Molecular basis of polymorphic drug metabolism

Daly, Ann K.

doi:10.1007/bf00195139

Cited by 95 publications

(55 citation statements)

References 172 publications

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“…Futhermore, cooperativity in oxidations catalysed by the enzyme was described and attributed to the existence of more than one binding site at the CYP3A4 molecule (Ueng et al 1997). Finally, the specificity of the two substrates used with respect to CYP3A5 and CYP3A7 is not clearly defined (Daly et al 1995). Both enzymes are present in human liver, although usually at much lower levels than CYP3A4 (Tateishi et al 1999).…”

Section: Discussionmentioning

confidence: 99%

Inhibitory Effects of Silibinin on Cytochrome P‐450 Enzymes in Human Liver Microsomes

Beckmann-Knopp¹,

Rietbrock²,

Weyhenmeyer³

et al. 2000

Pharmacology & Toxicology

129

101

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Silibinin, the main constituent of silymarin, a flavonoid drug from silybum marianum used in liver disease, was tested for inhibition of human cytochrome P-450 enzymes. Metabolic activities were determined in liver microsomes from two donors using selective substrates. With each substrate, incubations were carried out with and without silibinin (concentrations 3.7-300 mM) at 37ae in 0.1 M KH 2 PO 4 buffer containing up to 3% DMSO. Metabolite concentrations were determined by HPLC or direct spectroscopy. First, silibinin IC 50 values were determined for each substrate at respective K M concentrations. Silibinin had little effect (IC 50 Ͼ200 mM) on the metabolism of erythromycin (CYP3A4), chlorzoxazone (CYP2E1), S(π)-mephenytoin (CYP2C19), caffeine (CYP1A2) or coumarin (CYP2A6). A moderate effect was observed for high affinity dextromethorphan metabolism (CYP2D6) in one of the microsomes samples tested only (IC 50 Ω173 mM). Clear inhibition was found for denitronifedipine oxidation (CYP3A4; IC 50 Ω29 mM and 46 mM) and S(ª)-warfarin 7-hydroxylation (CYP2C9; IC 50 Ω43 mM and 45 mM). When additional substrate concentrations were tested to assess enzyme kinetics, silibinin was a potent competitive inhibitor of dextromethorphan metabolism at the low affinity site, which is not CYP2D6 (K i,c Ω2.3 mM and 2.4 mM). Inhibition was competitive for S(ª)-warfarin 7-hydroxylation (K i,c Ω18 mM and 19 mM) and mainly non-competitive for denitronifedipine oxidation (K i,n Ω9 mM and 12 mM). With therapeutic silibinin peak plasma concentrations of 0.6 mM and biliary concentrations up to 200 mM, metabolic interactions with xenobiotics metabolised by CYP3A4 or CYP2C9 cannot be excluded.

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Section: Discussionmentioning

confidence: 99%

Inhibitory Effects of Silibinin on Cytochrome P‐450 Enzymes in Human Liver Microsomes

Beckmann-Knopp¹,

Rietbrock²,

Weyhenmeyer³

et al. 2000

Pharmacology & Toxicology

129

101

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“…Variations in individual metabolism often result in unexpected toxicities because drug clearance is affected by a range of factors, including genetic variation, enzyme induction (activation), and inhibition of drug metabolism. Therefore, characterization of the P450 enzyme family has been of unceasing interest for the prediction and identification of drug metabolism and drug-drug interactions for discovery, development, and clinical therapy (Gonzalez and Nebert, 1990;Daly, 1995;Nebert, 1997;Kleyn and Vesell, 1998;Evans and Relling, 1999).…”

mentioning

confidence: 99%

“…Other 2D6 alleles contain point mutations resulting in one or more amino acid changes in the proteins compared with CYP2D6.1. This variety results in a range of phenotypes, from poor metabolizers with no 2D6 enzyme activity, as seen in up to 10% of Caucasians, to ultra rapid metabolizers and ranges in between (Daly, 1995;Raimundo et al, 2000;Zanger et al, 2001).…”

mentioning

confidence: 99%

Expression, Purification, Biochemical Characterization, and Comparative Function of Human Cytochrome P450 2D6.1, 2D6.2, 2D6.10, and 2D6.17 Allelic Isoforms

Kneller

Rettie

et al. 2002

J Pharmacol Exp Ther

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Polymorphism at the cytochrome P450 2D6 (CYP2D6) locus is one of the most widely known causes of pharmacogenetic variability in humans. Our goal is to investigate the intrinsic enzymatic differences that exist among active CYP2D6 isoforms to test the hypothesis that these enzymatic differences are substrate-dependent. Active CYP2D6.1, 2, 10, and 17 holoenzymes were expressed in vitro and purified to a high degree of homogeneity as confirmed with SDS-polyacrylamide gel electrophoresis, CO-difference spectroscopy, and mass spectral analysis. Purified enzyme was reconstituted with lipid and cytochrome P450 reductase in a 2:1 ratio before kinetic analysis. The reaction rate for dextromethorphan (DXM) O-demethylation, DXM N-demethylation, codeine O-demethylation, and fluoxetine N-demethylation catalyzed by each of the variants was determined. The CYP2D6.10 enzyme was the most impaired, exhibiting an estimated enzyme efficiency (as V max /K m ) 50-fold lower for DXM O-demethylation and 100-fold lower for fluoxetine N-demethylation when compared with CYP2D6.1, whereas no measurable catalytic activity was observed for this variant toward codeine. The atypical DXM N-demethylation pathway catalyzed by this variant decreased only 2-fold in comparison. In the case of CYPD6.17, estimated clearances for each metabolite were decreased 6 to 33%. Likewise, the intrinsic clearance of CYP2D6.2 enzyme was consistently decreased for each reaction examined, indicating that the ultra-rapid metabolizer phenotype sometimes associated with this genotype is not a function of the underlying amino acid substitutions. Overall enzyme efficiencies for the metabolism of each substrate therefore decreased in the order of 2D6.1 Ͼ 2D6.2 Ͼ 2D6.17 Ͼ 2D6.10.Cytochrome P450 enzymes, a superfamily of heme-thiolate proteins, are found in all living organisms and are involved in the biotransformation of a diverse range of xenobiotics and endobiotics. Human P450 isoforms, which are mainly expressed in the liver, play a central role in drug metabolism. Variations in individual metabolism often result in unexpected toxicities because drug clearance is affected by a range of factors, including genetic variation, enzyme induction (activation), and inhibition of drug metabolism. Therefore, characterization of the P450 enzyme family has been of unceasing interest for the prediction and identification of drug metabolism and drug-drug interactions for discovery, development, and clinical therapy (Gonzalez and

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“…The metabolic ratios of the probe drugs vary, thus patients can be classified into 4 different genotypes; poor metabolizer (PM), intermediate metabolizer (IM), extensive metabolizer (EM), and ultra-rapid metabolizer (UM) (7). Generally, when a PM or IM patient is administered a drug that is inactivated by CYP2D6, the blood concentration and risk of side effects will be increased as compared to EM patients.…”

Section: Introductionmentioning

confidence: 99%

Digital PCR for determination of cytochrome P450 2D6 and sulfotransferase 1A1 gene copy number variations

Motoi

Watanabe²,

Honma

et al. 2017

DD&T

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Molecular basis of polymorphic drug metabolism

Cited by 95 publications

References 172 publications

Inhibitory Effects of Silibinin on Cytochrome P‐450 Enzymes in Human Liver Microsomes

Inhibitory Effects of Silibinin on Cytochrome P‐450 Enzymes in Human Liver Microsomes

Expression, Purification, Biochemical Characterization, and Comparative Function of Human Cytochrome P450 2D6.1, 2D6.2, 2D6.10, and 2D6.17 Allelic Isoforms

Digital PCR for determination of cytochrome P450 2D6 and sulfotransferase 1A1 gene copy number variations

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