to occur over multiple days, which allows the technique to be applied to daily-wear and extended-wear contact lenses.

WHAT THE READER WILL GAIN

The focus of this article is to review the emerging field of molecularly imprinted contact lenses and highlight significant accomplishments, trends, as well as future strategies and directions.

TAKE HOME MESSAGE

In the past 8 years, molecular imprinting has been used to produce therapeutic contact lenses with enhanced loading and delayed release. Progress in the field has mostly included low-molecular-weight therapeutics such as anti-glaucoma, antihistamine, antibiotic and anti-inflammatory therapeutics used to treat anterior eye disorders. Recently, high molecular weight comfort molecules have also been successfully demonstrated. Current methods can produce lenses of suitable thickness, water content, and mechanical and optical properties compared with commercial lenses on the market today.

Designing dendrimers for ocular drug delivery

New series of phosphorus-containing dendrimers, having one quaternary ammonium salt as core and carboxylic acid terminal groups have been synthesized from generation 0 (3 carboxylic acid terminal groups) to generation 2 (12 carboxylic acid terminal groups). These dendrimers react with the neutral form of carteolol (an ocular anti-hypertensive drug used to treat glaucoma) to afford ion pair (saline) species. The solubility in water of these charged dendrimers depends on the generation considered: generation 0 (3 carteolol) is well soluble, whereas generation 1 (6 carteolol) and generation 2 (12 carteolol) are poorly soluble. These dendrimers have been tested in vivo, as vehicle for ocular drug delivery of carteolol to rabbits.

A Na+/Ca2+ exchanger isoform, NCX1, is involved in retinal cell death after N-methyl-D-aspartate injection and ischemia-reperfusion

We investigated the expression of Na(+)/Ca(2+) exchanger (NCX) and the functional role of NCX in retinal damage by using NCX1-heterozygous deficient mice (NCX1(+/-)) and SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy] phenoxy]-5-ethoxyaniline), a selective NCX inhibitor in vivo. We also examined the role of NCX in oxygen-glucose deprivation (OGD) stress with a retinal ganglion cell line (RGC-5) cell culture in vitro. The expression of NCX1 was confirmed and entirely localized in retina by immunoblotting and immunohistochemistry, respectively. NCX1(+/-) mice possessed significant protection against retinal damage induced by intravitreal injection of N-methyl-D-aspartate (NMDA). SEA0400 at 3 and 10 mg/kg significantly reduced NMDA- or high intraocular pressure-induced retinal cell damage in mice. Furthermore, SEA0400 reduced the number of TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling)-positive cells and the expression of phosphorylated mitogen-activated protein kinases (ERK1/2, JNK, p38) induced by NMDA injection. In RGC-5, SEA0400 at 0.3 and 1 microM significantly inhibited OGD-induced cell damage. OGD-induced cell damage was aggravated by ouabain (a Na(+),K(+)-ATPase inhibitor) at 100 microM, and this increased damage was significantly reduced by SEA0400 at 1 microM. In conclusion, these results suggest that NCX1 may play a role in retinal cell death induced by NMDA and ischemia-reperfusion.

Cabergoline: Pharmacology, ocular hypotensive studies in multiple species, and aqueous humor dynamic modulation in the Cynomolgus monkey eyes

The aims of the current studies were to determine the in vitro and in vivo ocular and non-ocular pharmacological properties of cabergoline using well documented receptor binding, cell-based functional assays, and in vivo models. Cabergoline bound to native and/or human cloned serotonin-2A/B/C (5HT(2A/B/C)), 5HT(1A), 5HT(7), alpha(2B), and dopamine-2/3 (D(2/3)) receptor subtypes with nanomolar affinity. Cabergoline was an agonist at human recombinant 5HT(2), 5HT(1A) and D(2/3) receptors but an antagonist at 5HT(7) and alpha(2) receptors. In primary human ciliary muscle (h-CM) and trabecular meshwork (h-TM) cells, cabergoline stimulated phosphoinositide (PI) hydrolysis (EC(50)=19+/-7 nM in TM; 76 nM in h-CM) and intracellular Ca(2+) ([Ca(2+)](i)) mobilization (EC(50)=570+/-83 nM in h-TM; EC(50)=900+/-320 nM in h-CM). Cabergoline-induced [Ca(2+)](i) mobilization in h-TM and h-CM cells was potently antagonized by a 5HT(2A)-selective antagonist (M-100907, K(i)=0.29-0.53 nM). Cabergoline also stimulated [Ca(2+)](i) mobilization more potently via human cloned 5HT(2A) (EC(50)=63.4+/-10.3 nM) than via 5HT(2B) and 5HT(2C) receptors. In h-CM cells, cabergoline (1 microM) stimulated production of pro-matrix metalloproteinases-1 and -3 and synergized with forskolin to enhance cAMP production. Cabergoline (1 microM) perfused through anterior segments of porcine eyes caused a significant (27%) increase in outflow facility. Topically administered cabergoline (300-500 microg) in Dutch-belted rabbit eyes yielded 4.5 microMM and 1.97 microM levels in the aqueous humor 30 min and 90 min post-dose but failed to modulate intraocular pressure (IOP). However, cabergoline was an efficacious IOP-lowering agent in normotensive Brown Norway rats (25% IOP decrease with 6 microg at 4h post-dose) and in conscious ocular hypertensive cynomolgus monkeys (peak reduction of 30.6+/-3.6% with 50 microg at 3h post-dose; 30.4+/-4.5% with 500 microg at 7h post-dose). In ketamine-sedated monkeys, IOP was significantly lowered at 2.5h after the second topical ocular dose (300 microg) of cabergoline by 23% (p<0.02) and 35% (p<0.004) in normotensive and ocular hypertensive eyes, respectively. In normotensive eyes, cabergoline increased uveoscleral outflow (0.69+/-0.7 microL/min-1.61+/-0.97 microL/min, n=13; p<0.01). However, only seven of the eleven ocular hypertensive monkeys showed significantly increased uveoscleral outflow. These data indicate that cabergoline's most prominent agonist activity involves activation of 5HT(2), 5HT(1A), and D(2/3) receptors. Since 5HT(1A) agonists, 5HT(7) antagonists, and alpha(2) antagonists do not lower IOP in conscious ocular hypertensive monkeys, the 5HT(2) and dopaminergic agonist activities of cabergoline probably mediated the IOP reduction observed with this compound in this species.

GpnmbR150X allele must be present in bone marrow derived cells to mediate DBA/2J glaucoma

BACKGROUND

The Gpnmb gene encodes a transmembrane protein whose function(s) remain largely unknown. Here, we assess if a mutant allele of Gpnmb confers susceptibility to glaucoma by altering immune functions. DBA/2J mice have a mutant Gpnmb gene and they develop a form of glaucoma preceded by a pigment dispersing iris disease and abnormalities of the immunosuppressive ocular microenvironment.

RESULTS

We find that the Gpnmb genotype of bone-marrow derived cell lineages significantly influences the iris disease and the elevation of intraocular pressure. GPNMB localizes to multiple cell types, including pigment producing cells, bone marrow derived F4/80 positive antigen-presenting cells (APCs) of the iris and dendritic cells. We show that APCs of DBA/2J mice fail to induce antigen induced immune deviation (a form of tolerance) when treated with TGFbeta2. This demonstrates that some of the immune abnormalities previously identified in DBA/2J mice result from intrinsic defects in APCs. However, the tested APC defects are not dependent on a mutant Gpnmb gene. Finally, we show that the Gpnmb mediated iris disease does not require elevated IL18 or mature B or T lymphocytes.

CONCLUSION

These results establish a role for Gpnmb in bone marrow derived lineages. They suggest that affects of Gpnmb on innate immunity influence susceptibility to glaucoma in DBA/2J mice.

Peribulbar poloxamer for ocular drug delivery

PURPOSE

The use of biopolymers in peribulbar injection for controlled drug delivery provides alternative options to eyedrops and intravitreal or surgical methods. Polymerizable biopolymers are especially likely to have a role because of their particular properties. In liquid form, they can be easily injected into the target site and, after polymerization, they provide a prolonged and controlled release of the drug. This study was undertaken to demonstrate the suitability of a thermopolymerizable biopolymer poloxamer (Lutrol F127) for peribulbar injections and controlled drug release.

METHODS

The toxicity of injected poloxamer compounds was evaluated by visual inspection and histological and immunohistochemical tissue evaluation. The release of marker substances such as 5(6)-carboxyfluorescein (376 Da) or fluorescein isothiocyanate-dextran (FITC-dextran) (4-40 kDa) from poloxamer was used to simulate drug release and penetration into the eye using in vivo fluorometry.

RESULTS

According to our clinical and pathological analyses, poloxamer was well tolerated in peribulbar injections and did not cause acute toxicity at the site of injection. The marker compounds were released from the site of injection during the first 24 hours.

CONCLUSIONS

Although poloxamer appears to be suitable for peribulbar injections, a more prolonged period of dissolution is desirable for clinical purposes.

Protective effect of retinal ischemia by blockers of voltage-dependent calcium channels and intracellular calcium stores

In the present study, the neuroprotective effect of blockers of voltage-dependent calcium channels (VDCC) and intracellular calcium stores on retinal ischemic damage induced by oxygen deprivation-low glucose insult (ODLG) was investigated. Retinal damage induced by ODLG was dependent on the calcium concentration in the perfusion medium. When incubated in medium containing 2.4 mM CaCl(2), cell death in ischemic retinal slices treated with blockers of VDCC, omega-conotoxin GVIA (1.0 microM), omega-conotoxin MVIIC (100 nM) and nifedipine (1.0 microM), was reduced to 62 +/- 2.3, 46 +/- 4.3 and 47 +/- 3.9%, respectively. In the presence of blockers of intracellular calcium stores, dantrolene (100 microM) and 2-APB (100 microM), the cell death was reduced to 46 +/- 3.2 and 55 +/- 2.9%, respectively. Tetrodotoxin (1.0 microM), reducing the extent of the membrane depolarization reduces the magnitude of calcium influx trough VDCC causing a reduction of the cell death to 55 +/- 4.3. Lactate dehydrogenase content of untreated ischemic retinal slices was reduced by 37% and treatment of ischemic slices with BAPTA-AM (100 microM) or 2-APB (100 microM) abolished the leakage of LDH. Dantrolene (100 microM) and nifedipine (1.0 microM) partially blocked the induced reduction on the LDH content of retinal ischemic slices. Histological analysis of retinal ischemic slices showed 40% reduction of ganglion cells that was prevented by BAPTA-AM or dantrolene. 2-APB partially blocked this reduction whilst nifedipine had no effect, p > 0.95. Conclusion Blockers of VDCC and intracellular calcium-sensitive receptors exert neuroprotective effect on retinal ischemia.

Anecortave acetate in the treatment of age-related macular degeneration

RETAANE 15mg (anecortave acetate suspension) is under investigation to treat exudative age-related macular degeneration (AMD), the single largest cause of blindness in the Western world, affecting over 15 million people in the USA. RETAANE suspension is a unique synthetic cortisene and has antiangiogenic properties that were established in multiple experimental models of angiogenesis. The molecule acts at multiple sites of the angiogenic cascade. Clinical trials in patients with exudative AMD have demonstrated the excellent safety record of both the drug anecortave acetate and the posterior juxtascleral depot (PJD) administration procedure. A pivotal study comparing RETAANE suspension with placebo showed a significantly higher chance of maintaining vision in the treatment (73%) as compared with placebo (47%). Another study compared RETAANE suspension with Visudyne photodynamic therapy, revealing no statistically significant differences between the two treatments over 24 months. AMD is a multi-faceted disease and therefore a molecule such as RETAANE suspension with a unique mechanism of action, demonstrated clinical efficacy, and retreatment every six months is an important potential treatment option which should be further investigated both as a monotherapy or in combination with other treatment strategies.