Effect of probenecid on fluorescein transport in the central nervous system using in vitro and in vivo models

Purpose. The purpose of this study was to characterize the function of mult idrug resistance-associated proteins (MR-Ps) (or MR-P-like organic anion tr ansport systems) in the blood-brain barrier (BBB) and blood-cerebrospinal f luid barrier (BCSFB) using both an in vitro BBB model and an in vivo microd ialysis model. Methods. In vitro functional studies were performed using bovine brain micr ovessel endothelial cells (BBMEC). The accumulation of fluorescein, an anio nic fluorescent dye, in BBMEC was determined with and without the presence of inhibitors of various efflux transport proteins. In vivo microdialysis s imultaneously monitored fluorescein concentrations in cortical extracellula r fluid and cerebrospinal fluid. The effect of probenecid on the in vivo di stribution of fluorescein was studied using a balanced crossover design in the rat. Results. In vitro experiments showed that probenecid, indomethacin, LY-3291 46, and all MR-P inhibitors significantly increased (two- to threefold) the accumulation of fluorescein in BBMEC, whereas LY-335979, a P-gp inhibitor, had no effect on the accumulation of fluorescein. Probenecid significantly increased fluorescein plasma concentration and the plasma free fraction in vivo. The distribution of fluorescein across the BBB and BCSFB was enhance d by 2.2- and 1.9-fold, respectively, when probenecid was coadministered, e ven after correction for increased fluorescein plasma concentrations and fr ee fraction. Conclusions. These results demonstrate that MRPs or MRP-like transport syst em(s) may play an important role in fluorescein distribution across both BB B and BCSFB. This study showed that microdialysis proved to be a powerful i n vivo technique for the study of transport systems in the central nervous system, and in vitro/in vivo correlations are possible using these model sy stems.