Glycyrrhizic acid in liquorice--evaluation of health hazard

Literature on case reports, clinical studies and biochemical mechanisms of the sweet-tasting compound glycyrrhizic acid in liquorice was critically reviewed to provide a safety assessment of its presence in liquorice sweets. A high intake of liquorice can cause hypermineralocorticoidism with sodium retention and potassium loss, oedema, increased blood pressure and depression of the renin-angiotensin-aldosterone system. As a consequence, a number of other clinical symptoms have also been observed. Glycyrrhizic acid is hydrolysed in the intestine to the pharmacologically active compound glycyrrhetic acid, which inhibits the enzyme 11 beta-hydroxysteroid dehydrogenase (in the direction of cortisol to cortisone) as well as some other enzymes involved in the metabolism of corticosteroids. Inhibition of 11 beta-hydroxysteroid dehydrogenase leads to increased cortisol levels in the kidneys and in other mineralocorticoid-selective tissues. Since cortisol, which occurs in much larger amounts than aldosterone, binds with the same affinity as aldosterone to the mineralocorticoid receptor, the result is a hypermineralocorticoid effect of cortisol. The inhibitory effect on 11 beta-hydroxysteroid dehydrogenase is reversible; however, the compensatory physiological mechanisms following hypermineralocorticoidism (e.g. depression of the renin-angiotensin system) may last several months. It is not possible, on the basis of existing data, to determine precisely the minimum level of glycyrrhizic acid required to produce the described symptoms. There is apparently a great individual variation in the susceptibility to glycyrrhizic acid. In the most sensitive individuals a regular daily intake of no more than about 100 mg glycyrrhizic acid, which corresponds to 50 g liquorice sweets (assuming a content of 0.2% glycyrrhizic acid), seems to be enough to produce adverse effects. Most individuals who consume 400 mg glycyrrhizic acid daily experience adverse effects. Considering that a regular intake of 100 mg glycyrrhizic acid/day is the lowest-observed-adverse-effect level and using a safety factor of 10, a daily intake of 10 mg glycyrrhizic acid would represent a safe dose for most healthy adults. A daily intake of 1-10 mg glycyrrhizic acid/person has been estimated for several countries. However, an uneven consumption pattern suggests that a considerable number of individuals who consume large amounts of liquorice sweets are exposed to the risk of developing adverse effects.

In vitro nasal transport across ovine mucosa: effects of ammonium glycyrrhizinate on electrical properties and permeability of growth hormone releasing peptide, mannitol, and lucifer yellow

Transport of growth hormone releasing peptide across ovine nasal mucosa in the absence or presence of ammonium glycyrrhizinate (AMGZ) was studied in vitro. Ovine nasal mucosa was stripped from underlying cartilage and mounted in Ussing chambers. Transepithelial conductance (Gt) and short-circuit current (Isc) were monitored during experiments to assess tissue viability and integrity. Radiolabeled mannitol (Man; MW 182) and growth hormone releasing peptide (GHRP, SK&F 110679; MW 873) were employed to measure transport rates across the epithelium, and fluorescence spectroscopy was employed to measure rates of lucifer yellow (LY; MW 521) transport. Effects of AMGZ on ovine nasal mucosal viability and transport were determined from changes in electrical properties of fluxes of [3H]GHRP, [3H]Man, and LY. Results demonstrate that electrical properties of ovine nasal mucosa are stable over the time course of the experiments (Gt = 8.3 +/- 0.5 mS/cm2 and Isc = 3.7 +/- 0.2 microEq/hr.cm2; n = 21). Man fluxes were comparable in the mucosal (m)-to-serosal (s) and s-to-m directions [0.10 +/- 0.01 (n = 17) and 0.10 +/- 0.01 (n = 4) %/hr.cm2, respectively]. Transport of GHRP and LY in the m-s direction was similar to that of Man [0.08 +/- 0.01 (n = 11) and 0.09 +/- 0.01 (n = 3) %/hr.cm2, respectively]. GHRP flux was equivalent in the m-s and s-m directions. GHRP did not significantly alter ion transport processes as indicated by the lack of any change in Gt or Isc.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic analysis of glycyrrhetic acid, an active metabolite of glycyrrhizin, in rats: role of enterohepatic circulation

The role of enterohepatic circulation of glycyrrhetic acid (GA) in rats was determined by kinetic analysis of GA. The concentrations of GA in the plasma of the control rat (without bile duct cannulation) during the first 5 h after intravenous (iv) administration of GA (2, 5, 10, and 20 mg/kg) were similar to those in the bile duct-cannulated rat at each dose. No significant difference was observed in the values of the terminal half-life, the total body clearance, the distribution volume at steady state, the area under the curve of concentration in plasma versus time, and the mean residence time in each dose between both groups. When GA (2, 5, 10, and 20 mg/kg) was administered i.v. to the bile duct-cannulated rat, excretion of unchanged GA in bile was < 1% of each dose, that of the acid-hydrolyzed products was 14-16%, and that of GA-3-O-glucuronide was only 1-2%. In the control rat, a secondary peak of GA concentration was observed 12 h after i.v. administration of GA (20 mg/kg). The enterohepatic circulation of GA was confirmed by the linked-rat method in which bile of the donor rat after i.v. administration of GA (20 mg/kg) was allowed to flow directly into the duodenum of the recipient rat. GA was found in the plasma of the recipient rat after 6 h, and its concentration reached the maximum (approximately 0.5 microgram/mL) 8-12 h after dosing the donor rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake of glycyrrhizin by isolated rat hepatocytes

The mechanism of uptake of glycyrrhizin (GLZ) by isolated rat liver cells was studied. The uptake rate was dependent on the unbound GLZ concentration. The initial uptake rate with respect to the unbound GLZ concentration reflected the operation of both saturable and nonsaturable processes, which followed Michaelis-Menten type kinetics; the process involves a Km of 11.3 microM, Vmax of 0.112 nmol/min/10(6) cells, and a first-order rate constant (Kd) of 0.195 nmol/min/10(6) cells/mM. GLZ adsorption on the cell membrane occurs at two types of binding sites with a linear adsorption coefficient = 2.81 nmol/10(6) cells/mM and a dissociation constant = 18.3 microM and its adsorption capacity = 0.12 nmol/10(6) cells describing specific adsorption. GLZ uptake did not require the presence of Na+ in the incubation medium and was not significantly inhibited by ouabain. The Arrhenius plot of uptake of 10 microM GLZ presented a single straight line in the range of 4-37 degrees C, with an activation energy of 15.9 kcal/mol. An energy requirement was also demonstrated, as all metabolic inhibitors studied (rotenone, antimycin A, 2,4-dinitrophenol, and KCN) significantly reduced the uptake of 10 microM GLZ (p < 0.01). The uptake was competitively inhibited by glycyrrhetinic acid (GLA), taurocholate (TCA), and probenecid (PBC) with inhibition constants, Ki, of 13.7, 48.5, and 115.9 microM, respectively, and it was noncompetitively inhibited by bromosulfophthalein (Ki 9.2 microM) and indocyanine green (Ki 13.5 microM) only at low GLZ concentrations (5 and 10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Glycyrrhetinic acid bound to 11 beta-hydroxysteroid dehydrogenase in rat liver microsomes

A binding protein which exhibits high affinity to [3H]glycyrrhetinic-acid in the rat liver microsomal fraction was solubilized with 0.2% Triton DF-18 and then purified to homogeneity. The equilibrium dissociation constant of the [3H]glycyrrhetinic-acid binding reaction and the maximal concentration for the binding of the purified protein, as determined by Scatchard plot analysis, were 27.6 nM and 7.79 nmol/mg protein, respectively. The molecular mass of the subunit (34 kDa) and 30 amino acids of N-terminal sequence of the purified protein were entirely the same as those of the reported 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD). In each purification step, the recovery and purification (fold) of the glycyrrhetinic-acid binding activity corresponded to the values of 11 beta-HSD activity. These results show that the purified [3H]glycyrrhetinic-acid binding protein is 11 beta-HSD. From the molecular mass of 11 beta-HSD (135 kDa) and the maximal concentration of the binding site, it was calculated that one glycyrrhetinic acid molecule binds to one 11 beta-HSD molecule. The inhibitory effects of various glycyrrhetinic-acid derivatives on [3H]glycyrrhetinic acid binding and 11 beta-HSD activity indicate that the C30-carboxyl and C11-carbonyl groups of glycyrrhetinic acid are the principal structures for the 11 beta-HSD inhibition.

Specific binding of glycyrrhetinic acid to the rat liver membrane

Glycyrrhetinic acid bound specifically to a particulate fraction of rat liver. The binding was dependent on time, temperature and pH, equilibrium being reached after 10 min at 37 degrees C. The equilibrium dissociation constant and the maximal concentration of the binding site, as determined by Scatchard plot analysis, were 31 nM and 43 pmol/mg protein, respectively, indicating a single binding site entity. The binding site was highly specific for glycyrrhetinic acid, glycyrrhizin, various steroids, various fatty acids and retinoids showing no or only very low affinity. The binding was inhibited by boiling or treatment with trypsin or phospholipases. The specific activity of glycyrrhetinic acid binding was the highest in the liver, followed by in the kidney. The results suggest that glycyrrhetinic acid plays a significant role in the rat liver through its specific binding protein.

Metabolism of glycyrrhetic acid by rat liver microsomes--III. Male-specific glycyrrhetinate dehydrogenase

Glycyrrhetinate (GA) dehydrogenase localized in microsomes of rat liver catalyses the oxidation and reverse reduction of 18 beta-glycyrrhetic acid (GA), an aglycone of glycyrrhizin and a main component of liquorice, to 3-keto-18 beta-glycyrrhetic acid (3-ketoGA). The enzyme activity was detected in microsomes of adult males, but not in those of adult females. It was not observed in infant males but appeared 6 weeks after birth, increased gradually and reached the maximum level at 12 weeks after birth, whereas it was not detected in the hepatic microsomes of females of any age. The administration of estradiol valerate to intact adult males decreased GA dehydrogenase activity remarkably. Castration of male rats also caused a marked reduction of the activity, but the administration of testosterone proprionate to these rats restored it to close to the normal level. On the other hand, ovariectomy of female rats did not bring the activity into existence, but the injection of testosterone proprionate to the ovariectomized rats brought it into a slight existence, in spite of no appearance of the activity by the treatment of testosterone proprionate to intact adult females. The sex-related difference in the activity in adults was eliminated by hypophysectomy of male and female rats, their microsomal activities after the operation being the same, 20-40% of the activity in intact males. Moreover, the administration of estradiol valerate to the hypophysectomized rats did not affect the activity. These results indicate that GA dehydrogenase is male-specific and regulated by sex-hormones through the pituitary.

Hydrolysis of glycyrrhizin to 18 beta-glycyrrhetyl monoglucuronide by lysosomal beta-D-glucuronidase of animal livers

Glycyrrhizin (GL), a main constituent of liquorice, was hydrolysed to 18 beta-glycyrrhetic acid mono-beta-D-glucuronide (GAMG, glycyrrhetyl monoglucuronide) by rat liver homogenate, and the hydrolytic activity was localized in the lysosomes among the same subcellular fractions as acid beta-D-glucuronidase activity (p-nitrophenyl beta-D-glucuronide (pNPG)-hydrolysing activity). Rat liver lysosomes hydrolysed GAMG to 18 beta-glycyrrhetic acid (GA) at only 30% rate compared with the rate of GL to GAMG. GA was also produced slowly from GL after time lag by the lysosomes. Thus, GL seems to be first hydrolysed to GAMG, which was successively hydrolysed slowly to GA. GL-hydrolysing activity was released together with acid beta-D-glucuronidase activity from the lysosomes by sonication. Both activities from the sonicated lysosomes were eluted coincidentally on Sephacryl S-300 and butyl-Toyopearl 650M column chromatography, indicating that both activities are exhibited by the same enzyme. Moreover, GL-hydrolysing activity was inhibited strongly with D-saccharic acid 1,4-lactone, a specific inhibitor beta-D-glucuronidases of various origins. pH optimum of GL-hydrolysing activity was found to be 5.6, different from that (less than 4.0) of pNPG-hydrolysing activity. Km for GL was found to be 2 x 10(-5) M. Although hepatic lysosomes from mouse and cattle hydrolysed GAMG to GA similarly to those from rat, the hydrolysis of GAMG was not detected in lysosomes of human and porcine livers. Accordingly, lysosomal beta-D-glucuronidases from human and porcine livers converted GL to GAMG only.

[Antioxidative properties of glycyrrhyzic acid salts and their effect on the liver monooxygenase system]

Antioxidative activity of potassium- and sodium glycyrrhizins was detected by means of chemoluminescence procedure. As shown by the spectral studies the glycyrrhizin salts formed complex of the I type with cytochrome P-450 from rat liver microsomes, inhibited inactivation of isolated cytochrome P-450LM2 and induced hemoprotein formation after administration into rats. The preparations of glycyrrhizic acid appear to be useful for treatment of toxic impairment of liver tissue.

Metabolism of glycyrrhetic acid by rat liver microsomes-II. 22 alpha- and 24-hydroxylation

18 beta-Glycyrrhetic acid (GA, an aglycone of glycyrrhizin) is converted to 3-oxo-18 beta-glycyrrhetic acid (3-oxoGA) in the presence of NADP+ by rat liver homogenates, but GA was converted in the presence of NADPH to two other metabolites showing lower Rf values on thin-layer chromatography (TLC) than those of GA and 3-oxoGA by postmitochondrial supernatant of rat liver. The GA-metabolizing activity in the presence of NADPH was localized in microsomes, similar to localization of GA-oxidizing activity to 3-oxoGA. The GA-metabolizing activity required NADPH as a cofactor and O2 for full activity and was inhibited with CO, suggesting the hydroxylation reaction of GA by cytochrome P450. Two metabolites (I and II, lower and higher Rf values on TLC, respectively) were purified on preparative TLC. Mass spectral (MS) analyses of II and methyl ester of acetylated I indicated the formation of monohydroxylated metabolites. On the basis of 3H- and 13C-NMR assignments I and II were identified to be 22 alpha- and 24-hydroxy-18 beta-glycyrrhetic acids, respectively. 3-OxoGA and 3-epi-18 beta-glycyrrhetic acid (3-epiGA) seem to be also hydroxylated at C-22 and C-24. A metabolite of 3-oxoGA showing a lower Rf value was also identified as 22 alpha-hydroxy-3-oxo-18 beta-glycyrrhetic acid by MS and 3H- and 13C-NMR spectral analyses. In 22 alpha-hydroxylation the best substrate was 3-oxoGA, followed by GA and 3-epiGA. On the other hand, for 24-hydroxylation the best substrate was GA, then 3-oxoGA, and 3-epiGA in order. However, 18 alpha-glycyrrhetic acid (18 alpha-GA) was a poor substrate for both 22 alpha- and 24-hydroxylation.

Isolation of bacterial strains, which hydrolyze glycyrrhizin and produce glycyrrhezic acid, from soil

We isolated eight bacterial strains which could hydrolyze glycyrrhizin to glycyrrhezic acid. The bacterial strains were identified as three strains of Pseudomonas saccharophila, two of Plesiomonas sp., one of Pseudomonas stutzeri, one of Klebsiella pneumoniae subsp. ozaenae and one of Kluyvera ascorbata. Their capacity for the conversion of glycyrrhizin to glycyrrhezic acid was assayed by high performance liquid chromatography. P. saccharophila 11 was the most effective among the eight strains. Then, beta-glucuronidase, which is responsible for hydrolysis of glycyrrhizin, activity was assayed with p-nitrophenyl-beta-D-glucuronide as a substrate. P. saccharophila 11 showed the highest beta-glucuronidase activity among the eight strains. This indicates that P. saccharophila 11 may be useful for production of glycyrrhezic acid from glycyrrhizin by industrial fermentation.

Characterization of glycyrrhizin-binding protein kinase from the crude membrane fraction of rat liver

Using GL-affinity column chromatography, a casein phosphorylating protein kinase was purified selectively from the crude membrane fraction of rat liver. The biochemical characteristics of the purified kinase (approximately Mr 210 kDa) are very similar to those reported for polypeptide-dependent protein kinase (kinase P). Moreover, low doses of GL selectively inhibit phosphorylation of Mr 35-36 kDa polypeptides (which are cross-reacted with anti-lipocortins I and II) by the kinase in vitro. These results suggest that the anti-inflammatory activity of GL may involve the impairment of the physiological functions of lipocortins through their specific modification by the kinase at the cell membrane level.

Biotransformation of 18 beta-glycyrrhetinic acid by cell suspension cultures of Glycyrrhiza glabra

Two biotransformation products formed from 18 beta-glycyrrhetinic acid by cell suspension cultures of Glycyrrhiza glabra were isolated and their structures determined by chemical and spectral data as 3-O-[alhpa-L-arabinopyranosyl-(1----2)-beta-D-Glucuronopy ranosyl]-24- hydroxy-18 beta-glycyrrhetinic acid and 30-O-beta-D-glycopyrano-syl-18 beta-glycyrrhetinic acid. The formation of glycyrrhizin, the main triterpene glucuronide of the licorice root, was not detected among the biotransformation products. This is the first report of the glucuronylation of an exogenous triterpene in plant cell cultures.

Licorice inhibits corticosteroid 11 beta-dehydrogenase of rat kidney and liver: in vivo and in vitro studies

In humans, glycyrrhetinic acid (GE), the active pharmacological ingredient of licorice, produces symptoms resembling those caused by excess mineralocorticoid secretion. We are proposing that 11 beta-dehydrogenase inhibition, and not intrinsic mineralocorticoid activity, is the primary mechanism of licorice induced pseudoaldosteronism. Glycyrrhizic acid (glycyrrhetinic acid glucuronide), when given orally to rats, partially inhibited renal 11 beta-dehydrogenase. In rats treated with dexamethasone before glycyrrhizic acid administration there was similar enzyme inhibition, suggesting that antimineralocorticoid effects of dexamethasone in licorice excess states are not mediated through a direct effect on 11 beta-dehydrogenase activity. Dispersed renal proximal tubular preparations, kidney homogenates, and microsomes readily converted corticosterone to 11-dehydrocorticosterone. GE and its synthetic analog carbenoxolone inhibited the conversion in these systems in a dose-dependent manner. Corticosteroid 11-oxoreductase, which was present in kidney homogenates at a level 10-20% that of 11 beta-dehydrogenase was not inhibited by any of the agents. With homogenate and microsomes, the Ki of GE was about 10(-9)-10(-8) M; with intact tubules, the Ki of GE was about 10(-5)-10(-6) M. It is suggested that a permeability barrier slows the entry of GE into the tubule cells. We conclude that the effects of licorice on corticosteroid metabolism in the kidney are based on its inhibition of 11 beta-dehydrogenase. Our data, supplemented by published evidence, is inconsistent with the conclusion that interaction with mineralocorticoid receptors accounts for the pharmacological effects of GE.

Glycyrrhizin stimulates growth of Eubacterium sp. strain GLH, a human intestinal anaerobe

Eubacterium sp. strain GLH was isolated from human feces and produced two kinds of beta-D-glucuronidase (EC 3.2.1.31), one new enzyme specific for glycyrrhizin (GL) and the other for phenyl beta-D-glucuronides. GL or p-nitrophenyl-mono-beta-D-glucuronide (pNPG) stimulated the production of GL or pNPG beta-glucuronidases and the growth of strain GLH in a basal medium lacking carbohydrate. D-Glucuronic acid also stimulated the growth of the bacterium, but glycyrrhetic acid did not. The increase of GL beta-glucuronidase paralleled the growth of the Eubacterium strain in pure culture. These results suggest that glucuronides such as GL and pNPG stimulate the growth of the Eubacterium strain in a nutrient-poor medium by providing D-glucuronic acid through the activity of beta-glucuronidases. The increase in GL beta-glucuronidase activity in the presence of GL was observed during the cultivation of human intestinal flora in a general anaerobic medium. During mixed cultivation of the Eubacterium strain with Streptococcus faecalis, which does not produce GL beta-glucuronidase, GL beta-glucuronidase was also increased by GL or pNPG, but not by glycyrrhetic acid and p-nitrophenol. It is suggested that GL stimulates the growth of strain GLH even in the mixed culture.

Inhibition of mutagenicity by glycyrrhiza extract and glycyrrhizin

The effects of Glycyrrhiza extract and one of its components, glycyrrhizin, on the mutagenicities of several mutagens were investigated by means of a modification of the Ames' test. Both inhibited the mutagenicities of 3-amino-1,4-dimethyl-5 H-pyrido[4,3-b]-indole (Trp-P-1) and 3-amino-1-methyl-5 H-pyrido[4,3-b]indole. Since the Glycyrrhiza extract and glycyrrhizin inhibited the mutagenicity of activated Trp-P-1, it was clear that their inhibitory effects were not due to inhibition of the enzyme activity of the S9 fraction. Both Glycyrrhiza extract and glycyrrhizin also inhibited the mutagenicities of benzo[a]pyrene, 3-methylcholanthrene, 2-naphthylamine, 2-amino-6-methyldipyrido[1,2-a:3',2'-d]-imidazole, dimethylnitrosoamine and dimethylaminoazobenzene. The mutagenicity of 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2) was inhibited by the Glycyrrhiza extract but not by glycyrrhizin. This suggested that a component different from glycyrrhizin, present in the Glycyrrhiza extract, inhibited the mutagenicity of AF-2.

Glycyrrhizic acid and its hydrolysate as mineralocorticoid agonist

Mineralocorticoid activity of glycyrrhetinic acid (GR) was studied in vivo (electrical potential difference in rat rectum) and in vitro (brush border Mg2+-HCO3- ATPase in rat small intestine, kidney cytosol binding of GR with and without RU-28362, anti-glucocorticoid compound) in order to clarify the mechanism of mineralocorticoid-like activity of GR. Scatchard analysis of [3H]aldosterone showed that Kd of higher affinity site (type I) 6.0 X 10(-9) M, Bmax 1.0 X 10(-14) mol/mg protein, and Kd of lower affinity site (type II) 1.6 X 10(-7) M, Bmax 7.5 X 10(-14) mol/mg protein. GR competed for [3H]aldosterone binding sites in kidney cytosol at the concentration of 10(4) times as that of unlabeled aldosterone. RU-28362 displaced aldosterone binding curve, whereas GR binding kinetic was not affected by this compound. Adrenalectomy caused a significant fall in brush border Mg2+-HCO3- ATPase activity (75% reduction compared with the initial level) which was not restored by GR administration. Electrical potential differences in the adrenalecomized rats were significantly lower than those in the control rats, which did not increase after GR administration.

Possible mechanism of steroid action of the plant herb extracts glycyrrhizin, glycyrrhetinic acid, and paeoniflorin: inhibition by plant herb extracts of steroid protein binding in the rabbit

To assess the action of some components of herbal medicine, glycyrrhizin, glycyrrhetinic acid, and paeoniflorin, on steroids, their binding to several classes of intracellular and serum steroid-binding proteins were studied in the rabbit. The affinity (inhibitor constant) for binding of dihydrotestosterone-sex hormone binding globulin in the serum (dissociation constant of 2.0 nmol/L for dihydrotestosterone) was approximately 520 nmol/L, and that for the binding of cortisol-corticosteroid-binding globulin in the serum (dissociation constant of 2.0 nmol/L for cortisol) was approximately 10 mumol/L. In the uterine cytosol, the inhibitor constant value for estradiol receptor binding (dissociation constant of 1.0 nmol/L) was 0.9 mumol/L, and these compounds did not influence progestin receptor binding (dissociation constant of 1.4 nmol/L). The inhibitor constant values for glucocorticoid receptor binding (dissociation constant of 1.0 nmol/L) in the liver cytosol were 3.0 nmol/L for paeoniflorin, 2.0 nmol/L for glycyrrhizin, and 1.7 nmol/L for glycyrrhetinic acid, and those for mineralocorticoid receptor binding (dissociation constant = 1.1 nmol/L) in the kidney cytosol were 3.5 nmol/L for paeoniflorin and glycyrrhetinic acid and 3.0 nmol/L for glycyrrhizin. These results suggest that herbal extracts such as the above compounds influence steroid effects by glucocorticoid and mineralocorticoid receptors and to a lesser extent by estrogen receptors or serum sex hormone-binding globulin and corticosteroid-binding globulin.

Biliary excretion and enterohepatic cycling of glycyrrhizin in rats

The enterohepatic cycling of glycyrrhizin was examined using rats with and without biliary fistulization. The plasma decay in the control rats without fistulization following an iv dose of 100 mg/kg of glycyrrhizin, was generally biphasic. However, secondary peaks were observed in all rats in the elimination phase, i.e., 0.5 to 12 h following dosing. The plasma concentrations in the rats with biliary fistulization administered the same dose showed a biexponential decline. The AUC and CLtot were significantly higher and lower in the control rats, respectively. The biliary excretion was 80.6 +/- 9.9% of the administered dose, and intestinal absorption was confirmed by using the bile collected after iv dosing. From these results, we concluded that glycyrrhizin was predominantly secreted from the liver into the bile, and that the secondary peaks in the elimination phase, the higher AUC, and the lower CLtot in the control rats were due to the effects of enterohepatic recycling of glycyrrhizin. Furthermore, the transport of the drug from the liver to the bile appears to be a saturable process.

Disposition of glycyrrhetic acid and its glycosides in healthy subjects and patients with pseudoaldosteronism

As a first step to elucidate the disposition of traditional Chinese formulations which contain licorice, the disposition of plain licorice was investigated in humans. Glycyrrhetic acid (GLA) was measured by an enzyme immuno-antibody technique. Glycyrrhetic glycosides (GLA-GS), such as glycyrrhizin, were measured after acid hydrolysis to GLA by the enzyme immuno-antibody assay. Five normal subjects were orally administered a decoction of licorice containing 133 mg of glycyrrhizin. It was found that the time required for maximum serum concentration of GLA-GS was less than 4 h after the administration. Although there were large individual differences, it was found that GLA-GS was eliminated from the blood for the most part within 72 h. On the other hand, GLA reached maximum serum concentration at about 24 h after administration and in two of the five cases it was still detected in the blood even after 96 h. Urinary excretion of GLA was about 2% of the total dose of glycyrrhizin administered. This suggested that there were great differences among the subjects in the absorption and urinary excretion of GLA-GS. The serum GLA levels in two clinical cases who presented pseudoaldosteronism by licorice containing formulations were as high as 70-80 ng/ml, with GLA-GS levels being very low. This fact suggests that pseudoaldosteronism develops in association with GLA rather than with GLA-GS.

Affinity of liquorice derivatives for mineralocorticoid and glucocorticoid receptors

Liquorice abuse causes a syndrome of pseudohyperaldosteronism. Much less commonly, glucocorticoid-like effects have been reported. The electrolyte-active principle of liquorice is glycyrrhizic acid (GI), which can be hydrolyzed to glycyrrhetinic acid (GE). Previous studies have reported that GE, but not GI, may occupy mineralocorticoid and glucocorticoid receptors. We here report that both GE and GI can bind to both mineralocorticoid and glucocorticoid receptors. The affinity of GI for mineralocorticoid receptors is four orders of magnitude lower than aldosterone and for glucocorticoid receptors five orders of magnitude lower than dexamethasone. The affinity, though low, is sufficient to explain the mineralocorticoid-like side effects, given the large amount of liquorice required to produce such a syndrome.