Combination strategy with complexation hydrogels and cell-penetrating peptides for oral delivery of insulin

In previous studies we showed that the complexation hydrogels based in poly(methacrylic acid-g-ethylene glycol) [P(MAA-g-EG)] rapidly release insulin in the intestine owing to their pH-dependent complexation properties; they also exhibit a high insulin-loading efficiency, enzyme-inhibiting properties, and mucoadhesive characteristics. Cell-penetrating peptides (CPPs), such as oligoarginines [hexa-arginine (R6), comprising six arginine residues], have been employed as useful tools for the oral delivery of therapeutic macromolecules. The aim of our study was to investigate the combination strategy of using P(MAA-g-EG) hydrogels with R6-based CPPs to improve the intestinal absorption of insulin. A high efficiency of loading into crosslinked P(MAA-g-EG) hydrogels was observed for insulin (96.1±1.4%) and R6 (46.6±3.8%). In addition, immediate release of the loaded insulin and R6 from these hydrogels was observed at pH 7.4 (80% was released in approximately 30min). Consequently, a strong hypoglycemic response was observed (approximately 18% reduction in blood glucose levels) accompanied by an improvement in insulin absorption after the co-administration of insulin-loaded particles (ILP) and R6-loaded particles (ALP) into closed rat ileal segments compared with that after ILP administration alone. These results indicate that the combination of P(MAA-g-EG) hydrogels with CPPs may be a promising strategy for the oral delivery of various insulin preparations as an alternative to conventional parenteral routes.