Validation of an automated image analysis micronucleus scoring system

The Loats Automated Micronucleus Scoring System was developed to assist with the evaluation of compounds for the ability to induce micronuclei in mouse bone marrow polychromatic erythrocytes (PCE). This image analysis system can identify PCE as well as normochromatic erythrocytes (NCE) and calculate the PCE/NCE ratio as an index for bone marrow toxicity. Two studies were conducted to provide slides for a comparison of micronucleated PCE values collected manually to those collected by the automated system. Mitomycin C was used as a micronucleus-inducing agent to elicit a positive response and Lilly compound 303497 was used as an example of a compound negative for the induction of micronuclei. No statistically significant differences were observed between micronucleus counts obtained manually and those obtained by the automated system. The PCE/NCE ratios calculated by the automated system were also similar to those determined from the manually collected PCE and NCE counts for the vehicle and positive controls, however, differences in the ratios were observed in compound treatment groups. These differences were attributed to a larger population of transitional cells in the treated groups. These results confirm that the Loats Automated Micronucleus Scoring System is an acceptable alternative to manual evaluation of mouse bone marrow slides for the incidence of micronucleated PCE.