Complexation hydrogels for intestinal delivery of interferon beta and calcitonin.

Recent studies have suggested that complexation hydrogels poly(methacrylic acid-g-ethylene glycol) (henceforth designated as P(MAA-g-EG)) exhibit high insulin incorporation efficiency, rapid insulin release in the intestine based on their pH-dependent complexation properties, enzyme-inhibiting effects and mucoadhesive characteristics. Therefore, they are promising carriers for insulin delivery via an oral route. As we designed these hydrogels as carriers suitable for oral administration of various peptide/protein drugs, in this study we aimed at investigating the applicability of P(MAA-g-EG) hydrogels to improving the intestinal absorption of various peptide/protein drugs. High loading efficiency into hydrogels was observed for insulin, calcitonin, and interferon beta. In addition, polymer microparticles loaded with calcitonin and interferon beta exhibited complexation/decomplexation and pH-sensitive release behavior. The molecular weight and chemical structure appeared to affect the efficiency of loading and release depending on the peptides and proteins. Furthermore, a drastic reduction of plasma calcium concentration accompanied by calcium absorption and a dose-dependent enhancement of plasma interferon beta concentration were observed after the administration of particles loaded with calcitonin or interferon beta into closed rat ileal segments. These findings indicate that P(MAA-g-EG) hydrogels are promising carriers for administration of various peptides and proteins via an oral route.

Confocal microscopic analysis of transport mechanisms of insulin across the cell monolayer.

Development of oral insulin formulations would significantly improve the quality of life of patients suffering from diabetes. Complexation hydrogels developed in our laboratory, are one of the most promising classes of materials for use in targeted oral delivery of proteins. Results from confocal microscopy analysis of insulin transport in Caco-2 cells indicated that the primary route of transport was the paracellular pathway and that the transcellular component of the transport was insignificant.

Synthesis and characterization of insulin-transferrin conjugates.

Receptor-mediated endocytosis can be exploited for improving the transcellular delivery of therapeutic proteins. Insulin conjugated to transferrin by forming disulfide bonds has been shown to improve insulin oral bioavailability in diabetic rats. We are developing a combination strategy involving complexation hydrogels as delivery vehicles for insulin-transferrin conjugates. The complexation hydrogels developed in our laboratory have been shown to be promising carriers for oral delivery of proteins and peptides. Integrating the strategies based on the complexation hydrogels and insulin-transferrin conjugates may prove to be a novel approach for oral delivery of insulin and other therapeutic proteins. In this work, electrospray ionization mass spectrometry (ESI-MS) was used to study the modification of insulin during its reaction with transferrin. The stability of the conjugated insulin to enzymatic degradation was also studied. ESI-MS studies confirmed the site-specific modifications of insulin. The transferrin conjugation of insulin was also shown to increase the stability of insulin to enzymatic degradation.

Nanoscale analysis of protein and peptide absorption: insulin absorption using complexation and pH-sensitive hydrogels as delivery vehicles.

Recent advances in the discovery and delivery of drugs to cure chronic diseases are achieved by combination of intelligent material design with advances in nanotechnology. Since many drugs act as protagonists or antagonists to different chemicals in the body, a delivery system that can respond to the concentrations of certain molecules in the body is invaluable. For this purpose, intelligent therapeutics or "smart drug delivery" calls for the design of the newest generation of sensitive materials based on molecular recognition. Biomimetic polymeric networks can be prepared by designing interactions between the building blocks of biocompatible networks and the desired specific ligands and by stabilizing these interactions by a three-dimensional structure. These structures are at the same time flexible enough to allow for diffusion of solvent and ligand into and out of the networks. Synthetic networks that can be designed to recognize and bind biologically significant molecules are of great importance and influence a number of emerging technologies. These synthetic materials can be used as unique systems or incorporated into existing drug delivery technologies that can aid in the removal or delivery of biomolecules and restore the natural profiles of compounds in the body.

Characterization of insulin protection properties of complexation hydrogels in gastric and intestinal enzyme fluids.

The objective of this study was to elucidate the mechanisms contributing to oral bioavailability of insulin by poly(methacrylic acid grafted with poly(ethylene glycol)) (P(MAA-g-EG)) hydrogels using the gastric and intestinal fluids from rats. P(MAA-g-EG) hydrogels successfully protected the incorporated insulin from enzymatic degradation by forming interpolymer complexes in the gastric fluid. The hydrogels also showed the insulin protection ability by itself. In the intestinal fluid, P(MAA-g-EG) hydrogels significantly decreased the insulin degradation rate and calcium ion levels, while protein levels was not changed. Insulin protecting effects were dependent on the fraction of the carboxylic group in the polymer networks. Moreover, the insulin degradation inhibitory effect was significantly correlated with Ca2+ deprivation ability of P(MAA-g-EG) hydrogels in the intestinal fluid, implying that the Ca2+ deprivation ability plays an important role in the inhibition of the intestinal enzyme activities. Insulin-loaded P(MAA-g-EG) (ILPs) hydrogels showed a rapid and almost complete insulin release even in the presence of intestinal proteases. These results suggested that the insulin protection ability of the hydrogels contributed to improve oral insulin absorption and that P(MAA-g-EG) hydrogels can be an excellent carrier for protecting insulin during their transit through the GI tract.

Novel delivery system based on complexation hydrogels as delivery vehicles for insulin-transferrin conjugates.

A variety of approaches have been investigated to address the problems associated with oral insulin delivery, but the bioavailability of oral insulin is still low. Insulin is rapidly degraded by the enzymes in the GI tract and is not transported across the epithelial barrier easily. The oral insulin formulation developed in this work makes use of complexation hydrogels for oral delivery of insulin bioconjugates. The insulin bioconjugates synthesized in this work consist of insulin bound to transferrin molecule which can be uptaken by the epithelial cells. The conjugates can increase the permeability of insulin across the epithelial barrier by receptor-mediated transcytosis. The transferrin in the conjugate is also shown to stabilize insulin in the presence of intestinal enzymes. Use of complexation hydrogels for delivery of insulin-transferrin conjugate may greatly increase the bioavailability of oral insulin. This is because, the complexation hydrogels are known to exhibit characteristics that make them ideal candidates for oral protein delivery. They can also inhibit the degradation of insulin in the GI tract. Thus, combination of these two approaches may provide an innovative platform for oral insulin delivery.

Gastrointestinal transit and mucoadhesive characteristics of complexation hydrogels in rats.

The aim of this study was to investigate the gastrointestinal (GI) transit and mucoadhesive properties of complexation hydrogels, poly(methacrylic acid-grafted-ethylene glycol). The fluorescent labeled complexation hydrogels containing different molar ratios of methacrylic acid/ethylene glycol and different particle diameters were synthesized by free radical solution polymerization. The GI transit profiles of microparticles after oral administration to rats were evaluated by determining the polymer remaining in the stomach and the small intestine. Moreover, the mucoadhesion to the duodenal mucosa was evaluated by an in situ perfusion method. The ethylene glycol content and particle size of the hydrogels influenced significantly the GI transit and mucoadhesive capacities. The microparticles composed of polymers prepared from 1:1 ratio of methacrylic acid/ethylene glycol and having diameters of <53 microm showed the strongest mucoadhesive capacity. These findings indicated that the hydrogels may be a promising tool for improving oral bioavailability of various drugs, which are poorly absorbed from the GI tract.