The endocannabinoid 2-arachidonoylglycerol activates human platelets through non-CB1/CB2 receptors.
BACKGROUND
The endocannabinoid 2-arachidonoylglycerol (2-AG) is an endogenous lipid that acts through the activation of G-protein-coupled cannabinoid receptors and plays essential roles in many physiological contexts. In the cardiovascular system 2-AG is generated by both activated endothelial cells and platelets, and participates in the regulation of inflammation and thrombosis. Although human platelets actively metabolize endocannabinoids, 2-AG also binds to platelet surface and leads to cell activation.


OBJECTIVE
To investigate the biological consequence of 2-AG interactions with human platelets and to clarify the role of cannabinoid receptors.


METHODS
Gel-filtered platelets were stimulated with 2-AG in the presence or absence of various inhibitors. Platelet aggregation and secretion were measured in a lumiaggregometer. Calcium ion movements were measured in FURA-2 loaded platelets. Thromboxane A(2) (TxA(2)) generation was evaluated as Thromboxane B(2) accumulation with a commercial EIA assay.


RESULTS
2-AG induced platelet shape change, aggregation and secretion with a dose-dependent mechanism that required engagement of platelet TxA(2) receptors. 2-AG caused also cytosolic calcium increase; however, it was totally dependent on availability of TxA(2). Indeed 2-AG was able to induce a robust generation of TxA(2) through the cyclooxygenase pathway. Treatment of platelets with inhibitors of monoacylglycerol lipase and fatty acid amide hydrolase did not affect the activation induced by 2-AG. Moreover, neither CB(1) and CB(2) proteins nor CB(1)/CB(2) mRNAs were detected in platelets.


CONCLUSIONS
2-AG can be considered a new physiologic platelet agonist able to induce full platelet activation and aggregation with a non-CB(1)/CB(2) receptor-mediated mechanism.
Baldassarri
S
S
Department of Clinical and Experimental Medicine, University of Eastern Piedmont, Novara, Italy.
Bertoni
A
A
Bagarotti
A
A
Sarasso
C
C
Zanfa
M
M
Catani
M V
MV
Avigliano
L
L
Maccarrone
M
M
Torti
M
M
Sinigaglia
F
F
D001095:Arachidonic Acids / Q000494:pharmacology*; D001792:Blood Platelets / Q000737:chemistry / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D063385:Cannabinoid Receptor Modulators / Q000494:pharmacology*; D002478:Cells, Cultured; D063388:Endocannabinoids; D005989:Glycerides / Q000494:pharmacology*; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation; D043882:Receptors, Cannabinoid / Q000502:physiology*; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000378:metabolism* / Q000502:physiology
D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D005989:Glycerides; D043882:Receptors, Cannabinoid; D044244:Receptors, Thromboxane A2, Prostaglandin H2; C094503:glyceryl 2-arachidonate; D002118:Calcium