Evaluation of cytochrome P450 1 (CYP1) and N-acetyltransferase 1 (NAT1) activities in HaCaT cells: implications for the development of in vitro techniques for predictive testing of contact sensitizers.

Xenobiotic metabolizing enzymes like cytochrome P450s and N-acetyltransferase are expressed in keratinocytes and professional antigen-presenting cells. Thus, biotransformation of chemicals applied to the skin can be relevant for their potential to cause skin toxicity and immune responses like allergic contact dermatitis. Considering the keratinocyte cell line HaCaT as a relevant in vitro tool for epidermal biotransformation, we specifically investigated CYP1 (EROD) and N-acetyltransferase 1 (NAT1) activities of three different HaCaT shipments and human primary keratinocytes (NHEK). Solvent treated HaCaT showed EROD levels near the detection limit (0.047 pmol/mg/min), primary keratinocytes (n=4) were in a range between 0 and 0.76 pmol/mg/min. B[a]P (1 microM) induced EROD activities of 19.0+/-0.9 pmol/mg/min (n=11) in HaCaT and 5.8+/-0.5 pmol/mg/min (n=4) in NHEK. N-acetylation activities for para-aminobenzoic acid (PABA) were in average 3.4-fold higher in HaCaT compared to NHEK (8+/-0.5 nmol/mg/min) and varied between the HaCaT shipments (range 12.0-44.5 nmol/mg/min). This was in good agreement with NAT1 promoter P1 dependent mRNA level and N-acetylation of the contact allergen para-phenylenediamine (PPD) under typical cell-based assay conditions. We conclude that HaCaT represent a suitable in vitro model for studying the qualitative contribution of epidermal phase1/phase2 metabolism to toxicological endpoints such as skin sensitization.