Quantification of the blood-brain barrier permeability to neutral and charged solutes.

摘要

The blood-brain barrier (BBB) is a dynamic barrier essential for maintaining the micro-environment of the brain. Its special anatomical features determine its protective role for the central nervous system (CNS) as well as a barrier to drug delivery to the brain. The BBB is such a complicated barrier that even after numerous attempts have been made to decode its complexity, very little has been determined conclusively. One difficulty is a lack of quantitative and well-defined model system. In the first part of this study, a non-invasive method was developed to measure the rat cerebral microvessel permeability to solutes. This new in vivo quantitative method overcame disadvantages of previous open-skull methods that would cause increased BBB permeability in a very short time.;Although the existence of charge in the BBB has been found a long time ago, there are no detailed quantitative data and models that investigate the contribution of the charge carried by the endothelial surface glycocalyx and basement membrane to the permeability of the BBB. The second part of the study applied the newly developed non-invasive method to measure the permeability of the BBB to charged molecules, and then to predict the charge density of the surface glycocalyx layer of the endothelium and that of the basement membrane in the BBB through mathematical modeling. Previous studies have shown that plasma glycoprotein orosomucoid modulates permeability of peripheral microvessels to charged molecules by contributing to the net charge on the microvessel wall. We also found that orosomucoid modulates the permeability of the BBB by altering its charge.;The cultured monolayer of b.End3, an immortalized mouse cerebral endothelial cell line, is becoming a more and more popular in vitro model of the BBB because of its advantages over the primary cultures in several aspects, e.g., easy growth and the ability to maintain the same characteristics over many passages. In the third part of this study, we examined whether or not b.End3 monolayer is a good in vitro model in studying transport across the BBB. We found that the b.End3 monolayer carries many characteristics of the BBB in terms of low solute permeability, comparable surface charge to that of the intact BBB endothelium, as well as similar transcellular transport of large nanoparticles as observed in the intact BBB.