Fostering the unleashing potential of nanocarriers-mediated delivery of ocular therapeutics

Ocular delivery is the most challenging aspect in the field of pharmaceutical research. The major hurdle for the controlled delivery of drugs to the eye includes the physiological static barriers such as the complex layers of the cornea, sclera and retina which restrict the drug from permeating into the anterior and posterior segments of the eye. Recent years have witnessed inventions in the field of conventional and nanocarrier drug delivery which have shown considerable enhancement in delivering small to large molecules across the eye. The dynamic challenges associated with conventional systems include limited drug contact time and inadequate ocular bioavailability resulting from solution drainage, tear turnover, and dilution or lacrimation. To this end, various bioactive-based nanosized carriers including liposomes, ethosomes, niosomes, dendrimer, nanogel, nanofibers, contact lenses, nanoprobes, selenium nanobells, nanosponge, polymeric micelles, silver nanoparticles, and gold nanoparticles among others have been developed to circumvent the limitations associated with the conventional dosage forms. These nanocarriers have been shown to achieve enhanced drug permeation or retention and prolong drug release in the ocular tissue due to their better tissue adherence. The surface charge and the size of nanocarriers (10-1000 nm) are the important key factors to overcome ocular barriers. Various nanocarriers have been shown to deliver active therapeutic molecules including timolol maleate, ampicillin, natamycin, voriconazole, cyclosporine A, dexamethasone, moxifloxacin, and fluconazole among others for the treatment of anterior and posterior eye diseases. Taken together, in a nutshell, this extensive review provides a comprehensive perspective on the numerous facets of ocular drug delivery with a special focus on bioactive nanocarrier-based approaches, including the difficulties and constraints involved in the fabrication of nanocarriers. This also provides the detailed invention, applications, biodistribution and safety-toxicity of nanocarriers-based therapeutcis for the ophthalmic delivery.

Optimization of stereolithography 3D printing of microneedle micro-molds for ocular drug delivery

Microneedles (MN) have emerged as an innovative technology for drug delivery, offering a minimally invasive approach to administer therapeutic agents. Recent applications have included ocular drug delivery, requiring the manufacture of sub-millimeter needle arrays in a reproducible and reliable manner. The development of 3D printing technologies has facilitated the fabrication of MN via mold production, although there is a paucity of information available regarding how the printing parameters may influence crucial issues such as sharpness and penetration efficacy. In this study, we have developed and optimized a 3D-printed MN micro-mold using stereolithography (SLA) 3D printing to prepare a dissolving ocular MN patch. The effects of a range of parameters including aspect ratio, layer thickness, length, mold shape and printing orientation have been examined with regard to both architecture and printing accuracy of the MN micro-mold, while the effects of printing angle on needle fidelity was also examined for a range of basic shapes (conical, pyramidal and triangular pyramidal). Mechanical strength and in vitro penetration of the polymeric (PVP/PVA) MN patch produced from reverse molds fabricated using MN with a range of shapes and height, and aspect ratios were assessed, followed by ex vivo studies of penetration into excised scleral and corneal tissues. The optimization process identified the parameters required to produce MN with the sharpest tips and highest dimensional fidelity, while the ex vivo studies indicated that these optimized systems would penetrate the ocular tissue with minimal applied pressure, thereby allowing ease of patient self-administration.

Can (Natural) deep eutectic systems increase the efficacy of ocular therapeutics?

The eye is one of the most complex organs in the human body, with a unique anatomy and physiology, being divided into anterior and posterior segments. Ocular diseases can occur in both segments, but different diseases affect different segments. Glaucoma and cataracts affect the anterior segment, while macular degeneration and diabetic retinopathy occur in the posterior segment. The easiest approach to treat ocular diseases, especially in the anterior segment, is through the administration of topical eye drops, but this route presents many constraints, namely precorneal dynamic and static ocular barriers. On the other hand, the delivery of drugs to the posterior segment of the eye is far more challenging and is mainly performed by the intravitreal route. However, it can lead to severe complications such as retinal detachment, endophthalmitis, increased intraocular pressure and haemorrhage. The design of new drug delivery systems for the anterior segment is very challenging, but targeting the posterior one is even more difficult and little progress has been made. In this review we will discuss various strategies including the incorporation of additives in the formulations, such as viscosity, permeability, and solubility enhancers, namely based on Deep eutectic systems (DES). Natural deep eutectic systems (NADES) have emerged to solve several problems encountered in pharmaceutical industry, regarding the pharmacokinetic and pharmacodynamic properties of drugs. NADES can contribute to the design of advanced technologies for ocular therapeutics, including hydrogels and nanomaterials. Here in, we revise some applications of (NA)DES in the development of new drug delivery systems that can be translated into the ophthalmology field.

A sterilizable platform based on crosslinked xanthan gum for controlled-release of polymeric micelles: Ocular application for the delivery of neuroprotective compounds to the posterior eye segment

TPGS (D-α-tocopheryl polyethylene glycol 1000 succinate) polymeric micelles show interesting properties for ocular administration thanks to their solubilization capability, nanometric size and tissue penetration ability. However, micelles formulations are generally characterized by low viscosity, poor adhesion and very short retention time at the administration site. Therefore, the idea behind this work is the preparation and characterization of a crosslinked film based on xanthan gum that contains TPGS micelles and is capable of controlling their release. The system was loaded with melatonin and cyclosporin A, neuroprotective compounds to be delivered to the posterior eye segment. Citric acid and heating at different times and temperatures were exploited as crosslinking approach, giving the possibility to tune swelling, micelles release and drug release. The biocompatibility of the platform was confirmed by HET-CAM assay. Ex vivo studies on isolated porcine ocular tissues, conducted using Franz cells and two-photon microscopy, demonstrated the potential of the xanthan gum-based platform and enlightened micelles penetration mechanism. Finally, the sterilization step was approached, and a process to simultaneously crosslink and sterilize the platform was developed.

Enhancing the hypotensive effect of latanoprost by combining synthetic phosphatidylcholine liposomes with hyaluronic acid and osmoprotective agents

The first line of glaucoma treatment focuses on reducing intraocular pressure (IOP) through the prescription of topical prostaglandin analogues, such as latanoprost (LAT). Topical ophthalmic medicines have low bioavailability due to their rapid elimination from the ocular surface. Nanotechnology offers innovative ways of enhancing the ocular bioavailability of antiglaucoma agents while reducing administration frequency. This study aims to combine LAT-loaded synthetic phosphatidylcholine liposomes with hyaluronic acid (0.2% w/v) and the osmoprotectants betaine (0.40% w/v) and leucine (0.90% w/v) (LAT-HA-LIP) to extend the hypotensive effect of LAT while protecting the ocular surface. LAT-HA-LIP was prepared as a mixture of 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine, cholesterol and α-tocopherol acetate. LAT-HA-LIP exhibited high drug-loading capacity (104.52 ± 4.10%), unimodal vesicle sizes (195.14 ± 14.34 nm) and a zeta potential of -13.96 ± 0.78 mV. LAT-HA-LIP was isotonic (284.00 ± 1.41 mOsm L-1), had neutral pH (7.63 ± 0.01) and had suitable surface tension (44.07 ± 2.70 mN m-1) and viscosity (2.69 ± 0.15 mPa s-1) for topical ophthalmic administration. LAT-HA-LIP exhibited optimal in vitro tolerance in human corneal and conjunctival epithelial cells. No signs of ocular alteration or discomfort were observed when LAT-HA-LIP was instilled in albino male New Zealand rabbits. Hypotensive studies revealed that, after a single eye drop, the effect of LAT-HA-LIP lasted 24 h longer than that of a marketed formulation and that relative ocular bioavailability was almost three times higher (p < 0.001). These findings indicate the potential ocular protection and hypotensive effect LAT-HA-LIP offers in glaucoma treatment.

In-situ forming biodegradable implants for sustained Fluocinolone acetonide release to the posterior eye: In-vitro and in-vivo investigations in rabbits

Delivering medication to the posterior segment of the eye presents a significant challenge. Intravitreal injection has emerged as the preferred method for drug delivery to this area. However, current injectable non-biodegradable implants for fluocinolone acetonide (FA) require surgical removal after prolonged drug release, potentially affecting patient compliance. This study aimed to develop an in-situ forming biodegradable implant (ISFBI) optimal formulation containing PLGA504H and PLGA756S (50:50 w/w%) with the additive NMP solvent. The goal was to achieve slow and controlled release of FA over a two-month period with lower burst release, following a single intravitreal injection. Through morphology, rheology, stability and in-vitro release evaluations, the optimal formulation demonstrated low viscosity (0.12-1.25 Pa. s) and sustained release of FA at a rate of 0.36 µg/day from the third day up to two months. Furthermore, histopathology and in-vivo studies were conducted after intravitreal injection of the optimal formulation in rabbits' eye. Pharmacokinetic analysis demonstrated mean residence time (MRT) of 20.02 ± 0.6 days, half-life (t1/2) of 18.80 ± 0.4 days, and clearance (Cl) of 0.29 ± 0.03 ml/h for FA in the vitreous humor, indicating sustained and slow absorption of FA by the targeted retinal tissue from vitrea over the two-month period and eliminating through the anterior section of the eye, as revealed by its presence in the aqueous humor. Additionally, FA exhibited no detection in the blood and no evidence of systemic side effects or damage on the retinal layer and other organs. Based on these findings, it can be concluded that in-situ forming injectable biodegradable PLGA implants can show promise as a long-acting and controlled-release system for intraocular drug delivery.

Next generation therapeutics for retinal neurodegenerative diseases

Neurodegenerative diseases affecting the visual system encompass glaucoma, macular degeneration, retinopathies, and inherited genetic disorders such as retinitis pigmentosa. These ocular pathologies pose a serious burden of visual impairment and blindness worldwide. Current treatment modalities include small molecule drugs, biologics, or gene therapies, most of which are administered topically as eye drops or as injectables. However, the topical route of administration faces challenges in effectively reaching the posterior segment and achieving desired concentrations at the target site, while injections and implants risk severe complications, such as retinal detachment and endophthalmitis. This necessitates the development of innovative therapeutic strategies that can prolong drug release, deliver effective concentrations to the back of the eye with minimal systemic exposure, and improve patient compliance and safety. In this review, we introduce retinal degenerative diseases, followed by a discussion of the existing clinical standard of care. We then delve into detail about drug and gene delivery systems currently in preclinical and clinical development, including formulation and delivery advantages/drawbacks, with a special emphasis on potential for clinical translation.

Selectively coated contact lenses by nanoelectrospray (nES) to fabricate drug-eluting contact lenses for treating ocular diseases

Drug-eluting contact lenses (DECLs) incorporated with poly(lactic-co-glycolic acid) (PLGA) and various model drugs (ketotifen fumarate, bimatoprost and latanoprost) were fabricated using nanoelectrospray (nES) approach. The resulting DECLs demonstrated outstanding optical transmittance within the optical zone, indicating that the employed coating procedure did not compromise visual acuity under the prescribed spraying parameters. In vitro drug release assessments of the model drugs (ketotifen fumarate (KF), bimatoprost (BIM), and latanoprost (LN)) revealed a strong correlation between the model drug's hydrophobicity and the duration of drug release. Changing the drug loading of the more hydrophilic model drugs, BIM and KF, showed no impact on the drug release kinetics of DECLs loaded with BIM and KF. However, for the hydrophobic model drug, LN, the highest LN loading led to the most extended drug release. The conventional steam sterilisation method was found to damage the PLGA coating on the DECLs fabricated by nES. An alternative sterilisation strategy, such as radiation sterilisation may need to be investigated in the future study to minimise potential harm to the coating.

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.

Carboxylated nanofibrillated cellulose empowers moxifloxacin to overcome Staphylococcus aureus biofilm in bacterial keratitis

Bacterial keratitis is one of the vision-threatening ocular diseases that is increasing at an alarming rate due to antimicrobial resistance. One of the primary causes of antimicrobial resistance could be biofilm formation, which alters the mechanism and physiology of the microorganisms. Even a potent drug fails to inhibit biofilm due to the extracellular polysaccharide matrix surrounding the bacteria, inhibiting the permeation of drugs. Therefore, we aimed to develop carboxylated nanocellulose fibers loaded with moxifloxacin (Mox-cNFC) as a novel drug delivery system to treat bacterial corneal infection. Nanocellulose fibers were fabricated using a two-step method involving citric acid hydrolysis followed by TEMPO oxidation to introduce carboxylated groups (1.12 mmol/g). The Mox-cNFC particles showed controlled drug release till 40 h through diffusion. In vitro biofilm inhibition studies showed the particle's ability to disrupt the biofilm matrix and enhance the drug penetration to achieve optimal concentrations that inhibit the persister cells (without increasing minimum inhibitory concentration), thereby reducing the bacterial drug-resistant property. In vivo studies revealed the therapeutic potential of Mox-cNFC to treat Staphylococcus aureus-induced bacterial keratitis with once-a-day treatment, unlike neat moxifloxacin. Mox-cNFC could improve patient compliance by reducing the frequency of instillation and a controlled drug release to prevent toxicity.

Protein Nanoparticles Laden In situ Gel for Topical Ocular Drug Delivery

Topical ocular delivery of drugs is most commonly preferred route by the patient and physician for the treatment of ocular diseases. The topical route is always followed with the disadvantages like tear turnover, nasolacrimal drainage, reduction in precorneal residence time, etc. To overcome these hindrances associated with topical ocular route, a novel drug delivery system is used for targeting the drug at a specific site. In the Novel Drug delivery System, protein-based nanoparticles are an attractive class of nanoparticles designed to deliver the drug at targeted site in slow and sustained release manner. They have a size in the range of 1-100 nm. Protein nanoparticles are leading, particularly for the topical ocular delivery like reduction in intra ocular pressure, providing sustained release and targeted drug delivery at the site of its action. Various methods are used for formulation of protein nanoparticles like desolvation, emulsification, complex coacervation, electrospray techniques. The characterization parameters include particle size, surface morphology, drug loading and entrapment efficiency. Protein nanoparticles can also be loaded in to the in situ gel forming polymers for increasing precorneal residence time of nanoparticles. The characterization parameters of in situ gelling systems are gelling time, rheological properties, gel strength. The review mainly describes the use of various proteins in preparation of protein nanoparticles, methods for preparation of protein nanoparticles, polymers used in in situ gelling system and evaluation as well as characterization parameters of protein nanoparticles, in situ gelling systems & patented information related to protein nanoparticles and in situ gelling system for ocular drug delivery.

Novel nanomicelle butenafine formulation for ocular drug delivery against fungal keratitis: In Vitro and In Vivo study

Fungal keratitis (FK) is a serious infectious corneal disease that leads to blindness. Butenafine (BTF) is an allylamine drug with high antifungal activity, but its poor water solubility and low bioavailability limit its clinical application in ophthalmology. To increase its aqueous solubility and corneal permeability, butenafine was encapsulated in d-ɑ-tocopheryl polyethylene glycol succinate (TPGS) polymeric nanomicelles to improve the bioavailability of the drug for the treatment of FK. Butenafine was successfully fabricated into nanomicelles with a high EE of 96.34 ± 1.65 % and DL of 6.71 ± 0.099 %. The BTF-NM showed an average particle size of 13.12 ± 0.24 nm, a zeta potential of -0.56 ± 0.44 mV and a narrow PDI of 0.12 ± 0.02 with a nearly spherical shape. The characterization results of FTIR, XRD and DSC indicated that BTF was encapsulated in the TPGS nanomicelles. The BTF-NM formulation also showed high storage stability, and the in vitro drug release study showed typical biphasic-release characteristics. In addition, the BTF-NM formulation displayed good cellular tolerance and excellent ocular tolerance in rabbits. Significantly elevated in vitro antifungal activity was also observed in the BTF-NM formulation, and remarkable improvements regarding in vivo corneal permeation were observed compared with the BTF suspension formulation. Finally, the in vivo antifungal activity studies indicated that the BTF-NM formulation had a good therapeutic effect on FK and had similar efficacy to that of commercial natamycin suspension eye drops. These results suggest that the BTF-NM ophthalmic formulation could be a promising ocular drug delivery system for the treatment of FK.

Progress in Ocular Drug Delivery: Challenges and Constraints

The eye has several dynamic and static barriers in place to limit the entry of foreign substances including therapeutics. As such, efficient drug delivery, especially to posterior segment tissues, has been challenging. This chapter describes the anatomical and physiological challenges associated with ocular drug delivery before discussing constraints with regard to formulation parameters. Finally, it gives an overview of advanced drug delivery technologies with a specific focus on recently marketed and late-stage clinical trial products.

A Mini-review on New Developments in Nanocarriers and Polymers for Ophthalmic Drug Delivery Strategies

The eye is an important and vital organ of the human body consisting of two segments - anterior and posterior segments and these segments are associated with many diseases. This review elaborates upon the various eye-related diseases with their medications and carriers used to deliver them. Delivery strategies include drugs encapsulated into liposomes, polymeric micelles of drugs, solid lipid nanoparticles, nanostructured lipid carriers, nano emulsions, and Nanosuspension used to improve penetrating properties, bioavailability, and residence time of the drugs as examples available in the literature. With regard to this, different forms of ocular drug delivery are classified and elaborated. Additionally, the possibility of addressing the physical and chemical complexities of ocular diseases and how they could be overcome with environmentally stable nanoformulations are briefly discussed. Enhanced drug delivery efficiency with various novel pharmaceuticals along with enhanced uptake by different routes/modes of drug administration. Current advancements in drug carrier systems, i.e., nanocarriers, have shown promise for improving the retention time, drug permeation and prolonging the duration of release of the drug in the ocular site. Bio-degradable polymers investigated for the preparation of nanocarriers for the entrapment of drugs and to enhance the efficacy through improved adherence of tissue in the eye, sustained release measures, enhanced bioavailability, lower toxicity, and targeted delivery is applicable. This review covers the introduction of various nanocarriers and polymers for ocular drug delivery with the purpose of enhancing the absorption, retention and bioavailability of medications in the eye.

Design and evaluation of in situ gel eye drops containing nanoparticles of Gemifloxacin Mesylate

Traditional eye drops used for topically administering drugs have poor ocular bioavailability due to the biological barriers of the eye. There is an interest to design and develop novel drug delivery systems that would extend the precorneal residence time, reduce the frequency of administration and decrease dose-related toxicity. This study aimed to prepare Nanoparticles of Gemifloxacin Mesylate and incorporate them into an in situ gel. The nanoparticles were prepared by ionic gelation technique, using 3² factorial design. Sodium tripolyphosphate (STPP) was used to crosslink Chitosan. The optimized formulation of the nanoparticles (GF4) contained 0.15% Gemifloxacin Mesylate, 0.15% Chitosan and 0.20% STPP, producing 71 nm particle size and 81.11% entrapment efficiency. The prepared nanoparticles showed biphasic release, with an initial burst release of 15% in 1.0 hr and a cumulative drug release of 90.53% at the end of 24 hrs. After that, the prepared nanoparticles were incorporated into an in situ gel, using Poloxamer 407, producing a sustained drug release with efficient antimicrobial activity against gram-positive and gram-negative bacteria as confirmed by the cup plate method.

NAD+-associated-hyaluronic acid and poly(L-lysine) polyelectrolyte complexes: An evaluation of their potential for ocular drug delivery

This study details the formation and characterisation of a novel nicotinamide adenine dinucleotide (NAD+)-associated polymeric nanoparticle system. The development of a polyelectrolyte complex (PEC) composed of two natural polyelectrolytes, hyaluronic acid and poly(L-lysine), and an evaluation of its suitability for NAD+ ocular delivery, primarily based on its physicochemical properties and in vitro release profile under physiological ocular flow rates, were of key focus. Following optimisation of formulation method conditions such as complexation pH, mode of addition, and charge ratio, the PEC was successfully formulated under mild formulation conditions via polyelectrolyte complexation. With a size of 235.1 ± 19.0 nm, a PDI value of 0.214 ± 0.140, and a zeta potential value of - 38.0 ± 1.1 mV, the chosen PEC, loaded with 430 µg of NAD+ per mg of PEC, exhibited non-Fickian, sustained release at physiological flowrates of 10.9 ± 0.2 mg of NAD+ over 14 h. PECs containing up to 200 µM of NAD+ did not induce any significant cytotoxic effects on an immortalised human corneal epithelial cell line. Using fluorescent labeling, the NAD+-associated PECs demonstrated retention within the corneal epithelium layer of a porcine model up to 6 h post incubation under physiological conditions. A study of the physicochemical behaviour of the PECs, in terms of size, zeta potential and NAD+ complexation in response to environmental stimuli,highlighted the dynamic nature of the PEC matrix and its dependence on both pH and ionic condition. Considering the successful formation of reproducible NAD+-associated PECs with suitable characteristics for ocular drug delivery via an inexpensive formulation method, they provide a promising platform for NAD+ ocular delivery with a strong potential to improve ocular health.

Experimental and mathematical approaches for drug delivery for the treatment of wet age-related macular degeneration

Several chronic eye diseases affect the posterior segment of the eye. Among them age-related macular degeneration can cause vision loss if left untreated and is one of the leading causes of visual impairment in the world. Most treatments are based on intravitreally injected therapeutics that inhibit the action of vascular endothelial growth factor. However, due to the need for monthly injections, this method is associated with poor patient compliance. To address this problem, numerous drug delivery systems (DDSs) have been developed. This review covers a selection of particulate systems, non-stimuli responsive hydrogels, implants, and composite systems that have been developed in the last few decades. Depending on the type of DDS, polymer material, and preparation method, different mechanical properties and drug release profiles can be achieved. Furthermore, DDS development can be optimized by implementing mathematical modeling of both drug release and pharmacokinetic aspects. Several existing mathematical models for diffusion-controlled, swelling-controlled, and erosion-controlled drug delivery from polymeric systems are summarized. Compartmental and physiologically based models for ocular drug transport and pharmacokinetics that have studied drug concentration profiles after intravitreal delivery or release from a DDS are also reviewed. The coupling of drug release models with ocular pharmacokinetic models can lead to obtaining much more efficient DDSs for the treatment of age-related macular degeneration and other diseases of the posterior segment of the eye.

Contact lens as an emerging platform for ophthalmic drug delivery: A systematic review

The number of people with eye diseases has increased with the use of electronics. However, the bioavailability of eye drops remains low owing to the presence of the ocular barrier and other reasons. Although many drug delivery systems have been developed to overcome these problems, they have certain limitations. In recent years, the development of contact lenses that can deliver drugs for long periods with high bioavailability and without affecting vision has increased the interest in using contact lenses for drug delivery. Hence, a review of the current state of research on drug delivery contact lenses has become crucial. This article reviews the key physical and chemical properties of drug-laden contact lenses, development and classification of contact lenses, and features of the commonly used materials. A review of the methods commonly used in current research to create contact lenses has also been presented. An overview on how drug-laden contact lenses can overcome the problems of high burst and short release duration has been discussed. Overall, the review focuses on drug delivery methods using smart contact lenses, and predicts the future direction of research on contact lenses.

Pyruvate-conjugation of PEGylated liposomes for targeted drug delivery to retinal photoreceptors

Despite several promising candidates, there is a paucity of drug treatments available for patients suffering from retinal diseases. An important reason for this is the lack of suitable delivery systems that can achieve sufficiently high drug uptake in the retina and its photoreceptors. A promising and versatile method for drug delivery to specific cell types involves transporter-targeted liposomes, i.e., liposomes surface-coated with substrates for transporter proteins highly expressed on the target cell. We identified strong lactate transporter (monocarboxylate transporter, MCT) expression on photoreceptors as a potential target for drug delivery vehicles. To evaluate MCT suitability for drug targeting, we used PEG-coated liposomes and conjugated these with different monocarboxylates, including lactate, pyruvate, and cysteine. Monocarboxylate-conjugated and dye-loaded liposomes were tested on both human-derived cell-lines and murine retinal explant cultures. We found that liposomes conjugated with pyruvate consistently displayed higher cell uptake than unconjugated liposomes or liposomes conjugated with lactate or cysteine. Pharmacological inhibition of MCT1 and MCT2 reduced internalization, suggesting an MCT-dependent uptake mechanism. Notably, pyruvate-conjugated liposomes loaded with the drug candidate CN04 reduced photoreceptor cell death in the murine rd1 retinal degeneration model while free drug solutions could not achieve the same therapeutic effect. Our study thus highlights pyruvate-conjugated liposomes as a promising system for drug delivery to retinal photoreceptors, as well as other neuronal cell types displaying high expression of MCT-type proteins.

A Biomimetic Peptide-drug Supramolecular Hydrogel as Eyedrops Enables Controlled Release of Ophthalmic Drugs

The rapid clearance of instilled drugs from the ocular surface due to tear flushing and excretion results in low drug bioavailability, necessitating the development of new drug delivery routes. Here, we generated an antibiotic hydrogel eye drop that can extend the pre-corneal retention of a drug after topical instillation to address the risk of side effects (e.g., irritation and inhibition of enzymes), resulting from frequent and high-dosage administrations of antibiotics used to obtain the desired therapeutic drug concentration. The covalent conjugation of small peptides to antibiotics (e.g., chloramphenicol) first endows the self-assembly ability of peptide-drug conjugate to generate supramolecular hydrogels. Moreover, the further addition of calcium ions, which are also widely present in endogenous tears, tunes the elasticity of supramolecular hydrogels, making them ideal for ocular drug delivery. The in vitro assay revealed that the supramolecular hydrogels exhibited potent inhibitory activities against both gram-negative (e.g., Escherichia coli) and gram-positive (e.g., Staphylococcus aureus) bacteria, whereas they were innocuous toward human corneal epithelial cells. Moreover, the in vivo experiment showed that the supramolecular hydrogels remarkably increased pre-corneal retention without ocular irritation, thereby showing appreciable therapeutic efficacy for treating bacterial keratitis. This work, as a biomimetic design of antibiotic eye drops in the ocular microenvironment, addresses the current issues of ocular drug delivery in the clinic and further provides approaches to improve the bioavailability of drugs, which may eventually open new directions to resolve the difficulty of ocular drug delivery. STATEMENT OF SIGNIFICANCE: Herein, we present a biomimetic design for antibiotic hydrogel eye drops mediated by calcium ions (Ca²⁺) in the ocular microenvironment, which can extend the pre-corneal retention of antibiotics after topical instillation. The mediation of Ca²⁺ which is widely present in endogenous tears, tunes the elasticity of hydrogels, making them ideal for ocular drug delivery. Since increasing the ocular retention of antibiotic eye drops enhances its action and reduces its adverse effects, this work may lead to an approach of peptide-drug-based supramolecular hydrogel for ocular drug delivery in clinics to combat ocular bacterial infections.

A novel approach to achieve semi-sustained drug delivery to the eye through asymmetric loading of soft contact lenses

Soft contact lenses are increasingly being explored as a vehicle for controlled delivery of ophthalmic drugs. However, traditional methods of drug-loading by soaking have limitations such as burst delivery and the release of drugs at the front side of the lens, leading to poor drug efficacy and systemic side effects. This study introduces a new methodology, termed asymmetric drug loading, whereby the ophthalmic drug 'Rebamipide' is attached to and released from the post-lens (=cornea-contacting) surface exclusively. The methodology involves using polymeric microparticles that carry a lipophilic crystalline ophthalmic drug at their surface. These drug-loaded microparticles first transfer the drug to the concave surface of the contact lens, and when worn, the drug is transferred again, now from the lens to the cornea. This is achieved through the diffusion of the drug from one hydrophobic microenvironment (the silicone moieties of the contact lens polymer network) to another hydrophobic microenvironment (the corneal epithelium) over a short pathway. The second drug transfer was observed and studied in experiments using an ex vivo porcine eye model. The results show that the drug amount that was absorbed by the cornea after applying the rebamipide-loaded contact lenses is approximately 3× (10.7 ± 3.1 μg) as much as the amount of rebamipide that gets transferred after the instillation of one eye drop (1% solution (p < 0.001). The new drug-loading method offers a practical and reproducible means of delivering ophthalmic drugs to the cornea through soft contact lenses. The drug payloads achieved are comparable to dosages used during eye drop therapy.

Recent trends and updates on ultradeformable and elastic vesicles in ocular drug delivery

Ocular drug delivery is enigmatic on account of various physiological precorneal barriers that ultimately hinder efficient drug penetration and corneal absorption. Ultradeformable vesicles embody non-ionic surfactants, edge activators and vesicular builders that provide enormous elasticity and deformability. The elastic vesicles can cross the ocular barriers owing to their peculiar squeezability and distorting ability and, thus, establish an infallible shot for ocular delivery. This review provides an overview of the recent advancements and updates of elastic vesicles as effective ocular drug delivery vehicles.

Ocular immunosuppressive microenvironment and novel drug delivery for control of uveitis

Ocular immune privilege is a phenomenon described by Peter Medawar in relation to the indefinite survival of the placement of foreign tissue grafts into the eye. Several mechanisms have been described that contribute to ocular immune privilege, such as a blood-ocular barrier and lack of lymphatics in the eye, the production of immune-suppressing molecules inside the ocular microenvironment, and the induction of systemic regulatory immunity against antigens found in the eye. Because ocular immune privilege is not absolute, failure of it can result in uveitis. Uveitis is a group of inflammatory disorders that can lead to vision loss if not treated properly. The current uveitis treatments involve the use of immunosuppressive and anti-inflammatory medications. Researching mechanisms of ocular immune privilege and the development of novel treatments for uveitis is ongoing. This review discusses mechanisms of ocular immune privilege, followed by an overview of uveitis treatments and ongoing clinical trials.

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.

Comparison of barrier properties of outer blood-retinal barrier models - Human stem cell-based models as a novel tool for ocular drug discovery

The retinal pigment epithelial (RPE) cell monolayer forms the outer blood-retinal barrier and has a crucial role in ocular pharmacokinetics. Although several RPE cell models are available, there have been no systematic comparisons of their barrier properties with respect to drug permeability. We compared the barrier properties of RPE secondary cell lines (ARPE19, and ARPE19mel) and both primary (hfRPE) and stem-cell derived RPE (hESC-RPE) cells by investigating the permeability of nine drugs (aztreonam, ciprofloxacin, dexamethasone, fluconazole, ganciclovir, ketorolac, methotrexate, voriconazole, and quinidine) across cell monolayers. ARPE19, ARPE19mel, and hfRPE cells displayed a narrow P_app value range, with relatively high permeation rates (5.2-26 × 10^-6 cm/s). In contrast, hESC-RPE cells efficiently restricted the drug flux, and displayed even lower P_app values than those reported for bovine RPE-choroid, with the range of 0.4-32 cm^-6/s. Therefore, ARPE19, ARPE19mel, and hfRPE cells failed to form a tight barrier, whereas hESC-RPE cells restricted the drug flux to a similar extent as bovine RPE-choroid. Therefore, hESC-RPE cells are valuable tools in ocular drug discovery.

Ocular barriers as a double-edged sword: preventing and facilitating drug delivery to the retina

In recent decades, the growing of the aging population in the world brings increasingly heavy burden of vision-threatening retinal diseases. One of the biggest challenges in the treatment of retinal diseases is the effective drug delivery to the diseased area. Due to the existence of multiple anatomical and physiological barriers of the eye, commonly used oral drugs or topical eye drops cannot effectively reach the retinal lesions. Innovations in new drug formulations and delivery routes have been continuously applied to improve current drug delivery to the back of the eye. Unique ocular anatomical structures or physiological activities on these ocular barriers, in turn, can facilitate drug delivery to the retina if compatible formulations or delivery routes are properly designed or selected. This paper focuses on key barrier structures of the eye and summarizes advances of corresponding drug delivery means to the retina, including various local drug delivery routes by invasive approaches, as well as systemic eye drug delivery by non-invasive approaches.

Recent advancements in polymeric nanofibers for ophthalmic drug delivery and ophthalmic tissue engineering

Nanofibers due to their unique properties such as high surface-to-volume ratio, porous structure, mechanical strength, flexibility and their resemblance to the extracellular matrix, have been researched extensively in the field of ocular drug delivery and tissue engineering. Further, different modifications considering the formulation and process parameters have been carried out to alter the drug release profile and its interaction with the surrounding biological environment. Electrospinning is the most commonly used technique for preparing nanofibers with industrial scalability. Advanced techniques such as co-axial electrospinning and combined system such as embedding nanoparticles in nanofiber provide an alternative approach to enhance the performance of the scaffold. Electrospun nanofibers offers a matrix like structure for cell regeneration. Nanofibers have been used for ocular delivery of various drugs like antibiotics, anti-inflammatory and various proteins. In addition, lens-coated medical devices provide new insights into the clinical use of nanofibers. Through fabricating the nanofibers researchers have overcome the issues of low bioavailability and compatibility with ocular tissue. Therefore, nanofibers have great potential in ocular drug delivery and tissue engineering and have the capacity to revolutionize these therapeutic areas in the field of ophthalmology. This review is mainly focused on the recent advances in the preparation of nanofibers and their applications in ocular drug delivery and tissue engineering. The authors have attempted to emphasize the processing challenges and future perspectives along with an overview of the safety and toxicity aspects of nanofibers.

Long-acting ocular drug delivery technologies with clinical precedent

INTRODUCTION

Ocular long-acting injectables and implants (LAIIs) deliver drug at a controlled release rate over weeks to years. A reduced dose frequency eases the treatment burden on patients, minimizes the potential for treatment-related adverse effects, and improves treatment adherence and persistence.

AREAS COVERED

This review provides a comprehensive landscape of ocular LAII drug delivery technologies with clinical precedent, including eight commercial products and 27 clinical programs. Analysis of this landscape, and the specific technologies with the greatest precedent, provides instructive lessons for researchers interested in this space and insights into the direction of the field.

EXPERT OPINION

Further technological advancement is required to create biodegradable LAIIs with extended release durations and LAIIs that are compatible with a broader array of therapeutic modalities. In the future, ocular LAII innovations can be applied to diseases with limited treatment options, prophylactic treatment at earlier stages of disease, and cost-effective treatment of ocular diseases in global health settings.

Improved ocular delivery of quercetin and resveratrol: A comparative study between binary and ternary cyclodextrin complexes

The number of patients affected by Dry Eye Disease (DED) had notably increased worldwide, addressing the need of novel therapeutic approaches. Polyphenols, quercetin (QUE) and resveratrol (RSV) show necessary antioxidant and anti-inflammatory properties to manage DED, but their application as topical eyedrops is restricted by low aqueous solubility and low chemical stability. Cyclodextrins (CD) are widely used to improve physicochemical characteristics of drugs. Consequently, the aim of this study was to make a comparison between binary complexes with quercetin, resveratrol and cyclodextrins and tertiary complexes adding hyaluronic acid (HA). Both complexes were able to enhance solubility and stability of QUE and RSV. AFM imaging and DLS measurements disclose the formation of spherical nanoaggregates within tertiary complexes of both QUE and RSV with mean diameters of 103 and 82 nm. Neither complex demonstrated cytotoxic effect in in vitro studies in corneal (HCE) and conjunctival (IM-ConjEpi) cell lines. In HCE cells, complexes containing QUE or RSV at their highest concentrations were able to scavenge more than 95 % of the ROS that were produced intracellularly (p < 0.005). Similar response was observed with IM-ConjEpi cells. The antioxidant effect was maintained in the complexes with HA. This confirmed their potential as viable topical treatment for DED.

A High-Throughput LC-MS/MS Method for the Simultaneous Quantification of Twenty-Seven Drug Molecules in Ocular Tissues

The purpose of this study was to develop a validated LC-MS/MS analytical method for the simultaneous analysis of a large cassette containing a wide range of drug substances with positive, negative, or neutral charge and further apply the method to assess octanol partition coefficient and eye tissue recovery of the drug cassette. A twenty-seven-drug cassette (N-in-one) including beta blockers, NSAIDs, and corticosteroids that range from extremely hydrophilic (sotalol) to very hydrophobic (triamcinolone hexacetanide) was used to develop an LC-MS/MS assay using QTrap 4500. An LC-MS/MS method based on gradient elution, with an eighteen-minute run time including equilibration time, was developed and validated for the rapid and simultaneous quantitation of drugs with a wide range of lipophilicities. Scheduled multiple reaction monitoring was used to maximize the scan time for each peak, ensuring sufficient scans. Method validation included lower limit of quantitation (LLOQ) and intra- and inter-day reproducibility. The LLOQ ranged from 0.5 (sotalol) to 40 fmols (dexamethasone) on column with a %RSD < 20%. The method was tested by measuring octanol:water and octanol:buffer (PBS, pH 7.4) partition coefficients and by quantitation of the drug cassette extracted from rabbit aqueous humor and cornea. Measured partition coefficients correlated positively with predicted values (r²=0.5-0.7). Drug recovery was ≥ 79% from aqueous humor and between 61 and 67% on average from cornea. A rapid, sensitive LC-MS/MS method suitable for N-in-one drug delivery screening was developed for simultaneous quantification of twenty-seven drugs in aqueous solutions and eye tissues.

Ocular biodistribution of cysteamine delivered by a sustained release microsphere/thermoresponsive gel eyedrop

The objective of the investigation was to determine the ocular biodistribution of cysteamine, a reducing agent used for treatment of cystine crystals in cystinosis, following topical administration of a sustained release formulation and traditional eyedrop formulation. To the right eye only, rabbits received a 50 µL drop of 0.44% cysteamine eyedrops at one drop per waking hour for 2, 6, 12, and 24 h. A second group received one 100 µL drop of a sustained release formulation containing encapsulated cysteamine microspheres suspended in a thermoresponsive gel. Upon serial sacrifice, ocular tissues from both eyes and plasma were obtained and quantified for cysteamine using LC-MS/MS. Cysteamine was detected in the cornea, aqueous humor and vitreous humor. Systemic plasma concentrations of cysteamine from treatment groups were below the limit of detection. As expected, 0.44% cysteamine eyedrops when administered hourly maintained drug concentrations within the cornea at a magnitude 5 times higher than a single dose of the sustained release formulation over 12 h. The sustained release formulation maintained cysteamine presentation across 12 h from a single drop. These studies demonstrate distribution of cysteamine to the eye following topical administration, including high drug uptake to the cornea and low systemic distribution.

Light-responsive biomaterials for ocular drug delivery

Light-responsive biomaterials can be used for the delivery of therapeutic drugs and nucleic acids, where the tunable/precise delivery of payload highlights the potential of such biomaterials for treating a variety of conditions. The translucency of eyes and advances of laser technology in ophthalmology make light-responsive delivery of drugs feasible. Importantly, light can be applied in a non-invasive fashion; therefore, light-triggered drug delivery systems have great potential for clinical impact. This review will examine various types of light-responsive polymers and the chemistry that underpins their application as ophthalmic drug delivery systems.

Development of an osmoprotective microemulsion as a therapeutic platform for ocular surface protection

Self-emulsified osmoprotective ophthalmic microemulsions (O/A) were prepared by combining betaine/leucine, clusterin/oleanolic acid, and hyaluronic acid or Dextran. The microemulsions contained an internal oily phase (1.2%), an external aqueous phase (96.3%), cosolvents (1%), and surfactants (1.5%). Physicochemical characterization and in vivo and in vitro tolerance were analyzed. The formulations' osmoprotective in vitro activity was assayed in a hyperosmolar model in human corneal cells. Average internal phase sizes were 16-26 nm for the microemulsions including Dextran. Addition of hyaluronic acid increased the size range (25-39 nm). Addition of osmoprotectants did not change nanodroplet size. The formulations were isotonic (280-290 mOsm/L) with neutral pH (≈7) and zeta potential (-10 to 0 mV), low surface tension (≈35-40mN·m^-1), and low viscosity (≈1 mPa·s), except for the microemulsions containing hyaluronic acid (≈4-5 mPa·s). SEM and cryo-TEM showed that all formulations exhibited sphere-shaped morphology with good cell tolerance (≈100%) and were stable at 8 °C for 9 months. Osmoprotective formulations were well tolerated in vitro and in vivo, protecting cells from hypertonic stress. We therefore developed stable microemulsions compatible with the ocular surface that could constitute a novel tool for treatment of ophthalmic diseases.

Customized cationic nanoemulsions loading triamcinolone acetonide for corneal neovascularization secondary to inflammatory processes

Customized cationic oil-in-water nanoemulsions (NEs) have been produced to improve the bioavailability of poorly water-soluble drugs, such as triamcinolone acetonide (TA). TA is a synthetic glucocorticoid with anti-inflammatory and antiangiogenic therapeutic properties and it is widely used as an effective treatment in ocular disorders. In this work, TA-NEs were characterized using two different custom-made cationic surfactants, showing a high positive surface charge favouring corneal penetration and a particle size below 300 nm. Both TA-NE formulations demonstrated to be stable at 4 °C during the first months of storage. Furthermore, TA-NEs were able to produce antiangiogenic effects in chicken membranes. The TA-NEs safety profile was evaluated using in vitro and in vivo ocular tolerance tests. Out of the two formulations, the one showing no irritant effects was screened in vivo demonstrating capacity to ameliorate ocular inflammation in New Zealand rabbits significantly, specially to reduce the risk of ocular inflammation processes, with antiangiogenic activity, and can therefore be exploited as a suitable formulation to avoid inflammatory reactions upon ocular surgical procedures, such as cataracts.

A methacrylated hyaluronic acid network reinforced Pluronic F-127 gel for treatment of bacterial keratitis

In this study, we developed a novel in situ thermoresponsive gel by introducing crosslinked methacrylated hyaluronic acid (HA-MA) networks into Pluronic F-127 (PF-127) gel (HP gel) to achieve levofloxacin (LFX) delivery in bacterial keratitis treatment. The interactions between PF-127 and HA-MA networks were studied by scanning electron microscopy, rheology, dynamic light scattering, differential scanning calorimetry, and small angle X-ray scattering. The results showed that the HP gel exhibited a higher critical gelling temperature and lower viscosity than the PF-127 gel (P gel), and could form a uniform thin layer on the ocular surface. Moreover, the drug release profile and gel dissolution rate revealed that the HA-MA network could retard the diffusion and dissolution of drug molecules and prolong the drug release time, which corresponded to an enhanced antibacterial ability of the HP-LFX gel. Furthermore, the HP gel exhibited low cytotoxicity to human corneal epithelial cells (HCECs). Finally, an in vivo pharmacodynamic study was conducted with rabbit keratitis models. An improved treatment efficacy was observed after application of the HP-LFX gels. This study highlights the potential of HP gels in ophthalmic drug delivery.

Iontophoretic ocular delivery of latanoprost-loaded nanoparticles via skin-attached electrodes

Prolonged drug efficacy to reduce the number of administrations is a key factor in the successful treatment of glaucoma through topical drug delivery to the eye. Therefore, we propose a new strategy for iontophoretic ocular delivery of drug-loaded nanoparticles. Considering safety and convenience, our strategy is involved with topical administration of the drug-loaded nanoparticles followed by their permeation into the eye tissues via noninvasive iontophoresis, using the skin-attached electrodes. Thus, those nanoparticles stayed longer in the eye, and during this period, the drug was released in a sustained manner, thereby prolonging drug exposure even with one-time treatment. The nanoparticles were made of poly(lactic-co-glycolic acid) (PLGA), which were loaded with a glaucoma drug, latanoprost. We varied the size of the nanoparticles at 100, 200, 300, and 500 nm and sought to find the optimum size under the fixed conditions for iontophoresis proposed in this work (4 mA; 30 min). Even with iontophoresis through the skin-attached electrodes, the nanoparticles were indeed deposited in the eye tissues, where with an increase in particle size, drug release was more sustained, but fewer particles could permeate into the eye tissues. Because of these two competing factors, iontophoretic delivery of the 300-nm particles exhibited the most prolonged drug efficacy in vivo for more than 7 days, and showed an approximately 23-fold increase in drug efficacy compared with that of Xalatan®, a commercially available eye drop of latanoprost developed for once-a-day administration every day. STATEMENT OF SIGNIFICANCE: To treat glaucoma, conventional eye drops are often prescribed; however, they often require multiple daily administrations due to rapid preocular clearance. To resolve this, we suggest a noninvasive iontophoretic ocular delivery of latanoprost-loaded PLGA nanoparticles using the skin-attached electrodes. Even with iontophoresis via the skin-attached electrodes, the nanoparticles can indeed be deposited into the eye tissues. However, with an increase in particle size, fewer particles can permeate into the eye tissues, although drug release is more sustained. Therefore, the particles with a size of 300 nm show the optimal in vivo delivery profile in this work, where the drug efficacy can be extended for more than 7 days with a single administration.

γ-Cyclodextrin-based polypseudorotaxane hydrogels for ophthalmic delivery of flurbiprofen to treat anterior uveitis

Anterior uveitis is a sight-threatening inflammation inside the eyes. Conventional eye drops for anti-inflammatory therapy need to be administered frequently owing to the rapid elimination and corneal barrier. To address these issues, polypseudorotaxane hydrogels were developed by mixing Soluplus micelles (99.4 nm) and cyclodextrins solution. The optimized hydrogels exhibited shear-thinning and sustained release properties. The hydrogels exhibited higher transcorneal permeability coefficient (P_app, 1.84 folds) than that of drug solutions. Moreover, animal study indicated that the hydrogels significantly increased the precorneal retention (AUC, 21.2 folds) and intraocular bioavailability of flurbiprofen (AUC_{Aqueous humor}, 17.8 folds) in comparison with drug solutions. Importantly, the hydrogels obviously boosted anti-inflammatory efficacy in rabbit model of endotoxin-induced uveitis at a reduced administration frequency. Additionally, the safety of hydrogels was confirmed by cytotoxicity and ocular irritation studies. In all, the present study demonstrates a friendly non-invasive strategy based on γ-CD-based polypseudorotaxane hydrogels for ocular drug delivery.

Design of Novel Nanoemulsion Formulations for Topical Ocular Delivery of Itraconazole: Development, Characterization and In Vitro Bioassay

Purpose: The objective of this study was to design and develop nanoemulsion formulations of Itraconazole (ITZ), a water-insoluble, potent antifungal drug using the spontaneous emulsification method, to improve the ocular delivery and achieve a sustained release of the drug. Methods: The oil was selected on the basis of the ITZ solubility while the surfactant and co-surfactant were selected based on the thermodynamic stability and globule size. Following the selection of components, a pseudo-ternary phase diagram was constructed for the most promising formulation (F11) using benzyl benzoate (BB) as the oil, Eumulgin CO40 as the surfactant, and propylene glycol as the co-surfactant, by the design of experiments (DoE). Results: F7 and F11 formulations were found to have an average globule size of 223.5 ± 10.7 nm and 157.5 ± 14.2 nm, besides thermodynamic stability and suitable physicochemical properties. F11 possessed an almost seven-fold higher cumulative percentage of in vitro released ITZ, in comparison to ITZ aqueous suspension after 24 hours. The release data suggested that the best fitted kinetical model for F11 and F7 was the Higuchi and Korsmeyer-Peppas model. Conclusion: The extended-release of the drug beside an acceptable amount of loaded ITZ suggested that nanoemulsion is suitable for the delivery of the ITZ.

A review on albumin as a biomaterial for ocular drug delivery

Development of ocular drug delivery system is one of the most technically challenging tasks, when compared with other routes of drug delivery. Eye (an intricate organ) is highly sophisticated and sensitive organ due to presence of various structurally differed anatomical layers, which many times limits the drug delivery approaches. Despite several limitations, many advancements have been made as evidence from various recent studies involving improvement of both residence time and permeation of the drug at the ocular region. In the last few decades, albumin(s) based ophthalmic products have been gained most attention to solve the major challenges associated with conventional ocular drug delivery systems. Interestingly, an albumin-based micro, nano, conjugates, and genetically fused target specific to ligand(s) formulation being exploited through many studies for successful ocular delivery of bioactives (mostly repurposed drugs). Past and current studies suggested that albumin(s) based ocular drug delivery system is multifunctional in nature and capable of extending both drug residence time and sustaining the release of drugs to deliver desired pharmacological outcomes. Despite wide applications, still complete progress made in albumin based ocular drug delivery is limited in literature and missing in market. So, herein we presented an overview to explore the key concepts of albumin-based nanocarrier(s) including strategies involved in the treatment of ocular disease, that have yet to be explored.

Enhanced topical corticosteroids delivery to the eye: A trade-off in strategy choice

Topical corticosteroids are the primary treatment of ocular inflammation caused by surgery, injury, or other conditions. Drug pre-corneal residence time, drug water solubility, and drug corneal permeability coefficient are the major factors that determine the ocular drug bioavailability after topical administration. Although growing research successfully enhanced local delivery of corticosteroids utilizing various strategies, rational and dynamic approaches to strategy selection are still lacking. Within this review, an overview of the various strategies as well as their performance in retention, solubility, and permeability coefficient of corticosteroids are provided. On this basis, the tradeoff of strategy selection is discussed, which may shed light on the rational choice and application of ophthalmic delivery enhancement strategies.

Strengthened rebamipide ocular nanoformulation to effectively treat corneal alkali burns in mice through the HMGB1 signaling pathway

Corneal alkali burns are a major ophthalmic emergency, as current therapeutic treatments are limited. Novel treatment targets and new potential agents are required to combat this severe ocular injury. Glycyrrhizin and rebamipide (RBM) are both FDA-approved drugs with potential effects against corneal alkali burns, but RBM is limited by its low aqueous solubility and low bioavailability. This study aimed to utilize dipotassium glycyrrhizinate (DG, a dipotassium salt of glycyrrhizin) as a nanocarrier encapsulating RBM to formulate an ophthalmic solution (marked DG-RBM) with strengthened activities to treat corneal alkali burns. Results showed that an easy DG-RBM preparative process generated particles with high encapsulation efficacy and ultra-small micellar size. The solubility of RBM in DG-RBM in aqueous solution was 3.1 × 10⁵-fold enhanced than its free solution. DG-RBM exhibited excellent storage stability. In vitro cytotoxicity, ex vivo conjunctival responses, and rabbit eye tolerance tests showed that DG-RBM possessed good ocular safety profiles. DG-RBM exhibited improved in vivo corneal permeation profiles and demonstrated a strong effect against H₂O₂-induced oxidative damage, with a significant effect on promoting epithelial wound healing in corneal cells in vitro. As expected, in a mouse model of corneal alkali burns, the topical administration of DG-RBM achieved a strengthened efficacy against alkali burn damages. The mechanism of this therapeutic effect involved regulating high-mobility group box 1 (HMGB1) signaling and its related angiogenic and proinflammatory cytokines. These findings demonstrate the ease of preparing DG-RBM and its great potential as a novel ocular topical formulation to treat corneal alkali burns by regulating HMGB1 signaling.

Analysis of topical dosing and administration effects on ocular drug delivery in a human eyeball model using computational fluid dynamics

Predicting the spatial and temporal drug concentration distributions in the eyes is essential for quantitative analysis of the therapeutic effect and overdose issue via different topical administration strategies. To address such needs, an experimentally validated computational fluid dynamics (CFD) based virtual human eye model with physiologically realistic multiple ophthalmic compartments was developed to study the effect of administration frequency and interval on drug concentration distributions. Timolol was selected as the topical dosing drug for the numerical investigation of how administration strategy can influence drug transport and concentration distribution over time in the human eye. Administration frequencies employed in this study are 1-4 times per day, and the administration time intervals are Δt = 900 s, 1800 s, and 3600 s. Numerical results indicate that the administration frequency can significantly affect the temporal timolol concentration distributions in the ophthalmic compartments. More administrations per day can prolong the mediations at relatively high levels in all compartments. CFD simulation results also show that shorter administration intervals can help the medication maintain a relatively higher concentration during the initial hours. Longer administration intervals can provide a more stable medication concentration during the entire dosing time. Furthermore, numerical parametric analysis in this study indicates that the elimination rate in the aqueous humor plays a dominant role in affecting the drug concentrations in multiple ophthalmic compartments. However, it still needs additional clinical data to identify how much drugs can be transported into the cardiac and/or respiratory systems via blood circulation for side effect assessment.

A composite System Combining Self-Targeted Carbon Dots and Thermosensitive Hydrogels for Challenging Ocular Drug Delivery

We developed a composite system combining self-targeted carbon dots and thermosensitive in situ hydrogels for ocular drug delivery of diclofenac sodium (DS). DS-CD_C-HP nanoparticles were prepared by loading DS on the surface of CD_C-HP via electrostatic interactions. An orthogonal experimental design was selected to screen the optimal thermosensitive hydrogel matrices and then DS-CD_C-HP nanoparticles were embedded to form the composite system. The physicochemical properties and release behavior of this system were characterized, and in vivo fluorescence imaging was carried out. Corneal penetrability and in vitro cellular studies (cytotoxicity, cell imaging and cell uptake) were performed to test the feasibility and potential of this ocular delivery system. Finally, the optimal gel matrix consisting of Poloxamer 407: Poloxamer 188: HPMC E50 was 21:1:1 (w/v %), and the gelation temperature before adding artificial tear fluid was 26.67°C and 34.29°C, respectively. This system has the characteristics of biphasic drug release. In addition, the corneal penetrability and in vivo fluorescence study indicated that corneal transmittance was enhanced and drug retention time was extended. Cellular studies revealed that the DS-CD_C-HP-Gel has good cytocompatibility and CD44 targeting. In summary, this composite system combines carbon dots with hydrogels, offering new potential for ocular drug delivery.

Topical ocular delivery of vancomycin loaded cationic lipid nanocarriers as a promising and non-invasive alternative approach to intravitreal injection for enhanced bacterial endophthalmitis management

Vancomycin (VCM) is a drug of choice for treating infections caused by Staphylococcus species, reported being the most causative agent of bacterial endophthalmitis. However, the ocular bioavailability of topically applied VCM is low due to its high molecular weight and hydrophilicity. The current study sought to explore whether the nanostructured lipid carriers (NLCs) fabricated via cold homogenization technique could improve ocular penetration and prolong the ophthalmic residence of VCM. A 2³ full factorial design was adopted to evaluate the influence of different process and formulation variables on VCM-loaded NLC formulae. The optimized formula with the particle size of 96.4 ± 0.71 nm and narrow size distribution showed spherical morphology obtained by AFM and represented sustained drug release up to 67% in 48 h fitted to the Korsmeyer-Peppas model with probably non-Fickian diffusion kinetic. FTIR studies visualized the drug-carrier interactions in great detail. High encapsulation of VCM (74.8 ± 4.3% w/w) in NLC has been established in DSC and PXRD analysis. The optimal positively charged (+ 29.7 ± 0.47 mV) colloidal dispersion was also stable for 12 weeks at both 4 °C and 25 °C. According to in vivo studies, incorporation of VCM in NLC resulted in a nearly 3-fold increase in the intravitreal concentration of VCM after eye-drop instillation over control groups. Besides, microbiological evaluation admitted its therapeutic effect within five days is comparable to intravitreal injection of VCM. Further, the optimized formula was found to be nonirritant and safe for ophthalmic administration in RBC hemolytic assay. Also, fluorescent tracking of NLCs on rabbit's cornea showed an increase in corneal penetration of nanoparticles. Thus, it is possible to infer that the evolved NLCs are promising drug delivery systems with superior attainments for enhanced Vancomycin ophthalmic delivery to the eye's posterior segment and improved bacterial endophthalmitis management.

Repurposing of nifedipine loaded in situ ophthalmic gel as a novel approach for glaucoma treatment

Glaucoma is a chronic eye disease characterized by elevated intraocular pressure (IOP) which causes severe complications to the eyes and may lead to vision loss. The effective treatment of such diseases motivated the search for novel and unique drugs and delivery systems. It has been reported that, nifedipine (NF) is effective in reducing the elevated IOP due to vasodilatation of eye vascular smooth muscles. NF loaded thermo-sensitive in situ gels were prepared by the cold method using poloxamer 407 (P407) and hydroxypropyl methyl cellulose (HPMC) polymers adopting Box-Behnken experimental design. All the prepared formulae were tested for homogeneity, clarity, pH, isotonicity, gelling capacity, rheological behavior, in vitro drug release and were tested in vivo on rabbits. The prepared in situ gels were homogenous, transparent, having a pH ranged from 5 to 5.5 and undergo sol-gel transition within few seconds physiological temperature. The in situ gels showed sustained in vitro release of NF where about 76% of the loaded drug was released over 12 h. NF loaded in situ gels showed a 45.83 ± 2.91% reduction in the IOP, with no sign of toxicity or irritation to the eye in rabbits. The current investigations clarified the efficiency of this novel and unique NF loaded in situ gel for the control of the IOP compared to the conventional ophthalmic dosage forms.

Pharmaceutical-loaded contact lenses as an ocular drug delivery system: A review of critical lens characterization methodologies with reference to ISO standards

Therapeutic contact lenses for ocular drug delivery have received considerable interest as they can potentially enhance ocular bioavailability, increase patient compliance, and reduce side effects. Along with the successful in vitro and in vivo studies on sustained drug delivery through contact lenses, lens critical properties such as water content, optical transparency and modulus have also been investigated. Aside from issues such as drug stability or burst release, the potential for the commercialization of pharmaceutical-loaded lenses can be limited by the alteration of lens physical and chemical properties upon the incorporation of therapeutic or non-therapeutic components. This review outlines advances in the use of pharmaceutical-loaded contact lenses and their relevant characterization methodologies as a potential ocular drug delivery system from 2010 to 2020, while summarizing current gaps and challenges in this field. A key reference point for this review is the relevant ISO standards on contact lenses, relating to the associated characterization methodologies. The content of this review is categorized based on the chemical, physical and mechanical properties of the loaded lens with the shortcomings of such analytical technologies examined.

Mucoadhesive properties of nanogels based on stimuli-sensitive glycosaminoglycan-graft-pNIPAAm copolymers

Mucoadhesive formulations capable of situ gelation are promising for improving ocular drug delivery. Here we investigated two types of nanogels based on anionic glycosaminoglycans with grafted thermo-responsive poly(N-isopropylacrylamide) chains. One type of nanogels were formed by thermo-induced gelling of heparin-graft-poly(N-isopropylacrylamide) and chondroitin sulfate-graft-poly(N-isopropylacrylamide) copolymers. Another type of nanogels was based on the same copolymers, but terminal groups of thermosensitive macromolecular chains were modified to form covalent disulfide cross-links. All types of nanogels were studied towards their ability to encapsulate and release model drug - dexamethasone. Mucoadhesivity of both thermo-gelled and covalently cross-linked polymeric systems, as well as their ability to interact with dexamethasone, was assessed by microscale thermophoresis (MST). Mucoadhesion properties were also evaluated by isothermal titration calorimetry (ITC), which were in good correlation with MST data. The presence of disulfide linkages and thiol groups were shown to favor improved binding of cross-linked nanogels to mucin. Moreover, in vivo intraocular pressure studies showed that presence of polymers in solution can alter the ocular absorption of carbonic anhydrase inhibitor from eyedrops. The pharmacological effect was in line with mucoadhesive properties of these copolymers.

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.

Nanoscale Drug Delivery Systems for Glaucoma: Experimental and In Silico Advances

In this review, nanoscale-based drug delivery systems, particularly in relevance to the antiglaucoma drugs, have been discussed. In addition to that, the latest computational/in silico advances in this field are examined in brief. Using nanoscale materials for drug delivery is an ideal option to target tumours, and the drug can be released in areas of the body where traditional drugs may fail to act. Nanoparticles, polymeric nanomaterials, single-wall carbon nanotubes (SWCNTs), quantum dots (QDs), liposomes and graphene are the most important nanomaterials used for drug delivery. Ocular drug delivery is one of the most common and difficult tasks faced by pharmaceutical scientists because of many challenges like circumventing the blood-retinal barrier, corneal epithelium and the blood-aqueous barrier. Authors found compelling empirical evidence of scientists relying on in-silico approaches to develop novel drugs and drug delivery systems for treating glaucoma. This review in nanoscale drug delivery systems will help us understand the existing queries and evidence gaps and will pave the way for the effective design of novel ocular drug delivery systems.

Ocular drug delivery to the anterior segment using nanocarriers: A mucoadhesive/mucopenetrative perspective

There is a growing demand for effective treatments for ocular conditions that improve patient compliance and reduce side-effects. While methods such as implants and injections have proven effective, topical administration remains the method of choice for the delivery of therapeutics to the anterior segment of the eye. However, topical administration suffers from multiple drawbacks including low bioavailability of the target therapeutic, systemic toxicity, and the requirement for high therapeutic doses due to the effective clearance mechanisms that exist in the eye. Nanoparticles that have tunable mucoadhesion and/or mucopenetration offer outstanding potential to overcome the anatomical and physiological barriers present to improve ocular bioavailability, reduce toxicity, and increase ocular retention, among other benefits. The current review highlights recent advances in the field of developing nanocarriers with tunable mucoadhesion and mucopenetration for drug delivery to the eye.