Bioadhesive characteristics of chitosan microspheres to the mucosa of rat small intestine

Chitosan (Chi) microspheres were examined in vitro and in vivo in terms of their bioadhesive characteristics to the mucosa of rat small intestine. Chi was labeled with fluorescein isothiocyanate (FITC), and the microspheres ( FTC-MS) were prepared by the dry-in-oil method using the obtained fluoresce in thiocarbamyl-chitosan (FTC-Chi). FTC-MS with a mean diameter of 27 mum a nd size distribution of a few micrometers to several tens of micrometers wa s used for the bioadhesion experiment. FTC-MS exhibited a tendency to adher e to each part of the small intestine to a greater extent than dissolved FT C-Chi, and the ratio of adhering FTC-MS increased as the amount of added FT C-MS decreased. FTC-MS showed slower transit following intraduodenal inject ion than oral administration. Following the intraduodenal injection of FTC- MS, more than half remained in the upper or middle part of the small intest ine for over 8 h. Further, insulin-containing chitosan microspheres with a mean diameter of 20 mum and size distribution of 5 mum to 45 mum were check ed in situ for drug absorption, but intraduodenal or intraileal application hardly gave any decrease in plasma glucose level at a very high dose. The present chitosan microsphere system showed good adhesion to the intestinal mucosa, but scarcely facilitated absorption of insulin.