PubMed Health⌕ Search

Biomedical subjects

Bernard Rousseau

Publications and source records attributed to Bernard Rousseau.

At least 19 recordsLinked to original sources
PubMed2006

On a variational approach to the Soret coefficient.

In this paper, a variational approach to the Soret coefficient initiated by Kempers [J. Chem. Phys. 90, 6541 (1989)] is critically revisited. We show that the physical coherence of the whole procedure leads to a very peculiar choice of the type of constraint one can select to mimic the nonequilibrium stationary state. However, we demonstrate that its precise definition would require a statistical evaluation of the heat of transfer, or a variational approach based on more microscopic ingredients.

Journal Article↗
PubMed2006

Optimization of the anisotropic united atoms intermolecular potential for n-alkanes: improvement of transport properties.

The parameters of the anisotropic united atom (AUA) intermolecular potential for n-alkanes originally proposed by Toxvaerd [J. Chem. Phys. 93, 4290 (1990)] [AUA(3)] was optimized by Ungerer et al. [J. Chem. Phys. 112, 5499 (2000)] [AUA(4)] on the basis of equilibrium properties (vapor pressures, vaporization enthalpies, and liquid densities). In this work we analyze the influence of the torsion potential in the internal and collective dynamics of the AUA model. The modified potential [AUA(4m)] preserves all the intermolecular parameters and only explores an increment in the trans-gauche and gauche(+)-gauche(-) transition barrier of the torsion potential. This modification better reproduce different transport properties (shear viscosity, self-diffusion coefficient, and internal relaxation times), keeping the accuracy achieved in our previous work for equilibrium properties. An extensive investigation of the shear viscosity of ethane, n-pentane, n-dodecane, and n-eicosane in a wide range of pressures and temperatures shows that the AUA(4m) improves the accuracy of the original AUA(4), reducing the absolute average deviation from 30% to 14.5%. Finally, the self-diffusion coefficient of n-hexane computed with the new model in the range of 223-333 K and from 0.1 to 295 MPa is in better agreement with respect to the experimental data than the original model.

Journal Article↗
PubMed2006

Low-temperature vapor-liquid equilibria from parallelized molecular dynamics simulations. Application to 1- and 2-methylnaphthalene.

A parallelized sampling version of the Gibbs Ensemble (Mol. Phys. 2000, 98, 1887) has been implemented to predict low-temperature vapor-liquid equilibria of 1- and 2-methylnaphthalene modeled by anisotropic united atom potentials. The simulation were performed at the low temperature of 364.2 K at which common direct simulation methods fail due to particle transfer problems. The simulation results are compared with published results obtained from the Gibbs-Duhem integration method and with experimental data. Both methods are compared and discussed in terms of computational efficiency and with respect to their future use at other thermodynamic conditions.

Journal Article↗
PubMed2005

Investigation of anti-hyaluronidase treatment on vocal fold wound healing.

SUMMARY: Phytochemical constituents of medicinal plants demonstrate inhibition of tissue and bacterial hyaluronidase. Echinacoside is a caffeoyl conjugate of Echinacea with known anti-hyaluronidase properties. The purpose of this study was to investigate the wound healing effects of Echinacea on vocal fold wound healing and functional voice outcomes. Pig animal model. METHODS: Vocal fold injury was induced in 18 pigs by unilateral vocal fold stripping. The uninjured vocal fold served as control. Three groups of six pigs randomly received a topical application of 300, 600, or 1,200 mg of standardized Echinacea on the injured side. Animals were euthanized after 3, 10, and 15 days of wound healing. Phonation threshold pressure and vocal economy measurements were obtained from excised larynges. Treatment outcomes were examined by comparing the animals receiving treatment with a set of 19 untreated and 5 historical controls. Treatment effects on wound healing were evaluated by histologic staining for hyaluronan and collagen. Treated larynges revealed improved vocal economy and phonation threshold pressure compared with untreated larynges. Histologically, treated vocal folds revealed stable hyaluronan content and no significant accumulation of collagen compared with control. Findings provide a favorable outcome of anti-hyaluronidase treatment on acute vocal fold wound healing and functional measures of voice.

Animals↗
PubMed2005

Cyclic nucleotides, the photosynthetic apparatus and response to a UV-B stress in the Cyanobacterium Synechocystis sp. PCC 6803.

Cyclic nucleotides cAMP and cGMP are ubiquitous signaling molecules that mediate many adaptative responses in eukaryotic cells. Cyanobacteria present the peculiarity among the prokaryotes of having the two types of cyclic nucleotide. Cellular homeostasis requires both cyclases (adenylyl/guanylyl, for their synthesis) and phosphodiesterases (for their degradation). Fully segregated null mutants have been obtained for the two genes, sll1624 and slr2100, which encode putative cNMP phosphodiesterases. We present physiological evidence that the Synechocystis PCC 6803 open reading frame slr2100 could be a cGMP phosphodiesterase. In addition, we show that Slr2100, but not Sll1624, is required for the adaptation of the cells to a UV-B stress. UV-B radiation has deleterious effects for photosynthetic organisms, in particular on the photosystem II, through damaging the protein structure of the reaction center. Using biophysical and biochemical approaches, it was found that Slr2100 is involved in the signal transduction events which permit the repair of the UV-B-damaged photosystem II. This was confirmed by quantitative reverse transcriptase-PCR analyses. Altogether, the data point to an important role for cGMP in signal transduction and photoacclimation processes during a UV-B stress.

Adaptation, Physiological↗
PubMed2005

Computing the Soret coefficient in aqueous mixtures using boundary driven nonequilibrium molecular dynamics.

We have computed the Soret coefficient in aqueous mixtures using a boundary driven nonequilibrium molecular dynamics algorithm and standard molecular force fields. The choice of this specific approach is justified by the nature of the mixtures studied here. Four aqueous solutions, including methanol, ethanol, acetone, and dimethyl-sulfoxide (DMSO) have been studied at ambient conditions for different compositions. The experimental behavior of water-alcohol mixtures was reproduced, including the change of sign of the Soret coefficient with composition, in excellent agreement with existing experimental data. The methodology has been applied to obtain pure predictions for water-acetone and water-DMSO where no experimental data are accessible. A change of sign is also observed in the same range of composition as in water-alcohol mixtures. It is suggested that the nature and strength of the molecular interactions, rather than the mass or shape ratio of the components, dominates the behavior of the Soret coefficient versus composition for the aqueous associating mixtures studied here.

Journal Article↗
PubMed2005

Dosing and scheduling influence the antitumor efficacy of a phosphinic peptide inhibitor of matrix metalloproteinases.

The in vivo disposition and antitumor efficacy of a newly developed phosphinic matrix metalloproteinase inhibitor (RXP03) were examined. RXP03 potently inhibits MMP-11, MMP-8 and MMP-13, but not MMP-1 and MMP-7. Twenty-four hours after i.p. injection into mice, most of the RXP03 was recovered intact in plasma, feces (biliary excretion) and tumor tissue. Pharmacokinetic parameters indicated that, after an i.p. dose of 100 microg/day, the plasma concentration of RXP03 over 24 hr remained higher than the Ki values determined for MMP-11, MMP-8 and MMP-13. Efficacy of RXP03 on the growth of primary tumors induced by s.c. injection of C(26) colon carcinoma cells in mice was observed to depend both on RXP03 doses and treatment schedules. Tumor volumes in mice treated for 18 days with 50, 100 and 150 microg/day of RXP03 were decreased compared with control tumor volumes, 100 microg/day being the most effective dose. Treatment at higher dose (600 microg/day) did not significantly reduce the tumor size as compared to control. Short treatments with RXP03 100 microg/day, 3 to 7 days after C(26) inoculation, were more effective on tumor growth than continuous treatment over 18 days. Strikingly, RXP03 treatment started 6 days after the C(26) injection and continued until day 18 led to stimulation of tumor growth, as compared to control. These paradoxical effects, depending on the RXP03 treatment schedule, underline the need to define carefully the spatiotemporal function of each MMP at various stages of tumor growth to achieve optimal therapeutic effects by MMP inhibitor treatment.

Alkylating Agents↗
PubMed2005

An isosparteine derivative for stereochemical assignment of stereogenic (chiral) methyl groups using tritium NMR: theory and experiment.

(N-CHDT)-(alpha)-isosparteinium ditosylamide can be used in conjunction with tritium NMR spectroscopy to assign the configuration of an intact stereogenic (chiral) methyl group. The S-CHDT group has a (3)H chemical shift that is 49 ppb downfield of the R-CHDT resonance. The sign and magnitude of this chemical shift difference of these diastereotopic tritium nuclei are found to be in agreement with predictions made via a purely ab initio computational approach. The chemical shift difference is due to an equilibrium isotope effect originating from a novel CH(3)(...)N hydrogen bond. Despite the improved tritium chemical shift dispersion, this method is not useful for determining the enantiopurity of CHDTN(Tos)(2) due to partial racemization that occurs during the derivatization step. Milder methylation conditions are described for reactions using methyl p-toluenesulfonate or methyl-d(3) triflate. These studies suggest that (-)-(alpha)-isosparteine is a potential new reagent for chirality analysis of methyl groups originating from suitably reactive electrophiles.

Journal Article↗
PubMed2005

The light-harvesting antenna of the diatom Phaeodactylum tricornutum. Evidence for a diadinoxanthin-binding subcomplex.

Diatoms differ from higher plants by their antenna system, in terms of both polypeptide and pigment contents. A rapid isolation procedure was designed for the membrane-intrinsic light harvesting complexes (LHC) of the diatom Phaeodactylum tricornutum to establish whether different LHC subcomplexes exist, as well to determine an uneven distribution between them of pigments and polypeptides. Two distinct fractions were separated that contain functional oligomeric complexes. The major and more stable complex ( approximately 75% of total polypeptides) carries most of the chlorophyll a, and almost only one type of carotenoid, fucoxanthin. The minor complex, carrying approximately 10-15% of the total antenna chlorophyll and only a little chlorophyll c, is highly enriched in diadinoxanthin, the main xanthophyll cycle carotenoid. The two complexes also differ in their polypeptide composition, suggesting specialized functions within the antenna. The diadinoxanthin-enriched complex could be where the de-epoxidation of diadinoxanthin into diatoxanthin mostly occurs.

Carotenoids↗
PubMed2004

In vivo biodistribution and pharmacokinetics of 18F-labelled Spiegelmers: a new class of oligonucleotidic radiopharmaceuticals.

PURPOSE: Single-stranded mirror-image oligonucleotides (Spiegelmers) are highly resistant to nuclease degradation and are capable of tightly and specifically binding to protein targets. Here we explored the potential of Spiegelmers as in vivo imaging probes for positron emission tomography (PET). METHODS: We investigated the biodistribution and pharmacokinetics of [18F]-L-DNA and [18F]-L-RNA Spiegelmers by dynamic quantitative whole-body PET imaging after intravenous administration in non-human primates. Their metabolic profile was explored in primates and rats, and ex vivo autoradiography of [(125)I]-L-RNA was performed in rat kidneys, the major organ for Spiegelmer uptake. RESULTS: Both [18F]-L-DNA and [18F]-L-RNA Spiegelmers were metabolically stable in plasma during 2 h after injection. No evidence of non-specific binding was found with either type of Spiegelmer in any tissue. CONCLUSION: The biodistribution and metabolic profiles of [18F]-L-DNA and [18F]-L-RNA Spiegelmers highlight their potential as radiotracers for in vivo imaging applications.

Animals↗
PubMed2004

Monte Carlo versus molecular dynamics simulations in heterogeneous systems: an application to the n-pentane liquid-vapor interface.

The Monte Carlo (MC) and molecular dynamics (MD) methodologies are now well established for computing equilibrium properties in homogeneous fluids. This is not yet the case for the direct simulation of two-phase systems, which exhibit nonuniformity of the density distribution across the interface. We have performed direct MC and MD simulations of the liquid-gas interface of n-pentane using a standard force-field model. We obtained density and pressure components profiles along the direction normal to the interface that can be very different, depending on the truncation and long range correction strategies. We discuss the influence on predicted properties of different potential truncation schemes implemented in both MC and MD simulations. We show that the MD and MC profiles can be made in agreement by using a Lennard-Jones potential truncated via a polynomial function that makes the first and second derivatives of the potential continuous at the cutoff distance. In this case however, the predicted thermodynamic properties (phase envelope, surface tension) deviate from experiments, because of the changes made in the potential. A further readjustment of the potential parameters is needed if one wants to use this method. We conclude that a straightforward use of bulk phase force fields in MD simulations may lead to some physical inconsistencies when computing interfacial properties.

Journal Article↗
PubMed2004

Catharanthinol and dihydrocatharanthinol: two Iboga-class alkaloids.

The title compounds are indole alkaloids of the Iboga class. In both compounds, viz. catharanthinol methanol solvate, C(20)H(24)N(2)O.CH(4)O, (I), and dihydrocatharanthinol monohydrate, C(20)H(26)N(2)O.H(2)O, (II), a nitrogen-containing seven-membered ring is fused to the indole system and shares two sides with a tricyclic isoquinuclidine group. The main difference between (I) and (II) is the presence of a C=C bond in the isoquinuclidine ring in (I). The presence of amine and hydroxy groups in these molecules and of methanol [in (I)] or water [in (II)] solvent molecules results in intra- and/or intermolecular hydrogen bonding.

Alkaloids↗
PubMed2004

The super-excess energy dissipation in diatom algae: comparative analysis with higher plants.

When grown at intermittent light regime, diatom alga Phaeodactylum tricornutum is able to form photoprotective non-photochemical chlorophyll fluorescence quenching (NPQ) three to five times larger than that observed in the higher plants. This quenching is sustained in the dark for 5 to 10 min, reverses completely within approximately 1 h and seems to be very tightly related to the presence of the zeaxanthin analogue, diatoxanthin. Addition of the uncoupler NH4Cl before illumination can completely abolish formation of NPQ, revealing the DeltapH-dependency of the xanthophyll cycle activity. Once established, NPQ can also be almost completely reversed by the uncoupler. However, the higher NPQ is formed the more time is required for its reversal. At the point when the fluorescence was approximately 90% recovered the level of illumination-induced diatoxanthin was found to be only partially reduced. This indicates that the proton gradient is a key triggering factor of NPQ. It was also noticed that NPQ in Phaeodactylum cells was absent even when majority of reaction centers were closed and the plastoquinone pool was significantly reduced. The absence of NPQ at these conditions could be due to very low levels of DeltapH. It is likely that in diatoms alternative sources of protons such as the PS I cyclic electron transfer and/or chlororespiration are important in generating the proton gradient sufficient to trigger NPQ. Absorption changes associated with the xanthophyll cycle activity were found to be larger than those for higher plants. The position of the positive maximum in the difference spectrum illuminated-minus-dark was 512-514 nm in comparison to the 505-508 nm for leaves. The 535 nm band associated with NPQ in plants is absent in Phaeodactylum. An uncoupler-sensitive absorption change at 522 nm was discovered. Kinetics of NPQ showed linear correlation with the 522 nm absorption change.

Journal Article↗
PubMed2004

Characterization of chronic vocal fold scarring in a rabbit model.

The purpose of the current study was to assess the histologic and rheologic properties of the scarred vocal fold lamina propria during a chronic phase of wound repair in a rabbit model. Eighteen rabbit larynges were scarred using a procedure that involved stripping the vocal fold lamina propria down to the thyroarytenoid muscle, using 3-mm microforceps. The approximate dimension of injury to the vocal fold was 3 x 1.5 x 0.5 mm [length x width x depth]. At 6 months postoperatively, histologic analysis of the scarred and control lamina propria in eight of these rabbits was completed for collagen, procollagen, elastin, and hyaluronic acid. Compared with control samples, scarred tissue samples revealed fragmented and disorganized elastin fibers. Additionally, collagen was significantly increased, organized, and formed thick bundles in the scarred vocal fold lamina propria. Measurements of the viscoelastic shear properties of the scarred and control lamina propria in the remaining 10 rabbits revealed increased elastic shear modulus (G') in 8 of 10 scarred samples and increased dynamic viscosity (eta') in 9 of 10 scarred samples. Although rheologic differences were not statistically significant, they revealed that on average, scarred samples were stiffer and more viscous than the normal controls. Histologic data are interpreted as indicating that by 6 months postinjury, the scarred rabbit vocal fold has reached a mature phase of wound repair, characterized by an increased, organized, and thick bundle collagen matrix. Rheologic data are interpreted as providing support for the potential role of increased, thick bundle collagen, and a disorganized elastin network on shear stiffness and dynamic viscosity in the chronic vocal fold scar. Based on these results, a 6-month postoperative time frame is proposed for future studies of chronic vocal fold scarring using the rabbit animal model.

Animals↗
PubMed2004

Prevention of vocal fold scarring by topical injection of hepatocyte growth factor in a rabbit model.

OBJECTIVES/HYPOTHESIS: Vocal fold scarring disrupts the layer structure of the vocal fold lamina propria that is essential for optimal mucosal vibration. Prevention of vocal fold scarring remains challenging. Hepatocyte growth factor (HGF) has strong antifibrotic activity. The authors' previous studies have found that HGF stimulates hyaluronic acid production and suppresses collagen production from vocal fold fibroblasts, suggesting that HGF has therapeutic potential in prevention of vocal fold scarring. The present study aimed to demonstrate the effects of HGF on vocal fold scarring in an in vivo rabbit model. STUDY DESIGN: Animal experiment. METHODS: The vocal fold mucosa was stripped unilaterally in 20 rabbits, then HGF or saline (sham-treated group) was immediately injected into the injured site. At 6 months after the procedure, histological, rheological, and physiological examinations of vibratory behavior were completed. RESULTS: Histological examination revealed excessive collagen deposition and disorganized elastin in the sham-treated group, whereas the HGF-treated group presented with better wound healing exhibiting less collagen deposition. Contraction of the injured vocal folds observed in the sham-treated group did not occur in the HGF-treated group. Rheological data indicated that the HGF-treated vocal folds were less stiff and viscous compared with the sham-treated group. Mucosal vibration of HGF-treated vocal folds appeared much better than the sham-treated group in terms of phonation threshold pressure, vocal efficiency, mucosal wave amplitude, and glottal closure. CONCLUSION: Hepatocyte growth factor proved to be useful in preventing vocal fold scarring and maintaining viscoelastic shear properties of the vocal fold.

Animals↗
PubMed2004

Hyaluronan levels in acute vocal fold scar.

OBJECTIVES/HYPOTHESIS: The objective was to measure the level of hyaluronan during the first 15 days after vocal fold biopsy in a rabbit model. STUDY DESIGN: Experimental, nonrandomized prospective study. METHODS: Twenty-eight rabbits underwent unilateral vocal fold biopsy. The contralateral vocal fold was preserved as a control sample. On days 3, 5, 10, and 15 after biopsy, hyaluronan levels in the injured and normal vocal folds were measured immunohistologically and with an ELISA assay. RESULTS: Hyaluronan levels in the injured vocal fold were lowest on day 3 and highest on day 5 after injury. Statistical analysis revealed that the injured vocal fold demonstrated significantly lower levels of hyaluronan on day 3 than on days 5, 10, and 15. On day 5, the injured vocal fold demonstrated significantly greater levels of hyaluronan than those observed on days 3, 10, and 15. Compared with the normal vocal fold, the injured vocal fold demonstrated significantly lower levels of hyaluronan on days 3, 10, and 15. No differences were observed between the injured and normal vocal fold on day 5, when the hyaluronan level was maximized in the injured vocal fold. CONCLUSION: Maximizing hyaluronan levels in the early stages of wound repair may have therapeutic potential for decreasing the incidence of vocal fold scar. Decreased hyaluronan levels may provide a less than optimal environment for normal tissue regeneration and may contribute to the formation of scar tissue in vocal fold lamina propria.

Animals↗
PubMed2004

Calcium-independent cytoskeleton disassembly induced by BAPTA.

In living organisms, Ca2+ signalling is central to cell physiology. The Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) has been widely used as a probe to test the role of calcium in a large variety of cell functions. Here we show that in most cell types BAPTA has a potent actin and microtubule depolymerizing activity and that this activity is completely independent of Ca2+ chelation. Thus, the depolymerizing effect of BAPTA is shared by a derivative (D-BAPTA) showing a dramatically reduced calcium chelating activity. Because the extraordinary depolymerizing activity of BAPTA could be due to a general depletion of cell fuel molecules such as ATP, we tested the effects of BAPTA on cellular ATP levels and on mitochondrial function. We find that BAPTA depletes ATP pools and affects mitochondrial respiration in vitro as well as mitochondrial shape and distribution in cells. However, these effects are unrelated to the Ca2+ chelating properties of BAPTA and do not account for the depolymerizing effect of BAPTA on the cell cytoskeleton. We propose that D-BAPTA should be systematically introduced in calcium signalling experiments, as controls for the known and unknown calcium independent effects of BAPTA. Additionally, the concomitant depolymerizing effect of BAPTA on both tubulin and actin assemblies is intriguing and may lead to the identification of a new control mechanism for cytoskeleton assembly.

Adenosine Triphosphate↗