Sphingosylphosphorylcholine, a naturally occurring lipid mediator, inhibits human platelet function

Abstract

1 The lysophospholipids, lysophosphatidic acid and sphingosine 1-phosphate, have been reported to activate platelets. Here we examined e ects of the naturally occurring related sphingosylphosphorylcholine (SPC) on human platelet function. 2 Platelet activation was determined as aggregation, elevation of intracellular Ca 2+ concentrations, surface expression of P-selectin, GP 53, and GP IIb/IIIa neoepitope PAC-1, and of ®brinogen binding to the platelet surface. 3 Platelets were activated by ADP (5 and 20 mM), the thrombin receptor-activating peptide TRAP-6 (5 and 20 mM), the thromboxane A 2 mimetic U-46619 (1 mM) and collagen (20 and 50 mg ml 71 ) but not by SPC (up to 20 mM). 4 SPC concentration-dependently (IC 50 approximately 1 ± 10 mM) inhibited activation of washed human platelets in response to all of the above agonists, with almost complete inhibition occurring at 20 mM SPC. 5 The SPC stereoisomers, D-erythro SPC and L-threo SPC, exhibited similar concentration ± response curves in inhibiting 20 mM ADP-induced platelet aggregation, suggesting that SPC did not act via speci®c lysophospholipid receptors. 6 Although SPC slightly activated platelet protein kinase A (as assessed by VASP phosphorylation), this e ect could not explain the marked platelet inhibition. Possible protein kinase C inhibition also did not explain the inhibition of platelet activation by SPC. On the other hand, SPC suppressed agonist-induced Ca 2+ mobilization and phospholipase C stimulation. 7 These results indicate that the lysophospholipid SPC is an e ective inhibitor of human platelet activation, apparently primarily by uncoupling agonist-activated receptors from their e ectors.

Phosphorylation of Vasodilator-Stimulated Phosphoprotein Prevents Platelet-Neutrophil Complex Formation and Dampens Myocardial Ischemia-Reperfusion Injury

“…11 Dynamic changes of the cytoskeleton alter the expression of GP IIb/IIIa on platelets and of CD11b/CD18 on neutrophils. 12 Bennett et al demonstrated that the cytoskeleton determines the affinity of the GP IIb/IIIa receptor to fibrinogen. 13 A key regulatory protein for rapid dynamic changes of the cytoskeleton is vasodilator-stimulated phosphoprotein (VASP).…”

“…[15][16][17][18] Vasodilator-stimulated phosphoprotein phosphorylation also influences the presence of the CD11b receptor on neutrophils and of GP IIb/IIIa on platelets. 12,19,20 Screening for VASP phosphorylation is used clinically as efficiency control for aggregation inhibitors (clopidogrel) and is known as the platelet reactivity index. 21,22 Given the importance of PNCs for the extent of inflammatory organ injury and the fact that VASP might affect the formation of PNCs, we pursued the role of VASP on the formation of PNCs and the functional impact of this during myocardial IR injury.…”

Lysophospholipid Receptors: Signaling and Biology

“…Moreover, SPC mobilizes Ca 2ϩ from internal stores as does S1P, suggesting common sites of action and mechanisms for SPC and S1P [reviewed in (13,14)]. It is notable, however, that SPC has also been shown to act differentially from S1P, as observed in human platelets in which S1P initiates, but SPC inhibits, activation (43). SPC can be produced from sphingomyelin by sphingomyelin deacylase, but little is known about the synthesis/degradation of SPC in a physiological context [reviewed in (13)].…”

Sphingosine kinase 1 (Sphk1) negatively regulates platelet activation and thrombus formation

“…On the one hand, S1P and the related compound sphingosylphosphorylcholine were described as inhibiting factors of platelet function and aggregation (3,35,51). On the other hand, S1P was described as activator of platelet aggregation, shape change, and calcium influx (38,53).…”