Kazuhisa Ishihara

Balicalin, the predominant flavone glucuronide of scutellariae radix, is absorbed from the rat gastrointestinal tract as the aglycone and restored to its original form.

When baicalin was orally administered to conventional rats, it was detected in their plasma for 24 h after administration, but baicalein, the aglycone of baicalin, was not detected. However, when baicalin was given to germ‐free rats, only a small amount of baicalin was detected in their plasma within 2 h after the administration, its AUC0‐lim (the area under the concentration‐time curve from 0 to last determination time) being 12.0% of that in conventional rats. Subsequently, a considerable amount (55.1 ± 6.2%) of baicalin was recovered from the gastrointestinal tract even 4 h after administration. When baicalein was orally administered to conventional rats, however, baicalin appeared rapidly in their plasma at an AUC0‐lim value similar to that obtained after oral administration of baicalin, despite the absence of baicalein in plasma. When intestinal absorption was evaluated by the rat jejunal loop method, baicalein was absorbed readily, but only traces of baicalin were absorbed. Moreover, in conventional rats a small amount (13.4 ± 3.1%) of baicalin and an appreciable amount (21.9 ± 3.4%) of baicalein were recovered from the gastrointestinal tract even 4 h after oral administration of baicalin, but only a small amount (3.93 ± 1.43%) of baicalein was detected in the intestinal tract 1 h after administration of baicalein.

BIOAVAILABILITY STUDY OF GLYCYRRHETIC ACID AFTER ORAL ADMINISTRATION OF GLYCYRRHIZIN IN RATS; RELEVANCE TO THE INTESTINAL BACTERIAL HYDROLYSIS

To clarify the metabolic fate of glycyrrhizin when orally ingested, we investigated the bioavailability of glycyrrhetic acid, the aglycone of glycyrrhizin, after intravenous or oral administration of glycyrrhetic acid (5.7 mg kg−1, equimolar to glycyrrhizin) or glycyrrhizin (10 mg kg−1) at a therapeutic dose in rat.

Interaction of drugs and Chinese herbs: pharmacokinetic changes of tolbutamide and diazepam caused by extract of Angelica dahurica.

The inhibitory effects of Angelica dahurica root extract on rat liver microsomal cytochrome P450 and drug‐drug interactions were studied.

Toxicological aspects of Kampo medicines in clinical use

Among 210 medicinal prescriptions used in present-day Japan, the clinical uses and the acute, chronic and mutagenic toxicity study of 16 Kampo (Japanese herbal) medicines are summarized. These Kampo medicines are classified into two categories; eight prescriptions containing Bupleurum root (Bupleurum falcatum L.) such as Sho-saiko-to and Saiko-keishi-to, and eight prescriptions not containing Bupleurum root such as Juzen-taiho-to and Ninjin-yoei-to. Studies of some potential interaction between herbal medicine and western drugs are also described.

Simultaneous determination of byak-angelicin and oxypeucedanin hydrate in rat plasma by column-switching high-performance liquid chromatography with ultraviolet detection

A simple and sensitive column-switching HPLC method was developed for the simultaneous determination of two furocoumarin compounds, byak-angelicin and oxypeucedanin hydrate, which are the main components of hot water extract of Angelica dahurica root (AE), in rat plasma. Plasma sample was simply deproteinated with perchloric acid. After centrifugation, the supernatant was injected into a column-switching HPLC system consisting of a clean-up column (Symmetry Shield RP 8, 20x3.9 mm I.D.) and analytical column (Symmetry C18, 75x4.6 mm I.D.) which were connected with a six-port switching valve. The flow-rate of the mobile phase (acetonitrile-water, 20:80) was maintained at 1 ml/min. Detection was carried out at wavelength 260 nm with a UV detector. The column temperature was maintained at 40 degrees C. The calibration curves of byak-angelicin and oxypeucedanin hydrate were linear over the ranges 19.6 to 980 ng/ml (r2>0.997). The accuracy of these analytes was less than 4.4%. The intra- and inter-day relative standard deviations of byak-angelicin and oxypeucedanin hydrate were within 12.0% and 12.7%, respectively. The present method was applied for the analysis of plasma concentration from rats after administration of AE.

High-performance liquid chromatographic assay with fluorescence detection for the determination of cephaeline and emetine in human plasma and urine.

A high-performance liquid chromatographic assay method for the quantitation of ipecac alkaloids (cephaeline and emetine) in human plasma and urine is described. Human plasma or urine was extracted with diethylether under alkaline conditions following the addition of an internal standard. Concentrations of alkaloids and internal standard were determined by octadecylsilica chromatographic separation (Symmetry C18 columns, plasma analysis; 15 cmx4.6 mm I.D., 5 microm particle size, urine analysis; 7.5 cmx4.6 mm I.D., 5 microm particle size). The mobile phase consisted of buffer (20 mmol/l 1-heptanesulfonic acid sodium salt, adjusted to pH 4.0 with acetic acid)-methanol (51:49, v/v). Eluate fluorescence was monitored at 285/316 nm. The lowest quantitation limits of cephaeline and emetine were 1 and 2.5 ng/ml, respectively, in plasma, and 5 ng/ml in urine. Intra- and inter-day relative standard deviations were below 15%. The assay is sensitive, specific and applicable to pharmacokinetic studies in humans.

Effects of subacutely administered saiboku-to, an oriental herbal medicine, on pharmacodynamics and pharmacokinetics of diazepam in rodents.

SummarySubacute treatment with saiboku-to (2000 mg/kg, p.o., once a day) for 7 days induced an anxiolytic-like effect in rats. It did not, however, produce any other effects, such as sedative and hypnotic effects, anticonvulsive and muscle relaxant effects except for anxiolytic effect observed in diazepam-injected rats or mice. Diazepam (1.0 mg/kg, s.c.) induced anxiolytic-like effect was enhanced in saiboku-to treated rats as an additional effect of that induced by saiboku-to. To elucidate whether the enhancement of the anxiolytic-like effect following combined administration of diazepam and saiboku-to is due to the inhibition of hepatic drug-metabolizing enzymes, the pharmacokinetics of diazepam were further investigated in saiboku-to treated rats. The pharmacokinetic studies clearly demonstrated that subacute treatment with saiboku-to did not affect plasma concentration and protein binding rate of diazepam, and the activities of hepatic drug-metabolizing enzymes related to diazepam metabolism. These results, taken together, suggest that the enhancement of diazepam-induced anxiolytic-like effect observed in saiboku-to-treated rats is not due to an inhibition of diazepam metabolism.

Biotransformation of the ipecac alkaloids cephaeline and emetine from ipecac syrup in rats

SummaryThe metabolism of cephaeline and emetine, which are the primary active components of ipecac syrup, were investigated in rats. Cephaeline-6′-O-glucuronide was found to be a biliary metabolite of cephaeline. Cephaeline (6′-O-demethylemetine) and 9-O-demethylemetine were observed to be enzyme-hydrolyzed biliary metabolites of emetine. Cephaeline was conjugated to glucuronide, while emetine was demethylated to cephaeline and 9-O-demethylemetine, and may be conjugated to glucuronides afterwards. Urine, feces and bile were collected from rats within 48 hours following the administration of ipecac syrup containing tritium (3H)-labeled cephaeline or emetine. Metabolites were separated and quantified by thin layer chromatography (TLC) or high-performance liquid chromatography (HPLC). Biliary and urinary excretion rates of3H-cephaeline were 57.5% and 16.5% of the dose, respectively. Cephaeline-6′-O-glucuronide was comprised 79.5% of biliary radioactivity and 84.3% of urinary radioactivity. Unchanged cephaeline was detected in 42.4% of the dose in feces. Biliary excretion rate of3H-emetine was 6.9% of the dose. Emetine, cephaeline and 9-O-demethylemetine comprised 5.8%, 43.2% and 13.6% in hydrolyzed bile, respectively. There were no emetine-derived metabolites in urine or feces. The occurrence of unchanged emetine was 6.8% and 19.7% of the dose in urine and feces, respectively.

Absorption, distribution and excretion of3H-labeled cephaeline- and emetine-spiked ipecac syrup in rats

SummaryThe maximum plasma radioactivity levels of tritium (3H)-labeled cephaeline, (24.3, 28.7 and 40.6 ng eq./mL) were reached at 2.00-3.33 hours following oral dosing of ipecac syrup. The maximum plasma radioactivity levels of3H-emetine (2.71, 6.47 and 9.62 ng eq./mL) were reached at 1.08–2.33 hours following ipecac syrup administration. The Cmax values of3H-cephaeline were followed by a biexponential decrease with half-lives t1/2(λz) of 3.45–9.40 hours. On the other hand, the t1/2(λz) of3H-emetine were 65.4–163 hours, which revealed a biexponential decrease. The radioactivity of both tritium-labeled compounds was distributed maximally in most tissues at 24 hours. For3H-cephaeline, the maximum radioactivity levels in tissues were approximately 100–150 times greater than in plasma. For3H-emetine, the radioactivity levels in tissues were approximately 1000–3000 times greater than in plasma. Tissue radioactivity levels decreased at a substantially slower rate than that observed in plasma. Tissue radioactivity of3H-emetine decreased more slowly than that of3H-cephaeline. For3H-cephaeline, the cumulative biliary excretion of radioactivity was 57.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity in these rats was 16.5% and 29.1%, respectively, of the dose at 48 hours following dosing. For3H-emetine, the cumulative biliary excretion of radioactivity was 12.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity was 9.4% and 34.1%, respectively, of the administered dose at 48 hours. The radioactivity level of3H-emetine remaining in the carcasses at 48 hours was equivalent to approximately 50% of the dose. A portion of each tritium-labeled compound was subjected to entero-hepatic circulation. Thus, the absorption rate of3H-cephaeline and3H-emetine was estimated to be approximately 70% on the basis of the data obtained from excretion studies. There was no difference in the absorption process between these two compounds. However, the difference was admitted in the biliary clearance, which is the main excretion route of both compounds. Delayed excretion of3H-emetine may be primarily due to its resorption as related to entero-hepatic circulation and tissue retention. This study has determined the absorption, distribution and excretion of3H-cephaeline and3H-emetine in rats.