Synthesis, characterization, mucoadhesion and biocompatibility of thiolated carboxymethyl dextran-cysteine conjugate

This study was aimed at improving the mucoadhesive properties of carboxymethyl dextran by the covalent attachment of cysteine. Mediated by a carbodiimide, L-cysteine was covalently attached to the polymer. The resulting CMD-cysteine conjugate (CMD-(273) conjugate) displayed 273 +/- 20 mu mol thiol groups per gram of polymer (mean +/- S.D.; n=3). Within 2 h the viscosity of an aqueous mucus/CMD-(273) conjugate mixture pH 7.4 increased at 37 degrees C by more than 85% compared to a mucus/carboxymethyl dextran mixture indicating enlarged interactions between the mucus and the thiolated polymer. Due to the immobilization of cysteine, the swelling velocity of the polymer was significantly accelerated (p<0.05). In aqueous solutions the CMD-(273) conjugate was capable of forming inter- and/or intramolecular disulfide bonds. Because of this crosslinking process within the polymeric network, the cohesive properties of the conjugate were also improved. Tablets comprising the unmodified polymer disintegrated within 15 min, whereas tablets of the CMD-(273) conjugate remained stable for 160 min (means +/- S.D.; n =3). Results from LDH and MIT assays on Caco-2 cells revealed 4.96 +/- 0.98% cytotoxicity and 94.1 +/- 0.9% cell viability for the CMD-(273) conjugate, respectively. Controlled release of model compound from CMD-(273) conjugate tablets was observed over 6h. These findings suggest that CMD-(273) conjugate is a promising novel polymer for drug delivery systems providing improved mucoadhesive and cohesive properties, greater stability and biocompatibility. (C) 2010 Elsevier B.V. All rights reserved.