Study on genotype and phenotype of novel CYP2D6 variants using pharmacokinetic and pharmacodynamic models with metoprolol as a substrate drug.

To investigate the pharmacokinetic and pharmacodynamic profiles of volunteers carrying CYP2D6 genotypes with unknow metabolic phenotypes, a total of 22 volunteers were recruited based on the sequencing results. Peripheral blood and urine samples were collected at specific time points after oral administration of metoprolol. A validated high-performance liquid chromatography (HPLC) method was used to determine the concentrations of metoprolol and α-hydroxymetoprolol. Blood pressure and electrocardiogram were also monitored. The results showed that the main pharmacokinetic parameters of metoprolol in CYP2D6*1/*34 carriers are similar to those in CYP2D6*1/*1 carriers. However, in individuals carrying the CYP2D6*10/*87, CYP2D6*10/*95, and CYP2D6*97/*97 genotypes, the area under the curve (AUC) and half-life (t1/2) of metoprolol increased by 2-3 times compared to wild type. The urinary metabolic ratio of metoprolol in these genotypes is consistent with the trends observed in plasma samples. Therefore, CYP2D6*1/*34 can be considered as normal metabolizers, while CYP2D6*10/*87, CYP2D6*10/*95, and CYP2D6*97/*97 are intermediate metabolizers. Although the blood concentration of metoprolol has been found to correlate with CYP2D6 genotype, its blood pressure-lowering effect reaches maximum effectiveness at a reduction of 25 mmHg. Furthermore, P-Q interval prolongation and heart rate reduction are not positively correlated with metoprolol blood exposure. Based on the pharmacokinetic-pharmacodynamic model, this study clarified the properties of metoprolol in subjects with novel CYP2D6 genotypes and provided important fundamental data for the translational medicine of this substrate drug.

Chronic Pain Management in a CYP2D6 Poor Metabolizer: A Case Report for Oxycodone.

The objective of this case report is to illustrate pharmacogenomics (PGx)-guided oxycodone treatment, given the conflicting data on the analgesic response from oxycodone in Cytochrome P450 (CYP)2D6 poor metabolizers (PMs). PGx-guided therapy can help improve treatment outcomes. This case report describes a 58-year-old patient who was prescribed oxycodone for chronic pain management. The patient presented with a history of inadequate pain control despite analgesic treatment with oxycodone (morphine milliequivalent [MME] = 22.5). Pharmacogenetic testing revealed that the patient was a CYP2D6 Poor Metabolizer (PM), which may shed light on the observed lack of analgesic response to oxycodone. The clinical pharmacist recommended switching to an alternative opioid not metabolized via the CYP2D6 pathway. The patient was subsequently switched to hydromorphone (MME = 16), resulting in improved pain control and fewer side effects. The newer hydromorphone dose accounted for a 30% MME dose reduction. The patient's initial average and worst pain score were 7 and 9 out of 10, respectively, per the numeric rating scale (NRS). Upon follow-up with the patient in two weeks, her average and worst pain scores improved to 3 and 3.5 out of 10, respectively, per the NRS. Further PGx testing results led to an overall positive outcome, such as her willingness to participate in physical therapy as a result of improved pain scores. This case highlights the importance of considering individual variability in drug metabolism when prescribing medications, particularly opioids such as oxycodone, to ensure optimal therapeutic outcomes and minimize the risk of adverse events in CYP2D6 PMs.

The genomic landscape of CYP2D6 variation in the Indian population.

Aim: The CYP2D6 gene is highly polymorphic, causing large interindividual variability in the metabolism of several clinically important drugs. Materials & methods: The authors investigated the diversity and distribution of CYP2D6 alleles in Indians using whole genome sequences (N = 1518). Functional consequences were assessed using pathogenicity scores and molecular dynamics simulations. Results: The analysis revealed population-specific CYP2D6 alleles (*86, *7, *111, *112, *113, *99) and remarkable differences in variant and phenotype frequencies with global populations. The authors observed that one in three Indians could benefit from a dose alteration for psychiatric drugs with accurate CYP2D6 phenotyping. Molecular dynamics simulations revealed large conformational fluctuations, confirming the predicted reduced function of *86 and *113 alleles. Conclusion: The findings emphasize the utility of comprehensive CYP2D6 profiling for aiding precision public health.

Influence of CYP2D6 Metabolizer Status on Risperidone and Paliperidone Tolerability in Children and Adolescents.

Background: Risperidone and, to a lesser extent, paliperidone are metabolized by CYP2D6; however, there are limited data related to variation in CYP2D6 phenotypes and the tolerability of these medications in children and adolescents. Furthermore, the impact of CYP2D6 on the association of risperidone and paliperidone with hyperprolactinemia in youth is not well understood. Methods: A retrospective chart review was performed in psychiatrically hospitalized children and adolescents prescribed risperidone (n = 263, age = 3-18 years, mean age = 13 ± 3 years, 49% female) or paliperidone (n = 124, age = 5-18 years, mean age = 15 ± 2 years, 44% female) who had CYP2D6 genotyping performed as part of routine care. CYP2D6 phenotypes were determined based on Clinical Pharmacogenetics Implementation Consortium guidelines and CYP2D6 inhibitors causing phenoconversion. Adverse effects were obtained from a review of the electronic health record, and patients were selected, in part, to enrich non-normal metabolizers. Results: Among risperidone-treated patients, 45% experienced an adverse effect, whereas 36% of paliperidone-treated patients experienced adverse effects. Discontinuation of risperidone due to lack of efficacy was more frequent in the CYP2D6 normal metabolizers and ultrarapid metabolizers compared with intermediate metabolizers (IMs) and phenoconverted poor metabolizers (pPMs) (54.5% vs. 32.7%, p < 0.001). Discontinuation due to weight gain was more common among risperidone- than paliperidone-treated patients (17% vs. 7%, p = 0.011). Among those taking paliperidone, CYP2D6 was associated with discontinuation due to side effects (p = 0.008), and youth with slower CYP2D6 metabolism (i.e., pPMs and IMs) were more likely to discontinue. Hyperprolactinemia was found in 10% of paliperidone-treated patients and 5% of risperidone-treated patients, and slower CYP2D6 metabolizers required higher risperidone doses to cause hyperprolactinemia (p = 0.011). Conclusions: CYP2D6 phenotype is associated with discontinuation of risperidone due to lack of efficacy and the dose of risperidone that induced hyperprolactinemia, as well as discontinuation of paliperidone due to adverse effects. Future studies should evaluate exposure-response and toxicity relationships in risperidone- and paliperidone-treated youth.

Pharmacogenetic Factors Influence Escitalopram Pharmacokinetics and Adverse Events in Youth with a Family History of Bipolar Disorder: A Preliminary Study.

Introduction: Escitalopram is an effective and generally well-tolerated antidepressant, but children of parents with bipolar disorder (BD) may be at increased risk for adverse events associated with antidepressants, including increased irritability, restlessness, impulsivity, and manic symptoms. This risk may be influenced by polymorphisms in genes encoding cytochrome P450 enzymes (CYP2C19 or CYP2D6), the serotonin transporter (SLC6A4), and the serotonin receptor 2A subtype (HTR2A). We explored whether gene-drug interactions influence the emergence of adverse events in depressed and/or anxious youth with a family history of BD. Materials and Methods: Children and adolescents aged 12-17 years with a first-degree relative with bipolar I disorder were treated with escitalopram and monitored for adverse effects, underwent pharmacogenetic testing, and provided serum escitalopram levels. Emergence of adverse events was determined by study clinicians, and symptoms were tracked using the Treatment-Emergent Activation and Suicidality Assessment Profile (TEASAP) and Pediatric Adverse Events Rating Scale. Clinical Pharmacogenetics Implementation Consortium guidelines were used to determine CYP2C19 and CYP2D6 phenotypes. Results: Slower CYP2C19 metabolizers had greater dose-normalized 24-hour area under the curve (AUC0-24; p = 0.025), trough concentrations (Ctrough; p = 0.013), and elimination half-lives (t1/2; p < 0.001). CYP2D6 phenotype was not significantly associated with any pharmacokinetic parameter. Slower CYP2D6 metabolizers had increased TEASAP akathisia (p = 0.015) scores. HTR2A A/A and A/G genotypes were associated with increased TEASAP "self-injury, suicidality, and harm to others" subscale scores (p = 0.017). Escitalopram maximum concentration, AUC0-24, CYP2C19 phenotype, and SLC6A4 genotype were not associated with adverse events. Conclusions: CYP2C19 phenotype influences escitalopram pharmacokinetics whereas CYP2D6 phenotype does not. Slower CYP2D6 metabolism was associated with increased akathisia, and HTR2A A/A or A/G genotypes were associated with increased risk of self-harm or harm to others. Larger cohorts are needed to identify associations between genetic test results and antidepressant-associated adverse events. Trial Registration: ClinicalTrials.gov identifier: NCT02553161.

High-throughput assay to simultaneously evaluate activation of CYP3A and the direct and time-dependent inhibition of CYP3A, CYP2C9, and CYP2D6 using liquid chromatography-tandem mass spectrometry.

In the early stages of drug discovery, adequate evaluation of the potential drug-drug interactions (DDIs) of drug candidates is important. Several CYP3A activators are known to lead to underestimation of DDIs. These compounds affect midazolam 1'-hydroxylation but not midazolam 4-hydroxylation.We used both metabolic reactions of midazolam to evaluate the activation and inhibition of CYP3A activators simultaneously. For our CYP inhibition assay using cocktail probe substrates, simultaneous liquid chromatography-tandem mass spectrometry monitoring of 1'-hydroxymidazolam and 4-hydroxymidazolam for CYP3A was established in addition to monitoring of 4-hydroxydiclofenac and 1'-hydroxybufuralol for CYP2C9 and CYP2D6.The results of our cocktail inhibition assay were well correlated with those of a single inhibition assay, as were the estimated inhibition parameters for typical CYP3A inhibitors. In our assay, a proprietary compound that activated midazolam 1'-hydroxylation and tended to inhibit 4-hydroxylation was evaluated along with known CYP3A activators. All compounds were well characterised by comparison of the results of midazolam 1'- and 4-hydroxylation.In conclusion, our CYP cocktail inhibition assay can detect CYP3A activation and assess the direct and time-dependent inhibition potentials for CYP3A, CYP2C9, and CYP2D6. This method is expected to be very efficient in the early stages of drug discovery.

[Metabolic Activities Catalyzed by Human Cytochrome P450 (CYP) 2D6 and CYP3A Subfamily Members and Effect of Various Compounds, Including Endogenous Steroid Hormones, on These Activities].

My research focused on the effects of various drugs on (1) dopamine formation from p-tyramine catalyzed by polymorphic cytochrome P450 (CYP or P450) 2D6 variants and (2) endogenous steroid hormone hydroxylation catalyzed by CYP3A subfamily members (CYP3A4, CYP3A5, CYP3A7). The activation (cooperativity) of metabolic reactions catalyzed by P450s was especially emphasized. The effects of various psychotropic agents on dopamine formation from p-tyramine, catalyzed by wild-type CYP2D6.1 and CYP2D6 variants, including CYP2D6.2 (Arg296Cys;Ser486Thr), CYP2D6.10 (Pro34Ser;Ser486Thr), and CYP2D6.39 (Ser486Thr) were compared. Michaelis (Km) and inhibition (Ki) constants of the psychotropic agents in the presence of CYP2D6.10 were higher than those observed in the presence of other CYP2D6 variants. Fluvoxamine, fluoxetine, milnacipran, and haloperidol activated CYP2D6-catalyzed dopamine formation [decreasing the Km and/or increasing the maximal velocity (kcat)], and this activation was CYP2D6 variant-dependent. Regarding the CYP3A subfamily, the effects of various compounds including endogenous steroid hormones on the 6ß-hydroxylation of steroid hormones, such as testosterone, progesterone, and cortisol, were determined; it was found that testosterone, dehydroepiandrosterone, and/or α-naphthoflavone activated 6ß-hydroxylation of cortisol and/or progesterone, but the effects varied in the presence of different CYP3A subfamily members. Further studies are required to confirm the mechanisms and therapeutic relevance of these activation phenomena.

CYP2D6 Phenotype Influences Pharmacokinetic Parameters of Venlafaxine: Results from a Population Pharmacokinetic Model in Older Adults with Depression.

In this study, we aimed to improve upon a published population pharmacokinetic (PK) model for venlafaxine (VEN) in the treatment of depression in older adults, then investigate whether CYP2D6 metabolizer status affected model-estimated PK parameters of VEN and its active metabolite O-desmethylvenlafaxine. The model included 325 participants from a clinical trial in which older adults with depression were treated with open-label VEN (maximum 300 mg/day) for 12 weeks and plasma levels of VEN and O-desmethylvenlafaxine were assessed at weeks 4 and 12. We fitted a nonlinear mixed-effect PK model using NONMEM to estimate PK parameters for VEN and O-desmethylvenlafaxine adjusted for CYP2D6 metabolizer status and age. At both lower doses (up to 150 mg/day) and higher doses (up to 300 mg/day), CYP2D6 metabolizers impacted PK model-estimated VEN clearance, VEN exposure, and active moiety (VEN + O-desmethylvenlafaxine) exposure. Specifically, compared with CYP2D6 normal metabolizers, (i) CYP2D6 ultra-rapid metabolizers had higher VEN clearance; (ii) CYP2D6 intermediate metabolizers had lower VEN clearance; (iii) CYP2D6 poor metabolizers had lower VEN clearance, higher VEN exposure, and higher active moiety exposure. Overall, our study showed that including a pharmacogenetic factor in a population PK model could increase model fit, and this improved model demonstrated how CYP2D6 metabolizer status affected VEN-related PK parameters, highlighting the importance of genetic factors in personalized medicine.

Mechanism-Based Inactivation of CYP2D6 by Phellopterin and Related Drug-Drug Interaction with Metoprolol.

Phellopterin (PLP) is a linear furanocoumarin widely found in citrus fruits and herbal medicines. The study aims to comprehensively investigate the mechanism of inhibition of CYP2D6 enzyme activity by PLP and its alteration of metoprolol pharmacokinetics. PLP was found to irreversibly inhibit CYP2D6 in time-, concentration-, and nicotinamide adenine dinucleotide phosphate-dependent manners. Coincubation with quinidine, which is a competitive inhibitor of CYP2D6, attenuated this time-dependent inhibition. Glutathione (GSH) and catalase/superoxide dismutase failed to reverse the PLP-induced CYP2D6 inactivation. GSH trapping experiments provided strong evidence that PLP metabolic activation produces epoxide or γ-ketoaldehyde intermediates. In addition, pretreatment with PLP resulted in significant increases in Cmax and area under curve of plasma metoprolol in rats.

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.

Novel Tree Shrew Cytochrome P450 2Ds (CYP2D8a and CYP2D8b) Are Functional Drug-Metabolizing Enzymes that Metabolize Bufuralol and Dextromethorphan.

Tree shrews are a nonprimate species used in a range of biomedical studies. Recent genome analysis of tree shrews found that the sequence identities and the numbers of genes of cytochrome P450 (CYP or P450), an important family of drug-metabolizing enzymes, are similar to those of humans. However, tree shrew P450s have not yet been sufficiently identified and analyzed. In this study, novel CYP2D8a and CYP2D8b cDNAs were isolated from tree shrew liver and were characterized, along with human CYP2D6, dog CYP2D15, and pig CYP2D25. The amino acid sequences of these tree shrew CYP2Ds were 75%-78% identical to human CYP2D6, and phylogenetic analysis showed that they were more closely related to human CYP2D6 than rat CYP2Ds, similar to dog and pig CYP2Ds. For tree shrew CYP2D8b, two additional transcripts were isolated that contained different patterns of deletion. The gene and genome structures of CYP2Ds are generally similar in dogs, humans, pigs, and tree shrews. Tree shrew CYP2D8a mRNA was most abundantly expressed in liver, among the tissue types analyzed, similar to dog CYP2D15 and pig CYP2D25 mRNAs. Tree shrew CYP2D8b mRNA was also expressed in liver, but at a level 7.3-fold lower than CYP2D8a mRNA. Liver microsomes and recombinant protein of both tree shrew CYP2Ds metabolized bufuralol and dextromethorphan, selective substrates of human CYP2D6, but the activity level of CYP2D8a greatly exceeded that of CYP2D8b. These results suggest that tree shrew CYP2D8a and CYP2D8b are functional drug-metabolizing enzymes, of which CYP2D8a is the major CYP2D in liver. SIGNIFICANCE STATEMENT: Novel tree shrew CYP2D8a and CYP2D8b cDNAs were isolated from liver. Their amino acid sequences were 75%-78% identical to human CYP2D6. For CYP2D8b, two additional transcripts contained different patterns of deletion. Tree shrew CYP2D8a mRNA was abundantly expressed in liver, similar to dog CYP2D15 and pig CYP2D25 mRNAs. Recombinant tree shrew CYP2Ds catalyzed the oxidation of bufuralol and dextromethorphan. Tree shrew CYP2D8a and CYP2D8b are functional drug-metabolizing enzymes, of which CYP2D8a is the major CYP2D in liver.

Exploring the impact of CYP2D6 and UGT2B7 gene-drug interactions, and CYP-mediated DDI on oxycodone and oxymorphone pharmacokinetics using physiologically-based pharmacokinetic modeling and simulation.

Oxycodone is one of the most commonly used opioids to treat moderate to severe pain. It is metabolized mainly by CYP3A4 and CYP2D6, while only a small fraction of the dose is excreted unchanged into the urine. Oxymorphone, the metabolite primarily formed by CYP2D6, has a 40- to 60-fold higher mu-opioid receptor affinity than the parent compound. While CYP2D6-mediated gene-drug-interactions (GDIs) and drug-drug interactions (DDIs) are well-studied, they only account for a portion of the variability in oxycodone and oxymorphone exposure. The combined impact of CYP2D6-mediated GDIs and DDIs, CYP3A4-mediated DDIs, and UGT2B7 GDIs is not fully understood yet and hard to study in head-to-head clinical trials given the relatively large number of scenarios. Instead, we propose the use of a physiologically-based pharmacokinetic model that integrates available information on oxycodone's metabolism to characterize and predict the impact of DDIs and GDIs on the exposure of oxycodone and its major, pharmacologically-active metabolite oxymorphone. To this end, we first developed and verified a PBPK model for oxycodone and its metabolites using published clinical data. The verified model was then applied to determine the dose-exposure relationship of oxycodone and oxymorphone stratified by CYP2D6 and UGT2B7 phenotypes respectively, and administered perpetrators of CYP-based drug interactions. Our simulations demonstrate that the combination of CYP2D6 UM and a UGT2B7Y (268) mutation may lead to a 2.3-fold increase in oxymorphone exposure compared to individuals who are phenotyped as CYP2D6 NM / UGT2B7 NM. The extent of oxymorphone exposure increases up to 3.2-fold in individuals concurrently taking CYP3A4 inhibitors, such as ketoconazole. Inhibition of the CYP3A4 pathway results in a relative increase in the partial metabolic clearance of oxycodone to oxymorphone. Oxymorphone is impacted to a higher extent by GDIs and DDIs than oxycodone. We predict oxymorphone exposure to be highest in CYP2D6 UMs/UGT2B7 PMs in the presence of ketoconazole (strong CYP3A4 index inhibitor) and lowest in CYP2D6 PMs/UGT2B7 NMs in the presence of rifampicin (strong CYP3A4 index inducer) covering a 55-fold exposure range.

Inhibition Effect of Okanin Toward Human Cytochrome P450 3A4 and 2D6 with Multi-spectroscopic Studies and Molecular Docking.

Okanin, a major flavonoid of a popular herb tea, Coreopsis tinctoria Nutt., showed strong inhibition on CYP3A4 and CYP2D6. The strong interaction between okanin and CYPs were determined by enzyme kinetics, multispectral technique and molecular docking. The inhibition type of two enzymes, CYP3A4 and CYP2D6, by okanin are mixed and non-competitive inhibition type, respectively. The IC50 values and the binding constant of okanin to CYP3A4 can be deduced that the interaction was stronger than that of CYP2D6. The Conformations of CYP3A4 and CYP2D6 were changed by okanin. The evidence from fluorescence measurement along with molecular docking verified that these two CYPs were bound with okanin by hydrogen bonds and hydrophobic forces. Our investigation suggested that okanin may lead to interactions between herb and drug by inhibiting CYP3A4 and CYP2D6 activities, thus its consumption should be taken with caution.

Effect of CYP2D6 genotype on duloxetine serum concentration.

Duloxetine is metabolized by cytochrome P450 (CYP)1A2 and CYP2D6. The aim of this study was to investigate the effect of the CYP2D6 genotype on duloxetine serum concentration adjusting for age and sex. Patients were included retrospectively from a therapeutic drug monitoring service. Multiple linear regression analysis was used to investigate the effect of CYP2D6 genotype, age and sex on the duloxetine concentration-to-dose (C/D) ratio. In total, 269 patients were included and assigned to the following genotype-predicted phenotype subgroups: CYP2D6 poor metabolizers (PMs, n = 23), intermediate metabolizers (IMs, n = 121), normal metabolizers (NMs, n = 120) and ultrarapid metabolizers (UMs, n = 5). Multiple linear regression analysis revealed a 95% higher duloxetine C/D ratio in PMs compared with NMs (p = 0.009). Patients ≥65 years had a 56% higher C/D ratio than younger patients (p = 0.01), while women had a 46% higher C/D ratio than men (p = 0.04). In conclusion, the CYP2D6 PM phenotype is associated with a twofold higher concentration at recommended dosing compared with the NM phenotype. CYP2D6 PM females above 65 years are at particular risk of high duloxetine levels as they may obtain a threefold higher C/D ratio compared with younger, male NMs.

Effect of isotretinoin on CYP2D6 and CYP3A activity in patients with severe acne.

AIMS: Previously, retinoids have decreased CYP2D6 mRNA expression in vitro and induced CYP3A4 in vitro and in vivo. This study aimed to determine whether isotretinoin administration changes CYP2D6 and CYP3A activities in patients with severe acne. METHODS: Thirty-three patients (22 females and 11 males, 23.5 ± 6.0 years old) expected to receive isotretinoin treatment completed the study. All participants were genotyped for CYP2D6 and CYP3A5. Participants received dextromethorphan (DM) 30 mg orally as a dual-probe substrate of CYP2D6 and CYP3A activity at two study timepoints: pre-isotretinoin treatment and with isotretinoin for at least 1 week. The concentrations of isotretinoin, DM and their metabolites were measured in 2-h postdose plasma samples and in cumulative 0-4-h urine collections using liquid chromatography-mass spectrometry. RESULTS: In CYP2D6 extensive metabolizers, the urinary dextrorphan (DX)/DM metabolic ratio (MR) (CYP2D6 activity marker) was numerically, but not significantly, lower with isotretinoin administration compared to pre-isotretinoin (geometric mean ratio [GMR] [90% confidence interval (CI)] 0.78 [0.55, 1.11]). The urinary 3-hydroxymorphinan (3HM)/DX MR (CYP3A activity marker) was increased (GMR 1.18 [1.03, 1.35]) and the urinary DX-O-glucuronide/DX MR (proposed UGT2B marker) was increased (GMR 1.22 [1.06, 1.39]) with isotretinoin administration compared to pre-isotretinoin. CONCLUSIONS: Administration of isotretinoin did not significantly reduce CYP2D6 activity in extensive metabolizers, suggesting that the predicted downregulation of CYP2D6 based on in vitro data does not translate into humans. We observed a modest increase in CYP3A activity (predominantly CYP3A4) with isotretinoin treatment. The data also suggest that DX glucuronidation is increased following isotretinoin administration.

The interplay between tamoxifen and endoxifen plasma concentrations and coagulation parameters in patients with primary breast cancer.

BACKGROUND: Tamoxifen is an effective treatment for primary breast cancer but increases the risk for venous thromboembolism. Tamoxifen decreases anticoagulant proteins, including antithrombin (AT), protein C (PC) and tissue factor (TF) pathway inhibitor, and enhances thrombin generation (TG). However, the relation between plasma concentrations of both tamoxifen and its active metabolite endoxifen and coagulation remains unknown. METHODS: Tamoxifen and endoxifen were measured in 141 patients from the prospective open-label intervention TOTAM-study after 3 months (m) and 6 m of tamoxifen treatment. Levels of AT and PC, the procoagulant TF, and TG parameters were determined at both timepoints if samples were available (n = 53-135 per analysis). Levels of coagulation proteins and TG parameters were correlated and compared between: 1) quartiles of tamoxifen and endoxifen levels, and 2) 3 m and 6 m of treatment. RESULTS: At 3 m, levels of AT, PC, TF and TG parameters were not associated with tamoxifen nor endoxifen levels. At 6 m, median TF levels were lower in patients in the 3rd (56.6 [33] pg/mL), and 4th (50.1 [19] pg/mL) endoxifen quartiles compared to the 1st (lowest) quartile (76 [69] pg/mL) (P=0.027 and P=0.018, respectively), but no differences in anticoagulant proteins or TG parameters were observed. An increase in circulating TF levels (3 m: 46.0 [15] versus 6 m: 54.4 [39] pg/mL, P < 0.001) and TG parameters was observed at the 6 m treatment timepoint, while AT and PC levels remained stable. CONCLUSIONS: Our results indicate that higher tamoxifen and endoxifen levels are not correlated with an increased procoagulant state, suggesting tamoxifen dose escalation does not further promote hypercoagulability.

Inhibitory effects of the main metabolites of Apatinib on CYP450 isozymes in human and rat liver microsomes.

PURPOSE: The inhibitory effect of Apatinib on cytochrome P450 (CYP450) enzymes has been studied. However, it is unknown whether the inhibition is related to the major metabolites, M1-1, M1-2 and M1-6. METHODS: A 5-in-1 cocktail system composed of CYP2B6/Cyp2b1, CYP2C9/Cyp2c11, CYP2E1/Cyp2e1, CYP2D6/Cyp2d1 and CYP3A/Cyp3a2 was used in this study. Firstly, the effects of APA and its main metabolites on the activities of HLMs, RLMs and recombinant isoforms were examined. The reaction mixture included HLMs, RLMs or recombinant isoforms (CYP3A4.1, CYP2D6.1, CYP2D6.10 or CYP2C9.1), analyte (APA, M1-1, M1-2 or M1-6), probe substrates. The reactions were pre-incubated for 5 min at 37 °C, followed by the addition of NAPDH to initiate the reactions, which continued for 40 min. Secondly, IC50 experiments were conducted to determine if the inhibitions were reversible. The reaction mixture of the "+ NADPH Group" included HLMs or RLMs, 0 to 100 of µM M1-1 or M1-2, probe substrates. The reactions were pre-incubated for 5 min at 37 °C, and then NAPDH was added to initiate reactions, which proceeded for 40 min. The reaction mixture of the "- NADPH Group" included HLMs or RLMs, probe substrates, NAPDH. The reactions were pre-incubated for 30 min at 37 °C, and then 0 to 100 µM of M1-1 or M1-2 was added to initiate the reactions, which proceeded for 40 min. Finally, the reversible inhibition of M1-1 and M1-2 on isozymes was determined. The reaction mixture included HLMs or RLMs, 0 to 10 µM of M1-1 or M1-2, probe substrates with concentrations ranging from 0.25Km to 2Km. RESULTS: Under the influence of M1-6, the activity of CYP2B6, 2C9, 2E1 and 3A4/5 was increased to 193.92%, 210.82%, 235.67% and 380.12% respectively; the activity of CYP2D6 was reduced to 92.61%. The inhibitory effects of M1-1 on CYP3A4/5 in HLMs and on Cyp2d1 in RLMs, as well as the effect of M1-2 on CYP3A in HLMs, were determined to be noncompetitive inhibition, with the Ki values equal to 1.340 µM, 1.151 µM and 1.829 µM, respectively. The inhibitory effect of M1-1 on CYP2B6 and CYP2D6 in HLMs, as well as the effect of M1-2 on CYP2C9 and CYP2D6 in HLMs, were determined to be competitive inhibition, with the Ki values equal to 12.280 µM, 2.046 µM, 0.560 µM and 4.377 µM, respectively. The inhibitory effects of M1-1 on CYP2C9 in HLMs and M1-2 on Cyp2d1 in RLMs were determined to be mixed-type, with the Ki values equal to 0.998 µM and 0.884 µM. The parameters could not be obtained due to the atypical kinetics of CYP2E1 in HLMs under the impact of M1-2. CONCLUSIONS: M1-1 and M1-2 exhibited inhibition for several CYP450 isozymes, especially CYP2B6, 2C9, 2D6 and 3A4/5. This observation may uncover potential drug-drug interactions and provide valuable insights for the clinical application of APA.

Relevance of pharmacogenetic analyses and therapeutic drug monitoring of antidepressants for an individualized treatment of peripartum psychopathology.

OBJECTIVE: Psychiatric disorders burden the peripartum period, often requiring psychopharmacological treatment, including antidepressants. Efficacy and tolerability of antidepressants are influenced by the physiological changes of the peripartum and individual metabolic profiles, which in turn can be modified by pregnancy. The objective of this study is to assess the relationship between antidepressants' pharmacokinetic profiles during pregnancy and individual metabolic profiles, along with the efficacy of the treatment. METHODS: In total 87 outpatients with diagnoses of bipolar disorder, major depression, anxiety, obsessive-compulsive disorder and post-traumatic stress disorder who required antidepressant treatment during pregnancy were recruited. Genotyping analysis of hepatic cytochrome P450 (CYPs) individual isoforms was performed. Antidepressants' blood concentrations and psychometric assessments were collected at five time points. Antidepressants' cord blood concentrations were assessed at birth. RESULTS: Sertraline showed greater stability in plasma concentrations and a lower placental penetrance index. Most of the antidepressants' concentrations below the therapeutic range were found in women with an extensive/ultrarapid metabolic profile. Antidepressants mainly metabolized by CYP2C19 were less frequently below the therapeutic range compared with antidepressants metabolized by CYP2D6. CONCLUSIONS: Pregnancy modulates cytochrome activity and drugs' pharmacokinetics. Genotyping analysis of CYPs isoforms and therapeutic drug monitoring might be used to guide clinicians in a well-tolerated treatment of psychiatric symptoms in pregnant women.

Pharmacogenomic testing for CYP2C19 and CYP2D6 in cyclic vomiting syndrome.

BACKGROUND: Amitriptyline (AT) is recommended as first-line prophylactic therapy in patients with cyclic vomiting syndrome (CVS). However, significant side effects limit its use and dosing is based on trial and error. Though the Clinical Pharmacogenetic Implementation Consortium (CPIC) Guidelines recommend dosing for AT based on CY2D6 and CYP2C19 genotype profile, this is not followed in clinical practice. METHODS: This pilot study determined CYP2C19 and CYP2D6 genotypes and ascertained its association with adverse drug reactions (ADRs), clinical response, and serum concentration of AT and nortriptyline in a well-characterized cohort of adults with CVS. KEY RESULTS: Of 46 subjects with CVS, age 33 ± 12 years, 61% female, 85% Caucasian, a third (33%) had normal CYP2C19 metabolizer status, while 4% were poor, and 43% were ultrarapid metabolizers. Most (61%) had normal CYP2D6 genotype while 9% were poor and 2% were ultra-rapid metabolizers. There was no statistically significant association between genotype and ADRs, clinical response or serum drug concentration. There was a trend towards significance between genotype and clinical response, with 64% of responders having normal CYP2D6 metabolism versus 36% of nonresponders (p = 0.06). ADRs were encountered in 46% of patients with 28% discontinuing the medication as a result. CONCLUSIONS AND INFERENCES: A subset of patients with CVS have dysfunctional alleles of CYP2C19 and CYP2D6. Larger prospective studies to evaluate the clinical impact of pharmacogenomic testing in CVS are needed. This has the potential to optimize clinical management, predict ADRs and allow for personalized therapy.

Nutrimetric Validation of Solanidine as Dietary-Derived CYP2D6 Activity Marker In Vivo.

CYP2D6 is involved in the metabolism of many drugs. Its activity is affected by pharmacogenetic variability leading to highly polymorphic phenotypes between individuals, affecting safety and efficacy of drugs. Recently, solanidine, a steroidal alkaloid from potatoes, and its metabolites, has been identified as a dietary-derived activity marker for CYP2D6. The intraday variability in plasma within individuals has not been studied yet in healthy subjects. As part of a CYP phenotyping cocktail study with 20 healthy participants, plasma concentrations of solanidine, 4-OH-solanidine and 3,4-secosolanidine-3,4-dioic acid (SSDA) were determined using a sensitive liquid chromatography-mass spectrometry method in urine and in plasma at timepoints 0, 2.5, 5, 8, and 24 hours after intake of test substances. The participants were phenotyped for CYP2D6 with oral metoprolol (12.5 mg) with 15 plasma sampling points over 24 hours (DRKS00028922). Metabolic ratios (MRs) of metabolite to parent plasma concentrations were formed from single timepoints and the area under the curve (AUC). All participants were genotyped for CYP2D6. The intra-individual variability of the CYP2D6 metabolite SSDA was highly stable with a median SD of 11.62% over 24 hours. MR SSDA/solanidine was more variable (median SD 31.90%) but correlated significantly at all measured timepoints with AUC MR α-OH-metoprolol/metoprolol. The AUC MR SSDA/solanidine showed a significant linear relationship with the genetically predicted CYP2D6 activity score. This study substantiates the MR SSDA/solanidine as CYP2D6 activity marker. The high correlation with metoprolol MR indicates a valid prediction of the CYP2D6 phenotype at any timepoint during the study day.