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

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

Topical Drug Delivery: Innovative Controlled Release Systems

One of the most innovative strategies for administrating bioactive molecules is the design of adequate drug delivery systems [...].

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.

Buccal Permeation of Polysaccharide High Molecular Weight Compounds: Effect of Chemical Permeation Enhancers

The greatest achievement in the advanced drug delivery field should be the optimization of non-invasive formulations for the delivery of high molecular weight compounds. Peptides, proteins, and other macromolecules can have poor membrane permeation, principally due to their large molecular weight. The aim of this work was to explore the possibility of administering fluorescently labeled dextrans (molecular weight 4-150 kDa) across the buccal mucosa. Permeation experiments across pig esophageal mucosa were carried out using fatty acids and bile salts as penetration enhancers. The data obtained show that it is possible to increase or promote the mucosa permeation of high molecular weight dextrans by using caprylic acid or sodium taurocholate as the chemical enhancers. With these enhancers, dextrans with molecular weight of 70 and 150 kDa, that in passive conditions did not permeate, could cross the mucosa in detectable amounts. FD-70 and FD-150 showed comparable permeability values, despite the molecular weight difference. The results obtained in the present work suggest that the buccal administration of high molecular weight compounds is feasible.

Cyclosporine-loaded micelles for ocular delivery: Investigating the penetration mechanisms

Cyclosporine is an immunomodulatory drug commonly used for the treatment of mild-to-severe dry eye syndrome as well as intermediate and posterior segment diseases as uveitis. The ocular administration is however hampered by its relatively high molecular weight and poor permeability across biological barriers. The aim of this work was to identify a micellar formulation with the ability to solubilize a considerable amount of cyclosporine and promote its transport across ocular barriers. Non-ionic amphiphilic polymers used for micelles preparation were tocopherol polyethylene glycol 1000 succinate (TPGS) and Solutol® HS15. Furthermore, the addition of alpha-linolenic acid was assessed. A second aim was to evaluate micelles fate in the ocular tissues (cornea and sclera) to shed light on penetration mechanisms. This was possible by extracting and quantifying both drug and polymer in the tissues, by studying TPGS hydrolysis in a bio-relevant environment and by following micelles penetration with two-photon microscopy. Furthermore, TPGS role as permeation enhancer on the cornea, with possible irreversible modifications of tissue permeability, was analyzed. Results showed that TPGS micelles (approx. 13 nm in size), loaded with 5 mg/ml of cyclosporine, promoted drug retention in both the cornea and the sclera. Data demonstrated that micelles behavior strictly depends on the tissue: micelles disruption occurs in contact with the cornea, while intact micelles diffuse in the interfibrillar pores of the sclera and form a reservoir that can sustain over time drug delivery to the deeper tissues. Finally, cornea quickly restore the barrier properties after TPGS removal from the tissue, demonstrating its potential good tolerability for ocular application.

DEVELOPMENT AND VALIDATION OF A HPLC-UV BASED METHOD FOR THE EXTRACTION AND QUANTIFICATION OF METHOTREXATE IN THE SKIN

An innovative and sensitive HPLC-UV method for the extraction and quantification of methotrexate (MTX) in skin layers was developed and validated. Due to the physico-chemical characteristics of the drug and the nature of the tissue, it was necessary to use folic acid (FA) as internal standard for MTX quantification in the dermis. MTX (and FA) analysis was performed on a Phenomenex Jupiter C18 column, using 50 mM sodium acetate buffer (pH 3.6) and methanol mixture (87:13, v/v) as mobile phase, pumped at 1 ml/min. The absorbance was monitored at 290 nm. The method resulted to be selective, linear in the range 0.11-8.49 μg/ml for extraction solvent and 0.05-8.94 μg/ml for pH 7.4 PBS, precise and accurate, with a LLOQ of 0.11 μg/ml (extraction solvent) and 0.05 μg/ml (pH 7.4 PBS). The method developed resulted to be suitable for the quantification of MTX in the skin layers at the end of in vitro permeation experiments; the overall mass balance was 96.5 ± 1.4 %, in line with the requirement of the OECD guideline for the testing of the chemicals (Skin absorption: in vitro method) (OECD, 2004).

Preliminary Investigation on Simvastatin-Loaded Polymeric Micelles in View of the Treatment of the Back of the Eye

There is increasing consensus in considering statins beneficial for age-related macular degeneration and in general, for immune and inflammatory mediated diseases affecting the posterior segment of the eye. However, all available data relate to oral administration, and safety and effectiveness of statins directly administered to the eye are not yet known, despite their ophthalmic administration could be beneficial. The aim was the development and the characterization of polymeric micelles based on TPGS or TPGS/poloxamer 407 to increase simvastatin solubility and stability and to enhance the delivery of the drug to the posterior segment of the eye via trans-scleral permeation. Simvastatin was chosen as a model statin and its active hydroxy acid metabolite was investigated as well. Results demonstrated that polymeric micelles increased simvastatin solubility at least 30-fold and particularly TPGS/poloxamer 407 mixed micelles, successfully stabilized simvastatin over time, preventing the hydrolysis when stored for 1 month at 4 °C. Furthermore, both TPGS (1.3 mPas) and mixed micelles (33.2 mPas) showed low viscosity, suitable for periocular administration. TPGS micelles resulted the best performing in delivery simvastatin either across conjunctiva or sclera in ex vivo porcine models. The data pave the way for a future viable ocular administration of statins.

Polymeric micelles in drug delivery: An insight of the techniques for their characterization and assessment in biorelevant conditions

Polymeric micelles, i.e. aggregation colloids formed in solution by self-assembling of amphiphilic polymers, represent an innovative tool to overcome several issues related to drug administration, from the low water-solubility to the poor drug permeability across biological barriers. With respect to other nanocarriers, polymeric micelles generally display smaller size, easier preparation and sterilization processes, and good solubilization properties, unfortunately associated with a lower stability in biological fluids and a more complicated characterization. Particularly challenging is the study of their interaction with the biological environment, essential to predict the real in vivo behavior after administration. In this review, after a general presentation on micelles features and properties, different characterization techniques are discussed, from the ones used for the determination of micelles basic characteristics (critical micellar concentration, size, surface charge, morphology) to the more complex approaches used to figure out micelles kinetic stability, drug release and behavior in the presence of biological substrates (fluids, cells and tissues). The techniques presented (such as dynamic light scattering, AFM, cryo-TEM, X-ray scattering, FRET, symmetrical flow field-flow fractionation (AF4) and density ultracentrifugation), each one with their own advantages and limitations, can be combined to achieve a deeper comprehension of polymeric micelles in vivo behavior. The set-up and validation of adequate methods for micelles description represent the essential starting point for their development and clinical success.

Validation of a HPLC-UV method for the quantification of budesonide in skin layers

A simple and sensitive HPLC method for the quantification of budesonide in skin layers was developed and validated. Budesonide was extracted from stratum corneum, epidermis and dermis by means of a mixture of acetonitrile:water (recovery > 90%). Budesonide quantification was performed with a RP-C18 column using methanol and water mixture (69:31, v/v) as mobile phase, pumped at 0.8 ml/min. The absorbance was monitored at 254 nm. The method resulted to be selective, linear in the range 0.05-5 or 10 μg/ml, precise and accurate. LLOQ resulted to be 0.05 μg/ml. The developed method appeared to be appropriate for the quantification of budesonide in skin layers at the end of in vitro permeation experiments since the recovery of the applied dose was 97 ± 1%, in line with requirement of the OECD guideline for the testing of the chemicals (Skin absorption: in vitro method).

In Vitro Skin Retention of Crisaborole after Topical Application

Crisaborole, a nonsteroidal phosphodiesterase 4 inhibitor, represents the first nonsteroidal medication approved for the treatment of atopic dermatitis in over a decade. In this work, crisaborole skin permeation and retention was studied in vitro from a 2% ointment using porcine skin as barrier. Crisaborole was also characterized in terms of thermal behavior, solubility, and logP. Control experiments were performed also on tape stripped skin to clarify the role of stratum corneum in drug partitioning and permeation across the skin. The results obtained indicate that crisaborole accumulates into the skin in considerable amounts after application of a topical lipophilic ointment. Crisaborole shows more affinity for the dermis compared to the epidermis despite its relatively high value of partition coefficient; stratum corneum analysis revealed a low affinity of the drug for this skin layer. Skin penetration across hair follicles or sebaceous glands can be a reason for the high dermis retention and is worth further investigation. The comparison with data obtained from a solution in acetonitrile suggests that the formulation plays a certain role in determining the relative distribution of crisaborole in the skin layers and in the receptor compartment.

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.

Development and validation of a simple method for the extraction and quantification of crisaborole in skin layers

Crisaborole is a boron compound recently approved by the US Food and Drug Administration as a 2% ointment for the treatment of mild to moderate atopic dermatitis. This work describes a simple method for the quantification of the drug in the skin layers at the end of in-vitro permeation experiments. Chromatographic separation was carried out on a reverse-phase C₁₈ column using a mixture of trifluoroacetic acid 0.05%-acetonitrile (55:45, v/v) as mobile phase, pumped at 1 ml/min. Column temperature was 35°C and UV detection was performed at 250 nm. The method was linear in the range of concentration from 0.06 to 6 μg/ml (R²  = 1) and was selective, precise and accurate. Depending on the solvent used, the LOQ ranged from 0.014 to 0.030 μg/ml and the LOD from 0.005 to 0.010 μg/ml. The extraction from all the skin layers was quantitative. The developed method was successfully tested in an in-vitro permeation study, proving to be an effective tool in the development of new formulations containing crisaborole.

Ucuùba (Virola surinamensis) Fat-Based Nanostructured Lipid Carriers for Nail Drug Delivery of Ketoconazole: Development and Optimization Using Box-Behnken Design

Ucuùba fat is fat obtained from a plant found in South America, mainly in Amazonian Brazil. Due to its biocompatibility and bioactivity, Ucuùba fat was used for the production of ketoconazole-loaded nanostructured lipid carriers (NLC) in view of an application for the treatment of onychomycosis and other persistent fungal infections. The development and optimization of Ucuùba fat-based NLC were performed using a Box-Behnken design of experiments. The independent variables were surfactant concentration (% w/v), liquid lipids concentration (% w/v), solid lipids concentration (% w/v), while the outputs of interest were particle size, polydispersity index (PDI) and drug encapsulation efficiency (EE). Ucuùba fat-based NLC were produced and the process was optimized by the development of a predictive mathematical model. Applying the model, two formulations with pre-determined particle size, i.e., 30 and 85 nm, were produced for further evaluation. The optimized formulations were characterized and showed particle size in agreement to the predicted value, i.e., 33.6 nm and 74.6 nm, respectively. The optimized formulations were also characterized using multiple techniques in order to investigate the solid state of drug and excipients (DSC and XRD), particle morphology (TEM), drug release and interactions between the formulation components (FTIR). Furthermore, particle size, surface charge and drug loading efficiency of the formulations were studied during a one-month stability study and did not show evidence of significant modification.

Topical application of polymeric nanomicelles in ophthalmology: a review on research efforts for the noninvasive delivery of ocular therapeutics

INTRODUCTION

Polymeric micelles represent nowadays an interesting formulative approach for ocular drug delivery, as they act as solubility enhancers of poorly soluble drugs and promote drug transport across cornea and sclera. In particular, in the last 5 years polymeric nanomicelles have been increasingly investigated to overcome some of the important challenges of the topical treatment of ocular diseases.

AREAS COVERED

The aim of this review was to gather up-to-date information on the different roles that polymeric micelles (commonly in the nanosize scale) can play in ocular delivery. Thus, after a general description of ocular barriers and micelles features, the attention is focused on those properties that are relevant for ophthalmic application. Finally, their efficacy in improving the ocular delivery of different classes of therapeutics (anti-inflammatory, immunosuppressant, antiglaucoma, antifungal, and antiviral drugs) are reported.

EXPERT OPINION

Although still a few, in vivo experiments have clearly demonstrated the capability of polymeric nanomicelles to overcome a variety of hurdles associated to ocular therapy, notably increasing drug bioavailability. However, there are still some very important issues to be solved, such as tolerability and stability; additionally, the role of micelles in drug uptake by the ocular tissues and their potential for the treatment of posterior eye diseases still need to be clarified/verified.

New Insights on the Mechanism of Fatty Acids as Buccal Permeation Enhancers

Buccal mucosa has recently received much attention as a potential route for systemic delivery of drugs, including biologics and vaccines. The aim of this work was to gain insight into the mechanism of fatty acids as buccal permeation enhancers, by studying the effect of a series of medium and long chain fatty acids on the permeation of a model high molecular weight and hydrophilic molecule, fluorescein isothiocyanate labelled dextran (FD-4, m.w. 4 kDa) across porcine esophageal epithelium. A parabolic relationship between fatty acid lipophilicity and enhancement was obtained, regardless of the presence and number of double bonds. The relationship, which resembles the well-known relationship between permeability and lipophilicity of transdermal delivery, presents a maximum value in correspondence of C10 (logP approx. 4). This is probably the ideal lipophilicity for the fatty acid to interact with the lipid domains of the mucosa. When the same analysis was performed on skin data, the same trend was observed, although the maximum value was reached for C12 (logP approx. 5), in agreement with the higher lipophilicity of the skin. The results obtained in the present work represent a significant advancement in the understanding of the mechanisms of action of fatty acids as buccal penetration enhancers.

Microemulsion containing triamcinolone acetonide for buccal administration

The aim of the present work was to investigate the potential of microemulsions for the buccal administration of triamcinolone acetonide. Microemulsions were developed by the construction of pseudoternary phase diagrams, using the aqueous titration method. Among all microemulsions prepared and tested for stability, three were selected and submitted to characterization and in vitro permeation/retention experiments, using pig esophageal epithelium, an accepted model of the buccal mucosa. Furthermore, one microemulsion was added of excipients (stearylamine, CTAB and chitosan) able to alter the charge of droplets. The results obtained show that the permeation of triamcinolone acetonide across pig esophageal epithelium was not influenced by the droplet size nor by the composition, but only by the presence of chitosan, polysaccharide able to increase the transport across mono and stratified epithelia. The determination of the permeation parameters allowed us to show that chitosan acts on the diffusion parameter across the tissue and not on the partitioning parameter; for the same reason the tissue retention of triamcinolone acetonide was not modified. Triamcinolone flux (2.6 μg cm^-2 h^-1) was too low to make systemic administration feasible (dose required 2.5 to 60 mg/day). The amount of triamcinolone acetonide recovered in the mucosa after only 10 min. of microemulsion application was much higher than after overnight application of the commercial paste Omicilon® A. This suggests that triamcinolone acetonide microemulsions can be an interesting alternative to the commercial formulation to treat diseases of the buccal mucosa. Owing to the fast uptake by the tissue, the formulation can be used as a mouthwash.

Cell penetrating peptides in ocular drug delivery: State of the art

Despite the increasing number of effective therapeutics for eye diseases, their treatment is still challenging due to the presence of effective barriers protecting eye tissues. Cell Penetrating Peptides (CPPs), synthetic and natural short amino acid sequences able to cross cellular membrane thanks to a transduction domain, have been proposed as possible enhancing strategies for ophthalmic delivery. In this review, a general description of CPPs classes, design approaches and proposed cellular uptake mechanisms will be provided to the reader as an introduction to ocular CPPs application, together with an overview of the main problems related to ocular administration. The results obtained with CPPs for the treatment of anterior and posterior segment eye diseases will be then introduced, with a focus on non-invasive or minimally invasive administration, shifting from CPPs capability to obtain intracellular delivery to their ability to cross biological barriers. The problems related to in vitro, ex vivo and in vivo models used to investigate CPPs mediated ocular delivery will be also addressed together with potential ocular toxicity issues.

Development of microemulsions of suitable viscosity for cyclosporine skin delivery

Psoriasis is a widespread chronic disease affecting 2-4% of the population in Western countries. Its mild-to-moderate form, representing approximately 80% of the total cases, is treated by topical application, with corticosteroid being the standard treatment. However, in case of psoriasis, no single treatment works for every patient and optimizing topical therapy is a key aspect. A possible alternative is represented by cyclosporine, an immunosuppressant cyclic peptide administered orally in the treatment of the severe form. Its topical application could avoid the problems related to systemic immunosuppression, but the unfavourable physico-chemical properties (MW: 1202 Da; LogP ≈ 3) hinder its permeation across the stratum corneum. The aim of the paper was the preparation, characterization and ex-vivo evaluation of cyclosporine loaded microemulsions using oleic acid as oil phase, either Tween^®80 or a soluble derivative of vitamin E (TPGS) as surfactants and either Transcutol^®, propylene glycol or 1,3 propanediol as co-surfactants. The issue of formulation viscosity was also addressed 1) by evaluating the thickening of Tween^®80-based microemulsions by direct addition of different rheological modifiers, 2) by building pseudo-ternary phase diagrams using TPGS, to identify the water/oil/surfactants proportions resulting in viscous self-gelifying systems. Nine formulations (five Tween^®80-based and four TPGS-based) were selected, characterized in terms of droplets size (low viscosity systems) or rheological properties (high viscosity systems), loaded with 6 mg/g cyclosporine and applied ex-vivo on porcine skin for 22 h. A relevant skin accumulation was obtained either with a low-viscosity Tween^®80-based microemulsion (9.78 ± 3.86 µg/cm²), or with a high viscosity TPGS-based microemulsion (18.3 ± 5.69 µg/cm²), with an increase of about 3 and 6 times respectively for comparison with a control cyclosporine solution in propylene glycol. The role of water content, surfactant, co-surfactant and viscosity was also addressed and discussed. The kinetic of skin uptake from the best performing formulation was finally evaluated, highlighting a relatively quick skin uptake and the achievement, after 2 h of contact, of potentially therapeutic cyclosporine skin concentrations.

Mydriatics release from solid and semi-solid ophthalmic formulations using different in vitro methods

The aim of the present paper was the development of semi-solid (hydrogels) and solid (film) ophthalmic formulations for the controlled release of two mydriatics: phenylephrine and tropicamide. The formulations - based on polyvinylalcohol and hyaluronic acid - were characterized, and release studies were performed with three different in vitro set-ups, i.e. Franz-type diffusion cell, vial method and inclined plane; for comparison, a solution and a commercial insert, both clinically used to induce mydriasis, were evaluated. Both gels and film allowed for a controlled release of drugs, appearing a useful alternative for mydriatics administration. However, the release kinetic was significantly influenced by the method used, highlighting the need for optimization and standardization of in vitro models for the evaluation of drug release from ophthalmic dosage forms.

Design and Synthesis of New Cell Penetrating Peptides: Diffusion and Distribution Inside the Cornea

The role of cell penetrating peptides (CPPs) has been challenged in recent years for drug delivery to ocular tissues for the targeting of both anterior and posterior segments. The enhancement of trans-corneal transport for anterior segment targeting is a very important issue possibly leading to important outcomes on efficacy and to the opportunity of topical administration of molecules with unfavorable penetration properties. The aim of the present work was the design and synthesis of new CPPs, deriving from the structure of PEP-1 peptide. Synthesized peptides were labeled with 5-carboxyfluorescein (5-FAM), and their diffusion behavior and distribution inside the cornea were evaluated by a validated ex vivo model and a confocal microscopy approach. Newly synthesized peptides showed similar corneal permeation profiles as PEP-1 (P_app = 0.75 ± 0.56 × 10^-6 cm/s), about 2.6-fold higher than 5-FAM (P_app = 0.29 ± 0.08 × 10^-6 cm/s) despite the higher molecular weight. Confocal microscopy experiments highlighted the tendency of PEP-1 and its derived peptides to localize in the intercellular space and/or in the plasma membrane. Noteworthy, using penetratin as positive control, a higher trans-corneal permeation (P_app = 6.18 ± 1.46 × 10^-6 cm/s) was evidenced together with a diffusion by intracellular route and a different accumulation between wings and basal epithelial cells, probably depending on the stage of cell development. Finally, PEP-1 and pep-7 proved to be safe and well tolerated when tested on human conjuctival cell line.

Mechanisms of imiquimod skin penetration

Imiquimod (IMQ) ia an immunostimulating drug used for the treatment of neoplastic skin diseases, such as actinic keratosis (AK) and superficial basal cell carcinoma (sBCC), and as adjuvant for vaccination. Imiquimod formulation and skin delivery is highly challenging because of its very low solubility in most pharmaceutical excipients and poor penetration properties. Objectives of the work were: (1) to evaluate IMQ solubility in different solvents and pharmaceutical excipients; (2) to evaluate IMQ skin retention after the application of simple saturated solutions; (3) to evaluate the role of stratum corneum and solvent uptake on IMQ skin retention and (4) to formulate IMQ in microemulsions - prepared using previously investigated components - and compare them with the commercial formulation. The results show that IMQ solubility is not related to the solubility parameter of the solvents considered. The highest solubility was found with oleic acid (74mg/ml); in the case of PEGs, the solubility increased linearly with MW (PEG 200: 1.9mg/ml; PEG 400 7.3mg/ml, PEG 600 12.8mg/ml). Imiquimod skin retention from saturated solutions (Tween 80, oleic acid, propylene glycol, PEG 200, PEG 400, PEG 600, Transcutol, 2-pyrrolidone, DMSO) resulted relatively similar, being 1.6μg/cm(2) in case of oleic acid (solubility 74mg/ml) and 0.18μg/cm(2) in case of propylene glycol (solubility 0.60mg/ml). Permeation experiments on stripped skin (no stratum corneum) and isolated dermis as well as uptake experiments on isolated stratum corneum sheets demonstrated that IMQ accumulation is related to skin solvent uptake. Finally, microemulsions (MEs) prepared with the above-studied components demonstrated a very good performance. In particular, a ME composed of 10% oleic acid, 35% Transcutol, 35% Tween 80 and 20% water is able to accumulate the same amount of drug as the commercial formulation but with far more efficiency, since its concentration was 12 times lower.

Effect of pH and penetration enhancers on cysteamine stability and trans-corneal transport

Ocular cystinosis is a rare metabolic disorder characterized by the presence of insoluble cystine crystals inside the corneal stroma, with consequent photophobia, keratopathies and frequent corneal erosions. The current therapy consists in the lifetime ophthalmic administration of cysteamine, drug characterized by extremely high hydrophilicity, low molecular weight (77g/mol), and easy oxidization to disulfide. Ocular delivery of cysteamine is very challenging, for its poor permeability and stability in solution. The purpose of the present paper was to study the impact of formulation pH and composition on (1) the trans-corneal delivery and (2) the stability in solution of cysteamine, with particular focus on the use of alpha-cyclodextrin (α-CD), benzalkonium chloride (BAC) and disodium edetate (EDTA). Permeation experiments were performed ex vivo through freshly excised porcine cornea; stability was evaluated for six months at -20°, +4° and +25°C; irritation potential was evaluated using HET-CAM assay. The results showed that cysteamine trans-corneal diffusion is strictly dependent on both pH (7.4 preferred to 4.2) and buffering capacity, that negatively impact on the permeation; EDTA did not enhance the trans-corneal diffusion of cysteamine neither at pH 7.4 nor at pH 4.2, while benzalkonium chloride (BAC), antimicrobial agent present within commercial eye-drops, significantly enhanced it. Notably, α-CD was able to promote the trans-corneal diffusion of cysteamine and, at a 5.5%, a 4-fold higher penetration compared to the BAC-containing formulation was obtained. EDTA and acidic pH demonstrated to be essential for cysteamine stability. The formulation obtained by combining α-CD and EDTA was characterized by significant permeation, good stability profile, and no irritation potential, even if the tolerability should be further confirmed by in vivo test.

In-vitro characterization of buccal iontophoresis: the case of sumatriptan succinate

Buccal administration of sumatriptan succinate might be an interesting alternative to the present administration routes, due to its non-invasiveness and rapid onset of action, but because of its low permeability, a permeation enhancement strategy is required. The aim of this work was then to study, in-vitro, buccal iontophoresis of sumatriptan succinate. Permeation experiments were performed in-vitro across pig esophageal epithelium, a recently proposed model of human buccal mucosa, using vertical diffusion cells. The iontophoretic behavior of the tissue was characterized by measuring its isoelectric point (Na(+) transport number and the electroosmotic flow of acetaminophen determination) and by evaluating tissue integrity after current application. The results obtained confirm the usefulness of pig esophageal epithelium as an in-vitro model membrane for buccal drug delivery. The application of iontophoresis increased sumatriptan transport, proportionally to the current density applied, without tissue damage: electrotransport was the predominant mechanism. Integrating the results of the present work with literature data on the transport of other molecules across the buccal mucosa and across the skin, we can draw a general conclusion: the difference in passive transport across buccal mucosa and across the skin is influenced by permeant lipophilicity and by the penetration pathway. Finally, buccal iontophoretic administration of sumatriptan allows to administer 6mg of the drug in 1h, representing a promising alternative to the current administration routes.

Permeation of proteins, oligonucleotide and dextrans across ocular tissues: experimental studies and a literature update

Proteins and oligonucleotides represent powerful tools for the treatment of several ocular diseases, affecting both anterior and posterior eye segments. Despite the potential of these compounds, their administration remains a challenge. The last years have seen a growing interest for the noninvasive administration of macromolecular drugs, but still there is only little information of their permeability across the different ocular barriers. The aim of this work was to evaluate the permeation of macromolecules of different size, shape and charge across porcine ocular tissues such as the isolated sclera, the choroid Bruch's membrane and the cornea, both intact and de-epitelialized. Permeants used were two proteins (albumin and cytochrome C), an oligonucleotide, two dextrans (4 and 40 kDa) and a monoclonal antibody (bevacizumab). Obtained data and its comparison with the literature highlight the difficulties in predicting the behavior of macromolecules based on their physicochemical properties, because the interplay between the charge, molecular radius and conformation prevent their analysis separately. However, the data can be of great help for a rough evaluation of the feasibility of a noninvasive administration and for building computational models to improve understanding of the interplay among static, dynamic and metabolic barriers in the delivery of macromolecules to the eye.

In vitro evaluation of mucoadhesive films for gingival administration of lidocaine

The aim of this study was the optimization of a lidocaine-based film formulation for the prevention of pain from needle prick during the injection of local anesthetic in dentistry. Film performances were evaluated in vitro by studying lidocaine permeation across pig esophageal epithelium as model for nonkeratinized buccal mucosa. The results obtained showed that the molecular weight of the film-forming polymer had no effect on lidocaine transport. The introduction of the adhesive Plastoid® into the film determined a significant increase of drug permeation rate, which was further improved by the addition of Azone®. On the contrary, the effect of sodium taurocholate was negligible.

Liposomal-benzocaine gel formulation: correlation between in vitro assays and in vivo topical anesthesia in volunteers

The aim of the present study was to characterize a liposome-based benzocaine (BZC) formulation designed for topical use on the oral mucosa and to evaluate its in vitro retention and permeation using the Franz-type diffusion cells through pig esophagus mucosa. To predict the effectiveness of new designed formulations during preclinical studies, a correlation between in vitro assays and in vivo efficacy was performed. Liposomal BZC was characterized in terms of membrane/water partition coefficient, encapsulation efficiency, size, polydispersity, zeta potential, and morphology. Liposomal BZC (BL10) was incorporated into gel formulation and its performances were compared to plain BZC gel (B10) and the commercially available BZC gel (B20). BL10 and B10 presented higher flux and retention on pig esophagus mucosa with a shorter lag time, when compared to B20. BZC flux was strongly correlated with in vivo anesthetic efficacy, but not with topical anesthesia duration. The retention studies did not correlate with any of the in vivo efficacy parameters. Thus, in vitro permeation study can be useful to predict anesthetic efficacy during preclinical tests, because a correlation between flux and anesthetic efficacy was observed. Therefore, in vitro assays, followed by in vivo efficacy, are necessary to confirm anesthetic performance.

Amikacin reverse iontophoresis: optimization of in vitro extraction

The aim of this work was to optimize amikacin reverse iontophoretic extraction across the skin in vitro, for non-invasive drug monitoring. Reverse iontophoresis experiments were performed using vertical diffusion cells. The lower chamber, simulating body fluids, contained amikacin bisulphate and acetaminophen, as marker for electroosmosis, while the upper chamber was filled with the appropriate extraction solution. The effect of concentration of amikacin in the dermal bathing solution and the effect of extraction solution composition and pH were studied. The results show that the extraction of amikacin was independent of pH and always in the anode-to-cathode direction, in agreement with the positive charge of the drug. The presence of amikacin in the bathing solution did not modify acetaminophen extraction at pH 4.0, while the extraction was reduced at pH 8.0. In conclusion, amikacin can be extracted across the skin in vitro by reverse iontophoresis. Owing to the charge of the molecule, extraction takes place at the cathode. Using acetaminophen as neutral marker, it was shown that amikacin can interact with the skin and alter its permselectivity at pH 8.0.

Combined patch containing salicylic acid and nicotinamide: role of drug interaction

The aim of the present study was to formulate a combined patch containing salicylic (SA) acid and nicotinamide (NA), useful for the treatment of mild acne, and to verify their mutual effect on drug permeation and skin retention. The performance of the patch was tested in vitro in permeation experiments using pig ear skin as barrier. To better understand the data obtained from the film, permeation from solutions and isopropyl myristate/water partition coefficient were also determined. The results obtained in the present work suggest a mutual influence of NA and SA on their permeation across the skin from an innovative transdermal film. The partition coefficient obtained when the two molecules were simultaneously present was typically lower than the respective value obtained with NA and SA alone.

In-vitro permeation of bevacizumab through human sclera: effect of iontophoresis application

Objectives

Bevacizumab (Avastin) is a recombinant humanized monoclonal antibody used in ophthalmology (off-label) for the treatment of neovascularization in diseases such as diabetic retinopathy and age-related macular degeneration (wet form). Bevacizumab is currently administrated by repeated intravitreal injection, which can cause severe complications; a non-invasive delivery route is therefore desirable. The passive permeation of bevacizumab through isolated human sclera was evaluated and the iontophoretic technique was explored as a method to enhance its transscleral transport in vitro.

Methods

Bevacizumab was fluorescently labelled using fluorescein isothiocyanate (FITC). Permeation experiments were conducted for 2 h in Franz-type diffusion cells using human sclera as the barrier. The donor compartment contained FITC-bevacizumab (2.5 mg/ml) in phosphate-buffered saline at pH 7.4. In the iontophoretic experiments, a current intensity of 2.3 mA (current density 3.8 mA/cm2) was applied. The permeation samples were analysed with a fluorescence detector (excitation and emission wavelengths were 490 and 520 nm, respectively). The stability of FITC-bevacizumab conjugate was checked by thin layer chromatography.

Key findings

The main finding of this work is that anodal iontophoresis can significantly enhance bevacizumab transport through isolated human sclera (enhancement factor 7.5), even though the drug is essentially uncharged. Due to the relatively constant characteristics of antibodies, these results can probably be extended to other molecules of the same family.

Conclusions

Preliminary results indicate that anodal iontophoresis could be a promising strategy to non-invasively deliver bevacizumab through the sclera. The presence in the eye of other barriers, both static and dynamic, necessitates further evaluation of the technique on more complex ex-vivo and in-vivo models.