Establishment of an in vitro model of cultured viable human, porcine and canine skin and comparison of different media supplements.

Transdermal drug delivery provides several advantages over conventional drug administration, such as the avoidance of first-pass metabolism and better patient compliance. In vitro research can abbreviate and facilitate the pharmaceutical development considerably compared to in vivo research as drug screening and clinical studies can be reduced. These advantages led to the development of corresponding skin models. Viable skin models are more useful than non-viable ones, due to the influence of skin metabolism on the results. While most in vitro studies concentrate on evaluating human-based models, the current study is designed for the investigation of both human and animal diseases. So far, there is little information available in the literature about viable animal skin cultures which are in fact intended for application in the veterinary and not the human field. Hence, the current study aims to fill the gap. For the in vitro viable skin model, specimens of human, porcine and canine skin were cultured over two weeks under serum-free conditions. To evaluate the influence of medium supplementation on skin viability, two different supplement mixtures were compared with basic medium. The skin specimens were maintained at a viability-level >50% until the end of the study. From the tested supplements, the addition of bovine pituitary extract and epidermal growth factor increased skin viability whereas hydrocortisone and insulin induced a decrease. This in vitro viable skin model may be a useful tool for the investigation of skin diseases, especially for the veterinary field.

Non-animal models of epithelial barriers (skin, intestine and lung) in research, industrial applications and regulatory toxicology.

Models of the outer epithelia of the human body - namely the skin, the intestine and the lung - have found valid applications in both research and industrial settings as attractive alternatives to animal testing. A variety of approaches to model these barriers are currently employed in such fields, ranging from the utilization of ex vivo tissue to reconstructed in vitro models, and further to chip-based technologies, synthetic membrane systems and, of increasing current interest, in silico modeling approaches. An international group of experts in the field of epithelial barriers was convened from academia, industry and regulatory bodies to present both the current state of the art of non-animal models of the skin, intestinal and pulmonary barriers in their various fields of application, and to discuss research-based, industry-driven and regulatory-relevant future directions for both the development of new models and the refinement of existing test methods. Issues of model relevance and preference, validation and standardization, acceptance, and the need for simplicity versus complexity were focal themes of the discussions. The outcomes of workshop presentations and discussions, in relation to both current status and future directions in the utilization and development of epithelial barrier models, are presented by the attending experts in the current report.

[Comparative in vitro and in vivo studies on the permeation and penetration of ketoprofen and ibuprofen in human skin]. / Vergleichende In-vitro- und In-vivo- Studien zur Permeation und Penetration von Ketoprofen und Ibuprofen an humaner Haut.

The aim of the present in vitro and in vivo studies was to compare the permeation and penetration of a 2.5% ketoprofen (CAS 22071-15-4) gel [Phardol Schmerz-Gel (Test-D)] with the permeation and penetration of two other ketoprofen gels (Ref-I, Ref-E) and an ibuprofen (CAS 15687-27-1) gel (Ref-D) on excised human skin. Furthermore, in vivo studies were performed. The permeation studies utilizing static Franz diffusion cells allow the determination of the transdermal (systemic) transport, whereas the penetration studies in vitro (according to the Saarbrücker model) and in vivo permit setting up a concentration-depth profile. For this purpose the permeation kinetics of ketoprofen from three different gels (each containing 2.5% ketoprofen) over a period of two days were determined at heat-separated human skin of different donors. The in vitro permeability coefficients for Test-D (6.50 x 10(-7) cm x s(-1)) and Ref-I (5.72 x 10(-7) cm x s(-1)) were comparable and the transport occurred for both by a factor of 8-9 faster than with Ref-E (0.78 x 10(-7) cm x s(-1)). In parallel to the permeation studies with ketoprofen, the permeability coefficient of caffeine from an ointment was assessed using the skin biopsies of the same donors as a quality assurance. In a second part of the studies, the in vitro penetration of ketoprofen from Test-D was determined over a period of 3 h at three different skin biopsies in comparison to a commercially available 5% ibuprofen gel (Ref-D). As a main result a concentration-depth profile for ketoprofen and ibuprofen could be issued. The ketoprofen (37.7 +/- 12.1 microg/cm2) and the ibuprofen (30.1 +/- 6.0 microg/cm2) penetrate to the same order of magnitude into the upper part of the Stratum corneum, whereas ibuprofen stronger accumulates in the deeper layers (ketoprofen: 27.3 +/- 8.5 microg/cm2; ibuprofen: 73.7 +/- 31.1 microg/cm2). An additional in vivo penetration study was performed with Test-D to set up an in vitro-in vivo (IVIV) correlation. Over a period of 3 h, the amount of ketoprofen in the Stratum corneum in vivo was 78.4 +/- 19.1 microg/cm2 being comparable to the in vitro data.

Validation of cell culture models for the intestine and the blood-brain barrier and comparison of drug permeation.

Cell culture models are useful tools to study the uptake of drugs across the barriers of the human body, like the intestine, the skin or the blood-brain barrier. Cell-based in vitro models not only help to reduce the number of animals used but are also much faster to perform, more cost effective and give more reproducible data than animal studies. Given the increasing number of new drugs and chemicals under development, there is an urgent need for the establishment of such in vitro models. However, the validity of such in vitro models is reflected by its ability to accurately predict the behaviour of a substance at the corresponding in vivo barrier. Here, we compare a well-established cell culture model for the intestine, based on Caco-2 colon carcinoma cells, with a primary cell culture model of the blood-brain barrier. We find that Caco-2 cells and cells of the blood-brain barrier have different barrier properties. Therefore, cells used for cell-based assays should be derived from the corresponding tissue to reflect the in vivo barrier characteristics.