Recent Advances in Topical Ocular Drug Delivery

Tuning of thermoresponsive pNIPAAm hydrogels for the topical retention of controlled release ocular therapeutics

Low patient compliance and poor bioavailability of ophthalmic medications are the main limitations of topical eye drops. A potential solution to these disadvantages could be provided by thermoresponsive hydrogels, which could be used as the basis for a gelling eye drop for long-term release of therapeutics. We previously reported such a system capable of being retained in the lower fornix of rabbits, continuously releasing an anti-glaucoma drug for one month. Here, we sought to improve the properties of the existing gels as most relevant to patient use without altering the drug release profile. Specifically, we optimized the sol-to-gel transition temperature and de-swelling kinetics of pNIPAAm gels to avoid risk of the gelled drop reverting to liquid during cold or windy weather, and ensure quick gelation upon administration. A reduction of the gel LCST, faster gelation kinetics, and suitable viscosity for the administration as an eye drop were successfully achieved through modification of the poly(ethylene glycol) content in the water phase and its molecular weight. Our data suggest that drug release is not affected by these changes, with representative drug concentration profiles of the previous and new formulations demonstrating comparable anti-glaucoma release kinetics.

Impediment of selenite-induced cataract in rats by combinatorial drug laden liposomal preparation

Cataract is the leading cause of blindness globally with surgery being the only form of treatment. But cataract surgery is accompanied by complications, chiefly intra-ocular infections. Hence, preventive nanoformulations may be extremely beneficial. In the present study, novel chitosan-coated liposomal formulations encapsulating a combination of drugs, lanosterol and hesperetin were prepared and characterized. The combinatorial liposomes were prepared by thin film evaporation active extrusion method. The characterization of liposomes was done by transmission electron microscopy, zeta potential, encapsulation efficiency, stability, cytotoxicity and in vitro release studies. The main difference between the chitosan-coated and uncoated combinatorial liposomes is the release of drugs as indicated by the in vitro release studies. The slow and sustained release of the drugs from chitosan-coated ones as against the burst release from uncoated indicates an increased retention time for combinatorial drugs in cornea. This leads to a delay in progression of cataract as seen from in vivo studies. Cytotoxicity studies indicate no cell toxicity of the coating of chitosan or the combination of drugs. Stability studies indicate that there were almost no changes in size, zeta potential and polydispersity index values of the combinatorial liposomes upon storage at room temperature for 60 days. Another important study is the estimation of antioxidant defense system. The estimated values of glutathione reductase, malondialdehyde and chief antioxidant enzymes point toward an upregulation of antioxidant defense system. From the results, it may be concluded that novel chitosan-coated combinatorial liposomes are effective in delaying or preventing of cataract.

Rapamycin Nano-Micelle Ophthalmic Solution Reduces Corneal Allograft Rejection by Potentiating Myeloid-Derived Suppressor Cells' Function

Allograft rejection is the major cause of corneal allograft failure. Rapamycin (RAPA) has been reported as an effective and novel immunosuppressive agent for patients undergoing corneal transplantation. However, its high water insolubility and low bioavailability have strongly constrained its clinical application. In this study, we successfully developed a RAPA nano-micelle ophthalmic solution and found that corneal allograft survival in recipients treated with RAPA nano-micelle ophthalmic solution was significantly prolonged for more than 2 months, with less inflammatory infiltration, decreased production of pro-inflammatory factors, and elevated recruitment of myeloid-derived suppressor cells (MDSCs). MDSCs from mice treated with RAPA nano-micelle ophthalmic solution could significantly inhibit the proliferation of CD4⁺T cells through increased expressions of inducible nitric oxidase (iNOS) and arginase-1 (Arg-1). The activity blockade of Arg-1 and iNOS pharmacologically reversed their immunosuppressive ability. Moreover, the effects of RAPA were antagonized by the administration of anti-Gr-1 antibody or by inhibiting the activity of iNOS pharmacologically. In addition, RAPA nano-micelle also effectively alleviated allograft rejection in high-risk rabbit penetrating keratoplasty (PKP) models with corneal vascularization. Collectively, our results demonstrate that RAPA nano-micelle ophthalmic solution could improve the immunosuppressive activity of MDSCs through elevated expression of Arg-1 and iNOS, which highlights the possible therapeutic applications of RAPA against corneal allograft rejection.

Drug delivery devices for retinal diseases

Retinal degenerative diseases are a leading cause of irreversible blindness and visual impairment, affecting millions of people worldwide. Although intravitreal injection can directly deliver drugs to the posterior segment of the eye, it is invasive and associated with serious side effects. The design of drug delivery systems targeting the posterior segment of the eye in a less invasive manner has still been challenging because of various anatomical and physiological barriers. In this review, we provide an overview of the current implant device-based approaches used for treating retinal degenerative diseases. We then offer our perspectives on future directions and challenges that remain for developing more effective device-based therapies for retinal diseases.

Ocular Drug Distribution and Safety of a Noninvasive Ocular Drug Delivery System of Dexamethasone Sodium Phosphate in Rabbit

PURPOSE

To determine the ocular toxicity, systemic exposure, and amounts of dexamethasone sodium phosphate (DSP) in ocular tissues after administration of DSP with the Visulex system (DSP-Visulex).

METHODS

DSP-Visulex was applied onto healthy rabbit eyes. DSP concentrations (4%, 8%, 15%, and 25%) and treatment durations (5, 10, and 20 min) were evaluated for the amounts of DSP in the ocular tissues and in plasma after single administrations of DSP-Visulex. The drug in eye tissues and plasma was analyzed by high-performance liquid chromatography-UV/VIS and by liquid chromatography-mass spectrometry, respectively. The safety and tolerability were ascertained based on clinical observations and histopathological examinations from repeat weekly DSP-Visulex treatments (4%, 8%, 15%, and 25% for 20 min) for 12 weeks.

RESULTS

Significant amounts of DSP (ie, higher than 1 μg/g) were found in the anterior chamber, retina-choroid, cornea, vitreous, conjunctiva, and sclera after single applications of DSP-Visulex. The DSP concentrations in the ocular tissues and in plasma increased with increased DSP concentrations in the Visulex applicator and with increased application times. Systemic DSP was rapidly detected. The plasma half-life was 2-3 h. C_max was 148 and 1,844 ng/mL, and the area under the plasma drug concentration versus time curve (AUC) was 418 and 3,779 ng · h/mL for the low dose (4% DSP-Visulex for 5 min) and the high dose (15% DSP-Visulex for 20 min), respectively. Ocular findings over 12 weeks were mostly conjunctival injection and eye discharge. These were transient and mild. Histopathological examinations indicated the eyes to be normal.

CONCLUSIONS

DSP can be administered safely and effectively into the rabbit eye with the Visulex system. Treatment duration and DSP concentration are important factors in achieving therapeutic levels. Repeat applications of DSP-Visulex are safe and well tolerated for weekly administrations over 4-12 weeks. DSP-Visulex has clinical potential for the noninvasive treatment of ocular diseases.

Ophthalmic Drug Delivery Systems for Antibiotherapy-A Review

The last fifty years, ophthalmic drug delivery research has made much progress, challenging scientists about the advantages and limitations of this drug delivery approach. Topical eye drops are the most commonly used formulation in ocular drug delivery. Despite the good tolerance for patients, this topical administration is only focus on the anterior ocular diseases and had a high precorneal loss of drugs due to the tears production and ocular barriers. Antibiotics are popularly used in solution or in ointment for the ophthalmic route. However, their local bioavailability needs to be improved in order to decrease the frequency of administrations and the side effects and to increase their therapeutic efficiency. For this purpose, sustained release forms for ophthalmic delivery of antibiotics were developed. This review briefly describes the ocular administration with the ocular barriers and the currently topical forms. It focuses on experimental results to bypass the limitations of ocular antibiotic delivery with new ocular technology as colloidal and in situ gelling systems or with the improvement of existing forms as implants and contact lenses. Nanotechnology is presently a promising drug delivery way to provide protection of antibiotics and improve pathway through ocular barriers and deliver drugs to specific target sites.

Principles of pharmacology in the eye

The eye is a highly specialized organ that is subject to a huge range of pathology. Both local and systemic disease may affect different anatomical regions of the eye. The least invasive routes for ocular drug administration are topical (e.g. eye drops) and systemic (e.g. tablets) formulations. Barriers that subserve as protection against pathogen entry also restrict drug permeation. Topically administered drugs often display limited bioavailability due to many physical and biochemical barriers including the pre-corneal tear film, the structure and biophysiological properties of the cornea, the limited volume that can be accommodated by the cul-de-sac, the lacrimal drainage system and reflex tearing. The tissue layers of the cornea and conjunctiva are further key factors that act to restrict drug delivery. Using carriers that enhance viscosity or bind to the ocular surface increases bioavailability. Matching the pH and polarity of drug molecules to the tissue layers allows greater penetration. Drug delivery to the posterior segment is a greater challenge and, currently, the standard route is via intravitreal injection, notwithstanding the risks of endophthalmitis and retinal detachment with frequent injections. Intraocular implants that allow sustained drug release are at different stages of development. Novel exciting therapeutic approaches include methods for promoting transscleral delivery, sustained release devices, nanotechnology and gene therapy.

Dexamethasone distribution characteristic following controllable continuous sub-tenon drug delivery in rabbit

Drug delivery systems are required to be safe, minimally invasive and effectively delivery drug to the target tissues. But delivery drugs to the eye has not yet satisfied this need. Here, we focused on examining the distribution of dexamethasone (DEX) in ocular and plasmic samples following controllable continuous sub-Tenon drug delivery (CCSDD) of dexamethasone disodium phosphate (DEXP) in rabbit, and to compare that with two traditional routes: subconjunctival injection and intravenous injection. The DEX concentration was analyzed by Shimadzu LC-MS 2010 system. In CCSDD group, during observed 24 h, the mean DEX level in collected samples from highest to lowest following in order: sclera, cornea, retina/choroid, iris, plasma, aqueous humor, lens and vitreous body. In ocular solid tissue, the DEX level in posterior segment is higher than in anatomic corresponding anterior segment, but it is opposite in ocular fluid tissue. High levels of DEX were maintained at 12 h in the ocular tissue immediately after the administration. Even at 24 h, the mean DEX concentration was 31.72 ng/ml and 22.40 ng/ml in aqueous and vitreous, respectively. In CCSDD group, the ocular DEX exposure (AUC0-24) is much higher and plasma exposure is much less than IV group, and it is also similar in SC group except iris. The amount of DEX levels are markedly increased in ocular tissues but it yield lower plasma levels indicating reduction of systemic absorption by CCSDD. Thus, CCSDD is an effective method of delivering DEX into anterior and posterior segment of the eye.

Dendrimers for Ocular Drug Delivery

Existing methods of administering ocular drugs are limited in either their safety or efficiency. Nanomedicine therapies have the potential to address this deficiency by creating vehicles that can control drug biodistribution. Dendrimers are synthetic polymeric nanoparticles with a unique highly organized branching structure. In recent years, promising results using dendrimer vehicles to deliver ocular drugs through different routes of administration have been reported. In this review, we briefly summarize these results with emphasis on the dendrimer modifications used to target different ocular structures.

Novel nanosystems for the treatment of ocular inflammation: Current paradigms and future research directions

Ocular discomforts involve anterior/posterior-segment diseases, symptomatic distress and associated inflammations and severe retinal disorders. Conventionally, the formulations such as eye drops, eye solutions, eye ointments and lotions, etc. were used as modalities to attain relief from such ocular discomforts. However, eye allows limited access to these traditional formulations due to its unique anatomical structure and dynamic ocular environment and therefore calls for improvement in disease intervention. To address these challenges, development of nanotechnology based nanomedicines and novel nanosystems (liposomes, cubosomes, polymeric and lipidic nanoparticles, nanoemulsions, spanlastics and nano micelles) are currently in progress (some of them are already marketed such as Eye-logic liposomal eye spray@Naturalife, Ireland). Today, it is one of the central concept in designing more accessible formulations for deeper segments of the eyes. These nanosystems has largely enabled the availability of medicaments at required site in a required concentration without inversely affecting the eye tissues; and therefore, attaining the excessive considerations from the formulation scientists and pharmacologists worldwide. The entrapment of drugs, genes, and proteins inside these novel systems is the basis that works at the bio-molecular level bestows greater potential to eradicate disease causatives. In this review, we highlighted the recent attempts of nanotechnology-based systems for treating and managing various ocular ailments. The progress described herein may pave the way to new, highly effective and vital ocular nanosystems.

Ocular disposition of ciprofloxacin from topical, PEGylated nanostructured lipid carriers: Effect of molecular weight and density of poly (ethylene) glycol

Ciprofloxacin (CIP) is an antibacterial agent prescribed for the treatment of ocular infections. The objective of the present project is to investigate the effect of surface PEG functionalization of the Nano structured lipid carriers (NLCs) on formulation stability, ocular penetration and distribution. CIP NLCs were tested with different molecular weight (poly ethylene glycol) PEGs ranging from (2K to 20K) grafted onto the phospholipid and with different chain lengths (14-18 carbons) of phospholipids derivatized with PEG-2K. Drug load in the formulations was maintained at 0.3%w/v. Formulations prepared were evaluated with respect to in vitro release, transcorneal permeation, autoclavability, morphological characteristics and in vivo ocular tissue distribution. Scanning Transmission electron microscopy (STEM) studies revealed that the PEG-CIP-NLCs were spherical in shape. Transcorneal penetration of CIP was optimum with PEG molecular weight in between 2K-10K. Carbon chain length of the phospholipid, however, did not affect transcorneal penetration of CIP. In vivo ocular tissue CIP concentrations attained from the various formulations was consistent with the in vitro data obtained. The results suggest that surface functionalization of PEGs, within a specified range of molecular weight and surface packing density, significantly enhance trans-ocular penetration and impart sterilization-stabilization characteristics into the formulations.

Physicochemical attributes and dissolution testing of ophthalmic ointments

The investigation of semisolid ophthalmic ointments is challenging due to their complex physicochemical properties and the unique anatomy of the human eye. Using Lotemax® as a model ophthalmic ointment, three different manufacturing processes and two excipient sources (Fisher® (OWP) and Fougera® (NWP)) were used to prepare loteprednol etabonate ointments that were qualitatively and quantitatively the same across the manufactured formulations. Physicochemical properties including drug content and uniformity, particle size and distribution, as well as rheological parameters (onset point, crossover modulus, storage modulus and Power law consistency index) were investigated. In addition, USP apparatus 2 with enhancer cells was utilized to study the in vitro drug release characteristics of the ophthalmic ointments. Both manufacturing processes and excipient sources had a significant influence on the physicochemical attributes and the in vitro drug release profiles of the prepared ointments. Ointments prepared via the hot melt processes exhibited higher rheological parameters and lower drug release rates compared to ointments prepared without hot melting. Ointments prepared with OWP demonstrated higher rheological parameters and lower in vitro drug release rates compared to ointments prepared with NWP. A strong correlation between the rheological parameters and in vitro drug release rate was shown using logarithmic linear regression. This correlation may be useful in predicting in vitro drug release from measured physicochemical properties, and identifying the critical quality attributes during the development of ointment formulations.

Recent perspectives on the delivery of biologics to back of the eye

INTRODUCTION

Biologics are generally macromolecules, large in size with poor stability in biological environments. Delivery of biologics to tissues at the back of the eye remains a challenge. To overcome these challenges and treat posterior ocular diseases, several novel approaches have been developed. Nanotechnology-based delivery systems, like drug encapsulation technology, macromolecule implants and gene delivery are under investigation. We provide an overview of emerging technologies for biologics delivery to back of the eye tissues. Moreover, new biologic drugs currently in clinical trials for ocular neovascular diseases have been discussed. Areas covered: Anatomy of the eye, posterior segment disease and diagnosis, barriers to biologic delivery, ocular pharmacokinetic, novel biologic delivery system Expert opinion: Anti-VEGF therapy represents a significant advance in developing biologics for the treatment of ocular neovascular diseases. Various strategies for biologic delivery to posterior ocular tissues are under development with some in early or late stages of clinical trials. Despite significant progress in the delivery of biologics, there is unmet need to develop sustained delivery of biologics with nearly zero-order release kinetics to the back of the eye tissues. In addition, elevated intraocular pressure associated with frequent intravitreal injections of macromolecules is another concern that needs to be addressed.

Stimuli-Responsive Polymeric Systems for Controlled Protein and Peptide Delivery: Future Implications for Ocular Delivery

Therapeutic proteins and peptides have become notable in the drug delivery arena for their compatibility with the human body as well as their high potency. However, their biocompatibility and high potency does not negate the existence of challenges resulting from physicochemical properties of proteins and peptides, including large size, short half-life, capability to provoke immune responses and susceptibility to degradation. Various delivery routes and delivery systems have been utilized to improve bioavailability, patient acceptability and reduce biodegradation. The ocular route remains of great interest, particularly for responsive delivery of macromolecules due to the anatomy and physiology of the eye that makes it a sensitive and complex environment. Research in this field is slowly gaining attention as this could be the breakthrough in ocular drug delivery of macromolecules. This work reviews stimuli-responsive polymeric delivery systems, their use in the delivery of therapeutic proteins and peptides as well as examples of proteins and peptides used in the treatment of ocular disorders. Stimuli reviewed include pH, temperature, enzymes, light, ultrasound and magnetic field. In addition, it discusses the current progress in responsive ocular drug delivery. Furthermore, it explores future prospects in the use of stimuli-responsive polymers for ocular delivery of proteins and peptides. Stimuli-responsive polymers offer great potential in improving the delivery of ocular therapeutics, therefore there is a need to consider them in order to guarantee a local, sustained and ideal delivery of ocular proteins and peptides, evading tissue invasion and systemic side-effects.