Abstracts / Toxicology Letters 205S (2011) S60–S179 S157 reactivation activity after Paraoxon inhibition was shown by Obidixime, TMB-4 and the new compound – BT-07-4M (1,4-bis (4-hydroxyiminomethyl-pyridinium) butane dibromide). They act as superior reactivators in comparison to HI-6, BT-03, BT-O7, BT 93, etc. Based on data obtained, we have discussed the structure- activity relationship. Analysis of the results showed that the most active newly synthesized reactivators of Dichlorvos inhibited AChE are bispiridinium oximes, containing oxime groups on 2nd position and methylene bridge between the piridinium rings. In the case of Paraoxon, the compounds containing oxime groups on 4th position in piridinium rings, act as more effective reactivators. doi:10.1016/j.toxlet.2011.05.550 P1317 Metabolomics of human embryonic and induced pluripotent stem cells to predict developmental toxicity: A comparison J. Palmer 1 , A. Weir-Hauptman 2 , A. Smith 1 , P. West 1 , K. Conard 1 , B. Fontaine 1 , E. Donley 1,* , G. Cezar 3 1 Stemina Biomarker Discovery Inc., Madison, USA, 2 NanoOncology, Madison, USA, 3 Animal Science, University of Wisconsin-Madison, Madison, USA Purpose: Exposure to developmental disruptors has a signifi- cant role in the pathogenesis of defects in human development. Human embryonic stem cell (hESC) technology is an innovative and robust alternative to predict developmental toxicity of chemicals during human pregnancy. We have developed the first all-human in vitro developmental toxicity screen that utilizes hES cells and metabolomics to discover biomarkers of developmental toxicity. Induced pluripotent stem cells (iPSC) are derived by genetic manip- ulation of human somatic cells. These cells are being investigated as a more ethically attractive alternative to hES cells. Method: We measured the secreted metabolites, across three hESC and two iPSC lines using liquid chromatography–mass spectrometry, to deter- mine what differences exist between cell types. Additionally, we exposed each cell line to 23 compounds with known teratogenicity to test the hypothesis that iPSC exhibit a similar response to that of hESC when exposed to compound. We also evaluated the cyto- toxicity of the test set using a cell viability assay. Results: Our initial comparisons between the three genetically distinct hES cell lines have shown that no metabolites were unique to a single cell line. However, there are differences in how cell lines respond to treat- ment. Also, cell viability assays show a difference between iPSC and hESC lines following treatment. Many compounds are more cytotoxic to iPS cells than hES cells. doi:10.1016/j.toxlet.2011.05.551 P1318 Chlorpyrifos and its metabolite, chlorpyrifos-oxon, modify the genic expression of mouse embryonic stem cells after 12 h of exposure C. Estevan Martínez 1,* , E. Vilanova 2 , M.A. Sogorb 2 1 Instituto De Bioingeniería. Unidad De Toxicología Y Seguridad Química, Universidad Miguel Hernández de Elche, Elche, Spain, 2 Instituto De BioingenierÍa, Universidad Miguel Hernández De Elche, Elche, Spain Chlorpyrifos (CPF) is an organophosphate insecticide that has been used in the last 4 decades for the protection of crops in agri- culture and for indoor use. This pesticide is not classified as toxic to development although there are some doubts concerning the potential effects of chlorpyrifos on the developmental process. In this study, the effects of CPF and its toxic metabolite, chlorpyrifos- oxon (CPO) on the development have been assessed by evaluating the modifications of the expression of several marker genes in the differentiation process of D3 mouse embryonic stem cells. D3 cells seeded in monolayer and in differentiation were incubated during 12 h in presence of CPF and CPO. The treated cells were collected after 12 h. The expression of different genes was quantified using qPCR. The expression of -fetoprotein, gene marker of the differen- tiation to visceral endoderm was significantly increased (p < 0.01) by 32 and 12 times after exposure to 100 M CPF and 400 M CPO, respectively. These exposures were the maximum tolerable concentration under cytotoxicity criteria, causing only slight cyto- toxicity with reduction of cell viability in both cases lower than 20%. The same exposure to CPO caused significant (p < 0.05) increases (by 1.9 times) and reductions (by 89%) in the expression of Nanog (marker of pluripotentiality) and Flk1 (marker of differentiation to mesoderm), respectively. In addition, some other markers have been assessed in order to characterize the embryotoxic potential of these organophosphates. doi:10.1016/j.toxlet.2011.05.552 P1319 Application of precision-cut liver slices for the investigation of test substance induced hepatocyte proliferation E.J. Fabian 1,* , F. Schuck 2 , A. Hess 1 , C. Jäckh 1 , S. Gröters 1 , B. van Ravenzwaay 1 , R. Landsiedel 1 1 Experimental Toxicology and Ecology, BASF SE, Ludwigshafen, Germany, 2 University of Mainz, Mainz, Germany Purpose: Precision cut liver slices (PCLiS) were evaluated for their applicability to detect test substance induced hepatocyte proliferation, since cell proliferation is a potential non-genotoxic contributor to hepatocarcinogenesis. Methods: A rotating culture system (Vitron) was applied and liver slices were incubated in FCS- supplemented Williams’ Medium E and characterized by viability parameters such as membrane integrity (LDH, ALT), energy sta- tus (ATP) and mitochondrial activity (MTT) over a period of up to 2 weeks. The proliferation in cultured liver slices was assessed as an integral over five days by DNA incorporation of BrdU, followed by immuno-staining of histological sections of PCLiS and count- ing stained cells. Results: Under the applied test conditions, liver slices sustained for 4–6 days. Within the testing period, LDH lev- els in the tissue declined to about 5% of the initial activity. ATP contents showed similar results. whereas the mitochondrial reduc- tion activity (MTT assay) stayed relatively constant over three days and was about 40% of the initial value after six days. Incubations of 1–100 M Wy-14,643 resulted in a concentration-dependent increase of proliferating hepatocytes up to a factor of 1.5-fold com- pared to the untreated control. This study demonstrated a proof of principle for the analysis of test-substance induced induction of hepatocyte proliferation in PCLiS. doi:10.1016/j.toxlet.2011.05.553