title: Endocannabinoids control platelet activation and limit aggregate formation under flow.
abstract: BACKGROUND
  The endocannabinoid system has previously been implicated in the regulation of neurons and inflammatory cells. Additionally, it has been reported that endocannabinoid receptors are present on circulating platelets, but there has been conflicting evidence on their contribution to platelet function.
  
  
  OBJECTIVE
  Our aim was to examine the role of endocannabinoids in platelet function in vitro and in vivo.
  
  
  RESULTS
  We studied the effects of the well-characterized endogenous endocannabinoid anandamide on platelet aggregation in suspension, α-granule release, calcium mobilization, Syk phosphorylation, as well as platelet spreading and aggregate formation under flow. Anandamide inhibits platelet aggregation and α-granule release by collagen, collagen-derived peptide CRP-XL, ADP, arachidonic acid and thromboxane A2 analogue U46619. However, activation via thrombin receptor PAR-1 stays largely unaffected. Calcium mobilization is significantly impaired when platelets are stimulated with collagen or CRP-XL, but remains normal in the presence of the other agonists. In line with this finding, we found that anandamide prevents collagen-induced Syk phosphorylation. Furthermore, anandamide-treated platelets exhibit reduced spreading on immobilized fibrinogen, have a decreased capacity for binding fibrinogen in solution and show perturbed platelet aggregate formation under flow over collagen. Finally, we investigated the influence of Cannabis sativa consumption by human volunteers on platelet activation. Similar to our in vitro findings with anandamide, ex vivo collagen-induced platelet aggregation and aggregate formation on immobilized collagen under flow were impaired in whole blood of donors that had consumed Cannabis sativa.
  
  
  CONCLUSIONS
  Endocannabinoid receptor agonists reduce platelet activation and aggregate formation both in vitro and ex vivo after Cannabis sativa consumption. Further elucidation of this novel regulatory mechanism for platelet function may prove beneficial in the search for new antithrombotic therapies.
authors.affiliation: Department of Clinical Chemistry and Haematology, Utrecht University Medical Center, Utrecht, The Netherlands.
authors.forename: Valentina
authors.initials: V
authors.lastname: De Angelis
authors.affiliation: Department of Clinical Chemistry and Haematology, Utrecht University Medical Center, Utrecht, The Netherlands.
authors.forename: Arnold C
authors.initials: AC
authors.lastname: Koekman
authors.affiliation: Department of Clinical Chemistry and Haematology, Utrecht University Medical Center, Utrecht, The Netherlands.
authors.forename: Cees
authors.initials: C
authors.lastname: Weeterings
authors.affiliation: Department of Clinical Chemistry and Haematology, Utrecht University Medical Center, Utrecht, The Netherlands.
authors.forename: Mark
authors.initials: M
authors.lastname: Roest
authors.affiliation: Department of Clinical Chemistry and Haematology, Utrecht University Medical Center, Utrecht, The Netherlands.
authors.forename: Philip G
authors.initials: PG
authors.lastname: de Groot
authors.affiliation: Department of Clinical Chemistry and Haematology, Utrecht University Medical Center, Utrecht, The Netherlands.
authors.forename: Eszter
authors.initials: E
authors.lastname: Herczenik
authors.affiliation: Department of Clinical Chemistry and Haematology, Utrecht University Medical Center, Utrecht, The Netherlands.
authors.forename: Coen
authors.initials: C
authors.lastname: Maas
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D001095:Arachidonic Acids / Q000494:pharmacology*; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002188:Cannabis / Q000378:metabolism; D003094:Collagen / Q000494:pharmacology; D013759:Dronabinol / Q000494:pharmacology; D063388:Endocannabinoids / Q000494:pharmacology*; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D039661:Integrin beta3 / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects*; D040201:Platelet Membrane Glycoprotein IIb / Q000378:metabolism; D053284:Polyunsaturated Alkamides / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D043885:Receptor, Cannabinoid, CB2 / Q000819:agonists / Q000378:metabolism; D044463:Receptor, PAR-1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000072377:Syk Kinase; D013927:Thrombosis / Q000188:drug therapy / Q000517:prevention & control*
chemical_list: D001095:Arachidonic Acids; D063388:Endocannabinoids; D039661:Integrin beta3; D047908:Intracellular Signaling Peptides and Proteins; D040201:Platelet Membrane Glycoprotein IIb; D053284:Polyunsaturated Alkamides; D043885:Receptor, Cannabinoid, CB2; D044463:Receptor, PAR-1; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D013759:Dronabinol; D005340:Fibrinogen; D003094:Collagen; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D002118:Calcium; C078814:anandamide