Unconjugated bilirubin efflux by bovine brain microvascular endothelial cells in vitro.
OBJECTIVE
The passage of unconjugated bilirubin (UCB) across the blood-brain barrier into the central nervous system is a crucial first step in the development of kernicterus. The objective of the current study was to characterize the passage of UCB across primary bovine brain microvascular endothelial cell (BBMVEC) monolayers in vitro.


METHODS
Experimental study.


METHODS
Research institute.


METHODS
BBMVECs.


METHODS
Tritiated UCB (H-UCB) transport at 60, 80, 100, 200, 300, and 400 nM concentrations was tested in both the apical to basolateral (A--> B) and basolateral to apical (B-->A) directions in BBMVEC monolayers in vitro with or without preincubation with pharmacologic active transport inhibitors cyclosporine A, indomethacin, or MK571.


RESULTS
The rate of H-UCB transport in the B-->A direction was 6.2- to 7.3-fold higher than in the A-->B direction, suggesting active efflux of UCB. Cyclosporine A (5 microM), a model inhibitor of P-glycoprotein, enhanced A-->B while decreasing B-->A UCB transport, resulting in an overall decrease in BBMVEC UCB efflux of between 46% and 54%. Indomethacin (10 microM) and MK-571 (50 microM), respectively a substrate and potent inhibitor of multidrug resistance-associated protein-1, had no effect.


CONCLUSIONS
We conclude that 1) UCB is transported by BBMVEC monolayers in vitro in a net B-->A direction (i.e., active efflux); and 2) cyclosporine A partially inhibits such transport. We speculate that the blood-brain barrier limits the passage and central nervous system retention of UCB by active transport and that this may be accounted in part by P-glycoprotein.
Sequeira
Deryk
D
Department of Pediatrics, University of Pittsburgh School of Medicine, Magee-Womens Research Institute, Pittsburgh, PA, USA.
Watchko
Jon F
JF
Daood
Monica J
MJ
O'Day
Terrence L
TL
Mahmood
Burhan
B
D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage / Q000378:metabolism*; D001663:Bilirubin / Q000008:administration & dosage / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D001812:Blood-Brain Barrier / Q000378:metabolism; D015153:Blotting, Western; D001921:Brain / Q000098:blood supply*; D002417:Cattle; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007647:Kernicterus
D000975:Antioxidants; D001663:Bilirubin