Repurposing insulin for Alzheimer's disease treatment: intranasal delivery of a thermoresponsive nanocarrier-based insulin formulation to the brain.

The Intranasal route provides an effective pathway for insulin delivery to the brain compared to oral/subcutaneous routes as it provides direct access to the brain, bypassing the restrictive blood-brain barrier (BBB), while minimizing systemic exposure. The present study investigated the potential of a thermoresponsive polymer, PNPHO, as a nanocarrier for brain-targeted insulin delivery through the intranasal route, with the aim of repurposing insulin for Alzheimer's disease treatment. Insulin-loaded nanoparticles (NP) were formulated using an advanced crossflow mixing technology with lower (F1) and higher (F2) PNPHO concentrations and characterised in vitro for size, zeta potential, encapsulation efficiencies, stability, drug deposition, and transport and in vivo for biodistribution. Both F1 and F2 NP demonstrated particle sizes ranging from 35.9 to 49.8 nm with low polydispersity index (< 0.3), negative surface charges, high encapsulation efficiencies (> 99%), and conserved structural integrity post 4 weeks of stability study. NP demonstrated significantly greater in vitro nasal deposition compared to insulin alone. Notably, the PNPHO nanocarrier protected insulin from enzymatic degradation, overcoming a key barrier associated with protein/peptide delivery. In vitro drug transport studies showed an initial delay in NP transport across nasal cells due to PNPHO-mucoadhesive properties, followed by increased transport. Significantly enhanced time-dependent NP transport across the BBB cells compared to insulin alone (p < 0.0001) confirmed NP's ability to cross the BBB. In vivo, NP demonstrated prolonged nasal retention and higher brain: serum ratio in mice, suggesting sustained drug release and improved brain delivery compared to insulin alone. Collectively, the study highlight the potential of PNPHO as a promising nanocarrier for achieving targeted and efficient intranasal delivery of insulin to the brain.