Metabolism Of Many Drugs Research Articles

Relationship between mRNA expression levels of CYP3A4, CYP3A5 and SXR in peripheral mononuclear blood cells and aging in young kidney transplant recipients under tacrolimus treatment.

The activity of several key enzymes involved in the metabolism of many drugs is subject to change closely related to the age of patients. This possibility must also be considered in the case of tacrolimus, the most important calcineurins inhibitor, which is widely used in pediatric kidney transplantation. As well as in the liver and intestine, some of the enzymes involved in the metabolism of tacrolimus were also isolated in the peripheral blood mononuclear cells (PBMCs), where also appear to play an important regulatory action. Therefore, the influence of some external factors on the expression of specific mRNA can be determined noninvasively. The correlation between the levels of mRNA specific for key enzymes SXR, CYP3A and ABCB1 involved in the metabolism of tacrolimus was evaluated in PBMCs obtained from a selected population of 29 young kidney transplant recipients. A possible correlation between the expression of these specific mRNAs and tacrolimus pharmacokinetics was also investigated. The patients' age and their blood concentrations of SXR mRNA were directly correlated with the expression of CYP3A4, CYP3A5 mRNAs, but not of ABCB1 mRNA in the PBMCs. tacrolimus-normalized daily dose was strongly correlated with patient's age and multivariable regression indicates the CYP3A4-specific mRNA as the sole independent variable influencing tacrolimus concentration-to-dose ratio. Aging and SXR mRNA significantly affect the expression of CYP3A4- and CYP3A5-specific mRNA as measured by their concentration in PBMC.

SNP genetic polymorphisms of MDR-1, CYP1A2 and CYPB11 genes in four canine breeds upon toxicological evaluation.

The fields of pharmacogenetics and pharmacogenomics have become increasingly promising regarding the clinical application of genetic data to aid in prevention of adverse reactions. Specific screening tests can predict which animals express modified proteins or genetic sequences responsible for adverse effects associated with a drug. Among the genetic variations that have been investigated in dogs, the multidrug resistance gene (MDR) is the best studied. However, other genes such as CYP1A2 and CYP2B11 control the protein syntheses involved in the metabolism of many drugs. In the present study, the MDR-1, CYP1A2 and CYP2B11 genes were examined to identify SNP polymorphisms associated with these genes in the following four canine breeds: Uruguayan Cimarron, Border Collie, Labrador Retriever and German Shepherd. The results revealed that several SNPs of the CYP1A2 and CYP2B11 genes are potential targets for drug sensitivity investigations.

Prevalence of CYP2B6 polymorphisms in Argentinians: the role of genetic testing.

CYP2B6 is a highly polymorphic isoenzyme involved in the metabolism of many drugs including cyclophosphamide, bupropion, and efavirenz. A single nucleotide polymorphism (SNP) in CYP2B6 (516G>T) resulted in decreased expression and function associated with the CYP2B6*6 haplotype. Among the clinical implications of this phenotype, decreased activation of cyclophosphamide and increased plasma levels of efavirenz associated with increased central nervous system toxicity have been reported. The frequency of the CYP2B6 (516G>T) SNP has been studied in several different populations, but there is no data regarding distribution among Argentinians. In this study, 102 DNA samples from healthy volunteers were analyzed using a polymerase chain reaction-restriction fragment length polymorphism reaction specific for the CYP2B6 (516G>T) SNP. Our results showed a prevalence of 71.08% for the G allele and 28.92% for the T allele. This was distributed as 52.9% for the GG genotype (reduced dosage required), 36.6% for the GT genotype (normal dosage range), and 10.8% for the TT genotype (high drug toxicity). There was no preferential gender distribution observed. The relatively high prevalence of the TT genotype in our population supports the clinical use of genotyping as an additional tool in personalized medicine.

Evaluation of the Pharmacokinetic Interaction Between Ticagrelor and Venlafaxine, a Cytochrome P-450 2D6 Substrate, in Healthy Subjects

PurposeTicagrelor is a reversibly binding P2Y12 receptor antagonist used clinically for the prevention of atherothrombotic events in patients with acute coronary syndromes (ACS). Ticagrelor has been shown in vitro to be a weak inhibitor of cytochrome P-450 (CYP) 2D6, a clinically important enzyme for the metabolism of many drugs. This study assessed the effects of coadministration of ticagrelor on the pharmacokinetics of the CYP2D6 substrate venlafaxine. The impact of venlafaxine on ticagrelor pharmacokinetic parameters was also investigated. MethodsHealthy subjects (N = 22) received a single 180-mg oral dose of ticagrelor on days 1 and 9 and oral doses of venlafaxine on day 4 (37.5 mg BID) and days 5 through 10 (75 mg BID). Plasma concentrations of ticagrelor, venlafaxine, and their metabolites (AR-C124910XX and O-desmethylvenlafaxine [ODV], respectively) were quantified for pharmacokinetic analyses. Safety and tolerability were assessed throughout the study. FindingsOverall, 19 of 25 subjects were male; 14 were white, 10 were black, and 1 was Asian. Mean (SD) age was 26 (6) years, and mean (SD) body mass index was 24.3 (2.9) kg/m2. Ticagrelor had no effect on overall exposure to venlafaxine, as assessed by the AUC0–τ (geometric least squares mean ratio, 110.32 ng · h/mL [90% CI, 106.27–114.52]). Venlafaxine Cmax was increased by 22% in the presence of ticagrelor (121.83 ng/mL [90% CI, 111.80–132.75]). ODV AUC0–τ and Cmax were unaffected by coadministration with ticagrelor (98.71 ng · h/mL [90% CI, 96.61–100.85] and 101.44 ng/mL [90% CI, 98.34–104.65], respectively). Venlafaxine had no effect on the Cmax or AUC0–∞ of ticagrelor (96.54 ng/mL [90% CI, 85.03–109.61] and 89.67 ng · h/mL [90% CI, 82.78–97.14]) or AR-C124910XX (106.39 ng/mL [90% CI, 96.10–117.78] and 106.32 ng · h/mL [90% CI, 97.28–116.21], respectively). Ticagrelor and venlafaxine were well tolerated whether given alone or in combination. ImplicationsTicagrelor had no clinically relevant effect on the plasma levels of venlafaxine and its CYP2D6-generated active metabolite, ODV. On the basis of these data, ticagrelor is not expected to affect CYP2D6-mediated drug metabolism to a clinically relevant extent. Venlafaxine had no effect on the pharmacokinetics of ticagrelor.

Genetic polymorphisms in warfarin and tacrolimus-related genes VKORC1, CYP2C9 and CYP3A5 in the Greek-Cypriot population

BackgroundTwo variants in the gene encoding the cytochrome P450 2C9 enzyme (CYP2C9) are considered the most significant genetic risk factors associated with bleeding after warfarin prescription. A variant in the vitamin K epoxide reductase (VKORC1) has been also associated by several studies with warfarin response. Another variant in the P450 3A5 enzyme (CYP3A5) gene is known to affect the metabolism of many drugs, including tacrolimus.FindingsWe conducted a population genetic study in 148 unrelated healthy Greek-Cypriot volunteers (through PCR-RFLP assays), in order to determine the frequencies of the above pharmacogenetics variants and to compare allele frequencies with those in other major ethnic groups. The allele frequencies of CYP2C9*2, CYP2C9*3 and CYP3A5*3 were found to be 0.162, 0.112 and 0.943 respectively, whereas VKORC1 - 1639A was 0.534. The latter frequency differs significantly when compared with Caucasians, Asians and Africans (p < 0.001) and is still significant when compared with the geographically and culturally closely related to Greek-Cypriots, Hellenes of Greece (p = 0.01). Interestingly ~18% of our population are carriers of four or three risk alleles regarding warfarin sensitivity, therefore they have a high predisposition for bleeding after taking high or even normal warfarin doses.ConclusionsOur data show no significant difference in the frequency of CYP2C9 and CYP3A5 allelic variants when compared to the Caucasian population, but differ significantly when compared with Africans and Asians (p < 0.001). Also, the frequency of variant VKORC1 - 1639A differs between Greek-Cypriots and every other population we compared. Finally, about 1/5 Greek-Cypriots carry three or four risk alleles and ~50% of them carry at least two independent risk alleles regarding warfarin sensitivity, a potentially high risk for over-anticoagulation.

Regulatory polymorphisms in CYP2C19 affecting hepatic expression

Cytochrome P450 2C19 is responsible for the metabolism of many drugs, including the activation of clopidogrel. The allele CYP2C19*17 is associated with ultra-rapid metabolizer phenotypes by increasing gene transcription. This study tests to what extent CYP2C19*17 enhances CYP2C19 expression in human liver and whether additional regulatory variants contribute to variation in CYP2C19 expression. CYP2C19 mRNA was measured with quantitative real-time PCR (qRT-PCR), enzyme activity as metabolic velocity with S-mephenytoin as the substrate and allelic mRNA expression ratio with SNaPshot in human livers. CYP2C19 transcribed exons and a 4kb promoter region were sequenced using IonTorrent PGM or Sanger sequencing and screened for polymorphisms associated with total hepatic CYP2C19 mRNA, enzyme activity and allelic mRNA ratios. Livers heterozygote and homozygous for CYP2C19*17 had mRNA levels 1.8-fold (p=0.028) and 2.9-fold (p=0.006), respectively, above homozygous reference allele livers. CYP2C19*17 heterozygotes were also associated with increased allelic mRNA expression (allelic ratio ~1.8-fold, SD±0.6, p<0.005), whereas CYP2C19 enzyme activity was elevated 2.3-fold, with borderline significance (p=0.06) in CYP2C19*17 carriers. One liver sample of African ancestry displayed a 2-fold allelic expression ratio, and another sample, a ~12-fold increase in metabolic velocity. Neither case was accounted for by *17, which indicates the presence of additional regulatory variants. Our findings confirm *17 as a regulatory polymorphism enhancing hepatic CYP2C19 expression 2-fold with potential to compensate for the loss of function allele CYP2C19*2. Additional regulatory factors may also enhance CYP2C19 expression in African American populations.

CYP3A4*22 : Promising Newly Identified CYP3A4 Variant Allele for Personalizing Pharmacotherapy

Many studies have attempted to explain the interindividual variability observed in drug metabolism by assessing the impact of SNPs in genes implicated in drug absorption, distribution, metabolism and excretion pathways. Particular attention has been paid to the CYP450s. CYP3A4 is the main CYP isoform in human liver and intestine and is involved in the metabolism of many drugs. Its activity, however, is characterized by widespread variation in the general population, which is thought to have a genetic basis. A new CYP3A4 allele (CYP3A4*22; rs35599367 C>T in intron 6) with a frequency of 5-7% in the Caucasian population was recently discovered through its association with low hepatic CYP3A4 expression and CYP3A4 activity, and showing effects on statin, tacrolimus and cyclosporine metabolism. This review will summarize the current literature on phenotypes linked to this new promising CYP3A4 genetic marker SNP and discusses the potential clinical relevance.

Understanding of Molecular Pain Medicine: Genetic Basis of Variation in Pain Sensation and Analgesia Response

Understanding of Molecular Pain Medicine: Genetic Basis of Variation in Pain Sensation and Analgesia Response

Drug Metabolites Formed in Vivo Promote the Clearance of Human Platelets by Metabolite-Dependent Antibodies in NOD/SCID Mice

AbstractAbstract 1083Drug induced immune thrombocytopenia (DITP) is a relatively common and often serious complication of treatment with many drugs. It can be extremely helpful clinically to identify the responsible agent, especially in patients taking multiple drugs. It is sometimes possible to demonstrate a drug-dependent antibody (DDAb) that binds to platelets only when drug is present but results are often negative even in patients with a history that strongly favors DITP. An important reason for this is that a drug metabolite rather than the parent drug can be the sensitizing agent. Because drugs often have many metabolites, most of which are not readily available, identification of the metabolite-specific, DDAbs can be very difficult.Animal models for studying immune clearance of human cells have not been available because of naturally occurring xenoantibodies. However, recent studies have shown that destruction of human platelets by human antibodies can be studied in the NOD/SCID mouse, which lacks xenoantibodies (Boylan et al 2009). Metabolism of many drugs is similar in mice and humans. We have shown that mice injected with acetaminophen and naproxen produce metabolites that promote in vivo destruction of human platelets by DDAbs specific for metabolites of these drugs (Bougie et al 2010). These findings suggested that the NOD/SCID mouse might be a useful screening tool to identify putative DDAbs specific for metabolites of other drugs in patients suspected of DITP.To detect metabolite-specific antibodies, mice are transfused with human platelets suspended in test serum. After collecting a baseline blood sample to define the relative number of human platelets in each mouse, the implicated drug is injected (intraperitoneal). Drug metabolites made by the mouse diffuse into the circulation and shorten the survival of human platelets if a metabolite-specific, platelet-reactive antibody is present in the test serum. For a result to be considered “positive” for DDAbs, human platelet survival should be unaltered in mice given test serum alone and normal serum plus drug and should be significantly shortened in mice given test serum plus drug (Figure). [Display omitted] Findings made to date with 94 archived serum samples from DITP suspects exposed to 5 widely used medications are summarized in Table 1. No platelet-reactive antibodies were detected in vitro using unmodified drug. However, 13 patient samples caused accelerated clearance of human platelets when mice were injected with the implicated drug (2 furosemide, 6 clopidogrel, 2 pantoprazole, 3 ibuprofen). [Display omitted] These findings suggest that DITP resulting from sensitization to drug metabolites may be much more common than has been thought and indicate that the NOD/SCID mouse model provides a highly efficient tool to screen candidate sera for metabolite-specific, platelet-reactive antibodies. Disclosures:No relevant conflicts of interest to declare.

A rapid multiplex PCR assay that can reliably discriminate the cytochrome P450 2D6 whole-gene deletion allele from 2D6*10 alleles

BackgroundGenetic polymorphisms of the human CYP2D6 gene can affect the metabolism of many drugs in clinical use. As a first step toward identifying poor drug metabolizers in the clinical setting, we developed a new multiplex PCR-based genotyping method to detect CYP2D6 whole-gene deletion. MethodsWe validated the new method by analyzing 500 genomic DNA samples from a Japanese population with the conventional long-PCR method and the new multiplex PCR method. The long-PCR system used a forward primer for CYP2D7P (a pseudogene closely related to CYP2D6) and a common reverse primer for the untranslated region. The multiplex PCR system used the same two primers as the long PCR and an additional forward primer for CYP2D6. ResultsWith the long-PCR system, DNA samples identified as containing CYP2D6*5 (whole-gene deletion) formed 3.5-kb PCR products. With the multiplex PCR system, many samples yielded 4.7-kb PCR products (implying the existence of normal CYP2D6) and some DNA samples yielded 6.2-kb PCR products (probably indicating CYP2D6*10D). The long-PCR assay detected 64 CYP2D6*5 alleles among 1000 Japanese alleles; however, the new multiplex PCR system identified 5 of these 64 alleles as CYP2D6*10D. ConclusionsThe new multiplex PCR method is useful for detecting CYP2D6*5. This system could reliably discriminate CYP2D6*5 from homologous pseudogene CYP2D7P and functional CYP2D6*10D.

Molecular design of O-phosphorylated oximes—Selective inhibitors of butyrylcholinesterase

Anticholinesterase compounds, including organophosphorus inhibitors (OPIs), are used to treat glaucoma, schistosomiasis, Alzheimer’s disease, myasthenia gravis, and other diseases. These compounds arealso widely used in agriculture as insecticides and inindustry [1]. The varied use of such compounds isbased on their common mechanism of action, which isassociated with the inhibition of acetylcholinesterase(AChE, EC 3.1.1.7), the biological role of which is thehydrolysis of the key neurotransmitter acetylcholine.In the treatment of Alzheimer’s disease (AD) underconditions of deficiency of central acetylcholine andreduced cholinergic transmission, the inhibition ofAChE in the brain provides cognition enhancement,which, however, may be accompanied by manifestations of acute toxicity and other side effects associatedwith inhibition of peripheral AChE [2].Many OPIs interact in the body with otheresterases. These interactions may lead to differentpharmacological and toxicological effects. For example, the neuropathy target esterase (NTE, EC 3.1.1.5),which normally catalyzes deacylation of phosphatidylcholine of cell membranes [3], is an “antitarget”responsible for the development of organophosphateinduced delayed neurotoxicity (OPIDN). This phenomenon is due to the fact that its inhibition and subsequent rapid “aging” initiates distal degeneration ofsensory and motor axons in the peripheral nervous system and/or spinal cord, causing paralysis [1]. This disease is characterized by a latent period of up to severalweeks; specific drugs for its treatment are still notknown. Thus, the possibility of initiation of delayedneurotoxicity is an important risk factor in industrialand medical applications of OPIs.Other serine esterases, such as butyrylcholinesterase (BChE, EC 3.1.1.8) and carboxylesterase (CaE,EC 3.1.1.1), function as stoichiometric scavengers,providing protection against the toxic effect of anticholinesterase agents [4]. BChE and CaE of bloodplasma and liver are also in volved in the metabolism ofmany drugs containing ester groups, significantlyaffecting their pharmacokinetics.Recent studies have shown that BChE is alsoinvolved in cholinergic transmission and is able tocompensate for some functions of AChE, optimizingthe cholinergic neurotransmission by hydrolysis ofacetylcholine under conditions when AChE is, forsome reason, unable to perform this function(for example, in severe forms of AD, when the activityof AChE is significantly reduced). It was found thatselective inhibitors of BChE increase the level of acetylcholine in the brain and provide cognition enhancement in rodents, having no side effects of classicalinhibitors of AChE. In this regard, the development ofselective inhibitors of BChE is a new strategy toimprove the quality of life of patients with AD, especially in severe cases, when the activity of AChE in thebrain is depleted along with a decrease in the level ofacetylcholine, whereas the activity of BChE isincreased [2].Within the considered scheme of interaction withthe four serine esterases, the esterase profile of aninhibitor can be described by four activity values(the inhibitory activity with respect to AChE

CYP2D6 gene variants in urban/admixed and Amerindian populations of Venezuela: Pharmacogenetics and anthropological implications

Background: Differences in genes encoding enzymes involved in the biotransformation of a large number of compounds, such as CYP2D6, are related to inter-individual and inter-ethnic variability in the metabolism of many drugs, which have also been linked to susceptibility to cancer and other health outcomes. Therefore, populations are likely to benefit from inclusion in pharmacogenetic research studies.Aim: To determine the frequency of functionally important allele variants of CYP2D6 gene in a sample of an Urban/admixed and five Amerindian Venezuelan populations.Subjects and methods: DNA of 328 unrelated volunteers was analysed for the presence of CYP2D6 *2, *3, *4, *5, *6 and *10 variants.Results: The frequency in the Urban/admixed population for *2, *3, *4, *5, *6 and *10 alleles was 37.9%, 0%, 13.4%, 2.0%, 1.2% and 4.0%, respectively. In the Bari population, the prevalence of *4 allele associated with decreased enzyme activity was observed in 42.5%, whereas the poor metabolizer genotype *4/*4 was found in 25%. In the Panare, Pemon, Warao and Wayuu populations the *4 allele was found in 5.4%, 2.5%, 1.7% and 4.2%, respectively. The *10 allele frequency found in Amerindians (0.0–6.3%) was lower than reported for Asians.Conclusion: The results are consistent with the known genetic admixture origin of most Venezuela populations. Nevertheless, the observed significant differences among Amerindians highlight the need for pharmacogenetic studies taking into account biogeographical and anthropological considerations.

Novel CYP3A4 intron 6 single nucleotide polymorphism is associated with simvastatin-mediated cholesterol reduction in The Rotterdam Study

CYP3A4 is involved in the oxidative metabolism of many drugs and xenobiotics including the HMG-CoA reductase inhibitor simvastatin. The objective of this study was to investigate whether a new CYP3A4 functional single nucleotide polymorphism (SNP) in intron 6 (CYP3A4*22) modifies the effect of simvastatin on total cholesterol (TOTc) or LDL cholesterol (LDLc) reduction in a population-based cohort study. In a total of 80 incident simvastatin users, the association between the CYP3A4 intron 6 C>T SNP (rs35599367) and reduction in cholesterol levels was analyzed using linear regression analysis and adjusting for potential confounding factors. The CYP3A4*22 allele was associated with a trend towards a stronger simvastatin lipid-lowering response, as reflected by the greater reduction in both TOTc and LDLc levels when compared with homozygous wild type. We observed that the CYP3A4*22 allele carriers had an increased reduction in TOTc and LDLc: -0.25 mmol/l (95% confidence interval [CI(95%)]=[-0.52; 0.01], P=0.058) and -0.29 mmol/l (CI(95%)=[-0.58; 0.01], P=0.054) when compared with homozygous CC. When we adjusted the model for potential confounding factors, the corresponding reduction in TOTc was -0.31 mmol/l (CI(95%)=[-0.59;-0.04], P=0.028) and for LDLc -0.34 mmol/l (CI(95%)=[-0.66; -0.02], P=0.034) greater for CYP3A4*22 allele carriers when compared with homozygotes wild type. The CYP3A4*22 intron 6 SNP T-variant allele was associated with reduced CYP3A4 activity, resulting in a better lipid lowering response to simvastatin, when data were adjusted for confounding factors. This observation is a step towards the clarification of the reasons of interindividual variability in statins response and may potentially lead to improved tailoring of simvastatin therapy.

Ontogenesis of phase I hepatic drug metabolic enzymes in sheep

Cytochrome P450 (CYP) enzymes are important for the metabolism of many drugs. While there is information on their identity and ontogeny in humans and rodents, similar data in sheep are lacking. In the present study, cDNA sequences of several CYP enzymes (CYP2A6, CYP2C19, CYP2D6) were cloned by rapid amplification of cDNA ends. In adult, newborn and fetal sheep the mRNA and protein levels of these CYPs and the regulatory factor, hepatic nuclear factor 4α (HNF4α) were determined in liver samples using real-time PCR and western blotting. The effect of antenatal glucocorticoid on these enzymes was also studied by i.v. infusion of cortisol (0.45 mgh(-1); 80 h) to another group of fetuses. The mRNA and protein levels of the CYPs and HNF4α were low or absent in the fetus, followed by increasing levels in the newborn and adult. Fetal cortisol administration significantly increased the mRNA and protein levels of CYP2D6. Moreover, the correlation observed between the CYP and HNF4α mRNA levels suggests a possible regulatory role for this transcription factor. The findings suggest that fetal and newborn lambs have a low ability to metabolise drugs that are substrates of these enzymes, and that this ability increases with advancing postnatal age, similar to the situation in humans.

Effect of a New Functional CYP3A4 Polymorphism on Calcineurin Inhibitors‘ Dose Requirements and Trough Blood Levels in Stable Renal Transplant Patients

CYP3A4 is involved in the oxidative metabolism of many drugs and xenobiotics including the immunosuppressants tacrolimus (Tac) and cyclosporine (CsA). The objective of the study was to assess the potential influence of a new functional SNP in CYP3A4 on the pharmacokinetic parameters assessed by dose requirements and trough blood levels of both calcineurin inhibitors (CNI) in stable renal transplant patients. A total of 99 stable renal transplant patients receiving either Tac (n = 49) or CsA (n = 50) were genotyped for the CYP3A4 intron 6 C>T (rs35599367) and CYP3A5*3 SNPs. Trough blood levels ([Tac](0) or [CsA](0) in ng/ml), dose-adjusted [Tac](0) or [CsA](0) (ng/ml per mg/kg bodyweight) as well as doses (mg/kg bodyweight) required to achieve target concentrations were compared among patients according to allelic status for CYP3A4 and CYP3A5. Dose-adjusted concentrations were 2.0- and 1.6-fold higher in T-variant allele carriers for the CYP3A4 intron 6 C>T SNP compared with homozygous CC for Tac and CsA, respectively. When CYP3A4/CYP3A5 genotypes were combined, the difference was even more striking as the so-defined CYP3A poor metabolizer group presented dose-adjusted concentration 1.6- and 4.1-fold higher for Tac, and 1.5- and 2.2-fold higher for CsA than the intermediate metabolizer and extensive metabolizer groups, respectively. Multiple linear regression analysis revealed that, taken together, both CYP3A4 intron 6 and CYP3A5*3 SNPs explained more than 60 and 20% of the variability observed in dose-adjusted [Tac](0) and [CsA](0), respectively. The CYP3A4 intron 6 C>T polymorphism is associated with altered Tac and CsA metabolism. CYP3A4 intron 6 C>T along with CYP3A5*3 (especially for Tac) pharmacogenetic testing performed just before transplantation may help identifying patients at risk of CNI overexposure and contribute to limit CNI-related nephrotoxicity by refining the starting dose according to their genotype. Original submitted 5 May 2011; Revision submitted 29 June 2011.

Cytochrome P450 2D6 Phenotyping in an Elderly Population With Dementia and Response to Galantamine in Dementia: A Pilot Study

Background The cytochrome P450 (CYP) 2D6 enzyme is involved in the metabolism of many drugs used by the elderly population. Variations in its activity can lead to altered drug response. However, few studies on the activity of this enzyme system have enrolled the elderly population. Objective The goal of this pilot study was to assess the feasibility of in vivo phenotyping of CYP2D6 in an elderly population with dementia and to determine if part of the variability in response to treatment with galantamine is attributable to CYP2D6 phenotype. Methods Patients with dementia attending geriatric clinics and receiving galantamine treatment for at least 6 months were enrolled in this case-control study. CYP2D6 phenotype was determined by analysis of the urinary concentrations of the probe drug dextromethorphan and its primary metabolite dextrorphan after ingestion of 30 mg of dextromethorphan. Patients were classified as robust responders to galantamine if their cognitive testing, as measured by using scores on the Mini–Mental State Examination or Alzheimer's Disease Assessment Scale–Cognitive subscale, had not changed or had improved after 6 months of treatment. Results Forty-three patients (23 men, 20 women; mean age, 78.4 years; 98% white) underwent phenotyping. The mean number of concomitantly prescribed medications was 5.7, and 16 patients (37%) were receiving other CYP2D6 substrate or inhibitor drugs. The distribution of CYP2D6 phenotype was similar to that seen in other white populations. There was no correlation between the phenotypic metabolic ratio and age, the number of routinely taken medications, whether patients were receiving other prescribed substrate or inhibitor drugs of CYP2D6 ( P = 0.63), or whether they were a robust responder ( P = 0.47). Conclusions Urinary assays of CYP2D6 phenotype are technically feasible in older individuals with dementia who are taking multiple medications, and may be a useful clinical tool in this population. However, the study was unable to make inferences about an association between CYP2D6 phenotype and galantamine responsiveness.

Fluoxetine Potentiates Pentobarbital Lethality and Sedation in the Rat

The 5-hydroxytryptamine-transport inhibitor fluoxetine interferes with the hepatic metabolism of many drugs and can potentiate the effects of anaesthetics. Because of the significance of this behaviour and because previous reports are inconsistent, the effect has been further investigated. Rats given fluoxetine (15 mg kg−1, i.p.) for six days did not regain consciousness after sodium pentobarbital anaesthesia (65 mg kg−1, i.p.). Serum pentobarbital levels were increased by 50% by fluoxetine (10 mg kg−1, 24 and 16 h before pentobarbital, 30 mg kg−1), and fluoxetine (0–10 mg kg−1) dose-dependently (ED50 = 2·9±0·5 mg kg−1) increased nocturnal behavioural sedation induced by pentobarbital (50 mg kg−1, 4 h later). Gastrointestinal abnormalities and weight loss also were found after repeated fluoxetine administration, particularly intraperitoneally. These observations indicate that fluoxetine can lethally potentiate pentobarbital anaesthesia, and suggest additional adverse effects of repeated injections of high doses.

Ontogenesis of UDP-glucuronosyltransferase enzymes in sheep

UDP glucuronosyltransferases (UGTs) are important for the metabolism of many drugs. To understand the ontogeny of these enzymes in sheep ( Ovis aries), knowledge of their expression levels at different developmental stages is important. cDNA sequences of six UGTs (UGT1A1, UGT1A3, UGT1A4, UGT1A6 and UGT1A9) were cloned in sheep liver by rapid amplification of cDNA ends. The mRNA and protein levels of the enzymes in sheep liver (adult n = 4; newborn n = 3; fetus n = 3) were determined using PCR and Western blots. mRNA levels in adult were very high followed by newborn and then fetus. However, no protein bands were detected on the Western blots of sheep hepatic microsomal proteins using several different antibodies against human UGTs. The effect of antenatal glucocorticoid administration was also studied by infusion of cortisol (0.45 mg/h; 80 h) to another group of fetuses (n = 5). This did not result in any significant changes in fetal mRNA levels. However, the correlation observed between the UGT enzymes and hepatocyte nuclear factor 4α (HNF4α) suggests a possible regulatory role for this transcription factor in sheep. We postulate that fetal and newborn lambs may have a reduced ability to metabolize drugs that are substrates of these enzymes.

DNA Alkylation with N-Methylquinolinium Quinone Methide to N2-dG Adducts Resulting in Extensive Stops in Primer Extension with DNA Polymerases and Subsequent Suppression of GFP Expression in A549 Cells

Quinone methides (QMs) are involved in the metabolism of many drugs and carcinogens as reactive intermediates to form covalent nucleobase adducts in DNA that associate with high mutagenicity. Recently, a plethora of synthetic QM DNA alkylating agents have been developed to form various nucleobase adducts as potential antitumor agents. However, the mutagenic potential of these synthetic QM alkylating agents has not been fully investigated. In this report, N-methylquinolinium QM was developed as a synthetic model to study biological consequences of the formation of nucleobase adducts in a DNA target. N-Methylquinolinium QM was generated in situ via an elimination process from a bis-quaternary ammonium precursor that was synthesized from a quinoline derivative. Alkylation with N-methylquinolinium QM on a DNA target produced mostly a stable N(2)-dG adduct as revealed by gel electrophoresis and DNA digestion assays and confirmed by mass and NMR analyses. The formation of N(2)-dG adducts of a DNA target was found to cause extensive stops in the primer extension with high fidelity DNA polymerase T7 and even low fidelity error prone Dpo4. The direct biological impact of a prealkylated green fluorescence protein plasmid with N-methylquinolinium QM was demonstrated as significant suppression of protein expression in A549 cells. Overall, our results suggested that nucleobase-QM adducts could potentially block nucleobase mismatch/translesion in the error-prone process to reduce the mutagenic potential if designed carefully.

Frequency of CYP2C9 variant alleles, including CYP2C9*13 in a Korean population and effect on glimepiride pharmacokinetics

Cytochrome P450 (CYP) 2C9 is a clinically important enzyme involved in the metabolism of many drugs commonly used in humans. Of several allelic variants known to affect the catalytic activity of the CYP2C9 enzyme, the frequencies of the CYP2C9*3 and CYP2C9*13 alleles in the Korean population have been reported as 1·1% and 0·6%, respectively. Our objective was to re-evaluate the frequencies of CYP2C9 allelic variants in the Korean population, including the CYP2C9*13 allele by pyrosequencing, and to investigate the pharmacokinetics of glimepiride in relation to CYP2C9 genotypes, including CYP2C9*3/*3. 295 subjects were genotyped for CYP2C9*2 and CYP2C9*3 using the TaqMan procedure, and for CYP2C9*13 using pyrosequencing. These data were combined with our previously reported data to assess the CYP2C9 allele and genotype frequencies in 869 Korean subjects. Data from 24 of the 295 genotyped subjects (22 CYP2C9*1/*1 homozygotes, one CYP2C9*1/*3 heterozygote and one CYP2C9*3/*3 homozygote) who had participated in a bioequivalence study were analysed retrospectively to examine the effects of CYP2C9 genotype on glimepiride pharmacokinetics. The frequencies of the CYP2C9*1/*3, *3/*3, and *1/*13 genotypes in the study population (n = 295) were 0·081 (n = 24), 0·010 (n = 3) and 0·003 (n = 1), respectively. In the 869 subjects from the combined studies, allele frequencies for CYP2C9*3 and CYP2C9*13 were 0·025 (95% CI: 0·018, 0·033) and 0·002 (95% CI: 0·000, 0·010), respectively. Relative to CYP2C9*1 homozygotes, the one CYP2C9*3 homozygous subject was found to have a higher AUC(0-∞) value (490% of the reference value) and a lower oral clearance rate (18% of the reference). This study is the first examination of CYP2C9*3 homozygotes in the Korean population. Our data on the one subject with this genotype suggest that CYP2C9*3/*3 momozygotes have lower clearance of glimepiride and are exposed to higher levels of the drug than wild-type homozygotes. Although we identified a subject with the CYP2C9*13 allele using a new pyrosequencing assay, we were unfortunately unable to investigate its effects on glimepiride pharmacokinetics.