Bioconversion of glycyrrhizinic acid in liquorice into 18-beta-glycyrrhetinic acid by Aspergillus parasiticus speare BGB

A filamentous fungi strain, Aspergillus parasiticus Speare BGB, producing beta-glucuronidase was screened to transform glycyrrhizinic acid (GL) in liquorice into 18-beta-glycyrrhetinic acid (GA). Under the following cultivate conditions in shake flask, 1% GL (purity 30%), medium capacity 40% of flask, the initial pH value at 4.5, cultivate temperature of 32 degrees C, inoculum size of 5% and culturing time for 96 h the bioconversion ratio of GL into GA could reach 95%. A variety of parameters of submerged state fermentation, including the growth characteristics of A. parasiticus Speare BGB, the change amount of GL and GA, and the activity of beta-glucuronidase, were monitored simultaneously. GA was separated and purified by macroporous resin, silica gel column chromatography followed by recrystalization with the final purity over 98%. Purified product was identified as GA by the infrared absorption spectrum, molecular weight, and nuclear magnetic resonance. This study provided a new and efficient approach of obtaining GA by microbial transformation.

Bioavailability of glycyrrhizin from Shaoyao-Gancao-Tang in laxative-treated rats

Shaoyao-Gancao-Tang (SGT), a traditional Chinese formulation composed of Shaoyao (Paeoniae Radix) and Gancao (Glycyrrhizae Radix), is frequently used in conjunction with laxatives such as sodium picosulfate in colonoscopy to relieve abdominal pains. We have investigated the alterations of the bioavailability of glycyrrhizin when SGT was co-administered with sodium picosulfate and we tried to identify a regimen that might minimize the alterations. Glycyrrhizin is one of the active glycosides in Gancao and SGT and is hydrolysed into the bioactive metabolite, 18β-glycyrrhetic acid (GA) by intestinal bacteria following oral administration. We found that the maximum plasma concentration (Cmax) and the area under the mean concentration vs time curve from zero to 24 h (AUC0–24 h) of GA from a single dose of SGT administered 5 h after a single pretreatment with sodium picosulfate were significantly reduced to 15% and 20% of the control level in rats, respectively. These reductions were still significant four days after sodium picosulfate pretreatment, but were restored by repetitive administration of SGT following sodium picosulfate pretreatment. Similar reductions and recovery were observed for the glycyrrhizin-metabolizing activity of intestinal bacteria in rat faeces. The results warrant clinical studies for co-administration of laxatives such as sodium picosulfate and SGT.

Bioactive microbial metabolites from glycyrrhetinic acid

Biotransformation of 18beta-glycyrrhetinic acid, using Absidia pseudocylinderospora ATCC 24169, Gliocladium viride ATCC 10097 and Cunninghamella echinulata ATCC 8688a afforded seven metabolites, which were identified by different spectroscopic techniques (1H, 13C NMR, DEPT, 1H-1H COSY, HMBC and HMQC). Three of these metabolites, viz. 15alpha-hydroxy-18alpha-glycyrrhetinic acid, 13beta-hydroxy-7alpha,27-oxy-12-dihydro-18beta-glycyrrhetinic acid and 1alpha-hydroxy-18beta-glycyrrhetinic acid are new. The 13C NMR data and full assignment for the known metabolite 7beta, 15alpha-dihydroxy-18beta-glycyrrhetinic acid are described here for the first time. The major metabolites were evaluated for their hepatoprotective activity using different in vitro and in vivo models. These included protection against FeCl3/ascorbic acid-induced lipid peroxidation of normal mice liver homogenate, induction of nitric oxide (NO) production in rat macrophages and in vivo hepatoprotection against CCl4-induced hepatotoxicity in albino mice.

Structural determination of two new triterpenoids biotransformed from glycyrrhetinic acid by Mucor polymorphosporus

Five hydroxylated derivatives of glycyrrhetinic acid by Mucor polymorphosporus were isolated. Among them, 6beta, 7beta-dihydroxyglycyrrhentic acid (2) and 27-hydroxyglycyrrhentic acid (3) are new compounds. Their chemical structures were identified by spectral methods including 2D-NMR.

Glycyrrhizin and licorice significantly affect the pharmacokinetics of methotrexate in rats

Glycyrrhizin (GZ) and licorice (root of Glycyrrhiza uralensis) are worldwide food additives and important oriental phytomedicines. This study investigated the biological fate of GZ by orally giving GZ and licorice decoction (LD) to rats. The serum concentrations of GZ and glycyrrhetic acid (GA) were determined by high performance liquid chromatography. The results showed that GZ was not detected and GA was present in serum until 3 days postdosing of GZ and LD. To evaluate the effects of GZ and licorice on the pharmacokinetics of methotrexate (MTX), an important immunosuppressant with a narrow therapeutic window, rats were orally given MTX with and without GZ and LD in different dosage regimens. The serum MTX concentration was determined by fluorescence polarization immunoassay. The results revealed that the AUC and MRT of MTX were significantly increased by GZ and LD. In conclusion, the concurrent use of GZ or licorice with MTX should be with caution.

Selective inhibition of 11beta-hydroxysteroid dehydrogenase 1 by 18alpha-glycyrrhetinic acid but not 18beta-glycyrrhetinic acid

Elevated cortisol concentrations have been associated with metabolic diseases such as diabetes type 2 and obesity. 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1, catalyzing the conversion of inactive 11-ketoglucocorticoids into their active 11beta-hydroxy forms, plays an important role in the regulation of cortisol levels within specific tissues. The selective inhibition of 11beta-HSD1 is currently considered as promising therapeutic strategy for the treatment of metabolic diseases. In recent years, natural compound-derived drug design has gained considerable interest. 18beta-glycyrrhetinic acid (GA), a metabolite of the natural product glycyrrhizin, is not selective and inhibits both 11beta-HSD1 and 11beta-HSD2. Here, we compare the biological activity of 18beta-GA and its diastereomer 18alpha-GA against the two enzymes in lysates of transfected HEK-293 cells and show that 18alpha-GA selectively inhibits 11beta-HSD1 but not 11beta-HSD2. This is in contrast to 18beta-GA, which preferentially inhibits 11beta-HSD2. Using a pharmacophore model based on the crystal structure of the GA-derivative carbenoxolone in complex with human 11beta-HSD1, we provide an explanation for the differences in the activities of 18alpha-GA and 18beta-GA. This model will be used to design novel selective derivatives of GA.

The disposition of diammonium glycyrrhizinate and glycyrrhetinic acid in the isolated perfused rat intestine and liver

The major component of liquorice root extract, glycyrrhizinate (GZ), has been formulated as an injection for the treatment of hepatitis. If given orally, GZ has poor bioavailability and is catalysed to glycyrrhetinic acid (GA) by intestinal bacteria. GA is subsequently responsible for significant side effects. This study was conducted to clarify the relationship between GZ and GA absorption and bioavailability. GZ and GA absorption were investigated using the in situ single pass isolated perfused intestine (IPI). Hepatic disposition was investigated using isolated perfused liver (IPL) and in vivo biliary excretion models. The apparent permeability and absorption rate constants in the IPI for GZ were 0.36 +/- 0.31 cm/min and 0.35 +/- 0.33 min (-1), while those for GA were 5.73 +/- 0.11 cm/min and 1.53 +/- 0.05 min (-1), respectively. The hepatic extraction ratios of unbound GZ and GA in the IPL were 0.22 +/- 0.01 and 0.44 +/- 0.15, respectively. Seven hours after intra-portal venous injection in vivo, the cumulative biliary excretion ratio for GZ was 96 %. There was negligible biliary excretion of unchanged GA during the same period. It was apparent in all models used that in the absence of intestinal bacteria GZ was not metabolised to GA, or vice versa. Hence, GZ can be absorbed unchanged from the intestine provided it has sufficient time and is protected from intestinal bacteria. This opens up the possibility that the use of pharmaceutical carrier systems or similar formulation approaches may allow effective oral administration of therapeutic levels of GZ without the side effects associated with GA.

[Expression, characterization and application of thermostable beta-glucuronidase from Thermotoga maritima]

The gene of beta-glucuronidase from Thermotoga maritima was cloned into the plasmid pHsh, and expressed in Escherichia coli JM109. The recombinant protein was purified to homogeneity by a simple step, heat treatment. The recombinant enzyme had a molecular mass of 65.9 kD. The optimal activity of beta-glucuronidase was found at pH 5.0 and 80 degrees C. The purified enzyme was stable over a pH range from 5.8 to 8.2 and had a half life of 2 h at 80 degrees C. The kinetic experiments at 80 degrees C with p-nitrophenyl-beta- glucuronide as substrate gave a K(m) and V(max) of 0.18 mmol/L and 312 u per mg of protein. The purified enzyme could transform glycyrrhizin to glycyrrhetinic acid.

Endogenous inhibitors (GALFs) of 11beta-hydroxysteroid dehydrogenase isoforms 1 and 2: derivatives of adrenally produced corticosterone and cortisol

Two isoforms of 11beta-HSD exist; 11beta-HSD1 is bi-directional (the reductase usually being predominant) and 11beta-HSD2 functions as a dehydrogenase, conferring kidney mineralocorticoid specificity. We have previously described endogenous substances in human urine, "glycyrrhetinic acid-like factors (GALFs)", which like licorice, inhibit the bi-directional 11beta-HSD1 enzyme as well as the dehydrogenase reaction of 11beta-HSD2. Many of the more potent GALFs are derived from two major families of adrenal steroids, corticosterone and cortisol. For example, 3alpha5alpha-tetrahydro-corticosterone, its derivative, 3alpha5alpha-tetrahydro-11beta-hydroxy-progesterone (produced by 21-deoxygenation of corticosterone in intestinal flora); 3alpha5alpha-tetrahydro-11beta-hydroxy-testosterone (produced by side chain cleavage of cortisol); are potent inhibitors of 11beta-HSD1 and 11beta-HSD2-dehydrogenase, with IC50's in range 0.26-3.0 microM, whereas their 11-keto-3alpha5alpha-tetrahydro-derivatives inhibit 11beta-HSD1 reductase, with IC50's in range 0.7-0.8 microM (their 3alpha5beta-derivatives being completely inactive). Inhibitors of 11beta-HSD2 increase local cortisol levels, permitting it to act as a mineralocorticoid in kidney. Inhibitors of 11beta-HSD1 dehydrogenase/11beta-HSD1 reductase serve to adjust the set point of local deactivation/reactivation of cortisol in vascular and other glucocorticoid target tissues, including adipose, vascular, adrenal tissue, and the eye. These adrenally derived 11-oxygenated C21- and C19 -steroidal substances may serve as 11beta-HSD1- or 11beta-HSD2-GALFs. We conclude that adrenally derived products are likely regulators of local cortisol bioactivity in humans.

A possible involvement of 3-monoglucuronyl-glycyrrhetinic acid, a metabolite of glycyrrhizin (GL), in GL-induced pseudoaldosteronism

Glycyrrhizin (GL), a major ingredient of Glycyrrhiza Radix (licorice), is widely used to treat various disorders or as a sweetener. It is also known that GL occasionally induces pseudoaldosteronism. It is conceivable that the active form of GL in pseudoaldosteronism induction is glycyrrhetinic acid (GA). Although it is reported that 3-monoglucuronyl-glycyrrhetinic acid (3MGA) is detectable specifically in the plasma of patients with GL-induced hypokalemia, pharmacokinetics and a hypokalemia induction mode of action for 3MGA have not been clarified. We investigated the toxicokinetics of GL, GA and 3MGA in a single or multiple oral administration of GL. The results suggested that higher blood concentrations of 3MGA were maintained by the multiple administration compared to the single dose, whereas the concentrations of GA and GL showed no difference. We injected 3MGA intravenously and found that it can decrease the plasma potassium level (PPL) in vivo. It is clinically recommended to avoid a combination treatment of GL and furosemide. While treatment with a low dosage of furosemide had no effect on PPL, the multiple administration of GL and furosemide markedly decreased PPL compared to the effect of administering GL alone. In the single dosage regime, there was no difference between PPL after the combination treatment and after administering GL alone. Collectively, these findings suggested that accumulation of 3MGA may be involved in the pathogenesis of pseudoaldosteronism induced by chronic GL treatment.

Clostridium glycyrrhizinilyticum sp. nov., a glycyrrhizin-hydrolysing bacterium isolated from human faeces

Screening of faecal bacteria for glycyrrhetic acid (GA) production by hydrolysing of glycyrrhizin (GL) resulted in the isolation of two strains, designated ZM35T and ZM38. Strains ZM35T and ZM38 were Gram-positive, obligate anaerobic, non-spore-forming and rod-shaped bacteria. Analysis of the 16S rRNA gene sequences indicated that strains ZM35T and ZM38 belonged to cluster XIVa of the genus Clostridium. The 16S rRNA gene sequences of strains ZM35T and ZM38 were identical. Strain ZM35T exhibited approximately 94% to 95% identity with the validly described species, Clostridium oroticum(94.5%), Eubacterium contortum(93.8%), Ruminococcus gnavus(94.5%) and R. torques(95.1%). In an experiment of DNA-DNA hybridization, it was confirmed that strains ZM35T and ZM38 were the same species. The guanine-plus-cytosine (G+C) content of strain ZM35T is 45.7 mol%. Based on the phylogenetic and phenotypic findings, we propose that strains ZM35T and ZM38 be assigned to a novel species named Clostridium glycyrrhizinilyticum. The type strain is ZM35T (=JCM 13368T=DSM 17593T).

Antioxidant and redox properties of supramolecular complexes of carotenoids with beta-glycyrrhizic acid

Supramolecular complexes between carotenoids and a triterpene glycoside, beta-glycyrrhizic acid (GA), were found to exhibit unusual antioxidant activity. Complexation with GA increases a scavenging rate of canthaxanthin and 7',7'-dicyano-7'-apo-beta-carotene toward OOH radicals more than 10 times, but has no effect on the scavenging rate of zeaxanthin. Scavenging rate constants were measured in DMSO solution of carotenoids using the EPR spin-trapping technique. EPR parameters of spin adducts were determined as a(H) = 2.3 G, a(N) = 13.9 G for PBN (N-tert-butyl-alpha-phenylnitrone)-OOH, and a(H) = 3.4 G, a(N) = 14.9 G for the PBN-CH3 adduct. Taking into account the previously measured dependence of the scavenging rate constants toward OOH radicals on the oxidation potential of carotenoids, this result can be explained by the hypothesis that the complexation with GA affects the value of oxidation potentials. This hypothesis was confirmed by CV measurements.

Binding analysis of glycyrrhetinic acid to human serum albumin: Fluorescence spectroscopy, FTIR, and molecular modeling

Fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and molecular modeling methods were employed to analyze the binding of glycyrrhetinic acid (GEA) to human serum albumin (HSA) under physiological conditions with GEA concentrations from 4.0x10(-6) to 4.5x10(-5) mol L(-1). The binding of GEA to HSA was via two types of sites: the numbers of binding site for the first type was near 0.45 and for the second type it was approximately 0.75. The binding constants of the second type binding site were lower than those of the first type binding site at corresponding temperatures, the results suggesting that the first type of binding site had high affinity and the second binding site involved other sites with lower binding affinity and selectivity. The fluorescence titration results indicated that GEA quenched the fluorescence intensity of HSA through static mechanism. The FTIR spectra evidence showed that the protein secondary structure changed with reduction of alpha-helices about 26.2% at the drug to protein molar ratio of 3. Thermodynamic analysis showed that hydrogen bonds were the mainly binding force in the first type of binding site, and hydrophobic interactions might play a main role in the second type of binding site. Furthermore, the study of computational modeling indicated that GEA could bind to the site I of HSA and hydrophobic interaction was the major acting force for the second type of binding site, which was in agreement with the thermodynamic analysis.

Microbial transformation of glycyrrhetinic acid by Mucor polymorphosporus

Glycyrrhetinic acid (GA; 1) is one of the major constituents of a traditional Chinese medicine, the roots of Glycyrrhiza uralensis, called Gancao in Chinese. In the present paper, the biotransformation of GA by Mucor polymorphosporus (AS 3.3443) was investigated and eight metabolites were obtained. Based on their chemical and spectral data, the structures of the derivatives were respectively elucidated as 24-hydroxyglycyrrhetinic acid ( 2), 6beta-hydroxyglycyrrhetinic acid ( 3), 7alpha-hydroxyglycyrrhetinic acid ( 4), 7beta-hydroxyglycyrrhetinic acid ( 5), 3- O-acetyl-7beta-hydroxyglycyrrhetinic acid ( 6), 3-oxo-7beta-hydroxyglycyrrhetinic acid ( 7), 15alpha-hydroxyglycyrrhetinic acid ( 8), 3 -oxo -15alpha-hydroxyglycyrrhetinic acid ( 9), among which metabolites 3, 4, 6, 7 and 9 are new compounds.

Glycyrrhetic acid (a metabolic substance and aglycon of glycyrrhizin) induces apoptosis in human hepatoma, promyelotic leukemia and stomach cancer cells

We have investigated the effect of glycyrrhetic acid (GR) which is metabolic substance of glycyrrhizin, on DNA of human hepatoma (HLE), promyelotic leukemia (HL-60) and stomach cancer (KATO III) cells. GR displayed apoptotic effects against HLE, HL-60 and KATO III cells. The fragmentation of DNA by GR to oligonucleosomal-sized fragments, a characteristic of apoptosis, was dose- and time-dependent in these cell lines. These findings suggest that growth inhibition of these cell lines by GR result from the induction of apoptosis by the compound. Inhibitors of caspases did not suppress the DNA fragmentation caused by GR. N-acetyl-L-cysteine, an antioxidant drug, weakly inhibited the DNA fragmentation caused by GR suggesting that active oxidants work partly as an apoptosis-inducing transfer substance.

Effects of glucose, fructose and 5-hydroxymethyl-2-furaldehyde on the presystemic metabolism and absorption of glycyrrhizin in rabbits

Our previous study reported that co-administration of honey significantly increased the serum levels of glycyrrhetic acid (GA) after oral administration of glycyrrhizin (GZ) in rabbits. The components of honey are sucrose, glucose, fructose and 5-hydroxymethyl-furaldehyde (HMF). To clarify the causative component(s) in honey that altered the metabolic pharmacokinetics of GZ, rabbits were given GZ (150 mg kg(-1)) with and without glucose (5 g/rabbit), fructose (5 g/rabbit) and HMF (1 mg kg(-1)), respectively, in crossover designs. An HPLC method was used to determine concentrations of GZ and GA in serum as well as GA and 3-dehydroglycyrrhetic acid (3-dehydroGA) in faeces suspension. A noncompartment model was used to calculate the pharmacokinetic parameters and analysis of variance was used for statistical comparison. Our results indicated that the area under curve (AUC) of GA was significantly increased by 29% when HMF was coadministered, whereas the pharmacokinetics of GZ and GA were not significantly altered by coadministration of glucose or fructose. An in-vitro study, using faeces to incubate GZ and GA individually, indicated that HMF significantly inhibited the oxidation of GA to 3-dehydroGA and this may explain the enhanced GA absorption in-vivo. It was concluded that HMF is the causative component in honey that affects the presystemic metabolism and pharmacokinetics of GZ in-vivo.

Anti-allergic activity of 18beta-glycyrrhetinic acid-3-O-beta-D-glucuronide

Glycyrrhizin (18beta-glycyrrhetinic acid-3-O-beta-D-glucuronopyranosyl-(1 --> 2)-beta-D-glucuronide, GL) was transformed to 18beta-glycyrrhetinic acid-3-O-beta-D-glucuronide (GAMG) by Streptococcus LJ-22. The antiallergic activities of GL and GAMG was measured using a RBL cell assay system and contact hypersensitivity model mice. GAMG exhibited anti-allergic activity with IC50 values of 0.28 mM. GAMG, which is sweeter than GL, and 18beta-glycyrrhetinic acid, which is a GAMG metabolite by human intestinal bacteria, also inhibited the passive cutaneous anaphylaxis and skin contact inflammation. In conclusion, GAMG may be useful as a new sweet food additive and an anti-allergic agent.

HDACi phenylbutyrate increases bystander killing of HSV-tk transfected glioma cells

Malignant glioma patients have a dismal prognosis with an urgent need of new treatment modalities. Previously developed gene therapies for brain tumors showed promising results in experimental animal models, but failed in clinical trials due to low transfection rates and insufficient expression of the transgene in tumor cells, as well as low bystander killing effects. We have previously shown that the histone deacetylase inhibitor 4-phenylbutyrate (4-PB) enhances gap junction communication between glioma cells in culture. In this study, we demonstrate an activation of recombinant HSV-tk gene expression, and a dramatic enhancement of gap junction-mediated bystander killing effect by administration of the HSV-tk prodrug ganciclovir together with 4-PB. These findings that 4-PB potentiates "suicide gene" expression as well as enhances gap junctional communication and bystander killing of tumor cells justify further testing of this paradigm as an adjunct to suicide gene therapy of malignant gliomas.

Metabolic Activities of Ginsenoside Rb1, Baicalin, Glycyrrhizin and Geniposide to Their Bioactive Compounds by Human Intestinal Microflora

To evaluate the pharmacological actions of herbal medicines, metabolic activities of herbal medicine components, ginsenoside Rb1, glycyrrhizin, geniposide and baicalin to their bioactive compounds compound K, 18beta-glycyrrhetic acid, genipin and baicalein by fecal specimens were measured. Their metabolic activities were 646.1+/-591.4, 29.4+/-51.7, 926.3+/-569.6 and 3884.6+/-1400.1 micromol/h/g, respectively. The profiles of these metabolic activities of baicalin and ginsenoside Rb1 were not significantly different to those of water extracts of Scutellariae Radix and Ginseng Radix. None of the metabolic activities tested were different between males and females, or between ages. However, the difference in these metabolic activities in individuals was significant. These results suggest that the human intestinal microflora enzymes that convert herbal components to their bioactive compounds may be used as selection markers of responders to traditional medicines.

Simultaneous determination of glycyrrhizin metabolites formed by the incubation of glycyrrhizin with rat feces by semi-micro high-performance liquid chromatography

A method for semi-micro high-performance liquid chromatography (HPLC) has been established for the simultaneous determination of 3alpha-hydroxyglycyrrhetic acid and 3-dehydroglycyrrhetic acid together with glycyrrhizin, glycyrrhetic acid and glycyrrhetic acid mono-glucuronide formed by incubation of glycyrrhizin with rat feces. The analysis was accomplished within 25 min with a TSKgel ODS-80TsQA (150 x 2.0 mm i.d.) column by linear gradient elution using a mobile phase containing aqueous phosphoric acid and acetonitrile at a flow rate of 0.2 ml.min(-1), a thermostatic oven at 25 degrees C, and detection at 254 nm. The detection limits of these compounds were 0.2 pmol per injection (5 microl). The metabolites of glycyrrhizin, by anaerobic or aerobic incubation with rat fecal suspension over 48 h, were determined. Glycyrrhizin was almost completely converted to metabolite glycyrrhetic acid, and metabolites 3alpha-hydroxyglycyrrhetic acid and 3-dehydroglycyrrhetic acid in negligible amounts in anaerobic conditions. However, the metabolic time courses of 3-dehydroglycyrrhetic acid when incubated in aerobic conditions revealed that it apparently continued increasing during the whole incubation period.

Metabolic inhibition induces opening of unapposed connexin 43 gap junction hemichannels and reduces gap junctional communication in cortical astrocytes in culture

Rat cortical astrocytes in pure culture are functionally coupled to neighboring cells via connexin (Cx) 43 gap junctions under ordinary conditions. Small fluorescent molecules such as Lucifer yellow (LY) pass between cell interiors via gap junctions, but do not enter the cells when externally applied. Subjecting rat and mouse cortical astrocytes to "chemical ischemia" by inhibition of glycolytic and oxidative metabolism induced permeabilization of cells to Lucifer yellow and ethidium bromide before loss of membrane integrity determined by dextran uptake and lactate dehydrogenase release. The gap junction blockers octanol and 18alpha-glycyrrhetinic acid markedly reduced dye uptake, suggesting that uptake was mediated by opening of unapposed hemichannels. Extracellular La(3+) also reduced dye uptake and delayed cell death. The purinergic blocker, oxidized ATP, was ineffective. Astrocytes isolated from mice with targeted deletion of the Cx43 coding DNA exhibited greatly reduced dye coupling and ischemia-induced dye uptake, evidence that dye uptake is mediated by Cx43 hemichannels. Dye coupling was reduced but not blocked by metabolic inhibition. Blockade of lipoxygenases or treatment with free radical scavengers reduced dye uptake by rat astrocytes, suggesting a role for arachidonic acid byproducts in hemichannel opening. Furthermore, permeabilization was accompanied by reduction in ATP levels and dephosphorylation of Cx43. Although hemichannel opening would tend to collapse electrochemical and metabolic gradients across the plasma membrane of dying cells, healthy cells might rescue dying cells by transfer of ions and essential metabolites via Cx43 gap junctions. Alternatively, dying astrocytes might compromise the health of neighboring cells via Cx43 gap junctions, thereby promoting the propagation of cell death.

Effect of pH on metabolism of glycyrrhizin, glycyrrhetic acid and glycyrrhetic acid monoglucuronide by collected human intestinal flora

Collected human intestinal flora (whole bacteria) was incubated with glycyrrhizin (GL), glycyrrhetic acid (GA), glycyrrhetic acid monoglucuronide (GAMG) and a combination of the three for 10 min at 37 degrees C under pH 5.6 and 7.0. The effect of these components on GL beta-D-glucuronidase activity, GAMG beta-D-glucuronidase activity and metabolite production in whole bacteria was examined. GL and GA were not metabolized at pH 5.6 and 7.0 by whole bacteria, while the level of GAMG changed at both pH 5.6 and 7.0. However, preincubated whole bacteria converted GA and a combination containing GA to other metabolites removed 3alpha-hydroxyglycyrrhetic acid and 3-oxoglycyrrhetic acid. The level of GL beta-D-glucuronidase activity remaining in whole bacteria after exposure to both GA and GAMG was above its initial level at pH 5.6 and 7.0, and the level of GAMG beta-D-glucuronidase activity remaining after exposure to GL, GA and GAMG was suppressed against control at pH 5.6 and 7.0. It is found that intestinal bacteria had similar action against GL, GA and GAMG at between pH 5.6 and 7.0.

Inhibitory effect of glycyrrhizin on the phosphorylation and DNA-binding abilities of high mobility group proteins 1 and 2 in vitro

The physiological correlation between glycyrrhizin (GL) and high mobility group proteins I and 2 (HMG1/2) and the inhibitory effect of GL on their phosphorylation by three protein kinases (CK-I, CK-II and PKC) were investigated biochemically in vitro. It was found that GL binds directly to HMG1/2, because (i) HMG1/2 have a high affinity with a GL-affinity column; and (ii) GL induces the conformational changes in HMG1/2. Both purified HMG1/2 functioned as phosphate acceptors for these two protein kinases (CK-I and PKC), but not phosphorylated by CK-II. Phosphorylation of HMG1/2 by two protein kinases (CK-I and PKC) was completely inhibited by a glycyrrhetinic acid derivative (oGA) at one-tenth the concentration of GL. Also, the DNA-binding abilities of HNG1/2 were reduced by GL in a dose-dependent manner. These results show that the binding of GL to HMG1/2 results in the inhibition of their physiological activities (DNA-binding ability and phosphorylation by PKC or CK-I) in vitro. The GL-induced inhibition of the physiological activities of HMG1/2 may be involved in the anti-inflammatory effect of GL in vivo.

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.

The effect of absorption enhancers on the initial degradation kinetics of insulin by alpha-chymotrypsin

The goal of this investigation was to establish a fast method to screen various insulin absorption enhancers by following their effect on the initial kinetics of insulin incubated with alpha-chymotrypsin at 37 degrees C. A simple, sensitive and reproducible reversed phase high performance liquid chromatography (HPLC) method has been developed to carry out this goal. Linear responses (r > 0.999) were observed over the range of 0.4-4 U/ml for insulin. There was no significant difference (P < 0.05) between inter- and intra-day studies for insulin. The mean relative standard deviations (RSD%) of the results of within-day precision and accuracy of insulin were 12%. The assay was sensitive to detect the existence of any metabolite due to the addition of any absorption enhancers, even if it was not seen with insulin alone. Three metabolites (A-C) were detected only when insulin was incubated with alpha-chymotrypsin at 37 degrees C. Metabolite D was observed when either glycocholic acid (0.5, 1%) or taurochenodeoxycholate (0.5, 1%) was incubated with insulin in the absence of alpha-chymotrypsin at 37 degrees C. The compounds that significantly increased insulin T50% were glycyrrhizic acid (0.5%) > deoxycholic acid (1%) > deoxycholic acid (0.5%) > glycyrrhizic acid (1%) > cholic acid (0.5, 1%). Capric acid (0.5%), hydroxypropyl-alpha-cyclodextrin (0.5, 1%) and dimethyl-alpha-cyclodextrin (0.5, 1, 5%) did not significantly affect insulin T50%. The bile salts increased insulin T50% in this order: deoxycholate > cholate > glycocholate > taurocholate > taurodeoxycholate > taurochenodeoxycholate > glycodeoxycholate. The results obtained would support the feasibility of utilizing such method for screening any compound incorporated in insulin formulation. These compounds should be used in the minimum possible concentration to avoid or minimize insulin degradation.