Isoliquiritigenin selectively inhibits H(2) histamine receptor signaling

Plants with potential anti-ulcerogenic activity and possible mechanism of actions based on their phyto-constitutional profile

Gastric ulcer, the most common disorder of the digestive tract is formed due to an imbalance between acid and mucus content of the stomach. However, the currently used western therapeutic regimens have many drawbacks like adverse effects, recurrence of gastric ulcers, are expensive, and also, may have interactions with other drugs. Hence, there is a need for effective alternative therapy. Medicinal herbs have been used since ancient times to treat several diseases and are also evidenced to be effective against gastric ulcers. It is also evident that medicinal herbs have been proved to be equally effective or superior as compared to the existing synthetic medicines. In this review, five herbs have been taken into consideration and assumed to be effective against gastric ulcers. Abrus mollis, Korean Thistle (Cirsium japonicum var. maackii), Astralagus complanatus Bunge, Bauhinia monandra, and Embelia ribes Burm f. are the herbs whose data is been collected and reviewed for their potential gastro-protective action. Although, their side effects and toxicity profile need to be further evaluated. Hence, the purpose of this review is to gather evidence of these five medicinal herbs and their probable mechanism of action against gastric ulcers based on their phyto-constitutional profile.

Heterocyclic compounds as a magic bullet for diabetes mellitus: a review

Diabetes mellitus (DM) is a major metabolic disorder due to hyperglycemia, which is increasing all over the world. From the last two decades, the use of synthetic agents has risen due to their major involvement in curing of chronic diseases including DM. The core skeleton of drugs has been studied such as thiazolidinone, azole, chalcone, pyrrole and pyrimidine along with their derivatives. Diabetics assays have been performed in consideration of different enzymes such as α-glycosidase, α-amylase, and α-galactosidase against acarbose standard drug. The studied moieties were depicted in both models: in vivo as well as in vitro. Molecular docking of the studied compounds as antidiabetic molecules was performed with the help of Auto Dock and molecular operating environment (MOE) software. Amino acid residues Asp349, Arg312, Arg439, Asn241, Val303, Glu304, Phe158, His103, Lys422 and Thr207 that are present on the active sites of diabetic related enzymes showed interactions with ligand molecules. In this review data were organized for the synthesis of heterocyclic compounds through various routes along with their antidiabetic potential, and further studies such as pharmacokinetic and toxicology studies should be executed before going for clinical trials.

Diabetes mellitus (DM) is a major metabolic disorder due to hyperglycemia, which is increasing all over the world.

Perspectives on the Role of Isoliquiritigenin in Cancer

Isoliquiritigenin (2',4',4-trihydroxychalcone, ISL), one of the most important bioactive compounds with a chalcone structure, is derived from licorice root. Licorice is commonly known as Glycyrrhiza, including Glycyrrhiza uralensis, Glycyrrhiza radix, and Glycyrrhiza glabra, which are generally available in common foods and Chinese herbal medicines based on a wide variety of biological functions and pharmacological effects, and its derivative (ISL) is utilized as a food additive and adjunct disease treatment. In this review, we summarized the progress over the last 10 years in the targeted pathways and molecular mechanisms of ISL that are involved in the regulation of the onset and progression of different types of cancers.

De novo biosynthesis of liquiritin in Saccharomyces cerevisiae

Liquiritigenin (LG), isoliquiritigenin (Iso-LG), together with their respective glycoside derivatives liquiritin (LN) and isoliquiritin (Iso-LN), are the main active flavonoids of Glycyrrhiza uralensis, which is arguably the most widely used medicinal plant with enormous demand on the market, including Chinese medicine prescriptions, preparations, health care products and even food. Pharmacological studies have shown that these ingredients have broad medicinal value, including anti-cancer and anti-inflammatory effects. Although the biosynthetic pathway of glycyrrhizin, a triterpenoid component from G. uralensis, has been fully analyzed, little attention has been paid to the biosynthesis of the flavonoids of this plant. To obtain the enzyme-coding genes responsible for the biosynthesis of LN, analysis and screening were carried out by combining genome and comparative transcriptome database searches of G. uralensis and homologous genes of known flavonoid biosynthesis pathways. The catalytic functions of candidate genes were determined by in vitro or in vivo characterization. This work characterized the complete biosynthetic pathway of LN and achieved the de novo biosynthesis of liquiritin in Saccharomyces cerevisiae using endogenous yeast metabolites as precursors and cofactors for the first time, which provides a possibility for the economical and sustainable production and application of G. uralensis flavonoids through synthetic biology.

Isoliquiritigenin suppresses human T Lymphocyte activation via covalently binding cysteine 46 of IκB kinase

The efficacious practice of precision personalized medicine requires a more exact understanding of the molecular mechanisms of drug, hence then it is necessary to identify the binding site of the drugs derived from natural sources. In the study, we investigated the suppressive effect and underlying mechanism of isoliquiritigenin (2′,4′,4-trihydroxychalcone; ILG), a phyto-flavonoid, on human T lymphocyte activation in vitro and in vivo. The results showed that ILG dose-dependently suppressed human T cell activation via suppressing IκBα phosphorylation and degradation, NF-κB nuclear translocation and IKKβ activity. Molecular docking results predicted that cysteine 46 (Cys-46) is probably the binding site of ILG on IKKβ, and this prediction has been validated by competition assay and kinase assay. To further verify the binding site of this compound in vivo, IKKβC46A transgenic (IKKβ^C46A) mice were generated. We found that ILG had a less potent immune-suppressive effect in homozygous IKKβ^C46A mice than IKKβ wild type (IKKβ wt) littermates with the delay-type hypersensitivity (DTH), suggesting that ILG cannot significantly suppress the inflammation due to the mutation of Cys-46 in the transgenic mice. Collectively, our findings indicate that the ILG inhibited T cell activation in vivo and in vitro via directly binding to IKKβ Cys46.

Diverse Molecular Targets for Chalcones with Varied Bioactivities

Natural or synthetic chalcones with different substituents have revealed a variety of biological activities that may benefit human health. The underlying mechanisms of action, particularly with respect to the direct cellular targets and the modes of interaction with the targets, have not been rigorously characterized, which imposes challenges to structure-guided rational development of therapeutic agents or chemical probes with acceptable target-selectivity profile. This review summarizes literature evidence on chalcones’ direct molecular targets in the context of their biological activities.

Identification of quinoline-chalcone hybrids as potential antiulcer agents

Antiulcer activity of novel quinoline-chalcone hybrids (13-37) was investigated. Among them, eight compounds (14, 16, 17, 23, 29, 31, 32 and 35) were found to be active in various ulcer models in Sprague-Dawley (SD) rats. To understand the mechanism of action of these hybrids, the effects of the compounds on antisecretory and cytoprotective activities were studied. All these active hybrids improved the depleted levels of mucin and consequently inhibited the formation of erosions in a pyloric ligated ulcer model. In addition, they also significantly increased the gastric PGE2 content in an aspirin induced ulcer model. The additional experiments including the in vitro metabolic stability and in vivo pharmacokinetics led to the identification of compound 17 as an orally active and safe candidate that is worthy of further investigation to be developed as an antiulcer agent.

In vivo anti-diabetic activity of derivatives of isoliquiritigenin and liquiritigenin

Isoliquiritigenin (ISL), a chalcone and liquiritigenin (LTG), a flavonoid found in licorice roots and several other plants. ISL displays antioxidant, anti-inflammatory, antitumor and hepatoprotective activities whereas LTG is an estrogenic compound, acts as an agonist selective for the β-subtype of the oestrogen receptor. Both the phenolics were isolated from the rhizomes of Glycyrrhiza glabra. Five derivatives from ISL and four derivatives from LTG were synthesized. All the compounds were established by extensive spectroscopic analyses and screened through oral glucose tolerance test to gain preliminary information regarding the antihyperglycemic effect in normal Swiss albino male mice. ISL (1), ISL derivatives 3, 4, 5, 7 and LTG derivatives 9 and 10 showed significant blood glucose lowering effect. The structure-activity relationship indicated that the presence of ether and ester groups in ISL and LTG analogues are important for exhibiting the activity. Compounds 1, 4 and 10 were selected for in vivo antidiabetic activity and found to be potential candidates for treatment of diabetes. It is the first report on antidiabetic activity of ISL derivative 4 and LTG derivative 10.

Pharmacokinetics, biodistribution and bioavailability of isoliquiritigenin after intravenous and oral administration

CONTEXT

Isoliquiritigenin (ISL) has been shown to exhibit a variety of biological activities. However, there is little research on the pharmacokinetic behavior and tissues distribution of ISL.

OBJECTIVE

Pharmacokinetics, biodistribution and bioavailability of ISL after intravenous and oral administration were determined by systematic investigation in Sprague-Dawley rats.

MATERIALS AND METHODS

ISL was dissolved in medicinal ethanol-Tween 80-0.9% sodium chloride saline in a volume ratio of 10:15:75. The ISL solution was injected in rats via a tail vein at a single dose of 10, 20 and 50 mg/kg and administered orally in rats at a single dose of 20, 50 and 100 mg/kg, respectively. Blood samples were collected at time intervals of 0.08, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 6, 8 and 12 h after intravenous injection. Tissues of interests in mice were collected immediately at each determined time point (0.5, 1, 2, 3 and 6 h) after cervical dislocation.

RESULTS

The dose-normalized AUC values were 7.3, 7.6 and 8.7 μg × h/ml (calculated based on the dose of 10 mg/kg) for intravenous doses of 10, 20 and 50 mg/kg, respectively. The elimination half-lifes (t1/2λ) were 4.9, 4.6 and 4.8 h at 10, 20 and 50 mg/kg intravenous doses, respectively. The F values were 29.86, 22.70, 33.62% for oral doses of 20, 50 and 100 mg/kg, respectively. Liver, heart and kidney were major distribution tissues of ISL in mice. The plasma protein binding of ISL in rats was 43.72%.

CONCLUSION

The work may useful for further study of the bioactive mechanism of ISL.

The regulation of epidermal melanogenesis via cAMP and/or PKC signaling pathways: insights for the development of hypopigmenting agents

Abnormal pigmentation, particularly hyperpigmentation, is major issue of concern for people with colored skin. Several hypopigmenting agents, which exert their action by inhibiting tyrosinase activity and/or transcription, have been used for treatment. However, results have been discouraging. To manage abnormal pigmentation properly, the mechanisms of melanogenesis should be understood. Endogenous and exogenous factors affect melanogenesis via intracellular machineries. cAMP and PKC are critical factors of important transduction pathways and cross-talk between them could amplify the melanogenic effect. Here, factors involved in melanogenesis regulation via cAMP and/or PKC pathways are reviewed with their action mechanisms.

Molecular and cellular analysis of human histamine receptor subtypes

The human histamine receptors hH(1)R and hH(2)R constitute important drug targets, and hH(3)R and hH(4)R have substantial potential in this area. Considering the species-specificity of pharmacology of H(x)R orthologs, it is important to analyze hH(x)Rs. Here, we summarize current knowledge of hH(x)Rs endogenously expressed in human cells and hH(x)Rs recombinantly expressed in mammalian and insect cells. We present the advantages and disadvantages of the various systems. We also discuss problems associated with the use of hH(x)R antibodies, an issue of general relevance for G-protein-coupled receptors (GPCRs). There is much greater overlap in activity of 'selective' ligands for other hH(x)Rs than the cognate receptor subtype than generally appreciated. Studies with native and recombinant systems support the concept of ligand-specific receptor conformations, encompassing agonists and antagonists. It is emerging that for characterization of hH(x)R ligands, one cannot rely on a single test system and a single parameter. Rather, multiple systems and parameters have to be studied. Although such studies are time-consuming and expensive, ultimately, they will increase drug safety and efficacy.

Screening for natural chemoprevention agents that modify human Keap1

Upregulation of cytoprotective enzymes by therapeutic agents to prevent damage by reactive oxygen species and xenobiotic electrophiles is a strategy for cancer chemoprevention. The Kelch-like ECH-associated protein 1 (Keap1) and its binding partner, transcription factor NF-E2-related factor-2 (NRF2), are chemoprevention targets because of their role in regulating the antioxidant response element (ARE) in response to oxidative stress and exposure to electrophiles. Modification of the sensor protein Keap1 by electrophiles such as the isothiocyanate sulforaphane can direct Nrf2 accumulation in the nucleus and subsequent ARE activation. Since our previous matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF MS)-based screening method to discover natural products that modify Keap1 does not detect covalent modification of Keap1 by some highly reversible agents such as sulforaphane, a more sensitive screening assay was developed. In this new assay, electrophiles that have reversibly modified Keap1 can be released, trapped, and detected as β-mercaptoethanol adducts by mass spectrometry. Isoliquiritigenin and sulforaphane, known ARE activators that target Keap1, were used to validate the assay. To determine the ability of the assay to identify electrophiles in complex matrixes that modify Keap1, sulforaphane was spiked into a cocoa extract, and LC-MS/MS using high resolution mass spectrometry with accurate mass measurement was used to identify β-mercaptoethanol adducts of sulforaphane that had been released from Keap1. This screening assay permits identification of potential chemoprevention agents in complex natural product mixtures that reversibly modify Keap1 but cannot be detected using MALDI-TOF MS.

Isoliquiritigenin, a chalcone compound, is a positive allosteric modulator of GABAA receptors and shows hypnotic effects

Isoliquiritigenin (ILTG) is a chalcone compound and has valuable pharmacological properties such as antioxidant, anti-inflammatory, anticancer, and antiallergic activities. Recently, the anxiolytic effect of ILTG has been reported; however, its action mechanism and hypnotic activity have not yet been demonstrated. Therefore, we investigated the hypnotic effect and action mechanism of ILTG. ILTG significantly potentiated the pentobarbital-induced sleep in mice at doses of 25 and 50mg/kg. The hypnotic activity of ILTG was fully inhibited by flumazenil (FLU), a specific gamma-aminobutyric acid type A (GABA(A))-benzodiazepine (BZD) receptor antagonist. The binding affinity of ILTG was 0.453 μM and was found to be higher than that of the reference compound, diazepam (DZP, 0.012 μM). ILTG (10(-5)M) potentiated GABA-evoked currents to 151% of the control level on isolated dorsal raphe neurons. ILTG has 65 times higher affinity for GABA(A)-BZD receptors than DZP, and the dissociation constant for ILTG was 4.0 × 10(-10)M. The effect of ILTG on GABA currents was blocked by 10(-7)M FLU and ZK-93426. These results suggest that ILTG produces hypnotic effects by positive allosteric modulation of GABA(A)-BZD receptors.

Cardioprotective effects of Glycyrrhiza uralensis extract against doxorubicin-induced toxicity

The purpose of the present study was to investigate the cardioprotective effects of Glycyrrhiza uralensis extract (GUE) against doxorubicin (DOX)-induced cardiotoxicity. Imprinting control region (ICR) mice were treated with saline, DOX (20 mg/kg intraperitoneal [ip] for once), GUE (100 mg/kg intragastric [ig] for 8 days), co-treatments with DOX and GUE (100 mg/kg ig for 8 days), and amifostine (100 mg/kg intravenous [iv] for once), respectively. Serum levels of lactate dehydrogenase (LDH) and creatine kinase isoenzyme (CK-MB), glutathione peroxidase (GSH-P(X)) activity, and glutathione (GSH) level in heart tissue were measured. Histopathologic analysis of heart tissue was also performed. Treatment with GUE significantly protected the mice from DOX-induced cardiotoxicity, indicated by decreased levels of serum LDH and CK-MB, improved heart morphology and increased GSH-P(X) activity and GSH level. Additionally, GUE did not compromise the tumor-inhibitory effect of DOX. In conclusion, our studies imply the potentially clinical application of GUE to overcome the cardiotoxicity of doxorubicin.

AMPK-mediated GSK3beta inhibition by isoliquiritigenin contributes to protecting mitochondria against iron-catalyzed oxidative stress

Isoliquiritigenin (ILQ), a flavonoid compound originated from Glycyrrhiza species, is known to activate SIRT1. Arachidonic acid (AA) in combination with iron (a catalyst of auto-oxidation) leads cells to produce excess reactive species with a change in mitochondrial permeability transition. In view of the importance of oxidative stress in cell death and inflammation, this study investigated the potential of ILQ to protect cells against the mitochondrial impairment induced by AA+iron and the underlying basis for this cytoprotection. Treatment with ILQ inhibited apoptosis induced by AA+iron, as evidenced by alterations in the levels of the proteins associated with cell viability: ILQ prevented a decrease in Bcl-x(L), and cleavage of poly(ADP-ribose)polymerase and procaspase-3. Moreover, ILQ inhibited the ability of AA+iron to elicit mitochondrial dysfunction. In addition, superoxide generation in mitochondria was attenuated by ILQ treatment. Consistently, ILQ prevented cellular H2O2 production increased by AA+iron, thereby enabling cells to restore GSH content. ILQ treatment enhanced inhibitory phosphorylation of glycogen synthase kinase-3beta (GSK3beta), and prevented a decrease in the GSK3beta phosphorylation elicited by AA+iron, which contributed to protecting cells and mitochondria. GSK3beta phosphorylation by ILQ was preceded by AMP-activated protein kinase (AMPK) activation, which was also responsible for mitochondrial protection, as shown by reversal of its effect in the experiments using a dominant negative mutant of AMPK and compound C. Moreover, the AMPK activation led to GSK3beta phosphorylation. These results demonstrate that ILQ has the ability to protect cells from AA+iron-induced H2O2 production and mitochondrial dysfunction, which is mediated with GSK3beta phosphorylation downstream of AMPK.

Histamine H1 receptor induces cytosolic calcium increase and aquaporin translocation in human salivary gland cells

One of the common side effects of antihistamine medicines is xerostomia (dry mouth). The current consensus is that antihistamine-induced xerostomia comes from an antimuscarinic effect. Although the effect of antihistamines on salivary secretion is both obvious and significant, the cellular mechanism whereby this happens is still unclear because of the lack of knowledge of histamine signaling in human salivary glands. Here, we have studied histamine receptors and the effect of antihistamines on human submandibular acinar cells. In primary cultured human submandibular gland and a HSG cell line, histamine increased the intracellular Ca(2+) concentration. The histamine-induced cytosolic free Ca(2+) concentration ([Ca(2+)](i)) increase was inhibited by histamine H1 receptor-specific antagonists, and the expression of the functional histamine H1 receptor was confirmed by reverse transcription-polymerase chain reaction. Interestingly, histamine pretreatment did not inhibit a subsequent carbachol-induced [Ca(2+)](i) rise without "heterologous desensitization." Chlorpheniramine inhibited a carbachol-induced [Ca(2+)](i) increase at a 100-fold greater concentration than histamine receptor antagonism, whereas astemizole and cetrizine showed more than 1000-fold difference, which in part explains the xerostomia-inducing potency among the antihistamines. Notably, histamine resulted in translocation of aquaporin-5 to the plasma membrane in human submandibular gland cells and green fluorescent protein-tagged aquaporin-5 expressing HSG cells. We found that histidine decarboxylase and the histamine H1 receptor are broadly distributed in submandibular gland cells, whereas choline acetyltransferase is localized only at the parasympathetic terminals. Our results suggest that human salivary gland cells express histamine H1 receptors and histamine-synthesizing enzymes, revealing the cellular mechanism of antihistamine-induced xerostomia.

Two flavonoids extracts from Glycyrrhizae radix inhibit in vitro hepatitis C virus replication

AIM

Traditional herbal medicines have been used for several thousand years in China and other Asian countries. In this study we screened herbal drugs and their purified compounds, using the Feo replicon system, to determine their effects on in vitro HCV replication.

METHODS

We screened herbal drugs and their purified extracts for the activities to suppress hepatitis C virus (HCV) replication using an HCV replicon system that expressed chimeric firefly luciferase reporter and neomycin phosphotransferase (Feo) genes. We tested extracts and 13 purified compounds from the following herbs: Glycyrrhizae radix; Rehmanniae radix; Paeoniae radix; Artemisiae capillari spica; and Rhei rhizoma.

RESULTS

The HCV replication was significantly and dose-dependently suppressed by two purified compounds, isoliquiritigenin and glycycoumarin, which were from Glycyrrhizae radix. Dose-effect analyses showed that 50% effective concentrations were 6.2 +/- 1.0 microg/mL and 15.5 +/- 0.8 microg/mL for isoliquiritigenin and glycycoumarin, respectively. The MTS assay did not show any effect on cell growth and viability at these effective concentrations, indicating that the effects of the two compounds were specific to HCV replication. These two compounds did not affect the HCV IRES-dependent translation nor did they show synergistic action with interferon-alpha.

CONCLUSION

Two purified herbal extracts, isoliquiritigenin and glycycoumarin, specifically suppressed in vitro HCV replication. Further elucidation of their mechanisms of action and evaluation of in vivo effects and safety might constitute a new anti-HCV therapeutics.

Sites of alkylation of human Keap1 by natural chemoprevention agents

Under basal conditions, the interaction of the cytosolic protein Keap1 (Kelch-like ECH-associated protein 1) with the transcription factor nuclear factor-E(2)-related factor 2 (Nrf2) results in a low level of expression of cytoprotective genes whose promoter region contains the antioxidant response element (ARE). Alkylation of one or more of the 27 cysteine sulfhydryl groups of human Keap1 is proposed to lead to Nrf2 nuclear accumulation, to upregulation of cytoprotective gene expression by the ARE, and to prevention of degenerative diseases, such as cancer. Therefore, identification of the most reactive of these cysteine residues toward specific electrophiles should help clarify this mechanism of cancer prevention, also known as chemoprevention. To address this issue, preliminary analyses of tryptic digests of Keap1 alkylated by the model electrophile 1-biotinamido-4-(4'-[maleimidoethyl-cyclohexane]-carboxamido) butane were carried out using liquid chromatographic-tandem mass spectrometry (LC-MS/MS) with a cylindrical ion trap mass spectrometer and also using LC-MS/MS with a hybrid linear ion trap FT ICR mass spectrometer. Because the FT ICR instrument provided more complete peptide sequencing coverage and enabled the identification of more alkylated cysteine residues, only this instrument was used in subsequent studies of Keap1 alkylation by three electrophilic natural products that can upregulate the ARE, xanthohumol, isoliquiritigenin, and 10-shogaol. Among the various cysteine residues of Keap1, C151 was most reactive toward these three electrophiles. These in vitro results agree with evidence from in vivo experiments, and indicate that C151 is the most important site of alkylation on Keap1 by chemoprevention agents that function by activating the ARE through Nrf2.