ANALYSIS OF MICRONUCLEATED CELLS BY FLOW-CYTOMETRY .4. KINETIC-ANALYSIS OF CYTOGENETIC DAMAGE IN BLOOD

Micronucleated cells (MN cells) generated spontaneously or by clastoge n action accumulate in the peripheral blood of the mouse, and their pr esence reflects the level of chromosome damage. Traditionally, micronu cleated cells have been scored by visual inspection. With the developm ent of flow cytometry based scoring procedures, vast numbers of cells can be analyzed, making it possible to determine the change in the num ber of MN cells in the total peripheral blood pool. This report descri bes experiments whereby initial blood samples were obtained before dos ing, providing mouse-specific controls for measuring subsequent change s in MN cells. Mice were then dosed with saline (solvent control), met hyl methanesulfonate, cyclophosphamide or colchicine every 48 h and bl ed every 96 h for 12 days. For each blood sample, one million fixed er ythrocytes (RBCs) were interrogated for the presence of micronuclei, a nd regression analysis was used to determine the rate of MN cell influ x per day for each animal or sets of animals. To evaluate the effect o f treatment on MN induction, the mean slopes of solvent and chemically treated animals were compared using t-tests. The results of these exp eriments indicate that the kinetics of MN induction continues near the background frequency for saline dosed mice, whereas clastogenic agent s or spindle poisons cause a significant influx of MN events into the blood. The results suggest that some studies may benefit from a flow c ytometry based analysis of multiple blood samples, especially when the number of mice is limited, or when a weak clastogen is being investig ated.