Platelets play a pivotal role in atherothrombosis and the antiplatelet agents have been proved to be useful in preventing onset of acute clinical events including myocardial infarction and stroke. Increasing number of natural compounds has been identified to be potential antiplatelet agents. Here we report the antiplatelet effect of glaucocalyxin A (GLA), an ent-diterpenoid that we isolated and purified from the aerial parts of Rabdosia japonica (Burm. f.) var. glaucocalyx (Maxim.) Hara, and investigate the molecular mechanisms by which GLA inhibits platelet activation and thrombus formation. The effect of GLA on platelet activation was measured using platelets freshly isolated from peripheral blood of healthy donors. Results showed that pretreatment of human platelets with lower concentrations of GLA (0.01μg/ml, 0.1μg/ml) significantly inhibited platelet aggregation induced by collagen (P<0.001) and CRP (P<0.01), a synthetic GPVI ligand, but not by ADP and U46619. Accordingly, GLA inhibited collagen-stimulated tyrosine phosphorylation of Syk, LAT, and phospholipase Cγ2, the signaling events in collagen receptor GPⅥ pathway. GLA also inhibited platelet p-selectin secretion and integrin activation by convulxin, a GPVI selective ligand. Additionally, GLA was found to inhibit low-dose thrombin-induced platelet activation. Using a flow chamber device, GLA was found to attenuate platelet adhesion on collagen surfaces in high shear condition. In vivo studies showed that GLA administration increased the time for complete occlusion upon vascular injury in mice, but did not extend tail-bleeding time when mice were administered with relatively lower doses of GLA. Therefore, the present results provide the molecular basis for the inhibition effect of GLA on platelet activation and its in vivo effect on thrombus formation, suggesting that GLA could potentially be developed as an antiplatelet and antithrombotic agent.

Eupatorium lindleyanum DC., "Ye-Ma-Zhui" called by local residents in China, showed anti-inflammatory activity and is used to treat tracheitis. We had isolated and identified the flavonoids, diterpenoids and sesquiterpenes compounds from the herb. In the present study, we evaluated the protective effects of the flavonoids fraction of E. lindleyanum (EUP-FLA) on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice and the possible underlying mechanisms of action. EUP-FLA could significantly decrease lung wet-to-dry weight (W/D) ratio, nitric oxide (NO) and protein concentration in BALF, lower myeloperoxidase (MPO) activity, increase superoxide dismutase (SOD) activity and down-regulate the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β). Additionally, EUP-FLA attenuated lung histopathological changes and significantly reduced complement deposition with decreasing the levels of Complement 3 (C3) and Complement 3c (C3c) in serum. These results demonstrated that EUP-FLA may attenuate LPS-induced ALI via reducing productions of pro-inflammatory mediators, decreasing the level of complement and affecting the NO, SOD and MPO activity.

These results showed that EUP-SQT significantly attenuated LPS-induced ALI via reducing productions of pro-inflammatory mediators and decreasing the level of complement, indicating it as a potential therapeutic agent for ALI.

Three new acyclic diterpenoids were isolated from the whole plant of Eupatorium lindleyanum DC. The structures of the compounds were elucidated by means of (1)H and (13)C NMR spectroscopic analyses, including 2D NMR experiments.

No abstract