title: Human liver cytochrome P450 2D6 genotype, full-length messenger ribonucleic acid, and activity assessed with a novel cytochrome P450 2D6 substrate.
abstract: OBJECTIVE
  The goal of this study was to develop and validate a cytochrome P450 (CYP) 2D6 probe substrate with improved sensitivity to elucidate the relationship of CYP2D6 ribonucleic acid transcript levels, genotype, and enzyme activity in human liver biopsy samples.
  
  
  METHODS
  CYP2D6 activity in tissue homogenates of liver biopsy specimens collected from control subjects (with no apparent liver disease), liver biopsy subjects, liver transplant subjects, and liver bank specimens was assessed with a calcimimetic, R-568, a high-clearance and specific substrate of CYP2D6. The livers were genotyped for the 6 most common CYP2D6 genetic variants (ie, *3, *4, *5, *6, *7, and *8). The 1.5-kilobase CYP2D6 messenger ribonucleic acid (referred to as full-length) transcripts were estimated with a semiquantitative reverse transcription-polymerase chain reaction assay.
  
  
  RESULTS
  As a CYP2D6-specific catalytic probe, R-568 offers a 20-fold higher sensitivity compared with that of dextromethorphan. The improved assay sensitivity allowed evaluation of CYP2D6 enzyme activity in a few milligrams of tissue collected from biopsy specimens. The ratio of CYP2D6 enzyme activity to transcript remained relatively constant within each group of subjects, especially within the control group. However, mean activity to transcript varied greatly across the 4 groups of subjects. The liver samples in the control group showed significantly higher enzyme activity but a lower transcript level.
  
  
  CONCLUSIONS
  A combination of genotyping and messenger ribonucleic acid level determination could allow a quantitative estimation of functional CYP2D6 activity in healthy human livers with a reasonable degree of confidence. Kinetic study with R-568 indicates that this compound is probably the most sensitive CYP2D6 probe substrate available.
authors.affiliation: Department of Pharmaceutics, Medicine, Surgery and Pharmacy, University of Washington, Seattle, WA 98195-7610, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: McConnachie
authors.forename: Miklos
authors.initials: M
authors.lastname: Bodor
authors.forename: Kris
authors.initials: K
authors.lastname: Kowdley
authors.forename: Adam
authors.initials: A
authors.lastname: Levy
authors.forename: Bruce
authors.initials: B
authors.lastname: Tung
authors.forename: Kenneth
authors.initials: K
authors.lastname: Thummel
authors.forename: Brian
authors.initials: B
authors.lastname: Phillips
authors.forename: Manoj
authors.initials: M
authors.lastname: Bajpai
authors.forename: Victor
authors.initials: V
authors.lastname: Chi
authors.forename: Joel D
authors.initials: JD
authors.lastname: Esmay
authors.forename: Danny D
authors.initials: DD
authors.lastname: Shen
authors.forename: Rodney J Y
authors.initials: RJ
authors.lastname: Ho
mesh_terms: D001706:Biopsy; D016022:Case-Control Studies; D046508:Culture Techniques; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics*; D004789:Enzyme Activation; D005838:Genotype; D006801:Humans; D008099:Liver / Q000737:chemistry* / Q000201:enzymology* / Q000473:pathology; D011237:Predictive Value of Tests; D012333:RNA, Messenger / Q000032:analysis*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013379:Substrate Specificity
chemical_list: D012333:RNA, Messenger; D019389:Cytochrome P-450 CYP2D6