In vitro nasal transport across rabbit mucosa: Effect of oxygen bubbling, pH and hypertonic pressure on permeability of lucifer yellow, diazepam and 17 β-estradiol

Development and application of an ex vivo fosphenytoin nasal bioconversion/permeability evaluation method

There is an increasing interest in the intranasal delivery of central nervous system-active drugs due to the existence of a direct nose-to-brain connection. However, poor solubility limits the amount of drug that can be administered within an aqueous solution. In the present work, the objectives were to develop an ex vivo bioconversion/permeability evaluation method and to study the ex vivo bioconversion of the hydrophilic phosphate ester prodrug fosphenytoin (FOS) to the active drug phenytoin (PHT) and their comparative nasal permeation. Bioconversion/permeability studies were performed in excised porcine nasal mucosa mounted in Ussing chambers. The physical integrity of the tissues was evaluated by measurement of the transepithelial electrical resistance (TEER). The simultaneous quantitative assay of FOS, PHT and its major metabolite, 5-(4-hydroxyphenyl)-5-phenylhydantoin (HPPH) was developed and validated according to international guidelines using a liquid chromatography analytical method. The FOS bioconversion rate and PHT and FOS apparent permeability coefficients (Papp) were determined at different time points. FOS bioconversion was also qualitatively investigated in human nasal mucus. The developed liquid chromatography method combines a fast and inexpensive sample preparation with inactivation of the enzymatic metabolism of the prodrug during sample manipulation and storage. It was linear, precise, accurate, and presented a high analyte recovery. FOS was converted ex vivo to PHT but the metabolite HPPH was not detected. The bioconversion rate increased with FOS concentration and with time, which suggests a diffusion-limited process. FOS was also converted to its active drug by human nasal mucus. A novel mathematical data analysis method was developed to reduce the bias introduced by variable mucosal TEER in the permeability results. At comparable FOS and PHT concentrations the ln(Papp(PHT)) of both compounds showed little difference, which indicates that the use of a hydrophilic and charged prodrug did not hinder overall drug permeation. At the highest tested FOS concentration it was possible to quantify FOS in the receiver chambers, meaning that at a sufficiently high concentration the FOS permeation rate overcame its bioconversion rate. The ln(Papp(PHT)) tended to similar equilibrium values as the assay progressed, but with higher FOS concentrations that equilibrium was attained faster. Acidic pH reduced the permeability of both PHT and FOS. The developed bioconversion/permeability evaluation method will constitute an important tool to select the most promising formulations before proceeding to in vivo studies. Importantly, it allowed the demonstration of phosphatase activity and FOS bioconversion in nasal mucosa, as well as the prodrug's nasal permeation potential. Furthermore, this study demonstrates the possibility of formulating phosphate prodrugs of poorly soluble central nervous system-active drugs as a strategy to increase the solubilized drug doses administered through the nasal route.

Correlation between nasal membrane permeability and nasal absorption rate

The objective of this study was to investigate the relationship between in vitro permeability (Papp) values obtained from isolated nasal tissues and the absorption rates (ka) of the same compounds following nasal administration in animals and humans. The Papp of a set of 11 drug compounds was measured using animal nasal explants and plasma time-concentration profiles for each of the same compounds following intravenous (IV) and intranasal (IN) administration were experimentally determined or obtained from literature reports. The plasma clearance was estimated from the IV plasma time-concentration profiles, and ka was determined from the IN plasma time-concentration profiles using a deconvolution approach. The level of correlation between Papp and ka was established using Pearson correlation analysis. A good correlation (r=0.77) representing a point-to-point relationship for each of the compounds was observed. This result indicates that the nasal absorption for many drug candidates can be estimated from a readily measured in vitro Papp value.

An improved primary human nasal cell culture for the simultaneous determination of transepithelial transport and ciliary beat frequency

Objectives

The aim was to establish a preclinical in-vitro system of the nasal mucosa for the simultaneous evaluation of nasal absorption and effects on ciliary activity.

Methods

Human nasal epithelial cells were grown in collagen-coated transport inserts with transparent polyethylene terephthalate membranes (3 μm). Transepithelial transport and ciliary beat frequency values were measured every 15 min for 1 h.

Key findings

The apparent permeability coefficients (Papp) for atenolol (mainly paracellular transport) and propranolol (transcellular transport) amounted to 0.1 ± 0.1 and 23.7 ± 0.6 × 10−6 cm/s, respectively, illustrating that the system can be used to discriminate between high permeability and low permeability compounds. Transport of talinolol (substrate for the P-glycoprotein efflux carrier) did not reveal polarity (0.3 ± 0.2 and 0.2 ± 0.1 × 10−6 cm/s for absorptive and secretory transport, respectively) and was not affected by verapamil (10 μm), suggesting the absence of P-glycoprotein in the nasal cell culture. No significant effects of atenolol, propranolol and talinolol on ciliary beat frequency were observed (98 ± 20% of the control condition after 60 min). Chlorocresol significantly decreased the ciliary activity but this decrease was not accompanied by effects on the transepithelial transport of atenolol, propranolol and talinolol.

Conclusions

A new system was developed which offers possibilities as a fast screening tool for studying the potential of compounds for nasal drug administration, since permeability and a possible cilio-toxic effect can be assessed simultaneously.

Evaluation of human nasal RPMI 2650 cells grown at an air-liquid interface as a model for nasal drug transport studies

This study tests the hypothesis that human nasal RPMI 2650 cells grown at an air-liquid interface is a feasible model for drug transport studies via the nasal route. RPMI 2650 cells were cultured in Eagle's minimal essential medium (MEM) at both air-liquid and liquid-liquid interfaces. For each culture regimen, monolayer integrity was tested by measuring the transepithelial resistance (TEER) as well as the transport of paracellular and transcellular markers across the monolayer. The expression of tight junction proteins-differentiation markers-in cells of the different monolayers was studied by western blot analysis and confocal microscopy. The highest TEER values (192 +/- 3 Omega . cm2) were observed for RPMI 2650 cells seeded onto collagen-coated permeable polytetrafluoroethylene inserts and grown at an air-liquid interface for 10 days; a seeding density of 4 x 10(5)/cm2 generated and maintained a cell monolayer with suitable barrier properties at days 9-12. Microscopic examination showed that RPMI 2650 cells grown on filter inserts formed a fully confluent monolayer. The apparent permeability coefficients of the paracellular marker, [14C] mannitol, and the transcellular marker, [3H] propranolol, were 5.07 +/- 0.01 x 10(-6) cm/s and 16.1 +/- 0.1 x 10(-6) cm/s, respectively. Western blot analysis indicated the presence of four tight junction proteins: ZO-1, occludin, claudin-1 and E-cadherin; and the quantities of ZO-1, occludin, and E-cadherin were significantly higher in cells grown at an air-liquid interface than in cells grown at a liquid-liquid interface. Confocal microscopic studies showed ZO-1, F-actin, occludin and claudin-1 proteins at cell-cell contacts and revealed significant differences in the distributions and densities of ZO-1 protein in cells grown at the two types of interface. The data indicate that RPMI 2650 cells grown at an air-liquid interface form polarized monolayers with the cells interconnected by tight junction proteins. This human nasal cell line model could provide a useful tool for in vitro screening of nasal drug candidates.

TR146 cells grown on filters as a model of human buccal epithelium: III. Permeability enhancement by different pH values, different osmolality values, and bile salts

The aim of the present study was to evaluate the TR146 cell culture model as an in vitro model of human buccal epithelium with respect to the permeability enhancement by different pH values, different osmolality values or bile salts. For this purpose, the increase in the apparent permeability (P(app)) of the hydrophilic marker mannitol due to exposure to solutions with pH values or osmolality values different from the physiological values was studied. As in studies with solutions of either taurocholate (TC), glycocholate (GC) or glycodeoxycholate (GDC) the results were compared to the increase in P(app) of mannitol obtained in analog studies using porcine buccal mucosa in an Ussing chamber. The effect of the exposure on the electrical resistance of the TR146 cell culture model and the porcine buccal mucosa was measured, and the degree of protein leakage due to GC exposure was investigated in the TR146 cell culture model. The porcine buccal mucosa was approximately ten times less permeable to mannitol than the TR146 cell culture model. The P(app)TC. Increased P(app) values correlated with a decrease in the electrical resistance of the TR146 cell culture model and the porcine buccal mucosa. GC was shown to induce concentration dependent protein leakage in the TR146 cell culture but only from the site of application, and the results indicate that duration of exposure further than 120 min was of minor importance. The present results indicate that the TR146 cell culture model may be a suitable in vitro model for efficacy studies and mechanistic studies of enhancers with potential use in human buccal drug delivery.

Nasal drug delivery--evaluation of an in vitro model using porcine nasal mucosa

An in vitro model for permeation studies using porcine nasal mucosa was developed and evaluated. The viability and integrity of the mucosa were determined by electrophysiological measurements, permeation studies involving 14C-mannitol and D-(2-3H) glucose, histological studies and a biochemical assay. Enzymatic activity in the mucosa was determined by serosal addition of ouabain. Three different types of porcine nasal mucosa (cavity mucosa, natural septum mucosa and dermatomed septum mucosa) were examined. The results showed that cavity mucosa was the most suitable; this type remained viable for up to 8 h after removal. Lower limits for electrophysiological data were defined in order to establish criteria for tissue viability. This in vitro method using porcine nasal mucosa appears potentially valuable as a tool for further permeation and mechanistic studies within nasal drug delivery research.

Permeation of several drugs through keratinized epithelial-free membrane of hamster cheek pouch

The hamster cheek pouch mucosa was selected as a substitute for the human buccal mucosa in an in vitro permeation study. Considering that a keratinized layer is not present in the human buccal mucosa, keratinized epithelial-free hamster cheek pouch (KEF-membrane) was prepared by chemical splitting. To confirm the usefulness of the KEF-membrane, a permeation study was conducted using several drugs with different lipophilicities. The permeability coefficient of hydrophilic drugs through the KEF-membrane (Pkef) was significantly greater than that through a viable KEF-membrane (Pkef-viable), which was estimated by using the permeability coefficient of the viable full-thickness membrane and that of the keratinized layer. On the other hand, the Pkef values of lipophilic drugs were comparable with the Pkef-viable values. Furthermore, the ratio of these P values (Pkef/Pkef-viable) decreased with increasing lipophilicity of drugs. These findings indicate that the KEF-membrane may be useful for buccal permeation studies of lipophilic drugs.

In vitro cell models to study nasal mucosal permeability and metabolism

Whereas in vivo studies represent the most crucial test for any nasal drug application or formulation, mechanistic aspects of nasal absorption may be more clearly approached by well defined and controlled in vitro studies. In this review the progress of nasal in vitro models to investigate drug permeation and metabolism in the epithelium is summarized and their potential and limitations are discussed. The following subjects will be covered: (i) primary cell cultures of human nasal epithelium, including sampling techniques and culture conditions, (ii) human nasal cell lines (in particular the human nasal cell line RPMI 2650), and (iii) excised nasal epithelium (rabbit, bovine, ovine, canine, human), also summarizing suitable preparation techniques and tissue characterization, test media, tissue equilibration, viability testing, and integrity tests. Furthermore, an overview on the various experimental set-ups suitable for in vitro transport studies (permeation rates; identification of permeation pathways; mechanisms and toxicity of absorption enhancers) and for metabolism studies (rates, saturation and pathways of enzymatic cleavage) is presented. Some attention is given to identify potential endocytotic uptake mechanisms. To date, the permeation and metabolic barrier function of excised nasal tissue derived from various animals has shown to mimic the in vivo situation 'ex vivo' at the highest degree possible. Supply of human tissue will continue to be short. Therefore, further studies are necessary to evaluate and improve culture conditions, handling, performance and physiologic relevance of primary human cell and cell line cultures.