title: Mechanism of platelet activation induced by endocannabinoids in blood and plasma.
abstract: Platelets play a central role in atherosclerosis and atherothrombosis, and circulating endocannabinoids might modulate platelet function. Previous studies concerning effects of anandamide (N-arachidonylethanolamide) and 2-arachidonoylglycerol (2-AG) on platelets, mainly performed on isolated cells, provided conflicting results. We therefore investigated the action of three main endocannabinoids [anandamide, 2-AG and virodhamine (arachidonoylethanolamine)] on human platelets in blood and platelet-rich plasma (PRP). 2-AG and virodhamine induced platelet aggregation in blood, and shape change, aggregation and adenosine triphosphate (ATP) secretion in PRP. The EC50 of 2-AG and virodhamine for platelet aggregation in blood was 97 and 160 µM, respectively. Lower concentrations of 2-AG (20 µM) and virodhamine (50 µM) synergistically induced aggregation with other platelet stimuli. Platelet activation induced by 2-AG and virodhamine resembled arachidonic acid (AA)-induced aggregation: shape change, the first platelet response, ATP secretion and aggregation induced by 2-AG and virodhamine were all blocked by acetylsalicylic acid (ASA) or the specific thromboxane A2 (TXA2) antagonist daltroban. In addition, platelet activation induced by 2-AG and virodhamine in blood and PRP were inhibited by JZL184, a selective inhibitor of monoacylglycerol lipase (MAGL). In contrast to 2-AG and virodhamine, anandamide, a substrate of fatty acid amidohydrolase, was inactive. Synthetic cannabinoid receptor subtype 1 (CB1) and 2 (CB2) agonists lacked stimulatory as well as inhibitory platelet activity. We conclude that 2-AG and virodhamine stimulate platelets in blood and PRP by a MAGL-triggered mechanism leading to free AA and its metabolism by platelet cyclooxygenase-1/thromboxane synthase to TXA2. CB1, CB2 or non-CB1/CB2 receptors are not involved. Our results imply that ASA and MAGL inhibitors will protect platelets from activation by high endocannabinoid levels, and that pharmacological CB1- and CB2-receptor ligands will not affect platelets and platelet-dependent progression and complications of cardiovascular diseases.
authors.affiliation: Institute for Prevention of Cardiovascular Diseases, Ludwig Maximilians University of Munich , Munich , Germany.
authors.forename: S Annette
authors.initials: SA
authors.lastname: Brantl
authors.forename: Anna L
authors.initials: AL
authors.lastname: Khandoga
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Siess
mesh_terms: D000328:Adult; D001095:Arachidonic Acids / Q000097:blood / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002186:Cannabinoids / Q000097:blood / Q000494:pharmacology; D051545:Cyclooxygenase 1 / Q000097:blood; D063388:Endocannabinoids / Q000097:blood* / Q000494:pharmacology; D005989:Glycerides / Q000097:blood / Q000494:pharmacology; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000097:blood / Q000494:pharmacology
chemical_list: D001095:Arachidonic Acids; D002186:Cannabinoids; D063388:Endocannabinoids; D005989:Glycerides; D010975:Platelet Aggregation Inhibitors; D053284:Polyunsaturated Alkamides; C456739:virodhamine; C094503:glyceryl 2-arachidonate; D051545:Cyclooxygenase 1; C078814:anandamide