Cytochrome P450 Enzymes Involved in Metoprolol Metabolism and Use of Metoprolol as a CYP2D6 Phenotyping Probe Drug.

Benjamin Berger,Manuel Haschke,Urs Duthaler,Fabio Bachmann,Stephan Krähenbühl

doi:10.3389/fphar.2018.00774

Abstract

Metoprolol is used for phenotyping of cytochrome P450 (CYP) 2D6, a CYP isoform considered not to be inducible by inducers of the CYP2C, CYP2B, and CYP3A families such as rifampicin. While assessing CYP2D6 activity under basal conditions and after pre-treatment with rifampicin in vivo, we surprisingly observed a drop in the metoprolol/α-OH-metoprolol clearance ratio, suggesting CYP2D6 induction. To study this problem, we performed in vitro investigations using HepaRG cells and primary human hepatocytes (before and after treatment with 20 μM rifampicin), human liver microsomes, and CYP3A4-overexpressing supersomes. While mRNA expression levels of CYP3A4 showed a 15- to 30-fold increase in both cell models, mRNA of CYP2D6 was not affected by rifampicin. 1′-OH-midazolam formation (reflecting CYP3A4 activity) increased by a factor of 5–8 in both cell models, while the formation of α-OH-metoprolol increased by a factor of 6 in HepaRG cells and of 1.4 in primary human hepatocytes. Inhibition studies using human liver microsomes showed that CYP3A4, 2B6, and 2C9 together contributed 19.0 ± 2.6% (mean ± 95%CI) to O-demethylation, 4.0 ± 0.7% to α-hydroxylation, and 7.6 ± 1.7% to N-dealkylation of metoprolol. In supersomes overexpressing CYP3A4, metoprolol was α-hydroxylated in a reaction inhibited by the CYP3A4-specific inhibitor ketoconazole, but not by the CYP2D6-specific inhibitor quinidine. We conclude that metoprolol is not exclusively metabolized by CYP2D6. CYP3A4, 2B6, and 2C9, which are inducible by rifampicin, contribute to α-hydroxylation, O-demethylation, and N-dealkylation of metoprolol. This contribution is larger after CYP induction by rifampicin but is too small to compromise the usability of metoprolol α-hydroxylation for CYP2D6 phenotyping.

Highlights

Metoprolol is a cardioselective beta-blocker that is used mainly in the treatment of arterial hypertension (Hansson et al, 1999), heart failure (MERIT-HF Study Group, 1999), and myocardial infarction (Chen et al, 2005)
We performed a clinical study using 15 healthy volunteers, where we investigated the effect of pre-treatment with rifampicin on the Basel phenotyping cocktail, which contains caffeine, efavirenz, losartan, omeprazole, metoprolol, and midazolam as probe drugs
We observed an increase in the clearance of midazolam (Figure 1B) in all subjects tested, which is a marker of CYP3A4 activity (Link et al, 2008)

Summary

Introduction

Metoprolol is a cardioselective beta-blocker that is used mainly in the treatment of arterial hypertension (Hansson et al, 1999), heart failure (MERIT-HF Study Group, 1999), and myocardial infarction (Chen et al, 2005). Intestinal absorption of metoprolol is rapid and almost complete; due to an extensive first pass metabolism (Regardh and Johnsson, 1980), Metoprolol Metabolism and CYP2D6 Phenotyping the bioavailability of metoprolol is only approximately 50%. The half-life is in the range of 3–4 h in young adults and between 7–9 h in elderly patients (Rigby et al, 1985). Metoprolol is heavily biotransformed with less than 5% of an oral dose being excreted in non-metabolized form by the kidneys (Regardh and Johnsson, 1980; McGourty et al, 1985; Rigby et al, 1985; Johansson et al, 2007). 70% of orally administered metoprolol is metabolized by CYP2D6 (Johnson and Burlew, 1996). Major oxidative pathways are O-demethylation to O-demethylmetoprolol and its further oxidation to the corresponding metoprolol phenylacetate (65% of the oral dose recovered in urine); N-dealkylation to N-deisopropylmetoprolol (10%), which may be transaminated and the resulting aldehyde oxidized to the corresponding acid; and α-hydroxylation to α-OH-metoprolol (10%) (Borg et al, 1975) (Figure 1A)

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