Modification, Antitumor Activity, and Targeted PPARγ Study of 18β-Glycyrrhetinic Acid, an Important Active Ingredient of Licorice

Licorice is a traditional Chinese medicine, which is often used as sweetener and cosmetic ingredients in food and pharmaceutical industries. Among them, glycyrrhetic acid is one of the most important agents. Studies have shown that glycyrrhetic acid exhibited antitumor activities as PPARγ agonist. However, the limited number of PPARγ glycyrrhetinic agonists and their high toxicity greatly limit the design based on the structure. Therefore, clarifying the binding mode between PPARγ and small molecules, we focused on the introduction of a natural active piperazine skeleton in the position of glycyrrhetinic acid C-3. According to the Combination Principle and the Structure-Based Drug Design, 19 glycyrrhetic acid derivatives were designed and synthesized as potential PPARγ agonists. Compounds 4c and 4q were screened as high-efficiency and low-toxicity lead compounds.

Synthesis and Antiproliferative Activity of Novel A-Ring Cleaved Glycyrrhetinic Acid Derivatives

A series of new glycyrrhetinic acid derivatives was synthesized via the opening of its ring A along with the coupling of an amino acid. The antiproliferative activity of the derivatives was evaluated against a panel of nine human cancer cell lines. Compound 17 was the most active compound, with an IC50 of 6.1 µM on Jurkat cells, which is 17-fold more potent than that of glycyrrhetinic acid, and was up to 10 times more selective toward that cancer cell line. Further biological investigation in Jurkat cells showed that the antiproliferative activity of compound 17 was due to cell cycle arrest at the S phase and induction of apoptosis.

Novel findings of 18β-glycyrrhetinic acid on sRAGE secretion through inhibition of transient receptor potential canonical channels in high-glucose environment

Enhancing soluble receptor for advanced glycation endproducts (sRAGE) is considered as a potent strategy for diabetes therapy. sRAGE secretion is regulated by calcium and transient receptor potential canonical (TRPC) channels. However, the role of TRPC channels in diabetes remains unknown. 18β-Glycyrrhetinic acid (18β-GA), produced from liquorice, has shown antidiabetic properties. This study was aimed to investigate the effect of 18β-GA on sRAGE secretion via TRPC channels in high glucose (HG)-induced THP-1 cells. HG treatment enhanced TRPC3 and TRPC6 expression and consequently caused reactive oxygen species (ROS) accumulation mediated through p47 nicotinamide-adenine dinucleotide phosphate oxidase and inducible nitric oxide synthase (iNOS) associated with uncoupling protein 2 (UCP2) decline and lower sRAGE secretion. Interestingly, 18β-GA showed the dramatic effects similar to Pyr3 or 2-aminoethyl diphenyl borinate inhibitors and effectively reversed HG-elicited mechanisms including that blocking TRPC3 and TRPC6 protein expressions, suppressing intracellular [Ca2+] concentration, decreasing expressions of ROS, p47s, and iNOS, but increasing UCP2 level and promoting sRAGE secretion. Therefore, 18β-GA provides a potential implication to diabetes mellitus and its complications.

Glycyrrhetinic Acid Improves Insulin-Response Pathway by Regulating the Balance between the Ras/MAPK and PI3K/Akt Pathways

Glycyrrhetinic acid (GA), a bioactive component in the human diet, has been reported to improve hyperglycemia, dyslipidemia, insulin resistance and obesity in rats with metabolic syndrome. However, GA-specific target proteins and the mechanisms involved in the downstream signaling and cross-talk to improve insulin sensitivity have not been fully elucidated. In this study, the potential targets of GA were identified by chemical proteomics strategies using serial GA probes for target fishing and cell molecular imaging. Intracellular enzyme activity evaluation and insulin resistance models were used for validating the function of the target proteins on the downstream insulin signaling pathways. Collectively, our data demonstrate that GA improved the insulin-responsive pathway and glucose consumption levels via multiple diabetogenic factors that activated the insulin signaling pathway in HepG2 cells. GA improved Glucose transporter 4(GLUT4) expression by targeting the Ras protein to regulate the mitogen-activated protein kinase (MAPK) pathway. GA exhibited a strong inhibitory effect on IRS1ser307 phosphorylation in cells treated with the Protein kinase C (PKC) activator Phorbol 12-myristate 13-acetate (PMA.) Consistently, IRS1ser307 phosphorylation was also inhibited by GA in Free fatty acid (FFA)-treated HepG2 cells. GA also inhibited the PMA-induced phosphorylation of IκB kinase α/β (IKKα/β), c-Jun N-terminal kinase (JNK) and p38 proteins (P38), suggesting that IKKα/β, JNK and P38 activation is dependent on PKC activity.

Isoliquiritigenin exerts antioxidant activity in Caenorhabditis elegans via insulin-like signaling pathway and SKN-1

BACKGROUND

Glycyrrhiza uralensis is a well-known medicinal plant. Different therapeutic effects have been reported for its secondary metabolites, including neuroprotective activity. Antioxidant properties have also been documented for some of its compounds and it could be a possible mechanism of neuroprotection.

PURPOSE

The present study was conducted to investigate the antioxidant effect and underlying pathways of G. uralensis and its main compounds.

METHODS

The experiments were conducted with Caenorhabditis elegans, a simple in vivo model, widely used in this context. The methanol extract of G. uralensis and its main compounds isoliquiritigenin, liquiritigenin, glycyrrhizic acid, and glycyrrhetinic acid were tested for their effects on heat shock protein expression under mild oxidative stress and survival rate under lethal oxidative stress. To clarify the underlying pathways, the effect on the transcription factors DAF-16, SKN-1, and HSF-1 was tested.

RESULTS

Isoliquiritigenin was the most potent compound in both assays, leading to a 31% decrease in expression of the stress marker heat shock protein and an 87% increase in survival rate. It significantly activated DAF-16 and SKN-1, but not HSF-1.

CONCLUSION

The present study identified isoliquiritigenin as the most active antioxidant compound in G. uralensis. It exerts its effect by activating the transcription factors DAF-16/FOXO and SKN-1/Nrf2 which regulate many genes, including those which code for proteins of antioxidative response. This implicates isoliquiritigenin as a possible supplement drug against oxidative stress especially in neurodegenerative diseases.

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.

Harnessing the gatekeepers of glucocorticoids for chemoprevention of non-melanoma skin cancer

Despite effective surgical methods for non-melanoma skin cancer (NMSC), patients suffer from tissue damage, scarring, or even disfigurement; thus, there is a need for chemopreventive approaches. Because of the complex interplay between glucocorticoids (GCs), inflammation, and cancer, we sought to determine the role of 11β-hydroxysteroid dehydrogenase 1 and 2 (11βHSD1 and 2) in regulating GCs during skin cancer development and progression. 11βHSDs modulate the activation of GCs in a tissue-specific manner and have been reported to play a role in development and progression of other types of cancer, but their role has not yet been reported in NMSC. Here, we found a significant upregulation of 11βHSD2 protein in skin cancer cells when compared to normal skin cells, suggesting a role for this enzyme in the multifactorial process of skin cancer development. In addition, inhibition of 11βHSD2 with siRNA resulted in significant reduction in colony formation in vitro. Finally, our in vivo study elucidated that inhibition of 11βHSD2 with pharmacological inhibitor, Glycyrrhetinic acid (GA) could significantly diminish tumorigenesis in a well-studied in vivo mouse model of NMSC. Overall, these studies highlight for the first time a potential novel role for 11βHSD2 in NMSC development and may allow for new GC treatment approaches capable of avoiding deactivation by the enzyme. If 11βHSD2 can be inhibited as we have done here, or circumvented using modified GCs, this may lead to more efficacious outcomes for NMSC patients by preventing deactivation of the GC and minimizing resistance.

Efflux excretion of bisdemethoxycurcumin-O-glucuronide in UGT1A1-overexpressing HeLa cells: Identification of breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins 1 (MRP1) as the glucuronide transporters

Bisdemethoxycurcumin (BDMC) was a natural curcuminoid with many bioactivities present in turmeric (Curcuma longa L.). However, the disposition mechanisms of BDMC via uridine 5'-diphospho-glucuronosyltransferase (UGT) metabolism still remain unclear. Therefore, we aimed to determine the potential efflux transporters for the excretion of BDMC-O-glucuronide. Herein, chemical inhibition assays (Ko143, MK571, dipyridamole, and leukotriene C4) and biological inhibition experiments including stable knocked-down of breast cancer resistance protein (BCRP), multidrug resistance-associated proteins (MRPs) transporters were both performed in a HeLa cell line stably overexpressing UGT1A1 established previously. The results indicated that Ko143 (5 and 20 μM) caused a marked reduction in excretion rate (18.4-55.6%) and elevation of intracellular BDMC-O-glucuronide (28.8-48.1%), whereas MK-571 (5 and 20 μM) resulted in a significant decrease in excretion rate (6.2-61.6%) and increase of intracellular BDMC-O-glucuronide (maximal 27.1-32.6%). Furthermore, shRNA-mediated silencing of BCRP transporter led to a marked reduction in the excretion rate (21.1-36.9%) and an obvious elevation of intracellular glucuronide (24.9%). Similar results were observed when MRP1 was partially silenced. In addition, MRP3 and MRP4 silencing both displayed no obvious changes on the excretion rate and intracellular levels of glucuronide. In conclusion, chemical inhibition and gene silencing results both indicated that generated BDMC-O-glucoside were excreted primarily by the BCRP and MRP1 transporters. © 2018 BioFactors, 44(6):558-569, 2018.

[Study on Autophagy and Apoptosis Induced by Amiodarone Combined with Glycyrrhetinic Acid in HepG2 Cells]

OBJECTIVE

To investigate the effects of amiodarone combined with glycyrrhetinic acid on the activity, apoptosis and autophagy in human hepatoma HepG2 cells.

METHODS

After using amiodarone and glycyrrhetinic acid alone or in combination treatment for HepG2 cells, MTT assay was used to detect cell proliferation, Annexin Ⅴ/PI flow cytometry was used to detect apoptosis; Western blot was used to detect the expression of autophagy-related proteins Beclin-1, LC3 and p62. The formation of EGFP-LC3 green fluorescent aggregates was observed under a fluorescence microscope. The effects of autophagy on cell proliferation and apoptosis were studied by autophagy inhibitor hydroxychloroquine (HCQ) and autophagy promoter Rapamycin.

RESULTS

The cell viability in combination group was lower than that in single drug group, and the apoptosis rate was higher than that in single drug group. Compared with single-drug group, the expressions of Beclin-1 and LC3Ⅱ protein in the combination group were higher than that in the single-drug group, while the expression of p62 protein was lower in the single-drug group. Fluorescence microscopy results showed that the number of EGFP-LC3 fluorescent aggregates in the combination group were more than that in the single-drug. Using amiodarone and glycyrrhetinic acid treated HepG2 cells, inhibition of auotophagy could decrease cell viability, increase apoptosis rate of cells; promoting autophagy would decrease the apoptosis rate and increase cells viability.

CONCLUSION

By increasing apoptosis of hepatocellular carcinoma HepG2 cells and autophagy level, and decreasing the cell activity, amiodarone combining with glycyrrhetinic acid treatment inducing autophagy a protective mechanism for cells.

Controlled release of 18-β-glycyrrhetic acid by nanodelivery systems increases cytotoxicity on oral carcinoma cell line

The topical treatment for oral mucosal diseases is often based on products optimized for dermatologic applications; consequently, a lower therapeutic effect may be present. 18-β-glycyrrhetic acid (GA) is extracted from Glycirrhiza glabra. The first aim of this study was to test the cytotoxicity of GA on PE/CA-PJ15 cells. The second aim was to propose and test two different delivery systems, i.e. nanoparticles and fibers, to guarantee a controlled release of GA in vitro. We used chitosan and poly(lactic-co-glycolic) acid based nanoparticles and polylactic acid fibers. We tested both delivery systems in vitro on PE/CA-PJ15 cells and on normal human gingival fibroblasts (HGFs). The morphology of GA-loaded nanoparticles (GA-NPs) and fibers (GA-FBs) was investigated by electron microscopy and dynamic light scattering; GA release kinetics was studied spectrophotometrically. MTT test was used to assess GA cytotoxicity on both cancer and normal cells. Cells were exposed to different concentrations of GA (20-500 μmol l^-1) administered as free GA (GA-f), and to GA-NPs or GA-FBs. ROS production was evaluated using dichlorodihydrofluorescein as a fluorescent probe. Regarding the cytotoxic effect of GA on PE/CA-PJ15 cells, the lowest TC₅₀ value was 200 μmol l^-1 when GA was added as GA-NPs. No cytotoxic effects were observed when GA was administered to HGFs. N-acetyl Cysteine reduced mortality induced by GA-f in PE/CA-PJ15 cells. The specific effect of GA on PE/CA-PJ15 cells is mainly due to the different sensitivity of cancer cells to ROS over-production; GA-NPs and GA-FBs formulations increase, in vitro, this toxic effect on oral cancer cells.

18β-Glycyrrhetinic acid mitigates radiation-induced skin damage via NADPH oxidase/ROS/p38MAPK and NF-κB pathways

Radiation-induced inflammation plays an important role in radiation-induced tissue injury. 18β-glycyrrhetinic acid (18β-GA) has shown an anti-inflammatory activity. This study aimed to assess the activity of 18β-GA against radiation-induced skin damage, and explore the underlying mechanisms. In vitro assay revealed 18β-GA treatment decreased the production of IL-1β, IL-6, PGE2 and decreased p38MAPK phosphorylation, DNA-binding activity of AP-1, and NF-κB activation in irradiated RAW264.7 macrophages. Additionally, 18β-GA suppressed NF-κB activation by inhibiting NF-κB/p65 and IκB-α phosphorylation and alleviated ROS overproduction in irradiated RAW264.7 macrophages. In vivo assay showed 18β-GA alleviated severity of radiation-induced skin damage, reduced inflammatory cell infiltration and TNF-α, IL-1β and IL-6 levels in cutaneous tissues. Our findings demonstrate that 18β-GA exhibits anti-inflammatory actions against radiation-induced skin damage probably by inhibiting NADPH oxidase activity, ROS production, activation of p38MAPK and NF-κB signaling, and the DNA binding activities of NF-κB and AP-1, consequently suppressing pro-inflammatory cytokine production.

[Glycyrrhetinic acid selectively inhibits proliferation of hepatocellular carcinoma cells in vitro]

OBJECTIVE

To investigate the selective inhibitory effect of glycyrrhetinic acid on 4 hepatocellular carcinoma (HCC) cells with different proliferation rates and explore the underlying mechanisms.

METHODS

MTT method was used to detect the proliferation rates of 4 HCC cell lines, namely SMMC-7721, SK-HEP1, HEPG2 and HEP3B. Following treatment of the cells with glycyrrhetinic acid (5, 10, 20, 30, 40, and 60 µmol/L), the cell viability was analyzed using MTT assay and the expressions of total ERK protein, p-ERK protein and topoisomerase IIα were detected using Western blotting.

RESULTS

Among the 4 cell lines, SMMC-7721 had the lowest and SK-HEP1 had the highest proliferation rate. Treatment with glycyrrhetinic acid for 48 h dose-dependently inhibited the proliferation of all the 4 cell lines in vitro and produced the strongest inhibitory effect in SMMC-7721 cells with the IC₅₀ of 28.04 µmol/L. The proliferation rate of the cells was positively correlated with the expression levels of p-ERK and topoisomerase IIα, which were the lowest in SMMC-7721 cells and the highest in SK-HEP1 cells. Treatment with 50 µmol/L glycyrrhetinic acid significantly down-regulated the expressions of p-ERK and topoisomerase IIα in the 4 HCC cell lines (P<0.05), while 25 µmol/L glycyrrhetinic acid significantly reduced the expression of topoisomerase IIα and p-ERK in SMMC-7721, HEPG2 and HEP3B cells (P<0.05) but not in SK-HEP1 cells.

CONCLUSION

Glycyrrhetinic acid can inhibit the proliferation of different HCC cells particularly in cells with a low proliferation rate. The inhibitory effect of glycyrrhetinic acid might be mediated by reducing the expressions of topoisomerase IIα and inhibiting the ERK pathway.

[18β-glycyrrhetinic acid piperazine derivative A30 inhibits the proliferation of SMMC-7721 hepatoma cells]

Objective To investigate the mechanism of 18β-glycyrrhetinic acid (GA) piperazine derivative A30 on the antiproliferation of hepatocellular carcinoma SMMC-7721 cells in vitro. Methods The experiment included three groups: control group, 18β-GA group and A30 group. The proliferation activity was detected by MTT assay. Cell apoptosis and the change in the cycle of SMMC-7721 cells were evaluated by flow cytometry. Western blotting was used to observe the expressions of Bcl2 and caspase-8. Results The proliferation of SMMC-7721 cells was inhibited by A30 at the concentration of 2-128 μg/mL in a dose-dependent manner. 18β-GA and A30 could induce the apoptosis of SMMC-7721 cells, and the apoptosis rate of A30 group was significantly higher than that of the 18β-GA group. In the cell cycle analysis, the G2/M phase cells of 18β-GA and A30 groups increased remarkably as compared with the control group. A30 and 18β-GA could significantly enhance the expression of caspase-8, and decreased the expression of Bcl2. Conclusion The 18β-GA piperazine derivative A30 can inhibit the proliferation of SMMC-7721 cells in vitro, and the inhibitory effect is stronger than that of 18β-GA. The mechanism may be related to the inhibition of intracellular Bcl2 protein expression and the enhancement of caspase-8 expression.

Plasma metabolomics study of the hepatoprotective effect of glycyrrhetinic acid on realgar-induced sub-chronic hepatotoxicity in mice via 1H NMR analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Realgar, a type of mineral drug that contains arsenic, is concurrently used with Glycyrrhizae Radx et Rhizoma to reduce its toxicity in many Chinese herbal formulations. Glycyrrhetinic acid (GA) is the bioactive ingredient in Glycyrrhizae Radx et Rhizoma. In this study, the protective effects of GA on realgar-induced hepatotoxicity was investigated using ¹H nuclear magnetic resonance (¹H NMR)-based metabolomic approaches.

MATERIALS AND METHODS

Mice were divided into control, GA, realgar, and GA and realgar co-administration groups. Their plasma samples were used for a metabolomics study.

RESULTS

GA can protect the mice against realgar-induced hepatotoxicity to some extent by relieving alterations in the clinical biochemical parameters and the damage to hepatocytes. Metabolic profiling via principal components analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) indicated that the metabolic perturbation caused by realgar was reduced by GA. Six metabolites, including 3-hydroxybutyrate (3-HB), very low density/low density lipoprotein (VLDL/LDL), N-acetylglycoprotein (NAc), lactate, choline and D-glucose, were considered as potential biomarkers that are involved in the toxicity reduction effect of GA on realgar-induced hepatotoxicity. The correlation analysis showed that these potential biomarkers were all positively correlated with ALT and AST activities (correlation coefficient > 0.5). Lipid and energy metabolism pathways were found to be primarily associated with the hepatoprotective effect of GA.

CONCLUSIONS

GA has an effective protection function by regulating the lipid and energy metabolism to liver injuries that are induced by realgar.

Glycyrrhizin and glycyrrhetinic acid inhibits alpha-naphthyl isothiocyanate-induced liver injury and bile acid cycle disruption

Alpha-naphthyl isothiocyanate (ANIT) is a common hepatotoxicant experimentally used to reproduce the pathologies of drug-induced liver injury in humans, but the mechanism of its toxicity remains unclear. To determine the metabolic alterations following ANIT exposure, metabolomic analyses was performed by use of liquid chromatography-mass spectrometry. Partial least squares discriminant analysis (PLS-DA) of liver, serum, bile, ileum, and cecum of vehicle- and ANIT-treated mice revealed significant alterations of individual bile acids, including increased tauroursodeoxycholic acid, taurohydrodeoxycholic acid, taurochenodeoxycholic acid, and taurodeoxycholic acid, and decreased ω-, β- and tauro-α/β- murideoxycholic acid, cholic acid, and taurocholic acid in the ANIT-treated groups. In accordance with these changes, ANIT treatment altered the expression of mRNAs encoded by genes responsible for the metabolism and transport of bile acids and cholesterol. Pre-treatment of glycyrrhizin (GL) and glycyrrhetinic acid (GA) prevented ANIT-induced liver damage and reversed the alteration of bile acid metabolites and Cyp7a1, Npc1l1, Mttp, and Acat2 mRNAs encoding bile acid transport and metabolism proteins. These results suggested that GL/GA could prevent drug-induced liver injury and ensuing disruption of bile acid metabolism in humans.

Cellular uptake mechanism and clearance kinetics of fluorescence-labeled glycyrrhetinic acid and glycyrrhetinic acid-modified liposome in hepatocellular carcinoma cells

Glycyrrhetinic acid (GA) is a natural pentacyclic triterpene derivative that exerts significant effects in the suppression of liver cancer. The receptors of GA on liver cells and hepatocellular carcinoma (HCC) cells have drawn broad attention. The effects of GA might depend on its transport into and out of cells. However, the question has not been previously addressed despite its obvious and fundamental importance. In this paper, GA and GA-modified liposome (GA-Lip) were labeled with fluorescein isothiocyanate (FITC) or coumarin 6 (Cou6) using chemical or pharmaceutical techniques. The transport courses of FITC-GA and GA-Cou6-Lip were studied in HepG2 cells in vitro. We found that the fluorescence labeled GA and GA-Lip uptake and clearance were time-dependent. FITC-GA uptake involved passive diffusion and active transport, and the receptors were in the cytomembrane proteins. GA-Cou6-Lip uptake was mediated by caveolae-dependent endocytosis. In addition, FITC-GA and GA-Cou6-Lip clearance of the HCC cells fitted exponential decay and second-order processes, respectively. These findings provide new insights into the anti-HCC actions of GA.

An Overview of Structurally Modified Glycyrrhetinic Acid Derivatives as Antitumor Agents

Glycyrrhetinic Acid (GA), a triterpenoid aglycone component of the natural product glycyrrhizinic acid, was found to possess remarkable anti-proliferative and apoptosis-inducing activity in various cancer cell lines. Though GA was not as active as other triterpenes, such as betulinic acid and oleanolic acid, it could trigger apoptosis in tumor cells and it can be obtained easily and cheaply, which has stimulated scientific interest in using GA as a scaffold to synthesize new antitumor agents. The structural modifications of GA reported in recent decades can be divided into four groups, which include structural modifications on ring-A, ring-C, ring-E and multiple ring modifications. The lack of a comprehensive and recent review on this topic prompted us to gather more new information. This overview is dedicated to summarizing and updating the structural modification of GA to improve its antitumor activity published between 2005 and 2016. We reviewed a total of 210 GA derivatives that we encountered and compiled the most active GA derivatives along with their activity profile in different series. Furthermore, the structure activity relationships of these derivatives are briefly discussed. The included information is expected to be of benefit to further studies of structural modifications of GA to enhance its antitumor activity.

Evidence of involvement of neurone-glia/neurone-neurone communications via gap junctions in synchronised activity of KNDy neurones

Pulsatile secretion of gonadotrophin-releasing hormone (GnRH)/luteinising hormone is indispensable for the onset of puberty and reproductive activities at adulthood in mammalian species. A cohort of neurones expressing three neuropeptides, namely kisspeptin, encoded by the Kiss1 gene, neurokinin B (NKB) and dynorphin A, localised in the hypothalamic arcuate nucleus (ARC), so-called KNDy neurones, comprises a putative intrinsic source of the GnRH pulse generator. Synchronous activity among KNDy neurones is considered to be required for pulsatile GnRH secretion. It has been reported that gap junctions play a key role in synchronising electrical activity in the central nervous system. Thus, we hypothesised that gap junctions are involved in the synchronised activities of KNDy neurones, which is induced by NKB-NK3R signalling. We determined the role of NKB-NK3R signalling in Ca²⁺ oscillation (an indicator of neuronal activities) of KNDy neurones and its synchronisation mechanism among KNDy neurones. Senktide, a selective agonist for NK3R, increased the frequency of Ca²⁺ oscillations in cultured Kiss1-GFP cells collected from the mediobasal hypothalamus of the foetal Kiss1-green fluorescent protein (GFP) mice. The senktide-induced Ca²⁺ oscillations were synchronised in the Kiss1-GFP and neighbouring glial cells. Confocal microscopy analysis of these cells, which have shown synchronised Ca²⁺ oscillations, revealed close contacts between Kiss1-GFP cells, as well as between Kiss1-GFP cells and glial cells. Dye coupling experiments suggest cell-to-cell communication through gap junctions between Kiss1-GFP cells and neighbouring glial cells. Connexin-26 and -37 mRNA were found in isolated ARC Kiss1 cells taken from adult female Kiss1-GFP transgenic mice. Furthermore, 18β-glycyrrhetinic acids and mefloquine, which are gap junction inhibitors, attenuated senktide-induced Ca²⁺ oscillations in Kiss1-GFP cells. Taken together, these results suggest that NKB-NK3R signalling enhances synchronised activities among neighbouring KNDy neurones, and that both neurone-neurone and neurone-glia communications via gap junctions possibly contribute to synchronised activities among KNDy neurones.

18β-Glycyrrhetinic acid, the major bioactive component of Glycyrrhizae Radix, attenuates airway inflammation by modulating Th2 cytokines, GATA-3, STAT6, and Foxp3 transcription factors in an asthmatic mouse model

18β-Glycyrrhetinic acid (18Gly), the major bioactive component of Glycyrrhizae Radix, possesses anti-ulcerative, anti-inflammatory, and other pharmacological properties. Although 18Gly is associated with immunoregulatory functions of allergic diseases, the pathophysiological mechanisms of 18Gly action in allergic inflammatory lung disease have not been examined. Moreover, there are no in vivo studies on the anti-asthmatic effects of 18Gly in allergic asthma. We investigated its effect and mechanism of action in airway inflammation in a BALB/c mouse model of allergic asthma. Interestingly, 18Gly strongly suppressed airway hyperresponsiveness, accumulation of inflammatory cells, and levels of T helper type 2 (Th2) cytokines (interleukin (IL)-5 and IL-13) in bronchoalveolar lavage fluid (BALF). It also attenuated lung IL-5, IL-13, and IL-4 expression, but it upregulated peroxisome proliferator-activated receptor gamma (PPARγ) mRNA expression in lungs. Moreover, it exerted immunomodulatory effects by suppressing Th2 cytokines (IL-5, IL-13) production through upregulation of forkhead box p3 (Foxp3), and downregulation of signal transducer and activator of transcription (STAT6), GATA-binding protein 3 (GATA-3), and retinoic acid-related orphan receptor γ t (RORγt) expression. These results suggest that the anti-asthmatic activity of 18Gly may occur by the suppression of IL-5, IL-13, and OVA-specific Immunoglobulin E (IgE) production through inhibition of the RORγt, STAT6, GATA-3 pathways and upregulation of the Foxp3 transcription pathway. Also, 18Gly treatment was protective against the oxidative stress by inducing significant decrease of reactive oxygen species (ROS) generation in MH-S alveolar macrophage cells. Our results suggest that 18Gly can improve allergic asthma and can be a novel therapeutic component for the treatment of allergic asthma.

Anti-inflammatory and hepatoprotective effects of glycyrrhetinic acid on CCl4-induced damage in precision-cut liver slices from Jian carp (Cyprinus carpio var. jian) through inhibition of the nf-kƁ pathway

In order to evaluate the antioxidant and anti-inflammatory effects of glycyrrhetinic acid (GA) on carbon tetrachloride (CCl₄)-induced damage in precision-cut liver slices (PCLS) from Jian carp (Cyprinus carpio. Jian), an acute liver damage model was established in this study. The viability of PCLS, levels of anti-oxidases in liver homogenates, expression of inflammation-related genes including nuclear factor-κB (nf-κB)/c-rel, inducible nitric oxide synthase (inos), interleukin-1β (il-1β), interleukin-6 (il-6) and interleukin-8 (il-8), and protein levels of (nf-κB)/c-rel in liver tissues were measured. The results showed that pretreatment of PCLS with GA at 5 and 10 μg/mL for 6 h significantly inhibited the cytotoxicity of CCl₄. GA attenuated CCl₄-induced oxidative stress in PCLS through promoting the recovery of superoxide dismutase (SOD) and glutathione (GSH) levels, and inhibiting malondialdehyde (MDA) synthesis. In inflammatory response, GA at both 5 and 10 μg/mL significantly inhibited the increase in mRNA levels of inflammatory cytokines including nf-kƁ/c-rel, inos, il-1β, il-6 and il-8, and the protein level of Nf-kƁ/C-rel induced by CCl₄. Furthermore, treatment with pyrrolyl dithiocarbamate (PDTC, 4 μg/mL), an inhibitor of nuclear transcription factor nf-kB, significantly inhibited nf-kB levels, and transcription of downstream cytokines inos, il-1β, il-6 and il-8, also the viability of PCLS was significantly increased. These results indicated that GA suppressed inflammation and reduced cytotoxicity by inhibiting the nf-kƁ signaling pathway, and plays a role in liver protection.

Methotrexate hepatotoxicity is associated with oxidative stress, and down-regulation of PPARγ and Nrf2: Protective effect of 18β-Glycyrrhetinic acid

18β-glycyrrhetinic acid (18β-GA) is a bioactive component of licorice with promising hepatoprotective activity. However, its protective mechanism on methotrexate (MTX) hepatotoxicity in not well defined. We investigated the hepatoprotective effect of 18β-GA, pointing to the role of peroxisome proliferator activated receptor gamma (PPARγ) and the redox-sensitive nuclear factor erythroid 2-related factor 2 (Nrf2). Wistar rats were orally administered 18β-GA (50 and 100 mg/kg) 7 days either before or after MTX injection. MTX induced significant increase in circulating liver function marker enzymes and bilirubin with concomitant declined albumin levels. Serum pro-inflammatory cytokines, and liver malondialdehyde and nitric oxide were significantly increased in MTX-induced rats. Treatment with 18β-GA significantly reduced serum enzymes of liver function, bilirubin and pro-inflammatory cytokines. 18β-GA attenuated MTX-induced oxidative stress and restored the antioxidant defenses. In addition, 18β-GA improved liver histological structure and decreased the expression of Bax whereas increased Bcl-2 expression. MTX-induced rats showed significant down-regulation of Nrf2, hemoxygenase-1 and PPARγ, an effect that was markedly reversed by 18β-GA supplemented either before or after MTX. In conclusion, 18β-GA protected against MTX-induced liver injury, possibly by activating Nrf2 and PPARγ, and subsequent attenuation of inflammation, oxidative stress and apoptosis. Therefore, 18β-GA can provide protection against MTX-induced hepatotoxicity.

Glycyrrhetinic acid suppressed hmgb1 release by up-regulation of Sirt6 in nasal inflammation

To extend our understanding of previous studies on the pathogenesis and mechanism of high mobility group box 1 (HMGB1) in chronic rhinosinusitis with nasal polyps (CRSwNP), here we show that Sirtuin 6 (Sirt6), one of the Sirtuin family members which are widely studied in aging, DNA repair, metabolism, inflammation and cancer, was expressed in normal nasal mucosa using immunohistochemical staining and Western blot assay. Sirt6 expression levels were decreased in CRSwNP tissue. Sirt6 expression levels were modulated by small interfering RNA transfection in human nasal epithelial cells (HNE). We found that depletion of Sirt6 suppressed the number of human nasal epithelial cell cilia, and dramatically induced HMGB1 translocation from nucleus to cytoplasm in the HNE cells. Glycyrrhizic acid (GA) and glycyrrhetinic acid (GTA) are specific chemical compounds that may be isolated from the licorice plant. GTA has been shown to have anti-inflammatory and anti-allergic activity: it binds selectively to HMGB1 protein released extra-cellularly and inhibits its cytokine activities through a scavenger mechanism on the protein accumulation. In an in vitro study we used the 18-β-stereoisomer of GTA to enhance Sirt6 expression levels, inhibiting through this mechanism the translocation of HMGB1 protein from nucleus and reversing its extracellular accumulation stimulated by lipopolysaccharides. These findings reveal a previously unknown role for nasal mucosa steady-state conditions in the control of Sirt6 activity, and provide evidence for a relationship between HMGB1 and Sirt6 in CRSwNP, and promising benefits of glycyrrhetinic acid for CRSwNP patients.

Connexin43high prostate cancer cells induce endothelial connexin43 up-regulation through the activation of intercellular ERK1/2-dependent signaling axis

Connexin(Cx)43 regulates the invasive potential of prostate cancer cells and participates in their extravasation. To address the role of endothelial Cx43 in this process, we analyzed Cx43 regulation in human umbilical vein endothelial cells in the proximity of Cx43^high (DU-145 and MAT-LyLu) and Cx43^low prostate cancer cells (PC-3 and AT-2). Endothelial Cx43 up-regulation was observed during the diapedesis of DU-145 and MAT-LyLu cells. This process was attenuated by transient Cx43 silencing in cancer cells and by chemical inhibition of ERK1/2-dependent signaling in endothelial cells. Cx43 expression in endothelial cells was insensitive to the inhibition of gap junctional intercellular coupling between Cx43^high prostate cancer and endothelial cells by 18α-glycyrrhetinic acid. Instead, endothelial Cx43 up-regulation was correlated with the local contraction of endothelial cells and with their activation in the proximity of Cx43^high DU-145 and MAT-LyLu cells. It was also sensitive to pro-inflammatory factors secreted by peripheral blood monocytes, such as TNFα. In contrast to Cx43^low AT-2 cells, Cx43^low PC-3 cells produced angioactive factors that locally activated the endothelial cells in the absence of endothelial Cx43 up-regulation. Collectively, these data show that Cx43^low and Cx43^high prostate cancer cells can adapt discrete, Cx43-independent and Cx43-dependent strategies of diapedesis. Our observations identify a novel strategy of prostate cancer cell diapedesis, which depends on the activation of intercellular Cx43/ERK1/2/Cx43 signaling axis at the interfaces between Cx43^high prostate cancer and endothelial cells.

Blockage of androgen and administration of estrogen induce transdifferentiation of testis into ovary

Induction of sex reversal of XY fish has been restricted to the sex undifferentiated period. In the present study, differentiated XY tilapia were treated with trilostane (TR), metopirone (MN) and glycyrrhetinic acid (GA) (inhibitor of 3β-HSD, Cyp11b2 and 11β-HSD, respectively) alone or in combination with 17β-estradiol (E2) from 30 to 90 dah (days after hatching). At 180 dah, E2 alone resulted in 8.3%, and TR, MN and GA alone resulted in no secondary sex reversal (SSR), whereas TR + E2, MN + E2 and GA + E2 resulted in 88.3, 60.0 and 46.7% of SSR, respectively. This sex reversal could be rescued by simultaneous administration of 11-ketotestosterone (11-KT). Compared with the control XY fish, decreased serum 11-KT and increased E2 level were detected in SSR fish. Immunohistochemistry analyses revealed that Cyp19a1a, Cyp11b2 and Dmrt1 were expressed in the gonads of GA + E2, MN + E2 and TR + E2 SSR XY fish at 90 dah, but only Cyp19a1a was expressed at 180 dah. When the treatment was applied from 60 to 120 dah, TR + E2 resulted in 3.3% of SSR, MN + E2 and GA + E2 resulted in no SSR. These results demonstrated that once 11-KT was synthesized, it could antagonize E2-induced male-to-female SSR, which could be abolished by simultaneous treatment with the inhibitor of steroidogenic enzymes. The upper the enzyme was located in the steroidogenic pathway, the higher SSR rate was achieved when it was inhibited as some of the precursors, such as androstenedione, testosterone and 5α-dihydrotestosterone, could act as androgens. These results highlight the key role of androgen in male sex maintenance.

Glycyrrhetinic acid alleviates radiation-induced lung injury in mice

Radiation-induced lung injury (RILI) is a common complication of thoracic radiotherapy, but efficacious therapy for RILI is lacking. This study ascertained whether glycyrrhetinic acid (GA; a functional hydrolyzed product of glycyrrhizic acid, which is extracted from herb licorice) can protect against RILI and investigated its relationship to the transforming growth factor (TGF)-β1/Smads signaling pathway. C57BL/6 mice were divided into four groups: a control group, a GA group and two irradiation (IR) groups. IR groups were exposed to a single fraction of X-rays (12 Gy) to the thorax and administered normal saline (IR + NS group) or GA (IR + GA group). Two days and 17 days after irradiation, histologic analyses were performed to assess the degree of lung injury, and the expression of TGF-β1, Smad2, Smad3 and Smad7 was recorded. GA administration mitigated the histologic changes of lung injury 2 days and 17 days after irradiation. Protein and mRNA expression of TGF-β1, Smad2 and Smad3, and the mRNA level of Smad7, in lung tissue were significantly elevated after irradiation. GA decreased expression of TGF-β1, Smad2 and Smad3 in lung tissue, but did not increase Smad7 expression. GA can protect against early-stage RILI. This protective effect may be associated with inhibition of the TGF-β1/Smads signaling pathway.