Testing for induction of DNA synthesis in human hepatocyte primary cultures by rat liver tumor promoters.
Parenchymal liver cells were isolated from human liver pieces of surgical waste as well as from rat livers. DNA synthetic activity was measured after different times in primary culture by [3H]thymidine incorporation and autoradiography. Labeling of control cultures of human hepatocytes at densities between 8,000 and 15,000 cells/cm2 was very low (0.4 to 1.3%). Human recombinant epidermal growth factor increased labeling 2- to 4-fold (P less than 0.01). Treatment with known inducers of liver growth in rats, namely, cyproterone acetate, alpha-hexachlorocyclohexane, nafenopin, phenobarbital, and rifampicin did not increase the number of labeled human liver cells. In some of the experiments, a 24-h exposure to the chemicals of rat or human hepatocytes was followed by a 24-h treatment with epidermal growth factor (EGF). In rat hepatocytes, incorporation rates were significantly increased. Cyproterone acetate and EGF acted in an additive manner, alpha-hexachlorocyclohexane and EGF were clearly overadditive, and phenobarbital had little effect. In human hepatocytes, little alteration in labeling indices was found; in some cases labeling was, rather, found to be lower than in cultures treated with EGF alone. These results show that human hepatocytes cultured in vitro are sensitive to stimulation of DNA synthesis by EGF; they differ from rat hepatocytes in their response to some drugs which show liver growth-promoting activity in rodents.