CYP2D6 genetic variation in healthy adults and psychiatric African-American subjects: implications for clinical practice and genetic testing

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ABSTRACT:Polymorphisms in the cytochrome P450 2D6 (CYP2D6) gene are a major cause of pharmacokinetic variability in human. Although the poor metabolizer phenotype is known to be caused by two null alleles leading to absence of functional CYP2D6 protein, the large variability among individuals with functional alleles remains mostly unexplained. Thus, the goal of this study was to examine the intrinsic enzymatic differences that exist among the several active CYP2D6 allelic variants. The relative catalytic activities (enzyme kinetics) of three functionally active human CYP2D6 allelic variants, CYP2D6.1, CYP2D6.10, and CYP2D6.17, were systematically investigated for their ability to metabolize a structurally diverse set of clinically important CYP2D6-metabolized drugs [atomoxetine, bufuralol, codeine, debrisoquine, dextromethorphan, (S)-fluoxetine, nortriptyline, and tramadol] and the effects of various CYP2D6-inhibitors [cocaine, (S)-fluoxetine, (S)-norfluoxetine, imipramine, quinidine, and thioridazine] on these three variants. The most significant difference observed was a consistent but substrate-dependent decease in the catalytic efficiencies of cDNAexpressed CYP2D6.10 and CYP2D6.17 compared with CYP2D6.1, yielding 1.32 to 27.9 and 7.33 to 80.4% of the efficiency of CYP2D6.1, respectively. The most important finding from this study is that there are mixed effects on the functionally reduced allelic variants in enzyme-substrate affinity or enzyme-inhibitor affinity, which is lower, higher, or comparable to that for CYP2D6.1. Considering the rather high frequencies of CYP2D6*10 and CYP2D6*17 alleles for Asians and African Americans, respectively, these data provide further insight into ethnic differences in CYP2D6-mediated drug metabolism. However, as with all in vitro to in vivo extrapolations, caution should be applied to the clinical consequences.

Section: Discussionmentioning

confidence: 97%

Comparative Metabolic Capabilities and Inhibitory Profiles of CYP2D6.1, CYP2D6.10, and CYP2D6.17

Shen

He²,

Liu³

et al. 2007

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129

“…Typically, 150 to 200 l was recovered from a single vial of human hepatocytes (5000 -15,000 DNA copies per l). The isolated genomic DNA was initially characterized for CYP2D6 alleles *1xn, *2xn, *4xn, *2, *3, *4, *5, *6, *7, *9, *10,*17, *30, *35,*40, *41, and *43 according to published methods (Lovlie et al, 1996;Chou et al, 2003;Cai et al, 2006) and the AmpliChip CYP450 prototype microarray (Roche Molecular Systems, Inc., Branchburg, NJ). For comparative purposes CYP2A6*2,*3,*4,*5, *9, and *12 alleles were also assessed in these samples (Fernandes-Salguero et al, 1995;Rao et al, 2000;Paschke et al, 2001;Goods and Tynsdale, 2002;Oscarson et al, 2002).…”

Section: Methodsmentioning

confidence: 99%

NEW CYTOCHROME P4502D6*56ALLELE IDENTIFIED BY GENOTYPE/PHENOTYPE ANALYSIS OF CRYOPRESERVED HUMAN HEPATOCYTES

Pan²,

Porter³

et al. 2006

ABSTRACT:Genotype/phenotype analysis with human hepatocytes has identified a new inactive CYP2D6 allele, CYP2D6*56. Cryopreserved human hepatocytes from 51 livers were evaluated for CYP2D6 activity with dextromethorphan as the probe substrate. Hepatocyte lots that lacked CYP2D6 activity were further evaluated for CYP2D6 expression and known genetic variations, including CYP2D6*2, *3, *4, *5, *6, *7, *8, *9, *10, *11, *14, *15, *17, *18, *19, *20, *25, *26, *29, *30, *35, *40, *41, *43, and various multiple copy CYP2D6 alleles (*1xn, *2xn, and *4xn) by the AmpliChip CYP450 prototype microarray (Roche Molecular Systems, Inc., Branchburg, NJ). Two discrepancies were uncovered between the CYP2D6 genotype and activity by this approach. In one sample, a previously unreported 3201C 224 T transition in exon 7 resulted in Arg344(CGA) being replaced by a stop codon (TGA), resulting in a CYP2D6 enzyme lacking the terminal 153 amino acids. This allele was given the designation of CYP2D6*56 and the GenBank accession number DQ282162. The lack of CYP2D6 activity in cryopreserved hepatocytes and microsomes found in the second sample, despite a normal level of CYP2D6 expression and a genotype (*10/*1) predictive of normal CYP2D6 activity, was attributed to enzyme inactivation by an unknown metabolite. The identification and characterization of the CYP2D6*56 allele indicates that commercial cryopreserved human hepatocytes may provide a valuable means to rapidly identify genetic variations with functional relevance. This integrated approach of identifying alleles and examining allele relationships to gene expression and function could be of tremendous value to understanding the mechanism responsible for functional differences in gene variation. The commercial availability of human cryopreserved hepatocytes also makes this potential readily available to any who are interested in it, not just those with access to private liver banks.

“…3). However, several researchers (Bogni et al, 2005;Cai et al, 2006;Shen et al, 2007) have reported that some allelic variants (e.g., CYP2D6*17) are associated with substrate-dependent decreases in catalytic properties. In addition, some CYP2D6 variant proteins may decrease heme incorporation into the CYP2D6 apoprotein, but this possibility could not be assessed in the present study.…”

Section: Functional Characterization Of Cyp2d6 Variantsmentioning

confidence: 99%

Functional Characterization of 17CYP2D6Allelic Variants (CYP2D6.2, 10, 14A–B, 18, 27, 36, 39, 47–51, 53–55, and 57)

Sakuyama¹,

Sasaki²,

Ujiie³

et al. 2008

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