Frequency and DNA content of micronuclei in rat parenchymal liver cells during experimental hepatocarcinogenesis.

Liver carcinogenesis is considered to be a good experimental model to study the sequential changes leading to cancer and was applied here for the analysis of chromosome/genome mutations. Since the micronucleus test was shown to be an adequate method to detect and analyse chromosome changes in dividing cells, the frequency of micronuclei (MN) together with their relative DNA content (DNA content of the MN divided by the DNA content of the corresponding nucleus) were analysed in hepatocytes isolated from rats at different stages of experimentally induced hepatocarcinogenesis. The protocol used for the induction of liver cancer was based on the triphasic 'Gerlans protocol', a Solt-Farber procedure supplemented with a phenobarbital (PB) promotion step. Male Wistar rats were initiated by a single i.p. dose of diethylnitrosamine (DENA), followed by selection of the resistant hepatocytes by 2-acetylaminofluorene (2-AAF). Subsequent promotion was accomplished by chronic exposure to phenobarbital. For each group of rats a mitotic stimulator (CCl4) is necessary at the end of their treatment period to express the clastogenic and/or aneugenic lesions which may lead to micronuclei. The results of these experiments do confirm that genetic alterations are occurring at the chromosome level (MN expression) during the different steps of experimental rat liver carcinogenesis. DNA measurements seem to be a good genetic parameter to detect eventual differences between the chromosomal content (whole chromosome or chromosome fragments) of MN populations appearing in different stages of the carcinogenic process. Moreover, a comparison between the mono- and bi-nucleated cell population showed that the frequency of micronuclei is higher in mononuclear parenchymal liver cells.