Lectin-mediated bioadhesion: Preparation, stability and Caco-2 binding of wheat germ agglutinin-functionalized poly(D,L-lactic-co-glycolic acid)-microspheres

To take advantage of the cytoadhesive characteristics of Wheat germ aggluti nin (WGA) for improved particulate drug delivery, the interaction between W GA-grafted poly(D,L-lactic-co-glycolic acid)-microspheres and Caco-2 monola yers was investigated using bovine serum albumin (BSA) or glycine coated mi crospheres as a control. Covalent immobilization of WGA by the carbodiimide /N-hydroxysuccinimide-method on 4 mu m microspheres yielded a surface densi ty of 9.67 +/- 1.21 x 10(6) molecules/particle, whereas 0.22 +/- 0.04 x 10( 6) WGA-molecules were bound by physical adsorption. After storage for 21 da ys in HEPES-buffer and treatment of the particles with 5 M urea, 86% of cov alently linked lectin was still attached to the particles. At 4 degrees C t he Caco-2 binding rate of both, WGA- and BSA-modified particles increased w ith addition of increasing numbers of particles until saturation was reache d at 38150 +/- 1740 (WGA) or 12066 +/- 1195 (BSA) microspheres bound/mm(2) Caco-2 monolayer. Inhibition of Caco-2 binding of WGA-functionalized micros pheres by chitotriose indicated for specificity of the interaction. As obse rved by confocal laser scanning microscopy, the fluorescein-loading of the particles was accumulated intracellularly after incubation of Caco-2 monola yers with WGA-modified microspheres contrary to glycine-grafted microsphere s. Additionally, in case of WGA-functionalized microspheres the amount of c ell associated fluorescein was 200-fold higher than that of the free soluti on. In conclusion. WGA-modified microspheres are expected to enhance intestinal transport of incorporated drugs due to cytoadhesion provided by the lectin coating.