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

Improving corneal permeability of dexamethasone using penetration enhancing agents: First step towards achieving topical drug delivery to the retina

With an ever-increasing burden of vision loss caused by diseases of the posterior ocular segment, there is an unmet clinical need for non-invasive treatment strategies. Topical drug application using eye drops suffers from low to negligible bioavailability to the posterior segment as a result of static and dynamic defensive ocular barriers to penetration, while invasive delivery systems are expensive to administer and suffer potentially severe complications. As the cornea is the main anatomical barrier to uptake of topically applied drugs from the ocular surface, we present an approach to increase corneal permeability of a corticosteroid, dexamethasone sodium-phosphate (DSP), using a novel penetration enhancing agent (PEA). We synthesised a novel polyacetylene (pAc) polymer and compared its activity to two previously described cell penetrating peptide (CPP) based PEAs, TAT and penetratin, with respect to increasing transcorneal permeability of DSP in a rapid ex-vivo porcine corneal assay over 60 min. The transcorneal apparent permeability coefficients (Papp) for diffusion of pAc, and fluorescein isothiocyanate (FITC) conjugated TAT and penetratin were up to 5 times higher (p < 0.001), when compared to controls. When pAc was used in formulation with DSP, an almost 5-fold significant increase was observed in Papp of DSP across the cornea (p = 0.0130), a significant 6-fold increase with TAT (p = 0.0377), and almost 7-fold mean increase with penetratin (p = 0.9540). Furthermore, we investigated whether the PEAs caused any irreversible damage to the barrier integrity of the corneal epithelium by measuring transepithelial electrical resistance (TEER) and immunostaining of tight junction proteins using zonula occludens-1 (ZO-1) and occludin antibodies. There was no damage or structural toxicity, and the barrier integrity was preserved after PEA application. Finally, an in-vitro cytotoxicity assessment of all PEAs in human retinal pigment epithelium cells (ARPE-19) demonstrated that all PEAs were very well-tolerated, with IC50 values of 64.79 mM for pAc and 1335.45 µM and 87.26 µM for TAT and penetratin, respectively. Our results suggest that this drug delivery technology could potentially be used to achieve a significantly higher intraocular therapeutic bioavailability after topical eye drop administration, than currently afforded.

Design and validation of a custom-made system to measure transepithelial electrical impedance in human corneas preserved in active storage machine

Corneal epithelial barrier represents one of the major limitations to ocular drug delivery and can be explored non-invasively through the evaluation of its electrical properties. Human corneas stored in active storage machine (ASM) could represent an interesting physiological model to explore transcorneal drug penetration. We designed a new system adapted to human corneas preserved in ASM to explore corneal epithelial barrier function ex-vivo. A bipolar set-up including Ag/AgCl electrodes adaptors to fit the corneal ASM and a dedicated software was designed and tested on freshly excised porcine corneas (n = 59) and human corneas stored 14 days in ASM (n = 6). Porcine corneas presented significant and proportional decrease in corneal impedance in response to increasing-size epithelial ulcerations and acute exposure to benzalkonium chloride (BAC) 0.01 and 0.05%. Human corneas stored 14 days in ASM presented a significant increase in corneal impedance associated with the restoration of a multi-layer epithelium and an enhanced expression of tight junctions markers zonula occludens 1, claudin 1 and occludin. These results support the relevance of the developed approach to pursue the exploration and development of human corneas stored in ASM as a physiological pharmacological model.

Dynamic Ex Vivo Porcine Eye Model to Measure Ophthalmic Drug Penetration under Simulated Lacrimal Flow

Animal models are still used in the research and development of ophthalmic drug products, mainly due to the difficulty in simulating natural physiological conditions with in vitro models, as there is a lack of dynamic protection mechanisms. Therefore, developing alternative ophthalmic models that evaluate drug penetration in the cornea while applying dynamic protection barriers is a contemporary challenge. This study aimed to develop a dynamic ex vivo model using porcine eyes with a simulated lacrimal flow to evaluate the performance of pharmaceutical drug products. A glass donor cell to support a simulated tear flow was designed, optimized, and custom-made. The system was challenged with different formulations (with fluconazole) including excipients with different viscosities (poloxamer 407) and mucoadhesive properties (chitosan). The results were compared to those obtained from a conventional excised cornea model mounted in Franz-type diffusion cells. The dynamic model could differentiate formulations, while the static model did not, overestimating ex vivo drug penetrated amounts. Hence, the dynamic model with simulated tear flow showed to be a simple and promising new alternative method for the drug penetration of ophthalmic formulations that ultimately can reduce the number of animals used in research.

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.

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.

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.

SCD1-Fatty Acid Desaturase Inhibitor MF-438 Alleviates Latent Inflammation Induced by Preservative-Free Prostaglandin Analog Eye Drops

Introduction

Prostaglandin analogs are the first line of treatment in patients with glaucoma. Recently, many preservative-free prostaglandin analogs have been marketed to increase their tolerance in chronic use. However, potentially safer formulations have been reported to induce inflammation within ocular surface and adnexa, associated with pronounced activation of tissue macrophages.

Aim

We aimed to evaluate the effect of a Stearoyl-CoA desaturase-1 (SCD1) inhibitor, MF-438, on the differentiation of monocytes exposed to eye drop detergents, representing saturated fatty acid derivatives.

Methods

A culture of human peripheral blood monocytes was exposed to eye drops containing fatty acid derivatives (eye drop detergents), pf-latanoprost (Monoprost^®, hydroxystearate macrogolglycerol – MGHS40) or pf-tafluprost (Taflotan^®, polysorbate 80 – PS80), as well as pf-latanoprost+MF-438, MGHS40, and PS80. For the negative control C(-), monocytes were cultured in basal medium, and for the positive controls, monocytes were stimulated with Lipopolysaccharide (LPS) and Interferon γ (IFNγ) (M1 macrophages) or Interleukin-4 (IL-4) (M2 macrophages). The concentration of desaturase in the cell homogenates was determined by ELISA. The number of cells was counted under a microscope at 20x magnification.

Results

The following concentrations of SCD1 (ng/mL) were measured: 7.8±0.3 – pf-latanoprost group; 1.5±0.4 – pf-tafluprost group; 6.8±0.7 – MGHS40 group; 0.4±0.002 – PS80 group; 0.9±0.02 – pf-latanoprost+MF-438 group; 5.4±1.6 – C(-) control; 0.5±0.04 – M1 control; 2.2±0.13 – M2 control. The percentages of macrophages in culture were 33.6%, 17.6%, 33%, 0%, 13.5%, 18.6%, 36.3%, and 39.3% for the pf-latanoprost, pf-tafluprost, MGHS40, PS80, pf-latanoprost+MF-438, C(-), M1, and M2 cultures, respectively. There was a strong correlation between SCD1 concentration and macrophage count in the culture (r=0.8, p<0.05).

Conclusion

Inhibition of SCD1 in monocytes prevents their transformation into macrophages after exposure to saturated fatty acid derivatives contained in eye drops, which may contribute to the limitation of latent inflammation within ocular adnexa and could possibly translate into better tolerability of the topical treatment.

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Preparation, in vitro and in vivo evaluation of chitosan-sodium alginate-ethyl cellulose polyelectrolyte film as a novel buccal mucosal delivery vehicle

This paper describes the development of a film comprising chitosan (CS), sodium alginate (SA), and ethyl cellulose (EC) for buccal mucosal administration. A film of CS-SA unidirectional release drug-containing water-repellent layer EC was produced by interfacial reaction solvent-drying technique using self-made equipment. The CS-SA-EC film had superior mechanical properties compared to CS-EC and SA-EC films. The existence of the amide bond was confirmed by FT-IR. DSC confirmed that the drug was dispersed in the carrier material in an amorphous form. The drug release studies emerged that the model drugs from CS-SA-EC films presented better release properties. The Ritger-Peppas model best describes all ratios of drugs release mechanisms. The permeability characteristics of the films were evaluated in the TR146 cells model and the rabbit buccal mucosae. The cumulative penetration amounts of the model drugs were significantly increased. The permeability mechanism of the film was studied preliminarily using immunofluorescence and Western Blot. The results showed that the film inhibited the expression of ZO-1 protein, and the expressive trend of ZO-1 protein was consistent with the results of in vitro permeation experiments. The pharmacokinetics of the drugs loaded films were evaluated and compared with oral administration in rats. The relative bioavailability of the model drugs was 246.00% (Zolmitriptan) and 142.12% (Etodolac) relative to oral administration. The results of this study demonstrate the potential of CS-SA-EC vehicle in buccal mucosa drug delivery.

Intraocular Scattering, Blinking Rate, and Tear Film Osmolarity After Exposure to Environmental Stress

Purpose

Dry environments, such as those in offices or aircraft cabins, can potentially generate ocular discomfort and alter the tear film. We compare light scatter, blinking rate, and tear osmolarity in young and older subjects after exposure to low humidity using a controlled environmental chamber.

Methods

Two groups of healthy subjects were recruited; younger (N = 13, 27 ± 6 years) and older (N = 23, 71 ± 7 years). Measurements were carried out before and after 90-minute exposure to low relative humidity (5%) and constant temperature (23 degrees). Ocular light scatter was measured using a double-pass instrument (OQAS, Visiometrics, Spain). Blinking rate was monitored using an infrared video camera. Tear osmolarity was measured using the TearLab system (Escondido, CA, USA).

Results

Ocular light scatter increased by a factor of 10% after exposure to low humidity in the older group (P = 0.03) but did not change significantly in the younger group. Blinking rate increased significantly (40% more blinks) in both groups but there was no difference between the groups. No significant differences in osmolarity were shown between two age groups or as result of environmental stress.

Conclusions

Exposure to dry environment increased light scatter in older subjects. Although more blinks were triggered in both younger and older groups to prevent corneal dehydration, there was no difference between the groups. Blink rate and osmolarity are not associated with the difference in light scatter.

Translational Relevance

Our work approaches a clinical care problem using basic research methods (measuring ocular scatter and blink ratio).

New Approach in Ocular Drug Delivery: In vitro and ex vivo Investigation of Cyclodextrin-Containing, Mucoadhesive Eye Drop Formulations

Background

Optimal transcorneal penetration is necessary for ocular therapy; meanwhile, it is limited by the complex structure and defensive mechanisms of the eye. Antimicrobial stability of topical ophthalmic formulations is especially important. According to previous studies, the mostly used preservative, benzalkonium-chloride is irritative and toxic on corneal epithelial cells; therefore, novel non-toxic, antimicrobial agents are required. In this study, prednisolone-containing ophthalmic formulations were developed with expected optimal permeation without toxic or irritative effects.

Methods

The toxicity and permeability of prednisolone-containing eye drops were studied on a human corneal epithelial cell line (HCE-T) and ex vivo cornea model. The lipophilic drug is dissolved by the formation of cyclodextrin inclusion complex. Zinc-containing mucoadhesive biopolymer was applied as an alternative preservative agent, whose toxicity was compared with benzalkonium-chloride.

Results

As the results show, benzalkonium-chloride-containing samples were toxic on HCE-T cells. The biopolymer caused no cell damage after the treatment. This was confirmed by immunohistochemistry assay. The in vitro permeability was significantly higher in formulations with prednisolone-cyclodextrin complex compared with suspension formulation. According to the ex vivo permeability study, the biopolymer-containing samples had significantly lower permeability.

Conclusion

Considering the mucoadhesive attribute of target formulations, prolonged absorption is expected after application with less frequent administration. It can be stated that the compositions are innovative approaches as novel non-toxic ophthalmic formulations with optimal drug permeability.

PLGA Nanoparticle Platform for Trans-Ocular Barrier to Enhance Drug Delivery: A Comparative Study Based on the Application of Oligosaccharides in the Outer Membrane of Carriers

Purpose

The trans-ocular barrier is a key factor limiting the therapeutic efficacy of triamcinolone acetonide. We developed a poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) surface modified respectively with 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD), chitosan oligosaccharide and trehalose. Determination of the drug/nanoparticles interactions, characterization of the nanoparticles, in vivo ocular compatibility tests, comparisons of their corneal permeability and their pharmacokinetics in aqueous humor were carried out.

Methods

All PLGA NPs were prepared by the single emulsion and evaporation method and the drug-nanoparticle interaction was studied. The physiochemical features and in vitro corneal permeability of NPs were characterized while the aqueous humor pharmacokinetics was performed to evaluate in vivo corneal permeability of NPs. Ocular compatibility of NPs was investigated through Draize and histopathological test.

Results

The PLGA NPs with lactide/glycolide ratio of 50:50 and small particle size (molecular weight 10 kDa) achieved optimal drug release and corneal permeability. Surface modification with different oligosaccharides resulted in uniform particle sizes and similar drug-nanoparticle interactions, although 2-HP-β-CD/PLGA NPs showed the highest entrapment efficiency. In vitro evaluation and aqueous humor pharmacokinetics further revealed that 2-HP-β-CD/PLGA NPs had greater trans-ocular permeation and retention compared to chitosan oligosaccharide/PLGA and trehalose/PLGA NPs. No ocular irritation in vivo was detected after applying modified/unmodified PLGA NPs to rabbit's eyes.

Conclusion

2-HP-β-CD/PLGA NPs are a promising nanoplatform for localized ocular drug delivery through topical administration.

In vitro evaluation of stearylamine cationic nanoemulsions for improved ocular drug delivery

Oil-in-water nanoemulsions (NEs) represent one of the formulation approaches to improve eye-related bio-availability of lipophilic drugs. The potential of cationic NEs is pronounced due to the electrostatic interaction of positively charged droplets with negatively charged mucins present in the tear film, providing prolonged formulation residence at the ocular surface. The aim of this study was to develop a cationic ophthalmic NE with cationic lipid stearylamine (SA) as a carrier of a positive charge. The addition of a nonionic surfactant provided the dual electro-steric stabilization of NEs and enabled tuning of SA concentration to achieve an optimal balance between its interaction with mucins and biocompatibility. Physicochemical characterization, stability profile, in vitro mucoadhesion study and biocompatibility study employing 3D HCE-T cell-based model of corneal epithelium pointed out the NE with 0.05 % (m/m) SA as the leading formulation. Minimizing SA content while retaining droplet/mucin interactions is of great importance for efficacy and safety of future ophthalmic drug products.

Ex Vivo Conjunctival Retention and Transconjunctival Transport of Poorly Soluble Drugs Using Polymeric Micelles

This paper addresses the problem of ocular delivery of lipophilic drugs. The aim of the paper is the evaluation of polymeric micelles, prepared using TPGS (d-α-Tocopheryl polyethylene glycol 1000 succinate), a water-soluble derivative of Vitamin E and/or poloxamer 407, as a vehicle for the ocular delivery of dexamethasone, cyclosporine, and econazole nitrate. The research steps were: (1) characterize polymeric micelles by dynamic light scattering (DLS) and X-ray scattering; (2) evaluate the solubility increase of the three drugs; (3) measure the in vitro transport and conjunctiva retention, in comparison to conventional vehicles; (4) investigate the mechanisms of enhancement, by studying drug release from the micelles and transconjunctival permeation of TPGS; and (5) study the effect of micelles application on the histology of conjunctiva. The data obtained demonstrate the application potential of polymeric micelles in ocular delivery, due to their ability to increase the solubility of lipophilic drugs and enhance transport in and across the conjunctival epithelium. The best-performing formulation was the one made of TPGS alone (micelles size ≈ 12 nm), probably because of the higher mobility of these micelles, an enhanced interaction with the conjunctival epithelium, and, possibly, the penetration of intact micelles.

Self-nanoemulsifying drug delivery system of bruceine D: a new approach for anti-ulcerative colitis

Background

Bruceine D (BD) is a major bioactive component isolated from the traditional Chinese medicinal plant Brucea javanica which has been widely utilized to treat dysentery (also known as ulcerative colitis [UC]).

Methods

To improve the water solubility and absolute bioavailability of BD, we developed a self-nanoemulsifying drug delivery system (SNEDDS) composing of MCT (oil), Solutol HS-15 (surfactant), propylene glycol (co-surfactant) and BD. The physicochemical properties and pharmacokinetics of BD-SNEDDS were characterized, and its anti-UC activity and potential mechanism were evaluated in TNBS-induced UC rat model.

Results

The prepared nanoemulsion has multiple beneficial aspects including small mean droplet size, low polydispersity index (PDI), high zeta potential (ZP) and excellent stability. Transmission electron microscopy showed that nanoemulsion droplets contained uniform shape and size of globules. Pharmacokinetic studies demonstrated that BD-SNEDDS exhibited enhanced pharmacokinetic parameters as compared with BD-suspension. Moreover, BD-SNEDDS significantly restored the colon length and body weight, reduced disease activity index (DAI) and colon pathology, decreased histological scores, diminished oxidative stress, and suppressed TLR4, MyD88, TRAF6, NF-κB p65 protein expressions in TNBS-induced UC rat model.

Conclusion

These results demonstrated that BD-SNEDDS exhibited highly improved oral bioavailability and advanced anti-UC efficacy. In conclusion, our current results provided a foundation for further research of BD-SNEDDS as a potential complementary therapeutic agent for UC treatment.