(565b) Oral Delivery of Insulin-Transferrin Bioconjugates Using Intelligent Complexation Hydrogels

Complexation graft copolymer of poly(methacrylic acid-g-ethylene glycol), designated as P(MAA-g-EG), has been shown to be effective in oral delivery of theraputic proteins. Their hydrogen bonding complexation/decomplexation characteristics render these responsive hydrogels able to protect the insulin in the harsh, acidic environment of the stomach before releasing the bioactive agent in the small intestine. Further, it can inhibit the activity of Ca2+ dependent proteolytic enzymes, increase the residence time of the drug in the small intestine by mucoadhesion, and reversibly open the tight junctions between the intestinal cells. Transport studies using Caco-2 cells, a widely used in vitro model for intestinal absorption of drugs, have proven the efficacy of the polymeric system. Further enhancement in the insulin bioavailability may be obtained by conjugating it to molecules that can recognize specific receptors on the epithelial cells and get transported across the intestinal epithelium. This approach eliminates the side effects associated with prolonged opening of the tight junctions. Since the conjugate complex crosses the cell barrier by the transcellular mechanism and is specific towards the protein of interest, unspecific transport of toxic compounds is avoided. Researchers have investigated receptor-mediated transcytosis of the insulin-transferrin conjugate in Caco-2 cells. Transferrin is a naturally occurring protein that is involved in the uptake of iron by the cells. The iron-bound transferrin (holo-transferrin) binds to the specific receptor on the epithelial cells and the complex is then endocytosed into the cells. The use of a complexation hydrogel as a delivery vehicle for the insulin conjugates is under investigation. The transferrin molecule (~80 kDa) is significantly bigger than the insulin (~5.8kDa). Hence, as a preliminary step towards developing the delivery system, the loading and release profile of the transferrin from the swollen and deswollen polymer microparticles was investigated by spectroscopic methods. Loading of the microparticles near the iso-electric point of the protein resulted into high loading efficiencies. Understanding the loading and release of transferrin from the complexation hydrogels is important in developing a delivery system for the insulin-transferrin conjugates. The loading and release profile of the insulin-transferrin conjugates from the polymer microparticles was also investigated. It was found that altering the polymer synthesis parameters such as crosslinker, solvent to monomer ratio, particle size, and specific copolymer had an effect on the release profile of the conjugates. Based on these release profiles, the synthesis parameters were adjusted to provide the maximal release of the insulin-transferrin conjugates from the complexation hydrogels.

This work was supported by a NIH grant (EB 000246) and a NSF/IGERT Fellowship to JS