Ocular Drug Delivery Barriers-Role of Nanocarriers in the Treatment of Anterior Segment Ocular Diseases

In situ gelling systems for ocular drug delivery

In situ gelling systems represent a burgeoning paradigm in ocular drug administration, addressing intrinsic challenges posed by extant ocular formulations, such as compromised bioavailability and constraints in traversing the corneal barrier. This systematic review endeavours to comprehensively examine the contemporary landscape of research in this domain, focusing on the nuanced capabilities of in situ gelling systems to optimize drug delivery and enhance therapeutic outcomes, without much technological complexity. Employing a meticulous search strategy across diverse databases for publications and patents spanning the years 2015 to 2023 a total of 26 research papers and 14 patents meeting stringent inclusion criteria were identified. Synthesizing the collective insights derived from these investigations, it becomes evident that in situ gelling systems confer an ability to protract the residence time of formulations or active pharmaceutical ingredients (APIs) within the ocular milieu. This sustained presence engenders extended drug release kinetics, thereby fostering improved patient compliance and mitigating the proclivity for side effects attendant to frequent dosing. These salutary effects extend to diminished systemic drug absorption, augmented ocular bioavailability, and the prospect of reduced dosing frequencies, thereby amplifying patient adherence to therapeutic regimens. Intriguingly, the protective attributes of in situ gelling systems extend to the establishment of an ocular surface barrier, thereby abating the susceptibility to infections and inflammatory responses. In summation, this review underscores the auspicious potential of in situ gelling systems as a transformative approach to advancing ocular drug delivery, warranting sustained research endeavours and developmental initiatives for the betterment of global patient outcomes.

Multifunctional nano-in-micro delivery systems for targeted therapy in fundus neovascularization diseases

Fundus neovascularization diseases are a series of blinding eye diseases that seriously impair vision worldwide. Currently, the means of treating these diseases in clinical practice are continuously evolving and have rapidly revolutionized treatment opinions. However, key issues such as inadequate treatment effectiveness, high rates of recurrence, and poor patient compliance still need to be urgently addressed. Multifunctional nanomedicine can specifically respond to both endogenous and exogenous microenvironments, effectively deliver drugs to specific targets and participate in activities such as biological imaging and the detection of small molecules. Nano-in-micro (NIM) delivery systems such as metal, metal oxide and up-conversion nanoparticles (NPs), quantum dots, and carbon materials, have shown certain advantages in overcoming the presence of physiological barriers within the eyeball and are widely used in the treatment of ophthalmic diseases. Few studies, however, have evaluated the efficacy of NIM delivery systems in treating fundus neovascular diseases (FNDs). The present study describes the main clinical treatment strategies and the adverse events associated with the treatment of FNDs with NIM delivery systems and summarizes the anatomical obstacles that must be overcome. In this review, we wish to highlight the principle of intraocular microenvironment normalization, aiming to provide a more rational approach for designing new NIM delivery systems to treat specific FNDs.

Consistent Intraocular Pressure Reduction by Solid Drug Nanoparticles in Fixed Combinations for Glaucoma Therapy

Efficient topical drug delivery remains a significant challenge in glaucoma management. Although nanoparticle formulations offer considerable promise, their complex preparation processes, co-delivery issues, and batch consistency have hindered their potential. A scalable fabrication strategy is developed here for preparing solid drug nanoparticles (SDNs) with enhanced drug delivery efficiency. Utilizing hydrophobic antiglaucoma drugs brimonidine (BM) and betaxolol (BX), uniform fixed combination BM/BX SDNs are fabricated through a continuous process, improving batch-to-batch consistency for combined glaucoma treatment. With trehalose being used as a lyoprotectant, BM/BX SDNs can be stored as dry powder and easily reconstituted in phosphate buffered saline. Importantly, reconstituted BM/BX SDNs form clear, homogenous solutions, and exhibit negligible cytotoxicity and irritation, making them well-suited for topical administration as eyedrops. Ex vivo and in vivo studies demonstrated that topically applied BM/BX SDNs permeate through the cornea significantly (about two fold to three fold) compared to their hydrophilic counterparts, i.e., brimonidine tartrate, and betaxolol hydrogen chloride. Notably, BM/BX SDNs displayed consistent intraocular pressure lowering effects in vivo in both normotensive rats and glaucoma mice. Collectively, this study demonstrates the potential of the scalable fabrication strategy and the resultant BM/BX SDNs for improving glaucoma management through eyedrops.

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.

Advancing ophthalmic delivery of flurbiprofen via synergistic chiral resolution and ion-pairing strategies

Flurbiprofen (FB), a nonsteroidal anti-inflammatory drug, is widely employed in treating ocular inflammation owing to its remarkable anti-inflammatory effects. However, the racemic nature of its commercially available formulation (Ocufen®) limits the full potential of its therapeutic activity, as the (S)-enantiomer is responsible for the desired anti-inflammatory effects. Additionally, the limited corneal permeability of FB significantly restricts its bioavailability. In this study, we successfully separated the chiral isomers of FB to obtain the highly active (S)-FB. Subsequently, utilizing ion-pairing technology, we coupled (S)-FB with various counter-ions, such as sodium, diethylamine, trimethamine (TMA), and l-arginine, to enhance its ocular bioavailability. A comprehensive evaluation encompassed balanced solubility, octanol-water partition coefficient, corneal permeability, ocular pharmacokinetics, tissue distribution, and in vivo ocular anti-inflammatory activity of each chiral isomer salt. Among the various formulations, S-FBTMA exhibited superior water solubility (about 1-12 mg/ml), lipid solubility (1< lg Pow < 3) and corneal permeability. In comparison to Ocufen®, S-FBTMA demonstrated significantly higher in vivo anti-inflammatory activity and lower ocular irritability (such as conjunctival congestion and tingling). The findings from this research highlight the potential of chiral separation and ion-pair enhanced permeation techniques in providing pharmaceutical enterprises focused on drug development with a valuable avenue for improving therapeutic outcomes.

Combination of PEGylation and Cationization on Phospholipid-Coated Cyclosporine Nanosuspensions for Enhanced Ocular Drug Delivery

Strong precorneal clearance mechanisms including reflex blink, constant tear drainage, and rapid mucus turnover constitute great challenges for eye drops for effective drug delivery to the ocular epithelium. In this study, cyclosporine A (CsA) for the treatment of dry eye disease (DED) was selected as the model drug. Two strategies, PEGylation for mucus penetration and cationization for potent cellular uptake, were combined to construct a novel CsA nanosuspension (NS@lipid-PEG/CKC) by coating nanoscale drug particles with a mixture of lipids, DSPE-PEG2000, and a cationic surfactant, cetalkonium chloride (CKC). NS@lipid-PEG/CKC with the mean size ∼173 nm and positive zeta potential ∼+40 mV showed promoted mucus penetration, good cytocompatibility, more cellular uptake, and prolonged precorneal retention without obvious ocular irritation. More importantly, NS@lipid-PEG/CKC recovered tear production and goblet cell density more efficiently than the commercial cationic nanoemulsion on a dry eye disease rat model. All results indicated that a combination of PEGylation and cationization might provide a promising strategy to coordinate mucus penetration and cellular uptake for enhanced drug delivery to the ocular epithelium for nanomedicine-based eye drops.

Nanozymes for Treating Ocular Diseases

Nanozymes, characterized by their nanoscale size and enzyme-like catalytic activities, exhibit diverse therapeutic potentials, including anti-oxidative, anti-inflammatory, anti-microbial, and anti-angiogenic effects. These properties make them highly valuable in nanomedicine, particularly ocular therapy, bypassing the need for systemic delivery. Nanozymes show significant promise in tackling multi-factored ocular diseases, particularly those influenced by oxidation and inflammation, like dry eye disease, and age-related macular degeneration. Their small size, coupled with their ease of modification and integration into soft materials, facilitates the effective penetration of ocular barriers, thereby enabling targeted or prolonged therapy within the eye. This review is dedicated to exploring ocular diseases that are intricately linked to oxidation and inflammation, shedding light on the role of nanozymes in managing these conditions. Additionally, recent studies elucidating advanced applications of nanozymes in ocular therapeutics, along with their integration with soft materials for disease management, are discussed. Finally, this review outlines directions for future investigations aimed at bridging the gap between nanozyme research and clinical applications.

RiTe conjugate mediated corneal collagen crosslinking, a novel therapeutic intervention for keratoconus - in vitro and in vivo study

Corneal collagen crosslinking (CXL) is an effective method to halt the disease progression of keratoconus, a progressive corneal dystrophy leading to cone shaped cornea. Despite the efficacy of standard protocol, the concerning step of this procedure is epithelial debridement performed to facilitate the entry of riboflavin drug. Riboflavin, a key molecule in CXL protocol, is a sparsely permeable hydrophilic drug in corneal tissues. The present study has employed cell penetrating peptide (CPP), Tat2, to enhance the penetration of riboflavin molecule, and thereby improve currently followed CXL protocol. This study demonstrates approximately two-fold enhanced uptake of CPP riboflavin conjugate, Tat2riboflavin-5'Phosphate (RiTe conjugate), both in vitro and in vivo. Two different CXL protocols (Epi ON and Epi OFF) have been introduced and implemented in rabbit corneas using RiTe conjugate in the present study. The standard and RiTe conjugate mediated CXL procedures exhibited an equivalent extent of crosslinking in both the methods. Reduced keratocyte loss and no endothelial damage in RiTe conjugate mediated CXL further ascertains the safety of the proposed CXL protocols. Therefore, RiTe conjugate mediated CXL protocols present as potential alternatives to the standard keratoconus treatment in providing equally effective, less invasive and patient compliant treatment modality.

Nanoparticles incorporated hydrogels for delivery of antimicrobial agents: developments and trends

The prevention and treatment of microbial infections is an imminent global public health concern due to the poor antimicrobial performance of the existing antimicrobial regime and rapidly emerging antibiotic resistance in pathogenic microbes. In order to overcome these problems and effectively control bacterial infections, various new treatment modalities have been identified. To attempt this, various micro- and macro-molecular antimicrobial agents that function by microbial membrane disruption have been developed with improved antimicrobial activity and lesser resistance. Antimicrobial nanoparticle-hydrogels systems comprising antimicrobial agents (antibiotics, biological extracts, and antimicrobial peptides) loaded nanoparticles or antimicrobial nanoparticles (metal or metal oxide) constitute an important class of biomaterials for the prevention and treatment of infections. Hydrogels that incorporate nanoparticles can offer an effective strategy for delivering antimicrobial agents (or nanoparticles) in a controlled, sustained, and targeted manner. In this review, we have described an overview of recent advancements in nanoparticle-hydrogel hybrid systems for antimicrobial agent delivery. Firstly, we have provided an overview of the nanoparticle hydrogel system and discussed various advantages of these systems in biomedical and pharmaceutical applications. Thereafter, different hybrid hydrogel systems encapsulating antibacterial metal/metal oxide nanoparticles, polymeric nanoparticles, antibiotics, biological extracts, and antimicrobial peptides for controlling infections have been reviewed in detail. Finally, the challenges and future prospects of nanoparticle-hydrogel systems have been discussed.

Recent Advances in Nanotechnology for the Treatment of Dry Eye Disease

Dry eye disease (DED) incidence is continuously growing, positioning it to become an emergent health issue over the next few years. Several topical treatments are commonly used to treat DED; however, reports indicate that only a minor proportion of drug bioavailability is achieved by the majority of eye drops available on the market. In this context, enhancing drug ability to overcome ocular barriers and prolonging its residence time on the ocular surface represent a new challenge in the field of ocular carrier systems. Therefore, research has focused on the development of multi-functional nanosystems, such as nanoemulsions, liposomes, dendrimers, hydrogels, and other nanosized carriers. These systems are designed to improve topical drug bioavailability and efficacy and, at the same time, require fewer daily administrations, with potentially reduced side effects. This review summarizes the different nanotechnologies developed, their role in DED, and the nanotechnology-based eyedrops currently approved for DED treatment.

Light-responsive polymeric nanoparticles for retinal drug delivery: design cues, challenges and future perspectives

A multitude of sight-threatening retinal diseases, affecting hundreds of millions around the globe, lack effective pharmacological treatments due to ocular barriers and common drug delivery limitations. Polymeric nanoparticles (PNPs) are versatile drug carriers with sustained drug release profiles and tunable physicochemical properties which have been explored for ocular drug delivery to both anterior and posterior ocular tissues. PNPs can incorporate a wide range of drugs and overcome the challenges of conventional retinal drug delivery. Moreover, PNPs can be engineered to respond to specific stimuli such as ultraviolet, visible, or near-infrared light, and allow precise spatiotemporal control of the drug release, enabling tailored treatment regimens and reducing the number of required administrations. The objective of this study is to emphasize the therapeutic potential of light-triggered drug-loaded polymeric nanoparticles to treat retinal diseases through an exploration of ocular pathologies, challenges in drug delivery, current production methodologies and recent applications. Despite challenges, light-responsive PNPs hold the promise of substantially enhancing the treatment landscape for ocular diseases, aiming for an improved quality of life for patients.

Recent progress of nanomedicine in managing dry eye disease

Background

Dry eye disease (DED) is a commonly reported ocular complaint that has garnered significant attention in recent research. The global occurrence of DED ranges from 5% to 50%, impacting a substantial proportion of individuals worldwide with increasing frequency. Although topical administration remains the mainstream drug delivery method for ocular diseases, it suffers from drawbacks such as low bioavailability, rapid drug metabolism, and frequent administration requirements. Fortunately, the advancements in nanomedicine offer effective solutions to address the aforementioned issues and provide significant assistance in the treatment of DED.

Main text

DED is considered a multifactorial disease of the ocular surface and tear film, in which the integrity of tear film function and structure plays a crucial role in maintaining the homeostasis of the ocular surface. The conventional treatment for DED involves the utilization of artificial tear products, cyclosporin, corticosteroids, mucin secretagogues, and nonsteroidal anti-inflammatory drugs. Furthermore, nanomedicine is presently a significant field of study, with numerous clinical trials underway for various nanotherapeutics including nanoemulsions, nanosuspensions, liposomes, and micelles. Notably, some of these innovative nanoformulations have already received FDA approval as novel remedies for DED, and the advancement of nanomedicine is poised to offer enhanced prospects to solve the shortcomings of existing treatments for DED partially.

Conclusions

This article provides an overview of the latest advancements in nanomedicine for DED treatment, while the field of DED treatment is expected to witness a remarkable breakthrough shortly with the development of nanomedicine, bringing promising prospects for patients worldwide suffering conditions.

Polymer Nanoparticles with 2-HP-β-Cyclodextrin for Enhanced Retention of Uptake into HCE-T Cells

Triamcinolone acetonide (TA), a medium-potency synthetic glucocorticoid, is primarily employed to treat posterior ocular diseases using vitreous injection. This study aimed to design novel ocular nanoformulation drug delivery systems using PLGA carriers to overcome the ocular drug delivery barrier and facilitate effective delivery into the ocular tissues after topical administration. The surface of the PLGA nanodelivery system was made hydrophilic (2-HP-β-CD) through an emulsified solvent volatilization method, followed by system characterization. The mechanism of cellular uptake across the corneal epithelial cell barrier used rhodamine B (Rh-B) to prepare fluorescent probes for delivery systems. The triamcinolone acetonide (TA)-loaded nanodelivery system was validated by in vitro release behavior, isolated corneal permeability, and in vivo atrial hydrodynamics. The results indicated that the fluorescent probes, viz., the Rh-B-(2-HP-β-CD)/PLGA NPs and the drug-loaded TA-(2-HP-β-CD)/PLGA NPs, were within 200 nm in size. Moreover, the system was homogeneous and stable. The in vitro transport mechanism across the epithelial barrier showed that the uptake of nanoparticles was time-dependent and that NPs were actively transported across the epithelial barrier. The in vitro release behavior of the TA-loaded nanodelivery systems revealed that (2-HP-β-CD)/PLGA nanoparticles could prolong the drug release time to up to three times longer than the suspensions. The isolated corneal permeability demonstrated that TA-(2-HP-β-CD)/PLGA NPs could extend the precorneal retention time and boost corneal permeability. Thus, they increased the cumulative release per unit area 7.99-fold at 8 h compared to the suspension. The pharmacokinetics within the aqueous humor showed that (2-HP-β-CD)/PLGA nanoparticles could elevate the bioavailability of the drug, and its Cmax was 51.91 times higher than that of the triamcinolone acetonide aqueous solution. Therefore, (2-HP-β-CD)/PLGA NPs can potentially elevate transmembrane uptake, promote corneal permeability, and improve the bioavailability of drugs inside the aqueous humor. This study provides a foundation for future research on transocular barrier nanoformulations for non-invasive drug delivery.

Overview of processed excipients in ocular drug delivery: Opportunities so far and bottlenecks

Ocular drug delivery presents a unique set of challenges owing to the complex anatomy and physiology of the eye. Processed excipients have emerged as crucial components in overcoming these challenges and improving the efficacy and safety of ocular drug delivery systems. This comprehensive overview examines the opportunities that processed excipients offer in enhancing drug delivery to the eye. By analyzing the current landscape, this review highlights the successful applications of processed excipients, such as micro- and nano-formulations, sustained-release systems, and targeted delivery strategies. Furthermore, this article delves into the bottlenecks that have impeded the widespread adoption of these excipients, including formulation stability, biocompatibility, regulatory constraints, and cost-effectiveness. Through a critical evaluation of existing research and industry practices, this review aims to provide insights into the potential avenues for innovation and development in ocular drug delivery, with a focus on addressing the existing challenges associated with processed excipients. This synthesis contributes to a deeper understanding of the promising role of processed excipients in improving ocular drug delivery systems and encourages further research and development in this rapidly evolving field.

Enhancing Ocular Drug Delivery: The Effect of Physicochemical Properties of Nanoparticles on the Mechanism of Their Uptake by Human Cornea Epithelial Cells

This study investigates the effect of nanoparticle size and surface chemistry on interactions of the nanoparticles with human cornea epithelial cells (HCECs). Poly(lactic-co-glycolic) acid (PLGA) nanoparticles were synthesized using the emulsion-solvent evaporation method and surface modified with mucoadhesive (alginate [ALG] and chitosan [CHS]) and mucopenetrative (polyethylene glycol [PEG]) polymers. Particles were found to be monodisperse (polydispersity index (PDI) below 0.2), spherical, and with size and zeta potential ranging from 100 to 250 nm and from -25 to +15 mV, respectively. Evaluation of cytotoxicity with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay indicated that incubating cells with nanoparticles for 24 h at concentrations up to 100 μg/mL caused only mild toxicity (70-100% cell viability). Cellular uptake studies were conducted using an in vitro model developed with a monolayer of HCECs integrated with simulated mucosal solution. Evaluation of nanoparticle uptake revealed that energy-dependent endocytosis is the primary uptake mechanism. Among the different nanoparticles studied, 100 nm PLGA NPs and PEG-PLGA-150 NPs showed the highest levels of uptake by HCECs. Additionally, uptake studies in the presence of various inhibitors suggested that macropinocytosis and caveolae-mediated endocytosis are the dominant pathways. While clathrin-mediated endocytosis was found to also be partially responsible for nanoparticle uptake, phagocytosis did not play a role within the studied ranges of size and surface chemistries. These important findings could lead to improved nanoparticle-based formulations that could improve therapies for ocular diseases.

Cationic microemulsion of voriconazole for the treatment of fungal keratitis: in vitro and in vivo evaluation

Aim: This investigation aimed to develop a voriconazole-loaded chitosan-coated cationic microemulsion (CVME) to treat fungal keratitis. Methods: Microemulsions were prepared using water titration, and the optimized microemulsion was coated with chitosan to prepare CVME. The physicochemical parameters, ocular irritation potential, in vitro antifungal efficacy and in vitro release studies were performed. The in vivo antifungal efficacy study was conducted in a fungal infection-induced rabbit eye model. Results: The developed CVME displayed acceptable physicochemical properties and excellent mucoadhesive behavior and showed a sustained release profile. Ex vivo and in vivo studies concluded that higher permeability and improved antifungal efficacy were observed for CVME than drug suspension (DS). Conclusion: The prepared CVME7 is a viable alternative to treating fungal keratitis with existing approaches.

Mucoadhesive Hybrid System of Silk Fibroin Nanoparticles and Thermosensitive In Situ Hydrogel for Amphotericin B Delivery: A Potential Option for Fungal Keratitis Treatment

The purpose of this work was to investigate the feasibility of a novel ophthalmic formulation of amphotericin B-encapsulated silk fibroin nanoparticles incorporated in situ hydrogel (AmB-FNPs ISG) for fungal keratitis (FK) treatment. AmB-FNPs ISG composites were successfully developed and have shown optimized physicochemical properties for ocular drug delivery. Antifungal effects against Candida albicans and in vitro ocular irritation using corneal epithelial cells were performed to evaluate the efficacy and safety of the composite formulations. The combined system of AmB-FNPs-ISG exhibited effective antifungal activity and showed significantly less toxicity to HCE cells than commercial AmB. In vitro and ex vivo mucoadhesive tests demonstrated that the combination of silk fibroin nanoparticles with in situ hydrogels could enhance the adhesion ability of the particles on the ocular surface for more than 6 h, which would increase the ocular retention time of AmB and reduce the frequency of administration during the treatment. In addition, AmB-FNP-PEG ISG showed good physical and chemical stability under storage condition for 90 days. These findings indicate that AmB-FNP-PEG ISG has a great potential and be used in mucoadhesive AmB eye drops for FK treatment.

Poly(ethylene glycol) Methyl Ether Acrylate-Grafted Chitosan-Based Micro- and Nanoparticles as a Drug Delivery System for Antibiotics

Nanotechnology is the science of creating materials at the nanoscale by using various devices, structures, and systems that are often inspired by nature. Micro- and nanoparticles (MPs, NPs) are examples of such materials that have unique properties and can be used as carriers for delivering drugs for different biomedical applications. Chitosan (CS) is a natural polysaccharide that has been widely studied, but it has a problem with low water solubility at neutral or basic pH, which limits its processability. The goal of this work was to use a chemically modified CS with poly(ethylene glycol) methyl ether acrylate (PEGA) to prepare CS micronic and submicronic particles (MPs/NPs) that can deliver different types of antibiotics, respectively, levofloxacin (LEV) and Ciprofloxacin (CIP). The particle preparation procedure employed a double crosslinking method, ionic followed by a covalent, in a water/oil emulsion. The studied process parameters were the precursor concentration, stirring speeds, and amount of ionic crosslinking agent. MPs/NPs were characterized by FT-IR, SEM, light scattering granulometry, and Zeta potential. MPs/NPs were also tested for their water uptake capacity in acidic and neutral pH conditions, and the results showed that they had a pH-dependent behavior. The MPs/NPs were then used to encapsulate two separate drugs, LEV and CIP, and they showed excellent drug loading and release capacity. The MPs/NPs were also found to be safe for cells and blood, which demonstrated their potential as suitable drug delivery systems for biomedical applications.

Nanostructured Lipid Carriers Mediated Drug Delivery to Posterior Segment of Eye and their In-vivo Successes

BACKGROUND

The disease of the posterior segment of the eye is a major concern worldwide, and it affects more than 300 million people and leads to serious visual deterioration. The current treatment available is invasive and leads to serious eye complications. These shortcomings and patient discomfort lead to poor patient compliance. In the last decade, Nanostructured lipid carriers (NLC) have established a remarkable milestone in the delivery of drug substances to the posterior segment of the eye. Additionally, NLC can reduce the clearance due to adhesive properties which are imparted due to nano-metric size. This attribute might reduce the adverse effects associated with intravitreal therapy and thus enhance therapeutic efficacy, eventually raising patient adherence to therapy. The current review provides an inclusive account of NLC as a carrier to target diseases of the posterior segment of the eye.

OBJECTIVE

The review focuses on the various barrier encountered in the delivery of drugs to the posterior segment of the eye and the detail about the physicochemical property of drug substances that are considered to be suitable candidates for encapsulation to lipid carriers. Therefore, a plethora of literature has been included in this review. The review is an attempt to describe methods adopted for assessing the in-vivo behavior that strengthens the potential of NLC to treat the disease of the posterior segment of the eye.

CONCLUSION

These NLC-based systems have proven to be a promising alternative in place of invasive intravitreal injections with improved patient compliance.

Enhancing Corneal Drug Penetration Using Penetratin for Ophthalmic Suspensions

Eye drops, including solutions and suspensions, are essential dosage forms to treat ophthalmic diseases, with poorly water-soluble drugs typically formulated as ophthalmic suspensions. In addition to low bioavailability, suspensions exhibit limited efficacy, safety, and usability due to the presence of drug particles. Improving bioavailability can reduce the drug concentrations and the risk of problems associated with suspended drug particles. However, practical penetration enhancers capable of improving bioavailability remain elusive. Herein, we focused on penetratin (PNT), a cell-penetrating peptide (CPP) that promotes active cellular transport related to macromolecule uptake, such as micropinocytosis. According to the in vitro corneal uptake study using a reconstructed human corneal epithelial tissue model, LabCyte CORNEA-MODEL24, PNT enhanced the uptake of Fluoresbrite® YG carboxylate polystyrene microspheres without covalent binding. In an ex vivo porcine eye model, the addition of 10 µM PNT to rebamipide ophthalmic suspension markedly improved the corneal uptake of rebamipide; however, the addition of 100 µM PNT was ineffective due to potentially increased particle size by aggregation. This article provides basic information on the application of PNT as a penetration enhancer in ophthalmic suspensions, including the in vitro and ex vivo studies mentioned above, as well as the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay and storage stability at different pH values.

Advanced Technologies of Drug Delivery to the Posterior Eye Segment Targeting Angiogenesis and Ocular Cancer

Retinoblastoma (RB), a childhood retinal cancer is caused due to RB1 gene mutation which affects the child below 5 years of age. Angiogenesis has been proven its role in RB metastasis due to the presence of vascular endothelial growth factor (VEGF) in RB cells. Therefore, exploring angiogenic pathway by inhibiting VEGF in treating RB would pave the way for future treatment. In preclinical studies, anti-VEGF molecule have shown their efficacy in treating RB. However, treatment requires recurrent intra-vitreal injections causing various side effects along with patient nonadherence. As a result, delivery of anti-VEGF agent to retina requires an ocular delivery system that can transport it in a non-invasive manner to achieve patient compliance. Moreover, development of these type of systems are challenging due to the complicated physiological barriers of eye. Adopting a non-invasive or minimally invasive approach for delivery of anti-VEGF agents would not only address the bioavailability issues but also improve patient adherence to therapy overcoming the side effects associated with invasive approach. The present review focuses on the eye cancer, angiogenesis and various novel ocular drug delivery systems that can facilitate inhibition of VEGF in the posterior eye segment by overcoming the eye barriers.

Applications of Nanotechnology-mediated Herbal Nanosystems for Ophthalmic Drug

In recent years, herbal nanomedicines have gained tremendous popularity for novel drug discovery. Nanotechnology has provided several advances in the healthcare sector, emerging several novel nanocarriers that potentiate the bioavailability and therapeutic efficacy of the herbal drug. The recent advances in nanotechnology with accelerated strategies of ophthalmic nanosystems have paved a new path for overcoming the limitations associated with ocular drug delivery systems, such as low bioavailability, poor absorption, stability, and precorneal drug loss. Ophthalmic drug delivery is challenging due to anatomical and physiological barriers. Due to the presence of these barriers, the herbal drug entry into the eyes can be affected when administered by following multiple routes, i.e., topical, injectables, or systemic. However, the advancement of nanotechnology with intelligent systems enables the herbal active constituent to successfully entrap within the system, which is usually difficult to reach employing conventional herbal formulations. Herbal-loaded nanocarrier drug delivery systems demonstrated enhanced herbal drug permeation and prolonged herbal drug delivery. In this current manuscript, an extensive search is conducted for original research papers using databases Viz., PubMed, Google Scholar, Science Direct, Web of Science, etc. Further painstaking efforts are made to compile and update the novel herbal nanocarriers such as liposomes, polymeric nanoparticles, solid lipid nanoparticles, nanostructure lipid carriers, micelles, niosomes, nanoemulsions, dendrimers, etc., which are mostly used for ophthalmic drug delivery system. This article presents a comprehensive survey of diverse applications used for the preventative measures and treatment therapy of varied eye disorders. Further, this article highlights the recent findings that the innovators are exclusively working on ophthalmic nanosystems for herbal drug delivery systems. The nanocarriers are promising drug delivery systems that enable an effective and supreme therapeutic potential circumventing the limitations associated with conventional ocular drug delivery systems. The nanotechnology-based approach is useful to encapsulate the herbal bioactive and prevent them from degradation and therefore providing them for controlled and sustained release with enhanced herbal drug permeation. Extensive research is still being carried out in the field of herbal nanotechnology to design an ophthalmic nanosystem with improved biopharmaceutical properties.

Current Advances in Regenerative Strategies for Dry Eye Diseases: A Comprehensive Review

Dry eye disease (DED) is an emerging health issue affecting millions of individuals annually. Ocular surface disorders, such as DED, are characterized by inflammation triggered by various factors. This condition can lead to tear deficiencies, resulting in the desiccation of the ocular surface, corneal ulceration/perforation, increased susceptibility to infections, and a higher risk of severe visual impairment and blindness. Currently, the clinical management of DED primarily relies on supportive and palliative measures, including the frequent and lifelong use of different lubricating agents. While some advancements like punctal plugs, non-steroidal anti-inflammatory drugs, and salivary gland autografts have been attempted, they have shown limited effectiveness. Recently, there have been promising developments in the treatment of DED, including biomaterials such as nano-systems, hydrogels, and contact lenses for drug delivery, cell-based therapies, biological approaches, and tissue-based regenerative therapy. This article specifically explores the different strategies reported so far for treating DED. The aim is to discuss their potential as long-term cures for DED while also considering the factors that limit their feasibility and effectiveness. These advancements offer hope for more effective and sustainable treatment options in the future.

Hydrogels in Ophthalmology: Novel Strategies for Overcoming Therapeutic Challenges

The human eye's intricate anatomical and physiological design necessitates tailored approaches for managing ocular diseases. Recent advancements in ophthalmology underscore the potential of hydrogels as a versatile therapeutic tool, owing to their biocompatibility, adaptability, and customizability. This review offers an exploration of hydrogel applications in ophthalmology over the past five years. Emphasis is placed on their role in optimized drug delivery for the posterior segment and advancements in intraocular lens technology. Hydrogels demonstrate the capacity for targeted, controlled, and sustained drug release in the posterior segment of the eye, potentially minimizing invasive interventions and enhancing patient outcomes. Furthermore, in intraocular lens domains, hydrogels showcase potential in post-operative drug delivery, disease sensing, and improved biocompatibility. However, while their promise is immense, most hydrogel-based studies remain preclinical, necessitating rigorous clinical evaluations. Patient-specific factors, potential complications, and the current nascent stage of research should inform their clinical application. In essence, the incorporation of hydrogels into ocular therapeutics represents a seminal convergence of material science and medicine, heralding advancements in patient-centric care within ophthalmology.

Dendritic Oligoethylenimine Decorated Liposome with Augmented Corneal Retention and Permeation for Efficient Topical Delivery of Antiglaucoma Drugs

The topically administered glaucoma medications usually encounter serious precorneal drug loss and low corneal penetration, leading to a low bioavailability. In addition, due to the complexity of glaucoma etiology, a single medication is often insufficient. In this work, we report a novel dendritic oligoethylenimine decorated liposome for codelivery of two antiglaucoma drugs, latanoprost and timolol. The liposome showed a uniform nanoscopic particle size, positive surface charge, and excellent dual-drug loading capacity. A prolonged precorneal retention is observed by using this liposomal delivery system. This liposomal delivery system presents increased cellular uptake and tight junctions opening capacity, contributing respectively to the transcellular and paracellular permeation, thereby enhancing the trans-corneal transportation. Following topical administration of one eye drop in brown Norway rats, the dual-drug-loaded liposome formulation resulted in a sustained and effective intraocular pressure reduction as long as 5 days, without inducing ocular inflammation, discomfort, and tissue damage.

PLGA Nanoparticles Containing Natural Flavanones for Ocular Inflammation

Flavanones are natural compounds that display anti-inflammatory activity. The aim of this work was to prepare PLGA nanoparticles (NPs) containing natural flavanones I ((2S)-5,7-dihydroxy-6-methyl-8-(3-methyl-2-buten-1-il)-2-phenyl-2,3-dihydro-4H-1-Benzopyran-4-one) and II (2S)-5,7-dihydroxy-2-(4'-methoxyphenyl)-6-methyl-8-(3-methyl-2-buten-1-yl)-2,3-dihydro-4H-1-Benzopyran-4-one) (NP I and NP II, respectively) so as to evaluate their potential for topical anti-inflammatory ocular therapy. An in silico study was carried out using the Molinspiration® and PASS Online web platforms before evaluating the in vitro release study and the ex vivo porcine cornea and sclera permeation. The HPLC analytical method was also established and validated. Finally, the in vitro anti-inflammatory efficacy of NPs was studied in the HCE-2 model. The flavanones I and II could be released following a kinetic hyperbolic model. Neither of the two NPs was able to permeate through the tissues. NP I and NP II were found to be respectful of any changes in the tissues' morphology, as evidenced by histological studies. In HCE-2 cells, NP I and NP II were not cytotoxic at concentrations up to 25 µM. NP I showed higher anti-inflammatory activity than NP II, being able to significantly reduce IL-8 production in LPS-treated HCE-2 cells. In summary, ocular treatment with NP I and NP II could be used as a promising therapy for the inhibition of ocular inflammation.

Drug delivery methods based on nanotechnology for the treatment of eye diseases

One of the most difficult tasks among the numerous medication delivery methods is ocular drug delivery. Despite having effective medications for treating ocular illness, we have not yet managed to develop an appropriate drug delivery strategy with the fewest side effects. Nanotechnology has the potential to significantly address the drawbacks of current ocular delivery systems, such as their insufficient therapeutic effectiveness and unfavourable side effects from invasive surgery or systemic exposure. The objective of the current research is to highlight and update the most recent developments in nano-based technologies for the detection and treatment of ocular diseases. Even if more work has to be done, the advancements shown here might lead to brand-new, very practical ocular nanomedicines.

Exploring the Potential of Nanoporous Materials for Advancing Ophthalmic Treatments

The landscape of ophthalmology is undergoing significant transformations, driven by technological advancements and innovations in materials science. One of the advancements in this evolution is the application of nanoporous materials, endowed with unique physicochemical properties ideal for a variety of ophthalmological applications. Characterized by their high surface area, tunable porosity, and functional versatility, these materials have the potential to improve drug delivery systems and ocular devices. This review, anchored by a comprehensive literature focusing on studies published within the last five years, examines the applications of nanoporous materials in ocular drug delivery systems (DDS), contact lenses, and intraocular lenses. By consolidating the most current research, this review aims to serve as a resource for clinicians, researchers, and material scientists engaged in the rapidly evolving field of ophthalmology.

Stimuli-Responsive Hydrogels for Protein Delivery

Proteins and peptides are potential therapeutic agents, but their physiochemical properties make their use as drug substances challenging. Hydrogels are hydrophilic polymeric networks that can swell and retain high amounts of water or biological fluids without being dissolved. Due to their biocompatibility, their porous structure, which enables the transport of various peptides and proteins, and their protective effect against degradation, hydrogels have gained prominence as ideal carriers for these molecules' delivery. Particularly, stimuli-responsive hydrogels exhibit physicochemical transitions in response to subtle modifications in the surrounding environment, leading to the controlled release of entrapped proteins or peptides. This review is focused on the application of these hydrogels in protein and peptide delivery, including a brief overview of therapeutic proteins and types of stimuli-responsive polymers.

Development of Osthole-Loaded Microemulsions as a Prospective Ocular Delivery System for the Treatment of Corneal Neovascularization: In Vitro and In Vivo Assessments

Osthole (OST), a natural coumarin compound, has shown a significant inhibitory effect on corneal neovascularization (CNV). But, its effect on treating CNV is restricted by its water insolubility. To overcome this limitation, an OST-loaded microemulsion (OST-ME) was created to improve the drug's therapeutic effect on CNV after topical administration. The OST-ME formulation comprised Capryol-90 (CP-90), Cremophor® EL (EL-35), Transcutol-P (TSP) and water, and sodium hyaluronate (SH) was also included to increase viscosity. The OST-ME had a droplet size of 16.18 ± 0.02 nm and a low polydispersity index (0.09 ± 0.00). In vitro drug release from OST-ME fitted well to the Higuchi release kinetics model. Cytotoxicity assays demonstrated that OST-ME was not notably toxic to human corneal epithelial cells (HCECs), and the formulation had no irritation to rabbit eyes. Ocular pharmacokinetics studies showed that the areas under the concentration-time curves (AUC0-t) in the cornea and conjunctiva were 19.74 and 63.96 μg/g*min after the administration of OST-ME, both of which were 28.2- and 102.34-fold higher than those after the administration of OST suspension (OST-Susp). Moreover, OST-ME (0.1%) presented a similar therapeutic effect to commercially available dexamethasone eye drops (0.025%) on CNV in mouse models. In conclusion, the optimized OST-ME exhibited good tolerance and enhanced 28.2- and 102.34-fold bioavailability in the cornea and conjunctiva tissues compared with suspensions in rabbit eyes. The OST-ME is a potential ocular drug delivery for anti-CNV.

Quantification of Metal(loid)s in Lubricating Eye Drops Used in the Treatment of Dry Eye Disease

The aim of the study was to evaluate the presence of metal(loid)s in lubricating eye drops used in the treatment of dry eye disease. The concentrations of Al, As, Ba, Cd, Co, Cu, Cr, Pb, Fe, Mg, Mn, Mo, Ni, Se, V, and Zn were determined in 19 eye drop samples using inductively coupled plasma optical emission spectrometry (ICP OES). The limit of detection (LOD) and limit of quantification (LOQ) values for the quantified elements ranged from 0.0002-0.0363 (mg/L) and 0.0007-0.1211 (mg/L), respectively. High values of concentrations of Al (2.382 µg/g), As (0.204 µg/g), Ba (0.056 µg/g), Cd (0.051 µg/g), Co (1.085 µg/g), Cr (0.020 µg/g), Cu (0.023 µg/g), Fe (0.453 µg/g), Mg (24.284 µg/g), Mn (0.014 µg/g), Mo (0.046 µg/g), Ni (0.071 µg/g), Pb (0.049 µg/g), Se (0.365 µg/g), V (0.083 µg/g), and Zn (0.552 µg/g) were quantified in samples of eye drops with and without preservatives. The concentrations of As (5 samples) and Cd (3 samples) were higher than those allowed by the Brazilian Pharmacopoeia for impurities (parenteral use). The value of Co content (µg/g) in a sample was higher than the value established by the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH Q3D (R2)) in the parenteral route. The daily eye drop instillation exposure (µg/day) was below the values from the parenteral-permitted daily exposure (PDE) set by the ICH Q3D guideline (R2). The presence of heavy metals in eye drops is an alert to regulatory agencies in several countries so that control and inspections can be carried out.

Technological Advances in a Therapy of Primary Open-Angle Glaucoma: Insights into Current Nanotechnologies

Glaucoma is a leading cause of irreversible blindness and is characterized by increased intraocular pressure (IOP) and progressive optic nerve damage. The current therapeutic approaches for glaucoma management, such as eye drops and oral medications, face challenges including poor bioavailability, low patient compliance, and limited efficacy. In recent years, nanotechnology has emerged as a promising approach to overcome these limitations and revolutionize glaucoma treatment. In this narrative review, we present an overview of the novel nanotechnologies employed in the treatment of primary open-angle glaucoma. Various nanosystems, including liposomes, niosomes, nanoparticles, and other nanostructured carriers, have been developed to enhance the delivery and bioavailability of antiglaucoma drugs. They offer advantages such as a high drug loading capacity, sustained release, improved corneal permeability, and targeted drug delivery to the ocular tissues. The application of nanotechnologies in glaucoma treatment represents a transformative approach that addresses the limitations of conventional therapies. However, further research is needed to optimize the formulations, evaluate long-term safety, and implement these nanotechnologies into clinical practice. With continued advancements in nanotechnology, the future holds great potential for improving the management and outcomes of glaucoma, ultimately preserving vision and improving the lives of millions affected by this debilitating disease.

Advancements in Nanogels for Enhanced Ocular Drug Delivery: Cutting-Edge Strategies to Overcome Eye Barriers

Nanomedicine in gel or particle formation holds considerable potential for enhancing passive and active targeting within ocular drug delivery systems. The complex barriers of the eye, exemplified by the intricate network of closely connected tissue structures, pose significant challenges for drug administration. Leveraging the capability of engineered nanomedicine offers a promising approach to enhance drug penetration, particularly through active targeting agents such as protein peptides and aptamers, which facilitate targeted release and heightened bioavailability. Simultaneously, DNA carriers have emerged as a cutting-edge class of active-targeting structures, connecting active targeting agents and illustrating their potential in ocular drug delivery applications. This review aims to consolidate recent findings regarding the optimization of various nanoparticles, i.e., hydrogel-based systems, incorporating both passive and active targeting agents for ocular drug delivery, thereby identifying novel mechanisms and strategies. Furthermore, the review delves into the potential application of DNA nanostructures, exploring their role in the development of targeted drug delivery approaches within the field of ocular therapy.

Biodegradable Polymer-Based Drug-Delivery Systems for Ocular Diseases

Ocular drug delivery is a challenging field due to the unique anatomical and physiological barriers of the eye. Biodegradable polymers have emerged as promising tools for efficient and controlled drug delivery in ocular diseases. This review provides an overview of biodegradable polymer-based drug-delivery systems for ocular diseases with emphasis on the potential for biodegradable polymers to overcome the limitations of conventional methods, allowing for sustained drug release, improved bioavailability, and targeted therapy. Natural and synthetic polymers are both discussed, highlighting their biodegradability and biocompatibility. Various formulation strategies, such as nanoparticles, hydrogels, and microemulsions, among others, are investigated, detailing preparation methods, drug encapsulation, and clinical applications. The focus is on anterior and posterior segment drug delivery, covering glaucoma, corneal disorders, ocular inflammation, retinal diseases, age-related macular degeneration, and diabetic retinopathy. Safety considerations, such as biocompatibility evaluations, in vivo toxicity studies, and clinical safety, are addressed. Future perspectives encompass advancements, regulatory considerations, and clinical translation challenges. In conclusion, biodegradable polymers offer potential for efficient and targeted ocular drug delivery, improving therapeutic outcomes while reducing side effects. Further research is needed to optimize formulation strategies and address regulatory requirements for successful clinical implementation.

Ultrasound-Mediated Ocular Drug Delivery: From Physics and Instrumentation to Future Directions

Drug delivery to the anterior and posterior segments of the eye is impeded by anatomical and physiological barriers. Increasingly, the bioeffects produced by ultrasound are being proven effective for mitigating the impact of these barriers on ocular drug delivery, though there does not appear to be a consensus on the most appropriate system configuration and operating parameters for this application. In this review, the fundamental aspects of ultrasound physics most pertinent to drug delivery are presented; the primary phenomena responsible for increased drug delivery efficacy under ultrasound sonication are discussed; an overview of common ocular drug administration routes and the associated ocular barriers is also given before reviewing the current state of the art of ultrasound-mediated ocular drug delivery and its potential future directions.

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

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

Exploring Penetration Ability of Carbonic Anhydrase Inhibitor-Loaded Ultradeformable Bilosome for Effective Ocular Application

Brinzolamide is an effective carbonic anhydrase inhibitor widely used in glaucoma therapy but limits its application due to inadequate aqueous solubility and permeability. The aim of the present research work is the development and characterization of brinzolamide-loaded ultradeformable bilosomes to enhance the corneal permeation of the drug. These ultradeformable bilosomes were prepared by ethanol injection method and evaluated for physicochemical properties, particle size, morphology, drug release, ultra-deformability, corneal permeation, and irritation potential. The optimized formulation exhibited an average particle size of 205.4 ± 2.04 nm with mono-dispersity (0.109 ± 0.002) and showed entrapment efficiency of 75.02 ± 0.017%, deformability index of 3.91, and release the drug in a sustained manner. The brinzolamide-loaded ultradeformable bilosomes released 76.29 ± 3.77% of the drug in 10 h that is 2.25 times higher than the free drug solution. The bilosomes were found non-irritant to eyes with a potential irritancy score of 0 in Hen's egg-chorioallantoic membrane assay. Brinzolamide-loaded ultradeformable bilosomes showed 83.09 ± 5.1% of permeation in 6 h and trans-corneal permeability of 8.78 ± 0.14 cm/h during the ex vivo permeation study. The acquired findings clearly revealed that the brinzolamide-loaded ultradeformable bilosomes show promising output and are useful in glaucoma therapy.

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.

Preparation of a Sunitinib loaded microemulsion for ocular delivery and evaluation for the treatment of corneal neovascularization in vitro and in vivo

Background: Corneal neovascularization (CNV) is a pathological condition that can disrupt corneal transparency, thus harming visual acuity. However, there is no effective drug to treat CNV. Sunitinib (STB), a small-molecule multiple receptor tyrosine kinase inhibitor, was shown to have an effect on CNV. The purpose of this study was to develop an STB microemulsion (STB-ME) eye drop to inhibit CNV by topical application. Methods: We successfully prepared an STB-ME by the phase inversion emulsification method, and the physicochemical properties of STB-MEs were investigated. The short-term storage stability, cytotoxicity to human corneal epithelial cells, drug release, ocular irritation, ocular pharmacokinetics and the inhibitory effect on CNV were evaluated in vitro and in vivo. Results: The optimal formulation of STB-ME is composed of oleic acid, CRH 40, Transcutol P, water and sodium hyaluronate (SH). It is a uniform spherical particle with a mean droplet size of 18.74 ± 0.09 nm and a polydispersity index of 0.196 ± 0.004. In the in vitro drug release results, STB-ME showed sustained release and was best fitted by a Korsmeyer-Peppas model (R ² = 0.9960). The results of the ocular pharmacokinetics in rabbits showed that the formulation containing SH increased the bioavailability in the cornea (2.47-fold) and conjunctiva (2.14-fold). STB-ME (0.05% and 0.1%), administered topically, suppressed alkali burn-induced CNV in mice more effectively than saline, and high-dose (0.1%) STB-ME had similar efficacy to dexamethasone (0.025%). Conclusion: This study provides a promising formulation of STB-ME for the inhibition of CNV by topical administration, which has the excellent characteristics of effectiveness, sustained release and high ocular bioavailability.

Where should siRNAs go: applicable organs for siRNA drugs

RNA interference mediated by small interfering RNAs (siRNAs) has been exploited for the development of therapeutics. siRNAs can be a powerful therapeutic tool because the working mechanisms of siRNAs are straightforward. siRNAs determine targets based on their sequence and specifically regulate the gene expression of the target gene. However, efficient delivery of siRNAs to the target organ has long been an issue that needs to be solved. Tremendous efforts regarding siRNA delivery have led to significant progress in siRNA drug development, and from 2018 to 2022, a total of five siRNA drugs were approved for the treatment of patients. Although all FDA-approved siRNA drugs target the hepatocytes of the liver, siRNA-based drugs targeting different organs are in clinical trials. In this review, we introduce siRNA drugs in the market and siRNA drug candidates in clinical trials that target cells in multiple organs. The liver, eye, and skin are the preferred organs targeted by siRNAs. Three or more siRNA drug candidates are in phase 2 or 3 clinical trials to suppress gene expression in these preferred organs. On the other hand, the lungs, kidneys, and brain are challenging organs with relatively few clinical trials. We discuss the characteristics of each organ related to the advantages and disadvantages of siRNA drug targeting and strategies to overcome the barriers in delivering siRNAs based on organ-specific siRNA drugs that have progressed to clinical trials.

Ophthalmic nano-bioconjugates: critical challenges and technological advances

Ophthalmic disease can cause permanent loss of vision and blindness. Easy-to-administer topical and systemic treatments are preferred for treating sight-threatening disorders. Typical ocular anatomy makes topical and systemic ophthalmic drug delivery challenging. Various novel nano-drug delivery approaches are developed to attain the desired bioavailability in the eye by increasing residence time and improved permeability across the cornea. The review focuses on novel methods that are biocompatible, safe and highly therapeutic. Novelty in nanocarrier design and modification can overcome their drawbacks and make them potential drug carriers for eye disorders in both the anterior and posterior eye segments. This review briefly discussed technologies, patented developments, and clinical trial data to support nanocarriers' use in ocular drug delivery.

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.

Innovative Strategies for Drug Delivery to the Ocular Posterior Segment

Innovative and new drug delivery systems (DDSs) have recently been developed to vehicle treatments and drugs to the ocular posterior segment and the retina. New formulations and technological developments, such as nanotechnology, novel matrices, and non-traditional treatment strategies, open new perspectives in this field. The aim of this mini-review is to highlight promising strategies reported in the current literature based on innovative routes to overcome the anatomical and physiological barriers of the vitreoretinal structures. The paper also describes the challenges in finding appropriate and pertinent treatments that provide safety and efficacy and the problems related to patient compliance, acceptability, effectiveness, and sustained drug delivery. The clinical application of these experimental approaches can help pave the way for standardizing the use of DDSs in developing enhanced treatment strategies and personalized therapeutic options for ocular pathologies.

Application of organic nanocarriers for intraocular drug delivery

The application of intraocular drug delivery is usually limited due to special anatomical and physiological barriers, and the elimination mechanisms in the eye. Organic nano-drug delivery carriers exhibit excellent adhesion, permeability, targeted modification and controlled release abilities to overcome the obstacles and improve the efficiency of drug delivery and bioavailability. Solid lipid nanoparticles can entrap the active components in the lipid structure to improve the stability of drugs and reduce the production cost. Liposomes can transport hydrophobic or hydrophilic molecules, including small molecules, proteins and nucleic acids. Compared with linear macromolecules, dendrimers have a regular structure and well-defined molecular mass and size, which can precisely control the molecular shape and functional groups. Degradable polymer materials endow nano-delivery systems a variety of size, potential, morphology and other characteristics, which enable controlled release of drugs and are easy to modify with a variety of ligands and functional molecules. Organic biomimetic nanocarriers are highly optimized through evolution of natural particles, showing better biocompatibility and lower toxicity. In this article, we summarize the advantages of organic nanocarriers in overcoming multiple barriers and improving the bioavailability of drugs, and highlight the latest research progresses on the application of organic nanocarriers for treatment of ocular diseases.

Recent Advances of Ocular Drug Delivery Systems: Prominence of Ocular Implants for Chronic Eye Diseases

Chronic ocular diseases can seriously impact the eyes and could potentially result in blindness or serious vision loss. According to the most recent data from the WHO, there are more than 2 billion visually impaired people in the world. Therefore, it is pivotal to develop more sophisticated, long-acting drug delivery systems/devices to treat chronic eye conditions. This review covers several drug delivery nanocarriers that can control chronic eye disorders non-invasively. However, most of the developed nanocarriers are still in preclinical or clinical stages. Long-acting drug delivery systems, such as inserts and implants, constitute the majority of the clinically used methods for the treatment of chronic eye diseases due to their steady state release, persistent therapeutic activity, and ability to bypass most ocular barriers. However, implants are considered invasive drug delivery technologies, especially those that are nonbiodegradable. Furthermore, in vitro characterization approaches, although useful, are limited in mimicking or truly representing the in vivo environment. This review focuses on long-acting drug delivery systems (LADDS), particularly implantable drug delivery systems (IDDS), their formulation, methods of characterization, and clinical application for the treatment of eye diseases.

The effect of charges on the corneal penetration of solid lipid nanoparticles loaded econazole after topical administration in rabbits

Fungal keratitis is an infectious disease caused by pathogenic fungi with a high blindness rate. Econazole (ECZ) is an imidazole antifungal drug with insoluble ability. Econazole-loaded solid lipid nanoparticles (E-SLNs) were prepared by microemulsion method, then modified with positive and negative charge. The mean diameter of cationic E-SLNs, nearly neutral E-SLNs and anionic E-SLNs were 18.73±0.14, 19.05±0.28, 18.54±0.10 nm respectively. The Zeta potential of these different charged SLNs formulations were 19.13±0.89, -2.20±0.10, -27.40±0.67 mV respectively. The Polydispersity Index (PDI) of these three kinds of nanoparticles were about 0.2. The Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) analysis showed that the nanoparticles were a homogeneous system. Compared with Econazole suspension (E-Susp), SLNs exhibited sustained release capability, stronger corneal penetration and enhanced inhibition of pathogenic fungi without irritation. The antifungal ability was further improved after cationic charge modification compared with E-SLNs. Studies on pharmacokinetics showed that the order of the AUC and t_1/2 of different preparations was cationic E-SLNs > nearly neutral E-SLNs > anionic E-SLNs > E-Susp in cornea and aqueous humor. It was shown that SLNs could increase corneal penetrability and ocular bioavailability while these capabilities were further enhanced with positive charge modification compared with negative charge ones.

Nanocarriers for ocular drug delivery: Recent advances and future opportunities

Topical route of administration is very important and the most commonly used method of drug delivery for treatment of ocular diseases. However, due to unique anatomical and physiological barriers of eye, it is difficult to achieve the therapeutic concentration in the targeted tissue within the eye. To overcome the effect of these barriers in absorption and to provide targeted and sustained drug delivery, various advances have been made in developing safe and efficient drug delivery systems. Various formulation strategies for ocular drug delivery are used, like basic formulation techniques for improving availability of drugs, viscosity enhancers, and use of mucoadhesives for drug retention and penetration enhancers to promote drug transport to the eye. In this review, we present a summary of the current literature to understand the anatomical and physiological limitations in achieving adequate ocular bioavailability and targeted drug delivery of topically applied drugs and use of new techniques in formulating dosage forms in overcoming these limitations. The recent and future advances in nanocarrier-mediated drug delivery may have the potential to provide patient-friendly and noninvasive techniques for the treatment of diseases related to the anterior and posterior segments of the eye.

Recent advancements in nanotechnology-based bacteriophage delivery strategies against bacterial ocular infections

Antibiotic resistance is growing as a critical challenge in a variety of disease conditions including ocular infections leading to disastrous effects on the human eyes. Staphylococcus aureus (S. aureus) mediated ocular infections are very common affecting different parts of the eye viz. vitreous chamber, conjunctiva, cornea, anterior and posterior chambers, tear duct, and eyelids. Blepharitis, dacryocystitis, conjunctivitis, keratitis, endophthalmitis, and orbital cellulitis are some of the commonly known ocular infections caused by S. aureus. Some of these infections are so fatal that they could cause bilateral blindness like panophthalmitis and orbital cellulitis, which is caused by methicillin-resistant S. aureus (MRSA) and vancomycin-resistance S. aureus (VRSA). The treatment of S. aureus infections with known antibiotics is becoming gradually difficult because of the development of resistance against multiple antibiotics. Apart from the different combinations and formulation strategies, bacteriophage therapy is growing as an effective alternative to treat such infections. Although the superiority of bacteriophage therapy is well established, yet physical factors (high temperatures, acidic pH, UV-rays, and ionic strength) and pharmaceutical barriers (poor stability, low in-vivo retention, controlled and targeted delivery, immune system neutralization, etc.) have the greatest influence on the viability of phage virions (also phage proteins). A variety of Nanotechnology based formulations such as polymeric nanoparticles, liposomes, dendrimers, nanoemulsions, and nanofibres have been recently reported to overcome the above-mentioned obstacles. In this review, we have compiled all these recent reports and discussed bacteriophage-based nanoformulations techniques for the successful treatment of ocular infections caused by multidrug-resistant S. aureus and other bacteria.

Emerging strategies of engineering retinal organoids and organoid-on-a-chip in modeling intraocular drug delivery: current progress and future perspectives

Retinal diseases are a rising concern as major causes of blindness in an aging society; therapeutic options are limited, and the precise pathogenesis of these diseases remains largely unknown. Intraocular drug delivery and nanomedicines offering targeted, sustained, and controllable delivery are the most challenging and popular topics in ocular drug development and toxicological evaluation. Retinal organoids (ROs) and organoid-on-a-chip (ROoC) are both emerging as promising in-vitro models to faithfully recapitulate human eyes for retinal research in the replacement of experimental animals and primary cells. In this study, we review the generation and application of ROs resembling the human retina in cell subtypes and laminated structures and introduce the emerging engineered ROoC as a technological opportunity to address critical issues. On-chip vascularization, perfusion, and close inter-tissue interactions recreate physiological environments in vitro, whilst integrating with biosensors facilitates real-time analysis and monitoring during organogenesis of the retina representing engineering efforts in ROoC models. We also emphasize that ROs and ROoCs hold the potential for applications in modeling intraocular drug delivery in vitro and developing next-generation retinal drug delivery strategies.