Kinetics of micronucleus induction and cytotoxic activity of colchicine in murine erythroblast in vivo.

In previous studies, we inferred some pharmacokinetic and pharmacodynamic parameters of alkylating agents and antimetabolites by comparing their kinetics of micronucleated polychromatic erythrocyte (MN-PCE) induction with the one obtained after the exposure to gamma rays in peripheral blood of mice, assuming that radiation acts immediately because it does not require absorption and distribution in the organism. According to our earlier studies, the kinetics of MN-PCE induction depends mainly on the following: (i) the cytotoxic effects that in turn could affect the duration of cell division; (ii) the pharmacokinetics including the metabolic activation requirement; and (iii) the mechanism of MN induction. The aim of the present study was to analyze the kinetics of MN-PCE induction by an aneuploidogen that induces micronuclei by acting on the achromatic spindle. The kinetics of MN-PCE induction by colchicine, as well as the reduction in the PCE frequency over time was determined in peripheral blood of mice treated with different doses of the aneuploidogen. The genotoxic effect, established as the area beneath the curve (ABC) of MN-PCE versus time-response, indicates an almost directly proportional relationship with respect to dose. Similarly, the relationship between dose and cytotoxic effect determined as the ABC of PCE versus time was inversely proportional, suggesting a relationship between both endpoints and doses administered. However, the number of cells affected by these two phenomena indicates that cytotoxicity is not necessarily caused, or at least not only by genotoxicity. The analysis of the kinetics of MN-PCE induction after the treatment with non-cytotoxic dose of colchicine, indicates that the MN-PCE appear in the blood stream at almost the same time, as occurs after the exposure to gamma rays; in spite of the differences in the cell cycle stage in which they can cause micronucleus (MN). Perhaps the fact that cells are not synchronized does not permit one to observe some difference in the time they appear in the blood. These results suggest that colchicine acts rapidly after exposure. The elimination half-life of colchicine is 17h, suggesting that colchicne is disposable for long time. With high doses of colchicine the pharmacokinetic parameters increases substantially. These data imply that low doses of colchicine are slightly cytotoxic, and that under this circumstances colchicines arrives rapidly to hemopoyetic tissues and acts for several hours.