In Vitro Investigation of Oral Insulin Delivery Systems Using Lectin Functionalized Complexation Hydrogels

The main advantage of oral protein delivery is that it improves patient compliance and comfort over other routes of administration (i.e. injection), thus leading to a more effective treatment regimen. Although oral protein delivery could benefit many individuals, maintaining the functionality of the protein and low bioavailability of the delivered drug have prevented it from becoming a successful therapy. We have developed a class of environmentally responsive complexation hydrogels composed of methacrylic acid and grafted ethylene glycol chains (P(MAA-g-EG)) functionalized with wheat germ agglutinin (WGA) to overcome these challenges. The drug carriers were designed to (1) minimize the effects of the harsh environment of the gastrointestinal tract and (2) target delivery of the protein drug to the upper small intestine by exploiting the pH shift between the stomach and the small intestine. In addition, functionalization of PEG chains with WGA will allow for specific binding to carbohydrate moieties present in the intestinal mucosa to improve residence time of the carrier at the delivery site. Hydrogel microparticles were prepared by UV-initiated free radical solution polymerization. PEG chains were then functionalized with WGA through a biotin-avidin interaction. Insulin, a model protein, was used to determine if the functionalization process affected the loading and release behavior of the microparticles. Insulin entrapment in the polymer network was unaffected by the WGA functionalization and loading efficiency was determined to be 75% in both functionalized and unfunctionalized microparticles. A release study was done to mimic the conditions of the pH shift between the stomach and the small intestine. The hydrogel carriers prevented release at a low pH (3.2) and rapidly released insulin when the pH was increased to 7.0. In vitro mucoadhesive characteristics of the functionalized polymer were evaluated using a mucin coated 96-well plate. As expected, WGA functionalized microparticles displayed a higher adhesion to the mucin than non-functionalized microparticles. In addition, a competitive carbohydrate assay was used to demonstrate that there was a specific interaction between the WGA and the carbohydrate groups present within the mucus layer. Insulin transport studies were carried out in both the presence and absence of microparticles by using a mucus secreting co-culture of Caco-2 and HT29-MTX cells seeded on a permeable Transwell® plate. The cellular model was designed to more accurately mimic the small intestinal epithelia by inclusion of a mucus secreting cell. Apparent permeability (Papp) increased for wells with P(MAA-g-EG) (15.01 ± 0.65 x 10-9 cm/s) and P(MAA-g-EG) WGA (15.20 ± 1.43 x 10-9 cm/s) as compared to an insulin only solution (2.98 ± 0.27 x 10-9 cm/s) (p<0.01), which correlates to approximately a 5-fold increase in Papp. Functionalizing complexation hydrogels with WGA improved the mucoadhesive properties of this polymer. In addition, the presence of the microparticles increased the amount of insulin transported across a cellular monolayer. Future work is focused on elucidating the exact mechanism by which insulin transport is increased across the cellular monolayer. Introduction Hydrogels are three dimensional polymer networks that are insoluble due to the presence of physical and/or chemical crosslinks . In addition, hydrogels are often used in biomedical applications due to their biocompatibility and ability to imbibe large amounts of water. Complexation hydrogels are a specific class of hydrogels that form physical crosslinks through non-covalent interactions, such as hydrogen bonding . Our lab has successfully developed a class of environmentally sensitive complexation hydrogels containing MAA and PEG tethers (designated as P(MAA-g-EG)) . More specifically, P(MAA-g-EG) is a pH responsive hydrogel that is capable of swelling and deswelling due to the formation of temporary physical crosslinks, or interpolymer complexes, between the PMAA pendant groups and the tethered PEG chains.