title: Oxygen tension, insulin, and glucagon affect the preservation and induction of cytochrome P450 isoforms in cultured rat hepatocytes.
abstract: The role of oxygen tension, insulin, and glucagon on the preservation and induction of cytochrome P450 isoenzyme activities and contents was investigated in rat hepatocytes cultured for 4 days on crude liver membrane fractions at 4 or 13% O2. At 13% O2, three out of six immunochemically analyzed P450 isoenzymes were significantly higher than in 4% O2. Exposure to phenobarbital (PB) from Days 1 to 4 dose dependently increased the protein content and decreased the albumin secretion in 13% O2 cultures only. The maximal induction of P450 isoenzymes CYP2B1/2B2 (20- to 25-fold) and CYP2C6 (6-fold) were found at 0.75 mM PB at both oxygen tensions. In contrast, the highest induction of CYP1A1/1A2 (3-fold), of CYP3A (2-fold), and EROD activity were found with 3 mM PB in 4% O2 cultures. CYP2B-dependent testosterone hydroxylation at positions 16 alpha/beta was elevated to a greater extent in 13% O2 cultures (96-fold at 0.75 mM PB) compared to 4% O2 cultures (42-fold). This activity was affected by the insulin concentrations and the insulin:glucagon ratio. With decreasing insulin concentration (100 to 1 nM) or with increasing insulin:glucagon ratios (1:100-1:0.1), the enzyme activity increased preferentially in 4% O2 cultures. The results of these investigations demonstrate that different tissue oxygen tension modulates the responsiveness of the cultured hepatocytes to the glucoregulatory hormones insulin and glucagon and this modulation results in a altered activity of cytochrome P450 isoforms.
authors.affiliation: Institute of Toxicology, Swiss Federal Institute of Technology, Schwerzenbach.
authors.forename: B
authors.initials: B
authors.lastname: Saad
authors.forename: H
authors.initials: H
authors.lastname: Thomas
authors.forename: H
authors.initials: H
authors.lastname: Schawalder
authors.forename: F
authors.initials: F
authors.lastname: Waechter
authors.forename: P
authors.initials: P
authors.lastname: Maier
mesh_terms: D000418:Albumins / Q000032:analysis; D000818:Animals; D002478:Cells, Cultured; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis / Q000187:drug effects*; D004790:Enzyme Induction; D004797:Enzyme-Linked Immunosorbent Assay; D005934:Glucagon / Q000494:pharmacology*; D006900:Hydroxylation; D007328:Insulin / Q000494:pharmacology*; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008297:Male; D010088:Oxidoreductases / Q000032:analysis; D010100:Oxygen / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013739:Testosterone / Q000378:metabolism
chemical_list: D000418:Albumins; D007328:Insulin; D007527:Isoenzymes; D013739:Testosterone; D005934:Glucagon; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D007770:L-Lactate Dehydrogenase; D019363:Cytochrome P-450 CYP1A1; D010100:Oxygen