Study of the mechanism of insulin encapsulation in poly(isobutylcyanoacrylate) nanocapsules obtained by interfacial polymerization

In previous studies, insulin-loaded poly(alkylcyanoacrylate) nanocapsules w ere found to reduce the blood glucose level after oral administration to di abetic rats and dogs. The reduction of the glycemia induced by the nanocaps ules was the same regardless of the insulin doses administered, but the eff ect appeared only after a delay of a few days. The purpose of this study wa s to investigate the mechanism of insulin encapsulation and the type of int eractions that may exist between the polymer forming the nanocapsule wall a nd the insulin. The results of this study showed, based on the interfacial polymerization of isobutyl-cyanoacrylate, that the insulin molecule is not chemically modified during the nanoencapsulation process. In addition, no i nteraction between the poly(isobutylcyanoacrylate) and the insulin could be observed. The observed high encapsulation efficiency of intact insulin may be explained by the fact that the ethanol used in the preparation of the n anocapsules is responsible for the initiation of the interfacial polymeriza tion of isobutylcyanoacrylate instead of the insulin. The zeta potential me asurements suggest that insulin is located within the core of the nanocapsu les. Thus the biological activity of the nanoencapsulated peptide and the h igh efficiency of insulin encapsulation achieved with this nanoencapsulatio n process cannot be explained by a specific interaction of the insulin with the polymer forming the nanocapsule's wall. It may be due, however, to the fact that the encapsulated insulin molecule is chemically intact and locat ed within the oily core of the nanocapsules. (C) 1999 John Wiley & Sons, In c.