Nathalie Ledirac

Induction of cytochrome P450 1A1 gene expression, oxidative stress, and genotoxicity by carbaryl and thiabendazole in transfected human HepG2 and lymphoblastoid cells.

Carbaryl and thiabendazole, two widely used pesticides, have been shown to induce cytochrome P450 1A1 (CYP1A1) expression, but neither compound is capable of displacing [3H] 2,3,7,8-tetrachlorodibenzo-P-dioxin from its aryl hydrocarbon receptor binding site. In the present study, we investigated the transcriptional regulation of CYP1A1 as well as other genes in various human hepatoma HepG2 cell lines stably transfected with the chloramphenicol acetyl transferase (CAT) reporter gene and cloned under the control of each of 14 promoters or response elements from relevant stress genes. Carbaryl and thiabendazole were found to activate CYP1A1 at the level of transcription, as demonstrated by the dose-dependent increase in reporter CAT and CYP1A1 mRNAs. Moreover, this effect appeared to be mediated via the xenobiotic responsive element (XRE), because both pesticides specifically activated various fusion constructs containing XRE sequences (CYP1A, glutathione S-transferase, and XRE). Carbaryl and to a lesser extent thiabendazole also activated other stress genes such as c-fos and NF-kappaBRE, HSP70 and GRP78, and GADD153 at a transcriptional level. These data suggest that these molecules induce early alert genes, including those known to be sensitive to oxidative stress. This led us to examine the genotoxic effect of carbaryl and thiabendazole by an in vitro DNA repair solid-phase assay. Both compounds provoked a strong DNA-damaging activity in the human lymphoblastoid cell line that constitutively expresses human CYP1A1 cDNA, but not in the parental line, indicating that CYP1A1 is chiefly implicated in carbaryl and thiabendazole genotoxicity. This effect was confirmed on HepG2 cells. These observations support the notion that intracellular signals leading to CYP1A1 induction, oxidative stress, and genotoxicity are intimately related.

Inferential, robust non-negative matrix factorization analysis of microarray data

MOTIVATION Modern methods such as microarrays, proteomics and metabolomics often produce datasets where there are many more predictor variables than observations. Research in these areas is often exploratory; even so, there is interest in statistical methods that accurately point to effects that are likely to replicate. Correlations among predictors are used to improve the statistical analysis. We exploit two ideas: non-negative matrix factorization methods that create ordered sets of predictors; and statistical testing within ordered sets which is done sequentially, removing the need for correction for multiple testing within the set. RESULTS Simulations and theory point to increased statistical power. Computational algorithms are described in detail. The analysis and biological interpretation of a real dataset are given. In addition to the increased power, the benefit of our method is that the organized gene lists are likely to lead better understanding of the biology. AVAILABILITY An SAS JMP executable script is available from http://www.niss.org/irMF

Cytotoxic effects and induction of cytochromes P450 1A1/2 by insecticides, in hepatic or epidermal cells: binding capability to the Ah receptor

Insecticides deserve particular attention since the general population is potentially exposed to such chemicals through many routes. We therefore tested the comparative acute and chronic toxicity of chemicals belonging to the major insecticides families (DDT, malathion and tetrachlorvinphos, carbaryl, cypermethrin, diflubenzuron), in hepatocytes, HepG2 and HaCaT cell lines. Two kinds of end-points were used: cytotoxicity parameters and CYP1A1 induction. Except for cypermethrin and diflubenzuron, all these chemicals exerted a cytotoxic effect in hepatocytes and HaCaT, but not in HepG2 cells. However, the induction of the EROD activity appeared more sensitive since a response was detected at lower concentrations. Significant differences were observed between the cell types and the insecticides. Furthermore, these chemicals were unable to displace [3H]TCDD from its binding sites, suggesting that they would not be a ligand of the Ah receptor. The experimental approach used herein may be a good means for predicting the acute and chronic toxicity of pesticides.

Endosulfan decreases cell growth and apoptosis in human hacat keratinocytes : Partial ROS-dependent ERK1/2 mechanism

Endosulfan is an organochlorine insecticide described as a potential carcinogen in humans. This insecticide was recently reported to alter the mitogen‐activated protein (MAP) kinase signaling pathways and is suspected to affect cell growth and differentiation in human keratinocytes. This study was designed to assess the mitogenic, apoptogenic, and genotoxic effects of endosulfan on the HaCaT cell line. We first found that 25 µM endosulfan led to persistent extracellular signal‐regulated kinase (ERK)1/2 phosphorylation with an accumulation of the phosphorylated form in the nucleus, probably caused by MAP kinase phosphatase (MKP) inhibition. As previously described under sustained ERK1/2 activation, cell growth was decreased: delayed confluency and 35% decrease of BrdU incorporation was demonstrated in endosulfan‐treated keratinocytes. In addition, endosulfan has been shown to generate transient reactive oxygen species (ROS), and blocking this oxidative stress by N‐acetyl cysteine (NAC) strongly prevented both persistent nuclear ERK1/2 phosphorylation and cell growth decrease. Additional experiments demonstrated that unchanged endosulfan rather than its metabolites has mutagenic effects (Ames positive without S9) and increased DNA strand breaks (Comet assay) in HaCaT cells, via a ROS‐dependent mechanism. Therefore, to assess the putative pro‐apoptotic response of damaged cells, caspases 3/7 activity and poly(ADP‐ribose)‐polymerase (PARP) cleavage were measured. The results clearly indicated that endosulfan inhibited both spontaneous and staurosporine‐induced apoptosis. Taken together, these findings strongly support that endosulfan induces ROS generation leading to sustained ERK1/2 phosphorylation and decrease in cell growth. Moreover, endosulfan was found to inhibit apoptosis and this could contribute to mutant cell survival and therefore have possible carcinogenic effects. J. Cell. Physiol. 213: 177–186, 2007.

Comparative study of CYP1A1 induction by 3-methylcholanthrene in various human hepatic and epidermal cell types

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 mum). 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.