Statistical comparison of dissolution profiles to predict the bioequivalence of extended release formulations

Appropriate setting of dissolution specification of extended release (ER) formulations should include precise definition of a multidimensional space of complex definition and interpretation, including limits in dissolution parameters, lag time (t-lag), variability, and goodness of fit. This study aimed to set dissolution specifications of ER by developing drug-specific dissolution profile comparison tests (DPC tests) that are able to detect differences in release profiles between ER formulations that represent a lack of bioequivalence (BE). Dissolution profiles of test formulations were simulated using the Weibull and Hill models. Differential equations based in vivo-in vitro correlation (IVIVC) models were used to simulate plasma concentrations. BE trial simulations were employed to find the formulations likely to be declared bioequivalent and nonbioequivalent (BE space). Customization of DPC tests was made by adjusting the delta of a recently described tolerated difference test (TDT) or the limits of rejection of f2. Drug ka (especially if ka is small), formulation lag time (t-lag), the number of subjects included in the BE studies, and the number of sampled time points in the DPC test were the factors that affected the most these setups of dissolution specifications. Another recently described DPC test, permutation test (PT), showed excellent statistical power. All the formulations declared as similar with PT were also bioequivalent. Similar case-specific studies may support the biowaiving of ER drug formulations based on customized DPC tests.

Crystal suspensions of poorly soluble peptides for intra-articular application: a novel approach for biorelevant assessment of their in vitro release

Crystal suspensions of 3 poorly soluble peptides (MSC1, 2 and 3), intended for intra-articular administration were prepared and in vitro release was tested by a modified USP IV apparatus, combined with a dialysis system. Half-lives of release profiles were ∼5 days for MSC1 and ∼0.5 days for MSC2 and MSC3, showing the potential to achieve sustained exposure from crystal suspensions after intra-articular administration. The in vitro release setup discriminated between (i) different formulations, (ii) different concentrations of API and (iii) different APIs. In addition it was shown that this method allows the modification of release conditions in order to gain more biorelevance for in vitro release testing in the field of intra-articular application: the influence of synovial fluid components hyaluronic acid and albumin was demonstrated, showing prolonged half-lives for suspensions containing 2.5% bovine serum albumin (5 days) and accelerated release rates for suspensions containing 1% sodium hyaluronate (2.5 days) in comparison to a suspension in phosphate buffered saline (4 days). Furthermore, it was demonstrated that release rates of a suspension containing an artificial synovial fluid were in accordance with suspensions containing bovine synovial fluid (t1/2∼4 days).

Finite dose skin mass balance including the lateral part: comparison between experiment, pharmacokinetic modeling and diffusion models

This work investigates in vitro finite dose skin absorption of the model compounds flufenamic acid and caffeine experimentally and mathematically. The mass balance in different skin compartments (donor, stratum corneum (SC), deeper skin layers (DSL), lateral skin parts and acceptor) is analyzed as a function of time. For both substances high amounts were found in the lateral skin compartment after 6h of incubation, which emphasizes not to elide these parts in the modeling. Here, three different mathematical models were investigated and tested with the experimental data: a pharmacokinetic model (PK), a detailed microscopic two-dimensional diffusion model (MICRO) and a macroscopic homogenized diffusion model (MACRO). While the PK model was fitted to the experimental data, the MICRO and the MACRO models employed input parameters derived from infinite dose studies to predict the underlying diffusion process. All models could satisfyingly predict or describe the experimental data. The PK model and MACRO model also feature the lateral parts.

Effects of the Mucoadhesive Polymer Polycarbophil on the Intestinal Absorption of a Peptide Drug in the Rat

The absorption across rat intestinal tissue of the model peptide drug 9-desglycinamide, 8-arginine vasopressin from bioadhesive formulations was studied in-vitro, in a chronically isolated internal loop in-situ and after intraduodenal administration in-vivo. A controlled-release bioadhesive drug delivery system was tested, consisting of microspheres of poly(2-hydroxyethyl methacrylate) with a mucoadhesive Polycarbophil-coating, as well as a fast-release formulation consisting of an aqueous solution of the peptide in a suspension of Polycarbophil particles. Using the controlled-release system, a slight improvement of peptide absorption was found in-vitro in comparison with a non-adhesive control system, but not in-situ or in-vivo. In contrast, bioavailability was significantly increased in all three models from the Polycarbophil suspension in comparison with a solution of the drug in saline. The effect appeared to be dose-dependent, indicative of intrinsic penetration-enhancing properties of the mucoadhesive polymer. A prolongation of the absorption phase in-vitro and in the chronically isolated loop in-situ suggested that the polymer was able to protect the peptide from proteolytic degradation. This could be confirmed by degradation studies in-vitro. The duration of the penetration enhancing/enzyme inhibiting effect was diminished with increasing complexity of the test model, in the same way as was previously found for the bioadhesive effect. This interrelationship suggests that the observed improvement in peptide absorption and the mucoadhesive properties of this polymer are associated. The development of a fast-release oral dosage form for peptide drugs on the basis of Polycarbophil appears to be possible.

Nanoparticles made from novel starch derivatives for transdermal drug delivery

The goal of this paper was aimed to the formulation of nanoparticles by using two different propyl-starch derivatives - referred to as PS-1 and PS-1.45 - with high degrees of substitution: 1.05 and 1.45 respectively. A simple o/w emulsion diffusion technique, avoiding the use of hazardous solvents such as dichloromethane or dimethyl sulfoxide, was chosen to formulate nanoparticles with both polymers, producing the PS-1 and PS-1.45 nanoparticles. Once the nanoparticles were prepared, a deep physicochemical characterization was carried out, including the evaluation of nanoparticles stability and applicability for lyophilization. Depending on this information, rules on the formation of PS-1 and PS-1.45 nanoparticles could be developed. Encapsulation and release properties of these nanoparticles were studied, showing high encapsulation efficiency for three tested drugs (flufenamic acid, testosterone and caffeine); in addition a close to linear release profile was observed for hydrophobic drugs with a null initial burst effect. Finally, the potential use of these nanoparticles as transdermal drug delivery systems was also tested, displaying a clear enhancer effect for flufenamic acid.

Nortriptyline for smoking cessation: release and human skin diffusion from patches

The objective of this work was to develop a simple and inexpensive transdermal formulation containing Nortriptyline Hydrochloride (NTH) for smoking cessation support therapy. Hydroxypropyl-methyl-cellulose was chosen as polymer and a mixture of transdermal enhancers (selected from previous research) was incorporated. The formulations were characterised in terms of appearance, thickness, uniformity of NTH content, release and skin permeation. Release studies demonstrated controlled release for four formulations. Diffusion studies were performed through human heat separated epidermis (HHSE) using Franz Diffusion Cells (FDC). Patches provided different fluxes varying from 20.39+/-7.09 microg/(cm(2) h) to 256.19+/-94.62 microg/(cm(2) h). The penetration profiles of NTH within the stratum corneum (SC) and deeper skin layers (DSL) were established after three administration periods (3 h, 6 h, and 24 h). Skin changes induced by the application of the patches were observed by confocal laser scanning microscopy (CLSM). The highest flux obtained would provide the recommended doses for smoke cessation support therapy (25-75 mg per day) with a 2 cm x 2 cm patch or a 3.5 cm x 3.5 cm patch, respectively, without skin damage evidence.

Dexamethasone-loaded nanoparticle-coated microparticles: Correlation between in vitro drug release and drug transport across Caco-2 cell monolayers

This work reports the preparation of dexamethasone in nanoparticle-coated microparticles and the study of the influence of such microencapsulation on drug absorption across Caco-2 cell monolayers. Nanoparticle-coated microparticles were prepared by spray-drying using nanocapsules (NC) or nanospheres (NS) in aqueous suspensions as coating material. Drug contents ranged from 64 to 134mgg(-1), yields between 49% and 67% and moisture content below 2.0%. SEM and AFM analysis demonstrated that the nanoparticle-coated microparticles (20-53microm) show nanostructures on their surface with a similar diameter compared to the aqueous suspensions. The type of nanocoating material had a significant influence on the drug release profile and on the drug permeation across Caco-2 cells: NC-coated microparticles led to a prolonged release and slower transport across Caco-2 cell monolayers, while the NS-coated microparticles showed a faster release and Caco-2 transport compared to uncoated microparticles. The correlation between the amount of drug permeated and the drug released (%) suggests that the drug absorption from such a delivery system is controlled mainly by the release rate rather than by epithelial permeability. Caco-2 transport studies appear to be a useful characterization tool for the development of microparticulate oral controlled release systems.

Cationic poly(lactide-co-glycolide) nanoparticles as efficient in vivo gene transfection agents

Poly(lactide-co-glycolide) (PLGA), a biocompatible and biodegradable polyester co-polymer of PLA and PGA, has been recognized for its ability to deliver genes. However, gene delivery by PLGA nanoparticles is limited by their negative charge and their poor transport through mucosal barriers. In this study, PLGA nanoparticles were surface modified with cationic chitosan in an effort to improve their gene delivery capability. PLGA nanoparticles were synthesized by emulsion-diffusion-evaporation technique using PVA-chitosan (PLGA1) or PVA-chitosan-PEG (PLGA2) blend as stabilizers. This method is reproducible and produces nanoparticles with hydrodynamic diameter <200 nm. The nanoparticles were characterized by zetasizer, photon correlation spectroscopy and atomic force microscopy. A549 epithelial cells were transfected in vitro with PLGA particles complexed with a reporter plasmid encoding green fluorescent protein. PLGA particles transferred EGFP gene, but were less efficient than the lipofectamine control. The nanoparticles were also tested for their ability to transport across the nasal mucosa in vivo in mice. The results show that both PLGA1 and PLGA2 facilitate gene delivery and expression in vivo with increased efficiency and without causing inflammation, as measured by IL-6. Together, these results indicate that chitosan-modified PLGA nanoparticles have greater potential as gene carriers.

Cationic silica nanoparticles as gene carriers: synthesis, characterization and transfection efficiency in vitro and in vivo

The potential of cationic SiO2 nanoparticles was investigated for in vivo gene transfer in this study. Cationic SiO2 nanoparticles with surface modification were generated using amino-hexyl-amino-propyltri-methoxysilane (AHAPS). The zeta potential of the nanoparticles at pH = 7.4 varied from -31.4 mV (unmodified particles; 10 nm) to +9.6 mV (modified by AHAPS). Complete immobilization of DNA at the nanoparticle surface was achieved at a particle ratio of 80 (w/w nanoparticle/DNA ratio). The surface modified nanoparticle had a size of 42 nm with a distribution from 10-100 nm. The ability of these particles to transfect pCMVbeta reporter gene was tested in Cos-1 cells, and optimum results were obtained in the presence of FCS and chloroquine at a particle ratio of 80. These nanoparticles were tested for their ability to transfer genes in vivo in the mouse lung, and a two-times increase in the expression levels was found with silica particles in comparison to EGFP alone. Very low or no cell toxicity was observed, suggesting silica nanoparticles as potential alternatives for gene transfection.

Preparation and characterization of cationic PLGA nanospheres as DNA carriers

Nanoparticles formulated from biodegradable polymers such as poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) are being extensively investigated as non-viral gene delivery systems due to their controlled release characteristics and biocompatibility. PLGA nanoparticles for DNA delivery are mainly formulated by an emulsion-solvent evaporation technique using PVA as a stabilizer generating negatively charged particles and heterogeneous size distribution. The objective of the present study was to formulate cationically modified PLGA nanoparticles with defined size and shape that can efficiently bind DNA. An Emulsion-diffusion-evaporation technique to make cationic nanospheres composed of biodegradable and biocompatible co-polyester PLGA has been developed. PVA-chitosan blend was used to stabilize the PLGA nanospheres. The nanospheres were characterized by atomic force microscopy (AFM), photon-correlation spectroscopy (PCS), and Fourier transform infrared spectroscopy (FTIR). Zeta potential and gel electrophoresis studies were also performed to understand the surface properties of nanospheres and their ability to condense negatively charged DNA. The designed nanospheres have a zeta potential of 10mV at pH 7.4 and size under 200nm. From the gel electrophoresis studies we found that the charge on the nanospheres is sufficient to efficiently bind the negatively charged DNA electrostatically. These cationic PLGA nanospheres could serve as potential alternatives of the existing negatively charged nanoparticles.

Lectin-mediated drug delivery: discrimination between cytoadhesion and cytoinvasion and evidence for lysosomal accumulation of wheat germ agglutinin in the Caco-2 model

Lectin-mediated drug delivery may become a promising strategy to improve the efficacy of poorly permeable drugs by utilising active high-capacity transport pathways of epithelial tissues. This requires the elucidation of the basic mechanisms of lectin uptake prior to their practical use. We studied the interaction between the dietary lectin wheat germ agglutinin (WGA) and Caco-2 cells (single cells and monolayers) by a newly established assay design that is able to discriminate between cellular binding and uptake as well as by confocal microscopy: (i) All binding sites available for WGA at the cell membrane were occupied within 10 min of incubation. (ii) Cytoadhesion was followed by immediate uptake. After 20 min, 60% (single cells) or 30% (monolayers) of the membrane bound lectin were internalised. However, regardless of cell arrangement, 80% of the surface bound lectin was taken up into the cells during the course of the experiment. (iii) About 50% of the internalised lectin accumulated within the lysosomes after 1 h. This was confirmed by assays in the presence of monensin, an inhibitor of endosomal acidification, and by colocalisation with lysosomal cathepsin followed by semiquantitative image analysis. Further analysis by immunocytochemistry suggested that the trans-Golgi complex and the caveoli were not involved. Due to cytoadhesion, cytoinvasion and partial lysosomal accumulation, WGA-mediated drug delivery may provide for improved intracellular availability of conjugated drugs or colloidal carrier systems.

Lectin-functionalized liposomes for pulmonary drug delivery: interaction with human alveolar epithelial cells

In this study the interaction of lectin-functionalized liposomes with two different alveolar epithelial cell culture models was evaluated. Plant lectins were coupled to liposomes exploiting the avidin/biotin technology. In contrast to lectin-free liposomes, lectin functionalized liposomes specifically bound to A549 cells, a tumor-derived cell line. Using this cell line, temperature-dependent binding assays as well as confocal laser scanning microscopy (CLSM) revealed that the lectin liposomes were only bound but not taken up by these cells. In contrast to these findings, confocal images of human alveolar epithelial cells in primary culture incubated together with lectin liposomes indicated binding as well as cellular uptake. Fluorescein-isothiocyanate (FITC)-labeled dextrans (Mw 40,000 Da), encapsulated in lectin-functionalized liposomes and incubated with monolayers of primary cultured human alveolar epithelial cells appeared to be localized intracellularly by CLSM. This suggests that lectin-mediated bioadhesion and uptake of liposomal carriers may provide a useful technology for improved delivery of hydrophilic macromolecules to the alveolar epithelium.

Cationic solid-lipid nanoparticles can efficiently bind and transfect plasmid DNA

The suitability of cationically modified solid-lipid nanoparticles (SLN) as a novel transfection agent was investigated. SLN were produced by hot homogenisation using either Compritol ATO 888 or paraffin as matrix lipid, a mixture of Tween 80 and Span 85 as tenside and either EQ1 (N,N-di-(beta-steaorylethyl)-N,N-dimethylammonium chloride) or cetylpyridinium chloride as charge carrier. The resulting particles were approximately 100 nm in size and showed zeta potentials around +40 mV at pH 7.4. DNA binding was tested by agarose gel electrophoresis. The resulting SLN-DNA complexes were further characterised by AFM and zeta potential measurements. Only the SLN batch SII-13, composed of 4% Compritol, 4% Tween/Span and 1% EQ1, was able to form stable complexes with DNA. Typical complexes were 300 to 800 nm in size. Cytotoxicity and transfection efficiency was tested in vitro on Cos-1 cells. Cationic SLN produced by modification with EQ1 were well tolerated, with LD50 values >3 mg/ml in the LDH release assay and >0.6 mg/ml in the WST-1 assay. Further, SLN-DNA complexes containing between 10 and 200 weight equivalents of SII-13 (matrix lipid) efficiently transfected the galactosidase expression plasmid pCMVbeta in the absence and presence of the endosomolytic agent chloroquine.

Biodegradable nanoparticles for targeted drug delivery in treatment of inflammatory bowel disease

The use of nanoparticles for targeted oral drug delivery to the inflamed gut tissue in inflammatory bowel disease was examined. Such a strategy of local drug delivery would be a distinct improvement compared with existing colon delivery devices for this disease. An experimental colitis was induced by trinitrobenzenesulfonic acid to male Wistar rats. Rolipram, an anti-inflammatory model drug, was incorporated within poly(lactic-coglycolic acid) nanoparticles, which were administered once a day orally for five consecutive days. A clinical activity score and myeloperoxidase activity were determined to assess the inflammation, whereas an adverse effect index reflected the remaining neurotropic effect of rolipram resulting from its systemic absorption. All nanoparticle formulations proved to be as efficient as the drug in solution in mitigating the experimental colitis. The clinical activity score and myeloperoxidase activity decreased significantly after the oral administration of rolipram nanoparticles or solution. During the next 5 days when animals were kept without drug treatment the drug solution group displayed a strong relapse, whereas the nanoparticle groups continued to show reduced inflammation levels. The rolipram solution group had a high adverse effect index, whereas the rolipram nanoparticle groups proved their potential to retain the drug from systemic absorption as evidenced by a significantly reduced index. This new delivery system enabled the drug to accumulate in the inflamed tissue with higher efficiency than when given as solution. The nanoparticle deposition in the inflamed tissue should be given particular consideration in the design of new carrier systems for the treatment of inflammatory bowel disease.

[Marker transport across biological barriers in vitro: comparison of cell culture models for the gastrointestinal barrier, the blood-brain barrier and the alveolar epithelium of the lung]

In order to respond to the flood of new active ingredients currently being generated by combinatorial chemistry or molecular biological synthesis, selection procedures able to filter out rapidly and economically those drug candidates with the highest development potential are required. This necessitates the measurement of fundamental biopharmaceutical parameters very early in the drug development process. Any pharmaceutically active agent must be able to overcome the body's natural protective mechanisms. A broad variety of biological barriers can be simulated in the laboratory by cell monolayer models. Apart from ethical aspects, the advantage of these in vitro test systems is that permeability studies can be performed at high throughput rates under controlled and reproducible conditions. The validity of such a model is ultimately reflected in its ability to accurately predict the behaviour of an active ingredient at the corresponding in vivo barrier.

Interrelation of permeation and penetration parameters obtained from in vitro experiments with human skin and skin equivalents

In a comparative study, two different in vitro cutaneous test systems were examined: (1) The Franz diffusion cell (FD-C), a test system to study drug permeation through the skin and to obtain data like steady state flux and lag time as well as permeability and diffusion coefficients. (2) The Saarbruecken penetration model (SB-M), a test system to investigate drug penetration into different skin layers and after varying incubation times to acquire values about the quasi steady state drug amounts in the stratum corneum (SC). Three drug concentrations (0.9, 0.45 and 0.225%) of a lipophilic model drug preparation, flufenamic acid in wool alcohols ointment, were applied on the skin's surface using 'infinite dose' conditions. Trypsin-isolated SC, heat-separated epidermis, full-thickness skin and reconstructed human skin (RHS) served as skin membranes in the FD-C, while the SB-M experiments were only carried out using full-thickness skin. Increasing steady state flux data and m(ss) values (steady state drug amount in the SC) were detectable after the application of rising drug amounts. Concerning the permeability of the used skin membranes in establishing barrier properties, the following rank order was observed: RHS>SC> or =epidermis>full skin. The flux data of the FD-C experiments for isolated SC, separated epidermis and RHS were linearly related with the m(ss) values of the SB-M investigations, allowing a direct comparison of permeation with penetration parameters. Concerning the drug amount in the SC, previous investigations succeeded in the establishment of an in vivo/in vitro correlation. Based on the results presented here, the prediction of drug amounts present in the SC after different incubation times in vivo is now possible after penetration as well as permeation experiments using the lipophilic model drug preparation, flufenamic acid in wool alcohols ointment.

Reconstructed skin equivalents for assessing percutaneous drug absorption from pharmaceutical formulations

Excised human skin has so far been considered to be one of the most suitable in vitro methods to evaluate the penetration of dermatologically applied substances. The limited supply and the relatively high donor variability stimulated many research groups to use animal skin as a substitute for human skin. Since nowadays reconstructed skin equivalents are commercially available, we examined these cultures for their suitability as a percutaneous absorption model for different pharmaceutical formulations. One such equivalent is EpiDerm (EPI-606, MatTek corporation, Ashland Massachusetts) which was investigated using the lipophilic model drug flufenamic acid. Permeation studies with the Franz diffusion cell were undertaken to evaluate the model for the establishment of a new in vitro method to study the percutaneous absorption of different dosage forms. The drug was applied in two pharmaceutical formulations to the intact surface of the skin disk: dissolved in wool alcohol ointment (0.1125 %), and dissolved in Soerensen phosphate buffer pH 7.4 (0.1125% solution). HPLC was used for the analysis of drug content. It was shown that the model forms a barrier towards diffusion by comparing the permeation across the tissue-free inserts to the equivalents. Flux values were calculated and the permeation across the skin equivalent from the solution was noted to be almost forty times higher than from the ointment. Two different batches of the skin equivalent showed no statistically significant difference. Finally the permeability of the reconstructed skin was compared to human epidermis, and a five times higher flux value was found for the skin equivalent model. Our results suggest that reconstructed skin equivalents based on human keratinocytes have potential as a pharmaceutical test system to study dermal drug transport from topical formulations.

Lectin-functionalized liposomes for pulmonary drug delivery: effect of nebulization on stability and bioadhesion

The generation of respirable aerosols of a functionalized colloidal carrier has been investigated in this study. Lectin-functionalized liposomes, which proved to show improved cell association (using A549 cell line and primary human alveolar cells) even in the presence of a commercial lung surfactant preparation, have been developed. The stability of non-functionalized liposomes during nebulization using a jet nebulizer (Pari II provocation nebulizer, operated using an air flow of 30 l/min) was firstly investigated, and the experimental and formulation conditions were optimized and applied for the preparation of lectin-functionalized liposomes. The incorporation of cholesterol enhanced the stability of the liposomes during nebulization (from 15-20% leakage of a hydrophilic marker to 8% upon cholesterol incorporation) and upon incubation with lung surfactant preparation. Nebulization of the functionalized liposomes did not significantly influence their physical stability. Their enhanced cell binding capability (compared to non-functionalized liposomes) was also maintained. A drop in cell association compared to fresh functionalized liposomes was detected after nebulization, nevertheless, the binding was still significantly higher than that of the non-functionalized liposomes. The deposition of the liposomal preparation in lung periphery, proved by the deposition of the liposomal preparation on the lower stages of an ASTRA type cascade impinger and a mean median aerodynamic diameter (MMAD) of 2.85 microm, makes it a potential candidate as a macromolecule-drug carrier for local and/or systemic administration.

Low-temperature micronization of a peptide drug in fluid propellant: case study cetrorelix

Aim of this study was to elaborate an efficient method for the micronization of the decapeptide cetrorelix (a GnRH-antagonist), in order to obtain a microsuspension as basis for other pharmaceutical preparations, such as e.g. inhalation aerosols. A modified pearl-mill coupled with a cryostat was used for the micronization of cetrorelix in fluid propellant and operated under different conditions. The obtained cetrorelix suspensions were analyzed for particle size distribution, purity of cetrorelix, and for metal contamination through abrasion from parts of the mill. The method allowed an effective micronization of cetrorelix. The mean particle size of the initial cetrorelix lyophilizate bulk ware was reduced from 52.5 microm (Volume Mean Diameter, VMD) down to 14.9, 6.1 and 3.1 microm, respectively, respectively. The HPLC analysis of all cetrorelix suspensions after micronization did not show signs of decomposition as compared to the initial product. The elementary analysis of the suspensions performed by inductively coupled plasma mass spectrometry revealed a negligible amount of contaminants in the suspension (Zr = max. 0.6 ppm; Fe, Cr, Ni, Ba, below limit of quantification, i.e. < 0.14 ppm). The only appreciable contaminant, Aluminum (Al = 1.1 ppm), was derived from the mechanical capping of aluminum canisters prior to analysis. The Zr determination in the suspension of 0.6 ppm, is still considered to be negligible as compared to the legally tolerated limit of air contamination. By low-temperature micronization in fluid propellant, fine drug suspensions of cetrorelix for pMDIs can be directly manufactured in one-step procedure without destruction of the peptide structure and without appreciable product contamination.

Oral endotracheal intubation of rats for intratracheal instillation and aerosol drug delivery

As reported in the literature, oral endotracheal intubation of rats is considered to be very difficult. Specialised equipment and complicated techniques have been described to perform this procedure. In our experiment we adopted a simple method, which allowed-without any complicated equipment-the insertion of a relatively wide tube into the trachea of rats, allowing drug administration.

Development of a new aerosol delivery system for systemic pulmonary delivery in anaesthetized and orotracheal intubated rats

Over the last decade, the systemic absorption of a broad range of therapeutics after pulmonary application has been demonstrated in animals as well as in humans. The most common method used in the laboratory is the intratracheal instillation of drugs in solution. This method is, however, unsatisfactory, because of discrepancies in particle distribution, clearance, kind of injury and bioavailability between instillation and inhalative application. On the other hand, a precise determination of the amount of drug applied by aerosol, and of the aerosol volume retained within the lungs is rather difficult, and is not possible for use with small animals such as mice or rats. We describe a system which allows the delivery of aerosols directly into the animal's lungs, and calculation of the amount of drug retained in the lungs. Our system was tested in vitro and in vivo and was shown to allow precise and efficient pharmacokinetic and toxicological studies to be carried out.

[In vitro models of intestinal and alveolar epithelium cultures in pharmaceutical research]

The progress of modern bio- and information-technology has made an enormous impact on the development of new drugs: At the one hand, computer-aided drug design and automated high-throughput screening has enormously facilitated the chemical synthesis of new drug candidates. At the other hand, the number of macromolecular biopharmaceuticals, such as peptides, proteins, antisense agents or gene vectors is continuously increasing. Whether or not such new entities can indeed be developed to safe and efficient medicines, is largely determined by the question, if these molecules are able to reach their actual target (receptor) within the patient"s body. Often, biological barriers, such as the mucosal epithelium of the gastrointestinal tract cannot be passed. In vitro test systems based on human epithelial cells may help to determine those candidate drugs which are well absorbed after oral application. Moreover, such cell culture models are helpful tools for the discovery for new delivery routes for those molecules, which cannot be administered by oral application. In this context, there is an increasing interest in the pulmonary delivery of drugs, as well as in the development of cell culture systems to model the blood-air barrier represented by the alveolar epithelium.

Size-dependent bioadhesion of micro- and nanoparticulate carriers to the inflamed colonic mucosa

PURPOSE

The size-dependent deposition of microparticles and nanoparticles after oral administration to rats using an experimental model colitis was examined. Local delivery of an entrapped drug could reduce side effects and would be a distinct improvement compared with existing colon delivery devices.

METHODS

Ulcerative colitis was induced in Lewis rats with trinitrobenzenesulfonic acid. Fluorescent polystyrene particles with a size of 0.1, 1, or 10 microm were administered for 3 days. The animals then were sacrificed and their guts resected. Particle distribution in the colon was imaged by confocal laser scanning microscopy and quantified by fluorescence spectrophotometry.

RESULTS

In the inflamed tissue, an increased adherence of particles was observed at the thicker mucus layer and in the ulcerated regions. A size dependency of the deposition was found, and an increased number of attached particles to the colon was determined compared with the control group. For 10-micorm particles, only fair deposition was observed (control group: 1.4 +/- 0.6%; colitis: 5.2 +/- 3.8% of administered particle mass). One-micrometer particles showed higher binding (control group: 2.0 +/- 0.8%; colitis: 9.1 +/- 4.2%). Highest binding was found for 0.1-microm particles (control group: 2.2 +/- 1.6%; colitis: 14.5 +/- 6.3%). The ratio of colitis/control deposition increased with smaller particle sizes.

CONCLUSIONS

The use of submicron-sized carriers holds promise for the targeted delivery of drugs to the inflamed colonic mucosal areas in inflammatory bowel disease.

Systemic delivery of cetrorelix to rats by a new aerosol delivery system

PURPOSE

To study the pulmonary absorption and tolerability of various formulations of the decapeptide cetrorelix acetate in rats by a new aerosol delivery system (ASTA-ADS) for intratracheal application.

METHODS

Using the ASTA-ADS, cetrorelix liquid formulations (aqueous solutions for ultrasonic nebulization) were firstly selected and subsequently delivered as nebulized aerosol to orotracheally cannulated rats. The pharmacologic effect (decrease of testosterone serum level) of four cetrorelix formulations was determined in rats by enzyme linked immunosorbant assay, and pharmacokinetic data were determined after measurement of cetrorelix serum level by radioimmunoassay. Histological examination of the lung was performed at the end of the experiments, and in a supplementary experiment the respiratory parameters (resistance and compliance) of rats were monitored by a validated pulmonary monitoring system during the aerosol application of the same formulations.

RESULTS

After an exposure time of 5 min, the applied formulations reduced the testosterone concentration in serum to subnormal levels (< or =1 ng/ml) over a period of 24 h. Comparing the plasma concentration after intratracheal aerosolization with data of intravenous administration, the mean calculated bioavailabilities for the four formulations using the corrected dose (delivered--exhaled amount) were between 48.4 +/- 27.0% and 77.4 +/- 44.0%. The histologic examination of the lungs revealed different tolerability of the various tested formulations ranging from locally intolerable to well tolerated. The measurement of the lung function parameters did not reveal any compound or formulation related changes.

CONCLUSIONS

Our studies show that cetrorelix can be effectively administered as aerosol and that intratracheal aerosolization via the ASTA-ADS provides results that are well comparable to other application routes, as demonstrated by statistical comparison of the newly obtained data with previous results from intratracheal instillation of cetrorelix solutions in rats.

Influences of process parameters on preparation of microparticle used as a carrier system for omega - 3 unsaturated fatty acid ethyl esters used in supplementary nutrition

Microparticles were prepared by complex coacervation to encapsulate eicosapentaenoic acid ethyl ester (EPA-EE) for incorporation into foods as a nutrition supplement. Gelatin and acacia were used in the coacervation process. With an increasing oil/polymer ratio, both yield and encapsulation rate decreased; with an increasing homogenization time, the yield remained constant while the encapsulation rate slightly increased. Several particle hardening techniques were examined and their influence on particle structure, yield and encapsulation rate were examined. Ethanol hardening was compared to cross-linking with dehydroascrobic acid with respect to both yield and encapsulation rate. The particle diameters for both formulations were similar (ethanol: 38.4 +/- 4.1 microm; cross-linking: 41.8 +/- 3.0 microm). Spray-drying of the coacervates led to the smallest particles (5.2 +/- 1.1 microm), lowest yield and encapsulation rate. All microencapsulation products were assayed for their storage stability over 4 weeks with respect to the oxidation of the encapsulated omega - 3 unsaturated fatty acid ester inside the particles. Hardening with ethanol showed the lowest amount of peroxides: particle wall cross-linking by dehydroascorbic acid and spray-drying were observed to be less protective. All microparticles were characterized for their internal structure with confocal laser scanning microscopy (CLSM) after fluorescence labelling of the polymers, in order to localize the oil phase and visualize the distribution of the polymers in the coacervates. With increasing homogenization time, the internal structure changed stepwise from a capsule structure (core/wall) towards a matrix structure. For all experiments, a homogeneous distribution for both polymers, gelatin and acacia was observed inside the particle wall. No influence of the different particle hardening procedures on the polymer distribution was found.

Design of rolipram-loaded nanoparticles: comparison of two preparation methods

The aim of the present work was to investigate the preparation of nanoparticles as a potential drug carrier and targeting system for the treatment of inflammatory bowel disease. Rolipram was chosen as the model drug to be incorporated within nanoparticles. Pressure homogenization-emulsification (PHE) with a microfluidizer or a modified spontaneous emulsification solvent diffusion method (SESD) were used in order to select the most appropriate preparation method. Poly(epsilon-caprolactone) has been used for all preparations. The drug loading has been optimized by varying the concentration of the drug and polymer in the organic phase, the surfactants (polyvinyl alcohol, sodium cholate) as well as the volume of the external aqueous phase. The rolipram encapsulation efficiency was high (>85%) with the PHE method in all cases, whereas with the SESD method encapsulation efficiencies were lower (<40%) when lower surfactant concentrations and reduced volume of aqueous phase were used. Release profiles were characterized by a substantial initial burst release with the PHE method (25-35%) as well as with the SESD method (70-90%). A more controlled release was obtained after 2 days of dissolution with the PHE method (70-90%), no further significant drug release was observed with the SESD method.

Charge-dependent interaction of self-emulsifying oil formulations with Caco-2 cells monolayers: binding, effects on barrier function and cytotoxicity

A positively charged self-emulsifying oil formulation (SEOF), aimed to enhance oral bioavailability of drugs poorly soluble in water, was recently developed. In the present study the Caco-2 cell model was used for the investigation of the charge-dependent interactions of this SEOF with human intestinal epithelial cells. The positively charged emulsions affected the barrier properties of the cell monolayer at high concentrations and reduced the cell viability. However, at the dilution with aqueous phase used in the present study (1:2000), the positively charged SEOF did not induce any detectable cytotoxic effect. The binding of the fluorescent dye DiIC(18)(3) was much higher from the positively charged SEOF, compared to the negatively charged formulation, suggesting an increased closer adhesion of the droplets to the cell surface due to the electrostatic attraction. No transepithelial transport of this compound across Caco-2 cell monolayers was observed with any SEOF formulation.

Biodegradable microparticles as a two-drug controlled release formulation: a potential treatment of inflammatory bowel disease

A multiple unit dosage form for oral delivery based on the microencapsulation of anti-inflammatory drugs using different biodegradable polymers, poly(epsilon-caprolactone), polylactic acid and poly(lactic-co-glycolic acid), prepared either by the water-in-oil-in-water (w/o/w) or the solid-in-oil-in-water (s/o/w) solvent evaporation method was developed. Microparticles were characterized for their size, morphology, encapsulation efficiency and drug release. The physical state of drugs and polymers was determined by differential scanning calorimetry (DSC), imaging of the particles was performed by scanning electron microscopy and confocal laser scanning microscopy. Sulfasalazine and betamethasone used for the treatment of inflammatory bowel disease, were chosen as model drugs. The microparticles were spherical with diameters in the range of 91 to 258 microm by the w/o/w-method, and in the range of 102 to 277 microm by the s/o/w-method. The encapsulation efficiency (EE) varied between 11 and 16% for sulfasalazine and 50 and 67% for betamethasone with the w/o/w-method, and between 73 and 79% for sulfasalazine and 60 and 70% for betamethasone with the s/o/w-method. DSC showed no interaction between polymers and drugs, while the drugs were dispersed in the polymer. In vitro release studies showed a controlled release of sulfasalazine and betamethasone from microparticles prepared by the s/o/w-method; a pronounced burst release of sulfasalazine was observed from microparticles prepared by the w/o/w-method.

Drug distribution in human skin using two different in vitro test systems: comparison with in vivo data

PURPOSE

Two in vitro test systems used to study drug penetration into human skin--the Franz diffusion cell (FD-C) and the Saarbruecken penetration model (SB-M)--were evaluated, and the results were compared with data gained under analogous in vivo conditions.

METHODS

Excised human skin was used in all in vitro experiments. Flufenamic acid dissolved in wool alcohols ointment, was chosen as a model drug, and the preparation was applied using 'infinite dose' conditions. To acquire quantitative information about the drug penetration, the skin was segmented into surface parallel sections at the end of each experiment, first by tape stripping the stratum corneum (SC), and second by cutting the deeper skin layers with a cryomicrotome. The flufenamic acid was extracted from each sample and assayed by high performance liquid chromatography (HPLC). For in vivo experiments, only the tape stripping technique was used.

RESULTS

a) Drug penetration into the SC: In both in vitro test systems the total drug amounts detected in the SC were found to increase over the different incubation times. Similar conditions were obtained in vivo, but on a lower level. Using Michaelis-Menten kinetics, the m(max) value was calculated for the skin of two donors. The relations of the m(max) values for the FD-C and the SB-M closely correspond (1.26 [donor 1] and 1.29 [donor 2]). A direct linear correlation of the drug amount in the SC and the time data were found for in vivo with both in vitro test systems. b) Drug penetration into the deeper skin layers: The detected drug amounts in the deeper skin layers continuously increased with the incubation time in the SB-M, while in the FD-C, only very small drug amounts were observed after incubation times of 30 and 60 minutes. It was also noticed, that the drug amounts rose steeply at time points 3 and 6 hours. Additional studies showed a remarkable penetration of water into the skin from the basolateral acceptor compartment in the FD-C. This could explain the different drug transport into the deeper skin layers between the two in vitro test systems.

CONCLUSIONS

Both in vitro models showed comparable results for the drug penetration into the SC and a robust correlation with in vitro data. Different results were obtained for the deeper skin layers. Whether a correlation between in vitro and in vivo data is also possible here has to be investigated by further experiments.

A nonviral DNA delivery system based on surface modified silica-nanoparticles can efficiently transfect cells in vitro

Diverse polycationic polymers have been used as nonviral transfection agents. Here we report the ability of colloidal silica particles with covalently attached cationic surface modifications to transfect plasmid DNA in vitro and make an attempt to describe the structure of the resulting transfection complexes. In analogy to the terms lipoplex and polyplex, we propose to describe the nanoparticle-DNA complexes by the term "nanoplex". Three batches, Si10E, Si100E, and Si26H, sized between 10 and 100 nm and with zeta potentials ranging from +7 to +31 mV at pH 7.4 were evaluated. The galactosidase expression plasmid DNA pCMVbeta was immobilized on the particle surface and efficiently transfected Cos-1 cells. The transfection activity was accompanied by very low cytotoxicity, with LD(50) values in the milligrams per milliliter range. The most active batch, Si26H, was produced by modification of commercially available silica particles with N-(6-aminohexyl)-3-aminopropyltrimethoxysilane, yielding spherical nanoparticles with a mean diameter of 26 nm and a zeta potential of +31 mV at pH 7.4. Complexes of Si26H and pCMVbeta plasmid DNA formed at w/w ratios of 10 were most effective in promoting transfection of Cos-1 cells in the absence of serum. At this ratio, >90% of the DNA was associated with the particles, yielding nanoplexes with a net negative surface charge. When the transfection medium was supplemented with 10% serum, maximum gene expression was observed at a w/w ratio of 30, at which the resulting particle-DNA complexes possessed a positive surface charge. Transfection was strongly increased in the presence of 100 microM chloroquine in the incubation medium and reached approximately 30% of the efficiency of a 60 kDa polyethylenimine. In contrast to polyethylenimine, no toxicity was observed at the concentrations required. Atomic force microscopy of Si26H-DNA complexes revealed a spaghetti-meatball-like structure. The surface of complexes prepared at a w/w ratio of 30 was dominated by particles half-spheres. Complex sizes correlated well with those determined previously by dynamic light scattering.

Structural analysis of microparticles by confocal laser scanning microscopy

This study demonstrates the potential of confocal laser scanning microscopy (CLSM) as a characterization tool for different types of microparticles. Microparticles were prepared by various methods including complex coacervation, spray drying, double emulsion solvent evaporation technique, and ionotropic gelation. Protein drugs and particle wall polymers were covalently labeled with a fluorescent marker prior to particle preparation, while low molecular weight drugs were labeled by mixing with a fluorescent marker of similar solubility properties. As was demonstrated in several examples, CLSM allowed visualization of the polymeric particle wall composition and detection of heterogeneous polymer distribution or changes in polymer matrix composition under the influence of the drug. Furthermore, CLSM provides a method for three-dimensional reconstruction and image analysis of the microparticles by imaging several coplanar sections throughout the object. In conclusion, CLSM allows the inspection of internal particle structures without prior sample destruction. It can be used to localize the encapsulated compounds and to detect special structural details of the particle wall composition.

Silica nanoparticles modified with aminosilanes as carriers for plasmid DNA

We synthesised silica nanoparticles (SiNP) with covalently linked cationic surface modifications and demonstrated their ability to electrostatically bind, condense and protect plasmid DNA. These particles might be utilised as DNA carriers for gene delivery. All nanoparticles were sized between 10 and 100 nm and displayed surface charge potentials from +7 to +31 mV at pH 7.4. They were produced by modification of commercially available (IPAST) or in-house synthesised silica particles with either N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or N-(6-aminohexyl)-3-aminopropyltrimethoxysilane. All particles formed complexes with pCMVbeta plasmid DNA as evidenced by ratio dependent retardation of DNA in the agarose gel and co-sedimentation of soluble DNA with nanoparticles. High salt and alkaline pH did inhibit complex formation. Absorption onto the particles also decreased the hydrodynamic dimensions of plasmid DNA as shown by photon correlation spectroscopy. Complexes formed in water at a w/w ratio of Si26H:DNA (pCMVbeta) of 300 were smallest with a mean hydrodynamic diameter of 83 nm. For effective condensation a w/w ratio of Si26H:DNA of 30 was sufficient. Further, the absorbed DNA was protected from enzymatic degradation by DNase I.

Visualization and quantification of polymer distribution in microcapsules by confocal laser scanning microscopy (CLSM)

Confocal laser scanning microscopy (CLSM) was employed in order to characterize microcapsules. Microcapsules were prepared by complex coacervation: gelatin and arabic gum were labelled with fluorescent markers. In the capsule wall a homogeneous distribution for both gelatin and arabic gum throughout the capsule wall was depicted. By the use of CLSM and a computational image analysis the quantification of the labelled polymer in the wall material was possible. Adding fluorescently labelled casein as a macromolecular model compound to the coacervation process, a gradiental distribution in the wall material was observed with highest concentration of casein at the oil-wall interface. The influence of casein concentration on its deposition behaviour in the capsule wall was imaged successfully and thereafter quantified by computational image analysis.

Lectin-mediated drug delivery: the second generation of bioadhesives

This paper reviews some recent developments in the area of bioadhesive drug delivery systems. The area of bioadhesion in drug delivery had started some 20 years ago by using so-called mucoadhesive polymers. Many of these polymers were already used as excipients in pharmaceutical formulations. This has facilitated the development of the first bioadhesive drug products, which are now commercially available. A major disadvantage of the hitherto known mucoadhesives, however, is their non-specificity with respect to the substrate. In particular for gastro-intestinal applications, this may cause some premature inactivation and moreover limits the duration of mucoadhesive bonds to the relatively fast mucus turnover. Nevertheless, for some mucoadhesive polymers other interesting functionalities were discovered, such as their ability to modulate epithelial permeability and to inhibit proteolytic enzymes. In contrast to the mucoadhesive polymers, lectins and some other adhesion molecules specifically recognize receptor-like structures of the cell membrane and therefore bind directly to the epithelial cells themselves ("cytoadhesion") rather than to the mucus gel layer. Furthermore, when bioadhesion is receptor-mediated, it is not only restricted to mere binding, but may subsequently trigger the active transport of large molecules or nanoscalic drug carrier systems by vesicular transport processes (endo-/transcytosis). Rather than only acting as a platform for controlled release systems, the concept of lectin-mediated bioadhesion therefore bears the potential for the controlled delivery of macromolecular biopharmaceuticals at relevant biological barriers, such as the epithelia of the intestinal or respiratory tract.

Systemic delivery of the GnRH antagonist cetrorelix by intratracheal instillation in anesthetized rats

Pulmonary absorption of the decapeptide cetrorelix acetate was studied in rats by a non-surgical intratracheal instillation method. The pharmacological effect (decrease of testosterone plasma concentration) following intratracheal (i.t.) instillation was determined in four groups of seven rats each at three different concentrations (0.5, 1.0 and 2.5 mg/kg body weight). The applied doses reduced testosterone plasma concentration to subnormal level (</=1 ng/ml), for 24, 34 and 72 h, respectively. Pharmacokinetic data of cetrorelix were determined in two additional groups of ten and nine rats, respectively, at doses of 0.5 and 1 mg/kg body. After i.t. administration the mean terminal t(1/2) was 12.94+/-1.74 (0.5 mg/kg) and 13.03+/-3.15 h (1 mg/kg); mean residence time (MRT) was 6. 85+/-3.01 and 8.72+/-2.33 h; the C(max) (277.72+/-252.11 and 274. 23+/-113.49 ng/ml) were observed in the first or the second plasma sample, suggesting that the drug was rapidly absorbed (t=1 and 2 h). Comparing the plasma concentration after i.t. administration with data after i.v. administration from a previous study undertaken in the same laboratory, the mean i.t. bioavailability was calculated as 75.80+/-45.42 and 58.97+/-18.25%. The data from the group of 0.5 mg/kg were confirmed in a subsequent experiment. Our studies show that intratracheal instillation via the adopted method of non-surgical cannulation provides reproducible results. In addition, we demonstrated that pharmacologically active amounts of cetrorelix were absorbed from the lungs.

Organic cation transport in rabbit alveolar epithelial cell monolayers

PURPOSE

To characterize organic cation (OC) transport in primary cultured rabbit alveolar epithelial cell monolayers, using [14C]-guanidine as a model substrate.

METHODS

Type II alveolar epithelial cells from the rabbit lung were isolated by elastase digestion and cultured on permeable filters precoated with fibronectin and collagen. Uptake and transport studies of [14C]-guanidine were conducted in cell monolayers of 5 to 6 days in culture.

RESULTS

The cultured alveolar epithelial cell monolayers exhibited the characteristics of a tight barrier. [14C]-Guanidine uptake was temperature dependent, saturable, and inhibited by OC compounds such as amiloride, cimetidine, clonidine, procainamide, propranolol, tetraethylammonium, and verapamil. Apical guanidine uptake (Km = 129 +/- 41 microM, Vmax = 718 +/- 72 pmol/mg protein/5 min) was kinetically different from basolateral uptake (Km = 580 +/- 125 microM, Vmax = 1,600 +/- 160 pmol/mg protein/5 min). [14C]-Guanidine transport across the alveolar epithelial cell monolayer in the apical to basolateral direction revealed a permeability coefficient (Papp) of (7.3 +/- 0.4) x 10(-7) cm/sec, about seven times higher than that for the paracellular marker [14C]-mannitol.

CONCLUSIONS

Our findings are consistent with the existence of carrier-mediated OC transport in cultured rabbit alveolar epithelial cells.

Monolayers of human alveolar epithelial cells in primary culture for pulmonary absorption and transport studies

PURPOSE

To develop a cell culture model of human alveolar epithelial cells in primary culture for the in vitro study of pulmonary absorption and transport.

METHODS

Type II pneumocytes isolated from normal human distal lung tissue by enzyme treatment and subsequent purification were plated on fibronectin/collagen coated polyester filter inserts, and cultured using a low-serum growth medium. Characterization of the cell culture was achieved by bioelectric measurements, cell-specific lectin binding, immunohistochemical detection of cell junctions, and by assessment of transepithelial transport of dextrans of varying molecular weights.

RESULTS

In culture, the isolated cells spread into confluent monolayers, exhibiting peak transepithelial resistance of 2,180 +/- 62 ohms x cm2 and potential difference of 13.5 +/- 1.0 mV (n = 30-48), and developing tight junctions as well as desmosomes. As assessed by lectin-binding, the cell monolayers consisted of mainly type I cells with some interspersed type II cells, thus well mimicking the situation in vivo. The permeability of hydrophilic macromolecular FITC-dextrans across the cell monolayer was found to be inversely related to their molecular size, with Papp values ranging from 1.7 to 0.2 x 10(-8) cm/sec.

CONCLUSIONS

A primary cell culture model of human alveolar epithelial cells has been established, which appears to be a valuable in vitro model for pulmonary drug delivery and transport studies.

Transport of proteolytic enzymes across Caco-2 cell monolayers

PURPOSE

To investigate the mechanisms by which proteolytic enzymes, such as trypsin, chymotrypsin, papain, and bromelain, are able to cross the intestinal mucosal barrier after oral administration to man.

METHODS

Filter-grown Caco-2 cell monolayers were incubated with proteolytic enzymes and then the transepithelial electrical resistance (TEER) and the transport of the paracellular marker fluorescein were monitored. The effects of the enzymes on the cells were investigated by light microscopy and by biochemical assays. Transport of intact proteases across the cells was verified by monitoring the proteolytic activity and MALDI-TOF mass spectroscopic identification of undegraded trypsin.

RESULTS

Depending on time, concentration, and side of exposure to Caco-2 cell monolayers, all proteases decreased the TEER and increased the transport of fluorescein. Some morphological and metabolic changes were observed. The effects were reversible, but until 24 hours after removal of the proteases. Under the conditions of this in-vitro model, approximately 10% of the apically applied dose reached the basolateral compartment as biologically active, non-degraded molecules.

CONCLUSIONS

Proteolytic enzymes were found to exert considerable effects on the barrier function of Caco-2 monolayers, facilitating the transport of normally non-absorbable compounds. This suggests the also reported, but so far unexplained, systemic absorption of proteolytic enzymes after oral administration in vivo may occur by self-enhanced paracellular transport.

Binding, uptake, and transport of hypericin by Caco-2 cell monolayers

The biological evaluation of hypericin in various test models is hampered by its very poor water solubility. In the present study cyclodextrin formulations and liposomal preparations were investigated for improved delivery and solubility of hypericin in aqueous buffer systems. Caco-2 cells, grown to tight monolayers on 96-well tissue culture plates as well as on Transwell polycarbonate filters, were used to study the membrane binding and the epithelial transport of hypericin. Cumulative transport of hypericin, which could not be measured without the use of cyclodextrins, in apical-to-basolateral direction from cyclodextrin-hypericin buffer solutions was 3-5% at 37 degrees C and approximately 0.12% at 4 degrees C after 5 h. After an incubation time of 1 h at 37 and 4 degrees C, 12.7% +/- 2.6% and 6.5% +/- 0.8%, respectively, of hypericin were found to be bound to or taken up by Caco-2 cells. Liposomal formulations markedly increased the solubility of hypericin in Krebs-Ringer buffer, but there was no effect observed on the binding and transport of hypericin delivered by liposomes in the Caco-2 cell model. Due to the fluorescence properties of hypericin, its interaction with the cells could be visualized by confocal laser scanning microscopy. The results indicate that a significant accumulation of the drug in the cell membrane and the cell nucleus membrane takes place. We conclude that hypericin is absorbed through the intestinal epithelium by passive transcellular diffusion and that increasing its solubility by cyclodextrin appears as a promising approach to increase its oral bioavailability for pharmaceutical formulations.

Simultaneous in vivo visualization and localization of solid oral dosage forms in the rat gastrointestinal tract by magnetic resonance imaging (MRI)

PURPOSE

Bioavailability of orally administered drugs is much influenced by the behavior, performance and fate of the dosage form within the gastrointestinal (GI) tract. Therefore, MRI in vivo methods that allow for the simultaneous visualization of solid oral dosage forms and anatomical structures of the GI tract have been investigated.

METHODS

Oral contrast agents containing Gd-DTPA were used to depict the lumen of the digestive organs. Solid oral dosage forms were visualized in a rat model by a 1H-MRI double contrast technique (magnetite-labelled microtablets) and a combination of 1H- and 19F-MRI (fluorine-labelled minicapsules).

RESULTS

Simultaneous visualization of solid oral dosage forms and the GI environment in the rat was possible using MRI. Microtablets could reproducibly be monitored in the rat stomach and in the intestines using a 1H-MRI double contrast technique. Fluorine-labelled minicapsules were detectable in the rat stomach by a combination of 1H- and 19F-MRI in vivo.

CONCLUSIONS

The in vivo 1H-MRI double contrast technique described allows solid oral dosage forms in the rat GI tract to be depicted. Solid dosage forms can easily be labelled by incorporating trace amounts of non-toxic iron oxide (magnetite) particles. 1H-MRI is a promising tool for observing such pharmaceutical dosage forms in humans. Combined 1H- and 19F-MRI offer a means of unambiguously localizing solid oral dosage forms in more distal parts of the GI tract. Studies correlating MRI examinations with drug plasma levels could provide valuable information for the development of pharmaceutical dosage forms.

From sticky stuff to sweet receptors--achievements, limits and novel approaches to bioadhesion

About 10 years ago, the concept of bioadhesion was introduced into the pharmaceutical literature and has since stimulated much research and development both in academia and in industry. The first generation of bioadhesive drug delivery systems (BBDS) were based on so-called mucoadhesive polymers, i.e. natural or synthetic macromolecules, often already well accepted and used as pharmaceutical excipients for other purposes, which show the remarkable ability to 'stick' to humid or wet mucosal tissue surfaces. While these novel dosage forms were mainly expected to allow for a possible prolongation, better localization or intensified contact to mucosal tissue surfaces, it had to be realized that these goals were often not so easily accomplished, at least not by means of such relatively straightforward technology. However, although not always convincing as a 'pharmaceutical glue', some of the mucoadhesive polymers were found to display other, possibly even more important biological activities, namely to inhibit proteolytic enzymes and/or to modulate the permeability of usually tight epithelial tissue barriers. Such features were found to be particularly useful in the context of peptide and protein drug delivery. But still, the interest in realizing 'true' bioadhesion continues: instead of mucoadhesive polymers, plant or bacterial lectins, i.e. adhesion molecules which specifically bind to sugar moieties of the epithelial cell membrane, are now widely being investigated as drug delivery adjuvants. These second-generation bioadhesives not only provide for cellular binding, but also for subsequent endo- and transcytosis. This makes the novel, specifically bioadhesive molecules particularly interesting for the controlled delivery of DNA/RNA molecules in the context of antisense or gene therapy.

Mucoadhesive polymers in peroral peptide drug delivery. II. Carbomer and polycarbophil are potent inhibitors of the intestinal proteolytic enzyme trypsin

PURPOSE

The evaluation of the inhibitory action of two mucoadhesive poly(acrylates), polycarbophil and carbomer, registered by the Food and Drug Administration (FDA), on the intestinal proteolytic enzyme trypsin.

METHODS

The effect of the polymers on trypsin activity by measuring the degradation of a trypsin specific substrate. Binding of Ca2+ ions and proteins (125I-BSA) to the poly(acrylates). The influence of the polymers on the secondary trypsin structure by circular dichroism.

RESULTS

Trypsin inhibition was found to be time-dependent upon addition of Ca2+ in the degradation experiment. Only when Ca2+ was added within 10 min after trypsin incubation, recovery of the enzyme could be observed. Both polymers showed a strong Ca2+ binding ability. Carbomer, which had a higher inhibitory effect on trypsin activity, also revealed a higher Ca2+ binding affinity than polycarbophil. The amount of Ca2+ depleted out of the trypsin structure and the reduction of enzyme activity were comparable. Immobilization of trypsin by binding to the polymers could not be observed at pH 6.7. Circular dichroism studies suggested that, under depletion of Ca2+ from trypsin, the secondary structure changed its conformation, followed by an increased autodegradation of the enzyme.

CONCLUSIONS

The poly(acrylates) investigated may have potential to protect peptides from tryptic degradation and may be used to master the peroral delivery of peptide drugs.