Impact of the CYP2D6 ultra-rapid metabolizer genotype on doxepin pharmacokinetics and serotonin in platelets

Evidence for solanidine as a dietary CYP2D6 biomarker: Significant correlation with risperidone metabolism

AIMS

The extensive variability in cytochrome P450 2D6 (CYP2D6) metabolism is mainly caused by genetic polymorphisms. However, there is large, unexplained variability in CYP2D6 metabolism within CYP2D6 genotype subgroups. Solanidine, a dietary compound found in potatoes, is a promising phenotype biomarker predicting individual CYP2D6 metabolism. The aim of this study was to investigate the correlation between solanidine metabolism and the CYP2D6-mediated metabolism of risperidone in patients with known CYP2D6 genotypes.

METHODS

The study included therapeutic drug monitoring (TDM) data from CYP2D6-genotyped patients treated with risperidone. Risperidone and 9-hydroxyrisperidone levels were determined during TDM, and reprocessing of the respective TDM full-scan high-resolution mass spectrometry files was applied for semi-quantitative measurements of solanidine and five metabolites (M402, M414, M416, M440 and M444). Spearman's tests determined the correlations between solanidine metabolic ratios (MRs) and the 9-hydroxyrisperidone-to-risperidone ratio.

RESULTS

A total of 229 patients were included. Highly significant, positive correlationswere observed between all solanidine MRs and the 9-hydroxyrisperidone-to-risperidone ratio (ρ > 0.6, P < .0001). The strongest correlation was observed for the M444-to-solanidine MR in patients with functional CYP2D6 metabolism, i.e., genotype activity scores of 1 and 1.5 (ρ 0.72-0.77, P < .0001).

CONCLUSION

The present study shows strong, positive correlations between solanidine metabolism and CYP2D6-mediated risperidone metabolism. The strong correlation within patients carrying CYP2D6 genotypes encoding functional CYP2D6 metabolism suggests that solanidine metabolism may predict individual CYP2D6 metabolism, and hence potentially improve personalized dosing of drugs metabolized by CYP2D6.

Pain Management in Children Admitted to the Emergency Room: A Narrative Review

Pain is a biopsychosocial experience characterized by sensory, physiological, cognitive, affective, and behavioral components. Both acute and chronic pain can have short and long-term negative effects. Unfortunately, pain treatment is often inadequate. Guidelines and recommendations for a rational approach to pediatric pain frequently differ, and this may be one of the most important reasons for the poor attention frequently paid to pain treatment in children. This narrative review discusses the present knowledge in this regard. A literature review conducted on papers produced over the last 8 years showed that although in recent years, compared to the past, much progress has been made in the treatment of pain in the context of the pediatric emergency room, there is still a lot to do. There is a need to create guidelines that outline standardized and easy-to-follow pathways for pain recognition and management, which are also flexible enough to take into account differences in different contexts both in terms of drug availability and education of staff as well as of the different complexities of patients. It is essential to guarantee an approach to pain that is as uniform as possible among the pediatric population that limits, as much as possible, the inequalities related to ethnicity and language barriers.

Pharmacogenomics: Driving Personalized Medicine

Personalized medicine tailors therapies, disease prevention, and health maintenance to the individual, with pharmacogenomics serving as a key tool to improve outcomes and prevent adverse effects. Advances in genomics have transformed pharmacogenetics, traditionally focused on single gene-drug pairs, into pharmacogenomics, encompassing all "-omics" fields (e.g., proteomics, transcriptomics, metabolomics, and metagenomics). This review summarizes basic genomics principles relevant to translation into therapies, assessing pharmacogenomics' central role in converging diverse elements of personalized medicine. We discuss genetic variations in pharmacogenes (drug-metabolizing enzymes, drug transporters, and receptors), their clinical relevance as biomarkers, and the legacy of decades of research in pharmacogenetics. All types of therapies, including proteins, nucleic acids, viruses, cells, genes, and irradiation, can benefit from genomics, expanding the role of pharmacogenomics across medicine. Food and Drug Administration approvals of personalized therapeutics involving biomarkers increase rapidly, demonstrating the growing impact of pharmacogenomics. A beacon for all therapeutic approaches, molecularly targeted cancer therapies highlight trends in drug discovery and clinical applications. To account for human complexity, multicomponent biomarker panels encompassing genetic, personal, and environmental factors can guide diagnosis and therapies, increasingly involving artificial intelligence to cope with extreme data complexities. However, clinical application encounters substantial hurdles, such as unknown validity across ethnic groups, underlying bias in health care, and real-world validation. This review address the underlying science and technologies germane to pharmacogenomics and personalized medicine, integrated with economic, ethical, and regulatory issues, providing insights into the current status and future direction of health care. SIGNIFICANCE STATEMENT: Personalized medicine aims to optimize health care for the individual patients with use of predictive biomarkers to improve outcomes and prevent adverse effects. Pharmacogenomics drives biomarker discovery and guides the development of targeted therapeutics. This review addresses basic principles and current trends in pharmacogenomics, with large-scale data repositories accelerating medical advances. The impact of pharmacogenomics is discussed, along with hurdles impeding broad clinical implementation, in the context of clinical care, ethics, economics, and regulatory affairs.

Genetic Susceptibility Toward Nausea and Vomiting in Surgical Patients

Postoperative nausea and vomiting (PONV) are frequently occurring adverse effects following surgical procedures. Despite predictive risk scores and a pallet of prophylactic antiemetic treatments, it is still estimated to affect around 30% of the patients, reducing their well-being and increasing the burden of post-operative care. The aim of the current study was to characterize selected genetic risk factors of PONV to improve the identification of at risk patients. We genotyped 601 patients followed during the first 24 h after surgery for PONV symptoms in the absence of any antiemetic prophylaxis. These patients were recruited in the frame of a randomized, placebo controlled clinical study aiming to test the efficacy of dexamethasone as a treatment of established PONV. We examined the impact of selected single nucleotide polymorphisms (SNPs) located around 13 different genes and the predicted activity of 6 liver drug metabolizing enzymes from the cytochromes P450 family (CYP) on the occurrence and recurrence of PONV. Our genetic study confirms the importance of genetic variations in the type 3B serotonin receptor in the occurrence of PONV. Our modelling shows that integration of rs3782025 genotype in preoperative risk assessments may help improve the targeting of antiemetic prophylaxis towards patients at risk of PONV.

Optimizing doxepin therapy in dermatology: introducing blood level monitoring and genotype testing

Doxepin, a tricyclic antidepressant, is the most efficacious antipruritic available to dermatologists; however its use is often suboptimal because of significant interindividual variability in doxepin plasma levels and clinical response between patients taking the same dose. As result, the Food and Drug Administration approves a maximum dose of 300 mg of doxepin per day and a 10 mg per cc liquid doxepin concentrate. These allow patients to significantly increase or decrease their dose, due to either a lack of clinical efficacy or side effects at typical dermatologic doses (often 10-25 mg per day). This review initially discusses the unique advantages of doxepin in dermatology. Then, it explores internal and external reasons why doxepin plasma levels and clinical response vary so significantly between patients, including genetic polymorphisms, drug interactions, comorbidities, sex, and ethnicity. Blood level monitoring is introduced, a tool dermatologists can use to optimize doxepin dosing in patients responding subtherapeutically to typical dermatologic doses. Without blood level monitoring, patients initially unresponsive to treatment could be labeled treatment failures when in fact they may be cases of inadequate dosing. Blood level monitoring allows for safe dose adjustments in these individuals to maximize patients' chances of achieving therapeutic success with this agent.

The effect of smoking on the plasma concentration of tricyclic antidepressants: a systematic review

Smoking is highly prevalent in the psychiatric population, and hospital admittance usually results in partial or complete smoking cessation. Tobacco use is known to affect the metabolism of certain psychoactive drugs, but whether smoking influences the plasma concentration of tricyclic antidepressants (TCAs) remains unclear. This article investigates the possible effect of smoking on the plasma concentration of TCAs. A systematic review of the literature available on PubMed and EMBASE as of October 2020 was carried out using PRISMA guidelines. Studies reporting plasma concentrations of any TCA in both a smoking and a non-smoking group were included and compared. Ten eligible studies were identified and included. In the eight studies investigating the effect of smoking on amitriptyline and/or nortriptyline, five studies found no significant effect. Two studies investigating the effect of smoking on imipramine found a significant effect, and one study investigating the effect of smoking on doxepin found no significant effect. The majority of studies included in this review were influenced by small study populations and other methodical issues. The effect of smoking on the plasma concentration of TCAs is still not entirely clear. There is a possibility that smoking affects the distribution of TCA metabolites, but this is probably not of clinical importance.

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Farmacogenômica e Doença Cardiovascular: Onde Estamos e Para Onde Vamos

A farmacogenômica (FGx) investiga a interação entre genes e medicamentos. Através da análise de regiões específicas do DNA, informações sobre o perfil de metabolização do paciente para um determinado fármaco podem ser descritas, assim como o perfil esperado de resposta ao tratamento. Objetivamente, esse tipo de teste pode ter impacto no tratamento de pacientes que não estão respondendo adequadamente a um determinado medicamento, seja pela ausência dos efeitos esperados ou em virtude do aparecimento de efeitos adversos. Neste cenário, o objetivo desta revisão é o de informar o cardiologista clínico sobre esta importante área do conhecimento e atualizá-lo sobre o tema, procurando preencher as lacunas no que diz respeito à relação custo-benefício da aplicação da FGx nas doenças cardiovasculares, além de fornecer informações para a implementação da terapia guiada pela FGx na prática clínica.

Personalized prescribing: a new medical model for clinical implementation of psychotropic drugs

The use of pharmacogenetic tests was already being proposed in psychiatry in the early 2000s because genetic factors were known to influence drug pharmacokinetics and pharmacodynamics. However, sufficient levels of evidence to justify routine use have been achieved for only a few tests (eg, major histocompatibility complex, class I, B, allele 1502 [HLA-B*1502] for carbamazepine in epilepsy and bipolar disorders); many findings are too preliminary or, when replicated, of low clinical relevance because of a small effect size. Although drug selection and dose adaptation according to cytochrome P450 genotypes are sound, a large number of patients need to be genotyped in order to prevent one case of severe side effect and/or nonresponse. The decrease in cost for genetic analysis shifts the cost: benefit ratio toward increasing use of pharmacogenetic tests. However, they have to be combined with careful clinical evaluations and other tools (eg, therapeutic drug monitoring and phenotyping) to contribute to the general aim of providing the best care for psychiatric patients.

Polymorphism in CYP2D6 and CYP2C19, members of the cytochrome P450 mixed-function oxidase system, in the metabolism of psychotropic drugs

Numerous studies in the field of psychopharmacological treatment have investigated the possible contribution of genetic variability between individuals to differences in drug efficacy and safety, motivated by the wide individual variation in treatment response. Genomewide analyses have been conducted in several large-scale studies on antidepressant drug response. However, no consistent findings have emerged from these studies. In a recent meta-analysis of genomewide data from the three studies capturing common variation for association with symptomatic improvement and remission revealed the absence of any strong genetic association and failed to replicate results of individual studies in the pooled data. However, there are good reasons to consider the possible importance of pharmacogenetic variants separately. These variants explain a large portion of the manifold variability in individual drug metabolism. More than 20 psychotropic drugs have now been relabelled by the FDA adding information on polymorphic drug metabolism and therapeutic recommendations. Furthermore, dose recommendations for polymorphisms in drug metabolizing enzymes, first and foremost CYP2D6 and CYP2C19, have been issued with the advice to reduce the dosage in poor metabolizers to 50% or less (in eight cases), or to choose an alternative treatment. Beside the well-described role in hepatic drug metabolism, these enzymes are also expressed in the brain and play a role in biotransformation of endogenous substrates. These polymorphisms may therefore modulate brain metabolism and affect the function of the neural substrates of cognition and emotion.

CYP2D6 variation, behaviour and psychopathology: implications for pharmacogenomics-guided clinical trials

Individual and population differences in polymorphic cytochrome P450 enzyme function have been known for decades. The biological significance of these differences has now been deciphered with regard to drug metabolism, action and toxicity as well as disposition of endogenous substrates, including neuroactive compounds. While the cytochrome P450 enzymes occur abundantly in the liver, they are expressed in most tissues of the body, albeit in varying amounts, including the brain. The latter location of cytochrome P450s is highly pertinent for susceptibility to neuropsychiatric diseases, not to mention local drug metabolism at the site of psychotropic drug action in the brain. In the current era of personality medicine with companion theranostics (i.e. the fusion of therapeutics with diagnostics), this article underscores that such versatile biological roles of cytochrome P450s offer multiple points of entry for personalized medicine and rational therapeutics. We focus our discussion on CYP2D6, one of the most intensively researched drug and endogenous compound metabolism pathways, with a view to relevance for, and optimization of, pharmacogenomic-guided clinical trials. Working on the premise that CYP2D6 is related to human behaviour and certain personality traits such as serotonin and dopamine system function, we further suggest that the motivation of healthy volunteers to participate in clinical trials may in part be influenced by an under- or over-representation of certain CYP2D6 metabolic groups.

Pharmacokinetic behavior presents drug therapy challenges

There are conditions that cause a substantial change in drug clearance to such a degree that how a specific drug is managed to optimize drug response and minimize drug toxicity presents a challenge. This review will focus on recent literature (within the past 5 years) that evaluates pathophysiologic and genetic conditions and drug interactions which can change drug clearance to the magnitude that response is affected. Situations discussed that cause an increase in drug clearance will include: augmented renal clearance in critically ill patients; ultrafast drug metabolism caused by gene duplication; and enzyme induction interactions caused by rifampin. Situations discussed that result in a reduction in clearance will include: multiple organ failure in critically ill, patients with non-functioning CYP2D6 and CYP2C8/9 alleles, and CYP3A4 drug interactions with erythromycin and clarithromycin. In each case evaluated clearance is changed to the magnitude such that managing drug therapy can be difficult.

Complexities of CYP2D6 gene analysis and interpretation

Cytochrome P450 2D6 (CYP2D6) plays an important role in the metabolism and bioactivation of about 25% of clinically used drugs including many antidepressants, antipsychotics and opioids. CYP2D6 activity is highly variably ranging from no activity in so-called poor metabolizers to ultrarapid metabolism at the other end of the extreme of the activity distribution. A large portion of this variability can be explained by the highly polymorphic nature of the CYP2D6 gene locus for which > 100 variants and subvariants identified to date. Allele frequencies vary markedly between ethnic groups; some have exclusively or predominantly only been observed in certain populations. Pharmacogenetic testing holds the promise of individualizing drug therapy by identifying patients with CYP2D6 diplotypes that puts them at an increased risk of experiencing dose-related adverse events or therapeutic failure. Inferring a patient's CYP2D6 metabolic capacity, or phenotype, however, is a challenging task due to the complexity of the CYP2D6 gene locus. Allelic variation includes SNPs, small insertions and deletions, gene copy number variation and rearrangements with CYP2D7, a highly related non-functional gene. This review provides a summary of the intricacies of CYP2D6 variation and genotype analysis, knowledge that is invaluable for the translation of genotype into clinically useful information.

Genetic variability of drug-metabolizing enzymes: the dual impact on psychiatric therapy and regulation of brain function

Polymorphic drug-metabolizing enzymes (DMEs) are responsible for the metabolism of the majority of psychotropic drugs. By explaining a large portion of variability in individual drug metabolism, pharmacogenetics offers a diagnostic tool in the burgeoning era of personalized medicine. This review updates existing evidence on the influence of pharmacogenetic variants on drug exposure and discusses the rationale for genetic testing in the clinical context. Dose adjustments based on pharmacogenetic knowledge are the first step to translate pharmacogenetics into clinical practice. However, also clinical factors, such as the consequences on toxicity and therapeutic failure, must be considered to provide clinical recommendations and assess the cost-effectiveness of pharmacogenetic treatment strategies. DME polymorphisms are relevant not only for clinical pharmacology and practice but also for research in psychiatry and neuroscience. Several DMEs, above all the cytochrome P (CYP) enzymes, are expressed in the brain, where they may contribute to the local biochemical homeostasis. Of particular interest is the possibility of DMEs playing a physiological role through their action on endogenous substrates, which may underlie the reported associations between genetic polymorphisms and cognitive function, personality and vulnerability to mental disorders. Neuroimaging studies have recently presented evidence of an effect of the CYP2D6 polymorphism on basic brain function. This review summarizes evidence on the effect of DME polymorphisms on brain function that adds to the well-known effects of DME polymorphisms on pharmacokinetics in explaining the range of phenotypes that are relevant to psychiatric practice.

Pharmacogenomics of adverse drug reactions: implementing personalized medicine

Pharmacogenomics aims to investigate the genetic basis of inter-individual differences in drug responses, such as efficacy, dose requirements and adverse events. Research in pharmacogenomics has grown over the past decade, evolving from a candidate-gene approach to genome-wide association studies (GWASs). Genetic variants in genes coding for drug metabolism, drug transport and more recently human-leukocyte antigens (HLAs) have been linked to inter-individual differences in the risk of adverse drug reactions (ADRs). The tight association of specific HLA alleles with Stevens-Johnson syndrome, toxic epidermal necrolysis, drug hypersensitivity syndrome and drug-induced liver injury underscore the importance of HLA in the pathogenesis of these idiosyncratic drug hypersensitivity reactions. However, as with the search for the genetic basis for common diseases, pharmacogenomic research, including GWAS, has so far been a disappointment in discovering major gene variants responsible for the efficacy of drugs used to treat common diseases. This review focuses on the pharmacogenomics of ADRs, the underlying mechanisms and the potential use of genomic biomarkers in clinical practice for dose adjustment and the avoidance of drug toxicity. We also discuss obstacles to the implementation of pharmacogenomics and the direction of future translational research.

Tamoxifen resistance and CYP2D6 copy numbers in breast cancer patients

BACKGROUND

Breast cancer accounts about one million from total annual ten million new diagnosed cases of neoplasia worldwide and is the main cause of death due to cancer in women. Tamoxifen is the most popular selective estrogen receptor modulator used in anti estrogen treatments. Tamoxifen must be converted into its metabolite endoxifen for biologic effects; this conversion process is catalysed by highly polymorphic cytochrome P450 2D6 (CYP2D6). This study surveyed copy number variation of the CYP2D6 gene and its possible correlation with Tamoxifen resistance in breast cancer patients.

METHODS

This case control study was performed on samples taken from 79 patients with breast cancer who used tamoxifen in Yazd and Tehran Cities, Iran. Real time reactions were conducted for 10 healthy samples using the comparative Ct (Cycles threshold) method, each pair of genes being compared and samples with ratios around 1 were taken as control samples. Proliferation reactions were done by Real-Time PCR ABI Prism 7500. All registered data were transformed into SPSS 15 program and analyzed.

RESULTS

Efficiency of PCR for both CYP2D6 and ALB genes was 100%. From all 23 drug resistant patients 21.7% had one copy, 47.8% two copies and 30.4% had three copies. Also from all 56 drug sensitive patients, 26.8% had one copy, 51.8% two copies and 21.4% had three copies. The percentage of patients with one and two copies was similar between two groups but patients with three copies were more likely to belong to the drug resistant group more. Odd ratios for one and two copies were 0.759 and 0.853 respectively, indicating possible protective effects while that for three copies was 1.604.

CONCLUSIONS

Based on our study there is no significant link between CYP2D6 gene copy numbers and tamoxifen resistance in women with breast cancer. But more studies considering other influencing factors appear warranted.

CYP2D6 and the severity of suicide attempts

Aim: Among people who die by suicide, an increased frequency of CYP2D6 active gene multiplication has been described. Therefore, the present study analyzed the relationship between the severity of the suicidal intent and CYP2D6 number of active genes among survivors. Materials & methods: A group of 342 individuals were evaluated with Beck Suicide Intent Scale within 24 h of the failed attempt. ‘Severe’ suicide attempters were classified as those scoring above percentile 75 in the objective circumstances section of the Suicide Intent Scale Scale. A group of 377 healthy controls were also genotyped. Results: A higher number of ‘severe’ suicide attempters carrying ≥2 active CYP2D6 genes as compared with the rest of the patients population (p < 0.01) or the healthy control group (p < 0.01) was found. Conclusion: Considering that ‘severe’ suicide attempters are more likely eventually to die by suicide, CYP2D6 genetic polymorphism might be of use as a biomarker of death by suicide, which is in agreement with previous findings.

Original submitted: 17 July 2011; Revision submitted: 21 September 2011

Cytochrome oxidase 2D6 gene polymorphism in primary open-angle glaucoma with various effects to ophthalmic timolol

AIMS

Timolol is used topically for the treatment of glaucoma and metabolized by cytochrome P450 (CYP) 2D6 in the liver. The aim of this study is to test the hypothesis that CYP 2D6 single-nucleotide polymorphism (SNP) is associated with drug effects of ophthalmic timolol.

METHODS

A total of 133 primary open-angle glaucoma (POAG) subjects underwent the ophthalmic single timolol administration and the drug effects were observed, including lowering the effects of intraocular pressure (IOP) and side effects (i.e., appearing bradycardia). Eight SNPs of CYP2D6 were investigated in 73 subjects by a SNPstream genotyping system. The relationship between the effects of timolol and CYP2D6 Arg296Cys and Ser486Thr genotype distribution in these POAG subjects was analyzed.

RESULTS

Topical timolol administration had significant effect on IOP (P = 0.000) and heart rate (HR) (P = 0.000) in all 133 subjects, and individual ocular hypotensive effect of timolol varied between 0 and 23 mmHg. Individual effect of HR varied between -31 and 10 beats per minute, in the present study. According to SNP genotyping in 73 subjects, there was no significant difference of IOP between subjects with different CYP2D6 Arg296Cys (P = 0.308) or Ser486Thr genotypes (P = 0.741). The effect of timolol on HR was significantly different between subjects with different Arg296Cys genotypes (P = 0.046). Timolol-induced bradycardia tended to occur in subjects with Arg296Cys CT and TT genotype when compared with CC genotype (P = 0.009).

CONCLUSIONS

CYP2D6 SNP Arg296Cys appeared to be correlative with the intersubject variability seen with timolol in POAG subjects. Subjects with CC genotype trended to avoid timolol-induced bradycardia, and subjects with TT genotype trended to have poorer timolol-induced ocular hypotensive effects.

Association between the CYP2D6*4 polymorphism and depression or anxiety in the elderly

INTRODUCTION

5-methoxytryptamine (5-MT), a precursor of serotonin, is considered to be an endogenous substrate of cytochrome P450 2D6 (CYP2D6). Homozygous carriers of the variant allele CYP2D6*4 lack CYP2D6 enzyme activity. Relative to extensive metabolizers, these poor metabolizers may have lower baseline serotonin concentrations in various brain regions, and may be more prone to depression or anxiety.

AIM

To test whether the CYP2D6*4/*4 genotype is associated with a predisposition to depression or anxiety disorders in the elderly.

MATERIALS & METHODS

We conducted a cross-sectional study within the Rotterdam Study, a population-based cohort study, among persons aged 55 years or older, who were screened for depression and anxiety disorders at two consecutive examination rounds. Logistic regression was used to analyze the association between the CYP2D6*4 polymorphism and the risk of depression or anxiety disorders.

RESULTS

The risk of major depression in CYP2D6*4/*4 was not significantly different from extensive metabolizers (OR = 0.85; 95% CI: 0.36-2.00; p = 0.72). Neither did we find an association between CYP2D6 genotype and minor depression (OR = 1.56; 95% CI: 0.69-3.52; p = 0.28). No increased risk of anxiety disorders was found (OR = 1.19; 95% CI: 0.68-2.09; p = 0.55).

CONCLUSION

Variation in the CYP2D6 gene is not related to a predisposition to depression or anxiety disorders in the elderly.

Chromosome 17: association of a large inversion polymorphism with corticosteroid response in asthma

A 900-kb inversion exists within a large region of conserved linkage disequilibrium (LD) on chromosome 17. CRHR1 is located within the inversion region and associated with inhaled corticosteroid response in asthma. We hypothesized that CRHR1 variants are in LD with the inversion, supporting a potential role for natural selection in the genetic response to corticosteroids. We genotyped six single nucleotide polymorphisms (SNPs) spanning chromosome 17: 40,410,565-42,372,240, including four SNPs defining inversion status. Similar allele frequencies and strong LD were noted between the inversion and a CRHR1 SNP previously associated with lung function response to inhaled corticosteroids. Each inversion-defining SNP was strongly associated with inhaled corticosteroid response in adult asthma (P values 0.002-0.005). The CRHR1 response to inhaled corticosteroids may thus be explained by natural selection resulting from inversion status or by long-range LD with another gene. Additional pharmacogenetic investigations into regions of chromosomal diversity, including copy number variation and inversions, are warranted.

Relation between CYP2D6 phenotype and genotype and personality in healthy volunteers

Objectives: Our group has previously show that interindividual variability in CYP2D6 hydroxylation capacity was related to personality differences in cognitive social anxiety. Thus, we aimed to analyze whether this relationship between personality and CYP2D6 phenotype and genotype was found in a similar population of healthy volunteers from a different latitude and culture by using the same methodology. Methods: A total of 253 university students and staff from Havana Psychiatric Hospital and Calixto García Medical School in Cuba completed the Karolinska Scales of Personality (KSP), and were evaluated on debrisoquine hydroxylation capacity and CYP2D6 genotypes. KSP scores were compared between four groups, divided according to their CYP2D6 metabolic capacity: one of poor and three of extensive metabolizers. Furthermore, KSP scores were compared between another four different groups divided according to their number of CYP2D6 active genes: zero, one, two, and more than two. Results: In Cubans, the differences in cognitive social anxiety-related personality traits across the four CYP2D6 hydroxylation capacity groups were strikingly similar to those found in Spaniards. These differences also came out to be significant for psychic anxiety (p = 0.02) and socialization (p = 0.02). The same pattern of results obtained for the subscales of psychic anxiety, socialization, psychasthenia and inhibition of aggression with regard to phenotype in both the Cuban and Spanish studies were seen with regard to CYP2D6 genotypes. Conclusions: Corroborating these results further strengthens evidence of the relationship between CYP2D6 metabolic capacity and personality. In this population of healthy Cuban volunteers, the CYP2D6 hydroxylation capacity was related to the degree of anxiety and socialization. These results support the postulated reduction of serotonin in CYP2D6 poor metabolizers, which may be associated with a cluster of behavioral traits (e.g., anxiety, impulsivity). Thus, research is warranted to determine CYP2D6 functional implications for interindividual differences in vulnerability to neuropsychiatric diseases and drug response.

CYP2D6 polymorphism: implications for antipsychotic drug response, schizophrenia and personality traits

The CYP2D6 gene is highly polymorphic, causing absent (poor metabolizers), decreased, normal or increased enzyme activity (extensive and ultrarapid metabolizers). The genetic polymorphism of the CYP2D6 influences plasma concentration of a wide variety of drugs metabolized in the liver by the cytochrome P450 (CYP) 2D6 enzyme, including antipsychotic drugs used for schizophrenia treatment. Additionally, CYP2D6 is involved in the metabolism of endogenous substrates in the brain, and reported to be located in regions such as the cortex, hippocampus and cerebellum, which are impaired in schizophrenia. Moreover, recently we have found that CYP2D6 poor metabolizers are under-represented in a case-control association study of schizophrenia. Furthermore, null CYP2D6 activity in healthy volunteers is associated with personality characteristics of social cognitive anxiety, which may bear some resemblance to milder forms of psychotic-like symptoms. In keeping with this, CYP2D6 may influence, not only variability to drug response, but also vulnerability to disease in schizophrenia patients.

CYP2D6 and DRD2 genes differentially impact pharmacodynamic sensitivity and time course of prolactin response to perphenazine

OBJECTIVES

We observed that CYP2D6 contributes to pharmacodynamic tissue sensitivity to perphenazine as measured by the areas under the curve (AUCs) expressed as a ratio (prolactin-AUC0-6/perphenazine-AUC0-6) in Chinese Canadians [Pharmacogenetics and Genomics 2007; 17:339-347]. As genetic heterogeneity in drug targets can influence drug response, we sought to further evaluate the contribution of CYP2D6 to pharmacodynamic sensitivity in our previous study sample in tandem with DRD2, the primary molecular target for perphenazine.

METHODS

Genotyping for DRD2 Taq1A, -141C ins/del and Ser311Cys functional polymorphisms was performed using PCR-restriction-fragment length polymorphism methods.

RESULTS

After controlling for DRD2 polymorphisms, CYP2D6 was a significant predictor of pituitary pharmacodynamic tissue sensitivity to perphenazine (P=0.024; power=80.4%). Taq1A polymorphism significantly influenced the time course of prolactin response (P=0.039; power=70%). A1/A1 genotype displayed a higher prolactin elevation 2 h after perphenazine administration (P=0.02). Patients with -141C ins/ins genotype showed a strong trend toward a 38% larger prolactin AUC compared with the -141C ins/del genotypic group (P=0.07).

CONCLUSIONS

CYP2D6 seems to be an independent contributor to pituitary pharmacodynamic tissue sensitivity to perphenazine after accounting for DRD2 functional polymorphisms. The A1 allele of the Taq1A polymorphism was previously shown to decrease D2 receptor density in vitro and in neuroimaging studies in vivo. At a given antipsychotic dose, individuals with A1 allele might thus achieve a higher DRD2 antipsychotic occupancy, which is consistent with an increased prolactin elevation in the A1/A1 genotype in this study. These findings provide a basis for further studies on the endogenous substrates of CYP2D6 and the rational selection of candidate genes for long-term consequences of antipsychotic-induced hyperprolactinemia (e.g. susceptibility to breast and prostate cancers).

Comprehensive assessment of metabolic enzyme and transporter genes using the Affymetrix Targeted Genotyping System

The combined effects of multiple polymorphisms in several drug-metabolizing enzyme and transporter genes can contribute to considerable interindividual variation in drug disposition and response. Therefore, it has been of increasing interest to generate scalable, flexible and cost-effective technologies for large-scale genotyping of the drug-metabolizing enzyme and transporter genes. However, the number of drug-metabolizing enzyme and transporter gene variants exceeds the capacity of current technologies to comprehensively assess multiple polymorphisms in a single, multiplexed assay. The Targeted Genotyping System (Affymetrix, CA, USA) provides a solution to this challenge, by combining molecular inversion probe technology with universal microarrays to provide a method that is capable of analyzing thousands of variants in a single reaction, while remaining relatively insensitive to cross-reactivity between reaction components. This review will focus on the Targeted Genotyping System and how this technology was adapted to enable comprehensive analysis of drug-metabolizing enzyme and transporter gene polymorphisms.

Multiplex assay for comprehensive genotyping of genes involved in drug metabolism, excretion, and transport

BACKGROUND

Drug metabolism is a multistep process by which the body disposes of xenobiotic agents such as therapeutic drugs. Genetic variation in the enzymes involved in this process can lead to variability in a patient's response to medication.

METHODS

We used molecular-inversion probe technology to develop a multiplex genotyping assay that can simultaneously test for 1227 genetic variants in 169 genes involved in drug metabolism, excretion, and transport. Within this larger set of variants, we performed analytical validation of a clinically defined core set of 165 variants in 27 genes to assess accuracy, imprecision, and dynamic range.

RESULTS

In a test set of 91 samples, genotyping accuracy for the core set probes was 99.8% for called genotypes, with a 1.2% no-call (NC) rate. The majority of the core set probes (133 of 165) had < or = 1 genotyping failure in the test set; a subset of 12 probes was responsible for the majority of failures (mainly NC). Genotyping results were reproducible upon repeat testing with overall within- and between-run variation of 1.1% and 1.4%, respectively-again, primarily NCs in a subset of probes. The assay showed stable genotyping results over a 6-fold range of input DNA.

CONCLUSIONS

This assay generates a comprehensive assessment of a patient's metabolic genotype and is a tool that can provide a more thorough understanding of patient-to-patient variability in pharmacokinetic responses to drugs.

CYP2D6 genotype in relation to perphenazine concentration and pituitary pharmacodynamic tissue sensitivity in Asians: CYP2D6–serotonin–dopamine crosstalk revisited

OBJECTIVES

Hyperprolactinemia is a common side effect of first-generation antipsychotics mediated by antagonism of dopaminergic neurotransmission in the pituitary. Most first-generation antipsychotics are metabolized by CYP2D6 in the liver. Further, CYP2D6 is expressed in the human brain as a 5-methoxyindolethylamine O-demethylase potentially contributing to regeneration of serotonin from 5-methoxytryptamine. As dopaminergic neurotransmission is subject to regulation by serotonin, CYP2D6 may exert a nuanced (serotonergic) influence on dopaminergic tone in the pituitary. CYP2D6*10 is an allele associated with reduced enzyme function and occurs in high frequency (about 50%) in Asians. We prospectively evaluated significance of CYP2D6 genetic variation for prolactin response to perphenazine (a model first-generation antipsychotic) in Asians.

METHODS

A single oral dose of perphenazine (0.1 mg/kg) or placebo was administered to 22 medication-free nonsmoker healthy male Chinese-Canadian volunteers, following a double-blind within-subject randomized design. Blood samples were drawn at baseline and 2, 3, 4, 5 and 6 h after drug administration.

RESULTS

In volunteers with CYP2D6*10/CYP2D6*10 genotype, the mean area under curve (AUC0-6) for perphenazine concentration was 2.9-fold higher than those who carry the CYP2D6*1 allele (P<0.01). Notably, volunteers homozygous for CYP2D6*10 exhibited a significant reduction (66%) in mean pharmacodynamic tissue sensitivity as measured by the (prolactin-AUC0-6/perphenazine-AUC0-6) ratio (P=0.02).

CONCLUSIONS

CYP2D6 genotype is a significant contributor to perphenazine concentration in Chinese-Canadians. Importantly, prolactin response, when normalized per unit perphenazine concentration, appears to be blunted in volunteers homozygous for CYP2D6*10. We suggest that CYP2D6 genetic variation may potentially influence pharmacodynamic tissue sensitivity in the pituitary, presumably through disposition of an endogenous substrate (e.g. 5-methoxytryptamine).

Could endogenous substrates of drug-metabolizing enzymes influence constitutive physiology and drug target responsiveness?

Integration of genomic data from pharmacokinetic pathways and drug targets is an emerging trend in bioinformatics, but is there a clear separation of pharmacokinetic pathways and drug targets? Should we also consider the potential interactions of endogenous substrates of drug-metabolizing enzymes with receptors and other molecular drug targets as we combine pharmacogenomic datasets? We discuss these overarching questions through a specific pharmacogenomic case study of the cytochrome P450 (CYP)2D6, serotonin and dopamine triad. Importantly, CYP2D6 may contribute to the regeneration of serotonin from 5-methoxytryptamine by virtue of its catalytic function as a 5-methoxyindolethylamine O-demethylase. Furthermore, serotonergic neurons provide a regulatory feedback on dopaminergic neurotransmission. Hence, we hypothesize that independent of its role as a pharmacokinetic gene, CYP2D6 may nuance the regulation of serotonergic and dopaminergic neurophysiology. Additionally, we reflect upon the contribution of hyperspecialization in biomedicine to the present disconnect between research on pharmacokinetics and drug targets, and the potential for remedying this important gap through informed dialogue among clinical pharmacologists, human geneticists, bioethicists and applied social scientists.

Pharmacokinetics of codeine and its metabolite morphine in ultra-rapid metabolizers due to CYP2D6 duplication

Codeine is an analgesic drug acting on mu-opiate receptors predominantly via its metabolite morphine, which is formed almost exclusively by the genetically polymorphic enzyme cytochrome P450 2D6 (CYP2D6). Whereas it is known that individuals lacking CYP2D6 activity (poor metabolizers, PM) suffer from poor analgesia from codeine, ultra-fast metabolizers (UM) due to the CYP2D6 gene duplication may experience exaggerated and even potentially dangerous opioidergic effects and no systematical study has been performed so far on this question. A single dose of 30 mg codeine was administered to 12 UM of CYP2D6 substrates carrying a CYP2D6 gene duplication, 11 extensive metabolizers (EM) and three PM. Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism methods and a single-base primer extension method for characterization of the gene-duplication alleles. Pharmacokinetics was measured over 24 h after drug intake and codeine and its metabolites in plasma and urine were analyzed by liquid chromatography with tandem mass spectrometry. Significant differences between the EM and UM groups were detected in areas under the plasma concentration versus time curves (AUCs) of morphine with a median (range) AUC of 11 (5-17) microg h l(-1) in EMs and 16 (10-24) microg h l(-1) in UM (P=0.02). In urine collected over 12 h, the metabolic ratios of the codeine+codeine-6-glucuronide divided by the sum of morphine+its glucuronides metabolites were 11 (6-17) in EMs and 9 (6-16) in UM (P=0.05). Ten of the 11 CYP2D6 UMs felt sedation (91%) compared to six (50%) of the 12 EMs (P=0.03). CYP2D6 genotypes predicting ultrarapid metabolism resulted in about 50% higher plasma concentrations of morphine and its glucuronides compared with the EM. No severe adverse effects were seen in the UMs in our study most likely because we used for safety reasons a low dose of only 30 mg. It might be good if physicians would know about the CYP2D6 duplication genotype of their patients before administering codeine.