A novel role of sesamol in inhibiting NF-B-mediated signaling in platelet activation

Background: Platelet activation is relevant to a variety of coronary heart diseases. Our previous studies revealed that sesamol possesses potent antiplatelet activity through increasing cyclic AMP formation. Although platelets are anucleated cells, they also express the transcription factor, NF-B, that may exert non-genomic functions in platelet activation. Therefore, we further investigated the inhibitory roles of sesamol in NF-B-mediated platelet function. Methods. Platelet aggregation, Fura 2-AM fluorescence, and immunoblotting analysis were used in this study. Results: NF-B signaling events, including IKK phosphorylation, IB degradation, and p65 phosphorylation, were markedly activated by collagen (1 g/ml) in washed human platelets, and these signaling events were attenuated by sesamol (2.5∼25 M). Furthermore, SQ22536 and ODQ, inhibitors of adenylate cyclase and guanylate cyclase, respectively, strongly reversed the sesamol (25 M)-mediated inhibitory effects of IKK phosphorylation, IB degradation, and p65 phosphorylation stimulated by collagen. The protein kinase A (PKA) inhibitor, H89, also reversed sesamol-mediated inhibition of IB degradation. Moreover, BAY11-7082, an NF-B inhibitor, abolished IB degradation, phospholipase C (PLC)2 phosphorylation, protein kinase C (PKC) activation, [Ca²⁺]i mobilization, and platelet aggregation stimulated by collagen. Preincubation of platelets with the inhibitors, SQ22536 and H89, both strongly reversed sesamol-mediated inhibition of platelet aggregation and [Ca²⁺]i mobilization. Conclusions: Sesamol activates cAMP-PKA signaling, followed by inhibition of the NF-B-PLC-PKC cascade, thereby leading to inhibition of [Ca²⁺]i mobilization and platelet aggregation. Because platelet activation is not only linked to hemostasis, but also has a relevant role in inflammation and metastasis, our data demonstrating that inhibition of NF-B interferes with platelet function may have a great impact when these types of drugs are considered for the treatment of cancer and various inflammatory diseases.