P450 Oxidoreductase Polymorphisms Research Articles

Cytochrome P450 oxidoreductase genetic polymorphism and pantoprazole pharmacokinetics in healthy volunteers

ABSTRAKTWstęp: Genetycznie uwarunkowana aktywność enzymów metabolizujących leki może mieć znaczenie dla bezpieczeństwa i skuteczności leczenia. We wcześniejszych badaniach wykazano, że na aktywność enzymatyczną CYP2C19 może wpływać nie tylko polimorfizm genu kodującego ten cytochrom, lecz także zawartość reduktazy cytochromu P450 (POR) w mikrosomach ludzkich hepatocytów. Ludzki gen POR wykazuje dużą zmienność, a allel POR*28 jest związany ze zwiększoną aktywnością reduktazy, co w konsekwencji może prowadzić do zwiększonej aktywności układu CYP P450, w tym enzymu CYP2C19.Celem badania było określenie związku pomiędzy polimorfizmem genu POR a parametrami farmakokinetycznymi pantoprazolu, substratu CYP2C19 w grupie zdrowych ochotników. W analizie uwzględniono także warianty genu CYP2C19.Materiały i metody: U 30 osób, u których wykonano badanie pod kątem występowania jedno­nukleotydowych polimorfizmów: rs4244285 (681G>A, CYP2C19*2), rs12248560 (−806C>T, CYP2C19*17) oraz rs1057868 (31696C>T, POR*28). Stężenia pantoprazolu w osoczu zmierzono metodą wysokosprawnej chromatografii cieczowej w ciągu 8 godz. od przyjęcia pojedynczej doustnej dawki leku (40 mg).Wyniki: Nie stwierdzono istotnych różnic w stężeniu pantoprazolu pomiędzy osobami o różnych genotypach POR (*1/*1, *1/*28 i *28/*28). Analiza wieloczynnikowa wykazała, że genotyp CYP2C19 istotnie wpływał na wartość wszystkich analizowanych parametrów farmakokinetycznych (p < 0.05), podczas gdy genotyp POR nie był istotnie związany z żadnym z nich.Wnioski: Wyniki badania wskazują, że polimorfizm genu POR nie wpływa istotnie na farmakokinetykę pantoprazolu.

Influence of two variants of CYP450 oxidoreductase on the stable dose of acenocoumarol in a Spanish population.

To evaluate the influence of two variants of P450 oxidoreductase (POR), rs2868177 and POR*28, on the stable dosage of acenocoumarol. For this observational, cross-sectional study, patients were undergone stable anticoagulant treatment with acenocoumarol. Univariate and multiple regression analyses were performed to assess the influence of POR polymorphisms. About 340 patients were enrolled. Multiple regression had a coefficient of determination (R2) of 51.5% and an Akaike information criterion of 234.22. The inclusion of POR*28 polymorphisms increased the R2 to 52.0% and reduced the Akaike information criteria to 230.58. The POR*28 heterozygote showed statistical significance in the algorithm. The POR*28 heterozygote appears to be associated with the stable dose of acenocoumarol, but its clinical contribution to the prediction of the dosing of this drug is minimal.

Effects of the selected cytochrome P450 oxidoreductase genetic polymorphisms on cytochrome P450 2B6 activity as measured by bupropion hydroxylation.

Cytochrome P450 oxidoreductase (POR) is required for drug metabolism by all microsomal cytochrome P450 (CYP) enzymes. The aim of this study was to investigate whether single-nucleotide polymorphisms in the POR gene were correlated with interindividual variations in CYP2B6 activity, as measured by bupropion hydroxylation. Thirty-five healthy individuals with selected CYP2B6 and POR polymorphisms were involved in the clinical study. The activity of CYP2B6 was evaluated on the basis of the area under the time-concentration curve (AUC) ratio of hydroxybupropion versus bupropion (AUC_hyd/AUC_bup). Individuals carrying CYP2B6*1/*1 showed a significantly higher mean AUC_hyd/AUC_bup than individuals carrying the CYP2B6*1/*6 and CYP2B6*6/*6 variants (17.1 ± 6.23 vs. 10.3 ± 4.53, P = 0.003 and 17.1 ± 6.23 vs. 9.41 ± 2.84, P = 0.002, respectively). POR g.6593A>G (rs2868177) AA homozygotes showed a significantly lower mean AUC_hyd/AUC_bup than POR g.6593A>G AG heterozygotes or GG homozygotes (8.54 ± 2.65 vs. 14.9 ± 6.06, P = 0.005 and 8.54 ± 2.65 vs. 16.8 ± 6.45, P = 0.002, respectively). Moreover, POR g.6593A>G AA homozygotes had a significantly lower mean AUC_hyd/AUC_bup than the POR g.6593A>G AG/GG genotypes in the CYP2B6*1/*1, CYP2B6*1/*6 and CYP2B6*6/*6 groups (10.9 ± 1.82 vs. 19.7 ± 5.53, P < 0.001; 6.18 ± 0.284 vs. 12.1 ± 4.31, P = 0.011; and 6.94 ± 1.48 vs. 10.9 ± 2.39, P = 0.043, respectively). There was no significant difference in the mean AUC_hyd/AUC_bup among different POR c.1508C>T (*28 or rs1057868) genotypes, even after the effect of CYP2B6*6 was excluded. These results indicate, for the first time, that the POR g.6593A>G polymorphism significantly influences CYP2B6 activity, as measured by bupropion hydroxylation, in humans, and the CYP2B6*6 and POR g.6593A>G polymorphisms might be considered simultaneously for the individualized therapy with CYP2B6 substrate drugs such as bupropion.

Effects of CYP2C19 and P450 Oxidoreductase Polymorphisms on the Population Pharmacokinetics of Clobazam and N-Desmethylclobazam in Japanese Patients With Epilepsy

Clobazam (CLB) is a 1,5-benzodiazepine with antiepileptic properties. More than 70% of administered CLB is dealkylated to yield N-desmethylclobazam (N-CLB), a pharmacologically active metabolite, by cytochrome P450 (CYP) 3A4 and CYP2C19. The subsequent inactivation of N-CLB is primarily catalyzed by CYP2C19. Meanwhile, P450 oxidoreductase (POR) is the obligatory electron donor to all microsomal CYP enzymes. The aim of this study was to evaluate the impact of the CYP2C19 and POR genotypes on the pharmacokinetic parameters of CLB and N-CLB. This retrospective study included 85 Japanese patients with epilepsy who were treated with CLB. CYP2C19*2, *3, and P450 oxidoreductase (POR) *28 (rs1057868C>T) polymorphisms were evaluated. A total of 128 steady-state concentrations for both CLB and N-CLB were collected from the patients. A nonlinear mixed-effects model identified the pharmacokinetics of CLB and N-CLB; the covariates included CYP2C19 and POR genotypes, weight, gender, daily CLB dose, and coadministered antiepileptic drugs. Among the 85 patients, the allele frequencies of CYP2C19*2, CYP2C19*3, and POR*28 were 27.6%, 12.9%, and 41.2%, respectively. A one-compartment model with first-order absorption and/or elimination showed that the clearance of CLB and N-CLB was significantly lower by 18.1% and 84.9%, respectively, in the CYP2C19 poor metabolizers compared with the homozygous extensive metabolizers. The CLB clearance was 44% higher in subjects homozygous for the POR*28 T allele than in those homozygous for the POR*28 C allele, although the genotypes did not affect the N-CLB clearance. The concomitant use of phenobarbital, phenytoin, and zonisamide significantly affected the CLB clearance, whereas that of carbamazepine, phenytoin, and valproic acid affected the N-CLB clearance. The weight also significantly influenced the CLB clearance and volume of distribution of both CLB and N-CLB. Our results showed that the CYP2C19 and/or POR genotypes have an impact on the CLB and/or N-CLB clearance. These results suggest that determining the CYP2C19 and/or POR genotypes is helpful for obtaining appropriate serum CLB and N-CLB concentrations and preventing an overdose when starting CLB therapy.

Single-nucleotide polymorphisms in P450 oxidoreductase and peroxisome proliferator-activated receptor-α are associated with the development of new-onset diabetes after transplantation in kidney transplant recipients treated with tacrolimus

New-onset diabetes after transplantation (NODAT) is an important complication after kidney transplantation. The etiology of the malady is multifactorial and includes both environmental and genetic factors. NODAT is a polygenic disease and many single-nucleotide polymorphisms could constitute potential risk factors. Peroxisome proliferator-activated receptor α (PPARα) and P450 oxidoreductase (POR) play a central role in the control of energy metabolism in humans. Some recent data highlighted a possible functional impact of two single-nucleotide polymorphisms in PPARα (rs4253728 G>A and rs4823613 A>G) and one coding variant in POR (rs1057868; POR*28; A503V) on the activity of their respective encoded proteins. In the present study, we assessed the association between these variants and the risk of developing NODAT after kidney transplantation. Development of NODAT was investigated in 101 renal transplant recipients receiving tacrolimus-based immunosuppressive therapy. Patients were genotyped for PPARα and POR. The incidence of NODAT was compared between different genotypes. Kaplan-Meier and Cox's proportional-hazard analysis were used to evaluate the association of NODAT with potential risk factors. Potential nongenetic risk factors were also considered. The PPARα rs4253728A>G and POR*28 variant alleles were both independently associated with an increased risk for NODAT with respective odds ratios of 8.6 [95% confidence interval (CI)=1.4-54.2; P=0.02] and 8.1 (95% CI=1.1-58.3; P=0.04). Other risk predictors included sex and body weight. This candidate-gene study shows that polymorphisms in PPARα and POR might predispose patients being treated with tacrolimus to the development of NODAT after kidney transplantation. Patient management after organ transplantation might benefit from genotype data.

Cytochrome P450 oxidoreductase genetic polymorphisms A503V and rs2868177 do not significantly affect warfarin stable dosage in Han-Chinese patients with mechanical heart valve replacement

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.

Influence of cytochrome P450 oxidoreductase genetic polymorphisms on CYP1A2 activity and inducibility by smoking

Cytochrome P4501A2 (CYP1A2) presents a high interindividual variability in its activity and also in its inducibility by smoking. Cytochrome P450 oxidoreductase (POR) is an electron transfer protein that catalyzes the activity of several cytochromes P450. We aimed to study the influence of POR genetic polymorphisms on CYP1A2 activity while smoking and after smoking cessation, as well as on CYP1A2 inducibility. CYP1A2 activity was determined by the paraxanthine/caffeine ratio in 184 smokers and in 113 of these smokers who were abstinent during a 4-week period. Participants were genotyped for POR rs17148944G>A, rs10239977C>T, rs3815455C>T, rs2286823G>A, rs2302429G>A, and rs1057868C>T (POR*28) polymorphisms. While smoking, none of the tested POR polymorphisms showed a significant influence on CYP1A2 activity. After smoking cessation, significantly higher CYP1A2 activity was found in POR rs2302429A carriers (P=0.038) and in carriers of rs17148944G-rs10239977C-rs3815455T-rs2286823G-rs2302429A-rs1057868T haplotype (P=0.038), whereas carriers of POR rs2286823A (P=0.031) and of the rs17148944G-rs10239977C-rs3815455C-rs2286823A-rs2302429G-rs1057868C haplotype (P=0.031) had decreased CYP1A2 activity. In the complete regression model, only POR rs2302429G>A showed a significant effect (P=0.017). No influence of POR genotypes or haplotypes was observed on the inducibility of CYP1A2. POR genetic polymorphisms influence CYP1A2 basal but not induced activity and do not seem to influence CYP1A2 inducibility. Future work is warranted to identify other clinical and genetic factors that may explain the variability in CYP1A2 activity and inducibility by smoking.

Nomenclature for alleles of the cytochrome P450 oxidoreductase gene

Recent focus on the cytochrome P450 oxidoreductase (POR) gene has resulted in the discovery of numerous new polymorphic alleles. Many of these were found [1–6] because of their association with steroidogenic disorders and congenital skeletal malformations resembling the phenotype of Antley-Bixler syndrome [7], whereas other alleles have been found as a consequence of sequencing the POR gene in normal unrelated individuals [8,9]. The association of POR variants with clinical phenotypes is the result of POR serving as the major electron donor for cytochrome P450 (CYP) enzymes with important endogenous functions in hormone biosynthesis. Consequently, defective POR alleles can be the cause of abnormal glucocorticoid, mineralocorticoid, and sex steroid synthesis [10], thus leading to a form of congenital adrenal hyperplasia. In addition, POR deficiency can cause skeletal defects, the mechanism of which is yet unknown but has been suggested to result from impaired sterol synthesis [11] because of decreased electron flow from POR to lanosterol 14-alpha-demethylase (CYP51A1) and squalene monooxygenase (SQLE). In addition, as POR is equally important as an electron donor to CYP enzymes involved in the metabolism of drugs, POR variants may affect drug bioavailability. The effect of POR mutations on the activity of some drug-metabolizing CYP enzymes has been documented in vitro [12–14], but not yet in vivo. In addition, POR is an electron donor for heme oxygenase, cytochrome b5, and several additional small molecules that can be directly metabolized by POR without CYP enzymes. Thus, an increasing focus on the importance of POR in drug response and adverse drug reactions is to be expected. Until now, no systematic guidelines have been proposed for the naming of POR alleles. To standardize POR allelic nomenclature, the Human CYP Allele Nomenclature Chair and Committee have taken the initiative to devise a system for the designation of POR alleles that follows the guidelines for CYP allelic star (CYP*) nomenclature (http://www.cypalleles.ki.se/criteria.htm). The POR allele nomenclature web page (http://www.cypalleles.ki.se/por.htm) was launched in September 2008, listing 35 different alleles. On this POR web page, the alleles are presented together with their corresponding nucleotide and amino acid changes, and the phenotypic consequences observed by in vitro and in vivo studies. Among the more important POR variants are POR*2 and *5 (Arg457His and Ala287Pro, respectively), the former being the most frequent mutation in Japanese and Chinese POR-deficient patients [5,15], whereas the latter is the POR mutation most frequently found in Caucasians. Alleles with frameshift mutations (POR*9, *10, and *20–24), deletions, insertions, and several of the alleles that result in amino acid substitutions are also associated with in vivo phenotypes, as is a splice defect in the POR*3 allele. To maintain a common nomenclature system within the field, fellow scientists investigating POR polymorphisms are highly recommended to submit novel POR allelic variants to the Human CYP Allele Nomenclature Committee (http://www.cypalleles.ki.se/criteria.htm) by contacting the Webmaster for designation and reservation of novel POR allele names. The authors of this Letter, a number of whom have identified the novel POR alleles, are supportive of this new nomenclature system, and will use this system in their future work.

P450 oxidoreductase: genetic polymorphisms and implications for drug metabolism and toxicity

Background: Cytochrome P450 oxidoreductase (POR) is the only electron donor for all microsomal cytochrome P450 monooxygenases (CYP), some of which are phase I drug-metabolizing enzymes, responsible for oxidation of more than 80% of drugs. Objectives: To provide a more thorough understanding of the genetic factors influencing drug metabolism, we address the role of genetic polymorphisms in the POR gene, and their implications for drug metabolism and cytotoxicity. Methods: The scope of this review is intended to cover polymorphisms currently identified in the POR gene, assess their functional significance on POR activity, and address their impact on CYP-mediated drug metabolism. POR is also responsible for directly metabolizing several anticancer prodrugs via a 1-electron reduction reaction, so the effect of POR polymorphisms on the direct bioactivation of drugs is also considered. Results/conclusion: POR is a polymorphic enzyme that can affect CYP-mediated drug metabolism as well as direct bioactivation of prodrugs. Genetic polymorphisms in the POR gene may help to explain altered drug-metabolizing phenotypes.

Single nucleotide polymorphisms in cytochrome P450 oxidoreductase influence drug metabolism

Cytochrome P450 oxidoreductase (POR) is the only protein that donates electrons to all microsomal P450 enzymes, which metabolize more than 80% of prescription drugs. Our objective was to determine if polymorphisms in POR could affect gene expression and activity of POR, and/or P450‐catalyzed drug metabolism. POR polymorphisms were identified from non‐diseased human livers (n=99) by sequencing the POR gene and mRNA levels were quantified by the branched DNA method. POR activity was quantified by measuring cytochrome c reduction in liver microsomes and activities of ten drug‐metabolizing P450 enzymes were quantified by HPLC. Of the 34 identified polymorphisms, 9 were novel, 9 were in exons, and 4 changed an amino acid: K49N, L420M, A503V, and L577P. We report a novel exonic polymorphism, L577P (patent pending), which is associated with decreased POR (p=0.003) and several P450 activities. Our data suggest that [1] POR is functionally polymorphic in the general population and [2] has the potential to serve as a biomarker to optimize pharmacologic dosing strategies. This work was supported by NIH COBRE 5P20 RR021940 and Pharmaceutical Research and Manufacturers of America Foundation (PhRMA).

Genetic polymorphisms in cytochrome P450 oxidoreductase influence microsomal P450-catalyzed drug metabolism

Cytochrome P450 oxidoreductase (POR) is the only flavoprotein that donates electrons to all microsomal P450 enzymes, which catalyze the biosynthesis of steroids, fatty acids, and bile acids, as well as metabolism of more than 80% of prescription drugs. Although mutations in POR have been identified in several disease states with disordered steroidogenesis, effects of polymorphisms on drug metabolism in the general population are unclear. In this report, we performed a comprehensive study to correlate POR polymorphisms with POR gene expression, POR activity, and P450-catalyzed drug metabolism. A set of human liver samples (n=99) were used in this study. POR polymorphisms were identified by sequencing the exons and surrounding introns of the POR gene and mRNA levels were quantified by branched DNA technology. POR activity was quantified by measuring cytochrome c reduction in liver microsomes and activities of 10 drug-metabolizing P450 enzymes were quantified by high performance liquid chromatography methods with drugs known to be specific for each enzyme. Of the 34 polymorphisms identified in this cohort, four polymorphisms changed an amino acid: K49N, L420M, A503V, and L577P. L577P likely resulted in an alpha helix change, possible disruption of the nicotinamide adenine dinucleotide phosphate interaction, and decreased POR activity (P=0.003) and several drug-metabolizing P450 activities. We also found an intronic polymorphisms rs41301427, which was associated with altered POR, but not P450 activities. Polymorphisms in the POR gene can affect POR and P450-catalyzed drug oxidation. These results suggest that POR has the potential to serve as a predictive biomarker for pharmacogenomic testing.

Novel SNPs in Cytochrome P450 Oxidoreductase

Cytochrome P450 oxidoreductase (POR) is the single flavoprotein which donates electrons to the microsomal cytochrome P450 enzymes for oxidation of their substrates. In this study, we sequenced all 15 exons and the surrounding intronic sequences of POR in 100 human liver samples to identify novel and confirm known genetic polymorphisms in POR. Thirty-four single nucleotide polymorphisms (SNPs) were identified including 9 in the coding exons (5 synonymous and 4 nonsynonymous), 20 in the intronic regions, and 5 in the 3'-UTR. Of these, 9 were novel SNPs, including three nonsynonymous SNPs, SNH313003 (817733G>C; K49N), SNH313020 (848661C>A; L420M), and SNH313029 (849577T>C; L577P) with minor allele frequencies of 0.005, 0.045, and 0.020, respectively. We also confirmed a previously reported non-synonymous SNP rs1057868 (A503V) as well as five synonymous SNPs (G5G, T29T, P129P, S485S, and S572S) all with allele frequencies similar to those previously reported. Structurally, these polymorphisms occur in different regions: SNH313003 (K49N) in the amino-terminal tail, SNH313020 (L420M) in the connecting domain, SNH313029 (L577P) in the NADPH-binding domain, and rs1057868 (A503V) in the FAD binding domain.