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Joyce A Goldstein

Publications and source records attributed to Joyce A Goldstein.

31 records · Page 2Linked to original sources
PubMed2003

Differences in flurbiprofen pharmacokinetics between CYP2C9*1/*1, *1/*2, and *1/*3 genotypes.

OBJECTIVE: This study was conducted to examine differences in flurbiprofen metabolism among individuals with the CYP2C9*1/*1, *1/*2, and *1/*3 genotypes. METHODS: Fifteen individuals with the CYP2C9*1/*1 ( n=5), *1/*2 ( n=5), and *1/*3 ( n=5) genotypes received a single 50-mg oral dose of flurbiprofen. Plasma and urine samples were collected over 24 h, and flurbiprofen and 4'-hydroxyflurbiprofen pharmacokinetic data were compared across genotypes. RESULTS: CYP2C9 genotype was a significant predictor of flurbiprofen metabolism and accounted for 59% of the variability in flurbiprofen AUC(0- infinity ), and approximately 50% of the variability in flurbiprofen oral clearance, formation clearance to 4'-hydroxyflurbiprofen, and the 0 to 24-h urinary metabolic ratio of flurbiprofen to 4'-hydroxyflurbiprofen. Flurbiprofen AUC(0- infinity )was significantly higher and all measures of flurbiprofen clearance were significantly lower in the CYP2C9*1/*3 individuals than in those with *1/*1. Significant differences in these parameters were not detected between *1/*2 subjects and *1/*1 subjects. CONCLUSIONS: CYP2C9 genotype is a significant predictor of flurbiprofen disposition in humans by altering CYP2C9-mediated metabolism and reducing systemic clearance. The effects are most pronounced in individuals carrying the *3 allele.

Adolescent↗
PubMed2003

Genetic findings and functional studies of human CYP3A5 single nucleotide polymorphisms in different ethnic groups.

OBJECTIVES: Genetic polymorphisms of cytochromes P450 (CYPs) are a principal reason for inter-individual variations in the metabolism of therapeutic drugs and environmental chemicals in humans. The present study identifies 34 single nucleotide polymorphisms (SNPs) of CYP3A5 including 27 previously unidentified SNPs by direct sequencing of the exons, intron-exon junctions and 5'-upstream region of CYP3A5 from 92 racially diverse individuals (24 Caucasians, 24 Africans, 24 Asians, and 20 individuals of unknown racial origin). RESULTS: Four new CYP3A5 SNPs produced coding changes: R28C, L82R, A337T, and F446S. CYP3A5 R28C occurred in African populations (allelic frequency of 4%). CYP3A5 A337T occurred in Asians (2% allelic frequency), CYP3A5 L82R (occurred in the racially unidentified group) and CYP3A5 F446S (identified in Caucasians with a 2% allelic frequency) were on an allele containing the splice change g.6986A>G known as CYP3A5*3. The newly identified allelic proteins were constructed by site-directed mutagenesis, expressed in Escherichia coli and purified. CYP3A5 L82R was expressed only as denatured CYP420, suggesting it may be unstable. CYP3A5*1 exhibited the highest maximal clearance for testosterone followed by CYP3A5 A337T > CYP3A5 R28C >> CYP3A5 F446S. CYP3A5*1 exhibited a higher V(max) for nifedipine oxidation than CYP3A5 A337T > CYP3A5 R28C >> CYP3A5 F446S. CYP3A5 A337T and CYP3A5 R28C exhibited a 42-64% lower V(max) for nifedipine oxidation than CYP3A5*1. CYP3A5 F446S exhibited a > 95% decrease in the intrinsic clearance for both 6beta-hydroxytestosterone and nifedipine oxidation. CONCLUSION: This study identifies four new potentially defective coding alleles. CYP3A5 F446S is predicted to be more catalytically defective than the splice change alone.

Alleles↗
PubMed2003

Identification of constitutive androstane receptor and glucocorticoid receptor binding sites in the CYP2C19 promoter.

CYP2C19 is an important human drug-metabolizing enzyme that metabolizes a number of clinically used drugs including the antiulcer drug omeprazole, the anxiolytic drug diazepam, the beta-blocker propranolol, the antimalarial drug proguanil, certain antidepressants and barbiturates, and the prototype substrate S-mephenytoin. Previous studies show that compounds such as rifampicin and dexamethasone induce CYP2C19 both in vivo in humans and in vitro in human hepatocytes. This study examines the transcriptional regulation of CYP2C19. Analysis of the CYP2C19 promoter revealed a single constitutive androstane receptor (CAR) binding site (CAR-RE; -1891/-1876 bp) and a glucocorticoid-responsive element (GRE; -1750/-1736 bp). Gel-shift assays showed that CAR-RE binds CAR and pregnane X receptor (PXR). Cotransfection with hCAR, mCAR, or hPXR in HepG2 cells up-regulated transcription of CYP2C19 promoter constructs, whereas mutation of the -1891-bp CAR-RE abolished up-regulation. Expression with hCAR also up-regulated endogenous CYP2C19 mRNA content in HepG2 cells. Androstenol repressed the mCAR-mediated constitutive activation of the CYP2C19 promoter in HepG2 cells, whereas the potent mCAR ligand 1,4-bis[2-3,5-dichloropyridyloxyl)] benzene derepressed this response. Rifampicin produced a modest increase in promoter activity in cells cotransfected with hPXR. Dexamethasone activated the -2.7-kb CYP2C19 promoter constructs in HepG2 cells only in the presence of cotransfected glucocorticoid receptor (GR), whereas the GR antagonist mifepristone inhibits this response. Mutation of the GRE abolishes dexamethasone activation. This is the first study to identify nuclear receptor binding sites (CAR/PXR and GR) in the CYP2C19 promoter and to suggest that these receptors may up-regulate CYP2C19 constitutively and possibly its response to drugs.

Aryl Hydrocarbon Hydroxylases↗
PubMed2003

Tolbutamide, flurbiprofen, and losartan as probes of CYP2C9 activity in humans.

The metabolic activity of CYP2C9 in 16 subjects expressing four different genotypes (CYP2C9*1/*1, *1/*2, *1/*3, and *2/*2) was evaluated. Single oral doses of tolbutamide, flurbiprofen, and losartan were administered in a randomized, crossover design. Plasma and urine were collected over 24 hours. The urinary metabolic ratio and amount of metabolite(s) excreted were correlated with formation clearance. The formation clearance of tolbutamide to its CYP2C9-mediated metabolites demonstrated a stronger association with genotype compared to flurbiprofen and losartan, respectively (r2 = 0.64 vs. 0.53 vs. 0.42). A statistically significant correlation was observed between formation clearance of tolbutamide and the 0- to 12-hour urinary amount of 4'-hydroxytolbutamide and carboxytolbutamide (r = 0.84). Compared to tolbutamide, the correlations observed between the respective measures of flurbiprofen and losartan metabolism were not as strong. Tolbutamide is a better CYP2C9 probe than flurbiprofen and losartan, and the 0- to 12-hour amount of 4'-hydroxytolbutamide and carboxytolbutamide is the best urinary measure of its metabolism.

Adult↗
PubMed2003

Losartan and E3174 pharmacokinetics in cytochrome P450 2C9*1/*1, *1/*2, and *1/*3 individuals.

STUDY OBJECTIVE: To determine if differences in the pharmacokinetics of losartan and its pharmacologically active E3174 metabolite exist among individuals expressing the cytochrome P450 (CYP) 2C9*1/*1, *1/*2, and *1/*3 genotypes. DESIGN: Single-dose pharmacokinetic study. SETTING: University general clinical research center. SUBJECTS: Fifteen healthy volunteers, five from each genotype: CYP2C9*1/*1, *1/*2, and *1/*3. INTERVENTION: A single oral dose of losartan 50 mg. MEASUREMENTS AND MAIN RESULTS: Plasma and urine samples were collected for 24 hours, and losartan and E3174 pharmacokinetic data were compared across the three genotypes. Orthostatic blood pressure was measured over 12 hours after dosing. No significant differences were observed among the three groups in losartan or E3174 area under the plasma concentration-time curve, losartan or E3174 elimination half-life, or losartan oral clearance. A significant association between CYP2C9 genotype and losartan to E3174 formation clearance was observed, such that 50% of the variability was accounted for by the genotype. No significant relationship between that genotype and blood pressure was observed at any time. CONCLUSION: Differences in the pharmacokinetics of losartan and its active E3174 metabolite were not observed in healthy subjects with the genotype of CYP2C9*1/*2 and *1/*3 compared with those expressing *1/*1. Alterations in losartan dosing in CYP2C9*1/*2 and *1/*3 individuals does not appear necessary.

Adolescent↗
PubMed2002

Evaluation of cytochrome P4502C9 metabolic activity with tolbutamide in CYP2C91 heterozygotes.

OBJECTIVES: Multiple single-nucleotide polymorphisms in the gene encoding cytochrome P450 (CYP) 2C9 have been identified, but the functional significance of the various putative defective genotypes in humans merits further study. METHODS: Using tolbutamide as a probe of CYP2C9 activity, we evaluated CYP2C9 phenotype in 15 healthy individuals expressing the CYP2C9(*)1/(*)1, (*)1/(*)2, and (*)1/(*)3 genotypes (n = 5 per group). CYP2C9 genotype was determined by polymerase chain reaction-restriction fragment length polymorphism methods. Subjects received 500 mg of tolbutamide, with plasma and urine collected over a 24-hour period. Plasma tolbutamide and urinary tolbutamide, 4'-hydroxytolbutamide, and carboxytolbutamide concentrations were determined by an HPLC method. RESULTS: Tolbutamide area under the plasma concentration-time curve from time zero to infinity [AUC(0- infinity )] significantly increased by 1.5-fold and 1.9-fold, respectively, in subjects expressing the CYP2C9(*)1/(*)2 and (*)1/(*)3 genotypes compared with (*)1/(*)1 subjects. Statistically significant reductions in tolbutamide oral clearance (29% and 48%) and formation clearance (38% and 56%) were detected in the (*)1/(*)2 and (*)1/(*)3 individuals, respectively, compared with (*)1/(*)1 subjects. The increases in AUC(0- infinity) and decreases in oral clearance observed in the (*)1/(*)3 individuals were also significantly greater than those expressing the (*)1/(*)2 genotype (P <.05). The amount of urinary 4'-hydroxytolbutamide and carboxytolbutamide excreted in the 0- to 12-hour and 6- to 12-hour collection intervals was significantly less in (*)1/(*)2 and (*)1/(*)3 individuals compared with (*)1/(*)1 subjects. With tolbutamide used as a CYP2C9 probe, CYP2C9 genotype was the major determinant of CYP2C9 phenotype (r(2) = 0.77). CONCLUSIONS: CYP2C9 activity was significantly reduced in (*)1 heterozygotes compared with (*)1 homozygotes, and metabolism was more severely impaired in (*)1/(*)3 individuals compared with those expressing (*)1/(*)2.

Adolescent↗
PubMed2002

Evaluation of potential losartan-phenytoin drug interactions in healthy volunteers.

BACKGROUND: Phenytoin, a cytochrome P450 (CYP) 2C9 substrate, has a narrow therapeutic index and nonlinear pharmacokinetics. Therefore there is the potential for significant concentration-related adverse effects when phenytoin is coadministered with other CYP2C9 substrates. Losartan, an antihypertensive agent, is also a substrate for CYP2C9. OBJECTIVE: Our objective was to assess the effects of losartan on the pharmacokinetics of phenytoin and the effects of phenytoin on the pharmacokinetics of losartan in a healthy population of volunteers. METHODS: A prospective, randomized, 3-period crossover study was conducted in 16 healthy volunteers with phenytoin alone, phenytoin in combination with losartan, and losartan alone. Each treatment was given for 10 days with a 3-week washout period between treatments. On day 10, plasma concentrations of phenytoin and plasma and urine concentrations of losartan and its active carboxylic-acid metabolite E3174 were measured to determine steady-state pharmacokinetic parameters. RESULTS: Coadministration of losartan had no effect on the pharmacokinetics of phenytoin. Coadministration of phenytoin increased the mean area under the concentration-time curve from time zero to 24 hours [AUC(0-24)] of losartan by 17% (355 +/- 220 ng x h/mL versus 427 +/- 177 ng x h/mL; P =.1), but this difference was not statistically significant. In the 14 CYP2C9*1/*1 subjects, the mean AUC(0-24) of losartan was increased by 29% (284 +/- 84 ng x h/mL versus 402 +/- 128 ng x h/mL; P =.008). Coadministration of phenytoin significantly reduced the AUC(0-24) of E3174 by 63% (1254 +/- 256 ng x h/mL versus 466 +/- 174 ng x h/mL; P =.0001) and the formation clearance of losartan to E3174 (1.91 +/- 0.8 mL/h per kilogram versus 0.62 +/- 0.4 mL/h per kilogram; P =.0001). CONCLUSIONS: Losartan, a CYP2C9 substrate, had no effect on the pharmacokinetics of phenytoin. However, phenytoin inhibited the CYP2C9-mediated conversion of losartan to E3174.

Adult↗
PubMed2002

Analysis of the CYP2C19 polymorphism in a North-eastern Thai population.

CYP2C19 is a polymorphically expressed cytochrome P450 responsible for the metabolism of several clinically used drugs, including some barbiturates, diazepam, proguanil, propranolol and several proton pump inhibitors. Genetic polymorphism of this enzyme shows marked interracial differences, with the poor metabolizer (PM) phenotype representing 2-5% of Caucasian and 11-23% of Oriental populations. In the present study, CYP2C19 phenotype and genotype were investigated in 107 North-eastern Thai subjects using the omeprazole hydroxylation index (HI) and polymerase chain reaction-restriction fragment length polymorphism technique, respectively. It was found that the distribution of HI in these subjects was bimodal. Seven subjects [6.54%, 95% confidence (CI) 1.86-11.22%] were identified as PM, with an HI > 7. Analysis of CYP2C19 genotypes in these 107 Thai subjects revealed that the allele frequencies for CYP2C19*1, CYP2C19*2 and CYP2C19*3 were 0.71 (95% CI 0.65-0.77), 0.27 (95% CI 0.21-0.33) and 0.02 (95% CI 0.01-0.05), respectively. The PM phenotype and the frequencies of CYP2C19 defective alleles in Thais, particularly CYP2C19*3, were lower than those observed in other Oriental populations. It is noteworthy that there was a case of nonaccordance between phenotype and genotype in one of the PMs. Whether this PM represents a novel defective allele requires further investigation.

Adult↗
PubMed2002

Cytochrome P450 2C9 polymorphisms: a comprehensive review of the in-vitro and human data.

The discovery of six distinct polymorphisms in the genetic sequence encoding for the cytochrome P450 2C9 (CYP2C9) protein has stimulated numerous investigations in an attempt to characterize their population distribution and metabolic activity. Since the CYP2C9*1, *2 and *3 alleles were discovered first, they have undergone more thorough investigation than the recently identified *4, *5 and *6 alleles. Population distribution data suggest that the variant *2 and *3 alleles are present in approximately 35% of Caucasian individuals; however, these alleles are significantly less prevalent in African-American and Asian populations. In-vitro data have consistently demonstrated that the CYP2C9*2 and *3 alleles are associated with significant reductions in intrinsic clearance of a variety of 2C9 substrates compared with CYP2C9*1; however, the degree of these reductions appear to be highly substrate-dependent. In addition, multiple in-vivo investigations and clinical case reports have associated genotypes expressing the CYP2C9*2 and *3 alleles with significant reductions in both the metabolism and daily dose requirements of selected CYP2C9 substrates. Individuals expressing these variant genotypes also appear to be significantly more susceptible to adverse events with the narrow therapeutic index agents warfarin and phenytoin, particularly during the initiation of therapy. These findings have subsequently raised numerous questions regarding the potential clinical utility of genotyping for CYP2C9 prior to initiation of therapy with these agents. However, further clinical investigations evaluating the metabolic consequences in individuals expressing the CYP2C9*2, *3, *4, *5, or *6 alleles are required before large-scale clinical genotyping can be recommended.

Alleles↗
PubMed2002

Identification and functional characterization of new potentially defective alleles of human CYP2C19.

CYP2C19 is a clinically important enzyme responsible for the metabolism of a number of therapeutic drugs, such as mephenytoin, omeprazole, diazepam, proguanil, propranolol and certain antidepressants. Genetic polymorphisms in this enzyme result in poor metabolizers of these drugs. There are racial differences in the incidence of the poor metabolizer trait, which represents 13-23% of Asians but only 3-5% of Caucasians. In this study, single nucleotide polymorphisms (SNPs) in CYP2C19 were identified by direct sequencing of genomic DNA from 92 individuals from three different racial groups of varied ethnic background, including Caucasians, Asians and blacks. Several new alleles were identified containing the coding changes Arg114 His (CYP2C19*9), Pro227 Leu (CYP2C19*10), Arg150 His (CYP2C19*11), stop491 Cys (CYP2C19*12), Arg410 Cys (CYP2C19*13), Leu17 Pro (CYP2C19*14) and Ile19 Leu (CYP2C19*15). When expressed in a bacterial cDNA expression system, CYP2C19*9 exhibited a modest decrease in the V(max) for 4'-hydroxylation of -mephenytoin, and no alteration in its affinity for reductase. CYP2C19*10 exhibited a dramatically higher K(m) and lower V(max) for mephenytoin. CYP2C19*12was unstable and expressed poorly in a bacterial cDNA expression system. Clinical studies will be required to confirm whether this allele is defective in vivo. CYP2C19*9, CYP2C19*10 and CYP2C19*12 all occurred in African-Americans, or individuals of African descent, and represent new potentially defective alleles of CYP2C19 which are predicted to alter risk of these populations to clinically important drugs.

Alleles↗
PubMed2002

In vitro human metabolism and interactions of repellent N,N-diethyl-m-toluamide.

Oxidative metabolism of the insect repellent N,N-diethyl-m-toluamide (DEET) by pooled human liver microsomes (HLM), rat liver microsomes (RLM), and mouse liver microsomes (MLM) was investigated. DEET is metabolized by cytochromes P450 (P450s) leading to the production of a ring methyl oxidation product, N,N-diethyl-m-hydroxymethylbenzamide (BALC), and an N-deethylated product, N-ethyl-m-toluamide (ET). Both the affinities and intrinsic clearance of HLM for ring hydroxylation are greater than those for N-deethylation. Pooled HLM show significantly lower affinities (K(m)) than RLM for metabolism of DEET to either of the primary metabolites (BALC and ET). Among 15 cDNA-expressed P450 enzymes examined, CYP1A2, 2B6, 2D6*1 (Val(374)), and 2E1 metabolized DEET to the BALC metabolite, whereas CYP3A4, 3A5, 2A6, and 2C19 produced the ET metabolite. CYP2B6 is the principal cytochrome P450 involved in the metabolism of DEET to its major BALC metabolite, whereas CYP2C19 had the greatest activity for the formation of the ET metabolite. Use of phenotyped HLMs demonstrated that individuals with high levels of CYP2B6, 3A4, 2C19, and 2A6 have the greatest potential to metabolize DEET. Mice treated with DEET demonstrated induced levels of the CYP2B family, increased hydroxylation, and a 2.4-fold increase in the metabolism of chlorpyrifos to chlorpyrifos-oxon, a potent anticholinesterase. Preincubation of human CYP2B6 with chlorpyrifos completely inhibited the metabolism of DEET. Preincubation of human or rodent microsomes with chlorpyrifos, permethrin, and pyridostigmine bromide alone or in combination can lead to either stimulation or inhibition of DEET metabolism.

Animals↗
PubMed2002

Regulation of human CYP2C9 by the constitutive androstane receptor: discovery of a new distal binding site.

The CYP2C subfamily metabolizes many clinically important drugs. These genes respond to prototypical inducers such as phenobarbital and rifampicin, yet little has been reported on the mechanisms of induction. This report examines the regulation of CYP2C9 with respect to two specific receptors thought to be involved in phenobarbital (PB) induction, the constitutive androstane receptor (CAR) and pregnane X receptor (PXR). Transfection of either mouse CAR (mCAR) or human CAR (hCAR) into HepG2 cells results in increased CYP2C9 mRNA content. Inducers further increased this response in CAR transfected cells. mCAR but not hCAR conferred drug inducibility to the proximal -2145 bp of the CYP2C9 promoter in luciferase assays. Further examination of a -2925-bp promoter construct revealed that hCAR cotransfection increased activity 20-fold. Gel shift assays confirmed the presence of a distal PB-responsive enhancer module-like enhancer module, CAR-responsive enhancer (CAR-RE), between -2900 and -2841 bp consisting of two DR-5 nuclear receptor binding motifs capable of binding hCAR, mCAR, and, to a lesser extent, human PXR. The majority of binding and hCAR activation is derived from the NR1 portion of the CAR-RE. PB treatment did not further increase the hCAR activation in any of the constructs. In summary, a new CAR/PXR binding site was identified in the CYP2C9 promoter, and this site seems to constitutively regulate transcription via a CAR-dependent mechanism; however, it could not be shown to account for PB inducibility of the gene.

Aryl Hydrocarbon Hydroxylases↗