Dipyridamole synergizes with nitric oxide to prolong inhibition of thrombin-induced platelet shape change.
We and others have previously demonstrated that nitric oxide (NO)-induced inhibition of platelet shape change is important in regulating platelet adhesion and aggregation, and therapeutic intervention of this pathway is clinically relevant for secondary prevention of stroke with dipyridamole. In the present study, we investigated whether dipyridamole affected the shape change of aspirinated platelets. Platelet shape change was inhibited using both authentic NO and sodium nitroprusside, as monitored by light scattering and mean platelet volume measurements. Dipyridamole synergized with NO, even at supra-therapeutic levels, to inhibit thrombin-induced shape change and further potentiated cAMP dependent protein kinase (PKA) mediated phosphorylation of vasodilator stimulated phosphoprotein (VASP) Ser157, even without altered levels of platelet cAMP. The effect of dipyridamole on NO-inhibited shape change depended on cGMP synthesis as evaluated by inhibition of soluble guanylyl cyclase. Measured increases in cGMP levels by dipyridamole and NO was assessed by mathematical modeling and found to be consistent with inhibition of phosphodiesterase 5 (PDE5). The model could explain the unexpected efficiency of dipyridamole in inhibiting PDE5 at the measured cGMP levels, by the majority of cGMP being bound to cGMP-dependent protein kinase (PKG). Still, selective activators of PKG failed to extend NO-mediated inhibition of the thrombin-induced platelet shape change, suggesting that PKG was not responsible for the inhibitory effect of NO and dipyridamole on shape change. The effects of dipyridamole were independent of the prostanoid and ADP pathways. Thus, the effect of dipyridamole on NO-mediated inhibition of platelet shape change may be an important and additional beneficial therapeutic effect of dipyridamole, which we suggest, is acting though localized amplification of the NO/cGMP/Phosphodiesterase3/cAMP/PKA-pathway. Probably, the efficiency of dipyridamole could be amplified clinically with NO donors.
Department of Biomedicine, University of Bergen, Bergen, Norway.
Baard Olav
BO
Jensen
Rune
R
Kleppe
Reidun
R
Kopperud
Gyrid
G
Nygaard
Stein Ove
SO
Døskeland
Holm
H
Holmsen
Frode
F
Selheim
D001792:Blood Platelets / Q000187:drug effects* / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000378:metabolism; D048430:Cell Shape / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000378:metabolism; D004176:Dipyridamole / Q000494:pharmacology*; D004357:Drug Synergism; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism; D008958:Models, Molecular; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology*; D009599:Nitroprusside / Q000378:metabolism / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology; D020521:Stroke / Q000517:prevention & control; D013917:Thrombin / Q000378:metabolism / Q000494:pharmacology*; D000098662:Vasodilator-Stimulated Phosphoprotein
D015815:Cell Adhesion Molecules; D008840:Microfilament Proteins; D010726:Phosphodiesterase Inhibitors; D010750:Phosphoproteins; D000098662:Vasodilator-Stimulated Phosphoprotein; D009599:Nitroprusside; D009569:Nitric Oxide; D004176:Dipyridamole; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D013917:Thrombin; D006152:Cyclic GMP