Novel approaches to retinal drug delivery

Encapsulated cell technology: Delivering cytokines to treat posterior ocular diseases

Encapsulated cell technology (ECT) is a targeted delivery method that uses the genetically engineered cells in semipermeable polymer capsules to deliver cytokines. Thus far, ECT has been extensively utilized in pharmacologic research, and shows enormous potentials in the treatment of posterior segment diseases. Due to the biological barriers within the eyeball, it is difficult to attain effective therapeutic concentration in the posterior segment through topical administration of drug molecules. Encouragingly, therapeutic cytokines provided by ECT can cross these biological barriers and achieve sustained release at the desired location. The encapsulation system uses permeable materials that allow growth factors and cytokines to diffuse efficiently into retinal tissue. Moreover, the ECT based treatment can be terminated timely when we need to retrieve the implant, which makes the therapy reversible and provides a safer alternative for intraocular gene therapy. Meanwhile, we also place special emphasis on optimizing encapsulation materials and enhancing preservation techniques to achieve the stable release of growth factors and cytokines in the eyeball. This technology holds great promise for the treatment of patients with dry AMD, RP, glaucoma and MacTel. These findings would enrich our understandings of ECT and promote its future applications in treatment of degenerative retinopathy. This review comprises articles evaluating the exactness of artificial intelligence-based formulas published from 2000 to March 2024. The papers were identified by a literature search of various databases (PubMed/MEDLINE, Google Scholar, Cochrane Library and Web of Science).

Current Insights into Targeting Strategies for the Effective Therapy of Diseases of the Posterior Eye Segment

The eye is one a unique sophisticated human sense organ with a complex anatomical structure. It is encased by variety of protective barriers as responsible for vision. There has been a paradigm shift in the prevalence of several major vision threatening ocular conditions with enhanced reliance on computer-based technologies in our workaday life and work-from-home modalities although aging, pollution, injury, harmful chemicals, lifestyle changes will always remain the root cause. Treating posterior eye diseases is a challenge faced by clinicians worldwide. The clinical use of conventional drug delivery systems for posterior eye targeting is restricted by the ocular barriers. Indeed, for overcoming various ocular barriers for efficient delivery of the therapeutic moiety and prolonged therapeutic effect requires prudent and target-specific approaches. Therefore, for efficient drug delivery to the posterior ocular segment, advancements in the development of sustained release and nanotechnology-based ocular drug delivery systems have gained immense importance. Therapeutic efficacy and patient compliance are of paramount importance in clinical translation of these investigative drug delivery systems. This review provides an insight into the various strategies employed for improving the treatment efficacies of the posterior eye diseases. Various drug delivery systems such as systemic and intraocular injections, implants have demonstrated promising outcomes, along with that they have also exhibited side-effects, limitations and strategies employed to overcome them are discussed in this review. The application of artificial intelligence-based technologies along with an appreciation of disease, delivery systems, and patient-specific outcomes will likely enable more effective therapy for targeting the posterior eye segment.

Recent Updates on Nanocarriers for Drug Delivery in Posterior Segment Diseases with Emphasis on Diabetic Retinopathy

In recent years, various conventional formulations have been used for the treatment and/or management of ocular medical conditions. Diabetic retinopathy, a microvascular disease of the retina, remains the leading cause of visual disability in patients with diabetes. Currently, for treating diabetic retinopathy, only intraocular, intravitreal, periocular injections, and laser photocoagulation are widely used. Frequent administration of these drugs by injections may lead to serious complications, including retinal detachment and endophthalmitis. Although conventional ophthalmic formulations like eye drops, ointments, and suspensions are available globally, these formulations fail to achieve optimum drug therapeutic profile due to immediate nasolacrimal drainage, rapid tearing, and systemic tearing toxicity of the drugs. To achieve better therapeutic outcomes with prolonged release of the therapeutic agents, nano-drug delivery materials have been investigated. These nanocarriers include nanoparticles, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), dendrimers, nanofibers, in-situ gel, vesicular carriers, niosomes, and mucoadhesive systems, among others. The nanocarriers carry the potential benefits of site-specific delivery and controlled and sustained drug release profile. In the present article, various nanomaterials explored for treating diabetic retinopathy are reviewed.

Spanlastic-laden in situ gel as a promising approach for ocular delivery of Levofloxacin: In-vitro characterization, microbiological assessment, corneal permeability and in-vivo study

The objective of this study was to encapsulate the antibacterial drug levofloxacin hemihydrate (LF) into spanlastics (SLs) followed by incorporation into gelrite in situ gel to enhance its antibacterial activity and sustain ocular delivery. A combination of Span 60 as main vesicle component and Tweens as an edge activator (EA) was used to prepare SLs using the thin film hydration method. A 32 factorial design was applied to study the effect of formulation variables (ratio of Span 60: EA and type of EA) on SLs characteristics (encapsulation efficiency (EE%), particle size (PS), zeta potential (ZP) and percentage of drug released). In-vitro antimicrobial study was conducted to determine the antibacterial activity of the optimized formula. Finally confocal laser scanning microscopy (CLSM) was applied to monitor SLs corneal penetration. The optimum formulation (F5), contains 240 mg Span 60 and 60 mg Tween 60 as EA. F5 exhibited EE% = 59.7 ± 4.2%, PS = 177.6 ± 1.8 nm, PDI = 0.27 ± 0.022 and ZP = -40.6 ± 0.68 mV. Furthermore, only 39.37 ± 0.72% of LF amount was released after 4 h compared to complete release from drug solution. The apparent permeation coefficient was (14.7 × 10-3 cm/h) compared to (9.7 × 10-3 cm/h) for LF solution. Moreover, F5 exhibited 200% and 100% increase in the antibacterial efficacy against Pseudomonas aeruginosa and Staphylococcus aureus respectively.

Trends in Formulation Approaches for Sustained Drug Delivery to the Posterior Segment of the Eye

The eye, an intricate organ comprising physical and physiological barriers, poses a significant challenge for ophthalmic physicians seeking to treat serious ocular diseases affecting the posterior segment, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR). Despite extensive efforts, the delivery of therapeutic drugs to the rear part of the eye remains an unresolved issue. This comprehensive review delves into conventional and innovative formulation strategies for drug delivery to the posterior segment of the eye. By utilizing alternative nanoformulation approaches such as liposomes, nanoparticles, and microneedle patches, researchers and clinicians can overcome the limitations of conventional eye drops and achieve more effective drug delivery to the posterior segment of the eye. These innovative strategies offer improved drug penetration, prolonged residence time, and controlled release, enhancing therapeutic outcomes for ocular diseases. Moreover, this article explores recently approved delivery systems that leverage diverse polymer technologies, such as chitosan and hyaluronic acid, to regulate drug-controlled release over an extended period. By offering a comprehensive understanding of the available formulation strategies, this review aims to empower researchers and clinicians in their pursuit of developing highly effective treatments for posterior-segment ocular diseases.

An Update on Strategies to Deliver Protein and Peptide Drugs to the Eye

In the past few decades, advancements in protein engineering, biotechnology, and structural biochemistry have resulted in the discovery of various techniques that enhanced the production yield of proteins, targetability, circulating half-life, product purity, and functionality of proteins and peptides. As a result, the utilization of proteins and peptides has increased in the treatment of many conditions, including ocular diseases. Ocular delivery of large molecules poses several challenges due to their high molecular weight, hydrophilicity, unstable nature, and poor permeation through cellular and enzymatic barriers. The use of novel strategies for delivering protein and peptides such as glycoengineering, PEGylation, Fc-fusion, chitosan nanoparticles, and liposomes have improved the efficacy, safety, and stability, which consequently expanded the therapeutic potential of proteins. This review article highlights various proteins and peptides that are useful in ocular disorders, challenges in their delivery to the eye, and strategies to enhance ocular bioavailability using novel delivery approaches. In addition, a few futuristic approaches that will assist in the ocular delivery of proteins and peptides were also discussed.

Lipid nanoparticles (LNPs) for in vivo RNA delivery and their breakthrough technology for future applications

RNA therapeutics show a significant breakthrough for the treatment of otherwise incurable diseases and genetic disorders by regulating disease-related gene expression. The successful development of COVID-19 mRNA vaccines further emphasizes the potential of RNA therapeutics in the prevention of infectious diseases as well as in the treatment of chronic diseases. However, the efficient delivery of RNA into cells remains a challenge, and nanoparticle delivery systems such as lipid nanoparticles (LNPs) are necessary to fully realize the potential of RNA therapeutics. While LNPs provide a highly efficient platform for the in vivo delivery of RNA by overcoming various biological barriers, several challenges remain to be resolved for further development and regulatory approval. These include a lack of targeted delivery to extrahepatic organs and a gradual loss of therapeutic potency with repeated doses. In this review, we highlight the fundamental aspects of LNPs and their uses in the development of novel RNA therapeutics. Recent advances in LNP-based therapeutics and preclinical/clinical studies are overviewed. Lastly, we discuss the current limitations of LNPs and introduce breakthrough technologies that might overcome these challenges in future applications.

Challenges and strategies for ocular posterior diseases therapy via non-invasive advanced drug delivery

Posterior segment diseases, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) are vital factor that seriously threatens human vision health and quality of life, the treatment of which poses a great challenge to ophthalmologists and ophthalmic scientists. In particular, ocular posterior drug delivery in a non-invasive manner is highly desired but still faces many difficulties such as rapid drug clearance, limited permeability and low drug accumulation at the target site. At present, many novel non-invasive topical ocular drug delivery systems are under development aiming to improve drug delivery efficiency and biocompatibility for better therapy of posterior segment oculopathy. The purpose of this review is to present the challenges in the noninvasive treatment of posterior segment diseases, and to propose strategies to tackle these bottlenecks. First of all, barriers to ocular administration were introduced based on ocular physiological structure and behavior, including analysis and discussion on the influence of ocular structures on noninvasive posterior segment delivery. Thereafter, various routes of posterior drug delivery, both invasive and noninvasive, were illustrated, along with the respective anatomical obstacles that need to be overcome. The widespread and risky application of invasive drug delivery, and the need to develop non-invasive local drug delivery with alternative to injectable therapy were described. Absorption routes through topical administration and strategies to enhance ocular posterior drug delivery were then discussed. As a follow-up, an up-to-date research advances in non-invasive delivery systems for the therapy of ocular fundus lesions were presented, including different nanocarriers, contact lenses, and several other carriers. In conclusion, it seems feasible and promising to treat posterior oculopathy via non-invasive local preparations or in combination with appropriate devices.

Nanotechnology-based ocular drug delivery systems: recent advances and future prospects

Ocular drug delivery has constantly challenged ophthalmologists and drug delivery scientists due to various anatomical and physiological barriers. Static and dynamic ocular barriers prevent the entry of exogenous substances and impede therapeutic agents' active absorption. This review elaborates on the anatomy of the eye and the associated constraints. Followed by an illustration of some common ocular diseases, including glaucoma and their current clinical therapies, emphasizing the significance of drug therapy in treating ocular diseases. Subsequently, advances in ocular drug delivery modalities, especially nanotechnology-based ocular drug delivery systems, are recommended, and some typical research is highlighted. Based on the related research, systematic and comprehensive characterizations of the nanocarriers are summarized, hoping to assist with future research. Besides, we summarize the nanotechnology-based ophthalmic drugs currently on the market or still in clinical trials and the recent patents of nanocarriers. Finally, inspired by current trends and therapeutic concepts, we provide an insight into the challenges faced by novel ocular drug delivery systems and further put forward directions for future research. We hope this review can provide inspiration and motivation for better design and development of novel ophthalmic formulations.

Transscleral Delivery of Dexamethasone-Loaded Microparticles Using a Dissolving Microneedle Array

Microneedles (MNs) have attracted considerable interest as a means of ocular drug delivery, a challenging delivery route due to the limitations imposed by the various biological barriers associated with this organ. In this study, a novel ocular drug delivery system was developed by formulating a dissolvable MN array containing dexamethasone-loaded PLGA microparticles for scleral drug deposition. The microparticles serve as a drug reservoir for controlled transscleral delivery. The MNs displayed sufficient mechanical strength to penetrate the porcine sclera. Dexamethasone (Dex) scleral permeation was significantly higher than in topically instilled dosage forms. The MN system was able to distribute the drug through the ocular globe, with 19.2% of the administered Dex detected in the vitreous humour. Additionally, images of the sectioned sclera confirmed the diffusion of fluorescent-labelled microparticles within the scleral matrix. The system therefore represents a potential approach for minimally invasive Dex delivery to the posterior of the eye, which lends itself to self-administration and hence high patient convenience.

In Situ Formation of Injectable Gelatin Methacryloyl (GelMA) Hydrogels for Effective Intraocular Delivery of Triamcinolone Acetonide

A novel drug delivery system designed for intraocular injection, gelatin methacryloyl (GelMA), has attracted much attention due to its sustained-release character and low cytotoxicity. We aimed to explore the sustained drug effect of GelMA hydrogels coupled with triamcinolone acetonide (TA) after injection into the vitreous cavity. The GelMA hydrogel formulations were characterized using scanning electron microscopy, swelling measurements, biodegradation, and release studies. The biological safety effect of GelMA on human retinal pigment epithelial cells and retinal conditions was verified by in vitro and in vivo experiments. The hydrogel exhibited a low swelling ratio, resistance to enzymatic degradation, and excellent biocompatibility. The swelling properties and in vitro biodegradation characteristics were related to the gel concentration. Rapid gel formation was observed after injection, and the in vitro release study confirmed that TA-hydrogels have slower and more prolonged release kinetics than TA suspensions. In vivo fundus imaging, optical coherence tomography measurements of retinal and choroid thickness, and immunohistochemistry did not reveal any apparent abnormalities of retinal or anterior chamber angle, and ERG indicated that the hydrogel had no impact on retinal function. The GelMA hydrogel implantable intraocular device exhibited an extended duration, in situ polymerization, and support cell viability, making it an attractive, safe, and well-controlled platform for treating the posterior segment diseases of the eye.

Ocular Delivery of Therapeutic Proteins: A Review

Therapeutic proteins, including monoclonal antibodies, single chain variable fragment (ScFv), crystallizable fragment (Fc), and fragment antigen binding (Fab), have accounted for one-third of all drugs on the world market. In particular, these medicines have been widely used in ocular therapies in the treatment of various diseases, such as age-related macular degeneration, corneal neovascularization, diabetic retinopathy, and retinal vein occlusion. However, the formulation of these biomacromolecules is challenging due to their high molecular weight, complex structure, instability, short half-life, enzymatic degradation, and immunogenicity, which leads to the failure of therapies. Various efforts have been made to overcome the ocular barriers, providing effective delivery of therapeutic proteins, such as altering the protein structure or including it in new delivery systems. These strategies are not only cost-effective and beneficial to patients but have also been shown to allow for fewer drug side effects. In this review, we discuss several factors that affect the design of formulations and the delivery of therapeutic proteins to ocular tissues, such as the use of injectable micro/nanocarriers, hydrogels, implants, iontophoresis, cell-based therapy, and combination techniques. In addition, other approaches are briefly discussed, related to the structural modification of these proteins, improving their bioavailability in the posterior segments of the eye without affecting their stability. Future research should be conducted toward the development of more effective, stable, noninvasive, and cost-effective formulations for the ocular delivery of therapeutic proteins. In addition, more insights into preclinical to clinical translation are needed.

Promising Role of Silk-Based Biomaterials for Ocular-Based Drug Delivery and Tissue Engineering

Silk is a wonderful biopolymer that has a long history of medical applications. Surgical cords and medically authorised human analogues made of silk have a long history of use in management. We describe the use of silk in the treatment of eye diseases in this review by looking at the usage of silk fibroin for eye-related drug delivery applications and medication transfer to the eyes. During this ancient art endeavour, a reduced engineering project that employed silk as a platform for medicine delivery or a cell-filled matrix helped reignite interest. With considerable attention, this study explores the present usage of silk in ocular-based drug delivery. This paper also examines emerging developments with the use of silk as a biopolymer for the treatment of eye ailments. As treatment options for glaucoma, diabetic retinopathy, retinitis pigmentosa, and other retinal diseases and degenerations are developed, the trans-scleral route of drug delivery holds great promise for the selective, sustained-release delivery of these novel therapeutic compounds. We should expect a swarm of silk-inspired materials to enter clinical testing and use on the surface as the secrets of silk are unveiled. This article finishes with a discussion on potential silk power, which adds to better ideas and enhanced ocular medicine delivery.

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

Targeted Nanotherapies for the Posterior Segment of the Eye: An Integrative Review on Recent Advancements and Challenges

The eye is a one-of-a-kind sensory organ with intricate anatomy and physiology. It is protected by a variety of barriers, ranging from static barriers to dynamic barriers. Although these barriers are very effective at protecting the eye from exogenous substances and external stress, they are highly compromised by various vision-impairing diseases of both the anterior and the posterior segment of the eye. Due to ocular elimination systems and intricate obstacles that selectively limit drug entry into the eye, effective drug delivery to the posterior segment of the eye (PSE) continues to be a challenge in ophthalmology. Since more than half of the most debilitating eye illnesses are thought to originate in the posterior segment (PS), understanding the physiology and clearance mechanism of the eye could help design improved formulations that could be noninvasive and intended for targeted posterior segment therapeutics. Moreover, the major drawback associated with the conventional drug delivery system to PSE is minimal therapeutic drug concentration in the desired ocular tissue and life-threatening ophthalmic complications. One possible approach that can be implemented to overcome these ocular barriers for efficient ocular therapy, non-invasive and targeted drug action to the posterior tissues is by designing nanomedicines. This review summarizes the recent non-invasive and patient compliant advances in designing nanomedicines targeting PSE. The various routes and pathways of drug administration to the ocular tissue are also summarized.

Long-acting formulation strategies for protein and peptide delivery in the treatment of PSED

The invigoration of protein and peptides in serious eye disease includes age-related macular degeneration, choroidal neovascularization, retinal neovascularization, and diabetic retinopathy. The transportation of macromolecules like aptamers, recombinant proteins, and monoclonal antibodies to the posterior segment of the eye is challenging due to their high molecular weight, rapid degradation, and low solubility. Moreover, it requires frequent administration for prolonged therapy. The long-acting novel formulation strategies are helpful to overcome these issues and provide superior therapy. It avoids frequent administration, improves stability, high retention time, and avoids burst release. This review briefly enlightens posterior segments of eye diseases with their diagnosis techniques and treatments. This article mainly focuses on recent advanced approaches like intravitreal implants and injectables, electrospun injectables, 3D printed drug-loaded implants, nanostructure thin-film polymer devices encapsulated cell technology-based intravitreal implants, injectable and depots, microneedles, PDS with ranibizumab, polymer nanoparticles, inorganic nanoparticles, hydrogels and microparticles for delivering macromolecules in the eye for intended therapy. Furthermore, novel techniques like aptamer, small Interference RNA, and stem cell therapy were also discussed. It is predicted that these systems will make revolutionary changes in treating posterior segment eye diseases in future.

Recent achievements in nano-based technologies for ocular disease diagnosis and treatment, review and update

Ocular drug delivery is one of the most challenging endeavors among the various available drug delivery systems. Despite having suitable drugs for the treatment of ophthalmic disease, we have not yet succeeded in achieving a proper drug delivery approach with the least adverse effects. Nanotechnology offers great opportunities to overwhelm the restrictions of common ocular delivery systems, including low therapeutic effects and adverse effects because of invasive surgery or systemic exposure. The present review is dedicated to highlighting and updating the recent achievements of nano-based technologies for ocular disease diagnosis and treatment. While further effort remains, the progress illustrated here might pave the way to new and very useful ocular nanomedicines.

Retinal Diseases: The Next Frontier in Pharmacodelivery

The future continuous growth of the global older population augments the burden of retinal diseases worldwide. Retinal characteristics isolating and protecting the sensitive neuro-retina from the rest of the ocular tissues challenge drug delivery and promote research and development toward new horizons. In this review, we wish to describe the unmet medical needs, discuss the novel modes of delivery, and disclose to the reader a spectrum of older-to-novel drug delivery technologies, innovations, and the frontier of pharmacodelivery to the retina. Treating the main retinal diseases in the everlasting war against blindness and its associated morbidity has been growing steadily over the last two decades. Implants, new angiogenesis inhibitor agents, micro- and nano-carriers, and the anchored port delivery system are becoming new tools in this war. The revolution and evolution of new delivery methods might be just a few steps ahead, yet its assimilation in our daily clinical work may take time, due to medical, economical, and regulatory elements that need to be met in order to allow successful development and market utilization of new technologies. Therefore, further work is warranted, as detailed in this Pharmaceutics Special Issue.

Self-Plugging Microneedle (SPM) for Intravitreal Drug Delivery

Intravitreal injection (IVI) is a common technology which is used to treat ophthalmic diseases inside eyeballs by delivering various drugs into the vitreous cavity using hypodermic needles. However, in some cases, there are possible side effects such as ocular tissue damage due to repeated injection or eyeball infection through the hole created during the needle retraction process. The best scenario of IVI is a one-time injection of drugs without needle retraction, keeping the system of the eyeball closed. Microneedles (MNs) have been applied to ocular tissues over 10 years, and no serious side effects on ocular tissue due to MN injection have been reported. Therefore, a self-plugging MN (SPM) is developed to perform intraocular drug delivery and to seal the scleral puncture simultaneously. The SPMs are fabricated by a thermal drawing process and then coated with a polymeric carrier of drugs and a hydrogel-based scleral plugging component. Each coated functional layer is characterized and demonstrated by in vitro and ex vivo experiments. Finally, in vivo tests using a porcine model confirms prompt sealing of SPM and sustained intraocular drug delivery.

Recent advances in ophthalmic preparations: Ocular barriers, dosage forms and routes of administration

The human eye is a complex organ with unique anatomy and physiology that restricts the delivery of drugs to target ocular tissues/sites. Recent advances in the field of pharmacy, biotechnology and material science have led to development of novel ophthalmic dosage forms which can provide sustained drug delivery, reduce dosing frequency and improve the ocular bioavailability of drugs. This review highlights the different anatomical and physiological factors which affect ocular bioavailability of drugs and explores advancements from 2016 to 2020 in various ophthalmic preparations. Different routes of drug administration such as topical, intravitreal, intraocular, juxtascleral, subconjunctival, intracameral and retrobulbar are discussed with their advances and limitations.

Implementing Spanlastics for Improving the Ocular Delivery of Clotrimazole: In vitro Characterization, Ex vivo Permeability, Microbiological Assessment and In vivo Safety Study

Purpose

The aim of this study was to encapsulate clotrimazole (CLT), an antifungal drug with poor water solubility characteristics, into spanlastics (SPs) to provide a controlled ocular delivery of the drug.

Methods

Span 60 was used in the formulation of SPs with Tween 80, Pluronic F127, or Kolliphor RH40 as an edge activator (EA). The presence of EA offers more elasticity to the membrane of the vesicles which is expected to increase the corneal permeation of CLT. SPs were prepared using ethanol injection method applying 3² complete factorial design to study the effect of formulation variables (ratio of Span 60: EA (w/w) and type of EA) on SPs characteristics (encapsulation efficiency percent (EE%), average vesicle size (VS), polydispersity index (PDI) and zeta potential (ZP)). Design-Expert software was used to determine the optimum formulation for further investigations.

Results

The optimum formulation determined was S1, which contains 20 mg of Tween 80 used as an EA and 80 mg of Span 60. S1 exhibited EE% = 66.54 ± 7.57%, VS = 206.20 ± 4.95 nm, PDI = 0.39 ± 0.00 and ZP = −29.60 ± 0.99 mV. S1 showed highly elastic sphere-shaped vesicles. Furthermore, S1 displayed a sustained release profile and a higher ex vivo permeation across rabbit cornea relative to CLT suspension. Also, S1 revealed superior inhibition of Candida albicans development compared to CLT suspension applying 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction technique. Moreover, in vivo histopathological examination assured the safety of S1 after ophthalmic application in mature male albino rabbits.

Conclusion

Overall, the outcomes revealed the marked efficacy of SPs for ocular delivery of CLT.

In vitro dissolution testing models of ocular implants for posterior segment drug delivery

The delivery of drugs to the posterior segment of the eye remains a tremendously difficult task. Prolonged treatment in conventional intravitreal therapy requires injections that are administered frequently due to the rapid clearance of the drug molecules. As an alternative, intraocular implants can offer drug release for long-term therapy. However, one of the several challenges in developing intraocular implants is selecting an appropriate in vitro dissolution testing model. In order to determine the efficacy of ocular implants in drug release, multiple in vitro test models were emerging. While these in vitro models may be used to analyse drug release profiles, the findings may not predict in vivo retinal drug exposure as this is influenced by metabolic and physiological factors. This review considers various types of in vitro test methods used to test drug release of ocular implants. Importantly, it discusses the challenges and factors that must be considered in the development and testing of the implants in an in vitro setup.

Genetics, pathogenesis and therapeutic developments for Usher syndrome type 2

Usher syndrome (USH) is a rare, autosomal recessively inherited disorder resulting in a combination of sensorineural hearing loss and a progressive loss of vision resulting from retinitis pigmentosa (RP), occasionally accompanied by an altered vestibular function. More and more evidence is building up indicating that also sleep deprivation, olfactory dysfunction, deficits in tactile perception and reduced sperm motility are part of the disease etiology. USH can be clinically classified into three different types, of which Usher syndrome type 2 (USH2) is the most prevalent. In this review, we, therefore, assess the genetic and clinical aspects, available models and therapeutic developments for USH2. Mutations in USH2A, ADGRV1 and WHRN have been described to be responsible for USH2, with USH2A being the most frequently mutated USH-associated gene, explaining 50% of all cases. The proteins encoded by the USH2 genes together function in a dynamic protein complex that, among others, is found at the photoreceptor periciliary membrane and at the base of the hair bundles of inner ear hair cells. To unravel the pathogenic mechanisms underlying USH2, patient-derived cellular models and animal models including mouse, zebrafish and drosophila, have been generated that all in part mimic the USH phenotype. Multiple cellular and genetic therapeutic approaches are currently under development for USH2, mainly focused on preserving or partially restoring the visual function of which one is already in the clinical phase. These developments are opening a new gate towards a possible treatment for USH2 patients.

Effective Ocular Delivery of Eplerenone Using Nanoengineered Lipid Carriers in Rabbit Model

Background

Eplerenone (Epl) is a selective mineralocorticoid-receptor antagonist used for chronic central serous chorioretinopathy treatment. Our goal was to enhance the corneal performance of Epl-loaded nanostructured lipid carriers (NLCs) through surface modification using different coating polymers.

Methods

Epl-loaded modified NLCs (Epl-loaded MNLCs) were prepared by coating the surface of Epl-loaded NLCs using different polymers, namely hyaluronic acid, chitosan oligosaccharide lactate, and hydrogenated collagen. A 3¹×4¹ full factorial design was used to evaluate the effect of the surface modification on the properties of the prepared systems. Selected optimal Epl-loaded MNLCs were further evaluated for in vitro drug release, morphology, pH, rheological properties, corneal mucoadhesion, irritation, and penetration.

Results

Epl-loaded MNLCs were successfully prepared with high drug-entrapment efficiency and nanosized particles with low size distribution. Transmission electron microscopy revealed nanosized spherical particles surrounded by a coating layer of the surface modifier. The pH, refractive index, and viscosity results of the Epl-loaded MNLCs confirmed the ocular compatibility of the systems with no blurring of vision. The safety and ocular tolerance of the optimal MNLCs were confirmed using the hen’s egg test on chorioallantoic membrane and by histopathological evaluation of rabbit eyes treated with the optimal systems. Confocal laser-scanning microscopy of corneal surfaces confirmed successful transcorneal permeation of the Epl-loaded MNLCs compared to the unmodified Epl-loaded NLCs, revealed by higher corneal fluorescence intensity at all time intervals.

Conclusion

Overall, the results confirmed the potential of Epl-loaded MNLCs as a direct approach for Epl ocular delivery.

Recent trends in drug-delivery systems for the treatment of diabetic retinopathy and associated fibrosis

Diabetic retinopathy is a frequent microvascular complication of diabetes and a major cause of visual impairment. In advanced stages, the abnormal neovascularization can lead to fibrosis and subsequent tractional retinal detachment and blindness. The low bioavailability of the drugs at the target site imposed by the anatomic and physiologic barriers within the eye, requires long term treatments with frequent injections that often compromise patient's compliance and increase the risk of developing more complications. In recent years, much effort has been put towards the development of new drug delivery platforms aiming to enhance their permeation, to prolong their retention time at the target site and to provide a sustained release with reduced toxicity and improved efficacy. This review provides an overview of the etiology and pathophysiology of diabetic retinopathy and current treatments. It addresses the specific challenges associated to the different ocular delivery routes and provides a critical review of the most recent developments made in the drug delivery field.

Age-related ocular conditions: Current treatments and role of cyclodextrin-based nanotherapies

Age-related eye disorders are chronic diseases that affect millions of people worldwide. They cause visual impairment and, in some cases, irreversible blindness. Drug targeting to the retina is still a challenge due to the difficulties with drug distribution, crossing eye barriers, and reaching intraocular tissues in an effective therapeutic concentration. Although intravitreal injections can directly deliver drugs to the posterior segment of the eye, it remains an invasive technique and leads to several side effects. Conventional formulations such as emulsions, suspensions, or ointments have been related to frequent instillation and inability to reach intraocular tissues. New drug delivery systems and medical devices have also been designed. Nevertheless, these treatments are not always effective and sometimes require the presence of a specialist for the administration of the dose. Therefore, treatments for age-related ocular diseases remain as one of the major unmet clinical needs to manage these widespread eye conditions. Nanotechnology may become the adequate tool for developing effective and non-invasive therapies suitable for self-administration. In this review, we discuss emerging therapeutic options based on nanoengineering of cyclodextrin nanocarriers for the treatment of age-related eye disorders, including their pathophysiology, pharmacological options, and feasibility of clinical translation.

Extraocular, periocular, and intraocular routes for sustained drug delivery for glaucoma

Although once daily anti-glaucoma drug therapy is a current clinical reality, most therapies require multiple dosing and there is an unmet need to develop convenient, safe, and effective sustained release drug delivery systems for long-term treatment to improve patient adherence and outcomes. One of the first sustained release drug delivery systems was approved for the reduction of intraocular pressure in glaucoma patients. It is a polymeric reservoir-type insert delivery system, Ocusert™, placed under the eyelid and on the ocular surface for zero-order drug release over one week. The insert, marketed in two strengths, released pilocarpine on the eye surface. While many clinicians appreciated this drug product, it was eventually discontinued. No similar sustained release non-invasive drug delivery system has made it to the market to date for treating glaucoma. Drug delivery systems under development include punctal plugs, ring-type systems, contact lenses, implants, microspheres, nanospheres, gels, and other depot systems placed in the extraocular, periocular, or intraocular regions including intracameral, supraciliary, and intravitreal spaces. This article discusses the advantages and disadvantages of the various routes of administration and delivery systems for sustained glaucoma therapy. It also provides the reader with some examples and discussion of drug delivery systems that could potentially be applied for glaucoma treatment. Interestingly, one intracamerally injected implant, Durysta™, was approved recently for sustained intraocular pressure reduction. However, long-term acceptance of such devices has yet to be established. The ultimate success of the delivery system will depend on efficacy relative to eye drop dosing, safety, reimbursement options, and patient acceptance. Cautious development efforts are warranted considering prior failed approaches for sustained glaucoma drug delivery. Neuroprotective approaches for glaucoma therapy including cell, gene, protein, and drug-combination therapies, mostly administered intravitreally, are also rapidly progressing towards assessment in humans.

Dopamine-Functionalized Gellan Gum Hydrogel as a Candidate Biomaterial for a Retinal Pigment Epithelium Cell Delivery System

In this study, dopamine-functionalized gellan gum (DFG) hydrogel was prepared as a carrier for retinal pigment epithelium (RPE) cell delivery via a carbodiimide reaction. The carboxylic acid of gellan gum (GG) was replaced with catechol in a 21.3% yield, which was confirmed by NMR. Sol fraction and weight loss measurements revealed that dopamine improved degradability in the GG hydrogel. Measurements of the viscosity, injection force, and compressibility also showed that dopamine-functionalized GG hydrogels had more desirable rheological/mechanical properties for improving injectability. These characteristics were confirmed to arise from the GG's helix structure loosened by the dopamine's bulky nature. Moreover, dopamine's hydrophilic characteristics were confirmed to create a more favorable microenvironment for cell growth by promoting swelling capability and cell attachment. This improved biocompatibility became more pronounced when the hydrophilicity of dopamine was combined with a larger specific surface area stemming from the less porous structure of the dopamine-grafted hydrogels. This effect was apparent from the live/dead staining images of the as-prepared hydrogels. Meanwhile, the nonionic cross-linked DFG (DG) hydrogel showed the lowest protein expression in the immunofluorescence staining images obtained after 28 days of culture, supporting that it had the highest degradability and associated cell-releasing ability. That tendency was also observed in the gene expression data acquired by real-time polymerase chain reaction (RT-PCR) analysis. RT-PCR analysis also revealed that the DG hydrogel carrier could upregulate the visual function-related gene of RPE. Overall, the DG hydrogel system demonstrated its feasibility as a carrier of RPE cells and its potential as a means of improving visual function.

Ocular Drug Delivery to the Retina: Current Innovations and Future Perspectives

Treatment options for retinal diseases, such as neovascular age-related macular degeneration, diabetic retinopathy, and retinal vascular disorders, have markedly expanded following the development of anti-vascular endothelial growth factor intravitreal injection methods. However, because intravitreal treatment requires monthly or bimonthly repeat injections to achieve optimal efficacy, recent investigations have focused on extended drug delivery systems to lengthen the treatment intervals in the long term. Dose escalation and increasing molecular weight of drugs, intravitreal implants and nanoparticles, hydrogels, combined systems, and port delivery systems are presently under preclinical and clinical investigations. In addition, less invasive techniques rather than intravitreal administration routes, such as topical, subconjunctival, suprachoroidal, subretinal, and trans-scleral, have been evaluated to reduce the treatment burden. Despite the latest advancements in the field of ophthalmic pharmacology, enhancing drug efficacy with high ocular bioavailability while avoiding systemic and local adverse effects is quite challenging. Consequently, despite the performance of numerous in vitro studies, only a few techniques have translated to clinical trials. This review discusses the recent developments in ocular drug delivery to the retina, the pharmacokinetics of intravitreal drugs, efforts to extend drug efficacy in the intraocular space, minimally invasive techniques for drug delivery to the retina, and future perspectives in this field.

Small interfering RNAs (siRNAs) based gene silencing strategies for the treatment of glaucoma: Recent advancements and future perspectives

RNA-interference-based mechanisms, especially the use of small interfering RNAs (siRNAs), have been under investigation for the treatment of several ailments and have shown promising results for ocular diseases including glaucoma. The eye, being a confined compartment, serves as a good target for the delivery of siRNAs. This review focuses on siRNA-based strategies for gene silencing to treat glaucoma. We have discussed the ocular structures and barriers to gene therapy (tear film, corneal, conjunctival, vitreous, and blood ocular barriers), methods of administration for ocular gene delivery (topical instillation, periocular, intracameral, intravitreal, subretinal, and suprachoroidal routes) and various viral and non-viral vectors in siRNA-based therapy for glaucoma. The components and mechanism of siRNA-based gene silencing have been mentioned briefly followed by the basic strategies and challenges faced during siRNA therapeutics development. We have emphasized different therapeutic targets for glaucoma which have been under research by scientists and the current siRNA-based drugs used in glaucoma treatment. We also mention briefly strategies for siRNA-based treatment after glaucoma surgery.

Corticosteroids in ophthalmology: drug delivery innovations, pharmacology, clinical applications, and future perspectives

Corticosteroids remain the mainstay of the treatment for various ocular conditions affecting the ocular surface, anterior and posterior segments of the eye due to their anti-inflammatory, anti-oedematous, and anti-neovascularization properties. Prednisolone, prednisolone acetate, dexamethasone, triamcinolone acetonide, fluocinolone acetonide, and loteprednol etabonate are amongst the most widely used ophthalmic corticosteroids. Corticosteroids differ in their activity and potency in the eye due to their inherent pharmacological and pharmaceutical differences. Different routes and regimens are available for ocular administration of corticosteroids. Conventional topical application to the eye is the route of choice when targeting diseases affecting the ocular surface and anterior segment, while periocular, intravitreal, and suprachoroidal injections can be potentially effective for posterior segment diseases. Corticosteroid-induced intraocular pressure elevation and cataract formation remain the most significant local risks following topical as well as systemic corticosteroid administration. Invasive drug administration via intracameral, subconjunctival, and intravitreal injection can enhance ocular bioavailability and minimize dose and dosing frequency of administration, yet may exacerbate ocular side effects of corticosteroids. This review provides a critical appraisal of the ophthalmic uses of corticosteroid, routes of administration, drug delivery fundamentals and novel ocular implantable steroid delivery systems, factors influencing side effects, and future perspectives for ocular corticosteroid therapy.

Nanocarriers for ocular drug delivery: current status and translational opportunity

Ocular diseases have a significant effect on vision and quality of life. Drug delivery to ocular tissues is a challenge to formulation scientists. The major barriers to delivering drugs to the anterior and posterior segments include physiological barriers (nasolacrimal drainage, blinking), anatomical barriers (static and dynamic), efflux pumps and metabolic barriers. The static barriers comprise the different layers of the cornea, sclera, and blood-aqueous barriers whereas dynamic barriers involve conjunctival blood flow, lymphatic clearance and tear drainage. The tight junctions of the blood-retinal barrier (BRB) restrict systemically administered drugs from entering the retina. Nanocarriers have been found to be effective at overcoming the issues associated with conventional ophthalmic dosage forms. Various nanocarriers, including nanodispersion systems, nanomicelles, lipidic nanocarriers, polymeric nanoparticles, liposomes, niosomes, and dendrimers, have been investigated for improved permeation and effective targeted drug delivery to various ophthalmic sites. In this review, various nanomedicines and their application for ophthalmic delivery of therapeutics are discussed. Additionally, scale-up and clinical status are also addressed to understand the current scenario for ophthalmic drug delivery.

Tuning surface functionalities of sub-10 nm-sized nanocarriers to target outer retina in designing drug delivery agents for intravitreal administration

Age-related macular degeneration (AMD) is one of the leading causes of irreversible blindness, generally affecting people over 50 years of age in industrialized countries. Despite the effectiveness of anti-vascular endothelial growth factor (VEGF) therapy in attenuating the growth of new blood vessels, substantial visual improvements are rare with this complex disease. Furthermore, the current regimen of repeated monthly intravitreal injections of drugs can result in serious side effects. Combination therapies-to complement anti-VEGF alone-with a prolonged therapeutic effect and efficient delivery to the intended site are urgently needed, which could be realized through the use of carefully designed nanocarriers. To understand the physicochemical effects (e.g., size, charge, geometry) of intravitreally administered nanocarriers on their bioavailability, distribution, and targeting efficiency across multiple layers of the retina, here we prepared seven different types of surface-functionalized water-soluble dendritic nanocarriers with hydrodynamic sizes mostly under 5 nm. A similar stoichiometric amount of fluorophore was covalently attached to each of these biocompatible nanocarriers for quantitative analyses by confocal microscopy of cryosectioned healthy mouse eyes. Interestingly, at 24 h post-injection, the nanocarrier with multiple copies of glucosamine on the surface (D_NSG) accumulated predominantly in the photoreceptor layer and the retinal pigment epithelium (RPE), which are speculated to be associated with AMD pathogenesis (i.e., target sites). Furthermore, extended residence at these outer retinal layers was demonstrated by D_NSG, which appeared to gradually turn into micron-scale particles potentially through aggregation. Our systematic findings may provide useful guidelines for the rational design of intravitreal nanocarriers to treat vision-threatening retinal diseases, including AMD.

Efficacy and safety of injecting increasing volumes into the extravascular spaces of the choroid using a blunt adjustable depth injector

PURPOSE

To evaluate the efficacy and safety of injecting increasing volumes into the extravascular spaces of the choroid (EVSC) in rabbit eyes in vivo using a blunt adjustable depth injector.

METHODS

Indocyanine green (ICG) was injected in the superior-temporal quadrant, 2 mm posterior to the limbus at increasing volumes (0.1-0.3 ml) into the EVSC of New Zealand rabbit eyes in vivo. Intraocular pressure (IOP) measurements, spectral domain optical coherence tomography (SD-OCT), fundus imaging and histology analysis were performed to assess the safety and efficacy of the injection.

RESULTS

Volumes up to 0.3 ml were administered consistently. ICG injection was successfully monitored in vivo using infrared fundus imaging and SD-OCT. ICG was detected across the EVSC compartment, reaching the retinal pigment epithelium, optic nerve head and visual streak. Injection of 0.3 ml yielded maximal dye distribution with a coverage area of 61.8% ± 6.7% (mean ± standard error, SE) of the posterior segment. Maximal IOP elevation was recorded 5 min following injection of 0.2 and 0.3 ml ICG (+ 20.0 mmHg, + 19.4 mmHg, respectively). Twenty minutes post-injection, the IOP was < 15 mmHg in all injection volumes. No retinal detachment or hemorrhages were detected in any of the injected eyes.

CONCLUSIONS

This study demonstrates consistent and safe delivery of large volumes within the EVSC using a blunt adjustable depth injector that distributes the dye over 60% of the retinal surface. This injection system may offer a minimally invasive and easy way to deliver large volumes of pharmaceuticals into the posterior segment.

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.

Thermal Effects on Fluid Mixing in the Eye

Age-related macular degeneration (AMD) is the leading cause of central vision loss in the developed world. Wet AMD can be managed through serial intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) agents. However, sometimes the treatment is ineffective. Given that the half-life of the drug is limited, inefficient mixing of the injected drug in the vitreous chamber of the eye may contribute to the ineffectiveness. Here, we introduce thermal heating as a means of enhancing the mixing-process in the vitreous chamber and investigate parameters that potentially influence its effectiveness. Our in vitro studies reveal the importance of the heating location on the eye. A significant increase in the mixing and delivery of drugs to the targeted area (the macula) could be achieved by placing heating pads to induce a current, against gravity, in the vitreous. The presented results can potentially help in the development of a better strategy for intravitreal injection, subsequently improving the quality of patient care.

Drug Delivery to the Posterior Segment of the Eye: Biopharmaceutic and Pharmacokinetic Considerations

The treatment of the posterior-segment ocular diseases, such as age-related eye diseases (AMD) or diabetic retinopathy (DR), present a challenge for ophthalmologists due to the complex anatomy and physiology of the eye. This specialized organ is composed of various static and dynamic barriers that restrict drug delivery into the target site of action. Despite numerous efforts, effective intraocular drug delivery remains unresolved and, therefore, it is highly desirable to improve the current treatments of diseases affecting the posterior cavity. This review article gives an overview of pharmacokinetic and biopharmaceutics aspects for the most commonly-used ocular administration routes (intravitreal, topical, systemic, and periocular), including information of the absorption, distribution, and elimination, as well as the benefits and limitations of each one. This article also encompasses different conventional and novel drug delivery systems designed and developed to improve drug pharmacokinetics intended for the posterior ocular segment treatment.

Advances in ocular drug delivery systems

Recent advances in pharmacological agents have led to successful treatment of a variety of retinal diseases such as neovascular age-related macular degeneration (AMD), diabetic macular oedema (DMO), and retinal vascular occlusions (RVO). These treatments often require repeated drug injections for an extended period of time. To reduce these repeated treatment burdens, minimally invasive drug delivery systems are needed. An ideal therapy should maintain effective levels of drug for the intended duration of treatment following a single application, recognising that a significant number of months of therapy may be required. There are numerous approaches under investigation to improve treatment options. This review will highlight the advantages and limitations of selected drug delivery systems of novel biomaterial implants and depots. The main emphasis will be placed on less invasive, longer acting, sustained release formulations for the treatment of retinal disorders.

Effect of Formulation Variables and Gamma Sterilization on Transcorneal Permeation and Stability of Proniosomal Gels as Ocular Platforms for Antiglaucomal Drug

This study aims to evaluate the effect of different formulation variables (surfactant type and HLB value) adopting full factorial design (5¹. 2¹) using coacervation phase technique on in vitro characterization of dorzolamide hydrochloride (DZ)-loaded proniosomal gels, namely, entrapment efficiency percentage (EE%), vesicle size distribution, polydispersion index (PDI), and in vitro DZ release. The optimum formula F2 with a desirability value of 0.937 composed of 40 mg DZ, 500 mg span 60, 500 mg of L-α-Lethicin, and 55.5 mg cholesterol showing EE% of 84.5 ± 1.5%, PS of 189.5 ± 35.76 nm with PDI 0.8 ± 0.28 and 58.51% ± 1.00 of DZ released after 8 h was further evaluated using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The effect of gamma sterilization on transcorneal permeation and stability of DZ from the selected formulation (F2) revealed that F2 was significantly tolerable, stable, and competent to corneal permeation confirmed by histological examination, confocal laser microscopy, and intraocular pressure (IOP) measurement. Significant corneal bioavailability was attained from formula F2 (370.6 mg. h/m) compared to the market product Trusopt® eye drops (92.59 mg. h/ml) following IOP measurement, thereby proniosomal gels could be considered as tolerable and competent ocular platforms for improving the transcorneal permeation of DZ.

S, Akshara MR, N. K, Zaidi ZS, Iqbal SF, Misra SK. Advances in chemistry and composition of soft materials for drug releasing contact lenses

Ocular drug delivery has always been a challenging feat to achieve in the field of medical sciences. One of the existing methods of non-invasive ocular drug delivery is the use of eye drops. However, drugs administered through these formulations have low bioavailability in the ocular system. This limitation can been overcome by using contact lenses as drug delivery vehicles. According to USA FDA definitions they can be categorized into two main categories-hard and soft contact lenses. Based on the material properties, hard contact lenses are mostly produced from polymers of acrylate monomers such as MMA (methyl methacrylate). These have the least water retention capacity, thereby, having minimal ability to diffuse oxygen into the corneal layer and are not ideal for long term use. Soft material contact lenses are flexible and are mainly hydrogel based. They have higher water retention capacities as compared to rigid contact lenses, which gives them the ability to transmit oxygen to the corneal layer. These hydrogel based soft materials are mainly produced from polymers of acrylate monomers such as HEMA (hydroxyethyl methacrylate) and found to be better for drug delivery contact lenses. These polymer-based soft materials have been efficiently modified in terms of their chemistry to achieve diverse physicochemical properties to produce efficient ocular drug delivery systems. However, complications such as drug leaching during storage and distribution, sterilisation, preservation of integrity of the lens and the possibility of surface roughness due to the incorporated drug molecules still need to be optimised. This review highlights the chemistries of various polymeric molecules through which physicochemical properties can be modified to achieve optimum drug loading and sustained release of the drug for application in the ocular system.

Contact lens as controllable route for ocular drug delivery.

Bio-Inspired Strategies against Diabetes and Associated Complications: A Review

Bio-molecules are the most important target to be considered while designing any drug delivery system. The logic lies in using such bio-sensing or bio-mimicking systems in their formulations that can mimic the active site of those receptors to which the drug is going to bind. Polymers mimicking the active site of target enzymes are regarded as bio-inspired polymers and can be used to ameliorate many diseased conditions. Nowadays, this strategy is also being adopted against diabetes and its complications. Under hyperglycemic conditions, many pathways get activated which are responsible for the progression of diabetes-associated secondary complications viz. retinopathy, neuropathy, and nephropathy. The enzymes involved in the progression of these complications can be mimicked for their effective management. For an instance, Aldose Reductase (ALR2), a rate-limiting enzyme of the polyol pathway (downstream pathway) which gets over-activated under hyperglycemic condition is reported to be mimicked by using polymers which are having same functionalities in their structure. This review aims at critically appraising reports in which target mimicking bio-inspired formulations have been envisaged against diabetes and its complications. The information summarized in this review will provide an idea about the bio-sensing approaches utilized to manage blood glucose level and the utility of bio-inspired polymers for the management of diabetic complications (DC). Such type of information may be beneficial to pharmaceutical companies and academia for better development of targeted drug delivery systems with sustained-release property against these diseased conditions.

Effects of Exogenous Neuroglobin (Ngb) on retinal inflammatory chemokines and microglia in a rat model of transient hypoxia

Neuroglobin is an endogenous neuroprotective protein. We determined the safety of direct delivery of Neuroglobin in the rat retina and its effects on retinal inflammatory chemokines and microglial during transient hypoxia. Exogenous Neuroglobin protein was delivered to one eye and a sham injection to the contralateral eye of six rats intravitreally. Fundus photography, Optical Coherence Topography, electroretinogram, histology and Neuroglobin, chemokines level were determined on days 7 and 30. Another 12 rats were subjected to transient hypoxia to assess the effect of Neuroglobin in hypoxia exposed retina by immunohistochemistry, retinal Neuroglobin concentration and inflammatory chemokines. Intravitreal injection of Neuroglobin did not incite morphology or functional changes in the retina. Retinal Neuroglobin protein was reduced by 30% at day 7 post hypoxia. It was restored to normoxic control levels with intravitreal exogenous Neuroglobin injections and sustained up to 30 days. IL-6, TNFα, IL-1B, RANTES, MCP-1 and VEGF were significantly decreased in Neuroglobin treated hypoxic retinae compared to non-treated hypoxic controls. This was associated with decreased microglial activation in the retina. Our findings provide proof of concept suggesting intravitreal Neuroglobin injection is non-toxic to the retina and can achieve the functional level to abrogate microglial and inflammatory chemokines responses during transient hypoxia.

Proniosomal gel-derived niosomes: an approach to sustain and improve the ocular delivery of brimonidine tartrate; formulation, in-vitro characterization, and in-vivo pharmacodynamic study

Brimonidine tartrate (BRT) is a hydrophilic α2 adrenergic agonist used for the treatment of glaucoma. Glaucoma is an ocular disease affecting the anterior segment of the eye requiring lifetime treatment. Owing to the obstacles facing ocular delivery systems and hydrophilicity of BRT, frequent administration of the eye drops is required. Niosomes have been widely used to improve the ocular bioavailability of the topically applied drugs and to enhance the ocular residence time. However, they have drawbacks as physical instability, aggregation, and loss of the entrapped drug. For this reason, BRT proniosomes were prepared to overcome niosomal instability issues. A D-optimal design was utilized to determine the optimum conditions for preparation of the proniosomal gels. Independent variables were amount of surfactant, surfactant:cholesterol ratio, and type of surfactant used. The dependent variables were entrapment efficiency (EE%), particle size, percentage of drug released after 2 h (Q2h), and percentage of drug released after 24 h (Q24h). The optimum formula was suggested with desirability 0.732 and the composition of 540 mg Span 60 and 10:1 surfactant:cholesterol ratio. The results obtained after reconstitution were; EE% of 79.23 ± 1.12% particle size of 810.95 ± 16.758 nm, polydispersity index (PDI) 0.6785 ± 0.213, zeta potential 59.1 ± 0.99 mV, Q2h40.98 ± 1.29%, Q8h 63.35 ± 6.07%, and Q24h = 91.11 ± 1.76%. Transmission electron microscope imaging of the formula showed the typical spherical shape of niosomes. In-vivo pharmacodynamic study assured the improved ocular bioavailability of BRT selected formula when compared with Alphagan®P with relative AUC0-24 of 5.024 and 7.90 folds increase in the mean residence time (MRT). Lack of ocular irritation of the formula was assured by Draize test.

Melt-Cast Films Significantly Enhance Triamcinolone Acetonide Delivery to the Deeper Ocular Tissues

Delivering an effective drug load to the posterior section of the ocular tissues, while using a non-invasive technique, has always been a challenge. In this regard, the goal of the present study was to develop sustained release triamcinolone acetonide (TA) loaded polymeric matrix films for ocular delivery. The TA-films were prepared in two different polymer matrices, with drug loadings of 10% and 20% w/w, and they were evaluated for ocular distribution in vivo in a conscious rabbit model. A 4% w/v TA suspension (TA-C) was used as a control for in vitro and in vivo studies. The TA-films, prepared with melt-cast technology, used polyethylene oxide (PEO) and Soluplus^® as the polymer matrix. The films were evaluated with respect to assay, content uniformity, excipient interaction, and permeability across isolated rabbit sclera. The distribution of TA in the ocular tissues, post topical administration, was determined in New Zealand male albino rabbits as a function of dose, and was compared against TA-C. The assay of the 10% and 20% w/w film was in the range from 70–79% and 92–94% for the Soluplus^® and PEO films, respectively, and content uniformity was in the range of 95–103% for both the films. The assay of the TA from Soluplus^® films was less compared with the PEO films and showed an interaction with TA, as revealed by Differential Scanning Calorimetry (DSC). Hence, Soluplus^® films were not selected for further studies. No interaction was observed between the drug and PEO polymer matrix. The enhancement of trans-scleral flux and permeability of TA was about 1.16 and 1.33-folds, respectively, from the 10% w/w PEO and 3.5 and 2.12-folds, respectively, from the 20% w/w PEO films, as compared with TA-C formulations. The in vivo studies demonstrate that significantly higher TA levels were observed in the anterior and posterior segments of the eye at the end of 6h with the PEO films. Therefore, the PEO based polymeric films were able to deliver TA into the back of the eye efficiently and for prolonged periods.