Effects of Prototypical Microsomal Enzyme Inducers on Cytochrome P450 Expression in Cultured Human Hepatocytes

Abstract

ABSTRACT:Cultured human hepatocytes are a valuable in vitro system for evaluating new molecular entities as inducers of cytochrome P450 (P450) enzymes. The present study summarizes data obtained from 62 preparations of cultured human hepatocytes that were treated with vehicles (saline or dimethylsulfoxide, 0.1%), ␤-naphthoflavone (33 M), phenobarbital (100 or 250 M), isoniazid (100 M) and/or rifampin (20 or 50 M), and examined for the expression of P450 enzymes based on microsomal activity toward marker substrates, or in the case of CYP2C8, the level of immunoreactive protein. The results show that CYP1A2 activity was markedly induced by ␤-naphthoflavone (on average 13-fold, n ‫؍‬ 28 preparations), and weakly induced by phenobarbital (1.9-fold, n ‫؍‬ 25) and rifampin (2.3-fold, n ‫؍‬ 22); CYP2A6 activity tended to be increased with phenobarbital (n ‫؍‬ 7) and rifampin (n ‫؍‬ 3) treatments, but the effects were not statistically significant; CYP2B6 was induced by phenobarbital (6.5-fold, n ‫؍‬ 13) and rifampin (13-fold, n ‫؍‬ 14); CYP2C8 was induced by phenobarbital (4.0-fold, n ‫؍‬ 4) and rifampin (5.2-fold, n ‫؍‬ 4); CYP2C9 was induced by phenobarbital (1.8-fold, n ‫؍‬ 14) and rifampin (3.5-fold, n ‫؍‬ 10); CYP2C19 was markedly induced by rifampin (37-fold, n ‫؍‬ 10), but relatively modestly by phenobarbital (7-fold, n ‫؍‬ 9); CYP2D6 was not significantly induced by phenobarbital (n ‫؍‬ 5) or rifampin (n ‫؍‬ 5); CYP2E1 was induced by phenobarbital (1.7-fold, n ‫؍‬ 5), rifampin (2.2-fold, n ‫؍‬ 5), and isoniazid (2.3-fold, n ‫؍‬ 5); and, CYP3A4 was induced by phenobarbital (3.3-fold, n ‫؍‬ 42) and rifampin (10-fold, n ‫؍‬ 61), but not by ␤-naphthoflavone. Based on these observations, we generalize that ␤-naphthoflavone induces CYP1A2 and isoniazid induces CYP2E1, whereas rifampin and, to a lesser extent phenobarbital, tend to significantly and consistently induce enzymes of the CYP2A, CYP2B, CYP2C, CYP2E, and CYP3A subfamilies but not the 2D subfamily. Drugs and NMEs5 are often screened for their ability to induce P450 and other drug-metabolizing enzymes with the aim of predicting or explaining drug-drug interactions and pharmacokinetic tolerance.

Impact of CYP2A6 genotype on pretreatment smoking behaviour and nicotine levels from and usage of nicotine replacement therapy

“…Although the 3HC/COT ratio can be utilized as an indicator of CYP2A6 phenotype, 4 there are limitations to using this ratio as a measure of genetically determined CYP2A6 activity, as enzymatic activity is also influenced by diet, steroids, gender and environment. For instance, grapefruit juice can inhibit CYP2A6-mediated coumarin metabolism, 67 drugs such as phenobarbital and rifampin can induce CYP2A6, 68 and oral contraceptives can increase nicotine clearance. 45 Such dietary and drug histories were not available for the participants in this study.…”

Porcine Cytochrome P450 and Metabolism

“…In contrast to CYP2A the CYP3A activity remained constant during the first 72 hrs. of incubation, and the activity could be induced by rifampicin 3-4 times [28,6] , a potent inducer of CYP3A4 in human hepatocyte cultures [29]. Rifampicin also induces both the 1-and 4-hydroxylation of midazolam, whereas dexamethasone, another inducer of human CYP3A4, could induce neither the testosterone hydroxylation nor the midazolam hydroxylation [2,30,12].…”

Delamanid Does Not Inhibit or Induce Cytochrome P450 Enzymes <i>in Vitro</i>

“…[20][21][22][23][24][25] Three lots of human fresh hepatocytes were used for the assessment of CYP1A2, CYP2C9, and CYP3A4 activities and the relative mRNA levels. Hepatocytes were seeded at approximately 1.3×10 6 viable cells/mL on collagencoated 60 mm culture dishes and were placed in a humidified culture chamber (37°C, at 95% relative humidity, 95/5% air/ carbon dioxide).…”