Gesellschaft für Umwelt-Mutationsforschung e.V. (GUM) A German-speaking section of the European Environmental Mutagen Society (EEMS) Abstracts of papers presented at the 11th meeting October 12–14, 1988, Mainz, FRG

Mutagenesis vol.4 no.4 pp.306-324, 1989 Gesellschaft fiir Umwelt-Mutationsforschung e.V. (GUM) A German-speaking section of the European Environmental Mutagen Society (EEMS) Abstracts of papers presented at the 11th meeting October 12—14, 1988, Mainz, FRG (A) Papers to the main topic of the conference: xenobiotic metabolism in chemical mutagenesis Pyrrolizidine alkaloids such as seneciphylline, senecionine and monocrotaline (unsaturated alkaloids) are known mutagens and carcinogens which are metabolized by P-450-dependent oxidations to reactive species (overview: Mattocks, 1986). As activation reactions C-hydroxylations at different positions occur leading to mutagenic metabolites, as for example to 19-hydroxysenecionine. So far most studies were undertaken using rats, mice and sheep. In the present study the mutagenic activity of seneciphylline, senecionine, senkirkine and monocrotaline was compared in the yeast strain Saccharomyces cerevisiae D7 (Zimmermann, 1975). Because it is already known that S. cerevisiae contains its own P-450 system, which seems also to be capable of activating some promutagens (Callen and Philpot, 1977; Niggli et al., 1987), an additional aim of this study was to characterize the endogenous metabolism of the alkaloids in yeast using intact cells or isolated microsomes. Seneciphylline and senecionine showed distinct mutagenic effects (induction of trp5 convertants) in the dose range of 1—2 mg/ml whereas corresponding doses of senkirkine were without effect. At the maximum dose level, survival was reduced by —50 and >90% with seneciphylline and senecionine respectively. Senkirkine was non-toxic. In addition, these results were compared with the activity of monocrotaline which is a wellknown mutagenic pyrrolizidine alkaloid. This compound was also positive between 1 and 2 mg/ml, the mutagenic potency being less when compared to seneciphylline and senecionine. A chloroform extract of whole cells and isolated microsomes after incubation with seneciphylline were separated by TLC followed by GC/MS analysis. A different spectrum of metabolites (four different TLC spots) was found compared with an incubation with rat liver homogenate (Aroclor-1254-treated animals). Due to the small amounts of the respective metabolites and due to die fact that the polar metabolites did not yield detectable mass fragments (probably as a consequence of their instability), only one metabolite could be identified so far: the 13,19-epoxide of seneciphylline. References Callen.D.F. and Philpot.R.M. (1977) Mum. Res., 45, 309-324. Mattocks, A.R. (1986) In Chemistry and Toxicology of Pyrrolizidine Alkaloids. Academic Press, NY. Niggli.B. et al (1986) Mutat. Res., 175, 223-229. Zimmermann.F.K. (1975) Mutat. Res., 28, 381-388. 306 Synergistic interactions have been reported in the tumorigenicity to mouse skin of the epoxy resin components bis epoxycyclopentylether and bisphenol A diglycidylether. Neither compound was carcinogenic when tested individually, whilst the mixture induced a large number of tumours (Holland et al., 1979). To elucidate the mechanism of this synergism we have studied the hydrolysis of bisphenol A diglycidylether by epoxide hydrolases, its inhibition by bis epoxycyclopentylether and the effects on the binding of the glycidylether to mouse skin DNA. Bisphenol A diglycidylether was rapidly hydrolysed by epoxide hydrolases in microsomal and cytosolic fractions of both liver and skin. In the liver the activities in three different mouse strains were 28.3—48.5 and 33.0 — 38.8 nmol/mg protein/min for microsomal and cytosolic fractions respectively; the corresponding activities in skin subcellular fractions were 7.9-10.2 and 0.85-0.98 nmol/mg protein/min. The microsomal activity in both tissues was inhibited by bis epoxycyclopentylether, the liver enzyme appearing to be slightly more sensitive to this inhibition. Bisphenol A diglycidylether formed one major DNA adduct when applied to mouse skin. This was identified as a glycidaldehyde adduct, indicating that glycidaldehyde was produced by O-dealkylation of the ether. Adduct formation was not observed at the lowest bisphenol A digylcidylether dose tested, unless bis epoxycyclopentylether was simultaneously applied. This implies that at low doses the bisphenol A diglycidylether is hydrolysed before dealkylation can occur and no glycidaldehyde is formed, inhibition of the epoxide hydrolase activity prevents this inactivan'on and results in increased production of the reactive metabolite. This in turn could account for the potentiation of the carcinogenic response in the epoxide mixture. Reference HollandJ.M., Gosslee,D.G. and Williams.N.J. (1979) Cancer Res., 39, 1718-1725. 3. In vivo genotoxicity of A'-nitrosodimethylamine in primary cells of liver, lung and kidney S.Y.Brendler, P.Schmezer and B.L.Pool Institute of Toxicology and Chemotherapy, German Cancer Research Centre, Im Neuenheimer Feld 280, D-69 Heidelberg 1, FRG N-Nitrosamines are carcinogens with strong organ-specific effects. The reason for the selectivity of these compounds is 1. Mutagenicity and endogenous metabolism of pyrrolizidine alkaloids in the yeast Saccharomyces cerevisiae D7 I.Baljak, J.Brauchli, U.Zweifel, U.Friederich and F.E.Wurgler Institute of Toxicology, El Hand University of Zurich, CH-8603 Schwerzenbach, Switzerland 2. Studies on the mechanism of the synergistic interaction between bis epoxycyclopentylether and bisphenol A diglycidylether in mouse skin tumorigenicity P.Bentley, F.Bieri, H.Kuster, S.Muakkassah-Kelly, P.Sagelsdorff, W.Staubli and F.Waechter Central Toxicology Unit, ClBA-GEIGYLtd, Basel, Switzerland GUM abstracts 4. Formation of mkronuclei in mouse bone marrow by benzo[a]pyrene and benzo[a]pyrene metabolites, and the role of induction of xenobiotic-metabolizing enzymes E.Bruchlos, S.Dogra, K.Pauly, A.Seidel, F.Oesch and H.R.Glatt Institute of Toxicology, University of Mainz, Obere Zahlbacher Strasse 67, D-6500 Mainz, FRG Benzo[a]pyrene (BP) and two metabolites, BP-3,6-quinone and rra/w-BP-7,8-dihydrodiol (BP-7,8-diol) were investigated for the induction of micronuclei in polychromatic erythrocytes of the bone marrow of male NMRI mice. All test compounds were applied by the i.p. route. BP showed a marked positive response when two applications were used, at - 2 4 and - 4 8 h (with respect to the time of killing), but was virtually inactive, when a single dose was applied at - 2 4 h. It was suspected that the first dose was important for the induction of BP-metabolizing enzymes (arylhydrocarbon hydroxylase, AHH) rather than as substrate for the formation of active metabolites. Indeed, 24 h after application of BP, AHH activity was elevated in bone marrow and liver. A similar effect on AHH activity was observed 24 h after i.p. application of /3-naphthoflavone (BNF). Treatment of mice with this compound, at - 2 4 and/or - 4 8 h, did not affect the frequency of micronucleated cells. However, treatment with BNF at (...truncated)