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Prenatal developmental toxicity (PDT) as observed with some petroleum substances (PS) has been associated with the presence of 3-7 ring polycyclic aromatic hydrocarbons (PAHs). In the present study, the applicability of ES-D3 cell differentiation assay of the EST to evaluate in vitro embryotoxicity potencies of PS and gas-to-liquid (GTL) products as compared to their in vivo potencies was investigated. DMSO-extracts of a range of PS, containing different amounts of PAHs, and GTL-products, which are devoid of PAHs, were tested in the ES-D3 cell proliferation and differentiation assays of the EST. The results show that PS inhibited the differentiation of ES-D3 cells into cardiomyocytes in a concentration-dependent manner at non-cytotoxic concentrations, and that their potency was proportional to their PAH content. In contrast, as expected, GTL-products did not inhibit ES-D3 cell viability or differentiation at all. The in vitro PDT potencies were compared to published in vivo PDT studies, and a good correlation was found between in vitro and in vivo results (R=0.97). To conclude, our results support the hypothesis that PAHs are the primary inducers of the PDT in PS.

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In the present study, the ability of green tea catechins to induce electrophile-responsive element (EpRE)mediated gene expression and the role of their quinones in the mechanism of this induction were investigated. To this end, Hepa1c1c7 mouse hepatoma cells were used, stably transfected with a luciferase reporter gene under the expression regulation of an EpRE from the human NAD(P)H:quinone oxidoreductase 1 (NQO1) gene. The results obtained show that several, but not all, catechins tested are able to induce EpRE-mediated gene transcription, with epigallocatechin gallate (EGCG) and gallocatechin gallate (GCG), both containing a pyrogallol and a galloyl moiety, being the most powerful inducers. Moreover, it was demonstrated that the EpRE-mediated response to catechins was increased in cells with reduced cellular glutathione (GSH) levels and decreased in cells with increased levels of GSH, corroborating a role for catechin quinones. The intrinsic capacity of catechins to form quinone type metabolites upon their oxidation was demonstrated using incubations of epigallocatechin (EGC) and EGCG with tyrosinase and the GSH-trapping method. Glutathione conjugates formed in these incubations were identified as 2′-glutathionyl-EGC, 2′,6′-diglutathionyl-EGC, 2′-glutathionyl-EGCG, and 2′,6′diglutathionyl-EGCG, supporting the formation of quinone type metabolites involving especially the pyrogallol moiety of these catechins. Formation of the EGCG-quinone-glutathionyl adducts was also observed in the EpRE-LUX cellular system. This further supports the importance of the pyrogallol moiety for the quinone chemistry of the catechins. Finally, the presence of the pyrogallol moiety in the catechins also results in a relatively lower half-wave oxidation potential (E 1/2 ) and calculated heat of formation (DHF) for conversion of the catechins to their corresponding quinones, pointing at an increased ability to become oxidized. Altogether, our studies reveal that catechins, especially those containing a pyrogallol moiety, induce EpRE-mediated detoxifying gene expression and that this induction is likely to be the result of their quinone chemistry.

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A number of metabolites of 17b-estradiol were tested for their estrogenic activity using the ER-CA-LUX assay based on the increased expression of luciferase in exposed T47D breast cancer cells. E 2 b and estrone showed similar potencies in the test, whereas E 2 a was 100 times less active. Incubation of cells with estrone (0.35 mM) resulted in the formation of E 2 b, whereas the reverse reaction was observed for E 2 b. The resulting equilibrium may explain the similar estrogenic potency of estrone in the test. The synthetic 17-hydroxy benzoate ester of E 2 b was 3 times less active than the parent compound. The 17-hydroxy palmitate and oleate esters of E 2 b, were respectively 25 and 200 times less active than the parent compound. The 2-hydroxy metabolites of E 2 b and estrone showed a 5,000 to 10,000 fold lower activity. The 4-hydroxy metabolites were more potent than the 2-hydroxy metabolites, showing only a 20-200 times lower activity. The 2-and 4-methoxyesters of estrone were 700 times less active. It is concluded that the estrogenic potency of metabolites formed in cattle after treatment with E 2 b, like estrone, E 2 a and especially the esters of E 2 b, may be significant with respect to the potential risk of the use of estradiol for growth promotion in domestic animals in certain countries.Key words: Estrogenicity; ER-CALUX; catecholestrogens; estradiol; estradiol-esters. L. A. P. Hoogenboom, RIKILT, Bornsesteeg 45, 6708PD Wageningen, The Netherlands, e-mail: L.A.P. Hoogenboom/rikilt.wag-ur.nl The use of 17b-estradiol for growth-promoting purposes in cattle may result in the increased formation of residues of not only the parent compound but also its metabolites. In order to investigate the potential risk for the consumer, it is essential to obtain information on the identity, levels and biological properties of these compounds. In cattle the major metabolites of E 2 b are estrone, the 17a-congener and their glucuronide conjugates (1-3). Previous studies showed increased levels of the parent compound, and the two major bovine metabolites,

Pyrrolizidine alkaloids (PAs) are naturally occurring genotoxic compounds, and PA-containing plants can pose a risk to humans through contaminated food sources and herbal products. Upon metabolic activation, PAs can form DNA adducts, DNA and protein cross links, chromosomal aberrations, micronuclei, and DNA double-strand breaks. These genotoxic effects may induce gene mutations and play a role in the carcinogenesis of PAs. This study aims to predict in vivo genotoxicity for two well-studied PAs, lasiocarpine and riddelliine, in rat using in vitro genotoxicity data and physiologically based kinetic (PBK) modelling-based reverse dosimetry. The phosphorylation of histone protein H2AX was used as a quantitative surrogate endpoint for in vitro genotoxicity of lasiocarpine and riddelliine in primary rat hepatocytes and human HepaRG cells. The in vitro concentration-response curves obtained from primary rat hepatocytes were subsequently converted to in vivo doseresponse curves from which points of departure (PoDs) were derived that were compared to available in vivo genotoxicity data. The results showed that the predicted PoDs for lasiocarpine and riddelliine were comparable to in vivo genotoxicity data. It is concluded that this quantitative in vitro-in silico approach provides a method to predict in vivo genotoxicity for the large number of PAs for which in vivo genotoxicity data are lacking by integrating in vitro genotoxicity assays with PBK modelling-facilitated reverse dosimetry.