Contribution Of Cytochrome P450 Isoforms Research Articles

Metabolism of triflumuron in the human liver: Contribution of cytochrome P450 isoforms and esterases

Triflumuron (TFM) is a benzoylurea insecticide commonly used in Tunisian agriculture and around the world to control crop pests and flies as a promising alternative to conventional insecticides for its arthropod specificity and low toxicity. From the evidence available in animal models, it can be expected that the metabolism of TFM is catalyzed by cytochrome P450 (CYP) and esterases. However, no data are available on human metabolism of TFM with regards to phase I metabolism and CYP isoform specificity. Hence, this manuscript describes experimental investigations to underpin in vitro phase I TFM metabolism in human samples for the first time. TFM biotransformation by recombinant human CYPs was characterized, then human liver microsomes (HLM) and chemical specific inhibitors have been used to identify the relative contribution of CYPs and esterases. Our results showed that all CYP isoforms were able to metabolize TFM with different affinity and efficiency. The relative contribution based both on the kinetic parameters and the CYP hepatic content was 3A4 > >2C9 > 2C8 > 2A6 > 1A2 > 2B6 > 2D6 > 2C19 > 2C18 > 1A1 at low TFM concentration, whilst at high TFM concentration it was 1A2 > >2C9 = 3A4 = 2A6 > 2C19 > 2B6 = 2C8 > 2D6 > 1A1 > 2C18. Experiments with HLMs confirmed the involvement of the most relevant CYPs in the presence of specific chemical inhibitors with a catalytic efficiency (Cliapp) lower by an order of magnitude compared with recombinant enzymes. Esterases were also relevant to the overall TFM kinetics and metabolism, with catalytic efficiency higher than that of CYPs. It is foreseen that such isoform-specific information in humans will further support in silico models for the refinement of the human risk assessment of single pesticides or mixtures.

Contribution of cytochrome P450 isoforms to gliquidone metabolism in rats and human

1. Gliquidone, a second generation sulfonylurea, is a widely used oral antidiabetic drug. Due to the differences in its rate of metabolism, gliquidone shows inter-subject variability in pharmacokinetic and pharmacodynamic profiles.2. Cytochrome P450 (CYP450) isoforms are involved in the metabolism of a majority of drugs in clinical use and plays a significant role in reducing possible drug interactions. This research aimed to systematically study the contribution of various human CYP450 isoforms to gliquidone metabolism in vitro in rats and human.3. In rat liver microsomes, gliquidone was metabolized mainly by the most abundant CYP2C. The other isoforms involved in the metabolism included CYP3A, CYP2D, CYP1A and CYP2E.4. Further investigation of rat recombinant enzymes showed that CYP3A1 and CYP2C11 played a major role in gliquidone metabolism in vitro, while CYP2D1, CYP1A2 and CYP2E1 were also involved.5. But the metabolism of gliquidone in the human liver microsomes was mainly mediated by CYP3A4. The other isoforms involved in this process were CYP2C9, CYP2C19 and CYP2D6.6. The further study of human recombinant enzymes demonstrated that CYP3A4 was the principal isoform enzyme for the metabolism of gliquidone. The intrinsic clearance (Vmax/Km) of CYP3A4 during gliquidone metabolism was 3–12 times greater than that of other CYP450 isoforms including CYP2C9, CYP2D6 and CYP2C19.7. These findings may assist in valuable prediction of potential interactions of gliquidone with other drugs that are CYP3A4 inhibitors or inducers and help to design more efficacious and safer pharmacotherapy for patients of diabetes mellitus.

The relative contribution of human cytochrome P450 isoforms to the four caffeine oxidation pathways: An in vitro comparative study with cDNA-expressed P450s including CYP2C isoforms

The aim of the present study was to estimate the relative contribution of cytochrome P450 isoforms (P450s), including P450s of the CYP2C subfamily, to the metabolism of caffeine in human liver. The experiments were carried out in vitro using cDNA-expressed P450s, liver microsomes and specific P450 inhibitors. The obtained results show that (1) apart from the 3-N-demethylation of caffeine – a CYP1A2 marker reaction and the main oxidation pathway of caffeine in man – 1-N-demethylation is also specifically catalyzed by CYP1A2 (not reported previously); (2) 7-N-demethylation is catalyzed non-specifically, mainly by CYP1A2 and, to a smaller extent, by CYP2C8/9 and CYP3A4 (and not by CYP2E1, as suggested previously); (3) C-8-hydroxylation preferentially involves CYP1A2 and CYP3A4 and, to a smaller degree, CYP2C8/9 and CYP2E1 (and not only CYP3A, as suggested previously) at a concentration of 100 μM corresponding to the maximum therapeutic concentration in humans. At a higher caffeine concentration, the contribution of CYP1A2 to this reaction decreases in favour of CYP2C8/9. The obtained data show for the first time the contribution of CYP2C isoforms to the metabolism of caffeine in human liver and suggest that apart from 3-N-demethylation, 1-N-demethylation may also be used for testing CYP1A2 activity. Moreover, they indicate that the C-8-hydroxylation is not exclusively catalyzed by CYP3A4.

Pharmacokinetic differences between lansoprazole enantiomers and contribution of cytochrome P450 isoforms to enantioselective metabolism of lansoprazole in dogs.

The purpose of this study was to evaluate the pharmacokinetics of lansoprazole enantiomers and contribution of cytochrome P450 enzymes to enantioselective metabolism in dogs. The mean Cmax and area under the curve (AUC) values of (+)-lansoprazole were 4-5 times greater than those of (-)-lansoprazole following oral administration of 30-mg racemic lansoprazole to dogs. The CLtot/F values of (+)-lansoprazole were significantly smaller than those of (-)-lansoprazole (p<0.05). The mean unbound fraction of (-)-lansoprazole was significantly greater than that of the (+)-lansoprazole. The amount of (+)-lansoprazole remaining was significantly greater than that of the (-)-lansoprazole after incubation of racemic lansoprazole in dog liver microsomes. When the effects of ticlopidine or ketoconazole on the metabolism of lansoprazole were studied using dog liver microsomes, ticlopidine significantly inhibited the formation of 5-hydroxylansoprazole, but not another metabolite, lansoprazole sulfone; however ketoconazole significantly inhibited formation of both metabolites. When the amount of (+)- and (-)-enantiomers remaining was measured in the presence and absence of ticlopidine, the amount of (+)-lansoprazole was significantly greater than that of the (-)-lansoprazole. On the other hand, there was no significant difference between the amount of (+)- and (-)-enantiomers remaining in combination with ketoconazole. These results suggest that the enantioselective pharmacokinetics of lansoprazole enantiomers are probably ascribable to their enantioselective protein binding and/or metabolism, and among the cytochrome P450 enzymes, CYP3A contributed to the enantioselective metabolism of lansoprazole.