Stimulation of in vitro rat hepatocyte proliferation by conditioned mediumobtained from an immortalized macrophage cell line

The hepatomitogenic effect of conditioned medium (CDM), obtained from the N -11 mouse macrophage cell line was analysed in rat hepatocyte primary cultu res. CDM concentrations from 0.01% to 100% were used and the stimulating ac tion in terms of mitotic index (MI) was evaluated. A clear mitogenic effect was observed only with concentrations higher than 10% with peak effects ar ound 60%. Further increase in CDM concentrations resulted in an MI decrease , and at 100% CDM the effect was totally abolished. Tests addressed to iden tify the presence of hepatocyte growth factor (HGF) yielded negative result s. In order to identify the mitogenic factor(s) involved, we tested CDM obt ained after lipopolysaccharide (LPS) stimulation of N-11 cells. Comparison of the results obtained with untreated or LPS stimulated CDMs suggested tha t macrophage activation does not affect the release of hepatomitogenic acti vity. To further characterize this macrophage-derived activity, we checked whether CDM could interact with the mitogenic effects of epidermal growth f actor (EGF). CDM (10 or 50%) showed no stimulatory effect to hepatocytes cu ltured in the presence of a maximally stimulatory concentration of EGF. Con versely, both CDM concentrations were able to increase the MI of hepatocyte cultures treated with a suboptimal dose of EGF. These results suggest that macrophages release factor(s) which interact, in hepatocytes, with the EGF signal transduction mechanisms, or with the EGF receptor itself. (C) 1999 Elsevier Science Ltd. All rights reserved.