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Studies of the metabolizing effect of the S9 liver fraction, hepatic microsomes and microsomal supernatant in the Ames test
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A rational extrapolation from mutagenicity data obtained in a test system to a situation of interest requires the knowledge of these variables in both cases.
4 Arni, P., A. Lfith, E. Deparade and D. Mfiller, CIBA-GEIGY Ltd., CH-4002 Basle (Switzerland)
Studies of the metabolizing effect of the $9 liver fraction, hepatic microsomes and microsomal supernatant in the Ames test In investigations with micro-organisms or mammalian cells in vitro, liver fractions ($9 fractions) from rats or mice are generally used to metabolize the test substances. The aim of the present study was to compare the metabolizing activity of microsomes alone with that of the $9 fraction in the Ames test, and also to include the microsomal supernatant ($105 fraction) in the investigations. Liver fractions from guinea pigs, mice, untreated rats and rats treated with Aroclor were tested. The mutagenicity tests with 2-acetylaminofluorene and b e n z o [ a ] p y r e n e were performed on strain TA1538 and those with cyclophosphamide and ~-naphthylamine on strain TA1535. The $9 fractions generally displayed the greatest activity. Microsomes alone exerted a similar action with cyclophosphamide, b u t were less active with the other substances. The S105 fractions for the most part produced scarcely any metabolizing action, except for those from guinea pigs and induced rats in the tests with ~-naphthylamine and 2-acetylaminofluorene. The S105 fractions from guinea pigs also proved capable of metabolizing b e n z o [ a ] p y r e n e . In the metabolization of benzo[a]pyrene, the microsomal supernatant generally appears to exert a predominantly stabilizing effect. The tests with ~-naphthylamine and 2-acetylaminofluorene, on the other hand, demonstrated a complementary effect of the enzymes present in the S105 fraction.
5 Aeschbacher, H.U., Nestl~ Products, Technical Assistance Co., Ltd., Biological Experimentation, Services Orbe, CH-1350 Orbe (Switzerland)
Technical problems in mutagenicity tests of complex substances in vitro Foods, or its components, are more and more frequently subjected to in vitro "carcinogenicity screening" tests. Such substances, however, can cause a variety of artefacts which may lead to misinterpretations. For instance, in the Ames test, free histidine increases the number of revertants in Salmonella TA98, TA100, T A 1 5 3 5 and TA1538, up to the doubling rate, which is reached with 100 pg histidine/plate. Now most foods contain enough free histidine to cause an increase in the number of revertants. Such an increase due to histidine could falsely be interpreted as a "mutagenic effect". Hence, the histidine must be eliminated and the content of free histidine must be chemically checked. Further problems occur when a complex test substance needs to be fractionated for reasons like solubility, concentration, isolation of compounds, etc.
A rational extrapolation from mutagenicity data obtained in a test system to a situation of interest requires the knowledge of these variables in both cases.
4 Arni, P., A. Lfith, E. Deparade and D. Mfiller, CIBA-GEIGY Ltd., CH-4002 Basle (Switzerland)
Studies of the metabolizing effect of the $9 liver fraction, hepatic microsomes and microsomal supernatant in the Ames test In investigations with micro-organisms or mammalian cells in vitro, liver fractions ($9 fractions) from rats or mice are generally used to metabolize the test substances. The aim of the present study was to compare the metabolizing activity of microsomes alone with that of the $9 fraction in the Ames test, and also to include the microsomal supernatant ($105 fraction) in the investigations. Liver fractions from guinea pigs, mice, untreated rats and rats treated with Aroclor were tested. The mutagenicity tests with 2-acetylaminofluorene and b e n z o [ a ] p y r e n e were performed on strain TA1538 and those with cyclophosphamide and ~-naphthylamine on strain TA1535. The $9 fractions generally displayed the greatest activity. Microsomes alone exerted a similar action with cyclophosphamide, b u t were less active with the other substances. The S105 fractions for the most part produced scarcely any metabolizing action, except for those from guinea pigs and induced rats in the tests with ~-naphthylamine and 2-acetylaminofluorene. The S105 fractions from guinea pigs also proved capable of metabolizing b e n z o [ a ] p y r e n e . In the metabolization of benzo[a]pyrene, the microsomal supernatant generally appears to exert a predominantly stabilizing effect. The tests with ~-naphthylamine and 2-acetylaminofluorene, on the other hand, demonstrated a complementary effect of the enzymes present in the S105 fraction.
5 Aeschbacher, H.U., Nestl~ Products, Technical Assistance Co., Ltd., Biological Experimentation, Services Orbe, CH-1350 Orbe (Switzerland)
Technical problems in mutagenicity tests of complex substances in vitro Foods, or its components, are more and more frequently subjected to in vitro "carcinogenicity screening" tests. Such substances, however, can cause a variety of artefacts which may lead to misinterpretations. For instance, in the Ames test, free histidine increases the number of revertants in Salmonella TA98, TA100, T A 1 5 3 5 and TA1538, up to the doubling rate, which is reached with 100 pg histidine/plate. Now most foods contain enough free histidine to cause an increase in the number of revertants. Such an increase due to histidine could falsely be interpreted as a "mutagenic effect". Hence, the histidine must be eliminated and the content of free histidine must be chemically checked. Further problems occur when a complex test substance needs to be fractionated for reasons like solubility, concentration, isolation of compounds, etc.