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P Aymard

Publications and source records attributed to P Aymard.

At least 19 recordsLinked to original sources
PubMed2001

Influence of thermal history on the structural and mechanical properties of agarose gels.

Using a multitechnique approach, two temperature domains have been identified in agarose gelation. Below 35 degrees C, fast gelation results in strong, homogeneous and weakly turbid networks. The correlation length, evaluated from the wavelength dependence of the turbidity, is close to values of pore size reported in the literature. Above 35 degrees C, gelation is much slower and is associated with the formation of large-scale heterogeneities that can be monitored by a marked change in the wavelength dependence of turbidity and visualised by transmission electron microscopy. Curing agarose gels at temperatures above 35 degrees C, and then cooling them to 20 degrees C, produces much weaker gels than those formed directly at 20 degrees C. Dramatic reductions in the elastic modulus and failure strain and stress are found in this case as a result of demixing during cure. An interpretation, based on the kinetic competition between osmotic forces (in favor of phase separation) and elastic forces (that prevent it) is proposed.

Elasticity↗
PubMed2000

New insight into agarose gel mechanical properties.

The current study focuses on the effects of the molecular weight on the mechanical behavior of agarose gels. The small strain rheology and large strain deformation/failure behavior of three different molecular weight agarose gels have been examined, with the results expressed in term of molar concentration. For small deformation strains, the gelation temperature at low concentrations and the critical concentration for gel formation are strongly affected by the molecular weight. In addition, the elasticity of the network is also very sensitive to this parameter. It has been demonstrated that the experimental gelation cure curves can be superimposed on a universal gelation master curve, independent of the cure time. This would indicate self-similarity of the network at different scales, irrespective of concentration. A relationship between the elastic modulus and the molecular weight has been extracted from these results, where the molecular weight dependence exhibits a power law exponent of 2.42. For large deformation strains, the Poisson ratio has been estimated to be 0.5 for each of the agarose types examined, which indicates that these gels are incompressible. The strain at failure is largely dependent on the molecular weight, and is essentially independent of the biopolymer concentration. This result highlights the fact that the strain at failure is sensitive to the connectivity distances in the gel network. However, the failure stress and Young's modulus of agarose gels show a dependence on both concentration and molecular weight. The observations regarding Young's modulus are in good agreement with those found for small deformation strain rheology for the shear modulus. One of the primary advantages of using the lowest molecular weight agarose is that higher molar concentrations can be reached (more molecules per unit volume). However, the mechanical response of agarose gels is very sensitive to the molecular weight at fixed molar concentration, and if the present results are extrapolated to very low molecular weight, it can be suggested that below a limiting molecular weight a percolating network will not be formed, as suggested by the Cascade model (Carbohydr. Polym. 1994, 23, 247-251). This speculation is based on the influence of the "connectivity" at long distances, which influences the strain at failure (when the strain at failure is zero, the system is not connective).

Algorithms↗
PubMed1999

Compound SFTPB 1549C-->GAA (121ins2) and 457delC heterozygosity in severe congenital lung disease and surfactant protein B (SP-B) deficiency.

Several human respiratory disorders have been linked to an abnormality of pulmonary surfactant synthesis or turnover. Among those conditions, hereditary deficiency in the hydrophobic surfactant protein B (SP-B) has been recognized as a rare cause of respiratory failure in term newborn infants. Homozygosity for a common mutation (1549C-->GAA, or 121ins2) of the SP-B-encoding gene (SFTPB) results in rapidly fatal respiratory failure, with complete absence of the mRNA and protein observed in lung fluid or biopsy specimens. Hereditary SP-B deficiency is also associated with aberrant processing of proSP-C and deficiency of the active SP-C peptide. In the present study, we characterized the SFTPB gene in an infant with severe unexplained respiratory distress and identified a paternally derived 1549C-->GAA lesion, as well as a hitherto unreported mutation (457delC) inherited from the mother. Analysis of bronchoalveolar lavage fluid demonstrated the complete absence of SP-B. However, unlike previous infants with hereditary SP-B deficiency, proSP-C was processed to the active SP-C peptide, suggesting that the defect in SP-B, rather than SP-C, caused the respiratory distress in this infant. The present findings demonstrate the importance of SFTPB in pulmonary function and support the need for further genotype-phenotype correlations in patients with SP-B deficiency.

Base Sequence↗
PubMed1999

Stability and compatibility of teicoplanin in parenteral nutrition solutions used in pediatrics.

AIMS: To investigate teicoplanin added to pediatric parenteral nutrition solutions in terms of its stability, its compatibility with parenteral nutrition solution components, and its diffusion through an antibacterial filter material. METHODS: Three binary solutions with and without teicoplanin were studied. Different solution compositions and teicoplanin concentrations were used: A (98.3 +/- 8.2 mg/l), B (116.3 +/- 12.4 mg/l), and C (162.7 +/- 16.2 mg/l). Concentrations of teicoplanin and of solution components, osmolality, and pH of each solution were measured at H0, after 24 h at room temperature, after 24 h at +4 degrees C followed by 24 h at room temperature, and after 144 h at +4 degrees C followed by 24 h at room temperature (H168). Teicoplanin concentrations were also measured before and after passage of each solution through a 0.22 micro filter. RESULTS: Teicoplanin concentrations remained unchanged from H0 to H168 in solutions A (99.6 +/- 8.3 mg/l), B (116.9 +/- 12. 3 mg/l), and C (162.4+12.9 mg/l). During the H0-H168 interval, iron and methionine were the only components that showed significant decreases, which were similar in solutions without teicoplanin [iron, -6.1% (A), -6.8% (B), and -4.5% (C); methionine, -7.3% (A) and -8. 7% (B)] and in those with teicoplanin [iron, -6.2% (A), -7.1% (B), and -4.0% (C, nonsignificant); methionine, -10.5% (A) and -10.7% (B)], indicating that they were not dependent on the presence of teicoplanin. Teicoplanin levels after filtration were identical to prefiltration values in solutions A (86.4 +/- 5.0 vs 89.8 +/- 3.4 mg/l) and B (112.6 +/- 4.3 vs 115.3 +/- 9.0 mg/l) but were 10.0% lower in solution C (161.6 +/- 3.9 vs 145.4 +/- 4.0; P << 0.001). CONCLUSIONS: Teicoplanin can be added to pediatric parenteral nutrition solutions to treat central venous catheter-related infections due to teicoplanin-susceptible organisms since its concentrations and those of solution components remain stable over time.

Anti-Bacterial Agents↗
PubMed1999

Improved fluorescent PCR-based assay for sizing CGG repeats at the FRAXA locus.

Fragile X syndrome is the most frequent heritable genetic disease involving mental retardation and is usually caused by an expanded CGG repeat in the first exon of the FMR1 gene. Therefore, searching for CGG expansion at the FRAXA locus among the mentally retarded has become a routine investigation in neuro-paediatric practice. Consequently, we have developed a fluorescent PCR-based assay for sizing repeats as an alternative to laborious and time-consuming Southern blot. The procedure utilises a reverse fluorescent labelled primer, and the Expand Long Template PCR system (Roche) with addition of dimethylsulfoxide and 7-deaza-dGTP It allows precise determination of the CGG repeat number in males and females for alleles from normal to premutation size range and detection of full mutations in males. We believe that this PCR protocol, allowing a high sample throughput, is useful for first-line screening among mentally retarded males, possibly complemented by Southern blot analysis to assess the methylation status of large mutated alleles.

Electrophoresis, Polyacrylamide Gel↗
PubMed1999

Linkage analysis of 5 novel van der Woude syndrome kindreds to 1q32-q41 markers further supports locus homogeneity of the disease trait.

van der Woude syndrome (vWS, MIM 119300) is a rare autosomal dominant clefting condition with cardinal features of mucous cysts (lower-lip pits) and clefts to the lip and/or palate. The vWS gene has been assigned to a locus in 1q32-q41 by linkage analysis and physical mapping. We have investigated 5 novel vWS families through probands attended for cleft lip and/or palate repair at the Department of Maxillofacial Surgery of Hôpital Trousseau, Paris, in order to tentatively refine the genetic map of the vWS region in 1q32-q41 and possibly identify unlinked pedigrees. Linkage analysis was carried out to 6 microsatellite markers (D1S249, D1S425, D1S491, D1S205, D1S414, D1S425), yielding a maximum cumulative LOD score of Z = 3.27 at theta = 0.00 for D1S245. The innermost four markers were found to be tightly linked to one another, with no evidence for recombination. Our results support linkage of vWS within a region of tightly linked markers and do not favour locus heterogeneity of the disease trait.

Chromosome Mapping↗
PubMed1997

Stability of brain content of magnesium in experimental hypomagnesemia.

Magnesium is important in cerebral function. If there is a deficiency and neurological symptoms accrue, we hypothesised that Mg2+ deficiency causes neurological symptoms by decreasing the level of Mg2+ in cerebral tissue. The content of magnesium was determined in 12 brain structures in magnesium-deficient rats. Experiments were carried out for 40 days in two groups of Wistar male rats made magnesium-deficient (MD) by a well-controlled diet (50 mg of Mg2+/kg of food), and a control group (CG) rats fed normal diet (1 g of Mg2+/kg of food). At the end of the 40 days, the clinical signs of hypomagnesemia were sought in the MD rats and Mg2+ concentration levels were measured in the blood and brain. The results showed variable distribution of Mg2+ in the different brain structures, both in CG and MD rats; in the MD rats there is an important stability of global Mg2+ content of the brain. Although the global values for Mg2+ in the brain did not decline in MD rats, there was a significant decrease in Mg2+ in the brainstem. We conclude that the brain is able to maintain a stable concentration of Mg2+ during chronic hypomagnesemia, but its topographic variations could account for some of neurological signs accompanying this condition.

Animals↗
PubMed1997

Paracellular calcium transport across Caco-2 and HT29 cell monolayers.

Intestinal calcium absorption has been shown to include two processes, a saturable transcellular movement and a non-saturable paracellular pathway. The potential utility of cell monolayers for studying transepithelial intestinal calcium transport has already been demonstrated; however, simultaneous evaluation of the contribution of the saturable transcellular and of the non-saturable paracellular processes to the total transepithelial transport has not yet been attempted. The aim of this study was to investigate the contribution both of transcellular and paracellular transport processes to the total transepithelial calcium transport in two cell culture monolayers. Caco-2 cells and a clone derived from HT-29 cells (HT29-Cl.19A), two cell lines derived from colon adenocarcinomas which are known to be able to exhibit typical enterocytic differentiation, were used. Cell monolayers were grown on a permeable support and used after 15 days of culture when these cells express enterocytic differentiation and high transepithelial resistance. Isotopic transport rate measurements were performed in the absence of a chemical gradient. The paracellular route was evaluated using [3H]mannitol. Calcium and [3H]mannitol transport rates across cell monolayers were not significantly different. Augmentation of calcium uptake by 200 mM sorbitol did not significantly increase calcium or mannitol transepithelial transport; however, calcium accumulation in the cells was increased by about 200%. Modulation of the monolayer permeability by addition of 10 nM vasoactive intestinal polypeptide (VIP) or 0.5 mM carbachol treatment, which respectively increased and decreased the transepithelial resistance, consequently modified calcium and mannitol transport in a parallel manner. Our results show that Caco-2 and HT29-Cl.19A cell monolayers are good models for studying the calcium paracellular transport pathway.

Caco-2 Cells↗
PubMed1997

CFTR gene analysis in cystic fibrosis patients: detection of 91% of molecular defects and identification of the novel mutation D979V.

More than 600 mutations have been identified in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene and are known to cause cystic fibrosis (CF). This large number of mutations makes the search of the molecular defects in CF patients difficult. We have used the techniques of denaturing gradient gel electrophoresis (DGGE) and direct DNA sequencing to detect the mutations in 334 CF chromosomes mostly of French origin. The whole coding sequence of the CFTR gene corresponding to the 27 exons and their exon-intron boundaries was studied. 45 different mutations were identified. This method allowed us to detect the molecular defect in 90.5% of the mutant alleles and to report a novel mutation D979V.

Adolescent↗
PubMed1996

The effect of temperature and ionic strength on the dimerisation of beta-lactoglobulin.

Bovine beta-lactoglobulin is a globular whey protein that associates partly and reversibly in dimers in the native state. Static and dynamic light scattering techniques have been used to determine the relative amount of monomers and dimers, and to estimate their size and shape in different conditions. The effect of the ionic strength on the dimerisation has been studied at pH 2, where the protein is highly charged. A simple model, taking into account the monomer-dimer equilibrium and virial interactions has been used. The strength of the interactions depends on the amount of added salt, i.e. ionic strength, and influences the dimer dissociation. When the ionic strength decreases, the equilibrium is shifted towards the monomeric form. The dissociation, however, is only complete at very low concentration. The effect of temperature has been studied at pH 7 and low concentration where virial interactions are negligible. The dissociation increases with increasing temperature (5 degrees C - 76 degrees C). At high temperatures, protein-protein aggregation is fast, even at low concentration. The temperature dependence can be described using a simple Van't Hoff model, even at temperatures where aggregation occurs. The ionic strength and temperature dependence both indicate that beta-lactoglobulin solutions have to be considered as a mixture of monomers and dimers.

Hydrogen-Ion Concentration↗
PubMed1996

Sucrase-isomaltase deficiency: changing pattern over two decades.

Twenty-two cases of sucrase-isomaltase deficiency (SID) were observed over a period of 20 years. Since 1977 delay of introduction of sucrose and its decrease in infants' diets have modified the symptomatology. In general, onset of diarrhea has not taken place immediately but 15 days to 2 months after introduction of sucrose. Out of 12 cases with dehydration, five occurred 3 to 7 months after the beginning of sucrose diet. Hypotrophy was not constant (11 of 22 cases), thus diagnosis was delayed in 17 of 22 cases. A yellow complexion due to rising carotene levels in the blood is a striking feature. Because of falsely positive sucrose load tests (four out of 14 nonSID infants) and failure of the hydrogene breath test (one out of five studied cases), disaccharidase determination remains the key to diagnosis. Despite the genetic difference symptoms seem to depend on infant feeding practices.

Carbohydrate Metabolism, Inborn Errors↗
PubMed1995

Determination of iodide in serum and urine by ion-pair reversed-phase high-performance liquid chromatography with coulometric detection.

An HPLC method is described for the determination of iodide in serum and urine using ion-pair chromatography with coulometric detection. After adding hexadecyltrimethylammonium chloride, the ions pairs formed with the iodide in the sample are extracted using an organic solvent. The solvent is then evaporated and the dry residue obtained is mixed with an appropriate volume of mobile phase so as to concentrate the sample prior to injection into the chromatograph. For a sample of 0.5 ml of serum, the method features a limit of detection (signal-to-noise ratio of 3) of 0.2 microgram l-1, sufficient to be applied in paediatric assays for the diagnosis of both iodide deficiency and excess.

Child↗
PubMed1995

Evaluation of human IgG subclass assays on Beckman array.

Automated immunonephelometric assays were developed to measure human IgG subclasses in serum, on the Beckman Array Protein System (APSR), with sheep antihuman IgG subclass antisera. The interassay imprecision was judged to be satisfactory in each case (CV: IgG1: 2.3%; IgG2: 2.9%; IgG3: 4.0% and IgG4 5.4%). The standard curves were found to be linear in the ranges 1.5-30.0 g/L for IgG1, 1.5-15.0 g/L for IgG2, 0.1-1.0 g/L for IgG3 and 0.1-1.0 g/L for IgG4. The lower limit for quantification of the immunephelometric assays was 0.5 g/L for IgG1, 0.04 g/L for IgG2, 0.06 g/L for IgG3 and 0.03 g/L for IgG4. We found no antigen excess to at least 60.0 g/L for IgG1 and IgG2, 3.5 g/L for IgG3 and 2.0 g/L for IgG4. Nephelometric results correlated with those of radial immunodiffusion (r = 0.96 for IgG1, r = 0.93 for IgG2, r = 0.90 for IgG3 and r = 0.96 for IgG4). The reaction monitored by the Beckman Array Protein System is easy to perform, rapid and precise. The performance makes the immunonephelometric method suitable for the determination of IgG subclass concentrations in routine analysis.

Adolescent↗
PubMed1994

Effects of administration of branched-chain amino acids vs. glucose during acute exercise in the rat.

Several studies of the relationship of food intake to physical exercise strongly suggest that the two are closely linked. Serotonin transmission seems to be particularly important in the regulation of both appetite and central fatigue. Thus, the ingestion of branched-chain amino acids has been reported to decrease serotonin production and to improve physical performance. In the present study, the effects of three treatments (water, glucose, and branched-chain amino acids) were compared in 34 male Wistar rats. Maximal exercise duration, blood insulin, and glucose levels were measured. Results showed that following the ingestion of branched-chain amino acids, physical performance is lower and blood insulin level is higher than after glucose administration.

Amino Acids↗
PubMed1994

Duodenal calcium binding protein and active calcium transport in rats: are they functionally related?

The effects of calcitriol and a novel calcitriol analogue, 22-oxacalcitriol (OCT) on duodenal Ca transport, calbindin-D9k mRNA, and calbindin-D9k content were studied in two animal models reflecting common human pathologies, namely arterial hypertension and chronic renal failure, as well as in normal rats. The hormone or its analogue were administered intraperitoneally to vitamin-D-replete rats. Active Ca transport was increased in both spontaneously hypertensive rats (SHR) and in normotensive control WKY rats 5 h after calcitriol dosing of either 60 and 600 ng per rat. In WKY, calbindin-D9k content was slightly increased after the injection of 60 ng calcitriol, but not of 600 ng calcitriol whereas calbindin-D9k mRNA stayed essentially unchanged. In contrast, active Ca transport was significantly stimulated after the higher dose of 600 ng calcitriol. In SHR, while both doses of calcitriol increased active Ca transport, they had no stimulatory effect on calbindin-D9k mRNA or protein. In chronically uraemic rats, active Ca transport, duodenal calbindin-D9k and calbindin-D9k mRNA were stimulated after the injection of two subsequent doses of 300 ng calcitriol per rat. OCT treatment at same dosage led to a similar stimulation of calbindin-D9k and calbindin-D9k mRNA, but failed to induce an increase in active Ca transport. These results show that the stimulation of intestinal active Ca transport and calbindin-D9k can be entirely dissociated at the protein synthesis and the mRNA expression level (1) after calcitriol administration to normal and hypertensive rats, and (2) after OCT administration to uraemic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗