Topical delivery of Avastin to the posterior segment of the eye in vivo using annexin A5-associated liposomes

Enhanced Ocular Delivery of Beva via Ultra-Small Polymeric Micelles for Noninvasive Anti-VEGF Therapy

Pathological ocular neovascularization resulting from retinal ischemia constitutes a major cause of vision loss. Current anti-VEGF therapies rely on burdensome intravitreal injections of Bevacizumab (Beva). Herein ultrasmall polymeric micelles encapsulating Beva (P@Beva) are developed for noninvasive topical delivery to posterior eye tissues. Beva is efficiently loaded into 11 nm micelles fabricated via self-assembly of hyperbranched amphiphilic copolymers. The neutral, brush-like micelles demonstrate excellent drug encapsulation and colloidal stability. In vitro, P@Beva enhances intracellular delivery of Beva in ocular cells versus free drug. Ex vivo corneal and conjunctival-sclera-choroidal tissues transport after eye drops are improved 23-fold and 7.9-fold, respectively. Anti-angiogenic bioactivity is retained with P@Beva eliciting greater inhibition of endothelial tube formation and choroid sprouting over Beva alone. Remarkably, in an oxygen-induced retinopathy (OIR) model, topical P@Beva matching efficacy of intravitreal Beva injection, is the clinical standard. Comprehensive biocompatibility verifies safety. Overall, this pioneering protein delivery platform holds promise to shift paradigms from invasive intravitreal injections toward simplified, noninvasive administration of biotherapeutics targeting posterior eye diseases.

Study on the interaction mechanism of whey protein isolate with phosphatidylcholine: By multispectral methods and molecular docking

The elucidation of the interaction mechanism between phospholipids and milk proteins within emulsions is pivotal for comprehending the properties of infant formula fat globules. In this study, multispectral methods and molecular docking were employed to explore the relationship between phosphatidylcholine (PC) and whey protein isolate (WPI). Observations indicate that the binding constant, alongside thermodynamic parameters, diminishes as temperature ascends, hinting at a predominantly static quenching mechanism. Predominantly, van der Waals forces and hydrogen bonds constitute the core interactions between WPI and PC. This assertion is further substantiated by Fourier transform infrared spectroscopy, which verifies PC's influence on WPI's secondary structure. A detailed assessment of thermodynamic parameters coupled with molecular docking reveals that PC predominantly adheres to specific sites within α-lactalbumin, β-lactoglobulin, and bovine serum albumin, propelled by a synergy of hydrophobic interactions, hydrogen bonding, and van der Waals forces, with binding energies noted at -5.59, -6.71, and -7.85 kcal/mol, respectively. An increment in PC concentration is observed to amplify the emulsification properties of WPI whilst concurrently diminishing the zeta potential. This study establishes a theoretical foundation for applying the PC-WPI interaction mechanism in food.

Recent advances and strategies for nanocarrier-mediated topical therapy and theranostic for posterior eye disease

Posterior eye disorders, such as age-related macular degeneration, diabetic retinopathy, and glaucoma, have a significant impact on human quality of life and are the primary cause of age-related retinal diseases among adults. There is a pressing need for innovative topical approaches to treat posterior eye disorders, as current methods often rely on invasive procedures with inherent risks. Limited success was attained in the realm of topical ophthalmic delivery through non-invasive means. Additionally, there exists a dearth of literature that delves into the potential of this approach for drug delivery and theranostic purposes, or that offers comprehensive design strategies for nanocarrier developers to surmount the significant physiological ocular barriers. This review offers a thorough and up-to-date state-of-the-art overview of 40 studies on therapeutic loaded nanocarriers and theranostic devices that, to the best of our knowledge, represent all successful works that reached posterior eye segments through a topical non-invasive administration. Most importantly, based on the successful literature studies, this review provides a comprehensive summary of the potential design strategies that can be implemented during nanocarrier development to overcome each ocular barrier.

Recent advances in nanocrystal-based technologies applied for ocular drug delivery

INTRODUCTION

The intricate physiological barriers of the eye and the limited volume of eye drops impede efficient delivery of poorly water-soluble drugs. In the last decade, nanocrystals have emerged as versatile drug delivery systems in various administration routes from bench to bedside. The unique superiorities of nanocrystals, mainly embodied in high drug-loading capacity, good mucosal adhesion and penetration, and greatly improved drug solubility, reveal a promising prospect for ocular delivery of poorly water-soluble drugs.

AREAS COVERED

This article focuses on the ophthalmic nanocrystal technologies and products that are in the literature, clinical trials, and even on the market. The recent research progress in the preparation, ocular application, and absorption of nanocrystals are highlighted, and the pros and cons of nanocrystals in overcoming the physiological barriers of the eye are also summarized.

EXPERT OPINION

Nanocrystals have demonstrated success as glucocorticoid eye drops in the treatment of anterior segment diseases. However, the thermodynamic stability of nanocrystals remains the major challenge in product development. New technologies for efficiently optimizing stabilizers and sterilization processes are still expected. Strategies to confer more diverse functions via surface modification are also worth exploration to improve the potential of nanocrystals in delivering poorly water-soluble drugs to posterior segment of the eye.

A comparison between the effects of two liposome-encapsulated bevacizumab formulations on ocular neovascularization inhibition

Bevacizumab (BVZ), an anti-VEGF antibody, has demonstrated reliable outcomes in the treatment of irritating ocular neovascularization. Frequent intravitreal injections are necessitated due to rapid clearance and short local accessibility. We recruited liposome as a highly prevailing drug delivery system to enhance drug availability. Two liposome formulations were characterized and their in vitro stability was analyzed. The toxicity of the formulations on some ocular cell lines was also evaluated. In addition, the anti-angiogenic effects of formulations were examined. Drug permeation was measured across ARPE-19 and HCE cell lines as in vitro cellular barrier models. Results revealed that NLP-DOPE-BVZ acquired high stability at 4 °C, 24 °C, and 37 °C for 45 days. It also showed more capacity to entrap BVZ in NLP-DOPE-BVZ (DEE% 69.1 ± 1.4 and DLE% 55.66 ± 1.15) as compared to NLP-BVZ (DEE% 43.57 ± 14.64, and DLE% 37.72 ± 12.01). Although both formulations inhibited the migration and proliferation of HUVECs, NLP-DOPE-BVZ was more effective at inhibiting angiogenesis. Furthermore, NLP-DOPE-BVZ better crossed our established barrier cellular models. Based on the findings, the inclusion of DOPE in NLPs has significantly enhanced the features of drug carriers. This makes them a potential candidate for treating ocular neovascularization and other related ailments.

Age-Related Macular Degeneration - Therapies and Their Delivery

Age-related macular degeneration (ARMD) is a degenerative ocular disease that is the most important cause of irreversible vision loss in old-aged people in developed countries. Around fifty percent of vision impairments in developed countries are due to ARMD. It is a multifaceted disease that is associated with both genetic and environmental risk factors. The most important treatments option for ARMD includes laser photocoagulation, photodynamic therapy (PDT), Anti-VEGF Injections, and combination therapies. In this review, we also propose that topical ocular drug delivery with nanocarriers has more attention for the treatment of ARMD. The nanocarriers were specially designed for enhanced corneal residential time, prolonged drug release and action, and minimizing the frequency of administrations. Different types of nanocarriers were developed for the topical ocular delivery system, such as nanomicelles, nanoemulsions, nanosuspensions, liposomes, and polymeric nanoparticles. These topical ocular nanocarriers were administered topically, and they can fix the hydrophobic substances, increase solubility and improve the bioavailability of an administered drug. Hence the topical ocular delivery systems with nanocarriers provide a safe and effective therapeutic strategy and promising tool for the treatment of posterior segment ocular diseases ARMD.

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.

Discovery and Potential Utility of a Novel Non-Invasive Ocular Delivery Platform

To this day, the use of oily eye drops and non-invasive retinal delivery remain a major challenge. Oily eye drops usually cause ocular irritation and interfere with the normal functioning of the eye, while ocular injections for retinal drug delivery cause significant adverse effects and a high burden on the healthcare system. Here, the authors report a novel topical non-invasive ocular delivery platform (NIODP) through the periorbital skin for high-efficiency anterior and posterior ocular delivery in a non-human primate model (NHP). A single dose of about 7 mg JV-MD2 (omega 3 DHA) was delivered via the NIODP and reached the retina at a Cmax of 111 µg/g and the cornea at a Cmax of 66 µg/g. The NIODP also delivered JV-DE1, an anti-inflammatory agent in development for dry eye diseases, as efficiently as eye drops did to the anterior segments of the NHP. The topical NIODP seems to transport drug candidates through the corneal pathway to the anterior and via the conjunctiva/sclera pathway to the posterior segments of the eye. The novel NIODP method has the potential to reshape the landscape of ocular drug delivery. This is especially the case for oily eye drops and retinal delivery, where the success of the treatment lies in the ocular tolerability and bioavailability of drugs in the target tissue.

Biomaterial Drug Delivery Systems for Prominent Ocular Diseases

Ocular diseases, such as age-related macular degeneration (AMD) and glaucoma, have had a profound impact on millions of patients. In the past couple of decades, these diseases have been treated using conventional techniques but have also presented certain challenges and limitations that affect patient experience and outcomes. To address this, biomaterials have been used for ocular drug delivery, and a wide range of systems have been developed. This review will discuss some of the major classes and examples of biomaterials used for the treatment of prominent ocular diseases, including ocular implants (biodegradable and non-biodegradable), nanocarriers (hydrogels, liposomes, nanomicelles, DNA-inspired nanoparticles, and dendrimers), microneedles, and drug-loaded contact lenses. We will also discuss the advantages of these biomaterials over conventional approaches with support from the results of clinical trials that demonstrate their efficacy.

Nanoparticles Enhance Solubility and Neuroprotective Effects of Resveratrol in Demyelinating Disease

Resveratrol is a natural polyphenol which may be useful for treating neurodegenerative diseases such as multiple sclerosis (MS). To date, current immunomodulatory treatments for MS aim to reduce inflammation with limited effects on the neurodegenerative component of this disease. The purpose of the current study is to develop a novel nanoparticle formulation of resveratrol to increase its solubility, and to assess its ability to prevent optic nerve and spinal cord degeneration in an experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Resveratrol nanoparticles (RNs) were made using a thin rehydration technique. EAE mice received a daily oral administration of vehicle, RNs or unconjugated resveratrol for one month. They were assessed daily for clinical signs of paralysis and weekly for their visual acuity with optokinetic responses (OKR). After one month, their spinal cords and optic nerves were stained for inflammation and demyelination and retinal ganglion cells immunostained for Brn3a. RNs were stable for three months. The administration of RNs did not have any effect on clinical manifestation of EAE and did not preserve OKR scores but reduced the intensity of the disease. It did not reduce inflammation and demyelination in the spinal cord and the optic nerve. However, RNs were able to decrease RGC loss compared to the vehicle. Results demonstrate that resveratrol is neuroprotective by reducing RGC loss. Interestingly, neuroprotective effects and decreased disease severity occurred without reduction of inflammation or demyelination, suggesting this therapy may fill an unmet need to limit the neurodegenerative component of MS.

Ocular therapies with biomacromolecules: From local injection to eyedrop and emerging noninvasive delivery strategies

The last two decades have witnessed a continuously increasing number of biomacromolecules approved for the treatment of ocular diseases. The eye possesses multiple protective mechanisms to resist the invasion of exogenous substances, but meanwhile these physiological defense systems also act as strong barriers, impeding absorption of most biomacromolecules into the eye. As a result, local injections play predominant roles for posterior ocular delivery of biomacromolecules in clinical practice. To achieve safe and convenient application of biomacromolecules, alternative strategies to realize noninvasive intraocular delivery are necessary. Various nanocarriers, novel penetration enhancers and physical strategies have been explored to facilitate delivery of biomacromolecules to both anterior and posterior ocular segments but still suffered difficulties in clinical translation. This review compares the anatomical and physiological characteristics of the eyes from those frequently adopted experimental species and profiles the well-established animal models of ocular diseases. We also summarize the ophthalmic biomacromolecules launched on the market and put emphasis on emerging noninvasive intraocular delivery strategies of peptides, proteins and genes.

Ocular permeability, intraocular biodistribution of lipid nanocapsule formulation intended for retinal drug delivery

Recently, cGMP analogues have been investigated for the treatment of inherited retinal degenerations (IRD) using intravitreal injections. However, higher vitreous elimination rates limit the possibility to treat the retina with small molecule drugs. Here, we investigated the potential of lipid nanocapsules (LNCs) as vehicles to reduce clearance and prolong the delivery of cGMP analogue, CN03 to the retinal photoreceptors. Initially LNCs were investigated for both topical/periocular and intravitreal administration routes. While LNC-mediated drug permeation through the cornea proved to be too low for clinical applications, intravitreal application showed significant promise. Intravitreally administered LNCs containing fluorescent tracer in ex vivo porcine eyes showed complete intravitreal dispersal within 24 h. Ocular bio-distribution on histological sections showed that around 10 % of the LNCs had reached the retina, and 40 % accumulated in the ciliary body. For comparison, we used fluorescently labeled liposomes and these showed a different intraocular distribution with 48 % accumulated in the retina, and almost none were in the ciliary body. LNCs were then tested in retinal explants prepared from wild-type (WT) and rd1 mouse. In WT retina LNCs showed no significant toxic effects up to a concentration of 5 mg/mL. In rd1 retina, the LNC/CN03 formulation protected rd1 photoreceptors with similar efficacy to that of free CN03, demonstrating the usefulness of LNC/CN03 formulation in the treatment of IRD. Overall, our results indicate the suitability of LNCs for intraocular administration and drug delivery to both the retina and the ciliary body.

Polymer- and lipid-based nanocarriers for ocular drug delivery: Current status and future perspectives

Ocular diseases seriously affect patients' vision and life quality, with a global morbidity of over 43 million blindness. However, efficient drug delivery to treat ocular diseases, particularly intraocular disorders, remains a huge challenge due to multiple ocular barriers that significantly affect the ultimate therapeutic efficacy of drugs. Recent advances in nanocarrier technology offer a promising opportunity to overcome these barriers by providing enhanced penetration, increased retention, improved solubility, reduced toxicity, prolonged release, and targeted delivery of the loaded drug to the eyes. This review primarily provides an overview of the progress and contemporary applications of nanocarriers, mainly polymer- and lipid-based nanocarriers, in treating various eye diseases, highlighting their value in achieving efficient ocular drug delivery. Additionally, the review covers the ocular barriers and administration routes, as well as the prospective future developments and challenges in the field of nanocarriers for treating ocular diseases.

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.

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.

Annexins as potential targets in ocular diseases

Annexins (AnxAs) are Ca2+/phospholipid-binding proteins extensively studied and generally involved in several diseases. Although evidence exists regarding the distribuition of AnxAs in the visual system, their exact roles and the exact cell types of the eye where these proteins are expressed are not well-understood. AnxAs have pro-resolving roles in infectious, autoimmune, degenerative, fibrotic and angiogenic conditions, making them an important target in ocular tissue homeostasis. This review summarizes the current knowledge on the distribution and function of AnxA1-8 isoforms under normal and pathological conditions in the visual system, as well as perspectives for ophthalmologic treatments, including the potential use of the AnxA1 recombinant and/or its mimetic peptide Ac2-26.

Decorating hexahistidine-metal assemblies with tyrosine enhances the ability of proteins to pass through corneal biobarriers

In recent decades, the use of protein drugs has increased dramatically for almost every clinical indication, including autoimmunity and cancer infection, given their high specificity and limited side effects. However, their easy deactivation by the surrounding microenvironment and limited ability to pass through biological barriers pose large challenges to the use of these agents for therapeutic effects; these deficits could be greatly improved by nanodelivery using platforms with suitable physicochemical properties. Here, to assess the effect of the hydrophilicity of nanoparticles on their ability to penetrate biological barriers, the hydrophobic amino acid tyrosine (Y) was decorated onto hexahistidine peptide, and two nanosized YHmA and HmA particles were generated, in which Avastin (Ava, a protein drug) was encapsulated by a coassembly strategy. In vitro and in vivo tests demonstrated that these nanoparticles effectively retained the bioactivity of Ava and protected Ava from proteinase K hydrolysis. Importantly, YHmA displayed a considerably higher affinity to the ocular surface than HmA, and YHmA also exhibited the ability to transfer proteins across the barriers of the anterior segment, which greatly improved the bioavailability of the encapsulated Ava and produced surprisingly good therapeutic outcomes in a model of corneal neovascularization. STATEMENT OF SIGNIFICANCE: Improving the ability to penetrate tissue barriers and averting inactivation caused by surrounding environments, are the keys to broaden the application of protein drugs. By decorating hydrophobic amino acid, tyrosine (Y), on hexahistidine peptide, YHmA encapsulated protein drug Ava with high efficiency by co-assembly strategy. YHmA displayed promising ability to maintain bioactivity of Ava during encapsulation and delivery, and protected Ava from proteinase K hydrolysis. Importantly, YHmA transferred Ava across the corneal epithelial barrier and greatly improved its bioavailability, producing surprisingly good therapeutic outcomes in a model of corneal neovascularization. Our results contributed to not only the strategy to overcome shortcomings of protein drugs, but also suggestion on hydrophilicity as a nonnegligible factor in nanodrug penetration through biobarriers.

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.

Topical Nanoemulsion of an Runt-related Transcription Factor 1 Inhibitor for the Treatment of Pathologic Ocular Angiogenesis

Purpose

To test the efficacy of runt-related transcription factor 1 (RUNX1) inhibition with topical nanoemulsion containing Ro5-3335 (eNano-Ro5) in experimental ocular neovascularization.

Design

Preclinical experimental study.

Participants

In vitro primary culture human retinal endothelial cell (HREC) culture. C57BL/6J 6- to 10-week-old male and female mice.

Methods

We evaluated the effect of eNano-Ro5 in cell proliferation, cell toxicity, and migration of HRECs. We used an alkali burn model of corneal neovascularization and a laser-induced model of choroidal neovascularization to test in vivo efficacy of eNano-Ro5 in pathologic angiogenesis in mice. We used mass spectrometry to measure penetration of Ro5-3335 released from the nanoemulsion in ocular tissues.

Main Outcome Measures

Neovascular area.

Results

RUNX1 inhibition reduced cell proliferation and migration in vitro. Mass spectrometry analysis revealed detectable levels of the active RUNX1 small-molecule inhibitor Ro5-3335 in the anterior and posterior segment of the mice eyes. Topical treatment with eNano-Ro5 significantly reduced corneal neovascularization and improved corneal wound healing after alkali burn. Choroidal neovascularization lesion size and leakage were significantly reduced after treatment with topical eNano-Ro5.

Conclusions

Topical treatment with eNano-Ro5 is an effective and viable platform to deliver a small-molecule RUNX1 inhibitor. This route of administration offers advantages that could improve the management and outcomes of these sight-threatening conditions. Topical noninvasive delivery of RUNX1 inhibitor could be beneficial for many patients with pathologic ocular neovascularization.

Non-Viral Delivery of CRISPR/Cas Cargo to the Retina Using Nanoparticles: Current Possibilities, Challenges, and Limitations

The discovery of the CRISPR/Cas system and its development into a powerful genome engineering tool have revolutionized the field of molecular biology and generated excitement for its potential to treat a wide range of human diseases. As a gene therapy target, the retina offers many advantages over other tissues because of its surgical accessibility and relative immunity privilege due to its blood–retinal barrier. These features explain the large advances made in ocular gene therapy over the past decade, including the first in vivo clinical trial using CRISPR gene-editing reagents. Although viral vector-mediated therapeutic approaches have been successful, they have several shortcomings, including packaging constraints, pre-existing anti-capsid immunity and vector-induced immunogenicity, therapeutic potency and persistence, and potential genotoxicity. The use of nanomaterials in the delivery of therapeutic agents has revolutionized the way genetic materials are delivered to cells, tissues, and organs, and presents an appealing alternative to bypass the limitations of viral delivery systems. In this review, we explore the potential use of non-viral vectors as tools for gene therapy, exploring the latest advancements in nanotechnology in medicine and focusing on the nanoparticle-mediated delivery of CRIPSR genetic cargo to the retina.

Antiangiogenic Nanomicelles for the Topical Delivery of Aflibercept to Treat Retinal Neovascular Disease

The traditional intravitreal injection delivery of antivascular endothelial growth factor (anti-VEGF) to the posterior segment of the eye for treatment of retinal diseases is invasive and associated with sight-threatening complications. To avoid such complications, there has been significant interest in developing polymers for topical drug delivery to the retina. This study reports a nanomicelle drug delivery system made of a copolymer EPC (nEPCs), which is capable of delivering aflibercept to the posterior segment topically through corneal-scleral routes. EPC is composed of poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and polycaprolactone (PCL) segments. In this study, aflibercept-loaded nEPCs (nEPCs + A) are capable of penetrating the cornea in ex vivo porcine eye models and deliver a clinically significant amount of aflibercept to the retina in laser-induced choroidal neovascularization (CNV) murine models, causing CNV regression. nEPCs + A also demonstrate biocompatibility in vitro and in vivo. Interestingly, this study also suggests that nEPCs have intrinsic antiangiogenic properties. The ability to deliver anti-VEGF drugs and the intrinsic antiangiogenic properties of nEPCs may result in synergistic effects, which can be harnessed for effective therapeutics. nEPCs may be a promising topical anti-VEGF delivery platform for the treatment of retinal diseases.

One Week Sustained In Vivo Therapeutic Release and Safety of Novel Extended-Wear Silicone Hydrogel Contact Lenses

Since the seminal work of Wichterle in 1965 describing the first soft contact lenses and their potential for ocular drug delivery, the field has yet to realize his vision. Maintaining all lens commercial properties combined with a mechanism for controlled drug release of therapeutically relevant concentrations for duration of wear is a major challenge. Here, successful in vivo week-long sustained release of a small molecular weight therapeutic in rabbits from extended-wear silicone hydrogel contact lenses meeting all commercial specifications by utilizing a novel macromolecular memory strategy is reported for the first time. Lens-treated eyes show a continuous, therapeutically relevant bromfenac tear concentration of 256.4 ± 23.1 µg mL^-1 for 8 days. Bromday (bromfenac ophthalmic solution, 0.09%, Bausch+Lomb) topical drops exhibit a quick peak concentration of 269.3 ± 85.7 µg mL^-1 and 100 min duration. Bioavailability (AUC_0-8days ) and mean residence time of lenses are 26 and 155 times higher than drops, respectively. Lenses are safe, well tolerated, and no corneal histological differences are observed. This work highlights the enormous potential of drug releasing lenses as a platform strategy, and offers a new dropless clinical strategy for post-cataract, uveitis, post-LASIK, and corneal abrasion treatment.

Aqueous eye drops containing drug/cyclodextrin nanoparticles deliver therapeutic drug concentrations to both anterior and posterior segment

Using topical application to deliver therapeutic concentrations of drugs to the posterior segment of the eye remains very challenging. As a result, posterior segment diseases are usually treated by intravitreal injection or implant. While topical treatments are commonly used for anterior segment conditions, they sometimes require frequent applications. Eye drop formulations based on γ-cyclodextrin (γCD)-based nanoparticle aggregates were developed, which in animal models and clinical studies deliver therapeutic concentrations of drugs (dorzolamide and dexamethasone) to both anterior and posterior segments of the eye. An early study in humans showed dorzolamide/γCD eye drops could achieve comparable intraocular pressure decreases to commercial dorzolamide eye drops, but with less frequent application. Pilot studies with dexamethasone/γCD eye drops suggested that they could be effective in a range of conditions, including diabetic macular oedema, cystoid macular oedema and vitritis secondary to uveitis, postcataract surgery inflammation and postoperative treatment in trabeculectomy. Phase II studies with similar dexamethasone/γCD nanoparticle eye drops in diabetic macular oedema and postcataract surgery inflammation have recently been completed. This technology has the potential to be used with other classes of drug molecules and to replace or complement invasive treatments, providing safer, non-invasive therapies, particularly for posterior segment conditions, that can be self-administered as eye drops by patients.

Topical Drug Delivery to the Posterior Segment of the Eye

Topical drug delivery to the posterior segment of the eye is a very complex challenge. However, topical delivery is highly desired, to achieve an easy-to-use treatment option for retinal diseases. In this review, we focus on the drug characteristics that are relevant to succeed in this challenge. An overview on the ocular barriers that need to be overcome and some relevant animal models to study ocular pharmacokinetics are given. Furthermore, a summary of substances that were able to reach the posterior segment after eye drop application is provided, as well as an outline of investigated delivery systems to improve ocular drug delivery. Some promising results of substances delivered to the retina suggest that topical treatment of retinal diseases might be possible in the future, which warrants further research.

Topical drug delivery to the retina: obstacles and routes to success

INTRODUCTION

Retinal diseases are one of the main reasons for vision loss where all available drug treatments are based on invasive drug administration such as intravitreal injections. Despite huge efforts and some promising results in animal models, almost all delivery technologies tested have failed in human trials. There are however examples of clinically effective topical delivery systems such as fast dissolving aqueous eye drop suspensions.

AREAS COVERED

Six obstacles to topical drug delivery to the eye have been identified and discussed in some details. These obstacles consist of static membrane barriers to drug permeation into the eye, dynamic barriers such as the lacrimal drainage and physiochemical barriers such as low thermodynamic activity. It is explained how and why these obstacles hamper drug permeation and how different technologies, both those that are applied in marketed drug products and those that are under investigation, have addressed these obstacles.

EXPERT OPINION

The reason that most topical drug delivery systems have failed to deliver therapeutic drug concentrations to the retina is that they do not address physiochemical barriers such as the thermodynamic activity of the permeating drug molecules. Topical drug delivery to the retina has only been successful when the static, dynamic, and physiochemical barriers are addressed simultaneously.

Deliver protein across bio-barriers via hexa-histidine metal assemblies for therapy: a case in corneal neovascularization model

Because of their high specificity and low side effects, protein drugs possess a substantial global market. However, the low bioavailability of protein is still a major obstacle to their expanded applications, which is expected to be answered with proper protein formulations. Taking corneal neovascularization (CNV) as an example, we demonstrated a co-assembled system of hexa-histidine and Ava (Avastin) with metal ions (HmA@Ava) could cross the cornea, the most important bio-barrier during the treatment of most diseases of the anterior segment in clinics. We found that the nanosized HmA@Ava efficiently encapsulated Ava with impressive loading capacity without destroying the bioactivity of Ava and assisted Ava penetration through the corneal barriers to effectively inhibit CNV development in an alkali burn rat model with sustained and pH-dependent Ava release. Our results suggested that the co-assembled strategy of protein and HmA is a proper formulation to protein drugs, with promising penetration ability to deliver protein across bio-barriers, which could open a path for topical administration of protein drugs for treatment of various ocular diseases and hold enormous potential for delivery of therapeutic proteins not only for ocular diseases but also for other diseases that require protein treatment.

•

HmA@Ava can bring protein drug, Ava, across over the primary bio-barrier of the anterior segment ​and efficiently treat CNV.

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HmA@Ava was nanoparticles, with impressive loading capacity without destroying bioactivity of Ava ​and strong pH-dependent release.

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HmA can open a path for the treatment of eye diseases and hold huge potential to protein drugs to other diseases.

Novel Postoperative Dropless Protocol for Micro-Incision Vitrectomy Surgery

BACKGROUND AND OBJECTIVE

To evaluate the outcomes of a novel postoperative dropless protocol for 25-gauge and 27-gauge micro-incision vitrectomy surgery (MIVS).

PATIENTS AND METHODS

The institutional review board approved a single-center, retrospective study. A total of 493 surgeries were identified, and 451 cases from 369 patients met eligibility criteria. Instead of pre- or postoperative drops, patients were given a novel postoperative dropless protocol consisting of subconjunctival injections of a 1:1 cefazolin:dexamethasone mix at each sclerotomy and intravitreally, and injection of posterior sub-Tenon's Kenalog. Primary outcome measure was cases of postoperative endophthalmitis.

RESULTS

There was one presumed case of endophthalmitis. Anterior chamber paracentesis sample was negative for culture and Gram stain. For all patients, mean logMAR best-corrected visual acuity improved from 0.65 (±0.69) to 0.57 (±0.61) postoperatively (P = 0.004). Mean intraocular pressure increased from 14.5 (±4.3) to 15.5 (±4.8) postoperatively (P < 0.001). Mean follow-up was 96 days.

CONCLUSION

This novel postoperative dropless protocol could potentially be a convenient alternative to topical eye drops for patients undergoing MIVS, but further study is required to establish its safety. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:587-592.].

Diabetic eye: associated diseases, drugs in clinic, and role of self-assembled carriers in topical treatment

Introduction: Diabetes is a pandemic disease that causes relevant ocular pathologies. Diabetic retinopathy, macular edema, cataracts, glaucoma, or keratopathy strongly impact the quality of life of the patients. In addition to glycemic control, intense research is devoted to finding more efficient ocular drugs and improved delivery systems that can overcome eye barriers. Areas covered: The aim of this review is to revisit first the role of diabetes in the development of chronic eye diseases. Then, commercially available drugs and new candidates in clinical trials are tackled together with the pros and cons of their administration routes. Subsequent sections deal with self-assembled drug carriers suitable for eye instillation combining patient-friendly administration with high ocular bioavailability. Performance of topically administered polymeric micelles, liposomes, and niosomes for the management of diabetic eye diseases is analyzed in the light of ex vivo and in vivo results and outcomes of clinical trials. Expert opinion: Self-assembled carriers are being shown useful for efficient delivery of not only a variety of small drugs but also macromolecules (e.g. antibodies) and genes. Successful design of drug carriers may offer alternatives to intraocular injections and improve the treatment of both anterior and posterior segments diabetic eye diseases.

Organic Nanocarriers for Bevacizumab Delivery: An Overview of Development, Characterization and Applications

Bevacizumab (BCZ) is a recombinant humanized monoclonal antibody against the vascular endothelial growth factor, which is involved in the angiogenesis process. Pathologic angiogenesis is observed in several diseases including ophthalmic disorders and cancer. The multiple administrations of BCZ can cause adverse effects. In this way, the development of controlled release systems for BCZ delivery can promote the modification of drug pharmacokinetics and, consequently, decrease the dose, toxicity, and cost due to improved efficacy. This review highlights BCZ formulated in organic nanoparticles providing an overview of the physicochemical characterization and in vitro and in vivo biological evaluations. Moreover, the main advantages and limitations of the different approaches are discussed. Despite difficulties in working with antibodies, those nanocarriers provided advantages in BCZ protection against degradation guaranteeing bioactivity maintenance.

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

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

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.

Multifunctional nanocomposite eye drops of cyclodextrin complex@layered double hydroxides for relay drug delivery to the posterior segment of the eye

Topical drug delivery system to the posterior segment of the eye is facing many challenges, such as rapid drug elimination, low permeability, and low concentration at the targeted sites. To overcome these challenges, Multifunctional nanocomposite eye drops of dexamethasone-carboxymethyl-β-cyclodextrin@layered double hydroxides-glycylsarcosine (DEX-CM-β-CD@LDH-GS) were developed for relay drug delivery. Herein, our studies demonstrated that DEX-CM-β-CD@LDH-GS could penetrate through human conjunctival epithelial cells with an intact structure and exhibited integrity in the sclera of rabbits' eyes with in vivo fluorescence resonance energy transfer imaging. Consequently, tissue distribution indicated that DEX-CM-β-CD@LDH-GS nanocomposite eye drops could maintain the effective therapeutic concentration of DEX in choroid-retina within 3 h. As a relay drug delivery system, drug-CD@LDH nanocomposites offer an efficient strategy for drug delivery from ocular surface to the posterior segment.

Lipid-Based Nanocarriers as Topical Drug Delivery Systems for Intraocular Diseases

Effective drug delivery to intraocular tissues remains a great challenge due to complex anatomical and physiological barriers that selectively limit the entry of drugs into the eye. To overcome these challenges, frequent topical application and regular intravitreal injections are currently used to achieve the desired drug concentrations into the eye. However, the repetitive installation or recurrent injections may result in several side effects. Recent advancements in the field of nanoparticle-based drug delivery have demonstrated promising results for topical ophthalmic nanotherapies in the treatment of intraocular diseases. Studies have revealed that nanocarriers enhance the intraocular half-life and bioavailability of several therapies including proteins, peptides and genetic material. Amongst the array of nanoparticles available nowadays, lipid-based nanosystems have shown an increased efficiency and feasibility in topical formulations, making them an important target for constant and thorough research in both preclinical and clinical practice. In this review, we will cover the promising lipid-based nanocarriers used in topical ophthalmic formulations for intraocular drug delivery.

Nanotechnology: revolutionizing the delivery of drugs to treat age-related macular degeneration

Introduction: Age-related macular degeneration (AMD) is a progressive retinal disease that degrades the eye's ability to grasp visual acuity. The antivascular endothelial growth factor (VEGF) therapies have made significant strides in improving the quality of life, and there is a continued opportunity to improve delivery, outcomes, and patient convenience and compliance. The treatments available could gain better clinical outcome from novel therapeutics through nanotechnology application.Areas covered: This review summarizes AMD biology and the pathophysiology of the disease along with the successes and limitations of available therapies. It further discusses the promising nanotechnology modalities that could become the cornerstone of future AMD research for improving delivery and reducing frequency of administration thus, enabling development of novel therapeutics.Expert opinion: The robust translation from preclinical work to clinical outcome for AMD remains an unmet need. Continuing to investigate in deeper understanding of biology and advancing high-quality targets into the clinic in combination with the application of advanced nanotechnology to design patient-centric offerings for both dry and wet AMD is needed. Because of the lack of regulatory precedence, and challenging manufacturing and supply chain need, the future of nano-enabled technologies is challenging but presents exciting treatment options for AMD.

Emerging innovations in nano-enabled therapy against age-related macular degeneration: A paradigm shift

Age-related macular degeneration (AMD), a degenerative eye disease, is the major cause of irreversible loss of vision among individuals aged 50 and older. Both genetic and environmental factors are responsible for the progressive damage to central vision. It is a multifactorial retinal disease with features such as drusen, hypopigmentation and/or hyperpigmentation of the retinal pigment epithelium, and even choroidal neovascularization in certain patients. AMD is of two major forms: exudative (wet) and atrophic (dry) with changes affecting the macula leading to impaired vision. Although the retina remains an accessible portion for delivering drugs, there are no current options to cure or treat AMD. The existing expensive therapeutics are unable to treat the underlying pathology but display several side effects. However, recent innovations in nanotherapeutics provide an optimal alternative of drug delivery to treat the neovascular condition. These new-age technologies in the nanometer scale would enhance bioactivity and improve the bioavailability of drugs at the site of action to treat AMD. The nanomedicine also provides sustained release of the drug with prolonged retention after penetrating across the ocular tissues. In this review, the insights into the cellular and molecular mechanisms associated with the pathophysiology of AMD are provided. It also serves to review the current progress in nanoparticle-based drug delivery systems that offer feasible treatments in AMD.

Safety and Tolerability of Topical Ophthalmic Triamcinolone Acetonide-Loaded Liposomes Formulation and Evaluation of Its Biologic Activity in Patients with Diabetic Macular Edema

Intravitreal injections (IVTs) of corticosteroids as triamcinolone acetonide (TA) are frequently used for the treatment of many vitreous and retinal disorders. However, IVTs are related to severe ocular complications. Lately, a topical ophthalmic TA-loaded liposomes formulation (TALF) was designed to transport TA into the posterior segment of the eye when instilled on the ocular surface. To evaluate the safety, tolerability, and biological activity of TALF, an animal study and a phase I clinical assay were performed. Moreover, four patients with diabetic macular edema (DME) were treated with TALF in order to explore the biological activity of the formulation. No inflammation, lens opacity, swelling, or increase in intraocular pressure were recorded after the instillation of TALF in any of the animal or clinical studies. Mainly, mild and transient adverse events such as dry eye and burning were reported. TALF significantly improves visual acuity and diminishes central foveal thickness in patients with DME. The current data demonstrate the safety, tolerability, and biological activity of TALF. It seems that TALF can be used topically to treat vitreous and retinal diseases that respond to TA such as DME, avoiding the use of corticosteroid IVTs and their associated hazards.

Smart nano-micro platforms for ophthalmological applications: The state-of-the-art and future perspectives

Smart nano-micro platforms have been extensively applied for diverse biomedical applications, mostly focusing on cancer therapy. In comparison with conventional nanotechnology, the smart nano-micro matrix can exhibit specific response to exogenous or endogenous triggers, and thus can achieve multiple functions e.g. site-specific drug delivery, bio-imaging and detection of bio-molecules. These intriguing techniques have expanded into ophthalmology in recent years, yet few works have been summarized in this field. In this work, we provide the state-of-the-art of diverse nano-micro platforms based on both the conventional materials (e.g. natural or synthetic polymers, lipid nanomaterials, metal and metal oxide nanoparticles) and emerging nanomaterials (e.g. up-conversion nanoparticles, quantum dots and carbon materials) in ophthalmology, with some smart nano/micro platformers highlighted. The common ocular diseases studied in the field of nano-micro systems are firstly introduced, and their therapeutic method and the related drawback in clinic treatment are presented. The recent progress of different materials for diverse ocular applications is then demonstrated, with the representative nano- and micro-systems highlighted in detail. At last, an in-depth discussion on the clinical translation challenges faced in this field and the future direction are provided. This review would allow the researchers to design more smart nanomedicines in a more rational manner for specific ophthalmology applications.

Biotechnology and Biomaterial-Based Therapeutic Strategies for Age-Related Macular Degeneration. Part I: Biomaterials-Based Drug Delivery Devices

Age-related Macular Degeneration (AMD) is an up-to-date untreatable chronic neurodegenerative eye disease of multifactorial origin, and the main causes of blindness in over 65 years old people. It is characterized by a slow progression and the presence of a multitude of factors, highlighting those related to diet, genetic heritage and environmental conditions, present throughout each of the stages of the illness. Current therapeutic approaches, mainly consisting of intraocular drug delivery, are only used for symptoms relief and/or to decelerate the progression of the disease. Furthermore, they are overly simplistic and ignore the complexity of the disease and the enormous differences in the symptomatology between patients. Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, the development of biomaterials-based approaches for a personalized and controlled delivery of therapeutic drugs and biomolecules represents the main challenge for the defeat of this neurodegenerative disease. Here we present a critical review of the available and under development AMD therapeutic approaches, from a biomaterials and biotechnological point of view. We highlight benefits and limitations and we forecast forthcoming alternatives based on novel biomaterials and biotechnology methods. In the first part we expose the physiological and clinical aspects of the disease, focusing on the multiple factors that give origin to the disorder and highlighting the contribution of these factors to the triggering of each step of the disease. Then we analyze available and under development biomaterials-based drug-delivery devices (DDD), taking into account the anatomical and functional characteristics of the healthy and ill retinal tissue.

Formulation of nanoliposome-encapsulated bevacizumab (Avastin): Statistical optimization for enhanced drug encapsulation and properties evaluation

Bevacizumab (Avastin®), an anti-vascular endothelial growth factor, is one of the most effective drugs widely used to inhibit ocular angiogenesis. Nanoliposomes were recruited to improve the accessibility of bevacizumab (BVZ) during treatment. To optimize drug entrapment efficiency (DEE %), the effect of some independent variables was evaluated utilizing response surface methodology. The optimized formulation containing BVZ (NLP-BVZ) was characterized, and its safety was assessed. Employingarising retinalpigment epithelial (ARPE) cells, the permeability of the nanoliposome was analyzed. Structural stability and integrity of NLP-BVZ were also estimated with different methods. Optimal condition for the maximum DEE (39.9%) was obtained with cholesterol/DPPC (1,2-Dipalimitoyl-Sn-glycero-3-phosphocholine) (%w/w) 13.64, BVZ/DPPC (%w/w) 83.78 and 9 freeze-thaw cycles. Neutral fabricated NLP-BVZ with an average size of 141.5 ± 45.8 nm showed a smooth spherical structure and released the drug in a slow and sustained fashion. The formulation exhibited no obvious effect against human umbilical vein endothelial cells (HUVECs) and ARPEs. Additionally, the pattern of the circular dichroism (CD) and intrinsic fluorescence spectra confirmed the structural integrity of protein remained conserved after encapsulation. Taken together, the analysis indicated that the process of entrapment into nanoliposome meaningfully made the drug safer, more stable, and, therefore, appropriate for treating ocular disorders.

Evolution of Nanotechnology in Delivering Drugs to Eyes, Skin and Wounds via Topical Route

The topical route is the most preferred one for administering drugs to eyes, skin and wounds for reaching enhanced efficacy and to improve patient compliance. Topical administration of drugs via conventional dosage forms such as solutions, creams and so forth to the eyes is associated with very low bioavailability (less than 5%) and hence, we cannot rely on these for delivering drugs to eyes more efficiently. An intravitreal injection is another popular drug delivery regime but is associated with complications like intravitreal hemorrhage, retinal detachment, endophthalmitis, and cataracts. The skin has a complex structure that serves as numerous physiological barriers to the entry of exogenous substances. Drug localization is an important aspect of some dermal diseases and requires directed delivery of the active substance to the diseased cells, which is challenging with current approaches. Existing therapies used for wound healing are costly, and they involve long-lasting treatments with 70% chance of recurrence of ulcers. Nanotechnology is a novel and highly potential technology for designing formulations that would improve the efficiency of delivering drugs via the topical route. This review involves a discussion about how nanotechnology-driven drug delivery systems have evolved, and their potential in overcoming the natural barriers for delivering drugs to eyes, skin and wounds.

Regulation of the Ocular Cell/Tissue Response by Implantable Biomaterials and Drug Delivery Systems

Therapeutic advancements in the treatment of various ocular diseases is often linked to the development of efficient drug delivery systems (DDSs), which would allow a sustained release while maintaining therapeutic drug levels in the target tissues. In this way, ocular tissue/cell response can be properly modulated and designed in order to produce a therapeutic effect. An ideal ocular DDS should encapsulate and release the appropriate drug concentration to the target tissue (therapeutic but non-toxic level) while preserving drug functionality. Furthermore, a constant release is usually preferred, keeping the initial burst to a minimum. Different materials are used, modified, and combined in order to achieve a sustained drug release in both the anterior and posterior segments of the eye. After giving a picture of the different strategies adopted for ocular drug release, this review article provides an overview of the biomaterials that are used as drug carriers in the eye, including micro- and nanospheres, liposomes, hydrogels, and multi-material implants; the advantages and limitations of these DDSs are discussed in reference to the major ocular applications.

Nanoparticulate Drug Delivery to the Retina

Retinal diseases, such as age-related macular degeneration and diabetic retinopathy, are the leading causes of blindness worldwide. The mainstay of treatment for these blinding diseases remains to be surgery, and the available pharmaceutical therapies on the market are limited, partially owing to various biological barriers in hindering the delivery of therapeutics to the retina. The nanoparticulate drug delivery system confers the capability for delivering therapeutics to the specific ocular targets and, hence, potentially revolutionizes the current treatment landscape of retinal diseases. While the research to date indicates the enormous therapeutics potentials of the nanoparticulate delivery systems, the successful translation of these systems from the bench to bedside is challenging and requires a combined understanding of retinal pathology, physiology of the eye, and particle and formulation designs of nanoparticles. To this end, the review begins with an overview of the most prevalent retinal diseases and related pharmacotherapy. Highlights of the current challenges encountered in ocular drug delivery for each administration route are provided, followed by critical appraisal of various nanoparticulate drug delivery systems for the retinal diseases, including their formulation designs, therapeutic merits, limitations, and future direction. It is believed that a greater understanding of the nano-biointeraction in eyes will lead to the development of more sophisticated drug delivery systems for retinal diseases.

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.

Noble Metals and Soft Bio-Inspired Nanoparticles in Retinal Diseases Treatment: A Perspective

We are witnessing an exponential increase in the use of different nanomaterials in a plethora of biomedical fields. We are all aware of how nanoparticles (NPs) have influenced and revolutionized the way we supply drugs or how to use them as therapeutic agents thanks to their tunable physico-chemical properties. However, there is still a niche of applications where NP have not yet been widely explored. This is the field of ocular delivery and NP-based therapy, which characterizes the topic of the current review. In particular, many efforts are being made to develop nanosystems capable of reaching deeper sections of the eye such as the retina. Particular attention will be given here to noble metal (gold and silver), and to polymeric nanoparticles, systems consisting of lipid bilayers such as liposomes or vesicles based on nonionic surfactant. We will report here the most relevant literature on the use of different types of NPs for an efficient delivery of drugs and bio-macromolecules to the eyes or as active therapeutic tools.