title: Active transport of fentanyl by the blood-brain barrier.
abstract: Previous studies have shown that uptake of the lipophilic opioid, fentanyl, by pulmonary endothelial cells occurs by both passive diffusion and carrier-mediated processes. To evaluate if the latter mechanism also exists in brain endothelium, transport of [3H]fentanyl was examined in primary cultured bovine brain microvessel endothelial cell (BBMEC) monolayers. Uptake of fentanyl appears to occur via a carrier-mediated process as uptake of [3H]fentanyl by BBMECs was significantly inhibited in a dose-dependent manner by unlabeled fentanyl. Fentanyl uptake was also significantly inhibited by either 4 degrees C or sodium azide/2-deoxyglucose, suggesting that carrier-mediated uptake of fentanyl was an active process. Fentanyl was also tested to determine whether it might be a substrate of the endogenous blood-brain barrier efflux transport system, P-glycoprotein (P-gp). Release of [3H]fentanyl or rhodamine 123, a known substrate of P-gp, previously loaded in the BBMECs was studied in the presence or absence of either fentanyl or verapamil, a known competitive inhibitor of P-gp. Both fentanyl (10 microM) and verapamil (100 microM) decreased release of rhodamine 123 from BBMECs, indicating that fentanyl is a substrate of P-gp in the BBMECs. This was further supported by the observation that uptake of [3H]fentanyl was significantly increased in Mg2+-free medium, a condition known to reduce P-gp activity. However, release of [3H]fentanyl was significantly increased when incubated with either unlabeled fentanyl or verapamil. These results suggest that the active P-gp-mediated extrusion of fentanyl in these cells is overshadowed by an active inward transport process, mediated by an as yet unidentified transporter. In addition, verapamil was shown to be a substrate of both P-gp and the fentanyl uptake transporter.
authors.affiliation: University of Colorado Health Sciences Center, Department of Pharmaceutical Sciences, School of Pharmacy, Denver, Colorado, USA. tkhenthorn@shi.uhcolorado.edu
authors.forename: T K
authors.initials: TK
authors.lastname: Henthorn
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: M
authors.initials: M
authors.lastname: Mahapatro
authors.forename: K Y
authors.initials: KY
authors.lastname: Ng
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors; D000465:Algorithms; D000701:Analgesics, Opioid / Q000378:metabolism* / Q000493:pharmacokinetics; D000818:Animals; D001693:Biological Transport, Active; D001812:Blood-Brain Barrier / Q000502:physiology*; D002196:Capillaries / Q000201:enzymology / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004730:Endothelium, Vascular / Q000201:enzymology / Q000378:metabolism; D004734:Energy Metabolism; D005283:Fentanyl / Q000378:metabolism* / Q000493:pharmacokinetics; D008274:Magnesium / Q000494:pharmacology; D006899:Mixed Function Oxygenases / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000701:Analgesics, Opioid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; D008274:Magnesium; D005283:Fentanyl