Crossing the Blood-brain Barrier: Emerging Nanotechnological Approaches for Neurodegenerative Disease Therapy.

Neurodegenerative disorders such as Parkinson's Disease (PD), Alzheimer's Disease (AD), Amyotrophic Lateral Sclerosis (ALS), and Huntington's Disease (HD) are characterized by progressive neuronal degeneration and severe therapeutic limitations due to the Blood-Brain Barrier (BBB). Recent advances in nanotechnology have enabled the development of nanoscale drug delivery systems capable of improving BBB penetration and enhancing therapeutic efficacy. This review discusses recent progress in Lipid Nanoparticles (LNPs), polymeric nanoparticles, exosomes, magnetic nanoparticles, gold nanoparticles, graphene quantum dots, and RNAloaded nanocarriers for brain-targeted delivery. Special emphasis is placed on receptor-mediated transcytosis, intranasal delivery, magnetic targeting, and ionizable lipid nanoparticle systems for nucleic acid delivery. Recent nanoformulations including curcumin-loaded nanoparticles, siRNA- loaded lipid nanoparticles, dopamine-loaded liposomes, and lactoferrin-functionalized polymeric nanoparticles are critically compared based on BBB penetration, therapeutic efficacy, toxicity, and translational potential. Furthermore, current clinical challenges including nanotoxicity, pharmacokinetics, large-scale manufacturing, and regulatory barriers are discussed. Nanotechnology- based therapeutics represent a promising strategy for improving diagnosis and treatment of neurodegenerative disorders and may facilitate the future development of precision nanomedicine.