Abstract

Transport of new quinolone antibacterial agents (quinolones) at the blood-brain barrier (BBB) was studied in vitro by using immortalized rat brain capillary endothelial cells RBEC1, and in vivo by using the brain perfusion method in rats and multidrug-resistantmdr1a/1b gene-deficient mice. The permeability coefficient of grepafloxacin measured by brain perfusion was increased by an excess of unlabeled grepafloxacin, suggesting a participation of a saturable BBB efflux system. Uptake coefficients of [¹⁴C]grepafloxacin, [¹⁴C]sparfloxacin, and [¹⁴C]levofloxacin by RBEC1 cells at the steady state were increased in the presence of the unlabeled quinolones. The steady-state uptake of [¹⁴C]grepafloxacin was increased in the presence of various quinolones. Brain distributions of [¹⁴C]grepafloxacin and [¹⁴C]sparfloxacin evaluated in terms of the brain-to-plasma free concentration ratio inmdr1a/1b gene-deficient mice were significantly higher than those in wild-type mice, demonstrating an involvement of P-glycoprotein as the efflux transporter. Anionic compounds, including 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) and genistein, increased the steady-state uptake of [¹⁴C]grepafloxacin by RBEC1 cells. Because [¹⁴C]grepafloxacin was transported by multidrug resistance-associated protein (MRP), in MRP1-overexpressing cells and because RBEC1 and primary cultured brain capillary endothelial cells expressed MRP1, this protein may be an additional efflux transporter for quinolones. Furthermore, the permeability coefficient of [¹⁴C]grepafloxacin 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 restricted by the action of multiple efflux transporters, including P-glycoprotein, MRP1, and an unknown anion exchange transporter.