Joo Youn Cho

MRP2 haplotypes confer differential susceptibility to toxic liver injury

Objectives Multidrug resistance protein 2 (MRP2, ABCC2) plays an important role in the biliary clearance of a wide variety of endogenous and exogenous toxic compounds. Therefore, polymorphisms and mutations in the MRP2 gene may affect individual susceptibility to hepatotoxic reactions. Methods Associations between genetic variations of MRP2 and toxic hepatitis were investigated using integrated population genetic analysis and functional molecular studies. Results Using a gene scanning method, 12 polymorphisms and mutations were found in the MRP2 gene in a Korean population. Individual variation at these sites was analyzed by conventional DNA screening in 110 control subjects and 94 patients with toxic hepatitis induced mostly by herbal remedies. When haplotypes were identified, over 85% of haploid genes belonged to the five most common haplotypes. Among these, a haplotype containing the g.−1774delG polymorphism showed a strong association with cholestatic or mixed-type hepatitis, and a haplotype containing the g.−1549G>A, g.−24C>T, c.334−49C>T, and c.3972C>T variations was associated with hepatocellular-type hepatitis. A comprehensive functional study of these sites revealed that genetic variations in the promoter of this gene are primarily responsible for the susceptibility to toxic liver injuries. The g.−1774delG variation and the combined variation of g.−1549G>A and g.−24C>T decreased MRP2 promoter activity by 36 and 39%, respectively. In addition, the promoter carrying the g.−1774delG allele showed a defect in the bile acid-induced induction of promoter activity. Conclusions These results suggest that genetic variations of MRP2 are an important predisposing factor for herbal-induced or drug-induced toxic liver injuries.

Apple juice greatly reduces systemic exposure to atenolol

AIM Fruit juice reduces the plasma concentrations of several β-adrenoceptor blockers, likely by inhibiting OATP2B1-mediated intestinal absorption. The aim of this study was to investigate the effects of apple juice on the pharmacokinetics of atenolol. METHODS Twelve healthy Korean volunteers with genotypes of SLCO2B1 c.1457C> T (*1/*1 (n = 6) and *3/*3 (n = 6)) were enrolled in this study. In a three-phase, one-sequence crossover study, the pharmacokinetics (PK) of atenolol was evaluated after administration of 50 mg atenolol. Subjects received atenolol with either 300 ml water, 1200 ml apple juice or 600 ml apple juice. RESULTS Apple juice markedly reduced the systemic exposure to atenolol. The geometric mean ratios (95% confidence intervals) of apple juice : water were 0.18 (0.13, 0.25, 1200 ml) and 0.42 (0.30, 0.59, 600 ml) for the AUC(0,t(last)). In this study, the PK parameters of atenolol responded in a dose-dependent manner to apple juice. CONCLUSIONS Apple juice markedly reduced systemic exposure to atenolol. The genetic variation of SLCO2B1 c.1457C>T had a minimal effect on the pharmacokinetics of atenolol when the drug was administered with water or apple juice.

Population pharmacokinetic modelling of aripiprazole and its active metabolite, dehydroaripiprazole, in psychiatric patients

AIMS The aims of this study were to develop a combined population pharmacokinetic model for both aripiprazole and its active metabolite, dehydroaripiprazole, in psychiatric patients and to identify to what extent the genetic polymorphisms of cytochrome P450 (CYP) enzymes contribute to the variability in pharmacokinetics (PK). METHODS A population pharmacokinetic analysis was performed using NONMEM software based on 141 plasma concentrations at steady state from 80 patients receiving multiple oral doses of aripiprazole (10-30 mg day(-1)). RESULTS A one-compartment model with first-order kinetics for aripiprazole and dehydroaripiprazole each was developed to describe simultaneously the concentration data. The absorption rate constant was fixed to 1.06 h(-1). The typical value of apparent distribution volume of aripiprazole was estimated to be 192 l. Covariate analysis showed that CYP2D6 genetic polymorphisms significantly influenced the apparent clearance of aripiprazole (CL/F), reducing the interindividual variability on CL/F from 37.8% CV (coefficient of variation) to 30.5%. The CL/F in the CYP2D6 IMs was approximately 60% of that in CYP2D6 EMs having two functional alleles. Based on the CYP2D6 genotype, the metabolic ratios were calculated at 0.20-0.34. However, the plasma concentration : dose ratios of dehydroaripiprazole were not different across the CYP2D6 genotype. CONCLUSIONS This population pharmacokinetic model provided an adequate fit to the data for both aripiprazole and dehydroaripiprazole in psychiatric patients. The usefulness of CYP genotyping as an aid to select the starting dose should be further investigated.

Modeling of brain D2 receptor occupancy-plasma concentration relationships with a novel antipsychotic, YKP1358, using serial PET scans in healthy volunteers

YKP1358 is a novel serotonin (5‐HT2A) and dopamine (D2) antagonist that, in preclinical studies, fits the general profile of an atypical antipsychotic. We conducted a D2 receptor occupancy study with YKP1358 in healthy volunteers using positron emission tomography (PET) to measure the D2 receptor occupancy of YKP1358 and to characterize its relationship to plasma drug concentrations. A single oral dose, parallel group, dose‐escalation (100, 200, and 250 mg) study was performed in 10 healthy male volunteers with the PET radiotracer [11C]raclopride. The D2 receptor occupancy of striatum was measured pre‐dose, and at 2, 5, and 10 h after YKP1358 administration. Serial blood samples were taken for measurement of plasma YKP1358 concentrations. D2 receptor occupancy by YKP1358 increased to 53–83% at 2 h, and then decreased afterwards, ranging from 40–64% at 5 h to 20–51% at 10 h. The YKP1358 dose‐plasma concentration relationship exhibited extensive variability, but there was a good relationship between plasma concentrations and D2 receptor occupancy that was well predicted by a sigmoid Emax model using nonlinear mixed effects modeling. To our knowledge, this is the first study in which the relationship between plasma concentration and the biomarker of D2 receptor occupancy was modeled using nonlinear mixed effects modeling. It is anticipated that these results will be useful in estimating for subsequent studies the initial doses of YKP1358 required to achieve a therapeutically effective range of D2 receptor occupancy.

Optimal dose of intravenous pantoprazole in patients with peptic ulcer bleeding requiring endoscopic hemostasis in Korea.

Background and Aim:  The lowest effective dose of proton pump inhibitors (PPI) for prevention of peptic ulcer rebleeding remains unclear. The objective of the present study was to evaluate whether low‐dose PPI has a similar efficacy to high‐dose i.v. administration for maintaining intragastric pH above 6.

Sensitive liquid chromatography assay with ultraviolet detection for a new phosphodiesterase V inhibitor, DA-8159, in human plasma and urine.

A sensitive high-performance liquid chromatographic (HPLC) method with ultraviolet absorption detection (292 nm) was developed and validated for the determination of the new phosphodiesterase V inhibitor, DA-8159 (DA), in human plasma and urine. A single step liquid-liquid extraction procedure using ethyl ether was performed to recover DA and the internal standard (sildenafil citrate) from 1.0 ml of biological matrices combined with 200 microl of 0.1M sodium carbonate buffer. A Capcell Pak C18 UG120 column (150 mm x 4.6 mm I.D., 5 microm) was used as a stationary phase and the mobile phase consisted of 30% acetonitrile and 70% 20mM potassium phosphate buffer (pH 4.5) at a flow rate of 1.0 ml/min. The lower limit for quantification was 5 ng/ml for plasma and 10 ng/ml for urine samples. Within- and between-run accuracy and precision were < or =15 and < or =10%, respectively, in both plasma and urine samples. The recovery of DA from human plasma and urine was greater than 70%. Separate stability studies showed that DA is stable under the conditions of analysis. This validated assay was used for the pharmacokinetic analysis of DA during a phase I, rising dose study.

Intravenous Amantadine for Freezing of Gait Resistant to Dopaminergic Therapy: A Randomized, Double-Blind, Placebo-Controlled, Cross-Over Clinical Trial

Background Freezing of gait (FOG) is one of the most disabling symptoms in Parkinsonism. Open-label studies have suggested that intravenous (IV) amantadine is effective against FOG resistant to dopaminergic therapy in Parkinsons disease (PD). We evaluated the efficacy of IV amantadine on FOG resistant to dopaminergic therapy. Methodology/Principal Findings This was a randomized, double-blind, placebo-controlled, cross-over study on IV amantadine. The placebo (normal saline) and amantadine (400 mg/day) were injected for 2 days with a 52-hour washout period. The instruments for the outcome measures were the Freezing of Gait Questionnaire (FOGQ), Unified Parkinsons disease rating Scale (UPDRS), and the duration of the 4×10 m walking test. The placebo arm was compared to the amantadine arm. Ten patients were enrolled but two patients withdrew, one from each arm. The FOGQ and UPDRS scores and the duration of the 4×10 m walking test improved in both arms compared to the baseline (P<0.05 in all). However, there were no differences in these values between the amantadine arm and placebo arm (P = 0.368, P = 0.583, P = 0.206, respectively). Follow-up measures 2weeks after discharge in an open-label study showed the beneficial effects of an amantadine tablet on FOG (FOGQ, P = 0.018; UPDRS, P = 0.012 respectively). Conclusions/Significance This double blind, placebo-controlled study did not show the efficacy of IV amantadine on FOG when compared with the placebo. This study provides Class II evidence due to small sample size for the lack of benefit of IV amantadine on FOG resistant to dopaminergic therapy Trial Registration Clinicaltrials.gov NCT01313819

Inhibition of the multidrug and toxin extrusion (MATE) transporter by pyrimethamine increases the plasma concentration of metformin but does not increase antihyperglycaemic activity in humans.

We hypothesized that the pharmacodynamic (PD) characteristics of metformin would change with inhibition of the multidrug and toxin extrusion (MATE) transporter, which mediates renal elimination of metformin. Twenty healthy male subjects received two doses (750/500 mg) of metformin, with and without 50 mg of pyrimethamine (a potent MATE inhibitor), with 1 week of washout in between each dose. The PD characteristics of metformin were assessed using oral glucose tolerance tests (OGTTs) before and after the metformin dose. Metformin concentrations in plasma and urine were determined using liquid chromatography‐electrospray ionization‐tandem mass spectrometry. When metformin was co‐administered with pyrimethamine, its area under the concentration–time curve from 0 to 12 h was 2.58‐fold greater (p < 0.05), whereas the antihyperglycaemic effects of metformin were decreased. The mean differences (90% confidence interval) in mean and maximum serum glucose concentrations and in 2‐h‐post‐OGTT serum glucose concentration were −0.6 (−1, −0.2), −0.9 (−1.6, −0.3) and −0.5 (−1.1, 0.1) mmol/l, respectively. These findings indicate that the response to metformin is not only related to the plasma exposure of metformin but is also related to other factors, such as inhibition of uptake transporters and the gastrointestinal‐based pharmacology of metformin.

Aspirin Decreases Systemic Exposure to Clopidogrel Through Modulation of P‐Glycoprotein But Does Not Alter Its Antithrombotic Activity

Decreased oral clopidogrel absorption caused by induction of intestinal permeability glycoprotein (P‐gp) expression after aspirin administration was observed in rats. This study evaluated the effect of aspirin coadministration on the pharmacokinetics/pharmacodynamics of clopidogrel in humans. A single 75‐mg dose of clopidogrel was orally administered before and after 2 and 4 weeks of once‐daily 100‐mg aspirin administration in 18 healthy volunteers who were recruited based on CYP2C19 and PON1 genotypes. Plasma concentrations of clopidogrel and its active metabolite, H4, and relative platelet inhibition (RPI) were determined. The P‐gp microRNA miR‐27a increased by up to 7.67‐fold (P = 0.004) and the clopidogrel area under the concentration–time curve (AUC) decreased by 14% (P > 0.05), but the AUC of H4 remained unchanged and RPI increased by up to 15% (P = 0.002) after aspirin administration. These findings indicate low‐dose aspirin coadministration may decrease clopidogrel bioavailability but does not decrease its efficacy.

Korean, Japanese, and Chinese populations featured similar genes encoding drug-metabolizing enzymes and transporters: a DMET Plus microarray assessment.

Background Interethnic differences in genetic polymorphism in genes encoding drug-metabolizing enzymes and transporters are one of the major factors that cause ethnic differences in drug response. This study aimed to investigate genetic polymorphisms in genes involved in drug metabolism, transport, and excretion among Korean, Japanese, and Chinese populations, the three major East Asian ethnic groups. Methods The frequencies of 1936 variants representing 225 genes encoding drug-metabolizing enzymes and transporters were determined from 786 healthy participants (448 Korean, 208 Japanese, and 130 Chinese) using the Affymetrix Drug-Metabolizing Enzymes and Transporters Plus microarray. To compare allele or genotype frequencies in the high-dimensional data among the three East Asian ethnic groups, multiple testing, principal component analysis (PCA), and regularized multinomial logit model through least absolute shrinkage and selection operator were used. Results On microarray analysis, 1071 of 1936 variants (>50% of markers) were found to be monomorphic. In a large number of genetic variants, the fixation index and Pearson’s correlation coefficient of minor allele frequencies were less than 0.034 and greater than 0.95, respectively, among the three ethnic groups. PCA identified 47 genetic variants with multiple testing, but was unable to discriminate ethnic groups by the first three components. Multinomial least absolute shrinkage and selection operator analysis identified 269 genetic variants that showed different frequencies among the three ethnic groups. However, none of those variants distinguished between the three ethnic groups during subsequent PCA. Conclusion Korean, Japanese, and Chinese populations are not pharmacogenetically distant from one another, at least with regard to drug disposition, metabolism, and elimination.