Human fetal liver cultures: basal activities and inducibility of epoxide hydrolases and aryl hydrocarbon hydroxylase.

The environmental influence of various drugs on the epoxide hydrolase with styrene oxide (EHSO) or benzo(a)pyrene-4,5-oxide (EHBPox) as substrate and the aryl hydrocarbon hydroxylase (AHH) activity was studied in monolayer cultures of human fetal hepatocytes (HFH) obtained at legal abortions. Hepatocytes were isolated by trypsin treatment of liver fragments and primary HFH cultures were maintained in Eagle's minimum essential medium supplemented with 15% newborn calf serum. The HFH were plated on culture dishes and allowed to 'settle' for one day before adding various drugs (in 1 microliter dimethylsulfoxide/ml) or solvent only and assay 1-2 days later. The basal AHH activity [assayed with 3H-benzo(a)pyrene as substrate] varied between 2 and 8.4 pmoles/min/mg protein and the basal EHSO activity was 0.3-4.9 nmoles/min/mg protein (n = 6) after one or two days' culture. The corresponding activity of EHBPox was 0.23-1.48 nmoles/min/mg protein (n = 5). Exposure of cultures to 2 mM phenobarbital (Pb), 2.5-25.0 microM benzanthracene (BA), 0.1 mM trans-stilbene oxide (TSO), or 5 microM beta-naphtoflavone (beta NF) resulted in a 1.2-3.7-fold induction of EHSO. Induction of EHBPox was also observed with Pb, beta NF, BA and TSO as inducers. Pb gave a dose-dependent induction of both EH at 0.1, 1.0 and 2.0 mM. Our results demonstrate that EH and AHH activities in HFH cultures are inducible by classical in vivo inducers. Although difficult to prove, it is plausible that such induction takes place also in intrauterine life.