ABSTRACT
The blood-brain barrier (BBB) is a specialized structure of the blood vessel wall that
limits transport and diffusion from the vasculature to the central nervous system and is a
major limitation for the delivery of many therapeutic and imaging agents into the central
nervous system (1-3). It consists of a functional and structural barrier at the level of the
basal lamina and intercellular attachments of the endothelial cells known as “tight
junctions.” The factors that limit passage through the barrier are lipid solubility,
molecular size, and charge. The BBB prevents passage of ionized water-soluble
molecules with molecular weight greater than 180Da (2). These limitations exclude
many of the available therapeutic and diagnostic agents from being used in the brain.
