INTERACTIVE EFFECTS OF ETHANOL AND CAFFEINE ON RAT FETAL HEPATOCYTE REPLICATION AND EGF RECEPTOR EXPRESSION

This study reports on the interactive effects of ethanol and caffeine on growth of rat fetal hepatocytes. Exposure of cultured rat fetal hepatocytes (RFH) to ethanol in concentrations above 1 mg/ml, causes a blockade of EGF-dependent cell replication along with an overexpression of surface EGF receptors (EGF-R). However, RFHs exposed for 24 hours to ethanol at a concentration of 1 mg/ml alone had little effect on cell replication. Caffeine, when combined with this concentration of alcohol, progressively impaired RFH growth by up to 100%. Caffeine alone up to 10-mu-g/ml, on the other hand, caused a progressive increase in RFH replication associated with a 69% enhancement of DNA synthesis. Caffeine concentrations in excess of 50-mu-g/ml had no effect on replicative capacity. Concomitant caffeine exposure had no effect on the ethanol-related increase in cell DNA content, yet it caused a further enhancement of the cell protein accrual induced by ethanol alone. Caffeine (10-mu-g/ml) alone had no effect on EGF-R expression, while ethanol (2 mg/ml) increased it by almost 200%. Addition of caffeine to ethanol reduced this enhanced EGF binding by 45%. Scatchard analysis indicated that no treatment altered ligand affinity for the receptor, but that the alterations in binding caused by ethanol and the caffeine/ethanol combination reflected changes in binding capacity, in both low and high affinity components. It is concluded that (1) ethanol blocks EGF-mediated replication accompanied by a reduction in DNA synthesis, (2) caffeine alone at low concentrations has the opposite effect and can actually potentiate the EGF-mediated mitogenic response, (3) caffeine in combination with ethanol acts synergistically to reduce RFH replication. We suggest that the ethanol-induced perturbation of the EGF-R may be due to an altered cAMP kinase that plays a regulatory role in EFG-R expression.