Controlled Delivery of Basal Level of insulin From Chitosan-Zinc-Insulin-Complex-Loaded Thermosensitive Copolymer

Present study was aimed at developing a delivery system for controlled release of insulin, based on chitosan-zinc-insulin complex incorporated into poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (4500 Da) thermosensitive polymer. In vitro release of insulin from the delivery system was studied in phosphate-buffered saline (pH 7.4). The effect of zinc and chitosan on the stability of insulin in the delivery systems during release and storage at 4°C and 37°C was investigated. Circular dichroism, calorimetry, polyacrylamide gel electrophoresis (PAGE), high-performance liquid chromatography, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry were used to determine the stability of insulin released and extracted from the gel. A significant decrease (p < 0.05) in the initial burst was observed from the formulation containing chitosan-zinc-insulin complex, compared with all other formulations. The formulations containing chitosan-zinc-insulin complex showed a long-term controlled release (∼84 days) of insulin. Insulin released and extracted from the gel was conformationally and structurally stable. Bands at 12 kDa were observed in native PAGE, but sodium dodecyl sulfate-PAGE indicated noncovalent nature of insulin aggregates. Thus, the chitosan-zinc-insulin complex significantly reduced the initial burst release and prolonged the release of insulin. It also improved the stability of insulin in the delivery system and protected insulin from aggregation during the entire release period and storage.