Effects of Taurine and Ginkgo biloba Extract on Platelet Aggregation

Effects of the leaf extract Ginkgo biloba, ginkgolides A and B, and the amino acid taurine (2-aminoethane sulfonic acid) on platelet aggregation was studied. All potential anitcoagulants were incubated in day one platelet-rich plasma and subjected to various agonist-induced clotting and tests and other measures of platelet viability. G. biloba extract and its respective ginkgolides had no effect on platelet aggregation in response to ADP and thrombin, while taurine exhibited prolongation of thrombin time (TT) and reduced thrombin-induced aggregation by 10%. Taurine prolonged time of initial clot formation on thrombolestographic tests, but overall clot viability remained unaffected. These data suggest that G. biloba and its active ginkgolides do not inhibit platelet aggregation induced by ADP and thrombin, while taurine mildly inhibits thrombin-induced platelet aggregation. These findings correlate with taurine's osmoregulatory and cryoprotective properties and indicate a role as a hemostasis stabilizer rather than an anticoagulant. Possible mechanism of taurine action is suggested. Abbreviations: EGb 761, Ginkgo bi/oba extract; GA, ginkgolide A; GB, ginkgolide B; PT, prothrombin time; APTT, activated partial thromboplastin time; TT, thrombin time; ESC, extent of shape change; HSR, hypotonic shock response; PRP, plateletrich plasma; PPP, platelet-poor plasma. Introduction Leaves from the plant Ginkgo biloba have been an integral part of Chinese herbal medicine for over 5,000 years, but it is only fairly recently that Western medicine has acknowledged it's physiological effects and pharmacological implications. Similarly, taurine, an amino acid ubiquitous throughout the animal kingdom, has an ancient evolutionary history, but only in recent decades has it stimulated interest in the biomedical community. Many biological effects of G. bi/oba have been reported in current literature including cerebrovascular and memory enhancement, 1,2 antioxidant action,>' 3 neurotransmitter stimulation,>' 3 and inhibition of platelet aggregation. 1-5 Taurine exerts a similarly copious influence on biological phenomena with effects including bile conjugation, 68 osmoregulation, 6,8-9 membrane stabilization, 6,9 cellular calcium modulation, 6,10 anti oxidation , 6,7 and inhibition of platelet aggregation., 10-13 G. biloba and taurine's influence on platelet aggregation is the exclusive focus of this study. The number of studies on G. biloba is rapidly increasing, due in no small part to the American public's increasing fascination with complimentary and alternative medicine and accordingly, the traditional healer's sensitivity to the needs of his or her patients. Due to its classification as a supplement, G. biloba extract (EGb 761), the commercially available form of the herb, is not regulated by the FDA, and because it can be purchased over-the counter, adverse side effects and/or drug-interactions are usually not considered before taking the supplement. Similarly, physicians may not realize their patients are using herbal extracts until a potentially dangerous situation presents itself, such as in situations of perioperative care. EGb 761 is purified and concentrated 1 :50 (extract: leaves) and consists of 24% Osprey Journal of Ideas and Inquiry 1 flavonoid glycosides compounds, 2.4% bilobalide, and 2, 0.8, and 1 % ginkgolides A, B, and C, respectively (Fig. 1). The extract is processed as a powder and manufactured in pill-form by various pharmaceutical companies. Figure 1. Chemical structures of Ginkgo biloba extract (EGb 761) constituents