IN-VITRO EXPRESSION OF DRUG-METABOLIZING ENZYME-ACTIVITIES IN HUMAN ADULT KERATINOCYTES UNDER VARIOUS CULTURE CONDITIONS AND THEIR RESPONSE TO INDUCERS

In this study we analysed the expression and induction of several drug metabolizing enzymes involved in either phase I or phase II reactions, in adult human keratinocytes cultured in submerged conditions. We also evaluated the influence of confluence, subcultivation and cryopreservation on the expression of these enzymes. Besides ethoxyresorufin-O-deethylase (EROD) and glutathione S-transferase (GST) activities, which have been shown previously to be maintained in such cultures, three additional enzyme activities were measured (i.e. phenacetin deethylase, a phase I enzyme, and procainamide N-acetyltransferase and paracetamol sulfotransferase, two phase II enzymes). Post-confluent keratinocytes showed decreased activities in comparison with preconfluent cells and the different enzymes tested revealed different patterns. After confluence, some activities, such as those of procainamide N-acetyltransferase, phenacetin deethylase and paracetamol sulfotransferase, showed only a slight decrease, whereas EROD and GST activities were decreased by 65 and 50%, respectively. No major differences were observed between keratinocytes in primary culture and those in second subculture. After freezing, xenobiotic metabolizing enzyme activities were only slightly reduced, if at all. Induction of EROD and GST enzymes was also analysed. Maximum EROD activity was obtained with 1 mu M 3-methylcholanthrene (3-MC) and 20 mu M benzanthracene (BA), in both pre-confluent and post-confluent cultures. At their optimal concentration 3-MC was a stronger inducer than BA. GST activity was slightly induced by the different compounds tested only in pre-confluent keratinocytes. In conclusion, the presence of a variety of drug metabolizing enzymes in adult human keratinocytes cultured in submerged conditions suggests that this model is suitable for investigating epidermal biotransformation of drugs and other chemicals and for determining the potential cutaneous toxicity of metabolites.