Comparison of magnitude of rat P-450 enzyme induction in vivo with that observed in vitro in cultured hepatocytes prepared from freshly isolated or cryopreserved cells
| P-450 Enzyme1-a | In Vivo Induction1-b in Male Rats | In Vitro Induction | Comparison of In Vivo with In Vitro | ||
|---|---|---|---|---|---|
| Freshly Isolated Hepatocytes1-c | Cryopreserved Hepatocytes1-c | In Vivo/Freshly Isolated | In Vivo/ Cryopreserved | ||
| Enzyme activity (pmol/min/mg protein) | Ratio of enzyme activity | ||||
| CYP1A | |||||
| Control | 233 | 43.3 | 52.3 | 5.4 | 4.5 |
| β-Naphthoflavone | 3,940 (17)1-d | 1140 (26) | 994 (19) | 3.5 | 4.0 |
| CYP2B | |||||
| Control | 17.6 | 15.7 | 5.6 | 1.1 | 3.1 |
| Phenobarbital | 1,490 (85) | 405 (26) | 567 (100) | 3.7 | 2.6 |
| CYP3A | |||||
| Control | 2,480 | 683 | 450 | 3.6 | 5.5 |
| Dexamethasone | 12,200 (4.9) | 4,300 (6.3) | 3,930 (8.7) | 2.8 | 3.2 |
| CYP4A | |||||
| Control | 475 | 166 | 187 | 2.9 | 2.5 |
| Clofibric acid | 11,100 (23) | 2370 (14) | 3,750 (20) | 4.7 | 3.0 |
↵1-a Enzyme activity of CYP1A, CYP2B, CYP3A, and CYP4A enzymes was determined as EROD, PROD, testosterone 6β-hydroxylation, and lauric acid 12-hydroxylation respectively, as described inMaterials and Methods.
↵1-b Liver microsomes from male Sprague-Dawley rats treated with P-450 enzyme inducers. Rats were dosed once per day for 4 days with isotonic saline, β-naphthoflavone, phenobarbital, dexamethasone, or clofibric acid at a dosage of 5 ml/kg, 100 mg/kg, 80 mg/kg, 50 mg/kg, and 200 mg/kg, respectively. Microsomes were provided by XenoTech, LLC, which also provided data on activity of P-450 enzymes. Data shown are averages of duplicate determinations from three to five experiments.
↵1-c Liver microsomes from cultured rat hepatocytes (prepared from either freshly isolated or cryopreserved cells) were treated with P-450 enzyme inducers and activity of P-450 enzymes was determined as described in Materials and Methods. Data shown are averages of duplicate determination from a single experiment (Fig. 2A, 4A, 5A, and 6A). Data for induced samples are maximum rates extrapolated from the EC50 curves.
↵1-d Values in parentheses show fold induction compared with controls.