Disease mechanisms and translational barriers guide nanocarrier design for nose to brain delivery in Alzheimer’s disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with limited disease-modifying treatment options, partly because many therapeutic agents show insufficient brain exposure and dose-limiting systemic adverse effects after conventional administration. Nose-to-brain (N2B) delivery has emerged as a non-invasive strategy to transport therapeutics to the central nervous system through the olfactory and trigeminal pathways, thereby partially bypassing the blood-brain barrier. Recent advances in nanomedicine and biomaterial engineering have further improved this approach by enhancing drug stability, nasal residence, mucosal transport, and brain-targeting efficiency. This review examines nanocarrier-enabled N2B delivery strategies for AD from a mechanism-guided perspective, highlighting how AD-related pathological processes shape the selection of therapeutic cargos and formulation designs. We discuss recent progress in the intranasal delivery of repurposed small molecules, natural products, insulin-related agents, peptides and proteins, extracellular vesicles, antibodies, and nucleic acid-based therapeutics. We further summarize major nanocarrier and formulation platforms, including lipid-based systems, polymeric nanoparticles, micelles, extracellular vesicles, in situ gels, and device-assisted delivery technologies. Particular attention is given to the design parameters that influence N2B performance, including particle size distribution/PDI, surface charge, mucus interaction, cargo protection, targeting modification, biodistribution, and deposition reproducibility. Finally, we critically evaluate the translational challenges that continue to limit clinical application, including species differences in nasal anatomy, dose-volume restrictions, device-dependent variability, limited human pharmacokinetic evidence, manufacturing complexity, long-term safety, and regulatory requirements. By integrating disease mechanisms, nanocarrier design, and translational considerations, this review provides a structured perspective for developing more rational and clinically feasible N2B nanodelivery systems for AD.