Cotovio, J., P. Justine, D. Duche, R. Roguet, M. Cottin, and P. Catroux. Phase I, Phase II and Antioxidant Enzyme Activities in the Human Reconstructed Epidermis Episkin: Comparison with Human Keratinocyte Monolayers. ATLA 1999. 27: 82.

The skin, usually considered to be an effective barrier against external influences, contains enzyme systems capable of metabolizing a wide range of endogenous substrates and xenobiotic agents. In order to avoid the use of animals in cutaneous toxicological and pharmacological studies, and to enrich scientific knowledge, in vitro models of skin and epidermis have been developed. A relevant in vitro model should have as many characteristics of the in vivo situations as possible and thus it is of particular importance to characterize its specific enzyme content. In this work, the human reconstructed epidermis model EPISKIN was characterized with regard to its monolayers. We measured the activity of some phase I (ethoxyresorufin-O-deethylase (EROD), ethoxycoumarin-O-deethylase (ECOD) and non-specific esterases) and phase II (glutathione-S-transferase (GST), UDP-glucuronyltransferase (UDP-GT), sulfotransferase (ST), DT-diaphorase (DTD) and N-acetyltransferase (NAT) drug metabolizing enzymes, as well as the antioxidant enzymes (superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (Cat)). Our results show that EPISKIN, as well as NHK, retains in vitro 3-MC inducible EROD (mainly supported by CYP1A1) and ECOD (predominantly 1A and 2B-dependent) activities. Both models express esterase activity. Catalytic activities of phase II enzymes were detected. Compared to NHK, GST activity in EPISKIN was 1.5 times higher. ST activity in NHK was very weak (<0.02 pmol/minute/mg protein) and undetectable in EPISKIN. UDP-GT and DTD were present in both models at similar levels. Furthermore EPISKIN expressed NAT activity. All antioxidant enzymes were present in EPISKIN with levels at least as high as those in NHK, except for GR, which was three times lower. In conclusion, the three-dimensional model EPISKIN expresses drug metabolizing enzymes, as well as enzymatic antioxidant defenses, with profiles similar to those of NHK monolayers. This enzymatic equipment makes EPISKIN an attractive tool, suitable for pharmacotoxicological studies, in particular for in vitro testing interactions between cosmetic ingredients and cutaneous metabolic capacities, and xenobiotic molecular reactivity.