Hinokitiol is a novel glycoprotein VI antagonist on human platelets

Abstract

Hinokitiol (4-isopropyl-tropolone) is a bioactive compound with various pharmacological activities that is found in the wood of cupressaceous plants. Platelet activation plays an important role in thrombogenesis. In our previous study, hinokitiol specifically inhibited collagen-induced platelet aggregation ex vivo and prolonged thrombogenesis in vivo. The glycoprotein (GP) VI and integrin α₂β₁ are major collagen receptors that mediate platelet adhesion and aggregation. In our current study, we investigated which of these collagen receptors is involved in the hinokitiol-mediated inhibition of platelet activation. Treatment with 2–100 µM hinokitiol caused a dose-dependent right, parallel shift in the collagen concentration–response curve (0.5–10 µg/ml), with no change in the maximal responses. Furthermore, hinokitiol inhibited platelet aggregation and relative [Ca²⁺]i mobilization stimulated by convulxin, an agonist of GP VI, but not by aggretin, an agonist of integrin α₂β₁, indicating that hinokitiol mediates the inhibition of platelet activation through GP VI, rather than through integrin α₂β₁. Hinokitiol also specifically inhibited the convulxin-mediated activation of protein kinase C, phospholipase Cγ2, Akt, mitogen-activated protein kinases, and Lyn. Hinokitiol markedly diminished the co-immunoprecipitation of GP VI-bound Lyn after convulxin stimulation. In conclusion, hinokitiol, an antagonist of collagen GP VI may represent a novel antiplatelet drug for the prevention of thrombi associated with coronary and cerebral artery diseases.

• Collagen receptors
• convulxin
• glycoprotein VI
• hinokitiol
• platelet activation

Acknowledgements

The authors thank Prof. Tur-Fu Huang (Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan) for his kindness to provide the convulxin and aggretin in this study. This work was supported by grants from the National Science Council, Taiwan (NSC100-2320-B-038-021-MY3, NSC101-2811-B-038-002, NSC101-2811-B-038-006 and NSC102-2320-B-341-001-MY3), and the Chi-Mei Medical Center of Taipei Medical University (100CM-TMU-08); and Shin Kong Wu Ho-Su Memorial Hospital (SKH-8302-102-NDR-04). The funders had no role in study, data collection and analysis, decision to publish, or preparation of the manuscript.