Novel functional polymorphisms in the UGT1A7 and UGT1A9 glucuronidating enzymes in Caucasian and African-American subjects and their impact on the metabolism of 7-ethyl-10-hydroxycamptothecin and flavopiridol anticancer drugs

Heterodimerization of Human UDP-Glucuronosyltransferase 1A9 and UDP-Glucuronosyltransferase 2B7 Alters Their Glucuronidation Activities

Human UDP-glucuronosyltransferases (UGTs) play a pivotal role as prominent phase II metabolic enzymes, mediating the glucuronidation of both endobiotics and xenobiotics. Dimerization greatly modulates the enzymatic activities of UGTs. In this study, we examined the influence of three mutations (H35A, H268Y, and N68A/N315A) and four truncations (signal peptide, single transmembrane helix, cytosolic tail, and di-lysine motif) in UGT2B7 on its heterodimerization with wild-type UGT1A9, using a Bac-to-Bac expression system. We employed quantitative fluorescence resonance energy transfer (FRET) techniques and co-immunoprecipitation assays to evaluate the formation of heterodimers between UGT1A9 and UGT2B7 allozymes. Furthermore, we evaluated the glucuronidation activities of the heterodimers using zidovudine and propofol as substrates for UGT2B7 and UGT1A9, respectively. Our findings revealed that the histidine residue at codon 35 was involved in the dimeric interaction, as evidenced by the FRET efficiencies and catalytic activities. Interestingly, the signal peptide and single transmembrane helix domain of UGT2B7 had no impact on the protein-protein interaction. These results provide valuable insights for a comprehensive understanding of UGT1A9/UGT2B7 heterodimer formation and its association with glucuronidation activity. SIGNIFICANCE STATEMENT: Our findings revealed that the H35A mutation in UGT2B7 affected the affinity of protein-protein interaction, leading to discernable variations in fluorescence resonance energy transfer efficiencies and catalytic activity. Furthermore, the signal peptide and single transmembrane helix domain of UGT2B7 did not influence heterodimer formation. These results provide valuable insights into the combined effects of polymorphisms and protein-protein interactions on the catalytic activity of UGT1A9 and UGT2B7, enhancing our understanding of UGT dimerization and its impact on metabolite formation.

Mutual Modulation of the Activities of Human CYP2D6 and Four UGTs during the Metabolism of Propranolol

Cytochromes P450 (CYP) and UDP-glucuronosyltransferases (UGT) are two enzyme families that play an important role in drug metabolism, catalyzing either the functionalization or glucuronidation of xenobiotics. However, their mutual interactions are poorly understood. In this study, the functional interactions of human CYP2D6 with four human UGTs (UGT1A7, UGT1A8, UGT1A9, and UGT2A1) were investigated using our previously established co-expression model system in the fission yeast Schizosaccharomyces pombe. The substrate employed was propranolol because it is well metabolized by CYP2D6. Moreover, the CYP2D6 metabolite 4-hydroxypropranolol is a known substrate for the four UGTs included in this study. Co-expression of either UGT1A7, UGT1A8, or UGT1A9 was found to increase the activity of CYP2D6 by a factor of 3.3, 2.1 or 2.8, respectively, for the conversion of propranolol to 4-hydroxypropranolol. In contrast, UGT2A1 co-expression did not change CYP2D6 activity. On the other hand, the activities of all four UGTs were completely suppressed by co-expression of CYP2D6. This data corroborates our previous report that CYP2D6 is involved in functional CYP-UGT interactions and suggest that such interactions can contribute to both adverse drug reactions and changes in drug efficacy.

An update on the pharmacogenetic considerations when prescribing dopamine receptor agonists for Parkinson's disease

INTRODUCTION

Parkinson's disease is a chronic neurodegenerative multisystemic disorder that affects approximately 2% of the population over 65 years old. This disorder is characterized by motor symptoms which are frequently accompanied by non-motor symptoms such as cognitive disorders. Current drug therapies aim to reduce the symptoms and increase the patient's life expectancy. Nevertheless, there is heterogeneity in therapy response in terms of efficacy and adverse effects. This wide range in response may be linked to genetic variability. Thus, it has been suggested that pharmacogenomics may help to tailor and personalize drug therapy for Parkinson's disease.

AREAS COVERED

This review describes and updates the clinical impact of genetic factors associated with the efficacy and adverse drug reactions related to common medications used to treat Parkinson's disease. Additionally, we highlight current informative recommendations for the drug treatment of Parkinson's disease.

EXPERT OPINION

The pharmacokinetic, pharmacodynamic, and safety profiles of Parkinson's disease drugs do not favor the development of pharmacogenetic tests with a high probability of success. The chances of obtaining ground-breaking pharmacogenetics biomarkers for Parkinson's disease therapy are limited. Nevertheless, additional information on the metabolism of certain drugs, and an analysis of the potential of pharmacogenetics in novel drugs could be of interest.

Cannabis Pharmacogenomics: A Path to Personalized Medicine

Cannabis and related compounds have created significant research interest as a promising therapy in many disorders. However, the individual therapeutic effects of cannabinoids and the incidence of side effects are still difficult to determine. Pharmacogenomics may provide the answers to many questions and concerns regarding the cannabis/cannabinoid treatment and help us to understand the variability in individual responses and associated risks. Pharmacogenomics research has made meaningful progress in identifying genetic variations that play a critical role in interpatient variability in response to cannabis. This review classifies the current knowledge of pharmacogenomics associated with medical marijuana and related compounds and can assist in improving the outcomes of cannabinoid therapy and to minimize the adverse effects of cannabis use. Specific examples of pharmacogenomics informing pharmacotherapy as a path to personalized medicine are discussed.

Cannabinoids and Multiple Sclerosis: A Critical Analysis of Therapeutic Potentials and Safety Concerns

Multiple sclerosis (MS) is a complicated condition in which the immune system attacks myelinated axons in the central nervous system (CNS), destroying both myelin and axons to varying degrees. Several environmental, genetic, and epigenetic factors influence the risk of developing the disease and how well it responds to treatment. Cannabinoids have recently sparked renewed interest in their therapeutic applications, with growing evidence for their role in symptom control in MS. Cannabinoids exert their roles through the endogenous cannabinoid (ECB) system, with some reports shedding light on the molecular biology of this system and lending credence to some anecdotal medical claims. The double nature of cannabinoids, which cause both positive and negative effects, comes from their actions on the same receptor. Several mechanisms have been adopted to evade this effect. However, there are still numerous limitations to using cannabinoids to treat MS patients. In this review, we will explore and discuss the molecular effect of cannabinoids on the ECB system, the various factors that affect the response to cannabinoids in the body, including the role of gene polymorphism and its relation to dosage, assessing the positive over the adverse effects of cannabinoids in MS, and finally, exploring the possible functional mechanism of cannabinoids in MS and the current and future progress of cannabinoid therapeutics.

Effects of common genetic variants of human uridine diphosphate glucuronosyltransferase subfamilies on irinotecan glucuronidation

The adverse effects (diarrhea and neutropenia) of irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin) are associated with genetic variants of uridine diphosphate glucuronosyltransferase 1A subfamilies (UGT1As). UGT1As are enzymes that metabolize the active form of irinotecan, 7-ethyl-10 hydroxycamptothecin (SN-38), by glucuronidation in the liver. They are widely known as predictive factors of severe adverse effects, such as neutropenia and diarrhea. Some studies have suggested that variants of UGT1As affect SN-38 glucuronidation activities, thus exerting severe adverse effects. We aimed to identify UGT1A isoforms that show SN-38 glucuronidation activity and determine the relationship between UGT1A variants and SN-38 glucuronidation in vitro. We found that UGT1A1 and UGT1A6-UGT1A10 displayed SN-38 glucuronidation activity. Among these, UGT1A1 was the most active. Furthermore, the variants of these isoforms showed decreased SN-38 glucuronidation activity. In our study, we compared the different variants of UGT1As, such as UGT1A1.6, UGT1A1.7, UGT1A1.27, UGT1A1.35, UGT1A7.3, UGT1A8.4, UGT1A10M59I, and UGT1A10T202I, to determine the differences in the reduction of glucuronidation. Our study elucidates the relationship between UGT1A variants and the level of glucuronidation associated with each variant. Therefore, testing can be done before the initiation of irinotecan treatment to predict potential toxicities and adverse effects.

Pharmacological counseling in hepatotoxicity induced by macitentan and selexipag: a case report

Background

Pulmonary arterial hypertension is a progressive, debilitating condition characterized by increased resistance in the pulmonary arterial circulation. Current treatments for pulmonary arterial hypertension include endothelin receptor antagonists such as bosentan, sitaxentan, ambrisentan, macitentan, and oral prostacyclin receptor agonists such as selexipag. Endothelin receptor antagonists have been associated with liver injury, while hepatotoxicity was not reported for selexipag. Although genetic variability has been indisputably associated with variability in drug response, no study has been designed until now to assess its effects on the pharmacokinetics of endothelin receptor antagonists or selexipag.

Case presentation

We report the case of a 58-year-old female Caucasian patient with a dramatic increase in plasma levels of transaminases after treatment with macitentan and selexipag, drugs whose risk of causing liver injury has so far been considered limited. After therapy discontinuation, plasma levels of transaminases returned to baseline, thus suggesting a role of these drugs in the observed hepatotoxicity. After pharmacological counseling, we decided to introduce ambrisentan for the patient’s treatment. After 7 months of treatment, no liver injury has been reported. To evaluate the role of genetic factors in the observed hepatotoxicity, we genotyped the patient for single-nucleotide polymorphisms previously associated with macitentan, ambrisentan, or selexipag metabolism. We found a genetic profile associated with a poor metabolizer (PM) phenotype for CYP2C8 and CYP2C9, key enzymes for elimination of both macitentan and selexipag. The reported results suggest that an allelic profile associated with low activity for CYP2C8 and CYP2C9 enzyme could be a potential risk factor for macitentan and selexipag-induced liver injury and could provide a possible marker for early identification of subjects at higher risk of developing hepatotoxicity.

Conclusions

A multidisciplinary approach based on clinical evaluation, as well as pharmacological counseling and evaluation of the patient’s genetic profile, might be useful for identification of patients with a high chance of drug-induced liver injury, avoiding unnecessary risks in therapy selection and prescription.

An ethnopharmacological review on the therapeutical properties of flavonoids and their mechanisms of actions: A comprehensive review based on up to date knowledge

Flavonoids -a class of low molecular weight secondary metabolites- are ubiquitous and cornucopia throughout the plant kingdom. Structurally, the main structure consists of C6-C3-C6 rings with different substitution patterns so that many sub-classes are obtained, for example: flavonols, flavonolignans, flavonoid glycosides, flavans, anthocyanidins, aurones, anthocyanidins, flavones, neoflavonoids, chalcones, isoflavones, flavones and flavanones. Flavonoids are evaluated to have drug like nature since they possess different therapeutic activities, and can act as cardioprotective, antiviral, antidiabetic, anti-inflammatory, antibacterial, anticancer, and also work against Alzheimer's disease and others. However, information on the relationship between their structure and biological activity is scarce. Therefore, the present review tries to summarize all the therapeutic activities of flavonoids, their mechanisms of action and the structure activity relationship.

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Latest updated ethnopharmacological review of the therapeutic effects of flavonoids.

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Flavonoids are attracting attention because of their therapeutic properties.

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Flavonoids are valuable candidates for drug development against many dangerous diseases.

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This overview summarizes the most important therapeutic effect and mechanism of action of flavonoids.

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General knowledge about the structure activity relationship of flavonoids is summarized.

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Substitution of chemical groups in the structure of flavonoids can significantly change their biological and chemical properties.

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The chemical properties of the basic flavonoid structure should be considered in a drug-based structural program.

Common UGT1A9 polymorphisms do not have a clinically meaningful impact on the apparent oral clearance of dapagliflozin in type 2 diabetes mellitus

Dapagliflozin is an inhibitor of the human renal sodium-glucose cotransporter type 2 (SGLT2), first approved for the treatment of type 2 diabetes mellitus (T2DM). Dapagliflozin is primarily metabolized by uridine diphosphate glucuronosyltransferase 1A9 (UGT1A9). The effect of UGT1A9 polymorphisms on dapagliflozin apparent oral clearance (CL/F) was studied with dapagliflozin population pharmacokinetic data and UGT1A9 genotype data (I.399C>T, rs2011404, rs6759892, rs7577677, rs4148323, UGT1A9*2 and UGT1A9*3) from a Phase 2 study conducted in subjects with T2DM (n=187). An ANCOVA model accounting for known covariates influencing dapagliflozin CL/F was applied to these data to quantify the impact of each UGT1A9 polymorphism relative to the wildtype UGT1A9 genotype. The analysis showed that the geometric mean ratio of dapagliflozin CL/F for all of the UGT1A9 polymorphisms studied were within the range of wildtype UGT1A9 CL/F values. Consequently, the polymorphisms of UGT1A9 studied had no clinically meaningful impact on the CL/F of dapagliflozin.

Meta-Analysis of Noncompartmental Pharmacokinetic Parameters of Ertugliflozin to Evaluate Dose Proportionality and UGT1A9 Polymorphism Effect on Exposure

Ertugliflozin, a sodium‐glucose cotransporter 2 inhibitor, is primarily metabolized via glucuronidation by the uridine 5′‐diphospho‐glucuronosyltransferase (UGT) isoform UGT1A9. This noncompartmental meta‐analysis of ertugliflozin pharmacokinetics evaluated the relationship between ertugliflozin exposure and dose, and the effect of UGT1A9 genotype on ertugliflozin exposure. Pharmacokinetic data from 25 phase 1 studies were pooled. Structural models for dose proportionality described the relationship between ertugliflozin area under the plasma concentration‐time curve (AUC) or maximum observed plasma concentration (C_max) and dose. A structural model for the UGT1A9 genotype described the relationship between ertugliflozin AUC and dose, with genotype information on 3 UGT1A9 polymorphisms (UGT1A9‐2152, UGT1A9*3, UGT1A9*1b) evaluated as covariates from the full model. Ertugliflozin AUC and C_max increased in a dose‐proportional manner over the dose range of 0.5‐300 mg, and population‐predicted AUC and C_max values for the 5‐ and 15‐mg ertugliflozin tablets administered in the fasted state demonstrated good agreement with the observed data. The largest change in ertugliflozin AUC was in subjects carrying the UGT1A9*3 heterozygous variant, with population‐predicted AUC (90% confidence interval) values of 485 ng·h/mL (458 to 510 ng·h/mL) and 1560 ng·h/mL (1480 to 1630 ng·h/mL) for ertugliflozin 5 and 15 mg, respectively, compared with 436 ng·h/mL (418 to 455 ng·h/mL) and 1410 ng·h/mL (1350 to 1480 ng·h/mL), respectively, in wild‐type subjects. Overall, the mean effects of the selected UGT1A9 variants on ertugliflozin AUC were within ±10% of the wild type. UGT1A9 genotype did not have any clinically meaningful effects on ertugliflozin exposure in healthy subjects. No ertugliflozin dose adjustment would be required in patients with the UGT1A9 variants assessed in this study.

Pharmacokinetics of Roxadustat: A Population Analysis of 2855 Dialysis- and Non-Dialysis-Dependent Patients with Chronic Kidney Disease

BACKGROUND

Roxadustat is a novel, small-molecule, first-in-class therapeutic that stimulates erythropoiesis by inhibiting hypoxia-inducible factor prolyl hydroxylase enzymes. This agent (roxadustat) is in clinical development for the treatment of anemia in patients with non-dialysis-dependent (NDD) and dialysis-dependent (DD) chronic kidney disease. A population pharmacokinetic analysis was undertaken to evaluate the effect of intrinsic and extrinsic factors on roxadustat pharmacokinetics.

METHODS

Non-linear mixed-effects models implemented in NONMEM software were fitted to 8209 pharmacokinetic samples from 2855 DD and NDD subjects enrolled in four phase III studies with roxadustat dose concentrations of 20-400 mg as orally administered tablets. Effects of intrinsic and extrinsic factors were evaluated using a stepwise covariate modeling procedure in combination with the full covariate approach, and defined no-effect boundaries for exposure were based on the difference in exposure between 70 and 100 mg of roxadustat (i.e., - 30%, + 43%).

RESULTS

A two-compartment model with first-order absorption adequately described roxadustat pharmacokinetics, with parameter estimates (relative standard error) for apparent clearance of 1.1 (0.0223) L/h in NDD subjects, and apparent central and peripheral volumes of distribution of 14.9 (0.0278) L and 9.5 (0.0872) L, respectively. Stepwise covariate modeling identified bodyweight, dialysis status, race, and dose as statistically significant covariates on apparent clearance, and bodyweight, sex, and albumin as statistically significant covariates on apparent central volume of distribution. However, the effects of these covariates did not result in roxadustat area under the curve or maximum plasma concentration changes outside of the defined no-effect boundaries. The effects of concomitant oral iron, clopidogrel, and staggered sevelamer, calcium carbonate, or calcium acetate were investigated using a full covariate approach but did not result in roxadustat area under the curve or maximum plasma concentration changes outside of the defined no-effect boundaries.

CONCLUSIONS

A population pharmacokinetic model was developed for the pharmacokinetics of roxadustat in the target population. None of the investigated intrinsic or extrinsic factors resulted in a significant change in roxadustat exposure outside of the defined no-effect boundaries.

Pharmacogenetics and pharmacokinetics modeling of unexpected and extremely severe toxicities after sorafenib intake

A 53-year-old woman with papillary thyroid cancer treated with 800 mg sorafenib therapy rapidly experienced grade 3 toxicities. Dosing was reduced in a step-wise manner with several treatment discontinuations down to 200 mg every 2 days but severe toxicities continued. Plasma drug monitoring showed high exposure, even at low dose. Dosing was then further reduced at 200 mg every 3 days and tolerance was finally acceptable (i.e., grade 1 toxicity) with stable disease upon RECIST imaging. Pharmacogenetic investigations showed polymorphisms affecting both UGT1A9 (UGT1A9-rs3832043) and nuclear receptor PXR (NR1I2-rs3814055, NR1I2-rs2472677 and NR1I2-rs10934498), possibly resulting in downregulation of liver metabolizing enzymes of sorafenib (i.e., CYP and UGT). Patient's clearance (0.48 l/h) estimated by Bayesian approach was consistently lower than usually described. This is the first time that, in addition to mutations affecting UGT1A9, genetic polymorphisms of NR1I2 have possibly been associated with both plasma overexposure and severe toxicities upon sorafenib intake.

Human variability in isoform-specific UDP-glucuronosyltransferases: markers of acute and chronic exposure, polymorphisms and uncertainty factors

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro-in vivo extrapolations in chemical risk assessment are discussed.

Circadian Clock Component Rev-erbα Regulates Diurnal Rhythm of UDP-Glucuronosyltransferase 1a9 and Drug Glucuronidation in Mice

UDP-glucuronosyltransferases (UGTs) are a family of phase II enzymes that play an important role in metabolism and elimination of numerous endo- and xenobiotics. Here, we aimed to characterize diurnal rhythm of Ugt1a9 in mouse liver and to determine the molecular mechanisms underlying the rhythmicity. Hepatic Ugt1a9 mRNA and protein displayed robust diurnal rhythms in wild-type mice with peak levels at zeitgeber time (ZT) 6. Rhythmicity in Ugt1a9 expression was confirmed using synchronized Hepa-1c1c7 cells. We observed time-varying glucuronidation (ZT6 > ZT18) of propofol, a specific Ugt1a9 substrate, consistent with the diurnal pattern of Ugt1a9 protein. Loss of Rev-erbα (a circadian clock component) downregulated the Ugt1a9 expression and blunted its rhythm in mouse liver. Accordingly, propofol glucuronidation was reduced and its dosing time dependency was lost in Rev-erbα ^-/- mice. Dec2 (a transcription factor) was screened to be the potential intermediate that mediated Rev-erbα regulation of Ugt1a9. We confirmed Rev-erbα as a negative regulator of Dec2 in mice and in Hepa-1c1c7 cells. Based on promoter analysis and luciferase reporter assays, it was found that Dec2 trans-repressed Ugt1a9 via direct binding to an E-box-like motif in the gene promoter. Additionally, regulation of Ugt1a9 by Rev-erbα was Dec2-dependent. In conclusion, Rev-erbα generates and regulates rhythmic Ugt1a9 through periodical inhibition of Dec2, a transcriptional repressor of Ugt1a9. Our study may have implications for understanding of circadian clock-controlled drug metabolism and of metabolism-based chronotherapeutics. SIGNIFICANCE STATEMENT: Hepatic Ugt1a9 displays diurnal rhythmicities in expression and glucuronidation activity in mice. It is uncovered that Rev-erbα generates and regulates rhythmic Ugt1a9 through periodical inhibition of Dec2, a transcriptional repressor of Ugt1a9. The findings may have implications for understanding of circadian clock-controlled drug metabolism and of metabolism-based chronotherapeutics.

The Effect of UGT1A9, CYP2B6 and CYP2C9 Genes Polymorphism on Propofol Pharmacokinetics in Children

Purpose

This study was conducted to determine the effect of UGT1A9 98T>C, CYP2B6 516G>T and CYP2C9 430C>T genetic polymorphisms on the pharmacokinetics of propofol in children of different sexes and ages who undergone total intravenous anesthesia (ТIVA) and deep sedation during diagnostic and therapeutic procedures.

Patients and Methods

The prospective study included 94 children, ASA I-II status, 1 to 17 years of age, who undergone standard anesthetic protocol for TIVA, which implied the continuous use of propofol. Before the administration of propofol, venous blood was sampled to determine the presence of genetic variations in UGT1A9, CYP2B6 and CYP2C9 gene using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). From each patient included in the study blood samples were taken: 10 mins after the induction of anesthesia, immediately before the discontinuation of the propofol infusion, 10 mins after discontinuation of the propofol infusion and 20 mins after discontinuation of the propofol infusion to determine the pharmacokinetics of the drug in the plasma of the subjects The plasma propofol concentration was determined by HPLC analytical technique.

Results

UGT1A9 genotype is an independent predictor of the propofol concentration in children immediately after the end of the continuous infusion and 10 mins afterwards. In the carriers of the polymorphic UGT1A9 C allele, the propofol distribution constant was higher. The carriers of the polymorphic CYP2B6 T allele received a significantly lower overall and initial dose of propofol. Unlike polymorphism of the UGT1A9 gene, the tested CYP2C9 and CYP2B6 gene polymorphisms are not independent predictors of the pharmacokinetics of propofol.

Conclusion

Further investigations of UGT1A9, CYP2B6 and CYP2C9 and other genes that participate in propofol metabolism as well as detailed analyses of the general conditions, administered therapies and associated diseases could explain the large interindividual variability of propofol metabolism in children.

Multiplex analysis of genetic polymorphisms within UGT1A9, a gene involved in phase II of Δ9-THC metabolism

We present a novel multiplex assay for the simultaneous detection of 12 polymorphisms within the UGT1A9 sequence, which codes for enzymes involved in phase II biotransformation. The assay combines a multiplexed amplification step with single-base extension sequencing. The method described here is fast, cost-effective, and easy-to-use, combining the relevant features of screening methods for research and diagnostics in pharmacogenetics. To validate the assay, we tested reproducibility and sensitivity and analysed allele frequencies of 110 Caucasian individuals. Furthermore, we describe combining genetic information of individuals consuming Cannabis sativa products with respective plasma concentrations of a metabolite.

Regioselectivity significantly impacts microsomal glucuronidation efficiency of R/S-6, 7-, and 8-hydroxywarfarin

Coumadin (R/S-warfarin) metabolism plays a critical role in patient response to anticoagulant therapy. Several cytochrome P450s oxidize warfarin into R/S-6-, 7-, 8-, 10, and 4'-hydroxywarfarin that can undergo subsequent glucuronidation by UDP-glucuronosyltransferases (UGTs); however, current studies on recombinant UGTs cannot be adequately extrapolated to microsomal glucuronidation capacities for the liver. Herein, we estimated the capacity of the average human liver to glucuronidate hydroxywarfarin and identified UGTs responsible for those metabolic reactions through inhibitor phenotyping. There was no observable activity toward R/S-warfarin, R/S-10-hydroxywarfarin or R/S-4'-hydroxywarfarin. The observed metabolic efficiencies (V_max/K_m) toward R/S-6-, 7-, and especially 8-hydroxywarfarin indicated a high glucuronidation capacity to metabolize these compounds. UGTs demonstrated strong regioselectivity toward the hydroxywarfarins. UGT1A6 and UGT1A1 played a major role in R/S-6- and 7-hydroxywarfarin glucuronidation, respectively, whereas UGT1A9 accounted for almost all of the generation of the R/S-8-hydroxywarfarin glucuronide. In summary, these studies expanded insights to glucuronidation of hydroxywarfarins by pooled human liver microsomes, novel roles for UGT1A6 and 1A9, and the overall degree of regioselectivity for the UGT reactions.

Genetics and Treatment Response in Parkinson's Disease: An Update on Pharmacogenetic Studies

Parkinson's disease (PD) is a complex neurodegenerative disorder characterized by a progressive loss of dopamine neurons of the central nervous system. The disease determines a significant disability due to a combination of motor symptoms such as bradykinesia, rigidity and rest tremor and non-motor symptoms such as sleep disorders, hallucinations, psychosis and compulsive behaviors. The current therapies consist in combination of drugs acting to control only the symptoms of the illness by the replacement of the dopamine lost. Although patients generally receive benefits from this symptomatic pharmacological management, they also show great variability in drug response in terms of both efficacy and adverse effects. Pharmacogenetic studies highlighted that genetic factors play a relevant influence in this drug response variability. In this review, we tried to give an overview of the recent progresses in the pharmacogenetics of PD, reporting the major genetic factors identified as involved in the response to drugs and highlighting the potential use of some of these genomic variants in the clinical practice. Many genes have been investigated and several associations have been reported especially with adverse drug reactions. However, only polymorphisms in few genes, including DRD2, COMT and SLC6A3, have been confirmed as associated in different populations and in large cohorts. The identification of genomic biomarkers involved in drug response variability represents an important step in PD treatment, opening the prospective of more personalized therapies in order to identify, for each person, the better therapy in terms of efficacy and toxicity and to improve the PD patients' quality of life.

Relationship between UGT1A9 gene polymorphisms, efficacy, and safety of propofol in induced abortions amongst Chinese population: a population-based study

The present study aimed to investigate the influence of UGT1A9 gene polymorphisms on the efficacy of propofol in patients undergoing the painless induced abortion method. A total of 156 women seeking voluntary pregnancy termination procedures were selected for the study, and subsequently underwent painless induced abortions, following anesthesia by means of propofol administration. PCR-restriction fragment length polymorphism (PCR-RFLP) was performed to detect the polymorphisms of UGT1A9 gene at -440C/T, -1818C/T, and -1887T/G loci. The time, effect-site concentration, and bispectral index (BIS) for the Observer's Assessment of Alertness/Sedation (OAA/S) (up to 4 points) were observed and recorded in patients following discontinuation of propofol. The time and effect-site concentration for BIS reaching 80 in patients following the discontinuation of propofol were observed and recorded. Postoperative observations of adverse reactions, such as nausea, vomiting, and respiratory depression were all made record of. In comparison with patients with UGT1A9 -440C/T CT and TT, those with UGT1A9 -440C/T CC displayed shorter durations of OAA/S by up to 4 points, shorter BIS times reaching 80, as well as higher corresponding effect-site concentrations. No significant differences were detected in the patients with -440C/T, -1818T/C, and -1887T/G in incidence of nausea, vomiting, and respiratory depression. The findings of the study highlighted correlation between UGT1A9 -440C/T gene polymorphisms and positive propofol efficacy in patients undergoing painless induced pregnancy termination procedures.

The effect of UGT1A9, CYP2B6 and CYP2C9 genes polymorphism on individual differences in propofol pharmacokinetics among Polish patients undergoing general anaesthesia

Propofol (2,6-diisopropylphenol) is one of the safest and most commonly used anaesthetic agents for intravenous general anaesthesia. However, in clinical practice, a large inter-individual variability in response to propofol is observed. To limit the risk of adverse effects, pharmacogenetic investigations are recommended. The aim of our study was to verify the impact of genetic changes c.516G>T in the CYP2B6, c.98T>C in the UGT1A9 and c.1075A>C in the CYP2C9 genes on the individual propofol pharmacokinetic profile in the Polish patients undergoing general anaesthesia. Eighty-five patients from the Department of Anaesthesiology and Intensive Therapy, Regional Hospital in Poznan, Poland, anaesthetised with propofol for surgery, were enrolled in the study. We have genotyped CYP2B6, UGT1A9 and CYP2C9 polymorphisms with the use of pyrosequencing. HPLC measurements of propofol plasma concentration were applied for a pharmacokinetic analysis of the anaesthetic. We identified poor (20), intermediate (42) and rapid (23) metabolisers of propofol, which constituted 24%, 49% and 27% of the group, respectively. Homozygotes c.516 T/T in the CYP2B6 gene were statistically more often found in the rapid metabolisers group (p < 0.05). However, polymorphisms c.98T>C in the UGT1A9 and c.1075A>C in the CYP2C9 genes did not affect the pharmacokinetic profile of propofol. The mean propofol retention time (MRT) correlated with the patient’s body mass index (BMI) (p < 0.05). From all the analysed changes, only polymorphism c.516G>T in the CYP2B6 gene and BMI affect the metabolism rate of propofol and may play an important role in the optimisation of propofol anaesthesia.

Prevalence of UDP-glucuronosyltransferase polymorphisms (UGT1A6∗2, 1A7∗12, 1A8∗3, 1A9∗3, 2B7∗2, and 2B15∗2) in a Saudi population

Glucuronidation is an important phase II pathway responsible for many endogenous substances and drug metabolism. The present work evaluated allele frequencies of certain UDP-glucuronosyl-transferases (UGT 1A6∗2, A7∗12, A8∗3, A9∗3, 2B7∗2, and 2B15∗2) in Saudi Arabians that could provide essential ethnic information. Blood samples from 192 healthy unrelated Saudi males of various geographic regions were collected. Genomic DNA was isolated and genotyping of various UGTs was carried out using polymerase chain reaction (PCR) followed by direct sequencing. For UGT1A6∗2 A/G genotype, the most common variant was the homozygous repeat (AA) and the most common allele was (A) with a frequency of 46.5% and 67.3%, respectively. Similarly, the most common variant for UGT1A7∗12 T/C genotype was the heterozygous repeat (TC) with a frequency of 78.7% while the mutant allele (C) was present in 60.6% of the study population. Both UGT1A8∗3 (G/A) and UGT1A9∗3 (T/C) showed only a wild homozygous pattern in all screened subjects. For UGT2B7∗2, the heterozygous repeat (TC) was found with a frequency of 57.3% and the alleles (A) showed a frequency of 50.8%. In contrast, for UGT2B15∗2 (G253T), the heterozygous repeat (TG) presented 62.3% of the subjects where the most common allele (G) was with a frequency of 66.2%. In conclusion, our data indicate that Saudis harbor some important UGT mutations known to affect enzyme activity. Additional studies are therefore, warranted to assess the clinical implications of these gene polymorphisms in this ethnic group.

Dimerization of human uridine diphosphate glucuronosyltransferase allozymes 1A1 and 1A9 alters their quercetin glucuronidation activities

Uridine diphosphate glucuronosyltransferase 1A (UGT1A) is a major phase II drug-metabolism enzyme superfamily involved in the glucuronidation of endobiotics and xenobiotics in humans. Many polymorphisms in UGT1A genes are reported to inhibit or decrease UGT1A activity. In this study, two UGT1A1 allozymes, UGT1A1 wild-type and a splice mutant, as well as UGT1A9 wild-type and its three UGT1A9 allozymes, UGT1A9*2(C3Y), UGT1A9*3(M33T), and UGT1A9*5(D256N) were single- or double-expressed in a Bac-to-Bac expression system. Dimerization of UGT1A1 or UGT1A9 allozymes was observed via fluorescence resonance energy transfer (FRET) and co-immunoprecipitation analysis. SNPs of UGT1A altered the ability of protein-protein interaction, resulting in differential FRET efficiencies and donor-acceptor r distances. Dimerization changed the chemical regioselectivity, substrate-binding affinity, and enzymatic activity of UGT1A1 and UGT1A9 in glucuronidation of quercetin. These findings provide molecular insights into the consequences of homozygous and heterozygous UGT1A1 and UGT1A9 allozymes expression on quercetin glucuronidation.

Impact of obesity on accumulation of the toxic irinotecan metabolite, SN-38, in mice

AIM

Our aim is to investigate the impact of high fat diet-induced obesity on plasma concentrations of the toxic irinotecan metabolite, SN-38, in mice.

MAIN METHODS

Diet-induced obese (DIO, 60% kcal fed) and lean mice (10% kcal fed) were treated orally with a single dose of 10mg/kg irinotecan to determine pharmacokinetic (PK) parameters. Feces and livers were collected for quantification of irinotecan and its metabolites (SN-38 & SN-38G). SN-38G formation by Ugt1a1 enzyme was analyzed in liver S9 fractions. Expression of the pro-inflammatory cytokine, TNF-α was determined in liver and plasma. Hepatic β-glucuronidase and carboxylesterase enzymes (CES) were also determined.

KEY FINDINGS

AUC0-8 and Cmax of SN-38 increased by 2-fold in DIO mice compared to their lean controls. This was accompanied by a~2-fold reduction in AUC0-8 and Cmax of SN-38G in DIO mice. There were no differences in the PK parameters of irinotecan in DIO or lean mice. Conversion of SN-38 to SN-38G by Ugt1a1 enzyme was reduced by ~2-fold in liver S9 fractions in DIO mice. Furthermore, in DIO mice, β-glucuronidase activity increased by 2-fold, whereas there was no change in CES activity. TNF-α mRNA expression was 3 fold higher in DIO mice.

SIGNIFICANCE

Our study demonstrates that reduced hepatic Ugt1a activity during obesity likely contributes to reduced glucuronidation, and results in higher levels of the toxic metabolite, SN-38. Thus, irinotecan dosage should be closely monitored for effective and safe chemotherapy in obese cancer patients who are at a higher risk of developing liver toxicity.

In vitro metabolism of canagliflozin in human liver, kidney, intestine microsomes, and recombinant uridine diphosphate glucuronosyltransferases (UGT) and the effect of genetic variability of UGT enzymes on the pharmacokinetics of canagliflozin in humans

O-glucuronidation is the major metabolic elimination pathway for canagliflozin. The objective was to identify enzymes and tissues involved in the formation of 2 major glucuronidated metabolites (M7 and M5) of canagliflozin and subsequently to assess the impact of genetic variations in these uridine diphosphate glucuronosyltransferases (UGTs) on in vivo pharmacokinetics in humans. In vitro incubations with recombinant UGTs revealed involvement of UGT1A9 and UGT2B4 in the formation of M7 and M5, respectively. Although M7 and M5 were formed in liver microsomes, only M7 was formed in kidney microsomes. Participants from 7 phase 1 studies were pooled for pharmacogenomic analyses. A total of 134 participants (mean age, 41 years; men, 63%; white, 84%) were included in the analysis. In UGT1A9*3 carriers, exposure of plasma canagliflozin (Cmax,ss , 11%; AUCτ,ss , 45%) increased relative to the wild type. An increase in exposure of plasma canagliflozin (Cmax,ss , 21%; AUCt,ss , 18%) was observed in participants with UGT2B4*2 genotype compared with UGT2B4*2 noncarriers. Metabolites further delineate the role of both enzymes. The pharmacokinetic findings in participants carrying the UGT1A9*3 and UGT2B4*2 allele implicate that UGT1A9 and UGT2B4 are involved in the metabolism of canagliflozin to M7 and M5, respectively.

Genotype and allele frequencies of drug-metabolizing enzymes and drug transporter genes affecting immunosuppressants in the Spanish white population

Interpatient variability in drug response can be widely explained by genetically determined differences in metabolizing enzymes, drug transporters, and drug targets, leading to different pharmacokinetic and/or pharmacodynamic behaviors of drugs. Genetic variations affect or do not affect drug responses depending on their influence on protein activity and the relevance of such proteins in the pathway of the drug. Also, the frequency of such genetic variations differs among populations, so the clinical relevance of a specific variation is not the same in all of them. In this study, a panel of 33 single nucleotide polymorphisms in 14 different genes (ABCB1, ABCC2, ABCG2, CYP2B6, CYP2C19, CYP2C9, CYP3A4, CYP3A5, MTHFR, NOD2/CARD15, SLCO1A2, SLCO1B1, TPMT, and UGT1A9), encoding for the most relevant metabolizing enzymes and drug transporters relating to immunosuppressant agents, was analyzed to determine the genotype profile and allele frequencies in comparison with HapMap data. A total of 570 Spanish white recipients and donors of solid organ transplants were included. In 24 single nucleotide polymorphisms, statistically significant differences in allele frequency were observed. The largest differences (>100%) occurred in ABCB1 rs2229109, ABCG2 rs2231137, CYP3A5 rs776746, NOD2/CARD15 rs2066844, TPMT rs1800462, and UGT1A9 rs72551330. In conclusion, differences were recorded between the Spanish and other white populations in terms of allele frequency and genotypic distribution. Such differences may have implications in relation to dose requirements and drug-induced toxicity. These data are important for further research to help explain interindividual pharmacokinetic and pharmacodynamic variability in response to drug therapy.

The effect of UGT1A and UGT2B polymorphisms on colorectal cancer risk: haplotype associations and gene–environment interactions

UDP-glucuronosyltransferases (UGTs) play an important role in the phase II metabolism of exogenous and endogenous compounds. As colorectal cancer (CRC) etiology is thought to involve the biotransformation of dietary factors, UGT polymorphisms may affect CRC risk by altering levels of exposure. Genotyping of over 1800 Caucasian subjects was completed to identify the role of genetic variation in nine UGT1A and five UGT2B genes on CRC risk. Unconditional logistic regression and haplotype analyses were conducted to identify associations with CRC risk and potential gene-environment interactions. UGT1A haplotype analysis found that the T-G haplotype in UGT1A10 exon 1 (block 2: rs17864678, rs10929251) decreased cancer risk for the colon [proximal (OR = 0.28, 95% CI = 0.11–0.69) and for the distal colon (OR = 0.32, 95% CI = 0.12–0.91)], and that the C-T-G haplotype in the 3′ region flanking the UGT1A shared exons (block 11: rs7578153, rs10203853, rs6728940) increased CRC risk in males (OR = 2.56, 95% CI = 1.10–5.95). A haplotype in UGT2B15 containing a functional variant (rs4148269, K523T) and an intronic SNP (rs6837575) was found to affect rectal cancer risk overall (OR = 2.57, 95% CI = 1.21–5.04) and in females (OR = 3.08, 95% CI = 1.08–8.74). An interaction was found between high NSAID use and the A-G-T haplotype (block 10: rs6717546, rs1500482, rs7586006) in the UGT1A shared exons that decreased CRC risk. This suggests that UGT genetic variation alters CRC risk differently by anatomical sub-site and gender and that polymorphisms in the UGT1A shared exons may have a regulatory effect on gene expression that allows for the protective effect of NSAIDs on CRC risk.

Pharmacogenetics research on chemotherapy resistance in colorectal cancer over the last 20 years

During the past two decades the first sequencing of the human genome was performed showing its high degree of inter-individual differentiation, as a result of large international research projects (Human Genome Project, the 1000 Genomes Project International HapMap Project, and Programs for Genomic Applications NHLBI-PGA). This period was also a time of intensive development of molecular biology techniques and enormous knowledge growth in the biology of cancer. For clinical use in the treatment of patients with colorectal cancer (CRC), in addition to fluoropyrimidines, another two new cytostatic drugs were allowed: irinotecan and oxaliplatin. Intensive research into new treatment regimens and a new generation of drugs used in targeted therapy has also been conducted. The last 20 years was a time of numerous in vitro and in vivo studies on the molecular basis of drug resistance. One of the most important factors limiting the effectiveness of chemotherapy is the primary and secondary resistance of cancer cells. Understanding the genetic factors and mechanisms that contribute to the lack of or low sensitivity of tumour tissue to cytostatics is a key element in the currently developing trend of personalized medicine. Scientists hope to increase the percentage of positive treatment response in CRC patients due to practical applications of pharmacogenetics/pharmacogenomics. Over the past 20 years the clinical usability of different predictive markers has been tested among which only a few have been confirmed to have high application potential. This review is a synthetic presentation of drug resistance in the context of CRC patient chemotherapy. The multifactorial nature and volume of the issues involved do not allow the author to present a comprehensive study on this subject in one review.

Association analysis of UGT1A genotype and haplotype with SN-38 glucuronidation in human livers

AIM

7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan, is mainly eliminated hepatically through glucuronidation by UGT1A1 and UGT1A9 enzymes. This study comprehensively investigates the effects of UGT1A1 and UGT1A9 genetic polymorphism on SN-38 glucuronidation activity.

MATERIALS & METHODS

Genetic polymorphisms and combinational haplotypes of UGT1A1 and UGT1A9, SN-38 glucuronidation activities, and protein levels of UGT1A1 and UGT1A9 were determined using a set of over 45 Chinese livers.

RESULTS

UGT1A1 reduced function variants UGT1A1*6, *28, *60 and *1B exhibited additive effect. The number of UGT1A1 reduced function alleles was associated with decreased SN-38G formation rates and UGT1A protein levels. UGT1A9 I399C>T and UGT1A9*1b, which were highly linked, were associated with increased SN-38 glucuronidation activity and UGT1A protein levels. However, further analysis based on UGT1A9-1A1 haplotypes confirmed that their increased effect was partly due to their close linkage with UGT1A1 reduced function alleles.

CONCLUSION

UGT1A1 genetic polymorphisms have a more important function in human liver SN-38 glucuronidation activity than UGT1A9. Original submitted 7 November 2013; Revision submitted 30 January 2014.

Sorafenib metabolism is significantly altered in the liver tumor tissue of hepatocellular carcinoma patient

Background

Sorafenib, the drug used as first line treatment for hepatocellular carcinoma (HCC), is metabolized by cytochrome P450 (CYP) 3A4-mediated oxidation and uridine diphosphate glucuronosyl transferase (UGT) 1A9-mediated glucuronidation. Liver diseases are associated with reduced CYP and UGT activities, which can considerably affect drug metabolism, leading to drug toxicity. Thus, understanding the metabolism of therapeutic compounds in patients with liver diseases is necessary. However, the metabolism characteristic of sorafenib has not been systematically determined in HCC patients.

Methods

Sorafenib metabolism was tested in the pooled and individual tumor hepatic microsomes (THLMs) and adjacent normal hepatic microsomes (NHLMs) of HCC patients (n = 18). Commercial hepatic microsomes (CHLMs) were used as a control. In addition, CYP3A4 and UGT1A9 protein expression in different tissues were measured by Western blotting.

Results

The mean rates of oxidation and glucuronidation of sorafenib were significantly decreased in the pooled THLMs compared with those in NHLMs and CHLMs. The maximal velocity (V_max) of sorafenib oxidation and glucuronidation were approximately 25-fold and 2-fold decreased in the pooled THLMs, respectively, with unchanged K_m values. The oxidation of sorafenib in individual THLMs sample was significantly decreased (ranging from 7 to 67-fold) than that in corresponding NHLMs sample. The reduction of glucuronidation in THLMs was observed in 15 out of 18 patients’ samples. Additionally, the level of CYP3A4 and UGT1A9 expression were both notably decreased in the pooled THLMs.

Conclusions

Sorafenib metabolism was remarkably decreased in THLMs. This result was associated with the down regulation of the protein expression of CYP3A4 and UGT1A9.

The impact of genetic factors on response to anaesthetics

In recent years, exceptional progress has been observed in pharmacogenetics, i.e. investigations of inherited conditioning of the organism's response to drugs or xenobiotics. On the other hand, modern molecular biology techniques have been implemented, making it possible to perform studies determining the involvement of genetic factors in differing responses to agents employed in general anaesthesia. Unexpected and incorrect response of the organism to the administration of specific anaesthetics is most commonly associated with a genetic defect of the metabolic pathway of a given agent or its receptor. The majority of agents used in anaesthesia are metabolised in the liver by the cytochrome P450 superfamily enzymes (CYPs) and phase II drug-metabolising enzymes: glutathione S-transferases (GSTs), sulphotransferases (SULTs), UDP-glucuronosyltransferases (UGTs) and NAD(P)H:quinone oxidoreductase (NQO1). Propofol is presently widely used for gastrointestinal (GI) and several other procedures. Among genes associated with metabolism of the most commonly applied anaesthetics such as propofol and sevoflurane, the following ones can be mentioned: CYP2E1, CYP2B6, CYP2C9, GSTP1, UGT1A9, SULT1A1 and NQO1. Moreover, the basic mechanism of propofol action involves its interaction with an ionotropic receptor GABAA inhibiting transfer of nerve impulses. Molecular studies have shown that polymorphic changes in GABRG2 receptor gene turn out to be important in the propofol anaesthesia. Planning of optimal anaesthesia can be considerably assisted by the determination of genetic factors of prognostic value taking advantage of genotyping and making it possible to select anaesthetics and reduce risk of side effects as well as undesirable actions.

Molecular markers of chemotherapeutic response and toxicity in colorectal cancer

Outcomes in colorectal cancer have improved over the last 15 years; this is in part due to the optimization of 5-fluorouracil schedules and the introduction of new and effective chemotherapeutic agents, such as irinotecan and oxaliplatin. However, not all patients respond to these agents and a proportion may suffer severe side effects from particular chemotherapy drugs. These observations have resulted in a concerted research effort to identify markers of chemotherapy efficacy and toxicity. Here we review the evidence for using molecular markers to individualize chemotherapy treatment in colorectal cancer.

UGT1A9, UGT2B7, and MRP2 genotypes can predict mycophenolic acid pharmacokinetic variability in pediatric kidney transplant recipients

BACKGROUND

Mycophenolic acid (MPA) exposure in pediatric patients with kidney transplant receiving body surface area (BSA)-based dosing exhibits large variability. Several genetic variants in glucuronosyltransferases (UGTs) and of multidrug resistance-associated protein 2 (MRP2) have independently been suggested to predict MPA exposure in adult patients with varying results. Here, the combined contribution of these genetic variants to MPA pharmacokinetic variability was investigated in pediatric renal transplant recipients who were on mycophenolic mofetil maintenance therapy.

METHODS

MPA and MPA-glucuronide concentrations from 32 patients were quantified by high-performance liquid chromatography. MPA exposure (AUC) was estimated using a 4-point abbreviated sampling strategy (predose/trough and 20 minutes, 1 hour, and 3 hours after dose) using a validated pediatric Bayesian estimator. Genotyping was performed for all of the following single nucleotide polymorphisms (SNPs): UGT1A8 830G>A(*3), UGT1A9 98T>C(*3), UGT1A9-440C>T, UGT1A9-2152C>T, UGT1A9-275T>A, UGT2B7-900A>G, and MRP2-24T>C.

RESULTS

Recipients heterozygous for MRP2-24T>C who also had UGT1A9-440C>T or UGT2B7-900A>G (n = 4), and MRP2-24T>C-negative recipients having both UGT1A9-440C>T and UGT2B7-900A>G (n = 5) showed a 2.2 and 1.7 times higher dose-dependent and BSA-normalized MPA-AUC compared with carriers of no or only 1 UGT-SNP (P < 0.001 and P = 0.01, respectively) (n = 7). Dose-dependent and BSA-normalized predose MPA concentrations were 3.0 and 2.4 times higher, respectively (P < 0.001). Interindividual variability in peak concentrations could be explained by the presence of the UGT1A9-440C>T genotype (P < 0.05).

CONCLUSION

Our preliminary study demonstrates that combined UGT1A9-440C>T, UGT2B7-900A>G, and MRP2-24T>C polymorphisms can be important predictors of interindividual variability in MPA exposure in the pediatric population.

Interaction of cigarette smoking and carcinogen-metabolizing polymorphisms in the risk of colorectal polyps

The causal role of cigarette smoking in the risk of colorectal neoplasm has been suggested but not established. In a case-control study including 2060 colorectal polyp patients and 3336 polyp-free controls, we evaluated 21 functional genetic variants to construct a tobacco-carcinogen-metabolizing genetic risk score. Data regarding cigarette smoking were obtained through telephone interviews. Cigarette smoking was associated with an elevated risk of both adenomas and hyperplastic polyps. The association with smoking was stronger in participants with a high carcinogen-metabolizing risk score than those with a low risk score. Smoking 30 or more cigarettes per day was associated with a 1.7-fold elevated risk of any polyps (95% confidence interval = 1.3-2.2) among those with a low genetic risk score and 2.9-fold elevated risk (95% confidence interval = 1.8-4.8) among those with a high genetic risk score (P interaction = 0.025). A similar pattern of interaction was observed in analyses conducted separately for those with adenomas only (P interaction = 0.039) and hyperplastic polyps only (P interaction = 0.024). Interaction between carcinogen-metabolizing genetic risk and cigarette smoking was found in relation to high-risk adenomas (P interaction = 0.010) but not low-risk adenomas (P interaction = 0.791). No apparent interaction was found for duration of smoking. This study shows that the association between cigarette smoking and colorectal polyp risk is modified by tobacco-carcinogen-metabolizing polymorphisms, providing support for a causal role of cigarette smoking in the etiology of colorectal tumors.

Substrate selectivity of human intestinal UDP-glucuronosyltransferases (UGTs): in silico and in vitro insights

The current drug development process aims to produce safe, effective drugs within a reasonable time and at a reasonable cost. Phase II metabolism (glucuronidation) can affect drug action and pharmacokinetics to a considerable extent and so its studies and prediction at initial stages of drug development are very imperative. Extensive glucuronidation is an obstacle to oral bioavailability because the first-pass glucuronidation [or premature clearance by UDP-glucuronosyltransferases (UGTs)] of orally administered agents frequently results in poor oral bioavailability and lack of efficacy. Modeling of new chemical entities/drugs for UGTs and their kinetic data can be useful in understanding the binding patterns to be used in the design of better molecules. This review concentrates on first-pass glucuronidation by intestinal UGTs, including their topology, expression profile, and pharmacogenomics. In addition, recent advances are discussed with respect to substrate selectivity at the binding pocket, structural requirements, and mechanism of enzyme actions.

Population pharmacokinetics of unbound mycophenolic acid in adult allogeneic haematopoietic cell transplantation: effect of pharmacogenetic factors

AIM

To evaluate pharmacogenetic factors as contributors to the variability of unbound mycophenolic acid (MPA) exposure in adult allogeneic haematopoietic cell transplantation (alloHCT) recipients.

METHODS

A population-based pharmacokinetic (PK) model of unbound MPA was developed using non-linear mixed-effects modelling (nonmem). Previously collected intensive unbound MPA PK data from 132 adult alloHCT recipients after oral and intravenous dosing of the prodrug mycophenolate mofetil (MMF) were used. In addition to clinical covariates, genetic polymorphisms in UGT1A8, UGT1A9, UGT2B7 and MRP2 were evaluated for their impact on unbound MPA PK.

RESULTS

Unbound MPA concentration-time data were well described by a two compartment model with first order absorption and linear elimination. For the typical patient (52 years of age, creatinine clearance 86 ml min(-1)), the median estimated values [coefficient of variation, %, (CV)] of systemic clearance, intercompartmental clearance, central and peripheral volumes of MPA were 1610 l h(-1) (37.4%), 541 l h(-1) (75.6%), 1230 l (37.5%), and 6140 l (120%), respectively. After oral dosing, bioavailability was low (0.56) and highly variable (CV 46%). No genetic polymorphisms tested significantly explained the variability among individuals. Creatinine clearance was a small but significant predictor of unbound MPA CL. No other clinical covariates impacted unbound MPA PK.

CONCLUSIONS

In adult alloHCT recipients, variability in unbound MPA AUC was large and remained largely unexplained even with the inclusion of pharmacogenetic information. Targeting unbound MPA AUC in a patient will require therapeutic drug monitoring.

A pharmacokinetic/pharmacodynamic model of tumor lysis syndrome in chronic lymphocytic leukemia patients treated with flavopiridol

PURPOSE

Flavopiridol, the first clinically evaluated cyclin-dependent kinase inhibitor, shows activity in patients with refractory chronic lymphocytic leukemia, but prevalent and unpredictable tumor lysis syndrome (TLS) presents a major barrier to its broad clinical use. The purpose of this study was to investigate the relationships between pretreatment risk factors, drug pharmacokinetics, and TLS.

EXPERIMENTAL DESIGN

A population pharmacokinetic/pharmacodynamic model linking drug exposure and TLS was developed. Plasma data of flavopiridol and its glucuronide metabolite (flavo-G) were obtained from 111 patients treated in early-phase trials with frequent sampling following initial and/or escalated doses. TLS grading was modeled with logistic regression as a pharmacodynamic endpoint. Demographics, baseline disease status, and blood chemistry variables were evaluated as covariates.

RESULTS

Gender was the most significant pharmacokinetic covariate, with females displaying higher flavo-G exposure than males. Glucuronide metabolite exposure was predictive of TLS occurrence, and bulky lymphadenopathy was identified as a significant covariate on TLS probability. The estimated probability of TLS occurrence in patients with baseline bulky lymphadenopathy less than 10 cm or 10 cm or more during the first 2 treatments was 0.111 (SE% 13.0%) and 0.265 (SE% 17.9%), respectively, when flavo-G area under the plasma concentration versus time curve was at its median value in whole-patient group.

CONCLUSIONS

This is the first population pharmacokinetic/pharmacodynamic model of TLS. Further work is needed to explore potential mechanisms and to determine whether the associations between TLS, gender, and glucuronide metabolites are relevant in patients with chronic lymphocytic leukemia treated with other cyclin-dependent kinase inhibitors.

Using gene-environment interaction analyses to clarify the role of well-done meat and heterocyclic amine exposure in the etiology of colorectal polyps

BACKGROUND

The role of well-done meat intake and meat-derived mutagen heterocyclic amine (HCA) exposure in the risk of colorectal neoplasm has been suggested but not yet established.

OBJECTIVE

With the use of gene-environment interaction analyses, we sought to clarify the association of HCA exposure with colorectal polyp risk.

DESIGN

In a case-control study including 2057 colorectal polyp patients and 3329 controls, we evaluated 16 functional genetic variants to construct an HCA-metabolizing score. To derive dietary HCA-exposure amount, data were collected regarding dietary intake of meat by cooking method and degree of doneness.

RESULTS

A 2-fold elevated risk associated with high red meat intake was found for colorectal polyps or adenomas in subjects with a high HCA-metabolizing risk score, whereas the risk was 1.3- to 1.4-fold among those with a low risk score (P-interaction ≤ 0.05). The interaction was stronger for the risk of advanced or multiple adenomas, in which an OR of 2.8 (95% CI: 1.8, 4.6) was observed for those with both a high HCA-risk score and high red meat intake (P-interaction = 0.01). No statistically significant interaction was found in analyses that used specific HCA exposure derived from dietary data.

CONCLUSION

High red meat intake is associated with an elevated risk of colorectal polyps, and this association may be synergistically modified by genetic factors involved in HCA metabolism.