The aggregation of pig articular chondrocyte and synthesis of extracellular matrix by a lactose-modified chitosan.

A reductive amination reaction (N-alkylation) obtained exploiting the aldheyde group of lactose and the amino group of the glucosamine residues of chitosan (d.a. 89%) afforded a highly soluble engineered polysaccharide (chitlac) for a potential application in the repair of the articular cartilage. Chitosan derivatives with 9% and 64% of side chain groups introduced have been prepared and characterized by means of potentiometric titration, (1)H-NMR and intrinsic viscosity. Both polymers, with respect to the unmodified chitosan, induce cell aggregation when in contact with a primary culture of pig chondrocytes, leading to the formation of nodules of considerable dimensions (up to 0.5-1 mm in diameter). The nodules obtained from chondrocytes treated with chitlac with the higher degree of substitution have been studied by means of optical and electron microscopy (SEM, TEM) and the production of glycosaminoglycans (GAGs) and collagen has been measured by means of colorimetric assays. The chondro-specificity of GAG and collagen was determined by RT-PCR. The results show that the lactose-modified chitosan is non-toxic and stimulates the production of aggrecan and type II collagen.

Regiospecific transglycolytic synthesis and structural characterization of 6-O-alpha-glucopyranosyl-glucopyranose (isomaltose).

The enzymatic synthesis of 6-O-alpha-glucopyranosyl-glucopyranose (isomaltose) was achieved. The regiospecific transglycosylation reaction was catalyzed by a crude preparation of alpha-D-glucosidase from Aspergillus niger, using p-nitrophenyl alpha-D-glucopyranose as the donor and glucopyranose as the acceptor. The yield of the reaction was 59% on a molar basis with respect to the donor. The structural identity of the product was fully determined by HPLC, HPAEC-PAD, ionspray mass spectrometry and (13)C NMR.

Physicochemical properties of aqueous xanthan solutions: static light scattering.

The secondary structure of xanthan in solutions of relatively low salt concentration and at room temperature has been investigated using static light scattering experiments. Additional evidence has been found for a dimeric structure at 25 degrees C in 0.01 M NaCl. From the experimental z-average mean square (ms) radius of gyration, a value for the persistence length p has been estimated, taking explicitly into account the polydispersity of the three samples used, which has been established by gel permeation chromatography (GPC) measurements. The experimental particle scattering functions of the three samples are consistent with theoretical estimates for polydisperse systems with the same value of p = 65 +/- 10 nm and the molar mass per unit length for a dimeric structure. This secondary structure remains unaffected by the ionic strength in the 0.005-0.01 M range. Partial aggregation seems to occur at higher NaCl concentrations. Light scattering and GPC data show that heating the xanthan 0.01 M NaCl solutions to about 70 degrees C considerably reduces the Mw of the low molar mass sample (2.3 x 10(5) g.mol-1), contrary to what is observed for the high molar mass sample (1.8 x 10(6) g.mol-1). These experimental findings can be accounted for by a partial temperature-induced dissociation of the xanthan dimers according to an all-or-none mechanism.

Solution conformation and properties of the galactoglucan from Rhizobium meliloti strain YE-2(S1).

The physicochemical solution properties of the galactoglucan excreted by Rhizobium meliloti strain YE-2(S1) have been investigated by capillary viscometry, potentiometric titration, isothermal mixing microcalorimetry, and circular dichroism. Potentiometric and chiro-optical data, as a function of the degree of ionisation, indicate the absence of a co-operative conformational transition. Solution properties, as a function of ionic strength and temperature, suggest that the galactoglucan adopts a disordered conformation characterised by moderate flexibility. Polyelectrolyte theory is used to fit the enthalpy of dilution data with a suitable linear charge-density parameter. Conformational calculations and chain modelling, using molecular mechanics, give an unperturbed characteristic ratio, (C infinity) of 20, which was smaller than that estimated from intrinsic-viscosity and molecular-weight data for an expanded-coil chain model.

Physico-chemical properties of aqueous solutions of xanthan: an n.m.r. study.

The conformations of xanthan in aqueous solution as a function of temperature have been studied. Measurements of optical activity indicate that the conformational transition, induced by varying the polymer concentration, is analogous to that induced by changes in ionic strength and pH. Within a certain range of concentrations, the low-temperature conformation has a molecular-weight-dependent stability, which shows the usual sigmoidal melting profile with increase in temperature. The 13C-n.m.r. data reflect the increase of the mobility of C-1 and the side-chain carbon atoms in the transition-temperature region. The 23Na relaxation behaviour changes on melting the ordered xanthan conformation. At least two correlation times are needed in order to describe the field-strength dependence of the longitudinal and transverse 23Na relaxation. At 25 degrees, a value of 6.8 ns is obtained for the largest correlation time for the fluctuation of the electric-field gradient. The high-temperature conformation also generates correlation times of the order of ns. From 17O relaxation measurements, a reduction of the mobility of water molecules in the presence of xanthan chains is also observed.

A possible pH-controlled drug delivery system based on a derivative of the polysaccharide scleroglucan.

Four carboxylated derivatives of scleroglucan have been obtained by oxidation, to different extents, of the glucopyranose side chains of the natural polysaccharide. The diffusion of model molecules through aqueous solutions of these new products was measured at various pH values. The reversible pH induced sol-gel transition of some of the polyelectrolyte solutions tested effects a remarkable variation in the diffusion rate of the permeating species; in this sense the most interesting polysaccharide appears to be the product with 70% oxidized glucopyranose moieties. The behaviour of scleroglucan and its derivatives has been compared with that of carboxymethylcellulose and the mechanism involved in drug permeation and release discussed. The possible application of one of the new products in controlled release formulations for oral use is also reported.