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Validation of an efficient in vivo genotoxicity test with somatic cells of Drosophila
211 (SMART) to increase the sensitivity of this system, cotreatment with inducers and indirect mutagens/carcinogens was performed. Treatment of larvae with 0.1 mM of dimethylnitrosamine (DMN) dissolved in sucrose solution gave nearly a 100-fold increase of spots, involving both single and twin spots. Cotreatment with 1000 ppm phenobarbital caused a significant increase of the effect of DMN. The use of dimethyl sulfoxide (DMSO) as a solvent instead of the sucrose solution caused a drastic decrease of the effect of DMN in accordance with previous observations (Magnusson and Ramel, 1978). Benzo[a]pyrene is metabolized in Drosophila preferentially to quinones instead of dihydrodiols as in mammals (HallstriSm and Grafstr6m, 1981) and this compound is not mutagenic in standard sex-linked recessive lethal tests in Drosophila. In the SMART system it is however weakly mutagenic, but this effect was not increased by cotreatment with the inducer Aroclor (PCB).
23 FrNich, A., and F.E. Wiirgler, Institute of Toxicology, Swiss Federal Institute of Technology and University of Zurich, CH-8603 Schwerzenbach (Switzerland) Validation of an efficient in vivo genotoxicity test with somatic cells of Drosophila
In the Drosophila wing spot test larvae transheterozygous for the recessive markers on chromosome 3 are exposed to test compounds. Spots on the wing expressing phenotypically the markers are indicative of genotoxic effects (Wiargler, F.E., and E. Vogel (1986) in: F.J. de Serres (Ed.), Chemical Mutagens, Vol. 10, Plenum, New York, pp. 1-72). In Drosophila larvae promutagens can be activated by cytochrome P-450-dependent enzyme systems. Optimizing the metabolic activities, e.g. by altering the genetic control of the P-450 systems could improve the test performance. Therefore first and second chromosomes of the test strains were substituted by those of a wild-type strain with constitutively increased cytochrome P450 activities linked to a locus on the second chromosome. Diethylnitrosamine which is acti-
vated by cytochrome P-450-dependent a-C-hydroxylation shows increased toxic and genotoxic effects in the new strains. (Work supported by Swiss Cancer League.)
24 Ioannides, C., R. Hyde and J.N. Smith, Biochemistry Department, University of Surrey, Guildford, Surrey GU2 5XH (Great Britain) A comparison of Aroclor 1254-induced hepatic preparations from rat and hamster in the activation of precarcinogens in the Ames test
A number of studies have revealed marked species differences in the activation of chemical carcinogens in the Ames test. The hamster appears to be the most effective laboratory animal species in metabolically converting nitrosamines and aromatic amines to their mutagenic intermediates. However, the above studies were conducted in animals that were not treated with any inducing agent. In the standard Ames test procedure activation systems derived from rats induced with Aroclor 1254, a mixture of polychlorinated biphenyls that are potent inducers of mixed-function oxidase activity, are routinely used. The present study was undertaken in order to investigate the effect of Aroclor 1254 on the mixed-function oxidases in the rat and hamster and compare the efficiency of hepatic preparations from these animals in activating established carcinogens into mutagens in the Ames test. In both animal species treatment with Aroclor 1254 gave rise to increases in benzphetamine N-demethylase and NADPH cytochrome c reductase activities and cytochromes P-450 and b5. Although the O-deethylation of ethoxyresorufin, an indicator of cytochrome P-448 activity (cytochromes P-450c and P-450a), was stimulated in both animal species, the extent of induction was markedly different being 150-fold in the rat but only 3-fold in the hamster. A comparison of hepatic preparations from the induced animals in activating various groups of chemical carcinogens to mutagens revealed that no generalisations could be made as to which is the superior activating
23 FrNich, A., and F.E. Wiirgler, Institute of Toxicology, Swiss Federal Institute of Technology and University of Zurich, CH-8603 Schwerzenbach (Switzerland) Validation of an efficient in vivo genotoxicity test with somatic cells of Drosophila
In the Drosophila wing spot test larvae transheterozygous for the recessive markers on chromosome 3 are exposed to test compounds. Spots on the wing expressing phenotypically the markers are indicative of genotoxic effects (Wiargler, F.E., and E. Vogel (1986) in: F.J. de Serres (Ed.), Chemical Mutagens, Vol. 10, Plenum, New York, pp. 1-72). In Drosophila larvae promutagens can be activated by cytochrome P-450-dependent enzyme systems. Optimizing the metabolic activities, e.g. by altering the genetic control of the P-450 systems could improve the test performance. Therefore first and second chromosomes of the test strains were substituted by those of a wild-type strain with constitutively increased cytochrome P450 activities linked to a locus on the second chromosome. Diethylnitrosamine which is acti-
vated by cytochrome P-450-dependent a-C-hydroxylation shows increased toxic and genotoxic effects in the new strains. (Work supported by Swiss Cancer League.)
24 Ioannides, C., R. Hyde and J.N. Smith, Biochemistry Department, University of Surrey, Guildford, Surrey GU2 5XH (Great Britain) A comparison of Aroclor 1254-induced hepatic preparations from rat and hamster in the activation of precarcinogens in the Ames test
A number of studies have revealed marked species differences in the activation of chemical carcinogens in the Ames test. The hamster appears to be the most effective laboratory animal species in metabolically converting nitrosamines and aromatic amines to their mutagenic intermediates. However, the above studies were conducted in animals that were not treated with any inducing agent. In the standard Ames test procedure activation systems derived from rats induced with Aroclor 1254, a mixture of polychlorinated biphenyls that are potent inducers of mixed-function oxidase activity, are routinely used. The present study was undertaken in order to investigate the effect of Aroclor 1254 on the mixed-function oxidases in the rat and hamster and compare the efficiency of hepatic preparations from these animals in activating established carcinogens into mutagens in the Ames test. In both animal species treatment with Aroclor 1254 gave rise to increases in benzphetamine N-demethylase and NADPH cytochrome c reductase activities and cytochromes P-450 and b5. Although the O-deethylation of ethoxyresorufin, an indicator of cytochrome P-448 activity (cytochromes P-450c and P-450a), was stimulated in both animal species, the extent of induction was markedly different being 150-fold in the rat but only 3-fold in the hamster. A comparison of hepatic preparations from the induced animals in activating various groups of chemical carcinogens to mutagens revealed that no generalisations could be made as to which is the superior activating