Blood-Arachnoid Barrier as a Dynamic Physiological and Pharmacological Interface Between Cerebrospinal Fluid and Blood

Abstract

The blood-arachnoid barrier (BAB) consists of arachnoid epithelial cells linked by tight junctions, and forms one of the interfaces between blood and cerebrospinal fluid (CSF). The BAB was long believed to be impermeable to water-soluble substances and to play a largely passive role until our in vivo studies demonstrated that it is an active interface. Our quantitative proteomic analyses revealed that multiple transporters (OAT1, OAT3, P-gp, BCRP, MATE1, OCT2, PEPT2, etc.) are expressed more abundantly at the BAB than at the blood-cerebrospinal fluid barrier, their membrane localizations are polarized in the BAB, and there are regional differences between the cerebral and spinal cord BAB. These findings would provide a better understanding about the central nervous system kinetics of drugs and endogenous compounds, which cannot be explained by blood-brain and blood-cerebrospinal fluid barriers. Here, we introduce the BAB transport systems and discuss the physiologically and pharmacologically crucial roles of the BAB.