Nanotherapies for the treatment of ocular diseases

Polymeric nanocapsules: a potential new therapy for corneal wound healing

Corneal injuries are one of the most frequently observed ocular diseases, leading to permanent damage and impaired vision if they are not treated properly. In this sense, adequate wound healing after injury is critical for keeping the integrity and structure of the cornea. The goal of this work was to assess the potential of polymeric nanocapsules, either unloaded or loaded with cyclosporine A or vitamin A, alone or in combination with mitomycin C, for the treatment of corneal injuries induced by photorefractive keratectomy surgery. The biopolymers selected for the formation of the nanocapsules were polyarginine and protamine, which are known for their penetration enhancement effect. The results showed that, following topical instillation to a mouse model of corneal injury, all the nanocapsule formulations, either unloaded or loaded with cyclosporine A or vitamin A, were able to stimulate corneal wound healing. In addition, the healing rate observed for the combination of unloaded protamine nanocapsules with mitomycin C was comparable to the one observed for the positive control Cacicol®, a biopolymer known as a corneal wound healing enhancer. Regarding the corneal opacity, the initial grade of corneal haze (>3) induced by the photorefractive keratectomy was more rapidly reduced in the case of the positive control, Cacicol®, than in corneas treated with the nanocapsules. In conclusion, this work shows that drug-free arginine-rich (polyarginine, protamine) nanocapsules exhibit a positive behavior with regard to their potential use for corneal wound healing.

Pediatric ocular nanomedicines: Challenges and opportunities

The eye is a highly complex, yet readily accessible organ within the human body. As such, the eye is an appealing candidate target for a vast array of drug therapies. Despite advances in ocular drug therapy research, the focus on pediatric ocular drug delivery continues to be highly underrepresented due to the limited number of degenerative ocular diseases with childhood onset. In this review, we explore more deeply the reasons underlying the disparity between ocular therapies available for children and for adults by highlighting diseases that most commonly afflict children (with focus on the anterior eye) and existing prognoses, recent developments in ocular drug delivery systems and nanomedicines for children, and barriers to use for pediatric patients.

Epigallocatechin Gallate-Loaded Gelatin-g-Poly(N-Isopropylacrylamide) as a New Ophthalmic Pharmaceutical Formulation for Topical Use in the Treatment of Dry Eye Syndrome

Given that biodegradable in situ gelling delivery systems may have potential applications in the design of ophthalmic pharmaceutical formulations, this study, for the first time, aims to develop gelatin-g-poly(N-isopropylacrylamide) (GN) carriers for topical epigallocatechin gallate (EGCG) administration in the treatment of dry eye disease (DED). By temperature triggered sol-gel phase transition of copolymers, EGCG-loaded GN was prepared at 32 °C and characterized by FTIR, NMR, and HPLC analyses. Results of WST-1 and live/dead assays showed that GN materials have good compatibility with corneal epithelial cells. Gradual biodegradation of delivery carriers allowed sustained release of EGCG without drug toxicity. Anti-inflammatory and antioxidant activity studies also indicated effective therapeutic drug levels at each time point within 3 days of release. In a rabbit dry eye model, corneal epithelial defects was ameliorated by treatment with single-dose administration of EGCG-containing GN. Furthermore, drug molecules released from carrier materials could prevent further tear evaporation and loss of mucin-secreting goblet cells in diseased animals. Our findings suggest that GN carrier is responsible for enhanced pharmacological efficacy of topically instilled EGCG, thereby demonstrating the benefits of using biodegradable in situ gelling delivery system to overcome the drawbacks of limited dry eye relief associated with eye drop dosage form.

Non-invasive strategies for targeting the posterior segment of eye

The safe and effective treatment of eye diseases has been remained a global myth. Several advancements have been done and various drug delivery and treatment techniques have been suggested. The Posterior segment disorders are the leading cause of visual impairments and blindness. Targeting the therapeutic agents to the anterior and posterior segments of the eye has attracted extensive attention from the scientific community. Significant key factors in the success of ocular therapy are the development of safe, effective, economic and non-invasive novel drug delivery systems. These specialized non-invasive ocular drug delivery systems revolutionized the drug delivery strategies by overcoming the limitations, provided targeted delivery to the ocular tissues by avoiding larger doses, and reducing the toxicity encountered by the conventional approaches. These non-invasive systems are fabricated by ingredients encompassing biodegradability, biocompatibility, mucoadhesion, solubility and permeability enhancement and stimuli responsiveness. The variety of routes are utilized to provide minimally invasive drug delivery to the patients without any discomfort and pain. This review is focused on the brief introduction, types, significance, preparation techniques, components and mechanism of drug release of non-invasive systems, including in situ gelling systems, microspheres, iontophoresis, nanoparticles, nanosuspensions and specialized novel emulsions.

Synthetic nanocarriers for the delivery of polynucleotides to the eye

This review is a comprehensive analysis of the progress made so far on the delivery of polynucleotide-based therapeutics to the eye, using synthetic nanocarriers. Attention has been addressed to the capacity of different nanocarriers for the specific delivery of polynucleotides to both, the anterior and posterior segments of the eye, with emphasis on their ability to (i) improve the transport of polynucleotides across the different eye barriers; (ii) promote their intracellular penetration into the target cells; (iii) protect them against degradation and, (iv) deliver them in a long-term fashion way. Overall, the conclusion is that despite the advantages that nanotechnology may offer to the area of ocular polynucleotide-based therapies (especially AS-ODN and siRNA delivery), the knowledge disclosed so far is still limited. This fact underlines the necessity of more fundamental and product-oriented research for making the way of the said nanotherapies towards clinical translation.

Multifunctional organic-inorganic hybrid nanoparticles and nanosheets based on chitosan derivative and layered double hydroxide: cellular uptake mechanism and application for topical ocular drug delivery

To study the cellular uptake mechanism of multifunctional organic-inorganic hybrid nanoparticles and nanosheets, new chitosan-glutathione-valine-valine-layered double hydroxide (CG-VV-LDH) nanosheets with active targeting to peptide transporter-1 (PepT-1) were prepared, characterized and further compared with CG-VV-LDH nanoparticles. Both organic-inorganic hybrid nanoparticles and nanosheets showed a sustained release in vitro and prolonged precorneal retention time in vivo, but CG-VV-LDH nanoparticles showed superior permeability in the isolated cornea of rabbits than CG-VV-LDH nanosheets. Furthermore, results of cellular uptake on human corneal epithelial primary cells (HCEpiC) and retinal pigment epithelial (ARPE-19) cells indicated that both clathrin-mediated endocytosis and active transport of PepT-1 are involved in the internalization of CG-VV-LDH nanoparticles and CG-VV-LDH nanosheets. In summary, the CG-VV-LDH nanoparticle may be a promising carrier as a topical ocular drug delivery system for the treatment of ocular diseases of mid-posterior segments, while the CG-VV-LDH nanosheet may be suitable for the treatment of ocular surface diseases.

Visual tracing of diffusion and biodistribution for amphiphilic cationic nanoparticles using photoacoustic imaging after ex vivo intravitreal injections

To visually trace the diffusion and biodistribution of amphiphilic cation micelles after vitreous injection, various triblock copolymers of monomethoxy poly(ethylene glycol)-poly(ε-caprolactone)-polyethylenimine were synthesized with different structures of hydrophilic and hydrophobic segments, followed by labeling with near-infrared fluorescent dye Cyanine5 or Cyanine7. The micellar size, polydispersity index, and surface charge were measured by dynamic light scattering. The diffusion was monitored using photoacoustic imaging in real time after intravitreal injections. Moreover, the labeled nanoparticle distribution in the posterior segment of the eye was imaged histologically by confocal microscopy. The results showed that the hydrophilic segment increased vitreous diffusion, while a positive charge on the particle surface hindered diffusion. In addition, the particles diffused through the retinal layers and were enriched in the retinal pigment epithelial layer. This work tried to study the diffusion rate via a simple method by using visible images, and then provided basic data for the development of intraocular drug carriers.

Improving the topical ocular pharmacokinetics of an immunosuppressant agent with mucoadhesive nanoemulsions: Formulation development, in-vitro and in-vivo studies

Topical ocular conditions such as cornea transplant rejection and keratoconjunctivitis sicca (so called dry eye disease) require therapeutic concentration of immunosuppressant onto the ocular surface for prolonged period. Based on this rational, we optimized cyclosporine A (Cy-A) loaded polymeric mucoadhesive nanoemulsion (Cy-A-mN) with higher Cy-A payload, improved ocular retention, corneal and conjunctival bioavailability. The concentrations of oil, surfactant and co-surfactant needed for the stable nanoemulsion were screened followed by phase behavior study of the formulations components by the construction of pseudo-ternary phase diagrams. The concentration of chitosan was optimized according to the blinking force of eyelids. The size distribution, surface charge, mucoadhesiveness and Cy-A release were studied for Cy-A-mN along with other formulations. The corneal retention of Cy-A-mN was evaluated by gamma scintigraphy, revealing that the clearance was slowest in the case of Cy-A-mN. Biodistribution performed in rabbits showed that Cy-A-mN was able to maintain the therapeutic concentrations (≥50-300ng/g) of Cy-A in the cornea and conjunctiva over the period of 24h. The safety of formulation was confirmed by Draize's test and by measuring the ocular surface temperature.

Safety of nanosuspensions in drug delivery

Nanosuspension technology is currently undergoing dramatic expansion in pharmaceutical science research and development. However, most of the research efforts generally focus on formulation and potential beneficial description, while the research into potential toxicological effects and implications (i.e., in vivo safety and health effects) is lacking. This review identifies some of the key factors for studying nanosuspension safety and the potential undesired effects related to nanosuspension exposure. The key factors for discussion herein include particle characterization, preparation approach, composition, and excipients of the formulation and sterilization methods. A few comments on the primary and required safety aspects of each administration route are also reviewed.

Poly(ortho ester) nanoparticles targeted for chronic intraocular diseases: ocular safety and localization after intravitreal injection

Treatment of posterior eye diseases is more challenging than the anterior segment ailments due to a series of anatomical barriers and physiological constraints confronted by drug delivery to the back of the eye. In recent years, concerted efforts in drug delivery have been made to prolong the residence time of drugs injected in the vitreous humor of the eye. Our previous studies demonstrated that poly(ortho ester) (POE) nanoparticles were biodegradable/biocompatible and were capable of long-term sustained release. The objective of the present study was to investigate the safety and localization of POE nanoparticles in New Zealand white rabbits and C57BL/6 mice after intravitreal administration for the treatment of chronic posterior ocular diseases. Two concentration levels of POE nanoparticles solution were chosen for intravitreal injection: 1.5 mg/ml and 10 mg/ml. Our results demonstrate that POE nanoparticles were distributed throughout the vitreous cavity by optical coherence tomography (OCT) examination 14 days post-intravitreal injection. Intraocular pressure was not changed from baseline. Inflammatory or adverse effects were undetectable by slit lamp biomicroscopy. Furthermore, we demonstrate that POE nanoparticles have negligible toxicity assessed at the cellular level evidenced by a lack of glia activation or apoptosis estimation after intravitreal injection. Collectively, POE nanoparticles are a novel and nontoxic as an ocular drug delivery system for the treatment of posterior ocular diseases.

Safety and toxicity of nanomaterials for ocular drug delivery applications

Multifunctional nanomaterials are rapidly emerging for ophthalmic delivery of therapeutics to facilitate safe and effective targeting with improved patient compliance. Because of their extremely high area to volume ratio, nanomaterials often have physicochemical properties that are different from those of their larger counterparts. There exists a complex relationship between the physicochemical properties (composition, size, shape, charge, roughness, and porosity) of the nanomaterials and their interaction with the biological system. The eye is a very sensitive accessible organ and is subjected to intended and unintended exposure to nanomaterials. Currently, various ophthalmic formulations are available in the market, while some are underway in preclinical and clinical phases. However, the data on safety, efficacy, and toxicology of these advanced nanomaterials for ocular drug delivery are sparse. Focus of the present review is to provide a comprehensive report on the safety, biocompatibility and toxicities of nanomaterials in the eye.

Reformulating cyclosporine A (CsA): More than just a life cycle management strategy

Cyclosporine A (CsA) is a well-known immunosuppressive agent that gained considerable importance in transplant medicine in the late 1970s due to its selective and reversible inhibition of T-lymphocytes. While CsA has been widely used to prevent graft rejection in patients undergoing organ transplant it was also used to treat several systemic and local autoimmune disorders. Currently, the neuro- and cardio-protective effects of CsA (CiCloMulsion®; NeuroSTAT®) are being tested in phase II and III trials respectively and NeuroSTAT® received orphan drug status from US FDA and Europe in 2010. The reformulation strategies focused on developing Cremophor® EL free formulations and address variable bioavailability and toxicity issues of CsA. This review is an attempt to highlight the progress made so far and the room available for further improvements to realize the maximum benefits of CsA.