Fingerprinting of cytochrome P450 and microsomal epoxide hydrolase gene expression in human blood cells

To examine the character and variability of human cytochrome P450 (CYP) and microsomal epoxide hydrolase (mEH) gene expression in human blood cells, w e used a highly sensitive, quantitative, competitive reverse transcriptase- coupled polymerase chain reaction (QC RT-PCR) assay to assess mRNA profiles for a battery of 8 genes, in peripheral lymphocytes isolated from 10 healt hy donors. Of the genes profiled, in lymphocytes CYP2D6 was typically expre ssed at the highest levels (3.8 x 10(5) molecules/mu g total RNA), with CYP 2E1 and mEH also maintained at relatively high abundance (1.2 x 10(5) and 1 .8 x 10(5) molecules/mu g total RNA, respectively), CYP1A1 levels were appr oximately an order of magnitude lower (3.9 x 10(4) molecules/mu g total RNA ), followed by CYP2F1 and CYP3A levels that were near the detection limit o f the assay. CYP1A2 and CYP2A6/7 mRNAs were not detected in any of the lymp hocyte samples. Overall, relatively low levels of inter-individual variatio n (2- to 6-fold) existed among these endpoint parameters in the subjects te sted. To test whether established human blood cell lines were suitable mode ls to assess basal expression and chemical induction responsiveness of thes e genes, we determined that constitutive CYP and mEH mRNA profiles were ess entially conserved across 4 established human blood cell lines, and highly analogous to the basal expression patterns identified in freshly isolated p eripheral lymphocytes. mEH protein was detected in all of the cell lines us ing Western immunoblotting and chemiluminescent visualization, whereas CYP1 A1, CYP2D6, CYP2E1 or CYP3A proteins were not detected in these analyses. W hen blood cell-derived cultures were exposed to the prototypical CYP1A and CYP3A inducers, i.e,, beta-naphthoflavone (beta-NF), dexamethasone (DEX) or phenobarbital, generally little or no inductive response was manifested. T hus, the data obtained from this investigation indicate that, although huma n blood cell lines in general exhibit poor responsiveness to prototypical i nducer exposures, the constitutive patterns of CYP and mEH expression in pe ripheral lymphocytes appear to exhibit relatively low levels of variation a mong individuals. In addition, these in vivo patterns of expression are wel l maintained in established cultured blood-cell lines.