The use of nanocarriers for drug delivery through the blood-brain barrier

Due to its importance, the central nervous system (CNS) is protected by the blood‒brain barrier (BBB), a multicellular structure that controls the passage of molecules and ions and acts as a barrier for toxins and pathogens. However, the BBB represents an obstacle to achieving the delivery of therapeutic substances into the nervous system to treat neurological diseases. Strategies such as modulation, bypass of the BBB, and changes in the physical–chemical parameters of drugs can be used to enhance permeation. However, all of these methods have some drawbacks, and another growing strategy involves the use of drug nanocarrier systems. This review identifies the main nanocarriers administered orally or parenterally to increase BBB permeation. The literature describes the use of polymeric nanoparticles, micelles, liposomes, solid lipid nanoparticles, dendrimers, nanostructured lipid carriers, inorganic nanoparticles, nanoemulsions, and hybrid systems. However, polymers are widely applied. Ligand conjugation represents a common strategy for increasing cellular uptake, and the mechanisms involved are receptor-mediated and adsorptive-mediated transcytosis. Despite the potential and promising data for applying this strategy to treat CNS diseases, no commercial nanoformulations with these characteristics are available to treat CNS diseases.