Adsorption of cationized bovine epithelial crypt fractions of the serum albumin onto rat colon

The purpose of the study was to characterize mucosal attachment of a cation ized model protein, bovine serum albumin (BSA), onto the various fractions of colonic crypts epithelium in the rat. BSA was labeled with fluorescein i sothiocyanate (FITC) and its surface not electric charge was modified from negative to positive. Attachment of the cationized protein (CF-BSA) onto ra t colonic epithelium was performed by incubation of colonic everted sacs in medium containing cationized or non-cationized FITC-labeled BSA. Using a n onenzymatic isolation procedure, colonocytes were harvested from five horiz ontal fractions of the colonic crypts. BSA adhesion to the isolated colonoc ytes was quantified spectrofluorometrically. In addition, the effect of inc reasing concentrations of Mg2+ on the adsorption of the cationized BSA onto the surface of colonic epithelium was evaluated by measuring its ability t o displace the adhered BSA from its binding sites. BSA cationization facili tated protein adherence to the colon epithelium in a crypt depth-dependent manner. The largest extent of adherence was observed in the outer layer (fi rst fraction) of the colon. Binding persisted to approximately half the dep th of the crypts. The relation between CF-BSA concentration in the incubati on medium and the amount of CF-BSA adsorbed onto the colonic epithelium was exponential in nature. The addition of electrolyte (Mg2-) caused a detachm ent of the CF-BSA. The adsorption process was characterized by Langmuir's a dsorption isotherm. It is concluded that cationized BSA could be useful as a targetable drug platform in cases where the target site is the gastrointe stinal epithelium. (C) 2001 Wiley-Liss, Inc. and the American Pharmaceutica l Association.