Sphingolipids signal rapid loss of P‐glycoprotein transport activity at the blood‐brain barrier

Abstract

Blood‐brain barrier P‐glycoprotein is a major obstacle to CNS pharmacotherapy. We previously showed that TNF‐α signals through TNFR1, ET‐BR, iNOS and PKCβ1 to rapidly reduce P‐glycoprotein transport activity in rat brain capillaries (Hartz et al., Mol Pharmacol 69, 462, 2006; Rigor et al., J Cereb Blood Flow Metab 30, 1373, 2010). Here we investigate sphingolipid signaling downstream of PKCβ1. Exposing capillaries to sphingosine or sphingosine‐1‐phosphate (S1P) rapidly (minutes) and reversibly reduced P‐glycoprotein transport activity by a S1PR1‐dependent mechanism. Blocking sphingosine kinase activity or S1PR1 attenuated the ability of TNF‐α exposure or PKCβ1 activation to reduce P‐glycoprotein activity. Using in situ brain perfusion in rats, we found that infusing S1P into the cerebral vasculature increased brain accumulation of 14C‐verapamil, indicating loss of P‐glycoprotein activity; this effect was blocked by S1PR1 antagonists. S1P did not alter 3H‐sucrose accumulation, indicating no change in paracelllular permeability. We are currently testing S1PR1 agonists for possible use in improving delivery to the brain of CNS‐acting drugs that are P‐glycoprotein substrates.