Abstract
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.
Highlights
Non-animal models of epithelial barriers are currently enjoying increasing interest from various groups, including scientists in academia, product developers in industry, regulatory authorities and, last but not least, society in general
Large scale studies focusing on the barrier properties of normal skin, skin metabolism, and potential for development of skin inflammation and irritation, sensitization and skin diseases are required to define a normal, standard range that accounts for inherent donor variability
Such large epidemiological studies focused on characterization of human skin would bring unique knowledge backed by statistical power, and reference data needed for development of better in silico models and reliable assays, while accelerating the process of their formal validation – an achievement that is often hindered by a lack of reliable in vivo reference data
Summary
Non-animal models of epithelial barriers are currently enjoying increasing interest from various groups, including scientists in academia, product developers in industry, regulatory authorities and, last but not least, society in general. It is important to show that the natural barrier function of a given epithelium is not changed as a result of application or exposure – not even indirectly, for example via the induction of an immunological response – as this would cause unacceptable local irritation but as its consequence inevitably lead to an increased absorption of potentially noxious compounds Such considerations define the common interest of some industry sectors (i.e., cosmetics, industrial chemicals, biocides and plant protection products) in epithelial barriers in the context of their R&D efforts for new products. The outcome goal of this workshop and report was to analyze the current status of barrier models (skin, intestine and lung) in the various areas of application introduced above (environmental chemicals/cosmetics, pharmaceuticals and food) Based on such analysis, it became possible to identify specific needs for new models, as well as to define further research needed to validate existing models. The long term goal in this respect must be to create valid, robust alternatives to animal testing
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