Differences in the metabolism of glycyrrhizin, glycyrrhetic acid and glycyrrhetic acid monoglucuronide by human intestinal flora

Glycyrrhizin (1.0 mm GL), glycyrrhetic acid (1.0 mm GA) and glycyrrhetic acid monoglucuronide (1.0 mM GAMG), as well as a combination of all components added to medium at the start of growth and at the maximal stage of intestinal flora were cultured for 24 and 12 h, respectively. GL alone enhanced GL beta-D-glucuronidase activity about 2.7- to 6.8-fold and was metabolized to between 55 and almost 100% GA. GAMG alone was metabolized to almost 100% GA by GAMG beta-D-glucuronidase activity. Intestinal flora grown to a maximal stage converted GL to about 15% GA and GAMG to about 13% GA at almost 0 h. GL in combined GL and GA was consumed about 20% at 12 h and about 100% at 24 h under different culture conditions. Metabolite GA and unchanged GA were metabolized to a negligible amount of 3-oxoglycyrrhetic acid, 3alpha-hydroxyglycyrrhetic acid (3alpha-hydroxyGA) or both by 3beta-hydroxysteroid dehydrogenase and 3alpha-hydroxyGA dehydrogenase activities. Combined GL and GAMG consumed about 90% and 100% GAMG at 24 h and 12 h, respectively, regardless of culture conditions, and the consumption of GL was non-existent or negligible. Consumption of combined GL, GA and GAMG was similar to that of both combined GL and GA and combined GL and GAMG. It was found that intestinal flora can metabolize GL alone, but does not readily metabolize GL when present among its metabolites containing GL.

Competition in the metabolism of glycyrrhizin with glycyrrhetic acid mono-glucuronide by mixed Eubacterium sp. GLH and Ruminococcus sp. PO1-3

Eubacterium sp. GLH possessing glycyrrhizin (GL) and glycyrrhetic acid mono-glucuronide (GAMG) beta-D-glucuronidases, Ruminococcus sp. PO1-3 possessing GL and GAMG beta-D-glucuronidases and 3beta-hydroxysteroid dehydrogenase and these mixed bacteria were cultured in GAM medium with and without GL, GAMG or both. GL added to Eubacterium sp. GLH accelerated the peaks of enhanced GL beta-D-glucuronidase activity and suppressed GAMG beta-D-glucuronidase activity, and GAMG delayed the peaks of the enhanced growth with GL and GAMG beta-D-glucuronidase activities. GL added to Ruminococcus sp. PO1-3 enhanced gradually the growth with GL and GAMG beta-D-glucuronidase activities, and GAMG enhanced slowly GL beta-D-glucuronidase activity and rapidly the growth with GAMG beta-D-glucuronidase activity. The metabolite glycyrrhetic acid (GA) was produced by Eubacterium sp. GLH and Ruminococcus sp. PO1-3 in larger amounts and faster from GAMG than from GL. GL (1.0 mM) and 1.0 mM GAMG added to these mixed bacteria enhanced the growth with GL and GAMG beta-D-glucuronidase activities and were metabolized almost completely to GA in culture of 2 d and 1 d, respectively. It was found that the metabolism of GAMG was faster than that of GL. GL with GAMG added to mixed Eubacterium sp. GLH and Ruminococcus sp. PO1-3 cultured for 0 and 1 d led to a lower level of these enzyme activities and the consumption of GAMG more quickly, not GL. Low GAMG beta-D-glucuronidase had the ability to hydrolyze GAMG well.

Physiologically based pharmacokinetic modeling of glycyrrhizic acid, a compound subject to presystemic metabolism and enterohepatic cycling

Glycyrrhizic acid is currently of clinical interest for treatment of chronic hepatitis. It is also applied as a sweetener in food products and chewing tobacco. In some highly exposed subgroups of the population, serious side effects such as hypertension and electrolyte disturbances have been reported. In order to analyze the health risks of exposure to this compound, the kinetics of glycyrrhizic acid and its active metabolites were evaluated quantitatively. Glycyrrhizic acid and its metabolites are subject to complex kinetic processes, including enterohepatic cycling and presystemic metabolism. In humans, detailed information on these processes is often difficult to obtain. Therefore, a model was developed that describes the systemic and gastrointestinal tract kinetics of glycyrrhizic acid and its active metabolite glycyrrhetic acid in rats. Due to the physiologically based structure of the model, data from earlier in vitro and in vivo studies on absorption, enterohepatic cycling, and presystemic metabolism could be incorporated directly. The model demonstrates that glycyrrhizic acid and metabolites are transported efficiently from plasma to the bile, possibly by the hepatic transfer protein 3-alpha-hydroxysteroid dehydrogenase. Bacterial hydrolysis of the biliary excreted metabolites following reuptake of glycyrrhetic acid causes the observed delay in the terminal plasma clearance of glycyrrhetic acid. These mechanistic findings, derived from analysis of experimental data through physiologically based pharmacokinetic modeling, can eventually be used for a quantitative health risk assessment of human exposure to glycyrrhizic acid containing products.

Hasty effect on the metabolism of glycyrrhizin by Eubacterium sp. GLH with Ruminococcus sp. PO1-3 and Clostridium innocuum ES24-06 of human intestinal bacteria

Eubacterium sp. GLH with Ruminococcus sp. PO1-3 and Clostridium innocuum ES24-06 possessing enzymes involved in the metabolism of glycyrrhizin (GL) was cultured in GAM medium with and without 1.0 mM GL or 1.0 mM glycyrrhetic acid (GA). GL (1.0 mM) enhanced 3alpha-hydroxyglycyrrhetinate (3alpha-hydroxyGA) dehydrogenase activity, GA (1.0 mm) suppressed 3alpha-hydroxyGA dehydrogenase activity, GL beta-D-glucuronidase activity and the mixed bacterial growth, and GL and GA showed almost no change in a lower level of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity during 5 d of culture. GL (1.0 mM) and GA (1.0 mM) were metabolized to a small amount of GA and a negligible amount of 3-oxo-glycyrrhetic acid (3-oxo-GA) and 3alpha-hydroxyGA, and to a negligible amount of 3-oxo-GA, respectively, by these mixed bacteria. These amounts coincided with those of metabolites produced from 1.0 mM GL and 1.0 mM GA added to these mixed bacteria after 24 h culture. Whole bacteria and sonicated bacteria derived from the collection of these mixed bacteria reached a maximal stage and metabolized GL to a relatively large amount of GA and 3-oxo-GA, and a negligible amount of 3alpha-hydroxyGA and GA to a small amount of 3-oxo-GA and 3alpha-hydroxyGA within 180 min. GL beta-D-glucuronidase with 3beta-HSD and 3alpha-hydroxyGA dehydrogenase partially purified from each bacterium was converted GL to 3alpha-hydroxyGA, producing metabolites of about 60% after 10 min of incubation. These mixed bacteria possessed high enzyme activities could produce the metabolites of GL in under one hour under conditions.

Effects of glycyrrhizin and glycyrrhetic acid on the growth, glycyrrhizin beta-D-glucuronidase and 3 beta-hydroxysteroid dehydrogenase of human intestinal bacteria

The peak of glycyrrhizin (GL) beta-D-glucuronidase activity for Ruminococcus sp. PO1-3 and Eubacterium sp. GLH changed to 24 h from 12 h of culture and to 12 h from 48 h, respectively, at almost the same level by the addition of 1.0 mM GL. This enzyme activity was about 20-fold higher in Eubacterium sp. GLH than in Ruminococcus sp. PO1-3. GL beta-D-glucuronidase activity of Ruminococcus sp. PO1-3 with Eubacterium sp. GLH and the intestinal flora showed a maximal peak at 12 h of culture in the presence and absence of 1.0 mM GL. This enzyme activity was about 2.5-fold higher in mixed bacteria than in intestinal flora. 3Beta-hydrosteroid dehydrogenase activity of Ruminococcus sp. PO1-3 and Ruminococcus sp. PO1-3 with Eubacterium sp. GLH was suppressed greater in the presence of GL than without GL. Also, Ruminococcus sp. PO1-3, Eubacterium sp. GLH, and a mixture of both and intestinal flora, metabolized 1.0 mM GL to glycyrrhetic acid (GA) in yields of about 10, 70, 40 and 100%, respectively, with 24 h culture. From the level of GL beta-D-glucuronidase activity, it is considered that the metabolism of GL by intestinal flora is due to both enzymatic and non-enzymatic reactions. Moreover, GA at a concentration of 1.0 mM suppressed growth of Ruminococcus sp. PO1-3, Eubacterium sp. GLH, and the mixture of both and intestinal flora, which metabolized 1.0 mM GA to a negligible amount of 3-oxo-glycyrrhetic acid, indicating the accumulation of unchanged GA. GL beta-D-glucuronidase activity of intestinal flora was enhanced by GA, which stimulated bacteria possessing particular this characteristic.

Mechanisms of coordination of Ca2+ signals in pancreatic islet cells

Within pancreatic islet cells, rhythmic changes in the cytosolic Ca2+ concentration have been reported to occur in response to stimulatory glucose concentrations and to be synchronous with pulsatile release of insulin. We explored the possible mechanisms responsible for Ca2+ signal propagation within islet cells, with particular regard to gap junction communication, the pathway widely credited with being responsible for coordination of the secretory activity. Using fura-2 imaging, we found that multiple mechanisms control Ca2+ signaling in pancreatic islet cells. Gap junction blockade by 18 alpha-glycyrrhetinic acid greatly restricted the propagation of Ca2+ waves induced by mechanical stimulation of cells but affected neither Ca2+ signals nor insulin secretion elicited by glucose elevation. The source of Ca2+ elevation was also different under the two experimental conditions, the first being sustained by release from inner stores and the second by nifedipine-sensitive Ca2+ influx. Furthermore, glucose-induced Ca2+ waves were able to propagate across cell-free clefts, indicating that diffusible factors can control Ca2+ signal coordination. Our results provide evidence that multiple mechanisms of Ca2+ signaling operate in beta-cells and that gap junctions are not required for intercellular Ca2+ wave propagation or insulin secretion in response to glucose.

Influence of various bile acids on the metabolism of glycyrrhizin and glycyrrhetic acid by Ruminococcus sp. PO1-3 of human intestinal bacteria

Ruminococcus sp. PO1-3, an intestinal bacterium isolated from human feces, metabolized glycyrrhizin (GL) to glycyrrhetic acid (GA) and GA to 3-oxo-glycyrrhetic acid (3-oxo-GA) and possessed GL beta-D-glucuronidase and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) involved in the metabolism of GL. This bacterial growth was enhanced by GL at a concentration of 0.4 mm and was suppressed by GA at concentration of 1.0 mM. Chenodeoxycholic acid, deoxycholic acid and lithocholic acid among the bile acids added to this bacterium suppressed the growth and GL beta-D-glucuronidase activity and 3beta-HSD activity incident to it at a concentration of 1.0 mM, while cholic acid, hyodeoxycholic acid and glycine and taurin conjugates of cholic acid, chenodeoxycholic acid, deoxycholic acid and lithocholic acid had almost no effect on this bacterium at a concentration of 0.2 to 1.0 mm. However, these enzyme activities of this sonicated bacteria were inhibited by all of these bile acids. Although each bile acid and GL added to bacteria at the same time suppressed the growth and the amount of metabolite GA by all bile acids used except cholic acid, taurocholic acid and taurodeoxycholic acid with GL, a combination of each bile acid and GA eased the growth inhibition caused by GA at a concentration of 0.2 mM and enhanced the amount of metabolite 3-oxo-GA by the glycine conjugate of bile acids with GA. GL or GA added after 6 h culture with each of these bile acids and bacteria was metabolized to a relatively large amount of GA by chenodeoxycholic acid and lithocholic acid and their glycine and taurine conjugates, glycocholic acid and taurodeoxycholic acid, or had almost no effect on the amount of metabolite 3-oxo-GA, respectively. These results showed that although GL added after the exposure to bile acid and GA and bile acid added at the same time as bacteria had different bile acid action, these conditions enhanced the amount of metabolite GA from GL and metabolite 3-oxo-GA from GA.

Biotransformation of glycyrrhizin to 18beta-glycyrrhetinic acid-3-O-beta-D-glucuronide by Streptococcus LJ-22, a human intestinal bacterium

By human intestinal bacteria, glycyrrhizin (18beta-glycyrrhetinic acid-3-O-[beta-D-glucuronopyranosyl-(1-->2)-betaD-glucuro nopyranoside], GL) was metabolized to 18beta-glycyrrhetinic acid (GA): the main pathway metabolized GL to GA by glucuronidases of Bacteroides J-37 and Eubacterium sp. GLH and the minor pathway metabolized GL to 18beta-glycyrrhetinic acid-3-O-beta-D-glucuronide (GAMG) by beta-glucuronidase of Streptococcus LJ-22. Beta-Glucuronidase from Streptococcus LJ-22 hydrolyzed GL to GAMG (not GA). The molecular weight and optimal pH of the enzyme were 240 kDa and 5-6.

Purification and characterization of glycyrrhetic acid mono-glucuronide beta-D-glucuronidase in Eubacterium sp. GLH

Glycyrrhetic acid mono-glucuronide (GAMG), 1-(18beta-glycyrrhet-3-yl)-beta-D-glucopyranuroic acid, was hydrolyzed to glycyrrhetic acid (GA) by GAMG beta-D-glucuronidase in Eubacterium sp. GLH from human intestinal bacteria. The enzyme had an optimum pH of 5.0 and was purified from a crude extract by Butyl Toyopearl 650 S, Toyopearl HW-55 S, Hydroxyapatite and DEAE-Toyopearl 650 M column chromatography. The purified enzyme showed a specific activity of 495 nmol/min/mg protein and a single band on Coomassie brilliant blue staining and a molecular weight of about 43 kDa on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The apparent molecular weight was 49.5 kDa, as estimated by Toyopearl HW-55 S column chromatography. Also, the enzyme seemed to have a sulfhydryl group(s) in its active site with a Km value of 77 x 10(-3) M.

Biochemical characterization of recombinant HIV-1 reverse transcriptase (rRT) as a glycyrrhizin-binding protein and the CK-II-mediated stimulation of rRT activity potently inhibited by glycyrrhetinic acid derivative

By means of successive Mono Q and glycyrrhizin (GL)-affinity column chromatography (HPLC), recombinant HIV-1 RT (rRT) was purified to apparent homogeneity from the Superdex 200 pg fraction of the crude protein extract of E. coli BL21 transfected with pET 21a(+)/HIV-1 PR-RT. It was found that (i) rRT functioned as an effective phosphate acceptor for recombinant human casein kinase II (rhCK-II) in vitro; (ii) this phosphorylation was inhibited by anti-HIV-1 substances [a glycyrrhetinic acid derivative (oGA) and quercetin] and a high dose (100 microM) of GL; (iii) RNA-dependent DNA polymerase (RDDP) activity was stimulated about 2.5-fold after full phosphorylation of rRT by rhCK-II; and (iv) oGA as well as NCS-chromophore effectively prevented the CK-II-mediated stimulation of RDDP activity. These results suggest that the anti-HIV-1 effect of oGA may be involved in the selective inhibition of the CK-II-mediated stimulation of HIV-1 RT at the cellular level.

Distribution of enzymes involved in the metabolism of glycyrrhizin in various organs of rat

Glycyrrhizin (GL) was hydrolyzed to glycyrrhetic acid (GA), glycyrrhetic acid mono-beta-D-glucuronide (GAMG) or both by glucuronidases in various organs of rat. GL beta-D-glucuronidase I, hydrolyzing GL to GA; GAMG beta-D-glucuronidase, hydrolyzing GAMG to GA; and 3alpha-hydroxyglycyrrhetinate (3alpha-hydroxyGA) dehydrogenase, oxidizing 3alpha-hydroxyGA to 3-oxo-GA were found in the organs of this animal. GL beta-D-glucuronidase II was distributed in the lysosomal fraction of all organs except brain; 3alpha-hydroxyGA dehydrogenase was distributed in the microsomal fraction of the liver; but other enzymes were distributed in the nuclear, lysosomal, microsomal and soluble fractions of a variety of organs. GL beta-D-glucuronidase I, GL beta-D-glucuronidase II and GAMG beta-D-glucuronidase activities in a mixture of lysosomes and microsomes of rat liver exhibited different patterns on hydroxyapatite column chromatography. These results showed the metabolic pathways of GL to be of two types: a beta-D-glucuronidase hydrolyzing GL to GA, and the other consisting of two different beta-D-glucuronidases hydrolyzing GL to GAMG and GAMG to GA.

The role of 11 beta-hydroxysteroid dehydrogenase in the pathogenesis of hypertension

The two 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) isozymes catalyze the interconversion of cortisol and cortisone. Type 1 11 beta-HSD (11 beta-HSD1) has bidirectional activity, while type 2 11 beta-HSD (11 beta-HSD2) mainly converts cortisol into cortisone. Of these two hormones only cortisol has affinity to mineralocorticoid receptors (MRs) and thus induces mineralocorticoid effects. A normal activity of 11 beta-HSD2 is crucial for prevention of mineralocorticoid activity of cortisol. Absent or decreased 11 beta-HSD2 activity results in cortisol-mediated hypermineralocorticoid hypertension. In several hypertensive syndromes a decreased 11 beta-HSD2 activity has been described as the pathogenetic mechanism of the increased blood pressure. In the apparent mineral corticoid excess (AME) syndrome type 1, absence of 11 beta-HSD2 activity is caused by mutations in the gene coding for 11 beta-HSD2. In licorice-induced hypertension glycyrrhetinic acid, the active substituent of licorice, inhibits 11 beta-HSD2 resulting in an acquired hypermineralocorticoid state. 11 beta-HSD2 activity is not decreased in glucocorticoid hypertension (Cushing's syndrome). In essential hypertension some evidence for decreased systemic and skin activity of 11 beta-HSD1 and/or 11 beta-HSD2 has been found, while renal activity of both isozymes appears to be normal. 11 beta-HSD2 activity is also present in cardiovascular myocytes of humans and dogs, and inhibition of 11 beta-HSD potentiates the vascular response to catecholamines. Although MRs in the central nervous system have been incriminated in the pathogenesis of mineralocorticoid hypertension, a pathophysiological role for 11 beta-HSD2 has not yet been described. Finally, in the placenta 11 beta-HSD2 reduces fetal exposure to maternal glucocorticoids and a decreased activity of this isozyme may result in low birth weight and increased risk of high blood pressure at adult age.

Hydrolysis of glycyrrhetyl mono-glucuronide to glycyrrhetic acid by glycyrrhetyl mono-glucuronide beta-D-glucuronidase of Eubacterium sp. GLH

Glycyrrhetyl mono-glucuronide (GAMG) is an intermediate in the hydrolysis of glycyrrhizin (GL) to glycyrrhetic acid (GA). An enzyme responsible for its hydrolysis, characterized as a GAMG beta-D-glucuronidase of Eubacterium sp. (species) GLH, has been isolated from human intestinal bacteria. The pattern of GAMG beta-D-glucuronidase activity was different from that of GL beta-D-glucuronidase activity by Butyl-Toyopearl 650 S column chromatography. Thus, these enzymes showed differences in the purification ratio and substrate specificity. After this step, GAMG beta-D-glucuronidase was completely separated from GL beta-D-glucuronidase by gel filtration through Toyopearl HW-55 S, indicating that the GAMG beta-D-glucuronidase is a novel type of beta-D-glucuronidase which hydrolyzes one glucuronic acid linkage of GA.

Identification of glycyrrhizin as a thrombin inhibitor

Glycyrrhizin (GL), an anti-inflammatory compound isolated from Glycyrrhiza glabra, was identified as a new thrombin inhibitor: (a) It prolonged plasma recalcification and thrombin and fibrinogen clotting times, and (b) it inhibited thrombin-induced, but not collagen-, PAF- or convulxin-induced platelet aggregation. On the other hand, GL did not block thrombin's amidolytic activity upon S-2238. Furthermore, the fluorescence emission intensity of dansyl-thrombin was increased upon GL binding. Moreover, GL displaced hirudin as an inhibitor of thrombin-catalyzed hydrolysis of S-2238. Our data provide evidence that GL is a selective inhibitor of thrombin (the first one isolated from plants) that is able to exert its anti-thrombin action by interacting with the enzyme's anion binding exosite 1. A pharmacophoric search identified GL as a sialyl Lewis X (SLe[X]) mimetic compound able to inhibit selectin binding to SLe(X). However, SLe(X) did not affect thrombin clotting activities, which indicates a lack of its interaction with thrombin and distinguishes both molecules. It is suggested that the anti-inflammatory effect of GL may be due to its effective anti-thrombin action.

Localization of enzymes involved in metabolism of glycyrrhizin in contents of rat gastrointestinal tract

Most digested food 2 h after overnight feeding in rat remained in the stomach, duodenum, upper small intestine, lower small intestine, cecum and colon, all of which indicated pH between 4 and 7 and had glycyrrhizin (GL) hydrolyzing activity. This enzyme activity was highest in the cecal and colonic contents among all gastrointestinal contents. Also, 3 alpha-hydroxyglycyrrhetic acid (3 alpha-hydroxyGA) and 3 beta-hydroxyglycyrrhetic acid (3 beta-hydroxyGA) oxidizing enzymes were localized in the same cecal content. Namely, rat gastrointestinal bacteria had the ability to hydrolyze GL to 3 beta-hydroxyGA by glycyrrizin beta-D-glucuronidase and to oxide 3 beta-hydroxyGA and 3 alpha-hydroxyGA to 3-oxoGA by 3 beta-hydroxyglycyrrhetinate dehydrogenase and 3 alpha-hydroxyglycyrrhetinate dehydrogenase, respectively. In medium of pH 1 to pH 10, metabolites 3 beta-hydroxyGA, 3-oxoGA and 3 alpha-hydroxyGA obtained from the metabolism of GL were the highest in pH 8. The intestinal contents of pH 6 or pH 7 were able to produce metabolites 3 beta-hydroxyGA in the metabolism of GL. However, the stomach content at pH 4.2 was lowest in metabolite 3 beta-hydroxyGA. It is unknown whether or not GL is metabolized to 3 beta-hydroxyGA by the stomach content in vivo.

Identification of glycyrrhizin-binding protein kinase as casein kinase II and characterization of its associated phosphate acceptors in mouse liver

Two forms (G-I and G-II kinases) of casein kinase II(CK-II) in a partially purified CK-II fraction (Mono Q fraction) of mouse liver were separated by means of glycyrrhizin (GL)-affinity column chromatography. Biochemical characterization revealed that these two GL-binding kinases were identical to CK-II. Two phosphate acceptors [p99 (pI 7.0) and p56] copurified with CK-II were identified as ERp99 (Hsp-90-family protein) and calreticulin, respectively. Another protein [p100 (pI 9.0)], which crossreacted with anti-serum against human glucocorticoid receptor (GR), was associated with ERp99. Phosphorylation of p99 [a hetero-complex of p99 (pI 7.0) and p100 (pI 9.0)] and p56 by CK-II in vitro was stimulated significantly by low levels (1-3 microM) of GL, but inhibited significantly at doses above 20 microM. However, no effect of GL on autophosphorylation of ERp99 was detected. The data provided here suggest that GL can regulate CK-II-mediated phosphorylation involved in the GL-induced biological effects in mammalian cells.

Physiological correlation between glycyrrhizin, glycyrrhizin-binding lipoxygenase and casein kinase II

By means of glycyrrhizin (GL)-affinity column chromatography, a GL-binding lipoxygenase (gbLOX) was selectively purified from the partially purified soybean LOX-1 fraction. Polypeptide analysis of the purified gbLOX by SDS-PAGE detected two distinct polypeptides (p96 and p94), which were identical to LOX-3 as determined by their partial N-terminal amino acid sequences. Moreover, it was found that (i) phosphorylation of gpLOX by casein kinase II (CK-II) is significantly stimulated by 3 microM GL, but inhibited by 30 microM GL or 10 microM oGA; and (ii) gbLOX activity is enhanced when the enzyme is phosphorylated by CK-II in the presence of 3 microM GL. These results suggest that (i) CK-II is a kinase responsible for the activation of gbLOX through its specific phosphorylation; and (ii) GL is one of the regulatory substances for specific phosphorylation of gbLOX (LOX-3) by CK-II in plant cells.

Pharmacokinetics of glycyrrhizin in rats with D-galactosamine-induced hepatic disease

The pharmacokinetic behavior of glycyrrhizin (GZ) was examined in D-galactosamine-intoxicated (GAL) rats. When GZ was administered intravenously, the apparent volume of distribution (Vdss) and the total body clearance (CLtotal) were more significantly decreased in GAL rats than those in normal rats. When GZ was administered orally, the area under the plasma concentration-time curve (AUC), the mean residence time (MRT) and the time to reach the maximum plasma concentration (Tmax) for GZ were higher, but the maximum plasma concentration (Cpmax) in GAL rats was lower than that in normal rats. The bioavailability of GZ, however, was not significantly changed. On the other hand, the AUC for glycyrrhetic acid (GA), a main metabolite of GZ, after oral administration of GZ was higher in GAL rats than in normal rats, although there was no significant difference in MRT or Tmax, Cpmax or the bioavailability for GA between GAL and normal rats. The reasons for these differences in GAL rats would be changes in the absorption rate (reduced gastric emptying rate) and reduction of the hepatic elimination rates (biliary excretion of GZ and hepatic metabolism of GA).

Therapeutic basis of glycyrrhizin on chronic hepatitis B

Glycyrrhizin, a major component of a herb (licorice), has been intravenously used for the treatment of chronic hepatitis B in Japan and improves liver function with occasional complete recovery from hepatitis. This substance modifies the intracellular transport and suppresses sialylation of hepatitis B virus (HBV) surface antigen (HBsAg) in vitro. This study was designed to clarify the pharmacological basis for its effectiveness. The structure-bioactivity relationship of glycyrrhizin, glycyrrhetic acid 3-O-monoglucuronide and glycyrrhetic acid was determined, and glycyrrhetic acid was found to be the most active of them. The amounts of three substances bound to the liver were evaluated in guinea pigs after intravenous administration of glycyrrhizin. Glycyrrhizin and glycyrrhetic acid 3-O-monoglucuronide were detected at concentrations of 31.8-1.3 micrograms/g of liver, but glycyrrhetic acid was not detected. When glycyrrhizin attained these concentrations in the cellular fraction of the PLC/PRF/5 cell culture, it suppressed the secretion of HBsAg as reported previously. These results indicated that glycyrrhizin administered intravenously might bind to hepatocytes at the concentration at which glycyrrhizin could modify the expression of HBV-related antigens on the hepatocytes and suppress sialylation of HBsAg.

A 96-kDa glycyrrhizin-binding protein (gp96) from soybeans acts as a substrate for casein kinase II, and is highly related to lipoxygenase 3

A 96-kDa glycyrrhizin (GL)-binding protein (gp96) was purified to apparent homogeneity from an aqueous extract of soybeans by means of successive DEAE-cellulose column chromatography, gel filtration on Superdex 200pg, GL-affinity column chromatography, and ion-exchange chromatography on a Mono S column (HPLC). The protein was identified as a GL-binding protein since it specifically binds to [3H]GA. Moreover, it is a lipoxygenase (an enzyme that catalyzes the oxygenation of unsaturated fatty acids) since (i) it displays lipoxygenase (LOX) activity at pH 6.5; (ii) it is recognized on Western blot analysis by antibodies against LOX-1 and LOX-2; and (iii) the sequence of the N-terminal 21 amino acid residues (SNDVYLPRDEAFGHLKSSDFL) of a 42-kDa fragment (p42) proteolytically generated from gp96 is identical to a sequence of soybean LOX-3. In addition, GL, glycyrrhetinic acid (GA) and soyasaponin beta g slightly inhibited LOX activity of the purified gp96 fraction, whereas oGA (a GA derivative) greatly inhibited its activity. Furthermore, CK-II catalyzed phosphorylation of gp96 was stimulated significantly by GL at doses between 1 and 10 microM, but this phosphorylation was inhibited completely by 50 microM GL. All these results taken together suggest that (i) gp96 purified from soybeans as a GL-binding protein belongs to the LOX family; and (ii) triterpenoid saponins, including GL, are involved in the regulation of the activities of CK-II and LOXs in plants, such as soybeans and roots of liquorice, which contain large quantities of saponins.

Purification and characterization of a 100 kDa glycyrrhizin (GL)-binding protein (gp100) as an effective phosphate acceptor for CK-II and the effect of GL on the phosphorylation of gp100 by CK-II in vitro

By means of successive GL-affinity and Mono S column chromatographies (HPLC), a 100 kDa GL-binding protein (gp100) was purified from the partially purified CK-II fraction of EAT cells as an effective phosphate acceptor for CK-II. It was found that (i) gp100 (pI 9.0) is copurified with CK-II, Hsp-90 and p34 or p70; (ii) gp100 cross-reacts with anti-human GR; (iii) phosphorylation of gp100 by CK-II is significantly stimulated by 1 microM GL or 0.3 microM oGA; and (iv) GL as well as DEX inhibit it at doses above 3 microM. Data are provided to suggest that the GL-induced selective inhibition of the CK-II catalyzed phosphorylation of gp100 may be involved in the anti-inflammatory effects of GL.

Intestinal bacterial hydrolysis is indispensable to absorption of 18 beta-glycyrrhetic acid after oral administration of glycyrrhizin in rats

Gnotobiote rats were prepared by infecting germ-free rats with Eubacterium sp. strain GLH, a human intestinal bacterium capable of hydrolysing glycyrrhizin to 18 beta-glycyrrhetic acid. Their faeces and caecal contents showed glycyrrhizin-hydrolysing activities (31.7 and 31.3 pmol min-1 (mg protein)-1, respectively) similar to those (81.0 and 39.9 pmol min-1 (mg protein)-1, respectively) of conventional rats, although there was no detectable activity in germ-free rats. When glycyrrhizin (100 mg kg-1) was orally administered to conventional, germ-free and gnotobiote rats, no glycyrrhizin could be detected in plasma 4 or 17 h after the administration, using EIA and HPLC assays. Plasma 18 beta-glycyrrhetic acid was not detected 4 or 17 h after the administration of glycyrrhizin to germ-free rats nor could this compound be detected in caecal contents or in the faeces. However, 18 beta-glycyrrhetic acid (0.6-2.6 nmol mL-1) was detected in plasma of the conventional and the gnotobiote rats 4 and 17 h after the administration, and the caecal contents after 4 h and the cumulative faeces up to 17 h of the conventional and the gnotobiote rats contained considerable amounts of 18 beta-glycyrrhetic acid. These findings indicate that orally administered glycyrrhizin is poorly absorbed from the gut, but is hydrolysed to 18 beta-glycyrrhetic acid by intestinal bacteria such as E. sp. strain GLH, and the resulting 18 beta-glycyrrhetic acid is absorbed.

Biotransformation of 18 beta-glycyrrhetinic acid by ginseng hairy root culture

On administration of 18 beta-glycyrrhetinic acid to hairy root cultures of Panax ginseng, three new biotransformation products, 30-O-[beta-D-glucopyranosyl-(1-->2)-beta-D- glucopyranosyl]18 beta-glycyrrhetinic acid, 30-O-(6- O-malonyl-beta-D-glucopyranosyl)18 beta-glycyrrhetinic acid and 3-O-[6-O- malonyl-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl]18 beta-glycyrrhetinic acid, were isolated together with three known compounds. Ginseng hairy roots showed the biotransformation abilities of glycosylation and malonylation to 18 beta-glycyrrhetinic acid.