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H Vial

Publications and source records attributed to H Vial.

At least 19 recordsLinked to original sources
PubMed2003

[Malaria prophylaxis and treatment: problems, recent developments and perspectives].

Rapid development of significant resistance to antimalarials has been a major force driving research to identify and develop new drugs. Recent progress in this field promises to lead to a much greater range of antimalarial agents. The availability of a broader battery of drugs should provide a partial solution to the dilemma faced by malarial control agencies, i.e., distributing antimalarial drugs as widely as possible without enhancing resistance. Avenues of research for development of new antimalarials include lipid metabolism, degradation of hemoglobin and proteins, interaction with molecule transport, iron metabolism, apicoplasty and signal transduction. Throughout the course of evolution, micro-organisms have thwarted traps set by the environment including those designed by man. One can but hope that the different approaches now being implemented on a worldwide bases will overcome the defense mechanisms that Plasmodium have deployed in their long co-evolution with humans and anopheles.

Animals↗
PubMed2000

Antimalarial activity of compounds interfering with Plasmodium falciparum phospholipid metabolism: comparison between mono- and bisquaternary ammonium salts.

On the basis of a previous structure-activity relationship study, we identified some essential parameters, e.g. electronegativity and lipophilicity, required for polar head analogues to inhibit Plasmodium falciparum phospholipid metabolism, leading to parasite death. To improve the in vitro antimalarial activity, 36 cationic choline analogues consisting of mono-, bis-, and triquaternary ammonium salts with distinct substituents of increasing lipophilicity were synthesized. For monoquaternary ammonium salts, an increase in the lipophilicity around nitrogen was beneficial for antimalarial activity: IC(50) decreased by 1 order of magnitude from trimethyl to tripropyl substituents. Irrespective of the polar head substitution (methyl, ethyl, hydroxyethyl, pyrrolidinium), increasing the alkyl chain length from 6 to 12 methylene groups always led to increased activity. The highest activity was obtained for the N,N,N-tripropyl-N-dodecyl substitution of nitrogen (IC(50) 33 nM). Beyond 12 methylene groups, the antimalarial activities of the compounds decreased slightly. The structural requirements for bisquaternary ammonium salts in antimalarial activity were very similar to those of monoquaternary ammonium salts, i.e. polar head steric hindrance and lipophilicity around nitrogen (methyl, hydroxyethyl, ethyl, pyrrolidinium, etc.). In contrast, with bisquaternary ammonium salts, increasing the lipophilicity of the alkyl chain between the two nitrogen atoms (from 5 to 21 methylene groups) constantly and dramatically increased the activity. Most of these duplicated molecules had activity around 1 nM, and the most lipophilic compound synthesized exhibited an IC(50) as low as 3 pM (21 methylene groups). Globally, this oriented synthesis produced 28 compounds out of 36 with an IC(50) lower than 1 microM, and 9 of them had an IC(50) in the nanomolar range, with 1 compound in the picomolar range. This indicates that developing a pharmacological model for antimalarial compounds through choline analogues is a promising strategy.

Animals↗
PubMed2000

Characterization of Plasmodium falciparum CDP-diacylglycerol synthase, a proteolytically cleaved enzyme.

Cytidine diphosphate-diacylglycerol (CDP-DAG), an obligatory intermediate compound in the biosynthesis of the major anionic and zwitterionic phospholipids, is synthesized by CDP-DAG synthase (CDS). The gene encoding CDS was isolated from the human malaria parasite Plasmodium falciparum, based on sequence conservation to CDS from other organisms. The P. falciparum gene is located as a single copy on chromosome 14. The open reading frame (ORF) of PfCDS gene encodes a putative protein of 667 amino acids and 78 kDa. Only the C-terminal 422 amino acids share 40% homology with eukaryotic CDSs. The very long and non-conserved N-terminal region of 245 amino acids is hydrophilic and contains asparagine-rich and repetitive sequences. Two mRNA of 3.5 and 4 kb were detected. Transcription is developmentally regulated during the asexual intraerythrocytic cycle, being the weakest in the ring-stage. PfCDS enzyme activities in infected erythrocytes correlates with the transcription pattern, consistent with an increased synthesis of phospholipids in trophozoites and schizonts. Antisera raised against two synthetic peptides from the C-terminal region of PfCDS detected a single protein of 51 kDa in Western blot analysis, specific for parasitized erythrocytes. A protein of 28 kDa was recognized by an antiserum against an N-terminal peptide, indicating that PfCDS is proteolytically processed. Expression of 51- and 28-kDa proteins was developmentally regulated similar to regulation of the transcripts and the enzyme activity. The conserved C-terminal region of PfCDS, cloned into a eukaryote expression vector and transfected in COS-7 cells, showed a two-fold increase CDP-DAG synthase activities, indicating that the isolated gene most likely encoded the P. falciparum CDS enzyme.

Amino Acid Sequence↗
PubMed1999

Cationomycin and monensin partition between serum proteins and erythrocyte membrane: consequences for Na+ and K+ transport and antimalarial activities.

The ionophore properties of cationomycin and monensin were studied on human erythrocytes by measuring Na+ influx by 23Na NMR and concomitant K+ efflux by potentiometry in the presence of increasing amounts of serum. Both ion currents (Na+ or K+) decreased linearly with the reciprocal of serum amount. The serum effects on ion currents were stronger with cationomycin than with monensin. Assuming this decreased transport activity was due to drug binding to serum proteins, a partition coefficient between the protein and the membrane phase was determined for each ionophore by using a novel model. This partition coefficient is about 30 times higher for cationomycin than for monensin; the same result was obtained with purified human serum albumin, indicating that albumin may be the major ionophore binding protein of serum. In parallel, we also measured IC50 for 50% in vitro growth inhibition of Plasmodium falciparum, the agent of malaria. In the presence of increasing serum concentrations, the antimalarial activity was decreased for both ionophores. Serum effect was less severe for monensin than for cationomycin, in agreement with the weaker interaction of monensin with proteins as shown from the partition coefficient values. A correlation was established between the ion transport currents (sodium and potassium) and the IC50 measured on P. falciparum in the presence of the various concentrations of serum. The relative value of the ion transport currents (expressed as percentage of control in absence of serum) can be indicative of the ionophore unbound fraction in the medium.

Animals↗
PubMed1997

Antimalarial activity of molecules interfering with Plasmodium falciparum phospholipid metabolism. Structure-activity relationship analysis.

A series of 80 compounds, primary, secondary, and tertiary amines and quaternary ammonium and bisammonium salts, most of them synthesized as potential choline or ethanolamine analogs, were tested against the in vitro growth of Plasmodium falciparum, the human malaria parasite. They were active over the 10(-3)-10(-8) M concentration range. A structure-activity relationship study was carried out using autocorrelation vectors as structural descriptors, and multidimensional analysis. Principal component analysis, ascending hierarchical classification, and stepwise discriminant analysis showed that both the size and shape of the molecule were essential for antimalarial potency, making the lipophilicity and electronegativity distribution in the molecular space essential. Using the autocorrelogram describing the molecular shape and the electronegativity distribution on the molecular graph, 98% of the molecules were correctly classified either as poorly active or active with only three explanatory variables. The most active compounds were quaternary ammoniums salts whose nitrogen atom had only one long lipophilic chain of 11 or 12 methylene groups (E5, E6, E10, E13, E20, E21, E22, E23, F4, F8), or the bisammoniums whose polar heads were linked by linear alkyl chains of 10 to 12 carbon atoms (G4, G23). The hydroxyethyl group of choline was not very beneficial, whereas the charge and substitutions of nitrogen (aimed at increasing lipophilicity) were essential for optimal interactions. A crude topographic model of the ligand (choline) binding site was thus drawn up.

Animals↗
PubMed1997

Continuous in vitro culture of Babesia divergens in a serum-free medium.

Babesia divergens was cultivated in RPMI 1640 (25 mM HEPES) supplemented with 10% human serum (RPMI-10% HS) with a high percentage of parasitized erythrocytes (PPE) (> or = 40%). Standardization of in vitro tests, purification of exoantigens, biochemical studies and the safety of the culture handler motivated the development of a serum-free defined medium. Removal of serum greatly reduced the PPE but, after a period of adaptation, the culture was continuous and the parasite was able to develop a 3% routine PPE. Addition of vitamins or reduced glutathione in basal medium (RPMI) did not improve the PPE. The supplementation of basal medium with lipidic carrier (Albumax I or bovine serum albumin-Cohn's fraction V) promoted the growth of B. divergens with high PPE (> 30%) close to those obtained in RPMI-10% HS. Neither protein nor lipid fractions alone were able to restore the growth of B. divergens. Nevertheless, the whole lipid fraction from serum or Albumax I added to delipidated albumin partially restored the growth (7% PPE), indicating that the presentation of specific lipids by a carrier is crucial for the parasite. All the data indicate that Albumax I can replace human serum offering the advantages of safety, standardization for chemosensitivity tests, and exoantigen purification.

Animals↗
PubMed1996

Ionophore properties of monensin derivatives studied on human erythrocytes by 23Na NMR and K+ and H+ potentiometry: relationship with antimicrobial and antimalarial activities.

Eight derivatives of monensin with a modified C25-C26 moiety were synthesized. Their ionophore properties were studied on human erythrocytes by measuring Na+ influx with 23Na NMR and concomitant K+ and H+ efflux by potentiometry. Modification of OH-26 led to inversion of selectivity of transport in favor of K+/Na+ in comparison with monensin. This selectivity disappeared by suppression of the C26-OH moiety. Finally the ionophore ability was lost if the head-to-tail chelation of the monensin skeleton was prevented by blocking the terminal OH-25 and -26 functions. All the compounds were inactive on Gram-negative bacteria and fungi. MIC measured on Bacillus cereus showed that derivatives with increased K+/Na+ selectivity were clearly the most active against Bacillus growth. Most of the compounds showed potential antimalarial properties in the nanomolar range when tested in vitro against Plasmodium falciparum. The IC50S measured were correlated with the whole Na+ and K+ transport efficiency rather than with the ionic selectivity. In both cases determination of initial fluxes of transport for both cations (Na+ and K+) was necessary to investigate the relationship between biological and ionophore properties.

Adult↗
PubMed1996

Recent developments and rationale towards new strategies for malarial chemotherapy.

The major problem facing world research for new antimalarials lies in encountered difficulties in the search for new promising paths. The past 20 years have witnessed a very impressive increase in our understanding of the biochemistry and molecular biology of malaria parasites, with attention focused on specific parasite molecules that are keys to the parasite life cycle or the induction of its pathogenesis. Directed pharmacology research has involved the identification and characterization of targets that can be specifically pharmacologically affected, including the replicating machinery of the parasites, various metabolisms such as the purine salvage pathway, and biosynthesis of pyrimidines or phospholipids. Protease inhibitors (e.g. those degrading haemoglobin), the use of iron chelators or inhibition of heme polymerization, induction of oxidative stress or inhibition of antioxidant enzymes are also investigated. Some pathways have already been validated with current antimalarials but, due to the development of resistance, complete characterization of the molecular structure of the target should allow attack of these exceptional molecules at novel and distinct sites with new drug concepts. The problem in the quest to develop new antimalarials is the fact that the results are not being materialized, but there is no lack of pharmacological targets.

Animals↗
PubMed1993

[Influence of the position of the arm on the level of clinical arterial pressure].

The position of the arm in relation to the heart is one of the factors responsible for variations in arterial blood pressure. The purpose of this study was to confirm these variations and their diagnostic and therapeutic consequences. The blood pressure of 59 subjects was measured in supine position with or without support, this support being a device, recently developed by Swedish physicians, that brings the radial notch of the ulna at heart level. The results obtained confirmed the existence of variations in blood pressure values according to the position of the arm in relation to the heart. When measured with the support, blood pressure fell by 5 mmHg for systolic pressure and 4.6 mmHg for diastolic pressure. These results prove the need for standardization of blood pressure measurement in supine position. It is permissible to believe that at this moment a non-negligible proportion of patients (12 percent in our series) is either wrongly regarded as hypertensive or overtreated. In addition, the blood pressure variations induced by the brachial support should be taken into account in the analysis of future epidemiological studies. We conclude that using the brachial support can be recommended for a better evaluation of supine blood pressure measurements.

Arm↗
PubMed1991

Distinct lipid compositions of parasite and host cell plasma membranes from Plasmodium chabaudi-infected erythrocytes.

Mouse erythrocytes infected with early or late trophozoites of the malaria parasite Plasmodium chabaudi were fractionated into free parasites and host cell plasma membranes, and both fractions were analyzed for cholesterol content and the composition of phospholipids and total fatty acids. The major results are: (i) parasites contain only a very low level of cholesterol which is about one-tenth of that of host cell plasma membranes. (ii) Parasites also contain less sphingomyelin and phosphatidylserine as well as more phosphatidylcholine than host cell plasma membranes. (iii) Parasites contain less 18:0 and 18:1 and more 18:2 and 20:4 fatty acids than host cell plasma membranes. (iv) During intraerythrocytic growth of parasites from early to late trophozoites, the relative proportions of cholesterol and phospholipids remain largely unchanged in both parasites and host cell plasma membranes. However, significant changes occur in the fatty composition of both compartments. There is an increase in the 20:4 and a decrease in the 18:0 and 18:1 fatty acids. (v) Plasma membranes of infected and non-infected erythrocytes exhibit about the same cholesterol content and phospholipid composition, but differ in the total fatty acid composition. Our data suggest the existence of distinct mechanisms controlling the different lipid compositions of parasites and host cell plasma membranes in whole Plasmodium chabaudi-infected erythrocytes during intraerythrocytic development of parasites, though both compartments are known to depend on the supply of various lipids from the host.

Animals↗
PubMed1991

Oxysterol activation of arachidonic acid release and prostaglandin E2 biosynthesis in NRK 49F cells is partially dependent on protein kinase C activity [corrected].

We previously demonstrated that the oxysterol potentiation of arachidonic acid release and prostaglandin biosynthesis induced by foetal calf serum activation of normal rat kidney (NRK) cells (fibroblastic clone 49F) was not related to a direct effect of oxysterols on cell free Ca2+ level. Since both Ca2+ variations and protein kinase C are involved in arachidonic acid release in some models, we looked for a possible modulation by protein kinase C in the oxysterol effect on arachidonic acid release. We show that when the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA), a protein kinase C activator, was added to the culture medium, the oxysterol effect on arachidonic acid release and prostaglandin synthesis clearly increased. Moreover, the effect of TPA was dose-dependent and TPA EC50 (4 x 10(-9) M) was unchanged in the presence of the oxysterol. Preincubation of cells with TPA for 24 h prevented the arachidonic acid release induced by TPA alone, whereas the oxysterol effect was decreased but not abolished. In the absence of serum, TPA and ionomycin added together induced the same noticeable (arachidonic acid) release and PGE2 synthesis as serum alone. Nevertheless, the potentiating effect of cholest-5-ene-3 beta, 25-diol was much higher when serum itself was used to activate NRK cells than it was in the present serum-mimicking experimental conditions. Thus, the presence of growth factors is probably required to obtain a full oxysterol effect. We conclude that the oxysterol effect was synergistic with, but not fully dependent on, protein kinase C and Ca2+ ion fluxes, therefore oxysterols could affect earlier events triggered by serum growth factor binding to their cell membrane receptors.

Animals↗
PubMed1990

Abnormal behavior of protein kinase C in the human myeloma cell line, RPMI 8226.

Protein kinase C activity of the human myeloma cell line, RPMI 8226, was studied after prepurification on DEAE-cellulose. The total protein kinase activity, eluted at 0.12 M NaCl, was 493 nmol/min/10(10) cells, but 38% was associated with membranes. The lipid dependence of cytosolic and membrane activities was only 52% and 21%, respectively. This activity increased with time, to as much as 200% for the membrane fraction after 7 days, whereas lipid dependence and the PDBu binding properties were lost. This modified activity was not due to the extinction of a copurifying endogenous inhibitor nor to classical PKC proteolysis. TPA-treatment of these cels is accompanied by a rapid, selective and complete loss of lipid-dependent activity of the cytosol, thus benefiting co-migrating lipid independent activity, with no membrane fraction recovery or PKM formation.

Animals↗
PubMed1988

Phosphoinositide breakdown and superoxide anion release in formyl-peptide-stimulated human alveolar macrophages. Comparison between quiescent and activated cells.

Human alveolar macrophages (AMs) from allergic asthmatics (AAs) showed continuous Li+-sensitive production of IP1, indicating that the cells were continuously activated. Furthermore, whereas the accumulation of IP1, IP2 and IP3 rapidly increased by as much as 125-175% in chemotactic-factor-stimulated AMs from healthy subjects, stimulation of cells from AAs increased these inositol phosphates only slightly. This moderate production could be due to a permanent state of activation leading to a depleted pool of polyphosphoinositides, corroborating the greater capacity of these cells to generate superoxide anion after stimulation by a chemoattractant. The activation state could be due to the action of priming agents, which are known to be released into the inflammatory sites.

Cells, Cultured↗
PubMed1987

Phospholipid organization in monkey erythrocytes upon Plasmodium knowlesi infection.

The phospholipid organization in monkey erythrocytes upon Plasmodium knowlesi infection has been studied. Parasitized and nonparasitized erythrocytes from malaria-infected blood were separated and pure erythrocyte membranes from parasitized cells were isolated using Affi-Gel beads. In this way, the phospholipid content and composition of the membrane of nonparasitized cells, the erythrocyte membrane of parasitized cells and the parasite could be determined. The phospholipid content and composition of the erythrocyte membranes of nonparasitized and parasitized cells and erythrocytes from chloroquine-treated monkeys cured from malaria, were the same as in normal erythrocytes. The phospholipid content of the parasite increased during its development, but its composition remained unchanged. Three independent techniques, i.e., treatment of intact cells with phospholipase A2 and sphingomyelinase C, fluorescamine labeling of aminophospholipids and a phosphatidylcholine-transfer protein-mediated exchange procedure have been applied to assess the disposition of phospholipids in: erythrocytes from healthy monkeys, nonparasitized and parasitized erythrocytes from monkeys infected with Plasmodium knowlesi, and erythrocytes from monkeys that had been cured from malaria by chloroquine treatment. The results obtained by these experiments do not show any abnormality in phospholipid asymmetry in the erythrocyte from malaria-infected (splenectomized) monkeys, neither in the nonparasitized cells, nor in the parasitized cells at any stage of parasite development. Nevertheless, a considerable degree of lipid bilayer destabilization in the membrane of the parasitized cells is apparent from the enhanced exchangeability of the PC from those cells, as well as from their increased permeability towards fluorescamine.

Androgen-Binding Protein↗
PubMed1987

Isolation and characterization of parasites and host cell ghosts from erythrocytes infected with Plasmodium chabaudi.

A new procedure has been developed which allows the concomitant isolation of viable parasites and host cell plasma membranes from erythrocytes infected with Plasmodium chabaudi trophozoites. The average final yield of parasites is 56%. Free parasites reveal a well preserved ultrastructure, incorporate [14C]isoleucine for at least 3 h, and synthesize about the same proteins as parasites within erythrocytes as monitored by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE)-autoradiography. The host cell plasma membranes can be isolated in the form of ghosts with an average yield of 27%. The ghosts possess a structurally intact plasma membrane as revealed by freeze-etch electron microscopy. The ghosts are regularly associated with seven neo-proteins as identified by SDS-PAGE and isoelectric focusing (IEF)/SDS-PAGE. These neo-proteins have the following apparent molecular masses: 154 kDa, 145 kDa, 90 kDa, 72 kDa (pI 4.5), 67 kDa, 52 kDa, and 33 kDa (pI 5.7), respectively. The contamination of ghosts by parasite material and, conversely, the contamination of parasites by host cell plasma membranes is very low as demonstrated by light and electron microscopy, lactoperoxidase-mediated radioiodination and the distribution of the typical parasite marker enzymes such as choline kinase, cholinephosphotransferase and ethanolaminephosphotransferase.

Animals↗