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Search Results: 1 - 10 of 298721 matches for " Henri J.;Ancelin "
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Infected erythrocyte choline carrier inhibitors: exploring some potentialities inside Plasmodium phospholipid metabolism for eventual resistance acquisition
Vial, Henri J.;Ancelin, Marie L.;Elabbadi, Noureddine;Orcel, Hélène;Yeo, Hye-Jeong;Gumila, Catherine;
Memórias do Instituto Oswaldo Cruz , 1994, DOI: 10.1590/S0074-02761994000600021
Abstract: we have developed a model for designing antimalarial drugs based on interference with an essential metabolism developed by plasmodium during its intraerythrocytic cycle, phospholipid (pl) metabolism. the most promising drug interference is choline transporter blockage, which provides plasmodium with a supply of precursor for synthesis of phosphatidylcholine (pc), the major pl of infected erythrocytes. choline entry is a limiting step in this metabolic pathway and occurs by a facilitated-diffusion system involving an asymmetric carrier operating according to a cyclic model. choline transport in the erythrocytes is not sodium dependent nor stereospecific as demonstrated using stereoisomers of α and beta methylcholine. these last two characteristics along with distinct effects of nitrogen substitution on transport rate demonstrate that choline transport in the infected erythrocyte possesses characteristics quite distinct from that of the nervous system. this indicates a possible discrimination between the antimalarial activity (inhibition of choline transport in the infected erythrocyte) and a possible toxic effect through inhibition of choline entry in synaptosomes. apart from the de novo pathway of choline, pc can be synthesized by n-methylation from phosphatidylethanolamine (pe). there is a de novo pathway for pe biosynthesis from ethanolamine in infected cells but phosphatidylserine (ps) decarboxylation also occurs. in addition, pe can be directly and abundantly synthesized from serine decarboxylation into ethanolamine, a pathway which is absent from the host. the variety of the pathways that exist for the biosynthesis of one given pl led us to investigate whether an equilibrium can occur between all pl metabolic pathways. indeed, if alternative (compensative) pathway(s) can operate after blockage of the de novo pc biosynthesis pathway this would indicate a potential mechanism for resistance acquisition. up until now, there is no evidence of such a compensative pro
Present development concerning antimalarial activity of phospholipid metabolism inhibitors with special reference to in vivo activity
Ancelin, Marie L.;Vial, Henri J.;Calas, Michele;Giral, Louis;Piquet, Gilles;Rubi, Eric;Thomas, Alan;Peters, Wallace;Slomianny, Christian;Herrera, Socrates;Louis, F.;Mouanda, Vincent;
Memórias do Instituto Oswaldo Cruz , 1994, DOI: 10.1590/S0074-02761994000600020
Abstract: the systematic screening of more than 250 molecules against plasmodium falciparum in vitro has previously shown that interfering with phospholipid metabolism is lethal to the malaria parasite. these compounds act by impairing choline transport in infected erythrocytes, resulting in phosphatidylcholine de novo biosynthesis inhibition. a thorough study was carried out with the leader compound g25, whose in vitro ic50 is 0.6 nm. it was very specific to mature parasites (trophozo?tes) as determined in vitro with p. falciparum and in vivo with p. chabaudi -infected mice. this specificity corresponds to the most intense phase of phospholipid biosynthesis activity during the parasite cycle, thus corroborating the mechanism of action. the in vivo antimalarial activity (ed50) against p. chabaudi was 0.03 mg/kg, and a similar sensitivity was obtained with p. vinckei petteri, when the drug was intraperitoneally administered in a 4 day suppressive test. in contrast, p. berghei was revealed as less sensitive (3- to 20-fold, depending on the p. berghei-strain). this difference in activity could result either from the degree of synchronism of every strain, their invasion preference for mature or immature red blood cells or from an intrinsically lower sensitivity of the p. berghei strain to g25. irrespective of the mode of administration, g25 had the same therapeutic index (lethal dose 50 (ld50)/ed50) but the dose to obtain antimalarial activity after oral treatment was 100-fold higher than after intraperitoneal (or subcutaneous) administration. this must be related to the low intestinal absorption of these kind of compounds. g25 succeeded to completely inhibiting parasitemia as high as 11.2% without any decrease in its therapeutic index when administered subcutaneously twice a day for at least 8 consecutive days to p. chabaudi -infected-rodent model. transition to human preclinical investigations now requires a synthesis of molecules which would permit oral absorption.
Astronomy and the Media: a love story?
Henri M. J. Boffin
Physics , 2009,
Abstract: With the availability of nice images and amazing, dramatic stories, the fundamental questions it addresses, and the attraction is exerces on many, it is often assumed that astronomy is an obvious topic for the media. Looking more carefully, however, one realises that the truth is perhaps not as glamorous as one would hope, and that, although well present in the media, astronomy's coverage is rather tiny, and often, limited to the specialised pages or magazines.
A Renaissance study of Am stars. I. The mass ratio distribution
Henri M. J. Boffin
Physics , 2010, DOI: 10.1051/0004-6361/201015529
Abstract: Triggered by the study of Carquillat & Prieur (2007, MNRAS, 380, 1064) of Am binaries, I reanalyse their sample of 60 orbits to derive the mass ratio distribution (MRD), assuming as they did a priori functional forms, i.e. a power law or a Gaussian. The sample is then extended using orbits published by several groups and a full analysis of the MRD is made, without any assumption on the functional form. I derive the MRD using a Richardson-Lucy inversion method, assuming a fixed mass of the Am primary and randomly distributed orbital inclinations. Using the large sub-sample of double-lined spectroscopic binaries, I show that this methodology is indeed perfectly adequate. Using the inversion method, applied to my extended sample of 162 systems, I find that the final MRD can be approximated by a uniform distribution.
When a couple's squabbling leads to cosmic bubbles
Henri M. J. Boffin
Physics , 2014,
Abstract: Binarity and mass transfer appear to play a key role in the shaping and, possibly, formation of planetary nebulae (PNe), thereby explaining the large fraction of axisymmetric morphologies. I present the binary hypothesis for PNe and its current status. Recent discoveries have led to a quadrupling of the number of post-common envelope binary central stars of PNe compared to the end of the last century, thereby allowing us to envisage statistical studies. Moreover, these binary systems let us study in detail the mass transfer episodes before and after the common envelope, and I present the evidences for mass transfer - and accretion - prior to the common envelope phase.
Mass-ratio distribution of extremely low-mass white dwarf binaries
Henri M. J. Boffin
Physics , 2015, DOI: 10.1051/0004-6361/201525762
Abstract: Knowing the masses of the components of binary systems is very useful to constrain the possible scenarios that could lead to their existence. While it is sometimes possible to determine the mass of the primary star, for single-lined spectroscopic binaries it is not trivial to have good estimates of the mass of the secondary. If a large enough sample of such binaries is available, it is possible, however, to use statistical methods to determine the mass ratio distribution, and thus, the secondary mass distribution. Recently, Andrews et al. (2014) studied the mass distribution of companions to extremely low-mass white dwarfs, using a sample of binaries from the ELM WD Survey. I reanalyse the same sample, using two different methods: in the first one, I assume some functional form for the mass distribution, while in the second, I apply an inversion method. I show that the resulting companion-mass distribution can be as well approximated by either a uniform distribution or a Gaussian distribution. The mass ratio distribution derived from the inversion method, without assuming any a priori functional form, shows some additional fine-grain structure, although, given the small sample, it is difficult to claim that this structure is statistically significant. I conclude that it is not possible yet to fully constrain the distribution of the mass of the companions to extremely low-mass white dwarfs, although it appears that the probability to have a neutron star in one of the systems is indeed very small.
Spiral waves in accretion discs - theory
Henri M. J. Boffin
Physics , 2001,
Abstract: Spirals shocks have been widely studied in the context of galactic dynamics and protostellar discs. They may however also play an important role in some classes of close binary stars, and more particularly in cataclysmic variables. In this paper, we review the physics of spirals waves in accretion discs, present the results of numerical simulations and consider whether theory can be reconcilied with observations.
Mass Transfer by Stellar Wind
Henri M. J. Boffin
Physics , 2014, DOI: 10.1007/978-3-662-44434-4_7
Abstract: I review the process of mass transfer in a binary system through a stellar wind, with an emphasis on systems containing a red giant. I show how wind accretion in a binary system is different from the usually assumed Bondi-Hoyle approximation, first as far as the flow's structure is concerned, but most importantly, also for the mass accretion and specific angular momentum loss. This has important implications on the evolution of the orbital parameters. I also discuss the impact of wind accretion, on the chemical pollution and change in spin of the accreting star. The last section deals with observations and covers systems that most likely went through wind mass transfer: barium and related stars, symbiotic stars and central stars of planetary nebulae (CSPN). The most recent observations of cool CSPN progenitors of barium stars, as well as of carbon-rich post-common envelope systems, are providing unique constraints on the mass transfer processes.
Tongan traditions - On model-building and historical evidence
Henri J.M. Claessen
Bijdragen tot de Taal-, Land- en Volkenkunde , 1988,
Abstract:
The merry maidens of Matavai; A survey of the views of eighteenth-century participant observers and moralists
Henri J.M. Claessen
Bijdragen tot de Taal-, Land- en Volkenkunde , 1997,
Abstract:
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