On the Barrier Properties of the Cornea: A Microscopy Study of the Penetration of Fluorescently Labeled Nanoparticles, Polymers, and Sodium Fluorescein

Utilizing an Ex Vivo Skin Penetration Analysis Model for Predicting Ocular Drug Penetration: A Feasibility Study with Curcumin Formulations

Objective: This study aimed to investigate the feasibility of using the digital image processing technique, developed to semi-quantitatively study dermal penetration, to study corneal penetration in an ex vivo porcine eye model. Here, we investigated various formulation strategies intended to enhance dermal and corneal bioavailability of the model hydrophobic drug, curcumin.

METHODS

Several formulation principles were explored, including oily solutions, oily suspensions, aqueous nanosuspension, micelles, liposomes and cyclodextrins. The dermal penetration efficacy was tested using an ex vivo porcine ear model previously developed at Philipps-Universität Marburg with subsequent digital image processing. This image analysis method was further applied to study corneal penetration using an ex vivo porcine whole-eye model.

RESULTS

For dermal penetration, oily solutions, oily suspensions and nanosuspensions exhibited the least penetration, whereas liposomes and cyclodextrins showed enhanced penetration. Corneal curcumin penetration correlated with dermal penetration, with curcumin loaded into cyclodextrins penetrating the deepest.

CONCLUSIONS

Overall, our study suggests that the image analysis method previously developed for ex vivo skin penetration can easily be repurposed to study corneal penetration of hydrophobic drugs.

A Nanogel Formulation of Anti-VEGF Peptide for Ocular Neovascularization Treatment

Age-related macular degeneration (AMD) is an eye disorder that can lead to visual impairment in elder patients, and current treatments include repeated injections of monoclonal antibody-based antivascular endothelial growth factor (anti-VEGF) agents. This study investigates the potential of a nanoformulation of a peptide anti-VEGF molecule for neovascular AMD. Anti-VEGF peptide HRHTKQRHTALH (HRH), which has high affinity to VEGF-Fc receptor, was used as the bioactive agent to control neovascularization of the retina. The nanoformulation consisting of hyaluronic acid nanogel was generated by incorporating divinyl sulfone and cholesterol to increase the stability and control the size of the nanodrug. The encapsulation efficacy of nanogel was 65%, and drug release was 34.72% at the end of 192 h. Obtained nanogels were efficiently internalized in 15 min by human umbilical vascular endothelial cells (HUVECs) and ARPE-19 cells, and results indicate that nanoformulation is not toxic to ARPE-19 cells, whereas it inhibits HUVEC proliferation owing to anti-VEGF peptide in the nanogel structure. In the coculture experiment in which retinal penetration was modeled, it was observed that the nanogel reached HUVECs and negatively affected their proliferation without disturbing the monolayer of ARPE-19 cells. In vivo experiments with chick chorioallantoic membrane revealed that nanogel formulation has higher antiangiogenesis activity compared to free HRH. Additionally, in an oxygen-induced retinopathy model, the excessive growth of blood vessels was notably suppressed in mice treated with HRH-loaded nanogel. This research indicates that nanogels formulated in this study are promising candidates as a topical treatment for AMD.

Imaging-Based Drug Penetration Profiling in an Excised Sheep Cornea Model

Formulations designed to address ocular conditions and diseases are predominantly administered topically. While in vitro test systems have been developed to assess corneal permeation under extended contact conditions, methods focusing on determining the penetration depth and kinetics of a substance within the cornea itself rather than through it, are scarce. This study introduces a method for time-dependent penetration depth analysis (10 and 60 min) by means of a semiquantitative imaging method in comparison with a quantitative corneal depth-cut technique, employing fluorescein sodium at concentrations of 0.2 and 0.4 mg/mL as a small molecule model substance and sheep cornea as a human surrogate. Excised tissues exhibited sustained viability in modified artificial aqueous humor and maintained thickness (746 ± 43 µm) and integrity (electrical resistance 488 ± 218 Ω∙cm2) under the experimental conditions. Both methods effectively demonstrated the expected concentration- and time-dependent depth of penetration of fluorescein sodium, displaying a significantly strong correlation. The traceability of the kinetic processes was validated with polysorbate 80, which acted as a penetration enhancer. Furthermore, the imaging-based method enabled detecting the retention of larger structures, such as hyaluronic acid and nanoemulsions from the commercial eyedrop formulation NEOVIS® TOTAL multi, inside the lacrimal layer.

Hollow microneedles for ocular drug delivery

Microneedles (MNs) are micron-sized needles, typically <2 mm in length, arranged either as an array or as single needle. These MNs offer a minimally invasive approach to ocular drug delivery due to their micron size (reducing tissue damage compared to that of hypodermic needles) and overcoming significant barriers in drug administration. While various types of MNs have been extensively researched, significant progress has been made in the use of hollow MNs (HMNs) for ocular drug delivery, specifically through suprachoroidal injections. The suprachoroidal space, situated between the sclera and choroid, has been targeted using optical coherence tomography-guided injections of HMNs for the treatment of uveitis. Unlike other MNs, HMNs can deliver larger volumes of formulations to the eye. This review primarily focuses on the use of HMNs in ocular drug delivery and explores their ocular anatomy and the distribution of formulations following potential HMN administration routes. Additionally, this review focuses on the influence of formulation characteristics (e.g., solution viscosity, particle size), HMN properties (e.g., bore or lumen diameter, MN length), and routes of administration (e.g., periocular transscleral, suprachoroidal, intravitreal) on the ocular distribution of drugs. Overall, this paper highlights the distinctive properties of HMNs, which make them a promising technology for improving drug delivery efficiency, precision, and patient outcomes in the treatment of ocular diseases.

Hyaluronan-Sphingosine Polymersomes for Treatment of Ocular Neovascularization: Synthesis and Evaluation

Ocular neovascularization is a hallmark of several sight-threatening diseases, including diabetic retinopathy and age-related macular degeneration. Currently, available treatments are limited and often associated with side effects. Therefore, a novel approach to ocular neovascularization treatment through utilization of polymersomes from self-assembled sphingosine-grafted hyaluronic acid (HA-Sph) amphiphilic polymers is presented. The polymersomes are generated in spherical morphologies and sizes between 97.95 - 161.9 nm with homogenous size distributions. Experiments reveal that HA-Sph polymersomes, with concentrations ≥150 µg mL-1, significantly inhibit the proliferation of human umbilical vein endothelial cells (HUVECs), while concurrently promoting the proliferation of retinal pigment epithelial cells. The polymersomes demonstrate gradual disintegration in vitro, leading to sustained release of sphingosine, which prolongs the inhibition of HUVEC proliferation (from 87.5% at 24 h to 35.2% viability at 96 h). The efficacy of polymersomes in inhibiting angiogenesis is confirmed through tube formation assay, revealing a substantial reduction in tube length compared to the control group. The findings also validate the ocular penetration capability of polymersomes through ex vivo whole porcine eye ocular penetration study, indicating their suitability for topical administration. Potentially, HA-Sph polymersomes can be harnessed to develop intricate drug delivery systems that protect the retina and effectively treat ocular diseases.

Nanomicelles empower natamycin in treating fungal keratitis: An in vitro, ex vivo and in vivo study

Fungal infections of cornea are important causes of blindness especially in developing nations with tropical climate. However, the challenges associated with current treatments are responsible for poor outcome. Natamycin is the only FDA-approved antifungal drug to treat fungal keratitis, but unfortunately due to its poor water solubility, it is available as suspension. The marketed suspension (5% Natamycin) has rapid precorneal clearance, poor corneal permeability, a higher frequency of administration, and corneal irritation due to undissolved suspended drug particles. In our study, we developed clear and stable natamycin-loaded nanomicelles (1% Natcel) to overcome the above challenges. We demonstrated that 1% Natcel could permeate the cornea better than 5% suspension. The developed 1% Natcel was able to provide sustained release for up to 24 h. Further, it was found to be biocompatible and also improved the mean residence time (MRT) than 5% suspension in tears. Therefore, the developed 1% Natcel could be a potential alternative treatment for fungal keratitis.

Models for barrier understanding in health and disease in lab-on-a-chips

The maintenance of body homeostasis relies heavily on physiological barriers. Dysfunction of these barriers can lead to various pathological processes, including increased exposure to toxic materials and microorganisms. Various methods exist to investigate barrier function in vivo and in vitro. To investigate barrier function in a highly reproducible manner, ethically, and high throughput, researchers have turned to non-animal techniques and micro-scale technologies. In this comprehensive review, the authors summarize the current applications of organ-on-a-chip microfluidic devices in the study of physiological barriers. The review covers the blood-brain barrier, ocular barriers, dermal barrier, respiratory barriers, intestinal, hepatobiliary, and renal/bladder barriers under both healthy and pathological conditions. The article then briefly presents placental/vaginal, and tumour/multi-organ barriers in organ-on-a-chip devices. Finally, the review discusses Computational Fluid Dynamics in microfluidic systems that integrate biological barriers. This article provides a concise yet informative overview of the current state-of-the-art in barrier studies using microfluidic devices.

OCTN2- and ATB0,+-targeted nanoemulsions for improving ocular drug delivery

Traditional eye drops are administered via topical instillation. However, frequent dosing is needed due to their relatively rapid precorneal removal and low ocular bioavailability. To address these issues, stearoyl L-carnitine-modified nanoemulsions (SC-NEs) were fabricated. The physicochemical properties of SC-NEs in terms of size, morphology, zeta potential, encapsulation efficiency, and in vitro drug release behavior were characterized. The cellular uptake and mechanisms of SC-NEs were comprehensively studied in human corneal epithelial cells and the stearoyl L-carnitine ratio in SC-NEs was optimized. The optimized SC-NEs could target the novel organic cation/carnitine transporter 2 (OCTN2) and amino acid transporter B (0 +) (ATB0,+) on the corneal epithelium, which led to superior corneal permeation, ocular surface retention ability, ocular bioavailability. Furthermore, SC-NEs showed excellent in vivo anti-inflammatory efficacy in a rabbit model of endotoxin-induced uveitis. The ocular safety test indicated that the SC-NEs were biocompatible. In general, the current study demonstrated that OCTN2 and ATB0,+-targeted nanoemulsions were promising ophthalmologic drug delivery systems that can improve ocular drug bioavailability and boost the therapeutic effects of drugs for eye diseases.

Nebulised delivery of RNA formulations to the lungs: From aerosol to cytosol

In the past decade RNA-based therapies such as small interfering RNA (siRNA) and messenger RNA (mRNA) have emerged as new and ground-breaking therapeutic agents for the treatment and prevention of many conditions from viral infection to cancer. Most clinically approved RNA therapies are parenterally administered which impacts patient compliance and adds to healthcare costs. Pulmonary administration via inhalation is a non-invasive means to deliver RNA and offers an attractive alternative to injection. Nebulisation is a particularly appealing method due to the capacity to deliver large RNA doses during tidal breathing. In this review, we discuss the unique physiological barriers presented by the lung to efficient nebulised RNA delivery and approaches adopted to circumvent this problem. Additionally, the different types of nebulisers are evaluated from the perspective of their suitability for RNA delivery. Furthermore, we discuss recent preclinical studies involving nebulisation of RNA and analysis in in vitro and in vivo settings. Several studies have also demonstrated the importance of an effective delivery vector in RNA nebulisation therefore we assess the variety of lipid, polymeric and hybrid-based delivery systems utilised to date. We also consider the outlook for nebulised RNA medicinal products and the hurdles which must be overcome for successful clinical translation. In summary, nebulised RNA delivery has demonstrated promising potential for the treatment of several lung-related conditions such as asthma, COPD and cystic fibrosis, to which the mode of delivery is of crucial importance for clinical success.

An active transport dual adaptive nanocarrier designed to overcome the corneal microenvironment for neovascularization therapy

The eyes have a complicated microenvironment with many clearance mechanisms, making it challenging for effective drug delivery to the targeted areas of the eyes. Substrate transport mediated by active transporters is an important way to change drug metabolism in the ocular microenvironment. We designed multifunctional, dual-adaptive nanomicelles (GSCQ@NTB) which could overcome multiple physiological barriers by acting on both the efflux transporter and influx transporter to achieve deep delivery of the P-gp substrate in the cornea. Specifically, an effective "triple" antiangiogenic agent, nintedanib (NTB), was loaded into the biocompatible micelles. The expression of the efflux transporter was reversed by grafting quercetin. The peptide (glycylsarcosine, GS) was modified to target the influx transporter "Peptide Transporter-1" (PepT-1). Quercetin (QRT) and nintedanib (NTB) were transported to the cornea cooperatively, achieving long retention on the ocular surface and high compatibility. In a New Zealand rabbit model, within 8 hours after local administration, GSCQ@NTB was enriched in corneal stromal neovascularization and effectively inhibited the progress of neovascularization. Its effectiveness is slightly better than that in the first-line clinical application of steroids. In this study, we introduce the preparation of a dual adaptive nano-micelle system, which may provide an effective non-invasive treatment for corneal neovascularization.

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.

Patient Factors Influencing Intraocular Penetration of Brimonidine-Related Eye Drops in Adults: A Post Hoc Pooled Analysis

INTRODUCTION

The factors related to the ocular penetration of drugs after the administration of eye drops in humans have not been examined in detail. Therefore, this study assessed the influence of patient factors on the intraocular penetration of eye drops.

METHODS

A pooled analysis was performed on the data of 42 participants from three studies to evaluate the ocular pharmacokinetics in humans after the topical application of brimonidine-related eye drops. The patients were scheduled for vitrectomy and received brimonidine-related eye drops (0.1% brimonidine tartrate ophthalmic solution, 0.1% brimonidine tartrate and 0.5% timolol fixed-combination ophthalmic solution, or 0.1% brimonidine tartrate and 1% brinzolamide fixed-combination suspension) twice daily for 1 week. We analyzed the effects of patient factors (sex, the presence or absence of lens, age, corneal thickness, corneal endothelial cell density, tear secretion, eye axial length, height, weight and body mass index [BMI]) on brimonidine, timolol and brinzolamide concentrations in the aqueous and vitreous humor after topical application.

RESULTS

The drug concentrations in the aqueous and vitreous humor were not significantly different, regardless of sex or the presence or absence of lens. Age correlated positively with brimonidine (r = 0.3948, p = 0.012) and brinzolamide (r = 0.6809, p = 0.030) concentrations in the aqueous humor; the correlation with timolol showed a trend towards significance (r = 0.6425, p = 0.086). Corneal thickness, corneal endothelial cell density, tear secretion, eye axial length, height and BMI did not correlate with the drug concentrations in the aqueous or vitreous humor. Timolol concentration in the vitreous humor was negatively correlated with weight (r =  - 0.8333, p = 0.010).

CONCLUSION

The findings of this study emphasize the necessity of considering individual differences in ocular pharmacokinetics during drug therapy (formulation design of the eye drops and dose regimen).

Molecular Trojan Horses for treating lysosomal storage diseases

Lysosomal storage diseases (LSDs) are caused by monogenic mutations in genes encoding for proteins related to the lysosomal function. Lysosome plays critical roles in molecule degradation and cell signaling through interplay with many other cell organelles, such as mitochondria, endoplasmic reticulum, and peroxisomes. Even though several strategies (i.e., protein replacement and gene therapy) have been attempted for LSDs with promising results, there are still some challenges when hard-to-treat tissues such as bone (i.e., cartilages, ligaments, meniscus, etc.), the central nervous system (mostly neurons), and the eye (i.e., cornea, retina) are affected. Consistently, searching for novel strategies to reach those tissues remains a priority. Molecular Trojan Horses have been well-recognized as a potential alternative in several pathological scenarios for drug delivery, including LSDs. Even though molecular Trojan Horses refer to genetically engineered proteins to overcome the blood-brain barrier, such strategy can be extended to strategies able to transport and deliver drugs to specific tissues or cells using cell-penetrating peptides, monoclonal antibodies, vesicles, extracellular vesicles, and patient-derived cells. Only some of those platforms have been attempted in LSDs. In this paper, we review the most recent efforts to develop molecular Trojan Horses and discuss how this strategy could be implemented to enhance the current efficacy of strategies such as protein replacement and gene therapy in the context of LSDs.

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

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

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.

Nanomaterial-based ophthalmic drug delivery

The low bioavailability and side effects of conventional drugs for eye disease necessitate the development of efficient drug delivery systems. Accompanying the developments of nanofabrication techniques, nanomaterials have been recognized as promising tools to overcome these challenges due to their flexible and programmable properties. Given the advances achieved in material science, a broad spectrum of functional nanomaterials capable of overcoming various ocular anterior and posterior segment barriers have been explored to satisfy the demands for ocular drug delivery. In this review, we first highlight the unique functions of nanomaterials suitable for carrying and transporting ocular drugs. Then, various functionalization strategies are emphasized to endow nanomaterials with superior performance in enhanced ophthalmic drug delivery. The rational design of several affecting factors is essential for ideal nanomaterial candidates and is depicted as well. Lastly, we introduce the current applications of nanomaterial-based delivery systems in the therapy of different ocular anterior and posterior segment diseases. The limitations of these delivery systems as well as potential solutions are also discussed. This work will inspire innovative design thinking for the development of nanotechnology-mediated strategies for advanced drug delivery and treatment toward ocular diseases.

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.

Pickering emulsions stabilised with oligoglycine-functionalised nanodiamond as a model system for ocular drug delivery applications

Oil-in-water emulsions, stabilised with conventional surfactants, are commonly used in eye drops for ocular drug delivery. However, the presence of surfactants can sometimes irritate tissues. Furthermore, conventional emulsions often have poor retention on ocular tissue. Pickering emulsions stabilised with nanoparticles have been gaining attention in recent years for a range of biomedical applications because of their biocompatibility. Here, Pickering emulsions were evaluated for the first time for the confinement of organic components for potential application in ocular drug delivery. For a model system, we used nanodiamond (ND) nanoparticles functionalised with covalently-bonded two-tail (2T) oligoglycine C10(NGly4)2 to make Pickering oil-in-water emulsions, which were stable over three months of storage under neutral pH. We proved the non-toxicity of ND-2T Pickering emulsions, comparable to buffer solution, via an ex vivo bovine corneal permeability and opacity test. The retention of the oil phase in the ND-2T stabilised emulsions on corneal tissue is significantly increased because of the mucoadhesive properties arising from the positively-charged terminal amino groups of 2T. Our formulated emulsions have a surface tension, pH and salt concentration comparable to that of tear fluid. The high retention of the ND-2T-stabilised emulsions on the corneal surface, in combination with their non-toxicity, gives them distinct advantages for ocular drug delivery. The principles of this model system could be applied in the future design of a range of formulations for 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.

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

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

Smart Contact Lens Systems for Ocular Drug Delivery and Therapy

Ocular drug delivery and therapy systems have been extensively investigated with various methods including direct injections, eye drops and contact lenses. Nowadays, smart contact lens systems are attracting a lot of attention for ocular drug delivery and therapy due to their minimally invasive or non-invasive characteristics, highly enhanced drug permeation, high bioavailability, and on-demand drug delivery. Furthermore, smart contact lens systems can be used for direct light delivery into the eyes for biophotonic therapy replacing the use of drugs. Here, we review smart contact lens systems which can be classified into two groups of drug-eluting contact lens and ocular device contact lens. More specifically, this review covers smart contact lens systems with nanocomposite-laden systems, polymeric film-incorporated systems, micro and nanostructure systems, iontophoretic systems, electrochemical systems, and phototherapy systems for ocular drug delivery and therapy. After that, we discuss the future opportunities, challenges and perspectives of smart contact lens systems for ocular drug delivery and therapy.

Nanotechnology based drug delivery systems for the treatment of anterior segment eye diseases

Diseases affecting the anterior segment of the eye are the primary causes of vision impairment and blindness globally. Drug administration through the topical ocular route is widely accepted because of its user/patient friendliness - ease of administration and convenience. However, it remains a significant challenge to efficiently deliver drugs to the eye through this route because of various structural and physiological constraints that restrict the distribution of therapeutic molecules into the ocular tissues. The bioavailability of topically applied ocular medications such as eye drops is typically less than 5%. Developing novel delivery systems to increase the retention time on the ocular surfaces and permeation through the cornea is one of the approaches adopted to boost the bioavailability of topically administered medications. Drug delivery systems based on nanotechnology such as micelles, nanosuspensions, nanoparticles, nanoemulsions, liposomes, dendrimers, niosomes, cubosomes and nanowafers have been investigated as effective alternatives to conventional ocular delivery systems in treating diseases of the anterior segment of the eye. This review discussed different nanotechnology-based delivery systems that are currently investigated for treating and managing diseases affecting the anterior ocular tissues. We also looked at the challenges in translating these systems into clinical use and the prospects of nanocarriers as a vehicle for the delivery of phytoactive compounds to the anterior segment of the eye.

Repeated Topical Administration of 3 nm Cerium Oxide Nanoparticles Reverts Disease Atrophic Phenotype and Arrests Neovascular Degeneration in AMD Mouse Models

Increased oxidative stress in the retina and retinal pigment epithelium is implicated in age-related macular degeneration (AMD). Antioxidant cerium oxide nanoparticles (CeO2NPs) have been used to treat degenerative retinal pathologies in animal models, although their delivery route is not ideal for chronic patient treatment. In this work, we prepared a formulation for ocular topical delivery that contains small (3 nm), nonaggregated biocompatible CeO2NPs. In vitro results indicate the biocompatible and protective character of the CeO2NPs, reducing oxidative stress in ARPE19 cells and inhibiting neovascularization related to pathological angiogenesis in both HUVEC and in in vitro models of neovascular growth. In the in vivo experiments, we observed the capacity of CeO2NPs to reach the retina after topical delivery and a subsequent reversion of the altered retinal transcriptome of the retinal degenerative mouse model DKOrd8 toward that of healthy control mice, together with signs of decreased inflammation and arrest of degeneration. Furthermore, CeO2NP eye drops' treatment reduced laser-induced choroidal neovascular lesions in mice by lowering VEGF and increasing PEDF levels. These results indicate that CeO2NP eye drops are a beneficial antioxidant and neuroprotective treatment for both dry and wet forms of AMD disease.

Functional Peptide-Loaded Gelatin Nanoparticles as Eyedrops for Cornea Neovascularization Treatment

Background

Corneal neovascularization (NV) is a process of abnormal vessel growth into the transparent cornea from the limbus and can disturb the light passing through the cornea, resulting in vision loss or even blindness. The use of nanomedicine as an effective therapeutic formulation in ophthalmology has led to higher drug bioavailability and a slow drug release rate. In this research, we designed and explored the feasibility of a new nanomedicine, gp91 ds-tat (gp91) peptide-encapsulated gelatin nanoparticles (GNP-gp91), for inhibiting corneal angiogenesis.

Methods

GNP-gp91 were prepared by a two-step desolvation method. The characterization and cytocompatibility of GNP-gp91 were analyzed. The inhibition effect of GNP-gp91 on HUVEC cell migration and tube formation was observed by an inverted microscope. The drug retention test in mouse cornea was observed by in vivo imaging system, fluorescence microscope, and DAPI/TAMRA staining. Finally, the therapeutic efficacy and evaluation of neovascularization-related factors were conducted through the in vivo corneal NV mice model via topical delivery.

Results

The prepared GNP-gp91 had a nano-scale diameter (550.6 nm) with positive charge (21.7 mV) slow-release behavior (25%, 240hr). In vitro test revealed that GNP-gp91 enhanced the inhibition of cell migration and tube formation capacity via higher internalization of HUVEC. Topical administration (eyedrops) of the GNP-gp91 significantly prolongs the retention time (46%, 20 min) in the mouse cornea. In chemically burned corneal neovascularization models, corneal vessel area with a significant reduction in GNP-gp91 group (7.89%) was revealed when compared with PBS (33.99%) and gp91 (19.67%) treated groups via every two days dosing. Moreover, GNP-gp91 significantly reduced the concentration of Nox2, VEGF and MMP9 in NV's cornea.

Conclusion

The nanomedicine, GNP-gp91, was successfully synthesized for ophthalmological application. These data suggest that GNP-gp91 contained eyedrops that not only have a longer retention time on the cornea but also can treat mice corneal NV effectively delivered in a low dosing frequency, GNP-gp91 eyedrops provides an alternative strategy for clinical ocular disease treatment in the culture.

Chitosan-coated bovine serum albumin nanoparticles for topical tetrandrine delivery in glaucoma: in vitro and in vivo assessment

Glaucoma is one of the leading causes of blindness. Therapies available suffer from several drawbacks including low bioavailability, repeated administration and poor patient compliance with adverse effects thereafter. In this study, bovine serum albumin nanoparticles (BSA-NPs) coated with chitosan(CS) were developed for the topical delivery of tetrandrine (TET) for glaucoma management. Optimized nanoparticles were prepared by desolvation. pH, BSA, CS and cross-linking agent concentrations effects on BSA-NPs colloidal properties were investigated. CS-BSA-NPs with particle size 237.9 nm and zeta potential 24 mV was selected for further evaluation. EE% exceeded 95% with sustained release profile. In vitro mucoadhesion was evaluated based on changes in viscosity and zeta potential upon incubation with mucin. Ex vivo transcorneal permeation was significantly enhanced for CS coated formulation. In vitro cell culture studies on corneal stromal fibroblasts revealed NPs biocompatibility with enhanced cellular uptake and improved antioxidant and anti-proliferative properties for the CS-coated formulation. Moreover, BSA-NPs were nonirritant as shown by HET-CAM test. Also, bioavailability in rabbit aqueous humor showed 2-fold increase for CS-TET-BSA-NPs compared to TET with a sustained reduction in intraocular pressure in a rabbit glaucoma model. Overall, results suggest CS-BSA-NPs as a promising platform for topical ocular TET delivery in the management of glaucoma.

Effect of Polydeoxyribonucleotide (PDRN) Treatment on Corneal Wound Healing in Zebrafish (Danio rerio)

This study aimed to develop a corneal epithelial injury model in zebrafish (Danio rerio) and investigate the effectiveness of polydeoxyribonucleotide (PDRN) treatment on in vivo corneal epithelial regeneration and wound healing. Chemical injury to zebrafish cornea was produced by placing a small cotton swab containing 3% acetic acid solution. PDRN treatment was performed by immersing corneal-injured zebrafish in water containing PDRN (2 mg/mL) for 10 min at 0, 24, 48, and 72 h post-injury (hpi). The level of corneal healing was evaluated by fluorescein staining, histological examination, transcriptional profiling, and immunoblotting techniques. Fluorescein staining results demonstrate that PDRN treatment significantly (p < 0.05) reduced the wounded area of the zebrafish eye at 48 and 72 hpi, suggesting that PDRN may accelerate the corneal re-epithelialization. Histopathological evaluation revealed that injured corneal epithelial cells were re-organized at 72 hpi upon PDRN treatment with increased goblet cell density and size. Moreover, transcriptional analysis results demonstrate that PDRN treatment induced the mRNA expression of adora2ab (6.3-fold), pax6a (7.8-fold), pax6b (29.3-fold), klf4 (7.3-fold), and muc2.1 (5.0-fold) after the first treatment. Besides, tnf-α (2.0-fold) and heat-shock proteins (hsp70; 2.8-fold and hsp90ab1; 1.6-fold) have modulated the gene expression following the PDRN treatment. Immunoblotting results convincingly confirmed the modulation of Mmp-9, Hsp70, and Tnf-α expression levels upon PDRN treatment. Overall, our corneal injury model in zebrafish allows for understanding the morphological and molecular events of corneal epithelial healing, and ophthalmic responses for PDRN treatment following acid injury in zebrafish.

Linoleic Acid-Based Transferosomes for Topical Ocular Delivery of Cyclosporine A

Delivering high-molecular-weight hydrophobic peptides, such as cyclosporine A, across the corneal epithelium remains a challenge that is complicated by other physio-anatomical ocular structures that limit the ocular bioavailability of such peptides. Transferosomes have previously been used to improve transdermal permeability, and have the potential for improving the ocular corneal permeability of applicable drugs. In this study, transferosomes for the potential ocular delivery of cyclosporine A were investigated. Linoleic acid was evaluated for its effect on the stability of the transferosomes and was substituted for a portion of the cholesterol in the vesicles. Additionally, Span® 80 and Tween® 80 were evaluated for their effect on transferosome flexibility and toxicity to ocular cells as edge activators. Attenuated Total Reflectance–Fourier Transform Infrared spectroscopy (ATF-FTIR), differential scanning calorimetry (DSC), and dynamic light scattering (DLS) were used to evaluate the physicochemical parameters of the blank and the cyclosporine A-loaded transferosomes. Cyclosporine A release and corneal permeability were studied in vitro and in a New Zealand albino rabbit corneal model, respectively. The linoleic acid contributed to improved stability and the nano-size of the transferosomes. The Tween®-based formulation was preferred on the basis of a more favorable toxicity profile, as the difference in their corneal permeability was not significant. There was an initial burst release of cyclosporine A in the first 24 h that plateaued over one week. The Tween®-based formulation had a flux of 0.78 µg/cm2/h. The prepared transferosomes demonstrated biocompatibility in the ocular cell line, adequately encapsulated cyclosporine A, ensured the corneal permeability of the enclosed drug, and were stable over the period of investigation of 4 months at −20 °C.

Therapeutic Ultrasound for Topical Corneal Delivery of Macromolecules

Purpose

The objective of this study was to utilize therapeutic ultrasound in enhancing delivery of topical macromolecules into the cornea.

Methods

Rabbit corneas were dissected and placed in a diffusion cell with a small ultra-red fluorescent protein (smURFP; molecular weight of 32,000 Da) as a macromolecule solution. The corneas were treated with continuous ultrasound application at frequencies of 400 or 600 kHz and intensities of 0.8 to 1.0 W/cm2 for 5 minutes, or sham-treated. Fluorescence imaging of the cornea sections was used to observe the delivery of macromolecules into individual epithelial cells. Spectrophotometric analysis at smURFP maximal absorbance of 640 nm was done to determine the presence of macromolecules in the receiver compartment. Safety of ultrasound application was studied through histology analysis.

Results

Ultrasound-treated corneas showed smURFP delivery into epithelial cells by fluorescence in the cytoplasm, whereas sham-treated corneas lacked any appreciable fluorescence in the individual cells. The sham group showed 0% of subcellular penetration, whereas the 400 kHz ultrasound-treated group and 600 kHz ultrasound-treated group showed 31% and 57% of subcellular penetration, respectively. Spectrophotometry measurements indicated negligible presence of smURFP macromolecules in the receiver compartment solution in both the sham and ultrasound treatment groups, and these macromolecules did not cross the entire depth of the cornea. Histological studies showed no significant corneal damage due to ultrasound application.

Conclusions

Therapeutic ultrasound application was shown to increase the delivery of smURFP macromolecules into the cornea.

Translational Relevance

Our study offers a clinical potential for a minimally invasive macromolecular treatment of corneal diseases.

Fluorescent Nanosystems for Drug Tracking and Theranostics: Recent Applications in the Ocular Field

The greatest challenge associated with topical drug delivery for the treatment of diseases affecting the posterior segment of the eye is to overcome the poor bioavailability of the carried molecules. Nanomedicine offers the possibility to overcome obstacles related to physiological mechanisms and ocular barriers by exploiting different ocular routes. Functionalization of nanosystems by fluorescent probes could be a useful strategy to understand the pathway taken by nanocarriers into the ocular globe and to improve the desired targeting accuracy. The application of fluorescence to decorate nanocarrier surfaces or the encapsulation of fluorophore molecules makes the nanosystems a light probe useful in the landscape of diagnostics and theranostics. In this review, a state of the art on ocular routes of administration is reported, with a focus on pathways undertaken after topical application. Numerous studies are reported in the first section, confirming that the use of fluorescent within nanoparticles is already spread for tracking and biodistribution studies. The first section presents fluorescent molecules used for tracking nanosystems’ cellular internalization and permeation of ocular tissues; discussions on the classification of nanosystems according to their nature (lipid-based, polymer-based, metallic-based and protein-based) follows. The following sections are dedicated to diagnostic and theranostic uses, respectively, which represent an innovation in the ocular field obtained by combining dual goals in a single administration system. For its great potential, this application of fluorescent nanoparticles would experience a great development in the near future. Finally, a brief overview is dedicated to the use of fluorescent markers in clinical trials and the market in the ocular field.

A Novel Eye Drop Formulation for Potential Treatment of Neovascular Age-Related Macular Degeneration

Purpose

Drug delivery to posterior ocular tissues via topical eye drop administration is arduous due to the unique anatomy and physiology of the eye. Therefore, treatments for posterior eye disease have to be administered via intravitreal injection or systemic route, both of which have their drawbacks. Herein, the objective of this work was to demonstrate that a specially designed eye drop formulation could effectively deliver small-molecule vascular endothelial growth factor (VEGF) inhibitor to posterior ocular tissues for antiangiogenic therapy.

Methods

The unique eye drop formulation, termed ITRI AXN eye drops, was obtained from self-assembly of (2-hydroxypropyl)-β-cyclodextrin with a VEGF tyrosine kinase inhibitor, a hydrophilic polymer, hypromellose, and a complex stabilizer, caffeine. In vivo ocular pharmacokinetics studies were performed with New Zealand White (NZW) rabbits and Non Human Primates (NHP). The antiangiogenesis effect was evaluated on the Long-Evans rat with laser-induced choroidal neovascularization and pigmented Dutch-Belted rabbits with VEGF-induced retinal neovascularization.

Results

The successful drug transport from ocular surface to posterior ocular cavity was indicated by a drug biodistribution pattern in pharmacokinetic studies. Excellent drug exposure in the choroid and retina with the concentrations of 900- and 750-fold greater than drug IC50 0.5 hours post the eye drop administration (drug level: 0.8%) was observed on the NHP study. The obtained formulation also demonstrated a comparable antiangiogenic outcome with the intravitreal injection of anti-VEGF antibody on rat and rabbit disease models.

Conclusions

Our eye drop formulation has demonstrated great promise in antiangiogenic therapy against retinal and choroidal neovascularization in animal models. The results suggest that the aim of this work can be successfully achieved by the novel eye drop formulation.

Translational Relevance

The preclinical results provide evidence that ITRI AXN eye drops could effectively deliver therapeutics to the choroid and retina for antiangiogenic therapy.

Nanotechnology for Topical Drug Delivery to the Anterior Segment of the Eye

Topical drug delivery is one of the most challenging aspects of eye therapy. Eye drops are the most prevalent drug form, especially for widely distributed anterior segment eye diseases (cataracts, glaucoma, dry eye syndrome, inflammatory diseases, etc.), because they are convenient and easy to apply by patients. However, conventional drug formulations are usually characterized by short retention time in the tear film, insufficient contact with epithelium, fast elimination, and difficulties in overcoming ocular tissue barriers. Not more than 5% of the total drug dose administered in eye drops reaches the interior ocular tissues. To overcome the ocular drug delivery barriers and improve drug bioavailability, various conventional and novel drug delivery systems have been developed. Among these, nanosize carriers are the most attractive. The review is focused on the different drug carriers, such as synthetic and natural polymers, as well as inorganic carriers, with special attention to nanoparticles and nanomicelles. Studies in vitro and in vivo have demonstrated that new formulations could help to improve the bioavailability of the drugs, provide sustained drug release, enhance and prolong their therapeutic action. Promising results were obtained with drug-loaded nanoparticles included in in situ gel.

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

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

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

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

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

Hyaluronan-Cholesterol Nanogels for the Enhancement of the Ocular Delivery of Therapeutics

The anatomy and physiology of the eye strongly limit the bioavailability of locally administered drugs. The entrapment of therapeutics into nanocarriers represents an effective strategy for the topical treatment of several ocular disorders, as they may protect the embedded molecules, enabling drug residence on the ocular surface and/or its penetration into different ocular compartments. The present work shows the activity of hyaluronan-cholesterol nanogels (NHs) as ocular permeation enhancers. Thanks to their bioadhesive properties, NHs firmly interact with the superficial corneal epithelium, without penetrating the stroma, thus modifying the transcorneal penetration of loaded therapeutics. Ex vivo transcorneal permeation experiments show that the permeation of hydrophilic drugs (i.e., tobramycin and diclofenac sodium salt), loaded in NHs, is significantly enhanced when compared to the free drug solutions. On the other side, the permeation of hydrophobic drugs (i.e., dexamethasone and piroxicam) is strongly dependent on the water solubility of the entrapped molecules. The obtained results suggest that NHs formulations can improve the ocular bioavailability of the instilled drugs by increasing their preocular retention time (hydrophobic drugs) or facilitating their permeation (hydrophilic drugs), thus opening the route for the application of HA-based NHs in the treatment of both anterior and posterior eye segment diseases.

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

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

Novel Formulation of Eye Drops Containing Choline Salicylate and Hyaluronic Acid: Stability, Permeability, and Cytotoxicity Studies Using Alternative Ex Vivo and In Vitro Models

This work investigated the potential of a novel formulation of eye drops containing a non-steroidal anti-inflammatory drug-choline salicylate (CS)-and hyaluronic acid (HA). Thus, these drops may exert both anti-inflammatory and regenerative activity. The experiment was conducted through the careful characterization of physicochemical properties, stability, and quality of eye drops. Moreover, microbiological analysis, as well as penetration and cytotoxic studies, were performed. The UV, HPLC-UV, and HPLC-MS/MS methods were used to determine the purity and stability of CS. The penetration rate of CS was assessed using a hydrophilic membrane and ex vivo porcine cornea model. Additionally, the cytotoxic effects were evaluated using the SIRC cell line. The interaction between HA and CS was tested using size-exclusion chromatography and IR spectrophotometry. As a result, HA increased the viscosity of the drops, which prolonged their contact with the ocular surface, thus ensuring more effective penetration of CS into the corneal structure. After long-term storage, an interaction in the pharmaceutical phase between CS and HA was observed. However, this interaction did not affect the viability of rabbit corneal cells. Our findings showed that eye drops with CS and HA, stored at 2-8 °C in light-protected conditions, met the criteria of stability and safety.

A Review of Ocular Drug Delivery Platforms and Drugs for Infectious and Noninfectious Uveitis: The Past, Present, and Future

Uveitis refers to a broad group of inflammatory disorders of the eye that often require medical and surgical management to improve or stabilize vision and prevent vision-threatening pathological changes to the eye. Drug delivery to the eye to combat inflammation and subsequent complications from uveitic conditions is complex as there are multiple barriers to absorption limiting availability of the needed drug in the affected tissues. As such, there has been substantial interest in developing new drugs and drug delivery platforms to help reduce intraocular inflammation and its complications. In this review, we discuss the challenges of drug delivery, novel technologies recently approved for uveitis patient care and promising drug delivery platforms for uveitis and sequelae of ocular inflammation.

Isolation and Characterization of a New Human Corneal Epithelial Cell Line: HCE-F

PURPOSE

To isolate and characterize an epithelial cell (EC) line from a human donor cornea, which may serve as a reliable test cell line to address biomolecular issues and study the response of corneal epithelium to stressing events and therapeutic treatments.

METHODS

A corneal button from a donor patient was treated with enzymes to separate the epithelial sheet and to free EC, which were put in tissue culture. ECs were characterized by optic and electronic microscopies, cytokeratins and PAX6 were detected by SDS-PAGE and western immunoblotting, the barrier function was evaluated by transepithelial electric resistance and by the immune detection of membrane junction proteins, and the karyotype was characterized according to the classical methods.

RESULTS

Morphological analyses returned the picture of classical homogeneous polygonal morphology as expecetd by EC that was maintained over time and several in vitro passages. Transepithelial electric resistance values were characteristic of a typical barrier-forming cell line. The cytokeratin expression pattern was the one expected for corneal EC with a predominance of CK3 and CK5 and different from a human keratocyte cell line. The male karyotype showed 2 trisomies, of chromosomes 8 and 11.

CONCLUSIONS

All the data so far obtained with the HCE-F cells concur to certify this cell line as a stable, true primary human corneal EC line, which could then be used as a test cell line to study and address the questions concerning the biological response of human corneal epithelium to stressing and/or therapeutic treatments and as a term of comparison for EC derived from pathological corneas.

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.

Mucoadhesive and mucus-penetrating interpolyelectrolyte complexes for nose-to-brain drug delivery

Nasal administration offers a possibility of delivering drugs to the brain. In the present work, nasal drug delivery systems were designed based on cationic Eudragit® EPO (EPO) and anionic Eudragit® L100-55 (L100-55) methacrylate copolymers. Two types of nanocarriers were prepared using interpolyelectrolyte complexation between these polymers. The first type of nanoparticles was prepared by forming interpolyelectrolyte complexes between unmodified EPO and L100-55. The second type of nanoparticles was formed through the complexation between PEGylated L100-55 and EPO. For this purpose, PEGylated L100-55 was synthesized by chemical conjugation of L100-55 with O-(2-aminoethyl)polyethylene glycol. The mucoadhesive properties of these nanoparticles were evaluated ex vivo using sheep nasal mucosa. Nanoparticles based on EPO and L100-55 exhibited mucoadhesive properties towards nasal mucosa, whereas PEGylated nanoparticles were non-mucoadhesive hence displayed mucus-penetrating properties. Both types of nanoparticles were used to formulate haloperidol and their ability to deliver the drug to the brain was evaluated in rats in vivo.

Lipid-Based Nanocarriers for Ophthalmic Administration: Towards Experimental Design Implementation

Nanotherapeutics based on biocompatible lipid matrices allow for enhanced solubility of poorly soluble compounds in the treatment of ophthalmic diseases, overcoming the anatomical and physiological barriers present in the eye, which, despite the ease of access, remains strongly protected. Micro-/nanoemulsions, solid lipid nanoparticles (SLN) or nanostructured lipid carriers (NLC) combine liquid and/or solid lipids with surfactants, improving drug stability and ocular bioavailability. Current research and development approaches based on try-and-error methodologies are unable to easily fine-tune nanoparticle populations in order to overcome the numerous constraints of ocular administration routes, which is believed to hamper easy approval from regulatory agencies for these systems. The predictable quality and specifications of the product can be achieved through quality-by-design (QbD) implementation in both research and industrial environments, in contrast to the current quality-by-testing (QbT) framework. Mathematical modelling of the expected final nanoparticle characteristics by variation of operator-controllable variables of the process can be achieved through adequate statistical design-of-experiments (DoE) application. This multivariate approach allows for optimisation of drug delivery platforms, reducing research costs and time, while maximising the understanding of the production process. This review aims to highlight the latest efforts in implementing the design of experiments to produce optimised lipid-based nanocarriers intended for ophthalmic administration. A useful background and an overview of the different possible approaches are presented, serving as a starting point to introduce the design of experiments in current nanoparticle research.

Synthesis of fluorescently-labelled poly(2-ethyl-2-oxazoline)-protected gold nanoparticles

Gold nanoparticles (GNPs) protected by poly(2-ethyl-2-oxazoline) (POZ) of different molecular weights (Mw = 5, 50, 200 and 500 kDa) were synthesised and characterised by dynamic light scattering, nanoparticle tracking analysis, zeta potential measurement and transmission electron microscopy. It was established that the use of POZ with 50 kDa resulted in formation of GNPs with low polydispersity while POZ with greater molecular weights led to formation of more polydisperse GNPs. Fluorescent labelling of these nanoparticles was achieved through their reaction with polyethyleneglycol dithiol (8-12 kDa) as a linker molecule with subsequent reaction with 6-(iodoacetamido) fluorescein. The fluorescent nature of obtained GNPs was confirmed by the appearance of the fluorescence peak at 510 nm that is typical for fluorescein molecules and glowing of the aqueous solution under the UV irradiaton. The fluorescently-labelled GNPs are promising tool in biomedical application to monitor the biological systems using fluorescent microscopy.

Correlation between Keratoconus and Pollution

Introduction: Keratoconus is a corneal ectasia with multifactorial origin. Three risk factors for keratoconus are currently recognized: ultraviolet rays (UV), eye rubbing and atopy. In the current literature, other factors are evoked such as pollution, whose role in the physiopathology of keratoconus is unclear. The effects of particles matter (PM) 2.5 and 10 are the most studied and questioned in the scientific literature.Material and method: A correlation study was carried out to determine the influence of pollution on keratoconus. Fine particulate matter levels were measured according to available WHO data and were correlated with the prevalences of epidemiological studies. These measures were included in the study according to strict selection criteria.Results: The mean pollution rate of the selected studies was 29.1 ± 24.3 μg/m³ for PM_2.5 and 57.2 ± 56.2 μg/m³ for PM₁₀. The Pearson test shows a moderate correlation between the prevalence of keratoconus and the levels of PM_2.5 (R = 0.51; p = .022) and a strong correlation with the levels of PM₁₀ (R = 0.71; p < .001).Discussion: Fine particulate matter appears to be an emerging risk factor for keratoconus. They are thought to act indirectly by exacerbating known risk factors such as atopy and eye rubbing. And could have a direct action on the cornea by increasing the apoptosis of epithelial cells and interacting directly with the structure of collagen of the stroma.

Thiolated and PEGylated silica nanoparticle delivery to hair follicles

Targeting drug delivery to hair follicles is valuable to treat conditions such as alopecia's and acne, and this shunt route may also allow drug delivery to deeper skin layers and the systemic circulation by avoiding the intact stratum corneum. Here, we investigated the effects of nanoparticle surface chemistry on their delivery into hair follicles by synthesizing fluorescent thiolated silica nanoparticles and functionalizing with 750 Da and 5000 Da methoxypolyethylene glycol maleimide (PEG). The stability of the nanoparticles in skin homogenate was verified before tape stripping of porcine-dosed tissue showed the distribution of the free fluorescent dye and different nanoparticles in the skin. Analysis of microscopic images of the skin sections revealed penetration of nanoparticles functionalized with PEG into the appendages whereas thiolated nanoparticles stayed on the surface of the skin and were removed by tape stripping. Nanoparticles functionalized with PEG 5000 Da penetrated deeper into the hair follicles compared to counterparts functionalized with PEG 750 Da. PEGylation can thus enhance targeted delivery of nanoparticulates into hair follicles.

Emerging Trends in Nanomedicine for Improving Ocular Drug Delivery: Light-Responsive Nanoparticles, Mesoporous Silica Nanoparticles, and Contact Lenses

Vision is the most dominant of our senses, and it is crucial in every stage of our lives. Ocular diseases, regardless of whether they cause vision impairment or not, lead to personal and financial hardships. The anatomy and physiology of the eye strongly limit the efficacy of current ocular drug delivery strategies. Nanotechnology has been the ground for the development of powerful strategies in several fields, namely in medicine. This review highlights emerging nanotechnology-based solutions for improving ocular drug delivery and thus the bioavailability and efficacy of drugs. We focus our review on ambitious but promising approaches currently emerging to leverage the efficacy of nanoparticle-based systems in ocular therapy: (i) light-responsive nanoparticles, which enable spatiotemporal control of drug release; (ii) mesoporous silica nanoparticles, which offer high surface area-to-volume ratio, simple surface modification, good biocompatibility, and improved bioavailability; and (iii) contact lenses, which serve as a compliant method of nanoparticles use and as drug delivery systems for the treatment of ocular diseases.

Ocular Inserts of Voriconazole-Loaded Proniosomal Gels: Formulation, Evaluation and Microbiological Studies

BACKGROUND

Voriconazole (VRC) is a triazole broad spectrum antifungal drug, used in the management of versatile fungal infections, particularly fungal keratitis. The obligatory use of niosomal delivery of VRC may reduce the frequency of dosing intervals resulting from its short biological half time and consequently improve patient compliance.

METHODS

VRC loaded proniosomes (VRC-PNs) were set by the coacervation technique and completely characterized. The developed formula was comprehensively assessed concerning in- vitro release behavior, kinetic investigation, and its conflict against refrigerated and room temperature conditions. A selected noisomal formula was incorporated into ocusert (VRC-PNs Ocu) formulated by 1% w/w hydroxypropyl methyl cellulose HPMC and 0.1% w/w carbopol 940. Eventually, in vitro antifungal activity against Candida albicans and Aspergillus nidulans was assessed by the cup diffusion method.

RESULTS

The optimized VRC-PNs (Pluronic F127: cholesterol weight ratio 1:1 w/w) exhibited the highest entrapment efficiency (87.4±2.55%) with a spherical shape, proper size in nano range and a suitable Zeta potential of 209.7±8.13 nm and -33.5±1.85 mV, respectively. Assurance of drug encapsulation in nanovesicles was accomplished by several means such as attenuated total reflection Fourier-transform infrared spectroscopy, differential scanning calorimetry in addition to powder X-ray diffraction investigations. It displayed a biphasic in vitro release pattern and after 6 months of storage at a refrigerated temperature, the optimized formula preserved its stability. VRC-PNs Ocu proved a very highly significant antifungal activity matched with the free drug or nanosuspension which was extra assured by comparing its mean inhibition zone with that of 5% natamycin market eye drops.

CONCLUSION

In conclusion, VRC-PNs Ocu could be considered as a promising stable sustained release topical ocular nanoparticulate system for the management of fungal infections.

Overcoming negatively charged tissue barriers: Drug delivery using cationic peptides and proteins

Negatively charged tissues are ubiquitous in the human body and are associated with a number of common diseases yet remain an outstanding challenge for targeted drug delivery. While the anionic proteoglycans are critical for tissue structure and function, they make tissue matrix dense, conferring a high negative fixed charge density (FCD) that makes drug penetration through the tissue deep zones and drug delivery to resident cells extremely challenging. The high negative FCD of these tissues is now being utilized by taking advantage of electrostatic interactions to create positively charged multi-stage delivery methods that can sequentially penetrate through the full thickness of tissues, create a drug depot and target cells. After decades of work on attempting delivery using strong binding interactions, significant advances have recently been made using weak and reversible electrostatic interactions, a characteristic now considered essential to drug penetration and retention in negatively charged tissues. Here we discuss these advances using examples of negatively charged tissues (cartilage, meniscus, tendons and ligaments, nucleus pulposus, vitreous of eye, mucin, skin), and delve into how each of their structures, tissue matrix compositions and high negative FCDs create barriers to drug entry and explore how charge interactions are being used to overcome these barriers. We review work on tissue targeting cationic peptide and protein-based drug delivery, compare and contrast drug delivery designs, and also present examples of technologies that are entering clinical trials. We also present strategies on further enhancing drug retention within diseased tissues of lower FCD by using synergistic effects of short-range binding interactions like hydrophobic and H-bonds that stabilize long-range charge interactions. As electrostatic interactions are incorporated into design of drug delivery materials and used as a strategy to create properties that are reversible, tunable and dynamic, bio-electroceuticals are becoming an exciting new direction of research and clinical work.

Silica Nanoparticles in Transmucosal Drug Delivery

Transmucosal drug delivery includes the administration of drugs via various mucous membranes, such as gastrointestinal, nasal, ocular, and vaginal mucosa. The use of nanoparticles in transmucosal drug delivery has several advantages, including the protection of drugs against the harsh environment of the mucosal lumens and surfaces, increased drug residence time, and enhanced drug absorption. Due to their relatively simple synthetic methods for preparation, safety profile, and possibilities of surface functionalisation, silica nanoparticles are highly promising for transmucosal drug delivery. This review provides a description of silica nanoparticles and outlines the preparation methods for various core and surface-functionalised silica nanoparticles. The relationship between the functionalities of silica nanoparticles and their interactions with various mucous membranes are critically analysed. Applications of silica nanoparticles in transmucosal drug delivery are also discussed.