Recent advances in delivery through the blood-brain barrier

Current routes of delivering therapeutics to the brain to treat a variety of neurologic conditions include intracerebral, intrathecal, and intranasal delivery. Though successes have been achieved through the use of these methods, each has limitations that warrant a more universal delivery system involving the intravenous pathway. Two main barriers to intravenous delivery are the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier. This review discusses potential methods for overcoming barriers of intravenous-mediated brain targeting as well as highlights aspects of the highly restrictive BBB anatomy that are important to consider in the design of successful drug delivery systems. Recent advances in intravenous delivery to the brain have exploited receptor-mediated transcytosis and BBB disruption, as well as control of carrier properties. Currently, three predominant synthetic carriers are being studied to transport therapeutics across the BBB: liposomes, metallic nanoparticles, and polymersomes. This article also focuses on receptors that may be upregulated by brain endothelial cells and their ability to significantly increase brain tissue drug distribution when specific targeting moieties to these receptors are attached to synthetic nanocarriers.