Low temperature promotes the production and efflux of terpenoids in yeast

Altering the fermentation environment provides an effective approach to optimizing the production efficiency of microbial cell factories globally. Here, lower fermentation temperatures of yeast were found to significantly improve the synthesis and efflux of terpenoids, including glycyrrhetinic acid (GA), β-caryophyllene, and α-amyrin. The production of GA at 22°C increased by 5.5 times compared to 30°C. Yeast subjected to lower temperature showed substantial changes at various omics levels. Certain genes involved in maintaining cellular homeostasis that were upregulated under the low temperature conditions, leading to enhanced GA production. Substituting Mvd1, a thermo-unstable enzyme in mevalonate pathway identified by transcriptome and proteome, with a thermo-tolerant isoenzyme effectively increased GA production. The lower temperature altered the composition of phospholipids and increased the unsaturation of fatty acid chains, which may influence GA efflux. This study presents a strategy for optimizing the fermentation process and identifying key targets of cell factories for terpenoid production.

Natural Sweetener Glycyrrhetinic Acid Monoglucuronide Improves Glucose Homeostasis in Healthy Mice

Noncaloric or low-caloric sweeteners have become popular worldwide, although debates persist regarding their impact on health. To investigate whether the sweeteners are favorable for glucose homeostasis, our study assessed the effects of glycyrrhetinic acid monoglucuronide (GAMG) and several commonly used sweeteners [glycyrrhetinic acid (GA), stevioside, erythritol, sucralose, and aspartame] on glycometabolism and elucidated the underlying mechanisms. The C57BL/6J male mice were exposed to different sweeteners for 10 weeks, and our results showed that GAMG significantly reduced fasting blood glucose (FBG) levels (FBG-control: 3.81 ± 0.42 mmol/L; FBG-GAMG: 3.37 ± 0.38 mmol/L; p < 0.05) and the blood glucose levels 15 and 30 min after sucrose or maltose loading (p < 0.05). Furthermore, it improved glucose tolerance (p = 0.028) and enhanced insulin sensitivity (p = 0.044), while the other sweeteners had negligible or adverse effects on glucose homeostasis. Subsequent experiments showed that GAMG inhibited α-glucosidases potently (IC50 = 0.879 mg·mL-1), increased three SCFA-producing bacteria and SCFAs levels (p < 0.05), and promoted the gene expression of SCFA receptor GPR43 (p = 0.018). These results suggest that GAMG may regulate blood glucose by inhibiting α-glucosidases and modulating gut microbial SCFAs. Our findings prove that GAMG, beneficial to blood glucose regulation, is a promising natural sweetener for future utilization.

Preventing acute liver injury via hepatocyte-targeting nano-antioxidants

Acute liver injury (ALI) is a severe liver disease that is characterized by sudden and massive hepatocyte necrosis and deterioration of liver functions. Oxidative stress is increasingly recognized as a key factor in the induction and progression of ALI. Scavenging excessive reactive oxygen species (ROS) with antioxidants has become a promising therapeutic option, but intrinsically hepatocyte-targeting antioxidants with excellent bioavailability and biocompatibility are yet to be developed. Herein, self-assembling nanoparticles (NPs) composed of amphiphilic polymers are introduced to encapsulate organic Selenium compound L-Se-methylselenocysteine (SeMC) and form SeMC NPs, which protect the viabilities and functions of cultured hepatocytes in drug- or chemical-induced acute hepatotoxicity models via efficient ROS removal. After further functionalization with the hepatocyte-targeting ligand glycyrrhetinic acid (GA), the resultant GA-SeMC NPs exhibit enhanced hepatocyte uptake and liver accumulation. In mouse models of ALI induced by acetaminophen (APAP) or carbon tetrachloride (CCl4 ), treatment with GA-SeMC NPs significantly decrease the levels of hepatic lipid peroxidation, tissue vacuolization and serum liver transaminases, while prominently increase that of endogenous antioxidant enzymes. Our study therefore presents a liver-targeting drug delivery strategy for the prevention and treatment of hepatic diseases.

[Adverse effects of licorice consumed as food: An update]

The word "licorice" refers to the plant, its root, and its aromatic extract. From a commercial point of view, Glycyrrhiza glabra is the most important species with a wide range of uses (herbal medicine, tobacco industry, cosmetics, food and pharmaceutical). Glycyrrhizin is one of the main constituents of licorice. Glycyrrhizin is hydrolyzed in the intestinal lumen by bacterial β-glucuronidases to 3β-monoglucuronyl-18β-glycyrrhetinic acid (3MGA) and 18β-glycyrrhetinic acid (GA), which are metabolized in the liver. Plasma clearance is slow due to enterohepatic cycling. 3MGA and GA can bind to mineralocorticoid receptors with very low affinity, and 3MGA induces apparent mineralocorticoid excess syndrome through dose-dependent inhibition of 11β-hydroxysteroid dehydrogenase type 2 in renal tissue. The cases of apparent mineralocorticoid excess syndrome reported in the literature are numerous and sometimes severe, even fatal, most often in cases of chronic high dose consumption. Glycyrrhizin poisonings are characterized by hypertension, fluid retention, and hypokalemia with metabolic alkalosis and increased kaliuresis. Toxicity depends on the dose, the type of product consumed, the mode of consumption (acute or chronic) and a very large inter-individual variability. The diagnosis of glycyrrhizin-induced apparent mineralocorticoid excess syndrome is based on the history, clinical examination, and biochemical analysis. Management is primarily based on symptomatic care and stopping licorice consumption.

Glycyrrhetinic acid ameliorates diosbulbin B-induced hepatotoxicity in mice by modulating metabolic activation of diosbulbin B

Exposure to diosbulbin B (DBB), the primary component of the herbal medicine Dioscorea bulbifera L. (DB), can cause liver injury in humans and experimental animals. A previous study found DBB-induced hepatotoxicity was initiated by CYP3A4-mediated metabolic activation and subsequent formation of adducts with cellular proteins. The herbal medicine licorice (Glycyrrhiza glabra L.) is frequently combined with DB used in numerous Chinese medicinal formulas in an effort to protect against DB-elicited hepatotoxicity. Importantly, glycyrrhetinic acid (GA), the major bioactive ingredient in licorice, inhibits CYP3A4 activity. The study aimed to investigate the protection of GA against DBB-induced hepatotoxicity and the underlying mechanism. Biochemical and histopathological analysis showed GA alleviated DBB-induced liver injury in a dose-dependent manner. In vitro metabolism assay with mouse liver microsomes (MLMs) indicated that GA decreased the generation of metabolic activation-derived pyrrole-glutathione (GSH) conjugates from DBB. Toxicokinetic studies demonstrated that GA increased maximal serum concentration (Cmax ) and area under the serum-time curve (AUC) of DBB in mice. In addition, GA attenuated hepatic GSH depletion caused by DBB. Further mechanistic studies showed that GA reduced the production of DBB-derived pyrroline-protein adducts in a dose-dependent manner. In conclusion, our findings demonstrated that GA exerted protective effect against DBB-induced hepatotoxicity, mainly correlated with suppressing the metabolic activation of DBB. Therefore, the development of a standardized combination of DBB with GA may protect patients from DBB-induced hepatotoxicity.

18β-Glycyrrhetinic acid monoglucuronide (GAMG) alleviates single-walled carbon nanotubes (SWCNT)-induced lung inflammation and fibrosis in mice through PI3K/AKT/NF-κB signaling pathway

Carbon nanotubes (CNTs) have become far and wide used in a number of technical and merchant applications as a result of substantial advances in nanotechnology, therein single-walled carbon nanotubes (SWCNT) are one of the most promising nanoparticles. Inhaling CNTs has been linked to a variety of health problems, including lung fibrosis. Glycyrrhetinic acid 3-O-mono-β-D-glucuronide (GAMG), a natural sweetener, has anti-inflammatory and antioxidant capacities. The purpose of this study was to evaluate the potential for GAMG to alleviate SWCNT-induced lung inflammation and fibrosis. During days 3-28 after SWCNT intratracheal administration, we observed a remarkable increase of IL-1β, IL-6 and TNF-α in bronchoalveolar lavage fluid (BALF) on day 3 and collagen deposition on day 28. GAMG treatment remarkably ameliorated SWCNT-induced pulmonary fibrosis and attenuated SWCNT-induced inflammation and collagen deposition, and suppressed the activation of PI3K/AKT/NF-κB signaling pathway in the lungs. Therefore, GAMG has a therapeutic potential for the treatment of SWCNT-induced pulmonary fibrosis. Targeting PI3K/AKT/NF-κB signaling pathway may be a potential therapeutic approach to treat pulmonary fibrosis in mice with SWCNT.

Glycyrrhetinic acid regulates impaired macrophage autophagic flux in the treatment of non-alcoholic fatty liver disease

Macrophages are involved in hepatocyte steatosis and necroinflammation and play an important role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Impaired autophagy function (decreased autophagy or blocked autophagic flow) leads to cell damage and death and promotes NAFLD progression. The experimental and clinical research of glycyrrhetinic acid (GA) in the treatment of NAFLD has gradually attracted attention with clear pharmacological activities such as immune regulation, antiviral, antitumor, antioxidant, liver protection, and anti-inflammatory. However, the effects of GA on the STAT3-HIF-1α pathway and autophagy in macrophages are still unclear, and its mechanism of action in the treatment of NAFLD remains to be further elucidated. We constructed a NAFLD mouse model through a high-fat and high-sugar diet to investigate the therapeutic effects of GA. The results showed that GA reduced weight, improved the pathological changes and hepatic lipid deposition of liver, and abnormally elevated the levels of serum biochemical (AST, ALT, TG, T-CHO, LDL-C, and HDL-C) and inflammatory indexes (IL-1β, IL-4, IL-6, MCP-1, and TNF-α) in NAFLD mice. Further examination revealed that GA ameliorates excessive hepatic macrophage infiltration and hepatocyte apoptosis. The results of the cell experiments further elaborated that GA modulated the PA-induced macrophage STAT3-HIF-1α pathway and ameliorated impaired autophagic flux (blockade of autophagosome–lysosome fusion) and overactivation of inflammation. Excessive hepatocyte apoptosis caused by the uncontrolled release of inflammatory cytokines was also suppressed by GA.

Conclusion

This study demonstrated that GA could regulate the STAT3-HIF-1α pathway of macrophages, ameliorate the impaired autophagy flux, and reduce the excessive production of inflammatory cytokines to improve the excessive apoptosis of liver cells, thus playing a therapeutic role on NAFLD.

Structure-based design of glycyrrhetinic acid derivatives as potent anti-sepsis agents targeting high-mobility group box-1

Novel Glycyrrhetinic Acid (GA) derivatives with fused heterocycles on A ring were structure-based designed and synthesized. Their potential anti-inflammatory effects were investigated by a classical LPS stimulated macrophage model. Surface plasmon resonance (SPR) was used to verify the binding of GA analogues with HMGB1. A preliminary structure-activity relationship was summarized and an analogue GA-60 with ortho-methoxybenzyl pyrozole showed stronger anti-inflammatory effect and higher affinity for HMGB1 with a K_d value of 12.5 μM. In addition, this compound exhibited excellent inhibitory functions on NO (96%), TNF-α (94%), and IL-6 (100%), by interfering with phosphorylation of p38, ERK, JNK MAPKs, as well as that of NF-κB p65 and IKKα/β. Moreover, GA-60 extended the survival of either the classic CLP-induced or LPS-induced sepsis mouse models. Molecular modeling predictions further supported these findings, clearly indicating that inhibiting HMGB1 release, using fused heterocyclic GA derivatives, is a promising strategy for treatment of sepsis.

Enhanced targeted delivery of adenine to hepatocellular carcinoma using glycyrrhetinic acid-functionalized nanoparticles in vivo and in vitro

Hepatocellular carcinoma (HCC), a common malignancy in China and globally, is primarily treated through surgical resection and liver transplantation, with chemotherapy as a significant synergistic option. Adenine (Ade), a nucleobase, exhibits antitumor effects by blocking human hepatic carcinoma cells in S phase and inhibiting tumor cell proliferation. However, its use is limited owing to its low solubility, poor targeting ability, and nephrotoxicity. Therefore, liver-targeting drug delivery systems have attracted considerable attention for the treatment of HCC. In this study, we explored the liver-targeting efficacy and antitumor effect of adenine-loaded glycyrrhetinic acid-modified hyaluronic acid (Ade/GA-HA) nanoparticles in vitro and in vivo. The GA-HA nanoparticles possessed obvious targeting specificity toward liver cancer cells, which was mainly achieved by the specific binding of the GA ligand to the GA receptor that was highly expressed on the liver cell membrane. In vitro and in vivo results showed that Ade/GA-HA nanoparticles could inhibit liver cancer cell proliferation and migration, promote apoptosis, and significantly inhibit the growth of tumor tissues. Altogether, this study is the first to successfully demonstrate that the targeting activity and antitumor effect of Ade against HCC are enhanced by using GA-HA nanoparticles in vitro and in vivo.

Galactosylation of Monosaccharide Derivatives of Glycyrrhetinic Acid by UDP-Glycosyltransferase GmSGT2 from Glycine max

Glycyrrhetinic acid (GA), a pentacyclic triterpenoid aglycone, is the major functional component in licorice which mainly exists in the form of functional glycosides in licorice. The introduction of a sugar moiety to the C-3 OH of GA to yield glycosylated derivatives has been reported, but the late-stage glycosylation of GA-3-O-sugar to form rare GA glycosides with more complexed glycosyl decoration has been rarely reported. In this study, a unique UDP-galactosyltransferase GmSGT2 from Glycine max was found to transfer a galactose to the C2 position of the sugar moiety of GA-3-O-monoglucuronide (GAMG) and GA-3-O-monoglucose. In addition to UDP-galactose, GmSGT2 also recognizes UDP-glucose, UDP-xylose, and UDP-arabinose with relative activities of 32.1-89.2%. Based on a test of 12 typical natural products, GmSGT2 showed high specificity toward the pentacyclic triterpenoid skeleton as the sugar acceptor. Molecular docking was performed to elucidate the substrate recognition mechanism of GmSGT2 toward GAMG.

Glycyrrhetinic acid attenuates disturbed vitamin a metabolism in non-alcoholic fatty liver disease through AKR1B10

Abnormal vitamin A (retinol) metabolism plays an important role in the occurrence of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). In this study, NAFLD and NASH models were established to investigate the effects of food additives glycyrrhizic acid (GL) on retinol metabolism in NAFLD/NASH mice. Potential targets of GL and its active metabolite glycyrrhetinic acid (GA) were analyzed by RNA sequence, bioinformatics, and molecular docking analyses. Gene transfection and enzymatic kinetics were used to identify the target of GL. The results showed that GL could resolve the fatty and inflammatory lesions in the mouse liver, thereby improving the disorder of retinol metabolism. RNA sequence analysis of model mice liver revealed significant changes in AKR1B10 (retinol metabolic enzymes). Bioinformatics and molecular docking analyses showed that AKR1B10 is a potential target of GA but not GL. GA could inhibit AKR1B10 activity, which then affects retinol metabolism, whereas GL only had the same effect after hydrolysis into GA. In AKR1B10-KO hepatocytes, GA, GL, and hydrolysates of GL had no regulatory effect on retinol metabolism. Therefore, GA, the active metabolite of GL, as a novel AKR1B10 inhibitor, could promote retinoic acid synthesis. GL restored the balance of retinol metabolism in NAFLD/NASH mice by metabolizing to GA.

Mining of Sucrose Synthases from Glycyrrhiza uralensis and Their Application in the Construction of an Efficient UDP-Recycling System

Sucrose synthase (SUS) plays an important role in carbohydrate metabolism in plants. The SUS genes in licorice remain unknown. To reveal the sucrose metabolic pathway in licorice, all the 12 putative SUS genes of Glycyrrhiza uralensis were systematically identified by genome mining, and two novel SUSs (GuSUS1 and GuSUS2) were isolated and characterized for the first time. Furthermore, we found that the flexible N-terminus was responsible for the low stability of plant SUSs, and deletion of redundant N-terminus improved the stability of GuSUS1 and GuSUS2. The half-life of both GuSUS1 and GuSUS2 mutants was increased by 2-fold. Finally, the GuSUS1 mutant was coupled with UGT73C11 for the glycosylation of glycyrrhetinic acid (GA) with uridine 5'-diphosphate disodium salt hydrate (UDP) in situ recycling, and GA conversion was increased by 7-fold. Our study not only identified the SUS genes in licorice but also provided a stable SUS mutant for the construction of an efficient UDP-recycling system for GA glycosylation.

Anti-Inflammatory 18β-Glycyrrhetinin Acid Derivatives Produced by Biocatalysis

In this study, the biocatalysis of 18β-glycyrrhetinic acid by two strains of filamentous fungi, namely Rhizopus arrhizus AS 3.2893 and Circinella muscae AS 3.2695, was investigated. Scaled-up biotransformation reactions yielded 14 metabolites. Their structures were established based on extensive nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry data analyses, and seven of them are new compounds. The two fungal strains exhibited distinct biocatalytic features. R. arrhizus could catalyze hydroxylation and carbonylation reactions, whereas C. muscae preferred to catalyze hydroxylation and glycosidation reactions. These highly specific reactions are difficult to achieve by chemical synthesis, particularly under mild conditions. Furthermore, we found that most of the metabolites exhibited pronounced inhibitory activities on lipopolysaccharides-induced nitric oxide production in RAW264.7 cells. These biotransformed derivatives of 18β-glycyrrhetinic acid could be potential anti-inflammatory agents.

Computation-Aided Rational Deletion of C-Terminal Region Improved the Stability, Activity, and Expression Level of GH2 β-Glucuronidase

In this study, computation-aided design on the basis of structural analysis was employed to rationally identify a highly dynamic C-terminal region that regulates the stability, expression level, and activity of a GH2 fungal glucuronidase from Aspergillus oryzae Li-3 (PGUS). Then, four mutants with a precisely truncated C-terminal region in different lengths were constructed; among them, mutant D591-604 with a 3.8-fold increase in half-life at 65 °C and a 6.8 kJ/mol increase in Gibbs free energy showed obviously improved kinetic and thermodynamic stability in comparison to PGUS. Mutants D590-604 and D591-604 both showed approximately 2.4-fold increases in the catalytic efficiency k_cat/ K_m and 1.8-fold increases in the expression level. Additionally, the expression level of PGUS was doubled through a C-terminal region swap with bacterial GUS from E. coli (EGUS). Finally, the robust PGUS mutants D590-604 and D591-604 were applied in the preparation of glycyrrhetinic acid with 4.0- and 4.4-fold increases in concentration through glycyrrhizin hydrolysis by a fed-batch process.

Boosting 11-oxo-β-amyrin and glycyrrhetinic acid synthesis in Saccharomyces cerevisiae via pairing novel oxidation and reduction system from legume plants

Glycyrrhetinic acid (GA) and its precursor, 11-oxo-β-amyrin, are typical triterpenoids found in the roots of licorice, a traditional Chinese medicinal herb that exhibits diverse functions and physiological effects. In this study, we developed a novel and highly efficient pathway for the synthesis of GA and 11-oxo-β-amyrin in Saccharomyces cerevisiae by introducing efficient cytochrome P450s (CYP450s: Uni25647 and CYP72A63) and pairing their reduction systems from legume plants through transcriptome and genome-wide screening and identification. By increasing the copy number of Uni25647 and pairing cytochrome P450 reductases (CPRs) from various plant sources, the titers of 11-oxo-β-amyrin and GA were increased to 108.1 ± 4.6mg/L and 18.9 ± 2.0mg/L, which were nearly 1422-fold and 946.5-fold higher, respectively, compared with previously reported data. To the best of our knowledge, these are the highest titers reported for GA and 11-oxo-β-amyrin from S. cerevisiae, indicating an encouraging and promising approach for obtaining increased GA and its related triterpenoids without destroying the licorice plant or the soil ecosystem.

A novel glucuronosyltransferase has an unprecedented ability to catalyse continuous two-step glucuronosylation of glycyrrhetinic acid to yield glycyrrhizin

Glycyrrhizin is an important bioactive compound that is used clinically to treat chronic hepatitis and is also used as a sweetener world-wide. However, the key UDP-dependent glucuronosyltransferases (UGATs) involved in the biosynthesis of glycyrrhizin remain unknown. To discover unknown UGATs, we fully annotated potential UGATs from Glycyrrhiza uralensis using deep transcriptome sequencing. The catalytic functions of candidate UGATs were determined by an in vitro enzyme assay. Systematically screening 434 potential UGATs, we unexpectedly found one unique GuUGAT that was able to catalyse the glucuronosylation of glycyrrhetinic acid to directly yield glycyrrhizin via continuous two-step glucuronosylation. Expression analysis further confirmed the key role of GuUGAT in the biosynthesis of glycyrrhizin. Site-directed mutagenesis revealed that Gln-352 may be important for the initial step of glucuronosylation, and His-22, Trp-370, Glu-375 and Gln-392 may be important residues for the second step of glucuronosylation. Notably, the ability of GuUGAT to catalyse a continuous two-step glucuronosylation reaction was determined to be unprecedented among known glycosyltransferases of bioactive plant natural products. Our findings increase the understanding of traditional glycosyltransferases and pave the way for the complete biosynthesis of glycyrrhizin.

Aqueous extract from Aconitum carmichaelii Debeaux reduces liver injury in rats via regulation of HMGB1/TLR4/NF-ΚB/caspase-3 and PCNA signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum carmichaelii Debeaux is a well-known Chinese herb that has been used to treat liver diseases for many years in China. We investigated the effects of aqueous extract from Aconitum carmichaelii Debeaux (AEACD) on acute liver failure and identified the possible mechanisms of these effects.

MATERIAL AND METHODS

Specific pathogen-free (SPF) male Wistar rats were used to establish acute liver failure model by intraperitoneal injection of D-galactosamine (D-GalN) and treated with Stronger Neo-Minophagen C (SNMC) and AEACD by gavage. Then, the serum biochemical parameters, the pathological scores in the liver tissue, the mRNA expressions of toll- like receptor 4 (TLR4), nuclear factor kappa B (NF-κB), high mobility group box 1 (HMGB1) and caspase-3, the proliferating cell nuclear antigen (PCNA) positive rates were analyzed.

RESULTS

The liver function was improved, the pathological scores were decreased, the expressions the TLR4, NF-κB, HMGB1, and caspase-3 were inhibited, and the PCNA positive rates were increased by both SNMC and AEACD, but AEACD induced greater effects.

CONCLUSIONS

AEACD protected liver function by inhibiting inflammatory reaction, apoptosis and promoting liver tissue regeneration in the acute liver failure rats induced by D-galactosamine.

One-step Conjugation of Glycyrrhetinic Acid to Cationic Polymers for High-performance Gene Delivery to Cultured Liver Cell

Gene therapies represent a promising therapeutic route for liver cancers, but major challenges remain in the design of safe and efficient gene-targeting delivery systems. For example, cationic polymers show good transfection efficiency as gene carriers, but are hindered by cytotoxicity and non-specific targeting. Here we report a versatile method of one-step conjugation of glycyrrhetinic acid (GA) to reduce cytotoxicity and improve the cultured liver cell -targeting capability of cationic polymers. We have explored a series of cationic polymer derivatives by coupling different ratios of GA to polypropylenimine (PPI) dendrimer. These new gene carriers (GA-PPI dendrimer) were systematically characterized by UV-vis,(1)H NMR titration, electron microscopy, zeta potential, dynamic light-scattering, gel electrophoresis, confocal microscopy and flow cytometry. We demonstrate that GA-PPI dendrimers can efficiently load and protect pDNA, via formation of nanostructured GA-PPI/pDNA polyplexes. With optimal GA substitution degree (6.31%), GA-PPI dendrimers deliver higher liver cell transfection efficiency (43.5% vs 22.3%) and lower cytotoxicity (94.3% vs 62.5%, cell viability) than the commercial bench-mark DNA carrier bPEI (25 kDa) with cultured liver model cells (HepG2). There results suggest that our new GA-PPI dendrimer are a promising candidate gene carrier for targeted liver cancer therapy.

In Vitro and in Vivo Inhibitory Effects of Glycyrrhetinic Acid in Mice and Human Cytochrome P450 3A4

Glycyrrhetinic acid (GA) has been used clinically in the treatment of patients with chronic hepatitis. This study evaluated the effect of GA on the activity of five P450(CYP450) cytochrome enzymes: CYP2A6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, in human liver microsomes (HLMs) and recombinant cDNA-expressed enzyme systems using a HPLC-MS/MS CYP-specific probe substrate assay. With midazolam as the probe substrate, GA greatly decreased CYP3A4 activity with IC50 values of 8.195 μM in HLMs and 7.498 μM in the recombinant cDNA-expressed CYP3A4 enzyme system, respectively. It significantly decreased CYP3A4 activity in a dose- but not time-dependent manner. Results from Lineweaver-Burk plots showed that GA could inhibit CYP3A4 activity competitively, with a Ki value of 1.57 μM in HLMs. Moreover, CYP2C9 and CYP2C19 could also be inhibited significantly by GA with IC50 of 42.89 and 40.26 μM in HLMs, respectively. Other CYP450 isoforms were not markedly affected by GA. The inhibition was also confirmed by an in vivo study of mice. In addition, it was observed that mRNA expressions of the Cyps2c and 3a family decreased significantly in the livers of mice treated with GA. In conclusion, this study indicates that GA may exert herb-drug interactions by competitively inhibiting CYP3A4.

[Microbial transformation of glycyrrhetinic acid by Cunninghamella blakesleeana]

A study on the microbial transformation of glycyrrhetinic acid (GA) was conducted by a fungus, Cunninghamella blakesleeana CGMCC 3.970 systematically. After incubation with the cell cultures of C. blakesleeana CGMCC 3.970 at 25 degrees C for 7 days on a rotary shaker operating at 135 r x min(-1), GA was converted into one major product and five minor products. The products were extracted and purified by solvent extraction, macroporous adsorbent resin, silica gel column chromatography, and semi-preparative RP-HPLC chromatography. Their structures were identified as 3-oxo-15α-hydroxy-18β-glycyrrhetinic acid(1), 3-oxo-15β-hydroxy-18β-glycyrrhetinic acid (2), 7β,15α-dihydroxy-18β-glycyrrhetinic acid (3), 3-oxo-7β, 15α-dihydroxy-18β-glycyrrhetinic acid (4), 7β-hydroxy-18β-glycyrrhetinic acid(5) and 15α-hydroxy-18β-glycyrrhetinic acid(6) by the analyses of MS, 1H-NMR and 13C-NMR spectroscopic data respectively. Among them, 2 was a new compound. These results suggest that C. blakesleeana CGMCC 3.970 has the capability of selective ketonization and hydroxylation for GA. [Key words] glycyrrhetinic acid; Cunninghamella blakesleeana CGMCC 3. 970; microbial transformation

Formulation strategies to modulate the topical delivery of anti-inflammatory compounds

The aim of this study was to assess the ability of some vehicles (emulsion and emulgel), containing hydrogenated lecithin as penetration enhancer, in increasing the percutaneous absorption of the two model compounds dipotassium glycyrrhizinate (DG) and stearyl glycyrrhetinate (SG). Furthermore SG-loaded solid lipid nanoparticles (SLNs) were prepared and the effect of this vehicle on SG permeation profile was evaluated as well. Percutaneous absorption has been studied in vitro, using excised human skin membranes (i.e., stratum corneum epidermis or [SCE]), and in vivo, determining their anti-inflammatory activity. From the results obtained, the use of both penetration enhancers and SLNs resulted in being valid tools to optimize the topical delivery of DG and SG. Soy lecithin guaranteed an increase in the percutaneous absorption of the two activities and a rapid anti-inflammatory effect in in vivo experiments, whereas SLNs produced an interesting delayed and sustained release of SG.

Glycyrrhetic acid synergistically enhances β₂-adrenergic receptor-Gs signaling by changing the location of Gαs in lipid rafts

Glycyrrhetic acid (GA) exerts synergistic anti-asthmatic effects via a β₂-adrenergic receptor (β₂AR)-mediated pathway. Cholesterol is an important component of the structure and function of lipid rafts, which play critical roles in the β₂AR-Gs-adenylate cyclase (AC)-mediated signaling pathway. Owing to the structural similarities between GA and cholesterol, we investigated the possibility that GA enhances β₂AR signaling by altering cholesterol distribution. Azide-terminal GA (ATGA) was synthesized and applied to human embryonic kidney 293 (HEK293) cells expressing fusion β₂AR, and the electron spin resonance (ESR) technique was utilized. GA was determined to be localized predominantly on membrane and decreased their cholesterol contents. Thus, the fluidity of the hydrophobic region increased but not the polar surface of the cell membrane. The conformations of membrane proteins were also changed. GA further changed the localization of Gαs from lipid rafts to non-raft regions, resulting the binding of β₂AR and Gαs, as well as in reduced β₂AR internalization. Co-localization of β₂AR, Gαs, and AC increased isoproterenol-induced cAMP production and cholesterol reloading attenuated this effect. A speculation wherein GA enhances beta-adrenergic activity by increasing the functional linkage between the subcomponents of the membrane β₂AR-protein kinase A (PKA) signaling pathway was proposed. The enhanced efficacy of β₂AR agonists by this novel mechanism could prevent tachyphylaxis.

[The old man and the syrup]

Intoxication by glycyrrhizin is a rare cause of hypokalemia. We describe a patient with severe hypokalemia caused by long-term consumption of syrup containing liquorice. The physiopathological mechanism of the intoxication and the differential diagnosis are presented.

Blockade of gap junction hemichannel suppresses disease progression in mouse models of amyotrophic lateral sclerosis and Alzheimer's disease

Background

Glutamate released by activated microglia induces excitotoxic neuronal death, which likely contributes to non-cell autonomous neuronal death in neurodegenerative diseases, including amyotrophic lateral sclerosis and Alzheimer's disease. Although both blockade of glutamate receptors and inhibition of microglial activation are the therapeutic candidates for these neurodegenerative diseases, glutamate receptor blockers also perturbed physiological and essential glutamate signals, and inhibitors of microglial activation suppressed both neurotoxic/neuroprotective roles of microglia and hardly affected disease progression. We previously demonstrated that activated microglia release a large amount of glutamate specifically through gap junction hemichannel. Hence, blockade of gap junction hemichannel may be potentially beneficial in treatment of neurodegenerative diseases.

Methods and Findings

In this study, we generated a novel blood-brain barrier permeable gap junction hemichannel blocker based on glycyrrhetinic acid. We found that pharmacologic blockade of gap junction hemichannel inhibited excessive glutamate release from activated microglia in vitro and in vivo without producing notable toxicity. Blocking gap junction hemichannel significantly suppressed neuronal loss of the spinal cord and extended survival in transgenic mice carrying human superoxide dismutase 1 with G93A or G37R mutation as an amyotrophic lateral sclerosis mouse model. Moreover, blockade of gap junction hemichannel also significantly improved memory impairments without altering amyloid β deposition in double transgenic mice expressing human amyloid precursor protein with K595N and M596L mutations and presenilin 1 with A264E mutation as an Alzheimer's disease mouse model.

Conclusions

Our results suggest that gap junction hemichannel blockers may represent a new therapeutic strategy to target neurotoxic microglia specifically and prevent microglia-mediated neuronal death in various neurodegenerative diseases.

Intercellular communication amplifies stressful effects in high-charge, high-energy (HZE) particle-irradiated human cells

Understanding the mechanisms that underlay the biological effects of particulate radiations is essential for space exploration and for radiotherapy. Here, we investigated the role of gap junction intercellular communication (GJIC) in modulating harmful effects induced in confluent cultures wherein most cells are traversed by one or more radiation tracks. We focused on the effect of radiation quality (linear energy transfer; LET) on junctional propagation of DNA damage and cell death among the irradiated cells. Confluent normal human fibroblasts were exposed to graded doses of 1 GeV protons (LET ~0.2 keV/μm) or 1 GeV/u iron ions (LET ~151 keV/μm) and were assayed for clonogenic survival and for micronucleus formation, a reflection of DNA damage, shortly after irradiation and following longer incubation periods. Iron ions were ~2.7 fold more effective than protons at killing 90% of the cells in the exposed cultures when assayed within 5–10 minutes after irradiation. When cells were held in the confluent state for several hours after irradiation, substantial repair of potentially lethal damage (PLDR), coupled with a reduction in micronucleus formation, occurred in cells exposed to protons, but not in those exposed to iron ions. In fact, such confluent holding after exposure to a similarly toxic dose of iron ions enhanced the induced toxic effect. However, following iron ion irradiation, inhibition of GJIC by 18-α-glycyrrhetinic acid eliminated the enhanced toxicity and reduced micronucleus formation to levels below those detected in cells assayed shortly after irradiation. The data show that low LET radiation induces strong PLDR within hours, but that high LET radiation with similar immediate toxicity does not induce PLDR and its toxicity increases with time following irradiation. The results also show that GJIC among irradiated cells amplifies stressful effects following exposure to high, but not LET radiation, and that GJIC has only minimal effect on cellular recovery following low LET irradiation.

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.