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Brazilin isolated from Caesalpinia sappan L. acts as a novel collagen receptor agonist in human platelets
- Equal contributors
1 Department of Anesthesiology, Shin Kong Wu Ho-Su Memorial Hospital, 95 Wen-Chang Rd, Taipei, 11101, Taiwan
2 School of Medicine, Fu-Jen Catholic University, 510 Zhong-Zheng Rd, Taipei, 24205, Taiwan
3 Division of Urology, Department of Surgery, Chi-Mei Medical Center, 901 Zhong-Hua Rd, Tainan, 71004, Taiwan
4 Department of Pharmacology, College of Medicine, Taipei Medical University, 250 Wu-Hsing St, Taipei, 11031, Taiwan
5 Graduate Institute Medical Sciences, College of Medicine, Taipei Medical University, 250 Wu-Hsing St, Taipei, 11031, Taiwan
6 Division of Pulmonary Medicine, Department of Internal Medicine, Taipei Medical University Hospital, 252 Wu-Hsing St, Taipei, 11031, Taiwan
7 School of Respiratory Therapy, College of Medicine, Taipei Medical University, 250 Wu-Hsing St, Taipei, 11031, Taiwan
8 Central Laboratory, Shin Kong Wu Ho-Su Memorial Hospital, 95 Wen-Chang Rd, Taipei, 11101, Taiwan
Journal of Biomedical Science 2013, 20:4 doi:10.1186/1423-0127-20-4Published: 25 January 2013
Brazilin, isolated from the heartwood of Caesalpinia sappan L., has been shown to possess multiple pharmacological properties.
In this study, platelet aggregation, flow cytometry, immunoblotting analysis, and electron spin resonance (ESR) spectrometry were used to investigate the effects of brazilin on platelet activation ex vivo. Moreover, fluorescein sodium-induced platelet thrombi of mesenteric microvessels was also used in in vivo study.
We demonstrated that relatively low concentrations of brazilin (1 to 10 μM) potentiated platelet aggregation induced by collagen (0.1 μg/ml) in washed human platelets. Higher concentrations of brazilin (20 to 50 μM) directly triggered platelet aggregation. Brazilin-mediated platelet aggregation was slightly inhibited by ATP (an antagonist of ADP). It was not inhibited by yohimbine (an antagonist of epinephrine), by SCH79797 (an antagonist of thrombin protease-activated receptor [PAR] 1), or by tcY-NH2 (an antagonist of PAR 4). Brazilin did not significantly affect FITC-triflavin binding to the integrin αIIbβ3 in platelet suspensions. Pretreatment of the platelets with caffeic acid phenethyl ester (an antagonist of collagen receptors) or JAQ1 and Sam.G4 monoclonal antibodies raised against collagen receptor glycoprotein VI and integrin α2β1, respectively, abolished platelet aggregation stimulated by collagen or brazilin. The immunoblotting analysis showed that brazilin stimulated the phosphorylation of phospholipase C (PLC)γ2 and Lyn, which were significantly attenuated in the presence of JAQ1 and Sam.G4. In addition, brazilin did not significantly trigger hydroxyl radical formation in ESR analysis. An in vivo mouse study showed that brazilin treatment (2 and 4 mg/kg) significantly shortened the occlusion time for platelet plug formation in mesenteric venules.
To the best of our knowledge, this study provides the first evidence that brazilin acts a novel collagen receptor agonist. Brazilin is a plant-based natural product, may offer therapeutic potential as intended anti-thrombotic agents for targeting of collagen receptors or to be used a useful tool for the study of detailed mechanisms in collagen receptors-mediated platelet activation.