Licorice-derived Compounds Research Articles

Molecular docking analysis of acetylcholinesterase inhibitors for Alzheimer's disease management.

Alzheimer's disease (AD) is a neurological disease that is related to aging and is the leading cause of dementia globally. AD has a significant influence on cognitive functions, particularly memory, resulting in a variety of functional deficits. Given the increasing prevalence of AD, there is an urgent need for the development of effective therapeutic therapies. In a quest to uncover a holistic remedy for AD, a total of 41 bioactive compounds derived from three distinct medicinal plant sources were screened to evaluate their potential to inhibit the active sites of acetylcholinesterase (AChE). The insilico screening protocol included 24 licorice-derived compounds, 5 ginkgo biloba-derived compounds, and 11 ginseng-derived compounds. Two compounds (Ginkgolide A and Licorice glycoside D2) were observed to display greater binding energy (BE) relative to the control by interacting with crucial residues in the active site of AChE. Ginkgolide A and Licorice glycoside D2 exhibited BEs of -11.3 and -11.2 kcal/mol, respectively, whereas the control, Donepezil, demonstrated a BE of -10.8 kcal/mol. Further, these compounds exhibit favorable drug-likeness properties. This study suggests that further experimental investigations can be conducted on Ginkgolide A and Licorice glycoside D2 to explore their potential therapeutic applications for AD.

Isoangustone A induces autophagic cell death in colorectal cancer cells by activating AMPK signaling

Phytochemicals, especially flavonoids, have been widely investigated for their diversified pharmacological activities including anticancer activities. Previously we identified isoangustone A from licorice-derived compounds as a potent inducer of cell death. In the present study, the exact mechanism by which isoangustone A induced cell death was further investigated, with autophagy as an indispensible part of this process. Isoangustone A treatment activated autophagic signaling and induced a complete autophagic flux in colorectal cancer cells. Knockdown of ATG5 or pre-treatment with autophagy inhibitors significantly reversed isoangustone A-induced apoptotic signaling and loss of cell viability, suggesting autophagy plays an important role in isoangustone A-induced cell death. Isoangustone A inhibited Akt/mTOR signaling, and overexpressing of a constitutively activated Akt mildly suppressed isoangustone A-induced cell death. More importantly, isoangustone A inhibited cellular ATP level and activated AMPK, and pre-treatment with AMPK inhibitor or overexpression of dominant negative AMPKα2 significantly reversed isoangustone A-induced autophagy and cell death. Further study shows isoangustone A dose-dependently inhibited mitochondrial respiration, which could be responsible for isoangustone A-induced activation of AMPK. Finally, isoangustone A at a dosage of 10 mg/kg potently activated AMPK and autophagic signaling in and inhibited the growth of SW480 human colorectal xenograft in vivo. Taken together, induction of autophagy through activation of AMPK is an important mechanism by which isoangustone A inhibits tumor growth, and isoangustone A deserves further investigation as a promising anti-cancer agent.

Abstract 2603: Discovery of chemopreventive agents from licorice (Glycyrrhiza Uralensis)

Abstract Traditional Chinese Medicine (TCM) provides a rich resource of potential chemoprevention agents; however, the complexity arise from its multi-components and multi-targets nature hindered in-depth investigations and translations. Licorice is one of the most commonly utilized TCM herbal medicine which possesses many pharmacological activities including cancer prevention. We isolated over 120 licorice-derived compounds and systemically screened these compounds using cellular and molecular models including cytotoxicity, nitric oxide production, NF-κB and ARE luciferase reporters, and other models. Isoangustone A (IAA) is an isoprenyled isoflavonoid which has been reported to induce apoptosis and cell cycle arrest in prostate cancer cells, and it was identified as a NF-κB inhibitor in our assays. IAA significantly inhibited NF-κB signaling in SW480 colorectal adenocarcinoma cells, and decreased the expression of Cox-2 and iNOS. Overexpression of constitutively activated IKKβ potently stimulated NF-κB signaling and reversed IAA-mediated inhibition. Oral administration of IAA significantly inhibited dextran sodium sulfate-induced NF-κB signaling and the expression of Cox-2 and iNOS in mouse colon tissue, and alleviated symptoms of colitis without observable acute toxicity. IAA and similar compounds also induced autophagy in various cancer cells, and inhibition of autophagy significant reversed IAA-induced cell death, suggesting the existence of autophagic cell death. IAA caused cleavage and aggregation of LC-3 accompanied with p62 degradation, and typical autophagic morphology was observed by transmission electronic microscopy. Overexpression of dominant negative AMPK or treatment with AMPK inhibitor demonstrated that activation of AMPK was important for IAA-induced autophagy, while inhibition of Akt was not. Further studies suggest that metabolic stresses is essential for the pharmacological activities of IAA, and primary molecular target were identified. Notably, IAA significantly inhibited tumor growth in nude mice xenograft model. These results suggest that IAA is potentially an anti-inflammatory bowel disease and anti- colorectal cancer agent. Based on the structural similarity, several other compounds were found to possess even stronger anti-inflammation, pro-apoptotic and autophagy-inducing activities. The present work discovered several promising chemopreventive compounds from licorice that deserve future study, and provides an example of study on TCM in chemoprevention. Several other compounds were identified as Nrf2/ARE signaling modulators or apoptosis/autophagy inducers and further investigated. The present works were supported by the National Natural Science Foundation of China (No. 81272468, 81472657). Citation Format: Shunan Tang, Shuai Ji, Yongrui Wang, Ye Min, Siwang Yu, Tony A-N. Kong. Discovery of chemopreventive agents from licorice (Glycyrrhiza Uralensis). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2603.

Isoangustone A induces apoptosis in SW480 human colorectal adenocarcinoma cells by disrupting mitochondrial functions

Licorice and its components have been reported to posses various anti-tumor activities, but its active ingredients and underlying mechanisms are not well understood yet. In the present study, a group of representative licorice-derived compounds that could be detected in rat plasma or urine were screened for anti-tumor activity. Among these compounds, isoangustone A (IAA) was found to promptly inhibit the viability of SW480 human colorectal adenocarcinoma cells in a time- and concentration-dependent manner. Further analyses indicate that IAA activated caspase-dependent pro-apoptotic signaling and induced significant apoptosis, while had little effect on cell cycle. IAA strongly inhibited Akt phosphorylation within 5min; however, overexpression of constitutively activated Akt could not rescue IAA-mediated inhibition, indicating that inhibition of Akt was not involved in IAA-induced apoptosis. Further examinations show that IAA induced dissipation of mitochondria membrane potential and release of cytochrome C within 1h, accompanied by swelling of mitochondrial matrix and disrupting of mitochondrial outer membrane, and followed by decreasing of cellular ATP. The above results suggest that IAA induced apoptosis in colorectal cancer cells principally by inducing mitochondrial outer membrane permeabilization, and deserves further investigations as a novel anti-colorectal cancer agent.

NMR identification of anti-influenza lead compound targeting at PAC subunit of H5N1 polymerase

Abstract PA C subunit from avian influenza (H5N1) viral RNA polymerase was used in this work as a target in the screening for anti-influenza agents from licorice-derived compounds. As a result, 18 β -glycyrrhetinic acid was suggested to be PA C ligand by flexible docking, and was then confirmed by relaxation-edited NMR. The result of ApG primer extension assay indicated that this PA C ligand can inhibit the polymerase activity, and thus may potentially be valuable as anti-influenza lead compound. This work validated the possibility of screening polymerase inhibitors by using PA C as a target, and provided a starting point for the further discovery of new anti-influenza drugs.

18β-Glycyrrhetinic acid potentiates apoptotic effect of trichostatin A on human epithelial ovarian carcinoma cell lines

The licorice-derived compounds glycyrrhizin and 18β-glycyrrhetinic acid have been shown to induce apoptosis in various cancer cells. However, the effect of these licorice compounds on the apoptotic effect of histone deacetylase inhibitors in epithelial ovarian carcinoma cells has not been determined. We assessed the effect of 18β-glycyrrhetinic acid on trichostatin A-induced apoptosis in the human epithelial carcinoma cell lines OVCAR-3 and SK-OV-3. Trichostatin A induced nuclear damage, decreased Bid and Bcl-2 protein levels, increased in Bax levels, induced cytochrome c release, activated caspase-8, -9 and -3, and increased tumor suppressor p53 levels. 18β-Glycyrrhetinic acid potentiated the trichostatin A-induced apoptosis-related protein activation and cell death. Unlike 18β-glycyrrhetinic acid, up to 25 μM of the pro-compound glycyrrhizin did not induce cell death and did not affect trichostatin A-induced apoptosis. The results suggest that 18β-glycyrrhetinic acid may potentiate the apoptotic effects of trichostatin A against ovarian carcinoma cell lines by increasing the activation of the caspase-8-dependent pathway as well as the activation of the mitochondria-mediated cell death pathway, leading to activation of caspases. 18β-Glycyrrhetinic acid may enhance the therapeutic effect of trichostatin A against epithelial ovarian adenocarcinoma.

Separation of fluorescent derivatives of hydroxyl-containing small molecules on a microfluidic chip

Capillary electrophoresis (CE) on a microchip has been employed in this work because of the need to separate and detect fluorescent derivatives on some licorice-derived compounds, namely glycyrrhizin (GL), isoliquiritigenin (IQ). These compounds, which contain only phenolic or aliphatic hydroxyl (secondary) groups, are hard to derivatize in aqueous solutions. Although there are some fluorescent reagents that will react with hydroxyl groups, these reactions are usually achieved in aprotic solvents, but not in aqueous solutions. The only fluorescent reagent that works in aqueous solvents is 5-([4,6-dichlorotriazin-2-yl]amino)fluorescein (DTAF), but it has mostly been employed to label macromolecules. For the first time, we have successfully fluorescently label two hydroxyl-containing small molecules, GL and IQ in aqueous solutions. The reaction products were separated by CE and detected fluorescently on a microfluidic chip within 100 s. For comparison, the separation was also carried out on a commercial CE system using UV absorbance detection.

Licorice-derived compounds inhibit linoleic acid (C:18:2ω6) desaturation in soybean chloroplasts

Although glycyrrhizic acid, a major constituent of licorice root, has important pharmacological effects in humans, the biological activity of glycyrrhizic acid and its aglycone glycyrrhetinic acid in plants is unknown. Here we report that these licorice-derived compounds and the analog carbenoxolone inhibit desaturation of linoleic acid (C18:2ω6) in soybean chloroplasts using monogalactosyldiacylglycerol and phosphatidylcholine substrates in an in vitro assay for desaturase activity. At 10 nM glycyrrhetinic acid, there is significant inhibition of desaturation of linoleic acid suggesting that licorice-derived compounds could prove useful in investigating biochemical pathways of linoleic acid desaturation in plant chloroplasts and plant desaturase regulation, which has application in modification of plant response to environmental stress, as well as optimization of oil seed composition.

Endocrine Activity of Plant-Derived Compounds: An Evolutionary Perspective

Although plants have long been known to have important pharmacological effects in humans, the mechanism by which plant-derived compounds act in humans is still being elucidated. Two important pathways for the biological actions of plant-derived compounds involved binding either to hormone receptors or to enzymes that metabolize hormones. What are the origins of this interaction between plant-derived compounds and animals? And what insights can we gain from investigating this question? Some answers come from recent sequence analyses, revealing that 17 beta-hydroxysteroid dehydrogenase, which regulates estrogen and androgen levels in humans, and 15-hydroxyprostaglandin dehydrogenase, which regulates prostaglandin E2 and F2 alpha levels in humans, have a common ancestor with proteins in rhizobia that are important in forming nitrogen-fixing nodules in legume roots, and 3 beta-hydroxysteroid dehydrogenase, which regulates progestin and androgen levels in humans, has a common ancestor with enzymes important in the synthesis of anthocyanins. This evolutionary kinship, when combined with the structural similarities between flavonoids, licorice-derived compounds, and steroid hormones, provides another perspective on the hormone-like activity of flavonoids and other plant-derived compounds in humans: some of the hormone-like activity of plant-derived compounds is due to binding to steroid and prostaglandin dehydrogenases.

Inhibitory effect of isoliquiritin, a compound in licorice root, on angiogenesis in vivo and tube formation in vitro.

A water extract of licorice root inhibits granuloma angiogenesis in adjuvant-induced chronic inflammation (Phytother. Res., 5, 195. 1991). The present study has investigated the effects of licorice-derived compounds on granuloma angiogenesis. Isoliquiritin (0.31-3.1 mg/kg), a licorice-derived flavonoid, inhibited the carmine content of granuloma tissue 50-fold greater than licorice extract. Glyeyrrhizin (20-80 mg/kg), a licorice-derived saponin, inhibited carmine content with a weak potency. The licorice extract (0.01-1 mg/ml) also inhibited tube formation from vascular endothelial cells in a concentration-dependent manner. From the chemical structure-activities of used licorice-derived flavonoids (0.1-100 microM), their potencies for anti-tube formation were in the order isoliquiritigenin > isoliquiritin > liquiritigenin >> isoliquiritin-apioside. Glycyrrhizin (0.1-100 microM) and glycyrrhetinic acid (0.1-10 microM) increased tube formation. A glycyrrhizin (82 micrograms/ml)-induced increase in tube formation was inhibited by isoliquiritin. The combined effect of a mixture of 82 micrograms/ml glycyrrhizin and 4.2 micrograms/ml isoliquiritin, a similar concentration ratio to their yield ratio in the licorice extract, corresponded to the effect of 100 micrograms/ml extract. In conclusion, the anti-angiogenic effect of licorice extract depended on the anti-tube formation effect of isoliquiritin.

Licorice and enzymes other than 11β-hydroxysteroid dehydrogenase: An evolutionary perspective

Licorice has long been known to promote the healing of ulcers. In the 1950s, studies with licorice-derived compounds revealed that the anti-ulcer effects of licorice are due to inhibition of 15-hydroxyprostaglandin dehydrogenase and Δ 13- prostaglandin reductase. 15-Hydroxyprostaglandin dehydrogenase converts prostaglandins E 2 and F 2α to 15-ketoprostaglandins, which are inactive. Δ 13- Prostaglandin reductase metabolizes the inactive Δ 13- prostaglandin to 13,14-dihydro,15-ketoprostaglandin, which is further metabolized and excreted in urine. Thus, licorice-derived compounds have the effect of raising the local concentration of prostaglandins that promote mucous secretion and cell proliferation in the stomach, leading to healing of ulcers. 11β-Hydroxysteroid dehydrogenase, which also is inhibited by licorice-derived compounds, shares a common ancestor with 15-hydroxyprostaglandin dehydrogenase. Both enzymes are homologous to Streptomyces hydrogenans 3α,20β-hydroxysteroid dehydrogenase, which also is inhibited by licorice, Thus, licorice inhibits enzymes that diverged at least 2 billion years ago from a common ancestor. Other oxidoreductases in bacteria, plants, and animals that are inhibited by licorice-derived compounds are likely to be discovered in the future.

Inhibition of Streptomyces hydrogenans 3α,20β-hydroxysteroid dehydrogenase by licorice-derived compounds and crystallization of an enzyme-cofactor-inhibitor complex

Streptomyces hydrogenans 3α, 20β-hydroxysteroid dehydrogenase reduces the C20 ketone on glucocorticoids and progestins. We find that two licorice-derived compounds, glycyrrhizic acid and carbenoxolone, inhibit this enzyme with μM K i s. Inhibition is competitive, indicating that these compounds are binding at or close to the catalytic site. Carbenoxolone's high aqueous solubility and affinity for 3α,20β-hydroxysteroid dehydrogenase enabled us to prepare crystals of a carbenoxolone-NADH-enzyme ternary complex, which preliminary X-ray analysis indicates has a crystal structure that is significantly different from that of the 3α,20β-hydroxysteroid dehydrogenase-NADH complex. A comparison of the tertiary structures of these two complexes should prove useful in understanding this enzyme's catalytic mechanism, as well as those of two homologous enzymes, mammalian 11β-hydroxysteroid dehydrogenase and 15-hydroxyprostaglandin dehydrogenase that also are inhibited by carbenoxolone.