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Hepatocytes and keratinocytes are among the most widely used cells in pharmaco-toxicology, but a limitation of these models is the provision of human tissues on a regular basis. The suitability of HepG2, HaCaT and HESV cell lines as an acceptable substitute for primary cultures was examined. In these cell types, the effects of 3-methylcholanthrene (3-MC) were analysed on CYP1A1 gene expression, a crucial CYP subfamily in the activation of chemical carcinogens. Ethoxyresorufin O -deethylase (EROD) activity was never detected in HESV cells, but in other cell types it was stimulated in a concentration-dependent manner (maximal induction, 1–2.5 μ m ). Above this peak induction the effect fell rapidly. Northern blot analysis of CYP1A1 mRNA agreed with the trends obtained for EROD values. However, the decrease of the EROD activity observed at the highest 3-MC concentrations was not correlated with CYP1A1 mRNA reduction. This study also demonstrated that 3-MC is capable of significantly inducing CYP1A1 in HaCaT cells (17-fold over control), as in human hepatocytes (six- to 18-fold) and HepG2 (fourfold). Therefore, in contrast to SV40-immortalized keratinocytes (HESV), spontaneously immortalized keratinocytes (HaCaT) may constitute a valuable tool for studying epidermal CYP1A1 gene regulation by xenobiotics.

With the increasing demand for insecticide products, the question of their safety has become one of the serious world public health concerns. The capability of compounds belonging to the major insecticide families [such as chlorinated hydrocarbons (DDT), carbamates (carbaryl: CBR), organophosphorus compounds (malathion, tetrachlorvinfos: MAL, TCV), pyrethroids (cypermethrin: CPR) and benzoylurea (diflubenzuron: DFU)] in inducing CYP1 Al in rat and human hepatocyte cultures has been tested. Cells were treated during 3 days with six non-toxic increasing doses of insecticides and CYP1A1 expression was assessed by ethoxyresorufin O-deethylase (EROD) activity and by Northern blots. A strong and dose-dependent induction was observed with TCV and DFU, both in human (approx. five- and sevenfold over control, respectively) and in rat hepatocytes (approx. sevenfold). However, EROD induction and CYP/A1 mRNA levels were correlated for DFU but not for TCV, suggesting different regulation mechanisms for PCYP1A1 gene expression by the two compounds. CBR and CPR exerted less induction in both cell types (approx. 2.5-fold induction compared with approximately 16-fold for 3-methylcholanthrene), whereas DDT and MAL showed no action on human hepatocytes but decreased EROD activity in rat cells. Finally, cytotoxicity studies performed using the MTT and the neutral red tests demonstrated significant differences between insecticides.