ABSTRACT:Chitosan is a natural, cationic polysaccharide derived from fully or partially deacetylated chitin. Chitosan is capable of inducing large phospholipid aggregates, closely resembling the function of nonionic polymers tested previously as additives to therapeutic lung surfactants. The effects of chitosan on improving the surface activity of a dilute lung surfactant preparation, bovine lipid extract surfactant (BLES), and on resisting albumin-induced inactivation were studied using a constrained sessile drop (CSD) method. Also studied in parallel were the effects of polyethylene glycol (PEG, 10 kD) and hyaluronan (HA, 1240 kD). Both adsorption and dynamic cycling studies showed that chitosan is able to significantly enhance the surface activity of 0.5 mg/mL BLES and to resist albumin-induced inactivation at an extremely low concentration of 0.05 mg/mL, 1000 times smaller than the usual concentration of PEG and 20 times smaller than HA. Optical microscopy found that chitosan induced large surfactant aggregates even in the presence of albumin. Cytotoxicity tests confirmed that chitosan has no deleterious effect on the viability of lung epithelial cells. The experimental results suggest that chitosan may be a more effective polymeric additive to lung surfactant than the other polymers tested so far. (1) suggested the use of low-cost, water-soluble nonionic polymers, such as dextran, PEG, and polyvinylpyrrolidone (PVP), as additives to therapeutic lung surfactants. Both in vitro (1-6) and in vivo (7-9) trials have shown that these nonionic polymers can significantly improve the surface activity of different therapeutic lung surfactants and effectively reverse inactivation due to a variety of inhibitory substances.More recently, Lu et al. (10,11) reported the use of an anionic polymer, HA, as a surfactant additive. Both in vitro (10) and in vivo (11) tests showed that the addition of HA at different molecular weights to various therapeutic lung surfactants can effectively reverse serum-and meconium-induced inactivation. These studies, therefore, tentatively proved the feasibility of using an ionic polymer as a lung surfactant additive. Following these studies, we investigate here the use of a cationic polymer, chitosan, as a potential lung surfactant additive.Chitosan is a natural polysaccharide composed of linear ␤-(1¡4)-linked 2-amino-2-deoxy-␤-D-glucan combined with glycosidic linkages (12). It is derived from fully or partially deacetylated chitin, which is extracted from crustacean shells. Chitosan is also a polyelectrolyte with a positively charged backbone and is readily soluble in slightly acidic conditions (12). Chitosan was proven to be biodegradable, biocompatible, bioadhesive, and nontoxic in a range of toxicity tests (13). Because of these desirable properties, it has been extensively used in a variety of food, cosmetic, and pharmaceutical fields. Specifically, chitosan has been extensively used in drug delivery (13), including pulmonary drug delivery (12).Chan and co-workers (14 -17) have recently...