In vitro modeling of the blood-brain barrier: simplicity versus complexity.

Proper understanding of blood-brain barrier (BBB) regulation is crucial to reduce/prevent its disruption during injury. Since high brain complexity makes interpretation of in vivo data challenging BBB studies are frequently performed using simplified in vitro models. Although such models represent an important and frequently employed alternative for investigation of BBB function and alterations, our ability to translate in vitro findings to in vivo situation remains sub-optimal. Consequently, despite the fact that our knowledge of the cellular and molecular mechanisms underlying BBB physiology and pathophysiology is constantly increasing, our ability to modulate barrier function remains virtually non-existent. Classical in vitro model systems have provided a wealth of knowledge until now, but it is now evident that newer in vitro models that are more representative of the in vivo situation are needed to further our understanding of barrier physiology. This paper will provide an overview of the BBB cellular components and the most frequently used in vitro BBB model systems. I will discuss their advantages and disadvantages, as well as highlight recently developed models that more closely mimic the BBB in vivo.