In vivo and in vitro evidence for ATP-dependency of P-glycoprotein-mediated efflux of doxorubicin at the blood-brain barrier.
We investigated the role of ATP in the active efflux of doxorubicin (DOX) mediated by P-glycoprotein (P-gp), the multidrug-resistance (MDR) gene product, at the blood-brain barrier. In transient brain ischemic rats prepared with 4-vessel occlusion of vertebral and common carotid arteries for 20 min, a procedure that depleted their brain ATP content to 3% that of normal rats, the estimated permeability coefficient of DOX was increased 17-fold (to 243 +/- 2.5 microL/min/g brain). When the ATP content recovered to a normal level by means of 30-min and 24-hr cerebral recirculation of blood, the permeability coefficient recovered to 14.0 +/- 5.0 and 18.4 +/- 2.3 microL/min/g brain (mean +/- SEM, N = 3-6), respectively, very close to the control permeability (14.3 +/- 1.5 microL/min/g brain). The uptake of DOX by primary cultured brain capillary endothelial cells expressing P-gp at the luminal membrane was increased significantly (up to 2-fold), which correlated well with the decrease of cellular ATP contents caused by treating the cells with metabolic inhibitors. Evidence for the ATP-dependent transport of DOX obtained from the present in vivo and in vitro studies strongly indicates that P-gp in the brain capillaries functions actively as an efflux pump in the physiological state, providing a major mechanism to restrict the transfer of DOX into the brain.
Ohnishi
T
T
Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, School of Medicine, Kanazawa University, Japan.
Tamai
I
I
Sakanaka
K
K
Sakata
A
A
Yamashima
T
T
Yamashita
J
J
Tsuji
A
A
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000494:pharmacology / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000187:drug effects; D002478:Cells, Cultured; D004317:Doxorubicin / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000378:metabolism; D002546:Ischemic Attack, Transient / Q000378:metabolism; D008297:Male; D051381:Rats
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004317:Doxorubicin; D000255:Adenosine Triphosphate