Limited distribution of new quinolone antibacterial agents into brain caused by multiple efflux transporters at the blood-brain barrier

Transport of new quinolone antibacterial agents (quinolones) at the blood-b rain barrier (BBB) was studied in vitro by using immortalized rat brain cap illary endothelial cells RBEC1, and in vivo by using the brain perfusion me thod in rats and multidrug-resistant mdr1a/1b gene-deficient mice. The perm eability coefficient of grepafloxacin measured by brain perfusion was incre ased by an excess of unlabeled grepafloxacin, suggesting a participation of a saturable BBB efflux system. Uptake coefficients of [C-14]grepafloxacin, [C-14]sparfloxacin, and [C-14]levofloxacin by RBEC1 cells at the steady st ate were increased in the presence of the unlabeled quinolones. The steady- state uptake of [C-14]grepafloxacin was increased in the presence of variou s quinolones. Brain distributions of [C-14]grepafloxacin and [C-14]sparflox acin evaluated in terms of the brain-to-plasma free concentration ratio in mdr1a/1b gene-deficient mice were significantly higher than those in wild-t ype mice, demonstrating an involvement of P-glycoprotein as the efflux tran sporter. Anionic compounds, including 4,4'-diisothiocyanatostilbene-2,2'-di sulfonic acid (DIDS) and genistein, increased the steady-state uptake of [C -14]grepafloxacin by RBEC1 cells. Because [C-14]grepafloxacin was transport ed by multidrug resistance-associated protein (MRP), in MRP1-overexpressing cells and because RBEC1 and primary cultured brain capillary endothelial c ells expressed MRP1, this protein may be an additional efflux transporter f or quinolones. Furthermore, the permeability coefficient of [C-14]grepaflox acin across the BBB was increased by DIDS or in the absence of bicarbonate ions in the brain perfusion method. DIDS or bicarbonate ion did not affect MRP1 function. Accordingly, the brain distribution of quinolones is restric ted by the action of multiple efflux transporters, including P-glycoprotein , MRP1, and an unknown anion exchange transporter.