Tomoo Itoh

Kitasato University, Edo, Tōkyō, Japan

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Publications (25)54.17 Total impact

  • Ryoichi Fujiwara, Tomoo Itoh
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    ABSTRACT: Cytochrome P450 (CYP) 3A4 is a membrane protein that catalyzes hydroxylation of endogenous and exogenous substrates. Protein–protein interaction is a crucial factor that regulates the function of enzymes. However, protein–protein interactions involving human CYPs have not been fully understood. In this study, extensive protein–protein interactions involving CYP3A4 were determined by a shotgun analysis of immunoprecipitate utilizing anti-CYP3A4 antibody. Our shotgun analysis revealed that 149 proteins were immunoprecipitated with anti-CYP3A4 antibody in human liver microsomes. We further determined that 51 proteins of 149 proteins were specifically immunoprecipitated with the anti-CYP3A4 antibody. Our analysis demonstrated that other CYP isoforms are interacting with CYP3A4, which is in agreement with previous findings. Based on our current and previous findings, we propose that drug-metabolizing enzymes such as CYP3A4 and UDP-glucuronosyltransferase 2B7 form a metabolosome, which is a functional unit of metabolism consisting of multiple metabolism-related proteins.
    Pharmacology Research & Perspectives. 10/2014; 2(5).
  • Drug metabolism and pharmacokinetics. 07/2014;
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    ABSTRACT: UDP-glucuronosyltransferases (UGTs) are phase II drug-metabolizing enzymes that catalyze glucuronidation of various drugs. Although experimental rodents are used in preclinical studies to predict glucuronidation and toxicity of drugs in humans, species differences in glucuronidation and drug-induced toxicity have been reported. Recently, humanized UGT1 mice in which the original Ugt1 locus was disrupted and replaced with the human UGT1 locus (hUGT1 mice) have been developed. In this study, acyl-glucuronidations of etodolac, diclofenac, and ibuprofen in liver microsomes of hUGT1 mice were examined and compared with those of human and regular mice. The kinetics of etodolac, diclofenac, and ibuprofen acyl-glucuronidation in hUGT1 mice were almost comparable to those in humans, rather than in mice. We further investigated hepatotoxicity of ibuprofen in hUGT1 mice and regular mice by measuring serum alanine amino transferase (ALT) levels. As ALT levels were increased at 6 h after dosing in hUGT1 mice and at 24 h after dosing in regular mice, the onset pattern of ibuprofen-induced liver toxicity in hUGT1 mice was different from that in regular mice. These data suggest that hUGT1 mice can be valuable tools for understanding glucuronidations of drugs and drug-induced toxicity in humans.
    Drug metabolism and disposition: the biological fate of chemicals 04/2014; · 3.74 Impact Factor
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    ABSTRACT: Folic acid (FA) is a water-soluble vitamin, and orally ingested FA is absorbed from the small intestine by the proton-coupled folate transporter (PCFT). In the present study, we investigated whether epigallocatechin gallate (EGCG), one of the tea catechins, affects the transport of FA by PCFT. EGCG inhibited the uptake of FA into Caco-2 cells and human PCFT-expressing HEK293 cells (PCFT-HEK293 cells). The initial rate of uptake of FA into PCFT-HEK293 cells followed Michaelis-Menten kinetics (Km = 1.9 µM). Dixon plots revealed that PCFT-mediated FA uptake was competitively inhibited by EGCG (Ki ~ 9 µM). The uptake of the PCFT substrate methotrexate (MTX) was competitively inhibited by EGCG as well (Ki ~ 15 µM). In conclusion, it is suggested that when FA or MTX is ingested with tea, it is likely that the intestinal absorption of these compounds by PCFT is inhibited, which could result in insufficient efficacy.
    Drug Metabolism and Pharmacokinetics 04/2014; · 2.07 Impact Factor
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    ABSTRACT: The stereoselective transport of methotrexate (L-amethopterin, L-MTX) and its antipode (D-amethopterin, D-MTX) by human reduced folate carrier (hRFC) has been examined in HEK293 cells expressing H27-hRFC and R27-hRFC. The uptake of both L-MTX and D-MTX increased as the extracellular pH increased from 6.0 to 7.4. The initial uptake rate of L-MTX into the H27- and R27-hRFCs of the HEK293 cells followed Michaelis-Menten kinetics with Km values of approximately 0.24 and 0.47 µM, respectively. Dixon plots revealed that the [(3)H]-L-MTX uptake mediated by the H27- and R27-hRFCs was inhibited competitively by unlabeled L-MTX with Ki values of approximately 0.1 and 0.5 µM, respectively. D-MTX also competitively inhibited the H27- and R27-hRFC mediated uptake of [(3)H]-L-MTX with Ki values of approximately 3.4 and 3.2 µM, respectively. The RFC-mediated uptake clearance of L-MTX was approximately 15-fold greater than that of D-MTX in the H27-hRFC-HEK293 cells, and was more than 30-fold greater than that of D-MTX in the R27-hRFC-HEK293 cells. The results of the current study have revealed that the enantiomers of MTX enantiomers can be transported in a stereoselective manner by the H27- and R27-hRFCs because of significant differences in the affinities of the enantiomers to the hRFC.
    Biological & Pharmaceutical Bulletin 01/2014; 37(3):439-46. · 1.85 Impact Factor
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    ABSTRACT: Solute carrier (SLC) transporters play important roles in absorption and disposition of drugs in cells; however, the expression pattern of human SLC transporters in the skin has not been determined. In the present study, the expression patterns of 28 human SLC transporters were determined in the human skin. Most of the SLC transporter family members were either highly or moderately expressed in the liver, while their expression was limited in the skin and small intestine. Treatment of human keratinocytes with a reactive metabolite of ibuprofen significantly reduced cell viability. Expression array analysis revealed that S100 calcium binding protein A7A (S100A7A) was induced nearly 50-fold in dermal cells treated with ibuprofen acyl-glucuronide. Determination of the expression of drug-metabolizing enzymes as well as drug transporters prior to the administration of drugs would make it possible to avoid the development of idiosyncratic skin diseases in individuals.
    Scientific reports. 01/2014; 4:5251.
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    ABSTRACT: Inadequate calorie intake or starvation has been suggested as a cause of neonatal jaundice, which can further cause permanent brain damage, kernicterus. This study experimentally investigated whether additional glucose treatments induce the bilirubin-metabolizing enzyme - UDP-glucuronosyltransferase (UGT) 1A1 - to prevent the onset of neonatal hyperbilirubinemia. Neonatal humanized UGT1 (hUGT1) mice physiologically develop jaundice. In this study, UGT1A1 expression levels were determined in the liver and small intestine of neonatal hUGT1 mice that were orally treated with glucose. In the hUGT1 mice, glucose induced UGT1A1 in the small intestine, while it did not affect the expression of UGT1A1 in the liver. UGT1A1 was also induced in the human intestinal Caco-2 cells when the cells were cultured in the presence of glucose. Luciferase assays demonstrated that not only the proximal region (-1300/-7) of the UGT1A1 promoter, but also distal region (-6500/-4050) were responsible for the induction of UGT1A1 in the intestinal cells. Adequate calorie intake would lead to the sufficient expression of UGT1A1 in the small intestine to reduce serum bilirubin levels. Supplemental treatment of newborns with glucose solution can be a convenient and efficient method to treat neonatal jaundice while allowing continuous breastfeeding.
    Scientific reports. 01/2014; 4:6343.
  • Ryoichi Fujiwara, Tomoo Itoh
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    ABSTRACT: UDP-glucuronosyltransferase (UGT) 2B7 is a membrane protein that catalyzes glucuronidation of endogenous and exogenous substrates. Because UGTs are expressed in endoplasmic reticulum (ER), their substrates and metabolites need to be transported through the ER membrane. However, insight into the mechanism underlying the transport of substrates/metabolites of UGTs through the ER membrane has not been elucidated. Metabolosome is a functional unit of metabolism consisting of multiple metabolism-related proteins. UGTs might form a metabolosome to facilitate the transport of their substrates and/or metabolites through the ER membrane. In the present study, therefore, extensive protein-protein interactions involving UGT2B7 were determined by a shotgun analysis of immunoprecipitate. Our shotgun analysis revealed that 92 proteins were immunoprecipitated with anti-UGT2B7 antibody in human liver microsomes. We further determined that 42 proteins out of 92 proteins were specifically immunoprecipitated with the anti-UGT2B7 antibody. In addition to UGT2B7, other microsomal enzymes such as UGT1A, CYP3A4, CYP1A2, and a monoamine oxidase, were included in the list of proteins immunoprecipitated with the anti-UGT2B7 antibody, suggesting that these proteins might form a metabolosome to regulate their functions in the liver. Further analyses are needed to elucidate the roles of those proteins in the enzymatic activity of human UGTs.
    Drug Metabolism and Pharmacokinetics 12/2013; · 2.07 Impact Factor
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    ABSTRACT: ATP-binding cassette (ABC) transporters transport a variety of substrates across cellular membranes coupled with hydrolysis of ATP. Currently 49 ABC transporters consisting of seven subfamilies, ABCA, ABCB, ABCC, ABCD, ABCE, ABCF, and ABCG, have been identified in humans and they are extensively expressed in various tissues. Skin can develop a number of drug-induced toxicities' such as Stevens–Johnson syndrome and psoriasis. Concentration of drugs in the skin cells is associated with the development of adverse drug reactions. ABC transporters play important roles in absorption and disposition of drugs in the cells; however, the expression pattern of human ABC transporters in the skin has not been determined. In this study, the expression patterns of 48 human ABC transporters were determined in the human skin as well as in the liver and small intestine. Most of the ABCA, ABCB, ABCC, ABCD, ABCE, and ABCF family members were highly or moderately expressed in the skin, while ABCG family members were slightly expressed in the skin. Significant interindividual variability was also observed in the expression levels of those ATP transporters in the skin, except for ABCA5 and ABCF1, which were found to be expressed in all of the human skin samples tested in this study. In conclusion, this is the first study to identify the expression pattern of the whole human ABC family of transporters in the skin. The interindividual variability in the expression levels of ABC transporters in the human skin might be associated with drug-induced skin diseases.
    Pharmacology Research & Perspectives. 10/2013; 1(1).
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    ABSTRACT: Uridine 5′-diphosphate-glucuronosyltransferases (UGTs) are phase II drug-metabolizing enzymes that catalyze glucuronidation of various endogenous and exogenous substrates. Among 19 functional human UGTs, UGT1A family enzymes largely contribute to the metabolism of clinically used drugs. While the UGT1A locus is conserved in mammals such as humans, mice, and rats, species differences in drug glucuronidation have been reported. Recently, humanized UGT1 mice in which the original Ugt1 locus was disrupted and replaced with the human UGT1 locus (hUGT1 mice) have been developed. To evaluate the usefulness of hUGT1 mice to predict human glucuronidation of drugs, UGT activities, and inhibitory effects on UGTs were examined in liver microsomes of hUGT1 mice as well as in those of wild-type mice and humans. Furosemide acyl-glucuronidation was sigmoidal and best fitted to the Hill equation in hUGT1 mice and human liver microsomes, while it was fitted to the substrate inhibition equation in mouse liver microsomes. Kinetic parameters of furosemide glucuronidation were very similar between hUGT1 mice and human liver microsomes. The kinetics of S-naproxen acyl-glucuronidation and inhibitory effects of compounds on furosemide glucuronidation in hUGT1 liver microsomes were also slightly, but similar to those in human liver microsomes, rather than in wild-type mice. While wild-type mice lack imipramine and trifluoperazine N-glucuronidation potential, hUGT1 mice showed comparable N-glucuronidation activity to that of humans. Our data indicate that hUGT1 mice are promising tools to predict not only in vivo human drug glucuronidation but also potential drug-drug interactions.
    Pharmacology Research & Perspectives. 10/2013; 1(1).
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    ABSTRACT: UDP-glucuronosyltransferase (UGT) 1A1 is the sole enzyme that can metabolize bilirubin. Human infants physiologically develop hyperbilirubinemia due to inadequate expression of UGT1A1 in the liver. While phototherapy using blue light is effective in preventing jaundice, sunlight has also been suggested, but without conclusive evidence, to reduce serum bilirubin levels. We investigated the mRNA expression pattern of human UGT1A1 in human skin, human skin keratinocyte (HaCaT) cells, and skin of humanized UGT1 mice. The effects of ultraviolet B (UVB)-irradiation on the expression of UGT1A1 in the HaCaT cells were also examined. Multiple UGT1A isoforms including UGT1A1 were expressed in human skin and HaCaT cells. When HaCaT cells were treated with UVB-exposed tryptophan, UGT1A1 mRNA and activity were significantly induced. The treatment of the HaCaT cells with 6-formylindolo[3,2-b]carbazole (FICZ), which is one of the tryptophan derivatives formed by UVB, resulted in an induction of UGT1A1 mRNA and activity. In neonates the expression of UGT1A1 was greater in the skin, while in adults UGT1A1 was mainly expressed in the liver. Treatment of humanized UGT1 mice with UVB resulted in a reduction of serum bilirubin levels, along with increased UGT1A1 expression and activity in the skin. Our data revealed a protective role of UGT1A1 expressed in the skin against neonatal hyperbilirubinemia. Sunlight, a natural and free source of light, makes it possible to treat neonatal jaundice, while allowing mothers to breast-feed neonates.
    Molecular pharmacology 08/2013; · 4.53 Impact Factor
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    ABSTRACT: While breast milk has been known as a cause of neonatal hyperbilirubinemia, the underlying mechanism of breast milk-induced jaundice has not been clarified. Here, the impact of fatty acids on human UDP-glucuronosyltransferase (UGT) 1A1 - the sole enzyme that can metabolize bilirubin - were examined. Oleic acid, linoleic acid, and docosahexaenoic acid (DHA) strongly inhibited UGT1A1 activity. Forty-eight hours after a treatment with a lower concentration of DHA (10 mg/kg), total bilirubin significantly increased in neonatal hUGT1 mice, which are human neonatal jaundice models. In contrast, treatments with higher concentrations of fatty acids (0.1-10 g/kg) resulted in a decrease in serum bilirubin in hUGT1 mice. It was further demonstrated that the treatment with higher concentrations of fatty acids induced UGT1A1, possibly by activation of peroxisome proliferator-activated receptors. Our data indicates that activation of peroxisome proliferator-activated receptors would increase UGT1A1 expression, resulting in reduction of serum bilirubin levels in human infants.
    Scientific Reports 01/2013; 3:2903. · 5.08 Impact Factor
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    ABSTRACT: Hepatic intrinsic clearance (CLint) of drugs is often predicted based on in vitro data that are obtained from the Michaelis-Menten analysis. While most of the metabolic rate-substrate concentration kinetic curves fit to the Michaelis-Menten equation, cytochrome P450 (CYP) and uridine 5'-diphosphate (UDP)-glucuronosyltransferases exhibit sigmoidal kinetics for certain drugs. In our study, the kinetics of CYP3A4-catalyzed carbamazepine 10,11-epoxidation in human liver microsomes was sigmoidal and fitted to the Hill equation, revealing the S50 value of 358 µM, n of 2.0, and the Vmax value of 463 pmol/min/mg. While the intrinsic clearance calculated from Michaelis-Menten parameters (CLint) overestimated the observed in vivo intrinsic clearance (CLint, in vivo), the maximum intrinsic clearance calculated based on the Hill equation (CLmax) exhibited better predictions of CLint, in vivo. Such better prediction using the CLmax was also observed for other four drugs, all of which also exhibited sigmoidal metabolic rate-concentration curves, according to the literature data. However, even if we assume such Hill equation, intrinsic clearances predicted at their therapeutic concentrations from in vitro data were still much lower than their CLint, in vivo, suggesting the existence of unknown factors causing discrepancy between in vitro intrinsic clearance in human liver microsomes and in vivo data. Thus, even if we assume sigmoidal kinetics, that would not be enough for accurate prediction of CLint, in vivo, and it would be preferable to use CLmax to quantitatively extrapolate the in vitro data to in vivo clearance.
    Biological & Pharmaceutical Bulletin 01/2013; 36(12):1959-63. · 1.85 Impact Factor
  • Tomoya Narawa, Tomoo Itoh
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    ABSTRACT: Stereoselective transport of methotrexate (L-amethopterin, L-MTX) and its antipode (D-amethopterin, D-MTX) by the proton-coupled folate transporter (PCFT) was examined using PCFT-expressing HEK293 cells (PCFT-HEK293 cells). Uptake of both L-MTX and D-MTX was pH-dependent and decreased with an increase in the extracellular pH from 5.0 to 7.4. The initial uptake rate of L-MTX into PCFT-HEK293 cells followed Michaelis-Menten kinetics with a K(m) value of approximately 5.0 microM. Dixon plots revealed that L-MTX uptake was inhibited competitively by unlabeled L-MTX, D-MTX, and folic acid (FA), with K(i) values of approximately 3.6, 180, and 2.1 microM, respectively. The initial uptake rate of D-MTX into PCFT-HEK293 cells also followed Michaelis-Menten kinetics with a K(m) value of 211 microM. The V(max) value of D-MTX was similar to that of L-MTX. The present study revealed that the transport of MTX enantiomers by PCFT is highly stereoselective with the uptake clearance of L-MTX being approximately 40-fold greater than that of D-MTX. It was also revealed that this high stereoselectivity results from the difference in K(m) values, and not V(max) values, between the enantiomers. The observed stereoselectivity was consistent with the differences in the intestinal absorption of MTX enantiomers in humans.
    Drug Metabolism and Pharmacokinetics 01/2010; 25(3):283-9. · 2.07 Impact Factor
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    ABSTRACT: The method for predicting the fraction absorbed (Fa) of the PEPT1 substrates was established based on the in vitro uptake into Caco-2 cells. Uptake of a drug into Caco-2 cells was measured, and the carrier-mediated initial uptake clearance (DeltaCL uptake) was calculated as the difference between the uptake clearance in the absence of glycyl-sarcosine (Gly-Sar) and that in the presence of 30 mM Gly-Sar. The DeltaCL uptake of each drug was then divided by that of cephradine to obtain DeltaCL*uptake, which was a normalized parameter to correct for inter-day and/or inter-cell variability. Then, cephradine (CED), cefixime (CFIX), and cefotiam (CTM) were selected as marker compounds having excellent, medium and poor absorption, respectively. The DeltaCL*uptake and Fa values for CED, CFIX and CTM were fitted to the equation derived from the complete radial mixing (CRM) model, and the scaling factor (A') was obtained. Using the A' value, Fa was predicted from the DeltaCL*uptake value of each drug. Good correlation was observed between the predicted and reported Fa values, which demonstrated that Fa of PEPT1 substrates can be predicted based on the in vitro uptake in Caco-2 cells.
    International Journal of Pharmaceutics 05/2008; 354(1-2):104-10. · 3.99 Impact Factor
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    ABSTRACT: Stereoselectivity of the human reduced folate carrier (RFC1) in Caco-2 cells was examined using methotrexate (L-amethopterin, L-MTX) and its antipode (D-amethopterin, D-MTX) as model substrates. The initial uptake rate of L-MTX into Caco-2 cells followed Michaelis-Menten kinetics with a Km value of approximately 1 microM. The Eadie-Hofstee plot of the RFC1-mediated L-MTX uptake showed that it was mediated by a single transport system, RFC1. Dixon plots revealed that L-MTX uptake was inhibited competitively by folic acid (FA), L-MTX and D-MTX, with Ki values of approximately 0.8, 1.5 and 180 microM, respectively. The results showed that the affinities of FA and L-MTX to RFC1 were approximately 120-fold greater than that of D-MTX. The uptake of L- and D-MTX into Caco-2 cells was also measured using LC-MS/MS analysis, which revealed that the L-MTX uptake was at least 7-fold greater than that of D-MTX. The present study revealed significant stereoselectivity of RFC1 toward amethopterin enantiomers with the L-isomer being much more favored.
    Drug Metabolism and Pharmacokinetics 03/2007; 22(1):33-40. · 2.07 Impact Factor
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    ABSTRACT: Stereoselectivity of the human reduced folate carrier (RFC1) was examined in Caco-2 cells using methotrexate (l-amethopterin or l-MTX) and its antipode (d-amethopterin or d-MTX) as model substrates. The initial uptake rate of folic acid (FA) was concentration dependent, with a K(m) value of approximately 0.6 microM. The Eadie-Hofstee plot of the RFC1-mediated FA uptake revealed a single component for FA uptake into Caco-2 cells, demonstrating that only RFC1 is involved in FA uptake. l-MTX inhibited FA uptake in a competitive manner with a K(i) value of approximately 2 microM, similar to the K(m) value of l-MTX. d-MTX also competitively inhibited FA uptake with a K(i) value being approximately 120 microM, indicating that the affinity of d-MTX is ca. 60-fold less than that of l-MTX. The stereoselectivity of human RFC1 observed in the present study was consistent not only with the stereoselectivity of rabbit RFC1 observed in rabbit intestinal brush border membrane vesicles but also with the reported differences in oral absorption of amethopterin enantiomers in humans.
    Chirality 11/2005; 17(8):444-9. · 1.72 Impact Factor
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    ABSTRACT: Previously, we have shown that the inhibition of the transporter-mediated hepatic uptake of cerivastatin (CER) by cyclosporin A (CsA) could, at least partly, explain a pharmacokinetic interaction between these drugs in humans. In the present study, we have examined the effect of CsA on the in vivo disposition of CER in rats and the in vitro uptake of [14C]CER in isolated rat hepatocytes in an attempt to evaluate the effect of inhibition of transporter-mediated hepatic uptake on the in vivo CER disposition. The steady-state plasma concentration of CER increased 1.4-fold when coadministered with CsA up to a steady-state blood concentration of 4 microM. Studies of [14C]CER uptake into isolated rat hepatocytes showed saturable transport, with the saturable portion accounting for more than 80% of the total uptake. CsA competitively inhibited the uptake of [14C]CER with a Ki of 0.3 microM. The IC50 for the uptake of [14C]CER in the absence and presence of rat plasma was 0.2 and 2.3 microM, respectively. The in vivo hepatic uptake of [14C]CER evaluated by the liver uptake index method was also inhibited by CsA in a dose-dependent manner. On the other hand, CsA did not inhibit the metabolism of [14C]CER in rat microsomes. The in vitro and in vivo correlation analysis revealed that this pharmacokinetic interaction between these drugs in rats could be quantitatively explained by the inhibition of transporter-mediated hepatic uptake. Thus, this drug-drug interaction in rats is predominantly caused by the transporter-mediated uptake process.
    Drug Metabolism and Disposition 01/2005; 32(12):1468-75. · 3.36 Impact Factor
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    ABSTRACT: Clinical studies have revealed that plasma concentrations of midazolam after oral administration are greatly increased by coadministration of erythromycin and clarithromycin, whereas azithromycin has little effect on midazolam concentrations. Several macrolide antibiotics are known to be mechanism-based inhibitors of CYP3A, a cytochrome P450 isoform responsible for midazolam hydroxylation. The aim of the present study was to quantitatively predict in vivo drug interactions in humans involving macrolide antibiotics with different inhibitory potencies based on in vitro studies. alpha- and 4-Hydroxylation of midazolam by human liver microsomes were evaluated as CYP3A-mediated metabolic reactions, and the effect of preincubation with macrolides was examined. The hydroxylation of midazolam was inhibited in a time- and concentration-dependent manner following preincubation with macrolides in the presence of NADPH, whereas almost no inhibition was observed without preincubation. The kinetic parameters for enzyme inactivation (K'app and kinact) involved in midazolam alpha-hydroxylation were 12.6 microM and 0.0240 min-1, respectively, for erythromycin, 41.4 microM and 0.0423 min-1, respectively, for clarithromycin, and 623 microM and 0.0158 min-1, respectively, for azithromycin. Similar results were obtained for the 4-hydroxylation pathway. These parameters and the reported pharmacokinetic parameters of midazolam and macrolides were then used to simulate in vivo interactions based on a physiological flow model. The area under the concentration-time curve (AUC) of midazolam after oral administration was predicted to increase 2.9- or 3.0-fold following pretreatment with erythromycin (500 mg t.i.d. for 5 or 6 days, respectively) and 2.1- or 2.5-fold by clarithromycin (250 mg b.i.d. for 5 days or 500 mg b.i.d. for 7 days, respectively), whereas azithromycin (500 mg o.d. for 3 days) was predicted to have little effect on midazolam AUC. These results agreed well with the reported in vivo observations.
    Drug Metabolism and Disposition 08/2003; 31(7):945-54. · 3.36 Impact Factor
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    ABSTRACT: The mechanism involved in the clinically relevant drug-drug interaction (DDI) between cerivastatin (CER) and cyclosporin A (CsA) has not yet been clarified. In the present study, we examined the possible roles of transporter-mediated hepatic uptake in this DDI. The uptake of [(14)C]CER into human hepatocytes prepared from three different donors was examined. Kinetic analyses revealed K(m) values for the uptake of [(14)C]CER within the range of 3 to 18 microM, suggesting that more than 70% of the total uptake at therapeutic CER concentrations was accounted for by a saturable process, i.e., transporter-mediated uptake. This uptake was inhibited by CsA with K(i) values of 0.3 to 0.7 microM. The uptake of [(14)C]CER was also examined in human organic anion transporting polypeptide-2 (OATP2)-expressing Madin-Darby canine kidney cells (MDCKII). Saturable OATP2-mediated uptake of [(14)C]CER was observed and was also inhibited by CsA, with a K(i) value of 0.2 microM. These results suggest that the DDI between CER and CsA involves the inhibition of transporter-mediated uptake of CER and, at least in part, its OATP2-mediated uptake. The effect of CsA on the in vitro metabolism of [(14)C]CER was also examined. The metabolism of [(14)C]CER was inhibited by CsA with an IC(50) value of more than 30 microM. From these results, we conclude that the DDI between CER and CsA is mainly due to the inhibition of transporter (at least partly OATP2)-mediated uptake in the liver.
    Journal of Pharmacology and Experimental Therapeutics 03/2003; 304(2):610-6. · 3.89 Impact Factor

Publication Stats

387 Citations
54.17 Total Impact Points

Institutions

  • 1998–2014
    • Kitasato University
      • • Department of Pharmacy
      • • Department of Pharmaceutical Sciences
      Edo, Tōkyō, Japan
  • 2005
    • Showa University
      • Division of Pharmaceutical Sciences
      Shinagawa, Tōkyō, Japan