title: Evidence for bidirectional endocannabinoid transport across cell membranes.
abstract: Despite extensive research on the trafficking of anandamide (AEA) across cell membranes, little is known about the membrane transport of other endocannabinoids, such as 2-arachidonoylglycerol (2-AG). Previous studies have provided data both in favor and against a cell membrane carrier-mediated transport of endocannabinoids, using different methodological approaches. Because AEA and 2-AG undergo rapid and almost complete intracellular hydrolysis, we employed a combination of radioligand assays and absolute quantification of cellular and extracellular endocannabinoid levels. In human U937 leukemia cells, 100 nm AEA and 1 μm 2-AG were taken up through a fast and saturable process, reaching a plateau after 5 min. Employing differential pharmacological blockage of endocannabinoid uptake, breakdown, and interaction with intracellular binding proteins, we show that eicosanoid endocannabinoids harboring an arachidonoyl chain compete for a common membrane target that regulates their transport, whereas other N-acylethanolamines did not interfere with AEA and 2-AG uptake. By combining fatty acid amide hydrolase or monoacyl glycerol lipase inhibitors with hydrolase-inactive concentrations of the AEA transport inhibitors UCM707 (1 μm) and OMDM-2 (5 μm), a functional synergism on cellular AEA and 2-AG uptake was observed. Intriguingly, structurally unrelated AEA uptake inhibitors also blocked the cellular release of AEA and 2-AG. We show, for the first time, that UCM707 and OMDM-2 inhibit the bidirectional movement of AEA and 2-AG across cell membranes. Our findings suggest that a putative endocannabinoid cell membrane transporter controls the cellular AEA and 2-AG trafficking and metabolism.
authors.affiliation: Institute of Biochemistry and Molecular Medicine, National Center of Competence in Research TransCure, University of Bern, CH-3012 Bern, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Chicca
authors.forename: Janine
authors.initials: J
authors.lastname: Marazzi
authors.forename: Simon
authors.initials: S
authors.lastname: Nicolussi
authors.forename: Jürg
authors.initials: J
authors.lastname: Gertsch
mesh_terms: D001095:Arachidonic Acids / Q000378:metabolism* / Q000494:pharmacology; D001593:Benzyl Compounds / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D063388:Endocannabinoids / Q000378:metabolism*; D005663:Furans / Q000494:pharmacology; D005989:Glycerides / Q000378:metabolism*; D006801:Humans; D008563:Membrane Lipids / Q000378:metabolism*; D053284:Polyunsaturated Alkamides / Q000378:metabolism* / Q000494:pharmacology; D020298:U937 Cells
chemical_list: D001095:Arachidonic Acids; D001593:Benzyl Compounds; D063388:Endocannabinoids; D005663:Furans; D005989:Glycerides; D008563:Membrane Lipids; C443680:N-(3-furylmethyl)eicosa-5,8,11,14-tetraenamide; C474343:OMDM-2 cpd; D053284:Polyunsaturated Alkamides; C094503:glyceryl 2-arachidonate; C078814:anandamide