Contribution of P-glycoprotein to bunitrolol efflux across blood-brain barrier.
In this study, we investigated the mechanism of the blood-brain barrier (BBB) transport of bunitrolol (BTL), as a model of beta-blocker, in vivo and in vitro. In order to define the contribution of P-glycoprotein (P-gp) to the active efflux of BTL from brain to blood, we examined the in vivo brain distribution of BTL in mdr1a(-/-) mice with a disrupted mdr1a gene. After intravenous administration of BTL to mdr1a(-/-) mice, the brain concentration and Kp value of BTL were significantly increased as compared with those in mdr1a(+/+) mice. Next, the contribution of the mdr1a P-gp to in vitro uptake of BTL was compared in LV500 cells and L cells (mouse mdr1a-expressing cells and host cells, respectively). The intracellular accumulations of [3H]vinblastine and BTL by LV500 cells were lower than those by L cells, but were significantly increased by verapamil, a P-gp inhibitor. Furthermore, the BTL uptake by KB-VJ300 cells, which express human P-gp, was also significantly lower than that by KB host cells, and was increased by verapamil. The steady-state uptake of BTL by LLC-GA5-COL300 cells, expressing human P-gp, was significantly increased in the presence of 20 microM cyclosporin A (another P-gp inhibitor), which had no effect in the LLC-PK1 host cells. On the other hand, the steady-state intracellular accumulation of BTL by MBEC4 cells, which express mdr1b P-gp instead of mdr1a P-gp, was not significantly changed in the presence of verapamil. This finding suggested that BTL is not a good substrate for mdr1b P-gp. In conclusion, our results suggest that BTL is transported from brain to blood by mdr1a P-gp in mice and by MDR1 in humans, and this presumably accounts for the low brain distribution of BTL.
Matsuzaki
J
J
Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Yamamoto
C
C
Miyama
T
T
Takanaga
H
H
Matsuo
H
H
Ishizuka
H
H
Kawahara
Y
Y
Kuwano
M
M
Naito
M
M
Tsuruo
T
T
Sawada
Y
Y
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000502:physiology*; D000319:Adrenergic beta-Antagonists / Q000097:blood / Q000493:pharmacokinetics*; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics; D001693:Biological Transport, Active / Q000187:drug effects; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007624:KB Cells; D007700:Kinetics; D007739:L Cells; D051379:Mice; D011412:Propanolamines / Q000097:blood / Q000493:pharmacokinetics*; D014316:Tritium; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000493:pharmacokinetics
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000319:Adrenergic beta-Antagonists; D000972:Antineoplastic Agents, Phytogenic; D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D011412:Propanolamines; D014316:Tritium; D014747:Vinblastine; D016572:Cyclosporine; D014700:Verapamil; C084811:bunitrolol