Glabrol

Bioorg Med Chem. 2017 Jul 15;25(14):3706-3713.

Screening for bioactive natural products from a 67-compound library of Glycyrrhiza inflata.[Pubmed: 28522265]

Licorice shows a variety of pharmacological activities. This work aims to discover bioactive natural products from one botanical source of licorice, Glycyrrhiza inflata. A total of 67 free phenolics were isolated to form a compound library.
METHODS AND RESULTS:
Based on the bioactivities of licorice, these compounds were screened using cell- or enzyme-based bioassay methods. A total of 11 compounds exhibited potent cytotoxic activities against three human cancer cell lines (HepG2, SW480 and MCF7), while showed little toxicity on human normal cell lines LO2 and HEK293T.
CONCLUSIONS:
A number of chalcones showed remarkable anti-inflammatory activities. Among them, 2 (licochalcone B, IC50 8.78μM), 10 (licoagrochalcone C, IC50 9.35μM) and 13 (licochalcone E, IC50 9.09μM) exhibited the most potent inhibitory activities on LPS-induced NO production, whereas 1, 8, 10, 12 and 13 (IC50 13.9, 7.27, 2.44, 6.67 and 3.83μM) showed potent inhibitory activities on NF-κB transcription. Nine prenylated phenolics were found to be PTP1B inhibitors. Particularly, licoagrochalcone A (4), kanzonol C (7), 2'-hydroxyisolupalbigenin (35), gancaonin Q (45), glisoflavanone (50) and Glabrol (53) showed IC50 values of 0.31-0.97μM. Compounds 24 (semilicoisoflavone B, IC50 0.25μM), 26 (allolicoisoflavone B, IC50 0.80μM) and 64 (glabridin, IC50 0.10μM) showed noticeable tyrosinase inhibitory activities. Most of the above bioactive compounds were reported for the first time.

Arch Pharm Res. 2010 Feb;33(2):237-42.

Inhibitory activity of diacylglycerol acyltransferase by glabrol isolated from the roots of licorice.[Pubmed: 20195824 ]

Acyl-coenzyme A: diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes triglyceride synthesis in the glycerol phosphate pathway. It has relations with the excess supply and accumulation of triglycerides. Therefore, DGAT inhibitors may act as a potential therapy for obesity and type 2 diabetes.
METHODS AND RESULTS:
Five flavonoids were isolated from the ethanol extracts of licorice roots, using an in vitro DGAT inhibitory assay. One isoprenyl flavonoid showed most potential inhibition of DGAT on five flavonoids (1-5). On the basis of spectral evidences, the compound was identified as Glabrol (5). Compound 5 inhibited rat liver microsomal DGAT activity with an IC50 value of 8.0 microM, but the IC50 value for four flavonoids (1-4) was more than 100 microM. In addition, Glabrol showed a noncompetitive type of inhibition against DGAT.
CONCLUSIONS:
These data suggest that potential therapy for the treatment in obesity and type 2 diabetes patients by licorice roots might be related with its DGAT inhibitory effect.

J Nat Prod. 1980 Mar-Apr;43(2):259-69.

Antimicrobial agents from higher plants. Antimicrobial isoflavanoids and related substances from Glycyrrhiza glabra L. var. typica.[Pubmed: 7381508]

METHODS AND RESULTS:
Bioassay-directed fractionation of Glycyrrhiza glabra L. var. typica resulted in the isolation and characterization of glabridin (I), Glabrol (2), glabrene (3), 3-hydroxyGlabrol (4), 4'-O-methylglabridin (5), 3'-methoxyglabridin (6), formononetin (7), phaseollinisoflavan (8), hispaglabridin A (9), hispaglabridin B (13), salicylic acid and O-acetyl salicylic acid. Of these, hispaglabridin A, hispaglabridin B, 4'-O-methylglabridin, glabridin, Glabrol and 3-hydroxyGlabrol possess significant antimicrobial activity in vitro; hispaglabridin A, hispaglabridin B, 3'-methoxyglabridin, 4'-O-methylglabridin 3-hydroxyGlabrol, phaseollinisoflavan, salicylic acid, and O, acetyl salicylic acid are newly found in Glycyrrhiza sp.; and hispaglabridin A, hispaglabridin B, 3'-methoxyglabridin, 4'-O-methylglabridin, and 3-hydroxyGlabrol are new to the literature and their structures are proposed herein.

Bioorg Med Chem Lett. 2017 Dec 15;27(24):5400-5403.

Glycyrrhiza glabra extract and quercetin reverses cisplatin resistance in triple-negative MDA-MB-468 breast cancer cells via inhibition of cytochrome P450 1B1 enzyme.[Pubmed: 29150398 ]

The development of multi-drug resistance to existing anticancer drugs is one of the major challenges in cancer treatment. The over-expression of cytochrome P450 1B1 enzyme has been reported to cause resistance to cisplatin. With an objective to discover cisplatin-resistance reversal agents, herein, we report the evaluation of Glycyrrhiza glabra (licorice) extracts and its twelve chemical constituents for inhibition of CYP1B1 (and CYP1A1) enzyme in Sacchrosomes and live human cells.
METHODS AND RESULTS:
The hydroalcoholic extract showed potent inhibition of CYP1B1 in both Sacchrosomes as well as in live cells with IC50 values of 21 and 16 μg/mL, respectively. Amongst the total of 12 constituents tested, quercetin and Glabrol showed inhibition of CYP1B1 in live cell assay with IC50 values of 2.2 and 15 μM, respectively. Both these natural products were found to be selective inhibitors of CYP1B1, and does not inhibit CYP2 and CYP3 family of enzymes (IC50 > 20 μM). The hydroalcoholic extract of G. glabra and quercetin (4) showed complete reversal of cisplatin resistance in CYP1B1 overexpressing triple negative MDA-MB-468 breast cancer cells.
CONCLUSIONS:
The selective inhibition of CYP1B1 by quercetin and Glabrol over CYP2 and CYP3 family of enzymes was studied by molecular modeling studies.

Bioorg Med Chem. 2012 Jun 1;20(11):3493-501.

Hypnotic effects and GABAergic mechanism of licorice (Glycyrrhiza glabra) ethanol extract and its major flavonoid constituent glabrol.[Pubmed: 22543233]

Licorice (Glycyrrhiza glabra, GG) is one of the most frequently used herbal medicines worldwide, and its various biological activities have been widely studied. GG is reported to have neurological properties such as antidepressant, anxiolytic, and anticonvulsant effects. However, its hypnotic effects and the mechanism of GG and its active compounds have not yet been demonstrated.
METHODS AND RESULTS:
In this study, GG ethanol extract (GGE) dose-dependently potentiated pentobarbital-induced sleep and increased the amount of non-rapid eye movement sleep in mice without decreasing delta activity. The hypnotic effect of GGE was completely inhibited by flumazenil, which is a well-known γ-aminobutyric acid type A-benzodiazepine (GABA(A)-BZD) receptor antagonist, similar to other GABA(A)-BZD receptor agonists (e.g., diazepam and zolpidem). The major flavonoid Glabrol was isolated from the flavonoid-rich fraction of GGE; it inhibited [(3)H] flumazenil binding to the GABA(A)-BZD receptors in rat cerebral cortex membrane with a binding affinity (K(i)) of 1.63 μM. The molecular structure and pharmacophore model of Glabrol and liquiritigenin indicate that the isoprenyl groups of Glabrol may play a key role in binding to GABA(A)-BZD receptors. Glabrol increased sleep duration and decreased sleep latency in a dose-dependent manner (5, 10, 25, and 50mg/kg); its hypnotic effect was also blocked by flumazenil.
CONCLUSIONS:
The results imply that GGE and its flavonoid Glabrol induce sleep via a positive allosteric modulation of GABA(A)-BZD receptors.