AN IN-VIVO IN-VITRO METHOD FOR ASSESSING MICRONUCLEUS AND CHROMOSOME ABERRATION INDUCTION IN RAT BONE-MARROW AND SPLEEN .2. STUDIES WITH CHLORAMBUCIL AND MITOMYCIN-C

An in vivo/in vitro system using rat bone marrow cells and spleen cell s to assess micronucleus (MN) and structural chromosome aberrations (S CA) simultaneously (Moore et al., 1995) was further developed. In two separate experiments, two rats/dose/experiment were treated i.p. with 0, 5, 10 and 15 mg chlorambucil (CA)/kg or with mitomycin C (MMC) at 0 , 1, 2, 4 mg/kg (experiment I) or 0, 4, 6, and 8 mg/kg (experiment 2) and killed 6 h later. Cultures were then established in the presence o f growth stimulants (interleukin-3 and granulocyte-macrophage colony s timulating factor for bone marrow; lipopolysaccharide and concanavalin A for spleen) and cytochalasin B, a cytokinesis inhibitor. Bone marro w cells were harvested 24 h after establishment of cultures, while spl een cells were harvested at 48 h. In addition, spleen cells were concu rrently assayed for chromosome aberrations. With the MN endpoint, sple en cells appeared more sensitive than bone marrow cells to the effects of CA due both to a lower background and an increased response. For M MC, bone marrow cells exhibited both a higher background of MN and a g reater numerical response than did spleen cells. However, on the basis of a fold-increase over control values, spleen cells were more sensit ive than bone marrow cells. In general, the MN endpoint appeared more sensitive than the SCA in spleen cells after treatment with CA or MMC. Thus, the approach described here shows great potential in detecting genotoxicity.