Characterization of peroxidase activities in normal human skin compared with reconstructed human skin models

Skin metabolism is becoming a major consideration in the development of new cosmetic ingredients, skin being the first organ exposed to them. Consequently, the use of ex vivo samples of normal human skin (NHS) or reconstructed human skin models (skin models) as alternative tools to animal testing requires to characterize and compare their abilities to metabolize xenobiotics. In this work, we determined if they possessed a functional peroxidase activity. Previous studies showed that NHS and skin models from SkinEthic™ Laboratories such as Episkin™, SkinEthic-RHE™ and the full thickness model of Episkin™ expressed the mRNAs of several peroxidase isoforms (mainly in GPx and COX families). The catalytic activity of these enzymes was measured from dose-response studies using cumene hydroperoxide as substrate. Apparent Vmax, Km and ratio Vmax/Km (assessing metabolic clearance) were calculated for each biological model from 2-phenyl-2-propanol quantification. Results showed that in NHS and skin models, a peroxidase activity was demonstrated to be functional and that the obtained enzymatic parameters could be influenced by the lack of the glutathione co-factor. To conclude, a peroxidase activity is present and functional in NHS and skin models which can be easily used for studying the biotransformation process of peroxides and assessing their impact on cellular biomarkers.