Activation of PKC isoform beta(I) at the blood-brain barrier rapidly decreases P-glycoprotein activity and enhances drug delivery to the brain

Abstract

P-glycoprotein is an ATP (adenosine triphosphate)-driven drug efflux transporter that is highly
expressed at the blood–brain barrier (BBB) and is a major obstacle to the pharmacotherapy of
central nervous system diseases, including brain tumors, neuro-AIDS, and epilepsy. Previous
studies have shown that P-glycoprotein transport activity in rat brain capillaries is rapidly reduced
by the proinflammatory cytokine, tumor necrosis factor-a (TNF-a) acting through protein kinase C
(PKC)-dependent signaling. In this study, we used isolated rat brain capillaries to show that the TNF-ainduced
reduction of P-glycoprotein activity was prevented by a PKCbI/II inhibitor, LY333531, and
mimicked by a PKCbI/II activator, 12-deoxyphorbol-13-phenylacetate-20-acetate (dPPA). Western
blotting of brain capillary extracts with phospho-specific antibodies showed that dPPA activated
PKCbI, but not PKCbII. Moreover, in intact rats, intracarotid infusion of dPPA potently increased brain
accumulation of the P-glycoprotein substrate, [3
H]-verapamil without compromising tight junction
integrity. Thus, PKCbI activation selectively reduced P-glycoprotein activity both in vitro and in vivo.
Targeting PKCbI at the BBB may prove to be an effective strategy for enhancing the delivery of small
molecule therapeutics to the brain.