Ursodeoxycholic acid and 18β-glycyrrhetinic acid alleviate ethinylestradiol-induced cholestasis via downregulating RORγt and CXCR3 signaling pathway in iNKT cells

Estrogen-induced intrahepatic cholestasis (IHC) is a mild but potentially serious risk and urges for new therapeutic targets and effective treatment. Our previous study demonstrated that RORγt and CXCR3 signaling pathway of invariant natural killer T (iNKT) 17 cells play pathogenic roles in 17α-ethinylestradiol (EE)-induced IHC. Ursodeoxycholic acid (UDCA) and 18β-glycyrrhetinic acid (GA) present a protective effect on IHC partially due to their immunomodulatory properties. Hence in present study, we aim to investigate the effectiveness of UDCA and 18β-GA in vitro and verify the accessibility of the above targets. Biochemical index measurement indicated that UDCA and 18β-GA presented efficacy to alleviate EE-induced cholestatic cytotoxicity. Both UDCA and 18β-GA exhibited suppression on the CXCL9/10-CXCR3 axis, and significantly restrained the expression of RORγt in vitro. In conclusion, our observations provide new therapeutic targets of UDCA and 18β-GA, and 18β-GA as an alternative treatment for EE-induced cholestasis.

Identification of 18β-glycyrrhetinic acid as an AGT inhibitor against LPS-induced myocardial dysfunction via high throughput screening

Sepsis induced myocardial dysfunction (SIMD) is a serious complication of sepsis. There is increasing evidence that the renin-angiotensin system (RAS) is activated in SIMD. Angiotensinogen (AGT) is a precursor of the RAS, and the inhibition of AGT may have significant cardiovascular benefits. But until now, there have been no reports of small molecule drugs targeting AGT. In this study, we designed a promoter-luciferase based system to screen for novel AGT inhibitors to alleviate SIMD. As a result of high-throughput screening, a total of 5 compounds from 351 medicinal herb-derived natural compounds were found inhibiting AGT. 18β-glycyrrhetinic acid (18βGA) was further identified as a potent suppressor of AGT. In vitro experiments, 18βGA could inhibit the secretion of AGT by HepG2 cells and alleviate the elevated level of mitochondrial oxidative stress in cardiomyocytes co-cultured with HepG2 supernatants. In vivo, 18βGA prolonged the survival rate of SIMD mice, enhanced cardiac function, and inhibited the damage of mitochondrial function and inflammation. In addition, the results showed that 18βGA may reduce AGT transcription by downregulating hepatocyte nuclear factor 4 (HNF4) and that further alleviated SIMD. In conclusion, we provided a more efficient screening strategy for AGT inhibitors and expanded the novel role of 18βGA as a promising lead compound in rescuing cardiovascular disease associated with RAS overactivation.

18β-glycyrrhetinic acid suppresses Lewis lung cancer growth through protecting immune cells from ferroptosis

PURPOSE

18β-glycyrrhetinic acid (GA), the main metabolite of glycyrrhizic acid extracted from the root of licorice, has been reported to possess anti-cancer and immunomodulatory activity, but the mechanisms are not well understood. Recent studies have shown that ferroptosis of immune cells is involved in tumor-associated immune suppression. The purpose of this study was to investigate whether the enhanced immune response via inhibiting immune cell ferroptosis contributed to the anticancer effect of 18β-GA.

METHODS

Lewis Lung carcinoma mouse model and Murine CD8 + T cell culture model were used to examine the changes of immune response and ferroptosis of immune cells.

RESULTS

We found that 18β-GA was effective against lung cancer accompanied by enhanced activation of tumor-infiltrating CD8+ T cells in Lewis Lung carcinoma mouse model. Furthermore, we demonstrated that the boosted immune response by GA was attributed to its ability to inhibit arachidonic acid (AA)-mediated CD8+ T ferroptosis via suppressing CD36 expression.

CONCLUSION

The findings of the present study unraveled a novel mechanism underlying the anti-cancer and immunomodulatory activity of 18β-GA and support that 18β-GA holds potential to be used as an immune enhancer for lung cancer prevention or treatment.

Licorice metabolite 18β-glycyrrhetinic acid activates G protein-gated inwardly rectifying K+ channels

BACKGROUND AND PURPOSE

Licorice (liquorice) is a common food additive and is used in Chinese medicine. Excess licorice intake can induce atrial fibrillation. Patients with atrial fibrillation possess constitutively activated G protein-gated inwardly rectifying K+ (GIRK) channels. Whether licorice affects GIRK channel activity is unknown. We aimed to clarify the effects of licorice ingredients on GIRK current and the mechanism of action.

EXPERIMENTAL APPROACH

A major component of licorice, glycyrrhizic acid (GA), and its metabolite, 18β-glycyrrhetinic acid (18β-GA), were tested. We performed electrophysiological recordings in Xenopus oocytes to examine the effects of GA and 18β-GA on various GIRK subunits (Kir 3.1-Kir 3.4), mutagenesis analyses to identify the crucial residues for drug action and motion analysis in cultured rat atrial myocytes to clarify effects of 18β-GA on atrial functions.

KEY RESULTS

GA inhibited Kir 3.1-containing channels, while 18β-GA activated all Kir 3.x subunits. A pore helix residue Phe137 in Kir 3.1 was critical for GA-mediated inhibition, and the corresponding Ser148 in Kir 3.2 was critical for 18β-GA-mediated activation. 18β-GA activated GIRK channel in a Gβγ -independent manner, whereas phosphatidylinositol 4,5-bisphosphate (PIP2 ) was essential for activation. Glu236 located at the cytoplasmic pore of Kir 3.2 appeared to be important to interactions with 18β-GA. In rat atrial myocytes, 18β-GA suppressed spontaneous beating via activation of GIRK channels.

CONCLUSION AND IMPLICATIONS

GA acts as a novel GIRK inhibitor, and 18β-GA acts as a novel GIRK activator. 18β-GA alters atrial function via activation of GIRK channels. This study elucidates the pharmacological activity of licorice ingredients and provides information for drug design.

18β-Glycyrrhetinic acid exerts cardioprotective effects against BPA-induced cardiotoxicity through antiapoptotic and antioxidant mechanisms

Bisphenol A (BPA) is a synthetic environmental pollutant widely used in industry, as well as is an endocrine disrupting chemicals and has a toxic effects on heart tissue. The aim of this study is to reveal the cardioprotective effects of 18β-glycyrretinic acid (GA) against BPA-induced cardiotoxicity in rats. In this study, 40 male rats were used and five different groups (each group includes eight rats) were formed. The rats were applied BPA (250 mg/kg b.w.) alone or with GA (50 and 100 mg/kg b.w.) for 14 days. Rats were killed on Day 15 and heart tissues were taken for analysis. GA treatment decreased serum lactate dehydrogenase and creatine kinase MB levels, reducing BPA-induced heart damage. GA treatment showed ameliorative effects against lipid peroxidation and oxidative stress caused by BPA by increasing the antioxidant enzyme activities (glutathione peroxidase, superoxide dismutase, and catalase) and GSH level of the heart tissue and decreasing the MDA level. In addition, GA showed antiapoptotic effect by increasing Bcl-2, procaspase-3, and -9 protein expression levels and decreasing Bax, cytochrome c, and P53 protein levels in heart tissue. As a result, it was found that GA has cardioprotective effects on heart tissue by exhibiting antioxidant and antiapoptotic effects against heart damage caused by BPA, an environmental pollutant. Thus, it was supported that GA could be a potential cardioprotective agent.

Synthesis of novel 18β-glycyrrhetinic acid sulfonate derivatives displaying significant anti-oomycete activity against Phytophthora capsici

Using 18β-glycyrrhetinic acid (GA) as the lead compound, fourteen GA sulphonate derivatives (3a-n) were prepared by modifying its C-3 OH group, and their structures were well confirmed by 1H NMR, 13C NMR, HRMS and melting points. Moreover, we screened the anti-oomycete activity of these compounds against Phytophthora capsici by using the mycelial growth rate method. Among the fourteen GA sulphonate derivatives evaluated, four compounds 3f, 3j, 3k and 3l exhibited more potent anti-oomycete activity than that of the positive control zoxamide (EC50 = 25.17 mg/L), and had the median effective concentration (EC50) values of 23.04, 16.16, 22.55, and 13.93 mg/L, respectively. Especially compound 3l showed the best anti-oomycete activity against P. capsici with EC50 value of 13.93 mg/L. Overall, the introduction of sulfonyloxy groups at the C-3 position of GA has a significant impact on its anti-oomycete activity, and the corresponding derivative activity varies significantly with different substituents R.

Synthesis and Antiviral and Antitumor Activities of Novel 18β-Glycyrrhetinic Acid Derivatives

A series of novel derivatives of 18β-glycyrrhetinic acid (GA) were synthesized by introducing aromatic or heterocyclic structures to extend the side chain, thereby enhancing their interaction with amino acid residues in the active pocket of the target protein. These compounds were structurally characterized using 1H NMR, 13C NMR, and HRMS. The compounds were subsequently evaluated for their inhibitory effects on HIV-1 protease and cell viability in the human cancer cell lines K562 and HeLa and the mouse cancer cell line CT26. Towards HIV-1 protease, compounds 28 and 32, which featured the introduction of heterocyclic moieties at the C3 position of GA, exhibited the highest inhibition, with inhibition rates of 76% and 70.5%, respectively, at 1 mg/mL concentration. Further molecular docking suggests that a 3-substituted polar moiety would be likely to enhance the inhibitory activity against HIV-1 protease. As for the anti-proliferative activities of the GA derivatives, incorporation of a thiazole heterocycle at the C3- position in compound 29 significantly enhanced the effect against K562 cells with an IC50 value of 8.86 ± 0.93 µM. The introduction of electron-withdrawing substituents on the C3-substituted phenyl ring augmented the anti-proliferative activity against Hela and CT26 cells. Compound 13 exhibited the highest inhibitory activity against Hela cells with an IC50 value of 9.89 ± 0.86 µM, whereas compound 7 exerted the strongest inhibition against CT26 cells with an IC50 value of 4.54 ± 0.37 µM. These findings suggest that further modification of GA is a promising path for developing potent novel anti-HIV and anticancer therapeutics.

Unlocking Synergistic Potential: Enhancing Regorafenib Efficacy in Hepatocellular Carcinoma Through Combination Therapy With 18β-Glycyrrhetinic Acid

BACKGROUND/AIM

Hepatocellular carcinoma (HCC) is a primary liver cancer with limited treatment options and poor prognosis. Regorafenib, a multi-kinase inhibitor, has shown promise in HCC treatment; however, its efficacy can be enhanced by combining it with other agents. 18β-glycyrrhetinic acid (18β-gly) is a natural compound with potential anti-cancer properties.

MATERIALS AND METHODS

The toxicity and mechanism of regorafenib and 18β-gly was assessed on Hep3B cells, Huh7 cells, and Hep3B bearing animal model.

RESULTS

The combination of regorafenib and 18β-gly exhibited synergistic toxicity in HCC cells and animal model. Importantly, no significant differences in body weight or major tissue damage were observed after treatment with the combination of two drugs. Furthermore, the combination treatment modulated apoptosis-related markers and the mTOR signaling pathway.

CONCLUSION

The study provides evidence for the synergistic effect of 18β-gly and regorafenib in a HCC model. The combination treatment modulated apoptosis-related markers and the mTOR signaling pathway, highlighting potential mechanisms underlying its therapeutic efficacy.

18β-glycyrrhetinic acid ameliorates MPTP-induced neurotoxicity in mice through activation of microglial anti-inflammatory phenotype

RATIONALE

18β-glycyrrhetinic acid (18β-GA) has been reported to have anti-inflammatory and neuroprotective effects. However, the therapeutic effect of 18β-GA in Parkinson's disease (PD) has not been defined.

OBJECTIVE

The current study aimed to evaluate the potential therapeutic effects of 18β-GA in treating PD by mitigating 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity.

RESULTS

The study showed that 18β-GA has anti-inflammatory effects by upregulating TREM2 expression in BV2 cells, which correlates with the presence of NF-E2-related factor-2 (Nrf2). 18β-GA reduced inflammation in BV2 cells treated with 1-methyl-4- phenylpyridinium (MPP+) by enhancing TREM2 expression, which promotes an anti-inflammatory microglial phenotype. Repeated administration of 18β-GA in MPTP-treated mice led to therapeutic effects by enhancing TREM2 expression, resulting in the activation of anti-inflammatory microglia. Moreover, 18β-GA attenuated the decrease in brain-derived neurotrophic factor (BDNF) levels in both MPP+-induced BV2 cells and MPTP-intoxicated mice, indicating the involvement of BDNF in the beneficial effects of 18β-GA.

CONCLUSIONS

It is probable that activating microglial anti-inflammatory response through TREM2 expression might serve as a novel therapeutic strategy for PD. Additionally, 18β-GA seems to hold potential as a new therapeutic agent for PD.

A Biomimetic Nanoparticle Exerting Protection against Acute Liver Failure by Suppressing CYP2E1 Activity and Scavenging Excessive ROS

Acute liver failure (ALF) is a severe liver disease caused by many reasons. One of them is the overdosed acetaminophen (APAP), which is metabolized into N-acetyl-p-benzoquinone imine (NAPQI), an excessive toxic metabolite, by CYP2E1, resulting in excessive reactive oxygen species (ROS), exhausted glutathione (GSH), and thereafter hepatocyte necrosis. N-acetylcysteine is the Food and Drug Administration-approved drug for detoxification of APAP, but it has limited clinical application due to the short therapeutic time window and concentration-related adverse effects. In this study, a carrier-free and bilirubin dotted nanoparticle (B/BG@N) is developed, which is formed using bilirubin and 18β-Glycyrrhetinic acid, and bovine serum albumin (BSA) is then adsorbed to mimic the in vivo behavior of the conjugated bilirubin for hitchhiking. The results demonstrate that B/BG@N can effectively reduce the production of NAPQI as well as exhibit antioxidant effects against intracellular oxidative stress via regulating the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 signal axis and reducing the production of inflammatory factors. In vivo study shows that B/BG@N can effectively improve the clinical symptom of the mice model. This study suggests that B/BG@N own increases circulation half-life, improves accumulation in the liver, and dual detoxification, providing a promising strategy for clinical ALF treatment.

Development of an Antiviral Ion-Activated In Situ Gel Containing 18β-Glycyrrhetinic Acid: A Promising Alternative against Respiratory Syncytial Virus

The human respiratory syncytial virus (hRSV) is a major cause of serious lower respiratory infections and poses a considerable risk to public health globally. Only a few treatments are currently used to treat RSV infections, and there is no RSV vaccination. Therefore, the need for clinically applicable, affordable, and safe RSV prevention and treatment solutions is urgent. In this study, an ion-activated in situ gelling formulation containing the broad-spectrum antiviral 18β-glycyrrhetinic acid (GA) was developed for its antiviral effect on RSV. In this context, pH, mechanical characteristics, ex vivo mucoadhesive strength, in vitro drug release pattern, sprayability, drug content, and stability were all examined. Rheological characteristics were also tested using in vitro gelation capacity and rheological synergism tests. Finally, the cytotoxic and antiviral activities of the optimized in situ gelling formulation on RSV cultured in the human laryngeal epidermoid carcinoma (HEp-2) cell line were evaluated. In conclusion, the optimized formulation prepared with a combination of 0.5% w/w gellan gum and 0.5% w/w sodium carboxymethylcellulose demonstrated good gelation capacity and sprayability (weight deviation between the first day of the experiment (T0) and the last day of the experiment (T14) was 0.34%), desired rheological synergism (mucoadhesive force (Fb): 9.53 Pa), mechanical characteristics (adhesiveness: 0.300 ± 0.05 mJ), ex vivo bioadhesion force (19.67 ± 1.90 g), drug content uniformity (RSD%: 0.494), and sustained drug release over a period of 6 h (24.56% ± 0.49). The optimized formulation demonstrated strong anti-hRSV activity (simultaneous half maximal effective concentration (EC50) = 0.05 µg/mL; selectivity index (SI) = 306; pre-infection EC50 = 0.154 µg/mL; SI = 100), which was significantly higher than that of ribavirin (EC50 = 4.189 µg/mL; SI = 28) used as a positive control against hRSV, according to the results of the antiviral activity test. In conclusion, this study showed that nasal in situ gelling spray can prevent viral infection and replication by directly inhibiting viral entry or modulating viral replication.

18β-glycyrrhetinic acid promotes gastric cancer cell autophagy and inhibits proliferation by regulating miR-328-3p/signal transducer and activator of transcription 3

BACKGROUND

Gastric cancer (GC) is one of the most common cancer types worldwide, and its prevention and treatment methods have garnered much attention. As the active ingredient of licorice, 18β-glycyrrhetinic acid (18β-GRA) has a variety of pharmacological effects. The aim of this study was to explore the effective target of 18β-GRA in the treatment of GC, in order to provide effective ideas for the clinical prevention and treatment of GC.

AIM

To investigate the mechanism of 18β-GRA in inhibiting cell proliferation and promoting autophagy flux in GC cells.

METHODS

Whole transcriptomic analyses were used to analyze and screen differentially expressed microRNAs (miRNAs) in GC cells after 18β-GRA intervention. Lentivirus-transfected GC cells and the Cell Counting Kit-8 were used to detect cell proliferation ability, cell colony formation ability was detected by the clone formation assay, and flow cytometry was used to detect the cell cycle and apoptosis. A nude mouse transplantation tumor model of GC cells was constructed to verify the effect of miR-328-3p overexpression on the tumorigenicity of GC cells. Tumor tissue morphology was observed by hematoxylin and eosin staining, and microtubule-associated protein light chain 3 (LC3) expression was detected by immunohistochemistry. TransmiR, STRING, and miRWalk databases were used to predict the relationship between miR-328-3p and signal transducer and activator of transcription 3 (STAT3)-related information. Expression of STAT3 mRNA and miR-328-3p was detected by quantitative polymerase chain reaction (qPCR) and the expression levels of STAT3, phosphorylated STAT3 (p-STAT3), and LC3 were detected by western blot analysis. The targeted relationship between miR-328-3p and STAT3 was detected using the dual-luciferase reporter gene system. AGS cells were infected with monomeric red fluorescent protein-green fluorescent protein-LC3 adenovirus double label. LC3 was labeled and autophagy flow was observed under a confocal laser microscope.

RESULTS

The expression of miR-328-3p was significantly upregulated after 18β-GRA intervention in AGS cells (P = 4.51E-06). Overexpression of miR-328-3p inhibited GC cell proliferation and colony formation ability, arrested the cell cycle in the G0/G1 phase, promoted cell apoptosis, and inhibited the growth of subcutaneous tumors in BALB/c nude mice (P < 0.01). No obvious necrosis was observed in the tumor tissue in the negative control group (no drug intervention or lentivirus transfection) and vector group (the blank vector for lentivirus transfection), and more cells were loose and necrotic in the miR-328-3p group. Bioinformatics tools predicted that miR-328-3p has a targeting relationship with STAT3, and STAT3 was closely related to autophagy markers such as p62. After overexpressing miR-328-3p, the expression level of STAT3 mRNA was significantly decreased (P < 0.01) and p-STAT3 was downregulated (P < 0.05). The dual-luciferase reporter gene assay showed that the luciferase activity of miR-328-3p and STAT3 3’ untranslated regions of the wild-type reporter vector group was significantly decreased (P < 0.001). Overexpressed miR-328-3p combined with bafilomycin A₁ (Baf A₁) was used to detect the expression of LC3 II. Compared with the vector group, the expression level of LC3 II in the overexpressed miR-328-3p group was downregulated (P < 0.05), and compared with the Baf A₁ group, the expression level of LC3 II in the overexpressed miR-328-3p + Baf A₁ group was upregulated (P < 0.01). The expression of LC3 II was detected after intervention of 18β-GRA in GC cells, and the results were consistent with the results of miR-328-3p overexpression (P < 0.05). Additional studies showed that 18β-GRA promoted autophagy flow by promoting autophagosome synthesis (P < 0.001). qPCR showed that the expression of STAT3 mRNA was downregulated after drug intervention (P < 0.05). Western blot analysis showed that the expression levels of STAT3 and p-STAT3 were significantly downregulated after drug intervention (P < 0.05).

CONCLUSION

18β-GRA promotes the synthesis of autophagosomes and inhibits GC cell proliferation by regulating the miR-328-3p/STAT3 signaling pathway.

Discovery of Novel Pentacyclic Triterpene Acid Amide Derivatives as Excellent Antimicrobial Agents Dependent on Generation of Reactive Oxygen Species

Developing new agricultural bactericides is a feasible strategy for stopping the increase in the resistance of plant pathogenic bacteria. Some pentacyclic triterpene acid derivatives were elaborately designed and synthesized. In particular, compound A₂₂ exhibited the best antimicrobial activity against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac) with EC₅₀ values of 3.34 and 3.30 mg L^-1, respectively. The antimicrobial mechanism showed that the compound A₂₂ induced excessive production and accumulation of reactive oxygen species (ROS) in Xoo cells, leading to a decrease in superoxide dismutase and catalase enzyme activities and an increase in malondialdehyde content. A₂₂ also produced increases in Xoo cell membrane permeability and eventual cell death. In addition, in vivo experiments showed that A₂₂ at 200 mg L^-1 exhibited protective activity against rice bacterial blight (50.44%) and citrus canker disease (84.37%). Therefore, this study provides a paradigm for the agricultural application of pentacyclic triterpene acid.

18β-glycyrrhetinic acid inhibits proliferation of gastric cancer cells through regulating the miR-345-5p/TGM2 signaling pathway

BACKGROUND

Gastric cancer (GC) is a common gastrointestinal malignancy worldwide. Based on cancer-related mortality, the current prevention and treatment strategies for GC still show poor clinical results. Therefore, it is important to find effective drug treatment targets.

AIM

To explore the molecular mechanism of 18β-glycyrrhetinic acid (18β-GRA) regulating the miR-345-5p/TGM2 signaling pathway to inhibit the proliferation of GC cells.

METHODS

CCK-8 assay was used to determine the effect of 18β-GRA on the survival rate of GES-1 cells and AGS and HGC-27 cells. Cell cycle and apoptosis were detected by flow cytometry, cell migration was detected by a wound healing assay, the effect of 18β-GRA on subcutaneous tumor growth in BALB/c nude mice was investigated, and the cell autophagy level was determined by MDC staining. TMT proteomic analysis was used to detect the differentially expressed autophagy-related proteins in GC cells after 18β-GRA intervention, and then the protein-protein interaction was predicted using STRING (https://string-db.org/). MicroRNAs (miRNAs) transcriptome analysis was used to detect the miRNA differential expression profile, and use miRBase (https://www.mirbase/) and TargetScan (https://www.targetscan.org/) to predict the miRNA and complementary binding sites. Quantitative real-time polymerase chain reaction was used to detect the expression level of miRNA in 18β-GRA treated cells, and western blot was used to detect the expression of autophagy related proteins. Finally, the effect of miR-345-5p on GC cells was verified by mir-345-5p overexpression.

RESULTS

18β-GRA could inhibit GC cells viability, promote cell apoptosis, block cell cycle, reduce cell wound healing ability, and inhibit the GC cells growth in vivo. MDC staining results showed that 18β-GRA could promote autophagy in GC cells. By TMT proteomic analysis and miRNAs transcriptome analysis, it was concluded that 18β-GRA could down-regulate TGM2 expression and up-regulate miR-345-5p expression in GC cells. Subsequently, we verified that TGM2 is the target of miR-345-5p, and that overexpression of miR-345-5p significantly inhibited the protein expression level of TGM2. Western blot showed that the expression of autophagy-related proteins of TGM2 and p62 was significantly reduced, and LC3II, ULK1 and AMPK expression was significantly increased in GC cells treated with 18β-GRA. Overexpression of miR-345-5p not only inhibited the expression of TGM2, but also inhibited the proliferation of GC cells by promoting cell apoptosis and arresting cell cycle.

CONCLUSION

18β-GRA inhibits the proliferation of GC cells and promotes autophagy by regulating the miR-345-5p/TGM2 signaling pathway.

Anti-Photoaging Effects of Nanocomposites of Amphiphilic Chitosan/18β-Glycyrrhetinic Acid

Improving the transdermal absorption of weakly soluble drugs for topical use can help to prevent and treat skin photoaging. Nanocrystals of 18β-glycyrrhetinic acid (i.e., NGAs) prepared by high-pressure homogenization and amphiphilic chitosan (ACS) were used to form ANGA composites by electrostatic adsorption, and the optimal ratio of NGA to ACS was 10:1. Dynamic light scattering analysis and zeta potential analysis were used to evaluate the nanocomposites' suspension, and the results showed that mean particle size was 318.8 ± 5.4 nm and the zeta potential was 30.88 ± 1.4 mV after autoclaving (121 °C, 30 min). The results of CCK-8 showed that the half-maximal inhibitory concentration (IC50) of ANGAs (71.9 μg/mL) was higher than that of NGAs (51.6 μg/mL), indicating that the cytotoxicity of ANGAs was weaker than that of NGAs at 24 h. After the composite had been prepared as a hydrogel, the vertical diffusion (Franz) cells were used to investigate skin permeability in vitro, and it was shown that the cumulative permeability of the ANGA hydrogel increased from 56.5 ± 1.4% to 75.3 ± 1.8%. The efficacy of the ANGA hydrogel against skin photoaging was studied by constructing a photoaging animal model under ultraviolet (UV) irradiation and staining. The ANGA hydrogel improved the photoaging characteristics of UV-induced mouse skin significantly, improved structural changes (e.g., breakage and clumping of collagen and elastic fibers in the dermis) significantly, and improved skin elasticity, while it inhibited the abnormal expression of matrix metalloproteinase (MMP)-1 and MMP-3 significantly, thereby reducing the damage caused by UV irradiation to the collagen-fiber structure. These results indicated that the NGAs could enhance the local penetration of GA into the skin and significantly improve the photoaging of mouse skin. The ANGA hydrogel could be used to counteract skin photoaging.

Pharmacological Features of 18β-Glycyrrhetinic Acid: A Pentacyclic Triterpenoid of Therapeutic Potential

Glycyrrhiza glabra L. (belonging to the family Leguminosae), commonly known as Licorice, is a popular medicinal plant that has been used in traditional medicine worldwide for its ethnopharmacological efficacy in treating several ailments. Natural herbal substances with strong biological activity have recently received much attention. The main metabolite of glycyrrhizic acid is 18β-glycyrrhetinic acid (18βGA), a pentacyclic triterpene. A major active plant component derived from licorice root, 18βGA has sparked a lot of attention due to its pharmacological properties. The current review thoroughly examines the literature on 18βGA, a major active plant component obtained from Glycyrrhiza glabra L. The current work provides insight into the pharmacological activities of 18βGA and the potential mechanisms of action involved. The plant contains a variety of phytoconstituents such as 18βGA, which has a variety of biological effects including antiasthmatic, hepatoprotective, anticancer, nephroprotective, antidiabetic, antileishmanial, antiviral, antibacterial, antipsoriasis, antiosteoporosis, antiepileptic, antiarrhythmic, and anti-inflammatory, and is also useful in the management of pulmonary arterial hypertension, antipsychotic-induced hyperprolactinemia, and cerebral ischemia. This review examines research on the pharmacological characteristics of 18βGA throughout recent decades to demonstrate its therapeutic potential and any gaps that may exist, presenting possibilities for future drug research and development.

Carboxymethyl starch as a solid dispersion carrier to enhance the dissolution and bioavailability of piperine and 18β-glycyrrhetinic acid

OBJECTIVE

To investigate the applicability of carboxymethyl starch (CMS) as a carrier to prepare solid dispersions (SDs) of piperine (PIP) and 18β-glycyrrhetinic acid (β-GA) (PIP-CMS and β-GA-CMS SDs) and to explore the influence of drug properties on carrier selection.

SIGNIFICANCE

The low oral bioavailability of natural therapeutic molecules, including PIP and β-GA, severely restricts their pharmaceutical applications. Moreover, CMS, a natural polymer, is rarely reported as a carrier for SDs.

METHODS

PIP-CMS and β-GA-CMS SDs were prepared using the solvent evaporation method. Differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) were used for formulation characterization. Additionally, drug release characteristics were investigated.

RESULTS

In vitro dissolution studies showed that the dissolutions of PIP-CMS and β-GA-CMS SDs were 1.90-2.04 and 1.97-2.22 times higher than pure PIP and β-GA, respectively, at a drug:polymer ratio of 1:6. DSC, XRPD, FT-IR, and SEM analyses confirmed the formation of SDs in their amorphous states. Significant improvements in C_max and AUC_0-24 h of PIP-CMS and β-GA-CMS SDs (17.51 ± 8.15 μg/mL and 210.28 ± 117.13 μg·h/mL, respectively) and (32.17 ± 9.45 μg/mL and 165.36 ± 38.75 μg·h/mL, respectively) were observed in the pharmacokinetic study. Compared with weakly acidic β-GA, loading weakly basic PIP seemed to have a profound effect on stability through intermolecular forces.

CONCLUSIONS

Our findings showed CMS could be a promising carrier for SDs, and loading weakly basic drug may be more suitable, especially in binary SDs system.

Biotransformation of 18β-Glycyrrhetinic Acid by Human Intestinal Fungus Aspergillus niger RG13B1 and the Potential Anti-Inflammatory Mechanism of Its Metabolites

18β-Glycyrrhetinic acid (GA) is a triterpenoid possessing an anti-inflammatory activity in vivo, while the low bioavailability limits its application due to its intestinal accumulation. In order to investigate the metabolism of GA in intestinal microbes, it was incubated with human intestinal fungus Aspergillus niger RG13B1, finally leading to the isolation and identification of three new metabolites (1-3) and three known metabolites (4-6) based on 1D and 2D NMR and high-resolution electrospray ionization mass spectroscopy spectra. Metabolite 6 could target myeloid differentiation protein 2 (MD2) to suppress the activation of nuclear factor-kappa B (NF-κB) signaling pathway via inhibiting the nuclear translocation of p65 to downregulate its target proteins and genes in lipopolysaccharide (LPS)-mediated RAW264.7 cells. Molecular dynamics suggested that metabolite 6 interacted with MD2 through the hydrogen bond of amino acid residue Arg90. These findings demonstrated that metabolite 6 could serve as a potential candidate to develop the new inhibitors of MD2.

Neuroprotective effects of 18β-glycyrrhetinic acid against bisphenol A-induced neurotoxicity in rats: involvement of neuronal apoptosis, endoplasmic reticulum stress and JAK1/STAT1 signaling pathway

The exposure to bisphenol A (BPA) is inevitable owing to its common use in the production of polycarbonate plastics. Studies to reduce side effects are gaining importance since BPA causes severe toxicities in important tissues such as testes, lungs, brain, liver and kidney. The current study was planned to study ameliorative effect of 18β-glycyrrhetinic acid (18β-GA) on BPA induced neurotoxicity. Fourty Wistar albino rats were divided into five equal groups as follows: I-Control group, II-18β-GA group (100 mg/kg), III- BPA group (250 mg/kg), IV-250 mg/kg BPA + 50 mg/kg 18β-GA group, V-250 mg/kg BPA + 100 mg/kg 18β-GA group. BPA intoxication was associated with increased MDA level while reduced GSH concentration, activities of glutathione peroxidase, superoxide dismutase, and catalase. BPA supplementation caused apoptosis in the brain by up-regulating caspase-3 and Bax levels and down-regulating Bcl-2. BPA also caused endoplasmic reticulum (ER) stress by increasing mRNA transcript levels of PERK, IRE1, ATF-6 and GRP78. Additionally, it was observed that BPA administration activated JAK1/STAT1 signaling pathway and levels of TNF-α, NF-κB, p38 MAPK and JNK in the brain. However, co-treatment with 18β-GA at a dose of 50 and 100 mg/kg considerably ameliorated oxidative stress, inflammation, apoptosis, ER stress and JAK1/STAT1 signaling pathway in brain tissue. Overall, the data of this study indicate that brain damage associated with BPA toxicity could be ameliorated by 18β-GA administration.

Nrf2-mediated liver protection by 18β-glycyrrhetinic acid against pyrrolizidine alkaloid-induced toxicity through PI3K/Akt/GSK3β pathway

BACKGROUND

Misusage of pyrrolizidine alkaloid (PA)-containing plants or unaware intake of PA-contaminated foodstuffs causes thousands of PA poisoning cases in humans. PA intoxication is accompanied by oxidative stress and subsequent extensive hepatocellular damage. Our previous study has demonstrated that 18β-glycyrrhetinic acid (GA), a bioactive constituent of liquorice, prevented PA-induced hepatotoxicity in rats, however the underlying mechanisms remain unclear.

OBJECTIVE

This study aims to explore the mechanisms underlying the hepato-protective effect of GA in combating retrorsine (RTS, a representative toxic PA)-induced liver injury.

METHODS

Histological and biochemical assessments were employed to evaluate the protective effect of GA on RTS-induced hepatotoxicity in rats. Sulforhodamine B assay, real-time PCR, western blotting, and immunostaining were used to explore the underlying mechanisms in human hepatocytes and rats.

RESULTS

Our findings demonstrated that GA alleviated RTS-induced elevation of serum ALT and bilirubin levels, as well as hepatocytes necrosis and sinusoidal endothelial cells (SECs) damage in rats. GA also enhanced the activities and expressions of several antioxidant enzymes through upregulating nuclear factor-erythroid 2-related factor2 (Nrf2). Moreover, inhibition of Nrf2 blocked the hepatoprotective effect of GA against RTS intoxication. Mechanistically, GA increased the phosphorylation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) and enhanced glycogen synthase kinase 3 beta (GSK3β) inhibitory phosphorylation at serine 9, thus promoting the nuclear accumulation of Nrf2 and activating its downstream targets.

CONCLUSION

This study for the first time demonstrated that GA exerted protective effects against RTS-induced liver injury by potentiating the Nrf2-mediated antioxidant system through PI3K/Akt/GSK3β pathway. The findings indicated that GA may serve as a potential candidate drug for the treatment of PA intoxication.

18β-glycyrrhetinic acid regulates mitochondrial ribosomal protein L35-associated apoptosis signaling pathways to inhibit proliferation of gastric carcinoma cells

BACKGROUND

Gastric carcinoma (GC) is a common gastrointestinal malignancy worldwide. Based on the cancer-related mortality, the current prevention and treatment strategies for GC still show poor clinical results. Therefore, it is important to find effective drug treatment targets.

AIM

To explore the mechanism by which 18β-glycyrrhetinic acid (18β-GRA) regulates mitochondrial ribosomal protein L35 (MRPL35) related signal proteins to inhibit the proliferation of GC cells.

METHODS

Cell counting kit-8 assay was used to detect the effects of 18β-GRA on the survival rate of human normal gastric mucosal cell line GES-1 and the proliferation of GC cell lines MGC80-3 and BGC-823. The apoptosis and cell cycle were assessed by flow cytometry. Cell invasion and migration were evaluated by Transwell assay, and cell scratch test was used to detect cell migration. Furthermore, a tumor model was established by hypodermic injection of 2.5 × 10⁶ BGC-823 cells at the selected positions of BALB/c nude mice to determine the effect of 18β-GRA on GC cell proliferation, and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to detect MRPL35 expression in the engrafted tumors in mice. We used the term tandem mass tag (TMT) labeling combined with liquid chromatography–tandem mass spectrometry to screen for differentially expressed proteins (DEPs) extracted from GC cells and control cells after 18β-GRA intervention. A detailed bioinformatics analysis of these DEPs was performed, including Gene Ontology annotation and enrichment analysis, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis, and so on. Moreover, STRING database (https://string-db.org/) was used to predict protein-protein interaction (PPI) relationships and Western blot was used to detect the expression of proteins of interest in GC cells.

RESULTS

The results indicated that 18β-GRA could inhibit the proliferation of GC cells in a dose- and time-dependent manner. It could induce GC cell apoptosis and arrest the cell cycle at G0/G1 phase. The proportion of cells arrested at S phase decreased with the increase of 18-GRA dose, and the migration and invasiveness of GC cells were inhibited. The results of animal experiments showed that 18β-GRA could inhibit tumor formation in BALB/c nude mice, and qRT-PCR results showed that MRPL35 expression level was significantly reduced in the engrafted tumors in mice. Using TMT technology, 609 DEPs, among which 335 were up-regulated and 274 were down-regulated, were identified in 18β-GRA intervention compared with control. We found that the intervention of 18β-GRA in GC cells involved many important biological processes and signaling pathways, such as cellular processes, biological regulation, and TP53 signaling pathway. Notably, after the drug intervention, MRPL35 expression was significantly down-regulated (P = 0.000247), TP53 expression was up-regulated (P = 0.02676), and BCL2L1 was down-regulated (P = 0.01699). Combined with the Retrieval of Interacting Genes/Proteins database, we analyzed the relationship between MRPL35, TP53, and BCL2L1 signaling proteins, and we found that COPS5, BAX, and BAD proteins can form a PPI network with MRPL35, TP53, and BCL2L1. Western blot analysis confirmed the intervention effect of 18β-GRA on GC cells, MRPL35, TP53, and BCL2L1 showed dose-dependent up/down-regulation, and the expression of COPS5, BAX, and BAD also increased/decreased with the change of 18β-GRA concentration.

CONCLUSION

18β-GRA can inhibit the proliferation of GC cells by regulating MRPL35, COPS5, TP53, BCL2L1, BAX, and BAD.

Liquorice Extract and 18β-Glycyrrhetinic Acid Protect Against Experimental Pyrrolizidine Alkaloid-Induced Hepatotoxicity in Rats Through Inhibiting Cytochrome P450-Mediated Metabolic Activation

Misuse of pyrrolizidine alkaloid (PA)-containing plants or consumption of PA-contaminated foodstuffs causes numerous poisoning cases in humans yearly, while effective therapeutic strategies are still limited. PA-induced liver injury was initiated by cytochrome P450 (CYP)-mediated metabolic activation and subsequent formation of adducts with cellular proteins. Liquorice, a hepato-protective herbal medicine, is commonly used concurrently with PA-containing herbs in many compound traditional Chinese medicine formulas, and no PA-poisoning cases have been reported with this combination. The present study aimed to investigate hepato-protective effects of liquorice aqueous extract (EX) and 18β-glycyrrhetinic acid (GA, the primary bioactive constituent of liquorice) against PA-induced hepatotoxicity and the underlying mechanism. Histopathological and biochemical analysis demonstrated that both single- and multiple-treatment of EX (500 mg/kg) or GA (50 mg/kg) significantly attenuated liver damage caused by retrorsine (RTS, a representative hepatotoxic PA). The formation of pyrrole-protein adducts was significantly reduced by single- (30.3% reduction in liver; 50.8% reduction in plasma) and multiple- (32.5% reduction in liver; 56.5% reduction in plasma) treatment of GA in rats. Single- and multiple-treatment of EX also decreased the formation of pyrrole-protein adducts, with 30.2 and 31.1% reduction in rat liver and 51.8 and 53.1% reduction in rat plasma, respectively. In addition, in vitro metabolism assay with rat liver microsomes demonstrated that GA reduced the formation of metabolic activation-derived pyrrole-glutathione conjugate in a dose-dependent manner with the estimated IC₅₀ value of 5.07 µM. Further mechanism study showed that GA inhibited activities of CYPs, especially CYP3A1, the major CYP isoform responsible for the metabolic activation of RTS in rats. Enzymatic kinetic study revealed a competitive inhibition of rat CYP3A1 by GA. In conclusion, our findings demonstrated that both EX and GA exhibited significant hepato-protective effects against RTS-induced hepatotoxicity, mainly through the competitive inhibition of CYP-mediated metabolic activation of RTS.

Simultaneous solubilization and extended release of insoluble drug as payload in highly soluble particles of γ-cyclodextrin metal-organic frameworks

The inclusion and nanocluster formed in cyclodextrin-metal organic framework (CD-MOF) make it a remarkable vehicle in improving the solubility and bioavailability of insoluble drugs, but rarely in elongation of drug release kinetics. In this research, an insoluble compound, 18β-glycyrrhetinic acid (GA), encapsulated in CD-MOF (GA@nano-CD-MOF) had prominent effects in the treatment of bleomycin-induced idiopathic pulmonary fibrosis in rats with an enhanced bioavailability by 6.8 times. The solubility of GA@nano-CD-MOF was 7780 times higher than that of GA, which was explained by the solubility parameter of amorphous cells constructed in silico simulation. CD-MOF imparted GA unique biphasic release kinetics, namely, GA released instantly to 52% and slowly released to 100% for a period of 5 days, which made the drug loaded particles much more flexible in pharmaceutical applications. The distribution of GA molecules in CD-MOF and drug loading priority obtained by molecular docking illustrated the formation of biphasic release mode at the molecular level combined with other characterizations of SEM, PXRD, TGA and DSC. In conclusion, CD-MOF has a unique effect to simultaneously solubilize an insoluble drug and extend its release for days as payload in highly soluble particles of γ-cyclodextrin metal-organic frameworks, which broaden the applications of drugs in specific treatment and then enhance the therapeutic effects.

18β-Glycyrrhetinic Acid Has Anti-Cancer Effects via Inducing Apoptosis and G2/M Cell Cycle Arrest, and Inhibiting Migration of A549 Lung Cancer Cells

Background

18β-glycyrrhetinic acid (18β-Gly), which is extracted from licorice root, has various pharmacological properties; however, its anti-cancer effects on lung cancer cells have not been fully established.

Purpose

In this study, we investigated the underlying molecular mechanisms of 18β-Gly.

Results

Our results showed that 18β-Gly had significant cytotoxic effects and no apparent side effects. 18β-Gly induced mitochondria-dependent apoptosis of A549 lung cancer cells. In addition, after treatment with 18β-Gly, intracellular reactive oxygen species (ROS) levels were significantly increased, and G2/M cell cycle arrest and inhibition of cell migration were induced via the mitogen-activated protein kinase (MAPK)/signal transducer and activator of transcription 3 (STAT3)/nuclear factor kappa (NF-κB) signaling pathways. After pretreatment with the ROS scavenger N-acetyl-L-cysteine or MAPK inhibitors, the expression levels of phosphorylated p38 (p-p38), phosphorylated c-Jun N-terminal kinase, inhibitor of nuclear factor kappa B, cleaved caspase-3 (cle-cas-3), cleaved poly (ADP ribose) polymerase (cle-PARP), p-p53, p27, p21, and E-cadherin were decreased; and levels of phosphorylated extracellular signal-regulated kinase, p-STAT3, NF-κB, Bcl-2, cyclin B1, cyclase-dependent kinase 1/2 (CDK1/2), N-cadherin, vimentin, and snail homolog 1 (SNAI 1) were increased. In addition, the percentage of cells in the G2/M phase was decreased, and inhibition of migration was reduced.

Conclusion

In summary, 18β-Gly induced apoptosis and G2/M cell cycle arrest and inhibited migration via the ROS/MAPK/STAT3/NF-κB signaling pathways in A549 lung cancer cells. Therefore, 18β-Gly is a novel promising candidate for the treatment of lung cancer.

18β-glycyrrhetinic acid improves high-intensity exercise performance by promoting glucose-dependent energy production and inhibiting oxidative stress in mice

It has been shown that 18β-glycyrrhetinic acid (18β-GA), the main bioactive compound of licorice, can modulate oxidative stress and metabolic processes in liver and skin. Given the critical role of oxidative stress and energy metabolism in exercise-induced fatigue, we hypothesized that 18β-GA could exert an ergogenic action by inhibiting excess reactive oxygen species (ROS) induction and promoting energy production in muscles. Mice were gavage-fed with 18β-GA for four consecutive days. Running ability was assessed based on the exhaustive treadmill test with high- and moderate-intensity. Western blot analysis, enzyme-linked immunosorbent assay, and immunofluorescence staining were used to measure the changes of muscle fatigue-related markers, oxidative stress status, and energy metabolism in response to 18β-GA exposure. Treatment with 18β-GA significantly increased the exhaustive running distance (~37%) in the high-intensity exercise, but not in the moderate-intensity exercise. Mechanistically, reduction of oxidative stress and induction of antioxidants (SOD, CAT, and GSH) by 18β-GA were observed. Moreover, 18β-GA treatment caused an improved preservation of muscle glycogen (12%), which was associated with upregulation of glucose transporter 4 (GLUT4) (91%) and increased insulin level (17%). The findings of the present study clearly suggest that 18β-GA holds excellent potential as a novel bioactive agent against high-intensity exercise-induced fatigue.

Effect of glycyrrhizic acid and 18β-glycyrrhetinic acid on the differentiation of human umbilical cord-mesenchymal stem cells into hepatocytes

BACKGROUND

End-stage liver disease is a global health complication with high prevalence and limited treatment options. Cell-based therapies using mesenchymal stem cells (MSCs) emerged as an alternative approach to support hepatic regeneration. In vitro preconditioning strategies have been employed to strengthen the regenerative and differentiation potential of MSCs towards hepatic lineage. Chemical compounds of the triterpene class; glycyrrhizic acid (GA) and 18β-glycyrrhetinic acid (GT) possess diverse therapeutic properties including hepato-protection and anti-fibrosis characteristics. They are capable of modulating several signaling pathways that are crucial in hepatic regeneration. Preconditioning with hepato-protective triterpenes may stimulate MSC fate transition towards hepatocytes.

AIM

To explore the effect of GA and GT on hepatic differentiation of human umbilical cord-MSCs (hUC-MSCs).

METHODS

hUC-MSCs were isolated and characterized phenotypically by flow cytometry and immunocytochemistry for the expression of MSC-associated surface molecules. Isolated cells were treated with GA, GT, and their combination for 24 h and then analyzed at three time points; day 7, 14, and 21. qRT-PCR was performed for the expression of hepatic genes. Expression of hepatic proteins was analyzed by immunocytochemistry at day 21. Periodic acid Schiff staining was performed to determine the functional ability of treated cells.

RESULTS

The fusiform-shaped morphology of MSCs in the treatment groups in comparison with the untreated control, eventually progressed towards the polygonal morphology of hepatocytes with the passage of time. The temporal transcriptional profile of preconditioned MSCs displayed significant expression of hepatic genes with increasing time of differentiation. Preconditioned cells showed positive expression of hepatocyte-specific proteins. The results were further corroborated by positive periodic acid Schiff staining, indicating the presence of glycogen in their cytoplasm. Moreover, bi-nucleated cells, which is the typical feature of hepatocytes, were also seen in the preconditioned cells.

CONCLUSION

Preconditioning with glycyrrhizic acid, 18β-glycyrrhetinic acid and their combination, successfully differentiates hUC-MSCs into hepatic-like cells. These MSCs may serve as a better therapeutic option for degenerative liver diseases in future.

Protective effect of 18β-glycyrrhetinic acid against H2O2-induced injury in Schwann cells based on network pharmacology and experimental validation

The aim of the present study was to assess the protective effects of 18β-GA against hydrogen peroxide (H₂O₂)-induced injury. First, the SMILES annotation for 18β-GA was used to search PubChem and for reverse molecular docking in Swiss Target Prediction, the Similarity Ensemble Approach Search Server and the TargetNet database to obtain potential targets. Injury-related molecules were obtained from the GeneCards database and the predicted targets of 18β-GA for injury treatment were selected by Wayne diagram analysis. Subsequently, Kyoto Encyclopedia of Genes and Genomes analysis was performed by WebGestalt. The experimental cells were assorted into control, model, 10 µM SB203580-treated, 5 µM 18β-GA-treated and 10 µM 18β-GA-treated groups. Hoechst 33258 staining was performed and intracellular reactive oxygen species (ROS) levels, cell apoptosis, Bcl-xl, Bcl-2, Bad, Bax, cleaved-caspase 3, cleaved-caspase 7, transient receptor potential ankyrin 1 (TRPA1) and transient receptor potential vanilloid 1 (TRPV1) levels, as well as p38 MAPK phosphorylation were measured. The ‘Inflammatory mediator regulation of TRP channels’ pathway was selected for experimental verification. The results indicated that 10 µM 18β-GA significantly increased cell viability as compared with the H₂O₂-treated model group. As suggested by the difference in intracellular ROS fluorescence intensity, 18β-GA inhibited H₂O₂-induced ROS production in Schwann cells. Hoechst 33258 staining indicated that 18β-GA reversed chromatin condensation and the increase in apoptotic nuclei following H₂O₂ treatment. Furthermore, flow cytometry suggested that 18β-GA substantially inhibited H₂O₂-induced apoptosis. Pre-treatment with 18β-GA obviously reduced Bad, Bax, cleaved-caspase3, cleaved-caspase 7, TRPA1 and TRPV1 levels and p38 MAPK phosphorylation after H₂O₂ treatment and increased Bcl-2 and Bcl-xl levels. In conclusion, 18β-GA inhibited Schwann cell injury and apoptosis induced by H₂O₂ and may be a potential drug to prevent peripheral nerve injury.

Development of sodium carboxymethyl cellulose based polymeric microparticles for in situ hydrogel wound dressing formation

18β-glycyrrhetinic acid (Gly), a natural compound obtained from licorice, is known both for the anti-inflammatory and antioxidant activities and for this reason useful for wound treatment. Due to its poor solubility, Gly is not suitable for formulations used in conventional topical products such as gels, foams and creams. Polymeric bioadhesive microparticles (MP), loaded with Gly, were developed to be introduced in the wound bed and swell, once in contact with the exudate, to form a hydrogel in situ able to close the wound. The MP were prepared by spray drying method from the polymeric solution of polysaccharide sodium carboxymethyl cellulose (CMC) and copolymer Soluplus® (SL). Soluplus® introduction in MP composition, using a 3:1 ratio (CMC/SL wt./wt.), allowed to stabilize Gly in non-crystalline form, favoring the improvement of water solubility, and to obtain a spherical with rugged surface MP morphology. Ex vivo studies showed these MP maintain high swelling capability and are able to form in situ a hydrogel for wound repair. The controlled release of Gly from the hydrogel stimulates keratinocyte growth, potentially supporting the physiological healing processes.

Synthesis and biological evaluation of pentacyclic triterpenoid derivatives as potential novel antibacterial agents

A series of ursolic acid (UA), oleanolic acid (OA) and 18β-glycyrrhetinic acid (GA) derivatives were synthesized by introducing a range of substituted aromatic side-chains at the C-2 position after the hydroxyl group at C-3 position was oxidized. Their antibacterial activities were evaluated in vitro against a panel of four Staphylococcus spp. The results revealed that the introduction of aromatic side-chains at the C-2 position of GA led to the discovery of potent triterpenoid derivatives for inhibition of both drug sensitive and resistant S. aureus, while the other two series derivatives of UA and OA showed no significant antibacterial activity even at high concentrations. In particular, GA derivative 33 showed good potency against all four Staphylococcus spp. (MIC = 1.25-5 μmol/L) with acceptable pharmacokinetics properties and low cytotoxicity in vitro. Molecular docking was also performed using S. aureus DNA gyrase to rationalize the observed antibacterial activity. This series of GA derivatives has strong potential for the development of a new type of triterpenoid antibacterial agent.

Grafting of 18β-Glycyrrhetinic Acid and Sialic Acid onto Chitosan to Produce a New Amphipathic Chitosan Derivative: Synthesis, Characterization, and Cytotoxicity

Chitosan is the only cationic polysaccharide found in nature. It has broad application prospects in biomaterials, but its application is limited due to its poor solubility in water. A novel chitosan derivative was synthesized by amidation of chitosan with 18β-glycyrrhetinic acid and sialic acid. The chitosan derivatives were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and measurement of the zeta potential. We also investigated the solubility, cytotoxicity, and blood compatibility of chitosan derivatives. 18β-glycyrrhetinic acid and sialic acid could be grafted onto chitosan molecular chains. The thermal stability of the synthesized chitosan derivatives was decreased and the surface was positively charged in water and phosphate-buffered saline. After chitosan had been modified by 18 β-glycyrrhetinic acid and sialic acid, the solubility of chitosan was improved greatly in water and phosphate-buffered saline, and percent hemolysis was <5%. Novel amphiphilic chitosan derivatives could be suitable polymers for biomedical purposes.

Synthesis and antitumor effects of novel 18β-glycyrrhetinic acid derivatives featuring an exocyclic α,β-unsaturated carbonyl moiety in ring A

A series of novel 18β-glycyrrhetinic acid (GA) derivatives featuring an exocyclic α,β-unsaturated carbonyl moiety in ring A were synthesized and evaluated for their antitumor activities. Compounds 5c and 5l showed stronger cytotoxicity than other compounds and reported GA analogue CDODA-Me (methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate). 5c and 5l induced apoptosis in cancer cells accompanying with c-Flip reduction and Noxa induction, associated with decreased HDAC3 expression and increased acetylation of H3. 5l displayed better stability properties than 5c and CDODA-Me in microsomes and plasma, 5l also showed favorable pharmacokinetic profiles and inhibited tumor growth in mice. Compound 5l represents a new type of GA derivatives with improved antitumor activity.

18β-Glycyrrhetinic acid acts through hepatocyte nuclear factor 4 alpha to modulate lipid and carbohydrate metabolism

Hepatocyte nuclear factor 4 alpha (HNF4α) regulates the expression of essential genes involved in very-low-density lipoprotein (VLDL) homeostasis and gluconeogenesis.　18β-glycyrrhetinic acid (GA) is an active ingredient of Glycyrrhiza uralensis an herbal medicine used for treating liver aliments. In this study, we established that GA functions as a partial antagonist of HNF4α through HNF4α-driven reporter luciferase assay and co-immunoprecipitation experiments with co-activator PGC1α. By virtual docking and site-directed mutagenesis analysis, we confirmed that serine 190 and arginine 235 of HNF4α are both essential for GA to exert its antagonistic action on HNF4α. Importantly, GA suppressed the expression of HNF4α target genes such as apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTP) and phospholipase A₂ G12B (PLA2G12B) modulating hepatic VLDL secretion in mice fed on a high fat diet. In addition, GA also suppressed gluconeogenesis and ameliorated glucose intolerance via down-regulating the expression of HNF4α target genes glucose-6-phosphatase (G6pc) and phosphoenolpyruvate carboxykinase (Pepck). Furthermore, GA significantly lowered blood glucose and improved insulin resistance in db/db mice. In all, we established that GA acts as a partial HNF4α antagonist modulating lipid and carbohydrate metabolism.

Efficient synthesis of piperazinyl amides of 18β-glycyrrhetinic acid

In the present study, a practical method to prepare piperazinyl amides of 18β-glycyrrhetinic acid was developed. Two main procedures for the construction of important intermediate 8 are discussed. One procedure involves the amidation of 1-Boc-piperazine with 3-acetyl-18β-glycyrrhetinic acid, prepared by the reaction of 18β-glycyrrhetinic acid with acetic anhydride without any solvent at 130 °C. The other procedure to prepare compound 8 involves the amidation of 18β-glycyrrhetinic acid followed by the esterification with acetic anhydride. Finally, compound 8 underwent N-Boc deprotection to prepare product 4. To ascertain the scope of the reaction, another C-3 ester derivative 17 was tested under the optimized reaction conditions. Furthermore, the reasons for the appearance of byproducts were elucidated. Crystallographic data of a selected piperazinyl amide is reported.

Transcriptional suppression of androgen receptor by 18β-glycyrrhetinic acid in LNCaP human prostate cancer cells

Androgen receptor (AR) plays a pivotal role as a target for amplification/mutation in pathogenesis and tumor progression in prostate, and thus, controlling AR activity or expression might be a feasible therapeutic approach for the treatment of prostate cancer. Here, we report the novel mechanisms by which 18β-glycyrrhetinic acid (GA) targets AR to stimulate cell death in both hormone-responsive and -refractory prostate cancer cells. We found that miR-488, a tumor suppressive microRNA, was markedly induced by GA treatment, resulting in the down-regulation of AR expression and inhibition of cellular responses mediated by androgens. Moreover, GA not only suppressed the expression of androgen target genes (TMPRSS2, PSA, and NKX3.1), but also enhanced the suppressive effect of anti-androgens (bicalutamide and flutamide) on LNCaP cell growth. Our data further provides evidence that down-regulation of AR expression by GA may occur through transcriptional suppression at AR promoter region between - 1014 and - 829. Ectopic expression of SFR and E2F3α reversed the inhibitory effect of GA on AR promoter activity as well as protein expression, suggesting that GA may target transcription factors SRF and E2F3α to regulate AR expression. Taken together, our study provides new insights on AR regulation and GA as a potential therapeutic candidate for human prostate cancer.

Reactivation of Atp4a concomitant with intragenic DNA demethylation for cancer inhibition in a gastric cancer model

Accumulating evidence suggests that aberrant DNA methylation and gene silencing of tumor suppressors are pervasive in gastric malignancies, supporting reactivation of tumor suppressors through DNA demethylation as a potential therapeutic opportunity. Atp4a is an important tumor suppressor gene, encoding H⁺, K⁺-ATPase, and mediating gastric acid secretion in the stomach. Using transgenic gastric cancer model K19-Wnt1/C2mE (Gan) mice, by combining the transcriptome and MeDIP (methylated DNA immunoprecipitation) sequencing, together with qRT-PCR, we showed that Atp4a was expressed at low levels in tumor tissues and multiple GC cells, while both 5-aza-CdR and 18β-glycyrrhetinic acid (GRA) pharmacological treatment triggered Atp4a activation with downregulation of DNMT1. In addition, CpG island (CGI) search showed that the CpG rich region is absent in the promoter region but present in exons 9-14 of Atp4a. Methylation specific PCR (MSP) indicated that Atp4a was fully or partly methylated in multiple GC cells. Further MassArray suggested that the demethylation in the CpG site 75, 183, 196, 262-268 might be responsible for the reactivation of Atp4a. Our research identified that GRA, a bioactive component found in abundance in Radix Glycyrrhiza, reactivated Atp4a expression and inhibited gastric tumorigenesis as a potential demethylation agent.

A 18β-glycyrrhetinic acid conjugate with Vorinostat degrades HDAC3 and HDAC6 with improved antitumor effects

Semisynthetic 18β-glycyrrhetinic acid (GA) analogues bearing 1-en-2-cyano-3-oxo substitution on ring A have enhanced antitumor effects with reduced levels of HDAC3 and HDAC6 proteins. Aiming to inhibit both HDAC protein and activity, we developed a hybrid molecule by tethering active GA analogue methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate (CDODA-Me) and Vorinostat (SAHA). We tested the proper hybrid approaches of GA with hydroxamic acid and turned out that GA conjugated with SAHA by a piperazine linker was the best. The conjugate (15) of CDODA-Me and SAHA linked through a piperazine group was a potent cytotoxic agent against cancer cells with apoptosis induction. Compound 15 was more effective than the simple combination of CDODA-Me and SAHA to induce apoptosis. Mechanistic studies revealed that 15 was less effective than SAHA to inhibit HDAC activity, but was more effective than CDODA-Me to decrease the levels of HDAC3 and HDAC6 proteins with upregulated levels of acetylated H3 and acetylated α-tubulin. Compound 15 represents a new HDAC3 and HDAC6 inhibitor by reducing protein levels.

Exploring New Structural Features of the 18β-Glycyrrhetinic Acid Scaffold for the Inhibition of Anaplastic Lymphoma Kinase

Novel 18β-glycyrrhetinic acid derivatives possessing a carbamate moiety and structurally similar ester derivatives were developed and evaluated for their efficacy as antitumor inhibitors. In the cellular assays, most of the N-substituted carbamate derivatives at the C3-position exhibited potent activities. The results of SAR investigation revealed that the introduction of the morpholine group at the C30-COOH led to a significant loss of the inhibitory potency. Among the ester derivatives, the ester group at C3-position also determined a noticeable reduction in the efficacy. Compound 3j exhibited the most prominent antiproliferative activity against six human cancer cells (A549, HT29, HepG2, MCF-7, PC-3, and Karpas299). Furthermore, compound 3j exerted a moderate inhibiting effect on the ALK. The results of molecular docking analyses suggested that it could bind well to the active site of the receptor ALK, which was consistent with the biological data. These results might inspire further structural optimization of 18β-glycyrrhetinic acid aiming at the development of potent antitumor agents. The structures 4d, 4g, 4h, 4j, and 4n were studied by X-ray crystallographic analyses.

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.

Protective Effects of 18β-Glycyrrhetinic Acid on Monocrotaline-Induced Pulmonary Arterial Hypertension in Rats

Pulmonary arterial hypertension (PAH) is a destructive and rare disorder characterized by a progressive increase in pulmonary artery pressure and vasoconstriction, ultimately leading to right ventricular failure and death. 18β-Glycyrrhetinic acid (18β-GA) is an active ingredient in the commonly used Chinese herbal medicine radix glycyrrhizae, and it possesses antioxidant, anti-inflammatory, anti-tumor, and other pharmacological properties. This study aimed to determine whether 18β-GA has protective effects against monocrotaline (MCT)-induced PAH and whether it is associated with oxidative stress. The PAH of rats was induced by MCT (60 mg/kg) and oral administration of 18β-GA (100, 50, or 25 mg/kg/day), sildenafil (30 mg/kg), or saline for 21 consecutive days. The development of PAH was evaluated by hemodynamic parameters and right ventricular hypertrophy index. Hematoxylin and eosin staining, Masson trichrome staining, and electron microscopy were used to determine the degree of vascular remodeling and proliferation in lung tissue. Moreover, the antioxidant capacity and malondialdehyde levels in the lungs were measured according to the instructions provided by the test kits, and the expression levels of nicotinamide adenine dinucleotide phosphate oxidase-2 (Nox2) and Nox4 were detected through Western blot analysis. Results of our study indicated that 18β-GA treatment significantly improved the hemodynamic and pathomorphological data of the rats, reduced the changes in oxidative stress biomarkers, and inhibited Nox2 and Nox4 expression. Our research indicated that 18β-GA has a protective effect against MCT-induced PAH by inhibiting oxidative stress in rats.

The beneficial effects of 18β-glycyrrhetinic acid on the experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mouse model

AIM

The aim of this study was to investigate the beneficial effects of 18β-glycyrrhetinic acid (GA) on the experimental allergic encephalomyelitis (EAE) in C57BL/6 mice. GA is a natural substance found in the root of licorice and is used in traditional Chinese medicine. It has many pharmacological activities such as antioxidant, anti-inflammatory, and anti-cancer effects.

MATERIALS AND METHODS

A total of 40 C57BL/6 mice were divided equally into four groups: (1) Control, (2) EAE, (3) GA and (4) GA + EAE. 14 days after induction of EAE with MOG35-55 and pertussis toxin, mice were treated with GA at doses of 100 mg/kg/day for 7 days intraperitoneally.

RESULTS

To our results, oxidative stress and lipid peroxidations (elevated TBARS levels, decreased GPx, SOD, CAT, and GSH levels) were significantly (p < .01) increased, causing EAE in brain tissue. Also, histopathological damage (Caspase-3 and IL-17 activity, p ≤ .01) and cytokine levels (TNF-α and IL-1β, p < .01) were induced with EAE in mice brain tissue. On the other hand, GA treatment significantly (p < .01) reversed oxidative histological and immunological alterations caused by EAE.

CONCLUSIONS

In conclusion, the GA treatment can protect the brain tissue against EAE in mice with its antioxidant and anti-inflammatory properties.

18β-Glycyrrhetinic Acid Inhibits Osteoclastogenesis In Vivo and In Vitro by Blocking RANKL-Mediated RANK-TRAF6 Interactions and NF-κB and MAPK Signaling Pathways

Bone metabolism is determined by a delicate balance between bone resorption by osteoclasts and bone formation by osteoblasts. The imbalance due to over-activated osteoclasts plays an important role in various diseases. Activation of NF-κB and MAPK signaling pathways by receptor activator of nuclear factor -κB ligand (RANKL) is vital for osteoclastogenesis. Here, we for the first time explored the effects of 18β-glycyrrhetinic acid (18β-GA), a pentacyclic triterpenoid found in the Glycyrrhiza glabra L roots, on RANKL-induced osteoclastogenesis, osteoclast functions and signaling pathways in vitro and in vivo. In bone marrow monocytes (BMMs) and RAW264.7 cells, 18β-GA inhibited osteoclastogenesis, decreased expression of TRAP, cathepsin K, CTR and MMP-9, blocked actin ring formation and compromised osteoclasts functions in a dose-dependent manner at an early stage with minimal effects on osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). For underlying molecular mechanisms, 18β-GA inhibited RANKL-induced phosphorylation of p65, p50, and IκB, blocked p65 nuclear translocation and decreased the DNA-binding activity of NF-κB. Besides, 18β-GA inhibited the activation of the MAPK pathways. Co-immunoprecipitation showed that 18β-GA treatment blocked RANK-TRAF6 association at an upstream site. In vivo, 18β-GA treatment inhibited ovariectomy-induced osteoclastogenesis and reduced bone loss in mice. Overall, our results demonstrated that 18β-GA inhibited RANKL-induced osteoclastogenesis by inhibiting RANK expression in preosteoclasts and blocking the binding of RANK and TRAF6 which lead to the inhibition of NF-κB and MAPK signaling pathways. 18β-GA is a promising novel candidate in the treatment of osteoclast-related diseases such as postmenopausal osteoporosis.

Comparative study of selective in vitro and in silico BACE1 inhibitory potential of glycyrrhizin together with its metabolites, 18α- and 18β-glycyrrhetinic acid, isolated from Hizikia fusiformis

Hizikia fusiformis (Harvey) Okamura is a brown seaweed widely used in Korea and Japan, and it contains different therapeutically active constituents. In the present study, we investigated the activities of glycyrrhizin isolated from H. fusiformis, including its metabolites, 18α- and 18β-glycyrrhetinic acid against Alzheimer's disease (AD) via acetyl and butyrylcholinesterase and β-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibition. Among these three compounds, 18β-glycyrrhetinic acid (IC₅₀ = 8.93 ± 0.69 µM) demonstrated two fold potent activity against BACE1 compared to the positive control, quercetin (IC₅₀ = 20.18 ± 0.79 µM). Additionally, glycyrrhizin with an IC₅₀ value of 20.12 ± 1.87 µM showed similarity to quercetin, while 18α-glycyrrhetinic acid showed moderate activity (IC₅₀ = 104.35 ± 2.84 µM). A kinetic study revealed that glycyrrhizin and 18β-glycyrrhetinic acid were non-competitive and competitive inhibitiors of BACE1, demonstrated via K _i values of 16.92 and 10.91 µM, respectively. Molecular docking simulation studies evidently revealed strong binding energy of these compounds for BACE1, indicating their high affinity and capacity for tighter binding to the active site of the enzyme. These data suggest that glycyrrhizin isolated from the edible seaweed, H. fusiformis and its metabolite, 18β-glycyrrhetinic acid demonstrated selective inhibitory activity against BACE1 to alleviate AD.

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.

18β-glycyrrhetinic acid suppresses gastric cancer by activation of miR-149-3p-Wnt-1 signaling

18β-glycyrrhetinic acid (GRA) exerts anti-tumor effects on various types of cancer. In the present study, we found that GRA attenuated the severity of gastritis and suppressed gastric tumorigenesis in transgenic mice. We also discovered that miR-149-3p was downregulated in gastric cancer tissues and cell lines as compared to normal gastric tissues and epithelial cells, but was upregulated by GRA. miR-149-3p expression also correlated negatively with lymphnode metastasis. Our functional assays showed that miR-149-3p overexpression inhibited cell proliferation and cell cycle progression while inducing apoptosis, while inhibition of miR-149-3p had the opposite effects. In addition, we identified Wnt-1 as a direct target of miR-149-3p. These data suggest that GRA inhibits the initiation and progression of gastric tumors by ameliorating the inflammatory microenvironment through downregulation of COX-2 expression and by inhibiting Wnt-1 expression through the upregulation of tumor suppressor miR-149-3p. GRA may thus have the potential to serve as a useful therapeutic agent for the prevention and treatment of gastric cancer.

Protective Effects of Glycyrrhizic Acid and 18β-Glycyrrhetinic Acid against Cisplatin-Induced Nephrotoxicity in BALB/c Mice

The clinical use of antineoplastic drug cisplatin (CP) is commonly complicated by nephrotoxic side effects that limit its application and therapeutic efficiency. This study used a model of CP-induced renal injury in male BALB/c mice to investigate the protective effects of the active components of licorice, glycyrrhizic acid (GA), and 18β-glycyrrhetinic acid (18βGA) against CP-induced nephrotoxicity, and the chemoprotectant, amifostine, was used as a control. Oral administration of GA or 18βGA significantly reduced CP-induced increases in the levels of blood urea nitrogen, creatinine, and lactate dehydrogenase. Hematoxylin and eosin staining revealed that GA and 18βGA delayed the progression of renal injury, including tubular necrosis, hyaline casts, and tubular degeneration in response to CP exposure. Oxidative status and inflammatory responses in CP-treated mice were restored to near-normal levels by treatment with GA or 18βGA. These protective effects might be associated with upregulation of nuclear factor E2-related protein (Nrf2) and downregulation of nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κB) in the kidney. Notably, we demonstrated that GA and 18βGA rendered renal cells resistant to CP-induced HMGB1 cytoplasmic translocation and release. These findings suggest that GA and 18βGA might be act as the chemoprotectants against CP-induced nephrotoxicity.

18β-glycyrrhetinic acid attenuates anandamide-induced adiposity and high-fat diet induced obesity

SCOPE

Previous reports suggest that licorice extract has various metabolically beneficial effects and may help to alleviate adiposity and hyperlipidemia. However, underlying anti-obesity mechanisms still remain elusive. Moreover, it is unknown which single ingredient in licorice extract would mediate such effects. We aimed to demonstrate that licorice extract and its active ingredients can inhibit adipocyte differentiation and fat accumulation.

METHODS AND RESULTS

18β-glycyrrhetinic acid (18β-GA) alleviated the effects of CB1R agonist, anandamide (AEA) on CB1R signaling in a concentration-dependent manner. Consistently, 18β-GA suppressed AEA-induced adipocyte differentiation in 3T3-L1 cells through the downregulation of AEA-induced MAPK activation and expression of adipogenic genes including C/EBP-α and PPAR-γ. The protein levels of fatty acid synthase and stearoyl-CoA desaturase 1 were also decreased and the phosphorylation of acetyl-CoA carboxylase was increased in 18β-GA pretreated cells. The supplementation of 18β-GA significantly lowered body weight, fat weight, and plasma lipids levels in obese animal models.

CONCLUSION

These results may provide a novel insight into the molecular mechanism involved in anti-adipogenic and anti-obesity effects of 18β-GA by suppressing the activation of CB1R induced by AEA. Thus, 18β-GA may exert beneficial effects against obesity-related metabolic disorders.

Bioactivity and potential health benefits of licorice

Licorice is an herbal plant named for its unique sweet flavor. It is widely used in the food and tobacco industries as a sweetener. Licorice is also used in traditional Chinese medicine (TCM) and complementary medicine. Because the use of licorice has long been a part of TCM, the details of its therapeutic applications have been thoroughly established. In modern science, licorice is of interest because of its broad range of applications. Extracts of and compounds isolated from licorice have been well studied and biologically characterized. In this review, we discuss the nutraceutical and functional activities of licorice as well as those of the extracts of and the isolated compounds from licorice, including agents with anti-inflammatory activity, cell-protective abilities, and chemopreventive effects. The side effects of licorice are also enumerated. A comparison of the activities of licorice described by modern science and TCM is also presented, revealing the correspondence of certain characteristics.

Pharmacological blockade of gap junctions induces repetitive surging of extracellular potassium within the locust CNS

The maintenance of cellular ion homeostasis is crucial for optimal neural function and thus it is of great importance to understand its regulation. Glial cells are extensively coupled by gap junctions forming a network that is suggested to serve as a spatial buffer for potassium (K(+)) ions. We have investigated the role of glial spatial buffering in the regulation of extracellular K(+) concentration ([K(+)]o) within the locust metathoracic ganglion by pharmacologically inhibiting gap junctions. Using K(+)-sensitive microelectrodes, we measured [K(+)]o near the ventilatory neuropile while simultaneously recording the ventilatory rhythm as a model of neural circuit function. We found that blockade of gap junctions with either carbenoxolone (CBX), 18β-glycyrrhetinic acid (18β-GA) or meclofenamic acid (MFA) reliably induced repetitive [K(+)]o surges and caused a progressive impairment in the ability to maintain baseline [K(+)]o levels throughout the treatment period. We also show that a low dose of CBX that did not induce surging activity increased the vulnerability of locust neural tissue to spreading depression (SD) induced by Na(+)/K(+)-ATPase inhibition with ouabain. CBX pre-treatment increased the number of SD events induced by ouabain and hindered the recovery of [K(+)]o back to baseline levels between events. Our results suggest that glial spatial buffering through gap junctions plays an essential role in the regulation of [K(+)]o under normal conditions and also contributes to a component of [K(+)]o clearance following physiologically elevated levels of [K(+)]o.

Gap junctions support the sustained phase of hypoxic pulmonary vasoconstriction by facilitating calcium sensitization

AIMS

To determine the role of gap junctions (GJs) in hypoxic pulmonary vasoconstriction (HPV).

METHODS AND RESULTS

Studies were performed in rat isolated intrapulmonary arteries (IPAs) mounted on a myograph and in anaesthetized rats. Hypoxia induced a biphasic HPV response in IPAs preconstricted with prostaglandin F2α (PGF2α, 3 µM) or 20 mM K⁺. The GJ inhibitors 18β-glycyrrhetinic acid (18β-GA, 30 µM), heptanol (3.5 mM), or 2-aminoethoxydiphenyl borate (2-APB) (75 µM) had little effect on the transient Phase 1 of HPV, but abolished the sustained Phase 2 which is associated with Ca²⁺ sensitization. The voltage-dependent Ca²⁺ channel blocker diltiazem (10 µM) had no effect on HPV, and did not alter the inhibitory action of 18β-GA. Sustained HPV is enhanced by high glucose (15 mM) via potentiation of Ca²⁺ sensitization, in the presence of high glucose 18β-GA still abolished sustained HPV. Simultaneous measurement of tension and intracellular Ca²⁺ using Fura PE-3 demonstrated that whilst 18β-GA abolished tension development during sustained HPV, it did not affect the elevation of intracellular Ca²⁺. Consistent with this, 18β-GA abolished hypoxia-induced phosphorylation of the Rho kinase target MYPT-1. In anaesthetized rats hypoxia caused a biphasic increase in systolic right ventricular pressure. Treatment with oral 18β-GA (25 mg/kg) abolished the sustained component of the hypoxic pressor response.

CONCLUSION

These results imply that GJs are critically involved in the signalling pathways leading to Rho kinase-dependent Ca²⁺ sensitization during sustained HPV, but not elevation of intracellular Ca²⁺, and may explain the dependence of the former on an intact endothelium.

Effect of 18beta-glycyrrhetinic acid on electromechanical coupling in the guinea-pig renal pelvis and ureter

We have tested the effect of the gap junction inhibitor, 18beta-glycyrrhetinic acid (18betaGA) on electromechanical coupling in the guinea-pig renal pelvis and ureter by the sucrose gap technique. In the ureter 18betaGA (3 - 30 microM) produced a concentration-dependent inhibition of the spike component of the action potential (AP) and reduced contraction evoked by electrical stimulation. Neurokinin A (NKA) produced a slow depolarization with superimposed APs and phasic contractions of the ureter. 18betaGA (30 microM) markedly inhibited the depolarization and APs evoked by NKA. However the contractile response was more sustained in the presence than in the absence of 18betaGA. At 100 microM, 18betaGA inhibited the mechanical responses to NKA. KCl (80 mM) produced APs and phasic contractions followed by sustained depolarization and tonic contraction. At 30 microM 18betaGA markedly inhibited the KCl-evoked APs and phasic contractions without affecting the sustained responses. At 100 microM 18betaGA inhibited the tonic contraction to KCl. In the renal pelvis 18betaGA (30 microM) inhibited the amplitude of pacemaker potentials and accompanying contractions and induced the appearance of low-amplitude APs not associated with contraction. We conclude that, up to 30 microM, the action of 18betaGA is consistent with an inhibition of cell-to-cell electrical coupling via gap junctions. The single-unit character of smooth muscles in the guinea-pig upper urinary tract is partly converted to a multi-unit pattern. At high concentrations 18betaGA possesses non specific effects which limit its usefulness as a tool for studying the role of gap junctions in smooth muscles. British Journal of Pharmacology (2000) 129, 163 - 169