研究者詳細 - 大谷　壽一

論文 - 大谷　壽一

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A comparative pharmacodynamic study of the arrhythmogenicity of antidepressants, fluvoxamine and imipramine, in guinea pigs

Ohtani H., Odagiri Y., Sato H., Sawada Y., Iga T.

Biological and Pharmaceutical Bulletin （Biological and Pharmaceutical Bulletin） 24 （ 5 ） 550 - 554 2001年06月

ISSN 09186158

Among several classes of antidepressants, tricyclic antidepressants are known to prolong QTc intervals (QT interval corrected by heart rate) in electrocardiograms, while selective serotonin uptake inhibitors (SSRI) are considered to be devoid of arrhythmogenicity. In this study, we aimed to compare the arrhythmogenic potencies of imipramine (IMI), a typical tricyclic antidepressant, and fluvoxamine (FLV), an SSRI, at therapeutic and supratherapeutic concentrations using guinea pigs in vivo. Guinea pigs were anesthetized, and IMI (10 and 20 mg/kg/h) or FLV (20 mg/kg/h) was intravenously administered for 90 minutes to obtain the time-courses of drug concentrations in plasma and the changes in the QTc intervals during and after the drug administration. IMI induced distinct QTc prolongation in a dose-dependent manner, while FLV prolonged QTc intervals only slightly. A pharmacokinetic-pharmacodynamic analysis revealed that the potency for QTc prolongation of IMI was 1.7-fold higher than that of FLV. Taking the therapeutic concentration into account, the clinical risk of FLV for QTc prolongation was suggested to be 5-fold lower than that of IMI. Therefore, this SSRI agent was suggested to be safer than the tricyclic antidepressant for patients with cardiac risk factors, including arrhythmia, or for those taking other arrhythmogenic drugs concomitantly.

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In-vivo kinetics of the interaction between midazolam and erythromycin in rats, taking account of metabolic intermediate complex formation

Takedomi S., Matsuo H., Yamano K., Ohtani H., Sawada Y.

Journal of Pharmacy and Pharmacology （Journal of Pharmacy and Pharmacology） 53 （ 5 ） 643 - 651 2001年05月

ISSN 00223573

To predict, quantitatively, the extent of drug interaction during repeated administration of a metabolic inhibitor, we analysed the effects of erythromycin treatment under several regimens on the area under the concentration curve (AUC) of midazolam in rats. Midazolam was administered into the portal vein 12 h after erythromycin treatment for 1, 2 or 3 days, or 12, 24, 36, 48, 72 and 96 h after erythromycin treatment for 4 days, and the plasma-concentration profiles of midazolam were analysed to assess the AUC. Moreover, the contents of total cytochrome P450 and inactive metabolic intermediate (MI) complex were simultaneously quantitated. While the AUC value of midazolam was not affected by the administration of erythromycin for 1 day, repeated administration of erythromycin evoked an increase in AUC ratio (AUC in erythromycin-treated rats/AUC in vehicle-treated rats), which reached a maximum value of 1.99 at 12 h after 4 days' treatment with erythromycin. The total content of cytochrome P450 in liver microsomes was unaffected by erythromycin treatment. Although the MI complex was undetectable after 1 day's treatment with erythromycin, its content increased with duration of erythromycin treatment, and the complex disappeared after the end of erythromycin treatment with a half-life of 12.3 h. In conclusion, the interaction between erythromycin and midazolam could be well predicted when the formation of MI complex in the liver was taken into account.

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Prediction of midazolam - CYP3A inhibitors interaction in the human liver from in vivo/in vitro absorption, distribution, and metabolism data

Yamano K., Yamamoto K., Katashima M., Kotaki H., Takedomi S., Matsuo H., Ohtani H., Sawada Y., Iga T.

Drug Metabolism and Disposition （Drug Metabolism and Disposition） 29 （ 4 I ） 443 - 452 2001年04月

ISSN 00909556

The extent of decreases in apparent hepatic clearance and intrinsic hepatic clearance of midazolam (MDZ) after intravenous administration of MDZ with concomitant oral administration of cimetidine (CIM), itraconazole (ITZ), or erythromycin (EM) was predicted using plasma unbound concentrations and liver unbound concentrations of inhibitors. When MDZ was concomitantly administered with CIM, the observed increase in MDZ concentration was successfully predicted using inhibition constants assessed by human liver microsome and liver-to-plasma unbound concentration ratios in rats. However, the extent of interaction with ITZ or EM was still underestimated even taking into account the concentrative uptake of inhibitors into liver. We could predict the degree of "mechanism-based" inhibition by EM on the hepatic metabolism of MDZ, after repeated administration of EM, by a physiological model incorporating the amount of active enzyme as well as the concentration of inhibitor. The maximum inactivation rate constant and the apparent inactivation constant of EM on MDZ metabolism were 0.0665 min-1 and 81.8 μM, respectively. These kinetic parameters for the inactivation of the enzyme were applied to the physiological model with pharmacokinetic parameters of EM and MDZ obtained from published results. Consequently, we estimated that cytochrome P450 3A4 in the liver after repeated oral administration of EM was inactivated, resulting in 2.6-fold increase in the plasma concentration of MDZ. The estimated extent of increase in MDZ concentration in our study correlated well with the observed value based on metabolic inhibition by EM from published results.

Uptake mechanism of valproic acid in human placental choriocarcinoma cell line (BeWo)

Ushigome F., Takanaga H., Matsuo H., Tsukimori K., Nakano H., Ohtani H., Sawada Y.

European Journal of Pharmacology （European Journal of Pharmacology） 417 （ 3 ） 169 - 176 2001年04月

ISSN 00142999

Valproic acid is an anticonvulsant widely used for the treatment of epilepsy. However, valproic acid is known to show fetal toxicity, including teratogenicity. In the present study, to elucidate the mechanisms of valproic acid transport across the blood-placental barrier, we carried out transcellular transport and uptake experiments with human placental choriocarcinoma epithelial cells (BeWo cells) in culture. The permeability coefficient of [3H]valproic acid in BeWo cells for the apical-to-basolateral flux was greater than that for the opposite flux, suggesting a higher unidirectional transport in the fetal direction. The uptake of [3H]valproic acid from the apical side was temperature-dependent and enhanced under acidic pH. In the presence of 50 μM carbonyl cyanide p-trifluoromethoxylhydrazone, the uptake of [3H]valproic acid was significantly reduced. A metabolic inhibitor, 10 mM sodium azide, also significantly reduced the uptake of [3H]valproic acid. Therefore, valproic acid is actively transported in a pH-dependent manner on the brush-border membrane of BeWo cells. Kinetic analysis of valproic acid uptake revealed the involvement of a non-saturable component and a saturable component. The Michaelis constant for the saturable transport (Kt) was smaller under acidic pH, suggesting a proton-linked active transport mechanism for valproic acid in BeWo cells. In the inhibitory experiments, some short-chain fatty acids, such as acetic acid, lactic acid, propanoic acid and butyric acid, and medium-chain fatty acids, such as hexanoic acid and octanoic acid, inhibited the uptake of [3H]valproic acid. The uptake of [3H]valproic acid was also significantly decreased in the presence of 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid, salicylic acid and furosemide, which are well-known inhibitors of the anion exchange system. Moreover, p-aminohippuric acid significantly reduced the uptake of [3H]valproic acid. These results suggest that an active transport mechanism for valproic acid exists on the brush-border membrane of placental trophoblast cells and operates in a proton-linked manner. © 2001 Published by Elsevier Science B.V.

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Assessment of systemic adverse reactions induced by ophthalmic β-adrenergic receptor antagonists

Yamada Y., Takayanagi R., Tsuchiya K., Ito K., Ohtani H., Sawada Y., Iga T.

Journal of Ocular Pharmacology and Therapeutics （Journal of Ocular Pharmacology and Therapeutics） 17 （ 3 ） 235 - 248 2001年

ISSN 10807683

To assess quantitatively the risks of ophthalmic beta-blocking agents for cardiovascular and respiratory adverse reactions, we analyzed the binding kinetics of beta-blocking agents to the beta-1 and beta-2 adrenoceptors. The relationship between the occupancies for beta-1 and beta-2 adrenoceptors and the effects on the exercise pulse rate or the forced expiratory volume in one second (FEV1) after topical administration of carteolol, befunolol, timolol and betaxolol was analyzed using a ternary complex model. The beta-1 and beta-2 receptor occupancies after ophthalmic administration were calculated to be quite high as well as those after oral administration. The maximum occupancies for beta-1 and beta-2 receptors after ordinary ophthalmic administration were 52% and 88% for carteolol, 52% and 61% for befunolol, 62% and 82% for timolol, and 44% and 3% for betaxolol, respectively. Concave relationships were obtained between a decrease in exercise pulse rate and the beta-1 receptor occupancy and between a decrease in FEV1 and beta-2 receptor occupancy, respectively. Nasolacrimal occlusion was estimated to decrease the exercise pulse rate and FEV1 by 65% and 50%, respectively. The beta-1 and beta-2 adrenoceptor occupancies were proved to be the most appropriate indicators for cardiac and pulmonary adverse reactions evoked by ophthalmic beta-blocking agents.

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Characteristics of choline transport across the blood-brain barrier in mice: Correlation with in vitro data

Murakami H., Sawada N., Koyabu N., Ohtani H., Sawada Y.

Pharmaceutical Research （Pharmaceutical Research） 17 （ 12 ） 1526 - 1530 2000年12月

ISSN 07248741

Purpose. We examined the functional properties of choline transport across the blood-brain barrier (BBB) in mice. We compared the kinetic parameters and transport properties with those found in our in vitro uptake experiments using mouse brain capillary endothelial cells (MBEC4). Methods. The permeability coefficient-surface area product (PS) values of [3H]choline at the BBB were estimated by means of an in situ brain perfusion technique in mice. Results. [3H]Choline uptake was well described by a two-component model: a saturable component and a nonsaturable linear component. The [3H]choline uptake was independent of pH and Na+, but was significantly decreased by the replacement of Na+ with K+. Various basic drugs, including substrates and inhibitors of the organic cation transporter, significantly inhibited the [3H]choline uptake. These in situ (in vivo) results corresponded well to the in vitro results and suggest that the choline transporter at the BBB is a member of the organic cation transporter (OCT) family. Conclusion. The choline transport mechanism at the BBB is retained in MBEC4.

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Quantitative prediction of catalepsy induced by amoxapine, cinnarizine and cyclophosphamide in mice

Nasu R., Matsuo H., Takanaga H., Ohtani H., Sawada Y.

Biopharmaceutics and Drug Disposition （Biopharmaceutics and Drug Disposition） 21 （ 4 ） 129 - 138 2000年12月

ISSN 01422782

Parkinsonism can be a side effect of antipsychotic drugs, and has recently been reported with peripherally acting drugs such as calcium channel blockers, antiarrhythmic agents and so on. In this study, we examined the quantitative prediction of drug-induced catalepsy by amoxapine, cinnarizine and cyclophosphamide, which have been reported to induce parkinsonism. Dose-dependent catalepsy was induced by these drugs in mice. In vivo dopamine D1, D2 and muscarinic acetylcholine (mACh) receptor occupancies by these drugs in the striatum were also examined. The in vitro binding affinities (Ki values) of amoxapine and cinnarizine to dopamine D1, D2 and mACh receptors in rat striatal synaptic membrane were 200 and 2900 nM, 58.4 and 76.4 nM and 379 and 290 nM, respectively. Cyclophosphamide did not bind to these receptors at concentrations up to 100 μM. Twenty drugs, including those mentioned above, showed a significant correlation between the observed intensity of catalepsy and the values predicted with a pharmacodynamic model (Haraguchi K, Ito K, Kotaki H, Sawada Y, Iga T. Prediction of drug-induced catalepsy based on dopamine D1, D2, and muscarinic acetylcholine receptor occupancies. Drug Metab Disp 1997; 25: 675-684) based on in vivo occupancy of dopamine D1, D2 and mACh receptors. We conclude that occupancy of dopamine D1 and D2 receptors contributes to catalepsy induction by amoxapine and cinnarizine. Copyright © 2000 John Wiley & Sons, Ltd.

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Human placental transport of vinblastine, vincristine, digoxin and progesterone: Contribution of P-glycoprotein

Ushigome F., Takanaga H., Matsuo H., Yanai S., Tsukimori K., Nakano H., Uchiumi T., Nakamura T., Kuwano M., Ohtani H., Sawada Y.

European Journal of Pharmacology （European Journal of Pharmacology） 408 （ 1 ） 1 - 10 2000年11月

ISSN 00142999

To elucidate the role of P-glycoprotein in human placenta, we examined its expression in placenta, and the transcellular transport and uptake of P-glycoprotein substrates in cultured human placental choriocarcinoma epithelial cells (BeWo cells). The uptake of [3H]vinblastine and [3H]vincristine into BeWo cells was increased in the presence of a metabolic inhibitor, sodium azide. The basolateral-to-apical transcellular transport of [3H]vinblastine, [3H]vincristine and [3H]digoxin was greater than the apical-to-basolateral transcellular transport. In the presence of cyclosporin A, the basolateral-to-apical transcellular transport of [3H]vinblastine, [3H]vincristine and [3H]digoxin was significantly increased, and the apical-to-basolateral transcellular transport was decreased. The uptake of [3H]vinblastine, [3H]vincristine and [3H]digoxin into BeWo cells was significantly enhanced in the presence of several inhibitors, such as verapamil or mouse monoclonal antibody anti-P-glycoprotein MX-MDR (MRK16) as well as cyclosporin A. Although progesterone significantly enhanced the uptake of [3H]vinblastine, [3H]vincristine and [3H]digoxin into BeWo cells, the uptake of [3H]progesterone was not affected by these inhibitors. Immunoblot analysis revealed that P-glycoprotein with a molecular weight of 172 kDa was expressed in BeWo cells and isolated trophoblast cells. Furthermore, P-glycoprotein was detected in human placental brush-border membrane vesicles, but not in human placental basolateral membrane vesicles. In conclusion, these data suggest that P-glycoprotein is expressed on the brush-border membrane (maternal side) of human placental trophoblast cells. P-Glycoprotein is considered to regulate the transfer of several substances including vinblastine, vincristine and digoxin from mother to fetus, and to protect the fetus from toxic substances. (C) 2000 Elsevier Science B.V.

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Inhibition of P-glycoprotein by orange juice components, polymethoxyflavones in adriamycin-resistant human myelogenous leukemia (K562/ADM) cells

Ikegawa T., Ushigome F., Koyabu N., Morimoto S., Shoyama Y., Naito M., Tsuruo T., Ohtani H., Sawada Y.

Cancer Letters （Cancer Letters） 160 （ 1 ） 21 - 28 2000年11月

ISSN 03043835

We investigated the effects of the ethyl acetate extract of grapefruit juice (GFJ), that of orange juice (OJ) and their components on the uptake of [3H]vincristine into adriamycin-resistant human myelogenous leukemia cells. Its uptake was increased by the extracts of GFJ and OJ up to 7- and 3-fold, respectively, as well as verapamil and cyclosporin A. OJ components, i.e. 3,3',4',5,6,7,8-heptamethoxyflavone, nobiletin and tangeretin, also increased the uptake of [3H]vincristine in a concentration-dependent manner. Although GFJ components, dihydroxybergamottin and bergamottin, significantly increased the uptake, their potencies were considerably weaker than those of OJ components. These data suggest that OJ components inhibit P-gp-mediated efflux of [3H]vincristine, resulting in the intracellular accumulation of chemotherapeutic drugs. These components may become candidates of multi-drug resistance reversing agents in cancer chemotherapy. Copyright (C) 2000 Elsevier Science Ireland Ltd.

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Propiverine-induced Parkinsonism: A case report and a pharmacokinetic/pharmacodynamic study in mice

Matsuo H., Matsui A., Nasu R., Takanaga H., Inoue N., Hattori F., Ohtani H., Sawada Y.

Pharmaceutical Research （Pharmaceutical Research） 17 （ 5 ） 565 - 571 2000年07月

ISSN 07248741

Purpose. We present a case report of propiverine-induced Parkinsonism. We previously reported the induction of catalepsy by amiodarone, aprindine and procaine, which possess a diethylaminomethyl moiety and demonstrated selective blockade of dopamine D2 receptors by these drugs in mice. We hypothesized that drugs possessing a diethylaminomethyl structure may generally induce Parkinsonism and/or catalepsy. Methods. Thus, we performed a study to examine whether oxybutynin, pentoxyverine and etafenone, as well as propiverine, induce catalepsy in mice. Results. The intensity of drug-induced catalepsy was in the order: haloperidol > etafenone > pentoxyverine > propiverine > oxybutynin. In vivo occupancy of dopamine D1, D2 and mACh receptors in the striatum was also examined. The in vitro binding affinities to the D1, D2 and mACh receptors in the striatum synaptic membrane were within the ranges of 2.4-140 μM, 380-4,200 nM, and 1.2-2,800 nM, respectively. Conclusions. These results support the idea that any drug possessing a diethylaminomethyl moiety may contribute to the induction of catalepsy, possibly by occupying dopamine receptors.

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Effect of bioflavonoids on vincristine transport across blood-brain barrier

Mitsunaga Y., Takanaga H., Matsuo H., Naito M., Tsuruo T., Ohtani H., Sawada Y.

European Journal of Pharmacology （European Journal of Pharmacology） 395 （ 3 ） 193 - 201 2000年05月

ISSN 00142999

Several grapefruit juice bioflavonoids, including quercetin, are reported to stimulate P-glycoprotein-mediated drug efflux from cultured tumor cells. To see whether these bioflavonoids alter the permeation of vincristine across the blood-brain barrier, we conducted experiments with cultured mouse brain capillary endothelial cells (MBEC4 cells) in vitro and ddY mice in vivo. The steady-state uptake of [3H]vincristine by MBEC4 cells was decreased by 10 μM quercetin, but increased by 50 μM quercetin. Similarly, the in vivo brain-to-plasma concentration ratio of [3H]vincristine in ddY mice was decreased by coadministration of 0.1 mg/kg quercetin, but increased by 1.0 mg/kg quercetin. Kaempferol had a similar biphasic effect on the in vitro uptake of [3H]vincristine. Other aglycones tested (chrysin, flavon, hesperetin, naringenin) increased [3H]vincristine uptake in the 10-50 μM range, and glycosides (hesperidin, naringin, rutin) were without effect. We then addressed the mechanism of the concentration-dependent biphasic action of quercetin. Verapamil, a P-glycoprotein inhibitor, inhibited the efflux of [3H]vincristine from MBEC4 cells, while 10 μM quercetin significantly stimulated it. The uptake of [3H]vincristine by MBEC4 cells was increased by inhibitors of protein kinase C, but decreased by phorbol 12-myristate-13- acetate (PMA), as well as by 10 μM quercetin. The phosphorylation level of P-glycoprotein was increased in the presence of 5 μM quercetin or 100 nM PMA, but decreased by the protein kinase C inhibitor H7 (1-(5- isoquinolinesulfonyl)-2-methylpiperazine, 30 μM). We conclude that low concentrations of quercetin indirectly activate the transport of [3H]vincristine by enhancing the phosphorylation (and hence activity) of P- glycoprotein, whereas high concentrations of quercetin inhibit P- glycoprotein. Our results indicate that patients taking drugs which are P- glycoprotein substrates may need to restrict their intake of bioflavonoid- containing foods and beverages, such as grapefruit juice. (C) 2000 Elsevier Science B.V.

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Induction of apoptosis in mouse brain capillary endothelial cells by cyclosporin A and tacrolimus

Kochi S., Takanaga H., Matsuo H., Ohtani H., Naito M., Tsuruo T., Sawada Y.

Life Sciences （Life Sciences） 66 （ 23 ） 2255 - 2260 2000年04月

ISSN 00243205

Although cyclosporin A and tacrolimus are used clinically as potent immunosuppressants, there have been reports of neurotoxicity and encephalopathy. A possible mechanism is that these drugs damage the blood- brain barrier (BBB), inducing dysfunction and increased permeability, and are then able to enter the brain. We studied the cytotoxicity of cyclosporin A and tacrolimus, focused on apoptosis induction, using an immortalized cell line established from BALB/c mouse cerebral microvessel endothelial cells (MBEC4). We found that these two drugs induced cell shrinkage, chromatin condensation and DNA fragmentation, which are characteristics of apoptosis. Our data suggest that the induction of apoptosis on the brain capillary endothelial cells may be at least partly involved in the occurrence of immunosuppressant-induced encephalopathy.

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Polymethoxylated flavones in orange juice are inhibitors of P- glycoprotein but not cytochrome P450 3A4

Takanaga H., Ohnishi A., Yamada S., Matsuo H., Morimoto S., Shoyama Y., Ohtani H., Sawada Y.

Journal of Pharmacology and Experimental Therapeutics （Journal of Pharmacology and Experimental Therapeutics） 293 （ 1 ） 230 - 236 2000年04月

ISSN 00223565

The presence in orange juice of compounds that specifically inhibit the P-glycoprotein (P-gp) drug efflux transporter, but not the cytochrome P450 (CYP) isozyme CYP3A4, was investigated. The uptake of [3H]vinblastine, a substrate of P-gp, by Caco-2 cells was measured. An ethyl acetate extract of orange juice did not affect the initial uptake rate of [3H]vinblastine but significantly increased the steady-state uptake, as did cyclosporin A (20 μM), an inhibitor of P-gp. No significant effect on the uptake of 3-O- [3H]methylglucose or [14C]phenylalanine by Caco-2 cells was found, compared with the control. When the extract was separated on a Cosmosil column, the eluate with 70% methanol showed the most potent ability to increase [3H]vinblastine uptake. Additional separation of the 70% methanol eluate on a silica gel column with hexane-acetone (3:1) gave 3,3',4',5,6,7,8- heptamethoxyflavone (HMF) and 4',5,6,7,8-pentamethoxyflavone (tangeretin). HMF, tangeretin, and 3',4',5,6,7,8-hexamethoxyflavone (nobiletin), another methoxyflavone contained in orange juice, all increased the steady-state uptake of [3H]vinblastine by Caco-2 cells in a concentration-dependent manner. The order of potency of these compounds at the concentration of 50 μM was tangeretin > HMF > nobiletin. None of these methoxyflavones inhibited 6β-hydroxylation of testosterone catalyzed by CYP3A4. The ethyl acetate extract of orange juice and these methoxyflavones also increased steady-state [3H]vinblastine uptake by LLC-GA5-COL300 cells (a cell line transfected with human MDR1 cDNA). We conclude that these methoxyflavones enhanced vinblastine uptake by specifically inhibiting drug efflux via P-gp. They may have potential as agents for reversing multidrug resistance or for recovering the bioavailability of certain drugs.

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Determination of erythromycin, clarithromycin, roxithromycin, and azithromycin in plasma by high-performance liquid chromatography with amperometric detection

Taninaka C., Ohtani H., Hanada E., Kotaki H., Sato H., Iga T.

Journal of Chromatography B: Biomedical Sciences and Applications （Journal of Chromatography B: Biomedical Sciences and Applications） 738 （ 2 ） 405 - 411 2000年02月

ISSN 13872273

In this study, a high-performance liquid chromatographic method was developed for the quantitative determination of erythromycin (EM), roxithromycin (RXM), and azithromycin (AZM) in rat plasma with amperometric detection under a standardized common condition using clarithromycin (CAM) as an internal standard. This method was also proved to be applicable for the determination of CAM by employing RXM as an internal standard. Each drug was extracted from 150 μl of plasma sample spiked with internal standard under an alkaline condition with tert.-butyl methyl ether. The detector cell potential for the oxidation of the drugs was set at +950 mV. The linearity of the calibration curves were preserved over the concentration ranges of 0.1-10 μg/ml for EM and RXM, and 0.03-3.0 μg/ml for CAM and AZM. Coefficients of variation and relative error were less than 9% and ±7%, respectively. The analytical method presented here was proved to be useful for the investigation of the pharmacokinetic characteristics of EM, CAM, RXM, and AZM in rats. (C) 2000 Elsevier Science B.V.

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Influence of extracellular K<sup>+</sup> concentrations on quinidine-induced K<sup>+</sup> current inhibition in rat ventricular myocytes

Hirota M., Ohtani H., Hanada E., Sato H., Kotaki H., Uemura H., Nakaya H., Tatsuji I.

Journal of Pharmacy and Pharmacology （Journal of Pharmacy and Pharmacology） 52 （ 1 ） 99 - 105 2000年01月

ISSN 00223573

Hypokalaemia is one of the important risk factors for development of torsades de pointes. We recently reported that hypokalaemia increased the electrocardiographic QT interval in rats treated with quinidine, but did not alter the arrhythmogenic potency of quinidine. In this study, we have investigated the influence of extracellular potassium concentration ([K+](o)) on the inhibition of several types of cardiac potassium currents by quinidine. Such types of currents include the delayed rectifier potassium current (I(K)), the transient outward current (I(to)), and the inward rectifier potassium current (I(K1)), as measured in isolated rat ventricular cells using patch-clamp techniques. Concentration-dependent effects of quinidine on I(K), I(to), and I(K1) were evaluated under both normal ([K+](o) = 5.4 mM) and hypokalaemic ([K+](o) = 3.5 mM) conditions. In contrast to both I(K) and I(to), which were barely influenced by changes in [K+](o), I(K1) was significantly inhibited by hypokalaemia. Furthermore, while quinidine suppressed both I(K) and I(to) in a concentration-dependent manner, the inhibitory potency of quinidine on these currents was not influenced by changes in [K+](o). The respective normal and hypokalaemic IC50 values for quinidine were 11.4 and 10.0 μM (I(K)), and 17.6 and 17.3 μM (I(to)). Although higher concentrations of quinidine were required to inhibit I(K1), the inhibitory potency of quinidine was also found to be insensitive to changes in [K+](o). Thus, in rats, the inhibitory potency of quinidine for the K+ current-types I(K), I(to) and I(K1) is barely influenced by changes in [K+](o). These findings are consistent with our previous report showing that the QT-prolonging potency of quinidine was not altered under hypokalaemic conditions. However, whilst hypokalemia does not affect I(K) or I(to), it can inhibit I(K1) and can result in QT prolongation in-vivo.

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Comparative pharmacodynamic analysis of Q-T interval prolongation induced by the macrolides clarithromycin, roxithromycin, and azithromycin in rats

Ohtani H., Taninaka C., Hanada E., Kotaki H., Sato H., Sawada Y., Iga T.

Antimicrobial Agents and Chemotherapy （Antimicrobial Agents and Chemotherapy） 44 （ 10 ） 2630 - 2637 2000年

ISSN 00664804

In order to evaluate the arrhythmogenic potency of macrolide antibiotics in a quantitative manner, we analyzed the influence of clarithromycin (CAM), roxithromycin (RXM), and azithromycin (AZM) on Q-T intervals from pharmacokinetic and pharmacodynamic points of view and in comparison with the potency of erythromycin (EM) previously reported by us for rats. Male Sprague-Dawley rats were anesthetized, and CAM (6.6, 21.6, and 43.2 mg/kg of body weight/h), RXM (20 and 40 mg/kg/h), and AZM (40 and 100 mg/kg/h) were intravenously injected for 90 min to obtain the time courses of drag concentrations in plasma and the changes in the Q-T intervals during and after the drug injections. Distinct Q-T interval prolongation of up to 10 ms was observed with CAM at its clinical concentrations. RXM and AZM evoked Q-T interval prolongation at concentrations higher than their clinical ranges. The potencies for Q-T interval prolongation, assessed as the slope of the concentration-response relationship, were 6.09, 0.536, and 0.989 ms · ml/μg for CAM, RXM, and AZM, respectively. There was hysteresis between the change in the Q-T intervals and the time course of the plasma concentration of each drug. The rank order of clinical arrhythmogenicity was estimated to be EM > CAM > RXM > AZM, as assessed from the present results and our previous report for EM. In conclusion, RXM and AZM were estimated to be less potent at provoking arrhythmia than EM and CAM. These results should be useful for malting a safer choice of an appropriate agent for patients with electrocardiographic risk factors.

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Effect of furanocoumarin derivatives in grapefruit juice on the uptake of vinblastine by Caco-2 cells and on the activity of cytochrome P450 3A4

Ohnishi A., Matsuo H., Yamada S., Takanaga H., Morimoto S., Shoyama Y., Ohtani H., Sawada Y.

British Journal of Pharmacology （British Journal of Pharmacology） 130 （ 6 ） 1369 - 1377 2000年

ISSN 00071188

1. The presence of inhibitors of drug efflux transporters, such as P-glycoprotein (P-gp), in grapefruit juice (GFJ) was confirmed based on the uptake of [3H]-vinblastine (VBL) by Caco-2 cells. 2. The uptake of [3H]-VBL by Caco-2 cells was significantly increased by the ethyl acetate extract of GFJ as well as by cyclosporin A. The extract was separated on a Cosmosil column and the eluate with 60% methanol increased [3H]-VBL uptake, while the activity to inhibit CYP3A4 was greatest in the 70 and 80% eluates. 3. These results show that the major inhibitor of efflux transport of VBL is different from that of CYP3A4. 4. Further separation of the 60% methanol eluate afforded dihydroxybergamottin (DHBG). Both ethyl acetate extract of GFJ and DHBG increased steady-state [3H]-VBL uptake by LLC-GA5-COL300 cells. Besides DHBG, other furanocoumarins contained in GFJ, such as bergamottin, FC726, bergaptol and bergapten, increased the steady-state uptake of [3H]-VBL by Caco-2 cells. 5. The order of inhibitory potency of these compounds was FC726 > DHBG > bergamottin > bergapten > bergaptol. While, the IC50 values for inhibition of CYP3A4 were 0.075, 0.45, 1.0, 1.0 and > 20 μM, respectively. Bergaptol specifically inhibited VBL efflux. 6. DHBG was thus identified as a candidate for inhibitors of VBL transport, together with other furanocoumarins. Moreover, partly involvement of the P-gp inhibition was suggested. 7. Therefore, the inhibition of efflux transport of drugs as well as of drug metabolism by CYP3A4 could be an important cause of drug-GFJ interaction.

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Comparison of blood-brain barrier permeability in mice and rats using in situ brain perfusion technique

Murakami H., Takanaga H., Matsuo H., Ohtani H., Sawada Y.

American Journal of Physiology - Heart and Circulatory Physiology （American Journal of Physiology - Heart and Circulatory Physiology） 279 （ 3 48-3 ） H1022 - 8 2000年

ISSN 03636135

Here we present a method for measuring the permeability coefficient-surface area product (PS) values at the blood-brain barrier in mice, using the in situ brain perfusion technique originally developed for rats by Takasato et al. (Am J Physiol Heart Circ Physiol 247: H484-H493, 1984). Retrograde infusion into the right external carotid artery increased the carotid perfusion pressure in proportion to the perfusion rate. Intravascular volume and cerebral perfusion fluid flow at a perfusion rate of 1.0 ml/min in mice were similar to those in rats. In addition, the contribution of systemic blood to total flow in the hemisphere was small (only 3.2%). These findings indicated that this perfusion rate is suitable for mice. The PS values of more than 20 different compounds were determined in mice by using the in situ brain perfusion technique, and comparisons were made with data from rats. There was a close relationship (1:1) between the PS values in mice and rats, indicating that brain capillary permeabilities are similar in mice and rats.

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Efficient introduction of macromolecules and oligonucleotides into brain capillary endothelial cells using HVJ-liposomes.

Matsuo H, Okamura T, Chen J, Takanaga H, Ohtani H, Kaneda Y, Naito M, Tsuruo T, Sawada Y

Journal of drug targeting 8 （ 4 ） 207 - 16 2000年

ISSN 1061-186X

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Pharmacokinetic/pharmacodynamic analysis of tacrolimus-induced QT prolongation in guinea pigs

Minematsu T., Ohtani H., Sato H., Iga T.

Biological and Pharmaceutical Bulletin （Biological and Pharmaceutical Bulletin） 22 （ 12 ） 1341 - 1346 1999年12月

ISSN 09186158

Recently, several reports of clinical cases of QT prolongation and torsades de pointes, associated with the use of tacrolimus (FK506), have come to light. We have previously demonstrated FK506-induced QT prolongation in guinea pigs [Minematsu T., et al., Life Sci., 65, PL197-PL202 (1999)]. We now examined the relationship between QTc prolongation and the pharmacokinetics of FK506 in guinea pigs, in order to evaluate the arrhythmogenicity of FK506 when compared with that of quinidine sulfate (QND). Thus, dose-response relationships for FK506 (0.01 or 0.1 mg/h/kg) or QND (30 mg/h/kg) were investigated during and after intravenous infusion and also following intravenous bolus administration of FK506 (0.2 mg/kg). The dose-response relationship between plasma drug concentration and QTc prolongation for FK506 and QND were subsequently analyzed using an effect compartment model. The pharmacodynamic parameters thus obtained were as follows: k(E0) 2.72 X 10-4 (min-1), E(max) 27.1 (ms), EC50 0.376 (ng/ml) for FK506; and k(E0) 0.148 (min-1), K 8.41 (ms · ml/μg) for QND. The anti-clockwise hysteresis observed for FK506-induced QT prolongation was successfully analyzed by the present pharmacokinetic/pharmacodynamic model, which may provide a rational basis for developing a clinical dosing regimen to avoid possible QT prolongation induced by FK506.

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