Crossing Barriers: Advancements in Macromolecular Therapeutics for Neurodegenerative Diseases and Strategies to Overcome the Blood–Brain Barrier

Neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, present considerable challenges for our societies and health systems due to their progressive nature, the demographic shift toward older populations, and limited treatment options. Recent advances in macromolecular therapeutics, including antibodies, peptides, and proteins, offer novel therapeutic modalities for a broad range of diseases. Their high potency and specificity hold promise for disease-modifying therapies to combat neurodegenerative diseases. However, the blood–brain barrier poses a significant challenge for the effective delivery of these large molecules to the central nervous system. This review discusses the physiological role of the blood–brain barrier and its influence on restricting the exposure of macromolecules in the brain. Furthermore, emerging strategies for enhancing blood–brain barrier permeability to macromolecules are highlighted. This review summarizes modifications designed to utilize receptor-mediated uptake, adsorptive-mediated transcytosis, carrier-mediated transport, and nanoparticle-based delivery systems to overcome the blood–brain barrier. Additionally, we emphasize the importance of testing macromolecular therapeutics for their blood-brain barrier permeability and review the methods for such in vitro and in vivo testing. Finally, we shed light on therapeutics in preclinical and clinical development for neurodegenerative diseases and their challenges.