The use of reconstructed human epidermis for skin absorption testing: Results of the validation study.

A formal validation study was performed, in order to investigate whether the commercially-available reconstructed human epidermis (RHE) models, EPISKIN, EpiDerm and SkinEthic, are suitable for in vitro skin absorption testing. The skin types currently recommended in the OECD Test Guideline 428, namely, ex vivo human epidermis and pig skin, were used as references. Based on the promising outcome of the prevalidation study, the panel of test substances was enlarged to nine substances, covering a wider spectrum of physicochemical properties. The substances were tested under both infinite-dose and finite-dose conditions, in ten laboratories, under strictly controlled conditions. The data were subjected to independent statistical analyses. Intra-laboratory and inter-laboratory variability contributed almost equally to the total variability, which was in the same range as that in preceding studies. In general, permeation of the RHE models exceeded that of human epidermis and pig skin (the SkinEthic RHE was found to be the most permeable), yet the ranking of substance permeation through the three tested RHE models and the pig skin reflected the permeation through human epidermis. In addition, both infinite-dose and finite-dose experiments are feasible with RHE models. The RHE models did not show the expected significantly better reproducibility, as compared to excised skin, despite a tendency toward lower variability of the data. Importantly, however, the permeation data showed a sufficient correlation between all the preparations examined. Thus, the RHE models, EPISKIN, EpiDerm and SkinEthic, are appropriate alternatives to human and pig skin, for the in vitro assessment of the permeation and penetration of substances when applied as aqueous solutions.

Human skin equivalent as an alternative to animal testing.

The 3-D skin equivalent can be viewed as physiologically comparable to the natural skin and therefore is a suitable alternative for animal testing. This highly differentiated in vitro human skin equivalent is used to assess the efficacy and mode of action of novel agents. This model is generated from primary human keratinocytes on a collagen substrate containing human dermal fibroblasts. It is grown at the air-liquid interface which allows full epidermal stratification and epidermal-dermal interactions to occur. Future emphasis is the establishment of different test systems to investigate wound healing, melanoma research and infection biology. Key features of this skin model are that it can be used as an alternative for in vivo studies, donor tissue can be tailored to the needs of the study and multiple analyses can be carried out at mRNA and protein level. Driven by both ethical and economical incentives, this has already resulted in a shift of the test strategies used by the Pharmaceutical Industry in the early drug development process as reflected by the increased demand for application of cell based assays. It is also a suitable model for testing a wide variety of endpoints including cell viability, the release of proinflammatory mediators, permeation rate, proliferation and biochemical changes.

The potential of bioartificial tissues in oncology research and treatment.

This review article addresses the relevance and potential of bioartificial tissues in oncologic research and therapy and reconstructive oncologic surgery. In order to translate the findings from basic cellular research into clinical applications, cell-based models need to recapitulate both the 3D organization and multicellular complexity of an organ but at the same time accommodate systematic experimental intervention. Here, tissue engineering, the generation of human tissues and organs in vitro, provides new perspectives for basic and applied research by offering 3D tissue cultures resolving fundamental obstacles encountered in currently applied 2D and 3D cell culture systems. Tissue engineering has already been applied to create replacement structures for reconstructive surgery. Applied in vitro, these complex multicellular 3D tissue cultures mimic the microenvironment of human tissues. In contrast to the currently available cell culture systems providing only limited insight into the complex interactions in tissue differentiation, carcinogenesis, angiogenesis and the stromal reaction, the more realistic (micro)environment afforded by the bioartificial tissuespecific 3D test systems may accelerate the progress in design and development of cancer therapies.