title: Rapid, reversible modulation of blood-brain barrier P-glycoprotein transport activity by vascular endothelial growth factor.
abstract: Increased brain expression of vascular endothelial growth factor (VEGF) is associated with neurological disease, brain injury, and blood-brain barrier (BBB) dysfunction. However, the specific effect of VEGF on the efflux transporter P-glycoprotein, a critical component of the BBB, is not known. Using isolated rat brain capillaries and in situ rat brain perfusion, we determined the effect of VEGF exposure on P-glycoprotein activity in vitro and in vivo. In isolated capillaries, VEGF acutely and reversibly decreased P-glycoprotein transport activity without decreasing transporter protein expression or opening tight junctions. This effect was blocked by inhibitors of the VEGF receptor flk-1 and Src kinase, but not by inhibitors of phosphatidylinositol-3-kinase or protein kinase C. VEGF also increased Tyr-14 phosphorylation of caveolin-1, and this was blocked by the Src inhibitor PP2. Pharmacological activation of Src kinase activity mimicked the effects of VEGF on P-glycoprotein activity and Tyr-14 phosphorylation of caveolin-1. In vivo, intracerebroventricular injection of VEGF increased brain distribution of P-glycoprotein substrates morphine and verapamil, but not the tight junction marker, sucrose; this effect was blocked by PP2. These findings indicate that VEGF decreases P-glycoprotein activity via activation of flk-1 and Src, and suggest Src-mediated phosphorylation of caveolin-1 may play a role in downregulation of P-glycoprotein activity. These findings also imply that P-glycoprotein activity is acutely diminished in pathological conditions associated with increased brain VEGF expression and that BBB VEGF/Src signaling could be targeted to acutely modulate P-glycoprotein activity and thus improve brain drug delivery.
authors.affiliation: Laboratory of Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Hawkins
authors.forename: Destiny B
authors.initials: DB
authors.lastname: Sykes
authors.forename: David S
authors.initials: DS
authors.lastname: Miller
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000098:blood supply* / Q000187:drug effects / Q000378:metabolism*; D002196:Capillaries / Q000187:drug effects / Q000378:metabolism; D051242:Caveolin 1 / Q000187:drug effects / Q000378:metabolism; D002536:Cerebral Arteries / Q000187:drug effects / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007276:Injections, Intraventricular; D008297:Male; D008833:Microcirculation / Q000187:drug effects / Q000502:physiology; D009020:Morphine / Q000493:pharmacokinetics; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism* / Q000494:pharmacology; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D014700:Verapamil / Q000493:pharmacokinetics; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: C412373:AG 1879; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D051242:Caveolin 1; D004791:Enzyme Inhibitors; D011743:Pyrimidines; D042461:Vascular Endothelial Growth Factor A; D009020:Morphine; D014700:Verapamil; D040301:Vascular Endothelial Growth Factor Receptor-2; D019061:src-Family Kinases