Self-assembled lecithin/chitosan nanoparticles for oral insulin delivery: preparation and functional evaluation

Liyao Liu, Cuiping Zhou, Xuejun Xia, Yuling Liu State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Beijing Key Laboratory of Drug Delivery Technology and Novel Formulations, Department of Pharmaceutics, Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, People’s Republic of China Purpose: Here, we investigated the formation and functional properties of self-assembled lecithin/chitosan nanoparticles (L/C NPs) loaded with insulin following insulin–phospholipid complex preparation, with the aim of developing a method for oral insulin delivery.Methods: Using a modified solvent-injection method, insulin-loaded L/C NPs were obtained by combining insulin–phospholipid complexes with L/C NPs. The nanoparticle size distribution was determined by dynamic light scattering, and morphologies were analyzed by cryogenic transmission electron microscopy. Fourier transform infrared spectroscopy analysis was used to disclose the molecular mechanism of prepared insulin-loaded L/C NPs. Fast ultrafiltration and a reversed-phase high-performance liquid chromatography assay were used to separate free insulin from insulin entrapped in the L/C NPs, as well as to measure the insulin-entrapment and drug-loading efficiencies. The in vitro release profile was obtained, and in vivo hypoglycemic effects were evaluated in streptozotocin-induced diabetic rats.Results: Our results indicated that insulin-containing L/C NPs had a mean size of 180 nm, an insulin-entrapment efficiency of 94%, and an insulin-loading efficiency of 4.5%. Cryogenic transmission electron microscopy observations of insulin-loaded L/C NPs revealed multilamellar structures with a hollow core, encircled by several bilayers. In vitro analysis revealed that insulin release from L/C NPs depended on the L/C ratio. Insulin-loaded L/C NPs orally administered to streptozotocin-induced diabetic rats exerted a significant hypoglycemic effect. The relative pharmacological bioavailability following oral administration of L/C NPs was 6.01%.Conclusion: With the aid of phospholipid-complexation techniques, some hydrophilic peptides, such as insulin, can be successfully entrapped into L/C NPs, which could improve oral bioavailability, time-dependent release, and therapeutic activity. Keywords: insulin–phospholipid complex, lecithin, chitosan, nanoparticles, oral delivery, streptozotocin-induced diabetes