RT Journal Article
SR Electronic
T1 ONLY TRUNCATED, NOT COMPLETE CYTOCHROME P450 2D6 RNA TRANSCRIPT AND NO DETECTABLE ENZYME ACTIVITY ARE EXPRESSED IN HUMAN LYMPHOCYTES
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1103
OP 1107
DO 10.1124/dmd.31.9.1103
VO 31
IS 9
A1 Lisa A. McConnachie
A1 Brian Phillips
A1 Manoj Bajpai
A1 Danny D. Shen
A1 Rodney J. Y. Ho
YR 2003
UL http://dmd.aspetjournals.org/content/31/9/1103.abstract
AB Genotyping of the highly polymorphic cytochrome P450 2D6 (CYP2D6) permits a gross classification of individual phenotype (viz. ultra-rapid, extensive, and poor metabolizers). It does not, however, provide a precise prediction of CYP2D6 activity, particularly in an individual possessing at least one functional CYP2D6 allele. It has been suggested that the level of mRNA expression or enzyme activity in lymphocytes, isolated from blood, could potentially provide a better quantitative estimate of in vivo hepatic enzymatic activity in human subjects. Although short sequences of CYP2D6 mRNA have been detected in human lymphocytes by reverse transcriptase-polymerase chain reaction (RT-PCR) that suggests the potential use of lymphocyte RNA as a readily accessible biomarker, it is not known whether a functional enzyme is expressed in human lymphocytes. In this study, human lymphocyte activity was assessed with a CYP2D6-specific, high-turnover probe substrate that is severalfold more sensitive than traditional markers of CYP2D6 (e.g., dextromethorphan). CYP2D6 catalytic activity could not be detected in homogenates of human lymphocytes, even at high protein concentrations and with supplementation of enzyme cofactors. Further RT-PCR analysis of lymphocytes collected from eight human donors revealed the presence of only a fragment, but not the complete transcript, of CYP2D6 mRNA. Northern blot RNA transcript analysis also failed to indicate the presence of the full-length transcript in lymphocytes. Collectively, these data indicate that human lymphocytes express neither the full-length CYP2D6 mRNA transcript nor functional enzyme activity. Therefore, the utility of lymphocytes as a functional biomarker for CYP2D6 enzyme activity is not clear at present. The American Society for Pharmacology and Experimental Therapeutics