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Xenobiotica
the fate of foreign compounds in biological systems
Volume 49, 2019 - Issue 2
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General Xenobiochemistry

Predicted contributions of cytochrome P450s to drug metabolism in human liver microsomes using relative activity factor were dependent on probes

, , , , , & show all
Pages 161-168 | Received 11 Dec 2017, Accepted 25 Jan 2018, Published online: 08 Feb 2018
 

Abstract

  1. Contributions of cytochrome P450 (CYP450) isoforms to drug metabolism are often predicted using relative activity factor (RAF) method, assuming RAF values were independent of probe. We aimed to report probe-dependent characteristic of RAF values using CYP3A4 or CYP2C9 probes.

  2. Metabolism of four CYP3A4 probes (testosterone, midazolam, verapamil and atorvastatin) and three CYP2C9 probes (tolbutamide, diclofenac and S-warfarin) in human liver microsomes (HLM) and cDNA-expressed recombinant CYP450 (Rec-CYP450) systems were characterized and RAFCL value was estimated as ratio of probe intrinsic clearance in HLM to that in Rec-CYP450. CYP450i contributions to metabolic reaction of a probe were predicted using other probes and compared with data from specific inhibitions. Contributions of CYP3A4 and CYP2C9 to metabolism of deoxypodophyllotoxin and nateglinide were also predicted.

  3. RAF values were dependent on probes, leading to probe-dependently predicted contributions. Predicted contributions of CYP3A4 to formations of 6β-hydroxytestosterone, 1′-hydroxymidazolam, norverapamil, ortho-hydroxyatorvastatin and para-hydroxyatorvastatin using other probes were 47.46–219.46%, 21.62–98.87%, 186.49–462.44%, 21.87–101.15% and 53.62–247.97%, respectively. Predicted contributions of CYP3A4 and CYP2C9 to nateglinide metabolism were 8.18–37.84% and 36.08–94.04%, separately.

  4. In conclusion, CYP450i contribution to drug metabolism in HLM estimated using RAF approach were probe-dependent. Therefore, contribution of each isoform must be confirmed by multiple probes.

Disclosure statement

The authors report no declaration of interest.

Additional information

Funding

This work was supported by the National Science Foundation of People’s Republic of China [No.81573490 and No.81473273], Natural Science Foundation of Jiangsu Province (BK20161457), “333”, “Six Talent Peaks” and “Cyan Blue” Project of Jiangsu Province.

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