Determination of permeability coefficients of ophthalmic drugs through different layers of porcine, rabbit and bovine eyes

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.

Transporter Protein Expression of Corneal Epithelium in Rabbit and Porcine: Evaluation of Models for Ocular Drug Transport Study

The transcorneal route is the main entry route for drugs to the intraocular parts, after topical administration. The outer surface, the corneal epithelium (CE), forms the rate-limiting barrier for drug permeability. Information about the role and protein expression of drug and amino acid transporter proteins in the CE is sparse and lacking. The aim of our study was to characterize transporter protein expression in rabbit and porcine CE to better understand potential drug and nutrient absorption after topical administration. Proteins, mainly Abc and Slc transporters, were characterized with quantitative targeted absolute proteomics and global untargeted proteomics methods. In the rabbit CE, 24 of 48 proteins were detected in the targeted approach, and 21 of these were quantified. In the porcine CE, 26 of 58 proteins were detected in the targeted approach, and 20 of these were quantified. Among these, 15 proteins were quantified in both animals: 4f2hc (Slc3a2), Aqp0, Asct1 (Slc1a4), Asct2 (Slc1a5), Glut1 (Slc2a1), Hmit (Slc2a13), Insr, Lat1 (Slc7a5), Mct1 (Slc16a1), Mct2 (Slc16a7), Mct4 (Slc16a3), Mrp 4 (Abcc4), Na+/K+-ATPase, Oatp3a1 (Slco3a1), and Snat2 (Slc38a2). Overall, the global proteomics results supported the targeted proteomics results. Organic anion transporting polypeptide Oatp3a1 was detected and quantified for the first time in both rabbit (1.4 ± 0.4 fmol/cm2) and porcine (11.1 ± 5.3 fmol/cm2) CE. High expression levels were observed for L-type amino acid transporter, Lat1, which was quantified with newly selected extracellular domain peptides in rabbit (48.9 ± 11.8 fmol/cm2) and porcine (37.6 ± 11.5 fmol/cm2) CE. The knowledge of transporter protein expression in ocular barriers is a key factor in the successful design of new ocular drugs, pharmacokinetic modeling, understanding ocular diseases, and the translation to human.

A Comprehensive Meta-Analysis on the Role of Analgesics and Anti-Inflammatories in Pan-Retinal Photocoagulation

PURPOSE

Pan-retinal photocoagulation (PRP) is the mainstay of treatment for proliferative diabetic retinopathy (PDR), reducing the risk of severe vision loss. Pain poses a potential obstacle to effective laser delivery and patient compliance. Therefore, implementing pain relief strategies can enhance both treatment efficacy and patient comfort.

DESIGN

A systematic review and meta-analysis.

METHODS

We conducted a systematic review and meta-analysis according to PRISMA guidelines. The PubMed, Embase and Cochrane Central Register of Controlled Trials databases were searched for randomized controlled trials (RCTs) that enrolled patients undergoing PRP due to DR and compared analgesics or non-steroidal anti-inflammatory drugs (NSAID) to placebo. Pain was evaluated with the visual analogue scale. The version 2 of the Cochrane Collaboration's Risk of Bias in Randomized Controlled Trials tool and its version for crossover trials were used to assess the risk of bias. The Grading of Recommendations, Assessment, Development, and Evaluation tool was used to measure the certainty of evidence.

RESULTS

A total of 13 studies were included, comprising 1404 eyes from RCTs, nine of which were crossover. Patients who were administered analgesia reported a significantly lower pain sensitivity compared to those who received placebo (Standardized mean difference [SMD] -0.38; 95% confidence interval [CI] -0.58, -0.17; P < .01; I2 = 69%). Subgroup analysis of systemic administration of analgesics/NSAIDs (metamizole, Entonox, acetaminophen, ibuprofen, caffeine, mefenamic acid, intramuscular ketorolac tromethamine, and potassium diclofenac) also showed a statistically significant reduction in pain when compared to placebo (SMD -0.28; 95% CI -0.50, -0.07; P < .01; I2 = 43%). Exclusive eye drops administration (ketorolac tromethamine 0.5% and sodium diclofenac 0.1%) also showed a significant difference in pain sensitivity (SMD -0.46; 95% CI -0.88, -0.05; I2 = 83%), however with a more significant heterogeneity.

CONCLUSIONS

The results of this meta-analysis including over 1000 patients demonstrated that the use of analgesics significantly reduced pain sensitivity during PRP, and systemic analgesia is potentially better than topical administration when compared to placebo.

Molecular nature of ocular surface barrier function, diseases that affect it, and its relevance for ocular drug delivery

The structural and functional integrity of the ocular surface, a continuous epithelial structure comprised of the cornea, the conjunctiva, and the ductal surface of the lacrimal as well as meibomian glands, is crucial for proper vision. The ocular surface barrier function (OSBF), sum of the different types of protective mechanisms that exist at the ocular surface, is essential to protect the rest of the eye from vision-threatening physical, chemical, and biological insults. OSBF helps maintain the immune privileged nature of the cornea and the aqueous humor by preventing entry of infectious agents, allergens, and noxious chemicals. Disruption of OSBF exposes the dense nerve endings of the cornea to these stimuli, resulting in discomfort and pain. This review summarizes the status of our knowledge related to the molecular nature of OSBF, describes the effect of different ocular surface disorders on OSBF, and examines the relevance of this knowledge for ocular drug delivery.

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.

In Vitro and Ex Vivo Models for Assessing Drug Permeation across the Cornea

Drug permeation across the cornea remains a major challenge due to its unique and complex anatomy and physiology. Static barriers such as the different layers of the cornea, as well as dynamic aspects such as the constant renewal of the tear film and the presence of the mucin layer together with efflux pumps, all present unique challenges for effective ophthalmic drug delivery. To overcome some of the current ophthalmic drug limitations, the identification and testing of novel drug formulations such as liposomes, nanoemulsions, and nanoparticles began to be considered and widely explored. In the early stages of corneal drug development reliable in vitro and ex vivo alternatives, are required, to be in line with the principles of the 3Rs (Replacement, Reduction, and Refinement), with such methods being in addition faster and more ethical alternatives to in vivo studies. The ocular field remains limited to a handful of predictive models for ophthalmic drug permeation. In vitro cell culture models are increasingly used when it comes to transcorneal permeation studies. Ex vivo models using excised animal tissue such as porcine eyes are the model of choice to study corneal permeation and promising advancements have been reported over the years. Interspecies characteristics must be considered in detail when using such models. This review updates the current knowledge about in vitro and ex vivo corneal permeability models and evaluates their advantages and limitations.

Corneal Permeability and Uptake of Twenty-Five Drugs: Species Comparison and Quantitative Structure-Permeability Relationships

The purpose of this study was to determine corneal permeability and uptake in rabbit, porcine, and bovine corneas for twenty-five drugs using an N-in-1 (cassette) approach and relate these parameters to drug physicochemical properties and tissue thickness through quantitative structure permeability relationships (QSPRs). A twenty-five-drug cassette containing β-blockers, NSAIDs, and corticosteroids in solution at a micro-dose was exposed to the epithelial side of rabbit, porcine, or bovine corneas mounted in a diffusion chamber, and the corneal drug permeability and tissue uptake were monitored using an LC-MS/MS method. Data obtained were used to construct and evaluate over 46,000 quantitative structure-permeability (QSPR) models using multiple linear regression, and the best-fit models were cross-validated by Y-randomization. Drug permeability was generally higher in rabbit cornea and comparable between bovine and porcine corneas. Permeability differences between species could be explained in part by differences in corneal thickness. Corneal uptake between species correlated with a slope close to 1, indicating generally similar drug uptake per unit weight of tissue. A high correlation was observed between bovine, porcine, and rabbit corneas for permeability and between bovine and porcine corneas for uptake (R² ≥ 0.94). MLR models indicated that drug characteristics such as lipophilicity (LogD), heteroatom ratio (HR), nitrogen ratio (NR), hydrogen bond acceptors (HBA), rotatable bonds (RB), index of refraction (IR), and tissue thickness (TT) are of great influence on drug permeability and uptake. When data for all species along with thickness as a parameter was used in MLR, the best fit equation for permeability was Log (% transport/cm²·s) = 0.441 LogD - 8.29 IR + 8.357 NR - 0.279 HBA - 3.833 TT + 10.432 (R² = 0.826), and the best-fit equation for uptake was Log (%/g) = 0.387 LogD + 4.442 HR + 0.105 RB - 0.303 HBA - 2.235 TT + 1.422 (R² = 0.750). Thus, it is feasible to explain corneal drug delivery in three species using a single equation.

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

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

Hyaluronic acid - PVA films for the simultaneous delivery of dexamethasone and levofloxacin to ocular tissues

Ocular drug delivery is challenging due to the poor drug penetration across ocular barriers and short retention time of the formulation at the application site. Films, applied as inserts or implants, can be used to increase residence time while controlling drug release. In this work, hydrophilic films made of hyaluronic acid and two kinds of PVA were loaded with dexamethasone (included as hydroxypropylcyclodextrin complex) and levofloxacin. This association represents one of the main treatments for the post cataract surgery management, and it is also promising for eye infections whith pain and inflammation. Films were characterized in terms of swelling and drug release and were then applied to porcine eye bulbs and isolated ocular tissues. Film swelling leads to the formation of either a gel (3D swelling) or a larger film (2D swelling) depending on the type of PVA used. Films, prepared in an easy and scalable method, demonstrated high loading capacity, controlled drug release and the capability to deliver dexamethasone and levofloxacin to the cornea and across the sclera, to potentially target also the posterior eye segment. Overall, this device can be considered a multipurpose delivery platform intended for the concomitant release of lipophilic and hydrophilic drugs.

Nanostructured Lipid Carriers for Enhanced Transscleral Delivery of Dexamethasone Acetate: Development, Ex Vivo Characterization and Multiphoton Microscopy Studies

Corticosteroids, although highly effective for the treatment of both anterior and posterior ocular segment inflammation, still nowadays struggle for effective drug delivery due to their poor solubilization capabilities in water. This research work aims to develop nanostructured lipid carriers (NLC) intended for periocular administration of dexamethasone acetate to the posterior segment of the eye. Pre-formulation studies were initially performed to find solid and liquid lipid mixtures for dexamethasone acetate solubilization. Pseudoternary diagrams at 65 °C were constructed to select the best surfactant based on the macroscopic transparency and microscopic isotropy of the systems. The resulting NLC, obtained following an organic solvent-free methodology, was composed of triacetin, Imwitor® 491 (glycerol monostearate >90%) and tyloxapol with Z-average = 106.9 ± 1.2 nm, PDI = 0.104 ± 0.019 and zeta potential = -6.51 ± 0.575 mV. Ex vivo porcine sclera and choroid permeation studies revealed a considerable metabolism in the sclera of dexamethasone acetate into free dexamethasone, which demonstrated higher permeation capabilities across both tissues. In addition, the NLC behavior once applied onto the sclera was further studied by means of multiphoton microscopy by loading the NLC with the fluorescent probe Nile red.

A model for designing intraocular pressure-regulating glaucoma implants

Glaucoma is a group of eye conditions that damage the optic nerve, the health of which is vital for vision. The key risk factor for the development and progression of this disease is increased intraocular pressure (IOP). Implantable glaucoma drainage devices have been developed to divert aqueous humor from the glaucomatous eye as a means of reducing IOP. The artificial drainage pathway created by these devices drives the fluid into a filtering bleb. The long-term success of filtration surgery is dictated by the proper functioning of the bleb and overlying Tenon’s and conjunctival tissue. To better understand the influence of the health condition of these tissues on IOP, we have developed a mathematical model of fluid production in the eye, its removal from the anterior chamber by a particular glaucoma implant–the PRESERFLO^® MicroShunt–, drainage into the bleb and absorption by the subconjunctival vasculature. The mathematical model was numerically solved by commercial FEM package COMSOL. Our numerical results of IOP for different postoperative conditions are consistent with the available evidence on IOP outcomes after the implantation of this device. To obtain insight into the adjustments in the implant’s hydrodynamic resistance that are required for IOP control when hypotony or bleb scarring due to tissue fibrosis take place, we have simulated the flow through a microshunt with an adjustable lumen diameter. Our findings show that increasing the hydrodynamic resistance of the microshunt by reducing the lumen diameter, can effectively help to prevent hypotony. However, decreasing the hydrodynamic resistance of the implant will not sufficiently decrease the IOP to acceptable levels when the bleb is encapsulated due to tissue fibrosis. Therefore, to effectively reduce IOP, the adjustable glaucoma implant should be combined with a means of reducing fibrosis. The results reported herein may provide guidelines to support the design of future glaucoma implants with adjustable hydrodynamic resistances.

Physicochemical and Stability Evaluation of Topical Niosomal Encapsulating Fosinopril/γ-Cyclodextrin Complex for Ocular Delivery

This study aimed to develop a chemically stable niosomal eye drop containing fosinopril (FOS) for lowering intraocular pressure. The effects of cyclodextrin (CD), surfactant types and membrane stabilizer/charged inducers on physiochemical and chemical properties of niosome were evaluated. The pH value, average particle size, size distribution and zeta potentials were within the acceptable range. All niosomal formulations were shown to be slightly hypertonic with low viscosity. Span® 60/dicetyl phosphate niosomes in the presence and absence of γCD were selected as the optimum formulations according to their high %entrapment efficiency and negative zeta potential values as well as controlled release profile. According to ex vivo permeation study, the obtained lowest flux and apparent permeability coefficient values confirmed that FOS/γCD complex was encapsulated within the inner aqueous core of niosome and could be able to protect FOS from its hydrolytic degradation. The in vitro cytotoxicity revealed that niosome entrapped FOS or FOS/γCD formulations were moderate irritation to the eyes. Furthermore, FOS-loaded niosomal preparations exhibited good physical and chemical stabilities especially of those in the presence of γCD, for at least three months under the storage condition of 2–8 °C.

Brain and Retinal Organoids for Disease Modeling: The Importance of In Vitro Blood–Brain and Retinal Barriers Studies

Brain and retinal organoids are functional and dynamic in vitro three-dimensional (3D) structures derived from pluripotent stem cells that spontaneously organize themselves to their in vivo counterparts. Here, we review the main literature data of how these organoids have been developed through different protocols and how they have been technically analyzed. Moreover, this paper reviews recent advances in using organoids to model neurological and retinal diseases, considering their potential for translational applications but also pointing out their limitations. Since the blood–brain barrier (BBB) and blood–retinal barrier (BRB) are understood to play a fundamental role respectively in brain and eye functions, both in health and in disease, we provide an overview of the progress in the development techniques of in vitro models as reliable and predictive screening tools for BBB and BRB-penetrating compounds. Furthermore, we propose potential future directions for brain and retinal organoids, in which dedicated biobanks will represent a novel tool for neuroscience and ophthalmology research.

Understanding dexamethasone kinetics in the rabbit tear fluid: drug release and clearance from solution, suspension and hydrogel formulations

Rapid precorneal loss of topically applied eye drops limits ocular drug absorption. Controlling release and precorneal residence properties of topical formulations may improve ocular drug bioavailability and duration of action. In this study, we evaluated in vivo ocular pharmacokinetics of dexamethasone in rabbits after application of a drug solution (0.01%), suspension (Maxidex® 0.1%), and hydrogels of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AAc) copolymers. The rabbits received a single eyedrop (solution or suspension) or dexamethasone-loaded hydrogel topically. Dexamethasone in tear fluid was sampled with glass capillaries and quantitated by LC-MS/MS. Higher dexamethasone exposure (AUC) in the tear fluid was observed with the suspension (≈ 3.6-fold) and hydrogel (12.8-fold) as compared to the solution. During initial 15 min post-application, the highest AUC of dissolved dexamethasone was seen after hydrogel application (368 min*µg/mL) followed by suspension (109.9 min*µg/mL) and solution (28.7 min*µg/mL. Based on kinetic simulations, dexamethasone release from hydrogels in vivo and in vitro is comparable. Our data indicate that prolonged exposure of absorbable dexamethasone in tear fluid is reached with hydrogels and suspensions. Pharmacokinetic understanding of formulation behavior in the lacrimal fluid helps in the design of dexamethasone delivery systems with improved ocular absorption and prolonged duration of action.

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.

Nose-to-brain co-delivery of drugs for glioblastoma treatment using nanostructured system

Mutations on the epidermal growth factor receptor (EGFR), induction of angiogenesis, and reprogramming cellular energetics are all biological features acquired by tumor cells during tumor development, and also known as the hallmarks of cancer. Targeted therapies that combine drugs that are capable of acting against such concepts are of great interest, since they can potentially improve the therapeutic efficacy of treatments of complex pathologies, such as glioblastoma (GBM). However, the anatomical location and biological behavior of this neoplasm imposes great challenges for targeted therapies. A novel strategy that combines alpha-cyano-4-hydroxycinnamic acid (CHC) with the monoclonal antibody cetuximab (CTX), both carried onto a nanotechnology-based delivery system, is herein proposed for GBM treatment via nose-to-brain delivery. The biological performance of Poly (D,L-lactic-co-glycolic acid)/chitosan nanoparticles (NP), loaded with CHC, and conjugated with CTX by covalent bonds (conjugated NP) were extensively investigated. The NP platforms were able to control CHC release, indicating that drug release was driven by the Weibull model. An ex vivo study with nasal porcine mucosa demonstrated the capability of these systems to promote CHC and CTX permeation. Blot analysis confirmed that CTX, covalently associated to NP, impairs EGRF activation. The chicken chorioallantoic membrane assay demonstrated a trend of tumor reduction when conjugated NP were employed. Finally, images acquired by fluorescence tomography evidenced that the developed nanoplatform was effective in enabling nose-to-brain transport upon nasal administration. In conclusion, the developed delivery system exhibited suitability as an effective novel co-delivery approaches for GBM treatment upon intranasal administration.

Asymmetry in Drug Permeability through the Cornea

The permeability through the cornea determines the ability of a drug or any topically applied compound to cross the tissue and reach the intraocular area. Most of the permeability values found in the literature are obtained considering topical drug formulations, and therefore, refer to the drug permeability inward the eye. However, due to the asymmetry of the corneal tissue, outward drug permeability constitutes a more meaningful parameter when dealing with intraocular drug-delivery systems (i.e., drug-loaded intraocular lenses, intraocular implants or injections). Herein, the permeability coefficients of two commonly administered anti-inflammatory drugs (i.e., bromfenac sodium and dexamethasone sodium) were determined ex vivo using Franz diffusion cells and porcine corneas in both inward and outward configurations. A significantly higher drug accumulation in the cornea was detected in the outward direction, which is consistent with the different characteristics of the corneal layers. Coherently, a higher permeability coefficient was obtained for bromfenac sodium in the outward direction, but no differences were detected for dexamethasone sodium in the two directions. Drug accumulation in the cornea can prolong the therapeutic effect of intraocular drug-release systems.

Permeability of the Retina and RPE-Choroid-Sclera to Three Ophthalmic Drugs and the Associated Factors

In this study, Retina-RPE-Choroid-Sclera (RCS) and RPE-Choroid-Sclera (CS) were prepared by scraping them off neural retina, and using the Ussing chamber we measured the average time-concentration values in the acceptor chamber across five isolated rabbit tissues for each drug molecule. We determined the outward direction permeability of the RCS and CS and calculated the neural retina permeability. The permeability coefficients of RCS and CS were as follows: ganciclovir, 13.78 ± 5.82 and 23.22 ± 9.74; brimonidine, 15.34 ± 7.64 and 31.56 ± 12.46; bevacizumab, 0.0136 ± 0.0059 and 0.0612 ± 0.0264 (×10^-6 cm/s). The calculated permeability coefficients of the neural retina were as follows: ganciclovir, 33.89 ± 12.64; brimonidine, 29.83 ± 11.58; bevacizumab, 0.0205 ± 0.0074 (×10^-6 cm/s). Between brimonidine and ganciclovir, lipophilic brimonidine presented better RCS and CS permeability, whereas ganciclovir showed better calculated neural retinal permeability. The large molecular weight drug bevacizumab demonstrated a much lower permeability than brimonidine and ganciclovir. In conclusion, the ophthalmic drug permeability of RCS and CS is affected by the molecular weight and lipophilicity, and influences the intravitreal half-life.

Partitioning and Spatial Distribution of Drugs in Ocular Surface Tissues

Ocular drug absorption after eye drop instillation has been widely studied, but partitioning phenomena and spatial drug distribution are poorly understood. We investigated partitioning of seven beta-blocking drugs in corneal epithelium, corneal stroma, including endothelium and conjunctiva, using isolated porcine tissues and cultured human corneal epithelial cells. The chosen beta-blocking drugs had a wide range (-1.76-0.79) of n-octanol/buffer solution distribution coefficients at pH 7.4 (Log D_7.4). In addition, the ocular surface distribution of three beta-blocking drugs was determined by matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) after their simultaneous application in an eye drop to the rabbits in vivo. Studies with isolated porcine corneas revealed that the distribution coefficient (K_p) between the corneal epithelium and donor solution showed a positive relationship and good correlation with Log D_7.4 and about a 50-fold range of K_p values (0.1-5). On the contrary, K_p between corneal stroma and epithelium showed an inverse (negative) relationship and correlation with Log D_7.4 based on a seven-fold range of K_p values. In vitro corneal cell uptake showed a high correlation with the ex vivo corneal epithelium/donor K_p values. Partitioning of the drugs into the porcine conjunctiva also showed a positive relationship with lipophilicity, but the range of K_p values was less than with the corneal epithelium. MALDI-IMS allowed simultaneous detection of three compounds in the cornea, showed data in line with other experiments, and revealed uneven spatial drug distribution in the cornea. Our data indicate the importance of lipophilicity in defining the corneal pharmacokinetics and the K_p values are a useful building block in the kinetic simulation models for topical ocular drug administration.

Atorvastatin-Eluting Contact Lenses: Effects of Molecular Imprinting and Sterilization on Drug Loading and Release

Statins are receiving increasing attention in the ophthalmic field. Their activity as 3-hydroxy-3-methylglutaryl–CoA (HMG–CoA) reductase inhibitors is clinically used to regulate cholesterol levels and leads to pleiotropic effects, which may help in the management of diabetes-related ocular pathologies. This work aims to design bioinspired contact lenses (CLs) with an affinity for atorvastatin by mimicking the active site of HMG–CoA reductase. Sets of imprinted and nonimprinted 2-hydroxyethyl methacrylate (HEMA) hydrogels were synthesized, varying the contents in functional monomers that bear chemical groups that resemble those present in HMG–CoA reductase, namely, ethylene glycol phenyl ether methacrylate (EGPEM), 2-aminoethyl methacrylate hydrochloride (AEMA), and N-(3-aminopropyl) methacrylamide hydrochloride (APMA). The hydrogels were characterized in terms of suitability as CLs (solvent uptake, light transmission, mechanical properties, and biocompatibility) and capability to load and release atorvastatin. Three sterilization protocols (steam heat, gamma radiation, and high hydrostatic pressure) were implemented and their effects on hydrogel properties were evaluated. Copolymerization of AEMA and, particularly, APMA endowed the hydrogels with a high affinity for atorvastatin (up to 11 mg/g; K_N/W > 200). Only high hydrostatic pressure sterilization preserved atorvastatin stability and hydrogel performance. Permeability studies through the porcine cornea and sclera tissues revealed that the amount of atorvastatin accumulated in the cornea and sclera could be effective to treat ocular surface diseases.

Muscle Tissue as a Surrogate for In Vitro Drug Release Testing of Parenteral Depot Microspheres

Despite the importance of drug release testing of parenteral depot formulations, the current in vitro methods still require ameliorations in biorelevance. We have investigated here the use of muscle tissue components to better mimic the intramuscular administration. For convenient handling, muscle tissue was used in form of a freeze-dried powder, and a reproducible process of incorporation of tested microspheres to an assembly of muscle tissue of standardized dimensions was successfully developed. Microspheres were prepared from various grades of poly(lactic-co-glycolic acid) (PLGA) or ethyl cellulose, entrapping flurbiprofen, lidocaine, or risperidone. The deposition of microspheres in the muscle tissue or addition of only isolated lipids into the medium accelerated the release rate of all model drugs from microspheres prepared from ester-terminated PLGA grades and ethyl cellulose, however, not from the acid-terminated PLGA grades. The addition of lipids into the release medium increased the solubility of all model drugs; nonetheless, also interactions of the lipids with the polymer matrix (ad- and absorption) might be responsible for the faster drug release. As the in vivo drug release from implants is also often faster than in simple buffers in vitro, these findings suggest that interactions with the tissue lipids may play an important role in these still unexplained observations.

Thiolated cyclodextrins: Mucoadhesive and permeation enhancing excipients for ocular drug delivery

Thiolated β-cyclodextrin (β-CD) has the potential to enhance mucoadhesive and permeation enhancing properties on ocular mucosa. Thiolated β-CD was synthesized via replacement of all primary hydroxyl groups on β-CD backbone by halogen followed by substitution with thiol groups. The structure was confirmed by FT-IR and ¹H NMR spectroscopy. Thiolated CD was characterized for hemolytic effect, ocular irritation, solubility enhancement, viscoelastic behavior and mucoadhesive properties. Moreover, the permeation enhancing effect of thiolated oligomer on different ocular tissues including conjunctiva, sclera and cornea was evaluated with sodium fluorescein (Na-Flu) as a marker. Thiolated β-CD displayed 5360 ± 412 µmol/g thiol groups. The newly synthesized oligomer did not show any hemolytic effect on red blood cells at a concentration of 0.5% (m/v) for an incubation period of 3 h and minimal corneal irritation effects without any inflammation within 72 h. Thiolated β-CD exhibited a 5.3-fold improved aqueous solubility as compared to the unmodified β-CD. Thiolated oligomer (0.5% m/v) enhanced the viscosity of mucus up to 6.2-fold within 4 h and provided a 26-fold prolonged ocular residence time due to mucoadhesion. Moreover, 0.5% (m/v) thiolated β-CD enhanced the permeation of Na-Flu 9.6-, 7.1- and 5.3-fold on conjunctiva, sclera and cornea, respectively. Based on these findings, thiolated β-CD might be a promising auxiliary agent for ocular drug delivery.

Enhancement in corneal permeability of riboflavin using cyclodextrin derivates complexes as a previous step to transepithelial cross-linking

Corneal cross-linking has been described as an effective treatment to slow the progression of keratoconus. The standard protocol entails corneal epithelial removal to allow the diffusion of riboflavin into the stroma. Although, de-epithelization can generate risks or complications that transepithelial cross-linking tries to solve or avoid. Different formulations were developed after verifying that hydroxypropyl-β-cyclodextrin (HPβCD) and sulfobuthylether-β-cyclodextrin (SBEβCD) in a 20% concentration, increased the solubility of practically insoluble in water drugs such as riboflavin from 0.12 mg/mL to 0.35 mg/mL and 0.29 mg/mL respectively. These values were higher when chitosan and arginine were added to the formulation, showing solubility of 0.78 mg/mL when HPβCD concentration was not modified. Ex vivo corneal permeability was measured after having kept in contact bovine corneas with intact epithelium for 5 h with the 0.1 mg/mL riboflavin solution, the formulations developed and a reproduced nanoemulsion from another work. Riboflavin's permeability was increased when cyclodextrins, chitosan, and arginine were part of the formulations, compared to the control drug solution. The best permeability coefficient was reached when riboflavin was combined with 40% (w/v) HPβCD, 0.5% (w/w) arginine, and 0.5% (w/w) chitosan. After having carried out toxicity studies as bovine corneal opacity and permeability (BCOP) and Heńs Egg Test - Chorioallantoic Membrane Test (HET-CAM) it was verified that both, the active ingredients and the excipients of the different formulations were not harmful without generating irritation, loss of transparency or corneal permeability alterations. The results show the great potential of the ocular developed solution for their use in transepithelial cross-linking for keratoconus treatment.

Distribution of polymeric nanoparticles in the eye: implications in ocular disease therapy

Advantages of polymeric nanoparticles as drug delivery systems include controlled release, enhanced drug stability and bioavailability, and specific tissue targeting. Nanoparticle properties such as hydrophobicity, size, and charge, mucoadhesion, and surface ligands, as well as administration route and suspension media affect their ability to overcome ocular barriers and distribute in the eye, and must be carefully designed for specific target tissues and ocular diseases. This review seeks to discuss the available literature on the biodistribution of polymeric nanoparticles and discuss the effects of nanoparticle composition and administration method on their ocular penetration, distribution, elimination, toxicity, and efficacy, with potential impact on clinical applications.

Ciprofloxacin self-dissolvable Soluplus based polymeric films: a novel proposal to improve the management of eye infections

Infections of the eye are among the leading causes of vision impairment and vision loss worldwide. The ability of a drug to access the anterior parts of the eye is negligible after systemic administration. Effective drug delivery to the eye is a major challenge due to the presence of protective mechanisms and physiological barriers that result in low ocular availability after topical application. The main purpose of this work was the improvement of the corneal and conjunctival permeation of the antibiotic Ciprofloxacin, a wide spectrum antibiotic used for the most common eye infection, using a self-dissolving polymeric film. Films were prepared by the solvent casting technique, using polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft co-polymer (Soluplus), polyvynyl alcohol, and propylene glycol. Films were homogeneous in drug content and thickness, as demonstrated by adapting the Swiss Roll technique followed by microscopy observation. These films proved in vitro to control the release of the Ciprofloxacin. Ex vivo permeability studies using Franz diffusion cells and porcine cornea and sclera showed an effective permeability of the drug without inducing irritation of the tissues. Films swelled in contact with artificial tears forming an in situ gel over 20 min, which will improve drug contact and reduce the need of multiple dosing. The antibiotic activity was also tested in vitro in five types of bacterial cultures, assuring the pharmacological efficacy of the films. The developed films are a promising drug delivery system to topically treat or prevent ocular infections.

Therapeutic nanoemulsions in ophthalmic drug administration: Concept in formulations and characterization techniques for ocular drug delivery

The eye is the specialized part of the body and is comprised of numerous physiological ocular barriers that limit the drug absorption at the action site. Regardless of various efforts, efficient topical ophthalmic drug delivery remains unsolved, and thus, it is extremely necessary to advance the contemporary treatments of ocular disorders affecting the anterior and posterior cavities. Nowadays, the advent of nanotechnology-based multicomponent nanoemulsions for ophthalmic drug delivery has gained popularity due to the enhancement of ocular penetrability, improve bioavailability, increase solubility, and stability of lipophilic drugs. Nanoemulsions offer the sustained/controlled drug release and increase residence time which depend on viscosity, compositions, and stabilization process, etc.; hence, decrease the instillation frequency and improve patient compliance. Further, due to the nanosized of nanoemulsions, the sterilization process is easy as conventional solutions and cause no blur vision. The review aims to summarizes the various ocular barriers, manufacturing techniques, possible mechanisms to the retention and deep penetration into the eye, and appropriate excipients with their under-lying selection principles to prevent destabilization of nanoemulsions. This review also discusses the characterization parameters of ocular drug delivery to spike the interest of those contemplating a foray in this field. Here, in short, nanoemulsions are abridged with concepts to design clinically advantageous ocular drug delivery.

Imprinted Contact Lenses for Ocular Administration of Antiviral Drugs

A variety of ocular diseases are caused by viruses, and most treatments rely on the use of systemic formulations and eye drops. The efficient ocular barriers that oppose antiviral drug penetration have prompted the development of improved topical delivery platforms. The aim was to design hydrogel contact lenses endowed with an affinity for acyclovir (ACV) and its prodrug valacyclovir (VACV), first-choice drugs against herpes simplex virus (HSV) ocular keratitis, and that can sustain the release of therapeutic doses during daily wearing. Functional monomers suitable for interaction with these drugs were screened using computational modeling. Imprinted and non-imprinted hydrogels were prepared with various contents in the functional monomer methacrylic acid (MAA) and characterized in terms of swelling, transmittance, mechanical properties, and ocular compatibility (hen’s egg test on chorioallantoic membrane (HET-CAM) assay). The values were in the range typical of soft contact lenses. Compared to ACV, the capability to load VACV was remarkably higher due to stronger electrostatic interactions with MAA. The advantages of the imprinting technology were evidenced for VACV. Stability of VACV loading solution/hydrogels under steam heat sterilization and subsequent drug release was investigated. Permeability studies through bovine and porcine cornea and sclera of the drug released from the hydrogels revealed that VACV accumulates in the cornea and can easily cross the sclera, which may facilitate the treatment of both anterior and posterior eye segments diseases.

Corneal and scleral permeability of Desmoteplase in different species

OBJECTIVE

Intraocular fibrin clots caused by severe uveitis can be a sight-threatening condition that needs to be resolved quickly and reliably. Intracameral injection of tissue-plasminogen activator (tPA) is commonly used to resolve intraocular fibrin. However, the drug does not reach fibrinolytic concentrations after topical application. Desmoteplase (DSPA) is a structurally similar but smaller fibrinolytic agent with a higher fibrin selectivity, a longer half-life, and better biocompatibility compared with tPA. This study was designed to evaluate the corneal and scleral permeability of DSPA in rabbits, pigs, dogs, horses, and humans ex vivo.

PROCEDURES

Corneal and scleral tissues (n = 5 per group) were inserted into Franz-type diffusion chambers and exposed to 1.4 mg/mL DSPA for 30 minutes. Drug concentrations on the receiver side were determined by liquid chromatography-tandem mass spectrometry.

RESULTS

Concentrations of DSPA after corneal and scleral permeation through fresh tissues ranged from 0.0 to 16.3 µg/mL and 0.0 to 11.4 µg/mL (rabbits), 0.3 to 5.6 µg/mL and 3.1 to 9.2 µg/mL (dogs), 2.1 to 14.9 µg/mL and 4 to 8.7 µg/mL (horses), and 0.6 to 3 µg/mL and 2.9 to 18.1 µg/mL (pigs), respectively. A concentration of 0.07-12.9 µg/mL DSPA was detectable after diffusion through tissue culture preserved human donor bank corneas (Table 1).

CONCLUSIONS

Desmoteplase has the ability to permeate both cornea and sclera ex vivo in all species tested. Implications of the ex vivo permeability of DSPA suggest that in vivo permeability may be possible, and if so, it could lead to a novel topical application for lysing fibrin.

Potential Therapeutic Usage of Nanomedicine for Glaucoma Treatment

Glaucoma is a group of diseases characterized by progressive degeneration of retinal ganglion cells, leading to irreversible blindness. Currently, intraocular pressure reduction is the only established treatment available for glaucoma. With this treatment, the progression of the disease can only be delayed and there is no recovery. In addition, the commercially available eye drops have the disadvantage of low compliance and short therapeutic time, while glaucoma surgery always has the risk of failure due to wound fibrosis. Nanotechnology can overcome the limitations of the current treatment through the encapsulation and conjugation of drugs used for lowering intraocular pressure and antifibrotic agents using biodegradable or biocompatible nanoparticles for the sustained release of the drugs to protect the damaged ocular cells. Furthermore, using nanotechnology, treatment can be administered in various forms, including eye drops, contact lens, and ocular inserts, according to the convenience of the patients. Despite the promising results of delaying the progression of glaucoma, the regeneration of damaged ocular cells, including trabecular meshwork and retinal ganglion cells, is another critical hurdle to overcome. Bone marrow-derived mesenchymal stem cells and Müller glia cells can secrete neurogenic factors that trigger the regeneration of associated cells, including trabecular meshwork and retinal ganglion cells. In conclusion, this review highlights the potential therapeutic applications of nanotechnology- and stem cell-based methods that can be employed for the protection and regeneration of ocular cells.

Micelles of Progesterone for Topical Eye Administration: Interspecies and Intertissues Differences in Ex Vivo Ocular Permeability

Progesterone (PG) may provide protection to the retina during retinitis pigmentosa, but its topical ocular supply is hampered by PG poor aqueous solubility and low ocular bioavailability. The development of efficient topical ocular forms must face up to two relevant challenges: Protective barriers of the eyes and lack of validated ex vivo tests to predict drug permeability. The aims of this study were: (i) To design micelles using Pluronic F68 and Soluplus copolymers to overcome PG solubility and permeability; and (ii) to compare drug diffusion through the cornea and sclera of three animal species (rabbit, porcine, and bovine) to investigate interspecies differences. Micelles of Pluronic F68 (3–4 nm) and Soluplus (52–59 nm) increased PG solubility by one and two orders of magnitude, respectively and exhibited nearly a 100% encapsulation efficiency. Soluplus systems showed in situ gelling capability in contrast to the low viscosity Pluronic F68 micelles. The formulations successfully passed the hen’s egg-chorioallantoic membrane test (HET-CAM) test. PG penetration through rabbit cornea and sclera was faster than through porcine or bovine cornea, although the differences were also formulation-dependent. Porcine tissues showed intermediate permeability between rabbit and bovine. Soluplus micelles allowed greater PG accumulation in cornea and sclera whereas Pluronic F68 promoted a faster penetration of lower PG doses.

Intravitreal hydrogels for sustained release of therapeutic proteins

This review highlights how hydrogel formulations can improve intravitreal protein delivery to the posterior segment of the eye in order to increase therapeutic outcome and patient compliance. Several therapeutic proteins have shown excellent clinical successes for the treatment of various intraocular diseases. However, drug delivery to the posterior segment of the eye faces significant challenges due to multiple physiological barriers preventing drugs from reaching the retina, among which intravitreal protein instability and rapid clearance from the site of injection. Hence, frequent injections are required to maintain therapeutic levels. Moreover, because the world population ages, the number of patients suffering from ocular diseases, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) is increasing and causing increased health care costs. Therefore, there is a growing need for suitable delivery systems able to tackle the current limitations in retinal protein delivery, which also may reduce costs. Hydrogels have shown to be promising delivery systems capable of sustaining release of therapeutic proteins and thus extending their local presence. Here, an extensive overview of preclinically developed intravitreal hydrogels is provided with attention to the rational design of clinically useful intravitreal systems. The currently used polymers, crosslinking mechanisms, in vitro/in vivo models and advancements are discussed together with the limitations and future perspective of these biomaterials.

Delineating penetration enhancer-enriched liquid crystalline nanostructures as novel platforms for improved ophthalmic delivery

Liquid crystalline nanostructures (LCNs), for instance cubosomes, have been widely used as a promising carrier for drug delivery through the last few years. To date, the ophthalmic application of these platforms was not well explored, and the effect of integrating penetration enhancers (PEs) into LCNs has not been investigated yet. Hence, the present work aimed coupling novel PEs into glyceryl monooleate-based cubosomes for ocular administration. Various enhancers viz, free fatty acids (oleic and linoleic acids), natural terpenes (D-limonene and cineole), medium-chain triglycerides (Captex® 1000 and Captex® 8000), mono-/di-glycerides (Capmul® MCM, Capmul® PG-8, and Capmul® PG-12) were tested at different amounts. The morphology of the formed LCNs was investigated using transmission electron microscopy (TEM). The crystallinity and thermal behavior studies were also conducted. The ocular safety of optimized formulae was tested via hen's egg test-chorioallantoic membrane (HET-CAM), rabbit eye Draize test, and histopathological examinations of ocular tissues. Confocal laser scanning microscopy (CLSM) was utilized to assess the enhanced permeation of fluorescently-labeled LCNs across corneal layers. The acceptable formulations exhibited relatively homogenous particle nano-sizes ranging from 139.26 ± 3.68 to 590.56 ± 24.86 nm carrying negative surface charges. TEM images, X-ray patterns and DSC thermograms demonstrated the influential effect of PEs in developing altered crystalline structures. The ocular compatibility of optimized LCNs was confirmed. The corneal distribution using CLSM proved the disseminated fluorescence intensity of LCNs enriched with oleic acid, Captex® 8000 and Capmul® MCM. Selected LCNs showed good physical stability upon storage and lyophilization. The results demonstrated the efficiency of tailored PE-modified LCNs in enhancing the ocular transport with no evidence of any irritation potential, and hence suggested their prospective applicability in ophthalmic drug delivery.

In Vitro and Ex Vivo Evaluation of Nepafenac-Based Cyclodextrin Microparticles for Treatment of Eye Inflammation

The aim of this study was to design and evaluate novel cyclodextrin (CD)-based aggregate formulations to efficiently deliver nepafenac topically to the eye structure, to treat inflammation and increase nepafenac levels in the posterior segment, thus attenuating the response of inflammatory mediators. The physicochemical properties of nine aggregate formulations containing nepafenac/γ-CD/hydroxypropyl-β (HPβ)-CD complexes as well as their rheological properties, mucoadhesion, ocular irritancy, corneal and scleral permeability, and anti-inflammatory activity were investigated in detail. The results were compared with a commercially available nepafenac suspension, Nevanac^® 3 mg/mL. All formulations showed microparticles, neutral pH, and negative zeta potential (–6 to –27 mV). They were non-irritating and nontoxic and showed high permeation through bovine sclera. Formulations containing carboxymethyl cellulose (CMC) showed greater anti-inflammatory activity, even higher than the commercial formulation, Nevanac^® 0.3%. The optimized formulations represent an opportunity for topical instillation of drugs to the posterior segment of the eye.

Vitreous humor endogenous compounds analysis for post-mortem forensic investigation

The chemical and biochemical analysis of bodily fluids after death is an important thanatochemical approach to assess the cause and time since death. Vitreous humor (VH) has been used as a biofluid for forensic purposes since the 1960s. Due to its established relevance in toxicology, a literature review highlighting the use of VH with an emphasis on endogenous compounds has not yet been undertaken. VH is a chemically complex aqueous solution of carbohydrates, proteins, electrolytes and other small molecules present in living organisms; this biofluid is useful tool for its isolated environment, preserved from bacterial contamination, decomposition, autolysis, and metabolic reactions. The post-mortem analysis of VH provides an important tool for the estimation of the post-mortem interval (PMI), which can be helpful in determining the cause of death. Consequently, the present review evaluates the recent chemical and biochemical advances with particular importance on the endogenous compounds present at the time of death and their modification over time, which are valuable for the PMI prediction and to identify the cause of death.

Cytosine-functionalized bioinspired hydrogels for ocular delivery of antioxidant transferulic acid

Contact lenses (CLs) are being pointed out as feasible platforms for controlled delivery of ophthalmic drugs. Bioinspired strategies may endow CLs with affinity for a given drug by mimicking its physiological receptor using adequate functional monomers and tuning their conformation in the space through the molecular imprinting technology. However, there are some active substances, such as efficient antioxidant agents, that cannot be used as templates because they degrade during polymerization or even hinder the polymerization itself. Therefore, the development of CLs able to sustain the release of antioxidants for the prevention and/or treatment of several age-related and light-induced eye diseases has not been explored yet. Searching for an alternative bioinspired strategy, the present work relies on the fact that some drugs owe their therapeutic action to their ability to interact with nucleotides that build up DNA and RNA. Thus, the aim of this work was to design hydrogels functionalized with the nitrogenous base cytosine for the controlled uptake and release of transferulic acid (TA) having a complementary chemical structure in terms of hydrogen bonding and π-π stacking ability. Hydrogels were prepared from mixtures of 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA) and ethyleneglycolphenylether methacrylate (EGPEM). GMA was used as a bridge to immobilize cytosine after hydrogel synthesis, while EGPEM was added to reinforce hydrophobic interactions with TA. The hydrogels were characterized in terms of suitability to be used as CLs (swelling, light transmission, mechanical properties, biocompatibility) and capability to host TA and sustain its release in lachrymal fluid while maintaining the antioxidant activity. Relevantly, the bioinspired CLs favored TA accumulation in cornea and sclera tissues.

Nanotechnology for Medical and Surgical Glaucoma Therapy-A Review

Glaucoma is the second leading cause of blindness worldwide. Even though significant advances have been made in its management, currently available antiglaucoma therapies suffer from considerable drawbacks. Typically, the success and efficacy of glaucoma medications are undermined by their limited bioavailability to target tissues and the inadequate adherence demonstrated by patients with glaucoma. The latter is due to a gradual decrease in tolerability of lifelong topical therapies and the significant burden to patients of prescribed stepwise antiglaucoma regimens with frequent dosing which impact quality of life. On the other hand, glaucoma surgery is restricted by the inability of antifibrotic agents to efficiently control the wound healing process without causing severe collateral damage and long-term complications. Evolution of the treatment paradigm for patients with glaucoma will ideally include prevention of retinal ganglion cell degeneration by the successful delivery of neurotrophic factors, anti-inflammatory drugs, and gene therapies. Nanotechnology-based treatments may surpass the limitations of currently available glaucoma therapies through optimized targeted drug delivery, increased bioavailability, and controlled release. This review addresses the recent advances in glaucoma treatment strategies employing nanotechnology, including medical and surgical management, neuroregeneration, and neuroprotection.

Influence of the mechanical properties of biomaterials on degradability, cell behaviors and signaling pathways: current progress and challenges

We have clarified the influence of the mechanical properties of biomaterials on degradability and cell response, and also mechanical design targets and approaches.

Hollow Microcapsules as Periocular Drug Depot for Sustained Release of Anti-VEGF Protein

Diseases affecting the posterior segment of the eye such as age-related macular degeneration and diabetic retinopathy are leading causes of blindness all over the world. The current treatment regimen for such diseases involves repeated intravitreal injections of anti- Vascular Endothelial Growth Factor (VEGF) proteins. This method is highly invasive and can lead to severe complications. In an attempt to develop less invasive alternatives, we propose the use of a controlled release system consisting of anti-VEGF loaded hollow microcapsules that can be administered periocularly to form drug eluting depots on the episcleral surface. The microcapsules with either positive or negative surface charge were prepared by a layer by layer approach and showed pH responsive permeability switching. An ex vivo experiment using porcine sclera indicated positively charged microcapsules remained on the episcleral surface over four days while the negatively charged microcapsules were washed away. These positively charged microcapsules were then loaded with anti-VEGF protein ranibizumab using pH dependent permeability switching and protein release from the microcapsules were studied using an in vitro setup. An ex vivo experiment utilizing porcine sclera demonstrated sustained release of ranibizumab over seven days with zero-order kinetics.

Penetration Enhancers in Ocular Drug Delivery

There are more than 100 recognized disorders of the eye. This makes the development of advanced ocular formulations an important topic in pharmaceutical science. One of the ways to improve drug delivery to the eye is the use of penetration enhancers. These are defined as compounds capable of enhancing drug permeability across ocular membranes. This review paper provides an overview of anatomical and physiological features of the eye and discusses some common ophthalmological conditions and permeability of ocular membranes. The review also presents the analysis of literature on the use of penetration-enhancing compounds (cyclodextrins, chelating agents, crown ethers, bile acids and bile salts, cell-penetrating peptides, and other amphiphilic compounds) in ocular drug delivery, describing their properties and modes of action.

Cyclodextrin⁻Amphiphilic Copolymer Supramolecular Assemblies for the Ocular Delivery of Natamycin

Natamycin is the only drug approved for fungal keratitis treatment, but its low water solubility and low ocular penetration limit its efficacy. The purpose of this study was to overcome these limitations by encapsulating the drug in single or mixed micelles and poly(pseudo)rotaxanes. Soluplus and Pluronic P103 dispersions were prepared in 0.9% NaCl and pH 6.4 buffer, with or without α-cyclodextrin (αCD; 10% w/v), and characterized through particle size, zeta potential, solubilization efficiency, rheological properties, ocular tolerance, in vitro drug diffusion, and ex vivo permeation studies. Soluplus micelles (90–103 nm) and mixed micelles (150–110 nm) were larger than Pluronic P103 ones (16–20 nm), but all showed zeta potentials close to zero. Soluplus, Pluronic P103, and their mixed micelles increased natamycin solubility up to 6.00-fold, 3.27-fold, and 2.77-fold, respectively. Soluplus dispersions and poly(pseudo)rotaxanes exhibited in situ gelling capability, and they transformed into weak gels above 30 °C. All the formulations were non-irritant according to Hen’s Egg Test on the Chorioallantoic Membrane (HET-CAM) assay. Poly(pseudo)rotaxanes facilitated drug accumulation into the cornea and sclera, but led to lower natamycin permeability through the sclera than the corresponding micelles. Poly(pseudo)rotaxanes made from mixed micelles showed intermediate natamycin diffusion coefficients and permeability values between those of Pluronic P103-based and Soluplus-based poly(pseudo)rotaxanes. Therefore, the preparation of mixed micelles may be a useful tool to regulate drug release and enhance ocular permeability.

Biopharmaceutical evaluation of surface active ophthalmic excipients using in vitro and ex vivo corneal models

The objective of this study was to systematically investigate the effects of surface active ophthalmic excipients on the corneal permeation of ophthalmic drugs using in vitro (HCE-T cell-based model) and ex vivo (freshly excised porcine cornea) models. The permeation of four ophthalmic drugs (i.e., timolol maleate, chloramphenicol, diclofenac sodium and dexamethasone) across in vitro and ex vivo corneal models was evaluated in the absence and presence of four commonly used surface active ophthalmic excipients (i.e., Polysorbate 80, Tyloxapol, Cremophor® EL and Pluronic® F68). The concentration and self-aggregation-dependent effects of surface active ophthalmic excipients on ophthalmic drug permeability were studied from the concentration region where only dissolved monomer molecules of surface active ophthalmic excipients exist, as well as the concentration region in which aggregates of variable size and dispersion are spontaneously formed. Neither the surface active ophthalmic excipients nor the ophthalmic drugs at all concentrations that were tested significantly affected the barrier properties of both corneal models, as assessed by transepithelial electrical resistance (TEER) monitoring during the permeability experiments. The lowest concentration of all investigated surface active ophthalmic excipients did not significantly affect the ophthalmic drug permeability across both of the corneal models that were used. For three ophthalmic drugs (i.e., chloramphenicol, diclofenac sodium and dexamethasone), depressed in vitro and ex vivo permeability were observed in the concentration range of either Polysorbate 80, Tyloxapol, Cremophor® EL or Pluronic® F68, at which self-aggregation is detected. The effect was the most pronounced for Cremophor® EL (1 and 2%, w/V) and was the least pronounced for Pluronic® F68 (1%, w/V). However, all surface active ophthalmic excipients over the entire concentration range that was tested did not significantly affect the in vitro and ex vivo permeability of timolol maleate, which is the most hydrophilic ophthalmic drug that was investigated. The results of the dynamic light scattering measurements point to the association of ophthalmic drugs with self-aggregates of surface active ophthalmic excipients as the potential mechanism of the observed permeability-depressing effect of surface active ophthalmic excipients. A strong and statistically significant correlation was observed between in vitro and ex vivo permeability of ophthalmic drugs in the presence of surface active ophthalmic excipients, which indicates that the observed permeability-altering effects of surface active ophthalmic excipients were comparable and were mediated by the same mechanism in both corneal models.

Corneal and conjunctival drug permeability: Systematic comparison and pharmacokinetic impact in the eye

On the surface of the eye, both the cornea and conjunctiva are restricting ocular absorption of topically applied drugs, but barrier contributions of these two membranes have not been systemically compared. Herein, we studied permeability of 32 small molecular drug compounds across an isolated porcine cornea and built a quantitative structure-property relationship (QSPR) model for the permeability. Corneal drug permeability (data obtained for 25 drug molecules) showed a 52-fold range in permeability (0.09-4.70 × 10^-6 cm/s) and the most important molecular descriptors in predicting the permeability were hydrogen bond donor, polar surface area and halogen ratio. Corneal permeability values were compared to their conjunctival drug permeability values. Ocular drug bioavailability and systemic absorption via conjunctiva were predicted for this drug set with pharmacokinetic calculations. Drug bioavailability in the aqueous humour was simulated to be <5% and trans-conjunctival systemic absorption was 34-79% of the dose. Loss of drug across the conjunctiva to the blood circulation restricts significantly ocular drug bioavailability and, therefore, ocular absorption does not increase proportionally with the increasing corneal drug permeability.

Dry eye following cataract surgery: The effect of light exposure using an in-vitro model

PURPOSE

Cataract surgery can lead to the temporary development or worsening of dry eye symptoms. Contributing factors may include corneal incisions, agents used before, during or after surgery, light from the operating microscope, disruption of ocular surface tissues and inflammatory processes. The purpose of this study was to observe the effect of light exposure on conjunctival fibroblasts in order to determine whether light has an effect on wound healing closure, assuming that operating microscopes might have an effect on the ocular surface.

METHOD

An in vitro scratch assay was performed on porcine conjunctival fibroblasts. Ten minutes of light exposure from a light microscope with a halogen bulb was performed after the scratch assay. Fibroblasts were kept in culture for 48 hours post-exposure and the wound closure rates were visualized by live/dead staining. The fibroblasts which were exposed to light were compared to those without light exposure. Cell viability was also analysed by MTT assay.

RESULTS

A Slower wound closure rate was found when fibroblasts were exposed to light compared to the non-light exposed controls. Cell viability reduced by 20% with light exposure compared to controls in p3 cells (p = 0.04; however, the trend was not observed with p4 and p5 cells (p > 0.05).

CONCLUSIONS

These results suggest that light exposure might be one of the possible contributory factors for dry eye after ophthalmic surgery. Further evaluation of light effects should be carried out with different ocular surface cells.