Exploring nose-to-brain insulin delivery as a new strategy for the treatment of Alzheimer's disease.

A growing body of evidence shows that Insulin, Insulin Receptor (IR) and IR signaling are involved in brain cognitive functions and their dysfunction is implicated in Alzheimer's disease (AD) degeneration. Thus, administration of insulin could be a strategy for AD treatment. For this aim we designed, synthesized and characterized a nanogel system (NG) to deliver insulin to the brain, as a tool for the development of a new therapy for AD. A carboxyl-functionalized poly(N-vinyl pyrrolidone) nanogel system produced by high energy ionizing radiation was chosen as substrate for the covalent attachment of insulin or fluorescent molecules, relevant for its tracing. Biocompatibility of the naked carrier was verified by absence of cytotoxicity, oxidative stress and mitochondrial dysfunction. Hemocompatibility was demonstrated by hemolysis, coagulation time, leukocyte proliferation and inflammatory response tests. By immunofluorescence measurements we confirmed that insulin conjugated to the NG (NG-In) is protected by protease degradation, is able to bind and activate insulin receptor and triggers the insulin signaling via AKT activation. Neuroprotection of NG-In against dysfunction induced by amyloid ?, the peptide mainly involved in AD, was in vitro verified. Finally, the potential of NG-In to be efficiently transported across the Blood Brain Barrier was demonstrated by using an in vitro system. Moreover, we explored the possibility of utilizing the intranasal (i.n.) administration as viable alternative to the parenteral administration that could alter blood glucose levels. By intraperitoneal injection of a fluorescent-labeled nanogel, the biodistribution of NG in the whole body and its clearance through the different organs was demonstrated. The administration of NG-In through the i.n. route to study its brain distribution showed that insulin level is improved in the different brain areas with respect to the administration of free insulin. In addition, the histopathological analysis of the nasal mucosa has not shown any morphological change indicating that the nano-formulation is well tolerated in mouse. These results indicate that the synthesized NG-In enhanced insulin delivery to the brain by i.n. administration, thus strongly encouraging its use as therapeutic agent against AD.