Abstract
[Aim] Acetamide (AA) is a potent hepatocarcinogen in rats. We previously found that AA induces characteristic large micronuclei (LMN) in the rat liver, and showed the chromosome rearrangements through micronuclei formation may contribute to its hepatocarcinogenesis. In this study, to elucidate the mechanism of micronucleus formation, we investigated the time dependent changes in rat hepatocytes after a single dose of AA.
[Methods] Male 6-week-old F344 rats were gavaged a single dose of 6000 mg/kg body weight of AA, and the livers were examined at 1, 2, 4, 6, 12, 24, 48, 72, or 120 hrs after administration.
[Results] Binucleated hepatocytes in which one of two nuclei was irregularly shaped and shrunk were observed from 6 hrs after administration, and reached the maximum ratio at 24 hrs. At 48 hrs, apoptotic hepatocytes were frequently observed, and binucleated hepatocytes with shrunk nuclei were decreased. On the other hand, hepatocytes with LMN were newly observed at this time. The mitotic hepatocytes reached the maximum ratio at 72 hrs. Immunohistopathological examination showed abnormal expression of BAF from 6 hrs. Increases in heterochromatic regions from 12 hrs and abnormality of nuclear lamina at 48 hrs were observed in shrunk nuclei.
[Discussion] Histopathological and nuclear morphological analysis revealed that the LMN induced by AA were formed through nuclear shrinkage of binucleated hepatocytes. The fact that abnormal expression of BAF was observed not only in shrunk nuclei but in some morphologically normal nuclei suggested the involvement of nuclear envelope aberration in nuclear shrinkage and LMN formation.
