Akihiro Kikuchi

Tokyo University of Science, Edo, Tōkyō, Japan

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Publications (5)14.61 Total impact

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    ABSTRACT: Tebipenem pivoxil (TBPM-PI) is an oral carbapenem antibiotic for treating otolaryngologic and respiratory infections in pediatric patients. This agent is a prodrug to improve intestinal absorption of TBPM, an active form, and an absorption rate of TBPM-PI is higher than those of other prodrug-type β-lactam antibiotics. In the present study, we hypothesized that a certain mechanism other than simple diffusion is involved in the process of improved intestinal absorption of TBPM-PI and examined the mechanism. TBPM-PI uptake by Caco-2 cells was decreased by ATP-depletion and lowering the temperature to 4 °C, suggesting the contribution of carrier-mediated transport mechanisms. This uptake was partially decreased by ACE inhibitors, and the reduction of the absorption by captopril was observed by in vivo study and in situ single-pass intestinal perfusion study in rat, supporting the contribution of influx transporters. Since some ACE inhibitors and β-lactam antibiotics are reported to be substrates of PEPT and OATP families, we measured transporting activity of TBPM-PI by intestinally expressed transporters, PEPT1, OATP1A2, and OATP2B1. As a result, significant transport activities were observed by both OATP1A2 and OATP2B1 but not by PEPT1. Interestingly, pH dependence of TBPM-PI transports was different between OATP1A2 and OATP2B1, showing highest activity by OATP1A2 at pH 6.5, while OATP2B1-mediated uptake was higher at neutral and weak alkaline pH. OATP1A2 exhibited higher affinity for TBPM-PI (K(m) = 41.1 μM) than OATP2B1 (K(m) > 1 mM) for this agent. These results suggested that TBPM-PI has high intestinal apical membrane permeability due to plural intestinal transport routes, including the uptake transporters such as OATP1A2 and OATP2B1 as well as simple diffusion.
    Molecular Pharmaceutics 09/2010; 7(5). DOI:10.1021/mp100130b · 4.79 Impact Factor
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    ABSTRACT: The purpose of the present study was to examine whether the intestinal absorption of low-permeability drugs could be improved by utilization of the intestinal influx transporter PEPT1. We investigated whether peptide derivatives of poorly absorbable nonamino acid-like drugs might be substrates of PEPT1, using rebamipide (Reb) as a model drug. We synthesized several peptide derivatives of rebamipide and examined their inhibitory effect on the uptake of [(3)H]Gly-Sar by PEPT1-expressing HeLa cells. Some of the peptide derivatives inhibited PEPT1-mediated uptake of [(3)H]Gly-Sar. Next, uptake of the inhibitory peptide derivatives was evaluated in PEPT1-expressing Xenopus oocytes and HeLa cells. Ser(Reb)-Gly exhibited significantly increased uptake by PEPT1-expressing cells in comparison with that by mock cells. The permeability of Ser(Reb)-Gly across a Caco-2 cell monolayer was significantly higher than that of rebamipide itself, and the transport was decreased in the presence of PEPT1 substrates. Further, a rat intestinal perfusion study revealed increased absorption of Ser(Reb)-Gly compared with rebamipide. These results demonstrate that the addition of a dipeptide moiety to a poorly absorbable nonpeptide/nonamino acid-like drug can result in absorption via the intestinal transporter PEPT1, though there is some selectivity as regards the structure of the added peptide moiety.
    Journal of Pharmaceutical Sciences 05/2009; 98(5):1775-87. DOI:10.1002/jps.21551 · 3.01 Impact Factor
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    ABSTRACT: To assess the contribution of organic anion transporting polypeptide 1a5 (Oatp1a5/Oatp3) in the intestinal absorption of an orally active endothelin receptor antagonist, (+)-(5S,6R,7R)-2-butyl-7-[2-((2S)-2-carboxypropyl)-4-methoxyphenyl]-5-(3,4-methylene-dioxyphenyl)cyclopenteno[1,2-b]pyridine-6-carboxylic acid (compound-A) in rats. Uptakes of [(14)C]compound-A by Oatp1a5-expressing Xenopus laevis oocytes and isolated rat enterocytes were evaluated. The uptake of compound-A by Oatp1a5-expressing oocytes was significantly higher than that by water-injected oocytes and Oatp1a5-mediated uptake was saturable with K(m) value of 116 microM. Compound-A was taken up into isolated enterocytes in time- and concentration-dependent manners and the estimated K(m) value was 83 microM, which was close to that for the Oatpt1a5-mediated uptake in oocytes. Both uptakes of compound-A by Oatp1a5-expressing oocytes and enterocytes were pH-sensitive with significantly higher uptake at acidic pH than those at neutral pH. Uptakes of compound-A into Oatp1a5-expressing oocytes and enterocytes were significantly decreased in the presence of Oatp1a5 substrates such as bromosulfophthalein and taurocholic acid. These results consistently suggested that Oatp1a5 is contributing to the intestinal absorption of compound-A at least in part, and the transporter-mediated absorption seems to be maximized at the acidic microenvironment of epithelial cells in the small intestine in rats.
    Pharmaceutical Research 06/2008; 25(5):1085-91. DOI:10.1007/s11095-007-9472-4 · 3.95 Impact Factor
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    ABSTRACT: Both influx and efflux transporters are thought to be involved in the intestinal absorption of fexofenadine. The present study examined the influx transporter-mediated intestinal absorption of fexofenadine in rats, focusing on the role of rat oatp3 (Oatp1a5). The intestinal permeability of fexofenadine was evaluated by means of the Ussing chamber method in the presence of a P-glycoprotein inhibitor to block efflux transport. The permeability of fexofenadine from the mucosal to the serosal side was higher than that from the serosal side to the mucosal side. Transport of fexofenadine was saturable, and was significantly decreased by an organic anion transporting polypeptide (oatp) inhibitor. Furthermore, uptake of fexofenadine by Xenopus oocytes expressing rat oatp3 was significantly greater than that by water-injected oocytes, and the affinity of oatp3 for fexofenadine (Km) was about 60 microM, which is comparable with the value obtained by the Ussing chamber method using rat intestinal tissues. These results indicate that oatp3 plays a role as an influx transporter in the intestinal absorption of fexofenadine in rats.
    Drug Metabolism and Pharmacokinetics 09/2006; 21(4):308-14. DOI:10.2133/dmpk.21.308 · 2.86 Impact Factor
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    ABSTRACT: Tebipenem pivoxil (TBPM-PI) is a novel carbapenem antibiotic for treating respiratory tract and otolaryngologic infections caused by bacteria resistant to currently available antibiotics. TBPM-PI is esterified with pivaloyloxymethyl at carboxylic group of TBPM, an active form of TBPM-PI, to improve bioavailability. Since TBPM-PI exhibits an excellent intestinal absorption, we examined the mechanism of an intestinal membrane transport. Firstly, we evaluated the uptake of TBPM-PI by Caco-2 cells to examine whether the uptake transporter is involved in the intestinal absorption. TBPM-PI uptake by Caco-2 cells was inhibited by ATP-depletion and the incubation at 4C, suggesting the contribution of influx transporters. This uptake was partially decreased by some ACE inhibitors in Caco-2 cells, and the reduction of the absorption by ACE inhibitors was observed by in vivo study and in situ single-pass intestinal perfusion analysis in rats, supporting the contribution of influx transporters. ACE inhibitors are reported to be substrates of PEPT and OATP family. Next, we measured transporting activity of TBPM-PI using PEPT1, OATP1A2 (OATP-A), and OATP2B1 (OATP-B) expression systems. No transport activity was detected in PEPT1. On the other hand, significant transport activities were observed in OATP1A2 and OATP2B1. Interestingly, TBPM was not transported by these transporters and TBPM-PI was transported preferentially at acidic pH for OATP1A2 and neutral pH for OATP2B1. These data suggested that TBPM-PI has an excellent oral absorption due to plural routes of the intestinal membrane transport via influx transporters, OATP1A2 and OATP2B1, as well as passive diffusion.
    8th International International society for the study of xenobiotics Meeting;