Antiplatelet effect of AMP-activated protein kinase activator and its potentiation by the phosphodiesterase inhibitor dipyridamole.

AMP-activated protein kinase (AMPK) activates endothelial nitric oxide synthase (eNOS) via phosphorylation at the activating site. The eNOS-nitric oxide (NO)/soluble guanylate cyclase (sGC)-cGMP/cGMP-dependent protein kinase (PKG) signaling axis is a major antiaggregatory mechanism residing in platelets. Based on the hypothesis that direct activation of AMPK might be a potential strategy to inhibit platelet aggregation, the antiplatelet effect of AMPK activators was investigated. Treatment of isolated platelets with the AMPK activator, 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) resulted in AMPK activation and a decrease in aggregation, which was abolished by pretreatment with the AMPK inhibitors compound C (CC) and ara-A. Such an AMPK-dependent antiaggregatory effect was also observed with other AMPK activators such as A-769662 and PT1. AICAR induced eNOS activation was followed by NO synthesis, cGMP production, and subsequent phosphorylation of vasodilator-stimulated phosphoprotein (VASP), a PKG substrate. All these events were blocked by CC or ara-A pretreatment, and each event was inhibited by the eNOS inhibitor L-NAME, the sGC inhibitor ODQ, and the PKG inhibitor Rp-8-pCPT-cGMPS. Simultaneous treatment of dipyridamole, a phosphodiesterase (PDE) inhibitor, with AICAR potentiated the antiaggregatory effect by enhancing the cGMP elevation. Administration of AICAR increased platelet cGMP and prolonged FeCl3-induced arterial occlusion time in rats, which further increased in combination with dipyridamole. In conclusion, AMPK activators inhibited platelet aggregation by stimulating the eNOS-NO/sGC-cGMP/PKG signaling pathway. The antiplatelet effect of AMPK activators could be potentiated in combination with a PDE inhibitor through the common mechanism of elevating cGMP. Thus, AMPK may serve as a potential target for antiplatelet therapy.