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Noboru Okamura

Publications and source records attributed to Noboru Okamura.

At least 19 recordsLinked to original sources
PubMed2006

Genetic polymorphisms associated with adverse events and elimination of methotrexate in childhood acute lymphoblastic leukemia and malignant lymphoma.

Methotrexate is administered in high doses to treat childhood acute lymphoblastic leukemia and malignant lymphoma. Hepatotoxicity and bone marrow suppression often limit its use, however. The objective of this study was to determine the genetic polymorphisms associated with the hepatotoxicity and elimination of methotrexate. Genetic polymorphisms of glutathione S-transferase (GST) genes including GSTT1 positive/null, GSTM1 positive/null, and GSTP1 A313G, and genes for reduced folate carrier 1 G80A (RFC1 G80A), methylenetetrahydrofolate reductase C677T (MTHFR C677T), and breast cancer resistant protein C421A (BCRP C421A) were determined for 26 patients by the polymerase chain reaction (PCR) method or by direct sequencing. A high frequency of hepatotoxicity (P = 0.035) was observed for patients with GSTM1 positive and RFC1 AA(80), and serum concentrations of methotrexate 48 h after the start of infusion were higher for patients with the TT(677) genotype of MTHFR (P = 0.028). In conclusion, GSTM1 positive/null and RFC1 G80A polymorphisms could be predictors for hepatotoxicity, and the MTHFR C677T polymorphism is associated with elimination of methotrexate.

Adolescent↗
PubMed2006

Prediction of systemic exposure to cyclosporine in Japanese pediatric patients.

The monitoring of the blood concentration at 2 h (C(2)) after the oral administration of a cyclosporine (CsA) microemulsion was reconfirmed to be useful for the prediction of systemic exposure, the area under the blood concentration-time curve from 0 to 4 h (AUC(0-4)), in a group of Japanese patients, consisting of 33 children aged 5-15 years and 19 young adults aged 16-27 years, with a greater correlation for C(2) (r = 0.927) than the trough concentration (r = 0.488). The dose-normalized AUC(0-4) was independent of gender or indications for CsA, while it depended on body size, i.e., the age (P = 0.065) and total body weight (P = 0.026). MDR1 C3435T had a weak, but insignificant effect (P = 0.072); it was about 22-31% lower in the patients with TT(3435). Co-administration of a steroid and further treatment with nifedipine had a more intensive effect (P = 0.018); co-administration resulted in a 51% increase in the dose-normalized AUC(0-4). A strong effect was also observed for the serum total cholesterol level (P = 0.001). Collectively, the discrepancies in the results on MDR1 C3435T among investigators might be due to variability in the age/total body weight, co-administration drugs or serum lipid level.

Administration, Oral↗
PubMed2006

Role of type II topoisomerase mutations and AcrAB efflux pump in fluoroquinolone-resistant clinical isolates of Proteus mirabilis.

OBJECTIVES: We conducted a study to determine the role played by amino acid mutations in DNA gyrase and topoisomerase IV, and the AcrAB efflux pump in resistance to fluoroquinolones in clinical isolates of Proteus mirabilis. METHODS: Nine clinical isolates of P. mirabilis containing eight fluoroquinolone-resistant isolates and one fluoroquinolone-susceptible isolate as the causative pathogen were collected from different patients with urinary tract infections. Fluoroquinolone resistance was characterized by PCR and DNA sequencing. The role of the AcrAB efflux pump was investigated by semi-quantifying the transcriptional expression of the acrB gene. RESULTS: Double mutations were found in GyrA, at S83I and E87K, and single mutations in GyrB (S464F) and ParC (S80I) in four isolates with ciprofloxacin MICs of 16 to >128 mg/L. In three isolates (ciprofloxacin MICs of >128 mg/L), the level of acrB expression was 2.1- to 3.2-fold higher than that in the wild-type control strain (ciprofloxacin MIC of < or =0.12 mg/L) and these isolates also had increased MICs of minocycline (>64 versus 8-16 mg/L) and chloramphenicol (>256 versus 4-8 mg/L) compared with the five other fluoroquinolone-resistant isolates. CONCLUSION: Our findings demonstrate that two mechanisms--mutations in GyrA (at S83I and E87K), GyrB and ParC, and overproduction of the AcrAB efflux pump--might synergistically contribute to a highest level of resistance to fluoroquinolones in clinical isolates of P. mirabilis.

Anti-Bacterial Agents↗
PubMed2006

Serum cystatin C levels to predict serum concentration of digoxin in Japanese patients.

Cystatin C (Cys-C) has been recently paid great attention as a better endogenous marker of the glomerular filtration rate than creatinine (Cr). In this study, the usefulness of Cys-C was compared with Cr in terms of the estimation of the steady-state serum trough concentrations of digoxin in Japanese patients. Forty patients treated with digoxin and 56 healthy elderly subjects were participated in this study. The serum levels of Cys-C and Cr in the patients were higher than those in the healthy elderly subjects, but the increase of Cys-C was more predominant in the patients. Their levels were well-correlated for both of the healthy elderly subjects (r=0.691) and patients (r=0.774), but the serum concentrations of digoxin were better correlated with those of the reciprocal values of Cr (r=0.667) than those of Cys-C (r=0.383), presumably due to the fact that digoxin and Cr were excreted via both glomerular filtration and tubular secretion. Cys-C is useful for the substratification of the patients diagnosed to have normal renal function with Cr of < 1.3 mg/dL into those with normal and pseudo-normal renal function, resulting in the corresponding serum concentrations of digoxin.

Journal Article↗
PubMed2006

Effects of acid and lactone forms of eight HMG-CoA reductase inhibitors on CYP-mediated metabolism and MDR1-mediated transport.

PURPOSE: With the growing clinical usage of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), the number of reports concerning serious drug-drug interaction has been increasing. Because recent studies have shown that conversion between acid and lactone forms occurs in the body, drug-drug interaction should be considered on both acid and lactone forms. Thus, we investigated the inhibitory effects of acid and lactone forms of eight statins, including one recently withdrawn, cerivastatin, and two recently developed, pitavastatin and rosuvastatin, on cytochrome P450 (CYP) 2C8, CYP2C9, and CYP3A4/5 metabolic activities and multidrug resistance protein 1 (MDR1) transporting activity. METHODS: The inhibitory effects of statins on CYP metabolic activities and MDR1 transporting activity were investigated using human liver microsomes and MDR1-overexpressing LLC-GA5-COL150 cells, respectively. RESULTS: The acid forms had minimal inhibitory effects on all CYP activities tested, except for fluvastatin on CYP2C9-mediated tolbutamide 4-hydroxylation (IC50 = 1.7 microM) and simvastatin on CYP3A4/5-mediated paclitaxel 3-hydroxylation (12.0 microM). Lactone forms showed no or minimal inhibitory effects on CYP2C8, CYP2C9, and CYP2C19 activities, except for rosuvastatin on the CYP2C9 activity (20.5 microM), whereas they showed stronger inhibitory effects on the CYP3A4/5 activity with the rank order of atorvastatin (5.6 microM), cerivastatin (8.1 microM), fluvastatin (14.9 microM), simvastatin (15.2 microM), rosuvastatin (20.7 microM), and lovastatin (24.1 microM). Pitavastatin and pravastatin had little inhibitory effect, and a similar order was found also for testosterone 6beta-hydroxylation. MDR1-mediated transport of [3H]digoxin was inhibited only by lactone forms, and the rank order correlated with that of inhibitory effects on both CYP3A4/5 activities. Inhibitory effects on MDR1 activity, and on both CYP3A4/5 activities, could be explained by the lipophilicity; however, a significant correlation was found between the lipophilicity and inhibitory effects on CYP2C8-mediated paclitaxel 6alpha-hydroxylation. CONCLUSIONS: We showed the difference between the acid and lactone forms in terms of drug interaction. The lipophilicity could be one of the important factors for inhibitory effects. In the case of statins, it is important to examine the effects of both forms to understand the events found in clinical settings, including the pleiotropic effects.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

Involvement of recognition and interaction of carnitine transporter in the decrease of L-carnitine concentration induced by pivalic acid and valproic acid.

PURPOSE: Prodrugs with pivalic acid and valproic acid decrease L-carnitine concentration in plasma and tissues by urinary excretion of acylcarnitine as pivaloylcarnitine (PC) and valproylcarnitine (VC), respectively. We investigated the role of the Na+/L-carnitine cotransporter in the porcine kidney epithelial cell line, LLC-PK1 for the decrease of L-carnitine concentration. METHODS: The uptake of L-[3H]carnitine, acetyl-L-[3H]carnitine (AC), L-[3H]PC and L-[3H]VC were investigated in LLC-PK1 cells seeded in a 6-well culture plate. RESULTS: L-Carnitine and AC uptake in LLC-PK1 cells exhibited Na+ dependency. The Km values for L-carnitine and AC uptake were 11.0 and 8.18 microM, respectively. These results indicated expression of Na+/ L-carnitine cotransporter in LLC-PK1 cells. PC and VC inhibited Na+/L-carnitine cotransporter in the competitive (Ki = 90.4 microM) and noncompetitive (Ki = 41.6 microM) manners, respectively. PC and VC uptake by Na+/L-carnitine cotransporter were not observed in LLC-PK1 cells. CONCLUSIONS: These data suggested that PC and VC formed in the body could not be reabsorbed in the kidney, resulting in the decrease of L-carnitine concentration. In addition, inhibition of L-carnitine reabsorption by VC with lower Ki value could induce the decrease of L-carnitine concentration. Collectively, the recognition and interaction of Na+/L-carnitine cotransporter are important factors for carnitine homeostasis.

Acetylcarnitine↗
PubMed2006

Typing of bfpA genes of enteropathogenic Escherichia coli isolated in Thailand and Japan by heteroduplex mobility assay.

We developed a rapid genetic approach for screening bfpA variants of enteropathogenic E. coli(EPEC) using a heteroduplex mobility assay (HMA). A total of 204 human EPEC strains were isolated in Thailand and Japan. Of 34 bfpA-positive EPEC strains, bfpA variants were classified into 5 HMA-types. Different HMA-types were found in EPEC of the same serotypes. The results suggest that HMA is a simple and easy method to analyze polymorphism of bfpA gene, and can be used in laboratories without large apparatus such as sequencers.

Base Sequence↗
PubMed2006

MDR1 T-129C polymorphism can be predictive of differentiation, and thereby prognosis of colorectal adenocarcinomas in Japanese.

The expression level of MDR1 mRNA was evaluated in colorectal adenocarcinomas and adjacent noncancerous colorectal tissues obtained from 21 Japanese patients. It was lower in the former than in the latter (p=0.012), suggesting its down-regulation as a consequence of malignant transformation of colorectal tissues, possibly with the suppression of differentiation. Relatively lower expression was suggested in moderately-differentiated colorectal adenocarcinomas than well-differentiated ones, but there was no statistical difference (p=0.111). MDR1 mRNA up-regulation was found in a colorectal adenocarcinoma cell line, HCT-15, after treatment with two typical differentiating agents, sodium butyrate and all-trans retinoic acid, suggesting its involvement in the cellular events, resulting in differentiation without malignant transformation. MDR1 T-129C, but not G2677A,T and C3435T, was associated with the lower expression of MDR1 mRNA both in colorectal adenocarcinomas (p=0.040) and adjacent noncancerous colorectal tissues (p=0.023), possibly being an useful invasive marker predicting poorly-differentiated colorectal adenocarcinomas and thereby the poor prognosis of the patients, especially when no extra biopsy samples will be obtained. Further investigations with relatively large number of patients should be undertaken to confirm these preliminary results.

Adenocarcinoma↗
PubMed2006

MDR1 C3435T polymorphism is predictive of later onset of ulcerative colitis in Japanese.

Recently, a silent polymorphism of C3435T of the MDR1 gene, encoding the multidrug resistant transporter MDR1/P-glycoprotein, has been found to be associated with susceptibility to ulcerative colitis (UC), but this remains controversial. This study was conducted to find a possible reason for the discrepancies, and it was suggested that the age of onset was important for the association, namely, C3435T was predictive of susceptibility to later onset UC, but not for early onset UC. Linkage disequilibrium of C3435T with T-129C, C1236T and G2677A, T was suggested to be altered in UC, but the analysis of their haplotype provided no advantage in terms of prediction over that with only C3435T. The effect of C3435T on susceptibility could not be explained by that on mRNA expression in rectal mucosa, but it was greater in the C(3435)-noncarriers in the early onset group, allowing the individualization of steroid-based pharmacotherapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

Comparison of synthetic DNA templates with authentic cDNA templates in terms of quantification by real-time quantitative reverse transcription polymerase chain reaction.

Synthetic DNA templates were compared with authentic cDNA templates as standards for the real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). The single-stranded DNA template used here targeted the multidrug resistant transporter P-glycoprotein/MDR1. The double-stranded DNA template, targeting glyceraldehyde-3-phosphate dehydrogenase (GAPDH), was synthesized using an exonuclease-free large fragment E. coli DNA polymerase I. The human colon carcinoma cell line Caco-2 and human duodenum biopsies were used to prepare the authentic cDNA templates. The standard lines were comparable for the synthetic DNA templates and authentic cDNA templates. Long-term cryopreservation at -80 degrees C resulted in the destabilization of the synthetic single-stranded DNA template compared with the authentic cDNA templates in the case of MDR1, whereas for GAPDH, the stability of the synthetic double-stranded DNA template was comparable with that of the authentic cDNA templates. Even for the synthetic DNA templates, repetitive freeze-thawing resulted in destabilization, especially at lower concentrations, and degradation products might have interfered with the RT-PCR's efficiency. The synthetic DNA templates are better than the authentic cDNA templates, but more than 5 cycles of repetitive freeze-thawing should be avoided.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

MDR1 haplotype frequencies in Japanese and Caucasian, and in Japanese patients with colorectal cancer and esophageal cancer.

The genotype frequencies of MDR1 T-129C, C1236T, G2677A,T and C3435T SNPs were compared in 154 healthy Japanese and 100 healthy Caucasians to provide basic information on the inter-ethnic differences of pharmacotherapeutic outcome. The variants were found at allelic frequencies of 5.5%, 65.6%, 16.6%, 40.6% and 40.6%, for T-129C, C1236T, G2677A, G2677T and C3435T, respectively, in Japanese, and at 5.1%, 45.9%, 3.6%, 46.4% and 56.6%, respectively, in Caucasians, with a statistically significant difference for C1236T, G2677A,T and C3435T (p<0.001). G2677A was about 5-fold more frequent in Japanese than Caucasians. These genotype frequencies were also investigated in 95 Japanese patients with colorectal cancer (CRC) and esophageal squamous cell carcinoma (ESCC), but no significant difference was detected, when compared with healthy Japanese subjects. The haplotype frequency reached a total of about 85% in Japanese with the following 4 major haplotypes; T(-129)-T1236-T2677-T3435 (36.1%), T(-129)-T1236-G2677-C3435 (22.5%), T(-129)-C1236-G2677-C3435 (14.2%) and T(-129)-C1236-A2677-C3435 (13.3%). The second and fourth haplotypes were hardly inferred in Caucasian, whereas T(-129)-C1236-G2677-T3435 (12.8%) was found to be Caucasian-specific. There was a tendency for higher frequencies of the T(-129)/C-(129)-C1236-A2677-C3435 haplotype in Japanese CRC patients and T(-129)-T1236-T2677-T3435 haplotype in Japanese ESCC patients, compared with that in healthy Japanese subjects.

Adult↗
PubMed2006

Genotype-dependent down-regulation of gene expression and function of MDR1 in human peripheral blood mononuclear cells under acute inflammation.

Recent advances in pharmacogenomics have suggested the association of clinical outcome of glucocorticoid-based anti-inflammatory therapy with a single nucleotide polymorphism at position 3435 in exon 26 (C3435T) of the MDR1 gene. In the present study, the effects of the MDR1 C3435T genotype on the time-dependent profiles of gene expression and function of MDR1/P-glycoprotein were evaluated in peripheral blood mononuclear cells (PBMCs) under lipopolysaccharide (LPS)-induced experimental acute inflammation. LPS treatment resulted in the rapid elevation of IL-1beta and TNF-alpha mRNA levels relative to beta-actin mRNA at 1 h, with a subsequent slight decrease at 3 h after the treatment, while the down-regulation of the relative concentration of MDR1 mRNA was found at 3 h, not at 1 h, after LPS treatment. Here, the C3435T genotype-dependent down-regulations of MDR1 mRNA level were found for CC(3435) and CT(3435), but not for TT(3435), and were 64.1+/-10.1%, 71.4+/-5.9% and 100.0+/-22.5% (+/-S.D.), respectively, of their respective baseline levels, which were independent of C3435T (0.010+/-0.005, 0.011+/-0.013 and 0.009+/-0.006 (+/-S.D.), respectively). The C3435T genotype-dependent down-regulation was supported by the increase of the intracellular accumulation of calcein in PBMCs treated with LPS for 72 h, and the increase was more predominant for CC(3435) than TT(3435). These data suggested that glucocorticoid-based anti-inflammatory therapy might be more effective for C(3435)-allele carriers than non-carriers.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

Effect of therapeutic moderate hypothermia on multi-drug resistance protein 1-mediated transepithelial transport of drugs.

To clarify the effect of therapeutic moderate hypothermia on drug distribution, transepithelial transport via multi-drug resistance protein 1 (MDR1) (also called P-glycoprotein or ABCB1) was evaluated at various temperatures in vitro using LLC-GA5-COL150 cells, which were established by transfecting human MDR1 complementary deoxyribonucleic acid into kidney epithelial LLC-PK(1) cells and express MDR1 on the apical membrane. MDR1 is expressed in the blood-brain barrier to limit drug distribution to the brain by exporting exogenous substances including calcium blockers and antiarrhythmic drugs. Digoxin was used as a typical substrate, as well as the non-substrate tetracycline and paracellular marker inulin. MDR1-mediated transport of digoxin decreased at lower temperatures. Transport of tetracycline also decreased at lower temperatures, probably due to changes in membrane fluidity. However, no change was found at over 32 degrees C, suggesting that passive diffusion does not change during moderate hypothermia. The distribution of MDR1 substrates should be considered during hypothermic conditions, as the clinical outcome could be affected.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

[Mutations of DNA gyrase and topoisomerase IV in clinical isolates of fluoroquinolone-resistant Proteus mirabilis].

The presence of fluoroquinolone resistance-associated mutations within the quinolone resistance-determining region of DNA gyrase and topoisomerase IV was investigated genetically in clinical isolates of Proteus mirabilis recovered from patients with urinay tract infections. Two isolates of fluoroquinolone-resistant P. mirabilis possessed the mutations in GyrA (Ser-83 --> Arg or Ile), GyrB (Ser-464 --> Tyr or Phe) and ParC (Ser-80 --> Ile). A novel mutation with Glu-87 --> Lys in GyrA, where suggested to be responsible for fluoroquinolone resistance, was identified. These results demonstrate that the presence of an additional mutation at Glu-87 in GyrA may contribute to high-level fluoroquinolone resistance, too.

DNA Gyrase↗
PubMed2005

EGFR mRNA is upregulated, but somatic mutations of the gene are hardly found in renal cell carcinoma in Japanese patients.

PURPOSE: Heterozygous somatic mutations of epidermal growth factor receptor (EGFR) in exons 18, 19, and 21 were recently reported to be associated with response to gefitinib in patients having nonsmall cell lung cancer. Such mutations are more frequently found among Japanese than Europeans. In this work, the frequency of mutations was investigated in renal cell carcinoma (RCC) samples obtained from Japanese subjects to examine the potential of gefitinib as a therapeutic agent for RCC. METHODS: Nineteen patients with RCC, who gave written informed consent, were enrolled in this study. mRNA expression levels of EGFR were measured in RCC and its adjacent noncancerous renal tissue via the real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. Somatic mutations were determined using genomic DNA extracted from RCC by direct sequencing method. RESULTS: mRNA expression was confirmed to be about 19 times higher in RCC than in adjacent noncancerous renal tissues, but no such mutations were detected in both. CONCLUSION: Results from this study do not support the validity of further clinical trials on gefitinib for RCC with genotyping even in Japanese patients, although EGFR plays a key role in tumor progression.

Carcinoma, Renal Cell↗
PubMed2005

Effects of an endothelin B receptor agonist on secretory phospholipase A2-IIA-induced apoptosis in cortical neurons.

Endothelin (ET), a vasoconstrictive peptide, acts as an anti-apoptotic factor, and endothelin receptor B (ETB receptor) is associated with neuronal survival in the brain. Human group IIA secretory phospholipase A2 (sPLA2-IIA) is expressed in the cerebral cortex after brain ischemia and causes neuronal cell death via apoptosis. In primary cultures of rat cortical neurons, we investigated the effects of an ETB receptor agonist, ET-3, on sPLA2-IIA-induced cell death. sPLA2-IIA caused neuronal cell death in a concentration- and time-dependent manner. ET-3 significantly prevented neurons from undergoing sPLA2-IIA-induced cell death. These agonists reversed sPLA2-IIA-induced apoptotic features such as the condensation of chromatin and the fragmentation of DNA. Before cell death, sPLA2-IIA potentiated the influx of Ca2+ into neurons. Blockers of the L-type voltage-dependent calcium channel (L-VSCC) not only suppressed the Ca2+ influx, but also exhibited neuroprotective effects. As well as L-VSCC blockers, ET-3 significantly prevented neurons from sPLA2-IIA-induced Ca2+ influx. An ETB receptor antagonist, BQ788, inhibited the effects of ET-3. The present cortical cultures contained few non-neuronal cells, indicating that the ETB receptor agonist affected the survival of neurons directly, but not indirectly via non-neuronal cells. In conclusion, we demonstrate that the ETB receptor agonist rescues cortical neurons from sPLA2-IIA-induced apoptosis. Furthermore, the present study suggests that the inhibition of L-VSCC contributes to the neuroprotective effects of the ETB receptor agonist.

Animals↗
PubMed2005

Assessment of the hepatic and intestinal first-pass metabolism of midazolam in a CYP3A drug-drug interaction model rats.

In the current study, to understand the characteristics of dexamethasone (DEX)-treated female rats as an animal model for drug-drug interactions, a double-cannulation method was applied and separately assessed for the intestinal and hepatic first-pass metabolism of midazolam. Midazolam was administered intravenously or orally to the animals, and midazolam concentrations in the portal and systemic plasma were simultaneously determined. Next, the rates of elimination from the intestine and liver were estimated using the AUC values. After oral administration of midazolam, the entire drug was absorbed without intestinal first-pass metabolism, and 93% of the administered midazolam was extracted in the liver of the DEX-treated female rats. Seven per cent of the midazolam administered reached the systemic circulation. When ketoconazole was given orally to the animals, in conjunction with midazolam, the extraction ratio in the liver decreased from 93% to 77% in the control rats, and the bioavailability of midazolam increased to 23%. On the other hand, after intravenous administration, the elimination half-life of midazolam was not changed by ketoconazole pretreatment. These results indicated that midazolam is only extracted in the liver of DEX-treated female rats and that ketoconazole inhibits the hepatic first-pass metabolism, but not the systemic metabolism. In conclusion, DEX-treated female rats can be used as a drug-drug interaction model via CYP3A4 enzyme inhibition, especially for the hepatic first-pass metabolism of orally administered drugs.

Animals↗