Characterization of enzyme activities of Cytochrome P450 enzymes, Flavin-dependent monooxygenases, N-acetyltransferases and UDP-glucuronyltransferases in human reconstructed epidermis and full-thickness skin models

With the perspective to use human reconstructed skin models for genotoxicity testing which require metabolic activation of xenobiotics, this study aimed to characterize activities of biotransforming enzymes within two human reconstructed skin models, the epidermis model EpiDerm™ (MatTek) and the Phenion® Full-Thickness skin model Phenion®FT (Henkel). According to existing gene expression profiles, Cytochrome P450 (CYP) enzymes, Flavin-dependent monooxygenases (FMO), N-acetyltransferases (NAT) and UDP-glucuronyltransferases (UDP-GT) were investigated in S9 or microsomal fractions. CYP-catalyzed monooxygenation was assayed using 7-ethoxyresorufin, pentoxyresorufin and benzyloxyresorufin as substrates. FMO activity was tested using benzydamine. Conjugating activities of NAT and UDP-GT were determined by acetylation of p-aminobenzoic acid or glucuronation of 4-methylumbelliferone, respectively. Although CYPs were detected by expression profiling, no CYP activity was detected in either the epidermal nor the full-thickness reconstructed skin model while expression and activity of FMO, UDP-GT and NAT were demonstrated in both.