Structure-based drug design targeting the cell membrane receptor GPBAR1: exploiting the bile acid scaffold towards selective agonism

Bile acids can regulate nutrient metabolism through the activation of the cell membrane receptor GPBAR1 and the nuclear receptor FXR. Developing an exogenous control over these receptors represents an attractive strategy for the treatment of enterohepatic and metabolic disorders. A number of dual GPBAR1/FXR agonists are known, however their therapeutic use is limited by multiple unwanted effects due to activation of the diverse downstream signals controlled by the two receptors. On the other hand, designing selective GPBAR1 and FXR agonists is challenging since the two proteins share similar structural requisites for ligand binding. Here, taking advantage of our knowledge of the two targets, we have identified through a rational drug design study a series of amine lithocholic acid derivatives as selective GPBAR1 agonists. The presence of the 3α-NH2 group on the steroidal scaffold is responsible for the selectivity over FXR unveiling unprecedented structural insights into bile acid receptors activity modulation.

Anti-inflammatory and analgesic activities with gastroprotective effect of semi-purified fractions and isolation of pure compounds from Mediterranean gorgonian Eunicella singularis

OBJECTIVE

To explore anti-inflammatory activities of organic extract and its semi-purified fractions (ethanol, acetone, methanol/dichloromethane) from the Mediterranean gorgonian Eunicella singularis.

METHODS

The anti-inflammatory and analgesic activities were evaluated, using the carrageenan-induced rat paw edema model and the acetic acid writhing test in mice. The gastroprotective activity was determined using HCl/EtOH induced gastric ulcers in rats. The purification and structure elucidation of compound(s) from the more effective fraction were determined by chromatographic and spectroscopic methods and in comparison with data reported in the literature.

RESULTS

The fraction F-EtOH showed an important anti-inflammatory activity associated with significant analgesic and gastroprotective properties. The purification and structure elucidation of compound(s) from this fraction lead to the identification of one diterpenoid and four sterols.

CONCLUSIONS

These results suggested that components from the active fraction can be used to treat various anti-inflammatory diseases.

Antioxidant activity and chemical components as potential anticancer agents in the olive leaf (Olea europaea L. cv Leccino.) decoction

Epidemiological studies have shown that a reduced risk of chronic diseases such as cancer and cardiovascular diseases is correlated with a regular consumption of fruits and vegetable, many of which are rich in polyphenols. The additive and synergistic effect of phytochemicals in fruits and vegetables may reduce chronic diseases related to oxidative stress in human body. Olea europaea L. leaf are rich in phenolic components, which have been proposed to play a role in cancer prevention. The purpose of this study was to identify the main components in the Olea europaea L. leaf (cv. Leccino) preserved during the decoction preparation, in order to delineate the antioxidant activities of the crude extracts and its isolated compounds by using different in vitro assays including DPPH radicalscavenging capacity, total antioxidant capacity (TAC), xanthine oxidase (XO) inhibitory effect and the ability to delay the linoleic acid peroxidation process (ALP). The aqueous decoction was partitioned obtaining four extracts and the n-butanol extract showed the highest antioxidant activity and the highest total phenolic content. Phytochemical investigation leads to the isolation of thirteen secondary metabolites including simple phenolics, flavonoids, secoiridoids whose structures were elucidated by spectroscopic data (1D and 2D NMR) and spectrometric techniques. A significant free radical scavenging effect against DPPH has been evidenced in fraxamoside (1) (EC50 62.6 µM) and taxifolin (5) (EC50 50.0 µM), isolated for the first time from the water decoction. The most active compound in the TAC evaluation, was the 3,4 dihydro-phenyl glycol (8) (0.90 caffeic acid equiv.) while taxifolin and fraxamoside resulted as the most efficient inhibitors of XO activity (IC50 2.7 and 5.2 µM, respectively). Secoxyloganin (4), oleuropein (2) and tyrosol (6) showed the highest ALP activity. This study adds to the growing body of data supporting the bioactivities of phytochemicals and their potential impact on human health.

Molecular decodification of gymnemic acids from Gymnema sylvestre. Discovery of a new class of liver X receptor antagonists

The individual chemical components of commercial extract of Gymnema sylvestre, a medicinal plant used in the traditional systems of the Indian medicine for its antidiabetic and hypolipidemic properties, were isolated and evaluated for their capability to act as modulators of nuclear and membrane receptors involved in glucose and lipid homeostasis. The study disclosed for the first time that individual gymnemic acids are potent and selective antagonists for the β isoform of LXR. Indeed the above activity was shared by the most abundant aglycone gymnemagenin (10) whereas gymnestrogenin (11) was endowed with a dual LXRα/β antagonistic profile. Deep pharmacological investigation demonstrated that gymnestrogenin, reducing the expression of SREBP1c and ABCA1 in vitro, is able to decrease lipid accumulation in HepG2 cells. The results of this study substantiate the use of G. sylvestre extract in LXR mediated dislypidemic diseases.

Pharmacological evaluation of the semi-purified fractions from the soft coral Eunicella singularis and isolation of pure compounds

BACKGROUND

Gorgonians of the genus Eunicella are known for possessing a wide range of pharmacological activities such as antiproliferative and antibacterial effect. The aim of this study was to evaluate the anti-inflammatory and gastroprotective effect of the organic extract and its semi-purified fractions from the white gorgonian Eunicella singularis and the isolation and identification of pure compound(s) from the more effective fraction.

METHODS

Anti-inflammatory activity was evaluated, using the carrageenan-induced rat paw edema test and in comparison to the reference drug Acetylsalicylate of Lysine. The gastroprotective activity was determined using HCl/EtOH induced gastric ulcers in rats. The purification of compound(s) from the more effective fraction was done by two chromatographic methods (HPLC and MPLC). The structure elucidation was determined by extensive spectroscopic analysis (1H and 13C NMR, COSY, HMBC, HMQC and NOESY) and by comparison with data reported in the literature.

RESULTS

The evaluation of the anti-inflammatory activity of different fractions from Eunicella singularis showed in a dependent dose manner an important anti-inflammatory activity of the ethanol fraction, the percentage of inhibition of edema, 3 h after carrageenan injection was 66.12%, more effective than the reference drug (56.32%). In addition, this ethanolic fraction showed an interesting gastroprotective effect compared to the reference drugs, ranitidine and omeprazol. The percentage of inhibition of gastric ulcer induced by HCl/ethanol in rats was 70.27%. The percentage of the reference drugs (ranitidine and omeprazol) were 65 and 87.53%, respectively. The purification and structure elucidation of compound(s) from this ethanolic fraction were leading to the isolation of five sterols: cholesterol (5α-cholest-5-en-3β-ol) (1); ergosterol (ergosta-5,22-dien-3β-ol) (2); stigmasterol (24-ethylcholesta-5,22-dien-3b-ol) (3); 5α,8α-epidioxyergosta 6,22-dien-3β-ol (4) and 3β-hydroxy-5α,8α-epidioxyergosta-6-ene (5); and one diterpenoid: palmonine D (6).

CONCLUSION

Based on data presented here, we concluded that diterpenoids and sterols detected in the ethanolic fraction can be responsible for its pharmacological activity.

Modification on ursodeoxycholic acid (UDCA) scaffold. discovery of bile acid derivatives as selective agonists of cell-surface G-protein coupled bile acid receptor 1 (GP-BAR1)

Bile acids are signaling molecules interacting with the nuclear receptor FXR and the G-protein coupled receptor 1 (GP-BAR1/TGR5). GP-BAR1 is a promising pharmacological target for the treatment of steatohepatitis, type 2 diabetes, and obesity. Endogenous bile acids and currently available semisynthetic bile acids are poorly selective toward GP-BAR1 and FXR. Thus, in the present study we have investigated around the structure of UDCA, a clinically used bile acid devoid of FXR agonist activity, to develop a large family of side chain modified 3α,7β-dihydroxyl cholanoids that selectively activate GP-BAR1. In vivo and in vitro pharmacological evaluation demonstrated that administration of compound 16 selectively increases the expression of pro-glucagon 1, a GP-BAR1 target, in the small intestine, while it had no effect on FXR target genes in the liver. Further, compound 16 results in a significant reshaping of bile acid pool in a rodent model of cholestasis. These data demonstrate that UDCA is a useful scaffold to generate novel and selective steroidal ligands for GP-BAR1.

Scalarane sesterterpenes from Thorectidae sponges as inhibitors of TDP-43 nuclear factor

The chemical analysis of two Thorectidae sponges led to the isolation of five new scalarane derivatives along with fifteen known compounds. Their binding capability to TDP-43 was assessed by bio-physical techniques and resulted in the identifications of potent inhibitors.

Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of (13)C chemical shifts

In this paper the stereostructural investigation of two new oxygenated polyketides, plakilactones G and H, isolated from the marine sponge Plakinastrella mamillaris collected at Fiji Islands, is reported. The stereostructural studies began on plakilactone H by applying an integrated approach of the NOE-based protocol and quantum mechanical calculations of (13)C chemical shifts. In particular, plakilactone H was used as a template to extend the application of NMR-derived interproton distances to a highly flexible molecular system with simultaneous assignment of four non-contiguous stereocenters. Chemical derivatization and quantum mechanical calculations of (13)C on plakilactone G along with a plausible biogenetic interconversion between plakilactone G and plakilactone H allowed us to determine the absolute configuration in this two new oxygenated polyketides.

Oxygenated polyketides from Plakinastrella mamillaris as a new chemotype of PXR agonists

Further purification of the apolar extracts of the sponge Plakinastrella mamillaris, afforded a new oxygenated polyketide named gracilioether K, together with the previously isolated gracilioethers E-G and gracilioethers I and J. The structure of the new compound has been elucidated by extensive NMR (1H and 13C, COSY, HSQC, HMBC, and ROESY) and ESI-MS analysis. With the exception of gracilioether F, all compounds are endowed with potent pregnane-X-receptor (PXR) agonistic activity and therefore represent a new chemotype of potential anti-inflammatory leads. Docking calculations suggested theoretical binding modes of the identified compounds, compatible with an agonistic activity on hPXR, and clarified the molecular basis of their biological activities.

Binding mechanism of the farnesoid X receptor marine antagonist suvanine reveals a strategy to forestall drug modulation on nuclear receptors. Design, synthesis, and biological evaluation of novel ligands

Here, we report suvanine, a marine sponge sesterterpene, as an antagonist of the mammalian bile acid sensor farnesoid-X-receptor (FXR). Using suvanine as a template, we shed light on the molecular bases of FXR antagonism, identifying the essential conformational changes responsible for the transition from the agonist to the antagonist form. Molecular characterization of the nuclear corepressor NCoR and coactivator Src-1 revealed that receptor conformational changes are associated with a specific dynamic of recruitment of these cofactors to the promoter of OSTα, a FXR regulated gene. Using suvanine as a novel hit, a library of semisynthetic derivatives has been designed and prepared, leading to pharmacological profiles ranging from agonism to antagonism toward FXR. Deep pharmacological evaluation demonstrated that derivative 19 represents a new chemotype of FXR modulator, whereas alcohol 6, with a simplified molecular scaffold, exhibits excellent antagonistic activity.

A simultaneous multielement non-dispersive atomic-fluorescence spectrometer using modulated sources and frequency discrimination of fluorescence signals

Commercial radiofrequency-excited electrodeless discharge lamps can be run from a square-wave modulated power supply so as to give a low level of continuous emission when modulated in the frequency range 3-10 kHz. Use of a different modulation frequency and lock-in amplifier for each lamp allows multielement non-dispersive atomic-fluorescence spectrometry to be performed. Very low detection limits have been obtained for arsenic, selenium, tin and mercury. The use of low-cost electronic components in the system largely offsets the high cost of the individual excitation power supplies and tuned a.c. detectors.

Plakilactones from the marine sponge Plakinastrella mamillaris. Discovery of a new class of marine ligands of peroxisome proliferator-activated receptor γ

In this paper we report the isolation and the molecular characterization of a new class of PPARγ ligands from the marine environment. Biochemical characterization of a library of 13 oxygenated polyketides isolated from the marine sponge Plakinastrella mamillaris allowed the discovery of gracilioether B and plakilactone C as selective PPARγ ligands in transactivation assays. Both agents covalently bind to the PPARγ ligand binding domain through a Michael addition reaction involving a protein cysteine residue and the α,β-unsaturated ketone in their side chains. Additionally, gracilioether C is a noncovalent agonist for PPARγ, and methyl esters 1 and 2 are noncovalent antagonists. Structural requirements for the interaction of these agents within the PPARγ ligand binding domain were obtained by docking analysis. Gracilioether B and plakilactone C regulate the expression of PPARγ-dependent genes in the liver and inhibit the generation of inflammatory mediators by macrophages.

Imbricatolic acid from Juniperus communis L. prevents cell cycle progression in CaLu-6 cells

Imbricatolic acid was isolated from the methanolic extract of the fresh ripe berries of Juniperus communis (Cupressaceae) together with sixteen known compounds and a new dihydrobenzofuran lignan glycoside named juniperoside A. Their structures were determined by spectroscopic methods and by comparison with the spectral data reported in literature. Imbricatolic acid was evaluated for its ability to prevent cell cycle progression in p53-null CaLu-6 cells. This compound induces the upregulation of cyclin-dependent kinase inhibitors and their accumulation in the G1 phase of the cell cycle, as well as the degradation of cyclins A, D1, and E1. Furthermore, no significant imbricatolic acid-induced apoptosis was observed. Therefore, this plant-derived compound may play a role in the control of cell cycle.

Carbon dioxide insufflation versus air insufflation during endoscopic retrograde cholangiopancreatography under general anesthesia

AIM

The aim of this paper was to evaluate the effect of carbon dioxide (CO2) vs. air insufflation on post-endoscopic retrograde cholangiopancreatography (ERCP) abdominal pain and distension. In addition, we investigated the changes in the partial pressure of end-tidal CO2 (PetCO2) and the partial pressure of arterial CO2 (PaCO2).

METHODS

From October 2009 to January 2010, all patients admitted to our centre for ERCP were screened for enrollment; the patients recruited were randomised to CO2 or air insufflation. The patients were asked to rate their abdominal pain intensity and distension using a 100-mm Visual Analogue Scale (VAS) before, in the recovery room and at 1, 3, 6 and 24 hours after the ERCP. All anesthesiological and endoscopic details and complications were evaluated.

RESULTS

We included 76 patients, 39 in the Air group and 37 in the CO2 group. The groups were similar for age, gender, indications and duration of the procedure. Post-procedure mean values of pain (in the recovery room and at 1, 3 and 6 hours) and distension (at recovery room, and at 1 and 3 hours) according to the VAS were significantly reduced in the CO2 group as compared to the Air group. At baseline, the PetCO2 values were similar between the two groups while, during the ERCP, they increased significantly in CO2 group as compared to the Air group; these values were reduced by simply increasing the ventilation.

CONCLUSION

CO2 insufflation during ERCP significantly reduces post-procedural abdominal pain and distension. Increased PetCO2 and PaCO2 values remained within acceptable or readily controllable ranges.

Lauroside B, a megastigmane glycoside from Laurus nobilis (bay laurel) leaves, induces apoptosis in human melanoma cell lines by inhibiting NF-κB activation

Malignant melanoma is a highly aggressive tumor that frequently resists chemotherapy, so the search for new agents for its treatment is of great importance. In the present study, the antiproliferative propensity against human melanoma cell lines of lauroside B (1), a megastigmane glycoside isolated from Laurus nobilis (bay laurel) leaves, was investigated. This compound suppressed the proliferation of three human melanoma cell lines, namely, A375, WM115, and SK-Mel-28. The 1-induced inhibition of human melanoma cell proliferation was due to the induction of apoptosis, as demonstrated by FACS analysis with annexin V/PI staining and confirmed by activation of caspase-3 and by the cleavage of poly(ADP-ribose) polymerase (PARP). Growing evidence implicates NF-κB as an important contributor to metastasis and increased chemoresistance of melanoma. Thus, it was hypothesized that 1-induced apoptosis could be associated with suppression of NF-κB activation. The results showed that exposure of human melanoma cells to 1 inhibited IκB-α degradation and constitutive NF-κB DNA-binding activity as well as the expression, regulated by NF-κB, of two antiapoptotic genes, XIAP and c-FLIP. Induction of apoptosis by 1 in human aggressive melanoma cell lines has a potential high biological value.

Solomonamides A and B, new anti-inflammatory peptides from Theonella swinhoei

Two unprecedented cyclic peptides, solomonamides A and B, were isolated from the marine sponge Theonella swinhoei. The structures were elucidated on the basis of comprehensive 1D and 2D NMR analysis and high-resolution mass spectrometry. A combined approach, involving Marfey's method, QM J based analysis, and DFT J/(13)C calculations, was used for establishing the absolute configuration of the entire molecule. Solomonamide A showed in vivo anti-inflammatory activity.

Solomonsterols A and B from Theonella swinhoei. The first example of C-24 and C-23 sulfated sterols from a marine source endowed with a PXR agonistic activity

The finding of new PXR modulators as potential leads for treatment of human disorders characterized by dysregulation of innate immunity and with inflammation is of wide interest. In this paper, we report the identification of the first example of natural marine PXR agonists, solomonsterols A and B, from a Theonella swinhoei sponge. The structures were determined by interpretation of NMR and ESIMS data, and the putative binding mode to PXR has been obtained through docking calculations.