Simulation study of the effects of multiple treatments in the mouse bone marrow micronucleus test.

The effect of multiple treatment with chemicals in the micronucleus test was evaluated by simulation involving an estimation of the additive accumulation of micronucleated polychromatic erythrocytes (MNPCEs) on the basis of time-response data available on single treatments with mitomycin C, 1-beta-D-arabinofuranosylcytosine, 6-mercaptopurine, and methotrexate. The frequency of MNPCEs calculated for different multiple treatment regimens by the model could predict the effects observed in real experiments. On the other hand, the effect of multiple treatments on bone marrow depression, expressed as a decrease in the frequency of polychromatic erythrocytes, was exponential according to both the simulation and actual data. These results suggest that although increasing the number of treatments may additively enhance the MNPCE response obtained with some agents it may, in the case of bone marrow-toxic chemicals and doses, make micronucleus analysis more time-consuming and even impossible due to the exponential decrease of analyzable cells, especially in the case of manual scoring.