Interethnic variability ofCYP2D6alleles and of predicted and measured metabolic phenotypes across world populations

Evaluation of the effect of CYP2D6*3, *4,*10, and *17 polymorphisms on the pharmacokinetic of tamoxifen and its metabolites in patients with hormone-positive breast cancer

BACKGROUND AND OBJECTIVE

A high rate of interindividual variability in response to tamoxifen (TAM) in breast cancer patients with CYP2D6 polymorphism has been reported, which affects the patient's therapeutic outcome. The objective of this study was to investigate the pharmacogenomics of CYP2D6 genotyping in Iranian patients with breast cancer treated with adjuvant TAM.

METHODS

A peripheral blood sample was obtained to determine the steady-state plasma concentrations of TAM and its metabolites (Endoxifen (EN) and 4-Hydroxytamoxifen (4-OHT)) using high-performance liquid chromatography with fluorescence detection (HPLC-FLU) assay. We detected CYP2D6 * 3, * 4, * 10, and * 17 single nucleotide polymorphisms via polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

A total of 84 Iranian estrogen receptor‑positive breast cancer patients receiving the daily dose of 20 mg tamoxifen were recruited. Although a consequent decrease in the median EN and 4-OHT concentrations was observed by comparing poor or intermediate metabolizer patients with an extensive metabolizer population, this difference did not reach a significant level. The mean plasma EN concentrations in poor and intermediate metabolizers were 46.1% (95% CI, 7.4-27.8%) and 59.4% (95% CI, 11.9-37.3%) of extensive metabolizer subjects, respectively. Poor and intermediate metabolizers had the mean plasma 4-OHT concentrations that were 46.6% (95% CI, 0.9-61.7%) and 73.2% (95% CI, 2.7-93.1%) of those of subjects who were extensive metabolizer, respectively.

CONCLUSIONS

The possible role of genotyping in Iranian patients' response to treatment may explain inter-individual differences in the plasma concentrations of active metabolites of TAM.

Whole blood hydroxychloroquine: Does genetic polymorphism of cytochrome P450 enzymes have a role?

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with a wide range of clinical manifestations and multifactorial etiologies ranging from environmental to genetic. SLE is associated with dysregulated immunological reactions, with increased immune complex formation leading to end-organ damages such as lupus nephritis, cutaneous lupus, and musculoskeletal disorders. Lupus treatment aims to reduce disease activity, prevent organ damage, and improve long-term patient survival and quality of life. Antimalarial, hydroxychloroquine (HCQ) is used as a first-line systemic treatment for lupus. It has shown profound efficacy in lupus and its associated conditions. However, wide variation in terms of clinical response to this drug has been observed among this group of patients. This variability has limited the potential of HCQ to achieve absolute clinical benefits. Several factors, including genetic polymorphisms of cytochrome P450 enzymes, have been stipulated as key entities leading to this inter-individual variation. Thus, there is a need for more studies to understand the role of genetic polymorphisms in CYP450 enzymes in the clinical response to HCQ. Focusing on the role of genetic polymorphism on whole blood HCQ in lupus disorder, this review aims to highlight up-to-date pathophysiology of SLE, the mechanism of action of HCQ, and finally the role of genetic polymorphism of CYP450 enzymes on whole blood HCQ level as well as clinical response in lupus.

Implementation of pre-emptive testing of a pharmacogenomic panel in clinical practice: Where do we stand?

Adverse drug reactions (ADRs) account for a large proportion of hospitalizations among adults and are more common in multimorbid patients, worsening clinical outcomes and burdening healthcare resources. Over the past decade, pharmacogenomics has been developed as a practical tool for optimizing treatment outcomes by mitigating the risk of ADRs. Some single-gene reactive tests are already used in clinical practice, including the DPYD test for fluoropyrimidines, which demonstrates how integrating pharmacogenomic data into routine care can improve patient safety in a cost-effective manner. The evolution from reactive single-gene testing to comprehensive pre-emptive genotyping panels holds great potential for refining drug prescribing practices. Several implementation projects have been conducted to test the feasibility of applying different genetic panels in clinical practice. Recently, the results of a large prospective randomized trial in Europe (the PREPARE study by Ubiquitous Pharmacogenomics consortium) have provided the first evidence that prospective application of a pre-emptive pharmacogenomic test panel in clinical practice, in seven European healthcare systems, is feasible and yielded a 30% reduction in the risk of developing clinically relevant toxicities. Nevertheless, some important questions remain unanswered and will hopefully be addressed by future dedicated studies. These issues include the cost-effectiveness of applying a pre-emptive genotyping panel, the role of multiple co-medications, the transferability of currently tested pharmacogenetic guidelines among patients of non-European origin and the impact of rare pharmacogenetic variants that are not detected by currently used genotyping approaches.

Interethnic differences in drug response: projected impact of genetic variations in the Saudi population

Ethnicity is known to have an impact on drug responses. This is particularly important for drugs that have a narrow therapeutic window, nonlinearity in pharmacokinetics and are metabolized by enzymes that demonstrate genetic polymorphisms. However, most clinical trials are conducted among Caucasians, which might limit the usefulness of the findings of such studies for other ethnicities. The representation of participants from Saudi Arabia in global clinical trials is low. Therefore, there is a paucity of evidence to assess the impact of ethnic variability in the Saudi population on drug response. In this article, the authors assess the projected impact of genetic polymorphisms in drug-metabolizing enzymes and drug targets on drug response in the Saudi population.

CYP2D6 Genotype and Pharmacovigilance Impact on Autism Spectrum Disorder: A Naturalistic Study with Extreme Phenotype Analysis

The long-term use of psychopharmacology medications in autism spectrum disorder (ASD) hitherto remains controversial due to a lack of evidence about safety and tolerability. In this regard, genotyping the metabolizing enzyme cytochrome P450 (CYP) 2D6, especially its extreme phenotypes, could help to prevent drug-related adverse reactions or adverse events (AEs). There are several medications warranting CYP2D6 screening that are consumed by people with ASD, such as risperidone and aripiprazole to name a few. A naturalistic observational study was carried out in participants with ASD to analyze the influence of the CYP2D6 phenotype in drug tolerability using a local pharmacovigilance system created for this study. In this case, AEs were identified from participants' electronic health records (EHRs) and paper registries. Other variables were collected: socio-demographic information, comorbidities, and psychopharmacology prescriptions (polypharmacy defined as ≥4 simultaneous prescriptions) and doses. The genetic analysis included allelic discrimination (CYP2D6*1, *2, *3, *4, *5, *6, *10, *17, and *41) and copy number variations. All of these were used to determine theoretical phenotypes of the metabolic profiles: poor (PM); intermediate (IM); normal (NM); and ultra-rapid (UM). Sex differences were analyzed. A total of 71 participants (30 ± 10 years old, 82% male, 45% CYP2D6 NM phenotype (32 participants)) with a median of 3 (IQR 2-4) comorbidities per person, mainly urinary incontinence (32%) and constipation (22%), were included. CYP2D6 UM showed the highest rate of polypharmacy, whilst, IM participants had the highest rates of neurological and psychiatric AEs, even worse if a CYP2D6 inhibitor drug was prescribed simultaneously. CYP2D6 pharmacogenomics and the monitoring of new antipsychotic prescriptions may make a difference in medication safety in adults with ASD. Particularly in those with psychopharmacology polymedication, it can help with AE avoidance and understanding.

Characterization of pharmacogenomic variants in a Brazilian admixed cohort of elderly individuals based on whole-genome sequencing data

Introduction: Research in the field of pharmacogenomics (PGx) aims to identify genetic variants that modulate response to drugs, through alterations in their pharmacokinetics (PK) or pharmacodynamics (PD). The distribution of PGx variants differs considerably among populations, and whole-genome sequencing (WGS) plays a major role as a comprehensive approach to detect both common and rare variants. This study evaluated the frequency of PGx markers in the context of the Brazilian population, using data from a population-based admixed cohort from Sao Paulo, Brazil, which includes variants from WGS of 1,171 unrelated, elderly individuals. Methods: The Stargazer tool was used to call star alleles and structural variants (SVs) from 38 pharmacogenes. Clinically relevant variants were investigated, and the predicted drug response phenotype was analyzed in combination with the medication record to assess individuals potentially at high-risk of gene-drug interaction. Results: In total, 352 unique star alleles or haplotypes were observed, of which 255 and 199 had a frequency < 0.05 and < 0.01, respectively. For star alleles with frequency > 5% (n = 97), decreased, loss-of-function and unknown function accounted for 13.4%, 8.2% and 27.8% of alleles or haplotypes, respectively. Structural variants (SVs) were identified in 35 genes for at least one individual, and occurred with frequencies >5% for CYP2D6, CYP2A6, GSTM1, and UGT2B17. Overall 98.0% of the individuals carried at least one high risk genotype-predicted phenotype in pharmacogenes with PharmGKB level of evidence 1A for drug interaction. The Electronic Health Record (EHR) Priority Result Notation and the cohort medication registry were combined to assess high-risk gene-drug interactions. In general, 42.0% of the cohort used at least one PharmGKB evidence level 1A drug, and 18.9% of individuals who used PharmGKB evidence level 1A drugs had a genotype-predicted phenotype of high-risk gene-drug interaction. Conclusion: This study described the applicability of next-generation sequencing (NGS) techniques for translating PGx variants into clinically relevant phenotypes on a large scale in the Brazilian population and explores the feasibility of systematic adoption of PGx testing in Brazil.

Personalizing atomoxetine dosing in children with ADHD: what can we learn from current supporting evidence

PURPOSE

There is marked heterogeneity in treatment response of atomoxetine in patients with attention deficit/hyperactivity disorder (ADHD), especially for the pediatric population. This review aims to evaluate current evidence to characterize the dose-exposure relationship, establish clinically relevant metrics for systemic exposure to atomoxetine, define a therapeutic exposure range, and to provide a dose-adaptation strategy before implementing personalized dosing for atomoxetine in children with ADHD.

METHODS

A comprehensive search was performed across electronic databases (PubMed and Embase) covering the period of January 1, 1985 to July 10, 2022, to summarize recent advances in the pharmacokinetics, pharmacogenomics/pharmacogenetics (PGx), therapeutic drug monitoring (TDM), physiologically based pharmacokinetics (PBPK), and population pharmacokinetics (PPK) of atomoxetine in children with ADHD.

RESULTS

Some factors affecting the pharmacokinetics of atomoxetine were summarized, including food, CYP2D6 and CYP2C19 phenotypes, and drug‒drug interactions (DDIs). The association between treatment response and genetic polymorphisms of genes encoding pharmacological targets, such as norepinephrine transporter (NET/SLC6A2) and dopamine β hydroxylase (DBH), was also discussed. Based on well-developed and validated assays for monitoring plasma concentrations of atomoxetine, the therapeutic reference range in pediatric patients with ADHD proposed by several studies was summarized. However, supporting evidence on the relationship between systemic atomoxetine exposure levels and clinical response was far from sufficient.

CONCLUSION

Personalizing atomoxetine dosage may be even more complex than anticipated thus far, but elucidating the best way to tailor the non-stimulant to a patient's individual need will be achieved by combining two strategies: detailed research in linking the pharmacokinetics and pharmacodynamics in pediatric patients, and better understanding in nature and causes of ADHD, as well as environmental stressors.

Theranostics for COVID-19 Antiviral Drugs: Prospects and Challenges for Worldwide Precision/Personalized Medicine

Coronavirus disease 2019 (COVID-19) is a systemic disease that impacts multiple organ systems with a complex clinical presentation and outcomes that can vary from person to person and between populations. To optimize COVID-19 treatment outcomes, and in light of the availability of antiviral drugs, there is a need for greater attention to the field of theranostics, the fusion of therapeutics and diagnostics. Theranostics tests would be invaluable, we suggest in this expert review, so as to optimize the efficacy and safety of current and future antiviral drugs against COVID-19. Theranostics would also assist in the design and implementation of clinical trials with antiviral drug candidates. We discuss here theranostics considering drugs such as remdesivir, Paxlovid™, and molnupiravir. All in all, we underscore that theranostics as a concept and practice is essential for efficient and safe health interventions against COVID-19 and other ecological crises in the 21st century.

Considerations into pharmacogenomics of COVID-19 pharmacotherapy: Hope, hype and reality

COVID-19 medicines, such as molnupiravir are beginning to emerge for public health and clinical practice. On the other hand, drugs display marked variability in their efficacy and safety. Hence, COVID-19 medicines, as with all drugs, will be subject to the age-old maxim “one size prescription does not fit all”. In this context, pharmacogenomics is the study of genome-by-drug interactions and offers insights on mechanisms of patient-to-patient and between-population variations in drug efficacy and safety. Pharmacogenomics information is crucial to tailoring the patients' prescriptions to achieve COVID-19 preventive and therapeutic interventions that take into account the host biology, patients’ genome, and variable environmental exposures that collectively influence drug efficacy and safety. This expert review critically evaluates and summarizes the pharmacogenomics and personalized medicine aspects of the emerging COVID-19 drugs, and other selected drug interventions deployed to date. Here, we aim to sort out the hope, hype, and reality and suggest that there are veritable prospects to advance COVID-19 medicines for public health benefits, provided that pharmacogenomics is considered and implemented adequately. Pharmacogenomics is an integral part of rational and evidence-based medical practice. Scientists, health care professionals, pharmacists, pharmacovigilance practitioners, and importantly, patients stand to benefit by expanding the current pandemic response toolbox by the science of pharmacogenomics, and its applications in COVID-19 medicines and clinical trials.

Joint Analysis of Phenotypic and Genomic Diversity Sheds Light on the Evolution of Xenobiotic Metabolism in Humans

Variation in genes involved in the absorption, distribution, metabolism, and excretion of drugs (ADME) can influence individual response to a therapeutic treatment. The study of ADME genetic diversity in human populations has led to evolutionary hypotheses of adaptation to distinct chemical environments. Population differentiation in measured drug metabolism phenotypes is, however, scarcely documented, often indirectly estimated via genotype-predicted phenotypes. We administered seven probe compounds devised to target six cytochrome P450 enzymes and the P-glycoprotein (P-gp) activity to assess phenotypic variation in four populations along a latitudinal transect spanning over Africa, the Middle East, and Europe (349 healthy Ethiopian, Omani, Greek, and Czech volunteers). We demonstrate significant population differentiation for all phenotypes except the one measuring CYP2D6 activity. Genome-wide association studies (GWAS) evidenced that the variability of phenotypes measuring CYP2B6, CYP2C9, CYP2C19, and CYP2D6 activity was associated with genetic variants linked to the corresponding encoding genes, and additional genes for the latter three. Instead, GWAS did not indicate any association between genetic diversity and the phenotypes measuring CYP1A2, CYP3A4, and P-gp activity. Genome scans of selection highlighted multiple candidate regions, a few of which included ADME genes, but none overlapped with the GWAS candidates. Our results suggest that different mechanisms have been shaping the evolution of these phenotypes, including phenotypic plasticity, and possibly some form of balancing selection. We discuss how these contrasting results highlight the diverse evolutionary trajectories of ADME genes and proteins, consistent with the wide spectrum of both endogenous and exogenous molecules that are their substrates.

CYP2D6 gene polymorphism and apatinib affect the metabolic profile of fluvoxamine

This study aimed 1) to investigate the influence of CYP2D6 variants on the catalyzing of fluvoxamine, and 2) to study the interaction between fluvoxamine and apatinib. An enzymatic reaction system was setup and the kinetic profile of CYP2D6 in metabolizing fluvoxamine was determined. In vivo, drug-drug interaction was investigated using Sprague–Dawley (SD) rats. Fluvoxamine was given gavage with or without apatinib. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to determine the concentrations of fluvoxamine and desmethyl-fluvoxamine. The results demonstrated that the relative clearance rates of CYP2D6.A5V, V104A, D337G, F164L, V342M, R440C and R497C increased significantly compared with CYP2D6.1, ranging from 153.626% ± 6.718% to 394.310% ± 33.268%. The activities of other variants reduced to different extent, or even lost function, but there was no statistical difference. The IC₅₀ of apatinib against fluvoxamine disposition was determined, which is 0.190 μM in RLM and 6.419 μM in HLM, respectively. In vivo, apatinib can enhance the plasma exposure of fluvoxamine remarkably characterized by increased AUC, Tmax and Cmax. Meanwhile, the produce of desmethyl fluvoxamine was dramatically inhibited, both AUC and C_max decreased significantly. Mechanistically, apatinib inhibit the generation of fluvoxamine metabolite with a mixed manner both in RLM and HLM. Furthermore, there were differences in the potency of apatinib in suppressing fluvoxamine metabolism among CYP2D6.1, 2 and 10. In conclusion, CYP2D6 gene polymorphisms and drug-drug interaction can remarkably affect the plasma exposure of fluvoxamine. The present study provides basis data for guiding individual application of fluvoxamine.

A potential paradigm shift in opioid crisis management: The role of pharmacogenomics

Pharmacogenetic investigations into the opioid crisis suggest genetic variation could be a significant cause of opioid-related morbidity and mortality. Variability in opioid system genes, including single nucleotide polymorphisms, manifest after pharmacogenetic testing, as previously invisible risk factors for addiction and overdose. Pharmacodynamic genes regulate opioid-sensitive brain networks and neural reward circuitry. Pharmacokinetic genes expressed in drug metabolic pathways regulate blood levels of active vs. inactive opioid metabolites. Elucidating the complex interplay of genetic variations in pharmacokinetic and pharmacodynamic pathways will shed new light on the addictive and toxic properties of opioids. This narrative review serves to promote understanding of key genetic mechanisms affecting the metabolism and actions of opioids, and to explore causes of the recent surge in opioid-related mortality associated with COVID-19. Personalised treatment plans centred around an individual's genetic makeup could make opioid-based pain management and opioid use disorder (OUD) treatments safer and more effective at both the individual and system levels.

Pharmacogenetics of Breast Cancer Treatments: A Sub-Saharan Africa Perspective

Breast cancer is the most frequent cause of cancer death in low- and middle-income countries, in particular among sub-Saharan African women, where response to available anticancer treatment therapy is often limited by the recurrent breast tumours and metastasis, ultimately resulting in decreased overall survival rate. This can also be attributed to African genomes that contain more variation than those from other parts of the world. The purpose of this review is to summarize published evidence on pharmacogenetic and pharmacokinetic aspects related to specific available treatments and the known genetic variabilities associated with metabolism and/or transport of breast cancer drugs, and treatment outcomes when possible. The emphasis is on the African genetic variation and focuses on the genes with the highest strength of evidence, with a close look on CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, CYP19A1, UGT1A4, UGT2B7, UGT2B15, SLC22A16, SLC38A7, FcγR, DPYD, ABCB1, and SULT1A1, which are the genes known to play major roles in the metabolism and/or elimination of the respective anti-breast cancer drugs given to the patients. The genetic variability of their metabolism could be associated with different metabolic phenotypes that may cause reduced patients’ adherence because of toxicity or sub-therapeutic doses. Finally, this knowledge enhances possible personalized treatment approaches, with the possibility of improving survival outcomes in patients with breast cancer.

Tafenoquine for the treatment of Plasmodium vivax malaria

INTRODUCTION

Plasmodium vivax malaria causes significant disease burden worldwide, especially in Latin America, Southeast Asia, and Oceania. P. vivax is characterized by the production of liver hypnozoites that cause clinical relapses upon periodic activation. Primaquine, an 8-aminoquinoline drug, has been the standard of care for decades to treat liver-stage P. vivax malaria; however, it requires long treatment regimens (one to two weeks) that lead to poor adherence and thus clinical relapses. Tafenoquine (TFQ), a newly available and efficacious single-dose 8-aminoquinoline, aims to address this challenge. Safe administration is possible when paired with the use of glucose-6-phosphate dehydrogenase (G6PD) diagnostics to prevent 8-aminoquinoline-induced hemolysis in patients with underlying G6PD deficiency (G6PDd).

AREAS COVERED

In this review, the authors present the recent literature regarding the pharmacology, efficacy, safety, and tolerability of TFQ and highlight regional differences in these areas. The authors also discuss the potential for TFQ, complemented with primaquine PQ and effective screening for G6PDd, to improve P. vivax clinical management and facilitate targeted mass drug administration in communities to decrease transmission.

EXPERT OPINION

Clinical studies show therapeutic efficacy of TFQ as well as a good performance in terms of safety and tolerability. Additional research regarding the effectiveness and safety TFQ in malaria elimination strategies such as targeted or mass drug administration are needed.

A cross-sectional study of the relationship between CYP2D6 and CYP2C19 variations and depression symptoms, for women taking SSRIs during pregnancy

Depression during pregnancy affects 10-15% of women, and 5% of women take antidepressants during pregnancy. Clinical guidelines provide recommendations for selective serotonin reuptake inhibitor (SSRI) drug choice and dose based on CYP2D6 and CYP2C19 genotype; however, they are based on evidence from non-pregnant cohorts. This study aimed to test the hypothesis that women with function-altering variants (increased, decreased, or no function) in these pharmacogenes, taking SSRIs prenatally, would have more depression symptoms than women whose pharmacogenetic variants are associated with normal SSRI metabolism. Comprehensive CYP2D6 and CYP2C19 genotyping using a range of methods, including gene copy number analysis, was performed as secondary analyses on two longitudinal cohorts of pregnant women (N = 83) taking the SSRIs paroxetine, citalopram, escitalopram, or sertraline. The Kruskal-Wallis test compared mean depression scores across four predicted metabolizer groups: poor (n = 5), intermediate (n = 10), normal (n = 53), and ultrarapid (n = 15). There were no significant differences between mean depression scores across the four metabolizer groups (H(3) = .73, p = .87, eta-squared = .029, epsilon-squared = .0089). This is the first study of the relationship in pregnancy between CYP2C19 pharmacogenetic variations and depression symptoms in the context of SSRI use. Findings from this initial study do not support the clinical use of pharmacogenetic testing for SSRI use during the second or third trimesters of pregnancy, but these findings should be confirmed in larger cohorts. There is an urgent need for further research to clarify the utility of pharmacogenetic testing for pregnant women, especially as companies offering direct-to-consumer genetic testing expand their marketing efforts.

Untangling SNP Variations within CYP2D6 Gene in Croatian Roma

CYP2D6 is a highly polymorphic gene whose variations affect its enzyme activity. To assess whether the specific population history of Roma, characterized by constant migrations and endogamy, influenced the distribution of alleles and thus phenotypes, the CYP2D6 gene was sequenced using NGS (Next Generation Sequencing) method-targeted sequencing in three groups of Croatian Roma (N = 323) and results were compared to European and Asian populations. Identified single nucleotide polymorphisms (SNPs) were used to reconstruct haplotypes, which were translated into the star-allele nomenclature and later into phenotypes. A total of 43 polymorphic SNPs were identified. The three Roma groups differed significantly in the frequency of alleles of polymorphisms 6769 A > G, 6089 G > A, and 5264 A > G (p < 0.01), as well as in the prevalence of the five most represented star alleles: *1, *2, *4, *10, and *41 (p < 0.0001). Croatian Roma differ from the European and Asian populations in the accumulation of globally rare SNPs (6089 G > A, 4589 C > T, 4622 G > C, 7490 T > C). Our results also show that demographic history influences SNP variations in the Roma population. The three socio-culturally different Roma groups studied differ significantly in the distribution of star alleles, which confirms the importance of a separate study of different Roma groups.

Pharmacogenetics research in Brazil: a systematic review

Aim: Pharmacogenomics (PGx) is a rising scientific area in many countries, such as Brazil. Objectives: To identify biomarkers, therapeutic areas, probe drugs and regions/ethnicities most studied in the country in order to guide future studies. Materials & methods: Systematic review of 1060 studies (from 1968 to 2020) comprising 80 genes, six probe drugs and 3,819,233 individuals. Results: MTHFR and HLA-A/B were the most studied genes and metoprolol and dextromethorphan the most studied probe drugs. Oncology was the most studied therapeutic area considering PGx biomarkers. The country’s regions and ethnic groups were studied unevenly, with south/southeast and White people over-represented in respect to their demographic relevance, in detriment of the center-west/northeast/north and Black/mixed individuals. Conclusion: Many of the gaps and possible paths to be covered to reach even PGx data are pointed out by this review.

Genotypic and phenotypic landscapes of 51 pharmacogenes derived from whole-genome sequencing in a Thai population

Differences in drug responses in individuals are partly due to genetic variations in pharmacogenes, which differ among populations. Here, genome sequencing of 171 unrelated Thai individuals from all regions of Thailand was used to call star alleles of 51 pharmacogenes by Stargazer, determine allele and genotype frequencies, predict phenotype and compare high-impact variant frequencies between Thai and other populations. Three control genes, EGFR, VDR, and RYR1, were used, giving consistent results. Every individual had at least three genes with variant or altered phenotype. Forty of the 51 pharmacogenes had at least one individual with variant or altered phenotype. Moreover, thirteen genes had at least 25% of individuals with variant or altered phenotype including SLCO1B3 (97.08%), CYP3A5 (88.3%), CYP2C19 (60.82%), CYP2A6 (60.2%), SULT1A1 (56.14%), G6PD (54.39%), CYP4B1 (50.00%), CYP2D6 (48.65%), CYP2F1 (46.41%), NAT2 (40.35%), SLCO2B1 (28.95%), UGT1A1 (28.07%), and SLCO1B1 (26.79%). Allele frequencies of high impact variants from our samples were most similar to East Asian. Remarkably, we identified twenty predicted high impact variants which have not previously been reported. Our results provide information that contributes to the implementation of pharmacogenetic testing in Thailand and other Southeast Asian countries, bringing a step closer to personalized medicine.

Frequencies of CYP2D6 genetic polymorphisms in Arab populations

CYP2D6 is a key drug-metabolizing enzyme implicated in the biotransformation of approximately 25% of currently prescribed drugs. Interindividual and interethnic differences in CYP2D6 enzymatic activity, and hence variability in substrate drug efficacy and safety, are attributed to a highly polymorphic corresponding gene. This study aims at reviewing the frequencies of the most clinically relevant CYP2D6 alleles in the Arabs countries. Articles published before May 2021 that reported CYP2D6 genotype and allelic frequencies in the Arab populations of the Middle East and North Africa (MENA) region were retrieved from PubMed and Google Scholar databases. This review included 15 original articles encompassing 2737 individuals from 11 countries of the 22 members of the League of Arab States. Active CYP2D6 gene duplications reached the highest frequencies of 28.3% and 10.4% in Algeria and Saudi Arabia, respectively, and lowest in Egypt (2.41%) and Palestine (4.9%). Frequencies of the loss-of-function allele CYP2D6*4 ranged from 3.5% in Saudi Arabia to 18.8% in Egypt. The disparity in frequencies of the reduced-function CYP2D6*10 allele was perceptible, with the highest frequency reported in Jordan (14.8%) and the lowest in neighboring Palestine (2%), and in Algeria (0%). The reduced-function allele CYP2D6*41 was more prevalent in the Arabian Peninsula countries; Saudi Arabia (18.4%) and the United Arab Emirates (15.2%), in comparison with the Northern Arab-Levantine Syria (9.7%) and Algeria (8.3%). Our study demonstrates heterogeneity of CYP2D6 alleles among Arab populations. The incongruities of the frequencies of alleles in neighboring countries with similar demographic composition emphasize the necessity for harmonizing criteria of genotype assignment and conducting comprehensive studies on larger MENA Arab populations to determine their CYP2D6 allelic makeup and improve therapeutic outcomes of CYP2D6- metabolized drugs.

GSTM1 and GSTT1 polymorphisms in healthy volunteers - a worldwide systematic review

The GSTM1 and GSTT1 genes encode homonymous enzymes, which are responsible for the detoxification of several substances potentially harmful to the human body, such as air pollution, drugs, pesticides, and tobacco. However, some individuals may present a complete deletion of these genes and, consequently, an enzyme deficiency leading to an inadequate metabolism and, therefore, a higher susceptibility to some clinical conditions. Interethnic variations have also been described for both genes, making necessary the study of the deletion frequencies of GSTM1 and GSTT1 in different populations around the world. So, the aim of this study was to enable the synthesis and discussion of the main population differences of GSTM1 and GSTT1 polymorphisms in healthy volunteers. Searches were performed in the PubMed database, including 533 articles and 178,566 individuals in the analyses. We found an overrepresentation of European individuals and studies, and an underrepresentation of non-European ethnicities. Moreover, there are significant frequency differences among distinct ethnic groups: East Asians present the highest frequencies worldwide for GSTM1 and GSTT1 deletions, which could suggest higher disorders risk for this population; in contrast, Sub-Saharan Africans presented the lowest frequency of GSTM1 worldwide, corroborating evolution inferences performed previously for other genes codifying metabolism enzymes. Also, admixture is a relevant component when analyzing frequency values for both genes, but further studies focusing on this subject are warranted.

Genetic Variation of G6PD and CYP2D6: Clinical Implications on the Use of Primaquine for Elimination of Plasmodium vivax

Primaquine, an 8-aminoquinoline, is the only medication approved by the World Health Organization to treat the hypnozoite stage of Plasmodium vivax and P. ovale malaria. Relapse, triggered by activation of dormant hypnozoites in the liver, can occur weeks to years after primary infection, and provides the predominant source of transmission in endemic settings. Hence, primaquine is essential for individual treatment and P. vivax elimination efforts. However, primaquine use is limited by the risk of life-threatening acute hemolytic anemia in glucose-6-phosphate dehydrogenase (G6PD) deficient individuals. More recently, studies have demonstrated decreased efficacy of primaquine due to cytochrome P450 2D6 (CYP2D6) polymorphisms conferring an impaired metabolizer phenotype. Failure of standard primaquine therapy has occurred in individuals with decreased or absent CYP2D6 activity. Both G6PD and CYP2D6 are highly polymorphic genes, with considerable geographic and interethnic variability, adding complexity to primaquine use. Innovative strategies are required to overcome the dual challenge of G6PD deficiency and impaired primaquine metabolism. Further understanding of the pharmacogenetics of primaquine is key to utilizing its full potential. Accurate CYP2D6 genotype-phenotype translation may optimize primaquine dosing strategies for impaired metabolizers and expand its use in a safe, efficacious manner. At an individual level the current challenges with G6PD diagnostics and CYP2D6 testing limit clinical implementation of pharmacogenetics. However, further characterisation of the overlap and spectrum of G6PD and CYP2D6 activity may optimize primaquine use at a population level and facilitate region-specific dosing strategies for mass drug administration. This precision public health approach merits further investigation for P. vivax elimination.

Contribution of CYP2D6 Functional Activity to Oxycodone Efficacy in Pain Management: Genetic Polymorphisms, Phenoconversion, and Tissue-Selective Metabolism

Oxycodone is a widely used opioid for the management of chronic pain. Analgesic effects observed following the administration of oxycodone are mediated mostly by agonistic effects on the μ-opioid receptor. Wide inter-subject variability observed in oxycodone efficacy could be explained by polymorphisms in the gene coding for the μ-opioid receptor (OPRM1). In humans, oxycodone is converted into several metabolites, particularly into oxymorphone, an active metabolite with potent μ-opioid receptor agonist activity. The CYP2D6 enzyme is principally responsible for the conversion of oxycodone to oxymorphone. The CYP2D6 gene is highly polymorphic with encoded protein activities, ranging from non-functioning to high-functioning enzymes. Several pharmacogenetic studies have shown the importance of CYP2D6-mediated conversion of oxycodone to oxymorphone for analgesic efficacy. Pharmacogenetic testing could optimize oxycodone therapy and help achieve adequate pain control, avoiding harmful side effects. However, the most recent Clinical Pharmacogenetics Implementation Consortium guidelines fell short of recommending pharmacogenomic testing for oxycodone treatment. In this review, we (1) analyze pharmacogenomic and drug-interaction studies to delineate the association between CYP2D6 activity and oxycodone efficacy, (2) review evidence from CYP3A4 drug-interaction studies to untangle the nature of oxycodone metabolism and its efficacy, (3) report on the current knowledge linking the efficacy of oxycodone to OPRM1 variants, and (4) discuss the potential role of CYP2D6 brain expression on the local formation of oxymorphone. In conclusion, we opine that pharmacogenetic testing, especially for CYP2D6 with considerations of phenoconversion due to concomitant drug administration, should be appraised to improve oxycodone efficacy.

The impact of catha edulis (vahl) forssk. ex endl. (celestraceae) (khat) on pharmacokinetics of clinically used drugs

INTRODUCTION

Catha edulis (Vahl) Forssk. ex Endl. (Celestraceae) is used as a recreational drug on daily basis for its euphoric and psychostimulant effects. It is also chewed by individuals who are on medications, raising the possibility of drug-khat interaction. However, limited data are available in the literature, although clinically significant interactions are expected, as khat contains a complex mixture of pharmacologically active constituents.

AREAS COVERED

It provides an overview of the phytochemistry, pharmacokinetics, pharmacodynamics, and pharmacogenetics of khat based on the literature mined from PubMed, Google Scholar, and Cochrane databases. It also presents a detailed account of drug-khat interactions with specific examples and their clinical significance. The interactions mainly occur at the pharmacokinetics level and particular attention is paid for the phases of absorption and cytochrome P450 enzyme-mediated metabolism.

EXPERT OPINION

Despite the increasing trend of khat chewing with medications among the populace and the potential risk for the occurrence of clinically significant interactions, there is paucity of data in the literature demonstrating the magnitude of the risk. The available data, however, clearly demonstrate that the consequence of drug-khat interaction is dependent on genotype. Genotyping, where feasible, could be used to improve clinical outcome and minimize adverse reactions.

CYP2D6 Allele Frequency in Five Malaria Vivax Endemic Areas From Brazilian Amazon Region

Genetic variability was linked with individual responses to treatment and susceptibility to malaria by Plasmodium vivax. Polymorphisms in the CYP2D6 gene may modulate enzyme level and activity, thereby affecting individual responses to pharmacological treatment. The aim of the study was to investigate whether or not CYP2D6 single nucleotide polymorphisms rs1065852, rs38920-97, rs16947 and rs28371725 are unequally distributed in malaria by Plasmodium vivax individuals from the Brazilian Amazon region. The blood samples were collected from 220 unrelated Plasmodium vivax patients from five different endemic areas. Genotyping was performed using SNaPshot^® and real-time polymerase chain reaction methods. In all five areas, the rs1065852 (CYP2D6*10, C.100C > T), rs3892097 (CYP2D6*4, 1846C > T) and rs16947 (CYP2D6*2, C.2850G > A), as a homozygous genotype, showed the lowest frequencies. The rs28371725 (CYP2D6*41, 2988G > A) homozygous genotype was not detected, while the allele A was found in a single patient from Macapá region. No deviations from Hardy-Weinberg equilibrium were found, although a borderline p-value was observed (p = 0.048) for the SNP rs3892097 in Goianésia do Pará, Pará state. No significant associations were detected in these frequencies among the five studied areas. For the SNP rs3892097, a higher frequency was observed for the C/T heterozygous genotype in the Plácido de Castro and Macapá, Acre and Amapá states, respectively. The distribution of the CYP2D6 alleles investigated in the different areas of the Brazilian Amazon is not homogeneous. Further investigations are necessary in order to determine which alleles might be informative to assure optimal drug dosing recommendations based on experimental pharmacogenetics.

Chinese breast cancer patients with CYP2D6*10 mutant genotypes have a better prognosis with toremifene than with tamoxifen

Purpose

To evaluate the prognosis of estrogen receptor‐positive breast cancer patients with CYP2D6*10 mutant genotypes under tamoxifen or toremifen therapy.

Methods

Estrogen receptor‐positive breast cancer patients were selected and CYP2D6*10 genotypes (C/C, C/T, and T/T) were determined by Sanger sequencing. Patients were divided into tamoxifen, toremifene, or tamoxifen + toremifene groups according to prior therapy. The correlation between CYP2D6*10 genotype and disease‐free survival was analyzed.

Results

In total, 293 estrogen receptor‐positive breast cancer patients treated with tamoxifen or toremifene between 2008 and 2017 were studied. Median follow‐up was 39 months (10–141). Of these, 107 (36.52%), 112 (38.23%), and 74 (25.26%) patients had C/C, C/T, and T/T genotypes, respectively. Genotype was significantly associated with disease‐free survival in tamoxifen patients. Patients with C/T and T/T genotypes showed worse disease‐free survival than patients with a C/C genotype. Genotype and disease‐free survival in toremifene and tamoxifen+toremifene patients were not correlated. Of patients with a C/T genotype, toremifene or tamoxifen+toremifene groups showed better disease‐free survival than tamoxifen patients. Although disease‐free survival of patients with a T/T genotype in the three groups was not statistically different, tamoxifen patients showed worse disease‐free survival. There was no correlation between different treatments and disease‐free survival in patients with a C/C genotype. Cox proportional hazard analysis revealed toremifene patients had a better prognosis than tamoxifen patients; toremifene was an independent protective factoremifene for disease‐free survival.

Conclusions

Tamoxifen was less effective in patients with CYP2D6*10 C/T and T/T genotypes. Estrogen receptor‐positive breast cancer patients with a CYP2D6*10 mutation genotype have a better prognosis with toremifen than tamoxifen.

The Pharmacokinetics of Gefitinib in a Chinese Cancer Population Group: A Virtual Clinical Trials Population Study

Gefitinib, a selective inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, is used to treat non-small-cell lung cancer (NSCLC). Lung cancer rates are high in China and are expected to increase over the next decade. CYP 2D6 intermediate metaboliser (IM) phenotypes are more prevalent in the Chinese population compared to Caucasians; the increased risk of drug-drug interactions (DDI) with chemotherapy polypharmacy may lead to different clinical pharmacokinetics outcomes for Chinese patients. This study developed and validated a virtual Chinese cancer population for the pragmatic assessment of gefitinib DDI as a victim drug in Chinese and Caucasian cancer populations. When assessing the impact of 2D6 phenotypes on bupropion mediated CYP 2D6 DDI in Chinese cancer population, we found that AUC increased by at least 60% in extensive metabolizers (EM) and 30% in IM. As a result, fmCYP2D6 was reduced by 15% in IM in the presence of bupropion, translating into > 70% of EM subjects and > 48% of IM subjects with trough concentrations at steady state (Ctrough,ss) below the gefitinib target trough level. The PBPK model predicted that a 500 mg once daily dose in both EM and IM subjects successfully reduced the percent of subjects below the Ctrough,ss. Such changes in Ctrough,ss warrant further investigation and highlight the ability of pharmacokinetic modelling to investigate populations that may be difficult to recruit for traditional clinical studies.

Genetic variability of CYP2D6, CYP3A4 and CYP3A5 among the Egyptian population

Aim: This study investigated major allelic variants of CYP2D6, CYP3A4 and CYP3A5 in Egyptians, an Arabic population for which there is little information regarding these important pharmacogenes. Patients & methods: CYP2D6*2, *4, *5, *10, *41 and gene copy number variation, as well as CYP3A4*22 and CYP3A5*3 were determined with commercially available TaqMan assays in 145 healthy study participants. Results: The CYP2D6 alleles identified suggest that the prevalence of poor metabolizers is low as none were found among the 145 subjects investigated. The frequency for CYP3A5 nonexpressers was 74.5% and the CYP3A4*22 allele frequency was low at 2.0%. Conclusion: These preliminary findings indicate that pharmacogene variation in Egyptians is different from those of other Middle Eastern/Arabic populations and warrants further investigation.

Metabolizer phenotype prediction in different Peruvian ethnic groups through CYP2C9 polymorphisms

OBJECTIVES

The CYP2C9 gene have three common alleles, CYP2C9*1, CYP2C9*2 and CYP2C9*3, associated with different homozygous (*1/*1, *2/*2 and *3/*3) and heterozygous (*1/*2 and *1/*3) genotypes, which in turn are related to extensive (gEM), intermediate (gIM) and poor (gPM) metabolizers. Likewise, the inter-ethnic variability was intimately associated with different drug metabolism. Therefore, the aim of the present study was predict the metabolizer phenotypes in different Peruvian ethnic groups from lowland (<2,500 m) and highland (>2,500 m).

METHODS

TaqMan genotyping assays were performed in a group of 174 healthy unrelated Peruvian individuals.

RESULTS

In this study, the allelic comparison between the three eco-regions showed that the CYP2C9*1 was the most common in Andean (96.32%); the *2 was the most frequent in Coast (7.45%, p<0.05). Regarding the *3 was the most common in Amazonian (6.25%, p<0.05). In a corroborative manner, the gEM was the most common in Andean (94.74%), the gIM in Coast (17.02%) and gPM in Amazonian (6.25%) populations.

CONCLUSIONS

Our study provides a valuable source of information about to metabolizer phenotype drugs in different Peruvian ethnic groups. In this way, it could be established suitable genetic-dosage medicaments for various common diseases in these heterogenetic populations.

Pharmacogenetics Approach for the Improvement of COVID-19 Treatment

The treatment of coronavirus disease 2019 (COVID-19) has been a challenge. The efficacy of several drugs has been evaluated and variability in drug response has been observed. Pharmacogenetics could explain this variation and improve patients’ outcomes with this complex disease; nevertheless, several disease-related issues must be carefully reviewed in the pharmacogenetic study of COVID-19 treatment. We aimed to describe the pharmacogenetic variants reported for drugs used for COVID-19 treatment (remdesivir, oseltamivir, lopinavir, ritonavir, azithromycin, chloroquine, hydroxychloroquine, ivermectin, and dexamethasone). In addition, other factors relevant to the design of pharmacogenetic studies were mentioned. Variants in CYP3A4, CYP3A5, CYP2C8, CY2D6, ABCB1, ABCC2, and SLCO1B1, among other variants, could be included in pharmacogenetic studies of COVID-19 treatment. Besides, nongenetic factors such as drug–drug interactions and inflammation should be considered in the search for personalized therapy of COVID-19.

Meta-analysis of probability estimates of worldwide variation of CYP2D6 and CYP2C19

Extensive migration has led to the necessity of knowledge regarding the treatment of migrants with different ethnical backgrounds. This is especially relevant for pharmacological treatment, because of the significant variation between migrant groups in their capacity to metabolize drugs. For psychiatric medications, CYP2D6 and CYP2C19 enzymes are clinically relevant. The aim of this meta-analysis was to analyze studies reporting clinically useful information regarding CYP2D6 and CYP2C19 genotype frequencies, across populations and ethnic groups worldwide. To that end, we conducted a comprehensive meta-analysis using Embase, PubMed, Web of Science, and PsycINFO (>336,000 subjects, 318 reports). A non-normal metabolizer (non-NM) probability estimate was introduced as the equivalent of the sum-prevalence of predicted poor, intermediate, and ultrarapid metabolizer CYP2D6 and CYP2C19 phenotypes. The probability of having a CYP2D6 non-NM predicted phenotype was highest in Algeria (61%) and lowest in Gambia (2.7%) while the probability for CYP2C19 was highest in India (80%) and lowest in countries in the Americas, particularly Mexico (32%). The mean total probability estimates of having a non-NM predicted phenotype worldwide were 36.4% and 61.9% for CYP2D6 and CYP2C19, respectively. We provide detailed tables and world maps summarizing clinically relevant data regarding the prevalence of CYP2D6 and CYP2C19 predicted phenotypes and demonstrating large inter-ethnic differences. Based on the documented probability estimates, pre-emptive pharmacogenetic testing is encouraged for every patient who will undergo therapy with a drug(s) that is metabolized by CYP2D6 and/or CYP2C19 pathways and should be considered in case of treatment resistance or serious side effects.

Pharmacogenetics of tamoxifen therapy in Asian populations: from genetic polymorphism to clinical outcomes

BACKGROUND

Compared with western countries, Asian breast cancer patients have unique pathological and biological characteristics. Most of them are premenopausal women with HR positive. Tamoxifen as the first-line drug for premenopausal women with HR+ is involved in multiple enzymes and transporters during metabolizing and transporting process. Variants that cause decreased or inactive gene products leading to abnormal responses in tamoxifen therapy have well been studied in western countries, whereas such information is much less reported in Asian populations.

OBJECTIVE

In order to elucidate the relationship between genetic variants and tamoxifen-induced individual drug reactions in different Asian populations and further identify genotypes/phenotypes with potential therapeutic significance.

METHODS

We reviewed the frequencies of genetic variants in major enzymes and transporter genes involved in the metabolism and transport of tamoxifen across Asian populations as well as significant correlations between genotypes/metabolic phenotypes and metabolites concentrations or BC clinical outcomes.

RESULTS

Significant inter-ethnic differences in allele frequencies was found among Asian populations, such as CYP2D6*4, *10, *41, CYP2C9*2, ABCB1 C3435T and SLCO1B1*5, and CYP2D6*10/*10 is the most common genotype correlated with adverse clinical outcomes. Moreover, we summarized the barriers and controversies of implementing pharmacogenetics in tamoxifen therapy and concluded that more population-specific pharmacogenetic studies are needed in the future.

CONCLUSION

This review revealed more systematic pharmacogenomics of genes involved in the metabolism and transport besides CYP2D6, are required to optimize the genotyping strategies and guide the personalized tamoxifen therapy in Asian populations.

Genetic Diversity of Drug-Related Genes in Native Americans of the Brazilian Amazon

Introduction

The genetic admixture of the Brazilian population has considerable relevance to the implementation of the principles of pharmacogenomics (PGx), as it may compromise the extrapolation of data obtained in more homogeneous world populations.

Purpose

This study aims to investigate a panel of 117 polymorphisms in 35 pharmacogenes, which contains label recommendations or clinical evidence by international drug regulatory agencies, in Amazonian Native American populations, and compare the results obtained with continental population data from the 1000 Genomes Project Consortium.

Patients and Methods

The study population is composed of 109 Native American individuals from three Brazilian Amazon groups. The genotyping of the PGx polymorphisms was performed by allelic discrimination using TaqMan^® OpenArray Genotyping with a panel of 120 customized assays on the QuantStudio™ 12K Flex Real-Time PCR System.

Results

Statistical differences within the Native American populations were observed regarding both genotypes and phenotypes of some genes of the CYP family. The discriminant analysis of principal components (DAPCs) between the NAM group and the continental populations of the 1000 Genomes Project resulted in the clustering of the three Native American populations. Additionally, in general, the NAM group was determined to be closely situated between East Asia, America, and South Asia groups, which enabled us to infer a genetic similarity between these populations. The DAPC analysis further demonstrated that eight polymorphisms and six polymorphisms were more relevant in differentiating the NAM from the continental populations and the NAM populations among themselves, respectively.

Conclusion

Some investigated polymorphisms show differences among world populations, particularly with populations of European origin, for whom precision medicine protocols are primarily designed. The accumulated knowledge regarding these variations may assist in the design of specific protocols for Native American populations and populations admixed with them.

Crystal Structures of Drug-Metabolizing CYPs

The complex enzyme kinetics displayed by drug-metabolizing cytochrome P450 enzymes (CYPs) (see Chapter 9 ) can, in part, be explained by an examination of their crystallographic protein structures. Fortunately, despite low sequence similarity between different families of drug-metabolizing CYPs, there exists a high degree of structural homology within the superfamily. This similarity in the protein fold allows for a direct comparison of the structural features of CYPs that contribute toward differences in substrate binding, heterotropic and homotropic cooperativity, and genetic variability in drug metabolism. In this chapter, we first provide an overview of the nomenclature and the role of structural features that are common in all CYPs. We then apply these definitions to understand the different substrate specificities and functions in the CYP3A, CYP2C, and CYP2D families of enzymes.

Frequencies of Genetic Polymorphisms of Clinically Relevant Gene-Drug Pairs in a German Psychiatric Inpatient Population

INTRODUCTION

Genetic variation is known to affect enzymatic activities allowing differentiating various metabolizer types (e. g., slow or rapid metabolizers), in particular CYP2C19 and CYP2D6.

METHODS

PGx-testing was conducted in adult major depressive disorder inpatients admitted to the Vitos Klinik Eichberg between 11/2016 and 7/2017 (n=108, 57% female). We conducted a two-sided Z-Test (p=0.05) to analyze and compare frequencies of CYP2D6, CYP2C19, CYP3A4, CYP3A5 and CYP2C9 metabolizer groups with other European and psychiatric inpatient cohorts. The HLA-A and -B genes were also analyzed.

RESULTS

Non-normal metabolizer status of CYP2D6 were present in 47%. More specifically, 35 % were intermediate, 7% poor and 4% ultra-rapid metabolizers. 68% were CYP2C19 non-normal metabolizers. 8% were ultra-rapid and 31% rapid metabolizers. Notably, only 13% were NM for CYP2C19 and NM for CYP2D6 (activity score of 1 or more). For CYP2C9 we found 16% to be intermediate metabolizers, 1.0% poor metabolizer. CYP3A4 and CYP3A5 genetic polymorphisms were present in 25% and 19% respectively. HLA-B TAG- SNPs for *15:01 was positive in 25 patients, showing the need for different Tag-SNPs in Caucasians. HLA-B *57:01 TAG-SNP was positive in 8% of the patients, HLA-A TAG-SNP for *31:01 in Caucasians was positive in 9%. Z-Test showed statistical significance for our results.

DISCUSSION

Our results suggest that our psychiatric inpatients were enriched with genotypes consistent with non-normal drug metabolism compared to reference populations. We therefore conclude that pharmacogenetic testing should be implemented in clinical practice to guide drug therapy.

Pharmacogenomic Biomarkers and Their Applications in Psychiatry

Realizing the promise of precision medicine in psychiatry is a laudable and beneficial endeavor, since it should markedly reduce morbidity and mortality and, in effect, alleviate the economic and social burden of psychiatric disorders. This review aims to summarize important issues on pharmacogenomics in psychiatry that have laid the foundation towards personalized pharmacotherapy and, in a broader sense, precision medicine. We present major pharmacogenomic biomarkers and their applications in a variety of psychiatric disorders, such as depression, attention-deficit/hyperactivity disorder (ADHD), narcolepsy, schizophrenia, and bipolar disorder. In addition, we extend the scope into epilepsy, since antiepileptic drugs are widely used to treat psychiatric disorders, although epilepsy is conventionally considered to be a neurological disorder.

High prevalence of CYP2D6 ultrarapid metabolizers in a mestizo Colombian population in relation to Hispanic mestizo populations

Background: Interethnic differences in CYP2D6 allele frequency have been demonstrated across Latin-American countries. Only one previous study describing CYP2D6 genotypes in Colombian population has been performed. Thus, this study aimed to evaluate the CYP2D6 genetic variability in a mestizo Colombian population, as well as the similarities and differences concerning other Hispanic mestizo (HM) populations. Methodology: Two hundred and twelve unrelated healthy Colombian subjects were studied, in which different CYP2D6 polymorphisms were analyzed by extra long-PCR and real-time PCR. Results & discussion: A high percentage of ultrarapid metabolizers (18.4%) was found, representing the highest frequency calculated within the HM populations studied. However, the percentage of poor metabolizers (4.7%) was similar to those previously reported in HM populations.

Relationships between CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 metabolic phenotypes and genotypes in a Nicaraguan Mestizo population

Interethnic variability in the drug-metabolizing capacity of CYP450 enzymes may lead to discrepancies in the relationship between genotypes and phenotypes worldwide. The present study was aimed to analyze for the first time whether there is a relationship between clinically relevant CYP450 genetic polymorphisms and their drug oxidation capacity (metabolic phenotype) in a population of healthy Nicaraguan volunteers. Two hundred and twelve participants were genotyped for CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, and their actual metabolic phenotype (evaluated by the Metabolic Ratio, MR) was analyzed by using the CEIBA cocktail approach. The results showed the wide interindividual variability in all the studied enzymes and a significant difference (p < 0.004) in the activity of CYP1A2 between male and female subjects. The number of CYP2C19 (p < 0.0001) and CYP2D6 (p < 0.0001) active alleles were shown inversely correlated with their corresponding MR, although there were marked genotype-phenotype discrepancies. There was an actual enzyme capacity overlapping (MR) between genotypically Poor (gPMs) and Extensive Metabolizers (gEMs) of 3.14% subjects for CYP2D6 and 0.94% for CYP2C9. Similarly, there was an overlapping for metabolic phenotypes of 11.48% of genotypically ultrarapid metabolizers (gUMs) for CYP2C19 and 2.09% for CYP2D6 and gEMs. Therefore, the current approach for metabolic phenotype prediction based just on genotype does not predict properly for all individuals within this Nicaraguan Mestizo population, thus representing a potential barrier for the clinical implementation of personalized medicine in this region. However, it is necessary to improve the prediction of phenotype from genotype in order to improve the pharmacogenetic implementation in populations with specific ethnic backgrounds.

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.

Adverse Drug Reactions in the Emergency Department: Is There a Role for Pharmacogenomic Profiles at Risk?-Results from the ADRED Study

Individual differences in required drug dosages exist based on the pharmacogenomic (PGx) profiles. This study aimed to assess associations between PGx profiles and adverse drug reactions (ADR) that lead to admissions to the emergency department (ED). ADR cases of the prospective multi-center observational trial in EDs (ADRED study) were analyzed (n = 776) together with the relevant PGx phenotypes of the enzymes CYP2D6, CYP2C19, CYP2C9, and VKORC1. Overall, the allele frequency distribution in this cohort did not differ from the population frequencies. We compared the frequencies of phenotypes in the subgroups with the drugs suspected of certain ADR, in the remaining cases. The frequency distribution of CYP2C19 differed for the ADR bleeding cases suspected of clopidogrel (p = 0.020). In a logistic regression analysis, higher CYP2C19 activity (OR (95% CI): 4.97 (1.73−14.27)), together with age (1.05 (1.02−1.08)), showed an impact on the clopidogrel-suspecting ADRs, when adjusting for the clinical parameters. There was a trend for an association of phenprocoumon-risk profiles (low VKORC1 or CYP2C9 activity) with phenprocoumon-suspecting ADRs (p = 0.052). The PGx impact on serious ADRs might be highest in drugs that cannot be easily monitored or those that do not provoke mild ADR symptoms very quickly. Therefore, patients that require the intake of those drugs with PGx variability such as clopidogrel, might benefit from PGx testing.

Pharmacogenomics of breast cancer: highlighting CYP2D6 and tamoxifen

PURPOSE

To review recent pharmacogenomics studies on breast cancer patients undergoing tamoxifen therapy, highlighting how our knowledge on cytochrome P450 2D6 (CYP2D6) can help to guide the development of adjuvant therapies for these patients.

METHODS

A comprehensive literature search was conducted. Articles reporting findings pertaining to the effect of CYP2D6 on the therapeutic efficacy of tamoxifen, those reporting how targeting CYP2D6 could inform tamoxifen-based therapy development, and those on the tamoxifen effects on cell lines and animal models were included in the review.

RESULTS

With CYP2D6 being the primary enzyme for tamoxifen metabolism, single-nucleotide polymorphisms (SNPs) in this gene were one of the determinants in the rate of tamoxifen metabolism, thereby potentially having an effect on the efficacy of tamoxifen-based therapies. Our review indicates the potential effectiveness of targeting these SNPs, including those for the CYP2D6*10 allele (c. 100C > T), in modifying the level of tamoxifen metabolism. These findings suggest the importance of pharmacogenomics research in our understanding of the efficacy of adjuvant therapies. However, the involvement of multiple enzymes in tamoxifen metabolism, dietary factors, ethnic differences in gene frequencies, and patients' compliance to tamoxifen therapies in studies do present challenges in pharmacogenomics research.

CONCLUSIONS

Pharmacogenomics could play important roles in mediating the advancement of tamoxifen-based adjuvant therapies. Research efforts should be directed towards the exploration of further SNPs of CYP2D6 that affect tamoxifen metabolism, as well as epigenetic changes in CYP2D6, enabling the design of precision medicine and confirming clinical validity in the use of pharmacogenomics for tamoxifen.

The Metabolization Profile of the CYP2D6 Gene in Amerindian Populations: A Review

BACKGROUND

the CYP2D6 gene is clinically important and is known to have a number of variants. This gene has four distinct metabolization profiles that are determined by the different allelic forms present in the individual. The relative frequency of these profiles varies considerably among human populations around the world. Populations from more isolated regions, such as Native Americans, are still relatively poorly studied, however. Even so, recent advances in genotyping techniques and increasing interest in the study of these populations has led to a progressive increase in publication rates. Given this, the review presented here compiled the principal papers published on the CYP2D6 gene in Amerindian populations to determine the metabolic profile of this group.

METHODS

a systematic literature review was conducted in three scientific publication platforms (Google Scholar, Science Direct, and Pubmed). The search was run using the keywords "CYP2D6 Amerindians" and "CYP2D6 native Americans".

RESULTS

a total of 13 original papers met the inclusion criteria established for this study. All the papers presented frequencies of the different CYP2D6 alleles in Amerindian populations. Seven of the papers focused specifically on Amerindian populations from Mexico, while the others included populations from Argentina, Chile, Costa Rica, Mexico, Paraguay, Peru, and the United States. The results of the papers reviewed here showed that the extensive metabolization profile was the most prevalent in all Amerindian populations studied to date, followed by the intermediate, slow, and ultra-rapid, in that order.

CONCLUSION

the metabolization profiles of the Amerindian populations reviewed in the present study do not diverge in any major way from those of other populations from around the world. Given the paucity of the data available on Amerindian populations, further research is required to better characterize the metabolization profile of these populations to ensure the development of adequate therapeutic strategies.

CYP2D6 haplotypes with enhancer single-nucleotide polymorphism rs5758550 and rs16947 (*2 allele): implications for CYP2D6 genotyping panels

INTRODUCTION

CYP2D6 metabolizes ∼25% of all clinically used drugs, with numerous genetic polymorphisms affecting enzyme activity and drug response. Clinical utility of current CYP2D6 genotyping is partially compromised the unresolved complex haplotype structure of the CYP2D6 locus. We have identified a distal enhancer single-nucleotide polymorphism rs5758550 that robustly increases CYP2D6 expression, whereas rs16947 (CYP2D6*2), previously considered inert, reduces correct mRNA splicing and expression, thereby affecting presumed activity of other alleles on the *2 haplotype.

OBJECTIVE

This study aims to determine the structure and frequency of haplotypes containing either rs5758550 or rs16947, or both, together with other relevant CYP2D6 alleles, assigning predictive enzyme activity scores to each, and addressing ambiguities in estimating diplotypes in different populations.

METHODS

The structure and frequency of haplotypes containing rs5758550 and/or rs16947 in different populations were determined by using phased genotype data from 'The 1000 Genomes Project'. The assigned haplotype-phenotype relationship was tested by associating assigned CYP2D6 activity score with CYP2D6 enzyme activity in a cohort of 122 human liver microsomes.

RESULTS

Addition of enhancer single-nucleotide polymorphism rs5758550 and *2 to a CYP2D6 panel improves prediction of CYP2D6 activity. Moreover, the haplotype containing rs5758550 and rs16947 predict extensive CYP2D6 activity more accurately than CYP2D6*2A, a surrogate marker for extensive activity.

CONCLUSION

With further studies, the results support possible incorporation of rs5758550 and rs16947 into CYP2D6 biomarker panels for more accurate prediction of CYP2D6 metabolizer status.

The effect of CYP2D6 variation on antipsychotic-induced hyperprolactinaemia: a systematic review and meta-analysis

Hyperprolactinemia is a known adverse drug reaction to antipsychotic treatment. Antipsychotic blood levels are influenced by cytochrome P450 enzymes, primarily CYP2D6. Variation in CYP450 genes may affect the risk of antipsychotic-induced hyperprolactinemia. We undertook a systematic review and meta-analysis to assess whether CYP2D6 functional genetic variants are associated with antipsychotic-induced hyperprolactinemia. The systematic review identified 16 relevant papers, seven of which were suitable for the meta-analysis (n = 303 participants including 134 extreme metabolisers). Participants were classified into four phenotype groups as poor, intermediate, extensive, and ultra-rapid metabolisers. A random effects meta-analysis was used and Cohen's d calculated as the effect size for each primary study. We found no significant differences in prolactin levels between CYP2D6 metabolic groups. Current evidence does not support using CYP2D6 genotyping to reduce risk of antipsychotic-induced hyperprolactinemia. However, statistical power is limited. Future studies with larger samples and including a range of prolactin-elevating drugs are needed.

Defining screening panel of functional variants of CYP1A1, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 genes in Serbian population

Plethora of drugs and toxic substances is metabolized by cytochrome P450 enzymes (CYP450). These enzymes are coded by highly variable genes abundant with single nucleotide variants (SNVs) and small insertions/deletions (indels) that affect the functionality of the enzymes, increasing or decreasing their activity. CYP genes genotyping, followed by haplotype inference, provides substrate specific metabolic phenotype prediction. This is crucial in pharmacogenetics and applicable in molecular autopsy. However, high number of alleles in CYP450 superfamily and interethnic variability in frequency distribution require precise gene panel customization. To estimate informativeness of SNVs and alleles in CYP gene families 1, 2, and 3, associated with metabolic alterations, 500 unrelated individuals from 5 regions of Serbia were genotyped using TaqMan assays to determine frequencies of CYP2C9 *2 and *3, CYP2C19 *2 and *17 alleles, four variants in CYP2D6 (rs3892097, rs1065852, rs28371725, rs28371706) gene, and CYP3A4*1B allele. In addition, CYP1A1 rs4646903 and rs1048943 (m1 and m2) variants were genotyped by RFLP. Our results showed that frequencies of tested variants in Serbian population corresponded to general European population and somewhat differed from neighboring populations. SNV rs1065852, the main contributor to non-functional CYP2D6 *4, significantly departed from Hardy-Weinberg equilibrium. With the exception of rs28371706 in CYP2D6 and rs2740574 in CYP3A4, which were very rare in our sample, all other tested variants in CYP2 family are informative and appropriate for pharmacogenetic testing, molecular autopsy, and medico-legal genetic analyses.

Pharmacogenetic relevant polymorphisms of CYP2C9, CYP2C19, CYP2D6, and CYP3A5 in Bhutanese population

Background Marked differences among genotype frequencies (Caucasians, Asians, and Africans) have been observed in cytochrome P450 (CYP) genes. Data on the frequency of pharmacogenetic relevant polymorphisms in Bhutanese population is absent. This study aimed to investigate the frequencies of pharmacogenetic relevant polymorphisms of CYP2C9 (*2 and *3), CYP2C19 (*2 and *3), CYP2D6 (*10), and CYP3A5 (*3) in Bhutanese population. Methods Genotyping was performed in 443 DNA samples using polymerase chain reaction-restriction fragment length polymorphism. Results For CYP2C9, allele frequencies of *2 and *3 variants were 0.339% and 0%, respectively. For CYP2C19, frequencies of *2 and *3 variants were 30.135% and 15.689%, respectively. Allele frequencies of CYP2D6*10 and CYP3A5*3 were 21.332% and 77.314%, respectively. Allele frequencies of CYP2C9*2 are similar to most Asians while CYP2C9*3 was absent. CYP2C19*2 showed a close resemblance to Japanese and Burmese, while CYP2C19*3 is near to Japanese and Korean. CYP2D6*10 is noticeably lower than other Asians. CYP3A5*3 is similar to East Asians (Chinese, Japanese, and Korean). Conclusions The Bhutanese population is polymorphic for these CYP genes, except for CYP2C9*3. Similar to other populations, genetic testing for these genes may, therefore, be helpful to obtain the benefit from pharmacological treatments and prevent adverse drug reactions.

Circulating Extracellular Vesicles Containing Xenobiotic Metabolizing CYP Enzymes and Their Potential Roles in Extrahepatic Cells Via Cell-Cell Interactions

The cytochrome P450 (CYP) family of enzymes is known to metabolize the majority of xenobiotics. Hepatocytes, powerhouses of CYP enzymes, are where most drugs are metabolized into non-toxic metabolites. Additional tissues/cells such as gut, kidneys, lungs, blood, and brain cells express selective CYP enzymes. Extrahepatic CYP enzymes, especially in kidneys, also metabolize drugs into excretable forms. However, extrahepatic cells express a much lower level of CYPs than hepatocytes. It is possible that the liver secretes CYP enzymes, which circulate via plasma and are eventually delivered to extrahepatic cells (e.g., brain cells). CYP circulation likely occurs via extracellular vesicles (EVs), which carry important biomolecules for delivery to distant cells. Recent studies have revealed an abundance of several CYPs in plasma EVs and other cell-derived EVs, and have demonstrated the role of CYP-containing EVs in xenobiotic-induced toxicity via cell–cell interactions. Thus, it is important to study the mechanism for packaging CYP into EVs, their circulation via plasma, and their role in extrahepatic cells. Future studies could help to find novel EV biomarkers and help to utilize EVs in novel interventions via CYP-containing EV drug delivery. This review mainly covers the abundance of CYPs in plasma EVs and EVs derived from CYP-expressing cells, as well as the potential role of EV CYPs in cell–cell communication and their application with respect to novel biomarkers and therapeutic interventions.

Genomic Ancestry, CYP2D6, CYP2C9, and CYP2C19 Among Latin Americans

We present the distribution of CYP2D6, CYP2C9, and CYP2C19 variants and predicted phenotypes in 33 native and admixed populations from Ibero-America (n > 6,000) in the context of genetic ancestry (n = 3,387). Continental ancestries are the major determinants of frequencies of the increased-activity allele CYP2C19*17 and CYP2C19 gUMs (negatively associated with Native American ancestry), decreased-activity alleles CYP2D6*41 and CYP2C9*2 (positively associated with European ancestry), and decreased-activity alleles CYP2D6*17 and CYP2D6*29 (positively associated with African ancestry). For the rare alleles, CYP2C9*2 and CYPC19*17, European admixture accounts for their presence in Native American populations, but rare alleles CYP2D6*5 (null-activity), CYP2D6-multiplication alleles (increased activity), and CYP2C9*3 (decreased-activity) were present in the pre-Columbian Americas. The study of a broad spectrum of Native American populations from different ethno-linguistic groups show how autochthonous diversity shaped the distribution of pharmaco-alleles and give insights on the prevalence of clinically relevant phenotypes associated with drugs, such as paroxetine, tamoxifen, warfarin, and clopidogrel.