Differentiation of the mechanism of micronuclei induced by cysteine and glutathione conjugates of methylenedi-p-phenyl diisocyanate from that of 4,4 '-methylenedianiline

Methylenedi-p-phenyl diisocyanate (MDI) is widely used in the production of polyurethane, products. Diisocyanates are reactive compounds, MDI can reac t under physiological conditions with various functional groups found on bi ological molecules resulting in conjugate formation or undergo non-enzymati c hydrolysis to form 4,4'-methylenedianiline (MDA). We have previously repo rted that addition of MDI directly to Chinese hamster lung fibroblasts (V79 ) cultures did not induce micronuclei (MN), but MDA, and the glutathione an d cysteine conjugates of NDI (BisGS-MDI and BisCYS-MDI), induced a concentr ation-dependent increase in the frequency of MN. The conventional MN assay does not discriminate between MN produced by acentric chromosome fragments from those arising due to whole lagging chromosomes that were not incorpora ted into daughter nuclei at the time of cell division. The mechanism of MN induction from these potential MDI metabolites/reaction products was explor ed in the present study using immunofluorescent staining of kinetochore in MN of cytokinesis-blocked V79 cells. This assay discerns the presence of ce ntromere within the MN to distinguish the MN containing centric chromosomes from those containing acentric fragments. Eighty five percent of NMA-induc ed MN were negative with respect to anti-kinetochore antibody binding (KC-) . This is consistent with an interaction between MDA and DNA resulting in c hromosome breakage. However, BisGS-MDI and BisCYS-MI induced a higher perce ntage of MN that were positively stained by the anti-kinetochore antibody ( KC+). These results suggest that the mechanism of MN formation induced by B isGS-MDI and BisCYS-MDI is mediated through disruption and/or by affecting the function of the mitotic spindle. This mechanism is distinctly different from the mechanism of MN induction by MDA. Published by Elsevier Science B .V.