Nuclear DNA content of altered hepatic foci in a rat liver carcinogenesis model

Abstract

In individual altered hepatic foci (AHF), aneuploidy occurs before malignant changes can be diagnosed histologically (O. Sudilovsky and T. K. Hei. Fed. Proc., 42:2225, 1983). In the current experiments Sprague-Dawley rats of both sexes were given i.p. injections of diethylnitrosamine (50 mg/kg body weight) 18 h after partial hepatectomy and were given a choline-sufficient diet (CS) for 1 wk. Four treatment groups were then formed and fed CS, CS containing 0.05% phenobarbital (PHB), choline-deficient diet (CD), and CD with 0.05% PHB. An extra female group received infusions of saline after the hepatectomy and fared CD. Control animals were partially hepatectomized, inoculated i.p. with saline, and placed on CS. The rats were sacrificed 16 wk later, liver sections were stained with a combined Feulgen-gamma-glutamyl transpeptidase stain, and the DNA content of gamma-glutamyl transpeptidase-positive foci was measured cytospectrophotometrically. There were no AHF in the control animals. Hepatocytes from control livers and cells adjacent to foci in treated livers had peaks corresponding to the 2C, 4C, and 8C range. In AHF the ploidy, however, was predominantly diploid, tetraploid, or heterogeneous. The ratio of diploid to tetraploid cells in foci of rats provided with CS + PHB was 5.5 and in those supplied with CD + PHB was 0.09. This suggested that dietary manipulations change the nuclear DNA distribution of AHF. Aneuploidy was also present, as expected, in 4 of 33 AHF in the animals placed on CD + PHB. It was observed as well in 2 of 26 AHF of rats given CD but in none of the 20 AHF fed CS + PHB. These data indicate that CD (which acts as both initiator and promoter) may be responsible for the appearance of aneuploidy. A general model, based on these results and the clonality of each individual focus, is proposed for the development of cells through the preneoplastic stage.