Antiplatelet And Antithrombotic Activities Of Salvianolic Acid A

It is widely accepted that thrombus formation facilitates the progression of variouscardiovascular or cerebrovascular disorders, including unstable angina, myocardialinfarction, transient ischemic attack, and atherosclerosis. Platelets play an importantrole in thrombus formation at the site of damaged blood vesslels, especially arterialand microvascular thrombi, which are major causes of cardiovascular andcerebrovascular diseases. Collaborative meta-analysis of randomized trials has shownthat antiplatelet therapy prvents serious vascular events, arterial occlusion, and venousthromboembolism among a wide range of patients at high risk for occlusive vascularevent. Therefore, agents with antiplatelet and antithrombotic effects could have widetherapeutic potential for circulatory diseases.There are various antiplatelet drugs that used in clinical, including aspirin,clopidogrel, abciximab and so on. Although these drugs are effective in inhibiton ofplatelet aggregation mediated by various signaling receptors, they have more sideeffects such as allergic reactions, gastric mucosal injury, severe bleeding andhematopoietic dysfunction. Simultaneously, most antiplatelet agents are single targetdrugs. They tend to inhibit only one of platelet activation pathways. In the patientstaking available antiplatelet agents, multiple outstanding pathways remain able to beactivated and overcome inhibiton, and finally aggregation takes place. Recurrentischemic events and related mortality remain high. In addition, some patients areaspirin-resistant or clopidogrel-resistant or dual drug-resistant. Base on the above,there is need to development more novel and effective antiplatelet drugs. Thus, toseek antiplatelet agents with more effective but safety remains to be a major area ofinvestigation with increased emphasis. Danshen is the dried root of Salvia miltiorrhizae (Labiatae) and is one of the mostversatile Chinese herbal drugs. It has been used clinically to treat and preventcardiovascular diseases, hyperlipidemia, and cerebrovascular diseases. Salvianolicacid A (SAA), one of major water-soluble phenolic acids of Danshen, has shown themost potent protection against peroxidative damage to biomembranes. Modernpharmacological tests have revealed that SAA possesses a variety of pharmacologicalactivities. It is found to scavenge oxygen free radicals to protect against oxidativedamage to mitochondria of heart and liver in rats, prevent focal cerebral ischemicinjury and reduce myocardial ischemia and reperfusion injury, which was moreeffective than other phenolic compounds.However, the antithrombotic and antiplatelet activities of SAA have not beenreported. Thus, the present study was to assess the effects of SAA on platelet function,thrombus formation, hemorheology and coagulation, and to provide pharmacologicalevidence for its clinical application. In addition, the underlying mechanism of SAAwas also investigated.In this study, the evaluation of antiplatelet and antithrombotic effect of SAA isshown as following:1. We fist determined the effects of SAA on rat platelet aggregation induced byadenosine diphosphate (ADP), thrombin or arachidonic acid (AA) in vivo and invitro, together with the effect of SAA on cyclic adenosine monophosphate (cAMP)level.2. Subsequently, we evaluated the activity of SAA on washed human plateletinduced by ADP.3. Then, we established arterio-venous shunt model to examined antithromboticactivity of SAA via determination of thrombus weight and thromboxane B2(TXB2),6-keto prostaglandin F1α(6-keto-PGF1α) and cAMP levels in plasma.Simultaneously, we treated rats with adrenaline hydrochloride injection and coldstress to alter rat blood rheology.4. The effect of SAA on microcirculation was evaluated by measuringhemorheologic parameters. 5. Finally, to determine whether SAA could affect coagulation cascade, coagulationparameters: prothrombin time (PT), activated partial thromboplastin time (APTT),fibrinogen (FIB) concentration and thrombin time (TT), were determined in ratstreated with SAA for several days.The results are shown as following:1. Effect of SAA on platelet function in vitro: SAA effectively inhibited ADP-andthrombin-induced platelet aggregation, and exerted mild inhibitory effects onAA-induced platelet aggregation. For human platelet aggregation assay, SAAshowed potent inhibiton on ADP-induced platelet aggregation. In addition, SAAsignificantly increased cAMP level.2. Effect of SAA on platelet aggregation in vivo: SAA markedly inhibitADP-induced rat platelet aggregation in a dose-dependent manner.3. Effect of SAA on thrombus formation and possible mechanism of antithrombosis:SAA significantly inhibited artery-venous shunt thrombus formationdose-dependently. SAA had no effect on plasma levels of TXB2,6-keto-PGF1αlevels or the ratio of TXB2/6-keto-PGF1α. In contrast, it could markedly increasecAMP level.4. Effect of SAA on hemorheology: SAA improved hemorheology and demonstratedthe ability to significantly reduced blood viscosity, plasma viscosity, andhematocrit.5. Effect of SAA on coagulation parameters: SAA had no effect on PT, APTT, FIB orTT.In conclusion, SAA possesses significant antithrombotic and antiplatelet activities,and the ability to modulate hemorheology. Simultaneously, SAA does not affect thecoagulation system. The mechanisms underlying such activities may involve theinduction of cAMP.