Reconstructed Human Epidermis for Skin Absorption Testing: Results of the German Prevalidation Study
Monika Schäfer-Korting, Udo Bock, Armin Gamer, Annekathrin Haberland, Eleonore Haltner-Ukomadu, Monika Kaca, Hennicke Kamp, Manfred Kietzmann, Hans Christian Korting, Hans-Udo Krächter, Claus-Michael Lehr, Manfred Liebsch, Annette Mehling, Frank Netzlaff, Frank Niedorf, Maria K. Rübbelke, Ulrich Schäfer, Elisabeth Schmidt, Sylvia Schreiber, Klaus-Rudolf Schröder, Horst Spielmann8 and Alexander Vuia1
Exposure to chemicals absorbed by the skin can threaten human health. In order to standardise the predictive testing of percutaneous absorption for regulatory purposes, the OECD adopted guideline 428, which describes methods for assessing absorption by using human and animal skin. In this study, a protocol based on the OECD principles was developed and prevalidated by using reconstructed human epidermis (RHE). The permeation of the OECD standard compounds, caffeine and testosterone, through commercially available RHE models was compared to that of human epidermis and animal skin. In comparison to human epidermis, the permeation of the chemicals was overestimated when using RHE. The following ranking of the permeation coefficients for testosterone was obtained: SkinEthic > EpiDerm, EPISKIN > human epidermis, bovine udder skin, pig skin. The ranking for caffeine was: SkinEthic, EPISKIN > bovine udder skin, EpiDerm, pig skin, human epidermis. The inter-laboratory and intra-laboratory reproducibility was good. Long and variable lag times, which are a matter of concern when using human and pig skin, did not occur with RHE. Due to the successful transfer of the protocol, it is now in the validation process.
The Use of Reconstructed Human Epidermis for Skin Absorption Testing: Results of the Validation Study
Monika Schäfer-Korting, Udo Bock, Walter Diembeck, Hans-Jürgen Düsing, Armin Gamer, Eleonore Haltner-Ukomadu, Christine Hoffmann, Monika Kaca, Hennicke Kamp, Silke Kersen, Manfred Kietzmann, Hans Christian Korting, Hans-Udo Krächter, Claus-Michael Lehr, Manfred Liebsch, Annette Mehling, Christel Müller-Goymann, Frank Netzlaff, Frank Niedorf, Maria K. Rübbelke, Ulrich Schäfer, Elisabeth Schmidt, Sylvia Schreiber, Horst Spielmann, Alexander Vuia and Michaela Weimer
A formal validation study was performed, in order to investigate whether the commerciallyavailable 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 finitedose 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.
Reconstructed Epidermis and Full-Thickness Skin for Absorption Testing: Influence of the Vehicles used on Steroid Permeation
Monika Schäfer-Korting, Ashraf Mahmoud, Simone Lombardi Borgia, Barbara Brüggener, Burkhard Kleuser, Sylvia Schreiber and Wolfgang Mehnert
A protocol for percutaneous absorption studies has been validated, based on the use of reconstructed human epidermis (RHE) and aqueous solutions of test substances. However, it is often the case that it is more-complex formulations of drugs or chemicals which will make contact with the skin surface. To investigate whether RHE and the reconstructed full-thickness skin model (FT-model) can be used to predict uptake from formulations, we compared the permeation of hydrocortisone and testosterone when applied in emulsion form and as a solution containing the penetration enhancer, ethanol. Human and pig skin and a non-cornified alveolar model served as references. The results were compared with steroid release from the formulations. The permeation rates of the steroids were ranked as: alveolar model >> RHE > FT-model, pig skin > human skin. In accordance with the rapid hydrocortisone release from the formulations, the permeation rates of this steroid exceeded those of testosterone. Only minor differences were observed when comparing the testosterone formulations, in terms of release and permeation. However, the ranking of the permeation of the hydrocortisone formulations was: solution > w/o emulsion > o/w emulsion, which permitted the elucidation of penetration enhancing effects, which is not possible with drug release studies. Differences in penetration were most obvious with native skin and reconstructed tissues, which exhibited a well-developed penetration barrier. In conclusion, RHE and skin preparations may be useful in the development of topical dermatics, and in the framework of hazard analysis of toxic compounds and their various formulations.