化学物質によるｉｎ ｖｉｔｒｏ及びｉｎ ｖｉｖｏにおける突然変異の定量的解析に関する研究

Abstract

The mutagenicities of methyl, ethyl, isopropyl, and butyl methanesulfonates and the corresponding alkylderivatives of N-nitrosoureas were examined using E. coli Hs30R strain deficient in the excision repair system. Their mutagenic capacities were standardized by converting the experimentally obtained mutation frequencies into those per unit of the concentration-time integrated dose with various dimensions, μM×h, mM×h, and M×h. The mutation frequencies under various conceptual exposure conditions were computed by using those at unit integrated dose, on the assumption that the dose-response relation is linear on a log-log scale.An attempt was made to establish a procedure for kinetic formulation of the mutagenic chemical modification of the mutational target(s). Using the proposed kinetic formulation, a quantitative analysis was made of the temperature dependence of mutation frequency in terms of the activation energies for mutagenic modification induced in the cell by mutagens. E. coli Hs30R strain was treated with alkyl methanesulfonates and N-alkyl-N-nitrosoureas at 37, 25, and 15°C for 1 hour and the induced mutation frequencies were normalized in terms of the concentration-time integrated dose. The plot of the normalized mutation frequency versus the reciprocal of the reaction temperature gave a straight line which corresponds to the Arrehnius plot, enabling us to estimate the apparent activation energy of the initial chemical event leading to mutation.In order to study the mutagenic interaction between two chemicals, an analytical method for the classification of the mutagenic interactions as “equivalent” or “independent” is proposed. The mutation frequencies induced by simultaneous (combined) treatments of Salmonella typhimurium TA100 with two simple alkylating agents were compared with those induced by separate treatments with the two mutagens. Furthermore, the comparison was made of the frequencies of micronucleated reticulocytes (MNRETs) produced in ddY mice treated with model chemicals such as alkylating agents, spindle poisons, and an oxidizing agent. The results indicate that the analytical method proposed here is appropriate to evaluate the combined effects of chemicals both in bacterial mutagenesis and micronucleus induction.