Prerequisite Characteristics of Nanocarriers Favoring Oral Insulin Delivery: Nanogels as an Opportunity

Protamine nanocapsules as carriers for oral peptide delivery

Peptides represent a promising therapeutic class with the potential to alleviate many severe diseases. A key limitation of these active molecules relies on the difficulties for their efficient oral administration. The objective of this work has been the rational design of polymer nanocapsules (NCs) intended for the oral delivery of peptide drugs. For this purpose, we selected insulin glulisine as a model peptide. The polymer shell of the NCs was made of a single layer of protamine, a cationic polypeptide selected for its cell penetration properties, or a double protamine/polysialic acid (PSA) layer. Insulin glulisine-loaded protamine and protamine/PSA NCs, prepared by the solvent displacement method, exhibited a size that varied in the range of 200-400 nm and a neutral surface charge (from +8 mV to -6 mV), depending on the formulation. The stability of the encapsulated peptide was assessed using circular dichroism and an in vitro cell activity study. Colloidal stability studies were also performed in simulated intestinal media containing enzymes and the results indicated that protamine NCs were stable and able to protect insulin from the harsh intestinal environment, and that this capacity could be further enhanced with a double PSA-Protamine layer. These NCs were freeze-dried and stored at room temperature without alteration of the physicochemical properties. When the insulin-loaded protamine NCs were administered intra-intestinally to diabetic rats (12 h fasting) it resulted in a prolonged glucose reduction (60%) as compared to the control insulin solution. This work raises prospects that protamine NCs may have a potential as oral peptide delivery nanocarriers.

Nose-to-brain delivery of insulin enhanced by a nanogel carrier

Recent evidences suggest that insulin delivery to the brain can be an important pharmacological therapy for some neurodegenerative pathologies, including Alzheimer disease (AD). Due to the presence of the Blood Brain Barrier, a suitable carrier and an appropriate route of administration are required to increase the efficacy and safety of the treatment. Here, poly(N-vinyl pyrrolidone)-based nanogels (NG), synthetized by e-beam irradiation, alone and with covalently attached insulin (NG-In) were characterized for biocompatibility and brain delivery features in a mouse model. Preliminarily, the biodistribution of the "empty" nanocarrier after intraperitoneal (i.p.) injection was investigated by using a fluorescent-labeled NG. By fluorescence spectroscopy, SEM and dynamic light scattering analyses we established that urine clearance occurs in 24h. Histological liver and kidneys inspections indicated that no morphological alterations of tissues occurred and no immunological response was activated after NG injection. Furthermore, after administration of the insulin-conjugated nanogels (NG-In) through the intranasal route (i.n.) no alteration or immunogenic response of the nasal mucosa was observed, suggesting that the formulation is well tolerated in mouse. Moreover, an enhancement of NG-In delivery to the different brain areas and of its biological activity, measured as Akt activation levels, with reference to free insulin administration was demonstrated. Taken together, these results indicate that the synthesized NG-In enhances brain insulin delivery upon i.n. administration and strongly encourage its further evaluation as therapeutic agent against some neurodegenerative diseases.

Ionizing radiation-engineered nanogels as insulin nanocarriers for the development of a new strategy for the treatment of Alzheimer's disease

A growing body of evidence shows the protective role of insulin in Alzheimer's disease (AD). A nanogel system (NG) to deliver insulin to the brain, as a tool for the development of a new therapy for Alzheimer's Disease (AD), is designed and synthetized. A carboxyl-functionalized poly(N-vinyl pyrrolidone) nanogel system produced by ionizing radiation is chosen as substrate for the covalent attachment of insulin or fluorescent molecules relevant for its characterization. Biocompatibility and hemocompatibility of the naked carrier is demonstrated. The insulin conjugated to the NG (NG-In) is protected by protease degradation and able to bind to insulin receptor (IR), as demonstrated by immunofluorescence measurements showing colocalization of NG-In(FITC) with IR. Moreover, after binding to the receptor, NG-In is able to trigger insulin signaling via AKT activation. Neuroprotection of NG-In against dysfunction induced by amyloid β (Aβ), a peptide mainly involved in AD, is verified. Finally, the potential of NG-In to be efficiently transported across the Blood Brain Barrier (BBB) is demonstrated. All together these results indicate that the synthesized NG-In is a suitable vehicle system for insulin deliver in biomedicine and a very promising tool to develop new therapies for neurodegenerative diseases.