Rapid, Reversible Modulation of Blood-Brain Barrier P-Glycoprotein Transport Activity by Vascular Endothelial Growth Factor

Laboratory of Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 01/2010; 30(4):1417-25. DOI: 10.1523/JNEUROSCI.5103-09.2010
Source: PubMed


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.


Available from: Brian T Hawkins, Mar 23, 2016
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    • "VEGF was increased several fold in the CSF in experimental chronic hydrocephalus and the increase was significantly correlated with ventricular volume (78). Excess VEGF in the CSF is known to decrease p-gp activity, thus contributing to hydrocephalus (79). "
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    • "A possible explanation of this discrepancy is that the ratio of the intrinsic transport activity per P-gp molecule to the passive diffusion rate at the BBB in EL mice may be lower than that in the in vitro P-gp–transfected LLC-PK1 cells used for the reconstruction of the K p brain values in the present study. The intrinsic P-gp transport activity in brain capillaries has been suggested to decrease under inflammatory conditions (e.g., upon TNF-a stimulation) and also under pathologic conditions associated with increased expression of vascular endothelial growth factor in brain (Hawkins et al., 2010; Miller, 2010). In the rodent model of epilepsy, protein levels of vascular endothelial growth factor and inflammatory mediators, including TNF-a, in brain are increased after the induction of seizures (Croll et al., 2004; Vezzani and Granata, 2005; Rigau et al., 2007; Vezzani et al., 2011). "
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    • "The time to reach a steady state solute concentration in the lumen increases with increasing k pgp /k m . Results from experiments reported in the literature show a time to reach steady state of 30–60 min (Hartz et al., 2004; Bauer et al., 2007; Hawkins et al., 2010; Cannon et al., 2012), consistent with k pgp /k m ≈ 5. From examination of the model it can be seen that rate constant k m = 2P 0 , where P 0 is the permeability for passive diffusion across the cell. P 0 can be equated to values obtained from in vitro transwell experiments or in vivo perfusion experiments where transport is dominated by passive diffusion. "
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