Proton pump inhibitors (PPIs), such as omeprazole, lansoprazole, rabeprazole, esomeprazole, and pantoprazole, are mainly metabolized by CYP2C19 in the liver. There are genetically determined differences in the activity of this enzyme. The genotypes of CYP2C19 are classified into the three groups, rapid extensive metabolizer (RM), intermediate metabolizer (IM), and poor metabolizer (PM). The pharmacokinetics and pharmacodynamics of PPIs depend on CYP2C19 genotype status. Plasma PPI levels and intragastric pHs during PPI treatment in the RM group are lowest, those in the IM group come next, and those in the PM group are highest of the three groups. These CYP2C19 genotype-dependent differences in pharmacokinetics and pharmacodynamics of PPIs influence the cure rates for the gastro-esophageal reflux disease and H. pylori infection by PPI-based therapies. For the better PPI-based treatment, doses and dosing schemes of PPIs should be optimized based on CYP2C19 genotype status.

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  We previously established a method to predict the drug metabolism capacity of injured liver based on pharmacokinetic estimation of the amount of cytochrome P450 (CYP) in vivo (PKCYP test), by introducing the apparent liver-to-blood free concentration gradient in vivo (qg) as a parameter. Here we show that the amount of CYP3A2 in CCl₄-treated rats can be estimated appropriately by applying the PKCYP test using midazolam (MDZ) as a probe, assuming that the qg value in control rats does not change. We applied the results to predict the clearance of theophylline as a model drug with a physiologically based pharmacokinetic model.
   Male Sprague-Dawley rats were pretreated with CCl₄, and the amount of CYP (A-CYP_vivo) was quantified by Western blotting. The qg value of MDZ was determined in control rats and used to estimate the amounts of CYP3A2 in CCl₄-treated rats; the result agreed well with the observed values. The qg value of CYP3A2 estimated with MDZ as a probe was used together with our previously reported value for CYP1A2 (theophylline metabolism in the liver is known to be almost entirely mediated by CYP3A2 and CYP1A2) to predict the total body clearance (CL_tot) of theophylline in CCl₄-treated rats. The predicted CL_tot was about one-third of the observed value, which was considered acceptable. The time-course of theophylline concentration in serum simulated with a physiologically-based pharmacokinetic model agreed well with the observed values. Thus, the PKCYP test using MDZ as a probe can be used to predict the amount of CYP3A2 and the CL_tot of theophylline in CCl₄-treated rats.

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  It is important to estimate the defective metabolism caused by genetic polymorphism of drug metabolizing enzymes before the clinical stage. We evaluated the utility of cryopreserved human hepatocytes of CYP2D6 poor metabolizer (PM) for the estimation of the metabolism in PM using dextromethorphan (DEX) as the probe drug for CYP2D6 substrate.
   The results of low formations of dextrorphan (DXO) and 3-hydroxymorphinan (3-HM) in CYP2D6 PM hepatocytes incubated with dextromethorphan reflected the clinical data. Formation of 3-methoxymorphinan (3-MEM) normalized by CYP3A4/5 activity in the PM hepatocytes reached about 2.8-fold higher than that in CYP2D6 extensive metabolizer (EM) hepatocytes, which clearly showed the compensatory metabolic pathway of O-demethylation catalyzed by CYP2D6 as seen in clinical study. On the contrary, in the condition of the EM hepatocytes with CYP2D6 inhibitors, the enhancement of 3-MEM formation was not observed. In phase II reaction, the glucuronide formation rate of DXO in the PM hepatocytes was lower than that in the EM hepatocytes, which was consistent with clinical data of DXO-glucuronide (DXO-glu) concentration. These results would suggest that CYP2D6 PM hepatocytes could be a good in vitro tool for estimating CYP2D6 PM pharmacokinetics.

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  To evaluate the effect of protein binding of pilsicainide on its clearance and the contribution of protein binding to optimized pilsicainide therapy, clinical laboratory and pharmacokinetic data were studied in 160 Japanese inpatients (Study 1) and 18 Japanese inpatients (Study 2). To determine the relation between protein concentration and the protein binding ratio of pilsicainide in vitro, the effect of human α₁-acid glycoprotein (AAG) and human albumin on the binding ratio was studied. The mean ratio of serum pilsicainide concentration to dose per body weight (C/D) increased with increases in the C-reactive protein (CRP) concentration in Study 1. The AAG level increased with increases in the CRP concentration and the binding ratio increases in the AAG concentration in the Study 2. The binding ratios increased with increased AAG and albumin concentrations; the AAG concentration relative to the ratio was particularly large in vitro study. These results suggest C/D is increased in patients with high CRP levels because of binding of pilsicainide to protein, resulting decreased clearance.

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  We aimed to analyze the risks of extrapyramidal symptoms (EPS) induced by typical and atypical antipsychotic drugs using a common pharmacokinetic-pharmacodynamic (PK-PD) model based on the receptor occupancy.
   We collected the data for EPS induced by atypical antipsychotics, risperidone, olanzapine and quetiapine, and a typical antipsychotic, haloperidol from literature and analyzed the following five indices of EPS, the ratio of patients obliged to take anticholinergic medication, the occurrence rates of plural extrapyramidal symptoms (more than one of tremor, dystonia, hypokinesia, akathisia, extrapyramidal syndrome, etc.), parkinsonism, akathisia, and extrapyramidal syndrome. We tested two models, i.e., a model incorporating endogenous dopamine release owing to 5-HT_2A receptor inhibition and a model not considering the endogenous dopamine release, and used them to examine the relationship between the D₂ receptor occupancy of endogenous dopamine and the extent of drug-induced EPS.
   The model incorporating endogenous dopamine release better described the relationship between the mean D₂ receptor occupancy of endogenous dopamine and the extent of EPS than the other model, as assessed by the final sum of squares of residuals (final SS) and Akaike's Information Criteria (AIC). Furthermore, the former model could appropriately predict the risks of EPS induced by two other atypical antipsychotics, clozapine and ziprasidone, which were not incorporated into the model development.
   The developed model incorporating endogenous dopamine release owing to 5-HT_2A receptor inhibition may be useful for the prediction of antipsychotics-induced EPS.

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  Background/Aim: Creatinine is excreted into urine via tubular secretion in addition to glomerular filtration. In the present study, characteristics of the creatinine transport in renal epithelial cells were investigated.
   Methods: The transcellular transport and accumulation of [¹⁴C]creatinine and [¹⁴C]tetraethylammonium (TEA) were assessed using LLC-PK₁ cell monolayers cultured on porous membrane filters.
   Results: [¹⁴C]Creatinine was transported directionally from the basolateral to apical side of LLC-PK₁ cell monolayers. Basolateral uptake of [¹⁴C]creatinine was dependent on membrane potential, and was saturable with apparent K_m and V_max values of 13.2±2.8 mM and 13.1±3.1 nmol/mg protein/5 min, respectively. Concomitant administration of organic cations (1 mM) such as cimetidine, quinidine and trimethoprim inhibited both the transcellular transport and accumulation of [¹⁴C]creatinine. Furthermore, apical excretion of [¹⁴C]creatinine was not dependent on acidification of the apical medium.
   Conclusions: Creatinine was subjected to directional transport across renal epithelial cells from the basolateral to apical side. The organic cation transporter should be involved in the basolateral uptake of creatinine.

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  The metabolism of ethyl 2-(4-chlorophenyl)-5-(2-furyl)-4-oxazoleacetate (TA-1801), a potent hypolipidemic agent, was studied in humans after oral administration and compared with that found in rats, rabbits, and dogs previously. Hydrolysis of the ethyl ester to produce metabolite M1 (TA-1801 active form; TA-1801A) is the first metabolic step and the subsequent biotransformation includes the glucuronidation to form the metabolite M4 and the oxidation to form the metabolites M2 and M3. The metabolism of TA-1801 in humans was qualitatively similar to that in the experimental animals studied, although species differences were seen in the amount of metabolites. M4, the glucuronide of TA-1801A was the most abundant metabolite in human urine (24.3% of the dose). In vitro studies using human liver and jejunum microsomes indicated that the TA-1801A glucuronosyltransferase activity in human jejunum microsomes was 2-fold higher than that in liver microsomes. With regard to the interspecies differences in the TA-1801A glucuronosyltransferase activities, the intrinsic clearance for the TA-1801A glucuronidation in liver microsomes was in the following order: rabbit>monkey>human=rat=dog. In jejunum microsomes, the intrinsic clearance for the TA-1801A glucuronidation was in the following order: human>monkey>rabbit>rat=dog. These results suggest that the species differences in the intestinal TA-1801A glucuronidation contribute to the species differences in the excretion rate of TA-1801A glucuronide into the urine.

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  We characterized the hepatic and intestinal UDP-glucuronosyltransferase (UGT) isoform(s) responsible for the glucuronidation of 2-(4-chlorophenyl)-5-(2-furyl)-4-oxazoleacetic acid (TA-1801A) in humans through several in vitro mechanistic studies. Assessment of a panel of recombinant UGT isoforms revealed the TA-1801A glucuronosyltransferase activity of UGT1A1, UGT1A3, UGT1A7, UGT1A9, and UGT2B7. Kinetic analyses of the TA-1801A glucuronidation by recombinant UGT1A1, UGT1A3, UGT1A9, and UGT2B7 showed that the K_m value for UGT2B7 was apparently consistent with those in human liver and jejunum microsomes. The TA-1801A glucuronosyltransferase activity in human liver microsomes was inhibited by bilirubin (typical substrate for UGT1A1), propofol (typical substrate for UGT1A9), diclofenac (substrate for UGT1A9 and UGT2B7), and genistein (substrate for UGT1A1, UGT1A3, and UGT1A9). The inhibition by bilirubin, propofol, and diclofenac of the TA-1801A glucuronidation was less pronounced in jejunum microsomes than liver microsomes, suggesting that the contribution of UGT1A1, UGT1A9, and UGT2B7 to the TA-1801A glucuronidation is smaller in the intestine than the liver. In contrast, genistein strongly inhibited the TA-1801A glucuronosyltransferase activity in both human liver and jejunum microsomes. These results suggest that the glucuronidation of TA-1801A is mainly catalyzed by UGT1A1, UGT1A9, and UGT2B7 in the liver, and by UGT1A1, UGT1A3, and UGT2B7 in the intestine in humans.

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  The on-chip genotyping system (“the electrochemical DNA chip”) has been developed as a more cost-effective genotyping system and was applied to MDR1 genotyping in the present study, which is required for wide use in clinical application and for personalized medication based on genotype. The electrochemical DNA chip was optimized and applied to simultaneous genotyping of four MDR1 polymorphisms (T-129C, C1236T, G2677(A,T) and C3435T) using synthetic model oligonucleotide DNA and human genomic DNA. The electrochemical DNA chip successfully gave the T-129C, C1236T, G2677(A,T) and C3435T genotypes, which were completely consistent with those determined by direct sequencing. In conclusion, the electrochemical DNA chip is useful for simultaneous determination of some genotypes and haplotypes, and efficient genotyping using this system can support future genotype-phenotype studies at a large scale.

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