CYP2D6 genotyping by a multiplex primer extension reaction

Leveraging in Vitro Models for Clinically Relevant Rare CYP2D6 Variants in Pharmacogenomics

Cytochrome P450 2D6 (CYP2D6) is responsible for the metabolism of up to 20% of small-molecule drugs and therefore, may impact the safety and efficacy of medicines in broad therapeutic areas. CYP2D6 is highly polymorphic, and the frequency of variants can differ across racial and ethnic populations, significantly affecting enzymatic function and drug metabolism. However, rare variants of CYP2D6 present a unique challenge for academia, industry, and regulatory agencies alike due to the lack of feasibility of characterizing their clinical relevance in clinical trials, particularly in variants that exhibit population-specific frequencies in racial and ethnic groups that are poorly represented in clinical trials. Despite significant advancement in pharmacogenomics, the substrate specificity and related clinical relevance of these CYP2D6 rare variants remain largely unclear, and further efforts are warranted to characterize the burden of these variants on adverse drug reactions and drug efficacy. Thus, cell-based in vitro systems can be used to inform substrate-specific effects and the overall relevance of a rare variant. Liver microsomes, cell-based expression systems, ex vivo primary samples, and purified variant protein have all been used with various substrates to potentially predict the clinical impact of new substrates. In this review, we identify rare variants of CYP2D6 that demonstrate differences across races in prevalence and thus are often unassessed in clinical trials. Accordingly, we examine current pharmacogenomic in vitro models used to analyze the functional impact of these rare variants in a substrate-specific manner. SIGNIFICANCE STATEMENT: Variants of CYP2D6 play a clinically relevant role in drug metabolism, leading to potential safety and efficacy concerns. Although the influence of prevalent variants is often well characterized, rare variants are traditionally not included in clinical trials. This review captures the clinical relevance of rare variants in CYP2D6 by highlighting in vitro models that analyze their impact on the metabolism of CYP2D6 substrates.

Effects of pharmacogenetic profiles on pediatric pain relief and adverse events with ibuprofen and oxycodone

Introduction

Individual genetic variation may influence clinical effects for pain medications. Effects of CYP2C9, CYP3A4, and CYP2D6 polymorphisms on clinical effectiveness and safety for ibuprofen and oxycodone were studied.

Objective

Primary objectives were to AU2 evaluate if allelic variations would affect clinical effectiveness and adverse events (AEs) occurrence.

Methods

This pragmatic prospective, observational cohort included children aged 4 to 16 years who were seen in a pediatric emergency department with an acute fracture and prescribed ibuprofen or oxycodone for at-home pain management. Saliva samples were obtained for genotyping of allelic variants, and daily telephone follow-up was conducted for 3 days. Pain was measured using the Faces Pain Scale-Revised.

Results

We included 210 children (n = 140 ibuprofen and n = 70 oxycodone); mean age was 11.1 (±SD 3.5) years, 33.8% were female. Median pain reduction on day 1 was similar between groups [ibuprofen 4 (IQR 2,4) and oxycodone 4 (IQR 2,6), P = 0.69]. Over the 3 days, the oxycodone group experienced more AE than the ibuprofen group (78.3% vs 53.2%, P < 0.001). Those with a CYP2C9*2 reduced function allele experienced less adverse events with ibuprofen compared with those with a normal functioning allele CYP2C9*1 (P = 0.003). Neither CYP3A4 variants nor CYP2D6 phenotype classification affected clinical effect or AE.

Conclusion

Although pain relief was similar, children receiving oxycodone experienced more AE, overall, than those receiving ibuprofen. For children receiving ibuprofen or oxycodone, pain relief was not affected by genetic variations in CYP2C9 or CYP3A4/CYP2D6, respectively. For children receiving ibuprofen, the presence of CYP2C9*2 was associated with less adverse events.

A frequent CYP2D6 variant promotes skipping of exon 3 and reduces CYP2D6 protein expression in human liver samples

CYP2D6 is one of the most polymorphic drug-metabolizing enzymes in the liver. While genetic CYP2D6 variants serve as clinical biomarkers to predict CYP2D6 activity, large inter-person variability in CYP2D6 expression remains unaccounted for. Previous results suggest that there is variable expression of a CYP2D6 splice isoform with an in-frame deletion of exon 3 (CYP2D6ΔE3) encoding a protein lacking numerous active site residues. Here, using fragment analysis and RT-qPCR, we revealed that rs1058164 G (MAF = 27%-43%) is associated with increased formation of CYP2D6∆E3 in human liver samples (1.4-2.5-fold) and transfected cells. Furthermore, western blots showed that rs1058164 G was associated with a 50% decrease in full-length hepatic CYP2D6 protein expression. In addition, by studying a larger liver cohort, we confirmed our previous results that rs16947 (CYP2D6*2) reduces full-length CYP2D6 mRNA by increasing the production of an unstable splice isoform lacking exon 6 (CYP2D6ΔE6) and that the impact of CYP2D6ΔE6 is offset in carriers of the downstream enhancer variant rs5758550. The three frequent SNPs (rs1058164, rs16947, and rs5758550) form various 3-SNP-haplotypes, each with distinct CYP2D6 expression characteristics. Using an expression score (ES) system, we tested the impact of the 3-SNP-haplotype on improving the standard model to predict hepatic CYP2D6 protein expression based on genotype. A model that incorporates the 3-SNP-haplotype provided the best fit for CYP2D6 expression and also accounted for more variability in CYP2D6 protein levels (59%) than a model based on the accepted standard (36%) or one that only adds rs16947 and rs5758550 (42%). Clinical studies are needed to determine whether including the 3-SNP-haplotype alongside current standard CYP2D6 models improves the predictive value of CYP2D6 panels.

Prediction of the CYP2D6 enzymatic activity based on investigating of the CYP2D6 genotypes around the vivax malaria patients in Yunnan Province, China

BACKGROUND

In recent years, the incidence rate of vivax malaria recurrence still had 3.1% in Yunnan Province population after eradication therapy using primaquine (PQ). In order to understand the specific failure reasons for preventing vivax malaria relapses, a preliminary exploration on the CYP2D6 enzyme activity was carried out in the vivax malaria patients in Yunnan Province population by analysing mutational polymorphism in the coding region of CYP2D6 gene.

METHODS

Blood samples were collected from vivax malaria patients with suspected relapse (SR) and non-relapsed (NR) malaria in Yunnan Province. The DNA fragments containing 9 exons regions of human CYP2D6 gene were amplified by performing PCR and sequenced. The sequencing results were aligned by using DNAStar 11.0 to obtain the coding DNA sequence (CDS) of CYP2D6 gene. DnaSP 6.11.01 software was used to identify mutant polymorphisms and haplotypes of the CDS chain. The waterfall function of GenVisR package in R was utilized to visualize the mutational landscape. The alleles of CYP2D6 gene were identified according to the criteria prescribed by Human Cytochrome P450 (CYP) Allele Nomenclature Committee Database and the CYP2D6 enzyme activity was predicted based on diploid genotype.

RESULTS

A total of 320 maternal CDS chains, including 63 from SR group and 257 from NR group, were obtained. Twelve mutant loci, including c.31 (rs769259), c.100 (rs1065852), c.271 (rs28371703), c.281 (rs28371704), c.294 (rs28371705), c.297 (rs200269944), c.336 (rs1081003), c.408 (rs1058164), c.505 (rs5030865), c.801 (rs28371718), c.886 (rs16947), and c.1,457 (rs1135840) were observed on the 640 CDS chains (including 320 maternal and 320 paternal chains). The high-frequency mutation at rs1135840 (0.703) and low-frequency mutation, such as rs28371703, were detected only in the SR group. The frequency of mutant rs1058164 and rs1135840 were significantly increased in the SR group ([Formula: see text]= 4.468, 5.889, P < 0.05), as opposed to the NR group. Of the 23 haplotypes (from Hap_1 to Hap_23), the nomenclatures of 11 allelic forms could be found: Hap_3 was non-mutant, Hap_2 accounted for the highest frequency (36.9%, 236/640), and Hap_9 had the most complex sequence structure, containing 7 loci mutations. Allele *10 was the most frequent among these genotypes (0.423). Among the allele *10 standard named genotypes, *1/*10, *1/*1 and *2/*10 were significantly more frequent in the NR group ([Formula: see text]= 3.911, P < 0.05) and all showed uncompromised enzyme activity; the impaired genotype *10/*39 was more frequent in the SR group ([Formula: see text]= 10.050, P < 0.05), and genotype *4/*4was detected only in the SR group.

CONCLUSION

In the patients receiving PQ dosage in Yunnan Province population, both rs1135840 single nucleotide polymorphism and *10 allele form was common in the CYP2D6 gene. Low-frequency mutation sites, such as rs28371703, were only presented in patients with vivax malaria relapse.

Oral Yohimbine as a New Probe Drug to Predict CYP2D6 Activity: Results of a Fixed-Sequence Phase I Trial

Objective

Yohimbine pharmacokinetics were determined after oral administration of a single oral dose of yohimbine 5 mg and a microdose of yohimbine 50 µg in relation to different cytochrome P450 (CYP) 2D6 genotypes. The CYP2D6 inhibitor paroxetine was used to investigate the influence on yohimbine pharmacokinetics. Microdosed midazolam was applied to evaluate a possible impact of yohimbine on CYP3A activity and the possibility of combining microdosed yohimbine and midazolam to simultaneously determine CYP2D6 and CYP3A activity.

Methods

In a fixed-sequence clinical trial, 16 healthy volunteers with a known CYP2D6 genotype [extensive (10), intermediate (2) and poor (4) metaboliser] received an oral dose of yohimbine 50 µg, yohimbine 5 mg at baseline and during paroxetine as a CYP2D6 inhibitor. Midazolam (30 µg) was co-administered to determine CYP3A activity at each occasion. Plasma concentrations of yohimbine, its main metabolite 11-OH-yohimbine, midazolam and paroxetine were quantified using validated liquid chromatography-tandem mass spectrometry assays.

Results

Pharmacokinetics of yohimbine were highly variable and a CYP2D6 genotype dependent clearance was observed. After yohimbine 5 mg, the clearance ranged from 25.3 to 15,864 mL/min and after yohimbine 50 µg, the clearance ranged from 39.6 to 38,822 mL/min. A more than fivefold reduction in clearance was caused by paroxetine in CYP2D6 extensive metabolisers, while the clearance in poor metabolisers was not affected. Yohimbine did not alter CYP3A activity as measured by microdosed midazolam.

Conclusions

The pharmacokinetics of yohimbine were highly correlated with CYP2D6, which was further supported by the clearance inhibition caused by the CYP2D6 inhibitor paroxetine. With these data, yohimbine is proposed to be a suitable probe drug to predict CYP2D6 activity. In addition, the microdose can be used in combination with microdosed midazolam to simultaneously evaluate CYP2D6 and CYP3A activity without any interaction between the probe drugs and because the microdoses exert no pharmacological effects.

Clinical Trial Registration

EudraCT2017-001801-34.

Electronic supplementary material

The online version of this article (10.1007/s40262-020-00862-6) contains supplementary material, which is available to authorized users.

The association of CYP2D6 gene polymorphisms in the full-length coding region with higher recurrence rate of vivax malaria in Yunnan Province, China

Background

Accumulating evidence suggest that compromised CYP2D6 enzyme activity caused by gene mutation could contribute to primaquine failure for the radical cure of vivax malaria. The current study aims to preliminarily reveal the association between the recurrence of vivax malaria in Yunnan Province and CYP2D6 gene mutation by analysing polymorphisms in the entire coding region of human CYP2D6 gene.

Methods

Blood samples were collected from patients with vivax malaria, who received "chloroquine and 8-day course of primaquine therapy" in Yunnan Province. The suspected relapsed cases were determined by epidemiological approaches and gene sequence alignment. PCR was conducted to amplify the CYP2D6 gene in the human genome, and the amplified products were then sequenced to compare with the non-mutation “reference” sequence, so as to ensure correct sequencing results and to determine 9 exon regions. Subsequently, the DNA sequences of 9 exons were spliced into the coding DNA sequence (CDS), which, by default, is known as maternal CDS. The paternal CDS was obtained by adjusting the bases according to the sequencing peaks. The mutation loci, haplotypes (star alleles), genotypes and odds ratios (OR) of all the CDSs were analysed.

Results

Of the119 maternal CDS chains in total with 1491 bp in length, 12 mutation sites in the 238 maternal and paternal CDS chains were detected. The c.408G > C mutation was most frequently detected in both suspected relapsed group (SR) and non-relapsed group (NR), reaching 85.2% (75/88) and 76.0% (114/150), respectively. The c.886C > T mutation was most closely related to the recurrence of vivax malaria (OR = 2.167, 95% CI 1.104–4.252, P < 0.05). Among the 23 haplotypes (Hap_1 ~ Hap_23), Hap_3 was non-mutant, and the sequence structure of Hap_9 was the most complicated one. Five star alleles, including *1, *2, *4, *10 and *39, were confirmed by comparison, and CYP2D6*10 allele accounted for the largest percentage (45.4%, 108/238). The frequency of CYP2D6*2 allele in the SR group was significantly higher than that in the NR group (Χ² = 16.177, P < 0.05). Of the defined 24 genotypes, 8 genotypes, including *4/*4, *4/*o, *2/*39, *39/*m, *39/*x, *1/*r, *1/*n, and *v/*10, were detected only in the SR group.

Conclusion

Mutation of CYP2D6*10 allele accounts for the highest proportion of vivax malaria cases in Yunnan Province. The mutations of c. 886C > T and CYP2D6*2 allele, which correspond to impaired PQ metabolizer phenotype, are most closely related to the relapse of vivax malaria. In addition, the genotype *4/*4 with null CYP2D6 enzyme function was only detected in the SR group. These results reveal the risk of defected CYP2D6 enzyme activity that diminishes the therapeutic effect of primaquine on vivax malaria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03685-3.

Effects of genetic variability of CYP2D6 on neural substrates of sustained attention during on-task activity

The polymorphic drug-metabolizing enzyme CYP2D6, which is responsible for the metabolism of most psychoactive compounds, is expressed not only in the liver, but also in the brain. The effects of its marked genetic polymorphism on the individual capacity to metabolize drugs are well known, but its role in metabolism of neural substrates affecting behavior personality or cognition, suggested by its CNS expression, is a long-standing unresolved issue. To verify earlier findings suggesting a potential effect on attentional processes, we collected functional imaging data, while N = 415 participants performed a simple task in which the reward for correct responses varied. CYP2D6 allelic variants predicting higher levels of enzymatic activity level were positively associated with cortical activity in occipito-parietal areas as well as in a right lateralized network known to be activated by spatial attentional tasks. Reward-related modulation of activity in cortical areas was more pronounced in poor metabolizers. In conjunction with effects on reaction times, our findings provide evidence for reduced cognitive efficiency in rapid metabolizers compared to poor metabolizers in on-task attentional processes manifested through differential recruitment of a specific neural substrate.

Predicting steady-state endoxifen plasma concentrations in breast cancer patients by CYP2D6 genotyping or phenotyping. Which approach is more reliable?

In previous studies, steady-state Z-endoxifen plasma concentrations (ENDOss) correlated with relapse-free survival in women on tamoxifen (TAM) treatment for breast cancer. ENDOss also correlated significantly with CYP2D6 genotype (activity score) and CYP2D6 phenotype (dextromethorphan test). Our aim was to ascertain which method for assessing CYP2D6 activity is more reliable in predicting ENDOss. The study concerned 203 Caucasian women on tamoxifen-adjuvant therapy (20 mg q.d.). Before starting treatment, CYP2D6 was genotyped (and activity scores computed), and the urinary log(dextromethorphan/dextrorphan) ratio [log(DM/DX)] was calculated after 15 mg of oral dextromethorphan. Plasma concentrations of TAM, N-desmethyl-tamoxifen (ND-TAM), Z-4OH-tamoxifen (4OH-TAM) and ENDO were assayed 1, 4, and 8 months after first administering TAM. Multivariable regression analysis was used to identify the clinical and laboratory variables predicting log-transformed ENDOss (log-ENDOss). Genotype-derived CYP2D6 phenotypes (PM, IM, NM, EM) and log(DM/DX) correlated independently with log-ENDOss. Genotype-phenotype concordance was almost complete only for poor metabolizers, whereas it emerged that 34% of intermediate, normal, and ultrarapid metabolizers were classified differently based on log(DM/DX). Multivariable regression analysis selected log(DM/DX) as the best predictor, with patients' age, weak inhibitor use, and CYP2D6 phenotype decreasingly important: log-ENDOss = 0.162 - log(DM/DX) × 0.170 + age × 0.0063 - weak inhibitor use × 0.250 + IM × 0.105 + (NM + UM) × 0.210; (R2  = 0.51). In conclusion, log(DM/DX) seems superior to genotype-derived CYP2D6 phenotype in predicting ENDOss.

An Explorative Study of CYP2D6’s Polymorphism in a Sample of Chronic Pain Patients

Background

A proper antalgic treatment is based on the use of titrated drugs to provide adequate relief and a good tolerability profile. Therapies have a variable effectiveness among subjects depending on medical and genetic conditions. CYP2D6 variations determine a different clinical response to most analgesic drugs commonly used in daily clinical practice by influencing the drugs’ pharmacokinetics. This study was a monocentric clinical trial exploring the CYP2D6 variants in 100 patients with a diagnosis of chronic pain.

Methods

DNA was extracted to evaluate the genotype and to classify patients as normal-fast (gNMs-F), normal-slow (gNMs-S), ultrarapid (gUMs), intermediate (gIMs), and poor metabolizers (gPMs) using the Activity Score (AS). Information on therapies and general side effects experienced by patients was collected. Nongenetic co-factors were evaluated to examine the discrepancy between metabolic profile predicted from genotype (gPh) and metabolic profile (phenocopying).

Results

The distribution of our data underlined the prevalence of the gNMs-F (67%), whereas gNMs-S were 24%, gIMs 6%, gPMs 3%, and no gUMs were found, resulting in 33% of patients with reduced metabolic activity. In the analyzed population sample, 86% and 56% of patients, respectively, took at least one or two drugs inhibiting in vitro activity of the CYP2D6 enzyme.

Conclusions

Over one-third of the enrolled patients showed altered CYP2D6 enzymatic metabolic activity, with a risk of phenocopying potentially due to polypharmacology.

Trial registration

ClinicalTrials.gov ID: NCT03411759.

Identification of mutations in SLC4A1, GP1BA and HFE in a family with venous thrombosis of unknown cause by next-generation sequencing

Various risk factors, including high age, female gender, obesity and certain genetic defects have been linked to venous thrombosis. A Taiwanese family with venous thrombosis of unknown cause were enrolled in the present study. In this pedigree, two women without any specific underlying diseases suffered from venous thrombotic events at the same age. No specific risk factors or coagulation abnormalities were identified. The main proband's younger brother also had intestinal arterial thrombosis at 54 years of age. Therefore, it was hypothesized that familial genetic defects may be the cause of venous thrombosis within this family. Blood samples collected from certain members of this pedigree were subjected to whole-exome sequencing, and three genetic variants were identified, including a missense variant of solute carrier family 4 member 1 (SLC4A1) (c.388G>A), a deletion on glycoprotein Ib platelet α subunit (GP1BA) (c.1322_1344del23) and an insertion in the splice site of homeostatic iron regulator (HFE). To date, none of these three genetic variants have been reported to be associated with venous thrombosis, to the best of our knowledge. The present study suggests that these genetic variants of SLC4A1, GP1BA and HFE may be associated with venous thrombosis in an Asian pedigree.

Genetic variability of CYP2D6, CYP2B6, CYP2C9 and CYP2C19 genes across the Italian Peninsula

BACKGROUND

Environmental conditions and past migratory events may have shaped genetic heterogeneity of clinically relevant enzymes involved in the phase I metabolism of the most common therapeutic drugs.

AIM

To investigate the genetic variability of CYP2D6, CYP2B6, CYP2C19 and CYP2C9 across the Italian Peninsula, by sampling only ancestrally and geographically homogeneous individuals from northern, central and southern Italy.

SUBJECTS AND METHODS

A total of 25 SNPs were genotyped in 174 unrelated Italian individuals by means of multiplex PCR and minisequencing reactions. CYP2D6 genotypic data were used to predict phenotypes and the phylogenetic relationships among reconstructed haplotypes were represented by means of a Median Joining Network.

RESULTS

Pairwise Fisher Exact tests revealed significant differences between northern and southern Italy in the distribution of CYP2C19 genotypes, with the CYP2C19*2 allele appearing over-represented in northern Italy. Likewise, significant differences in the distribution of CYP2D6 genotypes (*4/*3, *4/*4 and *6/*4) responsible for the poor metabolizer phenotype were observed in northern with respect to both central and southern Italy.

CONCLUSIONS

The north-south structuring pattern showed by CYP2D6 and CYP2C19 underline how a deeper knowledge of the geographic distribution of alleles may improve clinical practice and help to avoid hypothetical bias in drug trials.

Analysis of Genetic Variation in CYP450 Genes for Clinical Implementation

Background

Genetic determinants of drug response remain stable throughout life and offer great promise to patient-tailored drug therapy. The adoption of pharmacogenetic (PGx) testing in patient care requires accurate, cost effective and rapid genotyping with clear guidance on the use of the results. Hence, we evaluated a 32 SNPs panel for implementing PGx testing in clinical laboratories.

Methods

We designed a 32-SNP panel for PGx testing in clinical laboratories. The variants were selected using the clinical annotations of the Pharmacogenomics Knowledgebase (PharmGKB) and include polymorphisms of CYP2C9, CYP2C19, CYP2D6, CYP3A5 and VKORC1 genes. The CYP2D6 gene allele quantification was determined simultaneously with TaqMan copy number assays targeting intron 2 and exon 9 regions. The genotyping results showed high call rate accuracy according to concordance with genotypes identified by independent analyses on Sequenome massarray and droplet digital PCR. Furthermore, 506 genomic samples across three major ethnic groups of Singapore (Malay, Indian and Chinese) were analysed on our workflow.

Results

We found that 98% of our study subjects carry one or more CPIC actionable variants. The major alleles detected include CYP2C9*3, CYP2C19*2, CYP2D6*10, CYP2D6*36, CYP2D6*41, CYP3A5*3 and VKORC1*2. These translate into a high percentage of intermediate (IM) and poor metabolizer (PM) phenotypes for these genes in our population.

Conclusion

Genotyping may be useful to identify patients who are prone to drug toxicity with standard doses of drug therapy in our population. The simplicity and robustness of this PGx panel is highly suitable for use in a clinical laboratory.

Genetic polymorphism of CYP2D6 in patients with systemic lupus erythematosus and systemic sclerosis

Human organism is constantly exposed to harmful exogenous factors (xenobiotics) including drugs and carcinogenic compounds that can induce development of a large number of diseases. The processes of biotransformation in the organism are multidirectional and xenobiotics can be transformed into active or inactive metabolites via the oxidative route. The knowledge of oxidation polymorphism in the course of systemic lupus erythematosus and systemic sclerosis may be helpful in choosing more efficient and safer therapy, particularly in the case of a disease involving various organs and treated with drugs belonging to diverse therapeutic groups. The aim of the study was to evaluate the CYP2D6 polymorphism in the SLE (systemic lupus erythematosus) and SSc (systemic sclerosis) patients and to investigate a possible correlation with disease susceptibility. The study was carried out in 296 patients: 65 patients with SLE, 81 patients with SSc, and 150 healthy volunteers. The CYP2D6 genotypes were analyzed by polymerase chain reaction fragment length polymorphism (PCR-RFLP) method. The relative risk of developing SSc, expressed by the odds ratio, was three-fold higher for persons with the CYP2D6*1/CYP2D6*4 genotype (OR = 2.9; statistically significant difference, p = 0.0002). A statistically significant correlation between the CYP2D6*4 allele prevalence and the risk for developing SSc was found (OR = 1.53; p = 0.047). No effect of the CYP2D6 gene mutations on the incidence of SLE was noted. The obtained results may suggest the influence of CYP2D6*4 gene variants alleles on increased incidence of systemic sclerosis.

CYP2D6 allele distribution in Macedonians, Albanians and Romanies in the Republic of Macedonia

Cytochrome P450 2D6 (CYP2D6) is an enzyme of great importance for the metabolism of clinically used drugs. More than 100 variants of the CYP2D6 gene have been identified so far. The aim of this study was to investigate the allele distribution of CYP2D6 gene variants in 100 individuals of each of the Macedonian, Albanian and Romany population, by genotyping using long range polymerase chain reaction (PCR) and a multiplex single base extension method. The most frequent variants and almost equally distributed in the three groups were the fully functional alleles *1 and *2. The most common non functional allele in all groups was *4 that was found in 22.5% of the Albanians. The most common allele with decreased activity was *41 which was found in 23.0% of the Romany ethnic group, in 11.0% of the Macedonians and in 10.5% of the Albanians. Seven percent of the Albanians, 6.0% of the Romani and 4.0% of the Macedonians were poor metabolizers, while 5.0% of the Macedonians, 1.0% of Albanians and 1.0% of the Romanies were ultrarapid metabolizers. We concluded that the CYP2D6 gene locus is highly heterogeneous in these groups and that the prevalence of the CYP2D6 allele variants and genotypes in the Republic of Macedonia is in accordance with that of other European populations.

Paroxetine markedly increases plasma concentrations of ophthalmic timolol; CYP2D6 inhibitors may increase the risk of cardiovascular adverse effects of 0.5% timolol eye drops

Although ophthalmic timolol is generally well tolerated, a significant fraction of topically administered timolol can be systemically absorbed. We investigated the effect of the strong CYP2D6 inhibitor paroxetine on the pharmacokinetics of timolol after ophthalmic administration. In a four-phase crossover study, 12 healthy volunteers ingested either paroxetine (20 mg) or placebo daily for 3 days. In phases 1-2, timolol 0.1% gel, and in phases 3-4, timolol 0.5% drops were administered to both eyes. Paroxetine increased the plasma concentrations of timolol with both timolol formulations to a similar degree. The geometric mean ratio (95% confidence interval) of timolol peak concentration was 1.53-fold (1.23-1.91) with 0.1% timolol and 1.49-fold (0.94-2.36) with 0.5% timolol, and that of timolol area under the plasma concentration-time curve (AUC) from time 0 to 12 hours was 1.61-fold (1.26- to 2.06-fold) and 1.78-fold (1.21-2.62), respectively. During paroxetine administration, six subjects on 0.5% timolol drops, but none on 0.1% timolol gel, had plasma timolol concentrations exceeding 0.7 ng/ml, which can cause systemic adverse effects in patients at risk. There was a positive correlation between the AUC from time 0 to 13 hours of paroxetine and the placebo phase AUC from time 0 to infinity of timolol after timolol 0.5% drops (P < 0.05), and a nonsignificant trend after timolol 0.1% gel, consistent with the role of CYP2D6 in the metabolism of both agents. In the orthostatic test, heart rate immediately after upright standing was significantly lower (P < 0.05) during the paroxetine phase than during the placebo phase at 1 and 3 hours after 0.5% timolol dosing. In conclusion, paroxetine and other CYP2D6 inhibitors can have a clinically important interaction with ophthalmic timolol, particularly when patients are using 0.5% timolol formulations.

Developing and Evaluating the HRM Technique for Identifying Cytochrome P450 2D6 Polymorphisms

BACKGROUND

Cytochrome P450 2D6 is one of the important enzymes involved in the metabolism of many widely used drugs. Genetic polymorphisms of CYP2D6 can affect its activity. Therefore, an efficient method for identifying CYP2D6 polymorphisms is clinically important.

METHODS

We developed a high-resolution melting (HRM) analysis to investigate CYP2D6 polymorphisms. Genomic DNA was extracted from peripheral blood samples from 71 healthy individuals. All nine exons of the CYP2D6 gene were sequenced before screening by HRM analysis. This method can detect the most genotypes (*1, *2, *4, *10, *14, *21 *39, and *41) of CYP2D6 in Chinese.

RESULTS

All samples were successfully genotyped. The four most common mutant CYP2D6 alleles (*1, *2, *10, and *41) can be genotyped. The single nucleotides polymorphism (SNP) frequencies of 100C > T (rs1065852), 1039C > T (rs1081003), 1661G > C (rs1058164), 2663G > A (rs28371722), 2850C > T (rs16947), 2988G > A (rs28371725), 3181A > G, and 4180G > C (rs1135840) were 58%, 61%, 73%, 1%, 13%, 3%, 1%, 73%, respectively. We identified 100% of all heterozygotes without any errors. The two homozygous genotypes (1661G > C and 4180G > C) can be distinguished by mixing with a known genotype sample to generate an artificial heterozygote for HRM analysis. Therefore, all samples could be identified using our HRM method, and the results of HRM analysis are identical to those obtained by sequencing. Our method achieved 100% sensitivity, specificity, positive prediction value and negative prediction value.

CONCLUSION

HRM analysis is a nongel resolution method that is faster and less expensive than direct sequencing. Our study shows that it is an efficient tool for typing CYP2D6 polymorphisms.

Common CYP2D6 polymorphisms affecting alternative splicing and transcription: long-range haplotypes with two regulatory variants modulate CYP2D6 activity

Cytochrome P450 2D6 (CYP2D6) is involved in the metabolism of 25% of clinically used drugs. Genetic polymorphisms cause substantial variation in CYP2D6 activity and serve as biomarkers guiding drug therapy. However, genotype-phenotype relationships remain ambiguous except for poor metabolizers carrying null alleles, suggesting the presence of yet unknown genetic variants. Searching for regulatory CYP2D6 polymorphisms, we find that a SNP defining the CYP2D6*2 allele, rs16947 [R296C, 17-60% minor allele frequency (MAF)], previously thought to convey normal activity, alters exon 6 splicing, thereby reducing CYP2D6 expression at least 2-fold. In addition, two completely linked SNPs (rs5758550/rs133333, MAF 13-42%) increase CYP2D6 transcription more than 2-fold, located in a distant downstream enhancer region (>100 kb) that interacts with the CYP2D6 promoter. In high linkage disequilibrium (LD) with each other, rs16947 and the enhancer SNPs form haplotypes that affect CYP2D6 enzyme activity in vivo. In a pediatric cohort of 164 individuals, rs16947 alone (minor haplotype frequency 28%) was associated with reduced CYP2D6 metabolic activity (measured as dextromethorphan/metabolite ratios), whereas rs5758550/rs133333 alone (frequency 3%) resulted in increased CYP2D6 activity, while haplotypes containing both rs16947 and rs5758550/rs133333 were similar to the wild-type. Other alleles used in biomarker panels carrying these variants such as CYP2D6*41 require re-evaluation of independent effects on CYP2D6 activity. The occurrence of two regulatory variants of high frequency and in high LD, residing on a long haplotype, highlights the importance of gene architecture, likely shaped by evolutionary selection pressures, in determining activity of encoded proteins.

Development of a tetraplex PCR assay for CYP2D6 genotyping in degraded DNA samples

CYP2D6 polymorphism analysis is gaining increasing interest in forensic pharmacogenetics. Nevertheless, DNA recovered from forensic samples could be of poor quality and not suitable for long polymerase chain reaction required to type CYP2D6 gene prior to SNaPshot minisequencing analysis performed to define alleles with different enzymatic activity. We developed and validated following the guidelines of the Scientific Working Group on DNA Analysis Methods a tetraplex PCR yielding four amplicons of 597, 803, 1142, and 1659 bp encompassing the entire CYP2D6 gene to analyze eleven SNP positions by SNaPshot minisequencing. Concordance, sensitivity, and specificity were assessed. The method, applied to thirty-two forensic samples failed to amplify with long PCR, allowed the amplification of CYP2D6 gene in 62.5% of degraded samples. The new tetraplex PCR appears a suitable method for CYP2D6 analysis in forensic pharmacogenetics.

A clinical tool for reducing central nervous system depression among neonates exposed to codeine through breast milk

Background

Neonates are commonly exposed to maternal codeine through breast milk. Central Nervous System (CNS) depression has been reported in up to 24% of nurslings following codeine exposure. In 2009, we developed guidelines to improve the safety of codeine use during breastfeeding based on previously established pharmacogenetic and clinical risk factors. The primary objective of this study was to prospectively evaluate the effectiveness of these guidelines in ensuring neonatal safety.

Methods and Findings

Women taking codeine for pain following caesarean section were given safety guidelines, including advice to use the lowest codeine dose for no longer than four days and to switch to a non-opioid when possible. Mothers provided a saliva sample for analysis of genes involved in opioid disposition, metabolism and response. A total of 238 consenting women participated. Neonatal sedation was reported in 2.1% (5/238) of breastfeeding women taking codeine according to our safety guidelines. This rate was eight fold lower than that reported in previous prospective studies. Women reporting sedated infants were taking codeine for a significantly longer period of time (4.80±2.59 days vs. 2.52±1.58 days, p = 0.0018). While following the codeine safety guidelines, mothers were less likely to supplement with formula, reported lower rates of sedation in themselves and breastfed more frequently throughout the day when compared to previously reported rates. Genotyping analysis of cytochrome p450 2D6 (CYP2D6), uridine-diphosphate glucuronosyltransferase (UGT) 2B7, p-glycoprotein (ABCB1), the mu-opioid receptor (OPRM1) and catechol-o-demethyltransferase (COMT) did not predict codeine response in breastfeeding mother/infant pairs when following the safety guidelines.

Conclusions

The only cases of CNS depression occurred when the length of codeine use exceeded the guideline recommendations. Neonatal safety of codeine can be improved using evidence-based guidelines, even in those deemed by genetics to be at high risk for toxicity.

Alternative reliable method for cytochrome P450 2D6 poor metabolizers genotyping

High-resolution melting curve analysis (HRM) of polymerase chain reaction (PCR) amplicons has been described as a fast, cheap, and reliable closed-tube method of genotyping with no need for labeled primers or labeled probes. We adapted this melting analysis assay for the detection of the most common nonfunctional alleles of cytochrome P-450 (CYP) 2D6 in the Caucasian population that affect the metabolism of many commonly used drugs. We used this method to genotype 91 patients under paroxetine therapy. The presence and the constitution of the most common single-nucleotide polymorphisms (1846G>A, 2988G>A, 100C>T, 2549delA, 2615_2617delAAG, and 1707delT) in poor and intermediate metabolizers from the Caucasian population were detected in short amplicons (≤148 bp). After fluorescence normalization, the wild-type, homozygous, and heterozygous samples were easily distinguishable from each other by their specific melting curve shape. A total of 92.6% of the 1846G>A heterozygotes, 96% of the 100C>T heterozygotes, and 100% of the 2988G>A, 2549delA, 2615_2617delAAG, and 1707delT heterozygotes have been correctly distinguished from the wild types. One hundred percent of all the homozygotes in this group of patients have been detected without any error. HRM of short amplicons is a simple tool for effective, rapid, and reliable CYP2D6 genotyping that does not require real-time PCR, labeled probes, processing or any separations after PCR. The reaction is performed in a closed-tube system and is highly specific and sensitive. We proved that this technique is highly reliable for use in routine diagnostics.

Unexpectedly high blood concentration of bisoprolol after an incorrect prescription: A case report

An elderly person died of uncontrolled bradycardia in a hospital. The doctor had prescribed 1.35 mg of bisoprolol fumarate orally, but a nurse mistakenly gave the patient 10 mg of the drug 9 hours prior to her death. Bisoprolol was detected in her blood by liquid chromatography-mass spectrometry at a concentration of 176 ng/mL. Even if the patient had chronic heart failure, this concentration is double the expected value. This patient was found to have a mutation within cytochrome P2D6, with thymidine substituted for cytosine at position 100 and cytosine for guanine at position 4180, causing proline to serine and threonine to serine amino acid substitutions. This mutation in the intermediate metabolizer allele reportedly reduces enzyme activity by half. However, in addition to the type of cytochrome P450 allelic variant, the amount of enzyme product influences metabolism of this drug. In this case, the high blood concentration of bisoprolol was only partly attributable to an error in prescription; its concentration was inexplicably high.

Apnea and oxygen desaturations in children treated with opioids after adenotonsillectomy for obstructive sleep apnea syndrome: a prospective pilot study

BACKGROUND

Recent case reports have alerted the medical community of fatality in children receiving codeine after tonsillectomy and/or adenoidectomy for obstructive sleep apnea syndrome.

OBJECTIVE

The objective of this study was to compare the rates of oxygen desaturation before and after adenotonsillectomy in children with obstructive sleep apnea syndrome (OSAS), and to examine the relationship between cytochrome P450 2D6 (CYP2D6) genotype and respiratory events.

STUDY DESIGN

This was a prospective observational study.

METHODS

Twenty-six children with OSAS (mean age 78 months, range 1.8-17 years) who underwent adenotonsillectomy were studied. CYP2D6 genotype was characterized in 21 of these children. The primary endpoints of the study were the change in the rate of desaturation and in the nadir oxygen saturation values before and in the first 24 hours after surgery as measured by pulse oximetry.

RESULTS

Twenty-two children received codeine and four were managed with hydrocodone. There was no post-operative improvement in the mean rate of desaturation (1.84 ± 1.45/hour pre-operative vs 2.97 ± 3.3/hour post-operative; p = 0.119; 95% CI -2.56, 0.313), or the post-operative nadir of oxygen saturation (85.2 ± 5.8% pre-operative vs 84.0 ± 6.8% post-operative; p = 0.632; 95% CI -3.00, 4.84) on the night after surgery. Prior to surgery, six children had an oxygen saturation nadir <80%, while post-surgery, the number increased to eight children. Ten children improved their parameters after surgery. CYP2D6 genotype by itself did not predict the changes in desaturation or nadir.

CONCLUSION

Post-operative use of opioids following OSAS may not be safe for all children. It is conceivable that if the child is among the significant proportion that experiences increased oxygen desaturations, the CNS depressing effects of codeine or hydrocodone and their respectively potent morphine or hydromorphone metabolites can further compromise respiratory drive. Larger studies are needed to investigate the potential contribution of CYP2D6 genotype.

Label-free genotyping of cytochrome P450 2D6*10 using ligation-mediated strand displacement amplification with DNAzyme-based chemiluminescence detection

Genotyping of cytochrome P450 monooxygenase 2D6*10 (CYP2D6*10) plays an important role in pharmacogenomics, especially in clinical drug therapy of Asian populations. This work reported a novel label-free technique for genotyping of CYP2D6*10 based on ligation-mediated strand displacement amplification (SDA) with DNAzyme-based chemiluminescence detection. Discrimination of single-base mismatch is firstly accomplished using DNA ligase to generate a ligation product. The ligated product then initiates a SDA reaction to produce aptamer sequences against hemin, which can be probed by chemiluminescence detection. The proposed strategy is used for the assay of CYP2D6*10 target and the genomic DNA. The results reveal that the proposed technique displays chemiluminescence responses in linear correlation to the concentrations of DNA target within the range from 1 pM to 1 nM. A detection limit of 0.1 pM and a signal-to-background ratio of 57 are achieved. Besides such high sensitivity, the proposed CYP2D6*10 genotyping strategy also offers superb selectivity, great robustness, low cost and simplified operations due to its label-free, homogeneous, and chemiluminescence-based detection format. These advantages suggest this technique may hold considerable potential for clinical CYP2D6*10 genotyping and association studies.

Population pharmacokinetic/pharmacogenetic model for optimization of efavirenz therapy in Caucasian HIV-infected patients

Despite extensive clinical experience with efavirenz (EFV), unpredictable interindividual variabilities in efficacy and toxicity remain important limitations associated with the use of this antiretroviral. The purpose of this study was to determine the factors affecting EFV pharmacokinetics and to develop a pharmacokinetic/pharmacogenetic (PK/PG) model in a Caucasian population of HIV-infected patients. In total, 869 EFV plasma concentrations from 128 HIV-infected patients treated with EFV were quantitatively assessed using a validated high-performance liquid chromatography technique. All patients were genotyped for 90 single nucleotide polymorphisms (SNPs) in genes coding for proteins involved in the metabolism and transport of EFV, using a MassArray platform provided by Sequenom. The influence of these polymorphisms on EFV pharmacokinetics and the effects of demographic, clinical, biochemical, lifestyle, and concurrent drug covariates were evaluated. Plasma concentrations were fitted by a one-compartment model, with first-order absorption and elimination using nonlinear mixed-effect modeling (NONMEM program). The CYP2B6*6 allele, multidrug resistance-associated protein 4 (MRP4) 1497C → T, and gamma-glutamyltranspeptidase (GGT) were identified as major factors influencing the apparent EFV oral clearance (CL/F), reducing the initial interindividual variability by 54.8%, according to the model CL/F = (12.2 - 0.00279 · GGT) · 0.602(CYP2B6*6 [G/T]) · 0.354(CYP2B6*6 [T/T]) · 0.793(MRP4 1497C → T), where CYP2B6*6 [G/T], CYP2B6*6 [T/T], and MRP4 1497C → T take values of 0 or 1 to indicate the absence or presence of polymorphisms. The detailed genetic analysis conducted in this study identified two of 90 SNPs that significantly impacted CL/F, which might indicate that the remaining SNPs analyzed do not influence this PK parameter, at least in Caucasian populations with characteristics similar to those of our study population.

Inhibition of cytochrome P450 3A by clarithromycin uniformly affects the pharmacokinetics and pharmacodynamics of oxycodone in young and elderly volunteers

The aim of this study was to investigate the effect of the cytochrome P450 3A4 inhibitor clarithromycin on the pharmacokinetics and pharmacodynamics of oral oxycodone in young and elderly subjects. Ten young and 10 elderly healthy subjects participated in this placebo-controlled, randomized, 2-phase crossover study. Subjects took clarithromycin 500 mg or placebo twice daily for 5 days. On day 4, subjects ingested an oral dose of 10 mg oxycodone. Plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 hours, and pharmacological response for 12 hours. Clarithromycin decreased the apparent clearance of oxycodone by 53% in young and 48% in elderly subjects (P < 0.001) and prolonged its elimination half-life. The mean area under the plasma concentration-time curve (AUC0-∞) of oxycodone was increased by 2.0-fold (range, 1.3-fold to 2.7-fold) (P < 0.001) in young and 2.3-fold (range, 1.1-fold to 3.8-fold) (P < 0.001) in elderly subjects. The formation of noroxycodone was decreased by 74% in young and 71% in elderly subjects (P < 0.001). The ratio of AUC0-∞ of oxycodone during the clarithromycin phase compared with the one with placebo did not differ between the age groups. Clarithromycin did not alter the pharmacological response to oxycodone. Clarithromycin increased the exposure to oral oxycodone, but the magnitude of this effect was not age related. Although the pharmacological response to oxycodone was not significantly influenced by clarithromycin, dose reductions may be necessary in the most sensitive patients to avoid adverse effects when oxycodone is used concomitantly with clarithromycin.

Genetically polymorphic OCT1: another piece in the puzzle of the variable pharmacokinetics and pharmacodynamics of the opioidergic drug tramadol

We investigated whether tramadol or its active metabolite, O-desmethyltramadol, are substrates of the organic cation transporter OCT1 and whether polymorphisms in OCT1 affect tramadol and O-desmethyltramadol pharmacokinetics. Tramadol showed high permeability through parallel artificial membrane permeability assays (PAMPAs). Tramadol uptake in HEK293 cells did not change after OCT1 overexpression, and the concentrations of tramadol in the plasma of healthy volunteers were independent of their OCT1 genotypes. In contrast, O-desmethyltramadol showed low membrane permeability, and OCT1 overexpression increased O-desmethyltramadol uptake 2.4-fold. This increase in uptake was reversed by OCT1 inhibitors and absent when loss-of-function OCT1 variants were overexpressed. Volunteers carrying loss-of-function OCT1 polymorphisms had significantly higher plasma concentrations of O-desmethyltramadol (P = 0.002, n = 41) and significantly prolonged miosis, a surrogate marker of opioidergic effects (P = 0.005, n = 24). In conclusion, polymorphisms in OCT1 influence the pharmacokinetics of O-desmethyltramadol, presumably by affecting its uptake into liver cells, and thus may modulate the efficacy of tramadol treatment.

Grapefruit juice enhances the exposure to oral oxycodone

Grapefruit juice alters the concentrations of many CYP3A substrates. The objective of this study was to examine the effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of oral oxycodone in a randomized cross-over study with two phases at an interval of 4 weeks. Twelve healthy volunteers ingested 200 ml of grapefruit juice or water t.i.d. for 5 days. An oral dose of oxycodone hydrochloride 10 mg was administered on day 4. Oxycodone, noroxycodone, oxymorphone and noroxymorphone concentrations were analysed from the plasma samples for 48 hr and behavioural and analgesic effects were recorded for 12 hr. Grapefruit juice increased the mean area under the oxycodone concentration-time curve (AUC(0-∞) ) by 1.7-fold (p<0.001), the peak plasma concentration by 1.5-fold (p<0.001) and the half-life of oxycodone by 1.2-fold (p<0.001) as compared to the water. The metabolite-to-parent AUC(0-∞) ratios (AUC(m)/AUC(p) ) of noroxycodone and noroxymorphone decreased by 44% (p<0.001) and 45% (p<0.001), respectively. Oxymorphone AUC(0-∞) increased by 1.6-fold (p<0.01) after grapefruit juice, but the AUC(m)/AUC(p) remained unchanged. Pharmacodynamic changes were modest and only self-reported performance significantly impaired after grapefruit juice. Analgesic effects were not influenced. Grapefruit juice inhibited the CYP3A4-mediated first-pass metabolism of oxycodone, decreased the formation of noroxycodone and noroxymorphone and increased that of oxymorphone. We conclude that dietary consumption of grapefruit products may increase the concentrations and effects of oxycodone in clinical use.

Exposure to oral oxycodone is increased by concomitant inhibition of CYP2D6 and 3A4 pathways, but not by inhibition of CYP2D6 alone

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Oxycodone is an opioid analgesic that is metabolized mainly in the liver by cytochrome P450 (CYP) 2D6 and 3A4 enzymes. So far, the effects of CYP2D6 or CYP3A4 inhibitors on the pharmacokinetics of oxycodone in humans have not been systematically studied.

WHAT THIS STUDY ADDS

Drug interactions arising from CYP2D6 inhibition most likely have minor clinical importance for oral oxycodone. When both of CYP2D6 and CYP3A4 pathways are inhibited, the exposure to oral oxycodone is increased substantially.

AIM

The aim of this study was to find out whether the inhibition of cytochrome P450 2D6 (CYP2D6) with paroxetine or concomitant inhibition of CYP2D6 and CYP3A4 with paroxetine and itraconazole, altered the pharmacokinetics and pharmacological response of orally administered oxycodone.

METHODS

A randomized placebo-controlled cross-over study design with three phases was used. Eleven healthy subjects ingested 10 mg of oral immediate release oxycodone on the fourth day of pre-treatment with either placebo, paroxetine (20 mg once daily) or paroxetine (20 mg once daily) and itraconazole (200 mg once daily) for 5 days. The plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 h, and pharmacological (analgesic and behavioural) effects were evaluated.

RESULTS

Paroxetine alone reduced the area under concentration-time curve (AUC(0,0-48 h)) of the CYP2D6 dependent metabolite oxymorphone by 44% (P < 0.05), but had no significant effects on the plasma concentrations of oxycodone or its pharmacological effects when compared with the placebo phase. When both oxidative pathways of the metabolism of oxycodone were inhibited with paroxetine and itraconazole, the mean AUC(0,infinity) of oxycodone increased by 2.9-fold (P < 0.001), and its C(max) by 1.8-fold (P < 0.001). Visual analogue scores for subjective drug effects, drowsiness and deterioration of performance were slightly increased (P < 0.05) after paroxetine + itraconazole pre-treatment when compared with placebo.

CONCLUSIONS

Drug interactions arising from CYP2D6 inhibition most likely have minor clinical importance for oral oxycodone if the function of the CYP3A4 pathway is normal. When both CYP2D6 and CYP3A4 pathways are inhibited, the exposure to oral oxycodone is increased substantially.

Evolution of detoxifying systems: the role of environment and population history in shaping genetic diversity at human CYP2D6 locus

OBJECTIVE

The transition from food collection to food production (FP) modified the nature of selective pressures, and several studies illustrate that genetic adaptation to new lifestyle has occurred in humans since the agricultural revolution. Here we test the hypothesis that high levels of genetic variation at CYP2D6, a locus coding for a detoxifying enzyme of the cytochrome P450 complex, reflect this change.

METHODS

We compared DNA sequences and predicted the levels of enzyme activity across 10 African, Asian and European populations, six of which currently rely on hunting and gathering (HG) while four on food production (FP).

RESULTS AND CONCLUSION

HG and FP showed similar levels of CYP2D6 diversity, but displayed different substitution patterns at coding DNA sites possibly related to selective differences. Comparison with variation at presumably neutral independent loci confirmed this finding, despite the confounding effects of population history, resulting in higher overall variation in Africans than in Eurasians. The differences between HG and FP populations suggest that new lifestyle and dietary habits acquired in the transition to agriculture affected the variation pattern at CYP2D6, leading to an increase in FP populations of the frequency of alleles that are associated with a slower rate of metabolism. These alleles reached a balanced co-existence with other important and previously selected variants. We suggest that the pronounced substrate-dependent activity of most of these enzymes expanded the spectrum of the metabolic response.

CYP2D6 genotyping in breast cancer patients by liquid chromatography-electrospray ionization mass spectrometry

The application of cytochrome P450 2D6 (CYP2D6) genotyping to allow a personalized treatment approach for breast cancer patients undergoing endocrine therapy has been repeatedly discussed. However, the actual clinical relevance of the CYP2D6 genotype in the endocrine treatment of breast cancer still remains to be elucidated. A major prerequisite for the successful and valid evaluation of the CYP2D6 genotype with regard to its pharmacokinetic and clinical relevance is the availability of a comprehensive, accurate and cost-effective CYP2D6 genotyping strategy. Herein we present a CYP2D6 genotyping assay employing polymerase chain reaction (PCR)-ion pair reversed-phase high-performance liquid chromatography-electrospray ionization time-of-flight mass spectrometry (ICEMS). The genotyping strategy involves the simultaneous amplification of nine variable regions within the CYP2D6 gene by a two-step PCR protocol and the direct analysis of the generated PCR amplicons by ICEMS. The nucleotide composition profiles generated by ICEMS enable the differentiation of 37 of the 80 reported CYP2D6 alleles. The assay was applied to type the CYP2D6 gene in 199 Austrian individuals including 106 breast cancer patients undergoing tamoxifen treatment. The developed method turned out to be a highly applicable, robust and cost-effective approach, enabling an economical CYP2D6 testing for large patient cohorts.

Miconazole oral gel increases exposure to oral oxycodone by inhibition of CYP2D6 and CYP3A4

Our aim was to assess the effect of miconazole oral gel on the pharmacokinetics of oral oxycodone. In an open crossover study with two phases, 12 healthy volunteers took a single oral dose of 10 mg of immediate-release oxycodone with or without thrice-daily 85-mg miconazole oral gel treatment. The plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 h. Pharmacological effects of oxycodone were recorded for 12 h. Pharmacokinetic parameters were compared by use of the geometric mean ratios (GMRs) and their 90% confidence interval (CIs). Pretreatment with miconazole oral gel caused a strong inhibition of the CYP2D6-dependent metabolism and moderate inhibition of the CYP3A4-dependent metabolism of oxycodone. The mean area under the concentration-time curve (AUC) from time zero to infinity (AUC(0-∞); GMR, 1.63; 90% CI, 1.48 to 1.79) and the peak concentration of oxycodone (GMR, 1.31; 90% CI, 1.19 to 1.44) were increased. The AUC of the CYP2D6-dependent metabolite oxymorphone was greatly decreased (GMR, 0.17; 90% CI, 0.09 to 0.31) by miconazole gel, whereas that of the CYP3A4-dependent metabolite noroxycodone was increased (GMR, 1.30; 90% CI, 1.15 to 1.47) by miconazole gel. Differences in the pharmacological response to oxycodone between phases were insignificant. Miconazole oral gel increases the exposure to oral oxycodone, but the clinical relevance of the interaction is moderate. Miconazole oral gel produces a rather strong inhibitory effect on CYP2D6, which deserves further study.

Will a new genotyping test help the clinician predict response to antidepressant drugs?

OBJECTIVE

The aim of this paper is to evaluate the accuracy of a new genotyping test (Antidepressant PredictAR) in assigning patients as likely 'poor', 'rapid' or 'normal' metabolizers of antidepressant drugs.

METHOD

Eighty-nine patients were clinically assigned (on the basis of their historical response to antidepressant drugs) as 'poor', 'rapid' or 'normal' metabolizers and comparison was then made to their test-based 2D6 and C19 genotyping status reports.

RESULTS

The overall capacity of the test to allocate patients to four differing phenotypic categories reporting for the genotyping test was not significant in relation to either C19 or 2D6 analyses. However, the C19 test did appear to have some capacity to identify rapid metabolizers, and we note how we then sought to manage such patients clinically.

CONCLUSIONS

The test may have some capacity to identify patients with a rapid metabolizing profile. Any further advantages were not identified by this study, whether reflecting methodological and/or assay limitations.

Oxycodone concentrations are greatly increased by the concomitant use of ritonavir or lopinavir/ritonavir

PURPOSE

this study aimed to investigate the effect of antivirals ritonavir and lopinavir/ritonavir on the pharmacokinetics and pharmacodynamics of oral oxycodone, a widely used opioid receptor agonist used in the treatment of moderate to severe pain.

METHODS

a randomized crossover study design with three phases at intervals of 4 weeks was conducted in 12 healthy volunteers. Ritonavir 300 mg, lopinavir/ritonavir 400/100 mg, or placebo b.i.d. for 4 days was given to the subjects. On day 3, 10 mg oxycodone hydrochloride was administered orally. Plasma concentrations of oxycodone, noroxycodone, oxymorphone, and noroxymorphone were determined for 48 h. Pharmacokinetic parameters were calculated with standard noncompartmental methods. Behavioral effects and experimental cold pain analgesia were assessed for 12 h. ANOVA for repeated measures was used for statistical analysis.

RESULTS

ritonavir and lopinavir/ritonavir increased the area under the plasma concentration-time curve of oral oxycodone by 3.0-fold (range 1.9- to 4.3-fold; P <0.001) and 2.6-fold (range 1.9- to 3.3-fold; P <0.001). The mean (± SD) elimination half-life increased after ritonavir and lopinavir/ritonavir from 3.6 ± 0.6 to 5.6 ± 0.9 h (P <0.001) and 5.7 ± 0.9 h (P <0.001), respectively. Both ritonavir (P <0.001) and lopinavir/ritonavir (P <0.05) increased the self-reported drug effect of oxycodone.

CONCLUSIONS

ritonavir and lopinavir/ritonavir greatly increase the plasma concentrations of oral oxycodone in healthy volunteers and enhance its effect. When oxycodone is used clinically in patients during ritonavir and lopinavir/ritonavir treatment, reductions in oxycodone dose may be needed to avoid opioid-related adverse effects.

Elucidation of CYP2D6 genetic diversity in a unique African population: implications for the future application of pharmacogenetics in the Xhosa population

Genetic variation of the CYP2D6 gene has been associated with altered drug metabolism; however, limited studies have investigated CYP2D6 sequence diversity in African populations. We devised a CYP2D6 genotyping strategy to analyse the South African Xhosa population and genotype a Xhosa schizophrenia cohort, as CYP2D6 metabolises many antipsychotics and antidepressants. The entire CYP2D6 gene locus was sequenced in 15 Xhosa control individuals and the data generated were used to design a comprehensive genotyping strategy. Over 25 CYP2D6 alleles were genotyped in Xhosa controls and Xhosa schizophrenia patients using long-range PCR, DNA sequencing and single nucleotide primer extension analysis. Bioinformatic algorithms were used to predict the functional consequences of relevant mutations and samples were assigned CYP2D6 activity scores. A unique allele distribution was revealed and two rare novel alleles, CYP2D6*73 and CYP2D6*74, were identified. No significant differences in allele frequencies were detected between Xhosa controls and schizophrenia patients. This study provides i) comprehensive data on a poorly characterised population, ii) a valuable CYP2D6 genotyping strategy and iii) due to their unique genetic profile, provides the basis for pharmacogenetic intervention for Xhosa individuals.

Immunosuppressive cytokine gene polymorphisms and outcome after related and unrelated hematopoietic cell transplantation in a chinese population

Cytokine gene polymorphisms can affect the outcome of allogeneic hematopoietic stem cell transplantation. We analyzed 6 single nucleotide polymorphisms in 3 immunosuppressive cytokine genes, TGFβ1-509(C>T), +869(T>C), TGFβ1 receptor II (TGFβ1RII) +1167(C>T, codon389 AAC/AAT), and IL-10-1082(A>G), -819(T>C), -592(A>C), in a cohort of 138 pairs of recipients and their unrelated donors and a second cohort of 102 pairs of recipients and their HLA-identical sibling donors. TGFβ1-509 T/T genotype in the donors or T allele-positivity in the recipients was associated with a significant protective effect against acute graft-versus-host disease (aGVHD) and grades II-IV aGVHD in the unrelated transplantation cohort. In the combined cohort, multivariate analysis confirmed that donors with the TGFβ1-509 T/T genotype also conferred protection against the risk of aGVHD and grades II-IV aGVHD. In both the unrelated transplantation cohort and the sibling transplantation cohort, the IL-10-819 C/C and -592 C/C genotypes in either recipients or donors were significantly associated with a higher incidence of aGVHD. In the combined cohort, the IL-10 promoter haplotype polymorphisms at positions -1082, -819, and -592 influenced the occurrence of aGVHD and death in remission. Recipients without the A-T-A haplotype or those transplanted from donors without the A-T-A haplotype had a higher incidence of aGVHD than those who were A-T-A homozygotes or heterozygotes. Estimates for death in remission showed a clear advantage for recipients transplanted from donors with the A-T-A haplotype. In multivariate analysis, recipients without the A-T-A IL-10 haplotype had a higher risk of aGVHD (relative risk [RR] = 0.764; 95% confidence interval [CI]: 0.460-1.269; P = .096) and grades II-IV aGVHD (RR = 0.413; 95% CI: 0.245-0.697; P = .001). These results provide the first report of an association between TGFβ1, TGFβ1RII, and IL-10 polymorphic features and outcome of allo-HSCT in a Chinese population, and suggest an interaction between TGFβ1-509 genotypes and IL-10 promoter haplotype polymorphisms at positions -1082, -819, and -592 and the risk of aGVHD.