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1.  Structure-Dependent Inhibition of Bladder and Pancreatic Cancer Cell Growth by 2-Substituted Glycyrrhetinic and Ursolic Acid Derivatives 
Derivatives of oleanolic acid, ursolic acid and glycyrrhetinic acid substituted with electron withdrawing groups at the 2-position in the A-ring which also contains a 1-en-3-one structure are potent inhibitors of cancer cell growth. In this study, we have compared the effects of several 2-substituted analogs of triterpenoid acid methyl esters derived from ursolic and glycyrrhetinic acid on proliferation of KU7 and 253JB-V bladder and Panc-1 and Panc-28 pancreatic cancer cells. The results show that the 2-cyano and 2-trifluoromethyl derivatives were the most active compounds. The glycyrrhetinic acid derivatives with the rearranged C-ring containing the 9(11)-en-12-one structure were generally more active than the corresponding 12-en-11-one isomers. However, differences in growth inhibitory IC50 values were highly variable and dependent on the 2- substitutent (CN vs. CF3) and cancer cell context.
PMCID: PMC2408873  PMID: 18359628
glycyrrhetinate analogs; growth inhibition; bladder cancer; pancreatic cancer
2.  Screening of gap junction antagonists on dye coupling in the rabbit retina 
Visual neuroscience  2007;24(4):609-618.
Many cell types in the retina are coupled via gap junctions and so there is a pressing need for a potent and reversible gap junction antagonist. We screened a series of potential gap junction antagonists by evaluating their effects on dye coupling in the network of A-type horizontal cells. We evaluated the following compounds: meclofenamic acid (MFA), mefloquine, 2-aminoethyldiphenyl borate (2-APB), 18-α-glycyrrhetinic acid, 18-β-glycyrrhetinic acid (18-β-GA), retinoic acid, flufenamic acid, niflumic acid, and carbenoxolone. The efficacy of each drug was determined by measuring the diffusion coefficient for Neurobiotin (Mills & Massey, 1998). MFA, 18-β-GA, 2-APB and mefloquine were the most effective antagonists, completely eliminating A-type horizontal cell coupling at a concentration of 200 μM. Niflumic acid, flufenamic acid, and carbenoxolone were less potent. Additionally, carbenoxolone was difficult to wash out and also may be harmful, as the retina became opaque and swollen. MFA, 18-β-GA, 2-APB and mefloquine also blocked coupling in B-type horizontal cells and AII amacrine cells. Because these cell types express different connexins, this suggests that the antagonists were relatively non-selective across several different types of gap junction. It should be emphasized that MFA was water-soluble and its effects on dye coupling were easily reversible. In contrast, the other gap junction antagonists, except carbenoxolone, required DMSO to make stock solutions and were difficult to wash out of the preparation at the doses required to block coupling in A-type HCs. The combination of potency, water solubility and reversibility suggest that MFA may be a useful compound to manipulate gap junction coupling.
PMCID: PMC2213422  PMID: 17711600
Horizontal cells; Retina; Gap junction antagonist
3.  18β-glycyrrhetinic acid inhibits rotavirus replication in culture 
Virology Journal  2012;9:96.
Glycyrrhizin (GA) and primary metabolite 18β-glycyrrhetinic acid (GRA) are pharmacologically active components of the medicinal licorice root, and both have been shown to have antiviral and immunomodulatory properties. Although these properties are well established, the mechanisms of action are not completely understood. In this study, GA and GRA were tested for the ability to inhibit rotavirus replication in cell culture, toward a long term goal of discovering natural compounds that may complement existing vaccines.
Epithelial cells were treated with GA or GRA various times pre- or post-infection and virus yields were measured by immunofluorescent focus assay. Levels of viral proteins VP2, VP6, and NSP2 in GRA treated cells were measured by immunoblot to determine if there was an effect of GRA treatment on the accumulation of viral protein.
GRA treatment reduced rotavirus yields by 99% when added to infected cultures post-- virus adsorption, whereas virus yields in GA treated cultures were similar to mock treated controls. Time of addition experiments indicated that GRA-mediated replication inhibition likely occurs at a step or steps subsequent to virus entry. The amounts of VP2, VP6 and NSP2 were substantially reduced when GRA was added to cultures up to two hours post-entry.
GRA, but not GA, has significant antiviral activity against rotavirus replication in vitro, and studies to determine whether GRA attenuates rotavirus replication in vivo are underway.
PMCID: PMC3478227  PMID: 22616823
Rotavirus; Licorice; 18beta-glycyrrhetinic acid; Antiviral
4.  Synthesis and Pro-Apoptotic Activity of Novel Glycyrrhetinic Acid Derivatives 
Chembiochem  2011;12(5):784-794.
Triterpenoids are used for medicinal purposes in many countries. Some, such as oleanolic and glycyrrhetinic acids, are known to be anti-inflammatory and anticarcinogenic. However, the biological activities of these naturally occurring molecules against their particular targets are weak, so the synthesis of new synthetic analogues with enhanced potency is needed. By combining modifications to both the A and C rings of 18βH-glycyrrhetinic acid, the novel synthetic derivative methyl 2-cyano-3,12-dioxo-18βH-olean-9(11),1(2)-dien-30-oate was obtained. This derivative displays high antiproliferative activity in cancer cells, including a cell line with a multidrug-resistance phenotype. It causes cell death by inducing the intrinsic caspase-dependent apoptotic pathway.
PMCID: PMC3085123  PMID: 21328513
antitumor agents; apoptosis; biological activity; glycyrrhetinic acid derivatives; medicinal chemistry
5.  Antitumor Agents 255. Novel Glycyrrhetinic Acid-Dehydrozingerone Conjugates as Cytotoxic Agents 
Bioorganic & medicinal chemistry  2007;15(18):6193-6199.
Esterification of glycyrrhetinic acid (GA) with dehydrozingerone (DZ) resulted in a novel cytotoxic GA-DZ conjugate. Based on this exciting finding, we conjugated eleven different DZ analogs with GA or other triterpenoids, including oleanoic acid (OA) or ursolic acid (UA). In an in vitro anticancer assay using nine different human tumor cell lines, most of the GA-DZ conjugates showed significant potency. Particularly, compounds 5, 29, and 30 showed significant cytotoxic effects against LN-Cap, 1A9, and KB cells with ED50 values of 0.6, 0.8, and 0.9 μM, respectively. Similar conjugates between DZ and OA or UA were inactive suggesting that the GA component is critical for activity. Notably, although GA-DZ conjugates showed potent cytotoxic activity, the individual components (GA and DZ analogs) were inactive. Thus, GA-DZ conjugates are new chemical entities and represent interesting hits for anticancer drug discovery and development.
PMCID: PMC2034305  PMID: 17591444
Glycyrrhetinic acid; Dehydrozingerone; Conjugation; Cytotoxicity
6.  Induction of apoptosis with mitochondrial membrane depolarization by a glycyrrhetinic acid derivative in human leukemia K562 cells 
Cytotechnology  2012;64(4):421-428.
Glycyrrhetinic acid (GA) is the active compound in Glycyrrhizae radix, a famous traditional Chinese medicine. Recently the anticancer activity of GA became the focus of scientific interest and many GA derivatives were developed as anti-tumor lead compounds. We previously reported that AEGA, a GA derivative, has proliferation inhibition and apoptosis-inducing activity in various human tumor cells. The present study was undertaken to further investigate the molecular mechanisms involved in AEGA-induced apoptosis in human leukemia K562 cells. AEGA can inhibit the growth of K562 cells in dose- and time-dependent manners determined by the MTT assay. Induction of apoptosis was evidenced by morphological changes and biochemical markers such as cell shrinkage, chromatin condensation and DNA ladder formation. Further mechanistic analysis revealed that AEGA induced apoptosis through the collapse of mitochondrial membrane potential, the accumulation of the cytosolic cytochrome c and the activation of caspase-9 and caspase-3. The apoptosis induction by AEGA was associated with the alteration in the ratio of Bcl-2/Bax protein expression. These results suggest that AEGA may induce apoptosis through a mitochondria-mediated pathway, and might have the therapeutic value against hematological malignancies.
PMCID: PMC3397113  PMID: 22274625
AEGA; Glycyrrhetinic acid derivative; Apoptosis; Mitochondrial membrane potential; Bcl-2/Bax; Human leukemic cells
7.  Chemical modifications of natural triterpenes - glycyrrhetinic and boswellic acids: evaluation of their biological activity 
Tetrahedron  2008;64(51):11541-11548.
Synthetic analogues of naturally occurring triterpenoids; glycyrrhetinic acid, arjunolic acid and boswellic acids, by modification of A-ring with a cyano- and enone- functionalities, have been reported. A novel method of synthesis of α-cyanoenones from isoxazoles is reported. Bio-assays using primary mouse macrophages and tumor cell lines indicate potent anti-inflammatory and cytotoxic activities associated with cyanoenones of boswellic acid and glycyrrhetinic acid.
PMCID: PMC2900779  PMID: 20622928
8.  Unifying Mechanisms of Action of the Anticancer Activities of Triterpenoids and Synthetic Analogs 
Triterpenoids such as betulinic acid (BA) and synthetic analogs of oleanolic acid [2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO)] and glycyrrhetinic acid [2-cyano-3,11-dioxo-18β-oleana-1,12-dien-30-oc acid (CDODA)] are potent anticancer agents that exhibit antiproliferative, antiangiogenic, anti-inflammatory and pro-apoptotic activities. Although their effects on multiple pathways have been reported, unifying mechanisms of action have not been reported. Studies in this laboratory have now demonstrated that several triterpenoids including BA and some derivatives, celastrol, methyl ursolatee, β-boswellic acid derivatives, and the synthetic analogs CDDO, CDODA and their esters decreased expression of specificity protein (Sp) transcription factors and several pro-oncogenic Sp-regulated genes in multiple cancer cell lines. The mechanisms of this response are both compound- and cell context-dependent and include activation of both proteasome-dependent and -independent pathways. Triterpenoid-mediated induction of reactive oxygen species (ROS) has now been characterized as an important proteasome-independent pathway for downregulation of Sp transcription factors. ROS decreases expression of microRNA-27a (miR-27a) and miR-20a/miR-17-5p and this results in the induction of the transcriptional “Sp-repressors” ZBTB10 and ZBTB4, respectively, which in turn downregulate Sp and Sp-regulated genes. Triterpenoids also activate or deactive nuclear receptors and G-protein coupled receptors, and these pathways contribute to their antitumorigenic activity and may also play a role in targeting Sp1, Sp3 and Sp4 which are highly overexpressed in multiple cancers and appear to be important for maintaining the cancer phenotype.
PMCID: PMC3532564  PMID: 22583404
Sp transcription factors; downregulation; reactive oxygen species
9.  (3β,18β,20β)-N-Eth­oxy­carbonyl­methyl-3-nitrato-11-oxoolean-12-ene-29-carboxamide methanol monosolvate 
The title compound, C34H52N2O7·CH4O, is the methanol solvate of a difunctionalized derivative of the therapeutic agent 18β-glycyrrhetinic acid, a penta­cyclic triterpene. The five six-membered rings of the glycyrrhetinic acid moiety show normal geometries, with four rings in chair conformations and the unsaturated ring in a half-chair conformation. This moiety is substituted by a nitrate ester group and an O-ethyl­glycine group. In the crystal, the nonsolvent mol­ecules are packed parallel to (010) in a herringbone fashion with the nitrato, ethyl­glycine and methanol-O atom being proximate. The methanol solvent mol­ecule is anchored via a donated O—H⋯Oac­yl and an accepted N—H⋯O hydrogen bond, giving rise to infinite zigzag chains of hydrogen bonds parallel to [100]. Two weak intermolecular C—H⋯O interactions to the methanol and to an acyl oxygen establish links along [100] and [010], respectively.
PMCID: PMC3344161  PMID: 22606164
10.  Inhibitory Effects of Glycyrrhetinic Acid on DNA Polymerase and Inflammatory Activities 
We investigated the inhibitory effect of three glycyrrhizin derivatives, such as Glycyrrhizin (compound 1), dipotassium glycyrrhizate (compound 2) and glycyrrhetinic acid (compound 3), on the activity of mammalian pols. Among these derivatives, compound 3 was the strongest inhibitor of mammalian pols α, β, κ, and λ, which belong to the B, A, Y, and X families of pols, respectively, whereas compounds 1 and 2 showed moderate inhibition. Among the these derivatives tested, compound 3 displayed strongest suppression of the production of tumor necrosis factor-α (TNF-α) induced by lipopolysaccharide (LPS) in a cell-culture system using mouse macrophages RAW264.7 and peritoneal macrophages derived from mice. Moreover, compound 3 was found to inhibit the action of nuclear factor-κB (NF-κB) in engineered human embryonic kidney (HEK) 293 cells. In addition, compound 3 caused greater reduction of 12-O-tetradecanoylphorbol-13-acetate-(TPA-) induced acute inflammation in mouse ear than compounds 1 and 2. In conclusion, this study has identified compound 3, which is the aglycone of compounds 1 and 2, as a promising anti-inflammatory candidate based on mammalian pol inhibition.
PMCID: PMC3138047  PMID: 21785649
11.  Natural products that reduce rotavirus infectivity identified by a cell-based moderate-throughput screening assay 
Virology Journal  2006;3:68.
There is widespread interest in the use of innate immune modulators as a defense strategy against infectious pathogens. Using rotavirus as a model system, we developed a cell-based, moderate-throughput screening (MTS) assay to identify compounds that reduce rotavirus infectivity in vitro, toward a long-term goal of discovering immunomodulatory agents that enhance innate responses to viral infection.
A natural product library consisting of 280 compounds was screened in the assay and 15 compounds that significantly reduced infectivity without cytotoxicity were identified. Time course analysis of four compounds with previously characterized effects on inflammatory gene expression inhibited replication with pre-treatment times as minimal as 2 hours. Two of these four compounds, α-mangostin and 18-β-glycyrrhetinic acid, activated NFκB and induced IL-8 secretion. The assay is adaptable to other virus systems, and amenable to full automation and adaptation to a high-throughput format.
Identification of several compounds with known effects on inflammatory and antiviral gene expression that confer resistance to rotavirus infection in vitro suggests the assay is an appropriate platform for discovery of compounds with potential to amplify innate antiviral responses.
PMCID: PMC1564392  PMID: 16948846
12.  Antitumor Agents. 256. Conjugation of Paclitaxel with Other Antitumor Agents: Evaluation of Novel Conjugates as Cytotoxic Agents 
Fifteen different taxoid conjugates were prepared by linking various anticancer compounds, including camptothecin (CPT), epipodophyllotoxin (EP), colchicine (COL), and glycyrrhetinic acid (GA), at the 2’- or 7-position on paclitaxel (TXL, 1) through an ester, imine, amine, or amide bond. Newly synthesized conjugates were evaluated for cytotoxic activity against replication of several human tumor cell lines. Among them, TXL-CPT conjugates, 8–10, were more potent than TXL itself against the human prostate carcinoma cell line PC-3 (ED50 = 14.8, 3.1, 19.4 nM compared with 55.5 nM), and conjugate 10 was also eightfold more active than TXL against the LN-CAP prostate cancer cell line. These compounds also possessed anti-angiogenesis ability as well as lower inhibitory effects against a normal cell line (MRC-5). Thus, conjugates 8–10 are possible antitumor drug candidates, particularly for prostate cancer.
PMCID: PMC1955431  PMID: 17350834
Paclitaxel; Conjugation; Cytotoxity; Prostate cancer
Molecular carcinogenesis  2011;50(9):655-667.
Methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate (CDODA-Me) and the corresponding 2-trifluoromethyl analog (CF3DODA-Me) are derived synthetically from the triterpenoid glycyrrhetinic acid, a major component of licorice. CDODA-Me and CF3DODA-Me inhibited growth of highly invasive ARO, DRO, K-18 and HTh-74 thyroid cancer cells and this was due, in part, to decreased expression of specificity protein (Sp) transcription factors Sp1, Sp3 and Sp4 that are overexpressed in these cells. CDODA-Me and CF3DODA-Me also decreased expression of Sp-dependent genes, such as survivin and vascular endothelial growth factor, and induced apoptosis. In addition, pituitary tumor-transforming gene-1 (PTTG-1) protein and mRNA levels were also decreased in thyroid cancer cells treated with CDODA-Me or CF3DODA-Me and this was accompanied by decreased expression of PTTG-1-dependent c-Myc and fibroblast growth factor 2 genes. RNA interference studies against Sp1, Sp3 and Sp4 proteins showed that in thyroid cancer cells, PTTG-1 was an Sp-dependent gene. This study demonstrates for the first time that drugs, such as CDODA-Me and CF3DODA-Me, that decrease Sp protein expression also downregulate PTTG-1 in thyroid cancer cells and therefore have potential for clinical treatment of thyroid cancer and other endocrine neoplasias where PTTG-1 is a major pro-oncogenic factor.
PMCID: PMC3128656  PMID: 21268135
PTTG-1; Sp proteins; thyroid cancer; anticancer agents
Many of the traditional herbal formulations contain extracts of Piper longum and Glycyrrhiza glabra, piperine and glycyrrhetinic acid respectively, being active constituents of these two herbs. An attempt has been made to develop a simple, precise, rapid, and cost-effective high-performance thin-layer chromatographic (HPTLC) method for simultaneous estimation of these in a herbomineral formulation (Efiplus® Capsules). Precoated silica gel 60 F254 plates with toluene-ethyl acetate-glacial acetic acid 12.5:7.5:0.5, as mobile phase were used in chromatographic determinations. The plates were scanned and the compounds were quantified at their wavelengths of maximum absorption of 260 and 331 nm for glycyrrhetinic acid and piperine respectively. The respective RF, values of glycyrrhetinic acid and piperine were 0.51 and 0.55. Under these experimental conditions linearity was observed between 0.8-2.6 μg/ spot for glycyrrhetinic acid and between 10-50 ng/ spot for piperine and average recovery was 96.25% for glycyrrhetinic acid and 98.55% for piperine.
PMCID: PMC3255427  PMID: 22247845
HPTLC; glycyrrhetinic acid; piperine; herbomineral formulation
15.  Synthesis and proteasome inhibition of lithocholic acid derivatives 
A new class of proteasome inhibitors was synthesized using lithocholic acid as a scaffold. Modification at the C-3 position of lithocholic acid with a series of acid acyl groups yielded compounds with a range of potency on proteasome inhibition. Among them, the phenylene diacetic acid hemiester derivative (13) displayed the most potent proteasome inhibition with IC50 = 1.9 μM. Enzyme kinetic analysis indicates that these lithocholic acid derivatives are non-competitive inhibitors of the proteasome.
PMCID: PMC3072167  PMID: 21388808
Lithocholic acid; proteasome; proteasome inhibitor
16.  Propargylaminyl 3α-hy­droxy-11-oxo-18β-olean-12-en-29-oate 
The title compound, C33H49NO3, is the propargyl­amide of 18β-glycyrrhetinic acid, a penta­cyclic triterpenoid of inter­est as a therapeutic agent. The five six-membered rings of the glycyrrhetinic acid moiety show normal geometries, with four rings in chair conformations and the unsaturated ring C in a half-chair conformation. In the crystal, the terminal N-propargylcarboxamide group has remarkable structural effects on weak hydrogen-bond-like inter­actions. Particularly noteworthy are an inter­molecular O—H⋯π inter­action accepted side-on by the terminal alkyne group [O⋯C = 3.097 (2) and 3.356 (2) Å] and a short inter­molecular C—H⋯O inter­action [C⋯O = 3.115 (2) Å] donated by the alkyne C—H group. An N—H⋯O [N⋯O = 3.251 (2) Å] and a Calkyl—H⋯O [C⋯O = 3.254 (2) Å] interaction complement the crystal structure.
PMCID: PMC3247445  PMID: 22220063
17.  The Sleep-inducing Lipid Oleamide Deconvolutes Gap Junction Communication and Calcium Wave Transmission in Glial Cells  
The Journal of Cell Biology  1997;139(7):1785-1792.
Oleamide is a sleep-inducing lipid originally isolated from the cerebrospinal fluid of sleep-deprived cats. Oleamide was found to potently and selectively inactivate gap junction–mediated communication between rat glial cells. In contrast, oleamide had no effect on mechanically stimulated calcium wave transmission in this same cell type. Other chemical compounds traditionally used as inhibitors of gap junctional communication, like heptanol and 18β-glycyrrhetinic acid, blocked not only gap junctional communication but also intercellular calcium signaling. Given the central role for intercellular small molecule and electrical signaling in central nervous system function, oleamide- induced inactivation of glial cell gap junction channels may serve to regulate communication between brain cells, and in doing so, may influence higher order neuronal events like sleep induction.
PMCID: PMC2132638  PMID: 9412472
18.  Oncogenic MicroRNA-27a Is A Target For Anticancer Agent Methyl 2-Cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate in Colon Cancer Cells 
Methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate (CDODA-Me) is a synthetic derivative of glycyrrhetinic acid, a triterpenoid phytochemical found in licorice extracts. CDODA-Me inhibited growth of RKO and SW480 colon cancer cells and this was accompanied by decreased expression of Sp1, Sp3 and Sp4 protein and mRNA and several Sp-dependent genes including survivin, vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1 or Flt-1). CDODA-Me also induced apoptosis, arrested RKO and SW480 cells at G2/M, and inhibited tumor growth in athymic nude mice bearing RKO cells as xenografts. CDODA-Me decreased expression of microRNA-27a (miR-27a), and this was accompanied by increased expression of two miR-27a-regulated mRNAs, namely ZBTB10 (an Sp repressor) and Myt-1 which catalyzes phosphorylation of cdc2 to inhibit progression of cells through G2/M. Both CDODA-Me and antisense miR-27a induced comparable responses in RKO and SW480 cells, suggesting that the potent anticarcinogenic activity of CDODA-Me is due to repression of oncogenic miR-27a.
PMCID: PMC2766353  PMID: 19582879
CDODA-Me; anticarcinogenicity; miR-27a; colon cancer; cell cycle
19.  Induction of Apoptosis and Nonsteroidal Antiinflammatory Drug-Activated Gene 1 in Pancreatic Cancer Cells By A Glycyrrhetinic Acid Derivative 
Molecular carcinogenesis  2009;48(8):692-702.
Methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate (CDODA-Me) is a synthetic triterpenoid derived from glycyrrhetinic acid, a bioactive phytochemical in licorice, CDODA-Me inhibits growth of Panc1 and Panc28 pancreatic cancer cell lines and activates peroxisome proliferator-activated receptor γ (PPARγ)-dependent transactivation in these cells. CDODA-Me also induced p21 and p27 protein expression and downregulates cyclin D1; however, these responses were receptor-independent. CDODA-Me induced apoptosis in Panc1 and Panc28 cells, and this was accompanied by receptor-independent induction of the proapoptotic proteins early growth response-1 (Egr-1), nonsteroidal anti-inflammatory drug-activated gene-1 (NAG-1), and activating transcription factor-3 (ATF3). Induction of NAG-1 and Egr-1 by CDODA-Me was dependent on activation of phosphatidylinositol-3-kinase (PI3-K) and/or p42 and p38 mitogen-activated protein kinase (MAPK) pathways but there were differences between Panc28 and Panc1 cells. Induction of NAG-1 in Panc28 cells was p38-MAPK- and PI3-K-dependent but Egr-1-independent, whereas induction in Panc1 cells was associated with activation of p38-MAPK, PI3-K and p42-MAPK and was only partially Egr-1-dependent. This is the first report of the induction of the proapoptotic protein NAG-1 in pancreatic cancer cells.
PMCID: PMC2746008  PMID: 19125423
CDODA-Me; pancreatic cancer; apoptosis
20.  18beta-Glycyrrhetinic Acid Inhibits Periodontitis Via Glucocorticoid-Independent NF–κB Inactivation In IL-10 Deficient Mice 
Journal of periodontal research  2010;45(6):757-763.
Background and objective
18beta-glycyrrhetinic acid (GA) is a natural anti-inflammatory compound derived from licorice root extract (Glycyrrhiza glabra). The effect of GA on experimental periodontitis and its mechanism of action were determined in the present study.
Periodontitis was induced by oral infection with Porphyromonas gingivalis W83 in IL-10 deficient mice. The effect of GA, which was delivered by subcutaneous injections in either prophylactic or therapeutic regimens, on alveolar bone loss and gingival gene expressions was determined on day 42 after initial infection. The effect of GA on LPS-stimulated macrophages, T cell proliferation, and osteoclastogenesis was also examined in vitro.
GA administered either prophylactically or therapeutically dramatically reduced infection-induced bone loss in IL-10 deficient mice, which are highly disease-susceptible. Although GA has been reported to exert its anti-inflammatory activity via down-regulation of 11-beta hydroxysteroid dehydrogenase-2 (HSD2), which converts active glucocorticoids (GC) to their inactive forms, GA did not reduce HSD2 gene expression in gingival tissue. Rather, under GC-free conditions, GA potently inhibited LPS-stimulated proinflammatory cytokine production and RANKL-stimulated osteoclastogenesis, both of which are NF–κB-dependent. GA furthermore suppressed LPS- and RANKL-stimulated phosphorylation of NF–κB p105 in vitro.
These findings indicate that GA inhibits periodontitis by inactivation of NF–κB in an IL-10 and GC-independent fashion.
PMCID: PMC3075584  PMID: 20682015
18beta-glycyrrhetinic acid; periodontal disease; NF–κB; IL-10 deficient mouse
21.  Glycyrrhizin Attenuates MPTP Neurotoxicity in Mouse and MPP+-Induced Cell Death in PC12 Cells 
The present study examined the inhibitory effect of licorice compounds glycyrrhizin and a metabolite 18β-glycyrrhetinic acid on the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the mouse and on the 1-methyl-4-phenylpyridinium (MPP+)-induced cell death in differentiated PC12 cells. MPTP treatment increased the activities of total superoxide dismutase, catalase and glutathione peroxidase and the levels of malondialdehyde and carbonyls in the brain compared to control mouse brain. Co-administration of glycyrrhizin (16.8 mg/kg) attenuated the MPTP effect on the enzyme activities and formation of tissue peroxidation products. In vitro assay, licorice compounds attenuated the MPP+-induced cell death and caspase-3 activation in PC12 cells. Glycyrrhizin up to 100µM significantly attenuated the toxicity of MPP+. Meanwhile, 18β-glycyrrhetinic acid showed a maximum inhibitory effect at 10µM; beyond this concentration the inhibitory effect declined. Glycyrrhizin and 18β-glycyrrhetinic acid attenuated the hydrogen peroxide- or nitrogen species-induced cell death. Results from this study indicate that glycyrrhizin may attenuate brain tissue damage in mice treated with MPTP through inhibitory effect on oxidative tissue damage. Glycyrrhizin and 18β-glycyrrhetinic acid may reduce the MPP+ toxicity in PC12 cells by suppressing caspase-3 activation. The effect seems to be ascribed to the antioxidant effect.
PMCID: PMC2817536  PMID: 20157396
Glycyrrhizin; MPTP; MPP+; Brain tissue damage; Cell death; Inhibitory effect
22.  (+)-Methyl 3β-acet­oxy-13-carb­oxy-19-hy­droxy-11-oxo-C-norolean-18-en-30-oate γ-lactone 
The title compound, C33H46O7, is an unusual oxydation product of the therapeutic agent glycyrrhetinic acid that has, in comparison to the latter, a distinctly altered triterpene structure with one five- and four six-membered carbocycles complemented by a γ-lactone ring with a spiro-junction and a ring double bond. The junction between the five-membered ring C, a cyclo­penta­none ring, and the six-membered ring D, previously in question, was found to be cis, confirming earlier structure assignments based solely on chemical transformations. In the solid state, the compound exhibits five intra- and four inter­molecular C—H⋯O inter­actions with H⋯O distances less than or equal to 2.70 Å and C—H⋯O greater than 100°.
PMCID: PMC2983216  PMID: 21587575
23.  The Role of Gap Junction Communication and Oxidative Stress in the Propagation of Toxic Effects among High-Dose α-Particle-Irradiated Human Cells 
Radiation research  2011;175(3):347-357.
We investigated the roles of gap junction communication and oxidative stress in modulating potentially lethal damage repair in human fibroblast cultures exposed to doses of α particles or γ rays that targeted all cells in the cultures. As expected, α particles were more effective than γ rays at inducing cell killing; further, holding γ-irradiated cells in the confluent state for several hours after irradiation promoted increased survival and decreased chromosomal damage. However, maintaining α-particle-irradiated cells in the confluent state for various times prior to subculture resulted in increased rather than decreased lethality and was associated with persistent DNA damage and increased protein oxidation and lipid peroxidation. Inhibiting gap junction communication with 18-α-glycyrrhetinic acid or by knockdown of connexin43, a constitutive protein of junctional channels in these cells, protected against the toxic effects in α-particle-irradiated cell cultures during confluent holding. Upregulation of antioxidant defense by ectopic overexpression of glutathione peroxidase protected against cell killing by α particles when cells were analyzed shortly after exposure. However, it did not attenuate the decrease in survival during confluent holding. Together, these findings indicate that the damaging effect of α particles results in oxidative stress, and the toxic effects in the hours after irradiation are amplified by intercellular communication, but the communicated molecule(s) is unlikely to be a substrate of glutathione peroxidase.
PMCID: PMC3139025  PMID: 21388278
24.  Interaction of Natural Dietary and Herbal Anionic Compounds and Flavonoids with Human Organic Anion Transporters 1 (SLC22A6), 3 (SLC22A8), and 4 (SLC22A11) 
Active components of complementary/alternative medicines and natural supplements are often anionic compounds and flavonoids. As such, organic anion transporters (OATs) may play a key role in their pharmacokinetic and pharmacological profiles, and represent sites for adverse drug-drug interactions. Therefore, we assessed the inhibitory effects of nine natural products, including flavonoids (catechin and epicatechin), chlorogenic acids (1,3- and 1,5-dicaffeoylquinic acid), phenolic acids (ginkgolic acids (13 : 0), (15 : 1), and (17 : 1)), and the organic acids ursolic acid and 18β-glycyrrhetinic acid, on the transport activity of the human OATs, hOAT1 (SLC22A6), hOAT3 (SLC22A8), and hOAT4 (SLC22A11). Four compounds, 1,3- and 1,5-dicaffeoylquinic acid, ginkgolic acid (17 : 1), and 18β-glycyrrhetinic acid, significantly inhibited hOAT1-mediated transport (50 μM inhibitor versus 1 μM substrate). Five compounds, 1,3- and 1,5-dicaffeoylquinic acid, ginkgolic acids (15 : 1) and (17 : 1), and epicatechin, significantly inhibited hOAT3 transport under similar conditions. Only catechin inhibited hOAT4. Dose-dependency studies were conducted for 1,3-dicaffeoylquinic acid and 18β-glycyrrhetinic acid on hOAT1, and IC50 values were estimated as 1.2 ± 0.4 μM and 2.7 ± 0.2 μM, respectively. These data suggest that 1,3-dicaffeoylquinic acid and 18β-glycyrrhetinic acid may cause significant hOAT1-mediated DDIs in vivo; potential should be considered for safety issues during use and in future drug development.
PMCID: PMC3618943  PMID: 23573138
25.  Inhibition of peptic activity by carbenoxolone and glycyrrhetinic acid 
Gut  1970;11(4):344-351.
Carbenoxolone (Biogastrone, Berk) has been shown to reduce the peptic activity and total acidity of gastric juice obtained from anaesthetized pylorus-ligated rats without affecting significantly the volume of gastric juice secreted or the K+ concentration. Glycyrrhetinic acid was less potent in reducing peptic activity and caused no reduction in total acidity.
Antipeptic activity of carbenoxolone has also been demonstrated in vitro using the pepsin plate technique and the haemoglobin pepsin assay.
It is suggested that these actions of carbenoxolone may contribute to the increased rate of healing of peptic ulcer in patients treated with the drug.
PMCID: PMC1411413  PMID: 4913800

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