Effects of genetic variants of human P450 oxidoreductase on catalysis by CYP2D6 in vitro.

Department of Pediatrics, University of California, San Francisco, California 94143-0978, USA.
Pharmacogenetics and Genomics (Impact Factor: 3.45). 11/2010; 20(11):677-86. DOI: 10.1097/FPC.0b013e32833f4f9b
Source: PubMed

ABSTRACT Cytochrome P450 (P450) oxidoreductase (POR) donates electrons to all microsomal cytochrome P450s, including drug-metabolizing and steroidogenic enzymes. Severe POR mutations cause skeletal malformations and disordered steroidogenesis. The POR polymorphism A503V is found on approximately 28% of human alleles and decreases activities of CYP3A4 and steroidogenic CYP17, but not the activities of steroidogenic CYP21 or drug-metabolizing CYP1A2 and CYP2C19. CYP2D6 metabolizes about 25% of clinically used drugs; we assessed the capacity of POR variants to support the activities of human CYP2D6.
N-27 forms of wildtype (WT), Q153R, A287P, R457H and A503V POR, and WT CYP2D6 were expressed in Escherichia coli. POR proteins in bacterial membranes were reconstituted with purified CYP2D6. Support of CYP2D6 was measured by metabolism of EOMCC (2H-1-benzopyran-3-carbonitrile,7-(ethoxy-methoxy)-2-oxo-(9Cl)), dextromethorphan and bufuralol. Michaelis constant (K(m)) and maximum velocity (V(max)) were determined in three triplicate experiments for each reaction; catalytic efficiency is expressed as V(max)/K(m).
Compared with WT POR, disease-causing POR mutants A287P and R457H supported no detectable CYP2D6 activity with EOMCC, but A287P supported approximately 25% activity with dextromethorphan and bufuralol. Q153R had increased function with CYP2D6 (128% with EOMCC, 198% with dextromethorphan, 153% with bufuralol). A503V supported decreased CYP2D6 activity: 85% with EOMCC, 62% with dextromethorphan and 53% with bufuralol.
POR variants have different effects depending on the substrate metabolized. Disease-causing POR mutations R457H and A287P had poor activities, suggesting that diminished drug metabolism should be considered in affected patients. The common A503V polymorphism impaired CYP2D6 activities with two commonly used drugs by 40-50%, potentially explaining some genetic variation in drug metabolism.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract Spanning over 2000 years, the Jewish population has a long history of migration, population bottlenecks, expansions, and geographical isolation, which has resulted in a unique genetic architecture among the Jewish people. As such, many Mendelian disease genes and founder mutations for autosomal recessive diseases have been discovered in several Jewish groups, which have prompted recent genomic studies in the Jewish population on common disease susceptibility and other complex traits. Although few studies on the genetic determinants of drug response variability have been reported in the Jewish population, a number of unique pharmacogenetic variants have been discovered that are more common in Jewish populations than in other major racial groups. Notable examples identified in the Ashkenazi Jewish (AJ) population include the vitamin K epoxide reductase complex subunit 1 (VKORC1) c.106G>T (p.D36Y) variant associated with high warfarin dosing requirements and the recently reported cytochrome P450 2C19 (CYP2C19) allele, CYP2C19*4B, that harbors both loss-of-function [*4 (c.1A>G)] and increased-function [*17 (c.-806C>T)] variants on the same haplotype. These data are encouraging in that like other ethnicities and subpopulations, the Jewish population likely harbors numerous pharmacogenetic variants that are uncommon or absent in other larger racial groups and ethnicities. In addition to unique variants, common multi-ethnic variants in key drug metabolism genes (e.g., ABCB1, CYP2C8, CYP2C9, CYP2C19, CYP2D6, NAT2) have also been detected in the AJ and other Jewish groups. This review aims to summarize the currently available pharmacogenetics literature and discuss future directions for related research with this unique population.
    05/2014; DOI:10.1515/dmdi-2013-0069
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cytochrome P450 oxidoreductase (POR) supports reactions of microsomal cytochrome P450 which metabolize drugs and steroid hormones. Mutations in POR cause disorders of sexual development. P450 oxidoreductase deficiency (PORD) was initially identified in patients with Antley-Bixler syndrome but now it has been established as a separate disorder of sexual development (DSD). Here we are summarizing the work on variations in POR related to metabolism of drugs and xenobiotics. We have compiled mutation data on reported cases of PORD from clinical studies. Mutations found in patients with defective steroid profiles impact metabolism of steroid hormones as well as drugs. Some trends are emerging that establish certain founder mutations in distinct populations with Japanese (R457H), Caucasian (A287P) and Turkish (399-401) populations showing repeated findings of similar mutations. Most other mutations are found as single occurrences. A large number of different variants in POR gene with more than 130 amino acid changes are now listed in databases. Among the polymorphisms, the A503V allele is found in about 30% of all alleles but there are some differences across different population groups.
    Frontiers in Pharmacology 04/2014; 5(103). DOI:10.3389/fphar.2014.00103
  • [Show abstract] [Hide abstract]
    ABSTRACT: To investigate the influence of cytochrome P450 oxidoreductase (POR) polymorphisms (A503V and rs2868177) on warfarin stable dosage (WSD) in Han-Chinese patients with mechanical heart valve replacement (MHVR). Three hundred and seventeen Han-Chinese MHVR patients on stable maintenance dose of warfarin were enrolled. Blood samples were collected for genotyping analyses of VKORC1 -1639G>A, CYP2C9 *3, CYP4F2 rs2108622 and POR (A503V and rs2868177). Average WSD of carriers with variant POR genotypes or haplotypes were compared. Association analyses were performed by single and multiple linear regression analysis. The variant allele frequencies of POR polymorphisms (A503V and rs2868177) were 38.8 % and 44.8 %, respectively. D' between POR A503V and rs2868177 was 0.855, r(2) was 0.375, and the frequencies of the four POR haplotypes were 42.3 % for CG, 36.3 % for TA, 18.9 % for CA, and 2.5 % for TG, respectively. There were no significant differences in average WSD among carriers with three variant POR A503V genotypes or among carriers with three variant POR rs2868177 genotypes (both P > 0.05). Similarly, there were no significant differences in average WSD among carriers with variant POR haplotypes (all P > 0.05). Neither single nor multiple linear regression analyses showed significant effects of POR A503V or POR rs2868177 polymorphisms on WSD. POR polymorphisms (A503V and rs2868177) do not appear to significantly influence WSD in Han-Chinese patients with MHVR.
    European Journal of Clinical Pharmacology 08/2013; 69(10). DOI:10.1007/s00228-013-1544-2 · 2.70 Impact Factor