Cyclic nucleotides and mitogen-activated protein kinases: regulation of simvastatin in platelet activation.
BACKGROUND
3-Hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have been widely used to reduce cardiovascular risk. These statins (i.e., simvastatin) may exert other effects besides from their cholesterol-lowering actions, including inhibition of platelet activation. Platelet activation is relevant to a variety of coronary heart diseases. Although the inhibitory effect of simvastatin in platelet activation has been studied; the detailed signal transductions by which simvastatin inhibit platelet activation has not yet been completely resolved.


METHODS
The aim of this study was to systematically examine the detailed mechanisms of simvastatin in preventing platelet activation. Platelet aggregation, flow cytometric analysis, immunoblotting, and electron spin resonance studies were used to assess the antiplatelet activity of simvastatin.


RESULTS
Simvastatin (20-50 microM) exhibited more-potent activity of inhibiting platelet aggregation stimulated by collagen than other agonists (i.e., thrombin). Simvastatin inhibited collagen-stimulated platelet activation accompanied by [Ca2+]i mobilization, thromboxane A2 (TxA2) formation, and phospholipase C (PLC)gamma2, protein kinase C (PKC), and mitogen-activated protein kinases (i.e., p38 MAPK, JNKs) phosphorylation in washed platelets. Simvastatin obviously increased both cyclic AMP and cyclic GMP levels. Simvastatin markedly increased NO release, vasodilator-stimulated phosphoprotein (VASP) phosphorylation, and endothelial nitric oxide synthase (eNOS) expression. SQ22536, an inhibitor of adenylate cyclase, markedly reversed the simvastatin-mediated inhibitory effects on platelet aggregation, PLCgamma2 and p38 MAPK phosphorylation, and simvastatin-mediated stimulatory effects on VASP and eNOS phosphorylation.


CONCLUSIONS
The most important findings of this study demonstrate for the first time that inhibitory effect of simvastatin in platelet activation may involve activation of the cyclic AMP-eNOS/NO-cyclic GMP pathway, resulting in inhibition of the PLCgamma2-PKC-p38 MAPK-TxA2 cascade, and finally inhibition of platelet aggregation.
Department of Pharmacology, Taipei Medical University, Taipei, Taiwan. sheujr@tmu.edu.tw
Ye-Ming
YM
Lee
Wei-Fan
WF
Chen
Duen-Suey
DS
Chou
Thanasekaran
T
Jayakumar
Ssu-Yu
SY
Hou
Jie-Jen
JJ
Lee
George
G
Hsiao
Joen-Rong
JR
Sheu
D020013:Calcium Signaling / Q000187:drug effects; D015815:Cell Adhesion Molecules / Q000097:blood; D003094:Collagen / Q000494:pharmacology; D000242:Cyclic AMP / Q000097:blood; D006152:Cyclic GMP / Q000097:blood; D006801:Humans; D017665:Hydroxyl Radical / Q000097:blood; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology*; D066298:In Vitro Techniques; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008840:Microfilament Proteins / Q000097:blood; D020929:Mitogen-Activated Protein Kinase Kinases / Q000097:blood*; D009569:Nitric Oxide / Q000097:blood; D052250:Nitric Oxide Synthase Type III / Q000097:blood; D009712:Nucleotides, Cyclic / Q000097:blood*; D051966:Phospholipase C gamma / Q000097:blood; D010750:Phosphoproteins / Q000097:blood; D015539:Platelet Activation / Q000187:drug effects* / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000097:blood; D015398:Signal Transduction / Q000187:drug effects; D019821:Simvastatin / Q000494:pharmacology*; D013928:Thromboxane A2 / Q000097:blood; D000098662:Vasodilator-Stimulated Phosphoprotein
D015815:Cell Adhesion Molecules; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D008840:Microfilament Proteins; D009712:Nucleotides, Cyclic; D010750:Phosphoproteins; D010975:Platelet Aggregation Inhibitors; D000098662:Vasodilator-Stimulated Phosphoprotein; D009569:Nitric Oxide; D017665:Hydroxyl Radical; D013928:Thromboxane A2; D003094:Collagen; D019821:Simvastatin; D000242:Cyclic AMP; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III; D011493:Protein Kinase C; D020929:Mitogen-Activated Protein Kinase Kinases; D051966:Phospholipase C gamma; D006152:Cyclic GMP