Improvement of selectivity and sensitivity by column switching in the determination of glycyrrhizin and glycyrrhetic acid in human plasma by high-performance liquid chromatography

Can Antiviral Activity of Licorice Help Fight COVID-19 Infection?

The phytotherapeutic properties of Glycyrrhiza glabra (licorice) extract are mainly attributed to glycyrrhizin (GR) and glycyrrhetinic acid (GA). Among their possible pharmacological actions, the ability to act against viruses belonging to different families, including SARS coronavirus, is particularly important. With the COVID-19 emergency and the urgent need for compounds to counteract the pandemic, the antiviral properties of GR and GA, as pure substances or as components of licorice extract, attracted attention in the last year and supported the launch of two clinical trials. In silico docking studies reported that GR and GA may directly interact with the key players in viral internalization and replication such as angiotensin-converting enzyme 2 (ACE2), spike protein, the host transmembrane serine protease 2, and 3-chymotrypsin-like cysteine protease. In vitro data indicated that GR can interfere with virus entry by directly interacting with ACE2 and spike, with a nonspecific effect on cell and viral membranes. Additional anti-inflammatory and antioxidant effects of GR cannot be excluded. These multiple activities of GR and licorice extract are critically re-assessed in this review, and their possible role against the spread of the SARS-CoV-2 and the features of COVID-19 disease is discussed.

Recent advances in chemical analysis of licorice (Gan-Cao)

Gan-Cao, or licorice, the dried roots and rhizomes of Glycyrrhiza uralensis, G.glabra, and G.inflata, has received considerable interest due to its extensive application in traditional Chinese medicine (TCM) prescriptions (60% approximately), clinical therapy, and as food additives world-wide. Chemical analysis is an important approach to understand the active pharmaceutical components in licorice and its prescriptions, as well as to develop novel methodologies for their quality assessment and control. This comprehensive review describes the advances in the chemical analysis, including sample preparation methods, qualitative and quantitative analysis and biological specimen analysis, based on 113 references for the recent years. Newly established methods are summarized, such as high performance thin layer chromatography (HPTLC), high performance liquid chromatography (HPLC), liquid chromatography tandem mass spectrometry (LC-MS), capillary electrophoresis (CE) and near infrared spectroscopy (NIR), which allows the identification, authentication, and simultaneous detection of multiple compounds in licorice with higher throughput and sensitivity. It is anticipated that this review could provide imperative information for improving the existing quality evaluation methods of licorice and afford scientific basis for further researches on the pharmacodynamic substances of licorice.

Chromolithic Method Development, Validation and System Suitability Analysis of Ultra-Sound Assisted Extraction of Glycyrrhizic Acid and Glycyrrhetinic Acid from Glycyrrhiza glabra

An ultrasound-assisted extraction and chromolithic LC method was developed for simultaneous determination of glycyrrhizic acid (GA) and glycyrrhetinic acid (GL) from the root extract of Glycyrrhiza glabra using RPLC-PDA. The developed method was validated according to the International Conference on Harmonisation. The method exhibited good linearity (r2 >0.9989) with high precision and achieved good accuracies between 97.5 to 101.3% of quantitative results. The method is more sensitive and faster (resolved within ten minutes) than the earlier developed methods using normal LC columns.

Glycyrrhetinic acid induces anoikis-like death and cytoskeletal disruption in the central nervous system tumorigenic cells

We analyzed the effects of glycyrrhetinic acid (GA), a licorice compound, on the induction of anoikis-like death and cytoskeletal disruption in the central nervous system (CNS) tumorigenic cells. GA was cytotoxic in time- and dose-dependent manners, and the tumorigenic cells shed floating cells upon the GA treatment and even some of the adherent cells were easily detached from the fibronectin-coated culture dish by gentle shaking and aspiration. Reculture of the detached cells revealed that the longer the duration of GA exposure, the less the number of the proliferatable cells. These results indicate that GA perturbs cell adhesion and induces anoikis-like cell death. Further, GA also induced morphologic changes and disturbed cytoskeletal proteins.

Novel effects of glycyrrhetinic acid on the central nervous system tumorigenic progenitor cells: induction of actin disruption and tumor cell-selective toxicity

Licorice extracts are used worldwide in foods and medicines, and glycyrrhetinic acid (GA) is a licorice component that has been reported to induce various important biological activities. In the present study, we show that GA induces actin disruption and has tumor cell-selective toxic properties, and that its selectivity is superior to those of all the clinically available antitumor agents tested. The cytotoxic activity of GA and the tested antitumor agents showed better correlation with the partition coefficient (log P) values rather than the polar surface area (PSA) values. For selective toxicity against tumor cells, GA was most effective at 10 microM that was the same concentration as the previously reported maximum plasma GA level reached in humans ingesting licorice. These results suggest that GA could be utilized as a promising chemopreventive and therapeutic antitumor agent. The underlying mechanisms involved in the selective toxicity to tumor cells by GA are also preliminarily discussed.

Selective cytotoxicity of glycyrrhetinic acid against tumorigenic r/m HM-SFME-1 cells: potential involvement of H-Ras downregulation

With the intensive need for the development of more effective and safer agents for chemoprevention and therapy of human cancer, natural products from plants have been expected to play significant roles in creating new and better chemopreventive and therapeutic agents. Selectivity is also an important issue in cancer prevention and therapy. In the present study, normal serum-free mouse embryo (SFME) and tumorigenic human c-Ha-ras and mouse c-myc cotransfected highly metastatic serum-free mouse embryo-1 (r/m HM-SFME-1) cells were treated with various concentrations of clinically available antitumor agents or glycyrrhetinic acid (GA), and the antiproliferative effects of these compounds were determined by the MTT assay. Western blotting analysis, RT-PCR, fluorescence staining and confocal laser scanning microscopic observation were adopted to analyze H-Ras regulation. GA exhibited the tumor cell-selective toxicity through H-Ras downregulation, and its selectivity was superior to those of all the clinically available antitumor agents examined. For the selective toxicity of tumor cells, GA was most effective at 10 microM. Interestingly, this concentration was the same as the previously reported maximum plasma GA level reached in humans ingesting licorice. These results in the present study suggest that GA with its cytotoxic effects could be utilized as a promising chemopreventive and therapeutic antitumor agent.

Review of pharmacological effects of Glycyrrhiza sp. and its bioactive compounds

The roots and rhizomes of licorice (Glycyrrhiza) species have long been used worldwide as a herbal medicine and natural sweetener. Licorice root is a traditional medicine used mainly for the treatment of peptic ulcer, hepatitis C, and pulmonary and skin diseases, although clinical and experimental studies suggest that it has several other useful pharmacological properties such as antiinflammatory, antiviral, antimicrobial, antioxidative, anticancer activities, immunomodulatory, hepatoprotective and cardioprotective effects. A large number of components have been isolated from licorice, including triterpene saponins, flavonoids, isoflavonoids and chalcones, with glycyrrhizic acid normally being considered to be the main biologically active component. This review summarizes the phytochemical, pharmacological and pharmacokinetics data, together with the clinical and adverse effects of licorice and its bioactive components. Copyright © 2008 John Wiley & Sons, Ltd.

Glycyrrhetinic acid as inhibitor or amplifier of permeability transition in rat heart mitochondria

Glycyrrhetinic acid (GE), a hydrolysis product of glycyrrhizic acid, one of the main constituents of licorice root, is able, depending on its concentration, to prevent or to induce the mitochondrial permeability transition (MPT) (a phenomenon related to oxidative stress) in rat heart mitochondria (RHM). In RHM, below a threshold concentration of 7.5 microM, GE prevents oxidative stress and MPT induced by supraphysiological Ca2+ concentrations. Above this concentration, GE induces oxidative stress by interacting with a Fe-S centre of Complex I, thus producing ROS, and amplifies the opening of the transition pore, once again induced by Ca2+. GE also inhibits Ca2+ transport in RHM, thereby preventing the oxidative stress induced by the cation. However, the reduced amount of Ca2+ transported in the matrix is sufficient to predispose adenine nucleotide translocase for pore opening. Comparisons between observed results and the effects of GE in rat liver mitochondria (RLM), in which the drug induces only MPT without exhibiting any protective effect, confirm that it interacts in a different way with RHM, suggesting tissue specificity for its action. The concentration dependence of the opposite effects of GE, in RHM but not RLM, is most probably due to the existence of a different, more complex, pathway by means of which GE reaches its target. It follows that high GE concentrations are necessary to stimulate the oxidative stress capable of inducing MPT, because of the above effect, which prevents the interaction of low concentrations of GE with the Fe-S centre. The reported results also explain the mechanism of apoptosis induction by GE in cardiomyocytes.

Simultaneous HPLC analysis, with isocratic elution, of glycyrrhizin and glycyrrhetic acid in liquorice roots and confectionery products

Glycyrrhizin (1), the main active principle of Glycyrrhiza glabra (liquorice) roots, is extensively used in herbal medicines, in pharmaceutical preparations and confectionery products. A feasible and reliable method which allows the simultaneous analysis of 1 and its aglycone, 18beta-glycyrrhetic acid (2), by means of an isocratic HPLC procedure is described. The system uses a C8 column as the stationary phase, and a mixture of acetonitrile, methanol, water and glacial acetic acid as the mobile phase. Good linearity was found in the concentration ranges 1-50 and 0.05-2.50 microg/mL for 1 and 2, respectively. A simple and rapid sample pre-treatment, based on the extraction of the two analytes with a mixture of water and ethanol, was developed for the examination of liquorice confectionery products and root samples. The HPLC method was shown to be appropriate, in terms of precision and feasibility, for the quality control of the analytes in these matrices.

Separation and analysis of glycyrrhizin, 18beta-glycyrrhetic acid and 18alpha-glycyrrhetic acid in liquorice roots by means of capillary zone electrophoresis

Glycyrrhizin is the main active compound of Glycyrrhiza glabra root extracts; according to recent studies, glycyrrhizin and its aglycon, glycyrrhetic acid, have interesting therapeutic properties. A new capillary electrophoretic method has been developed for the separation and quantification of glycyrrhizin, beta-glycyrrhetic acid and its isomer a-glycyrrhetic acid. Separation of the analytes was achieved in less than 3 min on a fused silica capillary, by injecting the samples at the short end of the capillary (effective length: 8.5 cm). The background electrolyte was composed of pH 10.0 carbonate buffer, methanol and ethylene glycol (80/10/10) and contained 0.4% beta-cyclodextrin; indomethacin was used as the internal standard. Diode array detection was used, with quantitative assays carried out at 254 nm. Linearity was found over the 5-200 and 2.5-100 microg mL(-1) concentration ranges for glycyrrhizin and glycyrrhetic acid, respectively. This method has been applied to the determination of the analytes in different matrices (liquorice roots and commercial confectionery products), and to the purity control of beta-glycyrrhetic acid obtained from the hydrolysis of glycyrrhizin. When analysing beta-glycyrrhetic acid and its epimer in roots, the samples were purified by means of a suitable solid-phase extraction (SPE) procedure with Oasis HLB cartridges, which granted good selectivity, eliminating matrix interference.

Licorice compounds glycyrrhizin and 18beta-glycyrrhetinic acid are potent modulators of bile acid-induced cytotoxicity in rat hepatocytes

The accumulation of hydrophobic bile acids results in cholestatic liver injury by increasing oxidative stress, mitochondrial dysfunction, and activation of cell signaling pathways. Licorice root and its constituents have been utilized as antihepatotoxic agents. The purpose of this study was to evaluate the potential modulation by a primary component of licorice root, glycyrrhizin (GL), and its metabolite, 18beta-glycyrrhetinic acid (GA), in a hepatocyte model of cholestatic liver injury. Preincubation of fresh rat hepatocyte suspensions with GL or GA reduced glycochenodeoxycholic acid (GCDC)-dependent reactive oxygen species generation, with GA more potent than GL. Interestingly, GL and GA had opposing effects toward GCDC-induced cytotoxicity; GA prevented both necrosis and apoptosis, whereas GL enhanced apoptosis. GCDC promoted activation of caspase 10, caspase 3, and PARP; all were inhibited by GA but not GL. Induction of apoptosis by GCDC was also associated with activation of JNK, which was prevented by GA. Activation of caspase 9 and dissipation of mitochondrial membrane potential were prevented by GA but not GL. In liver mitochondrial studies, GL and GA were both potent inhibitors of the mitochondrial permeability transition, reactive oxygen species generation, and cytochrome c release at submicromolar concentrations. Results from this study suggest that GL exhibits pro-apoptotic properties, whereas GA is a potent inhibitor of bile acid-induced apoptosis and necrosis in a manner consistent with its antioxidative effect.

Glycyrrhetinic acid-induced permeability transition in rat liver mitochondria

Glycyrrhetinic acid, a hydrolysis product of one of the main constituents of licorice, the triterpene glycoside of glycyrrhizic acid, when added to rat liver mitochondria at micromolar concentrations induces swelling, loss of membrane potential, pyridine nucleotide oxidation, and release of cytochrome c and apoptosis inducing factor. These changes are Ca(2+) dependent and are prevented by cyclosporin A, bongkrekic acid, and N-ethylmaleimide. All these observations indicate that glycyrrhetinic acid is a potent inducer of mitochondrial permeability transition and can trigger the pro-apoptotic pathway.

The pharmacokinetics of glycyrrhizic acid evaluated by physiologically based pharmacokinetic modeling

Glycyrrhizic acid is widely applied as a sweetener in food products and chewing tobacco. In addition, it is of clinical interest for possible treatment of chronic hepatitis C. In some highly exposed subjects, side effects such as hypertension and symptoms associated with electrolyte disturbances have been reported. To analyze the relationship between the pharmacokinetics of glycyrrhizic acid in its toxicity, the kinetics of glycyrrhizic acid and its biologically active metabolite glycyrrhetic acid were evaluated. Glycyrrhizic acid is mainly absorbed after presystemic hydrolysis as glycyrrhetic acid. Because glycyrrhetic acid is a 200-1000 times more potent inhibitor of 11-beta-hydroxysteroid dehydrogenase compared to glycyrrhizic acid, the kinetics of glycyrrhetic acid are relevant in a toxicological perspective. Once absorbed, glycyrrhetic acid is transported, mainly taken up into the liver by capacity-limited carriers, where it is metabolized into glucuronide and sulfate conjugates. These conjugates are transported efficiently into the bile. After outflow of the bile into the duodenum, the conjugates are hydrolyzed to glycyrrhetic acid by commensal bacteria; glycyrrhetic acid is subsequently reabsorbed, causing a pronounced delay in the terminal plasma clearance. Physiologically based pharmacokinetic modeling indicated that, in humans, the transit rate of gastrointestinal contents through the small and large intestines predominantly determines to what extent glycyrrhetic acid conjugates will be reabsorbed. This parameter, which can be estimated noninvasively, may serve as a useful risk estimator for glycyrrhizic-acid-induced adverse effects, because in subjects with prolonged gastrointestinal transit times, glycyrrhetic acid might accumulate after repeated intake.

Effect of liquorice and glycyrrhizin on rat liver carcinogen metabolizing enzymes

We investigated the effect of single or repeated intake of conspicuous amounts of licorice root extract (LE, 3138 or 6276 mg/kg body weight (bw) per os) or its natural constituent glycyrrhizin (G, 240 or 480 mg/kg bw per os) on Sprague-Dawley rat liver monooxygenases. Whereas a single LE or G dose was unable to affect CYP superfamily, four daily doses induced CYP3A, CYP1A2 and to varying extents CYP2B1-linked monooxygenases. A boosting effect on testosterone 6beta- (CYP3A1/2, CYP1A1/2), 7alpha- (CYP1A1/2, CYP2A1), 16alpha- (CYP2B1, CYP2C11), 2alpha- (CYP2C11) and 2beta- (CYP3A1, CYP1A1) -dependent oxidases as well as on androst-4-ene-3,17-dione- (CYP3A1/2) -supported monooxygenases were also achieved. Harmful outcomes associated to CYP changes (e.g. cotoxicity, cocarcinogenicity and promotion) may be of concern.

Determination of urinary 18 beta-glycyrrhetinic acid by gas chromatography and its clinical application in man

A sensitive and quantitative gas chromatographic assay for the determination of 18 beta-glycyrrhetinic acid (18 beta-GA), the main metabolite of glycyrrhizin after oral licorice consumption in human urine, has been developed and validated. For the extraction of 18 beta-GA from urine two Sep-Pak C18 extractions, hydrolysis with Helix pomatia and three liquid-liquid extractions were performed, using 18 alpha-glycyrrhetinic acid (18 alpha-GA) as internal standard. Both 18 beta-GA and internal standard were converted into their pentafluorobenzyl-ester/trimethylsilyl-ether derivatives and detected by flame ionization detection using a WCOT-fused-silica capillary column. Good quality control data were obtained in precision and accuracy tests. The detection limit of the gas chromatographic method was 10 micrograms/l with a urine volume of 10 ml. A detection limit of 3 micrograms/l was obtained by performing GC-MS. The GC method was used to monitor the urinary excretion of 18 beta-GA after licorice consumption by two healthy volunteers and a patient suspected of licorice abuse. Furthermore, it was shown that this GC assay enables to detect other metabolites related to licorice consumption.

Solid-phase extraction of 18beta-glycyrrhetinic acid from plasma and subsequent analysis by high-performance liquid chromatography

A new method is described for the solid-phase extraction of 18beta-glycyrrhetinic acid from plasma or serum, with subsequent analysis by HPLC. New aspects of the method include the use of commercially available 18alpha-glycyrrhetinic acid as the internal standard and the use of a Bond Elut C2 (ethyl) extraction column, to avoid the need to use large volumes of organic solvent to elute the isolates from the columns. Separation was achieved on a Shandon Hypersil BDS C18 analytical column, with a mobile phase consisting of acetonitrile-0.02 M phosphate buffer, pH 5.7 (55:45, v/v). The column effluent was monitored at 248 nm. Compared with previous methods, the procedure is much easier to carry out, whereas the sensitivity (limit of detection, 10 ng/ml, and limit of quantitation, 50 ng/ml), the precision (0.3-6.2%) and the accuracy (97.2-101.9%) are of the same order of magnitude.

Effect of licorice and glycyrrhizin on murine liver CYP-dependent monooxygenases

This study is aimed to investigate the effect of the prolonged intake of conspicuous amounts of licorice (LE), or its natural constituent glycyrrhizin (G) on murine liver CYP-catalyzed drug metabolism. For this purpose the modulation of the regio- and stereo-selective hydroxylation of testosterone, together with the use of highly specific substrates as probes for different CYP isoforms such as ethoxyresorufin (CYP1A1), methoxyresorufin (1A2), pentoxyresorufin (2B1), p-nitrophenol (2E1) and aminopyrine (3A), were investigated. Daily doses of licorice root extract (3,138 or 6,276 mg/kg b.w. per os), or G (240 or 480 mg/kg b.w. per os), were administered to different groups of Swiss Albino CD1 mice of both sexes for 1, 4 or 10 consecutive days. While a single LE or G dose was unable to affect the multienzymatic CYP-system, using both schedules of repeated treatment, either LE or G were able to significantly induce hepatic CYP3A- and, to a lesser extent, 2B1- and 1A2-dependent microsomal monooxygenase activities, as well as 6beta- (mainly associated to CYP3A), 2alpha-, 6alpha- (CYP2A1, 2B1), 7alpha-, 16alpha- (CYP2B9) and 16beta-testosterone hydroxylase (TH) activities in male and female mice. Data on CYP3A modulation, the major isoform present in human liver, was confirmed by using Western immunoblotting with anti-CYP3A1/2 rabbit polyclonal antibodies raised against purified rat CYP3A. Northern blotting analysis using CYP3A cDNA biotinylated probe showed that the expression of such isozyme is regulated at the mRNA level. These results suggest that the induction of cytochrome P450-dependent activities by the prolonged intake of high LE or G doses, may result in accelerated metabolism of coadministered drugs with important implications for their disposition. The adverse effects associated with CYP changes such as toxicity/cotoxicity and comutagenicity may also have clinical consequences.

Determination of 18 beta-glycyrrhetinic acid in human serum using the fully automated ALCA-system

We report a method for the determination of 18 beta-glycyrrhetinic acid (glycyrrhetinic acid) in human serum using the ALCA-system. The technology of the ALCA-system is based on the principles of adsorptive and desorptive processes between liquid and solid phases. The assay is run fully automated and selective. Procedural losses throughout the analysis are negligible, thereby allowing for external calibration. The calibration curve is linear up to 10 mg/l and concentrations as low as 10 micrograms/l are detectable. CV is 2.5% for within- and 7.5% for between-assay precision at a level of 50 micrograms/l and 1.2% for within- and 8.5% for between-assay precision at a level of 500 micrograms/l. Specific and expensive reagents are not necessary and time-consuming manual operations are not involved. This assay can be selected from a wide spectrum of methods at any time. Thus, the present method is well-suited for drug monitoring purposes in the routine laboratory. In a pharmacokinetic study we measured serum levels of glycyrrhetinic acid in ten healthy young volunteers after ingestion of 500 mg glycyrrhetinic acid. Maximum levels of glycyrrhetinic acid were 6.3 mg/l 2 to 4 hours after ingestion. Twenty-four (24) hours after ingestion seven probands still had glycyrrhetinic acid levels above the detection limit with a mean level of 0.33 mg/l.

Systematic analysis of post-administrative saiboku-to urine by liquid chromatography to determine pharmacokinetics of traditional Chinese medicine

To disclose the mystery of a traditional Chinese medicine and to identify biologically active components, we analysed post-administrative urine for Saiboku-To, an anti-asthmatic Chinese herbal remedy. Systematic analysis of the components appearing in the urine was carried out by high-performance liquid chromatography (HPLC) with normal- and reversed-phase modes in combination. beta-D-glucuronidase-treated urine was subjected to rapid-flow fractionation (RFF) to achieve fractional extraction of lipophilic components with exhaustive recovery rates. The extracts were analysed by HPLC equipped with a multi-channel UV-detector. In the first stage of HPLC, we conducted a normal-phase mode run to find magnolol derived from Magnolia officinalis, as the most hydrophobic component showing minimum retention time among the urinary products of Saiboku-To. In the next stage, mobile phase solvent composition for reversed-phase HPLC was optimized so as to retain magnolol up to 60 min. Under these conditions, other Saiboku-To urinary products, which were more polar than magnolol, appeared within 60 min. Our HPLC method used marker compounds like magnolol and could indicate the terminal peak position on the reversed-phase chromatography. We found a total of eight components in the post-administrative Saiboku-To urine. Structure identification of the isolated pure materials was achieved using nuclear magnetic resonance (NMR)-, mass (MS)- and UV-spectra, and HPLC retention profiles. They were magnolol and 8,9-dihydroxydihydromagnolol stemming from M. officinalis, medicarpin and liquiritigenin from Glycyrrhiza glabra, baicalein, wogonin, and oroxylin A from Scutellaria baicalensis, and davidigenin of an unknown origin. The pharmacological mystery of Saiboku-To should be disclosed by resolving the pharmacokinetics and pharmacodynamics of these urinary products independently and synergistically.

Further studies on the mechanism of the mineralocorticoid action of licorice in humans

The pathogenesis of pseudohyperaldosteronism from licorice has been evaluated in 6 male volunteers taking daily 7 g of a commercial preparation of licorice for 7 days, corresponding to an intake of 500 mg/day of glycyrrhizic acid. Pseudohyperaldosteronism was evident during the treatment (increase of body weight, suppression of plasma renin activity and plasma aldosterone, reduction of serum potassium). The ratio (tetrahydrocortisol + allo tetrahydrocortisol)/tetrahydrocortisone in urine increased in 5 cases after 3 days of treatment, without an increase of plasma mineralocorticoid activity (PMA). In the 6th case the urinary ratio was unchanged and PMA increased from the pretreatment value. After 7 days of therapy the ratio remained high and PMA was not measurable in 3 cases, while in the other 3 cases the ratio returned to pretreatment and PMA was higher than pretreatment value. We conclude that the pseudohyperaldosteronism from licorice is initially related to decreased activity of 11 beta-hydroxysteroid-dehydrogenase and afterwards also a direct effect of licorice derivatives on mineralocorticoid receptors becomes evident in some cases. In other cases however the effect on the enzyme is prevailing probably due to individual factors.

Different effects of traditional Chinese medicines containing similar herbal constituents on prednisolone pharmacokinetics

Three major traditional Chinese medicines (TCM), Sho-saiko-To, Saiboku-To, and Sairei-To, consist of similar herbal prescriptions containing glycyrrhizin, which is a strong inhibitor of 11 beta-hydroxysteroid dehydrogenase. We performed cross-over open trials in healthy subjects to clarify prednisolone pharmacokinetics on co-administration of these preparations. All subjects received a single oral dose of 10 mg prednisolone before oral treatment with one of the test preparations. After a 2-week wash-out interval, they received one of the test preparations for three days at daily doses of 7.5 or 9.0 g. On the third study day, 10mg prednisolone was administered orally in combination with the test preparation. Area under the curves (AUC) of prednisolone before and after the treatment decreased from 0.94 to 0.78 mg h L-1 (P < 0.05) in the Sho-saiko-To group, increased from 0.92 to 1.06 mg h L-1 (P < 0.01) in the Saiboku-To group, and did not change in the Sairei-To group. AUC ratios of prednisone and prednisolone, which reflect the 11 beta-hydroxysteroid dehydrogenase activity, increased in the Sho-saiko-To group (P < 0.01), decreased in the Saiboku-To group (P < 0.01), and did not change in the Sairei-To group after the treatments. Similar results were observed in ratios of endogenous cortisone to cortisol. Because of the equal glycyrrhizin content in all three preparations, it was unexpected that the 11 beta-hydroxysteroid dehydrogenase effect was different amongst the three groups. These observations suggest that some unknown metabolic enzyme modifiers, promoters or inhibitors, may be involved in these traditional treatments.

Interaction of licorice on glycyrrhizin pharmacokinetics

The effects of components of aqueous licorice root extract (LE) on the pharmacokinetics of glycyrrhizin (G) and glycyrrhetic acid (GA) were investigated in rats and humans. The aim of this work was to define the role of pharmacokinetics in G toxicity. In the procedure, G and GA were detected in biological fluids by means of recently improved HPLC methods. Significantly lower G and GA plasma levels were found in rats and humans treated with LE compared to the levels obtained with those in which G alone was administered. The pharmacokinetic curves showed significant differences in the areas under the plasma-time curve (AUC), Cmax, and Tmax parameters. The data obtained from urine samples are in agreement with the above results and confirm a reduced bioavailability of G present in LE compared to pure G. This should be attributed to the interaction during intestinal absorption between the G constituent and the several components in LE. The modified bioavailability could explain the various clinical adverse effects resulting from the chronic oral administration of G alone as opposed to LE.

Determination of 18 beta-glycyrrhetic acid in human plasma by high-performance liquid chromatography

A sensitive high-performance liquid chromatographic method has been developed for the determination of 18 beta-Glycyrrhetic acid in human plasma. 18 alpha-Glycyrrhetic acid was used as an internal standard. The procedure includes pretreatment by liquid-liquid extraction and chromatographic separation on a reversed-phase column with ultraviolet detection. The detection limit of the drug was 5 ng/ml. The method was applied to the determination of 18 beta-glycyrrhetic acid in plasma after oral administration of a herbal medicine containing 18 beta-glycyrrhitic acid in human volunteers.

Determination of glycyrrhetinic acid in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method has been developed for measuring 18 beta-glycyrrhetinic acid (GRA) in human plasma in the range of 0.1-3 micrograms/ml. The acetate ester of GRA is added to the plasma as an internal standard, plasma proteins are denatured with urea to release GRA, and the GRA and the internal standard are extracted in an ion-pairing solid-phase extraction process. An isocratic, reversed-phase HPLC separation is used, followed by ultraviolet absorbance detection at 248 nm. The results from the analysis of five GRA-fortified plasma pools show a mean relative standard deviation of 7% and are accurate to within 10%. With evaporative concentration of the extract, the limit of detection for GRA in plasma is approximately 10 ng/ml.

High-performance liquid chromatographic determination of 18 alpha-glycyrrhetinic acid and 18 beta-glycyrrhetinic acid in rat plasma: application to pharmacokinetic study

A high-performance liquid chromatographic method for the separation and determination of 18 alpha-glycyrrhetinic acid and 18 beta-glycyrrhetinic acid has been developed. Indomethacin was used as an internal standard. The drugs were separated on a reversed-phase column and detected by UV detection at a wavelength of 254 nm. Methanol-water-perchloric acid-ammonia (80:20:0.4:0.4, v/v) was used as the mobile phase at pH of 7.0-7.5. The detection limit of both compounds was 0.1 microgram/ml in rat plasma. The method was applied to pharmacokinetic studies of glycyrrhetinic acids in rats. The results suggest that the pharmacokinetics appeared to be non-linear in nature.

Selective high-performance liquid chromatographic method for the determination of glycyrrhizin and glycyrrhetic acid-3-O-glucuronide in biological fluids: application of ion-pair extraction and fluorescence labelling agent

A selective high-performance liquid chromatographic method has been developed for the simultaneous determination of glycyrrhizin and glycyrrhetic acid-3-O-glucuronide in biological fluids of the rat. The procedure is based on the ion-pair formation using tetra-n-amylammonium bromide, extraction with ethyl acetate-n-heptane from the salt-saturated aqueous phase, labelling with 4-bromomethyl-7-methoxycoumarin, followed by chromatographic separation with fluorescence detection. Glycyrrhizin in plasma, bile and urine could be precisely determined in concentrations as low as 1, 1 and 2.5 micrograms/ml, respectively, in a 0.1-ml sample. The equivalent values for the glucuronide were 1, 2.5 and 2.5 micrograms/ml, respectively. The method is applicable in pharmacokinetic studies of glycyrrhizin in small animals.