Anti-inflammatory, antimicrobial and antioxidant activities of Diospyros bipindensis (Gürke) extracts and its main constituents.

ETHNOPHARMACOLOGICAL RELEVANCE: Diospyros bipindensis (Gürke) stem bark is used in Cameroon by Baka Pygmies for the treatment of respiratory disorders. AIM OF THE STUDY: To assess the anti-inflammatory, antibacterial and antioxidant properties of constituents from the bark extracts through bioassay-guided fractionation. MATERIALS AND METHODS: The anti-inflammatory activity of extracts, fractions and pure compounds was assessed through the inhibition of the pro-inflammatory mediator nuclear factor-kappa B (NF-κB) transcriptional activity and nitric oxide (NO) production. DPPH, ABTS and ORAC assays were used for determining the antioxidant properties. The activity against Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Klebsiella pneumoniae, was evaluated on the basis of the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) by the macrodilution method. RESULTS: The water extract showed antimicrobial activity against S. pneumoniae (MIC: 300 µg/ml) and S. pyogenes (MIC: 300 µg/ml). The dichloromethane extract efficiently inhibited NF-κB transcriptional activity and NO production and exhibited significant antioxidant activity in the ORAC assay. An interesting activity was also found against S. pneumoniae (MIC: 200 µg/ml), S. aureus (MIC: 400 µg/ml) and S. pyogenes (MIC: 200 µg/ml). The phytochemical investigation of the dichloromethane extract afforded plumbagin, canaliculatin, ismailin, betulinic acid and 4-hydroxy-5-methyl-coumarin as the main constituents. Plumbagin and ismailin were found to be responsible for the main biological activities observed. CONCLUSIONS: These results may provide a rational support for the traditional use of Diospyros bipindensis stem bark in the treatment of respiratory disorders, since the anti-inflammatory, antimicrobial and antioxidant compounds isolated from the dichloromethane extract were also present in the traditional water extract.

Antioxidant potential and radical-scavenging effects of flavonoids from the leaves of Psidium cattleianum grown in French Polynesia.

Psidium cattleianum J. Sabine (Myrtaceae) is a traditional medicinal plant in French Polynesia. The leaves and roots possess many medicinal properties. These effects may be correlated with the presence of antioxidant compounds. Seven flavonoids along with a benzoic acid were isolated from the leaves of P. cattleianum. The compounds indicated strong antioxidant and radical-scavenging activities in ALP, DPPH(·), ABTS(·-) and ORAC assays. This study demonstrates that the leaves of P. cattleianum possess main compounds with interesting antioxidant and radical-scavenging activities, as clarified by four biological assays. Our findings may justify the use of these leaves in the traditional medicine of French Polynesia. Among the total eight known compounds, reynoutrin and luteolin were isolated for the first time from the genus Psidium.

Targeting the multidrug ABCG2 transporter with flavonoidic inhibitors: in vitro optimization and in vivo validation.

This review describes the breast cancer resistance protein ABCG2 through its structure, functional roles and involvement in cell multidrug resistance, especially in cancer cells resistance to chemotherapeutics. The different types of known inhibitors are described, some being non-selective, since they also bind to other targets, and others being quite specific such as flavonoids. The different classes of active flavonoids and other polyphenols are described, some as plant natural compounds, but most of them being prepared and derivatized through medicinal chemistry. Quantitative structure-activity relationships of the ability of flavones, chalcones, xanthones, acridones and various benzopyrane/benzofurane derivatives to inhibit ABCG2-mediated drug efflux have led to pharmacophores and molecular models allowing to optimize the available hit compounds and to design new-generation lead compounds. Interestingly, inhibitory flavonoids are quite specific for ABCG2 versus ABCB1 and ABCC1, and appear either non-competitive or partially competitive towards mitoxantrone efflux. Most compounds do not inhibit ATPase activity, and are assumed not to be transported themselves by the transporter. Some acridones, firstly optimized in vitro as potent inhibitors, are indeed efficient in vivo, against human xenografts in SCID mice, more efficiently than gefitinib taken as a control. Future developments should open the way to more efficient/targeted modulators including (i) the potential interest of bimodulation by combining two different inhibitors, (ii) computer-assisted ligand-based drug design for getting more potent and more specific inhibitors, (iii) structure-based drug design from ABCG2 molecular models allowing in silico screening and docking of new inhibitors.

QSAR analysis and molecular modeling of ABCG2-specific inhibitors.

In addition to its critical role is controlling drug availability and protecting sensitive organs and stem cells through cellular detoxification, breast cancer resistance protein (BCRP/ABCG2) plays an important role in cancer cell resistance to chemotherapy, together with P-glycoprotein/ABCB1. A main approach to abolish multidrug resistance is to find out specific inhibitors of the drug-efflux activity, able to chemosensitize cancer cell proliferation. Many efforts have been primarily focused on ABCB1, discovered thirty years ago, whereas very few studies have concerned ABCG2, identified much more recently. This review describes the main types of inhibitors presently known for ABCG2, and how quantitative structure-activity relationship analysis among series of compounds may lead to build up molecular models and pharmacophores allowing to design lead inhibitors as future candidates for clinical trials. A special attention is drawn on flavonoids which constitute a structurally-diverse class of compounds, well suited to identify potent ABCG2-specific inhibitors.

Xanthones from Gentianella amarella ssp. acuta with acetylcholinesterase and monoamine oxidase inhibitory activities.

Two new xanthone glycosides, corymbiferin 3-O-beta-D-glucopyranoside (1) and swertiabisxanthone-I 8'-O-beta- d-glucopyranoside (2), were isolated from Gentianella amarella ssp. acuta, along with eight known xanthones: triptexanthoside C, veratriloside, corymbiferin 1-O-glucoside, swertianolin, norswertianolin, swertiabisxanthone-I, bellidin, and bellidifolin, four of them identified for the first time in G. amarella ssp. acuta. The isolation was conducted mainly by centrifugal partition chromatography, and the structures of the isolated compounds were established on the basis of spectrometric data including 2D NMR and mass spectrometry. Xanthones were weakly active against acetylcholinesterase (AChE), except triptexanthoside C, which inhibited AChE with an IC(50) of 13.8 +/- 1.6 microM. Some compounds were active against monoamine oxidases (MAO): bellidin and bellidifolin showed interesting inhibitory activity of MAO A, while swertianolin, the 8-O-glucopyranoside form of bellidifolin, gave 93.6% inhibition of MAO B activity at 10(-5) M.

Stereoselective block of hERG channel by (S)-methadone and QT interval prolongation in CYP2B6 slow metabolizers.

Methadone inhibits the cardiac potassium channel hERG and can cause a prolonged QT interval. Methadone is chiral but its therapeutic activity is mainly due to (R)-methadone. Whole-cell patch-clamp experiments using cells expressing hERG showed that (S)-methadone blocked the hERG current 3.5-fold more potently than (R)-methadone (IC50s (half-maximal inhibitory concentrations) at 37 degrees C: 2 and 7 microM). As CYP2B6 slow metabolizer (SM) status results in a reduced ability to metabolize (S)-methadone, electrocardiograms, CYP2B6 genotypes, and (R)- and (S)-methadone plasma concentrations were obtained for 179 patients receiving (R,S)-methadone. The mean heart-rate-corrected QT (QTc) was higher in CYP2B6 SMs (*6/*6 genotype; 439+/-25 ms; n=11) than in extensive metabolizers (non *6/*6; 421+/-25 ms; n=168; P=0.017). CYP2B6 SM status was associated with an increased risk of prolonged QTc (odds ratio=4.5, 95% confidence interval=1.2-17.7; P=0.03). This study reports the first genetic factor implicated in methadone metabolism that may increase the risk of cardiac arrhythmias and sudden death. This risk could be reduced by the administration of (R)-methadone.

The Hydrogen-Bond: computational approaches and applications to drug design.

This mini-review begins with a presentation of the hydrogen-bond in the context of other intermolecular recognition forces of significance in molecular biology and molecular pharmacology. This is followed by a survey of the various computational methods available to calculate the hydrogen-bonding capacity of compounds. Such methods use quantum mechanics, molecular mechanics, or algorithms based on experimental fragmental values. A recent and promising advance in the computation of H-bonding capacity is the development of specific molecular interaction fields (MIFs) known as molecular hydrogen-bonding potentials (MHBPs). Their interest in relating molecular properties to pharmacokinetic behaviour is highlighted with two examples, namely oral drug absorption and blood-brain barrier permeation.

The esterase-like activity of serum albumin may be due to cholinesterase contamination.

PURPOSE: The "esterase-like activity" of human serum albumin (HSA) is described in the literature, but a contamination of commercially available HSA preparations by plasma cholinesterase is conceivable in some cases. The purpose of the present work was to examine this hypothesis. METHODS: The hydrolytic activity of HSA and its inhibition by physostigmine were measured fluorimetrically by monitoring the hydrolysis of the ester substrate moxisylyte. Affinity chromatography was used to separate cholinesterase and HSA. The cholinesterase activity in the eluted fractions was assessed using Ellman's reagent and butyrylthiocholine as substrate. RESULTS: A significant variation in the esterase-like activity of different albumin batches was observed. This activity was strongly inhibited by physostigmine, a well-known inhibitor of cholinesterase. Affinity chromatography led to a complete separation between HSA and the esterase activity, which was found exclusively in the cholinesterase fraction. CONCLUSIONS: The apparent esterase-like activity of HSA toward moxisylyte and butyrylthiocholine was due to a contamination by cholinesterase. With these substrates, HSA showed a total lack of esterase-like activity.

Generalization of ionic partition diagrams to lipophilic compounds and to biphasic systems with variable phase volume ratios.

The ionic partition diagram methodology has been generalized to address both hydrophilic and lipophilic compounds and to consider biphasic systems with variable phase volume ratios. With this generalized approach electrochemical measurements of ion transfer potentials afford the determination of the standard partition coefficients of all forms of ionizable molecules, including the neutral form, as well as the evaluation of the dissociation constant of monoprotic substances. An interesting consequence of this approach is the definition of an extraction pK(a,ext) which is the apparent pK(a) of neutral acids and bases when dissolved in the organic phase.

Coumarins derivatives as dual inhibitors of acetylcholinesterase and monoamine oxidase.

A set of 17 coumarin and 2 chromone derivatives with known inhibitory activity toward monoamine oxidase (MAO) A and B were tested as acetylcholinesterase (AChE) inhibitors. All compounds inhibited AChE with values in the micromolar range (3-100 microM). A kinetic study showed that most compounds acted as noncompetitive AChE inhibitors. This finding may be of interest in the context of Alzheimer's disease because recent observations suggest that MAO and AChE inhibition might decrease beta-amyloid deposition.

Development of molecular hydrogen-bonding potentials (MHBPs) and their application to structure-permeation relations.

Hydrogen bonds are major forces of recognition in biochemistry and molecular pharmacology; they are an essential component of intermolecular interactions and determine to a significant extent the 3D-structure of bio-macromolecules. To explore three-dimensional H-bonding properties, a new tool called Molecular Hydrogen-Bonding Potentials (MHBPs) was created. The development of this tool is based on a stepwise procedure similar to the one used successfully to generate the Molecular Lipophilicity Potential (MLP). First, a H-bonding fragmental system was developed starting from published solvatochromic parameters. An atomic H-bonding donor fragmental value (alpha) is associated to each hydrogen atom in a polar moiety. Similarly, an atomic H-bonding acceptor fragmental value (beta) is associated to each polar atom. A distance function and an angle function were defined to take into account variations of the MHBPs in space. The fragmental system and the geometric functions were then combined to generate the MHBPs. These are calculated at each point of an adequate molecular surface or on a three-dimensional grid. The MHBPs were compared with GRID interactions energies and correlated with success to oral drug absorption data. Available examples demonstrate that the MHBPs are a promising computational tool in drug design. Their combination with CoMFA and VolSurf is being studied.

Interaction of psychotropic drugs with monoamine oxidase in rat brain.

Literature observations indicate that some psychotropic drugs may have inhibitory activity towards monoamine oxidase (MAO). This study was undertaken to assess the potency, isozyme selectivity and mechanism of inhibition of representative first- and second-generation antidepressant drugs towards rat brain MAO-A and MAO-B. Five tricyclic antidepressants (imipramine, trimipramine, clomipramine, amitriptyline and doxepine) and three selective serotonin reuptake inhibitors (fluoxetine, fluvoxamine and citalopram) were examined. They showed inhibitory activity towards MAO-A and MAO-B, with clear selectivity for MAO-B (Ki in the micromolar range). Their mechanism of inhibition was competitive towards MAO-B and of a mixed competitive type towards MAO-A. The results suggest that some of the drugs examined might also contribute an MAO inhibitory effect in chronically treated patients.

The apparent lipophilicity of quaternary ammonium ions is influenced by galvani potential difference, not ion-pairing: a cyclic voltammetry study.

PURPOSE: This work examines whether ion-pairing contributes to the apparent lipophilicity of cations, which is seen by a shake-flask or titrimetic method to be influenced by the nature and concentration of counter-ions. METHODS: To solve this problem, the lipophilicity of several quaternary ammonium drugs was measured by cyclic voltammetry in the 1,2-dichloroethane/water system. The standard ionic partition coefficient values so obtained (log Pdce(o,C)) were correlated with log Poct values calculated by the CLOGP algorithm for the respective neutral molecules. RESULTS: The standard (i.e., intrinsic) lipophilicity values are shown to depend on a, the structure of the ion (nature, volume, charge), and b, on the Galvani potential difference at the ITIES (interface between two immiscible electrolyte solutions). CONCLUSIONS: The standard lipophilicity values were not influenced by counter-ions. In contrast, simulations showed that the increased apparent lipophilicity of cations, as measured by the shake-flask method in the presence of lipophilic anions, is fully accounted for by the resulting increase in the Galvani potential difference.

Lipophilicity behaviour of the Zwitterionic antihistamine cetirizine in phosphatidylcholine liposomes/water systems.

PURPOSE: The partitioning of cetirizine in a phosphatidylcholine liposomes/water system was compared with that of hydroxyzine and acrivastine to gain insight into the mechanisms of interaction of its various electrical species with membranes. METHODS: The lipophilicity profiles of the compounds were obtained from equilibrium dialysis and potentiometry, and compared with changes in NMR relaxation rates. RESULTS: The neutral form of hydroxyzine interacted mainly via hydrophobic interactions with the bilayer lipid core of the membrane, whereas for the cationic form both hydrophobic and electrostatic interactions were involved. Zwitterionic and anionic cetirizine were less lipophilic than its cation, which behaved like the corresponding species of hydroxyzine. Zwitterionic cetirizine interacted more by weak electrostatic interactions with the polar headgroups of phospholipids than by hydrophobic interactions with the membrane interior. The lipophilicity of its anion reflected the balance of repulsive electrostatic interactions between the carboxylate and phosphate groups and the hydrophobic interactions with the lipid core. CONCLUSION: The study confirms that various mechanisms influence the interaction of solutes with liposomes. Combining experimental techniques and using suitable reference compounds proves useful.

Inhibition of monoamine oxidases by functionalized coumarin derivatives: biological activities, QSARs, and 3D-QSARs.

A large series of coumarin derivatives (71 compounds) were tested for their monoamine oxidase A and B (MAO-A and MAO-B) inhibitory activity. Most of the compounds acted preferentially on MAO-B with IC(50) values in the micromolar to low-nanomolar range; high inhibitory activities toward MAO-A were also measured for sulfonic acid esters. The most active compound was 7-[(3, 4-difluorobenzyl)oxy]-3,4-dimethylcoumarin, with an IC(50) value toward MAO-B of 1.14 nM. A QSAR study of 7-X-benzyloxy meta-substituted 3,4-dimethylcoumarin derivatives acting on MAO-B yielded good statistical results (q(2)() = 0.72, r(2)() = 0.86), revealing the importance of lipophilic interactions in modulating the inhibition and excluding any dependence on electronic properties. CoMFA was performed on two data sets of MAO-A and MAO-B inhibitors. The GOLPE procedure, with variable selection criteria, was applied to improve the predictivity of the models and to facilitate the graphical interpretation of results.

Very slow chiral inversion of clopidogrel in rats: a pharmacokinetic and mechanistic investigation.

Clopidogrel hydrogen sulfate, a thienopyridine derivative, is an ADP receptor antagonist that inhibits platelet aggregation. Clopidogrel is an enantiopure carboxylic ester of S-configuration. The R-enantiomer is devoid of antithrombotic activity and can provoke convulsions at high doses in animals. During preclinical safety evaluation, the possible chiral inversion of clopidogrel has, therefore, been investigated in vivo after repeated oral administration of different dose levels of clopidogrel to male and female rats. Due to rapid metabolism in the liver and low plasma levels of unchanged drug, possible chiral inversion was assessed by monitoring the plasma concentrations of the carboxylic acid metabolites, i.e., the (S)- and (R)-acid, by means of a stereoselective assay. The production of 4 to 8% of (R)-acid was observed. This could be the result of chiral inversion of either clopidogrel or its main metabolite, the (S)-acid. Thus, the possibility of nonenzymatic and enzymatic inversion of clopidogrel and its carboxylic acid metabolite was studied in vitro by chiral HPLC and (1)H NMR. Nonenzymatic chiral inversion of clopidogrel at 37 degrees C in 0.1 M phosphate buffers could be observed but was found to be slow, with estimated half-lives of 7 to 12 days, depending on the pH. The (S)-acid was configurationally fully stable up to 45 days in phosphate buffers. Neither clopidogrel nor its carboxylic acid metabolites were subject to enzymatic chiral inversion in isolated rat hepatocyte suspensions. We conclude that the nonenzymatic inversion of clopidogrel accounts for the 4 to 8% of chiral inversion seen in vivo in the rat.

[Chirality and drugs]. / Chiralité et Médicament.

The two enantiomers of a chiral drug may have vastly different pharmacodynamic and pharmacokinetic properties. As a result, the research and development of chiral drugs raises specific problems some of which are discussed here. Thus, various pharmacokinetic interactions may involve two enantiomers, as seen for example when one enantiomer inhibits the metabolism of the other and modifies its effects. A different situation occurs when a third compound stereoselectively inhibits the metabolism of one of the two enantiomers. Another problem examined here results from the lack of configurational stability of some chiral drugs, a little known phenomenon whose consequences can be of pharmacological or pharmaceutical significance depending on the rate of the reaction of racemization or epimerisation. In-depth investigations are needed before choosing between a eutomer or a racemate.

Predicting blood-brain barrier permeation from three-dimensional molecular structure.

Predicting blood-brain barrier (BBB) permeation remains a challenge in drug design. Since it is impossible to determine experimentally the BBB partitioning of large numbers of preclinical candidates, alternative evaluation methods based on computerized models are desirable. The present study was conducted to demonstrate the value of descriptors derived from 3D molecular fields in estimating the BBB permeation of a large set of compounds and to produce a simple mathematical model suitable for external prediction. The method used (VolSurf) transforms 3D fields into descriptors and correlates them to the experimental permeation by a discriminant partial least squares procedure. The model obtained here correctly predicts more than 90% of the BBB permeation data. By quantifying the favorable and unfavorable contributions of physicochemical and structural properties, it also offers valuable insights for drug design, pharmacological profiling, and screening. The computational procedure is fully automated and quite fast. The method thus appears as a valuable new tool in virtual screening where selection or prioritization of candidates is required from large collections of compounds.

The pH-partition profile of the anti-ischemic drug trimetazidine may explain its reduction of intracellular acidosis.

PURPOSE: The anti-ischemic drug trimetazidine (TMZ) acts by a combination of molecular mechanisms which begin to be understood. Thus, it acts in the micromolar range to significantly reduce intracellular acidification during ischemia. To search for a possible physicochemical explanation of this phenomenon, we investigated the transfer mechanisms of the various electrical forms of this dibasic drug. METHODS: The transfer characteristics of TMZ were studied by electrochemistry at the water/1,2-dichloroethane interface. Cyclic voltammetry was used to measure the formal transfer potentials of singly and doubly protonated forms of TMZ (noted TH+ and TH(2)2+, respectively) as a function of aqueous pH, and the partition coefficient of neutral TMZ (log P(T)) was measured by two-phase titration. RESULTS: log P(T) was measured to be 1.04 +/- 0.06, and the acid-base dissociation constants in water were deduced to be pK(w)a1 = 4.54 +/- .02 and pK(w)a2 = 9.14 +/- 0.02. The partition coefficients of TH+ and TH(2)2+ were found to be respectively log P0'TH+ = -3.78 +/- 0.16 and log P0'TH(2)2+ = -9.84 +/- 0.30, which agrees well with the charge being delocalized on two nitrogen atoms in TH+. The pH-partition profile of TMZ was then established in the form of its ionic partition diagram, which showed that the affinity of the ions for the organic phase is pH-dependent and strongly increased by the interfacial potential. CONCLUSIONS: This behavior suggests a physicochemical mechanism whereby efflux of protonated TMZ out of an acidified cell is facilitated, in effect exporting protons to extracellular space.