Yoshihisa Shitara

Publications (32)118.39 Total impact

• Article: The Mechanism of the Down-Regulation of Hepatic Transporters in Rats with Indomethacin-Induced Intestinal Injury.

  Nobuhiro Fujiyama, Yoshihisa Shitara, Toshiharu Horie
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  ABSTRACT: BACKGROUND: Previously, we reported that hepatic transporters were down-regulated consistent with intestinal injury in indomethacin (IDM)-treated rats. AIM: The purpose of this study was to characterize this mechanism of the down-regulation of hepatic transporters in IDM-treated rats. METHODS: Hepatic nuclear receptor expressions, oxidative stress condition and the expression of hepatic transporters were evaluated in rats with IDM-induced intestinal injury with or without the administration of mucosal protectant ornoprostil, a prostaglandin E(1) analogue, or aminoguanidine (AG), an iNOS inhibitor. RESULTS: All the nuclear receptors examined in the present study, which regulates hepatic transporters, were decreased by the administration of IDM. Hepatic glutathione, an indicator of oxidative stress, was significantly reduced compared with control. We then determined the expression of hepatic transporters by semi-quantitative real-time RT-PCR and Western blot analysis in IDM-treated rats with or without the administration of ornoprostil or AG. Ornoprostil recovered the gene expression of Oatp1a1, Oatp1b2 and Mrp2 and protein expression of Mrp2 while it had no effect on Oatp1a1 and Oatp1b2 proteins. These results indicated that the gene expression of hepatic transporters was down-regulated in association with the intestinal injury. On the other hand, there is no effect of AG on the reduced gene expression of hepatic Oatp1a1, Oatp1b2 and Mrp2. In protein expression, AG slightly recovered Mrp2 expression accompanied by a partial decrease in portal NO levels. CONCLUSIONS: We suggest that the transcriptional process influenced by a dysfunction of hepatic nuclear receptors as well as the effect of NO on the post-transcriptional process due to intestinal injury are partially involved in the down-regulation of hepatic transporters.
  Digestive Diseases and Sciences 02/2013; · 2.12 Impact Factor
• Article: Long-lasting inhibitory effects of saquinavir and ritonavir on OATP1B1-mediated uptake.

  Yoshihisa Shitara, Kumiko Takeuchi, Toshiharu Horie
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  ABSTRACT: Previously, we reported a long-lasting inhibition of transport mediated by organic anion-transporting polypeptides (OATPs) in humans and rats by cyclosporin A (CsA). In the present study, we examined the effects of several other compounds on OATP1B1-mediated transport, with a focus on long-lasting inhibition. Effects of coincubation, preincubation, or preincubation plus coincubation of 12 compounds on uptake of estrone 3-sulfate (E(1) S) in OATP1B1-expressing HEK293T cells were examined. The OATP1B1 inhibitors used in the present study inhibited OATP1B1-mediated uptake of E(1) S in a concentration-dependent manner. Among them, saquinavir and ritonavir in addition to CsA exhibited long-lasting inhibitory effects on OATP1B1-mediated transport of E(1) S at ≥5 and 25 μM, respectively, even after they were washed out from the incubation buffer. After preincubation with saquinavir, its inhibitory effect on OATP1B1 remained for at least 6 h, whereas the effect of ritonavir did not remain. Protein expression of OATP1B1 was not altered by preincubation with 25 μM saquinavir or ritonavir. The present study firstly showed that saquinavir and ritonavir as well as CsA have long-lasting inhibitory effects on OATP1B1. But, at plasma unbound concentrations of saquinavir and ritonavir in clinical situations, they may not cause long-lasting inhibition of OATP1B1. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci.
  Journal of Pharmaceutical Sciences 02/2013; · 3.06 Impact Factor
• Article: Role of organic cation/carnitine transporter 1 in uptake of phenformin and inhibitory effect on complex I respiration in mitochondria.

  Yoshihisa Shitara, Noritaka Nakamichi, Misaki Norioka, Hiroyo Shima, Yukio Kato, Toshiharu Horie
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  ABSTRACT: Phenformin causes lactic acidosis in clinical situations due to inhibition of mitochondrial respiratory chain complex I. It is reportedly taken up by hepatocytes and exhibits mitochondrial toxicity in the liver. In the present study, uptake of phenformin and [(14)C]tetraethylammonium (TEA), and complex I inhibition by phenformin were examined in isolated liver and heart mitochondria. Uptake of phenformin into isolated rat liver mitochondria was higher than that into heart mitochondria. It was inhibited by several cationic compounds, which suggests the involvement of multispecific transport system(s). Similar characteristics were also observed for uptake of TEA; however, uptake of phenformin into mitochondria of organic cation/carnitine transporter 1 (OCTN1) knockout mice was lower than that in wild-type mice whereas uptake of TEA was comparable between the two strains, suggesting the involvement of distinct transport mechanisms for these two cations in mitochondria. Inhibition by phenformin of oxygen consumption via complex I respiration in isolated rat liver mitochondria was greater than that in heart mitochondria, whereas inhibitory effect of phenformin on complex I respiration was similar in inside-out structured submitochondrial particles prepared from rat livers and hearts. Lactic acidosis provoked by intravenous infusion of phenformin was weaker in octn1(-/-) mice than that in wild-type mice. These observations suggest that uptake of phenformin into liver mitochondria is at least partly mediated by OCTN1 and functionally relevant to its inhibition potential of complex I respiration. The present study was thus the first to demonstrate OCTN1-mediated mitochondrial transport and toxicity of biguanide in vivo in rodents.
  Toxicological Sciences 12/2012; · 4.65 Impact Factor
• Article: Clinical significance of organic anion transporting polypeptides (OATPs) in drug disposition: their roles in the hepatic clearance and intestinal absorption.

  Yoshihisa Shitara, Kazuya Maeda, Kazuaki Ikejiri, Kenta Yoshida, Toshiharu Horie, Yuichi Sugiyama
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  ABSTRACT: Organic anion transporting polypeptides (OATP) family transporters accept a number of drugs and are increasingly being recognized as important factors in governing their pharmacokinetics. OATP1B1 and OATP1B3 play an important role in hepatic drug uptake while OATP2B1 and OATP1A2 might be key players in intestinal absorption and transport across blood-brain barrier of drugs, respectively. To understand the importance of OATPs in hepatic clearance of drugs, the rate-determining process for elimination should be considered; for some drugs, hepatic uptake rather than metabolic rate is more important determinant of hepatic clearances. Importance of the unbound concentration ratio (liver/blood), K(p,uu) , of drugs, which is partly governed by OATPs, is exemplified in interpreting the difference in IC(50) of statins between the hepatocyte and microsome systems for the inhibition of HMG-CoA reductase activity. Intrinsic activity and/or expression level of OATPs are affected by genetic polymorphisms and drug-drug interactions. Their effects on the elimination rate or intestinal absorption rate of drugs may sometimes depend on the substrate drug. This is partly because of the different contribution of OATP isoforms to clearance or intestinal absorption. When the contribution of the OATP-mediated pathway is substantial, the pharmacokinetics of substrate drugs should be greatly affected. We describe estimation of the contribution of OATP1B1 to the total hepatic uptake of drugs from the data of fold-increases in the plasma concentration of substrate drugs by the genetic polymorphism of this transporter. To understand the importance of the OATP family transporters, modeling and simulation with a physiologically-based pharmacokinetic model are helpful. Copyright © 2012 John Wiley & Sons, Ltd.
  Biopharmaceutics & Drug Disposition 10/2012; · 2.07 Impact Factor
• Article: P-glycoprotein mediated efflux in Caco-2 cell monolayers: The influence of herbals on digoxin transport.

  Enoche F Oga, Shuichi Sekine, Yoshihisa Shitara, Toshiharu Horie
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  ABSTRACT: ETHNOPHARMACOLOGICAL RELEVANCE: Several herbal medicines are concomitantly used with conventional medicines with a resultant increase in the recognition of herb-drug interactions. The phytomedicines Vernonia amygdalina Delile (VA), family Asteraceae; Azadiractha indica A. Juss (NL), family Meliaceae; Morinda lucida Benth (MLB), family Rubiaceae; Cymbopogon citratus Stapf (LG), family Poaceae; Curcuma longa L. (CUR), family Zingiberaceae; Carica papaya L. (CP), family Caricaceae and Tapinanthus sessilifolius Blume (ML), family Loranthaceae are used in African traditional medicine for the treatment of malaria. They are also used in several regions world over in managing other ailments like cancer and diabetes. This study investigated their interaction with digoxin (DIG) with a view to predict the potential of P-glycoprotein (p-gp) mediated drug-herb interactions occurring with p-gp substrate drugs. MATERIALS AND METHODS: To assess p-gp mediated transport and inhibition, bidirectional transport studies were carried out on Caco-2 cell monolayers using digoxin (DIG) as a model p-gp substrate. Cell functionality was demonstrated using the determinations of transepithelial electric resistance (TEER), cell cytotoxicity testing utilizing the MTT assay as well as the inclusion of inhibition controls. RESULTS: Under the conditions of this study, extracts of ML, VA and CP showed significant inhibition to (3)H-Digoxin basolateral-to-apical (B-A) transport at 0.02-20mg/mL; the concentrations examined. Their apical-to-basolateral (A-B) transport was further investigated. Increases in the mean A-B transport and significant decreases in the B-A transport and efflux ratio values were observed. The apparent permeability coefficient and efflux ratio were computed providing an estimate of drug absorption. CONCLUSION: The findings show that extracts of ML, VA and CP significantly inhibit p-gp in vitro and interactions with conventional p-gp substrate drugs are likely to occur on co-administration which may result in altered therapeutic outcomes.
  Journal of ethnopharmacology 10/2012; · 2.32 Impact Factor
• Article: Potential P-glycoprotein-mediated drug-drug interactions of antimalarial agents in Caco-2 cells.

  Enoche F Oga, Shuichi Sekine, Yoshihisa Shitara, Toshiharu Horie
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  ABSTRACT: Antimalarials are widely used in African and Southeast Asian countries, where they are combined with other drugs for the treatment of concurrent ailments. The potential for P-glycoprotein (P-gp)-mediated drug-drug interactions (DDIs) between antimalarials and P-gp substrates was examined using a Caco-2 cell-based model. Selected antimalarials were initially screened for their interaction with P-gp based on the inhibition of rhodamine-123 (Rho-123) transport in Caco-2 cells. Verapamil (100 μM) and quinidine (1 μM) were used as positive inhibition controls. Lumefantrine, amodiaquin, and artesunate all showed blockade of Rho-123 transport. Subsequently, the inhibitory effect of these antimalarials on the bi-directional passage of digoxin (DIG) was examined. All of the drugs decreased basal-to-apical (B-A) P-gp-mediated DIG transport at concentrations of 100 μM and 1 mM. These concentrations may reflect therapeutic doses for amodiaquin and artesunate. Therefore, clinically relevant DDIs may occur between certain antimalarials and P-gp substrates in general.
  The American journal of tropical medicine and hygiene 07/2012; 87(1):64-9. · 2.59 Impact Factor
• Article: Long-lasting inhibition of the intestinal absorption of fexofenadine by cyclosporin A in rats.

  Kei Suzuki, Yoshihisa Shitara, Kousuke Fukuda, Toshiharu Horie
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  ABSTRACT: The purpose of the present study is to examine the long-lasting inhibition of intestinal organic anion transporting polypeptides (Oatps) by cyclosporin A (CsA) in rats using fexofenadine (FEX) as a probe drug. We examined the pharmacokinetics of FEX after its intravenous or oral administration to rats at 3 or 24 h after the oral administration of CsA. When FEX was administered at 3 h after the administration of CsA, its plasma concentration increased regardless of whether it was administered intravenously or orally. When FEX was intravenously administered at 24 h after the oral administration of CsA, its plasma concentration was increased; however, that observed after its oral administration was not significantly different from the vehicle-treated control. When FEX was administered at 3 h after the administration of CsA, the hepatic availability (F(h)) and the fraction absorbed in the intestine as an unchanged form (F(a)·F(g)) of FEX were increased, resulting in increased bioavailability (=F(a)·F(g)·F(h)). At 24 h after the administration of CsA, the F(h) of FEX was increased, whereas its bioavailability was decreased, suggesting that its F(a)·F(g) was decreased because of the long-lasting inhibition. In conclusion, CsA has long-lasting inhibitory effects on Oatps in the rat intestine as well as in the liver.
  Journal of Pharmaceutical Sciences 04/2012; 101(7):2606-15. · 3.06 Impact Factor
• Article: Long-lasting inhibitory effects of cyclosporin A, but not tacrolimus, on OATP1B1- and OATP1B3-mediated uptake.

  Yoshihisa Shitara, Kumiko Takeuchi, Yoshiko Nagamatsu, Satomi Wada, Yuichi Sugiyama, Toshiharu Horie
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  ABSTRACT: Cyclosporin A (CsA) causes a number of clinically-relevant drug-drug interactions (DDIs) by inhibiting OATP1B1 and OATP1B3. In the present study, long-lasting inhibitory effects of CsA on these transporters were examined in comparison to tacrolimus (TCR). OATP1B1- and OATP1B3-expressing HEK293T cells, OATP1B1-expressing MDCK II cells, and human hepatocytes were preincubated with CsA or TCR, and uptake studies were carried out in their presence or absence. Western blot or immunohistochemical studies were in OATP1B1-expressing HEK293T cells. The pretreatment of OATP1B1- and OATP1B3-expressing cells with 0.5 - 10 µM CsA, but not TCR, resulted in a reduction in their activity, even after washing out CsA from the incubation media. Preincubating the cells with CsA significantly enhanced its inhibitory effects on OATP1B1 and OATP1B3 by coincubation at 0.1 - 1 µM. Preincubation with 1 µM CsA caused a reduction in OATP1B1 activity for at least 18 h after its removal. The expression of OATP1B1 was not affected by incubation with CsA and no obvious change in its intracellular localization was observed. The long-lasting inhibition by CsA was also observed in human hepatocytes. Thus, CsA has a long-lasting inhibitory effect on OATP1B1 and OATP1B3. It may attribute to the clinically-relevant DDIs between OATP substrates and CsA.
  Drug Metabolism and Pharmacokinetics 01/2012; · 2.32 Impact Factor
• Article: Population pharmacokinetic analysis of letrozole in Japanese postmenopausal women.

  Hiromi Tanii, Yoshihisa Shitara, Toshiharu Horie
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  ABSTRACT: Letrozole is an orally active aromatase inhibitor for the treatment of breast cancer. The objectives of this study were to examine the pharmacokinetic profile of letrozole in Japanese subjects and to identify factors that influence variability in the pharmacokinetics of letrozole using population pharmacokinetic (PPK) analysis. Twenty-five healthy postmenopausal Japanese women were enrolled in the study and received 2.5 mg letrozole once daily for 14 or 28 days. A PPK model was developed using NONMEM software. Age, body weight (WT), AST, ALT, total bilirubin, serum creatinine (CRE), and genotype of CYP2A6 were studied as covariates. Estrone, estrone sulfate, and estradiol in plasma were measured as pharmacodynamic markers. CYP2A6 genotype, CRE, and AST were significant covariates for apparent systemic clearance (CL/F), and WT was a significant covariate for apparent distribution volume (Vd/F). Population mean estimates of CL/F and Vd/F in subjects without CYP2A6 mutation were 1.03 × (CRE/0.70)(-1.27) × (AST/17.5)(-0.793) L/h and 94.2 × (WT/51.1)(1.12) L respectively. CL/F in subjects possessing 1 and 2 CYP2A6 mutation alleles were 84.3% and 44.8% of the value in the subjects without mutation respectively. Estrogen levels fell to below detection limits in most subjects after letrozole administration. Three mild and transient adverse events (upper respiratory tract inflammation, arthralgia, and vomiting) were reported in the study. CYP2A6 genotype largely influences CL/F of letrozole. Genetic polymorphism of CYP2A6 and body weight will be causes of ethnic difference in PK. However, dose adjustment is not necessary, because of the wide therapeutic range.
  European Journal of Clinical Pharmacology 04/2011; 67(10):1017-25. · 2.85 Impact Factor
• Article: Clinical importance of OATP1B1 and OATP1B3 in drug-drug interactions.

  Yoshihisa Shitara
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  ABSTRACT: OATP1B1 and OATP1B3 are transporters that are expressed on the sinusoidal membrane of hepatocytes; they accept a number of therapeutic reagents as their substrates. In vitro and in vivo studies have shown that some drugs inhibit these transporters and cause clinically relevant drug-drug interactions (DDIs). Among these drugs, cyclosporin A markedly increases the plasma concentrations of OATP1B1 substrates. In such cases, the area under the plasma concentration-time curve and the maximum concentration of the affected drugs are increased to a similar degree. Even for OATP1B1 substrates that are metabolized in the liver, the hepatic uptake rate is a determinant of overall hepatic clearance, and the DDIs are partly caused by the inhibition of OATP1B1. Gemfibrozil displays DDIs with some OATP1B1 substrates, although their extent is small. Rifampicin and some HIV protease inhibitors are also OATP1B1 inhibitors. Rifampicin is also an inducer of metabolic enzymes, and although its single coadministration produces an increase in the plasma concentration of the affected drugs, multiple coadministrations may result in reductions in the plasma concentrations of OATP1B1 and CYP3A4 bisubstrates. As a large number of therapeutic reagents are substrates and/or inhibitors of OATP1B1 and OATP1B3, we should be aware of DDIs caused by the inhibition of these transporters.
  Drug Metabolism and Pharmacokinetics 02/2011; 26(3):220-7. · 2.32 Impact Factor
• Article: Multiple mechanisms underlying troglitazone-induced mitochondrial permeability transition.

  Takuya Okuda, Misaki Norioka, Yoshihisa Shitara, Toshiharu Horie
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  ABSTRACT: Troglitazone, a thiazolidinedione class antidiabetic drug, was withdrawn from the market because of its severe idiosyncratic hepatotoxicity. It causes a mitochondrial permeability transition (MPT), which may in part contribute to its hepatotoxicity. In the present study, the mechanism of troglitazone mitochondrial toxicity was investigated in isolated rat liver mitochondria. Mitochondrial swelling induced by 10 μM troglitazone was attenuated by bromoenol lactone (BEL), an inhibitor of Ca²+-independent phospholipase A₂ (iPLA₂). In contrast, that induced by 50 μM troglitazone was exacerbated by BEL. This exacerbation was diminished by addition of 2mM glutathione, an antioxidant. Oxygen consumption by state 3 respiration in isolated mitochondria was also decreased by troglitazone, but it was not affected by BEL. Mitochondrial swelling induced by 10 μM troglitazone was completely attenuated in the absence of Ca²+ while that induced by 50 μM troglitazone was not affected. Addition of 1 μM cyclosporin A (CsA), an inhibitor of MPT pores, completely attenuated swelling induced by 10 μM troglitazone while it only partly diminished that induced by 50 μM troglitazone. Thus, the MPT induced by 10 and 50 μM troglitazone are regulated by different mechanism; the MPT induced by 10 μM troglitazone is regulated by the activation of iPLA₂ and caused by the opening of CsA-regulating MPT pores followed by accumulation of Ca²+ in mitochondria, while that induced by 50 μM troglitazone is partly regulated by reactive oxygen species and mainly caused by the opening of CsA-insensitive MPT pores.
  Toxicology and Applied Pharmacology 11/2010; 248(3):242-8. · 4.45 Impact Factor
• Article: Zonula Occludens-1 alterations and enhanced intestinal permeability in methotrexate-treated rats.

  Kazuma Hamada, Yoshihisa Shitara, Shuichi Sekine, Toshiharu Horie
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  ABSTRACT: The molecular mechanisms that underlie the methotrexate (MTX)-mediated disruption of intestinal barrier function have not been fully characterized. Epithelial barrier function is determined in large part by a multiprotein complex located at the most apical part of the lateral membrane, which is referred to as a tight junction (TJ). In the present study, we examined the alteration of zonula occludens-1 (ZO-1), which is a scaffolding protein that plays a pivotal role in the formation of TJs, to identify an additional molecular mechanism for epithelial barrier dysfunction. Male Wistar rats were administered MTX (15 mg kg(-1)) orally once daily for 3-5 days. Intestinal mucosal permeability was determined using the in vitro everted intestinal sac technique. Mucosal inflammation was assessed by myeloperoxidase activity and production of reactive oxygen species. Altered expression, tyrosine phosphorylation, and localization of ZO-1 were evaluated by RT-PCR, Western blotting, immunoprecipitation, and immunohistochemistry. A barrier function study revealed increased intestinal permeability in rats treated with MTX for 4 days, as indicated by enhanced fluorescein isothiocyanate-dextran flux. In addition, mucosal inflammation was linked to enhanced intestinal permeability. Quantitative analysis of ZO-1 expression showed the absence of significant differences in MTX-treated rats, whereas tyrosine dephosphorylation of ZO-1 was observed. Moreover, we also detected an obvious reduction of ZO-1 immunostaining along the apical membrane of intestinal villi. These results indicate that, in MTX-treated rats, ZO-1 alterations may contribute to disturbance of the TJ barrier, which leads to enhanced intestinal permeability.
  Cancer Chemotherapy and Pharmacology 11/2010; 66(6):1031-8. · 2.83 Impact Factor
• Chapter: Extrapolation of In Vitro Metabolic and P-Glycoprotein-Mediated Transport Data to In Vivo by Modeling and Simulations

  Motohiro Kato, Yoshihisa Shitara, Masato Kitajima, Tatsuhiko Tachibana, Masaki Ishigai, Toshiharu Horie, Yuichi Sugiyama
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  ABSTRACT: Recently, a prediction method using in vivo K i values for inhibitors of cytochrome P450 with a physiologically based pharmacokinetic modeling was proposed to improve the accuracy of the prediction. Also, a method to predict the alterations caused by drug–drug interactions mediated by intestinal cytochrome P450 3A4 or P-glycoprotein was introduced. In this chapter, these methods and computerized simulation method are shown.
  12/2009: pages 299-315;
• Chapter: Web-Based Database as a Tool to Examine Drug–Drug Interactions Involving Transporters

  Kazuya Maeda, Yoshihisa Shitara, Toshiharu Horie, Yuichi Sugiyama
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  ABSTRACT: The clinical importance of drug–drug interaction mediated by drug transporters has been gradually recognized; its quantitative prediction and an in silico database of drug–drug interaction have been much wanted. In this chapter, examples of, and prediction methods for, transporter-mediated drug–drug interactions are shown, and a Web-based transporter-mediated drug–drug interaction database in TP-search (http://www.TP-Search.jp/) is also described. KeywordsDrug–drug interaction-Transporter-TP-search-Physiologically based pharmacokinetic (PBPK) modeling
  12/2009: pages 387-412;
• Article: Long-lasting inhibition of the transporter-mediated hepatic uptake of sulfobromophthalein by cyclosporin a in rats.

  Yoshihisa Shitara, Yoshiko Nagamatsu, Satomi Wada, Yuichi Sugiyama, Toshiharu Horie
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  ABSTRACT: Cyclosporin A (CsA) is a well known inhibitor of the organic anion-transporting polypeptide (OATP/Oatp) family transporters, causing a large number of transporter-mediated drug-drug interactions in clinical situations. In the present study, we examined the inhibitory effect of CsA on the hepatic uptake of sulfobromophthalein (BSP) in rats, focusing on a long-lasting inhibition. Twenty-one hours after the subcutaneous administration of CsA, the hepatic clearance of BSP was decreased. The liver uptake index study revealed that hepatic uptake of BSP was reduced in CsA-treated rats for at least 3 days. Comparison of uptake studies using isolated hepatocytes prepared from control and CsA-treated rats showed that hepatic uptake in CsA-treated rats was decreased. In primary cultured hepatocytes, after preincubation with CsA, the uptake of [(3)H]BSP was reduced even after removal of CsA from the incubation buffer although a preincubation time dependence was not observed. However, the expression of Oatp1a1 and Oatp1b2, which are involved in the hepatic uptake of BSP, and the amount of intrahepatic glutathione, a driving force of Oatp1a1, did not change in CsA-treated rats. Thus, we can conclude that CsA modulates the transporter function sustainably. It can cause a potent in vivo drug-drug interaction. The modulation of transporters is not caused by reduced expression or driving force of transporters. It may be affected by CsA accumulated in the liver or its metabolites. The inhibitory effect of CsA on the transporter-mediated uptake of BSP cannot be explained by a simple competitive mechanism and a novel mechanism should be considered.
  Drug metabolism and disposition: the biological fate of chemicals 04/2009; 37(6):1172-8. · 3.74 Impact Factor
• Article: Physiologically based pharmacokinetic modeling to predict transporter-mediated clearance and distribution of pravastatin in humans.

  Takao Watanabe, Hiroyuki Kusuhara, Kazuya Maeda, Yoshihisa Shitara, Yuichi Sugiyama
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  ABSTRACT: Hepatobiliary excretion mediated by transporters, organic anion-transporting polypeptide (OATP) 1B1 and multidrug resistance-associated protein (MRP) 2, is the major elimination pathway of an HMG-CoA reductase inhibitor, pravastatin. The present study examined the effects of changes in the transporter activities on the systemic and liver exposure of pravastatin using a physiologically based pharmacokinetic model. Scaling factors, determined by comparing in vivo and in vitro parameters of pravastatin in rats for the hepatic uptake and canalicular efflux, were obtained. The simulated plasma and liver concentrations and biliary excretion profiles were very close to the observed data in rats under linear and nonlinear conditions. In vitro parameters, determined in human cryopreserved hepatocytes and canalicular membrane vesicles, were extrapolated to in vivo parameters using the scaling factors obtained in rats. The simulated plasma concentrations of pravastatin were close to the reported values in humans. Sensitivity analyses showed that changes in the hepatic uptake ability altered the plasma concentration of pravastatin markedly but had a minimal effect on the liver concentration, whereas changes in the ability of canalicular efflux altered the liver concentration of pravastatin markedly but had a small effect on the plasma concentration. In conclusion, the model allows the prediction of the disposition of pravastatin in humans. The present study suggests that changes in the OATP1B1 activities may have a small and a large impact on the therapeutic efficacy and side effect (myopathy) of pravastatin, respectively, whereas those in the MRP2 activities may have opposite impacts (i.e., large and small impacts on the therapeutic efficacy and side effect).
  Journal of Pharmacology and Experimental Therapeutics 12/2008; 328(2):652-62. · 3.83 Impact Factor
• Article: The quantitative prediction of CYP-mediated drug interaction by physiologically based pharmacokinetic modeling.

  Motohiro Kato, Yoshihisa Shitara, Hitoshi Sato, Kunihiro Yoshisue, Masaru Hirano, Toshihiko Ikeda, Yuichi Sugiyama
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  ABSTRACT: The objective is to confirm if the prediction of the drug-drug interaction using a physiologically based pharmacokinetic (PBPK) model is more accurate. In vivo Ki values were estimated using PBPK model to confirm whether in vitro Ki values are suitable. The plasma concentration-time profiles for the substrate with coadministration of an inhibitor were collected from the literature and were fitted to the PBPK model to estimate the in vivo Ki values. The AUC ratios predicted by the PBPK model using in vivo Ki values were compared with those by the conventional method assuming constant inhibitor concentration. The in vivo Ki values of 11 inhibitors were estimated. When the in vivo Ki values became relatively lower, the in vitro Ki values were overestimated. This discrepancy between in vitro and in vivo Ki values became larger with an increase in lipophilicity. The prediction from the PBPK model involving the time profile of the inhibitor concentration was more accurate than the prediction by the conventional methods. A discrepancy between the in vivo and in vitro Ki values was observed. The prediction using in vivo Ki values and the PBPK model was more accurate than the conventional methods.
  Pharmaceutical Research 09/2008; 25(8):1891-901. · 4.09 Impact Factor
• Article: Down-regulation of hepatic transporters for BSP in rats with indomethacin-induced intestinal injury.

  Nobuhiro Fujiyama, Yoshihisa Shitara, Kousei Ito, Yasuhiro Masubuchi, Toshiharu Horie
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  ABSTRACT: Previous reports have demonstrated that an intestinal injury causes hypofunctions of the liver associated with down-regulations of cytochrome P450, but an influence on hepatic transporters remains unclear. Here, we tested hepatic transporter functions in a rat model of bowel injury using indomethacin (IDM). After administration of IDM (8.5 mg/kg, i.p., 3 d), the rats suffered the intestinal impairment indicated by a reduction of alkaline phosphatase activity in mucosa. In vivo pharmacokinetic experiments of bromosulfophthalein (BSP) showed that there was a reduction in its plasma elimination rate and cumulative biliary excretion in IDM-treated rats and systemic and biliary clearances reduced to nearly 50% of the control group. Protein expressions in plasma membrane and mRNA levels of organic anion transporting polypeptide 1b2 (Oatp1b2) and multidrug resistance-associated protein 2 (Mrp2), which play hepatic BSP uptake and biliary excretion, respectively, in the liver were significantly reduced following the IDM treatment. In portal plasma, the levels of proinflammatory cytokines were unchanged, while the level of nitric oxide metabolites (NO2- + NO3-) increased to 6.5-fold that of the control. The time-course on IDM treatment indicated that, firstly, intestinal injury was induced, the NO level increased, and the hepatic Oatp1b2 and Mrp2 expression began to fall followed by an increase in plasma ALT. In conclusion, IDM-induced injury to the small intestine causes the hypofunction of hepatic Oatp1b2 and Mrp2 independently on the hepatic impairment, and NO arising from bowel injury may be one of key factors for it through the remote effect.
  Biological & Pharmaceutical Bulletin 04/2007; 30(3):556-61. · 1.66 Impact Factor
• Article: Pharmacokinetic and pharmacodynamic alterations of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors: drug-drug interactions and interindividual differences in transporter and metabolic enzyme functions.

  Yoshihisa Shitara, Yuichi Sugiyama
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  ABSTRACT: 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are widely used for the treatment of hypercholesterolemia. Their efficacy in preventing cardiovascular events has been shown by a large number of clinical trials. However, myotoxic side effects, sometimes severe, including myopathy or rhabdomyolysis, are associated with the use of statins. In some cases, such toxicity is associated with pharmacokinetic alterations. In this review, the pharmacokinetic aspects and physicochemical properties of statins are reviewed in order to understand the mechanism governing their pharmacokinetic alterations. Among the statins, simvastatin, lovastatin and atorvastatin are metabolized by cytochrome P450 3A4 (CYP3A4) while fluvastatin is metabolized by CYP2C9. Cerivastatin is subjected to 2 metabolic pathways mediated by CYP2C8 and 3A4. Pravastatin, rosuvastatin and pitavastatin undergo little metabolism. Their plasma clearances are governed by the transporters involved in the hepatic uptake and biliary excretion. Also for other statins, which are orally administered as open acid forms (i.e. fluvastatin, cerivastatin and atorvastatin), hepatic uptake transporter(s) play important roles in their clearances. Based on such information, pharmacokinetic alterations of statins can be predicted following coadministration of other drugs or in patients with lowered activities in drug metabolism and/or transport. We also present a quantitative analysis of the effect of some factors on the pharmacokinetics of statins based on a physiologically based pharmacokinetic model. To avoid a pharmacokinetic alteration, we need to have information about the metabolizing enzyme(s) and transporter(s) involved in the pharmacokinetics of statins and, along with such information, model-based prediction is also useful.
  Pharmacology [?] Therapeutics 11/2006; 112(1):71-105. · 8.56 Impact Factor
• Article: Drug-drug interaction between pitavastatin and various drugs via OATP1B1.

  Masaru Hirano, Kazuya Maeda, Yoshihisa Shitara, Yuichi Sugiyama
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  ABSTRACT: It has already been demonstrated that pitavastatin, a novel potent HMG-coenzyme A reductase inhibitor, is taken up into human hepatocytes mainly by organic anion transporting polypeptide (OATP) 1B1. Because OATP2B1 is also localized in the basolateral membrane of human liver, we took two approaches to further confirm the minor contribution of OATP2B1 to the hepatic uptake of pitavastatin. Western blot analysis revealed that the ratio of the band density of OATP2B1 in human hepatocytes to that in our expression system is at least 6-fold lower compared with OATP1B1 and OATP1B3. The uptake of pitavastatin in human hepatocytes could be inhibited by both estrone-3-sulfate (OATP1B1/OATP2B1 inhibitor) and estradiol-17beta-D-glucuronide (OATP1B1/OATP1B3 inhibitor). These results further supported the idea that OATP1B1 is a predominant transporter for the hepatic uptake of pitavastatin. Then, to explore the possibility of OATP1B1-mediated drug-drug interaction, we checked the inhibitory effects of various drugs on the pitavastatin uptake in OATP1B1-expressing cells and evaluated whether the in vitro inhibition was clinically significant or not. As we previously reported, we used the methodology for estimating the maximum unbound concentration of inhibitors at the inlet to the liver (I(u,in,max)). Judging from I(u,in,max) and inhibition constant (K(i)) for OATP1B1, several drugs (especially cyclosporin A, rifampicin, rifamycin SV, clarithromycin, and indinavir) have potentials for interacting with OATP1B1-mediated uptake of pitavastatin. The in vitro experiments could support the clinically observed drug-drug interaction between pitavastatin and cyclosporin A. These results suggest that we should pay attention to the concomitant use of some drugs with pitavastatin.
  Drug Metabolism and Disposition 08/2006; 34(7):1229-36. · 3.73 Impact Factor