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A comparison of the results of the spot test in the mouse with the results of other test systems
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compounds is similar for all test systems, E. coli being for this chemical class the most sensitive organism. Whereas metronidazole exhibits moderate mutagenic activity in E. coli, 2 of the analogues are strongly mutagenic even at noninactivating concentrations. One of these compounds also causes genetic changes in all the other organisms used, i.e.N, crassa, S. cerevisiae and D. melanogaster. This can be taken as a strong indication that the compound will also induce genetic changes in mammalian cells when exposed to comparable concentrations and also that mutagenic analogues of 5-nitroimidazole may induce Trichomonas mutants with increased resistance to these agents. The remaining 5-nitroimidazole derivative was not active in any of the genetic systems employed here and appears to be suitable for use as an alternative to metronidazole or as a starting point for synthesis of new non-mutagenic analogues. The biological effects of the compounds studied here may be partly explained on the basis of differences in their chemical structure and reactivity.
28 Dawson, G.W.P., and G.A.T. Mahon, Department of Genetics, Trinity College, Dublin 2 (Ireland) A comparison o f the results o f the spot test in the mouse with the results of other test systems The spot test on the mouse involves the exposure of embryos, heterozygous for coat colour genes, to the chemicals. There are two forms of the test: either the embryos are produced by crossing the T strain (homozygous for 7 recessives) with wild-type or with the HT strain (homozygous for 6 recessives) with only 1 in common with the T strain). The former cross leads to the recognition as variant coat co]our areas in the offspring of mutations of at least 4 genes; the latter to the recognition of mutations of at least 6 genes. It will be argued that the second form may- be the more efficient test. The importance of the time of gestation at which treatment is given will be illustrated. The results of the test will be compared with the results of other test systems. Approximate estimates of the frequencies of mutations induced per cell will be compared with data from the germ line specific-locus test and shown to be similar. As different cell metabolisms are known to have different sensitivities it is not necessarily expected that mutations in coat pigment primordial cells will be induced at the same frequencies as mutations during gametogenesis. However, should these preliminary comparisons be further confirmed the spot test will be not only established as a simple inexpensive test for the detection of mutagenic chemicals but also as a test yielding quantitative results applicable to estimating the degree of heritable genetic damage. It will also be noted that the spot test in the mouse is the only known whole mammal system in which both carcinogenicity and mutagenicity could be scored simultaneously: the offspring of treated pregnant females could be examined for m u t a n t areas of coat colour and for tumours.
119 29 Loprieno, N., R. Barale, S. Presciuttini, A.M. Rossi, I. Sbrana, G. Stretti, L. Zaccaro, A. Abbondandolo a, S. Bonatti a and R. Fiorio ~, Laboratorio di Genetica, University of Pisa, and ~ Laboratorio di Mutagenesi e Differenziamento of the CNR, Pisa (Italy) Comparative data with different test systems using micro-organisms and mammalian cells on references and environmental mutagens The mutagenic activity of some 11 chemicals of different interest (methyl methanesulfonate, ethyl methanesulfonate, dimethylnitrosamine, mitomycin C, hycanthone, atrazine, styrene, styrene oxide, trichloroethylene, e p o x y - l , l , 2 trichloroethane, difluoromonochloromethane) has been evaluated by using different genetic test systems. These included: (1) reverse mutations to histidine independence in S. typhimurium; (2) forward mutations at 5 loci in S. pombe; (3) mitotic gene conversions at 2 loci in S. cerevisiae; (4) forward mutations at the HGPRT locus in V79 Chinese hamster cells; (5) unscheduled DNA synthesis in EUE human cells; (6) chromosomal aberrations in bone-marrow cells in the mouse. Appropriate systems for metabolic activation (microsomal preparations, host-mediated assay) were used in combination with the different mutation tests in vitro; for evaluating the herbicide atrazine, a plant metabolic activation system was included in the methodology. Styrene, trichloroethylene and difluorochloromethane were found inactive in all investigated systems, whereas all remaining compounds resulted mutagenic in each test system. By this mutagenicity multisystem test it is possible to rule out also dubious results, due to the uncertainty of some of the experiments, thus increasing the reliability of each system.
3O Paes, D., and S. Thompson, Department of Genetics, Trinity College, Dublin 2 (Ireland) Forward mutagenesis as a test system in Salmonella typhimurium There are two alternative approaches to the development of bacterial mutagenicity assays: (a) back-mutation systems based on the reversion to prototrophy of auxotrophic strains, and (b) forward-mutation systems based on the inactivation of genes indispensable for normal cell functions. Failure to detect some chemical carcinogens as mutagens (false negatives) in the Ames test, the best characterized of the back-mutation assays, may reflect the specificity of the tester strains utilized in the test. Resistance to azetidine-carboxylic acid (ACr), 8-azaguanine (AG r ), chromate, L-arabinose, lactose, galactose (galr) and the galR s -~ galR- system in E. coli K12 343/113 were surveyed by us as potential forward-mutation systems. All the systems with varying degrees of sensitivity, detect the base substituting mutagens MNNG, EMS and the general frameshift mutagen ICR-191. The AC r, AG ~ and gal r systems in S. typhimurium detect 9-aminoacridine, a frame-
compounds is similar for all test systems, E. coli being for this chemical class the most sensitive organism. Whereas metronidazole exhibits moderate mutagenic activity in E. coli, 2 of the analogues are strongly mutagenic even at noninactivating concentrations. One of these compounds also causes genetic changes in all the other organisms used, i.e.N, crassa, S. cerevisiae and D. melanogaster. This can be taken as a strong indication that the compound will also induce genetic changes in mammalian cells when exposed to comparable concentrations and also that mutagenic analogues of 5-nitroimidazole may induce Trichomonas mutants with increased resistance to these agents. The remaining 5-nitroimidazole derivative was not active in any of the genetic systems employed here and appears to be suitable for use as an alternative to metronidazole or as a starting point for synthesis of new non-mutagenic analogues. The biological effects of the compounds studied here may be partly explained on the basis of differences in their chemical structure and reactivity.
28 Dawson, G.W.P., and G.A.T. Mahon, Department of Genetics, Trinity College, Dublin 2 (Ireland) A comparison o f the results o f the spot test in the mouse with the results of other test systems The spot test on the mouse involves the exposure of embryos, heterozygous for coat colour genes, to the chemicals. There are two forms of the test: either the embryos are produced by crossing the T strain (homozygous for 7 recessives) with wild-type or with the HT strain (homozygous for 6 recessives) with only 1 in common with the T strain). The former cross leads to the recognition as variant coat co]our areas in the offspring of mutations of at least 4 genes; the latter to the recognition of mutations of at least 6 genes. It will be argued that the second form may- be the more efficient test. The importance of the time of gestation at which treatment is given will be illustrated. The results of the test will be compared with the results of other test systems. Approximate estimates of the frequencies of mutations induced per cell will be compared with data from the germ line specific-locus test and shown to be similar. As different cell metabolisms are known to have different sensitivities it is not necessarily expected that mutations in coat pigment primordial cells will be induced at the same frequencies as mutations during gametogenesis. However, should these preliminary comparisons be further confirmed the spot test will be not only established as a simple inexpensive test for the detection of mutagenic chemicals but also as a test yielding quantitative results applicable to estimating the degree of heritable genetic damage. It will also be noted that the spot test in the mouse is the only known whole mammal system in which both carcinogenicity and mutagenicity could be scored simultaneously: the offspring of treated pregnant females could be examined for m u t a n t areas of coat colour and for tumours.
119 29 Loprieno, N., R. Barale, S. Presciuttini, A.M. Rossi, I. Sbrana, G. Stretti, L. Zaccaro, A. Abbondandolo a, S. Bonatti a and R. Fiorio ~, Laboratorio di Genetica, University of Pisa, and ~ Laboratorio di Mutagenesi e Differenziamento of the CNR, Pisa (Italy) Comparative data with different test systems using micro-organisms and mammalian cells on references and environmental mutagens The mutagenic activity of some 11 chemicals of different interest (methyl methanesulfonate, ethyl methanesulfonate, dimethylnitrosamine, mitomycin C, hycanthone, atrazine, styrene, styrene oxide, trichloroethylene, e p o x y - l , l , 2 trichloroethane, difluoromonochloromethane) has been evaluated by using different genetic test systems. These included: (1) reverse mutations to histidine independence in S. typhimurium; (2) forward mutations at 5 loci in S. pombe; (3) mitotic gene conversions at 2 loci in S. cerevisiae; (4) forward mutations at the HGPRT locus in V79 Chinese hamster cells; (5) unscheduled DNA synthesis in EUE human cells; (6) chromosomal aberrations in bone-marrow cells in the mouse. Appropriate systems for metabolic activation (microsomal preparations, host-mediated assay) were used in combination with the different mutation tests in vitro; for evaluating the herbicide atrazine, a plant metabolic activation system was included in the methodology. Styrene, trichloroethylene and difluorochloromethane were found inactive in all investigated systems, whereas all remaining compounds resulted mutagenic in each test system. By this mutagenicity multisystem test it is possible to rule out also dubious results, due to the uncertainty of some of the experiments, thus increasing the reliability of each system.
3O Paes, D., and S. Thompson, Department of Genetics, Trinity College, Dublin 2 (Ireland) Forward mutagenesis as a test system in Salmonella typhimurium There are two alternative approaches to the development of bacterial mutagenicity assays: (a) back-mutation systems based on the reversion to prototrophy of auxotrophic strains, and (b) forward-mutation systems based on the inactivation of genes indispensable for normal cell functions. Failure to detect some chemical carcinogens as mutagens (false negatives) in the Ames test, the best characterized of the back-mutation assays, may reflect the specificity of the tester strains utilized in the test. Resistance to azetidine-carboxylic acid (ACr), 8-azaguanine (AG r ), chromate, L-arabinose, lactose, galactose (galr) and the galR s -~ galR- system in E. coli K12 343/113 were surveyed by us as potential forward-mutation systems. All the systems with varying degrees of sensitivity, detect the base substituting mutagens MNNG, EMS and the general frameshift mutagen ICR-191. The AC r, AG ~ and gal r systems in S. typhimurium detect 9-aminoacridine, a frame-