Biomedical subjects

Ulrich F Schaefer

Publications and source records attributed to Ulrich F Schaefer.

15 recordsLinked to original sources

PubMed2006

Nanoparticles--an efficient carrier for drug delivery into the hair follicles.

The penetration and storage behavior of dye-containing nanoparticles (diameter 320 nm) into the hair follicles was investigated. The results were compared to the findings obtained with the same amount of dye in the non-particle form. In the first part of the experiments, the penetration of the dye into the hair follicles was investigated in vitro on porcine skin, which is an appropriate model for human tissue. It was found that the nanoparticles penetrate much deeper into the hair follicles than the dye in the non-particle form, if a massage had been applied. Without massage, similar results were obtained for both formulations. Subsequently, the storage behavior of both formulations in the hair follicles was analyzed in vivo on human skin by differential stripping. Using the same application protocol, the nanoparticles were stored in the hair follicles up to 10 days, while the non-particle form could be detected only up to 4 days. Taking into consideration the surface structure of the hair follicles, it was assumed that the movement of the hairs may act as a pumping mechanism pushing the nanoparticles deep into the hair follicles.

Administration, Cutaneous↗

PubMed2006

Permeability assessment for solid oral drug formulations based on Caco-2 monolayer in combination with a flow through dissolution cell.

The aim of our study was to develop an apparatus assessing in vitro permeation through Caco-2 monolayers of oral solid dosage forms as a possible tool to forecast in vivo performance. Therefore, flow through dissolution and permeation modules were connected by means of a stream splitter. Permeation was measured in a specially designed cell, dissolution took place in the apparatus 4, USP. In order to test the apparatus for its reproducibility and conclusiveness, different tablet strengths and varying release profiles of propranolol HCl tablets were produced and evaluated. It was shown that for both tablet species, immediate and extended release, the apparatus was able to measure permeation through Caco-2 monolayer as well as dissolution simultaneously with high precision and reproducibility. The permeated amount of the three immediate release tablets with increasing dosage strength showed linear dependency on the dosage strength. Furthermore, the effect of retarded release on permeation could be detected and conclusive data for dissolution and permeation were obtained. In summary, connecting cell culture based permeability assessment with compendial flow through dissolution equipment led to promising results and poses the base for more advanced studies for detecting influences of dosage forms on permeation process.

Caco-2 Cells↗

PubMed2006

Permeability of the reconstructed human epidermis model Episkin in comparison to various human skin preparations.

The objective of this work was to compare the barrier function of the small diameter reconstructed human epidermis model Episkin (d=12 mm) to human skin in vitro. For that purpose a modification for the Franz diffusion cell (d=15mm) had to be developed so as to allow direct comparison with the following human skin preparations: Full thickness skin (FTS), split thickness skin (STS), heat-separated epidermis (HSE), and trypsin isolated stratum corneum (TISC). Among the tested preparations, HSE appeared to be the most preferable due to its clear morphological structure and ease of preparation. The lipid profile of HSE and Episkin was analyzed and showed significant differences in terms of cholesterol, ceramides and triglycerides contents, whereas cholesterol esters and fatty acids were not different. Permeation data with HSE and Episkin were then gathered using caffeine and testosterone. Both test compounds permeated much faster through Episkin than through HSE. Moreover, opposed to Episkin, HSE differentiated between the two test compounds. In spite of the remarkable progress in developing RHEs in the past years at this time Episkin can obviously not yet fully replace human skin for in vitro permeability experiments.

Ceramides↗

PubMed2006

Development and characterization of film forming polymeric solutions for skin drug delivery.

Film forming polymeric solutions as a novel approach for skin drug delivery were developed and characterized concerning their mechanical properties and water vapor permeability. They were developed by varying type and content of the film forming polymer as well as nature and content of the plasticizer. The resulting formulations were evaluated according to five criteria: drying time, cosmetic attractiveness, outward stickiness, integrity on skin (after 18 h) and viscosity. Among the 14 tested polymers 10 film formers yielded formulations with a positive evaluation in all five test criteria. Selected formulations were then investigated for tensile strength and elongation at break in vitro and for water vapor permeability in vitro (WVP) and in vivo (TEWL). Their mechanical properties determined in vitro were found to be not predictive for the flexibility and abrasion resistance observed on living skin. Similar to this, the results derived from the WVP and the TEWL methods were not in accordance with each other. Obviously, the investigated in vitro methods do not characterize the properties of the thin films on living skin satisfactorily. Nevertheless, the identified film forming solutions are a promising approach and will provide the basis for the further development of this novel dosage form.

Adhesiveness↗

PubMed2006

In vitro studies on release and human skin permeation of Australian tea tree oil (TTO) from topical formulations.

Essential oils are widely used in pharmaceutical and cosmetic preparations e.g. as fragrance, active ingredient or penetration enhancer. However, reports on skin absorption are rare. Therefore, the aim of our study was to investigate the capability of terpinen-4-ol, the main compound of Australian tea tree oil (TTO), to permeate human skin. In static Franz diffusion cells permeation experiments with heat separated human epidermis were carried out using infinite dosing conditions and compared to liberation experiments. The flux values of three different semisolid preparations with 5% TTO showed the rank order semisolid O/W emulsion (0.067 microl/cm2 h) > white petrolatum (0.051 microl/cm2 h) > ambiphilic cream (0.022 microl/cm2 h). In comparison to the flux value obtained with the native TTO (0.26 microl/cm2 h), the flux values are remarkably reduced due to the lower amount of terpinen-4-ol. P(app) values for cream (2.74+/-0.06 x 10(-7) cm/s) and native TTO (1.62+/-0.12 x 10(-7) cm/s) are comparable whereas white petrolatum (6.36+/-0.21 x 10(-7) cm/s) and semisolid O/W emulsion (8.41+/-0.15 x 10(-7) cm/s) demonstrated higher values indicating a penetration enhancement. No relationship between permeation and liberation was found.

Administration, Cutaneous↗

PubMed2006

Multiphoton microscopy for the investigation of dermal penetration of nanoparticle-borne drugs.

Multiphoton microscopy (MPM) of a dually fluorescence-labeled model system in excised human skin is employed for high-resolution three-dimensional (3D) visualization in order to study the release, accumulation, and penetration properties of drugs released from nanoscale carrier particles in dermal administration. Polymer particles were covalently labeled with fluorescein, whereas Texas Red as a drug-model was dissolved in the particles to be released to the formulation matrix. Single nanoparticles on skin could easily be localized and imaged with diffraction-limited resolution. The temporal evolution of the fluorescent drug-model concentration in various skin compartments over more than 5 hours was investigated by multiphoton spectral imaging of the same area of the specimen. The 3D penetration profile of the drug model in correlation with skin morphology and particle localization information is obtained by multiple laser line excitation experiments. MPM combined with spectral imaging was found to allow noninvasive long-term studies of particle-borne drug-model penetration into skin with subcellular resolution. By dual color labeling, a clear discrimination between particle-bound and released drug model was possible. The introduced technique was shown to be a powerful tool in revealing the dermal penetration properties and pathways of drugs and nanoscale drug vehicles on microscopic level.

Fluorescence↗

PubMed2005

TEWL measurements as a routine method for evaluating the integrity of epidermis sheets in static Franz type diffusion cells in vitro. Limitations shown by transport data testing.

The suitability of transepidermal water loss (TEWL) measurements in vitro as a barrier integrity test for human heat separated epidermis (HSE) was investigated. A model system consisting of a Teflon membrane mounted in Franz diffusion cells (FDC) filled with phosphate buffer saline (PBS) was set up. The membrane was used intact and punctured with a needle (up to five holes). After each puncturing the TEWL was measured. Only the TEWL of intact and punctured membrane differed significantly regardless of the number of holes. From three donors intact human HSE and punctured HSE were compared and no significant difference of the TEWL was found. Permeation experiments with flufenamic acid (FFA) showed a significantly higher diffusion rate through punctured HSE. TEWL and drug permeation were compared for skin stripped three, seven and 15 times prior to heat separation to an intact control group. Only the TEWL values of intact HSE and HSE stripped 15 times differed significantly. However, seven and 15 times stripping resulted in significantly higher diffusion rate. In conclusion, TEWL measurements can detect severe damage of the stratum corneum (SC) but not small changes, which nevertheless may already influence drug diffusion. Therefore, TEWL measurements appears to be of limited use as a barrier integrity test for human HSE in in vitro test systems.

Diffusion↗

PubMed2005

Immediate drug release from solid oral dosage forms.

Fast drug release from solid dosage forms requires a very fast contact of the vast majority of the drug particles with the solvent; this, however, is particularly delayed in tablets and granulations. Starch and cellulose substances favor the matrix disintegration during the starting phase and the generation of the effective dissolution surface of the drug substance, thereby. To investigate the very complex interrelation between the functionality of commonly used excipients and the structural effects of the production processes, wettability, porosity, water uptake, and drug release rates of several ketoprofen-excipient preparations (powder blends, granulations, tablets) were measured. Significant linear correlation between these parameters, however, was not achieved; only qualitative tendencies of the effects could be detected. In consequence, a general mathematical model describing the mechanistic steps of drug dissolution from solid dosage forms in a fully correct way was not realized. However, the time-dependent change of the effective dissolution surface follows stochastic models: a new dissolution equation is based on the differential Noyes-Whitney equation combined with a distribution function, e.g. the lognormal distribution, and numerically solved with the software system EASY-FIT by fitting to the observations. This new model coincides with the data to a considerably higher degree of accuracy than the Weibull function alone, particularly during the starting, matrix disintegration, and end phases. In combination with a procedure continuously quantifying the dissolved drug, this mathematical model is suitable for the characterization and optimization of immediate drug release by the choice and modification of excipients and unit operations. The interdependence of some characteristic effects of excipients and production methods is discussed.

Algorithms↗

PubMed2005

Tissue distribution of moxaverine-hydrochloride in the rabbit eye and plasma.

OBJECTIVE: The aim of this study was to determine the tissue distribution and epithelial penetration of moxaverine-hydrochloride (MOX) in the rabbit eye. METHODS: For systemic application, a radioactively labeled MOX solution was injected into the ear vein of Dutch-belted pigmented male rabbits. For topical dosing, an identical solution was administered. At predetermined time points, rabbits were sacrificed, the eyes dissected, and the amount of MOX in the ocular tissues measured. To examine the MOX permeability across the corneal epithelium, transport studies using rabbit corneal epithelial cell culture were conducted and the respective apparent permeability coefficient in absorptive (a to b) or secretive (b to a) direction was calculated. RESULTS: Topical delivery resulted in high concentrations of MOX in the cornea and conjunctiva, although other tissues of the anterior part yielded lower MOX concentrations. In the tissues of the posterior part, high amounts were detected in the retina. Plasma levels were low. The apparent permeability coefficient across corneal epithelial cell layers was in the range of 10(5) cm/s, exhibiting no apparent directionality. CONCLUSION: A topical dosing of MOX to posterior regions of the eye seems feasible. MOX levels in the posterior part of the eye were remarkably high, without causing stringent plasma levels. The high apparent permeability coefficient of MOX across the corneal epithelial cell layers might be caused by the lipophilic nature of the drug and was in the range of other compounds with comparable physicochemical properties.

Animals↗

PubMed2004

Effects of various vehicles on the penetration of flufenamic acid into human skin.

The effect of various vehicles (polyacrylate gels and wool alcohol ointments) on the penetration of flufenamic acid into excised human skin was investigated. Physico-chemical properties of the formulations were examined and discussed. Penetration data was gathered using two different in vitro test systems: the Saarbruecken penetration model (SB-M) and the Franz diffusion cell (FD-C). With wool alcohol ointments, drug concentration in the formulation was the decisive parameter for drug liberation and penetration. The incorporation of water into wool alcohol ointment led to increased drug amounts within the deeper skin layers (DSL), especially after longer incubation times. The drug concentration within the stratum corneum (SC) was not influenced by the bleeding effect of lipophilic, liquid components of the various wool alcohol ointments. With polyacrylate gels different results for liberation and penetration were observed. These results could be related to the effects of the drug concentration within the formulation and the penetration enhancers incorporated into the gels. Especially the effects of penetration enhancers clearly illustrated that liberation experiments do not predict the situation in the skin, but make experiments with a biological barrier essential. The high water content of the gels led to hydration of the skin specimen for the SB-M and the FD-C and therefore, in contrast to previous findings, comparable data were obtained in the penetration studies with both models. Furthermore, the quasi steady-state drug amount in the SC could be calculated for all formulations using an equation derived from a Michaelis-Menten kinetics. The data from both test systems were linearly correlated to each other. In addition, a direct linear relationship between the SC drug amount and the drug amount in the DSL was found as long as the quasi steady-state drug amount in the SC was not reached. A combination of all results might offer the chance to reduce the costs and to simplify the development of a new drug formulation.

Chemistry, Pharmaceutical↗

PubMed2003

Comparison of effects of different ointment bases on the penetration of ketoprofen through heat-separated human epidermis and artificial lipid barriers.

In vitro tests were performed to understand the effects of topical vehicles on the permeability of ketoprofen through artificial lipid barriers and heat-separated human epidermis consisting of stratum corneum and viable epidermis. Ketoprofen was selected as the model penetrant. Human epidermis and artificial membranes made from several mixtures of free fatty acids, cholesterol, cholesteryl ester, ceramides, and triglycerides were used as permeation matrices in untreated conditions and after pretreatment with petrolatum, wool alcohols ointment, or triglycerides. Apparent permeability and diffusion coefficients as well as the solubility of the drug in the artificial lipid matrices were ascertained. The solubilities of drugs and vehicle components that depend on the composition of the lipid matrix predominantly control the permeability of the barrier. Ceramides and cholesterol reduce the permeability and solubility, whereas triglycerides have the opposite effect. The vehicle effects in artificial membranes correspond to those in epidermis observed with samples pretreated with the aforementioned bases. The logarithms of the permeabilities of untreated and pretreated lipid mixtures 3, 4, and 5 are very well correlated with those of the permeabilities of heat-separated epidermis (r > = 0.9868). The artificial mixture containing all five lipids mentioned gives the best approximation to human epidermis. This result indicates comparable vehicle effects although the composition of the artificial mixture was adapted only in a simplified manner to the horny layer lipid phase. This lipid matrix or similar mixtures, therefore, are convenient tools for investigation into the effects of dermatological vehicles.

Epidermis↗

PubMed2003

pH profiles in human skin: influence of two in vitro test systems for drug delivery testing.

Investigations to determine pH profiles across human stratum corneum (SC), in vivo as well as in vitro, were carried out using the tape stripping technique and a flat surface pH electrode. This method was extended to the deeper skin layers (=viable epidermis+dermis; DSL) in vitro. Statistically significant changes in the pH values were detected in the SC between in vivo and in vitro investigations and also between male and female skin in vivo. For the DSL, no gender-dependent differences in pH were observed. While the results achieved for the SC are in accordance with data already published in the literature, the values for the DSL were surprising: An alkaline pH, with a steep increase of about two pH units in the first 100 microm of the DSL and a plateau of this level was thereafter detected. Research was also done to examine the influence of different in vitro test systems on the results of pH measurements across the skin. A permeation model (Franz diffusion cell; FD-C) and a penetration model (Saarbruecken penetration model; SB-M) were compared. Experiments were carried out concerning the incubation time as well as the pH of the acceptor solution in the FD-C. Independent of the test system used, no change in the pH profiles could be observed for the SC, but a strong effect of the acceptor medium and its pH on the pH profiles across the DSL could be demonstrated using the FD-C, which showed itself partly after 30 min in statistically significant differences between incubated and formerly frozen skin. The results after the use of buffer solutions with different pH values, the pH across the DSL seemed to come into line with the one of the buffer solution, which was investigated for acidic as well as alkaline pH values. The results obtained with the flat surface pH electrode were confirmed using two different dyes: the pH-dependent fluorescent dye carboxy-SNARF-1 and the pH indicator bromthymolblue.

Adult↗

PubMed2002

Correlation between stratum corneum/water-partition coefficient and amounts of flufenamic acid penetrated into the stratum corneum.

The stratum corneum of various donors differs in particular in the composition of the lipoidal phase. Considering the drug amounts penetrating into the stratum corneum a simple methodology to correlate these differences in the stratum corneum composition with the drug amounts detectable within the stratum corneum is desirable. Penetration experiments investigating several incubation times were carried out with three different skin flaps using the Saarbruecken penetration model and the lipophilic model drug flufenamic acid. The drug amounts within the stratum corneum were obtained with the tape-stripping technique, while the drug amounts present in the deeper skin layers were achieved by cryosectioning. The stratum corneum/water-partition coefficient was determined with the same three skin flaps to characterize the lipoidal stratum corneum phase in general, and the differences were attributed to the different amounts of ceramides and sterols. In addition, for the lipophilic drug flufenamic acid, a direct linear correlation was found between the stratum corneum/water-partition coefficients and the drug amounts penetrated into the stratum corneum for all investigated time intervals (correlation coefficients of r(30 min) = 0.998, r(60 min) = 0.998 and r(180 min) = 0.987). In contrast to the stratum corneum/water-partition coefficients, the determination of a corresponding relationship for the stratum corneum and the deeper skin layers failed due to the reason that steady-state conditions could not be achieved for the deeper skin layers during the investigated time intervals. In summary, the stratum corneum/water-partition coefficients offer the possibility to predict drug amounts within the stratum corneum of different donor skin flaps without a time consuming determination of the lipid composition of the stratum corneum.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2002

Human skin penetration of flufenamic acid: in vivo/in vitro correlation (deeper skin layers) for skin samples from the same subject.

Previously, the interest in in vivo/in vitro correlations in the dermal field of research has increased steadily. Unfortunately, in most cases the skin from different human donors was taken for in vivo and in vitro experiments, which led to problems concerning the interindividual variability of the skin. Therefore, we established a methodology to utilize the same skin for both sets of data. In time dependency, drug amounts in the stratum corneum and the deeper skin layers were determined from eight donors using the same skin area for in vivo and the corresponding in vitro tests. Penetration experiments were carried out with the lipophilic drug flufenamic acid dissolved in wool alcohols ointment as the model formulation, which was administered to the skin under "infinite dose" conditions. At different time points prior to starting the surgery, the drug preparation was applied topically on the edges of the skin area, which was planned for excision using Finn chambers. After anesthetizing the patient and disinfecting the operation area, the incubated skin pieces were cut off first and immediately frozen to limit further drug diffusion. In vitro experiments were performed on the remaining skin flap, using two different test systems, a penetration and a permeation model. At the end of all experiments (in vivo and in vitro) the skin specimens were segmented horizontally and the drug was extracted and quantified. The in vivo and in vitro drug amounts in the stratum corneum and the deeper skin layers, respectively, were compared. The inevitable use of unknown volumes of disinfectant in vivo (medical reasons) might be the reason why a correlation failed for the stratum corneum. Nevertheless, for both in vitro test systems a direct linear correlation was found for the deeper skin layers, which showed slopes of a = 3.2272 +/- 0.3933 (penetration model vs in vivo) and a = 1.7776 +/- 0. 1926 (permeation model vs in vivo). This difference demonstrates the varying influence of the test systems and represents a factor about which in vivo and in vitro data are shifted against each other. As far as the model drug flufenamic acid is concerned, this methodology represents a tool to predict drug penetration into the deeper skin layers in vivo after carrying out corresponding in vitro experiments. Therefore, the potential is given to reduce the number of in vivo experiments, the risk for the volunteers, and the costs for the development of new drug preparations.

Administration, Topical↗

PubMedDate not supplied

Nanoparticles made of fluorescence-labelled Poly(L-lactide-co-glycolide): preparation, stability, and biocompatibility.

Nanoparticles have recently been demonstrated in a rat model to be a promising tool for targeting inflamed areas of the intestinal mucosa in inflammatory bowel diseases whilst concentrating anti-inflammatory drugs at their site of action. Still, however, this novel concept has to be proven in vivo in humans. As a first step biodegradable and biocompatible fluorescent nanoparticles were prepared and characterized to serve as markers for successful inflammation targeting in future clinical trials. To achieve stable fluorescence labelling, fluoresceinamine was covalently bound to poly(L-lactide-co-glycolide) (PLGA) as described by Horisawa et al. The modification rate of carboxyl-end groups of the PLGA chains determined by 1H NMR was 65%. From this modified polymer, nanoparticles (FA-PLGA nanoparticles) of approximately 270 nm size were prepared via nanoprecipitation. Apart from an initial burst effect, most of the label (> 88%) appeared to be strongly bound and was leaked only slowly from the particles. In contrast, we found an immediate leakage of encapsulated sodium fluorescein with nanoparticles prepared by a double emulsion method. In degradation experiments we studied and visualized the changes in morphology and elastic properties of the FA-PLGA nanoparticles within 15 weeks using atomic force microscopy. When FA-PLGA nanoparticles were applied on an in vitro model of the intestinal mucosa (Caco-2 cell culture), only minor amounts of their fluorescent degradation products (approximately 0.02% after 6 h) were transported. In a cytotoxicity study with Caco-2 cells, FA-PLGA nanoparticles yielded an IC50 value as for plain PLGA nanoparticles. In conclusion, the polymer modification method allows to prepare fluorescently labelled nanoparticles from a well-known biodegradable pharmaceutical polymer with sufficient stability to be monitored over a period of several days. Some initial leakage of fluorescence label appears to be unavoidable but negligible with respect to potential absorption and cytotoxicity when applied in vivo.

Caco-2 Cells↗