Comprehensive analysis of the genetic factors determining expression and function of hepatic CYP2D6

Novel Independent Trans- and Cis-Genetic Variants Associated with CYP2D6 Expression and Activity in Human Livers

Cytochrome P450 2D6 (CYP2D6) is a critical hepatic drug-metabolizing enzyme in humans, responsible for metabolizing approximately 20%-25% of commonly used medications such as codeine, desipramine, fluvoxamine, paroxetine, and tamoxifen. The CYP2D6 gene is highly polymorphic, resulting in substantial interindividual variability in its catalytic function and the pharmacokinetics and therapeutic outcomes of its substrate drugs. Although many functional CYP2D6 variants have been discovered and validated, a significant portion of the variability in the expression and activity of CYP2D6 remains unexplained. In this study, we performed a genome-wide association study (GWAS) to identify novel variants associated with CYP2D6 protein expression in individual human livers, followed by a conditional analysis to control for the effect of functional CYP2D6 star alleles. We also examined their impact on hepatic CYP2D6 activity. Genotyping on a genome-wide scale was achieved using the Illumina Multi-Ethnic Genotyping Array (MEGA). A data-independent acquisition (DIA)-based proteomics method was used to quantify CYP2D6 protein concentrations. CYP2D6 activity was determined by measuring the dextromethorphan O-demethylation in individual human liver s9 fractions. The GWAS identified 44 single nuclear polymorphisms (SNPs) that are significantly associated with CYP2D6 protein expressions with a P value threshold of 5.0 × 10-7 After the conditional analysis, five SNPs, including the cis-variants rs1807493 and rs1062753 and the trans-variants rs4073010, rs729559, and rs80274432, emerged as independent variants significantly correlated with hepatic CYP2D6 protein expressions. Notably, four of these SNPs, except for rs80274432, also exhibited a significant association with CYP2D6 activities in human livers, suggesting their potential as novel and independent cis- and trans-variants regulating CYP2D6. SIGNIFICANT STATEMENT: Using individual human livers, we identified four novel cis- and trans-pQTLs/aQTLs (protein quantitative trait loci/activity quantitative trait loci) of Cytochrome P450 2D6 (CYP2D6) that are independent from known functional CYP2D6 star alleles. This study connects the CYP2D6 gene expression and activity, enhancing our understanding of the genetic variants associated with CYP2D6 protein expression and activity, potentially advancing our insight into the interindividual variability in CYP2D6 substrate medication response.

Pharmacogenomics of Dementia: Personalizing the Treatment of Cognitive and Neuropsychiatric Symptoms

Dementia is a syndrome of global and progressive deterioration of cognitive skills, especially memory, learning, abstract thinking, and orientation, usually affecting the elderly. The most common forms are Alzheimer's disease, vascular dementia, and other (frontotemporal, Lewy body disease) dementias. The etiology of these multifactorial disorders involves complex interactions of various environmental and (epi)genetic factors and requires multiple forms of pharmacological intervention, including anti-dementia drugs for cognitive impairment, antidepressants, antipsychotics, anxiolytics and sedatives for behavioral and psychological symptoms of dementia, and other drugs for comorbid disorders. The pharmacotherapy of dementia patients has been characterized by a significant interindividual variability in drug response and the development of adverse drug effects. The therapeutic response to currently available drugs is partially effective in only some individuals, with side effects, drug interactions, intolerance, and non-compliance occurring in the majority of dementia patients. Therefore, understanding the genetic basis of a patient's response to pharmacotherapy might help clinicians select the most effective treatment for dementia while minimizing the likelihood of adverse reactions and drug interactions. Recent advances in pharmacogenomics may contribute to the individualization and optimization of dementia pharmacotherapy by increasing its efficacy and safety via a prediction of clinical outcomes. Thus, it can significantly improve the quality of life in dementia patients.

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

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

Perhexiline: Old Drug, New Tricks? A Summary of Its Anti-Cancer Effects

Cancer metabolic plasticity, including changes in fatty acid metabolism utilisation, is now widely appreciated as a key driver for cancer cell growth, survival and malignancy. Hence, cancer metabolic pathways have been the focus of much recent drug development. Perhexiline is a prophylactic antianginal drug known to act by inhibiting carnitine palmitoyltransferase 1 (CPT1) and 2 (CPT2), mitochondrial enzymes critical for fatty acid metabolism. In this review, we discuss the growing evidence that perhexiline has potent anti-cancer properties when tested as a monotherapy or in combination with traditional chemotherapeutics. We review the CPT1/2 dependent and independent mechanisms of its anti-cancer activities. Finally, we speculate on the clinical feasibility and utility of repurposing perhexiline as an anti-cancer agent, its limitations including known side effects and its potential added benefit of limiting cardiotoxicity induced by other chemotherapeutics.

Combined and independent effects of OCT1 and CYP2D6 on the cellular disposition of drugs

The organic cation transporter 1 (OCT1) mediates the cell uptake and cytochrome P450 2D6 (CYP2D6) the metabolism of many cationic substrates. Activities of OCT1 and CYP2D6 are affected by enormous genetic variation and frequent drug-drug interactions. Single or combined deficiency of OCT1 and CYP2D6 might result in dramatic differences in systemic exposure, adverse drug reactions, and efficacy. Thus, one should know what drugs are affected to what extent by OCT1, CYP2D6 or both. Here, we compiled all data on CYP2D6 and OCT1 drug substrates. Among 246 CYP2D6 substrates and 132 OCT1 substrates, we identified 31 shared substrates. In OCT1 and CYP2D6 single and double-transfected cells, we studied which, OCT1 or CYP2D6, is more critical for a given drug and whether there are additive, antagonistic or synergistic effects. In general, OCT1 substrates were more hydrophilic than CYP2D6 substrates and smaller in size. Inhibition studies showed unexpectedly pronounced inhibition of substrate depletion by shared OCT1/CYP2D6 inhibitors. In conclusion, there is a distinct overlap in the OCT1/CYP2D6 substrate and inhibitor spectra, so in vivo pharmacokinetics and -dynamics of shared substrates may be significantly affected by frequent OCT1- and CYP2D6-polymorphisms and by comedication with shared inhibitors.

Impact of Pregnancy and Vitamin A Supplementation on CYP2D6 Activity

The mechanism of cytochrome P450 2D6 (CYP2D6) induction during pregnancy has not been evaluated in humans. This study assessed the changes in CYP2D6 and CYP3A activities during pregnancy and postpartum, and the effect of vitamin A administration on CYP2D6 activity. Forty-seven pregnant CYP2D6 extensive metabolizers (with CYP2D6 activity scores of 1 to 2) received dextromethorphan (DM) 30 mg orally as a single dose during 3 study windows (at 25 to 28 weeks of gestation, study day 1; at 28 to 32 weeks of gestation, study day 2; and at ≥3 months postpartum, study day 3). Participants were randomly assigned to groups with no supplemental vitamin A (control) or with supplemental vitamin A (10 000 IU/day orally for 3 to 4 weeks) after study day 1. Concentrations of DM and its metabolites, dextrorphan (DX) and 3-hydroxymorphinan (3HM), were determined from a 2-hour post-dose plasma sample and cumulative 4-hour urine sample using liquid chromatography-mass spectrometry. Change in CYP2D6 activity was assessed using DX/DM plasma and urine metabolic ratios. The activity change in CYP3A was also assessed using the 3HM/DM urine metabolic ratio. The DX/DM urine ratio was significantly higher (43%) in pregnancy compared with postpartum (P = .03), indicating increased CYP2D6 activity. The DX/DM plasma ratio was substantially higher in the participants, with an activity score of 1.0 during pregnancy (P = .04) compared with postpartum. The 3HM/DM urinary ratio was significantly higher (92%) during pregnancy, reflecting increased CYP3A activity (P = .02). Vitamin A supplementation did not change CYP2D6 activity during pregnancy; however, plasma all-trans retinoic acid (atRA) concentrations were positively correlated with increased CYP2D6 activity during pregnancy and postpartum. Further research is needed to elucidate the mechanisms of increased CYP2D6 activity during pregnancy.

Association of cytochrome P450 2D15 (CYP2D15) nonsynonymous polymorphisms and exon 3 deleted RNA splice variant with CYP2D15 protein content and enzyme function in dog liver microsomes

CYP2D15 is a major drug metabolizing P450 in canine liver. Like the human orthologue (CYP2D6), this enzyme is highly polymorphic with at least five common nonsynonymous variants reported that result in amino acid changes, including p.Ile109Val, p.Leu115Phe, p.Gly186Ser, p.Ile250Phe and p.Ile307Val. Furthermore, a mRNA splice variant of CYP2D15 has been found in canine liver that lacks the exon 3 gene region resulting in an inactive enzyme. The objective of this study was to evaluate whether any of these amino acid variants or the exon 3 deletion mRNA variant (exon3-delta) was associated with differences in CYP2D15-selective activities or protein content in a bank of canine livers. Livers were obtained from 25 Beagles and 34 dogs of various other breeds. CYP2D15-selective activities measured included dextromethorphan o-demethylation and tramadol o-demethylation. Reverse transcription PCR showed that 76% of livers (44/58) expressed both exon3-delta and normally spliced CYP2D15 RNA, while the remaining 24% (14/58) expressed only normally spliced RNA. The presence of exon3-delta was not correlated with CYP2D15 activities or protein content. Compared with wild-type livers, Beagle dog livers heterozygous for the p.Ile109Val and p.Gly186Ser variants showed from 40 to 50% reductions in median enzyme activities, while heterozygous p.Gly186Ser livers were associated with a 41% reduction in median CYP2D15 protein content (p < .05; Dunn's test). In the entire liver bank, livers homozygous for p.Ile109Val were also associated with a 40% reduction in median dextromethorphan O-demethylation activities versus wild-type livers (p < .05). These results identify several nonsynonymous CYP2D15 gene variants associated with variable CYP2D15 metabolism in canine liver.

Nrf2 Regulates the Expression of CYP2D6 by Inhibiting the Activity of Krüppel-Like Factor 9 (KLF9)

AIMS

The aim of the present study is to gain insight into the biology of Parkinson's disease (PD) and cancer to drive translational advances enabling more effective prevention and/or potential treatments.

BACKGROUND

The expression of Cytochrome P450 2D6 (CYP2D6) is correlated with various diseases such as PD and cancer; therefore, exploring its regulatory mechanism at transcriptional levels is of interest. NF-E2-related factor 2 (Nrf2) has been known to be responsible for regulating phase II and phase III drug-metabolizing genes.

OBJECTIVES

The objectives of this study are to investigate the transcriptional regulation of CYP2D6 by Nrf2 and to analyze its role in PD and cancer.

METHODS

Nrf2 was transiently expressed in human hepatoma Hep3B cells, and the expression of CYP2D6 was examined by RT-qPCR. The promoter activity of CYP2D6 and the DNA binding of Nrf2 were examined by luciferase and ChIP assay, respectively. We then investigated the expression and correlation of Nrf2 and CYP2D6 in the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) datasets.

RESULTS

In the present study, we demonstrated that Nrf2 down-regulated CYP2D6 mRNA expression in hepatoma Hep3B cells. Mechanistically, Nrf2 binds to the antioxidant responsive element (ARE) in the proximity of krüppel- like factor 9 (KLF9)-binding site within the -550/+51 of CYP2D6 promoter. The inhibition and activation of Nrf2 enhanced and suppressed KLF9 effects on CYP2D6 expression, respectively. The expression levels of Nrf2 and CYP2D6 were upregulated and downregulated in the PD patient GEO datasets compared to the healthy control tissues, and Nrf2 was negatively correlated with CYP2D6. In liver cancer patients, decreased CYP2D6 levels were apparent and associated with a lower probability of survival.

CONCLUSION

Our work revealed the inhibitory role of Nrf2 in regulating CYP2D6 expression. Moreover, Nrf2- dependent regulation of CYP2D6 can be used as a prognostic factor and therapeutic strategy in PD and liver cancer.

Potential of cytochrome P450, a family of xenobiotic metabolizing enzymes, in cancer therapy

SIGNIFICANCE

Targeted cancer therapy with minimal off-target consequences has shown promise for some cancer types. Although cytochrome P450 (CYP) consists of 18 families, CYP1-4 families play key role in metabolizing xenobiotics and cancer drugs. This eventually affects the process of carcinogenesis, treatment outcome, and cancer drug resistance. Differential overexpression of CYPs in transformed cells, together with phenotypic alterations in tumors, presents a potential for therapeutic intervention.

RECENT ADVANCES

Recent advances in molecular tools and information technology have helped utilize CYPs as cancer targets. The precise expression in various tumors, X-ray crystal structures, improved understanding of the structure-activity relationship, and new approaches in the development of prodrugs have supported the ongoing efforts to develop CYPs-based drugs with a better therapeutic index.

CRITICAL ISSUES

Narrow therapeutic index, off-target effects, drug resistance, and tumor heterogeneity limit the benefits of CYP-based conventional cancer therapies. In this review, we address the CYP1-4 families as druggable targets in cancer. An emphasis is given to the CYP expression, function, and the possible mechanisms that drive expression and activity in normal and transformed tissues. The strategies that inhibit or activate CYPs for therapeutic benefits are also discussed.

FUTURE DIRECTIONS

Efforts are needed to develop more selective tools that will help comprehend molecular and metabolic alterations in tumor tissues with biological end-points in relation to CYPs. This will eventually translate to developing more specific CYP inhibitors/inducers.

Molybdenum Cofactor Catabolism Unravels the Physiological Role of the Drug Metabolizing Enzyme Thiopurine S-Methyltransferase

Therapy of molybdenum cofactor (Moco) deficiency has received US Food and Drug Administration (FDA) approval in 2021. Whereas urothione, the urinary excreted catabolite of Moco, is used as diagnostic biomarker for Moco-deficiency, its catabolic pathway remains unknown. Here, we identified the urothione-synthesizing methyltransferase using mouse liver tissue by anion exchange/size exclusion chromatography and peptide mass fingerprinting. We show that the catabolic Moco S-methylating enzyme corresponds to thiopurine S-methyltransferase (TPMT), a highly polymorphic drug-metabolizing enzyme associated with drug-related hematotoxicity but unknown physiological role. Urothione synthesis was investigated in vitro using recombinantly expressed human TPMT protein, liver lysates from Tpmt wild-type and knock-out (Tpmt-/- ) mice as well as human liver cytosol. Urothione levels were quantified by liquid-chromatography tandem mass spectrometry in the kidneys and urine of mice. TPMT-genotype/phenotype and excretion levels of urothione were investigated in human samples and validated in an independent population-based study. As Moco provides a physiological substrate (thiopterin) of TPMT, thiopterin-methylating activity was associated with TPMT activity determined with its drug substrate (6-thioguanin) in mice and humans. Urothione concentration was extremely low in the kidneys and urine of Tpmt-/- mice. Urinary urothione concentration in TPMT-deficient patients depends on common TPMT polymorphisms, with extremely low levels in homozygous variant carriers (TPMT*3A/*3A) but normal levels in compound heterozygous carriers (TPMT*3A/*3C) as validated in the population-based study. Our work newly identified an endogenous substrate for TPMT and shows an unprecedented link between Moco catabolism and drug metabolism. Moreover, the TPMT example indicates that phenotypic consequences of genetic polymorphisms may differ between drug- and endogenous substrates.

From Croatian Roma to 1000 Genomes: The Story of the CYP2D6 Gene Promoter and Enhancer SNPs

The CYP2D6 gene encodes an enzyme responsible for the metabolism of ~20% of clinically prescribed drugs. In this study, 18 SNPs from the enhancer and promoter regions of CYP2D6 in 323 Roma from Croatia were genotyped, to find out whether the demographic history of Roma affected the distribution of the studied SNPs and their linkage disequilibrium (LD) values, with the major SNPs defining the CYP2D6 star alleles. No differences were found between the three Roma groups in allele and genotype frequencies. The distribution of LD values of Roma was compared with LD values of European and Asian populations. Regulatory CYP2D6 SNPs (rs5758550, rs28624811, rs1080985 and rs1080983) showed similar distribution and the highest LDs with rs16947 from the gene-coding region in all populations. In the promoter region, a complete LD between rs1080989 and rs28588594, and between rs1080983 and rs28624811, was found in Croatian Roma and investigated populations from 1000 genomes. A high LD was also found between rs1080985 from the promoter and rs5758550 from the enhancer region. SNP rs28735595 from the gene promoter region had the highest LD, with two gene region SNPs, rs1058164 and rs1135840. To conclude, the Croatian Roma population shows an LD pattern of the CYP2D6 gene region similar to the 1000 Genomes European and Asian populations.

The reference liver-CYP450 and UGT enzymes in healthy donor and metastatic livers: the impact of genotype

Background

Hepatic enzymes involved in drug metabolism vary markedly in expression, abundance and activity, which affects individual susceptibility to drugs and toxicants. The present study aimed to compare mRNA expression and protein abundance of the most pharmacologically relevant drug-metabolizing enzymes in two main sources of the control liver samples that are used as the reference, i.e. organ donor livers and non-tumorous tissue from metastatic livers. An association analysis of the most common genetic variants with mRNA and protein levels was also performed.

Methods

The CYP450 and UGT enzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, CYP3A5, UGT1A1, UGT1A3, UGT2B7 and UGT2B15) were analyzed for mRNA (qPCR) and protein abundance (LC–MS/MS) in healthy donors (n = 11) and metastatic (n = 13) livers. Genotyping was performed by means of TaqMan assays and pyrosequencing.

Results

Significantly higher protein abundance in the metastatic livers was observed in case of CYP2C9, CYP2D6, and UGT2B7, and for UGT1A3 the difference was only significant at mRNA level. For all the enzymes except CYP2E1 some significant correlation between mRNA and protein content was observed, and for UGT1A1 an inverse correlation with age was noted. CYP2C19, CYP3A5 and CYP2D6 were significantly affected by genotype.

Conclusion

The selection of a control group for the study on drug-metabolizing enzymes (e.g. in pathological states) may possibly affect its conclusions on differences in mRNA and protein content. Genotyping for common functional variants of CYP450 enzymes should be performed in all studies on drug-metabolizing enzymes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-021-00337-w.

Interactions between cardiology and oncology drugs in precision cardio-oncology

Recent advances in treatment have transformed the management of cancer. Despite these advances, cardiovascular disease remains a leading cause of death in cancer survivors. Cardio-oncology has recently evolved as a subspecialty to prevent, diagnose, and manage cardiovascular side effects of antineoplastic therapy. An emphasis on optimal management of comorbidities and close attention to drug interactions are important in cardio-oncologic care. With interdisciplinary collaboration among oncologists, cardiologists, and pharmacists, there is potential to prevent and reduce drug-related toxicities of treatments. The cytochrome P450 (CYP450) family of enzymes and the P-glycoprotein (P-g) transporter play a crucial role in drug metabolism and drug resistance. Here we discuss the role of CYP450 and P-g in drug interactions in the field of cardio-oncology, provide an overview of the cardiotoxicity of a spectrum of cancer agents, highlight the role of precision medicine, and encourage a multidisciplinary treatment approach for patients with cancer.

Impact of the CYP2D6 single nucleotide polymorphism on the concentration of and therapeutic response to donepezil in mild-to-moderate Alzheimer's disease

BACKGROUND/PURPOSE

Donepezil was approved for the treatment of Alzheimer's disease (AD) but causes variable therapeutic responses. Thus, identifying specific genetic polymorphisms, which can predict a therapeutic response to donepezil, would enable a development of personalized strategy to treatment for patients with AD. The research aimed to exam the impact of the cytochrome P450 2D6 (CYP2D6) single nucleotide polymorphism (SNP) rs1080985 on the concentration of and therapeutic response to donepezil in AD.

METHODS

In total, 40 newly diagnosed AD patients who had a clinical dementia rating (CDR) of 0.5-2 and who were on donepezil were enrolled and followed up. Plasma concentrations of donepezil were determined after 6 months of donepezil treatment. Cognitive and functional statuses were evaluated annually during follow-up. The response to therapy was defined based on the change in CDR.

RESULTS

At a mean of 21.8 ± 5.7 months of follow-up, 10 of 40 patients (25.0%) were nonresponders to donepezil treatment. Patients who were homozygous for the G allele exhibited a higher concentration of donepezil and concentration-to-dose ratio than those with other genotypes. Furthermore, a significantly higher proportion of patients with the G/G genotype were responders than nonresponders (90.0% vs 50.0%, P = 0.015, effect size of V: 0.457) to donepezil treatment. Conversely, patients carrying the C allele had a significantly high risk of poor responses to donepezil treatment (odds ratio: 9.00, 95% confidence interval: 1.611-50.275).

CONCLUSION

The CYP2D6 SNP rs1080985 might be a useful pharmacogenetic marker of the long-term therapeutic response to donepezil in patients with AD.

Differential effects on human cytochromes P450 by CRISPR/Cas9-induced genetic knockout of cytochrome P450 reductase and cytochrome b5 in HepaRG cells

HepaRG cells are increasingly accepted as model for human drug metabolism and other hepatic functions. We used lentiviral transduction of undifferentiated HepaRG cells to deliver Cas9 and two alternative sgRNAs targeted at NADPH:cytochrome P450 oxidoreductase (POR), the obligate electron donor for microsomal cytochromes P450 (CYP). Cas9-expressing HepaRG^VC (vector control) cells were phenotypically similar to wild type HepaRG cells and could be differentiated into hepatocyte-like cells by DMSO. Genetic POR-knockout resulted in phenotypic POR knockdown of up to 90% at mRNA, protein, and activity levels. LC–MS/MS measurement of seven CYP-activities showed differential effects of POR-knockdown with CYP2C8 being least and CYP2C9 being most affected. Further studies on cytochrome b5 (CYB5), an alternative NADH-dependent electron donor indicated particularly strong support of CYP2C8-dependent amodiaquine N-deethylation by CYB5 and this was confirmed by genetic CYB5 single- and POR/CYB5 double-knockout. POR-knockdown also affected CYP expression on mRNA and protein level, with CYP1A2 being induced severalfold, while CYP2C9 was strongly downregulated. In summary our results show that POR/NADPH- and CYB5/NADH-electron transport systems influence human drug metabolizing CYPs differentially and differently than mouse Cyps. Our Cas9-expressing HepaRG^VC cells should be suitable to study the influence of diverse genes on drug metabolism and other hepatic functions.

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

Tri-Allelic Haplotypes Determine and Differentiate Functionally Normal Allele CYP2D6*2 and Impaired Allele CYP2D6*41

CYP2D6 metabolizes 20-25% of all clinically used drugs and its complex genetic polymorphism is a major determinant of drug safety and efficacy. We investigated the basis for the functional difference between the two common alleles *2 (g.2851C>T + g.4181G>C, normal function) and *41 (additional intronic g.2989G>A, reduced function). A recently reported far-distant enhancer polymorphism rs5758550A/G linked to *2 has been suggested to play a decisive role. Genotyping of two white cohorts confirmed strong linkage of rs5758550G to *2, whereas no influence was found on metabolic ratio of sparteine or hepatic expression. Genomic plasmid constructs carrying individual variants or combinations thereof were expressed in COS1 and Huh7 cells. Both g.2851C>T(R296C) and g.2989G>A reduced enzyme activity and protein levels similarly by ~ 50-65% compared to reference (*1), whereas the double variant had only ~ 20% activity. Although the unexpected loss of function caused by g.2851C>T was compensated by g.4181G>C (mimicking the EM-phenotype of *2), the additional loss of function due to intronic g.2989G>A in the triple variant was not compensated (mimicking the IM-phenotype of *41). We also confirmed increased erroneous splicing in carriers of g.2989G>A but not of g.2851C>T as a likely explanation for the impaired function of *41. In conclusion, our data demonstrate g.2989G>A as causal variant of impaired allele CYP2D6*41 whereas triple-haplotypes have to be considered to explain the functional difference between *2 and *41. These data are important for genotyping strategies and clinical implementation of CYP2D6 pharmacogenetics.

Therapeutic Drug Monitoring of Rivastigmine and Donepezil Under Consideration of CYP2D6 Genotype-Dependent Metabolism of Donepezil

Background

The efficacy of acetylcholinesterase inhibitors (AChE-I) might depend on blood concentration. While rivastigmine metabolism is independent of the cytochrome P450 system, its isoenzymes, especially CYP2D6, metabolize donepezil. CYP2D6 polymorphisms can cause altered enzyme activity resulting in lower or higher than expected drug concentrations of donepezil.

Objective

We investigated correlations between clinical efficacy and serum concentrations of rivastigmine and donepezil under special consideration of CYP2D6 genotype or gene dose–dependent metabolism of donepezil.

Methods

Serum concentrations of donepezil and rivastigmine were measured by liquid chromatography – tandem mass spectrometry (LC-MS/MS). Real-time quantitative polymerase chain reaction (PCR) and allele-specific PCR were performed to assess CYP2D6 genotype and gene dose.

Results

Patients treated with rivastigmine (n=28) or donepezil (n=48) were included in the study. Both gene dose and metabolism type significantly predicted the level of donepezil serum concentration (p=0.019 and p=0.013, respectively). In the rivastigmine group, changes of the word list delayed recall subtest before treatment and under stable medication were significantly associated with rivastigmine serum levels (β=0.465; p=0.018). Drug serum concentrations were outside the recommended range in a substantial percentage of participants, which might have contributed to poor correlations between changes in cognitive measures and drug concentrations. Donepezil serum concentrations significantly depended on CYP2D6 gene dose.

Conclusion

Testing AChE-I serum concentration should be considered in patients without clinical response to treatment or those with severe side effects. Patients with donepezil drug levels outside the recommended range might additionally profit from CYP2D6 genotyping or treatment with an AChE-I independent of CYP metabolism.

Gene Polymorphisms Affecting the Pharmacokinetics and Pharmacodynamics of Donepezil Efficacy

Donepezil (DNP) is the first-line drug used for Alzheimer's disease (AD). However, the therapeutic response rate of patients to DNP varies from 20 to 60%. The main reason for the large differences in the clinical efficacy of DNP therapy is genetic factors, some of which affect pharmacokinetics (PK), while others affect pharmacodynamics (PD). Thus, much emphasis has been placed on the investigation of an association between PK- and PD-related gene polymorphisms and therapeutic response to DNP, but a consistent view does not yet exist. In this review, we summarize recent findings regarding genetic factors influencing the clinical efficacy of DNP, including substantial differences in individual responses as a consequence of polymorphisms in Cytochrome P450 (CYP) 2D6, CY3A4, CY3A5, APOE, ABCA1, ABCB1, ESR1, BCHE, PON-1, CHRNA7, and CHAT. We also discuss possible strategies for the evaluation of the clinical efficacy of DNP, with a specific focus on possible biomarkers of PK/PD parameters, and provide perspectives and limitations within the field, which will also be beneficial for understanding the multiple mechanisms of DNP therapy in AD.

A review of the chemopreventative and chemotherapeutic properties of the phytochemicals berberine, resveratrol and curcumin, and their influence on cell death via the pathways of apoptosis and autophagy

Phytochemicals are a diverse group of compounds found in a variety of fruits, vegetables and herbs, and have been reported to possess a number of health benefits. Marketed as supplements by health food retailers, this group of naturally occurring compounds have been investigated for a number of years to determine if they possess any chemopreventative and/or chemotherapeutic benefits. In this comprehensive review, the phytochemicals resveratrol, berberine and curcumin will be discussed, with particular focus being given to their proposed anticancer applications. The purpose of this review is to help clarify whether there is any truth in the claims that are regularly made regarding the efficacy of these compounds. To this end, a number of significant studies that involved the use of these phytochemicals will be identified, discussed and evaluated, to determine if they show promise in the ongoing fight to reduce the incidence rates and severity of various cancers. Specifically, it is the aim of this review to present and discuss key studies performed over the last two decades using these compounds and to evaluate, compare and contrast their effectiveness as chemopreventatives and chemotherapeutics. This should provide the reader with an overarching picture of how these structurally similar phytochemicals might be used in both clinical and nonclinical settings, as a part of the ongoing effort by clinicians, to help to slow down the increasing rate of cancers observed over the last few decades.

The Associations Between CYP2D6*10 C188T Polymorphism and Pharmacokinetics and Clinical Outcomes of Tramadol: A Systematic Review and Meta-analysis

Background

Tramadol is one of the most extensively used centrally acting synthetic opioid analgesics. Recently, a number of studies have explored the associations of the CYP2D6*10 C188T polymorphism with pharmacokinetic and clinical outcomes of tramadol. However, the results of these previous reports remain controversial. Therefore, a meta-analysis was needed to reach a consensus.

Methods

PubMed, EMBASE, and the Cochrane Library were searched to identify eligible studies that explored the influence of the CYP2D6*10 C188T polymorphism on clinical outcomes of tramadol through April 2019. Articles meeting the inclusion criteria were comprehensively reviewed by two independent evaluators. A meta-analysis was performed using Review Manager 5.3.

Results

A total of nine studies involving 809 related subjects were included in this meta-analysis. Significant associations were found between CYP2D6*10 C188T mutation and longer serum tramadol half-lives, larger AUC0-∞, and the slower clearance rate of tramadol. In addition, we also found that CYP2D6*10 C188T had effects on the pharmacokinetic parameters of the metabolite of tramadol, O-desmethyltramadol, by sensitive analysis. Furthermore, CYP2D6*10 C188T polymorphism was associated with higher visual analog scale score, loading dose, and total consumption of tramadol. There was no significant association between CYP2D6*10 C188T polymorphism and postoperative nausea and vomiting.

Conclusions

CYP2D6*10 C188T polymorphism had a significant influence on tramadol pharmacokinetics and analgesic effect, but there was insufficient evidence to demonstrate that this polymorphism was associated with incidence of nausea and vomiting.

The Role of CYP450 Drug Metabolism in Precision Cardio-Oncology

As many novel cancer therapies continue to emerge, the field of Cardio-Oncology (or onco-cardiology) has become crucial to prevent, monitor and treat cancer therapy-related cardiovascular toxicity. Furthermore, given the narrow therapeutic window of most cancer therapies, drug-drug interactions are prevalent in the cancer population. Consequently, there is an increased risk of affecting drug efficacy or predisposing individual patients to adverse side effects. Here we review the role of cytochrome P450 (CYP450) enzymes in the field of Cardio-Oncology. We highlight the importance of cardiac medications in preventive Cardio-Oncology for high-risk patients or in the management of cardiotoxicities during or following cancer treatment. Common interactions between Oncology and Cardiology drugs are catalogued, emphasizing the impact of differential metabolism of each substrate drug on unpredictable drug bioavailability and consequent inter-individual variability in treatment response or development of cardiovascular toxicity. This inter-individual variability in bioavailability and subsequent response can be further enhanced by genomic variants in CYP450, or by modifications of CYP450 gene, RNA or protein expression or function in various 'omics' related to precision medicine. Thus, we advocate for an individualized approach to each patient by a multidisciplinary team with clinical pharmacists evaluating a treatment plan tailored to a practice of precision Cardio-Oncology. This review may increase awareness of these key concepts in the rapidly evolving field of Cardio-Oncology.

Potential role of pharmacogenomics testing in the setting of enhanced recovery pathways after surgery

In 2001, a group of European academic surgeons created the Enhanced Recovery After Surgery (ERAS) study group and established the first official ERAS protocol. One of the most significant challenges during ERAS implementation is variability of drugs used throughout the perioperative period. Pharmacogenomic testing (blood or saliva) results (obtained within approximately 48 hrs) provide guidelines on how to prescribe the optimal drug with the optimal dosage to each patient based on an individual's unique genetic profile. Pharmacogenomic testing of various methods of multimodal analgesia is an essential element of ERAS protocols spanning the entire perioperative period to ultimately optimize postoperative pain control. The key goal for anesthetic management in ERAS protocols is to facilitate rapid emergence by using the shortest acting agents available, thus accelerating recovery and reducing length of stay, hospital expenses, and postoperative complications. Postoperative nausea and vomiting (PONV) is an additional challenge that should be overcome to ensure an enhanced recovery and shorter length of stay with the use of antiemetics. Postoperative ileus (POI) can result in longer hospital stay with increasing susceptibility to associated morbidities along with an increase in associated hospitalization costs. Genetics-guided pharmacotherapy and its impact on clinical outcomes should be thoroughly studied for better understanding and managing drug administration in the settings of ERAS.

Coumarins and P450s, Studies Reported to-Date

Cytochrome P450 enzymes (CYPs) are important phase I enzymes involved in the metabolism of endogenous and xenobiotic compounds mainly through mono-oxygenation reactions into more polar and easier to excrete species. In addition to their role in detoxification, they play important roles in the biosynthesis of endogenous compounds and the bioactivation of xenobiotics. Coumarins, phytochemicals abundant in food and commonly used in fragrances and cosmetics, have been shown to interact with P450 enzymes as substrates and/or inhibitors. In this review, these interactions and their significance in pharmacology and toxicology are discussed in detail.

Influence of CYP2D6 genetic polymorphism on pharmacokinetics of active moiety of tolterodine

Tolterodine is metabolized to an active 5-hydroxymethyl tolterodine (5-HMT) by CYP2D6. This study investigated the relationship between CYP2D6 genotypes and pharmacokinetics of tolterodine and its active metabolite in healthy Korean subjects. All volunteers were genotyped for CYP2D6 and divided into four different genotype groups (CYP2D6*wt/*wt [*wt = *1 or *2], CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10). Each subject received a single oral dose of tolterodine tartrate (2 mg) in single-dose phase of the study. After the single-dose phase of the study, the same subjects received a single oral dose of tolterodine tartrate (2 mg) once daily for 1 week during multiple-dose tolterodine administration phase. Plasma concentrations of tolterodine and 5-HMT were measured by using liquid chromatography-tandem mass spectrometry method. Our study demonstrated that plasma exposure of tolterodine in CYP2D6*10/*10 and CYP2D6*5/*10 group significantly increased, compared with CYP2D6*wt/*wt group (P < 0.001). The pharmacokinetic parameters of 5-HMT were not significantly different in relation to CYP2D6 genotype, as 5-HMT itself is also metabolized by CYP2D6. With regard to active moiety (tolterodine + 5-HMT), C_max and AUC_0-24 was significantly increased in CYP2D6*10/*10 group, compared with CYP2D6*wt/*wt group (P < 0.001). Thus, our study showed the pharmacokinetics of tolterodine and its active moiety was significantly different in relation to CYP2D6 genotype.

PBPK and its Virtual Populations: the Impact of Physiology on Pediatric Pharmacokinetic Predictions of Tramadol

In pediatric PBPK models, age-related changes in the body are known to occur. Given the sparsity of and the variability associated with relevant physiological parameters, different PBPK software providers may vary in their system's data. In this work, three commercially available PBPK software packages (PK-Sim®, Simcyp®, and Gastroplus®) were investigated regarding their differences in system-related information, possibly affecting clearance prediction. Three retrograde PBPK clearance models were set up to enable prediction of pediatric tramadol clearance. These models were qualified in terms of total, CYP2D6, and renal clearance in adults. Tramadol pediatric clearance predictions from PBPK were compared with a pooled popPK model covering clearance ranging from neonates to adults. Fold prediction errors were used to evaluate the results. Marked differences in liver clearance prediction between PBPK models were observed. In general, the prediction bias of total clearance was greatest at the youngest population and decreased with age. Regarding CYP2D6 and renal clearance, important differences exist between PBPK software tools. Interestingly, the PBPK model with the shortest CYP2D6 maturation half-life (PK-Sim) agreed best with the in vivo CYP2D6 maturation model. Marked differences in physiological data explain the observed differences in hepatic clearance prediction in early life between the various PBPK software providers tested. Consensus on the most suited pediatric data to use should harmonize and optimize pediatric clearance predictions. Moreover, the combination of bottom-up and top-down approaches, using a convenient probe substrate, has the potential to update system-related parameters in order to better represent pediatric physiology.

CYP2D6 Protein Level Is the Major Contributor to Interindividual Variability in CYP2D6-Mediated Drug Metabolism in Healthy Human Liver Tissue

CYP2D6 genetic polymorphisms are considered a major contributor to the large interindividual variability in CYP2D6-mediated drug metabolism, but fail to explain a significant portion of the variability. The aim of this study was to assess the ability of the CYP2D6 activity score (AS) estimated from CYP2D6 genotype to predict CYP2D6 expression and enzyme activity. The CYP2D6 gene region was sequenced in 115 healthy human liver tissue samples to determine their CYP2D6 AS. Additionally, CYP2D6 enzyme activity, protein, and mRNA levels were estimated. CYP2D6 AS explained 23% of the interindividual variability in CYP2D6 activity, but only 7.5% in tissues assigned AS 1-2. The CYP2D6 protein level was found to be the major determinant of CYP2D6 activity, explaining 59% of variability. These findings suggest that while CYP2D6 AS is a good predictor of poor metabolizer phenotype, additional nongenetic factors may govern the rate of CYP2D6-mediated metabolism in those without the poor metabolizer phenotype.

CYP2D6 genotypes in revolving door patients with bipolar disorders: A case series

RATIONALE

In psychiatric disorders, interindividual differences in cytochrome P450 (CYP)2D6 (CYP2D6) enzymatic activity could be responsible of adverse drug reactions (ADRs) and therapeutic failures (TFs) for CYP2D6-metabolized drugs, contributing to the periodical hospital readmissions of the revolving door (RD) condition.

PATIENT CONCERNS

We investigated CYP2D6 genotypes in a controlled series of 5 consecutive RD patients with Bipolar Disorder (BD).

DIAGNOSES

Psychiatric patients affected by Bipolar Disorder.

INTERVENTIONS

We defined TFs as a difference at the Brief Psychiatric Rating Scale score ΔBPRS < 25% at each 1-week of stable treatment, and ADRs as the onset of extrapyramidal symptoms and/or metabolic impairment with weight gain.

OUTCOMES

At 3 months, a mean number of 2.75 ± 1.26 ADR and a mean ΔBPRS score of 16.07 ± 0.05% were observed. At 6 months of follow-up, compared to the only patient without BD (ΔBPRS < 32.10%), BD patients (n = 4) showed TFs (ΔBPRS < 25%). CYP2D6 genotyping revealed intermediate metabolizer phenotypes for BD patients and an extensive metabolizer phenotype for the patient without BD. In BD patients, the ratio of drugs maintained/discontinued for TFs or ADRs was 1.75 for non-CYP2D6 versus 0.33 for CYP2D6 interacting drugs, while the proportion of ADR:TF was 0:4 versus 6:3.

LESSONS

Our findings may suggest that CYP2D6 clinically relevant genotypes may be involved in the unwanted outcomes observed in RD patients with BD.

Health-Relevant Phenotypes in the Offspring of Mice Given CAR Activators Prior to Pregnancy

Hepatic induction in response to drugs and environmental chemicals affects drug therapies and energy metabolism. We investigated whether the induction is transmitted to the offspring. We injected 3-day- and 6-week-old F0 female mice with TCPOBOP, an activator of the nuclear receptor constitutive androstane receptor (CAR, NR1I3), and mated them 1-6 weeks afterward. We detected in the offspring long-lasting alterations of CAR-mediated drug disposition, energy metabolism, and lipid profile. The transmission to the first filial generation (F1) was mediated by TCPOBOP transfer from the F0 adipose tissue via milk, as revealed by embryo transfer, crossfostering experiments, and liquid chromatography-mass spectrometry analyses. The important environmental pollutant PCB153 activated CAR in the F1 generation in a manner similar to TCPOBOP. Our findings indicate that chemicals accumulating and persisting in adipose tissue may exert liver-mediated, health-relevant effects on F1 offspring simply via physical transmission in milk. Such effects may occur even if treatment has been terminated far ahead of conception. This should be considered in assessing developmental toxicity and in the long-term follow-up of offspring of mothers exposed to both approved and investigational drugs, and to chemicals with known or suspected accumulation in adipose tissue.

Ten Years' Experience with the CYP2D6 Activity Score: A Perspective on Future Investigations to Improve Clinical Predictions for Precision Therapeutics

The seminal paper on the CYP2D6 Activity Score (AS) was first published ten years ago and, since its introduction in 2008, it has been widely accepted in the field of pharmacogenetics. This scoring system facilitates the translation of highly complex CYP2D6 diplotype data into a patient’s phenotype to guide drug therapy and is at the core of all CYP2D6 gene/drug pair guidelines issued by the Clinical Pharmacogenetics Implementation Consortium (CPIC). The AS, however, only explains a portion of the variability observed among individuals and ethnicities. In this review, we provide an overview of sources in addition to CYP2D6 genotype that contribute to the variability in CYP2D6-mediated drug metabolism and discuss other factors, genetic and non-genetic, that likely contribute to the observed variability in CYP2D6 enzymatic activity.

Discovery and Development of Calcimimetic and Calcilytic Compounds

The extracellular calcium receptor (CaR) is a G protein-coupled receptor (GPCR) and the pivotal molecule regulating systemic Ca²⁺ homeostasis. The CaR was a challenging target for drug discovery because its physiological ligand is an inorganic ion (Ca²⁺) rather than a molecule so there was no structural template to guide medicinal chemistry. Nonetheless, small molecules targeting this receptor were discovered. Calcimimetics are agonists or positive allosteric modulators of the CaR, while calcilytics are antagonists and all to date are negative allosteric modulators. The calcimimetic cinacalcet was the first allosteric modulator of a GPCR to achieve regulatory approval and is a first-in-class treatment for secondary hyperparathyroidism in patients on dialysis, and for hypercalcemia in some forms of primary hyperparathyroidism. It is also useful in treating some rare genetic diseases that cause hypercalcemia. Two other calcimimetics are now on the market (etelcalcetide) or under regulatory review (evocalcet). Calcilytics stimulate the secretion of parathyroid hormone and were initially developed as treatments for osteoporosis. Three different calcilytics of two different chemotypes failed in clinical trials due to lack of efficacy. Calcilytics are now being repurposed and might be useful in treating hypoparathyroidism and several rare genetic diseases causing hypocalcemia. The challenges ahead for medicinal chemists are to design compounds that select conformations of the CaR that preferentially target a particular signalling pathway and/or that affect the CaR in a tissue-selective manner.

Comparison of the Guidelines of the Clinical Pharmacogenetics Implementation Consortium and the Dutch Pharmacogenetics Working Group

Both the Clinical Pharmacogenetics Implementation Consortium (CPIC) and Dutch Pharmacogenetics Working Group provide therapeutic recommendations for well-known gene-drug pairs. Published recommendations show a high rate of concordance. However, as a result of different guideline development methods used by these two consortia, differences between the published guidelines exist. The aim of this paper is to compare both initiatives and explore these differences, with the objective to achieve harmonization.

CYP2D6 phenotypes are associated with adverse outcomes related to opioid medications

BACKGROUND

Variation in the CYP2D6 gene may affect response to opioids in both poor and ultrarapid metabolizers, but data demonstrating such associations have been mixed, and the impact of variants on toxicity-related symptoms (e.g., nausea) is unclear. Therefore, we examined the association between CYP2D6 phenotype and poor pain control or other adverse symptoms related to the use of opioids in a sample of primary care patients.

MATERIALS AND METHODS

We identified all patients in the Mayo Clinic RIGHT Protocol who were prescribed an opioid medication between July 01, 2013 and June 30, 2015, and categorized patients into three phenotypes: poor, intermediate to extensive, or ultrarapid CYP2D6 metabolizers. We reviewed the electronic health record of these patients for indications of poor pain control or adverse symptoms related to medication use. Associations between phenotype and outcomes were assessed using Chi-square tests and logistic regression.

RESULTS

Overall, 257 (25% of RIGHT Protocol participants) patients received at least one opioid prescription; of these, 40 (15%) were poor metabolizers, 146 (57%) were intermediate to extensive metabolizers, and 71 (28%) were ultrarapid metabolizers. We removed patients that were prescribed a CYP2D6 inhibitor medication (n=38). After adjusting for age and sex, patients with a poor or ultrarapid phenotype were 2.7 times more likely to experience either poor pain control or an adverse symptom related to the prescription compared to patients with an intermediate to extensive phenotype (odds ratio: 2.68; 95% CI: 1.39, 5.17; p=0.003).

CONCLUSION

Our results suggest that >30% of patients with a poor or ultrarapid CYP2D6 phenotype may experience an adverse outcome after being prescribed codeine, tramadol, oxycodone, or hydrocodone. These medications are frequently prescribed for pain relief, and ~39% of the US population is expected to carry one of these phenotypes, suggesting that the population-level impact of these gene-drug interactions could be substantial.

CYP2D6 phenotypes are associated with adverse outcomes related to opioid medications

Background

Variation in the CYP2D6 gene may affect response to opioids in both poor and ultrarapid metabolizers, but data demonstrating such associations have been mixed, and the impact of variants on toxicity-related symptoms (e.g., nausea) is unclear. Therefore, we examined the association between CYP2D6 phenotype and poor pain control or other adverse symptoms related to the use of opioids in a sample of primary care patients.

Materials and methods

We identified all patients in the Mayo Clinic RIGHT Protocol who were prescribed an opioid medication between July 01, 2013 and June 30, 2015, and categorized patients into three phenotypes: poor, intermediate to extensive, or ultrarapid CYP2D6 metabolizers. We reviewed the electronic health record of these patients for indications of poor pain control or adverse symptoms related to medication use. Associations between phenotype and outcomes were assessed using Chi-square tests and logistic regression.

Results

Overall, 257 (25% of RIGHT Protocol participants) patients received at least one opioid prescription; of these, 40 (15%) were poor metabolizers, 146 (57%) were intermediate to extensive metabolizers, and 71 (28%) were ultrarapid metabolizers. We removed patients that were prescribed a CYP2D6 inhibitor medication (n=38). After adjusting for age and sex, patients with a poor or ultrarapid phenotype were 2.7 times more likely to experience either poor pain control or an adverse symptom related to the prescription compared to patients with an intermediate to extensive phenotype (odds ratio: 2.68; 95% CI: 1.39, 5.17; p=0.003).

Conclusion

Our results suggest that >30% of patients with a poor or ultrarapid CYP2D6 phenotype may experience an adverse outcome after being prescribed codeine, tramadol, oxycodone, or hydrocodone. These medications are frequently prescribed for pain relief, and ~39% of the US population is expected to carry one of these phenotypes, suggesting that the population-level impact of these gene–drug interactions could be substantial.

Complications of Psychotropic and Pain Medications in an Ultrarapid Metabolizer Patient at the Upper 1% of Cytochrome P450 (CYP450) Function Quantified by Combinatorial CYP450 Genotyping

A 44-year-old Caucasian woman presented with a history of empirical treatment with 20 pain and psychotropic medications, as well as dual comorbidity of intractable pain and depression. A multiple gain-of-function profile in the CYP450 family of cytochrome P450 (CYP450) drug metabolism isoenzymes was discovered. The patient was a homozygote of suprafunctional alleles for both CYP2D6 (^*35/^*35) and CYP2C19 (^*17/^*17) genes and functional alleles for CYP2C9 (^*1/^*1), which account for aggregate drug metabolism function at the upper 1% of the population. The patient improved clinically with discontinuation of psychotropics and pain medications that were substrates of CYP2D6 and/or CYP2C19, suggesting that much of her symptomatology was drug induced. Combinatorial genotyping of CYP450 genes is diagnostically useful in individuals with histories of multiple side effects or drug resistance, which could be avoided by genetically informed therapeutics in behavioral health.

Significance of functional disease-causal/susceptible variants identified by whole-genome analyses for the understanding of human diseases

Human genome variation may cause differences in traits and disease risks. Disease-causal/susceptible genes and variants for both common and rare diseases can be detected by comprehensive whole-genome analyses, such as whole-genome sequencing (WGS), using next-generation sequencing (NGS) technology and genome-wide association studies (GWAS). Here, in addition to the application of an NGS as a whole-genome analysis method, we summarize approaches for the identification of functional disease-causal/susceptible variants from abundant genetic variants in the human genome and methods for evaluating their functional effects in human diseases, using an NGS and in silico and in vitro functional analyses. We also discuss the clinical applications of the functional disease causal/susceptible variants to personalized medicine.

Retrospective use of PBPK modelling to understand a clinical drug-drug interaction between dextromethorphan and GSK1034702

1. In a clinical trial, a strong drug-drug interaction (DDI) was observed between dextromethorphan (DM, the object or victim drug) and GSK1034702 (the precipitant or perpetrator drug), following single and repeat doses. This study determined the inhibition parameters of GSK1034702 in vitro and applied PBPK modelling approaches to simulate the clinical observations and provide mechanistic hypotheses to understand the DDI. 2. In vitro assays were conducted to determine the inhibition parameters of human CYP2D6 by GSK1034702. PBPK models were populated with the in vitro parameters and DDI simulations conducted and compared to the observed data from a clinical study with DM and GSK1034702. 3. GSK1034702 was a potent direct and metabolism-dependent inhibitor of human CYP2D6, with inhibition parameters of: IC₅₀=1.6 μM, K_inact = 3.7 h^-1 and K_I = 0.8 μM. Incorporating these data into PBPK models predicted a DDI after repeat, but not single, 5 mg doses of GSK1034702. 4. The DDI observed with repeat administration of GSK1034702 (5 mg) can be attributed to metabolism-dependent inhibition of CYP2D6. Further, in vitro data were generated and several potential mechanisms proposed to explain the interaction observed following a single dose of GSK1034702.

Transcriptional Regulation of CYP2D6 Expression

CYP2D6-mediated drug metabolism exhibits large interindividual variability. Although genetic variations in the CYP2D6 gene are well known contributors to the variability, the sources of CYP2D6 variability in individuals of the same genotype remain unexplained. Accumulating data indicate that transcriptional regulation of CYP2D6 may account for part of CYP2D6 variability. Yet, our understanding of factors governing transcriptional regulation of CYP2D6 is limited. Recently, mechanistic studies of increased CYP2D6-mediated drug metabolism in pregnancy revealed two transcription factors, small heterodimer partner (SHP) and Krüppel-like factor 9, as a transcriptional repressor and an activator, respectively, of CYP2D6. Chemicals that increase SHP expression (e.g., retinoids and activators of farnesoid X receptor) were shown to downregulate CYP2D6 expression in the humanized mice as well as in human hepatocytes. This review summarizes the series of studies on the transcriptional regulation of CYP2D6 expression, potentially providing a basis to better understand the large interindividual variability in CYP2D6-mediated drug metabolism.

Cytochrome P450 and Non-Cytochrome P450 Oxidative Metabolism: Contributions to the Pharmacokinetics, Safety, and Efficacy of Xenobiotics

The drug-metabolizing enzymes that contribute to the metabolism or bioactivation of a drug play a crucial role in defining the absorption, distribution, metabolism, and excretion properties of that drug. Although the overall effect of the cytochrome P450 (P450) family of drug-metabolizing enzymes in this capacity cannot be understated, advancements in the field of non-P450-mediated metabolism have garnered increasing attention in recent years. This is perhaps a direct result of our ability to systematically avoid P450 liabilities by introducing chemical moieties that are not susceptible to P450 metabolism but, as a result, may introduce key pharmacophores for other drug-metabolizing enzymes. Furthermore, the effects of both P450 and non-P450 metabolism at a drug's site of therapeutic action have also been subject to increased scrutiny. To this end, this Special Section on Emerging Novel Enzyme Pathways in Drug Metabolism will highlight a number of advancements that have recently been reported. The included articles support the important role of non-P450 enzymes in the clearance pathways of U.S. Food and Drug Administration-approved drugs over the past 10 years. Specific examples will detail recent reports of aldehyde oxidase, flavin-containing monooxygenase, and other non-P450 pathways that contribute to the metabolic, pharmacokinetic, or pharmacodynamic properties of xenobiotic compounds. Collectively, this series of articles provides additional support for the role of non-P450-mediated metabolic pathways that contribute to the absorption, distribution, metabolism, and excretion properties of current xenobiotics.

Physiological Content and Intrinsic Activities of 10 Cytochrome P450 Isoforms in Human Normal Liver Microsomes

Due to a lack of physiologic cytochrome P450 (P450) isoform content, P450 activity is typically only determined at the microsomal level (per milligram of microsomal protein) and not at the isoform level (per picomole of P450 isoform), which could result in the misunderstanding of variations in P450 activity between individuals and further hinder development of personalized medicine. We found that there were large variations in protein content, mRNA levels, and intrinsic activities of the 10 P450s in 100 human liver samples, in which CYP2E1 and CYP2C9 showed the highest expression levels. P450 gene polymorphisms had different effects on activity at two levels: CYP3A5*3 and CYP2A6*9 alleles conferred increased activity at the isoform level but decreased activity at the microsomal level; CYP2C9*3 had no effect at the isoform level but decreased activity at the microsomal level. The different effects at each level stem from the different effects of each polymorphism on the resulting P450 protein. Individuals with CYP2A6*1/*4, CYP2A6*1/*9, CYP2C9*1/*3, CYP2D6 100C>T TT, CYP2E1 7632T>A AA, CYP3A5*1*3, and CYP3A5*3*3 genotypes had significantly lower protein content, whereas CYP2D6 1661G>C mutants had a higher protein content. In conclusion, we first offered the physiologic data of 10 P450 isoform contents and found that some single nucleotide polymorphisms had obvious effects on P450 expression in human normal livers. The effects of gene polymorphisms on intrinsic P450 activity at the isoform level were quite different from those at the microsomal level, which might be due to changes in P450 protein content.

Pharmacogenetics of CYP2D6 and tamoxifen therapy: Light at the end of the tunnel?

The clinical usefulness of assessing the enzymatic activity of CYPD6 in patients taking tamoxifen had been longly debated. In favour of preemptive evaluation of phenotypic profile of patients is the strong pharmacologic rationale, being that the formation of endoxifen, the major and clinically most important metabolite of tamoxifen, is largely dependent on the activity of CYP2D6. This enzyme is highly polymorphic for which the activity is largely depending on genetics, but that can also be inhibited by a number of drugs, i.e. antidepressants, which are frequently used in patients with cancer. Unfortunately, the clinical trials that have been published in the last years are contradicting each other on the association between CYP2D6 and significant clinical endpoints, and for this reason CYP2D6 genotyping is at present not generally recommended. Despite this, the CYP2D6 genotyping test for tamoxifen is available in many laboratories and it may still be an appropriate test to use it in specific cases.

Interindividual Variability in Cytochrome P450-Mediated Drug Metabolism

The cytochrome P450 (P450) enzymes are the predominant enzyme system involved in human drug metabolism. Alterations in the expression and/or activity of these enzymes result in changes in pharmacokinetics (and consequently the pharmacodynamics) of drugs that are metabolized by this set of enzymes. Apart from changes in activity as a result of drug-drug interactions (by P450 induction or inhibition), the P450 enzymes can exhibit substantial interindividual variation in basal expression and/or activity, leading to differences in the rates of drug elimination and response. This interindividual variation can result from a myriad of factors, including genetic variation in the promoter or coding regions, variation in transcriptional regulators, alterations in microRNA that affect P450 expression, and ontogenic changes due to exposure to xenobiotics during the developmental and early postnatal periods. Other than administering a probe drug or cocktail of drugs to obtain the phenotype or conducting a genetic analysis to determine genotype, methods to determine interindividual variation are limited. Phenotyping via a probe drug requires exposure to a xenobiotic, and genotyping is not always well correlated with phenotype, making both methodologies less than ideal. This article describes recent work evaluating the effect of some of these factors on interindividual variation in human P450-mediated metabolism and the potential utility of endogenous probe compounds to assess rates of drug metabolism among individuals.

Genetic polymorphisms associated with heart failure: A literature review

Objective

To review possible associations reported between genetic variants and the risk, therapeutic response and prognosis of heart failure.

Methods

Electronic databases (PubMed, Web of Science and CNKI) were systematically searched for relevant papers, published between January 1995 and February 2015.

Results

Eighty-two articles covering 29 genes and 39 polymorphisms were identified.

Conclusion

Genetic association studies of heart failure have been highly controversial. There may be interaction or synergism of several genetic variants that together result in the ultimate pathological phenotype for heart failure.