Makoto Chiba

Hokkaido University, Sapporo-shi, Hokkaido, Japan

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Publications (11)25.81 Total impact

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    ABSTRACT: Various mechanisms can influence the intestinal absorption and oral bioavailability of drugs. The barrier effects of efflux transporters may be one of the critical factors limiting the bioavailability of certain drugs. It has been reported that multidrug resistance-associated protein 2 (Mrp2) is expressed in the mucosal membrane of the epithelium of the small intestine and secretes various drugs into the jejunum lumen. However, it is possible that total intestinal secretion of Mrp2 substrates is accounted for the contribution of Mrp2 and other transporter(s) to the intestinal secretion of Mrp2 substrates. In this study, we found that phenolsulfonphthalein and pravastatin, both Mrp2 substrates, are transported by different transport systems in the intestine. These results suggest that contribution of transporters to the drug transport may be a critical factor affecting drug disposition and drug-drug interaction. In addition to evaluating the substrate specificity of a transporter, it is important to be aware of the contribution of a transporter to drug disposition.
    Biological & Pharmaceutical Bulletin 02/2008; 31(1):146-8. · 1.85 Impact Factor
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    ABSTRACT: It has been reported that the transport function for organic anions on the kidney is maintained in multidrug resistance-associated protein 2 (Mrp2)-deficient rats. Different from Mrp2-deficient rats, Long-Evans Cinnamon (LEC) rats have impaired urinary excretion of Mrp2-substrate, phenolsulfonphthalein (PSP). PSP is transported by the potential-sensitive urate transport system in rat brush-border membranes. We analyzed the function of PSP transport system in LEC rats. Unlike Long-Evans Agouti (LEA) rats, the initial uptake of PSP and urate into the renal brush-border membrane vesicles of LEC rats were not significantly enhanced in the presence of positive intravesicular potential, suggesting that the potential-sensitive urate transport system is impaired in LEC rats. LEC rats should be useful for elucidating the potential-sensitive urate transport system in rats at the molecular level.
    Biochimica et Biophysica Acta 02/2008; 1778(1):270-5. · 4.66 Impact Factor
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    ABSTRACT: Wilson's disease is an inherited, autosomal recessive disorder of copper accumulation and toxicity. Lifelong chelation therapy is essential in all Wilson's disease patients. Intestinal absorption of some compounds is limited partly because they are preferentially transported in the secretory direction. Several ATP-binding cassette (ABC) transporters are expressed in the apical membrane of the small intestine and secrete various drugs into the lumen. In this study, we investigated the characteristics of the intestinal efflux ABC transporters in LEC rats. We found that the expression of multidrug resistance-associated protein 2 (Mrp2) in the jejunum of Long-Evans Cinnamon (LEC) rats, an animal model for Wilson's disease, is decreased.
    Drug Metabolism and Pharmacokinetics 01/2008; 22(6):450-5. · 2.07 Impact Factor
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    ABSTRACT: The liver plays important roles in the detoxification of xenobiotics. Hepatobiliary transporters contribute to hepatic uptake and efflux processes of xenobiotecs. Expressions of these transporters may be modulated under the condition of hepatic failure. Long-Evans Cinnamon (LEC) rats provide a pertinent model for basic and clinical studies on hepatitis. However, only a few reports describing the properties of hepatobiliary transporters in LEC rats have appeared in the literature. We investigated the expression levels of hepatobiliary transporters in LEC rats by real-time RT-PCR. We found that hepatic expressions of three sinusoidal organic anion transporters, Ntcp, Oatp1a1 and Oatp1a4, were decreased in LEC rats. However, no significant difference of the expressions of Mrp2 and Bsep, organic anion transporters located on canalicular membrane, were found between Wistar rats and LEC rats.
    Drug Metabolism and Pharmacokinetics 11/2007; 22(5):387-90. · 2.07 Impact Factor
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    ABSTRACT: It has been reported that a significant portion of the lactone form of 7-ethyl-10-(4-[1-piperidino]-1-piperidino)-carbonyloxy-camptothecin (CPT-11) is excreted into the gastrointestinal lumen via the intestinal membrane and that carboxylesterase activity, which converts CPT-11 to SN-38, was detected in the intestine. It is possible that a reduction in the excretion of CPT-11 lactone into the gastrointestinal lumen induces the gastrointestinal toxicity. The purpose of this study was to investigate the characteristics of transporter(s) that contribute to the jejunal efflux of the lactone form of CPT-11. The serosal-to-mucosal permeation rate of CPT-11 lactone was investigated in everted sac studies. The secretory transport required metabolic energy and was diminished by sulfobromophthalein (BSP) and 1-naphthol, inhibitors of the ME3277 transport system. However, inhibitors of breast cancer resistance protein (Bcrp), multidrug resistance-associated protein 2 (Mrp2) and P-glycoprotein (P-gp) did not affect the secretion of CPT-11 lactone. The results suggest that a specific transport system, which is identical to the ME3277 transport system, plays a major role in the secretion of CPT-11 lactone.
    Cancer Chemotherapy and Pharmacology 02/2006; 57(1):129-33. · 2.80 Impact Factor
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    ABSTRACT: It is known that secretory transport limits the oral bioavailability of certain drugs. However, there is little information on the secretion of anionic compounds in the intestine. Phenolsulfonphthalein (PSP) and p-aminohippuric acid (PAH) have been used widely as substrates for organic anion transport systems. PAH is transported in the secretory direction in the intestine. It is possible that PSP and PAH share the same transport system at the mucosal membrane. The purpose of this study was to characterize the transport system for PSP in the intestine. In the jejunum, the serosal-to-mucosal permeation rate of PSP was significantly reduced in an ATP-depleted condition, whereas a significant difference was not observed in the ileum. Some multidrug resistance-associated protein 2 (Mrp2) inhibitors inhibited PSP permeation in the jejunum. However, pravastatin, a substrate of Mrp2, did not inhibit the PSP permeation. The jejunal secretory transport of pravastatin was significantly reduced in an ATP-depleted condition and by addition of probenecid, but PSP did not affect the jejunal permeation of pravastatin. These results suggest that PSP is secreted into the intestinal lumen by Mrp2-like transporter and that two Mrp2 substrates, PSP and pravastatin, are likely to be transported by different transport systems at the mucosal membrane.
    Drug Metabolism and Pharmacokinetics 03/2005; 20(1):72-8. · 2.07 Impact Factor
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    Makoto Chiba, Masahiro Seo
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    ABSTRACT: Nano-scratching in solution was performed to the single-crystal iron (100) surface passivated at 0.0–1.0V (SHE) in pH 8.4 borate buffer solution to evaluate the friction coefficient of the iron (100) surface kept in the passive state and its potential dependence. The friction coefficient obtained with nano-scratching for the passive iron surface depended on normal force, i.e., normal displacement, which resulted mainly from the geometry of the diamond tip. In order to avoid the effect of the tip geometry on friction coefficient, the normalized friction coefficient was newly defined with dividing friction coefficient by geometrical factor. The normalized friction coefficient obtained with nano-scratching in solution for the iron (100) surface kept in the passive sate was significantly larger than those obtained with nano-scratching in air after passivation. The normalized friction coefficient obtained with nano-scratching in air after passivation was almost independent of potential in the passive region. On the other hand, the normalized friction coefficient obtained with nano-scratching in solution increased with increasing potential in the passive region.The difference between normalized friction coefficients obtained with nano-scratching in solution and in air was discussed by taking into account a series of mechano-electrochemical reaction (film rupture, active dissolution and repassivation) which would take place at the moving front of the diamond tip during nano-scratching in solution. The large potential dependence of the normalized friction coefficient obtained with nano-scratching in solution was explained in terms of the increase in repassivation rate at the film rupture sites with increasing potential in the passive region.
    Electrochimica Acta - ELECTROCHIM ACTA. 01/2004; 50(4):967-975.
  • Makoto Chiba, Masahiro Seo
    Journal of The Electrochemical Society - J ELECTROCHEM SOC. 01/2003; 150(11).
  • Makoto Chiba, Masahiro Seo
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    ABSTRACT: An in situ nanoindentation technique combined with an AFM was applied to evaluate the effects of dichromate treatment on the mechanical properties of the single crystal iron (1 0 0) and (1 1 0) surfaces passivated in pH 8.4 borate solution. The dichromate treatment was performed with natural immersion of the iron specimens in 5×10−2 M K2Cr2O7 solution for 24 h prior to passivation at 0.25 V (SHE) for 1 h. The hardness, H and the works (elastic work, We, plastic work, Wp, and total work, Wt=We+Wp) made during nanoindentation were obtained from the measured load–depth curves.The values of H and We/Wt at the indentation depth larger than 30 nm for the passivated single crystal iron surfaces were increased by the dichromate treatment. The increases in H and We/Wt due to the dichromate treatment were attributed to the promotion of repassivation at the sites of passive film ruptured during nanoindentation process.
    Corrosion Science 10/2002; 44(10):2379–2391. · 3.62 Impact Factor
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    Masahiro Seo, Makoto Chiba
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    ABSTRACT: In situ nanoindentation tests were performed to evaluate the mechanical properties of the iron (100) and (110) surfaces passivated potentiostatically for 1 h in pH 8.4 borate solution after or without immersion in 5×10−2 M K2Cr2O7 solution for 24 h. It was found from the measured load–depth curves at a maximum load of 400 μN that the hardness (3.2–3.3 GPa) of the passivated iron (110) surfaces was larger by 10% than that (2.9–3.1 GPa) of the passivated iron (100) surfaces. Moreover, the hardness of the passivated iron (100) and (110) surfaces increased slightly with increasing formation potential of passive film, which was ascribed to the presence of passive film. The dichromate treatment increased the hardness of the iron (100) and (110) surfaces to some extent. The loading discontinuity appeared frequently at a load of about 90 μN in the load–depth curves for the passivated iron (110) surfaces as compared with the passivated iron (100) surfaces. The loading discontinuity in the load–depth curves for the iron (110) surface, however, disappeared completely due to the dichromate treatment.
    Electrochimica Acta 01/2001; 47:319-325. · 4.09 Impact Factor
  • Masahiro Seo, Makoto Chiba, Kakunari Suzuki
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    ABSTRACT: An in-situ nanoindentation test using a Berkovich pyramidal diamond indenter was performed to examine the mechano-electrochemical properties of the single crystal iron (100) surface passivated at a constant potential for 1 h in pH 8.4 borate solution. The load–depth curve measured at a maximum load, Wmax=50 μN and a load speed of 50 μN s−1 showed an evidence of plasticity irrespective of the potential at which the passive film was formed. The average hardness of the iron surface obtained from the unloading curve ranged from 2.0 to 2.5 GPa and it increased with increasing potential in the passive region higher than 0.25 V versus SHE, indicating that the passive film contributes to the increase in hardness of the iron surface. Moreover, the indentation at a maximum load, Wmax=200 μN and a load speed of 20 μN s−1 was performed in order to observe the time variation of the shape of the indent with AFM after the indentation. The indent shape for the iron surface cathodically reduced did not change significantly with time after the indentation. In contrast, the indent shape for the iron surface passivated at 1.0 V spread and became obscure with time, which was ascribed to the active dissolution of iron near and under the indenter, followed by the repassivation.
    Journal of Electroanalytical Chemistry 01/1999; 473(1):49-53. · 2.58 Impact Factor

Publication Stats

41 Citations
25.81 Total Impact Points

Institutions

  • 2001–2008
    • Hokkaido University
      • • Laboratory of Clinical Pharmaceutics and Therapeutics
      • • Faculty of Pharmaceutical Sciences
      • • Graduate School of Pharmaceutical Sciences
      • • Graduate School of Engineering
      Sapporo-shi, Hokkaido, Japan