Biomedical subjects

M Rinaudo

Publications and source records attributed to M Rinaudo.

At least 19 recordsLinked to original sources

PubMed2006

Synthesis and evaluation of the mucoadhesivity of a CD-chitosan derivative.

Combining mucoadhesive characteristics of a biodegradable polymer such as chitosan with the potential to enhance drug release by increasing the solubility of poorly water-soluble drugs has great potential for pharmaceutical technology and drug delivery design. Polymeric delivery systems have been extensively researched in an attempt to achieve modified drug release. Cyclodextrins (CD) offer an alternative approach. These cyclic oligosaccharides have the ability to form non-covalent complexes with a number of drugs altering their physicochemical properties. In the continuing challenge to improve the properties of delivery systems, this paper focuses on the modification of chitosan by introducing beta-cyclodextrin and to test the mucoadhesive strength and inclusion properties of this synthesised cyclodextrin-polymer. beta-Cyclodextrin was successfully grafted onto a chitosan chain polymer with a cyclodextrin grafting yield of 7% and a CD-chitosan yield of 85%. Although the complexation of (+)-catechin by the grafted beta-CD was found to be about five times weaker than that by the beta-CD monoaldehyde and natural beta-CD, the inclusion properties of the chitosan-CD remain promising. The mucoadhesive properties of chitosan-CD were compared to that of pectin (reference) and the parent chitosan with the use of a tensile separation test. The chitosan-CD showed mucoadhesive strengths of 12% stronger than pectin, but 13.5% weaker than the parent chitosan. The synthesised chitosan-CD-polymer exhibits characteristics of a possible mucoadhesive drug delivery system with some inclusion properties from beta-cyclodextrin.

Adhesiveness↗

PubMed2003

Hydration of polysaccharide hyaluronan observed by IR spectrometry. I. Preliminary experiments and band assignments.

This article is the first one in a series dedicated to the study of hyaluronan as observed by IR spectrometry. The goal is to determine its hydration mechanism and the structural changes this mechanism implies. Hyaluronan is a natural polysaccharide that is widely used in biomedical applications and cosmetics. Its macroscopic properties are significantly dependent on its degree of hydration. In this article we record the IR spectrum of a several micron thick dried film and deduce that four or five residual H(2)O molecules remain around each disaccharide repeat unit in the dried film. We then compare the spectra of sodium hyaluronan and its acid form to assign vibrational bands linked to the carboxylate group. We proceed with a qualitative analysis of the spectral changes induced by changes of temperature and hygroscopicity, two independent parameters that act by modifying the hydrogen bond network of the sample. This enables us to assign most of the vibrational bands of the hydrophilic groups and to distinguish the bands that are due to these hydrophilic groups when they are or are not hydrogen bonded. It constitutes a prerequisite for the quantitative analysis of hydration spectra that will be described in the following articles of this series.

Bacteria↗

PubMed2003

Hydration of hyaluronan polysaccharide observed by IR spectrometry. II. Definition and quantitative analysis of elementary hydration spectra and water uptake.

We recorded a series of spectra of sodium hyaluronan (HA) films that were in equilibrium with their surrounding humid atmosphere. The hygrometry of this atmosphere extended from 0 to 0.97% relative humidity. We performed a quantitative analysis of the corresponding series of hydration spectra that are the difference spectra of the film at a defined hygrometry minus the spectrum of the dried film (hygrometry = 0). The principle of this analysis is to use this series of hydration spectra to define a limited number (four) of "elementary hydration spectra" over which we can decompose all hydration spectra with good accuracy. This decomposition, combined with the measurements of the numbers of H(2)O molecules at the origin in these elementary hydration spectra of the three characteristic vibrational bands of H(2)O, allowed us to calculate the hydration number under different relative humidity conditions. This number compares well with that determined by thermogravimetry. Furthermore, the decomposition defines for each hygrometry value which chemical mechanisms represented by elementary hydration spectra are active. This analysis is pursued by determining for the elementary hydration spectra the number of hydrogen bonds established by each of the four alcohol groups found in each disaccharide repeat unit before performing the same analysis for amide and carboxylate groups. These results are later utilized to discuss the structure of HA at various stages of hydration.

Alcohols↗

PubMed2003

Hydration of hyaluronan polysaccharide observed by IR spectrometry. III. Structure and mechanism of hydration.

The results of the analysis of hydration spectra of Na(+) hyaluronan (HA) performed in a companion study are translated in terms of chemical mechanisms. We find that dried HA is characterized by chains having ordered parts of at least 6 disaccharide repeat units that extend over 60 A. The order is mainly due to C3O3H...O5 and C4O4H...O5 hydrogen bonds that hinder rotations around beta(1-4) and beta(1-3) glycoside bonds. Along one chain there are two-thirds of the N-H amide groups and carboxyl groups that are directly hydrogen bonded, with no water intermediate, to form N-H...(-)O-C=O hydrogen bonds, which are collateral to C3O3H...O5 hydrogen bonds. The existence of these N-H...(-)O-C=O bonds is somewhat in opposition to literature descriptions. In this dry state a "water wire" of 4-5 H(2)O molecules, which are anchored on C=O carboxyl groups and hydrating the Na(+) CO(-) ionic group, establishes hydrogen bonds on other hydrophilic groups of the same chain or other chains and remains embedded in HA, even at 104 degrees C. Hydration occurs at low hygrometry around the remaining one-third of the N-H...(-)O-C=O pairs that are not hydrogen bonded. Each of these N-H and (-)O-C=O groups is hydrated by a nanodroplet of some 25 H(2)O molecules that finds other sites for binding and hydrates 2 disaccharide repeat units. At higher hygrometry bigger nanodroplets hydrate all hydrophilic sites.

Hyaluronic Acid↗

PubMed2001

Associative phenomena in galactomannan-deacetylated xanthan systems.

The interaction between mesquite seed galactomannan (MSG; D-mannose to D-galactose ratio (M/G) approximately 1.1) and deacetylated xanthan (DX) in 5 mM NaCl leading to synergistic gel formation at 25 degrees C was investigated and compared with the far more studied system made of xanthan and locust bean gum (LBG; M/G approximately 3.5). Rheology and differential scanning calorimetry were used to measure temperatures of gel formation and transition enthalpy as a function of polymer composition, while circular dichroism was used to probe the conformation of DX in the LBG-DX system. MSG and DX associate at 25 degrees C with a well defined stoichiometry of 0.6:1.0 (w/w) at low ionic strength favouring the disordered coil state of DX. When LBG was used in place of MSG in water or 5 mM NaCl, two types of mechanisms of interpolymeric association are envisaged.

Calorimetry, Differential Scanning↗

PubMed2001

Comparative rheological behavior of hyaluronan from bacterial and animal sources with cross-linked hyaluronan (hylan) in aqueous solution.

Using a variety of rheological techniques, the behavior of hyaluronan (M(w) 0.8-2.2 x 10(6)), cross-linked hyaluronan (hylan) (M(w) 1.8-12.5 x 10(6)), and Healon (M(w) approximately 5 x 10(6)) (a proprietary hyaluronan) was studied over a large range of molecular weights. The object was to study the effect of the cross-links in hylan on the various rheological parameters, in comparison with linear hyaluronan. There are significant differences. The Huggins constant and the critical overlap parameter C*[eta] are considerably lower for hylan and an increase in moduli at low frequencies was observed for hylan compared with the hyaluronan samples at all molecular weights studied. The results point to a difference in structure in dilute solution for hylan due to the ability to form networks, which can be removed by pressure filtration. In contrast, we do not find an increase of the steady shear viscosity and elastic modulus at higher concentrations when a homogeneous entangled network is reached. We attribute this behavior to the semirigid character of the hyaluronan chain and to the predominance of entanglements over the cross-link points present in hylan in the semidilute domain. Due to the higher apparent molecular weights that are possible with hylan structures but not with the hyaluronans currently available, a wider range of applications can be achieved with hylans when viscoelasticity is required, particularly for the viscosupplementation of synovial fluid damaged by osteoarthritis.

Animals↗

PubMed2001

Two types of hydrophobic aggregates in aqueous solutions of chitosan and its hydrophobic derivative.

The aggregation phenomena in aqueous solutions of hydrophobically modified (HM) chitosan, containing 4 mol % of n-dodecyl side chains, were studied by viscometry and fluorescence spectroscopy with pyrene as a probe. The results are compared with those for unmodified chitosan. Surprisingly, fluorescence data reveal the appearance of intermolecular hydrophobic aggregates both in chitosan and in HM chitosan. Nevertheless, these polymers exhibit quite different rheological properties: upon the formation of aggregates the viscosity of HM chitosan sharply increases, while that of unmodified chitosan raises only slightly. The aggregation models for both chitosan and its hydrophobic derivative were proposed. It was shown that in solutions of HM chitosan two types of hydrophobic domains exist: hydrophobic domains typical for different associating polymers with hydrophobic side chains and hydrophobic domains inherent to chitosan itself.

Biopolymers↗

PubMed2000

Study on TEMPO-mediated selective oxidation of hyaluronan and the effects of salt on the reaction kinetics.

2,2,6,6-Tetramethyl-1-piperidinyloxy radical (TEMPO)-mediated oxidation of hyaluronan was studied at pH 10.2 and temperature of 0 degrees C with NaOCl as the primary oxidant. As with other polysaccharides, a high selectivity of oxidation was observed. The degradation of the polymer was essentially caused by the oxidation process. The primary oxidant and the pH of the reaction mixture did not alter the molecular weight of hyaluronan during oxidation. The kinetics of the oxidation process was investigated at different concentrations of reactants and the inorganic salts, NaBr, NaCl, and Na2SO4. An increase in the salt concentration in the mixture causes a major decrease in the rate of the oxidation, and this decrease is independent of the nature of the salt.

Catalysis↗

PubMed2000

A new bacterial exopolysaccharide (YAS34). II. Influence of thermal treatments on the conformation and structure. Relation with gelation ability.

This paper describes an original mechanism of evolution of a polysaccharide system occurring during thermal treatments. Under its native conformation, the YAS34 polymer presents a solution character in the dilute and semi-dilute regimes. However, the zero shear rate viscosity indicates existence of interchain interactions which disappear on the deacetylated polymer. Thermal treatments over the temperature of conformational change produce a progressive and irreversible evolution of the physical properties when the polymer is under its sodium salt form. This evolution was related to a modification of the arrangement of acetyl substituents. The heated polysaccharide gives thermoreversible gel which is very elastic. A gelation mechanism is proposed based on formation of helical segments connecting the network.

Acetylation↗

PubMed2000

A new bacterial polysaccharide (YAS34). I. Characterization of the conformations and conformational transition.

This paper concerns the study of the conformational transition of a new exopolysaccharide (YAS34) using experimental techniques such as optical rotation, conductimetric and microcalorimetric measurements as a function of temperature. The behaviors of this polysaccharide in the acid or sodium salt form are compared; a deacetylated sample is also prepared to demonstrate the role of substituents. For the native structure (never heated), a conformational transition is observed but the deacetylated polysaccharide exhibits no ordered conformation. Multidetection size exclusion chromatography (SEC) analyses and conductimetric experiments allowed to determine the nature of each conformation and the molecular dimensions. From these results, it is suggested that the native conformation is a double helix which by heating over T(m) (temperature corresponding to half conformational transition) dissociates into disordered single chains. In the acid and sodium salt forms, by cooling below T(m), an ordered conformation is restored. This conformation seems to be an intramolecular double helix 'hairpin-like turn' (called renatured conformation). Nevertheless an irreversible denaturation is obtained progressively in the sodium salt form when the time of heating over T(m) increases. The conformation of the deacetylated polysaccharide corresponds to that of a single flexible chain (disordered conformation). The conformational transition for the native conformation was studied also in relation to the polyelectrolytic character of the polysaccharide: stability as a function of salt nature and salt and polymer concentrations was investigated for the polymer initially in the sodium and acid forms.

Carbohydrate Conformation↗

PubMed2000

Solid state NMR for determination of degree of acetylation of chitin and chitosan.

The degree of acetylation (DA) of various samples has been evaluated by 1H liquid-state NMR and 13C and 15N CP-MAS solid-state NMR over the whole range of DA. A good agreement has been found for all the experiments. The 13C and 15N CP-MAS experiments have permitted the evaluation of the chitin DA and content in the structural polysaccharides in a fungus named Aspergillus niger. The fungus structural carbohydrates mainly consist in pure chitin associated with glucans. Comparison of the 13C CP-MAS spectra with standard (1-->3)-beta-D-glucans strongly suggests that chitin and glucans are linked via covalent bonds.

Acetylation↗

PubMed2000

Conformational behavior of hyaluronan in relation to its physical properties as probed by molecular modeling.

Hyaluronan (HA) is a linear charged polysaccharide whose structure is made up of repeating disaccharide units. Apparently conflicting reports have been published about the nature of the helical structure of HA in the solid state. Recent developments in the field of molecular modeling of polysaccharides offer new opportunities to reexamine the structural basis underlying the formation and stabilization of ordered structures and their interactions with counterions. The conformational spaces available and the low energy conformations for the disaccharide, trisaccharide, and tetrasaccharide segments of HA were investigated via molecular mechanics calculations using the MM3 force field. First, the results were used to access the configurational statistics of the corresponding polysaccharide. A disordered chain having a persistence length of 75 A at 25 degrees C is predicted. Then, the exploration of the stable ordered forms of HA led to numerous helical conformations, both left- and right-handed, having comparable energies. Several of these conformations correspond to the experimentally observed ones and illustrate the versatility of the polysaccharide. The double stranded helical forms have also been explored and theoretical structures have been compared to experimentally derived ones.

Carbohydrate Conformation↗

PubMed1999

Role of galactomannan composition on the binary gel formation with xanthan.

The influence of the galactomannan characteristic ratios (M/G) on the temperature of gelation (Tg) and the gel strength of mixtures of galactomannan with xanthan is reported. Two galactomannans were investigated: one highly substituted from the seeds of Mimosa scabrella (M/G = 11), and the other, less substituted, from the endosperm of Schizolobium parahybae, with (M/G = 30) [Ganter JLMS, Zawadzki-Baggio SF, Leitner SC, Sierakowski MR, Reicher F. J Carbohydr Chem 1993;12:753]. The xanthan:galactomannan systems (4:2 g l(-1), in 5 mM NaCl) showed a temperature of gel formation (Tg) of 24 degrees C for that of S. parahybae [Bresolin TMB, Milas M, Rinaudo M and Ganter JLMS. Int J Biol Macromol 1998;23:263] and 20 degrees C for the galactomannan of M. scabrella, determined by viscoelastic measurements and microcalorimetry. A Tg of 40-50 degrees C was found by Shatwell et al. [Shatwell KP, Sutherland IW, Ross-Murphy SB, Dea ICM. Carbohydr Polym 1991;14:29] for locust bean gum-LBG (M/G = 43). Lundin and Hermansson [Lundin L, Hermansson AM. Carbohydr Polym 1995;26:129] reported a difference of 13 degrees C for Tg of two LBG samples with M/G = 3 (40 degrees C) and 5 (53 degrees C), in mixtures with xanthan. It appears that the more substituted galactomannans have lower temperatures of gelation in the presence of xanthan. The mechanism of gelation depends also on the M/G ratio. For the lower values it involves only disordered xanthan chains in contrast to M/G ratios higher than 3. In addition, the presence of the galactomannan from M. scabrella increased slightly the temperature of the conformational change (Tm) of xanthan probably due to the ionic strength contribution of proteins (3.9%) present in the galactomannan. On the other hand, the galactomannans from S. parahybae, with 1.5% of proteins and M. scabrella, with 2.4% of protein, did not show this effect, the Tm of xanthan alone or in a mixture being practically unchanged.

Calorimetry, Differential Scanning↗

PubMed1999

On the interchain associations in aqueous solutions of a succinoglycan polysaccharide.

Formation of interchain associations between succinoglycan chains have been studied by comparing weight average molecular weight, intrinsic viscosity of succinoglycan as a function of the conditions to prepare the solutions (polymer concentration, the heating temperature adopted compared with Tm). The different solutions obtained were characterized by their Newtonian viscosity, the storage and loss moduli and their sensitivity to the temperature. It was found that interchain associations, first stabilized mainly during the disorder-order transition convert to more stable associations by aging at temperatures below but not too far from Tm. These associations appear from succinoglycan solutions characterized by an overlap parameter higher than about 8 and modify only very slightly the conformational transition parameters obtained from microcalorimetry measurements.

Calorimetry↗

PubMed1999

Comparison between the physicochemical behaviour of two microbial polysaccharides: RMDP17 and rhamsan.

This paper concerns the properties of two ionic polysaccharides with very close chemical structures. pH metric and conductimetric measurements showed that they behave similarly from a polyelectrolytic point of view. From optical rotation and differential scanning calorimetry (DSC) measurements, the two polymers probably adopt a double helical conformation which is destabilised by deacetylation. The main differences concern the stability of this ordered conformation and the ability of these double helices to associate to form gels. The results support a higher thermal stability of the ordered conformation for deacetylated RMDP17 (about 8 degrees C), whereas deacetylated rhamsan has a better ability to form gels.

Acetylation↗

PubMed1999

Conformational transition of native and modified gellan.

This paper concerns the characterisation of native gellan by differential scanning calorimetry (DSC) and rheology. The stability of the double helix is characterised by Tm and the enthalpy of conformational change. The role of the external salt concentration is investigated; it is shown that Tm is only slightly modified. At ambient temperature, in 10(-2) M NaCl, native gellan behaves as a loose gel (G' > G''). This behaviour disappears when temperature is larger than 60 degrees C. The comparison with deacylated gellan (commercial sample) shows that the position of conformational transition is much more influenced by the salt concentration; the helical structure is less stable and the conformational transition presents a hysteresis between heating and cooling runs when the external salt concentration increases. The rheological behaviour is that corresponding to a solution (G' < G'') at ambient temperature and in 10(-2) M NaCl. When the salt excess increases, then a stronger gel is formed. The differences between the two types of samples are clearly established as well as the relations between the conformation and the rheology of the systems.

Acetylation↗

PubMed1999

Physico-chemical characterization of Ca-alginate microparticles produced with different methods.

In the present paper the physico-chemical characterization of Ca-alginate microparticles produced with different methods is presented. Ca-alginate microparticles were obtained either by emulsification method or by dripping an aqueous alginate solution into a solution of calcium salt. Inverse Size Exclusion Chromatography (ISEC) was used for the determination of dimensions of the pores and porous volume of microparticles having a mean diameter of 220 microm when obtained by emulsification method. The same technique was used to study the variation of the pore size and porous volume with pH. The results were related with the content of calcium and sodium in the microparticles, before and after their treatment with different HCl solutions. For the particles with a mean diameter of 1.2 mm (obtained by dripping method) we adopted an other approach based on the steric exclusion of solute at equilibrium. For a convenient interpretation of the obtained data, determination of water regain, swelling degree, and scanning electron microscopy (SEM) were performed. Finally, a comparison of the characteristics of microparticles produced by ionic and epichlorohydrin crosslinkings was made. The maximum dimensions of the pores of the microparticles obtained by emulsification were found smaller than those obtained by other technics. The variation of the dimensions of the pores and porous volume with pH is not significant. The structure of the chemically crosslinked beads with epichlorohydrin is more elastic and the swelling is reversible; after drying and reswelling process, the dimensions of the pores and porous volume of these microparticles remain unchanged. On the opposite, for the microparticles obtained by emulsification or dripping method in the presence of calcium ions, these characteristics are changed after a first drying process.

Alginates↗

PubMed1998

Evaluation of molecular strategies to develop a live dengue vaccine.

BACKGROUND: Millions of individuals are estimated to become infected with dengue virus each year, particularly in tropical and subtropical regions. Mortality is low but infection can lead to a severe form of dengue, characterised by haemorrhage and shock. A safe and effective vaccine against dengue is still not available. OBJECTIVE: To use the successful construction of dengue type 4 virus (DEN4) cDNA, which yields infectious RNA transcripts, to provide a new approach to the development of safe and effective dengue vaccines. STUDY DESIGN: The 3' and 5' noncoding (NC) regions of the genome were targeted to construct DEN4 deletion mutants, because the sequences in these regions are thought to play an important role in the regulation of viral replication. DEN4 cDNA was also employed to construct a viable chimeric virus with dengue type 1, 2 or 3 antigenicity, by substitution of heterotypic structural protein genes. RESULTS: Most viable mutants, recovered from the cDNA constructs, were partially restricted for growth in simian cells as analysed by plaque morphology assay and viral yield analysis. Several 3' NC deletion mutants which exhibited a range of growth restriction in cell culture were further evaluated for infectivity and immunogenicity in rhesus monkeys. Occurrence and duration of viraemia were reduced for these deletion mutants, compared to the wild type DEN4. Analysis of antibody response to infection in rhesus monkeys also indicated that some of these mutants were attenuated. These DEN4 deletion mutants represent promising live dengue vaccine candidates that merit further clinical evaluation. Chimera DEN1/DEN4 or DEN2/DEN4 which expresses DEN1 or DEN2 antigenicity were also used to infect monkeys. Most monkeys immunised with these chimeric viruses, singly or in combination, developed high titres of neutralising antibodies and were protected against homotypic wild type DEN1 or DEN2 challenge. CONCLUSIONS: DEN4 and its derived chimeric viruses of other three dengue serotype specificity, that contain appropriate attenuating mutations, have a potential use in a tetravalent live vaccine against dengue.

Animals↗