Nobuo Aoyama

MDR1 genotype-related pharmacokinetics of digoxin after single oral administration in healthy Japanese subjects.

AbstractPurpose. To evaluate the MDR1 genotype frequency in the Japanese population and to study the relationship between the MDR1 genotype and the pharmacokinetics of digoxin after single oral administration in healthy subjects. Methods. The MDR1 genotype at exon 26 was determined in 114 healthy volunteers by polymerase chain reaction-restriction fragment length polymorphism. The serum concentration-time profile of digoxin was examined after single oral administration at a dose of 0.25 mg. Results. It was found that 35.1 % (40/114) of subjects were homozygous for the wild-type allele (C/C), 52.6 % (60/114) were compound heterozygotes with a mutant T-allele (C3435T) (C/T), and 12.3 % (14/114) were homozygous for the mutant allele (T/T). There was no effect of gender or age on the distribution. The serum concentration of digoxin after a single oral administration increased rapidly, attaining a steady state in all subjects; however, it was lower in the subjects harboring the T-allele. AUC0-4 h values (±SD) were 4.11 ± 0.57, 3.20 ± 0.49, and 3.27± 0.58 ng h/ml, respectively, with a significant difference between C/C and C/T or T/T. Conclusions. The serum concentration of digoxin after single oral administration was lower in the subjects harboring a mutant allele (C3435T) at exon 26 of the MDR1 gene.

Effect of the mutation (C3435T) at exon 26 of the MDR1 gene on expression level of MDR1 messenger ribonucleic acid in duodenal enterocytes of healthy Japanese subjects.

The effect of the C3435T mutation at exon 26 of the MDR1 gene on the expression levels of MDR1 messenger ribonucleic acid (mRNA) was evaluated by means of real‐time polymerase chain reaction in 51 biopsy specimens of duodenum obtained from 13 healthy Japanese subjects. The mRNA levels of MDR1 were 0.38 ± 0.15, 0.56 ± 0.14, and 1.13 ± 0.42 (mean value ± SE) in the subjects with the homozygote of wild‐type allele (C/C), compound heterozygote with mutant T allele (C/T), and the homozygote of the mutant allele (T/T), respectively, reasonably explaining the lower digoxin serum concentration after administration of a single oral dose to subjects harboring a mutant T allele. Good correlation (r = .797; P < .01) was observed between the mRNA concentrations of MDR1 and CYP3A4 in the individual biopsy specimens. This finding suggested a lower plasma concentration of the substrates for CYP3A4 in subjects harboring the C3435T mutation of the MDR1 gene.

Mice deficient in protein tyrosine phosphatase receptor type Z are resistant to gastric ulcer induction by VacA of Helicobacter pylori

The vacuolating cytotoxin VacA produced by Helicobacter pylori causes massive cellular vacuolation in vitro and gastric tissue damage in vivo, leading to gastric ulcers, when administered intragastrically. Here we report that mice deficient in protein tyrosine phosphatase receptor type Z (Ptprz, also called PTP-ζ or RPTP-β, encoded by Ptprz) do not show mucosal damage by VacA, although VacA is incorporated into the gastric epithelial cells to the same extent as in wild-type mice. Primary cultures of gastric epithelial cells from Ptprz+/+ and Ptprz−/− mice also showed similar incorporation of VacA, cellular vacuolation and reduction in cellular proliferation, but only Ptprz+/+ cells showed marked detachment from a reconstituted basement membrane 24 h after treatment with VacA. VacA bound to Ptprz, and the levels of tyrosine phosphorylation of the G protein–coupled receptor kinase–interactor 1 (Git1), a Ptprz substrate, were higher after treatment with VacA, indicating that VacA behaves as a ligand for Ptprz. Furthermore, pleiotrophin (PTN), an endogenous ligand of Ptprz, also induced gastritis specifically in Ptprz+/+ mice when administered orally. Taken together, these data indicate that erroneous Ptprz signaling induces gastric ulcers.

CYP2C19 genotype–related efficacy of omeprazole for the treatment of infection caused by Helicobacter pylori

Omeprazole is used for the treatment of infection caused by Helicobacter pylori, and it is metabolized by the polymorphic cytochrome P4502C19 (CYP2C19). We have found that the anti–H pylori efficacy by the combination of omeprazole and antibiotics is related to the CYP2C19 genotype.

Significant genetic linkage of MDR1 polymorphisms at positions 3435 and 2677: Functional relevance to pharmacokinetics of digoxin

The human MDR1 gene encodes MDR1, also called Pglycoprotein (P-gp), which functions in the energy-dependent export of substances from the inside of cells to the outside. MDR1 was originally isolated from resistant tumor cells as the protein responsible for conferring resistance against antitumor agents (1). Human MDR1 is also expressed in normal tissues including the mucosal cells in the small and large intestine, the epithelial cells of renal proximal tubules, the biliary canalicular side of hepatocytes, capillary endothelial cells of the brain and testis, and cells of the leukocyte lineage (2). MDR1 contributes to the limitation of drug absorption from the gastrointestinal tract, secretion of the drugs into bile and urine, and the prevention of penetration of drugs across the blood-brain barrier. Thus, MDR1 in these normal tissues defines the pharmacokinetics of many drugs, which are substrates for MDR1. In 1989, nine nucleotide differences on the human MDR1 gene were found from drug-selected multidrugresistant cultured cells (3). To date, more than 20 single nucleotide polymorphisms (SNPs) in the exonic regions have been identified (4–7). Among them, the mutation in exon 26, position 3435 (C3435T), neighboring on the ATP binding domain, has been focused due to its suppressive effect on the expression of MDR1 protein in duodenal biopsies and resultant increase of plasma concentration of digoxin under rifampin induction or at steady-state in Caucasian subjects, although this is a silent mutation (5). C3435T mutation was shown to decrease efflux of the MDR1 substrate rhodamine from CD56 natural killer cells and lower MDR1 mRNA expression in leukocytes (8). However, recent investigations have suggested that C3435T has no effect on placental MDR1 expression (7) and moreover that C3435T mutation is related to a higher level of MDR1 mRNA expression in duodenal biopsies in healthy Japanese subjects (9). The C3435T mutation has been reported to have no effect on the plasma concentration of digoxin (10) and to be lower in subjects with T/T genotype (11). As for other MDR1 substrates, the C3435T mutation has been reported to have no effect on the cyclosporin A trough concentration (12) and to be lower plasma concentration of fexofenadine (13). These investigations suggested the importance of MDR1 genotyping, especially for C3435T. However, the molecular mechanisms underlying the effects of this polymorphism remain unclear, and further investigations should be addressed to elucidate these discrepancies. The C3435T SNP has been suggested to be linked with the SNP at exon 21, position 2677 (G2677(A,T)) producing Ala893Thr and Ala893Ser, respectively (7,13), and haplotype analysis might provide a rational explanation for these discrepancies. This study was, therefore, designed to elucidate the linkage of SNPs at positions 3435, 2677, and -129 in 117 healthy Japanese subjects. Position 2677 locates in the intracellular domain between the 10th and 11th transmembrane spanning domains. Position –129 is in the promoter region, exon 1b. In addition, the effects of SNPs at positions 3435 and 2677 on the serum concentration-time profiles of digoxin after single oral administration were examined in healthy Japanese subjects.

HLA-DRB1*1502 allele, subtype of DR15, is associated with susceptibility to ulcerative colitis and its progression.

HLA-DRB1 allele typing was performed by the PCR-RFLP method on 59 ulcerative colitis (UC) patients and 136 healthy controls. Phenotypic frequencies of HLA-B52 and DR2 were significantly increased among the UC patients, serologically. DNA typing of HLA-DRB1 revealed that the genotypic frequency of DRB1*1502 was higher in UC than in the controls (49.2% vs 17.6%;P<0.0001). In the analysis of clinical parameters, 82.8% of patients bearing DRB1*1502 were treated with corticosteroids. DRB1*1501 and DRB1*1502 differ in only one amino acid at residue 86 (valine vs glycine), and 66% of the UC patients carried two glycines at position 86 in the HLA-DRβ-chain (vs 51% of control;P<0.05). These observations suggest that the presence of Gly-86 in the HLAβ-chain and surrounding amino acid sequence of HLA-DRB1*1502 is strongly associated with susceptibility to UC.

Levofloxacin based triple therapy as a second-line treatment after failure of helicobacter pylori eradication with standard triple therapy.

BACKGROUND Successful eradication of Helicobacter pylori infection after failure of standard triple therapy is difficult. The efficacy and safety of levofloxacin based triple therapy as a first-line therapy has-been studied. AIMS The aim was to evaluate the efficacy and tolerability of levofloxacin based therapy after a failed standard triple therapy. PATIENTS We conducted a prospective, uncontrolled study of a consecutive series of 33 patients who failed eradication with 1 week of lansoprazole-amoxicillin-clarithromycin triple therapy. METHODS The subjects were retreated with 1 week of LA-LVFX triple therapy (lansoprazole, 30 mg twice daily; amoxicillin, 1000 mg twice daily: levofloxacin, 200 mg twice daily). Cure of infection was defined as negative results from culture, histology and a urea breath test 4 to 8 weeks after the second-line therapy. RESULTS The eradication rate was 69.7% (23/33) by both intention-to-treat and per-protocol analyses (95% confidence interval=61-79%). Seven (21.2%) patients experienced mild side-effects, such as soft stools and taste disturbance. No patient stopped the medication on account of adverse effects. CONCLUSIONS Levofloxacin based triple therapy is an effective second-line treatment after a failed standard triple therapy.

CYP2C19 Genotype and Pharmacokinetics of Three Proton Pump Inhibitors in Healthy Subjects

AbstractPurpose. To predict the CYP2C19 genotype-dependence in anti-Helicobacter pylori(H. pylori) therapy when lansoprazole or rabeprazole was used instead of omeprazole as a proton pump inhibitor (PPI). Methods. A comparative pharmacokinetic study with each PPI was designed as an open, randomized, and crossover study of 18 Japanese healthy volunteers who were classified into the homozygous, heterozygous extensive metabolizer and the poor metabolizer based on the CYP2C19 genotype determined by PCR-RFLP method. Each subject received a single oral dose of 20 mg omeprazole, 30 mg lansoprazole, or 20 mg sodium rabeprazole, with at least 1 week washout period between treatments. Plasma concentrations of PPIs and their metabolites were monitored until 12 h after medication. Results. Pharmacokinetic profiles of omeprazole and lansoprazole were well correlated with the CYP2C19 genotype. The heterozygous extensive metabolizer was slightly different from the homozygote, but there was no statistically significant difference. The CYP2C19 genotype dependence found for lansoprazole was not obvious compared with omeprazole. As for rabeprazole, the pharmacokinetic profile was independent of the CYP2C19 genotype. Conclusions. CYP2C19 genotype dependence will be found in the anti-H. pylori therapy even when lansoprazole is used as the PPI.

Primary Levofloxacin Resistance and gyrA/B Mutations Among Helicobacter pylori in Japan

Background:  Recent years have witnessed a decrease in the rate of Helicobacter pylori eradication due to antimicrobial resistance, clarithromycin or metronidazole resistance in particular. As one of the alternatives to the standard regimens, levofloxacin‐containing therapy has been considered a promising regimen. Nevertheless, there is a little information concerning the prevalence of levofloxacin resistance and this resistance mechanism.

Recurrent Peptic Ulcers in Patients Following Successful Helicobacter pylori Eradication: A Multicenter Study of 4940 Patients

Objective.  Although curative treatment of Helicobacter pylori infection markedly reduces the relapse of peptic ulcers, the details of the ulcers that do recur is not well characterized. The aim of this study is to describe the recurrence rate and specific features of peptic ulcers after cure of H. pylori infection.