Biomedical subjects

M Rinaudo

Publications and source records attributed to M Rinaudo.

At least 37 records · Page 2Linked to original sources

PubMed1998

A phosphatidylcholine phospholipase C inhibitor, D609, blocks interleukin-3 (IL-3)-induced bcl-2 expression but not c-myc expression in human IL-3-dependent cells.

Activation of the interleukin-3 (IL-3) receptor is required for the induction of cell proliferation and suppression of apoptosis in primitive hematopoietic progenitor cells. A rapid activation of tyrosine kinases and a phosphatidylcholine-specific phospholipase C has been observed in these cells in response to IL-3. The signal transduction cascades regulating cell proliferation and the suppression of apoptosis are poorly understood. Using human IL-3-dependent TF-1 cells, we have found that the tyrosine kinase inhibitor genistein blocks both the IL-3 suppression of apoptosis and the expression of the cell survival gene bcl-2. In addition, we have found that D609, a specific inhibitor of phosphatidylcholine-specific phospholipase C, also inhibits IL-3-induced expression of the bcl-2 gene without affecting IL-3-induced tyrosine phosphorylation. D609 also drove these cells into apoptosis even in the presence of IL-3. Significantly, genistein inhibited the IL-3 induction of both bcl-2 and c-myc gene. The latter gene is related to the induction of cell proliferation. D609, however, blocked the induction only of the cell survival gene bcl-2. Thus, phosphatidylcholine hydrolysis appears linked to the induction of genes related to cell survival. These data fit with the hypothesis that there is a bifurcation in the signaling pathways downstream of IL-3 receptor-induced tyrosine phosphorylation.

Apoptosis↗

PubMed1998

Cassia spectabilis DC seed galactomannan: structural, crystallographical and rheological studies.

The seeds of Cassia spectabilis DC (family: Leguminoseae), an Indian fast growing spreading tree, contain about 40% of endosperm and possess the characteristics of becoming a potential source of commercial gum. The purified galactomannan shows Mw 1.1 x 10(6), intrinsic viscosity [eta] 615ml/g with k' = 1.706 x 10(-1), and a mannose to galactose ration of 2.65. The hydrolysis of the fully methylated polysaccharide reveals clearly the expected structure of legume galactomannans. The orthorhombic lattice constants of the hydrated gums are as follows: a = 9.12 A, b = 25.63 A and c = 10.28 A. The results of X-ray fiber studies show that the b dimension of the unit cell is very sensitive to relative humidity (RH), galactose substitution and orientation of the films. The probable space group symmetry of the unit cell is P2(1)2(1)2. Rheological studies of the galactomannan have shown that the transition from semi-dilute to dilute regime occurs at a critical concentration Cc* = 2.75. The slope of the log-log plot of specific viscosity versus C at zero shear rate is 5.87 in the more concentrated regime. The viscoelastic and critical shear rate behavior indicate the characteristics of a coil polymer. The large dependence of the viscosity on the coil overlap parameter is probably due to polymer-polymer interactions and peculiarity of the galactose distribution along the chain. Above 20 g/L concentration, the rheological behavior of the gum is like the one of a weak-gel.

Cassia↗

PubMed1998

Xanthan-galactomannan interactions as related to xanthan conformations.

The influence of xanthan conformation on the physicochemical behaviour of their mixtures with galactomannan from Schizolobium parahybae mannose:galactose ratio (M/G=3), was studied by viscoelastic measurements, differential scanning calorimetry (DSC) and chiroptical (circular dichroism) methods. The results suggested a more effective interaction of the galactomannan with disordered xanthan segments, which are more abundant in low salt concentrations but are still present in lower proportion at temperatures lower than the temperature of xanthan conformational transition (Tm). The dependence of ellipticity with temperature in a circular dichroism (CD) spectra suggested an ordering of the xanthan chains induced by galactomannan at the temperature of gel formation (Tg approximately 25 degrees C), under conditions where xanthan alone exhibits a disordered conformation. The lower Tg value found (approximately 25 degrees C) compared with that (60 degrees C) usually described in the literature is certainly related to the M/G ratio and the galactosyl unit distribution along the mannan main chain.

Calorimetry, Differential Scanning↗

PubMed1997

Order-disorder conformational transition in succinoglycan: calorimetric measurements.

Differential scanning microcalorimetry was performed on succinoglycan samples from different sources in order to better understand the thermally induced order-disorder conformational transition of the polysaccharide. The shape of thermograms, as well as the melting temperature, were related to the content or distribution of the succinate groups at least in salt-free solution. With increasing polysaccharide and/or salt concentration, the change in the shape of the thermogram was attributed to a progressive screening of the succinate contribution to the order-disorder conformational transition instead of a change in the transition mechanism. In the presence of salt, contrary to the rheological behavior, the calorimetric results were found to be independent of the thermal history of the samples. This suggests a very low enthalpic contribution of the interchain interactions present in succinoglycan solutions. Possible contributions that could explain some discrepancies with results already published in the literature are discussed.

Calorimetry, Differential Scanning↗

PubMed1997

On the specific role of coions and counterions on kappa-carrageenan conformation.

The role of the nature and concentration of counterions and coions on the conformation of kappa-carrageenan is discussed; particularly, that of iodide compared with chloride based on the results obtained from optical rotation, viscometry and microcalorimetry. Iodide gives a more stable helical conformation, with a larger degree of order; at the same time, it represses aggregation of the helices and the gelation ability. Concerning the ordered conformation obtained in the presence of iodide coions, the results obtained are not conclusive. From the enthalpy of the conformational change, it seems that, even in the presence of iodide, the ordered conformation remains a double helix. On the other hand, no doubling of molecular weight was obtained by MALLS/GPC. Thus, this aspect remains still under discussion.

Calorimetry↗

PubMed1996

Structural studies of the exocellular polysaccharide from Sphingomonas paucimobilis strain I-886.

The exocellular polysaccharide from Sphingomonas paucimobilis strain I-886 has been studied using methylation analysis, Smith degradation, partial acid hydrolysis, NMR spectroscopy, and mass spectrometry as the principal methods. It is concluded that the repeating unit has the following structure: [formula: see text] The absolute configuration of the uronic acid was deduced from 1H NMR chemical shifts and is most likely D. Some preparations of the polysaccharide also contain phosphate and O-acyl groups which have not been identified or localised.

Carbohydrate Conformation↗

PubMed1996

Characterization and solution properties of a new exopolysaccharide excreted by the bacterium Alteromonas sp. strain 1644.

This paper concerns the study of a new bacterial exopolysaccharide. The ionic properties of the polymer are considered in relation to the first structural results. This polysaccharide is a carboxylic polyelectrolyte with a charge parameter of 1.33, and exhibits usual polyelectrolyte properties with monovalent and Mg2+ ions. In contrast, its affinity for the divalent ions Ca2+, Sr2+ and Ba2+ is greater than predicted from electrostatic theory. In solution, the polysaccharide undergoes a local conformational transition related to the number of divalent ions bound per carboxylic group. This interaction is mainly an intramolecular process. The dimensions of the polymeric chain were also considered using light-scattering and viscometric measurements. The intrinsic persistence length Lp is equal to 80 +/- 5 A and allows this polymer to be classified as a semi-rigid chain.

Calcium↗

PubMed1996

Solution and gel rheology of a new polysaccharide excreted by the bacterium Alteromonas sp. strain 1644.

A new bacterial polysaccharide '1644' is studied in aqueous solutions and in the gel state. The viscometric measurements for dilute and semi-dilute solutions in presence of monovalent salts are usual; however, in presence of divalent cations like Ca2+ an original behaviour is observed, related to intermolecular bonds. For larger polymer concentrations a clear gel is obtained with divalent counterions. This gel exhibits unusual properties compared to other gelling polysaccharides: it is very elastic and resistant because of low crosslinking. The mechanical properties of this gel depend closely on the fraction of divalent ions linked to the polymer and so on thermodynamic parameters.

Calcium↗

PubMed1996

Characterisation of sorbed water molecules on neutral and ionic polysaccharides.

Ionic and neutral polysaccharides with well-defined structures were chosen to investigate the mechanism of water sorption at different relative humidities. From an experimental point of view, the freezing water was determined by DSC when the total sorbed water was obtained from thermogravimetry. The isotherms of sorption and enthalpies of interaction were determined using the combination of a microbalance and a microcalorimeter. It is shown that freezing water appears for P/P(zero) > 0.85 especially with the neutral polymers. The differential molar enthalpy of interaction is higher for P/P(zero) < 0.85 corresponding to the fixation of two water molecules forming double H-bonds; this result is confirmed by molecular modelling; saturation is obtained experimentally for 4 water molecules interacting per glucose unit. On ionic polymers, the water retention increases especially over P/P(zero) approximately 0.8 and the enthalpy of interaction is higher for the first water molecules sorbed. For P/P(zero) approximately equal to 0.8, the numbers of bound water molecules found are 2 per glucopyranosyl unit for neutral polysaccharides, 5 for glucuronan and 9-10 for carboxymethylcellulose (CMC) of DS = 2 and hyaluronan (HA).

Adsorption↗

PubMed1996

Hydrophobic derivatives of chitosan: characterization and rheological behaviour.

Chitosans which are substituted with alkyl chains having a minimum of six carbon atoms demonstrate hydrophobic interactions in solution. The chemical structure of synthetized polymers is determined from NMR spectroscopy and microanalysis and the distribution between the different types of substituted units is obtained. In relation to the rheological behaviour different parameters are studied such as the nature of the hydrophobic chain and the substitution degree, the polymer concentration, the temperature and the ionic content of the polymeric solution. All the observations tend to prove the hydrophobic nature of the interaction mechanism.

Biocompatible Materials↗

PubMed1995

Hydration of alpha-maltose and amylose: molecular modelling and thermodynamics study.

Hydration of alpha-maltose and amylose were investigated using molecular modelling and thermodynamics methods. The structure and energy of hydration of three low-energy conformers of alpha-maltose were determined by the MM3 molecular mechanics method. The hydration structure was found to be sensitive to the conformation of alpha-maltose and hydration numbers 10 or 11 were estimated for the different conformers. Differential scanning calorimetry and thermogravimetric analysis were used to determine the number of water molecules specifically bonded (non-freezing water) to amylose and different samples of alpha-maltose. Due to high crystallinity of alpha-maltose samples, the observed non-freezing water content was lower than predicted by molecular modelling. In contrast, the experimental number of non-freezing molecules of water per D-glucopyranose residue for amorphous amylose (nh = 3.8) is in good accordance with the value of 3.8 extracted from our calculations.

Adsorption↗

PubMed1995

Galactomannans from Brazilian seeds: characterization of the oligosaccharides produced by mild acid hydrolysis.

Galactomannans with Man:Gal ratios ranging from 1.1:1 to 3:1, obtained from the seeds of Mimosa scabrella, Stryphnodendron barbatiman, Schizolobium parahybum and Schizolobium amazonicum, were submitted to mild acid hydrolysis. The products were fractionated by gel permeation chromatography on BioGel P2 yielding fractions with degrees of polymerization (DP) of 1 to 6. Those with DP 2 to 6 from each species were analysed by ion-exchange high-performance liquid chromatography and characterized by 13C- and 1H-nuclear magnetic resonance (NMR) spectroscopy. The distribution of the oligosaccharides of each degree of polymerization was very similar for the products from S. parahybum and S. amazonicum, indicating the same D-galactosyl distribution on the D-mannan backbone, in agreement with the 13C-NMR splitting in the C4 region of the D-mannosyl units in the original polymers. The hydrolytic conditions adopted allowed characterization of compounds that are not generally produced by enzymatic treatments. The results show that the structures of the oligosaccharides, even if there is a preferential hydrolysis of Gal-Man linkages, reflect the composition of the parent polymer.

Brazil↗

PubMed1994

Influence of the method of purification on some solution properties of welan gum.

The origin and some consequences of the presence of aggregates and impurities (deriving from the fermentation procedure) on the solution properties of welan gum have been studied. For this purpose, a method of purification was developed for a fermentation welan broth. It was verified that this method is ineffective for the dissociation of aggregates in the commercial product. This demonstrates the irreversible nature of the intermolecular interactions of welan samples isolated by precipitation in the presence of impurities. The purified products were characterized (Mw, [eta], kH) and the results were compared to those obtained from commercial samples of welan. The influence of the method of purification on the rheological properties was analysed.

Carbohydrate Conformation↗

PubMed1994

Rheological study on mixtures of different molecular weight hyaluronates.

The shear flow of hyaluronate solutions prepared from mixtures of hyaluronates with different molecular weights has been studied. This paper shows that prediction of the rheological behaviour of polymer mixtures at a given polymer concentration is possible knowing the intrinsic viscosity of the different mixed samples and the general variation of the specific viscosity versus the overlap parameter C[eta]. These characteristics depend on the total ionic strength in solution and have been determined for three conditions: in 0.1 M NaCl and at ionic strengths corresponding to hyaluronate concentrations of 5 and 10 g l-1 in pure water. The differences between the predicted viscosities and the measured ones are usually lower than 5% for the three conditions tested.

Hyaluronic Acid↗

PubMed1993

Characterization of chitosan. Influence of ionic strength and degree of acetylation on chain expansion.

This paper concerns a new method of characterizing chitosans with different degrees of acetylation (DA = 2, 11.5 and 21%); it consists of steric exclusion chromatography using a multidetection instrument allowing determination of M, [eta] and RG for each point of the chromatograms. From these data, the Mark-Houwink parameters for intrinsic viscosity and the exponent relating RG and M are determined. In the same way, the role of the solvent is discussed and the solvent AcOH 0.3 M/AcONa 0.2 M is proposed to reduce the presence of aggregates which perturbs static molecular weight determination by light scattering. The role of the ionic concentration and of the degree of acetylation on the stiffness of chitosan is then discussed and a theoretical treatment is proposed allowing the determination of the intrinsic persistence length (Lp = 50 A) and the prediction of the dimensions in solution (RG and [eta]). Lp is found to be independent of DA in the range tested.

Acetylation↗

PubMed1992

On the solution properties of bacterial polysaccharides of the gellan family.

The influence of side chains and substituents on the polyelectrolyte behaviour of aqueous solutions of polysaccharides of the gellan family has been studied. The results of conductimetric and potentiometric titrations suggest that each of these polysaccharides adopts a double-helix conformation. Deacetylation destabilises the helix of rhamsan and gellan, and optical rotation data confirm these results. The side chain in rhamsan is more flexible and is remote from the carboxylate groups, and the behavior of this polysaccharide is similar to that of gellan. Gelation of deacetylated rhamsan occurs in the presence of calcium ions. The intrinsic viscosity as a function of ionic strength depends on the structure of the polysaccharide and on the presence of acetyl groups.

Carbohydrate Conformation↗

PubMed1992

Substituent distribution on O,N-carboxymethylchitosans by 1H and 13C n.m.r.

The use of the n.m.r. method in the investigation of chitosan carboxymethylation was evaluated. It seems to be the most effective technique to determine concurrently the degree and the position of substitution of the carboxymethylated chitosan derivatives. The 13C-n.m.r., by the DEPT method, 1H-1H and 1H-13C-n.m.r. correlations give much valuable information from the chemical shifts of the complex carboxymethylchitosan spectra. The relative reactivity of the functional groups of chitosan towards carboxymethylation was also determined assuming a higher reactivity of the C-6 position.

Animals↗

PubMed1990

On the physicochemical properties of gellan gum.

This paper concerns the behavior in dilute and demidilute solutions of deacetylated gellan. The conformational transition, controlled by temperature and ionic strength, is investigated. It corresponds to a double-helix single-chain transition. Large ionic selectivity is observed in the helical conformation th at controls the degree of aggregation upon gelation. Potentiometry and conductivity measurements are interpreted in terms of the Manning polyelectrolyte theory in the sol state.

Carbohydrate Conformation↗