Astrocytes increase the functional expression of P-glycoprotein in an in vitro model of the blood-brain barrier.
OBJECTIVE
To investigate the influence of astrocytes on P-glycoprotein (Pgp) expression and intracellular accumulation of Pgp substrates, separate from their net transcellular transport across the blood-brain barrier (BBB).


METHODS
An in vitro BBB model was used, comprising of brain capillary endothelial cells (BCEC) monolayers or BCEC co-cultured with astrocytes.


RESULTS
BCEC+astrocyte co-cultures seemed to express a higher level of Pgp compared to BCEC monolayers. Inhibition of Pgp results in an increased intracellular accumulation of Pgp substrates in both BCEC monolayers and BCEC+astrocyte co-cultures, and increased the sensitivity for vinblastine mediated disruption of the in vitro BBB (called the vinblastine exclusion assay). BCEC monolayers were more sensitive to vinblastine mediated disruption compared to BCEC+astrocyte co-cultures. In the latter, but not in BCEC monolayers, an inhibitable polar transport of Pgp substrates was only found from the brain to the blood side of the filter.


CONCLUSIONS
Astrocytes increase the functional expression of Pgp in our in vitro BBB model. These results also illustrate that an important role for Pgp on the BBB is to protect the barrier against intracellular accumulation of cytotoxic BBB disrupting compounds.
Gaillard
P J
PJ
Department of Pharmacology, Leiden/Amsterdam Center for Drug Research, Leiden University, The Netherlands.
van der Sandt
I C
IC
Voorwinden
L H
LH
Vu
D
D
Nielsen
J L
JL
de Boer
A G
AG
Breimer
D D
DD
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics; D001253:Astrocytes / Q000166:cytology / Q000502:physiology*; D001812:Blood-Brain Barrier / Q000502:physiology*; D001921:Brain / Q000098:blood supply; D018938:Caco-2 Cells / Q000378:metabolism; D002196:Capillaries / Q000166:cytology / Q000378:metabolism; D002417:Cattle; D018920:Coculture Techniques; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D006801:Humans; D020112:Rhodamine 123 / Q000493:pharmacokinetics; D014162:Transfection; D014747:Vinblastine / Q000493:pharmacokinetics
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000972:Antineoplastic Agents, Phytogenic; D005456:Fluorescent Dyes; D020112:Rhodamine 123; D014747:Vinblastine