Pregnane X receptor up-regulation of P-glycoprotein expression and transport function at the blood-brain barrier.
P-glycoprotein, an ATP-driven drug export pump, is a critical, selective component of the blood-brain barrier responsible for the poor penetration of many therapeutic drugs. In liver, ligand-activated, nuclear receptors are transcriptional regulators of drug metabolizing enzymes and drug export pumps, but only one, the pregnane X receptor (PXR in rodents, SXR in humans), regulates p-glycoprotein expression. We report for the first time that PXR is expressed in rat brain capillaries. Moreover, exposing isolated capillaries to the PXR ligands pregnenolone-16alpha-carbonitrile (PCN) and dexamethasone increased p-glycoprotein expression and p-glycoprotein-specific transport of a fluorescent cyclosporine A derivative into capillary lumens. Dosing rats with PCN and dexamethasone increased p-glycoprotein expression in liver plasma membranes and in brain capillaries and up-regulated specific transport in capillaries. This is the first evidence for PXR expression in brain and for regulation by nuclear receptors of a xenobiotic export pump at the blood-brain barrier. These results imply selective tightening of the barrier in patients exposed to the wide range of xenobiotics that are PXR/SXR ligands, including drugs, dietary constituents, and toxicants.
Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Björn
B
Bauer
Anika M S
AM
Hartz
Gert
G
Fricker
David S
DS
Miller
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000378:metabolism*; D015153:Blotting, Western; D015870:Gene Expression; D007150:Immunohistochemistry; D008297:Male; D000077297:Pregnane X Receptor; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000502:physiology*; D011987:Receptors, Steroid / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation; D015262:Xenobiotics / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D015262:Xenobiotics