Hikaru Yabuuchi

Kobe University, Kōbe, Hyōgo, Japan

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Publications (48)157.88 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel fluorescent bile acid derivative, 4-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole- conjugated bile acid was synthesized as a probe to develop a rapid screening method for function analysis of bile salt export pump (BSEP, ABCB 11). The transport properties of the synthetic fluorescent bile acid derivative in membrane vesicles obtained from hBSEP-expressing Sf9 cells were examined using the liquid chromatography-electrospray ionization-mass spectrometry method. The Michaelis-Menten constant and maximum uptake rate for the synthetic fluorescent bile acid derivative by hBSEP were 23.1+/-1.6 microM and 623.2+/-22.4 pmol/min/mg protein, respectively. These kinetic parameters of the synthetic fluorescent bile acid derivative were comparable with those of an unlabeled bile acid, taurocholic acid. Moreover, we examined inhibitory effects of various drugs on hBSEP-mediated uptake of the fluorescent bile acid derivative using a fluorescence detection method. The relative uptake activities (percent of control) for the fluorescent bile acid derivative in the presence of an inhibitor were in accordance with previous findings using (3)H-labeled taurocholic acid. Our results suggest that the synthetic fluorescent bile acid derivative may be useful for evaluation of the inhibitory effects of various drugs on hBSEP-mediated uptake.
    Drug Metabolism and Pharmacokinetics 12/2010; 25(2):214-9. DOI:10.2133/dmpk.25.214 · 2.57 Impact Factor
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    ABSTRACT: N-[6-[2-[(5-Bromo-2-pyrimidinyl)oxy]ethoxy]-5-(4-methylphenyl)-4-pyrimidinyl]-4-(2-hydroxy-1,1-dimethylethyl) benzenesulfonamide sodium salt (TA-0201) carboxylic acid form (TA-0201CA) is the primary and pharmacologically active metabolite of TA-0201, which is an orally active nonpeptide antagonist for endothelin receptors. A major elimination route of TA-0201CA in rats was biliary excretion. The aim of this study was to clarify the transporters responsible for the hepatobiliary transport of TA-0201CA by in vivo pharmacokinetic study and in vitro study using sandwich-cultured rat hepatocytes (SCRH) from normal rats [Sprague-Dawley rats (SDR)] and Eisai hyperbilirubinemic rats (EHBR). After intravenous administration, TA-0201CA was extensively excreted into bile with a high biliary clearance in SDR. In contrast, the biliary clearance in EHBR was lower than that in SDR. These results indicated that multidrug resistance-associated protein 2 (Mrp2) was partly involved in the biliary excretion of TA-0201CA. In SCRH, the hepatic uptake of TA-0201CA was significantly decreased by the presence of organic anion-transporting polypeptide (Oatp) substrates/inhibitors and a Na(+)-free condition, which is a driving force of the Na(+)-taurocholate cotransporting polypeptide (Ntcp). The canalicular secretion of TA-0201CA was inhibited by the bile salt export pump (Bsep) inhibitor glibenclamide and by the Mrp2 inhibitor 3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid (MK-571) in SCRH from SDR and EHBR. These results suggested that TA-0201CA was transported into hepatocytes via Oatps and Ntcp and excreted into bile via Mrp2 and Bsep in rats.
    Drug metabolism and disposition: the biological fate of chemicals 08/2010; 38(9):1505-1513. DOI:10.1124/dmd.110.033258 · 3.25 Impact Factor
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    ABSTRACT: Monovalent bile acids, such as taurine- and glycine-conjugated bile acids, are excreted into bile by bile salt export pumps (BSEP, ABCB11). Human BSEP (hBSEP) is physiologically important because it was identified as the gene responsible for the genetic disease: progressive familial intrahepatic cholestasis type 2 (PFIC-2). The evaluation of the inhibitory effect of hBSEP transport activity provides significant information for predicting toxic potential in the early phase of drug development. The role and function of hBSEP have been investigated by the examination of the ATP-dependent transport of radioactive isotopically (RI)-labeled bile acid such as a tritium labeled taurocholic acid, in membrane vesicles obtained from hBSEP-expressing cells. The chemiluminescence detection method using 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) had been developed for a simple analysis of bile acids in human biological fluids. This method is extremely sensitive and it may be applicable for the measurements of bile acid transport activities by hBSEP vesicles without using RI-labeled bile acid. The present paper deals with an application of the chemiluminescence detection method using 3alpha-HSD with enzyme cycling method to the measurement of ATP-dependent transport activities of taurocholic acid (T-CA) in membrane vesicles obtained from hBSEP-expressing Sf9 cells. Calibration curves for T-CA was linear over the range from 10 to 400 pmol/ml. The values of the kinetic parameters for hBSEP vesicles obtained by the chemiluminescence detection method were comparable with the values of that obtained by liquid chromatography-mass spectrometry method. This assay method was highly useful for the measurements of bile acid transport activities.
    Yakugaku zasshi journal of the Pharmaceutical Society of Japan 05/2010; 130(5):755-61. DOI:10.1248/yakushi.130.755 · 0.26 Impact Factor
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    ABSTRACT: Abscisic acid (ABA) is one of the most important phytohormones involved in abiotic stress responses, seed maturation, germination, and senescence. ABA is predominantly produced in vascular tissues and exerts hormonal responses in various cells, including guard cells. Although ABA responses require extrusion of ABA from ABA-producing cells in an intercellular ABA signaling pathway, the transport mechanisms of ABA through the plasma membrane remain unknown. Here we isolated an ATP-binding cassette (ABC) transporter gene, AtABCG25, from Arabidopsis by genetically screening for ABA sensitivity. AtABCG25 was expressed mainly in vascular tissues. The fluorescent protein-fused AtABCG25 was localized at the plasma membrane in plant cells. In membrane vesicles derived from AtABCG25-expressing insect cells, AtABCG25 exhibited ATP-dependent ABA transport. The AtABCG25-overexpressing plants showed higher leaf temperatures, implying an influence on stomatal regulation. These results strongly suggest that AtABCG25 is an exporter of ABA and is involved in the intercellular ABA signaling pathway. The presence of the ABA transport mechanism sheds light on the active control of multicellular ABA responses to environmental stresses among plant cells.
    Proceedings of the National Academy of Sciences 02/2010; 107(5):2361-6. DOI:10.1073/pnas.0912516107 · 9.67 Impact Factor
  • Kana Yamaguchi · Tsuyoshi Murai · Hikaru Yabuuchi · Takao Kurosawa
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    ABSTRACT: A method has been developed for the measurement of transport activities in membrane vesicles obtained from human multidrug resistance-associated protein 3-expressing Sf9 cells for 1beta-hydroxy-, 6alpha-hydroxy- and unsaturated bile acids by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Calibration curves for the bile acids were linear over the range of 10 to 2000 pmol/mL, and the detection limit was less than 2 pmol/mL for all bile acids using selected reaction monitoring analysis. The method was applied to measurements of adenosine triphosphate-dependent transport activities of the membrane vesicles for the above-mentioned hydroxylated and unsaturated bile acids. The present study demonstrated that the human multidrug resistance-associated protein 3 vesicles accepted 1beta-, 6alpha-hydroxylated and unsaturated bile acids along with common bile acids, such as glycocholic acid and taurolithocholic acid 3-sulfate. The developed method is useful for measurements of bile acid transport activities.
    Analytical Sciences 01/2010; 26(3):317-23. DOI:10.2116/analsci.26.317 · 1.39 Impact Factor
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    ABSTRACT: Hypertension in patients with chronic kidney disease (CKD) strongly associates with cardiovascular events. Among patients with CKD, reducing the accumulation of uremic toxins may protect against the development of hypertension and progression of renal damage, but there are no established therapies to accomplish this. Here, overexpression of human kidney-specific organic anion transporter SLCO4C1 in rat kidney reduced hypertension, cardiomegaly, and inflammation in the setting of renal failure. In addition, SLCO4C1 overexpression decreased plasma levels of the uremic toxins guanidino succinate, asymmetric dimethylarginine, and the newly identified trans-aconitate. We found that xenobiotic responsive element core motifs regulate SLCO4C1 transcription, and various statins, which act as inducers of nuclear aryl hydrocarbon receptors, upregulate SLCO4C1 transcription. Pravastatin, which is cardioprotective, increased the clearance of asymmetric dimethylarginine and trans-aconitate in renal failure. These data suggest that drugs that upregulate SLCO4C1 may have therapeutic potential for patients with CKD.
    Journal of the American Society of Nephrology 10/2009; 20(12):2546-55. DOI:10.1681/ASN.2009070696 · 9.34 Impact Factor
  • Kana Yamaguchi · Tsuyoshi Murai · Hikaru Yabuuchi · Takao Kurosawa
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    ABSTRACT: The high performance liquid chromatography-electrospray ionization-mass spectrometry method has been applied to the measurement of bile acid transport activities in membrane vesicles obtained from a human bile salt export pump expressing Sf9 cells. The amounts of bile acids transported using the human bile salt export pump expressing Sf9 cells were determined using liquid chromatography-electrospray ionization-mass spectrometry method and the values of the kinetic parameters were determined to be comparable with those obtained using radioisotope-labeled substrates. The developed method was highly useful for the measurements of bile acid transport activities.
    Analytical Sciences 10/2009; 25(9):1155-8. DOI:10.2116/analsci.25.1155 · 1.39 Impact Factor
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    ABSTRACT: Oseltamivir, an ester-type prodrug of the neuraminidase inhibitor [3R,4R,5S]-4-acetamido-5-amino-3-(1-ethylpropoxy)-1-cyclohexene-1-carboxylate phosphate (Ro 64-0802), has been developed for the treatment of A and B strains of the influenza virus but has neuropsychiatric and other side effects. In this study, we characterized the transport across intestinal epithelial cells and the absorption of oseltamivir in rats. Uptake by Caco-2 cells (human carcinoma cell line) and HeLa cells transfected with peptide transporter 1 (HeLa/PEPT1) was time- and temperature-dependent and was inhibited by typical PEPT1 inhibitors such as glycyl-sarcosine (Gly-Sar). The uptake by Caco-2 cells and HeLa/PEPT1 was saturable, with similar K(m) values. Oseltamivir absorption in adult rats was greatly reduced by simultaneous administration of milk, casein, or Gly-Sar. Furthermore, the plasma and brain concentrations of oseltamivir were higher in fasting than in nonfasting rats after oral administration. These results suggest that oseltamivir is a substrate of PEPT1 and that PEPT1 is involved in its intestinal absorption.
    Drug metabolism and disposition: the biological fate of chemicals 06/2009; 37(8):1676-81. DOI:10.1124/dmd.109.026922 · 3.25 Impact Factor
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    ABSTRACT: The dog bile salt export pump (BSEP; ABCB11) was cloned and expressed in a Sf9 insect cell system. The deduced amino acid sequence encodes a 1325-amino-acid protein, which shows 89.4% and 80.2% homology with human BSEP and rat Bsep, respectively. The transcript of the dog Bsep gene was detected at a high level in liver, but not other tissues, by quantitative RT-PCR. The BSEP-expressing membrane vesicles isolated from Sf9 cells exhibited saturable uptake of [(3)H]taurocholic acid with Michaelis constants (K(m)) of 33.7, 22.2 and 19.9 microM for the dog, rat and human transporters, respectively. The uptake of [(3)H]taurocholic acid by all three transporters was significantly inhibited by troglitazone, glibenclamide, and other several inhibitors, while pravastatin inhibited dog Bsep and human BSEP, but not rat Bsep at 100 microM. The IC(50) of troglitazone for dog Bsep, human BSEP, and rat Bsep were 32, 20, and 60 microM, and those of pravastatin were 441, 240 and >1,000 microM, respectively. In conclusion, while dog Bsep shows similar ATP-dependent bile acid transport characteristics to human BSEP and rat Bsep, there is a species difference in affinity for drugs such as pravastatin and troglitazone.
    Biopharmaceutics & Drug Disposition 11/2008; 29(8):441-8. DOI:10.1002/bdd.629 · 2.34 Impact Factor
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    ABSTRACT: The monkey is an important experimental model in the pharmacological evaluation of new drugs. We isolated monkey multidrug resistance-associated protein 2 (MRP2) cDNA to examine expression profiles among various tissues and measured ATPase activity to assess substrate specificity. The amino acid sequence encoded by monkey MRP2 cDNA was very similar (96% identity) to the reported human MRP2 cDNA (GenBank accession no. NM_000392). The tissue distribution of MRP2 in monkeys was partially different from that in humans. We found relatively high expression of MRP2 in the monkey kidney and small intestine using Northern blotting. Substrate specificity was compared between human and monkey MRP2. The affinity of 17beta-estradiol 17-(beta-d-glucuronide), methotrexate, vinblastine, and probenecid to monkey MRP2 was higher than that to human MRP2. Functional and expression differences between human and monkey MRP2 should be incorporated into the evaluation of candidate drugs.
    European Journal of Pharmaceutical Sciences 09/2008; 35(4):326-34. DOI:10.1016/j.ejps.2008.08.001 · 3.35 Impact Factor
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    ABSTRACT: It has been reported that organic cation/carnitine transporter 1 (OCTN1) is associated with rheumatoid arthritis and Crohn's disease. Additionally, we reported that OCTN1 is expressed in hematopoietic cells, and is associated with proliferation and differentiation of erythroid cells. However, physiological role of OCTN1 is still unclear. Ergothioneine, an anti-oxidant, was recently reported to be a good substrate of human OCTN1. However, the transport characteristics of ergothioneine in rat remains to be clarified. The present study, is to further investigate the role of rat Octn1 on transport of ergothioneine in rat Octn1 transfected cells and natively expressing cell line PC12 derived from rat adrenal pheochromocytoma. [(3)H]Ergothioneine uptake by rat Octn1 stably transfected HEK293 cells was saturable, sodium dependent with 1 : 1 stoichiometry of ergothioneine, and pH dependent. Since ergothioneine was reported to presumably play a protective role against oxidative stress-induced apoptosis in PC12 cells, its transport in this cell line was investigated. The expression of rat Octn1 and a saturable and Na(+)-dependent transport of ergothioneine were observed in PC12 cells, suggesting that ergothioneine transport in this cell line may be mediated by rat Octn1. These findings suggested that rat Octn1 may act as a survival factor by taking up ergothioneine to suppress oxidative stress in this cell line. In conclusion, functional characteristics of ergothioneine transport by rat Octn1 is similar to that of human OCTN1 and it is suggested that rat Octn1 is important by transporting anti-oxidant ergothioneine in PC12 cells, though its role in vivo is to be investigated.
    Biological & Pharmaceutical Bulletin 09/2008; 31(8):1580-4. DOI:10.1248/bpb.31.1580 · 1.83 Impact Factor
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    ABSTRACT: Intestinal membrane permeability is an important factor affecting the bioavailability of drugs. As a strategy to improve membrane permeability, membrane transporters are useful targets since essential nutrients are absorbed efficiently via specific transporters. For example, there are reports that intestinal hexose transporters could be used as a tool to improve permeability; however, there has been no direct evidence that the transporter protein, sodium/glucose cotransporter 1 (SGLT1), is involved in the transport of hexose analogs. Accordingly, we examined directly whether the intestinal membrane permeability of hexose analogs can be improved by utilizing SGLT1. Three hexose-quinoline derivatives were synthesized and their interactions with SGLT1 were evaluated. Among the three derivatives, the glucose-quinoline molecule exhibited an inhibitory effect on D-glucose uptake by both rat intestinal brush-border membrane vesicles (BBMVs) and Xenopus oocytes expressing SGLT1. In addition, significant uptake of the glucose-quinoline derivative by Xenopus oocytes expressing SGLT1 was observed by both an electrophysiological assay and direct measurement of the uptake of the compound, while the galactose-quinoline derivative did not show significant uptake via SGLT1. Thus, it was directly demonstrated that SGLT1 could be used as a tool for the improvement of intestinal membrane permeability of drugs by modification to the glucose analogs.
    Journal of Pharmaceutical Sciences 05/2008; 97(5):1821-30. DOI:10.1002/jps.21147 · 2.59 Impact Factor
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    ABSTRACT: To identify the rat hepatic basolateral transporters involved in the hepatic uptake of beta-lactam antibiotics using nafcillin as a model beta-lactam antibiotic that undergoes extensive biliary excretion. Uptake by isolated rat hepatocytes and Xenopus laevis oocytes expressing organic anion transporting peptides (Oatp1, 2, and 4) and organic anion transporter (OAT2) was evaluated. Nafcillin uptake by isolated rat hepatocytes was saturable with the Km of 210 microM and was significantly inhibited by anionic compounds (estrone-3-sulfate and sulfobromophthalein), but not by cationic compounds (tetraethylammonium and 1-methyl-4-phenylpyridinium). In an in vitro uptake study by Xenopus oocytes expressing hepatic basolateral membrane transporters, nafcillin was transported by multiple Oatps with Km values of 4120 microM (Oatp1/Oatp1a1), 198 microM (Oatp2/Oatp1a4), and 1,570 microM (Oatp4/Oatp1b2), though it was not transported by hOAT2. Comparison of affinity and analysis by the relative activity factor method indicated that Oatp2 is the predominant contributor to the hepatic uptake of nafcillin. Cefadroxil, cefazolin, cefmetazole, cefoperazone, cefsulodin, and cephalexin, though not cefotaxime or ceftriaxone, were also substrates of Oatp2. These findings suggest that Oatp2 plays a key role in the hepatic uptake of nafcillin and most other beta-lactam antibiotics in rats.
    Pharmaceutical Research 04/2008; 25(3):578-85. DOI:10.1007/s11095-007-9427-9 · 3.42 Impact Factor
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    ABSTRACT: To examine the mechanisms of the alteration of serum uric acid level by angiotensin II receptor blockers (ARBs), the effects of ARBs on renal uric acid transporters, including OAT1, OAT3, OAT4, and MRP4, were evaluated. Uptakes of uric acid by OAT1-expressing Flp293 cells, by Xenopus oocytes expressing OAT3 or OAT4, and by membrane vesicles from Sf9 cells expressing MRP4 were evaluated in the presence or absence of ARBs. All ARBs inhibited uptake of uric acid or estrone-3-sulfate by OAT1, OAT3 and OAT4 in concentration dependent manners. Among them, the IC50 values of valsartan, olmesartan and pratosartan for OAT3 were comparable to clinically observed unbound maximum plasma concentration of ARBs. Candesartan, losartan, and telmisartan inhibited ATP-dependent uptake of uric acid by MRP4 at 10 microM. The IC50 value of losartan for MRP4 was comparable to the estimated kidney tissue concentration of losartan. No ARBs showed trans-stimulatory effects on the uptake of estrone-3-sulfate by OAT4. Valsartan, olmesartan, and pratosartan could inhibit the OAT3-mediated uric acid secretion in clinical situations. Furthermore losartan could inhibit ATP-dependent uric acid secretion by MRP4. These effects may explain partially the alteration of serum uric acid level by ARBs.
    Pharmaceutical Research 04/2008; 25(3):639-46. DOI:10.1007/s11095-007-9401-6 · 3.42 Impact Factor
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    ABSTRACT: In the present study, we attempted to identify the membrane permeation process(es) primarily involved in the molecular-weight-dependent biliary excretion of beta-lactam antibiotics. A search of the literature indicated that the molecular weight threshold operates mainly in the transport process across bile canalicular membranes. We confirmed that biliary clearance of the model biliary-excretion-type cephalosporin cefoperazone was reduced to 10% of the control in Eisai hyperbilirubinemic rats, which are genetically deficient in multidrug resistance-associated protein (Mrp) 2, indicating that Mrp2 plays a major role as an efflux transporter on the canalicular membranes. ATP-dependent uptake of several cephalosporins including cefoperazone, cefbuperazone, cefpiramide, and ceftriaxone, all of which are mainly excreted into bile, was confirmed in membrane vesicles from Sf9 cells transfected with rat Mrp2. Both the inhibitory potency of the cephalosporins for Mrp2-mediated transport and the uptake of cephalosporins by Mrp2-expressing vesicles were molecular weight-dependent, suggesting that Mrp2 is one of the major transporters involved in molecular weight-dependent biliary excretion. An uptake study in membrane vesicles of Sf9 cells transfected with breast cancer resistance protein (Bcrp) revealed that Bcrp accepts cefoperazone, cefbuperazone, cefpiramide, cefotetan, ceftriaxone, cefotiam, cefamandole, and cefazolin as substrates, and Bcrp-mediated transport was also molecular weight-dependent, suggesting that Bcrp also contributes to molecular weight-dependent biliary excretion of beta-lactam antibiotics in rats.
    Drug metabolism and disposition: the biological fate of chemicals 03/2008; 36(6):1088-1096. DOI:10.1124/dmd.107.019125 · 3.25 Impact Factor
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    ABSTRACT: Recently, it was reported that OCTN1 transporter (SLC22A4) is associated with rheumatoid arthritis (RA) and Crohn's disease. Additionally, we reported that OCTN1 is expressed in hematopoietic cells, preferentially in erythroid cells. Accordingly, we assessed the physiological role of OCTN1 by examining the effect of knockdown of OCTN1 in blood cells using siRNA method. Vector-based short hairpin RNA (shRNA) was used to establish K562 cell line which shows stably decreased expression of OCTN1. The characteristic of knockdown of OCTN1 in K562 cells was investigated by cell proliferation, cell differentiation, and uptake of ergothioneine that is a good substrate of OCTN1. Several clones of K562 cells exhibited significantly reduced expression of OCTN1 mRNA and protein. They also showed a decreased growth rate and butyrate-dependent differentiation to erythrocytes compared with control-vector transfected cells. In addition, uptake of [(3)H]ergothioneine by K562 cells suggested that Na(+)-dependent and high-affinity transporter which is similar to the characteristics of OCTN1 is functional. Moreover, uptake of ergothioneine by K562 cells which exhibit decreased-expression of OCTN1 was decreased in comparison with wild type K562 cells. It was suggested that OCTN1 is involved in the transport of physiological compounds that are important for cell proliferation and erythroid differentiation.
    Pharmaceutical Research 10/2007; 24(9):1628-35. DOI:10.1007/s11095-007-9290-8 · 3.42 Impact Factor
  • Mika Sugiura · Masato Nagaoka · Hikaru Yabuuchi · Toshihiro Akaike
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    ABSTRACT: Embryonic stem (ES) cell differentiation is regulated by cytokines and growth factors, as well as small-compound chemicals incorporated into cells by transporter proteins. Little is known regarding the effect of transporters on ES cell differentiation. This study focused on the effect of transporters during the neural-lineage differentiation of ES cells. Among the 27 types of SLC family transporters, MCT8 expression was coincident with that of neural stem cell markers, and the overexpression of MCT8 accelerated the differentiation into neural cells. These results suggested that the transporters and their substrates also play a crucial role in the regulation of ES cell differentiation.
    Biochemical and Biophysical Research Communications 10/2007; 360(4):741-5. DOI:10.1016/j.bbrc.2007.06.109 · 2.30 Impact Factor
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    ABSTRACT: The liver of a chimeric urokinase-type plasminogen activator (uPA)(+/+)/severe combined immunodeficient (SCID) mouse line recently established in Japan could be replaced by more than 80% with human hepatocytes. We previously reported that the chimeric mice with humanized liver could be useful as a human model in studies on drug metabolism and pharmacokinetics. In the present study, the humanization of an excretory pathway was investigated in the chimeric mice. Cefmetazole (CMZ) was used as a probe drug. The CMZ excretions in urine and feces were 81.0 and 5.9% of the dose, respectively, in chimeric mice and were 23.7 and 59.4% of the dose, respectively, in control uPA(-/-)/SCID mice. Because CMZ is mainly excreted in urine in humans, the excretory profile of chimeric mice was demonstrated to be similar to that of humans. In the chimeric mice, the hepatic mRNA expression of human drug transporters could be quantified. On the other hand, the hepatic mRNA expression of mouse drug transporters in the chimeric mice was significantly lower than in the control uPA(-/-)/SCID mice. In conclusion, chimeric mice exhibited a humanized profile of drug excretion, suggesting that this chimeric mouse line would be a useful animal model in excretory studies.
    Toxicological Sciences 07/2007; 97(2):533-8. DOI:10.1093/toxsci/kfm041 · 3.85 Impact Factor
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    ABSTRACT: The non-steroidal antiandrogen flutamide is widely used for treatment of prostatic cancer, but causes side effects, including cholestatic hepatitis and fulminant hepatitis. We investigated the pathogenesis of flutamide-induced cholestatic hepatitis, focusing on the bile salt export pump (BSEP; ABCB11), which exports bile salts to the bile. We examined the inhibitory effects of flutamide and its active metabolite, hydroxyflutamide, on the transport of taurocholic acid (TCA) by membrane vesicles derived from hBSEP-expressing Sf9 cells. Flutamide inhibited the transport of TCA by hBSEP (IC50 value, about 50 microM), while hydroxyflutamide had no effect at up to 100 microM. When flutamide was administered to rats as a single oral dose of 100 mg/kg, the biliary excretion rate of bolus-injected [3H]TCA was decreased and the liver tissue concentration of flutamide exceeded 50 microM. Repeated doses of flutamide for 5 d (10 mg/kg/d) also decreased the biliary excretion rate of bolus-injected [3H]TCA. In this case, the liver tissue concentration of flutamide was below 0.1 microM. In both cases, no change in the mRNA level of rat Bsep was detected by RT-PCR. These results suggest that flutamide itself, but not its major metabolite, may cause cholestasis by inhibiting BSEP-mediated bile salt excretion.
    Biological & Pharmaceutical Bulletin 05/2007; 30(4):739-44. DOI:10.1248/bpb.30.739 · 1.83 Impact Factor
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    ABSTRACT: Breast cancer resistance protein (BCRP) confers resistance against topoisomerase I inhibitors in cancer cells. Very recently, we reported that gefitinib reverses BCRP-mediated drug resistance by direct inhibition. However, it remains undetermined how much BCRP contributes to the resistance to topoisomerase I inhibitors in non-small cell lung cancer (NSCLC). The present study was designed to examine whether BCRP levels in NSCLC cells are correlated with the resistance to topoisomerase I inhibitors and the reversal effect by gefitinib. BCRP levels and its function were evaluated by Western blotting and flowcytometry, respectively. Gefitinib-insensitive NSCLC cells expressed various levels of BCRP, which were closely correlated not only with the IC50 values of SN-38 (r=0.874, P<0.05) and those of topotecan (r=0.968, P<0.001), but also with the reversal effects of 1 microM gefitinib on SN-38 resistance (r=0.956, P<0.001) and topotecan resistance (r=0.977, P=0.0001). BCRP levels accounted for between 80 and 90% of the variation in the resistance to topoisomerase I inhibitors and the reversal effects by gefitinib. Also, gefitinib increased intracellular topotecan accumulation in proportion to the BCRP levels. These findings suggest that BCRP is the most important molecule responsible for topoisomerase I inhibitor resistance, and that the development of BCRP inhibitors is an effective approach for overcoming this resistance. In addition, the examination of BCRP levels in NSCLC tissues may identify an optimal patient population for treatment with topoisomerase I inhibitors alone or in combination with BCRP inhibitors.
    Cancer Chemotherapy and Pharmacology 11/2006; 58(5):594-600. DOI:10.1007/s00280-006-0212-y · 2.77 Impact Factor

Publication Stats

3k Citations
157.88 Total Impact Points


  • 2010
    • Kobe University
      • Center for Collaborative Research and Technology Development (CREATE)
      Kōbe, Hyōgo, Japan
    • Health Sciences University of Hokkaido
      • Division of Pharmaceutical Sciences
      Tōbetsu, Hokkaido, Japan
  • 2007
    • Yokohama Rubber Co. Ltd.
      Yokohama, Kanagawa, Japan
  • 2005
    • Tokyo University of Science
      • Department of Pharmaceutical Sciences
      Edo, Tōkyō, Japan
  • 2001–2003
    • Tokyo Institute of Technology
      • Department of Biomolecular Engineering
      Edo, Tōkyō, Japan
  • 1997–2000
    • Kanazawa University
      • Graduate School of Natural Science and Technology
      Kanazawa, Ishikawa, Japan