Kiminori Mohri

Effects of furanocoumarin derivatives in grapefruit juice on nifedipine pharmacokinetics in rats

AbstractPurpose. It has been reported that grapefruit juice (GJ) causes a pharmacokinetic interaction with many drugs after co-ingestion. It is postulated that the substances in GJ may inhibit the first-pass metabolism during the intestinal absorption process. In recent years, several furanocoumarin derivatives that inhibit P450 activity in intestinal microsomes were isolated from GJ. In this study, we report the effects of the furanocoumarin derivatives in GJ on the nifedipine (NFP) pharmacokinetics in rats. Methods. Three furanocoumarin derivatives (bergaptol [BT], bergamottin [BG], and 6′,7′-dihydroxybergamottin [DHB]) found in GJ were used in this study. Each furanocoumarin was reconstituted in orange juice at the same concentration as in the GJ. Two milliliters of each sample was administered into the rat duodenum. After 30 min, NFP was intraduodenally administered at a dose of 3 mg/kg body weight. The NFP concentrations in the plasma samples were determined by HPLC. Results. A significant increase in the AUC of NFP was observed only in the rats administered BG; 1.5 times that of the control group. The result was quite identical with that of the group that was administered GJ. BT and DHB had no significant effects on the NFP pharmacokinetics. Conclusions. The results strongly suggested that BG in GJ might be the substance that elevates the NFP plasma concentrations.

Effects of cranberry juice on nifedipine pharmacokinetics in rats.

Little information is available about drug interactions with cranberry juice (CJ). Using microsomes from the human liver and rat small intestine, this study was designed to determine whether CJ could inhibit CYP3A‐mediated nifedipine (NFP) oxidase activity; it showed that CJ was a potent inhibitor of human and rat CYP3A. Preincubation with 10% vol/vol of CJ and 1 mM NADPH for 10 min resulted in significant inhibition of the NFP oxidation activity of human and rat CYP3A (18.2 and 12.6% decreases, respectively, compared with preincubation experiments without NADPH). In addition, the pharmacokinetic interaction between CJ and NFP in vivo was confirmed in rats. In comparison with a control group, the area under the concentration‐time curve (AUC) of NFP was approximately 1.6‐fold higher when CJ (2 mL) was injected intraduodenally 30 min before the intraduodenal administration of NFP (30 mg kg−1). However, the mean residence time, the volume of distribution and the elimination rate constant were not changed significantly. These data suggest that CJ component(s) inhibit the function of enteric CYP3A. In conclusion, it was found that CJ inhibits the CYP3A‐mediated metabolism of NFP in both rats and humans. Furthermore, CJ alters NFP pharmacokinetics in rats.

Enzymatic Activities in the Microsomes Prepared from Rat Small Intestinal Epithelial Cells by Differential Procedures

In 1982, it was reported that the small intestinal extraction ratio of phenacetin in rats coincided with the result of a metabolic investigation using epithelial cells (enterocytes) of the rat small intestine (1). That is, when Klippert et al. administered phenacetin into the jugular vein, the portal vein, and the duodenum of rats pretreated with 3-methylcholanthrene, the extraction ratio by the gut was calculated to be 0.53. However, the extraction ratio obtained from the in vitro data on phenacetin metabolism using isolated mucosal cells of 3-methylcholanthrene-pretreated rats was between 0.31 and 0.53. Gupta et al. (2) first reported in humans that the contribution of the small intestine in the first pass metabolism of cyclosporine was significantly large. In recent years, the metabolism of a drug when it passes through enterocytes has been the focus of attention (3–8). Although drug metabolism studies using rat intestinal microsomes have been increasing, their results vary quite widely among the researchers. It is conceivable that different procedures in the preparation of intestinal microsomes contribute severely to enzymatic stability; however, a comparative study of the preparation procedures of the microsomes from rat enterocytes has never been reported. In this report, we describe the activities of cytochrome P450 and UDP-glucuronosyltransferase in the rat small intestinal microsomes prepared by four different procedures and the stability of the enzyme activities in the microsomes during storage at 4°C, −20°C, and −80°C for 30 days.

Simultaneous determination of amfenac sodium and its metabolite (7-benzoyl-2-oxindole) in human plasma by high-performance liquid chromatography.

A simple, selective, sensitive and rapid high-performance liquid chromatographic method for the simultaneous determination of amfenac sodium (AMF) and its metabolite (7-benzoyl-2-oxindole, S1) in plasma was established. To 100 microliters of plasma, purified water (100 microliters), ammonium sulphate (0.2 g) and ethanol (100 microliters) containing fenbufen (100 micrograms/ml, internal standard) were added. After centrifugation the ethanol layer was directly injected into a reversed-phase ODS column. AMF and S1 were eluted using a gradient buffer system of 20-80% acetonitrile-phosphate buffer (pH 7.0), and detected at 245 nm. The analytical recoveries of AMF at concentrations of 0.5, 2 and 10 micrograms/ml in plasma were ca. 92.1, 95.4 and 94.6%, respectively. The coefficients of variation of the AMF recoveries were below 4.6%. The S1 recoveries at the concentrations of 40, 200 and 400.ng/ml were ca. 93.4, 98.7 and 95.3%, and the coefficients of variation were below 6.0%. The coefficients of variation for intra- and inter-day variation of AMF (5 micrograms/ml) and S1 (100 ng/ml) were 4.5 and 3.6% and 4.2 and 4.2%, respectively. The detection limits of AMF and S1 in plasma were as low as 0.1 microgram/ml and 20 ng/ml, and the coefficients of variation were 4.0 and 4.4%, respectively. The method was applied to determine the plasma concentrations of AMF and S1 after oral administration of AMF capsules (100 mg of AMF) to human volunteers.

Factors affecting physicochemical properties of liposomes prepared with hydrogenated purified egg yolk lecithins by the microencapsulation vesicle method

We examined hydrogenated purified egg yolk lecithins, having practical advantages over non-hydrogenated ones, as liposomal membrane materials. Liposomes were prepared by the microencapsulation vesicle (MCV) method in which liposomes are formed through two-step emulsification and dispersion. Three types of purified egg yolk lecithins with different iodine values were examined after being dissolved in one of three lipid solvents. The liposome size increased as the temperature during the second emulsification increased, being closer to the boiling temperature of the solvent. The preparation temperature in relation to the transition temperature of each lecithin was also a factor affecting liposome sizes. As for the encapsulation efficiencies of the model compound calcein in liposomes, they differed mainly depending on the solubility of each lecithin in a lipid solvent and it was more obvious in hydrogenated lecithins. A high preparation temperature resulted in lower encapsulation efficiencies, suggesting that leakage of encapsulated calcein was facilitated at high temperature in the MCV methods. There was a significant correlation between liposome sizes and encapsulation efficiencies in non-hydrogenated purified egg yolk lecithin but not in hydrogenated ones. When using hydrogenated purified egg yolk lecithins as liposomal membrane materials, it was suggested that a lipid solvent should be chosen so that a lecithin completely dissolves under the preparation condition in order to achieve a higher encapsulation efficiency. Smaller liposome particles were obtained when the second emulsification was performed at a lower temperature compared with the boiling point of the lipid solvent. These findings can be applied to control encapsulation efficiencies and particle sizes in each particular liposome preparation enclosing therapeutic agents.

Hesperidin in orange juice reduces the absorption of celiprolol in rats

It has been reported that the intestinal absorption of celiprolol, an antihypertensive drug, is inhibited when it is taken with orange juice; it has been suggested that element(s) in citrus juice are responsible for this. In the present study, the pharmacokinetic interaction between celiprolol and orange juice was characterized through in vivo experiments with rats. Celiprolol 5 mg/kg was injected into the rat duodenum together with 5 ml/kg of neutralized orange juice or the same concentration of hesperidin as in the orange juice. Plasma celiprolol concentrations were measured by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). Concomitant administration of orange juice or hesperidin with celiprolol significantly decreased the area under the plasma concentration-time curve (AUC) by 74% and 75%, respectively, compared with control. These findings suggest that hesperidin is responsible for the decreased absorption of celiprolol and that orange juice taken with celiprolol has an inhibiting effect on intestinal absorption of the drug.

Determination of erythromycin in human plasma and whole blood by high-performance liquid chromatography

Abstract A simple, selective, sensitive, and rapid high-performance liquid chromatographic (HPLC) method is described for the quantitation of erythromycin (EM) in plasma and whole blood. The volume of plasma and whole blood and analytical time were only 0—2 ml and ∼15 min. Analytical recovery of EM at concentrations of 0.2, 1.0 and 5.0 μg/ml after the complete extraction procedures with diethyl ether from alkalinized plasma and whole blood was > 75%. The coefficients of variation (CVs) for intra- and inter- day assay riabilities at 0.2, 1.0 and 5.0 μg/ml of EM were <5.8% in plasma and <6.3% in whole blood, respectively. The calibration curves for the respective analyte were linear (r = 0.994) over concentrations ranging from 0.1 to 5.0 μg/ml in plasma and whole blood. The lower detection limit for EM in plasma and whole blood was 0.1 μg/ml (CVs <5.3%). This assay method is useful for the routine monitoring of EM in biological specimens.

Development of Patient‐Friendly Preparations: Preparation of a New Allopurinol Mouthwash Containing Polyethylene(oxide) and Carrageenan

Stomatitis is a harmful side effect induced by high and/or multiple dosing of cytotoxic drugs such as 5‐fluorouracil. Allopurinol mouthwash has been used to prevent stomatitis induced by cancer chemotherapy. In the present study, the pharmaceutical utility of allopurinol mouthwash (Alkox‐mw), which consists of polyethylene(oxide) (Alkox®) and iota‐carrageenan (INA), was investigated as a possible material for a new oral dosage preparation for improving the adhesiveness onto the oral mucosa. From the observation of the gel formation, which was studied as a function of the variety of the added Alkox® and/or INA, the preferential compositions of Alkox®‐mw (Alkox®:INA% ratio) seemed to be 1.0:(0–1.0) and (0–3.0):0.4, respectively. The adhesiveness and the spinnability of various allopurinol mouthwashes were also investigated using a creep meter. The adhesiveness of Alkox‐mw increased with the increase in the amount of added Alkox®. Furthermore, the adhesion force of Alkox®‐mw was greater than that of allopurinol mouthwash consisting of sodium carboxymethylcellulose (CMC–Na). From the in vitro assessment of mimicking the effusion of the allopurinol mouthwashes from the surface of the oral mucosa, the effusion of Alkox®‐mws was retarded by the added Alkox. The results obtained in the present study suggest that Alkox®‐mws may be useful as a new dosage form that adheres to the oral mucosa.

Stereoselective Taurine Conjugation of (R)-Benoxaprofen Enantiomer in Rats: In Vivo and in Vitro Studies Using Rat Hepatic Mitochondria and Microsomes

No HeadingPurpose.Identify (R)-BOP-T in rat bile after administration of (R)-BOT over a 12 h period.Methods.Each benoxaprofen (BOP) enantiomer was administered i.v. to bile duct-cannulated rats at a dose of 5 mg/kg. The optical isomers of BOP and its metabolites in plasma, urine, and bile were quantified using a chiral HPLC column. The amounts of BOP glucuronide (BOP-G), BOP taurine conjugate (BOP-T), and BOP enantiomers excreted into the bile over 12 h after administration of (R)-BOP were as follows: (R)-BOP-G and (S)-BOP-G, 2.1 ± 0.5 and 6.2 ± 1.4% of the dose; (R)-BOP-T and (S)-BOP-T, 5.6 ± 1.8 and 0.7 ± 0.3% of the dose; (R)-BOP and (S)-BOP, 0.7 ± 0.1 and 1.7 ± 0.2% of the dose, respectively, whereas after (S)-BOP administration, (S)-BOP-G and (S)-BOP were mainly excreted into the bile (14.3 ± 1.8 and 3.0 ± 0.4% of the dose, respectively). Only after (R)-BOP administration was the taurine conjugate of BOP found in the bile, and the configuration was R. BOP-T could not be found in the bile after (S)-BOP administration. To investigate the stereoselectivity of the conjugation enzymes responsible for BOP-T formation, in vitro studies were performed using rat hepatic organelles.Results.When (R)-BOP was used as a substrate, rat hepatic mitochondrial and microsomal fractions exhibited stereoselective BOP-T formation activity, with microsomal activity approximately 3.0 times greater than that of the mitochondria. That of (S)-BOP was approximately 2.1. Mean (R)/(S) ratios of BOP enantiomer for BOP-T formation in the mitochondrial and microsomal incubations were approximately 1.7 and 2.4, respectively.Conclusion.Although in the in vivo studies, only (R)-BOP-T originated from (R)-BOP was found in the bile, the configuration of BOP-T formed by the incubations of (R)-BOP or (S)-BOP with rat hepatic mitochondria or microsomes was S for both.

IDENTIFICATION OF THE RABBIT LIVER UDP-GLUCURONOSYLTRANSFERASE CATALYZING THE GLUCURONIDATION OF 4-ETHOXYPHENYLUREA (DULCIN)

Dulcin (DL), 4-ethoxyphenylurea, a synthetic chemical about 200 times as sweet as sucrose, has been proposed for use as an artificial sweetener. DL is excreted as a urinary ureido-N-glucuronide after oral administration to rabbits. The phenylurea N-glucuronide is the only ureido conjugate with glucuronic acid known at present; therefore, DL is interesting as a probe to search for new functions of UDP-glucuronosyltransferases (UGTs). Seven UGT isoforms (UGT1A3, UGT1A4, UGT1A6, UGT1A7, UGT2B13, UGT2B14, and UGT2B16) have been identified from rabbit liver, but these UGTs have not been investigated using DL as a substrate. In this work, the identities of UGT isoforms catalyzing the formation of DL glucuronide were investigated using rabbit liver microsomes (RabLM) and cloned/expressed as rabbit UGT isoforms. DL-N-glucuronide (DNG) production was determined quantitatively in RabLM and homogenates of COS-7 cells expressing each UGT isoform by using electrospray liquid chromatography-tandem mass spectrometry. Analysis of DNG formation using RabLM, by Eadie-Hofstee plot, gave a Vmax of 0.911 nmol/min/mg protein and the Km of 1.66 mM. DNG formation was catalyzed only by cloned expressed rabbit UGT1A7 and UGT2B16 (Vmax of 3.98 and 1.16 pmol/min/mg protein and a Km of 1.23 and 1.69 mM, respectively). Substrate inhibition of UGT1A7 by octylgallate confirmed the significant contribution of UGT1A7 to the formation of DNG. Octylgallate was further shown to competitively inhibit DNG production by RabLM (Ki = 0.149 mM). These results demonstrate that UGT1A7 is the major isoform catalyzing the N-glucuronidation of DL in RabLM.