Induction by xenobiotics of phase I and phase II enzyme activities in the human keratinocyte cell line NCTC 2544

This study analyses the expression and induction of several drug-metabolisi ng enzyme activities involved in either phase I or phase II biotransformati ons in NCTC 2544 human keratinocytes. The phase I activities 7-ethoxycoumar in O-deethylase (ECOD), 7-ethoxyresorufin O-deethylase (EROD) and 7-pentoxy resorufin O-depenthylase (PROD) were easily detectable in basal conditions. During incubations lasting up to 144 h in the presence of the classical cy tochrome P450 inducers beta -naphthoflavone (BNF), 3-methylcholanthrene (MC ) and phenobarbital (PB), a considerable and significant increase in all th e three activities was observed, PROD activity was induced up to 4.5-fold a fter 96 h in the presence of PB. The MC-induced ECOD and EROD activities we re also dose-dependently inhibited by alpha -naphothflavone, which was give n to the cells during the incubation with CYP 1A1 inducers. Also the PB-ind uced PROD activity was decreased by the simultaneous addition of the CYP 2B inhibitor metyrapone. Both cytochrome P450 inhibitors were used at non-cyt otoxic concentrations. The phase II enzymes glutathione S-transferase, alde hyde dehydrogenase and quinone reductase were all highly expressed and indu cible by MC. The exposure (24 h) of the cells to four hair dyes used in cos metic formulations resulted in a marked increase in ECOD activity. All data give sustained evidence for the suitability of NCTC 2544 cell line to skin toxicology studies. (C) 2001 Elsevier Science Ltd. All rights reserved.