Expression of BrdU and C-Ha-ras in Experimentally Induced Enzyme Altered Foci of the Liver and Hepatocellular Carcinoma

ABSTRACT

For sequential phenotypic changes including enzyme altered hepatocytic foci, hyperplastic nodules, hepatocellular adenomas and carcinomas were produced in Sprague-Dawley rats by Solt-Farber method (administration of diethylnitrosamine and acetylaminofluorene (AAF), and partial hepatectomy). The immunohistochemical expressions of glutathione S transferase P (GST-P) and bromodeoxyuridine (BrdU) were assessed for selective proliferative activity in the enzyme altered foci and the subsequently developed lesions by double immunohistochemical staining technique. Immunoreactive areas against GSTP gradually increase from early period of carciogenesis. BrdU labeling in such areas remained high during the first week. but decreased thereafter. BrdU labeling index remained low in the GSTP negative area throughout the experimental period. This suggests that cells in the enzyme altered foci keep away from the suppressor effect of AAF in contrast to the normal cells in which their growth are inhibited by AAF. BrdU labeling index remained very low in both hyperplastic nodule and adenoma which were prevalent during the mid-experimental period, but increase markedly in carcinoma. The long period of low BrdU labeling index seems to correspond to the "slowly growing step of persistent nodule" during hepatocarcinogenesis. The differentiation index, a ratio of S phase fraction between GSTP positive and negative areas, was low in adenoma-developing period and high in carcinoma-developing period. C-Ha-ras p21 was not expressed in foci of enzyme altered hepatocyte and hyperplasia, but highly positive in carcinoma. This indicates that the c-Ha-ras may involve the late step of hepatocarcinogenesis.