Effects of epidermal growth factor on CYP inducibility by xenobiotics, DNA replication, and caspase activations in collagen I gel sandwich cultures of rat hepatocytes11Abbreviations: BrdU, 5-bromo 2′-deoxyuridine; Cdk 1, Cyclin dependent kinase 1; CYP, cytochrome P450; DEVD-AMC, N-acetyl-Asp-Glu-Val-Asp-aminomethylcoumarin; EGF, epidermal growth factor; EROD, ethoxyresorufin O-deethylase; 3-MC, 3-methylcholantrene; β-NF, β-naphtoflavone; PB, phenobarbital; and PROD, pentoxyresorufin O-depentylase.

In this study, we investigated the combined effects of EGF and collagen I gel on the phenotype of cultured rat hepatocytes and we focussed our investigations on the regulation of xenobiotic-mediated induction of CYP, cell cycle progression and activation of capases 8 and 3. We found that EGF, added to basal culture medium or phenobarbital (3.2 mM) containing medium, provoked a moderate decrease of CYP1A1 and CYP2B1/2 activities. However, EGF did not exert any inhibitory effect on 3-methylcholantrene (5 μM) and β-naphtoflavone (25 μM) induction of CYP1A1 activities. In collagen gel sandwich cultures, hepatocytes remained arrested in mid-G1 phase of the cell cycle, even in the presence of EGF. In conventional primary cultures, caspases 8 and 3 were activated at 3 and 5 days after plating respectively. In collagen gel sandwich cultures, we found that neither collagen I nor EGF prevented activation of caspase 8 while collagen I gel inhibited activation of caspase 3, preventing spontaneous apoptosis of cultured rat hepatocytes. In contrast, EGF transiently increased caspase 3 activity at day 1 after plating. Altogether, our data demonstrate that collagen I gel triggers intracellular signals which strongly affect cultured hepatocyte phenotype, leading to a cell cycle arrest in G1 phase and long-term survival through the inhibition of caspase 3 activation and that EGF-free medium improves survival and liver-specific gene expression in hepatocytes maintained in collagen I gel sandwich cultures.