A new method for drug transport studies on pig nasal mucosa using a horizontal Ussing chamber

Recent Advances in Studying In Vitro Drug Permeation Across Mucosal Membranes

Transmucosal drug products, such as aerosols, films, semisolids, suppositories, and tablets, have been developed for the treatment of various human diseases and conditions. Transmucosal drug absorption is highly influenced by the biological structures of the mucosa and the physiological environment specific to the administration route (e.g., nasal, rectal, and vaginal). Over the last few decades, in vitro permeation testing (IVPT) using animal tissues or in vitro cell cultures have been utilized as a cost-effective and efficient tool for evaluating drug release and permeation behavior, assisting in formulation development and quality control of transmucosal drug delivery systems. This review summarizes the key mucosal permeation barriers associated with representative transmucosal administration routes, as well as considerations for IVPT method development. It highlights various IVPT methods, including vertical diffusion cell, flow-through diffusion cell, Ussing chamber, and transwell systems. Additionally, future perspectives are discussed, such as the use of optical methods to study in vitro drug permeation and the development of in vitro-in vivo correlation (IVIVC) for transmucosal drug development. The potential of IVPT as part of in vitro bioequivalence assessment strategies for locally acting transmucosal drug products is also highlighted.

Impact of Storage on In Vitro Permeation and Mucoadhesion Setup Experiments Using Swine Nasal Mucosa

Intranasal topical administration offers a promising route for local and systemic drug delivery, with in vitro permeation and mucoadhesion studies often using porcine models. However, the impact of storage on mucosal integrity after the procedure remains unaddressed. This study aimed to standardize the preparation process and evaluated whether storage of porcine nasal mucosa impairs its integrity and permeability for experimental comparisons. Additionally, an optimized in vitro mucoadhesion experiment using texture analyzer equipment was investigated. Porcine nasal mucosa was subjected to different storage conditions ("fresh"; refrigerated at 4°C for 24 h and 48 h, and frozen at -20°C for two or three weeks) and assessed using optical and transmission electron microscopy. In vitro permeation assays were performed in a Franz-type vertical diffusion system with lidocaine hydrochloride (LDC). In vitro mucoadhesion assays were conducted using fresh nasal mucosa and a commercial nasal topical formulation using TA.XT. Plus texture analyzer. The variables involved (probe speed, contact time, and application force) in assessing mucoadhesive capacity (maximum mucoadhesive force Fmax and work of mucoadhesion Wmuc) were optimized using a Central Composite Design. Fresh tissues showed no alterations in histological arrangement or in the ultrastructure of adherence junctions. Stored tissues exhibited histological disorganization, reduced thickness, and loss of epithelial integrity. LDC permeability increased in storage tissues (p < 0.05). Contact force had a positive effect on Fmax and Wmuc (p < 0.0001), with a minimum required value of 0.48 N. Variations in contact time and probe speed did not affect the responses (p > 0.05). In conclusion, the preparation technique was adequate to maintain mucosa integrity for permeability studies. However, storing the mucosa at 4 or -20°C overestimated LDC permeation, which could mislead critical data for formulation development. Therefore, the use of fresh mucosa is recommended to ensure more reliable results. For in vitro mucoadhesion assays, a minimum contact force of 0.48N is required for optimal responses.

Curcumin and Quercetin-Loaded Lipid Nanocarriers: Development of Omega-3 Mucoadhesive Nanoemulsions for Intranasal Administration

Curcumin (CUR) and quercetin (QU) are potential compounds for treatment of brain diseases such as neurodegenerative diseases (ND) because of their anti-inflammatory and antioxidant properties. However, low water solubility and poor bioavailability hinder their clinical use. In this context, nanotechnology arises as a strategy to overcome biopharmaceutical issues. In this work, we develop, characterize, compare, and optimize three different omega-3 (ω-3) fatty acids nanoemulsions (NEs) loaded with CUR and QU (negative, cationic, gelling) prepared by two different methods for administration by intranasal route (IN). The results showed that formulations prepared with the two proposed methods exhibited good stability and were able to incorporate a similar amount of CUR and QU. On the other side, differences in size, zeta potential, in vitro release kinetics, and permeation/retention test were observed. Considering the two preparation methods tested, high-pressure homogenization (HPH) shows advantages, and the CQ NE- obtained demonstrated potential for sustained release. Toxicity studies demonstrated that the formulations were not toxic for Caenorhabditis elegans. The developed ω-3 fatty acid NEs have shown a range of interesting properties for the treatment of brain diseases, since they have the potential to increase the nose-to-brain permeation of CUR and QU, enabling enhanced treatments efficiency.

Nose to Brain Delivery of Phenytoin Sodium Loaded Nano Lipid Carriers: Formulation, Drug Release, Permeation and In Vivo Pharmacokinetic Studies

An acute epileptic seizure is a seizure emergency fatal condition that requires immediate medical attention. IV phenytoin sodium remains the second line therapeutic agent for the immediate treatment of status epilepticus. Phenytoin sodium formulated as nanolipid carriers (NLCs) seems to be promising as an intranasal delivery system for controlling acute seizures. Three different nanosized phenytoin sodium loaded NLCs (<50 nm, 50-100 nm and >100 nm) were prepared by melt emulsification and was further characterised. In vitro drug release studies showed immediate drug release from phenytoin sodium loaded NLCs of <50 nm size, which is highly essential for acute seizure control. The ex vivo permeation study indicated greater permeation from <50 nm sized NLC through the olfactory epithelium compared to thecontrol drug solution. Invivo pharmacokinetic studies revealed higher drug concentration in CSF/brain within 5 min upon intranasal administration of <50 nm sized phenytoin sodium NLCs than the control drug solution and marketed IV phenytoin sodium, indicating direct and rapid nose to brain drug transport through the olfactory epithelium. The study has shown that formulation strategies can enhance olfactory uptake, and phenytoin sodium NLCs of desired particle sizes (<50 nm) offer promising potential for nose to brain direct delivery of phenytoin sodium in treating acute epileptic seizures.

Quality by Design Approach for the Development of Liposome Carrying Ghrelin for Intranasal Administration

The therapeutic use of peptides has increasingly recognized in the development of new therapies. However, the susceptible enzymatic cleavage is a barrier that needs to overcome. Nose-to-brain delivery associated with liposomes can protect peptides against biodegradation and improve the accessibility to brain targets. The aim was to develop a liposomal formulation as ghrelin carrier. The quality by design (QbD) approach was used as a strategy for method development. The initial risk assessments were carried out using a fishbone diagram. A screening design study was performed for the critical material attributes/critical process parameters (CMAs/CPPs) on critical quality attributes (CQAs). Liposomes were obtained by hydrating phospholipid films, followed by extrusion or homogenization, and coated with chitosan. The optimized liposome formulation was produced by high-pressure homogenization coated with chitosan, and the resulted were liposomes size 72.25 ± 1.46 nm, PDI of 0.300 ± 0.027, the zeta potential of 50.3 ± 1.46 mV, and encapsulation efficiency of 53.2%. Moreover, chitosan coating improved performance in ex vivo permeation and mucoadhesion analyzes when compared to the uncoated liposome. In this context, chitosan coating is essential for the performance of the formulations in the ex vivo permeation and mucoadhesion analyzes. The intranasal administration of ghrelin liposomes coated with chitosan offers an innovative opportunity to treat cachexia.

Development of Nasal Lipid Nanocarriers Containing Curcumin for Brain Targeting

BACKGROUND

Curcumin (CUR) has properties that can be useful for the treatment of Alzheimer's disease. Such properties are the inhibition of amyloid-β-protein (Aβ) aggregation, Aβ-induced inflammation, and activities of β-secretase and acetylcholinesterase. However, previous studies have revealed that CUR exhibited low bioavailability and difficulties in reaching the brain.

OBJECTIVE

To overcome such drawbacks, this study aims at developing nasal lipid nanocarriers loaded with CUR to effectively target the brain.

METHODS

The lipid nanocarriers (NE) were prepared using the hot solvent diffusion associated with the phase inversion temperature methods. Physico-chemical and morphological characterizations and in vitro drug release of the nanocarriers were carried out. The CUR permeation/retention was analyzed in Franz-type diffusion cell using porcine nasal mucosa. Confocal laser scan and histopathological studies were also performed.

RESULTS

The results showed that the NE sizes ranged between 18 nm and 44 nm with negative zeta potential. The CUR content ranged from 0.24 to 1.50 mg/mL with an encapsulation efficiency of 99%. The profiles of CUR release indicated a biphasic kinetics. CUR-NE permeation across the porcine nasal mucosa was higher when compared to free CUR. These results have also been validated through an analysis on a confocal microscopy. In addition, no toxicity on the nasal mucosa has been observed in a histopathological analysis.

CONCLUSION

These results suggest that it is possible to develop NEs with a high content of CUR and small particle size. Such an encapsulation increases the potential of CUR permeation across the porcine nasal mucosa.

Expression of P-glycoprotein in excised human nasal mucosa and optimized models of RPMI 2650 cells

To assess the transmucosal drug transport in the development of medications for intranasal administration, cellular in vitro models are preferred over the use of animal tissues due to inter-species variations and ethical concerns. With regard to the distribution of active agents and multidrug resistance, the ABC transporter P-glycoprotein plays a major role in several mammalian tissues. The present study compares the expression of this efflux pump in optimized in vitro models based on the human RPMI 2650 cell line with specimens of human turbinate mucosa. The presence of the ABCB1 gene was investigated at the mRNA and protein levels using RT-PCR and Western blot analysis in differently cultured RPMI 2650 cells and excised human nasal epithelium. Furthermore, the localization and activity of P-gp was examined by immunohistochemical staining and functionality assays using different substrates in both in vitro and ex vivo models. Both mRNA and protein expression of P-gp was found in all studied models. Furthermore, transporter functionality was detected in both RPMI 2650 cell culture models and excised human mucosa. The results demonstrated a highly promising comparability between RPMI 2650 models and explants of human nasal tissue concerning the influence of MDR1 on drug disposition. The RPMI 2650 cell line might become a useful tool in preclinical trials to improve reproducibility and achieve greater applicability to humans of experimental data regarding passive diffusion and active efflux of drug candidates.

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.

Visualization of drug translocation in the nasal cavity and pharmacokinetic analysis on nasal drug absorption using positron emission tomography in the rat

We performed positron emission tomography (PET) using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) to evaluate the pharmacokinetics of nasal drug absorption in the rat. The dosing solution of [(18)F]FDG was varied in volume (ranging from 5 to 25 μl) and viscosity (using 0% to 3% concentrations of hydroxypropylcellulose). We modeled the pharmacokinetic parameters regarding the nasal cavity and pharynx using mass balance equations, and evaluated the values that were obtained by fitting concentration-time profiles using WinNonlin® software. The regional nasal permeability was also estimated using the active surface area derived from the PET images. The translocation of [(18)F]FDG from the nasal cavity was visualized using PET. Analysis of the PET imaging data revealed that the pharmacokinetic parameters were independent of the dosing solution volume; however, the viscosity increased the absorption rate constant and decreased the mucociliary clearance rate constant. Nasal permeability was initially higher but subsequently decreased until the end of the study, indicating regional differences in permeability in the nasal cavity. We concluded that the visualization of drug translocation in the nasal cavity in the rat using PET enables quantitative analysis of nasal drug absorption, thereby facilitating the development of nasal formulations for human use.

Nasal administration of liquid crystal precursor mucoadhesive vehicle as an alternative antiretroviral therapy

The purpose of this study was to develop a mucoadhesive stimuli-sensitive drug delivery system for nasal administration of zidovudine (AZT). The system was prepared by formulating a low viscosity precursor of a liquid crystal phase, taking advantage of its lyotropic phase behavior. Flow rheology measurements showed that the formulation composed of PPG-5-CETETH-20, oleic acid and water (55, 30, 15% w/w), denominated P, has Newtonian flow behavior. Polarized light microscopy (PLM) revealed that formulation P is isotropic, whereas its 1:1 (w/w) dilution with artificial nasal mucus (ANM) changed the system to an anisotropic lamellar phase (PD). Oscillatory frequency sweep analysis showed that PD has a high storage modulus (G') at nasal temperatures. Measurement of the mucoadhesive force against excised porcine nasal mucosa or a mucin disk proved that the transition to the lamellar phase tripled the work of mucoadhesion. Ex vivo permeation studies across porcine nasal mucosa exhibited an 18-fold rise in the permeability of AZT from the formulation. The Weibull mathematical model suggested that the AZT is released by Fickian diffusion mechanisms. Hence, the physicochemical characterization, combined with ex vivo studies, revealed that the PPG-5-CETETH-20, oleic acid, and water formulation could form a mucoadhesive matrix in contact with nasal mucus that promoted nasal absorption of the AZT. For an in vivo assessment, the plasma concentrations of AZT in rats were determined by HPLC method following intravenous and intranasal administration of AZT-loaded P formulation (PA) and AZT solution, respectively, at a dose of 8mg/kg. The intranasal administration of PA resulted in a fast absorption process (Tmax=6.7min). Therefore, a liquid crystal precursor formulation administered by the nasal route might represent a promising novel tool for the systemic delivery of AZT and other antiretroviral drugs. In the present study, the uptake of AZT absorption in the nasal mucosa was demonstrated, providing new foundations for clinical trials in patients with AIDS.

Physiology and pathophysiology of respiratory mucosa of the nose and the paranasal sinuses

In this review, anatomy and physiology of the respiratory mucosa of nose and paranasal sinuses are summarized under the aspect of its clinical significance. Basics of endonasal cleaning including mucociliary clearance and nasal reflexes, as well as defence mechanisms are explained. Physiological wound healing, aspects of endonasal topical medical therapy and typical diagnostic procedures to evaluate the respiratory functions are presented. Finally, the pathophysiologies of different subtypes of non-allergic rhinitis are outlined together with treatment recommendations.

Evaluation of anEx VivoModel Implication for Carrier-Mediated Retinal Drug Delivery

PURPOSE

The purpose of this study was to evaluate the implication of an ex vivo model for carrier-mediated retinal drug delivery using an Ussing chamber system.

METHODS

Dutch Belted Pigmented rabbits weighing 2-2.5 kg were used in these studies. Excised posterior segment tissues (RPE-choroid-sclera and sclera), mounted on the Ussing chamber, were used as an ex vivo model. Transport studies were carried out across sclera and RPE-choroid-sclera (RCS) tissue preparations in the sclera to retina (S --> R) and retina to sclera (R --> S) directions for 3 hr at 37 degrees C. The model was validated by permeability studies with paracellular and transcellular markers ([(3)H]mannitol and [(14)C]diazepam, respectively), tissue viability studies (bioelectrical and biochemical assays), and tissue histology and electron microscopy studies. Functional presence of a carrier-mediated transport system for folic acid (folate receptor alpha) was investigated on the basolateral side of the rabbit retina.

RESULTS

Results from bioelectrical, biochemical, and histological evaluation of tissue provide evidence that the RCS tissue preparation remains viable during the period of transport study. Permeability values of [(3)H]mannitol across sclera were 4.18 +/- 1.09 x 10(- 5) cm/s (R --> S) and 4.11 +/- 1.09 x 10(- 5) cm/s (S --> R) and across RCS were 1.77 +/- 0.31 x 10(- 5) cm/s (S --> R) and 1.60 +/- 0.19 x 10(- 5) cm/s (R --> S). Permeability values of [(14)C]diazepam across sclera were 2.37 +/- 0.38 x 10(- 5) cm/s (R --> S) and 2.70 +/- 0.70 x 10(- 5) cm/s (S --> R) and across RCS were 3.12 +/- 0.12 x 10(- 5) cm/s (R --> S) and 2.77 +/- 0.25 x 10(- 5)cm/s (S --> R). The rate of [(3)H]folic acid transport across RCS was found to be significantly higher in the S -->R direction (16.34 +/- 0.94 fmoles min(-1) cm(-2)) as compared with R --> S direction (9.38 +/- 1.44 fmoles min(-1) cm(-2)) and nearly 10-fold higher across sclera as compared with RCS in both directions. Transport of [(3)H]folic acid was found to be pH and temperature dependent and was inhibited by 44.5%, 35.1%, and 50.3% in the presence of unlabeled folic acid, 5-methyltetrahydrofolate (MTF), and Methotrexate (MTX).

CONCLUSIONS

The RCS tissue preparation mounted on the Ussing chamber system, an ex vivo model, can be a useful tool for identification and characterization of carrier-mediated systems present on RPE (a major barrier for retinal drug delivery) and to study carrier-mediated retinal drug delivery via prodrug derivatization.

Kinetics of cellular retention during Caco-2 permeation experiments: role of lysosomal sequestration and impact on permeability estimates

The permeability estimation from cell monolayer permeation data is usually based on 100% recovery assumption. However, poor recovery is often seen in such experiments in practice but often neglected in data interpretation. In the present study, the cellular retention kinetics during Caco-2 permeation experiments of three passively transported compounds, weakly basic propranolol [(+/-)-1-isopropylamino-3-(1-naphthyloxy)-2-propanol], weakly acidic ibuprofen [alpha-methyl-4-(isobutyl)phenylacetic acid], and neutral testosterone (17beta-hydroxy-4-androsten-3-one), were determined. Furthermore, the effects of cellular retention kinetics on apparent permeability were evaluated, and the role of lysosomal sequestration in cellular retention of propranolol was explored. The cellular retention profiles were observed to be direction and concentration dependent, which may cause erroneous directionality and concentration dependence in permeability estimates. Furthermore, the lysosomal sequestration was demonstrated to contribute to the extent and kinetics of the cellular retention of propranolol.

Determination of drug permeability and prediction of drug absorption in Caco-2 monolayers

Permeability coefficients across monolayers of the human colon carcinoma cell line Caco-2, cultured on permeable supports, are commonly used to predict the absorption of orally administered drugs and other xenobiotics. This protocol describes our method for the cultivation, characterization and determination of permeability coefficients of xenobiotics (which are, typically, drug-like compounds) in the Caco-2 model. A few modifications that have been introduced over the years are incorporated in the protocol. The method can be used to trace the permeability of a test compound in two directions, from the apical to the basolateral side or vice versa, and both passive and active transport processes can be studied. The permeability assay can be completed within one working day, provided that the Caco-2 monolayers have been cultured and differentiated on the permeable supports 3 weeks in advance.

The permeation of nalmefene hydrochloride across different regions of ovine nasal mucosa

The permeability of nalmefene hydrochloride (NH) across different regions of ovine nasal mucosa was investigated in vitro. Five different regions of ovine nasal mucosa (superior turbinate mucosa, middle turbinate mucosa, inferior turbinate mucosa, posterior septum mucosa, and anterior septum mucosa) were studied. The results showed that the permeability coefficients of NH through different regions of nasal mucosa were different, and the suitable regions for the absorption of NH were the middle turbinate mucosa, the posterior septum mucosa and the superior turbinate. At the same time, the middle turbinate mucosa was the largest region among the five regions, thus it was the main absorption region for NH. The high uniformity of the middle turbinate mucosa also made it the most suitable model for the permeation of NH in vitro.

Transport of anti-allergic drugs across the passage cultured human nasal epithelial cell monolayer

The purpose of this study was to investigate the nasal absorption characteristics of a series of anti-allergic drugs across the human nasal epithelial cell monolayer, which was passage cultured by the liquid-covered culture (LCC) method on Transwell. Characterization of this cell culture model was achieved by bioelectric measurements and morphological studies. The passages 2--4 of cell monolayers exhibited the TEER value of 1731+/-635 Omega cm(2) after 2 days of seeding and maintained high TEER value for 4--6 days. Morphological study by TEM and SEM showed the existence of the tight junctions, and the cuboidal shaped epithelial cells monolayer. A series of anti-allergic drugs, albuterol hemisulfate, albuterol, fexofenadine HCl, dexamethasone, triamcinolon acetonide, and budesonide were selected as model compounds for transport studies. All the drugs were assayed using reversed-phase HPLC under isocratic conditions. Results indicated that within the logP (apparent 1-octanol/water partition coefficient) range from --1.58 (albuterol) to 3.21 (budesonide), there existed 100-fold difference in the apparent permeability coefficients (P(app)). A log-linear relationship was shown between the drug logP and the P(app) across passaged human nasal epithelial monolayers. The amount of fexofenadine HCl and dexamethasone across passaged human nasal cell monolayers was concentration-dependent in the direction of apical to basolateral. The direction dependent transport studies were investigated among all these drugs and no significant difference in the two directions was observed. In conclusion, this LCC passaged human nasal epithelial culture model may be a useful in vitro model for studying the passive transport processes in nasal drug delivery.

Correlation between epithelial toxicity and surfactant structure as derived from the effects of polyethyleneoxide surfactants on caco-2 cell monolayers and pig nasal mucosa

The cell toxic effects of nonionic surfactants were investigated by means of two in vitro models, namely pig nasal mucosa mounted in horizontal Ussing chambers, and Caco-2 cell monolayers. A series of homologous polyethyleneoxide (PEO) surfactants with a wide span in hydrophilic head-group size and hydrophobic chain lengths were screened for concentration-dependent effects on the transepithelial electrical resistance (TEER) and mannitol permeability across Caco-2 cell monolayers. Trends in effects on permeability in the presence of increasing surfactant concentration coincided with the effects seen on TEER. Correlation of surfactant molecular structure with cell toxicity showed the size of the PEO group to be a more critical parameter than the size of the hydrocarbon chain. More specifically, the presence of very long PEO groups (>30 EO units) were found to lead to a decrease in cell toxicity. Similar trends were observed in the studies of the effects of PEO surfactants on pig nasal mucosa mounted in horizontal Ussing chambers. However, the nasal mucosa was somewhat more tolerant towards high surfactant concentrations than the Caco-2 cells. The relation between surfactant molecular structure and cell toxic effects is discussed in terms of micellar surface adsorption and micellar solubilization. The effect of the surfactants on the solubility of budesonide was investigated at two different surfactant concentrations (0.01 and 1 mg/mL). At the lower concentration, the solubilizing capacity of all of the surfactants was marginal, and there was no correlation between solubilizing capacity and cmc. At the higher concentration, on the other hand, all surfactants substantially increased the solubility of budesonide. The C18 PEO-ester with 40 EO units in the head group was found to be an efficient micellar solubilizer for budesonide, without causing adverse effects on the Caco-2 cell monolayers.

Cell culture models of the respiratory tract relevant to pulmonary drug delivery

The respiratory tract holds promise as an alternative site of drug delivery due to fast absorption and rapid onset of drug action, with avoidance of hepatic and intestinal first-pass metabolism as an additional benefit compared to oral drug delivery. At present, the pharmaceutical industry increasingly relies on appropriate in vitro models for the faster evaluation of drug absorption and metabolism as an alternative to animal testing. This article reviews the various existing cell culture systems that may be applied as in vitro models of the human air-blood barrier, for instance, in order to enable the screening of large numbers of new drug candidates at low cost with high reliability and within a short time span. Apart from such screening, cell culture-based in vitro systems may also contribute to improve our understanding of the mechanisms of drug transport across such epithelial tissues, and the mechanisms of action how advanced drug carriers, such as nanoparticles or liposomes, can help to overcome these barriers. After all, the increasing use and acceptance of such in vitro models may lead to a significant acceleration of the drug development process by facilitating the progress into clinical studies and product registration.

In vitro permeation studies comparing bovine nasal mucosa, porcine cornea and artificial membrane: androstenedione in microemulsions and their components

The components of a carrier formulation can interact with an added drug as well as with the membrane surface they were applied on. Therefore, they can influence permeability of the membrane and permeation of the drug. The particular membrane structure might lead to different drug permeation out of one and the same carrier formulation. In this study, in vitro permeability of androstenedione (AD) as a highly lipophilic substance was investigated in excised bovine nasal mucosa, porcine cornea and the artificial cellulose membrane Nephrophan. Two microemulsions (ME) with either the addition of the co-surfactants hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD; ME-CD) or propylene glycol (PG, ME-PG) were tested in order to be used as carrier systems. Both MEs also consisted of 5% isopropyl myristate (IPM), 20% Cremophor EL (CrEL), and water. Buffer solution (EBS) with 0.0025% AD served as control solution and was furthermore compared to 0.0025% AD/buffer-solutions containing the ME components HP-gamma-CD in different concentrations (0.012, 0.024, 9%) as well as 20% CrEL. The AD-permeation behaviour through the three tissues was differently influenced by the MEs. The apparent permeability coefficients (Papp) of nasal mucosa for both ME systems did not differ from the Papp of the AD/buffer solution. In case of the other two barriers (cornea, Nephrophan, ME-PG as well as ME-CD provoked extended time lags for AD to permeate, so the Papp could not be calculated or declined to zero. Papp of AD/buffer solution without any additives resulted for cornea, nasal mucosa and Nephrophan in a ratio of 1:3:4. CrEL and 9% HP-gamma-CD diminished the Papp, except HP-gamma-CD in molar AD/HP-gamma-CD-ratios of 1:1 (0.012%) and 1:2 (0.024%). It seems that the composition of lipophilic and hydrophilic structures of the carrier systems or the additives had a higher impact on the Papp of cornea than on the Papp of the other tissues. Structure and character of the different membranes are considered to be mainly responsible for the differentiated permeation behaviour.

Uptake of ovalbumin-conjugated starch microparticles by pig respiratory nasal mucosa in vitro

The uptake of ovalbumin-conjugated starch microparticles (OVA-MP) was studied after application to porcine respiratory nasal mucosa in vitro. Nasal mucosa from freshly slaughtered pigs was mounted in horizontal Ussing chambers, which permit monitoring of the viability of the tissue exposed to microparticles and ensure that the microparticles are deposited on the mucosa. The antigen-conjugated starch microparticles have previously been shown to produce strong mucosal, cellular and systemic immune responses to conjugated model antigens following oral administration. Intranasal administration of vaccines for mucosal immunisation is an interesting alternative to oral administration, since nasal delivery systems generally require lower doses of antigen and the site of application is better suited for protection against air-borne antigens. Most of a nasally administered dose is deposited on the surface of the respiratory area of the nasal mucosa. It is therefore important to examine whether the microparticles are taken up in this area and, if so, by which cell type. Confocal laser scanning microscopy and transmission electron microscopy (TEM) of the nasal tissue both showed intracellular OVA-MP in non-ciliated epithelial cells after 45 min' incubation. The morphology of the cells in the TEM preparations did not support the presence of either M cells (specialised antigen sampling cells) or adjacent lymphocytes. Anticytokeratin-18 (Ac18) was used as a potential M cell marker. However, there was no indication of Ac18 binding to M cells, but it did bind to mucus-producing cells in the respiratory nasal mucosa. In conclusion, OVA-MP were taken up intracellularly by non-ciliated epithelial cells in the nasal respiratory mucosa of pigs, in vitro.

Evaluation of drug release from gels on pig nasal mucosa in a horizontal Ussing chamber

In this study, controlled release gel formulations containing dihydroalprenolol (DHA), hydrocortisone (HC) or testosterone (TS) in Carbopol 934P (C934) were evaluated using pig nasal mucosa in a horizontal Ussing chamber. The controlled release gel formulations were designed by including DHA in vesicle bilayers formed with sodium dodecyl sulphate (SDS) (1.4 and 36 mM) and by partitioning TS to the core of Brij 58 (B58, 1%) micelles. For comparison, unmodified gels and solutions of the drugs and additives were examined in parallel experiments. The viability and toxicity were evaluated with electrophysiological measurements and light microscopy. The results showed that C934 did not affect the viability of the mucosa and that the rate and profile of the appearance on the receiver side was independent of whether the substances were released from an unmodified gel or an unmodified solution. Continuous electrophysiological measurements made during exposure showed that B58 (1%) and SDS (1.4 mM) inactivated the mucosa, whereas SDS (36 mM) activated it. Investigations made after a 90-min exposure to the formulations showed that all the modified gels had inactivated the mucosa and had negative effects on the morphology. For the TS-B58 (1%) and the DHA-SDS (36 mM) gels, the rate-limiting step in transport was the release from the formulation. The results confirmed that gels from C934 are suitable for nasal administration and also clearly indicated the different degrees of toxicity of the controlled release formulations evaluated in this study. The horizontal Ussing chamber method was a suitable tool for the evaluation of gels for nasal administration.