Blood-brain and retinal barriers show dissimilar ABC transporter impacts and concealed effect of P-glycoprotein on a novel verapamil influx carrier.
OBJECTIVE
The respective impact and interplay between ABC (P-glycoprotein/P-gp/Abcb1a, BCRP/ABCG2, MRP/ABCC) and SLC transporter functions at the blood-brain barrier (BBB) and blood-retinal barriers (BRB) are incompletely understood.


METHODS
We measured the initial cerebral and retinal distribution of selected ABC substrates by in situ carotid perfusion using P-gp/Bcrp knockout mice and chemical ABC/SLC modulation strategies. P-gp, Bcrp, Mrp1 and Mrp4 were studied by confocal retina imaging.


RESULTS
Chemical or physical disruption of P-gp increased [(3) H]-verapamil transport by ~10-fold at the BBB and ~1.5-fold at the BRB. [(3) H]-Verapamil transport involved influx-mediated by an organic cation clonidine-sensitive/diphenhydramine-sensitive proton antiporter at both barriers; this effect was unmasked when P-gp was partially or fully inhibited/disrupted at the BBB. Studies of [(3) H]-mitoxantrone and [(3) H]-zidovudine transport suggested, respectively, that Bcrp efflux was less involved at the BRB than BBB, whereas Mrps were significantly and similarly involved at both barriers. Confocal imaging showed that P-gp and Bcrp were expressed in intra-retinal vessels (inner BRB/iBRB) but absent from the blood/basal membrane of cells of the retinal pigment epithelium (outer BRB/oBRB/RPE) where, in contrast, Mrp1 and Mrp4 were localized.


CONCLUSIONS
P-gp, Bcrp, Mrp1 and Mrp4 are differentially expressed at the outer and inner BRB, resulting in an altered ability to limit substrate distribution at the retina as compared with the BBB. [(3) H]-Verapamil distribution is not P-gp-specific and involves a proton antiporter at both the BBB and BRB. However, this transport is concealed by P-gp at the BBB, but not at the BRB, where P-gp activity is reduced.
Variabilité de Réponse aux Psychotropes, INSERM, U1144, Paris, France.|Faculté de Pharmacie, Université Paris Descartes, UMR-S 1144, Paris, France.|Université Paris Diderot, UMR-S 1144, Paris, France.
Hélène
H
Chapy
Variabilité de Réponse aux Psychotropes, INSERM, U1144, Paris, France.|Faculté de Pharmacie, Université Paris Descartes, UMR-S 1144, Paris, France.|Université Paris Diderot, UMR-S 1144, Paris, France.
Bruno
B
Saubaméa
INSERM, CEA, Université Paris Sud, UMR 1023 - ERL 9218 CNRS, IMIV, Orsay, France.
Nicolas
N
Tournier
Variabilité de Réponse aux Psychotropes, INSERM, U1144, Paris, France.|Faculté de Pharmacie, Université Paris Descartes, UMR-S 1144, Paris, France.|Université Paris Diderot, UMR-S 1144, Paris, France.
Fanchon
F
Bourasset
Université Paris Descartes, UMR-S 1138, Paris, France.|Physiopathologies des Maladies Oculaires, INSERM U1138, Paris, France.
Francine
F
Behar-Cohen
Variabilité de Réponse aux Psychotropes, INSERM, U1144, Paris, France.|Faculté de Pharmacie, Université Paris Descartes, UMR-S 1144, Paris, France.|Université Paris Diderot, UMR-S 1144, Paris, France.|Assistance Publique des Hôpitaux de Paris - AP-HP, Paris, France.
Xavier
X
Declèves
Variabilité de Réponse aux Psychotropes, INSERM, U1144, Paris, France.|Faculté de Pharmacie, Université Paris Descartes, UMR-S 1144, Paris, France.|Université Paris Diderot, UMR-S 1144, Paris, France.|Assistance Publique des Hôpitaux de Paris - AP-HP, Paris, France.
Jean-Michel
JM
Scherrmann
Variabilité de Réponse aux Psychotropes, INSERM, U1144, Paris, France.|Faculté de Pharmacie, Université Paris Descartes, UMR-S 1144, Paris, France.|Université Paris Diderot, UMR-S 1144, Paris, France.|Assistance Publique des Hôpitaux de Paris - AP-HP, Paris, France.
Salvatore
S
Cisternino
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000378:metabolism*; D001813:Blood-Retinal Barrier / Q000378:metabolism*; D008297:Male; D018345:Mice, Knockout; D008942:Mitoxantrone / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology*; D015215:Zidovudine / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D015215:Zidovudine; D008942:Mitoxantrone; D014700:Verapamil