Eugenol Suppresses Platelet Activation and Mitigates Pulmonary Thromboembolism in Humans and Murine Models.

Platelets assume a pivotal role in the pathogenesis of cardiovascular diseases (CVDs), emphasizing their significance in disease progression. Consequently, addressing CVDs necessitates a targeted approach focused on mitigating platelet activation. Eugenol, predominantly derived from clove oil, is recognized for its antibacterial, anticancer, and anti-inflammatory properties, rendering it a valuable medicinal agent. This investigation delves into the intricate mechanisms through which eugenol influences human platelets. At a low concentration of 2 µM, eugenol demonstrates inhibition of collagen and arachidonic acid (AA)-induced platelet aggregation. Notably, thrombin and U46619 remain unaffected by eugenol. Its modulatory effects extend to ATP release, P-selectin expression, and intracellular calcium levels ([Ca2+]i). Eugenol significantly inhibits various signaling cascades, including phospholipase Cγ2 (PLCγ2)/protein kinase C (PKC), phosphoinositide 3-kinase/Akt/glycogen synthase kinase-3ß, mitogen-activated protein kinases, and cytosolic phospholipase A2 (cPLA2)/thromboxane A2 (TxA2) formation induced by collagen. Eugenol selectively inhibited cPLA2/TxA2 phosphorylation induced by AA, not affecting p38 MAPK. In ADP-treated mice, eugenol reduced occluded lung vessels by platelet thrombi without extending bleeding time. In conclusion, eugenol exerts a potent inhibitory effect on platelet activation, achieved through the inhibition of the PLCγ2-PKC and cPLA2-TxA2 cascade, consequently suppressing platelet aggregation. These findings underscore the potential therapeutic applications of eugenol in CVDs.

Glabridin, a Bioactive Flavonoid from Licorice, Effectively Inhibits Platelet Activation in Humans and Mice.

Platelets are crucial for hemostasis and arterial thrombosis, which may lead to severe cardiovascular diseases (CVDs). Thus, therapeutic agents must be developed to prevent pathological platelet activation. Glabridin, a major bioalkaloid extracted from licorice root, improves metabolic abnormalities (i.e., obesity and diabetes) and protects against CVDs and neuronal disorders. To the best of our knowledge, no studies have focused on glabridin's effects on platelet activation. Therefore, we investigated these effects in humans and mice. Glabridin exhibited the highest inhibitory effects on collagen-stimulated platelet aggregation and moderate effects on arachidonic-acid-stimulated activation; however, no effects were observed for any other agonists (e.g., thrombin or U46619). Glabridin evidently reduced P-selectin expression, ATP release, and intracellular Ca2+ ([Ca2+]i) mobilization and thromboxane A2 formation; it further reduced the activation of phospholipase C (PLC)γ2/protein kinase C (PKC), phosphoinositide 3-kinase (PI3K)/Akt/glycogen synthase kinase-3ß (GSK3ß), mitogen-activated protein kinase (MAPK), and NF-κB. In mice, glabridin reduced the mortality rate caused by acute pulmonary thromboembolism without altering bleeding time. Thus, glabridin effectively inhibits the PLCγ2/PKC cascade and prevents the activation of the PI3K/Akt/GSK3ß and MAPK pathways; this leads to a reduction in [Ca2+]i mobilization, which eventually inhibits platelet aggregation. Therefore, glabridin may be a promising therapeutic agent for thromboembolic disorders.

Regulation of Human Platelet Activation and Prevention of Arterial Thrombosis in Mice by Auraptene through Inhibition of NF-κB Pathway.

Platelets are major players in the occurrence of cardiovascular diseases. Auraptene is the most abundant coumarin derivative from plants, and it has been demonstrated to possess a potent capacity to inhibit platelet activation. Although platelets are anucleated cells, they also express the transcription factor, nuclear factor-κB (NF-κB), that may exert non-genomic functions in platelet activation. In the current study, we further investigated the inhibitory roles of auraptene in NF-κB-mediated signal events in platelets. MG-132 (an inhibitor of proteasome) and BAY11-7082 (an inhibitor of IκB kinase; IKK), obviously inhibited platelet aggregation; however, BAY11-7082 exhibited more potent activity than MG-132 in this reaction. The existence of NF-κB (p65) in platelets was observed by confocal microscopy, and auraptene attenuated NF-κB activation such as IκBα and p65 phosphorylation and reversed IκBα degradation in collagen-activated platelets. To investigate cellular signaling events between PLCγ2-PKC and NF-κB, we found that BAY11-7082 abolished PLCγ2-PKC activation; nevertheless, neither U73122 nor Ro31-8220 had effect on NF-κB activation. Furthermore, both auraptene and BAY11-7082 significantly diminished HO• formation in activated platelets. For in vivo study, auraptene prolonged the occlusion time of platelet plug in mice. In conclusion, we propose a novel inhibitory pathway of NF-κB-mediated PLCγ2-PKC activation by auraptene in human platelets, and further supported that auraptene possesses potent activity for thromboembolic diseases.

Licochalcone A Prevents Platelet Activation and Thrombus Formation through the Inhibition of PLCγ2-PKC, Akt, and MAPK Pathways.

Platelet activation is involved in cardiovascular diseases, such as atherosclerosis and ischemic stroke. Licochalcone A (LA), an active ingredient of licorice, exhibits multiple biological activities such as anti-oxidation and anti-inflammation. However, its role in platelet activation remains unclear. Therefore, the study investigated the antiplatelet mechanism of LA. Our data revealed that LA (2-10 µM) concentration dependently inhibited platelet aggregation induced by collagen, but not thrombin and U46619. LA markedly attenuated collagen-stimulated ATP release, P-selectin secretion, calcium mobilization, and GPIIbIIIa activation, but did not interfere with the collagen binding to platelets. Moreover, LA significantly reduced the activation of PLCγ2, PKC, Akt and MAPKs. Thus, LA attenuates platelet activation, possibly by inhibiting collagen receptor downstream signaling but not by blocking the collagen receptors. In addition, LA prevented adenosine diphosphate (ADP)-induced acute pulmonary thrombosis, fluorescein sodium-induced platelet thrombus formation, and middle cerebral artery occlusion/reperfusion-induced brain injury in mice, but did not affect normal hemostasis. This study demonstrated that LA effectively reduced platelet activation and thrombus formation, in part, through the inhibition of PLCγ2-PKC, Akt, and MAPK pathways, without the side effect of bleeding. These findings also indicate that LA may provide a safe and alternative therapeutic approach for preventing thromboembolic disorders such as stroke.