Emergence of a population of small, diploid hepatocytes during hepatocarcinogenesis.

The sequential treatment of young Wistar rats with two different carcinogens (diethylnitrosamine - plus partial hepatectomy - as an initiator, and 2-acetylaminofluorene as a cytotoxic selection pressure) induces the appearance of foci and nodules of liver cells which are phenotypically altered. By means of an algorithm which takes into account binuclearity as well as cell-to-cell aggregation it is possible to compute cellular ploidy distributions from flow-cytometric analysis of either hepatocyte suspensions or suspensions of hepatocytic nuclei. Cell suspensions isolated from carcinogen-treated rats can be shown to contain, already after 8 weeks, approximately 70% small, diploid hepatocytes, whereas suspensions from normal or partially hepatectomized control livers contain only approximately 10% diploid cells (the remainder being mostly tetraploid). Isolated nodules, i.e., expanding clones of proliferating cells, believed to be neoplastic precursor lesions, contained almost only diploid cells. These observations suggest that the selective outgrowth of a population of small, diploid hepatocytes may be a significant early step in the development of liver cancer.