CYP450 and GST are induced by xenobiotics in normal human keratinocytes and play a different role in UVB-mediated apoptosis

Skin enzymatic detoxification systems may provide a barrier for protection against the external environment. UVB is the major cause for cutaneous malignancies in the human population. The skin is able to activate anti-oxidants and enzymatic detoxification reactions to neutralize reactive photochemical products. Very little is known about the behaviour of cutaneous metabolizing enzymes after ultraviolet B exposure. In the first part of the present study we analysed the induction and expression of cytocrome P450 (CYP450) phase I and gluthatione S transferase (GST) phase II enzymes in normal human keratinocytes in culture after exposure to classical inducers such as: β-naphthoflavone (BNF), 3-methylcholanthrene (MC), phenobarbital (PB) and also to ultraviolet B (UVB) radiation. Phase I enzymes (CYP450 1A1, 1A2, 1B2 and 2B1, 2B2) were investigated through 7-ethoxyresorufìn O-deethylase (EROD) and 7-pentoxyresorufìn O-depenthylase activities (PROD), while GST was analysed throught the coniugation of 1-chloro-2,4 dinitrobenzene with reduced gluthatione.MC, BNF and UVB exposure resulted in a dose-dependent and time dependent induction of CYP450 confirmed by immunoblotting assay. GST was induced by PB and inhibited by UVB. According to these results in the second part of this study we analysed the role of these enzymes in UVB induced apoptotic process. Apoptosis is a key mechanism in the cellular homeostasis and can be triggered by exogenous insults and in particular by genotoxic agents. The exact function of these enzymes in carcinogenesis remains unclear. Western blot analysis of Bcl2 expression showed that inhibition of CYP450 prevented UVB induced apoptotic cell death. On the contrary inhibition of GST, by ethacrynic acid, showed to improve UVB induced apoptosis. These experimental findings stress the value that CYP450 and GST enzymes may play an important role in keratinocytes apoptosis.