to a selective reduction of the liver load with preneoplas-Previous studies have shown 5-to 10-fold higher rates tic cells. (HEPATOLOGY 1996;23:840-847.) of apoptosis in prestages of liver cancer (putative preneoplastic cell foci [PPF]) than in unaltered liver; fasting or withdrawal of tumor promoters enhanced apoptosis
Foci of phenotypically altered hepatocytes are widely even further. We studied whether transforming growth considered to represent prestages of liver cancer in hufactor b 1 (TGF-b 1 ), an inducer of apoptosis in normal mans and experimental animals. [1][2][3][4][5] In rat liver, these liver, might be involved in induction of apoptosis in PPF. putative preneoplastic foci (PPF) have been well char-PPF were produced in 7-week-old female Sprague-Dawacterized and provide a useful model to study comley rats with a single oral dose of the genotoxic carcinopound effects on carcinogenesis. PPF show enhanced gen 7,12-dimethylbenz(a)anthracene (DMBA). At 24 rates of cell replication and apoptosis [6][7][8][9][10][11] ; treatment weeks of age, TGF-b 1 was injected into animals (40 mg/kg with tumor promoters enhances replication and inhibintravenously) either once and they were killed 4 hours later (single-dose experiment) or eight times at 24-hour its apoptosis, resulting in preferential foci growth durintervals and they were killed 24 hours after the last ing tumor promotion. 2,10 Conversely, promoter withadministration (multiple-dose experiment). Further subdrawal or food restriction decrease replication and groups received daily subcutaneous injections of tamoxenhance apoptosis in foci 2,8,12,13 ; this may lead to a reifen (TAM) (8 mg/kg) for 4 consecutive weeks before TGFduction of foci volume and complete extinction of foci. b 1 treatment. In normal liver, the apoptosis incidence Little is known about growth regulation in foci by enwas low in solvent-and TAM-only-treated animals, in dogenous factors. Recently, it has been found that the single-as well as the multiple-dose experiment. TGFtransforming growth factor b 1 (TGF-b 1 ), known as a b 1 increased the apoptosis incidence severalfold, and the stimulator of mesenchymal and inhibitor of epithelial combined administration of TGF-b 1 with TAM caused a cell proliferation, 14,15 can induce apoptotic cell death. further strong increase. The already-elevated basal apoptotic incidence in PPF was further increased by TGF-b 1 In normal rat liver, TGF-b 1 appears in cells preparing and particularly by TGF-b 1 plus TAM treatments, which for apoptosis, 16,17 and it triggers apoptosis of unaltered resulted in a reduction of foci number and size. In sumhepatocytes in vitro and in vivo. 18,19 In the present mary, these results show that TGF-b 1 can induce study, we asked whether TGF-b 1 can also induce apoptosis in PPF. This apoptosis-inducing activity is apoptosis in PPF. Female Sprague-Dawley rats were strongly enhanced by the additional treatment with the used as the model. They were treated with a single oral antiestrogen TAM, which by itself does not have any cell dose of the carcinogen 7,12-dimethylbenz(a)anthracene death-inducing effect in the liver or PPF. The elevated (DMBA), which leads to the development of PPF and apoptotic activity of PPF in response to TGF-b 1 can lead breast carcinomas. 20 In previous studies, induction of apoptosis by TGFb 1 was particularly effective during involution of liver Abbreviations: PPF, putative preneoplastic foci; TGF-b1, transforming hyperplasia following treatment with a hepatomitogen growth factor b1; DMBA, 7,12-dimethylbenz(a)anthracene; TAM, tamoxifen; such as cyproterone acetate. 18,19 Apparently, induction ABs, apoptotic bodies; GST-P, placental glutathione-S-transferase isoenzyme; of apoptosis is favored after mitogen withdrawal. Con-LI, labeling indices. sequently, we sought to determine whether treatment