RESTRICTED TRANSPORT OF CYCLOSPORINE-A ACROSS THE BLOOD-BRAIN-BARRIERBY A MULTIDRUG TRANSPORTER, P-GLYCOPROTEIN

The blood-brain barrier permeability of cyclosporin A (CsA), an immuno suppressive cyclic peptide, is restricted despite its highly lipophili c nature. In this study, the uptake of CsA by primary cultured bovine brain capillary endothelial cells (BCEC) was investigated in order to clarify whether P-glycoprotein (P-gp), an ATP-dependent drug efflux pu mp expressed in the luminal surface of BCEC, causes the decreased tran sport of CsA into the brain. P-gp, having a molecular mass of 130-140 kDa, was detected with anti-P-gp monoclonal antibody, C219, using west ern blot analysis of the membrane fraction isolated from the bovine br ain capillary. The uptake of CsA by primary cultured bovine BCEC was t ime-dependent, and the steady-state uptake of CsA was increased in the presence of several multidrug resistance reversing agents including v erapamil and steroid hormones and the substrate of P-gp in BCEC, vincr istine. The steady-stage uptake was increased significantly to approxi mately 4-fold when cellular ATP was depleted by treating with 2,4-dini trophenol, suggesting that the efflux process is ATP dependent. Furthe rmore, in the presence of an anti-P-gp monoclonal antibody, MRK16, at a 10 mug/mL concentration, the uptake of CsA was increased approximate ly 3-fold. These results suggest that the low permeability of CsA into the brain is caused by the active efflux from BCEC by P-gp present in the luminal surface of cells.