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Biomedical subjects

C Léger

Publications and source records attributed to C Léger.

At least 19 recordsLinked to original sources
PubMed2006

[Use of antiretroviral drugs invoices for the follow-up of a treatment programme. Example in Abidjan, Côte d'Ivoire].

A retrospective analysis of the prescriptions of the ARV treatment programme in Abidjan, Côte-d'Ivoire enabled the authors to assess the collected anonymous information in order to evaluate the efficacy of the programme. This collection of information helps to supervise each center at a lower cost, to alert on some working problems and to follow the quality of the observance. This supervision is possible regardless of the health care places, it can be carried out systematically from the administrative or financial services. In this study this follow-up reveals some problems.

Anti-Retroviral Agents↗
PubMed2003

Validation of a volumic reconstruction in 4-d echocardiography and gated SPECT using a dynamic cardiac phantom.

A dynamic cardiac phantom was used as a reference to compare the volumes reconstructed with 4-D echocardiography and gated single-photon emission computed tomography (SPECT). 4-D echocardiography used a new prototype of rotating scan head to acquire ultrasound (US) images during a cardiac cycle, associated with a new protocol (left ventricular 4-D or LV 4-D) to reconstruct the volume deformations of the heart as a function of time. Gated SPECT data were acquired with a standard single-head gamma camera, and the reconstructions were carried out using the Mirage software released by Segami. The influences of different LV 4-D parameters were tested and analyzed. End-diastolic volume, end-systolic volume, and ejection fraction were measured using both LV 4-D and gated SPECT. Results obtained showed a straight correlation between the two examinations. The agreement confirmed the relevance of the comparisons. This study is an initial step before conducting clinical trials to exhaustively compare the two modalities.

Echocardiography, Four-Dimensional↗
PubMed2001

A distal histidine mutant (H52Q) of yeast cytochrome c peroxidase catalyzes the oxidation of H(2)O(2) instead of its reduction.

A H52Q variant of yeast cytochrome c peroxidase (CcP), in which the distal histidine is replaced by glutamine, catalyzes oxidation of H(2)O(2) instead of reduction. This redirection of catalytic action is detected by protein film voltammetry. In the presence of H(2)O(2), wild-type CcP, adsorbed on a graphite electrode, shows a strong catalytic reduction wave commencing at about 0.8V (pH 5.4); by contrast, H52Q does not exhibit this activity but instead shows a catalytic oxidation current at potentials in the region of 0.9 V. The oxidation current is partly suppressed in the presence of tetranitromethane (a superoxide scavenger) and is not observed for other mutants studied, including H52A. The only significant structural change in the H52Q variant is that the Q-52 side chain occupies the space vacated by the H-52 imidazole; specifically, the N-epsilon atom that is believed to transfer a proton and induce O--O cleavage is replaced, to within 0.75 A, by the carbamide-O. Thus, while the weakly basic amide functionality is unable to serve in the reorganization of bound H(2)O(2), it is able to facilitate its oxidation, most obviously by serving as a H-bond acceptor to assist formation of a labile superoxide intermediate.

Binding Sites↗
PubMed2001

Enzyme electrokinetics: energetics of succinate oxidation by fumarate reductase and succinate dehydrogenase.

Protein film voltammetry is used to probe the energetics of electron transfer and substrate binding at the active site of a respiratory flavoenzyme--the membrane-extrinsic catalytic domain of Escherichia coli fumarate reductase (FrdAB). The activity as a function of the electrochemical driving force is revealed in catalytic voltammograms, the shapes of which are interpreted using a Michaelis-Menten model that incorporates the potential dimension. Voltammetric experiments carried out at room temperature under turnover conditions reveal the reduction potentials of the FAD, the stability of the semiquinone, relevant protonation states, and pH-dependent succinate--enzyme binding constants for all three redox states of the FAD. Fast-scan experiments in the presence of substrate confirm the value of the two-electron reduction potential of the FAD and show that product release is not rate limiting. The sequence of binding and protonation events over the whole catalytic cycle is deduced. Importantly, comparisons are made with the electrocatalytic properties of SDH, the membrane-extrinsic catalytic domain of mitochondrial complex II.

Flavin-Adenine Dinucleotide↗
PubMed2001

Determination of an optimal potential window for catalysis by E. coli dimethyl sulfoxide reductase and hypothesis on the role of Mo(V) in the reaction pathway.

Protein film voltammetry (PFV) of Escherichia coli dimethyl sulfoxide (DMSO) reductase (DmsABC) adsorbed at a graphite electrode reveals that the catalytic activity of this complex Mo-pterin/Fe-S enzyme is optimized within a narrow window of electrode potential. The upper and lower limits of this window are determined from the potential dependences of catalytic activity in reducing and oxidizing directions; i.e., for reduction of DMSO (or trimethylamine-N-oxide) and oxidation of trimethylphosphine (PMe(3)). At either limit, the catalytic activity drops despite the increase in driving force: as the potential is lowered below -200 mV (pH 7.0-8.9), the rate of reduction of DMSO decreases abruptly, while for PMe(3), an oxidative current is observed that vanishes as the potential is raised above +20 mV (pH 9.0). Analysis of the waveshapes reveals that both activity thresholds result from one-electron redox reactions that arise, most likely, from groups within the enzyme; if so, they represent "switches" that reflect the catalytic mechanism and may be of physiological relevance. The potential window of activity coincides approximately with the appearance of the Mo(V) EPR signal observed in potentiometric titrations, suggesting that crucial stages of catalysis are facilitated while the active site is in the intermediate Mo(V) oxidation state.

Binding Sites↗
PubMed2000

Fast voltammetric studies of the kinetics and energetics of coupled electron-transfer reactions in proteins.

A wealth of information on the reactions of redox-active sites in proteins can be obtained by voltammetric studies in which the protein sample is arranged as a layer on an electrode surface. By carrying out cyclic voltammetry over a wide range of scan rates and exploiting the ability to poise or pulse the electrode potential between cycles, data are obtained that are conveniently (albeit simplistically) analysed in terms of plots of peak potentials against scan rate. A simple reversible electron-transfer process gives rise to a 'trumpet'-shaped plot because the oxidation and reduction peaks separate increasingly at high scan rate; the electrochemical kinetics are then determined by fitting to Butler-Volmer or Marcus models. Much more interesting though are the ways in which this 'trumpet plot' is altered, often dramatically, when electron transfer is coupled to biologically important processes such as proton transfer, ligand exchange, or a change in conformation. It is then possible to derive particularly detailed information on the kinetics, energetics and mechanism of reactions that may not revealed clearly or even at all by other methods. In order to interpret the voltammetry of coupled systems, it is important to be able to define 'ideal behaviour' for systems that are expected to show simple and uncoupled electron transfer. Accordingly, this paper describes results we have obtained for several proteins that are expected to show such behaviour, and compares these results with theoretical predictions.

Electrochemistry↗
PubMed1995

Enhancement of domoic acid production by reintroducing bacteria to axenic cultures of the diatom Pseudo-nitzschia multiseries.

Axenic cultures of Pseudo-nitzschia multiseries (formerly Pseudonitzschia pungens f. multiseries) produce less domoic acid (DA) than the original bacteria-containing cultures. Bacterial strains isolated from two nonaxenic P. multiseries clones were reintroduced individually into cultures of three axenic P. multiseries strains. The bacteria did not substantially affect division rates or cell yields. However, they did cause a 2- to 95-fold enhancement of DA production (per cell basis) relative to the axenic culture, depending on the P. multiseries and bacterial strain used. Bacteria isolated from a nontoxic Chaetoceros sp. culture also enhanced DA per cell (by 115-fold), showing that it is not necessary for the bacteria to be isolated from a toxic culture in order to enhance toxin production. There was no evidence of intracellular bacteria in disrupted P. multiseries cells obtained from axenic cultures. Our results demonstrate an important, but nonessential, role of extracellular bacterial in DA production. Characterization of the bacterial strains using morphology, substrate utilization, and restriction fragment length polymorphism (RFLP) analyses clearly showed that we had isolated different species of bacteria from the various nonaxenic cultures. We conclude that not one but several bacterial species enhance DA production by P. multiseries.

Cells, Cultured↗
PubMed1995

Experimental bias in the evaluation of the cellular transient expression in DNA co-transfection experiments.

beta-Galactosidase (beta-gal) expressing vectors are commonly used to standardize the transfection efficiency in transient expression experiments. In the Chinese hamster ovary (CHO) cell line, we transfected beta-gal expressing vectors in combination with different plasmid DNAs. We reported here that the presence of specific DNAs led to statistically significant variations in the beta-gal expression level. Therefore, the measure of beta-gal activity is not necessarily an accurate method to monitor transfection efficiency, and its use to normalize the expression from reporter genes could be questionable.

Animals↗
PubMed1992

CT and MR imaging findings in adults with cerebellar medulloblastoma: comparison with findings in children.

The goal of this study was to determine if certain imaging features suggest the diagnosis of cerebellar medulloblastoma in adults and to determine how often the classic CT appearance seen in children is present in adults. The study included 28 adult patients with proved cerebellar medulloblastoma. The tumor was located in the cerebellar vermis in 14 patients and in a cerebellar hemisphere in 14 patients. Thirteen patients had unenhanced CT of the brain, all patients had contrast-enhanced CT, and eight patients had unenhanced MR imaging. The imaging features in adults were compared with those in children, as described in the literature. In our adult patients, all tumors were hyperdense compared with gray matter on unenhanced CT and showed a slight to moderate increase in density after injection of contrast medium. Thirteen lesions had well-defined margins, and 15 had poorly defined margins. Low-density areas consistent with cystic and necrotic degeneration were detected in 23 (82%) of the 28 tumors. By comparison, in children, medulloblastoma usually originates in the vermis. As in adults, the mass is hyperdense on unenhanced CT, but enhances markedly and homogeneously after injection of contrast medium. Usually no evidence of cyst formation or necrosis is seen, and the tumor margins are well defined. This classic CT appearance of medulloblastoma in children was identified in only three (11%) of the 28 adult patients. Medulloblastoma has a variable MR appearance in both children and adults. On T2-weighted images, lesions are hypo-, iso-, or hyperintense compared with normal gray matter. The CT findings of medulloblastoma in adults usually differ from those of medulloblastoma in children. The tumor has a variable and nonspecific appearance in adults and should always be considered in the differential diagnosis of a mass in the posterior fossa.

Adolescent↗
PubMed1988

Arachidonic acid metabolism and casein secretion in lactating rabbit mammary epithelial cells: effects of inhibitors of prostaglandins and leukotrienes synthesis.

The metabolism of arachidonic acid (AA) in fragments of lactating rabbit mammary glands in vitro was studied by considering the distribution of 13-[14C]AA in the cells, and the effects of inhibitors of cyclooxygenase and lipoxygenase pathway on the basal and prolactin (PRL)-stimulated casein secretion. 13-[14C]AA was incorporated in all classes of lipids and PRL increased transiently the percentage of free fatty acid after 1 and 5 min. Ten microM ETYA (5,8,11,14-Eicosatetraynoic acid), a tetrayne analogue of AA inhibited prostaglandins F2 alpha (PGF2 alpha) production but not leukotrienes B4 and C4 (LTB4 and LTC4) production and increased basal casein secretion. 10(-4) M DCHA (Docosahexaenoic acid) a competitive inhibitor of prostaglandin-synthetase inhibited PGF2 alpha production but did not affect basal nor PRL-stimulated casein secretion. Fourteen microM indomethacin inhibited PGF2 alpha and LTC4 production and PRL-stimulated casein secretion. Ten microM NdgA (nordihydroguaiaretic acid) an inhibitor of lipoxygenase pathway, inhibited LTB4 and LTC4 production, increased basal level of casein secretion and inhibited PRL-stimulated casein secretion. Hundred microM caffeic acid, an inhibitor of glutathione-S-transferase (GST), a class of enzymes implied in the transformation of LTA4 into LTC4, had the same effect that NDGA on basal and PRL-stimulated casein secretion. These findings show that inhibitors of AA metabolites alter casein secretion.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1985

Incidence of (n-3) essential fatty acid deficiency on trout reproductive processes.

A feeding experiment was conducted on rainbow trout broodstock for one year to investigate the influence of the quality of dietary lipids on egg and fry fatty acid composition, embryonic development and hatching efficiency. The broodstock were fed either a commercial control diet or a (n-3) fatty acid-deficient diet; their liver, eggs and fry were analysed to determine the fatty acid composition of their neutral and polar lipids. The fatty acid pattern in liver, eggs and fry was markedly different due to the qualitative difference of the dietary lipids. The most striking difference was the low amount of 22:6 (n-3) and the high levels of 20:4 (n-6) and 22:5 (n-6) in phospholipids of fish receiving the (n-3)-deficient diet containing a high level of 18:2 (n-6). While fertilization efficiency was equivalent in the first two days of development, whatever the diet, two peaks of mortality were observed, one at day 8 and the other at day 22 after fertilization, during the time the eggs produced by the deficient fish were incubated. A shorter period of vitellus resorption (50 vs 65 day) was observed in (n-3)-deficient alevins as compared to controls. Morphological study of the development of the (n-3)-deficient embryos showed some cleavage disorders at the 16 to 32-cell stage, a blocking effect before gastrulation, and later various alterations in organogenesis. It was concluded that (n-3) fatty acids, and especially 22:6 (n-3), play a crucial and specific role in trout embryo development. These fatty acids could be involved in cellular recognition processes through their oxygenated derivatives. The need for long-term nutritional deficiency to induce the reported biochemical and physiological alterations is discussed.

Animals↗
PubMed1984

[Recent findings on pancreatic lipase and colipase].

Lipase and colipase are two genetically independent proteins synthesized and secreted by the pancreas. Lipase catalyzes the hydrolysis of dietary triglycerides emulsified in the intestinal lumen. It is activated by interfaces and, to a lesser extent, by micelles and monomeric solutions of glycerides in the presence of an organic solvent. The enzyme is activated due to acceleration of the acyl-enzyme deacylation step after conformational modification of the catalytic site by contact with the interface. Lipase turnover is higher than that of other esterases. The enzyme denaturation rate increases as surface pressure at the interface decreases (as surface tension increases). On the other hand, the enzyme is stabilized by high surface pressure and by colipase. Beyond a certain surface pressure, only lipase is unable to adsorb to the surface. In this case, colipase is indispensable for the anchorage of lipase at the interface. The association colipase with lipase and substrate depends on two distinct sites, each site being formed by an hydrophobic region and by ionizable epsilon-amino and carboxylate groups. The KD of the [lipase.colipase] complex is 10(-7) M; in the presence of substrate, it is 10(-9) M. Colipase is synthesized as pro-colipase. The [ pro-colipase .lipase] complex pre-exists in pancreatic juice and probably in cells of the exocrine pancreas. Trypsin action on pro-colipase leads to the cleavage of the colipase with 96 residues and the N-terminal pentapeptide. The [lipase.colipase] complex obtained is more generally hydrophobic than the previous one. In duodenal contents, this newly formed complex would be stabilized by the pH of the milieu and by free fatty acids appearing in the gastric contents, whether associated or not with the bile lipoprotein complex. The [lipase-colipase] complex, which is also stabilized by the substrate, would be fixed at the triglyceride/water interface, i.e. by passing through the layer of adsorbed amphipathic compounds (bile salts, phospholipids, fatty acids, proteins) owing to their hydrophobic and ionic properties, and by positioning into the interface by ionizable colipase groups.

Animals↗
PubMed1982

Removal and addition of bile in the intestine, and pancreatic colipase activity in the pig: effect of a high-lipid diet.

The aim of the reported study was to investigate the effects of the removal and addition of bile in the intestine on the tissue pancreatic colipase of pigs fed a high-lipid diet (25% peanut oil). Experiments were carried out on fistulated pigs. In one group of animals, bile was removed for 8 days; in a second group an excess of bile was added in the intestine for 8 days. Results were compared to those obtained in pigs in which the collected bile was entirely returned. When bile was removed, the tissue enzyme activities of pancreatic lipase and colipase significantly decreased; the latter increased when bile was added in the intestine of pigs whose enterohepatic cycle was fully maintained.

Animals↗
PubMed1982

Ischemic fecal incontinence and rectal angina.

In 36 patients who consulted for fecal incontinence or rectal pain, or both, there was grossly visible scarring of the rectum and biopsy revealed mucosal atrophy and fibrosis. A steal from the hemorrhoidal arteries to the iliac vessels was demonstrated in 3 subjects. Maximum tolerable volumes within a rectal balloon were smaller than in control subjects, both in men (192 vs. 273 ml) and in women (142 vs. 217 ml) (p less than 0.01). The rectoanal inhibitory reflex was abnormal in all but 1 patient. Specific abnormalities were a decreased amplitude or a prolonged duration of the reflex. It was totally absent in 2 patients. This study is compatible with the hypothesis that chronic ischemia of the rectum may cause fecal incontinence or rectal pain.

Adult↗